Adhesive sheet

Abstract

A curable adhesive sheet includes an electrically insulating substrate including a first major surface and a second major surface opposite to the first major surface. The curable adhesive sheet further includes a first adhesive layer disposed on the first major surface. The first adhesive layer is thermally expandable. The first adhesive layer includes a plurality of first portions alternating with a plurality of second portions such that the first adhesive layer is patterned. Each second portion is disposed between two adjacent first portions. Each first portion includes a thermally expandable adhesive. Each second portion is less thermally expandable than each first portion. The curable adhesive sheet further includes a second curable adhesive layer disposed on the second major surface.

Description

PA102799W002ADHESIVE SHEETTechnical Field

[0001] The present disclosure generally relates to an adhesive sheet, and more particularly a thermally expandable adhesive sheet.Background

[0002] Adhesive sheets are used to adhere adherends to one another. Some adhesive sheets, e.g., expandable slot liners (ESL), include a dielectric film substrate provided with a thermally expandable adhesive partially or fully covered on one or both major surfaces of the dielectric film substrate. ESLs are flexible insulation sheets that are used to attach conductors inside a slot of a stator or a rotor of an electric motor. ESLs function as a dielectric insulation to minimize the chance of conductors from shorting and as an adhesive sheet that holds the conductors within the slot of the stator. Current ESLs may also include a porous cover layer disposed on the thermally expandable adhesive, or some other means, such as particles disposed on a major surface to avoid tackiness. The porous cover layer may reduce friction at a major surface of the ESL making it easier to insert the ESL into the slot or the hairpin electrodes into the slot with a slot liner without the risk of scraping, scuffing, abrading, or detaching the adhesive surface.

[0003] In current usage, the ESL is inserted into the slot of the stator followed by the conductors. Subsequently, the ESL is heated by resistance heating of the conductors, by induction heating, by convective heating, or combinations thereof. This heating step softens the thermally expandable adhesive and activates an expandable component of the adhesive causing the adhesive to expand and flow through the porous cover layer, thereby filling the gap between the conductors and a wall of the stator. The heat activation step also cures the thermally expandable adhesive. The thermally expandable adhesive on one side of the dielectric film substrate expands and adheres to the conductor while on the other side of the dielectric film substrate expands toward the stator wall. This allows the conductor and the wall of the stator to be adhesively connected and separated by the dielectric film substrate, and the dielectric film being locked into place by the expanded and cured adhesive.

[0004] Various techniques are utilized for cooling internal components of electric motors. Conventionally, a coolant may interface with both ends of the stator to dissipate heat from exposed parts of the stator. Recent approaches focus on pumping a cooling liquid through the stator from one end to the other with the cooling liquid flowing in close contact with the conductors. This can help to improve heat dissipation around the conductors. However, this approach may require a specific design of the conductor and also the ESL to provide flow channels for the cooling liquid. Current ESL designs provide continuous layers of the thermally expandable adhesive and the cover layer. Such a continuous layer design may interfere with the flow channels needed to allow the cooling liquid to flow through the stator. In the current ESL design containing continuous layers of the thermally expandable adhesive and the cover layer, the flow channelsmay get mechanically blocked during expansion of the thermally expandable adhesive. Thus, a new ESL design is needed which prevents interference and blocking of the flow channels by the ESL.Summary

[0005] In a first aspect, the present disclosure provides a curable adhesive sheet. The curable adhesive sheet includes an electrically insulating dielectric substrate including a first major surface and a second major surface opposite to the first major surface. The curable adhesive sheet further includes a first adhesive layer disposed on the first major surface of the electrically insulating substrate. The first adhesive layer is thermally expandable. The first adhesive layer includes a plurality of first portions alternating with a plurality of second portions. Each second portion of the plurality of second portions is disposed between two adjacent first portions of the plurality of first portions to form a pattern. Each first portion includes a thermally expandable adhesive. Each second portion is less thermally expandable than each first portion. The curable adhesive sheet further includes a second curable adhesive layer disposed on the second major surface of the electrically insulating substrate. The second curable adhesive layer may also be patterned as described above for the first adhesive layer, or the second curable adhesive layer may be non-pattemed. In the former case, first and second portions of the second curable adhesive layer may or may not align with the plurality of first and second portions of the first adhesive layer, respectively. The second curable adhesive layer may also be expandable as described above for the first adhesive layer, or the second curable adhesive layer may be non-expandable.

[0006] In a second aspect, the present disclosure provides an electric motor. The electric motor includes a stator core or a rotor core including at least one slot and a winding at least partially received within the at least one slot. The electric motor further includes an expandable insulative slot liner including the curable adhesive sheet of the first aspect arranged between the stator core or the rotor core and the winding.

[0007] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.Brief Description of the Drawings

[0008] Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0009] FIG. 1 is a schematic cross-sectional view of an electric motor, according to an embodiment of the present disclosure;

[0010] FIG. 2A is a schematic sectional view of a stator core of a stator of an electric motor taken along a section line X-X’ shown in FIG. 1, according to an embodiment of the present disclosure;

[0011] FIG. 2B is a schematic enlarged view of a portion of the stator core of FIG. 2A, according to an embodiment of the present disclosure;

[0012] FIG. 3A is a schematic side view of a portion of the curable adhesive sheet, according to an embodiment of the present disclosure;

[0013] FIG. 3B is a schematic bottom view of the portion of a curable adhesive sheet, according to an embodiment of the present disclosure;

[0014] FIG. 4A is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0015] FIG. 4B is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0016] FIG. 5A is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0017] FIG. 5B is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0018] FIG. 6A is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0019] FIG. 6B is a schematic top view of the portion of the curable adhesive sheet, according to an embodiment of the present disclosure;

