Energy curable inkjet compositions

Abstract

A UV-curable inkjet ink or inkjet coating composition comprises (i) 30-75 wt.% multifunctional (meth)acrylate monomers having an average functionality of >2, (ii) one or more difunctional, trifunction

Description

BACKGROUND OF THE INVENTION An issue with energy-curable (UV and electron beam) inkjet compositions to date has been the need to use relatively high concentrations of low viscosity monomers to achieve the desired low ink viscosity required of current inkjet printhead designs. Indeed, until recently, there was a push for continuously decreasing viscosity to accommodate newer printheads. Such low viscosity monomers are typically monofunctional and difunctional with respect to the polymerizable groups on each monomer molecule. For low migration printing applications, such as the printing of food packaging, these monomers may not be fully reacted into the cured ink film, making them prone to migrate from the print and contaminate the packaged contents. In a technology shift, manufacturers (e.g. Xaar) now produce an “Ultra High Viscosity” printhead technology that can jet fluids up to 100 mPa.s at jetting temperature. Other printhead manufacturers are likely to follow Xaar’s and release their own printhead products with similar if not further enhanced viscosity capability. Until recently, inkjet inks were typically formulated to a viscosity of less than 10 mPa.s and often less than 8 mPa.s at jetting temperature. Being able to formulate at higher viscosities, for example up to about 100 mPa.s, and potentially higher, at 45°C, means that the amount of monofunctional and difunctional monomers with molecular weight of less than 400* can be significantly reduced if not eliminated from inkjet compositions. Thus, by using predominantly tri-, tetra- and higher functional monomers (referred to as “multifunctional” monomers throughout the present application), UV-curable inkjet inks can be more effectively cured for low migration printing applications, under the action of UV-LED lamp emissions. Furthermore, this can be achieved at press line speeds of 50 m / min or greater, which is advantageous for current and future single pass inkjet presses. *Theoretic molecular weight based on structure GB2606623B (Fujifilm) mentions inks with multifunctional monomers1, however the incorporation of difunctional monomer as a preferred embodiment (5 to 20% (w / w)) is clearly stated. Indeed, the one given example contains 18% (w / w) of the difunctional monomer 3-methylpentanediol diacrylate. The ink also comprises 2% (w / w) of the difunctional monomer DVE-3 (triethyleneglycol divinyl ether) by way of the pigment dispersion. ‘623 clearly does not demonstrate any issue for inks comprising difunctional monomers at >5% (w / w), for the risk of undesirable levels of these uncured monomers in a UV-cured ink film. An aspect of the inks and coatings of the present invention is that they should minimize or be essentially free of any purely vinyl ether containing monomer. Furthermore, the ‘623 ink example does not comprise an acrylated amine, which the inventors have found to be highly beneficial in helping to reduce the amount of uncured monomer. Furthermore, there is no indication of the UV dose required to cure the inks satisfactorily. Yet furthermore, no analysis of the amount of uncured monomer present in the inks cured under the action of a UV-LED lamp was provided, thus there is no indication of the suitability of these inks for low migration printing. The inventors have shown that an ink prepared according to ‘623 performs very poorly in terms of the amount of uncured monomer in a print cured under the action of a UV-LED lamp emitting at 395nm. ’In the context of the present invention, a multifunctional monomer is defined as one where the average number of polymerizable groups per molecule is >2. Yet furthermore, the example provided in ‘623 comprises a total of 20% (w / w) of oligomeric and polymeric photoinitiator, which is an excessive amount. An aspect of the present invention is that <10% (w / w) of any blend of polymeric photoinitiators should be used. It is especially preferred that <10% of any polymeric thioxanthone photoinitiator be used. A reason for this is that high concentrations of such photoinitiators can significantly attenuate the amount of incident light from a UV-LED light source that can penetrate through an ink film. This can have a negative impact on the degree of monomer conversion and hence the suitability of such ink compositions for low migration printing. Furthermore, the use of such high concentrations of polymeric photoinitiators can contribute significantly to ink viscosity, reducing the amount of multifunctional monomers and oligomers that can be used whilst maintaining a viscosity ideally of less than about 100 mPa.s at jetting temperature. Clearly, such high concentrations of photoinitiator is excessive and the present invention shows how to formulate inkjet inks that effectively cure under the action of UV-LED lamps, with photo initiator concentrations of less than 10% (w / w). GB2607660A, GB2606449B and GB2606448A (all Fujifilm) all mention UV-curable inkjet compositions having viscosities greater than 30 mPa.s at 40°C. All examples comprise greater than 10% (w / w) of monofunctional or difunctional monomers, so fall outside the scope of the present invention. WO2023105206 (Fujifilm) mentions UV-curable inkjet compositions for the printing of food packaging which might be cured under the action of UV-LED light sources. This is achieved through the use of high concentrations of acylphosphine oxide photoinitiators. The inventive examples all comprise greater than 8.5% (w / w) of such photoinitiators along with a polymeric thioxanthone photoinitiator. Furthermore, all the inventive examples comprise more than 70% (w / w) of the difunctional monomer, 3-methylpentanediol diacrylate. An aspect of the present invention is that <5% (w / w) of any blend of acylphosphine oxide photoinitiators should be used to mitigate against the contamination risk arising from migration of mesitaldehyde, a photodecomposition by-product of this type of photoinitiator. It is interesting to note that the inks described by way of the examples do not comprise any amine synergist; the present invention uses acrylated amines to enhance the cure under the action of UV-LED light sources. This is shown by way of the examples. WO2023105207 (Fujifilm) also mentions UV-curable inkjet compositions for the printing of food packaging which might be cured under the action of UV-LED light sources. This is achieved with a blend of acylphosphine oxide photoinitators, including polymeric types, where the overall concentration of this blend of photoinitiators is >5.0% (w / w) of the ink composition. In all instances of the examples, >10% (w / w) concentration of all photoinitiators is used, along with >60% (w / w) of the difunctional monomer, 3-methylpentanediol diacrylate. Again, no amine synergist, and more specifically no aminoacrylate was used. Agfa hold a number of patents describing low migration capable energy-curable inkjet compositions comprising the difunctional monomer, 2-(2-Vinyloxyethoxy)ethyl acrylate (‘VEEA’) which has an acrylate and a vinyl ether polymerizable group per molecule. US8940811B2 is representative of that suite of patents and requires that >25% (w / w) of the polymerizable component should constitute VEEA, thus falling outside the scope of the present invention. Sun Chemical hold a number of patents covering low migration energy-curable inkjet compositions, all of which comprise significant concentrations of difunctional monomers, including US9714355B2. Indeed, ‘355 