The four basic components of pharmaceutical blister packages are :
  1. the forming film (80–85% of the blister package)
  2. the lidding material (15–20% of the total weight of the package)
  3. the heat-seal coating
  4. the printing ink

The forming film and the lidding material form an integrated package, they must match precisely.

Forming film
The forming film is the packaging component that receives the product in deep drawn pockets. Thing should be consider in selecting plastic film for the blisters are the type, grade, thickness, height and weight of the product, sharp or pointed edges of the final package, and the impact resistance, aging, migration, and cost of the film. The plastic also must be compatible with the product. Factors influencing package production and speed of assembly must be taken into account, including heat- sealing properties and the ease of cutting and trimming formed blisters.

Plastic forming films such as PVC, polypropylene (PP), and polyester (PET) can be thermoformed, but support materials containing aluminum are cold-formed. The forming film usually is colorless and transparent, but it can be obscured for use in child resistant packages or to protect light-sensitive drugs. The forming web for blister packs nearly always is PVC, sometimes coated or laminated with additional components that enhance the oxygen and water-vapor barrier.


Types of forming films. 

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.


PVC/chlorotrifluoroethylene (CTFE). Films made from PVC and CTFE have the lowest water-vapor permeability of all films used for blister packaging. When compared with the water-vapor permeability of 10-mil PVC, the permeability of 8-mil PVC/0.76- mil CTFE is lower by a factor of 15.

PP. The water-vapor permeability of uncoated PP is lower than that of PVC and is comparable to that of PVDC-coated PVC. The thickness of PP films used in the thermoforming process ranges from 10 to 12 mil.Advantages of PP include easy recyclability, no release of toxins during incineration, and good moisture-barrier properties. One problem is thermoforming. The temperatures required for thermoforming PP and for the subsequent cooling process must be controlled precisely. Warping also can occur, in which case the packages must be straightened before cartoning. Other difficulties associated with the use of PP include its thermal instability, higher rigidity than PVC, and susceptibility to post processing shrinkage. PP is difficult to run on a standard blister machine and cannot be processed as fast as PVC.

PET. It has relatively high water-vapor permeability compared to PVC. PVDC-coated PET could have the same water vapor barrier effect as PVC, but this does not appear to be promising in view of the larger goal to replace chlorous plastics with PET.

Polystyrene (PS) is perfectly compatible with thermoforming, but its high water-vapor permeability makes it unsuitable as a blister material for pharmaceutical purposes.

Oriented polyamide (OPA)/aluminum/PVC or nylon/aluminum/PVC. OPA/aluminum/PVC laminates are intriguing. With a laminate structure consisting of 1-mil OPA, 1.8- mil aluminum, and 2.4-mil PVC it is possible to eliminate water-vapor permeability almost entirely. Moreover, because of the large proportion of aluminum in the laminate, recycling this material has become feasible. Enormous efforts are being made to replace PVC with PP in such laminates to comply with environmental standards. OPA/aluminum/PVC laminate is cold-formed. Its cost per square meter can stand any critical comparison with PVDC-coated PVC. Cold-forming, however, requires more packaging material than does thermoforming to package the same number of the same size of tablets or capsules.

CTFE homopolymer (Aclar UltRx 3000) can be thermoformed easily and exhibits the highest moisture barrier of clear films. Various Aclar products have al- lowed wider use of blister packaging because they can be thermoformed into clear or tinted blister cavities and exhibit barrier properties close to those of the near-perfect barrier offered by foil.

COC. Cyclic olefin copolymers (COC) or polymers (COP) 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 semicrystalline resins such as PP or PE. Films can be manufactured via coextrusion or lamination. 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.

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