Some kinds of packaging must maintain a seal against the flow of gases, for example, packaging for some foods, pharmaceuticals, chemicals and consumer goods. The term can describe the result of some food preservation practices, such as vacuum packing and canning. Packaging materials include glass, aluminum cans, metal foils, and gas impermeable plastics.
Some buildings designed with sustainable architecture principles may use airtight technologies to conserve energy. Under some low energy building, passive house, low-energy house, self-sufficient homes, zero energy building, and superinsulation standards, structures must be more air-tight than other lesser standards. Air barriers are not effective if construction joints or service penetrations (holes for pipes, etc.) are not sealed. Airtightness is a measure of the amount of warm (or cool) air that can pass through a structure. Mechanical ventilation system can recover heat before discharging air externally. Green buildings may include windows that combine triple-pane insulated glazing with argon or krypton gas to reduce thermal conductivity and increase efficiency. In landscape and exterior construction projects, airtight seals may be used to protect general services and landscape lighting electrical connections/splices. Airtight implies both waterproof and vapor-proof.
Applications for hermetic sealing include semiconductor electronics, thermostats, optical devices, MEMS, and switches. Electrical or electronic parts may be hermetic sealed to secure against water vapor and foreign bodies to maintain proper functioning and reliability.
Hermetic sealing for airtight conditions is used in archiving significant historical items. In 1951, The U.S. Constitution, U.S. Declaration of Independence, and U.S. Bill of Rights were hermetically sealed with helium gas in glass cases housed in the U.S. National Archives in Washington, D.C. In 2003, they were moved to new glass cases hermetically sealed with argon.
Types of epoxy hermetic seals
Typical epoxy resins have pendant hydroxyl (-OH) groups along their chain that can form bonds or strong polar attractions to oxide or hydroxyl surfaces. Most inorganic surfaces—i.e., metals, minerals, glasses, ceramics—have polarity so they have high surface energy. The important factor in determining good adhesive strength is whether the surface energy of the substrate is close to or higher than the surface energy of the cured adhesive.
Certain epoxy resins and their processes can create a hermetic bond to copper, brass, stainless steel, specialty alloys, plastic, or epoxy itself with similar coefficients of thermal expansion, and are used in the manufacture of hermetic electrical and fiber optic hermetic seals. Epoxy-based seals can increase signal density within a feedthrough design compared to other technologies with minimal spacing requirements between electrical conductors. Epoxy hermetic seal designs can be used in hermetic seal applications for low or high vacuum or pressures, effectively sealing gases or fluids including helium gas to very low helium gas leak rates similar to glass or ceramic. Hermetic epoxy seals also offer the design flexibility of sealing either copper alloy wires or pins instead of the much less electrically conductive Kovar pin materials required in glass or ceramic hermetic seals. With a typical operating temperature range of −70 °C to +125 °C or 150 °C, epoxy hermetic seals are more limited in comparison to glass or ceramic seals, although some hermetic epoxy designs are capable of withstanding 200 °C.
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