Blister pack

Blister pack is a term for several types of pre-formed clear plastic packaging used for small consumer goods.

The two primary components of a blister pack are a pre-formed plastic blister and a printed paperboard card which has a heat-seal coating.

Blister packs for unit doses of drugs
Blister packs are commonly used as unit-dose packaging for pharmaceutical dosage forms such as tablets, capsules or lozenges. Blister packs can provide barrier protection for shelf life requirements, and a degree of protection where product tampering is a consideration. In the USA, blister packs are mainly used for packing physician samples of drug products or for the sale of Over The Counter (OTC) products in the pharmacy. In other parts of the world, blister packs are the main packaging type since pharmacy dispensing and re-packaging are not common. A series of blister cavities is sometimes called a blister card or blister strip as well as blister pack. In some parts of the world the blister pack is known as a Push-Through-Pack (PTP). Main advantages of unit-dose blister packs over other methods of packing pharmaceutical products are the assurance of product/packaging integrity (including shelflife) of each individual dose and the possibility to create a compliance pack or calendar pack by printing the days of the week above each dose.

Blister packs are created by means of a form-fill-seal process at the pharmaceutical company or designated contract packer. A form-fill-seal process means that the blister pack is created from rolls of flat sheet or film, filled with the pharmaceutical product and closed (sealed) on the same equipment. Such equipment is called a blisterline.

Blister packs comprise of two principle components : 1) a formed base web creating the cavity inside which the product fits and 2) the lidding foil for dispensing the product out of the pack. There are 2 types of forming the cavity into a base web sheet: thermoforming and cold forming.

Blister packs for general consumer goods
Other types of blister packs consist of carded packaging where goods such as toys, hardware, and electrical items are contained in between a specially made paperboard and clear pre-formed plastic such as PVC. The PVC, transparent so the item can be seen and examined easily, is vacuum-formed around a mold so it can contain the item snugly, and have room to be opened upon purchase. The card is brightly colored and designed depending on the item inside, and the PVC is affixed to the card using heat and pressure to activate an adhesive (heat seal coating) on the blister card. The adhesive is strong enough so that the pack may hang on a peg, but weak enough so that this way one can tear open the joint and access the item. Sometimes with large items the card has a perforated window for access.

A more secure package is known as a clamshell. Typically used for theft-prone items like consumer electronics, it consists of either two pre-formed plastic sheets or one sheet folded over onto itself and fused at the edges. They are usually designed to be difficult to open by hand so as to deter tampering and pilfering. A pair of scissors or a sharp knife is often required to open them. Care must be used to safely open some of these packages.

Techniques used to open blister packs
Puncturing the packaging along the edges of the seal with a retractable knife with a sharp tip, for example a utility knife, then opening along the seam is generally quite effective, when the plastic is not too thick. Thicker plastics may require scissors, again, cutting along the seam where the two halves meet (or trimming away the sections where the plastics have been heat-fused together) will often be sufficient.

Attempting to 'tear' blister packaging by hand is ill-advised, as the plastic is often quite sharp.

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 moldable. 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 mold. The mold is cooled such that the plastic becomes rigid again and maintains its shape when removed from the mold. In case of difficult shapes, the warm film will be physically pushed down partially into the cavity by a "plug-assist" feature.

Cold forming
In the case of cold forming, an aluminum-based laminate film is simply pressed into a mold by means of a stamp. The aluminum will be elongated and maintain the formed shape. In the industry these blisters are called cold form foil (CFF) blisters. The principal advantage of cold form foil blisters is that the use of aluminum is offering 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 (aluminum can not be formed with near 90 degree angles).