Safety device and method of manufacturing a safety device

Abstract

A safety device is disclosed. The safety device includes: a substrate; an array of observation elements disposed in or on the substrate; and an image layer disposed in or on the substrate and overlapping the array of observation elements. The image layer includes a first image channel and a second image channel. The first image channel is formed by a set of first image channel positions respectively associated with a corresponding observation element, and the second image channel is formed by a set of second image channel positions respectively associated with a corresponding observation element. The first image channel positions and the second image channel positions are staggered, thereby directing light from the first image channel to the observer at a first viewing angle and directing light from the second image channel to the observer at a second viewing angle. At least the first image channel is formed by a corresponding image layer material that collectively defines a first image. A set of first image elements occupies the image layer; wherein the image layer includes at least one region that is completely contained within a lateral region of the first image and overlaps with a plurality of said viewing elements, the at least one region having a first image tone ratio, the first image tone ratio being the ratio of the number of first image channel positions occupied by the first image elements to the number of first image channel positions within the region; and wherein: (i) the image layer includes a first region and a second region having different first image tone ratios; and / or (ii) the second image channels are occupied by a corresponding set of second image elements formed of an image layer material that commonly defines the second image, and within the at least one region of the image layer, the first image tone ratio differs from the second image tone ratio, the second image tone ratio being the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions within the region. A corresponding method for manufacturing such a device is also disclosed.

Description

Technical Field

[0001] This invention relates to a security device that can be used to verify the authenticity of valuable documents, such as banknotes, checks, passports, identity cards, certificates of authenticity, revenue stamps, and other security documents. A method for manufacturing such a security device is also disclosed. Background Technology

[0002] Valuable items, especially valuable documents such as banknotes, checks, passports, identity documents, certificates, and licenses, are often targeted by counterfeiters and those wishing to fraudulently copy and / or alter any data contained therein. Typically, such items are equipped with multiple visible security devices to verify their authenticity. The term "security device" here refers to a feature that cannot be accurately copied by obtaining a visible light copy (e.g., using standard photocopying or scanning equipment).

[0003] One type of security device is a lens-like device that uses a focusing element (such as a lens) to produce an optically variable effect, meaning that the device's appearance differs depending on the viewing angle and / or lighting conditions. This type of device is particularly effective as a security device because direct copies (such as photocopies) do not produce an optically variable effect and can therefore be easily distinguished from the genuine article.

[0004] In a lenticular device, an array of viewing elements (typically cylindrical lenses) overlays an image layer containing a corresponding array of image elements, each depicting only a portion of the image to be displayed. Image elements from two or more different images are interleaved, and when viewed through the array of viewing elements, only selected image elements are directed toward the observer at each viewing angle. In this way, different composite images can be viewed from different angles. Examples of lenticular devices are described in US-A-4892336, WO-A-2011 / 051669, WO-A-2011051670, and US-B-6856462. The advantage of lenticular devices is that they can display different images at different viewing angles, producing animations and other compelling visual effects, making the device easy to authenticate while being difficult to forge.

[0005] To enhance the security of lens-type security devices, it is desirable for one or more of the presented images to be multi-toned or multi-colored. This increases the complexity and recognizability of the image, thereby improving both the ease of authentication and the difficulty of counterfeiting. However, due to the increased size (e.g., linewidth) of printed image elements after printing, in some cases by up to 200%, it can be difficult to achieve the desired level of tonal control within the image. This so-called "dot gain" is particularly problematic for devices presenting a large number of different images, as it requires smaller individual image elements. It is also difficult to achieve the required registration of image elements with different tones or colors within the required tolerances of the image layers.

[0006] In addition, there is a desire to improve the ease with which security devices can be integrated into documents or items that carry such devices.

[0007] Therefore, in order to stay ahead of potential counterfeiters, continuous efforts are being made to improve security devices, especially lens-shaped security devices. Summary of the Invention

[0008] According to a first aspect of the invention, a safety device (e.g., lens-shaped) is provided, the safety device comprising: Substrate; An observation element array, the observation element array being disposed in or on the substrate; and An image layer is disposed in or on the substrate and overlaps with the observation element array. The image layer includes a first image channel and a second image channel. The first image channel is formed by a set of first image channel positions associated with corresponding observation elements, and the second image channel is formed by a set of second image channel positions associated with corresponding observation elements. The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed by image layer material that collectively defines the first image; wherein, The image layer includes at least one region that is completely contained within the horizontal region of the first image and overlaps with the plurality of viewing elements. The at least one region has a first image tone ratio, which is the ratio of the number of first image channel positions occupied by the first image elements to the number of first image channel positions within the region; and wherein: (i) The image layer includes a first region and a second region with different first image tone ratios; and / or (ii) The second image channel is occupied by a corresponding set of second image elements formed by image layer material that commonly defines the second image, and in the at least one region of the image layer, the first image tone ratio is different from the second image tone ratio, which is the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions in the region.

[0009] The security device of the present invention includes an image layer, in which at least one region has a first image tone ratio, the first image tone ratio being the ratio of the number of first image channel positions occupied by a first image element to the number of image channel positions within the region. By controlling the first image tone ratio across the entire image layer, the perceived tone of the presented first image can be advantageously controlled, for example, to provide a first region and a second region of the first image with different perceived tones, or to control the relative perceived tones of two or more images presented by the device when the viewing angle changes.

[0010] The occupation of image channel positions by image elements (e.g., at least partially) can be described as the "selective" occupation of image channel positions by image elements, wherein the selective occupation enables enhanced tonal control of the perceived image presented by the device as described above.

[0011] The safety device according to the first aspect of the present invention is generally a lens-shaped safety device.

[0012] In this article, when we refer to “different hues”, we mean the following areas of the image presented by the device: under rough examination with the naked human eye, these areas are perceived as being perceptibly different in “brightness” or “darkness”.

[0013] As discussed above, at least the first image channel is occupied by a corresponding set of first image elements (e.g., "selectively") formed of an image layer material that collectively defines the first image. The first image is perceived by an observer of the device at a corresponding viewing angle. At least some of the first image channel locations are not occupied by the first image elements. In other words, the invention advantageously includes first image channel locations where the corresponding image elements are absent, i.e., forming "blank" or "closed" channels for these locations. Each region overlaps with multiple viewing elements. The human eye averages the visual effects of the image elements on the corresponding multiple viewing elements to perceive the image. Therefore, including "closed" image channel locations means that the human eye will perceive a different hue in the corresponding area of ​​the image presented by the device compared to areas where each image channel location is occupied (e.g., "open").

[0014] Compared with conventional methods for controlling the size (e.g., line width) of individual image elements, the present invention provides a different technique for presenting tone control. This advantageously reduces problems associated with dot gain and means that the images presented by a device according to the present invention can present an increased number of different tones compared to conventional devices.

[0015] The image layer includes at least one region that is completely contained within the lateral region of the first image. The at least one region has a first image tone ratio, which is the ratio of the number of first image channel positions occupied by first image elements to the number of first image channel positions within the region. In other words, the first image tone ratio is the ratio of the number of first image channels that are "on" (i.e., occupied by first image elements) to the number of available image channel positions within the region. Each region is completely contained within the lateral region of the first image (e.g., within the perimeter of the first image). In other words, each region forms part of the image perceived by an observer. Thus, each region has at least one "on" image channel such that it corresponds to the region of the image perceived when viewed by an observing device. Typically, each region is perceived as having a uniform tone over its entire domain.

[0016] A first image tone ratio of 1:1 (i.e., each first image channel position within the region is occupied) will present the highest contrast / saturation (e.g., the "darkest" tone), while a first image tone ratio of 1:n, where n > 1 (i.e., one first image channel position is occupied compared to every (n - 1) first image channels that are unoccupied or "off") will present a lower contrast / saturation (e.g., a "lighter" tone). Typically, the first image tone ratio is 1:n, where generally 1 ≤ n ≤ 30, more typically 1 ≤ n ≤ 10, and even more typically 1 < n ≤ 5. In the notation "1:n", it should be noted that n need not be an integer.

[0017] The image layer may include a first region and a second region having different first image tone ratios. In this way, the resulting first image presented by the device will be perceived as having first regions and second regions of different tones corresponding to the respective first image tone ratios (each completely contained within the lateral region of the first image). This advantageously enables the device to present a multi-tone first image when viewed at a first range of viewing angles. Typically, both the first region and the second region include image channel positions that are not occupied by first image elements.

[0018] The second image channel can be a "blank" image channel, containing no image elements and therefore not displaying any image. This results in an optically variable "on / off" effect when the device is tilted, switching to a "blank" appearance when viewed from a second range of viewing angles and switching to a multi-toned first image when viewed from a first range of viewing angles. Alternatively, the second image channel can contain a set of second image elements formed of an image layer material that collectively defines a second image (different from the first image) displayed from a second range of viewing angles.

[0019] As discussed above, the image layer may include a first region and a second region with different first image hue ratios. Alternatively or additionally, the second image channel may be occupied by a corresponding set of second image elements formed by an image layer material that commonly defines the second image, and within the at least one region of the image layer, the first image hue ratio differs from the second image hue ratio, which is the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions within the region. Such an arrangement can be advantageously used to reduce the perceived difference in color saturation between the first and second images. For example, a first image formed from an image layer material of a first color with relatively high color saturation (e.g., red ink) may have a lower image hue ratio than a second image formed from an image layer material of a second color with relatively low color saturation (e.g., yellow ink).

[0020] In such an implementation, typically, the first image tone ratio differs from the second image tone ratio across the entire domain of the entire image layer.

[0021] Each image element is formed from an image layer material (e.g., ink), whereby the combination of image layer materials defines the image. In this document, the term "image" refers to the graphic form of an image as perceived by an observer of the device. Preferably, at least one image presented by the device is in the form of a sign or mark, and more preferably, at least one image presented by the device is one or more geometric shapes, letters, logos, currency symbols, or other symbols.

[0022] Preferably, in a first aspect of the invention, each first image element is formed from the same image layer material (e.g., ink). Therefore, in embodiments, the image layer material of each first image element has substantially the same color. However, in some embodiments, the image elements intended to form an image may be formed from different image layer materials. Similarly, in embodiments, each second image element may be formed from the same image layer material (typically different from the image layer material forming the first image elements). Typically, the image layer material forming a particular image may be a single ink. In this way, effective control over the color tone of the image presented by the device can be achieved.

[0023] Preferably, the at least one region comprises a plurality of repeating regions, each of which presents the first image tonal ratio. This provides a convenient way to provide the first image tonal ratio across the entire at least one region. The term "repeated" herein refers to the configuration of the "on" and "off" positions of the first image channel within each region, rather than a specific form of image layer material. This can be considered as a "periodic" arrangement of the "on" and "off" positions of the first image channel. Therefore, each repeating region presents the same first tonal ratio. Typically, both the first and second regions comprise a plurality of repeating regions, each presenting its own first image tonal ratio.

