Substrate with integrated security element

Abstract

A substrate (S) for use in forming a security product, e.g. a banknote, the substrate (S) having a laminated structure (1, 5, 3, 2) comprising: at least one upper layer (1, 5) of polymeric material; and at least one lower layer (3, 2) of polymeric material; wherein the laminated structure (1, 5, 3, 2) includes at least one at least partially diffractive optical security element (4) incorporated between the upper (1, 5) and lower (3, 2) layers.

Description

[0001] SUBSTRATE WITH INTEGRATED SECURITY ELEMENT

[0002] TECHNICAL FIELD

[0003] This invention relates to a substrate with one or more integrated optical security element(s) therewithin, i.e. a substrate with one or more optical security element(s) incorporated within its structure. Such substrates are particularly, though not exclusively, useful for forming banknotes and like products, e.g. securities, certificates, tickets, ID (identification) documents, or other items used for financial, security, identification, authentication or protection purposes. The invention also relates to a method for manufacturing such a substrate with one or more integrated optical security element(s) incorporated within it, as well as to a banknote or like product per se which comprises, or is formed from, such a substrate with one or more integrated optical security element(s) incorporated within it.

[0004] BACKGROUND AND PRIOR ART

[0005] One of the new directions currently being explored in the development of security elements for valuables and other products requiring high levels of security for authentication, identification or protection purposes is the development of substrates with integrated security elements therewithin. Such security elements are very often based on optical elements, especially holograms, and typically take the form of a DOVID (i.e. an at least partially diffractive optically variable image device). A DOVID is usually based on a single- or multilayer optical structure that creates different or varying visible optical effects depending on the conditions under which it is illuminated or has light applied thereto. Such a DOVID device typically includes at least one layer within its structure which includes diffractive optically active relief on a surface thereof.

[0006] Such DOVI D-based security elements are useful because they can exhibit a very high degree of security, thereby allowing security element designers wide flexibility in devising security features or systems that can provide degrees of security ranging from simply recognizable optical elements at the lay / public level right through to sophisticated security elements aimed at the expert level or even at the forensic level. DOVID-based security elements also allow the combining together of optical and e.g. electronic security features in a single security element, and this kind of interdisciplinary linking of security elements can significantly increase the levels of security that are attainable in end products to which such DOVID-based security elements are applied. For end applications such as new types of banknotes in particular, especially the newer types of plastics-based banknotes, developments in the art are further being directed towards the area of transparent substrates for use in forming such banknotes, where one or more DOVID- type security element(s) is / are integrated within the substrate’s structure and is / are intended for observation by a user or for verification by external means, e.g. through a transparent window in the banknote or directly through the entire product, which may even be transparent in its entirety.

[0007] In the case of newer type banknote applications, a typical polymer substrate material is often a PP (polypropylene), and in known such products a DOVID-type security element is applied to an outer surface of the transparent substrate, for example by direct or hot embossing. The surface of the substrate is then supplemented with one or more protective feature(s), e.g. one or more protective layer(s) or element(s), in the overall banknote production process, which protective feature(s) are intended to be sufficiently chemically and mechanically stable, or may even be fixed in position e.g. by a protective overprinted layer or coating. These processes are currently used for the manufacture of newer polymer-type banknotes, e.g. by companies such as CCL Secure and De la Rue.

[0008] But even so, the durability of these protective features on the surface of the base substrate is limited. This can lead to serious compromises in the overall resistance of the banknotes themselves to mechanical and / or chemical damage. Moreover, this known technology denies or limits the scope with which banknote designers can devise and incorporate additional protective elements - especially those of newer developed kinds - into the structures of banknotes, in particular with an eye to always needing to keep one step ahead of counterfeiters and the like.

[0009] Accordingly, it is a primary object of the present invention to address the above shortcomings in the known art of manufacturing banknotes and like products requiring high levels of security for authentication, identification or protection purposes, and to provide a new form of substrate and its manner of manufacture that enable the design and production of such banknotes and like products that exhibit enhanced integrity and longevity, as well as enhancing levels of security that are attainable by giving designers greater flexibility in incorporating plural security features in a given product’s structure.

[0010] SUMMARY OF THE INVENTION

[0011] Accordingly, in a first aspect the present invention provides a substrate for use in forming a security product, especially a banknote (or other product requiring a high level of security for authentication, identification or protection purposes), the substrate having a laminated structure comprising: at least one upper layer of polymeric material; and at least one lower layer of polymeric material; wherein the laminated structure includes at least one at least partially diffractive optical security element incorporated between the upper and lower layers.

[0012] In a second aspect the present invention provides a method for the manufacture of a substrate for use in forming a security product, especially a banknote (or other product requiring a high level of security for authentication, identification or protection purposes), the method comprising: laminating together at least one upper layer of polymeric material and at least one lower layer of polymeric material to form a laminated structure, wherein the lamination step includes incorporating between the upper and lower layers at least one at least partially diffractive optical security element.

[0013] In a third aspect the present invention provides a security product, especially a banknote (or other product requiring a high level of security for authentication, identification or protection purposes), comprising or formed from a substrate according to the first aspect of the invention or any embodiment thereof, or made according to the method of the second aspect of the invention or any embodiment thereof.

[0014] Accordingly, in its broadest sense the present invention aims to remove or ameliorate the above-discussed disadvantages of the known art by integrating one or more DOVID-type security element(s) by encapsulation between the substrate’s laminated layers. On the one hand, this solution may significantly strengthen the mechanical and chemical resistance properties of the overall substrate itself (e.g. when used to form banknotes), whilst on the other hand this solution may also make it possible or easier to integrate new protective or security elements, especially auxiliary ones or combinations of security elements, into a substrate’s structure - but now interiorly thereof -, which otherwise were it not to be for this invention could not be achieved if the known art of applying it / them to just an outer surface of a base plastics substrate were to be relied on instead.

[0015] Moreover, in certain specific embodiments of the invention, it may be a further advantage associated with such embodiments that such substrates can securely and durably incorporate optical security element(s) with deeper relief structures than would be the case using conventional thin holograms, thereby giving substrate designers even greater flexibility and more options for creating even more advanced optical security functions or effects for such embodiment substrates.

