Eye Catching

Every day, people walk the aisles of stores. No matter what they are looking for, somewhere during their shopping trips metallic glimmers are likely to catch their attention. Thousands of products sit on store shelves, but the ones that are likely to stand out the most in the competitive world of packaging are those adorned with foil. To achieve such an alluring look, package printers must make effective use of the hot foil stamping process.

What glimmers is gold

Brand owners know that adding hot foil stamping to packaging will elicit a second glance from consumers. “The primary reason to use expensive, shiny materials on a label or carton is to catch [people's eyes] and make potential customers want to take it home,” says Gerry Stanford, sales and marketing manager for DMS, Inc. “Cold foil and overprinted metallic substrates present a flat mirror-like surface. This surface reflects light back to the
potential customer’s eye from one and only one direction, often the floor.” The difference between hot stamping and other methods, he says, is that the impression created in the substrate and its foil-covered bent edges reflect light from various angles.

“When compared to metallic inks, the mirror reflection is unmatched for brilliance and reflectivity, making the finished product really stand out on the shelf,” says Chris Raney, vice president, Bobst Group, Inc. “When compared to cold foiling, the finished stamped surface is of a much higher quality. Cold foil is like a label stuck on the surface of the board. As a result, any imperfections in the board tend to show through, and the surface therefore, tends to be much less smooth than with hot foil.”

Metallic inks are most successfully applied with gravure or flexo, where there is the possibility of laying down metallic particles, according to Raney. The volume of ink applied in offset is extremely low, leading to limited results compared with hot foil stamping, he says.

Brass is the way to go

Relative to the cylinders used in the hot stamping process, industry experts find that brass is most effective in achieving the most accurate and detailed foiling. According to Stanford, this is because the typical size of the equipment, and the speeds required, make brass the material of choice.

“The material is ideally suited for the manufacturing processes of machining and engraving, [and] it provides adequate heat conductivity properties that are necessary to apply the foil,” says Steve Lee, vice president and director of technical support, RotoMetrics. “RotoMetrics is the exclusive worldwide distributer for UEI Group’s (Universal Engraving Inc. and UEI Fine Cut) rotary hot stamp and embossing tooling. We have chosen brass because of its inherent characteristics for engraving, hardness, durability, and heat conductivity.” As part of its full line of hot stamping and embossing rotary tools, RotoMetrics offers UEI’s custom-designed UniSphere rotary cylinders and UniFlex flexible dies that can adhere to a heated magnetic cylinder in minutes.

Although brass is the most favored material for hot stamping systems, converters may consider other materials depending on the nature of their projects. “The best material for a specific application is determined by several factors: the amount of thermal energy transfer required, the dwell time, and the recovery time at the desired speed being foremost,” says Stanford.

It’s all in the details

“Because of the inherent nature of hot foil, you will experience a measurable degree of foil bleed. So if the die image isn’t precisely duplicated, you’re simply adding to the problem,” explains Michael See, president of Precision Hot Stamp. “The best way to determine the accuracy of an image, whether it be CNC-engraved, photo-etched, or cold-foil-applied, is to proof the image with a film positive. Place a film positive over the die and view the comparison with a 10X loupe. If you see in excess of 10 to 20 percent bleed, you will be able to determine the final outcome.”

The die surface should be smooth and flat to avoid patch-ups during job setup, according to Raney. “The design is very important, and consideration should be given to whether a flat-on-flat, round-on-flat, or round technology will be used,” he says. “For the highest detail or for large surfaces, round-on-round would be the preferred choice.”

A CNC-engraved brass cylinder produces the best press speeds and quality when stamping shiny foil on clay coat or film, according to Stanford. “If you are trying to stamp extremely fine, dense artwork, and a lot of it, you may consider photoengraving,” he says. “Soft substrates may require skinning up the copy. Magnetic tape, or any other continuous applications, can be improved by press setup/tooling changes. Heat sealing and hot laminating operations benefit from other die materials.”

UEI recommends looking at the concentricity, or TIR value, when purchasing a new cylinder. “We consider an excellent TIR value to be 0.0005˝. The critical TIR value should be a consideration when choosing an engraver, as you want to make sure that the engraver can hold a high tolerance.”

It’s electric

Heat control is extremely important for correct foil application, which can be achieved with electric or hot oil heating systems. “There are two types of oil systems: one that is wet and the oil runs through a bored out cavity in the cylinder; the other is a dry oil system where the oil doesn’t come in direct contact with the cylinder but is contained and heated with an electric heating mechanism,” says Larry Hutchison, president of UEI Group. “Between the two systems, the first one needs more consideration as it must have a thicker internal wall to contain the oil and provide structural strength to the cylinder.” Although electric heating does not run as fast as the hot oil system, high-running speeds have been achieved by both, he says.

Stanford says electric heating systems are the safer, more-effective option. “Many people believe that hot oil is superior to an electric system. Hot oil is an inherently dirty and dangerous system. The reality is that a well-designed electric heat/cool system will perform as well or better than a hot oil system. As technology has advanced and plant safety and systems maintenance and reliability issues become more important, there is a move in all industries generally away from hot oil as a process heating source,” says Stanford.

Raney says electric systems are more responsive to changes that may be required during the run. “An increase in temperature (or decrease) is more quickly seen on the die,” he explains. “Oil is a very good heating means for certain types of presses particularly where higher temperatures are required. Unless equipped with an equivalent cooling system, temperature adjustments can take a while to be seen on the die.”

Handle with care

For converters, system maintenance is the key to running a smooth and successful hot stamping operation. “The maintenance of hot stamping dies is often ignored. Simply acquiring a super-fine polishing stone can make all the difference in the world,” says See. “After a certain amount of usage, say five thousand repeats and up, the images on a die will begin to lose focus. Friction will round over the edges of the image and start to blur the final result.”

UEI recommends taking monthly measurements to ensure that once placed in the machine, the hot stamp cylinder continues to rotate to the original value it was meant to achieve. “The rounder the cylinder and the impression rollers are, the better the system will perform,” Hutchison says.

It is also very important to keep the press as clean as possible, as the foiling process creates dust, according to Raney. He also suggests making sure the heating system is functioning properly, because heat control is a very important component in the hot foil stamping process. While there is much to consider with hot foil stamping maintenance, Stanford recommends converters keep three rules in mind: “Keep your die clean, always check compatibility of new substrate/foil combinations, and use your die maker’s advice.” n