[0024] In this implementation, each region within the first and second regions includes a first image channel position not occupied by the first image element. In other words, in this implementation, the overlapping regions within the first and second regions each include a "closed" or "blank" first image channel position.

[0025] In some implementations, the regions may have a predetermined size (e.g., corresponding to a predetermined number of observation elements). The predetermined size may be based on the number of different image tonal ratios (and therefore different perceptual tonal levels) to be achieved. Typically, each region may have a dimension of 500 µm or less, preferably 300 µm or less (e.g., maximum) (e.g., along a direction that alternates between the first and second image channel positions).

[0026] In an embodiment where the second image channel is occupied by a corresponding set of second image elements, preferably, the at least one region comprises a plurality of repeating regions, each of which presents both the first image tone ratio and the second image tone ratio. In such an embodiment, the at least one region may extend entirely across the lateral regions of the two images. In other words, in such an embodiment, the first image tone ratio is uniform across the entire first image layer, and the second image tone ratio (different from the first image tone ratio) is uniform across the entire second image.

[0027] Typically, within the at least one region, each region is laterally continuous.

[0028] As discussed above, the present invention utilizes the average perceived visual effects of the eye on multiple observation elements of the device. Therefore, the at least one region overlaps with the multiple observation elements. It should be understood that the size of the at least one region will depend on the presented image. Typically, each region has a dimension of 300 µm or greater, preferably 500 µm or greater, more preferably 1 mm or greater (e.g., minimum). In this way, the human eye will be able to perceive the resulting tonal differences caused by differences in image tonal proportions. Typically, the minimum size of each region is along a direction that intersects the positions of the first and second image channels.

[0029] In some implementations, the image layer may include multiple regions defining an intermediate segment located between two regions of the image layer with different first image tone ratios, wherein each region within the intermediate segment includes a different first image tone ratio to present a perceived (e.g., gradual) tone change between the two regions over the entire intermediate segment. Including such an intermediate segment advantageously increases the complexity of the image by presenting a gradual tone change rather than an abrupt change between the two regions. This can also be used to achieve a three-dimensional effect. In this way, the security level of the device can be improved. To achieve a gradual tone change, the first image tone ratio of the regions forming the intermediate segment preferably varies continuously from a “darker” tone to a “lighter” tone or vice versa. For example, (e.g., consecutive) regions of the intermediate segment may be presented with consecutive first image tone ratios of 4:5, 3:5, and 2:5, thereby forming an intermediate segment between a first region presenting a first image tone ratio of 1:1 and a second region presenting a first image tone ratio of 1:5.

[0030] According to a second aspect of the present invention, a safety device (e.g., lens-shaped) is provided, the safety device comprising: Substrate; An observation element array, the observation element array being disposed in or on the substrate; and An image layer is disposed in or on the substrate and overlaps with the observation element array. The image layer includes a first image channel and a second image channel. The first image channel is formed by a set of first image channel positions associated with corresponding observation elements, and the second image channel is formed by a set of second image channel positions associated with corresponding observation elements. The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed of an image layer material that commonly defines the first image; wherein a first subset of the first image elements is formed of an image layer material exhibiting a first color, and a second subset of the first image elements is formed of an image layer material exhibiting a second color different from the first color; and The image layer includes at least one first color region that overlaps with a plurality of the observation elements. The first color region includes a first image channel position occupied by a first image element of a first subset and a first image channel position occupied by a first image element of a second subset, according to a first color ratio. Thus, the first color region is perceived as having a resultant color due to the combination of the first color and the second color.

[0031] Similar to the first aspect of the invention, the safety device according to the second aspect of the invention utilizes the fact that the human eye averages the visual effect of image elements on multiple viewing elements. In this way, the observer perceives at least one first color region of the presented image as having a composite color, which is due to a combination of the first and second colors of a first subset and a second subset of corresponding first image elements. This advantageously increases the ease with which devices for presenting complex multicolor images can be manufactured. For example, in the case where the image layer material is ink, fewer different colored inks need to be printed because the invention utilizes color mixing to achieve additional colors.

[0032] In one embodiment, each of the first subset of the first image elements is formed of the same image layer material (e.g., colored ink that presents the first color). Therefore, each of the first subset of the first image elements presents the same first color. In another embodiment, each of the second subset of the first image elements is formed of the same image layer material (e.g., colored ink that presents the second color), the image layer material being different from the image layer material forming the first subset of the first image elements. Therefore, each of the second subset of the second image elements presents the same second color.

[0033] The safety device according to the second aspect of the present invention is generally a lens-shaped safety device.

[0034] The first color region includes first image channel positions occupied by first image elements of the first subset according to a first color ratio, and first image channel positions occupied by first image elements of the second subset (e.g., different). In other words, the first color ratio is the ratio of the number of first image elements of the first subset to the number of first image elements of the second subset within the region. Typically, the first color region is completely contained within the horizontal region of the first image.

[0035] In one implementation, the first image channel position occupied by the first image elements of the first subset is different from the first image channel position occupied by the first image elements of the second subset. In other words, in one implementation, the first color region includes a first set of first image channel positions occupied by (e.g., only) the first image elements of the first subset and a second set of (different) first image channel positions occupied by (e.g., only) the first image elements of the second subset.

[0036] The first color region includes both the first image elements of the first subset and the first image elements of the second subset. In this way, the synthesized color differs from both the first and second colors. Typically, the first color region is perceived as having a uniform synthesized color.

[0037] Although the first image presented by the device is typically a multicolor image, this is not always the case. For example, in one embodiment, the first color proportions may be uniform across the entire device, resulting in a first image with uniform composite colors.

[0038] The use of color mixing according to embodiments of the invention may be particularly advantageous when the substrate of the security device is the substrate of a security document, such as a banknote, carrying the device. For example, printed matter (e.g., lithographic printing) applied to the banknote substrate outside the lateral extent of the security device itself can be applied using a first ink and a second ink of different colors. The first image elements of the security device's image layer can then be printed in the same printing step, exhibiting (different) composite colors produced by the color mixing of the first and second colors. This advantageously reduces the number of printing steps and the number of different inks required to form a security document carrying the device. This advantageously increases the ease with which the security device can be integrated into the document or article carrying the device.

[0039] In this article, "different colors" refers to colors that have a perceptible difference when observed with the naked eye. Typically, if two colors are in the CIELAB color space (i.e., CIE1976L...), then... a The Euclidean distance ΔE in the color space b) If the ΔE is greater than 2.3, preferably greater than 3, more preferably greater than 5, and even more preferably greater than 10, then the two colors will be perceived as different. The value is measured using the following formula:

[0040] Where ΔL , Δa and Δb These are two regions along L a and b The distance between axes (see G. Sharma (2003), *Digital Color Imaging Handbook* (ed. 1.7.2), CRC Press, ISBN 0-8493-0900-X, pp. 30-32). Difference ΔE Measurements can be taken using any commercial spectrophotometer, such as those available from Hunterlab, Reston, Virginia, USA.

[0041] Preferably, the first color region comprises a plurality of repeating first color regions, each presenting the first color proportion. In a manner corresponding to the first aspect of the invention, the term "repeated" herein refers to the arrangement of a first subset and a second subset of the first image elements, rather than a specific form of image layer material. Thus, each repeating region presents the same first color proportion. Using repeating regions in this way provides a convenient way to achieve the desired composite color across the entire first color region. In some embodiments, the color regions may have a predetermined size (e.g., corresponding to a predetermined number of observation elements).

[0042] In a manner similar to that discussed with respect to the first aspect of the invention, each color area may typically have a dimension of 500 µm or less, preferably 300 µm or less (e.g., maximum) (e.g., along a direction that alternates between the first and second image channel positions).

[0043] In a preferred embodiment, the image layer further includes a second color region comprising a first image channel position occupied by the first image elements of the first subset and a first image channel position occupied by the first image elements of the second subset, according to a second color ratio; wherein the first color ratio and the second color ratio are different, thereby the first color region and the second color region are perceived as having different colors. In this way, embodiments of the invention advantageously enable the presentation of complex multicolor images through the "color mixing" of the image elements forming the image.

[0044] Typically, the second color region comprises multiple repeating second color regions, each of which represents a proportion of the second color.

[0045] In a manner similar to that discussed with respect to the first aspect of the invention, preferably, each color region has a dimension of 300 µm or greater, more preferably 500 µm or greater, and more preferably 1 mm or greater (e.g., minimum). In this way, the human eye can perceive color differences between different color regions.

[0046] In some implementations, the first image element may further include a third subset, in addition to the first and second subsets, formed of image layer material that presents colors different from the first and second colors. Such implementations allow for more complex effects, such as CMYK color mixing.

[0047] In a safety device according to a second aspect of the invention, at least the first image channel is occupied by a corresponding set of first image elements. The second image channel may be a "blank" image channel, producing an "on / off switching" optical variable effect. The second image channel may be occupied by image elements defining a second image different from the first image, thereby the safety device exhibits an image switching effect when tilted.

[0048] In embodiments where the second image channel presents the second image, the second image may utilize color mixing as described with respect to the first image. Therefore, in some embodiments, the second image channel is occupied by a corresponding set of second image elements formed of an image layer material that commonly defines the second image, wherein a first subset of the second image elements is formed of an image layer material presenting a third color, and a second subset of the second image elements is formed of an image layer material presenting a fourth color different from the third color, and wherein, within at least one color region of the image layer, the image layer includes second image channel positions occupied by the second image elements of the first subset in proportion to the second color, and second image channel positions occupied by the second image elements of the second subset (e.g., different), whereby the color region is perceived as having a composite color due to the combination of the third and fourth colors. The third and fourth colors may be the same as the first and second colors, or may be colors different from the first and second colors.

[0049] In one embodiment, each of the first subset of the second image elements is formed of the same image layer material, and each of the second subset of the second image elements is formed of the same image layer material, which is different from the image layer material forming the first subset of the second image elements.

[0050] In this way, the safety device can advantageously present more than one complex multicolor image when tilted, which is achieved by the visual effect of the image layer perceived by the eye on the entire plurality of observation elements in the observation element.

[0051] In some embodiments, the image layer may include multiple color regions defining intermediate color segments located between two portions of the image layer that present different colors. Each color region within the intermediate color segment includes a different color proportion to present a perceived (e.g., gradual) color change across the entire intermediate color segment between the two portions. Including such intermediate color segments advantageously increases the complexity of the image by presenting a gradual color change rather than an abrupt change between the two portions. The portions of the image flanking the intermediate color region may be areas that present color mixing or may be single-color areas that do not present color mixing. To achieve a gradual color change across the domain of the intermediate color segment, the color proportions of the (e.g., continuous) regions defining the intermediate color segment are preferably different in a continuous manner.

