Liquid set for inkjet printing comprising aqueous pretreatment liquid, aqueous inkjet ink and varnish

Abstract

A liquid set for inkjet printing comprising an aqueous pre-treatment liquid comprising a fixing agent, an aqueous inkjet ink comprising a pigment and a water-soluble organic solvent, and a varnish, the varnish includes water, resin particles selected from the group consisting of urethane resins, acrylic resins, and waxes, and a water-soluble polymer selected from the group consisting of linear PPO-PEO copolymers and aryl ethyl phenyl polyethylene glycol ethers. The liquid package is suitable for inkjet printing on liners for corrugated packaging, folded panels and corrugated boards.

Description

TECHNICAL FIELD

[0001] The present invention relates to a liquid set suitable for inkjet recording, and more particularly to inkjet printing on liners for corrugated packaging, folding board and corrugated board. BACKGROUND

[0002] Inkjet printing is an increasingly growing field for printing of liners for corrugated packaging and corrugated board. Preferably, inkjet printing is carried out by means of aqueous inkjet inks. Aqueous inkjet inks are inherently safer than reactive UV inks and inks whose main vehicle is a solvent.

[0003] Both dyes and pigments have been used as colorants for aqueous inkjet inks, and both have certain advantages. Pigment inks are advantageous in that they tend to provide more lightfast images than soluble dye inks.

[0004] However, since pigment inks adhere to the uppermost surface of the printed matter (hereinafter referred to as pigment ink printed matter), the printed text and images are easily peeled off, which means that the rub resistance of the pigment ink printed matter is poor.

[0005] In an attempt to improve the rub resistance of such pigment ink printed matter, for example, JP-2011-63016-A and JP-2011-105900-A disclose a method of protecting the surface of the printed matter by applying a transparent post-processing fluid to the recording medium after the printed image.

[0006] The easiest way to apply a transparent post-processing fluid to a recording medium carrying an inkjet printed image is by complete coating of the post-processing fluid as in US 2007 / 0282037 A1. Similar overprint varnishes are available commercially. In this case, the amount of post-processing fluid is significantly greater than in the case where only a post-treatment fluid is applied to the inkjet printed image. Furthermore, the time variation required for switching between different paper sizes is significant and leads to a less economically efficient printing process.

[0007] Therefore, it is beneficial to apply only a post-processing liquid to the inkjet printed image. The most suitable technique for applying a post-processing liquid by image is inkjet, and only an additional inkjet head or print bar needs to be introduced into the printing device.

[0008] EP3099735A discloses a post-processing fluid comprising a fluid vehicle and a anionic polyurethane-acrylic hybrid polymer binder dispersed in the fluid vehicle.

[0009] The post-treatment liquid includes components such as resins and waxes. Since the resins or waxes form a uniform coating film on the surface of the image formed by jetting the aqueous ink, the image is given glossiness. However, if the post-treatment liquid is applied to the surface of the image formed by jetting the aqueous ink in an unfixed state, the post-treatment liquid is mixed into the image.

[0010] Therefore, a uniform coating film cannot be formed on the surface of the image, resulting in the problem of poor glossiness of the image. In order to increase the glossiness, US2016 / 0177116 A proposes an imaging set including: an aqueous ink including a colorant, a water-soluble organic solvent, and a post-treatment liquid including a water-soluble organic solvent, a urethane resin, and an acrylic resin, and an isocyanate as a crosslinking agent. The use of an organic solvent and a reactive crosslinking agent in the post-treatment liquid is to be avoided for health and safety reasons.

[0011] Therefore, there is a strong need to obtain a durable inkjet printed image in which the post-treatment liquid shows a high glossiness value, while being free of reactive crosslinking agents such as isocyanates in its composition. SUMMARY

[0012] It is an object of the present application to provide a solution to the above problems. This object has been achieved by providing a liquid set as defined in claim 1.

[0013] Another embodiment of the present application is to provide a printing method as defined in claim 8 using the liquid set of claim 1.

[0014] Further features, elements, steps, characteristics and advantages of the present application will become more apparent from the following detailed description of preferred embodiments of the present application. Specific embodiments of the present application are also defined in the dependent claims. DETAILED DESCRIPTION

[0015] A. Liquid kit for inkjet printing The liquid set for inkjet printing according to the present application comprises an aqueous pre-treatment liquid, an aqueous inkjet ink, and a varnish.

[0016] A.1. Varnish The varnish as part of the liquid set according to the present application serves to protect the inkjet printed image from wet and dry rub, scratches, and solvents. Therefore, the varnish comprises water, resin particles, and a water-soluble polymer selected from linear PPO-PEO copolymers and arylethylphenyl polyglycol ethers.

[0017] Suitable linear PPO-PEO copolymers preferably have polymeric or oligomeric hydrophobic segments. They are also called multi-block copolymers. Typical examples are di- or tri-block copolymers based on EO and PO. Typical trade names are Pluronic RPE grades or Pluronic PE grades available from BASF and Synperonic grades from Croda. In case of tri-block copolymers, the outer blocks have a different polarity than the middle block. The most polar block can be located at the outer side, but also in the middle of the middle block. In addition to di- and tri-block copolymers, also multi-block copolymers can be used.

[0018] The hydrophilicity of the hydrophilic segment can be varied by varying the number of EO units, but also other hydrophilic alkylene oxide units can be used instead of EO, for example based on glycidol, other ethylene oxides, glycerol, glycerol alcohol, glycosides, etc. Typical trade names are Lutensol (BASF), Plurafac (BASF), Tergitol (Dow), Etocas (Croda), Pionin (NOF), Emulsogen (Clariant), Silcosperse (Keim Additec).

[0019] Other specific useful examples of water-soluble polymers that can be used in the varnish of the present application are aryl ethyl phenyl polyglycol ethers, for example Lucramul DA554 from LEVACO Chemicals GmbH.

[0020] Without being bound by theory, it is believed that the above water-soluble polymers improve the film formation of the resins present in the varnish by avoiding flocculation with the fixer of the pre-treatment liquid during the drying step of the varnish. The improved film formation leads to higher gloss values of the printed image covered with the varnish coating.

[0021] Particularly preferred water-soluble linear copolymers based on EO and PO have an average molecular weight between 3000 g / mol and 30000 g / mol, more preferably between 4000 g / mol and 15000 g / mol and have a PPO / PEO weight ratio between 0.1 and 2.5. Varnish compositions containing copolymers with these ranges of molecular weight and PPO / PEO weight ratio do indeed show improved gloss and increased resistance to wet and dry rub of the inkjet printed image. The average Mw (average molar mass) is determined from the OH value (mg KOH / g), which is obtained by titration, for example using the ISO 4326 method.

[0022] The water-soluble polymer in the varnish of the present invention is preferably a nonionic polymer. Due to its nonionic nature, the water-soluble polymer interacts less with the cationic fixing agent in the pretreatment liquid during the drying step of the varnish. This results in higher gloss values.

[0023] The water-soluble polymer is present in the varnish composition in an amount ranging from 1 wt % to 40 wt % based on the total dry solids content of the treatment composition, more preferably in an amount ranging from 2 wt % to 35 wt % based on the total dry solids content of the treatment composition, and most preferably in an amount ranging from 5 wt % to 20 wt % based on the total dry solids content of the treatment composition.

