Of all the security related print devices available for brand protection and securing packaging and labeling from threats of counterfeiting, tampering and alteration of important information such as sell-by dates, identification references and variable supply chain data, inks are the most versatile component in the armory of the printer and converter.
Regardless of the printing process, whether it is litho, letterpress, flexo, gravure or silk screen, there is a whole range of inks available to act as precursors of authenticity, indicators of alteration and covert messengers that can be used to conceal hidden information that is only accessible to those with the knowledge and equipment to reveal their secrets.
In itself, ink is a versatile commodity that can be adapted to carry security features that are sensitive enough to provide reactivity to external stimuli such as light and heat. If used correctly, these responses deliver an indication that a pack can be trusted or that a label is not all it purports to be.
In order to protect security inks from unauthorized use, it is necessary for the industry to establish that it is dealing with bona-fide printers that can be trusted before supplying product to any printer or converter.
This is a necessary prerequisite of any of the materials utilized in product protection and applies to paper, board and foils as well. Safeguarding such supplies whilst they are in stock or on the print shop floor awaiting conversion is an important responsibility for the printer too.
Since there is a tendency for packaging and labeling converters to generate product using the four color printing process it is necessary to point out that in order to provide security it is obligatory to deliver a security ink using spot color and this requires extra print stations to be available depending upon the number of colors needed in excess of cyan, magenta, yellow and black (CMYK).
This in itself is not a hindrance for most suppliers since they will already have equipment capable of delivering a number of additional colors over and above CMYK, but for those with a basic four color limit, or those with only digital print facilities, security Inks for primary validation work will require additional runs through the press or the utilization of alternative security devices if only digital methods of production are available.
As hinted at earlier, there is a wide choice of security inks, all designed to deliver specific reactions in order to safeguard against a whole range of potential threats. These threats range from unauthorized replication right through to detecting alteration and substitution attacks.
Instances include printed codes that may be erased or replaced in order to disguise an out of date product, or to mislead consumers by indicating that a component is suitable for a particular use when it is not.
An illustration of ‘change of use’ would be where a code on an electrical product label specified it was safe for industrial use when it had only been authorized for domestic applications. Such changes would immediately increase the ‘value’ of a product by just changing or altering the identification code on the label.
Before deciding on the suitability of ink as a method of adding a security feature to print it will be necessary to evaluate the protection from potential risks that such a solution will provide. Decisions should be made relating to whether protection is required at point of sale or right through the supply chain.
Additionally, it will be essential to establish whether an ink will be used as a primary, secondary or forensic identification feature, or maybe all three. Designers should appreciate that if they are also to incorporate supplementary devices such as holograms or serialized codes then consideration must be given to how these all complement each other in the system and whether any unnecessary duplication of function is encountered.
It is, for instance, a duplication of function if a hologram is used for primary recognition and combined with another optically based feature such as a visible color change ink. For low to medium type security protection, such combinations can add considerably to the cost of the final product with little additional benefit.
There follows an inventory of inks and vanishes that are suitable for security packaging and labeling applications. This list is non-exhaustive since new inks and pigments for such uses are under continual modification and development.
INKS THAT MAY BE USED FOR PRIMARY VALIDATION PURPOSES
These inks are designed to supply an initial indication of provenance that may be obtained visually within a few seconds.
Clear or optically variable varnishes
The use of varnish in print provides a matt/gloss effect that is highly resistant to scanning and attack through the use of ‘home office’ laser and ink jet printers that are often used for low end replication of counterfeit labels and packaging such as small cartons.
By adding a color shifting pigment to the varnish security can be increased even further. In the illustration (Figure 4.1) it should be noticed that braille is also present on the carton, as a prerequisite of pharmaceutical requirements for those that require tactile confirmation on the pack as they may be visually impaired.
Figure 4.1 - The use of a varnish seen here used as a logo appears in positive/negative form when tilted to light
Because of the size of the color shifting pigment particles in the ink it may not always be possible to use some printing techniques such as litho and flexo to deliver optically variable varnishes on some materials.
Optically Variable inks
As their name implies, optically variable inks (OVI’s), visibly change color when tilted by the observer to deliver an easily recognizable shift in appearance.
