HK1059630B - Uv curing intaglio ink - Google Patents

Description

UV-curing intaglio ink

The present invention relates to an intaglio ink composition, to a process for the production and application of said composition, to the use of said composition in an intaglio printing process and to a process for precipitating the resulting wiping solution, as well as to a security document obtained by intaglio printing using said composition. The ink composition includes a component polymerizable via a free radical reaction pathway by irradiation with electromagnetic radiation or electron beam radiation. The ink composition additionally exhibits suitable dispersibility in wiping solutions of low sodium hydroxide concentration.

The printing of security documents requires excellent printing quality and special measures to prevent counterfeiting and forgery of the printed documents.

The security document is preferably printed by a gravure printing process. The term "intaglio printing" as used in the present application applies to so-called "engraved steel die" or "copperplate" printing methods known to the person skilled in the art. The printing plates used here are usually chrome-plated engraved nickel plates or cylinders prepared by electrical replication of an initial copper plate, usually hand-engraved. The following will not apply to rotogravure or gravure printing processes, also known, which rely on different types of ink.

In engraved steel die rotogravure, a rotoengraved steel cylinder bearing the pattern or image to be printed is supplied with ink by one or more stencil inking cylinders, whereby a pattern of different colored inks is transferred to the printing cylinder. After inking, any excess ink on the smooth surface of the printing cylinder is wiped off by a rotating wiping cylinder coated with plastisol. The remaining ink in the engravings of the printing cylinder is then transferred under pressure onto the substrate to be printed, which may be paper or plastic in the form of a sheet or web. The wiping cylinder is then continuously cleaned using a dilute aqueous sodium hydroxide solution as an emulsifying medium for the wiped off excess ink, or a paper/cotton cloth wiping device, or an organic solvent such as trichloroethylene. These process steps and the machines for engraved steel die printing are known to the person skilled in the art.

The printing inks for printing security documents by the engraved steel die method of intaglio printing with the currently used fed sheets or fed webs must meet the following requirements:

suitable rheological properties (rheology) at the moment of transfer of the ink to the printing cylinder and at the moment of printing;

the ability to remove ink easily and quantitatively from the non-printing areas of the printing plate (printing die) surface (wipeability);

ease of cleaning (dirt-removing power) of the wiping cylinder with an aqueous solution containing 0.1-1% caustic soda and a detergent of similar concentration, or even with pure water;

the stability of the ink on the inking roller before printing until printing;

film-forming properties such that they can further process paper or web with printed film of up to 200 microns thickness during the last 24 hours after printing or preferably immediately after printing.

Anti-smudge properties: immediate rewinding of the printed substrate is mandatory when printing on a continuous web at speeds up to 150 m/min. The ink system must ensure that no ink is transferred from the new printing surface to the back of the rolled substrate in contact therewith. In case the web printing machine is equipped with a hot air drying device (as for example supplied by TEC-System, w.r.grace & co.) the web printing speeds up to 150m/min must be tolerated using engraving depths up to 200 micrometer. On sheet fed paper presses, depending on the specific printing substrate and the depth of the engravings, 500-;

-according to the date of the 1969 by INTERPOL at the 5^thOutstanding chemical and mechanical resistance of prints according to the specifications established by International conference on Current and counting or the test method of the Bureau of Engravingand Printing as described in BEP-88-214(TN) section M5;

acceptable toxicological and environmental properties.

As is known in the printing art, the printed substrate must generally be dried in order to allow subsequent processing and to obtain the desired resistance properties of the final product.

By the term "drying", three different mechanisms are proposed, which are well known to the person skilled in the art of printing. Two purely physical drying methods mean that the volatile solvent evaporates from the printing ink paste (ink paste), leaving its solid resin and pigment components behind, and that the non-volatile ink solvent is sucked back (absorbed) into the substrate. The third (chemical drying process), also known as hardening or curing, refers to the conversion of a liquid composition into a solid state by a chemical polymerization or crosslinking reaction. One or more of these drying methods may be included in the drying of the same specific printing ink, and generally the printer does not distinguish between physical drying and chemical drying.

Intaglio inks are typically cured by an oxidation reaction. This is a rather slow drying process and documents printed and stacked accordingly as paper are often not further processed until a drying time of one to several days.

