WO2011148201A1

WO2011148201A1 - Printing ink

Info

Publication number: WO2011148201A1
Application number: PCT/GB2011/051019
Authority: WO
Inventors: Bridgette Blaskette; Brian Woolrich; Jeremy Ward; Vincent Wright
Original assignee: Sericol Limited
Priority date: 2010-05-27
Filing date: 2011-05-27
Publication date: 2011-12-01
Also published as: GB2494344B; GB201008911D0; GB201222461D0; GB2494344A

Abstract

The present invention provides an ink-jet ink comprising isophoryl acrylate, a photoinitiator, and a colouring agent, in which the total photoinitiator concentration is from 4 to 12% by weight based on the total weight of the ink, and/or the isophoryl acrylate is present in an amount of from 10.0 to 35.0% by weight based on the total weight of the ink, and/or the ink-jet ink additionally comprises a monofunctional (meth)acrylate monomer other than isophoryl acrylate that is present in an amount of 1 to 18 % by weight based on the total weight of the ink.

Description

PRINTING INK

The present invention concerns inks for use in ink-jet printers, and methods of ink-jet printing. In particular, this invention concerns inks for use in ink-jet printers that are cured using ultraviolet radiation.

Digital ink-jet printing is becoming an increasingly popular method for the production of fine graphic images for advertising, due to its low implementation cost and versatility in comparison with traditional techniques such as lithographic and screen printing. Ink-jet printers comprise one or more printheads that include a series of nozzles through which ink is ejected onto a substrate. The printheads are typically provided on a printer carriage that traverses the print width (moves back and forth across the substrate) during the printing process. Over recent years, ultraviolet (UV) curable ink systems have largely replaced so!vent-based ink systems in the higher productivity range, wide format graphics market. Unlike solvent- based inks, there is no appreciable evaporation of potentially harmful volatile substances from UV curable inks during drying of the ink. instead, the material is transformed into a solid through exposure to an energy source. In most cases, the energy source is an intense UV light, which causes photo-crosslinking of curable molecules in the presence of a photo initiator to form a solid. UV ink solidification times of less than one second compare favourably with solvent inks that can take several minutes to dry. UV curable ink-jet systems are therefore advantageous because they deliver high production rates. Furthermore, printed films formed from UV curable ink-jet inks typically have good solvent resistance and good adhesion to substrates.

Ink-jet printers for UV curable inks are more complex and consequently more expensive than ink-jet printers for solvent-based ink-jet inks, however. For example, UV curable ink-jet inks must generally be jetted at elevated temperatures, for example around 45 °C, which requires the presence of heaters in the printhead, adding to printer complexity and cost.

JP2009-197194 relates to curable ink-jet compositions comprising an N-viny! compound as a polymerisable compound, optionally isophoryl acrylate as an additional polymerisable compound, a polymerisation initiator, and a quinone methylide compound as a polymerisation inhibitor. However, it does not disclose jetting of a UV curable ink-jet ink without pre-heating.

There therefore exists a need for a UV curable ink-jet ink system that overcomes the above disadvantages. Accordingly, the present invention provides an ink-jet ink comprising isophoryl acrylate, a photoinitiator, and a colouring agent, in which the total photoinitiator concentration is from 4 to 12% by weight based on the total weight of the ink, and/or the isophoryl acrylate is present in an amount of from 10.0 to 35.0% by weight based on the total weight of the ink, and/or the ink-jet ink additionally comprises a monofunciional (meth)acrylate monomer other than isophoryl acrylate that is present in an amount of 1 to 18 % by weight based on the total weight of the ink.

The ink of the present invention can advantageously be jetted at tower temperatures than typical UV curable ink-jet inks, which means that the ink does not have to be heated at the printhead, leading to lower printer costs. The ink of the invention has good cure speed and printed films formed from the ink of the invention have good adhesion to substrates and high elongation. Isophoryl acrylate, also know as 3,3,5-trimethylcyciohexyI acrylate, is a commercially available monomer that has the following structure:

Isophoryl acrylate is preferably present in the ink of the invention in an amount of 10 to 90 % by weight based on the total weight of the ink, preferably 10 to 80 % by weight, more preferably 10 to 50 % by weight, and even more preferably 10.0 to 35.0% by weight.

