FR3121386A1 - OPTICALLY VARIABLE DEVICE - Google Patents

Abstract

The present disclosure relates to an optically variable device, preferably for use in a security document such as a banknote. The optically variable device includes a substrate having a first side with an array of focusing elements, and a second side opposite the first side, the second side having a plurality of image elements. The picture elements include a first group of sub-elements which are magnified by the focusing elements at a first range of viewing angles, and a second group of sub-elements which are magnified by the focusing elements at a second viewing angle range. The picture elements include a plurality of recessed regions that are recessed on the second side and a corresponding plurality of non-recessed regions. At least a first part of the recessed regions and/or the non-recessed regions comprises diffraction gratings. Separated ink is present in recessed regions but not in non-recessed regions.

Description

OPTICALLY VARIABLE DEVICE

Cross-Reference to a Related Request

This application claims the priority of Australian Provisional Application no. 2021900998 filed April 6, 2021, the contents of which are incorporated herein in their entirety.

The invention generally relates to optically variable devices and methods of making or verifying the same. In particular, the present invention relates to optically variable devices having diffractive elements or diffractive structures which exhibit at least one visual effect when viewed using a point light source and at least one visual effect when viewed in diffuse lighting conditions. Such optically variable devices can be used as security articles when applied to documents and the like.

Background

Optically variable devices are commonly used in connection with valuable documents as a means of preventing unauthorized duplication or tampering. These optically variable devices generally produce optical effects and/or articles that may be difficult for a potential counterfeiter to reproduce. Optical effects and/or articles can also be used for the verification of valuable documents.

Counterfeiting of banknotes and other valuable documents has become a growing problem in recent times due to the ready availability of color photocopiers and computer scanning equipment. This technology offers forgers an easier way to copy valuable documents issued using traditional security printing technologies. In response, central banks and banknote printers have turned to technologies and devices that produce images that vary with a changing angle of view, and therefore cannot be easily photographed.

One available technology that is used as an anti-counterfeiting device on security documents, such as banknotes, is a diffractive lens-image article (DLIM). The DLIM article uses a lenticular array of lenses located on one surface of the banknote and a lenticular image on an opposite surface of the banknote. The lenticular image has diffraction gratings on a flat surface located in the focal plane of the lenticular lens array. Lenticular lenses focus on and magnify the lenticular image of diffraction gratings. Diffraction gratings produce an optical effect when viewed through the lenticular lens array under desired conditions, i.e. when viewed from an appropriate viewing angle and sample orientation by compared to a point light source.

PCT document WO2018/204982, by the present applicant, relates to an optical security device and a method of producing the same. The security elements described in this document are DLIM items that provide an optical effect. The contents of WO2018/204982 are incorporated herein by reference.

shows a cross-sectional view of an existing security device 500 having a diffractive image-lens (DLIM) article as described in WO2018/204982. The security device 500 includes a substrate 505, on a first side 506 of which an array of lenticular lenses 501 is provided. The lens array 501 having an elongated axis perpendicular to the page. On an opposite second side 507 of substrate 505, a series of diffraction gratings 503 formed in a radiation curable ink 502 applied to the substrate during manufacture are provided. The gratings 503 preferably being aligned perpendicular to the longitudinal axis L of the lens array 501. Optionally, a coating 504 is applied to the diffraction gratings 503. The diffraction gratings 503 form at least a portion of picture elements or pixels that are associated with a respective lens of lens array 501.

The possible optical effects that can be provided by such DLIM items include 3D images, color switching, contrast switching and animation effects. Optical effects being visible when DLIM items are viewed under favorable lighting conditions as the viewing angle to the 501 lenticular lens array is changed.

A problem with the present DLIM articles is that the optical effects they provide are only readily visible under point source lighting conditions. Under diffused lighting conditions, visibility of the optical effects of DLIM items is very difficult or impossible. This is because the imaging components of DLIM articles are diffraction gratings that diffract incident light into their constituent colors, but the colors will only be visible if: (a) the light source is a point source or essentially similar to a point source; and (b) the location of the observer's eye is within the angular range of the diffracted light. Requirement (b) depends on the orientation of the DLIM item relative to the point source.

Due to this problem and the requirements for viewing the optical effect of the DLIM article discussed above, the viewer will often have to continuously manipulate the orientation of the substrate holding the DLIM article, and/or the light source. , and/or the viewing angle of the observer in order to discover the optimal viewing conditions. These issues can make authenticating a DLIM item to a security document difficult and/or slow, especially for untrained individuals. These difficulties are further exacerbated by attempts to view the DLIM article under diffuse lighting and non-point light source conditions.

It is therefore desirable to provide a suitable authentication item for a security document that overcomes at least one of the problems associated with the prior art. For example, it is desired to provide an optically variable device providing one or more optical effect(s) which is/are visible under diffuse lighting and point light source conditions, and/or which can be authenticated under diffuse lighting and point light source conditions, and/or which can be more easily observed in general.

One aspect of the present disclosure provides an optically variable device comprising: a substrate having a first side and a second side opposite the first side; an array of focusing elements on the first side; and a plurality of picture elements on the second side, the picture elements including a first group of sub-elements which are magnified by the focusing elements at a first range of viewing angles, and a second group of sub-elements which are magnified by focusing elements to a second viewing angle range, wherein the picture elements include a plurality of recessed regions which are recessed on the second side and a corresponding plurality of non-recessed regions, at at least a first part of the recessed regions and/or the non-recessed regions comprising diffraction gratings, where a separate first ink is present in the recessed regions but not in the non-recessed regions.

According to embodiments, the diffraction gratings are in the first part of the recessed regions. Diffraction gratings can be found only in recessed regions.

According to embodiments, the focusing elements are lenticular lenses or cylindrical lenses.

According to embodiments, the separated first ink is separated in the first part of the recessed regions.

According to embodiments, the diffraction gratings are oriented perpendicular to a longitudinal axis of the focusing elements.

According to embodiments, the first separated ink is a reflective ink.

According to embodiments, at least one recessed region of the first portion of recessed regions comprises diffraction gratings having a first spatial frequency, and where at least one other recessed region of the first portion of recessed regions comprises diffraction gratings having a second spatial frequency different from the first spatial frequency.

According to embodiments, a second part of the recessed regions is devoid of diffraction gratings, the second part of recessed regions being overprinted with a second ink. Optionally, the second ink is separated in the second part of the recessed regions. Optionally, the second ink is the same ink as the separated first ink. Optionally, the second ink is a non-reflecting pigmented ink and/or an opacifying ink.

