ThreeBond Technical News
Issued January 1, 201279

Heat-Curable Expanding Adhesive Sheet
Introduction

Since our founding, ThreeBond has been hard at work developing a wide variety of liquid adhesives
and sealants. Currently, we are utilizing the liquid materials we have cultivated so far and applying
them to new technology to continue the development of functional sheets. This approach is about
more than simply creating a sheet out of liquid materials—it is about developing a more practicaladhesive by giving sheets additional functionality while utilizing the best features of both liquidand sheet adhesives. As our first step in this endeavor, we are pleased to introduce the ThreeBond
1652 heat-curable expanding adhesive sheet, an adhesive fixing sheet for motor-driven automobilemotors.
Hereafter, ThreeBond is abbreviated as TB.

Table of Contents

Introduction.................................................1
1. Background.............................................2
2. Development Background of the HeatCurable Expanding Adhesive Sheet........2
3. Expanding Adhesive Sheet TB1652........3
3-1 Expanding Adhesive Sheet
Features...........................................3
3-2 Properties.........................................43-3 Basic Characteristics.......................43-4 Curing Time......................................53-5 Relationship Between Clearance andInterlocking Bonding Strength.........5
4. Adhesive Characteristics.........................54-1 Interlocking Bonding Strength
Comparison......................................54-2 Measurement of Tensile Shear Bond
Strength During Curing....................64-3 Adhesion to Plastic..........................6
5. Durability.................................................6
5-1 Automatic Transmission Oil
Resistance........................................65-2 Adhesive Strength in Heat...............75-3 Adhesive Strength in Cold...............7
6. Transferring the Sheet.............................7
Closing........................................................81

1.

BackgroundIn recent years, conversion to petroleum substitutes andreduction of carbon dioxide (CO2) emissions have beenrequired of the automobile industry in the effort to prevent
global warming. This has spurred remarkable technologicalinnovations in hybrid, electric and fuel cell vehicles. And,as more electronics are added to vehicles, preparations
are underway to change the vehicle drive system from angasoline/diesel powered engine to a hybrid or full electrical
powered motor.
Conventionally, there are many kinds of automobile motors,
and a variety of adhesives as well as liquids. For thesematerials such as epoxy and liquid adhesives have been
the main adhesives. However, the structure of an electrical
motor drive system is different from a conventional motor,
so it is difficult to adapt conventional liquid adhesives forsuch use. For this reason, we have had to develop materials
that meet this different requirements.

2.

Development Background of the HeatCurable Expanding Adhesive Sheet

Permanent
MagnetLaminated Silicon
Steel PlateLiquid AdhesiveFig. 2 Liquid Adhesive applied to a LaminatedSilicon Steel Plate (Slot)
Decreased Adhesive AmountLiquid Adhesive Leakage

For the IPM (Interior Permanent Magnet) motors adopted
for many motor-driven vehicles, adhesive is used to affix
the laminated silicon steel plate and permanent magnet(neodymium magnet) that make up the rotor.
Laminated Silicon
Steel Plate

Fig. 3 Liquid Adhesive Leaking from a LaminatedSilicon Steel Plate (Slot)

PermanentMagnet

Fig. 1 IPM Motor Rotor

However, it is difficult to control the amount of liquidadhesive applied when bonding the laminated siliconsteel plate and permanent magnet. The laminated siliconsteel plate is a caulked structure of overlapping plates sothere are gaps between the steel plates. When it hardens,
capillarity causes the filled in liquid adhesive to penetrate
between these layers of laminated silicon steel plates. Thismeans that the required amount of liquid adhesive does notremain to the surface of the permanent magnet, and appliedadhesive coat is uneven (Fig. 2, 3).

2To solve this issue, we have approached it using a sheetadhesive. Sheet adhesives are solid at room temperature,so they can be cut to the needed size and applied on thesurface of the permanent magnet, keeping the thickness
and area of the adhesive constant. This makes it possible togreatly improve issues of coating unevenness common inliquid adhesives. However, in order to insert the permanent
magnet into the slot in the laminated silicon steel plate, thedimensions (volume/thickness) of the adhesive layer mustbe smaller than the slot. Sheet adhesive dimensions alter
less than liquid adhesive, with thickness and shape changing
very little. As a result, conventional sheet type adhesives do
not make sufficient contact with the laminated silicon steel
plate, so sufficient adhesive strength cannot be maintained(Fig. 4).

