In recent years, identity document issuance solutions have undergone significant advances, incorporating a wave of new technologies that enable identity documents to be more durable, as they need to perform for their validity period. How should a document be designed to meet this requirement and how can the design be proven in the laboratory? The designer needs to consider the durability requirements of the components – the substrate, preprint, personalisation, laminate and chip – and combine them in a low-risk, holistic, overall solution. In the second and final part of this series, Nick Nugent describes how the science of durability can help an identity document achieve a lifetime performance. Many of the scientific principles that applied in the first part of this series about security, are also relevant in designing appropriate durability into an identity document, beginning with a threat assessment.[1] The environment in which a document will be stored, carried and used is as important as its required validity period in designing the durability solution. ISO/IEC 24789 is a new, two-part standard on identification card service life which was formally issued as a standard in 2012, and can help all parties understand, specify and agree on durability requirements.

The emergence of ISO/IEC 24789 has begun to change the way in which card vendors and card issuers discuss and define durability. Part 1 of the standard establishes application profiles; how the card will be used and stored, while Part 2 then defines durability test methods that are suited to these anticipated profiles. In this way, the service life of a national identity card is specified differently from, for example, an employee identity card worn as a badge, and tested accordingly.Durability of identity documents is generally measured using test methods that examine such properties as resistance to flex, abrasion, chemicals, daylight and extremes of temperature and humidity. These methods may be used as stand-alone single tests or combined in sequence, and useful guidance is given in ISO/IEC 24789. A full description of the standard and how it can be used is beyond the scope of this article.
The durability performance is related to, and may be impacted by, the other performance characteristics of Quality, Security and Cost. For example, thin laminates are more difficult to remove but are they sufficiently durable for a long‑life (7+ years) card? Does the chosen laminate go to the edge of the card, is it near-edge, or clearly a ‘patch’?

Laminate and overlay durability
Steady evolution in chemistry over the last few years has allowed laminates and overlays to become thinner – increasing their anti-tamper properties – without compromising durability. One successful approach has been to use UV-curable materials, where ultra-thin films (less than 10 µm) are formed by action of ultraviolet radiation on photo-initiators within suitable resins. This polymerisation process occurs when the UV energy activates the initiators in the resin and causes the molecules to link up in a nanoscale interlocking matrix. The result is a film which, although thin, is incredibly tough and durable. UV-polymerised films have the added security advantage that they have a tendency to break or snap if attempts are made to peel, lift, fold back or otherwise remove them.

UV-cured solutions during and after manufacture
Various durable UV-cured solutions are available. One approach is a film which is UV-cured during manufacture within the factory and another is to cure the overlay later, within the personalisation hardware. Each offers advantages and both improve tamper resistance without compromising durability.
UV-curing within the factory allows the film to contain holographic security features if required, as these can be introduced by a micro-embossing step before the film is cured. Extensive research and development led to the invention of such clear and holographic, edge-to-edge overlays that provide an effective barrier against chemicals, moisture and abrasions that can otherwise result in costly card reissuance. This type of overlay offers up to four times the protection of a standard topcoat and unprecedented card life for such a thin film.
In contrast to this pre-cured product, another tough protective film available to the industry is UV-cured after application to the card, producing an exceptionally hard-wearing non-holographic overlay. This solution has been proving itself for around a decade now and has been shown to provide up to a 10‑year performance for millions of cards while offering the anti-tamper properties inherent in UV‑curable films. Although the lack of a hologram reduces security, it is straightforward to layer additional security features as required. These include an embedded holographic DOVID – which can have a ghost portrait lasered beneath – laser tactility and microtext, a UV-fluorescent ghost portrait and even fluorescent taggants added to the film. A further advantage of this design is that pigmented colour can sit alongside laser in a very strong personalisation solution, meeting many issuers’ requirements for high-security long-life identity documents. For shorter lifetime requirements, five years or less, other durability solutions exist. Costing less, and typically with either holographic or clear options, topcoats and other overlays of 3‑5 µm are available from multiple vendors in the industry.
As has been seen already in this article, there are many layers to protect within an identity card. Although a critical part of the defences, the laminate or overlay is not the only component to consider when designing durability, and this protection should not be selected in isolation from the other card components. The substrate and the personalisation are also vulnerable to deterioration during the lifetime of the card, and several options are available for each.

Substrate durability
There have been many articles written on the relative durability performances of different substrate materials, and it is not the intention of this article to add to the debate about which is best. What is important to know is that several polymer options exist, including poly­ester (PET), polycarbonate (PC) and polyvinyl chloride (PVC), with selection usually driven by personalisation technology, durability and cost requirements. It is also important to know that substrates from the same polymer class will not necessarily behave the same, and should be tested as part of the overall solution prior to going live.
Again the substrate should not be selected in isolation and must be considered in the light of any preferred personalisation and laminate technology. For example, it is not straightforward (and may indeed be impossible) to use unmodified polycarbonate with standard dye-based ribbon systems, or to achieve high‑quality laser marking of conventional substrates consisting of PVC or composite materials.
Although it is true that some substrates, such as poly­carbonate and polyester, are inherently more durable than others such as PVC, it is a very complex situation and there is no clear ‘winner’; all polymer materials used in card bodies have advantages and disadvantages when compared to alternatives. A detailed comparison is beyond the scope of this paper but much useful guidance is already published.
   Additionally, substrates will last for different periods of time in different environments and use cases, and when selecting the substrate the principles of ISO/IEC 24789 should be considered. For example, if an identity card is to be worn as a badge in bright sunshine for extended periods, then selection of the personalisation tech­nology becomes critical, the laminate can be selected with UV absorbers to prolong life, and the choice of the substrate is less critical to achieve durability in-use.

