Primer composition for inkjet printing of non-absorbent or low-absorbent substrates with aqueous pigmented inks

Abstract

The present invention relates to an aqueous coating composition comprising (a) 20 to 79 weight percent of a dispersed polymer binder, (b) 20 to 79 weight percent of aluminum oxide hydroxide particles, (c) 0.1 to 10 weight percent of dissolved polyvalent metal cations, and (d) inorganic and / or organic counteranions of the metal cations. The aqueous coating composition is used to form an inkjet-printable primer layer on a non-absorbent or low-absorbent substrate. Methods for coating the substrate and inkjet printing the coated substrate are also provided.

Description

[Technical Field]

[0001] The present invention relates to an aqueous coating composition used to form an inkjet printable primer layer on a non-absorbent or low-absorbent substrate, a coated substrate comprising an inkjet printable primer layer, and a method of coating a substrate and inkjet printing the coated substrate. [Background technology]

[0002] Inkjet printing on non-absorbent or low-absorbent substrates, such as polymer films, foils, coated papers, ceramics, and glass, is important due to the low viscosity of inkjet inks and the resulting printing artifacts, such as intercolor bleed, line sharpness issues, dot spreading, and coalescence. Furthermore, adhesion of inkjet inks to such non-absorbent substrates can be critical if no binder is present in the ink. To overcome these problems, it is known to apply inkjet coatings to non-absorbent substrates. Inkjet coatings, such as microporous inkjet coatings, can absorb ink in a short time, resulting in fast settling of ink droplets. These inkjet coatings generally require a density of at least 15 g / m to handle the ink laydown. 2

[0003] Coating weights of 1000 ppm or more are required, which are coated offline before printing, adding high costs to the substrate and final print. For commercial presses with single-pass printing, i.e., packaging or decorative applications, these costs are unacceptable. Primer coatings that are applied at lower coat weights and are therefore less expensive, have also been described, especially in combination with suitable inks. Inkjet primer compositions often contain coagulants, such as dissolved polyvalent metal cations, which play an important role in precipitating the anionically charged dispersed ink components, primarily dispersed anionic color pigments and, optionally, anionic binders.

[0003] WO 2022 / 003336 describes a method for preparing a digitally printed laminate, comprising applying a primer to a first substrate, printing an aqueous pigmented inkjet printing ink onto the primed substrate, and laminating a second substrate to the primed and printed first substrate, wherein the primer is an aqueous coating composition comprising (a) a water-dispersible polymer and a polyvalent metal salt, or (b) a water-soluble polymer and a polyvalent metal salt, and the aqueous pigmented inkjet printing ink comprises an anionic polymer dispersion or an anionic polymer solution. The aqueous primer composition may further comprise a dispersion of an inorganic material, such as colloidal silica or alumina, preferably modified anionic colloidal silica.

[0004] EP3928998A1 relates to a recording medium comprising a substrate, an ink-receiving layer (1) disposed on the substrate and containing first inorganic particles and a first binder, and an ink-receiving layer (2) disposed on the ink-receiving layer (1) and containing second inorganic particles and a second binder, wherein the first binder and the second binder are each a water-insoluble resin. The first inorganic particles can be selected from alumina hydrate, fumed alumina, and fumed silica, and the second inorganic particles are preferably colloidal silica.

[0005] U.S. Patent Application Publication No. 2022 / 119666 relates to an aqueous composition for pretreating a substrate prior to inkjet printing, the aqueous composition comprising one or more water-soluble salts of polyvalent metal cations, one or more nonionic or cationic water-soluble or water-dispersible polymeric binder materials, and surface-treated, fine, visible light-scattering particles to provide a white background for printing high-quality monochrome or polychrome images on transparent film substrates or dark substrates. The surface-treated, visible light-scattering particles comprise silicon dioxide, zinc oxide, titanium dioxide, zirconium oxide, aluminum oxide, barium sulfate, and / or magnesium oxide, preferably titanium dioxide. Summary of the Invention

[0006] It is an object of the present invention to provide a coating composition useful for preparing a thin print primer layer with a low coat weight for high-speed inkjet printing on non-absorbent or low-absorbent surfaces. Substrates coated with a low coat weight primer composition should be printable with high print quality and should exhibit good adhesion between the primer and the substrate in printed and unprinted areas, as well as non-stick properties (anti-blocking properties) when in contact with other surfaces during coating, storage, or further processing.

[0007] The above objects are achieved by an aqueous coating composition comprising: (a) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, and most preferably 40 to 59 wt % of a dispersed polymer binder; (b) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, and most preferably 40 to 59 wt % of aluminum oxide hydroxide particles; (c) 0.1 to 10 wt %, preferably 0.3 to 5 wt %, and more preferably 0.5 to 2 wt % of dissolved polyvalent metal cations; and (d) inorganic and / or organic counter anions of said metal cations, wherein the weight percentages are based on the solids content of the aqueous coating composition.

[0008] The present invention also relates to a substrate at least partially coated with an aqueous coating composition that forms an inkjet printable primer layer.

[0009] The present invention further relates to a method of coating a substrate, comprising applying the aqueous coating composition to a substrate to obtain an inkjet printable primer layer, as well as a method of preparing an inkjet printed substrate, further comprising printing the inkjet printable primer layer of the coated substrate by an aqueous inkjet printing process. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is an SEM micrograph (×20,000 magnification) of an inkjet printable primer layer formed from an aqueous coating composition of the present invention according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Dispersion polymer binder (a) The dispersed polymer binder (a) of the aqueous coating composition of the present invention comprises polymer particles, the term "polymer particles" being broadly understood to include particles in a solid, viscoelastic (rubbery), or liquid state, depending on the glass transition temperature and / or melting temperature of the polymer. This means that the polymer binder is suspended or emulsified in an aqueous medium. Typically, the polymer particles of the dispersed polymer binder (a) have a median particle size (D) of 10 nm to 500 nm, preferably 20 to 300 nm, more preferably 50 to 250 nm, and most preferably 75 to 230 nm, as measured by laser diffraction in accordance with ISO 13320:2020-01, for example, using a Beckman Coulter LS13320 device. v50 )

[0012] To improve the dispersibility of the polymer binder (a) and its stability in aqueous coating compositions, the polymer particles according to the present invention are typically cationic or nonionically stabilized. Cationic polymers are generally prepared by incorporating cationic groups or groups that can be converted to cationic groups, such as tert-amino groups that can be protonated or quaternized with acid, into the polymer structure. Accordingly, nonionically stabilized polymers are generally prepared by incorporating hydrophilic groups into the polymer structure, typically including polyoxyalkylene groups such as polyoxyethylene or polyoxypropylene groups. The stabilization mechanism of polymer particles in nonionic dispersions is usually based on the steric stabilization mechanism provided by hydrophilic soft segments. The portion of the chain containing the nonionic segment extends into the continuous phase, i.e., the aqueous phase, preventing the coalescence effect between the formed polymer particles.

[0013] The polymeric binder preferably comprises polyurethane particles or poly(meth)acrylate particles or copolymers or combinations thereof, more preferably non-ionically stabilized polyurethane particles, cationic polyurethane particles, non-ionically stabilized poly(meth)acrylate particles, cationic poly(meth)acrylate particles, and even more preferably non-ionically stabilized polyurethane particles and / or cationic polyurethane particles.

[0014] The polymer particles are typically added to the aqueous coating composition of the present invention in the form of an aqueous dispersion. Suitable dispersions of polymer particles preferably have a solids content of 30 to 60% by weight, a pH of 4.0 to 8.0, more preferably 5.0 to 7.0, and a minimum film-forming temperature (MFFT) of less than 35°C, more preferably less than 20°C. The aqueous dispersion of polymer particles should be compatible with the polyvalent metal cation (c), i.e., it should be stable in the presence of dissolved polyvalent metal cation (c) and dispersed aluminum oxide hydroxide particles (b), meaning that neither flocculation nor a significant increase in viscosity occurs.

[0015] The aqueous coating composition of the present invention comprises 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, and most preferably 40 to 59 wt % of the dispersed polymer binder (a), based on the solids content of the coating composition.

[0016] Polyurethane particles Suitable polyurethanes for use as the polymeric binder (a) in the present aqueous coating composition can be aromatic and / or aliphatic, i.e., can be made from aromatic, aliphatic, and / or cycloaliphatic polyisocyanates (e.g., hexamethylene diisocyanate and isophorone diisocyanate), low molecular weight glycols (e.g., ethylene glycol, 1,4-butanediol, and 1,6-hexanediol), polyether diols, polyester diols, polyacrylic diols, and polycarbonate diols, or any blends or hybrids thereof. Aliphatic or cycloaliphatic polyurethanes are preferred.

[0017] Cationic polyurethanes are typically prepared by incorporating side chains containing amino groups, e.g., tertiary or quaternary amino groups, into the polymer and protonating the amino groups with an amino acid. Non-ionically stabilized polyurethanes are generally prepared by incorporating side chains containing polar groups, preferably polyoxyalkylene moieties, into the polymer.

[0018] The polyurethane may have an amount of hydroxyl groups such that the hydroxyl number of the polyurethane is 50 mg KOH / g or less. Preferably, the hydroxyl number is less than 1 mg KOH / g, more preferably 0 mg KOH / g.

