CH707318B1 - Optical safety device. - Google Patents

Abstract

According to the present invention there is provided an optical safety device comprising: a transparent or translucent substrate (15), at least a first array of repeating picture elements (20) in or on a first side (16) of the substrate (15), at least one second array of repeating picture elements on a second side (17) of the substrate (15). The at least one second array (30) of repeating pixels is substantially in register with the at least one first array (20) of pixels. The at least one first array (20) and / or the at least one second array (30) of repeating picture elements is at least partially opaque. The repeating picture elements on at least one side of the substrate (15) are modulated in regions according to the brightness or color values of corresponding areas of an underlying gray scale or color image. Thus, when viewing the device in the overhead light, a first image is visible from the first side of the substrate (15), and when viewing the device in the top light, a second image is visible from the second side of the substrate. The first image is formed at the repeating pixels of the first array (20) and the second image (30) is formed at the repeating pixels of the second array.

Description

Description Field of the Invention The present invention is directed to optical security devices, their use in security documents, and methods of making same.

definitions

Security Document As used herein, the term security document encompasses all types of documents and tokens and identity documents including, but not limited to: currency such as banknotes or coins, credit cards, checks, passports, identity cards, securities and stock certificates, driver's licenses, title deeds, travel documents such as airline or credit cards Train tickets, entrance tickets and entrance tickets, birth, death and marriage certificates and study books.

Transparent Windows and Half Windows [0003] As used herein, the term window refers to a transparent (i.e., transparent) or translucent area in the security document delimited from the substantially opaque area being printed on. The window may be fully transparent so as to allow the substantially unimpaired passage of light, or it may be partially transparent or translucent, thus allowing the partial passage of light without, however, being able to clearly see objects through the window area.

[0004] A window area may be formed in a polymeric security document having at least one layer of transparent polymeric material and one or more opacifying layers deposited on at least one side of a transparent polymeric substrate by forming at least one opacifying layer in the area forming the window area. is omitted. When opacifying layers are applied to both sides of a transparent substrate, a fully transparent window can be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area.

[0005] A partially transparent or translucent area, hereinafter referred to as a "half window", can be formed in a polymeric security document having opacifying layers on both sides by omitting the opacifying layers on only one side of the security document in the window area, so that the "half-window" is not fully transparent, but allows some light to pass through, without objects being clearly visible through the half-window.

Alternatively, it is possible to produce the substrates from a substantially opaque material, such as paper or fiber material, wherein an insert of transparent plastic material is inserted into a cutout or a recess in the paper or fiber substrate to a transparent window or form a translucent half-window area.

Opacifying Layers [0007] One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is designed such that LT <L0, where L0 is the amount of light incident on the document and LT is the amount of light transmitted through the document. An opacifying layer may comprise one or more of a variety of different opacifying coatings. For example, the opacifying layers may comprise a pigment, such as titanium dioxide, dispersed in a binder or support of thermally activated crosslinkable polymer material. Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or another partially or substantially opaque material onto which indicia may subsequently be printed or otherwise applied.

Focus size or focal length H

As used herein, the term focus size (or focus distance) refers to the dimensions, usually an effective diameter or width, of the geometric distribution of points at which rays which are refracted when passing through a lens, an object plane in cut a special viewing angle. The focal point size can be derived from theoretical calculations, beam train simulations or actual measurements.

Focal length f In the present specification, when used with respect to a microlens in a lens array, focal distance means the distance from the top of the microlens to the position of the focus determined by the location of the maximum of the power density distribution when collimated radiation from the lens side of the lens Arrays occurs (see T. Miyashita "Standardization for microlenses and microlens arrays" (2007) Japanese Journal of Applied Physics 46, p. 5391).

Test Thickness t [0010] The test thickness is the distance from the vertex of a small lens on one side of the transparent or translucent material to the surface of the opposite side of the translucent material on which the pixels are substantially coincident with the object plane.

Lens frequency and pitch The lens frequency of a lens array is the number of small lenses over a given distance on the surface of the lens array. The pitch is the distance between the vertex of a small lens and the vertex of the adjacent small lens. In a uniform lens arrangement, pitch and lens frequency are in inverse proportion.

Lens width W

The width of a small lens in a microlens array is the distance from one edge of the small lens to the opposite edge of the small lens. In a lens array with hemispherical or semi-cylindrical small lenses, the width and diameter of the lens are identical.

Radius of curvature R

The radius of curvature of a small lens is the distance from a point on the surface of the lens to a point at which the perpendicular to the lens surface intersects a straight line that passes perpendicularly through the apex of the lens (lens axis).

Sag S The sag of a small lens (also referred to as a lens thickness) is the distance from the vertex to a point on the axis intersected by the shortest straight line coming from the edge of a small lens passing through the axis.

Refractive index n The refractive index of a medium n is the ratio of the speed of light in vacuum to the speed of light in the medium. The refractive index n of a lens determines the order of refraction of light rays which reach the lens surface according to Snell's law: n-1 * Sin (α) = n * Sin (Θ), where a is the angle between an incident beam and the perpendicular at the point of incidence on the lens surface; Θ is the angle between the refracted ray and the perpendicular at the point of incidence; and n-1 is the refractive index of air (for n-1, the value 1 can be used as an approximation).

Conic constant P

The conic constant P is a quantity for describing conic sections and is used in geometrical optics for the specification of lenses: spherical (P = 1), elliptic (0 <P <1 or P> 1), parabolic (P = 0) and hyperbolic (P <0). Occasionally the letter K for the conical constant is also found in the literature. The relationship of K to P is K = P -1.

