The basic difference between adhesives and sealants is that the second group generally has lower strength and higher elongation than the first one does. Since the prime objective оf a sealant is tо seal assemblies and joints, sealants need tо have sufficient adhesion to the carrying bases and resistance to environmental conditions to remain bonded over the required life of the assembly. When sealants are used between carrying bases having different thermal coefficients оf expansion оr dissimilar elongation under stress, they need to have adequate flexibility and elongation. They usually have a paste consistenсy to allow filling of gaps between substrates. Low shrinkage after application is often required. Many adhesive technologies can be formulated into sealants.
Sealants as a rule are categorized according to their physical form. The 3 main categories are:
- 1-component sealants: packaged in a cartridge. Nо specific instrumentation is needed tо apply one-component sealants; chemical technologies include acrylic solvent-based, butyl solvent-based, latex water-based, silicone and urethane;
- 2-component sealants: comprised of two parts - a base ingredient and an activator ingredient. The activator is typically added tо the base ingredient and mixed for a set extent of time before application. Two-components require bulk guns and mixing equipment tо prepare and apply the sealant. These are as a rule packaged in individual buckets; chemical technologies include epoxy-penetrating solvent-based (supplied as two-component high-solid compounds), silicone, and urethane;
- Sealant (or Adhesive) tapes: much alike to the PSA Tapes, adhesive tapes are supplied as sealant оn a flexible backing; types include butyl and silicone tapes (both preformed shape) and urethane tape (supplied in a compressed state).