Polycarbonate Films – Material For Intelligent, High-Quality Cards

by Cengiz Yesildag and Georgios Tziovaras, Bayer MaterialScience AG

Security is one of the key issues determining recent developments in high-quality cards for sensitive fields of application. Security in this context refers to data storage, unequivocal personal identification and protection against forgery. Thanks to their range of properties, polycarbonate films not only fulfill the most critical requirements, but also lend the cards good long-term performance and a long service life.

High-quality cards are manufactured from polycarbonate films such as Makrofol® ID from Bayer MaterialScience AG. The first official documents in credit-card format to be made of Makrofol® ID were the Swiss National ID card and the German driver’s license. A new trend focuses on the use of this material for documents in other formats, such as

passports or data storage media for wireless data transmission. Government institutions and an increasing number of businesses and health insurance companies are becoming interested in high-quality cards with security features. For example, site ID cards with an integrated chip and microantenna were recently introduced at the Bayer Chemical Parks in the Rhineland region of Germany. They permit contactless reading for security checks at the gate entrance. With an additional barcode for scanner reading, employees can use the cards to make cashless purchases in the company restaurant and to log flextime hours. Incidentally, “contactless cards” of this kind have gained a significant share of the market in recent years compared with dual interface, magnetic stripe and chip cards.

Higher-contrast laser print

There are several arguments in favor of using polycarbonate films to manufacture high-quality cards. For instance, compared with other card materials, polycarbonate films allow very good, high-contrast, black-and-white laser printing, making it possible to personalize the cards. Specific information, such as passport photos, signatures or personal data, can be lasered into different front and back layers. The process is rapid and precise, results in abrasion-resistant print and makes the cards largely forgery-proof. Using the Changeable Laser Image (CLI) or Multiple Laser Image (MLI) method, images similar to a simple hologram, which contain card-specific information, can be applied as an added security feature. All of the security features applied by laser printing can be combined with classical security features such as holograms, Kinegrams and embossed surface textures.

Good functional properties, long service life

Polycarbonate films likewise offer advantages when it comes to their mechanical and thermal properties. Above all, they boast high strength even at low temperatures, as well as high stiffness (tensile modulus: 2,300 MPa). These properties give the cards very good long-term flexural strength. They can even withstand severe, repeated deformation—such as what occurs when they are kept in a wallet—without sustaining damage, thereafter returning to their original shape. The chips and antennas integrated in the film structure of the contactless ID cards cannot be removed by force. Thanks to the polycarbonate material, the cards have very high heat resistance of up to 145 °C.

In other words, they don’t warp after extended exposure to high temperatures. Because of this ideal set of properties, polycarbonate is the material of choice for cards intended to have a service life of ten or more years.

Lamination without an adhesive

The cards are manufactured by combining individual layers of polycarbonate film. In contrast to other card materials, the lamination process can be carried out without an adhesive. The resulting film structure can not be separated without destroying it; the individual layers are bonded together so tightly that the card can be viewed as a single, compact piece of polycarbonate. This fact further enhances protection of the cards against forgery. Moreover, the film structure is stress-free because the polycarbonate displays virtually no shrinkage at all. Opaque white polycarbonate films usually serve as the core film, which is marketed by our company in thicknesses of 105 to 790 micrometers. The core layer is covered on both sides by transparent overlays with thicknesses of roughly 30 to 150 micrometers, which can be lasered as needed. Alternatively, duplex (two-layer) films can be used right from the outset.

A look ahead

Cards with chips and antennas, such as those used for RFID (Radio Frequency Identification) systems, are very complex to manufacture. It is particularly difficult to embed the antenna and the chip in the film structure. To simplify the process and make card manufacturing more economical, Bayer MaterialScience is working on the development of special duplex films, comprising a rigid polycarbonate film and a flexible layer based on polyurethane.

One product with great application potential is the “citizen’s card,” which has good prospects for use worldwide. In addition to functioning as a personal ID, the citizen’s card can also be used as a driver’s license, cash card, social security ID and health insurance card. Because it is equipped with a personal certificate, it also fulfills the requirements for an electronic signature, with which people in the future can identify themselves on the Internet and conclude legal contracts. Government institutions would have the opportunity to offer “e-government” services through a special Internet portal, which would enable citizens to electronically submit applications, tax returns and other official documents.