LIQUID SET FOR INK JET RECORDING

A liquid set for inkjet recording, includes (i) an aqueous treatment liquid including a polyurethane resin obtainable by reacting a polyester polyol, a diol containing a quaternary N-atom or tertiary amino group, and a polyisocyanate, wherein the quaternary N-atom or tertiary amino group is present in a side chain of the carbon chain linking the two hydroxyl groups of the diol, and the polyester polyol is obtained by reacting a polyol and an aromatic polycarboxylic acid; and (ii) an aqueous inkjet ink including a colorant. A method for inkjet printing includes using the liquid set.

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Description
CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application of PCT/EP2018/082764, filed Nov. 28, 2018. This application claims the benefit of European Application No. 17203985.1, filed Nov. 28, 2017, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid set comprising a treatment liquid comprising an aqueous polyurethane resin dispersion and an aqueous ink jet ink.

2. Description of the Related Art

In recent years, inkjet techniques have been increasingly utilized for industrial printing applications such as displays, posters, bulletin boards, packaging, textile, etc. In such applications durability such as light fastness, water resistance, and wear resistance are important requirements of the printed images and pigment based inks therefore have been developed.

Inks, such as solvent-based inkjet inks using an organic solvent as a vehicle, and ultraviolet curable inkjet inks including a polymerisable monomer as a main component have been used widely in industrial applications.

However, the solvent-based inkjet inks are not environmentally preferable because the solvent is evaporated in the atmosphere. The ultraviolet curable inkjet inks have limited application fields because they may have skin sensitizing properties depending on the monomer used and an expensive ultraviolet irradiation apparatus is required to be incorporated to the main body of a printer.

In view of such background, there have been developed pigment based aqueous inks for inkjet recording capable of being directly used for printing on porous and non-porous substrates and which give less environmental load. These inks are characterized by the presence of a resin which binds the pigments and prevents rubbing off the images from the substrate leading to an improved solvent and scratch resistance.

Usually, an ink-jet recording medium for aqueous ink jet inks includes a substrate such as paper, a plastic film or textile fabric and an ink-jet receiving layer provided thereon.

The layer is formed from an ink-jet receiving agent which mostly contains a water soluble resin such as polyvinyl alcohol, polyvinyl pyrrolidone and the like and any of various additives, in order to prevent bleeding and or ink coalescence caused by the water based ink or improve ink absorbing property. Problems are caused because bleeding and coalescence arises due to insufficient adsorption of the aqueous pigment ink into the ink-jet receiving layer.

Moreover, there is a problem that a printed image made by jetting aqueous ink jet inks has poor waterproof characteristics. The most popular method to improve the waterproof characteristics is a method wherein an ink-jet receiving agent is used which includes an aqueous cationic resin such as a poly(diallyldimethylammonium chloride) in addition to the aforementioned resin in the ink. Waterproof characteristics can be improved by fixing of the pigment of the aqueous ink due to the electrostatic bonding between an anionic group of the pigment in the ink and a cationic group of the water-soluble cationic resin. However, since the water-soluble cationic resin itself tends to be easily dissolved in water, the effect for improving waterproof characteristics was insufficient. Furthermore, these polymers do not crosslink with each other nor form a film, leading to poor physical properties of the printed image.

WO14042652 discloses a fixer fluid to be used for making an ink-receiving layer and comprising a liquid vehicle, a surfactant, and a cationic polymer. The cationic polymer can be selected from the group of quaternized polyamines, dicyandiamide polycations, diallyldimethyl ammonium chloride copolymers, quaternized dimethylaminoethyl(meth)acrylate polymers, quaternized vinylimidizol polymers, alkyl guanidine polymers, alkoxylated polyethylene imines.

JP2015163678A discloses an aqueous pigment composition for printing on a porous substrate such as textile which guarantees an improved washing fastness and rubbing resistance of the images on the fabric. The aqueous composition comprises pigment particles containing a urethane resin obtained by reacting polyester polyols with polyols comprising an ionic or non-ionic group and polyisocyanate.

US2009/0233065 discloses an ink jet pre-treatment liquid containing a cationic polyurethane. The cationic polyurethane is obtained by making use of a chain extending agent having a tertiary amino group, hence bringing a cationic group in the main chain of the resin. The resin assures a good adhesion of the resin to non-porous substrates. Storage stability of the pre-treatment liquid containing the cationic polyurethane is still to be improved.

US2008/0090949 discloses an ink-jet receiving agent including a cationic polyurethane resin aqueous dispersion. The resin provides excellent waterproof characteristics on a coating which is formed after removing water from the dispersion. The tertiary amino group containing polyol having secondary OH-groups will have limited reactivity, limiting the length of the polymer chains and hence reducing the physical properties of the resin such as adhesion, scratch resistance, and mechanical performance. Furthermore, the method of preparation of the cationic polyurethane as disclosed in US2008/0090949 is laborious, since first the tertiary amino group containing polyol needs to be prepared in advance. The incorporation of polyalkylene glycol units is limited into the main chain of the polyurethane, which will lead to inferior properties with respect to colloidal stability of the aqueous resin dispersion.

As described above, there is great need for the development of a treatment liquid of substrates for ink-jet printing with aqueous pigment inks and which can provide an ink-jet receiving layer which is excellent in printing quality (colour density increase, coalescence and bleeding decrease, fixing power) and which provides printed images showing excellent physical properties (adhesion, waterproof characteristics, solvent resistance and flexibility) and which can be produced via an efficient synthesis method.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a solution for the above stated problems. The object has been achieved by providing a liquid set as defined below and comprising a treatment liquid containing a polyurethane resin and an inkjet ink comprising a colorant.

According to another aspect, the present invention includes an inkjet recording method using the polyurethane resin as defined below. This method is also defined below.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. Specific embodiments of the invention are also defined below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Liquid Set for Inkjet Recording

The liquid set for inkjet recording according to the invention comprises an aqueous treatment liquid and an aqueous inkjet ink comprising a colorant.

A. 1. Aqueous Treatment Liquid

The aqueous treatment liquid from the liquid set according to the present invention contains a polyurethane resin as described in § A.1.1.1. and water. Additional components may be added to the treatment liquid are given below. The amount of polyurethane resin in the treatment liquid is equal to or lower than 30 wt. %.

A.1.1. Polyurethane Resin

The polyurethane resin incorporated in the treatment liquid of the liquid set of the present invention is characterised by the fact that the polyurethane resin comprises a cationic group in a side chain and a polyester. A polyalkylene oxide may also be present in a side chain of the polyester urethane backbone. Both the cationic group and the polyalkylene oxide increase the dispersibility and colloidal stability of the resin in water. The polyester urethane resin of the invention is obtainable by reacting a polyester polyol containing aromatic moieties with, a polyol containing a cationic group and a polyisocyanate.

A.1.1.1 Polyester Polyol

The polyester polyol used in the reaction of the invention, is obtained by reacting an aromatic polycarboxylic acid and a polyol.

The polyester polyol is a resin formed by an esterification reaction or transesterification reaction between at least one aromatic polycarboxylic acid component and at least one polyol component. Specific examples of the aromatic polycarboxylic acid include dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, 2,6-Naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid; tri- or higher -valent polybasic acids such as trimellitic acid and pyromellitic acid; and acid anhydrides thereof, for example, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride; and the like. As the aromatic polycarboxylic acid component, one or more dibasic acids selected from the dibasic acids mentioned above, lower alkyl ester compounds of these acids, and acid anhydrides are mainly used. If necessary, a monobasic acid such as benzoic acid, crotonic acid or p-t-butyl benzoic acid; a tri- or higher valent polycarboxylic acid such as trimellitic anhydride, methylcyclohexene tricarboxylic acid or pyromellitic anhydride; or the like can be further used in combination with the polycarboxylic acid component. It is preferred that the polyester is prepared using dicarboxylic acids which give linear polymer chains, in particular 1,4-terephtalic acid copolymers give a better performance regarding colloidal stability in aqueous medium, than phthalic acid anhydride copolymers. Besides terephthalic acids, one could use also other para- or linear substituted polycarboxylic acids to obtain the desired properties such as 2,6-naphthalenedicarboxylic acid or 1,5-naphthalenedicarboxylic acid.

