Blister Materials – Foil Lidding Structures
The History of Pharmaceutical Blister Packaging Materials – Foil Lidding Structures
The aluminum foil is general a “hard” aluminum. Again, the US and global markets were historically differentiated. In the US, where the imperial measurement system was common, most foil lid stocks were 1 mil thick, or 25.4 µm. In Europe the 20.0 µm thickness became common, and offered a slight yield advantage. In recent years the trend is to the thinner 20.0 µm film regardless of the market.
Today the vast majority of the aluminum foil has a “universal” Heat Seal Lacquer applied to assure a good seal.
Alcan Packaging SINGEN was the first company in the world to produce a rigid aluminium foil with a tight seal to uPVC film. A critical factor in this first lid stock was the ease which oral solid dose tablets were pushed through the foil. This foil was used by Schering and Organon for their contraceptive products.
Early challenges revolved around developing a foil with good tear properties – so that the product could be easily “pushed” through the foil – and good sealing properties – to allow a hermetic seal needed for product integrity.
Aluminum foil for packaging is characterized by its temper as either being “hard” or “soft.” The soft foil receives additional annealing and any of the lubricants used during the rolling process are evaporated. For hard tempered foil, lacquers are used to handle the rolling additives.
Application of protective lacquer is carried out in the first processing step. Drying (removal of solvents) is carried out at high air temperature and with airflow. The heat of the drying and the air flow also assist in removing the rolling oil from the inner side of the material.
Heat-seal lacquering is carried out in the second processing step. The lacquer contains resins which bind the residual rolling oil and which are characterized by a good adhesion to the surface. The heatseal lacquers are also chosen for their sensitivity to humidity.
Foil lidding is critical in understanding the three major “families” of blisters in use today:
- Push-Through (PTP): for sealing foil lids to various formable films with the general structure of:
- Prelacquer –> Aluminum (hard or soft tempered) –> Heat Seal Coating (HSC)
- Peel: for sealing foil lids to formable films (generally PVC or PP) with one of the following structures:
- Paper –> PET –> soft tempered Aluminum –>HSC
- PET –> soft tempered Aluminum –> HSC
- Paper –> soft tempered Aluminum –> HSC
- Peel/Push: for sealing foil lids to formable films (generally PVC or PP) with one of the following structures:
- Paper –> PET –> Special Adhesive –> soft tempered Aluminum –> HSC
- PET –> Special Adhesive –> soft tempered Aluminum –> HSC
As the market developed, lidding films differ according to:
- Type of opening
- Child Resistance
- Printability (pre-printed or printed in-line)
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