[0024] Water-soluble organic solvents For various reasons, one or more water-soluble organic solvents may be present in the varnish from the liquid set according to the invention. For example, it may be advantageous to add a small amount of an organic solvent to improve the dissolution of the compound in the varnish to be prepared, to achieve better penetration in porous substrates or to prevent the varnish from drying out quickly at the nozzles of the inkjet head. Preferred water-soluble organic solvents are polyols (e.g. ethylene glycol, glycerol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,5-pentanediol, 1,2-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 3- methyl-1,5-pentanediol, 3-methyl-1,3-butanediol and 2-methyl-1,3-propanediol), N-hydroxyethyl-pyrrolidone, N-butyl-pyrrolidone, amines (such as ethanolamine and 2-(dimethylamino)ethanol), monohydric alcohols (such as methanol, ethanol and butanol), 2,2'-thiodiethanol, amides such as N,N-dimethylformamide, heterocycles such as 2-pyrrolidone and N-methyl-2-pyrrolidone, and acetonitrile.

[0025] Examples of glycol ethers include monoalkyl ethers of glycols selected from ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol and tripropylene glycol. More specifically, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether and dipropylene glycol monopropyl ether can be preferably cited. Other useful examples listed in Swiss list A and therefore compatible with food packaging are: propylene glycol monomethyl ether; propylene glycol monoethyl ether; propylene glycol monopropyl ether; ethylene glycol monobutyl ether; propylene glycol monobutyl ether; diethylene glycol monoethyl ether; diethylene glycol monobutyl ether; dipropylene glycol mono-n-propyl ether; dipropylene glycol methyl ether; tripropylene glycol monomethyl ether. These solvents can be used alone or in combination of two or more. The wetting agent is preferably added to the pre-coating composition formulation in an amount of 0.1-25 wt % based on the total weight of the liquid.

[0026] Waxes The clear varnish included in the liquid set according to the present application can include a wax. The wax can improve the durability of the printed image. In general, any suitable wax can be used in the clear varnish composition. Thus, the wax can be a polyethylene wax, a petroleum wax, a paraffin wax, a carnauba wax, a polypropylene wax, a crystalline and microcrystalline wax, an amide wax (oleamide, stearamide, erucamide, cyclamide, etc.), and combinations thereof. In one aspect of the present application, the wax can be a high density polyethylene wax.

[0027] In one aspect of the present application, the wax can be a polyethylene wax or a modified paraffin wax. Examples of polyethylene waxes include high density polyethylene (HDPE) waxes having a density in the range of about 0.93 g / mL to 0.97 g / mL.

[0028] Examples of modified paraffin wax particles include paraffin waxes that have been modified, e.g., via emulsification, to improve dispersibility in water. The modified paraffin wax can be surface modified, chemically modified, etc.

[0029] Some specific examples of waxes that can be used include those of the JONCRYL Wax series (e.g., JONCRYL Wax 22, JONCRYL Wax 26, and JONCRYL Wax 120, available from BASF Corp.), those of the AQUACER series (e.g., AQUACER 498, AQUACER 501, AQUACER 505, AQUACER 513, AQUACER 530, AQUACER 531, AQUACER 535, AQUACER 537, AQUACER 539, and AQUACER 552, available from BYK-Gardner, Columbia, Md.), and Liquilube 404E from Lubrizol.

[0030] The wax can have i) a high melting temperature T and / or ii) a small average particle size. In one example, the wax can have a high melting temperature T, e.g., a high melting temperature T equal to or greater than 90 °C. In addition, the wax can have an average particle size (in terms of effective diameter, assuming that each wax particle is not a perfect sphere) in the range of 0.03 µm to 1.5 µm, more preferably 0.05 µm to 1 µm (D50). If the particle size exceeds these upper limits, jetting reliability problems of the clear varnish can occur.

[0031] The wax can be present in the clear varnish in an amount in the range of 3-25 weight percent, more preferably 5-20 weight percent, relative to the total solids weight of the overprint clear varnish.

[0032] Resin particles Examples of the resin particles included in the varnish include well-known resins such as urethane-based resins, acrylic resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, and vinyl chloride-based resins. Vinyl chloride-based resins include vinyl chloride copolymers such as vinyl chloride-vinyl acetate copolymers. These resins may be used alone or in combination of two or more thereof.

[0033] Among the above-mentioned resin particles, the resin included in the varnish is preferably a urethane-based resin, an acrylic resin, a styrene-acrylic resin, or a polyolefin-based resin.

[0034] As the urethane-based resin, commercially available products can be used, for example, commercially available products such as SUPER FLEX 460, 460s, 840, E-4000 (trade names, manufactured by DKS Co., Ltd.), RESAMINE D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (trade names, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), TAKELAC WS-6021, W-512-A-6 (trade names, manufactured by Mitsui Chemicals Polyurethanes INC.), SUNCURE 2710 (trade name, manufactured by LUBRIZOL Corporation), and Permalin UA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.) can be used.

[0035] Acrylic resin is a general term for polymers obtained by polymerizing at least acrylic monomers (such as (meth) acrylic acid and (meth) acrylate), and examples thereof include (meth) acrylic resins obtained from acrylic monomers, and copolymers of monomers other than acrylic monomers and acrylic monomers (such as vinyl-based monomers, such as styrene). Acrylamide and acrylonitrile can also be used as acrylic monomers. Acrylic resin can be non-reactive or self-crosslinking. As a resin emulsion using acrylic resin as a raw material, commercially available products can be used, and examples thereof include FK-854 (trade name, manufactured by CHIRIKA.Co., Ltd.), Mowinyl 952B, 718A (trade name, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.), Nipol LX852 and LX874 (trade name, manufactured by ZEON Corporation).

[0036] Examples of styrene-acrylic resins include poly(styrene-alkyl acrylate), poly(styrene-1,3-diene), poly(styrene-alkyl methacrylate), poly(styrene-alkyl acrylate-acrylic acid), poly(styrene-1,3-diene-acrylic acid), poly(styrene-alkyl methacrylate-acrylic acid), poly(styrene-alkyl acrylate-acrylonitrile-acrylic acid), and poly(styrene-1,3-diene-acrylonitrile-acrylic acid). Other examples include poly(styrene-propyl acrylate), poly(styrene-butyl acrylate), poly(styrene-butadiene-acrylic acid), poly(styrene-butadiene-methacrylic acid), poly(styrene-butadiene-acrylonitrile-acrylic acid), poly(styrene-butyl acrylate-acrylic acid), poly(styrene-butyl acrylate-methacrylic acid), poly(styrene-butyl acrylate-acrylonitrile), poly(styrene-butyl acrylate-acrylonitrile-acrylic acid). Commercial styrene-acrylic resins are Neocryl D2101 (Covestro) and Bonron PS001 and Bonron PS002 (Mitsui).

[0037] Other suitable resins include Esajet acrylic latexes from Lamberti, such as Esajet AC 20, Esajet AC 22, Esajet AC 29, Esajet AC 31, and Esajet AC 03.

[0038] Polyolefin-based resins have olefins (e.g., ethylene, propylene, and butylene) as a structural backbone, and a publicly known resin can be appropriately selected for use. As the olefin resin, a commercially available product can be used, and examples thereof include Arrowbase CB-1200 and CD-1200 (trade name, manufactured by UNITIKA LTD.).

[0039] The varnish contains the resin in an amount of 1% to 30% by weight with respect to the total mass of the liquid. When the content of the resin in the varnish is within the above range, the effect of improving the rubbing resistance of the image tends to become more excellent. More preferably, the varnish contains the resin in an amount of 3% to 15% by weight with respect to the weight of the liquid. Most preferably, the varnish contains the resin in an amount of 5% to 12% by weight with respect to the weight of the liquid.