The preferred carboxylic acid is an aromatic dicarboxylic acid such as terephthalic acid and isophthalic acid. The content of aromatic acids within the resin is equal to or higher than 30 mol % and preferably equal to or higher than 50 mol % with respect to the total amount of dicarboxylic acids or anhydrides. Treatment liquids comprising polyurethane resins obtained by reaction of polyesters polyols containing aromatic polycarboxylic acids do show an improved colloidal stability and lead to images with an improved solvent resistance and an improved dry and wet scratch resistance. The good results obtained with terephthalic acids and isophthalic acids has probably to do with obtaining a certain amount of crystallinity of the polyurethane resin or providing linear amorphous chains which contribute more to the desired physical properties such as scratch resistance and solvent resistance. Introducing phthalic acid anhydride or isophthalic acid in terephthalic acid based polyesters reduces the crystallinity or chain end-to-end distance and improves the solubility in organic solvents. For terephthalic acid based polyester polyols, it is preferred to use copolymers of terephthalic acid with isophthalic acid, more preferably having at least 20 mol % isophthalic acid. For the same reason polyester polyols with only phthalic acid anhydride are less preferred than copolymers where terephthalic acid is incorporated. Polyester polyols based on only phtalic acid anhydride could be very soluble in the polymerization solvent for the PU preparation, but a dried coating will have also a lower solvent resistance. Therefore, it is preferred that the aromatic polyester polyol contains between 20 and 80 mol % of terephthalate groups on the basis of the total amount of dicarboxylic acids (or acid anhydrides) in the polyester polyol.

Very suitable polyester polyols containing terephthalic ester units and isophthalic ester units in a ratio of 1:1 mol % are: Dynacoll 7150 supplied by Evonik, Marl, Germany, Vylon 220 from Toyobo, Osaka Japan and Elitel 1401 obtained from Unitika Ltd Dusseldorf Germany.

In order to obtain the desired properties of the polyester polyol and using a high content of terephthalic acid, one could use also a mixture of dicarboxylic acids. For example, to reduce the crystallinity one could use a mixture of terephthalic acid and adipic acid. Consequently, one could use also polyester polyols based on a mixture of aromatic polycarboxylic acids and aliphatic dicarboxylic acids such as adipic acid, succinic acid, methylcyclohexene tricarboxylic acid, fumaric acid and sebacic acid or anhydrides such as tetrahydrophthalic acid anhydride, hexahydrophtalic acid anhydride, maleic acid anhydride and succinic acid anhydride.

Polyester polyols with a high content of terephthalic acid could have a poor solubility in the preparation solvent (e.g. acetone) for the PU preparation or could have a too high degree of crystallinity in order to get good adhesive properties. In particular, this is the case when only non-branched diols are used for the polyester polyol, such as 1,2-ethylene glycol or 1,4-butane diol. When using terephthalic acid based polyester polyols with more than 35 mol % terephthalic acid, one can preferably use a mixture of different non-branched diols (e.g. a mixture of 1,2-ethylene glycol and 1,4-butane diol) or a mixture of a non-branched diol (e.g. ethylene glycol) with a branched diol (e.g. neopentyl glycol). When using mixtures of different diols for the polyester polyol, one could use high terephthalic acid contents, even up to 100 mol % based of the total dicarboxylic acid content.

Specific examples of the polyol component include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,4-hexanediol and 1,6-hexanediol; and tri- or higher-valent polyols such as glycerin, trimethylolethane, trimethylolpropane and pentaerythritol. For the polyol component, diols as mentioned above are mainly used, and if necessary, tri- or higher-valent polyols such as glycerin, trimethylolethane, trimethylolpropane and pentaerythritol can be further used in combination with the diols. Aromatic diols can also be used to increase the content of aromatic moieties in the polyester polyol. Suitable aromatic diols are: p-xylene glycol, 1,5-naphthalenedimethanol, 1,4-naphthalenedimethanol, 4,4′-bis(hydroxymethyl)biphenyl, bis(hydroxyethyl) terephthalate, bis(2-hydroxypropyl) terephthalate, 1,5-naphthalenedicarboxylic acid 1,5-bis(2-hydroxyethyl) ester, 4,4-bis(hydroxymethyl) diphenylmethane, 2,2-bis(4-β-hydroxyethoxyphenyl)propane (diethoxylated bisphenol A) and bis[p-(2-hydroxyethoxy)phenyl]methane.

Preferably diols with a Mw equal to or less than 400 are used together with the polyester polyol. These polyols can be used singly or as mixture of two or more kinds.

A.1.1.2. Diols Containing an Amino Group or Cationic Group

Examples of the cationic group in the polyurethane resin of the invention can be selected from protonated amines, protonated nitrogen containing heteroarmoatic compounds, quaternized tertiary amines, N-quaternized heteroaromatic compounds, sulfoniums and phosphoniums, quaternized tertiary amines and N-quaternized heteroaromatic compounds being more preferred.

The diol to be used for obtaining the polyurethane resin of the invention contains a quaternary N-atom or amino group, the quaternary N-atom or tertiary amino group being present in a side chain being present in the side chain of the carbon chain linking the two hydroxyl groups of the diol, hence not present in the carbon chain between the two hydroxyl groups of the diol.

Preferably a diol is used containing an amino group, preferably a tertiary amino group, ie a precursor for obtaining a cationic group after protonation using an acid, e.g. acetic acid. The amino group and more preferably the tertiary amino group is not present in the chain between the two hydroxygroups of the diol. Hence the amino group and more preferably the tertiary amino group or quaternary ammonium group is present in the side chain of the prepared polyurethane resin. After preparation of the polyurethane in a solvent like acetone, the amino group and preferably tertiary amino group is converted to a quaternary ammonium group by protonation with an acid, e.g. acetic acid. Subsequently water is added during a high shear treatment or stirring to obtain an aqueous dispersion. Subsequently the organic solvent (e.g. acetone) is removed by distillation under reduced pressure.

Examples of suitable diols having a N-atom in the side chain for introducing a cationic group in the resin are: 2-[(Dimethylamino)methyl]-1,3-propanediol, CAS Registry Number 69040-18-2, 2-Methyl-2-dimethylaminomethyl-1,3-propanediol, CAS Registry Number 36254-31-6, 2-Ethyl-2-dimethylaminomethyl-1,3-propanediol, CAS Registry Number 25941-41-7, 2-Diethylaminoethyl -2-methyl-1,3-propanediol, CAS Registry Number 29006-31-3 , 2-Diethylaminomethyl-2-ethyl-1,3-propanediol, CAS Registry Number 26102-95-4, 3-[methyl(phenylmethyl)amino]- 1,2-propanediol, CAS Registry Number 60278-98-0. Diols having a N-atom in the side chain have the advantage that the colloidal stabilisation of the produced polyurethane resin is further improved with respect to the diols having a N-atom in the main chain.

When using a tertiary amino group containing diol, the amino group is converted to a cationic group by protonation using an inorganic or organic acid. Examples of inorganic acids are hydrochloric acid, perchloric acid, sulphuric acid, hydrobromic acid, hydroiodic acid, phosphoric acid, nitric acid, boric acid, etc. Examples of organic acids include: acetic acid, formic acid, propionic acid, citric acid, oxalic acid, ascorbic acid, lactic acid, benzoic acid, toluene sulphonic acid, phenol, salicylic acid, acrylic acid, maleic acid, itaconic acid, stearic acid, glutamic acid, sulfoethyl methacrylate, carboxyethyl acrylate 2-acrylamido-2-methyl-1-propanesulfonic acid, monoacryloyloxyethyl hexahydrophthalate, methacryloyloxyethyl succinate, acryloyloxyethyl succinate or other organic compounds with an acidic proton such as sulphonamides or thiols.

