Abstract
A method of producing a security device (60) is disclosed. The method comprises inkjet printing a liquid crystal material onto a first region (61) of a substrate and ink jet printing the same liquid crystal material onto a second region (62) of the substrate. The volume of the liquid crystal material printed per unit area of the substrate in the first region of the substrate is different to the volume of the liquid crystal material printed per unit area of the substrate in the second region of the substrate such that the wavelength of the peak reflectance of the liquid crystal material on the first region is different to the wavelength of the peak reflectance of the liquid crystal material on the second region.
Claims
1-21. (canceled)
22. A security device comprising a first region comprising a first volume of a liquid crystal material per unit area of the security device and a second region comprising a second volume of the liquid crystal material per unit area of the security device, wherein the wavelength of the peak reflectance of the liquid crystal material in the first region is different to the wavelength of the peak reflectance of the liquid crystal material in the second region and wherein a visible colour of the liquid crystal material in the first region is different to a visible colour of the liquid crystal material in the second region.
23. The security device according to claim 22, wherein the first volume of the liquid crystal material per unit area of the security device and the second volume of the liquid crystal material per unit area of the security device are both within the range from 0.01 to 20 L/cm.sup.2.
24. The security device according to claim 22, wherein the liquid crystal material comprises a cholesteric liquid crystal material.
25. The security device according to claim 22, wherein the first volume of the liquid crystal material per unit area of the security device differs from the second volume of the liquid crystal material per unit area of the security device by at least 10% relative to the first volume of the liquid crystal material per unit area of the security device.
26. The security device according to claim 22, wherein the first volume of the liquid crystal material per unit area of the security device is at least 0.1 L/cm.sup.2 greater than the second volume of the liquid crystal material per unit area of the security device.
27. The security device according to claim 22, wherein the first volume of the liquid crystal material per unit area of the security device is at least 6 L/cm.sup.2 and the second volume of liquid crystal material per unit area of the security device is not more than 4 L/cm.sup.2.
28. The security device according to claim 22, wherein the first region abuts the second region.
29. The security device according to claim 22, wherein the first and second regions each have an area of from not less than 1 mm.sup.2 to not greater than 1 cm.sup.2.
30. (canceled)
31. The security device according to claim 22, wherein the wavelength of peak reflectance of the liquid crystal material in the first region is at least 10 nm shorter than the wavelength of peak reflectance of the liquid crystal material in the second region.
32. The security device according to claim 22, wherein the liquid crystal material exhibits a variation in colour with viewing angle and wherein the variation in colour is different in the first region to the second region.
33. The security device according to claim 32, wherein, when changing from a viewing angle of 90 to the security device to a viewing angle of 45 to the security device, the amount by which the wavelength of peak reflectance of the first region shifts differs from the amount by which the wavelength of peak reflectance of the second region shifts by at least 5 nm.
34. The security device according to claim 22, wherein the first and second regions are part of an insignia, marking or code wherein different regions of the insignia, marking or code have different volumes of liquid crystal material per unit area of the security device.
35. The security device according to claim 34, wherein in at least a region of the insignia, marking or code the volume of the liquid crystal material per unit area of the security device varies across the region.
36-41. (canceled)
42. A method of authenticating a product, the method comprising providing on the product a security device according to claim 22; inspecting the security device at a first viewing angle and identifying a first colour in the first region and a second colour in the second region; comparing the first and second colours to expected first and second colours; and, based on the comparison, verifying the authenticity of the product.
43. The method of authenticating a product according to claim 42, the method further comprising: inspecting the security device at a second viewing angle and identifying a first shift in the first colour in the first region and a second shift in the second colour in the second region; comparing the first and second shifts to expected first and second shifts; and, based on the comparison, verifying the authenticity of the product.
