High performance adhesives for security documents

Abstract

An adhesive (500) suitable for use in a security document (100) (e.g., currency, passport, travel ticket, etc.) includes a plurality of polymers (505) collectively exhibiting tack-imparting properties (510), aqueous agent resistance (515), and solvent resistance (520), and a crosslinker (525) selected to be activated to chemically react with one or more of the plurality of polymers at a temperature within a predetermined temperature range.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to adhesives. More specifically, the present disclosure relates to high performance adhesives for security documents. [Background technology]

[0002] Security documents, including but not limited to banknotes, stamps, passports, identification cards, tickets, utilize a multi-component construction comprising one or more substrates (e.g., fibrous substrates such as paper) to which security elements, such as holograms, security stripes, or micro-optical features, are affixed with one or more adhesives or at least partially integrated into the substrate. The components of the security document, including the features and arrangement of any security elements, can operate cooperatively to generate multiple detectable (e.g., by an observer's eye or by specialized machines) evidence of the authenticity of the security document.

[0003] The properties of the adhesive used in the manufacturing process are therefore crucial to the overall effectiveness of the security document. For example, an adhesive that cannot be dissolved by immersion in water or exposure to commonly available decomposing agents (e.g., oxidizing agents such as hydrogen peroxide) and does not allow removal or harvesting of the security elements increases the effectiveness of the security document by increasing its resistance to counterfeiting. Counterfeiting and counterfeiting of security documents imposes significant costs on the issuer of the security document, since documents that can be disassembled into parts for counterfeiting must be removed from circulation and replaced. Similarly, adhesives that yellow or decompose under foreseeable environmental conditions or mechanical stresses (e.g., folding, accidentally washing in the laundry, etc.) impair the effectiveness of the security document of which they are a part and impose increased disposal and replacement costs on the issuer. The replacement costs imposed by counterfeiting and wear are considerable and, depending on the security document in question (e.g., banknotes), can be on the order of millions of dollars per year in replacement costs.

[0004] Thus, the technical challenges associated with developing high performance adhesives for constructing security documents include, but are not limited to, developing adhesive compositions that match competing and often seemingly incompatible performance requirements (e.g., the adhesive must strongly adhere the security element to the paper substrate, while at the same time comprising a thin layer) with the constraints imposed by the manufacturing process (e.g., time limitations associated with the amount of web moving through a particular stage of a paper converting machine, or temperature limitations to avoid melting or damaging the microlens or other structural security elements). Summary of the Invention [Problem to be solved by the invention]

[0005] Historically, manufacturers of security documents have chosen to use adhesives that include thermoplastics that are generally water resistant but susceptible to solvents. To date, adhesives for security documents have not been able to combine the water and solvent resistance properties desired by security document manufacturers. Thus, an opportunity remains to improve the overall performance of adhesives used on security documents as a mechanism to increase the counterfeit resistance of security documents. [Means for solving the problem]

[0006] The present disclosure provides high performance adhesives for security documents.

[0007] In a first embodiment, the adhesive comprises one or more of the polymers that collectively exhibit tack, aqueous agent resistance, and solvent resistance, and a crosslinker selected to be activated to chemically react at temperatures in a predetermined temperature range.

[0008] In a second embodiment, a security document includes a paper substrate, a security device, and an adhesive layer including an adhesive, the adhesive layer providing a bond between the security device and the paper substrate, the adhesive further including a plurality of polymers that collectively provide tack, resist and solvent resistance properties, and a crosslinker selected to be activated at a temperature within a predetermined temperature range to chemically react with one or more of the plurality of polymers.

[0009] In a third embodiment, a method of making a security document includes introducing an adhesive to form an adhesive layer in a paper machine configured to pass a substrate containing water through one or more treatment sections, the adhesive including a plurality of polymers collectively exhibiting tack-imparting properties, resistance to aqueous agents, and solvent resistance, and a crosslinking agent selected to be activated to chemically react at a temperature in a predetermined temperature range. The method further includes positioning a security device on a first portion of the substrate on which the adhesive has been introduced, and passing the first portion of the substrate through a treatment section of the paper machine at a temperature in the predetermined temperature range to activate the crosslinking agent to chemically react with one or more of the plurality of polymers. Additionally, the adhesive is introduced to the substrate in a treatment section of the paper machine where the substrate includes sufficient water to activate a polymer of the plurality of polymers that exhibits tack-imparting properties to provide wet tack.

[0010] In a fourth embodiment, a security device includes a substrate, an authentication structure, and an adhesive layer including an adhesive, the adhesive layer providing a bond between the security device and the paper substrate, the adhesive further including a plurality of polymers that collectively exhibit tackiness, water resistance, and solvent resistance, and a crosslinker selected to be activated to chemically react with one or more of the plurality of polymers at a temperature within a predetermined temperature range.

[0011] Other technical features may be readily apparent to those skilled in the art from the following figures, descriptions and claims.

[0012] Before proceeding with the detailed description below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "comprise" and "have," as well as their derivatives, mean inclusive without limitation. The term "or" means all-inclusive and / or. The term "associated" and its derivatives mean including, contained within, interconnected, containing, contained within, connected, coupled, communicable, cooperating, interleaving, juxtaposing, adjacent, bound, having a property, having a relationship, and the like. The term "at least one," when used in conjunction with a list of items, means that various combinations of one or more of the listed items can be used and that only one item from the list is required. For example, "at least one of A, B, and C" means the following: Includes A, B, C, A and B, A and C, B and C, and A, B and C.

[0013] Definitions of other specific terms and phrases are provided throughout this patent document. Those of skill in the art should understand that in many cases such definitions apply to prior and future uses of such defined words and phrases.

[0014] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 illustrates an example of a security document including an adhesive according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 illustrates an example of a security device that can be affixed to a security document using an adhesive according to various embodiments of the present disclosure. [Diagram 3] FIG. 3 is a schematic diagram showing elements of a paper machine for implementing methods for producing security documents according to some embodiments of the present disclosure. [Figure 4]FIG. 4 is a diagram illustrating operations of a method for producing a security document according to some embodiments of the present disclosure. [Diagram 5] FIG. 5 is a diagram illustrating the composition and properties of component compounds of adhesives according to various embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] FIGS. 1 through 5 described below and the various embodiments used to describe the principles of the present disclosure in this patent document are for illustrative purposes only and should not be construed as limiting the scope of the disclosure.

[0017] FIG. 1 illustrates an example of a security document 100 according to this disclosure.

[0018] 1, a security document 100 comprises a paper substrate 105 to which one or more security devices (e.g., security thread 110) are affixed using an adhesive. According to various embodiments, constructional details of the security document 100, including but not limited to optical effects (e.g., flicker, synthetic image presentation, or moire effects) created by the security thread 110, watermarks (e.g., watermarks 115a and 115b), and precise alignment of constructional details (e.g., registration of the security device through a window in the second "0" of the "500"), act in concert to provide a detectable indication of authenticity and to deter counterfeiting.

