Printing process

Abstract

The invention provides a water-based, UV-curable inkjet ink.

Description

[0001] PRINTING PROCESS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of UV-curable inkjet inks.

[0004] BACKGROUND OF THE INVENTION

[0005] Inks for inkjet printing must be relatively low viscosity, and must cure rapidly, producing a high-quality image that is resistant to smearing immediately after curing. Durability (resistance to wear) of the printed image is also important. In addition, because inkjet inks typically sit in a printhead and / or cartridge for prolonged periods between use, it is important that the ink show good “restartability”, i.e. that the ink retain the above-mentioned characteristics over time, and not polymerize or form a precipitate during storage to avoid clogging the printhead.

[0006] For environmental and user safety reasons, there is an increasing demand for inkjet inks having reduced organic solvent content (i.e. water-based).

[0007] Thus there is a need for water-based inkjet inks that show good printing characteristics and good restartability.

[0008] SUMMARY OF THE INVENTION

[0009] In a first aspect, the invention provides a water-based UV-curable inkjet ink comprising:

[0010] (A) water;

[0011] (B) one or more di(meth)acrylates;

[0012] (C) one or more mono(meth)acrylates;

[0013] (D) one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1,000 g / mol;

[0014] (E) the following photoinitiators: e1) a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) anthracene methanol; and e3) a thioxanthone of general formula IV: where R3is Ci-Ce-alkyl and is repeated 1 or 2 times; and

[0015] (F) one or more pigments or dyes. In a second aspect, the invention provides a water-based UV-curable inkjet ink comprising:

[0016] (A) water;

[0017] (B) one or more di(meth)acrylates of general Formula I: where R is H or CH3, and n is from 1 to 20;

[0018] (C) one or more mono(meth)acrylates of formula II: where R1is H or CH3, and m is from 2 to 6;

[0019] (D) one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1,000 g / mol;

[0020] (E) the following photoinitiators: e1 ) a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) anthracene methanol; and e3) a thioxanthone of general formula IV: where R3is Ci-Ce-alkyl and is repeated 1 or 2 times; and

[0021] (F) one or more pigments or dyes.

[0022] In a third aspect, the invention provides an inkjet cartridge comprising the water-based UV-curable inkjet ink of the invention.

[0023] In a fourth aspect, the invention provides an inkjet printer comprising the water-based UV-curable inkjet ink of the invention.

[0024] In a fifth aspect, the invention provides a printed feature formed by applying the water-based UV- curable inkjet ink of the invention on a substrate and curing the ink.

[0025] In a sixth aspect, the invention provides a process for printing a feature on a substrate by a process comprising the steps of: a) applying the water-based UV-curable inkjet ink of the invention by inkjet printing so as to form an uncured ink layer; and b) exposing the uncured ink layer to U V light at a dose of at least 150 mJ / cm2, to form a cured ink layer.

[0026] DETAILED DESCRIPTION

[0027] Definitions

[0028] As used herein, the article "a" indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0029] As used herein, the term “about” means that the amount or value in question may be the value designated or some other value about the same. The phrases are intended to convey that similar values within a range of ± 5% of the indicated value promote equivalent results or effects according to the invention.

[0030] The term “UV” (ultraviolet) as used herein is intended to mean radiation having a wavelength component in the UV part of the electromagnetic spectrum; typically from 200 nm to 420 nm.

[0031] As used herein, the term “at least one” is meant to define one or more than one, for example one or two or three. As used herein, the term “and / or” means that either all or only one of the elements of said group may be present. For example, “A and / or B” shall mean “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

[0032] The term “comprising” as used herein is intended to be non-exclusive and open-ended. Thus, for instance an ink comprising a compound A may include other compounds besides A. However, the term “comprising” also covers, as a particular embodiment thereof, the more restrictive meanings of “consisting essentially of and “consisting of”, so that for instance “an ink comprising A, B and optionally C” may also (essentially) consist of A and B, or (essentially) consist of A, B and C.

[0033] The term "security document" refers to a document which is usually protected against counterfeit or fraud by at least one security feature. Examples of security documents include without limitation value documents and value commercial goods.

[0034] The term “security feature” is used to denote an image, pattern or graphic element that can be used for authentication purposes.

[0035] Where the present description refers to “preferred” embodiments / features, combinations of these “preferred” embodiments / features shall also be deemed as disclosed as long as this combination of “preferred” embodiments / features is technically meaningful.

[0036] The term “(meth)acrylate” encompasses molecules bearing acrylate and / or (meth)acrylate moieties.

