Please tell me types of knurling of the blisters and difference between them.
Maintain a good knurl pattern.
Understand the impact that your sealing tool has on the material. A too-aggressive sealing dies combined with high pressure and high line speed might lead to stress cracking of the lidding foil and compromise the seal integrity. Even worse, this might become noticeable only long-term: Even though the in-process testing for seal integrity (in pharmaceuticals it’s usually a methylene blue bath) finds the seal OK, microscopic fractures in the foil might over time compromise the shelf life of the package.
Key characteristics of a platen sealing tool should be good flatness and appropriate knurl. Use pressure-sensitive tape to assure the planarity of the tool. For best results, you may want to vary the type of knurl depending on the type of lidding you run. It also makes sense to vary the knurl depending on the web width. Use smaller knurls on a narrow web, since the air can escape more easily. On a wider web, use a slightly larger knurl to allow some places for the entrapped air to go.
Regularly inspect and clean your sealing die surfaces. Dirt or other residues, e.g., from over lacquers, inks, and paper particles, can build up over time, absorb heat, distort the knurl pattern, and lead to an uneven seal.