Club angle [0017] The lobe angle of a lens is the total viewing angle formed by the lens.

Abbe number The Abbe number of a transparent or translucent material is a measure of the dispersion (wavelength dependence of the refractive index) of the material. An appropriately selected Abbe number for a lens can help minimize color errors.

Background of the Invention The present invention aims to provide a security device with an attractive appearance that can be economically produced while ensuring increased security against counterfeiting.

It is known to use arrays of microlenses, which are arranged so that they focus on corresponding arrays of identical microimages in order to achieve optically variable effects. A particularly striking effect can be achieved by a slight registration deviation of the microlenses and microimages, so that a series of moiré strips are produced. The moiré strips take the form of enlarged versions of the microimages. This effect, known as "moiré magnification," has been reported by Hutley et al. (Pure and Applied Optics 3, pp 133-142, 1994) and Amidror (The Theory of the Moire Phenomenon, Kluwer, Dordrecht, 2000). When a transparent (transparent) or translucent material is used as the substrate for a security device or for a security document, the corresponding substrates are suitable as carriers for devices of the above-mentioned type. For example, it is possible to apply the microimages to one side of the substrate and apply the microlenses on the opposite side of the substrate, thereby functioning as an optical spacer, as described, for example, in US 5,712,731.

An alternative possibility for producing a security device or a security document with Moire magnification effect is the provision of a separate grid in the form of a microlens array. The grid may be an independent element or built-in part of the security device or security document and positioned by folding the document in register with the microimages located elsewhere on the document.

Summary of the Invention According to the present invention, there is provided an optical safety device comprising: a transparent or translucent substrate, at least a first array of repeating pixels in or on a first side of the substrate, at least a second array of repeating pixels a second side of the substrate, wherein the at least one second array of repeating pixels is substantially in register with the at least one first array of pixels, the at least one first array and / or the at least one second array of repeating pixels being at least partially opaque, wherein the repeating picture elements on at least one side of the substrate are modulated, area by area, according to the brightness or color values of corresponding areas of an underlying gray scale or color image such that upon viewing the device in the top light of FIG the first side is visible from a first image and when viewing the device in the overhead light from the second side of a second image is visible and wherein the first image is formed at the repeating pixels of the first array and wherein the second image at the repeating Picture elements of the second array is formed.

Preferably, the picture elements of both the first and second arrays are at least partially opaque. The picture elements of at least one of the arrays may be completely opaque. In one embodiment, the pixels of at least one of the arrays are partially opaque and partially transparent such that the first image and the second image combine to form a third image that is visible when the security device is viewed in transmitted light.

The picture elements of at least one of the first and second arrays may be color picture elements modulated in regions according to the color or brightness values of corresponding areas of an underlying color image.

Alternatively or additionally, the picture elements of the first and / or second array can be gray-scale picture elements which are modulated in regions according to the brightness values of corresponding areas of an underlying gray value picture.

The picture elements on at least one side of the substrate may be printed picture elements. The picture elements on both sides of the substrate may be printed picture elements. Alternatively, the picture elements may be imprinted picture elements on at least one side of the substrate. In other embodiments, the picture elements on at least one side of the substrate may be diffractive structures or structures in the sub-wavelength range.

In a further embodiment, the repeating picture elements on at least one side of the substrate are non-diffractive picture elements surrounded by a background area comprising a diffraction or subwavelength grating structure, wherein a background area of the image viewed when viewing the device is visible from this side, shows a visually variable color effect.

In one embodiment, the repeating elements may be amplitude modulated on at least one side of the substrate. In another embodiment, the thickness or area of the repeating elements may be modulated on at least one side of the substrate.

The first and / or second image may be optically variable. In one embodiment, the first image may be an optically variable image and the second image may be an optically invariant image.

In another embodiment, both the first and second images may be optically invariant images.

The optical security device may include on or in at least one side of the substrate two or more arrays of repeating elements.

The repeating elements on at least one side of the substrate may be embossed elements. In one embodiment, the embossed elements on at least one side of the substrate form repeating picture elements. In this case, each imprinted picture element has a depth and the depth is preferably modulated in regions.

The repeating elements on at least one side of the substrate may be printed picture elements. In another embodiment, the repeating elements are printed pixels on both sides of the substrate.

The repeating elements on at least one side of the substrate may be picture element-forming diffraction structures or structures in the sub-wavelength range. The diffraction or subwavelength structures may be surrounded by a non-diffractive background.

In another embodiment, the repeating elements on at least one side of the substrate are non-diffractive pixels surrounded by a background region comprising a diffraction or sub-wavelength grating structure, wherein a background region of the image is on that side of the substrate shows a visually variable color effect.

In a preferred embodiment, the at least one first array of repeating elements in or on a first side of the substrate is an array of focussing elements and the at least one second array of repeating elements in or on the second side of the substrate is an array of pels, which are substantially identical in shape to each other so that when the device is viewed from the first side, an enlarged image including at least one enlarged version of the pixel shape is visible, and when viewed from the second side, the gray scale image or Color image is visible.

An optical safety device is also described, comprising: a transparent or translucent substrate, an array of focusing elements in or on a first side of the substrate and at least one array of repeating pixels having a substantially identical shape to each other and in FIG or on a second side of the substrate, wherein the array of repeating picture elements is substantially in register with the array of focusing elements, and wherein the picture elements are modulated in regions according to the brightness or color values of corresponding areas of an underlying gray scale or color image such that when the device is viewed from the first side, an enlarged image is visible that includes at least one enlarged version of the pixel shape, and when viewing the device from the second side, the gray scale or color image is visible.