[0019] Furthermore, in certain embodiments, security document 100 is constructed to meet a wide range of performance criteria (e.g., performance criteria specified by a central bank, as well as constraints imposed by manufacturing methods suitable for producing large numbers of security documents). In some cases, the performance criteria for the security document include performance criteria for the adhesive used to secure the security device to the paper substrate (e.g., paper substrate 105) used in constructing the security document. Non-limiting real-world examples of performance criteria for adhesives used in security documents, such as security document 100, are described below.

[0020] The performance criteria for adhesives according to various embodiments of the present disclosure include that the adhesive attaching the security device (e.g., security strip 110 in FIG. 1) is substantially transparent when dried, and that the dried adhesive layer between the paper substrate and the security device is 2-10 microns thick.

[0021] In addition to or as an alternative to some or all of the above criteria, performance criteria for adhesives according to some embodiments of the present disclosure may include a requirement that the adhesive not yellow when exposed to heat, or humidity, or light. In some embodiments, the performance criteria for adhesives may include a requirement that the adhesive may be pre-applied to a security feature, and that the security feature may be affixed to a substrate that contains sufficient moisture to activate the adhesive properties of the adhesive.

[0022] In some embodiments, in addition to or as an alternative to some or all of the above criteria, the criteria for use on security documents may include a requirement that the adhesive provide wet tack between the wet substrate and the security device in the paper machine, allowing for precise alignment (sometimes referred to as registration) with other constructional features of the security document. Performance criteria for adhesives according to certain embodiments of the present disclosure may include a requirement that the adhesive not curl the security device in the paper machine. Performance criteria for various adhesives of the present disclosure may also include a requirement that the adhesive remain adhered to both the paper substrate and the security device on the finished security document after immersion in one or more organic solvents or aqueous solutions. Examples of aqueous agents that may be included in the adhesive performance criteria include, but are not limited to, acids (e.g., hydrochloric acid solution), bases (e.g., sodium hydroxide solution), and oxidizing agents (e.g., bleach). Examples of organic solvents that may be included in the adhesive performance criteria include, but are not limited to, toluene and acetone.

[0023] In addition to or as an alternative to the performance criteria mentioned above, performance criteria for adhesives according to certain embodiments of the present disclosure may include a requirement to withstand common currency mechanical tests, including but not limited to wash tests, crumple tests, cycling simulations, Sutherland rubbing and tape tests on the finished security document. Performance criteria for adhesives according to some embodiments of the present disclosure include, but are not limited to, a requirement that the adhesive be usable on security documents in which a security device (e.g., micro-optical threads) is woven into a paper substrate, as well as security documents in which a security device is affixed to the outside of a paper substrate. However, further performance criteria for adhesives according to various embodiments of the present disclosure include a requirement that the adhesive be able to adhere to the security device and paper substrate, preferably without a primer or surface treatment.

[0024] As mentioned above, the properties and performance of the adhesive used in manufacturing security documents contribute significantly to the overall performance of the security document and its ability to reliably provide evidence of authenticity and prevent counterfeiting.

[0025] Surprisingly, security documents that meet the performance requirements demanded by security document manufacturers, including the combination of performance criteria described above, can be produced by using adhesives according to certain embodiments of the present disclosure. The embodiments of the present disclosure allow for the use of polymers that are resistant to aqueous agents along with polymers that are solvent resistant, thereby providing security document manufacturers with adhesives that provide bonds between substrates and security devices with unexpected durability. In other words, adhesives according to various embodiments of the present disclosure provide unexpectedly strong, thin, and tough (as used herein, the term "strong" encompasses the property of good resistance to external degrading agents such as aqueous agents (e.g., oxidizing agents, acidic solutions, and organic solvents) between the paper substrate and the security device, as well as organic solvents, while at the same time being compatible with the high volume, high precision paper machines used in the production of security documents) adhesives.

[0026] FIG. 2 illustrates an example of a security device 200 that can be affixed to a security document using an adhesive according to various embodiments of the present disclosure.

[0027] Referring to the non-limiting example of Figure 2, security device 200 includes a multi-layer micro-optical (MO) security device, a portion of which (e.g., portion of security article 110 of Figure 1) is shown in Figure 2. According to certain embodiments according to the present disclosure, security device 200 comprises an authentication structure having at least two layers, including focusing layer 205 and second layer 210.

[0028] According to an embodiment, the focusing layer 205 includes an array of precisely formed focusing elements such as microlenses (including, for example, microlens 207) formed from a substantially transparent material having an appropriate index of refraction. In some embodiments according to the present disclosure, the focusing layer is disposed on a second layer 210 that includes a layer of substantially optically transparent material that includes image elements (e.g., image elements 213). In various embodiments, the image elements 213 are disposed on a top surface of the second layer 210. In certain embodiments, the image elements 213 are disposed within the second layer 210 (e.g., within voids created in the material of the layer). In some implementations, the image elements 213 are disposed on a bottom surface of the second layer 210. The positioning of the image elements relative to the focusing elements generates an optical effect, such as a composite image, when the image elements are viewed through the focusing elements.

[0029] Referring to the non-limiting example of FIG. 2, in certain embodiments, the security device 200 has a thickness of about 50 microns or less and is affixed to the underside of the second layer 210 via an adhesive applied to the paper substrate. Further, to enhance security, in certain embodiments, the security device 200 is precisely positioned on the substrate (e.g., relative to a window or printed content within the substrate). Thus, the thinness of the security device 200 and the operating principles (e.g., certain security devices according to this must be substantially flat and oriented with the focal element facing the viewer) can impose additional performance requirements on the adhesive used to attach the security device 200 to the paper substrate. For example, the adhesive must be thin enough to prevent the security device from curling or wrinkling during the manufacturing process. At the same time, in some embodiments, the security device includes the ability to transition to a "tacky" state, such as wet tack (as used herein, the term "wet tack" refers to the ability to transition from a dry state to a relatively sticky or tacky state when wetted) between the security device and a wet or semi-wet substrate, such that the security device 200 remains in the same position on the substrate for the remainder of the process of manufacturing the security document.

[0030] Certain embodiments according to the present disclosure include an adhesive that unexpectedly meets these additional performance requirements imposed by the thinness and operating principles of security devices (e.g., security device 200) suitable for use with security documents.

[0031] 2 shows an example of a security device, but various modifications can be made to FIG. 2. For example, security devices suitable for security documents according to the present disclosure include, but are not limited to, refractive security devices (e.g., as shown in FIG. 2), security devices with authentication structures using reflective focusing elements, and diffractive security devices such as holograms. Further examples of security devices that can be incorporated into security devices according to embodiments of the present disclosure include security devices using authentication structures with reflective, diffractive, and hybrid optical structures, as well as other single or multi-layer structures such as conductive traces, circuit patterns, microlenses, waveguides, negative pressure space air lenses, insulating ceramic structures, icon structures, microtext, anti-reflective structures, photorefractive prisms, micromirror structures, patterned or non-patterned metallization, fluorescent security prints, ruled gratings, periodic or non-periodic arrays, structures for increasing surface area, and element-changing structures.

[0032] FIG. 3 illustrates an example of a paper machine 300 for implementing methods for creating security documents according to various embodiments of the present disclosure.

