Printing ink

Abstract

The present invention provides an inkjet ink comprising: a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the cross-linking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the cross-linking agent, when deprotected, has a molecular weight of 600 to 2000. The present invention further provides a method of inkjet printing comprising the following steps in order: (i) providing an inkjet ink of the invention; (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate; (iii) drying the printed substrate to remove water; and (iv) deprotecting the two or more protected reactive groups. The present invention further provides a dispersion and a printed substrate having the inkjet ink of the invention printed thereon.

Description

[0001] Printing ink

[0002] The present invention relates to a printing ink and, in particular, an inkjet ink for printing onto textiles. The present invention also relates to a method of printing said ink.

[0003] Digital inkjet printing is commonly used in the textile industry as it offers many advantages over analogue printing such as a rapid and facile print process, print flexibility and much shorter preparation times. Digital inkjet printing is also more environmentally friendly than analogue printing as it offers substantial reductions in energy consumption and chemical, water and carbon dioxide waste.

[0004] There are two inkjet inks typically used in the textile industry, dye-based inkjet inks and pigmented inkjet inks.

[0005] Dye-based inkjet inks provide printed textiles with brilliant colours, good handle and wash- and rubfastness. However, the textile substrate dictates the particular dye used. Reactive dyes are used for cellulosic and protein fibres, acid dyes are limited to protein fibres and dispersed and sublimation dyes can only be applied to polyester substrates.

[0006] Printing processes involving dye-based inkjet inks also tend to be multi-step and complex. For example, reactive dyes necessitate pre-treating the textile followed by printing, steaming and then washing the textile. All of these steps are energy and water intensive. Sublimation dyes require printing onto a transfer medium and applying heat and pressure to transfer the print to the substrate.

[0007] Pigmented inkjet inks offer a significant advantage in terms of universal applicability to textile substrates. Printing using pigmented inkjet inks is also simpler, quicker and more environmentally friendly than using dye-based inkjet inks as the ink can just be printed on the textile and heat treated.

[0008] Pigmented inkjet inks typically contain a binder resin to enable the pigment to bind to the textile substrate. However, the binder resin tends to provide printed substrates with a poor handle that feel very stiff to the touch, and sub-optimal optical density, print wash, rub and perspiration fastness.

[0009] There is therefore a need in the art for a pigmented inkjet ink for printing onto textiles that provides a printed substrate with a good handle and optical density, without compromising the wash-fastness and adhesion.

[0010] Accordingly, the present invention provides an inkjet ink comprising: a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the cross-linking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the cross-linking agent, when deprotected, has a molecular weight of 600 to 2000.

[0011] The present invention also provides a method of inkjet printing comprising the following steps in order:

[0012] (i) providing an inkjet ink of the present invention;

[0013] (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate;

[0014] (iii) drying the printed substrate to remove water; and

[0015] (iv) deprotecting the two or more protected reactive groups.

[0016] The present invention will now be described with reference to the accompanying drawings, in which:

[0017] Fig. 1 shows the sound spectra for the cured ink films of inks 1-2 and 4-5 on treated cotton, as well as a test substrate, using TSA;

[0018] Fig. 2 shows an image of the cured film for ink 1 ;

[0019] Fig. 3 shows an image of the cured film for ink 2;

[0020] Fig. 4 shows an image of the cured film for ink 5;

[0021] Fig. 5 shows the sound spectra for the cured ink films of inks 1-4 on untreated cotton, as well as the test substrate, using TSA;

[0022] Fig. 6 shows the sound spectra for the cured ink films of inks 1-2 and 4 on treated jersey, as well as the test substrate, using TSA; and

[0023] Fig. 7 shows a photographs for the prints of inks 1 , 5, 6 and 7, before and after wash treatments.

[0024] The inventors have surprisingly found that the inclusion of a cross-linking agent of the present invention in an aqueous inkjet ink containing a dispersed encapsulated pigment of the present invention provides a pigmented inkjet ink for printing onto textiles, which provides a printed substrate with a good handle and optical density, without compromising the wash-fastness and adhesion.

[0025] The two or more protected reactive groups of the cross-linking agent, when deprotected, can react with the hydroxyl groups of the encapsulated pigment and any free hydroxyl groups on the substrate, thus binding pigment particles together and tethering the encapsulated pigment to the substrate. This improves the adhesion between the encapsulated pigment and the substrate leading to wash-fast and robust printed substrates. It is surprising that such a formulation can provide such good adhesion without requiring a binder resin and therefore the printed substrates also benefit from a good handle and optical density.

[0026] The inkjet ink of the present invention comprises a continuous aqueous phase and is hence an aqueous ink. Water and, when present, an organic solvent define the continuous aqueous phase. The continuous aqueous phase acts as a carrier for the components of the ink and ensures that the ink has the appropriate viscosity for printing. As with known aqueous inks, water is required to evaporate from the printed ink, typically on heating, in order to allow the ink to dry.

[0027] In a preferred embodiment, water is present in a total amount of 30 to 80% by weight, more preferably 40 to 70% by weight and most preferably 45 to 65% by weight, based on the total weight of the ink. The total amount of water includes water that is added as a separate component and any water that may be present in other components such as the encapsulated pigment and the cross-linking agent.

[0028] The continuous aqueous phase preferably comprises, in addition to water, an organic solvent. The organic solvent is in the form of a liquid at ambient temperature and is miscible with water. As with known solvent-based inkjet inks, the organic solvent is required to evaporate from the printed ink, typically on heating, in order to allow the ink to dry.

[0029] The organic solvent may be a single solvent or a mixture of two or more solvents. The solvent can be selected from any solvent commonly used in the printing industry, such as glycol ethers, glycol ether esters, alcohols, glycols, ketones and esters. In a preferred embodiment, the inkjet ink further comprises triethylene glycol and / or glycerol.

[0030] The organic solvent is preferably present in the inkjet ink in a total amount of 5 to 55% by weight, more preferably 20 to 50% by weight and most preferably 30 to 45% by weight, based on the total weight of the ink.

[0031] The inkjet ink of the present invention further comprises a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups.

[0032] The encapsulated pigment is dispersed in the continuous aqueous phase of the inkjet ink.

[0033] Encapsulating the pigment particles by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups ensures that the pigment is uniformly and stably dispersed in the continuous aqueous phase of the ink. The polymer is cross-linked to prevent desorption from the pigment particles. The dispersed encapsulated pigment comprises pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups.

[0034] In a preferred embodiment, the dispersed encapsulated pigment consists of pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups, i.e. only pigment particles are encapsulated by the cross-linked polymer and no additional components are encapsulated by the cross-linked polymer. In this way, the dispersed encapsulated pigment and the cross-linking agent having two or more protected reactive groups are separate components of the inkjet ink.

[0035] Dispersed encapsulated pigments for inclusion in the inkjet ink are known and include Pro-Jet® APD 1000, 3000 and 4000 pigment dispersions commercially available from FUJIFILM Imaging Colorants Limited. Additional dispersed encapsulated pigments suitable for inclusion in the inkjet ink include those described in EP 3 239 212, EP 3 395 852, EP 3 397 703, EP 3 527 633, EP 3 498 792, EP 3 650 509, EP 3 650 510 and GB 2 592 298.

[0036] The preparation of a dispersed encapsulated pigment for inclusion in the inkjet ink of the present invention is also known and is described in at least WO 2006 / 064193 and WO 2010 / 038071 .

[0037] Typically, the dispersed encapsulated pigment is prepared by mixing pigment particles with a crosslinkable polymer in a liquid medium and adding a cross-linking agent. In this process, the crosslinkable polymer absorbs onto a surface of the pigment particles and is then cross-linked using the cross-linking agent to form a polymer coating, having pendant hydrophilic groups including hydroxyl groups, around the pigment particles.

[0038] The cross-linked polymer can be likened to a cage or coating surrounding each individual pigment particle.

[0039] For the avoidance of doubt, the cross-linking agent used to prepare the dispersed encapsulated pigment is typically different to the cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, present in the inkjet ink of the present invention.

[0040] Pigment particles include any of the classes of pigment particles described in the Third Edition of the Colour Index (1971) and subsequent revisions of, and supplements thereto, under the chapter headed “Pigments”. Examples of organic pigment particles include those from the azo (including disazo and condensed azo), thioindigo, indanthrone, isoindanthrone, anthanthrone, anthraquinone, isodibenzanthrone, triphendioxazine, quinacridone, diketopyrrolopyrrole and phthalocyanine series, such as copper phthalocyanine and its nuclear halogenated derivatives, and also lakes of acid, basic and mordant dyes. Examples of inorganic pigment particles include carbon black, titanium dioxide, aluminium oxide, iron oxide and silicon dioxide.

[0041] Preferred pigment particles are phthalocyanines, azo, indanthrone, anthanthrone and quinacridone, diketopyrrolopyrrole, carbon black pigment particles or any combination thereof.

[0042] Preferably, the pigment particles are cyan, magenta, yellow, black, violet, red, orange, green and white pigment particles or any combination thereof.

[0043] The cross-linked polymer having pendant hydrophilic groups including hydroxyl groups is not limited and may be formed using any monomers and cross-linking agents as long as pendant hydrophilic groups including hydroxyl groups are introduced.

[0044] In a preferred embodiment, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains two or more monomers, which are polymerised and subsequently crosslinked with a cross-linking agent. More preferably, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains one or more (meth)acrylate monomers and a (meth)acrylic acid monomer, which are polymerised and subsequently cross-linked with an epoxide. In a particularly preferred embodiment, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains benzyl (meth)acrylate and (meth)acrylic acid monomers, which are polymerised and subsequently cross-linked with an epoxide. In this embodiment, the pendant hydrophilic groups include carboxyl groups (from the (meth)acrylic acid monomers) and hydroxyl groups (resulting from epoxide ring opening during cross-linking).

[0045] Preferably, the epoxide used to prepare the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups has two or more epoxy groups. Preferably, the epoxide is an epichlorohydrin derivative. Examples of suitable epoxides include ethylene glycol diglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1 ,6-hexanediol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, polybutadiene diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol, diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol poly glycidyl ether, trimethylolpropane polygycidyl ether and combinations thereof. Trimethylolpropane polygycidyl ether is particularly preferred.

[0046] In a preferred embodiment, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains two or more monomers, which are polymerised and subsequently crosslinked with a cross-linking agent, wherein at least one of the two or more monomers has hydroxyl groups. More preferably, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains one or more (meth)acrylate monomers and a (meth)acrylic acid monomer, which are polymerised and subsequently cross-linked with an epoxide, wherein at least one of the one or more (meth)acrylate monomers has hydroxyl groups. In a particularly preferred embodiment, the cross-linked polymer having pendant hydrophilic groups including hydroxyl groups contains benzyl (meth)acrylate and (meth)acrylic acid monomers in combination with an additional monomer having hydroxyl groups, which are polymerised and subsequently cross-linked with an epoxide. 2-Hydroxypropyl (meth)acrylate (HPMA) is particularly preferred as the additional monomer having hydroxyl groups. The epoxide is as described in the preceding paragraph.

