Cooler and method for manufacturing the same

Abstract

In a cooler having a polypropylene resin plate section and an aluminum alloy plate section, the adhesive strength is increased, and the airtightness or water pressure resistance is improved. [Solution] A cooler having a cooling channel for cooling a battery for an electric vehicle, comprising a resin plate portion and an alloy plate portion joined to one surface of the resin plate portion via an adhesive, wherein the resin plate portion mainly contains polypropylene resin, and the alloy plate portion mainly contains aluminum, the resin plate portion has a plasma-treated surface on at least a part of the one surface, the plasma-treated surface has pores with a diameter of less than 1.05 μm calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of less than 1.05 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface is 80% or more.

Description

Technical Field

[0001] The present invention relates to a cooler used for cooling batteries for electrified vehicles.

Background Art

[0002] In electrified vehicles such as electric vehicles and hybrid vehicles, the amount of heat generated by battery packs and the like, which are objects to be cooled, has increased due to miniaturization and higher performance, and the importance of cooling performance is increasing. Conventionally, a cooler having a structure in which a cooling flow path is formed between mutually stacked metal plates has been employed. In this cooler, one plate is stacked on a battery pack or the like, and the battery pack or the like is cooled when the one plate is cooled by a refrigerant flowing through the cooling flow path.

[0003] Further, there is a demand for weight reduction of electrified vehicles, and weight reduction of coolers is being studied. For example, International Publication No. 2020 / 196878 (Patent Document 1) proposes that one plate stacked on a battery pack or the like be made of metal, and the other plate be made of synthetic resin having a lower specific gravity than metal.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] In their research and development of a cooler having a resin plate section and a metal plate section, the inventors conceived of using a polypropylene resin as the material for the resin plate section from the viewpoint of strength and heat resistance, and using an aluminum alloy as the material for the metal plate section from the viewpoint of thermal conductivity. Furthermore, from the viewpoint of refrigerant leakage, they conducted extensive studies focusing on the adhesive interface between the polypropylene resin plate section (hereinafter sometimes referred to as the "polypropylene resin plate section") and the aluminum alloy metal plate section (hereinafter sometimes referred to as the "aluminum alloy plate section"), particularly the surface characteristics of the polypropylene resin plate section, in order to improve the airtightness or water pressure resistance of the cooler.

[0006] Specifically, the inventors focused on the technical relationship between the physical shape formed on the surface of the polypropylene resin plate portion by plasma treatment and the adhesive strength with respect to the aluminum alloy plate portion joined via adhesive, among various surface treatment methods. In the course of this research, the inventors unexpectedly discovered that, unlike conventional plasma treatments of general strength, deliberately applying excessive plasma treatment creates specific minute pores on the surface of the polypropylene resin plate portion. By forming a plasma-treated surface containing a specific proportion or more of these minute pores, the adhesive strength with respect to the aluminum alloy plate portion joined via adhesive is significantly increased, and the airtightness or water pressure resistance of the cooler is significantly improved.

[0007] Conventionally, various methods are known for surface modification of polypropylene resins, but no surface modification method is known that forms minute pores with a diameter of less than 1.05 μm as defined in the present invention. In particular, no surface modification method is known that forms such minute pores by applying excessive plasma treatment to a polypropylene resin, and furthermore, it is completely unknown that forming a plasma-treated surface containing a specific proportion or more of such minute pores significantly increases the adhesive strength with the aluminum alloy plate portion joined via an adhesive, thereby improving the airtightness or water pressure resistance of the cooler.

[0008] For example, conventional plasma treatments were generally understood by those skilled in the art to primarily aim at chemical modification by introducing hydrophilic functional groups to the target resin surface. Therefore, it was often recommended to perform plasma treatment with a distance of 10 mm from the plasma discharge nozzle and approximately 3 passes. Those skilled in the art believed that these recommended conditions provided a sufficient surface modification effect and therefore did not anticipate performing plasma treatments beyond these recommended conditions. Rather, it was recognized that exceeding the recommended conditions could lead to concerns about reduced productivity in the plasma treatment process, damage to the resin surface, and adverse effects on the resin's properties.

[0009] As a result of various studies, the present inventors have discovered, contrary to the understanding of those skilled in the art, that by applying plasma treatment to a polypropylene resin plate with conditions significantly exceeding the recommended plasma treatment conditions, a unique surface shape not formed under conventional recommended conditions, specifically, minute pores with a diameter of less than 1.05 μm, is formed. As a result of further investigation into the distribution morphology of these minute pores, the present inventors have found that by forming a plasma-treated surface containing minute pores with a diameter of less than 1.05 μm in a specific proportion, the adhesive strength with the aluminum alloy plate portion joined via an adhesive is significantly increased, and the airtightness or water pressure resistance of the cooler is significantly improved, leading to the present invention. [Means for solving the problem]

