This white paper is intended as a reference for government officials considering technologies available for issuing secure ID cards. There are three major components of this decision:
• ID card body or ID card substrate material
• Print or personalization technologies
• Laminate or topcoat material
All three elements must be compatible for a successful ID card printing program and each component impacts the cost, durability and security of the ID card. There are many trade-offs involved in a decision on the appropriate combination. There is no “best” method, so the technology choices should be carefully evaluated against program requirements, and rigorously tested using the components selected.
ID Card Materials – Substrates
1. PVC (Polyvinyl chloride) is the most widely used material for plastic blank ID cards, and has been used for photo ID cards for more than 10 years. Low in cost, the smooth surface of photo quality PVC material accepts dyes for high quality image printing on ID cards and is compatible with most laminate materials. Although there are a wide quality range of PVC materials, durability is limited for applications with high usage. Material can be printed as pre-cut cards or sheet material (on large digital presses). PVC is generally the lowest cost of the materials used for ID cards, and is primarily used for ID cards with 1 – 3 year durability requirements.
2. Composite Cards typically combine layers of PVC and PET. Developed initially for the college and university ID card market, ID card constructions combine varying amounts of each material to meet a range of durability requirements and price points. The outer layer of the construction is PVC to facilitate digital ID card printing, and the inner core is PET for greater flexibility and durability. It has the same offset printing and card construction characteristics as PVC, and can be easily configured with RFID, IC and contactless technology. Manufacturers continue to develop new composite constructions (e.g. PVC/PET/PC) to add specific performance characteristics. Composite ID cards are often used for government ID cards that require a longer life.
3. Teslin is a synthetic porous material produced by PPG Industries. It is receptive to conventional offset printing used for high security designs. In sheet form, it can be printed using standard color electrophotographic (laser) printers or inkjet printers. Because the surface is not smooth like PVC it cannot be directly printed with dye diffusion printers.
1. Dye Sublimation (sometimes called dye diffusion thermal transfer – or D2T2) uses heat to transfer dyes to a substrate. Used for high quality color printing, the process creates continuous tone colors by varying the amount of heat applied. Typically a 3 or 4 color ribbon (cyan, magenta, yellow and black) is passed under a thermal printhead and heat is applied to deposit dye. Ribbon dyes can be applied:
a. Direct – printed directly to an ID card surface; or,
b. RETRANSFER – printed to the backside of a clear re-transfer ribbon which is then fused to the ID card surface and is often associated with the HDP series. It is commonly used to personalize smart cards which may have irregular surfaces.
An advantage of the dye sublimation process is the extensive range of colors that can be created. Slight variations in heat create different shades of the same color and the transparent dyes can be applied over one another, creating solid color gradients. Technologies such as inkjet or color electrophotographic printing rely on dithered images where solid color dots are printed closely together creating a visual appearance of a solid color. The typical 300 dpi printhead then can achieve image quality superior to a 300 dpi resolution from dithered images. There are a wide range of desktop ID card printers and several central issuance printers using direct and retransfer ID card printing technologies. These printers include in-line personalization of magnetic stripes, contactless or contact chips, RFID, etc. A disadvantage of this technology is the supply cost for the multi-panel ribbon. Another limitation is that the dyes need to be protected from degradation that may result from chemical or ultraviolet radiation attack.
2. Resin or Pigment Transfer is another application of thermal transfer printing using heat to deposit resin or pigment on a substrate. Thermally applied resins are more stable than dyes and are much more resistant to fading. Resins can be applied:
a. Direct – printed in monochrome directly to an ID card surface; or,
b. Retransfer – using resins on a 3-4-5 panel ribbon printed to the backside of a clear retransfer ribbon which is then fused to the ID card surface. Specially formulated retransfer ribbons are more receptive to resins than PVC, and can be printed at higher dot resolution. Retransfer can be used to personalize smart cards which may have irregular surfaces.
