HK1147975B - Optical variable device - Google Patents

Description

Optically variable device

The divisional application is based on the divisional application of Chinese patent application with the application number of 200410089921.6, the application date of 2004, 7/13, and the invention name of 'interference product of vacuum roll coating anti-counterfeiting film with obvious and/or hidden pattern layer'.

Technical Field

The present invention relates to security threads, and in particular to security threads for embedding in or on paper or documents.

Background

The use of security threads for the protection of banknotes, credit cards and other documents of value is well known. Security thread is a strip of material that is placed on the surface of a banknote document or sheet, such as a banknote; alternatively, the security thread may be curved or woven into the banknote paper (window shape effect) to provide additional security (authenticity) to the banknote. Typical dimensions of the hot line are 1-5mm wide and 3-4 μm thick; the thickness of the PET-based window line is 0.5 mil or 12.5 micrometers. By way of example, the earliest form of security thread consisted of a reflective foil which was transferred to the surface of the banknote by hot stamping (GB 2119312A). Such reflective foils prevent counterfeit banknotes from being reproduced by printing processes such as printers, pc printers and copiers. Holography (EP- ｃA-0624688), holographic properties together with thermochromic features (GB2347646), opaque coatings with readable features and patterns by transmitted light combined with luminescent substances (US6474695), repeated patterns of magnetic/magnetic markings or metal dots (WO02103624), laser etched fine lines and text with laser light (german "auslegschrift" No.2205428) and (WO02101147), printing small markings on hardened clear plastics with transparent acid-resistant inks and then acid etching in unprinted areas to produce shiny small markings on the clear bottom (US4652015), binding nucleic acid molecules to bind complementary nucleic acid molecules to molecules that have been attached to the document (DE10122836), and optically variable security elements made with liquid crystal materials (EP0435029) have all been used to make security threads. However, these above-mentioned security threads take a lot of time to produce and are associated with other problems, such as laser etching times that have been found to be too long and cost-inefficient, etching using chemicals requiring multiple steps and not being considered environmentally friendly; holograms can be easily replicated and in many cases the features of security threads are not readily apparent to the eye of the average person and need to be read by an instrument.

Piwcyzk in U.S. patent 4,022,928 proposes a method of embossing a metal or carbon monolayer in a vacuum chamber. Piwcyzk will be referred to as FOMBLIN using various methods^TMOr Krytox^TMThe perfluoropolyether of (a) is applied to a substrate in a desired pattern, the substrate being used to vacuum deposit a layer. Perfluoropolyethers inhibit deposition of deposition materials onto a sheet or plastic substrate. The liquid being applied by spraying or vacuum evaporation in combination with a selected removal process, e.g. in combination with a laserOr an electron beam. A method of printing is also described. Printing techniques including relief printing such as relief printing or flexography, offset printing such as offset printing, gravure printing, and screen printing such as screen process printing are disclosed.

Later, Ronchi in U.S. Pat. No. 4,749,591, the contents of which are incorporated herein by reference, and PCT application WO8700208(A1) proposed this printing method by applying the inhibited oil FOMBLIN to a vacuum roll coater where it is desired to emboss a film on a plastic substrate.

Ronchi in US4,749,591 discloses only the application of a single layer of metal, for example, aluminum deposited as a vacuum film layer as shown in fig. 1. In the case of security threads embedded in banknotes, the demetallised aluminium layer can be easily imitated by simply using metallised polyester which is subsequently embossed by one of the methods described above. In attempting to replicate a single layer security thread made by the Ronchi technique, patterning by photolithography in combination with an alkaline etchant can be used, or by any of the methods described previously, or even by mimicking the security thread using a silver pen. Security threads having multiple layers of film, wherein one or more of the layers are patterned, have not been previously contemplated. The main obstacle to providing several thin film layers is the residue left on the image and the non-patterned areas of the sheet. This oil residue is detrimental to further coating the film, since the remaining oil causes "ghosting"; a method of transferring the inhibiting oil to the back side of the plastic film when roll coating, which in turn transfers the inhibiting oil further down to the front side of the web. The remaining inhibiting oil also promotes failure to adhere to subsequent film layers.

The present invention overcomes "ghosting" and the ability to remove residual inhibiting oil. By this development, for the first time, patterned multilayer optical stacks can be conveniently manufactured on security threads by roll coating in a cost-effective manner. In particular, new optically variable security threads with a high degree of pattern definition are produced which contain readable text or graphic images in which covert features such as magnetic signatures are also incorporated.

It is an object of the present invention to provide a security thread having optically variable features such as an optically variable pattern that can be recognized from the pattern against a background, or an optically variable pattern that protrudes from the pattern.

It is another object of the present invention to provide a relatively simple, inexpensive method of making multilayer patterned security threads for use on the interior or upper portion of sheets or foils, such as on currency, documents or packaging, to provide authenticity verification thereof.

