EP1753627A1 - Ameliorations apportees a des dispositifs de securite - Google Patents

Ameliorations apportees a des dispositifs de securite

Info

Publication number
EP1753627A1
EP1753627A1 EP05750255A EP05750255A EP1753627A1 EP 1753627 A1 EP1753627 A1 EP 1753627A1 EP 05750255 A EP05750255 A EP 05750255A EP 05750255 A EP05750255 A EP 05750255A EP 1753627 A1 EP1753627 A1 EP 1753627A1
Authority
EP
European Patent Office
Prior art keywords
layer
shape memory
memory polymer
security substrate
liquid crystal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05750255A
Other languages
German (de)
English (en)
Inventor
Christopher John Eastell
Lawrence George Commander
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
De la Rue International Ltd
Original Assignee
De la Rue International Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by De la Rue International Ltd filed Critical De la Rue International Ltd
Publication of EP1753627A1 publication Critical patent/EP1753627A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/364—Liquid crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D15/00—Printed matter of special format or style not otherwise provided for
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/373—Metallic materials
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/003—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using security elements
    • B42D2033/26—

Definitions

  • the present invention relates to improvements in security devices that can be used in varying shapes and sizes for various authenticating or security applications, particularly a device which on the application of heat uses a shape memory polymer material to induce a colourshift in a liquid crystal material.
  • liquid crystal materials exhibit a difference in colour when viewed in transmission and reflection as well as an angularly dependent coloured reflection.
  • Liquid crystal materials have been incorporated into documents, identification cards and other security elements with a view to creating distinctive optical characteristics.
  • EP-A-0435029 is concerned with a data carrier, such as an identification card, which comprises a liquid crystal polymer layer or film in the data carrier.
  • the liquid crystal polymer is in solid form at room temperature and is typically within a laminate structure.
  • the intention is that the liquid crystal layer, which is applied to a black background, will demonstrate a high degree of colour purity in the reflected spectrum for all viewing angles. Automatic testing for verification of authenticity is described using the wavelength and polarisation properties of the reflected light in a single combined measurement. This has the disadvantage of being optically complex using a single absolute reflective measurement requiring a uniform liquid crystal area on a black background.
  • AU-A-488652 is also concerned with preventing counterfeit copies by introducing a distinctive optically variable feature into a security element.
  • This patent specification discloses the use of a liquid crystal "ink” laminated between two layers of plastic sheet. The liquid crystal is coated on a black background so that only the reflected wavelengths of light are seen as a colour. The patent is primarily concerned with liquid crystals which have the characteristic of changing colour with variation in temperature.
  • WO-A-03061980 discloses a method for manufacturing a security substrate, which combines the use of demetallised indicia with the colourshift effect of liquid crystal materials.
  • WO-A-03061980 there is provided a method of manufacturing a substrate comprising the steps of applying a darkly coloured resist to at least a part of a metallic layer on one side of a substantially transparent polymeric film, removing metal from areas not covered by the resist to form demetallised regions and applying a polymeric liquid crystal material over the resist and the demetallised regions.
  • the substrate produced by the method in WO-A-03061980 can be incorporated into secure documents such as banknotes as a thread, stripe or patch.
  • EP-A-1281538 discloses an optically variable marking comprising a semi-opaque substrate with a first surface that is covered with a liquid crystal polymer layer, and a second surface that is partially covered with a metal layer in the shape of a pattern. If the marking is viewed in reflection the device looks uniform and the reflective colour of the liquid crystal is seen. In transmission the pattern in the metal layer is visible through the semi- opaque substrate and the transmitted light is of a different colour to the reflected light.
  • Cholesteric liquid crystals have certain unique properties in the chiral nematic phase. It is the chiral nematic phase that produces an angularly dependent coloured reflection and a difference in colour when viewed in either transmission or reflection. Cholesteric liquid crystals form a helical structure which reflects circularly polarised light over a narrow band of wavelengths. The wavelength is a function of the pitch of the helical structure which is formed by alignment within the liquid crystal material. An example of such a structure is depicted in Figure 1 with the cholesteric helical axis in the direction of the arrow X. The reflection wavelength can be tuned by appropriate choice of chemical composition of the liquid crystal. The materials can be chosen to be temperature sensitive or insensitive.
  • Both handednesses of circularly polarised light can be reflected by choice of the correct materials and thus high reflectivities at specific wavelengths can be achieved with double layers of liquid crystals.
  • the wavelength of reflected light is also dependent on the angle of incidence, which results in a colour change perceived by the viewer as the device is tilted ( Figure 2) .
  • cholesteric liquid crystal materials An interesting property of cholesteric liquid crystal materials is that a mechanical deformation of the liquid crystal material through the application of a stress, can cause a shift of the reflection band and ; therefore a change in colour of the liquid crystal material.
