SECURITY DEVICE FORMED BY PRINTING WITH SPECIAL EFFECT INKS

Abstract

A security device is disclosed that has an image formed upon a substrate. The image has a first printed region and a second different printed region both printed with a same ink formulation of field alignable flakes. At least one of the printed regions has optically variable effects. One of the first and second printed regions at least partially surrounds the other. The second printed region is formed of thin parallel lines and the first printed region has substantially wider lines than are printed in the second printed region. The area density of the ink in a line in the first group of wider lines is greater than the area density of a line in the second group of narrower lines. A surprising effect of this image is that particles or flakes in the ink are field aligned so as to produce a visible kinematic dynamic effect visible in the first region and not visible in the second region when the image is tilted or rotated.

Claims

1-31. (canceled)

32. A method of forming a security device comprising the steps of: printing upon a substrate a first printed region and one or more second printed regions at least partially bordering the first printed region, wherein a same ink formulation having magnetically-alignable flakes therein is applied to the first and one or more second printed regions, and applying a curved magnetic field so that the flakes in the first printed region are aligned in a convex or concave shape in a cross-section of a vertical plane of the first printed region, wherein the flakes in the one or more second printed regions are not aligned along the curved magnetic field applied to the second printed regions.

33. A method as defined in claim 32, wherein the printing is intaglio printing.

34. A method as defined in claim 32, wherein the ink formulation having magnetically-alignable flakes therein is applied to the first and one or more second printed regions in lines of different heights.

35. A method as defined in claim 34, wherein the printed lines in the first printed region are substantially higher than printed lines in the one or more second printed regions.

36. A method as defined in claim 35, wherein a contrast between the first and second printed regions as a function of their contrasting line heights forms a discernible printed image.

37. A method as defined in claim 32, wherein the method produces an image having a visible kinematic effect in the first printed region when the image is tilted or rotated.

38. A method as defined in claim 32, wherein the first region and one or more second printed regions are printed without masking the effects of the magnetic field.

39. The method as defined in claim 32, wherein printing the first printed region includes printing a plurality of printed lines that are at least twice as wide as printed lines of the one or more second printed regions.

40. The method as defined in claim 32, wherein printing the second printed region includes printing parallel lines or pixels in the second printed region, the parallel lines being less than half as wide as the printed lines of the first printed region.

41. The method as defined in claim 32, wherein printing a first printed region includes printing a plurality of printed lines that are at least twice as deep as printed lines of the second region.

42. The method as defined in claim 32, wherein an area density of the ink of the one or more second printed regions is less than an area density of the ink of the first printed region.

43. The method as defined in claim 32, wherein the flakes are chosen from color shifting flakes, color switching flakes and diffractive flakes.

44. The method as defined in claim 32, wherein a rolling bar is seen in the first printed region without magnification upon tilting, and wherein the rolling bar is not seen without magnification in the one or more second printed regions upon tilting.

45. The method as defined in claim 32, wherein the printed lines in the first printed region are at a 45° angle to the printed lines in the one or more second printed regions.

46. A method of forming a security device comprising the steps of: printing upon a substrate a continuous, non-interrupted line of ink of variable width regions or variable height regions, the variable width regions have wide areas and narrow areas that are not as wide as the wide areas, and the variable height regions having tall areas and shallow areas that are not as deep as the shallow areas, the ink comprising magnetic particles, applying a magnetic field to the line of ink, wherein the magnetic particles do not have substantial tilt in the shallow areas or narrow areas under the influence of the applied magnetic field and do have a tilt in the wide areas or tall areas under the influence of the applied magnetic field.

47. A method as defined in claim 46, wherein the variable width regions or variable height regions are printed without masking the effects of the magnetic field.

48. The method as defined in claim 46, wherein the continuous, non-interrupted line has a variable height region.

49. The method as defined in claim 46, wherein the continuous, non-interrupted line has a variable width region.

50. A method as defined in claim 46, wherein the printing is intaglio printing.

51. A method as defined in claim 46, wherein the method produces an image having a visible kinematic effect in the wide or tall areas when the image is tilted or rotated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Exemplary embodiments of the invention will now be described in conjunction with the drawings, in which:

[0021] FIG. 1a is a plan view of a security device showing the letter “B” printed in thick lines and having a background that surrounds the “B” in thinner parallel lines.