[0019] The polyurethane particles are typically introduced into the aqueous coating composition of the present invention in the form of an aqueous dispersion. Commercially available polyurethane dispersions that can be used in the present invention include various types, such as NeoRez®, Bayhydrol® (available from Covestro), Permax®, Sancure®, and PrintRite® (available from Lubrizol Germany, Hamburg), Syntegra® (available from The Dow Chemical Company), Joncryl® (available from BASF), Beetafin® (available from BIP (Oldbury)), Daotan® (available from Alnex, Wiesbaden), Witcobond® (available from Lanxess), ESACOTE® (available from Lamberti SpA), Patelacol®, Hydran®, and Vondic® (available from DIC, Japan).

[0020] Preferred commercially available nonionically stabilized polyurethane dispersions are NeoRez® R-9340 (nonionically stabilized flexible polyurethane dispersion, MFFT <5°C; acid number = 0 mg KOH / g, dry resin solids content 40%, pH 6.5-7.5), Baybond® PU404 (nonionic polyester polyurethane, viscosity <1500 mPa·s according to M092-ISO2555 at 23°C, spindle L3 / 30 rpm, pH 5.5-7.5 at 20°C). Further examples of non-ionically stabilized polyurethane dispersions are Esacote® NBD, Esacote® PU931, Esacote® PU3511, Esacote® PU5913, Permax® 232, Vondic® 1050B-NE, Vondic® 1310NE, Vondic® 8510, Vondic® 1230NE, Vondic® 1970NE, Vondic® 1980NE, Vondic® 2210, Vondic® 2220, Witcobond® 320, and Witcobond® 447-05. Examples of commercially available cationic polyurethane dispersions are Witcobond® W-213, Witcobond® 214 (aliphatic polyurethane), Esacote® PU2001, Esacote® PU C1, Esacote® MD23, PrintRite® DP675, Sancure® 20051, Patelacol® IJ50, and Hydran® CP7020.

[0021] Poly(meth)acrylate particles Suitable poly(meth)acrylates for use as the polymer binder (a) in the aqueous coating composition of the present invention include homopolymers and copolymers of acrylate and / or methacrylate(s), such as alkyl, aryl, aralkyl, or hydroxyalkyl esters of acrylic or methacrylic acid, and copolymers of the above monomers with additional ethylenically unsaturated monomers, such as one or more of acrylonitrile, acrylamide, vinyl ethers (e.g., vinyl methyl ether, vinyl acetate), and styrene. Acidic comonomers, such as acrylic acid or methacrylic acid, result in anionic poly(meth)acrylates. Therefore, poly(meth)acrylates suitable for the present invention are typically not derived from acidic monomers. To achieve a low MFFT of aqueous dispersions of poly(meth)acrylate particles (such as below 35°C), it is preferable to (co)polymerize monomers with a low Tg, such as below 20°C, as reported in standard sources, e.g., J. Brandrup, E.H. Immergut, Polymer Handbook, 3rd Edition, John Wiley & Sons, 1989, pp. VI / 215-219. Examples of such monomers are 2-ethylhexyl acrylate, butyl acrylate, isobutyl acrylate, ethyl diglycol acrylate, propyl acrylate, and ethyl acrylate.

[0022] Nonionic stabilization of poly(meth)acrylate particles can be achieved by copolymerizing hydrophilic monomers. Cationic poly(meth)acrylates can be prepared by copolymerizing amino-group-containing monomers such as 2-dimethylaminoethyl acrylate (DMAEA) or 2-dimethylaminoethyl methacrylate (DMAEMA), which can be quaternized or protonated with an acid.

[0023] Poly(meth)acrylate particles are typically introduced into the aqueous coating compositions of the present invention in the form of an aqueous dispersion. Examples of commercially available cationic poly(meth)acrylate dispersions are Synprint® AC4110 (available from Zimmer & Schwarz, Germany) and Neocryl® XK-30 (available from Covestro). Examples of nonionic poly(meth)acrylate dispersions are PrintRite® 595FF (available from Lubrizol) and Neocryl® XK-37 (available from Covestro).

[0024] Water-soluble polymer binder (e) A portion of the dispersed polymer binder (A) can be replaced with a water-soluble polymer binder (e), which can be incorporated into the aqueous coating composition in an amount replacing from greater than 0 to 50 wt. % of the dispersed polymer binder (A) on a solids basis, preferably from 2 to 25 wt. %. The presence of the water-soluble polymer binder (e) can be advantageous with respect to the stability, viscosity, printability, and adhesion of the aqueous coating composition.

[0025] Any polymeric binder having a solubility of greater than 1% by weight at 20°C can be used as the water-soluble polymeric binder (e). In practice, it should be compatible with the other components of the aqueous coating composition. Suitable polymers for use as the water-soluble binder (e) include poly(vinyl alcohol), poly(vinyl alcohol) derivatives, poly(ethylene oxide), poly(vinylpyrrolidone), poly(vinyl methyl ether), poly(vinylamine), poly(2-ethyl-2-oxazoline), cationic or nonionic water-soluble poly(meth)acrylates and copolymers thereof, poly(acrylamide) and copolymers thereof, cellulose derivatives such as methyl cellulose and ethyl cellulose, or nonionic or cationic polymers based on any combination thereof. Preferably, the polymeric binder comprises poly(vinyl alcohol), poly(vinyl alcohol) derivatives, or any combination thereof.

[0026] The term "poly(vinyl alcohol)" is generally accepted in the art as referring to fully or partially hydrolyzed poly(vinyl acetate). The degree of hydrolysis attributed to poly(vinyl alcohol) indicates the degree of hydrolysis of poly(vinyl acetate) according to standard procedures. The degree of hydrolysis is 80-99 mol%, preferably 86-99 mol%. The degree of hydrolysis (saponification) indicates what percentage of basic poly(vinyl acetate) molecules have been "saponified" into poly(vinyl alcohol). Examples of modified poly(vinyl alcohol) are cationic poly(vinyl alcohol), silicon-modified poly(vinyl alcohol), keto-modified poly(vinyl alcohol), and vinyl alcohol / N-vinylformamide copolymer.

[0027] Aluminum hydroxide oxide particles (b) The aluminum hydroxide oxide particles (b) are small primary aggregates of aluminum hydroxide oxide crystallites dispersed in the aqueous coating composition, i.e., the median particle size (D) used herein for the aluminum hydroxide oxide particles. v50 ) is the median primary aggregate diameter (D v50 ) means

[0028] Aluminum oxide hydroxide, also known as aluminum oxide hydroxide, aluminum acid hydroxide, or alumina hydrate, has the formula AlO(OH) (=Al2O3·H2O). Preferred types of aluminum oxide hydroxide for use in the present invention are boehmite and pseudoboehmite.

[0029] Boehmite is a mineral with an orthorhombic unit cell (a = 3.693 Å, b = 12.221 Å, and c = 2.865 Å) classified as γ-AlO(OH). Its crystal structure consists of double layers of oxygen octahedra with an aluminum atom at the center. The outward-facing oxygen atoms are bonded to hydroxyl groups in adjacent layers of the octahedron via hydrogen bonds. Due to the weak bonds, boehmite tends to intercalate, i.e., incorporate small molecules, usually water, between its layers. This results in large spacing in the

[0010] direction and complete cleavage perpendicular to the general direction of the hydrogen bonds. Boehmite with increased spacing in the

[0010] direction is called pseudoboehmite, while boehmite that is largely amorphous is usually called gel. Boehmite can be found in nature, precipitated and grown from solutions of aluminum salts and alumina under hydrothermal conditions, or precipitated from aluminum alkoxides by hydrolysis.

[0030] Preferably, the boehmite microcrystals are not needle-shaped but are preferably plate-shaped, more preferably having an average aspect ratio of 3.0 to 10 and a long-axis-to-horizontal ratio of 0.60 to 1.0. The aspect ratio can be determined by the method disclosed in Japanese Patent Publication No. 5160154 B2. The aspect ratio is expressed herein as the ratio of the diameter to the particle thickness. The diameter here refers to the diameter of a circle (equivalent circle diameter) having the same area as the projected area of the alumina hydrate particle when observed under a microscope or electron microscope. The ratio of the long axis to the short axis of the plate surface is defined as the ratio of the minimum diameter to the maximum diameter of the plate surface when observed under a microscope using the same method as described for the aspect ratio.

[0031] The median diameter of boehmite crystallites in the dry powder (D v50 ) can be, for example, 7 to 80 nm, preferably 8 to 50 nm, more preferably 10 to 20 nm, as measured by X-ray diffraction on an X-ray diffractometer supplied by Siemens or Philips.

[0032] Pseudoboehmite is characterized by a higher water content (AlO(OH)·xH2O (0 < x < 1.0)). It is essentially a fine crystalline boehmite consisting of the same or similar octahedral layers in the xz plane, but lacks three-dimensional order due to a limited number of unit cells in the y direction. It is composed of a single unit lattice along the y direction or a number of crystallites containing a single octahedral layer. It contains more water, and the water is generally inserted between the octahedral layers and is usually arranged randomly, but sometimes arranged regularly. The water content consists of adsorbed and chemically bound water. The higher water content compared to boehmite can be explained by the smaller crystallite size. Boehmite consists of relatively long AlOOH chains with terminal H2O groups, while the chains of pseudoboehmite are significantly shorter. This is converted into a significantly higher specific water content due to the terminal water groups.

[0033] Small primary aggregates of fine crystals of boehmite or pseudoboehmite can be obtained by the dispersion of large secondary aggregates having an average particle size in the range of 1 μm to 100 μm present in commercially available boehmite or pseudoboehmite powders, such as those supplied from a spray drying process.