  • the effect of stress on cholesteric liquid crystal materials has been reported in the Journal of Advanced Materials (Adv. Mater. 2001, 13, No.14, July 18).
  • the use of liquid crystals in security devices to generate a piezochromic effect i.e. a reversible colour change under the action of a pressure) is known and has been disclosed in FR-A-2698390.
  • FR-A-2698390 describes a security thread comprising a piezochromic liquid crystal layer in which a colour change is induced by the authenticator pressing down on selected areas of the thread.
  • the effectiveness of the device is dependent on the amount of pressure applied by the authenticator which can lead to unwanted variability in the degree of colour change observed.
  • the object of the security device of the present invention is to induce a known, controlled amount of stress in a liquid crystal polymer, independent of the authenticator, such that the observed colourshift is always identical.
  • This is achieved by combining a liquid crystal film with a shape memory polymer film in a laminate construction.
  • the application of body heat by touch results in a controlled stretch in the shape memory polymer film that induces a known stress in the liquid crystal film.
  • the induced stress in the liquid crystal film causes a shift in the reflection band and a change in the observed colour.
  • the elastic nature of the laminate system will return the shape memory polymer to its original shape and the liquid crystal film to its original colour.
  • the device offers increased security over the traditional liquid crystal thread by exhibiting both an angular dependent colour change and a touch-sensitive colour change.
  • SMP Shape memory polymers
  • the SMP' s can include at least one hard segment and at least one soft segment, or can include at least one kind of soft segment wherein at least one kind of the soft segments are crosslinked, without the presence of a hard segment.
  • the term "segment” refers to a block or sequence of polymer forming part of the SMP.
  • the terms hard segment and soft segment are relative terms, relating to the softening point (melting point or glass transition temperature) of the segments.
  • the hard segment (s) has a higher softening point than the soft segment (s) .
  • SMP's can be thermoplastic, thermoset, interpenetrating networks, semi-interpenetrating networks, or mixed networks. Polymers can be a single polymer or a blend of polymers.
  • Polymers can be linear, branched, thermoplastic elastomers with side chains or any kind of dendritic structural elements.
  • Stimuli causing shape change can be temperature, ionic change, pH, visible irradiation, UV irradiation, electric field, magnetic field or ultrasound.
  • Thermoplastic SMP' s are generally characterised as phase segregated block co-polymers comprising a hard segment and a soft segment.
  • the hard segment is typically crystalline, with a defined melting point
  • the soft segment is typically amorphous, with a defined glass transition temperature. In some embodiments, however, the hard segment is amorphous and has a glass transition temperature rather than a melting point. In other embodiments, the soft segment is crystalline and has a melting point rather than a glass transition temperature. The melting point or glass transition temperature of the soft segment is substantially less than the melting point or glass transition temperature of the hard segment.
  • thermoplastic SMP When the thermoplastic SMP is heated above the melting point or glass transition temperature of the hard segment, the material can be shaped.
  • This (original) shape can be memorized by cooling the SMP below the melting point or glass transition temperature of the hard segment.
  • the shaped SMP When the shaped SMP is cooled below the melting point or glass transition temperature of the soft segment while the shape is deformed, that (temporary) shape is fixed.
  • the original shape is recovered by heating the material above the melting point or glass transition temperature of the soft segment but below the melting point or glass transition temperature of the hard segment.
  • thermosetting SMP system is a polymer network prepared by covalently cross-linking macromonomers, i.e. polymers which contain polymerisable endgroups such as carbon-carbon double bonds.
  • The, polymerisation process can be induced by using light or heat sensitive initiators or by curing with ultra violet light.
  • Thermoset SMP's can be prepared by extruding the pre-polymerized material (macromonomers), and fixing the original shape at a temperature above the T trans (melting point or glass transition temperature) of the thermoset polymer, for example, by photocuring reactive groups on the macromonomer .
  • the temporary shape is fixed by cooling the material below T trans after deforming the material.
  • thermoset SMP systems such as those described in Nature vol 434, page 879, 14 th April 2005, exist where the cross-links are cleaved, and therefore the shape change is induced, by UV irradiation.
  • SMP systems particularly suitable for this invention include, but are not limited to, polyamides, polyester amides, poly(amino acid)s, synthetic poly(amino acids), polyanhydrides, polycarbonates, polycaprolactones, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyortho esters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyvinylpyrrolidone, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, ethylene vinyl acetate, poly (meth) acrylic acid, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylphenol, and copolymers and mixtures thereof.
  • US-A-2004014929 discloses that it is possible to blend certain SMP compositions with other commercially available polymers, such as polyolefins, in particular polyethylene and polypropylene, or vinyl polymers, such as polystyrene and PVC. It could be shown that with a content of from 50 to 90 wt-% of SMP, the shape memory properties could be retained. This enables in particular the preparation of low cost SMP materials.
