The time values on a technical data sheet directly determine the speed and quality of your line. Confusing them is one of the most common causes of problems in the field.
Open time
The maximum time after application within which parts can be joined. Exceed it and the adhesive skins over and can no longer wet the second surface. Seconds for hot melts, minutes for dispersions.
Flash-off time
For contact adhesives, the time to wait before joining so the solvent can evaporate. Join when the film no longer sticks to a finger.
Press time
How long parts must stay under pressure. For dispersions it depends on temperature, substrate moisture and coat weight.
Green strength
The strength at which parts can leave the press and move to the next step. Hot melts and PUR reach it within seconds, which is their key advantage.
Final strength
The time for the adhesive to reach full strength: 1–7 days for PUR hot melts depending on humidity, 3–5 days for crosslinked solvent-based PU.
What affects these times?
| Factor | Effect |
|---|---|
| Ambient temperature | Cold slows curing and shortens hot melt open time |
| Relative humidity | Speeds up moisture-curing systems |
| Substrate moisture | 8–12% is ideal for wood; more delays dispersion drying |
| Coat weight | More adhesive lengthens open time and slows drying |
| Part temperature | Cold parts freeze hot melts instantly |
Data-sheet values are measured under standard conditions (usually 20 °C, 65% RH). Run trials in your own conditions to set the best parameters for your line.
