GB2593582A

GB2593582A - A printing ink

Info

Publication number: GB2593582A
Application number: GB2101146.5A
Authority: GB
Inventors: Ward Jeremy; Canning Sarah
Original assignee: Fujifilm Speciality Ink Systems Ltd
Current assignee: Fujifilm Speciality Ink Systems Ltd
Priority date: 2020-01-28
Filing date: 2021-01-28
Publication date: 2021-09-29
Anticipated expiration: 2041-01-28
Also published as: GB202101146D0; GB2593582B; GB202001149D0

Abstract

An inkjet ink comprises monofunctional (meth)acrylate monomer(s), a (meth)acrylated amine having an amine value of 1-190 mg KOH/g, colourant, and ≥15 wt.% di- and/or multifunctional monomer(s). The ink preferably contains 1-20 wt.% (meth)acrylated amine and 5-35 wt.% monofunctional (meth)acrylate monomer(s). The monofunctional (meth)acrylate monomer(s) may comprise lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, cyclic-TMP formal acrylate, tetrahydrofurfuryl acrylate, (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate, 4-tert-butylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, octadecyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate, or isodecyl acrylate. The di- and/or multifunctional monomer(s) may comprise 3-methyl-1,5-pentanediol diacrylate, 1,10-decanediol diacrylate, hexanediol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, tricyclodecane dimethanol diacrylate, propoxylated neopentyl glycol diacrylate, trimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, ethoxylated trimethylolpropane triacrylate, or triethylene glycol divinyl ether. Preferably, the ink comprises lauryl acrylate and 3-methyl-1,5-pentanediol diacrylate. Use of a (meth)acrylated amine having an amine value of 1-190 mg KOH/g for maintaining water resistance of a cured inkjet ink film is also disclosed.

Description

A printing ink This invention relates to a printing ink and in particular to an inkjet ink which has a desirable balance of properties.

For high-speed printing, the inks must flow rapidly from the printing heads, and, to ensure that this happens, they must have in use a low viscosity, typically 200 mPas or less at 25°C, although in most applications the viscosity should be 50 mPas or less, and often 25 mPas or less. Typically, when ejected through the nozzles, the ink has a viscosity of less than 25 mPas, preferably 5-15 mPas and most preferably between 7-11 mPas at the jetting temperature which is often elevated to, but not limited to 40-50°C (the ink might have a much higher viscosity at ambient temperature). The inks must also be resistant to drying or crusting in the reservoirs or nozzles. For these reasons, inkjet inks for application at or near ambient temperatures are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent such as water or a low-boiling solvent or mixture of solvents.

Anothertype of inkjet ink contains unsaturated organic compounds, termed monomers and/or oligomers which polymerise when cured. This type of ink has the advantage that it is not necessary to evaporate the liquid phase to dry the print; instead the print is cured, a process which is more rapid than evaporation of solvent at moderate temperatures.

For high-speed printing applications, very high cure speeds are required, for example around 100 m/min or above. By cure speed is meant the speed at which the actinic radiation source moves relative to the substrate. The advantage of high-speed printing is that a low dose per unit area is required to achieve a fully cured film. Components are often added to the ink to increase cure speed but such components can have a negative impact on other properties of the ink such as water resistance.

For many packaging applications, water resistance of the cured ink film is of great importance. For example, products may be stored in moist environments such as a fridge. Any water sensitivity of the cured ink film can lead to a loss of integrity in the print, specifically a failure in adhesion to the packaging substrate. Therefore, it is important that the cured ink film remains firmly attached to the packaging.

There is therefore a need in the art for an inkjet ink that offers the desired balance of properties, namely a fast cure speed and excellent water resistance of the cured ink film.

Accordingly, the present invention provides an inkjet ink comprising: one or more monofunctional (meth)acrylate monomers; one or more di-and/or multifunctional monomers; a (meth)acrylated amine having an amine value of 1-190 mg KOH/g; and a colouring agent, wherein the one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink.

In order to boost cure speed and particularly surface cure response for high-speed inkjet printing applications, amine synergists may be added to the ink. However, it has been found that the presence of some amine synergists results in poor water resistance of the cured ink film.

Surprisingly, it has been found that through careful selection of the amine synergist, it is possible to achieve a fast cure speed whilst maintaining excellent water resistance of the cured ink film. In particular, (meth)acrylated amines having an amine value of 1-190 mg KOH/g were found to be particularly useful in achieving an improved cure response without any associated loss in performance of the printed material.

The inkjet ink comprises one or more monofunctional (meth)acrylate monomers.

As is known in the art, monomers may possess different degrees of functionality, which include mono, di, tri and higher functionality monomers.

For the avoidance of doubt, (meth)acrylate is intended herein to have its standard meaning, i.e. acrylate and/or methacrylate. Mono and difunctional are intended to have their standard meanings, i.e. one or two groups, respectively, which take part in the polymerisation reaction on curing. Multifunctional (which does not include difunctional) is intended to have its standard meaning, i.e. three or more groups, respectively, which take part in the polymerisation reaction on curing.

Monofunctional (meth)acrylate monomers are well known in the art and are preferably the esters of acrylic acid. Mixtures of (meth)acrylate monomers may be used.

The substituents of the monofunctional (meth)acrylate monomers are not limited other than by the constraints imposed by the use in an inkjet ink, such as viscosity, stability, toxicity etc. The monofunctional (meth)acrylate monomers may be a cyclic monofunctional (meth)acrylate monomer and/or an acyclic-hydrocarbon monofunctional (meth)acrylate monomer.

The substituents of the cyclic monofunctional (meth)acrylate monomer are typically cycloalkyl, aryl and combinations thereof, any of which may be interrupted by heteroatoms and/or substituted by alkyl. Non-limiting examples of substituents commonly used in the art include C3-18 cycloalkyl, C8-10 aryl and combinations thereof, any of which may substituted with alkyl (such as C1-18 alkyl) and/or any of which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted by any of the above described substituents. The substituents may together also form a cyclic structure.

The cyclic monofunctional (meth)acrylate monomer may be selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-tett-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA) and mixtures thereof.

In a preferred embodiment, the cyclic monofunctional (meth)acrylate monomer is selected from isobornyl acrylate (IBOA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-tett-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA) and mixtures thereof. These are particularly preferred for food packaging applications where the quality and safety of the materials is a concern.

In a preferred embodiment, the one or more monofunctional (meth)acrylate monomers comprise an acyclic-hydrocarbon monofunctional (meth)acrylate monomer.

The substituents of the acyclic-hydrocarbon monofunctional (meth)acrylate monomer are typically alkyl, which may be interrupted by heteroatoms. A non-limiting example of a substituent commonly used in the art is C1-18 alkyl, which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with The acyclic-hydrocarbon monofunctional (meth)acrylate monomer contains a linear or branched C6-C20 group. It may be selected from octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof. In a preferred embodiment, the acyclic-hydrocarbon monofunctional (meth)acrylate monomer contains a linear C6-C20 group. Lauryl acrylate is particularly preferred. Lauryl acrylate provides the cured ink film with good physical film properties such as good water resistance and flexibility.

In a preferred embodiment, the acyclic-hydrocarbon monofunctional (meth)acrylate monomer is selected from octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), lauryl acrylate and mixtures thereof These are particularly preferred for use in food packaging applications.

In a preferred embodiment, the one or more monofunctional (meth)acrylate monomers are selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yOmethyl acrylate (MEDA/Medol10), 4-tert-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof In a preferred embodiment, the one or more monofunctional (meth)acrylate monomers are preferably selected from isobornyl acrylate (IBOA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-tert-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), lauryl acrylate and mixtures thereof. These are particularly preferred for use in food packaging applications.

