Adding Sparkle To Print

The Foil Experts

Indexing, the real picture

As the term “Foil indexing” is being abused through-out the industry, we thought it would be  useful to put it back in the real world perspective so that the printers can base their decision on something else than salesmen hype and avoid costly mistakes.

As the designer / inventor of all Eagle System Foil Machines, I started at the early age of 15 years old, working for my father’s company building a hot foil puller called Brighten Leaf Pullers which were attached to small automatic die cutting presses and clam shells.
Within a couple of years I realized there was a need for a large format foil solution so I created the first electronic foil indexer called the BOA System in 1977. This new technology was most effective in creating actual foil savings with a resolution in indexing of  +/- 1/8 of an inch.In 1990 I created the Eagle Systems Hot Foil indexer with high resolution +/- .002 thousandths of an inch creating the most extreme results in foil savings.
In 2007 I started developing and created the Eco-Eagle Cold Foil System an in-line foiling solution for offset printing presses.

 

 

The original Indexer


The first electronic foil indexing introduced in late 1977 by Mike King on a Bobst press , was made of dc motors and vacuum clutches driving an index roller. The foil would wrap around the head of the press in the opposite direction of the paper direction and then be slightly pulled by a light nip on a continuous running roller called a take up roller (TK).  This system then and still today allows step and repeat of any combination of sizes.

 

 

 

Sample job

 Click to see an animation of how short and long pulls are combined in the indexing process

In the case of Hot foil stamping as illustrated, the process is INTERMITTENT and the process cycle includes two phases before it repeats:
  • Phase I:   The sheet and Foil are standing still and the press stamps
  • Phase II:  The press opens and the foil can be advanced or “pulled”. At the same time the sheet can move.
Some math

Assuming the press runs at 5000sph

  • One cycle equals 0.72 seconds
  • Time available to move the foil (Phase II): 0.55 seconds
  • Assuming an even spread between speedup and slow down, this implies an acceleration on the foil of:
    a=2*d/t2 = 2*0.3/(0.275)2 = 7.9 m/s2 =0.8*g

 

In the case of Cold foil,the process is CONTINUOUS and there are no phases:
  • The foil needs to run at the same speed with the sheets
  • It must be perfectly synchronized

Click to see an animation of the Foil movement on Cold Foil

In theory the foil could be stopped between the imprints, but:
  • The Nip between the sheet and Foil needs to be released!
  • The dynamics of the foil drive must satisfy extremely strict conditions
  • The Foil needs to resist these extreme conditions
Some math

Assuming the press runs at 10’000sph

  • One cycle equals 0.36 seconds
  • Time available to stop the foil: 0.14 seconds
  • Assuming an even spread between slow down and speedup , this implies and acceleration on the foil of:
    a=2*d/t2 = 2*0.38/(0.07)2 = 179 m/s2 =18*g

Conclusions about “Indexing” on Cold Foil
  • The stress on foil and mechanical components is more than 20 times higher on a Cold foiler trying to index compared to a Hot foiler
  • Releasing the nip to allow foil stoppage has several implications:
    • Playing with the packing and/or cutting the blanket means extra time required for setup
    • Blanket becomes specific to a job meaning additional tooling cost
  • Slower Machine speeds
  • Production stops are inevitable due to increased stress on the foil
  • Production waste is dramatically increased
  • Dust generated by the foil drive system will affect printing quality and requires more frequent stops for blanket wash
  • Cannot be done with narrow foil webs
  • Staff frustration
  • Customer dissatisfaction

The choice is yours:

Download article about “Where did Foil Indexing come from?”

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