Technical and commercial advantages of composite materials over ‘monoblock’ polycarbonate (PC) have led to their increased use in secure electronic and non-electronic ID documents. The multilayered structure can both challenge and enable security enhancing applications in properly designed documents. In this article, Rainer Rettig will demonstrate applications for ID cards made of a variety of composite materials, showing some options for enhanced security beyond the monoblock paradigm.

Security features in card-sized documents need to fulfil a list of requirements that are hard to balance. They should not be easily accessible to unauthorised people, the information on them should be hard to alter or erase, and copying should be virtually impossible. Furthermore, manipulation has to be easily identifiable, preferably without any, or limited access to, equipment. Considering the increased amount of passengers at border crossings and airport passport control, cards that fail to be recognised as suspicious at first sight will rarely find their way into the more sophisticated machine-supported investigations, unless by chance. For that reason, security features that are easily checked by human ‘sensors’ increase the security of the overall system.

In general, two groups of security features can be distinguished:
1. Security features that focus on the card (‘card-centric’ features).
Features that are an integral part of the standard document and that are identical for all corresponding documents;
2. Security features that focus on personalisation (‘personalisation-centric’ features).
Features that are part of the personalisation, different for every card and applied through the various personalisation steps.

For both groups, we will discuss how they would combine with the various composite documents. It will become clear that their security is equal to or even enhanced compared to the industry’s benchmark, the polycarbonate monoblock card.

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figure 1

Security features that focus on the card
Security printing
Security features that are applied during the printing process require certain substrate properties already possessed by a large number of polymers used in the card industry. The standard security printing machines can easily print on PC, PVC, PET, PETG and synthetic papers such as TeslinTM or SynapsTM. Although techniques such as guilloche or rainbow printing, OVI, fluorescent pigments and IR blocking inks require application expertise, they are within the standard skills of a printer, regardless of the substrate they are applied on (see figure 1).

The inks themselves have their physical limits. One, for example, is the maximum process temperature, above which degradation, colour change or loss of UV luminescence can occur. Polycarbonate cards, the de facto standard in ID cards, are laminated at temperatures above 180°C for longer periods of time, prohibiting the use of some security inks. Composite card materials, on the other hand, allow for lamination around 130°C. This difference of 50°C significantly widens the range of applicable products.

Holographic features between overlay layers
By default, holographic security features are applied underneath an outer layer, before the card body is laminated. This is done to protect the feature from wear and tear, as well as from fraudulent access. Structured in three dimensions, the carrier material for reasonably priced holographic structures – usually a polyester film – will be damaged by excessive heat and pressure. The use of these films in polycarbonate structures does require special products, adapted and designed for the process and sold at high cost. As composite cards can be laminated at a significantly lower temperature, the range of applicable products is increased and the cost involved reduced. Designing the composite structure professionally will reduce the holographic structure’s vulnerability to fraud. If the structure is applied proficiently, they will be visibly damaged if layers of the card body were to be delaminated.

Tactile structures
During lamination, tactile structures such as microprint, fine lines or Braille can be generated on a card surface using structured plates – an expensive, complicated and skilful process. Tactile structures do increase the complexity and security of the card body manufacturing process, especially when combined with laser technology, for example 3D effects such as CLI or MLI. Structures that can be generated on polycarbonate can be generated on cards manufactured with outer layers of crystalline polyester as well.

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figure 2.

Security features that focus on personalisation
Laser engraving
In the last two decades, one of the biggest steps forward in personalised security features was the introduction of laser technology. This technology is based on the local carbonisation or evaporation of substrates in three dimensions within the card body. It can be used to apply personalised information, thus offering protection against fraud and easy verification during first line inspection. Examples of laser technology are carbonised and non-carbonised
tactile surface structures, characters, grey scale pictures and laser perforated structures. Laser engraving can offer a high level of fraud protection for personalised data. Polycarbonate supports this technology by its sensitivity to laser energy, offering high contrast and definition.