  • SMP's suitable for use in the current invention can be produced as a film or as a coating and therefore can be combined in a straightforward manner with a colour- shifting liquid crystal film or coating to produce a multilayer security device suitable for incorporation into a document of value.
  • the invention therefore provides a security substrate comprising a polymeric liquid crystal material and a shape memory polymer film, wherein the application of a predetermined external stimuli to the substrate which causes the shape memory polymer film to change shape which, in turn causes the liquid crystal material to stretch or contract and thereby induce in the liquid crystal material a temporary colour change.
  • the invention also provides a method of manufacturing a security substrate comprising the application of a layer of polymeric liquid crystal material to a carrier layer of a polymeric film, applying a layer of shape memory polymer film, wherein the shape memory polymer film has first been stretched along one of its dimensional axes whilst being heated to above melting point or a glass transition temperature of a hard segment of the shape memory polymer and subsequently cooled under tension to a temperature below the melting point or glass transition temperature of the hard segment, but above the melting point or glass transition temperature of a soft segment of shape memory polymer, and further cooling the film to below the melting point or glass transition temperature of the soft segment whilst the tension is released.
  • the invention further provides a method of manufacturing a security substrate comprising the application of a layer of polymeric liquid crystal material to a layer of shape memory polymer film, wherein the shape memory polymer film has first been stretched along one of its dimensional axes whilst being heated to above melting point or a glass transition temperature of a hard segment of the shape memory polymer and subsequently cooled under tension to a temperature below the melting point or glass transition temperature of the hard segment, but above the melting point or glass transition temperature of a soft segment of shape memory polymer, and further cooling the film to below the melting point or glass transition temperature of the soft segment whilst the tension is released.
  • Figure 1 depicts chiral nematic alignment of a cholesteric liquid crystal material
  • Figure 2 shows how the reflection from a cholesteric liquid crystal material varies with the angle of incidence
  • Figure 3 depicts the transmission and reflection of light incident on a liquid crystal material
  • Figure 4 is a cross-sectional side elevation of a substrate according to the present invention for use in security or authenticating devices.
  • Figures 5 to 8 are cross-sectional side elevations of alternative embodiments of the substrate of Figure 4
  • Figures 9 and 10 are cross-sectional side elevations of machine readable constructions incorporating a substrate according to the present invention.
  • the substrate 10 comprises a transparent polymeric film 11.
  • Suitable polymeric films are for example those made from polyethylene terephthalate (PET) which are commercially available from Dupont under the trade name Melinex.
  • PET polyethylene terephthalate
  • a black or dark pigmented ink or coating 12 is then applied to one surface of the polymeric film 11 in order to visually accentuate the colour change of the liquid crystal material 13.
  • the coating 12 may be applied, by a number of techniques using, for example, a roll coater or alternatively using a printing press by flexographic, offset lithographic or gravure techniques.
  • a black or dark dye can be applied to the surface of the polymeric film 11.
  • the black or dark coating/dye may be a conducting material, such as carbon black, to produce a machine-readable conducting layer.
  • it may be a magnetic material, such as magnetite, to produce a machine-readable magnetic layer.
  • a layer of polymeric liquid crystal material 13 is then coated, transferred or laminated on top of the coated polymeric film 11.
  • a layer of a suitable adhesive (not shown in Figure 4) may be required for this process, applied between the black/dark coating 12 and the liquid crystal layer 13.
  • a transparent or translucent SMP polymer film 14 is then transferred or laminated to the surface of the liquid crystal film 13.
  • a layer of a suitable adhesive (not shown in Figure 4) may be required for this process, applied between the liquid crystal layer 13 and the SMP layer 14.
  • the SMP layer 14 will be applied or transferred to the liquid crystal film 13 in its temporary shape, which will have been fixed during the initial forming stages of the SMP film 14.
  • thermoplastic polymer system is used for the SMP film 14 which can be produced by known polymer film production processes, such as the blown film process, the cast film process and the tentering process.
  • SMP film 14 is heated above the melting point or glass transition temperature of the hard segment.
  • the film 14 is then cooled below the melting point or glass transition temperature of the hard segment.
  • the film 14 is kept under tension along one of its dimensional axes in order to fix the permanent "stretched” shape.
  • the film 14 is then cooled below the melting point or glass transition temperature of the soft segment, while the tension is released, fixing a temporary shape which has contracted along one of its dimensional axes relative to the permanent shape.
  • the "stretched" shape can then be recovered by heating the material above the melting point or glass transition temperature of the soft segment but below the melting point or glass transition temperature of the hard segment.
  • the activation temperature i.e. the melting point or glass transition temperature of the soft segment, at which the film 14 switches from its temporary shape to its permanent shape can be controlled by changing the composition of the hard and soft segments.
  • the activation temperature is in the range 25°C to 80°C, preferably 30°C to 50°C.
  • the material can be formulated such that the switch from the temporary shape to the permanent shape occurs at body temperature, ⁇ 35-37°C, and therefore can be activated by touch.
