ES2297722T3 - SECURITY DEVICE THAT CONSISTS OF A LAYER OF ACTIVABLE POLYMER AT A SPECIFIC TEMPERATURE. - Google Patents

Abstract

A security device (10) for use in a security substrate consisting of an activatable layer of a polymeric material having a hard segment (12) and a soft crystallizable segment (15), said segments being selected to provide an activation temperature predetermined, so that the layer is opaque at temperatures below the activation temperature and becomes transparent at temperatures above the activation temperature.

Description

Security device consisting of a layer of polymer activatable at a specific temperature.

The present invention has to do with improvements in safety devices, which can be used in ways and various sizes, for authentication or security applications. In particular, the invention relates to a safety device durable consisting of a layer that changes from opaque to transparent to a specified temperature

It is generally known to use, in banknotes, security elements in the form of bands or threads  which are made from a transparent film supplied with a continuous reflective metal layer, the most frequent example vacuum deposited aluminum on film polyester. In general, banknotes manufactured using such safety devices have been in circulation in many countries for many years. When such security elements they are embedded in security paper, and the paper is subsequently printed to provide the security document, for example, a banknote, the security element cannot be easily perceived with reflected light, but it is immediately  evident as a dark image when the document is examined with light transmitted. Such security elements are extremely effective. against counterfeiting by printing or photocopying, since the optically variable effect provided cannot be exactly simulated, for example, printing a line on the paper.

The composition, size and positioning of Security items in use vary depending on security desired for the document. Typical security elements are compounds of a polymeric film, such as polyester, which It can be metallic or colored, and can include an inscription Microenterprise that means a title or message. The inscription is can produce by printing on the substrate or demetalizing a metallic layer in the substrate. In GB-A-1095286 you can find a example of a microprinted security thread. The element of security can be split to produce a registered inscription with respect to the edge of the thread, or an unregistered inscription designed so that the message always appears independently of thread splitting. The widths of the security elements typically used vary from 0.5 mm to 6.0 mm, and may have thicknesses typically ranging from 12 microns to 50 microns.

The positioning of the security element within the document can be strictly controlled according to predetermined criteria, and may be coincident with additional security features, such as the brand of Water. The security elements can be completely embedded within the security paper in such a way that the paper fibers cover both sides of the security elements, making them considerably less visible with reflected light but clearly visible with transmitted light.

In recent years, however, for improve security documents compared to modern counterfeit techniques that make use of a sophisticated color separation, printing and photocopying technology in color, it has become frequent to use an element of security consisting of a thin layer of aluminum on a plastic support, which is exposed on one side of the sheet a intervals along the length of the security element, the exposure region being mentioned as a "window". GB-A-1552853 and GB-A-1604463 reveal banknotes of Bank containing such windows. The paper for use in producing such banknotes can be manufactured using the method disclosed in EP-A-0059056. The Typically used window dimensions are from 3 mm to 14 mm long, with "bridges", the paper areas being substrate covering the security element between the windows, ranging from 4 mm to 30 mm between them. Again, you can control the positioning of the windows to allow window registration with respect to the document and others features such as watermarks.

This latest development has produced a increased security, and in many countries paper has been used with Banknote windows. Such a banknote provides added security against counterfeiters since, when examined with transmitted light, the security element is looks like a dark line, and, when examined with light reflected in the appropriate face, the portions of Shining aluminum that are exposed in the windows. But nevertheless, there is a need for even greater security through employment of more sophisticated security devices to make it more difficult the task of an aspiring forger, since the appearance of the reflected light of the exposed aluminum portions of a safety device can be simulated extremely by techniques and modern materials, for example, by using stamping by heat

Other security features in use are coated with protective lacquers and these may contain, by for example, fluorescent inks that are only visible to the ultraviolet light illumination of a wavelength specific, for example, 366 nm.

It is also possible to manufacture elements of security that are readable by machine, incorporating, within or on the substrate, substances that can be identified by a detector, such as a magnetic material.

Other known security elements may be a single layer or multiple layers joined or laminated together, and in some cases, each layer may be coated with a metal such as aluminum, stainless steel, tin and / or a metal oxide such as tin oxide. The coating can be protected with a lacquer that also contains pigments colored or invisible luminescent, for example, chelates of rare earths such as europium acetylacetonate and others.