Personalisation durability
Personalisation of identity cards is typically achieved by one of four fundamental technologies:
• laser marking
• thermal ribbon
   – pigment or dye-based
   – Direct-To-Card (DTC) or Retransfer Technology (RT)
• inkjet
• toner

Laser marking
Laser marking is itself inherently durable. The mark formed by the personalisation process is typically carbon, which is chemically inert and does not fade, discolour or migrate. Protection against harsh environ­ments is achieved by creating the mark deep inside the layers of polycarbonate. The durability of a document is not automatically assured by the use of laser-marked polycarbonate. Construction design and processing conditions must also be correctly defined and diligently followed to ensure the required lifetime is achieved.
There are some drawbacks to laser as a personalisation technology. The substrate, typically polycarbonate, has a high price, and the laser marking hardware systems are also usually more costly than alternative engines. Also the result is not coloured. Novel ‘colour laser’ systems are beginning to be introduced into the market though, at the time of writing, these are yet to be implemented or proven in the field. Until they are, coloured personalisation will use one of the other three technologies, and will need protection with a laminate or overlay.

Ribbon systems
Ribbon systems are the standard personalisation technology for identity cards. Photographic quality, simplicity of use and a wide range of scalable hardware options – from desktop to high-volume central issuance – make this a very popular choice for identity card issuers. From a durability standpoint, the particular type of ribbon technology selected might prove to be a key decision.
It is very difficult to make valid comparisons of the durability performance of cards personalised by different printers and with different ribbon systems.
A recent card printer technology assessment was undertaken with the aim of doing just this: evaluating and comparing the durability performance of the output from several industry desktop card printers. Printers using either Direct to Card or Retransfer Technology were used to personalise standardised test designs onto a common substrate, in an attempt to compare visual quality and durability performance between technologies.
Personalisation was onto one composite card material which was then protected beneath a 25 µm polyester laminate. Cards were then subjected to a selection of durability tests taken from two common industry standards, ANSI INCITS 322 and ISO/IEC 24789, to evaluate relative durability performance. Tests were selected based on the likelihood of differentiating the card performance: peel strength (after preconditioning with flex or elevated temperature/humidity), daylight exposure, water soak and wet abrasion. The results of the tests were then collated and the printers ranked according to the durability of the cards they delivered.
Insufficient numbers of cards were tested for statistical significance or to draw definitive conclusions from this study, however some interesting observations were made which indicated the following trends:

• No single printer performed the best in all durability tests with both laminates.
• Four of the five best‑ranked printers were Direct to Card.
• Retransfer systems typically showed lower peel strength, in particular the higher temperature/relative humidity peels, due to the presence of the retransfer film layer which can be a ‘weak link’ if the laminate is not well-matched with the retransfer printer.
• All cards passed the daylight exposure test criteria, and print fading can be further supressed by:
    – use of pigmented ink;
    – use of RT system;
    – use of holographic laminate;

• Different vendors’ systems had strengths and weaknesses, for example one laminate performed consistently better for DTC, while the other material performed consistently better for RT.

This small study highlighted the challenges faced in the selection of personalisation hardware, and reinforces the importance of holistic design and of testing the solution.

Inkjet
Inkjet is steadily gaining interest within the world of plastic card personalisation. Attracted by a potential lower cost per card and improving quality performance, a few integrators have implemented inkjet schemes, with mixed results. The main problem currently associated with this personalisation technology is not related to the inkjet itself – which generally provides good quality printing – but instead with its durable protection. In short, real-life implementations and laboratory testing have shown that these solutions are not yet built to last an extended lifetime of more than five years, and are more likely to be successful on documents with a validity period of three years or less.
Toner systems
Toner systems emerged in the 1990s and fought battles with ribbon systems for control of colour identity docu­ments. Over recent years toner systems have become increasingly marginalised, and market research indi­cates toner accounts for as little as 5‑10% of identity document personalisation worldwide in 2014.

Summary
We have considered the best practices by which identity cards should be designed to deliver the required levels of security and durability. We have seen some of the pitfalls; the dangerous traps that lie in wait and are the cause of many card issuance programmes worldwide being less successful than they were intended to be. There are trade-offs, and compromises to security and durability often need to be made, with decisions forced by restricted budgets and in the absence of full and perfect data.
In amongst all of these real-world challenges we should not lose sight of the fact that risks can be minimised and performance optimised by following the best practices contained within this article. These best practices have emerged over many decades. They are derived from the experience gained through the issuance of billions of identity documents from thousands of programmes, and from assessing the data gained from hundreds of durability and adversarial tests in specialist laboratories worldwide. In other words, the best practices necessary to deliver security and durability have been built from the “systematic knowledge of the physical or material world gained through observation and experimentation”; also known as science.

Reference
1 Nugent, N. (2014). Designing identity documents:
Part 1: The science of durability. Keesing Journal of Documents & Identity, Vol. 46, pp. 32‑39.