Pre-treatment solution for inkjet printing

Abstract

Aqueous pretreatment solution and ink set for inkjet recording. The aqueous pretreatment solution comprises a polyvalent metal salt and a carboxylic acid-containing polymer or its salt or a carboxylic acid anhydride-containing polymer, wherein the polymer has an acid value of 950 mg KOH / g polymer or less. A recording method including the above pretreatment solution is included.

Description

Technical Field

[0001] The present invention relates to a pretreatment liquid suitable for inkjet recording and an ink set, and more specifically, to inkjet printing on liners for cardboard packaging, folding boards, and cardboard paper.

Background Art

[0002] Inkjet printing technology is a growing field for printing liners for cardboard packaging and cardboard paper. In the printing of liners for cardboard paper, usually, flexographic printing or offset printing is performed to apply a precoat or primer.

[0003] Today, digital printing of liners for cardboard packaging and cardboard paper has become a growing field. A primer or pretreatment liquid improves the image quality of the printed image. The possibility of applying the pretreatment liquid only on the parts where the image will be present makes it possible to reduce the total consumption of the pretreatment liquid in the printing operation.

[0004] In obtaining high-quality images, the pretreatment liquid can receive ink and hold or fix the colorants in the ink more highly than the substrate not treated with the pretreatment liquid. Specifically, the pretreatment liquid can hold or fix the colorants on or near the surface of the substrate, and as a result, the optical density and color gamut of the printed image can be improved compared to a porous substrate not treated with the pretreatment liquid.

[0005] Patent Document 1 and Patent Document 2 disclose a pretreatment liquid containing an organic acid and a water-soluble polymer and to be applied as a coating.

[0006] Patent Document 3 describes a sprayable pretreatment solution for corrugated cardboard liners or corrugated cardboard base paper packaging as packaging materials. The pretreatment solution composition contains a polyvalent metal salt, wax, dispersant, latex, and water. The latex contains monomers (such as styrene, 1,3-butadiene, acrylonitrile, or a combination thereof).

[0007] Patent Document 4 describes a treatment composition for packaging liners comprising a fixative, a wax, and latex. The latex is stabilized by anionic groups (e.g., those originating from carboxylic acid groups). The image quality obtained by aqueous inks ejected onto the treatment composition still suffers from mottling and poor ink spreading of the aqueous inks, resulting in uneven color density in solid areas of the printed image.

[0008] Patent Document 5 discloses a sprayable pretreatment composition for corrugated cardboard printing, comprising a water-soluble polyvalent metal salt, wax, a nonionic dispersant, and resin particles.

[0009] In the pretreatment solutions disclosed in both disclosures, wax improves the durability of the ink between laminations and has a positive effect on the quality of the printed image. The wax consists of particles made of hydrophobic materials (such as polyethylene, petroleum derivatives, paraffin, carnauba, and polypropylene). These wax particles tend to clog filters in the liquid supply unit and filters in through-flow inkjet heads. In such heads, the ink circulates continuously through several filters. Due to this clogging, a recirculation problem may occur after continuous operation for a certain period of time (<1000 minutes) using this type of pretreatment solution. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent Application No. 2021 / 0187971 [Patent Document 2] European Patent No. 2535379 [Patent Document 3] International Publication No. 2018 / 017089 [Patent Document 4] International Publication No. 2019 / 013785 [Patent Document 5] International Publication No. 2023 / 001650 [Overview of the Initiative]

[0011] The object of the present invention is to provide a solution to the above-mentioned problems. This object is achieved by providing the pretreatment solution described in claim 1.

[0012] Another embodiment of the present invention is to provide an ink set containing the aqueous inkjet ink described in claim 7 and the pretreatment solution described in claim 1.

[0013] Another embodiment of the present invention is to provide a printing method using the pretreatment solution described in claim 11, as described in claim 11.

[0014] Other features, elements, steps, characteristics, and advantages of the present invention will become more apparent from the detailed description below of preferred embodiments of the invention. Specific embodiments of the invention are also described in the dependent claims. [Brief explanation of the drawing]

[0015] [Figure 1] The pattern used for inkjet printing during the evaluation of image quality obtained using a pretreatment solution. This pattern contains solid areas and negative text of varying sizes ranging from 1pt to 16pt. [Modes for carrying out the invention]

[0016] Description of the Embodiment A. Aqueous pretreatment solution A.1. Carboxylic acid-containing polymers The pretreatment solution for inkjet printing according to the present invention comprises a carboxylic acid-containing polymer or a salt thereof, or a carboxylic acid anhydride-containing polymer. The carboxylic acid anhydride is thought to be at least partially hydrolyzed to a carboxylic acid or a salt thereof when dissolved in the aqueous vehicle of the pretreatment solution.