The color change is delivered by millions of small light reflecting platelets distributed within the ink. These shiny substances provide a very definite change in color when tilted and are widely used in product protection as can be seen from Figure 4.2.
Figure 4.2 - Optically variable inks, similar to those on banknotes change color significantly when titled
Such inks were originally formulated for banknote protection and understandably they are under continual refinement and development.
Basic OVI’s for brand protection are restricted to specialized suppliers and only the highest security products are used in currency applications.
Because such inks carry high levels of pigmentation to deliver their optically shifting effects it may be necessary to use printing processes that are designed to carry heavy ink weights such as silk screen. A high degree of consultation with the ink manufacturer is recommended before OVI work is undertaken.
Iridescent inks
Similar in visual results to optically variable varnishes, iridescent inks deliver a multitude of colors in an effect that is similar to that observed on bird’s feathers or the wings of a butterfly.
Such inks are widely available and used predominantly to decorate cosmetic and body care products. Unless an ink of this type is specially developed to provide a unique visual appearance it should only be considered for decoration and very low level protection applications.
Thermo-chromic inks
These products react to specific variations in heat and are mainly used to temporarily indicate a certain degree of chill has been reached before a beverage such as beer is consumed, or that conversely a warm drink such as coffee is still too hot to consume. Communication is achieved by a brief color change from clear to deeper shades of blue in the case of chilling and towards orange and red in the event of a heat warning.
Thermo-chromic products are also useful where permanent records of temperature exposure are required. In these instances color changes are designed to point out that a product pack or label has been exposed too long to a specific temperature threshold that makes the product unsafe or unusable. In medical applications it is useful as a tool to measure correct autoclaving temperatures have been reached.
In product security applications, thermo-chromic inks are used as an indication of genuineness since they can be formulated to react to body heat in the form of pressure from a thumb or finger and change from color to clear or the other way round from clear to color. Alternatively such inks can also react to heat created by the friction generated by scratching the ink with a rough object such as a coin or a thumbnail. (note: some ink encapsulation processes deliver a similar result)
It is also possible to embed thermo-chromic properties into plastic containers and closures which enhances their use even further.
Figure 4.3 - Some color reactions to changes in temperature are shown
Recent developments have delivered inks capable of indicating a variety of color changes depending on the temperature they are exposed to.
These are referred to as tri-thermochromic inks.
Coin reactive inks
A very basic level of security can be achieved by the use of coin reactive inks. These products are visible as a semi-gloss varnish after printing and when a coin is rubbed across the ink a reaction occurs, causing minute amounts of surface material caused by oxidation on the coin’s surface to be transferred to the clear ink creating a gray color.
Penetrating inks
Again, as their name implies these products are designed to infiltrate paper substrates so that they bleed through the material and can be easily viewed from the reverse. Generally these inks appear black on the exterior of the paper and show as a color on the opposite side.
Well performing penetrating inks will be absorbed into the matte of the paper and will be very difficult to erase or alter. Therefore they are useful for delivering secure product coding that may be at risk from alteration or erasure.
INKS THAT MAY BE USED FOR COVERT AUTHENTICATION APPLICATIONS
We should remember that early in this study we discovered that if there was any uncertainty regarding the provenance of a primary or overt (obvious) security feature, then some secondary degree of confirmation was required in order to make a sound judgement about authenticity.
These ‘secondary’ procedures require an instrument of some sort that can be used as an assurance that a security feature is present – or not.
INKS THAT ARE RESPONSIVE TO ULTRA VIOLET LIGHT
Over the years, one popular method of achieving this secondary authentication objective is to use non-visible light in the form of ultra violet energy delivered by a power cell or mains connected lamp. These are also known as ‘black lights’ and need to be shaded from direct visible light in order to work efficiently so Inks used for covert authentication that UV reactive print may be observed.
Inks can be formulated to respond to both short wave and long wave UV light.
However, since long wave UV activating inks have been present for a number of years they are not considered as secure as their short wave alternatives because the chemicals used in short wave UV inks are not so easily obtained and in some countries are strictly controlled.
More recently, UV inks have been modified to deliver much more secure responses to UV light and it is possible to ‘tune’ such inks to react to much narrower wavebands of light at both ends of the UV spectrum.
