Pharmaceutical aluminum-plastic blister packaging, commonly known as PTP (Press-Through-Pack) packaging, works by forming cavities in a packaging film via heated vacuum forming or cold forming, filling each cavity with a tablet or capsule, and heat-sealing a coated aluminum foil lidding over the top to create individual unit-dose compartments.
This format delivers precise single-dose medication 鈥?each pill isolated from the next 鈥?making it both portable and safer for patients. It provides excellent product protection, supports high-speed automated production, and keeps costs low. That combination of economy and convenience is why blister packaging dominates tablet and capsule packaging worldwide.
Standard blister packs use PVC rigid film as the forming web and aluminum foil as the lidding. But PVC’s limited barrier properties can’t always guarantee drug stability throughout shelf life. That’s where cold-form blister technology comes in.
Cold-form aluminum blister packaging replaces vacuum thermoforming with mechanical stamping, enabling the use of pure aluminum composite laminates as the forming material. The high-strength aluminum alloy foil in the structure delivers water vapor, oxygen, and light barrier performance that no other material can match.
1. Cold-Form Blister Foil Structure
Cold-form blister foil consists of three functional layers bonded together into a single composite:
1.1 Surface Support Layer
The surface layer must be smooth, transparent, with high mechanical strength, excellent impact resistance, and sufficient abrasion and puncture resistance. It protects the entire package. The standard choice is 25 渭m biaxially oriented polyamide (BOPA / nylon) film. Standard 15 渭m BOPA used in flexible packaging lacks the strength needed for cold-forming, where the material undergoes extreme impact and stretching forces. For shallow-draw applications, BOPET (polyester) or BOPP (biaxially oriented polypropylene) can substitute at lower cost.
1.2 Aluminum Foil Barrier Layer
Unlike conventional flexible packaging aluminum foil, cold-form foil must serve as both a barrier and a structural element 鈥?providing strength while stretching during forming. The aluminum is a special high-strength alloy with superior elongation. Standard thickness is 45 渭m, substantially thicker than conventional lamination foil (typically 6鈥? 渭m). For shallow-draw applications, thickness can be reduced to as low as 30 渭m. For deep-draw cavities (鈮?5 mm) or when higher stiffness is required, thickness can be increased to up to 70 渭m.
1.3 Inner Heat-Seal Layer
PVC rigid film (typically 60 渭m) serves as the inner heat-seal layer, allowing the cold-form blister to be heat-sealed with standard PTP aluminum foil lidding 鈥?just like conventional blister packaging. However, the PVC used here differs from standard grades: rather than adding conventional plasticizers and lubricants, internal plasticization is achieved by grafting plasticizing segments onto the PVC molecular chain. Impact modifiers are added at significantly higher levels than in standard PVC to ensure good lamination and forming performance. For applications requiring higher rigidity, PVC thickness can be increased to up to 100 渭m. In special cases, PP, PE, PET, or Surlyn resin can serve as the heat-seal layer.
2. Production Requirements
The three layers are bonded with adhesives. Choosing the right adhesive system is critical 鈥?it must withstand the extreme forming forces without delamination or fracture. Bond strength between aluminum and both the surface layer and heat-seal layer must reach at least 8 N/15 mm. The polyurethane adhesive formulation must carefully balance hard and soft segment ratios to accommodate cold-forming stresses. Standard adhesives cannot meet these requirements; cold-form blister adhesives are specially formulated products.
In 2002, China’s National Medical Products Administration issued industry standard YBB00242002 鈥?”Polyamide/Aluminum/Polyvinyl Chloride Cold-Forming Solid Pharmaceutical Composite Sheet” 鈥?which specifies requirements for appearance, water vapor transmission rate, oxygen transmission rate, heat-seal strength, peel strength, residual vinyl chloride monomer, residual solvents, extractables, microbial limits, and abnormal toxicity. Since 2003, cold-form foil manufacturers and importers have required production and import licenses.
3. Common Problems and Solutions
Despite excellent appearance and barrier properties, cold-form blister packaging presents unique production challenges: aluminum cracking and pinholes during cavity forming, and interlayer delamination.
3.1 Raw Material Quality
The 25 渭m BOPA surface layer scratches easily, and even minor surface damage dramatically reduces its strength. Scratches 鈥?often invisible to the naked eye 鈥?lead to aluminum and nylon fracture during forming. Scratches typically result from poorly rotating guide rollers, foreign matter on rollers, or contact with fixed equipment parts. They can occur at either the film manufacturer or the pharmaceutical packaging line.
BOPA is hygroscopic. Moisture absorption causes BOPA-aluminum delamination during forming and leads to aluminum cracking or pinhole formation. Even finished cold-form blisters can delaminate when stored in humid environments. Cold-form foil and finished blister packs must be stored under dry conditions.
3.2 Mold Design
During cold forming, the material is stretched close to its limit. Mold design 鈥?both material selection and punch geometry 鈥?is critical.
