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Technology Focus

Registered Holograms for Short-Run Work

by Jeff Peterson

November-December, 2007
Often, foil stamping registered holograms on financial documents or other security/decorative applications is thought of as large-format work that is performed several-up on a platen-style foil stamping press. Although this may be true for certain applications, opportunities exist for registered holographic work that can be done one- or two-up on a clamshell, a converted cylinder press, or other small format press.

Registration Systems
Without a quality hologram registration system that accurately reads the registration mark that is placed by each of the holographic images, the job will be set up for disaster even before it starts. Although several different types of registration systems are on the market today, there are a few items to which the press operator should pay close attention.

One of the first things to keep in mind when working on a registered hologram job is to make sure there is accurate foil control. To achieve this, the foil tension must be maintained at a consistent level. Foil tension that is either slack or too tight will result in inconsistent registration. Because a specific method for defining foil tension does not exist, the operator must work with the holographic foil to tighten it to a point where the hologram is registering correctly in place.

Obviously, the key to achieving the proper registration is the fiber-optic eye that reads the registration mark on the holographic foil roll. Several options exist for placing the ‘eye’ in relation to the foil.

One option is to place the optical sensor outside the impression area to protect it from possible heat and crush damage. This system is easy to set up and works well when using good quality foil with all the images evenly spaced. However, if the registration unit does not have the ability to compensate for any spacing differences on the foil, this system will have a registration error, which is unacceptable.

A second option is to mount the fiber-optic eye so the registration mark can be detected just before the stamping die. The advantage of this system is that any spacing errors between the images should not be a problem and the set-up is relatively simple. However, having the sensor in the stamping area can be a hostile environment with the heat and pressure, so placement and accessibility are critical in making sure the sensor continues to work properly through the run and is not damaged.

On a Kluge hologram registration unit, the fiber-optic sensor is mounted directly to the toggle base in line with the edge of the foil. The sensor is connected to the signal pick-up device, also known as the ‘amplifier,’ which then is electronically adjusted until the registration mark can be seen. This innovation allows the digital alignment of hologram foil on the die with registration accuracy of +/- .012". It also is recommended on the Kluge to mount two short pieces of wire soon after the hologram has been stamped on the sheet. The foil is sandwiched by the wire (one above and one below the foil stream) to prevent the foil from curling due to direct heat from the die. Curled foil causes inaccuracy in registration because the mark becomes inconsistently visible to the eye.

Lastly, there are hologram registration systems where the fiber-optic sensor is placed outside the impression area and uses special programming to compensate for any inaccuracies between the holographic images. This system continuously disregards the information from the image just imprinted and inputs the information for the next image entering the stamping area. The downside of this system is the additional set-up time and potential waste. However, once it is set-up correctly, it provides positioning control that is extremely accurate, regardless of any spacing issues between the images.

Therm-O-Type manufactures registration systems that are placed away from the impression area that can be built with or without the special programming for sheets up to 12" x 19" in size. The parameters of the job will determine the best method to use. Therm-O-Type systems also allow regular foils to be run with a programmable draw using a single draw repeat or with a variable draw pattern repeat – all through its proprietary holo/foil draw system software.

If a retrofit registration system is being attached to an existing clamshell or cylinder press, it must be kept in mind that the press itself limits the performance of the system. A newer press in good condition should run registered holograms within a tight acceptable tolerance. However, trying to retrofit a hologram registration unit to a very old press could create registration problems impossible to fix.

Registration Marks
As stated above, the eye that reads the registration mark is the key to the successful registration of a hologram. As this is true, the registration mark that accompanies each image must work with the fiber-optic eye and be easily read.

The most common and best type of registration mark is a diffraction grating that is embossed into the holographic foil at the same time as the image. In most cases, the larger the diffraction mark, the greater the likelihood that the image will be read properly. It is recommended that the registration mark be at least ?" square.

When a diffraction grating is illuminated straight on, light is produced at several different angles, depending on the fineness of the grating. A direct reflection also exists, so the diffraction grating should be produced at a 45-degree angle with the fiber-optic eye angled at the same 45 degrees. This will allow the laser output of the eye to bounce back directly to it as the registration mark passes by. When plain foil passes the eye, the beam simply bounces at a different angle and does not register. It is imperative that the fiber-optic eye is accurately angled at 45 degrees; otherwise, registration that is precise and consistent will not occur.

Other techniques have been used to produce marks, such as diffuse marks, which are common in the industry. These types of marks scatter incoming light in all directions, and while it is possible to detect these, many times the detector must be adjusted during the process. In contrast, the diffraction marks, in conjunction with the proper fiber-optic eye, produce a strong signal where adjustments rarely are required.

Obviously, for any given project, the geometric relationship between the image and its associated mark must be constant. In most cases, the mark is centered on the image and should be placed alongside the image, not between each image. Most registration systems have a ‘windowing’ feature, which allows them to ignore false signals like an embossed seam between the images. While this feature makes it possible in some circumstances to use a mark between images, set-up is difficult and waste is likely to increase. So, placing the mark alongside the image is a much safer practice.

Holographic Foils/Images
Working with holographic foil, even continuous pattern foils, entails special precautions for set-up and running the job on press. The nature of how holographic foils are manufactured creates a tighter release in many cases, which must be considered when running the job. Combine these ‘on press’ challenges with a specific registered hologram, and it creates a foil stamping job that must be analyzed carefully to ensure a quality stamp registered in the precise position.

Today, holographic images can be created through a dot matrix process or other computerized layers, which is much less costly to produce than several years ago when the holographic images were all created through a laser recording process. This was very time-consuming and expensive. With new computerized hologram mastering processes, a very unique, customized holographic image can be produced for a fraction of what it would have cost just 10 to 15 years ago. This opens up the possibilities for smaller businesses and smaller security applications to utilize a registered holographic image at a reasonable cost.

One of the most important items to keep in mind when working with a registered hologram is to check that the image is oriented correctly on the roll of foil. The hologram can dispense off the roll of foil, either head, foot, left side, or right side first. This is all based on how the printed sheet will feed into the foil stamping press and must be analyzed carefully before the foil is manufactured.

In addition, a tolerance should be acknowledged in order to compensate for the slight drift that a registered hologram will encounter on press. Although it may be a very small amount, the hologram design should reflect this. For instance, do not have the main subject or focus of the image too close to the edge of the foil stamping die. Similarly, do not try to stamp a circular shape around a circular subject that is too close to the edge of the die. This can show a difference from stamp to stamp, even if the tolerances are very tight.

Registered holograms are used today on everything from packaging and direct mail to trading cards and security applications. And although many of these types of applications are set-up for larger-sized runs, opportunities exist today to use registered holograms to secure or enhance all types of products – large and small.

InsideFinishing would like to thank Sam Beamond and Mutt Wilson of Brandtjen & Kluge (800-826-7320), Chris Van Pelt of Therm-O-Type (800-237-9630), and Vince Sementilli of Crown Holo-Grafx (973-684-2600) for their assistance and input with this article.