requires the almost exclusive use of difunctional monomers, including VEEA, 3-methylpentanediol diacrylate and dipropylene glycol diacrylate. EP3294815B1 (Sun Chemical) describes energy-curable inkjet compositions for low migration printing comprising aminoacrylates of the type preferred in the present invention. However, all the examples comprise high concentrations of difunctional monomers, >50% (w / w) of the ink compositions. Thus, the present invention and the advantage for low migration printing with concentrations of difunctional monomers of <10% (w / w) and preferably <5% (w / w) has not satisfactorily been described or alluded to in the identified references. The key finding from the research is the benefit of minimizing the content of difunctional monomers to reduce the amount of free, unbound monomer in UV-cured ink films. The inks of the present application, comprising predominantly monomers bearing three or more acrylate groups per molecule, have also been designed to cure under the action of UV-LED light sources. Thus, the invention will allow low migration capable UV-inkjet ink compositions, for sensitive applications such as the printing of food packaging, pharmaceutical packaging, for curing with UV-LED lamps. This has not been satisfactorily demonstrated to date, with most of the state of the art describing UV-curable inkjet compositions for low migration printing, comprising significant concentrations of difunctional monomers, which were required for lower viscosity specification printheads which have been the norm until recently. These difunctional monomers are less likely to be incorporated into a UV-cured ink film than higher functional monomers and hence reducing, or nearly eliminating, their use would clearly be advantageous. GB2006623B, by way of the description and example, comprises a significant concentration of difunctional monomers. The present invention shows by way of the examples that when the concentration of difunctional monomers is reduced to <10% (w / w), preferably <5% (w / w) of the ink composition, the amount of uncured monomers significantly reduces for inks cured under the action of a UV-LED light source. The examples show that introducing any difunctional monomer into an ink also has a negative impact on the amount of uncured multifunctional monomer. Furthermore, when the inventors prepared and tested an example according to that provided in GB2006623B, they found it to produce excessive amounts of uncured monomer when cured with a UV-LED (395nm) light source. The present invention preferably comprises an aminoacrylate, which dramatically reduces the amount of uncured monomer present in a UV-cured ink film. Furthermore, ‘623 requires >10% (w / w) of polymeric photoinitiator, with the example comprising 20% of a blend of polymeric thioxanthone and aminoketone photoinitiators. Such high concentrations of photoinitiators can not only increase the ink viscosity significantly but also significantly attenuate the incident UV light, especially at 395nm, such that very little of the incident UV light might penetrate through the ink. Modelling in the inventors’ labs indicates that the polymeric thioxanthone used in ‘623, under the conditions of the information provided in the Example could cause a 95%, or greater attenuation of 395nm UV light through a 12-micron ink layer. Other ink components, especially pigments, could attenuate this even further. Therefore, to mitigate against this potential problem the current invention’s use of <10% (w / w), of any blend of polymeric thioxanthone photoinitiators is clearly beneficial. At the same time, the higher viscosity capability of new printheads, such as Xaar’s “Ultra High Viscosity Printhead” technology, allows the use of higher concentrations of such polymeric photoinitators. Thus, the benefits of high viscosity inkjet ink compositions from a formulation perspective are beneficial. Furthermore, as the viscosity of an ink increases, the adverse effects of oxygen inhibition decrease as the rate of oxygen ingress from the atmosphere decreases. From the foregoing it can be seen that the design of inks according to the present invention can provide significant advantages for low migration printing of UV-curable inkjet ink compositions, using UV-LED light sources. Furthermore, the invention can deliver low migration prints with UV doses (from a 395nm UV-LED light source) of less than 500 mJ / cm2, and at line speeds of 50 m / min, or greater. GB2006623B states a cure speed of only 30 m / min and this was only to the point of achieving satisfactory surface cure and adhesion, not to the desired point of low levels of uncured monomer necessary for low migration printing, of food packaging for example. DETAILED DESCRIPTION The main aspect that has restricted the implementation of low migration capable UV-inkjet relates to the low viscosities required for current printhead technology, typically less than 10 mPa.s at jetting temperature, which is usually between 40-50°C. Although it is recognised that the use of monofunctional monomers should be largely avoided, significant concentrations of low viscosity difunctional monomers such as HDDA (hexanediol diacrylate), 3-methylpentanediol diacrylate (‘MPDA’), DPGDA (dipropylene glycol diacrylate) and VEEA (2-(2-Vinyloxyethoxy)ethyl acrylate) have been used to achieve the low viscosities that have been required to date. Such difunctional monomers are still prone to incomplete reaction into the cured ink film after UV irradiation. So, the use of trifunctional, tetrafunctional and higher functional acrylate monomers is preferred to better achieve more complete incorporation into the UV-cured ink film. Obviously, as the functionality (the number of polymerizable groups per molecule) of an acrylate, or other ethylenically unsaturated monomer increases, the greater the likelihood that one of the acrylate groups on any monomer molecule will free radically polymerize into the UV-cured ink film. Thus, a preferable embodiment of the current invention is that the inks should comprise <10% (w / w), and more preferably <5% (w / w) of any blend of difunctional and monofunctional monomers; including <2.5 (w / w), or even elimination of difunctional monomers all together. Further to this, it is an aspect of the invention that at least 90% of the polymerizable component (excluding the aminoacrylate) should be comprised of multifunctional monomers having an average of >2 polymerizable groups per monomer molecule, where the polymerizable groups may be any of acrylate, vinyl ether or acrylamide. The inks of the invention will advantageously allow the printing of food packaging and labels intended for food packaging when cured under the action of UV-LED lamps, especially those emitting between 360 to 410nm, and more specifically 395nm. This is especially useful, as the inkjet printing market moves from mercury doped UV-lamps to UV-LED types for health and safety and environmental reasons. Compared with references describing high viscosity UV-curable inkjet inks, the compositions of the present invention can achieve satisfactory cure under the action of a UV-LED light source whilst using <10% (w / w) of any blend of polymeric photoinitiator and <5% (w / w) of any blend of acylphosphine oxide photoinitiators. Both these photoinitiator factors form optional features of the invention. Satisfactory cure can be obtained with a total dose of UV light of <500 mJ / cm2 provided by any combination of UV-LED light sources, whether air- or water-cooled, at any combination of wavelengths between 360 and 410 nm., and where the amount of any migratable monomer is <8pg / dm2 of print area (which is the equivalent of about 50ppb food