s a sealant for potting electrical and electronic components when premium
thermal cycling performance is required. It delivers low embedment stress upon cure and
during thermal cycle exposures. This inherent resilience is gentle on sensitive circuitry while
it provides an exceptional shield to protect the electrical components from the environment.
Tough-Seal 21 is a two component, hybrid epoxy elastomer material that does not contain
isocyanates. It has a milder health and safety profile than urethanes.
Tough-Seal 21 is provided in a convenient mix ratio that is easy to mix. It sets quickly at room
temperature to form a hardened polymer with exceptional flexibility to - 40°C and elevated
temperature resistance to 300°F. As an epoxy, Tough-Seal picks up where urethanes drop
off, while its tough, rubbery nature delivers thermal cycling performance not typically found in
epoxy materials.
Key Polymer is ISO 9001 certified and has 45 years in the business of
supplying specification materials to the electronic industries.
Visit the Key Polymer website for a complete product list KEY POLYMER 17 Shepard Street, Lawrence, MA 01843 USA 978-683-9411 tough-seal@keypolymer.com
Tough-Seal 21 Technicals (Typical values, not intended for specifications)
Wet Properties
Color
Viscosity at 25°C (77°F)
Brookfield RVT
Specific Gravity
Density (lbs/gal)
Shelf Life
Part A
Milky White
7,000 cPs
#5 @ 20 rpm
1.32
11.0
3 months
Part B
Black
11,000 cPs
#5 @ 20 rpm
1.28
10.7
3 months
MIX
Black
10,000 cPs
#5 @ 20 rpm
1.29
10.8
Shelf Life Conditions: Unopened, factory sealed containers and cartridges in factory sealed foil pouches have a shelf life
of 3 months from the date of shipment at room temperature 68°F to 77°F (20°C to 25°C) OR 12 months from the date of
shipment when stored at 0°F to 38°F (-18°C to 3°C). The gel time of KEY Tough-Seal 21 becomes longer as the Aside
component ages beyond 3 month at room temperature. While ultimate cure and properties are unaffected by the gel time
extension, the cure rate is affected beyond 3 months age. Refrigerator or freezer storage can be used to preserve gel
time. Storage above 90°F (32°C) is not recommended. Contact Key Polymer to discuss the supply chain management of
Tough-Seal 21 in your operation.
Mix Ratio by Weight
Combine 51 Parts A-side with 100 Parts B-side by Weight
Mix Ratio by Volume
Combine 1 Part A-side with 2 Parts B-side by Volume
Gel Time (100 grams)
10 minutes
Mechanical Properties
Lap Shear Strength
Aluminum 2024T3 Bare 0.5 in
2
overlap 5 mil gap
Tensile Strength
Elongation at Break
Type I 0.125 inch thickness
Linear Shrinkage
Hardness, Shore A
ASTM
D1002
D638
D638
D2256
D2240
Temperature
25°C (77°F)
25°C (77°F)
25°C (77°F)
25°C (77°F)
0°C (32°F)
25°C (77°F)
80°C (176°F)
100°C (212°F)
120°C (248°F)
150°C (302°F)
Value
640 psi Cohesive
350 psi
350%
< 0.001 in/in
58A
52A
50A
50A
50A
48A
Electrical Properties
Volume Resistivity
Dielectric Strength
Dielectric Constant
Dissipation Factor
Frequency 1kHz
ASTM
D257
D149
D150
D150
Temperature
23°C (73°F)
23°C (73°F)
23°C (73°F)
23°C (73°F)
Value
1.33 x 10¹² -cm
350 Volts/mil
6
0.06
350%
S T R E T C H KEY POLYMER 17 Shepard Street, Lawrence, MA 01843 USA 978-683-9411 tough-seal@keypolymer.com
Tough-Seal 21 Guards Electrical Components!
Tough-Seal 21 has the service temperature of an epoxy and the flexibility
common to urethanes. Its the best of both worlds. Tough-Seal is a hybrid
epoxy elastomer and as such, it possesses the resilience of an
elastomeric matrix but Tough-Seal sets to form epoxy domains seeded
throughout the cured polymer that boost thermal resistance. This
Interpenetrating Polymer Network, IPN, remains flexible but capable of
delivering superior thermal cycling and it does so without the use of
isocyanates and their associated health & safety issues because Tough-Seal is not a urethane.
Tough-Seal is superior to ordinary epoxy and urethane potting compounds.
