GB2574719A - A printing ink - Google Patents

Abstract

An inkjet ink comprises (i) a monomer selected from N-vinyl amide, N-acryloyl amine and/or N-vinyl carbamate, (ii) monofunctional (meth)acrylate, (iii) radical photoinitiator, (iv) dispersed pigment, (v) 0.1-10 wt.% 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine and/or 2-[4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and (vi) 0.1-5 wt.% bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate. The N-vinyl amide may be N-vinyl caprolactam (NVC) and the N-vinyl carbamate may be N-vinyl-5-methyl-2-oxazolidinone (NVMO). The monofunctional (meth)acrylate may be isobornyl acrylate (IBOA), phenoxyethyl acrylate (PEA), cyclic trimethylolpropane formal acrylate (CTFA) and/or trimethylcyclohexyl acrylate (TMCHA). The ink may comprise a radiation-curable oligomer and a passive resin and is preferably free of water and volatile organic solvents. The ink may be free of light stabilisers other than 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate. A method of inkjet printing the ink onto a substrate followed by curing is also disclosed. Typically, no top coat is applied over the printed ink or if one is applied, it does not comprise light stabilisers.

Description

This invention relates to a printing ink, in particular to an inkjet ink which provides a weather-resistant image.

In inkjet printing, minute droplets of black, white or coloured ink are ejected in a controlled manner from one or more reservoirs or printing heads through narrow nozzles on to a substrate which is moving relative to the reservoirs. The ejected ink forms an image on the substrate. The inks must flow rapidly from the printing heads and to ensure that this happens, they have low viscosities in use, typically below 100 mPas at 25°C, although in most applications the viscosity is below 50 mPas, and often below 25 mPas. The inks must also be resistant to drying or crusting in the reservoirs or nozzles.

There has been an increasing demand from customers and printer manufacturers to achieve higher quality prints that are durable and can withstand extreme conditions, for long periods of time.

UV absorbers (UVAs) are used in the coatings industry for extending the outdoor durability of decorated articles. However, the approach for inkjet inks has traditionally been to include UV absorbers in a clear coat which is applied over the top of the printed article. Although this has been proven to be effective, this two-layer application process can significantly lengthen the time taken to generate prints.

Including UVAs directly into a pigmented ink, without a secondary print layer, has not found commercial application. It has been generally understood that UVAs must be included at high levels to be effective at the low film weights typically applied by the inkjet process. But at such high levels, cure sensitivity is affected.

A number of attempts have been made to include UVAs into inkjet inks (see, for example, US 2014/0113082, US 2016/0083596 and WO 2017/031224), but these approaches have not provided the necessary balance between image durability on the one hand, and adequate cure speed and low viscosity on the other.

There remains therefore a need in the art for inkjet inks that achieve this balance of properties.

Accordingly, the present invention provides an inkjet ink comprising: an N-vinyl amide monomer, an N-acryloyl amine monomer and/or an N-vinyl carbamate monomer; a monofunctional (meth)acrylate monomer; a radical photoinitiator; a dispersed pigment; 0.1-10% by weight of 2-(2-hydroxy-4-[1octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine and/or 2-[4-[(2-hydroxy-3(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, based on the total weight of the ink; and 0.1-5% by weight of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, based on the total weight of the ink.

This ink combines image durability, adequate cure speed and low viscosity.

The inkjet ink of the present invention contains an N-vinyl amide monomer, N-acryloyl amine monomer and/or an N-vinyl carbamate monomer. Multiple monomers in each category or mixtures of monomers in different categories may be used.

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 as discussed below. Preferred examples are N-vinyl caprolactam (NVC) and N-vinyl pyrrolidone (NVP).

The most preferred monomer in this category is NVC. NVC is a well-known monomer in the art and has the following chemical structure:

N-vinyl caprolactam (NVC), mol wt 139 g/mol

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 N-acryloylmorpholine (ACMO).

N-Vinyl carbamate monomers are defined by the following functionality:

O

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).