[0010] The gist of this invention is as follows: [1] to [7]. [1] A cooler having a cooling channel for cooling batteries for electric vehicles, The above-mentioned cooler comprises a resin plate portion and an alloy plate portion bonded to one surface of the resin plate portion via an adhesive, wherein the resin plate portion mainly contains polypropylene resin, and the alloy plate portion mainly contains aluminum. A cooler in which the above-mentioned resin plate portion has a plasma-treated surface on at least a portion of one of its surfaces, the plasma-treated surface has pores with a diameter of less than 1.05 μm calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of less than 1.05 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of less than 1.05 μm / total number of pores × 100) is 80% or more. [2] The cooler according to [1], wherein the plasma-treated surface has pores with a diameter of less than 0.17 μm calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of less than 0.17 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of less than 0.17 μm / total number of pores × 100) is 65% or more. [3] The cooler according to [2], wherein the plasma-treated surface has pores with a diameter of 0.17 μm or more, calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of 0.17 μm or more to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of 0.17 μm or more / total number of pores × 100) is 20% or more. [4] The above resin plate portion contains glass fiber, and is a cooler according to any one of [1] to [3]. [5] The cooler according to any one of [1] to [4], wherein the adhesive is at least one selected from the group consisting of epoxy-modified silicone adhesives, epoxy adhesives, silicone adhesives, urethane adhesives, and acrylic adhesives. [6] A cooler according to any of [1] to [5], wherein the maximum height roughness (Rz) of the plasma-treated surface is 3 to 200 μm. [7] A method for manufacturing a cooler according to any one of [1] to [6], comprising the steps of: applying plasma treatment to at least a part of one surface of the resin plate portion to form pores; and joining the plasma-treated surface of the resin plate portion and the alloy plate portion via an adhesive. [Effects of the Invention]

[0011] According to the cooler of the present invention, the adhesive strength between the polypropylene resin plate portion and the aluminum alloy plate portion joined via an adhesive can be increased, thereby improving the airtightness or water pressure resistance of the cooler. [Brief explanation of the drawing]

[0012] [Figure 1] This figure schematically shows a cooler according to one embodiment of the present invention. [Figure 2] This figure schematically shows a cooler according to one embodiment of the present invention. [Figure 3] This is an SEM image of the plasma-treated surface in Example 1 of the present invention. [Modes for carrying out the invention]

[0013] Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to these embodiments. In this specification, "main component" refers to a component that significantly affects the properties of the object, and the content of this component is usually 50% by mass or more of the object, preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and particularly preferably 68% by mass or more. The content may also be 70% by mass or more, 80% by mass or more, 100% by mass or more, etc.

[0014] <Cooler> A cooler according to an embodiment of the present invention (hereinafter sometimes referred to as "the present cooler") is a cooler having a cooling flow path for cooling a battery for an electrified vehicle, wherein the cooler includes a resin plate portion and an alloy plate portion joined to one surface of the resin plate portion via an adhesive, the resin plate portion contains a polypropylene-based resin as a main component, the alloy plate portion contains aluminum as a main component, the resin plate portion has a plasma-treated surface on at least a part of the one surface, the plasma-treated surface has pores with a pore diameter of less than 1.05 µm calculated based on electron microscope image analysis, and a ratio (α) of the number of pores having a pore diameter of less than 1.05 µm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface is 80% or more. [Formula] (α) = (number of pores with pore diameter less than 1.05 µm / total number of pores) × 100 [%]

[0015] According to an example embodiment of the present cooler, the combination of the polypropylene-based resin plate portion and the aluminum alloy plate portion contributes to weight reduction of the cooler (weight reduction of electrified vehicles), and dramatically improves the adhesive strength between the polypropylene-based resin plate portion and the aluminum alloy plate portion, thereby providing a cooler excellent in airtightness and water pressure resistance, which is extremely useful.

[0016] [Ratio (α) of the number of pores with pore diameter less than 1.05 µm on the plasma-treated surface] As described above, the polypropylene-based resin plate portion of the present cooler has a plasma-treated surface, and the ratio (α) of the number of pores with pore diameter less than 1.05 µm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface is 80% or more. From the viewpoint of further improving the airtightness and water pressure resistance of the cooler, the ratio (α) is more preferably 82% or more, still more preferably 85% or more. Further, the ratio (α) may be, for example, 90% or more, or 95% or more, and the upper limit is not particularly limited, and may be 100%.

[0017] The number of pores with a diameter of less than 1.05 μm on the plasma-treated surface of the polypropylene resin plate is not particularly limited, but for example, it is about 1 to 3000 per rectangular measurement field of view of 6.4 μm × 4.6 μm. The above number may also be 50 to 2000, 100 to 1000, etc.

[0018] [Percentage of pores with a diameter of less than 0.17 μm on the plasma-treated surface (β)] In this cooler, from the viewpoint of further improving the airtightness and water pressure resistance of the cooler, it is preferable that the ratio (β) of the number of pores with a diameter of less than 0.17 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface of the polypropylene resin plate portion is above a certain value. Specifically, it is preferable that the above ratio (β) is 65% or more. The above ratio (β) may be, for example, 80% or more, or 90% or more. There is no particular upper limit, and it may be 100%. [Formula] (β) = Number of pores less than 0.17 μm / Total number of pores × 100 [%]

[0019] In one example of a preferred embodiment of this cooler, for example, the above ratio (β) is more preferably 65-90%, and even more preferably 70-85%, from the viewpoint of further improving the airtightness and water pressure resistance of the cooler.

[0020] The number of pores with a diameter of less than 0.17 μm on the plasma-treated surface of the polypropylene resin plate is not particularly limited, but for example, it is about 1 to 3000 per rectangular measurement field of view of 6.4 μm × 4.6 μm. The above number may also be 50 to 2000, 100 to 1000, etc.