Potting compounds & encapsulants are specified to flow over an electrical device and fill up
a housing with a hardened thermoset plastic to serve as an environmental barrier. Epoxy and
urethane materials are prevalent throughout industry because they suitably withstand intrusive
environmental moisture, salts and chemicals that can attack sensitive electronics and cause
shorts. Epoxies are typically rigid materials with high service temperatures and urethanes are
more flexible with lower heat resistance. Ideally, one would specify a flexible potting compound
to maintain a seal with the housing wall but elevated service temperatures degrade urethanes.
Ordinary epoxy materials can handle the high service temperatures but they are vulnerable
to pull back from the housing in cold conditions. Pull back creates a gap that is readily exploited
by the aggressive environment. Tough-Seal wont pull back!
Chemistry aside, Tough-Seal is a Guard Dog that grips the wall in cold when others contract
to expose a gap, yet it wont wilt under the heat. Tough-Seal picks up where urethanes leave
off and guards up to 300°F.
Order an evaluation kit and everything you need to perform a high quality engineering
evaluation is expedited to you including direct access to the consultants on the technical
service Seal Team at Key Polymer. Time and time again, specifying engineers determine
that Tough-Seal comes out on top in side by side testing with your existing encapsulant.
See for yourself.
Hit the Milestone & Get the Guard Dog
Order Your Tough-Seal 21 Evaluation Kit Today! KEY POLYMER 17 Shepard Street, Lawrence, MA 01843 USA 978-683-9411 tough-seal@keypolymer.com
ZERO TOLERANCE FOR STRESS
ZERO EMBEDMENT STRESS: the stress that electrical components are subjected to
when they are embedded in the potting compound. It is the principle cause of component
failure even when an impermeable seal to the environment is attained. The sensitive
components can be dislodged from their connections when (1) the potting compound
hardens from a liquid to a solid and later when (2) the part is exposed to thermal cycling
and the persistent expansion and contraction of the encapsulant.
ZERO SHRINK - ZERO STRESS: Tough-Seal avoids initial embedment stress upon cure
because it has imperceptibly low shrinkage. Thermoset plastics have a slightly larger
volume in their freshly mixed liquid state than they possess in their hardened cured state.
This differential volume is manifest by shrinkage and is aggravated by the size of the
pour and the extent of the resulting exotherm. The higher service temperature traditional
epoxy system essentially squeezes the components that it is designed to protect right off
the board. More flexible urethane systems shrink less and are more compliant than typical
epoxies but they are not recommended for the service temperatures encountered in under-
the-hood automotive service. Moreover, as is indicated later, flexible urethane systems
become hard in the cold extremes of thermal cycles and they induce stress post-potting.
The novel, hybridized nature of Tough-Seal has zero shrinkage upon cure per ASTM
D2256 and it cures with little to no reaction exotherm even in large pours.
Tough-Seal doesnt get hot but it can take the heat ... under-the-hood.
COLD
CONTRACT
HOT EXPAND KEY POLYMER 17 Shepard Street, Lawrence, MA 01843 USA 978-683-9411 tough-seal@keypolymer.com
THERMAL CYCLING - ZERO STRESS: Why does Tough-Seal have superior thermal cycling
characteristics? Uncharacteristic of standard epoxies and urethanes, the hardness of Tough-
Seal is not a function of temperature. The hardness of other potting compound chemistries
are strong functions of temperature and they definitely get harder as they get colder and
become softer as they are heated. In the graph below, the hardness of Tough-Seal is nearly
constant. Again expansion and contraction forces are eliminated and thus they do not act on
embedded circuitry.
Tough-Seal forms a tough seal,
but it is gentle on electrical
components because it does not
change as conditions do. It
thermal cycles like no other and
it guards electrical components.
Is your project nearly complete
with your launch date fast
approaching but youre getting
hammered on environmental
testing with your existing
encapsulant? You thought the
hard part was over with all design
reviews signed off except the
potting compound selection and
now the specification of the
potting compound is the only
thing standing between you and
success. Your electronic design
is high tech, why not go with the
latest technology in polymer
encapsulation?
Order an evaluation kit and everything you need to perform a high quality engineering
evaluation is expedited to you including direct access to the consultants on the technical
service Seal Team at Key Polymer. Time and time again, specifying engineers determine
that Tough-Seal comes out on top in side by side testing with your existing encapsulant.
See for yourself.
Hit the Milestone & Get the Guard Dog
Order Your Tough-Seal 21 Evaluation Kit Today! KEY POLYMER 17 Shepard Street, Lawrence, MA 01843 USA 978-683-9411 tough-seal@keypolymer.com
Tough-Seal Applications
Applications for Tough-Seal: Tough-Seal 21 is an ideal material for the encapsulation of
sensitive electrical and electronic components that are subject to thermal cycling stress. Tough-
Seal 21 bonds exceptionally well to the walls of most plasti