Rigid PVC (unplasticized polyvinyl chloride, or PVC-U) is the material of choice for pharmaceutical and industrial blister packaging. Its widespread use is no coincidence: it offers an ideal cost-performance balance that is difficult for other polymers to match, together with processability that makes it ideal for high-speed thermoforming cycles. However, rigid PVC is also one of the most challenging materials to process: it is thermally unstable, has a narrow processing window and exhibits rheological behavior that requires rigorous control at every stage of the extrusion line.
BG Plast designs and manufactures complete extrusion lines for rigid PVC extrusion
What is rigid PVC for blister packaging, and why is it the industry standard?
PVC-U for blister packaging is a thermoplastic foil free from plasticizers, designed to provide maximum structural rigidity, crystal-clear transparency and dimensional stability. These characteristics make it ideal for thermoforming cavities for tablets, capsules or small industrial components: transparency allows visual inspection of the contents, while rigidity protects the product against impact and crushing during handling and logistics.
While blister packs for oral solid doses remain the best-known application, PVC-U is also used in numerous other fields where rigidity, transparency and chemical resistance are key requirements: packaging for consumer goods and dry food products, technical packaging for industrial components, embossed or satin finishes for general-purpose applications, as well as co-extruded foamed PVC structures for technical and decorative applications. The material’s versatility, combined with the wide range of finishes and thicknesses that can be produced, makes it a strategic polymer for industrial-scale technical and pharmaceutical packaging.
Key properties of rigid PVC for blister packaging
As mentioned, the success of rigid PVC comes from the balance between its mechanical characteristics and optical properties.
- High structural rigidity
The molecular structure of unplasticized PVC provides high resistance to deformation and crushing of thermoformed cavities. This effectively protects the packaged product during handling and transport.
- High transparency
The foil offers excellent transparency, allowing immediate visual inspection of the contents, an essential feature in both pharmaceutical and retail packaging.
- Chemical resistance
PVC has good chemical inertness against numerous external agents and is resistant to acids, mold and microorganisms.
- Self-extinguishing properties
Thanks to the chlorine in its molecular structure, PVC is naturally self-extinguishing, a characteristic that contributes to safety in many industrial applications.
- Standard barrier properties
PVC offers a good standard barrier to dust, contaminants and oxygen. Where greater moisture protection is required, the foil is typically laminated with barrier materials such as PVDC, PCTFE (Aclar®) or EVOH. Multilayer structures significantly improve performance.
How rigid PVC foil is produced: dry-blend formulation with K-value, stabilizers and lubricants
The typical thickness of monolayer foil for blister applications falls within a very narrow range, generally between 200 and 350 microns, with useful forming widths of approximately 350 to 1,200 mm. The combination of such low thickness and the need for absolute uniformity makes production of this material a real technical challenge for manufacturers of PVC extrusion lines.
Unlike many other polymers, PVC is never processed as pure resin. The compound fed to the extruder, commonly known as a dry-blend, is a mixture rich in functional additives, each of which directly affects the process parameters.
- PVC resin: K-values between 57 and 60 are typically used for blister applications, corresponding to a relatively low molecular weight that promotes melt flow and foil formability during thermoforming.
- Thermal stabilizers: typically calcium-zinc (Ca-Zn) or organotin-based, essential for slowing degradation during melting and approved for food and pharmaceutical contact in accordance with FDA regulations and European Pharmacopoeia requirements.
- Internal and external lubricants: polyethylene waxes or stearates that reduce friction between the polymer chains and between the melt and the metal surfaces of the extrusion line.
- Processing aids: acrylic polymers that improve melt strength at the die exit, a critical factor for the dimensional stability of thin foil.
Any change in this formulation alters the material’s rheological behavior and therefore requires precise adjustment of the machine parameters: zone temperatures, screw compression profile and rotational speed.
Blister transparency and strength: essential parameters achieved through proper extrusion and calendering
The thermal challenge: why rigid PVC is difficult to extrude
The most critical limitation in PVC-U processing is its sensitivity to heat and mechanical shear. Above 190-200°C, the material begins to degrade, releasing hydrochloric acid (HCl), a highly corrosive compound for mechanical components in contact with the melt. This imposes two fundamental design constraints for PVC extrusion:
- A low-shear-stress screw profile, to prevent localized overheating that can trigger degradation even when the average barrel temperature is under control.
