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

Abstract

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

Description

Technical Field

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

[0002] Due to the low viscosity of inkjet inks and the resulting printing artifacts (artefacts) (e.g., color bleeding, line sharpness problems, dot spread and coalescence), it is essential to perform inkjet printing on non-absorbent substrates or low-absorbent substrates such as polymer films, foils, coated paper, ceramics, glass, etc. In addition, if there is no binder in the ink, the adhesion of the inkjet ink to such non-absorbent substrates may be very important. In order 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, thereby quickly fixing ink droplets. Since these inkjet coatings usually need to have a coating weight of at least 15g / m² to handle ink deposition (ink laydown), they are coated offline before printing, which increases the cost of substrate materials and final printing. For commercial printers for single pass printing, i.e., in packaging or decorative applications, these costs are unacceptable. Primer coatings that are applied with lower coating weights and are therefore cheaper are also described, especially when used in combination with appropriate inks. Inkjet primer compositions typically contain a coagulant, such as a dissolved multivalent metal cation, which plays an important role in precipitating the anionically charged dispersed ink components, primarily dispersed anionic color pigments and optional anionic binders.

[0003] WO2022 / 003336A1 describes a process for preparing a digital printing laminate, which includes applying a primer to a first substrate; printing an aqueous pigment inkjet printing ink onto a substrate coated with a primer; laminating a second substrate onto the first substrate coated with a primer and printed; wherein the primer is an aqueous coating composition comprising: (a) a water-dispersible polymer and a multivalent metal salt; or (b) a water-soluble polymer and a multivalent metal salt; wherein the aqueous pigment inkjet printing ink comprises an anionic polymer dispersion or an anionic solution polymer. The aqueous primer composition may also include a dispersion of an inorganic material (e.g., 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 may be selected from alumina hydrate, fumed alumina and fumed silica, and the second inorganic particles are preferably colloidal silica.

[0005] US2022 / 119666A1 relates to an aqueous composition for pre-treating a substrate before inkjet printing, the aqueous composition comprising one or more water-soluble salts of multivalent metal cations; one or more nonionic or cationic water-soluble or water-dispersible polymer binder substances, and fine surface-treated visible light scattering particles to provide a white background on a transparent film substrate or a dark substrate for printing high-quality monochrome or multi-color images. 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] The object of the present invention is to provide a coating composition which can be used to prepare thin printing primer layers with low coating weights for high-speed inkjet printing on non-absorbent or low-absorbent surfaces. Substrates coated with primer compositions with low coating weights should be printed with high print quality, should show good adhesion between primer and substrate in printed and unprinted areas, and should not be sticky (anti-blocking) when in contact with other surfaces during coating, storage or further processing.

[0007] This object is achieved by an aqueous coating composition comprising: (a) 20% to 79% by weight, preferably 30% to 69% by weight, more preferably 35% to 64% by weight, most preferably 40% to 59% by weight of a dispersed polymer binder, (b) 20% to 79% by weight, preferably 30% to 69% by weight, more preferably 35% to 64% by weight, most preferably 40% to 59% by weight of aluminum hydroxide oxide particles, (c) 0.1% to 10% by weight, preferably 0.3% to 5% by weight, more preferably 0.5% to 2% by weight of dissolved multivalent metal cations, and (d) inorganic counter anions and / or organic counter anions of the 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 which forms an inkjet printable primer layer.

[0009] The present invention also relates to a method for coating a substrate, which comprises applying an aqueous coating composition to a substrate to obtain an inkjet-printable primer layer, and a method for preparing an inkjet-printed substrate, which further comprises the step of printing the inkjet-printable primer layer of the coated substrate by a water-based inkjet printing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a SEM micrograph of an inkjet printable primer layer formed from the aqueous coating composition of the present invention according to Example 1 (magnification 20000×) DETAILED DESCRIPTION

[0011] Dispersed polymer binder (a)

[0012] The dispersed polymer binder (a) of the aqueous coating composition of the present invention comprises polymer particles, wherein the term "polymer particles" is broadly understood to include solid, viscoelastic (rubbery) or liquid particles, 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. As measured by laser diffraction (e.g., on a LS13320 device of Beckman Coulter) according to ISO 13320:2020-01, the polymer particles of the generally dispersed polymer binder (a) have a median particle size (D v50 ) size range is 10nm to 500nm, preferably 20nm to 300nm, more preferably 50nm to 250nm, and most preferably 75nm to 230nm.

[0013] In order to improve the dispersibility of the polymer binder (a) and its stability in the aqueous coating composition, the polymer particles according to the present invention are generally cationically stabilized or non-ionically stabilized. Cationic polymers are generally prepared by including cationic groups or groups that can be converted into cationic groups in the polymer structure, for example, tertiary amino groups can be protonated with acids or tertiary amino groups can be quaternized. Therefore, non-ionically stabilized polymers are generally prepared by incorporating hydrophilic groups into the polymer structure, and the hydrophilic groups generally include polyoxyalkylene groups, such as polyoxyethylene groups or polyoxypropylene groups. The stabilization mechanism of polymer particles in non-ionic dispersions is based on a steric stabilization mechanism generally provided by a hydrophilic soft segment. Part of the chain containing the non-ionic segment diffuses into the continuous phase, i.e., the aqueous phase, hindering the coalescence effect between the formed polymer particles.

[0014] The polymer binder preferably comprises polyurethane particles or poly(meth)acrylate particles, or copolymers and combinations thereof, more preferably comprises nonionically stabilized polyurethane particles, cationic polyurethane particles, nonionically stabilized poly(meth)acrylate particles, cationic poly(meth)acrylate particles, even more preferably comprises nonionically stabilized polyurethane particles and / or cationic polyurethane particles.

[0015] The polymer particles are usually 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 solid content of 30% to 60% by weight, a pH value of 4.0 to 8.0, more preferably a pH value of 5.0 to 7.0, and a minimum film forming temperature (MFFT) of less than 35°C, more preferably a minimum film forming temperature (MFFT) of 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 cations (c) and dispersed aluminum hydroxide oxide particles (b), which means that neither flocculation nor a significant increase in viscosity occurs.

[0016] The aqueous coating composition of the present invention comprises 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, most preferably 40 to 59 wt % of dispersed polymer binder (a), based on the solid content of the coating composition.

[0017] Polyurethane granules

[0018] Suitable polyurethanes used as polymer binders (a) in the aqueous coating composition of the present invention may be aromatic and / or aliphatic, i.e. made from aromatic polyisocyanates, aliphatic polyisocyanates and / or alicyclic polyisocyanates (e.g., hexamethylene diisocyanate and isophorone diisocyanate), and may be made from low molecular weight diols (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 polyurethanes or alicyclic polyurethanes are preferred.

[0019] Cationic polyurethanes are typically prepared by incorporating amino groups (e.g., side chains containing tertiary or quaternary amino groups) into the polymer and protonating the amino groups with an acid. Nonionically stabilized polyurethanes are typically prepared by incorporating polar groups (preferably side chains containing polyoxyalkylene moieties) into the polymer.

[0020] The polyurethane may have a certain amount of hydroxyl groups, that is, the hydroxyl value of the polyurethane does not exceed 50 mg KOH / g. Preferably, the hydroxyl value is <1 mg KOH / g, more preferably 0 mg KOH / g.

[0021] The polyurethane particles are typically introduced into the aqueous coating composition of the present invention in the form of an aqueous dispersion. There are a variety of commercially available polyurethane dispersions that can be used in the present invention, including polyurethane dispersions sold under the following trademarks: NeoRez ® 、Bayhydrol ® (commercially available from Covestro AG); Permax ® 、Sancure ® and PrintRite ® (commercially available from Lubrizol Deutschland GmbH, Hamburg), Syntegra ® (commercially available from The Dow Chemical Company), Joncryl ® (commercially available from BASF SE), Beetafin ® (commercially available from BIP (Oldbury) Ltd., UK), Daotan ® (commercially available from Allnex GmbH, Wiesbaden), Witcobond ® (commercially available from Lanxess AG), ESACOTE ® (commercially available from Lamberti SpA, Italy), Patelacol ® , Hydran ® and Vondic ® (Commercially purchased from Japan DIC Co., Ltd.).

[0022] A preferred commercially available nonionically stabilized polyurethane dispersion is NeoRez ® R-9340 (flexible non-ionically stabilized polyurethane dispersion, MFFT < 5°C; acid value = 0 mg KOH / g, dry resin solids content 40%, pH 6.5 to 7.5), Baybond ® PU404 (nonionic polyester polyurethane, at 23°C, spindle L3 / 30 rpm, M092-ISO 2555, viscosity <1500 mPa·s, pH 5.5 to 7.5 at 20°C). Other examples of nonionic stabilized polyurethane dispersions are Esacote ® NBD, Esacote ® PU 931, Esacote ® PU 3511, Esacote ® PU 5913, 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 include Witcobond ® W-213, Witcobond ® 214 (aliphatic polyurethane), Esacote ® PU 2001, Esacote ® PU C1, Esacote ® MD23, ​​PrintRite ® DP675, Sancure ® 20051、Patelacol ® IJ50 and Hydran ® CP 7020.

