Background: Why are holograms applied to credit cards?
Considering the cost of credit cards, this is a very good question
to ask. The simple answer is that for well over a decade, since the
mid 1980's, holograms have provided a very successful deterrence to
the counterfeiting of plastic credit and debit cards worldwide. It had
often been said that holography was a solution looking for a problem.
With the protection of the credit card, the hologram found a problem
for which it was an ideal solution. Now the hologram forms an integral
part of the many features used by the payment industry to protect their
cards.
The main security benefits conferred by the hologram are:
- Visible recognition features
- Difficulty of limitation
- Technology of production limited in availability
- Adaptable to swift change
- Capable of development
- Easy and cost effective to apply to the card
Holography may be defined as "a method of making three-dimensional
photographs without a camera, by splitting a laser beam into two beams
and recording on a photographic plate the minute interference patterns
made by one beam going from the laser to the object to the plate."1
At a recent conference2 Ron Morris of the US Secret Service, presented
a paper that reviewed the history of holographic counterfeiting efforts.
This paper and the accompanying exhibit of the Secret Service's "Black
Museum" of counterfeit credit cards revealed that while many attempts
had been made to imitate both the Visa "Dove" and Master Card
"MC" and "Globe" holograms, none had been successful
in producing a completely faithful copy of the genuine hologram.
The attempts to simulate the hologram have used a variety of techniques
that have included screen printed inks, silver paint, silver foils,
hot stamp holographic pattern foils and even substitute commercial non-security
holograms. In the main, these have all been directed at attempting to
create a passable counterfeit that will defeat what Weiandt3 defines
as a "first line of inspection" where the card is checked
without equipment. This of course is the situation where the transaction
takes place at point of sale where there is no magnetic stripe reader
available.
The program of using holograms on credit cards is due, in no small
part, to the efforts of American Banknote Holographics, Inc. They were
able to convince Master Card and Visa of the viability of the concept
of using the hologram as a deterrent to counterfeiting of the card;
and also of the viability of bringing together the various elements
necessary to make that a practical proposition as an industrial process.
Foil manufacturers have also played their part in this process by continuously
developing hot stamp foils of greater durability and consistency, as
have equipment manufacturers by developing ever more sophisticated machinery
to enable improved application speeds and higher quality control.
Attempts at counterfeiting the hologram have become more sophisticated
with time. In response, the MasterCard hologram has been varied in the
composition of the image design of both the "MC" letters and
the "globes" as well as the overall size. The Visa "Dove"
image has also been changed in terms of size, position, wing span, etc.
Furthermore, one of the original benefits of using the hologram, namely
that their limited availability, may become compromised as the technology
for their recording and reproduction by embossing becomes more widespread
through technology transfers and sales of equipment in the open market.
It is therefore fortunate that the hologram forms part of the wider
group of diffractive elements known as Optical Variable Devices (OVD's).
This group includes many technically advanced security devices such
as Kinegrams, Pixelgrams, Exelgrams, Fourier Transform structures, etc.,
some of which are already finding application in banknote printing.
All of these devices can be produced in the form of a hot stamp foil
and may be combined with other techniques such as demetallization and
high refractive index coatings to enhance security. Higher levels of
integrated security and machine readability can also be provided by
combining a diffractive structure with the magnetic tape on the credit
card such as with Holomagnetics and Holonetics4.
Holographic and OVD image formats
The first and now the most prolific use of holograms has been with
the MasterCard and Visa payment programs, although other payment systems
such as Europay, Novus and Diners Club are also now using holograms.
As a result, a wider variety of new designs are beginning to appear,
particularly with many of the cards issued in Europe.
The holographic image
All holograms used to date on credit cards have been a form of rainbow
transmission hologram, commonly known as the Benton hologram, named
after Stephen Benton who invented this technique in 1968 while working
at Polaroid. These holograms are characterized by giving the impression
of depth parallax when tilted in one plane (normally horizontal) and
giving changing color when tilted in a plane at right angles (normally
vertical). There are three main image formats, each of which requires
a different type of image input data.
3D Holograms - are recorded from actual three-dimensional objects.
The Visa "Dove" is the best known example of this type. There
is a 1:1 ratio between the image size and the original object size,
so in the case of a small hologram for a credit card, the detailing
on the model has to be to a very high standard. The object has to be
physically stable and inanimate, and this is often a limiting factor
in producing this type of image.
2D/3D Holograms - are recorded from two-dimensional flat artwork.
