Printed Article With Special Effect Coating

Abstract

A printed article is disclosed having a light transmissive substrate having a reverse printed region on a surface thereof in the form of a plurality of very closely spaced printed lines or regions. The printed regions and spaces therebetween are subsequently flood coated with special effect ink such as optically variable ink wherein the ink particle size is on average greater than the gap between reverse printed regions. The image is viewed from the non-printed side of the substrate and very fine lines of the special effect flood coated special effect ink appear as very clear sharp lines having a fine resolution. This eliminates the typical jagged edges that would otherwise be seen if the inked region was not present. This effect is due to the first printed inked regions or lines forming a mask through which the flood coated ink is seen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional side view of a reverse printed image printed upon a light transmissive substrate, wherein the image is flood coated thereover with a color shifting pigment ink or adhesive.

FIG. 2 is a plan view of an image having fine lines printed on one side of a substrate and having a flood coat of special effect flakes thereover.

DETAILED DESCRIPTION

The term security device referred to hereafter is meant to include any form of identifier that can be used to authenticate the device; and although the device described hereafter can be used as a decorative label or cover it inherently provides a measure of security for authentication.

Referring now to FIG. 1 a security device 10 is shown having a light transmissive substrate 12 that is transparent allowing an image placed on one side to be seen from the other side of the substrate. The substrate is shown as having two planar surfaces, however the upper surface may optionally have a microstructure not shown in the figure, such as a grating defined therein, spaced portions of the upper surface thereby providing diffractive effects in desired regions. In the manufacture of the device 10, a pattern 14 is reverse printed upon the lower surface of the transparent substrate 12 using conventional ink. The reverse printed image is printed so that the text or image appears readable when viewing it through the substrate. It is preferable that a particle size within the conventional ink be as small as possible so that adjacent printed regions can be separated by very thin, clear, unprinted regions without scalloped edges.

After the inked pattern 14 is applied to the substrate and the ink has dried, a portion or all of the inked image including gaps between inked regions is flood coated with color shifting ink or paint 16 having color shifting flakes 18 within a carrier. Alternatively, a color shifting adhesive having flakes therein may be used, for example a hot-stamp adhesive having color shifting flakes therein. Although color shifting flakes are coated over the dried non-color shifting inked pattern 14 as shown, color shifting flakes or any other special effect flakes can be used. Combinations of different special effect flakes may also be used. For example color switching flakes such as highly reflective aluminum flakes in a tinted carrier, or diffractive flakes, or covert symboled flakes or combinations thereof can be used to coat over the fine lined conventional inked pattern. The particular advantage in providing a transparent substrate printed with “conventional small platelet” printing ink coated thereover with special effect flaked ink is that a very crisp image having what appears to be very fine lines of special effect ink or paint is seen when looking through the substrate. Such visually apparent fine lines of special effect flaked pigment seen through a fine lined mask could not otherwise be provided by printing the visible pattern with the special effect ink, as the flakes would be too large to allow fine line spaces therebetween. Stated differently, if one reverses the process and first prints the fine line pattern with conventional special effect color shifting flakes ranging in size from 5 to 100 microns, and subsequently coats the printed image with conventional printing ink, the image would not appear as crisp to the viewer and scalloped edges would be much more evident in the image. In the embodiment shown, it is important that the smaller particle size ink be used upon the substrate subsequently coated with large size pigment flakes. There is only one instance where the order of coating is of little or no consequence. That is in an embodiment where the fine lined coating is printed on a first viewing side of the substrate and wherein the flood coated special effect ink or paint is coated on a second opposite side of the light transmissive substrate. However, this embodiment is less preferable than applying the special effect ink directly upon the conventionally reverse inked printed image. Depending on the thickness of the substrate there may be a visible parallax between the coating layers. If spot printing of color shift in areas of windows is used, printing on the two sides of the substrate would have to be in registration which is an additional requirement. Furthermore, in this less preferred embodiment preventing abrasion or weathering of the front surface ink which is not protected by the transparent substrate might require a protective coating or lamination which adds cost and process complexity. In this embodiment both sides of the substrate must be suitable for receiving ink, which might compromise other properties such as abrasion resistance which is desirable on the outward facing surface. In general, printing on both sides of the substrate is a more complex process.

Referring once again to FIG. 1, in an alternative embodiment, the color shifting ink or paint 16 can be selected such that it shifts from a first predetermined color to a second predetermined color, wherein one of the first and second colors matches the color of the inked pattern 14. Thus, by tilting the image, the color shifting ink 16 is either distinguishable from the inked pattern 14, or closely matches the pattern 14. It should be understood that in this embodiment, when the printed coated image is viewed through the substrate, it appears as if the inked region and color shifting inked regions are side-by-side, although the color shifting coating is coated over the entire conventionally inked printed region and covers spaced therebetween.

