ThreeBond Technical News
Issued January 1, 2020

95

Epoxy Resins for Vehicle Electrical Devices
Introduction

The situation with regards to vehicles has changed significantly in recent years, from weight
reduction and electrification due to tightening CO2 emission regulations to the adoption of advanced
driving support systems to improve safety and automatic driving. The structure and mechanismsof vehicles are also changing.
Up to now, various epoxy resins have been used for electrical components in vehicles such as ECUs,
inverters, converters and motors. Use of epoxy resins in vehicles is expected to increase further
in future as the number of electrical components increases with the electrification of vehicles, theintroduction of automatic driving, the use of alternatives to welding in order to reduce weight andthe installation of new components due to structural changes.
Although epoxy resins are used for a variety of areas and applications in vehicles, the required
properties vary depending on the location and application.
For this reason, we have been developing products that deliver the required characteristics. This
article describes the features and concepts behind these products.

Table of Contents
Introduction.................................................1
1. Required Characteristics........................2
2. Epoxy Resin with High Heat Resistance....2
2-1. ThreeBond 2237J.............................2
2-2. Characteristic Values.......................2
3. Epoxy Resin with Low Linear Expansion
Coefficient................................................3
3-1. TB2235L...........................................4
3-2. Characteristic Values.......................4

4. Epoxy Resin with High Heat Dissipation....5
4-1. TB2270J...........................................5
4-2. Characteristic Values.......................5
5. Flame-Retardant Epoxy Resin................6
5-1. TB2272F...........................................6
5-2. Characteristic Values.......................6
Closing........................................................81

1.

Required Characteristics

Although the glass transition temperature of typical epoxy
resins is between 100 and 120°C, the environmental
temperature in some areas in which epoxy resins are usedin vehicles exceeds 120°C. If the bonded area is exposed totemperatures above the glass transition temperature of theadhesive, peeling and other defects may occur.

Epoxy resins are used for a variety of areas in vehicles andthe required properties vary depending on the environment
surrounding each location.

ThreeBond 2237J was developed to prevent this decrease inbond strength in high temperature environments and has ahigh glass transition temperature in order to maintain a highelastic modulus and high bond strength in high temperatureenvironments.

2-1. ThreeBond 2237J
ThreeBond 2237J (hereafter ThreeBond is abbreviated toTB) is a single-component heat-curing epoxy resin with thefollowing characteristics.
1. High glass transition temperature
2. Excellent tensile shear bond strength and peeladhesive strength

Fig. 1 Components in which Epoxy Resins are
Used

When used near the engine or in positions exposed to hightemperatures created by moving parts, high heat resistanceis required to ensure that adhesive strength is maintainedeven at high temperatures.
In areas that undergo large changes in temperature, resinwith a low linear expansion coefficient is required.

2-2. Characteristic Values
The characteristic values of TB2237J are shown in Table
1 and the bond strength to various materials is shown in
Table 2.

High heat dissipation is needed in areas where generated
heat must be dissipated.
In addition, flame-retardant material may be required insome areas to prevent the spread of any fire that occurs.

As shown in Table 2, TB2237J exhibits high bond strength
to a wide range of materials.

The following sections describe products with thesecharacteristics.

2.

TB2237J has a high glass transition temperature of 150°C
and can maintain bond strength in high temperatureenvironments, as shown in Fig. 2. The material also exhibitshigh heat resistance and no decrease in bond strength isobserved after 2,500 hours at 150°C (Fig. 3).

Epoxy Resin with High Heat ResistanceThe bond strength of adhesives changes drastically at theglass transition temperature, usually dropping significantly
at temperatures above the glass transition temperature.

Table 1 TB2237J Characteristic Values
Test item

Unit

Characteristic value

Testing method

Remark(s)Appearance

—

White

3TS-2100-020—

Viscosity

Pa·s

115

3TS-2F00-007

Shear velocity: 5.0 s-1

Cure shrinkage%

1.6

3TS-2600-001—

Tensile shear bond strength

MPa

26

3TS-4100-011

Fe/Fe (SPCC-SD)

T type peeling adhesive strength

kN/m

3.6

3TS-4130-021

Fe/Fe (SPCC-SD)

Glass transition temperature

°C

150

Linear expansion coefficient (α1)
Linear expansion coefficient (α 2)Storage elastic modulus (E’)

25°C
200°C

Peak loss elastic modulus (E”)
Peak loss tangent (tanδ)Curing conditions

2ppm/°C
GPa
°C
—

30

TMA
3TS-4740-001

121

20 to 60°C
260 to 300°C

8.3
0.25
177

3TS-4730-001

DMA 1Hz——

186
120℃ × 60min

Table 2 Bond Strength of TB2237J by Material
Material

26

Fe/Fe (SPCC-SB)

