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Technology Feature

High Speed Foil Fusing

by By Chris VanPelt, Therm-O-Type

August-September, 2009
Traditional foil fusing technology uses a series of heated rollers to fuse foil to toner image areas on certain papers and plastics. While this technology has important applications, it also has several limitations, which include slow speed, excessive foil waste, restrictions in suitable papers and finishes, and the inability to selectively apply foil within surrounding toner image areas. However, a new foil fusing technology called High Speed Foil Fusing (HSFF) from Therm-O-Type has been introduced into the marketplace, providing many new advantages.

The HSFF process significantly increases the utility of foil fusing and offers solutions to each of the traditional foil fusing limitations. HSFF technology can be adapted to most platen foil stamping equipment, easily and inexpensively. Using HSFF technology, installed on an NSF series press (or other foil stamping press), foil can be fused to paper at speeds up to 4,000 impressions per hour. Excess foil waste is eliminated; a much wider range of papers and finishes can be foil fused; and foil can be fused selectively to toner image areas on the sheet.

The Mechanics of High Speed Foil Fusing
As mentioned, the High Speed Foil Fusing process fuses foil to toner image areas on paper. The mechanics of the process involve the adhesion of a specialized foil to the toner using heat and pressure. Specialized makeready materials are used to transfer heat and pressure to the paper in a method that does not crush or iron the paper surrounding the impression area. The reactive chemistry within the toner does not diminish over time. As a result, sheets can be run through the HSFF process weeks or even months after being imprinted with toner.

Four special materials are required when using the HSFF process. HSFF makeready materials are designed so presses can switch easily between flat foil stamping and foil embossing (with dies) and High Speed Foil Fusing (without dies) in a few minutes.

Unlike traditional hot stamping foils that stick to paper, HSFF foils are manufactured to adhere to toner. As a result, traditional hot stamping foils cannot be used with the High Speed Foil Fusing process. Because the HSFF process differs from traditional foil fusing, many foils that work with traditional foil fusing do not work with the high-speed process. In spite of their special characteristics, a wide selection of metallic colors, pigments (including white), metallic glitters, metallic and transparent holographic patterns, and even security foils are available for High Speed Foil Fusing.

An interesting side note on HSFF foils is that these foils can be used with metal dies to apply foil over solid toner backgrounds. This is a hybrid process combining a traditional die with HSFF foils. Using the HSFF foils and a metal die to fuse foil text and/or graphics over a solid toner background will provide more of a traditional foil stamped effect because the die will compress the stock within the image areas. Using a metal die to fuse foil over a solid toner background allows the fusing process to run at a higher speed than normal HSFF. Problems with foil adhesion directly to the toner are eliminated because these foils are formulated to stick to the toner. Foil can be fused to text and/or graphics within a solid toner background and this is impossible with the HSFF process. A limitation to using this hybrid process is when the background has areas with and without toner where fusing foil is to be applied with a metal die. In these cases, the foil will adhere only to the areas that have toner in the background.

Thermal Transfer Plate
HSFF, like traditional foil stamping with metal dies, requires heat and pressure to create a foil image. With traditional foil stamping, the image area is defined by the metal die. Using the HSFF process, no die is required and a toner image defines where the foil will be applied.

The thermal transfer plate is the surface used to apply heat to the foil, toner, and paper. This plate is approximately .25" thick and replaces the die on the chase. Thermal transfer plate material is a composite with a metal backer with a high temperature, compressible, synthetic coating facing the foil/paper. They can be purchased to match customerís image area requirements. To maximize HSFF production, it is recommended that the thermal transfer plate be mounted on a chase configured with mounting holes. Honeycomb-style chases are not recommended for High Speed Foil Fusing due to the lower heat density/transfer through this type of chase.

The thermal transfer plate thickness and mounting method allows most foil stamping presses to switch easily between traditional foil stamping, with metal dies, and HSFF, without dies, in just a few minutes. It has several important characteristics required to successfully use the High Speed Foil Fusing process on the widest range of stocks at the highest speed with the longest durability.

The most confusing issue with HSFF is that even though the thermal transfer plate and foil may cover many different toner image areas on a sheet, the High Speed Foil Fusing process allows foil to be applied selectively to certain image areas without affecting the surrounding toner image areas.

The solution to selectively fusing foil is a simple makeready procedure and the use of bottom makeready material. As already stated, fusing foil to toner requires heat and pressure. Heat is provided through the thermal transfer plate and the platen press generates pressure. Bottom makeready material provides the means to localize where pressure is applied to the paper and foil against the thermal transfer plate. By cutting and applying the self-adhesive bottom makeready material to align only with the toner image areas where foil is to be fused, pressure can be applied selectively to these image areas.

Preparing a HSFF makeready is very easy and usually can be completed in a few minutes. It is recommended that HSFF makeready be mounted on acetate, as this allows a makeready to be used over and over again. Pre-configured acetate makeready sheets can be mounted on the press with masking tape in less than a minute.

