Page 78 - Handbook of Adhesives and Sealants

46 Chapter One

does a solvent. Non-reactive diluents are much like solvents and could
leach out of the adhesive or sealant during its life.
Fillers are relatively non-adhesive substances added to the adhesive
or sealant to improve their working properties, strength, permanence,
or other qualities. Fillers are also used to reduce material cost. By
selective use of fillers, the properties of an adhesive or sealant can be
changed tremendously. Thermal expansion, electrical and thermal
conduction, shrinkage, viscosity, and thermal resistance are only a few
properties that can be modified by the use of fillers.
A carrier or reinforcement is usually a thin fabric or paper used to
support the semi-cured adhesive composition to provide a tape or film.
The carrier may also serve as a bond-line spacer and reinforcement
for the adhesive.

1.7.3 End-use processes for adhesives and
sealants
It must be realized that the adhesive or sealant itself is only part of
the joint and somewhat surprisingly does not play a singularly im-
portant role in determining the success of the joint. The manufactur-
ing methods used in producing an assembly will also determine the
initial degree of adhesion and service characteristics of the joint. A
typical flow chart for the adhesive bonding or sealing process is shown
in Fig. 1.12. It must be realized, however, that the decisions made in
one process segment may affect the decision in other process seg-
ments. For example, the choice of substrate will most definitely affect
the method of surface preparation used. The choice of adhesive or seal-
ant could also affect the degree of surface preparation required. (Cer-
tain adhesives are less sensitive to contaminated or low energy sur-
faces than others.) The processing equipment, time required, etc. will
affect the type of adhesive or sealant that can be chosen and may also
affect the type of substrate that can be considered for the application.
For example, certain thermoplastics are used in the auto industry be-
cause they can be thermally welded in a few seconds—a necessity in
a large volume production operation. Thus, the general processes in-
volved in adhesive bonding or sealing are interrelated and often de-
pendent on one another. The user must find the proper processing
methods for the specific application and consistently use them to en-
sure acceptable results.

Apply
Form Surface Adhesive Hold Until Inspect
Substrates Preparation Assemble Set
or Sealant
Figure 1.12 Basic steps in the adhesive bonding or sealing process.