44-50. (canceled)
51. A method of producing a security device according to claim 22, the method comprising: inkjet printing a liquid crystal material onto a first region of a substrate; and inkjet printing the same liquid crystal material onto a second region of the substrate, wherein the volume of the liquid crystal material printed per unit area of the substrate in the first region of the substrate is different to the volume of the liquid crystal material printed per unit area of the substrate in the second region of the substrate such that the wavelength of the peak reflectance of the liquid crystal material on the first region is different to the wavelength of the peak reflectance of the liquid crystal material on the second region and wherein a visible colour of the liquid crystal material in the first region is different to a visible colour of the liquid crystal material in the second region.
Description
DESCRIPTION OF THE DRAWINGS
[0038] The invention will be further described by way of example only with reference to the following figures, of which:
[0039] FIG. 1 is a print pattern, or bitmap, used to create test images, not according to the invention, and security devices according to the invention;
[0040] FIG. 2 is a test image, not according to the invention, printed with magenta ink using the print pattern of FIG. 1 and viewed at a first angle;
[0041] FIG. 3 is the test image of FIG. 2, viewed at a second angle;
[0042] FIG. 4 is a test image, not according to the invention, printed with cyan ink using the print pattern of FIG. 1 and viewed at a first angle;
[0043] FIG. 5 is the test image of FIG. 4, viewed at a second angle;
[0044] FIG. 6 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 1;
[0045] FIG. 7 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 1 and viewed at a first angle;
[0046] FIG. 8 is the security device of FIG. 7 viewed at a second angle;
[0047] FIG. 9 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 1 and viewed at a first angle;
[0048] FIG. 10 is the security device of FIG. 9 viewed at a second angle;
[0049] FIG. 11 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 1 and viewed at a first angle;
[0050] FIG. 12 is the security device of FIG. 11 viewed at a second angle;
[0051] FIG. 13 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 1 and viewed at a first angle;
[0052] FIG. 14 is the security device of FIG. 13 viewed at a second angle;
[0053] FIG. 15a is a graph of reflectance intensity against wavelength in regions of the security device of FIG. 13 viewed at 90 to the substrate;
[0054] FIG. 15b is a graph of reflectance intensity against wavelength in regions of the security device of FIG. 13 viewed at 45;
[0055] FIG. 16 is a graph of reflectance intensity against wavelengths in regions of a test image, not according to the invention, with different volumes of magenta ink per unit area;
[0056] FIG. 17 is a graph of reflectance intensity against wavelengths in regions of a test image, not according to the invention, with different volumes of cyan ink per unit area;
[0057] FIG. 18 is a print pattern, or bitmap, used to create security devices according to the invention;
[0058] FIG. 19 is a security device according to the invention printed with a liquid crystal material using the print pattern of FIG. 18 and viewed at a first angle;
[0059] FIG. 20 is the security device of FIG. 19 viewed at a second angle;
[0060] FIG. 21 is a print patent used to create security devices according to the invention;
[0061] FIG. 22 is a security device according to the invention printed with a liquid crystal material using parallel repeats of the print pattern of FIG. 21;
[0062] FIG. 23 is a portion of the security device of FIG. 22 viewed through a microscope; and
[0063] FIG. 24 is another portion of the security device of FIG. 22 viewed through a microscope.
DETAILED DESCRIPTION
[0064] In FIG. 1 a print pattern, or bitmap, comprises a plurality of regions in the form of vertical bands. A first region 1 is to be printed with a high volume of material per unit area. A second region 2 is to be printed with a low volume of material per unit area. Further regions 3, 4, 5 are to be printed with different, intermediate volumes of material per unit area. The regions are printed in a repeating pattern so that there are repetitions of, for example, the first region 1, 1, 1 and the second region 2, 2, 2 across the pattern.
