Security document with functional watermark and manufacturing method thereof

Abstract

A security document (660) includes a fibrous substrate (705) including a functional watermark (710a) including a defined fiber density changing region (715, 720) relative to a body portion (705) of the fibrous substrate, where the functional watermark includes a first edge (735) that at least partially defines a shape of the defined fiber density changing region. The security document further includes a surface application security device (600, 1005) covering at least a portion of the defined fiber density change region relative to the body portion.

Description

Technical Field

[0001] The present disclosure relates to enhancing the anti-counterfeiting properties of security documents such as banknotes, passports, and other documents that include surface-applied micro-optical security devices. More specifically, the present disclosure relates to a security document having one or more functional watermarks and a method of producing the same. Background Art

[0002] Manufacturing structural features that include anti-counterfeiting authenticity markings on passports, banknotes, and other documents (referred to herein as "security documents") that are difficult to replicate remains a source of ongoing technical challenges and opportunities for improvement in the field of security document design.

[0003] Challenges associated with manufacturing security documents of the quality desired by, for example, central banks and passport offices include coordinating the need for rapid, high-speed manufacturing with consistency and high-quality control. In other words, any manufacturing or quality control issues with legitimate security documents provide cover for malicious actors to pass off imperfect copies as genuine documents. Accordingly, the security of a security document depends at least in part on newly issued legitimate documents being as uniform and defect-free as possible. Summary of the Invention

[0004] The present disclosure illustrates embodiments of a security document having a functional watermark and a method of making the same.

[0005] In a first embodiment, a security document includes a fibrous substrate. The fibrous substrate includes a functional watermark. The functional watermark includes a defined fiber density change region relative to a body portion of the fibrous substrate, wherein the functional watermark includes a first edge that at least partially defines or determines the shape of the defined fiber density change region. The security document further includes a surface-applied security device that covers at least a portion of the defined fiber density change region relative to the body portion.

[0006] In a second embodiment, a method of making a security document includes: forming an initial fibrous web from a wet fibrous slurry; changing the fiber density of the initial fibrous web in one or more defined regions to define one or more functional watermarks; pressing and drying the initial fibrous web to form a fibrous substrate including a body portion and the one or more functional watermarks, wherein the one or more functional watermarks include at least one of a light element or a dark element, the light element or the dark element having at least one edge that defines a fiber density change region; and applying a surface-applied security device that covers at least a portion of the one or more functional watermarks.

[0007] Other technical features will be readily apparent to those skilled in the art from the following drawings, description, and claims.

[0008] Before presenting the following detailed embodiments, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term "coupled" and its derivatives refer to any direct or indirect communication between two or more elements, regardless of whether those elements are in physical contact with each other. The terms "comprises" and "comprising" and their derivatives mean including without limitation. The term "or" is inclusive and means and / or. The phrase "associated with" and its derivatives mean including, being included within, interconnecting with, containing, being contained within, connected to or connecting with, coupled to or coupling with, capable of communicating with, cooperating with, interlacing, juxtaposing, adjacent to, bound to or binding with, having, having the property of, having a relationship with, and so on. When used with a list of items, the phrase "at least one of" means that different combinations of one or more of the listed items may be used, and only one item from the list may be required. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

[0009] Throughout this patent document, definitions of some other words and phrases are provided. Those of ordinary skill in the art should understand that in many, if not most, instances, such definitions apply to both the prior and future use of the words and phrases so defined. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] To more fully understand the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

[0011] Figures 1A to 1E Examples of staple mark defects on an uncut sheet of a security document and the areas where they occur are illustrated;

[0012] Figure 2 Examples of functional edge watermarks as observed on a partial sheet of an uncut security document according to the present disclosure are illustrated;

[0013] Figure 3A and Figure 3B Examples of functional edge watermarks according to the present disclosure are illustrated;

[0014] Figure 4 Examples of an exemplary method for producing a security document with a functional edge watermark from an uncut sheet of a stack of security documents according to the present disclosure are illustrated;

[0015] Figure 5 Examples of security documents according to the present disclosure are illustrated;

[0016] Figure 6Illustrates an example of a security feature according to the present disclosure;

[0017] Figure 7 Illustrates an example of an uncut section of a fiber substrate including multiple functional watermarks according to the present disclosure;

[0018] Figure 8 Illustrates six examples of functional watermark patterns relative to multiple peel vectors according to the present disclosure;

[0019] Figure 9A and Figure 9B Illustrates an example acquisition test of a security document including a functional watermark according to the present disclosure;

[0020] Figure 10 Illustrates an example acquisition test of a security document including a functional watermark according to the present disclosure;

[0021] Figure 11 Illustrates an example acquisition test of a security document including a functional watermark according to the present disclosure; and

[0022] Figure 12 Illustrates an example method for generating a security document including one or more functional watermarks according to the present disclosure. Detailed Description

[0023] The following discussion Figures 1A to 12 and the various embodiments used to describe the principles of the present disclosure are for illustrative purposes only and should not be construed in any way as limiting the scope of the present disclosure. Those skilled in the art should understand that the principles of the present disclosure can be implemented in any suitably arranged security document.

[0024] Although the present disclosure has been described through various embodiments, various changes and modifications can be suggested to those skilled in the art. The present disclosure is intended to cover such changes and modifications that fall within the scope of the claims.

[0025] As described above, manufacturing structural features including difficult-to-replicate document anti-counterfeiting authenticity marks for passports, banknotes, and other documents (referred to herein as "security documents") remains a source of ongoing technical challenges and opportunities for improvement in the field of security document design.

[0026] Challenges associated with manufacturing security documents of the quality desired by, for example, central banks and passport offices include coordinating the need for fast, high-speed manufacturing with consistency and high-quality control. In other words, any manufacturing or quality control issues with legitimate security documents provide cover for malicious actors to pass off imperfect copies as genuine documents. Therefore, the security of a security document depends at least in part on newly issued legitimate documents being as uniform and defect-free as possible.

[0027] Manufacturing challenges associated with making defect-free security documents on a large scale and quickly include, but are not limited to, minimizing the incidence of so-called "nail mark defects". Many security documents (including banknotes) are manufactured at least in part using a roll-to-roll process to produce uncut sheets with multiple security documents on the sheet (e.g., uncut sheets of 4, 8, 16, or 50 banknotes sold by the United States Mint). In operations that produce security documents by size and scale, the uncut sheets are assembled into stacks of a predetermined size (also known as "webs"), and are cut using a pressure-driven cutter-like blade that simultaneously compresses and cuts the stacked documents along one or more predetermined cutting lines.

[0028] The applied security features (e.g., surface-applied or embedded strips of micro-optical materials) often cross the cutting lines along which individual security documents are cut from the larger sheet. In addition, the applied security features are often made of polyethylene-binding resin materials, whose compressibility and deformation properties are significantly different from the paper or fiber substrates to which they are attached. Thus, when the leading edge of the cutting tool travels along the cutting line of the uncut security document web and reaches the point where the security feature crosses the cutting line, the relative incompressibility of the overlapping security features in the stack creates local discontinuities and variations in the cutting force required to expand the cut through the less compressible security feature. The local discontinuity in the material properties of the stack being cut in the area around the security feature results in what is known in the industry as a "nail mark defect", which typically manifests as wrinkling and deformation of the paper substrate and the security feature at the cut edge of the security document. This effect doubles as the number of uncut sheets in the web increases.

[0029] Although the incidence of "nail mark defects" can be slightly reduced by increasing the replacement and resharpening of the cutting blades or by putting fewer uncut sheets into the stack to be cut, both of these methods come at the cost of increased maintenance and reduced production volume, and are thus not ideal for large enterprises such as national banks that must print very large quantities of security documents.

[0030] Therefore, optimizing security documents for defect-free batch cutting, especially in the area where the applied security features intersect the cut edge of the security document, has also become a source of technical challenges and opportunities for improvement in the field.