[0033] 3, a paper machine 300 creates a web of paper substrate including a security device (e.g., security device 200 of FIG. 200) attached by an adhesive in accordance with certain embodiments of the present disclosure. According to various embodiments, the paper machine 300 forms a continuous web 349 of fibrous substrate by spreading an aqueous slurry across a table having a wire section.

[0034] According to various embodiments, the paper machine 300 includes a headbox 303 that contains an aqueous slurry including water, cellulose (e.g., bleached wood pulp), and in certain embodiments, binders and / or additional fibrous materials (e.g., flax fibers or microthreads) to enhance the strength and security properties of the finished security document. In some embodiments, the aqueous slurry passes from the headbox 303 onto a wetting line 342 that includes a moving wire mesh through which water is drained from the aqueous slurry to form a wet substrate. In various embodiments, a security device 341 (which in certain embodiments includes the features and structure of the security device 200 of FIG. 2) having an adhesive applied thereto according to various embodiments of the present disclosure is placed onto a moving wet substrate that includes sufficient water to activate one or more polymers in the adhesive that exhibit tackiness when wetted. As used in this disclosure, the term "tackiness" encompasses the property that a material can be activated to transition from an initially dry state to a relatively adhesive state, where the material exhibits a sticky, or "tacky" feel. According to various embodiments, materials that exhibit tackiness exhibit the following modes of activation - wet, or aqueous activation (producing what is referred to herein as "wet tack"), exposure to heat (referred to herein as "thermal tack"), or exposure to a solvent (referred to herein as "solvent tack").

[0035] According to certain embodiments, polymers that exhibit tack-imparting properties in response to aqueous activation (e.g., contacting the web of material at the wet end of the papermaking machine 300 in FIG. 3) include polyvinylpyrrolidone, Carboxymethylcellulose , Guar, gum arabic, and polyacrylic acid. In various embodiments according to the present disclosure, polymers that exhibit tackiness in response to thermal activation include, but are not limited to, polyethylene, ethylene copolymers, polystyrene, poly(vinyl chloride), polytetrafluoroethylene, styrene butadiene rubber (SBR), polyurethane, and ethyl vinyl acetate. According to an embodiment, polymers that exhibit thermal tackiness become tackiness at temperatures ranging from 50° C. to 200° C., and polymers that exhibit thermal tackiness at 80° C. are well suited for continuous web processing. Examples of polymers that exhibit solvent tackiness include, but are not limited to, SBR and polypropylene.

[0036] In some embodiments, the security device 341 comprises a continuous web (e.g., a strip) of material having one or more security features (e.g., micro-optics as described with respect to security device 200 of FIG. 2) that are continuously applied to a continuous web 349 of fibrous substrate at a point after the wetting line 342 and prior to the couch roll 344. In certain embodiments, the security device 341 may be applied between vacuum boxes 345a and 345b, which may aid in setting the security device within the fibrous substrate. In various embodiments, moisture provided by the continuous web 349 of fibrous substrate may, for example, activate at least one component of an adhesive, e.g., a polymer exhibiting tack-imparting properties, to create a wet tack between the security device 341 and the continuous web 349.

[0037] Although not shown in FIG. 3, in certain embodiments, the paper machine 300 includes one or more processing sections (e.g., a drying section including heated drying rollers) that are maintained at or above a temperature within a predetermined temperature range. In various embodiments, the predetermined temperature range is between 65 and 100° C. In some embodiments, the predetermined temperature range covers temperatures above 100° C. According to some embodiments, exposure of the adhesive to an area of ​​the paper machine 300 that is at or above the predetermined temperature activates a chemical reaction between the crosslinking agent and one or more of the adhesive's constituent polymers. According to various embodiments, the predetermined temperature range corresponds to a range of temperatures associated with sufficient thermal energy for substantially all of the activated crosslinking agent to react with one or more of the adhesive's constituent polymers at a rate compatible with time scales associated with the manufacture of security documents. As a non-limiting example, it is believed that a chemical reaction between a particular crosslinking agent and one or more of the adhesive's constituent polymers can be activated at 35° C. and reacted at a rate such that substantially all of the crosslinking agent reacts with the polymer within one hour. In this purely illustrative example, the chemical reaction may be activated at 50° C. to proceed at such a rate that substantially all of the crosslinker reacts with the polymer within 15 seconds. For most applications, particularly continuous web paper converting applications, 50° C. is within the range of temperatures, whereas 35° C. would be outside the range of temperatures since the web does not stay on the dryer roll for an hour or less. Those skilled in the art will appreciate that the range of temperatures, according to certain embodiments, depends on a variety of context-specific factors, including, but not limited to, the activation energy of the chemical reaction between the crosslinker and the one or more polymers, the time the adhesive is exposed to the activation energy source (e.g., heated dryer rollers), and the material properties of the surfaces to be bonded (e.g., the melting point of the polymer substrate of a holographic security strip). In certain embodiments, the chemical reaction between the crosslinker and one or more polymers in the adhesive occurs at one or more reactive sites of the polymer molecules of the adhesive, thereby rendering one or more of the constituent polymers of the adhesive less reactive.In this manner, adhesives according to various embodiments of the present disclosure, when dried, are capable of forming an adhesive bond between a paper substrate and a security device that is thin, strong, and resistant to, but not limited to, organic solvents, aqueous solvents, and oxidizing agents, which is part of the finished security document.

[0038] FIG. 4 illustrates operations of a method 400 for producing a security document according to various embodiments of the present disclosure.

[0039] Referring to the non-limiting example of FIG. 4, the operations associated with incorporating a security device (e.g., security device 200 of FIG. 2) into a security document are advantageously integrated into the process for making the paper substrate, rather than laminating the security device separately onto a pre-prepared substrate. From a manufacturing standpoint, the embodiment of the method shown in FIG. 4 is advantageous in that it avoids additional manufacturing steps and allows existing paper machines to be utilized. From a performance standpoint, the embodiment of the method described with respect to FIG. 4 is also advantageous in that it produces a security document that is thin (in some cases with a dry adhesive layer thickness of .about.3 microns) yet has a strong bond attached to the paper substrate. In contrast, other adhesives, such as some pressure adhesives, typically produce a weaker interface between the paper substrate and the security device, having a thickness on the order of .about.25 microns.

[0040] As shown in the non-limiting example of FIG. 4, method 400 includes an operation 410 in which an adhesive is introduced to a substrate (e.g., continuous web 349 of FIG. 3) that contains sufficient water to water-activate the polymers of the adhesive that exhibit tack-imparting properties to provide wet tack. In this illustrative example, the adhesive includes a plurality of polymers that collectively exhibit tack-imparting properties, resistance to aqueous agents, and solvent resistance, and a crosslinker selected to be activated to chemically react with one or more of the polymers at a temperature in a predetermined temperature range. In some implementations, the adhesive is pre-applied as a wet layer on a surface of the security device (e.g., bottom surface of second layer 210 of FIG. 2), for example, by spraying or with a Mayer rod. In various embodiments, the adhesive is pre-applied and left to dry as a layer of adhesive on a surface of the security device. Thus, when the security device is contacted with a wet substrate, the adhesive receives sufficient moisture to water-activate the polymers of the adhesive that exhibit tack-imparting properties to provide wet tack between the security device and the substrate.

