Interest in materials that react to environmental conditions such as light, heat, gases, pH and moisture is gathering pace. Some of the ‘smart’ and ‘active’ labels (SALs) have already found their way to market and many will emerge in the years to come adding a new dimension to packaging.
Labels become active in response to a trigger event (i.e. filling, release of pressure or gasses, exposure to UV or moisture).
Labels store information and can communicate with a reader. More sophisticated systems can be write and read. Do not require line of sight.
Label function is able to switch on and/or off in response to external/internal conditions. Ability to sense and inform.
Figure 12.1 - The role and function of smart, smart active and intelligent labels. Source- Encyclopedia of Labels and Label Technology
There are many ways of creating SAL labels using smart inks, smart coatings, smart materials and by integrating components into the label structure.
Typically SALs are designed to sense the environment, it and to convey information to the user. The definitions between the terms tend to be somewhat blurred, but a common theme is the ability of these technologies to add a functional dimension to the label, so that it no longer remains a simple conveyer of brand identity. The ability to actively adapt to external influences means that the label can play a practical role in extending the shelf-life of a product, in promoting it, tracking it or protecting it from counterfeiters.
The growing interest in SAL packaging concepts in western markets is being encouraged by a number of drivers:
Rising sales of convenience, fresh-food products that are placing increasing demands on the packaging industry for formats which act to preserve taste, appearance and nutritional qualities
The demand for more product information by the consumer
The need to improve product life tracking, communication and control within the packaging supply chain - particularly to indicate where product or packaging abuse has taken place
Increasing pressure to reduce costs, and the desire to improve brand image and appeal
These demands, combined with recent advances in material science and biotechnology, are fuelling new applications in both food and non-food areas alike.
This article aims to provide a brief overview of some of these emerging technologies.
The use of high-performance coatings can enable surfaces to be more responsive to their environment and add functionality. Smart coatings frequently rely on a visible color response to indicate a temperature change or respond to other stimuli, such as a pH change, oxidation, corrosion or electric current.
Applications for smart coatings include tamper evidence, time/temperature indicators, anti-counterfeiting solutions, anti-microbial properties, barrier performance and freshness indicators.
Active packaging is designed to change the condition of the contents in order to extend shelf life or improve product safety.
The main focus of active packaging tends to be on maintaining or extending product shelf-life. The most commonly used ‘active’ technologies are desiccants, moisture absorbers and oxygen scavengers.
Whilst active packaging features tend to relate to the incorporation of additives into packaging film or within packaging containers, there is evidence that the label is being used for specific applications.
There are currently a limited number of freshness indicators on the market, where for instance an indicator label reacts to volatile amines from fish with a visual color change.
Gas indicators attached inside the package can provide information on the integrity or correct gas concentration within the packaging headspace.
For many perishable products exclusion of oxygen improves the stability of the product. A typical visual indicator can be formed as a printed layer or laminated in a polymer film and involves a distinct color change.
Time Temperature Indicator (TTI)
The time temperature indicator (TTI) is one area where the label is well established as a carrier (see Figure 12.3).
Figure 12.3 - Typical time temperature tag.
If perishable foods are stored above suggested storage temperatures, rapid microbial growth takes place and the product is spoiled. Typically attached as labels onto the pack surface, TTI’s integrate the time temperature history of the packaging throughout the entire distribution chain and provide information about product quality.
TTI’s play an important role in the healthcare sector. Maintaining the cold chain is fundamental to all vaccination programs, because vaccines and biological products are very sensitive to heat. A vaccine, for example, must remain active from its place of manufacture right through to the most remote areas where it is administered. If the cold chain is broken, the vaccine will lose its protective capacity.
SMART INK TECHNOLOGIES
Development in smart ink technologies is extending the role of labels into new areas. Smart inks can be applied using most of the main printing processes. A summary of some of the main types are as follows;
Photochromic inks exhibit spectacular color changes when they are illuminated with either ultra-violet light or natural daylight (Figure 12.4).
The inks are colorless in their natural state and when exposed they produce their visible color. These inks are reversible; reverting to their colorless state when the light source is removed. They are often used for product verification or in promotional applications.