Curing of printing inks with UV radiation is known and widely introduced in the printing field. UV curing allows the printed ink film to dry quickly, almost instantaneously, thus opening up a way to increase production speed. The chemical curing reaction is in most cases initiated by free radicals generated by UV irradiation. In order to obtain sufficient sensitivity to UV radiation, it is necessary to introduce into the printing ink a photoinitiator which decomposes under the influence of UV irradiation, forming free radicals, which in turn initiate the curing reaction.

FR 2274669 describes intaglio printing inks based on varnish (binder) comprising tung oil and an unsaturated aliphatic dicarboxylic acid, which can be cured by UV irradiation in the presence of oxygen. The curing (polymerization) speed of such binders is rather low due to the type of compound used, and therefore it takes a long time to complete the reaction. It is further described that the intaglio ink may be dispersed in a caustic solution wherein the concentration of the caustic compound is typically in the range of 0.5-2 wt%. To facilitate dispersion in the wiping solution, surface tension-active molecules (surfactants) such as sulfonated castor oil or sodium lauryl sulfate have to be added.

EP 432093 describes another intaglio ink which can be dispersed in a caustic solution. The concentration range of the caustic solution is the same as that of the above patent. The intaglio ink is cured by a cationic polymerization process upon UV irradiation. However, the recommended photoinitiators are representative toxicological hazards, since they contain toxic chemical elements such As, Sb or F, respectively.

The object of the present invention is to overcome the drawbacks of the prior art; especially by disclosing an intaglio ink composition that can be easily and fully cured, that requires only low environmental requirements for the necessary post-wiping treatment on the printing press, and that does not contain additives with toxicity problems. Another property of the disclosed intaglio ink is the water solubility of the ink and the simple, fast and economical method of precipitating the dissolved ink from the wiping solution.

It is another object of the present invention to provide a printing ink curable by UV or short wave visible light irradiation for printing security documents using engraved steel die printing. It is also an object of the present invention to provide a printing ink having improved water solubility compared to known printing inks. It is a further object of the present invention to provide UV-curable printing inks based on photoinitiator compounds of low toxicity.

These and other objects are achieved by the invention based on the independent claims.

The printing ink of the invention for use in the gravure printing process comprises a binder selected from water-soluble or water-thinnable acrylate oligomers. Urethane acrylate oligomers and epoxy acrylate oligomers are preferred oligomers in accordance with the present invention because these products are commercially available or can be readily prepared starting from commercial products. Water-soluble urethane acrylates can be prepared from water-soluble or hydrophilic polyols (ethoxylated polyols such as ethoxylated trimethylolpropane supplied by Perstorp specialty Chemicals, Sweden) and 2-hydroxyethyl acrylate or ethoxylated monoacrylates (monoacrylates such as polyethylene glycol or polypropylene glycol, Bisomer supplied by LaportePerform Chemicals, UK) grafted onto the water-soluble polyol using diisocyanates (toluene diisocyanate TDI, 1, 6-hexane diisocyanate HDDI, isophorone diisocyanate IPDI, etc.).

Water-soluble epoxy acrylates can be prepared from ethoxylated di-or triglycidyl ethers (such as diglycidyl ethers of polyethylene glycol or polypropylene glycol, for example diethylene glycol diglycidyl ether supplied by Sigma-Aldrich, polyoxypropylene di-and triglycidyl ethers supplied by Witco, Eurepox and triglycidyl ethers based on 9-ethoxylated trimethylolpropane, for example supplied by EMS Chemie, Switzerland, Grilonit V51-56) by adding acrylic acid using standard procedures.

Alternative oligomers that can be used are polyester acrylates and acrylic acrylates. Each oligomer includes reactive acrylate functionality and two or more repeat units separating these functionalities. The term "oligomer" is used to denote a molecule obtained by chemically linking two or more reactive units (monomers) together, so that the number of linked reactive units remains relatively small. The oligomers are intermediate stages between the monomers and the final polymer. They have a higher molecular weight than the monomers but are lowThe weight average molecular weight Mw of the final polymer obtained. The acrylate monomer is a monomer containing a reactive acrylate (R)₁R₂C＝CR₃-CO-OR₀) Group (R)₀Is an organic residue, a hydrogen atom, or a negative charge). Acrylate oligomers are higher molecular weight products of two or more acrylate monomers crosslinked by acrylic double bonds.