23

SUS/SUS (SUS304)

24
15

PPS/PPS

5.3

Epoxy glass/epoxy glass

13

Fe/Fe (SPCC-SD)

3.6

kN/m

Al/Al (A1050P)

Testing method

3TS-4100-011

18

Al/Al (A1050P)

25

3TS-4130-021

2.4

40

Tensile shear bond strength (MPa)Tensile shear bond strength (MPa)MPa

Cu/Cu (1100P)

T type peeling adhesive strength

20

15

10

5

0

50

100

150

200

250

300

Measurement temperature (°C)

Fig. 2 TB2237J Lap Shear Strength Test

Curing conditions: 60min at 120°C
Test piece material: SPCC-SD/SPCC-SD

3.

Character

Fe/Fe (SPCC-SD)

Tensile shear bond strength

0

Unit

Epoxy Resin with Low Linear
Expansion Coefficient

The volume of substances expands as the temperature rises.
The rate of this expansion per degree change in temperature
is called the linear expansion coefficient. The linear
expansion coefficient of epoxy resin is relatively low amongorganic materials, but higher than that of metals (Table 3).
The greater the difference in linear expansion coefficient
between the adherend and the adhesive, the greater the

8

30

6

20

4

10

2
Tensile shear bond strength
T type peeling adhesive strength

0

0

500

1000

1500

0
2500

2000

T type peeling adhesive strength (kN/m)

Test item

Time (h)Fig. 3 Heat Resistance of TB2237J

Curing conditions: 60min at 120°C
Environmental conditions: 150°C
Measurement conditions: 3TS-4100-011, 3TS-4130-021
Test piece material: SPCC-SD/SPCC-SD

stress due to expansion and contraction during heat cycles.
This repeated stress causes defects such as cracking andpeeling.
Some parts of vehicles undergo large differences intemperature between when driving and when stationary andmaterials with a low linear expansion coefficient that have asmall difference in volume during expansion and shrinkage
are required. For this reason, TB2235L was developed withconsideration given to heat cycle resistance.

Table 3 Linear Expansion Coefficient by Material
Linear expansion
coefficient

Material

Metal Inorganic
material

Linear expansion
coefficient

Material

Aluminum

23

Epoxy

45 to 65

Iron

12

Acrylic

50 to 90

Magnesium alloy

27

Polypropylene

58 to 100

Stainless steel

17

Polyethylene

120 to 140

Hard glass

9

Polycarbonate

66

Organic material33-1. TB2235L
TB2235L is a single-component heat-curing epoxy resinwith the following characteristics.
1. Low linear expansion coefficient
2. High glass transition temperature

Tensile shear bond strength (MPa)

25

20
15

3-2. Characteristic Values
The characteristic values of TB2235L are shown in Table 4.
Tensile shear bond strength when heated, heat resistance andheat cycles are shown in Fig. 4, Fig. 5 and Fig. 6, respectively.

10

In addition to having a low linear expansion coefficient,
TB2235L has a high glass transition temperature. This meansthat is has high bond strength in high temperature environments(Fig. 4) and excellent heat resistance at 150°C (Fig. 5).

5
0

25

50

75

100

125

150

Temperature (°C)

Fig. 4 TB2235L Lap Shear Strength Test

Curing conditions: 30min at 140°C
Measurement conditions: 3TS-4100-011
Test piece material: SUS/SUS (SUS304)

With regards to heat cycles, Fig. 6 shows that the epoxy resin
has excellent heat cycle resistance, showing no significant
decrease from the initial bond strength even after 2,000 cycles.
3030

Tensile shear bond strength (MPa)Tensile shear bond strength (MPa)

0

25

25

20

20
15
10
5
0

0

500

1000

1500

15
10
–40125°C–40150°C

5
0

0

500

1000

1500

2000

Number of cycles (cyc)2000

Fig. 6 TB2235L Heat Cycles

Time (h)Curing conditions: 30min at 140°C
1 cycle: (30min at -40°C and 30min at 125°C)(30min at -40°C and 30min at 150°C)
Measurement conditions: 3TS-4100-011
Test piece material: SUS/SUS (SUS304)

Fig. 5 Heat Resistance of TB2235L

Curing conditions: 30min at 140°C
Environmental conditions: 150°C
Measurement conditions: 3TS-4100-011
Test piece material: SUS/SUS (SUS304)

Table 4 TB2235L Characteristic Values
Test item

Unit

Characteristic value

Testing method

Remark(s)Appearance

—

Black

3TS-2100-020—

Viscosity

Pa·s

80

3TS-2F00-007

Shear velocity: 10.0 s-1

Cure shrinkage%

1.7

3TS-2600-001—

Tensile shear bond strength

MPa

23

3TS-4100-011

Fe/Fe (SPCC-SD)

T type peeling adhesive strength

kN/m

2.0

3TS-4130-021

Fe/Fe (SPCC-SD)

Glass transition temperature

°C

149

Linear expansion coefficient (α1)
Linear expansion coefficient (α 2)Storage elastic modulus (E’)

25°C

Peak loss elastic modulus (E”)
Peak loss tangent (tanδ)Curing conditions

4ppm/°C
GPa
°C
—

16

TMA
3TS-4740-001

24

20 to 40°C
160 to 200°C

10154

3TS-4730-001

DMA 1Hz——

170
140℃ × 30min

4.

