Open time is the time between application of the adhesive and bonding. In the open time, a liquid hot melt adhesive spreads on the surfaces to be joined and ensures the necessary adhesion. As the viscosity of a hot melt adhesive increases after application, the open time for hot melt adhesives is limited.
The length of the open time depends on:
- Application temperature,
- Applied quantity,
- Temperature of the subtrate,
- Temperature of the product,
- Thermal conductivity of the substrate,
- Absorbency of the substrate,
- Room temperature,
- Application method,
- Ambient temperature,
- Machine speed,
- Composition of the hot melt adhesive.
Open time for hot melt adhesives
In the case of hot melt adhesives, the open time can range from fractions of a second to over 300 seconds.
Open time for pressure-sensitive adhesives
Pressure-sensitive adhesives consisting of TK (thermoplastic elastomer) are characterised by open times far above those mentioned above. These adhesives are referred to as “permanently tacky” because they do not completely harden. There is a distinction between permanently adhesive and removable types.