Monomers with low viscosity are also described as reactive diluents due to the fact that they can reduce the viscosity of the oligomer or prepolymer while being incorporated into the cured final film structure. Binders or resins (mainly medium to low molecular weight polymers of synthetic or natural origin) are used in ink and coating compositions in order to "bind" desired functional additives, such as pigments, to the substrate and/or to produce a high molecular weight crosslinked coating on the surface of the substrate, which gives it the desired properties and appearance.

The molecular weight of the radiation curable oligomer or prepolymer is much lower than that of the resin. They are composed of at most a few repeating monomer units, which combine ("polymerize") to form a crosslinked high molecular weight structure upon interaction resulting from irradiation with incident light of sufficient energy. The terms "oligomer" and "prepolymer" are often used interchangeably in the art of radiation curable coatings or inks and are understood to differ significantly from the term "monomer".

Strictly speaking, a monomer is a molecular species capable of forming chemical bonds with the same or similar types of molecules, resulting in chains, sheets or three-dimensional networks (polymers) that may include several to a large number of monomeric building blocks. In the context of the present invention, monomers are understood to be molecular units which are polymerizable by the effect of radiation and which are generally, but not necessarily, of lower molecular weight than oligomers and prepolymers. The monomers are generally lower in viscosity than the oligomers and can be used as reactive diluents in order to reduce the viscosity of the radiation curable formulations, improve the curing speed and increase the crosslinking density (Chemistry & Technology of UV & EB formation for coatings, inks and paints, Vol.2, p.31).

In the context of the present disclosure, the term "water-soluble" means that an amount of 5g of the mentioned compound can be dissolved in 95ml of wiping solution at a temperature between 20 ℃ and 50 ℃. The corresponding cloud point temperature should be below 20 ℃ or above 50 ℃. A common wiping solution for intaglio printing comprises caustic soda in a concentration range between 0.5 and 1.2%. For the intaglio ink of the present invention, the caustic soda concentration is between 0% (pure water) and 0.5%. The concentration of intaglio ink in the wiping solution generally does not exceed 5%. The water-soluble or water-dilutable acrylates of the invention are selected as described above.

Notable urethane acrylates include aliphatic urethane acrylates, aliphatic urethane diacrylates and urethane acrylate oligomers available from various suppliers. Epoxy acrylates include aliphatic epoxy acrylates, aliphatic epoxy diacrylates and epoxy acrylate oligomers as described above, which are experimental products supplied by Sicpa s.a.france. The binder can also be a mixture of the above-mentioned acrylate oligomers. The use of water-soluble or water-dilutable compounds reduces the amount of emulsifiers or surface tension-active compounds required to obtain suitable dispersion properties of the printing inks in aqueous solutions.

Another optional but preferred component of the printing ink composition is a monomer selected from water-soluble or water-thinnable polyethylene glycol (PEG) diacrylate or polyethoxylated polyol triacrylate monomers, which can be used to adjust the viscosity of the printing ink to a desired value. PEG diacrylate monomers include compounds such as PEG-X diacrylate monomers, where X is in the range of 200-700, which are available from different suppliers. The (poly) ethoxylated polyol triacrylate monomers include compounds such as 7-ethoxylated trimethylolpropane triacrylate (TMPTA), 14-ethoxylated TMPTA, 15-ethoxylated TMPTA, 20-ethoxylated TMPTA or 15-ethoxylated bisphenol-A diacrylate monomers. Most of the above listed compounds are commercially available. This list should not be considered as exhaustive and limiting the number of useful compounds in the class.

The viscosity of the ink composition depends inter alia on its detailed content of water, pigments, fillers and other formulation components. However, there are limits to the respective amounts of these substances in view of the desired properties of the printing process and the print. For example, in gravure printing, an excess of water in the ink is detrimental due to the high pressure during printing.

Other components of the printing ink are the photoinitiators required to initiate the polymerization of the binder after irradiation with electromagnetic or electron beam radiation.

Further components of the printing ink compositions are additives such as pigments for providing the ink color, fillers, photosensitizers, light stabilizers, emulsifiers and special additives for security purposes.

