Addressing Vinyl Properties
Differentiating Cast and Calendered
By Cassandra Carnes
Vinyl is a core substrate. Available in a variety of forms, both cast and calendered pressure-sensitive, adhesive-backed vinyl are prominent elements of high-impact graphics. Media manufacturers work diligently to create products that are easy to install, remove, and last outdoors for extended periods of time.
Over the past decade, the industry experienced vinyl improvements in a variety of areas. Pressure-sensitive vinyl manufacturers continuously adapt to the changing demands. For example, Ritchie Daize, international digital sales manager, Arlon Graphics, LLC, explains that new vehicle types—such as Sprinters and Transits—feature challenging body contours, which require more flexible media with stronger adhesives.
Substrates evolve alongside new printing technologies, in particular higher resolutions and new, longer lasting, environmentally friendly inks, notes Martin Kugler, corporate communications manager, Hexis S.A.
Ease of use during installation is an additional factor. Air egress technology enhances the installation experience, reducing the time and expense of wrapping applications and improving the final look of the finished product. The evolution of air release liners is also significant.
Whether utilizing cast or calendered film, it is important that both print providers and installers understand the media. Depending on the application requirements, specifically the end environment and expected installed lifecycle, the choice of media is often obvious.
Advancements to pressure-sensitive, adhesive-backed vinyl products are best outlined by first categorizing whether the media is cast or calendared.
The differences between the two are primarily determined in manufacturing, rather than within the products’ chemical make up.
Molly Waters, technical specialist, Avery Dennison Graphics and Reflective Solutions, offers some basic facts. Most vinyl films begin with the same ingredients, polyvinyl chloride (PVC) polymer, which is “basic plastic and by nature rigid.”
Other ingredients are added to make the film flexible, specifically plasticizer; add color, usually pigment; and additional additives to achieve other desired properties. Once raw materials are chosen, the manufacturing process—as well as the type of plasticizer used—creates the main differences between vinyl films, explains Waters. “Vinyl films can either be made by calendering or by casting. Each of these processes renders different qualities.”
In addition to the manufacturing process, cast and calendered vinyl films are differentiated by molecular weight. “It largely determines chemical stability in non-crystalline plastic structures such as vinyl in all forms—water pipe, house siding, window frames, Barbie dolls, and vinyl film,” adds Daize.
Bill Stalker, technical director, Ritrama Inc., explains that cast vinyl is made using solvents and can handle larger molecular weight plasticizers. Calendered vinyl mix is heated to become a fluid and has plasticizer limitations. As the molecular weight increases, the plasticizer becomes more permanent and is less likely to migrate into the adhesive of the vinyl’s surface.
Cast films are often categorized as high performance, providing advanced durability and conformability. Calendared films are typically used for intermediate, short-term, and economy projects. Both are advancing.
“In the last five years, improvements in the construction of calendered films has created products that work more consistently, especially digital films,” notes Matt Buckley, technical specialist, FDC Graphic Films, Inc. “We point to increased durability and compatibility with wide format solvent and eco-solvent inks,” he adds.
Jeffrey Stadelman, technical marketing manager, MACtac Graphic Products, agrees, noting the greatest advancements are found with high-performance calendered vinyl films and their general overall acceptance in the U.S. market. “With new manufacturing advances in the calendering process, better temperature and processing controls and improved formulating abilities, high-performance calendered vinyl films are rivaling high-quality cast films in durability, conformability, and overall dimensional stability in almost every application,” he adds.
Traditionally, cast vinyl was considered a better product, but also carried a higher price tag. “Now, thanks to advances in the manufacture of calendared vinyl, graphics providers can receive a less expensive calendered vinyl that yields similar results to a high-performance cast vinyl,” says Dione Metnick, product manager, LexJet Corporation.
The popularity of both cast and calendered film results in better products for the end user. Competition among media manufacturers in the space keeps the market fresh, as new products are continuously introduced.
Printing and Installation
Despite some differences in the manufacturing process and chemical make up of cast and calendered pressure-sensitive, adhesive-backed vinyl products, the act of printing on one media over the other does not vary significantly.
