EP0059856B1 - Flat card of thermoplastic material with visually readable security marks, and process for manufacturing the same - Google Patents

Abstract

In order to form safety markings at a planar card made of a plastics material, which card may be used, for instance, as credit card, this card is built up from at least two parts. The inner border area between these two parts comprises a relief-like structure which is the carrier of the safety marking. In order to generate a watermark-like effect the upper part is made of a opaque plastic material and the other part is made of a transparent plastics material. When viewing through this card the areas of the opaque layer having the largest thickness appear as darker areas, whereby when viewing the same way the areas having a smaller thickness show a certain brightness. After being embossed the two parts of the thermoplastic material are joined to each other such that they cannot be separated such that no access from the outside is possible to this safety marking. Accordingly, an additional safety factor is arrived at in cards which can be used as money substrate, identification means or a license for any kind of access.

Description

The invention relates to a card made of thermoplastic material with flat surfaces and visually perceptible, internal security signs, and a method for its production.

Recently, printed cards made of plastic have found widespread use as credit, money substrate and identification cards which convey a service, represent a value or contain an access right. The partial information identifying the carrier and the features which assign the card to a specific organization or system are arranged on the card in the form of imprints, embossings, die-cuts or magnetic, laser or holographic information. It is now relatively easy to recreate the appearance of such cards. It is obvious that there is the possibility of misusing such cards, which are increasingly replacing cash transactions, without requiring too much effort. The public in particular has no way of convincing themselves of the authenticity of such a card.

Cards are therefore already known which are designed as composite cards, a paper layer being enclosed between two plastic layers. The paper layer is provided by means of a security print known from the banknotes and, like the banknotes, has a watermark which appears in the review. Furthermore, parts of the plastic surfaces can also be provided with a print pattern.

Although such cards offer increased security, they have several inadmissibilities. As a result of the combination of different materials, such as paper and plastic, experience has shown that the embossing of the finished card causes a deformation. The card is given a curvature in the embossing direction due to the voltage that occurs, which impair the automatic readability of the information mentioned at the outset, provided that it is provided on it. Furthermore, the structure of the known card offers the possibility of unwanted interventions. For example, the card can be separated along the paper layer, which enables manipulation of this paper layer, or the protective plastic layers can be removed using a solvent, so that the paper layer is then exposed.

The same disadvantages have a card known from FR-A-2176463 or OE-PS 311 702, which has a paper insert of locally varying thickness, whereby these thickness variations should be felt and visible as a security feature through a plastic cover layer on the card surface. The uneven outer surfaces are disadvantageous in that machine readability is made more difficult and unevenness on the outer surface caused by unauthorized manipulation of the card is at least not noticeable to the layperson. A flat card surface, on the other hand, allows attempted interventions to be recognized immediately by everyone, since corrugations or roughening etc. are immediately recognizable therein and in turn serves as a reliable security feature.

On the other hand, it is known to provide areas in the interior of plastic cards in which machine-readable information in the form of an optically scannable relief is arranged on a reflecting inner boundary surface. Structures of this type cannot be perceived by the eye due to their small dimensions and because of their structure, which is also expressly sought for security reasons in accordance with DE-A 2659639. Nevertheless, the metallized, inner interface poses a considerable security risk because the resulting inhomogeneity of the material makes it easy to tear the card along the interface.

According to the invention, on the other hand, there is the task of creating a plastic card with security signs which are visually immediately recognizable in the manner of a watermark, which has flat outer surfaces and does not require internal inhomogeneities, so as to exclude or immediately recognize a separation of the card for manipulating the security signs let be.

This object is achieved in that the supporting part of the card consists of two half parts made of thermoplastic material of substantially the same thickness and flat outer surfaces, of which the first consists of transparent, the second made of thermoplastic material with an increased light absorption coefficient compared to the first half part, and each A positive or an oppositely negative relief structure is stamped into the inner surface of each half part, which has at least such height differences and dimensions in the map plane that the differences in brightness produced by the locally varying light absorption of the light passing through in the view are perceptible to the eye, the two Half parts with their embossed inner surfaces are laminated against each other over their entire surface to form a homogeneous piece.