[0047] In this embodiment, the pendant hydrophilic groups include carboxyl groups (from the (meth)acrylic acid monomers) and hydroxyl groups (from the additional monomer having hydroxyl groups together with hydroxyl groups resulting from epoxide ring opening during cross-linking). Additional hydroxyl groups means that more hydroxyl groups are available on the encapsulated pigment for reaction with the cross-linking agent of the present invention, when deprotected, leading to enhanced adhesion between the encapsulated pigment and the substrate and / or enhanced crosslinking between the encapsulated pigment particles on the substrate.

[0048] A cross-linked polymer containing an additional monomer having hydroxyl groups also means that the cross-linked polymer is potentially more hydrophilic depending on the degree of cross-linking and acid value. A more hydrophilic cross-linked polymer allows for deeper penetration of the encapsulated pigment in hydrophilic substrates such as textile substrates having free hydroxyl groups at the surface of the substrate, leading to enhanced reaction and adhesion between the encapsulated pigment and the substrate. Such a printed substrate therefore has improved washfastness and robustness.

[0049] The pendant hydrophilic groups including hydroxyl groups are pendant in that they extend from the cross-linked polymer around the pigment particles. They are thus available to react with the two or more protected reactive groups of the cross-linking agent present in the inkjet ink of the present invention, when deprotected.

[0050] The pendant hydrophilic groups including hydroxyl groups are hydrophilic in that they are attracted to water molecules. They are not limited other than they must include hydroxyl groups. Examples of non-limiting additional pendant hydrophilic groups include non-ionic and ionic groups.

[0051] Hydroxyl groups are non-ionic groups. Hydroxyl groups are particularly good at reacting with the two or more protected reactive groups of the cross-linking agent, when deprotected. This leads to improved binding between pigment particles and improved tethering of the encapsulated pigment to the substrate, leading to better adhesion between the encapsulated pigment and the substrate. The printed substrates are hence more wash-fast and robust than would otherwise be obtained with less reactive pendant hydrophilic groups such as carboxyl groups. The hydroxyl groups may be primary and / or secondary hydroxyl groups but the pendant hydrophilic groups preferably include primary hydroxyl groups. Primary hydroxyl groups react faster than secondary hydroxyl groups, leading to an improved reaction between the encapsulated pigment and the cross-linking agent, when deprotected.

[0052] Any ionic hydrophilic groups may be cationic or anionic but anionic groups are preferred. Examples of anionic groups include phenoxy, carboxyl, sulphonic acid, sulphuric acid, phosphonic acid, polyphosphoric and phosphoric acid groups. Carboxyl, sulphonic acid, sulphuric acid, phosphonic acid, polyphosphoric and phosphoric acid groups may be in the free acid or salt form.

[0053] Particularly preferred additional pendant hydrophilic groups are carboxyl and / or amino groups. That is, the pendant hydrophilic groups preferably includes hydroxyl groups in combination with carboxyl and / or amino groups, more preferably hydroxyl groups in combination with carboxyl groups. Carboxyl groups are particularly good at stabilising the dispersed encapsulated pigment in the continuous aqueous phase. Carboxyl groups can also react with the two or more protected reactive groups of the cross-linking agent, when deprotected.

[0054] In a preferred embodiment, the dispersed encapsulated pigment is added to the ink in the form of an encapsulated pigment dispersion. Preferably, the encapsulated pigment dispersion is added to the ink in an amount of 10 to 40% by weight, more preferably 15 to 35% by weight and most preferably 20 to 30% by weight, based on the total weight of the ink. A higher concentration of encapsulated pigment dispersion may be required for white inks, for example up to and including 70% by weight, based on the total weight of the ink. For the avoidance of doubt, the amount of encapsulated pigment dispersion includes any water or additional solvent added as part of the encapsulated pigment dispersion.

[0055] Preferably, the dispersed encapsulated pigment is present in an amount of 0.2 to 20% by weight, preferably 0.5 to 15% by weight, more preferably 2 to 8% by weight, and most preferably 3 to 7% by weight, based on the total weight of the ink. A higher concentration of the dispersed encapsulated pigment may be required for white inks, for example up to and including 30% by weight, or 25% by weight, based on the total weight of the ink. For the avoidance of doubt, these amounts correspond to the dispersed encapsulated pigment per se.

[0056] Dispersed encapsulated 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, more preferably less than 0.5 pm and particularly preferably less than 0.2 pm.

[0057] The inkjet ink of the present invention further comprises a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the cross-linking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the cross-linking agent, when deprotected, has a molecular weight of 600 to 2000.

[0058] In this regard, two or more of the reactive groups of the oligomer having three or more reactive groups, react with a blocking agent, which is capable of blocking the reactive groups, to form two or more blocked reactive groups. Reactive groups that react with a blocking agent are protected (blocked) from reacting further until they are deprotected (deblocked). The terms blocked and protected are often used interchangeably. In addition, one or more of the reactive groups of the oligomer having three or more reactive groups, react with the non-ionic diol to form a urethane linkage. The cross-linking agent, when deprotected, has a molecular weight of 600 to 2000. The inventors have surprisingly found that introduction of the non-ionic diol improves micro- and macrohandle.

[0059] The oligomer having three or more reactive groups is not particularly limited, other than the three or more reactive groups of the oligomer are reactive to hydroxyl groups. The three or more reactive groups can be the same or different. The oligomer having three or more reactive groups may be selected from those commercially available, preferably having from 3 to 11 reactive groups, which are reactive to hydroxyl groups, per molecule. The oligomer may be aromatic, aliphatic, cycloaliphatic or a mixture thereof. In a preferred embodiment, the oligomer having three or more reactive groups has from 3 to 7, preferably 3 to 5 and most preferably 3 to 4 reactive groups per molecule.

[0060] The term oligomer has its standard meaning in the art, namely that the component is partially reacted to form a pre-polymer having a plurality of repeating monomer units, which is capable of further polymerisation. Oligomers typically have a molecular weight of at least 500 and less than 4,000. In the present invention, the oligomers preferably have a molecular weight of 500 to 2000, preferably 600 to 2000, more preferably 500 or 600 to 1200. In a preferred embodiment, the oligomers have a molecular weight of 500 to 700. 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.

[0061] The repeat unit of the oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups, is not particularly limited other than by the constraints imposed by the use in an inkjet ink, such as viscosity, stability, toxicity etc. The repeat unit of the oligomer having three or more reactive groups, is typically alkylene, cycloalkylene, arylene or combinations with at least one of alkyl, cycloalkyl and / or aryl, any of which may be interrupted by heteroatoms. Non-limiting examples of repeat units commonly used in the art include Ci-is alkylene, C3-18 cycloalkylene, CB- arylene and combinations with at least one of C1-18 alkyl, C3-18 cycloalkyl and / or CB-W aryl, such as CB-W aryl- or Cs-is cycloalkyl-substituted C1-18 alkylene, any of which may be interrupted by 1-16 heteroatoms, such as oxygen or nitrogen, with nitrogen further substituted by any of the above described substituents.

[0062] In a preferred embodiment, the three or more reactive groups of the oligomer, which are reactive to hydroxyl groups are isocyanate groups. That is, in a preferred embodiment, the oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxy groups is an isocyanate having three or more isocyanate groups. Therefore, in a preferred embodiment, the cross-linking agent comprises two or more protected isocyanate groups obtainable by reacting an isocyanate having three or more isocyanate groups, an isocyanate blocking agent and a non-ionic diol.

[0063] In a preferred embodiment, the isocyanate is selected from: isocyanates obtainable by the reaction of a polyol having three to ten hydroxy groups and isocyanates selected from hexamethylene diisocyanate isocyanurate trimer, 1 ,6- hexamethylenediisocyanate, 1 -isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane, 4,4'- dicyclohexyl-methanediisocyanate, 2,4-toluenediisocyanate, 2,6-toluenediisocyanate, 4,4'- diphenyl-methanediisocyanate, meta-tetramethylxilylenediisocyanate, and mixtures thereof; hexamethylene diisocyanate isocyanurate trimer; and mixtures thereof.

[0064] In a preferred embodiment, the isocyanate is hexamethylene diisocyanate isocyanurate trimer.

[0065] In a preferred embodiment, the isocyanate is obtainable by the reaction of a polyol having three to ten hydroxy groups and isocyanates selected from: hexamethylene diisocyanate isocyanurate trimer; 1 ,6-hexamethylenediisocyanate; 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl- cyclohexane; 4,4'-dicyclohexyl-methanediisocyanate; 2,4-toluenediisocyanate; 2,6- toluenediisocyanate; 4,4'-diphenyl-methanediisocyanate; meta-tetramethylxilylenediisocyanate; and mixtures thereof; and mixtures thereof.

[0066] Thus, in a preferred embodiment, the cross-linking agent is obtainable by: preparing an isocyanate by reacting a polyol having three to ten hydroxy groups and isocyanates selected from hexamethylene diisocyanate isocyanurate trimer, 1 ,6-hexamethylenediisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane, 4,4'-dicyclohexyl- methanediisocyanate, 2,4-toluenediisocyanate, 2,6-toluenediisocyanate, 4,4'-diphenyl- methanediisocyanate, meta-tetramethylxilylenediisocyanate, and mixtures thereof; and reacting the isocyanate and mixtures thereof, an isocyanate blocking agent, and a non-ionic diol. The cross-linking agent, when deprotected, has a molecular weight of 600 to 2000. In a preferred embodiment, the polyol is trimethylol propane.

[0067] Thus, in a preferred embodiment, the cross-linking agent is obtainable by: preparing an isocyanate by reacting trimethylol propane and isocyanates selected from hexamethylene diisocyanate isocyanurate trimer, 1 ,6-hexamethylenediisocyanate, 1-isocyanato-3- isocyanatomethyl-3,5,5-trimethyl-cyclohexane, 4,4'-dicyclohexyl-methanediisocyanate, 2,4- toluenediisocyanate, 2,6-toluenediisocyanate, 4,4'-diphenyl-methanediisocyanate, meta- tetramethylxilylenediisocyanate, and mixtures thereof; and reacting the isocyanate and mixtures thereof, an isocyanate blocking agent, and a non-ionic diol. The cross-linking agent, when deprotected, has a molecular weight of 600 to 2000.

[0068] In a preferred embodiment, the isocyanate is obtainable by the reaction of trimethylol propane and 2,4-toluenediisocyanate, 2,6-toluenediisocyanate and 1 ,6-hexamethylenediisocyanate. Preferably the weight ratio of 2,4-toluenediisocyanate:2,6-toluenediisocyanate is 70:30 to 90:10, preferably 80:20.

[0069] Thus, in a preferred embodiment, the cross-linking agent is obtainable by: preparing an isocyanate by reacting trimethylol propane and 2,4-toluenediisocyanate, 2,6-toluenediisocyanate and 1 ,6- hexamethylenediisocyanate; and reacting: the isocyanate and mixtures thereof; an isocyanate blocking agent; and a non-ionic diol. The cross-linking agent, when deprotected, has a molecular weight of 600 to 2000.

