Printed magnetic ink overt security image

Abstract

A security image and method of forming said image is disclosed wherein a substrate having an image or indicia thereon is coated with a dilute solution of pigment flakes in an ink or paint. The flakes are subsequently aligned in a magnetic field and are fixed after the field is applied. Most or all of the flakes in a region are aligned so as to be partially upstanding wherein their faces are essentially parallel. coating the image with flakes yields a latent image which can be clearly seen at a small range of predetermined angles.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

4 34 or tilted with its upper edge toward the observer, aligned magnetic particles 6 reflect incident light 5 in the direction 8 of the observer 7 making the surface of the print very reflective. The text 2 is still visible through the ink because the ink concentration is not high enough to provide complete coverage of under-printed text but it is large enough to make it barely visible as shown in FIG. 4b. When the image is tilted with its upper edge away from the observer as shown in FIG. 5a, the magnetic particles have a different angular position relative to the distant light source and relative to the observer. In this instance, the incident light 5 is reflected from and between the magnetic particles in the direction 9 and this light is scattered inside of the print. The opening among the particles at this particular observation angle is much larger than in FIG. 4a and the observer is able to see much more of the text image 2 as shown in FIG. 5b. The text is seen as exemplified in FIG. 5b as a text image that is much darker than the text in FIG. 4a. The layer of magnetic ink in FIG. 5b looks much darker than in FIG. 4b because the incident light 5 is reflected into the print away from the observer.

Many other printed images with optical effects generated by alignment of pigment particles in an applied magnetic field are suitable for fabrication of latent prints.

Depending upon the concentration and size of the flakes, the physical bases of the latent image appearance and disappearance may vary slightly. For example the latent image when viewed from one particular angle may be barely noticeable and from another angle essentially looking into the edges of the flakes as in FIG. 5a, may be highly visible. In other instances based on flake size and concentration and alignment angle, the image may be totally obscured at one angle and very visible at another small range of angles.

Although various configurations of magnetic fields can be used to align the flakes, it is preferable that a substantially large region, for example a region covering at least a single letter or symbol to be viewed or obscured have the flakes substantially parallel to one another.

Another example of an optical effect with magnetic particles aligned in a V-shaped magnetic field is shown in FIG. 6. This arrangement of flakes is described in detail in U.S. Pat. No. 7,047,883. Referring now to FIG. 6, the substrate is printed with the text image 2, overprinted with magnetic ink consisting of the ink vehicle 3 and magnetic particles 6 and exposed to the V-shaped field to align the particles along the field lines. The center line of the V-shaped field was purposefully positioned in the middle of the text 2. Magnetic particles 4 44 of the ink area 22 are aligned at a predetermined angle to the particles in area 24. The angle between the particles of these two adjacent areas was set by the applied magnetic hardware described in U.S. Pat. No. 7,047,883. In an alternative embodiment not shown, instead of a V-shaped field a Λ-shaped field can be used.

As can be seen from FIGS. 7a and 7b, observations of the combined print on the substrate demonstrate a different appearance of the latent text printed underneath the magnetic ink. The tilt of the combined print in one particular direction with respect to positions of incident light and an observer shows that only half of the under-printed text becomes visible. In the FIG. 7a, where the cross-section of a printed insignia is shown, the substrate 1 with the text image 2 and the ink vehicle 3 containing dispersed and aligned particles 6 is tilted with its left side 22 away from the observer 5 25. Region 22 of the ink 3 contains magnetic particles oriented at a different angle to the particles in the region 24. Incident light, coming from the distant source 8 18 in the directions 9 and 13 and falling on the top of magnetic ink, is reflected differently in these two adjacent areas 22 and 24 of the magnetic print where the particles are aligned at predetermined angles. The portion 10 of the light coming in from the direction 9 reflects into the print in the direction of the substrate 1. As a result, part of the print 24 appears dark in FIG. 7b. However, at this particular angle of the tilt, the inclination of the particles is coincident with the observation direction of the print and the text image 2 becomes visible. Therefore, the right half of the under-printed text image 2 becomes visible to the observer 5 25 through the layer of the ink in the direction 11 in FIG. 7a. Another portion of the light 8 falls in the direction 13 on the region 22 of the substrate where magnetic particles are reflecting it in the direction 14 toward the observer 5 25. This part of the overt printed magnetic ink looks bright as is shown in FIG. 7b. The particles of the magnetic ink block the under-printed text image 2 making it barely visible as shown in FIG. 7b.