Other examples of quaternary amines are [p-(2,3-Dihydroxypropoxy)phenyl]trimethylammonium bromide=CAS regsiry number 109732-00-5, [m-(2,3-Dihydroxypropoxy)phenyl] trimethylammonium bromide=CAS registry number 109731-98-8, [2-[p-(2,3-Dihydroxypropoxy)phenoxy] ethyl]trimethylammonium iodide =CAS registry number 110056-43-4 and quarternary amino diols having the quarternary amino group in the side chain, e.g. 2,3-Dihydroxy -N,N,N-trimethyl-1-propanaminium=CAS registry number 44814-66-6.

In a further preferred embodiment, the diol having an amino group 3-(Dimethylamino)-1,2-propanediol.

A.1.1.3. Polyether Diol

The polyether diol which can be used in the present invention can be obtained by addition polymerization of an alkylene oxide with at least one compound having two or more active hydrogen atoms. Examples of this compound include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolethane and ethylolpropane. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin and tetrahydrofuran. Preferred polyether diols are compounds according to Formula 1.

wherein R1 is methyl or ethyl, R2 is H or C1-C4 alkyl and n represents an integer from 5 to 50, more preferably from 10 to 40 and most preferably from 15 to 30.

The polyether diol which can be preferably used in the present invention, is Ymer N120 or Tegomer D 3403, i.e. α-[2,2-bis (hydroxymethyl)butyl]-ω-methoxy-Poly(oxy-1,2-ethanediyl). These diols can be prepared from trimethylol propane oxetane (TMPO). A possible synthesis procedure is described by Fock, J.; Möhring, V., Polyether-1,2- and -1,3-diols as macromonomers for the synthesis of graft copolymers, 1. Synthesis and characterization of the macromonomers. Die Makromolekulare Chemie 1990, 191 (12), 3045-3057.

In general also other polyether 1,2- or 1,3-diols can be used. For a good stability the polyether graft needs to be well water soluble in order to give a good steric stabilisation. In the case of Ymer N120 the polyether is only composed of ethylene oxide segments, but this can also be a copolymer of different alkylene oxides. Furthermore in the current macro-monomer diol the end group is a methoxy group, this end group can also be other end groups such as a hydrophilic end group (such as anionic groups, e.g. carboxylic, sulphate, phosphate, etc. or cationic groups, e.g. quaternary amine groups or precursors for cationic groups e.g. tertiary amino groups) in order to have also electro-steric stabilisation. The content of the polyether diol in the polyurethane resin is preferably 30 wt. % or less, but more than 1 wt. % with respect to the total solid weight of the polyurethane resin, more preferably the polyether diol content is equal to or less than 15 wt. % and more than 2 wt. % with respect to the polyurethane resin. A content of the polyether diol of less than 30 wt. %, but more than 1 wt. % with respect to the polyurethane resin, has an additional improvement in scratch resistance and solvent resistance of the jetted and dried image with respect to polyether diol content outside this range. Too high polyether diol content (more than 30 wt %) would lead to a too high water solubility and lower glass transition temperature.

A.1.1.4. Polyisocyanates

Specific examples of the organic polyisocyanate compound that is reacted with the polyester polyol include aliphatic diisocyanates such as lysine diisocyanate, hexamethylene diisocyanate and trimethylhexane diisocyanate; cyclic aliphatic diisocyanates such as hydrogenated xylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2, 4 (or 2,6)-diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate) and 1,3-(isocyanatomethyl)cyclohexane; aromatic diisocyanates such as tolylene diisocyanate, xylene diisocyanate and diphenylmethane diisocyanate; organic polyisocyanates themselves, including tri- or higher-valent polyisocyanates such as lysine triisocyanate; adducts each composed of such an organic polyisocyanate with a polyhydric alcohol, a low molecular weight polyester resin or hydrogen; and cyclised polymers (for example, isocyanurate), biuret type adducts and the like, each formed from various diisocyanate compounds mentioned above.

It is preferable, from the viewpoint of storage stability of the treatment liquid composition, that the organic polyisocyanate compound according to the invention include at least one selected from non-yellowing type polyisocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate and lysine diisocyanate, and it is more preferable that the organic polyisocyanate compound include at least isophorone diisocyanate.

Furthermore, the organic polyisocyanate compounds can be used singly alone or as mixtures of two or more kinds.

A.1.1.5. Reaction Conditions

With regard to the conditions for the reaction between the polyester polyol, the polyol containing a cationic group and the organic polyisocyanate compound, those conventionally used reaction conditions can be used without particular limitation.

Besides the preferred terephthalate containing polyester polyols also a mixture of different polymeric polyols can be used to adjust the physical properties, adhesion, mechanical performance, etc. Examples are e.g. polycarbonate polyols, polyether polyols, polyacrylate polyols, aliphatic polyester polyols, polyolefin polyols or other polymeric polyols. Examples of polycarbonate polyols are e.g. Oxymer C112, Oxymer M112 (available via Perstorp), Kuraray polyol C-2050, C-2090, C-1090 (available from Kuraray), Converge HMA-1 and Converge HMA-1 (available from Novomer Inc.), Duranol T6002, T6001, T5652, T5651, T5650J, T4672, T4671, T4692 and T4691 (available from Asahi kasei). Additional aliphatic polyester polyols, are e.g. regular (semi)crystalline or amorphous grades, e.g. based on hexane diol adipates (e.g. Dynacoll 7372 from Evonik) but also polyester polyols based on natural products such as polyester polyols made by using dimer acid or dimer diols (e.g. trade name Priplast from Croda), examples are Priplast 3192 and Priplast 1838. The raw material used to prepare certain Priplast grades, i.e. dimer diols with trade name Pripol can also be used as monomer in the PU synthesis to modify the physical properties and adhesive properties.

In the reaction between the polyester polyol and the organic polyisocyanate compound, if necessary, a diol with Mw equal to or less than 400 can be used. Examples of suitable diols are: ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,4-hexanediol and 1,6-hexanediol; and tri- or higher-valent polyols such as glycerin, trimethylolethane, trimethylolpropane and pentaerythritol. 1,4-butane diol is most preferred.

In the polyurethane synthesis different high molar mass polyols and low molecular weight diols can be reacted, besides the polyether diols used for stabilization of the polyurethane dispersion. In the procedure used, the stabilizing polyols and the polyester polyol (Mw>400 g/mol) are reacted with in excess of isocyanate. This enables a good conversion of the reaction. Depending on the molecular weight and the copolymer composition, the polyester polyol, may have a poor solubility in the reaction solvent (e.g. acetone). Also the polyol with the anionic group has a poor solubility in acetone. After reacting using an excess of isocyanate, the excess is compensated to a NCO/OH molar ratio by addition of a low molecular weight diol, which would lead to a polyurethane resin with very low amount of residual isocyanate. In case some residual isocyanate is present some urea bonds could be formed. Examples of suitable diols are given above.