[0031] Additionally, challenges associated with manufacturing security documents include, but are not limited to, strengthening such documents to prevent "lifting", which refers to the process by which malicious actors disassemble a genuine security document in order to completely remove hard-to-replicate components of the security document, which provides a mechanism by which malicious actors can obtain materials to produce counterfeit security documents. If the hard-to-replicate components of a security document are removed substantially intact, such components, such as optical security devices (e.g., security strips and patches) or portions of a fibrous substrate that support optical security devices, can be used, for example, to produce upgraded counterfeits. As an example, security threads from lower-denomination banknotes can be incorporated into counterfeits or multiple counterfeits of higher-denomination banknotes (e.g., by using fragments of the embedded security threads from genuine banknotes to produce two or more counterfeit notes). Although counterfeit security documents produced from lifted components can generally be identified by central banks and security document professionals, to the extent that such counterfeits provide visible authenticity markings that substantially match those of genuine documents, such counterfeits have an acceptable quality for malicious actors because they can be easily passed off as genuine security documents by everyday users.

[0032] As printing and scanning technologies that produce "good enough" or "street quality" replicas of printed features on the paper substrate of security documents become increasingly commoditized and accessible to the general public, "lifting" of micro-optical security features has become a source of particular concern. Criminals and malicious actors are resourceful and have developed various techniques for removing security features from security documents. Such techniques include: "wet lifting", in which the security document is soaked in a solvent (e.g., water or alcohol) to weaken the adhesive bond between the security feature and the substrate; and "dry lifting", in which, instead of soaking the document, malicious actors attempt to carefully peel off surface-mounted security features (such as security threads). Given the resourcefulness of malicious actors and the improvement of imaging technology, strengthening security documents to prevent dry lifting and wet lifting by making it difficult to obtain security features substantially intact (and thus suitable for use in counterfeits) remains a source of technical challenges and opportunities for improvement in the art.

[0033] Figures 1A to 1D A non-limiting example illustrates a document defect called a "pinhole defect" that occurs when security documents are cut in batches. Figure 1E Illustrates aspects of an uncut sheet of a security document that produces Figures 1A to 1D the "pinhole defect" shown. For ease of cross-reference, Figures 1A to 1E common elements are numbered in a similar fashion.

[0034] Refer to Figure 1AAn exemplary example showing a portion of the security document 100 (in this case, a circulating banknote), while Figure 1B and Figure 1C provide a more detailed view of the nail mark defect visible in Figure 1A . Figures 1A to 1D is a photograph of a security document produced in high volume production, where a strip of one hundred uncut security document sheets has been cut using an industrial paper cutter. Industrial paper cutters and die cutters suitable for cutting security document strips typically apply a cutting force between 150 and 650 deca - newtons ("daN"). The security document 100 includes a fibrous substrate 105 which, in this example, comprises a linen - cotton fiber blend with colored fibers dispersed therein, having a weight and thickness similar to the fibrous substrate used for United States banknotes. The security document 100 also includes intaglio printing features 110 and surface - applied security features 115 (security features constructed similar to the optical security device 600 in Figure 6 ). In this example, the surface - applied security feature 115 includes a strip of transparent optical spacer material having a resin lens layer on one side of the optical spacer, and a resin icon layer disposed on the opposite side of the micro - optical spacer. As shown, the surface - applied security feature 115 and the fibrous substrate 105 have been cut together such that the edge 117 of the surface - applied security feature 115 co - extends with the edge of the security document 100.

[0035] In this example, there is no functional edge watermark where the surface - applied security feature 115 terminates at the edge 117. Thus, during the process of cutting the security document 100 from a sheet in the uncut sheet strip (e.g., the uncut sheet 150 in Figure 1E ), when the cutting line reaches the stacked micro - optical security devices in the strip, the paper cutter blade experiences a local maximum of resistance from the document strip. This sudden discontinuity in the resistance of the uncut sheet strip to the cutting tool produces a wrinkling or deformation effect known as a "nail mark defect", where the non - compressible / non - deformable material near the edge 117 bends over an internal die formed by the stacked micro - optical security devices in the strip. As the number of sheets in the strip increases, the effective size of this internal die also increases, and in particular among the documents near the top (i.e., closer to the side of the strip that first contacts the paper cutter), the edge effect becomes more significant.

[0036] Figure 1B provides a detailed view of the "nail mark defect" deformation of the security document 100 located along the edge 117 at the top of the security document in Figure 1A . The fibrous substrate 105 and the surface - applied security feature 115 are visibly squeezed or wrinkled, resulting in a wrinkled area that spans the edge 117 of the security document 100 and extends beyond that edge. Additionally,Figure 1B The nail mark defect will create a depression at the edge 117, which reduces or destroys the flatness of the security document 100, thereby adversely affecting the appearance of the security document and hindering the ability to stack and bundle batches of security documents for transportation and storage. In addition to the difficulty in maintaining an orderly stack, the lack of flatness of the security document 100 also causes jamming problems during the processing of multiple security documents via a high-speed banknote handling machine, or adversely affects the acceptance of the security document by an automated banknote handling machine (such as an ATM or a payment station).

[0037] Reference Figure 1C In the example of, the deformation of the security document 100 due to the "nail mark defect" described above is visible in the corrugations along the line 119, where the substrate and the surface-applied security feature 115 have been wrinkled inward. As Figure 1C Visible, the edge 117 is distorted near the area of the surface-applied security feature 115, thereby hindering the generation of a sharp straight edge across the entire security document 100.

[0038] Figure 1D Views of the opposite sides of the security document 100 and the same security documents 101 and 103 are provided. The defects of the security documents 100, 101, and 103 are more visually obvious, with the iconic "nail mark defect" effect associated with the deformation of the banknote during cutting. The nail mark defect 197 is clearly visible at the upper edge of the security document 100, and the associated nail mark defects 198 and 199 are also clearly visible at the upper edges of the security documents 101 and 103.

[0039] Figure 1E Illustrates an example of an uncut sheet 150 of a security document to show the possible occurrence of the "nail mark defect" with reference to the present disclosure Figures 1A to 1D described, and the area of the nail mark defect can be mitigated by using a functional edge watermark according to the present disclosure. Reference Figure 1E In the illustrative example of, an uncut sheet of a security document (e.g., a banknote, such as the security document 100) is shown in the figure. As shown, the uncut sheet 150 includes an area 151 that has been printed with a repeating pattern (represented by gray shading), and (in this example) five strips of surface-applied security feature material 153A-E have been applied to this area. To form individual security documents (e.g., the security document 100), the uncut sheet 150 is included in a strip of the same uncut sheet (usually but not necessarily including 100 uncut sheets), and then these uncut sheets are cut using an industrial paper cutter along the cutting lines shown as solid black lines in the figure (e.g., the cutting line 157). As discussed elsewhere in the present disclosure, the "nail mark defect" (e.g. Figure 1DThe nail mark defects (197 - 199) in [ ] typically occur in the intersection area where the cutting line intersects with the in - compressible applied security feature (e.g., area 159). However, by providing one or more functional edge watermarks according to the present disclosure in such intersection areas, the tendency to form nail mark defects in such intersection areas can be reduced or curbed.

[0040] Figure 2 Illustrates a partial view of an uncut sheet of the security document as shown, in transmitted light. The uncut sheet includes an exemplary functional edge watermark, which may also be referred to as a bright - on - paper element, for eliminating the occurrence of nail mark defects during batch cutting (i.e., by cutting a stack or web of uncut sheets with a paper cutter) when the functional edge watermark is aligned under a security feature such as a micro - optical line.

[0041] As Figure 2 observed in [ ], the uncut sheet 250 includes a plurality of printed banknote security documents as example security documents 200. In some embodiments, the security document 200 consists of a fibrous substrate 201 (e.g., a paper rich in linen or cotton fibers), which includes: a body portion 203 where the fiber density of the fibrous substrate does not change locally (e.g., due to watermarking); and at least one functional edge watermark 209. In Figure 2 the example of [ ], each functional edge watermark 209 (represented as a white rectangle) is registered or aligned under the security feature 215 and at each cutting line 257. The functional edge watermark 209 consists of areas where the fiber density changes locally, where the fibrous substrate 201 constituting the watermark has a lower fiber content than the surrounding fibrous substrate characterized by the body portion 203. Notably, the lower fiber content of the functional edge watermark 209 reduces the caliper of the substrate at the intersection area of the uncut sheet 250 (such as Figure 1E the intersection area indicated in area 159 of [ ]). In some embodiments of the present disclosure, positioning the functional edge watermark under the security feature and within its perimeter reduces the thickness of the fibrous substrate while allowing the security feature to increase the support for the reduced - fiber area of the functional edge watermark, and also improves the anti - acquisition property of the security feature.

