GB2461624A - Ink-jet ink - Google Patents

Abstract

An ink-jet ink comprises a bis(cycloalkyloxirane) monomer, limonene dioxide, a monofunctional oxetane, a cationic photoinitiator and a colourant. The viscosity is 200 mPas or less and the ink comprises at least 50 wt.% of the bis(cycloalkyloxirane) together with the limonene dioxide. Typically, the bis(cycloalkyloxirane) is 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexyl carboxylate. The oxirane and limonene dioxide may be present in a weight ratio of 30:70 to 70:30 and may constitute at least 60 wt.% of the total weight of ink. The ink may be substantially free of water and volatile organic solvents. In a preferred embodiment, the ink further comprises a difunctional oxetane and a dispersible pigment. The ink is intended to have improved adhesion properties on substrates such as glass and metal. A method of ink-jet printing by printing the ink onto a substrate following by curing is also disclosed.

Description

A printing ink This invention relates to an ink-jet ink and in particular to a cationic ink having improved adhesion properties.

In ink-jet printing, minute droplets of black or coloured ink are ejected in a controlled maimer 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. For high-speed printing, the inks must flow rapidly from the printing heads, and to ensure that this happens they must have a low viscosity at the jetting stage. The ink viscosity is typically below 25 mPas at jetting temperature.

Therefore, ink-jet inks for application at or near ambient temperatures are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent. In one common type of ink-jet ink this liquid is water, see for example the paper by Henry R. Kang in the Journal of Imaging Science, 35(3), pp. 179-188 (1991). In these inks, great effort must be made to ensure the inks do not dry in the head due to water evaporation.

In another common type the liquid is a low-boiling solvent or mixture of solvents - see, for example, EP 0 314 403, EP 0 424 714 and WO 0 1/36546. Unfortunately, ink-jet inks that include a large proportion of water or solvent cannot be handled after printing until the inks have dried, either by evaporation of the solvent or its absorption into the substrate. This drying process is often slow and in many cases (for example, when printing on to a heat-sensitive substrate such as paper) cannot be accelerated.

Another type of ink-jet ink contains unsaturated organic monomers, oligomers or prepolymers that polymerise by irradiation, commonly with UV light, in the presence of a photoinitiator. This type of ink has the advantage that it is not necessary to evaporate the liquid phase to dry the print; instead the print is exposed to radiation to cure or harden it, a process that is more rapid than evaporation of solvent at moderate temperatures. Thus, while such inks can tolerate traces of water and organic solvent, such inks are typically substantially free of water and organic solvent.

There are two main technologies that can be used in a TJV curing process. The first method uses free-radical species to initiate the polymerisation of reactive monomers.

These monomers may be acrylate or methacrylate esters, as is disclosed in WO 97/31071, and/or other components such as vinyl ethers as disclosed in WO 02/061001.

Another method used in UV curing technology is the generation of very strong acids F to initiate the cationic polymerisation of reactive monomers. Acids are generated from the decomposition of photoinitiators under the presence of UV light. Such commercially available photoinitiators include sulfonium and iodonium salts. The decomposition of the onium salts release acidic species and also an aryl radical that can be used to incorporate materials capable of being polymerised by free-radical mechanisms. The monomers that can be used in cationic curing are, for example, epoxides, allyl ethers and vinyl ethers. Oxetanes and hydroxy-bearing compounds are also typically used in cationic systems to maximise the reactivity by reacting with epoxy systems through ring opening and/or chain transfer reactions.

Some ink systems may contain elements of both cationic and free-radical chemistry such that when polymerisation of the ink occurs upon irradiation with UV light, both free radical and acid initiating species are generated by the photoinitiators of each respective type and the monomers in the system are of suitable chemical type to be polymerised by either cationic or free radical propagation. Such inks arc termed "hybrid inks".