[0037] Abbreviations

[0038] DEGDMA Diethylenglycol dimethacrylate

[0039] PEGDA Polyethylenglycol diacrylate

[0040] Trimethylolpropane ethoxylate triacrylate

[0041] 1,6-HDDMA 1,6-Hexanediol dimethacrylate

[0042] BAPO-Na a molecule of general formula III, where R is benzoyl substituted with three methyl groups, and M+is Na+

[0043] The inventors have created a water-based UV-curable inkjet ink showing good printing characteristics, good durability of the printed image and good restartability. Restartability is a measure of the retention of good printing properties after various periods of time between printing sessions. It can be measured using the method recited in the Examples.

[0044] The various features of the ink of the invention will now be described in more detail.

[0045] Solvent (A)

[0046] The inks of the invention comprise water as solvent and / or suspension agent. The inks of the invention preferably comprise from about 25 to about 50 wt%, more preferably from about 28 to about 45 wt% water, based on the total weight of the ink.

[0047] In addition to water, the inks of the invention may comprise water-miscible solvents. Examples of suitable water miscible solvents include, but are not limited to alcohols, other than anthracene methanol (such as mono and poly alcohols, including diols and triols), ketones, ethers (such as dioxanes, and tetrahydrofuran), esters and amides. If used, the water-miscible solvent is preferably used at from about 10 to about 50 wt%, more preferably from about 15 to about 35 wt%, based on the total weight of the ink. Preferably the concentration of water in the ink of the invention is equal to or greater than the concentration of water-miscible solvent. In one embodiment, the wt% ratio of the concentration of water to the concentration of the water-miscible solvent is about 3:1. In another embodiment the ratio is about 1:1.

[0048] In one embodiment, the ink of the invention comprises a Ci-Cs-alcohol, preferably methanol or ethanol, preferably at a wt% ratio of wateralcohol of from about 3:1 to about 1 :1 , in particular about 1 :1 water: ethanol.

[0049] In one embodiment, the ink of the invention comprises a Ci-Cs-alcohol, preferably methanol or ethanol, preferably at a concentration of from about 10 to about 50 wt%, more preferably from about 15 to about 35 wt%, based on the total weight of the ink.

[0050] In another embodiment, the ink of the invention comprises from about 25 to about 50 wt%, more preferably from about 28 to about 45 wt% water, and a Ci-Cs-alcohol, preferably methanol or ethanol, at a concentration of from about 10 to about 50 wt%, more preferably from about 15 to about 35 wt%, based on the total weight of the ink.

[0051] In another embodiment, the ink of the invention comprises from about 25 to about 35 wt% water and from about 25 to about 35 wt% of a Ci-Cs-alcohol, preferably methanol or ethanol.

[0052] One or more di(meth)acrylates (B)

[0053] The ink of the invention comprises one or more di(meth)acrylates. Suitable di(meth)acrylates are not particularly limited. Preferably the di(meth)acrylates comprise polyether linkages to improve water solubility, for example poly(ethyleneoxide) di(meth)acrylates, poly(propyleneoxide) di(meth)acrylates, or poly(butyleneoxide) di(meth)acrylates, more preferably poly(ethyleneoxide) di(meth)acrylates, poly(propyleneoxide) di(meth)acrylates.

[0054] In a preferred embodiment, the ink of the invention comprises one or more di(meth)acrylates of general Formula I: where R is H or CH3, and n is from 1 to 20.

[0055] Preferred molecules of general formula I are dimethacrylates (i.e. R=Me). In one embodiment, n is 2.

[0056] In another embodiment, R is Me and n is 2.

[0057] The di(meth)acrylate, preferably of general formula I, is preferably present at from about 4 to about 15 wt%, more preferably from about 7 to about 12 wt%, based on the total weight of the ink. In a preferred embodiment, in the di(meth)acrylate, preferably of general formula I, n is 2, and the di(meth)acrylate is present at from about 4 to about 15 wt%, more preferably from about 7 to about 12 wt%, based on the total weight of the ink.

[0058] One or more mono(meth)acrylates (C)

[0059] The ink of the invention comprises one or more mono(meth)acrylates. Suitable mono(meth)acrylates are not particularly limited. Acrylate monoesters with diols are preferred.

[0060] Preferably, the ink of the invention comprises one or more mono(meth)acrylates of formula II: where R1is H or CH3, and m is from 2 to 6.

