Identity document having a chip

The present invention relates to an identity document comprising a support, such as a page or a card, provided with a chip and an antenna, said support comprising a number of layers of plastic material laminated to each other, a first layer of plastic material being provided adjoining one side of said chip, on said first layer a second layer of plastic material is provided on the side away from said chip, an auxiliary layer being provided between said first and second plastic layers extending over a limited part of the extension of said support.

An identity document of this type may be an identity card, a bank card, credit card, driving license or part of a passport. A chip is accommodated therein, inter alia, for holding the personal data which, if required, may be compared to personal data provided in another manner on the identity document, such as a photograph, fingerprint and the like.

It is important that the support can be arranged around the chip in a simple manner. It is also important that such an identity document has sufficient mechanical properties and a sufficiently long service life. In addition, such an identity document has to be simple to produce against limited cost. A further condition which is sometimes set is that it has to be possible to write the plastic material used for the support by means of a laser, i.e. it has to be possible to transform certain parts of the plastic material by means of a laser in such a manner that its appearance changes, for example is colored black as a result of carbonization.

In the prior art, polycarbonate (PC) is often used as the plastic for the support material, while known alternatives include acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC) and polyester (PET).

In particular when using polycarbonate, but also with the other materials mentioned here, it has been observed that deformations occur during cooling subsequent to the application of the plastic material around the chip, which, depending on the technique and plastic used, takes place in the temperature range from 100-200 ⁰ C, resulting in

ripples in the material (deformation of the card) at the position of the chip.

In addition, it has been observed that under certain circumstances cracks may appear in the support material, either immediately during production or at a later stage. These may be small hairline cracks, but these may increase to become larger cracks. Although these imperfections do not have an immediate adverse effect on the cohesion of the card, they render the appearance of the card unattractive, as dirt and the like may accumulate in the former.

EP 1 227435 A2 discloses a chip card in which a metal foil is provided under the battery incorporated therein in order to prevent damage.

US 2005/093172 discloses a reinforcing plate arranged above a chip.

US 6,765,286 describes a system with a chip against which a layer is positioned, followed by a reinforcing layer consisting of metal.

It is the object of the present invention to overcome the problem of "stress cracking".

This object is achieved with an identity document as described above in that said auxiliary layer is made from a thermoplastic elastomer which comprises a material which is rubber-like at room temperature.

It has been found that the crack formation or warping of the identity document at the position of the chip is due to stresses. It is assumed that such stresses occur due to the different shrinking properties of the plastics used for the support and of the chip as a whole. It is assumed that the difference in these cooling properties between the time of production until use may lead to local stresses which may introduce cracks and may cause localized warping of the identity document, such as a card. Such an identity document has to be suitable for use at low temperatures of, depending on the use, between -40 and -25 ⁰ C. The softening temperature is in the range of 100-200 ⁰ C. By providing, according to the invention, an auxiliary layer between the first layer which directly adjoins the chip and the second layer which in turn adjoins the first layer, such

stresses can be minimized. This auxiliary layer preferably consists of a plastic material which can absorb differences in shrinking stresses. Preferably, this auxiliary layer consists of a thermoplastic elastomer and more particularly of a material which is rubber-like at room temperature. In addition, the presence of such an auxiliary layer makes it virtually impossible that any cracks starting in the first layer continue into the second layer. Since such cracks reach the auxiliary layer, local stresses are distributed over the entire surface area of the auxiliary layer as a result of the elastomer/rubber-like nature thereof, thus considerably limiting the risk of the pressure limit being exceeded. As a result, the cracks will not continue into the second layer which is furthest from the chip, so that the support remains sealed with respect to the environment, so that this second layer remains sealed.

