PVC forming film is called rigid PVC because it is almost free of softening agents and plasticizer. Without plasticizers, PVC blisters offer structural rigidity and physical protection for the pharmaceutical dosage form. 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. That is why, PVC sheet thickness is typically chosen between 200µ to 300µ depending on the cavity size and shape.
Rigid PVC is a very clear, stiff material with a low WVTR. It exhibits excellent thermoformability; a high flexural strength; good chemical resistance; low permeability to oils, fats, and flavoring ingredients; easy tintability; and low cost. These properties make rigid PVC the material of choice for blister packaging, and it essentially has 100% of the market for the plastic component. PVC films that are thermoformed have a thickness of about 10 mil. The main disadvantages are the poor barrier against moisture ingress and oxygen ingress; moreover PVC has a negative environmental connotation due to its chlorine content and highly toxic dioxins.
Most PVC sheets for pharmaceutical blisters are 250µ or 0.250 mm in thickness. Typical values for the Water Vapor Transmission Rate (WVTR) 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. PVC layer can be colored with pigments and/or UV filters.
Polyvinylidene chloride (PVDC)–coated PVC. PVDC plays a critical role in blister packaging as laminations or coatings on PVC. PVDC can reduce the gas and moisture permeability of PVC blister packages by a factor of 5–10. Coated PVC films have a thickness of 8–10 mil; the thickness of the PVDC coat amounts to 1–2 mil. The coating is applied on one side and usually faces the product and the lidding material.
PVDC provide excellent barrier to both oxygen and water vapor while most other barrier polymer offer just one or the other. The gas barrier properties are unaffected by relative humidity, do the performance can be relied on through a wide range of packaging and environmental conditions. All PVDC products on the market are actually copolymers of vinylidene chloride (VDC) and other comonomers. The relative amount of VDC in the copolymer dictates some key properties. With more VDC, the barrier properties are generally better, with less VDC, flexibility usually improves. However, the amount and type of comonomer as well as other additives and processing technology used, will influence other properties such as sealing, surface properties, transparency, glossm coefficient or friction, etc. PVDC coatings have been used with duplex (PVDC/PVC) and triplex (PVDC/PE/PVC) structure being the most common ones used. Approximately, 67% of the barrier blister packaging market uses these PVDC-coated films. Typical coating weights used include 40, 60, 90 and 120g/m2, with the WVTR for a ty pical 120 g/m2 PVDC-coated PVC film being arounf 0.16 g/m2 at 40 oC and 75% RH.