Inkjet recording method

Abstract

A recording method of inkjet printing an aqueous inkjet ink on an absorbent medium, the method comprising the steps of: a) transporting the absorbent medium in a transport direction, the medium having a width oriented transverse to the transport direction; and b) adhering a pretreatment liquid at least partially across the width of the absorption medium to form a layer having a thickness of from 1 to 5 [mu] m, the pretreatment liquid comprising water, a fixative, a hydrophilic binder selected from the group consisting of polyvinyl alcohol (PVOH) or modified polyvinyl alcohol, water dispersible ethylene vinyl alcohol (EVOH), a polysaccharide, and a surfactant. Comprising cellulose, a cellulose derivative, CMC, starch, a starch derivative and a combination of two or more of the cellulose, the cellulose derivative, the CMC, the starch and the starch derivative, and the viscosity of the pretreatment liquid is 40-300 mPa.s; and c) applying an aqueous inkjet ink to the layer by ejecting the ink from an inkjet head to form an image, the ink comprising a pigment, a water-soluble organic solvent; and d) drying the layer and the applied inkjet ink by applying heat and airflow to the image.

Description

Technical Field

[0001] The present invention relates to a recording method for inkjet printing aqueous inkjet inks on liner paper for corrugated packaging, folding board and corrugated cardboard. Background Art

[0002] Inkjet printing is a growing field for printing interlining paper for corrugated packaging and corrugated cardboard. Inkjet printing is preferably carried out using aqueous inkjet inks. Aqueous inkjet inks are inherently safer than reactive UV inks and inks whose primary solvent is solvent.

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

[0004] Because aqueous inks printed on a receiver dry primarily by evaporation of water, without much water penetration or absorption into the backing paper or cardboard, several problems are encountered. One such problem is that individual ink droplets spread slowly laterally across the coating surface, creating white lines in solid color areas and uneven patterns in solid color areas due to contact and coalescence with adjacent ink droplets. This results in visual image quality artifacts known as "coalescence" or "puddling." Another problem encountered when ink dries too slowly and when two different colors of ink are printed adjacent to each other is that the two colors tend to bleed into each other, resulting in a defect known as "intercolor bleed." Yet another problem is that when printing at high speeds in sheet-fed or roll-to-roll processes, the printed image does not dry sufficiently before it comes into contact with an unprinted surface, and ink is transferred from the printed area to the unprinted surface, causing unwanted "ink retransfer."

[0005] To achieve high-quality images, a pretreatment fluid can be used to initially treat or pretreat the media before the ink colorant is jetted onto the media to provide bleed and coalescence control, as well as improved adhesion and durability. The composition of the pretreatment fluid is capable of accepting ink and retaining or fixing the colorant in the ink to a greater extent than substrates not treated with the pretreatment fluid. In particular, the pretreatment fluid composition is capable of retaining the colorant at or near the surface of the substrate, resulting in improved optical density and color gamut of the printed image compared to absorbent substrates not treated with the pretreatment fluid.

[0006] However, if the pretreatment liquid is applied to the surface of a porous or absorptive recording medium, it may penetrate into the absorptive recording medium or at least partially dry out. When the aqueous pigment ink is applied to this pretreated recording medium, the reaction liquid is present within the recording medium rather than on its surface. Consequently, almost all of the color fixation reaction occurs within the recording medium. This leads to insufficient color development, resulting in low color density.

[0007] EP 1555137 A1 discloses a recording method in which a pretreatment liquid containing a polyvalent metal salt is applied to the recording medium and then a pigment ink having a lower surface tension than the reaction liquid is applied thereto within a time interval of between 5 ms and 200 ms. This short time interval represents demanding conditions for the printing apparatus. The necessary restrictions on the surface tension values ​​of the ink and pretreatment liquid represent severe constraints on the spreading and adhesion of the pretreatment liquid and on the reliable ejection of the ink.

[0008] WO14051547A discloses a wet-on-wet printing method comprising the steps of applying a simulated pretreatment fluid to a low-absorbing or non-absorbing medium, digitally inkjet printing a first inkjet ink on the coated medium sheet while the pretreatment fluid is still wet, and digitally inkjet printing a second inkjet ink on the first inkjet ink while the simulated pretreatment fluid and the first inkjet ink are still wet. The simulated pretreatment fluid contains latex as a binder and an associative thickener.

[0009] US2013 / 0156953 discloses a pretreatment fluid for use with less-porous or non-porous printing media, comprising a pigment ink composition comprising a liquid vehicle, a latex selected from an acrylic polymer, an acrylic copolymer, and a polyurethane, and an associative thickener. The pretreatment fluid has a viscosity of about 10 cps to about 1000 cps and a surface tension of about 16 dynes / cm to about 30 dynes / cm.

[0010] A disadvantage of latex-based binders in pretreatment liquids is that they cause the liquid to form a film at the air / liquid interface, clogging nozzles and pipes. This requires specific precautions in the liquid supply to the printing press and in the liquid application equipment. In addition to the disadvantage of film formation, latex binders also require associative thickeners (which are expensive compounds) to achieve the required viscosity of the pretreatment liquid, and most further require organic solvents such as dipropylene glycol dimethyl ether or dipropylene glycol methyl ether to promote film formation. Organic solvents should be avoided to minimize the release of toxic vapors during the drying of the pretreatment liquid during image formation.

[0011] There remains a need for a recording method comprising applying a pre-treatment liquid to an absorptive medium that produces acceptable image quality of inkjet printed images in a wet-on-wet printing mode and without latex or associative binders in the pre-treatment liquid. Summary of the Invention

[0012] The object of the present invention is to provide a solution to the problems set out above. This object has been achieved by providing a recording method as defined in claim 1, which comprises adhering a pretreatment liquid as a layer having a thickness of 1 μm to 5 μm and applying an aqueous inkjet ink to the layer, the pretreatment liquid comprising a fixing agent, a hydrophilic binder, a crosslinking agent, and having a viscosity of 40 to 300 mPa·s.

