Security fibre, in particular for use in security documents, and security document

Abstract

The invention relates to a security fibre comprising at least one surface (51, 52); wherein at least three types (10, 20, 30) of dots are located on the at least one surface (51, 52); wherein the three types (10, 20, 30) of dots are positioned such that the density of the dots of a first type (10) varies over a region of the surface (51, 52) and the density of the dots of a second type (20) varies over a region of the surface (51, 52), and wherein the dots of the first (10) type and the dots of the second (20) type gradually mix to form an area of mixed dots (10, 20); wherein the area of mixed dots (10, 20) is overlaid with a third type (30) of dots; wherein the at least three types (10, 20, 30) of dots have substantially no colour when irradiated with visible light having a wavelength of between 380 nm and 780 nm; and wherein, when irradiated with a UV wavelength of between 315 nm and 380 nm or between 280 to 315 nm, the first type (10) of dots is illuminated in a first colour (1), the second type (20) of dots is illuminated in a second colour (2), the area of mixed dots (10, 20) is illuminated in a third colour (3), and the third type (30) of dots is invisible; and wherein, when irradiated with a UV wavelength of between 100 nm and 280 nm, the first type (10) of dots is illuminated in the first colour (1), the second type (20) of dots is illuminated in the second colour (2), and the area of mixed dots (10, 20) overlaid with the third type (30) of dots is illuminated in a fourth colour (4).

Description

[0001] Security fiber especially for use in security documents and security document

[0002] The present invention relates to an improved security fiber, the use of the security fiber in security documents and security documents.

[0003] Security fibers are used as a security feature in security documents, such as banknotes, identification documents such as ID cards, passports and visa documents, lottery tickets and certificates.

[0004] The ideal security feature aims to make authenticity easy to verify, while also making it difficult for a counterfeiter to reproduce.

[0005] One example of a use for security fibers is their inclusion in security paper. Paper is made from paper pulp containing cellulose fibers, such as wood, hemp, straw, and cotton linters (note that although these cellulose fibers are used to make paper, they are not themselves made from paper). One well-known security technique is to replace some of the cellulose fibers used to make security paper with synthetic fibers made from materials such as polyester, nylon, and rayon. A relatively small number of the synthetic fibers can be incorporated into the paper pulp along with a majority of the cellulose fibers, resulting in the security paper made from the pulp having the synthetic fibers embedded and randomly scattered within it.The synthetic fibers may be dyed or coated, resulting in the paper containing a random pattern of small printed areas. The dye may be an ultraviolet (UV) light-sensitive dye, so that the random colored pattern is only visible under UV light. Such synthetic fibers are generally fibrous (i.e., predominantly one-dimensional, rather than two-dimensional or sheet-like), like the cellulose fibers they replace. WO 2004 / 025028 A1 describes security features referred to as "fibers" because they replace and combine with the cellulose fibers used in the manufacture of security paper, and because they provide a visual impression in the resulting paper suggesting that they are similar to such fibers. In fact, however, the fibers described in this document are small strips of paper and not fibrous.

[0006] Security fibers, which are invisible in daylight and appear solid-colored when exposed to ultraviolet light, are a well-known security feature. However, counterfeiters can use fluorescent highlighter-type markers to imitate the fibers on security documents. This feature requires close examination, for example, with a microscope, to identify the counterfeit, thus creating a need for a more secure or difficult-to-imitate security fiber.

[0007] To improve the security of security fibers, WO 2004 / 025028 A1 describes security fibers with two or more differently colored stripes or regions, the colors being visible only under ultraviolet light. The regions on these security fibers can abut each other at the edges of the regions without color overlap.

[0008] Furthermore, WO 2020 / 089625 A1 describes a security device which may be a security fiber for incorporation into a security document, the security device comprising a substrate having a first surface and a second surface. A first printed area may be provided on at least one of the first or second surfaces. The first printed area may have a varying tone density and / or be printed in an ink that fluoresces under ultraviolet light to emit light in a first color. A second printed area may be provided on at least one of the first or second surfaces. The second printed area may have a varying tone density and / or be printed in an ink that fluoresces under ultraviolet light to emit light in a second color.The first and second printed areas may be arranged on the at least first or second surface such that the colored light emitted by the fluorescent printed areas mixes to produce light of further different colors.