The artwork is separated into layers to give various depth planes that
show parallax in the final image. The MasterCard "MC" globe
images are representative of this type of hologram. The 2D/3D is the
most widespread form of image being used on other cards. This is almost
certainly because of the greater flexibility of dealing with artwork
with small format images and the fact that it can yield sharp, intricate
and brightly colored images.
Multiplex stereograms - the image data for this type of hologram
is derived from a series of several hundred sequential frames of cine
film or computer generated animation graphics. A good example of this
type of image is the rendition of an actor's face in the so-called "Shakespeare"
hologram used on certain cards in the UK. The technique is very versatile
and ahs the great advantage of avoiding the limitations of 1:1 size
requirement and animate stability, when recording real objects such
as the human face. This is an important benefit from a security standpoint.
The fraudulent imitation of artwork is far easier than that of three-dimensional
objects. The imitation of a particular human facial feature, particularly
if the visage is well known, is more difficult and very easily recognized
- therefore the fraud is easier to detect.
Optical Variable Devices (OVD's and DOVD's) - as noted above,
the hologram is part of a family of optical devices that may be collectively
grouped as Optical Variable Devices. More correctly, they are in the
category defined as deriving their particular optical effects from the
diffractive mature of their structure (hence Diffractive Optical Variable
Devices, DOVD's). These structures are composed of gratings of one form
or another and in most cases these structures can be converted into
very small relief grooves (order of 1 µm [microns] line spacing)
in a surface. This property opens the way for economically reproducing
them by the surface embossing process.
This group of structures is broad and offers an open-ended spectrum
of possibilities for creating DOVD's of enhanced security, including
the potential for machine readability. Some of these advanced technology
DOVD's, such as Kinegrams, Pixelgrams and Exelgrams, are now beginning
to be utilized in banknote printing and may well find application to
financial payment cards in the future. Although a full technical description
of these devices is beyond the scope of this article, the following
points are of note:
Kinegram is a high security DOVD produced via proprietary process
developed by Landis & Gyr in Switzerland and now finding considerable
use on a number of European currencies. Whereas the holographic image
is a result of diffraction from a single order, the Kinegram is able
to create visual effects using light diffracted into many orders. This
allows the Kinegram to produce very bright, iridescent colored and spatially
concentrated visual, graphical effects that can be encoded with strong
kinematic movement. These strong kinematic effects differentiate them
from holograms and are the basis of the Kinegram's security functionality.
Machine readability and covert features may also be included.
Pixelgram & Exelgram are high security DOVD's developed
by the Commonwealth Scientific and Industrial Research Organization
(CSIRO) in Australia and licensed to Leonhard Kurz GmbH. These DOVD's
differ entirely in the manner in which they are generated. Unlike the
hologram, these structures are not generated by optical interference
methods but are directly written groove structures produced by electron
beam lithography under the control of extremely sophisticated software.
They are not continuous surface structures but composed of very small
pixel cells (order of 60 µm square) in which high resolution grating
structures are contained. Besides a bewildering array of graphical and
kinematic effects, these structures can render photographic images that
will invert to a negative image when tilted. Besides a strong recognition
feature, this effect is very difficult to imitate.
Holomagnetics - This technology represents a second-generation
approach to the security of a financial transaction card and offers
an extremely high level of security confidence by linking the functionality
of the magnetic stripe with that of an optically readable stripe. It
is apparent that the information encoded on the magnetic stripe of a
credit card can be copied and duplicated onto another card. If, however,
the magnetic information is coupled to a cipher key encoded in a DOVD
machine readable stripe also included on the card; and if that optical
cipher is also made unique to that card, then the practicality of fraudulent
duplication of the data on the card becomes virtually impossible. Whereas
this system has found several commercially successful applications with
access control and identity cards, it remains unused in the financial
transaction card field. This, no doubt, is in small measure due to the
fact that magnetic reader modules would need to be refitted with associated
optical reader modules.
The Hologram or OVD substrate
Mechanical replication of holograms
To date, all holograms applied onto ISO specification credit cards
are manufactured using a process of embossing. In this process, the
holographic or DOVD image is recorded by means of either optical interference
or electron lithography into a photoresist plate. This plate is then
processed to reveal the recorded image in the form of a surface relief
structure, having extremely fine detail. The next step is to duplicate
this surface in a durable material such as nickel. At this or the preceding
step, the image is recombined with others to give the desired layout
required in the final foil product. A registration mark is also added
at this point. The nickel surface is now replicated several times to
give a thin metal shim that can be used on a rotary embossing machine.