[0061] In one embodiment, the mono(meth)acrylate, preferably of formula II, is a monoacrylate (i.e. R1=H).

[0062] In one embodiment, m is from 2 to 6, more preferably from 3 to 5, particularly preferably m is 4.

[0063] In one embodiment, R1is H and m is 4.

[0064] The mono(meth)acrylate, preferably of general formula II, is preferably present at from about 0.5 to about 6.5 wt%, more preferably from about 1 to about 3 wt%, particularly preferably about 2 wt%, based on the total weight of the ink. In a preferred embodiment, R1is H, m is 4, and the mono(meth)acrylate is present at from about 1 to about 3 wt%, particularly preferably about 2 wt%, based on the total weight of the ink.

[0065] One or more tetra(meth)acrylates (D)

[0066] The ink of the invention comprises one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol, more preferably from about 350 to about 900 g / mol.

[0067] The tetra(meth)acrylate is preferably a tetraacrylate. The tetraacrylate is not particularly limited. Preferred tetraacrylates include ditrimethylolpropane tetraacrylates, pentaerythritol tetraacrylates, alkoxylated pentaerythritol tetraacrylates and mixtures thereof, preferably selected from the group consisting of ditrimethylolpropane tetraacrylates, alkoxylated pentaerythritol tetraacrylates and mixtures thereof, in particular ditrimethylolpropane tetraacrylates, ethoxylated pentaerythritol tetraacrylates and mixtures thereof.

[0068] The one or more tetra(meth)acrylates is preferably present at from about 0.2 to about 8 wt%, more preferably at from about 1 to about 5 wt%, particularly preferably at from about 2 to about 4 wt%, based on the total weight of the ink.

[0069] In a preferred embodiment, the one or more tetra(meth)acrylates comprises di(trimethylolpropane)tetraacrylate, used at from about 0.2 to about 8 wt%, more preferably at from about 1 to about 5 wt%, particularly preferably at from about 2 to about 4 wt%, based on the total weight of the ink.

[0070] Photoinitiators (E)

[0071] The ink of the invention comprises the following photoinitiators: e1 ) a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups.

[0072] In one embodiment, R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups. In another embodiment, R is phenyl, substituted with 1 to 3 Ci to C2-alkyl groups. In yet another embodiment, R is phenyl, substituted with 3 methyl groups. In another embodiment, R is phenyl, substituted with 3 methyl groups, and M+is Li+.

[0073] In one embodiment, R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups. In another embodiment, R is benzoyl, substituted with 3 Ci to C2-alkyl groups. In yet another embodiment, R is benzoyl, substituted with 3 methyl groups. In another embodiment, R is benzoyl, substituted with 3 methyl groups and M+is Na+. e2) anthracene methanol; and e3) a thioxanthone of general formula IV: where R3is Ci-Ce-alkyl and is repeated 1 or 2 times.

[0074] The molecule of general formula III is preferably used at from about 1.7 to about 3.5 wt%, more preferably at from about 2 to about 3.4 wt%, more particularly preferably at from about 2.8 to about 3.3 wt%, based on the total weight of the ink.

[0075] In a preferred embodiment, the compound of general formula III is BAPO-Na, used at from about 1.7 to about 3.5 wt%, more preferably at from about 2 to about 3.4 wt%, more particularly preferably at from about 2.8 to about 3.3 wt%, based on the total weight of the ink.

[0076] Anthracene methanol is preferably used at from about 0.25 to about 0.75 wt%, more preferably from about 0.3 to about 0.6 wt%, more particularly preferably about 0.5 wt%, based on the total weight of the ink.

[0077] In the thioxanthone of general formula IV, R3is preferably present one time, and preferably Cs-alkyl, more preferably / -propyl.

[0078] The thioxanthone of general formula IV is preferably used at from about 1 to about 3.5 wt%, more preferably from about 1.2 to about 3 wt%, more particularly preferably at from about 1.5 to about 2.5 wt%, based on the total weight of the ink.

[0079] In a preferred embodiment, in the thioxanthone of general formula IV, R3is / -propyl, and the thioxanthone is used at from about 1 to about 3.5 wt%, more preferably from about 1.2 to about 3 wt%, more particularly preferably at from about 1.5 to about 2.5 wt%, based on the total weight of the ink.