[0009] Security fibers with different printed areas are also known from WO 2021 / 048 539 Al.

[0010] US 2008 / 0305313 A1 teaches security fibers with markings in the form of parallel stripes printed in two or more colors using UV and / or IR fluorescent inks.

[0011] DE 103 61 131 A1 relates to security elements and value documents, whereby the security element has a color-coded latent image with different image components.

[0012] US 4,897,300 concerns security papers in which security fibers are embedded.

[0013] The object to be achieved by the invention is to provide a security fiber that has an improved level of security compared to the security fibers described in the prior art. A further aim of the invention is to provide a security document with an improved level of security.

[0014] This object is achieved by a security fiber having the features of claim 1.

[0015] Furthermore, the above object is achieved by the security document containing the security fiber according to the invention.

[0016] According to the invention, a security fiber is provided which comprises at least one surface, wherein at least three types of dots are arranged on the at least one surface. The three types of dots are arranged such that the density of dots of a first type varies over a region of the surface and the density of dots of a second type varies over a region of the surface, and wherein the dots of the first and the dots of the second type gradually blend to form an area of ​​blended dots. The area of ​​blended dots is overlaid with a third type of dots.The at least three types of dots appear essentially colorless upon irradiation with visible light in the wavelength range between 380 nm and 780 nm, and upon irradiation with a UV wavelength in the range between 315 nm and 400 nm or between 280 and 315 nm, the first type of dots glows in a first color, the second type of dots glows in a second color, the area of ​​mixed dots glows in a third color, and the third type of dots is invisible, i.e. the third type of dots does not glow upon irradiation in this wavelength range. Furthermore, upon irradiation with a UV wavelength between 100 nm and 280 nm, the first type of dots glows in the first color, the second type of dots glows in the second color, and the area of ​​mixed dots superimposed with the third type of dots glows in a fourth color.

[0017] There are generally three types of UV light: Ultraviolet A (UV-A or long-wave UV), which can have a wavelength between 315 and 380 nm and is often provided at a wavelength of 365 nm; Ultraviolet B (UV-B or mid-wave UV), which can have a wavelength between 280 and 315 nm and is often provided at a wavelength of 313 nm; and Ultraviolet C (UV-C or short-wave UV), which has a wavelength between 100 and 280 nm and is often provided at a wavelength of 254 nm. Visible light, or artificial light, generally has a wavelength between 380 nm and 780 nm.

[0018] When irradiated with visible or artificial light, the security fiber is essentially colorless, i.e. the security fiber is colorless under daylight or artificial light and essentially does not absorb. Depending on the energy-rich wavelength of the UV light used to irradiate the respective dots, luminescent light may or may not be generated by the respective type of dot. For dots of the first and second type, excitation with UV-A or UV-B light is sufficient to generate the emission of luminescent light of the first and second colors. For the third type of dot, however, no luminescent light is emitted when irradiated with UV-A or UV-B light; the third type of dot therefore remains invisible under this lower-energy irradiation.

[0019] However, if the dots of the first, second and third type are excited with the high-energy UV-C light, the excitation energy is sufficient for the dots of the third type to also emit luminescent light.

[0020] When the fiber is irradiated with UV radiation in the wavelength range between 315 nm and 380 nm or between 280 and 315 nm, the first type of dots glows in the first color, the second type of dots glows in the second color, and the area of ​​mixed dots, ie the area in which the first and second type of dots are mixed, glows in a third color.

[0021] For example, the first type of dots can glow green due to the excitation of luminescence by irradiation with UV-A or UV-B radiation, and the second type of dots can glow red because green or red luminescence light is emitted, respectively.