Another prior art solution for Intensify document security is the use of devices  security consisting of layers that change from opaque to transparent, at a set temperature, to reveal hidden features, for example symbols or devices optically variable EP-A-0608078 reveals a security thread containing a coating thermochromic that changes from a colored state to a colorless state to reveal underlying symbols. WO-A-0116426 discloses an element of security also containing a thermochromic layer, which is combined with a second layer such as an optically layer variable or one readable layer per machine. In one embodiment WO-A-0116426 concrete, applies a thermochromic layer on a metallic holographic device, so that, when heating above a certain temperature, the thermochromic layer is activated so that it becomes transparent and reveal the underlying hologram. WO-A-0050249 describes the use of thermochromic liquid crystal materials that become transparent or opaque when heated, and its application in Security elements. In FR2698390 an approach is suggested alternative that describes the use of piezochromic materials in a authentication element, so that a change happens reversible from an opaque state to a transparent state, under the action of a pressure.

Thermochromic materials can be divided into two categories: leuco dye thermochromic and Thermochromic liquid crystal. The use of materials thermochromic leuco dye in inks, coatings and safety devices is limited due to its very low solidity to light while thermochromic glass materials Liquid and piezochromic require an expensive manufacturing process and complex not suitable for serial items. There is a need of a film or coating that can change by touch, from opaque to transparent, make it durable and easy to process.

In accordance with the present invention, it is provided a security device for use with a document of security, consisting of an activatable layer of polymeric material comprising a hard segment and a soft crystallizable segment or, at least, a soft segment that is crosslinked and contains a soft crystallizable segment; said segments being selected to provide an activation temperature default by which the layer is opaque at temperatures by below the activation temperature, and becomes transparent to temperatures above the activation temperature.

The present invention provides an improvement significant over the prior art because it is very durable and easy to process

The invention will now be described, by way of example only, with reference to the attached drawings, in those who:

Figure 1 is a cross-sectional profile of a safety device according to the present invention, in form of an embedded security element, in the line I-I of Figures 2 and 3;

Figures 2 and 3 are plants of a document of security that incorporates the security element of Figure 1, under different inspection conditions;

Figure 4 is a cross-sectional profile of an alternative embodiment of a device security in the form of a security element with windows, in the line IV-IV of Figures 5 and 6;

Figures 5 and 6 are plants of a document of security that incorporates the security element of Figure 4, under different inspection conditions;

Figures 7 and 8 are section profiles transverse of additional alternative embodiments of the security device in the form of a security element with windows;

Figure 9 is a cross-sectional profile of the safety device of Figure 8, on a material of transfer so that the device can be used in form patch or band;

Figure 10 is a cross-sectional profile in another alternative embodiment of a device security applied to a banknote, on the line X-X of Figures 11 and 12;

Figures 11 and 12 are plants of the document of safety of Figure 10, under different conditions of inspection;

Figures 13 and 14 are plants of a additional alternative security device, which incorporates a hologram applied to a security document, under different inspection conditions;

Figures 15 and 16 are section profiles cross section of two alternative safety devices additional, which incorporate a holographic layer for use as patch or band;

Figure 17 is a cross-sectional profile of a security substrate that incorporates an embodiment additional safety device, in order to be exposed in both faces;

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Figure 18 is a cross-sectional profile of an embodiment of an appropriate security element for use in the substrate of Figure 17; Y

Figures 19 to 22 are substrate plants of Figure 17, which incorporates the security element of Figure 18, under different inspection conditions.

The security device of the invention current uses a film or polymeric coating that changes from opaque to transparent at a specified temperature. The systems Polymers suitable for use in the present invention consist of of at least one hard segment and at least one soft segment crystallizable or, alternatively, at least one segment class soft that is crosslinked and contains a soft segment Crystallizable, without the presence of a hard segment. The term "segment" refers to a polymer block or sequence forming part of the polymer system. Such polymer systems they are used in shape memory polymers, and have been described in detail in US-B-6720402. The term "segment" refers to a polymer block or sequence forming part of the polymer system. The terms hard segment and soft segment are relative terms about the point of softening (melting point or transition temperature vitreous) of the segments. The hard segment (s) has a point softening greater than the soft segment (s).