Preferably, the repeating elements on at least one side of the substrate are modulated in regions according to the brightness or color values of corresponding areas of an underlying gray scale or color image.

Preferably, the pixels are amplitude modulated. In a preferred form of the invention, the amplitude modulation takes place in that the line thicknesses or area contents of the picture elements are varied.

Alternatively, the picture elements may be frequency modulated. For example, it is possible for the repeating pixels to have substantially the same overall period as the array of focussing elements, but omitted in some areas to produce brightness variations when viewing the second side of the device. This can result in slightly degraded quality of the enlarged image, but provide better contrast for viewing the gray scale or color image.

Thus, the effect produced by the safety device includes a moiré magnifying effect when the device is viewed from the first side while the device, when viewed from the opposite side (unexpected for a transparent region), has a completely different optical Effect as an optically invariable image (for example, a portrait) generates. This combination of two different types of optical effects within the same area of the device provides a more recognizable security feature with increased security over known security devices.

The device is also easier to manufacture, as an array of picture elements located in a single surface of the device, applied in a single manufacturing step (for example, by embossing), can be used to produce two different effects.

In a particularly preferred embodiment, the enlarged image is an optically variable image and the grayscale or color image is an optically invariable image.

By the interaction of diffractive and non-diffractive elements, a monochromatic macroscale image can be generated. Under conditions of illumination with multiple or diffuse light sources, the image appears as a negative (contrast-contrast reversed) image of the underlying image in the case of top light and as a positive image of the underlying image in transmitted light. Usually, a purely diffractive device would produce a very weak image with low diffraction power under such light conditions and be so weak under certain conditions that it is no longer recognizable.

The optical security device may include two or more array of repeating pixels. Thus, for example, when viewing a first region of the device from the first side, an enlarged image may be visible, while when viewing a second region of the device from the first side, a second, different, enlarged image is visible. When the device is viewed from the second side, a tonal gray value or color image is visible. Thus, adding more arrays of repeating pixels increases the complexity of the visual effect produced by the device and makes counterfeiting even more difficult.

In a preferred embodiment, the focal length of the focusing elements in an object plane located on the second side of the device is about the same, or in the range of 20 o / o, the width of the picture elements. This allows the use of larger picture elements at a given substrate thickness while still providing the desired image magnification effect.

The enlargement of the image elements in the enlarged image is preferably controlled by the fact that the array of focusing elements and the array of picture elements in the pitch and / or in the Drehausrichtung have a deviation from each other.

The picture elements in one embodiment are embossed picture elements, but the picture elements may also be printed picture elements. Embossed picture elements are particularly preferred since a higher resolution can be achieved with embossing processes, which produces a sharper magnified image when the device is viewed from the first side. In a method in which the picture elements are subjected to amplitude modulation, each embossed picture element has a depth, and the depth is modulated in regions.

Printing methods can also be used if the print resolution is high enough for the picture elements to fit under the focusing elements.

In a particularly preferred embodiment, the picture elements comprise diffraction or subwavelength grating elements which are surrounded by a non-diffractive background area, wherein the enlarged picture shows an optically variable color effect. The picture elements may alternatively be non-diffractive picture elements surrounded by a background area comprising diffraction or subwavelength grating elements, a background area of the magnified image exhibiting an optically variable color effect.

A "sub-wavelength" grid element, or zero-order grid element, is a surface-raised or surface-buried microstructure that produces light only in the zeroth diffraction order when illuminated with a light of a given wavelength. Generally, these zeroth-order structures have a period below the desired incident wavelength of light. For this reason, zeroth-order diffraction gratings are sometimes referred to as sub-wavelength gratings.

The use of diffraction or subwavelength grating elements (or of non-diffractive picture elements in front of a (light) diffractive background) advantageously provides a device which ensures a conspicuous visual effect both in specular reflection and in diffuse light conditions or in poor lighting conditions.

The focusing elements may be refractive microlenses. Alternatively, they may be Fresnel lenses, diffractive zone plates or photon screens. An exemplary photon screen is a screen having a series of apertures pseudo-randomized along the Fresnel zones of a Fresnel zone plate as described, for example, in US 7,368,744.

In another aspect of the invention, there is provided a method of manufacturing a security device, comprising the steps of:

Forming at least a first array of repeating picture elements in or on a first side of a transparent or translucent substrate; and

Forming at least one second array of repeating picture elements in or on a second side of the substrate, wherein the at least one second array of repeating elements is substantially in register with the at least one first array of repeating elements, and wherein the at least one first array and / or the at least one second array of repeating pixels is at least partially opaque, the step of forming the first and / or second array of repeating pixels on at least one side of the substrate, modulating the repeating pixels according to the brightness or color values of corresponding areas of a region underlying gray value or color image, so that when viewing the device in plan view from the first side of a first image is visible and viewing the device in plan view from the second side of a second image is visible and wherein the first e picture at the repetitive

Picture elements of the first array is formed and wherein the second image is formed at the repeating picture elements of the second array.

For the printing of the repeating picture elements, various printing methods can be used, including offset printing, flexographic printing, intaglio and gravure printing. Simultaneous printing is a particularly preferred printing method that can be used to print register-repeating picture elements concurrently on opposite sides of a substrate. The method may include the step of forming the repeating elements on at least one side of the substrate as diffractive pixels.

The method may include the step of embossing the repeating elements on at least one side of the substrate.