[0021] [Percentage of pores with a diameter of 0.17 μm or larger on the plasma-treated surface (γ)] In this cooler, from the viewpoint of further improving the airtightness and water pressure resistance of the cooler, it is preferable that the above ratio (β) requirement is met, and that the ratio (γ) of the number of pores with a diameter of 0.17 μm or larger to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface of the polypropylene resin plate portion is above a certain value. Specifically, it is preferable that the above ratio (γ) is, for example, 20% or more. The above ratio (γ) can be set appropriately within the above range, for example, it may be around 20-35% or 22-30%. [Formula] (γ) = Number of pores 0.17 μm or larger / Total number of pores × 100 [%]

[0022] The number of pores with a diameter of 0.17 μm or larger on the plasma-treated surface of the polypropylene resin plate is not particularly limited, but for example, it is about 1 to 1000 pores per rectangular measurement field of view of 6.4 μm × 4.6 μm. The above number may also be 17 to 660 pores, 33 to 330 pores, etc.

[0023] In this cooler, the pore diameter and number ratio of the pores on the plasma-treated surface of the polypropylene resin plate are the circular pore diameter and distribution extracted by the binarization process of electron microscope images. In other words, the ratio of pore diameter and number of pores on the plasma-treated surface of the polypropylene resin plate can be determined by calculating the pore diameter and distribution extracted by binarization of electron microscope images using known image analysis software, in accordance with conventional methods.

[0024] For example, a scanning electron microscope (SEM) can be used to capture a secondary electron image of the plasma surface of a polypropylene resin plate, and pores can be extracted by binarizing the image using image analysis software. SEM imaging conditions include, for example, an acceleration voltage of 10.0 kV, a magnification of 20,000x, and a field of view of 6.4 μm × 4.6 μm.

[0025] The binarization process only needs to be able to appropriately extract the minute pores that are the target of observation, and there are no specific conditions that limit it. For example, after denoising the SEM image, the pores can be extracted by performing binarization based on a predetermined threshold and then counting their number. Specifically, one method is to determine the grayscale for each pixel of the SEM image, create a histogram of the number of pixels and the grayscale, determine a threshold, and then perform binarization. Alternatively, it is preferable to use the functions of image analysis software to compare the images before and after binarization, check whether the pores have been appropriately extracted, and adjust the threshold as appropriate before performing binarization. Alternatively, the binarization process may be adaptive binarization. Adaptive binarization is a process in which, for each pixel of an input image, the values ​​of pixels within a certain surrounding area are obtained, the average or weighted average of the pixel values ​​within the area is calculated to obtain a threshold, and this threshold is applied to the corresponding pixel in the input image.

[0026] Next, the area of ​​each pore extracted by the binarization process is calculated using image analysis software, and the equivalent circular pore diameter is calculated from each area to determine the pore diameter. From the frequency distribution of pore diameters obtained in this way, the proportion of pores with a diameter of less than 1.05 μm (α), the proportion of pores with a diameter of less than 0.17 μm (β), and the proportion of pores with a diameter of 0.17 μm or more (γ) on the plasma-treated surface can be calculated using image analysis software.

[0027] In other words, one example of the embodiment of this cooler is characterized in that, in the binarized secondary electron image obtained by imaging the plasma-treated surface of the polypropylene resin plate using a scanning electron microscope, the proportion of pores with a circular pore diameter of less than 1.05 μm is 80% or more of the total number of pores. Furthermore, in one example of the embodiment of this cooler, it is preferable that, in the binarized secondary electron image obtained by imaging the plasma-treated surface of the polypropylene resin plate using a scanning electron microscope, the proportion of pores with a circular pore diameter of less than 0.17 μm is 65% or more of the total number of pores. Furthermore, in one example of the embodiment of this cooler, it is preferable that, in the binarized secondary electron image obtained by imaging the plasma-treated surface of the polypropylene resin plate using a scanning electron microscope, the proportion of pores with a circular pore diameter of less than 0.17 μm is 65% or more of the total number of pores, and the proportion of pores with a circular pore diameter of 0.17 μm or more is 20% or more of the total number of pores.

[0028] [Maximum height roughness (Rz) of the plasma-treated surface] Furthermore, in one example of this cooler embodiment, although not particularly limited, the maximum height roughness (Rz) of the plasma-treated surface is preferably 3 to 200 μm. The maximum height roughness (Rz) can be appropriately set within the above range, for example, 3 to 150 μm, 3 to 100 μm, 3 to 80 μm, 3 to 60 μm, 3 to 40 μm, 3 to 20 μm, 3 to 10 μm, etc. The maximum height roughness (Rz) can be determined in accordance with JIS B0601:2013 and by the method described in the examples below.

[0029] [Polypropylene resin] The polypropylene resin used to form the polypropylene resin plate is not particularly limited, but examples include homopolymers of propylene (homopolypropylene), block copolymers, random copolymers, graft copolymers, and other copolymers of propylene and α-olefins other than propylene, such as ethylene and 1-butene, and modified polypropylene modified with acid anhydrides such as maleic anhydride. These may be used individually or in combination of two or more.

[0030] Examples of the above-mentioned α-olefins include 2 to 20 carbon atoms such as ethylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, and 1-octadecene (excluding propylene, which has 3 carbon atoms). These may be used individually or in combination of two or more.