[0080] In one embodiment, the wt% ratio of [molecule of general formula lll]:anthracenemethanol:[thioxanthone of general formula IV] is about: 1.7-3.5:0.25-0.75:1-3.5, preferably 2-3.4:0.3-0.6: 12-3, more preferably 2.8-3.3:0.5:15-2.5. A preferred ratio [molecule of general formula lll]:anthracenemethanol:[thioxanthone of general formula IV] is about 3:0.5:18. One or more pigments or dyes (F)

[0081] The ink of the invention comprises one or more pigments or dyes. The pigments or dyes are not particularly limited, provided they are compatible with inkjet printing.

[0082] The dyes include but are not limited to azo dyes, anthraquinone dyes, xanthene dyes, azine dyes, combinations thereof and the like. Organic pigments may be one pigment or a combination of pigments, such as for instance Pigment Yellow Numbers 12, 13, 14, 17, 74, 83, 114, 126, 127, 174, 188; Pigment Red Numbers 2, 22, 23, 48: 1, 48:2, 52, 52: 1 , 53, 57:1 , 112, 122, 166, 170, 184, 202, 266, 269; Pigment Orange Numbers 5, 16, 34, 36; Pigment Blue Numbers 15, 15:3, 15:4; Pigment Violet Numbers 3, 23, 27; and / or Pigment Green Number 7. Inorganic pigments may be one of the following non-limiting pigments: iron oxides, titanium dioxides, chromium oxides, ferric ammonium ferrocyanides, ferric oxide blacks, Pigment Black Number 7 and / or Pigment White Numbers 6 and 7. Other organic and inorganic pigments and dyes can also be employed, as well as combinations that achieve the colors desired.

[0083] The pigments and / or dyes are preferably dispersed in a mixture comprising (meth)acrylates (B), (C), and (D) prior to their incorporation in the ink.

[0084] The pigments or dyes are preferably used at from about 2 to about 15 wt%, more preferably from about 3 to about 10 wt%, based on the total weight of the ink.

[0085] Additional ingredients

[0086] The inks of the invention may optionally comprise various other ingredients, including, but not limited to stabilizers, wetting aids, slip agents, inert resins such as acrylate polymers, defoaming agents, fillers, rheological aids, amine synergists, etc.

[0087] Specific examples of optional ingredients include:

[0088] Other (meth)acrylate monomers and oligomers in addition to (meth)acrylates (B), (C) and (D), such as, di(meth)acrylates, tri(meth)acrylates and tetra(meth)acrylates.

[0089] An example of a suitable di(meth)acrylate is poly(ethyleneglycol)diacrylate (PEGDA), in particular PEGDA having a number molecular weight of about 300 g / mol to about 1 ,000 g / mol, preferably about 350 to about 800 g / mol, more preferably about 400 g / mol.

[0090] An example of a suitable tri(meth)acrylate is trimethylolpropane ethoxylate triacrylate (TMP), in particular having the structure: having a molecular weight of about 428 g / mol, where n is about 0.63. If present, TMP is used at from about 2 to about 8 wt%, preferably at from about 3 to about 6 wt%, more preferably at about 5 wt%, based on the total weight of the ink.

[0091] An example of a suitable tetra(meth)acrylate is di(trimethylolpropane)tetraacrylate.

[0092] One or more surfactants, such as polysiloxanes, preferably (meth)acrylate-modified polysiloxanes, more preferably polyether modified acrylate functional polydimethylsiloxanes.

[0093] De-aerating or defoaming agents, such as, for example a poly(dimethylsiloxane) emulsion with silica.

[0094] The inks of the invention show good reliability of the printhead during its life; which means that:

[0095] - the printhead does not exhibit significant nozzle failure, during use or shelf-life;

[0096] - the printhead does not exhibit significant “decap failures” during pauses in printing.

[0097] Another aspect of the invention is a printed image or feature consisting of a cured ink layer made by curing an ink of the invention.

[0098] The invention also relates to an article or document comprising a substrate and one or more printed features of the invention.

[0099] Typical examples of substrate include, without limitation, fiber-based substrates, preferably substrates based on cellulosic fibers such as paper, paper-containing materials, polymer-based materials, composite materials (e.g. substrates obtained by the lamination of paper layers and polymer films), metals or metalized materials (for example aluminum), silicon, ceramic, glasses, ceramics and combinations thereof. Typical examples of polymer-based substrates are substrates made of ethylene- or propylene-based homo- and copolymers such as polypropylene (PP) and polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyamide (PA), polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET).

[0100] Preferably, the substrate of the article or document is a paper-containing material, a polymer-based material, a composite material, metal, glass, ceramic or any combination thereof.