So in the reaction conditions used a pre-condensation step with NCO/OH-ratio>1 and a chain extension step at NCO/OH-ratio =1.0 can be distinguished. Instead of using a 2-step process, one could use also a one-step or semi-continuous process. In the 2-step process, when using a high NCO/OH ratio more low molar mass diol (chain extender) is added and the weight ratio of the polyester polyol is reduced. In order to obtain the desired properties, the amount of polyester polyol as compared to low molar mass diols should be considerably higher, i.e. at least 50 wt. %. Surprisingly it was found that upon using high NCO/OH ratios in the pre-condensation step this resulted into polyurethane dispersions with poorer colloidal stability because of more coarse particles leading to an ink jet ink having poorer filterability. Reacting at a higher NCO/OH ratio in the pre-condensation step will lead also to a higher content of urethane units, which are able to form hydrogen bonds. When keeping the type of polyester polyol constant and also the chain extender, reacting at an NCO/OH ratio more close to NCO/OH=1.0, leads to better colloidal stability and better filtration properties of the formulated ink jet ink. Consequently when the NCO/OH ratio and the amount of urethane bonds play an important role, also the molecular weight of the polyester polyol and the low molar mass diol plays a role. In the most examples only one polyester polyol is used and only one low molar mass diol. When using mixtures of diols one can easily calculate the number average molecular weight which will affect the NCO/OH ratio.

Examples of the organic solvent used for the reaction between the polyester polyol, the polyether diol, the polyol comprising a cationic group and the organic polyisocyanate compound, here include ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, acetates such as ethyl acetate and butyl acetate, nitriles such as acetonitrile, and amides such as dimethyl formamide, N-methylpyrrolidone and N-ethylpyrrolidone. These may be used singly or in combinations of two or more.

Using higher molecular weight polyols than Ymer120N will give more phase separation, providing a better water dispersibility. However, for the making of the polyurethane resin, it is more difficult to dissolve these polyols in de organic solvent, e.g. acetone. This can be overcome by using a co-solvent during the polycondensation reaction. A preferred co-solvent is 2-pyrolidon or N-methylpyrrolidone, more preferably 2-pyrolidon.

The treatment liquid composition of the invention contains the polyurethane resin as an essential component. Therefore, the polyurethane resin is preferably dispersed in water to obtain an aqueous dispersion of the polyurethane resin. Every dispersing technology suitable for preparing an aqueous dispersion may be used.

A.1.2. Water Soluble Organic Solvent

The treatment liquid of the invention may contain, besides water as a solvent, also a water-soluble organic solvent. Examples of water-soluble organic solvents include polyhydric alcohols such as diethylene glycol, triethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1, 3-propanediol, 2-methyl-1, 3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 1,5-pentanediol 1,6-hexanediol, 2-ethyl-1, 3-hexanediol, 1,2-hexanediol and 2,5-hexanediol, polyhydric alcohol alkyl ethers such as dipropylene glycol n-propyl ether, tripropylene glycol methyl ether, tripropylene glycol n-propyl ether, propylene glycol phenyl ether, triethylene glycol methyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, diethylene glycol n-hexyl ether and ethylene glycol phenyl ether, and nitrogen-containing heterocyclic compounds such as 2-pyrrolidone and N-methylpyrrolidone.

Other preferred water soluble organic solvents include ethylene glycol, propylene glycol, 1,2-butanediol, 2,3-butanediol, 2-methyl-2, 4-pentanediol, dipropylene glycol monomethyl ether, propylene glycol n-butyl ether, propylene glycol t-butyl ether, diethylene glycol methyl ether, ethylene glycol n-propyl ether and ethylene glycol n-butyl ether.

The content of the water-soluble organic solvent, in the aqueous ink jet ink is preferably less than 70 wt. %. If the content exceeds 70% by mass, the ink loses its water based, hence more green character.

A.1.3. Surfactant

In the treatment liquid of the present invention, a surfactant may be added in order to ensure wettability onto the substrate. The amount of the surfactant added is preferably 0.1 wt. % to 5 wt. % as an active component in the ink.

If the amount added is below 0.1% by mass, wettability onto the substrate is not sufficient and causes degradation in image quality and in adhesion to the substrate. The surfactant that can be used is not particularly limited as long as it satisfies the above limitation.

While any of an amphoteric surfactant, a non-ionic surfactant, or a cationic surfactant can be used, non-ionic surfactants such as polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkyl amide, a polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester and an ethylene oxide adduct of acetylene alcohol are preferably used in terms of a relationship between dispersing stability and image quality. In addition, a fluorine-based surfactant and a silicon-based surfactant can be used in combination (or singly) depending on formulation.

Suitable surfactants are siloxane based surfactants such as Tego Twin 4000 from Evonik Industries, Tegowet 270 from Evonik industries, Hydropalat WE3220 from BASF, silane based surfactants such as Silwet HS312 from Momentive and fluor containing surfactants such as: Thetawet FS8150 from Neochem GMBH, Capstone FS3100 from Dupont, Tivida FL2500 from Merck and surfactants from the Dynol, Envirogem & Surfynol series from Air products.

A.1.4. Additives

Together with the polyurethane resin, a multivalent metal ion can be contained in the treatment liquid. Suitable examples are water-soluble metal salts formed from bi- or higher valent metal cations, such as magnesium, calcium, strontium, barium, zirconium, and aluminum, and anions, such as a fluoride ion (F−), a chloride ion (Cl−), a bromide ion (Br−) , a sulfate ion (SO42−, a nitrate ion (NO3−, and an acetate ion (CH3COO−).

These polyvalent metal ions have a function of aggregating ink by acting on anionic groups such as the carboxyl groups on the surface of the pigment or the dispersed polymer of capsules contained in the ink. As a result, the ink remains on the surface of the substrate to improve the colour-developing property. Therefore, it is preferred that the surface of the pigment in the ink and/or the dispersed polymer of the capsules contained in the ink have an anionic group selected from the group of carboxyl group, sulfonate group and phosphonate group, most preferably carboxyl group.

The treatment liquid may also contain organic acids. Preferred examples of the organic acids include, but are not limited to acetic acid, propionic acid, and lactic acid.

The treatment liquid may also contain colorants, such as pigments. Particularly useful for printing on dark substrates is a treatment liquid containing a white pigment. The preferred pigment for the aqueous treatment liquid ink is titanium dioxide. Titanium dioxide (TIO2) pigment useful in the present invention may be in the rutile or anatase crystalline form. Processes for making TiO2 are described in greater detail in “The Pigment Handbook”, Vol. I, 2nd Ed., John Wiley & Sons, N.Y. (1988), the relevant disclosure of which is incorporated by reference herein for all purposes as if fully setforth.

The titanium dioxide particles can have a wide variety of average particle sizes of about 1 micron or less, depending on the desired end use application of the treatment liquid. For applications demanding high hiding or decorative printing applications, the titanium dioxide particles preferably have an average size of less than about I μm. Preferably, the particles have an average size of from about 50 to about 950 nm, more preferably from about 75 to about 750 nm, and still more preferably from about 100 to about 500 nm.

In addition, unique advantages may be realized with multiple particle sizes, such as opaqueness and UV protection. These multiple sizes can be achieved by adding both a pigmentary and a nano grade of TIO2.

The titanium dioxide pigment may also bear one or more metal oxide surface coatings. These coatings may be applied using techniques known by those skilled in the art. Examples of metal oxide coatings include silica, alumina, aluminasilica, boria and zirconia, among others. These coatings can provide improved properties including reducing the photoreactivity of the titanium dioxide. Metal oxide coatings of alumina, aluminasilica, boria and zirconia result in a positive charged surface of the TiO2 pigments and hence are particularly useful in combination with the cationic stabilised capsules of the invention because no additional surface treatment of the pigment is required.

Commercial examples of such coated titanium dioxides include R700 (alumina-coated, available from E. I. DuPont deNemours, Wilmington Del.), RDI-S (alumina-coated, available from Kemira Industrial Chemicals, Helsinki, Finland), R706 (available from DuPont, Wilmington Del.) and W-6042 (a silica alumina treated nano grade titanium dioxide from Tayco Corporation, Osaka Japan). Other suitable white pigments are given by Table 2 in [0116] of WO 2008/074548. The white pigment is preferably a pigment with a refractive index greater than 1.60. The white pigments may be employed singly or in combination. Preferably titanium dioxide is used as pigment with a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in [0117] and in [0118] of WO 2008/074548.