[0017] The effect of using carboxylic acid-containing polymers or their salts or carboxylic acid anhydride-containing polymers in the pretreatment solution on image quality may be related to the interaction between these polymers and fixatives, which are polyvalent metal ions or cationic polymers present in the pretreatment solution. The function of these fixatives is to interact with the dispersed colorants (such as dyes or pigments) derived from the ink, which have an electrical load, to fix the colorants and prevent image bleeding (see §A.2). Although not bound by theory, it is thought that the activity of the fixative can be well controlled in the presence of carboxylic acid-functionalized polymers, and therefore, optimal conditions for image sharpness and ink spread can be obtained.

[0018] The carboxylic acid-containing polymer or its salt or carboxylic acid anhydride-containing polymer in the pretreatment solution is not limited to a specific polymer, but it should have an acid value of 950 mg KOH / g polymer or less, more preferably 450 mg KOH / g polymer or more and 950 mg KOH / g polymer or less, and most preferably 346 mg KOH / g polymer or more and 950 mg KOH / g polymer or less. It is assumed that polymers containing carboxylic acids, their salts, or carboxylic acid anhydrides exist in their acidic form. If the acid value exceeds this range, i.e., for maleic acid and fumaric acid-based homopolymers, the degree of polymerization will be too low, resulting in reduced interaction with the polyvalent salt used and poor ink spreading.

[0019] Although a lower limit value is not defined in the initially mentioned acid value range, in order to dissolve the polymer in the pretreatment liquid, the carboxylic acid-containing polymer or its salt or the carboxylic anhydride-containing polymer should have some acidic groups, and thus will have a small acid value. If the acid value is below this value, the solubility of the polymer in the pretreatment liquid may be too low to obtain sufficient image quality.

[0020] The acidity index is defined as mg KOH / polymer g corresponding to the amount of carboxylic acid groups or carboxylate groups. The acid value can be determined either through titration or calculation. An example of the titration method is described in ASTM D3644-06.

[0021] When the monomer composition of the carboxylic acid-containing polymer or its salt or the carboxylic anhydride-containing polymer is known, the acid value can be calculated. The molar composition of the carboxylic acid or its salt or the carboxylic anhydride can be determined through analytical methods such as NMR. In the calculation of the acid value, polymer end groups are ignored. The acid value of the polymer can be calculated from the wt.% of COOH assuming that the carboxylic acid or its salt or the carboxylic anhydride contributes to the acid value, and then converted to mg KOH / polymer g. The wt.% of COOH can be calculated by (45 / molar mass of 1 repeating unit)×100%. By calculating the acid value from the wt.% of COOH by wt.% of COOH / 15×56.11×10, the acid value in mg KOH / polymer g can be obtained. For polyacrylic acid, wt.% of COOH = 15 / 72×100% = 20.83%. As a result, the acid value of polyacrylic acid = 20.83 / 15×56.11×10 = 779 mg KOH / polymer g.

[0022] Preferred carboxylic acid-containing polymers are homopolymers (polyacrylic acid, polyitaconic acid, polycrotonic acid and polymethacrylic acid, as well as poly(N-(2-hydroxyethyl)maleamidic acid), poly(3-(aminocarbonyl)-3-butenoic acid), poly(4-amino-2-methylene-4-oxobutanoic acid and poly(maleamidic acid)), and salts of the corresponding homopolymers.

[0023] Other preferred carboxylic acid-containing polymers are modified anhydride homopolymers hydrolyzed with water or a base (such as KOH, NaOH) or a water-soluble organic base (such as a water-soluble monoamine (ethanolamine, ammonia, and amine-terminated polyethylene glycol (e.g., CAS registry numbers 65421-52-5, 171863-88-0, 33881-50-4, and 176703-83-6))). Typical anhydride homopolymers or copolymers that can be used for hydrolysis or post-modification are based on maleic anhydride and itaconic anhydride. When hydrolyzed with a base, the carboxylic acid may exist as a salt.

[0024] Other preferred carboxylic acid-containing polymers or carboxylic acid anhydride-containing polymers include copolymers (such as poly(ethylene-co-maleic anhydride), poly(isobutylene-co-maleic anhydride), poly(isobutene-co-anhydride), poly(vinyl methyl ether-co-maleic anhydride), poly(vinyl acetate-co-crotonic acid), poly(styrene-co-maleic anhydride), poly(acrylic acid-co-maleic acid), and maleic acid-methyl vinyl ether copolymers), as well as salts of the corresponding copolymers.