[0016] In accordance with the invention, the or each optical security element is an at least partially diffractive optical security element. This means it should possess or exhibit optically active behaviour or have an optical function that is to some degree diffractive in nature. In some practical embodiments such diffractive behaviour or function may be predominantly or even substantially total, whereby such one or more optical security element(s) may be classed as a “diffractive” optical security element. However, in other practical embodiments such one or more at least partially diffractive optical security element(s) may exhibit optically active behaviour or have an optical function that is to some degree - e.g. to a minor extent - refractive in nature. Thus, the term “at least partially diffractive optical security element” as used herein encompasses not only truly or fully diffractive such optical security elements but also ones that exhibit mixed or combined diffractive and refractive behaviour or properties, or ones that exhibit at least some (e.g. a minor) degree of refractive behaviour or properties. Thus, all references herein to simply “diffractive” in the context of the optical security element(s) or DOVIDs should therefore be construed accordingly with this broader sense and possible inherent nature, i.e. as encompassing optical security element(s) or DOVIDs which exhibit not only diffractive behaviour or properties but also to some extent some refractive behavior or properties.

[0017] In some practical embodiments of the invention, the or each (at least partially) diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure may be or comprise an at least partially diffractive relief-based optical security element, especially what may be termed an at least partially diffractive relief-based DOVID-type security element - i.e. the or each (at least partially) diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure may comprise an at least partially diffractive relief-based optical security element, especially an at least partially diffractive optical structure that includes (at least partially) diffractive optical relief on or in a surface of the material that forms that optical structure. Such relief-based optical structures may in practice be formed for example by conventional surface embossing techniques or known nano-imprinting lithography techniques, using conventional equipment, as are well-known in the art. Alternatively, in some alternative embodiments, the or each (at least partially) diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure may be or comprise an at least partially diffractive volume-type optical security element, especially what may be termed an at least partially diffractive volume-type DOVID-type security element - i.e. in which an at least partially diffractive optical structure is formed through at least a portion, especially through at least a substantial or majority portion, of the thickness of a body of material forming the optical element itself - the materials and techniques for making which are also well-known in the art.

[0018] Such optical structures based on surface relief may comprise relief features that are typically dimensioned such that they are represented by: widths and / or heights / depths of individual surface relief features in a range of from about 0.001 up to about 100 pm, optionally from about 0.01 up to about 80 or 90 or 100 pm, further optionally from about 0.05 up to about 70 or 80 or 90 or 100 pm, yet further optionally from about 0.1 up to about 50 or 60 or 70 or 80 or 90 or 100 pm.

[0019] In some such embodiments the or each (at least partially) diffractive optical structure may be formed directly on or in a surface of one of the layers (e.g. a carrier layer) of the laminated structure itself, especially on or in an upper surface of one of the layers (e.g. a carrier layer) of the laminated structure. Alternatively, in other such embodiments, the or each (at least partially) diffractive optical structure may be preformed as a discrete optical element which is then incorporated into the laminated structure during the lamination of the upper and lower layers thereof, with the preformed discrete optical element encapsulated or sandwiched between them. Such incorporation of such a preformed discrete optical element into the laminated structure during its layers’ lamination may in some embodiment forms involve bonding of the preformed discrete optical element (e.g. using a suitable adhesive or alternatively by direct thermal-bonding) to one or more surfaces of one or more of the layers of the laminated structure that contactingly sandwich the preformed discrete optical element therebetween. Alternatively or additionally, in some other embodiment forms, such incorporation may involve at least partially embedding the preformed discrete optical element in the one or more surfaces of one or more of the layers of the laminated structure that contactingly sandwich the preformed discrete optical element therebetween.

[0020] In certain ones of the above embodiments of the invention, the or each (at least partially) diffractive optical structure, which forms or constitutes the or each (at least partially) diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure, may be dimensioned such that it extends in the form of a patch over only a portion of, especially a minor portion of (e.g. up to about 10 or 20 or 30 or 40 or 50% of), the total area of the respective surface on or in which the optical structure is formed directly or to which the optical security element is affixed or bonded (as the case may be). However, in other ones of the above embodiments of the invention the or each (at least partially) diffractive optical structure, which forms or constitutes the or each (at least partially) diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure, may be dimensioned such that it extends over substantially the whole of the total area of the respective surface on or in which the optical structure is formed directly or to which the optical security element is affixed or bonded (as the case may be).

[0021] In some embodiments of the invention the or each optical security element that is / are incorporated between the upper and lower layers of the laminated structure may be of a light- transmissive type, i.e. the material of the body of material - especially the material of the relevant layer of the substrate - that forms or constitutes the optical security element or has formed in or on a surface thereof the optical security element in the form of (at least partially) diffractive optical relief, may allow the light (especially light in the visible region of the electromagnetic spectrum - as embodiments of the present invention generally may be designed for use with), with which the substrate is designed to be used, to pass through it. However, in other, alternative, embodiments the or each optical security element that is / are incorporated between the upper and lower layers of the laminated structure may be of a light- reflective type - i.e. the body of material that forms the optical security element and has the (at least partially) diffractive optical structure formed therein or thereon may comprise one or more metal layers, e.g. of Al, Au, Ag, Cr, Cu, etc, or alternatively some other material body that forms the optical security element may be provided with a suitable reflective coating (e.g. of those same metal(s)) - whereby the light (especially light in the visible region of the electromagnetic spectrum), with which the substrate is designed to be used, is reflected from the or the respective optical security element and does not substantially pass through it.

[0022] In some embodiments of the invention, in particular in those embodiments where the or each optical security element extends in the form of a patch only, there may be incorporated between the upper and lower layers of the laminated structure any suitable number of such patch-like optical security elements, e.g. one single such patch-like optical security element or alternatively a plurality of such patch-like optical security elements. The relevant number of such patch-like optical security element(s) may be applied or arranged in any suitable configuration, positioning, arrangement or pattern within the laminated structure, especially in terms of any suitable configuration, positioning, arrangement or pattern of any one or more of those optical security element(s) relative to the other(s) thereof. In practising many practical embodiments of the invention, especially those in which the or each (at least partially) diffractive optical security element comprises a surface relief-type optical structure, in order to maintain the efficacy of the optical function of the surface relief in the finished substrate, the or each respective optical security element may be provided with a or a respective - or even one or a plurality of - covering layer(s) or film(s) (especially relatively thin such layer(s) or film(s)) applied over the surface relief thereof, wherein the material of the covering layer(s) or film(s) has a refractive index that is significantly different from the refractive index of the material of the (at least partially) diffractive optical security element itself in which the optical relief is formed. Otherwise, the desired optical function of the surface relief may disappear after any overlying laminating layer of the substrate is applied over the surface relief of the or the respective optical security element. In many such embodiments, the significantly different refractive index material of the covering layer(s) or film(s) may have a refractive index that is significantly higher (e.g. higher by at least as much as 0.1 or 0.2 or 0.3 or 0.4 or 0.5 or even as much as 0.7 or 0.8) than the refractive index of the material of the optical security element itself in which the optical relief is formed. However, in other embodiments, it may in principle be possible instead for the significantly different refractive index material of the covering layer(s) or film(s) to have a refractive index that is significantly lower (e.g. lower by at least as much as 0.1 or 0.2 or 0.3 or 0.4 or 0.5) than the refractive index of the material of the optical security element itself in which the optical relief is formed.

