WO2013013128A2

WO2013013128A2 - Thermally expanding adhesive sheet and manufacturing method thereof

Info

Publication number: WO2013013128A2
Application number: PCT/US2012/047549
Authority: WO
Inventors: Takahiro Kasahara
Original assignee: 3M Innovative Properties Company
Priority date: 2011-07-20
Filing date: 2012-07-20
Publication date: 2013-01-24
Also published as: JP2013023559A; WO2013013128A3; JP6030288B2

Abstract

There is provided a curable thermally expanding adhesive sheet includes a substrate with a first surface and a second surface facing the first surface and having a linking opening, and a curable thermally expanding epoxy adhesive formed on the first surface of the substrate. The curable thermally expanding epoxy adhesive passes through the linking opening of the substrate during heating, and forms a second adhesive layer on the second surface of the substrate.

Description

THERMALLY EXPANDING ADHESIVE SHEET AND

MANUFACTURING METHOD THEREOF

TECHNICAL FIELD

5 The present invention relates to an adhesive sheet for filling a gap between two elements while adhering the elements together, and also relates to a manufacturing method thereof.

BACKGROUND

Epoxy adhesive has high bonding strength and excellent heat resistance, and therefore is widely used for structural adhesion. Various epoxy adhesives with high glass transition temperature (Tg) and/or

[ 0 low coefficient of thermal expansion (CTE) have been developed. Liquid epoxy adhesive can be

manufactured using simple manufacturing equipment, and has many applications. However, liquid epoxy adhesive may have problems with workability at the time of use, such as requiring precise viscosity adjustments and coating, and the like.

For example, an IPM (interior permanent magnet) motor has a rotor core, and a magnet is

[ 5 inserted into slots in the rotor core. A schematic cross section view of an IPM motor is illustrated in

FIG. 1. In FIG. 1 , an IPM motor 100 has a rotor core 120 and a coil 130 provided around the perimeter thereof, and magnets 1 10 are embedded in the rotor core 120. The magnets are generally attached to the rotor core using a liquid silicone adhesive or liquid epoxy adhesive. When magnets are attached to the rotor core using this type of liquid adhesive, magnets coated with the liquid adhesive are inserted into the

10 rotor core slots. However, the size of the slots in the rotor core is essentially the same as the magnet size (the clearance between the inner wall of the rotor core slots and the magnet is merely 80 to 150 μηι), and therefore most of the liquid adhesive coated on the magnet does not enter the inside of the slots, and is discarded without contributing to the adhesion between the magnet and the rotor core.

If the insertion angle of the magnet is not appropriate, a sufficient amount of liquid adhesive for

15 bonding the magnet and the rotor core with sufficient strength might not remain on a surface or portion of the magnet inserted into the slot. Furthermore, in high temperature environments that are used for curing the liquid rotor core slot and the magnet will further decrease. As a result, a portion of the uncured liquid adhesive will be discharged out of the slot, and the amount of adhesive in the slot may be diminished. Therefore, achieving a bond between the magnet and the rotor core with high reliability has conventionally been difficult.

Japanese Pat. Appln. No. H5- 179213 to Kobayashi et al. describes an expanding adhesive containing an uncured adhesive in a liquid or viscous semisolid form, and an expanding material.

Japanese Pat. Appn. No. 2007-106963 to Kimura et al. describes a heating expandable sheet type adhesive composition wherein film is formed from a component containing (a) a film forming resin that is solid at ambient temperature, (b) an epoxy resin that is liquid or semisolid at ambient temperature, (c) a latent curing agent, (d) thermally expanding capsules, and (e) lubricating fine particle powder.

U.S. Pat. Appln. No. 2004-0266899 to Muenz et al. describes expandable epoxy resin-based systems modified with thermoplastic polymers .

U.S. Pat. Appln. No. 2006-0188726 to Muenz et al. describes heat curable thermally expandable composition with high degree of expansion.

WO Pat. Appln. No. 2004-60984 to Eagle describes heat activated epoxy adhesive .

