Printing method with oxidative-drying intaglio ink and UV-VIS-curable intaglio inks

Abstract

The present invention relates to the field of the intaglio printing process. In particular, the present invention relates to a method that combines intaglio inks curable by oxidation with UV-VIS-curable intaglio inks on one intaglio plate or cylinder. The disclosed method results in an intaglio printed security element using advantageously the unalike properties of the different inks while enabling the printing on a standard printing press in one printing step.

Claims

1. Process for printing a security element on at least one side of a substrate with two or more different intaglio inks wherein at least one of said two or more different intaglio inks is an oxidative drying intaglio ink curable by an oxidative process, at least one other of said two or more different intaglio inks is a UV-VIS-curable intaglio ink curable by UV-VIS irradiation, the process comprising: transferring the oxidative drying intaglio ink through rubber-made rollers, inking a first selected portion of a printing plate of said intaglio printing device with the oxidative drying intaglio ink, transferring the UV-VIS-curable intaglio ink through EPDM (ethylene propylene diene monomer) material-made rollers, inking a second selected portion of said printing plate, which does not overlap with said first selected portion, of said intaglio printing device with the UV-VIS-curable intaglio ink, wiping off the excess of the oxidative drying intaglio ink and the UV-VIS-curable intaglio ink from said intaglio printing device using a paper or a tissue wiping system, printing the oxidative dying intaglio ink onto a first area of the substrate corresponding to the first selected portion of the printing plate and the UV-VIS-curable intaglio ink onto a second area of the substrate corresponding to the second selected portion of the printing plate in one printing step using one intaglio printing device, wherein intaglio relief of the second area has a predetermined thickness larger than intaglio relief of the first area, curing the UV-VIS curable intaglio ink by exposure to the UV-VIS irradiation, and curing the oxidative drying intaglio ink by the oxidative process, wherein said UV-VIS-curable intaglio ink is a transparent and colorless ink, wherein the printed cured ink layer made from said UV-VIS-curable intaglio ink is thicker than the printed cured ink layer made from said oxidative drying intaglio ink.

2. Process according to claim 1 wherein said inking the first selected portion and the inking the second selected portion are performed by an indirect inking process using a first and a second chablons covering different non-overlapping areas of the intaglio printing device.

3. Process according to claim 1 wherein said security element is printed on an area covering less than 80% of the whole surface of the substrate.

4. Process according to claim 1 wherein the average intaglio relief of the cured ink layer made of said UV-VIS-curable intaglio ink is between 1 m and 100 m.

5. Process according to claim 1 wherein said UV-VIS-curable intaglio ink comprises one or more machine readable security compounds.

6. Process according to claim 1 wherein said substrate is a security document.

7. Process according to claim 1, wherein the UV-VIS-curable intaglio ink is partially or completely cured by UV or VIS irradiation by a source of electromagnetic radiation immediately after the printing of the security element, and wherein the curing of the oxidatively curable intaglio ink is accelerated by a heat source located downstream of the source of electromagnetic radiation.

8. Process according to claim 4 wherein the average intaglio relief of the cured ink layer made of said UV-VIS-curable intaglio ink is between 10 m and 60 m.

9. Process according to claim 4 wherein the average intaglio relief of the cured ink layer made of said UV-VIS-curable intaglio ink is between 15 m and 45 m.

10. Process according to claim 6 wherein the security document is a banknote, a passport, a check a voucher, an ID- or a transaction card, a stamp, or a tax label.

11. Process according to claim 1, wherein the printed cured ink layer made from said UV-VIS curable intaglio inks is 10% to 50% thicker than the printed cured ink layer from said oxidative drying intaglio ink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be explained with the help of the following figures:

(2) FIG. 1 schematically depicts a security document comprising an intaglio printed security element printed with the process of the present invention.

(3) FIG. 2a schematically depicts an intaglio printing press useful for a direct inking process and comprising a heat source.

(4) FIG. 2b schematically depicts an intaglio printing press useful for a direct inking process and comprising a source of electromagnetic radiation.

(5) FIG. 3a schematically depicts an intaglio printing press useful for an indirect inking process (Orlof process) and comprising a heat source.

(6) FIG. 3b schematically depicts an intaglio printing press useful for an indirect inking process (Orlof process) and comprising a source of electromagnetic radiation.