Disclosure of Invention

According to the present invention there is provided a security thread for embedding in or on a sheet or document comprising:

an elongated substrate having a first side and a second side;

an optically variable structure deposited on one of the first side or the second side of the elongated substrate, wherein the optically variable structure comprises a thin film interference structure having the appearance of a plurality of separate interference filters arranged side by side and spaced apart from each other, having a visible color shifting characteristic to shift color in the form of a visible pattern of visually distinguishable identifying indicia against a foreground or background of a different color.

The present invention provides a security thread providing security to a sheet, document or package, wherein the thread has a visibly optically variable structure thereon, which structure is visible from at least one side of the paper; although the optically variable structure may be a continuous multilayer constituting a large Fabry-Perot cavity or interference filter, the interference filter appears as a separate filter by providing a patterned layer in front of the Fabry-Perot cavity. In another embodiment the plurality of separate filters are provided as optically variable structures that appear to be separate as well.

According to the present invention, there is provided a sheet having a security thread embedded therein or disposed on an upper portion thereof, the security thread comprising:

a substrate having a first side and a second side;

a plurality of separate n-layer Fabry-Perot cavities deposited side-by-side on the first side of the substrate, wherein the Fzbry-Perot cavities are spaced apart from each other, wherein each of the n-layer Fabry-Perot cavities is a thin film interference filter having visible discoloration properties; the plurality of cavities are arranged along the substrate to form a visible pattern as a result of the color shifting properties.

According to another aspect of the invention there is further provided a security thread for embedding in or disposing on a laminate, wherein the security thread comprises a plastic laminate on which is deposited a colour shifting thin film coating, the coating forming side-by-side isolated interference filters, wherein the patterned interference filters are visible when against a differently coloured background.

According to one embodiment of the invention, a continuous Fabry Perot structure having multiple layers defining one or more cavities may be applied to one side of a sheet or substrate. On the second side of the sheet, a pattern of aluminum or other material that is clearly distinguishable from the Fabry Perot structure may be applied using an oil-etching method. When one looks at the security thread from the aluminum side of the pattern on the surface, the portion lacking aluminum appears as an optically variable area and the portion with aluminum appears as a contrasting aluminum area. Thus in this embodiment, the viewer sees the continuous Fabry-Perot structure from the pattern side and from a plurality of FP cavities separated side by side, since the aluminum obscures the portion providing the pattern.

According to yet another aspect of the present invention there is provided a method for forming an optically variable device, comprising the steps of:

patterning a reflective layer on a thin substrate using an oil etching technique to form a patterned reflective layer, the substrate having a first side and a second side;

the oil residue is removed from the first side of the sheet and a thin film layer is deposited on the sheet substrate to form the optically variable device.

According to another aspect of the present invention, there is further provided a method of patterning a metal, comprising the steps of:

applying a non-wetting oil to selected portions of the first surface of the sheet substrate to form an oil pattern;

depositing metal on the first surface of the sheet substrate, wherein the non-wetting oil ablates the deposited metal from the oil pattern; and

the oil residue is removed and a first glow discharge is applied to a first surface of the sheet and a second glow discharge is applied to a second surface of the sheet.

According to another aspect of the present invention, there is provided a machine-readable security device comprising a sheet disposed thereon, a patterned layer of magnetic material sandwiched between two metal layers.

According to the present invention, there is also provided a machine-readable security device, wherein the security thread comprises a magnetic material on which a pattern is formed using an oil etching method.

The use of an oil etch process is the preferred embodiment, allowing for coating in the coating chamber and removal by rolling on the pattern to produce a patterned sheet with a significant pattern interference structure. Although it is within the scope of the invention to use other materials having the same properties as the oil, wherein its removal is compatible with the application of subsequent layers in situ. Alternatively, but not preferably, a water soluble polymeric coating that can be removed later by water washing is acceptable, however, the use of such a temporary coating is less effective than oil application, which can be removed in the deposition chamber.

The present invention encompasses the difficulties encountered in the wet chemical etching process for patterning by providing a novel security thread which is optically variable, whether in reflection or transmission of text or other patterns formed by a straight line through dry process using a vacuum roll coater. The color changes when the security thread is raised back and forth, and the human eye can easily see the optical characteristics of the color-changing security thread. In opposition to a transparent or brightThe text or pattern is optically variable in reflection against the background, or alternatively the background is optically variable relative to the text or pattern, which can be easily seen due to transmission. In addition, the security thread and the pattern thereon can be distinguished from the background of the sheet bearing it. Alternatively, security threads can be seen in reflection, with the image using foil or color shifting ink appearing colored or optically variable against a reflective background of aluminum or other non-colored metals such as copper, or against an optically variable or non-optically variable thin film optical laminate. Alternatively, one embodiment of the present invention provides a reverse or negative image of the above-mentioned structure. Optically variable laminates can be made using U.S. patent 4,705,356 to Phillips, an inventor of the present invention; 4,838,648, respectively; 5,135,812, respectively; 5,214,530, respectively; 5,278,590; 5,278,590; 6,157,489, respectively; 6,241,858, respectively; 6,243,204, respectively; 6,241,858, respectively; 6,569,529 and 6,699,313. In addition, discoloration such as titanium dioxide (TiO)₂) Or ferric oxide (Fe)₂O₃) Mica-coated mica-based interference pigments can be used as color-changing pigments in color-changing inks.

