Possible Problems When Bonding Hot-Melt Adhesive
- Cooling the adhesive during application prevents the formation of a good seam. A "good" tackiness can be created, which may be broken later when force is applied. Cooling can be caused by the following factors:
- adhesive open time is too short for application;
- application temperature is too low;
- not enough glue;
- air movement around the application area;
- low ambient temperature;
- bonding cold material.
- Package contents’ effects.
- physically introduces additional stress into the seam;
- chemicals or solvents soften the glue seam.
- insufficient pressing;
- movement of the bonded surfaces during joint consolidation.
- reusable material;
- more difficult for gluing material;
- coated material (wax, lacquer) or impregnation.
- insufficient heat resistance of the hot melt adhesive;
- poor resistance to low temperatures, causing cracking;
- insufficient adhesion to certain materials;
- residual heat inside the package, which can shift the solidification point up to 24 hours in some cases
When the box leaves the packaging machine, the valve opens
- Open time is too short - the adhesive cools down before pressing.
- The temperature of the adhesive is too high - gluing does not occur in time.
- There is too much hot-melt applied - the adhesive does not seize in time.
- Poor alignment of the packaging surface – it increases the tension in the "raw" joint.
- The ambient temperature is high - the adhesive does not seize in time.
- The temperature of the substrate to be bonded:
- too high - the adhesive does not seize in time;
- too low - the adhesive cools down before pressing.
- Bad pressing.
- An improper hot melt type is selected.
Filament formation from the glue applicator
- Application temperature is too low.
- Air flow from open doors in the room.
- The nozzle is too far from the application surface.
- Unsuitable adhesive for the application method.
- Applicator malfunction.
Lack of hot-melt in the applicator head
- The equipment is insufficient to melt the glue.
- The melting system temperature is too low.
- Low glue melting speed.
- The level of glue in the tank was allowed to drop too low for proper replenishment.
- The applicator voltage is too low.
- Glue blockage in the pre-melting device or feed system; possibly due to the wrong size or shape.
Excessive vapours or odour occurrence
The temperature of the glue is too high:
- incorrect adjustments may have been made;
- the thermostat may be defective;
- there may be a heater problem;
- the glue tank may need to be cleaned.
Colour change of hot melt during application
- Contamination of the hot melt adhesive.
- Thermal decomposition due to application at a higher temperature than recommended. This can lead to the following consequences:
- carbonization that forms solid particles;
- carbon deposits on the walls of the reservoir, the supply hose and the injector;
- viscosity change of the hot melt adhesive;
- congealing throughout the system;
- injector clogging.