This article presents a comprehensive guide to blister packaging. Read further to learn more about:
You will learn:
- Blister packaging and its advantages
- Blister packaging operation
- Components of a blister pack
- Methods of blister foil forming
- And much more…
Custom Thermoformed Packaging
(from Valk Industries, Inc)
Chapter One – What is Blister Packaging?
Blister packaging, or blister packs, are pre-formed packaging materials composed of a thermoformed plastic cavity and a pliable lid. In this type of packaging, the product is placed in deep-drawn pockets or cavities resembling a blister. A backing material or lidding mates to the flat area of the plastic cavity enclosing the product inside. Bonding the two structures is a heat-seal coating adhesive. Blister packaging has various types depending on the application. The most popular use of blister packs is packaging pharmaceutical products such as pills, tablets, capsules, and lozenges. Because of its low cost, cheap raw materials, and high operating speed, they are also used for packaging consumer goods such as foods, electronics, toys, and tools. Enumerated below are the benefits of using blister packaging.
Individual Packaging: The first notable use of blister packs is for packaging birth control pills. Blister packaging is a cheap and convenient way of packaging individual doses of the drug. Also, the packaging can be marked aiding effective administration. Individual packaging helps maintain the quality of the contents through containment in separate cavities or pockets. Damage to any part of the packaging material will not affect the whole.
Maintaining Product Integrity: Forming films and lidding structures are created according to the sensitivity of the product from moisture, oxygen, and light. The packaging components can be laminated with barriers that block the penetration of external elements. Opaque materials such as aluminum block light preventing product degradation through UV radiation.
Tamper Protection: Blister packs when opened cannot be returned to their original form. Blister packaging has an inherent tamper-evident mechanism since it is impossible to separate the lidding to the blister card without causing visible damage. This helps deter package pilferage not only in pharmaceuticals but also in consumer goods such as electronics.
Preventing Accidental Drug Misuse: Blisters and lidding structures can be designed in such a way that it cannot be opened easily without following the instructions specified by the manufacturer. This prevents children, and even seniors, from accidentally taking the drug. This design is known as child-resistant (CR) packaging.
Visibility: Blister packs, along with skin and clamshell packaging, are also used for retail products since it allows consumers to see the product through the packaging. The lid or backing material is colored and designed for attracting prospective buyers.
- Minimal Movement Within the Packaging: It is easy for blister packs to take the shape of the product. The product’s shape can be fed through a computer-aided machining program that controls a milling machine for creating a mold. The mold can be prepared to factor only small clearances between the product and the packaging.
Since packaging is often not a part of the production process, manufacturing plants often employ third-party services dedicated to the packaging process. Contract packaging is a service provided by packaging companies that usually comprises the supply of labor and equipment for product packaging. Contract packaging companies invest in sophisticated equipment such as blister packaging machines that are accredited by regulating bodies. This allows the manufacturer to focus its manpower and business process solely on production while getting the benefits of a specialized packaging system. A contract packaging setup also enables more investment into quality testing of packaging raw materials that are impractical for manufacturing plants. In broader scopes, the packaging company is responsible for producing graphic materials and product manuals, controlling inventory, warehousing, and distribution.
Chapter Two – The Blister Packaging Process
The packaging process starts by designing the packaging format. The manufacturer fabricates a negative die according to the shape of the product. To prepare the negative die, a metal stock is milled with an array of cavities using a CNC machine. The die is then installed into the forming machine.
The forming process can either be thermoforming or cold forming. Plastic films such as PVC are processed by thermoforming, while laminated aluminum forming films employ cold forming. For thermoforming machines, a preheating process is done at temperatures below the plastic's melting point. As the film moves through the machine, it is formed to shape by air pressure (thermoforming) or by pressing a positive die (cold forming).
Meanwhile, prior to packaging, the products are visually inspected in a staging area. For consumer goods, the products are placed manually or automatically into the pocket. For products with smaller profiles but large volumes such as medicine tablets, a packaging machine with hopper feeding is used. The products are loaded into the hopper and then carefully fed into the pockets of the blister sheets. Brushes and paddles help disperse and arrange the product through the whole blister card.
