Cold-stamped blister packs (referred to as “Farmaceutyczne pakiety pęcherzy”) are the mainstream packaging format for oral solid formulations (NP., tabletki, kapsułki). Their “aluminum-plastic composite film” must fulfill dual functions: ① physical protection (anti-impact, odporność na wilgoć); ② chemical barrier (blocking oxygen, para wodna, and light to prevent pharmaceutical oxidative degradation). Notably, according to the China Pharmaceutical Packaging Industry Development Report (2024), 38% of pharmaceutical shelf-life reduction incidents stem from excessive oxygen transmission rate (OTR) of blister packs—with aluminum foil pinholes being the primary cause.
The aluminum foil layer of pharmaceutical blister packs undertakes over 90% of the oxygen barrier task. konkretnie, 8079 folia aluminiowa for cold-stamped blister packs (6.50μm thick, O temper, Mn content 0.8%-1.2%, elongation ≥30%) becomes the core barrier substrate due to its compatibility with deep drawing (3-8mm depth) and near-zero oxygen transmission rate at room temperature. Jednakże, pinholes in aluminum foil (defined as “penetrating holes” by GB/T 31985-2015) form “oxygen transmission channels”—the more pinholes, the higher the OTR of the blister pack.
Obecnie, the industry-wide standard for aluminum foil pinholes is ≤5 holes/m². Yet, some pharmaceutical companies need to add an additional PVDC layer (increasing costs by 20%-30%) due to excessive OTR. This raises a critical question: Can controlling the pinhole count of 8079 aluminum foil for cold-stamped blister packs to ≤0.5 holes/m² break the OTR bottleneck? Answering this requires analysis from three interconnected aspects: oxygen transmission mechanism, quantitative relationship, and process verification.
Fundamentally, the OTR of pharmaceutical blister packs follows the “series barrier model”—oxygen must penetrate the plastic layer, adhesive layer, and aluminum foil layer sequentially. Among these layers, the barrier capability of 8079 aluminum foil for cold-stamped blister packs is far superior to others: the OTR of plastic layers is typically 10-50 cm³/(m²·24h·atm), while that of pinhole-free aluminum foil is ≤0.01 cm³/(m²·24h·atm). Więc, pinholes in the aluminum foil become the “bottleneck determinant” of overall blister OTR.
To quantify the relationship between pinhole count and OTR, we apply Fick’s Law and the “channel superposition principle”. Assuming the blister pack structure is “PCV (80um) + adhesive (5um) + 8079 aluminum foil for cold-stamped blister packs (6.5um)”—with a fixed plastic layer OTR of 12 cm³/(m²·24h·atm)—the OTR contributed by aluminum foil pinholes (O₂ₐₗ) is calculated using the formula:
O₂ₐₗ = N × S × D₀₂ / δ
Where:
The results of calculations for different N values are summarized in Table 1:
Notatka: When the OTR contributed by aluminum foil pinholes is ≤0.05 cm³/(m²·24h·atm), the OTR of the plastic layer (12 cm³/(m²·24h·atm)) is restricted by the aluminum foil due to the “series barrier effect”. W tym przypadku, the actual total OTR is dominated by the aluminum foil, with the plastic layer contributing <0.001 cm³/(m²·24h·atm).
To validate the theoretical conclusions above, a pharmaceutical packaging enterprise conducted experiments using 8079 aluminum foil for cold-stamped blister packs (6.50μm/O temper), divided into 4 groups by pinhole count. Blister packs were manufactured, and their OTR was tested in accordance with ASTM D3985-2017 Standard Test Method for Oxygen Transmission Rate Through Plastic Film and Sheeting. Dodatkowo, pinhole stability tests after cold stamping (simulating a 12-month shelf life) were performed to assess long-term performance.
The initial OTR data—measured before and after cold stamping—are presented in Table 2:
Two key conclusions emerge from these results:
Beyond initial OTR testing, long-term stability is critical for pharmaceutical packaging. Accelerated aging tests were therefore conducted on the blister packs of Group 4 (pinhole count 0.4 holes/m²), with regular monitoring of OTR and aluminum foil pinhole status. The results are shown in Table 3:
By comparison, for Group 1 (pinhole count 5.2 holes/m²): After 12 miesiące, OTR increased to 0.35 cm³/(m²·24h·atm), and the pharmaceutical oxidative degradation rate reached 3.2%—exceeding the pharmacopoeia requirement of ≤1%.
Wniosek: 8079 aluminum foil for cold-stamped blister packs with a pinhole count of ≤0.5 holes/m² maintains stable blister pack OTR throughout the shelf life, effectively inhibiting pharmaceutical oxidation.
To achieve the stringent pinhole control target of ≤0.5 holes/m², a closed-loop management system must be established across the “raw material-rolling-inspection-forming” process—aligning with the high compliance requirements of pharmaceutical packaging.
First and foremost, controlling raw material quality is essential to prevent pinhole formation at the source:
Następny, the rolling process—where thin-gauge aluminum foil is most prone to pinhole formation—requires targeted optimization. For 6.50μm aluminum foil, a strategy of “low speed, high tension, and stepwise reduction” is adopted to minimize rolling-induced stress and pinholes. The key parameters for each rolling stage are detailed in Table 4:
To ensure 100% detection of pinholes post-rolling, a multi-layered inspection system is implemented:
Wreszcie, optimizing the cold stamping process prevents secondary pinhole expansion:
W podsumowaniu, controlling the pinhole count of 8079 aluminum foil for cold-stamped blister packs (6.50μm/O temper) to ≤0.5 holes/m² delivers a “breakthrough improvement” in blister pack OTR, with three key benefits:
Looking ahead, future development will focus on three directions to further enhance performance:
Ostatecznie, the core principle of OTR control for pharmaceutical blister packs is to prioritize pinholes in 8079 aluminum foil for cold-stamped blister packs as the key control point. A pinhole count of ≤0.5 holes/m² is not only critical for meeting OTR standards but also a vital guarantee for pharmaceutical stability and medication safety—aligning with the “zero defect” compliance requirements of pharmaceutical packaging.