contamination, according to the standard EU food package model). In a further embodiment satisfactory cure of the printed ink sample can be obtained with UV-LED lamp(s) at a speed of >50 m / min. Compared with GB2606623B, a cure speed of only 30m / min was achieved and not to the same strictures as just outlined. Indeed, ‘623 merely defined acceptable cure in the loose terms of a print that passed a simple surface cure test. The more rigorous testing provided by way of the examples of the present invention clearly better define an inkjet ink which is capable of meeting the low migration requirements required in various markets, including the regulatory requirements in place in Europe for printing inks applied to food packaging. For the purposes of the present application, the regulatory requirement that is referenced throughout is Annex 10 of the Swiss Ordinance of the Federal Department of Home Affairs (FDHA), which pertains to materials and articles intended to come into contact with foodstuffs. This annex (henceforth referred to as “Annex 10”) lists the substances permitted for use in the production of packaging inks and outlines related requirements. The inks of the present invention have been rigorously designed to provide an inkjet ink that can meet the Annex 10 requirements. When inks were prepared according to GB2606623B, and cured with a dose of 300mJ / cm2 from a UV-LED lamp emitting at 395nm, the inventors found that the amount of migratable monomer was excessive and would be unsuitable for low migration printing of food packaging. The inks of the present invention have been designed to cure in atmospheric air. However, the inks may also be cured under an inert atmosphere, such as nitrogen, to exclude oxygen from the point of cure. In this case, the amount of photoinitiators, especially of the polymeric thioxanthones, may be reduced significantly; to less than 5% (w / w) and to even less than 2.5% (w / w). However, for cure under atmospheric air, the inks would preferably comprise preferably >2.5% polymeric thioxanthone, more preferably >4% (w / w), but less than 10% (w / w). A further reason for limiting the amount of thioxanthone type photoinitiators, as previously mentioned, is that as their concentration increases in an ink the attenuation of UV light between 360 and 410 nm increases. Indeed, for an ink comprising 10% (w / w) of Speedcure 7010, the polymeric thioxanthone photoinitiator used in GB2606623B, its absorption of UV light at 395nm would be in excess of 90%, according to calculations carried out by the inventors. The concentration of any combination of acylphosphine oxide photoinitiators should be maintained at 5% (w / w), or less and more preferably, 3% (w / w) or less to mitigate against the migration risk of mesitaldehyde, a photodecomposition by-product of this type of photoinitiator. Much of the detailed description has already been provided by way of the sections covering the technical and commercial advantages. In essence, the invention covers the following key aspects: 1. UV-curable inkjet compositions, suitable for low migration printing applications, having viscosities of greater than 20 mPa.s at 40°C. The inks are cured by the action of UV-LED light sources, with total, cumulative, UV doses of 500 mJ / cm2, or less. The inks, as shown in the Examples, have been cured using a 395nm UV-LED light source. 2. The inks preferably comprise less than 10% (w / w), more preferably less than 5% (w / w), and most preferably less than 2.5% (w / w) of any difunctional or monofunctional monomer having a molecular weight of <600 amu, preferably <500 amu, more preferably <400 amu. In one embodiment, the inks would be essentially free of difunctional or monofunctional monomer. 3. The inks preferably comprise >40% (w / w), more preferably >50%, and more preferably >60% (w / w) of any blend of multifunctional monomers, where the monomers comprise greater than 2 acrylate groups, on average (per molecule). Preferred multifunctional monomers may be selected from any of ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tri- and tertraacrylate. Other multifunctional monomers that may be optionally used include ditrimethylolpropane tetraacrylate, dipentaerythritol penta and hexaacrylate. 4. The inks preferably comprise <10% (w / w) of any blend of polymeric photoinitiators, wherein polymeric thioxanthones are most preferred. 5. The inks should comprise <5% (w / w), and more preferably <3% (w / w) of any blend of acylphosphine oxide photoinitiators. 6. The inks preferably comprise >2.5% (w / w), and more preferably >5.0% (w / w) of an aminoacrylate. 7. The inks achieve satisfactory cure, as defined in point (8) at lines speeds of 50 m / min, or greater, when cured with UV-LED lamps. This is an important embodiment as it will enable the inks of the invention to be successfully implemented on single pass presses, most especially for the printing of labels for the food packaging industries. 8. The inks can achieve levels of set-off migratable monomer of <50ppb (or <10ppb depending on the specific monomer) when tested according to guidelines laid out by EUPIA, as will be described in the Examples. Minimizing or excluding intentionally added mono- and difunctional monomers is key to achieving this. References in this space do not demonstrate this and more especially not for inkjet inks cured with UV- LED lamps. This breakthrough offers clear advantages for the UV-inkjet printing of food packaging. Inventors have prepared and tested a broad range of examples and have clearly demonstrated that when a difunctional monomer is included into the ink at >10% (w / w), these monomers become highly prone to migrating from an ink film cured using a UV-LED lamp, as a result of them not being incorporated into the cured print as a result of the photopolymerisation process. The higher viscosity capable printheads, such as those provided by Xaar and their “Ultra High Viscosity” printhead technology, allows the use of inks which are essentially free of any difunctional or monofunctional monomer. A further benefit of higher viscosity UV-curable inks, and especially when cured in air, is that they are less prone to oxygen inhibition. This is a well-understood problem for UV-inkjet and raising an ink’s viscosity will reduce the rate of oxygen ingress into the ink after printing, but prior to UV-curing, thereby alleviating the issue of oxygen inhibition. Yet a further benefit of the invention is that preferred multifunctional monomers such as ethoxylated trimethylolpropane triacrylate (TMPEOTA) and propxylated glycerol triacrylate (GPTA) have higher specific migration limits (SML), according to EU regulations, than most difunctional monomers. TMPEOTA and GPTA have SMLs of 50ppb; this is the maximum level of contamination allowed in a foodstuff resulting from any contamination of these monomers arising from migration from a print containing them. It should be noted that the term ‘Low Migration Printing Inks’ is one commonly used in the printing industry. However, In Europe the European Printing Ink Association (EUPIA) no longer uses this term but rather uses the phrase; “Printing inks for food contact materials”. It should be understood that in terms of the current invention both terms can be used interchangeably. To demonstrate the capability of inks prepared according to the invention to enable the printing of food packaging, inks were UV-cured on PET (polyester) film and cured under the light generated by a 395nm UV-LED lamp. The prints were then blocked to LDPE (low density polyethylene) film for 10 days. The blocked LDPE films into which any uncured monomer could migrate, by the well-known set-off migration process, were