[0022] FIG. 1b is a plan view of an alternative embodiment wherein the letter “B” is printed with a thicker ink coating than the background.

[0023] FIG. 2 is a plan view of an alternative embodiment of the invention wherein the letter “B” is printed in thick parallel lines in a first direction and wherein thinner parallel lines defining a background are at a different angle approximately 45 degrees to the thick parallel printed lines.

[0024] FIG. 3a is a cross-sectional view of a printing plate for the images in FIG. 2.

[0025] FIG. 3b is a cross-sectional view of the ink that is printed on the substrate using the printing plate in FIG. 3a before applying a magnetic field to align the flakes.

[0026] FIG. 4 is the cross-sectional view of FIG. 3b illustrating the orientation of the flakes in an. applied magnetic field.

[0027] FIG. 5 is the perspective view of the image of FIG. 3b after the magnetic field has been applied.

[0028] FIG. 6 is a prior art cross-sectional view of a flip-flop.

[0029] FIGS. 7 and 8 are simplified plan views of a flip-flop as seen from different angles.

[0030] FIG. 9 is a prior art cross-sectional view of a rolling bar showing only some of the aligned. flakes.

[0031] FIG. 10 is a top view of the rolling bar shown in FIG. 9.

DETAILED DESCRIPTION

[0032] In this application the term optically variable encompasses effects that are color shifting, color switching, diffractive, or kinematic. Color shifting and switching effects are effects that change or switch color with a change in viewing angle of angle of incident light. Kinematic effects are those wherein the viewer “appears” to see an aspect of the image move, or wherein the color in one region “appears” to switch colors with another region. In an image having kinematic effects the viewer appears to see motion or depth that would not be seen in a uniform coating that merely exhibited color shifting. In a kinematic image flakes are magnetically aligned such that they are not all uniformly aligned. Thus, tilting or rotating provides the illusion of movement or change.

[0033] The term “visible” used hereafter is to mean visible with the human eye; that is, out magnification.

[0034] The term “line” used here after is to encompass a straight or curved solid line, dotted line, dashed line or curved line.

[0035] The term “area density” is used hereafter to mean the mass per unit area defines as:

ρA where [0036] a. ρA=average area density [0037] b. M=total mass of the object [0038] c. A=total area of the object

[0039] Referring now to FIG. 1a a security image is formed having a substrate 1 supporting a fine lined region 2, wherein parallel lines of ink are applied via a silk screen printing, gravure process or preferably an Intaglio printing process. The region 2 borders or surrounds region 3 which is a region having thick lines therein visually forming or occupying the space of a letter B. The thick printed lines spaced by gaps there between absent ink form the image of the letter B, surrounded by the uniform background of thin lines in region 2. Although in preferred embodiments of this invention the lines are preferably solid continuous lines, dotted lines may be used to form the image shown. In this instance is it preferable that the thicker lines be solid lines and the thinner lines be dotted or dashed wherein the spacing between the dots be very small so as to be seen by the viewer as continuous solid lines. A fine silk screen mesh can be used and holes can be selectively plugged or masked preventing ink from being printed. Of course printing can be done with an ink jet printer or any known means of applying optical effect inks in lines of varying thicknesses or area densities.

[0040] A similar arrangement is shown in FIG. 2, however in FIG. 2 the lines are not all parallel. In FIG. 2 the letter B consists of thick parallel printed lines, wherein the background consists of thin printed lines having gaps or space between that is greater than the width of the printed lines. Thus, the background region 3 appears as if it consists of thick white lines and thinner black lines. Notwithstanding the apparent white lines are unprinted areas in region 2. In preferred embodiments of this invention the width of the fine lines and wider lines differ significantly however the height of the printed lines also differs. As can be seen in FIG. 3 the region 2 and 3 of the printing plate have different depths wherein region 3 is twice as deep as region 2, for example. Thus when the print is made, the ink in region 3 has a height approximately twice the height of the ink in region 2. Therefore the thin lines are finer in both dimensions, width and height off the substrate. It is the total volume of ink of a particular line that determines the perceived effects. Color shifting or color switching is seen whether lines are fine lines or wide lines, and kinematic effect requires a greater volume of ink in a line or lines to be perceived.

