Page 367 - Handbook of Adhesives and Sealants

Adhesive Composition and Formulation 323

TABLE 9.1 Fillers for Common Epoxy Adhesive
Formulations 2
Filler Improvement in epoxy adhesive
Aluminum Machinability, impact resistance
Alumina Abrasion resistance, electrical
Aluminum silicate Extender
Aluminum trioxide Flame retardant
Asbestos fibers Reinforcement
Barium sulfate Extender
Calcium carbonate Extender
Calcium sulfate Extender
Carbon black Color, reinforcement
Copper Machinability, elec conductivity
Glass fibers Reinforcement
Graphite Lubricity
Iron Abrasion resistance
Kaolin clay Extender
Lead Radiation shielding
Mica Electrical resistance
Phenolic microspheres Decrease density
Silica sand Abrasion, electrical properties
Silicon carbide Abrasion resistance
Silver Electrical conductivity
Titanium dioxide Color
Zinc Adhesion, corrosion resistance
Zirconium silicate Arc resistance

be changed significantly. Thermal expansion, electrical and thermal
conduction, shrinkage, viscosity, and thermal resistance are only a few
properties that can be modified by use of fillers. Common fillers are
wood flour, silica, alumina, titanium oxide, metal powders, china clay
and earth, slate dust, and glass fibers. Some fillers may act as ex-
tenders.
A carrier or reinforcement is usually a thin fabric, cloth, or paper
used to support the semicured adhesive composition to provide a tape
or film. In pressure sensitive tapes, the carrier is the backing on which
the adhesive is applied. The backing may be used for functional or
decorative purposes. In films or structural tape, the carrier is usually
porous and the adhesive saturates the carrier. Glass, polyester, and
nylon fabric are common carriers for supported B-staged adhesive
films. In these cases, the carrier provides a method of applying the
adhesive and also acts as reinforcement and an internal ‘‘shim’’ to
control the final thickness of the adhesive.
Plasticizers are incorporated into an adhesive formulation to provide
flexibility and/or elongation. Plasticizers may also reduce the melt vis-
cosity of hot melt adhesives. Similar to diluents, plasticizers are non-
volatile solvents for the base resin. By being incorporated into the