Aluminum lidding foil (often referred to as “aluminum blister foil” or “aluminum cover film”) for blister closure and sealing is an essential component of blister packaging, particularly in the pharmaceutical sector, where it represents a critical element of primary packaging.
What is aluminum lidding foil for blisters?
Aluminum lidding foil is a thin aluminum film, with typical thicknesses of 20, 25, or 30 microns, used to seal preformed cavities (blister pockets) made of plastic materials, generally PVC or PS, containing tablets, capsules, or other solid pharmaceutical dosage forms.
Function and composition
- Closure and protection: the primary function of aluminum lidding foil is to provide a high-performance barrier to protect the packaged product. Aluminum ensures excellent protection against moisture, oxygen, and light, which may compromise the stability of active pharmaceutical ingredients.
- Sealing: the inner side of the lidding foil is coated with a heat-sealable layer, generally consisting of a specific lacquer. The combined application of heat and pressure during the heat-sealing process ensures a hermetic and secure bond between aluminum and plastic.
- Integrity and tamper evidence: the material ensures package integrity and provides tamper-evident functionality, as access to the contents requires irreversible rupture of the seal.
How printing on aluminum lidding foil for blisters is performed
Printing on aluminum lidding foil is a technologically strategic step, as it enables the application of mandatory regulatory information, identifying graphic elements, and traceability codes. Printing is generally carried out on the outer matte side of the material, which is properly treated to ensure adequate ink adhesion.
- Main printing methods
The most widely used technologies for printing on aluminum lidding foil reels are:
Rotogravure printing: a technology suitable for high print runs and consistent graphic quality.
Flexographic printing: widely adopted in primary pharmaceutical packaging, it enables multicolor printing (for example up to four colors) with high precision and excellent performance on non-absorbent substrates such as aluminum.
- Purpose and printing requirements
Printing on aluminum lidding foil must include:
- Branding and graphics: logo, corporate colors, coordinated layout.
- Product information: medicinal product name, dosage, expiry date, batch number.
- Coding and marking: barcodes, QR codes, and other identification systems must ensure high resolution, readability, and compliance with applicable regulations and quality requirements.
- The printing process (roll-to-roll configuration)
The printing process for aluminum lidding foil is carried out on automated industrial lines in roll-to-roll configuration, often installed in controlled environments such as cleanrooms in the case of primary pharmaceutical packaging.
- Continuous process: the roll-to-roll system enables continuous processing of the reel, which is unwound, printed, and rewound in a single operational flow, ensuring high efficiency and optimization of production volumes.
- Substrate preparation: the lidding foil reel is unwound; the outer side is treated to ensure optimal ink adhesion.
- Ink application: the material passes through the printing units (printing plates in flexography), which transfer the ink with precise control of register and density.
- Drying and finishing: after deposition, the ink undergoes drying or curing. The printed material is then rewound into a reel, ready for use on blister packaging lines.
- Reduction of downtime: the elimination of single-sheet handling and the high level of automation reduce downtime and improve overall process reliability.
The printed aluminum lidding foil reels are subsequently used by blister packaging machines to seal the plastic cavities previously filled with the product.
UV curing and infrared drying
In the context of printing on aluminum lidding foil, both UV curing and IR drying play a decisive role. The selection or integration of the two technologies depends on parameters such as line speed, ink type, regulatory requirements, and the characteristics of the metallic substrate.
UV curing
- Instant curing: UV inks polymerize immediately upon exposure to ultraviolet radiation, enabling high production speeds.
- High graphic definition: immediate cross-linking maintains a stable and sharp print dot, reducing the risk of smearing or color variation.
- Low VOC emissions: UV inks are characterized by low or zero solvent content, a relevant aspect in primary packaging.
- High mechanical and chemical resistance: the cured ink exhibits surface hardness, abrasion resistance, and stability during heat-sealing phases.
UV technology is particularly effective on non-absorbent substrates such as aluminum, where absorption-based drying is not feasible.
Infrared drying (IR)
IR drying represents an equally strategic technology, especially when solvent-based or water-based inks are used:
- Controlled and uniform heating: infrared radiation transfers energy directly to the ink film, accelerating the evaporation of volatile components.
- Thermal control of the metallic substrate: in advanced systems, IR intensity can be modulated to prevent deformation or thermal stress on the lidding foil.
- Drying uniformity: ensures film stability and optimal adhesion prior to subsequent processing steps.
- Integration in hybrid lines: IR can be used as a standalone phase with conventional inks or as a pre-drying stage in combined UV/IR systems, improving overall process quality.
Advantages of UV and IR configuration in the pharmaceutical sector
The integration of UV curing and IR drying in roll-to-roll lines for aluminum lidding foil enables:
- High industrial productivity.
- Stability and sharpness of critical information: enables the reproduction of microtext, barcodes, QR codes, and high-resolution security features, essential for traceability and regulatory compliance.
- Resistance to heat-sealing cycles and handling.
- Compliance with safety and low-migration requirements for primary packaging.
- Operational flexibility in managing different ink formulations.
Roll-to-roll printing on aluminum lidding foil, using UV curing and/or infrared drying, represents a technologically advanced and highly reliable solution. The balance between these two technologies makes it possible to optimize quality, safety, productivity, and regulatory compliance, meeting the stringent requirements of pharmaceutical and food primary packaging.
Written by Marzia C. | Team Giugni®