In the embodiment shown in FIG. 2 a more complex image is shown, having a design of very even spaced fine printed lines 24 printed with conventional ink upon a substrate 22. A flood coat of highly reflective flakes 26 is printed over the lines 24 covering both the lines and fine spaces therebetween. By appropriately choosing the line width and width of spaces therebetween, a grating is formed having visible diffractive properties.

In another embodiment of the invention fine printed lines are provided on both sides of the substrate, either aligned or offset with each other. If the lines and spaces on both sides of the substrate are of a similar spacing and dimensions and suitably arranged compared to the thickness of a transparent substrate, a variety of variable image effects can be produced including something of a color-shifting and shape shifting moiré interference pattern due to the interaction of the two fine patterns as the substrate is tilted. Achieving such a moiré pattern or structure could not be done with coarse or fuzzy printed patterns alone, and also relies on the transparency of the substrate. In accordance with this invention the lines on the front (observer) side of the substrate must be printed with conventional ink with windows or alternatively a demetallized Al or other colored thin film layer(s). The opposite side would have a coating as described heretofore, wherein “apparently” fine lines of special effect ink are provided through a mask of conventionally printed ink having fine line gaps between regions.

A discussion of moiré patterns is found at http://en.wikipedia.org/wiki/Moir%C3%A9 pattern. The structure shown would require printing on both sides of the substrate so that the parallax gives the moiré a “motion”. The effect can be illustrated by overlaying two layers of window screen and moving them linearly and rotating/tilting them.

To produce moiré effects the lines need not be straight, in fact the configuration of the lines and their interaction is a design parameter. In this case, moiré is a desired effect unlike in most printing where it is an undesirable artifact.

The device of FIG. 1 may be hot stamped to an article, for example to an identity card, currency a poker chip creating a decorative label that offers a high degree of security and which can be authenticated. Hot stamping is a coating system that is transferred from a support to the finished article, in which case the “transparent substrate” to which the printing is applied is the stamping release/coating layers carried on a support foil.

Although in preferred embodiments of this invention shown heretofore, reverse printing was utilized, in an alternative less preferred embodiment of the invention as mentioned above, the inked pattern can be printed on top of the substrate on the viewing side and the flaked coating of special effect flakes can be printed on the opposite non-viewing side of the device. An advantage of the preferred embodiment wherein the special effect coating is printed over the conventional reverse printed ink on the same side of the substrate is that no protective lacquer coating is required. In further embodiment the substrate may be printed over on the face side to incorporate security features such as tamper-evidence.

Further Advantages of the Invention

Additional advantages of applying the optically variable component behind a high resolution reverse printed ink layer which defines the optical variable viewing area are:

An optically variable ink tends to lie flat against the viewing aperture as it settles after application, thus giving more vivid and specular optical reflection.

If using a magnetically aligned optical effect ink, it may be applied thickly to permit out-of-plane orientation of the platelets, otherwise not consistent with fine features and sharp edges.

The overlying substrate (or hot stamp protective layer) provides inherent protection against the abrasion, chemical attack, or removal of the optically variable component—a further protection against alteration.

By virtue of the ability to sharply define small optically variable areas and patterns, smaller patches, labels, planchettes, and patterned threads may be made, for example for embedding in currency or value document paper.

Any appropriate printing method may be used to print the first-applied conventional ink print areas.

In addition to the use of reverse printing with optically variable inks, as discussed above, reverse printing may also be used to define viewing areas through which a directly deposited (for example by vacuum or solvent coating means) optically variable multilayer coating may seen. It is impractical and costly to directly pattern such coatings by lithographic means, especially as they are composed of multiple layers of different metals and dielectric materials, which often must each be etched by different processes.

Further, as well as acting as an opaque mask to define visible area of optically variable coating or ink, the reverse printed ink may also printed in various colors, including colors which contrast or match with the optically variable coating(s) visible through the apertures in the ink layer, thus forming a unified design or image or information bearing pattern of which the optically variable layer is one component. In particular, a hidden image or text composed of optically variable elements may be incorporated into a printed image by using small image elements (pixels) of optically variable coating or ink which are visible through windows in the conventionally printed image as described above.

In addition, the color of the optically variable pigment, and its optical shift, may be modified by the addition of further components to the ink, including dyes, conventional pigments, ultraviolet or infrared active phosphors, including infrared excited visible emitting and ultraviolet excited visible emitting materials, for example, while retaining the effect of optical variation and the advantages of the reverse printing method described above for the production of fine features.

