Patent Publication Number: US-2006016557-A1

Title: Insertion of an elongate element into a fibrous substrate

Description:
This invention is directed to improvements in manufacturing substrates, such as paper, incorporating an elongate element, to a method of and apparatus for making such paper and to documents made therefrom.  
      It is generally known to include elongate security elements in security paper, as a security feature. Such elements can be threads, strips or ribbons of, for example, plastics film, metal foil, metallised plastic, metal wire. These security elements are included in the thickness of security paper to render imitation of documents produced from the paper more difficult. These elements help in the verification of security documents as they render the view of the documents in reflected light different from that in transmitted light. To increase the security provided by the inclusion of such an elongate element, it is also known to endow the element itself with one or more verifiable properties over and above its presence or absence. Such additional properties include magnetic properties, electrical conductivities, the ability to absorb x-rays and fluorescence.  
      As a further security feature, it has been found to be particularly advantageous to provide windows in one side of the surface of the paper, which expose such elongate elements at spaced locations. Examples of methods of manufacturing such paper incorporating security elements with or without windows are described below. It should be noted that references to “windowed thread paper” include windowed paper incorporating any elongate security element.  
      EP-A-0059056 describes a method of manufacture of windowed thread paper on a cylinder mould paper-making machine. The technique involves embossing the cylinder mould cover and bringing an impermeable elongate security element into contact with the raised regions of an embossed mould cover, prior to the contact entry point into a vat of aqueous stock. Where the impermeable security element makes intimate contact with the raised regions of the embossing, no fibre deposition can occur. After the paper is fully formed and couched from the cylinder mould cover, the water is extracted from the wet fibre mat and the paper is passed through a drying process. In the finished paper the contact points are present as exposed regions which ultimately form windows, visible in reflected light, on one side of a security or banknote paper.  
      WO-A-93/08327 describes a method of manufacturing windowed thread paper on a Fourdrinier paper-making machine. A rotating embedment means, with a modified profile for embossing, is used to drive an impermeable elongate security element into draining paper stock, on a Fourdrinier wire. The profile of the embedment means is such that raised portions are provided which remain in contact with the security element during the embedment process. Thus, paper fibres are prevented from collecting between the security element and embedment means, such that the security element is subsequently exposed in windowed regions of paper.  
      It has also become desirous to incorporate electronic chips, such as IC or RFID chips, into substrates, for security and authentication purposes and these provide a highly versatile security feature which is difficult to counterfeit. Some examples of known security substrates incorporating such chips are described below. WO-A-0007151 describes an electronic switching circuit embedded in security paper. A Carrier frequency input signal is transmitted to the switching circuit for checking authenticity and the circuit emits an output signal representing the authenticity feature in response to the received input signal.  
      DE-A-19601358 similarly describes a base substrate incorporating an integrated circuit, which is non-detachably and wholly embedded within the substrate. The circuit can be read without contact by the reading device. The circuit can be read capacitively, inductively or by light.  
      WO-A-0202350 also describes security paper which has a security element which is at least partially exposed on one surface of the paper and which provides at least one visually verifiable optical effect and incorporates an integrated circuit.  
      However, problems arise in the incorporation of such chips in a fibrous substrate, such as paper, due to their bulk. Such chips typically have a height of 40 microns. When this is embedded into security paper, which typically has a thickness of 190 microns, this results in an increase in the thickness in the area of the chips of 20%. This creates a particular problem in that the smoothness of the surface of the security paper is critical for achieving good printing. The lumpiness of paper containing chips makes printing very difficult. It is therefore vital to know where the chips are to avoid printing on or over them.  
      It is therefore an object of the present invention to provide a method of manufacturing substrates, such as paper, incorporating an elongate element, that may be the carrier of security features, chips, decorative features or information and the like, which is registered in the machine direction, apparatus for manufacturing such substrates and substrates made thereby.  
      The invention therefore provides a method of manufacturing a substrate comprising the steps of depositing fibres onto a moving support surface to form a substrate, introducing an elongate element such that it is at least partially embedded in the substrate, monitoring and providing information pertaining to the location of a control feature of the elongate element prior to embedment, monitoring and providing information pertaining to the location of the substrate, controlling the tension of the elongate element as it is introduced into the substrate using the location information to thereby control the rate at which the elongate element is introduced such that the at least one elongate element control feature thereof is in registration with at least one control feature of the substrate.  
      The invention also provides apparatus for manufacturing a substrate comprising a moving support surface, means for depositing fibres onto the support surface to form a substrate, feed apparatus for introducing an elongate element so that it is at least partially embedded in the substrate, at least one sensor for monitoring and providing information pertaining to the location of at least one primary feature of the elongate element prior to embedment, at least one sensor for monitoring and providing information pertaining to the location of the substrate, said feed apparatus comprising means for controlling the tension of the elongate element as it is introduced into the substrate using the location information to control the rate at which the elongate element is introduced such that the at least one primary feature thereof is in registration with at least one control feature of the substrate.  