The ink of the present invention is lower hazard compared to many other radiation curable UV inks due to the presence of isophoryl acrylate, which is a relatively low hazard monomer.

In an embodiment of the invention, the ink comprises one or more monofunctional monomers in addition to isophoryl acrylate. Free radical polymerisable monomers are preferred. Suitable monomers are well known in the art and include (meth)acry!ates, α,β-unsaturated ethers, vinyl amides, N-acryloyi amines and mixtures thereof. The substituents of the monofunctional monomers are not limited other than by the constraints imposed by the use in an ink-jet ink, such as viscosity, stability, toxicity etc. The substituents are typically alkyl, cycloalkyl, aryl and combinations thereof, any of which may be interrupted by heteroatoms. Non-limiting examples of substituents commonly used in the art include C-|.₁₈ alkyl, C₃.i₆ cyctoalky!, C₆-io aryl and combinations thereof, such as C₆-io aryl- or C₃.₁₈ cycloalkyl- substituted Ci-i₈ alkyl, any of which may be interrupted by 1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted by any of the above described substituents. The substituents may together aiso form a cyclic structure.

Monofunciional (meth)acryiate monomers are well known in the art. The esters of acrylic acid are preferred. Suitable examples include phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyl acrylate (!BOA), tetrahydrofurfuryl acrylate (THFA), 2-(2- ethoxyethoxy)ethyl acrylate, octadecyl acrylate (ODA), tridecyl acrylate (TDA), isodecy! acrylate (IDA) and lauryl acrylate. PEA is particularly preferred. The monofunciional (meth)acrylate monomer other than isophoryl acrylate is preferably present at a concentration of 1 to 18% by weight based on the total weight of the ink. Where more than one monofunciional (meth)acrylate monomer other than isophoryl acrylate is present, each is preferably present at a concentration of 1 to 18 % by weight. For example, PEA can be present at a concentration of 1 to 18% by weight, optionally in combination with an additional monofunciional (meth)acrylate monomer, such as isodecyl acrylate (IDA), which can also be present at a concentration of 1 to 18% by weight based on the total weight of the ink.

Examples of α,β-unsaturated ether monomers are well known and include vinyl ethers such as ethylene glycol monovinyl ether. N-vinyi amides and N-(meth)acryloyl amines may aiso be used in the inks of the invention. N- vinyl amides have a vinyl group attached to the nitrogen atom of an amide which may be further substituted as described above. Preferred examples are N-viny! caprolaciam (NVC) and N-vinyl pyrrolidone (NVP). NVC is particularly preferred. N-acryloyl amines also have a vinyl group attached to an amide but via the carbonyl carbon atom and again may be further substituted as described above. A preferred example is N-acryloylmorpholine (ACMO).

The one or more additional monofunciional monomers may be present in an amount of 5 to 70 % by weight based on the total weight of the ink, preferably 30 to 70 % by weight. In other words, the total amount of monofunctional monomer not including isophoryl acrylate is preferably 5 to 70 by weight based on the total weight of the ink, preferably 30 to 70 % by weight.

Preferably the isophoryl acrylate is present in an amount of at least 10 % by weight, based on the total weight of monofunctional monomer present in the ink, more preferably at least 15 % by weight.

In one embodiment, the ink of the present invention comprises a mixture of two or more monofunctional monomers in addition to isophoryl acrylate. Preferably the ink of the invention comprises an N-vinyl amide or N-(meth)acryloyl amine together with one or more monofunctional (meth)acrylate monomers other than isophoryl acrylate. Inks comprising NVC and one or more monofunctionai (meth)acrylate monomers other than isophoryl acrylate, particularly NVC and PEA, are preferred.

It is possible to modify the film properties of the ink-jet inks by inclusion of multifunctional monomers, oligomers or inert resins, such as thermoplastic acrylics. However, it should be noted that in the case of oligomers and multifunctional monomers the flexibility may be adversely affected and also that some adjustments to stoichiometry may be required to retain optimum cure speed. Where multifunctional monomer is included, the multifunctional monomer is present in an amount of no more than 15 wt%, preferably no more than 10 wt%, based on the total weight of the ink. The multifunctional monomer may be any multifunctional monomer which could be involved in the curing reaction, such as a multifunctional (meth)acrylate monomer or a multifunctional vinyl ether or a mixture thereof.