[0041] In certain embodiments according to the present disclosure, in operation 420, a security device (e.g., security device 200 of FIG. 2) is placed over the portion of the substrate where the adhesive was introduced. According to certain embodiments, the moisture of the wet substrate causes the tack-imparting adhesive polymer to be water activated, causing the adhesive to exhibit wet tack. In some embodiments, the polymer is activated in the sense that it absorbs enough water to allow for a physical bond to the substrate, thereby adhering the security device in substantially the same position relative to the substrate as the substrate continues through the paper machine into the finished product.

[0042] FIG. 5 illustrates aspects of the composition and properties of component compounds of an adhesive (500) according to various embodiments of the present disclosure.

[0043] 5, adhesive 500 includes a plurality of polymers and a crosslinker 525. According to various embodiments, the plurality of polymers 505 includes two or more polymers that collectively exhibit the properties of tack (510), resistance to aqueous agents (515), and solvent resistance (520) (as indicated by region 523).

[0044] As discussed elsewhere in this disclosure, in certain embodiments, a single polymer can exhibit one or more of tackiness 510, water agent resistance 515, and solvent resistance 520. For example, the material properties of a polymer exhibiting tackiness and water agent resistance are represented by region 511. Similarly, the material properties of a polymer exhibiting water agent resistance and solvent resistance are represented by region 517 in FIG. 5, and the material properties of a polymer exhibiting solvent resistance and tackiness are represented by region 521.

[0045] The non-limiting representation of the plurality of polymers 505 in FIG. 5 is intended to be descriptive, and the representation of the polymer properties of the plurality of polymers 505 should not be construed as requiring that the plurality of polymers 505 include a particular number of polymers within the range of two or more polymers.

[0046] In certain embodiments according to the present disclosure, adhesive 500 further includes a cross-linking agent 525 selected to be activated to chemically react with one or more polymers of the plurality of polymers 505 at a temperature within a predetermined temperature range.

[0047] According to certain embodiments, in operation 430, the portion of the substrate to which the adhesive has been introduced and to which the security device has been affixed passes through a section of a paper machine (e.g., a heated dryer section) that is set at or above a predetermined temperature range to activate a chemical reaction between the crosslinking agent and one or more of the polymers. In one embodiment, the heated dryer section comprises a portion of a paper machine at or above a predetermined temperature range. Once activated to react, the crosslinking agent reacts with some or all of the available reactive sites in the molecules of the constituent polymers of the adhesive, effectively "tying up" the reactive sites and thereby reducing the ability of the constituent polymers of the adhesive to subsequently react with externally applied degrading agents, such as boiling water, acid solutions, base solutions, oxidizing agents, or organic solvents (e.g., acetone or toluene).

[0048] As discussed elsewhere in this disclosure, adhesives according to certain embodiments of the present disclosure include multiple polymers that collectively exhibit, but are not limited to, tackiness, water resistance, and solvent resistance. According to various embodiments, the multiple polymers selected reflect an optimization or balance of desirable properties exhibited within a set of potentially suitable polymers (e.g., tackiness, water resistance, and solvent resistance). Furthermore, certain adhesives according to the present disclosure include one or more polymers that exhibit at least two desirable properties, such as tackiness and solvent resistance.

[0049] In some embodiments according to the present disclosure, the plurality of polymers includes polymers that exhibit tack-imparting properties and can be aqueous activated to provide wet tack using water present in the substrate. The wet tack provided by the tack-imparting polymer facilitates accurate positioning of the security device on the substrate while preventing the security device from wrinkling, obliterating, or twisting as the substrate passes through a paper machine.

[0050] Examples of polymers that exhibit tackiness and can be used to make adhesives according to some embodiments of the present disclosure include at least polyvinylpyrrolidone (PVP), polyvinyl alcohol, and carboxymethyl cellulose (CMC). Examples of polymers that exhibit tackiness and can be included to make adhesives according to various embodiments of the present disclosure also include, but are not limited to, guar gum, styrene butadiene rubber (SBR), gum arabic, and polyacrylic acid.

[0051] In the adhesive according to various embodiments of the present disclosure, the plurality of polymers comprises at least one polymer that exhibits solvent resistance. Examples of polymers that exhibit solvent resistance and are suitable for use in the adhesive according to some embodiments of the present disclosure include, but are not limited to, polypropylene (PP), carboxymethyl cellulose (CMC), polyvinyl alcohol, polyether ether ketone (PEEK), and polytetrafluoroethylene (PTFE). Further examples of polymers that exhibit solvent resistance and are suitable for use in the adhesive according to certain embodiments of the present disclosure include, but are not limited to, polyethylene (PE) and ethylene copolymers.

[0052] Adhesives according to various embodiments of the present disclosure include at least one polymer that exhibits resistance to aqueous agents (e.g., acids, bases, and oxidizing agents) and a solvent, including organic solvents such as chlorinated solvents, hydrocarbon solvents, and polar and non-polar solvents. In some embodiments, the polymer complements the performance component provided by the solvent-resistant polymer. Examples of polymers that exhibit resistance to aqueous agents and can be used in adhesives according to some embodiments of the present disclosure include, but are not limited to, polypropylene (PP), polyurethane (PU), polystyrene and styrene copolymers, polyethylene terephthalate (PET), and polyvinyl chloride (PVC). Further examples of polymers that exhibit resistance to aqueous agents and are suitable for use in adhesives according to certain embodiments of the present disclosure include, but are not limited to, polytetrafluoroethylene (PTFE), polyethylene (PE) and ethylene copolymers, polyvinylidene fluoride (PVDF), and copolymers of poly(vinyl acetate).

[0053] Developing an adhesive made of a polymer that is resistant to water-based agents and is compatible with a paper machine (e.g., paper machine 300 in FIG. 3) presents certain technical challenges, which stem from the fact that the polymer that is resistant to water-based agents typically does not "want" to mix in aqueous solutions or with the water provided by a wet substrate. In some embodiments, to overcome this water resistance and make the polymer fully compatible with the water of the wet substrate and aqueous solution, the polymer that is resistant to water-based agents is provided as an aqueous solution, emulsion, or dispersion in a liquid matrix.

[0054] Certain polymers suitable for use in adhesives according to embodiments of the present disclosure may exhibit more than one of the desirable properties of tackiness, resistance to aqueous agents, and resistance to solvents, including organic solvents. For example, certain polymers, including but not limited to carboxymethylcellulose (CMC) and polyvinyl alcohol, exhibit both tackiness and resistance to organic solvents, and can be combined with a second polymer that exhibits resistance to aqueous agents, and a crosslinker to produce an adhesive according to embodiments of the present disclosure. As another example, certain other polymers, including, for example, polytetrafluoroethylene (PTFE), polypropylene (PP), and polyethylene (PE), and ethylene copolymers, exhibit both resistance to organic solvents and aqueous agents, and can be combined with a second polymer that exhibits tackiness, and a crosslinker to produce one or more adhesives according to embodiments of the present disclosure.