[0070] Blocking agents, which are capable of blocking the three or more reactive groups of the polymer, are well known in the art. The blocking agent is not particularly limited and is preferably a thermally deblockable blocking agent. By thermally deblockable, it is meant that on the application of heat, the two or more blocked reactive groups of the cross-linking agent, which are formed on reacting the reactive groups of the polymer and the blocking agent, are deblocked, leaving one or more reactive groups, which are then free to react. The terms blocking and protecting agents are often used interchangeably. In a preferred embodiment, the blocking agent is deblockable at a temperature of 100°C to 170°C.

[0071] In a preferred embodiment, the blocking agent is an isocyanate blocking agent.

[0072] In a preferred the blocking agent is selected from an active methylene, an oxime, a lactam (e.g. an e-caprolactam), a pyrazole, an imidazole, or mixtures thereof. Forthe avoidance of doubt, an active methylene is a compound having a methylene bridge located between two electron-withdrawing groups. An example of a preferred active methylene is acetylacetone.

[0073] In a preferred embodiment, the blocking agent is selected from an oxime, a pyrazole or mixtures thereof. Particularly preferred are butanone oxime and 3,5-dimethylpyrazole. In a preferred embodiment, the non-ionic diol is selected from a polyether diol, a polyester diol, a polycarbonate diol, a polyesteramide diol, a polythioether diol, a polyacetal diol, a polyvinyl diol, a polysiloxane diol, or mixtures thereof.

[0074] In a particularly preferred embodiment, the non-ionic diol is an alkoxylated diol. By alkoxylated diol, it is meant two hydroxy groups connected by one or more alkylene glycols The alkylene glycol chain may be straight-chain or branched. In a particularly preferred embodiment, the alkoxylated diol has the following formula:

[0075] R1H2CO-(CH2CH2O)n-(CH2CHCH3O)m-R2wherein R1is a diol, R2is selected from methyl, ethyl, n-propyl, i-propyl, n-butyl and i-butyl, n is a number from 0 to 40, m is a number from 0 to 40 and n+m is a number from 20 to 80.

[0076] In a preferred embodiment, n is a number from 15 to 30. Preferably, m is a number from 0 to 10. Preferably, n+m is a number from 20 to 40, preferably 20 to 30.

[0077] Preferably, R2and R3are the same or different and are selected from methyl and ethyl. Preferably, R2is methyl and R3is ethyl.

[0078] More preferably, the alkoxylated diol has the following formula: wherein R2and R3are the same or different and are selected from methyl, ethyl, n-propyl, i-propyl, n-butyl and i-butyl, n is a number from 0 to 40, m is a number from 0 to 40 and n+m is a number from 20 to 80. Preferably, the alkoxylated diol has the following formula: wherein R2is methyl, R3is ethyl, n is a number from 15 to 30, m is a number from 0 to 10 and n+m is a number from 20 to 40.

[0079] In a preferred embodiment, the non-ionic diol has a molecular weight of 800 to 1500. Preferably, the non-ionic diol has a molecular weight of 1000 to 1400. Molecular weights (number average) can be calculated if the structure of the non-ionic diol is known or molecular weights can be measured using gel permeation chromatography using polystyrene standards.

[0080] In a preferred embodiment, the cross-linking agent is obtainable by: (i) reacting an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups, and a non-ionic diol at a temperature of up to 120°C; and (ii) reacting the obtained oligomer with a blocking agent, which is capable of blocking the three or more reactive groups.

[0081] Preferably, the cross-linking agent is obtainable by: (i) reacting an isocyanate having three or more isocyanate groups and a non-ionic diol at a temperature of up to 120°C; and (ii) reacting the obtained oligomer with an isocyanate blocking agent.

[0082] The cross-linking agent has two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups. The reactive groups can be the same or different. In a preferred embodiment, the cross-linking agent has two or more protected isocyanate groups. The two or more protected isocyanate groups, when deprotected, are reactive to hydroxyl groups thus forming a urethane linkage.

[0083] The cross-linking agent, when deprotected, has a molecularweight of 600 to 2000. In otherwords, when the two or more protected reactive groups of the cross-linking agent are deprotected, the cross-linking agent has a molecular weight of 600 to 2000, preferably 650 to 1900. Molecular weights (number average) can be calculated if the structure of the cross-linking agent is known or molecular weights can be measured using gel permeation chromatography using polystyrene standards.

[0084] In a preferred embodiment, the cross-linking agent is a non-ionic blocked di- and / or polyisocyanate, where the two or more isocyanate groups are protected. That is, the cross-linking agent is preferably a non-ionic blocked diisocyanate, a non-ionic blocked polyisocyanate or a mixture of a non-ionic blocked diisocyanate and a non-ionic blocked polyisocyanate. A non-ionic blocked di- and / or poly-isocyanate has two or more protected isocyanate groups.

[0085] In a preferred embodiment, the cross-linking agent is a non-ionic blocked diisocyanate. In another preferred embodiment, the cross-linking agent is a non-ionic blocked polyisocyanate. In a further preferred embodiment, the cross-linking agent is a mixture of a non-ionic blocked diisocyanate and a non-ionic blocked polyisocyanate.

[0086] As used herein, a non-ionic blocked diisocyanate comprises two blocked isocyanate groups and a non-ionic blocked polyisocyanate comprises three or more blocked isocyanate groups. When a non-ionic blocked polyisocyanate is present, the non-ionic blocked polyisocyanate preferably comprises three to six blocked isocyanate groups, more preferably three or four blocked isocyanate groups. A non-ionic blocked polyisocyanate having three blocked isocyanate groups is particularly preferred.

[0087] General synthesis of blocked isocyanates is well-known to the skilled person and has been reviewed by D.A. Wicks and Z.W. Wicks Jr., Progress in Organic Coatings, 1999, 36, 148-172 and E. Delebecq et al., Chem Rev., 2013, 113, 80-1 18.

[0088] Classic blocked isocyanates are defined as chemical components that are capable of forming isocyanates from a precursor upon thermal activation. In general, the reaction proceeds as shown below, where X is any suitable leaving group: R + H— X HX

[0089] The activation temperature, also called the deblocking temperature, is dependent on the leaving group. Suitable isocyanate precursors are shown below having a variable deblocking temperature from 100°C to 170°C: wherein R represents the remainder of the rest of the cross-linking agent, including one or more blocked reactive groups and one or more reactive groups which has reacted with the non-ionic diol, connected by repeat units.

[0090] Active methylene compounds as blocking agents are widely used as alternatives for classic blocked isocyanates, operating via an alternative reaction pathway, not yielding an intermediate isocyanate but crosslinking the system via ester formation as disclosed in D.A. Wicks and Z.W. Wicks, Progress in Organic Coatings, 1999, 36, 148-172. Suitable examples of active methylene blocked isocyanates are shown below: wherein R is as described above.

[0091] As discussed above, the leaving group of the cross-linking agent is not particularly limited. Preferably, the leaving group of the cross-linking agent can be any group capable of leaving at a temperature of 100°C to 170°C and one that is not hazardous. The leaving groups of the crosslinking agent may the same or different but are preferably the same. In a preferred embodiment, the leaving group of the cross-linking agent is 3,5-dimethylpyrazyl (DMP). DMP is favoured from a health and safety perspective and because of its relatively low deblocking temperature of 115°C.

[0092] As discussed above, in a preferred embodiment, the cross-linking agent used in the inkjet ink of the present invention contains 2 to 10 blocked reactive groups per molecule, wherein the blocked reactive groups, when deblocked, are reactive to hydroxyl groups, preferably 2 to 6, more preferably 2 to 4 blocked reactive groups per molecule. As discussed above, in a preferred embodiment, the cross-linking agent used in the inkjet ink of the present invention contains 2 to 10 blocked isocyanate groups per molecule, preferably 2 to 6, more preferably 2 to 4 blocked isocyanate groups per molecule.

[0093] Suitable cross-linking agents used in the inkjet ink of the invention include Roflex® products commercially available from Lamberti. A particularly preferred blocked polyisocyanate is Roflex® BK18, which is a water-based non-ionic blocked polyisocyanate.

[0094] The cross-linking agent is preferably added to the ink in the form of an aqueous dispersion and is thus preferably a water-based dispersion. It is preferably soluble in the continuous aqueous phase of the ink.

[0095] In a preferred embodiment, the cross-linking agent dispersion is added to the ink in an amount of

[0096] 5 to 20%, preferably 13 to 17% by weight, based on the total weight of the ink. For the avoidance of doubt, the amount of cross-linking agent dispersion includes any water added as part of the cross-linking agent dispersion. The inventors have found that this amount of cross-linking agent dispersion provides a balance between micro-handle and macro-handle.

[0097] Preferably, the two or more protected reactive groups, when deprotected, are present in the ink in an amount of 0.01 to 1 .00%, preferably 0.20 to 1 .00%, more preferably 0.50 to 1 .00% by weight, based on the total weight of the ink. When the cross-linking agent is a blocked di- and / or polyisocyanate, these amounts correspond to the isocyanate loading in the ink.

[0098] The two or more protected reactive groups of the cross-linking agent are only reactive to hydroxyl groups when they are deprotected, i.e. it is the two or more deprotected reactive groups that are reactive to hydroxyl groups. Deprotection typically happens after the inkjet ink is printed and dried to remove water.

[0099] The two or more protected reactive groups are preferably deprotected using heat, i.e. the crosslinking agent is preferably a cross-linking agent having two or more protected reactive groups, wherein the two or more protected reactive groups, when thermally deprotected, are reactive to hydroxyl groups.

[0100] Preferably, the two or more protected reactive groups are deprotected by heating to a temperature of 100°C or higher, preferably 120°C or higher, more preferably 135°C or higher. The maximum temperature is dictated by cost but preferably, the temperature sufficient to deprotect the two or more protected reactive groups is up to 170°C. Therefore, in a preferred embodiment, the two or more protected reactive groups are deprotected by heating to a temperature from 100°C to170°C, preferably from120°C to 170°C, more preferably from 135°C to 170°C. This temperature is higher than the temperature used to initially remove water, and optionally an organic solvent, from the printed ink. This allows the ink to be dried and then cured (cross-linked) in subsequent steps by applying the lower and then higher temperature, respectively.

[0101] Preferably, the printed ink is dried by heating to a temperature of less than 100 °C. In this embodiment, the printed ink needs to be heated to a temperature sufficient to dry the printed ink but preferably, the printed ink is dried by heating to a temperature of 60°C or higher. Therefore, in a preferred embodiment, the printed ink is dried by heating to a temperature between 60°C and less than 100°C.

[0102] The two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups. The two or more reactive groups can react with the hydroxyl groups of the encapsulated pigment, and / or any free hydroxyl groups on the substrate. The two or more reactive groups can also react with other pendant hydrophilic groups of the encapsulated pigment such as carboxyl groups. The two or more reactive groups of the cross-linking agent can also react with other available reactive groups on the substrate that are capable of reacting with the two or more reactive groups of the cross-linking agent. Examples of such groups include amino groups. In this way, the cross-linking agent can act as a bridge between pigment particles embedded in the substrate and between the encapsulated pigment and the substrate. Binding pigment particles together and tethering the encapsulated pigment to the substrate in this way provides good adhesion between the encapsulated pigment and the substrate, resulting in the printed image being both wash-fast and robust. The printed substrate also has a good handle and optical density.