[0041] Aside from the letter B being optically variable, the letter B in FIG. 2 also shows a dynamic kinematic effect in the form of a rolling bar through the mid-region of the letter B, Which appears as a bright bar. By tilting the image about an axis through the bright bar, the bar “appears” to move from right to left as the image is tilted in both directions. Such kinematic features are well know and are described in United States published patent application numbers 20060198998, 20060194040, 20060097515, 20060081151, and 20050123755 assigned to JDS Uniphase Corporation incorporated herein by reference.

[0042] Optical effect flakes can be aligned in a field, preferably a magnetic field to form many different type of kinematic effects. The more simple easily understood kinematic effects include the rolling bar and the flip-flop.

[0043] A flip-flop is shown in FIG. 6 illustrating a first printed portion 22 and a second printed portion 24, separated by a transition 25. Pigment flakes 26 surrounded by carrier 28, such as an ink vehicle or a paint vehicle have been aligned parallel to a first plane in the first portion, and pigment flakes 26′ in the second portion have been aligned parallel to a second plane. The flakes are shown as short lines in the cross-sectional view. The flakes are magnetic flakes, i.e. pigment flakes that can be aligned using a magnetic field. They might or might not retain remnant magnetization. Not all flakes in each portion are precisely parallel to each other or the respective plane of alignment, but the overall effect is essentially as illustrated. The Figures are not drawn to scale. A typical flake might be twenty microns across and about one micron thick, hence the figures are merely illustrative. The image is printed or painted on a substrate 29, such as paper, plastic film, laminate, card stock, or other surface. For convenience of discussion, the term “printed” will be used to generally describe the application of pigments in a carrier to a surface, which may include other techniques, including techniques others might refer to as “painting”.

[0044] Generally, flakes viewed normal to the plane of the flake appear bright, while flakes viewed along the edge of the plane appear dark. For example, light from an illumination source 30 is reflected off the flakes in the first region to the viewer 32. If the image is tilted in the direction indicated by the arrow 34, the flakes in the first region 22 will be viewed on-end, while light will be reflected off the flakes in the second region 24. Thus, in the first viewing position the first region will appear light and the second region will appear dark, while in the second viewing position the fields will flip-flop, the first region becoming dark and the second region becoming light, This provides a very striking visual effect. Similarly, if the pigment flakes are colour-shifting, one portion may appear to be a first colour and the other portion another colour.

[0045] The carrier is typically transparent, either clear or tinted, and the flakes are typically fairly reflective. For example, the carrier could be tinted green and the flakes could include a metallic layer, such as a thin film of aluminum, gold, nickel, platinum, or metal alloy, or be a metal flake, such as a nickel or alloy flake. The light reflected off a metal layer through the green-tinted carrier might appear bright green, while another portion with flakes viewed on end might appear dark green or other colour. If the flakes are merely metallic flakes in a clear carrier, then one portion of the image might appear bright metallic, while another appears dark. Alternatively, the metallic flakes might be coated with a tinted layer, or the flakes might include an optical interference structure, such as an absorber-spacer-reflector Fabry-Perot type structure. Furthermore, a diffractive structure may be formed on the reflective surface for providing an enhancement and an additional security feature. The diffractive structure may have a simple linear grating formed in the reflective surface, or may have a more complex predetermined pattern that can only be discerned when magnified but having an overall effect when viewing. By providing diffractive reflective layer, a colour change or brightness change is seen by a viewer by simply turning the sheet, banknote, or structure having the diffractive flakes.