[0023] Poly(meth)acrylate particles

[0024] Suitable poly(meth)acrylates for use as polymer binders (a) in the aqueous coating compositions of the present invention include homopolymers and copolymers of acrylates and / or methacrylates, 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 form anionic poly(meth)acrylates. Therefore, poly(meth)acrylates suitable for use in the present invention are generally not derived from acidic monomers. In order to achieve a low MFFT (e.g. <35° C.) of the aqueous dispersion of poly(meth)acrylate particles, it is preferred to (co)polymerize monomers whose homopolymers have a low Tg, e.g. below 20° C., as reported in standard sources, e.g. J. Brandrup, EH 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 diethylene glycol acrylate, propyl acrylate and ethyl acrylate.

[0025] Nonionic stabilization of poly(meth)acrylate particles can be achieved by copolymerization of hydrophilic monomers. Cationic poly(meth)acrylates can be prepared by copolymerization of monomers containing amino groups, such as 2-dimethylaminoethyl acrylate (DMAEA) or 2-dimethylaminoethyl methacrylate (DMAEMA), which can be quaternized or protonated with an acid.

[0026] The poly(meth)acrylate particles are usually introduced into the aqueous coating composition of the present invention in the form of an aqueous dispersion. Examples of commercially available cationic poly(meth)acrylate dispersions are Synprint ® AC 4110 (commercially available from Zschimmer & Schwarz GmbH & Co KG, Germany) and Neocryl ® XK-30 (commercially available from Covestro). Examples of nonionic poly(meth)acrylate dispersions include PrintRite ® 595FF (commercially available from The Lubrizol Corporation) and Neocryl ® XK-37 (commercially available from Covestro AG).

[0027] Water-soluble polymer binder (e)

[0028] 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 of >0 to 50% by weight, preferably 2% to 25% by weight, of the dispersed polymer binder (a), based on solids. The presence of the water-soluble polymer binder (e) is advantageous for the stability, viscosity, printing performance and adhesion of the aqueous coating composition.

[0029] Any polymer binder having a solubility in water of more than 1% by weight at 20° C. can be used as water-soluble polymer binder (e). In fact, it should be compatible with the other ingredients of the aqueous coating composition. Suitable polymers for use as water-soluble binder (e) are nonionic or cationic polymers based on poly(vinyl alcohol), poly(vinyl alcohol) derivatives, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, polyvinyl amine, poly(2-ethyl-2-oxazoline), cationic or nonionic water-soluble poly(meth)acrylates and their copolymers, poly(acrylamide) and their copolymers, cellulose derivatives (e.g., methylcellulose and ethylcellulose); or any combination thereof. Preferably, the polymer binder comprises poly(vinyl alcohol), poly(vinyl alcohol) derivatives or any combination thereof.

[0030] The term "poly(vinyl alcohol)" is generally considered in the art to be fully or partially hydrolyzed poly(vinyl acetate). According to standard convention, the degree of hydrolysis of poly(vinyl alcohol) refers to the degree of hydrolysis of poly(vinyl acetate). The degree of hydrolysis is from 80 mol % to 99 mol %, preferably from 86 mol % to 99 mol %. The degree of hydrolysis (saponification) refers to the percentage of basic poly(vinyl acetate) molecules that are "saponified" into poly(vinyl alcohol). Examples of modified poly(vinyl alcohol)s are cationic poly(vinyl alcohol), silicon-modified poly(vinyl alcohol), keto-modified poly(vinyl alcohol) and vinyl alcohol / N-vinyl formamide copolymers.

[0031] Aluminum hydroxide oxide particles (b)

[0032] Aluminium hydroxide oxide particles (b) within the meaning of the present invention are small primary aggregates of aluminium hydroxide oxide crystals dispersed in the aqueous coating composition, i.e. the median particle size (D v50 ) refers to the median primary aggregate size (D v50 ).

[0033] Aluminum hydroxide oxide is also called aluminum hydroxide, aluminum hydroxide or hydrated aluminum oxide, and its molecular formula is AlO(OH)(= ). Preferred types of aluminum hydroxide oxide used in the present invention are boehmite and pseudoboehmite.

[0034] Boehmite is a mineral with an orthorhombic unit cell. , and ), classified as γ-AlO(OH). Its crystal structure consists of a double layer of oxygen octahedrons centered on the aluminum atom. The outfacing oxygen is bonded to the hydroxyl groups of the adjacent octahedral layer by hydrogen bonds. Due to the weak bonding, boehmite is prone to intercalation, that is, small molecules (usually water) are intercalated between these layers. This results in a larger spacing in the

[010] direction, resulting in perfect cleavage perpendicular to the general direction of the hydrogen bonds. Boehmite with increased spacing in the

[010] direction is called pseudoboehmite, and most amorphous boehmite is generally referred to as gel. Boehmite can be found in nature, or it can be precipitated and grown from aluminum salts and alumina solutions under hydrothermal conditions, or it can be precipitated from aluminum alkoxides by hydrolysis.

[0035] Advantageously, the boehmite crystals are not needle-shaped, preferably they are tabular, more preferably having an average aspect ratio of 3.0 to 10 and a tabular surface with a major axis-to-horizontal ratio of 0.60 to 1.0. The aspect ratio can be determined by the method disclosed in Japanese Patent No. JP5160154B2. The aspect ratio herein is expressed as the ratio of the diameter to the thickness of the particle. The term "diameter" used herein refers to the diameter of a circle (equivalent circular diameter) having the same projected area as the alumina hydrate particle observed with a microscope or electron microscope. The major axis-to-minor axis ratio of the tabular surface is defined as the ratio of the minimum diameter to the maximum diameter of the tabular surface observed with a microscope in the same manner as the aspect ratio.

[0036] The median particle size (D) of the boehmite crystals in the dry powder is determined by X-ray diffraction using an X-ray diffractometer supplied by Siemens or Philips. v50 ) may, for example, be in the range of 7 nm to 80 nm, preferably in the range of 8 nm to 50 nm, more preferably in the range of 10 nm to 20 nm.

[0037] Pseudo-boehmite is characterized by a relatively high water content (AlO(OH)·xH2O (0 < x < 1.0)). It is essentially fine-crystalline boehmite, which consists of the same or similar octahedral layers in the xz plane, but lacks three-dimensional order due to the limitation of the number of unit cells in the y direction. It consists of a large number of crystals, which contain single unit cells or single octahedral layers along the y direction. It contains more water, and the water is usually sandwiched between the octahedral layers, usually randomly arranged, but sometimes regularly arranged. The water content consists of adsorbed water and chemically bound water. Compared with boehmite, its water content is relatively high, which can be explained by its smaller crystal size. Although boehmite consists of relatively long AlOOH chains with terminal H2O groups, the chains in pseudo-boehmite are significantly shorter. Due to the presence of terminal water groups, this means a significant increase in the specific water content.

[0038] Small primary aggregates of boehmite or pseudo-boehmite crystals can be obtained by dispersing secondary larger aggregates with an average particle size ranging from 1 μm to 100 μm present in commercially available boehmite or pseudo-boehmite powders (such as powders derived from spray drying processes).

[0039] As determined by laser diffraction according to ISO 13320:2020-01 (e.g., on an LS 13320 device from Beckman Coulter), the dispersed boehmite or pseudo-boehmite particles (small primary aggregates of boehmite or pseudo-boehmite crystals) typically have a median particle size (D v50 ) in the range of 20 nm to 500 nm, usually 30 nm to 300 nm, preferably 50 nm to 200 nm, and more preferably 80 nm to 180 nm.

[0040] The primary aggregates of boehmite or pseudo-boehmite have a porous structure. As determined by nitrogen adsorption according to the methods of Barrett, Joyner, and Halenda (BJH) and Gurwitsch as described in DIN 66134:1998-02 herein, typically the boehmite or pseudo-boehmite particles have an average pore volume of 0.5 ml / g to 1.5 ml / g, preferably 0.8 ml / g to 1.3 ml / g, and as determined by gas adsorption according to ISO 9277:2010, have a BET surface area of 100 m 2 / g to 400 m 2 / g, preferably 120 m 2 / g 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.

