I started working for my father’s company at the age of 15, building Brighten Leaf hot foil pullers that were attached to small, automatic die-cutting presses and clamshells. Within a couple of years, I realised there was a need for a large-format foiling solution, so I created the first electronic foil indexer, called the BOA system. This technology was highly-effective in creating foil savings with an indexing resolution of approximately 3mm.
In 1990, I created the Eagle Systems hot foil indexer with a high resolution of 0.05mm, which delivered significant foil savings. Then in 2007, I started developing the Eco-Eagle cold foil system, an inline foiling solution for offset presses.
Mechanical indexing
In the early years of hot foil stamping, the machines were called foil pullers (figure 1). The foil was on a supply roll on one end of the stamping area and on the other end was a mechanical device with rollers that the foil wrapped around to be pulled through the machine.
Although it worked, it applied a lot of stress to the carrier and was not controllable. This meant that foil pulls weren’t accurate and that the foil tended to stick to the substrate. If supply was too tight, then the foil would be damaged on the carrier. Another challenge was the slow speeds.
The choice at that time was one size pull every cycle. Later, newer mechanical foil pullers offered a step and repeat option. We learnt at an early stage that the stress on the hot foil carrier wasn’t conducive to a good-quality stamped product.
Electronic indexing
In late 1977, I introduced the first electronic foil indexing machine on a Bobst press. This system was made with DC motors, with vacuum clutches driving an index roller (figure 2), which had the supply millimetres away from the roller. The foil would then wrap around the head of the press in the opposite direction of the paper and be slightly pulled by a light nip on a continuous running roller called a take-up roller. This system allowed step and repeat of any combination of sizes, for example, 50.8mm ten times and then a 508mm clear pull.
Although the sky was the limit in foil saving flexibility, speed was held back by several factors, including the heat transfer process, substrate bonding, size area allowed and mechanical process registration limitations. Despite this, we have almost reached hot foil process speed limits.
Figures 1 and 2 show nip impression equalling approximately 60°, depending on the machine. This area enables time to “make the move” with foil. The mechanical restraint is 0.7 seconds to make the foil move at 3 600 sheets/hour (sph). While it seems fast
at less than a second, it is quite a bit of time to make this move. When the speed doubles to 7 200sph, the same move occurs at 0.35 seconds – tight, but still doable.
However, the press is off-impression a greater percentage of the time, and reinforces the fact that indexing is a hot foil term, which originated over 30 years ago.
Cold foil: blanket gap savings
Cold foil indexing should rather be referred to as blanket gap savings. After extreme testing and cold foil blanket gap trials, it became apparent that the time allowed by impression on or via nip doesn’t allow for a viable solution to save the foil waste in the gap. The cold foil diagram (figure 3) shows the time to make the move on cold foil is an extremely small window of opportunity. The time off-nip is 0.3 seconds at 3 600sph, 0.15 seconds at 7 200sph and 0.075 seconds at 10 800sph.
‘Average cold foil production speeds today are around 11 000sph. Cold foil can easily be run at higher speeds. The hold back on most jobs is the everyday variables not related to cold foil.
Unlike hot foil, which runs intermittently, cold foil runs continuously on a sheetfed offset press. What I described above as the “time to make the move” is the time available to stop the foil movement, which is otherwise running continuously with the press. This time doesn’t allow a stop without stretching the carrier, which disturbs the binding of the aluminium foil.
Imagine a piece of plastic wrap coated with a layer of paint. If you stretch it after it’s fully dry, you’ll see through the plastic wrap and the paint. You’ll also see the separation of the paint you are trying to transfer. Another disadvantage is that this damaging effect will allow the possibility of saving foil on the gap only at slow speeds. The foil carrier can be moved at these speeds mechanically, but the results will be inferior due to extreme pin-holing created by stretching the sheet lead edge. Piling and swirling will also occur.
The example below shows that savings are achievable in narrow-web jobs running at high speeds.
The damaging effects to the finishing process are increased production stops, the annoyance of foil dust, inferior products, production waste and longer make-ready times.
Touching the live side of the foil also results in damage because the dancers continuously bend the foil back and forth.
In conclusion, the most cost-effective way of saving money with hot or cold foil is optimising layouts that enable the highest production speeds and product quality.
Ed’s note:
Eagle Systems is represented in South Africa by PrintEquip.
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