[0055] The adhesive according to certain embodiments of the present disclosure further includes a crosslinker that is activated to chemically react with one or more of the polymers at a temperature in a predetermined temperature range. Thus, crosslinkers suitable for use in adhesives according to certain embodiments of the present disclosure may be selected or formulated to be activated and react at temperatures and time scales consistent with the manufacture of security documents. Thus, crosslinkers configured to activate at temperatures much higher than those realized on a paper machine may be inappropriate. Similarly, crosslinkers that react slowly at low temperatures are inappropriate given the speeds at which modern paper machines operate. For example, certain paper machines suitable for producing security documents can produce hundreds of feet of security documents per minute.

[0056] Thus, crosslinkers suitable for use in adhesives according to embodiments of the present disclosure are generally selected to be activated to chemically react with one or more of the adhesive's constituent polymers at temperatures and time scales relevant to a point in the production of security documents on a paper machine (e.g., paper machine 300 shown in FIG. 3). As such, activation temperatures and reaction rates associated with crosslinkers suitable for use in adhesives according to the present disclosure can present additional technical challenges, including, but not limited to, maintaining the crosslinker from reacting with other components of the adhesive until the material to be adhered to the paper substrate is properly positioned relative to the substrate. In certain embodiments according to the present disclosure, premature or undesired reactions between the crosslinker and other components of the adhesive can be avoided by preventing activation of the chemical reaction between one or more of the adhesive's constituent polymers and the adhesive material until an appropriate temperature in a predetermined temperature range for activating the chemical reaction is reached.

[0057] Examples of cross-linking agents suitable for use in adhesives according to various embodiments of the present disclosure include, but are not limited to, glyoxal, glyoxylic acid and its salts. Further examples of cross-linking agents suitable for use in adhesives according to certain embodiments of the present disclosure include, but are not limited to, glutaraldehyde, isocyanates, aziridines, and carbodiimides.

[0058] According to certain embodiments, the crosslinking agent is selected to be activated to chemically react with at least one of the polymers in the adhesive. In some embodiments, the crosslinking agent reacts with one or more polymers that are resistant to aqueous agents (e.g., polyurethane) and tacky (e.g., carboxymethyl cellulose). In some embodiments, the crosslinking agent reacts with one or more polymers that are solvent resistant (e.g., copolymers of ethylene). In various embodiments, the crosslinking agent reacts with at least one polymer that exhibits tackiness, at least one polymer that exhibits solvent resistance, and at least one polymer that exhibits resistance to aqueous agents.

[0059] An example adhesive according to some embodiments of the present disclosure includes an adhesive including a plurality of polymers that collectively exhibit tack, aqueous agent resistance, and solvent resistance, and a crosslinker selected to be activated to chemically react with one or more of the plurality of polymers at a temperature within a predetermined temperature range.

[0060] Examples of adhesives according to various embodiments of the present disclosure include adhesives in which a first polymer of a plurality of polymers exhibits tack and solvent resistance.

[0061] Examples of adhesives according to some embodiments of the present disclosure include adhesives in which the first polymer does not exhibit resistance to water-based agents.

[0062] Examples of adhesives according to certain embodiments of the present disclosure include adhesives in which a first polymer of the plurality of polymers exhibits resistance to aqueous agents and solvents.

[0063] Examples of adhesives according to various embodiments of the present disclosure include adhesives in which the first polymer does not exhibit tackifying properties.

[0064] Exemplary adhesives according to certain embodiments of the present disclosure include adhesives further comprising a third polymer, wherein a first polymer of the plurality of polymers exhibits resistance to aqueous agents, a second polymer of the plurality of polymers exhibits solvent resistance, and a third polymer of the plurality of polymers exhibits tackifying properties, and wherein a crosslinker is activated and selected to chemically react with one or more of the first polymer, the second polymer, or the third polymer at a temperature within a predetermined temperature range.

[0065] Exemplary adhesives according to some embodiments of the present disclosure include adhesives that exhibit wet tack upon contact with a substrate containing sufficient water to activate a polymer from the plurality of polymers that exhibits tackiness.

[0066] Examples of adhesives according to various embodiments of the present disclosure include adhesives in which the tack-imparting polymer from the plurality of polymers comprises at least one of polyvinylpyrrolidone, carboxymethylcellulose, guar, styrene butadiene rubber, gum arabic, or polyacrylic acid.

[0067] Exemplary adhesives according to some embodiments of the present disclosure include adhesives in which the polymers of the plurality of polymers that exhibit resistance to aqueous agents are provided as a solution, emulsion or dispersion in a liquid matrix.

[0068] Examples of adhesives according to certain embodiments of the present disclosure include adhesives in which the solvent-resistant polymer from the plurality of polymers includes at least one of polyethylene, ethylene copolymer, polypropylene, polytetrafluoroethylene, carboxymethylcellulose, or polyetheretherketone.

[0069] Examples of adhesives according to various embodiments of the present disclosure include adhesives in which the polymers that are resistant to aqueous agents include at least one of polyvinylidene fluoride, polyethylene terephthalate, polyvinyl chloride, polyethylene, ethylene copolymers, polypropylene, polytetrafluoroethylene, polyurethane, and copolymers of poly(vinyl acetate).

[0070] Example adhesives according to some embodiments of the present disclosure include adhesives having a temperature in the predetermined temperature range greater than 100°C.

[0071] Examples of adhesives according to certain embodiments of the present disclosure include adhesives in which the predetermined temperature range is from 65 to 100°C.

[0072] Exemplary adhesives according to certain embodiments of the present disclosure further include adhesives that contain a blocking agent that is deactivated at temperatures within a predetermined temperature range.

[0073] Examples of adhesives according to certain embodiments of the present disclosure include those in which the crosslinking agent contains one or more of an aziridine, a carbodiimide, an isocyanate, a glutaraldehyde, a glyoxal, a glyoxylic acid, or a salt thereof.

[0074] Exemplary adhesives according to some embodiments of the present disclosure include adhesives in which a crosslinking agent is selected to be activated at a temperature within a predetermined temperature range to chemically react with the tackifying polymers of the plurality of polymers.

[0075] Examples of adhesives according to various embodiments of the present disclosure include adhesives in which a cross-linking agent is selected to be activated to chemically react with those polymers of the plurality of polymers that exhibit solvent resistance at a temperature within a predetermined temperature range.

[0076] An example adhesive according to certain embodiments of the present disclosure includes an adhesive in which a cross-linking agent is selected to be activated at a temperature within a predetermined temperature range to chemically react with polymers of the plurality of polymers that are resistant to aqueous agents.

[0077] Examples of adhesives according to some embodiments of the present disclosure include adhesives in which a crosslinker is selected to be activated at a temperature within a predetermined temperature range to chemically react with one or more of a plurality of polymers that collectively exhibit tackifying properties and resistance to aqueous agents.

[0078] Exemplary adhesives according to various embodiments of the present disclosure include adhesives in which the crosslinking agent is selected to be activated so as not to chemically react with one or more of the solvent-resistant polymers.

