How does the viscosity of PUR flat lamination hot melt adhesive affect its application performance at different temperatures?

The viscosity of PUR flat lamination hot melt adhesive has a significant impact on its application performance at different temperatures. The following is a detailed analysis of this effect:

1. Relationship between viscosity and temperature
The viscosity of PUR flat lamination hot melt adhesive usually decreases with increasing temperature, and increases conversely. This is because changes in temperature affect the movement speed and interaction force of polymer molecules, thereby affecting the fluidity of the adhesive.

2. Effect of viscosity on application performance
Coating uniformity:
At high temperatures, the viscosity of PUR flat lamination hot melt adhesive decreases, the fluidity increases, and it is easier to form a uniform coating on the surface of the adherend. This helps to increase the bonding area and bonding strength.
At low temperatures, the viscosity increases and the fluidity weakens, which may lead to uneven coating and affect the bonding effect.
Initial bonding strength:
PUR flat lamination hot melt adhesive with higher viscosity may have higher initial bonding strength before curing because it forms a thicker coating on the surface of the adherend and has stronger intermolecular forces. However, too high viscosity may also cause coating difficulties and affect the uniformity of initial bonding strength.
At low temperatures, initial adhesion strength may be affected due to increased viscosity, as the adhesive is not easy to penetrate into the tiny pores of the adherend.

Permeability:
PUR flat-press hot melt adhesives with low viscosity can more easily penetrate into the tiny pores of the adherend, forming a tighter bond. This helps to improve bond strength and durability.
At high temperatures, permeability is enhanced due to reduced viscosity; at low temperatures, permeability is weakened.
Curing speed:
Although viscosity itself does not directly affect the curing speed, changes in viscosity may affect the coating and penetration process, and thus affect the bonding effect after curing. For example, high-viscosity adhesives may not be easy to apply evenly, resulting in uneven bond strength after curing.
Temperature also has a significant effect on curing speed. Generally speaking, as the temperature increases, the curing speed accelerates. However, too high a temperature may cause the adhesive to cure too quickly, affecting the bonding quality.

III. Considerations in practical applications
In practical applications, it is necessary to select the appropriate PUR flat-press hot melt adhesive viscosity grade based on the material, shape, size of the adherend and the required bonding strength, temperature resistance, chemical resistance and other performance requirements. At the same time, factors such as coating process, curing conditions and production costs also need to be considered.