[0020] FIG. 7A is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0021] FIG. 7B is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0022] FIG. 8A is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0023] FIG. 8B is a schematic side view of the portion of the curable adhesive sheet, according to another embodiment of the present disclosure;

[0024] FIG. 9A is a schematic side view of a substrate with a photo-initiator and an adhesive layer;

[0025] FIG. 9B is a schematic side view of the substrate of FIG. 9A upon application of an activation energy;

[0026] FIG. 9C is a schematic side view of the substrate of FIG. 9B upon heating and expansion of an adhesive of the adhesive layer;

[0027] FIG. 10A is a schematic side view of a substrate, a non-expandable adhesive layer, and a cover layer;

[0028] FIG. 10B is a schematic side view of a liner, an expandable adhesive layer, and another cover layer;

[0029] FIG. 10C is a schematic side view of a process film, an expandable adhesive layer, and another cover layer; and

[0030] FIG. 10D is a schematic side view of a substrate, a non-expandable adhesive layer, a cover layer, an expandable adhesive layer, and another cover layer.Detailed Description

[0031] In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0032] In the following disclosure, the following definitions are adopted.

[0033] As used herein, the term “adhesive sheet” is intended, in the context of this specification, to encompass all sheet-like structures in which an extent in a longitudinal direction and an extent in a transverse direction relative to the longitudinal direction is significantly greater than a thickness of the stmcture.

[0034] As used herein, the term “layer” generally refers to any material or a combination of materials on or overlaying a substrate.

[0035] As used herein, the term “substrate” generally refers to any layer on which another layer is formed.

[0036] Adhesive sheets, e.g., expandable slot liners (ESL), include a dielectric film substrate provided with a thermally expandable adhesive partially or fully covered on one or both major surfaces of the dielectric fdm substrate. ESLs are flexible insulation sheets that are used to attach conductors inside a slot of a stator or a rotor of an electric motor. Current ESLs may also include a porous cover layer disposed on the thermally expandable adhesive to reduce friction at a major surface of the ESL making it easier to insert the ESL into the slot or the hairpin electrodes into the slot with a slot liner without the risk of scrapping,scuffing, abrading, or detaching the adhesive surface. In current usage, the ESL is inserted into the slot of the stator followed by the conductors. Subsequently, the ESL is heated, which causes the thermally expandable adhesive to soften, expand, and cure, thereby filling a gap between the conductors and a stator wall of the stator, and locking the components into place.

[0037] Various techniques are utilized for cooling internal components of the electric motor. In recent approaches, a cooling liquid may be pumped through the stator from one end to the other with the cooling liquid flowing in close contact with the conductors. This can help improve heat dissipation around the conductors. This approach may require a specific design of the conductor and the ESL to provide flow channels for the flow of the cooling liquid. Current ESL designs provide continuous layers of the thermally expandable adhesive and the cover layer. Such a continuous layer design may interfere with the flow channels needed to allow the cooling liquid to flow through the stator. In the current ESL design containing continuous layers of the thermally expandable adhesive and the cover layer, the flow channels may get mechanically blocked during expansion of the thermally expandable adhesive, and thus, interfere with the performance of the flow channels between the conductors and the ESL.

[0038] The present disclosure provides a curable adhesive sheet. The curable adhesive sheet includes an electrically insulating substrate including a first major surface and a second major surface opposite to the first major surface. The curable adhesive sheet further includes a first adhesive layer disposed on the first major surface of the electrically insulating substrate. The first adhesive layer is thermally expandable. The first adhesive layer includes a plurality of first portions alternating with a plurality of second portions such that the first adhesive layer is patterned. Each second portion of the plurality of second portions is placed between two adjacent first portions of the plurality of first portions. Each first portion includes a thermally expandable adhesive. Each second portion is less thermally expandable than each first portion. The curable adhesive sheet further includes a second curable adhesive layer disposed on the second major surface of the electrically insulating substrate. The second curable adhesive layer may also be patterned as described above for the first adhesive layer, or the second curable adhesive layer may be non-pattemed. In the former case, first and second portions of the second curable adhesive layer may or may not be aligned with the plurality of first and second portions of the first adhesive layer, respectively.

[0039] The curable adhesive sheet of the present disclosure includes the first adhesive layer having the plurality of first portions alternating with the plurality of second portions. Thus, the first adhesive layer is patterned. Further, each second portion may expand less, or does not expand at all, or may shrink as compared to each first portion during application, curing, and usage of the curable adhesive sheet. In some cases, the curable adhesive sheet may function as an electric motor slot liner. Specifically, in such cases, the curable adhesive sheet may be disposed between a stator winding and a stator core of a stator of the electric motor. Specifically, the first adhesive layer may interface with the stator winding and the second curable adhesive layer may interface with the stator core. Further, the electric motor may receive a coolant for cooling components of the electric motor, e.g., the stator or a rotor.

[0040] Since each second portion is less thermally expandable than each first portion, the first adhesive layer may include regions with or without thermal expansion in a pattern. Specifically, the thermal expansion may be reduced in certain defined portions of the first adhesive layer, i.e., the plurality of second portions, thereby allowing localized gaps between the stator winding and the curable adhesive sheet. This may allow coolant to flow through such localized gaps, thereby enhancing an efficiency and an effectiveness of the coolant in cooling the stator winding or stator coil of the electric motor.

[0041] Referring now to Figures, FIG. 1 is a schematic cross-sectional view of an electric motor 10. In some embodiments, the electric motor 10 may be a part of a vehicle, such as a hybrid vehicle or a purely electric vehicle. However, the electric motor 10 may also be utilized in other suitable applications, including, but not limited to, power generation, aerospace, and general-purpose motor applications.

