Patent Application
20080246894
This invention relates to security documents, and is particularly concerned with security documents incorporating optical components which have at least one orientating layer provided on a substrate and at least one layer of a liquid crystal polymer (LCP) over the orientating layer.
U.S. Pat. No. 6,160,597 discloses a multi-layer optical component and a method of manufacture in which an orientating layer is applied on to at least one surface of a substrate, e.g. a glass plate, a layer of non-cross-linked liquid crystalline monomer is applied onto the orientating layer, and then the monomer is cross-linked to form a liquid crystalline polymer (LCP) layer. If required, additional orientating layers and liquid crystal layers may be applied to form more complex multi-layer structures.
These multi-layer structures can be used in optical and electro-optical devices, such as in the manufacture of liquid crystal calls, in which the various orientating and LCP layers serve different optical and orientating purposes.
It has also been proposed that the multi-layer optical components disclosed in U.S. Pat. No. 6,160,597 could be used as a safeguard against counterfeiting and copying. However, this has proved difficult in practice because we have found that a multi-layer structure of at least one orientating layer and at least one LCP layer lacks sufficient adhesion when provided on a flexible substrate of a security document, for example a polymeric substrate or a paper substrate with a polymeric coating. This problem is particularly exacerbated with security documents which are in frequent use, such as banknotes, which are required to be robust to withstand wear, folding and other rough treatment when in circulation.
It is therefore desirable to provide a security document incorporating an optical component of the type disclosed in U.S. Pat. No. 6,160,597 which is robust and able to withstand rough treatment without significantly affecting the optical properties of the optical component.
It is also desirable to provide an improved optical component for use as a security device in a security document.
It is further desirable to provide a method of manufacturing a security document or device incorporating an optical component of the type described above.
According to one aspect of the invention, there is provided a security document or device comprising:
a substrate including at least one layer of polymeric material;
an optical component formed by at least one orientating layer and at least one liquid crystal polymer layer in contact with the orientating layer; and
an intermediate layer provided between the optical component and the substrate which improves the adhesion of the optical component to the substrate.
The intermediate layer preferably comprises a primer layer, and more preferably the primer layer includes a hydroxyl terminated polymer. The primer layer may also include a cross-linker, for example a multi-functional isocyanate. Examples of primers suitable for use in the invention include: hydroxyl terminated polyester based co-polymers; polyethylene imine; cross-linked or uncross-linked hydroxylated acrylates; polyurethanes; and UV curing anionic or cationic acrylates. Examples of suitable cross-linkers include: isocyanates; polyaziridines; ziconium complexes; aluminium acetylacetone; melamines; and carbodi-imides,
The type of primer may vary for different substrates and orientating layers. Preferably, a primer is selected which does not substantially affect the alignment of the orientating layer.
In one preferred embodiment, the substrate is formed from a polymeric material. Preferably, the substrate includes at least one layer of biaxially oriented polymeric material. For example, the substrate may comprise a base layer of at least two films of transparent biaxially oriented polymeric material laminated together, such as described in WO 83/00659. The substrate may also include one or more co-polymer layers on one or both sides of the base layer of biaxially oriented polymeric material. Alternatively, the substrate may comprise a base layer of paper with at least one polymeric coating, e.g. a co-polymer, provided on one or both sides of the base layer.
The substrate may also include at least one opacifying coating applied on at least one side of the base layer, particularly when the base layer is formed from a transparent polymeric material. The at least one opacifying coating may completely cover the surface of the transparent substrate. Alternatively, the at least one opacifying coating may only partially cover the transparent substrate so as to form at least one transparent portion or window which is not covered by the opacifying coating.
The orientating layer and the liquid crystal polymer layer may be applied to cover the entire surface of the substrate, for example to form a stand-alone security device which may be attached to another article, such as a security document.
Alternatively, the orientating layer and the LCP layer may be applied over a selected region or regions of the substrate. For example, for a security document which includes a transparent portion or window, the orientating layer and the LCP layer may be applied wholly within the area of the window, partially within and partially outside the area of the window, or wholly outside the window.
The orientating layer is preferably in intimate contact with the LCP layer. The orientating layer preferably comprises a photo-alignment layer, such as a photo-orientated polymer network (PPN—synonymous with LPP in other literature), such as described in U.S. Pat. No. 5,602,661, the contents of which are incorporated herein by reference. Instead of the PPN layer, the orientating layer may comprise a more conventional orientating layer, such as a polyimide layer rubbed in one direction or a layer having an orientating effect and obtained by oblique sputtering with SiOx. Another possibility is to apply a PPN layer to a conventionally orientated layer previously deposited on the substrate.
The LCP layer preferably comprises an anisotropic layer of orientated cross-linked liquid crystal monomers. The LCP layer has an arrangement of molecules having an orientation determined by the orientation of the underlying orientating layer or transferred therefrom to the LCP layer. The LCP layer may be photo-cross-linked by the action of light of a suitable wavelength and retains the orientation of molecules predetermined by the orientating layer. The photo cross-linking fixes the orientation of the LCP layer so that it is unaffected by extreme external influences such as light or high temperatures.
