Patent Application
20220347990
This disclosure relates to flexible sheets made of layers of polyethylene terephthalate (PET) and heat-activated adhesive, and to thermal cooling structures using such flexible sheets.
In high-voltage battery applications (such as in electric and hybrid automotive vehicles), certain components may be heat-producing (i.e., generating their own heat, such as high-voltage batteries), while other components may be heat-bearing (i.e., not generating their own heat but absorbing heat from other nearby components, such as battery trays and enclosures). Adhesive-backed PET films may be used in such environments to physically interface between heat-bearing or heat-producing components and other components (e.g., heat sinks), in order to transfer heat from such heat-bearing or heat-producing components and into the other components. In addition to providing sufficient thermal conductivity, adhesive-backed PET films should also provide sufficient electrical isolation between electrical components (like high-voltage batteries) and other components. Further, adhesive-backed PET films should also provide sufficient bonding strength due to the g-forces that may be produced in environments such as automotive vehicles. However, it is a challenge to find adhesive-backed PET films which have the desired combination of thermal conductivity, electrical isolation and bonding strength.
According to one embodiment, a flexible sheet having enhanced thermal conductivity, electrical isolation and bonding strength includes a first layer of polyethylene terephthalate having opposed first and second sides and an electrical isolation of at least 500 ohms at 2.0 kV DC, and a second layer of heat-activated adhesive attached to and covering the first side, wherein the heat-activated adhesive has a bonding strength of greater than 50 psi, and wherein the first and second layers together have a thermal conductivity of at least 0.7 W/mK.
The second side may have a surface roughness of at least one of Ra≥0.5 μm and Rz≥3.0 μm, and the thermal conductivity of the first layer and second layers together may be at least 1.0 W/mK. The flexible sheet may further include a third layer of thermal interface material attached to and covering the second side. The thermal interface material may be at least one of: (i) a phase change material; and (ii) an adhesive, a silicone, a urethane or an acrylic, containing at least one of pyrolitic graphite, aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, diamond powder and silver. The flexible sheet may further include a metallic cooling plate attached to the second layer of heat-activated adhesive. The metallic cooling plate may include one or more cooling channels therein, wherein each of the one or more cooling channels is configured for containing a flow of coolant therethrough.
One or more of the following may be true with regard to the flexible sheet: (i) the first layer may be colored; (ii) the heat-activated adhesive may be capable of activation by exposure to laser light; (iii) the heat-activated adhesive may be a thermoset heat-activated adhesive; (iv) the heat-activated adhesive may be a thermoplastic heat-activated adhesive; (v) the polyethylene terephthalate may be crystalline; (vi) the polyethylene terephthalate may be amorphous; (vii) the polyethylene terephthalate may be a combination of crystalline and amorphous; and (viii) the polyethylene terephthalate may be a biaxially oriented polyethylene terephthalate.
According to another embodiment, a pliable sheet having enhanced thermal conductivity, electrical isolation and bonding strength includes: a first layer of polyethylene terephthalate having opposed first and second sides and an electrical isolation of at least 500 ohms at 2.0 kV DC; and a second layer of heat-activated adhesive attached to and covering the first side, wherein the heat-activated adhesive has a bonding strength of greater than 50 psi; wherein the polyethylene terephthalate is amorphous, the heat-activated adhesive is a thermoset heat-activated adhesive, and the first and second layers together have a thermal conductivity of at least 1.0 W/mK. The second side may have a surface roughness of at least one of Ra≥0.5 μm and Rz≥3.0 μm.
According to yet another embodiment, a thermal cooling structure for use with high-voltage battery applications includes: (i) a first layer of polyethylene terephthalate having opposed first and second sides and an electrical isolation of at least 500 ohms at 2.0 kV DC; (ii) a second layer of heat-activated adhesive attached to and covering the first side, wherein the heat-activated adhesive has a bonding strength of greater than 50 psi and the first and second layers together have a thermal conductivity of at least 0.7 W/mK; (iii) a third layer of thermal interface material attached to and covering the second side; and (iv) a metallic cooling plate attached to the second layer of heat-activated adhesive.
The thermal interface material may be at least one of: (i) a phase change material; and (ii) an adhesive, a silicone, a urethane or an acrylic, containing at least one of pyrolitic graphite, aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, diamond powder and silver. The metallic cooling plate may include one or more cooling channels therein, wherein each of the one or more cooling channels is configured for containing a flow of coolant therethrough. The polyethylene terephthalate may be amorphous, and the heat-activated adhesive may be a thermoset heat-activated adhesive.
The above features and advantages, and other features and advantages, of the present teachings are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings, as defined in the appended claims, when taken in connection with the accompanying drawings.
Referring now to the drawings, wherein like numerals indicate like parts in the several views, a flexible or pliable sheet 70 having enhanced thermal conductivity, electrical isolation and bonding strength, and a thermal cooling structure 80 for use with high-voltage battery applications, are shown and described herein. Note that as used herein, the descriptors “flexible” and “pliable” may be used interchangeably.