[0052] The safety device of the present invention can be designed for observation under visible light illumination only, in which case each image defined by the corresponding set of image elements can be perceived by the observer under visible light illumination. In some embodiments of the invention, the device can utilize luminescent materials in the image layer (this term includes materials or substances having fluorescent or phosphorescent properties) to produce complex visual effects to further enhance the safety level of the device. Such luminescent materials typically respond to illumination of a specific wavelength or wavelength range outside the visible spectrum (typically in the ultraviolet (UV) region of the electromagnetic spectrum) by emitting light of a specific color characteristic of the material in question. Typically, the at least one excitation wavelength is at least one wavelength within the ultraviolet (UV) portion of the electromagnetic spectrum. In such cases, for simplicity, the excitation illumination condition can be referred to as “UV light” or “illumination under UV illumination.”

[0053] In some embodiments of the second aspect, the image layer material of the first subset of the first image element includes a first luminescent material that emits light in response to illumination at at least one excitation wavelength, and the image layer material of the second subset of the first image element includes a second luminescent material that emits light in response to illumination at at least one excitation wavelength; wherein the first luminescent material and the second luminescent material are different from each other, such that when illuminated with an excitation illumination condition including illumination at the at least one excitation wavelength, the first subset and the second subset of the first image element exhibit different visible luminescent colors; and further wherein when illuminated with a first illumination condition including illumination with visible light in the absence of the at least one excitation wavelength, the image layer material of the first subset and the image layer material of the second subset of the first image element have substantially the same appearance.

[0054] In this way, when observed under excitation illumination conditions, the observer perceives at least one first color region of the presented image as having a composite color resulting from the combination of the first and second colors of corresponding first and second subsets of the first image elements. Particularly advantageously, when observed under the first illumination conditions, the image layer materials of the first and second subsets have substantially the same visual appearance (e.g., substantially the same non-luminous visible colors). Therefore, a particularly striking change is observed between the observation device under the first illumination conditions (where the image appears to have substantially uniform color) and the excitation illumination conditions (where the (luminous) image exhibits a polychromatic appearance due to the mixing of luminous visible colors).

[0055] In such an embodiment, the image layer material is preferably an ink containing the luminescent material.

[0056] The term "non-luminescent visible color" refers only to the color (e.g., red, blue, yellow, green, brown, etc.) that appears when the device is illuminated with visible light in the absence of the at least one excitation wavelength. Similarly, the term "luminescent visible color" refers to the color that appears when the device is illuminated with an excitation wavelength (e.g., when observing the device under a UV lamp). "Visible light" refers to light with wavelengths within the visible spectrum (approximately 400 nm to 750 nm). Most preferably, visible light is white light, i.e., containing substantially all visible wavelengths in a substantially uniform proportion. For the sake of brevity, the first illumination condition "including illumination with visible light in the absence of the at least one excitation wavelength" may also be referred to herein as "visible light," "visible light only," or "non-UV light." The ultraviolet spectrum typically includes wavelengths from about 200 nm to about 400 nm.

[0057] As discussed above, the security device according to both the first and second aspects of the present invention includes a first image channel and a second image channel. In some embodiments, the device may include only the first image channel and the second image channel, and is therefore referred to as a "dual-channel" device. However, the present invention is also applicable to devices that include additional (e.g., a third, fourth, etc.) image channels. Generally, the present invention is applicable to all n-channel (e.g., lens-shaped) security devices, where n is greater than or equal to 2.

[0058] In this invention, the observation element array can take various forms. In a preferred embodiment, the observation element array includes a focusing element array (e.g., a lens). The focusing element can be adapted to focus light in one dimension, in which case the focusing element is preferably a cylindrical focusing element (e.g., an elongated one). Embodiments of the invention can also be applied to two-dimensional lens-like devices. In such embodiments, the observation element is adapted to focus light in at least two (e.g., non-parallel, preferably orthogonal) directions, in which case the observation element is preferably a spherical or aspherical focusing element.

[0059] The pitch of the observation element array (e.g., lens array) is typically in the range of 10 μm to 200 μm, preferably 20 μm to 200 μm, and more preferably 50 μm to 200 μm. The pitch of the observation elements is typically uniform across the entire array.

[0060] While observation elements typically take the form of focusing elements such as lenses, in some embodiments, the array of observation elements can be in the form of a mask grid. In such embodiments, each observation element typically includes substantially opaque regions and substantially transparent regions, such that the mask grid comprises a plurality of substantially opaque regions spaced apart by gap regions. The image layer can be observed through the substantially transparent regions.

[0061] Preferably, when the observation element is a focusing element, the image layer is located approximately within the focal plane of the focusing element array. The required spacing between the focusing element and the image layer can be provided by the substrate itself and / or any optical spacer layer or base layer as known in the art.

[0062] In a typical embodiment, the substrate is at least translucent (preferably completely transparent), and the observation element array is disposed in or on a first surface of the substrate, while the image layer is disposed in or on the opposite second surface of the substrate. It should be noted that the term "on" does not necessarily imply direct contact; for example, a primer layer may be present between the substrate and the observation element array. It should be understood that in such a configuration, the substrate needs to be at least translucent (the term "transparent" herein is used to mean optically transparent and free of scattering, although it may have a color tint). In this case, the substrate is typically formed of one or more polymeric materials, such as BOPP, PET, PE, PC, etc. In an alternative embodiment, the observation element may be disposed on the same side of the substrate as the image layer, for example, by incorporating an optical spacer layer in its design, or by providing a base layer that is at least translucent between the observation element and the image layer. In such embodiments, the substrate does not need to be translucent and can be of any type, opaque or otherwise. This includes paper substrates, although polymer-based substrates are preferred.

[0063] The image layer is preferably provided by a printed article, and is preferably printed by gravure printing, engraving gravure printing, screen printing, micro-engraving gravure printing, flexographic printing, or (wet or dry) offset printing techniques, or by digital printing techniques (e.g., inkjet or laser printing). With careful design and implementation, these techniques can be used to print image elements with linewidths between 10 μm and 100 μm (e.g., in staggered directions). For example, using flexographic printing or wet offset printing, linewidths as small as approximately 5 μm to 25 μm can be achieved. In this way, the image element can be described as a “micro-image” element. The image layer is typically formed as a single layer (“image layer”) disposed in or on a substrate. When provided as a printed article, the image layer is preferably formed in a single printing operation (e.g., one paper feed on a printing press). Other (non-printing) methods for forming the image layer can also be used. For example, the image element may be in the form of a metallized or demetallized region, a filled recess, a laser-marked region, or (e.g., a diffractive) surface relief structure (including first-order, zero-order, and subwavelength gratings, such as a plasmonic structure), or the image element may include a metallized or demetallized region, a filled recess, a laser-marked region, or (e.g., a diffractive) surface relief structure (including first-order, zero-order, and subwavelength gratings, such as a plasmonic structure). Other examples include cast or imprinted recesses (which may or may not be filled with marking material) and / or columnar structures.

[0064] A third aspect of the invention provides a security article comprising the security device as described above, wherein the security article is preferably a security thread, strip, foil, insert, transfer element, label, patch, or data page for a security document. The security article with the security device (e.g., as described above) can then be applied to a security document or any other object, or the security article with the security device can then be incorporated into a security document or any other object, for example, by hot stamping, cold stamping, via adhesive or lamination, or by introduction during the papermaking process.

[0065] A fourth aspect of the invention provides a security document comprising the security device or security article as described above, wherein the security document is preferably a banknote, check, passport, identity card, driver's license, certificate of authenticity, stamp duty, or other document used to protect value or personal identity. The security device can be formed directly on the security document, in which case the document substrate can be used as the substrate for the security device, or it can be formed on the security article and then applied to or incorporated into the security document as described above.

[0066] According to a fifth aspect of the present invention, a method for manufacturing (e.g., lens-shaped) a safety device is provided, the method comprising: (a) Providing a substrate; (b) Applying an array of observation elements to the substrate; and (c) An image layer is formed in or on the substrate, the image layer overlapping the observation element array, the image layer including a first image channel and a second image channel, the first image channel being formed by a set of first image channel positions respectively associated with a corresponding observation element, and the second image channel being formed by a set of second image channel positions respectively associated with a corresponding observation element, wherein... The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed by image layer material that collectively defines the first image; wherein, The image layer includes at least one region that is completely contained within the horizontal region of the first image and overlaps with the plurality of viewing elements. The at least one region has a first image tone ratio, which is the ratio of the number of first image channel positions occupied by the first image elements to the number of first image channel positions within the region; and wherein: (i) The image layer includes a first region and a second region with different first image tone ratios; and / or (ii) The second image channel is occupied by a corresponding set of second image elements formed by image layer material that commonly defines the second image, and in the at least one region of the image layer, the first image tone ratio is different from the second image tone ratio, which is the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions in the region.

[0067] The result of the method in the fifth aspect is a safety device as described above with respect to the first aspect of the invention, possessing all the advantages discussed. Any of the preferred features described above can be provided through appropriate modifications to the method.

[0068] In a preferred embodiment of the fifth aspect, the method may further include, prior to step (c), forming an image layer template by identifying regions of different tones within the first image; and in step (c), forming the image layer based on the image layer template. The image layer template is typically in the form of a computer file.

[0069] According to a sixth aspect of the present invention, a method for manufacturing (e.g., lens-shaped) a safety device is provided, the method comprising: (a) Providing a substrate; (b) Applying an array of observation elements to the substrate; and (c) An image layer is formed in or on the substrate, the image layer overlapping the observation element array, the image layer including a first image channel and a second image channel, the first image channel being formed by a set of first image channel positions respectively associated with a corresponding observation element, and the second image channel being formed by a set of second image channel positions respectively associated with a corresponding observation element, wherein... The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed of an image layer material that commonly defines the first image; wherein a first subset of the first image elements is formed of an image layer material exhibiting a first color, and a second subset of the first image elements is formed of an image layer material exhibiting a second color different from the first color; and The image layer includes at least one first color region that overlaps with a plurality of the observation elements. The first color region includes a first image channel position occupied by a first image element of a first subset and a first image channel position occupied by a first image element of a second subset, according to a first color ratio. Thus, the first color region is perceived as having a resultant color due to the combination of the first color and the second color.

[0070] The result of the method in the sixth aspect is a safety device as described above with respect to the second aspect of the invention, possessing all the advantages discussed. Any of the preferred features described above can be provided through appropriate modifications to the method.

