Ultrasonic heating and hardening of hot melt adhesive

The application of hot melt adhesives is based on heating the adhesive from solid state to liquid state for wetting, and cooling back to its solid state to develop cohesive and adhesive strength. Conventional hot melt adhesive application methods use a separate heat source to melt the adhesive and apply it onto one of the substrates. Frequently, the adhesive cools while the second substrate is brought into contact with it resulting in inadequate wetting. With ultrasonic vibration, viscoelastic internal heating of the adhesive is used to melt it and to aid in wetting of the pre-placed hot melt adhesive film on the surfaces of both substrates. In this work, a conventional 40 kHz -ultrasonic welder was used to heat a coated hot melt adhesive film in a laminate. The effects of the processing parameters of heating time, vibration amplitude, heating pressure, and hold pressure on bond performance were studied. It was found that the holding pressure plays an important role in sealing and bonding performance. Through the use of ultrasonic vibration it was possible to produce high quality seals in very short cycle times of less than 7 seconds.