  • the SMP film 14 in Figure 4 has a temporary shape which has been formed by a 1% contraction of the permanent "stretched" shape in one of its dimensional axes in the plane of the film.
  • the substrate in Figure 4 is viewed through 'the transparent or translucent SMP film in its temporary shape a highly visible colour shift effect is observed from the liquid crystal layer 13 as the device 10 is tilted.
  • the colour shift can be from red, when viewed at a normal angle of incidence to the plane of substrate, to green when viewed at a low angle of incidence to the plane of the substrate.
  • the shape memory polymer 14 On warming the security device above the activation temperature, preferably 35-37°C, the shape memory polymer 14 reverts to its "stretched" permanent shape and induces a stress in the liquid crystal film 13.
  • the induced stress in the liquid crystal film 13 produces a known colour change.
  • the liquid crystal film 13 is stretched and the colour goes to shorter wavelengths for example red goes to green and green goes to blue, resulting in a colour shift from green to blue as the substrate 10 is tilted in its stretched state.
  • the change in colourshift when the substrate 10 is warmed is dependent on the stress induced in the liquid crystal film 13 by the shape change in the SMP film 14. Different colour shifts can be achieved by varying the degree of shape change and the amount of contraction and expansion in the SMP film 14. In addition the contraction and or expansion can occur along one or more dimensional axes depending how the SMP film 14 is formed.
  • the position of the liquid crystal polymer layer 13 and the SMP film 14 are reversed such that the SMP polymer film 14 is applied to the black/dark coating 12.
  • the functionality of the device is not significantly affected by this alteration. It is also possible to replace the polymeric carrier film 11 (for example PET) with a SMP film 14 such that a separate SMP film layer 14 is no longer required, as shown in Figure 5.
  • a second SMP film with the same characteristics as SMP film 14, is laminated on top of the liquid crystal film such that the liquid crystal film is sandwiched between the two shape memory polymer films.
  • This construction minimises any unwanted bending of the laminate system arising from the liquid crystal material being stretched to a different extent than the SMP.
  • the liquid crystal polymer is one of the polymer segments of the shape memory polymer such that a single material layer can be formed which exhibits the properties of the both the liquid crystal polymer and the shape memory polymer.
  • the liquid crystal layer 13 and the SMP layer 14 may be replaced by a single layer of material which exhibits both their characteristics.
  • a combined liquid crystal/SMP layer could also be achieved by blending the liquid crystal material with the SMP.
  • Figure 6 shows a further embodiment of the substrate of the present invention.
  • the structure is the same as that shown in Figure 4 except in that the combination of a transparent polymeric film 11 with a black/dark coating 12 has been replaced with a semi-opaque polymeric film 15.
  • This is preferably a plastic film that is darkened, for example to about 95% absorbance, by incorporation of light absorbing particles like, for example, carbon black.
  • the semi-opaque film 15 has the same function as the black/dark coating 12 in Figure 4 which is to visually accentuate the colour change of the liquid crystal material 13.
  • the overall function and appearance of the substrate in Figure 6 is otherwise the same as that discussed with reference to Figure 4.
  • Figure 7 shows a further embodiment of the substrate 10 of the current invention.
  • the structure is the same as that shown in Figure 6 except that the opposite surface of the semi-opaque polymeric film 15 has been metallised, using vapour deposited aluminium 16, and contains demetallised indicia 17, produced by a method, such as that described in EP-A-0319157.
  • the vapour deposited metallised layer can be replaced with conducting or non-conducting metallic ink.
  • the colour shift can be from red, when viewed at a normal angle of incidence to the plane of substrate 10, to green when viewed at a low angle of incidence to the plane of the substrate 10.
  • the demetallised indicia 17 becomes visible and the transmitted light will be of a complementary colour to the reflected light. In this example when viewed normally the main body of the substrate 10 will appear red due to the reflected light but the demetallised indicia 17 will appear green from the transmitted light.
  • the SMP film 15 On warming the security substrate 10 above the activation temperature, preferably 35-37°C, the SMP film 15 reverts to its "stretched" permanent shape and induces a stress in the liquid crystal film 13.
  • the induced stress in the liquid crystal film 13 produces a known colour change.
  • the liquid crystal film 13 is stretched and when viewed in reflection the colour goes to shorter wavelengths for example red goes to green and green goes to blue, resulting in a colour shift from green to blue as the substrate 10 is tilted in its stretched state.
  • the colour of the demetallised indicia 17, when viewed in transmission, will also change in this case from green to red.
  • the elastic nature of the laminate system will force the substrate 10 to relax to its original dimension and the liquid crystal film 13 to its original colour.
  • FIG 8 illustrates a further embodiment of the substrate 10 of the present invention for use in security or authenticating devices.
  • the structure shown is a combination of a SMP film 14 with an existing approach for the manufacture of liquid crystal security substrates disclosed in WO-A-03061980.
  • the substrate 10 comprises a transparent polymeric film 11 which has been metallised using for example vapour deposited aluminium. Suitable polymeric films are for example those made from polyethylene terephthalate (PET) which are commercially available from Dupont under the trade name Melinex.
