Ink Jet Technology Revolutionized: A Review of the Hot Melt Ink Method and Drop-on-Demand Ink Jet Printing

By Wink Faulkner, Markem Corporation | 11.02.09

The introduction of Touch Dry Hot Melt Ink technology and DOD ink jet printing enabled high-definition and crisp, instantly dry prints using a solid, wax-resin-based ink block

Product marking and coding processes greatly benefited from the confluence of two new ink technologies in 1988: hot melt ink technology and the drop-on-demand (DOD) method of ink jet printing.

Despite its drawbacks, the most popular method used for printing product identification is continuous ink jet (CIJ) technology. Some negative aspects of CIJ printing include code smearing as a result of wet ink; messy operation complete with ink leaks and splashing; the presence of hazardous solvents; hazardous waste disposal; the need for pre-printed boxes and a great deal of required maintenance.

Markem Corporation eliminated these hassles by uniting two new technologies that offer reduced associated operation costs; high quality, reliable prints; clean operation; ease-of-use and high system quality.

Ink Jet Technology Revolutionized

The packaging industry was ready for new, innovative ways for product marking and coding to be performed. Clean operation, high-quality, reliable prints, ease-of-use and system quality were all desirable characteristics for new product identification methods. The introduction of Touch Dry Hot Melt Ink technology and DOD ink jet printing enabled high-definition and crisp, instantly dry prints using a solid, wax-resin-based ink block.

This advanced ink adheres securely to virtually any substrates without weeping and is not affected by recycled content or variation in corrugated packaging, creating 100 percent scannable bar codes and graphic images with a high-quality appearance. These inks are solid at room temperature, allowing them to be picked up with no special handling requirements, melted for printing and harden immediately upon contact to the substrate surface, resulting in an instantly dry code.

No chemical solvents or water are needed for this process, allowing it to be free of organic compounds and therefore environmentally friendly. Replenishing the ink supply is both a simple and clean task. The solid ink block is placed into the system above the reservoir. Ink is melted internally by the system as required, eliminating any spilling and/or ink mess.

The DOD method of ink jet printing, illustrated in Diagram 1, is highly reliableand utilizes piezoelectric technology with hot melt ink jet technology. Heat is applied to liquefy the solid ink pellet; the ink, now in liquid form, is expelled from the nozzle by piezoelectric action. The ink solidifies on the printed surface, forming well-defined spots and solidifying to become “dry to the touch” in a fraction of a second.

The drop-on-demand method of ink jet printing ejects ink droplets from a nozzle to the substrate on an “as needed” basis, instead of a “continuous” basis, eliminating the need for an ink recirculation system. DOD print heads consist of many nozzles. Each individual nozzle is capable of emitting up to 30,000 finely controlled drops per second.

In comparison to DOD ink jet, traditional CIJ print systems have extensive morning start-up times of up to an hour, loss of packaging due to code smearing as a result of wet ink and higher overall system downtime. Other drawbacks associated with CIJ print systems include a great deal of required maintenance and the inherent worry of mixing toxic ink with products.

Large and Small Character Product Line Solutions

Both small character and large character marking and coding equipment manufactured by Markem are recognized for their high reliability, and utilize hot melt ink jet technology, which provides crisp, clean printing of both fixed and variable information such as sell by dates, lot codes and even graphics.

The product line of small character hot melt ink jet technology provides reliable performance and consistent production line activity, because the ink supply can be replenished without stopping the production line. Small and large character applications include those in the food (candy, coffee, frozen foods, dairy, ice cream), pharmaceutical, cosmetics, beverage, household cleaning products and tobacco industries.

Small character hot melt ink jet capabilities include applying date and lot codes to primary products, which are most commonly film wrapped products, and chip board boxes containing primary products. Both of these often carry the same codes. The 5000 Series line of case printers includes a small character option for the 5200 and 5400 models, which allows these systems to be used successfully with film and other flexible substrates.

The 5200 and 5400 SC case printers allow for printing on conveyers and both horizontal and vertical form fill machines. These machines function well in cold or damp wash-down environments. The 90XX Series is an industrial ink jet system known for its clean operation and superior code quality. Its design is specifically engineered to perform with rugged reliability, even in harsh production environments, live system diagnostics and superior uptime. The Model 90XX has a mean time between failure (MTBF) of 7,500 hours, and is accompanied by an intuitive user interface.

Large character hot melt ink jet capabilities, which include the 5000 Series case printers, include flexible and user-friendly coding solutions without the need for pre-printed cases or the application of labels. The 5000 Series of case printers have the capability of printing variable information on shipping cartons with up to four print heads, and provide total flexibility and quality in printing cartons directly on production lines, and has a MTBF of 17,000 hours. This series is also known for its superior code quality and clean operation.

Both the Model 5200 and 5400 can print on two sides of a box at the same time, are designed for real world manufacturing environments and utilize 256 addressable channels to produce high-resolution graphics and logos. The unique Touch Dry ink technology keeps prints from weeping and is not affected by recycled content or variation in corrugate packaging, creating 100 percent scannable bar codes and high-quality appearance of variable information.

Ink Solutions for a Wide Variety of Substrates

There are a large variety of hot melt inks formulated especially for many different substrates and applications. Some of the substrates include:
• Flexible packaging materials.
• Packaging films including polypropylene, polyester, polyethylene, saran, surface printed materials, laminated foils and Mylar laminates.
• Food - (Series 90012 food grade ink).
• Cold temperature films.
• Coated and uncoated cartons.
• Rigid packaging materials including HDPE/LDPE, polypropylene, polyester, glass, aluminum and high varnished cartons.
• Corrugated cardboard, shrink wrap material and porous substrates.
• Clay-coated materials.
• Metalized foil.

Hot melt ink jet technology and the DOD method of ink jet printing have changed the face of marking and coding technology by offering an alternative to CIJ equipment. These united technologies have brought cleanliness and environmental safety and high quality, crisp prints and machine reliability, all together for variable printing solutions applicable to many industries. Easy maintenance rounds off the experience that customers realize the benefits of each day.

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