[0023] In embodiments comprising such different refractive index covering layer(s) or film(s), the or each covering layer / film may extend either (a) over just the respective area extent of the or the respective individual optical security element, so that the respective covering layer / film is in register with the or each respective optical security element and co-extensive / co-terminous therewith in their area extents, or alternatively (b) the or each covering layer / film may be a part of a larger single overall covering layer / film that extends over substantially the whole area extent of the substrate’s laminated structure, and even into and across those regions / portions thereof which do not have applied thereto any such optical security element(s).

[0024] Moreover, in some such embodiments where any given covering layer / film or covering / layer film portion is applied so as to extend (a) over just the respective maximum area extent of a or a respective individual optical security element (so that the respective covering layer / film or portion is in register with the or the respective optical security element and co- extensive / co-terminous therewith in their maximum area extents), such a or a respective covering layer / film or portion may be applied either as (c) one single respective such covering layer / film or portion that extends over substantially the whole maximum area extent of the or the respective optical security element, or alternatively (d) a plurality of selectively arranged and applied covering layer / film or portion sections or segments that are spaced apart from each other and form a pattern or design or other discontinuous arrangement yet which collectively extend over substantially the whole maximum area extent of the or the respective optical security element.

[0025] Such thin covering layer(s) or film(s) with the different refractive index may generally be applied to the or the respective optical security element using e.g. vacuum deposition technology, many examples of which are known in the art. Typically, for example, a metallic material such as various metals, e.g. aluminium (Al) or copper (Cu), or high refractive index metal oxides (or other dielectric materials) such as TiC>2 or SiC>2, or even ZnS, may be used for such covering layers / films, in order to achieve an optimum required different refractive index (which for these materials may typically be up to around 2.5) and to facilitate their vacuum deposition (since such materials are well suited to such a deposition technique). Thus, by application of such high-refractive index covering layer(s) / film(s) onto the surface relief of the or the respective optical security element before the final laminating of the other (i.e. upper and lower layers, at least) of the substrate, the surface relief maintains and fulfils its desired optical function even after the laminated structure of the substrate has been finally formed.

[0026] In many practical embodiments of the invention the or each upper layer that forms part of the laminated structure may be formed of a substantially light-transparent polymeric material. Alternatively or additionally, the or each lower layer that forms part of the laminated structure may likewise be formed of a substantially light-transparent polymeric material. Suitable examples of such light-transparent polymers include PP (polypropylene), BOPP (biaxially- oriented polypropylene), PC (polycarbonate), PET (polyethylene terephthalate), PMMA (polymethyl methacrylate) or certain other acrylic-based polymers, and possibly other polymers that are known in the art of plastics and polymers for use in optics-related products. In this manner light for interacting with, or having already interacted with, the or each (at least partially) diffractive optical security element incorporated within the laminated structure of the substrate can readily pass through to, or back from, the or the respective optical security element without substantial energy or intensity loss, and so that any relevant designed security feature or property of the substrate can be properly viewed, detected or otherwise used and exploited for its security, authentication, identification or protection purpose.

[0027] In some, possibly relatively simple, embodiments of the invention in its various aspects, the laminated structure of the substrate may comprise just one upper polymer layer and one lower polymer layer, whereby the complete substrate comprises a laminated structure consisting of those two polymer layers (upper and lower) with the one or more (at least partially) diffractive optical security element(s) incorporated or sandwiched between those two layers, optionally (though preferably) with the above-mentioned covering layer(s) or film(s) (with the different refractive index) having been pre-applied onto the surface relief of the or each optical security element prior to its / their lamination by and between the upper and lower polymer layers.

[0028] However, in other, relatively more advanced, embodiments of the invention in its various aspects, the laminated structure of the substrate may comprise either or both of:

[0029] (i) two or more upper polymer layers, especially each being of an optically transparent polymer material (and each of which independently may or may not be the same polymer or a different polymer as / from that / those polymer(s) of the one or two or more (as the case may be) lower layer(s)), and / or

[0030] (ii) two or more lower polymer layers, especially each being of an optically transparent polymer material (and each of which independently may or may not be the same polymer or a different polymer as / from that / those polymer(s) of the one or two or more (as the case may be) upper layer(s)), whereby the complete substrate comprises a laminated structure consisting of those at least three or four - or possibly even as many as five or six or seven or eight (or even more) - polymer layers (being those layers among the upper and lower ones of the overall laminated structure) with the one or more (at least partially) diffractive optical security element(s) incorporated or sandwiched between at least two of those polymer layers - especially two of the centrally, or nearest to being centrally, located layers in the overall laminated structure - and again optionally (though preferably) with the above-mentioned covering layer(s) or film(s) (with the different refractive index) having been pre-applied onto the surface relief of the or each optical security element prior to its / their lamination by the various upper and lower polymer layers.

[0031] In some such embodiments as in the preceding paragraph, it may be that at least one of the two or more upper polymer layers, or at least one of the two or more lower polymer layers, or even at least two of the polymer layers being both upper and lower polymer layers, may constitute or comprise, or may be formed as, or may be applied as, an adhesive layer which bonds together a respective pair of neighbouring or adjacent layers immediately above and below it in the overall laminated structure. Such one or more adhesive layer(s) may be especially useful to employ and include if the polymer materials of the relevant neighbouring or adjacent layers do not permit or lend themselves readily to direct bonding by e.g. thermal adhesion.

[0032] Thus, in some such embodiment cases it may be that the or each such adhesive layer constitutes at least one of the layers of the laminated structure that is located immediately adjacent or encapsulates or covers or bounds or sandwiches or fixes in position within the substrate one or more of the (at least partially) diffractive optical security elements (optionally (though preferably) with the above-defined covering layer(s) or film(s) (with the different refractive index) having been pre-applied onto the surface relief of the or each such optical security element prior to its / their encapsulation or covering or bounding or sandwiching or fixing in position by that adhesive layer). Examples of suitable such adhesives for forming such adhesive layer(s) in the laminated structure include various acrylate-based adhesives or various UV-activated adhesives, many specific practical examples of each of which are well-known in the art of optics-based products and widely commercially available.