According to an advantageous embodiment of the invention, the auxiliary layer has a much larger coefficient of expansion than the plastic material of the support or, as a result of intrinsic, temperature-dependent chemical or physical changes, exhibits a relatively large amount of shrinkage in the relevant temperature range. The shrinkage of the above-described material during cooling from manufacturing temperature to ambient temperature is greater than that of the plastic material of the support. More particularly, this coefficient of expansion is at least twice that of the plastic material of the support and more particularly greater than 1.10 ^"4 1/°C. Examples of such a material are polyurethane grades, rubber grades, such as isoprene and butyl rubber, acrylates, vinyl acetates (EVA) and combinations thereof, as well as epoxy grades. The thickness of the auxiliary layer may be relatively small. It is between 5-30 μm and more particularly between 10-15 μm. The auxiliary layer may be applied in any way imaginable on either the first or the second layer. However, it is preferably applied on the second layer. According to a preferred embodiment of the invention, application is carried out by means of screen printing. Other printing techniques or application techniques, such as on film/foil, are possible. The material used for the screen printing may be solvent-based, such as a water-based system. However, it is also possible to use two-component systems or radiation-curable systems, such as UV/electron beam- curable systems. The first layer preferably has a thickness of approximately 50 μm, whereas the second layer has a total thickness (including an optional further layer) of approximately 200 μm. The second layer is preferably colored and more particularly

white, so that any crack formation in the first layer is not visible.

The above-described warping problem occurs mainly when the chip either has a nonsymmetrical shape or is not positioned symmetrically in the support, i.e. at equal distances from the top and bottom thereof. It has been observed that when such an auxiliary layer is used, the identity document is substantially flat, even at the position of the chip, i.e. the abovementioned symptoms of an elevation from the surface of the support no longer occur. In addition, no crack formation has been observed in the second layer, not even in tests which simulated a relatively long service life of the identity document.

Tests have shown that when polycarbonate is used as the plastic material for the support, the polycarbonate material shrinks approximately 0.8% in the range up to approximately 25 ⁰ C during the production by lamination of a support at a temperature of approximately 185°C. The shrinkage of the actual chip is less than 0.1%. The presence of a chip in the identity card will create a considerable stress in the polycarbonate material around the chip. Polycarbonate has a thermal coefficient of expansion of 7 x 10 ^"5 1/°C. If an auxiliary layer is now used, preferably having an effective coefficient of expansion which is greater than that of the polycarbonate material, in particular greater than 1 x 10 ^"4 IZ ⁰ C, it is possible to compensate for this shrinkage near this chip if the former is suitably thick.

According to a further advantageous embodiment of the invention, an additional auxiliary layer is present. The latter is provided on the side of the chip turned away from the side on which the above-described auxiliary layer is provided. Thus, it is possible to further reinforce the structure. This additional auxiliary layer may be provided directly adjoining the chip or at some distance, subject to the interposition of another layer. The dimensions of this additional layer are preferably at least equal to the dimensions of the chip in situ and preferably greater. More particularly, the dimensions of this additional auxiliary layer are greater than the greatest dimension of the chip. Such an additional auxiliary layer may be made from the same material as described above for the auxiliary layer.

The invention also relates to a method for producing an identity document comprising providing a first continuous plastic layer and a second continuous plastic layer and a third layer provided with an opening, wherein said these layers are laminated together when a chip is accommodated in this opening, an auxiliary layer being provided between this first and second layer.

In particular, the production of the identity document comprises laminating a number of plastic sheets. In this case, one or more plastic sheets may be provided with an opening for arranging the chip therein. Although it is possible to provide a space in the first or second layer for accommodating the auxiliary layer, this has not proved necessary in practice.

In particular, in a first step, this first layer, third layer and additional layer are provided during the accommodation of this chip and the subsequent lamination of these other layers.

The invention will be explained in more detail below with reference to exemplary embodiments illustrated in the drawing, in which:

Fig. 1 diagrammatically shows a perspective view of a first embodiment of an identity document or part thereof;

Fig. 2 shows the various parts from which the identity document according to Fig. 1 is produced;

Fig. 3 shows a detail of this identity document at the position of the chip;

Fig. 4, in a structure corresponding to that from Fig. 2, shows a further embodiment of an identity document; and

Fig. 5 shows a detail of this second embodiment according to Fig. 3.

In Fig. 1, an identity document is denoted by reference numeral 1. This may be any

(bank) card, credit card, driving license or part of a passport, such as a holder page. This consists of a plastic support material 2 on or in which, for example, a photograph 3 of the owner or another biometrical feature and further data of the lawful holder are provided.