Thermochromics are inks that change color with changes in temperature. They are available in two main types; reversible and irreversible.
Reversible thermochromic inks are generally used to show when the temperature of a pack or label has reached an optimum level. For example, when the temperature of a beverage (beer or wine) is at the appropriate level and ready to serve, the thermochromic ink label will change from white to blue. When the product warms up the message will disappear (Figures 12.5 and 12.6).
Figure 12.5 - Thermochromic inks that appear at predetermined temperature thresholds can indicate that a product has reached an ideal serving temperature or play an important role in security labeling
Figure 12.6 - Thermochromic labels - on both these label designs the mountains turn blue when the beer is cool
Irreversible thermochromic inks are used as time/temperature indicators in food and other packaging to provide a record of whether the products have been stored at the correct temperature, as well as in anti-counterfeiting or anti-tampering devices (Figure 12.7).
It should be noted that the EU has recently issued a new standard stating that all thermochromic inks should not have over a recommended level of formaldehyde.
Figure 12.7 - Irreversible thermochromic ink cha
Although thermochromic inks can be set at a variety of temperature thresholds, they are often set so that they can be activated at human body temperature, so that promotional messages or product verification can be achieved simply by touching the label or pack. In Figure 12.8 below black ink is printed over a ‘hidden’ image which is revealed when the ink is touched or rubbed.
RADIO FREQUENCY LABELS
Labels that contain an RFID (Radio Frequency Identification) tag are often referred to as ‘smart’ because they can store information (such as a unique serial number) and communicate with a reader.
RFID labels are increasingly being used in a wide range of applications to replace product barcodes.
WHAT IS RFID?
Radio Frequency Identification (RFID) is a term used for any device that can be sensed at a distance by radio frequencies. Not to be confused with EAS (Electronic Article Surveillance) tags found on many high value items such as CD’s and DIY products, radio frequency identification permits electronic detection of identification numbers and other data held on the tag.
An RFID tag contains a microchip attached to an antenna that is able to pick up signals from and send signals to a reader. The tag contains a unique serial number and may also contain other information, for example, a customer’s account number. Tag readers use the message they receive from the tag in accordance with their programer’s instructions (Figure 12.9).
Figure 12.8 - Image revealed by normal body heat
Figure 12.9 - Typical structure of an RFID tag
Generally, these readers must be no more than 2 meters (6 feet) away from the tags to be read. Unlike bar codes, RFID tags do not require line-of-sight reading, so a pallet load of RFID tagged goods can be read in a second or so.
Rather than a generic code, which relates to a specific product line – as with bar codes – each RFID tag has its own specific code. This offers retailers the opportunity of tracing and recalling certain batches of goods very quickly in the case of safety or quality concerns.
WHERE WILL IT BE USED?
It is clear that supply chain management will be the principal future use for RFID with applications in inventory management, warehouse management, theft, out of stocks issues and transport and logistics.
RFID applications will be invaluable in improving inventory insight. Balancing supply, demand, and customer service requires real-time information and operational control that will be facilitated by this technology.
Items, racks, and shelves can be labeled to automate picking and put away with forklift-mounted and wearable printers. With RFID labeling routes can be identified and pallets, bins and shipping containers managed without human intervention.
Antennae printed onto label structures using a conductive ink are increasingly being used (see Figure 12.10).
Figure 12.10 - SPGPrints collaborates with major suppliers of conductive inks to make RFID antenna
RFID antennae can be printed using silver conductive ink and there is work progressing on carbon graphite formulations.
In other instances smart inks contain radio frequency micro-taggants, which are responsive to electro-magnetic energy, enabling them to be detected when subject to an energy source. Information contained within the printed ink signature on the label can be read remotely when a low powered energy source is aimed at the printed area.
Developments in low cost RFID are split into tags that have microchips and those that don’t.
The more versatile chip tags comprise an antenna and a silicon chip mounted onto a substrate, but in the future it may be necessary to look towards ‘chipless’ RFID to reach the low unit prices required.
