It is well known that Diffractive Optically Variable Image Devices (DOVIDs) can be copied, duplicated or simulated by the counterfeiters. Some customers consider that such devices are no longer secure and will not use them to protect their product. To avoid counterfeiting, DOVIDs are being made more complicated with the introduction of a large number of simultaneous images, where recognition by customers is strongly compromised. Future trends appear to favor multiple technologies in one device while allowing the consumer to readily identify and remember the device. One approach calls for a combination of the diffractive foil interference found in DOVIDs with thin film interference to create new security devices called SecureShift ChromaGrams. A second approach calls for a combination of diffractive and thin film interference in the form of pigments combined with magnetic fields during the printing process to create another new security device called a "PrintaGramTM".
Each type of enhanced DOVIDs will be discussed in terms of its optical performance, manufacturability, its counterfeit deterrence, and its application.
OVP security pigment, the active ingredient in OVI security ink, is an assembly of high performance microscopic filters. The market acceptance of these filters has led them to become perhaps the most widely distributed interference devices on the planet. Recently, interference devices have been developed that provide the security industry with features beyond proven overt protection. New products are being launched that unite the attributes of optical interference with those of other technologies. One approach integrates thin film interference and diffractive interference to create a host of new security devices. The combined effects are complex and often surprising. The science behind the fusion is explored and the effects demonstrated. Interference pigment technology has also been combined with the science of magnetics to create a new line of OVP security pigments. To facilitate the practical use of such pigments, novel application technology has been developed which allows for the creation of new overt effects. This paper examines pigment designs and describes the physics behind the advanced application technology.
The science of layering security features has long been demonstrated effective in deterring counterfeiting. Now it is possible to provide multiple layers of security within the same device through the integration of proven technologies.
Most people in developed nations are familiar with the hologram. It appears on VISA, Discover and MasterCard credit cards. It is doubtful however, that a great number of people could identify the respective images. The public tends to confirm the presence of such a security device rather than verifying the actual image. As noted by Steve McGrew, "It is very rare that security holograms are subjected to close inspection in actual use" .Thus,there is now the opportunity for the use of poor counterfeits or the substitution of commercial holograms for the genuine security hologram. In an effort to thwart counterfeiters, the hologram industry has resorted to more complex products with multiple images as the device is rotated. These enhanced images provide the observer with a high level of "flash" or aesthetic appeal. Unfortunately, this added complexity does not confer added security because this complex imagery is hard to communicate and recollection of such imagery is difficult, if not impossible, to remember2 Every type of first order diffraction structure, including conventional holograms and grating images, has a major shortcoming even if encapsulated in a rigid plastic. Under an overcast sky or other diffuse illumination all diffraction orders expand and overlap so that the diffraction colors are lost. Under such viewing conditions all such devices look silvery or pastel at best. An additional hurdle that security holograms must overcome, to be truly secure, is the ease of which holograms can be counterfeited. One step and two step optical copying, direct mechanical copying and even re-origination have been extensively discussed over the Internet.3 Ways to counteract all these methods have been discussed but the conclusion was that none of the countermeasures, taken alone, was an effective deterrent. It has been discovered that by combining diffraction effects with thin film interference effects, a security device can be made with new enhanced features that allow for ready identification by the average person while still preserving complex optical patterns. This new security device, using LightGateTM technology, also appears to overcome the cited disadvantages of holographic technology.
An optically variable film (OVF) is designed to exhibit a significant color shift with changing observation angle. This color shift was characterized by multi-angle reflectance measurements using a goniospectrophotometer system that also calculated the angle dependent performance of the optically variable film. The reflectance and color of the optically variable film were predicted by optical thin film modelling and compared to the measured values. The optical constants of the materials used in the OVF were then modified based on the goniospectrophotometer measurements to estimate the reflectance more accurately and thus improve the modeled color predictions. Automating this iterative procedure to assess the refractive indices of the OVF components using multi-angle reflectance measurements could create an additional tool for monitoring the fabrication process.
Optically variable thin film coatings have been prepared on rolls of polyester film by depositing thin
multi-layers in a vacuum roll coater. Such coatings can be removed from the polyester film and
ground into optically variable pigments for printing inks. Various printing inks including gravure,
flexographic, and Intaglio inks have been prepared from these pigments, and printed images using
these inks have been obtained from commercial printing presses. These optically variable systems have
been used on various security documents to prevent counterfeiting with color copiers. Unique colors,
color shifting effects, and other optical properties have been obtained by combining non-optically
variable pigment and dyes with this light interference pigment. The merits of this new ink relative to
other optically variable systems are color uniformity, print quality, its ready use on existing printing
presses, and high security.
Conference Committee Involvement (1)
Optical Security and Counterfeit Deterrence Techniques VI
18 January 2006 | San Jose, California, United States
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