[0042] Figure 3A and Figure 3B Illustrate two examples of functional edge watermarks according to the present disclosure. For consistency and ease of cross - reference, Figure 3A and Figure 3B the common shading in both [ ] indicates that the shading convention and item numbers are shown to be the same in both figures.

[0043] Reference Figure 3ANon-limiting examples are shown in the figure, which depicts a section of the first uncut sheet 300 of a security document (e.g., the uncut sheet 150 in Figure 1E ). In various embodiments, the first uncut sheet 300 includes a fibrous substrate 301, which includes a body portion 303 (shown in white in the figure). In some embodiments, the thickness of the body portion 303 is 120 microns, but thicker or thinner embodiments are also possible and within the scope of this disclosure. As Figure 3A shown, the first uncut sheet 300 also includes a surface-applied security device 307 (e.g., the optical security device 600 in Figure 6 ). In this example, the applied security device 307 is formed as a multi-layer stack of a photocurable resin and a transparent film (e.g., a polyester film or BOPP), and it has a width of approximately 12 mm and a thickness between 35 and 50 microns. However, wider, narrower, thicker, and thinner examples of the surface-applied security device 307 are also possible and within the scope of this disclosure.

[0044] As Figure 3A shown, the first uncut sheet 300 also includes a functional edge watermark 309. In various embodiments, the unique features of the functional edge watermark 309 include one or more of the following:

[0045] a. The functional edge watermark 309 includes a bright region (shown as medium gray in the figure) that spans at least one cutting line 311, along which individual security documents (e.g., the security document 200 in Figure 2 ) are formed from the first uncut sheet 300. In some embodiments, the bright region of the functional edge watermark 309 is formed using an electrotype watermark tool (e.g., an electrotype tool such as that described in U.S. Patent No. 10,794,005). In certain embodiments, the bright region of the functional edge watermark 309 is formed using a wire mesh watermark tool (also such as the wire mesh watermark tool described in U.S. Patent No. 10,794,005).

[0046] b. The functional edge watermark 309 always occupies at least half of the width of the surface-applied security device 307 (shown as w in the figure) along the cutting line 311. In some embodiments, this criterion can be met by increasing the registration accuracy of the applied functional edge watermark 309 or increasing one or more of the widths w as needed.

[0047] c. In some embodiments, the height of the functional watermark 309 (in Figure 3Ashown as h) at least equal to the vertical registration accuracy of the tool for providing the functional edge watermark 309 (e.g., if the center of the functional edge watermark 309 can only be aligned with the cutting line 311 with a deviation within 2 mm, the height of the functional watermark is 2 mm). In some embodiments, the height of the functional watermark 309 is at least 1.25 times the vertical registration accuracy of the watermark tool. In various embodiments, the height of the functional watermark 309 is at least equal to 1.5 times the vertical registration accuracy of the watermark tool. In some embodiments, the height of the functional watermark 309 is equal to or greater than 1.5 times the vertical registration accuracy of the watermark tool.

[0048] Figure 3B illustrates additional examples of functional edge watermark 359 in accordance with the present disclosure. Referring Figure 3B to the non-limiting example of, the functional edge watermark 359 is disposed on a section of the uncut sheet 350 that includes a compressible fibrous substrate 301, a body portion 303, a surface-applied security device 307, and a cutting line 311, as described in reference Figure 3A Although some embodiments of the present disclosure propose that, in order to mitigate nail mark defects, the fiber density can be reduced by using a functional edge watermark including a bright region as described in reference Figure 3A to increase the compressibility of the uncut sheet below the surface-applied security device 307, this does not mean that the embodiments of the functional edge watermark of the present disclosure for mitigating nail mark defects cannot also include dark regions (i.e., regions of increased fiber density). If the functional edge watermark sufficiently reduces the change in deformation that occurs between the body portion 303 and the region where the surface-applied security device 307 intersects the cutting line 311 during cutting of the uncut sheet 350, the functional edge watermark 359 may include one or more dark regions 361A and 361B of increased fiber density. However, in some embodiments, the functional edge watermark 359 defines a region where the average fiber density is sufficiently reduced relative to the body portion 303 to counteract the local variations due to the deformability of the uncut sheet 350. In various embodiments, the total area of the one or more dark regions 361A and 361B is less than the area of the bright region 363. In some embodiments, the one or more dark regions 361A and 361B are substantially parallel to the cutting line 311. In some embodiments, the one or more dark regions 361A and 361B are close to or intersect the cutting line 311. Additionally, in some embodiments, the one or more dark regions 361A and 361B are not disposed below the center of the surface-applied security device 307 (or substantially between the edges of the surface-applied security device).

[0049] Figure 4 illustrates an example method 400 for producing a security document without nail mark defects in accordance with the present disclosure. Although referenceFigure 4 The steps described are described in sequence, but the order of the steps may be reversed, the steps may occur simultaneously or nearly simultaneously, and additional steps may be added.

[0050] Reference Figure 4 In the illustrative example of [[ID=]], at step 405, one or more functional watermarks are formed on the fibrous substrate. In various embodiments, the fibrous substrate includes a sheet of cellulosic material, such as paper made from wood, linen, and / or cotton fibers. The functional watermark includes a light region or “bright” region having a fiber density lower than the baseline fiber density of the body portion of the fibrous substrate (i.e., the non-watermarked portion). In certain embodiments, the functional watermark may also include some dark elements, but the net effect of the functional watermark is to reduce the average local fiber density in the region of the functional watermark relative to the fiber density of the body portion of the fibrous substrate. In this way, local variations in deformability resulting from the addition of a surface-applied security device are alleviated, and the body portion and the functional watermark region exhibit similar overall deformation properties and are cut in a manner substantially similar to a sheet of uniform material.

[0051] As Figure 4 shown, at step 410, a security feature (e.g., a strip of micro-optical lines, such as Figure 6 the optical security device 600 in [[ID=]]) is applied to the fibrous web to form an uncut sheet of the security document. In some embodiments, the security feature is applied while the fibrous substrate is still formed from wet fibrous slurry. In an embodiment, the security feature may be applied to a fully dry fibrous substrate, thereby minimizing the likelihood of unpredictably altering the fiber density near the fibrous substrate due to the application of the security feature.

[0052] In various embodiments, at step 415, a stack of uncut sheets of security documents formed in accordance with various embodiments of the present disclosure are stacked together to form a strip of uncut sheets. In certain embodiments, the strip of uncut sheets includes 100 uncut sheets, and the sheets are identically oriented in the stack such that the applied security features are aligned along a line perpendicular to the face of the strip (i.e., the flat upper surface where the cutting tool initially contacts the strip).

[0053] In some embodiments, at step 420, the uncut sheet is then cut along one or more cutting lines using an industrial paper cutter or die cutter, the cutting lines traversing the applied security feature at locations where the applied security feature at least partially covers the functional watermark. In some embodiments, the compressive force applied during cutting of the uncut sheet is between 150 and 600 dekanewtons (“daN”) and no nail mark defects are produced in the cut security document, due to the functional watermark counteracting local variations in the deformability of the stack of documents in the band due to the presence of the applied security feature. As described elsewhere in the present disclosure, the functional watermark helps to homogenize the cutting properties of each sheet in the stack along the entire length of the cutting line.

[0054] Figure 5 An example of a security document in accordance with the present disclosure is illustrated. One of the operating premises for obtaining the operation of a security device from a genuine security document is that the security feature needs to be separated from the substrate of the genuine document in a substantially intact state suitable for reuse in a forged document. Another operating premise is that the new security device and security document are completely uniform in appearance, without any obvious defects or variations due to manufacturing problems.