      In addition, the invention provides a substrate in which an elongate element bearing at least one security feature is at least partially embedded, wherein the at least one control feature is in register with at least one control feature of the substrate. 
    
    
      The invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
       FIG. 1  is a schematic representation of the apparatus used in the method of manufacturing paper according to the present invention; and  
      FIGS.  2  to  4  are schematic representations of alternative combinations of control strategies used in the method of the present invention. 
    
    
      The method of manufacturing a substrate, such as paper, according to the present invention is illustrated with reference to  FIG. 1 . A porous support surface, for example in the form of a cylinder mould cover  10 , is produced in a known way. If the substrate is to have windows, watermarks or apertures, the mould cover  10  may have portions  12  formed by embossing, such as those described in EP-A-0059056, or other drainage limitation means such as electrotype. The portions  12  are spaced around the mould cover  10  and define the shape of the windows  16  or watermarks formed in the final substrate  15 . In this specification the term “window” includes a transparent or translucent region in the substrate of a predefined shape and occurrence.  
      In a known manner, the cylinder mould cover  10  is rotated in a vat  12  of aqueous fibrous stock  11  as illustrated in  FIG. 1 , and fibres are continuously deposited thereon in a known manner to form a fibrous mat, as water drains through the mould cover  10 . The stock  11  may comprise fibres of natural materials, such as cotton, synthetic fibres or a mixture of both. As the cylinder mould cover  10  rotates, a flexible elongate, usually impermeable, element (or thread)  13 , is brought into contact with the cylinder mould cover  10  above or below the level of the stock depending on whether the element is to be wholly embedded or exposed in windows. As the mould cover  10  rotates, the elongate element  13  is introduced into the stock, and is embedded in the fibrous mat as it forms.  
      This mat, which forms the basis of the substrate, is couched from the cylinder mould cover  10  and is transferred to other processing elements of the cylinder mould machine, during which water is removed by pressing and drying over hot cylinders followed by impregnation with sizing agents, drying in an air float dryer, calendering and finally reeling.  
      The method of the present invention differs from the prior art methods in that the elongate element  13  is embedded in the substrate  14  in a manner such that a control feature thereof, which may be a security, decorative or other feature, is registered in the machine direction with respect to a control feature of the substrate, which can be a security feature such as a watermark, or a chop mark which is used to guide the cutting of the substrate into sheets. In the latter case the control feature or the security element  13  will ultimately be registered with respect to the edges of the sheet so that its position can be exactly determined. Other substrate control features can also be used. Control marks may also comprise marks especially added for the purpose of thread registration and, like typical chop marks, this could be an electrotype bar. Where such cutting guides provide the control feature, other surface features subsequently applied to the substrate or sheets or documents made therefrom, will be in register with the elongate element. Such surface features include printed information, holograms, patches or indicia formed from liquid crystal materials, thermochromics, UV, IR or luminescent materials and the like.  
      In order to achieve this, the elongate element  13  must be made of a material which allows it to be stretched by the feed apparatus. The material of the elongate element  13  therefore preferably has a youngs modulus in the range of 0.1 to 10 GPAThe elongate element  13  is provided with at least one control feature which may be, but is not limited to, a decorative feature, a security feature, an information carrying feature or, an electronic chip, such as an IC, RFID, or any other form of electronic chip, mounted thereon. The element  13  may have a feature that is designed purely to facilitate registration by providing the means of detecting the repeat unit of the element  13 . Such a feature may be a printed feature, a demetallised feature, a magnetic feature or some other device which will enable the position of the element  13  to be accurately determined. The element  13  may alternatively, or in addition, have one or more other features as control features, such as metallised or demetallised indicia, holograms, luminescence, magnetic coding, printed indicia, photochromic features, thermochromic features, optically variable features or the like. However, these must not significantly interfere with the ability of the elongate element  13  to be stretched. One material from which the elongate element  13  is preferably made is PET or a laminate including polyester. The thickness of the element  13  is preferably in the range of 12 to 200 microns, and more typically in the range of 30 to 70 microns. The width of the element  13  is preferably in the range of 12 to 200 microns, and more typically in the range of 30 to 70 microns. The width of the element  13  is preferably in the range of 0.5 mm to 6 mm and more preferably in the range of 1 mm to 4 mm.  