[0041] Suitable commercially available boehmite powders for use in the ink receiving layer (b) include DISPERAL ® LEVEL AND DISPAL ® Level (e.g. DISPERAL ® HP8, HP10, HP14, HP14 / 7 and HP18, preferably HP14) and BOEHMITE B8014 LM35 available from Tianjin Boyuan, China.

[0042] The aqueous coating composition of the present invention comprises 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, most preferably 40 to 59 wt % of aluminum hydroxide oxide particles (b), based on the solid content of the coating composition.

[0043] Acidic dispersant (f)

[0044] In order to disperse the aluminum hydroxide oxide particles, the aqueous coating composition may contain an acidic dispersant (f), preferably pk a The value of the dispersant is less than 5.0, more preferably less than 4.9, even more preferably less than 4.0, still more preferably less than 3.0, and most preferably less than 2.0, such as HCl, HBr, HNO3, formic acid, acetic acid, propionic acid, lactic acid, citric acid and aminosulfonic acid and any combination thereof. The amount of the acidic dispersant can be greater than 0 to 10% by weight, preferably 0.2% to 5% by weight, and more preferably 0.3% to 1% by weight, based on the content of the aluminum hydroxide oxide particles, respectively. Alternatively, a suitable acid can be added during the production of the aluminum hydroxide oxide powder, which can produce a self-dispersible powder (e.g., DISPERAL HYDROXIDE from Sasol) ® HP14 / 7, which was surface modified with citric acid).

[0045] Polyvalent metal ions (c) and counter anions (d)

[0046] The aqueous coating composition generally comprises a 2+ Mg 2+ 、Zn 2+ 、Al 3+ , Fe 2+ , Fe 3+ 、Ti 4+ 、Zr 4+ and combinations thereof, preferably selected from Ca 2+ Mg 2+ 、Al 3+The aqueous coating composition of the present invention comprises 0.1 to 10 wt %, preferably 0.3 to 5 wt %, more preferably 0.5 to 2 wt % of dissolved multivalent metal cation (c), based on the solid content of the coating composition.

[0047] The polyvalent metal cation must be dissolved in the aqueous coating composition. Therefore, the counter anions (d) are selected so that they will not precipitate as solids with the metal cations (c) from the aqueous coating composition. Examples of counter anions are chloride, bromide, borate, nitrate, bisulfate, sulfate, bicarbonate, acetate, formate, propionate, butyrate, benzoate, gluconosulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate and combinations thereof, preferably chloride, acetate and combinations thereof.

[0048] A preferred combination of polyvalent metal cation (c) and counter anion (d) is a combination whose salt has a solubility in water of at least 10 g / l at 20°C. The most preferred combination of polyvalent metal cation (c) and counter anion (d) is: Ca 2+ / Chloride ion, Ca 2+ / Acetate, Mg 2+ / Chloride ion, Mg 2+ / Acetate, Al 3+ / Chloride ions and Al 3+ / acetate. The polyvalent metal cation (c) and the counter anion (d) are usually 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.

[0049] Other additives

[0050] Other additives to the aqueous coating composition of the invention are, for example, biocides, surfactants (wetting agents), defoamers, viscosity improvers, crosslinking agents and organic solvents.

[0051] Examples of crosslinking agents include compounds such as formaldehyde, glyoxal and glutaraldehyde, polyisocyanates, aziridines, carbodiimides, epoxy compounds, dihydrazides (i.e., adipic acid dihydrazides), and inorganic compounds such as boric acid and zirconium salts. Specifically, when poly(vinyl alcohol) is used as the water-soluble binder (e), glyoxal, boric acid and adipic acid dihydrazides are preferred crosslinking agents.

[0052] Preferably, the aqueous coating composition of the present invention does not contain an organic solvent. If present, based on the gross weight of the aqueous coating composition, the maximum content of the organic solvent is 10 weight %. Suitable organic solvents include alcohols (such as ethanol, isopropanol and n-propanol), acetone and methyl ethyl ketone and a mixture of these solvents.

[0053] Waterborne coating composition

[0054] Typically, the solid content of the aqueous coating composition of the present invention is 1% to 50% by weight, preferably 5% to 40% by weight, 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 in the range of 3.0 to 5.5, more preferably in the range of 3.5 to 5.0. It is adjusted to stabilize the particles in the aqueous medium.

[0055] The aqueous coating composition of the present invention is preferably prepared by mixing the monocomponents (a) to (d), the optional components (e) and other optional components that have been dissolved or dispersed. If these forms are not yet commercialized, these components are preferably pre-dispersed or dissolved, and then these aqueous compositions are mixed into the final coating composition. This can be done in any order. Preferably, the dispersion of the polymer binder (a) is slowly added to the mixture of the salt solution of the polyvalent metal cation (c) and the counter anion (d) and the dispersion of the aluminum hydroxide oxide particles (b).

[0056] All ingredients should be compatible in the final aqueous coating composition, meaning that no precipitation or gelling will occur over time. A minimum stability of 6 months is preferred. The final pH 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 dispersant (f).

[0057] Base

[0058] The aqueous coating composition of the present invention can be coated onto various non-absorbent substrates or low-absorbent substrates, and then the water and optional solvent are dried to obtain a dry primer coating (primer layer) before inkjet printing.

[0059] Non-absorbent substrates include plastic substrates, such as polymer films (including polymer film laminates), such as flexible packaging laminates and decorative films; paper or paperboard coated or laminated with a polymer layer, such as double-sided resin-coated photographic base paper; metal foils, such as aluminum foil; substrates coated or laminated with a metal layer; glass substrates; and ceramic substrates, such as tiles. Examples of low-absorption substrates are permeation-resistant paper; highly sized or coated or impregnated paper or paperboard, such as wallpaper, decorative paper, and linings for corrugated boards; 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 also includes various plastic parts.

[0060] Non-absorbent substrates or low-absorbent substrates do not absorb or only slowly absorb aqueous coatings or water into their interior. For low-absorbent paper and board, the Cobb 30 value is less than 10 g / m², preferably less than 5 g / m² according to DIN EN ISO 535:2014-06. Preferably, the paper substrate is a white or colored paper, which is sized in themass, surface sized, impregnated, pretreated or coated, i.e. barrier coated. In particular, the substrate paper can be a commercial paper dedicated to graphic applications, i.e. for photography, advertising, documents, packaging (i.e. food packaging, cardboard boxes), decoration (i.e. flooring, wall decoration, furniture) or other applications. For paper, the paper weight can be 30 g / m² to 300 g / m², and for board, the paper weight can be 250 g / m² to 500 g / m².

[0061] In particular, the aqueous coating composition of the present invention is suitable for coating on polymer films, including polymer film laminates comprising more than one polymer film. The polymer film including the polymer film laminate may comprise a homogenous top layer as an adhesion promoting layer, the homogenous top layer being a coating or a coextruded layer.

[0062] The polymer film can be any polymer material that can be processed into a film and can be an unoriented film, a uniaxially oriented film or a biaxially oriented film. Typically, the polymer film comprises a thermoplastic material. Useful thermoplastic materials include polyesters, polyolefins, polystyrenes, polyamides, polyacrylates, polycarbonates, polyvinyl chlorides, cellulose derivatives (e.g., cellulose triacetate), biodegradable polymers (e.g., starch and poly(amino acids)) and blends and copolymers of these polymers.

[0063] Suitable biaxially stretched polymer films are commercially available with high initial tear strength and low propagation tear resistance. The biaxially stretched thermoplastic material may be selected from polyesters, polyolefins, polystyrenes, polyamides, polycarbonates and polyvinyl chlorides, including homopolymers, copolymers and blends thereof. Preferably, the thermoplastic material is selected from the group consisting of polyesters, more preferably poly(ethylene terephthalate), poly(ethylene naphthalate) and polylactic acid (commonly known as "poly(lactic acid)" -PLA); polyolefins; more preferably polypropylene; polyamides such as PA6; polyvinyl chloride, and blends and copolymers thereof. The most preferred biaxially stretched polymer film is biaxially stretched polypropylene (BOPP) (e.g. sold under the trade name Rayoface ® BOPP films commercially available from Innovia), biaxially oriented poly(ethylene terephthalate) (BOPET) (e.g., under the trade name Hostaphan ® BOPET films commercially available from Mitsubishi and under the trade name Mylar ® and Melinex ® Commercially available from DuPont (DuPont) BOPET film), biaxially stretched polylactic acid (BOPLA) and biaxially stretched polyamide (BOPA) (e.g. BOPA6). The biaxially stretched polymer film can also be a coextruded polymer film. Coextruded biaxially stretched polymer film, wherein the first layer is a polymer as described above and the second layer is a polymer with better adhesion to the aqueous coating composition, i.e. propylene / ethylene copolymer is preferred.