In a particularly preferred method, the step of forming the at least one first array of repeating elements and the step of forming the at least one second array of picture elements are performed substantially simultaneously.

A method of manufacturing a security device is also described, comprising the following steps:

Forming an array of focusing elements in or on a first side of a transparent or translucent substrate; and

Forming at least one array of repeating picture elements having a substantially identical shape to one another and arranged in or on a second side of the substrate, the array of repeating picture elements being substantially in register with the array of focusing elements, and wherein the picture elements reside in regions are modulated to the Flelligkeitswerten corresponding areas of an underlying gray value or color image, so that when viewing the device from the first page at least an enlarged version of the pixel shape is visible and when viewing the device from the second side of the gray scale or color image is visible.

The method may include the further step of applying an embossable radiation-curable ink to the first side and / or the second side.

Preferably, the method further comprises the step of: embossing the focusing elements in the embossable radiation-curable ink in the first side. The method may further include the step of embossing the pixels in the embossable radiation-curable ink in the second side.

Embossable radiation-curable printing ink The term embossable radiation-curable printing ink encompasses any paint, varnish or coating which can be applied to the substrate in a printing process and which can be embossed while still unconsolidated and cured by radiation to fix the embossed relief structure , The curing process does not occur before the radiation-curable ink is coined, but it is possible for the curing process to take place either after embossing or substantially simultaneously with the embossing step. The radiation-curable ink is preferably curable by ultraviolet (UV) radiation. Alternatively, the radiation-curable ink can be cured by other forms of radiation, such as electron beam or X-ray.

The radiation-curable ink is preferably a transparent or translucent ink formed of a transparent resin material. Such a transparent or translucent ink is particularly suitable for printing translucent security elements such as subwavelength gratings, diffractive transmission grids and lens structures.

In a particularly preferred embodiment, the transparent or translucent ink preferably comprises a UV-curable embossable acrylic-based lacquer or a UV-curable embossable acrylic-based coating.

Such UV-curable coatings can be obtained from various manufacturers, including Kingfisher Ink Limited, product UVF-203 or the like. Alternatively, radiation curable embossable coatings based on other compounds, e.g. Nitrocellulose, based, can be used.

The radiation-curable paints and lacquers used here have proven to be particularly suitable for embossing microstructures, including diffractive structures such as diffraction gratings and holograms, as well as microlenses and lens arrays. However, they can also be embossed with larger relief structures such as non-diffractive optically variable devices.

Preferably, the ink is embossed substantially simultaneously and cured by ultraviolet (UV) radiation. In a particularly preferred embodiment, the deposition and embossing of the radiation-curable ink occur substantially simultaneously in a gravure printing process.

For gravure printing, the radiation-curable ink preferably has a viscosity that is substantially in the range of about 20 to about 175 centipoise, and more preferably about 30 to about 150 centipoise. The

Determination of viscosity can be made by measuring the flow time of the varnish from a No. 2 toothed cup. A sample with 20 seconds flow time has a viscosity of 30 centipoise and a sample with 63 seconds flow time has a viscosity of 150 centipoise.

For some polymeric substrates, it may be necessary to apply an intermediate layer to the substrate prior to application of the radiation-curable ink to ensure improved adhesion of the imprint structure formed by the ink on the substrate. The intermediate layer preferably comprises a primer layer, and more preferably the primer layer comprises a polyethyleneimine. The primer layer may also include a crosslinking agent, for example a multifunctional isocyanate. Examples of other primers suitable for use in the invention include: hydroxyl-terminated polymers, polyester-terminated copolymers having hydroxyl end groups, crosslinked or uncrosslinked hydroxylated acrylates, polyurethanes, and UV-curing anionic or cationic acrylates. Examples of suitable crosslinkers include: isocyanates, polyaziridines, zirconium complexes, aluminum acetylacetone, melamines and carbodiimides.

The type of primer can vary depending on the substrate and embossed ink structure. Preferably, a primer is selected which does not significantly affect the optical properties of the embossed ink structure. The steps of forming the array of focusing elements and forming the array of picture elements are preferably carried out successively. However, in some embodiments, for example, when the focussing elements and picture elements are embossed, the steps may be performed simultaneously.

The method may further include the step of: curing the embossable radiation-curable ink. This is preferably done substantially simultaneously with the embossing step.

In a preferred embodiment, the picture elements comprise diffraction or subwavelength grating elements surrounded by a non-diffractive background area. The picture elements may alternatively be non-occult picture elements surrounded by a background area comprising diffraction or subwavelength grating elements.

The picture elements may be formed by printing or embossing the picture element form as a non-diffractive structure onto a background of diffraction or subwavelength grating elements. Alternatively, the pixels may be formed by embossing diffraction or subwavelength grating elements onto a non-diffractive background.

In another aspect, there is provided a security document incorporating a security device according to the first, second or third aspect of the invention or including a security device made in accordance with the fourth or fifth aspects of the invention. The security device may be formed or applied in or on a window of the security document.

Brief Description of the Drawings Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a cross-section through an embodiment of a security device according to the invention;

Fig. 2 shows the security device of Fig. 1 as part of a security document;

Fig. 3 shows a series of picture elements for use with a security device according to a

Embodiment of the invention;

Fig. 4 shows the picture elements of Fig. 3 as viewed through an array of focusing elements;

Figs. 5 and 6 show a variation of the embodiment of Figs. 3 and 4;

Fig. 7 shows another embodiment of a security device in which the picture elements are printed;

Fig. 8 shows an optically invariant image that becomes visible to a person looking at the security device of Fig. 3 from the side opposite the array of focussing elements; and

Fig. 9 shows an embodiment of a plant which is suitable for the production of security devices or security documents according to the above embodiments.