[0031] The melt flow rate (MFR) of the polypropylene resin is not particularly limited, but is preferably 1 to 10 g / 10 min, more preferably 3 to 8 g / 10 min, and even more preferably 4 to 7 g / 10 min. The MFR of polypropylene resins is measured in accordance with JIS K 7210, under conditions of a measurement temperature of 230°C and a load of 2.16 kg.

[0032] The polypropylene resin content is preferably 50 to 100% by mass, and more preferably 65 to 95% by mass, relative to the total amount (100% by mass) of the material forming the polypropylene resin plate portion. Alternatively, the polypropylene resin content may be 70 to 90% by mass, 75 to 85% by mass, etc.

[0033] From the viewpoint of increasing its strength, the polypropylene resin plate portion preferably contains a reinforcing filler. Examples of reinforcing fillers include glass fiber filler, carbon fiber filler, potassium titanate, glass beads, milled fiber, and talc. Among these, glass fiber filler is preferred.

[0034] Examples of glass fibers used as glass fiber fillers include D glass (low dielectric constant glass), NE glass (acid-resistant alkali glass), A glass (alkali glass), S glass (high-strength, high-elasticity glass), and alkali-resistant glass.

[0035] When reinforcing fillers are used, the content of the reinforcing fillers is preferably 1 to 35% by mass, more preferably 10 to 32% by mass, and even more preferably 20 to 30% by mass, relative to the total content (100% by mass) of the polypropylene resin and the reinforcing fillers.

[0036] [Aluminum alloy] The aluminum alloy used to form the aluminum alloy plate is not particularly limited, but examples include Al-Mg aluminum alloys (JIS designation 5000 series), Al-Mg-Si aluminum alloys (JIS designation 6000 series), and Al-Zn aluminum alloys (JIS designation 7000 series). These may be used individually or in combination of two or more. The aluminum content in the aluminum alloy is not particularly limited, but is preferably around 80 to 99% by mass.

[0037] 〔glue〕 As the adhesive, a thermosetting adhesive is preferred and is not particularly limited, but examples include epoxy-modified silicone adhesives, epoxy adhesives, urethane adhesives, silicone adhesives, and acrylic adhesives. These may be used individually or in combination of two or more.

[0038] Adhesives may be one-component or two-component. For example, one-component epoxy adhesives include thermosetting adhesives containing a liquid epoxy resin and a curing agent such as ketimine, oxazolidine, or aldimine compounds. Two-component epoxy resin adhesives may have bisphenol A type epoxy resin or bisphenol F type epoxy resin as the main component, and curing agents may include, for example, linear aliphatic amines, cyclic aliphatic amines, aromatic amines, imidazole compounds, or modified silicone polymers. One-component urethane adhesives may include, for example, thermosetting adhesives containing a urethane prepolymer having an isocyanate group. Two-component urethane adhesives may include, for example, thermosetting adhesives containing a main component containing a polyol and a curing agent containing an isocyanate.

[0039] <Manufacturing method> This cooler comprises the steps of: applying plasma treatment to at least a portion of one surface of a polypropylene resin plate to form the aforementioned pores; and joining the plasma-treated surface of the polypropylene resin plate to the aluminum alloy plate via an adhesive.

[0040] Examples of plasma treatments include atmospheric pressure plasma treatment and vacuum plasma treatment. The plasma gas used in the plasma treatment is not particularly limited, but examples include nitrogen gas, helium gas, argon gas, and mixed gases obtained by mixing these gases with one or more of oxygen gas, carbon dioxide gas, and hydrogen gas. The plasma treatment speed (the speed at which the plasma discharge nozzle is moved) can be appropriately set, for example, within the range of 10 to 1000 mm / second. The distance between the plasma discharge nozzle and the surface of the polypropylene resin plate can also be appropriately set within the range of 1 to 10 mm.

[0041] As a method for controlling the plasma processing surface of this cooler to satisfy the above requirements (α) to (γ), it is preferable to perform plasma processing more than the conventional recommended conditions, and is not limited to the following, but for example, increasing the number of plasma processing passes, shortening the distance between the plasma discharge nozzle and the surface of the polypropylene resin plate, or a combination thereof is simple and preferable. Specifically, for example, it is simple and preferable to perform plasma processing with 2 to 10 times the number of passes (for example, 6 to 30 passes) compared to the predetermined number of passes (for example, about 3 passes) which is the conventional recommended conditions. The number of passes refers to the number of unit plasma processing cycles, specifically the number of times the plasma discharge nozzle (plasma discharge) is swept. For example, if the plasma discharge nozzle is swept once from one end to the other of the resin plate, the number of passes is 1. If the plasma discharge nozzle is swept once from one end to the other of the resin plate, and then swept again from the other end to the first end, the number of passes is 2.

[0042] In this embodiment of the cooler, other surface treatments may be performed in conjunction with plasma treatment; for example, plasma treatment may be performed after blast treatment. The blast treatment method is not particularly limited and examples include sandblasting and scratch blasting. When other surface treatments are performed in conjunction with plasma treatment, the order of the two treatments should be such that the plasma treatment is performed after the other surface treatment.

[0043] Specific examples of embodiments of the present invention will be described in detail below with reference to the drawings. However, this cooler is not limited to the embodiments shown in the drawings.

[0044] Figures 1 and 2 show a cooler 10, which is an example of an embodiment of the present invention. The cooler 10 is placed on top of a heat-generating object 12 (heat-generating element) that generates heat, such as in an electric vehicle or a hybrid vehicle, to cool the object 12. The object 12 is, for example, a battery that supplies power to equipment mounted on the vehicle, specifically, a battery that supplies power to a traction motor in an electric vehicle configured to drive wheels using the power of an electric engine.