[0034] Dispersed particles of boehmite or pseudoboehmite (small primary aggregates of boehmite or pseudoboehmite crystallites) are typically measured by laser diffraction according to ISO 13320:2020-01, using, for example, an LS13320 device manufactured by Beckman Coulter, and have a median particle size (D v50 ) in the range of 20 to 500 nm, typically 30 nm to 300 nm, preferably 50 nm to 200 nm, more preferably 80 to 180 nm.

[0035] The boehmite or pseudo-boehmite primary aggregates have a porous structure. Typically, the boehmite or pseudo-boehmite particles herein have an average pore volume of 0.5 to 1.5 ml / g, preferably 0.8 to 1.3 ml / g, measured by nitrogen adsorption according to the Barrett, Joyner and Halenda (BJH) and Gurbich methods described in DIN 66134:1998-02, and a pore volume of 100 to 400 m, measured by gas adsorption according to ISO 9277:2010. 2 / g, preferably 120 to 180 m 2 / g. The average pore volume and BET surface area are determined by gas adsorption on the powder after calcination at 550°C for 3 hours.

[0036] Suitable commercially available boehmite powders for use in the ink-receiving layer (b) include DISPERAL® and DISPAL® grades available from Sasol, such as DISPERAL® HP8, HP10, HP14, HP14 / 7 and HP18, preferably HP14, and BOEHMITE B8014 LM35 available from Boyan, Tianjin, China.

[0037] The aqueous coating composition of the present invention comprises 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, and most preferably 40 to 59 wt % of aluminum oxide hydroxide particles (b) based on the solid content of the coating composition.

[0038] Acidic dispersant (f) To disperse the aluminum oxide hydroxide particles, the aqueous coating composition may contain an acidic dispersant (f), preferably having a pk of less than 5.0, more preferably less than 4.9, even more preferably less than 4.0, even more preferably less than 3.0, and most preferably less than 2.0. aThe acidic dispersing agent is an organic and / or inorganic acid having a dispersibility of 0 to 10% by weight, preferably 0.2 to 5% by weight, and more preferably 0.3 to 1% by weight, based on the amount of aluminum oxide hydroxide particles. Alternatively, a suitable acid can be added during the production process of the aluminum oxide hydroxide powder, which can result in a self-dispersing powder (e.g., DISPERAL® HP14 / 7, available from Sasol, which is surface-modified with citric acid).

[0039] Polyvalent metal ions (c) and counterions (d) The aqueous coating composition is typically 2+ , Mg 2+ , Zn 2+ , Al 3+ , Fe 2+ , Fe 3+ , Ti 4+ , Zr 4+ , and combinations thereof, preferably Ca 2+ , Mg 2+ , Al 3+ and combinations thereof. The aqueous coating composition of the present invention contains 0.1 to 10 wt %, preferably 0.3 to 5 wt %, and more preferably 0.5 to 2 wt % of dissolved polyvalent metal cations (c) based on the solids content of the coating composition.

[0040] The polyvalent metal cation must be dissolved in the aqueous coating composition. Therefore, the counter anion (d) is selected so that it does not precipitate as a solid from the aqueous coating composition along with the metal cation (c). Examples of counter ions include chloride, bromide, borate, nitrate, hydrogen sulfate, sulfate, bicarbonate, acetate, formate, propionate, butyrate, benzoate, gluconate, sulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate, and combinations thereof, preferably chloride, acetate, or a combination thereof.

[0041] Preferred combinations of polyvalent metal cations (c) and counterions (d) are those whose salts have a solubility in water of at least 10 g / l at 20° C. The most preferred combination of polyvalent metal cations (c) and counterions (d) is Ca 2+ / Chloride, Ca 2+ / Acetate, Mg 2+ / Chloride, Mg 2+ / Acetate, Al 3+ / chloride, and Al 3+ / acetate salts. The polyvalent metal cation (c) and counterion (d) are typically introduced into the aqueous coating composition of the present invention in the form of a salt. The most preferred salts are calcium chloride, magnesium chloride, calcium acetate, magnesium acetate, basic aluminum diacetate, aluminum chloride, and aluminum chlorohydrate. Another suitable salt is zirconium oxychloride.

[0042] Further Additives Further additives to the aqueous coating compositions of the present invention are, for example, biocides, surfactants (wetting agents), antifoaming agents, viscosity modifiers, crosslinking agents, and organic solvents.

[0043] Examples of crosslinking agents include formaldehyde, glyoxal, glutaraldehyde, polyisocyanates, aziridines, carbodiimides, epoxy compounds, dihydrazides, i.e., compounds such as adipic acid dihydrazide, and inorganic compounds such as boric acid and zirconium salts. In particular, when poly(vinyl alcohol) is used as the water-soluble binder (e), glyoxal, boric acid, and adipic acid dihydrazide are preferred crosslinking agents.

[0044] Preferably, the aqueous coating composition of the present invention does not contain organic solvent. If present, the organic solvent is contained in a maximum amount of 10 wt% based on the total weight of the aqueous coating composition. Suitable organic solvents include alcohols such as ethanol, isopropanol, and n-propanol, as well as acetone and methyl ethyl ketone, and mixtures of these solvents.

[0045] Aqueous Coating Composition Typically, the aqueous coating composition of the present invention has a solids content of 1 to 50% by weight, preferably 5 to 40% by weight, and more preferably 10 to 30% by weight. The pH value of the aqueous coating composition can be in the range of 2.8 to 6, preferably 3.0 to 5.5, and more preferably 3.5 to 5.0. It is adjusted to stabilize the particles in the aqueous medium.

[0046] The aqueous coating composition of the present invention is preferably prepared by mixing the individual components (a) to (d), optional component (e), and any additional optional components already dissolved or dispersed. If not already commercially available in these forms, these components are preferably pre-dispersed or pre-dissolved, and then these aqueous compositions are mixed into the final coating composition. This can be done in any order. Preferably, the dispersion of polymer binder (a) is slowly added to a mixture of a solution of a salt of polyvalent metal cation (c) and counterion (d) and a dispersion of aluminum oxide hydroxide particles (b).

[0047] All components should be compatible in the final aqueous coating composition, meaning that precipitation or gelation will not occur over time. A minimum stability of 6 months is preferred. The final pH value of the aqueous coating composition depends on the components used and their pre-dispersions or solutions and can be adjusted at each step of the formulation by adding an acidic dispersing agent (f).

[0048] Base material The aqueous coating composition of the present invention can be applied to different non-absorbent or low-absorbent substrates to obtain a dry primer coating (primer layer) prior to inkjet printing, followed by drying of the water and any solvent.

[0049] Non-absorbent substrates include plastic substrates, such as polymer films (including polymer film laminates), for example, flexible packaging laminates and decorative films; paper or cardboard coated or laminated with a polymer layer, for example, double-sided resin-coated photobase paper; metal foils, for example, aluminum foil; substrates coated or laminated with a metal layer; glass substrates; and ceramic substrates such as tiles. Examples of low-absorbent substrates include barrier paper; highly sized, coated, or impregnated paper or cardboard, such as wallpaper, decorative paper, and cardboard liners; coated canvas; and coated woven or nonwoven fabrics. The substrate can be a flexible substrate, such as the flexible substrates described above, or a rigid substrate, such as the rigid substrates described above, and can also include various plastic components.

[0050] Non-absorbent or low-absorbent substrates do not incorporate aqueous coatings or water into their mass, or only slowly do so. For low-absorbent paper and cardboard, the Cobb 30 value according to DIN EN ISO 535:2014-06 is 10 g / m². 2 Less than 5 g / m 2 The paper substrate is preferably a mass-produced, surface-sized, impregnated, pre-treated or coated, i.e. barrier-coated, white or colored paper. In particular, the substrate paper may be a commercial paper dedicated to graphic applications, i.e., photography, advertising, documents, packaging, i.e., food packaging, cardboard boxes, decoration, i.e., flooring, wall decoration, furniture, or other applications. The paper weight is preferably 30 g / m for paper. 2 ~300g / m 2 , 250 g / m for cardboard 2 ~500g / m 2 It could be.

[0051] The aqueous coating compositions of the present invention are particularly suitable for application to polymeric films, including polymeric film laminates containing two or more polymeric films, which may include a homogeneous top layer as an adhesion-promoting layer, which may be a coating layer or a coextruded layer.

[0052] The polymer film may be any polymer material that can be processed into a film, and may be unstretched, uniaxially stretched, or biaxially stretched. Typically, the polymer film comprises a thermoplastic material. Useful thermoplastic materials include polyesters, polyolefins, polystyrenes, polyamides, polyacrylates, polycarbonates, polyvinyl chloride, cellulose derivatives such as cellulose triacetate, biodegradable polymers such as starch and poly(amino acids), and blends and copolymers of these polymers.