  • PET polyethylene terephthalate
  • the metal layer 16 is printed with a resist 18 which contains a black or dark dye or pigment.
  • the printed metallised film 11 is then partially demetallised, according to a known demetallisation process using a caustic wash which removes the metal in the regions not printed with the resist 18.
  • the remaining regions coated with the resist provide a black layer which is visible when the demetallised film 19 is viewed from a first side (along arrow Y) interspersed with clear regions.
  • the shiny metal of the remaining parts of the metallised layer 16 are only visible from an opposite side of the demetallised film 19 (along arrow X) .
  • the resist 18 may be printed in the form of the indicia such as words, numerals, patterns and the like; in which case the resulting indicia will be positively metallised, with the metal still covered by the dark or black resist 18.
  • the resist 18 may be printed so as to form indicia negatively, in which case the resulting indicia will be provided by the demetallised regions 17.
  • the indicia, however formed, are clearly visible from both sides, especially in transmitted light, due to the contrast between the regions of the metal which have been removed and the remaining opaque regions.
  • the black or dark resist may be loaded with a conducting pigment, such as carbon black, to produce a machine-readable conducting layer.
  • Alternatively it may be loaded with a magnetic material, such as magnetite, to produce a machine-readable magnetic layer.
  • a layer of polymeric liquid crystal material 13 is then coated, transferred or laminated to the demetallised film 19 over the remaining parts of the black resist layer 18 and the demetallised regions 17.
  • a layer of a suitable adhesive may be required, for this process, applied between the black resist layer and the liquid crystal layer (not shown in Figure 8) .
  • a transparent or translucent SMP film 14 is then transferred or laminated to the surface of the liquid crystal film 13.
  • a layer of a suitable adhesive (not shown in Figure 8) may be required, for this process, applied between the liquid crystal layer 13 and the SMP layer 14.
  • the SMP film 14 in Figure 8 has a temporary shape which has been formed by a 1% contraction of the permanent "stretched" shape in one of its dimensional axes in the plane of the film 14.
  • a highly visible colour shift effect is observed from the regions of the liquid crystal layer 13 located above the dark as the substrate 10 is tilted.
  • the colour shift can be from red, when viewed at a normal angle of incidence to the plane of substrate, to green when viewed at a low angle of incidence to the plane of the substrate 10.
  • clear positive or negative indicia 17 can be seen in transmission from either side.
  • the shape memory polymer film 14 On warming the substrate 10 above the activation temperature, preferably 35-37°C, the shape memory polymer film 14 reverts to its "stretched" permanent shape and induces a stress in the liquid crystal film 13.
  • the induced stress in the liquid crystal film 13 produces a known colour change.
  • the liquid crystal film 13 is stretched and when viewed in reflection the colour goes to shorter wavelengths for example red goes to green and green goes to blue, resulting in a colour shift from green to blue as the device is tilted.
  • the elastic nature of the laminate system will force the substrate 10 to relax to its original dimension and the liquid crystal film 13 to its original colour.
  • the substrate 10 of the current invention can be slit or cut into patches, foils, stripes, strips or threads for incorporation onto or into plastic or paper substrates in accordance with known methods. Whilst these are preferably partially embedded into a paper or plastic substrate, they may be applied to a substrate or wholly embedded within. It will be further understood by those skilled in the art that the substrate of the present invention could be used in combination with existing approaches for the manufacture of security threads. Examples of suitable constructions that can be used include, but are not limited to, those cited within EP-A-0516790, WO-A- 9825236, and WO-A-9928852.
  • Figure 9 shows a machine readable construction laminated to a SMP film 14.
  • the machine-readable construction comprises a metallised PET base layer 11 which is demetallised with a suitable design ensuring "tramlines" 20 of metal are left along each edge of the security thread 21.
  • a black resist 18 is used during the demetallisation process.
  • an optional protective layer 22 may be applied prior to application of a magnetic layer 23.
  • a suitable protective layer 22 is VHL31534 supplied by Sun Chemical applied with a coat weight of 2gsm.
  • the protective layer 22 may optionally be pigmented.
  • a layer of polymeric liquid crystal material 13 is then coated, transferred or laminated to the demetallised film 19 over the magnetic layer 23 and the remaining parts of the black resist layer 18 and the demetallised regions.
  • a layer of a suitable adhesive may be required (not shown in Figure 9) , for this process, applied between the black resist layer 18 and the liquid crystal layer 13.
  • a transparent or translucent SMP film 14 is then transferred or laminated to the surface of the liquid crystal film 13.
  • a layer of a suitable adhesive (not shown in Figure 9) may be required, for this process, applied between the liquid crystal layer 13 and the SMP layer 14.
  • FIG 10 shows another preferred embodiment where the magnetic material 23 is applied over the resist 18 in a discontinuous manner to form blocks of magnetic material 23.
  • the functionality of the device 21 illustrated in Figure 9 is the same as that illustrated in Figure 8, except that it has a machine-readable component.
  • the SMP's utilised in the current invention can change shape in response to application of light, electric field, magnetic field and/or ultrasound.
  • the security substrate of the current invention can therefore also be produced such that it can be authenticated using any of the above stimuli.