WO Pat. Appln. No. 2010-014565 to Golden et al. describes toughened expandable epoxy resins.

There exists a need for an adhesive sheet with excellent handling properties that can fill in a gap between two elements and bond the elements together with high reliability, and to provide a

manufacturing method thereof.

SUMMARY OF THE INVENTION

The present disclosure provides an adhesive sheet with excellent handling properties that can fill in a gap between two elements such as a magnet and a rotor core of an IPM motor and bond the elements together with high reliability, and also provides a manufacturing method thereof. One aspect of the present disclosure provides a thermally expanding adhesive sheet having a first adhesive layer containing a curable thermally expanding epoxy adhesive formed on a first surface of a substrate having a first surface and a second surface opposite the first surface, the substrate having a linking opening, wherein the curable thermally expanding epoxy adhesive passes through the linking 5 opening of the substrate when heated and forms a second adhesive layer on the second surface of the substrate.

Another aspect of the present disclosure provides a manufacturing method for a curable thermally expanding adhesive sheet, including the steps of preparing a substrate with a first surface and a second surface opposite the first surface, the substrate having a linking opening, applying to the first

[ 0 surface of the substrate a curable thermally expanding epoxy resin composition containing (a) a curable epoxy resin, (b) a latent hardening agent, (c) thermally expanding capsules, and (d) solvent, and forming a first adhesive layer, wherein the epoxy resin is soluble in the solvent, and the latent hardening agent and the thermally expanding capsules are insoluble in the solvent.

Another aspect of the present disclosure is a method of bonding a first element and a second

[ 5 element, including the steps of placing the curable thermally expanding adhesive sheet between the first element and the second element, thermally curing the thermally expanding adhesive sheet, and thereby filling in a gap between the first element and the second element while bonding the first element and the second element.

Another aspect of the present disclosure provides an article containing a first element, second 10 element, and the thermally cured thermally expanding adhesive sheet, wherein the gap between the first element and the second element is filled in and the first element and the second element are bonded together by the thermally cured thermally expanding adhesive sheet.

The curable thermally expanding adhesive sheet of the present disclosure does not have an adhesive layer on the second surface of the substrate during the stage prior to heating. Therefore, the 15 element on which the adhesive sheet is applied with a first adhesive layer formed on the first surface of the substrate can be easily handled. For example, a magnet with the curable thermally expanding adhesive sheet of the present disclosure attached can smoothly be inserted into the narrow slots of the rotor core of an IPM motor. At this time, the surface on the opposite side as the adhesive surface of the adhesive sheet, or in other words the surface that does not have an adhesive layer functions as a slip surface when the magnet is inserted into the rotor core.

Furthermore, the first adhesive layer of the curable thermally expanding adhesive sheet of the present disclosure contains curable thermally expanding epoxy adhesive, and this thermally expanding epoxy adhesive passes through the linking opening of the substrate during melting and expanding during heating, and forms a second adhesive layer on the second surface of the substrate. Therefore, when the curable thermally expanding adhesive sheet of the present disclosure is used, the gap between the two elements is filled in by the epoxy adhesive while bonding by thermally curing, while at the same time the two elements can be bonded by the adhesive sheet provided therebetween. For example, if the curable thermally expanding adhesive sheet of the present disclosure is applied to a magnet, the magnet and the rotor core of the IPM motor can be bonded with high reliability by inserting the magnet into the slots of the rotor core of the IPM motor and then heating. Furthermore, unlike the case where a liquid adhesive is used, the epoxy adhesive included in the adhesive sheet can be effectively used for bonding between two elements.

Note that the above descriptions should not be construed to be a disclosure of all of the embodiments and benefits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross section view of an IPM motor.

FIG. 2 is a cross section view of a curable thermally expanding adhesive sheet according to an embodiment of the present disclosure.

FIG. 3 is a cross section view illustrating the condition where the curable thermally expanding epoxy adhesive has expanded when the thermally expanding adhesive sheet of an embodiment of the present disclosure is heated.