[0103] By optical density is meant OD = - log ( / / / 0), where l0is the intensity of incident light on a print, and I is the intensity of light reflected form a print. It is the measure of darkness of a print. The higher the optical density, the darker the print.

[0104] Binder resins are typically added to pigmented inkjet inks to facilitate adhesion between the ink and substrate. However, the inclusion of a binder resin in an inkjet ink results in a printed substrate with a poor handle and a sub-optimal optical density. Therefore, in a preferred embodiment, the ink contains less than 3% by weight, more preferably less than 2% by weight, more preferably less than 1 % by weight and most preferably is substantially free of a binder resin, where the amounts are based on the total weight of the ink.

[0105] By substantially free is meant that only small amounts will be present, for example as impurities in the components present. In otherwords, no binder resin is intentionally added to the ink. However, minor amounts of a binder resin, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight, more preferably less than 0.1 % by weight, most preferably less than 0.05% by weight of a binder resin, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of a binder resin.

[0106] By binder resin is meant a polymer capable of binding pigment to a substrate without formation of covalent bonds between the polymer and pigment. The binder resin may include reactive groups that may allow self-cross-linking of the polymer as the ink dries. The polymer typically contains polymerised ethylenically unsaturated monomers optionally with reactive groups remaining for cross-linking. Suitable monomers include vinyl monomers such as (meth)acrylates, styrenes, acrylamides, vinyl ethers and halogenated vinyl compounds. Examples of binder resins include Rovene® 4170 (a carboxylated self-cross-linking styrene butadiene copolymer available from Mallard Creek Polymers) and Lubrijet® T340 (an acrylic emulsion copolymer binder available from Lubrizol).

[0107] Binder resins are typically prepared by emulsion polymerisation, as is known in the art. In this case, the binder resin may be provided in the form of a latex. The latex includes polymer particles dispersed in a liquid carrier. The liquid carrier is typically water, which may contain small amounts of other solvents. The liquid carrier may include additives such as agents to control the pH, for example amines. The polymer particles can be self-dispersing or the particles can be dispersed with the aid of a surfactant. Suitable surfactants include conventional surfactants such as sulfates, sulfonates, and ethylene oxide / propylene oxide copolymers. Commercially available latexes typically comprise 40 to 60% by weight of polymer, based on the total weight of the latex. For the avoidance of doubt, the restrictions on the amount of binder resin above includes any water, additives and surfactants added as part of the binder resin component.

[0108] The binder resin typically has a weight-average molecular weight of more than 2000 to 500,000, preferably 4000 to 100,000, as determined by gel permeation chromatography with polystyrene standards.

[0109] In a preferred embodiment, the ink contains less than 2% by weight, more preferably less than 1 % by weight and most preferably is substantially free of polymer capable of binding pigment to a substrate without formation of covalent bonds between the polymer and pigment, where the amounts are based on the total weight of the ink.

[0110] By substantially free is meant that only small amounts will be present, for example as impurities in the components present. In other words, no polymer capable of binding pigment to a substrate without formation of covalent bonds between the polymer and pigment is intentionally added to the ink. However, minor amounts of such a polymer, which may be present as impurities in commercially available inkjet ink components, are tolerated. For example, the ink may comprise less than 0.5% by weight, more preferably less than 0.1 % by weight, most preferably less than 0.05% by weight of polymer capable of binding pigment to a substrate without formation of covalent bonds between the polymer and pigment, based on the total weight of the ink. In a preferred embodiment, the inkjet ink is free of polymer capable of binding pigment to a substrate without formation of covalent bonds between the polymer and pigment.

[0111] In the present invention, it has been found that the saturation of optical density is achieved more rapidly at lower print densities as the encapsulated pigment can penetrate the substrate more readily instead of being obscured by any binder resin. In this regard, a printed ink film containing a binder resin is confined to the surface of the substrate by the binder resin, which typically produces a rough topography and the pigment particles are enveloped in binder resin. These film properties scatter the light and have detrimental effects on the optical density. An ink containing minimal binder resin has improved wetting properties on the substrate owing to the lower amount of binder resin present in the ink, leading to deeper penetration and greater drop spread, which produces a smoother ink film topography with less scattering of light. The printed substrate therefore has good colour strength, even when using a small amount of ink. The printed substrate prepared using the inkjet ink of the present invention also has a better handle and is softer than a comparative ink containing a binder resin instead of a cross-linking agent of the present invention.

[0112] Minimising the amount of binder resin present in the inkjet ink of the present invention also improves the breathability of the printed substrate, which is particularly important in sportswear where the inclusion of a binder resin is thought to block sweat. In this regard, the inclusion of a binder resin in an ink limits the ink film to the surface of the substrate. Moreover, when such an ink is printed onto a textile substrate, the individual fibres in the substrate can be matted together by the binder resin. As discussed above in relation to optical density, an ink containing minimal binder resin will wet the substrate more readily and penetrate more deeply into the substrate. As such, a printed textile substrate is more breathable.

[0113] In a preferred embodiment, the inkjet ink of the present invention further comprises a wax. The inclusion of a wax in the ink improves dry crock and provides a conditioning effect. Examples of suitable waxes include Hytec Wax E-6314 and Hytec E-9015 commercially available from Toho Chemical Industry Co., Ltd., Adiwax H 606 F commercially available from Lamberti S.p.A and Nopcote PEM17 commercially available from San Nopco. Preferably, the wax is an aqueous emulsion, more preferably an aqueous polyethylene and / or polypropylene emulsion, most preferably an aqueous oxidised polyethylene and / or polypropylene emulsion. Hytec Wax E-6314 is an oxidised polyethylene wax emulsion. Hytec E-9015 is an aqueous emulsion of polyethylene wax. Adiwax H 606 F is an aqueous emulsion of oxidised polyethylene and paraffines wax, which is free of nonylphenols. Nopcote PEM17 is a polyethylene wax emulsion.

[0114] Additional examples of suitable waxes include: synthetic waxes such as polyolefin wax and stearic acid amide; natural waxes such as carnauba, animal and beeswax; petroleum waxes such as paraffin and Vaseline®; and mineral waxes such as montan wax.

[0115] In a preferred embodiment, the surface tension of the ink is controlled by the addition of one or more surface active materials such as commercially available surfactants. Therefore, the inkjet ink of the present invention preferably further comprises a surfactant.

[0116] Surfactants are well-known in the art and a detailed description is not required. A particularly preferred surfactant is Surfynol 440. Adjustment of the surface tension of the inks allows control of the surface wetting of the inks on various substrates. Too high a surface tension can lead to ink pooling and / or a mottled appearance in high coverage areas of the print. Too low a surface tension can lead to excessive ink bleed between different coloured inks. The surface tension is preferably in the range of 20-40 mNnr1and more preferably 30-35 mNnrr1. Preferably, the surfactant is present in the inkjet ink in an amount of 0.01 to 3% by weight, based on the total weight of the ink.

[0117] In a preferred embodiment, the inkjet ink of the present invention preferably further comprises a biocide.

[0118] Biocides are well-known in the art and a detailed description is not required. Biocides prevent microbial growth in the ink. An example of a suitable biocide is Proxel GXL commercially available from Arxanda. Proxel GXL is a 20% aqueous dipropylene glycol solution of 1 ,2-benzisothiazolin- 3-one.

[0119] Preferably, the biocide is present in the inkjet ink in an amount of 0.01 to 0.075%, more preferably 0.02 to 0.075%, most preferably 0.05 to 0.075% by weight, based on the total weight of the ink. Forthe avoidance of doubt, the amount of biocide includes any solvent added as part of the biocide component.

[0120] Other components of types known in the art may be present in the ink of the present invention to improve the properties or performance. These components may be, for example, pH buffers, humectants, defoamers, dispersants, synergists, stabilisers against deterioration by heat or light, reodorants, flow or slip aids, identifying tracers and viscosity modifiers.

[0121] In a preferred embodiment, the present invention provides an inkjet ink consisting of: a continuous aqueous phase including water and optionally, an organic solvent; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the crosslinking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the crosslinking agent, when deprotected, has a molecular weight of 600 to 2000; and optionally a wax, a surfactant, a biocide, a pH buffer, a humectant, a defoamer, a dispersant, a synergist, a stabiliser against deterioration by heat or light, a reodorant, a flow or slip aid, an identifying tracer, a viscosity modifier and combinations thereof.

[0122] More preferably, the present invention provides an inkjet ink consisting of: a continuous aqueous phase including water and optionally, an organic solvent; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the crosslinking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the crosslinking agent, when deprotected, has a molecular weight of 600 to 2000; and optionally a wax, a surfactant, a biocide, a viscosity modifier and combinations thereof.

[0123] In both of these embodiments, the preferred features of the inkjet ink are as discussed above, including that the pendant hydrophilic groups preferably further include carboxyl groups.

[0124] The amounts by weight provided herein are based on the total weight of the ink.

[0125] The inkjet ink may be prepared by known methods such as combining all of the components and stirring with a high-speed water-cooled stirrer, or milling on a horizontal bead-mill. The preparation of the inkjet ink of the present invention is remarkably simple. For example, one may simply use water, a commercially available encapsulated pigment dispersion, a commercially available crosslinking agent dispersion and any other additional components. The cross-linking agent dispersion may be added to the encapsulated pigment dispersion first or the cross-linking agent dispersion may be added to the encapsulated pigment dispersed in the continuous aqueous phase of the ink.

[0126] The inkjet ink preferably exhibits a desirable low viscosity (100 mPas or less, more preferably 50 mPas or less and most preferably 35 mPas or less at 25°C). The ink most preferably has a viscosity of less than 20 mPas at 25°C. Viscosity may be measured using a rotational viscometer fitted with a thermostatically controlled cup and spindle arrangement, running at 20 rpm at 25°C.

[0127] The present invention may also provide an inkjet ink set, wherein the inkjet ink set of the invention has at least one ink that falls within the scope of the inkjet ink according to the present invention. Preferably, all of the inks in the set fall within the scope of the inkjet ink according to the present invention.

[0128] 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.

[0129] The present invention also provides a dispersion comprising: a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the crosslinking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the crosslinking agent, when deprotected, has a molecular weight of 600 to 2000.

[0130] The dispersion is used to prepare the inkjet ink of the present invention. The preferred features of the components of the inkjet ink discussed above are also preferred features of the components of the dispersion. However, the amounts of the components present in the dispersion typically differ from the amounts of the components present in the inkjet ink.

[0131] In this regard, the dispersion typically contains a higher amount of encapsulated pigment than the inkjet ink. Preferably, the dispersed encapsulated pigment is present in an amount of 8 to 30% by weight, more preferably 10 to 25% by weight, and most preferably 12 to 20% by weight, based on the total weight of the dispersion. A higher concentration of the dispersed encapsulated pigment may be required for white dispersions, for example up to and including 55% by weight, based on the total weight of the dispersion.