However, when it comes to installation techniques, the differences become more relevant due to conformability. Adhesive properties also factor into installation. For any application, it is important to consider the surface a film will be applied to, the durability required, and the curves of the surface before deciding between a cast and calendered product.
In terms of printing, a few tips are worth mentioning. Since cast is thinner, it is more easily affected by solvents left in the film. Waters notes that cast films tend to maintain color and other properties better than other vinyl films, resulting in an ideal performance of pigments and UV absorbers.
Color management is a critical component to maintaining color and quality between cast or calendered. “As long as the printer uses the correct ICC profile and inks designed for the desired durability, there is no difference in printing between calendered and cast films,” states Stadelman.
The vinyl type chosen for an application affects installation. Properties, such as thickness, are important. “Calendered media is considered easier to install on flat surfaces because of its rigidity. Installers prefer this stiffer media because it makes installation easier,” explains Adam Larson, marketing supervisor, intermediate films and inks/warranties, 3M Commercial Graphics.
For the installer, calendered vinyl provides a broader range of opportunities when compared to cast, mainly because of its cost effectiveness. “Vehicle and wall wrapping are applications where calendered and cast vinyl overlap,” notes Stadelman. He explains that when compared head to head with cast, calendered vinyl feels more substantial and is easier to handle, as it does not wrinkle or fold over onto itself.
The downside is that calendered media does not conform well to complex curves. Also, when stretched into shape it tries to revert back to its original form. When exposed to heat, the film tends to shrink. More heat is typically required when wrapping complex surfaces with calendered films.
Print providers must ensure that the printing process doesn’t impede on installation. This includes attention to total ink coverage, especially when solvent-based inks are used. “Excessive ink coverage can increase the amount of typical shrinkage with calendered media and on cast films can soak through the adhesives,” admits Larson.
Adhesive strength is an important consideration. The length of time the application is intended to stay up and removability requirements should be addressed up front. Adhesives are developed with a variety of characteristics that influence bonding, performance, and removeability. While some are soft and conform to a surface easily and quickly, other adhesives are firm and may require heat and pressure, adhesive primer, and time to adhere.
Vinyl films generally use acrylic adhesives, which can be solvent or water based. “A general type is removable adhesive for short-term applications. Second, there are medium tack adhesives that are good for a variety of applications. Third, there are high-tack adhesives used for sticking to low-energy surfaces such as powder paints and polyethylene,” explains Stalker.
Adhesives are sometimes referred to as water- or solvent-based in reference to the carrier methods used in the manufacturing and not the characteristics of the finished product, explains Larson. He adds that a film’s adhesive is affected by the properties of the substrates, including the surface texture, surface energy, and outgassing.
Today’s on demand world indicates a push towards super removability traits. However, permanent adhesives are still viable. The level of permanence depends on a shop or customer’s interpretation of the word.
“Traditionally, permanent is defined as having a certain bond strength on a standard test substrate such as stainless steel or glass,” says Stadelman.
There is no doubt that removable materials have grown in popularity, especially with the expansion of the wrap market. However, many agree that there will always be a need for permanent adhesives. Long-term exterior signage and certain vehicle graphics are still best produced with them.
It is important to remember that permanent is a reference to the ultimate adhesion of an adhesive-backed film. The greater the adhesion, the more permanent it is. “Some substrates, such as engineered rigid board, require a more permanent adhesive to ensure the bond does not fail,” explains Buckley.
“For temporary graphics where the substrate is disposed of after use, there is no need for removable adhesive,” he adds. In the end, matching the adhesive to the substrate and understanding the requirements of the application will determine the selection of permanent versus removable.
Media performance is essential, especially when it comes to high-end products or complex curves. The decision between using a cast versus calendered film is determined based on the object or surface the media will eventually adhere to, as well as the installer’s preferences.
The vast amount of pressure-sensitive, adhesive-backed vinyl products available on the market leaves print providers with substantial choices. However, finding the best solution may prove to be a daunting task. Consider all aspects of a print job, and be sure to test media—including its adhesive bond, color quality, repositionability, and removability—before committing to a full run.
Apr2012, Digital Output