Fig. 10 is a schematic sectional view of a safety device according to another embodiment of the invention Ausfüh;

Fig. 11 is a schematic sectional view of a security document in which the security device of Fig. 10 is in a window of the document;

Fig. 12 shows the security document of Fig. 11 with a first image which is viewable from a first side when viewed in plan;

Fig. 13 shows the security document of Fig. 11 with a second image visible from the second side when viewed in top light;

Fig. 14 is an enlarged view of the window portion and security device of the security document of Fig. 12;

Fig. 15 is an enlarged view of the window portion and the security device of the security document of Fig. 13; and

Fig. 16 shows a modified embodiment of the security document of Figs. 12 and 15 with a

Transmitted light visible third image.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a partial cross section through a security device 10 with a transparent or translucent substrate 15 having a first side 16 and a second side 17. An array of focusing elements in the form of part-spherical microlenses 20 is formed on the first side 16, and a corresponding array of repeating pixels 30 is formed on the second side 17.

The focusing elements 20 may be formed directly in the surface of the first side 16 of the substrate 15, but are preferably formed in an embossable radiation-curable ink which is applied to the first side 16, preferably by gravure printing.

The picture elements 30 may be printed picture elements which are applied to the surface of the second side 17, for example by flexographic printing. Preferably, however, they are embossed pixels formed by applying an embossable radiation curable ink to the second side 17, embossing an array of relief structures into the embossable radiation curable ink, and curing the ink.

FIG. 2 is a partial cross-sectional view of a security document 100 incorporating the security device 10. The security document includes a transparent or translucent substrate 105 having a first side 106 and a second side 107. Layers of opacifying ink 108, 109 are applied to the first side 106 and second side 107, respectively, except in a window area in which the security device 10 is located. The opacifying ink 108, 109 is preferably applied before the security device 10 is formed in the window area to facilitate the registration of the security device 10 and window area.

Further details of the security device 10 will now be illustrated with reference to FIGS. 3, 4 and 8. The array of pixels 30 to be applied to the second side 17 of device 10 is made by forming a dither or halftone version of an underlying input image 200. In the example in FIG. 8, each pixel of the monochrome bitmap 200 is set to one of three brightness level values, each brightness value corresponding to a particular line thickness (line thickness) of the pixels (amplitude modulation), as shown to the right in the enlarged views of the areas 211, 212, 213 of the pixel elements. Arrays 210 shown. In an alternative embodiment, the spatial distribution of the pixels 30 on the second side 17 of the substrate could be modulated according to the brightness values of the underlying image 200 (frequency modulation), but the amplitude modulation is preferred.

Each image area 211, 212, 213 comprises pixels 25, which are square areas corresponding in mass to the dimensions of overlapping partially spherical lenses 20. The order of the pixels 25 is generally in the range of 45 square microns to 65 square microns, but it will be appreciated that smaller or larger dimensions can be selected to suit the particular application. As will also be apparent, the pixels need not be square, but in many applications the selection of square pixels is favorable.

The image area 211 corresponds to a part of the brightest area of the underlying image 200 and includes as such imprinted picture elements 30 that generate the greatest amount of reflected or transmitted light, i. H. which have the largest line thickness. Image area 212 lies within the second brightest part of image 200, and thus the corresponding image elements 31 have a line thickness slightly reduced with respect to image elements 30. Likewise, image area 213, which lies in the darkest areas of the underlying image 200, has pixels 32 with the lowest line weight.

The picture elements 30, 31, 32 all have substantially the same shape and differ only in their line width. The line weight may be modulated to the extent permitted by the resolution of the process used to apply the pixels. In flexographic printing, the smallest resolution is about 7 microns.

In an embossing process, the smallest resolution is limited by the resolution of the electron beam or other process used to make the embossing master, and may be on the order of nanometers. Embossing processes are therefore preferred because they allow a finer gradation between line widths and thus brightness values and thus create the impression of a smooth transition between areas of different coloration or brightness.

The array of lenses 20 and the array of pixels 30, 31, 32 can be made to produce a moiré magnified image if the two arrays have slightly different pitches or a different rotational orientation. The magnification degree for a lens array having period a and a pixel array having period b is given as a 2 / A, where Δ = a-b is the pitch distance difference. If the lens array and the image array have identical periods a but their axes are at an angle Θ to each other, the magnification is about 1 / (1-cos Θ).

The 3x3 grid of pixels 25 in Figure 3 includes three pixels 30, 31, and 32, respectively. Each pixel 30, 31, and 32, respectively, is an embossed or printed non-diffractive element extending from a surface 35, 36, and 37, respectively surrounded, which comprises an embossed surface relief structure. The surface relief structures in the background areas 35, 36, and 37 may have the same parameters (embossing depth, spatial frequency, curvature, azimuth angle) to each other, or the surface relief parameters may be different from area to area, if desired.

As can also be seen, the picture elements 30-32 can be formed by unembossed areas of pixels 25, that is, the entirety of a pixel 25 is embossed omitting a region whose edge is the shape of the picture element 30, 31 or 32 having.

The surface relief structure may be a diffractive structure to produce a light-colored background area that changes with the viewing angle. Alternatively, the surface relief structure may be a zero wavelength sub-wavelength grating having a particular color at all viewing angles. Advantageously, subwavelength structures typically also produce strong polarization effects, and thus the change (for example) in the azimuthal angle of the relief structure between pixels can give rise to another authenticity feature that can be considered among polarizing filters.

