Silicone Adhesive Sealant
Silicone adhesives are used for bonding, sealing and assembling many types of materials. They are resistant to moisture, chemicals and weathering and keep their elasticity and stability in high temperatures.
High temperature silicones are often called for in areas of an automobile where the sealant will be subject to high heat. Examples include valve covers, axle housings, water pump seals and timing chain cover gaskets.
Pressure Sensitive Adhesives
Pressure sensitive adhesives, or PSAs, are designed to adhere to substrates that may not have an easy time achieving sufficient contact area. They are generally based on rubber, acrylic or silicone polymers and provide various levels of performance depending on application requirements.
The PSA must be soft enough to flow onto the surface of the adherend and bond by making intermolecular contacts to produce a strong bond. These bonds must also be resilient enough to resist moisture, solvents, temperature and other environmental factors. These properties require a balance of softness and resistance, viscoelasticity (a combination of viscous and elastic properties) and good adhesion at high temperatures.
Typically, the PSA has a flexible facestock coated with the adhesive on one side. To activate the high temperature silicone adhesive sealant adhesive, the user removes the liner and presses the adhesive side against the substrate. This type of construction is common in packaging tapes and many other types of materials that require a single-sided adhesive for a specific function.
PSAs can be manufactured as a solvent-based, water-based or emulsion formulation. Water-based and emulsion PSAs offer lower environmental concerns than their solvent counterparts, while maintaining the same high level of performance. They can be used at temperatures up to -85°F and are fully cured within twenty-four hours of application. Regardless of the chemistry, it is important to use proper safety practices when working with all PSAs. This includes wearing protective eye-wear and avoiding skin contact and breathing fumes.
One Part Adhesives
One part silicone adhesives work best for applications that require a quick turnaround. Many of these adhesives feature a chemical reaction that takes between two and ten minutes to form, making them ideal for use on small surfaces or strips. These adhesives tend to have a shorter shelf life, so they must be kept in a cool and dry place.
Traditional one-part epoxies use thermal curing and provide exceptional strength at high temperatures. These adhesives are also able to resist chemicals, moisture, and weathering. Recent innovations in one-part epoxy technology are providing more versatile options, such as abrasion resistant formulas and materials that cure at lower temperatures for greater flexibility and impact resistance.
Silicones are more flexible than other adhesives and sealants, and they hold their elasticity even in very cold conditions. These properties make them suitable for a wide variety of applications, from sealing to bonding. Silicones are resistant to chemicals, water and UV radiation. They can also withstand extreme temperatures, ranging from high to low.
Master Bond offers several one component high temperature silicones, including the non-corrosive MasterSil 711 and the transparent MasterSil 151Med, which meets USP Class VI specifications for medical applications and biocompatibility. These silicones are also available as a spreadable paste. Other options include RTV silicones that cure to tough resilient rubber, such as MasterSil 1035, a low-odor, room-temperature cured adhesive that’s perfect for protecting copper connections on electronic circuit boards or sealing and encapsulating electronics.
Two Part Adhesives
Two part adhesives have a different chemical makeup than other, more organic polymer-based adhesives. This gives them high resistance to chemicals, moisture and weathering, as well as keeping their elasticity in both low and high temperatures. Because of this, they are a popular choice for use in a range of industrial applications including bonding, sealing and encapsulating.
These types of adhesives have two components that need to be mixed together in a specific ratio, as specified in the product information. Most of the products available in this range, such as the DELO-DUOPOX adhesives, come in cartridges which hold the epoxy resin and hardener in separate chambers that need to be combined by squeezing the syringe’s nozzle.
The speed at which these adhesives react means that they can be used on small surfaces or strips of material, and they can also cure quickly. This makes them a good choice for applications that need fast throughput or where work is being carried out under time constraints. They can be used on metals, plastics and ceramics, as well as being suitable for bonding glass. They also have a low odor and do not support mildew growth. They can also be used in a variety of environments and conditions, from humid and cold to dry and hot. However, they are not recommended for direct food contact or contact with skin.
LED Curing
Many assembly, bonding, and coating processes require adhesives that can be cured with UV light. LED curing technology offers advantages over traditional discharge lamps such as cooler temperatures, faster curing, reduced material distortion due to heat, and no drying step.
LEDs emit visible light with wavelengths near the 365 nm peak of the UV spectrum. When exposed to this light, photo-initiators in the adhesive formulation absorb the energy and kickstart the chemical reactions that polymerize the composite adhesive material. When these reactions are complete, the adhesive is fully cured.
Adhesive chemistries suited to LED curing include acrylate/urethanes, cyanoacrylates, silicones, anaerobics, and pressure sensitive adhesives as well as film adhesives and epoxies. This type high temperature silicone adhesive sealant of curing is also suitable for manufacturing production lines that use printed circuit boards, electronic components, wood/plastic composites, and other applications requiring quick and reliable curing.
Manufacturers considering switching from mercury vapour to LED curing should partner with an experienced provider that can assist in developing a reliable and flexible process via lab testing and in-plant trials. They should also work with chemistry formulation partners who can help to ensure the adhesive is compatible with LED light sources and capable of producing the same quality of cure as a mercury vapour cured product. This will help to minimize risk of the adhesive failing due to a poorly matched chemistry/LED combination.