There is a wide range of colors available and it is not necessary to adopt the traditional blue hues that have previously been used and can be easily compromised. Indeed there are products that turn from visible to invisible and those that offer a distinctive color change through three of four variations of shade when exposed to different intensities of UV exposure.
Figure 4.4 - The electromagnetic spectrum and the infra-red and ultra-violet wavelengths that can be utilized for security ink authentication systems
Ultra violet reactions are a form of photoluminescence. But this reaction ceases the moment the UV light source is switched off.
An additional reaction, known as phosphorescence can be made to deliver luminescence that continues to fluoresce after the UV light source has been extinguished. The intensity of the luminescence displayed by the printed image then decays over a period of time that it can be measured accurately. For this reason such inks are very useful to security printers because they can be tuned in both color and the period of time they take to decay. These properties make ideal authentication devices.
Metameric inks
Metamerism is a phenomenon that is used to describe color changes that occur in certain specially formulated inks when they are viewed under different light sources. For instance, under natural daylight a pair of color-matched inks will appear to be exactly the same. Expose the inks to an alternative light source and a very different image is observed.
Therefore metameric inks need to be ‘paired’ to work effectively. A metameric pair can be alternatively defined as two colors with different spectral compositions that generate the same color stimuli under certain conditions such as lighting, size and angle of viewing or the chromatic sensitivity of observers. In fact, we talk about a metameric pair because this effect is evident when comparing at least two color samples.
Such inks are available in a variety of combinations and since it is not always evident that such inks are metamerically paired on a piece of secure print it is possible to deliver a highly covert authentication feature that can act as an effective counterfeit detection measure.
Photochromic inks
Photochromism is the ability of a chemical to respond to light and display this response in the form of a color change. In the case of sunglasses, these chemicals react to light intensity by changing to a darker shade as the sun gets brighter.
The security-related print industry has long toyed with such reactions and tested these compounds on a number of occasions. When carried in inks, the photochromic chemicals (spiropyrans) can so far only be made to react to high intensity light such as a camera flash, and further limitations are that they are affected by daylight which causes loss of color fastness over time.
The color change reactions of photochromic inks are reversible and once a change develops it lasts much longer than the changes that are observed when phosphorescent light excitation is removed.
Work is currently underway at a university in the UK to improve the range of colors available and the results so far promise an early solution to these problems.
If successful, expect photochromic reactive inks to be more widely used in future.
Conductive inks
These products are widely used in the printed electronics market which is way beyond the terms of reference for this study.
However certain developments in this area are of interest to product security inasmuch as work carried out recently in Germany has delivered a conductive ink that can interface with the screen of a smartphone.
An invisible printed pattern is applied to the tag, label or board used in packaging for promotional purposes and authentication.
This pattern acts as a ‘pointer’ or trigger so that when the surface of the printed item is touched to the smartphone or tablet screen it interferes with the capacitive touch functions and acts in the same way as a finger is used to tap or navigate the system.
Figure 4.5 - Inks that react to the capacitive screens found on smartphones and tablets can be used to trigger authentication messages
Codes can vary and when activated can ‘virtually deliver’ the user to a webpage where product authentication can take place. They need to work in conjunction with an app which needs to be installed before touching the print to the tablet or smartphone screen.
Machine readable inks
In order to remove any ambiguity that may exist when authenticating inks and deciding their genuineness manually, a number of automated technologies now exist in the form of small hand held gadgets that recognize specific chemical signatures and respond with an audio or visual signal that confirms or rejects provenance of the ink.
Unique chemical signatures are formulated from a number of ‘rare earth’ materials that are then embedded in minute amounts within a printing ink or varnish.
The particles, which are invisible to the naked eye, glow brightly when lit up with specific frequencies of light. These specks can easily be manufactured and integrated into a variety of crystallized materials, and can withstand extreme temperatures, sun exposure, and heavy wear.
These crystals are doped with elements such as ytterbium, gadolinium, erbium, and thulium, which then emit visible colors under say, near-infrared light. By altering the ratios of these elements, it is possible to tune the crystals to emit a number of colors in the visible spectrum.
Such materials are then engineered to deliver highly specific reactions that can be used in millions of disparate applications, thus protecting the integrity of each system from reverse engineering.
