Consumer goods
ClamshellOther types of blister packs consist 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. The consumer can visually examine the product through the transparent plastic. The plastic shell is vacuum-formed around a mold so it can contain the item snugly. The card is 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 the package can be easily opened (in theory). Sometimes, with large items, the card (cold seal card) has a perforated window for access.
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. It consists of one sheet folded over onto itself and sometimes fused at the edges. They can be securely heat sealed, making them difficult to open by hand to deter tampering. A pair of scissors or a sharp knife is often required to open them (although these are often sold in similar packages).[4] Trauma shears are also effective at opening packaging of this type.[5] Care must be used to safely open some of these packages, as opening it without care can result in injury; 6,000 Americans are sent to the emergency room each year by injuries suffered in opening such packages.[6][7] Wrap rage is sometimes the result.
Medical blister trays
Medical blister trays 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 500 and 1000 µg and can not be collapsed, thus forming a solid tray. The lidding film provides a peel-open feature and is generally porous to allow sterilization (such as the Dupont medical Tyvek material). Such medical blister packs are used for sterile medical devices, used in hospitals.
Methods
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 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. 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 and cables.
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 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 (aluminum can not be formed with near 90-degree angles).[citation needed]
Thermo cold forming
In thermo cold forming process, the first packing is done by thermoforming technique after which the product is repacked with a cold forming package.[citation needed]
Materials
PVC
The most basic material for the forming web is polyvinyl chloride (PVC). 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. In the case of blister packaging the PVC sheet does not contain any plasticizer and is sometimes referred to as Rigid PVC or RPVC. In the absence of plasticizers, PVC blisters offer structural rigidity 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 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 colored with pigments and/or UV filters. The European Pharmacopoeia (Ph Eur) references the requirements for PVC blister packs for pharmaceutical primary packaging in the monograph EP 3.1.11 "MATERIALS BASED ON NON-PLASTICISED POLY(VINYL CHLORIDE) FOR CONTAINERS FOR DRY DOSAGE FORMS FOR ORAL ADMINISTRATION". In order to be suitable for pharmaceutical blister packs, the PVC formulation also needs to comply with the US Pharmacopoeia<661>; EU food legislation; US 21.CFR and Japanese food contact requirements.
PVDC
Polyvinylidene chloride (PVDC) can be coated onto a PVC film to obtain very high moisture and oxygen barrier properties depending on the coating weight. PVDC coated blister films are the most common and prevailing barrier films used for pharmaceutical blister packs. PVDC coatings are also the most economical method for adding water barrier and oxygen barrier properties to a PVC film. PVDC blister films are available in 2 or 3 layer specifications referred to as duplex or triplex. Since the PVDC is applied by a coating process, the coating weight is expressed in grams per square meter (gsm). Duplex structures are typically PVC/PVDC films, ranging from 250µPVC/40gsmPVDC to 250µPVC/120gsmPVDC with WVTR from 0,65 to 0,25 g/m2/d and OTR from 1 to 0,1 cc/m2/d. For very deep draw thermoformed cavities, the triplex specifications are used : PVC/PE/PVDC, where the PE layer assists when forming deeper cavities. The PE (polyethylene) forms a soft intermediate layer between the rigid PVC and PVDC layers. Triplex specifications exists in similar coating weights as duplex specifications: 250µPVC/25µPE/40gsmPVDC up to 250µPVC/25µPE/120gsmPVDC. In order to obtain high barrier properties, PVDC is always applied using an emulsion coating process using a PVDC resin dispersed in water. The film producer applies the coating in several steps, drying-off the water between each coating station.
PVDC grades are available in 2 types of polymer: (I) the historic grades offering medium to high barrier properties and (II) a super barrier coating grade offering the highest barrier. The SBC grade has over two times the barrier to moisture and oxygen per gram coating weight compared to the historic grades. The most common structures using the super barrier PVDC are triplex configurations 250µ PVC/25µ PE/120gsm PVDC up to 250µ PVC/25µ PE/180gsm PVDC, with WVTR of 0,11 down to 0,06 g/m2/day and available from various suppliers.