A.2. Ink Jet Ink Composition

The liquid set according to the invention further comprises an aqueous inkjet ink comprising a colorant.

A.2.1. Solvent

The aqueous medium of the ink contains water, but may preferably include one or more water-soluble organic solvents. The one or more organic solvents may be added for a variety of reasons. For example, it can be advantageous to add a small amount of an organic solvent to improve the dissolution of a compound in the inkjet ink to be prepared. Preferable water-soluble organic solvents are polyols (e.g., ethylene glycol, glycerin, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butyleneglycol, 1 ,6-hexanediol, 1 ,2-hexanediol, 1 ,5-pentanediol, 1,2-pentanediol, 2,2-dimethyl-1 ,3-prapanediol, 2-methyl-2,4-pentanediol, 3-methyl-1 ,5-pentanediol, 3-methyl-1 ,3-butanediol, and 2-methyl-1 ,3-propanediol), amines (e.g., ethanolamine, and 2-(dimethylamino) ethanol), monohydric alcohols (e.g., methanol, ethanol, and butanol), alkyl ethers of polyhydric alcohols (e.g., diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether), 2,2′-thiodiethanol, amides (e.g., N,N-dimethylformamide), heterocycles (e.g., 2-pyrrolidone and N-methyl-2-pyrrolidone), and acetonitrile.

A.2.2. Colorants

The colorants which can be included in the ink jet ink can be dyes or pigments.

The pigments may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. A colour pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley- VCH, 2004. ISBN 3527305769.

Suitable pigments for use in the ink jet ink of the invention are disclosed in paragraphs [0128] to [0138] of WO 2008/074548. The pigment particles are dispersed in an aqueous medium using a polymeric dispersant, a (anionic) surfactant, but preferably a self-dispersible pigment is used. The latter prevents interaction of the polymeric dispersant with the dispersing groups of resin particles of the invention which may be included in the inkjet ink (see below), since dispersion stability of the pigment is accomplished by the same technique of electrostatic stabilization as employed for the resin particles.

A self-dispersible pigment is a pigment having on its surface covalently bonded anionic hydrophilic groups, such as salt-forming groups or the same groups used as dispersing groups for the resin particles, that allow the pigment to be dispersed in an aqueous medium without using a surfactant or a resin.

The technology for making self-dispersible pigments is well-known. For example, EP1220879A discloses pigments having attached a) at least one steric group and b) at least one organic ionic group and at least one amphiphilic counterion, wherein the amphiphilic counterion has a charge opposite to that of the organic ionic group that are suitable for inkjet inks. Also EP906371A discloses suitable surface-modified coloured pigment having attached hydrophilic organic groups containing one or more ionic groups or ionizable groups. Suitable commercially available self-dispersible colour pigments are, for example, the CAB-O-JET™ inkjet colorants from CABOT.

Pigment particles in inkjet inks should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum colour strength and to slow down sedimentation.

The average pigment particle size is preferably between 0.050 and 1 μm, more preferably between 0.070 and 0.300 μm and particularly preferably between 0.080 and 0.200 μm. Most preferably, the numeric average pigment particle size is no larger than 0.150 μm. The average particle size of pigment particles is determined with a Brookhaven Instruments Particle Sizer BI90plus based upon the principle of dynamic light scattering. The ink is diluted with ethyl acetate to a pigment concentration of 0.002 wt %. The measurement settings of the BI90plus are: 5 runs at 23° C., angle of 90° , wavelength of 635 nm and graphics=correction function.

However, for white pigment inkjet inks, the numeric average particle diameter of the white pigment is from about 50 to about 950 nm, more preferably from about 75 to about 750 nm, and still more preferably from about 100 to about 500 nm.

Suitable white pigments are given by Table 2 in [0116] of WO 2008/074548. The white pigment is preferably a pigment with a refractive index greater than 1.60. The white pigments may be employed singly or in combination. Preferably titanium dioxide is used as pigment with a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in [0117] and in [0118] of WO 2008/074548. Also special colorants may be used, such as fluorescent pigments for special effects in clothing, and metallic pigments for printing a luxury look of silver and gold colours on textiles.

Suitable polymeric dispersants for the pigments are copolymers of two monomers but they may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers and their distribution in the polymer. Copolymeric dispersants preferably have the following polymer compositions:

statistically polymerized monomers (e.g. monomers A and B polymerized into ABBAABAB);

alternating polymerized monomers (e.g. monomers A and B polymerized into ABABABAB);

gradient (tapered) polymerized monomers (e.g. monomers A and B polymerized into AAABAABBABBB);

block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB) wherein the block length of each of the blocks (2, 3, 4, 5 or even more) is important for the dispersion capability of the polymeric dispersant;

graft copolymers (graft copolymers consist of a polymeric backbone with polymeric side chains attached to the backbone); and

mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable dispersants are DISPERBYK™ dispersants available from BYK CHEMIE, JONCRYL™ dispersants available from JOHNSON POLYMERS and SOLSPERSE™ dispersants available from ZENECA. A detailed list of non-polymeric as well as some polymeric dispersants is disclosed by MC CUTCHEON. Functional Materials, North American Edition. Glen Rock, N.J.: Manufacturing Confectioner Publishing Co., 1990. p.110-129.

The polymeric dispersant has preferably a number average molecular weight Mn between 500 and 30000, more preferably between 1500 and 10000.The polymeric dispersant has preferably a weight average molecular weight Mw smaller than 100,000, more preferably smaller than 50,000 and most preferably smaller than 30,000.

The pigments are preferably present in the range of 0.01 to 20%, more preferably in the range of 0.05 to 10% by weight and most preferably in the range of 0.1 to 5% by weight, each based on the total weight of the inkjet ink. For white inkjet inks, the white pigment is preferably present in an amount of 3% to 40% by weight of the inkjet ink, and more preferably 5% to 35%. An amount of less than 3% by weight cannot achieve sufficient covering power.

A.2.3. Resin

The ink jet ink composition according to the invention may further comprise an additional resin. The resin is often added to the ink jet ink formulation to achieve a good adhesion of the pigment to the substrate such as the fibres of the textile fabric. The resin is a polymer and suitable resins can be acrylic based resins, a urethane-modified polyester resin or a polyethylene wax, more preferably a urethane-modified polyester resin.

The polyurethane resin is to be incorporated in the ink formulation as a dispersion and may be selected from the group consisting of aliphatic polyurethane dispersions, aromatic polyurethane dispersions, anionic polyurethane dispersions, non-ionic polyurethane dispersions, aliphatic polyester polyurethane dispersions, aliphatic polycarbonate polyurethane dispersions, aliphatic acrylic modified polyurethane dispersions, aromatic polyester polyurethane dispersions, aromatic polycarbonate polyurethane dispersions, aromatic acrylic modified polyurethane dispersions, for example, or a combination of two or more of the above.

A preferred urethane resin to be used as dispersion in the ink of the invention is a polyester resin including a structural unit containing a urethane bond. Among such resins, a water-soluble or water-dispersible urethane-modified polyester resin is preferred. It is preferable that the urethane-modified polyester resin include at least one structural unit derived from a hydroxyl group-containing polyester resin (polyester polyol) and at least one structural unit derived from an organic polyisocyanate.

Furthermore, the hydroxyl group-containing polyester resin is a resin formed by an esterification reaction or transesterification reaction between at least one polybasic acid component and at least one polyhydric alcohol component.

A preferred polyurethane resin to be included in the ink of the invention is a polyurethane resin obtainable by reacting a polyester polyol, a polyether diol, a polyol containing an anionic group and a polyisocyanate. A particular preferred polyurethane resin is a polyurethane resin obtainable by reacting a polyester polyol, a polyether diol, a polyol containing an anionic group and a polyisocyanate, and wherein the polyester polyol is obtained by reacting an aromatic polycarboxylic acid and a polyol. Examples of suitable polyurethane resins and their preparations are disclosed in the unpublished patent application EP16196224.6.