Preferably, the one or more monofunctional (meth)acrylate monomers comprise lauryl acrylate.

Preferably, lauryl acrylate is the sole monofunctional (meth)acrylate monomer present in the ink and more preferably, lauryl acrylate is the sole monofunctional monomer present in the ink.

In a preferred embodiment, the inkjet ink comprises one or more monofunctional (meth)acrylate monomers present in 5-35% by weight, more preferably 10-30% by weight, most preferably 15-25% by weight, based on the total weight of the ink.

In a preferred embodiment, the inkjet ink comprises 10-30% by weight, preferably 15-25% by weight of one or more monofunctional (meth)acrylate monomers, based on the total weight of the ink, and 1030% by weight, preferably 15-25% by weight of one or more monofunctional (meth)acrylate monomers selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yfirnethyl acrylate (MEDA/Medol-10), 4-tert-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof, based on the total weight of the ink.

Tetrahydrofurfuryl acrylate (THFA) is often used to provide good adhesion to variety of substrates, as well as producing a flexible film which is less liable to cracking and delaminafion. A further advantage of THFA is that it can solubilise chlorinated polyolefins, which in turn provides good adhesion to polyoleftn substrates. However, THFA is a hazardous monomer and bears the GHS hazard statement H314 (Causes severe skin burns and eye damage). There is also growing evidence that it may damage fertility or the unborn child. Thus, there is an urgent need in the art to move away from THFA.

The ink will still function in the presence of tetrahydrofurfuryl acrylate (THFA), in terms of its printing and curing properties. However, to avoid the hazardous nature of THFA, the ink preferably contains less than 2% by weight, more preferably less than 1% by weight and most preferably is substantially free of THFA, based on the total weight of the ink.

By substantially free is meant that only small amounts will be present, for example as impurities in the radiation-curable materials present or as a component in a commercially available pigment dispersion.

In other words, no THFA is intentionally added to the ink. However, minor amounts of THFA, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight of THFA, more preferably less than 0.1% by weight of THFA, most preferably less than 0.05% by weight of THFA, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of THFA.

For food packaging applications, the Swiss Ordinance on Materials and Articles in Contact with Food (SR 817.023.21) sets out provisions for inks. Annex 10 lists permitted substances for the production of food packaging inks. Substances not listed should not be used for food packaging inks. Caution should still be used for some substances on the Swiss Ordinance list and there is some concern about the quality and safety of the monofunctional (meth)acrylate monomers isodecyl acrylate (IDA), octyl acrylate, phenoxyethyl acrylate (PEA) and 2-ethylhexyl acrylate (2-EHA).

The ink preferably contains less than 2% by weight, more preferably less than 1% by weight and most preferably is substantially free of each of IDA, octyl acrylate, PEA and 2-EHA, based on the total weight of the ink. More preferably, the ink contains less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1% by weight and most preferably is substantially free of IDA, octyl acrylate, PEA and 2-EHA in combination, based on the total weight of the ink.

In other words, no IDA, octyl acrylate, PEA and 2-EHA is intentionally added to the ink. However, minor amounts of IDA, octyl acrylate, PEA and 2-EHA, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight of each of IDA, octyl acrylate, PEA and 2-EHA, more preferably less than 0.1% by weight of each of IDA, octyl acrylate, PEA and 2-EHA, most preferably less than 0.05% by weight of each of IDA, octyl acrylate, PEA and 2-EHA, based on the total weight of the ink. Preferably, the ink may comprise less than 0.5% by weight of IDA, octyl acrylate, PEA and 2-EHA in combination, more preferably less than 0.1% by weight of IDA, octyl acrylate, PEA and 2-EHA in combination, most preferably less than 0.05% by weight of IDA, octyl acrylate, PEA and 2-EHA in combination, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of IDA, octyl acrylate, PEA and 2-EHA.

Preferably, the one or more monofunctional (meth)acrylate monomers are the sole monofunctional monomers present in the ink. However, the ink may further include at least one N-vinyl amide monomer, N-(meth)acryloyl amine monomer and/or N-vinyl carbamate monomer.

N-Vinyl amide monomers are well-known monomers in the art. N-Vinyl amide monomers have a vinyl group attached to the nitrogen atom of an amide which may be further substituted in an analogous manner to the (meth)acrylate monomers. Preferred examples are N-vinyl caprolactam (NVC), N-vinyl pyrrolidone (NVP), N-vinyl piperidone, N-vinyl formamide and N-vinyl acetamide.

Similarly, N-acryloyl amine monomers are also well-known in the art. N-Acryloyl amine monomers also have a vinyl group attached to an amide but via the carbonyl carbon atom and again may be further substituted in an analogous manner to the (meth)acrylate monomers. A preferred example is Nacryloylmorpholine (ACMO).

N-Vinyl carbamate monomers are defined by the following functionality: The synthesis of N-vinyl carbamate monomers is known in the art. For example, vinyl isocyanate, formed by the Curtius rearrangement of acryloyl azide, can be reacted with an alcohol to form N-vinyl carbamates (Phosgenations -A Handbook by L. Cotarca and H. Eckert, John Wiley & Sons, 2003, 4.3.2.8, pages 212-213).

If present, in a preferred embodiment, the N-vinyl carbamate monomer is an N-vinyl oxazolidinone. N-Vinyl oxazolidinones have the following structure: 07NNJ R1-) R2 in which R1 to R4 are not limited other than by the constraints imposed by the use in an ink-jet ink, such as viscosity, stability, toxicity etc. The substituents are typically hydrogen, alkyl, cycloalkyl, aryl and combinations thereof, any of which may be interrupted by heteroatoms. Non-limiting examples of substituents commonly used in the art include C1-18 alkyl, C3-18 cycloalkyl, C6-10 aryl and combinations thereof, such as C6_10 aryl-or C3-18 cycloalkyl-substituted C1-18 alkyl, any of which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted by any of the above described substituents. Preferably R1 to R4 are independently selected from hydrogen or Ctio alkyl. Further details may be found in WO 2015/022228 and US 4,831,153.

If present, most preferably, the N-vinyl carbamate monomer is N-vinyl-5-methyl-2-oxazolidinone (known as NVMO or VMOX). It is available from BASF and has the following structure: molecular weight 127 g/mol NVMO has the IUPAC name 5-methyl-3-vinyl-1,3-oxazolidin-2-one and CAS number 3395-98-0. NVMO includes the racemate and both enanfiomers. In one embodiment, the N-vinyl carbamate monomer is a racemate of NVMO. In another embodiment, the N-vinyl carbamate monomer is (R)-5-methyl-3-vinyl-1,3-oxazolidin-2-one. Alternatively, the N-vinyl carbamate monomer is (S)-5-methyl-3-vinyl-1,3-oxazolidin-2-one.

If present, the inkjet ink preferably comprises at least one of NVC, ACMO and/or NVMO. N-Vinyl amide monomers are particularly preferred, and most preferably NVC.

The inkjet ink may also comprise one or more N-vinyl monomers other than an N-vinyl amide monomer, N-(meth)acryloyl amine monomer and/or N-vinyl carbamate monomer. Examples include N-vinyl carbazole, N-vinyl indole and N-vinyl imidazole.

The inkjet ink of the present invention comprises one or more di-and/or multifunctional monomers, such as a di-/multifunctional (meth)acrylate monomer, a di-/multifunctional vinyl ether or a di-/multifunctional vinyl ether (meth)acrylate monomer.