According to embodiments, the second part of recessed regions is surrounded by non-recessed regions which include diffraction gratings. The second part of the recessed regions can be overprinted with a second ink. Surrounding uneven regions that include diffraction gratings can be overprinted with a third ink. The third ink is preferably a reflective ink.

According to embodiments, at least a subset of the non-recessed regions includes diffraction gratings. Optionally, the subset of non-hollowed regions comprising diffraction gratings is overprinted with a fourth ink. Optionally, the fourth ink is the same ink as the first separate ink. Optionally, the subset of non-hollowed regions has a width of at least 50 microns.

According to embodiments, the second side includes a protective layer over the picture elements. Optionally, the protective layer is transparent or translucent. Optionally, the protective layer is an opacifying layer.

According to embodiments, the recessed regions have a depth ranging from about 2 microns to about 12 microns. The recess depth can range from about 1 micron to about 20 microns. The recess depth can range from about 1 micron to about 15 microns. The recess depth can range from about 2 microns to about 15 microns. Preferably, the depth is in a range from about 3 microns to about 10 microns. More preferably, the depth is in the range from about 3 microns to about 7 microns.

According to embodiments, the substrate comprises a plurality of substrate layers.

According to embodiments, the recessed regions and the non-recessed regions are formed on the second side of the substrate in a radiation-curable ink. Optionally, the radiation curable ink is a UV curable ink. Optionally, radiation curable ink is embossable. Preferably, the diffraction gratings are formed in the radiation curable ink.

According to embodiments, the picture elements comprise more than two groups of sub-elements. Image elements can each have four sub-elements. Image elements can each have eight sub-elements. Image elements can each have two to ten sub-elements. Image elements can each have two to twenty sub-elements. Picture elements can have moiré picture sub-elements. Image elements can have full-image sub-elements. The variable optical device may include at least one lenticular integral image and at least one lenticular moiré image.

According to embodiments, the diffraction gratings are on the first part of the non-recessed regions. Diffraction gratings can be found only on non-hollowed regions. According to embodiments, the first separated ink is a non-reflective ink.

According to embodiments, the non-reflective ink is a pigmented non-reflective ink and/or an opacifying ink.

According to embodiments, the diffraction gratings occupy a surface of the non-recessed regions.

According to embodiments, the focusing elements are lenticular lenses or cylindrical lenses.

According to embodiments, the diffraction gratings are oriented perpendicular to a longitudinal axis of the focusing elements.

According to embodiments, the recessed regions with the separated first ink and the non-recessed regions with diffraction gratings are overprinted with a reflective ink.

According to embodiments, the recessed regions have a depth ranging from about 2 microns to about 12 microns, preferably where the depth is in a range from about 3 microns to about 10 microns, plus preferably where the depth is in the range from about 3 microns to about 7 microns.

According to embodiments, the picture elements comprise more than two groups of sub-elements.

Another aspect of the present disclosure provides a security document comprising the optically variable device of any of the above aspects or embodiments.

Possibly, the security document is a banknote.

Optionally, the optically variable device is provided in a window region or a half-window region of the security document.

One aspect of the present disclosure provides an optically variable device comprising: a substrate having a first side and a second side opposite the first side; an array of focusing elements on the first side; and a plurality of picture elements on the second side, the picture elements including a first group of sub-elements which are magnified by the focusing elements at a first range of viewing angles, and a second group of sub-elements which are magnified by focusing elements to a second range of viewing angles, wherein the picture elements include: a plurality of recessed regions which are recessed on the second side, at least a first portion of the recessed regions comprising diffraction gratings overprinted with a separate first ink; and a plurality of unrecessed regions on the second side.

According to another aspect of the present disclosure, an optically variable device is provided, which device comprises: a substrate having a first side and a second side opposite the first side; an array of focusing elements on the first side; and a plurality of picture elements on the second side, the picture elements including a first group of sub-elements which are magnified by the focusing elements at a first range of viewing angles, and a second group of sub-elements which are magnified by focusing elements to a second range of viewing angles, where the picture elements include:

a plurality of recessed regions which are recessed on the second side, where a non-reflecting ink is separated in each of the recessed regions; and a plurality of non-recessed regions on the second side, wherein at least a portion of the non-recessed regions includes diffraction gratings.

Definitions:

security document

As used herein, the term security document encompasses all types of documents and tokens of value and identification documents, including but not limited to the following: items of currency such as banknotes and coins, credit cards, checks, passports, identity cards, securities and stock certificates, driver's licenses, property documents, travel documents such as plane and train tickets, entrance cards and tickets, birth, death and marriage certificates and transcripts.

The invention can be applied in particular, but not exclusively, to security documents or tokens such as banknotes or to identification documents such as identity cards or passports formed from a substrate to which one or more printing layer(s) is/are applied.

The diffraction gratings and optically variable devices described here may also have application in other products, such as packaging.

Security Device or Security Item

As used herein, the term security article or device includes any of a large number of security devices, elements or articles intended to protect the security token or document against counterfeiting, copying, modifying or falsifying. The security articles or devices may be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate and may take a wide variety of forms, such as threads embedded in layers of the security document; security inks such as fluorescent, luminescent or phosphorescent inks, metallic inks, iridescent inks, photochromatic, thermochromatic, hydrochromic or piezochromic inks; printed or embossed articles, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable (OVD) devices comprising reflective optical structures comprising reflective surface relief structures and diffractive devices comprising diffraction gratings, holograms and diffractive optical elements (DOE).

Transparent Windows and Half Windows

As used herein, the term window refers to a transparent or translucent area in the security document relative to the substantially opaque region to which the print is applied. The window may be fully transparent so as to allow light transmission substantially unchanged, or it may be partially transparent or translucent, partially allowing light transmission but not allowing objects to be seen clearly through the window area.

A window area may be formed in a polymeric security document that has at least one layer of transparent polymeric material and one or more opacifying layer(s) applied to at least one side of a transparent polymeric substrate , omitting at least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate, a fully transparent window can be formed by omitting the opacifying layers from both sides of the transparent substrate in the window area.

A partially transparent or translucent area, hereinafter referred to as a "half window", can be formed in a polymeric security document which has 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 completely transparent, but allows some light to pass through without allowing objects to be clearly viewed through the half-window.