[0040] Polyether siloxane surfactant The varnish according to the present application can contain a polyether siloxane surfactant. A preferred surfactant is according to formula I: Formula I In formula I, R1to R9independently represent an alkyl group having 1-6 atoms, preferably methyl, or an aryl group, preferably phenyl. n and m independently represent an integer of 0 or more, but preferably 0-8. R10to R11independently represent a hydrogen atom or an alkyl group, preferably methyl. p and n preferably represent an integer of 0 or more.

[0041] In the case of m = 0 and n = 1, the structure is defined as a trisiloxane. In the case of n and m being greater than 0, the structure is defined as a graft copolymer. The polyether units have a degree of polymerization of p and the polyether units have a degree of polymerization of q. These units can be arranged in a block manner or randomly. In the case of R10= R11, then the graft contains only one type of alkylene oxide unit. Preferably, the graft A contains one or two different types of alkylene oxide units. In the case of the graft A containing one type of alkylene oxide, it is preferred that the alkylene oxide is ethylene oxide. In the case of two types of alkylene oxides being present, then it is preferred that ethylene oxide and propylene oxide are used. m in the spacer is preferably equal to 2 or 3, the polyether being terminated by a vinyl or allyl group, respectively.

[0042] The preferred content of the polyether siloxane based surfactant is equal to 0.03 wt% or more, more preferably equal to 0.2 wt% or more, based on the total weight of the liquid. If the content is lower, then the water resistance or wet rub resistance of the printed image is insufficient.

[0043] In addition to the compounds of formula I having trialkylsilyl end groups, there can also be similar structures with alkyl end groups, substituted alkyl groups, aryl groups or substituted alkyl groups.

[0044] Typical examples of trisiloxane structures are Byk 3450, Byk 3451, Tego wet 260, Tego wet 240, Tego wet KL245, Korasilon additive PS1, Korasilon additive PS2.

[0045] Typical examples of graft copolymer structures are Tego glide 410, Korasilon additive PS5, Coatosil 7607.

[0046] Another silicone polyether structure that can be used is shown in formula II, i.e. a silicone polyether block copolymer.

[0047] Formula II In Formula II, R1 to R9 independently represent an alkyl group having 1 to 6 atoms, preferably a methyl group, or an aryl group, preferably a phenyl group. n and m independently represent an integer of 0 or greater, but preferably 0 to 8. R10 and R11 independently represent a hydrogen atom or an alkyl group, preferably a methyl group. p and n preferably represent an integer of 0 or greater.

[0048] In a typical triblock copolymer, n=0, indicating a siloxane-polyether-siloxane triblock copolymer. An example of a block copolymer silicone surfactant is Byk 3420, which has an ABA structure (A=polyether, B=silicone).

[0049] Furthermore, the polyether siloxane surfactant may be a structure in which both polyether and siloxane segments are present as grafts. Examples of polyether siloxanes having siloxane grafts are Byk 3565, Byk 3566, and Byk 3568.

[0050] Polyether siloxane structures can also be designed to have better hydrolytic stability, such as those available under the trade names Silwet HS312 and Silwet HS212 from Momentive.

[0051] Commercially available suitable surfactants are Olfine PD-501 (Nissin Chemical Industry Co., Ltd.), Olfine PD-570 (Nissin Chemical Industry Co., Ltd.), BYK-333 (BYK Co., Ltd.), BYK-347 (BYK Co., Ltd.), BYK-348 (BYK Co., Ltd.).

[0052] The presence of polyether siloxane surfactants in the clearcoat of the present invention increases rubbing resistance under dry and wet conditions (water resistance). Without being bound by theory, it is believed that the polyether siloxane reduces the coefficient of friction of the clearcoat coating after drying, reducing the effects of mechanical damage to the image due to friction.

[0053] additive The varnish may further contain biocides, waxes, thickeners, pH adjusters and corrosion inhibitors.

[0054] Biocides may be added to the varnish to prevent unwanted microbial growth which may occur over time. Suitable biocides are listed in § A.2.

[0055] The biocide is preferably added to the aqueous medium in an amount of 0.001 to 3% by weight, more preferably 0.01 to 1.0% by weight, each based on the total weight of the varnish.

[0056] The varnish may contain a thickener to increase the viscosity within the desired range for the application method.

[0057] Suitable thickeners include urea or urea derivatives, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, derivatized chitin, derivatized starch, carrageenan, pullulan, proteins, poly(styrene sulfonic acid), poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamide, partially hydrolyzed polyacrylamide, poly(acrylic acid), poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate), poly(hydroxyethyl acrylate), poly(methyl vinyl ether), polyvinyl pyrrolidone, poly(2-vinyl pyridine), poly(4-vinyl pyridine), and poly(diallyldimethylammonium chloride).

[0058] The thickener is preferably added in an amount of 0.01 to 20% by weight, more preferably 0.1 to 10% by weight, based on the liquid.

[0059] Biocides may be added to the varnish to prevent unwanted microbial growth that may occur over time. Biocides may be used alone or in combination. Suitable biocides for use in the inkjet inks of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1-oxide, ethyl paraben, and 1,2-benzisothiazolin-3-one and its salts.

[0060] A preferred biocide is Proxel available from ARCH UK BIOCIDES TM GXL and Proxel TM Ultra 5 and Bronidox available from COGNIS TM .

[0061] The 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 total weight of the liquid.

[0062] The varnish may contain wax. Suitable examples of waxes are given in § A.3.3.

[0063] Layer thickness The coverage of the varnish coating after drying is preferably 0.2 g / m² to 2.5 g / m², more preferably 0.6-2.0 g / m². If the coverage is less than 0.2 g / m², the dry and wet rubbing resistance is insufficient. If the coverage is higher than 2.5 g / m², the applied varnish dries slowly, which limits the printing speed.

[0064] A.2. Aqueous pretreatment liquid The aqueous pretreatment liquid according to the present invention comprises water as a vehicle and a fixing agent.The aqueous vehicle may include one or more water-soluble organic solvents.

[0065] Fixative The fixing agent present in the pretreatment composition is preferably a polyvalent metal salt, a cationic polymer or an organic acid. The fixing agent serves to break up, precipitate or destabilize the ink colorants and thereby fix them to the substrate. This results in improved image quality (less bleeding, less agglomeration).

[0066] A polyvalent metal salt may be present in the pretreatment composition to improve inkjet printing quality. Typically, the polyvalent metal salt may be any water-soluble polyvalent metal salt. In a specific example, the polyvalent metal salt may include calcium chloride (CaCl ), magnesium chloride (MgCl ), magnesium sulfate (MgSO ), aluminum chloride (AlCl ), calcium nitrate (Ca(NO ) ), magnesium nitrate (Mg(NO ) ), magnesium acetate (Mg(CH COO) ), zinc acetate (Zn(CH COO) ), calcium propionate (Ca(C H COO) ) or a combination thereof. In a specific example, the polyvalent metal salt may be calcium chloride. In a further example, the polyvalent metal salt may include a metal cation selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminum, chromium or another polyvalent metal.