[0046] The process of fabricating diffractive flakes is described in detail in U.S. Pat. No. 6,692,830, U.S. patent application publication number 20030190473, describes fabricating chromatic diffractive flakes. Producing a magnetic diffractive flake is similar to producing a diffractive flake, however one of the layers is required to be magnetic. In fact, the magnetic layer can be disguised by way of being sandwiched between A1 layers; in this manner the magnetic layer and then it doesn't substantially affect the optical design of the flake; or could simultaneously play an optically active role as absorber, dielectric or reflector in a thin film interference optical design.

[0047] FIG. 7 is a simplified plan view of the printed image 20 on the substrate 29, which could be a document, such as a bank note or stock certificate, at a first selected viewing angle. The printed image can act as a security and/or authentication feature because the illusive image will not photocopy and cannot be produced using conventional printing techniques. The first portion 22 appears bright and the second portion 24 appears dark. The section line 40 indicates the cross section shown in FIG. 1A. The transition 25 between the first and second portions is relatively sharp. The document could be a bank note, stock certificate, or other high-value printed material, for example.

[0048] FIG. 8 is a simplified plan view of the printed image 20 on the substrate 29 at a second selected viewing angle, obtained by tilting the image relative to the point of view. The first portion 22 now appears dark, while the second portion 24 appears light. The tilt angle at which the image flip-flops depend on the angle between the alignment planes of the flakes in the different portions of the image. In one sample, the image flipped from light to dark when tilted through about 15 degrees.

[0049] FIG. 9 is a simplified cross section of a printed image 42 of a kinematic optical device that will be defined as a micro-arrayed cylindrical Fresnel reflector or as referred to as a “rolling bar” for purposes of discussion, according to another embodiment of the present invention. The image includes pigment flakes 26 surrounded by a transparent carrier 28 printed on a substrate 29. The pigment flakes are aligned in a curving fashion. As with the flip-flop, the region(s) of the rolling bar that reflect light off the faces of the pigment flakes to the viewer appear lighter than areas that do not directly reflect the light to the viewer. This image provides a Fresnel focal line that looks very much like a light band(s) or bar(s) that appear to move (“roll”) across the image when the image is tilted with respect to the viewing angle (assuming a fixed illumination source(s).

[0050] FIG. 10 is a simplified plan view of the rolling bar image 42 at a first selected viewing angle. A bright bar 44 appears in a first position in the image between two contrasting fields 46, 48. FIG. 2C is a simplified plan view of the rolling bar image at a second selected viewing angle. The bright bar 44′ appears to have “moved” to a second position in the image, and the sizes of the contrasting fields 46′, 48′ have changed. The alignment of the pigment flakes creates the illusion. of a bar “rolling” down the image as the image is tilted (at a fixed viewing angle and fixed illumination). Tilting the image in the other direction makes the bar appear to roll in the opposite direction (up).

[0051] The bar may also appear to have depth, even though it is printed in a plane. The virtual depth can appear to be much greater than the physical thickness of the printed image. It happens because the bar is a imaginary focal line of the cylindrical convex Fresnel reflector located at the focal length underneath the plane of the reflector. The tilting of the flakes in a selected pattern reflects light to provide the illusion of depth or “3D”, as it is commonly referred to. A three-dimensional effect can be obtained by placing a shaped. magnet behind the paper or other substrate with magnetic pigment flakes printed on the substrate in a fluid carrier. The flakes align along magnetic field lines and create the 3D image after setting (e.g. drying or curing) the carrier. The image often appears to move as it is tilted; hence kinematic 3D images may be formed.

[0052] Flip-flops and rolling bars can be printed with magnetic pigment flakes, i.e. pigment flakes that can be aligned using a magnetic field. A printed flip-flop type image provides an optically variable device with two distinct fields that can be obtained with a single print step and using a single ink formulation. A rolling bar type image provides an optically variable device that has a contrasting band that appears to move as the image is tilted, similar to the semi-precious stone known as Tiger's Eye. These printed images are quite noticeable and the illusive aspects would not photocopy. Such images may be applied to bank notes, stock certificates, software documentation, security seals, and similar objects as authentication and/or anti-counterfeiting devices. They are particularly desirable for high-volume printed documents, such as bank notes, packaging, and labels, because they can be printed in a high-speed printing operation, as is described below.