4. Laser Engraving When polycarbonate molecules are hit by a focused laser beam they change to tiny carbon bubbles. These form a black color, and permanently alter the substrate. By directing a laser beam at an opaque polycarbonate material laminated under the surface of the ID card, it is possible to print or “engrave” high resolution images or typeface below the top surface. Even microfeatures can be introduced. Varying the amount of laser energy enables true gray-scale printing which produces photo quality black and white images. The resulting text or image does not fade and is not subject to deterioration from UV light, moisture or surface abrasion.
A laser beam can also be focused at the outer laminate of the ID card with enough energy to disturb the ID card surface, creating a tactile effect. Unlike the other printing technologies described, there is no ongoing supply items (ribbons, toners, foils or overlay materials) required. There are a limited number of manufacturers of laser engraving personalization systems. These systems can be configured with in-line personalization of magnetic stripes, contactless or contact chips, RFID, etc. The equipment required to produce laser engraved cards or documents is more expensive and technically sophisticated than the other print methods described, making it very difficult to be procured for unauthorized use. This technology has been used in Europe for more than a decade for high security documents.
Laminate or Topcoat Materials
1. Thin Film Topcoats Color thermal transfer ribbons (dye and resin types) typically include a clear topcoat panel which is applied to the entire surface of the ID card once the color printing is complete. The topcoats are designed to prevent dye migration and provide only limited abrasion and chemical resistance. Topcoats are commonly used on corporate employee ID cards where the card is primarily for visual identification. Topcoats can be intentionally removed allowing alteration and/or replacement of printed information.
Thin film security topcoats incorporating optically variable features (e.g. ID card holograms or specialized inks) are also used to provide a level of counterfeit and tamper resistance. The films are only several microns thick and cannot be removed intact, providing a high level of tamper evidence. Combined with a clear topcoat these two layers offer slightly better chemical and abrasion resistance, but can still be removed. This type of security topcoat is used on many ID cards where security threats from tampering or alteration are not significant. They are also used on ID documents such as passports where the surface is not subjected to higher levels of abrasion common to ID cards.
2. UV-Cured Topcoats Ultra-violet cured topcoats are available on all central issuance Datacard® systems and provide a higher level of abrasion and chemical resistance than thin topcoats. The material is applied during personalization and then cured with a UV source. It offers a moderate level of protection for thermally printed images and text. They are commonly used in financial or loyalty cards, but are generally not recommended for ID card applications.
3. Polyester Laminates Polyester laminates are used in roll form and applied as “patches” to the surface of an ID card, or in sheet form to a cut-sheet substrate. In both cases the material is laminated with heat and pressure to the surface of the ID card. Applications for ID documents typically use laminates ranging from 0.0005 – 0.001” ( one-half to 1 mil). These laminates are best for abrasion and chemical resistance, and can incorporate UV blockers to protect against fading. They are extremely flexible, and can significantly extend the useful life of many types of ID documents.
A wide range of security features can be incorporated into the thicker laminates, including optically variable features, security printing, or serial numbers. These laminates are used on many secure government identification cards, providing a high level of counterfeit and tampering deterrence. The strongest level of lamination occurs when combining identical or chemically-linked materials where the laminate and substrate are fused under heat and pressure. Laminating polyester materials to other types of substrates requires specialized adhesives. Because the laminate material is thicker, it may be easier to remove intact leaving the original ID card or document vulnerable to tampering.
Putting It All Together
Defining a secure ID document should be viewed with a systems approach, evaluating how each component interacts or complements the others. Selecting what may be perceived as the “best” of each component category will not necessarily provide the best outcome. Factors such as durability, ability to incorporate security features, price (initial investment and ongoing supplies and maintenance cost), scalability, upgradeability and availability on the open market should be included in determining which components best fit an application. As noted earlier, there will be trade-offs with each choice. Testing the “system” before making a selection and on an ongoing basis will strengthen its reliability and security. Key characteristics should be tested, such as machine readability, durability, resistance to tampering or alteration, for the production of counterfeit ID cards.
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