[0045] The cooler 10 consists of an aluminum alloy plate portion 14 that is superimposed on the object to be cooled 12 and a plate-shaped polypropylene resin plate portion 18 with grooves 16, which are superimposed on each other and fixed together. The opening (upper opening 20) of the grooves 16 is covered by the aluminum alloy plate portion 14, forming a cooling channel 22 through which a heat transfer medium (refrigerant) flows between the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18.

[0046] The aluminum alloy plate portion 14 is a single, roughly rectangular plate, and its four sides are composed of a pair of long sides 24, 24 and a pair of short sides 26, 26 connecting these long sides 24. The thickness of the aluminum alloy plate portion 14 is not particularly limited, but in this embodiment, it is relatively thin, approximately 1 to 5 mm.

[0047] Furthermore, the aluminum alloy plate portion 14 has through holes 28 that penetrate the aluminum alloy plate portion 14 in the thickness direction at positions corresponding to the inlet 40 and outlet 42 of the polypropylene resin plate portion 18 that is superimposed on it. The through holes 28 can be provided, for example, at two diagonally opposite corners of the aluminum alloy plate portion 14, which is shaped like a roughly rectangular plate.

[0048] The polypropylene resin plate portion 18 is a substantially rectangular plate shape having a planar shape that is substantially corresponding to that of the aluminum alloy plate portion 14. The thickness dimension of the polypropylene resin plate portion 18 is not particularly limited, but in this embodiment, it is set to a relatively thin thickness dimension of about 2 to 10 mm. The polypropylene resin plate portion 18 has a pair of long sides 30, 30 and a pair of short sides 32, 32, and the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18 are superimposed on each other with the longitudinal direction of the aluminum alloy plate portion 14 and the longitudinal direction of the polypropylene resin plate portion 18 aligned. In this embodiment, the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18 are formed to be approximately the same size in plan view. When the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18 are superimposed, the pair of long sides 24, 24 of the aluminum alloy plate portion 14 and the pair of long sides 30, 30 of the polypropylene resin plate portion 18 are superimposed on each other, and the pair of short sides 26, 26 of the aluminum alloy plate portion 14 and the pair of short sides 32, 32 of the polypropylene resin plate portion 18 are superimposed on each other.

[0049] The polypropylene resin plate portion 18 has a groove 16 that opens upward (having an upward opening 20). The groove 16 is formed to a depth that does not penetrate the polypropylene resin plate portion 18 in the thickness direction (vertical direction), and has a bottomed groove shape. The shape of the groove 16 is not limited, but the groove 16 in this embodiment has a plurality of passages 34 in parallel that extend parallel to the long side 30 of the polypropylene resin plate portion 18. Between adjacent passages 34, 34 in the parallel direction of each passage 34, a partition portion 36 is provided that extends parallel to the long side 30 of the polypropylene resin plate portion 18. Each passage 34 is connected at both ends in the longitudinal direction of each passage 34 by connecting passages 38 that extend in a direction perpendicular to the longitudinal direction of each passage 34 (parallel to the short side 32 of the polypropylene resin plate portion 18).

[0050] Each of the outermost passages 34 in the parallel direction extends beyond the connecting passage 38 in one of its longitudinal directions, and the portion of each outermost passage 34 in the parallel direction that extends beyond the connecting passage 38 forms an inlet 40 and an outlet 42.

[0051] Furthermore, the portion of the polypropylene resin plate portion 18 where the groove 16 is not formed is a frame-shaped portion 44 that surrounds the groove 16 on all four sides. The frame-shaped portion 44 includes the portion outside the outermost passages 34 in the direction in which the short side 32 extends of the polypropylene resin plate portion 18, and the portion outside the connecting passages 38 in the direction in which the long side 30 extends of the polypropylene resin plate portion 18. In addition, each passage 34 and each partition portion 36 is formed with a relatively long length dimension in the direction in which the long side 30 extends of the polypropylene resin plate portion 18. The groove 16 is formed with a shape whose longitudinal direction is the direction in which the long side 30 extends of the polypropylene resin plate portion 18. Plasma-treated surfaces are formed on the surface of the frame-shaped portion 44 and on the surface of each partition portion 36.

[0052] An aluminum alloy plate portion 14 is superimposed on a polypropylene resin plate portion 18 from above, and the two are fixed together. The polypropylene resin plate portion 18 and the aluminum alloy plate portion 14 are fixed together by adhesive, and an adhesive layer is formed between the overlapping surfaces of the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18 (the lower surface 45a of the aluminum alloy plate portion 14 and the upper surface 45b of the polypropylene resin plate portion 18). As the aluminum alloy plate portion 14 and the polypropylene resin plate portion 18 are fixed together via this adhesive layer, the opening of the groove 16 (upper opening 20) is liquid-tightly sealed by the aluminum alloy plate portion 14.