[0101] Another aspect of the invention is an inkjet cartridge comprising the ink of the invention. An inkjet cartridge comprises a printhead. In one embodiment, the printhead is a thermal inkjet printhead. A thermal inkjet printhead typically comprises a printhead substrate; a nozzle layer, including a plurality of nozzles formed therethrough; a plurality of ink ejection chambers corresponding to the plurality of nozzles; a plurality of heater resistors formed on the printhead substrate and corresponding to the plurality of ink ejection chambers, each of the heater resistors being located in a different one of the ink ejection chambers so that ink drop ejection through each of the nozzles is caused by heating of one of the heater resistors that is located in the corresponding ink ejection chamber; and the inkjet printing ink according to the invention. The invention also provides a process for printing a feature on a substrate by a process comprising the steps of: a) applying the water-based UV-curable inkjet ink of the invention by inkjet printing so as to form an uncured ink layer; and b) exposing the uncured ink layer to U V light at a dose of at least 150 mJ / cm2, to form a cured ink layer.

[0102] In a preferred embodiment, step a) of the process is carried out with a thermal inkjet printhead.

[0103] In a preferred embodiment, step b) consists of exposing the ink layer to one or more wavelengths between about 380 nm and about 420 nm. Typically, commercially available Hg or UV-LED sources use one or more wavelengths such as for example 365 nm, 385 nm, 395 nm and 405 nm.

[0104] Preferably the curing / drying time of step b) of the process is comprised between about 0.02 sec and about 1 sec, more preferably between about 0.07 sec and about 0.44 sec.

[0105] In an embodiment of the invention, the printing frequency is higher than about 7 KHz. In a preferred embodiment, the printing frequency is higher than about 8 KHz. More preferably, the printing frequency is higher than about 9 KHz.

[0106] Preferred embodiments of the invention

[0107] 1 . A water-based UV-curable inkjet ink comprising:

[0108] (A) water;

[0109] (B) one or more di(meth)acrylates;

[0110] (C) one or more mono(meth)acrylates;

[0111] (D) one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol;

[0112] (E) the following photoinitiators: e1 ) a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) anthracene methanol; and e3) a thioxanthone of general formula IV: where R3is C-i-Cs-alky I and is repeated 1 or 2 times; and

[0113] (F) one or more pigments or dyes.

[0114] A water-based UV-curable inkjet ink comprising:

[0115] (A) water;

[0116] (B) one or more di(meth)acrylates of general Formula I: where R is H or CH3, and n is from 1 to 20;

[0117] (C) one or more mono(meth)acrylates of formula II: where R1is H or CH3, and m is from 2 to 6;

[0118] (D) one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol;

[0119] (E) the following photoinitiators: e1 ) a molecule of general formula III:

[0120] where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) anthracene methanol; and e3) a thioxanthone of general formula IV: where R3is C-i-Cs-alky I and is repeated 1 or 2 times; and (F) one or more pigments or dyes. A water-based UV-curable inkjet ink comprising:

[0121] (A) about 25 to about 50 wt% water;

[0122] (B) about 4 to about 15 wt% of one or more di(meth)acrylates;

[0123] (C) about 0.5 to about 6.5 wt% of one or more mono(meth)acrylates;

[0124] (D) about 0.2 to about 8 wt% of one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol;

[0125] (E) the following photoinitiators: e1 ) about 1.7 to about 3.5 wt% of a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) about 0.25 to about 0.75 wt% of anthracene methanol; and e3) about 1 to about 3.5 wt% of a thioxanthone of general formula IV: where R3is Ci-Ce-alkyl and is repeated 1 or 2 times; and

[0126] (F) about 2 to about 15 wt% of one or more pigments or dyes; the weight percentages being based on the total weight of the ink.

[0127] 4. A water-based UV-curable inkjet ink comprising:

[0128] (A) about 25 to about 50 wt% water;

[0129] (B) about 4 to about 15 wt% of one or more di(meth)acrylates of general Formula I: where R is H or CH3, and n is from 1 to 20;

[0130] (C) about 0.5 to about 6.5 wt% of one or more mono(meth)acrylates of formula II: where R1is H or CH3, and m is from 2 to 6;

[0131] (D) about 0.2 to about 8 wt% of one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol;

[0132] (E) the following photoinitiators: e1 ) about 1.7 to about 3.5 wt% of a molecule of general formula III: where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) about 0.25 to about 0.75 wt% of anthracene methanol; and e3) about 1 to about 3.5 wt% of a thioxanthone of general formula IV: where R3is Ci-Ce-alkyl and is repeated 1 or 2 times; and

[0133] (F) about 2 to about 15 wt% of one or more pigments or dyes; the weight percentages being based on the total weight of the ink.