In a preferred embodiment, the N-vinyl carbamate monomer is an N-vinyl oxazolidinone. N-Vinyl oxazolidinones have the following structure:

O

in which R¹ to R⁴ are not limited other than by the constraints imposed by the use in an inkjet 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 alkyl, C₃.₁₈ cycloalkyl, C_e.₁₀ aryl and combinations thereof, such as C_e.₁₀ aryl- or C₃.₁₈ cycloalkyl-substituted 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 Cmo alkyl. Further details may be found in WO 2015/022228 and US 4,831,153.

Most preferably, the N-vinyl carbamate monomer is N-vinyl-5-methyl-2-oxazolidinone (NVMO). 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 enantiomers. In one embodiment, the N-vinyl carbamate monomer is a racemate of NVMO. In another embodiment, the N-vinyl carbamate monomer is (R)-5methyl-3-vinyl-1,3-oxazolidin-2-one. Alternatively, the N-vinyl carbamate monomer is (S)-5-methyl-3vinyl-1,3-oxazolidin-2-one.

The inkjet ink preferably contains 10-50% by weight of the N-vinyl amide monomer, N-acryloyl amine monomer and/or an N-vinyl carbamate monomer, based on the total weight of the ink. The amount refers to the total amount of all monomers within these categories.

Monomers typically have a molecular weight of less than 600 Da, preferably more than 200 Da and less than 450 Da. 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 100 mPas 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 12° steel cone at 25°C with a shear rate of 25 s'¹.

The ink also contains monofunctional (meth)acrylate monomers.

The monofunctional (meth)acrylate monomers may be a cyclic monofunctional (meth)acrylate monomer and/or an acyclic-hydrocarbon monofunctional (meth)acrylate monomer.

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 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, C_e.₁₀ aryl and combinations thereof, any of which may substituted with alkyl (such as 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), tetra hydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolane-4-yl)methyl acrylate (MEDA/Medol-10), 4-te/Y-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA) and mixtures thereof.

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 alkyl, which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted.

The acyclic-hydrocarbon monofunctional (meth)acrylate monomer contains a linear or branched C_eC₂₀ 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.

Mixtures of cyclic-monofunctional (meth)acrylates and acyclic-hydrocarbon monofunctional (meth)acrylates are preferred. Preferred monofunctional (meth)acrylate monomers are IBOA, PEA, CTFA and TMCHA. A combination of all three is particularly preferred.

The monofunctional (meth)acrylate monomers are preferably present at 10-80%, more preferably 2060%, by weight, based on the total weight of the ink. The amount refers to the total amount of all monomers within this category (i.e. monofunctional (meth)acrylate monomers).

The inkjet ink may also contain difunctional and/or multifunctional (meth)acrylate monomers.

Difunctional (meth)acrylate monomers are well known in the art and a detailed description is therefore not required. Difunctional has its standard meaning, i.e. two groups, which take part in the polymerisation reaction on curing.

Examples include hexanediol diacrylate, 1,8-octanediol diacrylate, 1,9-nonanediol diacrylate, 1,10decanediol diacrylate (DDDA), 1,11-undecanediol diacrylate and 1,12-dodecanediol diacrylate, polyethyleneglycol diacrylate (for example tetraethyleneglycol diacrylate), dipropyleneglycol diacrylate (DPGDA), tricyclodecane dimethanol diacrylate (TCDDMDA), neopentylglycol diacrylate, 3-methyl1,5-pentanediol diacrylate (3MPDDA), 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, 1,11undecanediol dimethacrylate and 1,12-dodecanediol dimethacrylate, triethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate and mixtures thereof. Preferred difunctional (meth)acrylate monomers are NPGPODA and 3MPDDA, and the ink preferably contains NPGPODA and 3MPDDA.

Multifunctional (meth)acrylate monomers (tri- and higher-functional) are also well known in the art and a detailed description is therefore not required. Multifunctional has its standard meaning, i.e. tri or higher, that is three or more groups, respectively, which take part in the polymerisation reaction on curing. Usually, the multifunctional (meth)acrylate monomer has a degree of functionality of four or more, e.g. 4-8.

Examples of the multifunctional acrylate monomers include trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate, tri(propylene glycol) triacrylate, bis(pentaerythritol) hexaacrylate, and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, ethoxylated trimethylolpropane triacrylate, and mixtures thereof. Suitable multifunctional (meth)acrylate monomers also include esters of methacrylic acid (i.e. methacrylates), such as trimethylolpropane tri meth acrylate. Mixtures of (meth)acrylates may also be used. A preferred multifunctional (meth)acrylate monomer is TMPTA.

