Specialty Adhesives, Sealants and Compounds

Specialty adhesives, sealants and compounds are specialized and/or proprietary products with unique chemistries, cure technologies and/or compositions. Adhesives are organic or inorganic chemical compounds for joining components. Sealants are liquid compounds that prevent leaks and block the ingress of unwanted materials. There are many different types of specialty adhesives, sealants and compounds. Examples include levelers, fillers, chocking materials, mastics, caulks, grouts, and thread lockers. Common forms include binders, resins, greases, pastes, and pellets. Electrically conductive products provide low resistivity and are used to prevent electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). They are also used for electrical insulation and as dielectric materials. To improve heat dissipation, thermally conductive products are applied between a heat-generating electrical device and a heat sink. Encapsulating, dampening, flame retardant, and laminating products are also available.

Specialty adhesives, sealants and compounds use many different chemical systems. Some contain acetals, acrylics, elastomers, natural or synthetic rubbers, epoxy resins, water-based resins, wax-based binders, starches and starch pastes, volatile organic compounds (VOCs), silicone compounds, or vinyl systems. Others contain bituminous substances, butyls, ceramic or inorganic cements, cyanoacrylates, ethylene copolymers, styrene copolymers, fluropolymers, glues and gums, phenolics, formaldehyde resins, polyamides, or polyimides. Commonly used chemical systems for specialty adhesives, sealants and compounds include polybutadiene, polyethylene (PE), polyester, polyetherimide, polyolefin, polypropylene (PP), polysulfide, and polyurethane (PUR). Filled or reinforced compounds consist of resins with additional modifiers such as fillers, pigments, or chopped fibers.

There are several curing technologies for specialty adhesives, sealants and compounds. Examples include air setting, film drying, and anaerobic curing. Many thermoplastics and hot melt adhesives are cured using heat or heat and pressure. Vulcanization, a thermosetting reaction, uses heat and/or pressure in conjunction with a vulcanizing agent to produce materials with greatly increased strength, stability, and elasticity. Some materials cure or vulcanize at room temperature. Others cure with radiation, electron beam irradiation, visible light, or ultraviolet (UV) light. Single component curing systems consist of a resin that hardens through the application of heat or a reaction with surface moisture. Two-component and multi-component curing systems consist of two or more resins and a hardener, crosslinker, activator or catalyst. Pressure sensitive adhesives (PSA) and non-corrosive curing systems for specialty adhesives, sealants and compounds are also available.

Selecting specialty adhesives, sealants and compounds requires an analysis of physical, mechanical, thermal, electrical and optical properties. Physical properties include viscosity and gap fill, the space between the material and the substrate. Mechanical properties include tensile strength and elongation, the percentage amount of deformation. Thermal properties consist of use temperature, thermal conductivity, and the coefficient of thermal expansion (CTE). Resistivity, dielectric strength, and relative permittivity are important electrical properties. Optical properties for specialty adhesives, sealants and compounds include index of refraction, a measure of the speed of light in a material, and transmission.

Specialty adhesives, sealants and compounds are used in many industries and applications. Some products are used in aerospace, automotive, marine, military, photonics, optical, or tooling applications. Others are designed for use with electrical power products, high voltage applications, semiconductors, or integrated circuit (IC) packaging. Specialty adhesives, sealants and compounds that are suitable for medical, pharmaceutical and food processing applications meet requirements established by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA). Original equipment manufacturers (OEMs) and repair, maintenance and overhaul (MRO) organizations also use specialty adhesives, sealants and compounds.

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