Various embodiments of the present invention are described and illustrated in the detailed description and drawings. The security thread can enter the inside of the banknote in the form of a window, in the same way as in the european patent application EP1258334A3 in the name of Cunningham and Brian, or can be applied across the surface of the banknote.

Security threads of the kind described according to the invention cannot be reproduced exactly by means of photocopying, filming and printing, since these techniques cannot have optically variable effects. Furthermore, in the optically variable foil example, the optics in the copier prevents even the front side colors from being imaged at normal incidence; because the reflective surface of the optically variable line is just like a black pattern, light misses the entrance optics of the copier. In addition, complex patterns of text, with resolutions down to 60 microns, may prevent any attempt to use the method of interception to simulate the artifacts of this security device.

Drawings

Embodiments of the invention are described in detail with reference to the accompanying drawings, wherein:

figure 1 is a schematic representation of the prior art with an embossed aluminum layer on a PET substrate or sheet.

FIG. 2 is a cross-sectional view of one embodiment of the present invention in which the interfering structure is shown formed by an embossed aluminum layer on a PET sheet, the embossed aluminum layer covered by a MgF2 barrier layer, and a chromium layer covering the MgF₂And the three layers form a plurality of optical interference structures, and windows are arranged between the side-by-side optical interference structures.

Fig. 3 is a cross-sectional view of a laminate structure having embossed aluminum on one side of a PET sheet, an optically variable foil coating on the same side of the PET sheet, and a different optical coating on the other side of the PET sheet.

Fig. 3b is a cross-sectional view similar to fig. 3 with additional plastic layer embossing.

FIG. 4 is a schematic of an embodiment of an embossed magnetic layer on a PET sheet.

Figure 5 shows an embodiment of the invention in which an embossed magnetic layer is sandwiched between two aluminium layers on a PET sheet.

Fig. 6 shows an embodiment with an embossed aluminum layer on one side of the PET sheet and an optically variable foil with a hidden magnetic layer on the same side of the PET sheet.

Figure 7 is a schematic drawing showing an embossed aluminum layer deposited on a plastic substrate with color shifting ink applied to one side of the PET sheet.

Figure 8 shows the effect of applying a positive and negative embossed aluminum layer of color shifting ink on one side of a PET sheet.

FIG. 9 is a schematic view of an embodiment of the present invention in which an embossed aluminum layer is deposited on one side of a PET sheet and a color-changing ink layer is coated on the opposite side of the PET sheet.

Figure 10 is a cross-sectional view showing an embossed aluminum layer coated with a wear-resistant paint protective layer deposited on one side of a PET sheet, and color-shifting ink on the opposite side of the PET sheet.

Figure 11 shows an embossed aluminium layer coated with a Fabry-Perot pattern on one side of a PET sheet and a different Fabry-Perot pattern on the other side of the PET sheet.

Figure 12 is a cross-sectional view of an embossed aluminum layer on one side of a PET sheet and a continuous optical structure on the other side of the PET sheet.

Figure 13 shows a patterned color shifting foil on one side of the PET and an ink printed layer (black or the complement of the color shifting foil) on the other side of the PET.

FIG. 14 is a cross-sectional view showing a Fabry-Perot pattern on a PET sheet with an insulator spacer layer embossed on the PET sheet.

FIG. 15 is a cross-sectional view showing a Fabry-Perot pattern on a PET sheet with an absorber layer embossed to the PET sheet.

Fig. 16 is a schematic view illustrating a simplified coater according to an embodiment of the present invention.

Fig. 17 is a schematic diagram illustrating a cleaning arrangement for removing residual "suppressor oil" within the coating chamber.

FIG. 18 is a view of a one-dimensional magnetic barcode pattern hidden in an aluminum layer, which is suitably shown in this figure as transparent to allow the barcode to be seen.

FIG. 19 shows a two-dimensional magnetic barcode pattern hidden in an aluminum layer.

Fig. 20 is a photograph showing the clarity of text labels in an embossed optically variable security thread.

Figure 21 is a photograph of embossed optically variable lines embedded in a banknote in the form of windows.

Figure 22 is a photograph showing text of embossed optically variable lines in a banknote viewed in perspective.

FIG. 23 shows a graphic security label formed from a patterned optically variable foil structure on a releasable pressure sensitive adhesive label stock.