The substituents of the di-and/or multifunctional monomer are not limited other than by the constraints imposed by the use in an ink-jet ink, such as viscosity, stability, toxicity etc. The substituents are typically alkyl, cycloalkyl, aryl and combinations thereof, any of which may be interrupted by heteroatoms. Non-limiting examples of substituents commonly used in the art include C1-18 alkyl, C3-18 cycloalkyl, C8-83 aryl and combinations thereof, such as C8-10 aryl-or C3-18 cycloalkyl-substituted C1-18 alkyl, any of which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted by any of the above described substituents. The substituents may together also form a cyclic structure.

Examples of the di-and/or multifunctional radiation-curable monomer include difunctional (meth)acrylate monomers, multifunctional (meth)acrylate monomers, divinyl ether monomers, multifunctional vinyl ether monomers and di-and/or multifunctional vinyl ether (meth)acrylate monomers. Mixtures of di-and/or multifunctional monomers may also be used.

Difunctional (meth)acrylate monomers are well known in the art and a detailed description is therefore not required. Examples include hexanediol diacrylate (HDDA), 1,8-octanediol diacrylate, i,9-nonanediol diacrylate, 1,10-decanediol diacrylate (DDDA), 1,11-undecanediol diacrylate and 1,12-dodecanediol diacrylate, polyethylene glycol diacrylate (for example tetraethylene glycol diacrylate, PEG200DA, PEG300DA, PEG400DA, PEG600DA), dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), neopentylglycol diacrylate, 3-methyl-1,5-pentanediol diacrylate (3-MPDDA), and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, propoxylated neopentylglycol diacrylate (NPGPODA), and mixtures thereof. Also included are esters of methacrylic acid (i.e. methacrylates), such as hexanediol dimethacrylate, 1,8-octanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, 1,11-undecanediol dimethacrylate and 1,12-dodecanediol dimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate and mixtures thereof. 3-MPDDA is particularly preferred.

Multifunctional monomers (tri-and higher-functional) are also well known in the art and a detailed description is therefore not required. Usually, the multifunctional (meth)acrylate monomer has a degree of functionality of four or more, e.g. 4-8.

Examples of the multifunctional monomers include trimethylolpropane triacrylate (TMPTA), ditrimethylolpropane tetraacrylate (DiTMPTA), pentaerythritol triacrylate, tri(propylene glycol) triacrylate, di-pentaerythritol hexaacrylate (DPI-1A), and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, ethoxylated trimethylolpropane triacrylate (EOTMPTA) and ethoxylated pentaerythritol tetraacrylate (EOPETTA, also known as PPTTA), and mixtures thereof. Suitable multifunctional (meth)acrylate monomers also include esters of methacrylic acid (i.e. methacrylates), such as trimethylolpropane trimethacrylate. Mixtures of (meth)acrylates may also be used.

The di-and/or multifunctional monomer, based on the total weight of the ink, may have at least one vinyl ether functional group.

Examples of divinyl ether monomers include triethylene glycol divinyl ether (DVE-3), diethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, bis[4-(vinyloxy)butyl] 1,6- hexanediylbiscarbamate, bis[4-(vinyloxy)butyl] isophthalate, bis[4-(vinyloxy)butyl] (methylenedi-4,1-phenylene)biscarbamate, bis[4-(vinyloxy)butyl] succinate, bis[4-(vinyloxy)butyl]terephthalate, bis[4-(vinyloxymethyl)cyclohexylmethyl] glutarate, 1,4-butanediol divinyl ether and mixtures thereof DVE-3 is particularly preferred.

An example of a multifunctional vinyl ether monomer is tris[4-(vinyloxy)butyl] trimellitate.

Examples of vinyl ether (meth)acrylate monomers include 2-(2-vinyloxy ethoxy)ethyl acrylate (VEEA), 2-(2-vinyloxy ethoxy)ethyl methacrylate (VEEM) and mixtures thereof.

The di-and/or multifunctional monomer may possess different degrees of functionality, and a mixture including combinations of di, tri and higher functionality monomers may be used.

Preferably, the one or more di-and/or multifunctional monomers is selected from 1,10-decanediol diacrylate (DDDA), hexanediol diacrylate (HDDA), polyethylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), 3-methyl 1,5-pentanediol diacrylate (3-MPDDA), dipropylene glycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), trimethylolpropane triacrylate (TMPTA), di-trimethylolpropane tetraacrylate (DiTMPTA), di-pentaerythritol hexaacrylate (DPHA), ethoxylated trimethylolpropane triacrylate (EOTMPTA), ethoxylated pentaerythritol tetraacrylate (EOPETTA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof.

In a preferred embodiment, the one or more di-and/or multifunctional monomers is preferably selected from 1,10-decanediol diacrylate (DDDA), ethoxylated (5) hexanediol diacrylate (HD(E0)DA), polyethylene glycol (600) diacrylate (PEG600DA), tripropylene glycol diacrylate (TPGDA), 3-methyl 1,5-pentanediol diacrylate (3-MPDDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), di-trimethylolpropane tetraacrylate (DiTMPTA), dipentaerythritol hexaacrylate (DPHA), ethoxylated trimethylol propane triacrylate (EOTMPTA), ethoxylated pentaerythritol tetraacrylate (EOPETTA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof. A preferred NPGPODA is propoxylated (2) neopentyl glycol diacrylate. A preferred EOTMPTA is ethoxylated (3) trimethylolpropane triacrylate. These are particularly preferred for use in food packaging applications.

In a preferred embodiment, the one or more di-and/or multifunctional monomers comprise difunctional monomers. When difunctional monomers are present, preferably, the one or more difunctional monomers comprise one or more difunctional (meth)acrylate monomers.

In a preferred embodiment, the difunctional monomer is selected from 1,10-decanediol diacrylate (DDDA), hexanediol diacrylate (HDDA), polyethylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), 3-methyl 1,5-pentanediol diacrylate (3-MPDDA), dipropylene glycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof.

The difunctional monomer is preferably selected from 1,10-decanediol diacrylate (DDDA), ethoxylated (5) hexanediol diacrylate (HD(E0)DA), polyethylene glycol (600) diacrylate (PEG600DA), tripropylene glycol diacrylate (TPGDA), 3-methyl 1,5-pentanediol diacrylate (3-MPDDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof. These are particularly preferred for use in food packaging applications.

In a preferred embodiment, the one or more di-and/or multifunctional monomers comprise 3-MPDDA and DVE-3. Preferably, 3-MPDDA and DVE-3 are the sole di-and/or multifunctional monomers present in the ink. 3-MPDDA provides the ink with a good cure response/speed and further provides the cured ink film with good physical film properties such as good water resistance. DVE-3 is preferred because of its low viscosity.

The one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink. Preferably, the one or more di-and/or multifunctional monomers are present in a total amount of 20% by weight or more, more preferably 30% by weight or more, most preferably 40% by weight or more, based on the total weight of the ink. The one or more di-and/or multifunctional monomers may be present in a total amount of 65% by weight or less, more preferably 60% by weight or less, most preferably 55% by weight or less, based on the total weight of the ink.

In a preferred embodiment, the one or more di-and/or multifunctional monomers are present in a total amount of 15-65% by weight, preferably 20-60% by weight, more preferably 30-60% by weight, and most preferably 40-55% by weight, based on the total weight of the ink.

By total amount is meant the amount of difunctional monomers, if present, in combination with the amount of multifunctional monomers, if present. If both di-and multifunctional monomers are present, the total amount is the amount of difunctional monomers in combination with the amount of multifunctional monomers present in the ink. If difunctional monomers are present and multifunctional monomers are absent, the total amount is the amount of difunctional monomers present in the ink. If multifunctional monomers are present and difunctional monomers are absent, the total amount is the amount of multifunctional monomers present in the ink.