[0071] In a preferred embodiment of the sixth aspect, the method may further include, prior to step (c), forming an image layer template by identifying one or more color mixing regions within the first image; and in step (c), forming the image layer according to the image layer template. The image layer template is typically in the form of a computer file. When forming the image layer template, the identified color mixing regions are used to generate a desired color ratio to be defined by the first color region of the image layer, such that the desired composite color is presented.

[0072] Typically, the image layer can be formed using printing techniques, preferably gravure printing, engraving gravure printing, screen printing, micro-engraving gravure printing, flexographic printing, offset printing, or digital techniques. Typically, the image layer is formed in a single printing step. However, other (non-printing) methods can be used to form the image layer, such as metallization, demetallization, casting and filling recesses, laser marking, and forming (e.g., diffraction) surface relief structures (including first-order, zero-order, and subwavelength gratings, such as plasma structures). Other examples include casting or imprinting recesses (which may or may not be filled with marking material) and / or columnar structures.

[0073] Observational elements (typically focusing elements) can be produced by known means such as imprinting or casting curing, and can be formed directly on a substrate, or formed on a separate substrate and then transferred from that separate substrate to the device, or the separate substrate can be attached to the device and subsequently become part of the device substrate. In some cases, observational elements can be applied to the substrate by forming (e.g., imprinting) the observational element into the substrate material itself.

[0074] The observation element array and the image layer can be arranged in any order. In other words, the observation element array can be applied to the substrate before the image layer is applied, and vice versa. However, in a preferred embodiment, the observation element (e.g., a lens) is applied to a first side of the substrate at the same location along the substrate, while the image layer is simultaneously applied to the opposite second side of the substrate. This simultaneous application of the observation element and the image layer advantageously provides highly accurate registration between them. Attached Figure Description

[0075] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 A security document embodying a conventional lens-like device known in the art is illustrated schematically. Figure 2 This is a cross-sectional view of a traditional lens-shaped device; Figure 3 (a) to Figure 3 (f) schematically illustrates a safety device according to an embodiment of the present invention; Figure 4 (a) to Figure 4 (e) schematically illustrates a safety device according to another embodiment of the present invention; Figure 5 (a) and Figure 5 (b) schematically illustrates a safety device according to another embodiment of the present invention; Figure 5A A safety device according to another embodiment of the present invention is illustrated schematically; Figure 6 (a) to Figure 6 (f) schematically illustrates a safety device according to another embodiment of the present invention; Figure 7 (a) to Figure 7 (f) schematically illustrates a safety device according to another embodiment of the present invention; Figure 8 (a) to Figure 8 (e) in the text shows more details. Figure 7 (a) to Figure 7 The safety device shown in (f) is part of the diagram; Figure 9 A safety device according to another embodiment of the present invention is illustrated schematically; Figure 10 A cross-sectional view schematically illustrates an apparatus according to another embodiment of the present invention; Figure 11 This is a flowchart illustrating the main steps of the method according to an embodiment of the present invention; Figure 12 This is a flowchart illustrating the main steps of a method according to another embodiment of the present invention; Figures 13(a), 14(a), and 15(a) show three exemplary security documents carrying a security device manufactured according to an embodiment of the present invention in plan view and Figures 13(b), 14(b), and 15(b) / 13(c) show three exemplary security documents in cross section view. Figure 16(a) is a front view, Figure 16(b) is a rear view, and Figure 16(c) is a cross-sectional view illustrating further embodiments of a safety document carrying a safety device manufactured according to an embodiment of the present invention; and Figure 17 A to Figure 17 The number I in the figure illustrates different examples of relief structures that can be used to form image layers in embodiments of the present invention. Detailed Implementation

[0076] For clarity, the various figures in this document use different shading patterns or colors to schematically illustrate the positions of image elements where different groups of image elements exist. The use of shading does not necessarily indicate the arrangement or color of the image layer material forming the image elements. The cross-sectional views schematically illustrate the position of the image layer material if it is required to be present at any particular location to form the corresponding image.

[0077] Figure 1 The security document 1000 is schematically illustrated in a plan view, here in the form of a banknote, which carries a conventional lens-shaped security device 101 known in the art. Figure 2 A schematic cross-sectional view of device 101 along line Q-Q' is shown. Device 101 includes a transparent substrate 10, which may or may not be the base substrate of a document. On a first side 10a of substrate 10, an array 20 of cylindrical lenses 21 is disposed, extending parallel to each other and into the plane of the paper (along the z-axis). On the opposite side 10b of substrate 10, device 101 includes an image layer 30 comprising a plurality of image elements formed of an image layer material (e.g., ink), which combine to form an image presented by the device. The thickness T of substrate 10 substantially corresponds to the focal length of the lenses 21, such that image layer 30 is formed substantially within the focal plane of lens array 20. In this example, image layer 30 is formed as a single image layer.

[0078] Figure 2The device is a dual-channel device, comprising a set of first image channel positions i1 and a set of second image channel positions i2, which are periodically staggered along the x-direction. The set of first image channel positions i1 together form a first image channel, and the set of second image channel positions together form a second image channel. As those skilled in the art will understand, each image channel position of a particular image channel occupies the same relative position below the corresponding lens. Here, in Figure 2 In the view, each first image channel position i1 of the first image channel occupies the "left" half of the corresponding lens corresponding to the viewing angle θ1, and each second image channel position i2 of the second image channel occupies the "right" half of the corresponding lens corresponding to the viewing angle θ2. In this example, each image channel position is in the form of an elongated linear element extending parallel to the elongation direction of the cylindrical lens (i.e., along the z-direction). In this way, the image channel positions of the image layer 30 and the lens array 20 are coordinated with each other such that at the first viewing angle θ1, light from the first image channel is directed to the observer, and at the second viewing angle θ2, light from the second image channel is directed to the observer.

[0079] In device 101, both the first and second image channels are occupied by image elements formed from image layer materials that combine to define the corresponding images. The situation where each image channel position is occupied by a corresponding image element is as follows: Figure 2 The cross-sectional view is indicated by shading. The position of the first image channel is occupied by the image element of image I1, which is commonly defined as visible at the viewing angle θ1, and the position of the second image channel is occupied by the image element of image I2, which is commonly defined as visible at the viewing angle θ2. Therefore, the device 101 exhibits an optically variable "image switching" effect when tilted between the viewing angles θ1 and θ2.

[0080] Figure 3 (a) to Figure 3 (f) schematically illustrates a lens-shaped safety device 100 according to an embodiment of the present invention. Figure 3 (a) illustrates the optically variable effect presented by the device, in this example an "on / off switch" effect between image I1 presented at a first viewing angle θ1 and a "blank" or "closed" view at a viewing angle θ2. In other words, no image is presented at viewing angle θ2. Image I1, presented by the image element occupying the first image channel, is a multi-tone image of a turtle. Image layer 30 includes five regions R1, R2, R3, R4, and R5 (respectively in…) Figure 3 (b) to Figure 3 As shown in (f), each region is located within the horizontal region of image I1. The different configuration of image elements in each region results in different perceptual densities or "hues" in the regions, which will now be described in more detail.

[0081] Figure 3 (b) to Figure 3 Each of the figures (f) shows a cross-sectional view of the device 100 (with the substrate omitted for clarity) and a plan view of the image layer 30 showing the arrangement of the image elements in more detail. Here, the illustrations indicate the presence or absence of each image element, rather than the specific form of each element required to form an image. Figure 3 (b) to Figure 3 (f) in each of the images shows a portion of the corresponding region (R1 to R5) of the image layer 30.

[0082] Now consider Figure 3 In (b), the region R1 with the darkest tone is shown. Because this is a dual-channel device, each lens of the lens array 20 is associated with a first image channel position and a second image channel position. Each second image channel position i2 is blank, thus presenting... Figure 3 The “blank” visual effect at viewing angle θ2 is shown in (a) above. For simplicity and clarity, Figure 3 In (b), only the two second image channel positions i2 are marked. In region R1, each first image channel position is occupied by an image element S1. Therefore, the tonal ratio of region R1 is 1:1. Region R1 can be considered to consist of multiple repeating regions Z1. The concept of the repeating regions will refer to... Figure 3 (c) to Figure 3 (f) in the text describes this in more detail.

[0083] Figure 3 (c) schematically illustrates the configuration of image layer 30 in the second region R2. In this region, a subset of the first image channel positions are not occupied by the first image elements. The unoccupied (or “off”) first image channel positions are shown at U1, while the image elements occupying the first image channel positions are shown at S1. Therefore, due to the presence of unoccupied first image channel positions throughout this region, region R2 will be perceived as having a brighter hue than region R1. Region R2 consists of multiple laterally consecutive repeating regions Z2. Each region Z2 has the same arrangement of occupied (“on”) and unoccupied (“off”) image elements and is considered repeating in this way, even though the specific arrangement of image layer material in each region differs (i.e., varies depending on the image). Therefore, each region Z2 presents the same image hue ratio, here 4:5; in other words, for every one “off” image channel position, there are four “on” first image channel positions.

[0084] In this embodiment, the lens pitch is 60 µm, each zone overlaps with five lenses, and the “width” D of each zone is 300 µm. Therefore, five different tonal levels can be achieved, varying between an image tonal ratio of 1:1 and 1:5. If additional tonal levels are desired, a convenient way to achieve this is to increase the size of the overlap between each zone and more focusing elements.

[0085] Figure 3 (d) Figure 3 (e) and Figure 3 (f) shows the image layer arrangement of regions R3, R4, and R5, which contain an increasing number of "off" first image channel locations, thus exhibiting increasingly brighter tones. The image tonal ratio of region R3 is 3:5, that of region R4 is 2:5, and that of region R5 is 1:5.

[0086] It should be noted that in this embodiment, the same image layer material (e.g., the same ink) is used to form each image element of the image layer (although this is not necessary). In this way, by forming (e.g., printing) image layer regions with different image tonal ratios, an image layer presenting a multi-tone image can be formed in a single manufacturing step (e.g., a single print feed).

[0087] Figure 4 (a) to Figure 4 (e) schematically illustrates a device 100 according to an embodiment of the present invention, which is presented with Figure 3 The device uses the same optically variable effects, but the perceived tonal differences across different areas of the presented image are achieved through different configurations of image layer 30. Figure 3 Like other devices, each second image channel is "off", giving the device an "on / off" optical variable effect.