[0064] Suitable uniaxially stretched polymer films include shrink sleeves. The thermoplastic polymer of the shrink sleeve can be selected from the group consisting of (to) polyvinyl chloride, (to) polystyrene, (to) polyolefin, (to) polyester and their mixtures, blends and copolymers, more preferably selected from the group consisting of polyvinyl chloride (PVC), glycol-modified polyethylene terephthalate (PET-G), polystyrene (PS), styrene-butadiene copolymers, polypropylene (PP), polyethylene (PE), polylactic acid (PLA) and cycloolefin copolymer / polyethylene (COC / PE) and their mixtures, blends and copolymers. The (to) polymer and the film (alternatively uniaxially stretched or biaxially stretched) made thereof are all commercially available.

[0065] The most preferred non-absorbent substrates coated with the aqueous coating compositions of the present invention are polymeric films, including polymeric film laminates comprising 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.

[0066] The polymer film can be transparent, translucent or opaque, for example white opaque or colored opaque. Suitable films can be foamed, cavitated or dyed in themass, for example dyed with white pigments. The surface of the polymer film can be treated, for example, by corona treatment, flame treatment or chemical treatment (for example with a thin polyacrylate coating). Surface treatment can produce various effects, such as improving the wettability to the aqueous coating composition, especially in the case of BOPP films, especially increasing adhesion. The thickness of the suitable polymer film is generally in the range of 8 μm to 400 μm.

[0067] Inkjet printable primer layer

[0068] The water-based coating composition of the present invention can be coated on substrate to form an inkjet printable primer layer by any conventional coating method known in the art. For example, a curtain coater, die coater, roller coater, air knife coater, blade coater, rod coater, reverse gravure coater, bar coater can be used to apply the water-based coating composition by flexographic printing or gravure printing. Preferably, the application is by reverse gravure coating, gravure printing or flexographic printing.

[0069] After application to the substrate, the aqueous coating composition is dried to remove water and optional solvent to obtain the final inkjet printable primer layer. Preferably, an active drying step is performed, such as convection drying (in hot air), contact drying, infrared drying, near infrared drying or any combination thereof, usually at a temperature of at least 50° C., to reduce the drying time.

[0070] Preferably, the aqueous coating composition is directly coated on the substrate, which means that the inkjet printing layer is in direct contact with the substrate. Further preferably, the inkjet printing primer layer formed by the aqueous coating composition is a single inkjet printing layer. The aqueous coating composition can be applied to the substrate in the form of a layer in a single application step, or can be applied in the form of more than one layer of partial layers, that is, more than one aqueous coating composition of the present invention with different compositions is applied to the substrate successively. Two or more partial layers form the inkjet printing primer layer together. Preferably, the inkjet printing primer layer can be applied to the substrate in the form of a layer in a single application step.

[0071] The aqueous coating composition of the present invention can be applied in a separate coating process independent of the inkjet printing process, or it can be applied inline in an inkjet printer, i.e., applied at printing speed in a coating unit arranged upstream of the printing station. It is advantageous to apply it in a roll-to-roll process. Preferably, the aqueous coating composition is applied online during the printing process, more preferably in a roll-to-roll printing press.

[0072] Typically, the aqueous coating composition is applied to a substrate to obtain an inkjet printable primer layer having a dry coating weight of 0.3 g / m 2 Up to 8.0g / m 2 , preferably 0.5g / m 2 Up to 6.0g / m 2 , more preferably 0.8 g / m 2 Up to 5.0g / m 2 , most preferably 1.3g / m 2 Up to 4.0g / m 2 The actual dry coating weight can be adjusted according to the intended use of the coated substrate, for example, according to the type of printer and ink used to print on the inkjet printable primer layer. Within the scope of the present invention, the ink dot gain and precipitation reactivity can be controlled by selecting the appropriate dry coating weight and / or concentration of the multivalent metal cation (b) and the overall composition.

[0073] Preferably, the inkjet printable primer layer is glossy when applied to a glossy substrate, ie, a gloss of about 50 GU to 85 GU can be achieved when applied to a glossy substrate (gloss of about 65 GU).

[0074] The aluminum hydroxide oxide particles (b) provide porosity to the primer layer after coating and drying. "Porous" means that the pores in the aluminum hydroxide oxide particles (primary aggregates) and / or in the coating material comprising the aluminum hydroxide oxide particles and the binder have a pore size (diameter) ranging from 10 nm to 1 μm, preferably from 20 nm to less than 0.5 μm, more preferably from 50 nm to less than 0.2 μm, as determined by scanning electron microscopy (SEM). Figure 1 The porosity of the inkjet printable primer layer can be clearly seen in FIG.

[0075] The surface of the inkjet printable primer layer is non-sticky and smooth. This means that there is no blocking or adhesion to other surfaces, in particular to the back side of a substrate wound up into a roll, at room temperature or elevated temperature (e.g. 60° C.), even under increased pressure.

[0076] Typically, the inkjet printable primer layer is transparent. As measured according to ASTM D1003 Method A, when the substrate is a transparent film with a haze value of no more than 5%, the haze value of the coated substrate according to the present invention is preferably no more than 7%, more preferably no more than 10%, and most preferably no more than 15%.

[0077] print

[0078] The inkjet printable primer layer of the coated substrate of the present invention can be printed by a water-based inkjet printing process. Usually, it is printed with a high-speed printing process, more preferably with a single-pass printing process. Advantageously, the coated substrate is printed with a digital inkjet printer that runs at a high printing speed (e.g., 30m / min or 60m / min to 300m / min) such as a printing speed of 5m / min to 300m / min, preferably comprising a single-pass printing system, i.e., a printing system comprising a fixed printing bar (printing bar) exceeding the web width, the printing bar comprising a print head. High-speed printing processes include roll-to-roll printing and sheet printing (sheet printing) such as in a sheet-fed digital inkjet printer.

[0079] Exemplary high-speed single-pass inkjet digital printers for aqueous pigment inks are commercially available from Hewlett Packard (PageWide Industrial Presses), Kodak (Prosper, Versamark), Canon (ImagePress), Fujifilm (Jetpress), Screen (Truepress), Miyakoshi (MJP30-AXF), KBA (RotaJet), Palis (Padaluma Printing), AstroNova / Trojan, Afinia, Arrow Systems, and Rigoli. High speed single pass inkjet printers are typically operated with piezoelectric print heads, such as those commercially available from Fujifilm Dimatix (e.g. SAMBA print heads), Kyocera, Toshiba, Ricoh and Xaar, continuous inkjet print heads, such as those commercially available from Kodak, or with print heads and print bars, respectively, commercially available from Memjet.

[0080] After printing, the aqueous ink must be completely dried because the primer layer of the present invention and the non-absorbent substrate or low-absorbent substrate cannot absorb a large amount of water. Therefore, an active drying step can be carried out, such as convection drying (in hot air), contact drying, infrared drying, near infrared drying or any combination thereof, usually at a temperature of at least 50°C.

[0081] In the case of a transparent coated substrate, printing can be performed by face printing or reverse printing. Face printing refers to printing a non-mirror image on a jet-printable primer layer. In addition, due to the high transparency of the jet-printable primer layer, reverse printing can be performed on the coated substrate. Reverse printing refers to printing a mirror image on a jet-printable primer layer. As measured according to ASTM D1003 method A, when the haze of the coated substrate is less than 15%, more preferably less than 10%, and most preferably less than 6%, it is considered that the coated substrate is transparent.

[0082] Typically, an aqueous (water-based) pigment-based ink is used to print on the inkjet-printable primer layer of the present invention. The pigment-based ink contains dispersed pigments, preferably anionically stabilized dispersed pigments. Pigments within the meaning of the present invention are color pigments. The pigments can be organic pigments or inorganic pigments.

[0083] In addition, water-based pigment ink can include polymer binder, preferably include anionic polymer or anion-stabilized dispersed polymer dissolved or dispersed.Polymer binder is used for fixing pigment after printing and strengthening pigment to the anchoring of printing surface and / or as surface modification of pigment, to realize stable dispersion.In order to interact with water-based coating composition of the present invention, preferably include the ink of anionic binder polymer or anion-stabilized binder polymer.Anion or anion-stabilized binder polymer can be dispersed anionic polyurethane, polyurethane dispersed with anionic surfactant or dispersed anionic (methyl) acrylic polymer or copolymer (such as anionic styrene-(methyl) acrylate copolymer).Usually, based on the solid content of ink, the content of binder polymer in pigment-based ink is 1 % by weight to 25 % by weight, preferably 3 % by weight to 15 % by weight.Or, water-based pigment ink can be prepared without polymer binder.