[0022] If a surface is now present with mixed dots of the first and second type, the mixed dots will appear green at the dot of the first type and red at the dot of the second type when irradiated as in the above example. Since the dots are very small, the irradiated surface with the mixed dots glows in a third color, in this example yellow (additive color mixture green + red = yellow). However, under the microscope it can be observed that the light of the third color, namely yellow, is composed of the luminescence light of the first color green produced by irradiating the dot of the first type and the luminescence light of the second color, in this example red, produced by irradiating the dot of the second type.The separate green and red luminescences generated upon irradiation and visible under a microscope can be used to verify that the light appearing in the third color, for example, yellow, on two different colored luminescences, green and red, originating from the two different points of the first and second type, originate from additive color mixing. This aspect of the invention further increases the security of the security thread.

[0023] Of course, it is possible to add another type of dots which glow in another color when irradiated, the luminescence of which can gradually mix with the luminescence of the first and / or second type of dots to additionally produce another luminescent light in another color and, if necessary, the associated additional mixed colors.

[0024] As a security feature, the security fiber not only exhibits the above-described luminescence in a first, second, and third color that occurs upon exposure to UV-A or UV radiation, but also allows for verification under a microscope as to whether the resulting mixed color (third color) is truly based on the mixture of luminescent light of the first and second colors or whether it is a counterfeit. This increases the security of the security fiber, as it is difficult for a counterfeiter to imitate the security fiber in this respect.

[0025] A further security aspect of the security fiber according to the invention is that when irradiated with short-wave UV light of a wavelength between 100 nm and 280 nm, the first type of dots continues to glow in the first color and the second type of dots in the second color, but the area of ​​mixed dots superimposed with the third type of dots glows in a fourth color.

[0026] This is due to the fact that in the superimposed area, when irradiated with short-wave UV light, the area overlaid by the superimposed first and second dots luminesces in the third color (mixed color), which in turn is superimposed with the color of the third type of dot. According to the invention, the security fiber displays a first color scheme when irradiated with UV-A and UV-B light, in the above example green, red, and the additive mixed color yellow, and a different color scheme when irradiated with UV-C light (e.g. green, red, mixed color white) if the third type of dot luminesces blue, for example, since with additive color mixing red + green + blue = white.

[0027] Since the first type of dots (green) and the second type of dots (red) gradually blend, there are no "sharp" edges from one color to the other, but rather the colors in this example appear to blend from red to red-orange to yellow, yellow-green to green, the transition being diffuse.

[0028] The dots of the first and second type each exhibit the same color under UV-C irradiation as they do under UV-A and UV-B irradiation. The area of ​​the mixed dots is overlaid with dots of a third type, specifically dots that exhibit no color under UV-A and UV-B irradiation, but appear a different color when irradiated under UV-C irradiation. Thus, if the fiber appears to change from green to yellow-orange to red under UV-A and UV-B light, it could appear green to white to red under UV-C light if the third type of dot emits blue (with additive color mixing, red, green, and blue = white). This provides an additional level of security that can be easily authenticated by comparing the different colors exhibited by the security fiber under UV-A / UV-B light and under UV-C light.

[0029] The area of ​​mixed dots superimposed with dots of the third type can be created by printing the dots of the third type onto the area of ​​mixed dots of the first and second types. This means that the dots of the third type can overlap with the dots of the first and second types. Fig. 2 illustrates, by way of example, the dots of the third type overlapping the area of ​​mixed dots of the first type and the second type. In another variant, the dots of the first, second, and third types are printed simultaneously.

[0030] The variation in the density of the dots can be provided by halftone printing. Halftone printing is a well-known reprographic technique in which dots of different sizes, patterns, and / or spacing are used to give the appearance of different color shades. The density of the different types of dots (at least first, second, and third types) can vary continuously across the surface(s) of the fiber, i.e., increase and decrease, so that a color gradient can be achieved. Thus, the achievable color pattern can have diffuse transitions between different colors. The density of each type of dot can vary between 0% and 100%, for example, along the area of ​​at least one or all surfaces of the fiber. The density of a type of dot can also vary in one or more gradations or discrete steps, for example, in gradations of ten degrees (e.g., with densities of 10%, 20%, 30%, etc.).

