When ambient temperatures plummet, the physical state and processing characteristics of hot melt adhesives undergo fundamental changes. Understanding these changes is a prerequisite for ensuring their usability.
1. Risk of Brittle Fracture: Solids Losing Toughness
Low temperatures reduce the mobility of polymer chains, causing the adhesive to transition from a tough state to a brittle and rigid state. EVA, PSA sticks, or granules are more prone to cracking or shattering when subjected to external force (e.g., impact, dropping) at low temperatures. This not only affects their appearance but also poses challenges for automatic feeding systems.
2. Altered Melting Performance: Increased Energy Consumption and Thermal History Risk
Initial Viscosity Surge: When cold granules are fed into the melting equipment, they require more energy to reach a molten state, leading to an extremely high initial melt viscosity. This significantly increases the drive load and energy consumption of the equipment and may cause uneven adhesive application due to poor flow.
Overheating Risk and Degradation: Forcibly increasing the set temperature to achieve faster application speed can lead to surface oxidation and charring ( "scorching") of the adhesive, while the interior remains inadequately homogenized, compromising final bond performance.
3. Drastic Change in Curing Curve: Shortened Open Time and Poor Wetting
When molten adhesive is applied from the equipment onto a cold substrate, heat is rapidly drawn away, causing the adhesive temperature to plummet.
Shortened Open Time: The time window available for adjusting the adhesive shrinks dramatically, requiring higher operational precision.
Reduced Wettability: The instantaneous increase in viscosity prevents the adhesive from flowing adequately and wetting the microscopic pores of the substrate surface, directly leading to reduced bond strength and even apparent adhesion failure.
4. Phase Change and Deactivation of Specific Adhesives
Crystallization of PUR: Some PUR products may crystallize at low temperatures, manifesting as abnormally high viscosity or the appearance of granular matter, making them difficult to process and compromising their performance.
Freezing of Water-based PUD: Once frozen, the polymer particles in water-based adhesives (e.g., PUD) can break, coalesce, and agglomerate under the pressure of ice crystals. Their original performance cannot be restored after thawing, leading to permanent spoilage.
When ambient temperatures plummet, the physical state and processing characteristics of hot melt adhesives undergo fundamental changes. Understanding these changes is a prerequisite for ensuring their usability.
1. Risk of Brittle Fracture: Solids Losing Toughness
Low temperatures reduce the mobility of polymer chains, causing the adhesive to transition from a tough state to a brittle and rigid state. EVA, PSA sticks, or granules are more prone to cracking or shattering when subjected to external force (e.g., impact, dropping) at low temperatures. This not only affects their appearance but also poses challenges for automatic feeding systems.
2. Altered Melting Performance: Increased Energy Consumption and Thermal History Risk
Initial Viscosity Surge: When cold granules are fed into the melting equipment, they require more energy to reach a molten state, leading to an extremely high initial melt viscosity. This significantly increases the drive load and energy consumption of the equipment and may cause uneven adhesive application due to poor flow.
Overheating Risk and Degradation: Forcibly increasing the set temperature to achieve faster application speed can lead to surface oxidation and charring ( "scorching") of the adhesive, while the interior remains inadequately homogenized, compromising final bond performance.
3. Drastic Change in Curing Curve: Shortened Open Time and Poor Wetting
When molten adhesive is applied from the equipment onto a cold substrate, heat is rapidly drawn away, causing the adhesive temperature to plummet.
Shortened Open Time: The time window available for adjusting the adhesive shrinks dramatically, requiring higher operational precision.
Reduced Wettability: The instantaneous increase in viscosity prevents the adhesive from flowing adequately and wetting the microscopic pores of the substrate surface, directly leading to reduced bond strength and even apparent adhesion failure.
4. Phase Change and Deactivation of Specific Adhesives
Crystallization of PUR: Some PUR products may crystallize at low temperatures, manifesting as abnormally high viscosity or the appearance of granular matter, making them difficult to process and compromising their performance.
Freezing of Water-based PUD: Once frozen, the polymer particles in water-based adhesives (e.g., PUD) can break, coalesce, and agglomerate under the pressure of ice crystals. Their original performance cannot be restored after thawing, leading to permanent spoilage.