Alternatively, the substrates may be formed from a substantially opaque material, such as paper or fibrous material, with an insert of transparent plastic material inserted into a cutout or recess in the paper or substrate. fibrous to form a transparent window or translucent half-window area.

Opacifying layers

One or more opacifying layer(s) can be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that LT < LO, where LO is the amount of light incident on the document, and LT is the amount of light transmitted through the document. An opacifying layer can comprise any one or more of a variety of opacifying coatings. For example, opacifying coatings can include a pigment, such as titanium dioxide, dispersed in a binder or carrier of heat-activated crosslinkable polymeric material. Alternatively, a substrate of transparent plastic material could be gripped between opacifying layers of paper or other partially or substantially opaque material to which indicia can subsequently be printed or otherwise applied.

Radiation Curable Ink

The term radiation curable ink used herein refers to any ink, lacquer or other coating that can be applied to the substrate in an application process. In one embodiment, the ink can be embossed while soft to form a relief structure and radiation cured to set the embossed relief structure. In another embodiment, the ink can be printed on the substrate and radiation cured to fix the relief structure. The curing process preferably does not take place before the radiation-curable ink is formed (embossed or printed, for example), but either after application or substantially concurrent with the forming step. of the relief structure. Alternatively, the ink can be partially hardened before being formed. 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 beams or X-rays.

The radiation curable ink is preferably a transparent or translucent ink formed from a transparent resin material. Such transparent or translucent ink is particularly suitable for printing light transmitting security features such as sub-wavelength gratings, transmissive diffractive gratings and lens structures.

In a particularly preferred embodiment, the radiation-curable ink preferably comprises an acrylic-based UV-curable clearcoat or lacquer. Additionally, the radiation curable ink is preferably embossable.

These UV curable lacquers can be obtained from a variety of manufacturers including Kingfisher Ink Limited, UVF-203 ultraviolet type product or similar. Alternatively, radiation-curable embossable coatings can be based on other compounds, for example nitrocellulose.

The radiation-curable inks and lacquers used herein have been found to be particularly suitable for the formation of microstructures, including diffractive structures such as diffraction gratings and holograms, and microlenses and lens arrays. However, they can also be used to form larger relief structures, such as non-diffractive optically variable devices.

The ink is preferably cured by ultraviolet (UV) radiation substantially concurrently with the application of a tool incorporating the structure of interest to a substrate. In one embodiment, the radiation-curable ink is cured and embossed substantially simultaneously in a gravure process. In another embodiment, the ink is applied to a printing tool and cured when the printing tool is in contact with the substrate.

Curvature radius 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 normal to the lens surface intersects a line extending perpendicularly through the top of the small lens (the lens axis).

Image pixel and image sub-pixel

Throughout the description, terms such as image element(s) and image pixel(s) are used interchangeably and are intended to have the same meaning. Terms such as sub-pixels, image sub-pixels and sub-elements are also intended to have the same meaning as each other and are used interchangeably.

Embodiments of the invention will now be described with reference to the accompanying drawings. It should be understood that the embodiments are given by way of illustration only and that the invention is not limited by this illustration. In the drawings:

shows a cross section of a prior art optically variable device;

shows a cross section of an optically variable device according to one embodiment of the disclosure;

shows a top view of grating imaging sections located under a lenticular lens of the embodiment of the ;

shows an example of an integrated drawing visible to an observer of an optically variable device according to the present disclosure;

shows a cross section of an optically variable device according to another embodiment of the disclosure;

is another example of an integrated design visible to an observer of an optically variable device according to the present disclosure; and

shows a cross section of an optically variable device according to another embodiment of the disclosure.

Detailed Description of Embodiments

Aspects and embodiments of the present invention provide optically variable devices that provide optical effects that are visible to an observer under both diffuse lighting and point light source conditions. The present invention is therefore advantageous to at least provide those improvements over prior art DLIM articles of the optically variable device structure shown in Fig. , and discussed in the Background section above.

The shows an embodiment of an optically variable device 10 according to the present disclosure which can display to an observer optical effects under both diffuse illumination and point light source conditions. The optically variable device 10 has a substrate 11 with a first substrate side 12 and a second substrate side 13. On the first substrate side 12 is an array of focusing elements, in the form of an array of lenses lenses 14, which includes a plurality of lenses 15. In this embodiment, and all other embodiments described herein, the array of focusing elements may be any structures suitable for focusing light, such as refracting lenses or diffractive lenses. A longitudinal axis of each lens 15 of the lenticular lens array 14 being in or out of the page as seen in the . Opposite the first substrate side 12 is the second substrate side 13, each of the first substrate side and the second substrate side being substantially planar. On the second side of the substrate are a plurality of recessed regions 17 and non-recessed regions 18. Diffraction gratings 19 are located in the recessed regions 17. A reflective ink 20 is applied to the diffraction gratings so that it or, essentially, separated in the recessed regions only. Of course, the reflective ink 20 in a practical application or printing process may be present on the non-recessed regions 18 in an amount which does not affect the intended operation. That is, the reflective ink 20 may be present on the non-recessed regions in such small amounts that the amount of reflection, relative to the recessed regions 17, is insignificant.

When viewed at varying angles to the lenticular lens array 14 with a point light source, the optically variable device 10 having the structure as shown in Fig. will present a multicolored optical effect. The multicolor optical effect being provided by the diffraction gratings acting to diffract the light from the point light source into desired color components and a variation in the viewing angle will cause a change in perceived color from the different gratings diffraction 19 also due to the change in position of the focal point through the relevant microlens 15. It can be difficult to see the multicolor optical effect in diffuse lighting conditions. However, when viewed in diffuse lighting conditions, a single color optical effect, which is the color of the reflective ink 20, will be able to be viewed. The single-color optical effect will provide the same image, at a particular viewing angle, as the multi-color optical effect, but with a single color rather than multiple colors. The single-color effect may be easier to view compared to the multi-color optical effect and may require less manipulation of the optically variable device compared to a light source for the single-color effect to be seen.