If present, the ink contains 5-20% by weight of di- and/or multifunctional (meth)acrylate monomers, based on the total weight of the ink. The amount refers to the total amount of all monomers within this category (i.e. di- and multifunctional (meth)acrylate 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.

In one embodiment the ink is substantially free of monomers other than the N-vinyl amide monomer, N-acryloyl amine monomer, N-vinyl carbamate monomer and monofunctional (meth)acrylate monomers, meaning that only small amounts of other monomers will be present, for example as impurities in the radiation-curable materials present or as a component in a commercially available pigment dispersion. Where additional monomers are included, they are preferably present in an amount of less than 5% by weight and most preferably less than 2% by weight, based on the total weight of the ink.

The inkjet ink may also contain a radiation-curable (i.e. polymerisable) oligomer, e.g. a (meth)acrylate oligomer.

The term “curable oligomer” has its standard meaning in the art, namely that the component is partially reacted to form a pre-polymer often having a plurality of repeating monomer units, which is capable of further polymerisation. The oligomer typically has a molecular weight of at least 450 Da and more typically at least 600 Da (whereas monomers typically have a molecular weight below these values). The molecular weight is typically 4,000 Da 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 oligomer will also increase the viscosity of the ink and will require monomers to counteract that viscosity-increasing effect.

The degree of functionality of the oligomer determines the degree of crosslinking and hence the properties of the cured ink. The oligomer is typically multifunctional meaning that it contains on average more than one reactive functional group per molecule. The average degree of functionality is typically from 2-6.

Oligomers are typically added to inkjet inks to increase the viscosity of the inkjet ink or to provide filmforming properties such as hardness or cure speed. They therefore typically have a viscosity of 150 mPas or above at 25°C, for example a viscosity of 0.5-10 Pas at 50°C. Oligomer viscosities can be measured using an ARG2 rheometer manufactured by T.A. Instruments, which uses a 40 mm oblique 12° steel cone at 60°C with a shear rate of 25 s ¹.

Radiation-curable oligomers comprise a backbone, for example a polyester, urethane, epoxy or polyether backbone, and one or more radiation-curable groups. The oligomer preferably comprises a polyester backbone. The polymerisable group can be any group that is capable of polymerising upon exposure to radiation, and is usually (meth)acrylate. The oligomer may include amine functionality, as the amine acts as an activator without the drawback of migration associated with low-molecular weight amines. Polyurethane (meth)acrylate oligomers are preferred, e.g. Genomer 5695, which is an amine modified urethane acrylate oligomer.

Typical radiation-curable oligomers are polyester acrylate oligomers as these have excellent adhesion and elongation properties, e.g. di-, tri-, tetra-, penta- or hexa-functional polyester acrylates.

The radiation-curable oligomer is preferably present at 0.5-20% by weight, more preferably 1-10% by weight, based on the total weight of the ink. The amount refers to the total amount of all material within this category.

The inkjet ink of the present invention may also contain a passive resin.

Passive (or “inert”) resins are resins which do not enter into the curing process, i.e. the resin is free of functional groups which polymerise under the curing conditions to which the ink is exposed. In other words, resin is not a radiation-curable material. The resin is usually selected from epoxy, polyester, vinyl, ketone, nitrocellulose, phenoxy or acrylate resins, or a mixture thereof and is preferably a poly(methyl (meth)acrylate) resin. The resin has a weight-average molecular weight of 70-200 kDa and preferably 100-150 kDa, as determined by GPC with polystyrene standards.

The passive resin is preferably present at 0.5-10% by weight, more preferably 0.5-5% by weight, based on the total weight of the ink. The amount refers to the total amount of all material within this category.

The inkjet ink of the present invention comprises a radical photoinitiator. The radical photoinitiator is a free radical photoinitiator. The radical photoinitiator can be selected from any of those known in the art. For example, benzophenone, 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-

1-one, isopropyl thioxanthone, benzil dimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4trimethylpentylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide or mixtures thereof.