When both di-and multifunctional monomers are present, in one embodiment, the one or more difunctional monomers are preferably present in an amount of 5% by weight or more, more preferably 10% or more, based on the total weight of the ink. In another embodiment, when both di-and multifunctional monomers are present, the one or more multifunctional monomers are preferably present in an amount of 5% by weight or more, more preferably 10% or more, based on the total weight of the ink.

A particularly preferred monomer combination for the present invention is lauryl acrylate, 3-MPDDA and DVE-3. Preferably, the one or more monofunctional (meth)acrylate monomers comprise lauryl acrylate and the one or more di-and/or multifunctional monomers comprise 3-MPDDA and DVE-3. Preferably, lauryl acrylate is the sole monofunctional (meth)acrylate monomer present in the ink and 3-MPDDA and DVE-3 are the sole di-and/or multifunctional monomers present in the ink. More preferably, lauryl acrylate, 3-MPDDA and DVE-3 are the sole monomers present in the ink.

Monomers typically have a molecular weight of less than 600, preferably more than 200 and less than 450. Monomers are typically added to inkjet inks to reduce the viscosity of the inkjet ink. They therefore preferably have a viscosity of less than 150 mPas at 25°C, more preferably less than 100mPas at 25°C and most preferably less than 20 mPas at 25°C. Monomer viscosities can be measured using an ARG2 rheometer manufactured by T.A. Instruments, which uses a 40 mm oblique /2° steel cone at 25°C with a shear rate of 25 s-1.

The inkjet ink comprises a (meth)acrylated amine having an amine value of 1-190 mg KOH/g.

An amine (meth)acrylate may be formed by a pseudo-Michael addition reaction between a (meth)acrylate monomer or oligomer and a primary or secondary amine. Such a reaction may be represented as follows: Ri acrylate ester monomer/oligomer R2 Primary (R2= H) or Secondary amine pseudo-Michael addition H2

C

ON,,---Ri R3 I R2 Acrylated amine wherein RI represents the remainder of the (meth)acrylate monomer or oligomer (which may be a Cl_ a-alkyl, Ci-a-alkanol, Cm-cycloalkyl, C3.8-cycloalkyl-C1_8-alkyl, phenyl, polyester oligomer or polyether oligomer, substituted with a further 1-6 (meth)acrylate groups); and R2 and R3 may be the same or different and represent -H, Cl_a-alkyl, CLa-alkanol, C35-cycloalkyl, Ca-a-cycloalkyl-CI a-alkyl or phenyl (the alkyl groups may be straight chain or branched).

Secondary amines include diethylamine (R2 = -CH2C1-13, R3 = -CH3) and primary amines include monoethanolamine (R2 = -H, R3 = -CH2OH). If a primary amine is used then the amine can react with two acrylate groups to link two (meth)acrylate monomer/oligomers together.

Preferably, R1 represents a polyester or polyether backbone, substituted with a further 1-6 (meth)acrylate groups. Such (meth)acrylated amines are commercially available as CN2565 from Arkema, Ebecryl 80 from Allnex, Ebecryl 81 from Allnex and UVP6600 from Univar.

(Meth)acrylated amines may also be known as amine-modified (meth)acrylates.

The amine (meth)acrylate is a synergist and boosts cure speed. The amine (meth)acrylate can boost cure speed by acting as a hydrogen donor to form reactive alkyl-amino free radicals. These radicals can then react with the monomers present in the ink to initiate polymerisation. The resultant amine (meth)acrylate can also boost cure speed by reducing oxygen inhibition during curing. In this regard, it is thought that growing free-radical chains react with oxygen to form unreacfive peroxy radicals. Amine (meth)acrylates can react with these peroxy radicals to form reactive alkyl-amino free radicals, which can then go on to react with the monomers present in the ink.

The (meth)acrylated amine of the ink of the present invention has an amine value of 1-190 mg KOH/g. The amine value is a measure of the base content and is equal to the amount in milligrams of potassium hydroxide per gram of sample. This value may be calculated using the following method: (i) dissolving about 0.1 g of the (meth)acrylated amine in 20 mL of isopropyl alcohol, (ii) adding 0.5 mL of a 0.04% w/v solution of bromocresol green in isopropyl alcohol to give a blue solution; (ii) titrating the blue solution with 0.1 M hydrochloric acid until the blue solution turns yellow (the end point); and (Hi) using the following equation: Amine value (mg KOH/g) = (Titre value x 56.1 x Normality of HCI) / weight of (meth)acrylated amine dissolved.

The inclusion of the specific (meth)acrylated amine in the ink present invention boosts cure speed whilst surprisingly maintaining excellent water resistance properties in the cured ink film.

In order to measure the water resistance of a cured ink film, an inkjet ink containing one or more monofuncfional (meth)acrylate monomers; one or more di-and/or multifunctional monomers present in a total amount of 15% by weight or more, based on the total weight of the ink; a (meth)acrylated amine; and a colouring agent, is coated onto a suitable test substrate to produce a wet film. The wet film is cured to provide a tack-free film. Water resistance can then be assessed by a water soak test.

The water soak test is well known in the art. One immerses the tack-free film in water at room temperature. At regular intervals, one scratches the immersed film using a finger nail. Inks containing (meth)acrylated amines of the present invention remain intact after 60 minutes. Inks containing comparative (meth)acrylated amines are removed by finger nail scratch before 60 minutes.

Preferably, the (meth)acrylated amine has an amine value of 5-180 mg KOH/g, more preferably 10-170 mg KOH/g and most preferably 15-160 KOH/g.

The (meth)acrylated amine is preferably present in 1-20% by weight, more preferably 1-15% by weight, most preferably 5-15% by weight, based on the total weight of the ink.

In a preferred embodiment, the inkjet ink comprises: 10-30% by weight of one or more monofunctional (meth)acrylate monomers, based on the total weight of the ink; one or more di-and/or multifunctional monomers; 5-15% by weight of a (meth)acrylated amine having an amine value of 1-190 mg KOH/g, based on the total weight of the ink; a colouring agent; wherein the one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink; and 10-30% by weight of one or more monofunctional (meth)acrylate monomers selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-tett-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof, based on the total weight of the ink.

This inkjet ink is particularly preferred as it has been found by the inventors that this ink is particularly suitable for food packaging applications and has fast cure speed whilst maintaining excellent water resistance of the cured ink film.

In a particularly preferred embodiment, the inkjet ink comprises: 10-30% by weight of one or more monofunctional (meth)acrylate monomers, based on the total weight of the ink; one or more di-and/or multifunctional monomers; 5-15% by weight of a (meth)acrylated amine having an amine value of 1-190 mg KOH/g, based on the total weight of the ink; a colouring agent; wherein the one or more di-and/or multifunctional monomers comprise one or more difuncfional monomers, preferably one or more difunctional (meth)acrylate monomers; wherein the one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink; and 10-30% by weight of one or more monofunctional (meth)acrylate monomers selected from isobornyl acrylate (BOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-tettbutylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof, based on the total weight of the ink.

In a particularly preferred embodiment, the inkjet ink comprises: 10-30% by weight of one or more monofunctional (meth)acrylate monomers, based on the total weight of the ink; one or more di-and/or multifunctional monomers; 5-15% by weight of a (meth)acrylated amine having an amine value of 1-190 mg KOH/g, based on the total weight of the ink; a colouring agent; wherein the one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink; 10-30% by weight of one or more monofunctional (meth)acrylate monomers selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yOmethyl acrylate (MEDA/Medol-10), 4-tertbutylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethoxyethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof, based on the total weight of the ink; and wherein the one or more di-and/or multifunctional monomers are selected from 1,10-decanediol diacrylate (DDDA), hexanediol diacrylate (HDDA), polyethylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), 3-methyl-1,5-pentanediol diacrylate (3-MPDDA), dipropylene glycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), trimethylolpropane triacrylate (TMPTA), di-trimethylolpropane tetraacrylate (DiTMPTA), di-pentaerythritol hexaacrylate (DPHA), ethoxylated trimethylolpropane triacrylate (EOTMPTA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof Such inkjet inks are particularly preferred. In this regard, the inventors have found that such inkjet inks are particularly suitable for food packaging applications and has fast cure speed whilst maintaining excellent water resistance of the cured ink film.