[0084] Other ink ingredients include dispersants (surfactants and polymers), humectants and / or cosolvents to delay premature drying and prevent clogging of inkjet nozzles, defoamers and defoamers, wetting agents to enhance contact with the substrate, pH modifiers (usually amine derivatives), and biocides and bacteriostats. In commercial aqueous pigment-based inks, the ink ingredients vary widely, including a wide variety of pigments and dispersants. Specifically, the type and content of different cosolvents and humectants or mixtures thereof may vary significantly. Examples of suitable cosolvents and humectants are: alkanols (e.g. methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol), linear amides (e.g. dimethylformamide or dimethylacetamide), ketones and ketoalcohols (e.g. acetone, methyl ether ketone, cyclohexanone and diacetone alcohol), glycols (e.g. ethylene glycol, propylene glycol, diethylene glycol, 1,2-hexanediol, 1,5-pentanediol, triethylene glycol, tetraethylene glycol); triols (e.g. glycerol, 1,2,6-hexanetriol), glycol ethers (e.g., 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy)ethoxyethanol, 2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol, ethylene glycol monoallyl ether, tetraethylene glycol dimethyl ether), ethers (e.g., tetrahydrofuran and dioxane), cyclic esters (e.g., caprolactone), sulfoxides (e.g., dimethyl sulfoxide) and sulfolane.

[0085] Typically, four ink CMYK (cyan, magenta, yellow and black) systems are used to print on the inkjet printable primer layer of the present invention. However, special colors, such as blue, green, orange, red, particularly white or silver, may also be used.

[0086] The aqueous coating composition of the present invention can form an inkjet printable primer layer, which can provide high printing quality when inkjet printing is performed using pigment inks. The inkjet printable primer layer receives ink drops, thereby generating an appropriate contact angle to ensure a clear (defined) and appropriate dot size. Stable ink pigments and stable optional polymer binders are immediately chemically destabilized by interacting with multivalent 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 can quickly fix the applied ink droplets on its surface and ensure the clarity of the ink dots, although the ink is still in a liquid state (not yet dried). A not too small dot size for high-speed printing is achieved in single-pass printing, that is, a striped printed image caused by too small dots is avoided. The ink-receiving rate can reach a maximum of 10 ml / m 2 s or 20 ml / m 2 s. Therefore, the aqueous coating composition of the present invention is ideal for high-speed inkjet printing because it provides instant fixation of ink pigments and optional ink binders to achieve suitable dot sizes. High print quality can be obtained, meaning high image resolution, high color gamut, high color saturation and high color brightness, without any printing artifacts (such as stripes, bleeding, blurring, coagulation and mottled). The inkjet printing quality achieved with the aqueous coating composition of the present invention and suitable ink generally exceeds conventional flexographic printing and gravure printing. The good adhesion of the primer layer of the present invention to substrates and the applied ink after drying is also provided. With the aqueous coating composition of the present invention, the perfect balance between the adhesion of printing pigments to primer layer, the adhesion of primer layer to non-absorbent substrates or low-absorbent substrates and the utilization rate of polyvalent metal cations on the primer layer surface is achieved, that is, polyvalent metal cations are immediately released to the printing interface to contact with the ink dots that have just landed on the primer surface, thereby achieving high print quality. A primer layer with a non-stick surface after printing and drying is also obtained. This enables roll-to-roll processing of printed coated substrates without material blocking. This is particularly important if no additional overprint varnish is applied in-line after printing and ink drying. Nevertheless, an overprint varnish can be applied over the printed primer layer to protect the printed surface and / or to modify the surface properties.

[0087] In addition, the inkjet printable primer layer of the present invention has scratch and friction resistance properties both before and after printing. It also has good water resistance, which can provide these properties for suitable printing inks.

[0088] In order to achieve the best printing effect, the aqueous coating composition of the present invention must be adapted to the specific printing ink. This means that the mixing ratio of the individual components, namely the polymer binder (a), aluminum hydroxide oxide (b), polyvalent metal cation (c) and optional water-soluble polymer binder (e), must be adapted to the specific ink. This also applies to the type of polymer binder (a), the type of polyvalent metal cation (c) and counter anion (d) and the dry coating weight of the primer layer formed by the aqueous coating composition.

[0089] Commercial Applications

[0090] The aqueous coating composition of the present invention can be used for different applications. As mentioned above, it can be applied to a wide variety of non-absorbent substrates or low-absorbent substrates in an inkjet printer off-line or in-line. Preferably, the aqueous coating composition can be used for packaging applications and decorative applications on films and film laminates with low-absorbent surfaces and impregnated or pre-coated papers, such as food packaging films, decorative films, coated wallpapers and impregnated decorative papers.

[0091] In a further converting step, the print coated substrate can be laminated with a polymer film or a polymer film laminate, paper, a metal foil or a laminate comprising a metal foil, or can be embossed.

[0092] The coating composition of the present invention is particularly suitable for preparing an inkjet printable primer layer for high-speed single-pass printing in decorative paper and decorative film applications. Decorative paper is a special paper with a high filler content and high opacity, which can be pre-impregnated with melamine / melamine formaldehyde or urea resin as a roll-to-roll printing substrate and then converted into a rigid material by application to a rigid substrate. For decorative applications, in most cases, it is necessary to protect the printed primer layer; it is usually varnished by a radiation-cured coating and then cross-linked by ultraviolet or electron beam curing. Subsequently, the unprinted side of the decorative paper or decorative film is bonded to a rigid substrate. As a rigid substrate, high-pressure laminate (HPL), particle board, plywood (veneer), medium-density fiberboard (MDF), chipboard (chipboard), particle board, and even metal can be used. In addition to applying a varnish, the printed primer layer can also be protected by laminating with a film (for example, by extrusion lamination of a polymer (for example, polyurethane) using an adhesive and / or hot pressing, depending on the final application).

[0093] If used for food packaging, the applied aqueous coating composition and aqueous pigment ink must be safe for food packaging, i.e., they must not contain substances that can penetrate the substrate layer (e.g., film or film laminate) into the packaged goods and cause food non-compliance. Preferably, printing is performed using aqueous inks with a low migration tendency, and more preferably, pigment-based inks containing humectants that meet food standards such as glycerol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, poly(ethylene glycol) and poly(propylene glycol) are used.

[0094] Example

[0095] Reagents

[0096] Pseudo-boehmite powder: Surface-modified (acidic) water-dispersible pseudo-boehmite, corresponding to AlO(OH)·0.15H2O, with a specific surface area of ​​140 m2 after drying at 110°C for 2 hours 2 / g, pore volume 0.82cm 3 / g, HNO3 acid content (30% dispersion at pH=4.0), dispersibility in water is>96%.

[0097] Boehmite powder: DISPERAL ® HP14, a high porosity acidic dispersible boehmite, has a powder median particle size of 35 µm, a dispersed particle size of 100 nm (10 wt% dispersed in 0.4 wt% HNO3), a crystallite size of 14 nm

[120] , and a dispersibility of 98% (10 wt% dispersed in 0.4 wt% HNO3), and is commercially available from Sasol.

[0098] 13% strength by weight hydrochloric acid.

[0099] Calcium chloride: a hydrate containing 77% by weight of calcium chloride.

[0100] Magnesium chloride: hydrate containing 47% by weight of magnesium chloride.

[0101] Levasil ® CC310 (formerly known as Bindzil CC310): an anionic colloidal silica dispersion modified with (3-glycidyloxypropyl)trimethoxysilane having a solid content of 28 wt%, commercially available from Nouryon Chemicals BV.

[0102] Baybond ® PU 404: solid content 50 wt%, pH 5.5 to 7.5, MFFT < 0°C, average particle size (D v50 ) is a 135 nm non-ionic polyester polyurethane dispersion commercially available from Covestro.

[0103] Neorez ® R-9340: solid content 40 wt%, pH 6.5 to 7.5, MFFT <5°C, average particle size (D v50 ) is a 140 nm non-ionic polyester polyurethane dispersion commercially available from Covestro.

[0104] Neocryl ® XK-30: solid content 42 wt%, pH 4.0, MFFT 30°C, average particle size (D v50 ) is a 150 nm cationic acrylic dispersion commercially available from Covestro.

[0105] Esacote ® PU 4045: solid content 35 wt%, pH 7.0 to 9.5, MFFT about 0°C, average particle size (D v50 ) is an anionic aliphatic polyurethane dispersion with a diameter of 110 nm, commercially available from Lamberti.

[0106] Esacote ® PU C1: solid content 30% by weight, pH 4 to 6, MFFT about 0°C, average particle size (D v50 ) is a 180 nm aliphatic polyurethane cationic dispersion based on polycarbonate diols, commercially available from Lamberti.