[0053] The upper surface (plasma-treated surface) of the frame-shaped portion 44 and the upper surface (plasma-treated surface) of each partition portion 36 of the polypropylene resin plate portion 18 are superimposed on the aluminum alloy plate portion 14 via an adhesive layer, thereby covering the upper openings 20 of each passage 34 and each connecting passage 38, and forming a tunnel-shaped passage. By covering the upper openings 20 of each passage 34, multiple tunnel-shaped passages are formed in parallel in the direction in which the short side 32 of the polypropylene resin plate portion 18 extends. These tunnel-shaped passages are connected by tunnel-shaped passages that extend along the short side 32, formed by covering the upper openings 20 of each connecting passage 38. The tunnel-shaped passages are interconnected, forming a cooling channel 22 through which the refrigerant flows.

[0054] The method for applying the adhesive layer is not limited; for example, known methods such as application with a brush or spray application can be used. The thickness of the adhesive layer is not particularly limited, but for example, 10 to 1000 μm is preferred.

[0055] The cooling channel 22 is connected to the outside space through a through hole 28. An inlet 48 is formed by an inlet 40 and a through hole 28 located at a position corresponding to the inlet 40, allowing refrigerant to flow into the cooling channel 22 from the outside, while an outlet 50 is formed by an outlet 42 and a through hole 28 located at a position corresponding to the outlet 42, allowing refrigerant to flow out of the cooling channel 22 to the outside.

[0056] The refrigerant flowing through the cooling channel 22 is not limited, but for example, chiller water used in conventional chillers (cooling water circulation systems) installed in vehicles can be used. Specifically, water, alcohol (methanol, ethanol, etc.), glycol, etc. can be used. Furthermore, the refrigerant source for the refrigerant flowing through the cooling channel 22 is not limited, but for example, a chiller including a pump (not shown) may be provided separately, or a chiller already installed in the vehicle may be used. By using a chiller including a pump as the refrigerant source, the refrigerant can be made to flow through the cooling channel 22.

[0057] In the aluminum alloy plate portion 14 of the cooler 10 configured in this way, a heat-generating element (object to be cooled 12) that generates heat when energized, such as a battery pack, is placed on the surface (upper surface) opposite to the side on which the polypropylene resin plate portion 18 is superimposed. Furthermore, for example, if the aluminum alloy plate portion 14 is provided with through holes 28 to form an inlet 48 and an outlet 50, an inlet tube 52 is connected to the inlet 48 on the upper surface of the aluminum alloy plate portion 14, and one end of the inlet tube 52 extends outside the cooler 10 and is connected to a refrigerant source (not shown). In addition, an outlet tube 54 is connected to the outlet 50, and one end of the outlet tube 54 extends outside the cooler 10 and is connected to a refrigerant source (not shown). In other words, in this embodiment, the cooler 10 is configured as a circulation system in which the refrigerant that has flowed from the refrigerant source through the inlet tube 52 flows into the cooling channel 22 from the inlet 48, flows through the cooling channel 22, and then returns to the refrigerant source through the outlet 50 and the outflow tube 54.

[0058] In the cooler 10, a heat-generating element (object to be cooled 12), such as a battery pack, is placed on the aluminum alloy plate section 14. When the object to be cooled 12 generates heat, the heat generated in the object to be cooled 12 is transferred to the aluminum alloy plate section 14. The heat transferred to the aluminum alloy plate section 14 is cooled (heat exchanged) by the refrigerant flowing in each cooling channel 22, preventing a temperature rise in the object to be cooled 12 and the aluminum alloy plate section 14. Meanwhile, the refrigerant flowing into the cooling channel 22 from each inlet 48 is heated as it flows through the cooling channel 22 and flows out from each outlet 50 at a higher temperature than when it flowed in from each inlet 48, reaching a refrigerant source (not shown). At this refrigerant source, the refrigerant is cooled again and flows into the cooling channel 22 through each inlet 48.

[0059] In the cooler 10, a specific plasma-treated surface formed on a polypropylene-based resin plate portion 18 and the surface of an aluminum alloy plate portion 14 are bonded to each other via an adhesive. Therefore, the adhesive strength is high, and refrigerant leakage from the adhesive interface can be effectively suppressed, so that the cooler has excellent sealing performance or water pressure resistance.

[0060] Further, the cooler 10 is configured not by a combination of metal plates but by a combination of the polypropylene-based resin plate portion 18 and the aluminum alloy plate portion 14, so that weight reduction can be achieved, and the cooler is also excellent in that the degree of freedom in the shape of a cooling flow path is increased.

[0061] Further, in the usage environment of the cooler 10 (for example, the inside of an automobile is about -40°C to 80°C), due to the difference in linear expansion coefficient between the aluminum alloy and the polypropylene-based resin, a difference in deformation caused by contraction and expansion occurs between the two, and depending on the bonding mode of the two, the cooler may be deformed to warp. However, when the cooler includes, like the cooler 10, an aluminum alloy plate portion bonded to one surface of the polypropylene-based resin plate portion 18 via an adhesive, it tends to easily follow contraction and expansion, so that the cooler is also excellent in structural stability.

[0062] [Other Embodiments] Further, in an example of embodiment of the present cooler, for example, the plasma-treated surface has front-side pores identified based on first electron microscope image analysis using a first threshold as a reference, and inner pores identified based on second electron microscope image analysis using a second threshold (provided that the second threshold < the first threshold) as a reference, wherein the ratio (R1) of the number of front-side pores having a pore diameter of less than 0.17 µm to the total number of front-side pores identified based on the first electron microscope image analysis, and the ratio (R2) of the number of inner pores having a pore diameter of less than 0.17 µm to the total number of inner pores identified based on the second electron microscope image analysis, preferably satisfy the condition of R1 < R2.