Epoxy Resin with High Heat Dissipation

1. High heat conductivity
2. Low linear expansion coefficient and low cureshrinkage

The amount of heat generated by electrical components
has increased in recent years with the miniaturization andincrease in output of electrical components. Because thisheat generation affects the operation and performance of
mounted parts, the growing need for adhesives with heatdissipation properties needs to be addressed. Our silicone
rubber adhesive dissipates heat. However, as silicone heatradiating agents have low adhesive strength, there is demandfor heat radiating agents that combine high bond strengthwith heat resistance. We have developed the heat radiating
epoxy resin TB2270J to meet this demand.

4-2. Characteristic Values
The characteristic values of TB2270J are shown in Table 5.

4-1. TB2270J
TB2270J is a single-component heat-curing epoxy resinwith the following characteristics.

As shown in Fig. 8, the extremely low linear expansion
coefficient also provides excellent heat cycle resistance, withno significant decrease from the initial bond strength evenafter 2,000 cycles.

3. Excellent durability and curability at low temperatures

TB2270J is a thermally conductive material with a high storage
elastic modulus and bond strength. It also has excellent heat
resistance and no decrease in bond strength is observed evenafter 2,000 hours in a 125°C environment (Fig. 7).

Table 5 TB2270J Characteristic Values
Test item

Unit

Characteristic values

Testing method

Remark(s)Appearance

—

White

3TS-2100-020—

Viscosity

Pa·s

150

3TS-2F00-007

Shear velocity: 1.0 s-1

Cure shrinkage%

1.4

3TS-2600-001—

Tensile shear bond strengthMPa

93TS-4100-011

Fe/Fe (SPCC-SD)

Glass transition temperature

°C

117

Linear expansion coefficient (α1)
Storage elastic modulus (E’)

11ppm/°C

Linear expansion coefficient (α 2)
25°C

118

DMA 1HzHeat conductivity

W/m·K

4.2

3TS-4750-002—

Curing conditions—

100℃ × 40min

—

—

12

Tensile shear bond strength (MPa)Tensile shear bond strength (MPa)

3TS-4730-001

134

12

10

10
8
6
4
2
0

20 to 40°C
160 to 180°C

32°C

Peak loss tangent (tanδ)3TS-4740-001

58

GPa

Peak loss elastic modulus (E”)

TMA

0

500

1000

1500

Time (h)Fig. 7 Heat Resistance of TB2270J

Curing conditions: 40min at 100°C
Environmental conditions: 125°C
Measurement conditions: 3TS-4100-011
Test piece material: Al/Al (A1050P)

2000

8
6
4
2
0

0

500

1000

1500

2000

Number of cycles (cyc)Fig. 8 TB2270J Heat Cycles

Curing conditions: 40min at 100°C
One cycle: (30min at -40°C and 30min at 125°C)
Measurement conditions: 3TS-4100-011
Test piece material: Al/Al (A1050P)

5

50

Measurement method

45

TB2270J was applied at a thickness of 0.1mm between two
aluminum rods with a length of 50mm and diameter of φ20.
A Peltier element was attached to either end, with the upper
element set to 45°C to provide a temperature gradient (Fig. 9).
Results
A thermographic image is shown in Fig. 10. The sample
with TB2270J applied to a thickness of 0.1mm is shown on
the left. A sample with two aluminum rods in direct contact
without the application of a heat radiating agent is shownon the right. A graph of the temperature at the center line isshown in Fig. 11.
These results show that heat transfer does not occur at thejoint between the rods if TB2270J is not applied and that
there is almost no temperature difference in the joint between
the rods (the section where TB2270J is applied) when
TB2270J, which dissipates heat, is applied. This means thatthe heat is being transferred effectively.
Peltier element (heat source)

Aluminum rod

Thermographic camera

Evaluation
sample(TB2270J)

Peltier element (heat source)

Fig. 9 Thermographic Observation Model

Temperature (°C)

Figures 10 and 11 show the results of thermal conductivity
evaluation of TB2270J carried out using thermography.

40

35
30
25
20

With TB2270J
Without TB2270J
0

20

40

60

80

100

Distance (mm)Fig. 11 Aluminum Rod Temperature Distribution

5.