Some examples of suitable polyurethane dispersions are NEOREZ R-989, NEOREZ R-2005, and NEOREZ R-4000 (DSM NeoResins); BAYHYDROL UH 2606, BAYHYDROL UH XP 2719, BAYHYDROL UH XP 2648, and BAYHYDROL UA XP 2631 (Bayer Material Science); DAOTAN VTW 1262/35WA, DAOTAN VTW 1265/36WA, DAOTAN VTW 1267/36WA, DAOTAN VTW 6421/42WA, DAOTAN VTW 6462/36WA (Cytec Engineered Materials Inc., Anaheim Calif.); and SANCURE 2715, SANCURE 20041, SANCURE 2725 (Lubrizol Corporation), for example, or a combination of two or more of the above.

Acrylic based resins include polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers of the aforementioned monomers with other monomers. These resins are present as a suspension of particles having an average diameter of about 30 nm to about 300 nm. The acrylic latex polymer is formed from acrylic monomers or methacrylic monomer residues. Examples of monomers of the acrylic latex polymer include, by way of illustration, acrylic monomers, such as, for example, acrylate esters, acrylamides, and acrylic acids, and methacrylic monomers, such as, for example, methacrylate esters, methacrylamides, and methacrylic acids. The acrylic latex polymer may be a homopolymer or copolymer of an acrylic monomer and another monomer such as, for example, a vinyl aromatic monomer including, but not limited to, styrene, styrene butadiene, p-chloromethylstyrene, divinyl benzene, vinyl naphthalene and divinylnaphthalene.

Some examples of suitable acrylic latex polymer suspensions are, JONCRYL 537 and JONCRYL 538 (BASF Corporation, Port ArthurTX); CARBOSET GA-2111, CARBOSET CR-728, CARBOSET CR-785, CARBOSET CR-761, CARBOSET CR-763, CARBOSET CR-765, CARBOSET CR-715, and CARBOSET GA-4028 (Lubrizol Corporation); NEOCRYL A-1110, NEOCRYL A-1131, NEOCRYL A-2091, NEOCRYL A-1127, NEOCRYL XK-96, and NEOCRYL XK-14 (DSM); and BAYHYDROL AH XP 2754, BAYHYDROL AH XP 2741, BAYHYDROL A 2427, and BAYHYDROL A2651 (Bayer), for example, or a combination of two or more of the above.

The concentration of the resin in the ink jet ink according to the invention is at least 1 wt. % and preferably lower than 30 wt. %, more preferably lower than 20 wt. %.

A.2.4. Additives

The aqueous inkjet ink may further comprise a surfactant, a humectant, a biocide, a film-forming agent and a thickener as an additive.

Humectants are preferably incorporated in the inkjet ink to prevent the clogging of nozzles. The prevention is due to its ability to slow down the evaporation rate of the solvents, especially of the water in the ink. The humectant is preferably an organic solvent having a higher boiling point than water. Suitable humectants include triacetin, N-methyl-2-pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl urea, alkyl thiourea, dialkyl urea and dialkyl thiourea, diols, including ethanediols, propanediols, propanetriols, butanediols, pentanediols, and hexanediols; glycols, including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, tetraethylene glycol, and mixtures and derivatives thereof. A preferred humectant is glycerol. The humectant is preferably added to the liquid formulation in an amount of 0.1 to 20 wt. % based on the total weight of the liquid.

Any known surfactant may be used in the inkjet ink of the invention. Preferably a glycol surfactant and/or an acetylene alcohol surfactant can be used. The use of the acetylene glycol surfactant and/or the acetylene alcohol surfactant further reduces bleeding to improve printing quality, and also improves the drying property in printing to allow high-speed printing. The acetylene glycol surfactant and/or the acetylene alcohol surfactant is preferably one or more selected from 2, 4, 7, 9-tetramethyl-5-decine-4, 7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4, 7-diol, 2,4-dimethyl-5-decin-4-ol, and alkylene oxide adducts of 2,4-dimethyl-5-decin -4-ol. These are available, for example, from Air Products (GB) as Olfine (registered trademark) 104 series and E series, such as Olfine E1 010, or from Nissin Chemical Industry as Surfynol (registered trademark) 465 and Surfynol 61.

A biocide may be added to the ink to prevent unwanted microbial growth, which may occur in the liquid. The biocide may be used either singly or in combination. Suitable biocides for the ink-jet ink of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1-oxide, ethyl p-hydroxybenzoate and 1,2-benzisothiazolin -3-one and salts thereof. Preferred biocides are Proxel™ GXL and Proxel™ Ultra 5 available from ARCH UK BIOCIDES and Bronidox™ available from COGNIS.

A biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt. %, more preferably 0.01 to 1.0 wt. %, each based on the ink liquid.

The inkjet ink may further comprise at least one thickener for viscosity regulation in the liquid. Suitable thickeners include urea or urea derivatives, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, derived chitin, derived starch, carrageenan, pullulan, proteins, poly(styrenesulphonic acid), poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamid, partially hydrolyzed polyacrylamid, poly(acrylic acid), poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate), poly(hydroxyethyl acrylate), poly(methyl vinyl ether), polyvinylpyrrolidone, poly(2-vinylpyridine), poly(4-vinylpyridine) and poly(diallyldimethylammonium chloride).

The thickener is added preferably in an amount of 0.01 to 20 wt. %, more preferably 0.1 to 10 wt. % based on the ink.

B. Inkjet Recording Method B.1. Application Method of the Treatment Liquid

The treatment liquid according to the present invention is suitable for treating different substrates, porous and non-porous ones. Porous substrates include paper, card board, white lined chipboard, corrugated board, packaging board, wood, ceramics, stone, leather and textile. Non-porous substrates include metal, glass, polypropylene, polyvinylchloride, PET, PMMA, polycarbonate, polyamide, polystyrene or co-polymers thereof. The treatment liquid according to the present invention is also suitable for treating jetted images, commonly known as post treatment fluid.

All well-known conventional methods can be used for coating or impregnating the treatment liquid on a substrate or on an image formed by jetting an aqueous inkjet ink. Examples of the method include air knife coating, blade coating, roll coating, gravure coating. After applying the treatment liquid onto a substrate, the coating is preferably dried before printing the image onto the treated substrate.

The treatment liquid is particularly suitable for treating porous substrates, before or after printing images with inkjet printing.

The treatment liquid is also suitable for treating textile fabrics. The textile fabric used is made of one type of fibre or blended fibre of two or more selected from the group consisting of cotton, hemp, rayon fibre, acetate fibre, silk, nylon fibre, and polyester fibre. The fabric may be in any form, for example, a woven, knitted, or nonwoven form of the above-mentioned fibres. The treatment liquid containing the polyurethane resin according to the invention can be preferably applied to the fabric by spraying, coating, padding or pad printing.

Alternatively, the treatment liquid may also be applied to the substrate using an ink jet head or valve jet head. This means of applying the treatment liquid, which is according to an image, has the advantage that the amount of required treatment liquid is substantially lower than with the other application methods. By means of a jetting head, it is possible to apply treatment liquid onto areas of the substrate where the image should be printed. Suitable ink jet head types for applying the treatment liquid are piezoelectric type, continuous type, thermal print head type or valve jet type.

Substrates to which the treatment liquid has been applied may be dried and optionally undergo a heat treatment, before the subsequent ink jetting step with the colorant containing ink. Examples of the heating process include, but are not limited to, heat press, atmospheric steaming, high-pressure steaming, and THERMOFIX. Any heat source can be used for the heating process; for example, an infrared ray lamp is employed.

In another preferred embodiment of the invention, the treatment liquid, after having been applied onto a substrate, is not substantially dried before the image is printed by means of the jetting of the aqueous ink jetting step.