The advantages achieved by the invention can be seen in particular in the fact that the security features are visually recognizable when viewed from the outside, but are inaccessible in that they are covered by a transparent cover card part which is inseparably connected to the card part carrying the features, such that that the features are inaccessible for manipulation from the outside.

• Fig. 1 eine Ansicht eines Kartenteils gemäss einer ersten Ausführung, wie sie sich bei Durchsicht darstellt;
• Fig. 2a eine schematische vergrösserte Schnittansicht entlang der Linie 11-11 in Fig. 1;
• Fig. 2b eine der Fig. 2 entsprechende Ansicht, wobei die einzelnen Teile vor ihrer Vereinigung gezeigt sind, und
• Fig. 3 eine schematische vergrösserte Schnittansicht einer Variante der Ausführung gemäss Fig.1.

The invention is explained in more detail below on the basis of exemplary embodiments by means of the accompanying drawings. Show it:

• Fig. 1 is a view of a card part according to a first embodiment, as in through represents view;
• 2a shows a schematic enlarged sectional view along the line 11-11 in FIG. 1;
• 2b is a view corresponding to FIG. 2, the individual parts being shown before they are combined, and
• 3 shows a schematic enlarged sectional view of a variant of the embodiment according to FIG. 1.

• 1 = I_o·e^-βs

wobei

• '₀: einfallende Lichtintensität
• 1: Lichtintensität nach der Wegstrecke S
• β: Lichtabsorptionskoeffizient

In Fig. 1 a section of a card 1 according to the invention is shown in vertical supervision, one having to imagine a light source behind the card. Two zones, which can merge seamlessly into each other, emerge from the rest of the brightness image. A dark zone 4 and a light zone delimiting it. This corresponds to the appearance of the conventional watermark on paper, which is produced by the concentration of paper fibers at certain points, while fibers are drawn off at surrounding points, which creates the delimiting light zones. The different fiber concentrations lead to a different light transmission, which is the cause of the described effect. In the card according to the invention, which is not supposed to have a paper insert but is constructed entirely from thermoplastic, the aforementioned watermark cannot be produced in the manner described. Rather, as can be seen from FIGS. 2a and b, a card is constructed from two half parts 2, 3. One half part 2 is made of transparent plastic, the other half part 3 made of translucent, cloudy plastic. Such material has an increased light absorption coefficient β, so that the light is noticeably weakened when it passes through a relatively thin layer of, for example, 0.4 mm. One now takes advantage of the fact that the light absorption depends on the distance traveled, according to the law;

• 1 = I _o · e ^-βs

in which

• ' ₀ : incident light intensity
• 1: Light intensity after the distance S
• β: light absorption coefficient

A larger layer thickness therefore leads to greater light absorption. The influence of the transparent half part 2 can be disregarded here, since its light absorption coefficient β is negligibly small in comparison with that of the other layer 3. The half part 3 with an increased light absorption coefficient is now formed in such a way that regions 4 of increased thickness are formed to form a watermark-like effect. In contrast, zones 5 of smaller thickness are formed in adjacent areas 5, so that lighter areas 5 are created when looking around the dark-appearing areas, as is characteristic of the appearance of conventional watermarks. In Fig. 2b this is indicated schematically by arrows, which on the one hand represent the uniformly incident light and on the other hand the light passing through, the thickness of the arrows corresponding to the light intensity. The relief in the half part 3 is embossed in such a way that the total amount of material remains constant and there is only a shift in the amount of material from the areas 5 to the areas 4. This means that the average thickness over the areas 4 and 5 provided with a relief structure is equal to the thickness of the rest of the map. The molding is carried out with a stamping die of known type. The transparent half part 2 is provided with a corresponding, opposing stamping, the stamping mold used for this being preferably electrolytically molded from the first stamping mold. The two half parts are then inseparably formed into a single part by laminating. Polymerization of the plastic molecules takes place along the interface of the two half parts provided with the relief structure, so that a molecular connection is formed which makes separation impossible. It goes without saying that graphic patterns can also be printed on the inner interfaces, if this is desired. This will be discussed in more detail in connection with other exemplary embodiments. The surfaces of the card 1 thus formed are flat and can be printed or coated in a conventional manner. The characteristic mark is completely inaccessible in the card. In the normal case, this indicator is not recognizable in the supervision, since the differences in thickness cannot be perceived in supervision alone. This makes it difficult to imitate this characteristic by corresponding deceptive color printing, as is attempted with conventional watermarks on paper, where, as is well known, a small color contrast can also be seen in the top view.

