Hot melts are 100% solid thermoplastic compounds, which are compounded and applied in the molten state at elevated temperature, the resultant properties being obtained by cooling. Due to the quick cooling, bonds can be established in a very short time. Also a hot melt can be melted again, when already in the glue line. The advantages of hot melts are:
100% solid, contain no organic solvents; no water or solvent to be evaporated; low requirements concerning working and environmental safety easy to use, short set time allows high speed operation (up to 100m/min) rapid bond strength increase high bond strength
effective bonding even of difficult-to-bond surfaces: polyethylene (PE), polypropylene (PP), varnishes, and others combination of flexibility and toughness
adhesion to a wide variety of substrates even without a primer high variability in formulation (color, viscosity during application, temperature, and others)
practically unlimited storage life, easy storage no time limitations in application, hence no pot life problems no pollution of machinery and adherends, because of exactly metered application good temperature control during application, easy to use in automated production systems
The disadvantages of hot melts are:
cold flow: hot melts creep under mechanical load, even far below the melting temperature; bonds can open slowly, this effect being accelerated by higher temperatures
low heat resistance at elevated temperatures due to thermoplastic behavior; loss of bond strength
sensitivity of certain substrates to the required application temperature degradation at elevated temperature (color, viscosity)