According to the embodiment shown in the , a radiation curable ink 16 is applied to the second substrate side 13. The radiation curable ink 16 is preferably a UV curable ink. The recessed regions 17 are formed from radiation curable ink 16 (as described above). Diffraction gratings 19 are also formed in radiation curable ink 16. In one embodiment, recessed regions 17, non-recessed regions 18, and diffraction gratings 19 are printed on the second side of substrate 13, and where they are printed in the radiation curable ink 16, the ink 16 is cured to provide the structures shown in the . Alternatively, a radiation curable ink 16 is applied to the second substrate side 13, then the structure of recessed regions 17, non-recessed regions 18 and diffraction gratings 19 are embossed in the radiation curable ink 16, and cured . According to embodiments, recessed regions 17, non-recessed regions 18 and diffraction gratings 19 are formed in the same process. According to alternative embodiments, recessed regions 17 and non-recessed regions 18 are formed in a first process and diffraction gratings 19 are formed in a second process. The first and second processes may or may not be of the same type of process.

Optionally, a protective coating 21 is applied to the structure of recessed regions 17, non-recessed regions 18 and reflective ink 19. The protective coating may be transparent. The protective coating may be translucent. The protective coating may be an opacifying layer. A protective coating (not shown) may be applied to the lenticular lens array 14, or other focusing elements used in the optically variable device. The protective coating is preferably transparent.

The recessed regions have a depth x. For example, the distance perpendicular to the plane of the substrate between the recessed regions and the non-recessed regions is preferably the depth x. The preferred recess depth is in the range from about 1 micron to about 20 microns. More preferably, the recess depth is between about 2 microns and about 12 microns. Even more preferably, the recess depth is between about 3 microns and about 10 microns. Ideally, the recess depth is between about 3 microns and about 7 microns.

Substrate 11 is preferably formed at least partially from a polymeric material. The substrate may be formed entirely of a polymeric material. Substrate 11 may include at least one window area and/or at least one half-window area. The optically variable device 10 can be formed in the window region or the half-window region of the substrate. According to alternative embodiments, the substrate 11 can be multilayered and formed from layers of material. Substrate 11 may comprise a transparent polymer material and optionally at least one opacifying layer.

The diffraction gratings 19 are preferably oriented perpendicular to the longitudinal axis L of the lenses 15, as shown in the . This perpendicular orientation of the diffraction gratings 19 with respect to the longitudinal axis of the lenses 15 can ensure that each lens 15 of the lenticular lens array 14 projects a constant color towards an observer at each point along the lenticular axis L of the lenses. 15. The shows a top view of a picture element 30 under and associated with a single lens 15. Picture element 30 is divided into five channels or groups 31-35. Embodiments of the present disclosure will include at least two channels or groups. Each of the channels may provide a respective frame of a 3D image, animation, flip effect, contrast switching or other effect image. When pixel 30 is viewed through associated lens 15 at a first angle, first cluster 31 will be viewed. As the optically variable device is rotated relative to the user or viewed from a variable angle, the second group 32, third group 33, fourth group 34, and fifth group 35 will be viewed. In other words, a gradual rotation of the device with respect to the observer or a gradual change in the viewing angle will make it possible to gradually pass through and visualize each of the groups 31 to 35 one after the other. Each cluster 31-35 of pixel 30 has diffraction gratings 36, 37, 38 of varying spatial frequency and uneven areas 39 without gratings. The diffraction gratings 36, 37, 38 and non-recessed areas 39 of the group being viewed from each picture element 30 of each respective lenticular lens 15 combine together to provide an observer with an overall image at a given viewing angle. .

The spatial frequency of the diffraction gratings 36, 37, 38 can be selected such that a desired color is visible at the given viewing angle of the cluster in which that diffraction grating is located. On the , grating 36 will provide a red color to an observer, grating 37 will provide a green color to an observer, and grating 38 will provide a blue color to an observer. By using combinations of diffraction gratings that provide the colors red, green, and blue (RGB), a full color image can be created for an observer. A pixel of an image to be displayed to an observer can each have red, green and blue components. The red, green or blue components each being respectively a sub-pixel or a sub-element of the pixel. Other color spaces could be used in a similar way to create a full color image, such as CMY. Alternatively, gray scale images could be created. The brightness of each displayed color or sub-pixel or sub-element of a pixel can be controlled by any suitable method such as by varying grating depth, grating profile and/or grating curvatures . In addition, each of the sub-elements may have an effective grating area which includes the diffraction grating element, and a non-diffractive area which does not include any grating element, and a brightness value of each sub-element varies depending on changing the effective grating area in each sub-element and/or the non-diffractive area of the sub-element. The grating area of a sub-element (sub-pixel) is provided in a recessed region 17 of the optically variable device and the non-diffractive area is provided in a non-recessed region 18, in the embodiment shown in . Applicant's PCT document WO2018/204982 provides a detailed description of the creation of RGB and grayscale color space pixels, the contents of which are recreated herein by reference.

Functionally, the focusing elements, which are preferably lenticular lenses or cylindrical lenses, on the first substrate side will focus to picture elements located substantially in the focal plane of the lenses. The focus elements will sample and magnify parts of the picture elements. Each picture element is associated with a focusing element and each picture element is divided into at least two channels or groups, so that one of the channels or groups can be sampled and magnified by the focusing element at time and according to a viewing angle. This will generate a first optical effect image.

The picture element includes an imaging structure that includes recessed regions and non-recessed regions. The recessed regions are preferably recessed with respect to a second substrate side. The second substrate side may include a layer in which the recessed and non-recessed regions are formed. For example, the layer on the second substrate side can be formed from a radiation curable ink. The recessed regions and the non-recessed regions are located in a predetermined pattern in the imaging structure in correspondence with the first optical effect image. Preferably, the recessed regions each have a recess depth ranging from about 1 micron to about 20 microns. More preferably, the recess depth is between about 2 microns and about 12 microns. Even more preferably, the recess depth is between about 3 microns and about 10 microns. Ideally, the recess depth is between about 3 microns and about 7 microns. At least some of the recessed regions include diffraction gratings. All recessed regions may include diffraction gratings. The diffraction gratings may be oriented perpendicular to a longitudinal axis of the focusing elements. Diffraction gratings have predetermined locations, orientations and spatial frequencies in the imaging structure in correspondence with the first optical effect image. The recessed regions, whether or not they have diffraction gratings, are overprinted with an ink that separates into the recessed regions. The separated ink is preferably a reflective ink. Separated ink can be limited to recessed regions and can avoid non-recessed regions. As mentioned previously, the application of the separated ink in a practical process may result in a minor proportion of the separated ink being present on the non-recessed regions, in an amount which does not affect the intended operation. That is, the separated ink may be present on the non-recessed regions in such small amounts that the functional effect, compared to the recessed regions, is insignificant.