The device 10 of Figs. 1,3, 4 and 8 achieves the following optical effects.

If the device 10 is viewed from the first side 16 of the substrate 15, at least one enlarged and rotated version 130 of the individual picture elements 30, 31, 32 is seen as a result of the moiré magnification effect produced by the lenses 20. Although the bucket members 30, 31, 32 are not exactly identical, they can be made with sufficiently little difference in their respective line weights, so that the collective effect produced by the scanning of individual picture elements by the lenses 20 "Average" of each scanned image is. The image may also appear to float above or below the plane of the device 10 and / or exhibit orthoparallactic displacement as the device 10 is tilted forward and backward or side-to-side by the viewer. When using diffractive (diffractive) background areas 35, 36 and 37, the enlarged images 130 can also have a light-colored and optically variable background.

If the device 10 is viewed from the second side 17 of the substrate 15, there is no enlargement of the individual picture elements 30, 31, 32, which are dimensioned too small to be perceived by the naked eye (preferably of the order of 150 Microns or below, more preferably below 70 microns so that they are not visible at a 20 cm viewing distance), and together give the impression of a monochrome or color image 200.

Thus, the device 10 generates an optically variable magnified floating or moving image when viewed from the first side 16, and an optically invariant, tonal monochrome or full-color image when viewed from the second side 17 of the transparent or translucent one Considered substrate 15 from.

FIGS. 5 and 6 show an alternative embodiment in which embossed picture elements 40, 41 and 42 within the pixels 25 are surrounded by non-diffracting surfaces 45. The picture elements 40, 41 and 42 have different thicknesses and, in this embodiment, also comprise diffraction or sub-wavelength surface relief structures. The surface relief structures may have identical parameters (embossing depth, spatial frequency, curvature, azimuth angle) in each pixel, or the parameters may differ from pixel to pixel or between different pixel thicknesses. The embodiment of Figs. 5 and 6, when viewed through lenses 20, produces at least one enlarged and rotated version 140 of the individual picture elements 40, 41, 42, the color of which also corresponds to the color of the scanned individual picture elements. As with Figs. 3 and 4, the apparatus of Figs. 5 and 6, when viewed from the second side 17 of the transparent or translucent substrate 15, displays an optically invariant, tonal monochrome or full color image as shown in Fig. 8 ,

Fig. 7 shows part of another embodiment of a flexographic printing apparatus in which a 3x3 grid of pixels includes 25 pixels 50, 51, 52 composed of flexographic points 60 and corresponding background diffractive areas 55, 56, 57 are surrounded. The picture elements 50, 51, 52 have substantially the same shape (letter 'A'), but differ in the number of flexographic points, from which they are each composed.

As in the embodiments of Figs. 3 and 5, when viewed from the second side 17 of the transparent or translucent substrate 15, the device exhibits an optically invariant, tonal monochrome or full-color image as shown in Fig. 8.

Referring now to Figure 9, an embodiment of a security document manufacturing apparatus incorporating apparatus of the above type is shown.

The printing and embossing system 500 illustrated schematically in FIG. 9 includes a feeding unit 502 for feeding a sheet-like substrate 501 to various printing and embossing stations, which include an opacifying station 504, a first printing station 506, an embossing station 510, a second printing station 606, a second embossing station 610 and a third printing station 514.

The substrate 501 is preferably made from a substantially transparent or translucent polymeric material, such as biaxially oriented polypropylene (BOPP), and may be continuously fed from a roll of material 503 to the delivery unit 502 to the opacifying station 504. The opacification station 504 includes opacifying means for applying at least one opacifying layer to at least one side of the substrate 501. The opacifying agent is preferably in the form of a printing unit, e.g. with one or more gravure cylinders 505 for applying one or more opacifying ink coatings to one or both sides of the substrate. However, it is possible that the opacification station 504 could include opacifying means in the form of a laminating unit to apply one or more laminar layers of at least a partially opaque material, such as paper or other fibrous material, to at least one side of the transparent substrate.

Preferably, the opacifying means 505 is arranged at the opacifying station 504 such that at least one opacifying layer is omitted on one side or both sides of the substrate in at least one area to form a window or half-window area.

The first printing station 506 includes printing means 507, 508 for applying an embossable radiation curable ink to the substrate 501. The printing means may comprise at least one printing cylinder 507, e.g. a gravure cylinder, wherein the opacified transparent substrate is inserted between the impression cylinder 507 and a corresponding cylinder (or roller) 508 located on the opposite side of the substrate. The printing means 507, 508 is arranged so that it applies the radiation-curable ink to the first side 16 of the substrate 501, where the lenses 20 are to be impressed on the embossing station 510. The lenses may be applied in a window area formed by partially omitting the opacifying ink applied to the opacifying station 504.

The embossing station 510 comprises embossing means preferably in the form of a plate cylinder 511 and a counter-pressure cylinder 512. The embossing means 511, 512 includes embossing sections arranged to emboss different areas of the substrate as it passes through the press nip between the plate and impression cylinders 511, 512.

Embossing station 510 may also include radiation curing agent 513 to cure the embossable radiation curable ink substantially concurrently with, or immediately after, embossing the ink to form lenses 20. Alternatively, a separate curing station may be provided. The radiation curing agent preferably comprises an ultraviolet (UV) curing unit for curing a UV curable ink, but for X-ray or electron beam curable inks, x-ray or electron beam (EB) curing units can be used.