[0042] The electric motor 10 includes a housing 18, a rotor 14, and a stator 20. The rotor 14 and the stator 20 are arranged within the housing 18. A rotating shaft 26 of the rotor 14 is supported by the housing 18 via a pair of bearings 12 coupled to the housing 18. The rotating shaft 26 extends along and rotates about a central axis A-A’ of the housing 18. Thus, the rotor 14 is configured to rotate about the central axis A- A’. In some embodiments, the rotor 14 further includes a rotor core 16 and a magnet 17. The rotor core 16 is integrally formed with the rotating shaft 26 in an annular shape. The magnet 17 is arranged at an outer peripheral portion of the rotor core 16. In some embodiments, the magnet 17 may be a permanent magnet, for example, a rare earth magnet. Examples of the rare earth magnet may include, but are not limited to, neodymium magnets, samarium cobalt magnets, praseodymium magnets, and the like.

[0043] In some embodiments, the stator 20 is arranged circumferentially outside the rotor 14 with respect to the central axis A-A’. The stator 20 may be formed in an annular shape. An outer peripheral portion of the stator 20 is fixed to an inner wall surface of the housing 18. In some embodiments, the stator 20 includes a stator core 22 and a winding 24. In some embodiments, the stator core 22 is formed by laminating a plurality of plates along the central axis A-A’. In some embodiments, the winding 24 includes a plurality of conductors 25 (shown in FIG. 2B).

[0044] FIG. 2 A is a schematic sectional view of the stator core 22 of the stator 20 of the electric motor 10 (shown in FIG. 1) taken along a section line X-X’ (shown in FIG. 1). The winding 24 (shown in FIG. 1) is not shown in FIG. 2A for the purpose of clarity. Referring to FIGS. 1 and 2A, in some embodiments, the stator core 22 includes at least one slot 28. In the illustrated embodiment, the at least one slot 28 includes multiple slots 28. In some embodiments, the winding 24 is at least partially received within the at least one slot 28. The slots 28 may secure the winding 24 in place within the stator core 22.

[0045] FIG. 2B is a schematic enlarged view of a portion P (shown in FIG. 2 A) of the stator core 22. As shown in FIG. 2B, the at least one slot 28 receives the plurality of conductors 25 of the winding 24. In some embodiments, each conductor 25 of the plurality of conductors 25 is a wire with a square orrectangular cross-section. However, the plurality of conductors 25 may have any cross-sectional shape, including regular and irregular shapes. The electric motor 10 (shown in FIG. 1) further includes an expandable insulative slot liner 30 arranged between the stator core 22 and the winding 24. In some embodiments, the insulative slot liner 30 at least electrically insulates the winding 24 from the stator core 22. In the illustrated embodiment, the insulative slot liner 30 is a single-piece liner. However, in alternative embodiments, the insulative slot liner 30 may be made of multiple parts. In some embodiments, the insulative slot liner 30 includes a curable adhesive sheet. The curable adhesive sheet is described in greater detail in the following description.

[0046] FIG. 3A is a schematic side view of a portion of a patterned curable adhesive sheet 102, according to an embodiment of the present disclosure. In some embodiments, the curable adhesive sheet 102 is an electric motor slot liner, such as the insulative slot liner 30 shown in FIG. 2B. FIG. 3B is a schematic bottom view of the portion of the patterned curable adhesive sheet 102.

[0047] Referring to FIGS. 3A and 3B, the curable adhesive sheet 102 includes an electrically insulating substrate 104. The electrically insulating substrate 104 includes a first major surface 106 and a second major surface 108 opposite to the first major surface 106. In some embodiments, the electrically insulating substrate 104 may function as a dielectric insulating film between the winding 24 and the stator core 22 (shown in FIG. 2B). Examples of the electrically insulating substrate 104 include heat resistant film materials. Exemplary electrically insulating substrate 104 include one of a polyethylene naphthalate (PEN) film, a polyester film, a polycarbonate film, a polyimide fdm, a nylon film, a polyaramid film, a polymethyl methacrylate (PMMA) multilayer film, a polyether ether ketone (PEEK) film, a polyphenylene sulfide (PPS) film, a poly(phthalazinone ether sulfone ketone) film (PPESK), or combinations thereof. In some embodiments, the electrically insulating substrate 104 may be made of any heat and / or chemically resistant film material.

[0048] A thickness of the electrically insulating substrate 104 may be adjusted considering a gap between the winding 24 and the stator core 22 (shown in FIG. 2B). That is, in addition to a function of adhering the winding 24 and the stator core 22 as adherends, the curable adhesive sheet 102 may also have a function of filling the gap between the winding 24 and the stator core 22. Therefore, in case where the gap is large, the thickness of the electrically insulating substrate 104 may be increased to suitably fill the gap. In some embodiments, the thickness of the electrically insulating substrate 104 may also be adjusted considering dielectric parameters required for a given voltage of the electric motor 10 (shown in FIG. 1).

[0049] The curable adhesive sheet 102 further includes a first adhesive layer 110 disposed on the first major surface 106 of the electrically insulating substrate 104. The first adhesive layer 110 is thermally expandable. The curable adhesive sheet 102 further includes a second curable adhesive layer 112 disposed on the second major surface 108 of the electrically insulating substrate 104. In the illustrated embodiment, the second curable adhesive layer 112 is not thermally expandable. For example, the second curableadhesive layer 112 is a continuous non-thermally expandable layer. However, in alternative embodiments, the second curable adhesive layer 112 may be a continuous thermally expandable layer. In some embodiments, the second curable adhesive layer 112 may interface with the stator core 22 (shown in FIGS. 1-2B) while the first adhesive layer 110 may interface with the winding 24 (shown in FIGS. 1 and 2B).

[0050] In some embodiments, the first adhesive layer 110 and the second curable adhesive layer 112 may include an adhesive composition that is substantially solid at room temperature, is flowable upon heating, and hardened when cooled. In some embodiments, at least one of the first adhesive layer 110 and the second curable adhesive layer 112 includes a thermosetting epoxy resin.