[0055] Where possible, a forger will also attempt to retain the substrate from which the security device was obtained. In other words, a visibly damaged security feature and substrate cannot be used for reuse in forgery. Additionally, imperfect originals also introduce uncertainty as to the critical question of whether differences between documents are marks of forgery. As discussed in more detail herein, some embodiments of the present disclosure minimize the likelihood of the surface-applied security feature being obtained, and in particular, obtained undamaged by dry methods. More specifically, some embodiments of the present disclosure increase the likelihood of the thin multi-layer security feature being damaged in response to mechanical acquisition (i.e., attempting to mechanically break the security feature-substrate bond, rather than performing thermal or chemical acquisition where the security feature-substrate bond is eroded by heat or solvent), by using variations in the fiber density in the watermark region to create a pronounced discontinuity in the local forces when the security feature is obtained along the separation line.

[0056] Since many security features are made of thin materials (e.g., with a total thickness between 50 and 150 micrometers) having an array of microscale features (e.g., lenses or icon structures), obtaining and in particular dry obtaining of security features is a delicate operation that generally requires a relatively constant peeling force to be applied stably. As used in this disclosure, the term "peeling force" refers to the force applied to a security feature that has a first component parallel to the substrate (i.e., a "tensile force" that generates tension in the security feature and causes the separation line between the security feature and the substrate to expand along the peeling direction) and a second component perpendicular to the substrate (i.e., a "lifting force" that breaks one or more adhesive or structural joints between the security feature and the substrate, within the security feature, and / or within the substrate along the separation line).

[0057] In other words, given the thin and fragile optical structures of many micro-optical security features, pulling on the security line or otherwise applying an uneven, discontinuous, or excessive peeling force significantly increases the likelihood of damage to the security line during acquisition and is thus not suitable as a component for counterfeiting security documents. As discussed herein, some embodiments of the functional watermarks of the present disclosure facilitate a sufficiently sudden change in the peeling force applied to an adhered security device during acquisition so as to reliably cause the security device to tear, delaminate, or otherwise become unfit as an acquired component for reuse in counterfeiting security documents.

[0058] Reference Figure 5 to a non-limiting example of shows an example of a security document 500 according to the present disclosure. In this illustrative example, the security document 500 is a banknote, but other embodiments (e.g., tickets, identification documents, etc.) are also within the scope of the present disclosure. In some embodiments, the security document 500 includes a fibrous substrate 505 formed from a wet web of fibrous material (e.g., wood pulp, cotton fiber, linen fiber, hemp fiber, sisal fiber, cannabis fiber, abaca fiber, kozo fiber, mitsumata fiber, bamboo fiber, jute fiber, and / or synthetic fiber) laid at a first baseline fiber density (e.g., in a fourdrinier papermaking process). Before pressing, drying, and in some embodiments calendering, when the web is wet (e.g., by using a dandy roll, electrotype, or other watermarking tool), regions of the web where the first fiber density is not changed form the body region 510 of the security document 500. As used in this disclosure, the term "body region" encompasses a portion of the fibrous substrate that exhibits one or more of the baseline fiber density, baseline light absorption, or baseline thickness. In other words, as used in this disclosure, the term "body region" encompasses portions of the finished fibrous substrate in which the positions of the constituent fibers are not intentionally altered (e.g., by using an embossed wire cloth or electrotype) as part of the papermaking process.

[0059] AsFigure 5 As shown in the illustrative example of, the security document 500 also includes one or more security features 515 adhered to the surface of the security document 500. In some embodiments, the security feature 515 includes a strip of material that traverses the width (the shorter dimension of a rectangular-shaped object) of the security document 500 and coextends with one or more edges 517 of the security document 500. In some embodiments, the fibrous substrate and the security feature 515 are cut simultaneously, resulting in both coextending with the edge 517. The security feature 515 includes a thin material section having one or more optical structures, such as structures including an embossed or cast-cured outer surface that provides an optically variable effect. Examples of the optical structures provided on the security feature 515 include, but are not limited to, microlenses, diffraction structures, and micro-optical icons. Examples of the optically variable effects provided by the optical structures of the security feature 515 include, but are not limited to, holograms, color-shift effects, and synthetic images, characterized by a synthetic projection of image icon portions on an image icon array through focusing elements of an array of focusing elements, where the scale ratio (i.e., the ratio of the repetition period of the focusing elements to the repetition period of the image icons) is approximately 1.000.

[0060] The security document 500 also includes one or more functional watermarks 520. In various embodiments, the functional watermark 520 includes one or more regions in which the fiber density of the fibrous substrate 505 is intentionally changed (increased or decreased) relative to the fiber density in the body region 510 to form visible light patterns (i.e., allowing more light to pass through the fibrous substrate in a transmissive manner than in the body region 510) and / or dark (i.e., less light passing through the fibrous substrate in a transmissive manner than in the body region 510) elements. Additionally, at least a portion of the functional watermark 520 is covered by a portion of the security feature 515, where the security feature 515 remains in contact with the functional watermark 520 through an adhesive bond. In various embodiments, the functional watermark 520 in contact with the security feature 515 includes one or more light or dark elements whose edges are substantially perpendicular to one or more peel directions 525 of the security feature 515. As used in the present disclosure, the term "peel direction" encompasses the direction in which the separation of the security feature 515 is enlarged in a direction corresponding to a local minimum amount generally corresponding to the separation line. By lifting the security feature 515 from the fibrous substrate 505 in a peel direction 525 that is substantially perpendicular to the separation line between the security feature 515 and the fibrous substrate 505, the total peel force applied to the fibrous substrate 505 is minimized. All other conditions being equal, it is reasonable to expect that a malicious actor would attempt to separate the security feature 515 from the fibrous substrate 505 along the peel direction 525 to obtain the security feature 515 in order to minimize the force applied to the security feature 515. Depending on its shape, the security feature 515 may exhibit more than one peel direction.

[0061] In some embodiments, the functional watermark 520 includes a bright region (i.e., a region of reduced fiber density) near the intersection of the security feature 515 and the edge 517. As discussed in more detail herein, the presence of the bright region in the functional watermark 520 results in a local reduction in the substrate quality of the fiber substrate, which counteracts the incompressibility of the security feature 515 relative to the fiber substrate 505. Thus, the presence of the functional watermark 520 means that the force required to expand a cut along the edge 517 within a stack of uncut documents does not surge upward when the cut encounters the security feature 515, as compared to the force required to cut a stack of uncut documents lacking the functional watermark 520.

[0062] Figure 6 Illustrates a construction aspect of an exemplary micro-optical security device (e.g., the surface-applied security feature 115 in FIG. 1) including a portion of a security document according to the present disclosure.

[0063] Reference Figure 6 to the non-limiting example of, the optical security device 600 includes a plurality of focusing elements 605 (including, for example, the focusing element 607) and an image icon arrangement 620 (including, for example, the image icon 621). In various embodiments, each of the plurality of focusing elements 605 has a coverage area in which one or more image icons of the image icon arrangement 620 are positioned. Overall, the focusing elements among the plurality of focusing elements 605 magnify portions of the image icon arrangement 620 to produce a synthetic magnification effect (also referred to as a "synthetic image"), in which individual microscopic image icons are jointly magnified by the plurality of focusing elements 605 to produce an image that dynamically responds (e.g., by appearing to move or change color) in response to a change in the viewing angle. Given the small scale and strict manufacturing tolerances of the compositional structure of an optical security device providing a moiré magnification effect, many malicious actors are unable to produce a forged version of the optical security device 600. Thus, in many cases, the optical security device 600 is a trusted visual marker of the authenticity of a security document (e.g., the security document 660).

[0064] In some embodiments, the plurality of focusing elements 605 includes a planar array of micro-optical focusing elements. In some embodiments, the focusing elements among the plurality of focusing elements 605 include micro-optical refractive focusing elements (e.g., plano-convex lenses or GRIN lenses). In some embodiments, the refractive focusing elements among the plurality of focusing elements 605 are made of a photocurable resin having a refractive index in the range of 1.35 to 1.7 and have a diameter in the range of 5 μm to 200 μm. In various embodiments, the focusing elements among the plurality of focusing elements 605 include reflective focusing elements (e.g., very small concave mirrors) having a diameter in the range of 5 μm to 50 μm. Although in this illustrative example, the focusing elements among the plurality of focusing elements 605 are shown as including circular plano-convex lenses, other refractive lens geometries (e.g., biconvex lenses) are possible and within the scope of the present disclosure.

