Three Bond Technical News
Issued January 1, 2003

60

New Series of Fuel Cell Sealing Compounds – ThreeBond 1152/1153
Introduction
Major topics about automotive industry these days include reduction in total emission of CO2 as an all-out
incentive to arrest global warming, development of alternative energy sources as countermeasures against the
depletion of petroleum resources, and controlling regulations to check air pollution becoming increasingly
intensified in urban areas. The requirements to meet the situation are the utilization of alternative energy sources,
efforts for energy saving and to obtain higher energy efficiency, and the materialization of low emission vehicles(automobile engines).
Fuel cell is attracting much attention as a promising new energy source as it can provide high energy
efficiency and is ecofriendly as well. In particular, polymer electrolyte fuel cells are hopefully expected as a new
power source for the next-generation vehicles as these cells can work at relatively low temperatures and also
permit to materialize downsized cars with higher power because of their high current density.
Convinced of great potential of the polymer electrolyte fuel cell as a new vital power source for the
next-generation vehicles, at Three Bond we have been focusing our efforts on the research and development ofmaterials that can perfectly seal hydrogen, which is the fuel for these cells, and the establishment of their sealing
methods.
The performance characteristics and features of fuel cell sealing compounds ThreeBond 1152 and 1153(“TB1152/1153”) are described below.

Contents
Introduction....................................................................1
1. The Principle of Fuel Cell and Its Classification........2
2. Construction of Fuel Cell (PEFC)..............................2
3. Required Performance Characteristicsof Fuel Cell Sealing Compound .................................2

4. Leak Mechanism and Comparison of Gaskets ....... 4
5. Features of TB1152/1153 ....................................... 5
6. Epilogue ................................................................. 8

1

1. The Principle of Fuel Cell and Its Classification
Fuel cell battery is a new system to generate electric
power by means of the chemical reaction of oxygen (O2)to hydrogen (H2) that is obtained by reforming gasoline,
natural gases or the like and is used as main fuel (see Fig.
1). As compared to the existing internal combustion
engines such as gasoline and diesel engines, this new
system can provide a higher generating efficiency that
ranges between 30% and 60%. Besides, it practicallyemits no CO2 and other exhaust gases, drawing therefore
muchattentionasanenvironment-friendly,
next-generation power generating system.
The fuel cells currently in course of development
can be classified into the following groups according to
the type of electrolyte to be used: phosphonic acid fuelcell (PAFC), molten carbonate fuel cell (MCFC), solidoxide fuel cell (SOFC), and polymer electrolyte fuel cell
(PEFC), as shown in Table 1 below. Of these,development competition is heating up especially withthe polymer electrolyte type (PEFC) for automotive
application, home use and as portable power source. Thisis because the PEFC type can be smaller and lighter thanothers are, in addition that it can work at relatively low
temperatures within a range between 70°C and 100°C.

2. Construction of Fuel Cell (PEFC)
A polymer electrolyte fuel cell battery is a stack ofvarious cells. Each stacked cell is comprised of amembrane and electrode assembly (MEA), which
consists of an electrolytic membrane carrying platinum
catalysts on both sides, sandwiched between a fuelelectrode plate and an air electrode plate, two separators
having reaction gas feed channels, and the respective
sealing compound layers. (See Fig. 2.)
Hydrogen (H2) and oxygen (O2) are supplied to thisstack from outside to induce a series of reactions reverse
to electrolysis so that current is produced in the external
circuit. These reactions can be expressed by thefollowing formulae:

Table 1

Electrolytic membrane
Working temperature range
Fuel
Generating efficiency
Characteristics

In general terms, a d.c. voltage of around 0.7 voltscan be obtained per cell. So energetic efforts are being
concentrated on developing a stack that can generate
several kW to 200 kW using about 100 fuel cells.

3. Required Performance Characteristics of Fuel
Cell Sealing Compound
As described above, the electromotive force of afuel cell is obtained by means of the chemical reaction
between oxygen (O2) and hydrogen (H2), which is thereaction gas, supplied externally. Since hydrogen (H2),particularly when used as fuel gas, is colorless, odorless,flammable gas with small molecular weight, it can easilyleak even from a very fine clearance and is readily
ignitable even with a very small spark in a wide range of
mixing. Because of these characteristics of the hydrogen(H2) as fuel gas, a sealant that can provide almost perfectgas barrier is required between cells.

Classification of Fuel Cells(MCFC)(SOFC)

Phosphonic Acid Fuel Cell

Molten Carbonate Fuel Cell

Solid Oxide Fuel Cell

Phosphate water solution

Li-Na carbonate

Zirconia ceramic(PEFC)Polymer Electrolyte Fuel
Cell
Polymeric membrane

200˚C

650~700˚C

900~1000˚C

70~100˚C

Reformed hydrogen (natural gas, etc.)