[0031] The density of points is understood as the area covered by the points relative to the total area spanned by the points.

[0032] The dots of the first, second, and third types can be printed onto the first and / or second surface of the security fiber using a first, second, and third fluorescent ink. Printing the dots onto the fiber surface(s) allows for more precise positioning of the dots than, for example, dyeing the fibers. More precise positioning allows for better differentiation between the dots of the first and second types under a microscope, thus making the security fiber more secure.

[0033] Furthermore, the first and second types of dots are preferably arranged such that the color appearing upon irradiation varies continuously over a portion of at least one surface upon irradiation with a UV wavelength of 315 nm to 400 nm or 280 to 315 nm. A graduated spectrum or rainbow effect pattern may be produced. A rainbow pattern may be achieved by adding a fourth, fifth, etc., type of dot. The more types of dots, i.e., the more colors visible under UV-A and UV-B, the more difficult it is for a counterfeiter to imitate the security fiber of the present invention.

[0034] Furthermore, it is preferred that the first, second, and third types of dots are arranged such that the luminous color of the third type of dots does not exhibit a continuous transition to the other colors, but rather, upon irradiation with a UV wavelength of 100 nm to 280 nm, an abrupt color change occurs at the transition to the fourth color. Since the third type of dots exhibit no color under UV-A or UV-B light, the authenticity of the security fiber can be easily achieved by comparing the color produced under UV-A / UV-B light with the color exhibited under UV-C light.

[0035] The security fiber of the present invention can exhibit color upon irradiation under NIR (near-infrared light having a wavelength of 780 to 2,500 nm). Such a fiber can be provided by mixing luminescent particles with anti-Stokes properties into the fluorescent inks used in at least the first, second, and third types of dots. However, it is preferred that the first, second, and third types of dots do not fluoresce or exhibit color upon irradiation with NIR light. Instead, an additional type of dot may be used that fluoresces or exhibits color upon irradiation with NIR light. Adding another type of dot to one or both surfaces of the security fiber according to the present invention adds a further level of security.

[0036] It is further preferred that the dots of the first and second types be provided using an ink that fluoresces upon irradiation with UV-A, UV-B, and UV-C light and generates red, blue, or green light. Each of the first and second types of dots may be provided using an ink of a single color. As an alternative to red, blue, and green inks, cyan and magenta inks may also be used. Furthermore, each of the first and second types of dots may also be produced using an ink comprising a mixture of two or more differently colored pigments (e.g., yellow, red, green, and blue pigments) that fluoresce to generate light having a color resulting from the mixture of the different colors.

[0037] Likewise, the dots of the third type can be provided using an ink that fluoresces under UV-C light, for example, to produce red, blue, or green light. The third type of dots can be created using an ink that fluoresces to produce a color different from the color produced by the area of ​​mixed dots of the first and second types. Each of the third type of dots can be provided using an ink of a single color. As an alternative to red, blue, and green inks, cyan and magenta inks can also be used.The third type of dots can also be made using an ink comprising a mixture of two or more differently colored pigments (for example, yellow, red, green and blue pigments) that fluoresce to produce light with a color resulting from the mixture of the different colors.

[0038] Different types of dots exist when the dots have different luminescence spectra at the same excitation wavelength or different excitation wavelengths (UV-A, UV-B and UV-C).

[0039] The different types of dots can be provided using inks comprising microencapsulated fluorescent organic or organometallic dyes. The microencapsulated inks can each comprise a fluorescent dye of more than one color. The different types of dots can be provided using inks having a lightfastness of at least 3 on the blue wool scale. Further, it is preferred that the first type of dots have a different shape than the second type of dots. Further, the third type of dots can have a different shape than the first type of dots and the second type of dots. A different shape means, for example, that one type of dot can have a round shape and the other type can have an oval shape. There can be different degrees of oval shape, that is, different degrees of longitude of the oval shape.Additionally, a different shape may indicate a difference in the diameter of a round dot; for example, one shape may have smaller diameter round dots than the other. Furthermore, the orientation of the various oval shapes relative to the fiber's long axis may differ. Another shape difference may be caused by the dots having smooth or rough edges. These shape differences can be observed under a microscope, thereby adding another security feature to the security fiber of the present invention.