[0025] Further other preferred carboxylic acid-containing polymers or carboxylic acid anhydride-containing polymers include anhydride monoamine monomers (maleamidic acid = maleic acid monoamide, fumaric acid monoamide, 3-(carbamoyl)acrylic acid, 3-(aminocarbonyl)-3-butenoic acid, 4-amino-2-methylene-4-oxobutanoic acid, N-(2-hydroxyethyl)maleamidic acid, etc.) and maleimide monomers (3-pyrroline-2,5-dione, 3-maleimidopropionic acid, N-(2-hydroxyethyl)maleimide, N-(2-aminoethyl)maleimide, etc.) It is a reaction product of a rimer or a salt of the corresponding copolymer (e.g., CAS registry numbers 183558-78-3, 60256-14-6, 30446-39-0, 28929-31-9, 89360-06-5, 89360-07-6), or an anhydride copolymer (e.g., maleic anhydride or itaconic anhydride) with a water-soluble monoamine (ethanolamine, ammonia, and amine-terminated polyethylene glycol (e.g., CAS registry numbers 65421-52-5, 171863-88-0, 33881-50-4, and 176703-83-6)).

[0026] Preferably, the carboxylic acid-containing polymer or its salt or carboxylic acid anhydride-containing polymer has a molecular weight (Mw) of 5000 g / mol or more. The molecular weight is determined via GPC using a general calibration with polyethylene glycol standards. When the Mw is 5000 g / mol or more, further improvements in image quality are observed, particularly in ink spread in solid areas of printing.

[0027] The amount of carboxylic acid-containing polymer or its salt or carboxylic acid anhydride-containing polymer is preferably 0.1 to 5 wt.%, more preferably 0.2 to 4 wt.%. Below this range, the improvement in image quality will be insufficient. Above this range, (ii) a decrease in ejection performance due to an excessively high polymer content in the liquid, (iii) solubility issues causing sedimentation, and (iii) a decrease in image sharpness and an increase in bleeding and feathering may occur.

[0028] A.2. Fixative The aqueous pretreatment solution according to the present invention contains a fixative. The fixative works by crushing, settling, or destabilizing the ink colorants (such as dyes or pigments), thereby fixing the ink colorants to the substrate. This improves image quality (reduction of bleeding, reduction of adhesion).

[0029] The fixing agent is preferably a water-soluble polyvalent metal salt or a cationic polymer.

[0030] Polyvalent metal salts can be present in pretreatment solutions to improve the image quality of inkjet printed images. Generally, polyvalent metal salts can be any water-soluble polyvalent metal salt. Specific examples of polyvalent metal salts may include calcium chloride (CaCl2), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), aluminum chloride (ACl3), calcium nitrate (Ca(NO3)2), magnesium nitrate (Mg(NO3)2), magnesium acetate (Mg(CH3COO)2), zinc acetate (Zn(CH3COO)2), calcium propionate (Ca(C2H5COO)2), or combinations thereof. Further examples of polyvalent metal salts may include metal cations selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminum, chromium, or other polyvalent metals.

[0031] Suitable cationic polymers as fixatives in pretreatment solutions contain either guanidium or fully quaternized ammonium functionalized polymers (such as quaternized polyamine copolymers). Generally, the weight-average molecular weight (Mw) of a cationic polymer is such that, when measured with a Brookfield viscometer, it enables a viscosity of less than 25 cP at 25°C. Typical Mw is less than 500,000, and in one embodiment, less than 50,000.

[0032] Suitable classes of cationic polymers that can be used include, but are not limited to, quaternized polyamides. This includes dicyandiamide polycation, diallyldimethylammonium chloride copolymer, quaternized dimethylaminoethyl (meth)acrylate polymer, quaternized vinylimidisole polymer, alkylguanidine polymer, alkoxylated polyethyleneimine, and mixtures thereof.

[0033] A.3. Vehicle The aqueous medium of the pretreatment solution according to the present invention contains water as a vehicle, but may contain one or more water-soluble organic solvents.

[0034] One or more organic solvents may be added for a variety of reasons. For example, adding a small amount of organic solvent may be advantageous to improve the solubility of the compound in the pretreatment solution to be prepared, to obtain good penetration into a porous substrate, or to prevent the pretreatment solution from drying too quickly in the nozzle of an inkjet head. Preferred water-soluble organic solvents include polyols (e.g., ethylene glycol, glycerin, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, tetraethylene glycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, 1,6-hexanediol, 1,2-hexanediol, 1,5-pentanediol, 1,2-pentanediol, 2,2-dimethyl-1,3-prampanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol, and 2-methyl-1,3-propanediol), N-hydroxyethyl-pyrrolidone, N-butyl-pyrrolidone, and amines. These include (e.g., ethanolamine and 2-(dimethylamino)ethanol), monohydric alcohols (e.g., methanol, ethanol, and butanol), alkyl ethers of polyhydric alcohols (e.g., diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether), 2,2'-thiodiethanol, amides (e.g., N,N-dimethylformamide), heterocyclic compounds (e.g., 2-pyrrolidone and N-methyl-2-pyrrolidone), and acetonitrile. The humectants are preferably added to the precoat composition formulation in an amount of 0.1 to 35 wt.% based on the total weight of the liquid.