[0013] Another embodiment of the present invention is to provide a liquid set as defined in claim 12 comprising the aqueous inkjet ink of claim 1 and a pretreatment liquid.

[0014] 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. Particular embodiments of the present invention are also defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1: Pattern used for inkjet printing during the evaluation of image quality and physical properties of images obtained with pre-treatment liquid. The pattern contains solid areas and negative text with different sizes ranging from 1 pt to 16 pt. DETAILED DESCRIPTION A. Recording method for inkjet printing and liquid used therein A.1. Recording method for inkjet printing

[0016] The recording method of the present invention for inkjet printing an aqueous inkjet ink on an absorptive medium comprises the following steps:

[0017] First, an absorbent medium is transported in a conveying direction. The medium can be in the form of a sheet or a web. The medium has a width oriented transversely to the conveying direction.

[0018] Next, the pretreatment liquid is adhered at least partially across the width of the recording medium to form a layer having a thickness of 1 to 5 μm, and the pretreatment liquid is dried at a temperature of 25° C. for 1000 s. -1 The viscosity of the pretreatment liquid is 40 to 300 mPa.s at a shear rate of .

[0019] The method used to achieve adhesion can be selected from many known techniques including, but not limited to, spray coating, rod coating, roller coating, knife coating, bar coating, gravure coating (direct, reverse and indirect), flexographic coating, size press (puddle and metered), and curtain coating.

[0020] Flexographic coating involving the adhesion of the pretreatment liquid by means of an anilox roller is preferred.

[0021] Flexographic coating technology using anilox rollers is well-suited for uniformly applying pretreatment liquids with a viscosity of 40 to 300 mPa·s at wet layer thicknesses of 1 μm to 5 μm (preferably 1.5 μm to 4 μm). If the layer thickness is below these ranges, insufficient fixation of the ink pigments will result, leading to insufficient image quality. If the layer thickness is above the aforementioned ranges, the amount of liquid applied, such as water, is too high and insufficient drying will result, especially at the high printing speeds achievable using a fixed array of inkjet heads (so-called single-pass printing mode).

[0022] After the pretreatment liquid is applied to the medium, and while the pretreatment liquid is still wet (the layer thickness is preferably 0.5 μm to 5 μm), the aqueous pigment ink composition is applied to the wet pretreatment liquid-coated medium.

[0023] A preferred method of applying aqueous inkjet inks is by means of inkjet technology.

[0024] The preferred inkjet head for the injection of aqueous inkjet printing system is a piezoelectric inkjet head. Piezoelectric inkjet injection 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 that is then filled with aqueous inkjet ink. When the voltage is removed again, the ceramic expands to its original shape, ejecting aqueous inkjet ink drops from the inkjet head. However, the injection of aqueous inkjet 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.

[0025] The inkjet head can be a fixed nozzle array oriented transversely to the transport direction (preferably across the width of the absorbent medium) or can be incorporated into a scanning device that moves the inkjet head in a direction transverse to the transport direction. Such a fixed nozzle array oriented transversely to the transport direction has the advantage that a high production speed of images printed by inkjet can be achieved.

[0026] In particular, to reliably jet metal oxide-based white inks, the inkjet printing system preferably includes a shaking, mixing, or stirring device. This device is used to redisperse the white inkjet ink that may have settled between print jobs. In some examples, the printing system can be configured to shake an ink sac, ink tank, or ink buffer tank containing the white inkjet ink. In other examples, the printing ink sac or ink tank is configured to mix or stir the white inkjet ink prior to printing.

[0027] In a preferred embodiment, the printing system can be arranged to recirculate the aqueous ink prior to printing. Particularly useful inkjet heads for printing the aqueous inkjet inks of the present invention are of the type that include recirculation of the ink within the head (e.g., through-flow heads as disclosed in WO 2006 / 030235 A2 and WO 2006 / 064036 A1).

[0028] This type of inkjet head is very suitable for incorporation into a printing system, which includes a through-flow print head having one or more nozzles for ejecting drops of aqueous ink onto the pre-treatment liquid layer; and an ink circulation system for feeding and circulating the ink through the print head, which includes an ink tank for holding ink, a supply buffer tank for receiving ink from a main tank and supplying the ink to the through-flow print head, and a return manifold for receiving ink from the through-flow print head and returning the ink to the main ink tank via a pump.

[0029] The time interval between applying the pretreatment liquid and applying the aqueous pigment ink is preferably between 200 ms and 30 s. Longer time intervals are less preferred because the pretreatment liquid can then penetrate too much into the absorption medium. When high printing speeds are used for the recording method of the present invention, shorter time intervals are very difficult to achieve because the inkjet head must then be installed very close to the coating station or printing station in order to adhere the pretreatment liquid to the recording medium.

[0030] After the aqueous inkjet ink is applied onto the pre-treatment liquid layer so that an image is formed, the image is dried.

[0031] The image drying step can be performed by applying air flow and / or heat. The heating step must be performed using a heat source; examples include equipment for forced air heating, radiant heating (e.g., IR radiation, including NIR radiation, CIR radiation, and SWIR radiation), conductive heating, high-frequency drying, and microwave drying. Examples of heat treatments include, but are not limited to, hot pressing, atmospheric steaming, high-pressure steaming, and THERMOFIX. Any heat source can be used for the heat treatment, such as infrared lamps.

[0032] In order to further increase the dry and wet rubbing resistance of the inkjet image, a varnish can be applied to the formed image. Preferably, the varnish is an aqueous solution or dispersion of a resin. Preferably, the varnish is applied via a spraying technique that allows the varnish to be applied selectively to the image or via a coating or printing technique. The advantage of coating or printing techniques is that a thick varnish layer can be obtained in a single pass of the recording medium to ensure sufficient rubbing resistance of the image and additional protection of the non-image area. A.2. Pretreatment of liquid A.2.1. Carrier

[0033] The aqueous pretreatment composition according to the present invention comprises water as a solvent. The aqueous solvent may comprise one or more water-soluble organic solvents.