B.2. Ink Jetting & Drying

After the application of the treatment liquid to the substrate, the aqueous inkjet ink according to the invention is applied the substrate. The inkjet ink comprises a colorant, more preferably a pigment. A preferred method of applying the aqueous inkjet ink is by means of an ink jetting technique.

A preferred ink jet head for the inkjet printing system is a piezoelectric ink jet head. Piezoelectric inkjet jetting is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with ink. When the voltage is again removed, the ceramic expands to its original shape, ejecting a drop of ink from the ink jet head. However, the jetting of the ink according to the present invention is not restricted to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as a continuous type, a thermal print head type and a valve jet type.

EXAMPLES Measurement Methods 1. Viscosity

The viscosity of the treatment liquids was measured at 32° C. using a “Robotic Viscometer Type VISCObot” from CAMBRIDGE APPLIED SYSTEMS.

2. Storage Stability

Treatment liquid stability was evaluated numerically and visually. If the relative viscosity of the treatment liquid increases more than 40% after being stored for 2 weeks at 60° C. the treatment liquid is called unstable. If the treatment liquid solidifies, the treatment liquid is called unstable.

Materials

All materials used in the following examples were readily available from standard sources such as Sigma-Aldrich (Belgium) and Acros (Belgium) unless otherwise specified. The water used was demineralised water.

    • Acetone is acetone p.a. supplied by VWR International
    • Vylon 220 is a polyester polyol containing terephthalic ester and isophthalic ester units obtained from Toyobo
    • Ymer N120 is 1,3 diol polyether supplied by Perstorp
    • DBTL is dibutyl tin laurate (KEVER-KAT DBTL 162) supplied by Brenntag
    • IPDI is a Vestanat IPDI, isocyanate supplied by Evonik
    • BD is 1,4-butane diol supplied by Acros
    • Triethylamine is triethylamine supplied by Acros
    • Disperbyk 190 is a 40 wt. % solution of dispersing agent supplied by BYK CHEMIE GMBH
    • Imagisperse is a TiO2-dispersion supplied by Imagico

India and available under the trade name Imagisperse Aqua White

    • PYR is 2-pyrrolidone.
    • HD is 1,2-hexanediol
    • Proxel K is an aqueous solution of 5-10% 1,2-Benzisothiazolin -3-one
    • PU-9 is the reproduction of the polyurethane dispersion PU-9, prepared as disclosed in the unpublished patent application EP16196224.6 and having a solid content of 41.9 wt. %
    • PU-10 is the reproduction of the polyurethane dispersion PU-9, prepared as disclosed in the published patent application EP16196224.6 and having a solid content of 33.8 wt. %
    • COL is a commercial cyan dispersion supplied by Cabot

Corporation, available under the trade name Cab-O-Jet 450 C

    • SURF-1 is Capstone FS3100, a surfactant from Dupont
    • SURF-2 is Tego Twin 4000, a surfactant from Evonik Industries
    • SURF-3 is TEGO WET 270
    • SUBSTR-1 is Metamark MD5-100 (PVC)

Preparation of the Polyurethane Resin Dispersions PU-1 (INV)

In an Erlenmeyer of 500 ml the following compounds were weighed: 104.22 g of Vylon 220, 15.30 g of Ymer N120 and 201.45 g of acetone. The Ymer N120 was preheated in an oven at 80° C., in order to obtain a liquid which can be easily handled. The mixture weighed in the Erlenmeyer was stirred using a magnetic stirrer and heated to 45° C. A clear solution was obtained and cooled to room temperature which will be later on used in the reaction. In a 500 ml 3 necked round bottom flask equipped with a coiled condenser and stirrer, 4.61 g of 3-(Dimethylamino) 1,2-propanediol was added. The prepared polyol solution (Vylon 220+Ymer N120) was added to 3-(Dimethylamino)-1,2-propanediol present in the 500 ml 3 necked round bottom flask. 1.07 g of DBTL was diluted in 9.67 g of acetone and also added to the polyol mixture. Then the reactor was heated to 55° C. during appr. 35 minutes, allowing the 3-(Dimethylamino)-1,2-propanediol to dissolve homogenously. Subsequently 34.04 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount isocyanate added was an excess towards the hydroxyl amount, ie. NCO/OH=1.53). The reaction was allowed to take place during 2 hours at 55° C. The isocyanato terminated prepolymer and free IPDI which was available in excess was then further reacted using a diol as chain extender. As diol 4.78 g of BD was used. The reaction mixture was cooled to 40° C., in order to avoid evaporation of acetone. The reaction mixture was then allowed to react overnight during 20 hours at 40° C. s in order to reach full conversion. The tertiary amine group in the resin was protonated by adding 2.32 g of acetic acid to the resin solution.

From the protonated PU solution, 345.17 g (44.03% solids) was weighed in a stainless steel vessel. Subsequently the water based dispersion was made using Disperlux equipment adding water during high shear mixing. Under stirring at 900 RPM using a 9 cm diameter dissolver stirrer 282.27 g of water was added during 20 minutes to the acidified PU solution. The acetone in the obtained dispersion was evaporated on a rotary evaporator. In order to avoid foaming the evaporation was started at a lower vacuum. The evaporation was stopped when also water was evaporated at a pressure of 60 mbars and a 40° C. heating bath. Based on the weight the concentration was corrected by adding water to 35%. The obtained PU-dispersion showed an excellent colloidal stability. The exact solid content was determined by drying 1 g of solution on an aluminum dish at 130° C. during 120 minutes. The solid content obtained was 34.96 wt. %. The measured pH is 5.04. Particle size measurement using Zetasizer: 31 nm.

PU-2 (INV)

In an Erlenmeyer of 500 ml the following compounds were weighed: 107.39 g of Vylon 220 and 201.45 g of acetone. The Erlenmeyer was stirred using a magnetic stirrer and heated to 45° C. A clear solution was obtained and cooled to room temperature which will be later on used in the reaction. In a 500 ml 3 necked round bottom flask equipped with a coiled condenser and stirrer, 8.95 g of 3-(Dimethylamino)-1,2-propanediol was added. The prepared polyol solution (Vylon 220) was added to 3-(Dimethylamino) -1,2-propanediol present in the 500 ml 3 necked round bottom flask. 1.07 g of DBTL was diluted in 9.67 g of acetone and also added to the polyol mixture. Then the reactor was heated to 55° C. during appr. 35 minutes, allowing the 3-(Dimethylamino) -1,2-propanediol to dissolve homogenously. Subsequently 41.82 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount isocyanate added was an excess towards the hydroxyl amount, ie. NCO/OH=1.53). The reaction was allowed to take place during 2 hours at 55° C. The isocyanato terminated prepolymer and free IPDI which was available in excess was then further reacted using a diol as chain extender. As diol 4.78 g of BD was used. The reaction mixture was cooled to 40° C., in order to avoid evaporation of acetone. The reaction mixture was then allowed to react overnight during 20 hours at 40° C. s in order to reach full conversion. The tertiary amino group in the resin was protonated by adding 4.51 g of acetic acid to the resin solution.

From the protonated PU solution, 353.87 g (44.50 wt. % solids) was weighed in a stainless steel vessel. Subsequently the water based dispersion was made using Disperlux equipment adding water during high shear mixing. Under stirring at 900 RPM using a 9 cm diameter dissolver stirrer 292.48 g of water was added during 20 minutes to the acidified PU solution. The acetone in the obtained dispersion was evaporated on a rotary evaporator. In order to avoid foaming the evaporation was started at a lower vacuum. The evaporation was stopped when also water was evaporated at a pressure of 60 mbars and a 40° C. heating bath. Based on the weight the concentration was corrected by adding water to 35%. The obtained PU-dispersion showed an excellent colloidal stability. The exact solid content was determined by drying 1 g of solution on an aluminum dish at 130° C. during 120 minutes. The solid content obtained was 38.80 wt. %. The measured pH is 4.90. Particle size measurement using Zetasizer: 33 nm.