Under certain circumstances, HSFF foil may adhere to toner outside the areas defined by the bottom makeready material. This can be caused by various factors including paper flexing during the HSFF impression cycle or if toner image areas are very close to where foil is being fused. Applying thermal insulating material to the thermal transfer plate creates a thermal barrier that eliminates foil fusing in these areas. Thermal insulating material is a thin, self-adhesive, high-temperature insulation that can be cut with scissors and applied to the thermal transfer plate to stop foil from fusing to toner outside the areas defined by the high speed foil fusing makeready. In many applications, such as greeting card personalization, thermal insulating material is not needed.

ThermoEmbossing
While HSFF is normally used to produce a flat foil image, a process called ThermoEmbossing has been developed by Therm-O-Type that allows a foil embossed image to be created without dies. At this point, the Kodak NexPress is the only printer that has been able to apply the toner lay-down required to produce ThermoEmbossing.

To create a ThermoEmbossed image, background (flat foil) and foreground (embossed) layers must be created in pre-press. The background layer is designated to print as a 75 to 100 percent black toner image. The foreground layer is designated to print as a rich black (with or without Kodakís Clear Dimensional Dry Ink) toner image. Background and foreground toner is applied to the sheet in a single pass through the NexPress. When foil is fused to the background and foreground toner, the rich black areas appear embossed.

The High Speed Foil Fusing process also can be used to create a spot varnish effect on toner image areas. This process is called ThermoFusing, also known as toner glossing or post fusing. When ThermoFusing toner image areas, a special fusing film is used to keep toner from offsetting to the thermal transfer plate during the fusing process. In addition to glossing the toner image area, ThermoFusing also improves toner adhesion and durability.

Special Considerations
Some gap must always exist between toner image areas when one image area is to be foil fused and the adjacent image area is not. This gap will vary depending on the registration accuracy of the printer applying the toner to the sheet. It is important to understand the capabilities of your laser printer when foil fusing select toner image areas on a sheet.

An air blast foil separation system is recommended for HSFF. Fusing foils do not come in different release formulations. In spite of this fact, solid areas and fine line type can usually be foil fused with excellent quality provided that temperature, impression pressure, foil tension, and air blast controls are adjusted correctly.

While the HSFF process dramatically increases the range of papers that can be foil fused, there are still some paper restrictions, mainly due to incompatible coatings on certain papers. Paper surface finish, which is a huge issue with heated roller fusers, is not an issue when using the HSFF process. In fact, papers with very deep textures can be foil fused with the High Speed Foil Fusing process, provided the laser printer can apply toner within the textured surface.

As with heated roller foil fusing, HSFF is not compatible with all toners. Customers who wish to see if their laser printers are compatible with the HSFF process can send sample sheets to Thermo-O-Type for testing.

Using a foil press that can support multiple foil rolls, it is possible to combine HSFF and ThermoFusing in a single press pass. One application for this capability would be to foil fuse one panel of a greeting card verse insert while ThermoFusing a full color toner graphic on the opposite panel. Another multiple foil roll application includes fusing transparent holographic foil over a full color toner image while fusing one or more metallic colored foils to other toner image areas on the sheet. This is a format that has been demonstrated to produce graduation announcements with three foils fused to different image areas in one press pass.

The utility of the HSFF is normally based on product quantity. It is obvious that the cost of a metal die, and the ability to run faster on an NSF press, would negate the advantages of the HSFF process as quantities increase. However, small quantity orders are currently a strong growth market and this is where the HSFF process excels. Imagine personalizing a thousand invitations, with a different name on each, and then running these through the High Speed Foil Fusing process, at up to 4,000 iph with foil fused to each personalized invitation.

Because HSFF does not use a metal die, any texture in the paper will not be crushed flat by the foil fusing process. As a result, the texture of the paper will show through the foil. This characteristic allows some unique visual effects to be created.

Additional Benefits
High Speed Foil Fusing and ThermoEmbossing processes enhance and encapsulate toner in foil. These processes also provide significant protection to the toner image. Even the ThermoFusing process, which does not deposit a coating over the toner, enhances and improves the durability of the toner during the post fusing process.

As with any other printing process, High Speed Foil Fusing is not a perfect solution for all situations. However, it offers a completely new set of capabilities that have obvious applications in most foil stamping markets. Products ideally suited for the HSFF process include all types of short run foil stamping work, personalization/variable data foil stamping work, small quantity personal/business greeting/thank you cards, graduation invitations for small schools with custom logos, text, and graphics (without needing dies). Additional items include any product printed with toner where the product needs enhancement of image area(s), products printed with toner that need to protect toner image areas from scuff or abrasion damage, small quantity security applications using transparent or metallic security foils, and small quantity security applications using ThermoEmbossing.

All this being said, there are applications that are better suited to the traditional hot stamping process. Some examples include long run foil stamping orders (using a metal die will allow the job to run faster and will not require the sheet through a toner based printer before foil can be applied); products where foil text and/or graphics will be applied over offset printing; and products that require a foil embossed effect beyond the limitations of ThermoEmbossing. Also falling into this category would be products that require multiple colors of foil within tight registration and products printed on papers that are not compatible with the High Speed Foil Fusing process.

For additional information on the HSFF process, makeready material, set-up procedures, fusing foils, and films contact Therm-O-Type at (800) 237-9630 or visit www.thermotype.com. Patent claims have been submitted by Therm-O-Type to the United States Patent Office covering the High Speed Foil Fusing and ThermoEmbossing technologies.