When the print is tilted in the opposite direction as shown in FIG. 8a the particles 6 in the area 24 of the print reflects the majority of incident light from the direction 9 from the light source 8 18 in the direction 10 to the observer 5 25. The portion of the light arriving from the source 8 18 in the direction 13 propagates through the ink vehicle between the pigment particles toward the substrate 1 and the printed image 2 in the direction 14. As a result, the left part (region 22) of the text image 2 in FIG. 8b becomes visible surrounded by a dark area. The right part of the print becomes bright and reflective. The text image is now barely visible in the right part of the print. This flip-flop effect is due to the different parallel alignment of the flakes in the two parts of the image.

Other printed images, fabricated by printing on a substrate an informative text image or a graphical image and over-printed with ink containing magnetic particles aligned in an applied shaped magnetic field, also show a printed latent image visible through various optical effects generated in magnetic fields. For example, optical effects, generated in a hemispheric, semi-cylindrical magnetic fields, or other magnetic fields with a predetermined shape of magnetic lines penetrating through the layer of wet magnetic ink, show covert features similar to those described above. Certain areas of the under-printed image appear through the cover-printed magnetic ink at different observation angles.

Visibility of the under-printed image can be changed by changing its contrast to the substrate. For instance the image can be printed white on the black substrate or printed black on the white substrate. The image can be colored and the substrate can be with another color. The ink vehicle of magnetic ink can also be colored or clear. Specific colors of the substrate, the under-printed image and the ink vehicle can be selected to provide the best visibility of the latent image. Example of such a color fit is shown in FIG. 9. The substrate 1 is printed with image 2 in the form of a letter F. Magnetic ink 3 is printed on the top of the image 2 in a discontinuous manner with interruptions in the form of bars as shown in FIGS. 9 and 10. The substrate 1 is white, the under-print 2 is yellow and the magnetic ink vehicle is blue. Appearance of the completed print at normal observation angle is shown in FIG. 10a. The bright light-blue stripes form a square on the surface of the substrate with very narrow yellow lines. When the substrate with the print is tilted with its upper edge away from the observer, a green image of the F appears in the square of dark blue stripes. The upper layer of the semi-transparent magnetic ink can be printed with a tessellated pattern on the top of the solid coated under-print. For some prints, both layers may have matched patterns.

The pigment of the magnetic ink can be silver-like, colored, or color-shifting. Silver-like pigment is generally fabricated by deposition of reflective metal (Al, Ag) on the surface of magnetic flake. Colored pigments with metallic reflectance can be fabricated either by vacuum or chemical deposition of colored reflecting metals and materials (Cu, Au, TiN_x, ZrN_x, NbO_x, etc.) on the surface of magnetic platelet. Alternatively, colored pigments with high color performance can be fabricated by vacuum deposition of multi-layered structure Ab/D/R/M/R/D/Ab where Ab is semi-transparent absorber, D is transparent dielectric of predetermined thickness, R is opaque reflector (Al in most of the cases), M is magnetic material. Alternatively the particles may be silver-like or colored diffractive structure as described in U.S. Pat. No. 6,902,807. Other particles may have a structure of irregular low-frequency binary gratings without appearance of diffractive colors. The typical size of the particles for the ink is in the range of 10-100 microns, more preferably in the range of 18-30 microns. The flakes may be purposefully shaped to have a same, particular shape, for example, square-shaped. In this manner the aligned flakes are more predictably oriented to show or to obscure the indicia or image disposed thereunder.

We found that the concentration of the magnetic particles dispersed in the ink vehicle should be in the range of 2-30 wt %, more preferably in the range of 5-15 wt. %. In many instances the choice of concentration depends upon the thickness and weight of the pigment and the thickness of printed layer of the ink and further depends on upon the method of printing.

In summary, this invention provides an additional measure of security in addition to security only afforded to images formed of magnetically aligned flakes. Furthermore, combining a printed image and a magnetically aligned coating provides an unexpected synergy from these two printing methods.