The appropriate polymer systems for Current invention can be thermoplastic, thermosetting, interpenetrated networks, semi-interpenetrated networks, or mixed networks. The polymers can be a single polymer or a mixture of polymers The polymers can be linear, branched, thermoplastic elastomers with side chains or any kind dendritic structural element.

In accordance with the present invention, the device safety uses a polymeric film or coating thermoplastic The thickness of the polymeric film or coating thermoplastic is in the range of 0.5-100 um, and more preferably, in the range of 1-30 µm. The thermoplastic polymer is built so that, when in the form of a film or coating, the hard segment is substantially transparent and the soft segment is substantially opaque due to its high degree of crystallinity In this case, the film or coating they will appear opaque below the melting point of the soft segment crystalline, and they will become substantially transparent when warm above the melting point of the soft segment. The Hard and soft segments are oligomers preferably. The term oligomer refers to a linear chain molecule having a molecular weight of up to 15,000 daltons. The polymers that form the segments are selected based on the temperatures of desired softening. The activation temperature, that is, the melting point of the soft segment, can be controlled by changing the monomer composition and the monomer class. For the current invention, the activation temperature is in the range from 25 ° C to 80 ° C, preferably from 30 ° C to 50 ° C. In a form of preferred embodiment, the material can be formulated so that the change from opaque to transparent occurs at body temperature, ~ 35-37 ° C, and therefore, can be activated by touch

Alternatively, the security device of the present invention uses a film or coating thermosetting polymer. The thickness of the film or thermosetting polymeric coating is in the range of 0.5-100 µm, and more preferably, in the 1-30 µm range. A polymeric system thermosetting material suitable for the present invention comprises a covalently crosslinked network, consisting of one or more segments soft, and a crystallizable changing segment (soft segment). The activation temperature, at which the film or coating thermosetting polymer changes from opaque to transparent, it is the melting temperature of the crystalline changing element. For the current invention, the activation temperature is in the range from 25 ° C to 80 ° C, preferably from 30 ° C to 50 ° C. In a form of preferred embodiment, the material can be formulated so that the change from opaque to transparent occurs at body temperature, 3535-37 ° C, and therefore can be activated by touch

Examples of polymer segments that are suitable for this invention include, but are not limited to, polyamides, polyesteramides, poly (amino acids), synthetic poly (amino acids), polyanhydrides, polycarbonates, polycaprolactones, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, oxides polyalkylene, polyalkylene terephthalates, polyorthoesters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyvinylpyrrolidone, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, ethylene-vinyl acetate, poly (meth) acrylic acid , polyvinyl chloride, polyvinylphenol, and copolymers and mixtures of the
same.

In the review article "Shape Memory Polymers ", in Angew. Chem. Int. Ed. 2002, 41, 2,034-2,057, specific examples of thermoplastic polymer systems consisting of a soft segment, with a high degree of crystallinity, and a hard segment substantially transparent (i.e. predominantly amorphous). A concrete example suitable for the present invention is a segmented block copolyester urethane containing physical crosslinks (hard segment) and a segment Soft crystallizable consisting of polycaprolactone units.

In the same review article "Shape Memory Polymers "examples of polymer systems can be found thermosetting consisting of a reticulated network of one or more soft segments, and a crystallizable changing segment (segment soft). A particular example is an AB polymer network based on oligo (ε-caprolactone) diols as a component that forms a crystallizable changing element. In this example, the oligo (ε-caprolactone) diols they are functionalized with terminal groups to form a segment soft that you may experience a polymerization reaction. The segments of oligo (e-caprolactone) dimethacrylate are then combined with acrylate of n-butyl to form the polymer network. The weight molecular of the two segments controls the crystallinity, the activation temperature and mechanical properties.