The product then moves into the inspection station. Here, an inspector or visual sensors check any damaged or broken items and marks them for rejection at the end of the packaging line. After inspection, the sheets are transferred into the sealing station.
Before sealing, a cylinder with embossed texts or graphics prints on one side of the lidding before being fed into the machine. The cylinder picks up the ink and then presses it onto the lidding film. At the sealing station, the lidding film and the blister sheet meet by pressing them against each other. Heat is applied to re-activate the sealing resin creating a bond between the two substrates. After bonding, the sealed blister packs are then transferred into a cooling station which sets the bond.
The sealed blister sheets are then transferred into a trimming station where whole blister packs are cut into blister cards. Additional cuts are made by the machine depending on the intended application such as child-resistant packs. Afterward, the blister cards pass through a conveyor system where an automatic rejection system removes flagged items from the packaging line. The conveyor leads the blister cards through robotic arms that automatically collect and place them into boxes or larger packs.
Process operators select samples from the packaging line for quality checks. Packaging quality inspection is usually done for pharmaceutical products. A simple method is water submersion testing or blue dye testing. This is a leak test that involves subjecting the blister card to a vacuum for several minutes. Once a flaw in the sealing or damage on the film is present, a vacuum is created inside the blister. The blister card is then submerged in the dyed water. The packs are then removed from the water and manually opened for visual inspection. Advances in probing and scanning technology allow automated visual inspections for finished blister packs. The water submersion method is limited since it does inspect the whole production. Scanning and visual inspection systems are now able to reliably check each pocket and pinpoint the location of the cavity with defects.
Chapter Three – Components of Blister Packaging
There are four main components involved in blister packaging. These are the forming film, lidding, heat-seal coating and prints. The forming film and lidding are the main structural components that account for almost the total weight of the packaging. The heat seal layer creates a bond between the two structures. Lastly, the labels, batch numbers, codes, and other important information are added by printing.
Forming Film: This is the component formed to create the cavity. Property, grade, and thickness are the common bases for selecting forming films. The formed cavity copies the contour of the product with a slight clearance. This allows small deformations from impact without damaging the content. The film must have the right grade and thickness to provide sufficient rigidity into the whole packaging while at the same time allow convenient opening. Being too rigid makes it hard for the product to be pressed out of the pocket; while being too flexible allows it to be easily damaged.
Backing Material or Lidding: The lidding secures the product into the cavity. Classifications of lidding structures are divided into Push-Through-Packs (PTP), peelable lids, or a combination of both. PTPs are designed to be broken or torn while pressing into the pocket as seen in typical medicine packaging. Lidding can also be made peelable without deforming the pocket as seen in most consumer goods packaging. Push-peel lidding types are specially designed to be opened by performing a sequence of actions. These proprietary lid types are used for medicines for seniors and children known as child-resistant blister lidding.
Common lidding materials can be aluminum foil, PET, paper, or a combination of these materials. Aluminum foil is characterized by its temper that can be either soft or hard. Soft-tempered aluminum foil is more malleable and is suitable for packaging hard materials such as tablets and lozenges. Their malleability allows some amount of deformation before breaking. Because of this characteristic, soft aluminum lids are used for child-resistant blister packaging which helps prevent children from pushing tablets out of it. Soft aluminum foils used in blister lidding typically have 1.0 mil thickness.
Hard-tempered aluminum foils do not allow any elongation and can be torn easily with sufficient force. They are used for lids that are designed to be pushed through or peeled off. For a single layer, hard aluminum lid structure, the foil thickness is around 0.8 mils. This type of structure is used for push-through-packs.
Hard aluminum foils can also be combined with paper and PET to be used for child-resistant packages that can be pushed through, peeled off, or a combination of both. A common design features the paper and PET layers to be first peeled off from the aluminum. The tablet is then pushed through which tears the aluminum foil.