[0053] Although embodiments of the invention described heretofore have been primarily concentrated on Intaglio, other methods of applying ink in accordance with this invention can be used. For example gravure, silk screen, flexo, letterpress and other known method of applying ink can be utilized. What is required is that ink be applied to different regions within a larger region in lines of varying thickness and lines of varying height; that is the depth and width of the lines will vary so as to provide contrasting regions.

[0054] For intaglio or gravure printing, the simplest method is for the engraving to have greater depth in a first region than in a contrasting second region.

[0055] For Flexo printing, variation in ink thickness is achieved using a dot screen or half-tone technique wherein larger dot size, equating to higher area coverage is used in the region of greater desired ink thickness. In the case of silk screen printing wherein a physical screen having uniform open areas is used, variation in height is achieved in a different manner In screen printing, the achievement of different ink height in the two or more regions is provided by throttling the transfer of ink through the screen via the masking of the screen itself. By selective masking of the screen, the first area has uninhibited ink transfer and therefore greater ink height off the substrate while the second area has a lesser degree of ink transfer and therefore lower ink height due to masking of the screen in a predetermined manner. For other printing techniques such as letterpress and offset, similar schemes are used wherein areas of greater and lesser ink thickness are provided. by varying the ink transfer by means of dot sizes or percent ink coverage on the plate or transfer medium.

[0056] In a preferred embodiment of the invention, the weight of the ink in a line of a length of one unit in the first region is at least three times the weight of the ink in a line of a same length in the second region. Preferably, the first region consists of a plurality of parallel printed lines of width W.sub.L and the second region consists of a plurality of parallel printed lines having a width of less than W.sub.L/2, however in some instances the width of the lines in the second region may be orders of magnitude smaller than the width of the lines in the first region. Regardless of the exact ratio that is selected With regard to area density of ink in the two regions, a desired ratio is one wherein the narrow lines do not show visible magnetic or kinematic effects, while the wider and/or higher lines do exhibit visible kinematic effects.

[0057] FIG. 1b shows an alternative embodiment of the invention wherein the letter “B” shown as 3b and it's background 2b are printed in lines of a same width on substrate 1b. However, the “B” is printed in ink that is considerably thicker than the ink forming the background. The image was printed with a printing plate (Intaglio) or with gravure cylinder having a gradient of engravings. Engravings forming the B are deeper than engravings forming the background 2b as shown in FIG. 3b. As a result, the lines of the background 2b are shallow and contain small amount of a pigment. In contrast, the lines 3b forming the B are thicker and contain greater number of pigment particles per unit of the substrate area as shown in FIG. 3b.

[0058] FIG. 4 illustrates the orientation of the flakes 4b in an applied magnetic field 5b. Being dispersed in a liquid ink vehicle and placed in a curved magnetic field, the particles 4b rotate in the ink vehicle until they become aligned along the lines of the field as shown. The process of rotation occurs in these regions of the print where the ink vehicle has enough space for it. Usually these are the places where the ink is printed with deep engravings. The shallow lines of the background do not have room enough for the particles to rotate and align along the lines. They stay almost flat. As a result, the image of the B gets a kinematic optical effect shown in FIG. 5 while the background does not have it.

[0059] In an alternative embodiment not shown in the figures the letter “B” is printed. with a solid unlined coating whereby one thick line forms the letter “B”. Hence, the letter “B” is not made up of parallel lines however the background is and the same effects are present as in other embodiments.

[0060] Numerous other embodiments of the invention may be envisaged without departing from the scope of this invention. For example in an embodiment not shown, a first fine lined coating is applied to the bottom of a light transmissive substrate and wherein a wider lined coating representing the letter B is on the top side of the substrate. Conveniently the tine lined coating can cover the entire bottom for ease of printing. The wide “B” is printed on the other side of a light transmissive substrate.