[0051] Examples of epoxy resin contained in the thermosetting epoxy resin-based adhesive composition may include, but are not limited to, those obtained from an epoxy compound (monomer epoxy compound or polymer epoxy compound) having at least one oxirane ring that may be polymerized by a ring-opening reaction. The epoxy compound may be aliphatic, cycloaliphatic, aromatic, or heterocyclic. A bisphenol epoxy resin, such as, a bisphenol A-type epoxy resin and a bisphenol F-type epoxy resin, an epoxy resin having an aliphatic skeleton, such as, hexanediol diglycidyl ether, a glycidylamine-type epoxy resin, such as, triglycidylaminophenol, a novolac epoxy resin, such as, a phenol novolac epoxy resin, a cresol novolac epoxy resin, a brominated epoxy resin, and a cycloaliphatic epoxy resin, and mixtures thereof may also be used. In some embodiments, the adhesive composition of the first adhesive layer 110 and the second curable adhesive layer 112 may further include a curing agent or a curing accelerator, or both.

[0052] The adhesive composition of the first adhesive layer 110 may further optionally include additional components, such as, a thermoplastic resin (phenoxy resin (polyhydroxypolyether synthesized from bisphenols and epichlorohydrin), or the like), a toughening agent (such as, a core shell rubber, a rheology modifier such as nanosilica particles, a silane coupling agent, a flame retardant, an impact modifier, a heat stabilizer, a processing aid, a lubricant, a reinforcing agent, a colorant, a photopolymerization initiator, a crosslinking agent, and a thermally conductive filler (e.g., boron nitride or BN, alumina or AI2O3, or other oxides). Various agents known in the related art may be used as each of such additional components.

[0053] In some embodiments, the first adhesive layer 110 includes functional fillers 114, e.g., thermally expandable particles, contained within the adhesive composition of the first adhesive layer 110, or the second curable adhesive layer 112, or both. In the illustrated embodiments, the functional fillers 114 are shown only in the adhesive composition of the first adhesive layer 110. In some embodiments, the thermally expandable particles may be present in a substantially uniformly mixed state within the adhesive composition of the first adhesive layer 110, or the second curable adhesive layer 112, or both. The thermally expandable particles may thermally expanded upon heating. Upon thermal expansion, a volume of the first adhesive layer 110, or the second curable adhesive layer 112, or both may increase. Exemplary thermally expandable particles may include expandable graphite, or those having a capsule structure in which a thermoplastic resin, a vinylidene chloride polymer, an acrylonitrile copolymer, or an acrylic polymer, orthe like may be used as an outer shell, and isobutane, isopentane, or the like may be encapsulated as an expansion agent. One exemplary thermally expandable particle is available under the trade name Matsumoto Microsphere FN-100D from Matsumoto Yushi Seiyaku Co. Ltd.

[0054] In some embodiments, the curable adhesive sheet 102 further includes a cover layer 122 disposed on the first adhesive layer 110 opposite to the electrically insulating substrate 104. In some embodiments, the cover layer 122 may be a porous layer. Upon expansion of the first adhesive layer 110, the cover layer 122 may allow an adhesive of the first adhesive layer 110 to permeate from a major surface 140 of the cover layer 122 facing the first adhesive layer 110 to a major surface 142 of the cover layer 122 opposite to the major surface 140. More specifically, the cover layer 122 is provided with a structure having at least a plurality of holes passing through from the major surface 140 to the major surface 142. This may allow the adhesive to pass through the plurality of holes to reach the major surface 142 upon expansion of the first adhesive layer 110.

[0055] In some embodiments, the cover layer 122 is made up of a material having a glass transition temperature that is higher than a curing starting temperature of the adhesive of the first adhesive layer 110. In some embodiments, the cover layer 122 is made up of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof. For example, a cellulose-based non-woven paper may be as the cover layer 122. Exemplary non-woven fabrics may include non-woven glass fabrics, aramid-based non-woven fabrics, polyolefin-based non-woven fabrics, polysulfone-based non-woven fabrics, polyaramide non-woven fabrics, polyphenylsulfide-based non-woven fabrics, polyester-based non-woven fabrics, nylon-based non-woven fabrics, or liquid crystal polymer (LCP)-based non-woven fabrics. Since such a non-woven fabric / paper has a large number of through holes therein, the adhesive of the first adhesive layer 110 that is in contact with the major surface 140 may pass through the non-woven fabric / paper and reach the major surface 142 under certain conditions.

[0056] When using the curable adhesive sheet 102, the curable adhesive sheet 102 is disposed in a certain position between the components to be adhered with a predetermined gap. For example, the second curable adhesive layer 112 may be disposed adjacent to the stator core 22 (shown in FIGS. 1-2B) and the first adhesive layer 110 may be disposed adjacent to the winding 24 (shown in FIGS. 1 and 2B). Subsequently, the curable adhesive sheet 102 is heated such that the first adhesive layer 110 expands. As a result, the adhesive composition of the first adhesive layer 110 enters the cover layer 122 and flows to the other major surface 142 of the cover layer 122. Thus, the adhesive composition of the first adhesive layer 110 is interposed between the cover layer 122 and the component to be adhered (i.e., the winding 24). Subsequently, or concurrently, a curable adhesive composition (i.e., the adhesive composition of the first adhesive layer 110 and the second curable adhesive layer 112) in the curable adhesive sheet 102 is cured. After curing, the components to be adhered together are adhered by means of the curable adhesive sheet 102.

[0057] The first adhesive layer 110 includes a plurality of first portions 118 alternating with a plurality of second portions 120 such that the first adhesive layer 110 is patterned. Each second portion 120 of the plurality of second portions 120 is disposed between two adjacent first portions 118. As used herein, the term “patterned” generally refers to a repetitive configuration of the plurality of first portions 118 and the plurality of second portions 120. In some embodiments, the pattern may be regular or irregular. Each first portion 118 includes a thermally expandable adhesive. The thermally expandable adhesive may include the adhesive composition as described above.