According to the invention, the binder and optionally other monomers must be suitably selected in order to obtain a composition which is substantially 100% dispersible in the aqueous wiping solution. The value of 100% is the optimum value. The term "dispersible" should be understood as defined in R * mpp Lexikon, "Lacke und Druckfarben", published 1998, Thieme Verlag Stuttgart, p.147. The aqueous wiping solution may contain sodium hydroxide in a concentration range between 0 and 0.5 wt.%. However, the concentration of sodium hydroxide is preferably chosen between 0.1 and 0.3 wt% and more preferably between 0.1 and 0.2 wt%. The substantially complete dispersibility of the ink composition will avoid separation of the ink composition from the water wiping solution and thus possible clogging of parts of the system containing the water wiping solution. Furthermore, as described below, this may facilitate recovery of unused ink from the water wiping solution.

The low sodium hydroxide concentration of the wiping solution required for printing the inks of the invention has the advantage of being much less environmentally costly than the higher sodium hydroxide concentration of wiping solutions required for printing inks as described in the prior art. However, the low concentration sodium hydroxide solution used to print the inks of the present invention still provides sufficient alkaline conditions to obtain effective corrosion protection for the wiping system.

The main aspect of the invention relates to the regulation and control of the viscosity of intaglio printing inks. The viscosity of the printing ink composition is chosen to be between 7 and 60pa.s (40 ℃). A viscosity between 12 and 40pa.s is preferred and a viscosity of the composition (40 ℃) between 15 and 30pa.s is even more preferred in order for the ink to obtain a suitable rheological behaviour during printing.

As part of the invention, the viscosity of the binder is chosen to be between 5 and 40pa.s (40 ℃). This provides the possibility of reducing the amount of other formulation components required to obtain the necessary rheological properties of the ink.

The binder is preferably selected from the group of compounds described above having a molecular weight Mw of between 1,500 and 10,000g/mol, determined according to the procedure described in Polymer Synthesis, 2 nd revised edition, Ed. Huthig & Wepf1991, page 344, compiled by Paul Rempp and Edward W.Merrill. This molecular weight range provides an ink with sufficient capacity for thorough crosslinking and establishment of a stable three-dimensional network.

In the composition of the intaglio printing ink, the water-soluble or water-thinnable urethane acrylate or epoxy acrylate oligomer is contained in an amount of 30 to 70 wt% based on the total weight of the ink. The preferred content of binder is between 40 and 60%, and more preferably between 45 and 55%, each based on the total weight of the composition.

According to the invention, the content of water-soluble or water-thinnable PEG diacrylate or polyethoxylated polyol triacrylate monomers is preferably chosen between 5 and 25% by weight, relative to the total weight of the ink. Preferred contents of water-soluble or water-thinnable PEG diacrylate or polyethoxylated polyol triacrylate monomers are between 10 and 20 wt.%, and contents between 10 and 15 wt.% are even more preferred.

The amount of water-soluble or water-thinnable PEG diacrylate or polyethoxylated polyol triacrylate or tetraacrylate monomer makes it possible to adjust the viscosity of the total printing ink composition. At the same time, these components provide functional groups similar to those of the ink binder and thus participate in the formation of the polymeric binder matrix in an optimal manner.

The intaglio printing ink comprises a photoinitiator capable of initiating a radical polymerization reaction within the above-mentioned binder and monomer. A suitable type of photoinitiator makes it possible to start a polymerization reaction of a suitable type, which ideally proceeds at a high reaction speed and provides a rapid curing of the printing ink.

According to another aspect of the invention, the photoinitiator can be selected from the group consisting of compounds of the acetophenone or benzophenone type. It is well known that these types of photoinitiators split into free radicals after irradiation with UV or short wavelength visible light, which are capable of initiating the polymerization process.

In addition, the photoinitiators may have the highest absorption at wavelengths between 300nm and 450 nm. Radiation of these wavelengths is easily produced by means of devices such as Hg medium pressure lamps, or Ga/Pb, Fe/Co doped Hg lamps, respectively.

Another aspect of the invention is in the application of photosensitizers that allow higher amounts of captured UV or short wavelength visible photons. The photosensitizer is selected from thioxanthone compounds. Such compounds include, for example, isopropyl-thioxanthone (ITX), 1-chloro-2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX), and 2, 4-diethyl-thioxanthone (DETX), and mixtures thereof.