[0065] As Figure 6 shown in the illustrative example of, the image icon arrangement 620 includes a set of image icons (including image icon 621) positioned at predetermined locations within the coverage area of the focusing elements among the plurality of focusing elements 605. In various embodiments, an individual image icon in the image icon arrangement 620 includes a region of photocurable material associated with the focusing path of structured light (e.g., collimated UV light) that passes through the plurality of focusing elements 605 from a projection point associated with one or more predetermined viewing angle ranges. In some embodiments, an individual image icon in the image icon arrangement 620 is not disposed within a structured image icon layer. As used in the present disclosure, the term "structured image layer" encompasses a material layer (e.g., a photocurable resin) that has been embossed or otherwise formed to include structures (e.g., recesses, posts, grooves, or terraces) for positioning and holding image icon material. In various embodiments, an individual image icon in the image icon arrangement 620 is disposed within a structured image layer that includes one or more of voids, terraces, or posts that act as holding structures to retain micrometer-scale and nanometer-scale volumes of colored material.

[0066] As Figure 6 shown in the illustrative example of, in certain embodiments, the optical security device 600 includes an optical spacer 610. In various embodiments, the optical spacer 610 includes a film of a substantially transparent material (e.g., polyethylene terephthalate ("PET") or biaxially oriented polypropylene ("BOPP")) that is used to position the image icons in the image icon arrangement 620 in or around the focal plane of the focusing elements among the plurality of focusing elements 605. In some embodiments of the present disclosure, the optical spacer 610 includes a manufacturing substrate on which one or more layers of photocurable material can be applied to form one or more of the image icon arrangement 620 or the plurality of focusing elements 605.

[0067] In various embodiments, the optical security device 600 includes one or more regions of a light-curable protective material that occupy the space between the image icons in the image icon arrangement 620. In some embodiments, the image icon arrangement 620 is first formed (e.g., by selectively curing and removing a liquid photocurable material on the optical spacer 610), then a layer of a transparent photocurable material is applied to fill the space between the image icons in the image icon arrangement 620, and then overflow curing is performed to produce a protective layer that protects the image icons from moving from their positions within the coverage area of the focusing elements in the plurality of focusing elements 605. In certain embodiments, the photocurable material used to form the image icon arrangement 620 is a colored ultraviolet (UV)-curable polymer.

[0068] In some embodiments, the image icon arrangement 620 is secured to a second substrate 630 that serves to protect and fasten the image icon arrangement 620 and provides an interface for attaching the optical security device 600 to a substrate 650 as part of a security document 660. In some embodiments, the optical security device 600 is secured to the substrate 650 during the manufacture of the substrate in a paper machine (such as a fourdrinier paper machine). In some embodiments, the optical security device 600 is secured to the substrate 650 by a layer of adhesive between the image icon arrangement 620 and the top surface of the substrate 650.

[0069] In some embodiments of the present disclosure, the optical security device 600 includes a sealing layer 640. In certain embodiments, the sealing layer 640 includes a thin (e.g., 2 μm to 50 μm thick) layer of a substantially transparent material that abuts the focusing elements in the plurality of focusing elements 605 on the lower surface and includes an upper surface with less curvature variation (e.g., by being smooth, or by having a surface with a larger radius of curvature with local undulations) compared to the plurality of focusing elements 605. In various embodiments, one or more of the plurality of focusing elements 605, the sealing layer 640, and the image icon arrangement 620 are formed from a polyacrylate or other UV-curable resin.

[0070] While Figure 6 an example of an optical security device is provided, the present disclosure is not limited thereto. Other optical security devices are within the scope of the present disclosure, and these other optical security devices are prone to damage when pulled or otherwise subjected to a suddenly increased force and include micron-scale and nanoscale optical structures (e.g., holograms, devices that provide a thin-film effect, devices that produce diffraction-based optical effects) that are difficult to replicate, and these optical structures provide a target for malicious actors.

[0071] Figure 7An example of a fibrous substrate with a functional watermark in accordance with the present disclosure is illustrated. Referring to Figure 7 a non-limiting example, an uncut section 700 of a fibrous substrate (e.g., banknote paper with linen fibers) is shown. In this example, the uncut section 700 will be cut along a first cut line 701a and a second cut line 701b to form a substrate for one or more security documents. Additionally, at some point during the manufacturing process, one or more surface-applied security features are applied to the fibrous substrate such that the surface-applied security feature covers the area defined by the first cut line 701a and the second cut line 701b, as well as lines 703a and 703b. In some embodiments, the surface-applied security feature is applied before cutting along the cut lines 701a and 701b such that cutting the fibrous substrate also trims the ends of the surface-applied security feature to be flush with the edges of the security document. In some embodiments, the surface-applied security feature is applied after cutting along the cut lines 701a and 701b.

[0072] As Figure 7 shown, the uncut section 700 includes a body region 705 (shown in gray in the figure) that constitutes the fibrous substrate, where the fiber density and thickness of the fibrous substrate do not vary significantly, and where transmitted light passes uniformly through the fibrous substrate over the entire body region 705. Simply put, the underlying paper in the body region 705 (excluding any applied printing or security devices) appears to the human eye as a uniformly opaque material field.

[0073] In various embodiments, the uncut section 700 also includes a first functional watermark 710a and a second functional watermark 710b, which, in the Figure 7 example, span the first cut line 701a and the second cut line 701b. As Figure 7As shown, both the first functional watermark 710a and the second functional watermark 710b include a pattern of dark elements (shown in dark gray in the figure) and light elements (shown in white in the figure). In various embodiments, the light elements (e.g., light element 715) correspond to regions of the fibrous substrate where the wet web is altered during manufacture to produce a lower fiber density (i.e., fewer fibers per unit area) than the body region 705. Thus, when viewed in transmitted light (i.e., when the uncut section 700 is backlit), the light elements allow more light to pass through and appear brighter than the body region 705. In some embodiments, the light element regions constitute 50% to 70% of the background basis weight. In some embodiments, light element regions that constitute 55% to 65% of the background basis weight provide a high-performance combination of fibrous substrate strength and compressibility above the body region in the light element regions. Similarly, the dark elements (e.g., dark element 720) correspond to regions of the fibrous substrate where the wet web is altered during manufacture to produce a higher fiber density than the body region 705 and allow less light to pass through than the body region 705. Thus, the dark elements appear darker than the body region 705 in transmitted light.

[0074] Additionally, in some embodiments, the local topology of the uncut section 700 can vary significantly between the functional watermarks 710a and 710b, where the dark elements have a high point relative to the body region 705 (as recorded by placing a platen on each of the functional watermarks 710a and 710b), and a low point relative to the body region 705 on all the light elements (again detected by comparing the profile of the watermark with the platen). In various embodiments, the variation in the thickness difference between the high point of the dark elements and the low point of the light elements (where the thickness measurement provides a measure of the local thickness at various points within the uncut section 700) approximates or is equivalent to the thickness of the surface-applied security feature. Thus, when the fiber density change regions (i.e., the light or dark elements) have well-defined boundaries such as edges, the thickness variation between the fiber density change regions can create small local ramps that are sufficient to cause fluctuations in the peel angle (i.e., the angle between the removed security feature and the surface of the fiber substrate at the separation point). Such fluctuations in the peel angle change to the extent that the applied peel force is in a direction perpendicular to the fiber substrate. In practice, when a malicious actor attempts to peel the adhered security feature from the functional watermarks 710a and 710b, the separation line will fluctuate violently between "uphill" and "downhill" progression. These violent fluctuations in the peel angle during the transition between the light and / or dark elements translate into sudden changes in the lift and pull components of the force applied to the security feature. As described elsewhere in this disclosure, successful acquisition generally presupposes minimizing the pull and lift components of the force applied to the security feature and keeping these components stable. Fluctuations in the relative values of the total force or the pull and lift components may damage the fiber substrate and / or the security feature, rendering one or both unsuitable for reuse in creating forged documents, or if reused, presenting visible marks of prior tampering.

