Page 545 - Handbook of Adhesives and Sealants

470 Chapter Twelve

TABLE 12.9 Property Consideration of Sealants 6
Applicable ASTM
Typical units test methods
Uncured properties
Skin over time minutes
Tack free time hours C-679
Sag, weep inches C-713
Extrusion rate grams/minute C-603
Flow seconds C-639
Cured properties
Durometer hardness Shore A C-661
Tensile at maximum elongation psi C-908
Elongation at maximum tensile percent
Modulus psi
Tear lbs/inch
Peel piw C-794
Application Properties
UV resistance C-793
Ozone resistance C-793
Staining/dirt pick-up C-510
Color change C-771
Application temperature range
Service temperature range
Adhesion C-719
Durability C-973, C-732
Compatibility
Compression set C-972
Solvent release C-733
Life expectancy
Cost
Material
Installation

high or 100% solids such as many of the two component systems. Me-
dium shrinkage systems include hot melt sealants that shrink as they
go from a molten state to a gelatinous state. High shrinkage systems
are solvent or aqueous base sealants in which shrinkage is due to
evaporation of solvent or water.
For improved gap filling characteristics, some sealants are formu-
lated to expand prior to curing. These sealants include automotive
sealants with foaming agents in the formulation similar to the foam-
ing agents used in packaging materials. Hot-melt formulations are
also prepared with gases dissolved into the resin that will expand
when heated. All of these formulations will expand before cure to fill
in the joint gap (Fig. 12.1) and maintain positive pressure on the sub-
strate as the sealant cures.
Foam-in-place gaskets promised to eliminate production bottlenecks
in mass produced automobiles, appliances, electronics, and office