The second side 14 of the first layer 10 may be roughened (either as formed or through a post-processing step), so as to enhance its bondability with other materials or components. For example, the second side 14 may have a surface roughness of at least one of Ra≥0.5 μm and Rz≥3.0 μm. (For example, the second side 14 may have (i) an average surface roughness Ra of 0.5 μm or more, such as 2-3 μm or more, and/or (ii) a range of surface roughness Rz between the highest and lowest points of the surface of 3.0 μm or more, such as 5-6 μm or more.) Optionally, the thermal conductivity requirements of the first and second layers 10, 20 together may be altered; for example, the thermal conductivity of the first and second layers 10, 20 together may be at least 1.0 W/mK.
The flexible sheet 70 and thermal cooling structure 80 may further include a third layer 30 of thermal interface material 31 having opposed fifth and sixth sides 32, 34, with the fifth side 32 attached to and covering the second side 14 of the first layer 10. As illustrated by the block diagram of
The flexible sheet 70 and thermal cooling structure 80 may further include a metallic cooling plate 60 having a seventh side 68 which is attached to the fourth side 24 of the second layer 20. The metallic cooling plate 60 has a body portion 62 made of aluminum, copper, steel or the like, with the body portion 62 having one or more cooling channels 64 therein. Each of the one or more cooling channels 64 is configured for containing a flow of coolant 66 therethrough, such as a liquid coolant. The coolant 66 may be circulated through the one or more channels 64 by a pump or other system (not shown).
With the flexible sheet 70 and thermal cooling structure 80 arranged as variously described above, the flexible sheet 70 or thermal cooling structure 80 may be disposed in contact with a heat-bearing or heat-producing workpiece 90 as illustrated in
The materials and components used in the flexible sheet 70 and thermal cooling structure 80 may have various properties, such as the exemplary properties shown below in TABLE 1 below. An industry or engineering standard is provided for selected properties for the sake of reference. Note that these are merely exemplary or example properties and standards, and are not intended to limit or define the selected materials or components. For example, the electrical isolation (also known as dielectric resistance) may be 500 ohms or more at 2.0 kilovolts of direct current (i.e., kV DC), or 500 ohms or more at some higher DC voltage level such as 2.1 kV, 2.8 kV, 3.5 kV, etc. Similarly, the bond strength may be greater than 50 psi (thus excluding conventional pressure-sensitive adhesives), or the bond strength may be required to be greater than 300 psi in shear and/or greater than 270 psi in tensile strength.
According to another embodiment, a pliable sheet 70 having enhanced thermal conductivity, electrical isolation and bonding strength includes: a first layer 10 of polyethylene terephthalate 11 having opposed first and second sides 12, 14 and an electrical isolation of at least 500 ohms at 2.0 kV DC; and a second layer 20 of heat-activated adhesive 21 attached to and covering the first side 12, wherein the heat-activated adhesive 21 has a bonding strength of greater than 50 psi; wherein the polyethylene terephthalate 11 is amorphous (i.e., an amorphous polyethylene terephthalate 11a), the heat-activated adhesive 21 is a thermoset heat-activated adhesive 21TS, and the first and second layers 10, 20 together have a thermal conductivity of at least 1.0 W/mK. The second side 14 may have a surface roughness of at least one of Ra≥0.5 μm and Rz≥3.0 μm.
According to yet another embodiment, a thermal cooling structure 80 for use with high-voltage battery applications (and other applications) includes: (i) a first layer 10 of polyethylene terephthalate 11 having opposed first and second sides 12, 14 and an electrical isolation of at least 500 ohms at 2.0 kV DC; (ii) a second layer 20 of heat-activated adhesive 21 attached to and covering the first side 12, wherein the heat-activated adhesive 21 has a bonding strength of greater than 50 psi and the first and second layers 10, 20 together have a thermal conductivity of at least 0.7 W/mK; (iii) a third layer 30 of thermal interface material 31 attached to and covering the second side 14; and (iv) a metallic cooling plate 60 attached to the second layer 20 of heat-activated adhesive 21.
The thermal interface material 31 may be at least one of: (i) a phase change material 36; and (ii) an adhesive 38, a silicone 40, a urethane 42 or an acrylic 44, containing at least one of pyrolitic graphite 46, aluminum oxide 48, magnesium oxide 50, aluminum nitride 52, boron nitride 54, diamond powder 56 and silver 58. The metallic cooling plate 60 may include one or more cooling channels 64 therein, wherein each of the one or more cooling channels 64 is configured for containing a flow of coolant 66 therethrough. The polyethylene terephthalate 11 may be amorphous (i.e., an amorphous polyethylene terephthalate 11a), and the heat-activated adhesive 21 may be a thermoset heat-activated adhesive 21TS.
The above description is intended to be illustrative, and not restrictive. While the dimensions and types of materials described herein are intended to be illustrative, they are by no means limiting and are exemplary embodiments. In the following claims, use of the terms “first”, “second”, “top”, “bottom”, etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. As used herein, an element or step recited in the singular and preceded by the word “a” or “an” should be understood as not excluding plural of such elements or steps, unless such exclusion is explicitly stated. Additionally, the phrase “at least one of A and B” and the phrase “A and/or B” should each be understood to mean “only A, only B, or both A and B”. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
This written description uses examples, including the best mode, to enable those skilled in the art to make and use devices, systems and compositions of matter, and to perform methods, according to this disclosure. It is the following claims, including equivalents, which define the scope of the present disclosure.