[0034] One or more organic solvents may be added for a variety of reasons. For example, it may be advantageous to add a small amount of an organic solvent to improve the solubility of the compound in the pretreatment composition to be prepared.

[0035] Suitable water-soluble organic solvents are listed in §A.3. A.2.2. Adhesives

[0036] The pre-coat composition used in the present invention further comprises a hydrophilic polymer binder. The hydrophilic binder helps anchor the pigment from the ink to the substrate and helps achieve the desired viscosity of the pre-treatment liquid, for example to obtain a uniform layer on the absorbent medium, especially if the pre-treatment liquid is to be applied by flexographic printing technology.

[0037] Such hydrophilic polymer binders include polymers that can absorb water and preferably can form a continuous phase solution. Non-exclusive examples of such materials include gelatin, hydroxycellulose, polyvinyl alcohol, modified polyvinyl alcohol, water-dispersible ethylene vinyl alcohol (EVOH), polysaccharides, including cellulose, cellulose derivatives, carboxymethyl cellulose (CMC), starch, starch derivatives, acrylic-based (to) polymers, polyvinyl pyrrolidone, polyethylene imine, polyvinyl amine and derivatives of these materials and any two or more combinations of these compounds.

[0038] The hydrophilic polymer binder preferably comprises a polymer with hydroxyl functional groups, such as polyvinyl alcohol, and more particularly polyvinyl alcohol with a saponification degree of 88%, more preferably 98% or higher. The hydroxyl groups of the hydrophilic binder interact with the cationic fixative, forming a complex-like structure. This structure enhances the wet film strength of the pretreatment layer and the ink printed atop it. According to a preferred embodiment of the present invention, the binder is Poval 2098 from Kuraray, a polyvinyl alcohol with a saponification degree of 98.0 to 98.8 mol%.

[0039] The pretreatment liquid of the present invention comprises a hydrophilic polymer binder in an amount of 5 to 70 wt.%, preferably 8 to 60 wt.%, more preferably 15 to 45 wt.%, based on the weight of all dry components of the pretreatment liquid composition.

[0040] More preferably, the pretreatment liquid of the present invention comprises polyvinyl alcohol in an amount of 5 to 70 wt.%, more preferably 8 to 50 wt.%, and most preferably 15 to 45 wt.%, based on the weight of all dry components of the pretreatment liquid composition. The weight-average molecular weight of the polyvinyl alcohol in the pretreatment of the present invention is preferably from about 50,000 to about 250,000 g / mol, as measured using GPC with PE as a reference. If the amount and molecular weight of the polyvinyl alcohol are outside the above ranges, the viscosity of the pretreatment liquid will be outside the preferred range of 40 mPa.s to 300 mPa.s.

[0041] The hydrophilic polymer binder in the precoat formulation used in the present invention may be crosslinked to improve the abrasion resistance of the jetted image when wet, as well as to provide increased coating cohesion after drying.

[0042] Non-exclusive examples of cross-linking agents are dialdehydes such as glyoxal, Cartabond TSI (Clariant), Cartabond EPI (Clariant), Sequarez 755 (Omnova), glutaraldehyde sodium bisulfate complex (Aldrich), Sunrez 5700M (Omnova), Sunrez 700C (Omnova), CR-5L (Esprix), bis(vinyl)sulfone, bis(vinyl)sulfone methyl ether, adipic acid dihydrazide, boric acid, epichlorohydrin polyamide resins, carbodiimides, and urea-formaldehyde resins.

[0043] Preferably, the crosslinking agent is boric acid, borax, sodium tetraborate, phenylboric acid, butylboric acid, and combinations thereof. Without being bound by any particular theory, it is believed that these boron-containing compounds act as colorant fixing agents that can chemically, physically, and / or electrostatically bind the pigment in the inkjet ink at the surface of the absorbing medium or hydrophilic adhesive.

[0044] The viscosity of the pretreatment fluid should be such that the pretreatment fluid is sufficiently suitable for adhesion to the absorbent medium, preferably by coating or printing techniques. In particular, for adhesion via flexographic printing, the viscosity of the pretreatment is preferably in the range of 1000s at 25°C. -1 40 to 300 mPa.s at a shear rate of 1000 s at 25 ° C. -1 80 to 300 mPa.s at a shear rate, most preferably at 1000 s at 25 °C -1The viscosity of the pretreatment liquid is typically between 90 and 300 mPa.s at a shear rate of 100 to 200 mPa.s. If the viscosity of the pretreatment liquid is below this range, rapid penetration into the absorbing medium occurs, and limited interaction occurs between the fixative and the pigment of the ink printed on top of the pretreatment liquid, resulting in poor image quality. Viscosities exceeding 300 mPa.s can be achieved with the help of viscosity enhancers. However, viscosity enhancers lack the beneficial interaction between the hydroxyl groups of the hydrophilic binder and the cationic fixative, which forms a complex-like structure. This structure can lead to enhanced wet film strength of the pretreatment layer and the ink printed on top of it.

[0045] Viscosities exceeding 300 mPa.s further increase the risk of inhomogeneities in the pretreatment layer when applied at low wet layer thicknesses. A.2.3. Wax

[0046] Pretreatment compositions according to the present invention may comprise wax. Wax can improve the durability of ink and pretreatment packaging during general treatment. Usually, any suitable wax can be used in the pretreatment compositions. Therefore, wax can be polyethylene wax, petroleum wax, paraffin wax, carnauba wax, polypropylene wax, crystalline wax and microcrystalline wax, amide wax (oleamide, stearamide, erucamide, cyclic amide etc.) and combination thereof. In one aspect of the invention, wax can be high density polyethylene wax.

[0047] In one aspect of the present invention, the wax can be a polyethylene wax or a modified paraffin wax. Examples of polyethylene waxes include high-density polyethylene (HDPE) waxes, which have a density range of about 0.93 g / mL to 0.97 g / mL. The density of HDPE is generally higher than that of low-density polyethylene (LDPE), which is at least partially due to the lower amount of molecular branching in HDPE.