[0053] Suitable biaxially oriented polymer films are commercially available and have high initial tear strength and low tear resistance. The biaxially oriented thermoplastic material can be selected from the group consisting of polyester, polyolefin, polystyrene, polyamide, polycarbonate, and polyvinyl chloride (including homopolymers and copolymers and blends thereof). Preferably, the thermoplastic material is selected from the group consisting of polyester, even more preferably poly(ethylene terephthalate), poly(ethylene naphthalate), and polylactide (also colloquially referred to as "poly(lactic acid)" - PLA); polyolefin, even more preferably polypropylene; polyamide, such as PA6; polyvinyl chloride, and blends and copolymers thereof. The most preferred biaxially oriented polymer films are biaxially oriented polypropylene (BOPP), such as the BOPP film available from Innovia under the trade name Rayoface®, biaxially oriented poly(ethylene terephthalate) (BOPET), such as the BOPET film available from Mitsubishi under the trade name Hostaphan® and from DuPont under the trade names Mylar® and Melinex®, biaxially oriented polylactide (BOPLA), and biaxially oriented polyamide (BOPA), such as BOPA6. The biaxially oriented polymer film may also be a coextruded polymer film. Coextruded biaxially oriented polymer films are preferred, in which the first layer is a polymer described above and the second layer is a polymer with better adhesion to the aqueous coating composition, i.e., a propylene / ethylene copolymer.

[0054] Suitable uniaxially stretched polymer films include shrink sleeves. The thermoplastic polymer of the shrink sleeve can be selected from the group consisting of (co)polyvinyl chloride, (co)polystyrene, (co)polyolefin, (co)polyester, and mixtures, blends, and copolymers thereof, more preferably polyvinyl chloride (PVC), glycol-modified polyethylene terephthalate (PET-G), polystyrene (PS), styrene-butadiene copolymer, polypropylene (PP), polyethylene (PE), polylactic acid (PLA), and cyclic olefin copolymer / polyethylene (COC / PE), and mixtures, blends, and copolymers thereof. Both the above (co)polymers and their films, which may be optionally uniaxially or biaxially stretched, are commercially available.

[0055] The most preferred non-absorbing substrates to be coated with the aqueous coating compositions of the present invention are polymeric films, including polyolefins such as polypropylene (e.g., cast polypropylene (cPP) and biaxially oriented polypropylene (BOPP)) and polyethylene, polyesters such as poly(ethylene terephthalate) (PET, APET) (e.g., biaxially oriented poly(ethylene terephthalate) (BOPET)), or polyamides, including polymeric film laminates.

[0056] The polymer film can be transparent, translucent, or opaque, e.g., white opaque or colored opaque. Suitable films can be foamed, hollowed, or heavily dyed, e.g., with white pigments. The surface of the polymer film can be treated, e.g., by corona treatment, flame treatment, or chemical treatment, e.g., with a thin polyacrylate coating. Surface treatment can have various effects, such as improving wettability with aqueous coating compositions, particularly in the case of BOPP films, and especially increasing adhesion. Suitable polymer film thicknesses generally range from 8 to 400 μm.

[0057] Inkjet printable primer layer The aqueous coating composition of the present invention can be coated onto a substrate to form an inkjet printable primer layer by any conventional coating method known in the art. For example, the aqueous coating composition can be applied by means of a curtain coater, die coater, roll coater, air knife coater, blade coater, rod coater, reverse gravure coater, bar coater, or by flexographic or gravure printing. Application by reverse gravure coating, gravure printing, or flexographic printing is preferred.

[0058] After application to a substrate, the aqueous coating composition is dried to remove water and any solvent to obtain the final inkjet printable primer layer. Preferably, an active drying step, such as convection drying (with hot air), contact drying, IR drying, NIR drying, or any combination thereof, is carried out, typically at a temperature of at least 50° C., to reduce drying time.

[0059] Preferably, the aqueous coating composition is applied directly to the substrate, meaning that the inkjet-printable layer is in direct contact with the substrate. It is more preferred that the inkjet-printable primer layer formed from the aqueous coating composition is a single inkjet-printable layer. The aqueous coating composition can be coated onto the substrate in one layer in a single application step, or can be applied in two or more partial layers, i.e., two or more aqueous coating compositions of the present invention having different compositions are subsequently coated onto the substrate. The two or more partial layers together form the inkjet-printable primer layer. Preferably, the inkjet-printable primer layer is applied onto the substrate in one layer in a single application step.

[0060] The aqueous coating composition of the present invention can be applied separately from the inkjet printing process in a separate coating process, or inline in the inkjet printer, i.e., at the printing speed in a coating unit arranged upstream of the printing station.It is advantageous to apply it by a roll-to-roll method.Preferably, the aqueous coating composition is applied inline in the printing process, more preferably inline in the printer in a roll-to-roll process.

[0061] Typically, the aqueous coating composition has a coating weight of 0.3 to 8.0 g / m 2 , preferably 0.5 to 6.0 g / m 2 , more preferably 0.8 to 5.0 g / m 2 , and most preferably 1.3 to 4.0 g / m 2 The inkjet printable primer layer is applied to the substrate so as to obtain a dry coating weight of 1000 ppm or less. The actual dry coating weight can be adapted to the intended use of the coated substrate, for example, the type of printer and ink used to print on the inkjet printable primer layer. Ink dot gain and deposition reactivity can be controlled by selecting the appropriate dry coating weight and / or concentration of the polyvalent metal cation (b), as well as the overall composition within the scope of the present invention.

[0062] Preferably, the inkjet printable primer layer has a gloss, and when applied to a glossy substrate, i.e., when applied to a glossy substrate (having a gloss of about 65 GU), a gloss of about 50 to 85 GU is achieved.

[0063] The aluminum hydroxide oxide particles (b) provide pores in the primer layer after coating and drying. By "porous" we mean that the pores in the aluminum hydroxide oxide particles (primary aggregates) and / or in the coating comprising the aluminum hydroxide oxide particles and binder have a pore size (diameter) in the range of 10 nm to 1 μm, preferably 20 nm to less than 0.5 μm, and more preferably 50 nm to less than 0.2 μm, as measured by scanning electron microscopy (SEM). The porosity of the inkjet printable primer layer is evident in Figure 1.

[0064] The surface of the inkjet printable primer layer is non-tacky and smooth, meaning that after application and drying and optionally printing of the aqueous coating composition of the present invention, in particular against the backside of a substrate wound into a roll, there is no blocking or adhesion to other surfaces, even under pressure, at room temperature or at elevated temperatures, e.g., 60°C.

[0065] Typically, the inkjet printable primer layer is transparent. When the substrate is a transparent film having a haze value of 5% or less, the coated substrate according to the present invention preferably has a haze value of 7% or less, more preferably 10% or less, and most preferably 15% or less, as measured according to ASTM D1003, Procedure A.

[0066] printing The inkjet-printable primer layer of the coated substrate of the present invention can be printed by aqueous inkjet printing. Typically, it is printed using a high-speed printing process, more preferably a single-pass printing process. Advantageously, the coated substrate is printed using a digital inkjet printer operating at a high printing speed, such as 5 to 300 m / min, e.g., 30 or 60 to 300 m / min, preferably a single-pass printing system, i.e., a printing system including a stationary print bar that includes a printhead across the web width. High-speed printing processes include, for example, roll-to-roll printing and sheet printing in a sheet-fed digital inkjet press.

[0067] Exemplary high-speed, single-pass inkjet digital presses for aqueous pigment inks are commercially available from Hewlett-Packard (Pagewide Industrial Press), Kodak (Prosper, Versamark), Canon (ImagePress), Fujifilm (Jetpress), Screen (Truepress), Miyakoshi (MJP30-AXF), KBA (RotaJet), Paris (Padarma Printing), Astronova / Trojan, Affinia, Arrow Systems, and Rigoli. High-speed, single-pass inkjet printers are typically operated using piezo printheads available from, for example, Fujifilm, Dimatics (e.g., SAMBA® printheads), Kyocera, Toshiba, Ricoh, and Xaar, continuous inkjet printheads available from, for example, Kodak, or printheads and printbars available from Memjet, respectively.

[0068] After printing, thorough drying of the aqueous ink is necessary because neither the primer layer of the present invention nor the non- or low-absorbency substrate can absorb significant amounts of water. Therefore, an active drying step, such as convection drying (in hot air), contact drying, IR drying, NIR drying, or any combination thereof, can be carried out, typically at a temperature of at least 50°C.

[0069] In the case of a transparent coated substrate, it can be printed by either front printing or reverse printing. Front printing means that a non-mirror image is printed on the inkjet-printable primer layer. Also, due to the high transparency of the inkjet-printable primer layer, reverse printing of the coated substrate is possible. Reverse printing means that a mirror image is printed on the inkjet-printable primer layer. A coated substrate is said to be transparent if it has a haze of less than 15%, more preferably less than 10%, and most preferably less than 6%, as measured according to ASTM D1003, Procedure A.

[0070] Typically, aqueous (water-based) pigment-based inks are used to print on the inkjet printable primer layer of the present invention. Pigment-based inks contain dispersed pigments, preferably anionically stabilized dispersed pigments. Within the meaning of the present invention, pigments are colored pigments. The pigments can be organic or inorganic pigments.

[0071] Additionally, aqueous pigment-based inks can contain a polymeric binder, preferably a dissolved or dispersed anionic polymer or anionic stabilizing dispersion polymer. The polymeric binder is present to immobilize the pigment, promote adhesion of the pigment to the printed surface after printing, and / or as a surface modification of the pigment to achieve stable dispersion. Inks containing anionic polymers or anionic stabilizing binder polymers are preferred for their interaction with the aqueous coating composition of the present invention. The anionic polymer or anionic stabilizing binder polymer can be a dispersed anionic polyurethane, a polyurethane dispersed with an anionic surfactant, or a dispersed anionic (meth)acrylic polymer or copolymer, such as an anionic styrene-(meth)acrylate copolymer. Typically, the binder polymer is present in the pigment-based ink in an amount of 1 to 25% by weight, preferably 3 to 15% by weight, based on the solids content of the ink. Alternatively, aqueous pigment-based inks can be formulated without a polymeric binder.