Claims

1. A security device comprising:

a) a substrate supporting having an image thereon;

b) a coating of flakes supported by the substrate and in a carrier, covering the image thereby forming a latent image,;

wherein a first group of said flakes are aligned in a substantially same orientation at a first partially upstanding flake angle relative to said image, and wherein a second group of said flakes are aligned in a substantially same orientation at a second partially upstanding flake angle relative to said image;

wherein said flakes are aligned in such a manner as to obscure the image forming a wherein the concentration of flakes within the carrier is dilute enough and said first partially upstanding flake angle and said second partially upstanding flake angle are oriented such that said latent image is obscured when viewing the security device said security device is viewed from a first viewing angle, and to reveal the image when viewing the said latent image is revealed when said security device is viewed from a second viewing angle, different from the first viewing angle, wherein the coating of flakes includes a carrier supporting the flakes and wherein the concentration of flakes within the carrier is dilute enough so as to allow the latent image to be seen or to be obscured as the substrate is tilted from one direction to another, wherein a first group of the flakes are aligned in a substantially same orientation and wherein a second group of the flakes are oriented in a substantially same orientation that differs from the orientation of the first group of flakes.

2. A security device as defined in claim 1 wherein the first group of flakes overlies a first symbol and wherein a second group of flakes overlies a second symbol wherein said first partially upstanding flake angle of said first group of flakes has an orientation that differs from the orientation of said second partially upstanding flake angle of said second group of flakes.

3. A security device as defined in claim 2, wherein the first symbol is obscured while the second symbol is revealed when viewing the substrate at a first predetermined angle.

4. A security device as defined in claim 2, wherein the first symbol is revealed while the second symbol is obscured when viewing the substrate at a second different predetermined angle.

5. A security device as defined in claim 1, wherein the flakes are at least one of color shifting, diffractive, reflective, absorbing and color switching.

6. A security device as defined in claim 1, wherein the latent image is printed with pigment flakes that are oriented so as to be parallel with the substrate.

7. A security device as defined in claim 5 wherein the flakes are opaque.

8. A security device as defined in claim 1, wherein the coating is over at least 80% of the image and wherein regions of the image are uncoated with the coating.

9. A security device as defined in claim 8 wherein the substrate, the image and the coating are different colors and wherein the color of at least one of the image, the coating and the substrate change with a change of viewing angle.

10. A security device as defined in claim 1, wherein the coating forms a tessellated plane pattern.

11. A security device as defined in claim 1, wherein the flakes are electrically or magnetically aligned flakes.

12. A security device as defined in claim 1, wherein the image is printed upon the substrate and wherein the coating of flakes is coated over the latent image on a same side of the substrate.

13. A security device as defined in claim 1, wherein the substrate is transparent and wherein the coating of flakes is coated on a first side of the substrate and wherein the latent image is on a second side of the substrate.

14. A security device as defined in claim 1, wherein the device exhibits at least 70% of reflectance of light incident thereon when the latent image is obscured, and wherein the device exhibits less than 40% of light incident thereon when the latent image is revealed.

15. A security device as defined in claim 1, wherein the latent image is text.

16. A security device as defined in claim 1, wherein the latent image includes one or more symbols, or a logo.

17. A security device as defined in claim 1, wherein the substrate image is printed with an ink or paint and wherein the latent image is formed by an absence of ink or paint on the printed substrate.

18. A security device as defined in claim 1, wherein the particles are flakes and wherein at least 80% of the flakes have a same shape.

19. A security device as defined in claim 1 wherein the first group of flakes overlies a first symbol and wherein a second group of flakes overlies a second symbol.

20. A security device as defined in claim 19 wherein the first symbol is obscured while the second symbol is revealed when viewing the substrate at a first predetermined angle.

21. A security device as defined in claim 1 wherein said first and said second groups of flakes overlie a first symbol.

22. A security device comprising: a substrate;

a coating covering an image located on said substrate, said coating comprising a carrier carrying a plurality of magnetically aligned flakes;

wherein said magnetically aligned flakes are aligned in a substantially same orientation and are tilted, relative to said image, at a partially upstanding angle; and

wherein said magnetically aligned flakes cover said latent image in a dilute enough concentration, and are so aligned at said partially upstanding angle, such that said latent image is obscured when said security device is viewed from a first angle, and said latent image is revealed when said security device is viewed from a second, different angle.

23. A security device as defined in claim 19, wherein the first symbol is revealed while the second symbol is obscured when viewing the substrate at a second different predetermined angle.