The ink may comprise a radiation-curable (i.e. polymerisable) oligomer, such as a (meth)acrylate oligomer. Any radiation-curable oligomer that is compatible with the other ink components is suitable for use in the ink.

The term "curable oligomer" has its standard meaning in the art, namely that the component is partially reacted to form a pre-polymer having a plurality of repeating monomer units, which is capable of further polymerisation. The oligomer preferably has a molecular weight of at least 600. The molecular weight is preferably 4,000 or less. Molecular weights (number average) can be calculated if the structure of the oligomer is known or molecular weights can be measured using gel permeation chromatography using polystyrene standards.

The oligomers may possess different degrees of functionality, and a mixture including combinations of mono, di, tri and higher functionality oligomers may be used. The degree of functionality of the oligomer determines the degree of crosslinking and hence the properties of the cured ink. The oligomer is preferably multifunctional meaning that it contains on average more than one reactive functional group per molecule. The average degree of functionality is preferably from 2 to 6.

Radiation-curable oligomers comprise a backbone, for example a polyester, urethane, epoxy or polyether backbone, and one or more radiation-curable groups.

The polymerisable group can be any group that is capable of polymerising upon exposure to radiation. Preferably the oligomers are (meth)acrylate oligomers.

Particularly preferred radiation-curable oligomers are di-, tri-, tetra-, penta-or hexa-functional acrylates.

Other suitable examples of radiation-curable oligomers include epoxy based materials such as bisphenol A epoxy acrylates and epoxy novolac acrylates, which have fast cure speeds and provide cured films with good solvent resistance. However, for food packaging applications where quality and safety of the materials is a concern, the ink is preferably substantially free of bisphenol A based materials such as bisphenol A epoxy acrylates. Therefore, the ink is preferably substantially free of bisphenol A epoxy acrylates.

By substantially free is meant that only small amounts will be present, for example as impurities in the radiation-curable materials present or as a component in a commercially available pigment dispersion. In other words, no bisphenol A epoxy acrylates is intentionally added to the ink. However, minor amounts of bisphenol A epoxy acrylates which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight of bisphenol A epoxy acrylates, more preferably less than 0.1% by weight of bisphenol A epoxy acrylates, most preferably less than 0.05% by weight of bisphenol A epoxy acrylates, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of bisphenol A epoxy acrylates.

The amount of radiation-curable oligomer, when present, is preferably 0.1-10% by weight, based on the total weight of the ink.

Oligomers are typically added to inkjet inks to increase the viscosity of the inkjet ink or to provide film-forming properties such as hardness or cure speed. They therefore preferably have a viscosity of 150 mPas or above at 25°C. Preferred oligomers for inclusion in the ink of the invention have a viscosity of 0.5 to 10 Pas at 50°C. Oligomer viscosities can be measured using an ARG2 rheometer manufactured by T.A. Instruments, which uses a 40 mm oblique /2° steel cone at 60°C with a shear rate of 25 s -1.

The ink of the present invention cures by free radical polymerisation.

The ink may also contain a resin. The resin preferably has a weight-average molecular weight (Mw) of 10-50 KDa, and most preferably 15-35 KDa. The Mw may be measured by known techniques in the art, such as gel permeation chromatography (GPC), using a polystyrene standard. The resin is preferably solid at 25°C. It is preferably soluble in the liquid medium of the ink (the radiation-curable diluent and, when present, additionally the solvent).

The resin is a passive (i.e. inert) resin, in the sense that it is not radiation curable and hence does not undergo cross-linking under the curing conditions to which the ink is subjected.

The resin may improve adhesion of the ink to the substrate. It is preferably soluble in the ink. The resin, when present, is preferably present at 0.1-5% by weight, based on the total weight of the ink.

The ink of the present invention may also include a photoinitiator which under irradiation, for example using ultraviolet light, initiates the polymerisation of the radiation-curable diluent.

In a preferred embodiment, the inkjet ink of the present invention further comprises one or more photoinitiators. Preferred are photoinitiators which produce free radicals on irradiation (free radical photoinitiators) such as, for example, benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzy1-2- dimethylamino-(4-morpholinophenyl)butan-1-one, benzil dimethylketal, phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide or mixtures thereof. Such photoinitiators are known and commercially available such as, for example, under the trade names Omnirad (from IGM) and Esacure (from Lamberti).

Mixtures of free radical photoinitiators can be used and preferably, the ink comprises a plurality of free radical photoinitiators. The total number of free radical photoinitiators present is preferably from one to five, and more preferably, two or more free radical photoinitiators are present in the ink.

For food packaging applications, there is some concern about the negative odour/taint, migration potential and/or safety of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide.

Therefore, in a preferred embodiment, the ink preferably contains less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1% by weight and most preferably is substantially free of each of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1- hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide, where the amounts are based on the total weight of the ink.

By substantially free is meant that only small amounts will be present, for example as impurities in the radiation-curable materials present or as a component in a commercially available pigment dispersion. In other words, no 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2- morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide is intentionally added to the ink. However, minor amounts of each of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9Hthioxa nthen-9-one (2-ITX), 4-isopropyl 9H4hioxanthen-9-one (4-ITX), 2,4-diethyl 9H4hioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight, more preferably less than 0.1% by weight, most preferably less than 0.05% by weight of each of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of each of 2- hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide.

More preferably, the ink contains less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1% by weight and most preferably is substantially free of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9Hthioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide in combination, where the amounts are based on the total weight of the ink.

By substantially free is meant that only small amounts will be present, for example as impurities in the radiation-curable materials present or as a component in a commercially available pigment dispersion. In other words, no 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1- hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide is intentionally added to the ink. However, minor amounts of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide in combination, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight, more preferably less than 0.1% by weight, most preferably less than 0.05% by weight of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholinopropiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-IDC), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide in combination, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of 2-hydroxy 2-methyl propiophenone, 2-(dimethylamino)ethyl benzoate, benzophenone, 2-methyl benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy 2-phenyl acetophenone, 2-methyl 4'-(methylthio) 2-morpholino-propiophenone, 2-isopropyl 9H-thioxanthen-9-one (2-ITX), 4-isopropyl 9H-thioxanthen-9-one (4-ITX), 2,4-diethyl 9H-thioxanthen-9-one and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide.

Polymeric photoinitiators are preferred. Examples include Omnipol TP®, Omnipol 9100 and Speedcure 70100.

Omnipol IP® is commercially available from IGM. It is a polymeric phosphine oxide photoinifiator, and is known by the chemical name polymeric ethyl (2,4,6-trimethylbenzoyI)-phenyl phosphinate or polymeric TPO-L. It has the following structure: a+b+c = 1-20 The total value of a, b and c of the chemical formula for polymeric TPO-L is equal to 1-20.

Omnipol 910® is also commercially available from IGM. It is a piparazino-based aminoalkylphenone having the following structure: The value of n of the chemical formula for Omnipol 910® is equal to 1-10.