Detailed Description

Referring to fig. 2, a patterned aluminum layer 22 is shown on a PET sheet 20. This embodiment is not limited to the use of aluminum as the reflector material and other reflective materials, such as additional reflective metals, can be used in place of aluminum. The PET sheet forms the basis of the security thread on which the layers shown are deposited; however, other materials, such as other plastics, can be used in place of PET. The embossed aluminum layer 22 is formed from MgF deposited on the embossed aluminum and the sheet₂An isolation layer 24 covering the sheet, the sheet forming a window 28 in the area of the sheet where no deposited aluminum is present; a layer 26 of absorbing material, such as a thin layer of chromium, is deposited on the isolation layer 24. The optical interference structure is formed by a reflector/insulator separator/absorber (R/D/Ab) on the embossed metal remainder, but not on the sheet portion where the aluminum has been removed; these portions where aluminum has been removed are referred to as window portions. The optical interference structure(s) 21 may be colored fibers that provide a distinctive appearance of embossed metal, or colored fibers that provide a "optically variable" appearance of embossed metallic discoloration. The aluminum is patterned by printing a pattern or image on the clinker sheet 20 using "inhibited oil" and then depositing a thin aluminum film. This procedure works even though the exact mechanism by which the oil prevents adhesion of vacuum deposits to the substrate is not fully understood. Various theories have been proposed to explain this phenomenon. One theory cites the idea that the heat of compression of the deposited material converts oil to gas and actually melts the metal. Another explanation is that the oil only prevents the buildup of deposited metal and thus the arriving material is dispersed.

In the embodiment shown in FIG. 2, Al-IIMagnesium fluoride (MgF)₂) -each layer of the chrome laminate forms a Fabry-Perot ("F-P") absorbing layer-spacer layer-reflecting layer type optically variable device ("OVD") which is not formed in the window portion of the sheet, since in this region there is a loss of Fabry-Perot structure. The plastic sheet may be colorless, colored, translucent or transparent, and the choice of materials for the embossed metal layer and the overlying film is merely exemplary. After coating the film layer, a protective layer is optionally coated, such as a thin lacquer layer, not shown, or adhered to the plastic film (e.g., 0.5 mil) of the OVD using a laminating adhesive.

Fig. 3 shows a layer structure similar to fig. 2 on the front side of the sheet 30. The aluminum deposition is embossed after being applied with a roller coater in an oil pattern with a suppressor oil to prevent continued deposition of predetermined areas of the sheet 30 on the "front" side of the PET sheet. MgF₂Layers 34 and 36 of chrome are deposited on the front side to form an optical interference structure that is saturated with aluminum; aluminum acts as a reflective layer in the Fabry-Perot structure. Another optical structure 39 forms the "back" side of the sheet, such as a reflective layer, an optically variable layer (OV), a magnetic layer, all continuous or embossed, or sandwiched between aluminum layers or as a single or fluorescent layer. In this embodiment, protective layers are optionally applied to both sides of the OVD. The optical structure may be opaque or semi-transmissive.

In embodiments in which the magnetic layer is sandwiched between reflective layers, as described in us patent application 2002/0160194a1 and WO02090002(a2) in the name of the same inventor, an overlay mark is proposed, in accordance with the present invention. Numbers in a numeric code or in a bar code may be provided which cannot be identified with the naked eye and the serial number may be pre-verified on a voucher or banknote, for example, $ 50.00.

In this embodiment, the magnetic bar code is hidden in a pattern that has the same reflective characteristics as aluminum, but has magnetic identification marks that can be read by a dedicated detector. The magnetic detection may be due solely to the presence of magnetic material in the magnetic image, e.g. a covert barcode or covert marker, or may be a digital or analog signal of recorded information.

In the simplest embodiment, as shown in FIG. 4, a single layer 42 of magnetic material can be deposited onto a plastic sheet 40, patterned by oil imaging, and then patterned to form a security thread, label or hot-stamp image. In more complex structures, the patterned magnetic layer 52 supported by the substrate 50 is sandwiched between two aluminum layers 54 and 56 as shown in FIG. 5, or two aluminum layers in a Fabry-Perot optical stack as shown in detail in FIG. 6, with a patterned aluminum layer 62 deposited on the substrate 60 in FIG. 6; on the aluminum layer 62 is an insulator 64 of chromium layer 63, with a magnetic layer 66 sandwiched between two aluminum layers 65 and 67, which are located on the insulator 64. In the case where only one side of the security thread is visible, the magnetic layer 66 can be coated with a single layer of aluminum 67 without being sandwiched between two layers of aluminum.