[0132] Further, the dispersion typically has a higher surface tension than the inkjet ink. Preferably, the dispersion has a surface tension of 50 rnNm1or higher.

[0133] The present invention also provides a method of inkjet printing comprising the following steps in order:

[0134] (i) providing an inkjet ink of the present invention;

[0135] (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate;

[0136] (iii) drying the printed substrate to remove water; and

[0137] (iv) deprotecting the two or more protected reactive groups.

[0138] The method of the present invention is a method of inkjet printing.

[0139] 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.

[0140] For high-speed printing, the inks must flow rapidly from the printing heads, and, to ensure that this happens, they must have in use a low viscosity, typically 200 mPas or less at 25°C, although in most applications the viscosity should be 50 mPas or less, and often 25 mPas or less. Typically, when ejected through the nozzles, the ink has a viscosity of less than 25 mPas, preferably 3-15 mPas and most preferably between 4-11 mPas at the jetting temperature, which is often elevated to, but not limited to 30-50°C (the ink might have a much higher viscosity at ambient temperature). The inks must also be resistant to drying or crusting in the reservoirs or nozzles. For these reasons, inkjet inks for application at or near ambient temperatures are commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent such as water or another solvent or mixture of solvents.

[0141] The method of the present invention comprises (i) providing an inkjet ink of the present invention.

[0142] The inkjet ink used in the method of the present invention is the inkjet ink of the present invention as described above. The preferred inkjet ink used in the method of the present invention is as described above for the inkjet ink of the present invention.

[0143] The method of the present invention further comprises (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate.

[0144] The printing is performed by inkjet printing, e.g. on a single-pass inkjet printer, for example for printing (directly) onto a substrate, or a multiple-pass printer where the image is built up in print swathes. Inkjet printing is well-known in the art.

[0145] The ink is jetted from one or more reservoirs or printing heads through narrow nozzles onto a substrate to provide a printed substrate.

[0146] 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.

[0147] The inkjet ink of the present invention is compatible with print heads that are capable of jetting drop sizes of 90 picolitres or less because of its low viscosity.

[0148] Print heads account for a significant portion of the cost of an entry level printer and it is therefore desirable to keep the number of print heads (and therefore the number of inks in the ink set) low. Reducing the number of print heads can reduce print quality and productivity. It is therefore desirable to balance the number of print heads in order to minimise cost without compromising print quality and productivity.

[0149] The substrate can be any substrate suitable for printing. Textile substrates are particularly preferred including treated and untreated textile substrates. Suitable textile substrates include cotton, jersey, silk, rayon, wool, polyester and nylon. Jersey is a stretchable, close-knit fabric having a latticework of twisted vertical yarns connected by untwisted horizontal yarns. Jersey is composed of natural fibres such as wool (animal-derived) or cotton (plant-derived), both of which are optionally blended with synthetic fibres such as polyester or rayon.

[0150] The ink of the present invention is suitable for printing onto a wider range of textile substrates than typical inks containing a binder resin. In particular, the ink of the present invention is suitable for printing onto stretchable textile substrates such as jersey. Inks containing a binder resin typically adhere poorly to stretchable textile substrates as the ink film is confined to the surface and only physically embedded in the substrate. In contrast, the strong covalent bonds formed between the encapsulated pigment and the substrate in the present invention and the deep penetration of the ink film into the substrate means that stretchable textile substrates can be printed onto successfully.

[0151] In a preferred embodiment, the substrate is a textile substrate, wherein the textile substrate is composed of a polymeric material having reactive groups which are available to react with the two or more protected reactive groups of the cross-linking agent, when deprotected, preferably wherein the textile substrate comprises a cellulosic material. More preferably, the substrate is a textile substrate, wherein the textile substrate is composed of a polymeric material having free hydroxyl groups at the surface of the substrate. Cellulosic textile substrates are particularly preferred. Examples of cellulosic textile materials include cotton and jersey. Printing onto such textile substrates provides a printed substrate with particularly advantageous properties.

[0152] Once the two or more protected reactive groups are deprotected, the cross-linking agent is able to react with the hydroxyl groups on the encapsulated pigment and the reactive groups of the textile substrate, including any free hydroxy groups at the surface of the substrate. The cross-linking agent therefore tethers the encapsulated pigment to the textile substrate, providing good adhesion between the encapsulated pigment and the textile substrate. The encapsulated pigment particles also embed in the substrate and the cross-linking agent cross-links the encapsulated pigment particles together, increasing the density of the ink film. These cross-linking reactions results in the printed image being both washfast and robust.

[0153] Suitable substrates include silk, cotton, rayon, wool, polyester and / or nylon. The substrate may be treated with a pre-treat or untreated. Preferred substrates comprise silk and / or cotton. Silk may contain amino groups which can react with the two or more reactive groups of the cross-linking agent. A particularly preferred substrate comprises cotton and more preferably is jersey. Jersey composed of natural fibres is preferred. Natural fibres have the ability to decompose meaning jersey composed of natural fibres is more environmentally friendly. A particularly preferred jersey substrate is composed of 95% cotton and 5% Lycra®. The ink of the present invention adheres particularly well to this stretch jersey leading to wash-fast printed substrates. If there are no free reactive groups on the substrate, the two or more protected reactive groups of the cross-linking agent, when deprotected, can still react with the hydroxyl groups of the encapsulated pigment and cross-link the encapsulated pigment, so that a cross-linked film of the ink is formed on the substrate. Such a printed substrate would still have a good handle and optical density, even if the adhesion between the encapsulated pigment and the substrate is not optimal. However, substrates with no free reactive groups may need to be pre-treated prior to printing so that sufficient bonding to the substrate is achieved.

[0154] It is standard practice to use a pre-treat (also known as a primer) on a textile substrate to enhance wash- and crock-fastness of the printed ink. Pre- and post-treats are also commonly applied to enhance the handle, image and colour quality of the prints. Post-treats typically involve steaming, washing, drying and / or heating steps. Preferably, the method of the present invention does not use pre- or post-treats. It is surprising that the method of the present invention can provide printed images with a high-quality handle, image and colour without resorting to pre- or post-treats. The fact that the method of the present invention does not require any additional pre- or post-treatment steps means that it is also simpler, quicker, cheaper and more environmentally friendly than other methods using dye-based inkjet inks.

[0155] When discussing the substrate, it is the surface which is most important, since it is the surface which is wetted by the ink. Thus, at least the surface of substrate is composed of the abovediscussed material.

[0156] The method of the present invention further comprises (iii) drying the printed substrate to remove water.

[0157] By drying, it is meant the removal of the water (and optional organic solvent) by evaporation. Evaporation of the water can occur simply by exposure of the inks to the atmosphere, but the ink may also be heated to accelerate evaporation. If the ink is heated to accelerate evaporation, the ink is preferably heated to a temperature of less than 100 °C. The minimum temperature is less critical but if the ink is heated to accelerate evaporation, the printed ink is preferably heated to a temperature of 60°C or higher. Therefore, in a preferred embodiment, the printed ink is heated to a temperature between 60°C and less than 100°C.

[0158] Drying the printed substrate to remove water occurs before the two or more reactive groups are deprotected in order to minimise the two or more reactive groups reacting with water.

[0159] The method of the present invention further comprises (iv) deprotecting the two or more protected reactive groups. Deprotecting the two or more protected reactive groups can be done by any means. The means of deprotection depends on the nature and reactivity of the two or more protected reactive groups. Preferably however, the two or more protected reactive groups are reactive to hydroxyl groups when thermally deprotected, and deprotecting the two or more protected reactive groups is by heating the printed substrate to a temperature sufficient to deprotect the two or more protected reactive groups.

[0160] Therefore, the present invention preferably provides a method of inkjet printing comprising the following steps in order:

[0161] (i) providing an inkjet ink comprising: a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the cross-linking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the cross-linking agent, when deprotected, has a molecular weight of 600 to 2000;

[0162] (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate;

[0163] (iii) drying the printed substrate to remove water; and

[0164] (iv) heating the printed substrate to a temperature sufficient to deprotect the two or more protected reactive groups.

[0165] In a particularly preferred embodiment, the present invention preferably provides a method of inkjet printing comprising the following steps in order:

[0166] (i) providing an inkjet ink comprising: a continuous aqueous phase; a dispersed encapsulated pigment consisting of pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the cross-linking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the cross-linking agent, when deprotected, has a molecular weight of 600 to 2000;

[0167] (ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate;

[0168] (iii) drying the printed substrate to remove water; and

[0169] (iv) heating the printed substrate to a temperature sufficient to deprotect the two or more protected reactive groups.

[0170] The temperature is selected based on the cross-linking agent used and what temperature is required to deprotect the two or more protected reactive groups. For example, the blocked isocyanate groups of Roflex BK18 are deprotected at a temperature of around 170°C. Preferably, the temperature sufficient to deprotect the two or more protected reactive groups is 100°C or higher, more preferably 120°C or higher and most preferably 135°C or higher. The maximum temperature is dictated by cost but preferably, the temperature sufficient to deprotect the two or more protected reactive groups is up to 170°C.

[0171] The printed substrate is preferably heated to a temperature sufficient to deprotect the two or more protected reactive groups from 30 seconds to 10 minutes, more preferably from 1 to 7 minutes.

[0172] In this step, the two or more protected reactive groups of the cross-linking agent are deprotected. The reactive groups can then react with the hydroxyl groups of the encapsulated pigment and any free hydroxyl groups on the substrate, thereby binding pigment particles together and tethering the encapsulated pigment to the substrate. These cross-linking reactions provide good adhesion between the encapsulated pigment and the substrate, resulting in the printed image being both wash-fast and robust.

[0173] The present invention also provides a printed substrate having the inkjet ink as defined herein printed thereon. The present invention further provides a printed substrate obtainable by the method of the present invention. Preferred substrates are those given above. As discussed above, the printed substrate has a good handle and optical density, without compromising the washfastness and robustness of the printed substrate. The printed substrate therefore has superior properties than achieved using other pigmented inkjet inks. It is surprising that these properties can be achieved without requiring a binder resin.

[0174] The invention will now be described with reference to the following examples, which are not intended to be limiting.

[0175] Examples

[0176] Example 1

[0177] Preparation of cross-linkable polymers 1-3 used to prepare encapsulated pigment dispersions of the invention

[0178] Cross-linkable polymers 1-3 were prepared using the components set out in Table 1 . The amounts of the components are given in grams.

[0179] Table 1

[0180] HPMA, HEMA, BzMA and MAA are monomers. Specifically, HPMA is 2-hydroxypropyl methacrylate. HEMA is 2-hydroxyethyl methacrylate. BzMA is benzyl methacrylate. MAA is methacrylic acid. The chain transfer agent (CTA) is butyl 3-mercaptopropionate. The initiator is t- butylperoxy 2-ethylhexanaote. Dipropylene glycol (DPG) is a solvent.

[0181] For each cross-linkable polymer, the monomers and chain transfer agent were mixed. Each mixture was then dissolved in dipropylene glycol to provide a solution used as the monomer / CTA feed.