[0065] The first region 1 is printed at 25402540 DPI (dots per inch), which equates to a volume of material per unit area of 10 L/cm.sup.2. The second region 2 is printed at 5082540 DPI, which equates to a volume of material per unit area of 2 L/cm.sup.2. Intermediate regions 3, 4, 5 are printed at 12702540 DPI, 8472540 DPI and 6352540 DPI respectively, which equate to a volume of material per unit area of 5 L/cm.sup.2, 3.3 L/cm.sup.2 and 2.5 L/cm.sup.2 respectively. When printed with droplets of 10 L, 2540 DPI equates to a droplet spacing of 10 m and 635 DPI equates to a droplet spacing of 40 m. The print pattern is used to print test images, not according to the invention, using conventional magenta and cyan inks (available from Mimaki) and security devices according to the invention using liquid crystal materials. Examples of liquid crystal materials suitable for inkjet printing are disclosed in WO2008/110342 and WO2008/110317. Such formulations typically contain a non-reactive liquid crystal, mono-acrylate liquid crystal, diacrylate liquid crystal, chiral dopant, photo initiator and inhibitor. Other such formations typically contain mono-acrylate liquid crystal, diacrylate liquid crystal, chiral dopant, photo initiator and inhibitor. The test images and the security devices were printed in a multi-pass manner using a Fujifilm Dimatix DMP2831 printer (Fujifilm, United States). With the DMP2831 printing occurs on the outbound motion of the print head away from the blotter, which when complete, is followed by incremental advance of the platen in a manner perpendicular to the direction of printing. The procedure then repeats until the image has been completed. The controlling software regards the print resolution as being defined by the angle at which the print head is positioned relative to the direction of printing. However, if the data file, or bitmap, for the image has regions of varying pixel density, then even though the sabre angle of the printer does not vary whilst printing is underway, images where the print resolution varies throughout the image can still be achieved. An example bitmap is shown in FIG. 1.
[0066] In FIGS. 2 and 3 a test image 100, not according to the invention, has been printed using a conventional magenta ink and the print pattern of FIG. 1. While the first regions 101, 101, 101 are darker than the secondary regions 102, 102, 102, with the intermediate regions 103, 104, 105, having intermediate shades, all the regions show the same magenta hue. Moreover, the hue is the same whether viewed perpendicular to the substrate (FIG. 2) or at 45 to the substrate (FIG. 3).
[0067] In FIGS. 4 and 5 a test image 200, not according to the invention, has been printed using a conventional cyan ink and the print pattern of FIG. 1. As with the test image 100, the regions in the test image 200 show the same colour in lighter or darker shades. The first regions 201, 201, 201 are darker than the secondary regions 202, 202, 202, with the intermediate regions 203, 204, 205, having intermediate shades. However, all the regions show the same blue colour and the colours are the same whether viewed perpendicular to the substrate (FIG. 4) or at 45 to the substrate (FIG. 5).
[0068] In FIG. 6 a security device 10 according to the invention has been printed using a liquid crystal material and the print pattern of FIG. 1. The substrate onto which the liquid crystal material is printed is glass. The first regions 11, 11, 11 are a green-orange colour, while the second regions 12, 12, 12 are a brown colour. Intermediate regions 13 and 14 are a pale orange and orange colour, respectively, while intermediate region 15 is a pale brown colour. The colour thus transitions from the green-orange colour of the first regions 11, 11, 11 to the brown colour of the second regions 12, 12, 12 via intermediate colours in the intermediate regions 13, 14, 15. The different colours are readily apparent to the eye and thus form a striking visual effect despite all the regions 11, 12, 13, 14, 15 being printed with the same liquid crystal material.
[0069] In FIGS. 7 and 8 a security device 30 according to the invention, similar to the security device 10 in FIG. 6, is viewed perpendicular to the substrate (FIG. 7) and at 45 to the substrate (FIG. 8). The security device 30 is also printed onto a glass substrate. As described above in relation to FIG. 6, in FIG. 7 the first regions 31, 31, 31 are a green-orange colour and the second regions 32, 32, 32 are a brown colour. The intermediate regions 33, 34, 35 are pale orange, orange and pale brown respectively. When, in FIG. 8, the security device 30 is viewed at 45 to the substrate, the colour of the first regions 31, 31, 31 shifts to a blue-green colour and the colour of the second regions 32, 32, 32 shifts to an olive green colour. The intermediate regions 33, 34, 35 are intermediate colours. Thus the brown colour of the second regions 32, 32, 32 has shifted to an olive green and the green-orange colour of the first regions 31, 31, 31 has shifted to a blue-green. This results in a useful overt security feature since the different colour shifts, especially when viewed simultaneously next to each other as the security device 30 is tilted, produce a memorable visual effect that cannot be replicated with conventional inks. Since the effect is produced using a single liquid crystal material, the security device 30 can be manufactured in a cost and time effective manner.