Expanding
Adhesive Sheet(Pre-Curing)

Permanent Magnet

Sheet AdhesiveFig. 6 Permanent Magnet Applied with theExpanding Adhesive Sheet and Inserted
into the Laminated Silicon Steel Plate

Lack of Contact
Laminated Silicon
Steel Plate

ExpandingAdhesive Sheet(Post-Curing)

Fig. 4 Attaching Laminated Silicon Steel Platewith Sheet AdhesiveFig. 7 Heat is Applied, and the Sheet Expands toBond and Fix the Laminated Silicon Steel
Plate and the Permanent Magnet

In order to fill the gaps between the laminated silicon steel
plate and the permanent magnet after insertion, we combined
the sheet adhesive with capsules that expand when heat isapplied. The capsules expand just before the curing reaction
to increase the thickness of the sheet adhesive, whichchanges adhesive volume (Fig. 5). Thanks to this expansion
function, we succeeded in creating a heat- curable expanding
adhesive sheet. This new addition to the market has addedfunctionality that allows it to fill in gaps as it is applied andfixed (Fig. 6, 7) This heat-curable expanding adhesive sheet(hereafter abbreviated to expanding adhesive sheet) is mainlycomposed of a heat and chemical-resistant epoxy resin withstrong adhesion to multiple materials (Table 1, 2).

Fig. 8 Mock Workpiece Bonded with theExpanding Adhesive Sheet

3.

Fig. 5 Left: Expanding Capsules Spread
Throughout the Sheet
Right: Capsules After the Sheet hasExpanded

Expanding Adhesive Sheet TB1652

3-1 Expanding Adhesive Sheet Features• At room temperature it is a sheet-shaped solid forexcellent handling and workability.
• Sheet-type adhesive can be cut to the needed
dimensions prior to mounting.
• Can be inserted into gaps and affixed to simplify thebonding process.
• Heat and chemical-resistant to ensure incredible
reliability.

33-2 Properties

Table 1 TB1652 Properties
UnitTB1652

Testing Method

Appearance-White3TS-201-92

Sheet Film Thicknessμm

40

3TS-261-01

Heat Loss%

2.0 or less

3TS-216-01

Remark(s)80°C x 30min.

Wound CoreBacking Film
Adhesive Layer

Separator Film

Unwinding Direction
Fig. 9 Structure

3-3 Basic Characteristics
Unit

Table 2 Basic TB1652 Characteristics
TB1652

Testing Method

11Remarks
Fe/FeTensile Shear Bond
Strength

MPa

Interlocking Bond
StrengthMPa393TS-305-01

Stainless steel 304 pin, collar (adhesive area
φ6×15mm, clearance 1/10mm)

Glass Transition
Temperature°C

165

3TS-504-01

DMA (Dynamic Mechanical Analysis) E” peak
top, frequency: 1Hz

Storage Modulus

Pa

2.8×108

3TS-504-01

DMA E’ 25°C when the expanding adhesive
sheet is expanded by 4 times, frequency: 1Hz

Surface ResistivityΩ

3.0×1016

3TS-402-01

Volume Resistivity

Ω·m

4.8×1015

3TS-401-01

Expansion ScaleTimes

43TS-261-01

2.43TS-301-21

3.0

PPS/PPS (Contains 40% glass powder)
PBT/PBT (Contains 30% glass powder)

Expansion scale when in an open state and thetemperature is rising at 5°C/min. to cure.

*Curing conditions: 150°C×30min.
*Tensile shear adhesive strength test piece: t2.0×25×100mm, clearance 50μm, sheet film thickness 40μm

43-4 Curing TimeA temperature of 150°C or more is required to cure theexpanding adhesive sheet. Curing speeds at various
temperatures were calculated based on DSC (differentialscanning calorimetry) thermal analyzer measurement
results (Fig. 10). (The standard curing conditions are
150°C×30min. for the expanding adhesive sheet)

Compression load
PinCollar

100

Before Breaking

Fig. 12 Interlocking Bonding Strength
Measurement Method

Reaction Rate 50%

Measurement of breaking load by applying compression load
to pins

4.