[0035] A.4. Resin particles The pretreatment solution according to the present invention may contain resin particles dispersed in a liquid aqueous medium. The resin particles can improve the mechanical resistance and water resistance of printed images. The resin is preferably selected from the group consisting of poly(urethane) and its copolymers, acrylic and its copolymers, poly(ester) and its copolymers, poly(styrene) and its copolymers, poly(vinylamide) and its copolymers, poly(vinyl alcohol) derivatives and their copolymers, poly(acetal) and its copolymers, poly(ether) and its copolymers, poly(vinyl ether) and its copolymers, polyvinyl(ester) and its copolymers, poly(imide) and its copolymers, poly(imine) and its copolymers, polycarbonate and its copolymers, poly(vinyl chloride) and its copolymers, poly(vinylidene chloride) and its copolymers, poly(amidic acid) and its copolymers, poly(saccharide) and its derivatives, and cellulose and its derivatives. The resin particles are stabilized by nonionic groups or nonionic compounds or amphiphilic compounds. It should be understood that nonionic groups are groups that are covalently bonded to the resin particles.

[0036] To accommodate polyvalent metal salts or cationic polymers, the resin particles are preferably cationic or nonionic and sterically stabilized.

[0037] For poly(urethane) dispersions, nonionic stabilization can be achieved by using polyetherdiols in the preparation of the poly(urethane) resin. Preferably used polyetherdiols in this invention are Ymer N180, Ymer N120, Ymer N90, or Tegomer D3403 (i.e., α-[2,2-bis(hydroxymethyl)butyl]-ω-methoxy-poly(oxy-1,2-ethanediyl)). Such diols can be prepared from trimethylolpropaneoxetane (TMPO). Possible synthesis procedures are described in Fock, J.; Moehring, V., Polyether-1,2-and-1,3-diols as macromonomers for the synthesis of graft copolymers, 1. Synthesis and characterization of the macromonomers. Die Makromolekulare Chemie 1990, 191(12), 3045-3057. In general, other polyether 1,2- or 1,3-diols can also be used.

[0038] For addition polymerization (e.g., preparation of polyacrylates), mono-methacrylate-terminated polyethers or mono-acrylate-terminated polyethers can be used to prepare graft copolymers having polyether side chains. Examples of macromers suitable for addition polymerization are described in [0022~0024] of WO2023 / 001650A.

[0039] The preferred resin particle dispersion incorporated into the pretreatment solution according to the present invention is based on a polyurethane particle dispersion. In polyurethane synthesis, different polyols can be introduced to obtain suitable physical, mechanical, or optical properties (such as adhesion to the substrate, water resistance, solvent resistance, weather resistance, scratch resistance, gloss, or opacity). Commonly used polyols include polyether polyols, polyester polyols, polycarbonate polyols, polyamide polyols, polyacrylate polyols, and polyolefin polyols. In addition to polymer polyols, low molar diols and diols that have affinity for the aqueous phase (such as dimethylolpropionic acid) can also be used. To obtain good compatibility with polyvalent salts, the use of water-soluble polyether diols is preferred.

[0040] The amount of resin particles in the pre-coat composition is 1 wt.%, ~50 wt.%, preferably 5 wt.%, ~45 wt.%, and more preferably 20 wt.%, ~40 wt.%, relative to the total solid content of the pre-coat composition. Amounts exceeding these values ​​will negatively affect the ejection reliability if the pre-coat composition is applied via an ejection method.

[0041] Suitable commercially available PU dispersions include, for example, Vondic2220 and Vondic1980NE supplied by Toyobo, Printrite DP375 and Printrite PD379 supplied by Lubrizol, Esacote PU3511 supplied by Lamberti, Neorez R9340 available from DSM, and 2019WTT001-3 available from BASF.

[0042] A.5. Nonionic dispersants The pretreatment solution of the present invention may further contain a nonionic dispersant, preferably a nonionic polymer dispersant.

