Epoxies are one of the oldest synthetic chemistries for adhesives, dating back to the 1940s. The long history and substantial number of reactive chemistries available make epoxies one of the most diverse adhesive chemistries. Formulations are available for low and high temperatures, flexible and rigid, toughened and brittle, etc. Epoxy adhesives are most commonly used for structural applications where there is a very high load and/or small bond area. Common in aerospace, defense and industrial transportation, epoxy chemistry is also used when there are temperature or chemical exposure requirements.
Epoxy reactions are step-wise polymerizations, meaning that for every reactive group “A”, there must be a reactive group “B” that it can react with. For two-component systems, A and B are in separate sides and mixed through a nozzle. For one-component systems, one of the components is activated using heat, light, pressure or some other energy source that allows the reaction to proceed.
Urethanes are most well known in other formats such as foam, synthetic rubber or coatings. Urethanes also make great resins for adhesives, and the adhesives have many of the same properties: flexibility, energy absorption and durability, to name a few.
Urethane adhesives are most common in industries such as construction that require bonds to traditional materials (e.g. wood, brick, concrete). However, their unique flexibility and energy absorption properties have allowed highly engineered urethane adhesives to find a fit in many industrial applications such as transportation.
Similar to epoxy chemistry, urethane reactions are step-wise polymerizations, requiring a reactive group “A” and “B”. For two-component systems, A and B are in separate sides and mixed through a nozzle. For one-component systems, the other reactive group comes from ambient moisture (H2O), curing the adhesive from the outside in.
Cyanoacrylates (one example of the acrylic chemistry family) were discovered during World War II while searching for a plastic material to use in weapons. The technology was originally overlooked because it stuck to everything during processing! Since then, acrylic chemistry has advanced tremendously to include two-component, light curing, and many other forms of industrial adhesives.
Acrylic liquid adhesives are best known for their rapid cure speed. Some acrylic adhesives are capable of reaching 1000 psi in lap shear strength within a minute. This process speed with high ultimate strength makes acrylics suitable for processes that require fast throughput, such as electronics.
Two-component acrylic reactions are called “radical polymerization”. One of the components contains the “initiator” that allows the reaction to begin; once initiated, the polymerization process occurs very rapidly. One-component adhesives rely on ambient moisture (H2O) or UV light to initiate the reaction. Acrylics may also be emulsified in water and used as a sprayable or coatable adhesive, often used for large surface lamination bonds.
Liquid silicones have a very low surface tension, meaning that they will readily wet out many surfaces – even those with very low surface energy like PTFE. It’s no wonder silicone caulk adheres quite well to nearly every surface in a home from kitchen to bathroom.
Silicone liquid adhesives are best known as “sealants” used broadly in many industries. However, their ability to bond a wide range of materials and tolerate high temperatures and chemical exposure suits them for many industrial bonding applications. They are relatively low cost, commonly used in building and construction. Two-component silicones have very high temperature resistance, with many appliance or solar applications.
Silicone chemistries have reaction mechanisms very similar to urethanes, but their inorganic nature (silicon is the backbone, not carbon) means the bonds formed have greater resistance to high temperatures. To aid in processing, oils are often added to improve flow and wet out, especially for one-component systems. The leaching of these oils may cause aesthetic issues over the life of the adhesive.
Natural rubber has been used for adhesives since before the industrial revolution. To this day, most of the natural rubber used for adhesive formulations is “smoked” to eliminate fungi or bacteria that can adversely affect the bond over time. (The chemistry of this “smoking” is actually similar to the chemistry of smoking meats to preserve them.)
While many of the rubbers used for adhesives are naturally derived (such as from the Hevea rubber plant), “rubber” may also refer to synthetic materials such as polychloroprene (Neoprene) or various block co-polymers (e.g. SBR). Their ability to be “tackified” makes them attractive, low-cost solutions for large surface lamination bonds or bonds requiring immediate handling strength and lower ultimate strength.
Natural rubber (poly cis-isoprene) is mechanically worked to provide lower molecular weight polymers that can be readily dissolved or dispersed in a solvent. Synthetic polymers (such as styrene-isoprene block copolymers) may also be used. Tackifiers such as pinene (from pine sap, among other sources) are added to give the adhesive additional tackiness allowing it to be used as a PSA.
Expand your design capabilities by bonding dissimilar materials with ease. Explore new ways to join materials and discover how 3M adhesive technology assists you in your designs.
Thank you for your interest in 3M Industrial Adhesives & Tapes products. A 3M representative will contact you shortly regarding your inquiry.
An error has occurred while submitting. Please try again later...