The first optical effect image may be a full 3D image and/or an interlaced image. The first optical effect image can include animation optical effect, 3D interlaced image effect, 2-tilt image effect, contrast switch effect, any other desired transient image effect, or any combination of two or more effects thereof.

According to other possible embodiments of an optically variable device of the present disclosure, not shown in the , recessed regions that do not contain diffraction gratings can be provided. These recessed regions would be similarly overprinted with separate ink. The separated ink is preferably a reflective ink. The separated ink can be the same ink that is overprinted on the recessed regions that contain diffraction gratings as well as the recessed regions that do not contain diffraction gratings. Alternatively, a different separate ink can be used for each of the recessed regions that contain diffraction gratings and the recessed regions that do not contain diffraction gratings. The separate ink overprinted on at least the recessed regions which are free of diffraction gratings may be a non-reflective ink, such as a pigmented non-reflective ink. When viewed through the focusing elements at varying angles, the recessed regions devoid of diffraction gratings will display a single-color optical effect which is the color of the overprinted ink that is separated in these regions.

As another optional article, non-reflective ink can be applied to and separated into recessed regions. The recessed regions that receive the non-reflective ink may have diffraction gratings and/or may not have diffraction gratings. Areas overprinted with non-reflective ink that is separated into recessed regions with and/or without diffraction gratings will display a single-color optical effect, related to the color of the non-reflective ink, when viewed in all lighting conditions, in other words when viewed in both diffuse lighting and point light source conditions.

As an additional item, network imagery can be provided in non-recessed regions. These non-hollowed regions with diffraction gratings can function similarly to a standard DLIM article. The diffraction gratings on the non-recessed regions are preferably perpendicular to the longitudinal axis L of the focusing elements. Preferably, diffraction gratings are provided over non-recessed regions which exceed a width of about 50 microns. Diffraction gratings in non-recessed regions can be overprinted with reflective ink. Unlike diffraction gratings in recessed regions which have separately overprinted ink, reflective ink that is applied to diffraction gratings in non-recessed regions will not separate. In other words, the ink applied to the diffraction gratings in the non-hollowed regions will not separate and will also be deposited on the non-hollowed regions which do not have diffraction gratings which are adjacent to the unhollowed regions with diffraction gratings. For this reason, a single-color optical effect that can be viewed in diffused lighting is not produced by this article of diffraction gratings overprinted with reflective ink in non-recessed regions. In contrast, a multicolored optical effect is produced by these areas of diffraction gratings in non-hollowed regions overprinted with ink that is visible under point light source conditions but difficult to visualize under diffuse lighting conditions. By implementing this item in addition to diffraction gratings in recessed regions with separated ink, an additional authentication step, which requires the user to view the additional item in a point light source in order to detect his presence is planned.

The provides an example of an image 40 that can be viewed using an optically variable device with items as described above. Image 40 is preferably one of multiple frames of images that are displayed when the optically variable device is viewed from varying angles. The large print 'AU' design 41 is formed by recessed regions having diffraction gratings which are overprinted with separate reflective ink, as shown in the . The 'AU' 41 design is seen by an observer as a 3D optical effect that appears to float in front of the banknote. The 'AU' design 41 is visible as a multicolor image when viewed with a point light source and is visible as a single color image corresponding to the color of the reflective ink when viewed under light conditions diffuse.

The large print '50' design 43 is formed by gratings applied to non-recessed regions and overprinted with reflective ink which is not separated. The '50' 43 design is seen by an observer as a multicolored 3D optical effect that appears to float in front of the banknote when viewed in a point light source. The '50' design is not visible to an observer in diffuse lighting conditions or is extremely difficult to view in diffuse lighting conditions. The 'AU50' designs in small print 42 depicted on the are formed by recessed regions without diffraction gratings overprinted with separate ink. The 'AU50' 42 designs are seen by an observer as 3D optical effects that appear to float behind the banknote, and behind the 'AU' 41 design and the '50' 43 design. The background of the Image 40 may be formed by overprinting the second side of the optically variable device with an ink, preferably a reflective ink, into a desired shape, such as a rectangle as shown in .

The shows a cross section of an optically variable device according to one embodiment of the present invention and including items as discussed above. The optically variable device 60 has a substrate 61 with a first substrate side 62 and a second substrate side 63. On the first substrate side 62 is an array of focusing elements, in the form of an array of lenses lenses 64, which includes a plurality of lenses 65. A longitudinal axis of each lens 65 of the lens array 64 is in and/or out of the page as seen in the . Opposite first substrate side 62 is second substrate side 63, each of first substrate side 62 and second substrate side 63 being substantially planar. On the second substrate side 63 are a plurality of recessed regions 67 and non-recessed regions 68. Diffraction gratings 69 are located in a first portion of the recessed regions 67. Reflective ink 70 is applied to the diffraction gratings 69 in the first part of the recessed regions 67 so that the reflective ink is separated in at least the first part of the recessed regions 67. The diffraction gratings 69 in the recessed regions 67 overprinted with a separate reflective ink 70 provide a multicolor optical effect when viewed with a point light source at varying angles through the lens array 64 by an observer. When the same structures are viewed through lens array 64 by an observer under diffuse lighting conditions, a single-color optical effect that is the color of reflective ink 70 is seen. The multi-color optical effect being the same optical effect as the single-color optical effect except for the color difference.

A second part 73 of recessed regions 67 does not include diffraction gratings. The second portion 73 of recessed regions 67 is overprinted with separate ink 74. Ink 74 may be the same as reflective ink 70. Alternatively, ink 74 may be different from reflective ink 70. The second portion 73 of recessed regions overprinted with ink 74 provides a single color optical effect to an observer viewing through the lenticular lens array 64. The single color optical effect being the color of the ink 74. The ink 74 is of preferably reflective ink. Alternatively, the ink 74 may be a pigmented non-reflective ink.

A portion of the unrecessed regions 68 have diffraction gratings 75 therein. The diffraction gratings 75 are preferably oriented substantially perpendicular to the longitudinal axis L of the lenses 65. The diffraction gratings are preferably provided on non-recessed regions 68 which have a width dimension of at least about 50 microns. Adjacent to the diffraction gratings 75 on the unrecessed regions 68 are sections 77 which are devoid of diffraction gratings. The diffraction gratings 75 and the sections 77 being overprinted with an ink 76. Preferably, the ink 76 is a reflective ink. Ink 76 may be the same ink as ink 74 and/or reflective ink 70. Alternatively, ink 76 may be different from both ink 74 and reflective ink 70. When unrecessed regions 68 with diffraction gratings 75 and adjacent sections 77 devoid of gratings which are overprinted with ink 76 are viewed through lens array 64, a multicolor optical effect or a grayscale optical effect may be seen. In diffuse lighting conditions, it is extremely difficult to visualize the same multi-color optical effect.