[0070] In FIGS. 9 and 10 a security device 20 according to the invention is viewed perpendicular to the substrate (FIG. 9) and at 45 to the substrate (FIG. 10). The substrate is a Mylar based tamper evident label. In FIG. 9 the first regions 21, 21, 21 are an orange colour and the second regions 22, 22, 22 are a yellow-green colour. The intermediate regions 23, 24, 25 transition from the orange of the first regions 21, 21, 21 to the yellow-green of the second regions 22, 22, 22. When, in FIG. 10, the security device 20 is viewed at 45 to the substrate, the colour of the first regions 21, 21, 21 shifts to a bright green colour and the colour of the second regions 22, 22, 22 shifts to a deep blue-green colour. The intermediate regions 23, 24, 25 are intermediate colours. The result is a striking change from an overall impression of yellow-greens and oranges to an overall impression of greens and blue-greens, with a particularly noticeable effect in the visually greater shift in colour, from orange to bright green, in the first regions 21, 21, 21 when compared to the lesser shift in colour, from yellow-green to blue-green, in the nearby second regions 22, 22, 22. The ability to make a security device 20 with varying colours and with varying degrees in the shift of those colours with viewing angle using a single liquid crystal material is an important advantage of the invention.
[0071] In FIGS. 11 and 12 a security device 40 according to the invention is viewed perpendicular to the substrate (FIG. 11) and at 45 to the substrate (FIG. 12). The substrate is a dark substrate created by printed a black image onto Teknocard (Arjowiggins). In FIG. 11 the first regions 41, 41, 41 are a red-orange colour and the second regions 42, 42, 42 are a deep-red colour. The intermediate regions 43, 44, 45 are intermediate colours. The colour difference between the first regions 41, 41, 41 and the second regions 42, 42, 42 provides a first level of authentication capability. However, most advantageously, there is a striking visual effect when the security device 40 is tilted so as to be viewed at 45 to the substrate (FIG. 12). At that angle, the colour of the first regions 41, 41, 41 shifts to a bright green colour, while the colour of the second regions 42, 42, 42 shifts to a lesser extent to a red-orange colour. The intermediate regions 43, 44, 45 are intermediate colours. The visually greater shift in colour, from red-orange to bright green, in the first regions 41, 41, 41 when compared to the lesser shift in colour, from deep-red to red-orange, in the nearby second regions 42, 42, 42 creates an effect that is immediately recognisable even to an unskilled observer. The effect is achieved with a single liquid crystal material, which results in a security device 40 that is simple to manufacture yet effective in providing a recognisable effect for authentication that is difficult to replicate by other means.
[0072] In FIGS. 13 and 14 a security device 90 according to the invention is viewed perpendicular to the substrate (FIG. 13) and at 45 to the substrate (FIG. 14). The substrate is card. In FIG. 13 the first regions 91, 91, 91 are a green colour and the second regions 92, 92, 92 are an orange colour. The intermediate regions 93, 94, 95 are intermediate colours. The colour difference between the first regions 91, 91, 91 and the second regions 92, 92, 92 provides a first level of authentication capability. However, most advantageously, there is a striking visual effect when the security device 90 is tilted so as to be viewed at 45 to the substrate (FIG. 14). At that angle, the colour of the first regions 91, 91, 91 shifts to a blue-green colour, while the colour of the second regions 92, 92, 92 shifts to an olive green colour. The intermediate regions 93, 94, 95 are intermediate colours. The different shift in colour, from green to blue-green, in the first regions 91, 91, 91 when compared to the shift in colour, from orange to olive green, in the nearby second regions 92, 92, 92 creates an effect that is immediately recognisable even to an unskilled observer. The effect is achieved with a single liquid crystal material, which results in a security device 90 that is simple to manufacture yet effective in providing a recognisable effect for authentication that is difficult to replicate by other means.
