The substances used to make adhesives are usually synthetic in nature, but they may also have a natural origin, such as from animals, natural resin, or starch. Natural adhesive sources such as these, however, are fairly rare because synthetic adhesives are both easier and cheaper to produce and sell.
Rather, the three main materials used to produce industrial adhesives are: acrylics, silicone, and polyurethane. Industrial adhesives are often categorized according to these three materials, as well as their adhesive properties and curing mechanism.
Per their curing method, adhesives may be divided into: conductive adhesives, epoxy adhesives, hot melt adhesives, laminating adhesives, pressure sensitive adhesives, and ultraviolet adhesives.
Conductive adhesives are those that conduct heat and electricity.
Epoxy adhesives, on the other hand, are made from a dual chemical base epoxy. They are the most chemically resistant and strongest adhesive type available to consumers today.
Next, hot melt adhesives use heat to harden the surface they are treating, while laminating adhesives mount objects using a backing material.
Per their tactile nature, pressure sensitive adhesives attach themselves to their assigned surface when pressure is applied. Pressure sensitive adhesives often come with backing designed to allow users to remove or reposition them without reducing or losing stickiness or damaging surfaces.
Finally, ultraviolet adhesives work with the help of sunlight.
Depending on their composition, adhesives have different cure times. For instance, some adhesives require a full night to complete bonding with a surface, while others set and dry almost instantaneously.
In addition, these various adhesive types can be created as part of either one-part or two-part formulas.
One-part adhesives bond to surfaces using only their latent bonding properties, which are activated by various energy sources. Energy sources vary by the type of adhesive, but some common examples include heat, moisture, and radiation. A version of the one-part formula is used to create ultraviolet adhesives.
Two-part, or multi-part, adhesives, on the other hand require the mixture of two or more separate components. They are activated either through homogeneous mixing, which must take place immediately before application, or through the separate application and pressing together of these components. During the latter procedure, a chemical reaction occurs that allows the properties of the components to bond together. Multi-part adhesive formulas are used with acrylics, epoxies, and urethanes.
In the same way that different adhesives are activated by different methods and sources, different adhesives have different temperature range settings, depending on how much cooling or heating they require to harden. Generally, these temperatures range anywhere between 212ºF to -68ºF. Hot melt adhesives, for example, require a high level of heat, so that they can reach viscous liquid states.
Adhesives also heat and cool at a variety of set speeds, remaining tacky or soft for different amounts of time. The longer an adhesive remains tacky, the more time manufacturers have to assemble more complementary parts. Also, some setting speeds allow an adhesive to retain a level of tack, which facilitates repositioning options. Some adhesives are not sensitive to heat once they have hardened; these are called thermoset adhesives.
Adhesives are available in several forms, such as aerosol sprays, films, foams, liquids, pastes, and solids.
Film adhesives are chosen for use with applications that require a uniform glue line, which they supply upon their activation via pressure and/or heat. Also, film adhesives may or may not come with release paper. Laminating adhesives are an example of very common film adhesives.
Gap filling adhesives are usually a glue-like liquid or a foam. Because they do not shrink much when set, they can be used as a sealant.
Solid adhesive products include, among others, chips, granules, hot melt sticks, pellets, and powder.
Adhesives are applied using a variety of methods, including: transfer printing, screen printing, curtain coating, spraying, spreading with a brush, glue gun or other tool, and dispensing through a nozzle tool, such as a caulking gun, complex air-actuated nozzle or hand-held squeeze bottle.
Adhesives are critical to keeping machinery and systems together in industrial, commercial, and domestic settings. Adhesives are indispensable. From the back of stickers to in between a bone and an implant, the impact of adhesives on the modern world cannot be overstated. To find the best adhesive(s) for an application, customers should judge them by their cleavage strength, fatigue strength, impact strength, peel strength, shear strength, tensile strength, and wet strength.