Page 364 - Handbook of Adhesives and Sealants
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320 Chapter Nine
without the addition of some modifying substance such as plasticizer,
tackifier, or inert filler. The selection of the actual ingredients will
depend on the end-properties required, the application and processing
requirements, and the overall cost target. The various components
that constitute an adhesive formulation include the following:
Base or binder
Catalyst or hardener
Accelerators, inhibitors, and retarders
Solvents
Diluents
Extenders
Fillers
Carriers and reinforcements
Plasticizers
Tackifiers
Thickeners and thixotropic agents
Film formers
Antioxidants, antihydrolysis and antifungal agents, and stabilizers
Soaps, surfactants, and wetting agents
The adhesive base or binder is the principal component of an ad-
hesive. The binder provides many of the main characteristics of the
adhesive such as wettability, curing properties, strength and environ-
mental resistance. The binder is often by weight the largest compo-
nent in the adhesive formulation, but this is not always the case es-
pecially with highly filled adhesive or sealant systems. The binder is
generally the component from which the name of the adhesive is de-
rived. For example, an epoxy adhesive may have many components,
but the primary material or base is an epoxy resin. Once the binder
is chosen, the other necessary ingredients then can be determined.
The next chapter describes in detail the various polymeric resins that
are commonly used as bases or binders in adhesive formulations.
A hardener or curing agent is a substance added to an adhesive to
promote the curing reaction by taking part in it. They cause curing
by chemically combining with the base resin. Hardeners or curing
agents are specifically chosen to react with a certain resin. They will
have a significant effect on the curing characteristics and on the ul-
timate properties of the adhesive system.
Reactive polyamide is an example of a common hardener used in
two part epoxy systems. The criticality of the amount of hardener used