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Blister packaging: Advantage manufacturers
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Monday, 16 April, 2012, 08 : 00 AM [IST]
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Amita Venkatesh
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You generally know you have purchased a product encased in blister packaging when you are unable to open your purchase without the use of heavy scissors or a sharp knife. While blister packaging may be the bane of consumers, it has become a favourite of manufacturers. It allows a product to be highly visible, leading to more point of purchase sales, and also lessens packaging costs.
As another benefit, blister packaging reduces store losses from shoplifting. It prevents small items, often consumer electronics, from being opened and slipped into a pocket by those who seek to cheat stores via a “five finger discount.” For both retailers and manufacturers, any method that reduces theft is a boon to bottom-line profits.
Blister pack is a term for several types of pre-formed plastic packaging used for small consumer goods, foods, and for pharmaceuticals.
The primary component of a blister pack is a cavity or pocket made from a formable web, usually a thermoformed plastic. This usually has a backing of paperboard or a lidding seal of aluminum foil or plastic. A blister that folds onto itself is often called a clamshell.
There are varieties of blister packaging, but all function on the same premise. The product is encased in a cavity of hard plastic and sealed shut, usually via an assembly line heating process. Blister packs can be very small or very large, depending on the product in question, and their uses are seemingly endless.
The main uses are Unit dose packaging this is a Blister pack commonly used as unit-dose packaging for pharmaceutical tablets, capsules or lozenges. Blister packs can provide barrier protection for shelf life requirements, and a degree of tamper resistance. Consumer goods are another type of blister pack which consists of carded packaging where goods such as toys, hardware, and electrical items are contained between a specially made paperboard card and clear pre-formed plastic such as PVC. Clamshell is a hinged blister is known as a clamshell, used for a variety of products. It can be used as a security package to deter package pilferage for small high-value items, such as consumer electronics. Medical blisters are trays which differ from pharmaceutical blister packs in that these are not push-through packs. The thermoformed base web is made of a thicker plastic sheet, generally between 500µ and 1000µ and cannot be collapsed, thus forming a solid tray. The lidding film provides a peel-open feature and is generally porous to allow sterilisation (such as the Dupont medical Tyvek material). Such medical blister packs are used for medical devices, used in hospitals.
One of the most prevalent forms of blister packaging, and also the most user-friendly, is found in single-dose strips of both over-the-counter (OTC) and prescription pharmaceuticals.
The packs not only provide protection to the drugs themselves, but can be handy for the consumer in helping them make certain they have taken the correct dosage. These blister packs open quite easily, and do not require excessive ripping, tearing, cutting, or cursing.
This is not the case with many blister packaged consumer products, and the most detested form of blister packaging is referred to as the clamshell. One will often find clamshell packaging encasing products such as small electronic goods, children’s actions figures, and tools. A very hard, plastic shell is formed around a mould of the item to be sold. On the reverse side of the shell, a bright, product card is encased in a form-fitting, plastic sleeve. The shell is then heated, and an extremely strong adhesive bonds the two sides into a nearly impregnable package.
It is estimated that over 5,000 people injure themselves each year attempting to open blister packaging of the clamshell variety. In response to this fact, a device known at the Open X was created. This product is designed to safely and efficiently open clamshell blister packaging and reduce injuries. However, there is one problem with this otherwise fine idea. The Open X is only displayed and sold in a clamshell blister pack.
PRODUCTION
Thermoforming
In the case of thermoforming, a plastic film or sheet is unwound from the reel and guided though a pre-heating station on the blister line. The temperature of the pre-heating plates (upper and lower plates) is such that the plastic will soften and become pliable. The warm plastic will then arrive in a forming station where a large pressure (4 to 8 bar) will form the blister cavity into a negative mould. The mould is cooled such that the plastic becomes rigid again and maintains its shape when removed from the mould. In case of difficult shapes, the warm film will be physically pushed down partially into the cavity by a "plug-assist" feature. Plug-assist results in a blister cavity with more uniform wall distribution and is typically used when the cavity size and shape is larger than a small tablets.
Cold forming
In the case of cold forming, an aluminum-based laminate film is simply pressed into a mould by means of a stamp. The aluminium will be elongated and maintain the formed shape. In the industry these blisters are called cold form foil (CFF) blisters. The principal advantage of CFF blisters is that the use of aluminium offers a near complete barrier for water and oxygen, allowing an extended product expiry date. The principal disadvantages of cold form foil blisters are the slower speed of production compared to thermoforming; the lack of transparency of the package (a therapy compliance disadvantage); and the larger size of the blister card (aluminium cannot be formed with near 90 degree angles).
PVC
The most basic material for forming web is PVC or Polyvinyl Chloride. The principal advantages of PVC are the low cost and the ease of thermoforming. 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. In the case of blister packaging the PVC sheet does not contain any plasticiser and is sometimes referred to as Rigid PVC or RPVC. In the absence of plasticisers, PVC blisters offer structural rigidity and physical protection for the pharmaceutical dosage form. Meanwhile, 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 typically chosen 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. Typical 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 mL/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. Also, the PVC layer can be coloured with pigments and/or UV filters.
COC
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 comb
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