The polymeric material of the present invention it can be produced as a film or as a coating, and so therefore, it can be incorporated into a security substrate that be used to make a valuable document, such as a ticket of bank, using some known processes. The material polymeric is incorporated into such a security device as a thread, band or patch in the form of a substrate, or as a layer coated. In an embodiment of the invention, it is applied such a device to the surface of a document, as in the case of A band or patch. In another embodiment, it is partially embedded within the document so that it is visible only partially on the surface of the document, in the form of a security element with windows. In one embodiment additionally, the device is incorporated into the document of so that regions of the device are visible from both sides of the document.

In EP-A-1141480 a method for incorporating a security device of so that it is visible from both sides of the document. Alternatively, the polymeric material is applied directly, as ink or coating, to the surface of the document value.

The function of the polymeric layer of the invention current is to change from opaque to transparent at a temperature of activation set. The change from opaque to transparent can in itself act as a safety feature but, in ways of preferred embodiment, is used in combination with a second security element / layer that has additional properties that can be examined by any public, cashier and / or machine to authenticate the device. Examples of elements / layers of Security that can be used encompass, but are not limited to, holograms, optical effect pigments that change color, liquid crystal films that change color, designs demetalized, printed symbols, luminescent pigments and ink and magnetic encodings

The following are examples of ways to Preferred embodiments of the present invention.

Referring to Figures 1 to 3, a cross section of a security device 10 is shown for incorporation into a security document 11 as embedded thread 17. The security device 10 consists of a polymeric film 12 of the type described above, which changes from opaque to transparent at a set activation temperature. The polymeric film 12 has been metallized, using vapor deposited aluminum, to provide a metallic layer 13, and contains demetalized symbols 14 by a method such as that described in EP-A-0319157. Alternatively, the metallized layer 13 deposited in the vapor phase can be replaced with a conductive or non-conductive metallic ink, applied non-continuously to provide
Symbols

Then a metal layer 13 is applied polymeric coating 15 that changes from opaque to transparent to the same activation temperature as the polymeric film. He coating 15 can be applied by various techniques that use, for example, a roller coater or, alternatively, using a printing machine by techniques flexographic, lithographic offset or gravure. Later apply an adhesive layer 16 on both sides of the device security 10, to favor the cohesion of the device 10 to secure substrate, from which the secure document is manufactured, during the making.

With reflected and transmitted light, it is reduced considerably the visibility of the thread 17 due to the appearance opaque white film and polymeric coating (Figure 2). When heating the safety device 10 above the activation temperature, preferably 35-37 ° C, polymeric film 12 and coating 15 both change from opaque to transparent, revealing the negative symbols 14 (demetallized) when examined with transmitted light (Figure 3).

A construction is shown in Figure 4 alternative in which a metallized polyester film 20, with Demetalized symbols 14, is coated on both sides with a polymeric coating 15 that changes from opaque to transparent to an established activation temperature. Then a adhesive 16 on both sides of the security device 10, for favor the cohesion of the device 10 to the secure substrate, of that the secure document is manufactured, during manufacturing. The Figures 5 and 6 illustrate the incorporation of such device 10, within a secure document 11, such as thread 17 with windows. With light reflected, in the windows 18 you can see the thread 17 having the opaque white color of polymeric coating 15 (Figure 5). With transmitted light, wire visibility is greatly reduced 17 due to the opaque white appearance of the polymeric coating 15. When heating the safety device 10 above the activation temperature, preferably 35-37 ° C, polymeric coatings 15 change from opaque to transparent, revealing negative symbols 14 when examined with light transmitted (Figure 6). With reflected light, when heated by above the activation temperature, the windows 18 change from opaque to metallic, with an inscription or clear symbols.

A construction is shown in Figure 7 additional, in cross section, appropriate for incorporation as thread 17 with windows. The security device 10 consists of a polymeric film 12 that changes from opaque to transparent to a activation temperature set. The polymeric film 12 ha been metallized using aluminum 13 deposited in the vapor phase, and it contains symbols 14 demetalized by a method such as described in EP-A-0319157. How before, the metallized layer deposited in the vapor phase can be replaced with a metallic, conductive or non-conductive ink, applied in a non-continuous way to provide symbols. Then an adhesive 16 is applied on both sides of the device security 10, to favor the cohesion of the device 10 to secure substrate, from which the secure document is manufactured, during the making.