[0079] Exemplary adhesives according to certain embodiments of the present disclosure include adhesives in which a crosslinker is selected to chemically react with each of the polymers that collectively exhibit tackiness, resistance to aqueous agents, and solvent resistance at or above a predetermined temperature range.

[0080] Examples of adhesives according to some embodiments of the present disclosure include adhesives in which the plurality of polymers does not include a single polymer that exhibits all three of the following: tack, solvent resistance, and resistance to aqueous agents.

[0081] An example security document according to various embodiments of the present disclosure includes a paper substrate, a security device, and an adhesive layer containing an adhesive that provides a bond between the security device and the paper substrate, the adhesive layer including a plurality of polymers that collectively exhibit tack, water and solvent resistance, and a crosslinker selected to be activated to chemically react with one or more of the plurality of polymers at a predetermined temperature range.

[0082] An example security document according to certain embodiments of the present disclosure includes a security document, wherein a first polymer of the plurality of polymers exhibits tack and solvent resistance.

[0083] Examples of security documents according to some embodiments of the present disclosure include security documents in which the first polymer does not exhibit resistance to aqueous agents.

[0084] An example security document according to various embodiments of the present disclosure includes a security document in which a first polymer of the plurality of polymers exhibits aqueous agent and solvent resistance.

[0085] Examples of security documents according to certain embodiments of the present disclosure include security documents in which said first polymer does not exhibit tack-imparting properties.

[0086] An example security document according to some embodiments of the present disclosure includes a security document comprising a third polymer, a first polymer of the plurality of polymers exhibiting resistance to aqueous agents, a second polymer of the plurality of polymers exhibiting solvent resistance, and a third polymer of the plurality of polymers exhibiting tackifying properties, and a crosslinker selected to be activated to chemically react with one or more of the first polymer, the second polymer, and the third polymer at a temperature in a predetermined temperature range.

[0087] Examples of security documents according to various embodiments of the present disclosure include security documents having a thickness of 10 microns or less.

[0088] Examples of security documents according to certain embodiments of the present disclosure include security documents having an adhesive layer thickness of 5 microns or less.

[0089] Exemplary security documents according to some embodiments of the present disclosure include security documents in which the adhesive exhibits wet tack upon contact with a substrate containing sufficient water to activate a polymer from said plurality of polymers that exhibits tackiness.

[0090] An example of a security document according to various embodiments of the present disclosure includes a security document in which the polymer exhibiting tackiness among the plurality of polymers includes at least one of polyvinylpyrrolidone, carboxymethylcellulose, guar, styrene butadiene rubber, arabic rubber, or polyacrylic acid.

[0091] Examples of security documents according to certain embodiments of the present disclosure include security documents in which the polymers of said plurality of polymers that are resistant to aqueous agents are provided as a solution, emulsion or dispersion in a liquid matrix.

[0092] An example security document according to some embodiments of the present disclosure includes a security document in which the solvent-resistant polymer of the plurality of polymers includes at least one of polyethylene, ethylene copolymer, polypropylene, polytetrafluoroethylene, carboxymethylcellulose, or polyetherketone.

[0093] An example of a security document according to various embodiments of the present disclosure includes a security document in which the aqueous agent-resistant polymer of the plurality of polymers includes at least one of polyvinylidene fluoride, polyethylene terephthalate, polyvinyl chloride, polyethylene, ethylene copolymers, polypropylene, polytetrafluoroethylene, polyurethane, and copolymers of poly(vinyl acetate).

[0094] Examples of security documents according to certain embodiments of the present disclosure include security documents having a temperature within the predetermined temperature range above 100°C.

[0095] Examples of security documents according to some embodiments of the present disclosure include security documents where the temperature in the predetermined temperature range is between 65 degrees Celsius and 100 degrees Celsius.

[0096] Examples of security documents according to various embodiments of the present disclosure include security documents where the adhesive further contains a barrier agent that is deactivated at a temperature within a predetermined temperature range.

[0097] Examples of security documents according to certain embodiments of the present disclosure include security documents in which the cross-linking agent includes one or more of an aziridine, a carbodiimide, an isocyanate, a glutaraldehyde, a glyoxal, a glyoxylic acid, or a salt thereof.

[0098] An example security document according to some embodiments of the present disclosure includes a security document in which a cross-linking agent is selected to be activated at a temperature in a predetermined temperature range to chemically react with a polymer of said plurality of polymers that exhibits tack-imparting properties.

[0099] An example security document according to various embodiments of the present disclosure includes a security document in which a cross-linking agent is selected to be activated to chemically react with a solvent-resistant polymer of the plurality of polymers at a temperature in a predetermined temperature range.

[0100] An example security document according to certain embodiments of the present disclosure includes a security document wherein a cross-linking agent is selected to be activated to chemically react with polymers of said plurality of polymers that exhibit resistance to aqueous agents at a temperature in a predetermined temperature range.

[0101] Examples of security documents according to some embodiments of the present disclosure include security documents in which a cross-linking agent is selected to be activated at a temperature in a predetermined temperature range to chemically react with one or more polymers of the plurality of polymers that collectively exhibit tackifying properties and resistance to aqueous agents.

[0102] An example security document according to various embodiments of the present disclosure includes a security document in which a crosslinker is selected to chemically react with each of the polymers in the plurality of polymers that collectively exhibit tackiness, aqueous resistance, and solvent resistance at or above a predetermined temperature range.

[0103] An example of a security document according to certain embodiments of the present disclosure includes a security document, wherein the plurality of polymers does not include a single polymer that exhibits all three of tackiness, solvent resistance, and resistance to aqueous agents.

[0104] An example of a method of making a security document according to some embodiments of the present disclosure includes, in a paper machine configured to pass a substrate comprising water through one or more processing sections, introducing an adhesive to form an adhesive layer, the adhesive comprising a plurality of polymers configured to form an adhesive layer, the adhesive comprising a plurality of polymers collectively exhibiting tack-imparting properties, resistance to aqueous agents, and solvent resistance, a crosslinker selected to be activated to chemically react with one or more of the plurality of polymers, and a crosslinker selected to chemically react with one or more of the plurality of polymers at a temperature in a predetermined temperature range, positioning a first portion of a substrate having the adhesive introduced thereto over a first portion of the substrate having the adhesive introduced thereto, passing the first portion of the substrate through a processing section of the paper machine at a temperature in a predetermined temperature range to activate the crosslinker to chemically react with one or more of the plurality of polymers, the adhesive comprising a polymer exhibiting tack-imparting properties to impart wet tack, the adhesive comprising a plurality of polymers collectively exhibiting tack-imparting properties, resistance to aqueous agents, and solvent resistance, the crosslinker selected to chemically react with one or more of the plurality of polymers at a temperature in a predetermined temperature range.

[0105] An example method of making a security document according to certain embodiments of the present disclosure includes a method in which a first polymer of the plurality of polymers exhibits tack and solvent resistance.

[0106] Examples of methods of making security documents according to some embodiments of the present disclosure include methods in which the first polymer does not exhibit resistance to aqueous agents.