[0107] Kuraray Poval ® 30 / 92: high molecular weight poly(vinyl alcohol) with a saponification degree of 92%, commercially available from Kuraray.

[0108] Surfynol ® 420: an ethoxylated acetylene surfactant with dynamic wetting and molecular defoaming properties, commercially available from Evonik Operations GmbH, Germany.

[0109] Preparation of aluminum hydroxide oxide dispersion

[0110] Pseudo-boehmite dispersion

[0111] 18.4 kg of water-dispersible pseudo-boehmite powder (containing about 2 wt % of adsorbed water) was added to 58 kg of water and stirred for 3 hours to obtain a pseudo-boehmite particle dispersion having a solid content of 23.6 wt %. The pH of the dispersion was adjusted to 3.8 by adding hydrochloric acid. The average dispersed particle size (D) measured by laser diffraction was v50 ) is 128nm.

[0112] Boehmite dispersion

[0113] 18.6 kg of boehmite powder (containing about 4 wt % of 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 boehmite particle dispersion having a solid content of 23.6 wt %. The median particle size (D) measured by laser diffraction was v50 ) is 137nm.

[0114] Preparation of waterborne coating compositions

[0115] Coating composition A

[0116] 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. Pseudoboehmite dispersion (76.4 kg) was then added to the calcium chloride solution. 41 kg of Baybond ® PU 404 dispersion was slowly poured into the premix of pseudoboehmite and calcium chloride while stirring the mixture. 0.6 kg of Surfynol ® 420 surfactant. The pH of the aqueous coating composition was adjusted to 3.8 by adding hydrochloric acid, and the solid content was adjusted to 18 wt % by adding water.

[0117] It can be calculated that the solids content of coating composition A comprises 44% by weight of pseudo-boehmite particles, 50% by weight of polyurethane particles and 1.6% by weight of calcium ions.

[0118] Coating compositions B to H and comparative coating compositions I to M

[0119] The preparation methods of coating compositions B to H and comparative coating compositions I to M are similar to that of coating composition A, but the corresponding components shown in Table 1 are replaced or omitted. In Table 1, the solid portion of the added components is expressed in weight % based on the solid content of the aqueous coating composition.

[0120] In coating composition B, Kuraray Poval ® 30 / 92 poly(vinyl alcohol) partially replaced the polyurethane dispersion, Kuraray Poval ® 30 / 92 poly(vinyl alcohol). In comparative composition J, a 10 wt% poly(vinyl alcohol) solution was added as the sole polymer binder.

[0121] [Table 1]: Components of waterborne coating composition

[0122]

[0123] [Table 1]: Components of waterborne coating composition (continued)

[0124]

[0125] Example 1

[0126] The coating composition A was roll-to-roll coated onto a 100 µm thick white BOPET film (Melinex ® Model 339, which comprises a thin polyacrylate coating on both surfaces, has a gloss of 65 GU, commercially available from Dupont Teijin Film, with a dry coating weight of 2 g / m² and is dried at a maximum oven temperature of 80° C. The coating is non-sticky and the coated roll can be rewound without any blocking.

[0127] The coated film was then printed using a 4-color (CMYK) Epson inkjet printer (Ecotank ET-2720 model) that was not equipped with Epson inks but with a commercially available aqueous pigment ink containing color pigments, anionic polymer binder and about 40% by weight of 1,2-propylene glycol (Ink 1) or with an aqueous pigment DuraFlex from Memjet. ® Ink (Ink 2) containing no binder and containing triethylene glycol, 2-(2-butoxyethoxy)ethanol and glycerol at a total concentration of about 15 wt%. After printing, the ink fluid stayed on the surface of the coating 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.

[0128] Example 2 to Example 11

[0129] In Examples 2 to 11, BOPET films were coated and printed as described in Example 1, but using different dry coating weights (Examples 2 and 3), coating compositions B to H (Examples 4 to 11), as shown in Table 2.

[0130] Comparative Examples 12 to 16

[0131] In Comparative Examples 12 to 16, BOPET films were coated and printed as described in Example 1, but using comparative coating compositions I, J, L and M to achieve the corresponding dry coating weights as shown in Table 2.

[0132] Applied test methods

[0133] The coated or coated and printed samples were examined according to the following test methods and the results are reported in Table 2.

[0134] The dry coating weight of the primer layer was determined by the difference in weight of the coated and uncoated substrates.

[0135] The gloss of the dried primer layer on the substrate is determined in GU at an angle of 60° according to ISO 2813:2014.

[0136] The coated side of the substrate was stacked onto the back side of another substrate and heated in a climate chamber at 60°C and 80% relative humidity at 70 g / cm 2 The stickiness of the dried primer layer, i.e. the blocking tendency, was evaluated by placing it under pressure of 200° C. for 24 hours. The stack of coated substrates was then transferred to a standard climate (23° C., 50% relative humidity). After cooling, the stack was separated manually. The primer layer was visually inspected and rated as follows:

[0137] 1 The primer layer adheres to the back of another substrate, and forcible separation will cause damage to the entire primer layer

[0138] 2 Force must be applied to separate the layers, there may be separation noise, the primer surface is marked or damaged and / or there is slight transfer of primer paint to the back of another substrate

[0139] 3 Obstruction / separation force is obvious, there may be separation noise, and there are slight marks on the primer surface

[0140] 4 Slight local obstruction, minimal marks on the primer surface

[0141] 5 No blocking, no adhesion, no marks on the primer surface.

[0142] The friction, scratch and adhesion tests were carried out according to Finat Test Method No. 21 (FTM21) in a standard climate (23°C and 50% relative humidity).

[0143] The rub test was performed by sliding a fingertip back and forth 5 times under pressure over the surface of the unprinted primer layer and the printed primer layer (uniform red printed area). The primer layers were visually inspected and rated as follows:

[0144] Unprinted Primer Layer:

[0145] 1 The paint is completely rubbed off

[0146] 2 Paint only partially removed

[0147] 3. The marks and markings are clearly visible and have not been erased.

[0148] 4 Marks and traces are slightly visible and have not been erased

[0149] 5 No visible surface changes

[0150] Printed primer layer:

[0151] 1 Paint and ink are at least partially removed

[0152] 2 Printing ink can be completely wiped off / smudged

[0153] 3 Printing ink can be partially wiped off / rubbed off

[0154] 4 Slight smudging of printing ink

[0155] 5 No visible marks or markings

[0156] The scratch test is carried out on a hard, smooth, stable table by manually sliding the edge of a 1 Euro coin back and forth 5 times at a 60° angle to the table on the surface of the unprinted primer layer and the printed primer layer (uniform blue printed area) under light pressure. The surface of the coin faces the direction of movement. The primer layer is visually inspected and rated as follows:

[0157] Unprinted Primer Layer:

[0158] 1 The primer layer comes off in the entire scratch area

[0159] 2 Severe / obvious marks with primer removed

[0160] 3 Surface scratches and slight primer peeling can be detected

[0161] 4 Obvious scratches on the surface

[0162] 5 Only light scratches on the surface - not deep.

[0163] Printed primer layer:

[0164] 1 The ink and primer layers have fallen off in the entire scratch area

[0165] 2 Severe / obvious marks with ink and primer layers removed

[0166] 3. There are serious scratches and white marks on the printed surface

[0167] 4 Visible scratches / slight white marks on the printed surface

[0168] 5 No color defects / no visible white marks, only indentations are detectable

[0169] Adhesion of the printed area was evaluated using Tesa Film 4101 tape from Tesa SE, Germany. The results were rated as follows:

[0170] 1. Primer layer and ink fall off, adhesion problem between primer layer and substrate

[0171] 2. The ink falls off partially with the primer layer, the primer layer cracks, and the primer layer has adhesion problems

[0172] 3. Severe ink shedding and adhesion problems between ink and primer layer

[0173] 4 Ink transfers only slightly to the tape

[0174] 5 No visible ink transfer to the tape.

[0175] The dot diameter of individual cyan dots in the test prints was measured using a laser scanning microscope, model VK-9710, from Keyence Corporation, using a combined image of laser light and visible spectrum light.

[0176] Visual assessment of print performance: Criteria included overall color impression / color gamut, intercolor bleed + color bleed (colored areas bleed into each other + colored areas bleed into unprinted areas), print clarity (small printed characters, fine lines), and coalescence (In inkjet printing, coalescence or puddling is an image defect that occurs when adjacent wet ink droplets merge on the receiving surface, combining into larger ink droplets before the ink pigments settle. This can cause the image to appear mottled or "bubbled," resulting in uneven solid fill areas.)

