Thermal Transfer

Thermal transfer printing is a proven, versatile printing process that continues to expand its reach.

THERMAL TRANSFER PRINTING is a proven, industrial printing process that can be tailored to meet a wide range of application needs. Its tracks can be found in everything from coffee bags, medical devices, pharmaceuticals, snack foods, prepared foods, and processed meats and cheeses, says Glenn Breslauer, director of IT marketing for Bell-Mark Corp. (Pine Brook, N.J.).

One of the reasons for this widespread use is its ability to print variable information. "Thermal transfer allows a package to be coded with variable information in real-time," states Breslauer. "Not only are date codes and lot/expiration codes simple to apply, but graphics, barcodes, RSS, nutritional facts, and many other messages can be directly applied to a packaging substrate during the packaging process."

Joe Smith, products and service manager for DNP IMS America, Co., Ltd. (DNP, Concord, N.C.), adds, "Thermal transfer printing also offers the ability to control the variable data via a computer, dramatically reducing set-up time and streamlining the manufacturing process. It is the recognized printing standard for barcode labeling across all industries, and offers the highest durability compared to laser jet, bubble jet, lithographic, flexographic, and direct thermal. … Additionally, it is an inexpensive print process for short-run projects, and has the ability to print high-resolution information and barcodes onto small print surfaces; all of which are key qualities to any package printing application."

Nick Mandrycky, senior VP of marketing at IIMAK (Amherst, N.Y.), lists some generic uses of thermal transfer printing, along with some specific packaging applications:

• Coding—Most common; adds variable data directly on a package in food and beverage, pharmaceutical, and personal-care applications.

• Print and apply—This process prints and then automatically affixes shipping or product labels as they go down a conveyor belt. These applications are often done on extremely high-volume products. A good example of this is affixing a barcoded label with color information to the bottom of a nail polish bottle.

• Customization of pre-printed labels—To reduce label inventory and guard against obsolescence, some companies choose to combine thermal transfer printing with other printing technologies. The label or packaging is often preprinted with the logo and general company information, and the variable information such as the product's type, size, or variety is added on demand. Paint is a good example of this application.

• Private labeling—With short-run, specialty items or samples such as gourmet coffee or spices, thermal transfer is used to print the whole package. Logos, product name, description, and other information can be printed on the bags, in addition to the variable information. Private labeling and branding applications are found everywhere—in food and beverage markets, hardware, and in aftermarket supplies.

Application inroads

The application of thermal transfer printing appears to be cutting into the use of hot stamp printing of date and lot codes for flexible packages such as potato chip bags and crackers. "Thermal transfer printing is a very attractive solution in comparison to hot stamp," states Smith. "The driving force behind this shift is due, in part, to reducing set-up time, simplifying packaging changeover, and eliminating costly printing plates."

Another area of potential growth for thermal transfer printing is in the brand protection and security-labeling market. Appleton's (Appleton, Wis.) Joe Pleshek, brand protection market manager, believes that the ability to combine variable information with a security feature in thermal transfer substrates can provide a powerful security solution that is difficult to replicate. "The need for security is growing and this should open a growing niche market in the thermal transfer arena."

In May, Appleton introduced a new line of thermal-transfer label security papers that incorporate its TechMark® Taggants and Read/Write Threads. The taggants are invisible under normal lighting conditions, but can provide quick visual verification under UV lighting. They can also be formulated in the paper to create a unique identifying code that is difficult to duplicate or alter and can be read by a handheld reader. The TechMark Read/Write Threads carry a secure, encrypted code that also can be read by a handheld reader. The data is added to the thread by a proprietary process and cannot be erased, altered, or duplicated. Both grades of the security papers have been qualified by Zebra Technologies (Vernon Hills, Ill.) for use on its line of Zebra® brand thermal transfer printers.

Selection considerations

Even though thermal transfer printing is well established in package printing, potential users should not take its application for granted. Sony Chemicals (Mt. Pleasant, Pa.) continually emphasizes the importance of educating its customers on the dynamics of thermal transfer printing, so they can avoid common pitfalls and achieve the full benefits of thermal transfer printing.

