SECURITY PAPER

Abstract: A security paper (1) in the form of a laminate comprises at least two laminate layers (2, 3) with at least one paste layer (4) therebetween. At least one of the layers (2, 3, 4) is of a colour which differs from the adjacent layers. The strength of the bonding between the paste layer (4) and adjacent laminate layers (2, 3) is greater than the inner strength of the layers (2, 3, 4). Furthermore, the paste or adhesive in the paste layer (4) is of the curing or setting type.

Description: SECURITY PAPER TECHNICAL FIELD The present invention relates to a security paper for, for example, tickets, in the form of a laminate which comprises at least two laminate layers with at least one paste layer therebetween. BACKGROUND ART The term "security paper" is taken in this patent application to signify a sheet-shaped material, possibly stored in the rolled-up state, on which text and images are intended to be printed or applied, and which is intended to be used for travel tickets, lottery tickets and other securities for short-term use. The sheet-shaped material includes not only paper fibre but also other materials such as, for example, paste, plastic, glass fibre and metal foil. At the same rate as copying techniques have become highly refined and cheaper, and more readily accessible, the risk of competent forgeries of tickets and the like which are difficult to discover has also increased. It has happened that, before a train journey, a traveller purchases a ticket, makes a copy which is shown to the ticket inspector and, at the end of the journey, redeems the original ticket and gets his money back. One problem is that the tickets on board the train are inspected under such circumstances that heavy, bulky and technically advanced inspection devices are practically out of the question. Also at large sports events attracting a large number of spectators, forgeries of tickets have occurred to such an extent that more tickets have been in circulation than the number of places or seats available at the sports stadium. Also under such circumstances, many types of advanced inspection equipment are difficult to employ. There is thus an urgent need in the art to realise tickets which, in a simple manner, can be inspected as to their authenticity. One method of creating the possibilities for inspecting the authenticity of tickets is to print the tickets on a special type of paper, so-called security paper. Such paper may be of varying appearance, such as with water marks, printed text which is only visible in ultraviolet light, microtext which cannot be copied in a standard copier, embedded metal threads or holographic images. Many of these types of security paper are either expensive to produce or difficult to inspect manually without special equipment, or, at worst, both of these. It occurs in the art that two or more layers of paper, metal or plastic are laminated together. By a careful selection of materials and by the procedure in the production process, the properties of the laminate can be controlled. European Patent Application carrying publication number 0 453 131 discloses a security paper which is built up in two layers with a paste layer therebetween. On the inside of one or both of the paper layers, authenticity indicators are printed. The optical properties of the paste between the paper layers is such that the authenticity indicators are practically invisible in reflected light but are visible in transmitted light. It is also possible to design the authenticity indicator such that it can only be discovered with invisible light or with magnetic aids. The disadvantages inherent in a paper type according to this patent application is that it either requires good light conditions in order to discover an authenticity indicator which is visible in transmitted light, or special technical aids for discovering the authenticity indicators which can only be discovered with the aid of magnetism or invisible light. EP 0 491 099- Al shows a security tape which is built up from a plurality of layers of material, viz. a plastic film, two layers of adhesive material and a protective layer which is drawn off when the tape is put into use. The layer of adhesive material which lies most proximal the plastic film adheres best to this film and is, moreover, coloured. Between the plastic film and the coloured adhesive material there is disposed a non-continuous pattern of a translucent barrier material. The coloured adhesive material adheres less well to the barrier material than to the plastic film. The adhesive material which is most proximal the substrate to which the tape is bonded has a strongly adhesive capability. When the tape is torn off from the substrate, a pattern appears since the coloured adhesive material accompanies the plastic film apart from at those places which are provided with the barrier material. The invention is principally intended to create tamper-proof closures or seals which cannot be opened without this becoming apparent. It is also conceivable that the tape is employed for authenticity inspection, for example such that each authentic document is provided with a length of the tape which cannot be moved over to a forgery. A major disadvantage is that an authenticity inspection entails that the authenticity of the tape is inspected in that it is pulled off so that the characteristic pattern appears. This procedure entails that a genuine document would appear as a forgery on a second inspection. After all, during long train journeys, tickets are often inspected more than once. Another drawback inherent in the invention according to EP 0 491 099-Al is that it is difficult, in a rational production process, to provide the plastic film with the barrier layer in a non-continuous pattern. PROBLEM STRUCTURE The present invention has for its object to realise a security paper whose authenticity may simply be verified without access to specific technical aids. The method of production is also cost-effective, but is not available to the general public. SOLUTION The object forming the basis of the present invention is attained if the security paper disclosed by way of introduction is characterized in that at least one paste layer has a colour which differs from the adjacent layers. Further advantages will be attained according to the present invention if the subject matter of the present invention is also given one or more of the characterizing features as set forth in appended subclaims 2 to 4. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings: Fig. 1 is a cross section through a torn security paper according to the present invention, the rupture having taken place in a first manner; Fig. 2 is a view corresponding to that of Fig. 1, the rupture having taken place in a second manner; Fig. 3 is a straight top plan view of the security paper according to Fig. 1, when a corner has been torn off; Fig. 4 is a cross section through the security paper according to a second embodiment; and Fig.5 schematically illustrates the production of a laminate. DESCRIPTION OF PREFERRED EMBODIMENT Fig. 1 shows a security paper 1 according to the present invention. The security paper 1 consists of two laminate layers 2, 3 and a paste layer 4 located therebetween. The thickness of the laminate layers is considerably greater than the thickness of the paste layer. The Figure also shows the rupture surface 5 which occurs when the paper is torn. The interfaces between the layers 2 and 4 and between the layers 3 and 4, respectively have been exposed. This entails that the paper and the torn-off edge will have an appearance which is shown schematically in Fig. 3. In order to realise the desired effect, namely a rupture surface with an appearance according to Fig. 3, where the coloured paste is clearly seen in the rupture surface, the material in both the laminate layers and in the paste layer must be selected with great care. The laminate layers are, for example, plastic, paper or metal of such a thickness and mechanical strength that it is possible to tear up the finished laminate without major difficulty. The finished laminate must, however, withstand a certain normal handling without coming apart. The paste layer suitably consists of a curing or setting adhesive. In many cases, the so-called two can adhesives polyurethane or epoxy glue can be employed. In order to obtain the desired rupture surface, the inner mechanical strength in each respective layer must be balanced against the strength of the joints between the layers. The joint between the paste layer 4 and the laminate layers 2, 3 must be stronger than the inner strength of the layers, so that the coloured paste layer is reliably exposed when the paper 1 is torn. In other words, the strength at right angles to the plane of the paper must be less than the strength of the joint between the paste and the laminate layer. The paste 4 penetrates a slight distance into the laminate layers 2 and 3, on condition that these are more or less porous. In those - normally occurring - cases when at least one of the laminate layers 2, 3 surrounding the paste layer 4 consists of paper, this results in the paper fibres forming a reinforcement in the paste layer. The reinforcement affords increased strength to the joint between paper and paste. In such cases, the laminate layer 2, 3 ruptures at the border between the area which is unaffected by the paste and the area in which the paste has penetrated. This type of rupture is shown in Fig. 1, while Fig. 2 shows an example of a rupture which has taken place in the paste layer rather than in the joints. An important feature in the present invention is that the paste or adhesive 4 is of the curing or setting type, so that, after lamination, it can neither be dissolved nor melted. This is vital to prevent the replacement of any of the laminate layers and by such means make possible a forgery. The lamination of the security paper 1 proceeds in accordance with that technique which is illustrated schematically in Fig. 5. A laminate layer, the so-called noble film 8 is led from the magazine reel 9 through the roller pair 10, 11. The roller 11 is coated in the bath 12 with paste which is applied also to the film 8 when this passes through the roller pair 10, 11. The noble film coated with paste is thereafter led a shorter or longer distance, during which time a certain drying may possibly take place, to the so-called lamination nip between the rollers 13 and 14. In this step, the coated noble film is laminated together with an additional lamination layer 15 which is unwound from the magazine reel 16. After lamination, the laminate 1 has been formed and this is led to the magazine reel 17. A distinctive feature of the paper according to the present invention is that a colour pigment has been admixed into the paste. If a two can adhesive is employed, the colour pigment is suitably admixed into one of the two components which together make up the adhesive. DESCRIPTION OF ALTERNATIVE EMBODIMENTS Fig. 4 shows an alternative embodiment of the present invention. Here, the laminate 1 has been provided with an additional laminate layer 7 which is united with the other laminate layers with the aid of a paste layer 6. The paste layers 4 and 6 may have the same colour, but may also be of different colours in order to give a clearly distinguished rupture surface on being torn. The laminate layers 2, 3, 7 may have mutually identical colours, but also be of colours which differ from one another. In general, the point of interest is that the colours and the thickness of the laminate layers 2, 3, 7 and the paste 4, 6, respectively are selected such that the paste layers 4, 6 do not shine through the outer laminate layers 2, 7. Analogously, it is possible to provide the laminate 1 with additional paste layers and laminate layers. The laminate layers are often paper, but may also be of other materials, such as plastic or metal foil. In certain cases it is also conceivable that one or more of the paste layers consist of a plastic foil which may possibly be coloured. The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the scope of the appended Claims.