[0075] Reference Figure 7 to the illustrative example of, the light elements 715 and the dark elements 720 define a region having one or more edges that are substantially perpendicular to one or more peel lines. In Figure 7 the explanatory example of, to minimize the length of the separation line (and implicitly the total force of the peel force applied to the security feature), a logical approach to acquiring the surface-applied security feature that occupies the region defined by the lines 703a and 703b and the cut lines 701a and 701b is to start the acquisition by peeling the security feature upward at a first angle in a first peel direction 730a, and after separating a second angle, attempt to expand the separation by applying a peel force in a second peel direction 730b and acquire the security feature along its length.

[0076] Given that the geometry of the region defined by lines 703a and 703b and cut lines 701a and 701b determines that the first peel direction 730a and the second peel direction 730b are the logical ways to minimize the separation line width and the force applied to the security feature during an acquisition attempt, the dark element 720 includes a region having one or more edges (e.g., a first edge 735) that are set at an angle substantially perpendicular to the first peel direction 730a. Tests have shown that by providing at least one edge of a dark or light element of a functional watermark in a direction substantially perpendicular to the peel direction, the mutability of the discontinuity in size and directionality can be maximized, thereby maximizing the likelihood of damaging the security feature or the substrate. Similarly, the light element 715 has a second edge 740 that is substantially perpendicular to the second peel direction 730b. By making at least one edge of the transition between different fiber densities substantially perpendicular to the peel direction, the effect of a sudden change in the bevel will be felt on most, if not all, of the separation lines, as well as the adhesion between the security feature and the substrate in some cases, thereby maximizing the fluctuation of the applied force and implicitly maximizing the likelihood of damaging the security feature or the substrate during an acquisition.

[0077] Although certain embodiments of the present disclosure have been described with reference to Figure 7 striped security features and examples of functional watermarks disposed at the edges of security documents, the present disclosure is not limited thereto. Other combinations of functional watermarks (e.g., functional watermarks having only light elements or only dark elements) and security documents (e.g., security documents having functional watermarks disposed away from the edges) are within the scope of the present disclosure.

[0078] Figure 8 Illustrates a non-exhaustive set of six examples of functional watermark patterns suitable for use in security documents according to the present disclosure. Other functional watermark patterns suitable for use in security documents are possible and are within the scope of the present disclosure. In Figure 8 the illustrative example of Figure 8 the white blocks show regions of the functional watermark where the fiber density of the fiber substrate is the same as that of the body region of the security document. The gray blocks show regions having a first fiber density that was changed during the manufacture of the fiber substrate to be higher or lower than the fiber density of the body region. In

[0079] Reference Figure 8As a non-limiting example, the first functional watermark pattern 805 includes a honeycomb grid having regions of a second fiber density, the grid being scattered with filled regions having a first fiber density. The hexagonal shape of each cell of the first functional watermark pattern presents edges that are substantially perpendicular to a plurality of peel directions (e.g., presenting a peel direction angle of 45 degrees or greater), the plurality of peel directions including a first peel direction 891, a second peel direction 893, and a third peel direction 895. In this regard, the first functional watermark pattern 805 may be suitable for applied security features having a low aspect ratio (where the aspect ratio encompasses the ratio of the width to the length of the security device) and may be prone to acquisition at multiple peel angles.

[0080] As Figure 8 shown in the explanatory example of, the second functional watermark pattern 810 includes a series of wavy line regions having a first fiber density and a second fiber density. In some embodiments, the second functional watermark pattern is effective for applied security features having a high aspect ratio and may reasonably be expected to be acquired by a force applied substantially parallel to the first peel direction 891.

[0081] The third functional watermark pattern 815 embodies the same pattern as the Figure 7 functional watermarks 710a and 710b in. In some embodiments, the third functional watermark pattern 815 may effectively create discontinuities in a plurality of peel directions (such as a fourth peel direction 897 and the first peel direction 891) and may therefore be particularly suitable for applications involving security devices with angular exposures (e.g., where the line is not buried beneath a second fiber layer of the substrate) having a high aspect ratio (e.g., a linear device).

[0082] The fourth functional watermark pattern 820 includes a series of wide horizontal fiber bands that vary the first fiber density and the second fiber density. Tests have shown that, in addition to the perpendicularity of the leading edge of the functional watermark feature, the area of the fiber density change region can also be a factor affecting the degree to which the feature of the functional watermark enhances anti-acquisition by catalyzing a sudden change in the magnitude and directionality of the peel force. Tests to date have shown that higher anti-acquisition (e.g., a dry acquisition score of 10 to 15 according to the anti-acquisition index of the United States Bureau of Engraving and Printing) can be achieved when the area of the compositional region where the fiber density changes (i.e., the light element or the dark element) is between 60 and 140 mm 2 2. The fourth functional watermark pattern 820 may be particularly suitable for use in combination with narrow strips having a high aspect ratio that present a single peel direction.

[0083] The fifth functional watermark pattern 825 includes a series of spaced-apart "zigzag" regions having a second fiber density separated by a body region. In addition to presenting edges that are substantially perpendicular to the second peel direction 893, the third peel direction 895, and the fourth peel direction 897, the fifth functional watermark pattern 825 also presents numerous variations in the topography of the fiber substrate along the first peel direction 891, which variations, although not perpendicular to the first peel direction 891, still create local discontinuities in the direction and force of the peel force.

[0084] The sixth functional watermark pattern 830 exhibits performance similar to the second functional watermark pattern 810 along the first peel direction 891, but also incorporates elements of the third functional watermark pattern 815 to provide anti-acquisition along the fourth peel direction 897.

[0085] Reference Figure 8 The six patterns described are for illustration only, and functional watermarks for other patterns with bright and / or dark elements at the edges of the border are possible and within the scope of this disclosure.

[0086] Figure 9A And Figure 9B Illustrate aspects of the anti-acquisition of a security document incorporating a functional watermark according to this disclosure. For ease of cross-reference, Figure 9A And Figure 9B Common elements are numbered in a similar manner.

[0087] Reference Figure 9A As a non-limiting example, a functional watermark pattern 900 is shown in the figure. The functional watermark pattern 900 includes a series of regions of varying fiber density (shown in black) that are scattered between body regions of unaltered fiber density. Figure 9B Includes an enlarged image of a first damaged portion 905 of the security feature after an attempt to acquire the security feature from a fiber substrate including a body region 910 and a functional watermark 915, the functional watermark embodying Figure 9A The functional watermark pattern 900 of. In this example, the regions of varying fiber density include dark elements, such as dark element 920, which appears darker than adjacent strip 925, which has a fiber density substantially the same as the body region 910. In this example, an attempt to acquire the security feature is made by starting at the top edge 930 and moving in the peel direction 935. As Figure 9BAs shown, the act of peeling the security feature from the functional watermark 915 results in a discontinuity in the magnitude and / or directionality of the force applied to the security feature, thereby initiating a tear in the security feature starting from the rightmost portion of the dark element 920, which in turn causes the micro-optical device to separate into a first damaged portion 905 and a second damaged portion 940. Additionally, at certain locations, the adhesive strength of the bond holding the fiber substrate to the security feature is shown to exceed the internal strength of the fiber substrate. For example, at location 945, a patch of the fiber substrate is pulled away from the body region and remains attached to the first damaged portion 905.

