By Olivia Cahoon
Part 1 of 2
Polystyrene is a popular, printable rigid substrate commonly used in the sign industry. It remains a solid at room temperature, flows when heated above 100 degrees Celsius, and is also foamed between paper-based surfaces for digital printing.
Polystyrene is available in several configurations, including clear polystyrene sheets, prismatic polystyrene, and high-impact polystyrene (HIPS). This article focuses on HIPS.
HIPS Offers Variety
HIPS is a thermoplastic material used in low-heat applications that offers high-impact strength and stiffness. It is typically cost effective and available in a range of colors, sheet sizes, thicknesses, and surface finishes—making it an ideal substrate for digital printing.
HIPS thickness often depends on whether a corona treatment is applied. Corona treatment is a surface modification that increases the surface energy or dyne level of plastic films. While corona treated styrene is generally 0.010 to 0.060 inches thick, non-corona treatment HIPS products reach up to 0.250 inches, says Tony Lampariello, national rigid media manager, Agfa Graphics. Sheet sizes range from 48×96 to 60×120 inches.
Another important HIPS feature is opacity. It is available from translucent to 100 percent blockout. “Opacity drives the range of applications used in graphics,” reveals Lampariello. For example, translucent polystyrene is often used for backlit applications. “Increasing pigment and changing opacity creates single-sided signage applications to two-sided signage requiring a blockout polystyrene.”
Color also plays a role in HIPS’ popularity. Available colors include but aren’t limited to black, blue, brown, cream, green, grey, lilac, opal, orange, purple, red, silver, yellow, and white. While white is a popular HIPS color, black is not as common but still available, adds Mark Six, technical product manager, wide format, The Mosaica Group.
According to Wade Sisco, director of marketing, United Industries UltraBoard, HIPS facers are available in custom colors for production runs greater than 700 4×8-foot sheets. “Color matching processes also greatly differentiate from standardized color matching methods in ink or dye-based color systems—as HIPS colors are achieved utilizing elements of pre-colored plastics in combination with chemical, density, and opaqueness properties.” HIPS surface finishes typically include gloss and matte with matte more popular, especially in the graphic arts.
Several digitally printed applications are created with HIPS due to its flexibility, large assortment of colors, and surface finishes. These include point of purchase (POP) displays, product tags and labels, kiosks and retail fixtures, packaging and thermoformed graphics, and trade show panels. “HIPS is very flexible and bendable, and can conform to flat or curved for display purposes,” comments Six.
HIPS is an economical substrate in most cases, according to Six. “But sometimes, a thinner gauge expanded PVC foam may be used in its place to save on costs. There are also reasonably priced ‘green’ replacement products for styrene. Some of them are in the polypropylene and polyolefin families and some are paper based.”
“Polystyrene is the most cost-effective substrate for durable, longer term, moisture-resistant applications. When compared to paperboard product in the same thickness, polystyrene is slightly more expensive. Paperboard products may be slightly lower priced but will not compare in strength and durability,” admits Lampariello.
Rather than printing directly to polystyrene, some print providers opt for paper-based surfaces with a polystyrene center. Due to its high quality and durability, HIPS is often selected as the center and is available in foam sheets.
Paper-faced polystyrene sheets are the most common material used for temporary graphics and display solutions. According to Lampariello, this is because many retailers and signage display customers are looking for higher quality, moisture resistance, and longer term application material. “HIPS-faced polystyrene foam sheets is the solution. It is easily printed, finishes cleanly, and meets the high-quality, long-term requirement.”
When printing to HIPS, print providers should be aware of several challenges like surface contaminants, dyne level requirements, and static.
Surface contaminants are a constant challenge in substrate manufacturing that can affect print results by impeding ink contact with the styrene surface. “Unfortunately due to the nature of the manufacturing processes, a perfectly clean and print-ready sheet can be a bit of a unicorn within the sign industry,” shares Sisco.
Before printing to HIPS, Theresa Vanna, print market specialist, Primex Plastics Corporation, suggests print providers know the dyne requirements and the chemistry of the applied ink. “Ink adhesion and curing times are greatly impacted if the surface energy of the substrate and the ink chemistry are incompatible,” she offers.
Vanna adds that because there is no industry standard for product specifications or terminology as it applies to color, opacity, gloss, and surface textures, it is critical that the print provider knows its supplier’s specifications and sample the product.
Static is still a concern for printing to polystyrene and is determined by material as well as environment.
As printers increase in speed, so does static, which negatively affects image quality. Static results in overspray and ink separation, which Lampariello says can be remedied by using non-corona treated HIPS. “Non-corona treated HIPS removes the inherent surface energy and can help control static.”
Certain digital presses are also designed to combat static. When purchasing a flatbed printer, Sisco believes it’s important to assess the printer’s primary use as some are intended for printing directly to paper and have no static dissipation integrated into the design. “Always contact the manufacturers of your intended materials regarding their performance with different printer and ink types, as well as the operations environment of your printer,” he advises.
Static is also produced by the environment. In fact, Six believes it is more of an environmental issue than a material issue. To remedy it, he suggests print providers avoid humid environments and consider flatbed printers equipped with anti-static devices or tools that combat static electricity.
To avoid warping, polystyrene should be properly stored in a flat environment with controlled temperatures and humidity levels.
As with any large and rigid sign substrate, large sheets are ideally stored flat. “Storing any rigid materials on their ends or vertically encourages the substrates own weight—along with repetitive exposure to sunlight or varying temperatures and humidity—to warp the material overtime,” suggests Sisco.
This is especially true for products that are corona treated since dyne dissipates with time and storage conditions, says Vanna. In addition to temperature and humidity, products should also be protected from dust, dirt, and debris. “Since corona treated products tend to have an increased amount of static, static tends to draw airborne particles onto the surface of the sheet and therefore can affect print quality.”
If polystyrene is already warped the product can still be salvaged. According to Sisco, most substrates warped from incorrect storage are corrected by placing them horizontally on a flat surface. In this position, he says flatness should return as long as the environment is maintained at a consistent temperature and humidity for a period of time.
Polystyrene products like HIPS are available in a variety of colors, sheet sizes, and thicknesses in both gloss and matte surface finishes. While this substrate is a popular choice for POP displays and trade show graphics, it’s important to consider thickness, surface energy, opacity, static, and storage methods before using it.
Part two of this series features information on the newest polystyrene products.
Dec2018, Digital Output