- Effective corrosion protection on all parts in contact with the molten polymer – barrel, screw and flat-die flow channels – using bimetallic alloys, thick chrome plating or special surface treatments such as deep nitriding.
On the machine side, barrels and screws for these applications are generally made from high-strength alloy steels (41 CrAlMo7 for the screw and 38 CrAlMo7 for the barrel), nitrided as standard and, on request, provided with hard coatings or bimetallic technology for more demanding processing conditions. Ceramic band heaters and cooling – by air or water depending on production requirements – complete a thermal system capable of keeping PVC within its narrow processing window throughout the production cycle.
Single-screw or twin-screw: which technology for rigid PVC?
The choice of screw geometry depends mainly on the physical form of the incoming raw material. For processing powder dry-blend, counter-rotating twin-screw extruders are preferred because they ensure positive material conveying and more precise thermal control while reducing mechanical stress on the polymer. For pre-compounded granules, single-screw extruders with long screw profiles (typically L/D between 28 and 32) and progressive compression zones are more commonly used, ensuring homogeneous melting without hot spots.
Extrusion lines dedicated to rigid and soft PVC require specific application expertise, developed over time through direct field testing: each system must be calibrated to the exact rheological behavior of the formulation used by the customer, which can vary significantly from one producer to another.
Multilayer and barrier structures for pharmaceutical blister packaging
Monolayer PVC offers excellent rigidity, transparency and ease of thermoforming but, as mentioned, only limited moisture-barrier performance. For this reason, the pharmaceutical sector often relies on more complex multilayer structures.
- PVC/PVDC: polyvinylidene chloride provides an exceptional barrier to gases and moisture. It is applied by coating, with very precise control of the barrier-layer thickness.
- PVC/PE/PVDC: a solution used when maximum sealability and a high level of protection for the active ingredient are required.
- Structures with tie layers: intermediate adhesive layers that ensure adhesion between the rigid PVC mechanical support and the functional barrier layer.
Thickness tolerances and quality control: pharmaceutical industry standards
The pharmaceutical sector imposes extremely tight foil thickness tolerances, typically within ±2%. To achieve this level of precision, flat dies must integrate automatic die-lip adjustment systems, often controlled by in-line X-ray or beta-ray thickness gauges, capable of correcting thickness deviations in real time across the full foil width.
Equally critical is the absence of gels and unmelted particles in the matrix, a requirement achieved with an optimized plasticizing system. Finally, the cooling calender downstream of the extruder must precisely control the temperature of each individual roll to minimize internal stresses in the foil and limit shrinkage which, if excessive, compromises the subsequent thermoforming stage and, consequently, the packer’s production yield.
High-precision calendering improves the final result
BG Plast: application expertise in rigid PVC extrusion
BG Plast lines are specifically designed for the production of thin foils for thermoforming, with thicknesses from 0.15 to 1.80 mm, widths up to 2,000 mm, independent drive for each cylinder, dedicated thermoregulation and co-extrusion configurations with up to seven extruders. For applications requiring maximum thickness uniformity, the Cross-Axis device is also available, enabling even more precise adjustment during calendering.
Designing an extrusion line for rigid, soft or foamed PVC means tackling one of the most demanding processes in the entire plastics industry: every stage, from dry-blend dosing and melting through to calendering and cooling, must be calibrated to the material’s specific behavior to prevent thermal degradation and ensure stable production even during extended production runs.
This complexity is the foundation of the dedicated technical expertise we have built over the years, developing single-screw extruders, extrusion heads and calendering systems specifically sized for controlling PVC process temperatures. Co-extrusion configurations allow barrier layers and different materials to be integrated into the same product, while integration with haul-off, cutting, stacking and winding systems makes it possible to adapt each system to the end customer’s production requirements, whether for pharmaceutical blister foil, technical sheets or high-value niche applications.
For companies investing in a new PVC extrusion line or upgrading an existing system, the real difference in efficiency lies precisely here: in the ability to translate the chemical and physical characteristics of a complex polymer such as rigid PVC into a reliable and competitive production process over time. Start your new project with our experts: contact us.