[0072] Other components of inks include dispersants (surfactants and polymers), humectants and / or cosolvents (to retard premature drying and prevent clogging of inkjet nozzles), defoamers and antifoaming agents, humectants to enhance contact with the substrate, pH adjusters (usually amine derivatives), biocides and bacteriostats, etc. Commercially available aqueous pigment-based inks offer a great deal of variation in ink components, including a wide selection of pigment and dispersant types. In particular, the type and content of different cosolvents and humectants or their mixtures can vary significantly. Examples of suitable co-solvents and humectants are alkanols (such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol), linear amides (such as dimethylformamide or dimethylacetamide), ketones and ketone-alcohols (such as acetone, methyl ether ketone, cyclohexanone and diacetone alcohol), diols (such as ethylene glycol, propylene glycol, diethylene glycol, 1,2-hexanediol, 1,5-pentanediol, triethylene glycol, tetrahydrofuran ... ethylene glycol, etc.), triols (glycerol, 1,2,6-hexanetriol, etc.), ethers of diols (2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-[2-(2-methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]ethanol, ethylene glycol monoallyl ether, tetraethylene glycol dimethyl ether, etc.), ethers (tetrahydrofuran and dioxane, etc.), cyclic esters (caprolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), and sulfolane.

[0073] Primarily, the four ink CMYK (cyan, magenta, yellow, and black) system is used for printing onto the inkjet printable primer layer of the present invention, however, special colors such as blue, green, orange, red, and especially white or silver can also be used.

[0074] The aqueous coating composition of the present invention provides an inkjet-printable primer layer that provides high print quality when subjected to inkjet printing using pigmented inks. The inkjet-printable primer layer accepts ink droplets with an appropriate contact angle to ensure a defined and appropriate dot size. The stabilized ink pigment and any stabilized polymer binder are instantly chemically destabilized by interaction with polyvalent metal cations, cationic groups if present on the binder polymer in the primer layer, and protons if present in the primer layer. The inkjet-printable primer layer of the present invention quickly fixes applied ink droplets on its surface, ensuring a defined dot of ink even while the ink is still in the liquid phase (not yet dried). In single-pass printing, a dot size that is not too small for high-speed printing is achieved, i.e., streaky printed images that can be caused by dots that are too small are avoided. Up to 10 ml / m 2 seconds or up to 20ml / m 2Ink acceptance rates of seconds can be achieved. Therefore, the aqueous coating composition of the present invention is ideal for high-speed inkjet printing because it provides instantaneous fixation of ink pigments and, optionally, ink binders to achieve appropriate dot sizes. High print quality means high image resolution, high color gamut, color saturation, and color vibrancy, without any printing artifacts such as streaks, bleeding, blurring, coalescence, and mottle. The inkjet print quality achieved with the aqueous coating composition of the present invention and suitable inks often exceeds that of conventional flexographic and intaglio printing. Good adhesion of the primer layer of the present invention to the substrate and to the ink applied after drying is also provided. The aqueous coating composition of the present invention achieves a perfect compromise between adhesion of the print pigment to the primer layer, adhesion of the primer layer to non-absorbent or low-absorbent substrates, and availability of polyvalent metal cations on the surface of the primer layer, i.e., immediate release of the polyvalent metal cations to the printing interface in contact with the just-landed ink dot on the primer surface, to achieve high print quality. A tack-free surface of the primer layer after printing and drying is also obtained. This allows for roll-to-roll processing of the printed coated substrate without material blocking. This is especially important when an additional overprint varnish is not applied in-line after the ink is printed and dried. Nevertheless, an overprint varnish can be applied to the printed primer layer to protect the printed surface and / or modify the surface properties.

[0075] Furthermore, the inkjet printable primer layer of the present invention is scratch and rub resistant both before and after printing. It is further characterized by good water resistance and can provide these properties with suitable printing inks.

[0076] To achieve optimal printing results, the aqueous coating composition of the present invention must be adapted to a specific printing ink. This means that the mixing ratios of the individual components—polymeric binder (a), aluminum oxide hydroxide (b), polyvalent metal cation (c), and optional water-soluble polymeric binder (e)—must be adapted to the specific ink. This also applies to the type of polymeric binder (a), the type of polyvalent metal cation (c), and counteranion (d), as well as the dry coating weight of the primer layer formed from the aqueous coating composition.

[0077] commercial use The aqueous coating composition of the present invention is useful for a variety of applications. As described above, it can be applied to a wide variety of non-absorbent or low-absorbent substrates, either offline or in-line, in an inkjet printer. Preferably, the aqueous coating composition is useful for packaging and decorative applications of films and film laminates, as well as impregnated or pre-coated papers with low-absorbent surfaces, such as food packaging films, decorative films, coated wallpaper, and impregnated decorative papers.

[0078] In a further converting step, the coated and printed substrate may be laminated with a polymer film or polymer film laminate, paper, metal foil, or a laminate comprising metal foil, or may be embossed.

[0079] The coating composition is particularly applicable to preparing inkjet-printable primer layers for high-speed, single-pass printing in decorative paper and decorative film applications. Decorative paper is a specialty paper with a high filler content and high opacity. It can be pre-impregnated with melamine / melamine-formaldehyde resin or urea resin for roll-to-roll printing and then converted into a rigid material by application to a rigid substrate. For decorative applications, the printed primer layer almost always needs to be protected, typically by overvarnishing with a radiation-curable coating(s) and then crosslinking with UV light or electron beam curing. The unprinted side of the decorative paper or film is then bonded to a rigid substrate. Rigid substrates that can be used include high-pressure laminate (HPL), particleboard, plywood, medium-density fiberboard (MDF), chipboard, particleboard, or even metal. Instead of overvarnishing, the printed primer layer can be protected by lamination with a film, for example, using adhesives and / or heat presses, or by extrusion lamination with a polymer such as polyurethane, depending on the end use.

[0080] When intended for food packaging, the aqueous coating compositions and aqueous pigment inks applied must be safe for use in food packaging, i.e., they must not contain substances that migrate through the substrate, e.g., the layers of a film or film laminate, into the package, leading to non-compliant food. Preferably, aqueous inks with a low tendency to migrate are used for printing, more preferably pigment-based inks containing food-compatible humectants such as glycerol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, poly(ethylene glycol), and poly(propylene glycol). [Example]

[0081] [reagent] Pseudoboehmite powder: Surface-modified (acidic) water-dispersible pseudoboehmite equivalent to AlO(OH) 0.15H2O, specific surface area of 140m after drying at 110°C for 2 hours 2 / g, pore volume 0.82 cm 3 / g, containing HNO3 acid (pH=4.0, 30% dispersion), dispersibility in water >96%.

[0082] Boehmite powder: DISPERAL® HP14, an acid dispersible boehmite with a median powder size of 35 μm and high porosity, 100 nm dispersed particle size (10 wt% dispersion in 0.4 wt% HNO), 14 nm crystallite size and 98% dispersibility (10 wt% dispersion in 0.4 wt% HNO), available from Sasol.

[0083] Hydrochloric acid with a concentration of 13% by weight

[0084] Calcium chloride: A hydrated form containing 77% calcium chloride by weight

[0085] Magnesium chloride: hydrated form containing 47% by weight magnesium chloride

[0086] Levasil® CC310 (formerly Bindzil CC310): (3-glycidyloxypropyl)trimethoxysilane modified anionic colloidal silica dispersion, 28% solids by weight, available from Nouryon Chemicals BV.

[0087] Baybond® PU404: Nonionic polyester urethane dispersion, 50 wt% solids, pH 5.5-7.5, MFFT less than 0°C, and average particle size (D) of 135 nm v50 ), available from Covestro.

[0088] Neorez® R-9340: Nonionic polyester urethane dispersion, 40 wt% solids, pH 6.5-7.5, MFFT less than 5°C, and average particle size (D) of 140 nm v50 ), available from Covestro.

[0089] Neocryl® XK-30: Cationic acrylic dispersion, 42 wt. % solids, pH 4.0, MFFT at 30° C., and average particle size (D) of 150 nm v50 ), available from Covestro.

[0090] Esacote® PU4045: Anionic aliphatic polyurethane dispersion, 35 wt% solids, pH 7.0-9.5, MFFT of approximately 0°C, and average particle size (D) of 110 nm v50 ), available from Lamberti.

[0091] Esacote® PU C1: a cationic dispersion of aliphatic polyurethane based on polycarbonate diol, 30 wt. % solids, pH 4-6, MFFT near 0°C, and an average particle size (D) of 180 nm. v50 ), available from Lamberti.

[0092] Kuraray Poval® 30 / 92: High molecular weight poly(vinyl alcohol), saponification degree 92%, available from Kuraray Co., Ltd., Japan.

[0093] Surfynol® 420: Ethoxylated acetylenic surfactant, provides dynamic wetting and molecular defoaming, available from Evonik Operations GmbH, Germany.

[0094] [Preparation of Aluminum Oxide Hydroxide Dispersion] Pseudoboehmite dispersion 18.4 kg of water-dispersible pseudo-boehmite powder (containing approximately 2 wt. % of adsorbed water) was added to 58 kg of water and stirred for 3 hours to obtain a 23.6 wt. % solids dispersion of pseudo-boehmite particles. The pH of the dispersion was adjusted to 3.8 by adding hydrochloric acid. The average dispersed particle size (D) was measured by laser diffraction. v50 ) was 128 nm.