[0048] Examples of modified paraffin wax particles include paraffin wax that has been modified (e.g., via emulsification) to improve dispersibility in water. The modified paraffin wax may be surface-modified, chemically modified, or the like.

[0049] Some specific examples of waxes that can be used include those in the JONCRYL Wax series (e.g., JONCRYL Wax 22, JONCRYL Wax 26, and JONCRYL Wax 120, available from BASF Corp.), those in 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. The wax can also or otherwise be selected from water-dispersible waxes available from Micro Powders, Inc., Tarrytown, NY.

[0050] The wax may have i) a high melting temperature T and / or ii) a small average particle size. In one example, the wax may have a high melting T, such as a melting T equal to or greater than about 100°C. In one example, the T range of the wax may be from about 100°C to about 150°C. In another example, the T range of the wax may be from about 110°C to about 135°C. Further, the average particle size of the wax (in terms of effective diameter, assuming that the individual wax particles are not perfectly spherical) may range from 0.03 μm to 1.5 μm, more preferably from 0.05 μm to 1 μm, and most preferably from 0.07 μm to 0.50 μm (D50). The particle size of the wax may be measured by various techniques (e.g., dynamic light scattering). If the particle size exceeds these upper limits, problems with the jetting reliability of the pre-coating composition may arise.

[0051] The wax may be present in the pre-treatment liquid in an amount ranging from 3 to 25 wt.%, more preferably from 5 to 20 wt.%, relative to the total solid weight of the pre-treatment composition. A.2.4. Fixative

[0052] The fixing agent present in the pretreatment composition is preferably a polyvalent metal salt or a cationic polymer, which is capable of reacting with the anionic compound (which is the anionically charged pigment) in the inkjet ink.

[0053] 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 particular examples, the polyvalent metal salt may include calcium chloride (CaCl2), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), aluminum chloride (AlCl3), calcium nitrate (Ca(NO3)2), magnesium nitrate (Mg(NO3)2), magnesium acetate (Mg(CH3COO)2), zinc acetate (Zn(CH3COO)2), calcium propionate (Ca(C2H5COO)2), or a combination thereof. In further examples, the polyvalent metal salt may comprise a metal cation selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminum, chromium, or another polyvalent metal.

[0054] 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, for example C1 to C12. In a more particular example, the anion can be a carboxylate radical derived from a saturated aliphatic monocarboxylic acid having 1 to 6 carbon atoms or a carbocyclic monocarboxylic acid having 7 to 11 carbon atoms. Examples of saturated aliphatic monocarboxylic acids having 1 to 6 carbon atoms can include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, pivalic acid and / or caproic acid. The cationic salt can also be a mixture of two or more different cationic salts.

[0055] In some cases, the polyvalent metal salt may be present in an amount of 1 to 99 wt.% relative to the total weight of the pretreatment composition. In more specific embodiments, the polyvalent metal salt may be present in an amount of 5 to 65 wt.%, more preferably 25 to 60 wt.%, relative to the solids content of the pretreatment composition. If the amount is below the lower limit, insufficient fixation of the colorant may occur, resulting in reduced image quality.

[0056] Polymeric cationic polymers suitable as fixing agents in the pretreatment composition contain guanidinium or fully quaternized ammonium functional groups, such as quaternized polyamine copolymers. Typical Mw is less than 500.000, and in one aspect less than 50.000.

[0057] 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. A.3. Water-based inkjet ink

[0058] The aqueous inkjet ink used in the recording method according to the present invention and for printing on the layer of the pretreatment liquid layer contains a pigment.The aqueous medium of the ink contains water, but may contain one or more water-soluble organic solvents.

[0059] In a preferred embodiment of the present invention, the aqueous inkjet ink comprises a resin and or a wax. Suitable waxes are described in §A.2.3.

[0060] The aqueous inkjet ink may further contain surfactants, humectants, biocides, resins, defoaming additives, anti-corrosion additives, and thickeners as additives. A.3.1. Pigments

[0061] The pigment in the aqueous inkjet ink according to the present invention may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, etc. The color pigment may be selected from those disclosed in HERBST, Willy et al. Industrial Organic Pigments, Production, Properties, Applications, 3rd edition, Wiley-VCH, 2004 ISBN 3527305769.

[0062] Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO 2008 / 074548.

[0063] The pigment particles are dispersed in an aqueous medium using a polymeric dispersant, a surfactant, or a combination thereof. Self-dispersible pigments can also be used. The latter prevent the polymeric dispersant from interacting with the dispersing groups (see below) of the resin particles or capsules that may be contained in the inkjet ink.

[0064] Self-dispersible pigments are pigments having covalently bonded anionic hydrophilic groups or salt-forming groups on their surface which allow the pigment to be dispersed in aqueous media without the use of surfactants or resins.

[0065] The technology for preparing self-dispersible pigments is well known. For example, EP1220879A discloses pigments suitable for inkjet inks having attached a) at least one steric group and b) at least one organic ionic group and at least one amphiphilic counterion, wherein the charge of the amphiphilic counterion is opposite to the charge of the organic ionic group. EP906371A also discloses suitable surface-modified colored pigments having attached hydrophilic organic groups containing one or more ionic groups or ionizable groups. Suitable commercially available self-dispersible color pigments are, for example, CAB-O-JET from CABOT. TM Inkjet colorants.

[0066] 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 jet nozzle. It is also desirable to use small particles to maximize color intensity and slow down sedimentation.

[0067] The average pigment particle size is preferably between 0.050 μm and 1 μm, more preferably between 0.070 μm and 0.300 μm, and particularly preferably between 0.080 μm and 0.200 μm. Most preferably, the number average pigment particle size is no greater than 0.150 μm. The average pigment particle size is determined based on the principle of dynamic light scattering using a Brookhaven Instruments Particle Sizer BI90plus.

[0068] 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. Titanium dioxide is preferably 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.

[0069] 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.