Referring now to FIG. 5, a cross-sectional view is shown in which a plastic substrate 50 has a non-magnetic aluminum layer 54 deposited thereon. Other materials that are not magnetic may of course be used. A suppressed oil pattern is then applied to form a predetermined bar code oil pattern, the oil pattern depending on the design pattern and the roller from which the oil is obtained and applied to the plastic sheet 50. Magnetic layer 52 is then deposited and the magnetic material remains only in the portions that were not coated with oil during the vacuum coating and tumbling. The termination layer 56, without magnetic material, effectively sandwiches the magnetic layer 52 between two nonmagnetic layers.

In an alternative embodiment shown, it is possible to use an additional layer on the pattern layer as the alignment layer. This can be achieved by evaporation of the organic smoothing layer through lateral coupling during vacuum and curing as taught by Yializis in us patent 6,706,412. In the embodiment described according to the present invention, the depth of the vacuum deposition layer is much thinner than the thickness of the oil pattern; therefore, small protrusions of 1000 angstroms or less for vacuum deposition layers are negligible compared to about 10,000 angstroms in oil thickness. Patterning for multiple layers may occur over areas without patterning or even over previously patterned areas.

Fig. 6 is more complex than the structure of fig. 5, however the manufacturing process is essentially the same, both patterning and depositing subsequent layers.

In another embodiment of the present invention, a combination of patterned films and color shifting inks may be used, including but not limited to inks comprising coated mica-based pearlescent pigments,(registered by Flex products Co., Ltd.) pigment, optically variable ink (SICPA registration), diffractive based pigments or liquid crystal color changing inks. The pigments may constitute planar thin film optical structures or may constitute diffractive flakes as described in U.S. Pat. No. 6,692,830 and PCT application WO03011980A 1.

Referring now to fig. 7 and 8, one embodiment of the present invention utilizing a color shifting ink is shown. In this case, the color-changing ink 75 is visible through the holes or windows 76 in the embossed film 73. In the simplest case, the patterned aluminum 73 is formed on a plastic film 70 such as polyester terephthalate (PET) and the color shifting ink 75 is applied to the patterned aluminum so that the color shift is seen from the opposite side from a viewing angle through the text or graphic image or appears as a background around the reflective text or graphic.

The illustration in fig. 8 illustrates that the background may be color-invariant and the foreground color-shifting, or vice versa.

Alternatively, the color-changing ink is applied to the opposite surface of the aluminum bearing the pattern so that one can view the security device from the side of the aluminum bearing the pattern. In this case, the color shifting ink is shown through the patterned aluminum openings. As described in previous embodiments, the aluminum bearing the pattern may have an additional protective layer disposed thereon, such as a scratch resistant lacquer or laminating a typical thin PET sheet having a thickness of 0.5 mils or less. These structures are exemplified in fig. 9 and 10.

In fig. 9 the plastic sheet 90 has in its upper part an optically variable structure 92, for example in the form of an optically variable ink, a color-changing ink, an optically variable pigment or a thin film Fabry-Perot cavity. In the lower portion of the sheet is a patterned aluminum layer 94. In fig. 10 a layer 105 of a color-changing ink is deposited on a plastic substrate 100, a patterned aluminum layer 103 is deposited on the lower portion of the substrate 100, and a layer 106 of protective lacquer is applied thereon.

In one embodiment, the reflective layer is an opaque aluminum layer such that the window portions forming the patterned layer exhibit reflectivity. The back reflective layer has no MgF with the front side₂the-Cr layer typically constitutes the OV structure because the intermediate PET sheet is relatively thick for use as a spacer layer in the Fabry-Perot structure in the visible spectral region. The window portion displays the mirror and the front side F-P structure provides the OVD as shown in fig. 3.

Alternatively, the optical structures on the back side of the sheet are optical interference structures, such as a thin film absorber layer on a PET sheet, a spacer layer on the absorber layer, and a reflector layer on the absorber layer, thus forming a second F-P structure in addition to the F-P structure on the front side of the sheet as shown in FIG. 11. For security threads with OVDs, a reflective back layer 112a is particularly desirable because the mirror-like background provides a good visual reference for OVDs on the front side. This reflective back layer is also used for one layer of the optically variable structure defined by the two adjacent layers; the two adjacent layers are the chrome layer 115a and the insulating layer 111 a. Fig. 11 also shows a plastic substrate 110 with a patterned aluminum layer 112 followed by an insulating layer 111 with a chrome layer 115 on top of it.

Alternatively, a color-changing ink layer may be applied to the back of the sheet. Application of the color shifting ink to the back of the sheet produces an Optically Variable (OV) effect when the structure is viewed from either side. When viewed from the back, the OV effect of the color-changing ink was observed. When viewed from the front, in addition to the OV effect of the color-changing ink, the OV effect of the color-changing structure composed of the aluminum layer forming the pattern was observed.