Suitable multifunctional (meth)acrylate monomers include di-, tri- and tetra- functional monomers. Examples of the multifunctional acrylate monomers which may be included in the ink-jet ink formulation include hexanediol diacrylate, trimethylo!propane triacrylate, pentaerythritol triacrylate, polyethyleneglycol diacrylate, for example, tetraethyleneglycol diacrylate), dipropy!eneglycol diacrylate, tri(propylene glycol) triacrylate, neopentylglycol diacrylate, bis(pentaerythritol) hexa-acrylate, and the acrylate esters of ethoxylated or propoxylated glycols and polyols, for example, propoxylated neopentyl glycol diacrylate, ethoxylated trimethylolpropane triacrylate, and mixtures thereof. Suitable multifunctional methacryiate monomers include esters of methacrylic acid (i.e. methacrytates), such as hexanediol dimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycol dimethacrylate, diethylenegiycol dimethacrylate, ethylenegiycol dimethacrylate, 1 ,4-butanediot dimethacrylate. Mixtures of multifunctional (meth)acrylates may also be used.

Examples of multifunctional vinyl ether monomers include triethySene glycol divinyl ether, diethyiene glycol divinyl ether and 1 ,4-cyclohexanedimethanol divinyl ether.

The ink of the invention optionally comprises oligomeric material and/or an inert resin. By "oligomeric material" is meant material having a molecular weight of 600 or more and comprising radiation curable functional groups, for example acrylate oligomers. By "inert resin" is meant material having a molecular weight of 600 or more that does not include radiation curable functional groups, for example inert thermoplastic resins. Oligomeric materials and inert resins are known in the art and typically have a molecular weight of 600 to 4000. Where oligomeric material and/or an inert resin is included in the ink of the invention, the total amount of oligomeric material and/or inert resin is preferably no more than 20 wt%, more preferably no more than 10 wt%, most preferably no more than 5 wt% based on the total weight of the ink. In an embodiment the ink is substantially free of oiigomeric material and inert resin meaning that only trace amounts will be present.

The ink-jet ink of the present invention dries primarily by curing, i.e. by the polymerisation of the monomers present, and hence is a curable ink. The ink does not, therefore, require the presence of water or a volatile organic solvent to effect drying of the ink, although the presence of such components may be tolerated. For example, minor amounts of solvent may be introduced into the ink when the colouring agent is added. This is because commercially available pigment dispersants often contain solvents. Preferably, however, the ink-jet ink of the present invention contains less than 5 % by weight of volatile organic solvent based on the weight of the ink.

The ink is preferably substantially free of water. For example, the ink contains less than 5 % by weight of water, preferably less than 2 % by weight, more preferably less than 1 % by weight.

(Meth)acrylate is intended herein to have its standard meaning, i.e. acrylate and/or methacrylate. Mono and multifunctional are also intended to have their standard meanings, i.e. one and two or more groups, respectively, which take part in the polymerisation reaction on curing.

In addition to the monomers described above, the compositions include a photoinitiator, which, under irradiation by, for example, ultraviolet light, initiates the polymerisation of the monomers. Preferred are photoinitiators which produce free radicals on irradiation (free radical photoinitiators) and include, for example, benzophenone, phenyl benzophenone, 1- butanone, 2-{dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, 2-hydroxy-2-methylpropiophenone, 1 - hydroxycyclohexyl phenyl ketone, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1- one, benzii dimethylketal, bis{2_l6-dimethylbenzoyl)-2,4,4-trimeihylpentylphosphine oxide, bis(2,4,6-trimethylbenzoyi)-phenylphosphine oxide or mixtures thereof. Such photoinitiators are known and commercially available such as, for example, under the trade names Irgacure, Darocur (from Ciba) and Lucerin (from BASF).

Preferably the photoinitiator is present from 1 to 20 % by weight based on the total weight of the ink, more preferably from 4 to 12 % by weight. Where more than one photoinitiator is present, the total photoinitiator concentration is preferably from 1 to 20% by weight based on the total weight of the ink, more preferably from 4 to 12% by weight.

