Page 364 - Handbook of Adhesives and Sealants
P. 364

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
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