Flame-Retardant Epoxy Resin

The number of parts that can cause ignition in vehicles
is increasing with fires caused by heat generated fromelectronic components installed in vehicles, which havebecome more numerous, miniaturized and lightweight,
and the introduction of powertrains including high-voltage
and high-current batteries and motors in electric cars andother next-generation automobiles. When there is a sourceof ignition, flammable materials catch fire, which causes
the fire to spread. For this reason, materials used near areas
with potential sources of ignition must have flame-retardant
properties. TB2272F was developed in response to the fact
that, as adhesives are flammable, an epoxy resin with flameretardant properties is required in these areas.

5-1. TB2272F
TB2272F is a single-component heat-curable epoxy
compound resin that is certified to UL94-V-0 flammability
standard using the vertical flammability test. This makes
it suitable for bonding and sealing near parts that are apotential source of heat.
Fig. 12 shows an image of the flame from a gas burner being
applied to a material cured with TB2272F.
Whereas typical epoxy resin, which does not have flameretardant properties, spreads fire immediately after flame
is applied, the fire-retardant TB2272F does not easily catch
fire even when a flame is applied and any flames disappears
immediately.

With
TB2270J

Without
TB2270J

Fig. 10 Thermographic Observation

6

5-2. Characteristic Values
The characteristic values of TB2272F are shown in Table 6
and the results of the vertical flammability test are shownin table 7.

Vertical flammability test conditions• Sample conditioning: Left for at least 48 hours in an
atmosphere with a temperature of 23°C and relative
humidity of 50%• Testing method and evaluation method: According to3TS-2700-002• Sample size: 125 mm × 13 mm × 3 mm

• Testing environment: Temperature of 25°C andrelative humidity of 50%• Flame size: 20mm blue flame[Typical epoxy resin][TB2272F]

Fire spreads immediately
after the burner flame is turned on.

When flame is applied, the cured material does
not catch fire, or the fire disappears within
10 seconds of the removal of the burner.

Fig. 12 Flammability Comparison
Table 6 TB2272F Characteristic Values
Test item

Unit

TB2272F

Testing method

Remark(s)Appearance

—

Black

3TS-2100-002—

Viscosity

Pa·s

75

3TS-2F00-007

Shear velocity: 5.0 s-1

Tensile shear bond strength

MPa

21

3TS-4100-011

Fe/Fe (SPCC-SD)

Glass transition temperature

°C

117

Linear expansion coefficient (α1)
Linear expansion coefficient (α 2)Storage elastic modulus (E’)

25°C

Peak loss elastic modulus (E”)
Peak loss tangent (tanδ)ppm/°C
GPa
°C

29

TMA
3TS-4740-001

0 to 40°C

119

160 to 200°C

12

DMA 25℃

118

3TS-4730-001

1Hz

147

Non-flammable grade—

UL94V-0 certified——

Curing conditions—

100℃ × 60min——

Table 7 V-0 Flammability Standard Criteria for UL94 Vertical Flammability Test and Results for TB2272F
V-0 standard

Measured value for
TB2272F

t1 or t2 for each sample≤10 seconds≤4 seconds

Total burning time after 5 flame exposures (including second flame contact)≤50 seconds≤10 seconds

Total time of t2 and t3≤30 seconds≤8 seconds

Combustion or sparking reaching up to the clamp

No

No

Ignition of absorbent cotton by falling objects

No

No

Evaluation item

t1: burning time after first flame exposure, t2: burning time after second flame exposure, t3: afterglow time after second flame exposure

7

Closing

This article introduces products with high heat resistance, low linear expansion coefficient, heat dissipation and flame retardancy,
some of the key properties required for epoxy resins used in vehicle electrical devices.
Demand for adhesives for vehicles is expected to grow as vehicles continue to evolve. As the range of applications expands, itwill be necessary to develop products that suit the needs of each application.
ThreeBond will continue to contribute to the industry by focusing on product and technology development in line with market
trends.
<References>
1) Habara, Takeo. Global Trend of Electrified Vehicle and Our Country’s Action, Journal of Society of Automotive
Engineers of Japan, Vol. 72 (2), p.13-17, Society of Automotive Engineers of Japan (2018)
2) Ashida, Tadashi. Applications of Epoxy Adhesives, Epoxy Resin Review, Vol. 4, Advanced Edition II, p. 88-107, The
Japan Society of Epoxy Resin Technology (2003)

ThreeBond Co., Ltd. R&D Headquarters
2nd Development Division, 1st Electric Section
Kana Yasunaga
Yoshitomo Ono

ThreeBond Co., Ltd.
8

4-3-3 Minamiosawa, Hachioji,
Tokyo 192-0398
Tel: +81-42-670-5333