The second printing station 606 includes printing means 607, 608 for applying an embossable radiation-curable ink to the second side 17 of the substrate 501. The printing means may comprise at least one printing cylinder 607, e.g. a gravure cylinder, wherein the opacified transparent substrate is inserted between the impression cylinder 607 and a corresponding cylinder (or roller) 608 located on the opposite side 16 of the substrate 501. The printing means 607, 608 is arranged so that it applies radiation-curable ink in a region directly opposite and in register with the lenses 20 on the second side 17 of the substrate 501. If the lenses 20 are applied in a window region, the radiation-curable ink is applied in the window region on the opposite side of the substrate 501.

The embossing station 610 preferably comprises embossing means in the form of a plate cylinder 611 and a counter-pressure cylinder 612. The plate cylinder 611 carries the structures of the picture elements 30-32 and / or 40-42 and, if embossed background areas 35-37, 45 or 55-57 also the structures of these background areas. After passing through the embossing station 610, the substrate 501 carries an array of lens structures 20 on its first surface 16 and a corresponding array of pixels 30-32 and 40-42, respectively, which is substantially in register with the array lenses 20.

The embossing station 610 may also include radiation curing agent 613 to cure the embossable radiation curable ink substantially simultaneously with, or immediately after, embossing the ink to form the cured embossed image elements 30-32 and 40-42, respectively.

It will also be appreciated that the second printing station 606 and the second embossing station 610 may be replaced by a printing station, such as a flexographic printing station, if printed pixels 50-52 are to be used.

[0105] The third printing station 514 includes printing means for applying printed features to the substrate. The printing means preferably includes a printing cylinder 516, such as a gravure, offset or intaglio cylinder, and may be used to apply a variety of different printing features to the substrate. For example, the impression cylinder 516 may be used at the second print station 514 to apply printed security features that are in register with, adjacent to, or surrounding the imprinted security feature.

In operation of the system, the transparent substrate 501 is fed from the feed unit 502 through the opacifying station 504 where at least one opacifying layer is applied to at least one side of the substrate 501. The at least partially opacified substrate 501 is then passed through the first printing station 506 where the embossable radiation-curable ink is applied in a region (eg, a window region) that is to be embossed to form the lenses 20.

The substrate 501 is then passed through the embossing station 510 where the previously applied ink surface is embossed to form the microlenses 20 on the first side 16 of the substrate 501. The radiation-curable ink is then cured to fix the embossed lenses 20, preferably at the embossing station 510.

The substrate 501 is passed through the second printing station 606 and second embossing station 610 to form on the second side 17 of the substrate 501 embossed picture elements 30-32 and 40-42, respectively, in substantial registry with the embossed lenses 20.

The system 500 may also include other printing stations or embossing stations (not shown) to provide the substrate 501 with other printed or embossed features.

It is also possible to place an opacification station after the embossing station 510, this opacifying station applying at least one opacifying layer to at least one side of the substrate 501, thereby covering the area of the embossed lenses 20 and imprinted pixels 30-32 and 40, respectively -42 leaves to form a window.

In some embodiments, simultaneous embossing of both sides of the substrate may also be possible, such that the lenses 20 and pixels 30-32 or 40-42 are formed in substantial registration on opposite sides of the substrate at the same time.

Figures 10 to 16 illustrate further embodiments of security devices and security documents of the present invention which produce different images when viewed from opposite sides of the device in top light and when viewed in transmitted light.

FIG. 10 shows a partial cross-section through a security device 700 with a transparent or translucent substrate 705 having a first side 706 and a second side 707. On the first side 706, a first array 712 of repeating elements in the form of picture elements 720 is formed, and on the second side 707 a second array 713 of repeating elements in the form of picture elements 730 is formed, which are connected to the picture elements 730 of the first array 713 are essentially in register.

The pixels 720, 730 of the first and second arrays 712, 713 are preferably formed as fine lines or dots, with spaces 721, 722 between the dots allowing the passage of light through the transparent or translucent substrate. When lines are used, they may be straight, curved, wavy, or otherwise shaped. When points are used, they are preferably round, but may take other regular or irregular forms. In any event, the pixels 730 of the second array 713 preferably have substantially the same shape as the pixels 720 of the first array 712 and are substantially in register.

The picture elements 720, 730 of the first and second arrays 712, 713 can be colored or gray-scale picture elements, which are modulated in regions according to the color or brightness values of corresponding regions of an underlying color or gray scale image.

FIG. 11 is a partial cross-sectional view of a security document 800 including the security device 700. The security document includes a transparent or translucent substrate 805 having a first side 806 and a second side 807. On the first side 806 and second side 807, respectively, layers of opacifying ink 808, 809 are applied except in a window area 810 where the Security device 700 is located. The opacifying ink 808, 809 is preferably applied before the security device 700 is formed in the window 710 to facilitate the registration of the security device 700 and windows.

Figs. 12 and 13 show the security document 800 when viewed from the first and second sides 806, 807, respectively. Figs. 14 and 15 are enlarged views of the window area 810 and the security device 700 of the security document shown in Figs. 12 and 13, respectively.