According to the embodiment shown in the , a radiation curable ink 66 is applied to the second substrate side 63. The radiation curable ink 66 is preferably a UV curable ink. The radiation curable ink 66 is preferably embossable. The recessed regions 67, diffraction gratings 69 and diffraction gratings 75 are formed in the radiation curable ink 66 using techniques discussed herein. According to embodiments, recessed regions 67, non-recessed regions 68 and diffraction gratings 69, 75 are formed in the same process. According to alternative embodiments, recessed regions 67 and non-recessed regions 68 are formed in a first process and diffraction gratings 69, 75 are formed in a second process. The first and second processes may or may not be of the same type of process.

Another possible item of the present disclosure may be provided by recessed regions with diffraction gratings and/or recessed regions without diffraction gratings and/or non-recessed regions having diffraction gratings, which are overprinted with a plurality of separate ink layers. Separate ink layers may or may not overlap. The plurality of separate ink layers are preferably each a reflective ink or a pigmented non-reflective ink. Each separate ink layer can provide a distinct optical effect in that color when viewed in at least diffuse lighting conditions. A separate ink layer may be an opacifying layer of the security document on which the optically variable device is located. The separate ink layers may be in place of the separate ink 20, 70, 74 of the embodiments shown in Figures 2 and 5.

The shows a view 80 of one embodiment of an optically variable device with separate ink layers as described above. View 80 is preferably one of multiple frames of images that are displayed when the optically variable device is viewed from varying angles. The large print 'AU' design 81 is formed by recessed regions having diffraction gratings which are overprinted with separate reflective ink, as shown in . The 'AU' 81 design is seen by an observer as a 3D optical effect that appears to float in front of the banknote. The 'AU' 81 design is visible as a multicolor image when viewed with a point light source and is visible as a single color image matching the color of the reflective ink when viewed under light conditions diffuse.

The large print '50' design 83 is formed by gratings applied to non-recessed regions and overprinted with reflective ink which is not separated. The '50' 83 design is seen by an observer as a multicolored 3D optical effect that appears to float in front of the banknote when viewed in a point light source. The '50' design is not visible to an observer in diffuse lighting conditions or is extremely difficult to view in diffuse lighting conditions. The 'AU50' designs in small print 82 depicted on the are formed by recessed regions without diffraction gratings overprinted with separate ink. The 'AU50' 82 designs are seen by an observer as 3D optical effects that appear to float behind the banknote, and behind the 'AU' 81 design and the '50' 83 design.

The rectangular background section 84 behind AU design 81 and '50' design 83 of image 80 is formed by overprinting the second side of the optically variable device with reflective ink. In other words, this entire rectangular background section 84 shows the color of the reflective ink applied over this entire region on the second side of the security document. The reflective ink is preferably applied under a protective coating. The protective coating can be transparent or translucent.

Rectangular background section 85 is located between section 84 and section 86. Rectangular background section 85 has no ink applied to it. In this case, the optically variable device which forms the image 80 may be provided in a window region, in which case the section 85 displays a transparent appearance and will show a viewer the 3D optical effect in the color of the transmitted light. through the window region towards the observer. A transparent protective layer can be applied to the structure on the second side of the optically variable device in the window of section 85.

Rectangular background section 86 is located around the perimeter of image 80. Section 86 is formed by overprinting the second side of the optically variable device with an opacifying layer. In other words, this entire rectangular background section 86 shows the color of the opacifying layer that is applied over this entire region on the second side of the optically variable device. The opacifying layer is preferably applied under a protective coating, i.e. the protective coating is applied over the opacifying layer. The protective coating can be transparent or translucent.

The shows a cross section of an optically variable device 100 according to an alternate embodiment of the present disclosure. The optically variable device 100 has a substrate 101 with a first substrate side 102 and a second substrate side 103. On the first substrate side 102 is an array of focusing elements, in the form of an array of lenses lenses 104, which includes a plurality of lenses 105. A longitudinal axis L of each lens 105 of the lenticular lens array 104 is in and/or out of the page as seen in the . Opposite first substrate side 102 is second substrate side 103, each of first substrate side 102 and second substrate side 103 being substantially planar. On the second substrate side 103 are a plurality of recessed regions 107 and non-recessed regions 108.

Diffraction gratings 109 are disposed on the non-recessed regions 108. The diffraction gratings 109 are preferably perpendicular to the longitudinal axis L of the focusing elements 105. The recessed regions 107 shown on the do not contain diffraction gratings. A non-reflective ink 110 is separated in the recessed regions 107. The non-reflective ink 110 is preferably pigmented. The non-reflective ink 110 can be an opacifying ink. The non-reflective ink 110 can be applied in the recessed regions 107 by overprinting and is separated in the recessed regions. Reflective ink 111 is applied to recessed regions 107 already containing non-reflective ink 110 and to non-recessed regions 108 that have diffraction gratings 109. Reflective ink 111 can provide an outer layer on the second side of the optically variable device. Alternatively, one or more additional layer(s) may be applied over the reflective ink 111 (not shown in the figure). ). For example, a protective layer can be applied over the reflective ink 111. The protective layer can be transparent or translucent.

The recessed regions 107 are provided in a first predetermined imaging pattern and provide a first optical effect. The first optical effect of recessed regions 107 containing non-reflective ink 110 can be easily seen under all lighting conditions, in other words under both diffuse lighting and point light source conditions. The non-reflective ink 110 and the reflective ink layer 111 are preferably of different colors so that the non-reflective ink 110 is easily visible on the reflective ink layer 111. When viewing under a light source non-point through the lens array 105, the viewer can see a contrast between the color of the non-reflective ink 110 and the color of the reflective ink 111.

Under point light source conditions, an observer may be able to view a multicolored effect provided by the diffraction gratings in the non-recessed regions. The multicolor effect is provided by the lenses 105 sampling the diffracted colors produced by the diffraction gratings 109. The color projected from the diffraction gratings 109 will vary as a function of at least grating spatial frequency, viewing angle and the orientation of the optically variable device. When viewing recessed regions 107 and non-recessed regions 108 of optically variable device 100 through lens array 104 in a point light source, an observer will see the first optical effect image provided by recessed regions 107 having a non-reflecting ink 110 in the foreground and the multi-color effect of the non-recessed regions 108 with diffraction gratings 109 in the background behind the first optical effect image.