[0043] Suitable nonionic dispersants include polymeric dispersants, nonionic surfactants, and segmented polymers (such as graft copolymers, block copolymers, star-branched copolymers, comb copolymers, or gradient copolymers). These polymeric dispersants are preferably amphiphilic structures having at least one segment that is soluble, dispersible, or compatible with water-based media. The media does not necessarily have to be water alone, but can be mixed with other solvents. It can also be a mixture. In water-based inkjet inks, other water-soluble solvents (such as propylene glycol, glycerol, dipropylene glycol monomethyl ether, and 2-hydroxyethylpyrrolidone) can be added. At least one segment or portion of the polymer dispersant should be compatible with the solvent medium of the ink.

[0044] Examples of nonionic surfactants suitable as nonionic dispersants are described in [0033~0034] of WO2023001650.

[0045] Examples of suitable polymer dispersants are described in [0035-0039] of WO2023001650.

[0046] A.6. Additives The pretreatment solution according to the present invention may also contain a humectant. The pretreatment solution preferably incorporates a humectant, especially if the liquid needs to be applied by a jetting method (such as inkjet or valve jet). The humectant prevents nozzle clogging. This prevention is due to its ability to slow the evaporation rate of inkjet ink, particularly water in the liquid. The humectant is preferably an organic solvent having a higher boiling point than water. Suitable humectants include triacetin, N-methyl-2-pyrrolidone, glycerol, urea, thiourea, ethyleneurea, alkylurea, alkylthiourea, dialkylurea and dialkylthiourea, diols (including ethanediol, propanediol, propanetriol, butanediol, pentanediol, and hexanediol), glycols (including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, tetraethylene glycol, and mixtures and derivatives thereof). A preferred humectant is glycerol.

[0047] The humectant is preferably added to the pretreatment solution formulation in an amount of 0.1 to 40 wt.% based on the total weight of the liquid.

[0048] The pretreatment solution may contain a surfactant. Any known surfactant can be used, but preferably, a nonionic oxirane or mono(2-propylheptyl) ether is used.

[0049] To prevent undesirable microbial growth that may occur over time, biocides may be added to the precoat composition. Biocides may be used alone or in combination. Suitable biocides for the inkjet inks of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridinethion-1-oxide, ethyl p-hydroxybenzoate, and 1,2-benzoisothiazoline 3-one, as well as their salts.

[0050] Preferred biocides are Proxel® GXL and Proxel® Ultra5, available from ARCH UK BIOCIDES, and Bronidoc®, available from COGNIS.

[0051] The biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt.%, more preferably 0.01 to 1.0 wt.%, based on the total weight of the liquid.

[0052] The pre-coat composition may further contain at least one thickener for viscosity adjustment in the liquid. Suitable thickeners include urea or urea derivatives, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, derived chitin, derived starch, carrageenan, xanthan gum, pullulan, protein, poly(styrenesulfonic acid), and poly These include poly(styrene-co-maleic anhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamide, partially hydrolyzed polyacrylamide, poly(acrylic acid), poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate), poly(hydroxyethyl acrylate), poly(methyl vinyl ether), polyvinylpyrrolidone, poly(2-vinylpyridine), poly(4-vinylpyridine), and poly(diallyldimethylammonium chloride). Specific preferred thickeners are hydrophilically modified PU thickeners (HEUR) such as Thijet 170 supplied by Lamberti and polyacrylic acid esters such as BYK LP-R21675 supplied by BYK.

[0053] The thickening agent is added in an amount of preferably 0.01 to 20 wt.%, more preferably 0.1 to 10 wt.%, based on the liquid.

[0054] B. Liquid ink set containing pretreatment solution and water-based inkjet ink. The liquid set according to the present invention comprises the pretreatment solution described in §A, and an aqueous inkjet ink containing a water-soluble organic solvent and a colorant. Optionally, the liquid ink set may include an aqueous varnish applied during or after the ejection of the aqueous inkjet ink.

[0055] B.1. Water-based inkjet ink The aqueous inkjet ink, as part of the liquid set according to the present invention, comprises colorants (such as dyes and pigments). The pigment is preferably stabilized by an anionic dispersant group. Additional colloidal stability can also be achieved by further stabilizing the pigment with polymer dispersants, surfactants, or a combination thereof.

[0056] The aqueous medium of the ink contains water and one or more water-soluble organic solvents. Suitable water-soluble organic solvents are described in §A.3.

[0057] In a preferred embodiment of the present invention, the aqueous inkjet ink comprises a resin and / or wax.

[0058] Water-based inkjet inks may further contain surfactants, humectants, biocides, resins, and thickeners as additives.

