Medical Plastics and Biomaterials Magazine | MPB Article Index

Originally published July 1996

PACKAGING FILM

ROBERT J. BOCKSERMAN

The stringent requirements for effective packaging of pharmaceuticals and medical devices have led to the development and improvement of a wide range of medical polymer films. These films prevent a product from migrating or escaping from the enclosed packaging and entering the environment and also protect against outside influences that could enter a package and cause a deleterious effect on the product.

Environmental packaging films were created to address potentially harmful conditions that a package undergoes during the distribution chain, including temperature extremes, humidity, contact with water, and exposure to contaminants and microbes. Packages also may encounter shock, stress, vibration, compression, and magnetic fields. Barrier packaging involves the use of material--either a single film or a laminated structure of polymer films, foils, paper, or coatings--to prevent various constituents of the product from escaping. The barrier also prevents moisture, oxygen, and other gases from permeating the package structure. Barriers are also required when a product is sensitive to light (particularly ultraviolet light).

Within the last two decades, the health-care industry has replaced many of the traditional metal and glass packaging components with high-barrier plastic films composed of single polymers, new lamination combinations, metallized films, and an array of specialized coatings. These innovations were designed to provide better product protection, to meet the needs of the growing diversity of products, to comply with federal regulations, and to maintain and control costs. Continuous research and development by private industry and academic institutions have produced a great variety of new and improved medical films.

For many years, paper was the most widely used material for medical device packaging, but within the last decade, the use of plastic films has increased rapidly. New developments in medical packaging films were brought on by better understanding and subsequent modification of molecular structures to enhance desirable properties; new manufacturing techniques for flexible films; and the use of newly discovered plasticizers, heat stabilizers, lubricants, and additives for properties such as radiation resistance. Plastics that can now tolerate radiation sterilization have created a market for a multitude of polymer formulations for products such as rigid and semirigid thermoforms and films with thicknesses from 0.5 to 10.0 mil. Film structures combined with additives can be designed to be self-supporting and flexible, allowing them to be folded or creased without inducing a structural weakness in the film. Many of the newer film structures comprise fluoropolymers that are modified polychlorotrifluoro-ethylene. This material is converted to a film by melt extrusion, which requires special handling procedures because of its very high melt viscosity. Properties of such films include good tear strength, superior dimensional stability, and resistance to water vapor and to most chemicals. The films can stand up to steam, ethylene oxide, or radiation sterilization without being degraded.

FILM STRUCTURES

Among the types of film products available are single films, laminations, and coextrusions. Properties that can be manipulated include barrier characteristics, clarity, stability in hot and cold environments, tensile strength, thermoformability, sealability, and radiation and chemical resistance. Compliance with new environmental regulations for disposal and recycling is another important consideration.

Coextrusion. Because medical device packaging can require a wide range of properties, two or more polymers are often coextruded through a single die to form a multilayer film structure. Coextrusion is recommended for producing multilayer films because of its lower cost; it can be used instead of lamination, avoiding the problem of double handling that occurs when a film lamination is being produced. Coextrusion is sometimes preferred because laminations require a separate manufacturing process for each film used in the final laminate. Also, single-step coextrusions can replace adhesives and coatings that are frequently required in laminates. The materials best suited for coextrusion are low-density polyethylene, polypropylene, polyvinyl chloride, polyamides, and polystyrene. The coextrusion of high-density polyethylene and ethylene vinyl acetate brings out the best qualities of each polymer; the final film features an especially low gas-permeation rate, which is required for many health-care packaging applications.

Lamination. A lamination is created when two or more individual films are bonded together with special adhesives and run through rolling, heated cylinders to produce a composite film structure. This type of film composite offers excellent stability and often incorporates the best properties of each individual film layer. Lamination is preferred when a specific film composition cannot be effectively run on coextrusion systems due to equipment limitations, and also when the high temperatures required in coextrusion would be harmful to the films. Lamination is also recommended when it is desirable to produce a composite film with properties superior to those afforded by a single film layer of the same gauge. Some materials suitable for lamination are polyethylene-cellophane, polypropylene-cellophane-polyethylene, and polycarbonate-polyethylene.