[0033] In some yet other, even more advanced, embodiments of the invention in its various aspects, the substrate may comprise a laminated structure in the form of a laminated super-structure comprising a plurality of laminated sub-structures, wherein each laminated sub-structure comprises a respective laminated structure - as defined in the first aspect of the invention or any embodiment thereof defined hereinabove - comprising at least one upper polymer layer and at least one lower polymer layer with at least one (at least partially) diffractive optical security element incorporated between them, and wherein the laminated sub-structures are laminated together with the other(s) thereof in a stacked fashion to create the complete laminated super-structure of the substrate. In this manner, such even more advanced embodiment substrates within the scope of the invention may be designed and manufactured which include a plurality of spaced-apart (i.e. spaced apart in the thickness dimension of the substrate) groups or layers of sandwiched / laminated (at least partially) diffractive optical security element(s), especially located at different height locations within the overall thickness of the substrate’s laminated super-structure, with respective combinations of upper and lower polymer layer(s) above and below each respective group / layer of sandwiched / laminated (at least partially) diffractive optical security element(s) effecting the overall sandwiching and laminating of those plural groups / layers of sandwiched / laminated (at least partially) diffractive optical security element(s) within the overall laminated superstructure of the complete substrate. In such embodiments, each such group / layer of (one or two or more, or a plurality of) sandwiched / laminated (at least partially) diffractive optical security element(s) may thus comprise (at least partially) diffractive optical security element(s) that are either substantially the same as - or alternatively are different from (especially significantly different from) - that / those (at least partially) diffractive optical security element(s) in one or more other such layers thereof within the overall substrate’s laminated super-structure in terms of their respective optical functions. This may thus give even greater flexibility to substrate designers in devising and manufacturing substrates within the scope of the invention which have especially advanced or unique combinations of different optical functions derived from different groups or layers of (at least partially) diffractive optical security elements incorporated within the overall substrate super-structure.

[0034] Going further, in any of the embodiment substrates defined hereinabove, in order to constitute yet further useful embodiments within the scope of the invention, there may be incorporated between any two polymer layers (i.e. between any two upper layers or any two lower layers or any two layers being upper and lower layers) of the above-defined laminated structure, or of the above-defined laminated super-structure or any one of its laminated substructure^), one or more auxiliary security elements which may be, or may each independently be, either an auxiliary optical security element or an auxiliary non-optical security element. Examples of such auxiliary optical security elements include any of those as defined or described hereinabove or hereinbelow in the context of the (at least partially) diffractive optical security element(s) incorporated essentially within the substrate’s laminated structure. Examples of such auxiliary non-optical security elements include electronic or electrical security devices, e.g. one or more electronic chips or electronically- readable devices or tags which can be detected or read by appropriate external reading or detection equipment. Where provided and incorporated into the substrate’s laminated structure, such auxiliary security element(s) - both of the optical and non-optical kinds - may provide additional or auxiliary means by which certain additional or auxiliary security functions, e.g. security, detection, identification or authentication functions, can be attained.

[0035] In various embodiments of the invention which include either (i) plural upper layers and / or plural lower layers and / or one or more such auxiliary security element(s), all as defined in the preceding five paragraphs, or (ii) one or more cover layer(s) or film(s) applied over one or more of the (at least partially) diffractive optical security element(s) in the laminated structure, or (iii) one or more auxiliary security element(s), it may be that: any one or more of those layers or one or more portions of one or more of those layers - whether that be one or more of the upper or lower layers or an adhesive layer or a cover layer or film applied over one or more of the (at least partially) diffractive optical security element(s), and whether or not it be such a layer or film that extends over substantially the whole area of the substrate’s laminated structure or only over one or more selected areas or regions thereof (e.g. over just the area extent of one or more of the (at least partially) diffractive optical security elements incorporated in the laminated structure), or any one or more such auxiliary security element, or possibly even both thereof, is / are constructed and / or arranged or is / are designed such as to impart to the overall substrate of such embodiment(s) one or more additional or auxiliary optical or non-optical security functions over and above - i.e. distinct from or superimposed upon - that / those optical function(s) of the one or more (at least partially) diffractive optical security element(s) itself / themselves.

[0036] Such one or more additional or auxiliary optical security functions may for example comprise providing a specific colouration effect of at least one such layer of the laminated structure. In that example case, one or more of the (at least partially) diffractive optical security element(s) in or adjacent such a colouring layer may for instance be fully or partially covered or coated - e.g. selectively covered or coated in only one or more selected portions thereof - with one or more layers (especially relatively thin layers) or one or more systems of pluralities of layers such as to provide a desired colouration effect at a preselected location or region on the relevant (at least partially) diffractive optical security element or on a portion thereof. Such a colouring layer may, for example, be or comprise a printed layer or coating for changing the colour by virtue of being or comprising a printed absorbing colour filter (examples of which are in principle well-known in the art), which may be suitable in particular for providing a desired colour effect when viewed in transparency or also in reflection (according to which such type of optical security element is being used in that particular portion of the substrate’s laminated structure).

[0037] Alternatively such a colouring layer may be or comprise one or more deposited thin layer(s) orfilm(s) over the surface of the (at least partially) diffractive optical security element, thereby providing for example an interference-type colour filter or colour shift or colour flop function / effect in the desired region of the substrate’s laminated structure. Such a colour shift or colour flop effect may manifest itself as, or may comprise, a change in pre-defined colour(s) at pre-defined angles of view, which may be achieved for example by a combination of any suitable number of dielectric or metal layers, with its / their layer materials and / or layer thickness(es) being selected appropriately, either as referred to hereinabove for optional layers that comprise such dielectric or metal materials or as will be well understood by persons skilled in the art. Alternatively such a colour shift or colour flop effect may manifest itself as, or may comprise, a change in pre-defined colour(s) at pre-defined angles of view, which may be achieved for example by a combination of a plurality of metal layers with at least one dielectric layer between those metal layers (examples of which combinations may in principle be well-known in the art), thereby constituting or providing a Fabry-Perot resonator-based colour filter or colour shift / f lop effect.

[0038] Other types of colouring layer(s) or colouring layer material(s) may of course be possible, according to established knowledge in the art.

[0039] In other, alternative, embodiments, such one or more additional or auxiliary optical security functions may even comprise providing a combination of inter-disciplinary security or detection properties or functions, e.g. at least one layer of the substrate’s laminated structure may be or may be provided with (e.g. in the form of one or more coating(s)) one or more thin layers of a metal oxide, such as TiC>2, Fe2C>3or WO2, which is deposited in a modified vacuum deposition stoichiometry and may complement the diffractive optical security element(s) in or adjacent such a layer both optically - e.g. by a coloured absorption filter created by the deposited layer - and / or by the possibility of non-optical security / detection, e.g. electronic detection by use of a readout device that exploits the specific conductivity changes of the deposited layers.

