Classification of Sealants by Physical Form

1. Paste - type Sealants
   These sealants are basically used in static joints, with a service life of generally 2 years or more. Three main materials are commonly used: oils and resins, polybutene, and asphalt.
2. Liquid Elastomeric Sealants
   This type of sealant includes liquid polymers that can form a true elastic state after vulcanization. They have the ability to withstand repeated joint deformations. The polymer elastomers used in elastomeric sealants include liquid polysulfide rubber, mercapto - terminated polypropylene ether, liquid polyurethane, room - temperature vulcanized silicone rubber, and low - molecular - weight butyl rubber, etc. This type of sealant is usually formulated into two components, which are mixed during use.
3. Hot - melt Sealants
   Hot - melt sealants, also known as hot - applied sealants, refer to sealants based on a blend of elastomers and thermoplastic resins. These sealants are usually extruded directly into the joints through a certain die model when heated (150 - 200 °C). Hot - application can improve the wettability of the sealant to the adherend, so it has good adhesion to most adherends. Once placed in the appropriate position, it cools and forms a shape or film, becoming a firm elastomer with little shrinkage. The main materials of hot - applied sealants are mainly isobutylene - based polymers, ethylene - propylene - diene monomer (EPDM) rubber, and thermoplastic styrene block copolymers. They are usually blended with thermoplastic resins such as EVA, EEA, polyethylene, polyamide, and polyester.
4. Liquid Gasket Sealants
   This type of sealant is mainly used for the sealing of mechanical joint surfaces, replacing solid sealing materials (i.e., solid gaskets) to prevent the leakage of fluids inside the machinery from the joint surfaces. This type of sealant is usually made with polymer materials such as rubber and resin as the main materials, and is further compounded with fillers and other components. Liquid gasket sealants are usually divided into four categories: non - drying adhesive type, semi - drying viscoelastic type, drying adherent type, and drying peelable type, which are selected according to specific application sites and requirements.