then extracted into a 10% (w / w) aqueous solution of ethanol (commonly referred to as Simulant A) and the amount of migratable monomer determined, via GC-MS analysis. Reference is made to EP2956488B1 and EP3294815B1 for further description of the migration of low molecular weight contaminants from UV-cured inks and the testing protocols. Further detail about printing inks for food packaging materials can be found on EuPIA’s website (www. eupia.org) and more specifically their document; “Guidance on Migration Test Methods for the evaluation of substances in printing inks and varnishes for food contact materials”. Any combination of UV-LED lamps may be used to cure the inks of the invention, including those emitting between 360 and 410nm, and most especially those emitting at 395nm. Both air-cooled and water-cooled lamps are encompassed by the invention, although the inks allow satisfactory cure for the printing of food packaging materials to be achieved with air-cooled lamps. It should be understood that although the invention is preferentially directed to a UV-curing process using only UV-LED light sources, it also encompasses the situation where inks according to the invention are cured by two or more emissions from UV-LED lamps prior to a final cure with a medium-pressure, or low-pressure mercury lamp, including doped variants, as well as UV-LED lamps. Although the invention is directed towards thioxanthone and acylphosphine oxide photoinitiators suitable for the printing of food packaging, it should be understood that the invention covers other types of photoinitiators and sensitisers. A key part of the invention is the use of thioxanthone photoinitiators, especially those suited to the printing of food packaging, including polymeric, polymerizable and multifunctional types. Thus, suitable thioxanthone photoinitiators which may be used include, but are not limited to; 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4- diisopropylthioxanthone, 2-chlorothioxanthone, 2-chloro-4-isopropylthioxanthone. Oligomeric / polymeric thioxanthones such as Omnipol TX (ex. IGM Resins), Speedcure 7010 (ex. Arkema) and Genopol TX (ex. Rahn) may be used. Polymerizable thioxanthones such as Omnipol 3 ATX (ex. IGM Resins) may also be used. Suitable acylphosphine oxide photoinitiators include but are not limited to; diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide, ethyl-(2,4,6-triemthylbenzoyl) phenyl phosphinate, phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide, and oligomeric / polymeric types such as Omnipol TP and Omnirad 820 (ex. IGM Resins). The latter three photoinitiators are especially suited to low migration printing applications. It is preferred that the blend of thioxanthone and acylphosphine oxide photoinitiators should form <15.0% (w / w), more preferably <10.0% (w / w) of the ink composition. The thioxanthones and acylphosphine oxide photoinitiators may be blended in any ratio but preferably the ratio should be in the range 10:1 and 1:10 of thioxanthone to acylphospine oxide, more preferably in the range 5:1 and 1:5. It is preferred that the concentration of any blend of thioxanthone photoinitiators should be <10.0% (w / w) and that the concentration of any blend of acylphosphine oxide photoinitiators should be <5.0% (w / w) and more preferably <2.5% (w / w) of the ink composition. Where other photoinitiator types are used it is preferred that they should be suitable for the printing of food packaging and can include aminoketone types. To help the inks cure under the action of light produced by a UV-LED light source emitting at 395nm the use of any sensitiser might be considered. Such sensitisers are well known to those skilled in the art and include anthracenes such as diethoxyanthracene. Such sensitisers are not able themselves to produce initiating free radicals when exposed to UV light but can transfer energy, after photo-excitation, to photoinitiators, like acylphosphine oxides, to enhance radical generation and hence cure of the ink. The ink compositions of the invention should also preferably comprise an aminoacrylate. Aminoacrylates are the products of the reaction between an acrylate functional monomer or oligomer and a primary or secondary amine. As demonstrated by way of the examples, it is preferred that the aminoacrylate content of any inventive ink composition should be 2.5% (w / w), or greater, and more preferably 5.0% (w / w) or greater, and most preferably 10.0% (w / w) or more, especially when the aminoacrylate is one derived from the reaction of ethoxylated trimethylolpropane triacrylate and ethanolamine. Aminoacrylates and amine modified poly ether acrylates, including but not limited to may be used; EBECRYL 80, EBECRYL 81, EBECRYL 83, EBECRYL 85, EBECRYL 880, EBECRYL LEO 10551, EBECRYL LEO 10552, EBECRYL LEO 10553, EBECRYL 7100, EBECRYL Pl 15, EBECRYL Pl 16, EBECRYL LED 03, available from ALLNEX; CN501, CN550, CN UVA421, CN3705, CN3715, CN3755, CN381 and CN386, all available from Sartomer; GENOMER 3430, GENOMER 5142, GENOMER 5161, GENOMER 5271 and GENOMER 5275 from RAHN; PHOTOMER 4250, PHOTOMER 4771, PHOTOMER 4967, PHOTOMER 5006, PHOTOMER 4775, PHOTOMER 5662, PHOTOMER 5850, PHOTOMER 5930, and PHOTOMER 4250 all available from IGM, LAROMER LR8996, LAROMER LR8869, LAROMER LR8889, LAROMER LR8997, LAROMER PO 83F, LAROMER PO 84F, LAROMER PO 94F, LAROMER PO 9067, LAROMER PO 9103, LAROMER PO 9104, LAROMER PO 9106 and LAROMER PO77F, all available from BASF; AGISYN 008, AGISYN 701, AGISYN 702, AGISYN 703, NeoRad P-8 land NeoRad P-85 ex DSM-AGI. Furthermore, the aminoacrylates disclosed in WO2016186838, WO2017095786 and WO2017160784 by way of the descriptions and examples are also encompassed by the current invention. Aminobenzoate type amine synergists may also be optionally used, but their use is not a required embodiment of the invention. Indeed, inks with acceptable performance can be prepared which are essentially free of any aminobenzoate amine synergist. The invention is directed towards inkjet ink compositions, comprising any blend of ethylenically unsaturated monomers and oligomers, and especially those monomers and oligomers comprising acrylate groups. However, it should be understood that the invention also encompasses the printing of UV-flexo ink compositions. There is no restriction on the type, blend, or concentration of free radical photoinitiators used, other than those previously mentioned, and can include any of, but not limited to the following (and combinations thereof): a-hydroxyketones such as; 1-hydroxy-cyclohexyl-phenyl-ketone; 2-hydroxy-2-methyl-l-phenyl-1 -propanone; 2-hydroxy-2-methyl-4’-tert-butyl-propiophenone; 2-hydroxy-4’-(2-hydroxyethoxy)-2-methyl-propiophenone; 2-hydroxy-4’-(2-hydroxypropoxy)-2-methyl-propiophenone; oligo 2-hydroxy-2-methy 1-1-[4-(1-methyl-vinyl)phenyl]propanone; bis[4-(2-hydroxy-2-methylpropionyl)phenyl]methane; 2-Hydroxy-l-[l-[4-(2-hydroxy-2-methy Ipropanoy l)pheny 1] -1,3,3 -tr imethy lindan- 5 -y 1] -2-methy Ipr opan-1 - one and 2- Hydroxy-l-[4-[4-(2-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-l-one; acylphosphine oxides such as; 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; ethyl (2,4,6-trimethylbenzoyl)phenyl phosphinate, bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; and bis(2,6-dimethoxybenzoyl)-2,4,4- trimethylpentylphosphinoxide. a-aminoketones such as; 2-methyl-l-[4-methylthio)phenyl]-2-morpholinopropan-l-one; 2-benzyl-2-dimethylamino-l-(4-morpholinophenyl)-butan -1-one; and 2-dimethylamino-2-(4-methyl-benzyl)-l-(4-morpholin-4-yl-phenyl)-butan-l-one; thioxanthones such as; 2-4-diethylthioxanthone, isopropylthioxanthone, 2-chlorothioxanthone, and 1 -chloro-4-propoxythi oxanthone; benzophenones