[0040] Yet further alternatively still, such one or more additional or auxiliary optical functions may even for example comprise: providing one or more printed layers on or over a surface of the (at least partially) diffractive optical security element which have an optical function in the IR (infra-red) region of the spectrum and so can be detected under IR (infra-red) illumination; or alternatively by providing one or more printed layers on or over a surface of the (at least partially) diffractive optical security element which have an optical function in the visible region of the spectrum, e.g. luminescence, colour flip effects of pigments, etc; or yet further alternatively by providing one or more printed layers on or over a surface of the (at least partially) diffractive optical security element which have an optical function in the UV (ultraviolet) region of the spectrum and so can be detected under UV (ultra-violet) illumination; or still yet further alternatively by providing one or more printed layers on or over a surface of the (at least partially) diffractive optical security element which are composed of or which comprise certain non-pigment materials, e.g. other forms of printing of other materials or even liquid crystal layer application(s), etc.

[0041] By use of such combinations of one or more additional or auxiliary optical functions added into the overall substrate laminated structure of such embodiments as exemplified above (i.e. supplementary to the optical function(s) of the (at least partially) diffractive optical security element(s) itself / themselves), it may in particular be possible to ensure proper desired functioning of the (at least partially) diffractive optical security element(s) itself / themselves after its / their lamination into the laminated structure of the final substrate product, or alternatively it may be possible to provide extended optical functions of the (at least partially) diffractive optical security element(s) itself / themselves in the final substrate product. In some embodiment cases such added non-optical functions may even be achieved, e.g. by the electronic validation as mentioned above using the electrical response of thin layers used in the optical system of the diffractive optical security element(s) itself / themselves.

[0042] In many practical embodiments of the present invention in its various aspects, any given pair of adjacent or neighbouring or superimposed polymer layers of the substrate’s laminated structure may be united or bonded together during or as part of the overall lamination procedure by means of either (a) direct thermal bonding (e.g. by use of appropriate elevated temperature(s) to effect uniting of or bonding directly between the relevant material(s) of the adjacent / neighbouring / superimposed layers, or alternatively (b) a suitable adhesive layer placed or coated or applied between them - as already mentioned above that one or more of the layers of the laminated structure may itself constitute or be composed of.

[0043] Such one or more adhesive layer(s) may be especially useful to employ and include if the polymer materials of the relevant adjacent / neighbouring / superimposed layers do not permit or lend themselves readily to direct bonding by e.g. thermal adhesion. However, direct thermal adhesion or thermal bonding may be possible instead if the polymer materials of the relevant layers to be laminated permit that capability. Thus, whichever manner of bonding together or laminating of the relevant layers may dependent on the identity or chemical nature and properties of the individual polymer materials and polymer combinations that are used in the relevant adjacent / neighbouring / superimposed layers that are to be laminated together in the substrate’s overall laminated structure. Precise practical details of suitable such techniques, equipment - and if necessary adhesives - for effecting such lamination of the layers into the final overall substrate structure will be generally well-known in the art.

[0044] In many practical embodiments of the invention in its various aspects, each of the various upper and lower polymer layers of the substrate’s laminated structure may be generally of any suitable thickness. For example, in typical example embodiments each of the upper and lower polymer layers may take the form of - or may be provided in the form of - a sheet, film, foil, strip or plate, e.g. having a thickness in an approximate range of from about 1 or 5 or 10 pm up to about 200 or 250 or 300 pm, or possibly even up to as much as about 400 or 500 pm. More usually and typically a substrate layer thickness in an approximate range of from about 10 or 20 or 50 pm up to about 100 pm may be used, although sometimes a thickness greater than this, i.e. up to around 250 or even up to around 300 or 400 pm, may be found to be suitable, e.g. depending on the intended end use of the final substrate product (e.g. in many instances it will be as a material for banknote).

[0045] Within the scope of this specification it is envisaged that the various aspects, embodiments, examples, features and alternatives, and in particular the individual constructional or operational features thereof, set out in the preceding paragraphs, in the claims and / or in the following description and accompanying drawings, may be taken independently or in any combination of any number of same. For example, individual features described in connection with one particular embodiment are applicable to all embodiments, unless expressly stated otherwise or such features are incompatible.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Various practical embodiments of the present invention will now be described in detail, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0048] FIGURE 1 is a schematic cross-sectional view of one, relatively simple, embodiment form of a substrate according to a first embodiment of the invention;

[0049] FIGURE 2 is a schematic cross-sectional view of a more advanced embodiment form of a substrate according to a second embodiment of the invention;

[0050] FIGURE 3 is a schematic cross-sectional view of another more advanced embodiment form of a substrate according to a third embodiment of the invention;

[0051] FIGURE 4 is a schematic cross-sectional view of a yet further more advanced embodiment form of a substrate according to a fourth embodiment of the invention; and

[0052] FIGURE 5 is a schematic cross-sectional view of still yet further advanced embodiment form of a substrate according to a fifth embodiment of the invention.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS

[0054] Referring firstly to FIG. 1 , here there is shown schematically in cross-section a relatively simple first embodiment form of a substrate Si according to the invention. It comprises a directly-embossed first or lower polymer film 2 (i.e. a carrier layer) - e.g. of a light-transparent polymer such as PP, BOPP, PC, PET or PMMA etc - which has had pre-formed in / on an upper surface thereof by conventional embossing a pair of spaced-apart patches or strips of (at least partially) diffractive optical surface relief Di , D2 which form a pair of (at least partially diffractive) DOVID-type optical security elements Di, D2. Each DOVID element Di, D2 has been pre-coated with a respective HRI (high refractive index) cover layer 4 of a light- transparent high refractive index covering material (e.g. TiO2 or a metal layer such as Al or Cu) in order to maintain the optical function of the DOVID optical security elements Di , D2 once the lamination of the complete substrate layers has been completed. The sandwich is closed by a second or upper transparent polymer film 1 , which in this example embodiment is of the same polymer as that of the first (lower) polymer film 2, so that the two layers 1 , 2 may be simply thermally bonded together to effect the substrate’s overall secure lamination of its various layers.

[0055] FIG. 2 shows schematically in cross-section a more advanced embodiment form of substrate S2 according to the invention. It comprises the following compositional / constructional elements or features, many of which mirror in general principle(s) and material(s) those corresponding elements / features of the first embodiment of FIG. 1 , and so will be largely self- explanatory:

[0056] 1 = upper transparent polymer film;

[0057] 2 = lower transparent polymer film;

[0058] 3 = carrier (or another lower) layer with pair of (at least partially diffractive) DOVID optical security elements Di , D2 formed on the upper surface thereof;

[0059] 4 = respective coated HRI cover layers over each respective DOVID optical security element Di , D2;

[0060] 5 = central adhesion layer.

[0061] Thus, in this embodiment of FIG. 2 the central adhesion layer 5 is shown as being required, since in this example embodiment it may be that the polymers of the upper transparent film 1 and the carrier layer are different from each other and thus require an adhesive to be applied thereto in order to bond them securely together to effect the substrate’s overall secure lamination of its various layers.