(7) FIG. 4a schematically depicts an intaglio printing press useful for the process of the present invention to be used in a direct inking process. The printing press comprises a heat source and a source of electromagnetic radiation.

(8) FIG. 4b schematically depicts an intaglio printing press useful for the process of the present invention to be used in an indirect inking process (Orlof process). The printing press comprises a heat source and a source of electromagnetic radiation.

DETAILED DESCRIPTION

(9) The present invention takes advantage of the complementary properties of oxidatively drying inks and UV-VIS-curable inks. Moreover, the solution of the present invention of using the oxidatively drying and the UV-curable inks in parallel simultaneously, and not sequentially, on one intaglio cylinder, is advantageous for economical reasons.

(10) The present invention is furthermore related to the use of a security element disclosed herein for the protection against counterfeiting of a commercial good or a security document selected from the group consisting of the banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels.

(11) As used herein the term security element refers to an element on a security document printed with an intaglio printing process for the purpose of determining its authenticity and protecting it against counterfeits.

(12) It is known in the art that UV-VIS-irradiation permeates poorly into a highly coloured coating layer, in particular thick coating layer. Thus, in a preferred embodiment of the present invention, the UV-VIS-curable intaglio ink is a colourless or tinted intaglio ink. The colourless or tinted UV-VIS-curable intaglio ink may be transparent or non-transparent; preferably the colourless or tinted UV-VIS-curable intaglio ink is transparent; even more preferably the UV-VIS-curable intaglio ink is a colourless transparent ink. The UV-VIS-curable intaglio is preferably used to print thick-layered tactile areas of the security element.

(13) The average thickness of an intaglio relief is comprised between 1 m and 100 m, preferably between 10 m and 60 m, more preferably between 15 m and 45 m.

(14) As used herein the term intaglio relief refers to the sum of the intaglio ink layer and the substrate embossing.

(15) As used herein the term intaglio ink layer thickness refers to the thickness of the intaglio ink layer deposited on the substrate.

(16) The intaglio ink layer thickness corresponds to the thickness of the intaglio relief minus the substrate embossing.

(17) As used herein the term UV-VIS-curable intaglio relief refers to a security element printed with an intaglio printing process using a UV-VIS-curable intaglio ink. As used herein the term oxidatively drying intaglio relief refers to a security element printed with an intaglio printing process using a oxidatively drying intaglio ink.

(18) As used herein, the term transparent means providing for optical transparency at least in part of the visible spectrum (400-700 nm). Transparent ink layers may be colourless; or alternatively transparent ink layers may be tinted, entirely or in part, provided that there is transparency in at least part of the visible spectrum, such as to allow an observer to see through the ink layer.

(19) In a still further embodiment of the present invention, the printed cured UV-VIS-curable intaglio relief is thicker than the printed cured (dried) oxidatively drying intaglio relief. By selecting an appropriate design comprising a UV-curable intaglio ink layer and a oxidatively drying intaglio ink layer, the printed cured UV-VIS-curable intaglio ink relief being 10% to 50% thicker (the percentages refer to the thickness of the cured (dried) oxidatively drying intaglio relief), preferably 20% to 30% thicker, than the printed cured (dried) oxidatively drying intaglio relief, the mechanical pressure on the oxidatively drying intaglio relief in the stack of piled sheets or in the rolled web may be significantly reduced. Thus the present invention also discloses a method to reduce the set-off and/or the blocking of the oxidatively drying intaglio ink by reducing the mechanical pressure in the stack of piled sheets or in the rolled web, on the printed security feature made of an ink layer comprising an oxidatively drying intaglio ink.

(20) The UV-VIS-curable ink suitable for the present invention is preferably a colourless or tinted, transparent or non-transparent ink. UV-Vis curable compositions are known in the art and can be found in standard textbooks such as the series Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints, published in 7 volumes in 1997-1998 by John Wiley & Sons in association with SITA Technology Limited. UV-VIS-curable intaglio inks described herein typically comprise a) a binder compound which comprises oligomers (also referred in the art as prepolymers), preferably selected from the group consisting of radically-curable compounds, cationically-curable compounds and mixtures thereof. UV-Vis curing of a monomer, oligomer or prepolymer may require the presence of one or more photoinitiators and may be performed in a number of ways. UV-Vis curing may be done by a free radical mechanism, a cationic mechanism or a combination thereof. Depending of the binder compound(s) comprised in the UV-Vis curable composition, different photoinitiators might be used. The UV-VIS-curable intaglio ink may additionally comprise other additives; when a colourless transparent UV-VIS-curable intaglio ink is used, said additives are selected such that they do not alter the transparent properties of the UV-VIS-curable intaglio ink. Preferably the UV-VIS-curable intaglio ink may comprise one or more machine readable security compounds.