[0067] The polyvalent metal salt may also include an anion. In some examples, the anion may be fluoride, chloride, iodide, bromide, nitrate, chlorate, sulfate, acetate, or RCOO. - , wherein R is hydrogen or any low molecular weight hydrocarbon chain, such as C1-C12. In a more specific example, the anion can be a carboxylate radical derived from a saturated aliphatic monocarboxylic acid having 1-6 carbon atoms or a carbocyclic monocarboxylic acid having 7-11 carbon atoms. Examples of saturated aliphatic monocarboxylic acids having 1-6 carbon atoms can include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid and / or hexanoic acid. The cationic salt can also be a mixture of two or more different cationic salts.

[0068] In some cases, the polyvalent metal salt may be present in an amount of 1% to 99% by weight relative to the total weight of the pretreatment composition. In more specific examples, the polyvalent metal salt may be present in an amount of 5% to 65% by weight, more preferably 25% to 60% by weight, relative to the solids content of the pretreatment composition. If this amount is below the lower limit, insufficient fixation of the colorant may occur, resulting in reduced image quality.

[0069] Polymeric cationic polymers suitable as fixatives in the pretreatment composition contain guanidinium or fully quaternized ammonium functional groups, such as quaternized polyamine copolymers. Typically, the cationic polymer has a weight average molecular weight (Mw) such that the viscosity at 25°C is less than 25 cP, as measured on a Brookfield viscometer. Typical Mw is less than 500.000 g / mol, and in one aspect, less than 50.000 g / mol.

[0070] Suitable classes of cationic polymers that may be used include, but are not limited to, quaternized polyamines, dicyandiamide polycations, diallyldimethylammonium chloride copolymers, quaternized dimethylaminoethyl (meth)acrylate polymers, quaternized vinylimidazole polymers, alkylguanidine polymers, alkoxylated polyethyleneimines, and mixtures thereof.

[0071] resin The pretreatment liquid may contain resin particles. The resin particles are preferably selected from poly(urethane), poly(acrylate) or wax. Suitable examples of resin particles are given in § A.3.3.

[0072] In a preferred embodiment of the present invention, the pretreatment liquid may contain a water-soluble copolymer selected from PPO / PEO copolymers, arylethylphenyl polyethylene glycol ethers and fatty acid derivatives having EO / PO moieties. Suitable examples can be found in § A.1.

[0073] surfactants The pretreatment composition may contain a surfactant. Any known surfactant may be used, but preferably a glycol surfactant and / or an acetylene glycol surfactant and / or a polysiloxane surfactant is used. The use of an acetylene glycol surfactant and / or an acetylene glycol surfactant and / or a polysiloxane surfactant improves the drying properties during printing to allow high-speed printing.

[0074] The acetylenic diol surfactant and / or acetylenic alcohol surfactant is preferably one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, alkylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,4-dimethyl-5-decyne-4-ol and alkylene oxide adduct of 2,4-dimethyl-5-decyne-4-ol. These are available from Nissin Chemical Industry, for example as Olfine (Registered Trademark) E series, for example Olfine E1010, or from Evonik (formerly Air Products (GB)) as Surfynol (Registered Trademark) 104, Surfynol 465, Surfynol 61, Surfynol DF110, Dynol 604 Surfynol DF110L, Surfynol DF110D, Surfynol AD01 and ethoxylated derivatives such as CAS Registry Number 91629-35-5.

[0075] additives The pre-treatment liquid can comprise a thickening agent to increase the viscosity within the desired range of the application method.

[0076] Suitable thickening agents include urea or urea derivatives, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, derivatised chitins, derivatised starches, carrageenans, amylopectin, proteins, poly(styrene sulfonic acid), poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamide, partially hydrolysed polyacrylamide, poly(acrylic acid), poly( vinyl alcohol), partially hydrolysed poly( vinyl acetate), poly(hydroxyethyl acrylate), poly(methyl vinyl ether), polyvinylpyrrolidone, poly(2-vinylpyridine), poly(4-vinylpyridine) and poly(diallyldimethylammonium chloride).

[0077] The thickening agent is added based on the liquid, preferably in an amount of 0.01 to 20 wt%, more preferably 0.1 to 10 wt%.

[0078] A biocide can be added to the pre-coat composition to prevent undesirable microbial growth which can occur over time. Biocides can be used individually or in combination. Suitable biocides for use in the inkjet inks of the present application include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyrithione-1-oxide, ethyl p-hydroxybenzoate and 1,2-benzisothiazolin-3-one and salts thereof.

[0079] A preferred biocide is Proxel GXL and Proxel ULTRA GXL available from ARCH UK BIOCIDES TM GXL and Proxel TMBronidox available from COGNIS TM .

[0080] The 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 total weight of the liquid.

[0081] In a preferred embodiment of the present application, the pre-treatment liquid can contain a water-soluble copolymer selected from PPO / PEO copolymers, arylethylphenyl polyglycol ethers and fatty acid derivatives with EO / PO moieties. Suitable examples can be found in § A.1.

[0082] The pre-treatment liquid can also contain pigments. Particularly useful for printing on dark or transparent substrates are pre-coat compositions containing white pigments. The preferred pigment for use in aqueous pre-coat composition inks is titanium dioxide. The titanium dioxide (Ti02) pigments useful in the present application can be in either the rutile or anatase crystalline form. Methods of making Ti02are described in more detail in "The Pigment Handbook", Vol. I, 2ndEdition, John Wiley & Sons, NY (1988), the relevant disclosure of which is incorporated herein by reference for all purposes as if fully set forth.

[0083] The pre-treatment liquid can contain at least one pH adjusting agent. Suitable pH adjusting agents include organic amines such as triethanolamine, NaOH, KOH, NEt3, NH3, HC1, HN03, and H2S04. In a preferred embodiment, the pre-coat composition has a pH equal to or below 9.

[0084] A.3. Aqueous inkjet ink The aqueous inkjet ink as part of the liquid set according to the present application comprises a colorant, such as a dye and a pigment, for printing at least on the areas where the pre-treatment liquid has been applied to obtain a printed image. The pigment is preferably stabilized by anionic dispersing groups. The pigment can additionally also be stabilized by polymeric dispersants, surfactants or combinations thereof to achieve additional colloidal stability.

[0085] The aqueous medium of the ink contains water, but can include one or more water-soluble organic solvents. Suitable water-soluble organic solvents are described in § A.1.

[0086] In a preferred embodiment of the present application, the aqueous inkjet ink comprises a resin and / or a wax. Suitable waxes are described in § A.1.

[0087] The aqueous inkjet ink can further comprise surfactants, humectants, biocides, resins and thickeners as additives.

[0088] A.3.1. Pigments The pigments in the aqueous inkjet ink according to the application can be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, etc. The colored pigments can be selected from those disclosed by HERBST, Willy et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley - VCH, 2004. ISBN 3527305769.

[0089] Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO 2008 / 074548.

[0090] The pigment particles are dispersed in the aqueous medium using a polymeric dispersant, a surfactant or a combination thereof. Self-dispersible pigments can also be used. The latter prevent the interaction of the polymeric dispersant with the dispersing groups of the binders or capsules that can be included in the inkjet ink (see below).

[0091] Self-dispersible pigments are pigments having covalently bonded to their surface anionic hydrophilic groups or salt-forming groups that allow the pigments to be dispersed in an aqueous medium without the use of surfactants or resins.