[0134] 5. The ink of any one preceding embodiment, which comprises from about 25 to about 50 wt%, more preferably from about 28 to about 45 wt% water, based on the total weight of the ink.

[0135] 6. The ink of any one preceding embodiment, which additionally comprises at least one water- miscible solvent, preferably selected from alcohols, other than anthracene methanol (e.g. monols, diols, triols), ketones, ethers (e.g. dioxanes, and tetrahydrofuran), amides and esters.

[0136] 7. The ink of embodiment 6, wherein the at least one water-miscible solvent is present at from about 10 to about 50 wt%, more preferably from about 15 to about 35 wt%, based on the total weight of the ink.

[0137] 8. The ink of any one preceding embodiment, which comprises a Ci-Cs-alcohol, preferably methanol or ethanol, preferably at a ratio of water:alcohol of from about 3:1 to about 1:1 , in particular about 1:1 water:ethanol.

[0138] 9. The ink of any one preceding embodiment, wherein in the one or more di(meth)acrylates of general formula I, R is Me.

[0139] 10. The ink of any one preceding embodiment, wherein in the one or more di(meth)acrylates of general formula I, n is 2.

[0140] 11 . The ink of any one preceding embodiment, wherein the di(meth)acrylate of general formula I is present at from about 4 to about 15 wt%, preferably from about 7 to about 12 wt%, based on the total weight of the ink.

[0141] 12. The ink of any one preceding embodiment, wherein in the mono(meth)acrylate of formula II R1=H.

[0142] 13. The ink of any one preceding embodiment, wherein in the mono(meth)acrylate of formula II m is 4.

[0143] 14. The ink of any one preceding embodiment, wherein the mono(meth)acrylate of general formula II is present at from about 0.5 to about 6.5 wt%, more preferably from about 1 to about 3 wt%, particularly preferably about 2 wt%, based on the total weight of the ink.

[0144] 15. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol has a molecular weight of from about 350 to about 1,000 g / mol.

[0145] 16. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol is selected from ditrimethylolpropane tetraacrylates, pentaerythritol tetraacrylates, alkoxylated pentaerythritol tetraacrylates and mixtures thereof.

[0146] 17. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol is selected from the group consisting of ditrimethylolpropane tetraacrylates, alkoxylated pentaerythritol tetraacrylates and mixtures thereof.

[0147] 18. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol is selected ditrimethylolpropane tetraacrylates, ethoxylated pentaerythritol tetraacrylates and mixtures thereof.

[0148] 19. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates is present at from about 0.2 to about 8 wt%, preferably at from about 1 to about 5 wt%, more preferably at from about 2 to about 4 wt%, based on the total weight of the ink. The ink of any one preceding embodiment, wherein the one or more tetra(meth)acrylates comprises di(trimethylolpropane)tetraacrylate, preferably used at from about 0.2 to about 8 wt%, more preferably at from about 1 to about 5 wt%, particularly preferably at from about 2 to about 4 wt%, based on the total weight of the ink. The ink of any one preceding embodiment, wherein in the molecule of general formula III, M+is Na+. The ink of any one preceding embodiment, wherein in the molecule of general formula III is used at from about 1 .7 to about 3.5 wt%, preferably at from about 2 to about 3.4 wt%, more preferably at from about 2.8 to about 3.3 wt%, based on the total weight of the ink. The ink of any one preceding embodiment, wherein anthracene methanol is used at from about 0.25 to about 0.75 wt%, preferably from about 0.3 to about 0.6 wt%, more preferably about 0.5 wt%, based on the total weight of the ink. The ink of any one preceding embodiment, wherein in the thioxanthone of general formula IV, R3is Cs-alky I, preferably / -propyl. The ink of any one preceding embodiment, wherein in the thioxanthone of general formula IV, R3is / -propyl, and only one / -propyl substituent is present. The ink of any one preceding embodiment, wherein the thioxanthone of general formula IV is used at from about 1 to about 3.5 wt%, preferably from about 1.2 to about 3 wt%, more preferably at from about 1.5 to about 2.5 wt%, based on the total weight of the ink. The ink of any one preceding embodiment, wherein the wt% ratio of [molecule of general formula lll]:anthracenemethanol:[thioxanthone of general formula IV] is about 1.7-3.5:0.25- 0.75:1-3.5, preferably 2-3.4:0.3-0.6:1.2-3, more preferably 2.8-3.3:0.5: 1.5-2.5. An inkjet cartridge comprising the water-based UV-curable inkjet ink of any one preceding embodiment. A printed feature formed by applying the water-based UV-curable inkjet ink of any one of embodiments 1 to 27 on a substrate and curing the ink. A printed feature comprising:

[0149] (A) a substrate;

[0150] (b) an indicia on the substrate formed by a cured ink of any one of embodiments 1 to 27. 31 . The printed feature of embodiment 30, wherein the ink is cured by UV light.

