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US-12616995-B2 - Methods for producing overt security features exhibiting one or more indicia

US12616995B2US 12616995 B2US12616995 B2US 12616995B2US-12616995-B2

Abstract

Methods for producing eye-catching overt security features exhibiting one or more indicia for anti-counterfeit purposes on value documents or articles as well as decorative purposes are disclosed. In particular, the present invention provides methods for producing security features that can be easily, directly and unambiguously authenticated by the human without any external device or tool, wherein the security features comprised a cured ink and one or more cured indicia, the ink comprising cured cationically curable compounds or cured hybrid curable compounds and silver nanoplatelets.

Inventors

  • Hervé PITTET
  • Patrick Veya
  • Mélissa BERSIER

Assignees

  • SICPA HOLDING SA

Dates

Publication Date
20260505
Application Date
20221111
Priority Date
20211118

Claims (20)

  1. 1 . A method for producing a security feature exhibiting one or more indicia on a substrate comprising: a step a) of applying on a substrate surface a UV-Vis radiation curable ink, said UV-Vis radiation curable ink being in a first, liquid state so as to form a coating layer and said UV-Vis radiation curable ink comprising: i) from about 7.5 wt-% to about 20 wt-% of silver nanoplatelets bearing a surface stabilizing agent of general formula (V) wherein the residue R A is a C 2 -C 4 -alkyl group substituted with a hydroxy group; the residue R B is selected from a C 1 -C 4 -alkyl group, and a C 2 -C 4 -alkyl group substituted with a hydroxy group; and Cat + is an ammonium cation of general formula + NH 2 R C R D , wherein the residue R C is a C 2 -C 4 -alkyl group substituted with a hydroxy group; and the residue R D is selected from a C 2 -C 4 -alkyl group, and a C 2 -C 4 -alkyl group substituted with a hydroxy group; ii) from about 45 wt-% to about 80 wt-% of either a cycloaliphatic epoxide, or a mixture of a cycloaliphatic epoxide and one or more UV-Vis radiation curable compounds; iii) one or more cationic photoinitiators; iv) a perfluoropolyether surfactant functionalized with one or more functional groups selected from the group consisting of hydroxyl, acrylate, methacrylate, and trialkoxysilyl; v) from about 3 wt-% to about 12 wt-% of a polyvinyl chloride copolymer containing at least 60 wt-% of vinyl chloride; and optionally vi) up to about 25 wt-% of one or more organic solvents; the weight percents being based on the total weight of the UV-Vis radiation curable ink, subsequently to the step a), a step b) of applying by a contactless fluid microdispensing technology a top coating composition at least partially on top of the coating layer, wherein said top coating composition is applied in the form of one or more indicia, wherein said one or more indicia have an ink deposit greater than about 0.8 g/m 2 ; subsequently to step b), a step c) of curing the coating layer and the one or more indicia with one or more curing units, wherein the time between steps b) and c) is less than 5 seconds.
  2. 2 . The method according to claim 1 , wherein the one or more UV-Vis radiation curable compounds comprise one or more cationically curable monomers selected from the group consisting of vinyl ethers, propenyl ethers, cyclic ethers other than a cycloaliphatic epoxide, lactones, cyclic thioethers, vinyl thioethers, propenyl thioethers, hydroxyl-containing compounds, and mixtures thereof.
  3. 3 . The method according to claim 2 , wherein the one or more UV-Vis radiation curable compounds comprise one or more cationically curable monomers selected from the group consisting of vinyl ethers, cyclic ethers other than a cycloaliphatic epoxide and mixtures thereof.
  4. 4 . The method according to claim 1 , wherein the one or more UV-Vis radiation curable compounds comprise one or more radically curable monomers and/or oligomers, and the UV-Vis radiation curable ink further comprises vii) one or more free radical photoinitiators.
  5. 5 . The method according to claim 1 , wherein the UV-Vis radiation curable ink comprises an amount of perfluoropolyether surfactant from about 0.025 wt-% to about 5 wt-%, wherein the weight percents are based on the total weight of the UV-Vis radiation curable ink.
  6. 6 . The method according to claim 1 , wherein the top coating composition comprises one or more cationically curable compounds, one or more hybrid curable compounds, one or more solvents, one or more radically curable compounds or a mixture thereof.
  7. 7 . The method according to claim 6 , wherein the cationically curable compounds are selected from the group consisting vinyl ethers, glycidyl ethers, oxetanes and mixtures thereof; and/or the one or more hybrid curable compounds are hydroxy modified or (meth)acrylate modified vinyl ethers; and/or the one or more solvents are selected from the group consisting of alcohols ketones, glycols, glycol ethers, ether esters, glycol ether esters, alkylene carbonates and mixtures thereof, and/or the one or more radically curable compounds are selected from the group consisting of mono(meth)acrylates, di(meth)acrylates, tri(meth)acrylates and mixtures thereof.
  8. 8 . The method according to claim 1 , wherein the silver nanoplatelets have a number mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a number mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, the number mean diameter being determined by transmission electron microscopy and the mean thickness being determined by transmission electron microscopy.
  9. 9 . The method according to claim 8 , wherein the number mean diameter of the silver nanoplatelets is in the range of 70 to 120 nm with the standard deviation being less than 50%, the number mean thickness of the silver nanoplatelets is in the range of 8 to 25 nm with the standard deviation being less than 30%, and the mean aspect ratio of the silver nanoplatelets is higher than 2.5.
  10. 10 . The method according to claim 1 , wherein the surface stabilizing agent of general formula (V) is present in an amount from about 0.5% to about 5% of the weight percent (wt-%) of the silver nanoplatelets of i).
  11. 11 . The method according to claim 1 , wherein the step c) of curing the coating layer and the one or more indicia is carried out with one or more curing units selected from the group consisting of mercury lamps, UV-LED lamps and sequences thereof.
  12. 12 . The method according to claim 11 , wherein the step c) is carried out with one or more UV-LED lamps.
  13. 13 . The method according to claim 1 , wherein the one or more indicia are selected from the group consisting of codes, symbols, alphanumeric symbols, motifs, geometric patterns, letters, words, numbers, logos, drawings, portraits and combinations thereof.
  14. 14 . The method according to claim 1 , wherein the step a) is carried out by a process selected from the group consisting of rotogravure processes, flexography processes and screen printing processes and/or the step b) is carried out by an inkjet printing process.
  15. 15 . The method according to claim 14 , wherein the step a) is carried out by a process selected from the group consisting of screen printing processes and/or the step b) is carried out by a drop-on-demand inkjet printing process.
  16. 16 . The method according to claim 1 , wherein the UV-Vis radiation curable ink is applied on a transparent or partially transparent region of the substrate.
  17. 17 . The method according to claim 1 , wherein said one or more indicia have an ink deposit greater than or equal to 1.0 g/m 2 .
  18. 18 . The method according to claim 1 , wherein the time between steps b) and c) is less than about 4 seconds.
  19. 19 . The method according to claim 1 , wherein the time between steps b) and c) is equal to about 3.5 seconds or less than about 3.5 seconds.
  20. 20 . A security feature produced by the method recited in claim 1 .