such as; such as benzophenone, 4-phenylbenzophenone, and 4-methylbenzophenone; methyl-2-benzoylbenzoate; 4-benzoyl-4-methyldiphenyl sulphide; 4-hydroxybenzophenone; 2,4,6-trimethyl benzophenone, 4,4- bis(diethylamino)benzophenone; benzophenone-2-carboxy(tetraethoxy)acrylate; 4-hydroxybenzophenone laurate and l-[-4-[benzoylphenylsulpho]phenyl]-2-methyl-2-(4-methylphenylsulphonyl)propan-1 -one; phenylglyoxylates such as; phenyl glyoxylic acid methyl ester; oxy-phenyl-acetic acid 2-[hydroxyl-ethoxy]-ethyl ester, or oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester; oxime esters such as; 1-phenyl-l,2-propanedione-2-(O-ethoxycarbonyl)oxime; [1-(4-phenylsulfanylbenzoyl)heptylideneamino]benzoate, or [ 1 -[9-ethyl-6-(2- methylbenzoyl)carbazol-3-yl]-ethylideneamino]acetate; Examples of other suitable photoinitiators include diethoxy acetophenone; benzil; benzil dimethyl ketal; titanocen radical initiators such as titanium-bis(r) 5-2,4-cyclopentadien-l-yl)-bis-[2,6-difluoro-3-(lH-pyrrol-l-yl)phenyl]; 9-fluorenone; camphorquinone; 2-ethyl anthraquinone; and the like. Polymeric photoinitiators and sensitisers are also suitable, including, for example, polymeric aminobenzoates (GENOPOL AB-1 or AB-2 from RAHN, Omnipol ASA from IGM or Speedcure 7040 from Arkema), polymeric benzophenone derivatives (GENOPOL BP-1 or BP-2 from RAHN, Omnipol BP, Omnipol BP2702 or Omnipol 682 from IGM or Speedcure 7005 from Arkema), polymeric thioxanthone derivatives are especially preferred (GENOPOL TX-1 or TX-2 from RAHN, Omnipol TX from IGM or Speedcure 7010 from Arkema), polymeric aminoalkylphenones such as Omnipol 910 from IGM; polymeric benzoyl formate esters such as Omnipol 2712 from IGM; and the polymeric sensitiser Omnipol SZ from IGM. The invention is directed to low concentrations of monofunctional and difunctional monomers as already outlined. Examples of suitable monofunctional ethylenically unsaturated monomers include but are not limited to the following (and combinations thereof), where the terms ethoxylated refers to chain extended compounds through the use of ethyleneoxide, propoxylated refers to chain extended compounds through the use of propylene oxide, and alkoxylated refers to chain extended compounds using either or both ethyleneoxide and propylene oxide. Equivalent methacrylate compounds are also capable of being used, although those skilled in the art will appreciate that methacrylate compounds have lower reactivity than their equivalent acrylate counterparts: isobutyl acrylate; cyclohexyl acrylate; iso-octyl acrylate; n-octyl acrylate; isodecyl acrylate; iso-nonyl acrylate; octyl / decyl acrylate; lauryl acrylate; 2- propyl heptyl acrylate; tridecyl acrylate; hexadecyl acylate; stearyl acrylate; iso-stearyl acrylate; behenyl acrylate; tetrahydrofurfuryl acrylate; 4-t.butyl cyclohexyl acrylate; 3,3,5-trimethylcyclohexane acrylate; isobornyl acrylate; dicyclopentyl acrylate; dihydrodicyclopentadienyl acrylate; dicyclopentenyloxyethyl acrylate; dicyclopentanyl acrylate; benzyl acrylate; phenoxyethyl acrylate; 2-hydroxy-3-phenoxypropyl acrylate; alkoxylated nonylphenol acrylate; cumyl phenoxyethyl acrylate; cyclic trimethylolpropane formal acrylate; 2(2-ethoxyethoxy) ethyl acrylate; polyethylene glycol monoacrylate; polypropylene glycol monoacrylate; caprolactone acrylate; ethoxylated methoxy polyethylene glycol acrylate; methoxy triethylene glycol acrylate; tripropyleneglycol monomethyl ether acrylate; diethylenglycol butyl ether acrylate; alkoxylated tetrahydrofurfuryl acrylate; ethoxylated ethyl hexyl acrylate; alkoxylated phenol acrylate; ethoxylated phenol acrylate; ethoxylated nonyl phenol acrylate; propoxylated nonyl phenol acylate; polyethylene glycol o-phenyl phenyl ether acrylate; ethoxylated p-cumyl phenol acrylate; ethoxylated nonyl phenol acrylate; alkoxylated lauryl acrylate; ethoxylated tristyrylphenol acrylate; N- (acryloyloxyethyl)hexahydrophthalimide; N-butyl 1,2 (acryloyloxy) ethyl carbamate; acryloyl oxyethyl hydrogen succinate; octoxypolyethylene glycol acrylate; octafluoropentyl acrylate; 2-isocyanato ethyl acrylate; acetoacetoxy ethyl acrylate; 2-methoxyethyl acrylate; dimethyl aminoethyl acrylate; 2-carboxyethyl acrylate; 4-hydroxy butyl acrylate. Examples of difunctional ethylenically unsaturated monomers with molecular weights of less than 400amu include but are not limited to the following (and combinations thereof), where the terms ethoxylated refers to chain extended compounds through the use of ethyleneoxide, propoxylated refers to chain extended compounds through the use of propylene oxide, and alkoxylated refers to chain extended compounds using either or both ethylene oxide and propylene oxide. Equivalent methacrylate compounds are also capable of being used, although those skilled in the art will appreciate that methacrylate compounds have lower reactivity than their equivalent acrylate counterparts: 1,3-butylene glycol diacrylate; 1,4-butanediol diacrylate; neopentyl glycol diacrylate; ethoxylated neopentyl glycol diacrylate; propoxylated neopentyl glycol diacrylate; 2-methy 1-1,3-propanediyl ethoxy acrylate; 2-methyl-l,3-propanediol diacrylate; ethoxylated 2-methyl-l,3-propanediol diacrylate; 3 methyl 1,5- pentanediol diacrylate; 2-butyl-2-ethyl-1,3-propanediol diacrylate; 1,6-hexanediol diacrylate; alkoxylated hexanediol diacrylate; ethoxylated hexanediol diacrylate; propoxylated hexanediol diacrylate; 1,9-nonanediol diacrylate; 1,10 decanediol diacrylate; ethoxylated hexanediol diacrylate; alkoxylated hexanediol diacrylate; diethyleneglycol diacrylate; triethylene glycol diacrylate; tetraethylene glycol diacrylate; polyethylene glycol diacrylate; propoxylated ethylene glycol diacrylate; dipropylene glycol diacrylate; tripropyleneglycol diacrylate; polypropylene glycol diacrylate; poly (tetramethylene glycol) diacrylate; cyclohexane dimethanol diacrylate; ethoxylated cyclohexane dimethanol diacrylate; alkoxylated cyclohexane dimethanol diacrylate; polybutadiene diacrylate; hydroxypivalyl hydroxypivalate diacrylate; tricyclodecanedimethanol diacrylate; l,4-butanediylbis[oxy(2-hydroxy-3,1-propanediyl)]diacrylate 2-(2-Vinyloxyethoxy)ethyl acrylate; dioxane glycol diacrylate. Monomers having, on average, greater than 2 ethylenically unsaturated groups per molecule are the preferred monomer choice and can be selected from any of the following non-limiting list; ethoxylated glycerol triacrylate; glycerol propoxylate triacrylate; pentaerythritol triacrylate; trimethylolpropane triacrylate; caprolactone modified trimethylol propane triacrylate; ethoxylated trimethylolpropane triacrylate; propoxylated trimethylol propane triacrylate; tris (2-hydroxy ethyl) isocyanurate triacrylate; e-caprolactone modified tris (2-hydroxy ethyl) isocyanurate triacrylate; melamine acrylate oligomer; pentaerythritol tetraacrylate; ethoxylated pentaerythritol tetraacrylate; ditrimethylolpropane tetra acrylate; dipentaerythritol pentaaacrylate; dipentaerythritol hexaacrylate; ethoxylated dipentaerythritol hexaacrylate. Ethoxylated trimethylolpropane triacrylate, glycerol propoxylate triacrylate and ethoxylated pentaerythritol tri- and tetraacrylate are especially preferred. Examples of monomers comprising free-radically polymerizable groups other than acrylate include N-vinyl amides. Examples of N- vinyl amides include but are not limited to N-vinylcaprolactam (NVC), N-vinyl pyrollidone (NVP), diacetone acrylamide, N-vinyl carbazole, N-acryloxyoxy ethylcyclohexanedicarboximide, N-vinyl imidazole, N-vinyl-N-methylacetamide (VIMA) or acryloyl morpholine (ACMO). Vinyl ethers such as 2-(2-vinyloxyethoxy)ethyl(meth)acrylate (VEEA, VEEM), diethylene glycol divinyl ether(DVE2), triethylene glycol divinyl ether (DVE3), ethyl vinyl ether, n-butyl vinyl ether,iso-butyl vinyl ether, tert-butyl vinyl ether, cyclohexyl vinyl ether (CHVE), 2-ethylhexyl vinyl ether (EHVE),dodecyl vinyl ether (DDVE), octadecyl vinyl ether(ODVE), 1-2-butanediol divinyl ether (BDDVE), 1-4,cyclohexanedimethanol divinylether (CHDM-di), hydroxybutyl vinylether (HBVE), 1-4-cyclohexanedimethanolmono vinylether (CHDM-mono), 1,2,4-trivinylcyclohexane (TVCH), vinylphosphonic acid dimethylester (VPA) or vinylphosphonic acid dimethyl ester (VP AD ME). As well as, or in place of, free radically-polymerizable monomers any concentration and type of free-radically polymerizable oligomer, including but not restricted to polyurethane acrylates, polyester acrylates, polyether acrylates and epoxy acrylates may be used. Where the compositions of the invention require colourants, suitable colorants include, but are not limited to organic or inorganic pigments and dyes. 