[0088] Figure 10 Exemplary image 1000 obtained after attempting to obtain security feature 1005 from a security document including functional watermark 1010 in accordance with the present disclosure is illustrated. Referring Figure 10 to the exemplary example, security feature 1005 includes a multi-layer micro-optical security feature that includes optical spacers (e.g., Figure 6 optical spacer 610 in Figure 6 ), an array of focusing elements (in this case, microlenses) (e.g., Figure 6 array of focusing elements 605 in

[0089] As Figure 10 shown, an attempt is made to dry obtain the security feature 1005 in the peeling direction 1015. However, when the separation line crosses the perimeter 1020 of the functional watermark 1010, the lifting component of the peeling force exceeds the internal adhesion between the icon layer and the optical spacer, resulting in delamination of the security feature 1005, where the icon layer remains adhered to the fiber substrate. As Figure 10As shown, in the initial portion 1025 of the security feature 1005, all layers of the security feature 1005 have been successfully obtained, as indicated by the dark tint of the removed material, thus indicating the presence of the colored icon layer. However, in the second portion 1030, which is roughly defined by the point of contact between the security feature 1005 and the perimeter 1020 of the functional watermark 1010, the icon material is no longer present on the removed portion of the security feature 1005, as indicated by the light semi-transparent appearance of the security feature 1005 in the second portion 1030.

[0090] Figure 11 is an exemplary section 1100 of a security document, which further illustrates how in some embodiments of the present disclosure, the sharp-edged transition between the bright or dark elements in the functional watermark provides a starting point for structural damage to the surface-applied features. Refer to Figure 11 for an illustrative example that shows a section 1100 of a security document according to the present disclosure. The security document includes a body region 1105 of a formed fibrous substrate, where the fibrous substrate is banknote paper that includes a mixture of paper and linen or cotton fibers. In some embodiments, the fibrous substrate may include synthetic fibers (e.g., machine-readable fibers) added for strength or to provide authenticity marks that are difficult to replicate. The security document also includes a functional watermark 1110 that includes alternating body regions and bright elements in a repeating herringbone or "tread pattern". For clarity and ease of reference, the edges of some of the boundaries between the body regions and the bright elements of the functional watermark 1110 have been highlighted in the figure. A multi-layer micro-optical security device 1115 (e.g., optical security device 600) has been applied to and adhered to the functional watermark 1110. As Figure 10 in the security feature 1005 of

[0091] As Figure 11 shown, the micro-optical security device 1115 has undergone structural failure. Specifically, during acquisition, the optical spacer layer and the icon layer delaminated, as shown by the bright region 1125 on the acquired portion of the micro-optical security device 1115 and the similarly shaped dark region 1130 left on the fibrous substrate. Together, the bright region 1125 and the corresponding dark region 1130 indicate that the internal force holding the icon layer of the micro-optical security device 1115 to the optical spacer has been overcome by the lifting component of the peeling force.

[0092] Notably, as Figure 11As shown, the leading edge of the dark region 1130 exactly corresponds to the first leading edge 1135 of the bright elements of the functional watermark 1110, indicating that the boosting component of the peel force surges suddenly near the first leading edge 1135, thereby triggering the structural failure of the micro-optical security device 1115. Although it is slightly less clear in section 1100, there is a similar correspondence between the second leading edge 1140 of the bright element 1145 and the start of the second region 1150 of the icon material remaining on the substrate. Additionally, the 45-degree angles between the leading edges 1135 and 1140 and the peel direction 1120 indicate that while the basic perpendicularity between the peel direction and the edge of the fiber density change region facilitates the sudden change of the boosting component and the peeling component of the peel force (similar to a square-headed ship decelerating more suddenly than a pointed ship when encountering waves), this is by no means necessary to trigger the structural failure of the micro-optical security device during acquisition.

[0093] Figure 12 Illustrates an example method 1200 for forming a security document (e.g., Figure 5 the security document 500 in Figure 12 in accordance with the present disclosure. Although the steps described are described in sequence, the order of the steps can be reversed, the steps can occur simultaneously or nearly simultaneously, and additional steps can be added. Referring to Figure 12 a non-limiting example of

[0094] At step 1205, an initial fiber web is formed from a wet slurry, where the wet slurry comprises (without limitation) a mixture of a fiber material (e.g., paper fibers, cotton fibers, linen fibers, or synthetic fibers) and water. The initial fiber web can be formed by transferring the wet slurry from a forming vat to a screen on a forming board. The initial fiber web has a sufficient water content (e.g., 99% or more water by weight) such that after initial dewatering of the fiber web, the constituent fibers of the slurry can be repositioned in a later stage of the papermaking process (e.g., in the wet pressing section) in response to the "squeezing force" applied to the web by one or more of a wire cloth or an electroformed plate type tool on a watermark roll. Figure 7 At step 1210, the fiber density in one or more defined regions of the initial fiber web is changed to define the features of one or more functional watermarks. In some embodiments, the fiber density is changed by de-sizing to produce the bright elements of the functional watermark. In some embodiments, the fiber density is changed by sizing to produce the dark elements of the functional watermark. At step 1215, the initial fiber web including the fiber density change region is pressed and dried (e.g., by passing through the pressing section and the dryer section of a fourdrinier paper machine) to form a dry fiber substrate having one or more functional watermarks (e.g., Figure 7 the uncut section 700 in Figure 6The optical security device in) is applied to a fibrous substrate in at least one area covering the functional watermark to form a security document (e.g., Figure 5 the security document 500) in.

[0095] Examples of the security documents of the present disclosure include security documents comprising: a fibrous substrate comprising a functional watermark, the functional watermark comprising a defined fiber density change region relative to the body portion of the fibrous substrate, wherein the functional watermark comprises a first edge that at least partially defines or determines the shape of the defined fiber density change region; and a surface-applied security device that covers at least a portion of the defined fiber density change region relative to the body portion.

[0096] Examples of the security documents of the present disclosure include security documents wherein the functional watermark is disposed along a cut edge of the fibrous substrate.

[0097] Examples of the security documents of the present disclosure include security documents wherein the functional watermark is disposed away from the cut edge of the fibrous substrate.

[0098] Examples of the security documents of the present disclosure include security documents wherein the first edge is substantially perpendicular to a first peel direction of the surface-applied security device.

[0099] Examples of the security documents of the present disclosure include security documents wherein the functional watermark comprises a second edge that at least partially determines the shape of the defined fiber density change region, and wherein the second edge is substantially perpendicular to a second peel direction of the surface-applied security device.

[0100] Examples of the security documents of the present disclosure include security documents wherein the area of the defined fiber density change region in contact with the surface-applied security feature is between 60 and 140 mm 2 between.

[0101] Examples of the security documents of the present disclosure include security documents wherein the surface-applied security device comprises a multi-layer optical structure.

[0102] Examples of the security documents of the present disclosure include security documents wherein the surface-applied security device comprises the following layers: a first focusing element layer; and a second icon element layer, wherein the first focusing element layer projects a composite image of the icon elements in the second icon element layer.

[0103] Examples of the security documents of the present disclosure include security documents wherein the surface-applied security device comprises a transparent optical spacer.

[0104] Examples of the security documents of the present disclosure include security documents, wherein the functional watermark includes a repeating pattern that defines the shape of a fiber density change region relative to the fiber density of the fiber substrate.

[0105] Examples of the security documents of the present disclosure include security documents, wherein the surface-applied security device is configured to undergo structural failure in the area contacting the functional watermark in response to dry acquisition.

[0106] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region of the body portion relative to the fiber substrate corresponds to an electrotype pattern.

[0107] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region of the body portion relative to the fiber substrate corresponds to a wire mesh watermark tool pattern.

[0108] Examples of the security documents of the present disclosure include security documents that include an adhesive layer disposed between the surface-applied security device and the defined fiber density change region of the body portion relative to the fiber substrate, wherein the adhesive layer provides an adhesive force between the surface-applied security devices, and the adhesive force is less than the internal force that holds the fibers of the fiber substrate together.

[0109] Examples of the security documents of the present disclosure include security documents that include an adhesive layer disposed between the surface-applied security device and the defined fiber density change region of the body portion relative to the fiber substrate, wherein the adhesive layer provides a first adhesive force between the surface-applied security device and the defined fiber density change region, and wherein the adhesive layer provides a second adhesive force between the surface-applied security device and the body portion of the fiber substrate.

[0110] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region includes bright regions with a lower fiber density and greater compressibility compared to the body portion.

[0111] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region includes an electrotype watermark.

[0112] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region includes a wire cloth watermark.