[0040] Preferably, the points of the first and second type are arranged side by side. However, they can also be superimposed.

[0041] The security fiber generally has at least a first and a second surface. The first and second surfaces of the security fiber may be opposite surfaces. The first, second, and third types of dots may be provided on only one surface of the fiber or on the first and second surfaces of the fiber. Preferably, the dots are provided on both surfaces. This allows the fiber to be authenticated regardless of the fiber's orientation in the security document.

[0042] The fiber of the present invention may, for example, be made from a synthetic material such as polyester, nylon, and rayon, or from paper or cellulose. In a preferred embodiment, the security fiber of the present invention may be made from paper strips, in particular from soft paper; more preferably, it may be made from tissue paper strips, in particular small tissue paper strips, or an alternative thin paper. The paper may be without optical brighteners. A "small" paper strip is understood to mean a paper strip that is preferably between 3 and 10 mm long and between 0.15 and 0.5 mm wide, and in particular between 4 and 7 mm long and 0.3 mm wide.

[0043] Furthermore, the paper can be a highly porous, high-wet strength tissue paper with a nominal basis weight between 22 and 28 g / m². More preferably, the paper can be a highly porous, high-wet strength tissue paper with a nominal basis weight of 25 g / m². These properties enable optimal printing and cutting conditions for the paper. It is preferred that the fiber be made of paper, as paper fiber is easier to integrate into the papermaking process, meaning it allows for easier integration of the fiber into a security document made predominantly of paper.

[0044] The length of the security fiber of the present invention can be one of 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, and 10 mm, or variations of these lengths. The width can be one of 0.125 mm, 0.15 mm, 0.2 mm, 0.225 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, and 0.5 mm, or variations of these widths.

[0045] The security fiber may further comprise a lacquer layer on at least the first, second, and third types of dots. The security device may further comprise a lacquer layer on at least the first and / or second surface. Applying a lacquer layer protects the types of dots from abrasion and / or improves the affinity of the fibers to a paper product incorporating the fiber.

[0046] According to a further aspect of the invention, a security document is provided that contains the security fiber described above. Due to the advantageous security properties of the fiber, the security document is made more secure by incorporating the fiber. A security document according to the present invention can be, for example, a banknote, an identification document such as an ID card, passport, and visa document, a lottery ticket, and a certificate.

[0047] An example of a security fiber according to the present invention is shown in Fig. 1 and Fig. 2.

[0048] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The features shown in the description and the drawings can be used individually or in any combination according to the invention. They show:

[0049] Figure 1 shows an exemplary distribution of the first type 10 of dots and the second type 20 of dots on a surface 51 of a security fiber 8. Opposite the surface 51 shown in the figure, the security fiber has a second surface 52 on the other side, opposite this surface 51. When irradiated with visible or artificial light, all types 10, 20, and 30 of dots are colorless. Upon excitation with UV-A or UV-B light, the first type 10 of dots glows in a first color 1, and the second type 20 of dots glows in a second color 2. The area of ​​the mixed dots 10, 20 of the first type 10 and the second type 20 glows in a third color 3, as indicated below in Figure 1.

[0050] Figure 2 shows an exemplary distribution of the first 10, second 20, and third 30 types of points. As illustrated in Figure 1, the first 10 and second 20 types of points form a mixed area of ​​points. These mixed points are overlaid by the third 30 types of points.