This machine, by the application of the heat and pressure, is used to
emboss part-finished hot stamp foil as a mass production process. During
the embossing process, the manufacturer has to take great care that
the following factors are addressed:
- The surface relief profile and modulation of the structure of the
original hologram is accurately reproduced in the hot stamp foil.
- The holographic image is not distorted.
- Distortions of the foil are minimized or compensated for to maintain
accurate layout of the images and registration marks on the foil.
- The hot stamping properties of the foil are not deleteriously affected
during the embossing process.
- Embossing consistency is maintained with a given production batch
and between batches of foil.
- Extraneous inclusions such as scratches, pinholes, scuffs, dust,
stains, etc. are eliminated.
- Audited control of all production and waste is implemented.
Composition of holographic hot stamp foils
Holographic hot stamp foils designed for credit card application are
really modified versions of standard hot stamp foils used in the graphics
industry. Special attention has to be paid to the fact that the foil
must survive the heat and pressure of the holographic embossing process
without delaminating. The foil must also be capable of accommodating
the distortions of the card substrate during the macro-embossing of
the account number during the personalization process. The stamped foil
must also exhibit good abrasion resistance and have good adherence to
the PVC substrate of the card. The prevention of gas or vapor entrapment
during stamping is also an important factor if blistering is to be avoided
and good adhesion to the relatively non-porous surface of the card is
to be achieved.
A typical composition of the stamping foil would be as follows. A polyester
carrier of between 12 - 25 µm in thickness, depending upon application,
is coated with a release layer that has a melting point within a narrow
predetermined range. A series of lacquer layers are then coated which
impart the abrasion resistance to the finished foil and also provide
a medium into which the relief structure of the hologram can be embossed
by the action of the heat and pressure. The relief layer is then coated
with a thin layer of reflective metal, which enhances the brightness
of the hologram significantly. This is normally accomplished by the
vacuum evaporation of aluminum, although metals such as chromium or
gold can be used for special purposes. The metal layer is then coated
with a "tie" coat that serves to promote adhesion to the metal
surface and also protects it from any chemical action of the adhesive
coating. The final coating is a heat activated adhesive size coat.
Mechanism of hot stamping process
In use, the foil is acted upon by the heat and pressure applied by
the die and counter of the stamping machine. This causes the release
layer to melt and release the attached lacquer coating. At the same
time, the adhesive layer is activated and acts against the PVC surface.
The lacquer layers then fracture in regions defined by the outline of
the stamping die, and the lacquer layer containing the hologram is transferred
from the web of the foil carrier onto the plastic credit card surface.
An important design criteria for the foil manufacturer will be the design
of a foil that is capable of transferring the relatively large area
of the hologram, yet maintaining a well defined cutting of the die edges
to give a clean stamping with no flaking at the outline of the hologram.
It is interesting to note, that according to Gil Colgate5 of American
Banknote Holographics, in the early days of hologram application to
credit cards, the rejection rate for the foils was a high as 30 - 40
percent.
Enhanced security - transparent holographic foils
These films are an extension of the established technology of embossed
security holograms. Whilst not currently employed on financial transaction
cards, they have found extensive applications with identity cards, driving
license cards and banknotes. In the general scale of security print
features6, this technology has taken the existing high order of the
fully metallized DOVD to the next level. Unlike the fully metallized
hologram or DOVD, they do not obliterate the underlying detail of the
card to which they are attached. They are therefore eminently suited
to protecting either selected areas or the entire area of a document
or plastic card. Their visual transparency ensures that many traditional
visually orientated security measures can be retained and enhanced.
Most importantly, as protection against copying, they combine the specular,
ordered optical effects of the diffractive DOVD with the optically diffuse
effects of the non-diffractive print of the underlying substrate or
document.
There are currently two main types of transparent embossed Diffractive/Holographic
relief structure:
Selectively Demetallized films - These are based on the selective
removal of aluminum from a pre-metallized film. For transparent holograms,
foil is embossed and metallized in the normal way. The process then
essentially consists of printing a chemically resistant lacquer onto
the embossed and pre-metallized surface in a pre-determined pattern
and then chemically dissolving the unprotected aluminum with an alkali
solution. Developments in the past few years have allowed a dramatic
increase in the achievable resolution of the demetallized patterns giving
features beyond the resolution of the unaided eye and can form the basis
of a semi-transparent film. A good example of this can be seen in the
California driver's license. The method can further be extended and
high-resolution halftone or semi-half tone diffractive/metallic semi-transparent
images can be produced that cannot otherwise be achieved by traditional
printing or foiling methods.