FIG. 4 is a schematic view illustrating a condition where the curable thermally expanding adhesive sheet according to an embodiment the present disclosure is applied to a magnet, and the magnet is inserted into the slot of the rotor core.

FIG. 5 is a cross section view of a test sample fabricated for an overlap shear strength (OLSS) test of an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A detailed explanation for the purpose of illustrating representative embodiments of the present invention is given below, but these embodiments should not be construed to limit the present invention.

A cross section view of a curable thermally expanding adhesive sheet according to an embodiment of the present disclosure is illustrated in FIG. 2. A curable thermally expanding adhesive sheet 10 has a substrate 20 having a first surface and a second surface opposite the first surface and having a linking opening such as an air hole, gap, perforation, or the like, and a first adhesive layer 30 containing a curable thermally expanding epoxy adhesive formed on the first surface of the substrate. The condition where the curable thermally expanding epoxy adhesive expands when the thermally expanding adhesive sheet according to an embodiment of the present disclosure is heated is illustrated in FIG. 3. The curable thermally expanding epoxy adhesive of the first adhesive layer 30 melts and expands when heated, passes through the linking opening such as an air hole, gap, perforation, or the like, and reaches the second surface of the substrate 20 (middle level of FIG. 3). As a result, a second adhesive layer 40 is formed either contiguously or non-contiguously on the second surface of the substrate 20 (bottom level of FIG. 3). This curable thermally expanding adhesive sheet has a function of being temporarily attached to an object by only the first surface having the first adhesive layer in the stage prior to heating. The function of being temporarily attached refers to a function where the curable thermally expanding adhesive sheet can be temporarily attached to an object for bonding using ambient temperature contact adhesion or contact adhesion provided by a process of heating for a short period of time such as is found with a hot melt adhesive. Using this function of the first layer, the adhesive sheet can be applied to a first of the two elements that are to be bonded. After the second element is brought close to the adhesive sheet applied to the surface of the first element and oriented (the second element is not required to be in contact with the adhesive sheet applied surface), the adhesive sheet is heated to a 5 predetermined temperature, at least one of the dimensions, selected from the length, width, or thickness of the adhesive sheet will increase because of the expansion of the curable thermally expanding epoxy adhesive. As a result, a gap between the two elements can be filled in, and the two elements can be bonded together by the adhesive layer formed on both the first surface and the second surface of the substrate.

[ 0 The substrate with a linking opening can be a variety of conventionally known substrates such as paper, nonwoven material, porous films containing a polymer such as polytetrafluoroethylene or the like, metal mesh, or punched film. The linking opening refers to one or a plurality of openings that spatially connect the first surface and the second surface of the substrate contiguously. The size of the linking opening can be determined such that the latent curing agents described below can pass through.

[ 5 If the size of the linking opening is so small that the latent curing agents cannot pass through, the curable epoxy resin included in the curable thermally expanding epoxy adhesive and the latent curing agent will separate, and there may be problems with improper curing. For example, if the linking opening is round or almost round, a diameter of approximately 1 μηι or more, and approximately 10 μηι or less is advantageous. If there is a desire to provide slip properties to the element with the adhesive sheet

10 applied, the use of a substrate with low friction force on the surface, such as a nonwoven material or a porous polytetrafluoroethylene film for example is advantageous. The use of a nonwoven material as a substrate with low friction force on the surface is particularly advantageous from the perspective of low- cost. The friction force of the surface can also be reduced by performing a surface treatment on the substrate using a slip agent.

15 The thickness of the substrate can be a value such that the curable thermally expanding epoxy adhesive will pass through the linking opening of the substrate during heating and reach the second surface of the substrate, and when manufacturing the adhesive sheet, the curable thermally expanding epoxy adhesive will not penetrate to the second surface of the substrate. The thickness of the substrate can be for example approximately 1 μηι or more, approximately 5 μηι or more, or approximately 10 μηι or more, and approximately 5 mm or less, approximately 2 mm or less, or approximately 1 mm or less. In applications where the adhesive sheet is inserted into a narrow gap, such as for bonding the magnet and the rotor core of an IPM motor, the thickness can be for example approximately 1 μηι or more, or approximately 5 μηι or more, and approximately 200 μηι or less, or approximately 100 μηι or less. If the nonwoven material is used as the substrate, the basis weight of the nonwoven material can be approximately 2 g/m² or more , or approximately 4 g/m² or more, or approximately 100 g/m² or less, or approximately 200 g/m² or less.