Claims: WHAT IS CLAIMED IS: 1. A security paper (1) in the form of a laminate which comprises at least two laminate layers (2, 3, 7) with at least one paste layer (4, 6) therebetween, characterized in that at least one layer (2, 3, 4, 6, 7) is of a colour which differs from the adjacent layers. 2. The security paper (1) as claimed in Claim 1, characterized in that the strength of the bonding between each respective paste layer (4, 6) and the adjacent laminate layers (2, 3, 7) is greater than the inner strength of the layers (2, 3, 4, 6, 7). 3. The security paper (1) as claimed in Claim 1 or 2, characterized in that the paste or adhesive in the paste layer (4, 6) is of the curing or setting type. 4. The security paper (1) as claimed in any of Claims 1 to 3, characterized in that the paste is a single component adhesive in which colour pigment is admixed. 5. The security paper (1) as claimed in any of Claims 1 to 3, characterized in that the paste in the paste layer (4, 6) comprises two components; and that colour pigment is admixed to one of these components. 6. The security paper (1) as claimed in any of Claims 1 to 5, characterized in that the paste is polyurethane- or epoxy-based. 7. The security paper (1) as claimed in any of Claims 1 to 3, characterized in that at least one coloured layer (2, 3, 4, 6, 7) is a plastic- or metal foil.

Inventors: FREDIN STEN-INGE, FREDIN, STEN-INGE
Applicants: FREDIN STEN INGE, SCAND STICK AB, FREDIN, STEN-INGE
Application year: 1999
Main classification: D21H21
IPC codes: B32B29, B42D15, D21H21, D21H27