Lamination Applications. Many laminations have been designed for fabrication of pouches by form, fill, and seal machines. These pouches are used for packaging pharmaceutical tablets, capsules, powders, liquids, ointments, and creams, as well as for overwrapping medical devices. The pouch structure provides a good barrier and may be modified with the addition of a foil barrier when increased protection against gas and moisture permeability is required.

Pouch structures are constructed of substrates comprising combinations of paper, low-density polyethylene film, foil, polyester film, polyethylene copolymer film, adhesives, coatings, ionomer film, ethylene vinyl acetate, polypropylene, and polystyrene.

Testing. When polymer and nonpolymer films are combined into a lamination, predicting barrier capability of the total structure requires specialized testing methods. Modern laboratory procedures can now estimate the properties of a laminate by measuring within a few degrees of accuracy the moisture and gas permeability of each individual film. Techniques for testing barrier polymer films can be obtained from the following associations: American Society for Testing and Materials (Philadelphia); Association for the Advancement of Medical Instrumentation (Arlington, VA); Health Industry Manufacturers Association (Washington, DC); Technical Association of the Pulp and Paper Industry (Norcross, GA); and Flexible Packaging Association (Washington, DC). A thorough evaluation of the safety and suitability of the packaging materials selected for a medical device or pharmaceutical is required by FDA. Some of the testing criteria used to evaluate barrier polymers are oxygen/ CO₂/water vapor transmission, organic vapor/odor transmission, water absorption, stress-crack resistance, elongation, impact strength, puncture resistance, stiffness or flexibility, and light transmission (see Figure 1).

Adhesives. The selection of adhesives for lamination is important. General considerations include adhesion capability, mechanical bonding strength, formulating flexibility, heat and chemical resistance, and barrier properties. One must also determine the ability of the adhesive to flow uniformly over the film surface; whether it is solvent- or water-based; whether any solvent used can be removed from the adhesive after lamination; and whether corona discharge is required. Current laminate adhesives include dextrins, sodium silicates, latex rubber, vinyl acetate­vinyl chloride copolymer, and waterborne polyvinylidene chloride.

Metallization. Metallized film is developed by vaporizing molten metal, depositing it onto a polymer web, and then applying it to the film. Aluminum is most commonly used because of its cost-effectiveness. The entire process takes place in a vacuum chamber; the amount of metal applied is carefully controlled by instrumentation, and the vacuum temperature of the metal and speed of the web feed must also be closely monitored. Metallization improves the moisture- and gas-barrier properties of the film and prevents light from reaching the product.

Coating. The coating process involves the application of various materials to the film-web substrate to impart special features, improve properties, or change the handling characteristics (sticking, slipping, etc.) of a film. Commonly used coatings include polyvinylidene chloride, polyvinylidene fluoride, polyvinyl chloride, low-density polyethylene, and various Teflons. Coating equipment consists of a coating head, a drying unit, and the film-handling system.

BLISTER PACKAGING APPLICATIONS

Blister Packaging. Film for blister packaging of medical devices and pharmaceutical tablets or capsules has been developed for specific applications requiring compliance with shelf-life standards and protection from environmental conditions such as gas, moisture, chemicals, and extraneous microbiological and particulate contamination. The ability to precisely control film specifications for blister packaging enables this technique to be used to make specialized products such as child-resistant packaging. The technology for creating child-resistant packaging involves using seals, custom plastic banding, and container closures that must be pressed, twisted, or mechanically manipulated for entry. Foil webs require push-through or puncture to gain entry, and complete plastic tubes are used to totally enclose a package. Various combinations of polymer films, foils, and paper plies are employed in this type of packaging. Medical applications of blister packaging include surgical instruments, medical pouches, implantable devices, diagnostic test kits, and disposables.

Push-Through Lidding. One important application of blister film involves using various combinations of polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, and foils to create a lidding structure with a cover sheet through which a pharmaceutical tablet or capsule can be pushed. This system offers excellent protection of individual capsules or tablets until their ultimate use.