Heat-seal Coating: Heat-seal coatings bind the plastic blister pack and the lidding together. They are molten or liquid polymer resins that are applied on the surface of the lidding material using roll coaters, knives, gravure, brush, or sprays. The right amount must be applied to create an air-tight sealing. After application, the resin is allowed to dry on the surface of the foil. This resin will then be reactivated once the bonded foil-seal coat film is used for packaging.
Conventional characteristics of heat-seal coating resins used for blister packaging are low-temperature activation, low coefficient of friction, high gloss, and high transparency. For pharmaceutical and food packaging, the polymer resin must be approved by the FDA for direct food contact compliance. General types of heat seal coatings are solvent and water-based. Examples are polyvinylidene chloride (PVDC), acrylic, and ethylene acrylic acid (EAA). Other types are extrusion coated and co-extruded polyolefin films. These types of films can be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ethylene-vinyl acetate (EVA).
Prints: These are added to the lidding structure for providing information about the product and to attract the attention of buyers. They are usually applied by flexographic printing. Since these are applied before the heat-sealing process, they must be able to withstand the heat sealing temperatures which can be about 300°C.
Chapter Four – Methods of Foil Forming
There are two main methods used in foil forming: thermoforming and cold forming. The most common material used in blister packaging is PVC. PVC is formed by thermoforming which makes the process widely used. For applications requiring better barrier properties, laminated aluminum is the better option which is formed by cold forming.
Thermoforming: Thermoforming is the process of heating thin plastic sheets to its forming temperature and stretching it over a mold which takes its shape. This is the most common forming method used for blister packaging because of its simplicity and high volume.
This process starts by feeding the plastic sheet into a preheating station which initially heats to slightly above the plastic’s glass transition temperature. This makes the plastic soft and malleable without fully melting it. After heating, the film is transferred into the forming station. A die presses onto the sheet that imprints the profile of the blister pack. There are several types of thermoforming processes, but the ones used for blister pack manufacture are vacuum and pressure forming. In vacuum forming, the air is evacuated from the cavity that draws the heated film acquiring the profile of the die. Pressure forming, on the other hand, pushes the film into the cavity. For instances when the shape is difficult to form by air pressure alone, a plug-assist feature is used to push down the film into the die. This results in a more uniform wall thickness. After the forming process, refrigerated plates then press against the formed films which set into its new shape. It is then trimmed to size using a die cutter.
Cold Forming: This process is commonly used for packaging products that are sensitive to moisture and light. Instead of using clear plastic films, cold forming uses thin sheets of polymer-aluminum laminates. Laminated aluminum has a typical thickness of 1.8 mils of aluminum and 3 mils of combined polymer layers. With this thickness, it completely eliminates water permeability. In contrast to the thermoforming process, this type does not use heat to shape the film. Rather, the film is plastically deformed by pressing it into the die. Thus, this type of forming is mechanical which involves a negative tool (die), and a positive tool (plug). This brings the disadvantage of having another tool making the cold forming machine more expensive than the thermoforming. Another drawback is that the film cannot be formed with near 90° angles. There will always be draft angles that increase the size of the blister. Though the price per meter of the laminated aluminum is comparable with plastic films, a given area can only accommodate a smaller number of products. This, in turn, increases the material cost.
Chapter Five – Materials Used in Manufacturing Blister Packs
There are various materials used in blister packaging. PVC is the most suitable because of its low cost and ease of forming. However, there are moves to replace PVC due to its negative effects on the environment. Polymers containing chlorine and fluorine elements can discharge harmful acids to the atmosphere and are now being regulated in developed countries. Materials used for blister pack manufacturing are listed below.
Polyvinyl Chloride or PVC: This is the most widely used material for blister packaging due to its low cost and ease of forming. PVC dominates around 95% of the blister packaging market. The PVC forming film is rigid because of the absence of any plasticizers or softening agents. Due to its toughness and clarity, it is ideal for protecting goods while adding value by allowing prospective buyers to see the product. Moreover, PVC films have good barrier characteristics and chemical resistance. The typical thickness of the forming film is in the range of 0.2 to 0.3 millimeters. An important thing to note for using rigid PVC, however, is its tendency to degrade at high temperatures, known as dehydrochlorination, and produce hydrogen chloride. Since heating is an integral operation in PVC film forming processes, stabilizers are added to withstand the thermal and shear conditions throughout the process. Stabilizers must be FDA approved for food contact applications.