EXEMPLARY EMBODIMENT

Black and white images containing a pattern of fine lines similar to those often used in security printing applications were chosen to demonstrate the invention. To produce the ink mask, the image was printed on overhead transparency film using a laser printer at an approximate resolution of 600 dots per inch. The results are images on transparent film comprised of a black field (laser printer deposited black toner ink) with the fine lines comprising transparent areas in the image. A sample of these images is shown in FIG. 4 as printed on white paper for better viewing. The white regions in FIG. 4 are unprinted and are transparent when printed on a light transmissive substrate in accordance with this invention. In an embodiment not shown, the substrate can be tinted to provide color to the coating of flakes.

To produce a color shifting image the non-viewing image bearing side of the substrate was covered with a layer of optically variable pigment in binder, by silk-screening a thin layer of 20% concentration of pigment in ink binder over the entire image area. When viewed from the non-inked side of the transparent substrate, a fine line color shifting pattern on a black laser printed background is obtained.

This exemplary embodiment demonstrates the basic principle of reverse printing to produce fine line images which cannot be directly printed, the use of digital imaging processes in conjunction with color shifting inks and coatings to produce images, and the use of variable image reverse image printed masks to produce individually coded color shifting features. Inkjet and thermal transfer printing may be incorporated into a printing line to produce the ink masks.

It is easily seen that by incorporating colored inks into the image in whole or in part to replace the black toner mask, that metameric and hidden color shifting information may be produced at high resolution by this process. Further, by incorporating continuous line printing techniques such as flexography and lithographic printing, fine and continuous features may be produced.

Claims

1. A printed article comprising: a light transmissive substrate supporting on a first side thereof, a plurality of spaced printed regions, wherein spaces between some adjacent printed regions have a width W1 less than or equal to P1, and a special effect coating including a carrier having a plurality of flakes therein supported by the substrate and covering at least some of the spaces between the adjacent printed regions, wherein the flakes within the special effect coating have an average particle size of P1 greater or equal to 5 microns.

2. A printed article as defined in claim 1 wherein the printed regions are printed with an ink that has an average particle size of less than 5 microns.

3. A printed article as defined in claim 2 wherein the ink is an opaque ink and wherein the spaced printed regions are reverse printed regions.

4. A printed article as defined in claim 3 wherein the each of the plurality of printed regions are comprised of dots of ink.

5. A printed article as defined in claim 2 wherein the special effect coating has an appearance which varies with a change in viewing angle.

6. A printed article as defined in claim 5 wherein the special effect coating is color shifting, color switching diffractive, or combinations thereof.

7. A printed article as defined in claim 2 wherein at least some of the flakes bear covert indicia.

8. A printed article as defined in claim 2 wherein P1 is more than 10 microns and wherein the particles in the ink have an average size of less than 4 microns.

9. A printed article as defined in claim 2 wherein some of the spaced printed regions or some of the coated spaces between the printed regions form a diffractive grating.

10. A printed article as defined in claim 9 further comprising a plurality of printed lines on an opposite side of the substrate.

11. A printed article as defined in claim 2 wherein the article forms a moire pattern.

12. A printed article as defined in claim 2 further comprising an additional distinguishing visible feature on an opposing second side of the substrate.

13. A printed article as defined in claim 12 wherein a grating is formed on the opposing second side of the substrate.

14. A printed article as defined in claim 2 wherein the special effect coating serves as an adhesive.

15. A printed article as defined in claim 2 wherein the special effect coating includes special effect flakes in carrier which serves as a dry hot stamp adhesive.

16. A printed article as defined in claim 2 wherein the flakes are special effect pigment flakes that are magnetically aligned.

17. A method of forming a printed article having a first side and a second side comprising the steps of: providing a light transmissive substrate;printing a reverse printed image having regions of ink separated by unprinted spaces upon a region of the light transmissive substrate; and,coating the reverse printed image and regions of the substrate with a special effect coating such that at least some of the non printed spaces are covered, wherein patterned inked regions are visible and the special effect coating is visible simultaneously, when viewing one side of the device.

18. A method as defined in claim 17 wherein the average particle size of particles within the ink in the reverse printed image is at least two times smaller than the average particle size of fakes in the special effect coating.

19. A method of forming a printed article having a first side and a second side comprising the steps of: providing a reverse printed image on a light transmissive substrate printed with an ink having an average particle size P1, wherein the reverse printed image has spaces between inked regions that are smaller than P2 coating the substrate and reverse printed image by flood coating the reverse printed image and spaces therebetween with a special effect coating comprised of a carrier supporting flakes, wherein the average size of the flakes is larger than P2 or P1.