[0059] B.1.1. Pigments The pigments in the aqueous inkjet ink according to the present invention may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. The coloring pigments may be selected from those disclosed in HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN 3527305769.

[0060] Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO2008 / 074548.

[0061] Pigment particles are dispersed in an aqueous medium using polymer dispersants, surfactants, or a combination thereof. Self-dispersing pigments can also be used. The latter prevent interaction between the polymer dispersant and the dispersing groups of binders or capsules that may be included in inkjet inks (see below).

[0062] Self-dispersing pigments allow for the dispersion of pigment into an aqueous medium without the use of surfactants or resins. This pigment has covalently bonded anionic hydrophilic groups or salt-forming groups on its surface that enable dispersion.

[0063] Techniques for producing self-dispersing pigments are well known. For example, EP1220879A discloses a pigment to which a) at least one stereogroup and b) at least one organoionic group and at least one amphiphilic counterion are attached, the amphiphilic counterion having the opposite charge to that of the organoionic group suitable for inkjet inks. EP906371A also discloses suitable surface-modified coloring pigments to which one or more hydrophilic organic groups containing ionic or ionizable groups are attached. A suitable commercially available self-dispersing coloring pigment is, for example, CAB-O-JET® inkjet colorants supplied by CABOT.

[0064] The pigment particles in inkjet inks should be small enough to allow for free flow of ink through the inkjet printing device, particularly at the ejection nozzle. It is also desirable to use small particles to achieve maximum color intensity and to slow down sedimentation.

[0065] The average pigment particle size is preferably 0.050 to 1 μm, more preferably 0.070 to 0.300 μm, and particularly preferably 0.080 to 0.200 μm. Most preferably, the number-average pigment particle size is 0.150 μm or less. The average particle size of the pigment particles is determined using a Brookhaven Instruments Particle Sizer BI90plus based on the principle of dynamic light scattering.

[0066] Suitable white pigments are given by Table 2 in section

[0116] of WO2008 / 074548. The white pigments are preferably pigments having a refractive index greater than 1.60. The white pigments may be used alone or in combination. Preferably, titanium dioxide is used as the pigment having a refractive index greater than 1.60. Suitable titanium dioxide pigments are disclosed in sections

[0117] and

[0118] of WO2008 / 074548.

[0067] Special colorants may also be used, such as fluorescent pigments for special effects on clothing, and metallic pigments for printing a luxurious silver and gold appearance onto fabrics.

[0068] A suitable polymer dispersant is a copolymer of two monomers, but may also contain three, four, five, or even more monomers. The properties of the polymer dispersant depend on both the properties of the monomers and their distribution in the polymer. The copolymer dispersant preferably has the following polymer composition. • Monomers that have been statistically polymerized (for example, ABBAABAB, which is produced when monomer A and monomer B polymerize), • A polymer of monomers alternating (for example, ABABABAB formed by the polymerization of monomer A and monomer B), • Monomers polymerized in a gradient (tapered) manner (for example, AAABAABBABBB produced by the polymerization of monomer A and monomer B), • Block copolymers (e.g., AAAAABBBBBB formed by the polymerization of monomer A and monomer B) (the length of each block (2, 3, 4, 5, or more) is important for the dispersing ability of the polymer dispersant), • Graft copolymers (graft copolymers consist of a polymer skeleton having polymer side chains attached to the backbone), and • Mixed forms of these polymers (e.g., block gradient copolymers).

[0069] Suitable dispersants include DISPERBYK® dispersant available from BYK CHEMIE, JONCRYL® dispersant available from BASF, and Lubrizol. SOLSPERSE® dispersant is available. Another suitable dispersant is Edaplan 482 supplied by Muenzing. A detailed list of non-polymeric dispersants and several polymeric dispersants is disclosed in MC CUTCHEON. Functional Materials, North American Edition. Glen Rock, NJ: Manufacturing Confectioner Publishing Co., 1990. pp. 110-129.

[0070] The polymer dispersant preferably has a number-average molecular weight Mn of 500 to 30,000, more preferably 1,500 to 10,000.

[0071] The polymer dispersant preferably has a weight-average molecular weight Mw of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0072] The pigment is preferably present in an amount of 0.01 to 15%, more preferably 0.05 to 10% by weight, and most preferably 0.1 to 5% by weight, based on the total weight of the inkjet ink. For white inkjet inks, the white pigment is preferably present in an amount of 3% to 40% by weight, more preferably 5% to 35% of the inkjet ink. An amount of less than 0.01% by weight cannot achieve sufficient coverage.

[0073] In a preferred embodiment of the present invention, the aqueous ink comprises a pigment encapsulated by a crosslinked polymer shell. The encapsulated pigment provides a printed image with improved physical properties (such as water resistance and dry friction resistance) compared to a pigment dispersed by a non-crosslinked polymer.