[0182] For each cross-linkable polymer, the initiator was dissolved in dipropylene glycol to provide a solution used as the initiator feed. In a reaction flask, dipropylene glycol was either warmed to a temperature of 85°C for the preparation of cross-linkable polymer 1 or 93°C for the preparation of cross-linkable polymers 2 and 3, and purged with nitrogen gas. Whilst stirring, the corresponding monomer / CTA and initiator feeds were added over 4 and 5 hours, respectively, by pumping the solutions into the reaction flask. The nitrogen gas atmosphere was maintained throughout. The temperature was maintained at either 85°C or 93°C (±1 °C) throughout. On completion of the feeds, the flask contents were stirred fora further two hours at either 85°C or93°C. These steps copolymerised the monomers to prepare cross-linkable polymers 1-3, each in the form of a 40% by weight solution of cross-linkable polymer in dipropylene glycol, based on the total weight of the cross-linkable polymer solution.

[0183] Cross-linkable polymers 1-3 were acrylic copolymers having the properties shown in Tables 2 and 3.

[0184] Table 2

[0185] The molecular weights were determined using gel permeation chromatography (GPC) and measurements were performed on an Agilent GPC50 system fitted with two PL-Gel Mixed D columns (300 x 7.5 mm) and a Rl detector; using DMF (containing 1 wt% of each of acetic acid and trimethylamine) as the eluent with a flow rate of 1.0 mL / min. The number average and weight average molecular weights were determined by comparison to polystyrene standards.

[0186] Table 3

[0187] Neutralisation of cross-linkable polymers 1-3 to prepare cross-linkable polymer solutions 1-3

[0188] Cross-linkable polymer solutions 1-3 were prepared using cross-linkable polymers 1-3, respectively.

[0189] Cross-linkable polymer 1 (625 g) was neutralised by the addition of a solution containing 50% aqueous potassium hydroxide (56.11 g) and water (223.84 g) to provide a solids content of 31% by weight. Cross-linkable polymers 2 and 3 (625 g) were neutralised by the addition of a solution containing 50% aqueous potassium hydroxide (31.65 g) and water (109.24 g) to provide a solids content of 35% by weight, based on the total weight of the cross-linkable polymer solution.

[0190] Cross-linkable polymer solutions 1-3 had the properties shown in Table 4.

[0191] Table 4

[0192] Preparation of black mill-bases 1-4

[0193] Black mill-bases 1 and 2 were prepared using cross-linkable polymer solutions 1 and 2, respectively. Black mill-base 3 was prepared using cross-linkable polymer solution 1 . Black millbase 4 was prepared using cross-linkable polymer solution 3.

[0194] For black mill-base 1 , pigment powder (90 parts of NIPex™ 170IQ Carbon Black pigment, ex Degussa) and cross-linkable polymer solution 1 (116 parts) were mixed together to form a premixture. For black mill bases 2-4, pigment powder (90 parts of NIPex™ 170IQ Carbon Black pigment, ex Degussa) and a cross-linkable polymer solution (103 parts) were mixed together to form a premixture. Water was in some cases added to the premixture as appropriate to provide a suitable viscosity for mixing and milling.

[0195] For black mill-bases 1 , 2 and 4, the premixture was thoroughly mixed together using a Silverson™ mixer for 30 minutes. For black mill-base 3, the premixture was thoroughly mixed together using a Silverson™ mixer for 25 minutes, Imprafix® 2794 (0.192 parts) added, and mixed for a further five minutes. Imprafix® 2794 is a water-based aliphatic blocked polyisocyanate of 38% active strength.

[0196] After mixing, the mixture was transferred to a horizontal bead mill containing 1 mm beads. The mixture was then milled until the desired Z-average particle size was achieved.

[0197] The milled mixture was then removed from the horizontal bead mill, and the milled mixture was adjusted to 10% by weight of pigment by the addition of pure water. This resulted in a black millbase.

[0198] Black mill-bases 1-4 had the Z-average particle sizes shown in Table 5, measured using a Malvern Zetasizer™.

[0199] Table 5

[0200] Cross-linking the cross-linkable polymer solutions in black mill-bases 1-4 to prepare encapsulated pigment dispersions of the invention

[0201] Encapsulated black pigment dispersions B-E were prepared using black mill-bases 2, 3, 1 and 4, respectively, and the other components set out in Table 6. The amounts of the components are given in parts by weight, based on the total weight of the dispersion.

[0202] Table 6

[0203] *lmprafix® 2794 added during preparation of mill-base 3 Imprafix® 2794 is a water-based aliphatic blocked polyisocyanate of 38% active strength. Trimethylolpropane polyglycidyl ether is a cross-linking agent used to prepare encapsulated pigment dispersions of the invention. It is commercially available as Denacol EX-321 obtained from Nagase ChemteX, with weight per epoxy = 140, hereafter abbreviated as EX-321. Boric acid is used as a buffer. It was obtained from Aldrich.

[0204] For encapsulated pigment dispersions B and D, the black mill-base was heated to 70°C and stirred for 30 minutes. Imprafix® 2794 was added and the mixture was stirred for another 30 minutes.

[0205] For encapsulated pigment dispersions C and E, the black mill-bases were used directly in the crosslinking reaction as described below.

[0206] The cross-linkable polymer solutions in each of the mill-bases were then cross-linked using trimethylolpropane polyglycidyl ether. The cross-linking reaction was controlled by the presence of boric acid.

[0207] The cross-linking reaction was effected by heating the mixtures to a temperature of 70°C for a duration of six hours. This reaction cross-linked the carboxylic acid groups in the cross-linkable polymer and thereby encapsulated the pigment.

[0208] Ultrafiltration

[0209] The final stage in obtaining the encapsulated pigment dispersions of the invention is concentration to the desired pigment strength using membrane ultrafiltration. Each encapsulated black pigment dispersion was purified by means of ultrafiltration using membrane having a 0.1 micron pore size.

[0210] Each encapsulated black pigment dispersion was diafiltered with approximately 10 to 40 wash volumes of pure deionized water per 1 volume of the encapsulated black pigment dispersion. The ultrafiltration membrane was then used to concentrate the encapsulated black pigment dispersion back to a solids content of around 13 to 15% by weight, based on the total weight of the dispersion.

[0211] The concentration (or de-watering) was carried out until the pigment strength was slightly higher than (by from 1 to 3% by weight, based on the total weight of the dispersion) the desired final strength. Once the pigment content had reached 16% to 17% by weight, based on the total weight of the dispersion, the dispersion was drained from the membrane ultrafiltration equipment and then adjusted to the final strength target by the addition of demineralised water. Example 2

[0212] Inkjet inks were prepared according to the formulations set out in Tables 7 and 8. The inkjet ink formulations were prepared by mixing the components in the given amounts and filtering them through two 1 pm glass fibre filters from Whatman®.

[0213] For Inks 1-3 and 7-1 1 , Roflex® BK18 or Imprafix® 2794, respectively, was added as the final component of the ink prior to filtration. Amounts are given as weight percentages based on the total weight of the inks.

[0214] Table 7

[0215] Table 8

[0216] Pro-Jet® APD 1000 black and magenta dispersions are encapsulated pigments according to the invention, which are commercially available from FUJIFILM Imaging Colorants Limited.

[0217] Triethylene glycol and glycerol are organic solvents. Surfynol® 440 is a surfactant commercially available from Evonik. Proxel® GXL is a biocide commercially available from Arxanda. Snowtex XS is a colloidal silica commercially available from Nissan Chemical. Rovene® 4170 is a carboxylated self-cross-linking styrene butadiene copolymer binder resin commercially available from Mallard Creek. Imprafix® 2794 is a comparative cross-linking agent, specifically a waterbased aliphatic blocked polyisocyanate commercially available from Covestro. Rolflex® BK18 is a cross-linking agent of the present invention, specifically a cross-linking agent comprising two or more protected isocyanate groups obtainable by reacting an isocyanate having three or more isocyanate groups, an isocyanate blocking agent and a non-ionic diol, which is commercially available from Lamberti. Hytec Wax E-6314 is a is an oxidised polyethylene wax emulsion. PEG 20 000 S is polyethylene glycol

[0218] Inks 1 , 7 and 9-11 contain a cross-linking agent of the invention and are inks of the invention. Inks 2, 3 and 8 contain a comparative cross-linking agent and so are comparative inks. Inks 4 and 5 contain a binder resin instead of a cross-linking agent of the invention and so are comparative inks. Ink 6 contains no cross-linker or binder resin and is a comparative ink.

[0219] Test 1

[0220] Inks 1-2 and 4-5 were assessed for handle / softness.

[0221] Inks 1-2 and 4-5 were printed single pass on an Integrity printer with a KJ4B Kyocera head at large drop size and 600 X 600 DPI onto treated cotton (Premier coating 6798).

[0222] The prints were placed in an oven at 70°C for 15 minutes, immediately after printing. They were then transferred to the hot press for two minutes at 170°C. The prints were cooled under ambient conditions to room temperature before application testing.

[0223] For Inks 1 and 2, the conditions used were sufficient to deprotect the blocked polyisocyanate crosslinking agent to provide a polyisocyanate, which was then able to react with the hydroxyl groups of the encapsulated pigment and the hydroxyl groups of the substrate. In this way, the cross-linking agent bound the pigment particles together and tethered the encapsulated pigment to the substrate. These cross-linking reactions do not happen for Inks 4 and 5, in which a binder resin is present instead of a cross-linking agent.

[0224] In order to objectively measure the handle / softness of the cured ink films, the handle / softness of the cured ink films and a test substrate having no ink thereon was assessed using a Tactile Sensation Analyser (TSA) from Emtec. Both the softness (micro-surface variations) and roughness (macro-surface variations) were tested for each cured ink film and the test substrate.

[0225] The cured ink films and test substrate were each loaded onto the measuring cell of the Tactile Sensation Analyser.

[0226] The Tactile Sensation Analyser then measured both the roughness of the film (TS750) and the softness of the film (TS7), by sound analysis.

[0227] In this regard, the measuring head is lowered to the sample film until the rotor is pressed at a pressure of 100 mN onto the sample film, which is fixed in the measuring cell. The rotor of the measuring head is fixed in a vertical direction but rotates over the sample at a speed of 10 cm / s causing the blades to rub the sample. The generated sound is recorded and processed by the software of the TSA to generate a sound spectrum of frequency (Hz) vs intensity of sound (RMS), which includes TS750 and TS7 peaks. The TS750 peak (which occurs between 0 to 2000 Hz) represents the roughness of the sample. The TS7 peak (which occurs at around 6500 Hz) represents the softness of the sample.

[0228] For roughness (macro-surface vibrations), as the blades pass overthe sample, the vertical vibration of the sample film varies according to the surface structure and roughness (macro-variations) of the sample film. This vertical vibration causes a sound, which is recorded by the microphone of the TSA and a TS750 peak is generated. The higher the TS750 peak, the louder the sound, the stronger the vibration and hence rougher surface. As such, a lower peak is preferred for smoothness.