Example 1

This example illustrates the need for a polyurethane resin obtained by reacting a polyester polyol and a polyol containing a cationic group or a precursor of a cationic group such as tertiary amino group in order to assure sufficient storage stability of a treatment liquid and at the same time preserve excellent physical properties of the dried treatment liquid. The presence of a polyol containing a cationic group during the reaction implies that this compound is built in the PU-resin.

Preparation of Treatment Liquids

Treatment liquids were prepared by mixing the compounds given in Table 1. All weight percentages are relative to the total weight of the inkjet ink.

TABLE 1 PTL-1 (INV) PTL-2 (INV) Compound Content in wt. % Content in wt. % PU-1 (INV) 85.81 — PU-2 (INV) — 86.71 SURF-1 1.0 1.0 Water To complete to 100% To complete to 100%

Evaluation and Results

All treatment liquids comprising the inventive PU-resins show a good storage stability.

Example 2

This example shows that treatment liquids wherein the PU-resin according to the invention is combined with white pigments show an excellent storage stability.

Preparation of a White Pigment Dispersion (WIT-1)

275 g of white pigment (TRONOX CR 834) was added to a mixture of 68.75 g of Disperbyk 190 and 2.2 g of Proxel K in 204.05 g of water under high shear by means of a Disperlux. 200 g 0.4 mm yttrium stabilized zirconia beads (“high wear resistant zirconia grinding media” from TOSOH Co.) was added and the white pigment was milled for 75 minutes in a Dynomill Research Lab at a flow of 4500 t/min. The zirconia beads were removed by filtration and the dispersion was filtered over a 0.7 μm filter. The dispersion WIT-1 had an average particle size of 219 nm.

Preparation of the Treatment Liquids PTL-3 and PTL-4

Treatment liquids PTL-3 and PTL-4 were prepared by mixing the compounds given in Table 2. All weight percentages are relative to the total weight of the liquid.

TABLE 2 PTL-3 PTL-4 Compound Content in wt. % Content in wt. % PU-2 (INV) 34.32 34.32 Imagisperse 27.50 — WIT-1 — 22.00 PYR 15.0 15.0 HD 15.0 15.0 SURF-1 0.6 0.6 SURF-2 0.2 0.2 Water To complete to 100% To complete to 100%

Both treatment liquids show an excellent storage stability, showing that the PU-resins according to the invention can be combined with white pigments without causing storage stability problems in the treatment liquid.

Example 3

This example illustrates the fixing power towards colorants of the cationic polyurethane binder in the treatment liquid of the set of liquid according to the invention.

Preparation of the Treatment Liquids PTL-5 and PTL-6

Treatment liquids PTL-5 and PTL-6 were prepared by mixing the compounds given in Table 3.

All weight percentages are relative to the total weight of the liquid.

TABLE 3 PTL-5 (COMP) PTL-6 (INV) Compound Content in wt. % Content in wt. % PU-2 (INV) — 30.93 PU-9 dispersion 35.6 — PYR 20.0 20.0 HD 20.0 20.0 SURF-3 0.6 0.6 Water To complete to 100% To complete to 100%

Preparation of the INK-1

A cyan ink INK-1 was prepared by mixing the compounds given in Table 4. All weight percentages are relative to the total weight of the inkjet ink.

TABLE 4 INK-1 Compound Content in wt. % PU-9 dispersion 28.64 PYR 20.00 HD 20.00 SURF-3 0.60 COL 20.00 Water To complete to 100%

Evaluation and Results

The treatment liquids PTL-2 and PTL-5 were coated by using a 10 μm spiral bar (from Elcometer) with a motorised film applicator Elcometer 4340 on a sheet of chrome crusted leather supplied from Conceria Nuti Ivo S. P. A. (Italy). After drying the coated layer at 60° C. in an oven for 5 minutes, the treated substrate sheets were coated a second time each with the same treatment liquid PTL-2 and PTL-5. After drying the coated layer at 60° C. in an oven for 5 minutes, the treated substrate sheets were coated with INK-1 by means of the same 10 μm spiral bar. The coated samples were dried at 60° C. for 8 minutes.

The cyan optical density of the dried coatings was measured by means of an eXact apparatus (from X-rite) at ANSI A (no filter (M0)). After the measurements of the optical densities (D), the samples were stored for 3 days in a plastic pocket at room temperature and the optical density was again measured. It was observed that the optical density of the coated samples (D) was decreased, probably due to migration of the colorants of the inkjet ink into the porous substrate. In table 5, the measured decrease in optical density was summarized.

TABLE 5 Sample no Treatment liquid Inkjet ink ΔD due to storage 1 (COMP) PTL-5 INK-1 −0.24 2 (INV) PTL-6 INK-1 −0.13

From Table 5 it can be seen that the decrease in color density upon storage is less with the use of the set of liquids according to the invention (PTL-6+INK-1) than with a set of liquids not according to the invention.

Claims

1-10. (canceled)

11. A liquid set for inkjet recording comprising:

an aqueous treatment liquid including a polyurethane resin obtainable by reacting a polyester polyol, a diol including a quaternary N-atom or a tertiary amino group, and a polyisocyanate; and
an aqueous inkjet ink including a colorant; wherein
the quaternary N-atom or the tertiary amino group is present in a side chain of a carbon chain linking two hydroxyl groups of the diol; and
the polyester polyol is obtained by reacting a polyol and an aromatic polycarboxylic acid.

12. The liquid set according to claim 11, wherein the aromatic polycarboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, and a combination thereof.

13. The liquid set according to claim 12, wherein an amount of the isophthalic acid in the polyester polyol is at least 20 mol %.

14. The liquid set according to claim 11, wherein the colorant includes a pigment.

15. The liquid set according to claim 12, wherein the colorant includes a pigment.

16. The liquid set according to claim 14, wherein the aqueous treatment liquid includes a white pigment.

17. The liquid set according to claim 15, wherein the aqueous treatment liquid includes a white pigment.

18. The liquid set according to claim 11, wherein a polyether diol is present during the reaction of the polyester polyol, the diol, and the polyisocyanate.

19. The liquid set according to claim 18, wherein the polyether diol is a compound according to Formula 1:

wherein
R1 is methyl or ethyl;
R2 is C1-C4alkyl; and
n represents an integer from 5 to 50.

20. An inkjet recording method comprising:

providing a substrate and the liquid set according to claim 11;
applying on the substrate, the aqueous treatment liquid of the liquid set;
jetting the aqueous inkjet ink of the liquid set on an area of the substrate where the aqueous treatment liquid was applied; and
drying the aqueous inkjet ink.

21. The inkjet recording method according to claim 20, wherein the aromatic polycarboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, and a combination thereof.

22. The inkjet recording method according to claim 20, wherein the applying of the aqueous treatment liquid includes ink jetting the aqueous treatment liquid.

23. The inkjet recording method according to claim 21, wherein the applying of the aqueous treatment liquid includes ink jetting the aqueous treatment liquid.

24. The inkjet recording method according to claim 20, wherein the applying of the aqueous treatment liquid includes applying the aqueous treatment liquid to form an image.

Patent History
Publication number: 20200369903
Type: Application
Filed: Nov 28, 2018
Publication Date: Nov 26, 2020
Inventors: Hubertus VAN AERT (Mortsel), Ellen BERTELS (Mortsel), Marie LEHERICEY (Mortsel)
Application Number: 16/766,306
Classifications
International Classification: C09D 11/40 (20060101); C09D 11/54 (20060101); C09D 11/322 (20060101); C09D 11/102 (20060101); C08G 18/12 (20060101); C08G 18/32 (20060101); C08G 18/42 (20060101); C08G 18/48 (20060101); C08G 18/66 (20060101); C08G 18/75 (20060101); C08K 3/22 (20060101);