[0092] Techniques for preparing self-dispersible pigments are well known. For example, EP 1220879 A 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 the charge of the organic ionic group suitable for use in an inkjet ink. EP 906371 A also discloses suitable surface-modified colored pigments having attached hydrophilic organic groups containing one or more ionic or ionizable groups. Suitable commercially available self-dispersible colored pigments are for example CAB-O-JET® from CABOT TM Inkjet colorant.

[0093] The pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the nozzle. It is also desirable to use small particles to obtain maximum color strength and to slow down sedimentation.

[0094] 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 number average pigment particle size is no greater than 0.150 μm. The average particle size of the pigment particles is determined using a Brookhaven Instruments Particle Sizer BI90 Plus based on dynamic light scattering.

[0095] Suitable white pigments are given in Table 2 of

[0116] of WO 2008 / 074548. White pigments are preferably pigments having a refractive index greater than 1.60. White pigments can be used alone or in combination. Preferably, titanium dioxide is used as the pigment having a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in

[0117] and

[0118] of WO 2008 / 074548.

[0096] Specialty colorants can also be used, such as fluorescent pigments for special effects in clothing, and metallic pigments for printing silver and gold colors on textiles for a luxurious look.

[0097] Suitable polymeric dispersants are copolymers of two monomers, but they may contain three, four, five or even more monomers. The properties of the polymeric dispersant depend on both the properties of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition: • Statistical polymerization of monomers (e.g. monomers A and B polymerize to form ABBAABAB); • alternating monomers (e.g. monomers A and B polymerize to form ABABABAB); • Gradient (stepwise) polymerization of monomers (e.g. monomers A and B polymerize into AAABAABBABBB); • block copolymers (e.g. monomers A and B polymerized to AAAAABBBBBB), where the block length of each block (2, 3, 4, 5 or even more) is important for the dispersing ability of the polymeric dispersant; • Graft copolymers (graft copolymers consist of a polymer backbone with polymer side chains attached to the backbone); and •Mixed forms of these polymers, such as block gradient copolymers.

[0098] A suitable dispersant is DISPERBYK available from BYK CHEMIE TM Dispersant, JONCRYL available from BASF TM Dispersants and SOLSPERSE available from Lubrizol TMDispersants. Other suitable dispersants are Edaplan 482 from Münzing. A detailed list of non-polymeric dispersants as well as some polymeric dispersants is disclosed by McCutcheon. Functional Materials, North American Edition. Glen Rock, N.J.: Manufacturing Confectioner Publishing Co., 1990. pp. 110-129.

[0099] The polymeric dispersant preferably has a number average molecular weight Mn between 500 and 30,000, more preferably between 1,500 and 10,000.

[0100] The polymeric dispersant preferably has a weight average molecular weight Mw of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0101] The pigments are preferably present in the range of 0.01 to 15%, 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%. Amounts below 3% by weight do not enable sufficient coverage capability.

[0102] In a preferred embodiment of the present application, the aqueous ink comprises pigments encapsulated by a crosslinked polymeric shell. Encapsulated pigments provide printed images with improved physical properties such as water resistance and dry rub resistance relative to pigments dispersed by uncrosslinked polymers.

[0103] Suitable encapsulated pigments are provided by Lubrizol as Diamond HSDX-dispersion, and by Fujifilm as RxD pigment dispersions, such as APD1000 and APD400 premium dispersions.

[0104] A.3.2. Vehicle The aqueous ink according to the present application comprises water as a vehicle. The aqueous vehicle can further comprise one or more water-soluble organic solvents.

[0105] One or more organic solvents can be added for a variety of reasons. For example, it can be advantageous to add small amounts of organic solvents to improve the dissolution of compounds in the ink composition to be prepared or to prevent the ink from drying too quickly at the nozzles of the inkjet head. Preferred water-soluble organic solvents are listed in § A.1.

[0106] Preferably, if two or more organic solvents are present in the ink, the one of the organic solvents used in the largest amount has a boiling point of 150°C or higher and 250°C or lower. If the boiling point is below this range, the solvent is highly volatile and may impart an undesirable odor to the ink. When the boiling point of the solvent is above the aforementioned range, the solvent tends not to be eliminated during the drying step and remains in the printed image, resulting in reduced rub and scratch resistance of the printed image. The water-soluble organic solvent is preferably added to the ink composition formulation in an amount of 0.1-55% by weight, based on the total weight of the ink.

[0107] A.3.3. Resin The inkjet ink composition according to the present invention may contain a resin. Resins are generally added to inkjet ink formulations to achieve good adhesion of the pigment to the recording medium. The resin is preferably a polymer, and suitable resins may be acrylic resins, urethane resins, or waxes.

[0108] The polyurethane resin is introduced into the ink formulation as a dispersion and can be selected from, for example, aliphatic polyurethane dispersions, aromatic polyurethane dispersions, anionic polyurethane dispersions, nonionic 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, or a combination of two or more of the foregoing.

[0109] Preferred urethane resins for use as dispersants in the inks of the present invention are polyester resins comprising structural units containing urethane bonds. Of such resins, water-soluble or water-dispersible urethane-modified polyester resins are preferred. Preferably, the urethane-modified polyester resin comprises at least one structural unit derived from a hydroxyl-containing polyester resin (polyester polyol) and at least one structural unit derived from an organic polyisocyanate.

[0110] Furthermore, the hydroxyl-containing polyester resin is a resin formed by an esterification reaction or an ester exchange reaction between at least one polyacid component and at least one polyol component.

[0111] Preferred polyurethane resins for inclusion in the inks of the present invention are those obtainable by reacting polyester polyols, polyether diols, polyols containing anionic groups, and polyisocyanates. Particularly preferred polyurethane resins are those obtainable by reacting polyester polyols, polyether diols, polyols containing anionic groups, and polyisocyanates, wherein the polyester polyol is obtained by reacting aromatic polycarboxylic acids and polyols. Suitable polyurethane resins and examples of their preparation are disclosed in unpublished patent application EP16196224.6.

[0112] Some examples of suitable polyurethane dispersions are, for example, 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 (Covestro); DAOTAN VTW 1262 / 35WA, DAOTAN VTW 1265 / 36WA, DAOTAN VTW 1267 / 36WA, DAOTAN VTW 6421 / 42WA, DAOTAN VTW 6462 / 36WA (Allnex); and SANCURE 2715, SANCURE 20041, SANCURE 2725 (Lubrizol Corporation), or a combination of two or more thereof.

[0113] Acrylic resins include polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers of the above monomers with other monomers. These resins exist as suspensions of particles having an average diameter of about 30 nm to about 300 nm. Acrylic latex polymers are formed from acrylic monomers or methacrylic monomer residues. By way of illustration, examples of monomers for acrylic latex polymers include acrylic monomers, such as acrylates, acrylamides, and acrylic acid, and methacrylic monomers, such as methacrylates, methacrylamides, and methacrylic acid. Acrylic latex polymers can be homopolymers or copolymers of acrylic monomers and another monomer, such as a vinyl aromatic monomer, including but not limited to styrene, styrene-butadiene, p-chloromethylstyrene, divinylbenzene, vinylnaphthalene, and divinylnaphthalene.

[0114] Some examples of suitable acrylic latex polymer suspensions are, for example, JONCRYL 537 and JONCRYL 538 (BASF Corporation, Port Arthur TX); 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 BAYHYDROLAH XP 2754, BAYHYDROL AH XP 2741, BAYHYDROL A 2427, and BAYHYDROL A2651 (Bayer), or a combination of two or more of the above.