0140

160

180200220

Temperature (°C)

Fig. 10 DSC Reaction Rate Measurement

3-5 Relationship Between Clearance andInterlocking Bonding Strength
As the clearance of the expanding adhesive sheet widens
with respect to the sheet film thickness, the scale ofexpansion increases so material and interlocking adhesivestrength both decrease (Fig. 11)
10010180120160200240280

320360400

Clearance (µm)

Fig. 11 Relationship Between TB1652 Clearance
and Interlocking Bonding Strength*Measurement method: 3TS-305-01*Curing conditions: 150°C×30min.
*Test piece: Stainless steel 304 pin, collar (adhesive area
φ6×15mm, sheet film thickness 40μm)

Adhesive Characteristics

4-1 Interlocking Bonding StrengthComparison
We compared the interlocking bonding strength of the
expanding adhesive sheet and typical liquid epoxy resins.
The results of this comparison indicated that heat-curable
one-part epoxy resin demonstrated the highest adhesivestrength. However, when applying heat to cure, the epoxy
resin runs, making the adhesive area unstable which causes
the adhesive strength to vary with each measurement. On
the other hand, two-part epoxy resin can be cured at room
temperature, which makes the adhesive area stable, but low
in strength. Though the maximum adhesive strength of the
expanding adhesive sheet is inferior to that of a one-partepoxy resin, stability in the gaps in the adhesive surface
increases overall adhesive strength and ensures stability(Fig. 13). (For the measurement results, the test number n=3,
each result is indicated.)
Interlocking Bonding Strength (MPa)1Interlocking Bonding Strength (MPa)Time (min)Reaction Rate 99%
10

After Breaking

60504030
20
100
TB1652

One-Part Epoxy

Two-Part Epoxy

Fig. 13 Interlocking Bonding Strength Comparison*Measurement method: 3TS-305-01*Test piece: Stainless steel 304 pin, collar (adhesive areaφ6×15mm, clearance 1/10mm, sheet filmthickness 40μm)

5Tensile Shear Bond Strength (MPa)

4-2 Measurement of Tensile Shear BondStrength During Curing
The expanding adhesive sheet has excellent heat resistance.
Even in high temperature environments such as 150°C, it
still maintains approximately 70% adhesive strength atroom temperature (Fig. 14)
15sheets. It is considered that this reduction in the modulus ofelasticity is the result of sheet volume expansion.
As a result it has improved adhesiveness in PPS, PPT andother engineering plastics used for automobile parts, which
we expect will be utilized in future application (Fig. 15,Table 3).
Table 3 Improvement in Plastic Adhesion due to
Sheet Expansion
Unit

Typical Epoxy
Sheet

Expanded Epoxy
Sheet

PPS/PPS

MPa

0.8

2.4

PBT/PBT

MPa

1.1

3.0

10

50050

100

150200*Measurement method: 3TS-301-21*Curing conditions: 150°C×30min.
*Test piece: Typical epoxy sheet t2.0×25×100mm, noclearance, sheet film thickness 40μm
Expanded epoxy sheet t2.0×25×100mm,
clearance 50μm, sheet film thickness 40μm

250Temperature (°C)

Fig. 14 Changes in Tensile Shear Bond Strengthat Various Ambient Temperatures*Measurement method: 3TS-301-21*Curing conditions: 150°C×30min.
*Test piece: Fe/Fe t2.0×25×100mm, clearance 50μm, sheet
film thickness 40μm

4-3 Adhesion to Plastic
Though the expanding adhesive sheet has high heat
resistance and a high Tg (glass transition temperature),
modulus of elasticity is low compared to typical epoxy

5.

Durability

5-1 Automatic Transmission Oil Resistance
We measured the tensile shear bond strength of theexpanding adhesive sheet after immersion at 150°C inautomatic transmission oil. The expanding adhesive sheet
is highly resistant to automatic transmission oil, so swellingand other considerable deterioration is not evident. There
was no reduction in tensile shear bond strength when
immersed for 1,000 hours (Fig. 16).