[0058] Each second portion 120 is less thermally expandable than each first portion 118. In other words, each second portion 120 may expand less, or does not expand at all, as compared to each first portion 118 during application, curing, and usage of the curable adhesive sheet 102. Lower thermal expansion for each second portion 120 may be attributed to presence of functional fillers 114 that are ineffective for expansion, or absence of functional fillers 114, or even absence of thermally expandable adhesive. In some embodiments, each second portion 120 is pre-cured, such that each second portion 120 is less thermally expandable during use. In some embodiments, a concentration of the functional filler 114 in each first portion 118 is different from a concentration of the functional filler 114 in each second portion 120. This may allow each second portion 120 to be less thermally expandable than each first portion 118.

[0059] Since each second portion 120 is less thermally expandable than each first portion 118, the first adhesive layer 110 includes regions with or without thermal expansion in a pattern. Specifically, the thermal expansion may be reduced in certain defined portions of the first adhesive layer 110, i.e., the plurality of second portions 120, thereby allowing localized gaps between the winding 24 (shown in FIG. 2B) and the curable adhesive sheet 102, such that the coolant may flow therethrough. Further, this may enhance the efficiency and effectiveness of the coolant in cooling components of the electric motor 10 (shown in FIG. 1), such as the stator 20 (shown in FIGS. 1).

[0060] In the illustrated embodiment, the curable adhesive sheet 102 includes the plurality of first portions 118 and the plurality of second portions 120 extending along a width of the curable adhesive sheet 102 in a pattern. In alternative embodiments, the plurality of first portions 118 and the plurality of second portions 120 may extend along a longitudinal length of the curable adhesive sheet 102. In some embodiments, the pattern may be a symmetrical pattern or an asymmetric pattern.

[0061] FIG. 4A is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is not thermally expandable. Further, each second portion 120 of the first adhesive layer 110 is non-expandable. Specifically, each second portion 120 is devoid of any functional filler 114. For example, the thermally expandable particles of each second portion 120 may be functionally destroyed in a pattern, thus destroying their ability to expand, such that an adhesive of each second portion 120 may not expand during the expansion or curing step. Thus, each second portion 120 may not expand upon heating. Varioustechniques may be employed for locally destroying the functionality of the thermally expandable particles. An example of such a technique may be ultrasonic processing whereby ultrasonic energy destroys the functionality of the expandable agent.

[0062] FIG. 4B is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is not thermally expandable. Further, each second portion 120 of the first adhesive layer 110 is non-expandable. Specifically, each second portion 120 of the first adhesive layer 110 is cured prior to thermal activation of the functional fillers (or pre-cured), such that each second portion 120 is not thermally expandable during use. For example, a patterned thermal or photo accelerator or initiator may be utilized for pre-curing each second portion 120 of the first adhesive layer 110. The patterned thermal or photo accelerator may pre-cure each second portion 120 in place, thereby locking the thermally expandable particles in place, such that the thermally expandable particles may not be able to expand or their expansion is diminished due to a high viscosity of the cured adhesive.

[0063] FIG. 5A is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is not thermally expandable. Further, each second portion 120 of the first adhesive layer 110 is a void 136. In other words, each second portion 120 may not include any adhesive. Thus, each second portion 120 may not expand upon application, curing, and usage of the curable adhesive sheet 102.

[0064] Various techniques may be used for generating the plurality of first portions 118 and the plurality of second portions 120. For example, the plurality of first portions 118 and the plurality of second portions 120 may be generated by stripe coating during adhesive coating (down web or cross web), screen printing, flexo-printing, die cut transfer technology, and laser ablation technology. Other suitable manufacturing techniques may also be utilized based on application requirements.

[0065] In some embodiments, the plurality of first portions 118 and the plurality of second portions 120 may be prepared by masking a surface of the electrically insulating substrate 104 and overcoating with the adhesive composition of the first adhesive layer 110. Subsequently, the mask may be removed, leaving the plurality of first portions 118 and the plurality of second portions 120 on the surface of the electrically insulating substrate 104 in a pattern. This effect may also be accomplished by down web or cross web pattern die coating via a pulsed die flow.

[0066] In some embodiments, the curable adhesive sheet 102 further includes a plurality of partial cover portions 124 spaced apart from each other. Each partial cover portion 124 from the plurality of partial cover portions 124 is disposed on and aligned with a corresponding first portion 118 from the plurality of first portions 118 opposite to the electrically insulating substrate 104. In some embodiments, each partial cover portion 124 may include a similar material as that of the cover layer 122 (shown in FIGS. 3B-4B). In someembodiments, each partial cover portion 124 is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

[0067] FIG. 5B is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is not thermally expandable. Further, each second portion 120 of the first adhesive layer 110 is non-expandable. Specifically, each second portion 120 of the first adhesive layer 110 includes a sacrificial filling material 126. In some embodiments, the sacrificial filling material 126 may be removed from the first adhesive layer 110 during usage or application of the curable adhesive sheet 102. After removing the sacrificial filling material 126, each second portion 120 may include a void.

[0068] FIG. 6A is a schematic top view of the portion of the curable adhesive sheet 102, according to an embodiment of the present disclosure. FIG. 6B is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. Referring to FIGS. 6A and 6B, in the illustrated embodiment, each second portion 120 of the first adhesive layer 110 is less thermally expandable than each first portion 118 of the first adhesive layer 110. Further, the second curable adhesive layer 112 is thermally expandable. An adhesive composition of the second curable adhesive layer 112 may be similar to the adhesive composition of the first adhesive layer 110.

