Last Updated Thursday, October 8 2015

An Overview of Overt and Covert Security Inks

Unmasking the criminal frauds and forgeries for anti-counterfeiting product authentication

By Vinod Jyothikumar, PhD,

Published August 1, 2014
Related Searches: sheetfed offset specialty ink additives
An Overview of Overt and Covert Security Inks
Related Features
Counterfeiting, smuggling, warranty fraud, production overruns, product diversion and related problems are a huge concern for brand owners. Conservative estimates place counterfeiting alone at 5-7% of world trade, or more than $1 trillion per annum. Because the harmful effects of counterfeiting extend to entire economies and societies, fighting counterfeiting not only protects a brand name, but also can add to brand value if the company is perceived as an agent in product security.  

There are many features which used for security and they get involved in different steps production, i.e. security involved at substrate level when it is manufactured, the designing elements which are involved in document for security, the printing processes and special applications used and lastly, different post press special applications used. The contents of security printing, which are incorporated in document security, are differentiated on the basis of where and how these involved and added. There are different aspects where the security is involved as:

a) Substrate Based Security features
b) Diffraction Based Security features
c) Interference Based Security features
d) Printing inks
e) Printed Security patterns
Ink ingredients fall into three main categories: pigment, vehicle and modifiers/additives. Because there are so many different types of printing processes and print applications, the ingredients used in these three categories may vary widely.

Figure 1: Types of Security Features Used in Security Inks

Functions of Ink-Based Security Features

Security inks are formulated in relation to their specific security functions aiming at different categories of target users and varied authentication means:

• Public features for all users – authentication by eyesight and touch.
• Embedded features for shopkeepers and cash handling professionals – detection by aided devices.
• Machine-readable features – detection by sensors, machines and automated systems.

Security inks, especially inks for banknote printing, need to be highly resistant for the

Figure 2: The 3 A’s towards Developing a Security Ink
very reason that the security documents/banknotes are exposed to frequent handling. Like all products destined for public use, banknote inks are subject to Health, Safety and Environmental legislations to ensure the handling of the inks as well as the prints are safe and without negative impact on the environment.

Types of Security Inks

There are types of ink which have special properties related to physical aspect or chemical aspect. The response of these inks are in relation with environmental change of ink as change in temperature. In security applications, these inks can be inspected in first line by warming to body temperature, at which they become transparent and the color temporarily disappears. Change in chemical composition like in physical touch with chemicals.

Figure 3: Security Ink Considerations
Invisible Ink

One of the most widely used inks is invisible ultraviolet and will be revealed when the print is placed under a black lamp (or UV light source). The ink is invisible to the eye (covert) under normal lighting conditions. When passed under a UV lamp the ink glows and is used predominantly for cheque printing and document protection in the UK. It is relatively cheap and is available in many colors. The ink must be applied to a UV dull substrate, otherwise it will not be visible.

Thermochromic Ink

Thermochromic inks are sensitive to temperature changes and will appear or disappear at different temperature ranges. If you were to apply a finger and thumb to a 15°C dark blue printed thermo spot the ink would disappear to nothing, and as soon as you removed the heat source, the ink would re-appear again. Inks come in various temperature sensitivities and common temperatures available are 15°C, 31°C and 45°C. An important consideration would be where the ink is to be located. In hotter climates you may well have to go for a higher temperature as the ink could be invisible from the ambient temperature itself. Some are available as a permanent change, e.g. when it has reached a temperature the ink color does not reverse - this may be used on labelling for food product packaging where you could see if an item has thawed out and would be dangerous to re-freeze again.

Solvent Sensitive Ink (reactive)

As the name states, this would present a visible indicator that the ink has been attacked by a solvent (usually attempt to remove variably printed information such as a cheque). You will mainly find this being used on a printed watermark or fine guilloche artwork design. Once a solvent has been applied the ink will change color to show that alteration has been attempted.