[0088] Region R1 and Figure 3 The device presents a 1:1 image tone ratio in the same manner. However, in each of regions R2 to R5, the image tone ratio is defined by the arrangement of the positions of the first image channel "on" and "off" over the entire domain of the corresponding region, rather than by means such as Figure 3 The image layer 30 is defined by multiple repeating regions. In other words, the “off” image channel positions are not uniformly distributed across the entire area. In each of regions R2, R3, and R4, the image layer 30 includes a sub-region 32, which is spaced apart by sub-regions 34. In sub-region 32, the first image channel position is occupied by the first image element S1 (“on”); in sub-region 34, each first image channel position is not occupied by the first image element (“off”). Figure 4Region R5 shown in (e) includes a sub-region 32, which is laterally adjacent to sub-region 34. In sub-region 32, the first image channel position is occupied by the first image element S1, while in sub-region 34, each first image channel position is not occupied by a first image element. Although Figure 4 (b) to Figure 4 The arrangement shown in (e) achieves the desired image tonal ratio, but it is generally preferred to use an arrangement such as Figure 3 The multiple repeating areas shown are used to achieve the desired image tonal ratio, as this provides a more even distribution of color across the respective areas.

[0089] It should be noted that Figure 3 and Figure 4 The arrangement of the "on" and "off" channels shown is merely illustrative and is intended to illustrate the concept of the invention. It should be understood that in practice, the "on" and "off" channels will be arranged according to the dimensions of the area so that the eye perceives a uniform tone across the entire corresponding area.

[0090] Figure 5 (a) and Figure 5 (b) shows a lens-shaped security device 100 according to another embodiment of the present invention. In this embodiment, the device 100 presents an "image switching" optical variable effect, wherein a first image I1 is presented at a first viewing angle θ1, and a different second image I2 is presented at a second viewing angle θ2. Here, the first image I1 is in the form of a red numeral "5", while the second image I2 is in the form of a yellow diamond. Figure 5 (b) in the middle with Figure 3 and Figure 4 The configuration of image layer 30 is illustrated in a similar manner. Here, the first image channel position is occupied by a first image element (S1) formed by red ink, while the second image channel position is occupied by a second image element (S2) formed by yellow ink.

[0091] In this embodiment, different image tone ratios are used to reduce the difference in relative color saturation between the two images I1 and I2 (the red ink forming the first image I1 has a higher color saturation than the yellow ink defining the second image I2). Therefore, the first and second image channels are selectively filled with corresponding image elements, such that the first image channel presenting the first image has a lower image tone ratio than the second image channel presenting the second image. Figure 5Figure (b) shows a portion of image layer 30, which includes multiple repeating regions Z. As shown, the first image channel includes an occupied first image channel position (S1) and an unoccupied first image channel position (U1) in a 3:5 first image tone ratio. Conversely, each second image channel position is occupied by a second image element (S2), thus presenting a 1:1 color tone ratio.

[0092] In this way, when the device is observed and the viewing angle changes, the two images I1 and I2 are perceived as having a reduced color density difference compared to the case where both image channels are defined with a 1:1 color hue ratio.

[0093] Figure 5A An exemplary security device 100 according to an embodiment of the present invention is schematically illustrated. The device presents an "on / off" optically variable effect, wherein a multi-toned image I1 of a pen nib is presented at viewing angle θ1, while a blank appearance (not shown) is presented at viewing angle θ2. In this example, image layer 30 includes multiple regions R2, R3, R4 with different first image tone ratios to present a gradual tone change between the first region R1 and a laterally spaced second region R5, wherein regions R1 and R5 present different first image tone ratios (1:1 and 1:5, respectively). In this way, the multiple (continuous) regions R2, R3, and R4 define an intermediate segment ("IS") between the first region R1 and the second region R5. The gradual tone change (and the accompanying 3D effect in this case) across the entire intermediate segment IS is visible in image I1. Figure 5A In the example shown, the tonal ratio of the first image in the middle section changes from "4:5" in region R2 to "3:5" in region R3, and finally to "2:5" in region R4.

[0094] Figure 6 (a) to Figure 6 Image (f) schematically illustrates a security device 200 according to another embodiment of the invention, wherein image elements of different colors are advantageously used to generate complex multicolor images through color mixing. Figure 3 In a similar way, Figure 6 Image (a) shows the optical variable effect presented by device 200, while Figure 6 (b) to Figure 6 (f) in the diagram shows the configuration of the image layer 30 that provides the perceptual effect.

[0095] like Figure 6As shown in (a), the device 200 presents an "on / off" optically variable effect, in which a multicolor image I1 is presented at a first viewing angle θ1, while a blank appearance (no image) is presented at a second viewing angle θ2. Therefore, each second image channel position of the image layer is blank or "off". The first image channel positions are occupied by first image segments of different colors to generate multiple regions perceived as having different colors. In this example, a first subset (S1-1) of the first image elements has red (e.g., formed by red ink), while a second subset (S1-2) of the first image elements has yellow (e.g., formed by yellow ink). Image layer 30 includes four color regions R1, R2, R3, and R4, each located within a lateral region of the image, with different proportions of red and yellow image elements, thus presenting a color mixture. Image layer 30 also includes a region A1 in which only the first subset (S1-1) of image elements exists (in... Figure 6 As shown in (b) of the diagram), no color mixing is observed. Therefore, region A1 appears red.

[0096] Now refer to Figure 6 (c) to Figure 6 (f) describes in more detail the configuration of image layers 30 that present different composite colors in each color region R1 to R4 due to different color ratios.

[0097] like Figure 6 As shown in (c), the first color region R1 of image layer 30 comprises a plurality of repeating color regions Z1, each of which contains five first image channel positions. In each color region Z1, four of the five first image channel positions are occupied by image elements S1-1 of a first subset, while one of the five first image channel positions is occupied by image elements S1-2 of a second subset. This provides a 4:1 color ratio across the entire region R1. Therefore, color region R1 is perceived as representing a composite color resulting from the combination of the first image elements of the (red) first subset and the (yellow) second subset. In this example, each color region has a size D of 300 µm in the interlacing direction.

[0098] like Figure 6 As shown in (d), color region R2 comprises multiple color regions Z2, wherein the color ratio between the first subset and the second subset of the first image element is 3:2. Figure 6In color region R3 shown in (e), the color ratio in each color region Z3 is 2:3, while in color region R4, the color ratio in each color region Z4 is 1:4. Therefore, by using color mixing of two colors (red and yellow in this case) in different proportions, the image I1 presented by the device is perceived as including multiple regions of different colors.

[0099] In some alternative embodiments, the color mixing effect provided by the present invention can be used to generate an image I1 that presents a single uniform color across its entire domain. For example, in some embodiments, the color region R2 (presenting a 3:2 color ratio) can correspond to the entire image, such that image I1 is perceived as a single uniform synthetic color due to the color mixing between red and yellow inks.

[0100] If the image layer of the desired device and the printed matter outside the lateral area of ​​the image layer are formed in the same manufacturing step, and the printed matter is formed using red and yellow inks, then such an implementation may be advantageous.

[0101] Figure 7 (a) to Figure 7 (f) in the diagram shows the relationship with Figure 6 The similar safety device 200, but which exhibits an image switching effect when tilted. The first image channel is essentially as described in the reference. Figure 6 The image elements of the second image channel, which are defined as the second multicolor image I2 presented at the viewing angle θ1, are also occupied by the image elements of the second multicolor image I2 presented at the viewing angle θ2.

[0102] In the first region A1 of the image layer ( Figure 7 As shown in (b)), each first image channel position is occupied by a first image element of a first subset (defined by red ink), while each second image channel position is occupied by a second image element of a first subset (defined by yellow ink). This arrangement is... Figure 8 As shown more clearly in (a), a first subset of the first image elements is labeled S1-1, and a first subset of the second image elements is labeled S2-1. In the first color region R1 of the image layer 30 that presents color mixing ( Figure 7 As shown in (c), both the first and second image channels contain corresponding first and second subsets of image elements, and the region includes multiple repeating regions Z1. Figure 8(b) in the diagram more clearly shows the configuration of the image elements within region Z1. The first image channel position is occupied by a first subset (S1-1) of the first image elements defined by red ink and a second subset (labeled S1-2) of the first image elements defined by yellow ink. Similarly, the second image channel position is occupied by a second subset (S2-1) of the first image elements defined by yellow ink and a second subset (labeled S2-2) of the second image elements defined by red ink. In the first color region R1, both the first and second image channels exhibit a 4:1 color ratio.

[0103] Image layer color region R2 ( Figure 7 (c) shows that it includes multiple repeating regions Z2 (a single repeating region Z2 in Figure 8 (shown in more detail in (c)) where both the first and second image channels exhibit a 3:2 color ratio. The color region R3 of the image layer ( Figure 7 (d) in the diagram includes multiple repeating regions Z3 (in Figure 8 (shown in more detail in (d)) where both the first and second image channels present a 2:3 color ratio. In color region R4 ( Figure 7 As shown in (e), it includes multiple repeating regions Z4 (in Figure 8 (as shown in more detail in (e)), the first and second image channels each present a 1:4 color ratio.

[0104] exist Figure 7 In an exemplary embodiment, the first image elements of the first subset are formed with the same (red) ink as the second image elements of the second subset, and the first image elements of the second subset are formed with the same (yellow) ink as the second image elements of the first subset. Furthermore, in each region of the image layer, the first and second image channels exhibit the same color proportions. This produces a unique "reverse color" effect achieved when switching the viewing angle from θ1 to θ2 using only two inks. However, this symmetry between the first and second image channels is not required, and in other embodiments, the colors and color proportions of the second image channels may differ from those of the first image channels. It is also conceivable that the second image may differ from the first image in both graphic form and color.

[0105] So far, we have considered color mixing between the first and second colors within an image channel. In other words, the image elements occupying a specific image channel and defining the image include a first subset of image elements presenting the first color and a second subset of image elements presenting the second color. It is conceivable that image elements occupying a specific image channel could include more than two subsets of different colors, thereby utilizing more complex color mixing effects such as CMYK color mixing to present multicolor images. In this case, the color ratio within a specific region of the image layer would represent the relative proportions of three (or more) subsets of image elements. For example, in an RGB system, the region of the first image layer that is expected to present yellow would have a color ratio of 1:1:0.

[0106] Figure 9 An exemplary safety device 200 according to another embodiment of the present invention is illustrated schematically. This device is similar to... Figure 6 The device described herein features an "on / off" optically variable effect between presenting a multicolor image I1 of a turtle at a viewing angle θ1 and a blank appearance (not shown) at a second viewing angle θ2. In this example, image layer 30 includes multiple color regions for presenting a gradual color change between two monochrome regions (labeled A1 and A2) rather than an abrupt change between the two colors. Figure 9 A portion of image layer 30 is shown, illustrating this gradual transition between a first region (A1) and a second region (A2). In the first region, each first image channel position is occupied by a (red) image element of a first subset S1-1, and in the second region, each first image channel position is occupied by a (yellow) image element of a second subset S1-2. Between regions A1 and A2, the image layer includes multiple color regions R1, R2, R3, and R4, where the color ratio changes sequentially from a 4:1 ratio (i.e., a mixture with more red than yellow) in color region R1 to a 1:4 ratio (i.e., a mixture with more yellow than red) in color region R4. Here, color region R1 defines a 4:1 color ratio, color region R2 defines a 3:2 color ratio, color region R3 defines a 2:3 color ratio, and color region R4 defines a 1:4 color ratio.

