Security card comprising a thin glass layer

Details Security card comprising a thin glass layer Security card comprising a thin glass layer

1999-04-23

2001-07-31

Evans, Elizabeth (Department: 1772)

Stock material or miscellaneous articles

Composite

Of quartz or glass

C428S432000, C428S433000, C428S913000, C430S270120, C430S495100, C430S945000, C369S283000, C369S288000

Reexamination Certificate

active

06268058

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a security card which is difficult to counterfeit because it comprises a laminated thin glass layer as a security feature.
BACKGROUND OF THE INVENTION
Security cards are widely used for various applications such as identification purposes (ID cards) or financial transfers (credit cards). Such cards typically consist of a laminated structure consisting of various plastic layers wherein one or more layers carry information, e.g. alfanumeric information, logo's, a picture of the card holder, etc. Writable cards wherein the user can store random information are also known, e.g. cards comprising a magnetic strip, optically-recordable cards or cards comprising an electronic chip, sometimes called ‘smart cards’.
A principal objective of such security cards is that it cannot be easily modified or reproduced in such a way that the modification or reproduction is difficult to distinguish from the original. Therefore, security cards are provided with security features which are difficult to modify or reproduce, e.g. a “security seal” between the information layer and a protective sheet bonded to it. Upon an attempt to separate the protective sheet from the information layer, the security seal is destructed or removed so that it becomes clear that the information carried by the card has been tampered with or altered. Such a security seal can e.g. be provided by applying heat-sealable polymers so as to obtain a sealed envelope-type pouch, as described in e.g. U.S. Pat. No. 4,322,461 and references therein.
A problem associated with information recording materials is their susceptibility to mechanical impact which may cause defects such as scratches and may result in a considerable loss of the recorded data. The recordable layer of most of these security cards comprise a plastic foil as protective layer on top of the recording medium. The life-time of such recording materials, which is required to be 10 years for some applications, is insufficient because the plastic foil is not an efficient barrier against solvents, oxygen, moisture and other potential causes of data loss.
Some disclosures mention the use of glass as a base material for making a security card. JP-A 60/214996 describes a laser recording card wherein the base material, which carries the recording layer(s), can be glass. EP-A 272875 also describes an optical recording card wherein glass can be used as a constituting layer. In these patent applications, the glass layer is used as a suitable substrate because of its high transparency so that a light source can be used for writing and reading information. However, the glass layers disclosed therein are non-flexible layers which can easily be broken by accident, e.g. by slight bending during handling or while keeping the card in a wallet.
EP-A 669 205 describes a glass/plastic laminate for use as safety glass in vehicles, said laminate comprising a glass pane, an intermediate adhesive layer and a plastic pane, wherein the glass has a thickness from 30 to 1000 &mgr;m. A functional layer can be applied to the glass which, after lamination, is sandwiched between the glass and the plastic layer and is thereby protected from outside influences. Also U.S. Pat. Nos. 3,471,356 and 4,600,640 disclose thin-glass laminates for use in automotive and architectural applications.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a security card which is difficult to counterfeit and which is well protected against potential causes of information loss such as mechanical impact and permeation of solvents, oxygen, and moisture and which has sufficient flexibility so that it cannot be damaged by bending. This object is realised by the security card defined in claim
1
. Preferred embodiments of the present invention are defined in the dependent claims. Further advantages of the present invention will become clear from the description hereinafter.
DETAILED DESCRIPTION OF THE INVENTION
The security card of the present invention comprises a thin glass layer as a constituting layer. The glass layer offers several advantages. First, the glass layer itself is an efficient security feature. Attempts to counterfeit the card by delaminating the constituting layers causes breakage of the thin glass layer, which is easily detectable and difficult to repair. A second advantage is associated with the excellent barrier properties of the glass, which reduces the permeation of gases and liquids efficiently and which is characterised by a high hardness, thereby preventing damage by scratches and other forms of mechanical damage. As a result, information carrying or recording layers in the card are well protected from the environment and the card has a long life-time. In addition, the thin glass has sufficient flexibility so as to enable substantial bending of the card without damaging the glass layer. Finally, the high specific weight of the glass layer as well as its high transparency allows easy detection of its presence so as to distinguish a security card according to the present invention from a conventional, plastic-based security card or from copies made without such a glass layer.
The thin glass layer is a flexible glass layer. The word “flexible” as used herein shall be understood as meaning “capable of being wound around a core without breaking”. A preferred glass layer used in the card of the present invention is capable of being wound around a cylindrical core having a radius of 1.5 m without breaking. The basic requirements for obtaining flexible glass are a low thickness and a high strength. The lower the thickness of the glass, the higher is its flexibility and thus the lower the minimum radius of the core around which the glass can be wound without breaking. The maximum thickness of the glass layer which allows bending of the card with a low probability of breakage is dependent on several parameters, such as composition and manufacturing method of the glass as well as composition, thickness, number and position of the other constituting layers of the card. In order to obtain sufficient flexibility, the glass layer used in the security card of the present invention has an upper thickness limit of 350 &mgr;m. Above this limit, the probability of glass breakage is too high to allow sufficient bending. For higher flexibility said thickness is preferably not more than 200 &mgr;m and even more preferably not more than 100 &mgr;m. The minimum thickness is preferably at least 30 &mgr;m, more preferably at least 50 &mgr;m because glass having a lower thickness may be too brittle so that bending the card would cause glass breakage. As indicated above, the lower limit of the glass thickness is dependent on the composition and the manufacturing process of the glass layer.
Flexible glass is known in the art. EP-A 716 339 describes a process using a flexible glass web, which can be wound up around a core so as to obtain a roll of glass. Said glass can be unrolled and coated with a functional layer in a continuous web coating method. Said flexible glass is characterised by (i) a thickness lower than 1.2 mm, (ii) a failure stress (under tensile stress) equal to or higher than 1×10
7
Pa and (iii) an elasticity modulus (Young's modulus) equal to or lower than 1×10
11
Pa.
The glass may be e.g. sodium float glass, chemically strengthened glass or borosilicate glass. Such glass can be made by squeezing semi-molten glass between metal rollers to produce a thin web. U.S. Pat. No. 4,388,368 describes the following method to produce flexible glass sheets. A soda lime glass (Na
2
O.CaO.SiO
2
=15:13:72 by weight) molten at 1550° C. is drawn and rolled. The glass thus formed is supported by clips at both ends and heated at about 350° C. Thereafter the glass sheet is stretched to from 1.05 to 10 times the area of the original sheet while blowing a hot blast of air at a temperature lower than the aforesaid heating temperature onto the glass sheet, e.g. about 700° C. In this way, the glass sheet is cooled faster at th

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