Speedcure 7010LO is a particularly preferred photoinifiator for inclusion in the ink of the present invention. Speedcure 7010L® is commercially available from Lambson®. Speedcure 7010L® is a liquid at 20°C and is a solution of 1,3-diga-[1-chloro-9-oxo-9H-thioxanthen-4-yDoxylacetylpoly[oxy(1- methylethylene)]} oxy)-2,2-bisga-[1-chloro-9-oxo-9H-thioxanthen-4-yDoxylacetylpoly[oxy(1- methylethylene)]}oxymethyl) propane in trimethylolpropane ethoxylate triacrylate. 1,3-Di({a-[1-chloro9-oxo-9H-thioxanthen-4-yDoxy]acetylpoly[oxy (1-methylethylene)]1 oxy)-2,2-bis ({a-[1-ch loro-9-oxo-9 H-thioxanthen-4-yboxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl) propane is known as polymeric ITX and has the following structure: Cl 0 a+b+c+d = 1-20 Cl 0 The total value of a, b, c and d of the chemical formula for polymeric ITX is equal to 1-20. In a preferred embodiment, the value of a+b+c+d of the chemical formula for polymeric ITX is equal to 1-15.

Preferably the photoinitiator is present from 1 to 20% by weight, preferably from 5 to 15% by weight, of the ink.

However, the presence of one or more photoinifiators is optional as it is not necessary to include a photoinitiator in the inkjet ink in order to achieve a thorough cure of the ink. This is because the ink can cure without the presence of one or more photoinitiators by curing with a low-energy electron beam.

An inkjet ink that is cured with a low-energy electron beam may still contain 5% by weight or less of a photoinitiator, based on the total weight of the ink, if the ink is first pinned with actinic radiation.

By pinning is meant arresting the flow of the ink by treating the ink droplets quickly after they have impacted onto the substrate surface. Pinning provides a partial cure of the ink and thereby maximises image quality by controlling bleed and feathering between image areas. Pinning does not achieve full cure of the ink. By curing is meant fully curing the ink. Pinning leads to a marked increase in viscosity, whereas curing converts the inkjet ink from a liquid ink to a solid film. The dose of radiation used for pinning is generally lower than the dose required to cure the radiation-curable material fully.

In an alternative preferred embodiment, the photoinitiator is present in an amount of 10% by weight or less, preferably 5% by weight or less, more preferably 4% or less, more preferably 3% or less, more preferably 2% or less and more preferably 1% or less, based on the total weight of the ink. Most preferably, the inkjet ink is substantially free of photoinitiator.

In other words, no photoinitiator is intentionally added to the ink. However, minor amounts of a photoinitiator, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight, more preferably less than 0.1% by weight and most preferably less than 0.05% by weight of a photoinitiator, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of a photoinitiator.

An inkjet ink that is substantially free of photoinitiator is advantageous for various applications as there will be no unreacted photoinitiator or unreacted photoinitiator fragments present in the cured inkjet ink film. Photoinifiators create free radicals when exposed to radiation. These radicals react with reactive components of the ink (such as reactive monomers and oligomers). However, some photoinitiator and photoinitiator fragments will remain unreacted in the cured ink film and this is problematic for certain applications as such unreacted components can migrate into the substrate. In the ink of the present invention, photoinitiator is not necessary to achieve cure owing to curing with low-energy electron beam.

The inkjet ink of the present invention also includes a colouring agent, which may be either dissolved or dispersed in the liquid medium of the ink. The colouring agent can be any of a wide range of suitable colouring agents that would be known to the person skilled in the ad.

Preferably, the colouring agent is a dispersed pigment, of the types known in the art and commercially available such as under the trade-names Paliotol (available from BASF plc), Cinquasia, Irgalite (both available from Ciba Speciality Chemicals) and Hostaperm (available from Clariant UK). The pigment may be of any desired colour such as, for example, Pigment Yellow 13, Pigment Yellow 83, Pigment Red 9, Pigment Red 184, Pigment Blue 15:3, Pigment Green 7, Pigment Violet 19, Pigment Black 7. Especially useful are black and the colours required for trichromatic process printing. Mixtures of pigments may be used.

In one aspect the following pigments are preferred. Cyan: phthalocyanine pigments such as Phthalocyanine blue 15.4. Yellow: azo pigments such as Pigment yellow 120, Pigment yellow 151 and Pigment yellow 155. Magenta: quinacridone pigments, such as Pigment violet 19 or mixed crystal quinacridones such as Cromophtal Jet magenta 2BC and Cinquasia RT-355D. Black: carbon black pigments such as Pigment black 7.

Pigment particles dispersed in the ink should be sufficiently small to allow the ink to pass through an inkjet nozzle, typically having a particle size less than 8 pm, preferably less than 5 pm, more preferably less than 1 pm and particularly preferably less than 0.5 pm.

The colorant is preferably present in an amount of 0.2-20% by weight, preferably 0.5-10% by weight, based on the total weight of the ink. A higher concentration of pigment may be required for white inks, for example up to and including 30% by weight, or 25% by weight, based on the total weight of the ink.

The present invention may also provide an inkjet ink set wherein at least one of the inks in the set is an inkjet ink of the present invention. Preferably, allot the inks in the set fall within the scope of the inkjet ink according to the present invention.

Usually, the inkjet ink set of the present invention is in the form of a multi-chromatic inkjet ink set, which typically comprises a cyan ink, a magenta ink, a yellow ink and a black ink (a so-called trichromatic set). This set is often termed CMYK. The inks in a trichromatic set can be used to produce a wide range of colours and tones. Other inkjet ink sets may also be used, such as CMYK+white and light colours.

Print heads account for a significant portion of the cost of an entry level printer and it is therefore desirable to keep the number of print heads (and therefore the number of inks in the ink set) low. Reducing the number of print heads can reduce print quality and productivity. It is therefore desirable to balance the number of print heads in order to minimise cost without compromising print quality and productivity.

The inkjet ink of the present invention preferably dries primarily by curing, i.e. by the polymerisation of the monomers present, as discussed hereinabove, and hence is a curable ink. The ink does not, therefore, require the presence of water or a volatile organic solvent to effect drying of the ink. Preferably, the inkjet ink comprises less than 5% by weight of water and volatile organic solvent combined, preferably less than 3% by weight combined, more preferably, less than 2% by weight combined, more preferably less than 1% by weight combined and most preferably the inkjet ink is substantially free of water and volatile organic solvents, where the amounts are based on the total weight of the ink.

By substantially free is meant that only small amounts will be present, for example some water will typically be absorbed by the ink from the air and solvents may be present as impurities in the components of the inks, but such low levels are tolerated. In other words, no water or a volatile organic solvent is intentionally added to the ink. However, minor amounts of water or a volatile organic solvent, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight of water or a volatile organic solvent, more preferably less than 0.1% by weight of water or a volatile organic solvent, most preferably less than 0.05% by weight of water or a volatile organic solvent, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of water or a volatile organic solvent.

In a preferred embodiment, the ink of the present invention comprises a surfactant. The surfactant controls the surface tension of the ink. Surfactants are well known in the art and a detailed description is not required. An example of a suitable surfactant is BYK307. Adjustment of the surface tension of the inks allows control of the surface wetting of the inks on various substrates, for example, plastic substrates. Too high a surface tension can lead to ink pooling and/or a mottled appearance in high coverage areas of the print. Too low a surface tension can lead to excessive ink bleed between different coloured inks. Surface tension is also critical to ensuring stable jetting (nozzle plate wetting and sustainability). The surface tension is preferably in the range of 18-40 mNm-1, more preferably 20-35 mNm-1 and most preferably 20-30 mNm-1.

Other components of types known in the art may be present in the ink of the present invention to improve the properties or performance. These components may be, for example, defoamers, dispersants, synergists for the photoinifiator other than the (meth)acrylated amine of the ink of the present invention, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, biocides and identifying tracers.