Turning now to fig. 12, a PET sheet 120 is shown with patterned aluminum 112 on the front side and optical structures on the back side. In one embodiment, the optical structure is an organic layer 128 comprising Anti-Stokes (Anti-Stokes) material in powder form. When illuminated with longer wavelengths, the Anti-Stokes layer fluoresces at a short wavelength. There are many suitable materials and are typically applied to the back of the sheet as very fine particles in the carrier. Powdered Anti-Stokes material is available from STAR DUST TECHNOLOGIES. The particles are generally light colored, such as milky white or light tan, and fluoresce in colors such as blue, green, orange when irradiated with near infrared light outside the visible region. Thus, when the window portion is irradiated with the adjacent infrared light, the window portion fluoresces in a visible color. This can serve as a hidden security thread because the Anti-Stokes coating cannot be easily seen by casual observation.

Alternatively, a patterned optically variable foil is shown in FIG. 13, which includes a patterned aluminum layer 132, an insulating layer 134, and a chrome layer 135, which may be formed on one side of the PET, and a plain ink print layer 136 printed on the other side of the PET substrate 130. The printing ink 136 may be black or a color complementary to the conventional color (90 degrees) of the color shifting foil. In this embodiment, a black or complementary color is displayed through the window forming the pattern OVD or reverse image, and a black or complementary color layer is used to serve as a background for the color changing pattern text. For example, a foil that changes from green to blue would have magenta printing ink on the other side of the PET; for example, green and magenta are complementary colors. In both cases, the contrast between the printed ink layer and the color shifting foil can be easily seen in reflected light. The contrasting colors can also be printed so that the text reflective colors appear only at abnormal angles.

In the embodiment shown in fig. 3b, the plastic sheet plastic substrate 30 has an embossed surface coated with an aluminum layer 32 on the opposite side of the patterned coating 34 so that a holographic or diffraction image is displayed through the aperture 36.

FIG. 14 shows an OVD (optically variable device) formed on a thin plate 140, in which a reflective layer 142 of, for example, aluminum and MgF, for example, are deposited₂The overlying spacer layer of layer 144 is patterned by an oil "suppression" technique. E.g. thin layer of chromiumAn absorbing layer 146 is deposited on the underlayer to form the OVD, wherein the reflective layer, spacer layer and absorbing layer form the F-P structure. As shown by the OVD in fig. 3, where the optical structure of the back side is a reflective layer, the embodiment shown in fig. 14 may have a highly reflective region closest to the OVD structure, which provides a visual reference when viewing the OVD. In another embodiment, more insulating layer material can be deposited onto the patterned insulator to form a color shifting pattern on top of the different color shifting patterns once the final absorber layer has been deposited.

Fig. 15 shows an OVD formed on a sheet 150 having a reflective layer 152 and a spacer layer 154, respectively, formed on the sheet, and an overlying patterned absorber layer 156. The absorber layer is patterned using oil-melt techniques. OVDs are formed where the absorbent material remains.

Fig. 16 shows a simplified coater according to an embodiment of the invention. The coater includes an unwind roll 160a, a wind roll 160b, a print head 162, an evaporation dish 164, and glow discharge elements 166a and 166 b. In operation, the print head 162 receives "inhibited oil" from the pick-up roller 168 and applies the oil to the PET sheet 170.

The oil has a characteristic of not being easily evaporated in a vacuum state of the roll coater, but is easily evaporated when the evaporation material is subjected to compression heat. In addition, the oil has the property of not spreading on the surface of the plastic sheet, with little, if any, dot gain.

The oil must adhere to the substrate but not spread over the printed image area. Ideally, the oil should interact with the plastic sheet without diffusion. If the oil spreads over the image of the printing cylinder, the image is not faithfully reproduced. If the graphic image is in the form of pixels, it is important that the pixels are distinguishable from each other and that no edges or parts run into each other. This detrimental increase in pixel size is called dot gain. There may not be any difference to the very fine layer of oil, whether it is a wetting oil or not. However, it is preferred that the oil does not bead up into strings. If the oil is thick and not wet, the oil will simply gather beads and form stringsRun out of the web without remaining on the printed image. The diffusion of one material over another is determined by the respective surface energies γ a, γ B and γ AB, where γ a is the surface tension (i.e., surface energy) of the plastic sheet, γ B is the surface tension of the oil, and γ AB is the interfacial surface tension. Diffusion is represented by equation S_L/Sγ a- γ B- γ AB, wherein S_L/SIs the diffusion coefficient. If S is_L/SBeing positive, diffusion will occur. In other words, γ a is larger than the sum of γ B and γ AB, which means that (γ B plus γ AB) is lower than the surface energy of γ a. Thus, diffusion occurs to a minimum energy. Therefore, S is not generated in order that oil diffusion on the plastic substrate does not occur_L/SShould be negative. As mentioned above, spreading is detrimental because the dot gain reduces the sharpness of the original printed image on the patterned imaging roll. The oil also has a low vapor pressure so that the oil does not evaporate after the image is printed on the sheet. FOMBLIN or Krytox oil meets the diffusion standard; however, other low vapor pressure oils may be used depending on the substrate used.