[0229] For softness (micro-surface variations), as the blades pass overthe sample and scratch over fibres of the sample film, this causes vibration of the sample film and the paddles. If the fibres of the sample are hard, the paddles undergo strong vibrations after passing overthe fibres of the sample. If the fibres of the sample film are flexible, the paddles undergo less strong vibrations after passing over the fibres of the sample. The vibration again causes a sound, which is recorded by the microphone of the TSA and a TS7 peak is generated. The higher the TS7 peak, the harder the material. As such, a lower peak is preferred for softness.

[0230] The sound spectra for the cured ink films of inks 1 -2 and 4-5, as well as the test substrate, using the TSA are provided in Figure 1 .

[0231] As can be seen, the cured ink film of ink 1 of the invention has a much lower TS750 peak than that of comparative inks 2 and 4-5. The ink of the invention therefore provides the least rough macrohandle when printed onto treated cotton. It is particularly surprising that ink 1 of the invention provides improved smoothness when compared to comparative ink 2, as ink 1 of the invention has an increased amount of cross-linking agent when compared to ink 2. An increased amount of cross-linking agent is expected to increase the roughness of the sample.

[0232] The cured ink film of ink 1 of the invention has a slightly higher TS7 peak than that of the comparative inks and so provides the least soft micro-handle when printed onto treated cotton. It is surprising however that ink 1 of the invention provides comparable softness when compared to the comparative inks when ink 1 of the invention has an increased amount of cross-linking agent when compared to the comparative inks. An increased amount of cross-linking agent is expected to decrease the softness of the sample film.

[0233] Comparative ink 2 provides the lowest TS7 peak when compared to that of inks 1 and 4-5, and so has the softest micro-handle when printed onto treated cotton. It can thus be seen that the presence of the wax improves softness of the film sample. Without wishing to be bound by theory, the wax appears to contribute to the softness of the film by dampening the vibrations produced during the TSA measurement process for the TS7 peak.

[0234] As can be seen in Figure 1 , comparative inks 4 and 5, which do not contain a cross-linking agent and instead contain a binder, provide high TS750 and TS7 peaks, and thus have poor macrohandle (increased roughness) and poor micro-handle (reduced softness) when printed onto treated cotton. This can also be seen in the handle panel results of Test 4 discussed below, where binderbased inks were judged by 30 / 30 people as having poorer handle than cross-linker-based inks.

[0235] Thus, ink 1 of the invention provides an ink film having improved macro-handle (reduced roughness) when compared to that of the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact macro-handle. Ink 1 also has comparable softness when compared to the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact micro-handle. As shown in Test 4, it is expected that the micro-handle by TSA will improve further as the amount of crosslinking agent is decreased, whilst maintaining improved macro-handle.

[0236] The cured ink films for inks 1 , 2 and 5 were imaged using scanning electron microscope (Axia Chemie SEM) and the images can be seen in Figures 2-4 respectively. The magnification is provided on the images.

[0237] As can be seen from Figure 4, the fibres of the cured ink film having comparative ink 5 printed and cured thereon are stuck together. The fibres appear flat with large ink deposits stuck on top of the fibres, sticking the fibres together, creating an inflexible, rigid film. It is difficult to see gaps between the fibres. The ink is not absorbed into the fibres of the film. This visually shows that the ink film using comparative ink 4 has poor macro- and micro-handle. As can be seen from Figure 3, the fibres of the cured ink film having comparative ink 2 (which includes a comparative cross-linking agent but includes a wax) printed and cured thereon are not stuck together, as is the case for the fibres in Figure 4. There is a reduced amount of ink deposit on the outside of the fibres. The image appears three-dimensional and not flat. Without wishing to be bound by theory, the smooth nature of the fibres allows them to glide over each other, which provides improved micro-handle.

[0238] As can be seen from Figure 2, the fibres of the cured ink film having ink 1 of the invention printed and cured thereon have flexible connections between the fibres, creating a flexible film. There is again a reduced amount of ink deposit on the outside of the fibres when compared to Figure 4 as the ink absorbs into the fibres but has flexible connections between the fibres. Individual fibres can be easily discerned. Without wishing to be bound by theory, these flexible connections improve macro-handle.

[0239] The inventors have found that comparative ink 5 produces a rough surface and the ink does not penetrate into the fibres of the substrate. In contrast, ink 1 of the invention and comparative ink 2 penetrates into the fibres and does not have a rough surface when compared to a binder-based ink.

[0240] Test 2

[0241] Inks 1-4 were assessed for handle / softness.

[0242] Inks 1-4 were each printed single pass on an Integrity printer with a KJ4B Kyocera head at large drop size and 600 X 600 DPI onto untreated cotton (6978 from Premier Textiles).

[0243] The prints were placed in an oven at 70°C for 15 minutes, immediately after printing. They were then transferred to the hot press for two minutes at 170°C. The prints were cooled under ambient conditions to room temperature before application testing.

[0244] For Inks 1-3, the conditions used were sufficient to deprotect the blocked polyisocyanate crosslinking agent to provide a polyisocyanate, which was then able to react with the hydroxyl groups of the encapsulated pigment and the hydroxyl groups of the substrate. In this way, the cross-linking agent bound the pigment particles together and tethered the encapsulated pigment to the substrate. These cross-linking reactions do not happen for Ink 4, in which a binder resin is present instead of a cross-linking agent.

[0245] In order to objectively measure the handle / softness of the cured ink films, the handle / softness of the cured ink films and a test substrate having no ink thereon was assessed using a Tactile Sensation Analyser (TSA) from Emtec. Both the softness (micro-surface variations) and roughness (macro-surface variations) were tested for each cured ink film and the test substrate as detailed in Test 1 .

[0246] The sound spectra for the cured ink films of inks 1 -4, as well as the test substrate, using the TSA are provided in Figure 5.

[0247] As can be seen, the cured ink film of ink 1 of the invention has a much lower TS750 peak than that of comparative inks 2-4. The ink of the invention therefore provides the least rough macro-handle when printed onto untreated cotton. It is particularly surprising that ink 1 of the invention provides improved smoothness when compared to comparative inks 2 and 3, as ink 1 of the invention has an increased amount of cross-linking agent when compared to inks 2 and 3. An increased amount of cross-linking agent is expected to increase the roughness of the sample.

[0248] The cured ink film of ink 1 of the invention has a slightly higher TS7 peak than that of the comparative inks and so provides the least soft micro-handle when printed onto untreated cotton. It is surprising however that ink 1 of the invention provides comparable softness when compared to the comparative inks when ink 1 of the invention has an increased amount of cross-linking agent when compared to the comparative inks. An increased amount of cross-linking agent is expected to decrease the softness of the sample film.

[0249] Comparative ink 2 provides the lowest TS7 peak when compared to that of inks 1 and 3-4, and so has the softest micro-handle when printed onto untreated cotton. It can thus be seen that the presence of the wax improves softness of the film sample. Without wishing to be bound by theory, the wax appears to contribute to the softness of the film by dampening the vibrations produced during the TSA measurement process for the TS7 peak.

[0250] As can be seen in Figure 3, comparative ink 4, which does not contain a cross-linking agent and instead contains a binder, provides high TS750 and TS7 peaks, and thus has poor macro-handle (increased roughness) and poor micro-handle (reduced softness) when printed onto untreated cotton. This can also be seen in the handle panel results of Test 4 discussed below, where binderbased inks were judged by 30 / 30 people as having poorer handle than cross-linker-based inks.

[0251] Thus, ink 1 of the invention provides an ink film having improved macro-handle (reduced roughness) when compared to that of the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact macro-handle. Ink 1 also has comparable softness when compared to the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact micro-handle. As shown in Test 4, it is expected that the micro-handle by TSA will improve further as the amount of crosslinking agent is decreased. Test 3

[0252] Inks 1-2 and 4 were assessed for handle / softness.

[0253] Inks 1-2 and 4 were printed single pass on an Integrity printer with a KJ4B Kyocera head at large drop size and 600 X 600 DPI onto treated jersey (7026 from Premier textiles).

[0254] The prints were placed in an oven at 70°C for 15 minutes, immediately after printing. They were then transferred to the hot press for two minutes at 170°C. The prints were cooled under ambient conditions to room temperature before application testing.

[0255] For Inks 1 and 2, the conditions used were sufficient to deprotect the blocked polyisocyanate crosslinking agent to provide a polyisocyanate, which was then able to react with the hydroxyl groups of the encapsulated pigment and the hydroxyl groups of the substrate. In this way, the cross-linking agent bound the pigment particles together and tethered the encapsulated pigment to the substrate. These cross-linking reactions do not happen for Ink 4, in which a binder resin is present instead of a cross-linking agent.

[0256] In order to objectively measure the handle / softness of the cured ink films, the handle / softness of the cured ink films and a test substrate having no ink thereon was assessed using a Tactile Sensation Analyser (TSA) from Emtec. Both the softness (micro-surface variations) and roughness (macro-surface variations) were tested for each cured ink film and the test substrate as detailed in Test 1 .

[0257] The sound spectra for the cured ink films of inks 1 -2 and 4, as well as the test substrate, using the TSA are provided in Figure 6.

[0258] As can be seen, the cured ink film of ink 1 of the invention has a much lower TS750 peak than that of comparative inks 2 and 4. The ink of the invention therefore provides the least rough macrohandle when printed onto treated jersey. It is particularly surprising that ink 1 of the invention provides improved smoothness when compared to comparative ink, as ink 1 of the invention has an increased amount of cross-linking agent when compared to ink 2. An increased amount of cross-linking agent is expected to increase the roughness of the sample.

[0259] The cured ink film of ink 1 of the invention has a slightly higher TS7 peak than that of the comparative inks and so provides the least soft micro-handle when printed onto untreated cotton. It is surprising however that ink 1 of the invention provides comparable softness when compared to the comparative inks when ink 1 of the invention has an increased amount of cross-linking agent when compared to the comparative inks. An increased amount of cross-linking agent is expected to decrease the softness of the sample film. Comparative ink 2 provides the lowest TS7 peak when compared to that of inks 1 and 4, and so has the softest micro-handle when printed onto treated jersey. It is surprising that comparative ink 2 provides a lower TS7 peak when compared to that of comparative ink 3. In this regard, comparative ink 2 has much more cross-linking agent present, which typically decreases the softness. Comparative ink 2 has a wax present however and thus, it can be seen that the presence of the wax improves softness of the film sample. Without wishing to be bound by theory, the wax appears to contribute to the softness of the film by dampening the vibrations produced during the TSA measurement process for the TS7 peak.

[0260] As can be seen in Figure 6, comparative ink 4, which does not contain a cross-linking agent and instead contains a binder, provides high TS750 and TS7 peaks, and thus have poor macro-handle (increased roughness) and poor micro-handle (reduced softness) when printed onto untreated cotton. This can also be seen in the handle panel results of Test 4 discussed below, where binderbased inks were judged by 30 / 30 people as having poorer handle than cross-linker-based inks.

[0261] Thus, ink 1 of the invention provides an ink film having improved macro-handle (reduced roughness) when compared to that of the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact macro-handle. Ink 1 also has comparable softness when compared to the comparative inks, and this is despite the high amount of cross-linker present, which would be expected to negatively impact micro-handle. As shown in Test 4, it is expected that the micro-handle by TSA will improve further as the amount of crosslinking agent is decreased.