Such photoinitiators are known and commercially available such as, for example, under the trade names Irgacure and Darocur (from Ciba) and Lucirin (from BASF). Preferred photoinitiators are selected from bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone and mixtures thereof.

Preferably, the photoinitiator is present in an amount of 1-20% by weight, preferably 5-15% by weight, based on the total weight ofthe ink.

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

The inkjet ink dries primarily by curing, i.e. by the polymerisation of the monomers and oligomers 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 ofthe ink. The absence of water and volatile organic solvents means that the ink does not need to be dried to remove the water/solvent. However, water and volatile organic solvents have a significant viscosity-lowering effect making formulation of the ink in the absence of such components significantly more challenging.

Accordingly, the inkjet ink is preferably substantially free of water and volatile organic solvents. Preferably, the inkjet ink comprises less than 5% by weight combined of water and volatile organic solvent combined, preferably less than 3% by weight combined, more preferably, less than 2% by weight combined and most preferably less than 1% by weight combined, based on the total weight of the ink. Some water will typically be absorbed by the ink from the air and solvents may be present as impurities in the components ofthe inks, but such low levels are tolerated.

The ink may also contain a dispersed pigment, of the types known in the art and commercially available such as under the trade-names Paliotol (available from BASF pic), 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 pigment is preferably present in an amount of 1-30% by weight, preferably 2-20% by weight, based on the total weight of the ink. The higher concentration of pigment is required for white inks.

The inks may be 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). The inks in a trichromatic set can be used to produce a wide range of colours and tones.

The ink contains a specific combination of a UV absorber (UVA) and a hindered amine (or amide) light stabiliser (HALS). These are known types of light stabilisers in the art.

In one embodiment, the UVA is 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4phenylphenyl)-1,3,5-triazine, which may also be named as 6-methylheptyl 2-[4-[4,6-bis(4phenylphenyl)-1 H-1,3,5-triazin-2-ylidene]-3-oxocyclohexa-1,5-dien-1 -yl]oxypropanoate (CAS no. 204848-45-3). It is commercially available under the name Tinuvin 479.

Alternatively, or in addition, the UVA is 2-[4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine.

This UVA has a hydrocarbon radical which may be C₁₂ (dodecyl) or C₁₃ (tridecyl). Either compound may be used. Typically, the two compounds are not separated and a mixture of the dodecyl- and tridecyl-containing compounds are used. By “dodecyl/tridecyl” meant that the compound contains a dodecyl radical, or a tridecyl radical, or a mixture of the two compounds. A mixture of 2-[4-[(2hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and 2[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine has been allocated CAS no. 153519-44-9, and is commercially available under the name Tinuvin 400.

The UVAs of the invention, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4phenylphenyl)-1,3,5-triazine and/or 2-[4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, are present at 0.1-10% by weight, based on the total weight of the ink. The amount is preferably 1.5-5% by weight, and most preferably 4% by weight, based on the total weight of the ink. The amount refers to the total amount of the three UVAs.

The amount of 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5triazine is preferably 1-5% by weight, and most preferably 3% by weight, based on the total weight of the ink.

The amount of 2-[4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4dimethylphenyl)-1,3,5-triazine is preferably 0.5-3% by weight, and most preferably 1% by weight, based on the total weight of the ink. Both components are included in the calculation of the amount present by weight.

The HALS is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (CAS no. 41556-26-7). It is commercially available under the name Tinuvin 292. It may also contain without detriment some of the mono-substituted material, namely methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate.

The bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate is present at 0.1-5% by weight, based on the total weight of the ink. The amount is preferably 0.5-2.5% by weight, and most preferably 1% by weight, based on the total weight of the ink. Where methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate is present, it is include in the calculation of the amount present by weight.

It has been found that this combination of components in this ratio gives an unexpected increase in light fastness without compromising on cure response or viscosity. In a preferred embodiment, the ink contains 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine,

2- [4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)1,3,5-triazine and bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate.

Preferably, the identified compounds are the only UVAs and HALS in the composition, i.e. the ink is free of light stabilisers (the UVAs and HALSs) other than 2-(2-hydroxy-4-[1octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-

3- tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, bis(1,2,2,6,6pentamethyl-4-piperidyl) sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate.