[0063] Furthermore, in an example embodiment of the present cooler, for example, the plasma-treated surface has front-side pores identified based on a first electron microscope image analysis using a first threshold as a reference, and inner pores identified based on a second electron microscope image analysis using a second threshold (provided that second threshold < first threshold) as a reference, wherein among the front-side pores identified based on the first electron microscope image analysis, the number of front-side pores having a pore diameter of less than 0.17 μm (N1) and the number of inner pores having a pore diameter of less than 0.17 μm (N2) among the inner pores identified based on the second electron microscope image analysis preferably satisfy the condition of N1 < N2.

[0064] Note that the first threshold and the second threshold can be set as appropriate. For example, when an image has 256 gradations, the first threshold can be set to 125 and the second threshold can be set to 90, etc.

Examples

[0065] Examples of the present invention will be described below. However, the present invention is not limited to these examples.

[0066] [Example 1] Plasma treatment was performed on one surface of a polypropylene resin plate (disc-shaped member (containing 20% glass fiber), diameter 47 mm, thickness 3 mm) under the following conditions to obtain a test resin plate. [Plasma Treatment Conditions] ·Plasma treatment apparatus: Tough Plasma, FPE-20Type2, manufactured by FUJI ·Processing gas: nitrogen and air ·Gas flow rate: 30 L / min ·Processing pressure: atmospheric pressure ·Distance between nozzle and treated surface: 5 mm ·Number of passes: 15 times

[0067] [Analysis of Plasma-treated Surface] A scanning electron microscope (JEOL, JSM-7900F) was used to image the plasma-treated surface of a test resin plate (see Figure 3). The obtained images were analyzed, and the percentage of pores with a predetermined pore size was calculated. The results are shown in Table 1.

[0068] (SEM image acquisition conditions) • Observation mode: Secondary electron image observation • Acceleration voltage: 10.0kV ·Magnification: 20,000 times WD: 17.5mm

[0069] (Image analysis conditions) SEM images (image size 1280×1024 pixels, field of view approximately 6.4μm×4.6μm) were preprocessed with noise reduction (Non-Local Means Denoising). Noise reduction was performed using the Python library OpenCV (cv2.fastNlMeansDenoising()) with the following settings: h:3, Template Window size:7, Search Window size:21. Next, binarization was performed using the Python library OpenCV (cv2.adaptiveThreshold:128) to extract the dark areas as pores. Then, pore contour analysis was performed using OpenCV (cv2.findContours), the area of ​​each pore was calculated (cv2.ContArea), and the pore diameter was obtained by calculating the equivalent pore diameter from the area. The frequency distribution of the obtained pore diameters was calculated, and the proportion of pores with a diameter of less than 1.05 μm (α), the proportion of pores with a diameter of less than 0.17 μm (β), and the proportion of pores with a diameter of 0.17 μm or more (γ) were calculated relative to the total number of pores. The results are shown in Table 1.

[0070] [Water pressure resistance test] Adhesive (EP-001K from Cemedyne Co., Ltd.) was applied to the plasma-treated surface of the test resin plate obtained above, and the test resin plate and an aluminum alloy plate (disc-shaped member with nozzle, diameter 46 mm, nozzle diameter 13 mm, thickness 2 mm, AL5052) were laminated together via the adhesive to obtain a test sample formed by bonding the two together. Specifically, the test sample consisted of an annular plate-shaped base portion with a through hole in the center, an aluminum alloy plate having a cylindrical nozzle portion of approximately the same diameter connected to the through hole on one surface side of the annular plate-shaped base portion, and a test resin plate, with the test resin plate being bonded to the other surface of the aluminum alloy plate via adhesive. Next, the test sample was clamped with a binder clip, applying a clamping force in the direction that would cause the test resin plate and the aluminum alloy plate to adhere tightly, and left to stand for one week. After standing for one week, the clip was removed, the nozzle of the test sample was attached to a hydrostatic tester, and water was introduced from the nozzle opening towards the test resin plate, increasing the water pressure at 1.0 MPa / min. The water pressure (MPa) at which water leakage occurred from the adhesive interface between the aluminum alloy plate and the test resin plate was measured and evaluated according to the following criteria. The results are shown in Table 1. Note that the evaluation was performed using an exponential value, with the pressure (MPa) at which water leakage occurred from the adhesive interface in Comparative Example 1 set to "100". (evaluation) A: Over 150 B: Over 110 and 150 or less C:110 or less

[0071] [Maximum height roughness (Rz) measurement test] Using a laser microscope (Keyence VK-X200), measurement data was acquired from the plasma-treated surface at a magnification of 500x. Based on the acquired measurement data, the maximum height roughness (Rz) was determined using analysis software (included analysis application, Keyence) (JIS B0601, no cutoff, measurement range 700 μm). The results are shown in Table 1.

[0072] [Examples 2-3] A test resin plate was obtained in the same manner as in Example 1, except that the plasma treatment conditions for the polypropylene resin plate were changed as shown in Table 1. Each test was performed in accordance with the above test method. The results are shown in Table 1.

[0073] In Examples 2 and 3, the binarization process was performed using adaptive binarization, taking into account the bias in brightness, with the following conditions: Block size: 131, threshold correction: +5, and threshold calculation: arithmetic mean.