[0151] 32. A process for printing a feature on a substrate by a process comprising the steps of: a) applying the water-based UV-curable inkjet ink of any one of embodiments 1 to 27 by inkjet printing so as to form an uncured ink layer; and b) exposing the uncured ink layer to UV light at a dose of at least 150 mJ / cm2(i.e. 150 mJ / cm2or more), to form a cured ink layer.

[0152] EXAMPLES

[0153] The invention is now described in more detail with reference to the following non-limiting examples.

[0154] INK PREPARATION

[0155] The raw materials in the quantities listed in Table 2 were introduced into a glass vessel containing a magnetic stirring bar, at room temperature, in the following sequence: monomers, water; surfactant / dispersant, co-initiator, photoinitiator, dyes / pigments. The obtained mixture was stirred at room temperature for 45-60 minutes. The solution was then filtered, using Versapore filters with pore size diameter between 0.3-3.0 pm, and the filtrate was introduced into the printheads under vacuum conditions, using an inking machine (Xynertech semi-automatic filling system).

[0156] Table 2. Compositions of inkjet inks of the examples (E1-E4) and comparative examples (C1-C18), as well as performance data

[0157] 11

[0158] PRINTING TEST

[0159] The printhead types used during the printing tests were multiple-ink printheads. The printing tests were performed using a Card printer FARGO INK1000 system. Curing was carried out with a UV lamp with an emission band-width in a narrow range (390-400 nm) centered on 395 nm. The energy values of the irradiation were measured by the UV-Design radiometer UV-MC Microprocessor Integrator. The degree of cross-linking of the inks after printing and irradiation was determined by FTIR measurements using a Nicolet spectrometer FT-IR Nexus.

[0160] General experimental procedure:

[0161] A multiple-ink printhead containing the desired ink was introduced in the Card printer FARGO INK1000. A card was charged in the machine and was warmed to approximately 70°C. The card was then printed and irradiated by the UV lamp. After the irradiation treatment the card was ejected by the printer.

[0162] RESTARTABILITY PRINTING TEST

[0163] The printhead performances were evaluated over time by printing a reference “technical print” after defined pauses of time. The evaluated criteria are: print quality, ink dryness after UV irradiation, and nozzles blocked. A first “technical print” with minimized printing defects was realized according to the previously described procedure. The printhead was then stored in a capping station for a period of 5 minutes before printing another “technical print”. The resulting print was compared with the first one focusing on the above-mentioned criteria. The procedure was repeated for pauses of 30 minutes, 1 hour, 12 hours, 24 hours and 72 hours in order to verify the printhead performance over time. If restartability was inferior to 72 hours, the ink was ranked “fail”. The results are listed in Table 2.

[0164] CROSSLINKING MEASUREMENT PROCESS

[0165] Evaluation of the conversion degree of the material was measured by FTIR spectroscopic analysis. The FTIR instrument measures the typical monomer signal. The reaction of the monomers was monitored by observing the infrared vibration peak associated with the acrylate functionality disappearing, as a function of the UV-curing dose.

[0166] VISCOSITY METHOD PROCESS

[0167] The viscosity of the inks was measured with a RHEOLOGICA VISCOTECH-(RD312) tool, equipped with a thermostatic bath to maintain the temperature of the ink (25°C) during the measure. The viscosity measurement was carried out as follows: an ink volume of 0.925 ml was deposited on a temperature-controlled plate, with a graduate pipette, taking care not to create air bubbles. The head of the viscosimeter was lowered and, once the coupling of the rotating plate with the thermostated base is reached, the plate begins to rotate for some seconds, The ink’s creep resistance measurement, or viscosity, is expressed in mPa.s. ABRASION RESISTANCE TEST (TABER TEST)

[0168] The Taber test results refer to the number of abrasion cycles required to reach the stopping point for each ink tested. The stopping point is reached at 50% reduction of the initial optical density measurement (ANSI INCITS 322-2008, Card Durability Test Methods). Sample preparation: the samples were prepared printing polycarbonate (PC) cards at the temperature of 70°C with the printing mode 5 layers and by UV irradiation during the print.