Nevertheless, laser technology has its drawbacks, as it has evolved at significant speed. Machines that in the past represented huge investments and needed well-trained experts to operate are now available for a few thousand Euros as desktop machines, reduce the entrance barrier for fraudsters down to a critical level. Furthermore, low-contrast pictures on polycarbonate can be overwritten with higher contrast information, as shown in figure 2. Photos on a stolen valid document can easily be adapted to a new card holder if the real card holder and the illegal user are chosen thoroughly and meet certain optical criteria.

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figure 3.

Composite materials, which are highly sensitive to laser energy, can overcome this problem. Crystalline PET can be enhanced to match the contrast and resolution of polycarbonate, but will generate obvious blistering if a structure already engraved by laser is exposed to laser light for a second time. See figures 3 (polycarbonate re-exposed, showing no blistering) and 4 (polyester re-exposed, showing significant and easily detectable blistering). In none of the experiments blistering of the polyester composite cards could be avoided.

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figure 4.

Laser perforation
Laser perforation is a process that uses laser to generate photos by ‘drilling’ holes of a defined diameter into a card body. The holes can, for example, form a repetition of the holder’s printed photo and the image will be visible when the document is held in front of a light source. Laser perforation is a very strong security feature, as all the card layers are perforated. It can also be integrated physically into other security features to make alteration more difficult. Lifetime expectations of today’s polycarbonate documents are significantly reduced by laser perforation.

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figure 5.

The holes of the photo resemble paper that has been perforated, and any bending and torsion will reduce the mechanical stability and resistance (see figure 5). In contrast, composite cards made with outer layers of crystalline polyester are no longer sensitive to the negative impact of laser perforation and will survive even excessive wear and tear without significant reduction of mechanical properties (see figure 6).

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figure 6.

Additional laser options with composite materials
Composite cards with an outer layer of semicrystalline polyester can be engraved with a CO2 laser, thus providing individual clear tactile structures on the card surface. The tactile structures are easily detectable without the use of equipment and allow for an additional first level check of personalised data (see figure 7).

Chip application in card-sized documents
Another quantum leap in security was the introduction of chips into documents. Chips can be seen as both ‘card-centric’ – by identifying the application through a range of cryptographic information – and ‘personalisation-centric’, by containing the card holder’s data. The chip is either equipped with a contact interface – requiring direct contacting – or connected via a radio frequency (RF) interface.

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figure 7.

Both contact and contactless chips represent a significant challenge for card manufacturers when integrated into a card body. For chemical reasons, polycarbonate cards in particular show narrow production windows for contact chip insertion and are challenged by the fact that the card needs to provide secure adhesion for the chip for at least five years. The positioning of the chip on the card surface makes it vulnerable to fraudulent access. Composite cards with inner layers of PETG or PVC provide a much better chemical interface for glues used in the card industry, thus increasing the security of the chip/card connection.
Integrated contactless chips have not only been ICAO’s choice for international travel documents, but are also increasingly used in national solutions. The fact that the chip and its interface are surrounded by the card body provides significantly more shelter, but a more secure approach also exposes the chip to extreme parameters in lamination. The semiconductors used in ID cards and passports are specified for a usage temperature of up to 85°C. Although processing temperatures of up to 190°C are endured for short time survival, they influence long-time performance in a way that is not yet fully understood, which might pose a liability risk for the manufacturer. Composite cards, which can be laminated at temperatures that are 50°C lower, reduce the stress for the semiconductor during lamination, giving more security for the long-life card survival in the field.

Conclusion
The usage of polycarbonate in ID cards has improved document security over the last years. Though it has been of great value to the industry, it has not been the holy grail of ID document security, but rather a significant step in an evolutionary process. Problems with processing polycarbonate and the durability and fraud resistance of this type of material motivate the card manufacturing community to take a step towards the next level in ID card evolution. Composite solutions accomplished by intelligently combining materials of different physical and chemical profiles achieve more durable and tamperproof documents. Fine-tuned levels of laser sensitivity and different responses to laser light are revolutionising security levels in laser engraving. Furthermore, non-carbonised tactile structures can be personalised by laser to increase the efficiency and reliability of the first line document inspection at points of control. Last but not least, this new generation of cards made from composite materials offers ways to reduce stress applied to electronic structures in the card manufacturing process. This improves a document’s durability and increases the manufacturer’s and issuer’s confidence with regard to its lifetime expectation on the market.