[0115] The concentration of the resin in the inkjet ink according to the present invention is at least 1 wt.-%, and preferably below 30 wt.-%, more preferably below 20 wt.-%.

[0116] The aqueous inkjet ink of the present invention may also contain a wax. The wax in the ink improves the wet rubbing or wet scratch resistance of the printed layer. Suitable examples of waxes are listed in § A.1.

[0117] The inkjet ink composition according to the present invention may include capsules. Capsules (more preferably, nanocapsules) are typically introduced into inkjet ink formulations to encapsulate colorants (US2009227711A, JP200407575759) or to encapsulate reactive components that may crosslink. Particularly useful are the nanocapsules disclosed in WO2015158649 [0037-0110]: the nanocapsules have a polymer shell surrounding a core containing a reactive chemical. Shell materials include polyureas, polyurethanes, polyesters, polycarbonates, polyamides, melamine-based polymers, and mixtures thereof, with polyureas and polyurethanes being particularly preferred. Other particularly useful nanocapsules are disclosed in WO2016165970 [0051-0138]: the nanocapsules are self-dispersible and include dispersing groups covalently coupled to the shell polymer. The cores of the nanocapsules in WO2015158649 [0037-0110] and WO2016165970 [0051-0138] contain reactive chemicals that are capable of forming reaction products upon application of heat and / or light, allowing for the treatment of a wide variety of substrates. Other suitable reactive chemicals are reactive chemicals that are activated upon irradiation, as described in WO2015158649 [0068-0110].

[0118] The resin is preferably present in the inkjet ink in an amount of not more than 30 wt%, preferably between 5 and 25 wt%, based on the total weight of the ink.

[0119] A.3.4. Additives The ink composition may contain a surfactant. Any known surfactant may be used, but preferably a glycol surfactant and / or an acetylenic alcohol surfactant and / or a polysiloxane surfactant is used. Suitable surfactants are described in § A.2.

[0120] Biocides may be added to the ink composition to prevent unwanted microbial growth which may occur over time. Suitable biocides are listed in § A.2.

[0121] The 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 total weight of the ink.

[0122] The one or more light-to-heat conversion agents are preferably present in the range of 0.1-10 wt %, based on the total weight of the ink.

[0123] B. Recording Method B.1. Method of applying pretreatment liquid The pre-treatment liquid as part of the liquid kit according to the present application is suitable for treating different substrates, both absorbent substrates and non-absorbent substrates. A substrate is characterized as absorbent when the water uptake after a 60 seconds contact time is at least 10 g / m2. Absorbent substrates include paper, paperboard, white lined chipboard, corrugated board, packaging board, folding board, wood, ceramic, stone, leather and textiles. Non-absorbent substrates include metal, glass, polypropylene, polyvinyl chloride, PET, PMMA, polycarbonate, polyamide, polystyrene or copolymers thereof.

[0124] The pre-treatment liquid is particularly suitable for coating or jetting onto paper intended for use in packaging applications, more preferably packaging applications including absorbent substrates such as paperboard, paper liner, corrugated board, packaging board, folding board and paper. The paper can be single-ply or multi-ply paper.

[0125] The paper can be brown kraft paper, white top or bleached paperboard. The paper can be made from chemical, wood or recycled fibers. As an example, the paper can be a liner intended for printing on a page wide web press and converting into corrugated boxes. In this regard, the liner paper can be used as a double face liner and can be converted directly in a corrugator or laminated onto a double face liner after corrugation. The paper can also be a board for boxes and other packaging applications.

[0126] All known conventional methods can be used to coat or impregnate the pre-treatment liquid on the substrate. Examples of such methods include air knife coating, blade coating, roll coating, gravure coating and spraying. More preferably, the pre-treatment liquid is applied by a jetting technique.

[0127] The pre-treatment liquid is then applied using an inkjet head or a valve jet. This preferred way of applying the pre-treatment composition according to the image has the advantage that the amount of pre-treatment liquid required is significantly lower than for other application methods. By means of the jetting head, the pre-treatment liquid can be applied onto the area of the substrate where the image should be printed. Suitable inkjet head types for applying the pre-treatment liquid are piezoelectric, continuous, thermal printhead, Memjet, valve jet or through-flow heads as described in § B.2.

[0128] After the pre-treatment liquid has been applied to the substrate, the coating is preferably at least partially dried to form a pre-coat before the image is printed onto the treated substrate.

[0129] The substrate to which the pretreatment composition has been applied can be dried and optionally subjected to a heat treatment prior to the subsequent inkjet step, wherein the colorant-containing ink is applied to the formed precoat layer. Examples of heating methods include, but are not limited to, hot pressing, atmospheric steam, high-pressure steam, and THERMOFIX. Any heat source can be used for the heating process; for example, an infrared lamp can be used.

[0130] In another embodiment of the present invention, the pretreatment composition is not substantially dried prior to printing the image by jetting of the aqueous inkjet step.

[0131] B.2. Inkjetting and Drying After the pretreatment liquid has been applied to the substrate, an aqueous inkjet ink, which is part of the liquid set according to the present invention, is applied to the substrate, preferably to the portion to which the pretreatment liquid has been applied or to which a precoat layer has been formed. The inkjet ink comprises a colorant, more preferably a pigment. A preferred method of applying the aqueous inkjet ink is by inkjet technology.

[0132] The preferred inkjet head for ejecting the pretreatment composition printing system is a piezoelectric inkjet head. Piezoelectric inkjet ejection is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of voltage changes the shape of the piezoelectric ceramic transducer in the print head, creating a gap, which is then filled with aqueous inkjet ink. When the voltage is removed again, the ceramic expands to its original shape, ejecting droplets of the pretreatment composition from the inkjet head. However, the ejection of ink according to the present invention is not limited to piezoelectric inkjet printing. Other inkjet print heads can be used, and include various types, such as continuous type, thermal print head type, Memjet type head and valve jet type.

[0133] In a preferred embodiment, the printing system can be configured to recirculate the aqueous ink prior to printing. Particularly useful inkjet heads for printing the aqueous inkjet inks of the liquid set of the present invention are of the type that include ink recirculation within the head, such as the through-flow heads disclosed in WO 2006 / 030235 A2 and WO 2006 / 064036 A1. This type of inkjet head is well suited for incorporation into a printing system comprising a through-flow printhead having one or more nozzles for ejecting aqueous ink droplets onto the pretreatment liquid layer, and an ink circulation system for feeding and circulating the ink through the printhead, the ink circulation system comprising an ink tank for holding the ink, a supply buffer tank for receiving the ink from a main tank and supplying the ink to the through-flow printhead, and a return manifold for receiving the ink from the through-flow printhead and returning the ink to the main ink tank via a pump.

[0134] After applying the aqueous inkjet ink to at least a portion of the pre-treatment liquid or pre-coating layer so that an image is formed, the image is dried.

[0135] The image drying step can be performed by applying an air flow and / or applying heat. The heating step must be performed using a heat source; examples include equipment for forced air heating, radiant heating such as IR radiation (including NIR, CIR, and SWIR radiation), conductive heating, high-frequency drying, and microwave drying. Examples of heating methods include, but are not limited to, hot pressing, atmospheric steam, high-pressure steam, and THERMOFIX. Any heat source can be used for the heating process; for example, infrared lamps can be used.

[0136] B.3. Application of varnish After the image obtained by printing the aqueous inkjet ink has at least partially dried, a varnish forming part of the liquid set according to the invention is applied to at least a portion of the image.