[0177] Overall color impression / color gamut:

[0178] 1 Pale, dull, matte, stained and / or dirty colors, cracks on the printed surface, large color deviations in single, secondary or tertiary colors

[0179] 2 Pale, dull, matte and / or slightly stained, cracks on the printed surface visible upon magnification, slight color deviation in single, secondary or tertiary colors

[0180] 3 Obvious light, dull, matte, easily stained

[0181] 4 Bright color, but slightly dull, no staining

[0182] 5. Highly vivid colors and high gloss

[0183] Printing clarity:

[0184] 1 Small printed characters are unclear and difficult to read, and fine lines are blurred or blended together

[0185] 2 Small printed characters are severely blurred but legible

[0186] 3 All small characters and fine lines are clear and legible, but slightly blurred

[0187] 4 Good clarity,

[0188] 5. Excellent clarity

[0189] Coalescence:

[0190] 1 The printed area of ​​solid fill is not uniform and there is accumulation

[0191] 2 Only the solid fill print area of ​​the secondary and tertiary colors is uneven and has accumulation

[0192] 3 Solid fill areas are uneven and show accumulation only in high ink volume / tertiary color print areas

[0193] 4 Only minimal agglomeration

[0194] 5 No agglomeration

[0195] Color bleed + color bleed:

[0196] 1 Severe bleeding into each other and / or into unprinted areas

[0197] 2 Colors blend into each other and / or bleed into unprinted areas in a clearly identifiable manner

[0198] 3 Colors from very heavily inked areas blend into each other and / or bleed into unprinted areas in a clearly discernible manner

[0199] 4 Areas with high ink volume have only slight bleeding, which can only be discerned after magnification

[0200] 5 No bleeding.

[0201] For most applications, a judgment score of 3 is sufficient.

[0202] [Table 2]: Characteristics of unprinted primer layer and printed primer layer

[0203]

[0204] [Table 2]: Characteristics of unprinted primer layer and printed primer layer (continued)

[0205]

[0206] The anti-blocking performance, scratch and friction resistance, and adhesion were all acceptable to very good for all the examples of the present invention. The dot size was appropriate. The examples of the present invention also show that Ink 1 has very good printing performance and Ink 2 has still acceptable very good printing performance. The difference in printing performance is mainly due to the significant difference in the type and content of the co-solvents of Ink 1 and Ink 2. Although the tested aqueous coating composition of the present invention is considered to be the best for Ink 1, satisfactory printing results can also be achieved with Ink 2.

[0207] Comparative Example 12 (without aluminum hydroxide oxide particles) shows high adhesion and low rub resistance. The printing performance of both Ink 1 and Ink 2 is poor. Comparative Example 13 (only water-soluble polymer binder) shows that the unprinted primer layer has a lower scratch resistance and the printed area has a lower adhesion. In terms of the overall color impression / color gamut, the printing performance with Ink 2 is poor. In Comparative Example 14 (without calcium chloride), ink fixation could not be achieved. Comparative Example 15 corresponds to Example 10, with the only difference that silica particles are used instead of pseudo-boehmite particles. Comparative Example 15 shows considerable adhesion, which will lead to undesirable blocking in the roll-to-roll process. In terms of the overall color impression / color gamut, the printing performance with Ink 1 is significantly worse than that of Example 10. Both Example 10 and Comparative Example 15 with Ink 2 have problems with inter-color bleeding and color bleeding, which is due to the low coating weight of only 1.2 g / m 2 In Example 11 / Comparative Example 16, the coating weight was increased to 2.6 g / m 2 , the bleeding problem disappears. However, in Comparative Example 16, the overall color impression / color gamut using Ink 1 is still unacceptable.

[0208] Aspects of the invention:

[0209] 1. A water-based coating composition comprising

[0210] (a) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, most preferably 40 to 59 wt % of a dispersed polymer binder,

[0211] (b) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, most preferably 40 to 59 wt % of aluminum hydroxide oxide particles,

[0212] (c) 0.1 to 10 wt %, preferably 0.3 to 5 wt %, more preferably 0.5 to 2 wt % of dissolved multivalent metal cations, and

[0213] (d) inorganic counter anions and / or organic counter anions of the metal cations,

[0214] The weight percentages are based on the solid content of the aqueous coating composition.

[0215] 2. The aqueous coating composition according to aspect 1, wherein the median particle size (D v50 ) is 20 nm to 500 nm, preferably 30 nm to 300 nm, more preferably 50 nm to 200 nm, and most preferably 80 nm to 180 nm.

[0216] 3. The aqueous coating composition according to aspect 1 or aspect 2, wherein the dispersed polymer binder (a) comprises nonionically stabilized polymer particles or cationic polymer particles.

[0217] 4. The aqueous coating composition according to any one of aspects 1 to 3, wherein the dispersed polymer binder (a) comprises polyurethane particles, poly(meth)acrylate particles, or a combination thereof.

[0218] 5. An aqueous coating composition according to aspect 3 or aspect 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.

[0219] 6. The aqueous coating composition according to any one of aspects 3 to 5, wherein the median particle size (D v50 ) is in the range of 10 nm to 500 nm, preferably in the range of 20 nm to 300 nm, more preferably in the range of 50 nm to 250 nm, and most preferably in the range of 75 nm to 230 nm.

[0220] 7. The aqueous coating composition according to any one of aspects 1 to 6, wherein the aluminum hydroxide oxide particles (b) are selected from boehmite particles, pseudo-boehmite particles, and combinations thereof.

[0221] 8. The aqueous coating composition according to any one of aspects 1 to 7, wherein the polyvalent metal ion (c) is selected from Ca 2+ Mg 2+ 、Zn 2+ 、Al 3+ , Fe 2+ , Fe3+ 、Ti 4+ 、Zr 4+ and combinations thereof, preferably selected from Ca 2+ Mg 2+ 、Al 3+ and their combinations.

[0222] 9. An aqueous coating composition according to any one of Aspects 1 to 8, wherein the counter anion (d) is selected from chloride, bromide, borate, nitrate, bisulfate, sulfate, bicarbonate, acetate, formate, propionate, sulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate and combinations thereof, preferably selected from chloride, acetate and combinations thereof.

[0223] 10. The aqueous coating composition according to any one of aspects 1 to 9, wherein the solid content thereof is 1% to 50% by weight, preferably 5% to 40% by weight, and more preferably 10% to 30% by weight.

[0224] 11. The aqueous coating composition according to any one of Aspects 1 to 10, wherein the pH value thereof is 2.8 to 6.0, preferably 3.0 to 5.5, and more preferably 3.5 to 5.0.

[0225] 12. The aqueous coating composition according to any one of aspects 1 to 11, further comprising a water-soluble polymer binder (e), based on solids, replacing >0 to 50 wt%, preferably 2 to 25 wt%, of the dispersed polymer binder (a).

[0226] 13. The aqueous coating composition according to aspect 12, wherein the water-soluble polymer binder (e) is poly(vinyl alcohol), which preferably has a degree of hydrolysis of 78 mol % to 99 mol %.

[0227] 14. The aqueous coating composition according to any one of Aspects 1 to 13 further comprises an acidic dispersant (f), which is preferably an organic acid and / or an inorganic acid having a pka value 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, and its content is >0 to 10 wt %, preferably 0.2 wt % to 5 wt %, and more preferably 0.3 wt % to 1 wt %, based on the content of the aluminum hydroxide oxide particles (a).

[0228] 15. The aqueous coating composition according to aspect 14, wherein the acidic dispersant is selected from HCl, HBr, HNO3, formic acid, acetic acid, propionic acid, lactic acid, citric acid, aminosulfonic acid and any combination thereof.

[0229] 16. A substrate at least partially coated with the aqueous coating composition according to any one of aspects 1 to 15, the aqueous coating composition forming an inkjet printable primer layer, the dry coating weight of which is preferably 0.3 g / m 2 Up to 8.0g / m 2 , more preferably 0.5 g / m 2 Up to 6.0g / m 2 , more preferably 0.8g / m 2 Up to 5.0g / m 2 , most preferably 1.3g / m 2 Up to 4.0g / m 2 .

[0230] 17. The coated substrate according to aspect 16, wherein the substrate is a non-absorbent substrate or a low-absorbent substrate.

[0231] 18. A coated substrate according to aspect 17, wherein the substrate is a non-absorbent substrate, preferably selected from polymer films, which polymer films include polymer film laminates; paper or paperboard coated or laminated with a polymer layer, such as double-sided resin-coated photographic base paper; metal foil; substrates coated or laminated with metal layers; glass substrates; and ceramic substrates, such as tiles.

[0232] 19. A coated substrate according to aspect 18, wherein the substrate is a polymer film including a polymer film laminate and comprises a homogenous top layer as the adhesion promoting layer, the homogenous top layer being a coating or a coextruded layer.