Optically Variable Ink

OVIs contain minute flakes of metallic film. As the viewing angle is altered, the color morphs from one to another. This needs to be printed with a fairly heavy weight to get the best results. The inks are very expensive and are usually printed in small areas. Such examples would be in currency printing and visas. The most common color changes are brown to green (and vice versa) as well as red to purple. You will also notice that the ink feels almost embossed on the substrate, which is due to the amount of ink required to get the required effect.

Magnetic Ink

Magnetic inks are mainly used for serialization and numbering purposes. The ink contains small magnetic flakes and allows a number to be machine read. The most common application is cheque printing, and you will find it on the MICR numbering portion of the bottom of a cheque. This will usually contain the cheque number, account number and sort code of the bank.

Biometric Ink

Biometric inks contain DNA taggants that can be machine read or react to a reading solvent. This allows for verification of a genuine product and each batch of printed documents can contain different biometric properties. These are completely covert but require specialist methods to validate the authenticity. Over the past few decades there has been numerous advances in the biometric DNA proving technology, most notably among them is the development of PCR-based DNA proving methods.

Fugitive Ink (water-based)

Fugitive ink works similarly to solvent sensitive ink in the fact that any form of alteration (with water or an aqueous solution) will make the ink run so that the printed pattern or area becomes smudged, therefore indicating that a forgery or alteration has taken place. These, again, will be found on cheques, and if you are to wet your finger with saliva and wipe across the background, you would see the ink smudge.

Fluorescing Ink

Fluorescent is another type of ink that can provide a distinctive look for a variety of print applications. Fluorescent ink colors are most often printed on labels, posters and signs that are used for alerting people to hazards or attracting their attention to advertising pieces. There are several points to consider when using fluorescent colors. The ink tends to fade quickly, so they should be kept out of direct sunlight. Because of their tendency to fade, fluorescent inks have a short shelf life. Another point to consider is that fluorescent ink is very transparent, so it may require a double hit (a second run through the press) in order to achieve the desired results. In spite of this potential problem, fluorescent ink is a good choice for creating emphasis and increased visibility.
Phosphorescent Ink

Applications printed with phosphorescent inks acquire a “glow in the dark” property after the phosphorescent area has been exposed to light. The length of time that an application will glow in the dark depends upon the ink ingredients and the length of time that the application is exposed to light. In some cases, a 10-30 minute exposure to light can yield an afterglow of up to 12 hours. The ingredients of phosphorescent ink are nontoxic and are free of radioactive additives. It is very useful for road signs, sporting goods, exit signs, safety products, toys and novelty items.

Pearlescent Ink

Pearlescent ink is specialty ink that is used to add highlights and depth to the printed area of an application. It is able to provide an almost 3-dimensional effect to some applications.

Edible Ink

Edible ink is used on print applications that may come into contact with food or the ink may be part of the food product and therefore it must be made of totally nontoxic ingredients. An example where edible inks are used would be in the monogramming found on some confectionery items. Because the inks are used on food items, the government strictly regulates them.

Scratch and Sniff Ink

Also known as a microencapsulated ink, scratch and sniff ink releases a fragrance when the microcapsules are broken. The scratch and sniff ink is commonly used in magazines for perfume advertisements. When the consumer scratches the surface of the designated area of the ad, the capsules are broken, releasing the fragrance.

Medical Device Ink

Ink used for printing on medical devices is made of nontoxic ingredients so that direct printing on noninvasive surgical and medical disposable items is possible.

Moisture Resistant Ink

Moisture resistant ink is most often used for different types of packaging or for applications that may be used outdoors.

Desensitizing Ink

Desensitizing ink is a transparent ink that is applied to the face of CF (Coated Front) and/or CFB (Coated Front and Back) carbonless paper in order to deactivate the CF coating. The use of desensitizing ink is important when an application requires that handwritten or imprinted data not be transferred through the various pages of a carbonless form in specific areas.

