Substrate Options —‘Paper or Plastic?’September 2007 By Jean-Marie Hershey
Jet (formerly Jet Litho), Downers Grove, IL, does business in both worlds. The privately held company does around 75 percent of its business in plastic and 25 percent in paper. Over the past 15 years, Jet has become very heavily involved with plastic, due to the growth in its unsecured gift card business, in addition to which it also produces POP display and general printing work on plastic.
Complementary or Not?
Joe Tenyer, vice president of operations, says that the relationship between Jet's paper business and its plastic business is a complementary one. "Most gift cards are manufactured, then tipped on or affixed to a paper-type carrier, which you would see in a retail outlet, or folded into a direct mail piece. We print the plastic card, then marry it to the paper."
Jet expects to produce about 250 million laminated cards and upward of 500 million direct mail cards in the next year. The company prints on a wide variety of substrates, primarily PVC, styrene, polyester and polycarbonate, and prides itself on its ability to handle notoriously "difficult" materials, such as wood veneer and canvas.
Serigraph, headquartered in West Bend, WI, handles only plastic, and the graphic arts is just one of the multiple segments for which it produces printed plastic. "We've been exclusively plastic for about 20 years," explains Executive Vice President Robin Reis. "We exited paper based on our judgment that the plastic business would be more specialized and less competitive."
The company's Specialty Printing division is dedicated to the POP market--displays, signage, backlit signs (for McDonalds and Burger King, Coke and Pepsi) and floor graphics, among other applications. On the litho side, Serigraph uses a lot of polystyrene and static cling vinyl, and can print on substrates from film up to .030? on its offset presses, while its ink-jet equipment handles substrates up to 1/2? thick. Its finishing operation performs cutting, diecutting, embossing, hot stamping and laminating.
"Much of what we do isn't just plain-old printing," Reis points out. "We produce a lot of special effects by using different inks, or by combining offset with screen printing. Chemistry is important because we use so many different materials, and not every ink will stick to every plastic. Our technical team helps match the substrate with the right ink to achieve the desired effect."
Printing on plastic is far more difficult to execute well than switching from uncoated to glossy paper. Not only is plastic different from paper, but different plastics are suited for different applications. Of the dozen basic polymers suitable for printing, several are available in different grades developed for specific applications. Each has special properties that demand special treatment, including the use of custom inks and chemistry formulated by suppliers that specialize in UV-curable inks. Each new combination of inks and substrate has the potential to transform a normal pressroom into a science experiment.
The biggest difference between the paper world and the plastic world, however, is the price of the materials weighed against the potential for error. "Twelve-point paper is about 25 cents a sheet; 12-point PVC plastic is probably double that, so your material costs for makeready go up 10 percent, and your mistakes become more costly," Tenyer says. "A sheet of plastic for printing a credit card, once you laminate all four pieces together, costs more than $1 per sheet. Some polycarbonates are $3 to $4 a sheet. Most lenticulars are more than $1.50 per sheet."
A printer who handles both paper and plastic learns to accommodate the impact of the differences between them on the workflow in his shop. To begin with, "the ink sets and the plate curves are different," Tenyer points out. "As paper printers, we're all about the dot. We spend a lot of time tuning the differences in all these substrates to our prepress plate curves, making sure we're always printing the same dot gains, traps, etc."
It may also make sense to separate paper and plastic workflows. At Jet, "We try to keep most of our paper printing on certain presses and plastic printing on others," he adds. "If we do switch from UV to conventional printing, we know there will be different dot gains on the press because the rollers will swell from UV inks. We've learned to compensate for that."
Apart from getting the right ink to adhere to a given substrate, plastic printers are also faced with getting the ink to dry. "Conventional inks are designed to oxidize on paper; on nonporous plastic, the ink just sits there," Reis explains. And while ink and water balance has to be right to print decently on both paper and plastic, the fact remains that paper absorbs water, while most plastics won't. This means less water in the fountain solution, and the use of inks that will perform well with minimal water in the feed and press. According to Tenyer, this is something with which inexperienced press operators have a hard time adjusting.
Fast-drying synthetic UV inks are especially well-suited to printing on plastic, and there is no question that the biggest innovation in printing on plastic over the last 20 or 30 years has been UV energy. Take a closer look, however, and UV technology actually turns out to be something of a mixed blessing.
For one thing, UV printing generates considerable infrared (IR) energy needed to dry the ink. IR energy also has the potential to distort the plastic. "If you need a certain amount of UV energy to cure the ink, heat will be your nemesis," Barkley explains. "When you heat paper to a couple hundred degrees, it just gets hot. At 450 degrees, it burns. Get a piece of plastic to 200 degrees, and it's going to melt."
Static Electricity Warning
Under certain conditions, static electricity can transform most any plastic surface into a snarling, crackling enemy that attracts dirt, dust and debris. In the pressroom, sheets won't feed and ink won't lay down properly. To reduce static electricity, plastic printers routinely install static eliminators on their presses and equip their plants with temperature and humidity controls. Like most good commercial printers, Jet maintains temperatures between 70° F and 80° F, with humidity between 40 and 50 percent. It also feeds ionized air into the feeders on its presses to cut down on static.
Notes Tenyer, "There is more static in plastics and foils than in paper. On some of these metallized polyester sheets, you can see the sparks come off in our color viewing rooms. The guys who handle it wear cotton or rubber gloves." Adds Reis, "Material handling is a big issue with plastic. If we have to sheet the material off a roll, we do it in a clean room environment."
Proofing on plastic also presents some special challenges. At Serigraph, "We use a variety of different methods, but we have to proof on the material we're going to print," says Reis. "We produce both ink-jet and halftone dot proofs, and we spend a lot of time getting it right."
