The choice of adhesive type depends on the specific substrates and environmental resistance needed – temperature resistance, oil and plasticizer resistance, etc. Within each type of solvent based adhesive, formulations are available to match the application requirements of the process – brush, roll, bead or ribbon, spray. Adhesives are used throughout the sign industry for their bonding strength and material requirements.
Once the adhesive is applied, solvent evaporates relatively quickly causing an increase in viscosity of the adhesive film. Bonds can be made immediately after adhesive application or after some solvent has evaporated but before the adhesive has dried to the point where it will no longer wet (open time). Waiting for some evaporation prior to bonding (set time) increases the initial strength of the adhesive bond and allows assemblies to be processed more quickly.
The time window for proper bonding is specified by the adhesive manufacturer. Coating both substrates and waiting .until the adhesive sets before bonding typically provides the best initial bond strength with longest open time. The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than do adhesives. Since the main objective of a sealant is to seal assemblies and joints, sealants need to have sufficient adhesion to the substrates and resistance to environmental conditions to remain bonded over the required life of the assembly.
Sealants generally contain inert filler material and are usually formulated with an elastomer to give the required flexibility and elongation. They usually have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often required. Many adhesive technologies can be formulated into sealants.