[0113] Examples of the security documents of the present disclosure include security documents, wherein the defined fiber density change region further includes one or more dark regions with an increased fiber density relative to the body portion of the fiber substrate.

[0114] Examples of the security documents of the present disclosure include security documents in which the defined fiber density change region has a compressibility that is 25% to 50% higher than that of the body portion of the fiber substrate.

[0115] Examples of the security documents of the present disclosure include security documents in which the defined fiber density change region has a compressibility that is 50% to 65% higher than that of the body portion.

[0116] Examples of the security documents of the present disclosure include security documents in which the defined region and the surrounding area do not exhibit nail mark defects.

[0117] Examples of the security documents of the present disclosure include security documents in which the height of the defined region is at least equal to the vertical registration accuracy of the tool for providing the functional watermark.

[0118] Examples of the security documents of the present disclosure include security documents in which no nail mark defects are observed when the security document is part of a strip of sheets of one hundred identical security documents subjected to a cutting force of 300 daN.

[0119] Examples of the methods of the present disclosure include methods that include: forming an initial fiber web from a wet fiber slurry; changing the fiber density of the initial fiber web in one or more defined regions to define one or more functional watermarks; pressing and drying the initial fiber web to form a fiber substrate including a body portion and the one or more functional watermarks, wherein the one or more functional watermarks include at least one of a bright element or a dark element, and the bright element or the dark element has at least one edge defining a fiber density change region; and applying a surface-applied security device covering at least a portion of the one or more functional watermarks.

[0120] Examples of the methods of the present disclosure include methods that include cutting the fiber substrate along a line passing through at least one functional watermark and the surface-applied security device.

[0121] Examples of the methods of the present disclosure include methods in which the surface-applied security device is applied to the initial fiber web before pressing and drying the initial fiber web.

[0122] Examples of the methods of the present disclosure include methods in which the surface-applied security device is applied to the fiber substrate after pressing and drying the initial fiber web.

[0123] Examples of the methods of the present disclosure include methods in which changing the fiber density of the initial fiber web in the one or more defined regions is performed using at least one of an electroformed plate element or a wire cloth.

[0124] Examples of the method of the present disclosure include a method that includes: forming a functional watermark on a fibrous substrate, where the functional watermark includes defined regions having a lower fiber density than the non-watermarked body portion of the fibrous substrate; applying a security feature to the fibrous substrate to form an uncut sheet of a security document, where the security feature covers at least a portion of the functional watermark and includes material segments having a lower relative compressibility than the fibrous substrate; stacking a plurality of the uncut sheets to form a strip of uncut sheets such that the security features of the uncut sheets are aligned along a line orthogonal to the plane of the strip; and cutting the strip of uncut sheets along a cutting line passing through points where the security feature and the functional watermark overlap to form individual security documents, where the individual security documents do not exhibit nail mark defects at the points where the security feature and the functional watermark overlap.

[0125] Examples of the method of the present disclosure include a method where the defined region of changed fiber density includes an electrotype watermark.

[0126] Examples of the method of the present disclosure include a method where the defined region of changed fiber density includes a wire cloth watermark.

[0127] Examples of the method of the present disclosure include a method where the defined region of changed fiber density further includes one or more dark regions having an increased fiber density relative to the body portion of the fibrous substrate.

[0128] Examples of the method of the present disclosure include a method where the defined region of changed fiber density has a compressibility that is 25% to 50% higher than the body portion of the fibrous substrate.

[0129] Examples of the method of the present disclosure include a method where the defined region of changed fiber density has a compressibility that is 50% to 65% higher than the body portion.

[0130] Examples of the method of the present disclosure include a method where the height of the defined region is at least equal to the vertical registration accuracy of the tool for providing the functional watermark.

[0131] Examples of the method of the present disclosure include a method where no nail mark defects are observed when the strip includes 100 uncut sheets and is subjected to a cutting force of 300 daN.

[0132] Examples of the method of the present disclosure include a method where the security feature includes a plurality of layers, the plurality of layers including at least one of the following: a transparent optical spacer, a resin array of focusing elements, or a resin layer of an image icon.

[0133] Although the present disclosure has been described by means of various embodiments, various changes and modifications may be suggested to those skilled in the art. The present disclosure is intended to cover such changes and modifications that fall within the scope of the claims.

Claims

1. A security document (660), the security document comprising: A fibrous substrate (650), the fibrous substrate comprising: A functional watermark (710a), the functional watermark comprising defined fiber density change regions (715, 720) relative to a body portion (705) of the fibrous substrate, wherein the functional watermark comprises a first edge (735) at least partially defining the shape of the defined fiber density change regions; and A surface-applied security device (600, 1005), the surface-applied security device covering at least a portion of the defined fiber density change regions relative to the body portion.

2. The security document according to claim 1, wherein the functional watermark is disposed along a cutting edge (701a) of the fibrous substrate.

3. The security document according to claim 1, wherein the functional watermark is disposed away from the cutting edge of the fibrous substrate.

4. The security document according to claim 1, wherein the first edge is substantially perpendicular to a first peel direction (730a) of the surface-applied security device.

5. The security document according to claim 4, wherein: The functional watermark comprises a second edge, the second edge at least partially determining the shape of the defined fiber density change regions; and The second edge is substantially perpendicular to a second peel direction of the surface-applied security device.

6. The security document according to claim 1, wherein the area of the defined region of changed fibre density that is in contact with the surface to apply the security feature is between 60 and 140 mm 2 between.

7. The security document according to claim 1, wherein the surface-applied security device comprises a multi-layer optical structure.

8. The security document according to claim 5, wherein the surface-applied security device comprises the following layers: A first focusing element layer; and A second icon element layer, Wherein the first focusing element layer projects a composite image of icon elements in the second icon element layer.

9. The security document according to claim 5, wherein the surface-applied security device comprises a transparent optical spacer (610).

10. The security document according to claim 1, wherein the functional watermark comprises a repeating pattern defining the shape of the fiber density change regions relative to the fiber density of the fibrous substrate.

11. The security document according to claim 1, wherein the surface-applied security device is configured to undergo structural failure (1030) in a region contacting the functional watermark in response to dry acquisition.

12. The security document according to claim 1, wherein the defined fiber density change regions relative to the body portion of the fibrous substrate correspond to electrotype patterns.

13. The security document according to claim 1, wherein the defined fiber density change regions relative to the body portion of the fibrous substrate correspond to wire mesh watermark tool patterns.

14. The security document according to claim 1, further comprising an adhesive layer disposed between the surface-applied security device and the defined fiber density change regions relative to the body portion of the fibrous substrate, Wherein the adhesive layer provides an adhesive force between the surface-applied security devices, the adhesive force being less than the internal force holding the fibers of the fibrous substrate together.

15. The security document according to claim 1, further comprising an adhesive layer disposed between the surface-applied security device and the defined fiber density change region of the body portion relative to the fiber substrate, wherein the adhesive layer provides a first adhesive force between the surface-applied security device and the defined fiber density change region, and wherein the adhesive layer provides a second adhesive force between the surface-applied security device and the body portion of the fiber substrate.

16. A method of manufacturing a security document, the method comprising: forming an initial fiber web (1205) from a wet fiber slurry; changing the fiber density of the initial fiber web in one or more defined regions to define one or more functional watermarks (1210); pressing and drying the initial fiber web to form a fiber substrate (1215) comprising a body portion and the one or more functional watermarks, wherein the one or more functional watermarks include at least one of a light element or a dark element, the light element or the dark element having at least one edge defining a fiber density change region; and applying a surface-applied security device (1220) covering at least a portion of the one or more functional watermarks.

17. The method according to claim 16, further comprising cutting the fiber substrate along a line passing through at least one functional watermark and the surface-applied security device.

18. The method according to claim 16, wherein the surface-applied security device is applied to the initial fiber web before pressing and drying the initial fiber web.

19. The method according to claim 16, wherein the surface-applied security device is applied to the fiber substrate after pressing and drying the initial fiber web.

20. The method according to claim 16, wherein changing the fiber density of the initial fiber web in the one or more defined regions is performed using at least one of an electroformed element or a wire cloth.

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