Adds Tenyer, "Proofing can get a little tricky on synthetics, due to the melting points of various plastics. Trying to proof on a .010? styrene just doesn't happen because it distorts too quickly, but you can proof on 24 mil because it's more stable. That said, we've been able to tweak some off-the-shelf systems by managing the heat transfer of the rollers onto the substrates."
It may also make sense to press proof a plastic job. "If you think about what drives cost in this business, the client is spending a lot more for plastic than for paper printing," Barkley says, "so the idea of cost-justifying a proof is more often yes than no."
Although there are still many variables to contend with in plastic printing, plastic manufacturers of plastic substrates have succeeded in bringing some of the processing parameters--gauge, color, finish and dyne, among others--under control. As a result, the quality and consistency of the plastics available to the graphic arts marketplace has steadily improved over time.
Innovations in Plastics
Plastic manufacturers are also incorporating topcoats, treatments and other additives into their materials, enabling printers to be more flexible with their inks, fountain solutions and other materials. For example, rubber modifiers added to polystyrene render the material less likely to fracture. And, recent innovations--such as plastic sheet with pre-applied mag striping and versatile, less costly PVC lenticular plastic--also lower the bar to entry and yield significant savings.
A word about synthetic paper. Synthetic paper refers to plasticized paper substrates containing paper fiber or materials such as polypropylene-based Yupo synthetic papers, which can be printed and dried conventionally, and wiped clean when soiled. In addition to printing on a wide array of plastic materials, Quantum Graphics, Morton Grove, IL, uses Yupo synthetics extensively for publications work like catalogs, trail guides, workbooks, trucking manuals and other rough-duty applications. According to Tony Novack, COO, "It's a case of good product in, good product out."
When your destination is the "No Man's Land" of plastic printing, it's best to enlist the services of a guide. This is where a trusted supplier can be a valuable resource. "We probably have a closer relationship with our plastics suppliers than with our paper providers," Barkley points out, "because we tend to be one of their biggest customers."
Unless you're in a mood to experiment, it's probably best to stick with ink and material suppliers that have proven technologies and a track record to match. "I wouldn't go with the ink company of the month because they have a good price on plastic inks," Tenyer says. "Instead, I would make sure my suppliers had some experience with successful plastic printing companies. Again, it's all about controlling the variables. That's how the bottom line profits." PI
Are You Dyne-ing In?
The biggest hurdle for a plastic printer is to make sure he gets ink to adhere to all of the different types of materials with which he deals. While this is also a concern with UV, it is more of an issue when printing on plastic with conventional inks. This is where dyne levels and corona treatment play a critical role in the printability of a given piece of plastic.
Corona treatment changes the surface tension of plastic surfaces by subjecting them to a high voltage discharge, rendering them more ink- receptive. Surface energy is measured in dynes. Because the effects of corona treatment tend to dissipate over time, it's best to use a shipment of plastic as soon as it is received. In cases where the plastic cannot be used right away, however, printers will sometimes re-corona treat the substrate to reinvigorate or change its surface energy. This can be done by installing a corona treater in-line on a web press just before printing, or by affixing it to the first printing unit, such that every piece of plastic printed would receive corona treatment before passing through the remaining units for printing.
However, "printers really have to specify what dyne level they want, order their plastic timely, and try to use it right away," says Joe Tenyer, vice president of operations, Jet. "Our specification is 38-50 dynes, although we can make it work at less. We test the dyne level of incoming materials and prequalify all first-time materials before taking shipment."
Plastic suppliers have to be extremely sensitive and responsive about dyne level, notes Robin Reis, executive vice president, Serigraph. "I don't think I've had to reject a shipment over a dyne level issue in a number of years. It's really become a non-issue as plastics become more available."
"If we do reject a batch of plastic, it's because of slime spots or other defects in the surface," Tenyer adds. "Some of these plastics are calendered, others are extruded, and sometimes the finishes can be inconsistent. There might be dust around the edges from a paper cutter that will get into the work."
GOEX (www.goex.com), Janesville, WI, manufactures custom-extruded plastic sheet and roll stock materials, including PVC, polystyrene, polycarbonate, PETG, barex and XT materials for the graphic arts, medical, electronics and packaging industries.
INEOS Films (www.ineosfilms.com), Delaware City, DE, manufactures films for the packaging of pharmaceutical and medical products; chip cards, bank cards and identity systems; food and non-food packaging; and specialty applications.
Klöckner Pentaplast (www.kpfilms.com), Quebec, Canada, produces films for pharmaceutical, medical, food, electronics and general thermoform packaging, as well as printing and specialty applications using post-consumer polymers.
Lucchesi (www.lucchesi.it/en/gruppo.html), Bologna, Italy, specializes in the production of rigid PVC films for the printing industry.
Pace Industries (www.pace-industries-inc.com), Reedsburg, WI, provides the graphic arts industry with printable plastic in sheets and rolls. Engineered products are also available for printing, thermoforming and other related processes.
Pacur (www.pacur.com), Oshkosh, WI, is a custom sheet extruder specializing in light- and heavy-gauge polyester, co-polyester and polypropylene resins.
Rocheux International, Piscataway, NJ, provides rigid PVC with a range of printing surfaces for the offset, screen and flexographic markets. Suitable for both conventional and UV ink applications.
Spartech (www.spartech.com), Clayton, MO, produces extruded thermoplastic sheet and roll stock, polymeric compounds, and custom-engineered plastic products.
Transilwrap (www.transilwrap.com), Franklin Park, IL, manufactures and converts plastics for the thermal laminating, printing, industrial, specialty packaging and graphic arts markets.