The benefits of cationic curing over radical curing include low shrinkage post curing, excellent chemical resistance and good adhesion. Cationic systems are not sensitive towards oxygen inhibition and once initiated by the acidic species generated by the cleavage of the photoinitiator under UV light, the reaction proceeds until no more available reactive groups are able to be converted. This means that cationic technology can cure thick, pigmented ink films more easily than free radical technology. The lower shrinkage and high flexibility of these systems make cationic curable inks very suitable for printing onto flexible substrates. The high percentage conversion of the reactive groups in the system also means that the resultant cured coating has a high chemical resistance.

Although cationic inks tend to display superior adhesion compared to radically curable inks, some substrates, such as glass and metals, still cause difficulties for conventional cationically curable inks. These difficulties are compounded by the severe viscosity limitations imposed on the formulator of the ink by the ink-jet printing process. Thus, there remains a need in the art for an ink-jet ink which cures by a cationic mechanism, has good adhesion to difficult substrates such as glass and metals, but also has a suitably low viscosity for ink-jet printing.

Accordingly, the present invention provides an ink-jet ink comprising a bis(cycloalkyloxirane) monomer, limonene dioxide, a monofunctional oxetane, a cationic photoinitiator and a colourant, wherein the viscosity is 200 mPas or less and wherein the ink comprises at least 50% by weight of the bis(cycloalkyloxirane) together with the limonene dioxide based on the total weight of the ink.

That is, it has been found that this specific combination of monomers provides the required adhesion in a cationic system without unduly compromising viscosity.

The ink-jet ink used in the present invention comprises a blend of cationically polymerisable monomers. These monomers include a bis(cycloalkyloxirane) monomer and limonene dioxide. The bis(cycloalkyloxirane) monomer contains two cycloalkyl groups, each eycloalkyl group having oxirane functionality. The two cycloalkyl groups are preferably linked by an aliphatic linker, e.g. an ester. The cycloalkyl group is preferably C38 cycloalkyl and particularly preferably cyclohexyl.

The molecular weight is preferably no more than 500 and particularly preferably no more than 300. In a preferred embodiment, the bis(cycloalkyloxirane) monomer is Y,4'-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate. 3 4I..

Epoxycyclohexyl-methyl 3,4-epoxycyclohexylcarboxylate is commercially available from Diacel Chemicals as Celloxide 2021 and has the following formula: The monomer limoncne dioxide is commercially available from Millenium Chemicals and has the following formula: The ink comprises at least 50%, and preferably at least 60%, by weight of the 3,43 epoxycyclohexylmethyl 3,4-epoxycyclohcxylcarboxylatc together with the limonene dioxide (i.e. the sum of the weights of these two epoxy-functional monomers) based on the total weight of the ink. At lower levels, the inks tend to be tacky due to incomplete curing and tend to have reduced adhesion to certain substrates. The weight ratio of the 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylatc to the limoncne dioxide is preferably from 30:70 to 70:30, more preferably from 40:60 to 60:40, and most prcferably substantially equal amounts of both.

The ink-jet ink of the present invention may further comprise additional cationically curable components. Preferably the ink further comprises at least one cationically polymerisable monomer, oligomer or prepolymer. That is, at least one component which contains one or more ftmctional groups which react together by a cationic mechanism following initiation by a cationic photoinitiator to form a polymer, thereby providing a cured ink. The monomers, oligomers andlor prepolymcrs may possess different degrees of functionality, and a mixture including combinations of mono, di, tn and higher functionality monomers, oligomers and/or prepolymers may be used.

Suitable monomers, oligomers andlor prepolymers include epoxides, allyl ethers, vinyl ethers, oxetanes and hydroxy-containing compounds.