Another route to integrating RFID into labels and packaging is to insert the complete device into the label structure itself in the form of an inlay (Figures 12.11 and 12.12).
Figure 12.11 - A typical RFID inlay
Figure 12.12 - A typical RFID inlay
RFID labels are typically produced by incorporating a chip and antenna on a thin polyester film into a roll label construction (Figure 12.13).
The construction is then over-laminated with a print receptive face stock, printed, die-cut and applied as a standard self-adhesive label (Figure 12.14).
Figure 12.13 - Construction of a typical RFID roll label
Figure 12.14 - Converting a web of finished inlays into a label laminate structure
With the unit price per tag dropping and significant global players investing in RFID technology it is clear that low cost RFID is here to stay.
As we have seen with developments in printed RFID antennae, printed electronics are becoming an important facet of functional printing, creating a host of opportunities to add intelligent functions to a label.
Printed electronics involves printing conductive and dielectric inks on a flexible material to make an electrically active circuit or component.
When printing flexible electronics each printing process has pros and cons.
Screen printing is particularly good for laying down relatively thick ink films, which usually equates to better conductivity. However, screen printing is not ideal for fine features such as thin lines.
Flexo and gravure do better at reproducing small features, but have other challenges, including relatively thin ink films and inconsistent surface smoothness.
Inkjet printing is great for depositing fairly fine features and can make variable patterns, but it is quite slow compared to other processes.
Dr Malcolm Keif also details a list of printed electronics devices that can be reliably printed today.
Conductive traces (think flexible wiring)
Organic solar cells (OPVs)
Antennae for RFID, NFC or any inductive coupling (such as charging a wireless toothbrush)
Transparent conductive films
Printed resistors, capacitors, mechanical switches, and other simple devices
Developments in this arena will extend the role of the label from a static conveyor of brand values and information, into new realms where it can perform more complex functional tasks.
Paper substrates can be used for a variety of printed electronics applications (see Figure 12.15).
Figure 12.15 - Powercoat from Arjo Wiggins allows paper substrates to be used for printed electronic applications
OPPORTUNITIES FOR CONSUMER INTERACTION WITH PACKAGING
Coding printed on labels and packaging can offer a gateway to increased consumer interaction.
Print can provide opportunities to build relationships with customers via QR codes printed on labels or packaging.
QR (Quick Response) codes offer an instant way to get more information on a product by scanning the QR code with a smartphone and taking the user instantly to a web address (Figure 12.16).
Figure 12.16 - Typical QR Code
An on-pack back label can only offer a limited amount of space for information but when a QR code and smart phone combine, access to a wealth of web based information can be unleashed. For example recipes, nutritional information or even wine tasting notes, and links to other related products, can give the consumer the benefit of making a more informed purchase.
Digital printing of codes can be done quickly and at a much lower cost than conventional processes.
The introduction of new technologies such as the Smartphone and the trend of linking point of sale to online marketing resources is favoring more responsive and flexible print technologies.
Augmented Reality (AR) is an exciting new mechanism that is now being used to add value to packaging.
AR enables digital images/content triggered by a visual image to be seamlessly inserted into the real world through a smart phone, webcam or tablet. Brand marketers are bringing a spin to their packaging with a hidden level of graphics that can only be viewed through a phone’s camera (Fig 12.17).
Figure 12.17 - Augmented Reality
The technology can be added to any picture (even one that has already been printed) and it can also be programmed to allow the image to be scanned so it can be viewed afterwards, rather than having to hold the device over the image. This enables it to be used to demonstrate assembly instructions when building flat pack furniture, installing electronics or showing children how to build models.
The growth of smart phones and tablets will only increase the adoption of AR and there is currently talk of standardization in the industry to introduce a symbol that displays the presence of AR on packaging.
Current examples of AR packaging include drinks bottles that launch videos through an augmented AR smartphone app. and biscuit packs that use a QR code that directs the user to a video, photo or personalized message.
With little or no origination costs involved, digital print is a great way of reproducing the codes that link packaging at point of sale with web delivered content.