[0107] In this way, the eye perceives a smooth color change from red to yellow across the entire color region R1 to R4. The multiple color regions R1 to R4 can be considered as "intermediate color segments" ("ICS") defining the image layer. The visual effect of ICS is... Figure 9 Image I1 illustrates two such intermediate color segments. By gradually “blending” the colors between the two regions A1 and A2 (rather than presenting abrupt color changes between the two regions), the perceived image exhibits additional complexity, thus increasing the difficulty of forgery.

[0108] exist Figure 9 In the example, the two regions A1 and A2 on either side of the intermediate color segment ICS contain only a subset of image elements (region A1 contains only the first subset of image elements (red), and region A2 contains only the second subset of image elements (yellow)), thus not presenting color mixing. However, this is not necessary, and in other embodiments, the intermediate color segment ICS can be located between the two regions that display color mixing.

[0109] As described herein, in a preferred embodiment, the observation element is in the form of a focusing element such as a lens. In an alternative embodiment of the invention, the device 100 may alternatively include a mask grid 90 ( Figure 10 An array of observation elements (shown) in the form of a mask grating includes substantially opaque regions 93 spaced apart by substantially transparent regions 95 (e.g., defined by gaps between the opaque regions). The transparent regions 95 cooperate with the image layer 30 such that light from different image channels is directed to the observer at different viewing angles, as shown. Figure 10 In the example, at the first viewing angle θ1, light from the first image channel position i1 is directed to the observer, while at the second viewing angle θ2, light from the second image channel position i2 is directed to the observer, as shown in the figure.

[0110] Figure 11 This is a flowchart outlining the steps of a preferred method 300 for forming a safety device according to an embodiment of the present invention. The steps of the method will relate to... Figure 3 The example device shown is described below.

[0111] In step S301, an image to be displayed by the device is provided. In this example, the device 100 to be formed presents a single image I1 at a first viewing angle θ1, while presenting a "blank" appearance at a second viewing angle θ2. Therefore, image I1 is provided in step S301. However, this method can also typically be used to manufacture security devices that present two (or more) images depending on the viewing angle, such as reference... Figure 5 The aforementioned device.

[0112] In step S303, regions with different tones or perceived densities within the image are determined. Here, image I1 includes, for example... Figure 3 (b) to Figure 3 The five different hue regions identified in (f) are shown.

[0113] In step S305, the identified different tonal regions are used to form an image layer template. The image layer template defines the filling of image channel positions within the region of the image layer corresponding to the image region identified in step S303. More specifically, the image layer template defines the image tonal ratio corresponding to the identified image region for each region (R1, R2, R3, R4, R5) of the image layer. In a preferred embodiment, the template defines repeating regions within each region, each of which defines occupied and unoccupied image layer positions to achieve the desired tonal ratio. In some embodiments, the regions may have a predetermined size (e.g., corresponding to a predetermined number of observation elements).

[0114] Templates can typically be in the form of computer files.

[0115] In step S307, a substrate is provided. The substrate can be provided in any form and as part of any suitable process for manufacturing the safety device, such as a process based on roll or sheet feeding. As mentioned above, the substrate is typically transparent (e.g., polymer substrates such as BOPP, PET, PE, or PC), but in some alternative embodiments it can be translucent or opaque (e.g., opaque polymers or paper). Then, in steps S309 and S311, the observation element and the image layer are applied to the substrate, respectively. As discussed herein, the observation element is preferably a focusing element in the form of a cylindrical, spherical, or aspherical lens and can be formed using techniques known in the art such as imprinting or casting curing.

[0116] In step S311, an image layer is formed according to the image layer template formed in step S305. As described above, in a preferred embodiment, the image layer is provided in the form of a printed article, formed by a printing technique, preferably gravure printing, engraved gravure printing, micro-engraved gravure printing, flexographic printing, or offset printing, or digital printing such as inkjet printing. However, in other embodiments, the image layer can be formed by any of the following methods: laser marking; forming an embossed structure, preferably cured by imprinting or casting, wherein the embossed structure is configured to produce structural colors, preferably diffraction or plasma embossed structures; forming an embossed structure, preferably cured by imprinting or casting, and applying marking material to its recesses or protrusions; or demetallization of a metal or metal alloy layer. Suitable apparatus, materials, and methods disclosed herein for forming embossed structures such as focused features, and suitable printing techniques for forming printed articles are described in WO-A-2018 / 153840 and WO-A-2017 / 009616.

[0117] It should be understood that steps S309 and S311 can be performed in any order. For example, the image layer can be applied before the observation element, or the observation element and the image layer can be applied simultaneously. Simultaneous application can achieve high-precision registration between the observation element and the image segment. Additional steps, such as providing an additional layer or security feature on the substrate, can be performed before and / or after steps S309 and S311.

[0118] Figure 12 This is a flowchart outlining the steps of a preferred method 400 for forming a safety device according to an embodiment of the present invention. The steps of the method will be discussed in detail below. Figure 6 The example device shown is described below.

[0119] In step 401, an image to be displayed by the device is provided. In this example, the device 200 to be formed presents a single multicolor image I1 at a first viewing angle θ1, while presenting a "blank" appearance at a second viewing angle θ2. Therefore, image I1 is provided in step S401. However, this method can also be used to manufacture security devices that present two (or more) images depending on the viewing angle, such as reference... Figure 7 The aforementioned device.

[0120] In step S403, the color mixing regions within the image are determined. Here, image I1 contains four regions utilizing color mixing, such as... Figure 7 (c) to Figure 7 As shown in (f) in the diagram. Although Figure 6 The image I1 comprises multiple regions employing color mixing to present different colors, but as discussed herein, in some embodiments, the image presented by the device may be defined as a single uniform color achieved through uniform color mixing across the entire domain of the image. Such an implementation may be particularly advantageous in use cases where the image layer material (e.g., ink) of the different colors used to generate the composite color presented in the image is also used for printing outside the lateral spacing of the device. Therefore, the image layer and the additional printing separated laterally from the security device can be applied in a single paper feed.

[0121] In step S405, the identified color mixing regions are used to form an image layer template (e.g., in the form of a computer file). The image layer template defines the color ratios of a first subset and a second subset of a first image segment corresponding to the image region identified in step S303 in each color region (R1, R2, R3, R4) of the image layer. In a preferred embodiment, the template defines repeating color regions within each color region, wherein each color region defines the image layer position to be occupied by the first subset and the second subset to achieve the desired color ratio. In some embodiments, the color regions may have a predetermined size (e.g., corresponding to a predetermined number of observation elements).

[0122] In step S407, a substrate is provided, while in steps S409 and S411, an observation element is applied and an image layer is formed according to an image layer template. Steps S407, S409, and S411 are performed in the same manner as described above with reference to steps S307, S309, and S311.

[0123] The aforementioned types of security devices can be incorporated into or applied to any product requiring authenticity verification. In particular, such devices can be applied to or incorporated into valuable documents such as banknotes, passports, driver's licenses, checks, and identity cards. Image layers and / or complete security devices can be formed directly onto the security document (preferably using the methods described in WO-A-2018 / 153840 and WO-A-2017 / 009616), or can be provided as part of a security article (such as a security thread or patch), which can then be applied to or incorporated into such documents.

[0124] Such security features can be fully disposed on the surface of the base material of a security document (e.g., in the case of strips or patches), or can be only partially visible on the surface of the document base material, for example, in the form of a windowed security thread. Security threads are now present in many currencies around the world, as well as vouchers, passports, traveler's checks, and other documents. In many cases, the thread is provided in a partially embedded or windowed manner, where the thread appears to be woven into and out of the paper and is visible through a window on one or both surfaces of the base material. One method for producing paper with a so-called windowed thread can be found in EP-A-0059056. EP-A-0860298 and WO-A-03095188 describe different methods for embedding wider, partially exposed threads into a paper base material. Wide threads (typically 2 mm to 6 mm wide) are particularly useful because the additional exposed surface area allows for better utilization of optically variable devices, such as those disclosed in this invention.

[0125] Safety articles can be incorporated into or onto a paper or polymer-based substrate such that they are visible from both sides of the finished safety substrate at at least one window in the document. Methods of incorporating safety elements in this manner are described in EP-A-1141480 and WO-A-03054297. In the method described in EP-A-1141480, one side of the safety element is fully exposed at one surface of the substrate in which the safety element is partially embedded, and partially exposed at a window on the other surface of the substrate.

[0126] Suitable base substrates for manufacturing security substrates for secure documents can be formed from any conventional material, including paper and polymers. Techniques for forming substantially transparent areas in each of these types of base substrates are known in the art. For example, WO-A-8300659 describes a polymer banknote formed from a transparent substrate that includes an opaque coating on both sides of the substrate. The opaque coating is omitted in localized areas on both sides of the substrate to form transparent areas. In this case, the transparent substrate can be an integral part of a security device, or a separate security device can be applied to the transparent substrate of the document. WO-A-0039391 describes a method for manufacturing transparent areas in a paper substrate. Other methods for forming transparent areas in paper substrates are described in EP-A-723501, EP-A-724519, WO-A-03054297, and EP-A-1398174.

[0127] The safety device can also be applied to one side of the paper substrate, optionally partially located in an opening formed in the paper substrate. An example of a method for producing such an opening can be found in WO-A-03054297. An alternative method incorporating a safety element visible in an opening on one side of the paper substrate and fully exposed on the other side of the paper substrate can be found in WO-A-2000 / 39391.

[0128] Examples of valuable documents and technologies used in conjunction with security devices will now be described with reference to Figures 13 through 16.

[0129] Figure 13 depicts an exemplary valuable document 1500, here in the form of a banknote. Figure 13(a) shows the banknote in plan view, while Figure 13(b) shows a cross-section of the same banknote along line X-X', and Figure 13(c) shows a cross-section of a banknote variant. In this case, the banknote is a polymer (or hybrid polymer / paper) banknote having a transparent substrate 10. Two opaque layers 1505a and 1505b are applied to either side of the transparent substrate 10; they may take the form of an opaque coating, such as white ink, or may be a paper layer laminated to the substrate 10.