A benefit of the present invention is that an additional top coat does not have to be applied over the printed image. Or if a top coat is applied for reasons other than maintaining colour density, it does not need to contain light stabilisers (e.g. UVAs and HALSs). Accordingly, the present invention provides a method of printing the ink defined herein, wherein the method does not include the application of a top coat over the printed ink, or if a top coat is applied, the top coat does not contain any light stabilisers. Similarly, the present invention provides a substrate having the inkjet ink defined herein printed thereon, wherein the substrate does not have a top coat over the printed ink, or if a top coat is present, the top coat does not contain any light stabilisers.

The inkjet ink of the present invention exhibits a desirable low viscosity (200 mPas or less, preferably 100 mPas or less and more preferably 35 mPas or less at 25°C). In a preferred embodiment, the viscosity of the inkjet ink is 8-35 mPas at 25°C.

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.

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.

The surface tension ofthe inkjet ink may be controlled by the addition of one or more surface active materials such as commercially available surfactants. A particularly preferred surfactant is BYK-307 from BYK-Chemie GmbH. Adjustment ofthe surface tension ofthe inks allows control ofthe surface wetting ofthe 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 ofthe print. Too low a surface tension can lead to excessive ink bleed between different coloured inks. The surface tension is preferably in the range of 20-40 mNm'¹ and more preferably 21-32 rnNm’¹.

Other components of types known in the art may be present in the ink to improve the properties or performance. These components may be, for example, defoamers, dispersants, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, biocides and identifying tracers.

The present invention may also provide an inkjet ink set. 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. The inkjet ink ofthe present invention may be one or more the inks in the set.

The ink or inkjet ink sets may be prepared by known methods such as stirring with a high-speed water-cooled stirrer, or milling on a horizontal bead-mill.

The substrate is not limited. Examples of substrates include those composed of PVC, polyester, polyethylene terephthalate (PET), PETG, polyethylene, polypropylene, and cellulosic materials. Mixtures/blends are included.

In the method ofthe present invention, after inkjet printing the inkjet ink onto the substrate, the printed image is then exposed to a UV radiation source, preferably UV LED light, to cure the inkjet ink.

The present invention also provides a substrate having the inkjet ink ofthe present invention printed thereon.

Any suitable radiation source may be used. Suitable UV sources include mercury discharge lamps, fluorescent tubes, light emitting diodes (LEDs), flash lamps and combinations thereof. In a preferred embodiment, a UV LED light source is used to cure the ink.

Any of the sources of actinic radiation discussed herein may be used for the irradiation of the inkjet ink. A suitable dose would be greater than 200 mJ/cm , more preferably at least 300 mJ/cm and most preferably at least 500 mJ/cm . The upper limit is less relevant and will be limited only by the commercial factor that more powerful radiation sources increase cost. A typical upper limit would be 5 J/cm². Further details of the printing and curing process are provided in WO 2012/110815.

Upon exposure to a radiation source, 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 1-20 pm, preferably 110 pm, for example 2-5 pm. Film thicknesses can be measured using a confocal laser scanning microscope.

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

Examples

Example 1

Inks A-J 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

Component name	Amount (%)
InkA	Ink B	InkC	Ink D	Ink E	Ink F	Ink G	Ink H	Ink I	Ink J
PEA	17.39	12.89	10.39	19.89	15.39	19.89	12.89	19.89	17.39	13.39
IBOA	11.2	11.2	11.2	11.2	11.2	11.2	11.2	11.2	11.2	11.2
CTFA	10	10	10	10	10	10	10	10	10	10
NVC	20.4	20.4	20.4	20.4	20.4	20.4	20.4	20.4	20.4	20.4
UV-12	0.27	0.27	0.27	0.27	0.27	0.27	0.27	0.27	0.27	0.27
TMCHA	10	10	10	10	10	10	10	10	10	10
BR113	0.64	0.64	0.64	0.64	0.64	0.64	0.64	0.64	0.64	0.64
Genomer 5695	2	2	2	2	2	2	2	2	2	2
Pigment	12.5	12.5	12.5	12.5	12.5	12.5	12.5	12.5	12.5	12.5
Byk 307	1	1	1	1	1	1	1	1	1	1
TPO	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8
ITX	4	4	4	4	4	4	4	4	4	4
Irg 819	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8
Tinuvin 1130				2	5
Tinuvin 400	4	8	10					0.5	1	2
Tinuvin 479						1.5	8	1	3	6
Tinuvin 292	1	1.5	2	0.5	2	1	1.5	1	1	1
Total	100	100	100	100	100	100	100	100	100	100

Inks A-C and F-J are of the invention. The remaining inks are presented for comparison.