According to yet another aspect of the invention, a UV stabilizer is added to the ink. In the ink of the present invention, FlorstabUV-1 supplied by Kromachem Ltd, UK has been successfully used. The presence of the UV stabilizer serves to avoid premature polymerization on the press during preparation or during handling of the ink prior to use, and prior to the radiation curing step.

A further aspect of the invention relates to the pigment content of the printing ink composition. According to the invention, a pigment weight percentage of between 3 and 23% can be used. Preferred is a pigment content of between 5 and 12% and still more preferred between 7 and 10% with respect to the total weight of the ink. The type of pigment is selected from the class of pigments that can be applied to UV curable inks according to the prior art.

According to a further aspect of the invention, the filler content of the composition is chosen so as to be between 6 and 50% by weight of the ink. The amount of filler is preferably between 25 and 40%, more preferably between 25 and 35%, relative to the total weight of the ink.

According to yet another aspect of the invention, the filler is selected from natural and artificially prepared calcium carbonates. The type of calcium carbonate is preferably selected from grades with low oil absorption in order to avoid partial embedding of the binder in the filler (which would lead to incomplete polymerization of the binder).

Another part of the invention is a method of producing a gravure ink composition having a viscosity between 7 and 60pa.s at 40 ℃. A more preferred range of viscosity is between 12 and 40pa.s and a still more preferred range is between 15 and 30pa.s (40 ℃). According to the present invention, the ink viscosity is adjusted by adding water-soluble or water-thinnable PEG diacrylate or polyethoxylated polyol triacrylate monomers.

Yet another part of the invention is a method of applying a radiation curable intaglio printing ink in an intaglio printing process using a water wiping system. The water wiping system uses a wiping solution with a sodium hydroxide concentration between 0 and 0.5 wt.%, preferably between 0.1 and 0.3 wt.% and more preferably between 0.1 and 0.2 wt.%.

The ink waste dissolved in the wiping solution after the printing process can be precipitated by adding an inorganic metal halide or sulfate solution. This process is also called flocculation. The effect of this change in the solubility of the printing ink is the so-called "salting out" which is well known in the art of water-soluble organic polymers. The addition of such an inorganic salt solution makes it possible to recover a large amount of printing ink dispersed in the waste wiping solution, and thus to reduce the release of contaminated waste water. The precipitated ink can be recovered by standard solid-liquid separation methods known to those skilled in the art, such as filtration, ultrafiltration, centrifugation, and the like.

The remaining soluble organic content of the wiping solution after ultrafiltration, flocculation and filtration treatment can be determined by means of Chemical Oxygen Demand (COD), Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC) measurements belonging to standard procedures in the field of wastewater characterization. Environmentally friendly intaglio inks are characterized by low COD, TCO or DOC values of the residual wiping solution waste.

The invention also comprises a method of precipitating the above intaglio ink from a wiping solution of an intaglio printing press. The precipitation is notably brought about by the addition of an inorganic metal halide or sulfate solution, such as a solution of calcium chloride, ferric chloride, sodium chloride, potassium chloride or aluminium sulfate.

The invention also comprises a method of precipitating dispersed intaglio printing ink waste from a wiping solution, said method comprising adjusting the temperature of the aqueous wiping solution to between 20 and 50 ℃, preferably between 20 and 40 ℃, and more preferably between 25 and 35 ℃. The temperature significantly affects the solubility of the printing ink in the wiping solution.

In another aspect, the present invention provides a method of gravure printing on a substrate using the ink composition of the present invention. Said printing using said inks notably allows to deposit thin films of thickness comprised between 20 and 60 microns, preferably between 30 and 50 microns, on paper or polymeric substrates. The inks of the invention have the significant advantage that the relatively thick films can be cured thoroughly and rapidly by irradiation with electromagnetic and electron beam radiation, provide excellent and thoroughly dried prints, have excellent chemical and physical resistance, and a non-stick print surface immediately upon leaving the printer.

The invention will now be further explained by means of non-limiting composition examples, which are given for illustrative purposes.

