- December 01, 2009, By Kurt Schramer, MACtac
Companies specializing in film production are familiar with the environmental and economical trends impacting today's industry. Production costs continue to rise with the cost volatility of oil, and to combat price increases, some converters manufacture thinner films, known as downgauging, so the same weight of material results in more square feet of final product. These thinner films require companies to provide additional training on proper handling throughout the manufacturing, converting, and printing processes.
Limited knowledge, ever-changing industry trends, and misconceptions that paper manufacturing expertise translates into film production expertise are challenges for those entering the industry. However, working with an experienced supplier and understanding the basics — common film types, manufacturing processes, and end-use applications — will put interested parties on the path to future film success.
Film Types: Understanding the Application
Determining the right film for a particular application generally means considering the final application's needs as well as the needs of the retailer/distributor, applicator, printer, and converter (see Figure 1). Among numerous film substrates, five are most common in label production today: biaxially oriented polypropylene (BOPP), polyethylene (PE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS).
One of the fastest growing and most economical films, BOPP features high clarity and high gloss, and its moisture resistance and smooth surface make it suitable for health and beauty, beverage, and overlaminate applications. At low calipers, BOPP film has more efficient and economical dispensing; however, it becomes stiff at high calipers, and its temperature and tension must be closely controlled during converting.
BOPP films can be difficult to print because surface energy needs to be greater than 38 dynes/cm2 for print receptivity, and BOPP surface energy is generally 31. To improve printability, a surface treatment, such as a topcoat, is applied, which allows the ink to wet-out and adhere to the film but adds cost.
PE films, one of the largest production volume films, are economical, conformable, and puncture resistant. However, their low surface energy also requires a topcoat, and they must run at high calipers for dispensing ease. PE films usually have a hazy appearance and limited ultraviolet (UV) resistance. Common applications include conformable liners, health and beauty product labels, and chemical labels.
Soft and conformable, PVC films can be manufactured in any color with a variety of surface effects. Their exterior durability makes them suitable for fleet graphics, drum labeling, and point-of-purchase displays. Often more costly to produce, PVC films can stretch or shrink if not handled properly. Plasticizer migration also can take place when the plasticizers in the film migrate into the surrounding environment, altering the performance of the film over time.
Often referred to by its trade names of Mylar or Melinex, polyester or PET films offer high clarity, strength, and heat resistance, and their smooth surface provides a no-label appearance in end use. With moderate UV stability, PET films have low caliper, high-speed dispensing, and minimal web breaks while maintaining an excellent die-cutting surface. However, PET films often are stiff, unconformable, and expensive to manufacture. PET films are used in a variety of overlaminate applications, serving the automotive, pharmaceutical, and name plate industries.
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PS films are prominent in tamper-evident labeling, coupon dispensing, and scratch-off applications because they tear and print easily, feature good dispensing properties, and are economical to produce. However, they tend to be stiff and nonconformable and provide limited service temperature and UV resistance.
The Journey: How Films Are Manufactured
Film development is achieved through several standard processes, including basic and coextrusion, blown film processing, casting processing, and calendering processing.
One of the most popular manufacturing methods, extrusion, occurs when resins and additives are combined, pushed through a heated barrel that melts the mixture, and sent out, or extruded, through a die. During coextrusion, the same process occurs with an additional unit(s) going through the process concurrently for multiple layers of final product. Each layer can be engineered for specific properties like opacity, improved adhesion, color, and various barrier properties (see Figure 2).
In blown film processing, resins and additives are blended, heat is added to the mixture, and the material is extruded through an air ring where it is blown into a tube shape about three-stories high. The more the film is blown, the thinner the final film. The blown film is collapsed and then either divided into two separate sheets that are guided to a device that winds them, or the tube is heat sealed on one end to create a bag-shaped final product (see Figure 3).
Manufacturing a cast film requires incorporating solvents to make the resin and additives mixture into a liquid for processing. This mixture, or organosol, is metered onto a casting sheet and sent through a series of ovens in a long drying process in which the solvent(s) evaporates before the film and casting sheet are wound into large rolls. Cast films offer good to excellent UV resistance, good color matching capabilities, and long-term durability. They are also thin and dimensionally stable. However, the process can be expensive and time consuming.