[0070] Suitable polymeric dispersants are copolymers of two monomers, but they may contain three monomers, four monomers, five monomers or even more monomers. The properties of the polymeric dispersant depend on both the nature of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition: ● Statistically polymerized monomers (e.g., monomer A and monomer B polymerize to form ABBAABAB); ● Alternating monomers (e.g. monomer A and monomer B polymerize to form ABABABAB); ● Monomers that are polymerized in a gradient (e.g., monomer A and monomer B polymerize to form AAABAABBABBB); ● Block copolymers (e.g. monomer A and monomer B are polymerized to form AAAAABBBBBB), where each block (2, 3, 4 The block length of 1, 5 or even more (1, 2 or 3) 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.

[0071] A suitable dispersant is DISPERBYK available from BYK CHEMIE TM Dispersant, JONCRYL available from BASF TM Dispersants and SOLSPERSE available from Lubrizol TM Dispersants. A detailed list of non-polymeric dispersants as well as some polymeric dispersants is disclosed by MC CUTCHEON. Functional Materials (North American Edition) Glen Rock, NJ: Manufacturing Confectioner Publishing Co., 1990, pp. 110-129.

[0072] The number average molecular weight Mn of the polymeric dispersant is preferably between 500 and 30,000, more preferably between 1,500 and 10,000.

[0073] The weight average molecular weight Mw of the polymeric dispersant is preferably less than 100,000, more preferably less than 50,000 and most preferably less than 30,000.

[0074] The pigment is preferably present in the range of 0.01 to 15 wt %, more preferably in the range of 0.05 to 10 wt %, and most preferably in the range of 0.1 to 5 wt %, 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 wt %, and more preferably 5 to 35 wt %, based on the weight of the inkjet ink. An amount of less than 3 wt % may not achieve sufficient covering power.

[0075] In a preferred embodiment of the present invention, the aqueous ink comprises a pigment encapsulated by means of a cross-linked polymer shell.The encapsulated pigment undoubtedly provides a higher stability in the formulation in which the pigment dispersion is mixed with the resin dispersion.

[0076] Suitable encapsulated pigments are supplied by Lubrizol as Diamond HSDX dispersions and by Fujifilm as RxD pigment dispersions (eg APD1000 and APD400 premium dispersions). A.3.2. Solvent

[0077] The aqueous ink according to the present invention contains water as a solvent. The aqueous solvent may further contain one or more water-soluble organic solvents.

[0078] One or more organic solvents can be added for various reasons. For example, it can be advantageous to add a small amount of organic solvent to improve the dissolving of the compound in ink composition to be prepared or to prevent the rapid drying of ink at the nozzle of inkjet head. Preferred water-soluble organic solvents are polyols (such as ethylene glycol, glycerine, 2-ethyl-2-hydroxymethyl-1,3-propylene glycol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, 1,6-hexanediol, 1,2-hexanediol, 1,5-pentanediol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-pentanediol, 2,2-dimethyl-1,3-propylene glycol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol and 2-methyl-1, 3-propylene glycol), N-hydroxyethyl pyrrolidone, N-butyl pyrrolidone, amines (such as ethanolamine and 2-(dimethylamino)ethanol), monohydric alcohols (such as methanol, ethanol and n-butanol), alkyl ethers of polyhydric alcohols (such as 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 (such as N,N-dimethylformamide), heterocycles (such as 2-pyrrolidone and N-methyl-2-pyrrolidone) and acetonitrile.

[0079] Preferably, if two or more organic solvents are present in the ink, one of the organic solvents 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 stated range, the solvent tends to remain in the printed image without being eliminated during the drying process, 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 to 55 wt.%, based on the total weight of the ink. A.3.3. Resin

[0080] The inkjet ink composition according to the present invention may include a resin suspension. Resins are typically 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-based resins, polyurethane resins, or waxes.

[0081] The polyurethane resin is incorporated 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.

[0082] Preferred urethane resins to be used as dispersions in the inks of the present invention are polyester resins containing structural units containing urethane bonds. Among such resins, water-soluble or water-dispersible urethane-modified polyester resins are preferred. Preferably, the urethane-modified polyester resin contains 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.

[0083] Furthermore, the polyester resin containing a hydroxyl group 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.

[0084] Preferred polyurethane resins to be included in the inks of the present invention are polyurethane resins obtainable by reacting polyester polyols, polyether diols, polyols containing anionic groups and polyisocyanates. Examples of suitable polyurethane resins and their preparation are disclosed in the unpublished patent application EP16196224.6.

[0085] 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, BAYHYDROLUH XP 2648, and BAYHYDROLUA 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 CA); and SANCURE 2715, SANCURE 20041, SANCURE 2725 (Lubrizol Corporation), or a combination of two or more of the foregoing.

[0086] Acrylic-based resins include polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers of the foregoing monomers with other monomers. These resins exist as a suspension 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 example, 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 of acrylic monomers or copolymers of acrylic monomers with another monomer such as a vinyl aromatic monomer, including but not limited to styrene, styrene butadiene, parachloromethylstyrene, divinylbenzene, vinyl naphthalene, and divinylnaphthalene.

[0087] 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 BAYHYDROL AH XP 2754, BAYHYDROL AH XP 2741, BAYHYDROLA 2427 and BAYHYDROLA 2651 (Bayer), or a combination of two or more thereof.

[0088] The aqueous inkjet ink of the present invention may further comprise wax. The wax in the ink improves the wet rubbing resistance or wet scratch resistance of the printed layer.

[0089] The inkjet ink composition according to the present invention may include capsules. Capsules (more preferably nanocapsules) are often incorporated into inkjet ink formulations to encapsulate colorants (US2009227711A, JP2004075759) or to encapsulate crosslinkable reactive components. 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-dispersing and contain 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 form reaction products upon application of heat and / or light, enabling the treatment of a wide variety of substrates. Other suitable reactive chemicals are those that are activated upon irradiation, as described in WO2015158649[0068-0110].

