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Technology Focus

Tackling Multiple Pass Registration

by Jim Kingsby

August-September, 2003
Without a doubt, complex production jobs such as stamping multiple foil passes followed by registered embossing require exceptional care in order to achieve perfect registration. And while they do pose additional challenges for the operator, they can be processed with confidence and success. Through good communication, pre-planning, and a quality approach from all areas of the operation, projects of this nature do not have to interrupt the job flow in your shop.

The tips presented in this article are not meant to be the final word on how to tackle multiple foil passes with registered embossing but merely, are offered as practical solutions and guidelines. The following production techniques will cover operations for the clam shell type press. These solutions, which represent proven techniques used by converters worldwide, can stimulate the creative thinking process and ultimately, lead to a quality product and customer satisfaction.

The Clam Shell
For fine quality foil stamping and embossing, the very best option would be to run the project on three machines. The obvious conclusion is that registration and image alignment would not be a problem. However, machine breakdowns, maintenance problems, or simply a very full production schedule often will leave only one machine for the project. It is under this circumstance that we proceed.

Material Selection
Stamping board selection is critical for quality reasons. For instance, if a soft board is used on the first foil pass, you will create a difficult surface to stamp for the second and third foil runs - not impossible, but troublesome. When a soft board is used, you can observe the foil image and it will show excessive sub-surface impression. With this intaglio look and feel, you will notice on the second and third foil runs that the image could have uneven foil breaklines around the edges. This will distort sharpness of the image as you lay down the different foil colors - even if the foil products barely touch. This is one area where problems can occur. For best results, use a hard stamping board such as an epoxy glass board.

Machines
In the absence of two full-sized machines to run at the same time, a few different options exist. Many shops have a 10 x 15 hand-fed machine that is seldom used for anything. Do you have one? If so, set-up your embossing die and counter here. It will not be running continuously, so do not be alarmed. Once set-up, you could leave it set and during the run, check for proper position and confirm position for the foil as you set-up each color. This can be a great guide for foil alignment. But what if there is no second machine?

Film Positive/Negative
Without a second machine to register the foil runs to each other, a film positive/negative will be crucial to your success. A film positive can show alignment of each color of foil and tie them together for the final embossing run. With all the various types of materials and machinery now available, it is important to discuss some techniques that can help register all elements of this project perfectly.

Registration
Proceed with a good spot makeready and place it under the steel stamping plate. Turn the flywheel until the feed arm is at the position of your band blocks or gauge pins (if you prefer these). Mark your sheet and position it in-line with a dummy foot or a feed sucker. Position the sheet to feed so that the side guide will push only the minimum distance 1/32. The shorter push distance, the better the quality.

Figure #1 provides several aids to registration of the press sheet including guide wedgie (side guide), guide finger (band block), and tongue finger.

  • Guide Wedgie. This is simply a small dart cut in front of the side guide to give maximum registration. Construct it by placing a sheet of 80# cover under the side guide. Tape it in position with the tape following the sheet feed direction. This dart or wedgie will prevent your sheet from sliding under the guide during the impression stroke.
  • Guide Finger. The finger is an aid to hold the sheet in an exact position on the band block or gauge pin. It will prevent lighter weight papers from buckling when the side guide pushes it. The sheet will not be able to pass over the top of the band block or gauge pin. For construction, simply cut a strip of gray board 1/8 - 1/4 wide and 3- 4 long. Tape it next to the band block or gauge pin.
  • Tongue Finger. This mechanism, when constructed properly, will pull and hold the sheet snugly against the band block or gauge pin. It should pull the sheet downward and should be totally off the sheet during the impression stroke. Construct it by selecting the tongue of proper length. Cut a strip of gray board exactly as we did for the guide finger. Approximately 1/8-1/4 wide and 4 long. Figure #2 shows a magnified side view of the correct placement. Note: the finger portion of this mechanism will be slipped into the slot that you cut. Adjust tension on the tongue to allow it to freely slide on and off the sheet while gently guiding the sheet to the same spot on the band block during the entire sheet run.

In the end, complex jobs requiring multiple foil passes and registered embossing can be produced successfully, if you take your time and utilize the correct materials and makeready from the start. Know your press its capabilities and limitations and utilize the chart above to troubleshoot any problems that might arise while running a job. If you are faced with a challenge such as the one discussed in this article, hopefully you will find the above information useful. Remember, through good communication, pre-planning, and a quality approach from all areas of operation, projects such as these can be processed with confidence and success.

General Troubleshooting During a Run

Observation

Possible Causes

Possible Solutions

The image is moving up or down.

 

 

 

 

Tongue tension too tight.

Sheet release valve improperly set.

Sheet is bouncing on band block.

Sheet sliding under band block.

Machine running too fast.

Adjust tension or tongue.

Adjust release valve.

Construct sheet wedgie or finger.

Construct a ramp in front of the band block.

Slow machine.

The image is moving left to right.

Tongue tension too tight.

Sheet feeding under/over side guide.

Too far away from the side guide.

Side guide push cycle is too long.

Adjust tension on tongue.

Adjust sheet feeding.

Move the sheet away from side guide.

20# sheet buckles.

  

Tongue tension too tight.

Sheet slide under band. 

Adjust tension on tongue.

Construct sheet wedgie for side guide and band block.

Construct finger.

Double feeding.

  

Sheet improperly aired.

Air blower blast improperly set.

Magazine backrest improperly adjusted.

Remove sheet air / jog.

Adjust air blower.

Adjust backrest.

Erratic sheet movement.

 

 

 

 

Static on stamping board (polyurethane).

Sheet rubbing on metal in feeder (negative change).

Paper on paper.

Low humidity in pressroom.

Coated paper 

Keep pressroom above 40% relative humidity.

Silicone solution spray.

 

Critical foil on foil or foil and embossing registration.

One foil color mis-registers.

Troubleshoot by running sheet through the machine a second time.

Some additional troubleshooting tips include the following:

Use only a tongue of proper length (" on the sheet). If the tongue is too long, mis-registration problems can readily occur.
Never feed the sheet too close to the side guide or the tongue could cause mis-registration when sheet is pushed too soon.
Spot makeready is most effective under the stamping plate.

Jim Kingsby is a long-time consultant to the foil stamping and embossing industry, whose expertise in this area has taken him to over 20 countries. Jim can be reached at Jim_Kingsby@yahoo.com.