Natural gas, LP gas

Natural gas, LP gas

Pure hydrogen, refomed hydrogen35~45%

45~60%

45~65%

30~40%

Works at relatively low
temperatures.
decentralized powersource2

Fuel plate:
H2→2H++2eAir plate:
1/2O2+2H++2e-→H2O
Total reaction: H2+1/2O2→H2O(PAFC)

Cogeneration;
Main applications

Fig. 1 The principle of fuel cell

Provides high generating efficiency. Provides high generating efficiency. Works at low temperatures; downsizing possible.
Substitutes for large-scale thermal power plants;Substitutes for medium-scale thermal power plants; Automotive power source; home cogeneration;cogenerationcogeneration

Portable power sourceAn ionic-conductive polymer membrane (cationexchange membrane) is used as electrolyte in a polymer
electrolyte fuel cell. This membrane has a chemical
structure as shown in Fig. 3: it consists of the principal
chain of fluorocarbon resin with the side chain of
sulfonic acid radicals (SO3-) that allows addition of
protons (H+).
This
polymericmembrane
becomes
proton-conductive only after it absorbs water, permitting
connection between sulfonic acid radicals. Because ofthis fact, it is necessary to humidify the reaction gas sothat the membrane’s conductivity of protons can be
maintained. For this reason a polymer electrolyte fuelcell must be operated at around 100˚C, a temperaturelevel that can keep the membrane wet. The inside of thecell, on the other hand, is exposed to strong acid (pH 1~2)
by the influence of the side-chain sulfonic acid radicals.
The sealant or sealing compound for a polymer
electrolyte fuel cell must therefore own a low moisturepermeability to prevent leakage of water vapor required
for working of the membrane. Additionally, thischaracteristic must be combined with acid resistance,
moisture resistance and heat resistance in relation to theabove-mentioned working conditions.
Also, the less the ionic elution (especially, heavy
metal ions), the better the sealing compound. This isbecause ions eluted from sealing compound attack the
aforementioned polymer membrane’s sulfonic acidradicals, adversely affecting its proton-conductivity.
Secondly, the eluted ions deactivate the platinum
catalysts provided on the membrane which function tooxidize hydrogen and reduce it to oxygen. Both of theseionic actions could decrease the electromotive force ofeach of the cells composing the whole fuel cell system(battery), leading to a functional deterioration of thewhole system. A sealing compound allowing the least
possible ion elution is therefore desired.

Fig. 3 Chemical structure offluorocarbon ion exchange membrane

To obtain direct current voltage from eachcomponent cell, electrical insulation must be provided
between its separators. It is further desirable that theseseparators be made of some rubber elastic material sothat they can absorb shocks and vibrations, considering
applications of the fuel cell (and consequently, its sealing
compound) to vehicles and portable batteries.
Summarizing the above, the essential characteristics
required for a fuel cell sealing compound can be
described as follows:

Fig. 2

Construction of a fuel cell (PEFC)

3

* High level of gas barrier capability… For sealingof hydrogen (H2) and oxygen (O2) gases.
* Low moisture permeability… To let the polymer
membrane work in saturated vapor and keep theinside of the cell wet.
* Acid resistance… To protect the inside of the cellfrom exposure to strong acid, which occurs when
the polymer membrane functions in saturated vapor.
* Moisture resistance… Because the inside of thecell is saturated with vapor while the polymer
membrane is functioning.
* Heat resistance… Because of the working
conditions of the polymer membrane.
* Low ion elution… To maintain the polymer
membrane’s proton-conductivity and also keep theplatinum catalysts provided on the membrane
active.
* Electrical insulation… To prevent short circuit
between cells.
* Rubber elastic body… To absorb vibrations andimpacts.
* Others … Resistance to coolant, and methanol
resistance (this in anticipation of a modified
methanol or direct methanol fuel cell -DMFC-).