PEA, IBOA, TMCHA, CTFA and NVC are monomers identified hereinabove. UV-12 is a stabiliser. BR113 is an acrylic passive resin dispersed in PEA. Genomer 5695 is an amine modified urethane acrylate oligomer. The pigment is a yellow pigment in PEA and a dispersant. BYK307 is a surfactant. TPO is the photoinitiator, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. ITX is the photoinitiator, isopropylthioxanthone. Irg 819 is a bisacylphosphine oxide photoinitiator. Tinuvin 1130 is a benzotriazole UV absorber (CAS nos. 104810-48-2 and 104810-47-1). Tinuvin 400, Tinuvin 479 and Tinuvin 292 are identified hereinabove.

Example 2

Inks A-H were drawn down in a 12 pm film onto a onto an A5 self-adhesive vinyl substrate (Avery 400). The ink was then cured using a Baldwin 395 nm LED drier set at 20% power at 60 m/min speed (128.3 mJ/cm perpass) and the number of passes to achieve full cure was measured. After the first pass under the lamp, a small strip of Epson Premium Photo Paper is applied to the printed ink, with the coated side of the paper facing the printed ink, and rubbed down. Any ink removal or surface marking of the printed ink indicates an incomplete cure. The printed ink is repeatedly passed under the lamp and tested in this way until there is no ink removal or surface marking of the printed ink, indicating full cure.

For the preparation of samples for weathering, to ensure equivalent UV exposure was achieved, all inks were cured under the same conditions regardless of the determined cure speed, whilst maintaining an apparently fully cured film. Inks A-H were drawn down in a 12 pm film onto a onto an A5 self-adhesive vinyl substrate (Avery 700). The ink was then cured using a Baldwin LED drier at 100% power at 25 m/min speed, passed twice (683.9 mJ/cm per pass).

The viscosity of the ink was measured using a Brookfield DV1 viscometer running at 20 rpm at 25°C with spindle 00.

The colour density was measured on a Vipdens Densitometer. It was defined as 100% at time zero.

Further measurements were then taken after exposure to outdoor simulation equipment or ‘weatherometer’, a Q-Sun XE-3 test chamber. Weatherometers are designed to emulate and accelerate the natural weathering process of light, and dark and wet and dry and high temperature cycles. Specifically, the cycles that the XE-3 test chamber undergoes during testing for the given examples were: light cycle: 50% RH, 47°C air temperature, 70°C black panel, 0.55 W/m irradiance; light/spray cycle: 47°C air temperature, 70°C black panel, 0.55 W/m irradiance; light cycle: 50% RH, 47°C air temperature, 70°C black panel, 0.55 W/m² irradiance and dark cycle: 90% RH, 38°C air temperature. In the Q-Sun XE-3 test chamber 600 hours is equivalent to 1 year in real time (northern European climate).

Samples are removed from the test chamber at regular intervals and the colour density was measured. The colour density is assessed with respect to the value at t = 0. The density change is a measurement of how rapidly the colour faded, with the less fade the better. The results are set out in Table 3.