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Calendered film processing is a viable and often preferred alternative to cast film processing. Resins and additives are mixed, heated, and sent though a series of heated calendering rolls that press the mixture into a continuous sheet, which brings the film to a desired caliper while cooling it before it is sent over drums and wound into a roll. The final calendered film features good to excellent UV resistance, moderate color matching capabilities, and long-term durability. Processing is less expensive and up to two to three times faster than the cast alternative.
For added strength, films are sometimes oriented during manufacturing through the use of a tenter frame or similar process where a film is stretched, aligning the polymer matrix, and annealed, setting the orientation in place. Monoaxial orientation strengthens and stiffens the film in one direction whereas biaxial orientation orients in both directions. In addition to gaining stiffness and strength, oriented film tends to be very clear and has improved chemical and heat resistance, but orientation does diminish heat sealability and puncture resistance.
Labeling Needs: Film Versus Paper
Determining whether to incorporate a film or paper product depends almost exclusively on the final application's requirements. Some major film advantages include moisture resistance, wet strength, durability, conformability, and clarity.
Films excel in labeling applications where the final product may be subject to hot or cold, moist environments, because unlike paper, which wicks around the edges and peels up as moisture soaks into the facestock, films don't absorb moisture and maintain strength. Another advantage, their high strength at low calipers makes films more removable and repositionable than paper alternatives. In some packaging applications, their high temperature and UV resistance also provide additional barrier protection. Films also can be a consistent clear or solid color even if the surface is scratched or damaged, unlike the color-coated surfaces of many paper alternatives.
Conformability is another advantage, especially for applications with unique shapes, sizes, and labeling areas, because films can adjust shape and stretch to meet labeling requirements while maintaining strength and performance. This is essential for tube or bottle applications that require labels to perform well despite squeezing or shifting.
Durability and conformability properties can be disadvantages, however, when not handled properly. Films can be fragile during processing and are sometimes unknowingly stretched during production, coating, and application, affecting end performance. In addition, films do not absorb or wet-out when inks are applied, often necessitating special inks and adding cost.
With a thinner and smoother surface than paper, films continue gaining popularity for high-end, no-label look applications, like wine or spirit bottles. However, their clarity and thinness mean most defects are more apparent. Rolls of film generally have to be suspended following production because laying them down, even on smooth surfaces, can cause damage and inconsistencies a paper alternative would hide. The smooth surface also can cause issues during converting and printing because films tend to slide or wander on printing presses, unlike paper. There is also a substantial amount of static produced during film production, necessitating employee education on proper handling of finished films.
Future of Film: Meeting Industry Needs
Depending on the final application requirements, there is a place for both film and paper. In addition to a growing use in the health and beauty, beverage, and household product packaging and labeling industries, films also are gaining popularity in tamper-resistant labeling applications, which require a product that tears easily in a controlled manner, as well as international currency applications in which they are a flexible and durable paper alternative.
While cost often impacts paper supplier selection, price differentiators in the films market do not outweigh the benefits of working with an experienced supplier. Selecting a knowledgeable partner that can advise on best practices for working with a variety of film types is an essential first step for converters and printers looking to successfully enter the films industry. Pairing that partnership with a solid knowledge in film basics ensures that films have a bright future and the ability to serve as a value-added solution for applications in a number of industries.
Kurt Schramer, strategic business development director for MACtac, Stow, OH, has more than 30 years' experience assisting in creating short- and long-term goals for MACtac North America. With expertise in pressure-sensitive construction and film product development, Schramer is responsible for the growth of film products across all commercial areas. Contact him at firstname.lastname@example.org.
Common Film Abbreviations
CPP | Cast Polypropylene
EVA | Ethylene Vinyl Acetate
EVOH | Ethylene Vinyl Alcohol
HMWPE | High Molecular Weight Polyethylene
LDPE | Low-Density Polyethylene
LLDPE | Linear Low-Density Polyethylene
LMWPE | Low Molecular Weight Polyethylene
MMWPE | Medium Molecular Weight Polyethylene
UHMWPE | Ultra High Molecular Weight Polyethylene
The views and opinions expressed in Technical Reports are those of the author(s), not those of the editors of PFFC. Please address comments to the author(s).