With reflected light, if the thread 17 is metallic by the top face, in the windows 18 you can see symbols demetalized 14, which appear opaque whites on a background metal. The visibility of the thread 17 in the the embedded regions of the thread 17. If the thread 17 is arranged with the metal on the underside, then the thread 17 can be seen in windows 18 with reflected light, like a white band opaque When heating the safety device 10 above the activation temperature, preferably 35-37 ° C, the polymeric film 15 becomes transparent. With reflected light, the thread 17 can be seen in the windows 18 as bands Metallic with an inscription or clear symbols. With light transmitted, thread 17 appears as a continuous dark line with An inscription or clear symbols.

Figure 8 shows a sectional view cross section of a further embodiment of the device Safety 10 of the current invention. The device 10 is intended for use as a security label, and consists of a clear polymer substrate 20, such as polyester, on which they are printed identifier symbols 22 using inks or dyes Then, on the printed symbols 22 a polymeric coating 15 that changes from opaque to transparent to a set activation temperature, preferably 35-37 ° C. At room temperature, the device 15 it has a uniform opaque white appearance but, when heated by above the activation temperature, the polymeric coating 15 changes from opaque to transparent and reveals the printed symbols 22 hidden. An adhesive layer is applied to one side of the device 10 16 and, on this, a glass paper support layer 19 is applied. The crystal paper layer 19 allows the label to be easily removed for application again in a document or other article that requires protection.

Figure 9 shows the device tag 10 applied to a substrate. First, the paper layer is removed glass to expose the adhesive layer 16. Then, the device label 10 to the substrate, the adhesive used can be a pressure or hot melt adhesive, and can be permanent or temporary The use of temporary adhesives can be useful where a tag needs to be removed and applied back to another article. However, it is more likely that The label has to be applied permanently. For avoid removal and reapplication of the applied label permanently, the label must also be supplied with other characteristics of evidence of adulteration, for example, frangible substrate layers, incisions and others.

Figure 10 shows a form of further embodiment of the current invention, in which it is applied a polymeric film 15 of the type described above, which changes from opaque to transparent to body heat (35-37 ° C), on a serial number 25 of a bill of bench 26. Figure 10 shows the cross section of the 26 banknote in the polymeric film region 15. The polymeric film 15 can be prepared as a patch and applied using a protective layer 24 and a support film 23, as knows well in the production of devices for transfer of metallized tapes and described in US-A-4728377. At temperature ambient (<35 ° C), serial number 25 is obscured (Figure 11) but becomes visible when device 10 heats up by touch, and can be checked against a second number standard printed on the ticket (Figure 12). In a method alternatively, on serial number 25 of a banknote 26 a polymeric coating 15 is printed, which changes from opaque to transparent to body heat (35-37 ° C).

As an additional alternative, it would be possible to apply the printed polymeric patch or film 12, on the banknote 26, before the application of the serial number (s) 25. Then, under the patch or film 12 a serial number can be applied 25, or design, by using an appropriate laser marker apparatus. By properly tuning the laser power level, it should be possible to mark the surface of banknote 25 without affecting the patch or polymeric film 12 at the top. This can be made easier by printing banknote 26 with an appropriate laser marker additive (see Sherwood Technology Datalase on its website http://www.sherwoodtech.com/index.asp ). Such materials allow the use of a lower power laser and, thus, make marking through the patch or film 12 easier without affecting them. The second non-obscured number could also be applied by laser, or by more normal procedures such as typography. This would be a preferred approach since it would allow the numbering of documents as the final stage after all other printing processes. This avoids the problem of having to renumber documents due to deterioration during application of the opaque to transparent polymer.

Figure 13 shows an additional example of the current invention in which the polymeric film 12, which changes from opaque to transparent to body heat (35-37 ° C), it is applied to a secure document 11 so that it partially covers an optically variable feature, such as a hologram metallic 30. Touching the covered part of hologram 30 will will reveal (Figure 14) and may be compared with the exposed section. Polymeric film 15 can be prepared as a patch and applied using a protective layer 24 and a support film 23, such as It was described with reference to Figure 9.