Description

FIELD OF THE INVENTION The present invention relates to the field of methods for producing security features on substrates, in particular on value documents or articles. In particular, the present invention provides methods for producing eye-catching overt security features exhibiting a first color upon viewing in transmitted light and a second color different from the first color upon viewing in incident light and exhibiting one or more indicia as anti-counterfeit means on value documents or articles as well as decorative purposes. BACKGROUND OF THE INVENTION With the constantly improving quality of color photocopies and printings and in an attempt to protect value documents such as banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels that have no reproducible effects against counterfeiting, falsifying or illegal reproduction, it has been the conventional practice to incorporate various security means features in these documents. Security features, e.g. for value documents, can generally be classified into “covert” security features on the one hand, and “overt” security features on the other hand. The protection provided by covert security features relies on the concept that such features are difficult to detect, typically requiring specialized equipment and knowledge for detection, whereas “overt” security features rely on the concept of being easily detectable with the unaided human senses, e.g. such features may be visible and/or detectable via the tactile senses while still being difficult to produce and/or to copy. However, the effectiveness of overt security features depends to a great extent on their easy recognition as a security feature, because most users, and particularly those having no prior knowledge of the security features of a document or item secured therewith, will only then actually perform a security check based on said security feature if they have actual knowledge of their existence and nature. A special role in securing value documents is played by dichroic security features exhibiting a first color upon viewing in transmitted light and a second color different from the first color upon viewing in incident light. To provide a striking effect and draw the layperson's attention, the first color and the second color must have an attractive visual appearance, such as blue, metallic yellow, magenta, and green, and a significant color contrast (for e.g.: blue/metallic yellow, green/metallic yellow, violet/metallic yellow). Dichroic security features showing a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light may be obtained from silver platelets containing inks. WO 2020/224982 A1 discloses compositions comprising silver nanoplatelets as well as coatings comprising said nanoplatelets and exhibiting a blue color in transmission and a metallic yellow color in reflection. WO 2020/083794 A1 discloses compositions comprising silver nanoplatelets as well as coatings comprising said nanoplatelets and exhibiting a red or magenta color in transmission and a greenish-metallic color in reflection. WO 2021/213942 A1 discloses compositions comprising platelet-shaped transition metal particles as well as coatings comprising said particles and exhibiting a turquoise or blue color in transmission and a yellowish metallic color in reflection or exhibiting a red or magenta color in transmission and a greenish metallic color in reflection. WO 2021/214244 A1 discloses processes for manufacturing a security feature for securing a value document, wherein said security feature exhibits a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light. The disclosed processes comprises the steps of a) printing a specific UV-Vis radiation curable ink on a transparent or partially transparent region of a substrate of a value document; b) heating the ink layer obtained at step a) at a temperature of about 55° C. to about 100° C. for at least one second so that the ink layer exhibits a metallic yellow color upon viewing in incident light; and c) UV-Vis curing the ink layer obtained at step b) to form the security feature. The co-pending European Patent Application EP20206794.8 discloses UV-Vis radiation curable security inks for producing a security feature exhibiting a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light, wherein said ink comprises silver nanoplatelets, UV-Vis radiation curable compounds, one or more cationic photoinitiators, a perfluoropolyether surfactant and a polyvinyl chloride copolymer. WO 2021/175907 A1 discloses UV-Vis radiation cationically curable security inks and UV-Vis radiation curable hybrid security inks comprising an ink vehicle and pigments comprising a flake-shaped non-metallic or metallic substrate comprising one or more at least partial coating layers, an at least partial surface treatm