[0095] Boehmite dispersion 18.6 kg of boehmite powder (containing approximately 4 wt. % adsorbed water) and 0.9 kg of hydrochloric acid were added to 56.8 kg of water and stirred for 3 hours to obtain a 23.6 wt. % solids dispersion of boehmite particles. The median particle size (D) was measured by laser diffraction. v50 ) was 137 nm.

[0096] [Preparation of aqueous coating composition] Coating Composition A 2.4 kg of calcium chloride dihydrate was dissolved in 100 kg of water. The pH of the solution was adjusted to 3.8 by adding hydrochloric acid. Then, the pseudoboehmite dispersion (76.4 kg) was added to the calcium chloride solution. 41 kg of Baybond® PU404 dispersion was slowly poured into the pseudoboehmite and calcium chloride premix while stirring the mixture. 0.6 kg of Surfynol® 420 surfactant was slowly added to this mixture. The pH of the aqueous coating composition was adjusted to 3.8 by adding hydrochloric acid, and the solids content was adjusted to 18 wt. % by adding water.

[0097] Coating Composition A can be calculated to contain, by weight, 44% pseudoboehmite particles, 50% polyurethane particles, and 1.6% calcium ions in its solids content.

[0098] Coating compositions B to H and comparative coating compositions I to M Coating compositions B to H and comparative coating compositions I to M were prepared in the same manner as coating composition A, with each component being replaced or omitted as shown in Table 1. In Table 1, the solids content of the added components is shown in weight percent based on the solids content of the aqueous coating composition.

[0099] In Coating Composition B, Kuraray Poval® 30 / 92 poly(vinyl alcohol) partially replaced the polyurethane dispersion, where the Kuraray Poval® 30 / 92 poly(vinyl alcohol) was added as a 10 wt % aqueous solution before adding the polyurethane dispersion. In Comparative Composition J, a 10 wt % poly(vinyl alcohol) solution was added as the sole polymer binder.

[0100] [Table 1]

[0101] [Table 2]

[0102] [Example 1] Coating composition A was applied at 2 g / m 2 The coating was applied roll-to-roll onto a 100 μm thick white BOPET film (type: Melinex® 339, comprising a thin polyacrylate coating on both sides and having a gloss of 65 GU, available from DuPont Teijin Films) at a dry coating weight of 100 μm and dried at an oven temperature of up to 80° C. The coating was tack-free and the coated roll could be unwound without blocking.

[0103] The coated films were then printed with a four-color (CMYK) Epson inkjet printer (Type: Ecotank ET-2720), where the printer was equipped with either a commercially available aqueous pigment ink (Ink 1) containing color pigments, an anionic polymer binder, and approximately 40% by weight of propanediol-1,2, or an aqueous pigment DuraFlex® ink (Ink 2) from Memjet, Inc., containing no binder and an overall concentration of approximately 15% by weight of triethylene glycol, 2-(2-butoxyethoxy)ethanol, and glycerol. After printing, the ink fluid remained on the surface of the coated film, while the ink pigment and ink binder (if present) precipitated. The prints were transferred to a laboratory oven and dried at 60°C for 45 minutes.

[0104] [Examples 2 to 11] In Examples 2-11, BOPET films were coated and printed as described for Example 1 using different dry coating weights (Examples 2 and 3) and different coating compositions B-H (Examples 4-11), as shown in Table 2.

[0105] [Comparative Examples 12 to 16] In Comparative Examples 12-16, BOPET films were coated and printed as described for Example 1 using Comparative Coating Compositions I, J, L, and M to achieve the respective dry coating weights shown in Table 2.

[0106] [Applied test method] The coated or coated and printed samples were tested according to the following test methods and the results are reported in Table 2.

[0107] The dry coating weight of the primer layer was determined by the weight difference between the coated and uncoated substrate.

[0108] The gloss of the dried primer layer on the substrate was measured in GU at an angle of 60° according to ISO2813:2014.

[0109] The tackiness of the dried primer layer, i.e. the tendency to block, was measured at 70 g / cm in a climatic chamber at 60°C and room humidity of 80%. 2 The primer layer was evaluated by stacking the coated side of the substrate against the back of another substrate under a pressure of 0.05 psi for 24 hours. The stack of coated substrates was then transferred to a standard climate (23°C, 50% room humidity). After cooling, the stack was manually separated. The primer layer was visually inspected and rated as follows: 1. The primer layer adheres to the backside of other substrates, and forceful separation will damage the entire primer layer. Force must be applied to separate the two layers, separation noise may be present, the surface of the primer may be marked or show damage, and / or the primer coating may have migrated slightly to the backside of the other substrate. 3 Blocking / separation force is significant, separation noise may be present, slight marks on the primer surface 4 Slight localized blocking with minimal marks on the primer surface 5 No blocking, no adhesion, no marks on the primer surface

[0110] Friction, scratch and adhesion tests were carried out according to FINAT Test Method No. 21 (FTM21) in a standard climate (23°C and 50% room humidity).

[0111] The friction test was performed by sliding a fingertip back and forth under pressure five times on the surface of the unprinted and printed primer layers (the uniformly red printed areas). The primer layers were visually inspected and rated as follows: Unprinted primer layer: 1 The coating is completely rubbed off 2 The coating is only partially rubbed off 3 Clearly visible marks, no rub-off 4 Slightly visible marks, no rub-off 5 No visible changes on the surface Printed primer layer: 1 Coating and ink are at least partially rubbed off 2. Completely rub off / smear the printed ink 3. Partially rubbing off / staining printed ink 4 Slight stains of printed ink 5. No visible marks or imperfections

[0112] The scratch test was carried out by manually sliding the edge of a 1 euro coin back and forth five times on a hard, smooth, stable table at an angle of 60° to the table surface under light pressure over the surface of the unprinted primer layer and the printed primer layer (the uniformly blue printed area). The surface of the coin was facing the direction of movement. The primer layers were visually inspected and rated as follows: Unprinted primer layer: 1. The primer layer peels off over the entire scratched area. 2 Severe / significant marks with primer layer removal 3 Surface scratches and slight primer layer removal are detectable 4 Significant scratches are visible on the surface 5 Only minor surface scratches are visible, but not deep Printed primer layer: 1 Ink and primer layers peel off over the entire scratched area 2 Severe / significant marks with ink and primer layer removal 3. There are severe scratches or white marks on the printed surface. 4 Scratches / slight white marks are visible on the printed surface 5. No color defects / no white marks visible, only indentations can be detected

[0113] The adhesion of the printed areas was evaluated using adhesive tape Tesa Film 4101 manufactured by Tesa SE, Germany, and the results were evaluated as follows: 1. The primer layer and ink peel off, and there is a problem with the adhesion of the layer to the substrate. 2. The ink peels off along with part of the primer layer, the primer layer is split, and there is a problem with the cohesion of the primer layer. 3 Most of the ink has peeled off, and there is a problem with the ink's adhesion to the primer layer. 4. Only slight transfer of ink to tape 5 No significant transfer of ink to tape

[0114] The dot diameter of a single cyan dot in the test print was measured using a Keyence Model VK-9710 laser scanning microscope using combined laser and visible spectrum light imaging.

[0115] Print performance was assessed visually to judge general color impression / color gamut, intercolor bleed + color bleeding (bleeding of colored areas into each other + bleeding of colored areas into non-printed areas), print sharpness (small printed characters, thin lines), coalescence (coalescence or puddling in inkjet printing is an image defect that occurs when adjacent wet ink droplets coalesce on the receiving surface and combine into larger droplets before the ink pigment can settle. This causes the image to appear splotchy or "puddled" and results in unevenness in solid areas).

[0116] General color impression / color gamut: 1 Pale, dull, dull, smudged and / or dirty colors, cracked print, significant color shifts in single, secondary or tertiary colors 2 Pale, dull, dull and / or slightly stained colors, cracks visible on enlargement, slight color shifts in single, secondary or tertiary colors 3 Noticeably pale, dull and lackluster, prone to staining 4 Bright color but slightly dull, no stains 5. Extremely vibrant colors, high gloss

[0117] Print sharpness: 1. Small print is illegible and unrecognizable, thin lines are blurred or blended 2 Small print is severely blurred but still legible 3 All small print and thin lines are legible and recognizable, but slightly blurred 4 Good sharpness 5 Excellent sharpness

[0118] Coalescing: 1. The filled print area is not uniform and looks like a puddle 2 Only the printed areas filled with secondary and tertiary colors are not uniform, they look like puddles 3 Only the printing areas filled with high ink load / tertiary colors are not uniform, they look like puddles 4. Minimal adhesion only 5 No joining

[0119] Intercolor + Color Bleed: 1 Colors bleed strongly into each other and / or colors bleed strongly into non-printed areas The two colors bleed into each other and / or into non-printed areas in a clearly discernible manner 3. Colors in areas with high ink load bleed into each other and / or non-printed areas in a clearly noticeable manner 4 Only slight bleeding of color in areas with high ink load, discernible only under magnification 5. No bleeding

[0120] A rating of 3 is considered sufficient for most applications.