Figure 15 shows an embodiment of a safety device 10 that is appropriate for your application to a secure document 11, such as patch or band, in which the polymeric coating 15 that changes from opaque to transparent, to an established activation temperature is combined with a holographic layer or hologram 30. The security device 10 It consists of a polymeric coating 15, a thermoplastic lacquer embossed with a holographic structure 30, and a layer reflective aluminum 13 which ensures that the structure Holographic 30 can be observed with reflection. The structure multilayer is applied to a support band 23, so that the band support 23 and the polymeric coating 15 are separated by a protective layer 24. In a modified embodiment, the layer reflective aluminum 13 can be replaced with a thin intensifying layer of reflection, for example, a thin layer transparent zinc sulphide.

The security device 10 can be applied to document 11 using an adhesive layer 16. The adhesive layer 16 is applied to the metallic layer 13 or to the surface of the document insurance 11 to which device 10 has to be applied. After the transfer, the support band 23 is removed leaving the polymeric coating 15 as exposed layer. When heating the safety device 10 above the temperature of activation, preferably 35-37 ° C, the polymeric coating 15 becomes transparent and reveals the hologram

Figure 16 shows an embodiment additional safety device 10, appropriate for your application to a secure document 11 as a patch or band, in which polymeric coating 15, which changes from opaque to transparent at a set activation temperature, it is combined with a hologram The security device 10 consists of a layer polymer 15, 31, a thermoplastic lacquer embossed with a holographic structure 30, and a reflective aluminum layer 13 which ensures that the holographic structure 30 can be observed With the reflection. The polymeric layer 15, 31, consists of a polymeric coating 15, which changes from opaque to transparent to 35-37 ° C, applied in the form of symbols or any type of identifying information. The remaining areas of the layer polymeric 15, 31, consist of an opaque ink 31 having the same visual appearance that polymeric coating 15 when in its opaque state at room temperature. The multilayer structure is applied to a support band 23, in the same manner described above with reference to Figure 15. In a form of modified embodiment, the reflective aluminum layer 13 can be replaced with a thin layer intensifying the reflection, for example, a thin transparent layer of sulfide of zinc.

At room temperature (<35 ° C), the safety device 10 has a uniform opaque appearance by its entire surface, but when heating the device safety 10 above the activation temperature, preferably 35-37 ° C, only the regions that contain the polymeric coating 15 become transparent to reveal holographic areas that are shaped like the outline of Identifying symbols

A security device 10 consisting of a polymeric film 12 or coating 15 of the present invention it can also be incorporated into a secure substrate 26, of so that regions of device 10 are visible from both faces of the substrate 26, or of the document made thereof. In EP-A-1141480 describes a method to incorporate a safety device 10, so that it is visible from both sides of the substrate 26. Here it is exposed selectively a security thread 17 on a face of the substrate of security 26, and fully exposed on the second side to produce a window 18, as illustrated in Figure 17. This method allows the insertion of security threads considerably wider within the substrates.

Figure 18 shows a section view cross section of a safety device 10 that could be incorporated in the manner described in EP-A-1141480. The device of security 10 consists of a polymeric film 12 that changes from opaque to transparent at 35-37 ° C. A face of the polymeric film 12 has been metallized using aluminum 13 deposited in the vapor phase, and subsequently demetallized to form An identifying image. Then, on the metallized layer 13, You can apply an optional protective lacquer 34. In Figure 18, the another face of the polymeric film 13 is coated with a layer adhesive 16 to promote cohesion of device 10 with the secure document 11. Security thread 17 is attached to the document 11 so that face 32 is fully exposed in the front of the document (Figure 19), and the other side 33 is exposed in a window 18 on the back of document 11 (Figure twenty).

At room temperature, the polymeric film 15 is opaque and, when the security device 10 is viewed from the front of document 11 in the reflection, a metallic reflective layer containing some images Demetalised luminaires with opaque white appearance (Figure 19). By contrast, when viewed from the back of document 11 (Figure 20) in reflection, the security device 10 has a dull white appearance. When heating the safety device 10 above the activation temperature, preferably 35-37 ° C, polymeric film 12 becomes transparent so that, in reflection, you can see the layer metallized containing some luminous demetallized images from both sides of document 11. With transmitted light, the Demetalized images look bright against a dark background (Figures 21 and 22).