[0073] In FIG. 15a, spectra 201, 202, 203, 204, 205 of intensity against wavelength are plotted for different regions of the security device 90 of FIG. 13 viewed, as in FIG. 13, at 900 to the substrate. The security device 90 is viewed at 900 to the substrate with the light source and spectrometer probe coaxial to each other. The spectra are plotted for regions printed at 25402540 DPI or 10 L/cm.sup.2 (region 91, 91, 91, spectrum 201), 12702540 DPI or 5.0 L/cm.sup.2 (region 93, spectrum 203), 8472540 DPI or 3.3 L/cm.sup.2 (region 94, spectrum 204), 6352540 DPI or 2.5 L/cm.sup.2 (region 95, spectrum 205) and 5082540 DPI or 2.0 L/cm.sup.2 (region 92, 92, 92, spectrum 202). Spectrum 201 corresponds to the first region 91, 91, 91 of the security device 90 and spectrum 202 corresponds to the second region 92, 92, 92 of the security device 90. Spectra 203, 204 and 205 correspond to the intermediate regions 93, 94 and 95 respectively. As the volume of liquid crystal material printed per unit area decreases, the wavelength of peak reflectance (i.e. the peak in the wavelength spectrum) shifts towards longer wavelengths. To the eye, this effect is observed as a change to more red colours with decreasing volume of liquid crystal material printed per unit area.
[0074] In FIG. 15b, spectra 201, 202, 203, 204, 205 of intensity against wavelength are plotted for the different regions of the security device 90 of FIG. 13 viewed, as in FIG. 14, at 45 to the substrate. The security device 90 is viewed at 45 to the substrate with the light source and spectrometer probe at 90 to each other. Spectrum 201 corresponds to the first region 91, 91, 91 of the security device 90 and spectrum 202 corresponds to the second region 92, 92, 92 of the security device 90. Spectra 203, 204 and 205 correspond to the intermediate regions 93, 94 and 95 respectively. As the volume of liquid crystal material printed per unit area decreases, the wavelength of peak reflectance (i.e. the peak in the wavelength spectrum) still shifts towards longer wavelengths. However, all the wavelengths of peak reflectance are shifted to shorter wavelengths by the tilting of the viewing angle when compared to FIG. 15a. Moreover, the shift from FIG. 15a to FIG. 15b is different for the different regions 91, 92, 93, 94, 95 printed at different volumes of liquid crystal material per unit area. The result, as seen in FIGS. 13 and 14, is that the shift in colour on tilting the security device 90 is different in the different regions 91, 92, 93, 94, 95, which leads to a memorable, and difficult to counterfeit, visual effect.
[0075] On viewing the security device 90 at 90 to the substrate, the peak reflectance of the first regions 91, 91, 91 printed at 25402540 dpi is at a wavelength 30 nm shorter than the wavelength of peak reflectance of the second regions 92, 92, 92 printed at 5082540 dpi. On viewing the security device 90 at a 45 angle to the substrate, the peak reflectance of the first region 91, 91, 91 printed at 25402540 dpi is at a wavelength 25 nm shorter than the wavelength of the second region 92, 92, 92 printed at 5082540 dpi. Moreover, the peak reflectance of the first region 91, 91, 91 viewed at 45 is at a wavelength 50 nm shorter than the wavelength of peak reflectance of the same region 91, 91, 91 at a 90 viewing angle.