"The key to successful thermal transfer printing is the need to match the substrate, the thermal transfer ribbon, and the printer to each other in order to print the packages and labels correctly," emphasizes Lance Moyer, product manager, thermal transfer ribbons for Sony Chemicals. "Many users of thermal transfer printing run into problems because either their substrate or ribbon is not compatible with their printer."

One consideration that is of primary importance is the intended application, with special emphasis on the environmental exposures throughout the life of the product. The prime decision whether to use wax, wax/resin, or resin ribbons is a cost/performance issue based on the needs of the application.

Moyer spells out the general spectrum of this cost/performance equation. "General purpose wax ribbons offer broad performance characteristics to deliver the image quality and durability required for most applications, while providing an excellent total cost solution. … Wax/resin ribbon products produce superior results across a wide range of applications at a lower cost than all-resin ribbons. These include a darker image, ability to print at higher speeds, less printhead static, and suitability with a wide range of media from paper to low-end synthetics. Specialty resin ribbons provide enhanced image quality and durability for applications that require special performance characteristics such as extra resistance to environmental conditions, smudging, or scratching. Grades are available that resist solvents, chemicals, and exposure to damaging UV rays."

Both ribbon and printer suppliers have been introducing developments over the years that have improved the cost/performance issues and/or broadened the applicability of thermal transfer printing. Ann Marie Phaneuf, director of marketing for Weber Marking Systems (Arlington Heights, Ill.), believes that the costs of printer ribbons and labels have been a drawback in the past, but says that these costs have been coming down considerably in the past 18 months. Additional constraints have come from thermal transfer systems' inability to meet the needs of very high-speed production environments. "However," says Phaneuf, "printer speeds have been increasing while maintaining image quality."

In July, Weber introduced three additional Zebra thermal transfer print engines for use with its Model 5200 label printer-applicator. Each system includes a choice of a high-density, on-demand thermal/thermal transfer printer that provides text, barcodes, and graphics. The Zebra print engines are available in 203-, 300-, or 600-dpi models and can accommodate pressure-sensitive labels up to 6" wide at speeds up to 12" per second. The 5200 Series can provide precise label placement of ±0.03" and can apply labels to the top, bottom, or sides of a product.

Because of these continuing developments by ribbon and printer suppliers, it is imperative that users stay abreast of new product offerings so that they can take advantage of the lowest cost/best performance option that is available.

For instance, Brett Cameron, vice president sales/marketing for DNP, says that his company saw a gap in the thermal transfer ribbon market for a superior wax product that was still in line with wax ribbon cost expectations. DNP developed and introduced its newest product, W160 Ultra Durable Wax, to meet this need. It can print on a wider variety of label materials than many standard wax ribbons, and is designed to fill the gap between more expensive wax/resin ribbons and standard performing wax ribbons. Cameron says that the W160 ribbon is the fastest growing wax ribbon in DNP's product line.

Going up the price/performance scale, Phaneuf stresses the improvements that have been made in wax-based ribbons over the past few years. "It is important to note that there are a number of wax/resin ribbons on the market that offer a cost-effective alternative to resin ribbons when the application can be addressed by the wax/resin formulation." The emphasis, again, boils down to knowing the needs of the application to take advantage of lower cost possibilities.

Near-edge thermal transfer printing

Near-edge printers offer some real benefits for thermal transfer printing, including higher speeds, reduced set-up time, and longer printhead life. These benefits come from the approach taken to transfer the ink to the substrate. Cameron explains that in standard, flat-head printers, the printhead is stationary and a pressure roller is used to control contact between the ribbon and substrate. The printhead in near-edge printers "floats," and is adjusted to control the point of contact for ink transfer. Near-edge ribbons can be either wax or resin based.

Cameron reports that the print speed of near-edge printers is almost double that of flat-head printers. "That is why the majority of near-edge printers are used for packaging applications where speed is a determining factor," he notes.

Moyer explains that the longer printhead life is the result of less pressure being applied during the printing process. And the set-up time is reduced because no media thickness adjustments are required in the near-edge printing process.

by: Tom Polischuk