The inks of the invention may be prepared by known methods such as, for example, stirring with a highspeed water-cooled stirrer, or milling on a horizontal bead-mill.

The ink of the present invention is suitable for application by inkjet printing. The ink exhibits a desirable low viscosity, less than 100 mPas, preferably 50 mPas or less, more preferably 30 mPas or less and most preferably 20 mPas or less at 25°C. The ink most preferably has a viscosity of 8 to 20 mPas at 25°C. Viscosity may be measured using a digital Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as model DV1.

The present invention may also provide a cartridge containing the inkjet ink as defined herein.

The present invention also provides a method of inkjet printing, comprising jetting the ink as defined herein onto a substrate and curing the ink.

In the method of inkjet printing of the present invention, the inkjet ink is printed onto a substrate. Printing is performed by inkjet printing, e.g. on a single-pass inkjet printer, for example for printing (directly) onto a substrate, on a roll-to-roll printer or a flat-bed printer. As discussed above, inkjet printing is well known in the art and a detailed description is not required.

The ink is jetted from one or more reservoirs or printing heads through narrow nozzles on to a substrate to form a printed image.

Substrates include those for packaging applications and in particular, flexible packaging applications.

Examples include substrates composed of polyvinyl chloride (PVC), polystyrene, polyester, polyethylene terephthalate (PET), polyethylene terephthalate glycol modified (PETG) and polyolefin (e.g. polyethylene, polypropylene or mixtures or copolymers thereof). Further substrates include all cellulosic materials such as paper and board, or their mixtures/blends with the aforementioned synthetic materials.

Particularly preferred substrates are a food packaging. Food packaging is typically formed of flexible and rigid plastics (e.g. food-grade polystyrene and PE/PP films), paper and board (e.g. corrugated board). Printing onto a food packaging substrate represents a particular challenge on account of the strict safety limitations on the properties of materials which come into contact with food, including indirect additives like packaging inks. For printed food packaging, it is necessary to control and quantify the migration and/or odour of the components of the printed image on the food packaging into the food products. Specific exclusions based on their odour and/or migration properties include volatile organic solvents and many monomers typically used in UV curing inks. Preferably, the monomers of the ink of the present invention are suitable for food packaging applications. The (meth)acrylated amine includes amine functionality but without the drawback of migration associated with low-molecular weight amines.

When discussing the substrate, it is the surface which is most important, since it is the surface which is wetted by the ink. Thus, at least the surface of substrate is composed of the above-discussed material.

In a preferred embodiment, the substrate is a laminate carton material comprising the following layers, in order: an inner polyethylene layer; an aluminium layer; a board layer; and an outer polyethylene layer. By inner is meant a surface of the substrate that would come into contact with food and by outer is meant a surface of the substrate that would come into contact with the inkjet ink used in the method of the present invention. More preferably, the polyethylene layer is corona treated to a surface tension of 45 dynes/cm or higher using a Vetaphone unit. This provides improved adhesion of the ink.

The present invention may also provide a printed substrate having the ink as defined herein printed thereon. Preferably, the substrate is a food packaging.

In order to produce a high quality printed image a small jetted drop size is desirable. Preferably the inkjet ink is jetted at drop sizes below 90 picolitres, preferably below 35 picolitres and most preferably below 10 picolitres.

To achieve compatibility with print heads that are capable of jetting drop sizes of 90 picolitres or less, a low viscosity ink is required. A viscosity of 30 mPas or less at 25°C is preferred, for example, 8 to 12 mPas, 18 to 20 mPas, or 24 to 26 mPas. Ink viscosity may be measured using a Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as a DV1 low-viscosity viscometer running at 20 rpm at 25°C with spindle 00.

The ink of the present invention is cured by any means known in the art, such as exposure to actinic radiation and low-energy electron beam radiation.

It should be noted that the terms dry and "cure" are often used interchangeably in the art when referring to radiation-curable inkjet inks to mean the conversion of the inkjet ink from a liquid to solid by polymerisation and/or crosslinking of the radiation-curable material. Herein, however, by "drying" is meant the removal of the water by evaporation and by "curing" is meant the polymerisation and/or crosslinking of the radiation-curable material. Further details of the printing, drying and curing process are provided in WO 2011/021052.

The source of actinic radiation can be any source of actinic radiation that is suitable for curing radiation-curable inks but is preferably a UV source. Suitable UV sources include mercury discharge lamps, fluorescent tubes, light emitting diodes (LEDs), flash lamps and combinations thereof One or more mercury discharge lamps, fluorescent tubes, or flash lamps may be used as the radiation source.

Preferably, the source of actinic radiation is a mercury discharge lamp and/or LEDs. When LEDs are used, these are preferably provided as an array of multiple LEDs.

The source of low-energy electron beam (ebeam) can be any source of low-energy electron beam that is suitable for curing radiation-curable inks. Suitable low-energy electron beam radiation sources include commercially available ebeam curing units, such as the EB Lab from ebeam Technologies with energy of 80-300 keV and capable of delivering a typical dose of 30-50 kGy at line speeds of up to 30 m/min. By "low-energy" for the ebeam, it is meant that it delivers an electron beam having a dose at the substrate of 100 kGy or less, preferably 50 kGy or less.

Ebeam curing is characterised by dose (energy per unit mass, measured in kilograys (kGy)) deposited in the substrate via electrons. Electron beam surface penetration depends upon the mass, density and thickness of the material being cured. Compared with UV penetration, electrons penetrate deeply through both lower and higher density materials. Unlike UV curing, photoinifiators are not required for ebeam curing to take place.

Ebeam curing is well-known in the art and therefore a detailed explanation of the curing method is not required. In order to cure the printed ink, the ink of the invention is exposed to the ebeam, which produces sufficient energy to instantaneously break chemical bonds and enable polymerisation or cross I i n king.

The ink cures to form a relatively thin polymerised film. The ink of the present invention typically produces a printed film having a thickness of ito 20 pm, preferably 1 to 10 pm, for example 2 to 5 pm. Film thicknesses can be measured using a confocal laser scanning microscope.

The present invention also provides the use of a (meth)acrylated amine having an amine value of 1190 mg KOH/g for maintaining water resistance of a cured inkjet ink film. The (meth)acrylated amine is as described above for the inkjet ink of the present invention. By maintaining water resistance is meant that the water resistance of the cured ink film is not affected by the presence of the (meth)acrylated amine of the present invention. The cured ink film remains adhered to the substrate despite the presence of the (meth)acrylated amine of the present invention.

The invention will now be described with reference to the following examples, which are not intended to be limiting.

Examples

Example 1

Inks were prepared by mixing the components in the amounts shown in Table 1. Amounts are given as weight percentages based on the total weight of the ink Table 1. Ink formulations Component Comparative ink 1, wt% Comparative ink 2, wt% Comparative ink 3, wt% Ink 4, wt% Ink 5, wt% Ink 6, wt% Ink 7, wt% 3-MPDDA 47.5 57.5 47.5 47.5 47.5 47.5 47.5 Lauryl acrylate 25.0 20.0 20.0 20.0 20.0 20.0 20.0 DVE-3 5.0 - - - - -CN3715LM 10.0 CN2565 - - - 10.0 - - - Ebecryl 80 - - - - 10.0 - -Ebecryl 81 10.0 UVP6600 - - - - - - 10.0 lrgastab UV22 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Cyan pigment dispersion 7.8 7.8 7.8 7.8 7.8 7.8 7.8 Omnirad 819 (BAPO) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Esacure KIP 160 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Speedcure 7010L 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Byk 307 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Viscosity at 25°C / mPa.s 8.90 9.40 12.20 13.46 15.12 11.94 15.70 3-MPDDA, lauryl acrylate and DVE-3 are monomers, as defined herein. CN3715LM, CN2565, Ebecryl 80, Ebecryl 81 and UVP6600 are (meth)acrylated amines having the amine values shown in Table 2.

