Hot melts are applied to substrates in a liquid (molten) state.
Open time and set time are two key processing parameters for effective bonding.
- Open time: It is the time elapsed between applying the molten adhesive onto the substrate and the transformation to the solid-state, at which point the hot melt adhesive loses its ability to wet the substrate,
- Set time: It is the time it takes to form an acceptable bond when two or more substrates are combined with a hot melt adhesive.
1) Substrates to be bonded must be clean, dry, and free of dust, oil, and grease.
2) Hot melt adhesive must be applied at the correct temperature range.
3) The ambient temperature and the temperature of the substrates can affect adhesion:
-Too hot — a longer time to set
Too cold — the adhesive sets before substrates are bonded.
4) The amount of adhesive applied will affect the bond:
-Less adhesive cannot wet out the substrate sufficiently. The adhesive will cool quickly and may cause bonding failure.
-Too much adhesive will take more time to set. The adhesive can be pressed outward while the pressure takes place on the substrates for bonding. This excess adhesive can detach and adversely affect subsequent line operations.