[0062] FIG. 3 shows schematically in cross-section another more advanced embodiment form of substrate S3 according to the invention. It comprises the following compositional / constructional elements or features, which mirror in general principle(s) and material(s) those corresponding elements / features of the first and second embodiments of FIGS. 1 and 2, and so will be largely self-explanatory:

[0063] 1 = upper transparent polymer film;

[0064] 2 = lower transparent polymer film;

[0065] 3 = carrier (or another lower) layer with pair of (at least partially diffractive) DOVID optical security elements Di , D2 formed on the upper surface thereof;

[0066] 4 = respective coated HRI cover layers over each respective DOVID optical security element Di, D2 - but here in this variant embodiment each coated cover layer 4 is discontinuous over each respective DOVID element Di , D2 and is selectively applied thereto in a multi-section / segment pattern or design 4;

[0067] 5 = central adhesion layer.

[0068] Thus, in this variant embodiment of FIG. 3, the application of the coated cover layer 4 as a discontinuous layer over each respective DOVID element Di, D2, and which is selectively applied thereover in a multi-section / segment pattern or design 4, may serve as an example of how an appropriately constructed such additional discontinuous thin cover layer 4 may be used to useful effect for imparting desired colouration effects or other auxiliary optical functions at preselected locations or regions on each portion of the substrate S3 defined by the respective DOVID optical security elements Di, D2.

[0069] FIG. 4 shows schematically in cross-section another yet further more advanced embodiment form of substrate S4 according to the invention. It comprises the following compositional / constructional elements or features, which mirror in general principle(s) and material(s) those corresponding elements / features of the first, second and third embodiments of FIGS. 1 , 2 and 3, and so will be largely self-explanatory:

[0070] 1 = upper transparent polymer film;

[0071] 2 = lower transparent polymer film;

[0072] 3 = carrier (or another lower) layer with pair of (at least partially diffractive) DOVID optical security elements Di , D2 formed on the upper surface thereof;

[0073] 4a, 4b, 4c = respective plurality or stack of superimposed coated HRI and / or auxiliary cover layers over each respective DOVID optical security element Di , D2;

[0074] 5 = central adhesion layer.

[0075] In this variant embodiment each respective plurality or stack of superimposed coated HRI and / or auxiliary cover layers 4a, 4b, 4c over each respective DOVID optical security element Di , D2 not only imparts (e.g. by virtue of each first cover layer 4a) the necessary HRI covering effect on the respective DOVID surface relief (so it retains its optical function in the final complete laminated structure), but also imparts (e.g. by virtue of each pair of second and third auxiliary cover layers 4b, 4c) a respective one or more, or a respective combination of, auxiliary optical security functions or optical security effects, such as one or more desired colouration effects or even one or more auxiliary optical security functions of either an optical or a non-optical nature (some examples of which have already been mentioned hereinabove).

[0076] FIG. 5 shows schematically in cross-section another still yet further more advanced embodiment form of substrate Ss according to the invention. It comprises the following compositional / constructional elements or features, which mirror in general principle(s) and material(s) those corresponding elements / features of the first, second and third embodiments of FIGS. 1 , 2 and 3, and so will be largely self-explanatory:

[0077] 1 = upper transparent polymer film;

[0078] 2 = central transparent polymer film;

[0079] 3 = first (upper) carrier layer with a first pair of DOVID optical security elements DIA, D2A formed on the upper surface thereof;

[0080] 4 = respective coated HRI cover layers over each respective first pair of (at least partially diffractive) DOVID optical security element DIA, D2A;

[0081] 5 = upper adhesion layer;

[0082] 6 = lower adhesion layer;

[0083] 7 = second (lower) carrier layer with a second pair of (at least partially diffractive) DOVID optical security elements DIB, D2B formed on the upper surface thereof;

[0084] 8 = lower transparent polymer film;

[0085] 9 = respective coated HRI cover layers over each respective second pair of DOVID optical security element DIB, D2B.

[0086] Thus, in this variant embodiment of FIG. 5, the complete substrate laminated structure Ss is made up of two laminate sub-structures SSA, SSB, where each sub-structure SSA, SSB comprises the respective various layers in the layer combinations as shown in FIG. 5. The respective various layers that make up each respective sub-structure SSA, SSB are united together within each respective sub-structure SSA, SSB by appropriate bonding - i.e. either direct thermal bonding or bonding via an appropriate adhesive layer (depending on the identity or chemical properties of the polymers from which each layer is formed), as represented in FIG. 5, and the sub-structures SSA, SSB themselves are united together into the complete overall unitary laminated structure Ss of the substrate via the central transparent polymer film layer 2.

[0087] Thus, in this variant embodiment of FIG. 5, the incorporation of the two distinct pairs of DOVID optical security elements DIA, D2A and DIB, D2B at spaced apart locations within the thickness dimension of the substrate’s laminated structure Ss may serve as an example of how appropriately numbered and distributed such plural (at least partially) diffractive optical security elements within an overall substrate’s laminated structure may be used to useful effect for imparting to the substrate plural or particular combinations of different optical security functions, which may for instance be complementary to each other or superimposed upon each other - e.g. a main optical security function (e.g. derived from the first pair of DOVID optical security elements DIA, D2A) at the same time as an auxiliary optical (or perhaps even non-optical) security function (e.g. derived from the second pair of DOVID optical security elements DIB, D2B). Some specific examples of such plural / combination optical (or even non-optical) security functions have already been mentioned hereinabove.

[0088] All the above-described embodiment forms of substrates constructed with integrated diffractive optical security elements incorporated within their laminated structures, as illustrated schematically in FIGS. 1 to 5, may be used for forming a wide variety of security products that require high durability, high resistance to damage or wear, and possibly also enhanced levels of security by incorporation of plural security features into their laminated structures. Banknotes are an especially useful such product to whose manufacture substrates according to many embodiments of this invention are especially well suited, although other useful end products may include other like security products such as ID cards, pages of passports, visas, tickets, driving licences, etc.

[0089] Throughout the description and claims of this specification, the words “comprise” and “contain” and linguistic variations of those words, for example “comprising” and “comprises”, mean “including but not limited to”, and are not intended to (and do not) exclude other moieties, additives, components, elements, integers or steps.

[0090] Throughout the description and claims of this specification, the singular encompasses the plural unless expressly stated otherwise or the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless expressly stated otherwise or the context requires otherwise.

[0091] Throughout the description and claims of this specification, features, components, elements, integers, characteristics, properties, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith or expressly stated otherwise.