Claims (26)

1. A safety device (10) for use in a security substrate consisting of an activatable layer of a polymeric material having a hard segment (12) and a segment soft crystallizable (15), said segments being selected to provide a predetermined activation temperature, by what the layer is opaque at temperatures below the temperature of activation and become transparent at temperatures above the activation temperature. 2. A safety device (10) as claims in claim 1, wherein the polymeric material It has a hard amorphous segment. 3. A safety device (10) as claims in claim 1 or claim 2, wherein the polymeric material is a thermoplastic material in which the hard segment is substantially transparent and the soft segment it is substantially opaque due to its high degree of crystallinity, in where the activation temperature is the melting temperature of the soft segment. 4. A safety device (10) for use in a security substrate consisting of an activatable layer of a polymeric material having at least one hard segment (12) that is crosslinked and contains a soft crystallizable segment (15), said segments being selected to provide a temperature of default activation, so the layer is opaque to temperatures below the activation temperature and becomes transparent at temperatures above the temperature of activation. 5. A safety device (10) as claims in claim 4, wherein the polymeric material is a thermosetting material consisting of a covalently net lattice of one or more soft segments and one segment soft changeable crystallizable, where the temperature of activation is the melting temperature of the changing element crystalline. 6. A safety device (10) as claims in any of the preceding claims, in which the activation temperature is in the range of 25 ° C to 80 ° C 7. A safety device (10) as claims in claim 6, wherein the temperature of activation is in the range of 30 ° C to 50 ° C. 8. A safety device (10) as claims in claim 7, wherein the temperature of Activation is body temperature. 9. A safety device (10) as claims in any of the preceding claims, in which the hard and soft segments (12, 15) are oligomers. 10. A safety device (10) as claims in any of the preceding claims, comprising  also a support layer to which the activatable layer is applied. 11. A safety device (10) as claims in claim 10, wherein symbols are applied opaque to the support layer and the activatable layer is applied on the Symbols 12. A safety device (10) as claims in claim 10 or claim 11, wherein the Support layer is also an activatable layer. 13. A safety device (10) as claims in claim 11 or claim 12, wherein the symbols are supplied by a layer of metal that has been partially demetallized to form the symbols. 14. A safety device (10) as claims in any of claims 10 to 13, comprising an additional activatable layer of the copolymer applied to a surface of the support layer opposite the surface to which it The symbols apply. 15. A safety device (10) as claims in any of claims 1 to 10, wherein Symbols are formed by an opaque ink and the activatable layer is applied in correspondence with them, the opaque ink and the layer activatable being of the same visual appearance so that, to temperatures below the activation temperature, the safety device has a uniform opaque appearance while, above the activation temperature, it reveal opaque symbols. 16. A safety device (10) as claims in any of claims 1 to 14, wherein Symbols are applied to an activatable layer surface. 17. A safety device (10) as claims in any of the preceding claims, comprising  also an adhesive layer (16) applied on one side of the device, to which adhesive layer (16) a protective layer is applied. 18. A safety device (10) as claims in any of the preceding claims, comprising  also an optically variable feature located below the activatable layer. 19. A safety device (10) as claims in claim 18, wherein the feature Optically variable is a holographic feature. 20. A safety device (10) as claims in any of the preceding claims, wherein the polymeric layer is a film. 21. A safety device (10) as claims in any one of claims 1 to 19, wherein the layer Polymeric is a coating. 22. A security substrate comprising a base substrate and a security device (10) as claimed in any of the preceding claims. 23. A security substrate as claimed in claim 22, wherein the security device (10) is applies to at least one surface of the base substrate. 24. A security substrate as claimed in claim 22, wherein the security device (10) is at least partially embedded within the substrate of security, and visible at least in an opening or window in one or both surfaces of the substrate. 25. A security substrate as claimed in any of claims 22 to 24, comprising a plurality of safety devices (10). 26. A security document (11) manufactured at from a security substrate as claimed in any of the claims 22 to 25.