The ink fitrther comprises at least one monofunctional oxetane monomer, and preferably comprises a monoftmnetional oxetane and a difunetional oxetane. The fimetionality is defined as the number of functional groups which take part in curing reaction. The monofunctional oxetane plays a centrally important role in the composition in that imparts the necessary flexibility to the cured ink, i.e. it prevents embrittlement. Examples of oxetanes which may be used in the ink formulation are OXT-221 and QXT-212. OXT-221 is 3-ethyl-3-hydroxymethyl-oxetane, bis{[l-cthyl(3-oxetanil)]methyl}ether, a difunctional oxetane having the following formula: OXT-212 is 3-ethyl-3-[(2-ethylhexyloxy)methyl] oxetane, a monofunctional oxetane having the following formula: They are both commercially available from Toagosei Co. Ltd. In a preferred embodiment the ink is substantially free of oligomers, prepolymers and polymers.

The ink also contains at least one cationic photoinitiator, such as an onium salt, e.g. sulfonium and iodonium salts. Examples of iodoriium salts are Rhodorsil P1 2074 from Rhodia, MC AA, MC BB, MC CC, MC CC PF, MC SD from Siber Hegner and UV9380c from Alfa Chemicals. Sulfonium salts include TJVI-6972, UVT-6974, uvi- 6976, UVI-6990, UVI-6992 from Dow, Uvacure 1590 from UCB Chemicals, and Esacure 1064 from Lamberti spa.

The ink preferably further comprises at least one colouring agent. The colouring agent 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 under the trade-names Paliotol (available from BASF pie), 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.

As discussed hereinabove, the ink is preferably substantially free of water and volatile organic solvents.

The ink may also be a hybrid ink which further comprises at least one radically polymerisable monomer, oligomer anchor prepolymer and at least one radical photoinitiator. The radically polymerisable monomers, oligomers andlor prepolymers may be an ester of acrylic or methacrylic acid, such as octyl acrylate, decyl acrylate, hydroxyethyl methacrylate lauryl acrylate, phenoxyethyl acrylate, hexanediol diacrylate, polyethylene glycol diacrylate, tri(propylenc glycol) triacrylate, trimethylolpropane triacrylate, bisQentaerytbritol) hexa-acrylate; or an N-vinylamide such as, N-vinylcaprolactam or N-vinylformamide; or acrylamide or a substituted acrylamide, such as acryloylmorpholine. Preferred monomers, oligomers or prepolymers are the acrylate esters of the ethoxylated or propoxylated derivatives of di-, tn-or tetrahydric aliphatic alcohols, and the acrylate or methacrylate esters of epoxy, urethane, melamine or polyester resins or their ethoxylated or propoxylated derivatives, or combinations thereof These components may be sold under the names: Ebecryl 40, Ebecryl 1039, DPGDA, TPGDA, ODA-n, TTEGDA, Ebecryl 160,OTA 480, IRR 289, TMPTA, IRR 184, Ebecryl 111, Ebecryl 110, IBOA, HDDA, Ebecryl 81, ACTILANE 872, ACTILANE 735, ACTILANE 584, ACTILANE 525, ACTILANE 440, ACTILANE 432, ACTILANE 430, ACTILANE 423, ACTILANE 421 and ACTILANE 251. It should be understood, however, that although the materials would be compatible, the inclusion of an acrylate may reduce the adhesion of the ink to the substrate.

Photoinitiators for free radical curing include: benzophenone and substituted benzophenones, 1-hydroxycyclohexyl phenyl ketone, thioxanthones such as isopropylthioxanthonc, 2-hydroxy-2 -methyl-I -phenyipropan-1-one, 2-benzyl-2- dimethylamino-(4-morpholinophenyl)butan-1-one. benzil dimethylketal, bis(2,6- dimcthylbcnzoyl)-2,4,4-trimethylpentylphosphinc oxide, 2,4,6- trimethylbenzoyldiphenylphosphine oxide, 2-methyl-i-[4-(methylthio)phenyi] -2- morpholinopropan-1-one, 2,2-dimethoxy-1,2-diphenylethan-1-one or 5, 7-diiodo-3 -butoxy-6-fluorone, or combinations thereof.

The monomer, oligomer and/or polymer is preferably present at 40-95 wt%, preferably 5-80 wt% based on the total weight of the ink. As explained herein, this may be based on a cationie or hybrid system. The photoinitiator is preferably present at 1-20 wt%, preferably 4-10 wt% based on the total weight of the ink. The total proportion of pigment present is preferably from 0.5 to 30% by weight, more preferably from 1 to 5% by weight based on the total weight of the ink.

