The most basic material for the forming is PVC or Polyvinyl Chloride. The main advantages of PVC are the low cost and the simplicity of thermoforming. The key disadvantages are the inadequate barrier against moisture access and oxygen ingress. In the instance of blister packaging the PVC sheet does not contain any plasticizer and is sometimes referred to as Rigid PVC or RPVC. In the absenteeism of plasticizers, PVC blisters offer structural firmness and physical protection for the pharmaceutical dosage form.
On the other hand, the blister cavity must remain accessible by the push-through effect and the formed web may not be too hard to collapse when pressed upon; for this reason the PVC sheet thickness is characteristically preferred between 200µ to 300µ depending on the cavity size and shape.
Most PVC sheets for pharmaceutical blisters are 250µ or 0.250 mm in thickness. Usual values for the Water Vapor Transmission Rate (WVTR or MVTR) of a 250µ PVC film are around 3.0 g/m2/day measured at 38°C/90%RH and the Oxygen Transmission Rate (OTR) is around 20 cc/m2/day. In order to overcome the lack of barrier properties of PVC film, it can be coated with PVDC or laminated to PCTFE or COC to increase the protective properties. Multi-layer blister films based on PVC are often used for pharmaceutical blister packaging, whereby the PVC serves as the thermoformable backbone of the structure.
Furthermore, the PVC layer can be colored with pigments and/or UV filters. In order to be suitable for pharmaceutical blister packs, the PVC formulation also needs to meet the terms with the US Pharmacopoeia <661>; EU food legislation; US 21.CFR and Japanese food contact requirements.
Polychlorotrifluoro ethylene or PCTFE can be laminated to PVC to obtain very high moisture barrier. Typical constructions used for pharmaceutical products are 250µ PVC film laminated to 15µ-100µ PCTFE film. Duplex structures are PVC/PCTFE and triplex laminates are PVC/PE/PCTFE. Deeper cavities can be formed by using the triplex structures with PE. Typical WVTR values are between 0.06 – 0.40 g/m2/day.
Cyclic olefin copolymers (COC) or polymers (COP) can provide moisture barrier to blister packs, typically in multilayered combinations with polypropylene (PP), polyethylene (PE), or glycol-modified polyethylene terephthalate (PETg). Cyclic olefin resins are generally amorphous and are noted for good thermoforming characteristics even in deep cavities, leading some to use COC in blister packaging as a thermoforming enhancer, particularly in combination with semi crystal line resins such as PP or PE. Films can be manufactured via coextrusion or lamination. Cyclic olefin resins are obtainable which abide by with pharmaceutical packaging guidelines in Europe, and Japan.
WVTR values of commercial cyclic olefin-based pharmaceutical blister films typically range from 0.20 to 0.35 g/m2/day at 38C/90% RH. Unlike PVC and other common pharmaceutical barrier resins, cyclic olefin resins do not contain chlorine or other halogens in their molecular structure, being comprised solely of carbon and hydrogen.