In addition, a completely encapsulated chip with antenna 4 is provided. The former contains further data of the holder and can be read remotely.

Fig. 2 shows how such an identity document according to the invention can be produced. Fig. 2 describes this by means of a laminating process. However, it should be understood that it is also possible to use other processes, such as injection-molding, with the present invention.

A layer 5 is provided which is continuous. A subsequent layer 6 having a relatively small opening 7 is present. A layer 8 having a relatively large opening 9 is present while a first layer 18 is provided which is continuous. In this example, polycarbonate sheets are used. First layer 18 adjoins the part of the chip with the largest dimension. Adjoining layer 18, a second layer 13 is provided. At the position of the chip 10, mis second layer 13 is provided with an auxiliary layer 14 consisting of a rubber-like material. The elastomeric auxiliary layer preferably consists of a rubber-like polyurethane layer. The auxiliary layer 14 is applied to the second layer 13 by means of screen printing. The thickness of layer 13 is approximately 100 μm, whereas the thickness of the auxiliary layer is between 10 and 15 μm.

A chip 10 is also present. This chip has a relatively large top part and a slightly smaller bottom part. This is the result of the protrusions of the lead frame and the epoxy encapsulation used.

When the assembly illustrated in Fig. 2 is joined together, it is subsequently possible to fuse the different layers 5, 6, S, 13 and 18 together with a laminating press using heat and pressure, resulting in a single entity which makes it impossible to remove and/or replace the chip 10 without visible damage.

The laminating process results in the assembly illustrated in detail in Fig. 3.

If cooling takes place subsequently and if the entire space between the chip and the plastic material of the card has been filled during the laminating process, thermal stresses will occur due to the difference in thermal coefficient of expansion between the support material 2 and the chip 10. Due to either the asymmetrical shape of the chip or the fact that the chip has not been positioned at equal distances from the top and bottom of the support, these stresses may lead to protuberances, warping and possibly cracking.

By providing an auxiliary layer 14 according to the present invention, these stresses are absorbed to such an extent that warping and/or cracking hardly occur anymore. If, under certain circumstances, such stresses become so great that they exceed the strength of the first layer 18, these stresses will lead to the formation of cracks in layer 18. However, due to the presence of the auxiliary layer 14, such stresses will never be transmitted to the second layer 13 with the same stress concentrations. After all, as a result of the presence of the auxiliary layer 14, any stress peaks which occur inside first layer 18 will be absorbed and distributed over the entire surface area thereof. This is due to the elastomeric properties of the auxiliary layer. This prevents the second layer 13 from being subjected to stresses which are so high that they would lead to crack formation in the latter as well.

The following dimensions of the assembly illustrated here may be mentioned by way of example. The total thickness of the card may be approximately 800 μm. The thickness of layer 5 may be approximately 225 μm. The layer 8 may have a thickness of 100 μm, while the layer 6 has a thickness of 250 μm. The thickness of layer 13 is preferably at least approximately 100 μm, while the first layer 18 has a thickness of approximately 50 μm. It will be understood that the ratio between the thickness of layers 13 and 18 may vary depending on the desired properties.

Figs. 4, 5 show a further variant of the invention. Parts which are similar to those of the previous embodiment are denoted by the same reference numerals increased by 20.

This variant differs from the variant described earlier in that an additional auxiliary

layer 44 is present. In the illustrated example, the latter directly adjoins the chip 30, but it is also readily possible for it to be positioned at a small distance therefrom by the interposition of a layer. This additional auxiliary layer 44 is situated on the side of the chip turned away from the side of the chip on which the auxiliary layer 34 is provided. As can be seen in the figures, the extension of the additional auxiliary layer 44 is greater than the dimensions of the chip in situ and more preferably greater than the dimensions of the chip 30 in general.

This layer 44 is preferably made from the same material as the first auxiliary layer.

Upon reading the above description, the persons skilled in the art will immediately think of variants which are within the scope of the present invention as described in the claims. In this case, not only are exclusive rights expressly sought for claim 1 in combination with the subclaims, but also for the other claims not combined with the independent claims.