[0137] In one embodiment of the invention, the varnish is applied to the non-image areas, more particularly to the non-image areas containing the pre-treatment liquid or pre-coat.

[0138] All known conventional methods can be used to apply or print the varnish onto at least a portion of the image. Examples include air knife coating, blade coating, roller coating, gravure coating, and spraying. The advantage of coating or printing techniques is that a thick varnish layer can be obtained in a single pass over the recording medium, thereby ensuring sufficient abrasion resistance of the image.

[0139] The varnish is preferably applied via a spraying technique which allows the varnish to be applied selectively to the image.This preferably image-wise application of the varnish composition has the advantage that the amount of varnish material required is significantly lower than with other application methods.

[0140] Suitable spray heads for spraying clear varnish are the same as those described in § B.1.

[0141] Finally, the applied varnish is dried according to one of the ways described above for drying the pretreatment liquid or aqueous inkjet ink.

[0142] C. Examples C.1. Materials Unless otherwise stated, all materials used in the following examples are readily available from standard sources such as Aldrich Chemical Co. (Belgium) and Acros (Belgium). Where used, water was demineralized water (deionized water).

[0143] PB15:3 is Hostaperm TM B4G-KR, CI Pigment Blue 15:3 pigment from CLARIANT.

[0144] ●Edaplan is used for TM Abbreviation for 482, a polymeric dispersant from MUNZING CHEMIE GmbH.

[0145] ●Proxel is a 5 wt% aqueous solution of 1,2-benzisothiazolin-3-one. TM K is available from YDSCHEMICALS NV.

[0146] Liquilube 404E is a 35 wt% aqueous HDPE wax dispersion from Lubrizol Surfynol 104PG50 is a 50% by weight solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol from Evonik Printrite DP379 is an aqueous 30 wt% dispersion of a polyether-based polyurethane from Lubrizol Aquacer 530 is an aqueous dispersion from BYK containing 32% by weight of oxidized HDPE wax Synperonic PE P105 is a block copolymer of ethylene oxide and propylene oxide from Croda GmbH with 50% EO and a molecular weight of 6500 Pluronic F68 is a 100% PEO / PPO copolymer dispersant from BASF with an average Mw of 8750 g / mol and a PPO / PEO weight ratio of approximately 0.25 Dowanol DPMA is dipropylene glycol methyl ether acetate supplied by Dow Synperonic PE / F68-FL is a block copolymer of ethylene oxide and propylene oxide from Croda GmbH with 80% EO and a molecular weight of 8350 ●Pluronic P104 is a difunctional block copolymer surfactant from BASF, which is terminated at primary hydroxyl groups. ●Pluronic P123 is a block copolymer of ethylene oxide and propylene oxide from BASF with an average molecular weight of 5750 Synperonic PE F108 is a block copolymer of ethylene oxide and propylene oxide from Croda GmbH ●Pluronic P84 is a block copolymer of ethylene oxide and propylene oxide from BASF with an average molecular weight of 4200 Synperonic PE / F87-FL is a block copolymer of ethylene oxide and propylene oxide with 70% EO and a molecular weight of 7700 ●Pluronic PE9400 is a block copolymer of ethylene oxide and propylene oxide from BASF with a molar mass of 4600 g / mol Lucramul DA 554 is an aryl ethyl phenyl polyethylene glycol ether from Levaco Chemicals Solsperse 44000 is a 50 wt% aqueous solution of polyurethane-g-poly(ethylene glycol) graft copolymer Kauropal K933 is a nonionic ethylene oxide mono(2-propylheptyl) ether from BASF ●Tego Foamex 822 is a polyether siloxane copolymer from Evonik Mg(NO3)2.6H2O is magnesium nitrate hexahydrate from Merck Group ●Byk 333 is a polyether siloxane surfactant from Byk C.2. Evaluation Method C.2.1. Sample preparation Samples for gloss measurement and water resistance of the images were prepared by coating the pretreatment liquid onto a coated corrugated liner XLHD MM X-Liner HD (180 g / m2) from MM Karton using a 4 μm spiral rod. The coated liner was dried in an oven at 60°C for 2 minutes.

[0147] The inkjet ink was applied onto the coated liner by using a 10 μm spiral rod. The applied inkjet ink was then dried in an oven at 60°C for 5 minutes.

[0148] Unless otherwise stated, after drying the applied inkjet ink, a varnish was applied to the dried inkjet ink using a 10 µm spiral rod to give a solids coverage of 0.75 g / m². The varnish was dried in a ThermoScientific TM The samples were dried in Heratherm to obtain the samples for gloss and water resistance measurements.

[0149] C.2.2. Gloss measurement The gloss of the dried varnishes of the samples obtained in § C.2.1. was measured by GLOSS Zehntner at a viewing angle of 60°.

[0150] C.2.3. Water resistance The water resistance of the samples prepared according to § C.2.1 was evaluated by measuring the CIELAB delta E after wet rubbing.

[0151] The water resistance test was performed according to ISO 105-X12 with a Crockmeter SDL ATLAS M238AA. 0.02-0.04 ml water was applied to the top of the sample and subsequently the surface of the sample was treated with 10 double rubs using a crockmeter.

[0152] The whiteness of the rubbing cloth was measured 24 hours after the crocking test was performed, the whiteness is given in delta E according to the Cielab color space. The lower the delta E value, the better the water fastness.

[0153] The evaluation of the water resistance was performed according to the criteria shown in Table 1. A good pretreatment composition should provide an excellent (0) or good (1) level of water resistance.

[0154] Table 1 score Water resistance 0 (Excellent) ΔΕ < 10 1 (Good) 10 ≤ ΔE<20 2 (medium) 20 < ΔE < 40 3 (poor) ΔE>=40 C.3. Preparation of the pretreatment liquid PL-1 The pretreatment liquid PL-1 was prepared by mixing the ingredients given in Table 2. The weight percentages are relative to the total weight of the pretreatment liquid. The raw materials were used as supplied without any further treatment.

[0155] Table 2: Composition of the pretreatment liquid PL-1 Compound Amount (weight %) Printrite DP 379 17.78 Mg(NO3)2.6H2O 11.25 Synperonic PE P105 1 Aquacer 530 8 Kauropal K933 0.04 Tego Foamex 822 0.04 1,2-Propanediol 19 1,2-Hexanediol 2.85 Deionized water 40.04 C.4. Preparation of the inkjet ink INK-1 In a first step, a concentrated aqueous pigment dispersion was prepared by mixing the pigment PB15:3 with the dispersant Edaplan and 1,2-hexanediol using a Disperlux TM Yellow mixer and milled using a Dynomill TM KDL with 0.04 mm yttrium stabilized zirconium beads YTZ TM milling media (available from TOSOH Corp.). After milling, the dispersion was separated from the beads. The concentrated aqueous pigment dispersion was used as a basis for the preparation of the inkjet ink.

[0156] The aqueous cyan ink INK-1 was prepared by diluting the respective concentrated pigment dispersion with the other ink ingredients according to Table 3 expressed in weight % based on the total weight of the ink. Water was added to make up the ink to the desired pigment concentration.

[0157] Table 3: Composition of the inkjet ink INK-1 Compound Amount (weight %) Liquilube 404E 2.86 1,2-Propanediol 36 1,2-Hexanediol 3.0 Surfynol 104PG50 0.4 Proxel K 0.2 PB15:3 3.0 Edaplan 482 1.5 Deionized water to 100% by weight C.5. Preparation of the clear varnish The comparative varnishes and the varnishes of the present application were prepared by mixing the ingredients given in Table 4 and Table 5. The weight percentages are relative to the total weight of the pretreatment composition. The raw materials were used as delivered without any further treatment.