Storage Modulus (Pa)

5.0E+09

−40°C

25°C

100°C

150°C

Sheet expansion: Comparative storage modulus at various temperature ranges

1.0E+05

−40°C

25°C

100°C

150°C

Typical Epoxy Sheet

3.8E+9Pa

3.2E+9Pa

2.3E+9Pa

8.5E+8Pa

Expanded Epoxy Sheet

3.5E+8Pa

2.8E+8Pa

1.8E+8Pa

5.2E+7Pa0.0

50.0

100.0Temp °C

150.0

Fig. 15 DMA Storage Modulus Measurement

6*DMA E’, frequency: 1Hz200.0

181616Tensile Shear Bond Strength (MPa)Tensile Shear Bond Strength (MPa)18141210864200200

400

600

800

1000

1210864201200

0Time (h)200400600

800

1000

1200

Time (h)Fig. 16 Changes in Expanding Adhesive
Sheet Tensile Shear Bonding Strength
After Immersion in 150°C AutomaticTransmission Oil

Fig. 18 Changes in Tensile Shear Bonding
Strength over Time at -40°C*Measurement method: 3TS-301-21*Curing conditions: 150°C×30min.
*Test piece: Fe/Fe t2.0×25×100mm, clearance 50μm, sheet
film thickness 40μm

5-2 Adhesive Strength in Heat
We measured changes in the tensile shear bonding strength
in a 150°C environment. There was no reduction in tensile
shear bond strength after 1,000 hours (Fig. 17).
18Tensile Shear Bond Strength (MPa)1416*Measurement method: 3TS-301-21*Curing conditions: 150°C×30min.
*Test piece: Fe/Fe 2.0×25×100mm, clearance 50μm, sheet
film thickness 40μm

6.

Transferring the SheetThis section details the process for transferring the expanding
adhesive sheet to the permanent magnet. Use a double-sided
heating press (Fig. 19) to transfer the expanding adhesive
sheet to both sides of the permanent magnet. Next, remove
the backing film and transfer the expanding adhesive sheet
to the surface of the permanent magnet to complete theprocess (Fig. 20, 21).

141210864
200200

400

600

800

1000

1200

Time (h)Fig. 17 Changes in Tensile Shear Bond Strength
over Time at 150°C*Measurement method: 3TS-301-21*Curing conditions: 150°C×30min.
*Test piece: Fe/Fe 2.0×25×100mm, clearance 50μm, sheet
film thickness 40μm

5-3 Adhesive Strength in Cold
We measured changes in the tensile shear bonding strength
in a -40°C environment. There was no reduction in tensile
shear bonding strength after 1,000 hours (Fig. 18).

Fig. 19 Double-Sided Heating Press

7

Transferring the Expanding
Adhesive Sheet
Place the expanding adhesive sheet on bothsides of the permanent magnet.

Use a double-sided heating press (Fig. 19) totransfer the expanding adhesive sheet to bothsides of the permanent magnet.
Temperature: 60 to 80°C
Pressure:
50 to 100kPaTime:
Under a minute

Remove the backing film from the expanding
adhesive sheet.

Heating Press

Fig. 20 The Transfer Process

Detached Backing Film

Permanent Magnet

Expanding Adhesive Sheet(Post-Transfer)

Expanding Adhesive Sheet(Pre-Transfer)

Fig. 21 Transferring the Expanding Adhesive Sheet

Closing

As the use of electronics in the automobile industry continue to increase, we expect there will be more and more opportunities
to explore functional parts utilizing new materials that had never before been adopted for automobiles. This, of course, willlead to the necessity of developing new adhesives and sealants for these new materials and applications. So we at ThreeBondare developing functional sheet materials for our customers’ changing needs. As the first step in this endeavor, we are pleased
to introduce our heat-curable expanding adhesive sheet, an adhesive for motor-driven automobile motors. Moving forward, we
will continue to introduce new materials for a constantly evolving automobile industry that incorporate ThreeBond’s proprietary
technologies and unique ideas.
ThreeBond Co., Ltd. R&D Headquarters
Development Division, Functional Materials Department
Yoshihide Arai
Hiroshi KimuraThreeBond Co., Ltd.
84-3-3 Minamiosawa, Hachioji,
Tokyo 192-0398
Tel: +81-42-670-5333