In operation, the sheet is advanced to an evaporation dish to deposit aluminum or other material on the surface of the sheet. The process conditions are controlled so that the heat of compression of the aluminum vaporizes the oil located in the lower portion of the aluminum, removing the aluminum from the previously oiled area. An alternative explanation is that the oil prevents the buildup of deposited aluminum, i.e., the aluminum does not stick and re-evaporate into the chamber. However, even if the process is carried out under vacuum, it is found that there is a breakdown of the oil product and/or residual oil (typically "sludge") on some parts of the sheet, including on the back of the sheet after vacuum deposition. This residue can degrade the optical performance of OVDs subsequently formed on the web and prevent acceptable adhesion of subsequent film layers. Even detecting the presence of this residue, the absence of shaped OVDs and evaluating their optical performance is very difficult. Ghosting, smudging and other undesirable effects are observed when OVD film structures are deposited on a sheet with a patterned aluminum that does not remove the oil residue. Aluminum was deposited and patterned in one vacuum coater and OVD was deposited in another vacuum coater. It has been found that the cleaning of the dross can be performed in the aluminum coater after patterning, in the OVD coater before deposition, or by a vacuum roll coater which can be used for depositing and patterning aluminum and for depositing OVD layers with an intervening cleaning process.

Glow discharge scavenging techniques are used to successfully remove the oil cake. Several types of glow discharge scavenging techniques and other scavenging techniques were evaluated. Glow discharge removal techniques using argon are reliable, but do not adequately remove residues of the oil used in the patterning process. The infrared heater was used before coating, but oil migration still occurred, presumably due to oil migration between the layers of the sheet. For example, oil residue on the front side of the web on the winding roll will be transferred to the back side of the web. During the in-lay process, which applies OVD before the layers of the sheet are wound together, a front side removal of residue may be sufficient. However, according to the oil used in this example, it is considered that a certain amount of cross contamination occurred during the patterning, and cleaning of the front and rear was performed as shown in fig. 17.

Many additional features of the coater are omitted, such as the dancer roll and the chamber divider. Also, the sheet may be held against the rollers during aluminum deposition/patterning.

FIG. 17 shows a simplified deposition apparatus for cleaning an embossed sheet. The embossed web 170 exits from the unwind roll 170b and exits along a series of tension rolls. The back of the sheet is cleaned at first location 171 by a first glow rod shown open. The front of the web is cleaned by the surrounding glow rod at a second location 172 further along the web. The covering is optionally omitted if the glow discharge does not affect other system components. Also, the removal of the back side of the sheet may not be necessary in all embodiments. Oxygen is supplied to the glow rod enclosure, but may be provided at any location in the chamber. Oxygen supplied to the enclosure diffuses into the first glow rod region to cause a clearing discharge. The chamber divider 179 keeps material(s) from the OV from depositing on the tension rollers and other system components. During the OV layer deposition, the web is pulled taut against coating roller 178. As glow discharge using oxygen as a precursor (precursor) firstIt was found to perform well in sheets that clean up the oil sludge. Other precursors are preferably used for other oils or liquids, or even for this type of oil residues. In a particular embodiment, a PET sheet approximately 8.5 inches wide is fed through the glow discharge removal stage at a speed of 0.5 meters per second. The total current of the back side glow rod and the front side glow rod was 100 milliamps and the glow rod was operated at 2,200 volts. Pure oxygen is supplied to the front glow rod cover to produce a 5 x 10 glow rod^-3The chamber pressure is held to remove oil residue from both sides of the pattern sheet. OVDs formed on patterned sheets cleaned in this manner exhibit good optical properties and are suitable for use in commercial applications.

Further description of the embodiments

The present invention is generally directed to methods and apparatus for making image foils and security articles including optically variable foils and security labels. In an embodiment, the optically variable foil is manufactured using an all-vacuum embedding process.

A substrate comprised of 0.25 to 5 mils, preferably 0.5 to 1.0 mils (1 ═ 25.4 micrometers) of PET is first patterned onto the sheet, 2 "-60" wide or greater, to form a positive or negative image with perfluoropolyether as described in american publication "international conference on fourteenth world for vacuum sheet coating" by aeroeemachine in october 25-27, 2000. The printing position is similar to that described in US4,749,591, incorporated herein by reference. However, the printing method is not necessarily limited to the printing method described in US4,749,591. For example, other printing techniques may be used, including inkjet printing, flexographic, gravure or offset printing, or even dot matrix printing. In an embodiment of ink jet printing, it is possible to change the pattern or image without breaking the vacuum. Advantageously, this allows specific patterns to be made on plastic rollers, without the need for rollers in the printing position where pre-imaging of the roller is required. Such patterning using an inkjet method allows for sequential numbering of security labels and other security designs, which is highly advantageous. Multilayer patterns using a single patterned roll, or using different patterns in subsequently formed film layers in an inkjet printing process, can be used to make complex patterns in security threads or even microelectronics in security threads. In particular, security threads with optically variable features can be combined with hidden magnetic barcodes in any one-dimensional space, such as standard barcodes, or with hidden barcodes in two-dimensional spaces, such as two-dimensional barcode formats. The magnetic layer is hidden between other thin film patterned layers, such as shown in FIGS. 18 and 19 behind a reflective layer or sandwiched between two highly reflective aluminum layers.

