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Question and Answer

Rotary Hot Stamping Dies and Tooling

by Staff

February-March, 2013
Originally, the choices for hot stamping tooling for rotary narrow-web applications were limited to brass CNC engraved cylinders. However, there now are options in the marketplace to provide economical alternatives for certain applications.

InsideFinishing spoke with Eureka, MO-based RotoMetrics about the different kinds of dies and tooling that are available for label/narrow web hot stamping applications.

Q:  Although CNC-engraved brass dies are the more traditional choice for rotary hot stamping, when are they the absolute best choice?

A:  CNC-engraved brass hot stamping cylinders are indeed the more traditional decorating tool and the most common. They are the best choice when stamping a thick substrate or a board stock. With CNC-engraved cylinders, manufacturing steps can be taken to better accommodate these substrates, and the brass cylinder provides for a deeper clearance (height from the floor to the flat of the foiling surface).

Q:  There are flexible die options in the marketplace that can be used on a magnetic cylinder. What types of flexible dies are available, and what are the best applications for these?

A:  A couple of options exist for narrow web hot stamping with flexible dies. One option, Uniflex®, is a chemically etched flexible copper die that is manufactured with a thin steel backing that is securely held to a heated magnetic cylinder. These types of dies allow for fast, easy and reliable changeovers, making them a great choice for any job, including short- to medium-run hot stamp jobs. It also can be an economical choice because these types of flexible dies are a fixed cost (priced per square inch, regardless of image complexity). Flexible dies also provide the opportunity for companies to choose hot stamping versus cold foil and still keep tooling costs low.

Flexible die options also are available that do not require a magnetic cylinder to secure the dies. Developed for semi-rotary hot stamping applications, these dies are mounted around a mandrel using an existing OEM mechanical fastening system. Marketed as CopperFlex™ dies, this option can be a more economical choice than conventional CNC brass engravings and is recommended for short- to medium-sized run applications.

Both of these two options are manufactured with copper, which is a wonderful choice for hot stamping due to its excellent heat conductivity, particularly with the high speeds of rotary, and its ability to maintain temperature more evenly.

Q:  Are photopolymer dies still being used for rotary hot stamping applications?

A:  Some photopolymer plates that are mounted to steel anvils still are in use, but are typically limited to embossing applications with simple raised, flat embossing. Although there was a time where a few companies were marketing photopolymer plates for rotary hot stamping applications, the success was limited. The heat conductivity properties of photopolymer plates are not as good when compared to solid brass cylinders or flexible copper dies, which can result in slower production speeds. In addition, the polymer is a soft material which will shorten the lifespan of the plate.

Q:  Are there other options for hot stamping tooling besides brass engraved dies or flexible dies?

A:  Segmented dies refer to brass hot foil dies that are divided into segments and/or rings. The rings are cut from brass in a similar fashion as solid cylinders, but each ring is limited in size specific to the image. The rings then are slid onto a mandrel, which typically is aluminum. The ring system can accommodate both electrical and oil thermal units.

Q:  Explain how a texture or refractive pattern is added to a rotary brass die? Are there standard patterns available from which to choose?

A:  Textured and refractive patterns can be added to solid brass hot foil tools or flexible copper die plates as well. This proprietary process, Unifraxion®, offers a multitude of pattern and design options that can be tailored to the customer’s requirements. The patterns most commonly are used for decorative applications, but also can be used for anti-counterfeit purposes. There are several standard patterns offered for customer convenience, but customized patterns can be applied.

Typically, refractive applications accomplished via rotary result in dramatic “movement and effect” within the hot stamped image; however, textured patterns can result in a diminished “tactile” experience versus that of flatbed micro-embossing due to the difference in the pressure and dwell time necessary to form the paper fibers when micro-embossing.

Q:  Cold foiling is popular with rotary/label applications. Why is hot stamping still a preferred choice for many applications?

A:  Cold foiling equipment is another option for decorating, and the run speeds are increased compared to hot stamping. While there is a place in product decoration for cold foil, the overall quality and consistency still is not that of hot stamping. For high-end label applications, as is often the case in the health, beauty, wine and spirits industries, hot foil remains the preferred process. Another benefit to hot stamping is that the process “irons” the fibers of the substrate, which provides an ideal base to ensure the highest sheen and brilliance the foil has to offer. In cold foiling, the foil is laid on top of the adhesive and fibers of the paper, which can cause the resulting foil image to be less brilliant/shiny in appearance when compared to hot stamped images. Further, one has to consider adding what can be an expensive component – the adhesive – to the cold foil process. It is important to balance “true” expense versus desired effect when choosing the type of foiling that is best for your application.

RotoMetrics, Eureka, MO, is a global manufacturer of solid rotary cutters and flexible rotary cutters and an exclusive distributor of UEI Group manufactured UniSphere® rotary hot stamping and embossing cylinders; UniFlex® and CopperFlex™ flexible dies; and UniSphere® segmented dies. For more information, call 800.325.3851 or visit www.rotometrics.com.