The first adhesive layer formed on the first surface of the substrate contains a curable thermally expanding epoxy adhesive. The first adhesive layer provides the temporary attaching function to the first surface of an object as described above. The curable thermally expanding epoxy adhesive can include (a) an curable epoxy resin, (b) a latent curing agent, and (c) a thermally expanding capsule. The latent curing agent cures the epoxy adhesive using heat, and can increase the adhesive force of the adhesive layer. The heat expanding capsule promotes expansion of the epoxy adhesive melted by heating. The thickness of the first adhesive layer can be for example approximately 1 μηι or more, approximately 5 μηι or more, or approximately 10 μηι or more, approximately 5 mm or less,

approximately 2 mm or less, or approximately 1 mm or less. In applications where the adhesive sheet is inserted into a narrow gap, such as for bonding the magnet and the rotor core of an IPM motor, the thickness can be for example approximately 1 μηι or more, or approximately 5 μηι or more, and approximately 200 μηι or less, or approximately 100 μηι or less.

The physical properties of the epoxy resin used, such as fluidity, plasticity, softening point, melted viscosity, glass transition temperature (Tg), storage modulus, and the like are thought to be closely related to the functions of the curable thermally expanding adhesive sheet of the present disclosure, namely both the temporary fastening function of the first adhesive layer prior to heating and the function of forming the second adhesive layer during heating. For example, a softening point of the curable epoxy resin, an activation temperature of the latent curing agent to be described later, and an expansion

5 starting temperature of the thermally expanding capsule to be described later are all tightly related.

More specifically, the softening point of the curable epoxy resin is preferably not greater than the activation temperature of the latent curing agent and not greater than the expansion start temperature of the thermally expanding capsules, in order to effectively demonstrate the functions of the curable thermally expanding adhesive sheet of the present disclosure. If the softening point of the curable epoxy

[ 0 resin is not greater than the activation temperature of the latent curing agent, when a melted coating or solution coating is included in the manufacturing process of the heat expanding adhesive sheet, the curable epoxy resin can be prevented from gelling in the coating process and the associated drying process. If the softening point of the curable epoxy resin is not greater than the expansion start temperature of the thermally expanding capsules, the resin will exhibit fluidity at the temperature where

[ 5 the thermally expanding capsules expand, so the thermally expanding epoxy adhesive can be made to expand sufficiently. The softening point of the curable epoxy resin is measured using a spherical annulus softening point test method specified in JIS K 2207.

A plurality of epoxy resins can be blended in order to adjust the softening point of the curable epoxy resin. A curable epoxy resin with a relatively low softening point or a liquid epoxy resin can

10 provide to the epoxy resin either ambient temperature contact adhesion or contact adhesion that is

achieved by a short heating process, and can increase the fluidity during heating. A semisolid epoxy resin or an epoxy resin with a relatively high softening point can maintain the shape of the first adhesive layer at ambient temperature, and can suppress or prevent the thermally expanding epoxy adhesive from excessively penetrating into the substrate before heating. By using a blend of these curable epoxy

15 resins, the physical properties of the epoxy resin can easily and precisely be adjusted. The epoxy resins that can be used include bisphenol epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, and the like; epoxy resins with a fatty acid backbone such as hexanediol glycidyl ether and the like; glycidyl amine epoxy resins such as triglycidyl aminophenol and the like; novolac epoxy resins such as phenol novolac epoxy resin, creosol novolac epoxy resin, and the like;

5 brominated epoxy resins; cyclic epoxy resins; and blends thereof, but there is no restriction to these.