[0069] In some embodiments, the second curable adhesive layer 112 may include functional fillers 144, e.g., thermally expandable particles, contained within the second curable adhesive layer 112. In some embodiments, the functional fillers 144 may be similar to the functional fillers 114 contained within the first adhesive layer 110.

[0070] In some embodiments, the second curable adhesive layer 112 includes a plurality of additional first portions 130 alternating with a plurality of additional second portions 132 such that the second curable adhesive layer 112 is patterned. Each additional second portion 132 of the plurality of additional second portions 132 is disposed between two adjacent additional first portions 130 of the plurality of additional first portions 130. Each additional first portion 130 includes an additional thermally expandable adhesive. In some embodiments, the additional thermally expandable adhesive may be similar to the thermally expandable adhesive of each first portion 118 of the first adhesive layer 110. Each additional second portion 132 is less thermally expandable than each additional first portion 130.

[0071] In some embodiments, each additional first portion 130 of the second curable adhesive layer 112 aligns with a corresponding first portion 118 of the first adhesive layer 110 and each additional second portion 132 of the second curable adhesive layer 112 aligns with a corresponding second portion 120 of the first adhesive layer 110. However, in alternative embodiments, each additional first portion 130 and each additional second portion 132 of the second curable adhesive layer 112 may not align with the corresponding first portion 118 and second portion 120, respectively, of the first adhesive layer 110.

[0072] In some embodiments, the curable adhesive sheet 102 further includes an additional cover layer 116 disposed on the second curable adhesive layer 112 opposite to the electrically insulating substrate 104. In some embodiments, the additional cover layer 116 may be similar in material and construction to the cover layer 122. In some embodiments, the additional cover layer 116 is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

[0073] FIG. 7A is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is thermally expandable. Further, each additional second portion 132 of the second curable adhesive layer 112 is non-expandable. Specifically, each additional second portion 132 is devoid of any functional filler 144. For example, the thermally expandable particles of each additional second portion 132 may be destroyed in a pattern, such that an adhesive of each additional second portion 132 may cure during use but does not expand. Thus, each additional second portion 132 may not expand upon heating.

[0074] FIG. 7B is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is thermally expandable. Further, each additional second portion 132 of the second curable adhesive layer 112 is non-expandable. Specifically, each additional second portion 132 of the second curable adhesive layer 112 is pre-cured, such that each additional second portion 132 is not thermally expandable during use. For example, a patterned thermal or photo accelerator may be utilized for precuring each additional second portion 132 of the second curable adhesive layer 112. The patterned thermal or photo accelerator may pre-cure each additional second portion 132 in place, thereby locking the thermally expandable particles in place, such that the thermally expandable particles may not be able to expand much during use.

[0075] FIG. 8 A is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is thermally expandable. Further, each additional second portion 132 of the second curable adhesive layer 112 is non-expandable. Specifically, each additional second portion 132 of the second curable adhesive layer 112 is a void 146. In other words, each additional second portion 132 may not include any adhesive. Thus, each additional second portion 132 may not expand upon application, curing, and usage of the curable adhesive sheet 102.

[0076] The plurality of additional first portions 130 and the plurality of additional second portions 132 may be generated by stripe coating during adhesive coating (down web or cross web), screen printing, flexo-printing, die cut transfer technology, and laser ablation technology. Other suitable manufacturing techniques may also be utilized based on application requirements.

[0077] In some embodiments, the curable adhesive sheet 102 further includes a plurality of additional cover layers 134 spaced apart from each other. Each additional cover layer 134 from the plurality of additional cover layers 134 is disposed on and aligned with a corresponding additional first portion 130 from the plurality of additional first portions 130 opposite to the electrically insulating substrate 104. In some embodiments, each additional cover layer 134 may include a similar material as that of the cover layer 122. In some embodiments, each additional cover layer 134 is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

[0078] FIG. 8B is a schematic side view of the portion of the curable adhesive sheet 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the second curable adhesive layer 112 is thermally expandable. Further, each additional second portion 132 of the second curable adhesive layer 112 is non-expandable. Specifically, each additional second portion 132 of the second curable adhesive layer 112 includes a sacrificial filling material 148. In some embodiments, the sacrificial filling material 148 may be removed from each additional second portion 132 during usage or application of the curable adhesive sheet 102. After removing the sacrificial filling material 148, each additional second portion 132 may include a void. In some embodiments, the sacrificial filling material 148 may be similar to the sacrificial filling material 126 (shown in FIG. 5B).

[0079] Referring to FIGS. 1-8B, the curable adhesive sheet 102 of the present disclosure includes the first adhesive layer 110 having the plurality of first portions 118 alternating with the plurality of second portions 120. Thus, the first adhesive layer 110 is patterned. Further, each second portion 120 may expand less, or does not expand at all, as compared to each first portion 118 during application, curing, and usage of the curable adhesive sheet 102. In some cases, the first adhesive layer 110 may engage with the winding 24 of the electric motor 10 and the second curable adhesive layer 112 may engage with the stator core 22. In some cases, the housing 18 of the electric motor 10 may receive a coolant for cooling components of the electric motor 10, e.g., the stator 20. Since each second portion 120 is less thermally expandable than each first portion 118, the first adhesive layer 110 include regions with or without thermal expansion in a pattern. Specifically, the thermal expansion may be reduced in certain defined portions of the first adhesive layer 110, i.e., the plurality of second portions 120, thereby allowing localized gaps between the winding 24 and the curable adhesive sheet 102. This may allow the coolant to flow through such localized gaps, thereby enhancing an efficiency and an effectiveness of the coolant in cooling the components of the electric motor 10.Examples

[0080] The following methods and examples are offered for illustrative purposes only and is not intended to limit the scope of the disclosure in any way. Indeed, various modifications of the disclosure in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and the following examples and fall within the scope of the appended claims.EXAMPLE 1

[0081] FIG. 9A is a schematic side view of a substrate 202 with a photo-initiator 204 and an adhesive layer 206. The adhesive layer 206 may be similar to the first adhesive layer 110 shown in FIGS. 3 A-5B and 6B- 8B. The photo-initiator 204, i.e., Momentive epoxy photo-initiator (Momentive UV 9380C), was dissolved in methyl ethyl ketone (mek) (3% w / w). The photo-initiator 204 was wiped onto the substrate 202 made of polyethylene naphthalate (PEN) and allowed to dry. The substrate 202 has a thickness of about 75 microns. An adhesive having a composition similar to the adhesive composition of the first adhesive layer 110 was first dissolved in a solvent to 80% solid concentration until it became a paste. The adhesive was then coated onto the substrate 202 to generate the adhesive layer 206. A final uncured thickness of the adhesive layer 206 was approximately 30 microns.