[0121] [Table 3]

[0122] [Table 4]

[0123] It can be seen that the anti-blocking performance, scratch and rub resistance, and adhesion are very good in all inventive examples. The dot size is adequate. The inventive examples also show very good printing performance for Ink 1, and also for Ink 2. The difference in printing performance is mainly due to the type and content of co-solvent, which are significantly different for Ink 1 and Ink 2. The tested aqueous coating composition of the present invention is considered optimal for Ink 1, but satisfactory printing results can also be obtained with Ink 2.

[0124] Comparative Example 12 (without aluminum hydroxide oxide particles) shows high tack and low rub resistance. Printing performance is worse with both Ink 1 and Ink 2. Comparative Example 13 (water-soluble polymer binder only) shows low scratch resistance for the unprinted primer layer and poor adhesion in the printed areas. Printing performance with Ink 2 is poor in terms of general color impression / color gamut. In Comparative Example 14 (without calcium chloride), ink fixation could not be achieved. Comparative Example 15, corresponding to Example 10, with the only difference being that the pseudoboehmite particles were replaced with silica particles, shows considerable tack, which leads to undesirable blocking in the roll-to-roll process. Printing performance with Ink 1 is significantly worse than Example 10 in terms of general color impression / color gamut. With Ink 2, both Example 10 and Comparative Example 15 achieve only 1.2 g / m 2 In Example 11 / Comparative Example 16, the coating amount is 2.6 g / m 2 and the bleeding problem disappeared. However, in Comparative Example 16 the general color impression / gamut with Ink 1 is still unacceptable.

[0125] Aspects of the invention: 1. An aqueous coating composition comprising: (a) 20 to 79 wt. %, preferably 30 to 69 wt. %, more preferably 35 to 64 wt. %, and most preferably 40 to 59 wt. % of a dispersed polymer binder; (b) 20 to 79 wt. %, preferably 30 to 69 wt. %, more preferably 35 to 64 wt. %, and most preferably 40 to 59 wt. % aluminum oxide hydroxide particles; (c) 0.1 to 10 wt. %, preferably 0.3 to 5 wt. %, more preferably 0.5 to 2 wt. % of dissolved polyvalent metal cations, and (d) inorganic and / or organic counteranions of the metal cation; wherein the weight percentages are based on the solids content of the aqueous coating composition.

[0126] 2. The aluminum hydroxide oxide particles have a median particle size (D) of 20 to 500 nm, preferably 30 to 300 nm, more preferably 50 to 200 nm, and most preferably 80 to 180 nm, as measured by laser diffraction in accordance with ISO 13320:2020-01. v50 2. The aqueous coating composition of embodiment 1, having

[0127] 3. The aqueous coating composition of embodiment 1 or 2, wherein the dispersed polymer binder (a) comprises nonionically stabilized polymer particles or cationic polymer particles.

[0128] 4. The aqueous coating composition of any one of aspects 1-3, wherein the dispersed polymer binder (a) comprises polyurethane particles, poly(meth)acrylate particles, or a combination thereof.

[0129] 5. The aqueous coating composition of aspect 3 or 4, wherein the dispersed polymer binder (a) comprises nonionically stabilized polyurethane particles, cationic polyurethane particles, nonionically stabilized poly(meth)acrylate particles, cationic poly(meth)acrylate particles, or a combination thereof, preferably nonionically stabilized polyurethane particles, cationic polyurethane particles, or a combination thereof.

[0130] 6. The polymer particles of the dispersed polymer binder (a) have a median particle size (D) in the range of 10 to 500 nm, preferably 20 to 300 nm, more preferably 50 to 250 nm, and most preferably 75 to 230 nm, as measured by laser diffraction according to ISO 13320:2020-01. v50 6. The aqueous coating composition of any one of embodiments 3 to 5, wherein

[0131] 7. The aqueous coating composition of any one of aspects 1-6, wherein the aluminum oxide hydroxide particles (b) are selected from boehmite particles, pseudoboehmite particles, and combinations thereof.

[0132] 8. Polyvalent metal ions (c) are Ca 2+ , Mg 2+ , Zn 2+ , Al 3+ , Fe 2+ , Fe 3+ , Ti 4+ , Zr 4+ , and combinations thereof, preferably Ca 2+ , Mg 2+ , Al 3+

[0023] Aspect 8. The aqueous coating composition of any one of aspects 1-7, wherein the aqueous coating composition is selected from:

[0133] 9. The aqueous coating composition of any one of aspects 1-8, wherein the counter anion (d) is selected from chloride, bromide, borate, nitrate, hydrogensulfate, sulfate, bicarbonate, acetate, formate, propionate, sulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate, and combinations thereof, preferably chloride, acetate, and combinations thereof.

[0134] 10. The aqueous coating composition of any one of aspects 1 to 9, having a solids content of 1 to 50 wt %, preferably 5 to 40 wt %, and more preferably 10 to 30 wt %.

[0135] 11. The aqueous coating composition of any one of aspects 1 to 10, having a pH value of 2.8 to 6.0, preferably 3.0 to 5.5, and more preferably 3.5 to 5.0.

[0136] 12. The aqueous coating composition of any one of aspects 1-11, further comprising a water-soluble polymer binder (e) replacing more than 0 and up to 50 wt. %, preferably 2-25 wt. %, of the dispersed polymer binder (a), based on solids.

[0137] 13. The aqueous coating composition of embodiment 12, wherein the water-soluble polymeric binder (e) is a poly(vinyl alcohol), preferably a poly(vinyl alcohol) having a degree of hydrolysis of 78 to 99 mol %.

[0138] 14. Further comprising an acidic dispersant (f), preferably the acidic dispersant has a pk of less than 5.0, preferably less than 4.9, more preferably less than 4.0, even more preferably less than 3.0, and most preferably less than 2.0. a 14. The aqueous coating composition of any one of Aspects 1 to 13, wherein the acidic dispersant is an organic acid and / or an inorganic acid having a value of 0 to 10 wt %, preferably 0.2 to 5 wt %, and more preferably 0.3 to 1 wt %, based on the amount of aluminum oxide hydroxide particles (a).

[0139] 15. The aqueous coating composition of embodiment 14, wherein the acidic dispersing agent is selected from HCl, HBr, HNO3, formic acid, acetic acid, propionic acid, lactic acid, citric acid, sulfamic acid, and any combination thereof.

[0140] 16. A substrate at least partially coated with the aqueous coating composition of any one of embodiments 1 to 15, which forms an inkjet printable primer layer, preferably in an amount of 0.3 to 8.0 g / m 2 , more preferably 0.5 to 6.0 g / m 2 , and even more preferably 0.8 to 5.0 g / m 2, and most preferably 1.3 to 4.0 g / m 2 A substrate having a dry coating weight of

[0141] 17. The coated substrate of embodiment 16, wherein the substrate is a non-absorbent substrate or a low-absorbent substrate.

[0142] 18. The coated substrate of embodiment 17, wherein the substrate is a non-absorbent substrate, preferably selected from polymer films, including polymer film laminates, paper or cardboard coated or laminated with a polymer layer, e.g., photobase paper coated with a double-sided resin, metal foil, a substrate coated or laminated with a metal layer, a glass substrate, and a ceramic substrate such as a tile.

[0143] 19. The coated substrate of embodiment 18, wherein the substrate is a polymeric film comprising a polymeric film laminate and comprises a homogeneous top layer as an adhesion-promoting layer that is a coated layer or a coextruded layer.

[0144] 20. The coated substrate of embodiment 18 or 19, wherein the polymer film comprising the polymer film laminate comprises a polyolefin such as polypropylene (e.g., cast polypropylene (cPP) and biaxially oriented polypropylene (BOPP)) and polyethylene; polystyrene; polyester such as poly(ethylene terephthalate) (PET, APET) (e.g., biaxially oriented poly(ethylene terephthalate) (BOPET)); or polyamide.

[0145] 21. The coated substrate of embodiment 17, wherein the substrate is a low-absorbency substrate, preferably selected from barrier paper; highly sized or coated or impregnated paper or cardboard, such as wallpaper, decorative paper, and cardboard liner; coated canvas; and coated woven or nonwoven fabric; more preferably selected from barrier paper; highly sized or coated or impregnated paper or cardboard, such as wallpaper, decorative paper, and cardboard liner.

[0146] 22. The substrate is 10g / m 2 less than 5 g / m 2 22. The coated substrate of embodiment 21, which is a low absorbency paper or cardboard having a Cobb 30 value according to DIN EN ISO 535:2014-06 of less than 0.015.

[0147] 23. The coated substrate of any one of aspects 16-22, wherein the inkjet printable primer layer formed from the aqueous coating composition is a single inkjet printable layer.

[0148] 24. The coated substrate of any one of aspects 16-23, wherein the inkjet printable primer layer formed from the aqueous coating composition is in direct contact with the substrate.

[0149] 25. A method for coating a substrate, comprising applying the aqueous coating composition of any one of embodiments 1 to 15 to the substrate to obtain an inkjet printable primer layer, preferably the primer layer having a coating density of 0.3 to 8.0 g / m 2 , more preferably 0.5 to 6.0 g / m 2 , and even more preferably 0.8 to 5.0 g / m 2 , and most preferably 1.3 to 4.0 g / m 2 having a dry coating weight of

[0150] 26. The method of embodiment 25, wherein the aqueous coating composition is applied directly to the substrate.

[0151] 27. The method of embodiment 24 or 25, wherein the inkjet printable primer layer formed from the aqueous coating composition is a single inkjet printable layer.