According to embodiments, all of the non-recessed regions 108 surrounding the recessed regions 107 may include diffraction gratings 109. This would provide a colored background behind the first optical effect image of the recessed regions 107 with non-reflective ink 110 According to other possible embodiments, diffraction gratings 109 may be applied over the non-recessed regions in a second imaging pattern to provide a second effect image when viewed through lens array 104.

According to the embodiment shown in the , a radiation curable ink 106 is applied to the second substrate side 103. The radiation curable ink 106 is preferably a UV curable ink. The radiation curable ink 106 is preferably embossable. The recessed regions 107, non-recessed regions 108 and/or diffraction gratings 109 are formed in the radiation curable ink 106 using techniques discussed herein. According to embodiments, recessed regions 107, non-recessed regions 108 and diffraction gratings 109 are formed in the same process. According to alternative embodiments, recessed regions 107 and non-recessed regions 108 are formed in a first process and diffraction gratings 109 are formed in a second process. The first and second processes may or may not be of the same type of process.

According to other possible embodiments, the articles of the optically variable device 100 shown in the could be combined with one or more of the articles of the optically variable device shown and described in connection with the or the . For example, the articles of recessed regions 107 containing non-reflective ink 110, non-recessed regions 108 having diffraction gratings 109, and reflective ink layer 111 can be formed as part or section of a security device that contains a number of other authentication items.

According to other possible embodiments of the aspects described above, focusing elements other than lenticular lenses could be used. The focusing elements can be cylindrical lenses. Alternatively, diffractive lenticular focusing structures could be provided as the focusing elements. These diffractive lenticular focusing structures can be formed by applying a radiation-curable ink to the first side of the substrate and embossed when the radiation-curable ink is soft or by printing the radiation-curable ink on the first side of the substrate. The ink is then cured, usually while the tool is still in contact with the substrate, to set the diffractive lenticular focusing structures. Each diffractive lenticular focusing structure may comprise a diffractive cylindrical lens or a zone plate.

The recessed regions, non-recessed regions and diffraction gratings of each embodiment of the present disclosure can be formed by the use of a radiation curable ink. Radiation-curable ink can be printed in any desired thickness and pattern to create recessed regions, non-recessed regions, and diffraction gratings. The radiation curable ink can be applied as a layer and while soft can be embossed to form recessed regions, non-recessed regions and diffraction gratings. After the recessed regions, non-recessed regions and diffraction gratings have been formed, the radiation curable ink is cured to solidify the ink and fix the recessed regions, non-recessed regions and diffraction gratings in place . Of course, other suitable methods can be used to form the recessed regions, non-recessed regions and diffraction gratings. For example, recessed regions, non-recessed regions, and diffraction gratings may be embossed directly into the second substrate side, or may be embossed into a layer provided on the second substrate side. Alternatively, the recessed regions, the non-recessed regions and the diffraction gratings can be directly printed on the second side of the substrate. The use of radiation curable ink is preferable as it allows to form a high resolution image and structures in the micron size range. Using radiation curable ink can also provide a more consistent image when repeated on a large number of security documents.

Manufacturing process

A security document, such as a banknote, which incorporates the optically variable device according to the present disclosure may be formed by a roll gravure process. As indicated above, in preferred embodiments, the optically variable device according to the present disclosure may be formed at least in part by a UV radiation (such as UV) curable embossment, such as a soft embossment or a radiation curable print (such as UV). The radiation curable ink application process is preferably formed inline with the roll gravure process to create a security document having the optically variable device.

The manufacture of a banknote or other security document incorporating the optically variable device of the present disclosure may involve one or more of the following process steps:

1. A transparent polymer strip is provided as a substrate for the banknote or security document. The substrate has a first side and a second side.

2. The substrate is processed in a rotogravure printing press in roll form.

3. An adhesion promoting layer is applied to the first side of the substrate, using a first rotogravure printing station. Alternatively, the substrate may have an adhesion promoting layer pre-printed on the first side, in which case application of the adhesion promoting layer is not necessary.

4. A first coat of UV lacquer is applied to the first side of the substrate, using a second rotogravure print station. The first layer of UV lacquer is printed directly above the adhesion promoting layer on the first side.

5. The first layer of UV lacquer is contacted with an image embossing roller or an image embossing wedge to provide an image structure. The first layer of UV lacquer is simultaneously completely cured with a UV light source, thereby fixing the embossed image structure in the first layer of UV lacquer. Alternatively, or potentially additionally, a second layer of UV lacquer is applied to a printing tool having the desired image structure and the printing tool is brought into contact with the first side of the substrate, typically, there where the first layer of UV lacquer is present. Again, the UV lacquer layers are fully cured simultaneously with the print. The image structure includes recessed and non-recessed regions and/or diffraction gratings.

6. Optionally, the first/second layer of UV lacquer is UV post-cured in an additional UV curing station.

7. A second adhesion promoting layer is applied to the second side of the substrate using a third rotogravure printing station. Alternatively, the substrate may have an adhesion promoting layer pre-printed on the second side, in which case application of the adhesion promoting layer is not necessary.

8. A third coat of UV lacquer is applied to the second side of the substrate, using a fourth rotogravure print station. The third layer of UV lacquer is printed directly above the adhesion promoting layer on the second side.

9. The third layer of UV lacquer is contacted with a lens embossing roller or lens embossing wedge to provide lens structure. The third layer of UV lacquer is simultaneously completely cured with a UV light source, thus fixing the embossed lens structure in the third layer of UV lacquer. Alternatively, or potentially additionally, a fourth layer of UV lacquer is applied to a printing tool having the desired lens structure and the printing tool is brought into contact with the first side of the substrate, typically where the first layer of UV lacquer is present. Again, the UV lacquer layers are fully cured simultaneously with the print. Preferably, the lens structure includes an array of lenticular lenses. Alternatively, the lens structure may include focusing elements other than a lenticular lens array.

10. Optionally, the third/fourth layer of UV lacquer is UV post-cured in an additional UV curing station.

11. Steps 3 to 6 can be performed before steps 7 to 10. Alternatively, steps 7 to 10 can be performed before steps 3 to 6. In other words the image structure can be formed before the lens structure or vice versa.