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, 150, 155, 174, 180, 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, 71; Pigment Blue Numbers 15, 15:3, 15:4; Pigment Violet Numbers 3, 19, 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. The UV-curable compositions of the invention may also contain other components which enable them to perform in their intended application. These other ink components include, but are not restricted to; stabilizers, wetting aids, slip agents, inert resins, antifoams, fillers, rheological aids, amine synergists, etc. A stabilizer may also be used in the composition to ensure good pot life of the ink, examples of which are nitroxy based stabilizers such as OHTEMPO, TEMPO, and Irgastab UV10. Phenolic stabilizers such as hydroquinone (HQ), methyletherhydroquinone (MEHQ), butylhydroxytoluene (BHT) and 2,6-di-tert-butyl-N,N-dimethylamino-p-cresol. Nitrosophenylhydroxylamine (NPHA) base inhibitors NPHA, amine salts, and metal salts (Al salt, N-PAL) plus the aromatic amine inhibitors diphenylamine(DPA) and phenylenediamine (PPD). Other suitable stabilizers are florstab UV-1, UV-8, Genorad 16 and 18. Quinone methide such as found in BASF Irgastab UV-22. Included in the ink formulation can be a suitable de-aerator, these prevent the formation of air inclusions and pinholes in the cured coating. The following, non-limiting, products are available from EVONIK: TEGO AIREX 900, 910, 916, 920, 921, 931, 936, 940, 944, 945, 950, 962, 980, 986. Defoamers can also be included in the formulation, these prevent the formation of foam during manufacture of the ink and also while jetting. These are particularly important with recirculating printheads. Suitable, non-limiting, defoamers include TEGO FOAMEX N, FOAMEX 1488, 1495, 3062, 7447, 800, 8030, 805, 8050, 810, 815N, 822, 825, 830,831, 835, 840,842, 843, 845, 855, 860, 883, TEGO FOAMEX K3, TEGO FOAMEX K7 / K8 and TEGO TWIN 4000 available from EVONIK. Available from BYK is BYK-066N, 088, 055, 057, 1790, 020, BYK-A 530, 067A, and BYK 354. Surface Control Additives are often used to control the surface tension of the ink which is required to adjust the wetting on the face plate of the printhead and also to give the desired drop spread on the substrate or and in the case of multi pass inkjet printing wet on dry drop spread. They can also be used to control the level of slip and scratch resistance of the coating. Suitable surface control additives include but are not limited to TEGO FLOW300, 370,425, TEGO GLIDE 100, 110,130,406, 410,411, 415, 420, 432, 435, 440, 482, A115, B1484, TEGO GLIDE ZG400, TEGO RAD2010, 2011, 2100, 2200N, 2250, 2300, 2500, 2600, 2650, 2700, TEGO TWIN 4000, 4100, TEGO WET 240, 250, 260,265,270, 280, 500, 505, 510 and TEGO WET KL245 all available from EVONIK. Available from BYK are BYK 333,337, BYK UV3500, BYK 378, 347,361, BYK UV3530, 3570, CERAFLOUR 998, 996, NANOBYK 3601, 3610, 3650 and CERMAT 258. From Allnex EBECRYL 350, 1360, MODAFLOW 9200, EBECRYL 341. From SARTOMER the aliphatic silicone acrylate CN9800 may be used. The invention is further described by the examples given below. Citation or identification of any document in this application is not an admission that such represents prior art to the present invention. The present invention has been described in detail, including various embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and / or improvements on this invention that fall within the scope and spirit of the invention. EXAMPLES The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention. Ink preparation The inks were prepared by mixing the pigment dispersion with the ink components using a Silverson type disperser for 10 minutes. Viscosity Viscosity of the inks was measured using a Brookfield DV-II+ Pro Viscometer equipped with Spindle no. 18, at 40°C. Ink application and curing The inks were applied to 23 pm Melinex S (a polyester film) at a film weight of 10pm using a 10pm drawdown bar and then cured using a pinning dose of 50 mJ / cm2, followed by a further dose of 300 mJ / cm2, using a GEW UV-LED Lab Unit, equipped with a 395nm UV-LED lamp, with a stated maximum power emittance of 30W / cm2. To achieve the required doses of 50 and 300 mJ / cm2, a conveyor speed of 60 m / min was used with lamp power settings of 10% and 70%. An International Light Technologies ILT 800 Profiling Belt Radiometer was used to determine the UV dose. Migration testing The level of contamination from a print surface was determined by a ‘set-off migration test. This test involved blocking the printed surface to a 50 micron sheet of LDPE (low density poly (ethene)), under a lOKg weight for 10 days at room temperature. The poly(ethene) film was then extracted into 10% (w / w) aqueous solution of ethanol containing 0.025% (w / w) of MEHQ (stabilizer) for 24 hours before the solution was analyzed by GC-MS. The results are reported as ppb, the amount of migratable material that would be present in IKg of food according to the EU packaging model, where it is assumed that 600cm2 of substrate is required to package IKg of food. Molecular weight of non-polymeric or oligomeric compounds The molecular weight of non-polymeric or oligomeric compounds is defined and calculated by the molecular structure of the compound. Usually, this is given by the supplier technical data sheet of the compound or can be found on the webpage of the European Chemical Agency (ECHA). Molecular weight of polymeric and oligomeric compounds - GPC This was determined by size exclusion chromatography, specifically gel permeation chromatography (GPC), with a monodisperse polystyrene equivalent molecular weight calibration standard and GPC columns (manufactured by PSS (Polymer Standards Service-USA, Inc), applied column combination: SDV 5pm 1000A, SDV 5pm 500A, SDV 5pm lOOA). The flow rate in the columns is 1.0 ml / min, eluent: tetrahydrofuran, column temperature: 40°C, a differential refractive index detector (RI) and a UV-detector (254nm) were used. The dispersibility DISP = (Mw / Mn) is the quotient of molecular weight average and number average and was calculated from the measurement results. Unless otherwise stated, the molecular weight of polymeric and oligomeric compounds is the number average molecular weight. As used herein, room temperature is 25 °C. % (w / w) (or wt%) refers to the weight percentage of a component in a composition, relative to all components in the composition, including any solvents. Average acrylate functionality The average acrylate functionality is calculated by taking the amount of each acrylate monomer in 100g of sample, calculating the number of moles of each arylate monomer in 100g, and multiplying the number of moles of each monomer by the respective acrylate functionality, to provide the number of moles of acrylate groups. The average acrylate functionality is then calculated by adding together the number of moles of arylate groups and dividing by the total number of moles of acrylate monomers. An exemplary calculation is provided below. A composition comprises 50wt% of trimethylolpropane triacrylate (TMPTA) and 10 wt% of dipropyleneglycol diacrylate (DPGDA). 