To ensure good image fidelity, the print location should be directly on the chill roll prior to the deposition of the first layer, which is typically aluminum but can be any material with sufficient heat of compression to vaporize the imaging oil. Other substrates such as polyimide, polyhexamethylene, polypropylene, polyethylene, polystyrene, polycarbonate triacetate, diacetate and polyethylene naphthalate (PEN), which can be used in place of polyethylene terephthalate (PET). For other substrates and other surfaces, patterned oils based on the basic surface energies encountered and requiring low air pressures as described above will be used.

Depositing the first layer to be patterned is the next step to be performed. In embodiments where the OVD security image is optically variable, both the reflective layer and the absorbing layer may be imaged. In general, any layer can be imaged so long as the oil patterning process produces a careful oil image. For example, an image may appear in the insulating layer by placing an oil pattern on a previously deposited layer. In other words, the oil pattern may be placed on the reflective layer or the absorptive layer. The deposition of a metal layer on the patterned oil results in the explosive evolution of the liquid oil into a gas, causing ablation of the deposited layer. There may be some oil residue (oil monolayers) remaining in the pattern area that must be removed in order to prevent further transfer of the image oil down the web, which in turn may cause a ghost image (another image pattern) of any subsequently deposited layer.

In typical embodiments, the aluminum or chromium layer is imaged and then the remainder of the structure is added withComplete a Fabry-Perot structure, i.e. aluminum (opaque, patterned)/MgF₂1 Quantum Well (QW)400 nm to 8QW700 nm/Cr 30% T. Low index MgF₂The layers may be replaced by any insulating material that is highly transmissive to visible light. A high index insulating material will result in an optically variable foil that changes less in color than a foil with a larger optical change using a low index insulating material. A partial layer of aluminium having a thickness below the opaque point will provide a partially transparent colour shifting film, for example, having a thickness in the range of 200-800 nm, so that information can be read from paper, or printed on PET, by means of an optical laminate. All color changes shift from long to short wavelengths, i.e. from red to blue.

To remove oil residue in the pattern area, the oxygen glow was located just after the deposition source using a chill roll. The glow can also be used on the backside of the sheet before or after the deposition zone. In this case, the 02 glow will clear any oil from the back side of the sheet, which may be moving during the "inking process" or flashing throughout the deposition process, which ends at the back side of the run. Typically, the oxygen glow for a 12 "wide glow system runs at 2,200 volts and 100 milliamps. By calculating the color change, oil residues on the end coated sheet, such as large spots of the original image or double images like the original image, can be detected.

The image definition using the flexographic process showed 20 microns, although 70 microns was normal. This is shown in fig. 20. In addition to text, graphic images can be used in the software program COREL DRAW by processing^TMThe FloydSteinburg technique found in (1) scans images. This procedure converts the image into square pixels with good black (image) white (no image) contrast. After coating, the sheet is divided into 1 to 5mm wide strips, with the text generally centered in the strip. Figure 21 shows the optical lines of change of the window of the present invention embedded in a banknote and figure 22 shows the text symbols when viewed in transmission.

Instead of a tape, the device can function as a security sticker by applying adhesive to one side of the PET and die cutting the label from the laminate to release the liner, as shown in fig. 23. The adhesive may be a solvent glue or an aqueous glue. Among many other adhesives, a suitable adhesive is acrylic glue. Instead of a label, the product can be made into a hot stamp anti-counterfeit product by inserting a release layer between the carrier sheet and the vacuum deposited layer.

Of course, numerous other embodiments are contemplated without departing from the spirit and scope of the present invention.

Claims (5)

1. An optically variable device comprising:

a substrate having a first surface and a second surface;

an image printed on a first surface of the substrate; and

an optical stack for providing a color shifting effect, deposited on the first surface of the substrate to cover the image, comprising a reflective layer, an absorbing layer and an insulating layer between the reflective layer and the absorbing layer,

wherein the reflective layer is a partially transparent layer such that the image is viewable through the optical stack.

2. An optically variable device as claimed in claim 1, wherein the reflective layer is of a thickness below the opaque point.

3. The optically variable device of claim 1, wherein the image is printed using a conventional or optically variable ink.

4. The optically variable device of claim 1, wherein the image is text printed onto the substrate and is readable through the optical stack.

5. An optically variable device as claimed in claim 1, wherein the substrate is transparent to enable text to be read by the optically variable device.