[0158] Table 4: Composition of the varnishes of the present application and the comparative varnishes Table 5: Composition of the varnishes of the present application and the comparative varnishes C.6. Example 1 In Example 1, it is shown that the liquid set of the present application comprising a varnish with the claimed copolymer (= varnishes INV-V1 to INV-V9 of the present application) shows an improved gloss value of the image formed by coating and drying the pretreatment liquid and the aqueous inkjet ink from the liquid set according to the present application.

[0159] By combining the pretreatment liquid PL-1 prepared above with the inkjet ink INK-1 prepared above and the comparative varnishes and the varnishes of the present application, the comparative liquid set and the liquid set of the present application for inkjet printing were assembled. Samples were prepared by coating the comparative liquid set and the liquid set of the present application on the recording medium as described in § C.2.1.

[0160] Gloss was measured as described in § C.2.2 and § C.2.3. The measured values are listed in Table 6.

[0161] From Table 6 it can be seen that the gloss values of the coated liquid set comprising PL-1 + INK-1 and different varnishes, the liquid set of the present application comprising a pretreatment with a polyvalent metal salt as fixative, an aqueous inkjet ink comprising a pigment and a varnish comprising water, resin particles, a polyether siloxane surfactant and a water-soluble copolymer indeed show significantly higher gloss values than the comparative liquid set.

[0162] Table 6: Gloss values of the coated liquid set comprising PL-1 + INK-1 and different varnishes Liquid Varnish Set Gloss at 60° COMP-V1 25.3 COMP-V2 25.8 COMP-V3 24.9 COMP-V4 23.8 INV-V1 31.6 INV-V2 41.6 INV-V3 42.4 INV-V4 43.9 INV-V5 44.2 INV-V6 42.3 INV-V7 38.30 INV-V8 39.60 INV-V9 41.8 C.7. Example 2 In Example 2, it is shown that the presence of a polyether siloxane surfactant in the varnish of the liquid set of the present application improves the water resistance of the printed image.

[0163] The comparative varnishes and the varnishes of the present application were prepared by mixing the ingredients given in Table 7. The weight percentages are relative to the total weight of the pretreatment composition. The raw materials were used as delivered without any further treatment.

[0164] Table 7: Composition of comparative varnish and varnish of the present invention By combining the above prepared pretreatment liquid PL-1, the above prepared inkjet ink INK-1 and the respective comparative varnish and varnish of the present invention from Table 7, a comparative liquid set and a liquid set of the present invention for inkjet printing were assembled. Samples were prepared by coating the comparative liquid set and the liquid set of the present invention on a recording medium as described in § C.2.1.

[0165] The water resistance of the printed images was measured as described in § C.2.3. The measured values are listed in Table 8.

[0166] Table 8: Water resistance values of images obtained by coating the comparative liquid set and the liquid set of the present invention varnish Water resistance COMP-V5 3 INV-V10 1 INV-V11 0 INV-V12 1 INV-V13 1 From Table 8 it is clear that in order to achieve a good or excellent water resistance of the printed image the amount of polyether siloxane surfactant in the varnish should be 0.25 wt% or more.

[0167] C.8. Example 3 In Example 3 it was shown that the solid coverage of the varnish has to be equal to 0.6 g / m2or more to achieve a sufficient water resistance of the printed image.

[0168] A varnish of the present invention was prepared by mixing the ingredients given in Table 9. The weight percentages are relative to the total weight of the pretreatment composition. The raw materials were used as supplied without any further treatment.

[0169] Table 9: Composition of varnish of the present invention INV-14 Compound Amount (weight %) Neocryl D2101 14.29 Synperonic PE F108 1.0 Propylene glycol 25.5 Dowanol DPMA 5.0 Byk333 0.8 Deionized water to 100% by weight By combining the above prepared pretreatment liquid PL-1 with the above prepared inkjet ink INK-1 and the varnish of the present invention from Table 9, a liquid set of the present invention for inkjet printing was assembled. Samples were prepared by coating the liquid set of the present invention on a recording medium under different wet coat thicknesses of the varnish to achieve different solid weights after drying as described in § C.2.1.

[0170] The gloss and water resistance of the printed images were measured as described in § C.2.2 and § C.2.3. The measured values are listed in Table 10.

[0171] Table 10: Gloss and water resistance values of coated liquid set of the present invention Solid thickness of clear coat INV-V14 (g / m²) Gloss value Water resistance 0 9.0 3 0,24 27.1 3 0,36 28 3 0,6 35 0 1,2 35.5 0 From Table 10 it is seen that in order to achieve an excellent water resistance the thickness of the varnish should be equal to 0.6 g / m2or more.

Claims

1. A liquid kit for inkjet printing, comprising an aqueous pretreatment liquid, an aqueous inkjet ink, and a varnish, wherein the aqueous pretreatment liquid comprises a fixing agent, the aqueous inkjet ink comprises a pigment and a water-soluble organic solvent, and the varnish comprises water, a water-soluble polymer selected from a linear PPO-PEO copolymer and an arylethylphenyl polyethylene glycol ether, and resin particles selected from a urethane-based resin, an acrylic resin, a fluorene-based resin, a polyolefin-based resin, a rosin-modified resin, a terpene-based resin, a polyester-based resin, a polyamide-based resin, an epoxy-based resin, a vinyl chloride-based resin, and a wax. 2 . The liquid kit according to claim 1 , wherein the water-soluble polymer is a nonionic polymer.

3. The liquid kit according to any one of the preceding claims, wherein the varnish comprises a polyether siloxane surfactant.

4. The liquid kit according to any one of the preceding claims, wherein the fixing agent is a multivalent salt, a cationic polymer or an organic acid.

5. The liquid kit according to any one of the preceding claims, wherein the pre-treatment liquid comprises resin particles selected from poly(urethane), poly(acrylate) and wax.

6. The liquid kit according to any one of the preceding claims, wherein the pre-treatment liquid comprises a PPO / PEO copolymer, an arylethylphenyl polyethylene glycol ether or a fatty acid derivative having an EO / PO moiety.

7. The liquid set according to any one of the preceding claims, wherein the aqueous inkjet ink comprises resin particles selected from the group consisting of poly(urethanes), poly(acrylates) and waxes.

8. A printing method comprising the following steps: a) applying a pretreatment liquid as defined in claim 1 to claim 7 to at least a portion of the substrate; and b) optionally at least partially drying the applied pretreatment liquid to form a precoat layer; and c) jetting an aqueous inkjet ink as defined in claim 1 to claim 7 onto at least a portion of the applied pretreatment liquid or onto the precoat layer; and c) applying heat to dry the jetted aqueous inkjet ink to form an image; and d) applying a varnish as defined in claims 1 to 7 to at least a portion of the image; and e) applying heat to dry the varnish.

9. The printing method according to claim 8, wherein the solids amount of the applied varnish is equal to 0.6 g / m² or more.

10. A printing method according to claim 8 or claim 9, wherein the pre-treatment liquid is applied via a jetting technique.

11. A printing method according to claim 8 to claim 10, wherein the varnish is applied via spraying technology.

12. The printing method according to claim 8 to claim 11, wherein the substrate is an absorptive substrate.

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