The security document or device may include further orientating layers and/or LCP layers. For example, two or more orientating layers and LCP layers having different orientation patterns may be provided to form a stack of orientation layers and LCP layers on a substrate as disclosed in U.S. Pat. Nos. 5,602,661 and 6,160,597, the contents of which are incorporated herein by reference.
The security document or device may also include other layers, such as a reflector layer or a polarizing layer. For example, U.S. Pat. No. 6,144,428 discloses a reflective metal layer between the orientation layer and the substrate. The polarising layer may be a photo oriented polymer network (PPN) with a liquid crystal polymer (LCP) and a cross-linked dichroic dye added to form the polariser. However, other forms of polarisers may be used to form the polarising layer. WO 98/52077 discloses a linear polarizer between the orientation layer and the substrate. If the security document or device includes a reflector or a linear polarizer, the optical effects produced by the LCP layer and orientating layer in combination may be viewed using a single polarizer, instead of requiring cross-polarizers to view the effects.
The optical component formed by the combination of the LCP layer(s) and orientation layer(s) may contain two or more hidden images, such as described in WO 00/29878. These images may be successively revealed and concealed when the optical component is held between two polarizers and one of them is rotated.
According to another aspect of the invention, there is provided a method of manufacturing a security document or device comprising:
providing a substrate which includes at least one layer of polymeric material;
applying a primer layer on at least one side of the substrate;
applying an orientating layer over the primer layer;
aligning the molecules of the orientating layer; and
applying a liquid crystal polymer (LCP) layer over the orientating layer.
Preferably, the orientating layer comprises a photoalignment layer which is exposed to polarized light to align the molecules of the photoalignment layer.
The photoalignment may be subjected to a first exposure of polarized light through a mask to form local regions having a first orientation of molecules, The layer may then be subjected to a second exposure without a mask using a different component of the polarized light to form local regions having a second orientation to form an orientation pattern in the orientating layer.
Alternatively, an orientation pattern may be formed in the photo-alignment layer and/or the LCP layer without the use of a mask, for example in a variable printing process or a laser writing process, such as described in our International Patent Application No. WO03/106188, the contents of which are incorporated herein by reference.
The LCP layer may be formed by applying a coating of liquid crystal monomers to the orientating layer and cross-linking the monomers to fix the orientation of the liquid crystal molecules as determined by the underlying orientation layer.
Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The security device 10 shown in
The molecules of the PPN orientating layer 14 are oriented by selective irradiation by linearly polarized UV light. If a mask is placed over the PPN layer during the irradiation process, an orientation pattern may be formed in the PPN orientating layer 14. The PPN layer 14 may be subjected to more than one exposure to different components of linearly polarized light to produce more complex patterns. In cases where a uniform orientation pattern is required in the orientating layer 14, a PPN layer may be subjected to a single exposure of linearly polarized light without a mask, or alternatively the orientating layer 14 may be a conventional orientating layer such as a polyimide layer rubbed in one direction or a layer having an orientating effect obtained by oblique sputtering with SiOx.
The LCP layer 16 preferably comprises an anisotropic layer of orientated cross-linked liquid crystal monomers which has an orientation determined by the underlying orientating layer 14. The orientation of the liquid crystal molecules in layer 14 is fixed by a photo-cross-linking process, such as described in U.S. Pat. No. 5,602,661.
The polymeric substrate 12 preferably comprises a transparent, biaxially orientated polymeric material, such as described in WO 83/00659. Polymeric substrates of this type have been used successfully in the manufacture of flexible security documents, such as banknotes, for Australian currency and the currency of several other countries, We have, however, discovered that when a security device comprising an orientating (PPN) layer and an LCP layer is applied directly applied to a thin, flexible substrate formed from or including a polymeric layer in the manufacture of a flexible security document, the adhesion of the orientating (PPN) layer to the substrate is not sufficiently robust to withstand wear, folding and other rough treatment to which the flexible security document or banknote is subjected in use, without adversely affecting the optical properties of the optical component formed by the PPN and LCP layers.
In the security device of
The primer layer 18 preferably includes two components: a polymer component and a cross-linker. The polymer component is preferably a hydroxyl terminated polymer, such as a hydroxyl terminated polyester. Other suitable polymers include polyethyleneimine; hydroxylated acrylates, which may be cross-linked or not cross-linked; polyurethanes and UV curing anionic or cationic acrylates. Suitable cross-linkers include isocyanates; polyaziridines; zirconium complexes; aluminium acetylacetone; melamines; and carbodi-imides, The primer is preferably pre-selected so that it will not adversely affect the photo-alignment of the molecules in the PPN orientating layer.
In a preferred method of manufacturing the security device of
The PPN layer 16 is preferably applied to a thickness between about 2 nm and about 150 nm The photo-orientating polymer network (PPN) should not be soluble in the primer solvent, However, when the PPN layer 16 is dried, the primer layer 18 forms a strong adhesive bond between the PPN layer 16 and the polymeric substrate 12. Surprisingly it has also been found that the primer layer 18 also increases the robustness of the optical component formed by PPN layer 14 and the LCP layer 16.