[0169] Inks that reached the stopping point in 200 or fewer cycles were considered unacceptable, and were ranked as “fail”. The results are listed in Table 2. Results

[0170] The data in Table 2 show that the inks of the invention all pass the restartability test as well as the Taber test (durability), whereas the inks of the comparative examples fail one or both tests.

Claims

CLAIMS1. A water-based UV-curable inkjet ink comprising:(A) water;(B) one or more di(meth)acrylates;(C) one or more mono(meth)acrylates;(D) one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol;(E) the following photoinitiators: e1 ) a molecule of general formula III:where M+is selected from Li+, K+, Na+and NH4+, and R is phenyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups, or R is benzoyl, optionally substituted with 1 to 3 Ci to C2-alkyl groups; e2) anthracene methanol; and e3) a thioxanthone of general formula IV:where R3is Ci-C@-alky I and is repeated 1 or 2 times; and(F) one or more pigments or dyes.The ink of claim 1 , wherein: the one or more di(meth)acrylates (B) is of general Formula I:where R is H or CH3, and n is from 1 to 20; the one or more mono(meth)acrylates (C) is of formula II:where R1is H or CH3, and m is from 2 to 6.

3. The ink of claim 1 or 2, which comprises from about 25 to about 50 wt%, more preferably from about 28 to about 45 wt% water, based on the total weight of the ink.

4. The ink of claim 1, 2 or 3, which additionally comprises at least one water-miscible solvent, preferably selected from alcohols (e.g. monools, diols, triols), ketones, ethers (e.g. dioxanes, and tetrahydrofuran), amides and esters.

5. The ink of claim 4, wherein the at least one water-miscible solvent is present at from about 10 to about 50 wt%, more preferably from about 15 to about 35 wt%, based on the total weight of the ink.

6. The ink of any one preceding claim, wherein in the one or more di(meth)acrylates of general formula I, R is Me and n is 2.

7. The ink of any one preceding claim, wherein the di(meth)acrylate of general formula I is present at from about 4 to about 15 wt%, more preferably from about 7 to about 12 wt%, based on the total weight of the ink.

8. The ink of any one preceding claim, wherein in the mono(meth)acrylate of formula II, R1=H and m is 4.

9. The ink of any one preceding claim, wherein the mono(meth)acrylate of general formula II is present at from about 0.5 to about 6.5 wt%, more preferably from about 1 to about 3 wt%, particularly preferably about 2 wt%, based on the total weight of the ink.

10. The ink of any one preceding claim, wherein the one or more tetra(meth)acrylates having a molecular weight of from about 300 to about 1 ,000 g / mol is selected from ditrimethylolpropane tetraacrylates, pentaerythritol tetraacrylates, alkoxylated pentaerythritol tetraacrylates and mixtures thereof.11 . The ink of any one preceding claim, wherein the one or more tetra(meth)acrylates is present atfrom about 0.2 to about 8 wt%, preferably at from about 1 to about 5 wt%, more preferably at from about 2 to about 4 wt%, based on the total weight of the ink.

12. The ink of any one preceding claim, wherein in the molecule of general formula III, R is trimethylbenzoyl and M is Na+.

13. The ink of any one preceding claim, wherein in the molecule of general formula III, is used at from about 1.7 to about 3.5 wt%, preferably at from about 2 to about 3.4 wt%, more preferably at from about 2.8 to about 3.3 wt%, based on the total weight of the ink.

14. The ink of any one preceding claim, wherein anthracene methanol is used at from about 0.25 to about 0.75 wt%, preferably from about 0.3 to about 0.6 wt%, more preferably about 0.5 wt%, based on the total weight of the ink.

15. The ink of any one preceding claim, wherein the thioxanthone of general formula IV is used at from about 1 to about 3.5 wt%, preferably from about 1.2 to about 3 wt%, more preferably at from about 1.5 to about 2.5 wt%, based on the total weight of the ink.

16. The ink of any one preceding claim, wherein the wt% ratio of [molecule of general formula lll]:anthracenemethanol:[thioxanthone of general formula IV] is about 1.7-3.5:0.25-0.75:1-3.5, preferably 2-3.4:0.3-0.6:1.2-3, more preferably 2.8-3.3:0.5:1.5-2.5.

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