(21) The term intaglio device refers to an engraved intaglio flat plate or to an intaglio plate adapted on a printing cylinder of an intaglio printing press.

(22) The term machine readable security compound refers to security elements that may be detected by a machine, such as e.g. an ATM machine. Preferably, the machine readable security elements of the present invention are colourless components that are not visible to an un-aided human eye. The machine readable security compounds are selected from the group comprising UV-, VIS- or IR-absorbing materials, luminescent materials, magnetic compounds, forensic markers or taggants and combinations thereof. Examples of machine readable security compounds are disclosed in e.g. EP-0 927 749 B1, EP-1 246 876 B1 or WO 2010/115 286 A2.

(23) In a preferred embodiment of the present invention, the UV-VIS-curable intaglio ink is partially or completely cured by UV or VIS irradiation immediately after the printing of the security element; thus the UV-VIS-curable intaglio ink is partially or completely cured when the oxidative curing process of the oxidatively curable intaglio ink starts. Or alternatively, a thermal treatment may be first applied to the security element, thus initiating and/or accelerating the oxidative curing process of the oxidatively curable intaglio ink, before a UV irradiation step. Preferably the UV or VIS irradiation is performed before the thermal treatment. In this preferred alternative, the heat emitted by the UV or VIS irradiation source may contribute favourably to the drying of the oxidatively drying intaglio ink.

(24) According to the present invention, a typical intaglio printing press as known in the art may be used to print the oxidatively curable intaglio ink and the UV-VIS-curable intaglio ink in a single printing step with one intaglio device without significant modification of the press.

(25) FIG. 4a shows a printing press suitable for the present invention, i.e. that may be used with oxidatively drying intaglio inks and UV-curable intaglio inks. The elements made of polymeric material, in particular the rollers (110), (112) and (114) of the ink trains and the corresponding chablons (111), (113) and (115), are selected preferably among materials showing optimal compatibility with the corresponding intaglio inks to increase their lifetime. In particular, the rollers among the rollers (110), (112) and (114) and the chablons among the chablons (111), (113) and (115) used for oxidatively drying inks are preferably made of rubber, more preferably of PUR rubber; the rollers among the rollers(110), (112) and (114) and the chablons among the chablons (111), (113) and (115) used for the UV-curable inks are preferably made of material compatible with UV-curable inks, more preferably of EPDM material.

(26) The wiping cylinder (120) is made of usual material such as e.g. polyvinyl chloride (PVC) or rubber.

(27) The printing press of FIG. 4a is equipped with a source of electromagnetic radiation (150) for the UV-VIS curing of a UV-curable intaglio ink and with a thermal source (140) to accelerate the hardening of the oxidatively drying ink. The source of electromagnetic irradiation (150) is preferably located between the plate cylinder and the heat source (140); however, the heat source (140) may also be positioned between the plate cylinder (100) and the source of electromagnetic radiation (150).

(28) FIG. 4b shows a printing press suitable for the present invention, i.e. that may be used with oxidatively drying intaglio inks and UV-curable intaglio inks, comprising a device for the indirect inking (Orlof process). The printing press of FIG. 4b is equipped with a source of electromagnetic radiation (150) for the UV-VIS curing of a UV-curable intaglio ink and with a thermal source (140) to accelerate the hardening of the oxidatively drying ink. As in the FIG. 4a, for the rollers (110), (112) and (114) of the ink trains and the corresponding chablons (111), (113) and (115), the material is preferably selected according to the intaglio inks to be used on each ink train. Thus the rollers among the rollers (110), (112) and (114) and the chablons among the chablons (111), (113) and (115) used for oxidatively drying inks are preferably made of rubber, more preferably of PUR rubber; the rollers among the rollers(110), (112) and (114) and the chablons among the chablons (111), (113) and (115) used for the UV-curable inks preferably consist of material compatible with UV-curable inks, more preferably of EPDM material.