[0074] Suitable encapsulating pigments are provided by Lubrizol as Diamond HSDX dispersions and by Fujifilm as RxD pigment dispersions (such as APD1000 and APD4000 premium dispersions).

[0075] B.1.2.Resin The inkjet ink composition according to the present invention may contain a resin. The resin is often added to the inkjet ink formulation to achieve good adhesion of the pigment to the recording medium. The resin is preferably a polymer, and suitable resins may be acrylic-based resins, urethane resins, or waxes.

[0076] The polyurethane resin will be incorporated as a dispersion in the ink formulation and may be selected from the group consisting of, for example, aliphatic polyurethane dispersions, aromatic polyurethane dispersions, anionic polyurethane dispersions, nonionic polyurethane dispersions, aliphatic polyester polyurethane dispersions, aliphatic polycarbonate polyurethane dispersions, aliphatic acrylic-modified polyurethane dispersions, aromatic polyester polyurethane dispersions, aromatic polycarbonate polyurethane dispersions, aromatic acrylic-modified polyurethane dispersions, or two or more combinations of the above.

[0077] The preferred urethane resin to be used as a dispersion in the ink of the present invention is a polyester resin containing structural units that include urethane bonds. Among such resins, water-soluble or water-dispersible urethane-modified polyester resins are particularly preferred. The urethane-modified polyester resin preferably contains at least one structural unit derived from a hydroxyl group-containing polyester resin (polyester polyol) and at least one structural unit derived from an organic polyisocyanate.

[0078] Furthermore, the hydroxyl group-containing polyester resin contains at least one polybasic acid component, The resin is formed by an esterification or transesterification reaction with at least one polyhydric alcohol component.

[0079] Preferred polyurethane resins to be included in the ink of the present invention are polyurethane resins that can be obtained by reacting polyester polyols, polyether diols, anionic group-containing polyols, and polyisocyanates. Particularly preferred polyurethane resins are those that can be obtained by reacting polyester polyols, polyether diols, anionic group-containing polyols, and polyisocyanates, with polyester polyols being obtained by reacting aromatic polycarboxylic acids and polyols. Examples of preferred polyurethane resins and their preparation are disclosed in Japanese Patent Application EP3532545A.

[0080] Some examples of suitable polyurethane dispersions include NEOREZR-989, NEOREZR-2005, and NEOREZR-4000 (DSM NeoResins); BAYHYDROLUH2606, BAYHYDROL UH XP2719, BAYHYDROL UH XP2648, and BAYHYDROL UA XP2631 (Covestro); DAOTAN VTW1262 / 35WA, DAOTAN VTW1265 / 36WA, DAOTAN VTW1267 / 36WA, DAOTAN VTW6421 / 42WA, DAOTAN VTW6462 / 36WA (Allnex); and SANCURE 2715, SANCURE20041, SANCURE2725 (Lubrizol Corporation), or, for example, a combination of two or more of the above.

[0081] Acrylic resins include polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers of the aforementioned monomers with other monomers. These resins exist as suspensions of particles having an average diameter of about 30 nm to about 300 nm. Acrylic latex polymers are formed from acrylic monomer residues or methacrylic monomer residues. Examples of monomers for acrylic latex polymers include, for example, acrylic monomers (e.g., acrylic acid esters, acrylamides, and acrylic acids) and methacrylic monomers (e.g., methacrylic acid esters, methacrylamides, and methacrylic acids). Acrylic latex polymers can be homopolymers of acrylic monomers or copolymers of acrylic monomers with other monomers, such as vinyl aromatic monomers (but not limited to styrene, styrene-butadiene, p-chloromethylstyrene, divinylbenzene, vinylnaphthalene, and divinylnaphthalene).

[0082] Some examples of suitable acrylic latex polymer suspensions include JONCRYL 537 and JONCRYL 538 (BASF Corporation, Port Arthur TX); CARBOSET GA-2111, CARBOSET CR-728, CARBOSET CR-785, CARBOSET CR-761, CARBOSET CR-763, CARBOSET CR-765, CARBOSET CR-715, and CARBOSET GA-4028 (Lubrizol Corporation); NEOCRYL A-1110, NEOCRYL A-1131, NEOCRYL A-2091, NEOCRYL A-1127, NEOCRYL XK-96, and NEOCRYL XK-14 (DSM); and BAYHYDROL AH XP2754, BAYHYDROL AH XP2741, BAYHYDROL A2427, and BAYHYDROL A2651 (Bayer), or, for example, a combination of two or more of the above.

