Insufficient adhesion or cold bonding in hot melt adhesives can occur due to various factors. Below are the different causes of this issue along with corresponding solutions:

1. Low Temperature of Hot Melt in Use:

   • Solution: Increase the temperature of the hot melt to reach the suitable bonding temperature.

2. Excessive Open Time:

   • Solution: Reduce the open time to bring the adhesive closer to the substrate.

3. Slow Conveyor Belt Speed:

   • Solution: Increase the conveyor belt speed for a quicker bonding of the adhesive to the product.

4. Insufficient Applied Adhesive Amount:

   • Solution: Increase the applied amount of adhesive to achieve a better bond.

5. Materials to be Bonded and Low Ambient Temperature:

   • Solution: Raise the ambient temperature or the temperature of the materials to enhance adhesion.

6. Inadequate Pressure:

   • Solution: Adjust the pressure to the appropriate level for improved bonding.

Keep in mind that these factors may interact, so a combination of adjustments might be necessary. After implementing each change, fine-tune the settings through trial and error to achieve optimal adhesive performance.