(29) The collecting cylinder (160) may preferably be made of material that is compatible with both the UV-curable and the oxidatively drying ink, such as e.g. acrylonitrile butadiene (NBR) and silicone rubber.

(30) Compositions suitable for the present invention have been disclosed e.g. in EP 1 790 701 B1, EP 2 014 729 A2 or WO 2009/156 400 A1 (oxidatively drying inks); and in EP 1 260 563 B1 or EP 1 751 240 B1 (UV-curable inks).

(31) Typical formulations suitable for the present invention include without limitation the following formulations: formulation for an oxidatively drying intaglio ink:

(32) TABLE-US-00001 Component weight-%.sup.1 Pigments 4-40 Extenders (e.g. alumina, 10-50 calcium carbonate, china clay) Resins (e.g. cellulose 10-30 resins, long oil alkyd, polyamides, acrylic resins, vinyls, rosin- modified maleics Solvents 10-20 Dryer (e.g. Co-octoate) 0.1-3 Wax 1-7 Surfactants 1-10 Additives (e.g. slip 0.1-5 agent, anti-oxidant, stabilizer) .sup.1weight percents based on the total weight of the formulation. formulation for a UV curable intaglio ink:

(33) TABLE-US-00002 Component weight-%.sup.1 Pigments 0-30 Prepolymers 20-35 Monomers/oligomers 10-30 Fillers 5-10 Photoinitiators 1-10 UV_Stabilizer 1-3 Other additives (e.g. 1-5 emulsifiers) .sup.1weight percents based on the total weight of the formulation.

(34) The UV-curable intaglio ink and the oxidatively drying intaglio ink described herein may comprise further one or more additional security feature substances, preferably selected from, but not limited to, the group consisting of UV-, VIS- or IR-absorbing materials, luminescent materials, magnetic compounds, forensic markers or taggants and combinations thereof. Examples are disclosed in U.S. Pat. No. 6,200,628 and the like.

(35) Hence the processes of the present invention do not require the development of new sophisticated intaglio inks. Regular oxidatively drying intaglio inks and regular UV-curable intaglio inks may be used to produce the security element according to the present invention.

(36) A security element according to the present invention is depicted in an example in FIG. 1.

(37) FIG. 1 schematically represents a banknote comprising an intaglio printed security element consisting of a human face printed with a pigmented intaglio ink (C) and of a series of tactile dots printed with a colourless intaglio ink (T). The intaglio printed security element may be printed in one printing step on one intaglio cylinder using e.g. an oxidatively drying intaglio ink for the pigmented part (human face) and a UV-curable intaglio ink for the colourless part (tactile dots) according to one of the preferred embodiment of the present invention.

(38) The process of the present invention permits a faster printing of intaglio features combining UV-cured and oxidatively dried intaglio inks than with a sequential printing process of each intaglio ink.

(39) In particular, the process of the present invention permits a faster printing of an intaglio element while improving setting-off and blocking behaviour by combining thicker UV-cured intaglio ink layers with thinner oxidatively dried intaglio ink layers.

(40) The security elements produced with the process of the present invention are printed on a conventional intaglio printing press equipped with polymeric parts such as rollers and chablons compatible made of rubber, preferably of PUR rubber for the parts to be used with oxidatively drying intaglio inks, and with EPDM for the parts to be used with UV-curable intaglio ink.

(41) Typically, suitable washing solutions for cleaning the wiping cylinder of the intaglio press used for the present invention are alkaline aqueous wiping solutions comprising between 0.3 wt-% and 1.2 wt-% (weight percent) of a strong base, such as e.g. sodium hydroxide NaOH, and between 0.3 wt-% and 1 wt-% (weight percent) of a surfactant, such as e.g. sulphated castor oil (SCO), the weight percents being based on the total weight of the alkaline aqueous wiping solution.

(42) The security document of the present invention comprising the security element produced with the process of the present invention may comprise one or more additional security features such as e.g. threads, foils and/or windows. Alternatively, the security element printed with the process of the present invention may be printed on these one or more additional security features.