Peelable Lidding. Peelable blister packaging is used when an individual pharmaceutical dose must be removed from a sealed packet or a medical device removed from a tray. Peelable lidding can be sealed to blister packs with or without special adhesives and lacquers.

The types of adhesives commonly employed for peelable lidding include ethylene­vinyl acetate, polyester coatings, Tyvek coatings, vinyl chloride­vinyl acetate copolymers, and acrylics. When adhesives are used, the following criteria should be considered: (1) Should the lid be fusion sealed? (2) Should the lid be fully peelable? (3) Will the product require sterilization? (4) Is the lidding to be heat-sealable or pressure sensitive? and (5) Will the product require refrigeration or frozen storage?

QUALITY CONTROL

Quality control of polymer films involves the sum total of factors that contribute to the product's suitability, effectiveness, and safety. Quality control procedures should be outlined during the research and development stage and then continued through production, packaging, and ultimate storage and distribution. Manufacturers and fabricators must have total quality control programs that monitor each step of the process, employing detailed validation procedures and records and complete documentation.

FDA good manufacturing practices carefully outline procedures and regulations for the manufacturing, processing, packaging, and distributing of products and components used in pharmaceutical and medical device packaging. The criteria involve buildings, equipment, personnel, records, equipment maintenance and cleaning, production/quality control procedures, testing procedures, laboratory controls, expiration dating, and complaint files. The guides are published annually in the Code of Federal Regulations, subtitle 21, part 133.

CONCLUSION

There are a multitude of new films, laminations, barrier structures, composites, and coatings that are being introduced to the medical manufacturing industry. Premade pouches and rollstock, either in printed or unprinted form, are now able to withstand gamma- radiation sterilization as well as high-temperature pasteurization without weakening or changing the physical characteristics of the polymer.

Pouches are now constructed of various plastic, foil, paper, and Tyvek combinations that are easy to open, have specific barrier levels, and can be fabricated with multiple compartments to enclose noncompatible products that are mixed immediately before use by breaking inner seals or membranes. Laminated, flexible structures are designed with various types of coated composites in addition to plastic, foil, and paper layers that can be forming or nonforming and adaptable for the production of pouches, pockets, or strips with the use of form, fill, and seal equipment. These laminated structures can also be coated to provide permanent or peelable heat seals of various dimensions and configuration lidstock materials.

Continuing R&D in medical packaging is expected to produce sophisticated, technically advanced products such as smart films to absorb or emit various gases, antioxidants that are incorporated into a film and slowly diffused into the product, or antibiotic film that emits ozone. Other anticipated developments include water-soluble films with a controlled solubility rate, new films that can be gamma or electron-beam sterilized without degrading, downgauged film that retains its initial tensile strength, films that are not degraded by UV light, films that will tolerate high processing heat, films that are bio- or photodegradable, and silica-coated films that impart both barrier properties and clarity.

BIBLIOGRAPHY

Berins ML, Plastics Engineering Handbook, New York, Van Nostrand Reinhold, pp 102­132, 1991.

Hanlon JF, "Films and Foils," Handbook of Package Engineering, 2nd ed, Lancaster, PA, Technomic Publishing Co., 1992.

Harburn K, Quality Control of Packaging Materials in the Pharmaceutical Industry, New York, Marcel Dekker, 1991.

"Health-Care Packaging," in The Wiley Encyclopedia of Packaging Technology, Bakker M (ed), New York, John Wiley, pp 391­399, 1986.

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Robert J. Bockserman is the owner and president of Conatech Consulting Group, Inc. (Creve Coeur, MO), a consulting engineering firm specializing in product/ package development, systems design, material science, material handling, and auditing of quality, safety, and environmental control procedures. He is a member of the Packaging Industry Advisory Committee, School of Engineering, University of Missouri, Rolla, where he is a visiting lecturer teaching classes in packaging engineering. He is also a visiting lecturer in the food science department of the University of Missouri, at Columbia, where he teaches classes on food toxicology and sanitation.