[0130] Opaque layers 1505a and 1505b are omitted in selected areas 1502 (and 1502'), each forming a window in which security devices 100 and 100' are located. In Figure 13(b), security device 100 is disposed within window 1502, focusing element array 20 is arranged on one surface of transparent substrate 10, and image layer 30 is arranged on the other surface of transparent substrate 10. Figure 13(c) shows a variation in which a second security device 100' is also disposed on banknote 1500 in a second window 1502'. If desired, the arrangement of the second security device 100' can be reversed, such that its optically variable effect is visible from the side of the security document opposite to device 100.

[0131] It will be understood that, if necessary, any or all windows 1502, 1502' may alternatively be "half-windows" in which the opaque layer (e.g., 1505a or 1505b) is continuous over all or part of the image layer 30. Depending on the opacity of the opaque layer, the half-window area will tend to have a semi-transparent appearance relative to the surrounding areas on either side of the opaque layers 1505a and 1505b.

[0132] In Figure 14, banknote 1600 is a banknote based on conventional paper, which is provided with a security feature 1601 in the form of a security thread inserted during the papermaking process such that it is partially embedded in the paper, so that portions of paper 1605a and 1605b are located on either side of the thread. This can be accomplished using the technique described in EP0059056, in which no paper is formed in the window areas during the papermaking process, thus exposing the security thread 1601 in the window areas 1602a, 1602b, and 1602c of the banknote. Alternatively, the window areas 1602a, 1602b, and 1602c can be formed, for example, by abrading the surface of the paper in these areas after the thread is inserted. It should be noted that the window area does not have to be a “full-thickness” window: if preferred, the thread 1601 may be exposed on only one surface. For example, in some embodiments, the window is a “half-thickness” window, and the paper is continuous on one side of the image layer 30, with only the lens array 20 exposed. The safety device is formed on line 1601, which includes a transparent substrate, a focusing array 20 disposed on one side, and an image layer 30 disposed on the other side. Windows 1602a, 1602b, and 1602c expose portions of device 100, which may be formed continuously along the line. (In the figures, the lens array is depicted as discontinuous between each exposed area on the line, although this is not usually the case in practice, and the lens array (and image layer) will be formed continuously along the line.) Alternatively, multiple safety devices may be spaced apart from each other along the line, as in the depicted embodiment, with each device displaying a different or the same image.

[0133] In Figure 15, banknote 1700 is a conventional paper-based banknote, which is provided with a strip element or insert 1703. The strip element 1703 is based on a transparent substrate and is inserted between two paper layers 1705a and 1705b. The security device 100 is formed by a focusing feature array provided by lens array 20 on one side of the strip substrate 1703 and an image layer 30 provided by lens array 20 on the other side of the strip substrate 1703. The paper layers 1705a and 1705b are perforated in region 1702 to expose the security device 100. In this case, the security device 100 may be present throughout the entire strip element 1703 or may be located locally within the perforation region 1702. It should be noted that the paper layer 1705b does not need to be perforated and may be continuous across the security device.

[0134] Figure 16 illustrates another embodiment, with Figures 16(a) and 16(b) showing the front and back sides of document 1800, respectively, and Figure 16(c) being a cross-sectional view along line Z-Z'. The security item 1803 is a strip or band comprising the security device 100 according to any of the embodiments described above. Using the method described in EP-A-1141480, the security item 1803 is formed as a security document 1800 comprising a fiber substrate 1805. The strip is incorporated into the security document such that it is fully exposed on one side of the document (Figure 16(a)) and in one or more windows 1802 on the opposite side of the document (Figure 16(b)). Similarly, the security device 100 is formed on the strip 1803 comprising a transparent substrate, wherein a lens array 20 is formed on one surface, and a mating image layer 30 as previously described is formed on the other surface.

[0135] Alternatively, a similar structure can be achieved by providing a piece of paper 1800 with orifices 1802 and attaching a strip element 1803 across the orifices 1802 to one side of the paper 1800. The orifices can be formed during or after the papermaking process, for example by die-cutting or laser cutting.

[0136] In yet another embodiment, the complete security device 100 can be formed entirely on one surface of the security document, which can be transparent, translucent, or opaque, as is the case with banknotes regardless of any window area. The image layer 30 can be attached to the surface of the substrate, for example, by applying the image layer 30 directly to the substrate, or by forming the image layer 30 on another film and then adhering the film to the substrate by adhesive, thermal stamping, or cold stamping, either together with or in a separate process, wherein the focusing array 20 is subsequently applied.

[0137] Typically, when applying safety articles (e.g., strips or patches) carrying safety devices to a document, it is preferable to bond the articles to the document substrate to avoid contact between the focusing elements (e.g., lenses preferably used to produce the desired optical effect) and the adhesive, as such contact would render the lenses inoperable. For example, the adhesive can be applied in a pattern to the lens array such that the intended window areas of the lens array are uncoated, and then the strips or patches are applied in alignment (in the longitudinal direction of the substrate) so that the uncoated lens areas are aligned with the substrate holes or windows.

[0138] The safety device of the present invention can be made machine-readable by introducing a detectable material in any layer or by introducing a separate machine-readable layer. Detectable materials that respond to external stimuli include, but are not limited to, fluorescent, phosphorescent, infrared-absorbing, thermochromic, photochromic, magnetic, electrochromic, conductive, and piezochromic materials. In particular, including such detectable materials in the image layer can provide additional reliable visual effects.

[0139] Additional optically variable devices or materials, such as thin-film interference elements, liquid crystal materials, and photonic crystal materials, can be included in the safety device. These materials can be in the form of film layers or pigment materials suitable for application by printing. If these materials are transparent, they can be included in areas of the same device as the safety features of the present invention, or alternatively, if they are opaque, they can be positioned in separate, laterally spaced areas of the device.

[0140] The safety device may include a metal layer spaced laterally from the safety features of the present invention. The presence of the metal layer can be used to conceal the presence of a machine-readable dark magnetic layer. When magnetic material is incorporated into the device, the magnetic material can be applied in any design, but common examples include using magnetic tracks or using magnetic blocks to form a coded structure. Suitable magnetic materials include iron oxide pigments (Fe2O3 or Fe3O4), barium or strontium ferrite, iron, nickel, cobalt, and alloys of these. In this context, the term "alloy" includes materials such as nickel:cobalt, iron:aluminum:nickel:cobalt, etc. Sheet nickel material can be used; additionally, sheet iron material is also suitable. Typical nickel sheets have lateral dimensions ranging from 5 to 50 micrometers and a thickness of less than 2 micrometers. Typical sheet iron has lateral dimensions ranging from 10 to 30 micrometers and a thickness of less than 2 micrometers.

[0141] In alternative machine-readable embodiments, the transparent magnetic layer can be incorporated at any location within the device structure. WO03091953 and WO03091952 describe a suitable transparent magnetic layer comprising a distribution of magnetic material particles of a given size, and the magnetic layer having a concentration distribution that maintains the transparency of the magnetic layer.

[0142] Negative or positive markings can be created in a metallic layer or any suitable opaque layer. One method for producing partially metallized / demetallized films (where no metal is present in controlled and well-defined areas) is to selectively demetallize the areas using resist and etching techniques, as described in, for example, US-B-4652015. Other techniques for achieving similar effects include, for example, vacuum deposition of aluminum using a mask, or selective removal of aluminum from a composite strip of a plastic carrier and aluminum using an excimer laser. Metallic areas can alternatively be provided by printing with metallic effect inks that have a metallic appearance, such as Metalstar® inks sold by Eckart.

[0143] As previously stated, while printed matter is a preferred type of structure suitable for providing image layers, embossed structures can also be utilized in embodiments of the present invention. It will be understood that, in cases where more than one structure needs to present different corresponding colors, these can be embodied as different portions of a single embossed structure with correspondingly different characteristics. Various embossed structures suitable for forming image segments in embodiments of the present invention are applicable in... Figure 17 A to Figure 17 As shown in I. Therefore, Figure 17 A in the figure shows an image region of an image segment (IM) in the form of an imprinted or recessed area, while the unimprinted portion corresponds to the non-imaging area (NI) of the segment. Figure 17 B in the figure shows the image area of ​​the segment in the form of a concave or convex line. A colored marking material (e.g., ink or resin) may be applied to the embossed portion to provide the desired color to the image segment, as described in WO-A-2005052650.

[0144] In another approach, the relief structure can be a diffraction grating ( Figure 17 C in the middle) or moth eye / detail grating ( Figure 17 In the case where an image segment is formed by a diffraction grating, different parts of the image (within one image segment or in different segments) can be formed by gratings with different properties. Preferred methods for writing such gratings include electron beam writing or lattice writing techniques.

[0145] like Figure 17 E and Figure 17 As shown in the diagram, the F values ​​represent the diffraction gratings used for moth-eye / detail-range gratings. These gratings can also be located on recesses or protrusions (e.g., ...). Figure 17 A and Figure 17 (Those in B of the list).

[0146] Figure 17 G in the diagram illustrates a simple scattering structure that provides an achromatic effect.

[0147] In addition, in some cases, Figure 17 The recessed part of A in the figure can be filled with ink, or Figure 17 The recessed or raised areas in section B can be inked. The latter... Figure 17 As shown in H, ink layer 1910 is disposed on protrusion 1900. Therefore, each image segment can be produced by forming a suitable raised area or protrusion in a resin layer disposed on a transparent substrate. This can be achieved, for example, by casting curing or imprinting. Then, colored ink is typically transferred to the raised area using lithographic, flexographic, or gravure processes. Figure 17 The letter I in the figure illustrates the use of the Aztec structure.

[0148] As briefly discussed above, materials that respond to external stimuli can be used to produce striking optical effects. One example of such a material that can be used in this way is luminescent ink, which will now be described.

[0149] Considering the above reference Figure 5 The discussed implementation uses different image tone ratios to reduce the difference in relative color saturation between two images I1 and I2. This variation in image tone ratios can be advantageously utilized under different lighting conditions. For example, both the first image element (S1) and the second image element (S2) can be formed of luminescent ink. The ink forming the first image element can be a green ink that emits red light (under visible light illumination), while the ink forming the second image element can be a green ink that emits yellow light (under visible light illumination). Therefore, when the device is viewed under visible light, both images appear green. Then, under UV illumination, the first image I1 appears red, while the second image appears yellow. Due to the difference in image tone ratios across the entire image layer, the image perceived under UV illumination exhibits a reduced color density difference.

[0150] As another example of the use of luminescent materials, consider the above reference. Figure 6 The described implementation uses color regions of an image layer with different image element color ratios to generate a multicolor image through color mixing. Consider the following case: a first subset (S1-1) of the first image elements is formed by red-emitting green ink, while a second subset (S1-2) of the first image elements is formed by yellow-emitting green ink. When viewed under visible light illumination, the turtle image I1 will appear with a substantially uniform green color. However, when viewed under UV illumination, image I1 will have a multicolor appearance depending on the color ratios of color regions R1, R2, R3, and R4. This variation in color characteristics under different lighting conditions provides a particularly striking optical effect that is easy to authenticate and difficult to forge.