12. At least one layer of ink may be applied to the first side of the substrate on the image structure. The at least one ink layer may include a reflective ink layer or a non-reflective ink layer. The at least one ink layer may include an opacifying layer. The at least one ink layer may be applied using an additional rotogravure printing station, or where there are a plurality of ink layers, they may be applied in a plurality of printing stations by additional rotogravure.

Although the invention has been described in connection with a limited number of embodiments, those skilled in the art will understand that many variations, modifications and variations in light of the foregoing description are possible. Accordingly, the present invention is intended to encompass all such variations, modifications and variations which may fall within the spirit and scope of the invention as disclosed.

Any reference to or discussion of any document, act or piece of knowledge in this specification is included solely for the purpose of providing context for the present invention. There is no suggestion or representation that any of these or any combination thereof formed part of the common general knowledge on the priority date, or was known to be relevant to an attempt to solve any problem covered by this specification.

In this specification, the terms "includes", "comprising", "has", "comprising" or similar terms are intended to mean a non-exclusive inclusion, so that a method, system or apparatus which includes a list of items does not include these items only, but could very well include other items not listed.

List of references:

x – Recess depth

L - longitudinal axis of the focusing elements/lenticular lens array

10 – Optically variable device

11 – Substrate

12 – First side of substrate

13 – Second side of substrate

14 – Lenticular lens array

15 – Lens

16 – Radiation curable ink

17 – Hollow Regions

18 – Non-hollowed regions

19 – Diffractive gratings

20 – Separate Ink

21 – Protective Coating

22 – Second side of the optically variable device 10

30 – Image element

31 – First channel/group

32 – Second channel/group

33 – Third channel/group

34 – Fourth channel/group

35 – Fifth channel/group

36 – Red diffraction grating

37 – Green diffraction grating

38 – Blue diffraction grating

39 – Non-hollowed area

40 – Picture

41 – AU drawing

42 – Drawing AU50

43 – Drawing ‘50’

60 – Optically variable device

61 – Substrate

62 – First side of substrate

63 – Second side of substrate

64 – Lenticular lens array

65 – Lens

66 – Radiation curable ink

67 – Hollow Regions

68 – Unhollowed Regions

69 – Diffraction gratings in recessed regions

70 - Ink separated on diffraction gratings

71 – Protective Coating

72 – Hollow Region

72 – Second side of the optically variable device 60

73 – Hollow regions without diffraction gratings

74 - Separated ink in recessed regions with diffraction gratings

75 – Diffraction gratings in uneven regions

76 – Reflective ink on non-recessed areas

77 - non-recessed region without diffraction gratings with reflective ink applied

80 – Picture

81 – AU drawing

82 – Drawing AU50

83 – Design ‘50’

84 – Background section with reflective ink area

85 – Background section with window area

86 – Background section with opacifying ink area

100 – Optically variable device

101 – Substrate

102 – First side of substrate

103 – Second side of substrate

104 - Lenticular lens array

105 – Lens

106 – Radiation curable ink

107 – Hollow Regions

108 – Unhollowed Regions

109 – Diffractive gratings

110 – Separate Ink

111 – Reflective ink

500 - Optically variable device (prior art)

501 - Lenticular lens array (prior art)

502 - Radiation Curable Ink (Prior Art)

503 – Diffraction gratings (prior art)

504 – Ink (prior art)

505 – Substrate (prior art)

506 – 505 Substrate First Side (Prior Art)

507 - 505 Substrate Second Side (Prior Art)

Claims (20)

Optically variable device comprising:
a substrate having a first side and a second side opposite the first side;
an array of focusing elements on the first side; and
a plurality of picture elements on the second side, the picture elements including a first group of sub-elements which are magnified by the focusing elements at a first range of viewing angles, and a second group of sub- -elements which are magnified by focusing elements to a second range of viewing angles,
wherein the picture elements include a plurality of recessed regions which are recessed on the second side and a corresponding plurality of non-recessed regions, at least a first part of the recessed regions and/or the non-recessed regions comprising diffraction gratings, wherein a first separated ink is present in the recessed regions but not in the non-recessed regions. An optically variable device according to claim 1, wherein the diffraction gratings are in the first part of the recessed regions. An optically variable device according to claim 2, wherein the separated first ink is separated in the first part of the recessed regions. An optically variable device according to any of claims 1 to 3, wherein the diffraction gratings are oriented perpendicular to a longitudinal axis of the focusing elements. An optically variable device according to any of claims 1 to 4, wherein the separated first ink is a reflective ink. An optically variable device according to any of claims 1 to 5, wherein at least one recessed region of the first part of the recessed regions comprises diffraction gratings having a first spatial frequency, and wherein at least one further recessed region of the first portion of recessed regions includes diffraction gratings having a second spatial frequency different from the first spatial frequency. An optically variable device according to any one of claims 1 to 6, wherein a second part of the recessed regions is devoid of diffraction gratings, the second part of the recessed regions being overprinted with a second ink. An optically variable device according to claim 7, wherein the second ink is separated in the second part of the recessed regions. An optically variable device according to claim 7 or 8, wherein the second ink is the same ink as the separate first ink. An optically variable device according to claim 7 or 8, wherein the second ink is a pigmented non-reflecting ink and/or an opacifying ink. An optically variable device according to claim 10, wherein the second portion of recessed regions is surrounded by non-recessed regions which include diffraction gratings, and the second portion of recessed regions overprinted with a second ink and the surrounding non-recessed regions which comprise diffraction gratings are overprinted with a third ink. An optically variable device according to claim 11, wherein the third ink is a reflective ink. An optically variable device according to any preceding claim, wherein at least a first subset of the non-recessed regions comprises diffraction gratings. An optically variable device according to claim 13, wherein the first subset of the non-recessed regions comprising diffraction gratings are overprinted with a fourth ink. An optically variable device according to claim 14, wherein the fourth ink is the same ink as the separated first ink. An optically variable device according to any of claims 13 to 15, wherein the subset of non-recessed regions is at least 50 microns wide. An optically variable device according to any preceding claim, wherein the picture elements comprise more than two groups of sub-elements. An optically variable device according to claim 1, wherein the diffraction gratings are on the first part of the non-recessed regions. An optically variable device according to claim 18, wherein the regions recessed with the separated first ink and the non-recessed regions with diffraction gratings are overprinted with a reflective ink. An optically variable device according to claim 18 or 19, wherein the picture elements comprise more than two groups of sub-elements.