High Refractive Index Coated films - A truly transparent hologram
can be achieved by substituting a high refractive index coating of about
5µm thickness for the traditional aluminum coating normally applied
to an embossed hologram by vacuum evaporation. Light to reconstruct
the hologram is not provided by reflections with aluminum coatings but
relies on the property of refraction of light through a transparent
media. This property is governed by Snell's Law and determines the amount
of light transmitted or reflected when light traverses an interface
between transparent materials of differing refractive index. Several
high refractive index compounds are available, most all of which are
either metal oxides or refractive inorganic compounds such as Titanium
dioxide or Zinc sulfide. These coatings tend to be considerably more
expensive to produce compared to evaporated aluminum coatings.
Practical considerations for hologram and DOVD
The credit card represents one of the most ideal surfaces to apply
a hologram or other DOVD. The smooth surface of the card does not distort
the micro groove relief structure of the embossed foil as is often the
case when stamping onto an uncoated paper stock. Furthermore the stiff
nature of the card allows the image to be replayed without distortion
and clearly allows it to be seen in most viewing situations.
The practical considerations of hologram or DOVD hot stamp foil application
onto plastic credit cards is essentially that of "good housekeeping
practice" and common sense. Much is owed to the standard practices
of hot stamping in the graphic arts industry. Various parameters should
be considered in developing good working practices where the aim is
to enhance quality whilst reducing waste:
Foil type - As already discussed, the hot stamp foils designed
for application to PVC credit cards differ significantly from those
used in the graphic arts industry. Graphic foils make a poor substitute
in terms of abrasion resistance and adhesion and should not be considered
when using diffractive foils for credit card decoration.
Stamping Die - The stamping die is a critical element in the
stamping process. Great care should be exercised in maintaining the
die free of surface damage. The surface should be kept clean and polished
occasionally to remove stains, corrosion, finger marks, etc. The choice
of material is important too. Best results are produced with copper
for flat stamping and with steel for dies with semi-rotary machines
such as the Kurz MM3000. Cheaper dies made from zinc, zinc alloy or
magnesium should be avoided as these are only suitable for very short
production runs.
Die Temperature - This should accurately be maintained at the
temperature recommended by the manufacturer. Too high a temperature
will cause dulling and blistering, whereas too low a temperature will
result in incomplete transfer and poor adhesion. It is often good practice
to check the temperature directly on the die (taking care not to scratch
the surface) with a calibrated hand-held thermocouple. This often reveals
discrepancies with indicated temperatures on the machine control console.
Stripping Action - Embossed holographic hot stamp foils are
generally tighter release than a typical graphics foil. Careful adjustment
of the stripping plate mechanism, where fitted, can often improve both
stamped foil quality and allow increased stamping speed. Changing the
direction of the stripping plate action should be considered as this
may improve matters for a particular foil type. The use of a stripping
plate greatly assists in the control of the release action of the foil
carrier.
Static Control - Most stamping machines for credit cards separate
the cards from an input stack. Plastic cards are very good electrical
insulators, and the act of separating two such surfaces can generate
a considerable static electrical charge on the surfaces, especially
in a dry atmosphere. This charge can cause strong attraction of dust,
hairs and other airborne debris onto the card that is difficult to remove.
Some form of static control or ionization equipment is therefore recommended
between the input stack and the stamping head to avoid this problem.
Oil - Oil mist, especially from airlines supplying the ionization
unit, should be avoided by the employment of suitable filter traps in
the airlines. Oil contamination can cause a host of problems from lack
of adhesion of the foil to dulling and staining in the stamped hologram.
Equipment considerations
The functioning mode of application equipment falls into three main
categories:
- Flat bed, vertical reciprocating action
- Semi rotary, reciprocating action
- Rotary action
A key factor in the correction placement of the hologram on the card
is the accurate detection of the registration mark associated with the
hologram on the foil web and the control of the foil feed. A variety
of excellent registration units have been developed that use either
small Helium-Neon lasers, photodiodes, fiber optics, laser diodes. Sophisticated
foil feed mechanisms have also been developed which provide two-speed
movement. The foil is advanced at high speed initially till the registration
mark is detected and then de-accelerated as the correct foil position
is approached. These mechanisms can also be coupled with the action
of sliding "stripping plates" to allow "delayed"
release of the polyester carrier from the stamped foil to provide superior
stamping results and improved adhesion.