[0107] An example method of making a security document according to various embodiments of the present disclosure includes a method in which a first polymer of said plurality of polymers exhibits aqueous agent and solvent resistance.

[0108] Examples of methods of making security documents according to certain embodiments of the present disclosure include methods in which the first polymer does not exhibit tackifying properties.

[0109] An example method of making a security document according to some embodiments of the present disclosure includes a method in which the adhesive further comprises a third polymer, a first polymer of the plurality of polymers exhibits resistance to aqueous agents, a second polymer of the plurality of polymers exhibits solvent resistance, and a third polymer of the plurality of polymers exhibits tackifying properties, and a crosslinking agent is activated and selected to chemically react with one or more of the first polymer, the second polymer, and the third polymer at a temperature in a predetermined temperature range.

[0110] An example method of making a security document according to various embodiments of the present disclosure includes a method in which the tack-imparting polymer from the plurality of polymers comprises at least one of polyvinylpyrrolidone, carboxymethylcellulose, guar, styrene butadiene rubber, arabic rubber, or polyacrylic acid.

[0111] An example method of making a security document according to certain embodiments of the present disclosure includes a method in which the polymer of the plurality of polymers that is resistant to aqueous agents is provided as a solution, emulsion or dispersion in a liquid matrix.

[0112] An example method for producing a security document according to some embodiments of the present disclosure includes a method in which the solvent-resistant polymer from the plurality of polymers comprises at least one of polyethylene, ethylene copolymer, polypropylene, polytetrafluoroethylene, carboxymethylcellulose, or polyetherketone.

[0113] An example method for producing a security document according to various embodiments of the present disclosure includes a method in which the polymers from the plurality of polymers that are resistant to aqueous agents include at least one of polyvinylidene fluoride, polyethylene terephthalate, polyvinyl chloride, polyethylene, ethylene copolymers, polypropylene, polytetrafluoroethylene, polyurethane, polyvinyl acetate, and copolymers thereof.

[0114] An example method for producing a security document according to certain embodiments of the present disclosure includes a method in which the temperature within the predetermined temperature range exceeds 100°C.

[0115] An example method of producing a security document according to some embodiments of the present disclosure includes a method in which the temperature in the predetermined temperature range is between 65 and 100°C.

[0116] An example method of making a security document according to various embodiments of the present disclosure includes introducing an adhesive to form a dry adhesive layer having a thickness of 10 microns or less.

[0117] An example method of making a security document according to certain embodiments of the present disclosure includes a method in which an adhesive is introduced to form a dry adhesive layer having a thickness of 5 microns or less.

[0118] An example method of making a security document according to some embodiments of the present disclosure includes a method in which the adhesive further contains a barrier agent that is deactivated at a temperature within a predetermined temperature range.

[0119] Examples of methods of making security documents according to various embodiments of the present disclosure include methods in which the cross-linking agent comprises one or more of an aziridine, a carbodiimide, an isocyanate, glutaraldehyde, glyoxal, glyoxylic acid, or salts thereof.

[0120] An example method of producing a security document according to an embodiment of the present disclosure includes a method in which a cross-linking agent is selected to be activated to chemically react with the tackifying polymers of the plurality of polymers at a temperature in a predetermined temperature range.

[0121] An example method of producing a security document according to some embodiments of the present disclosure includes a method in which a cross-linking agent is selected to be activated to chemically react with a solvent-resistant polymer of the plurality of polymers at a temperature in a predetermined temperature range.

[0122] An example method of producing a security document according to various embodiments of the present disclosure includes a method in which a cross-linking agent is selected to be activated to chemically react with a polymer of the plurality of polymers that exhibits resistance to aqueous agents at a temperature in a predetermined temperature range.

[0123] An example method of producing a security document according to certain embodiments of the present disclosure includes activating a crosslinking agent selected to chemically react with one or more polymers of the plurality of polymers that collectively exhibit tackifying properties and resistance to aqueous agents at a temperature within a predetermined temperature range.

[0124] Examples of methods for producing security documents according to some embodiments of the present disclosure include methods in which a crosslinker is selected to chemically react with each polymer of a plurality of polymers that collectively exhibit tackifying, aqueous agent resistance, and solvent resistance at or above a predetermined temperature range.

[0125] Examples of methods of making security documents according to various embodiments of the present disclosure include methods in which the plurality of polymers does not include a single polymer that exhibits all three of the following properties: tack, solvent resistance, and resistance to aqueous agents.

[0126] An example security device according to an embodiment of the present disclosure includes a security device including an authentication structure and an adhesive layer including an adhesive that provides a bond between the security device and a substrate, the adhesive including a plurality of polymers that collectively exhibit tackiness, water resistance, and solvent resistance, and a crosslinker selected to be activated to chemically react with one or more of the plurality of polymers at a predetermined temperature range.

[0127] Exemplary security devices according to some embodiments of the present disclosure include security devices in which a first polymer of the adhesive exhibits tack and solvent resistance.

[0128] Exemplary security devices according to various embodiments of the present disclosure include a security device in which a first polymer of the adhesive does not exhibit resistance to aqueous agents.

[0129] An example of a security device according to certain embodiments of the present disclosure includes a security device, wherein a first polymer of the adhesive exhibits aqueous agent and solvent resistance.

[0130] Exemplary security devices according to some embodiments of the present disclosure include security devices in which a first polymer of the adhesive does not exhibit tackiness.

[0131] An example security device according to various embodiments of the present disclosure further includes a third polymer of the plurality of adhesive polymers, where a first polymer of the plurality of adhesive polymers exhibits resistance to aqueous agents, a second polymer of the plurality of adhesive polymers exhibits solvent resistance, and a third polymer of the plurality of adhesive polymers exhibits tackifying properties, and the crosslinker is selected to be activated to chemically react with one or more of the first polymer, the second polymer, and the third polymer at a temperature within a predetermined temperature range.

[0132] Examples of security devices according to certain embodiments of the present disclosure include security devices having a thickness of 10 microns or less.

[0133] Examples of security devices according to some embodiments of the present disclosure include security devices in which the adhesive layer has a thickness of 5 microns or less.

[0134] Examples of security devices according to various embodiments of the present disclosure include security devices in which the adhesive exhibits wet tack from contact with a fibrous substrate that contains sufficient water to activate a tack-imparting polymer among a plurality of polymers of the adhesive.

[0135] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the tack-imparting polymer of the adhesive comprises at least one of polyvinylpyrrolidone, carboxymethylcellulose, guar, styrene butadiene rubber, arabic rubber, or polyacrylic acid.

[0136] Exemplary security devices according to some embodiments of the present disclosure include security devices in which the polymers of the adhesive that are resistant to aqueous agents are provided as a solution, emulsion or dispersion in a liquid matrix.

[0137] Exemplary security devices according to various embodiments of the present disclosure include security devices in which the solvent-resistant polymer of the adhesive comprises at least one of polyethylene, ethylene copolymer, polypropylene, polytetrafluoroethylene, carboxymethylcellulose, or polyetherketone.