[0151] Examples of suitable ink formulations that can be used in embodiments of the present invention and exhibit different effects under different lighting conditions can be found in WO2004 / 050376, WO2018 / 206936 and WO2024 / 180326.

Claims

1. A safety device, the safety device comprising: Substrate; An observation element array, wherein the observation element array is disposed in the substrate or on the substrate; as well as An image layer is disposed in or on the substrate and overlaps with the observation element array. The image layer includes a first image channel and a second image channel. The first image channel is formed by a set of first image channel positions associated with corresponding observation elements, and the second image channel is formed by a set of second image channel positions associated with corresponding observation elements. The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed by image layer material that collectively defines the first image; wherein, The image layer includes at least one region, which is completely contained within the horizontal region of the first image and overlaps with the plurality of viewing elements. The at least one region has a first image tone ratio, which is the ratio of the number of first image channel positions occupied by the first image elements to the number of first image channel positions within the region; and wherein: (i) The image layer includes a first region and a second region with different first image tone ratios; and / or (ii) The second image channel is occupied by a corresponding set of second image elements formed by image layer material that commonly defines the second image, and in the at least one region of the image layer, the first image tone ratio is different from the second image tone ratio, which is the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions in the region.

2. The safety device according to claim 1, wherein, Each first image element is formed from the same image layer material.

3. The safety device according to claim 1 or 2, wherein, Each second image element is formed from the same image layer material.

4. The safety device according to any one of the preceding claims, wherein, The at least one region includes a plurality of repeating regions, each of which presents the first image tone ratio.

5. The safety device according to claim 4, wherein, Both the first region and the second region include multiple repeating areas, each of which presents its own first image tone ratio.

6. The safety device according to claim 5, wherein, Both the first region and the second region include the first image channel position that is not occupied by the first image element.

7. The safety device according to claim 4, wherein, The second image channel is occupied by a corresponding set of second image elements, and wherein the at least one region comprises a plurality of repeating regions, each of the plurality of repeating regions presenting the first image tone ratio and the second image tone ratio.

8. The safety device according to any one of claims 4 to 7, wherein, Within the at least one region, each of the regions is horizontally continuous.

9. The safety device according to any one of claims 4 to 8, wherein, Each region has a minimum dimension of 300 µm or greater, preferably 500 µm or greater, and more preferably 1 mm or greater.

10. The safety device according to any one of the preceding claims, wherein, The image layer includes multiple regions defining an intermediate segment located between two regions of the image layer with different first image tone ratios, wherein each region within the intermediate segment includes a different first image tone ratio to present a perceived tone variation across the entire intermediate segment between the two regions.

11. A safety device, the safety device comprising: Substrate; An observation element array, wherein the observation element array is disposed in the substrate or on the substrate; as well as An image layer is disposed in or on the substrate and overlaps with the observation element array. The image layer includes a first image channel and a second image channel. The first image channel is formed by a set of first image channel positions associated with corresponding observation elements, and the second image channel is formed by a set of second image channel positions associated with corresponding observation elements. The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed of an image layer material that commonly defines the first image; wherein a first subset of the first image elements is formed of an image layer material exhibiting a first color, and a second subset of the first image elements is formed of an image layer material exhibiting a second color different from the first color; and The image layer includes at least a first color region that overlaps with a plurality of the observation elements. The first color region includes a first image channel position occupied by the first image elements of the first subset and a first image channel position occupied by the first image elements of the second subset, according to a first color ratio. Thus, the first color region is perceived as having a composite color due to the combination of the first color and the second color.

12. The safety device according to claim 11, wherein, The first color region includes a plurality of repeating first color regions, each of the plurality of repeating first color regions presenting the first color proportion.

13. The safety device according to claim 11 or 12, wherein, The image layer further includes a second color region, which includes a first image channel position occupied by the first image elements of the first subset and a first image channel position occupied by the first image elements of the second subset, according to a second color ratio; wherein... The first color ratio and the second color ratio are different, so the first color region and the second color region are perceived as having different colors.

14. The safety device according to claim 13, wherein, The second color region includes a plurality of repeating second color regions, each of which presents the second color proportion.

15. The safety device according to any one of claims 12 to 14, wherein, Each color area has a minimum size of 300 µm or greater, preferably 500 µm or greater, and more preferably 1 mm or greater.

16. The safety device according to any one of claims 11 to 15, wherein, The second image channel is occupied by a corresponding set of second image elements formed of an image layer material that commonly defines the second image, wherein a first subset of the second image elements is formed of an image layer material exhibiting a third color, and a second subset of the second image elements is formed of an image layer material exhibiting a fourth color, which is different from the third color, and wherein... In at least one color region of the image layer, the image layer includes a second image channel position occupied by the second image elements of the first subset and a second image channel position occupied by the second image elements of the second subset according to the second color ratio, thereby the color region is perceived as having a composite color due to the combination of the third color and the fourth color.

17. The safety device according to any one of claims 11 to 16, wherein, The image layer includes multiple color regions defining intermediate color segments located between two portions of the image layer that present different colors. Each color region within the intermediate color segment includes a different color proportion to present a perceived color change across the entire intermediate color segment between the two portions.

18. The safety device according to any one of claims 11 to 17, wherein, The image layer material of the first subset of the first image element includes a first luminescent material that emits light in response to illumination at at least one excitation wavelength, and The image layer material of the second subset of the first image element includes a second luminescent material that emits light in response to illumination at at least one excitation wavelength; wherein, The first luminescent material and the second luminescent material are different from each other, such that when illuminated by excitation lighting conditions including illumination at the at least one excitation wavelength, the first subset and the second subset of the first image element exhibit different visible luminescent colors; and furthermore... When illuminated with a first illumination condition including visible light illumination in the absence of the at least one excitation wavelength, the image layer material of the first subset of the first image element and the image layer material of the second subset of the first image element exhibit substantially the same appearance.

19. The safety device according to any one of the preceding claims, wherein, At least one image presented by the device is in the form of a sign or mark, preferably, at least one image presented by the device is one or more geometric shapes, letters, logos, currency symbols or other symbols.

20. The safety device according to any one of the preceding claims, wherein, The observation element is a focusing element suitable for focusing light in one direction, preferably wherein the focusing element is a cylindrical focusing element.

21. The safety device according to any one of the preceding claims, wherein, The observation element array includes a lens array.

22. The safety device according to any one of the preceding claims, wherein, The substrate is at least semi-transparent, and the observation element array is disposed in or on a first surface of the substrate, and the image layer is disposed in or on a second surface opposite to the substrate.

23. The safety device according to any one of the preceding claims, wherein, The image layer is provided as a printed product, preferably printed by gravure printing, engraved gravure printing, screen printing, micro-engraved gravure printing, flexographic printing, offset printing or digital technology.

24. A safety article comprising a safety device according to any one of the preceding claims, wherein, Preferably, the security item is a security line, strip, foil, insert, transfer element, label, patch, or data page for a security document.

25. A security document comprising a security device according to any one of claims 1 to 23 or a security article according to claim 24, wherein, Preferably, the security document is a banknote, check, passport, ID card, driver's license, certificate of authenticity, stamp duty, or other document used to protect value or personal identity.

26. A method of manufacturing a safety device, the method comprising: (a) Providing a substrate; (b) Applying an array of observation elements to the substrate; as well as (c) An image layer is formed in or on the substrate, the image layer overlapping the observation element array, the image layer including a first image channel and a second image channel, the first image channel being formed by a set of first image channel positions respectively associated with a corresponding observation element, and the second image channel being formed by a set of second image channel positions respectively associated with a corresponding observation element, wherein... The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed by image layer material that collectively defines the first image; wherein, The image layer includes at least one region, which is completely contained within the horizontal region of the first image and overlaps with the plurality of viewing elements. The at least one region has a first image tone ratio, which is the ratio of the number of first image channel positions occupied by the first image elements to the number of first image channel positions within the region; and wherein: (i) The image layer includes a first region and a second region with different first image tone ratios; and / or (ii) The second image channel is occupied by a corresponding set of second image elements formed by image layer material that commonly defines the second image, and in the at least one region of the image layer, the first image tone ratio is different from the second image tone ratio, which is the ratio of the number of second image channel positions occupied by the second image elements to the number of second image channel positions in the region.

27. The method of claim 26, further comprising, prior to step (c), forming an image layer template by identifying regions of different hues within the first image; and In step (c), the image layer is formed according to the image layer template.

28. A method for manufacturing a safety device, the method comprising: (a) Providing a substrate; (b) Applying an array of observation elements to the substrate; as well as (c) An image layer is formed in or on the substrate, the image layer overlapping the observation element array, the image layer including a first image channel and a second image channel, the first image channel being formed by a set of first image channel positions respectively associated with a corresponding observation element, and the second image channel being formed by a set of second image channel positions respectively associated with a corresponding observation element, wherein... The positions of the first set of image channels and the positions of the second set of image channels are staggered, such that, at a first range of viewing angles, light from the first image channels is directed to the observer, and at a second range of viewing angles, light from the second image channels is directed to the observer; wherein, At least the first image channel is occupied by a corresponding set of first image elements formed of an image layer material that commonly defines the first image; wherein a first subset of the first image elements is formed of an image layer material exhibiting a first color, and a second subset of the first image elements is formed of an image layer material exhibiting a second color different from the first color; and The image layer includes at least a first color region that overlaps with a plurality of the observation elements. The first color region includes a first image channel position occupied by the first image elements of the first subset and a first image channel position occupied by the first image elements of the second subset, according to a first color ratio. Thus, the first color region is perceived as having a composite color due to the combination of the first color and the second color.

29. The method of claim 28, further comprising, prior to step (c), forming an image layer template by identifying one or more color mixing regions within the first image; and In step (c), the image layer is formed according to the image layer template.

30. The method according to any one of claims 26 to 29, wherein, The image layer is formed by printing technology, preferably gravure printing, engraved gravure printing, screen printing, micro-engraved gravure printing, flexographic printing, offset printing or digital technology.

31. The method according to any one of claims 26 to 30, wherein, The image is formed in a single printing process.

32. The method according to any one of claims 26 to 31, wherein, At the same location along the substrate, the observation element is applied to a first side of the substrate while the image layer is simultaneously applied to the opposite second side of the substrate.

33. The method according to any one of claims 26 to 32, wherein the method is suitable for manufacturing a safety device according to any one of claims 1 to 23.

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