4. Leak Mechanism and Comparison of Gaskets
According to the definition by the JIS (JapaneseIndustrial Standard), a gasket is “any of such objects
that is used to prevent leakage of internal fluid byinserting it between contact surfaces of pipes or
equipment devices or by bolting or tightening it byother methods.” There are three types of leakage (seeFig. 4):(i) Leakage along contact surface … Fluid leaks
from between gasket and flange faces.
(ii) Osmotic leakage (In-layer leakage) … Fluid
leaks through the gasket.
(iii) Breakdown leakage (Burst leakage) … Fluid
leakage occurs due to the burst of the gasket.
In terms of material, gaskets can be classified into
two: solid and liquid gaskets.
The sealing performance of the solid type gasket
is mainly discussed based on the compression righting
moment (restoring force) of the gasket itself whensubjected to a clamping force, and the principal
concern is the level of its set. Leakage along contact
surface also is an issue of vital importance to be taken
into consideration for this type of gasket as its close
contact with the joint surfaces plays a part in its
compression set. The advantages of a solid gasket
include easy removal and availability of relatively
thick gaskets, thus providing good sound insulationand vibration proofing.
The liquid type gasket, on the other hand, is very
4

Fig. 4

Types of leakage

effective in sealing performance because, being a fluid,
it can penetrate into uneven spots of the contact
surfaces and also, it can get into close contact with thesurfaces. There are two types of liquid gaskets: wet
type formed-in-place gasket (FIPG) and dry typecured-in-place gasket (CIPG).
4.1 FIPG (Formed-in-place Gasket)
Liquid gasket material is applied to sealing
surfaces (flange faces) and the faces are brought into
contact while the applied material still remains
unhardened. The material is then subjected tohardening. Because the liquid faithfully follows the
profile of the face, practically it does not require a highprecision of flange faces. Additionally, being abonding seal, its sealing performance is reliable, andflange width and thickness can be reduced.
4.2 CIPG (Gured-in-place Gasket)
Unhardened liquid gasket material is applied tosealing surfaces and is then heated for hardening. As
this type is directly applied to parts surfaces and cured
in place, it does not require molds that are needed forordinary molded gaskets. However, the sealing
performance of CIPG mainly depends on the shape,clamping pressure and compression set in the same
way as with a solid gasket. Special attention must be
paid to the accuracy in the shape of application beads
because the material is hardened as is as applied.
Shown in Table 2 are the characteristics of liquidgaskets (FIPG and CIPG) in comparison with those ofsolid type.
What is important here is that supposing that thesealing performance of the gasket material is fully
displayed, sealing width and thickness can be reduced
as the level of its barrier capability against the medium
to be sealed is higher. This is of vital importance forselection of the best sealing compound for a fuel cellbecause it needs to seal hydrogen (H2) and oxygen (O2)gases whose molecular weights are very small andwhich are wet. A smaller seal also contributes toincreasing the generating efficiency of a fuel cell,which will in turn do much toward downsizing of thewhole system.

Table 2 Comparison of Characteristics
Solid gaskets
Sealing method

Double face contact

Liquid gaskets
FIPG
CIPG
(Formed In Place Gasket)(Cured In Place Gasket)
One face contact, one face adhesion
Double face adhesion

Dimensional precision for sealing compound

High

Low

High

Flange face precision

High

Low

High

Surface pressure

High

Low

High

Compression set
Removability
Line production

RequiredO×

Not required×O

RequiredO
O

Solid gaskets (including CIPG) greatly depend on
the rigidity and pressure of the contact surface. Becauseof this, creeps are produced from immediately after they
are mounted, causing the sealed surface pressure to
decrease. These creeps are especially conspicuous atpoints that are subjected to heat and where internalpressure fluctuates frequently, which usually lead totorque decrease that is the most possible cause of leakage.
For a fuel cell battery, particularly, full consideration isrequired to these creeps in the design of sealing points
because the battery consists of a stack of tens tohundreds of cells.

5. Features of TB1152/1153
We have been successful in developing fuel cellsealing compounds TB1152 and TB1153 after years ofinvestigation and research in materials that can meet theperformance
characteristics
requiredfortheabove-mentioned two types of sealing gaskets.
TB1152 and TB1153 consist of telechelic polymer(main component) whose principal chain ispolyisobutylene having anyl groups at ends. The finishedsealing compound is formed by additional

Fig. 5polymerization and bridging of curing agent that contains
SiH radicals (see Fig. 5). Heating in the presence of
catalysts performs this forming. Table 3 shows therespective properties and general characteristics of these
sealing compounds.
It is known that usually, gas permeability of rubber
becomes lower as its molecular rotations become
difficult and molecular interactions become intensified.
This is because molecular movement is restrained.
Polyisobutylene, which is the main component of
TB1152/1153, has a C-C chain in its principal base.
Compared with the siloxane chain of silicone, the C-C
chain is shorter in intermolecular distance and smaller infree volume. Because of these properties, it can provide
higher performance of gas barrier and lower moisturepermeability while it is soft and flexible as silicone. (SeePhoto 1.)
Fig. 6 shows the relative comparison of the resultsof hydrogen (H2) gas permeability test (JIS K 7126) andwater vapor permeability experiment (JIS Z 0208)
between additional type common silicone sealant andTB1152/1153 hardened sheets (1-mm thick).