Mold material affects friction coefficient during forming. PTFE (Teflon) molds have a coefficient of friction of 0.4 against the PVC surface, versus 1.2 for POM (polyoxymethylene) and 2.1 for stainless steel. Lower friction means more uniform force distribution, greatly reducing aluminum cracking and delamination. For packaging the same tablet to the same depth, cavity area ratios are 1 : 1.2 : 1.4 (PTFE : POM : stainless steel). PTFE punches prevent forming defects while using less packaging material. The trade-off: PTFE is softer, more prone to surface damage, and damaged punches increase defect rates.
Punch geometry falls into two categories: smooth-transition and stepped-transition types. Smooth punches produce aesthetically pleasing cavities but have lower maximum draw depth and are more prone to forming defects. Stepped punches apply stretch in stages, reducing contact area during forming for more uniform material distribution. Computer software now optimizes punch geometry based on tablet dimensions to prevent localized over-stretching.
3.3 Process Control
Aluminum elongation at room temperature is limited 鈥?even the special alloy used in cold-form foil stretches only about 20%. Excessive draw depth leads to aluminum fracture and delamination. Forming depth should be minimized: deep enough to hold the tablet without the PTP lidding touching it during heat sealing, and no deeper.
Deeper cavities require either larger mold openings or thicker aluminum foil. Forming speed also matters 鈥?too fast and the material can’t stretch uniformly or relax internal stresses, increasing defect rates.
Preheating is a double-edged sword. Higher temperature aids PVC forming but reduces PVC-aluminum and aluminum-nylon bond strength, increasing delamination risk. It also typically increases the PVC-punch friction coefficient. Whether preheating helps depends on the specific punch material and PVC formulation. Even when beneficial, the temperature must be validated 鈥?above a certain threshold, friction can spike suddenly and bond strength can drop abruptly, causing defects.
3.4 Pinhole Detection
Micro-cracks and pinholes that don’t fully penetrate the composite can’t be caught by vacuum leak testing or visual inspection. Yet they critically compromise shelf life. Automated pinhole detectors using optical or far-infrared signals inspect formed cavities inline, with adjustable detection thresholds from 30鈥?00 渭m. When a defect exceeding the threshold is detected, the system automatically ejects the defective blister card.
3.5 Heat-Seal Issues
Cold-form blister PVC is only about 60 渭m thick 鈥?less than one-quarter the thickness of standard thermoformed PVC blister (200鈥?00 渭m). PTP lidding foil typically uses just 20 渭m aluminum with a 3鈥? 渭m heat-seal coating.
Most blister machines use dot-pattern heat-seal tooling for appearance rather than cross-hatch line patterns. With dot sealing, if the heat-seal layer is too thin or pressure is insufficient, not enough molten resin flows to fill gaps between dots 鈥?air can reach the tablet even when peel strength feels adequate. Market sampling has found that 18% of cold-form blister packs leak under vacuum testing. PTP foil heat-seal coating thickness should be increased for cold-form applications, with the exact requirement depending on dot size, height, and density.
3.6 Deformation
Cold forming produces significant stress beyond the cavity area. Non-cavity areas deform, causing wrinkles during heat sealing (affecting appearance and seal integrity) and waviness that causes tracking instability. Deformation results from poor material forming performance, inadequate mold design, or improper web tension control.
3.7 Lidding Crush Damage
Because cold-form blister packs are opaque on both sides, PTP foil crush damage during heat sealing is invisible. Two types occur: crushing in non-sealed cavity areas 鈥?detected by vacuum leak testing 鈥?and crushing at seal points due to burrs on the heat-seal tooling or excessive pressure. The latter doesn’t affect hermeticity but severely impacts barrier performance and shelf life, and is essentially impossible to detect. Prevention relies on rigorous process validation and using thicker PTP foil 鈥?25 渭m or even 30 渭m aluminum instead of the standard 20 渭m.
4. Conclusion
Cold-form aluminum blister packaging has matured over nearly two decades, with increasingly sophisticated automated equipment delivering near-perfect results. As domestic Chinese production of both cold-form foil and blister machines expands and prices decrease, cold-form blister packaging will reach more pharmaceutical products and more households.
References
- Wikipedia: Blister Pack 鈥?Overview of blister packaging technology including PTP and cold-form variants
- Wikipedia: Aluminum Foil 鈥?Material properties of aluminum foil including barrier and mechanical characteristics
- Wikipedia: Nylon 6 (BOPA) 鈥?Properties of biaxially oriented polyamide film used as cold-form surface support layer
- Wikipedia: BOPET (Polyester Film) 鈥?Alternative surface support material for shallow-draw cold-form applications
- FDA: Pharmaceutical Quality Resources 鈥?US regulatory guidance on drug packaging materials and container closure systems
- ISO 11607 鈥?Packaging for Terminally Sterilized Medical Devices: International standard for seal integrity and packaging material performance