In Fig. 3, an advantageous embodiment of the principle explained is enlarged and shown schematically in section. To do this, the raster technique is used to build up the relief-like structure of the interface. In areas 4, which should appear darker when viewed, the height h _{4 of} the individual punctiform grid elements 7 is chosen to be greater than the height h _{6 of} the grid elements in the main area of the map. In contrast, in adjacent areas 5 their height h _{5 is} chosen to be smaller. The thickness of the half part 3, averaged over the individual areas, is decisive for the light transmission if the individual halftone dots are no longer or only poorly resolved visually. These averaged thicknesses are chosen so that the effect already explained with reference to FIGS. 1 and 2 can be seen in the review. Again, there is only a material shift from the light areas 5 to the dark area during the embossing che 4 instead. The design of the relief as a grid allows this material rearrangement in a simple manner and also increases the interface along which the two half parts are joined, so that the one-piece map composed of the two half parts is held together even better. The transparent half part 2 is in turn designed to be opposite.

It goes without saying that the flat surfaces of plastic cards formed in this way can be printed in the known manner.

The arrangement described with a relief-like interface between two parts of the card, which are inseparably connected, results, as shown above, in many advantageous ways of visually securing cards of this type, which were not previously available. Absolutely flat surfaces are preserved. Embossments in the card do not lead to a curvature, as was the case with the previously known composite cards. The security features are inaccessible to manipulation.

A particularly advantageous application of the see-through marking by means of the relief-like design of the interface of the part 3 and the transparent part 2 according to FIGS. 1 to 3 is that the relief structure is formed in each case according to the portrait of the card owner. This portrait appears in watermark-like form when viewed and can be compared at any time with a photograph of the owner or himself. This enables an additional, individual identifier to be created. This is possible in particular because the relief-like structure of the interface can have continuously merging areas of different thicknesses, which - in contrast to conventional watermarks, which are usually designed in two stages - result in an image with continuous brightness variation between a maximum and a minimum .

Claims (5)

1. Card made of thermoplastic resin having planar surfaces and visually recognizable, internal safety markings, characterized in that the carrying portion of said card consists of two halves of thermoplastic resin having substantially the same thickness and planar outer surfaces, a first one of said halves (2) being made of transparent thermoplastic resin and a second one of said halves (3) being made of thermoplastic resin having a higher light absorbing coefficient than said first half and in that into the inner surfaces of said halves a positive and a corresponding negative relief structure (4, 5, 6), respectively is embossed, said relief structure having at least such differences of height and such extensions in the plane of the card that the variations in brightness caused by the locally varying light absorption of the transmitted light are visually recognizable when viewing through the card, wherein said halves are laminated with said embossed surfaces facing each other over their whole surface to form a homogeneous body.

2. Card made of thermoplastic resin of claim 1, characterized in that said halves comprise unem- bossed inner surface areas as a reference level, relative to which the relief structure consists of elevated and recessed zones, such that an elevated zone always is laterally adjacent to a recessed zone.

3. Card of the claims 1 and 2, characterized in that the relief structure has zones of various thickness which flow smoothly into each other.

4. Card of one of the claims 1 to 3, characterized in that at least one area of the relief structure of the inner surface comprises a screen raster- like shape (7, 9, 11).

5. Method of manufacturing the planar card of claim 2 wherein by means of an embossing mold a one-sided relief is embossed into a first section of a thermoplastic sheet and by means of a second, correspondingly complementary formed embossing mold a one-sided complementary shaped relief is embossed into a second section of the thermoplastic sheet, and wherein said two sheet sections are inseparably joined together, characterized in that in the embossing mold elevated zones are adjacent to recessed zones such that the embossing is carried out by displacing the thermoplastic sheet material from recessed zones relative to a reference level to adjacent elevated zones relative to said reference level, wherein the mean thickness of the sheet remains unchanged.

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