The epoxy resin can also contain a phenoxy resin (polyhydroxy polyether synthesized from a bisphenol and epichlorohydrin) as a thermoplastic component. If a phenoxy resin is added, the film forming properties of the thermally expanding epoxy adhesive can be enhanced.

The average molecular weight of the curable epoxy resin can generally be approximately 100 or

[ 0 higher, or approximately 300 or higher, and approximately 60,000 or less, or approximately 100,000 or less, calculated against a polystyrene standard. The epoxy equivalent weight of the epoxy resin can generally be approximately 50 g/eq or higher, or approximately 80 g/eq or higher, and approximately 30,000 g/eq or lower or approximately 50,000 g/eq or lower. The curable epoxy resin is a basic component of the curable thermal expanding epoxy adhesive. Therefore the amount of the other are

[ 5 described based on 100 mass parts of the thermal epoxy resin.

The latent curing agent does not have activity for curing the epoxy resin at ambient temperature, but is activated by heating, and is a curing agent that can cure the epoxy adhesive. For example, a fine particle latent curing agent that is conventionally known is insoluble in epoxy resins at ambient temperature, but can become soluble when heated, and can cure the epoxy resin. The latent curing agent

10 can be a conventionally known latent curing agent, such as dicyandiamide and derivatives thereof,

hydrazide compounds, trifluorinated boron-amine complexes, imidazole compounds that form fine particles at ambient temperature, the reaction products (amine-epoxy adducts) of amine compounds and epoxy compounds, and the reaction products (urea adducts) of an amine compound and an isocyanate compound or urea compounds, and the like. A combination of two or more latent curing agents can also

15 be used. The amount of latent curing agent that can be used can be approximately 0.5 mass parts or higher, approximately 1 mass parts or higher, or approximately 2 mass parts or higher, and approximately 30 mass parts or lower, approximately 20 mass parts or lower, and approximately 10 mass parts or lower, for 100 mass parts of the curable epoxy resin. A combination of dicyandiamide adducts (for example product name "PN-50", manufactured by Ajinomoto Fine Techno Co., Ltd.: Kawasaki-

5 shi,Kanagawa,Japan) can be advantageously used in order to have a favorable activation temperature and favorable storage modulus at room temperature.

The activation temperature of the latent curing agent is preferably selected such that the softening point of the curable epoxy resin is not greater than the activation temperature of the latent curing agent, as mentioned above. Herein the activation temperature of the latent curing agent refers to

[ 0 the temperature measured by DSC (different scanning calorimeter /measuring conditions mixture of the epoxy resin that is used and the latent curing agent is used as a test sample, rising rate of temperature is 10°C/minute from room temperature.) The activation temperature of the latent curing agent can be selected from a range of approximately 80°C or higher, or approximately 120°C or higher, and approximately 160°C or lower or approximately 180°C or lower.

[ 5 The curable thermally expanding capsule is a microcapsule with a thermally expanding agent encapsulated in a shell, where a thermoplastic resin with gas barrier properties is used as the shell.

When the thermally expanding capsule is heated, the thermoplastic resin of the shell will soften, the volume of the thermally expanding agent will increase, and thereby the capsule will expand. A substance with a low boiling point is used as the heat expanding agent, and the vaporization of the low

10 boiling point substance is used to expand the capsule. The expansion start temperature of the thermally expanding capsule is preferably lower than the activation temperature of the latent curing agent.

Thereby, curing the epoxy resin prior to the epoxy resin expanding can more effectively prevented or controlled. Furthermore, as described above, the expansion start temperature of the thermally expanding capsule is preferably selected such that the softening point of the curable epoxy resin is not greater than

15 the expansion start temperature of the thermally expanding capsule. Herein, the expansion start temperature of the thermally expanding capsule is the temperature where a volume change occurs in the thermally expanding capsule. The expansion start temperature of the thermally expanding capsule can be selected from a range for example of approximately 70°C or higher, or approximately 100°C or higher, and approximately 180°C or lower, or approximately 200°C or lower.