The ink-jet ink of the present invention also includes a colouring agent, which may be either dissolved or dispersed In the liquid medium of the ink. Preferably the colouring agent is a dispersible pigment, of the types known in the art and commercially available such as, for example, 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.

The total amount of pigment present is preferably from 0.5 to 15 % by weight, more preferably from 1 to 5 % by weight.

In one embodiment, the ink of the present invention is a so-called "hybrid" ink which cures by a radical and cationic mechanism. According to this embodiment the ink-jet ink of the present invention additionally comprises at least one cationically curable monomer, such as a vinyl ether, and at least one cationic photoinitiator, such as an iodonium or sulfonium salt, e.g. diphenyliodonium fluoride and triphenylsulfonium hexafluophosphate. Suitable cationic photoinitiators include the Union Carbide UVI-69-series, Deuteron UV 1240 and IJY2257, Ciba Irgacure 250 and CGI 552, IGM-C440, Rhodia 2047 and UV9380C. 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, surfactants, defoamers, dispersants, synergists for the photoinitiator, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, biocides and identifying tracers. The ink-jet ink preferably exhibits a viscosity of less than 10 mPa.s at 25 °C. Viscosity may be measured using a Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as a DV1 low-viscosity viscometer running at 20 rpm at 25 °C with spindle 00. The present invention further provides an ink-jet ink cartridge containing the ink-jet ink as defined herein. The cartridge comprises an ink container and an ink delivery port which is suitable for connection with an ink-jet printer.

The present invention also provides an ink set comprising a cyan ink, a magenta ink, a yellow ink and a black ink (a so-called trichromatic set), wherein at least one of the inks is an ink according to the present invention. Preferably all of the inks in the ink set are inks according to the present invention. The inks in a trichromatic set can be used to produce a wide range of secondary colours and tones by overlaying the printed dots on white substrate. The present invention aiso provides a method of ink-jet printing using the above-described ink and a substrate having the cured ink thereon.

The ink of the present invention can be printed using any ink-jet printer that is suitable for use with a radiation curable ink-jet ink, for example the Fujifilm Acuity Advance. As discussed previously, the printer does not require means for heating the ink at the printhead, however, and the Fujifilm Acuity Advance, for example, could therefore be used with the printhead heater switched off. The ink of the invention is preferably jetted at temperatures of 40 °C or less, preferably 35 °C or less and more preferably 30 °C or less. In a most preferred embodiment, the ink is jetted at ambient temperature and no heat is provided to the printhead. The ink is cured by exposure to radiation, preferably ultraviolet radiation.

Suitable substrates include styrene, PolyCarb (a polycarbonate), BannerPVC (a PVC) and VIVAK (a polyethylene terephthalate glycol modified).

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

Examples

A cyan ink having the composition shown in Table 1 was prepared by mixing the components in the given amounts. Amounts are given as weight percentages based on the total weight of the ink. The ink has a viscosity of 7.4 mPa.s at 25 °C. The ink was drawn down onto a self adhesive vinyl substrate using a no. 2 Kbar, depositing a wet film of 12 microns. The ink was cured using an !ntergration Technology SubZero 085, using a H bulb, with two passes over the substrate at a rate of 40 metres/ minute. The ink has a relatively high cure speed, good adhesion to the substrate and high elongation.

Claims

1. An ink-jet ink comprising isophoryl acrylate, a photoinitiator, and a colouring agent, wherein the total photoinitiator concentration is from 4 to 12% by weight based on the total weight of the ink.

2. The ink of claim 1 wherein the isophoryl acrylate is present in an amount of 10 to 90 % by weight based on the total weight of the ink, preferably 10 to 80 % by weight, more preferably 10 to 50 % by weight, and most preferably 10.0 to 35.0% by weight.

3. An ink-jet ink comprising isophoryl acrylate, a photoinitiator, and a colouring agent, wherein the isophoryl acrylate is present in an amount of 10.0 to 35.0 % by weight based on the total weight of the ink.

4. The ink of claim 3 in which the total photoinitiator concentration is from 4 to 12% by weight based on the total weight of the ink.

5. The ink according to any previous claim, additionally comprising one or more monofunctional monomers other than isophoryl acrylate.