50 g TMPTA (296.32 gmol'1) = 0.169 mol * 3 acrylate groups = 0.506 mol acrylate groups 10 g DPGDA (242.3 gmol'1) = 0.041 mol * 2 acrylate groups = 0.083 mol acrylate groups Total number of moles of acrylate groups = 0.506 + 0.107 mol = 0.589 mol Total number of moles of acrylate monomers = 0.169 + 0.041 mol = 0.21 mol Average acrylate functionality of acrylate monomers in composition = 0.589 / 0.21 = 2.80 Calculations can be performed for the average arylate functionality of all multifunctional acrylate monomers present and / or for the average arylate functionality of all acrylate monomers present in the composition. A calculation of the average vinyl functionality can also be made using the same procedure but including monomers comprising vinyl groups in the calculation. Vinyl groups include (meth)acrylate groups. It would be understood by the skilled person that the one or more acrylate monomers referred to in claim 1 refers to one or more different types of monomers. Thus, where only a single type of monomer is used in the calculation (e.g., where only a single type of acrylate monomer is present in the composition), an average is taken of all molecules of the same type that are present in the composition. As all monomers are the same, the average in this instance is the same as the acrylate functionality of a single molecule of said monomer. Raw Materials Polymeric thioxanthone photoinitiator Polymeric thioxanthone photoinitiator BAPO - Phenylbis(2,4,6-trimethylbenzoyl) phosphineoxide Polymeric aminoketone type photoinitiator Difunctional hydroxyketone photoinitiator Aminoacrylate = adduct of 1,6-hexanediol diacrylate (HDDA) with ethanolamine. Acrylate functionality = 2. Molecular weight = 800 gmol'1. VEEA - 2-(2-Vinyloxyethoxy)ethyl acrylate (difunctional monomer with a specific migration limit of lOppb). Molecular weight = 186.2 gmol'1. MePDDA - 3-Methylpentanediol diacrylate (difunctional monomer with a specific migration limit of 50ppb). Molecular weight = 226.3 gmol'1 DPGDA - Dipropyleneglycol diacrylate (difunctional monomer with a specific migration limit of lOppb). Molecular weight = 242.3 gmol'1 TMPEOTA - Ethoxylated trimethylolpropane triacrylate (trifunctional monomer with a specific migration limit of 50ppb). Molecular weight = 428 gmol'1 PPTTA - Ethoxylated pentaerythritol tetraacrylate (tetrafunctional monomer with a specific migration limit of lOppb). Molecular weight = 550 gmol'1 GPTA - Propoxylated glycerol triacrylate (trifunctional monomer with a specific migration limit of 50ppb). Molecular weight = 428 gmol'1 Cyan Dispersion 1 (DPGDA) - a dispersion containing 25.0% (w / w) of Pigment Blue 15:4, the remainder comprising the dispersant, stabilizers and DPGDA. Cyan Dispersion 2 (TMPEOTA) - a dispersion containing 25.0% (w / w) of Pigment Blue 15:4, the remainder comprising the dispersant, stabilizers and TMPEOTA. Poly ether Siloxane Copolymer Wetting Aid UV stabilizer Antioxidant stabilizer Note: all PPB thresholds are in accordance with Annex 10. Comparative Example 1 An ink prepared according to GB2606623B was cured and tested as outlined above. The formulation for this ink is: 53.5wt% TMPEOTA; 18.0wt% 3-MePDDA; 0.5wt% UV stabilizer; 10.0wt% polymeric aminoketone type photo initiator; 10.0wt% polymeric thioxanthone photoinitiator; and 8.0wt% Cyan dispersion 1. The viscosity of this ink was measured at 49.7 mPa.s. The amounts of migratable monomer were 14.1ppb TMPEOTA, 520ppb 3-MePDDA and 210ppb DPGDA. Although the amount of TMPEOTA is within a tolerable limit for the printing of food packaging, the amounts of the uncured migratable difunctional monomer are excessive. As stated in the description, the migration limit for TMPEOTA is 50ppb. Inventive Example 1 The composition for Inventive Example 1 is provided in Table 1, along with the viscosity and set-off migration results. Table 1: Inventive Example 1 Ink Formulation Component Wt. % TMPEOTA 50.0 Aminoacrylate 28.3 Polymeric Thioxanthone Photoinitiator 5.0 BAPO 1.5 Difunctional Hydroxyketone Photoinitiator 3.0 Cyan Dispersion 2 9.0 UV Stabilizer 1.0 Antioxidant 0.2 Poly ether Siloxane Copolymer Wetting Aid 2.0 Total 100.0 Viscosity (mPa.s) 93.4 Migratable TMPEOTA (ppb) 15.5 Average acrylate functionality of composition 2.77 Thus, for an ink comprising the multifunctional monomer TMPEOTA as the only monomer, and cured under the action of light emitted by a UV-LED lamp, the amount of uncured monomer that migrates is within acceptable limits. 5 Inventive Example 1A: same as Inventive Example 1, but with 1.0% difunctional hydroxyketone photoinitiator. This ink had a viscosity of 78.6 mPa.s and the cured ink produced a level of migratable TMPEOTA of 25.0ppb, again within acceptable limits for the printing of food packaging. 10 To show the impact of the aminoacrylate, Comparative Example 2 was prepared exactly as in Table 1 but leaving out the aminoacrylate, with the balance made up with TMPEOTA. The amount of migratable TMPEOTA was in excess of lOOOOppb. Thus, the benefit of using an aminoacrylate in the invention is clearly demonstrated. 15 Table 2 shows the migratable monomer results for inks prepared according to the composition provided in Table 1, where part of the TMPEOTA component was replaced with 2.5, 5, and 10% (w / w) of different difunctional monomers. Table 2: Migration Data Example Difunctional Monomer Viscosity Migratable TMPEOTA (ppb) Migratable VEEA (ppb) Migratable DPGDA (ppb) Migratable 3-MePDDA (ppb) Average acrylate monomer functionality Average vinyl monomer functionality 4 5% VEEA 66.0 11.5 < 1.0 2.47 2.63 5 10% VEEA 54.5 14.5 < 1.0 2.22 2.51 6 2.5% DPGDA 84.0 18.5 1.5 2.71 2.71 7 5% DPGDA 76.2 16.1 4.0 2.65 2.65 8 10% DPGDA 67.4 13.7 5.5 2.55 2.55 9 5% 3-MePDDA 35.5 16.1 1.6 2.65 2.65 10 10% 3-MePDDA 32.5 18.9 2.9 2.54 2.54 20 The results in Table 2 show that up to 10% (w / w) of difunctional monomers can be included in the inventive formulations without exceeding a migration of lOppb from an ink film cured according to the protocol set out previously. Although 3-MePDDA has migration limit of 50ppb according to European regulations, 25 many other difunctional monomers, like DPGDA and VEEA have the lower migration limit of lOppb. Therefore, restricting the amount of any difunctional monomer to less than 10% (w / w) can be seen to be beneficial and hence is an aspect of the current invention. To show that other multifunctional monomers can be used in compositions prepared 5 according to the invention, part of the TMPEOTA component of the composition of Table 1 was replaced with varying concentrations of PPTTA and GPTA. The results for the migration test are shown in Table 3. Table 3: Migration Data Example Multifunctional Monomer Viscosity Migratable TMPEOTA (ppb) Migratable GPTA (ppb) Migratable PPTTA(ppb) 15 5% GPTA 87.3 18.0 5.2 - 16 10% GPTA 86.9 21.0 4.5 - 17 20% GPTA 86.5 18.0 8.1 - 18 25% GPTA 90.4 6.8 8.5 - 19 5% PPTTA 88.0 23.0 - 2.5 20 10% PPTTA 92.5 23.5 - 2.1 21 20% PPTTA 98.6 20.0 - 2.0 10 The results in Table 3 show that inks comprised only of multifunctional monomers produce UV-cured prints having very low levels of migratable monomer. This supports the benefit that inks to be used in the printing of food packaging and cured under the action of light generated by a UV-LED lamp preferably comprise almost entirely of multifunctional monomers.