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 inks exhibit a desirable low viscosity (200 mPas or less, preferably 100 mPas or less, more preferably 50 mPas or less and most preferably 25 mPas or less at 25°C). Viscosity may be measured using a l3rookfield viseometer fitted with a thermostatically controlled cup and spindle arrangement, such as model LDV1+ with the ULA spindle and cup arrangement at 25°C. The particles dispersed in the ink should be sufficiently small to allow the ink to pass through an ink-jet nozzle, typically having a particle size of less than 8 jim, preferably less than 5 jim and particularly preferably less than I jim.

The nature of the substrate is not limited and includes any substrate which may be subjected to ink-jet printing. ilowever, the inks of the present invention are particularly suited for printing onto glass and metal substrates.

The ink of the present invention is preferably cured using actinie radiation, usually UV radiation.

The following non-limiting examples exemplify the present invention.

Examples

The invention will now be described, by way of example, with reference to the following examples (parts given are by weight).

Example 1

Five inks were prepared having the formulations set out in Table 1.

Table 1. Ink-jet ink formulations.

Component Function Ratio of Celloxide 2021 to LDO 40169 45/55 50/50 55/45 60/40 Celloxide 2021 Bis(cycloalkylox 24.0 27.0 30.0 33.0 36.0 irane) monomer LDO Low viscosity 36.0 33.0 30.0 27.0 24.0 Diepoxide OXT-2 12 Monoftmnctional 22.9 22.9 22.9 22.9 22.9 oxetane OXT-221 Diftmnctional 5.0 5.0 5.0 5.0 5.0 oxetane Byk 307 Silicone 0.1 0.1 0.1 0.1 0.1 Esacure 1064 Photoinitiator 8.0 8.0 8.0 8.0 8.0 Cinquasia Pigment magenta 3.0 3.0 3.0 3.0 3.0 RT3SSD Solsperse 32000 Pigment 1.0 1.0 1.0 1.0 1.0 dispersant The viscosity was then determined using a Brookfield DV-I Rheometer at 25°C and the results are set out in Table 2.

Table 2. Viscosity of the inks set out in Table 1.

Ratio of Celloxide 2021 to LDO 40/60 45/55 50/50 55/45 60/40 Viscosity in mPas 21.4 22.7 24.4 27.3 29.7 The film properties were also assessed. In each case the films were prepared by drawing down the ink on to the test substrate using an automated K-bar coater. A no. 2 K-bar was used depositing a 12 micron film. The films were cured using a UV drier fined with 2 x 80 W/cm medium pressure mercury lamps and left for 96 hours before testing. The results are set out in Table 3.

Table 3. Film properties of the inks set out in Table 1.

Ratio of Solvent resistance Flexibility Cross hatch adhesion Celloxide Double rubs 3 layers on 2021 to Aluminium Q Aluminium MEK Petrol IPA Glass LDO panel Qpanel 40/60 5 100 100 5 5 5 45/55 50 100 100 5 5 5 50/50 70 100 100 5 5 5 55/45100 100 100 5 5. 5 60/40 100 100 100 5 5 5 Key: 5 = perfect result; 1= very poor result.

Although the inks of the present invention provided a beneficial balance between viscosity and solvent resistance, the best compromise between viscosity and solvent resistance was achieved with a 5 0/50 ratio.

Example 2

A number of inks were prepared to investigate the effect of reducing total epoxy content and increasing the monooxetane content was determined. The formulations are set out in Table 4.

Table 4 Ink-jet inks of the present invention.