[0233] 20. A coated substrate according to aspect 18 or aspect 19, wherein the polymer film comprising the polymer film laminate comprises a polyolefin, such as polypropylene, such as cast polypropylene (cPP) and biaxially oriented polypropylene (BOPP), and polyethylene; polystyrene; polyesters such as poly(ethylene terephthalate) (PET, APET), such as biaxially oriented poly(ethylene terephthalate) (BOPET); or polyamide.

[0234] 21. A coated substrate according to aspect 17, wherein the substrate is a low-absorption substrate, preferably selected from anti-penetration paper; highly sized or coated or impregnated paper or paperboard, such as wallpaper, decorative paper and lining for corrugated board; coated canvas; and coated woven or non-woven fabrics, more preferably selected from anti-penetration paper; highly sized or coated or impregnated paper or paperboard, such as wallpaper, decorative paper and lining for corrugated board.

[0235] 22. A coated substrate according to aspect 21, wherein the substrate is a low-absorbency paper or paperboard having a relative humidity of less than 10 g / m2 according to DIN EN ISO 535:2014-06. 2 , more preferably less than 5g / m 2Cobb 30 value.

[0236] 23. The coated substrate according to any one of aspects 16 to 22, wherein the inkjet-printable primer layer formed from the aqueous coating composition is a single inkjet-printed layer.

[0237] 24. A coated substrate according to any one of aspects 16 to 23, wherein the inkjet-printable primer layer formed from the aqueous coating composition is in direct contact with the substrate.

[0238] 25. A method for coating a substrate, comprising applying the aqueous coating composition according to any one of aspects 1 to 15 to a substrate to obtain an inkjet printable primer layer, wherein the dry coating weight of the primer layer is preferably 0.3 g / m 2 Up to 8.0g / m 2 , more preferably 0.5 g / m 2 Up to 6.0g / m 2 , more preferably 0.8g / m 2 Up to 5.0g / m 2 , most preferably 1.3g / m 2 Up to 4.0g / m 2 .

[0239] 26. The method of aspect 25, wherein the aqueous coating composition is applied directly to the substrate.

[0240] 27. The method according to aspect 24 or aspect 25, wherein the inkjet printable primer layer formed from the aqueous coating composition is applied as a single inkjet print layer.

[0241] 28. The method according to any one of aspects 25 to 27, further comprising an active drying step, such as convection drying, contact drying, infrared drying, near infrared drying or any combination thereof.

[0242] 29. The method according to any one of aspects 25 to 28, wherein the substrate is as defined in any one of aspects 17 to 22.

[0243] 30. A method for preparing a coated substrate for inkjet printing, comprising the steps of:

[0244] (i) preparing a coated substrate by the method according to any one of aspects 25 to 29, and

[0245] (ii) printing an inkjet printable primer layer of the coated substrate obtained in step (i) by a water-based inkjet printing process.

[0246] 31. A method according to aspect 30, wherein the inkjet printing process is a high-speed printing process preferably with a printing speed of 5 m / min to 300 m / min, for example from 30 m / min or 60 m / min to 300 m / min, more preferably a single-pass printing process.

[0247] 32. The method according to aspect 30 or aspect 31 further comprises (iii) an active drying step after the printing step (ii), such as convection drying, contact drying, infrared drying, near infrared drying or any combination thereof.

[0248] 33. The method according to any one of aspects 30 to 32, further comprising (iv) the step of applying an overprint varnish after the printing step (ii) or the optional active drying step (iii).

[0249] 34. The method according to any one of aspects 30 to 33, wherein the aqueous ink used in the water-based inkjet printing process is an aqueous pigment-based ink.

[0250] 35. The method of aspect 34, wherein the aqueous pigment-based ink comprises anionically stabilized dispersed pigments.

[0251] 36. The method according to aspect 34 or aspect 35, wherein the aqueous pigment ink comprises a polymer binder, preferably a dissolved or dispersed anionic polymer or an anionically stabilized dispersion polymer.

[0252] 37. A method according to aspect 36, wherein the polymer 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.

[0253] 38. Use of the aqueous coating composition according to any one of aspects 1 to 15 for coating a non-absorbent substrate or a low-absorbent substrate to obtain an inkjet-printable primer layer, wherein the dry coating weight of the inkjet-printable primer layer is preferably 0.3 g / m 2 Up to 8.0g / m 2 , more preferably 0.5 g / m 2 Up to 6.0g / m 2 , more preferably 0.8g / m 2 Up to 5.0g / m 2 , most preferably 1.3g / m 2 Up to 4.0g / m 2 .

[0254] 39. The use according to aspect 38, wherein the inkjet printable primer layer is a single inkjet printed layer.

Claims

1. A water-based coating composition comprising (a) 20 to 79 wt %, preferably 30 to 69 wt %, more preferably 35 to 64 wt %, 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 %, most preferably 40 to 59 wt % of aluminum hydroxide oxide particles, (c) 0.1 to 10 wt %, preferably 0.3 to 5 wt %, more preferably 0.5 to 2 wt % of dissolved multivalent metal cations, and (d) inorganic counter anions and / or organic counter anions of the metal cations, The weight percentages are based on the solid content of the aqueous coating composition.

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

3. The aqueous coating composition according to claim 1 or claim 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 combinations thereof, preferably nonionically stabilized polyurethane particles, cationic polyurethane particles or combinations thereof.

4. The aqueous coating composition according to any one of claims 1 to 3, wherein the polyvalent metal ion (c) is selected from Ca 2+ Mg 2+ 、Zn 2+ 、Al 3+ , Fe 2+ , Fe 3+ 、Ti 4+ 、Zr 4+ and combinations thereof, preferably selected from Ca 2+ Mg 2+ 、Al 3+ and combinations thereof, and / or the counter anion (d) is selected from chloride, bromide, borate, nitrate, bisulfate, sulfate, bicarbonate, acetate, formate, propionate, sulfamate, succinate, citrate, lactate, glycerate, p-toluenesulfonate and combinations thereof, preferably selected from chloride, acetate and combinations thereof.

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

6. The aqueous coating composition according to any one of claims 1 to claim 5, further comprising an acidic dispersant (f), wherein the acidic dispersant (f) is preferably pk a An organic acid and / or an inorganic acid having a value 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, for example, selected from HCl, HBr, HNO3, formic acid, acetic acid, propionic acid, lactic acid, citric acid, aminosulfonic acid and any combination thereof, and the content of the acidic dispersant (f) is >0 to 10 wt %, preferably 0.2 wt % to 5 wt %, and more preferably 0.3 wt % to 1 wt %, based on the content of the aluminum hydroxide oxide particles (a).

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

8. The coated substrate according to claim 7, wherein the substrate is a non-absorbent substrate or a low-absorbent substrate selected from polymer films, the polymer films comprising polymer film laminates, preferably comprising polyolefins, such as polypropylene, such as cast polypropylene (cPP) and biaxially oriented polypropylene (BOPP), and polyethylene, polystyrene, polyesters, such as poly(ethylene terephthalate) (PET, APET), such as biaxially oriented poly(ethylene terephthalate) (BOPET), or polyamides; paper or paperboard coated or laminated with a polymer layer, such as double-sided resin-coated photographic base paper; metal foil; substrates coated or laminated with a metal layer; glass substrates; ceramic substrates, such as tiles; permeation-resistant paper; highly sized or coated or impregnated paper or paperboard, such as wallpaper, decorative paper and lining for corrugated board; coated canvas; and coated woven or non-woven fabrics.

9. A coated substrate according to claim 7 or claim 8, wherein the inkjet printable primer layer formed from the aqueous coating composition is a single inkjet printed layer and / or is in direct contact with the substrate.

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

11. The method according to claim 10, further comprising an active drying step, such as convection drying, contact drying, infrared drying, near infrared drying or any combination thereof.

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

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

14. The method according to claim 13, wherein the aqueous ink used in the water-based inkjet printing process is an aqueous pigment-based ink, preferably comprising anionically stabilized dispersed pigments.

15. A method according to claim 13 or claim 14, wherein the aqueous pigment ink comprises a polymer binder, preferably a dissolved or dispersed anionic polymer or an anionic stable dispersed 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. Use of the aqueous coating composition according to any one of claims 1 to 6 for coating a non-absorbent substrate or a low-absorbent substrate to obtain an inkjet printable primer layer, the dry coating weight of the inkjet printable primer layer is preferably 0.3 g / m 2 Up to 8.0g / m 2 , more preferably 0.5 g / m 2 Up to 6.0g / m 2 , more preferably 0.8g / m 2 Up to 5.0g / m 2 , most preferably 1.3g / m 2 Up to 4.0g / m 2 .

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

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