Page 464 - Handbook of Adhesives and Sealants

Adhesives Families 401

TABLE 10.19 Effect of Temperature and Aging on Silicone Pressure Sensitive Tape
(aluminum foil backing) 36

Testing temperature Adhesive strength, oz/in.
Uncatalyzed Catalyzed adhesive
C F adhesive (1% benzoyl peroxide)
70 94 Over 100* Over 100*
20 4 Over 100* Over 100*
100 212 60 48
150 302 60 45
200 392 Cohesive failure 40
250 482 Cohesive failure 35
Heat-aging cycle prior to
testing (tested at 25 C,
77 F):
No aging ................ 60 52
1 h at 150 C (302 F) ..... 55 50
24hat150 C (302 F) .... 60 50
7 days at 150 C (302 F) . . 70 50
1 h at 250 C (482 F) ..... 60 50
24hat250 C (82 F) ..... 65 65
7 days at 250 C (482 F) . . Cohesive failure 65

*Maximum limit of testing equipment.

strates. These adhesives are one-component pastes that cure by re-
acting with moisture in the air. Because of this unique curing mech-
anism, adhesive bond lines should not overlap by more than 1 in. RTV
silicone materials cure at room temperature in about 24 hrs. With
most RTV silicone formulations, acetic acid is released during cure.
Consequently corrosion of metals, such as copper and brass, in the
bonding area may be a problem. For corrosive substrates, certain RTV
silicone formulations are available that cure by liberating methanol
rather than acetic acid.
Two-part RTV systems that do not liberate byproducts during cure
are also available. These adhesive systems are generally cured by a
stannous octoate or dibutyltindilaurate catalyst at room or elevated
temperatures. These two-part systems normally contain water in the
formulation for more effective cure. Two-part RTV adhesives can cure
in thick sections, where the one-part system cannot because of a cured
skin that forms quickly, inhibiting atmospheric moisture from gaining
access to the center section of the bond-line.
Fully cured RTV adhesives can be used for extended periods up to
450 F and for shorter periods up to 550 F. Silicone adhesives are soft
and compliant and have good chemical and environmental resistance.
The low temperature limit for these adhesives is generally 80 F be-