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  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Liquid Crystal (AREA)
  • Polarising Elements (AREA)

Abstract

La présente invention concerne des améliorations apportées à des dispositifs de sécurité qui peuvent être utilisés sous différentes formes et tailles pour différentes applications d'authentification ou de sécurité, en particulier un dispositif qui, sous l'effet de l'application de chaleur, se sert d'une matière polymère à mémoire de forme pour induire un changement de couleur dans une matière de cristaux liquides. L'invention concerne à cet effet un substrat de sécurité (10) comprenant une matière de cristaux liquides polymère (13) et un film polymère à mémoire de forme (14), l'application d'un stimulus externe prédéterminé sur le substrat (10) provoquant le changement de forme du film polymère à mémoire de forme (14) qui de son côté provoque l'étirement ou la contraction de la matière de cristaux liquides (13) pour ainsi induire un changement de couleur temporaire de la matière de cristaux liquides (13).
EP05750255A 2004-06-10 2005-06-09 Ameliorations apportees a des dispositifs de securite Withdrawn EP1753627A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0412979.7A GB0412979D0 (en) 2004-06-10 2004-06-10 Improvements in security devices
PCT/GB2005/002271 WO2005120855A1 (fr) 2004-06-10 2005-06-09 Ameliorations apportees a des dispositifs de securite

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EP1753627A1 true EP1753627A1 (fr) 2007-02-21

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EP (1) EP1753627A1 (fr)
AU (1) AU2005252004A1 (fr)
GB (2) GB0412979D0 (fr)
WO (1) WO2005120855A1 (fr)

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Also Published As

Publication number Publication date
GB0412979D0 (en) 2004-07-14
WO2005120855A1 (fr) 2005-12-22
AU2005252004A1 (en) 2005-12-22
GB2414963A (en) 2005-12-14
GB0511755D0 (en) 2005-07-20
GB2414963B (en) 2006-07-19

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