[0138] Exemplary security devices according to certain embodiments of the present disclosure include security devices in which the aqueous agent-resistant polymer of the adhesive comprises at least one of polyvinylidene fluoride, polyethylene terephthalate, polyvinyl chloride, polyethylene, polyethylene, ethylene copolymers, polypropylene, polytetrafluoroethylene, polyurethane, polyvinyl acetate, or copolymers thereof.

[0139] Examples of security devices according to some embodiments of the present disclosure include security devices that have a temperature within the predetermined temperature range of greater than 100°C.

[0140] Examples of security devices according to various embodiments of the present disclosure include a security device where the predetermined temperature range temperature is between 65 degrees Celsius and 100 degrees Celsius.

[0141] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the adhesive further contains a barrier agent that deactivates at temperatures within a predetermined temperature range.

[0142] Examples of security devices according to some embodiments of the present disclosure include security devices in which the cross-linking agent contains one or more of an aziridine, a carbodiimide, an isocyanate, a glutaraldehyde, a glyoxal, a glyoxylic acid, or a salt thereof.

[0143] Exemplary security devices according to various embodiments of the present disclosure include security devices in which a cross-linking agent is selected to be activated at a temperature within a predetermined temperature range to chemically react with a tackifying polymer of the adhesive.

[0144] An example security device according to certain embodiments of the present disclosure includes a security device in which a cross-linking agent is selected to be activated to chemically react with a polymer of the adhesive that exhibits solvent resistance at temperatures in a predetermined temperature range.

[0145] Exemplary security devices according to some embodiments of the present disclosure include a security device in which a cross-linking agent is selected to be activated to chemically react with a polymer of the adhesive that exhibits resistance to aqueous agents at a temperature in a predetermined temperature range.

[0146] Exemplary security devices according to various embodiments of the present disclosure include security devices in which a crosslinking agent is selected to be activated to chemically react with one or more of the adhesive's polymers that collectively exhibit tackifying properties and resistance to aqueous agents at temperatures in a predetermined temperature range.

[0147] Exemplary security devices according to certain embodiments of the present disclosure include security devices in which a crosslinking agent is selected to chemically react with each of the polymers of the adhesive that collectively exhibit tackiness, aqueous agent resistance, and solvent resistance at or above a predetermined temperature range.

[0148] Exemplary security devices according to some embodiments of the present disclosure include security devices in which the multiple polymers of the adhesive do not include a single polymer that exhibits all three of the following: tack, solvent resistance, and resistance to aqueous agents.

[0149] Examples of security devices according to various embodiments of the present disclosure include security devices in which the substrate is a continuous web that is applied as a security article to a security document.

[0150] Examples of security devices according to certain embodiments of the present disclosure include security devices in which the authentication structure has a focusing layer.

[0151] Examples of security devices according to some embodiments of the present disclosure include security devices in which the focusing layer comprises one or more of an array of refractive focusing elements or an array of reflective focusing elements.

[0152] Examples of security devices according to various embodiments of the present disclosure include security devices in which the authentication structure generates a composite image.

[0153] The authentication structure includes a security device, where the authentication structure comprises one or more of a diffractive security device, a conductive trace, a circuit pattern, a waveguide, a negative space air lens, an insulating ceramic structure, an iconic image element, microtext, an anti-reflective structure, a light refractive prism, a micromirror structure, patterned metallization, unpatterned metallization, a fluorescent security print, a ruled grating, a periodic array, a non-periodic array, a structure for increasing surface area, or a tactile altering structure.

[0154] Nothing in this application should be read as implying that any particular element, step, or function is essential to being included in the scope of the claims. The scope of patented subject matter is defined solely by the claims. Further, none of the claims are intended to invoke 35 U.S.C. §112(f) unless "means for" is followed by a participle.

Claims

1. a plurality of polymers (505) including a polymer exhibiting tackiness (510) that is activated by the application of water to impart tackiness to the adhesive, a polymer exhibiting resistance to aqueous agents (515), and a polymer exhibiting solvent resistance (520), with no single polymer exhibiting all three of tackiness, solvent resistance, and water resistance; a cross-linking agent (525) that is activated at a temperature within a predetermined temperature range to chemically react with one or more of the polymers; Including, the tacky polymer comprises at least one of polyvinylpyrrolidone, carboxymethylcellulose, guar, gum arabic, or polyacrylic acid; the aqueous agent-resistant polymer is provided as an aqueous solution, emulsion, or dispersion in a liquid matrix and comprises at least one of polyvinylidene fluoride, polyethylene terephthalate, polyvinyl chloride, polyethylene, ethylene copolymers, polypropylene, polytetrafluoroethylene, polyurethane, or poly(vinyl acetate) copolymers; The solvent-resistant polymer comprises at least one of polyethylene, ethylene copolymer, polypropylene, polytetrafluoroethylene, carboxymethylcellulose, or polyetheretherketone; glue.

2. 10. The adhesive of claim 1, wherein water is provided to the tackifying polymer by contacting the adhesive with a substrate containing water.

3. The adhesive of claim 1 , wherein the predetermined temperature range is greater than 100° C.

4. The adhesive of claim 1, wherein the predetermined temperature range is 65 to 100°C.

5. the crosslinking agent comprises one or more of an aziridine, a carbodiimide, an isocyanate, a glutaraldehyde, a glyoxal, a glyoxylic acid, or a salt thereof; or the crosslinking agent is activated at a temperature in the predetermined temperature range to chemically react with the tackifying polymer; or the crosslinking agent is activated at a temperature in the predetermined temperature range to chemically react with the solvent resistant polymer; or the crosslinking agent is activated at a temperature in the predetermined temperature range to chemically react with the aqueous agent-resistant polymer; or the crosslinking agent is activated at a temperature in the predetermined temperature range to chemically react with one or more of the polymers that exhibit tack and aqueous agent resistance properties; The adhesive of claim 1.

6. The adhesive of claim 1 , wherein the crosslinking agent does not chemically react with the solvent resistant polymer when activated at temperatures in the predetermined temperature range.

7. The adhesive of claim 1 , wherein the crosslinking agent chemically reacts with each of the plurality of polymers at or above the predetermined temperature range at which the crosslinking agent is activated.

8. A paper substrate; A security device (200); An adhesive layer comprising the adhesive according to claim 1; A security document (100) comprising:

9. 2. In one or more processing sections of a papermaking machine configured to pass a water-containing post-paper substrate, the adhesive of claim 1 is introduced into the substrate to form an adhesive layer; placing a security device over the first portion of the substrate having the adhesive disposed thereon; passing the first portion of the substrate through the process section of the papermaking machine at a temperature in the predetermined temperature range to activate the crosslinking agent to chemically react with one or more of the plurality of polymers; wherein the adhesive is introduced to the substrate in the processing section of the papermaking machine, and in the processing section, water is supplied to the adhesive from the substrate, which contains sufficient water to activate the tack-imparting polymer contained in the plurality of polymers, to activate the tack-imparting polymer and impart tackiness to the adhesive. How to create security documentation.

10. 10. The method of claim 9, wherein the adhesive is introduced to form a dry adhesive layer having a thickness of 10 μm or less.

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