[0090] The resin is preferably present in the ink in an amount of not more than 30 wt.%, preferably between 0.3 wt.% and 25 wt.%, based on the total weight of the inkjet ink. A.3.4. Additives

[0091] The ink composition may contain a surfactant. Any known surfactant may be used, but preferably a glycol surfactant and / or an acetylene alcohol surfactant and / or a polysiloxane surfactant is used. The use of an acetylene glycol surfactant and / or an acetylene alcohol surfactant and / or a polysiloxane surfactant improves drying properties during printing, allowing high-speed printing.

[0092] The acetylene glycol surfactant and / or acetylene alcohol surfactant is preferably one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4-dimethyl-5-decyn-4-ol, and alkylene oxide adducts of 2,4-dimethyl-5-decyn-4-ol. These are available from Nissin Chemical Industry, for example as the Olfine (registered trademark) E series, such as Olfine E1010, or as Surfynol (registered trademark) 104, Surfynol 465, and Surfynol 61, available from Evonik (formerly Air Products (GB)).

[0093] Biocides may be added to the ink composition 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 parahydroxybenzoate, and 1,2-benzisothiazolin-3-one and its salts.

[0094] A preferred biocide is Proxel available from ARCH UK BIOCIDES TM GXL and Proxel TM Ultra 5 and Bronidox available from COGNIS TM .

[0095] 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.

[0096] The ink composition may further comprise at least one thickener for viscosity adjustment in the liquid. Suitable thickeners include urea or urea derivatives, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, derivatized chitin, derivatized starch, carrageenan, pullulan, protein, polystyrene sulfonic acid, poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamide, partially hydrolyzed polyacrylamide, polyacrylic acid, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate, polyhydroxyethyl acrylate, polymethyl vinyl ether, polyvinyl pyrrolidone, poly(2-vinyl pyridine), poly(4-vinyl pyridine), and poly(diallyldimethylammonium chloride).

[0097] The thickener is preferably added in an amount of 0.01 to 20 wt.%, more preferably 0.1 to 10 wt.%, based on the liquid.

[0098] The ink composition may also contain a photothermal conversion agent, which may be any suitable compound that absorbs within the wavelength range emitted by the infrared light source. The photothermal conversion agent is preferably an infrared dye, as this allows for easy processing into the liquid. Suitable examples of infrared dyes are disclosed in

[0179] of WO2015158649.

[0099] 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 liquid. A.4. Varnish

[0100] The varnish that can be used in the recording method according to the present invention contains a resin. Examples of the resin contained 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 can be used alone, or two or more thereof can be used in combination with a crosslinking agent such as an epoxide or a carbodiimide.

[0101] Among the aforementioned resins, the resin contained in the varnish is preferably a urethane-based resin, an acrylic resin, or a polyolefin-based resin.

[0102] Acrylic resin is a common name for a polymer obtained by polymerizing at least acrylic monomers (such as (meth) acrylic acid and (meth) acrylic esters), and examples thereof include (meth) acrylic resins obtained from acrylic monomers, and copolymers of acrylic monomers with monomers other than acrylic monomers (such as vinyl-based monomers, such as styrene). Acrylamide and acrylonitrile can also be used as acrylic monomers. As a resin emulsion using an acrylic resin as a raw material, a commercially available product can be used, and examples thereof include Neocryl D2101 (Covestro Coating Resins BV) FK-854 (trade name, manufactured by CHIRIKA. Co., Ltd.); Mowinyl 952B, 718A (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.); Nipol LX852 and LX874 (trade name, manufactured by ZEON Corporation).

[0103] As the urethane-based resin, commercially available products can be used, for example, the following commercially available products can be used: 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.).

[0104] The polyolefin-based resin has an olefin such as ethylene, propylene and butene as a structural skeleton, and well-known resins can be appropriately selected for use. As the olefin resin, commercially available products can be used, and examples thereof include Arrowbase CB-1200 and CD-1200 (trade names, manufactured by UNITIKA LTD.).

[0105] The resin contained in the varnish preferably includes a resin having a glass transition temperature (Tg) of 80° C. or lower, and more preferably includes a resin having a Tg of 40° C. to 80° C. When the first resin includes a resin having a Tg of 80° C. or lower, adhesion of the varnish to a recording medium can become excellent, and when the first resin includes a resin having a Tg of 40° C. or higher, it is possible to suppress the viscosity of clear ink attached to the recording medium.

[0106] The varnish contains the resin in an amount of 1 wt.% to 30 wt.% relative to the total mass of the varnish. When the content of the resin in the varnish is within the aforementioned range, the effect of improving the rubbing resistance of the image tends to become more excellent. A.5. Recording Media

[0107] The recording medium used in the method of the present invention is an absorption medium. When the amount of water absorbed after a contact time of 60 seconds is at least 10 g / m 2 Absorbent media are porous media or media that contain a binder that is capable of swelling when in contact with an aqueous liquid.

[0108] Porous substrates include paper, cardboard, white pulp lined chipboard, corrugated board, packaging board, folding board, wood, ceramics, stone, leather and textiles. The pretreatment composition of the present invention is particularly suitable for adhering to paper intended for packaging applications. The paper can be a single layer of a multi-layer paper.

[0109] Paper can be brown kraft paper, white top paper or bleached board. Paper can be made from chemical fiber, wood fiber or recycled fiber. As an example, paper can be a liner intended to be printed on a web press and converted into corrugated boxes. In this regard, the liner can be used as a double-sided liner and can be directly converted in a corrugator or laminated to the double-sided liner after corrugation. Paper can also be a board for boxes and other packaging applications. B. Examples B.1. Materials

