Security cards are widely used for various applications such as identification purposes (ID cards) and financial transfers (credit cards). Such cards typically consist of a laminated structure consisting of various plastic lamellae and layers wherein one or more of them carry visible information, such as alphanumeric information, logos and a picture of the card holder, and optionally also digital information stored in a magnetic strip or in an electronic chip (so-called smart card).
A principal objective of security cards is that they cannot be easily modified or reproduced in such a way that the modification or reproduction is difficult to distinguish from the original. Such modification usually involves de-laminating one or more plastic lamellae from the card, altering the visible information on the card and re-laminating, i.e. closing again, the card.
The most widely used material for lamellae in plastic cards is PVC (polyvinyl chloride), because of its low cost and its ease of printing and laminating. The biggest disadvantage of a PVC card body is the low durability, resulting in an effective lifetime of only 1-3 years, much lower than the lifetime of the often expensive electronic chips. PC (polycarbonate) can be used for longer-life and more secure ID cards, but has a high production cost and a low resistance to torsion, scratching and chemicals. Other materials occasionally used for security card, like Teslin™ and ABS are only suitable for very low-end or single-use cards.
PET-G (polyethylene terephthalate glycolised) is a kind of amorphous polyester which has not been toughened like crystalline polyester but rather processed to become more compatible with standard PVC card manufacturing. Durability of PET-G cards is comparable to that of PVC cards.
There is growing interest for crystalline polyethylene terephthalate (PET-C) as lamellae, especially as outermost lamellae, in security cards. PET-C is a material that is very durable and resistant to mechanical influences (flexion, torsion, scratches), chemical substances, moisture and temperature ranges. Untreated PET-C cannot be sealed or laminated to itself or to other materials, but requires additional adhesive coatings and layers to accomplish this.
Such adhesive layers have been optimized over the years for PVC, PC and other frequently used card materials. For example, U.S. Pat. No. 3,725,184 (ADDRESSOGRAPH MULTIGRAPH) discloses a laminated article in which a composition containing polyvinyl chloride, polyvinyl acetate and polyvinyl alcohol is interposed between a vinyl skin and the printing on the surface of a vinyl core to improve the adhesion between the skin and the printing ink.
US 2004081839 (TEIJIN DUPONT) discloses a polyester adhesive film readily adhering to an ink-receiving layer, having excellent adhesiveness to the ink-receiving layer, excellent transparency and weatherability. US 2003048343 (ANDERSON ET AL.) discloses a similar process for preparing a laminated ink jet printed image comprising first coating an ink jet image receiving layer onto a clear polyethylene terephthalate base, where after a printed image on the image receiving layer is laminated to a substrate with heat and pressure such that the image bearing layer is in between the substrate and the clear base and is protectively sealed by means of the clear base.
The requirement of an extra ink receiving layer not only adds costs and complexity, but also does not provide a solution for security cards where the ink is printed directly onto the plastic lamella, as e.g. shown by U.S. Pat. No. 3,725,184 (ADDRESSOGRAPH MULTIGRAPH) where lithographic offset inks are printed directly on the vinyl sheet without an ink receiving layer present.
WO 2009/063058 (AGFA GEVAERT) discloses a security laminate comprising at least one biaxially oriented polyester lamella and an adhesion system associated therewith and on at least one side thereof, said adhesion system comprising a layer system comprising a polyester, a polyester-urethane or a copolymer of a chlorinated ethylene. Although these security laminates adhere well to PVC, PC and PETG cards, they lose their adhesive properties when the card surface is printed completely or to a large extent with ink.
Therefore a need exists to provide security laminates based on crystalline polyethylene terephthalate (PET-C) that adhere well to both printed and unprinted PVC, PC and PETG cards without requiring an extra ink receiving layer on the card body.