Table 2

(Meth)acrylated amine Supplier Amine value / mg KOH/g CN3715LM Arkema 201 CN2565 Arkema 157 Ebecryl 80 Allnex 54 Ebecryl 81 Allnex 48 UVP6600 Univar 18 The amine values were determined by the following method: (i) dissolving about 0.1 g of the (meth)acrylated amine in 20 mL of isopropyl alcohol, (ii) adding 0.5 mL of a 0.04% w/v solution of bromocresol green in isopropyl alcohol to give a blue solution; (ii) titrating the blue solution with 0.1 M hydrochloric acid until the blue solution turns yellow (the end point); and (iii) using the following equation: Amine value (mg KOH/g) = (Titre value x 56.1 x Normality of HCI) / weight of (meth)acrylated amine dissolved.

Irgastab UV22 is a stabiliser from BASF.

The cyan pigment dispersion contains 30 wt% pigment, 20 wt% polymeric dispersing aid and 50 wt% DVE-3, based on the total weight of the pigment dispersion. The dispersion was prepared by mixing the components in the given amounts and passing the mixture through a bead mill until the dispersion had a particle size of less than 0.3 microns. Amounts are given as weight percentages based on the total weight of the dispersion.

Omnirad 819 (BAPO) and Esacure KIP 160 are photoinitiators from IGM. Speedcure 7010L is a photoinitiator from Lambson.

Byk 307 is a surfactant from Byk.

Example 2

Each of the above ink formulations was coated onto a laminate carton packaging material having a polyethylene outer layer. The polyethylene outer layer had been corona treated to a surface tension of 45 dynes/cm using a Vetaphone unit. The ink was coated onto the polyethylene outer layer using a K 2 applicator bar (12 pm wet film). The resulting films were cured using a Heraeus Noblelight UV lamp of power rating 180 W/cm. The UV dose required for full cure, i.e. a tack-free film, was recorded and the results are set out in Table 3.

Table 3

Comparative ink 1, wt% Comparative ink 2, wt% Comparative ink 3, wt% Ink 4, wt% Ink 5, wt% Ink 6, wt% Ink 7, wt% Dose / mJ/cm2 420 420 325 325 325 360 360 As can be seen from Table 3, comparative inks 1 and 2 show the same cure response, despite comparative ink 2 containing 10% more by weight of 3-MPDDA and 10% less by weight of monomers lauryl acrylate and DVE-3. 3-MPDDA is known to cure faster than lauryl acrylate and DVE-3, and so simply replacing slower curing monomers with faster curing monomers does not affect the cure response. This is contrast to comparative ink 3 and inks 4-7, which all contain (meth)acrylated amines and show an improved cure response compared to comparative inks 1 and 2, which do not contain (meth)acrylated amines.

Example 3

Each of the above ink formulations was printed in the same way as in Example 2 and the resulting films were cured using a Heraeus Noblelight UV lamp of power rating 180 W/cm and a total dose for cure of 1130 mJ/cm2.

Water resistance of the inks to the substrates was assessed using a water soak test. The test is as follows. AS cm x 5 cm square of print was immersed in a tray of cold water. At regular intervals up to a time of 60 minutes, the finger nail scratch resistance was assessed whilst the sample was submerged.

The time at which there was a noticeable deterioration in scratch resistance and ink was removed by finger nail scratch (the failure time) was recorded and the results are set out in Table 4.

Table 4

Comparative ink 1, wt% Comparative ink 2, wt% Comparative ink 3, wt% Ink 4, wt% Ink 5, wt% Ink 6, wt% Ink 7, wt% Time / minutes >60 >60 <5 >60 >60 >60 >60 As can be seen from Table 4, inks 4-7 which all contain a (meth)acrylated amine having an amine value of 1-190 mg KOH/g, have excellent water resistance. This is in contrast to comparative ink 3, which contains a (meth)acrylated amine having an amine value of 201 mg KOH/g. Comparative inks 1 and 2 also showed excellent water resistance but did not contain a (meth)acrylated amine and thus had a relatively slow cure speed.

Therefore, inks 4-7 are the only inks which have the desired balance of an improved cure speed with excellent water resistance.

Claims

Claims 1. An inkjet ink comprising: one or more monofunctional (meth)acrylate monomers; one or more di-and/or multifunctional monomers; a (meth)acrylated amine having an amine value of 1-190 mg KOH/g; and a colouring agent, wherein the one or more di-and/or multifunctional monomers are present in a total amount of 15% by weight or more, based on the total weight of the ink.
2. An inkjet ink as claimed in claim 1, wherein the (meth)acrylated amine has an amine value of 5-mg KOH/g.
3. An inkjet ink as claimed in claim 2, wherein the (meth)acrylated amine has an amine value of 10- 170 mg KOH/g.
4. An inkjet ink as claimed in any preceding claim, wherein the (meth)acrylated amine is present in 1-20% by weight, based on the total weight of the ink.
5. An inkjet ink as claimed in any preceding claim, wherein the one or more di-and/or multifunctional monomers are present in a total amount of 20% by weight or more, based on the total weight of the ink.
6. An inkjet ink as claimed in any preceding claim, wherein the one or more monofunctional (meth)acrylate monomers are present in 5-35% by weight, based on the total weight of the ink.
7. An inkjet ink as claimed in any preceding claim, wherein the one or more di-and/or multifunctional monomers comprise one or more difunctional monomers.
8. An inkjet ink as claimed in claim 7, wherein the one or more difunctional monomers comprise one or more difunctional (meth)acrylate monomers.
9. An inkjet ink as claimed in any preceding claim, wherein the one or more di-and/or multifunctional monomers are selected from 1,10-decanediol diacrylate (DDDA), hexanediol diacrylate (HDDA), polyethylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), 3-methyl-1,5-pentanediol diacrylate (3-MPDDA), dipropylene glycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), propoxylated neopentyl glycol diacrylate (NPGPODA), trimethylolpropane triacrylate (TMPTA), di-trimethylolpropane tetraacrylate (DiTMPTA), di-pentaerythritol hexaacrylate (DPHA), ethoxylated trimethylolpropane triacrylate (EOTMPTA), triethylene glycol divinyl ether (DVE-3) and mixtures thereof.
10. An inkjet ink as claimed in any preceding claim, wherein the one or more monofunctional (meth)acrylate monomers are selected from isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane- 4-yl)methyl acrylate (MEDAJMedo1-10), 4-tert-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), octadecyl acrylate (ODA), 2-(2-ethwryethoxy)ethyl acrylate, tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof.
11. An inkjet ink as claimed in any preceding claim, wherein the one or more monofunctional (meth)acrylate monomers comprise lauryl acrylate and wherein the one or more di-and/or multifunctional monomers comprise 3-MPDDA.
12. An inkjet ink as claimed in claim 11, wherein lauryl acrylate is the sole monofunctional (meth)acrylate monomer present in the ink and wherein 3-MPDDA is the sole di-and/or multifunctional monomer present in the ink.
13. An inkjet ink as claimed in any preceding claim, wherein the ink further comprises one or more photoinifiators.
14. A method of inkjet printing, comprising jetting the ink as claimed in any preceding claim onto a substrate and curing the ink.
15. Use of a (meth)acrylated amine having an amine value of 1-190 mg KOH/g for maintaining water resistance of a cured inkjet ink film.