List of abbreviations:

ebecryl 2001 UCB aliphatic urethane diacrylate oligomer

Ebecryl 2002 UCB aliphatic urethane acrylate oligomer

L300-627 SICPA France urethane acrylate oligomer

IRR210 UCB alkoxylated triacrylate

IRR280 UCB PEG-400 acrylate

Photomer 4155 Cognis 7-alkoxylated TMPTA

Photomer 4158 Cognis 14-ethoxylated TMPTA

·OVP^*Optionally modified pigments from Flex Corp, Santa Rosa

·OVI^*Optionally modified inks supplied by Sicpa s.a., Lausanne

Example I

Inks were prepared, printed and cured according to the following general formulation:

sample A B

Ebecryl 2002 46.6

L300-627 46.6

Wax (Montan) 4.04.0

Emulsifier 3.03.0

UV stabilizer 2.02.0

IRGALITE RED 8B 8.0 8.0

Filler (CaCO)₃) 30.0 30.0

ESACURE ITX 2.6 2.6

IRGACURE 369 3.8 3.8

Total 100.0100.0

Results	A	B
			Viscosity/[ Pa.s]	27	45
Viscosity/[ T.U.]	240	300
			Wiping/paper	5	5-6
Print quality/[ 60 ℃ C]*	5-6	5-6
			Drying/[ 2X 50m/min]*	3-4	3
Detergency at 0.1% NaOH	5-6	4-5
			COD[mg O2.L-1]	6’500	10’800

6 is very good; good 5; 4 is satisfactory; 3-difference; 2 is very poor;

the classification of the results for wiping, print quality, drying and detergency in 0.1% NaOH solution was made according to laboratory experience.

Example II

An ink was prepared according to the procedure described in example I.

Sample C D

Ebecryl 2002 35.6 35.6

IRR 210 11.0

IRR 280 11.0

Wax (Montan) 4.04.0

Emulsifier 3.03.0

UV stabilizer 2.02.0

IRGALITE RED 8B 8.0 8.0

Filler (CaCO)₃) 30.0 30.0

ESACURE ITX 2.6 2.6

IRGACURE 369 3.8 3.8

Total 100.0100.0

Results	C	D
			Viscosity/[ Pa.s]	16	20
Viscosity/[ T.U.]	110	130
			Wiping/paper	5-6	5-6
Print quality/[ 60 ℃ C]*	5-6	5-6
			Drying/[ 2X 50m/min]*	5	5
Detergency at 0.1% NaOH	5	5
			COD[mg O2.L-1]	10’675	10’685

6 is very good; good 5; 4 is satisfactory; 3-difference; 2 is very poor;

example III

Sample E F

Ebecryl 2001 32.0

Ebecryl 2002 35.6

Photomer 4155 14.6

Photomer 4158 11.0

Wax (Montan) 4.04.0

Emulsifier 3.03.0

UV stabilizer 2.02.0

IRGALITE RED 8B 8.0 8.0

Filler (CaCO)₃) 30.0 30.0

ESACURE ITX 2.6 2.6

IRGACURE 369 3.8 3.8

Total 100.0100.0

Results	E	F
			Viscosity/[ Pa.s]	27	14
Viscosity/[ T.U.]*	225	125
			Wiping/paper	5-6	5-6
Print quality/[ 60 ℃ C]*	5-6	5-6
			Drying/[ 2X 50m/min]*	5	5-6
Detergency at 0.1% NaOH	5	5
			COD[mg O2.L-1]	10’590	10’700

6 is very good; good 5; 4 is satisfactory; 3-difference; 2 is very poor;

example IV

The following samples using PEG 400DA (IRR280 or Cray Valley SR344) monomers and aliphatic urethane acrylate oligomers (Ebecryl 2002) are disclosed. Preparation and testing included Red, magnetic Green and OVI^*Different examples of formulations.