Claims

1. A UV-curable inkjet ink composition or inkjet coating composition comprising:i) 30 to 75% (w / w) of one or more multifunctional (meth)acrylate monomers, wherein the monomers have an average acrylate functionality of greater than 2.0;ii) one or more difunctional, trifunctional, or polymeric photoinitiators; andiii) an aminoacrylate;wherein the composition comprises 10% (w / w) or less of difunctional and / or monofunctional monomers with a molecular weight of less than 400 amu.

2. The composition of claim 1, wherein the average (meth)acrylate functionality of all (meth)acrylate monomers in the composition is greater than 2.0; optionally wherein the average vinyl functionality of all monomers is greater than 2.0.

3. The composition of claims 1 or 2, wherein the composition is curable with UV-LED light.

4. The composition of any one of claims 1 to 3, wherein the viscosity is 20 to 125 mPa.s at 40°C.

5. The composition of any one of claims 1 to 4, wherein the viscosity is 35 to 125 mPa.s at 40°C.

6. The composition of any one of claims 1 to 5, wherein the viscosity is 50 to 125 mPa.s. at 40°C.

7. The composition of any one of claims 1 to 6, wherein the viscosity is 50 to 100 mPa.s. at 40°C.

8. The composition of any preceding claim, wherein the one or more multifunctional (meth)acrylate monomers is / are selected from the group consisting of ethoxylatedtrimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol triacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexa-acrylate, ditrimethylolpropane triacylate, and ditrimethylolpropane tetra-acrylate, and combinations thereof; optionally wherein the multifunctional monomer is ethoxylated trimethylolpropane triacrylate.

9. The composition of claim 8, wherein the average degree of alkoxylation per acrylate group of the alkoxylated multifunctional monomers is greater than 1.0.

10. The composition of claims 8 or 9, comprising 10% (w / w) or less of one or more additional co-monomers, optionally 5% (w / w) or less, optionally 2% (w / w) or less of one or more co-monomers, optionally wherein the composition is substantially free of comonomers.

11. The composition of any preceding claim, wherein the aminoacrylate is obtainable from a reaction of an alkanolamine, such as ethanolamine, with an acrylate selected form the group consisting of ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, hexanediol diacrylate, and combinations thereof.

12. The composition of any preceding claim, wherein the difunctional monomer, when present, is selected from the group consisting of 2-(2-vinyloxyethoxy)ethyl acrylate, 3-methylpentanediol diacrylate, dipropyleneglycol diacrylate, and combinations thereof.

13. The composition of any preceding claim, further comprising an oligomer selected from the group consisting of polyurethane acrylate, epoxy acrylate, polyester acrylate, and combinations thereof.

14. The composition of any preceding claim, wherein the one or more difunctional, trifunctional, or polymeric photoinitiators comprises a polymeric thioxanthone photoinitiator.

15. The composition of claim 14, wherein the concentration of the polymeric thioxanthone photoinitiator is less than 10% (w / w) of the total ink composition.

16. The composition of any preceding claim, wherein the total amount of all photoinitiators is 10 % (w / w) or less.

17. The composition of any preceding claim, wherein the one or more difunctional, trifunctional, or polymeric photoinitiators comprises a difunctional or polymeric acylphosphine oxide photoinitiator.

18. The composition of claim 17, wherein the acylphosphine oxide photoinitiator is phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide.

19. The composition of claims 17 or 18, wherein the concentration of acylphosphine oxide photoinitiator is less than 5% (w / w); more preferably less than 3% (w / w) of the total ink composition.

20. The composition of any preceding claim, wherein the one or more difunctional, trifunctional or polymeric photoinitiators comprises an oligomeric or polymeric a-aminoketone photoinitiator, optionally wherein the concentration of acylphosphine oxide photoinitiator is 10 % (w / w) or less.

21. The composition of any preceding claim, comprising 5% (w / w) or less of difunctional monomers having a molecular weight of less than 400 Da, optionally 3% (w / w) or less; optionally 2% (w / w) or less of difunctional monomers having a molecular weight of less than 400 Da; optionally wherein the composition is substantially free of difunctional monomers having a molecular weight of less than 400 Da.

22. The composition of any preceding claim, comprising 5% (w / w) or less of any difunctional monomers; optionally 3% (w / w) or less; optionally 2% (w / w) or less ofdifunctional monomers, optionally wherein the composition is substantially free of difunctional monomers.

23. The composition of any preceding claim, comprising 5 % (w / w) or less of monofunctional monomers, optionally 3 % (w / w) or less, optionally 2 % (w / w) or less of monofunctional monomers, optionally wherein the composition is substantially free of monofunctional monomers.

24. The composition of any preceding claim, wherein the difunctional and / or monofunctional monomers are difunctional and / or monofunctional vinyl monomers.

25. The composition of claim 24, wherein the difunctional and / or monofunctional vinyl monomers are difunctional and / or monofunctional acrylate monomers.

26. The composition of any preceding claim, wherein the one or more multifunctional (meth)acrylate monomers are multifunctional acrylate monomers.

27. A process of preparing a printed article, comprising printing the composition of any one or more of claims 1-26 onto a substrate and curing with a UV light source.

28. The process of claim 27, where in the UV light source is UV-LED.

29. The process of claim 28, wherein the UV-LED light source emits light with a wavelength between 360 and 410nm.

30. The process of claims 28 or 29, wherein the UV-LED light source emits light with a wavelength of 395nm.

31. The process of any one of claims 27 to 30, wherein the overall cumulative dose of UV light is <500 mJ / cm232. The process of any one or more of claims 27 to 31, wherein the printing method is inkjet.

33. The process of claim 32, wherein the press speed is >50 m / min.

534. A printed article obtained from the process of any one or more of claims 27 to 33.

35. The printed article of claim 34, which is a food packaging article, a pharmaceutical packaging article, or a personal care packaging article.1036. The printed article of claims 34 or 35, wherein the amount of any residual migratable monomer is less than 50ppb.

37. The printed article of any one or more of claims 34 to 36, which complies with the 15 Swiss Ordinance for food contact materials.s