[0152] 28. The method of any one of aspects 25-27, further comprising an active drying step, such as convective drying, contact drying, IR drying, NIR drying, or any combination thereof.

[0153] 29. The method of any one of embodiments 25-28, wherein the substrate is defined as in any one of embodiments 17-22.

[0154] 30. A method for preparing an inkjet printed coated substrate, comprising the steps of (i) and (ii): (i) preparing a coated substrate by the method of any one of embodiments 25 to 29; and (ii) printing an inkjet printable primer layer on the coated substrate obtained in step (i) by an aqueous inkjet printing process.

[0155] 31. The method of embodiment 30, wherein the inkjet printing process is a high-speed printing process, preferably having a printing speed of 5 to 300 m / min, for example 30 or 60 to 300 m / min, and more preferably a single-pass printing process.

[0156] 32. The method of any one of aspects 30 to 31, further comprising (iii) an active drying step after the printing step (ii), such as convective drying, contact drying, IR drying, NIR drying, or any combination thereof.

[0157] 33. The method of any one of aspects 30-32, further comprising: (iv) applying an overprint varnish after the printing step (ii) or the optional active drying step (iii).

[0158] 34. The method of any one of aspects 30-33, wherein the aqueous ink used in the aqueous inkjet printing process is an aqueous pigment-based ink.

[0159] 35. The method of embodiment 34, wherein the aqueous pigment-based ink comprises an anionically stabilized dispersed pigment.

[0160] 36. The method of any one of embodiments 34 to 35, wherein the aqueous pigment ink comprises a polymeric binder, preferably a dissolved or dispersed anionic polymer or an anionically stabilized dispersed polymer.

[0161] 37. The method of embodiment 36, wherein the polymeric binder comprises a dispersed anionic polyurethane, a polyurethane dispersed with an anionic surfactant, a dispersed anionic (meth)acrylic polymer, or a dispersed anionic (meth)acrylic polymer or copolymer, such as an anionic styrene-(meth)acrylate copolymer.

[0162] 38. Preferably 0.3 to 8.0 g / m 2 , more preferably 0.5 to 6.0 g / m 2 , and even more preferably 0.8 to 5.0 g / m 2 , and most preferably 1.3 to 4.0 g / m 2 16. Use of the aqueous coating composition according to any one of aspects 1 to 15 for coating a non-absorbent or low-absorbent substrate to obtain an inkjet printable primer layer at a dry coating weight of

[0163] 39. The use according to embodiment 38, wherein the inkjet printable primer layer is a single inkjet printable layer.

Claims

1. An aqueous coating composition comprising: (a) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, and most preferably 40 to 59 wt % of a dispersed polymer binder; (b) 20 to 79 wt. %, preferably 30 to 69 wt. %, more preferably 35 to 64 wt. %, and most preferably 40 to 59 wt. % aluminum oxide hydroxide particles; (c) 0.1 to 10 wt. %, preferably 0.3 to 5 wt. %, more preferably 0.5 to 2 wt. % of dissolved polyvalent metal cations; and (d) inorganic and / or organic counter anions of the metal cation; wherein the weight percentages are based on the solids content of the aqueous coating composition.

2. The aluminum hydroxide oxide particles are selected from boehmite particles, pseudoboehmite particles, and combinations thereof, and / or have a median particle size (D) of 20 to 500 nm, preferably 30 nm to 300 nm, more preferably 50 nm to 200 nm, and most preferably 80 to 180 nm, as measured by laser diffraction according to ISO 13320:2020-01. ｖ５０ 10. The aqueous coating composition of claim 1, wherein

3. 3. The aqueous coating composition of claim 1 or 2, wherein the dispersed polymer binder (a) comprises nonionically stabilized polymer particles or cationic polymer particles, such as nonionically stabilized polyurethane particles, cationic polyurethane particles, nonionically stabilized poly(meth)acrylate particles, cationic poly(meth)acrylate particles, or a combination thereof, preferably nonionically stabilized polyurethane particles, cationic polyurethane particles, or a combination thereof.

4. The polyvalent metal ion (c) is Ca ２＋ , Mg ２＋ , Zn ２＋ , Al ３＋ , Fe ２＋ , Fe ３＋ , Ti ４＋ , Zr ４＋ and combinations thereof, preferably Ca ２＋ , Mg ２＋ , Al ３＋ and combinations thereof, and / or the counter anion (d) is selected from chloride, bromide, borate, nitrate, hydrogensulfate, sulfate, bicarbonate, acetate, formate, propionate, sulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate, and combinations thereof, preferably from chloride, acetate, and combinations thereof.

5. 5. The aqueous coating composition of any one of claims 1 to 4, further comprising a water-soluble polymeric binder (e) such as poly(vinyl alcohol), preferably having a degree of hydrolysis of 78 to 99 mol %, and replacing more than 0 to 50 wt %, preferably 2 to 25 wt %, of the dispersed polymeric binder (a), based on solids.

6. Further comprising an acidic dispersant (f), preferably the acidic dispersant has a pk of less than 5.0, preferably less than 4.9, more preferably less than 4.0, even more preferably less than 3.0, and most preferably less than 2.

0. ａ The acidic dispersant is an organic acid and / or an inorganic acid having a high acidity, for example, HCl, HBr, HNO ３ 6. The aqueous coating composition according to claim 1, wherein the amount of the acidic dispersing agent is selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, citric acid, sulfamic acid, and any combination thereof, and the amount of the acidic dispersing agent is more than 0 and not more than 10% by weight, preferably 0.2 to 5% by weight, and more preferably 0.3 to 1% by weight, based on the amount of the aluminum oxide hydroxide particles (a).

7. 7. A substrate at least partially coated with the aqueous coating composition of any one of claims 1 to 6 which forms an inkjet printable primer layer, preferably in an amount of 0.3 to 8.0 g / m ２ , more preferably 0.5 to 6.0 g / m ２ , and even more preferably 0.8 to 5.0 g / m ２ , and most preferably 1.3 to 4.0 g / m ２ A substrate having a dry coating weight of

8. 8. The coated substrate of claim 7, wherein the substrate is a non-absorbent or low-absorbent substrate selected from polymer films, including polymer film laminates; paper or cardboard coated or laminated with a polymer layer, for example, photobase paper coated with a double-sided resin; metal foil; substrates coated or laminated with a metal layer; glass substrates; ceramic substrates, such as tiles; barrier paper; highly sized, coated, or impregnated paper or cardboard, such as wallpaper, decorative paper, and corrugated cardboard liners; coated canvas; and coated woven or nonwoven fabrics, preferably wherein the polymer film laminate comprises a polyolefin, such as polypropylene (e.g., cast polypropylene (cPP) and biaxially oriented polypropylene (BOPP)) and polyethylene, polystyrene, polyester, such as poly(ethylene terephthalate) (PET, APET) (e.g., biaxially oriented poly(ethylene terephthalate) (BOPET)), or polyamide.

9. 9. The coated substrate of claim 7 or 8, wherein the inkjet printable primer layer formed from the aqueous coating composition is the sole inkjet printable layer and / or is in direct contact with the substrate.

10. A method for coating a substrate, comprising applying an aqueous coating composition according to any one of claims 1 to 6 to the substrate to obtain an inkjet printable primer layer, preferably the primer layer having a coating density of 0.3 to 8.0 g / m ２ , more preferably 0.5 to 6.0 g / m ２ , and even more preferably 0.8 to 5.0 g / m ２ , and most preferably 1.3 to 4.0 g / m ２ and preferably the aqueous coating composition is applied directly to the substrate and / or the inkjet printable primer layer formed from the aqueous coating composition is the only inkjet printable layer applied.

11. 11. The method of claim 10, further comprising an active drying step, such as convection drying, contact drying, IR drying, NIR drying, or any combination thereof.

12. 12. The method according to claim 10 or 11, wherein the substrate is defined as in claim 8.

13. 1. A method for preparing an inkjet printed coated substrate, comprising: (i) preparing a coated substrate by the method of any one of claims 10 to 12; and (ii) printing an inkjet printable primer layer on the coated substrate obtained in step (i) by an aqueous inkjet printing process, preferably by a high speed printing process such as a printing speed of 5 to 300 m / min or 30 or 60 to 300 m / min, more preferably by a single pass printing process; A method comprising the steps of:

14. 14. The method of claim 13, wherein the aqueous ink used in the aqueous inkjet printing process is an aqueous pigment-based ink, preferably comprising an anionic stabilized dispersed pigment.

15. 15. The method of claim 13 or 14, wherein the aqueous pigment ink comprises a polymeric binder, preferably a dissolved or dispersed anionic polymer or an anionic stabilized dispersing polymer, more preferably a dispersed anionic polyurethane, a polyurethane dispersed with an anionic surfactant, a dispersed anionic (meth)acrylic polymer, or a dispersed anionic (meth)acrylic polymer or copolymer, such as an anionic styrene-(meth)acrylate copolymer.

16. Preferably 0.3 to 8.0 g / m ２ , more preferably 0.5 to 6.0 g / m ２ , and even more preferably 0.8 to 5.0 g / m ２ , and most preferably 1.3 to 4.0 g / m ２ 7. Use of the aqueous coating composition according to any one of claims 1 to 6 for coating a non-absorbent or low-absorbent substrate to obtain an inkjet printable primer layer at a dry coating weight of

17. 17. The use according to claim 16, wherein the inkjet printable primer layer is a single inkjet printable layer.

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