The amount of thermally expanding capsules and the volumetric expansion factor can be appropriately selected based on the expansion factor required of the adhesive sheet and the strength and adhesive force required of the cured adhesive layer. For example, the amount of thermally expanding capsules used can be approximately 0.1 mass parts or more, approximately 0.5 mass parts or more, or approximately 1 mass part or more, and approximately 50 mass parts or less, approximately 30 mass parts or less, or approximately 20 mass parts or less, for 100 mass parts of the curable thermally expanding epoxy adhesive. The volumetric expansion factor of the thermally expanding capsule can be for example approximately 2 times or higher, or approximately 5 times or higher, and approximately 100 times or lower, or approximately 50 times or lower.

The curable thermally expanding epoxy adhesive can further contain as optional components antioxidants such as a phenol antioxidants or sulfur antioxidants, a toughening agent such as a core/shell type toughning agent, a silane coupling agent such as epoxy modified alkoxy silane, a thixotropic agent such as fumed silica, and a heat conductive filler such as boron nitride, and the like.

The thickness of the curable thermally expanding adhesive sheet containing a substrate and the first adhesive layer can be for example approximately 1 μηι or more, approximately 5 μηι or more, or approximately 10 μηι or more, and approximately 5 mm or less, approximately 2 mm or less, or approximately 1 mm or less. In applications where the adhesive sheet is inserted into a narrow gap, such as for bonding the magnet and the rotor core of an IPM motor, the thickness can be for example approximately 1 μηι or more, or approximately 5 μηι or more, and approximately 200 μηι or less, or approximately 100 μηι or less. The thermally expanding sheet can also have a liner on the first adhesive layer. The thermally expanding adhesive sheet of the present disclosure can be manufactured by applying the curable thermally expanding epoxy adhesive composition containing the curable epoxy resin, latent curing agent, thermally expanding capsules, and optional components as necessary onto the first surface of the substrate to form the first adhesive layer. The curable thermally expanding epoxy

5 adhesive composition can be applied to the substrate by a conventionally known method such as melt extrusion or coating such as bar coating, roller coating, and the like. If the melted viscosity of the curable epoxy resin is low, a solvent- free melted coating method can also be used. It is also possible to form the first adhesive layer by applying the curable thermally expanding epoxy adhesive composition onto a liner, and then laminating the substrate thereon in order to transfer the first adhesive layer onto the

[ 0 first surface of the substrate.

If a thin first adhesive layer or a first adhesive layer with uniform thickness is required, the viscosity of the composition is preferably adjusted by adding a solvent to the curable thermally expanding epoxy adhesive composition, applying the composition onto the first surface of the substrate or a liner using a solution coating method, and then forming the first adhesive layer by drying as necessary. In

[ 5 this case, the curable epoxy resin is preferably soluble in the solvent that is used, and the latent curing agent and the heat expanding capsules are preferably insoluble in order to manufacture an adhesive sheet with excellent storage stability. Examples of this type of solvent include esters such as ethyl acetate, butyl acetate, and the like.

The application properties of the curable thermally expanding epoxy adhesive composition can

10 also be improved by using a thixotropic agent such as fumed silica or the like either in place of the

solvent or together with the solvent. Furthermore, by using a thixotropic agent, the curable thermally expanding epoxy adhesive can be prevented or controlled from passing through the linking opening, for example air hole, gap, perforation, or the like, in the substrate when storing the adhesive sheet.

The curable thermally expanding adhesive sheet of the present disclosure can be used in a

15 variety of double-sided adhesive applications where a gap between two elements must be filled in. For example, as illustrated in FIG. 4, an adhesive sheet 10 is applied onto a magnet 1 10 such that the first adhesive layer of the curable thermally expanding adhesive sheet 10 is in contact with the magnet 110, the magnet is inserted into a slot 140 of a rotor core 120 of an IPM motor, and then the magnet 1 10 can bonded to the rotor core 120 by heating for 10 minutes to two hours at 120 to 180°C.

Examples

With the present embodiment, the materials shown in the following Table 1 were used.