Claims

1. CLAIMS1. A substrate for use in forming a security product, e.g. a banknote, the substrate having a laminated structure comprising: at least one upper layer of polymeric material; and at least one lower layer of polymeric material; wherein the laminated structure includes at least one at least partially diffractive optical security element incorporated between the upper and lower layers.

2. A substrate according to claim 1 , wherein the or each at least partially diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure is or comprises either:(i) an at least partially diffractive relief-based optical security element, especially an at least partially diffractive relief-based DOVID-type security element, whereby the or each at least partially diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure comprises an at least partially diffractive optical structure - optionally an optical structure which exhibits a mixture or combination of both diffractive and refractive behaviour or properties - that includes at least partially diffractive optical relief on or in a surface of the material that forms that optical structure; or(ii) an at least partially diffractive volume-type optical security element, especially an at least partially diffractive volume-type DOVID-type security element, wherein an at least partially diffractive optical structure - optionally an optical structure which exhibits a mixture or combination of both diffractive and refractive behaviour or properties - is formed through at least a portion, especially through at least a substantial or majority portion, of the thickness of a body of material forming the optical element itself.

3. A substrate according to claim 2, wherein: either (i) the or each at least partially diffractive diffractive optical structure is formed directly on or in a surface, optionally an upper surface, of one of the layers (e.g. a carrier layer) of the laminated structure itself; or (ii) the or each at least partially diffractive diffractive optical structure is preformed as a discrete optical element which is then incorporated into the laminated structure during the lamination of the upper and lower layers thereof, with the preformed discrete optical element encapsulated or sandwiched between them; optionally wherein (ii) is present or satisfied and (iii) the incorporation of the preformeddiscrete optical element into the laminated structure during its layers’ lamination involves bonding of the preformed discrete optical element to one or more surfaces of one or more of the layers of the laminated structure that contactingly sandwich the preformed discrete optical element therebetween, and / or (iv) the incorporation of the preformed discrete optical element into the laminated structure during its layers’ lamination involves at least partially embedding the preformed discrete optical element in the one or more surfaces of one or more of the layers of the laminated structure that contactingly sandwich the preformed discrete optical element therebetween.

4. A substrate according to claim 2 or claim 3, wherein: either (i) the or each at least partially diffractive optical structure, which forms or constitutes the or each at least partially diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure, is dimensioned such that it extends in the form of a patch over only a portion of, optionally a minor portion of (e.g. up to about 10 or 20 or 30 or 40 or 50% of), the total area of the respective surface on or in which the optical structure is formed directly or to which the optical security element is affixed or bonded (as the case may be); or (ii) the or each at least partially diffractive optical structure, which forms or constitutes the or each at least partially diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure, is dimensioned such that it extends over substantially the whole of the total area of the respective surface on or in which the optical structure is formed directly or to which the optical security element is affixed or bonded (as the case may be).

5. A substrate according to any preceding claim, wherein the or each at least partially diffractive optical security element that is / are incorporated between the upper and lower layers of the laminated structure is: either (i) of a light-transmissive type; or (ii) of a light-reflective type.

6. A substrate according to any preceding claim, wherein the or each at least partially diffractive optical security element comprises a surface relief-type optical structure, and wherein the or each respective at least partially diffractive optical security element is provided with a or a respective, or one or a plurality of, covering layer(s) or film(s) applied over the surface relief thereof, wherein the material of the covering layer(s) or film(s) has a refractive index that is significantly different, optionally significantly higher, from the refractive index of the material of the at least partially diffractive optical security element itself in which theoptical relief is formed; optionally wherein the or each covering layer / film extends either (a) over just the respective area extent of the or the respective individual at least partially diffractive optical security element, so that the respective covering layer / film is in register with the or each respective at least partially diffractive optical security element and co-extensive / co-terminous therewith in their area extents, or alternatively (b) the or each covering layer / film is part of a larger single overall covering layer / film that extends over substantially the whole area extent of the substrate’s laminated structure, and into and across those regions / portions thereof which do not have applied thereto any at least partially diffractive optical security element(s); and further optionally wherein, where any given covering layer / film or covering / layer film portion is applied so as to extend (a) over just the respective maximum area extent of a or a respective individual at least partially diffractive optical security element (so that the respective covering layer / film or portion is in register with the or the respective at least partially diffractive optical security element and co-extensive / co-terminous therewith in their maximum area extents), such a or a respective covering layer / film or portion is applied either as (c) one single respective such covering layer / film or portion that extends over substantially the whole maximum area extent of the or the respective at least partially diffractive optical security element, or alternatively (d) a plurality of selectively arranged and applied covering layer / film or portion sections or segments that are spaced apart from each other and form a pattern or design or other discontinuous arrangement yet which collectively extend over substantially the whole maximum area extent of the or the respective at least partially diffractive optical security element.

7. A substrate according to any preceding claim, wherein either one or both of the following (i) and / or (ii) is present or satisfied:(i) the or each upper layer that forms part of the laminated structure is formed of a substantially light-transparent polymeric material;(ii) the or each lower layer that forms part of the laminated structure is formed of a substantially light-transparent polymeric material.

8. A substrate according to any one of claims 1 to 7, wherein the laminated structure of the substrate comprises just one upper polymer layer and one lower polymer layer, whereby the complete substrate comprises a laminated structure consisting of those two polymer layers (upper and lower) with the one or more at least partially diffractive optical security element(s) incorporated or sandwiched between those two layers, optionally with a covering layer or film with a different refractive index therefrom having been pre-applied onto a surfacerelief of the or each optical security element prior to its / their lamination by and between the upper and lower polymer layers.

9. A substrate according to any one of claims 1 to 7, wherein the laminated structure of the substrate comprises either or both of:(i) two or more upper polymer layers, optionally each being of an optically transparent polymer material, and / or(ii) two or more lower polymer layers, optionally each being of an optically transparent polymer material, whereby the complete substrate comprises a laminated structure consisting of those at least three or four - or optionally as many as five or six or seven or eight - polymer layers (being those layers among the upper and lower ones of the overall laminated structure) with the one or more at least partially diffractive optical security element(s) incorporated or sandwiched between at least two of those polymer layers, optionally two of the centrally, or nearest to being centrally, located layers in the overall laminated structure, and further optionally with a covering layer or film (with a different refractive index therefrom) having been pre-applied onto a surface relief of the or each optical security element prior to its / their lamination by the various upper and lower polymer layers.

10. A substrate according to claim 9, wherein at least one of the two or more upper polymer layers, or at least one of the two or more lower polymer layers, or even at least two of the polymer layers being both upper and lower polymer layers, constitutes, or is formed as, or is applied as, an adhesive layer which bonds together a respective pair of layers immediately above and below it in the laminated structure; optionally wherein the or each such adhesive layer constitutes at least one of the layers of the laminated structure that is located immediately adjacent or encapsulates or covers or bounds or sandwiches or fixes in position within the substrate one or more of the at least partially diffractive optical security elements (optionally with a covering layer or film (with a different refractive index therefrom) having been pre-applied onto the surface relief of the or each such optical security element prior to its / their encapsulation or covering or bounding or sandwiching or fixing in position by that adhesive layer).