The PPN layer 14 is then subjected to at least one exposure of linearly polarized light to orientate the molecules of the PPN layer 14. Preferably, the PPN layer 14 is subjected to a first exposure through a mask to one component (e.g. the p-component) of polarised light to form local regions having a first orientation and then to a second exposure to the other component (e.g. the s-component) of polarized light without a mask so that other regions of the PPN layer have a second orientation to form an orientation pattern in the orientating PPN layer 14.
A solution containing liquid crystal monomers is then applied over the PPN layer. The liquid crystal molecules assume the orientation of the underlying PPN layer 14. The solvent is then removed and the liquid crystal monomers are photo-cross-linked by an exposure to light of a suitable wavelength. The photo-cross-linking process fixes the orientation of the LCP layer 16 so that it has the same orientation pattern of the PPN layer 14.
In an alternative method, an orientation pattern may be formed in the PPN layer and/or the LCP layer without the use of a mask, eg by a variable printing process in which the PPN layer and/or the LCP layer are printed in a pattern representing the orientation pattern for a latent image, or by a laser writing process using a scribe laser to write the orientation pattern forming the latent image in the PPN layer and/or the LCP layer. Both these processes are described in detail in WO 03/106188, the contents of which are incorporated herein by reference.
The orientation pattern of the security device of
The security device 10 of
Referring to
The second orientating (PPN) layer 24 is preferably exposed to linearly polarized light through a mask having a different pattern to the mask used to produce the orientation pattern in the first orientating (PPN) layer 14. Thus a different orientation pattern is formed in the second orientating (PPN) layer 24 and consequently when the second LCP layer 26 is applied in the form of a solution of liquid crystal monomers and photo-cross-linked to fix the orientation pattern, the second LCP layer 26 has a different pattern from the first LCP layer 16. Therefore, with a plurality of orientating layers 14, 24 and LCP layers 16, 26 with different orientation patterns, security devices which have more complex visual effects and which can store more information in the orientation patterns can be produced.
The substrate 31 of the security document 30 shown in
The opacifying layers 32 preferably comprise coatings containing at least one opacifying pigment. The opacifying coatings preferably include a major proportion of one or more pigmentary materials bound with a minor proportion of a cross-linkable polymeric binder, such as disclosed in WO 83/00659. The opacifying pigment or pigments may be selected from a group including titanium dioxide (Ti02), calcium carbonate (CaCO3), barium sulphate (BaSO4) and zinc oxide (ZnO), although it will be appreciated that other pigments may be used. One or more layers of printed indicia 39 may be provided on the opacifying layers 32.
The orientating layer 34 preferably comprises a photo-oriented polymer network (PPN). As in the security device of
The primer layer 38 may be formed from the same materials as described with reference to
A modified embodiment of a security document 40 in accordance with the invention is shown in
When viewed in polarized light the security device 42 in the security document 40 of
In a modified embodiment similar to that of
In another modified embodiment, the opacifying layer 32 on one or both sides of the substrate 31 may cover the entire surface or surfaces of the substrate 31, so that there is either a half window or no window at all. Again, it is desirable for the security device 42 to incorporate a reflective layer when the security device is provided wholly on an opacifying layer. In a further modified embodiment, the substrate 31 may comprise a base layer 35 of paper or fibrous material preferably covered on one or both sides by one or more polymeric layers 37 to improve the wear characteristics of the security document with a primer layer 38 provided between the orientating (PPN) layer 34 and the underlying polymeric layer 37.
Another embodiment of a security document 50 in accordance with the invention is shown schematically in
The transparent substrate 51 is preferably formed from a biaxially oriented polymeric material. The substrate 51 may also include co-polymer layers in similar fashion to the embodiments of
By providing a second polarizer 67 within a second laterally spaced window 63 on the security document 51, the flexible security document 51 may be folded so that the second window 63 overlies the first window 53, thus enabling the orientation pattern in the PPN and LCP layers 54, 56 to be viewed through the second polarizer 67. Therefore, the security document 51 is self-authenticating and no external verification means is required to verify the authenticity of the security device 55.
In a further modified embodiment, the linear polarizer 57 may be replaced by a reflective layer which also enables the security device 55 to be verified by folding the security document 51 so that the polarizer 67 in window 63 overlies the security device 55. In this case, it is not necessary for the security device 55 to be provided in a transparent region or window. Instead, it could be provided on an opacified part of the substrate 51.
The various embodiments of the present invention therefore provide security devices and security documents which may be authenticated either by use of external polarizers, or by a polarizer integrated within the security document itself. The security devices are difficult to copy and provide protection against counterfeiting. Moreover, a security document incorporating the security device is robust and able to withstand folding rough handling which is particularly important for flexible security documents, such as banknotes.
It will be appreciated that various modifications and alterations may be made to the preferred embodiments described above without departing from the scope and spirit of the invention. For instance, instead of an orientating layer in the form of a photo-oriented polymer network (PPN) other types of orientating layers, such as a polyimide material or an orientating layer obtained by oblique sputtering may be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004900133 | Jan 2004 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU2005/000021 | 1/11/2005 | WO | 00 | 6/19/2008 |
