Raw film manufacturing plays a critically important role in the development of the vinyl materials used extensively as printable substrates in the graphic arts industry. Indeed, the companies that manufacture these vinyl films are often leaders in the advancement of polymer science to support new capabilities and applications.
There are essentially two types of vinyl films that are used for a wide range of graphic art applications: cast and calendered.
The terms ‘cast’ and ‘calendered’ refer to different manufacturing processes. These processes, along with varying constituents added to the raw materials, render very different qualities to the films.
In cast manufacturing, a liquid is poured onto a carrier sheet, which is then heated in ovens. No stress is involved in the process, so the sheets suffer no shrinkage.
Calendered vinyl, on the other hand, is produced in a continuous process, which enables high-volume, low-cost manufacturing. On the calendering line, the raw materials are mixed together, extruded and then flattened out into a thin film by passing them through a series of heated rollers.
Historically, these two types of films have differed markedly in terms of their quality, including both durability and flexibility. Cast films have traditionally been considered the industry’s premium option, as they are more suitable for applications that require greater strength, resilience and superior handling, particularly for longer-term outdoor graphics. Calendered films, meanwhile, were largely relegated to short-term outdoor graphics and indoor applications, due to their less robust nature.
Today, however, the discrepancy between cast and calendered film quality is not nearly as great. Ongoing improvements in both the manufacturing process and the selection of ingredient additives have allowed the development of much higher-performance calendered films than in the past.
While cast vinyl has long been the preferred choice for graphic applications involving wrapping and stretching, calendered vinyl has now undergone sufficient improvements, to the point where it can now compete with cast vinyl.
While the difference between cast and calendered films is most frequently expressed in terms of their respective manufacturing processes, it is also a question of the particular ingredients added to the raw materials during manufacturing.
Most printable graphic films are made from the same basic raw material: polyvinyl chloride (PVC). In its unadulterated state, however, PVC is hard and inflexible. To provide the flexibility required for wraps and other graphic applications, a plasticizer must first be added to the PVC resin.
There are two primary types of plasticizer: monomeric and polymeric. The selection between the two will significantly affect the properties of the film.
Monomeric plasticizers consist of relatively simple, linear molecular chains, with a low molecular weight. They are considered the ‘economy-grade’ option, providing pliability for the film’s handling, but offering less durability than with polymeric plasticizers. Polymeric plasticizers are more complex, with a higher molecular weight, which leads to greater viscosity and better stability.
In the past, calendered vinyl was often associated with monomeric plasticizers, while only cast vinyl used polymeric plasticizers. Today, however, a new generation of calendered vinyl has been produced using polymeric plasticizers. As a result, the attributes and performance of calendered films have become closer to those of cast vinyl, including durability for several years, even though their manufacturing processes remain completely different.
Another differentiator between vinyl films is their sustainability. Traditional plasticizers are now recognized to be less than environmentally friendly, so many raw film manufacturers have sought to use alternative ingredients, such as non-phthalate plasticizers, in the production process.
Used primarily to soften PVC, phthalates are easily released into the air and pose health problems when ingested, particularly by children. By offering phthalate-free films, manufacturers are proactively taking steps to meet customers’ needs with a commitment to sustainable development and responsibility toward the environment.
Following years of research and development (R&D) and testing, phthalate-free films can now comply with industry regulations, such as Europe’s Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals (REACH), while providing the same quality and reliability as existing phthalate-based films.
As with higher-quality calendered films using polymeric plasticizers, these new options are helping transform the market.
Manufacturing advancements over the last few years have also allowed vinyl, both cast and calendered, to be held to higher specification standards. Working together, software and hardware can hone in on microscopic features and control them from batch to batch, to help ensure a high level of uniformity.
Intelligent control systems measure and monitor a number of parameters relating to both the machinery and the materials as they are manufactured. Film properties like thickness, colour, width and gloss level, all of which are crucial to overall quality, are constantly controlled. With greater uniformity throughout the whole manufacturing process, the films can be specified to even tighter standards without sacrificing consistency.
Just as designers drive the creativity behind today’s striking and decorative wide-format graphics, so too do vinyl film manufacturers use knowledge of the latest science to turn technological innovations into reality.