11. A substrate according to any preceding claim, wherein the substrate comprises a laminated structure in the form of a laminated super-structure comprising a plurality of laminated sub-structures, wherein each laminated sub-structure comprises a respective laminated structure as defined in any one of claims 1 to 10 and comprising at least one upper polymer layer and at least one lower polymer layer with at least one at least partiallydiffractive optical security element incorporated between them, and wherein the laminated sub-structures are laminated together with the other(s) thereof in a stacked fashion to create the complete laminated super-structure of the substrate; whereby the substrate includes a plurality of spaced-apart (optionally spaced apart in the thickness dimension of the substrate) groups or layers of sandwiched / laminated at least partially diffractive optical security element(s), optionally located at different height locations within the overall thickness of the substrate’s laminated super-structure, with respective combinations of upper and lower polymer layer(s) above and below each respective group / layer of sandwiched / laminated at least partially diffractive optical security element(s) effecting the overall sandwiching and laminating of those plural groups / layers of sandwiched / laminated at least partially diffractive optical security element(s) within the overall laminated super-structure of the complete substrate; and optionally wherein each group / layer of the one or two or more, or a plurality of, sandwiched / laminated at least partially diffractive optical security element(s) thereby comprises diffractive optical security element(s) that are either substantially the same as - or alternatively are different from - that / those at least partially diffractive optical security element(s) in one or more other such layers thereof within the overall substrate’s laminated super-structure in terms of their respective optical functions.

12. A substrate according to any preceding claim, wherein there is incorporated between any two polymer layers (i.e. between any two upper layers or any two lower layers or any two layers being upper and lower layers) of the laminated structure or super-structure, one or more auxiliary security elements which are, or are each independently, either an auxiliary optical security element or an auxiliary non-optical security element.

13. A substrate according to any preceding claim, which includes either (i) plural upper layers and / or plural lower layers and / or one or more auxiliary security element(s), all as defined in any one of claims 9 to 12, or (ii) one or more cover layer(s) or film(s) applied over one or more of the at least partially diffractive optical security element(s) in the laminated structure, or (iii) one or more auxiliary security element(s), wherein: any one or more of the said various layers or one or more portions of one or more of those layers - whether that be one or more of the upper or lower layers or an adhesive layer or a cover layer or film applied over one or more of the at least partially diffractive optical security element(s), and whether or not it be such a layer or film that extends over substantially the whole area of the substrate’s laminated structure or only over one or more selected areas or regions thereof (e.g. over just the area extent of one or more of the at least partially diffractive optical security elements incorporated in the laminated structure),or any one or more such auxiliary security element, or possibly even both thereof, is / are constructed and / or arranged or is / are designed such as to impart to the overall substrate one or more additional or auxiliary optical or non-optical security functions over and above - i.e. distinct from or superimposed upon - that / those optical function(s) of the one or more at least partially diffractive optical security element(s) itself / themselves.

14. A substrate according to claim 12 or claim 13, wherein the or each auxiliary security element is independently selected from an auxiliary optical security element or an auxiliary non-optical security element, for imparting to the overall substrate one or more additional or auxiliary optical or non-optical security functions over and above - i.e. distinct from or superimposed upon - that / those optical function(s) of the one or more at least partially diffractive optical security element(s) itself / themselves.

15. A substrate according to any one of claims 12 to 14, wherein the one or more additional or auxiliary optical security functions comprise any one or more of the following:(i) a specific colouration effect;(ii) a combination of inter-disciplinary - i.e. two or more optical, or at least one optical and at least one non-optical - security or detection properties or functions;(iii) one or more printed layers on or over a surface of the diffractive optical security element which have an optical function in the IR region, or the visible region, or the UV region of the spectrum;(iv) one or more printed layers on or over a surface of the diffractive optical security element which are composed of or which comprise one or more non-pigment materials, optionally another form of printing of other material(s) or liquid crystal layer application(s);(v) an electronic or electrical security device or function.

16. A substrate according to claim 15, wherein the one or more additional or auxiliary optical security functions comprise(s) (i) a specific colouration effect, and the said colouration effect is derived from one or more of the following features:(a) one or more printed or coated colouring layers or one or more systems of pluralities of printed or coated colouring layers which fully or partially cover or coat one or more of the at least partially diffractive optical security element(s) thereadjacent, and the or each of which is or comprises an absorbing colour filter material, whereby a desired colouration effect is produced at a preselected location or region on the relevant at least partially diffractive optical security element(s) or on a portion thereof; or(b) one or more printed or coated colouring layers or one or more systems of pluralities of printed or coated colouring layers, the or each of which is or comprises one or more deposited layer(s) or film(s) over the surface of one or more of the at least partially diffractive optical security element(s), thereby providing an interference-type colour filter or colour shift or colour flop function / effect in the desired region of the substrate’s laminated structure, optionally wherein the said colour shift or colour flop effect manifests itself as, or comprises, a change in pre-defined colour(s) at pre-defined angles of view, which is derived from either (c) a combination of a number of dielectric or metal layers, or (d) a combination of a plurality of metal layers with at least one dielectric layer between those metal layers, thereby constituting or providing a Fabry-Perot resonator-based colour filter or colour shift / f lop effect.

17. A substrate according to any preceding claim, wherein any given pair of adjacent or neighbouring or superimposed layers in the substrate’s laminated structure are united or bonded together by means of either (a) direct thermal bonding of the adjacent / neighbouring / superimposed layers, or (b) a suitable adhesive layer placed or coated or applied between them.

18. A substrate according to any preceding claim, wherein each of the upper and lower polymer layers of the substrate’s laminated structure takes the form of, or is provided in the form of, a sheet, film, foil, strip or plate having a thickness in a range of from about 1 or 5 or 10 pm up to about 200 or 250 or 300 pm, optionally up to about 400 or 500 pm, further optionally in a range of from about 10 or 20 or 50 pm up to about 100 pm.

19. A method for the manufacture of a substrate for use in forming a security product, e.g. a banknote, the method comprising: laminating together at least one upper layer of polymeric material and at least one lower layer of polymeric material to form a laminated structure, wherein the lamination step includes incorporating between the upper and lower layers at least one at least partially diffractive optical security element.

20. A security product comprising or formed from a substrate according to any one of claims 1 to 18, or made according to the method of claim 19.21 . A security product according to claim 20, which is a banknote.

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