[0051] In Fig. 2, for demonstration purposes, the third type (30) of dots is shown with a black outline on top of the area of ​​mixed dots (the dots in the mixed area are shown in a lighter shade of gray). No color appears when the first 10, the second 20, or the third 30 type of dots are irradiated with visible or artificial light. When excited with UV-A or UV-B light, the first type (10) of dots glows in a first color (1), and the second type (20) of dots glows in a second color (2). The area of ​​mixed dots of the first type (10) and the second type (20) glows in a third color (3) (see Fig. 1). The third type (30) of dots has no color. When excited with UV-C light, the first type (10) of dots glows in a first color (1), and the second type (20) of dots glows in a second color (2).The area of ​​mixed dots, which is overlaid with the third type 30 of dots, shines in a fourth color 4, see Fig. 2.

[0052] List of reference symbols

[0053] 1. First color

[0054] 2. Second color

[0055] 3. Third color

[0056] 4. Fourth color

[0057] 8. Security fiber

[0058] 10. First type of points

[0059] 20. Second type of points

[0060] 30. Third type of points

[0061] 51. First Surface

[0062] 52. Second surface

Claims

Claims: Safety fiber comprising: at least one surface (51, 52); wherein at least three types (10, 20, 30) of points are arranged on the at least one surface (51, 52); wherein the three types (10, 20, 30) of points are arranged such that the density of points of a first type (10) varies over a region of the surface (51, 52) and the density of points of a second type (20) varies over a region of the surface (51, 52), and wherein the points of the first (10) and the points of the second (20) type gradually mix to form an area of ​​mixed points (10, 20); wherein the area of ​​mixed points (10, 20) is superimposed with a third type (30) of points; wherein at least three types (10, 20, 30) of points exhibit essentially no color when irradiated with visible light with a wavelength between 380 nm and 780 nm;and wherein, when irradiated with a UV wavelength between 315 nm and 380 nm or between 280 and 315 nm, the first type (10) of points glows in a first color (1), the second type (20) of points glows in a second color (2), the area of ​​mixed points (10, 20) glows in a third color (3), and the third type (30) of points is invisible; and wherein, when irradiated with a UV wavelength between 100 nm and 280 nm, the first type (10) of points glows in the first color (1), the second type (20) of points glows in the second color (2), and the area of ​​mixed points (10, 20) superimposed with the third type (30) of points glows in a fourth color (4). Security fiber according to claim 1, wherein the dots (10, 20, 30) contain fluorescent printed ink. Security fiber according to claim 1 or 2, wherein the first (10) and second (20) types of dots are arranged such that the fluorescent color varies continuously over a section of at least one surface (51, 52) when irradiated with a UV wavelength between 315 nm and 380 nm or between 280 nm and 315 nm. Security fiber according to claim 3, wherein the first (10), second (20), and third (30) types of dots are arranged such that the fluorescent color does not vary continuously over a section of at least one surface (51, 52) when irradiated with a UV wavelength between 100 nm and 280 nm. Safety fiber according to one of claims 1 to 4, wherein the at least three types of dots (10, 20, 30) exhibit essentially no color when irradiated in NIR.Security fiber according to any one of claims 1 to 5, wherein the first type (10) of dots is printed in an ink that fluoresces upon irradiation with UV light to produce yellow light, red light, blue light, or green light, or a mixture thereof. Security fiber according to claim 6, wherein the second type (20) of dots is printed in an ink that fluoresces in a different color than the first type (10) of dots upon irradiation with UV light. Security fiber according to claim 6 or 7, wherein the third type (30) of dots is printed with an ink that fluoresces upon irradiation with a UV wavelength between 100 nm and 280 nm to produce a light of a different color than the luminescence of the dots of the first (10) and second (20) types. Security fiber according to any one of claims 1 to 8, wherein at least the first type (10) of dots and the second type (20) of dots have a different shape. Security fiber according to any one of claims 1 to 9, wherein the first (10), second (20), and third (30) type of dots are provided only on one surface (51, 52) of the fiber or on the first (51) and second (52) surfaces of the fiber. Security fiber according to any one of claims 1 to 10, wherein the fiber is made from paper strips, in particular from soft paper, more preferably from small paper strips or tissue paper strips, in particular small tissue paper strips. Security fiber according to any one of claims 1 to 11 for use in security documents. Security document containing the security fiber according to any one of claims 1 to 11.

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