[0082] FIG. 9B is a schematic side view of the substrate 202 upon application of an activation energy 208. Upon generation of the adhesive layer 206, the substrate 200 was exposed to the activation energy 208, i.e., germicidal lights (Ultraviolet-C or UVC) at 41 W / cm2(watt per square centimeter) for 2 minutes. The activation energy 208 may also be obtained from other sources, such as, for example, ultrasonic sources, heat sources, voltage sources, etc. The substrate 202 was removed from the light source 208 and heated to 160°C for 2 minutes. FIG. 9C is a schematic side view of the substrate 200 after heating. A thickness of the expanded adhesive layer 206 over an area with the photo-initiator 204 was 165 microns, while an area without the photo-initiator 204 was about 190 microns.EXAMPLE 2

[0083] Samples of curable adhesive sheets were prepared by first dissolving a curable adhesive having a similar composition as that of the first adhesive layer 110 shown in FIGS. 3A-5B and 6B-8B in a solvent to 80% solid concentration until it became a paste. Subsequently, a surface of a substrate was masked and overcoated with the curable adhesive. The mask was removed, leaving a patterned adhesive layer on the surface of the substrate. This effect may also be accomplished by down web or cross web pattern die coating via a pulsed die flow. The substrate was finally laminated with a nonwoven layer. The resulting method produced a sample with 7 millimeter (mm) wide stripes of the first adhesive layer with an average thickness of 160 microns, separated by 7.5 mm wide stripes where the average adhesive thickness was 0 microns (i.e., no presence of the adhesive).EXAMPLE 3

[0084] Samples of curable adhesive sheets were prepared by first dissolving a curable adhesive having a similar composition as that of the first adhesive layer 110 shown in FIGS. 3A-5B and 6B-8B in a solvent to 80% solid concentration until it became a paste. A stripe pattern was formed in a mesh screen by clogging pores on certain parts of the mesh screen in a striped pattern. The screen was then pressed against a substrate made of 75 microns thick polyethylene naphthalate (PEN). The adhesive was forced through the mesh screen onto the substrate with a scraper, and the mesh screen was then removed. The resulting method produced a sample with 10 mm wide stripes of the first adhesive layer with an average thickness of 185microns, separated by 12.5 mm wide stripes where the average adhesive thickness was 0 microns (i.e., no presence of the adhesive). The substrate was finally laminated with a non-woven layer. This method may be reproduced on-line with rotary screen printing techniques.EXAMPLE 4

[0085] FIG. 10A is a schematic side view of a substrate 302, a non-expandable adhesive layer 310, and a cover layer 314. The non-expandable adhesive layer 310 may be similar to the second curable adhesive layer 112 shown in FIGS. 3 A, 4A-5B and 6A-8B and the cover layer 314 may be similar to the additional cover layer 134 shown in FIGS. 8A and 8B. Samples of curable adhesive sheets were prepared by first dissolving an adhesive having a similar composition as that of the second adhesive layer 112 shown in FIGS. 4A-8B in a solvent to 80% solid concentration until it became a paste. Subsequently, the adhesive was coated on a major surface 304 of the substrate 302 to produce the non-expandable adhesive layer 310. Subsequently, the non-expandable adhesive layer 310 was laminated with the cover layer 314 opposite to the substrate 302.

[0086] FIG. 10B is a schematic side view of a release liner 316, an expandable adhesive layer 320, and another cover layer 322. The expandable adhesive layer 320 may be similar to the first adhesive layer 110 shown in FIGS. 3 A-6A and 7A-8B and the another cover layer 322 may be similar to the cover portion 124 shown in FIGS. 5A and 5B. A curable adhesive having a similar composition as that of the first adhesive layer 110 shown in FIGS. 3 A-5B and 6B-8B is first dissolved in a solvent to 80% solid concentration until it became a paste and then coated on the release liner 316 on a major surface 318 of the release liner 316 to produce the expandable adhesive layer 320. Subsequently, the expandable adhesive layer 320 was laminated with the another cover layer 322 opposite to the release liner 316.

[0087] FIG. 10C is a schematic side view of a process film 324, the expandable adhesive layer 320, and the another cover layer 322. After preparation of the release liner 316, the expandable adhesive layer 320, and the another cover layer 322 shown in FIG. 10B, the expandable adhesive layer 320 and the another cover layer 322 were transferred to the process film 324. The process film 324 may be a low adhesion pressure sensitive adhesive (PSA) tape. Subsequently, the expandable adhesive layer 320 and the another cover layer 322 were kiss cut while disposed on the release liner 316 to form a pattern.

[0088] FIG. 10D is a schematic side view of the substrate 302, the non-expandable adhesive layer 310, the cover layer 314, the expandable adhesive layer 320, and the another cover layer 322. After kiss cutting the expandable adhesive layer 320 and the another cover layer 322, the expandable adhesive layer 320 and the another cover layer 322 were transferred to the substrate 302. Specifically, the expandable adhesive layer 320 was heat laminated to a major surface 306 of the substrate 302, thereby forming a plurality of second portions 324 similar to the plurality of second portions shown in FIG. 5A. This technique may be referred to as “die cut transfer” technology.