6. The ink according to claim 5, wherein the one or more monofunctional monomers other than isophoryl acrylate are selected from (meth)acrylates, α,β-unsaturated ethers, vinyl amides, N-acryloyi amines and mixtures thereof.

7. The ink according to claim 6 comprising a monofunctional (meth)acrylate monomer other than isophoryl acrylate, selected from phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate {CTFA}, isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA), 2-(2- ethoxyethoxy)eihyl acrylate, octadecyl acryiate (ODA), tridecyl acrylate (TDA), isodecy! acrylate (IDA), lauryl acrylate and mixtures thereof.

8. The ink according to claim 7, comprising phenoxyethyl acrylate.

9. The ink according to any one of claims 6 to 8, in which each monofunctional (meth)acrylate monomer other than isophopry! acrylate is present in an amount of 1 to 18% by weight based on the total weigh of the ink.

10. An ink-jet ink comprising isophoryl acrylate, a photoinitiator, and a colouring agent, wherein the ink comprises a monofunctionat (meth)acrylate monomer other than isophoryl acrylate that is present in an amount of 1 to 18 % by weight based on the total weight of the ink.

11. The ink according to claim 10 wherein the ink comprises one or more further monofunctional monomers other than isophoryl acrylate selected from monofunctional (meth)acrylate monomers, α,β-unsaturated ethers, vinyl amides, N-acryloyl amines and mixtures thereof.

12. The ink of any of claims 10 and 11 , wherein the isophoryl acrylate is present in an amount of 10 to 90 % by weight based on the total weight of the ink, preferably 10 to 80 % by weight, more preferably 10 to 50 % by weight, and most preferably 10.0 to 35.0% by weight.

13. The ink according to any of claims 10 to 12, wherein the total photo initiator concentration is from 4 to 12% by weight based on the total weight of the ink.

14. The ink according to any one of claims 10 to 13 in which the one or more monofunctional (meth)acrylate monomers other than isophoryl acrylate are selected from phenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyi acrylate (I BOA), tetrahydrofurfuryl acrylate (THFA), 2-(2-ethoxyethoxy)ethyl acrylate, octadecy! acrylate (ODA), tridecyl acrylate (TDA), isodecyl acrylate (IDA), lauryl acrylate and mixtures thereof.

15. The ink according to claim 14, comprising phenoxyethyl acrylate.

16. The ink according to any of claims 5 to 9 and 11 to 15, comprising an N-vinyl amide selected from N-vinyl caprolactam (NVC), N-vinyl pyrrotidone (NVP) or a mixture thereof.

17. The ink according to claims 16 comprising N-vinyl caprolactam and phenoxyethyl acrylate.

18. The ink according to any one of claims 5 to 17 wherein the one or more monofunctional monomers other than isophoryl acrylate are present in an amount of 5 to 70 % by weight based on the total weight of the ink, preferably 30 to 70 % by weight.

19. The ink according to any previous claim wherein isophoryl acrylate is present in an amount of at least 15 % by weight, based on the total weight of monofunctional monomer present in the ink.

20. The ink according to any previous claim additionally comprising a multifunctional monomer.

21. The ink according to claim 20 wherein the multifunctional monomer is present in an amount of no more that 15 % by weight based on the total weight of the ink.

22. The ink according to any previous claim wherein the ink comprises less than 5 % of water based on the weight of the ink, preferably less than 2 % by weight, more preferably less than 1 % by weight.

23. The ink according to any previous claim wherein the photoinitiator is a free radical photoinitiator.

24. The ink according to any previous claim wherein the viscosity is less than 10mPa.s at 25 °C.

25. An ink-jet ink cartridge containing the ink-jet ink as claimed in any one of claims 1 to 24.

26. An ink-jet ink set comprising a cyan ink, a magenta ink, a yellow ink and a black ink wherein at least one of the inks is as defined in any one of claims 1 to 24,

27. A method of ink-jet printing comprising printing the ink-jet ink as claimed in any one of claims 1 to 24 on to a substrate and curing the ink.

28. The method according to claim 27 wherein the ink is jetted at a temperature of 40 °C or less, preferably 35 °C or less and more preferably 30 °C or less.

29. A substrate having the ink-jet ink as claimed in any one of claims 1 to 24 printed thereon.