Electronic Ink

Electronic ink can be transformed from bright white to dark and then back to bright white again with a small electrical charge. The ink consists of plastic microcapsules that contain both dark dye and white ink chips. The microcapsules are sandwiched between thin layers of flexible material, which substitutes for traditional paper. When an electrical charge is applied, some of the white chips float to the top of some capsules to create a white surface and in other capsules, the white chips remain at the bottom, allowing the dark fluid to remain visible. Applying the electrical charge under different combinations of capsules creates different characters. After the initial electrical charge is applied, no further charge is required to hold the image in place, (unlike a computer monitor, which requires a constant stream of energy in order to display an image). The content of the flexible page can be changed instantly and then be held on the page for as long as necessary. Although this technology is still being perfected, it could be a major advancement in variable imaging and in the reduction of paper usage for some print applications.

Sheetfed Ink

Sheetfed ink is manufactured specifically for sheet-fed presses and usually has a higher tack than web offset inks. The reason for this is that most sheet-fed presses run at slower speeds than web presses and a higher tack is necessary to provide the necessary quality.

Rubber-Based Ink

Ink formulated with a rubber base is a good choice when flexibility in the printing process is important. Rubber-based ink can be printed on coated and uncoated paper and it dries quickly. It is most often used on small sheet-fed presses.

Soybean-Based Ink

Soybean-based ink is becoming a popular alternative to petroleum-base ink because of the ease in which it is used and because it is environmentally friendly. Soy-based ink prints and handles similar to petroleum-based ink, but it is much less toxic because of the soybean oil. The soybean ink is biodegradable, meaning that it is eventually broken down and is much less hazardous to the environment. Some soy inks may contain petroleum additives, so if a client requires 100% soy-based ink for a print application, it is important to be fully informed on the type of soy ink that is used.

Water-Based Ink

Water-based ink has been around for a while, but it is still not as popular as other ink types. The usage of water-based ink may increase as environmental laws get tougher on the acceptable VOC (volatile organic compounds) emissions generated from petroleum-base ink. Water-based ink emits no VOCs. It is safe to work with and the print quality is comparable to other ink types. Water-based ink is used mainly in flexography and gravure printing. It is a good choice for printers and customers who want their projects manufactured with nontoxic materials.

Laser Ink

Laser ink is specially formulated to withstand the extreme heat of the laser printer. If conventional ink is used for the preprinted portion of a document (such as an invoice or statement), the ink will melt in a laser printer because of the excessive heat produced by the laser printer. This results in damage to the preprinted document and possible damage to the laser printer because of ink adhering to the internal parts of the printer.

Different printing processes give different ink deposition that results in considerable difference in densities. In the case of Security printing inks, amount of ink deposited on print plays significant role on performance of ink. Metamaric ink, optical variable ink, conductive ink, magnetic ink, thermochromic ink, etc. need to have proper ink density or ink deposition on to print to give proper performance for faithful authentication of document, i.e. density of ink gives significant effect on ink performance.
As the occurrence of counterfeiting is continuing to grow, the industry needs technologies that can help it to reduce such issues and maintain trust with consumers. Counterfeiting is an important problem addressed by several countries. This requires multiple measures to protect the supply chain. The implementation of security inks as anti-counterfeit technologies is an important strategy taken up by several manufacturers and regulatory authorities. The track and detect system are given importance and are widely used among all anti-counterfeit technologies in different countries.

Vinod Jyothikumar, Ph.D., has a broad background in Security and Risk, Biosecurity and biological safety, which encompasses past positions in the biotechnology industry, health care and academic research. He also has expertise in Multiplex imaging, sample preparations and advance microscopy techniques for Cellular Imaging, (FRET, FLIM, Calcium imaging, tissue and animal imaging). From 2004, he is consulting and contributing subject matter expertise on designing or implementation of experiments dealing with fluorescent probes and fluorescence detection. He is presently providing leadership and coordination of the biological safety program at George Washington University, D.C. as the director, Office of Lab Safety & Biosafety Officer.

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