[0110] Unless otherwise specified, 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 deionized. Poval 2098 is a polyvinyl alcohol from KURARAY with a degree of hydrolysis of 98%. to facilitate the preparation of the pretreatment liquid. Poval 5698 is a fully saponified grade of polyvinyl alcohol from Kuraray Europe GmbH; this product is pre- Dissolved in water to facilitate the preparation of pretreatment liquids. • Joncryl 538-A is a 45% aqueous styrene acrylic polymer dispersion from BASF SE. • Bayhydrol UH 2606 is a 35% aliphatic anionic polyurethane aqueous dispersion from Covestro AG. • Liquilube 404E is a 35% emulsion of high density polyethylene (HDPE) wax in water from Lubrizol Corporation. • Rheolate 666 is a polyetherurea polyurethane associative thickener containing 20% ​​active solids from Elementis plc. DMM is dipropylene glycol dimethyl ether from Dow Chemicals DPM is dipropylene glycol methyl ether from Dow Chemicals • Dynax DX 4000 is a fluorosurfactant from Dynak Corporation, Pound Ridge, NY. • Byk 022 is a silicone defoamer from BYK USA Inc., Wallingford CT. Mergal K9N is an in-can preservative for waterborne systems from Troy Chemical Company BV Ultralube GA 1042 is a 35 wt.% HDPE wax dispersion from KEIM-ADDITEC SURFACE GMBH body Surfynol 104PG50 is a 50 wt.% solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol from Evonik Kauropal K933 is a 100% nonionic ethylene oxide, mono(2-propylheptyl) ether from BASF. TegoFoamex 822 is a 20% defoamer from Evonik Industries AG that contains a polyether siloxane copolymer. Emulsion in water Glyoxal 40 is a 40% aqueous solution of glyoxal and is available as is from BASF Edaplan is Edaplan TM 482, which is a polymeric dispersant from MUNZING. ● Cyan pigment is Pigment Blue 15:3-FASTOGEN BLUELA5380 produced by Sun Chemical Corporation. Proxel is available as Proxel TM K was obtained from Azelis Corporate Services NV as a 5% aqueous solution of 1,2-benzisothiazolin-3-one HSDCX1 is a 19.7 wt.% Encapsulated Pigment Blue 15:3 aqueous dispersion from Lubrizol Corporation Mg(NO3)2.6H2O is magnesium nitrate hexahydrate from Merck Group Boric acid from Merck Group DI water is deionized water B.2. Evaluation Method B.2.1. Sample preparation

[0111] The pretreatment liquid was adhered to a coated corrugated liner paper XLHD MM X-Liner HD (180 g / m 2 ). Two adhesion methods were evaluated: rod coating and flexographic coating. In the rod coating method, a 4 μm spiral rod was used to coat the corrugated liner, resulting in a layer thickness of 4 μm. In the flexographic coating method, a K Printing Proofer (RK Printcoat Instruments) equipped with a Flexo head and a standard 200 lines per inch solid area plate was used to coat the corrugated liner, resulting in an applied layer thickness of approximately 1.5 μm.

[0112] After the pretreatment liquid was applied, the pretreated sample was printed without pre-drying, i.e., wet-on-wet printing. Taking into account operation times, such as the time required to transport the sample to the printing press and start printing, the time interval between the application of the pretreatment and the printing of the image using the aqueous inkjet ink was less than 30 seconds.

[0113] After the pretreatment liquid was applied, the pretreated liner paper samples were printed using an ImageXpert JetXpert with GIS printhead drive electronics for a FujiFilm Dimatix Samba printhead (SambaG3L) using a water-based cyan ink with a drop volume between 5.4 and 6.5 μl, a voltage between 19.5 and 23.5 V, at 32°C, and a jetting frequency of 7.8 kHz. The printed image was dried in an oven at 60°C for 2 minutes. The pattern of the printed image is shown in Figure 1. B.2.2. Image quality

[0114] The image quality of the printed images was evaluated by visually analyzing the following three properties: 1) ink spreading; 2) ink fixation and 3) image clarity.

[0115] Ink Spread: The ink should completely cover the solid areas in the printed image. The presence of white lines in the solid areas indicates a lack of ink spread. The assessment was performed by visually inspecting the solid areas and assigning a score from 0 (excellent ink spread, complete coverage) to 3 (poor ink spread, more than 20 white lines visible in the solid areas).

[0116] Ink Fixation: The ink should cover the solid areas of the printed image evenly and densely. The presence of uneven patterns in the solid areas indicates a lack of ink fixation. Ink fixation was assessed by visually inspecting the solid areas and assigning a score from 0 (excellent ink fixation, even coverage) to 3 (poor ink fixation, strong unevenness was observed).

[0117] Image clarity: Fine text should be readable. The disappearance of highlighted text indicates a lack of image clarity. Image clarity is assessed by visually inspecting the highlighted text and assigning a rating from 0 (excellent image clarity, 6 pt clearly readable) to 3 (poor image clarity, 16 pt partially or completely covered by ink). B.2.3. Viscosity

[0118] The viscosity of the pretreatment liquid was measured as follows: The dynamic viscosity of the pretreatment liquid was measured using a Thermo Scientific HAAKE RotoVisco 1 viscometer at a temperature of 25°C and using a 1000s -1 The dynamic viscosity of the pretreatment liquid was measured at a shear rate of 1. B.3. Example 1

[0119] Example 1 shows that the recording method using the pre-treatment liquid according to the present invention provides inkjet images exhibiting higher image quality than that of the pre-treatment liquid based on a latex binder. B.3.1. Preparation of pretreatment liquid and aqueous pigment ink

[0120] The pretreatment liquid composition was prepared by mixing the ingredients given in Table 1. The weight percentages are relative to the total weight of the pretreatment liquid. The raw materials were used as supplied without any further treatment. Table 1: Composition of pretreatment liquid COMP-PL1 INV-PL1 Poval2098 - 5.4 Joncryl538-A 11.11 - BayhydrolUH2606 28.57 - Liquilube404E 11.43 4.0 Rheolate666 2.14 - DMM 3.0 - DPM 2.0 - <![CDATA[Mg(NO3)2.6H2O]]> - 16.0 Kauropal K933 - 0.04 DynaxDX4000 2.57 - TegoFoamex822 - 0.04 Byk022 0.2 - MergalK9N - 0.01 Boric acid - 0.29 DI water To achieve 100% To achieve 100% <![CDATA[1000s -1 Viscosity under 40.1 101.0

[0121] Aqueous cyan inks were prepared by diluting the wax dispersion with the other ink ingredients (each ingredient is expressed in wt. % based on the total weight of the ink) according to Table 2. Water was added to bring the ink to the desired pigment concentration. Table 2: Composition of aqueous inkjet ink INV-INK1 B.3.2. Results of image quality assessment

[0122] Pretreatment liquids COMP-PL1 and INV-PL1 were adhered to the coated corrugated liner as described in §B.2.1. Pretreated samples were printed as described in §B.2.1 and the image quality of the obtained images was evaluated according to §B.2.2.