Table 1

Overlap Shear Strength iOLSS Test

The cross-section of a test piece fabricated for the overlap shear strength (OLSS) test is illustrated in FIG. 5. The thermally expanding adhesive sheet 10 was placed inside a rectangular solid space demarcated by a spacer 60 and two SPCC-SB steel plates 50 surface treated by wiping with methylethyl ketone (MEK), such that the first adhesive layer 30 was contacting one steel plate. The dimensions of the steel plate were a length of 50 mm, width of 25 mm, and a thickness of 1.6 mm, and the adhesive sheet was a rectangle 12.5 mm x 25 mm. The thickness of the spacer was twice that of the adhesive sheet (100 μηι), or three times the thickness of the adhesive sheet (150 μηι). Next, the epoxy adhesive of the adhesive sheet was melted, expanded, and cured by heating for 30 minutes at 160°C, to fabricate a test piece for the OLSS test. The tensile shear strength when the two steel plates of the test piece were pulled in mutually opposing directions at a rate of 5 mm/minute at 25°C was used as the OLSS (MPa).

Fabricating the thermally expanding adhesive sheet

The curable thermally expanding epoxy adhesive composition containing the components shown in the following Table 2 was applied onto a liner (SLB-50WD) using a bar coater, and then dried for 3 minutes at 65°C and then for 3 minutes at 80°C. The thickness of the dried adhesive layer was 30 μηι. Next, the nonwoven material was overlaid onto the adhesive layer that was formed on the liner. In this manner, the curable thermally expanding adhesive sheet with a thickness of 50 μηι was fabricated.

The results are shown in the following Table 2. Table 2

1) spacer thickness 100 μηι

2) spacer thickness 150 μηι

3) All amounts given are in mass parts.

LIST OF REFERENCE NUMBERS

10 Thermally expanding adhesive sheet

20 Substrate

30 First adhesive layer

40 Second adhesive layer

50 Steel plate

60 Spacer

100 IPM motor

1 10 Magnet

120 Rotor core

130 Coil

140 Slot

Claims

What is claimed is:

1. A curable thermally expanding adhesive sheet, comprising:

a substrate having a first surface and a second surface opposite the first surface, and having a linking opening; and

a first adhesive layer comprising a curable thermally expanding epoxy adhesive formed on the first surface of the substrate; wherein

the curable thermally expanding epoxy adhesive passes through the linking opening of the substrate during heating and forms a second adhesive layer on the second surface of the substrate.

2. The curable thermally expanding adhesive sheet according to claim 1, wherein the curable thermally expanding epoxy adhesive comprises:

(a) a curable epoxy resin,

(b) a latent curing agent, and

(c) thermally expanding capsules.

3. The curable thermally expanding adhesive sheet according to claim 1 or 2, wherein a softening point of the epoxy resin is not greater than an activation temperature of the latent curing agent, and the softening point of the epoxy resin not greater than an expansion start temperature of the thermally expanding capsules.

4. The curable thermally expanding adhesive sheet according to any one of claims 1 through 3, wherein the substrate is a nonwoven material.

5. A manufacturing method for a curable thermally expanding adhesive sheet, comprising: preparing a substrate with a first surface and a second surface facing the first surface and having a linking opening, and forming a first adhesive layer by applying a curable thermally expanding epoxy adhesive composition comprising (a) a curable epoxy resin, (b) a latent curing agent, (c) thermally expanding capsules, and (d) a solvent; wherein the epoxy resin is soluble in the solvent, and the latent curing agent and the thermally expanding capsules are insoluble in the solvent.

6. A method of bonding a first element and a second element, comprising: disposing a curable thermally expanding adhesive sheet described in any one of claims 1 through 4 between the first element and the second element; and thermally curing the thermally expanding adhesive sheet so as to fill in a gap between the first element and the second element while bonding the first element and the second element together.

7. An article, comprising: a first element, a second element, and a thermally cured thermally expanded adhesive sheet described in any one of claims 1 through 4, wherein

a gap between the first element and the second element is filled and the first element and the second element are bonded together by the thermally cured thermally expanding adhesive sheet.