[0076] By contrast, in FIG. 16, spectra 301, 302, 303, 304, 305 are plotted for conventional magenta ink in a test image not according to the invention and printed according to the print pattern of FIG. 1. Such a test image may be the image of FIGS. 2 and 3. Similarly, in FIG. 17, spectra 401, 402, 403, 404, 405 are plotted for conventional cyan ink in a test image not according to the invention and printed according to the print pattern of FIG. 1. Such a test image may be the image of FIGS. 4 and 5. In both cases, while the intensity of the peak reflectance decreases with decreasing volume of liquid crystal material printed per unit area, the shape of the reflectance spectrum remains substantially unaltered. To the eye this appears as a paler shade of the same colour. Because there is no peak reflectance with a wavelength that changes with volume of material printed per unit volume, the striking colour difference obtained in the security devices of the invention is not present in the test images.
[0077] In FIGS. 18, 19 and 20 a security device 60 according to the invention is printed using a print pattern (FIG. 18) comprising areas 51 in which a high volume of liquid crystal material is printed per unit area and areas 52 in which a low volume of liquid crystal material is printed per unit area. Between those regions are regions 53 in which the volume of liquid crystal material printed per unit area changes across the region. The resulting security device 60, when viewed perpendicular to the substrate (FIG. 19) is a striking image of spokes of a wheel. The spokes correspond to the first regions 51 of the print pattern and appear as first regions 61 of the security device 60 having a yellow-orange colour. The second regions 62 of the security device 60 correspond to second regions 52 of the print pattern and are a dark red colour. Between the first regions 61 and the second regions 62, intermediate regions 63 show a transition from the yellow-orange colour of the first regions 61 to the dark red colour of the second regions 62.
[0078] Even viewed perpendicular to the substrate as in FIG. 19, the security device 60 of the invention already provides a memorable visual image with just one liquid crystal material. However, as the security device 60 is tilted to 45 (FIG. 20), the visual effect is even more striking. In FIG. 20, the first regions 61 shift to a bright green colour, while the second regions 62 remain a red colour. The intermediate regions 63 now show a transition from the green of the first regions 61 to the red of the second regions 62, via yellow-green and orange colours. Because not only the wavelength of peak reflectance is different in the first 61 and second 62 regions, but also the extent to which that wavelength is shifted with changing viewing angle is different, the visual characteristics of the device are instantly recognisable to even an unskilled observer. However, those effects are difficult to reproduce by other means. Being able to create such a strong security device 60 by printing a single liquid crystal material in a single print step provides significant advantages in being able to apply the security device 60 to products or their packaging as they are produced even on a high speed production line.
[0079] In FIGS. 21 and 22, a security device 80 according to the invention is produced by varying the volume of liquid crystal material printed per unit area along a printed line. The volume of liquid crystal material printed per unit area is changed in discrete regions 71, 72, 73, 74, 75 of the print pattern, resulting in bands of colour in discrete regions 81, 82, 83, 84, 85 of the security device. The first region 81, having the highest volume of liquid crystal material per unit area appears a yellow colour, while the second region 82, having the lowest volume of liquid crystal material per unit area appears a pink colour. The intermediate regions 83, 84, 85 have intermediate colours.
[0080] The authenticity of the security device 80 can be further verified by examining the regions 81, 82, 83, 84, 85 under crossed linear polarisers in a microscope. In FIG. 23, the second region 82 shows a distinct pattern of varying colour at the microscopic scale that is distinct from the pattern in the first region 81 in FIG. 24. Thus, while the unskilled observer can confirm authenticity by reference to the overt visual effect, a further, forensic examination of authenticity can be undertaken by a skilled technician using the forensic effect if an even greater level of certainty is required.
[0081] It will be appreciated that the embodiments set out above are examples of the invention and that the skilled person would appreciate that variations are possible within the scope of the invention. For example, many different patterns of the first and second regions, and indeed of further regions are possible. Moreover, while the invention is concerned with the presence of a single liquid crystal material printed at different volumes per unit area in different regions of the security device, that can be achieved while also printing or coating further inks or liquid crystal materials in other regions of the security device.