      The elongate element  13  is introduced into the substrate  14  under tension. As can be seen from  FIG. 1 a  spool  15 , on which the elongate element  13  is wound, is mounted within the feed apparatus which incorporates a variable braking mechanism to slow the unwinding speed of the spool.  15 , or a variable driving mechanism which is variable to positively increase or decrease the unwinding speed. The feed apparatus is controlled by a control unit  16  to which signals are fed from at least a pair of sensors  17 , 18 . One sensor  17  is positioned so as to monitor the location of the control feature(s) of the substrate  14 . If the substrate control feature is a watermark, then the sensor  17  may be an optical detector. The other sensor  18  monitors the presence of the control feature(s) on the elongate element  13  before it is embedded in the substrate  14 . If the control feature comprises demetallised indicia, then the sensor  18  may be an optical or metal detector. If the control feature is an electronic chip, the sensor  18  may be a chip detector.  
      The signals from the two sensors  17 , 18  are used to control the tension applied to the elongate element  13  as it is fed through the machine. The tension applied can cause the element  13  to stretch, or allow it to remain contracted or relaxed, to precisely determine the positioning of the elongate element  13  relative to the substrate  14 , as it is fed into the fibrous stock, and therefore the location of the elongate element control features thereon to provide the desired registration.  
      In addition to embedding the elongate element  13  within the substrate, so that it is partially exposed in windows; or wholly embedded it may also be embedded in the surface of the substrate, so that it is wholly exposed along one surface thereof.  
      The following examples describe different control strategies all relying on the features described above. In each case the security feature which acts as the control feature of the elongate element  13  has a repeat length which has a single multiple of the control feature of the substrate  14 . This ensures that small adjustments to the tension, and thus the length of the elongate element  13 , enable its control feature position to be kept constant, in a machine direction relative to the substrate control feature. The variation between the following examples is where the control features are measured and how the multiple lines of features  13  are coordinated.  
     EXAMPLE 1  
      Referring to  FIG. 2 , the machine direction position of the elongate element  13  and the substrate control feature position are detected at some point shortly after the forming process. It is preferable, from a control point of view, to make this distance as short as possible, but it may be at any point before the drying section. This signal is passed to the control unit  16  which uses an algorithm to determine whether the element  13  is in a leading or trailing position. The control unit  16  then sends a signal to the driven unwind of the spool  16  causing it to brake more or less in order to correct any error in the element  13  to substrate  14  registration.  
     EXAMPLE 2  
      This strategy is shown in  FIG. 3  and differs from that described in Example 1 in that the position of substrate  14  is determined by a detector  17  monitoring the position of the-cylinder mould cover  10 .  
     EXAMPLE 3  
      This strategy is shown in  FIG. 4  and is also essentially the same as example 1 except that an additional elongate element monitor  18  is placed adjacent to the spool  15  monitoring the element unwind. In the previous embodiments each elongate element  13  is controlled independently. In this third embodiment, one elongate element  13  is used as the datum for several or all the others. The position of the “slave” elements  13  relative to the “master” element  13  is monitored and their position corrected so as to ensure that all elements  13  operating are parallel. The second element detector  18  positioned between the spool  15  and cylinder mould cover  10  will be used for all the elements  13 , whereas the other detectors  17 , 18  would only be used for the master.  
      The combinations described above serve as examples only and do not provide an exhaustive description of alternative detector configurations.  
      An example of a suitable commercially available machine for use in the present invention is the mark-3-B tear tape dispenser supplied by Applied Unwind Technologies B.V. of the Netherlands. This is a driven thread unwind, which only needs minor modification to enable it to be used with the control unit  16  as described above.  
      In most commercial papermaking processes, wide webs of paper are manufactured into which a plurality of elongate elements are fed simultaneously. The present invention can be used for embedding multiple elongate elements  13  either by controlling each feed mechanism individually, or controlling one master with slave mechanisms matched to the action of the master.  
      The method of the present invention can be used with wholly embedded elements  13  or with partially embedded elements  13  in which portions of the element  13  are exposed in windows or apertures at one or both surfaces of the substrate  14 . In the latter case the registration desired may be the registration of indicia on the element  13  with the windows or apertures.  
      As an alternative, indicia on the elongate element  13  may be registered with regard to the anticipated edges of sheets cut from the substrate  14 . This may be achieved by detecting a chop mark, as the control feature, or the like on or in the substrate which will subsequently be printed, the printing being in register with the anticipated edges of the sheets located by the notch. As a result the indicia will be in registration with the print.  
      It should also be noted that the problem of registering security features, including threads, watermarks, and print, applies equally to web printing as well as sheet printing. By using registration control features, possible those used to control the elongate element position, it is possible to ensure that web printed elements, embossings, foils etc, are also applied in register to elongate elements  13  such as threads.  
      The substrate  14  made in the manner described above can be cut and printed to make all forms of documents, including security documents, such as banknotes, cheques, travellers cheques, identity cards, passports, bonds, security labels, stamps, vouchers etc.