Readers that recognize these signatures, range from small inexpensive hand held devices that are powered from a battery, through to high speed automated machinery that is utilized to validate batches of banknotes before they are placed back into circulation after being received over the counter.
INKS THAT ARE DESIGNED TO DETECT AND DETER TAMPERING
Tamper evident inks have been used for decades to protect financial documents from alteration and erasure attacks. They have also found wide use in the construction of tamper evident labels so that messages can be displayed such as ‘opened’ and ‘void’ to reveal that a label used as a closure can display a warning message and be destroyed during the unfastening process.
More recently, with the popularity of product coding it has become necessary to protect products that carry date and product coding, serialization and batch specific data from alteration and/or erasure assaults.
This is because there is hidden value in these codes as they are used to identify when products should be withdrawn from sale because they have reached their ‘use by’ date. There is also value in protecting the codes used to identify the performance of products and there is money to be made in remarking those with low end specifications in order to disguise them as offering higher functionality. An illustration of this point is the remarking of computer processor components or graphic cards so that they pass off as more highly priced articles.
Inks used for coding then, need to be permanent and they also require a secure platform or base on which to reside.
Placing a screen of erasable ink under the code offers a degree of protection, which can be enhanced further by including a degree of chemical sensitivity in the ink to protect against solvent or bleach attacks that are aimed at erasing the code so that new data may be placed down or the original code altered to deliver a different message.
Figure 4.6 - Scratch off inks can be used to deter tampering especially where coded messages are used for internet checking of authenticity
Likewise, codes that are used for product authentication are often protected by a layer of scratch off ink that is removed during the verification process, ensuring that the same code cannot be reused again later.
For additional security the scratch off panel can be overprinted with a tamper evident design.
Forensic inks and taggants
For very high security applications it is necessary to add a form of forensic security to the ink. Marking an ink or other print related material such as paper or label adhesive with a forensic signature requires the addition of a tag or taggant.
These tags are microscopic particles that are embedded in the material and are distinguishable either through their chemical or biological signature or through high power magnification. They are sometimers referred to as nano-markers.
Figure 4.7 - When a reader is in close contact with a taggant carried in an ink then a signal in the form of a green light is delivered
In the same way that DNA can be used to recognize and prove the participation of a criminal in a crime, taggants can be used to prove conclusively the provenance of ink or label material on a label or package.
Indeed, biological materials in the form of synthetic DNA are used in product protection programs. The presence of the DNA is identified either by laboratory testing which takes some time, or through the use of specially doped chemical testing strips that work in a similar way to pregnancy testing. Color changes on the strip indicate the presence or absence of the validating DNA tag.
To simplify the process of categorizing taggants further it should be noted that there are two classes of nano-marker, organic and inorganic.
Organic markers such as synthetic DNA are easily dissolvable and can be carried in solutions that are capable of being applied by inkjet coders.
Inorganic markers are based on chemistry and the physical properties of small indicators that vary from the size of, say, a grain of salt through to material at micron levels. These particles are best carried in viscous inks or varnishes, since the process of reducing their size in order that they can be delivered through inkjet heads is a further specialized process.
At the top end of the scale, micro markers can be identified with magnification and tools such as loupes and microscopes are used to identify particles that can be visually coded with a variety of patterns, colors and stripes.
These coded particles be distributed randomly in an ink or varnish and when visually confirmed that they are present authentication is confirmed.
At a nano-level though, specialist readers are required to identify the tag and the signature carried by the markers. Signatures can range from those confirmed on a spectroscope through to specific chemicals that may be recognized by a hand held reader that displays a confirmation that the tag is present through the display of a red or green light.
Since the chemicals used in these inorganic authentication systems are based on materials that are distributed in very small amounts such as parts per billion, it is very difficult for anyone to reverse engineer the process, even if they have access to a reader and the chemical tag involved in the authentication procedure.
A further benefit of these tags is that since they are present at measurable levels, any variation in the amount of tag present in a sample can be readily recognized and can act as an indicator of dilution in vulnerable products such as liquids and powders.
It is a worthy practice to embed the same markers in the packaging as well as the product in order to obtain a systemized approach to product protection.
For instance it is a recognized practice for some producers of valuable vintages of wine to embed the DNA from their product in the ink that is used to print their wine bottle labels.
Inks for primary validation
Inks for covert authentication