	30.96	CO	o ό o	98.2	97.4	93.0	98.2	9'96	92.1
—	25.23	CM	o ό o	CD CO CD	CD CD CD	ID CD CD	ID CD CD	ID CD CD	o CM CD
I	22.32	CM	o ό o	cd S	O S	CD ό CD	O S	CD ό CD	CM CO
0	33.36		o ό o	CD co CD	ID CD	ID CD	CO S	ID CD	O CO CD
LL	22.68	CO	o ό o	CM CO CD	O ό O	CD CD	ID CD CD	CM CD	CD CO CO
LU	ID CM	CO	o ό o	cd	s	O CO CD	ID CD CO	σ> CO	T~
Q	21.36	co	o ό o	CD CD	CD CD	CD CD	CO CO CD	CO CO	O ID
O	29.58	co	o ό o	CM CO CD	CO cd	CD CD	CO cd	co CD CO	CO CO
m	27.72	co	o ό o	CM CO CD	CD LO CD	ID CD CD	ID CD CD	CM T~ CD	CD CO
<	24.39	co	o ό o	CM CO CD	CD CD	CD CD	ID ID CD	ID CO	CO s
Ink property	Viscosity at 25°C (mPas)	No. passes to achieve full cure on Baldwin LED	o	CM	O CO	ID CD	CO O O	CD CD CO	O O CO
Colour density (% change with time at t = 0, 211,430, 651,1003, 1399, 1800 h)

Table 3

Inks A-C and F-J (ofthe invention) show little reduction in colour density overtime. These inks retain more than 80% colour density after 1800 h, equivalent to 3 years in real time (Northern European climate). The comparative inks D and E, which do not contain any ofthe UV absorbers as claimed, show an inferior colour density compared to inks A-C and F-J, and they do not achieve a superior 5 viscosity or cure speed.

Inks G, I and J achieve the best results for colour density. Inks G, I and J contain a combination of Tinuvin 479, Tinuvin 292, and inks I and J also contain Tinuvin 400. Inks G, I and J retain more than 95% colour density after 1400 h, and more than 90% colour density after 1800 h. Ink I provides the 10 optimum balance of colour fastness, viscosity and cure speed.

The comparative inks D and E have inferior density change scores compared to inks A-C and F-J of the invention, with the same number of passes as inks A-C, F and J to achieve cure.

Claims (15)

Claims

1. An inkjet ink comprising: an N-vinyl amide monomer, an N-acryloyl amine monomer and/or an Nvinyl carbamate monomer; a monofunctional (meth)acrylate monomer; a radical photoinitiator; a dispersed pigment; 0.1-10% by weight of 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4phenylphenyl)-1,3,5-triazine and/or 2-[4-[(2-hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, based on the total weight of the ink; and 0.1-5% by weight of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, based on the total weight of the ink.

2. An inkjet ink as claimed in claim 1, wherein the ink comprises an N-vinyl amide monomer and the N-vinyl amide monomer is N-vinyl caprolactam (NVC).

3. An inkjet ink as claimed in claim 1, wherein the ink comprises an N-vinyl carbamate monomer and the N-vinyl carbamate monomer is N-vinyl-5-methyl-2-oxazolidinone (NVMO).

4. An inkjet ink as claimed in any preceding claim, wherein the ink contains a radiation-curable oligomer.

5. An inkjet ink as claimed in any preceding claim, wherein the ink contains a passive resin.

6. An inkjet ink as claimed in any preceding claim, wherein the inkjet ink is substantially free of water and volatile organic solvents.

7. An inkjet ink as claimed in any preceding claim, wherein the ink contains 1-5% by weight of 2-(2hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, and/or 2-[4-[(2hydroxy-3-(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5triazine, based on the total weight of the ink.

8. An inkjet ink as claimed in any preceding claim, wherein the ink contains 0.5-2.5% by weight of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, based on the total weight of the ink.

9. An inkjet ink as claimed in any preceding claim, wherein the ink contains 2-(2-hydroxy-4-[1- octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3(dodecyl/tridecyl)oxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate.

10. An inkjet ink as claimed in any preceding claim, wherein the ink is free of light stabilisers other than 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2- [4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate.

5

11. An inkjet ink as claimed in any preceding claim, wherein the monofunctional (meth)acrylate monomers are selected from IBOA, PEA, CTFA and/or TMCHA.

12. A method of inkjet printing, comprising printing the inkjet ink as claimed in any preceding claim on to a substrate and curing the ink.

13. A method as claimed in claim 12, wherein the method does not include the application of a top coat over the printed ink, or if a top coat is applied, the top coat does not contain any light stabilisers.

14. A substrate having the inkjet ink as claimed in any of claims 1 to 11 printed thereon.

15. A substrate as claimed in claim 14, wherein the substrate does not have a top coat over the printed ink, or if a top coat is present, the top coat does not contain any light stabilisers.