Component 60 % total epoxy 55% total epoxy 50% total epoxy 1:1 1:1 ratio 1:1 ratio ratio Celloxide 2021 30.0 27.5 25.00 LDO 30.0 27.5 25.0 OXT-212 22.9 27.9 32.9 OXT-221 5.0 5.0 5.0 Cinquasia magenta 3.0 3.0 3.0 RT355D Solsperse 32000 1.0 1.0 1.0 Byk307 0.1 0.1 0.1 Esacure 1064 8.0 8.0 8.0 Cure speed was assessed by drawing down films on to aluminium Q panels using a no. 3 K-bar, depositing 12 microns. Films were cured using a UV drier fitted with 2 x W/cm medium pressure mercury lamps. The cure speed was assessed as the speed in metres per minute that a tack free film was produced straight from the drier. The 60% epoxy containing formula was able to be cured to a tack-free state.

Example 3

As an alternative approach the level of the monoftmnctional oxetane was fixed and the level of the diflinetional oxetane (OXT-212) was increased as the level of the epoxy blend was decreased. The ink compositions are shown in Table 5.

Table 5. Ink-jet inks of the present invention.

Component 60 % total epoxy 55% total epoxy 50% total epoxy Celloxide 2021 30.0 27.5 25.0 LDO 30.0 27.5 25.0 OXT-212 22.9 22.9 22.9 OXT-221 5.0 10.0 15.0 Cinquasia magenta 3.0 3.0 3.0 RT35SD Solsperse 32000 1.0 1.03 1.03 Byk307(A92010) 0.1 0.1 0.! Esacureloó4(C95300) 8.0 8.0 8.0 As can be seen from Table 6, as the total level of epoxy is decreased to below 60% adhesion to aluminium Q panel is lost.

Table 6. Adhesion properties of the inks from Table 5.

Solvent resistance Flexibility Cross hatch adhesion 1:1 epoxy Double rubs 3 layers on content Aluminium Q Aluminium MEK Petrol WA Glass panel Qpanel 60% 70 100 100 5.5 5 55% 100 100 100 5 1 5 50% 100 100 100 5 1 5

Example 4

An ink composition according to the present invention including a single oxetane is

shown in Table 7.

Table 7. Ink-jet ink of the present invention containing a monofunctional oxetane.

Component Function Amount (wt%) Celloxide 2021 Bis(cycloalkyl) oxirane 30.0 LDO Low viscosity diepoxide 30.0 OXT-212 Monofunctional oxetane 27.9 Byk 307 Silicone 0.1 Esacure 1064 Photoinitiator 8.0 Cinquasia magenta RT3S5D Pigment 3.0 Solsperse 32000 Pigment dispersant 1.0 Total 100.0

Claims (10)

1. Claims I. An ink-jet ink comprising a bis(cycloalkyloxirane) monomer, limonene dioxide, a monofunctional oxetane, a cationic photoinitiator and a colourant, wherein the viscosity is 200 mPas or less and wherein the ink comprises at least 50% by weight of the bis(cycloalkyloxirane) together with the limonene dioxide based on the total weight of the ink.
2. 2. An ink as claimed in claim 1, wherein the bis(cycloalkyloxirane) is 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate.
3. 3. An ink as claimed in claim I or 2, wherein the ink comprises at least 60% by weight of the bis(cycloalkyloxirane) together with the limonene dioxide, based on the total weight of the ink.
4. 4. An ink as claimed in any preceding claim, the weight ratio of the bis(cycloalkyloxirane) to the limonene dioxide is from 30:70 to 70:30.
5. 5. An ink as claimed in any preceding claim, wherein the ink fUrther comprises a difunctional oxetane.
6. 6. An ink as claimed in any preceding claim, wherein the ink is substantially free of water and volatile organic solvents.
7. 7. An ink as claimed in any preceding claim, wherein the at least one colouring agent is a dispersible pigment.
8. 8. A method of ink-jet printing, comprising printing the ink-jet ink as claimed in any preceding claim on to a substrate and curing the ink.
9. 9. A substrate having the ink-jet ink as claimed in any of claims 1 to 7 printed thereon.
10. 10. An ink-jet ink cartridge containing the ink-jet ink as claimed in any of claims I to 7.