[0123] In Table 3, the image quality results for images printed onto the comparative pretreatment composition and the inventive pretreatment composition are listed. Table 3: Image quality assessment of images printed onto pre-treated liner paper

[0124] From Table 3, it can be concluded that the recording method in which the pretreatment liquid containing a hydrophilic binder is adhered as a layer having a thickness of 1 to 5 μm produces inkjet printed images with improved image quality relative to the recording method using the pretreatment liquid containing a latex binder. B.4. Example 2

[0125] Example 2 shows that boric acid as a cross-linking agent in the pre-treatment liquid produces inkjet printed images with improved image quality. B.4.1. Preparation of pretreatment liquid and inkjet ink

[0126] Three pretreatment liquids were prepared by mixing the ingredients given in Table 4. The weight percentages are relative to the total weight of the pretreatment liquid. Unless otherwise stated, the raw materials were used as supplied without any further treatment. After thorough mixing, a viscous, translucent liquid was obtained. Table 4: Composition of the inventive pretreatment liquid

[0127] Aqueous cyan inks were prepared by first preparing a concentrated aqueous pigment dispersion. The dispersion was prepared by mixing the composition according to Table 5 for 30 minutes using a Disperlux™ Yellow mixer. Table 5 lists the exact composition of the dispersion. Table 5: Composition of cyan pigment dispersion

[0128] An aqueous cyan pigment ink was prepared by mixing the ingredients according to Table 6 (expressed in wt. % based on the total weight of the ink). Table 6: Composition of Inventive Inkjet Inks Components INV-INK2 Cyan pigment dispersion 14.67 Proxel 0.2 Surfynol104PG50 0.4 glycerin 32.0 Ethylene glycol 15.4 1.2 Hexanediol 2.85 DI water To achieve 100% B.4.2. Results of image quality assessment

[0129] Pretreatment liquids INV-PL2 to INV-PL4 were adhered to the coated corrugated liner as described in §B.2.1 with the aid of a 4 μm spiral rod. The pretreated samples were printed as described in §B.2.1 and the image quality of the obtained images was evaluated according to §B.2.2.

[0130] It is clear from the evaluation of image quality that better ink spreading is obtained using the pre-treatment liquid containing boric acid than using the pre-treatment liquid containing glyoxal.

Claims

1. A recording method for inkjet printing on an absorbing medium, comprising the steps of: a) transporting the absorption medium in a conveying direction, the medium having a width oriented transversely to the conveying direction; and b) adhering a pretreatment liquid at least partially across the width of the absorbent medium to form a layer having a thickness of 1 to 5 μm, the pretreatment liquid comprising water, a fixing agent, a hydrophilic binder selected from the group consisting of polyvinyl alcohol (PVOH) or modified polyvinyl alcohol, water-dispersible ethylene vinyl alcohol (EVOH), a polysaccharide, and a combination of two or more thereof, at 25° C. for 1000 s -1 At a shear rate of , the viscosity of the pretreatment liquid is 40 to 300 mPa.s; c) applying an aqueous inkjet ink to the layer by ejecting the ink from an inkjet head to form an image, the ink comprising a pigment and a water-soluble organic solvent; and d) Drying the layer and the applied inkjet ink by applying heat and air flow to the image.

2. The recording method according to claim 1, wherein the absorption medium is a paper substrate, corrugated cardboard or paperboard. 3 . The recording method according to claim 1 , wherein the pretreatment liquid further contains a cross-linking agent. 4 . The recording method according to claim 3 , wherein the crosslinking agent is boric acid, and the hydrophilic binder is polyvinyl alcohol. 5 . The recording method according to claim 1 , wherein the inkjet ink is applied at a time interval of 200 ms to 30 s after the pretreatment liquid is adhered.

6. A recording method according to any preceding claim, wherein the head may be a fixed nozzle array oriented transversely to the transport direction or may scan in a direction transversely to the transport direction.

7. Recording method according to any one of the preceding claims, wherein the amount of hydrophilic binder is from 15 to 45 wt. % relative to the total amount of dry compounds.

8. The recording method according to any one of the preceding claims, wherein the water-soluble organic solvent has a boiling temperature of 150 to 250°C and an amount thereof of 20 wt.% or more relative to the total weight of the pretreatment liquid.

9. The recording method according to claim 1, wherein the adhering is performed by means of flexographic printing.

10. The recording method according to claim 9, wherein the flexographic printing comprises adhering the pretreatment liquid to the absorption medium by means of an anilox roller.

11. The recording method according to claim 1, wherein after step d), a varnish is applied to the image, the varnish comprising water and a resin.

12. A liquid kit comprising a pretreatment liquid and an aqueous inkjet ink, wherein the aqueous ink comprises a pigment, a wax, and a water-soluble organic solvent having a boiling point of 150° C. to 250° C., and the pretreatment liquid comprises water, a polyvalent metal salt, polyvinyl alcohol, and a crosslinking agent, wherein the pretreatment liquid comprises water, a polyvalent metal salt, polyvinyl alcohol, and a crosslinking agent, and wherein ... -1 At a shear rate of 1000 rpm, the viscosity of the pretreatment liquid is 40 to 300 mPa.s.

13. The liquid kit according to claim 12, wherein the pigment is encapsulated by means of a cross-linked polymer shell.

14. The kit according to claim 12 or claim 13, further comprising a varnish comprising water and a resin selected from polyacrylates, waxes and polyurethanes.

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