Sample G: red wine

L300-600 35.6

IRR 280 11.0

Wax (Montan) 4.0

Emulsifier 3.0

UV stabilizer 2.0

IRGALITE RED 8B 8.0

Filler (CaCO)₃) 30.0

ESACURE ITX 2.6

IRGACURE 369 3.8

Total 100.0

Sample H: magnetic green

Ebecryl 2002 46.6

Wax (Montan) 4.0

Emulsifier 3.0

UV stabilizer 2.0

Mapico yellow 215 9.5

IRGALITE GREEN GL 1.5

Carbon Black Raven 0.45

IRGALITE BLUE LGLD 0.35

Filler (CaCO)₃) 26.1

ESACURE ITX 2.6

IRGACURE 369 3.8

Total 100.0

Sample I: OVI^*Green-blue

Ebecryl 2002 46.6

Wax (Montan) 4.5

Emulsifier 3.0

UV stabilizer 2.0

OVP Green/blue 22.0

Filler (CaCO)₃) 6.5

Aerosil 200 9.0

ESACURE ITX 2.6

IRGACURE 369 3.8

Total of 100.0

Results	Sample G	Sample H	Sample I
				Viscosity/[ Pa.s]	6-7	30-40	30-40
Viscosity/[ T.U.]*	100	200	240
				Wiping/paper	5-6	5-6	5-6
Print quality/[ 60 ℃ C]*	5*	5-6	5
				Drying/[ 2X 50m/min]*	4-5*	4-5	5-6
Detergency at 0.1% NaOH	5*	5-6	5-6

6 is very good; good 5; 4 is satisfactory; 3-difference; 2 is very poor.

Example V

Sample J

Ebecryl 2002 35.6

IRR280 11.0

Wax (Montan) 4.0

Emulsifier 3.0

UV stabilizer 2.0

IRGALITE RED 8B 8.0

Filler (CaCO)₃) 30.0

ESACURE ITX 2.6

IRGACURE 369 3.8

Total 100.0

Inks of the above-listed compositions have been printed under industrial printing conditions. The first printing test was performed with a MiniOrlof Intaglio MOI printer available from De LaRue-Giori using both conditions of a pure water wiping solution and a 0.1% NaOH wiping solution. Under both conditions, print quality and wiping were excellent. The second printing test was performed using a SuperOrlofIntaglio SOI printer under the same conditions. In the case of a pure water wiping solution, the ink of example 1 was wiped off the plate and washed off the wiping cylinder in the correct manner. The wiping and washing of the ink is significantly improved when using 0.1 or 0.2% NaOH wiping solution. When the NaOH concentration was further increased (0.3% NaOH and 0.3% or more NaOH), the wiping and washing problems again occurred, which gradually worsened as the NaOH concentration was further increased.

The COD value of sample J was measured in two cases:

sample J/CaCl2(35％)	COD[mg O2.L-1]
		Pure water solution pH 6-7	2’750
0.2％NaOH，pH＝10-11	3’340

Example VI

Sample K was the same as sample J, except that IRR280 was replaced with Ebecryl 2002.

The COD of sample G was measured. 3g of fresh ink were dispersed in 97g of water for 1-2 hours (NaOH 0.1%) and heated at 50 ℃. The ink dispersion was allowed to cool under stirring. At 30 ℃, 1.5% mineral powder was added. Slowly add 10% CaCl in small portions₂Solution (1.5 ml total). Three different salts were used to precipitate the ink disclosed in sample G. The loose red precipitate was filtered using a paper filter. The solutions were analysed under identical conditions。

COD[mg O2.L-1]	Sample G	Sample J	Sample K
				NaCl 10％	10700	7530	5650
CaCl210％	10600	7490	6490
				FeCl310％	10670	7530	7600
Al2(SO4)3 10％	10570	7440	6940

As can be seen from these results, the COD appears to be unrelated to the nature or charge of the multivalent cations used to flocculate the ink waste. However, the nature of the acrylate oligomer or monomer is more critical.

Claims (25)

1. An intaglio printing ink composition comprising:

(a) a first binder compound selected from the group consisting of water-soluble or water-thinnable acrylate oligomers;

(b) a photoinitiator that initiates polymerization of the binder upon irradiation with electromagnetic or electron beam radiation;

(c) at least one pigment;

wherein the first binder (a) is selected such that the composition is substantially completely dispersible in a water wiping solution having a sodium hydroxide concentration of between 0 and 0.5% and the viscosity of the composition is between 7 and 60Pa.s at 40 ℃.

2. Intaglio printing ink according to claim 1 further comprising a second monomeric binder compound selected from the group consisting of water-soluble or water-thinnable polyethylene glycol diacrylate or polyethoxylated polyol triacrylate monomers to adjust the viscosity and selected so that said composition is substantially completely dispersed in a water wiping solution with a sodium hydroxide concentration between 0 and 0.5%.