Flat bed, reciprocating action - In this mode of action, a flat
die is brought vertically into contact with the foil and substrate by
the action of either: a mechanical toggle, cam or hydraulic ram. This
was the type of equipment originally used for the application of holograms
and signature panel foils to plastic cards. These stamping machines
were really modified versions of small-scale equipment used in the graphic
decorating market. It is the type of machine that has been most widely
used to date in the USA. Their main advantage, besides availability,
has been the relative simplicity of design, construction and operation.
Several drawbacks to this design are however apparent and require consideration.
The application of the flat die to the flat surface requires careful
make-ready preparation and maintenance to provide uniform foil application.
The method requires considerable overall applied force to provide sufficient
pressure for correct foil transfer. This, in turn can cause distortion
of the card and in worse case, an impression on the reverse side of
the card. Air entrapment can also be a problem and the doming of dies
to alleviate this can also lead to distortions of the card. For these
reasons, this mode of operation is generally unsuitable to large area
transfer, particularly onto the non-porous plastic surface of a finished
credit card.
Semi rotary, reciprocating action - This mode of operation is
a more recent development, designed to overcome many of the problems
associated with flat die application. The mechanical design is considerably
more complex and is based on a rocking die action combined with a form
of planetary lift and reset action. This mode of stamping necessitates
the use of an accurately curved die. The stamping action is essentially
one of line contact with a roll. As such, this allows for very low applied
stamping pressures and a consequent absence of visible print contouring
on the back of the card. Air entrapment is avoided as are some of the
problems of make-ready. These properties taken together allow for large
area stamping of virtually the whole of the surface of the card if required.
Rotary action - This method uses a roller nip and continuous
movement of substrate and foil. It is commonly used for the application
of magnetic and hot stamp signature panel foils but is not common for
applying registered holograms. Continuous pattern holographic foils
and holomagnetic foils can be applied either to the PVC overlay prior
to collation and lamination with a multi-track tapeplayer or to the
finished card with a roll-on hot stamping machine.
In one particular area - the application of full-face holograms to
pre-paid telephone cards for the Japanese market - this mode of application
has found considerable use, and a machine, the Kurz MCC-4, was developed
specifically for this purpose. Here the low card distortion and lack
of air entrapment were vital considerations. To ensure correct placement
of the hologram in this mode, the foil is made to continuously move
over the application roller. Upon detection of the hologram registration
mark, a card is moved forward on a belt to contact the foil at point
of closure of the roll nip. The card and foil move through the roll
nip with zero relative movement to each other. A delayed polyester carrier
stripping action is then employed.
On-line video inspection for quality control of hologram stamping
Monitoring and maintaining a defined high quality standard are essential
in today's card manufacturing business. Video inspection systems are
a recent development and have become available from several manufacturers.
This allows for varying degrees of automatic quality control of the
application of registered holograms (and signature panel).
These systems will verify the hologram stamped position spatially,
its dimensions and quality of application. The units will also verify
the position of the image within the stamped area to check registration,
as well as checking the diffracted image quality. Deleterious cosmetic
defects, such as scratches, dust marks, hairs, etc. can also be detected.
A particular system inspects in real time 786,000 individual pixels
in the holographic image in about 600 microseconds. The detected image
is then compared with a stored image and comparisons made with respect
to pre-set acceptance limits. The system also controls a mechanism to
physically remove rejected cards into a separate reject card magazine.
Conclusions
The hologram has been used effectively as a deterrent against credit
card counterfeiting and fraud for over a decade. During this period,
the increasing use of holograms on credit cards has been accompanied
by a continual improvement in foil technology and application equipment.
Recent developments of video inspection systems allow for completely
automatic quality control of the hologram application process. The hologram
is part of the larger group of elements known as Diffractive Optical
Variable Devices (DOVD's). As counterfeiting becomes more sophisticated,
DOVD's could well offer an opened-ended approach for continuing the
security enhancement of the financial transaction card.
References
1 Webster's New World Dictionary, 3rd College Edition, pp. 644, 1991.
2 Morris R., Paper 14, 8th HoloPack HoloPrint International Conf.,
Orlando, Nov. 1998.
3 Weilandt R.T, "The Evaluation of Document Fraud Resistance"
in Optical Document Security, van Renesse R.L. ed, Artech House, Inc.,
1994.
4 Holomagnetic® is a technology that combines magnetic and optical
data storage and is a patented joint development of American Banknote
Holographics. Inc. and Leonard Kurz GmbH.
5 Colgate G., "Document Protection by Holograms" pp. 151,
in Optical Document Security, van Renesse R.L. ed, Artech House, Inc.,
1994
6 van Renesse R., "Ordering the Order - A survey of Optical Security
Features," Paper #2406-33, SPIE Holography IX (1995).