- Polyvinylidene Chloride (PVDC): PVDC, though not a forming film material in itself, is applied to other substrates such as PVC and aluminum to impart better barrier properties by a factor of five to ten. PVDC coatings are one of the few compounds that can provide both moisture and oxygen barriers. Other desirable characteristics of PVDC are heat-sealability, high gloss, transparency, and flexibility. These are applied not only to the forming film but also to the lidding structure as well. PVDC is applied on the surface in contact with the product. Like PVC, it can also undergo thermally induced dehydrochlorination which poses threats to the environment.
- Polychlorotrifluoroethylene (PCTFE): This compound belongs to a family of polymers called fluoropolymers. Polychlorotrifluoroethylene is popularly known as Aclar film, a trade name from Honeywell. Like PVDC, PCTFE is laminated to PVC to enhance its barrier properties. PCTFE allows an extremely low transmission of moisture and gases, has inertness to strong chemicals and can resist external degrading factors such as UV light and ozone. In itself, it is not particularly strong or tough, but it has high abrasion resistance. Its other notable physical properties are transparency and better thermal stability. Aclar film is widely used in military, electronic, and aerospace applications. Its laminates are designed to perform in oxygen-rich environments for packaging items in liquid nitrogen. In pharmaceuticals, Aclar laminates are suited for aseptic blister packs since they can be sterilizable by heat.
Polypropylene (PP): Polypropylene emerges as an alternative forming film to PVC. Its water vapor permeability is comparable to PVDC-coated PVC. It is preferred in some regulated regions since it does not produce harmful chemicals when incinerated. Also, it can easily be recycled than PVC. Its main disadvantage is the difficulty of processing. PP cannot be readily fed to a standard blister packing machine. The range of operating temperatures for thermoforming PP is very narrow and must be controlled precisely. Warping and post-processing shrinkage can occur which decreases the quality of packaging.
- Polyethylene (PET): Another candidate to replace PVC is PET. Polyethylene is used for packaging food and consumer goods but is less often for blister packaging of medicines. This is because PET has a higher water vapor permeability than PVC. It can be solved by adding a layer of PVDC but it defeats the purpose of preventing the release of harmful gases.
Cyclic Olefin Copolymers (COC): COC is a family of fully amorphous polymer resins that are desired because of its comparable properties with PVC without the negative effects. COCs that have a multilayer structure are best suited for blister packaging because of its low water vapor permeability. The properties of a COC film can be altered by developing specific blends of polyolefins. Some of the properties that can be modified are its elasticity, transparency, vapor transmission rate, and coefficient of friction.
- Laminated Aluminum Foil: This type is a combination of aluminum, PVC, and polyamide or polyester films. Laminated aluminum films are cold-formed. They completely eliminate water-vapor permeability which makes them suitable for medicines with long storage life. It also provides complete protection from light and oxygen.
- Blister packaging, or blister packs, are pre-formed packaging materials composed of a thermoformed plastic cavity and a pliable lid. In this type of packaging, the product is placed in deep-drawn pockets or cavities that resemble a blister.
- Blister packaging offers the following benefits: individual packaging, maintaining product integrity, tamper protection, preventing accidental drug misuse, visibility, and allowing minimal movement within the packaging.
- Contract packaging is the process of outsourcing the packaging process to specialized service providers. This enables the manufacturer to focus on its operation and business process.
- There are four main components involved in blister packaging. These are the forming film, lidding, heat-seal coating and prints.
- There are two main methods used in foil forming: thermoforming and cold forming. Thermoforming is used for polymer-based materials, while cold forming is for laminated aluminum.
- PVC is the main material used for blister packaging. however, it is now being replaced due to its negative effects on the environment.