3. Intaglio printing ink according to claim 1 further comprising additives selected from the group consisting of fillers, photosensitizers, light stabilizers and emulsifiers.

4. The intaglio printing ink according to claim 1 wherein the first binder component is selected from the group consisting of water-soluble or water-thinnable urethane acrylate oligomers, water-soluble or water-thinnable epoxy acrylate oligomers, water-soluble or water-thinnable acrylic acrylate oligomers, water-soluble or water-thinnable polyester acrylate oligomers and mixtures thereof.

5. Intaglio printing ink according to any one of the claims 1 to 4 wherein the viscosity of the composition at 40 ℃ is between 12 and 40 Pa.s.

6. Intaglio printing ink according to any one of the claims 1 to 4 wherein the viscosity of the composition at 40 ℃ is between 15 and 30 Pa.s.

7. Intaglio printing ink according to claim 1 wherein the viscosity of the binder (a) at 40 ℃ is between 5 and 40 pa.s.

8. Intaglio printing ink according to claim 1 wherein the molecular weight Mw of the binder (a) is between 1,500 and 10,000 g/mol.

9. Intaglio printing ink according to any of the claims 1 to 4 characterized in that the content of water-soluble or water-thinnable acrylate oligomer is between 30 and 70% by weight based on the total weight of the ink.

10. Intaglio printing ink according to claim 2 characterized in that the content of water-soluble or water-thinnable polyethylene glycol diacrylate or polyethoxylated polyol triacrylate monomers is between 5 and 25% by weight, with respect to the total weight of the ink.

11. Intaglio printing ink according to claim 2 characterized in that the photoinitiator is capable of initiating a radical polymerization reaction of the first binder (a) and the second binder (b).

12. Intaglio printing ink according to claim 11 characterized in that said photoinitiator is selected from the group consisting of acetophenone and benzophenone-based compounds.

13. Intaglio printing ink according to claim 12 characterized in that said photoinitiator has a maximum absorption between the wavelengths of 300 and 450 nm.

14. Intaglio printing ink according to claim 3 characterized in that the photoinitiator is selected from the group of thioxanthone-based compounds.

15. Intaglio printing ink according to claim 14 characterized in that said thioxanthone based compound is selected from the group consisting of isopropyl-thioxanthone, 1-chloro-2-propoxy-thioxanthone, 2-chloro-thioxanthone and 2, 4-diethyl-thioxanthone, and mixtures thereof.

16. Intaglio printing ink according to claim 3 characterized in that UV stabilizers are added as light stabilizers to prevent premature polymerization of the ink.

17. Intaglio printing ink according to claim 1 characterized in that the pigment content of the composition is comprised between 3 and 15% by weight with respect to the total weight of the ink.

18. Intaglio printing ink according to claim 3 characterized in that the filler content of the composition is between 20 and 50% by weight with respect to the total weight of the ink.

19. Intaglio printing ink according to claim 18 characterized in that the filler is selected from calcium carbonates having a low oil absorption rating.

20. A process for producing an intaglio printing ink composition according to any one of claims 1 to 19 wherein the viscosity of the composition is adjusted to have a value between 7 and 60pa.s at 40 ℃; the viscosity adjustment includes the step of adding a water-soluble or water-thinnable polyethylene glycol diacrylate or polyethoxylated polyol triacrylate monomer.

21. Use of a composition according to any one of claims 1 to 19 in a gravure printing process comprising a wiping system comprising a water wiping solution having a sodium hydroxide concentration of between 0 and 0.5%.

22. A method of applying the radiation curable intaglio printing ink composition according to any of claims 1 to 19 in an intaglio printing process comprising a wiping system comprising a wiping solution having a sodium hydroxide concentration of between 0 and 0.5%, wherein waste ink is separated from the wiping solution by the addition of an inorganic metal halide or sulphate solution.

23. A method according to claim 22, comprising the step of adjusting the temperature of the wiping solution to between 20 and 50 ℃.

24. A method of making an intaglio print on a substrate using an intaglio printing ink according to any one of claims 1 to 19 comprising the steps of printing said ink onto said substrate at a film thickness of 20 to 60 microns and curing said print by irradiation with electromagnetic or electron beam radiation.

25. A security document comprising indicia made with an intaglio printing ink composition according to any of claims 1 to 19.