As with other types of adhesives (such as liquid, paste and powder), film and hot melt adhesives have numerous application methods. Because the compositions of films and hot melts vary, each application method varies according to the adhesive’s medium—as a result, some applications are well-suited to certain methods over others. Film adhesives are specifically for use on flat surfaces, while hot melts have a much broader range of applications. A description of each application method and appropriate use is offered below.
Film Adhesive Application Methods
Dry adhesive films offer several advantages because of their medium. The lack of mixing makes the application process relatively clean, and it doesn’t produce much waste. There are low emissions and environmental concerns associated with film adhesive application, and equipment is typically inexpensive.
Film adhesive traits can vary depending on the exact type of adhesive. Typically, film adhesives are heat-activated, solvent-activated, or pressure sensitive, with some adhesive films featuring a supportive mat.
When preparing to apply a film adhesive, the component should first be coated with a primer, which can be air-sprayed or applied using manufacturer recommended equipment. Primer thickness should be considered because it will affect how strongly the adhesive bonds to the component. Once the primer coating has air dried, application of the film adhesive can begin.
Depending on the type of film, the adhesive layer is applied using one of several methods. Typically, application begins with removing the protective supportive mat and a layer of protective film. Next, the adhesive is laid flat on the component’s surface, though it’s important to make sure that the film doesn’t wrinkle or trap any air. For solvent-activated films, a solvent is wiped on the film (care should be taken not to use too much solvent), and then pressure is used to enable the film to adhere to the component. Heat-activated films must be heated to properly adhere to a component.
Hot Melt Adhesive Application Methods
Hot melt adhesives, also called thermoplastic adhesives, are basically blocks of thermoplastic adhesive material that can be melted at very high temperatures and applied to a component. When a hot melt dries, it has adhered to the component in much the same way as glue. In fact, hot glue guns use a type of hot melt adhesive.
Typically, there are two main systems through which a hot melt adhesive is applied: melt-reservoir systems and pressure feed systems.
Reservoir systems can handle a large amount of adhesive, which begins in a heated reservoir holding area. After being pumped through a feed-hose, the adhesive is either applied via an extrusion gun or wheel, which deposits a layer of adhesive on the specific component. These types of systems are appropriate for low-performance adhesives, and can deposit about 4 to 5 kilograms (kg) of adhesive per hour.
Progressive feed systems are suited to handle a much smaller amount of adhesive. In industrial variants, adhesive pellets are transferred from a hopper to a heated grid, where they melt. Next, the heated adhesive is fed though a pump, pressurized, and then fed through a hose into a heated gun. Around 9 kg per hour, but keeps a very small amount in a melted state at any given time. For non-industrial systems, hand-held glue guns serve as a much smaller type of progressive feed system.