The pixels 720, 730 are at least partially opaque. Thus, if the security device 700 is viewed in a top light from a direction substantially perpendicular to the plane of the substrate from the first side 806, only the pixels 720 of the first array 712 are visible, such that a first color or gray scale image formed from the pixels 720 725 is visible as shown in FIGS. 12 and 14. Is the safety

Claims (7)

When device 700 is viewed in an overhead light from a direction substantially perpendicular to the plane of the substrate from the second side 807, only the pixels 730 of the first array 713 are visible, so that a first color or gray value image 735 formed from the pixels 730 is visible , as shown in Figs. 13 and 15. Figs. 12 and 14 show as a mere example a simple black and white image 725 in the form of a four-pointed star. Such an image may be formed by opaque black pixels forming the star shape and opaque white pixels forming the star background. Figures 13 and 15 show a simple gray image 735 in the form of an eight-pointed star formed by opaque gray lines or dots forming the star shape and opaque white lines or dots forming the star background. However, more complex gray level images can be formed by modulating the brightness values of gray pixels area by area according to the brightness values of corresponding regions of the underlying gray level image in a more complex manner. Also, the formation of colored or multicolor images is possible by using colored picture elements and modulating the color or brightness values of the colored lines or dots, in regions, according to the color or brightness values of corresponding areas of an underlying color image. If essentially vollopaque picture elements are used on both sides, only the first picture is visible from the first page in top light and transmitted light and only the second picture from the second page in top light and transmitted light. In other embodiments, as illustrated in FIG. 16, it is possible to form one or more images that are visible in transmitted light by using pixels on the first and / or second sides that are partially opaque and partially transparent or translucent allow the passage of light. For example, if the pixels of the first array forming the four-pointed constellation 725 are completely opaque and the second array pixels 730 forming the eight-pointed star 735 are partially opaque and partially transparent, when the device is viewed by light transmission from the second side, a combined third image 740 visible, consisting of the four-pointed star 725 and the eight-pointed star 735, as shown in Fig. 16. The pixels 720, 730 of the first or second or both arrays may be printed pixels applied to one or both surfaces of the substrate by, for example, flexographic printing or simultaneous printing. Alternatively, the pixels 720, 730 of the first or second or both arrays may be imprinted pixels. Embossed picture elements can be formed by applying an embossable radiation curable ink to the substrate, embossing an array of relief structures into the embossable radiation curable ink, and curing the ink. For example, a translucent colored radiation-curable ink can be used to form embossed picture elements that are partially transparent such that when combined with transmitted light from at least one side, a combined image is visible. In another modification, the picture elements on at least one side of the substrate are diffractive (diffractive) picture elements. Diffractive image elements can be used to form optically variable images, while printed image elements generally form optically invariable images. In one embodiment, the pixels of the first array may be printed images forming an optically invariant image and the pixels of the second array may be diffractive pixels to form an optically variable image. In another embodiment, the pixels on at least one side of the substrate are non-diffractive pixels surrounded by a diffraction or sub-wavelength grating structure, such that a background region of the resulting image visible from that side of the substrate, shows a visually variable color effect. Diffractive picture elements, or a diffractive or sub-wavelength structure, can be formed by applying an embossable radiation-curable ink to a surface of the substrate, embossing the required diffractive or sub-wavelength structure into the radiation-curable ink, and curing the ink. To produce security documents including embossed or diffractive picture elements or structures, a security document manufacturing facility similar to that described with reference to FIG. 9 may be used. If the picture elements in the first and second arrays are printed elements, a simpler system may be used in which the first and second printing and embossing stations 506, 510, 606 and 610 of Figure 9 are replaced by a simultaneous printing station. claims An optical safety device comprising: a transparent or translucent substrate, at least a first array of repeating pixels in or on a first side of the substrate, at least a second array of repeating pixels on a second side of the substrate, the at least one second array being more repetitive Picture elements substantially in register with the at least one first array of repeating picture elements, wherein the at least one first array and / or the at least one second array of repeating picture elements is at least partially opaque, the repeating picture elements on at least one side of the substrate in regions are modulated according to the brightness or color values of corresponding areas of an underlying gray value or color image, so that when viewing the device in the overhead light from the first side of the substrate, a first image is visible and d the device is seen in a top light from the second side of the substrate from a second image, wherein the first image is formed at the repeating pixels of the first array and wherein the second image is formed at the repeating pixels of the second array. The optical safety device of claim 1, wherein the repeating picture elements on at least one side of the substrate are amplitude modulated, or the thickness or area of the repeating picture elements is modulated. The optical safety device of claim 1 or 2, wherein the repeating pixels of at least one of the first and second arrays are partially opaque and partially transparent such that the first image and the second image combine to give a third image that is visible is when the safety device is viewed in transmitted light. A method of manufacturing a security device comprising the steps of: forming at least a first array of repeating pixels in or on a first side of a transparent or translucent substrate; and forming at least one second array of repeating picture elements in or on a second side of the substrate, wherein the at least one second array of repeating picture elements is substantially in register with the at least one first array of repeating picture elements and wherein the at least one first array and / or the at least one second array of repeating pixels is at least partially opaque, and wherein the step of forming the first and / or second array of repeating pixels on at least one side of the substrate comprises modulating the repeating pixels according to the brightness or chrominance values Contains areas of an underlying gray value or color image, so that when viewing the device in plan view from the first side of a first image is visible and viewing the device in plan view from the second side of a second image is visible un wherein the first image is formed at the repeating pixels of the first array, wherein the second image is formed at the repeating pixels of the second array. The method of claim 4, wherein the step of forming the first and / or second array of repeating pixels is performed by printing. The method of claim 5, wherein the first and second array of repeating picture elements are printed on both sides of the substrate by simultaneous printing. The method of claims 4 to 6, wherein the repeating pixels of at least one of the first and second arrays are formed as partially opaque and partially transparent pixels such that the first and second images combine to give a third image that is visible is when the safety device is viewed in transmitted light.