Curing mechanism of TB1152/1153

5

Compared with existing silicone sealing compounds
commonly in use, the hydrogen (H2) gas permeability of
TB1152/1153 is 1/20 and its water vapor permeability isaround 1/100, showing that TB1152/1153 areincomparably excellent in gas barrier performance.
TB1152/1153 also provide high resistance invarious physical conditions: the results obtained fromdumb-bell physical property testing show that theirtensile strength has not dropped in any of resistance test
conditions: acid resistance (Fig. 7), moisture resistance(Fig. 8), heat resistance (Fig. 9), and heat-cold cycle
resistance (Fig. 10). This means that TB1152/1153 canretain stable rubber-like physical properties for an
extended period of time.
Likewise, there has been no significant fluctuationin their hydrogen (H2) gas permeability (see Figs. 11
through 14), proving that their gas barrier capability ishighly reliable.
Finally, the measurement results of ions eluted fromthese sealing compounds are shown in Table 4. As can beseen in the table, no ionic elution (especially, heavy
metal ions) has been observed, meaning that they will
not cause any significant damage to the electrolytic
membrane, which is the heart of the polymer electrolyte
fuel cell (PEFC).
TB1152 is designed for use with FIPG, and TB1153
with CIPG so that each type can meet the stackvariations and different manufacturing processes as may
be required by fuel cell manufacturers. TB1153 (forCIPG) has higher levels of physical properties of sealing
agent than those of TB1152 (for FIPG) so as to increase
its compression set characteristic and improve its sealing
feature against compression. Shown in Photos 2 and 3
are the application images of the respective sealing
compounds.

Table 3

6

Table 4 Measurement Results of Eluted lons
Extracting conditions: pH = 1; H2SO4 aqueous solution; at 100˚C for 100 hrs

Ion type
Mg
Al
Si
Cr
Mn
Fe
Ni

Result
ND
ND
ND
ND
ND
ND
ND

Ion type
Result
Cu
ND
Zn
ND
Ag
ND
Cd
ND
Sn
ND
Hg
ND
Pb
ND
*ND: Not Detected

General Properties of TB1152/1153

–
Pa·s
–
˚C
A
MPa
%
Ω·m
mol·m/m2·s·Pa

TB1152(for FIPG)
Milky white
828
0.93
-67.2
35
3.0
315
2.6 × 1014
7.2 × 10-15

TB1153(for CIPG)
Gray
1110
1.00
-67.4
54
4.1
140
3.7 × 1014
9.6 × 10-15

g/m2/24h

3.5

0.21

JIS Z 0208

%

35

19

JIS K 6262

Unit
Appearance
Viscosity
Specific gravity
Glass transition point
Hardness
Tensile strength
Elongation
Characteristic volume resistivity
H2 gas permeability coefficient
Water vapor permeability(40˚C × 95%RH)
25% compression set(120˚C × 100h)Fig. 6 Hydrogen (H2) gas permeability coefficients
and water vapor permeability (Relative comparison)

Test method
3TS-201-01
3TS-210-03
3TS-213-02
3TS-501-04
3TS-215-01
3TS-320-01
3TS-320-01
3TS-401-01
JIS K 7126

7

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<Bibliography>●“Shin-Energy Gijyutu Nyumon” by Yoshihiro Adachi●“Nikkei Electronics” (Vol.807)●“Silicone Handbook” by Kunio Ito●“Rubber Kougyo Binran (Shinban)” by The Societyof Rubber Industry, Japan

Photo 2 Application image of TB1152

Photo 3 Application image of TB1153
for CIPG on a dummy separator

6. Epilogue
The recent news report that vehicles equipped withpolymer electrolyte fuel cell battery (PEFC) will belaunched even this year (2003) although in limited
quantity. Because of its high potential, its applications to
notebook personal computers, mobile phones, PDAs andother portable devices are also in study, and therefore,
heat-up of development competition and technologicalbreakthrough are anticipated.
Making the most of our long-experienced sealing
technologies and also taking advantage of our newly
developed TB1152/1153, we will challenge forestablishing more sophisticated hydrogen gas sealing
technology so that we can contribute to the development
and spread of fuel cells much more actively.

8<Writer>● Mr. Mamoru Adachi,
Material Development Department,
Product Development Division,
Research & Development Operations● Mr. Koichi Kaneko,
Material Development Department,
Product Development Division,
Research & Development Operations