Silicone sealants are now offered that combine the advantages of a pressure-sensitive adhesive (PSA) with the high performance of a structural, neutral-cure silicone sealant.
Always looking for ways to
improve productivity and quality, manufacturers are turning to sealants as an
alternative to bolts, screws, and rivets that often loosen, leak or corrode
In the past, traditional sealants were unable to substitute mechanical
fasteners due to limitations in substrate wetting, long-term performance and
cure time. New developments in reactive hot-melt sealants are overcoming these
issues to present a unique opportunity for manufacturers.
To address these issues, Dow Corning developed a new generation of hot-melt
silicone sealants that combines the advantages of a pressure-sensitive adhesive
(PSA) with the high performance of a neutral-cure silicone sealant. These
hot-melt silicone sealants provide immediate and excellent adhesion to
substrates such as metal, wood, painted surfaces and glass, as well as
low-energy surfaces such as PVC, ABS®
, PE, Teflon®
and many other plastics.
When first applied at temperatures of 120-130°C, the sealant is as strong as
double-sided tape, with adhesion of 6-18 psi. Within 30 seconds, the silicone
begins cooling and the viscosity rises to offer “instant bonding.” This
adhesive bond strength is from both the viscosity rise and the
pressure-sensitive adhesive character of the material. The PSA is “built into”
the sealant to provide instant green strength, which allows products to move
from one processing step to the next with no wait time. This can reduce
downtime and eliminate the bottlenecks in manufacturing caused by cure times
associated with other sealants, such as typical room temperature vulcanized
Once cured, the sealant has a tensile strength of 350-780 psi, but remains
flexible at temperatures well below 0°F and doesn’t break down at high
Even after crosslinking, silicone hot-melt sealants remain flexible due to
their silicone-oxygen backbone. Because the silicone is not adhered at focused
points, as with traditional fasteners, the stress is distributed along the bond
line, and the flexibility of the sealant absorbs much of the stress at high and
Silicone hot melts demonstrate excellent surface wetting characteristics, do
not require priming or surface activation, and are suitable for most
substrates, including PVC, aluminum, wood, and plastics. Hence, hot-melt
sealants have an growing number of uses, including marine, automotive, and
sports and leisure applications, as well as solar cells, circuit boards, and
home and industrial appliances. For home and industrial appliances, hot melts
are ideal for sealing air and water in or out of ovens, blenders, mixers,
sinks, coffee pots, stovetops, kitchen equipment, refrigerators, washing
machines, dishwashers, and steam cleaners.
A major advantage of silicone hot-melt sealants is their ease of use, allowing
manufacturers to devote more time and attention to customers’ needs. Hot-melt
sealants improve productivity because they are designed for easy processing
with automatic equipment, are not heat activated, and offer a long pot life and
open time. This allows for easy adjustment of the parts being bonded.
Silicone hot-melt sealants are very durable and have great longevity. They
resist environmental factors over time because they are virtually unaffected by
long-term exposure to ultraviolet rays or temperature extremes. In addition,
they meet volatile organic compound (VOC) standards and are available in ultra
To meet increasing application demands for hot-melt silicone sealants, Dow
Corning is adding several new formulations that have improved creep resistance,
higher viscosity and greater flowability. One patented technology is designed
to provide better resistance to low static shear and to have a lower
application temperature. At the same time, this new technology’s mechanical
properties will be closer to “standard” silicone sealants, meaning that it will
have better resistance to cohesive failure and creep.
Hot-melt technology continues to change and improve in response to industry
trends and demands, and is an excellent choice for manufacturers looking for
improved adhesion, an alternative to mechanical fasteners, fast cure times, and
low labor costs.
For more information, contact Dow Corning at www.dowcorning.com.