[0262] It is also useful to compare the TS750 peak difference (macro-handle peak difference) between the blank substrate and those of the individual inks (see Figures 1 , 5 and 6). As can be seen from Figures 1 , 5 and 6, ink 1 of the invention has the largest TS750 peak difference between an ink and that of the blank substrate for all three of the substrates. This means that ink 1 substantially softens the blank substrate from a macro-handle perspective, which can be regarded as a conditioning effect.

[0263] Test 4

[0264] Inks 5, 7 and 8 were assessed for handle / softness.

[0265] Inks 5, 7 and 8 were drawn down in 40 pm films using 40 pm wires wound K-bars onto transfer paper (cold-peel PET film suitable for water-based systems). The wetted transfer paper was pressed onto an untreated (Premier) cotton substrate. The inks were heated by placing the printed ink films in a pre-heated oven for 15 minutes at a temperature of 70°C. The draw down and heating steps were repeated a further time to form double layer draw-down. The inks were then heated (cured) in a hot-press either for one minute at 180°C (Ink 5), or three minutes at 170°C (Inks 7 and 8). The conditions used were dependent on the components of the ink but in each case, the conditions used were sufficient to fully dry / cure the ink.

[0266] For Inks 7 and 8, the conditions used were sufficient to deprotect the blocked isocyanate groups of the cross-linking agents, which were then able to react with the hydroxyl groups of the encapsulated pigment and the hydroxyl groups of the cotton substrate. In this way, the cross-linking agent bound the pigment particles together and tethered the encapsulated pigment to the substrate. These cross-linking reactions do not happen for Ink 5, in which a binder resin is present instead of a crosslinking agent.

[0267] Handle was assessed by performing a survey on a group of thirty people with basic textile handle training, referred to as the handle panel.

[0268] 26 / 30 people said that Ink 7 of the invention was the softest.

[0269] 26 / 30 people said that comparative Ink 8 was the second softest.

[0270] 30 / 30 people said that comparative Ink 5 was the least soft.

[0271] Accordingly, the handle test supports that the ink of the invention, which contains a cross-linking agent and an encapsulated pigment as claimed, produces softer cured ink films compared to inks containing comparative cross-linking agents or inks, which contain a binder resin and do not contain a cross-linking agent as claimed.

[0272] Test 5

[0273] Inks 1 , 5, 6 and 7 were assessed for wash-fastness. The inks were transferred to untreated cotton using the same transfer method, heating and curing conditions given in Test 4.

[0274] The cured ink films were then photographed.

[0275] Wash experiments (4 cycles) were performed on the prints in a rotawash (SDL Atlas) under ISO105 C06 C1 M conditions.

[0276] The prints were then photographed again after the 4 cycles.

[0277] The results are set out in Fig 7. Fig. 7 shows photographs taken for the prints of inks 1 , 5, 6 and 7, before and after the wash treatments. The small, detached section in the left-hand lower corner of each print is the washed part of the print and the rest of each print has been unwashed for comparison.

[0278] As can be seen, inks 1 and 7 of the invention, which contain a cross-linker of the invention (and no binder) have at least as good wash-fastness when compared to the comparative binder-based ink 5. Comparative Ink 6, which contains no binder or cross-linker has a much faded appearance postwash when compared to the other inks. Thus, the inclusion of a cross-linker of the invention improves wash-fastness.

[0279] The inventors have also found that the inks of the invention have improved crock results and thus good application results.

[0280] Test 6

[0281] Ink 11 was printed single pass using an Integrity printer with a SG1024 head (MA:400 X 400DPI) at large drop size onto three substrates: treated jersey (7026 from Premier textiles), treated and untreated cotton (6978T (treated) and 6978 (untreated) from Premier textiles).

[0282] The prints were placed in an oven at 70°C for 15 minutes, immediately after printing. They were then transferred to the hot press for two minutes at 170°C. The prints were cooled under ambient conditions to room temperature before application testing.

[0283] The conditions used were sufficient to deprotect the blocked polyisocyanate cross-linking agent to provide a polyisocyanate, which was then able to react with the hydroxyl groups of the encapsulated pigment and the hydroxyl groups of the substrate. In this way, the cross-linking agent bound the pigment particles together and tethered the encapsulated pigment to the substrate.

[0284] Ink 11 was assessed for wash and crock fastness.

[0285] Crock fastness was assessed using horizontal crock (ISO 105 X 12) and vertical crock (ISO 105 X 16) with visual greyscale assessment (ISO 105 A03).

[0286] Colour fastness to commercial and domestic laundering for Ink 11 was also measured with ISO 105-C06:2010 B1 M, which includes colour change and colour transfer with multi-staining fibre methodologies with visual assessment with greyscale standard ISO 105 A03.

[0287] The results are set out in Table 9. Table 9

[0288] For commercially viable wash and crock results, dry crock and wash fastness colour change are expected to be >4 and wet crock is expected to be > 2-3. Accordingly, Ink 11 of the invention is applicable in the apparel market.

Claims

Claims1 . An inkjet ink comprising: a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the crosslinking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the crosslinking agent, when deprotected, has a molecular weight of 600 to 2000.

2. An inkjet ink as claimed in claim 1 , wherein the dispersed encapsulated pigment consists of pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups.

3. An inkjet ink as claimed in claims 1 or 2, wherein the pendant hydrophilic groups further include carboxyl groups.

4. An inkjet ink as claimed in any preceding claim, wherein the non-ionic diol is selected from a polyether diol, a polyester diol, a polycarbonate diol, a polyesteramide diol, a polythioether diol, a polyacetal diol, a polyvinyl diol, a polysiloxane diol, and mixtures thereof.

5. An inkjet ink as claimed in any preceding claim, wherein the non-ionic diol is an alkoxylated diol.

6. An inkjet ink as claimed in claim 5, wherein the alkoxylated diol has the following formula:R1H2CO-(CH2CH2O)n-(CH2CHCH3O)m-R2wherein R1is a diol, R2is selected from methyl, ethyl, n-propyl, i-propyl, n-butyl and i-butyl, n is a number from 0 to 40, m is a number from 0 to 40 and n+m is a number from 20 to 80.

7. An inkjet ink as claimed in claim 6, wherein the alkoxylated diol has the following formula:wherein R2and R3are the same or different and are selected from methyl, ethyl, n-propyl, i-propyl, n-butyl and i-butyl, n is a number from 0 to 40, m is a number from 0 to 40 and n+m is a number from 20 to 80.

8. An inkjet ink as claimed in any preceding claim, wherein the cross-linking agent comprises two or more protected isocyanate groups obtainable by reacting an isocyanate having three or more isocyanate groups, an isocyanate blocking agent and a non-ionic diol.

9. An inkjet ink as claimed in claim 8, wherein the isocyanate is selected from: hexamethylene diisocyanate isocyanurate trimer; isocyanates obtainable by the reaction of a polyol having three to ten hydroxy groups and isocyanates selected from: hexamethylene diisocyanate isocyanurate trimer; 1 ,6-hexamethylenediisocyanate; 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl- cyclohexane; 4,4'-dicyclohexyl-methanediisocyanate; 2,4-toluenediisocyanate; 2,6- toluenediisocyanate; 4,4'-diphenyl-methanediisocyanate; meta-tetramethylxilylenediisocyanate; and mixtures thereof; and mixtures thereof.

10. An inkjet ink as claimed in claim 9, wherein the polyol is trimethylol propane.11 . An inkjet ink as claimed in claims 8 or 9, wherein the isocyanate is hexamethylene diisocyanate isocyanurate trimer.

12. An inkjet ink as claimed in claims 8 or 9, wherein the isocyanate is obtainable by the reaction of trimethylol propane and 2,4-toluenediisocyanate, 2,6-toluenediisocyanate and 1 ,6- hexamethylenediisocyanate.

13. An inkjet ink as claimed in any of claims 8 to 12, wherein the isocyanate blocking agent is selected from an active methylene, an oxime, an e-caprolactam, a lactam, a pyrazole, an imidazole, or mixtures thereof.

14. An inkjet ink as claimed in any preceding claim, wherein the dispersed encapsulated pigment is present in an amount of 0.2 to 20% by weight, based on the total weight of the ink.

15. An inkjet ink as claimed in any preceding claim, wherein the cross-linking agent is present in an amount of 5 to 20% by weight, preferably 13 to 17% by weight, based on the total weight of the ink.

16. An inkjet ink as claimed in any preceding claim, wherein the two or more protected reactive groups, when deprotected, are present in the ink in an amount of 0.01 to 1 .00%, preferably 0.50 to 1.00% by weight, based on the total weight of the ink.

17. An inkjet ink as claimed in any preceding claim, wherein water is present in a total amount of 30 to 80% by weight, based on the total weight of the ink.

18. An inkjet ink as claimed in any preceding claim, wherein the ink contains less than 3% by weight of a binder resin, based on the total weight of the ink.

19. A method of inkjet printing comprising the following steps in order:(i) providing an inkjet ink as claimed in any preceding claim;(ii) inkjet printing the inkjet ink onto a substrate to provide a printed substrate;(iii) drying the printed substrate to remove water; and(iv) deprotecting the two or more protected reactive groups.

20. A method of inkjet printing as claimed in claim 19, wherein the two or more protected reactive groups are reactive to hydroxyl groups when thermally deprotected, and wherein deprotecting the two or more protected reactive groups is by heating the printed substrate to a temperature sufficient to deprotect the two or more protected reactive groups.

21. A method of inkjet printing as claimed in claims 19 or 20, wherein the substrate is a textile substrate, and wherein the textile substrate is composed of a polymeric material having reactive groups which are available to react with the two or more protected reactive groups of the crosslinking agent, when deprotected, preferably wherein the textile substrate comprises a cellulosic material.

22. A method of inkjet printing as claimed in any one of claims 19 to 21 , wherein drying the printed substrate to remove water comprises heating the printed substrate to a temperature of less than 100°C.

23. A method of inkjet printing as claimed in any one of claims 19 to 22, wherein the temperature sufficient to deprotect the two or more protected reactive groups is 100°C or higher, preferably 120°C or higher, more preferably 135°C or higher.

24. A dispersion comprising:a continuous aqueous phase; a dispersed encapsulated pigment comprising pigment particles encapsulated by a cross-linked polymer having pendant hydrophilic groups including hydroxyl groups; and a cross-linking agent comprising two or more protected reactive groups, wherein the two or more protected reactive groups, when deprotected, are reactive to hydroxyl groups, wherein the crosslinking agent is obtainable by reacting: an oligomer having three or more reactive groups, wherein the three or more reactive groups are reactive to hydroxyl groups; a blocking agent, which is capable of blocking the three or more reactive groups; and a non-ionic diol; wherein the crosslinking agent, when deprotected, has a molecular weight of 600 to 2000.

25. A printed substrate having the inkjet ink as claimed in any one of claims 1 to 18 printed thereon.

26. A printed substrate obtainable by the method of any one of claims 19 to 23.

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