[0089] In the present detailed description of the preferred embodiments, reference is made to the accompanying drawings, which illustrate specific embodiments in which the invention may be practiced. The illustrated embodiments are not intended to be exhaustive of all embodiments according to the invention. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[0090] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0091] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including "and / or" unless the content clearly dictates otherwise.

[0092] Spatially related terms, including but not limited to, “proximate,” “distal,” “lower,” “upper,” “beneath,” “below,” “above,” and “on top,” if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of the device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if an object depicted in the figures is turned over or flipped over, portions previously described as below or beneath other elements would then be above or on top of those other elements.

[0093] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

What is claimed is:

1. A curable adhesive sheet comprising: an electrically insulating substrate comprising a first major surface and a second major surface opposite to the first major surface; a first adhesive layer disposed on the first major surface of the electrically insulating substrate, wherein the first adhesive layer is thermally expandable, wherein the first adhesive layer comprises a plurality of first portions alternating with a plurality of second portions such that the first adhesive layer is patterned, wherein each second portion of the plurality of second portions is disposed between two adjacent first portions of the plurality of first portions, wherein each first portion comprises a thermally expandable adhesive, and wherein each second portion is less thermally expandable than each first portion; and a second curable adhesive layer disposed on the second major surface of the electrically insulating substrate.

2. The adhesive sheet of claim 1, wherein each second portion is non-expandable.

3. The adhesive sheet of claim 2, wherein each second portion is a void.

4. The adhesive sheet of claim 3, further comprising a plurality of partial cover portions spaced apart from each other, wherein each partial cover portion from the plurality of partial cover portions is disposed on and aligned with a corresponding first portion from the plurality of first portions opposite to the electrically insulating substrate.

5. The adhesive sheet of claim 4, wherein each partial cover portion is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

6. The adhesive sheet of claim 2, wherein each second portion comprises a sacrificial filling material.

7. The adhesive sheet of claim 2, wherein each second portion is devoid of any functional filler.

8. The adhesive sheet of claim 2, wherein a concentration of a functional filler in each first portion is different from a concentration of the functional filler in each second portion.

9. The adhesive sheet of claim 2, wherein each second portion is pre-cured, such that each second portion is not thermally expandable during use.

10. The adhesive sheet of claim 1, wherein each second portion is pre-cured, such that each second portion is less thermally expandable during use.

11. The adhesive sheet of claim 1, further comprising a cover layer disposed on the first adhesive layer opposite to the electrically insulating substrate.

12. The adhesive sheet of claim 10, wherein the cover layer is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

13. The adhesive sheet of claim 1, wherein the electrically insulating substrate comprises one of a polyethylene naphthalate (PEN) film, a polyester film, a polycarbonate film, a polyimide film, a nylon film, a polyaramid film, a polymethyl methacrylate (PMMA) multilayer film, a polyether ether ketone (PEEK) film, a polyphenylene sulfide (PPS) film, a poly(phthalazinone ether sulfone ketone) film (PPESK), or combinations thereof.

14. The adhesive sheet of claim 1, wherein at least one of the first adhesive layer and the second curable adhesive layer comprises a thermosetting epoxy resin.

15. The adhesive sheet of claim 1, wherein the second curable adhesive layer is not thermally expandable.

16. The adhesive sheet of claim 1, wherein the second curable adhesive layer is thermally expandable.

17. The adhesive sheet of claim 15, wherein the second curable adhesive layer comprises a plurality of additional first portions alternating with a plurality of additional second portions such that the second curable adhesive layer is patterned, wherein each additional second portion of the plurality of additional second portions is disposed between two adjacent additional first portions of the plurality of additional first portions, wherein each additional first portion comprises an additional thermally expandable adhesive, and wherein each additional second portion is less thermally expandable than each additional first portion.

18. The adhesive sheet of claim 16, wherein each additional first portion of the second curable adhesive layer aligns with a corresponding first portion of the first adhesive layer, and wherein each additional second portion of the second curable adhesive layer aligns with a corresponding second portion of the first adhesive layer.

19. The adhesive sheet of claim 16, wherein each additional second portion of the second curable adhesive layer is non-expandable.

20. The adhesive sheet of claim 18, wherein each additional second portion is a void.

21. The adhesive sheet of claim 18, wherein each additional second portion comprises a sacrificial filling material.

22. The adhesive sheet of claim 18, wherein each additional second portion is devoid of any functional filler.

23. The adhesive sheet of claim 18, wherein each additional second portion is pre-cured, such that each additional second portion is not thermally expandable during use.

24. The adhesive sheet of claim 16, further comprising a plurality of additional cover layers spaced apart from each other, wherein each additional cover layer from the plurality of additional cover layers is disposed on and aligned with a corresponding additional first portion from the plurality of additional first portions opposite to the electrically insulating substrate.

25. The adhesive sheet of claim 4, wherein each additional cover layer is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

26. The adhesive sheet of claim 1, further comprising an additional cover layer disposed on the second curable adhesive layer opposite to the electrically insulating substrate.

27. The adhesive sheet of claim 23, wherein the additional cover layer is made of a non-woven fabric or a paper based on natural fibers, chemical fibers, or a mixture thereof.

28. The adhesive sheet of claim 1, wherein the curable adhesive sheet is an electric motor slot liner.

29. An electric motor comprising: a stator core comprising at least one slot; a winding at least partially received within the at least one slot; and an insulative slot liner comprising the curable adhesive sheet as claimed in any one of the claims 1 to 27 arranged between the stator core and the winding.

30. The electric motor of claim 29, wherein a curable adhesive composition in the curable adhesive sheet is cured.

Images