[0074] [Comparative Examples 1 and 2] A test resin plate for Comparative Example 1 was obtained in the same manner as in Example 1, except that the plasma treatment conditions for the polypropylene resin plate were changed as shown in Table 1. A water pressure resistance test was performed in accordance with the above test method. The results are shown in Table 1.

[0075] Furthermore, a test resin plate for Comparative Example 2 was obtained in the same manner as for Comparative Example 1, except that plasma treatment was performed after blast treatment. A water pressure resistance test was conducted in accordance with the above test method. The results are shown in Table 1. The above blasting process was performed using a wet blasting machine (Makot, manufactured by Macoh). The conditions were: alumina grid #60, projection pressure of 1.8 MPa, projection angle of 45 degrees, and processing time of approximately 10 seconds.

[0076] Furthermore, observation of SEM images obtained from comparative examples 1 and 2 confirmed that no pores existed on the plasma-treated surface. Additionally, image analysis of the plasma-treated surface revealed that no pores smaller than 1.05 μm could be detected.

[0077] [Table 1]

[0078] As shown in Table 1, the plasma-treated surfaces of Examples 1 to 3 have pores with a pore diameter of less than 1.05 µm, and the ratio (α) of the number of pores with a pore diameter of less than 1.05 µm was 80% or more. On the other hand, in Comparative Example 1 corresponding to plasma treatment under conventional recommended conditions, no pores with a pore diameter of less than 1.05 µm were confirmed. Similarly, in Comparative Example 2 in which blast treatment was performed before plasma treatment in Comparative Example 1, no pores with a pore diameter of less than 1.05 µm were confirmed.

[0079] As shown in Table 1, Examples 1 to 3 exhibit excellent water pressure resistance, and thus were found to be particularly useful for coolers. In contrast, Comparative Examples 1 and 2 were not satisfactory in terms of water pressure resistance, and were found to be still insufficient for coolers that require excellent water pressure resistance. From the above, it was found that by using a polypropylene resin plate having a plasma-treated surface that satisfies the requirements specified in the present invention: having pores with a pore diameter of less than 1.05 µm, and the ratio (α) of the number of pores with a pore diameter of less than 1.05 µm being 80% or more, an excellent cooler exhibiting high water pressure resistance can be provided.

[0080] In addition, from the comparison of Examples 1 to 3, it was found that when the ratio (β) of the number of pores with a pore diameter of less than 0.17 µm specified in the present invention is not less than a certain value (Examples 1 and 2), particularly excellent effects are exhibited. Furthermore, from the comparison of Examples 1 and 2, it was found that when the ratio of the number of pores with a pore diameter of less than 0.17 µm specified in the present invention is not less than a certain value, and the ratio (γ) of the number of pores with a pore diameter of 0.17 µm or more is not less than a certain value (Example 1), a remarkably excellent effect is achieved.

[0081] In Example 1, from the viewpoint of confirming the morphology of pores in the portion inside the blasted surface (the inner portion in the thickness direction), binarization processing with a separately set threshold (cv2.adaptiveThreshold:80) was performed. As a result, the condition R1 < R2 mentioned above was satisfied, and the condition N1 < N2 mentioned above was also satisfied. [Industrial Applicability]

[0082] The present invention is useful as a cooler used in electric vehicles, hybrid vehicles, and the like to cool objects to be cooled, such as battery packs. [Explanation of symbols]

[0083] 10 Cooler 12 Objects to be cooled 14. Aluminum alloy plate section 18 Polypropylene resin plate section 22 Cooling channel

Claims

1. A cooler having a cooling channel for cooling batteries for electric vehicles, The above-mentioned cooler comprises a resin plate portion and an alloy plate portion bonded to one surface of the resin plate portion via an adhesive, wherein the resin plate portion mainly contains polypropylene resin, and the alloy plate portion mainly contains aluminum. A cooler in which the resin plate portion described above has a plasma-treated surface on at least a portion of one of its surfaces, the plasma-treated surface has pores with a diameter of less than 1.05 μm calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of less than 1.05 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of less than 1.05 μm / total number of pores × 100) is 80% or more.

2. The cooler according to claim 1, wherein the plasma-treated surface has pores with a diameter of less than 0.17 μm calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of less than 0.17 μm to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of less than 0.17 μm / total number of pores × 100) is 65% or more.

3. The cooler according to claim 2, wherein the plasma-treated surface has pores with a diameter of 0.17 μm or more, calculated based on electron microscope image analysis, and the ratio of the number of pores with a diameter of 0.17 μm or more to the total number of pores calculated based on electron microscope image analysis of the plasma-treated surface (number of pores with a diameter of 0.17 μm or more / total number of pores × 100) is 20% or more.

4. The cooler according to claim 1 or 2, wherein the resin plate portion contains glass fibers.

5. The cooler according to claim 1 or 2, wherein the adhesive is at least one selected from the group consisting of epoxy-modified silicone adhesives, epoxy adhesives, silicone adhesives, urethane adhesives, and acrylic adhesives.

6. The cooler according to claim 1 or 2, wherein the maximum height roughness (Rz) of the plasma-treated surface is 3 to 200 μm.

7. A method for manufacturing a cooler according to claim 1 or 2, comprising the steps of: applying plasma treatment to at least a portion of one surface of the resin plate portion to form pores; and joining the plasma-treated surface of the resin plate portion and the alloy plate portion via an adhesive.

Images