[0083] The concentration of the resin in the inkjet ink according to the present invention is at least 1 wt.%. Preferably, it is less than 30 wt.%, and more preferably less than 20 wt.%.

[0084] The aqueous inkjet ink of the present invention may also contain wax. The wax in the ink improves the wet abrasion resistance or wet scratch resistance of the printed layer.

[0085] In general, any suitable wax can be used in ink and varnish compositions. Therefore, the wax may be polyethylene wax, petroleum wax, paraffin wax, carnauba wax, polypropylene wax, crystalline wax and microcrystalline wax, amide wax (oleic acid amide, stearic acid amide, erucic acid amide, cyclic amide, etc.), or combinations thereof. In one aspect of the present invention, the wax may be high-density polyethylene wax.

[0086] In one aspect of the present invention, the wax may be polyethylene wax or modified paraffin wax. An example of polyethylene wax is high-density polyethylene (HDPE) wax having a density in the range of about 0.93 g / mL to 0.97 g / mL.

[0087] An example of modified paraffin wax particles is paraffin wax that has been modified to improve its dispersibility in water (for example, through emulsification). Modified paraffin wax can be surface-modified or chemically modified.

[0088] Some specific examples of waxes that can be used include those from the JONCRYL Wax series (such as JONCRYL Wax22, JONCRYL Wax26, and JONCRYL Wax120 available from BASF Corp.), those from the AQUACER series (such as AQUACER498, AQUACER501, AQUACER505, AQUACER513, AQUACER530, AQUACER531, AQUACER535, AQUACER537, AQUACER539, and AQUACER552 available from BYK-Gardner, Columbia, Md), and Liquilube404E supplied by Lubrizol.

[0089] The wax may have i) a high melting temperature T and / or ii) a low average particle size. For example, the wax may have a high melting temperature T (such as 90°C or higher). Furthermore, the wax may have an average particle size in the range of 0.03 μm to 1.5 μm, more preferably 0.05 μm to 1 μm (referring to the effective diameter assuming that individual wax particles are not perfectly spherical) (D50). If the particle size exceeds these upper limits, varnish ejection reliability problems may arise.

[0090] Wax may be present in the ink in an amount ranging from 3 to 30 wt.%, more preferably 5 to 25 wt.%, relative to the total solid weight of the ink.

[0091] The inkjet ink composition according to the present invention may contain capsules. Capsules, more preferably nanocapsules, are often incorporated into the inkjet ink formulation to encapsulate colorants (US2009227711A, JP2004075759) or to encapsulate crosslinkable reactive components. Particularly useful are the nanocapsules disclosed in WO2015158649[0037~0110]: the nanocapsules have a polymer shell surrounding a core containing a reactive chemical. Shell materials include polyurea, polyurethane, polyester, polycarbonate, polyamide, melamine-based polymers, and mixtures thereof, with polyurea and polyurethane being particularly preferred. Other particularly useful nanocapsules are those disclosed in WO2016165970[0051~0138]: the nanocapsules are self-dispersible and contain dispersion groups covalently coupled to the shell polymer. WO2015158649[0037~0110] and WO20 The core of the nanocapsule in 16165970[0051~0138] contains a reactive chemical that enables the formation of reaction products upon application of heat and / or light to address a wide variety of substrates. Other suitable reactive chemicals are those activated upon irradiation as described in WO2015158649[0068~0110].

[0092] The capsules are preferably present in the inkjet ink in an amount of 30 wt.% or less, preferably 5 to 25 wt.%, based on the total weight of the ink.

[0093] B.1.3. Additives The ink composition may contain a surfactant. Any known surfactant may be used, but preferably, glycol surfactants and / or acetylene alcohol surfactants and / or polysiloxane surfactants are used. The use of acetylene glycol surfactants and / or acetylene alcohol surfactants and / or polysiloxane surfactants further improves print quality by reducing bleed and also improves drying properties during printing, enabling high-speed printing.

[0094] The acetylene glycol surfactant and / or acetylene alcohol surfactant is preferably one or more selected from 2,4,7,9-tetramethyl-5-decine-4,7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 2,4-dimethyl-5-decine-4-ol, and alkylene oxide adducts of 2,4-dimethyl-5-decine-4-ol. These are available, for example, from Air Products (GB) or Nissin Chemical Industry, and include the Olfin series® such as Olfin E1010, and the Surfynol® series such as Surfynol 465, Surfynol 104H, and Surfynol 61.

[0095] To prevent undesirable microbial growth that may occur over time, biocides may be added to the ink composition. Suitable biocides are described in §A.6.

[0096] The biocide is preferably added to the aqueous medium in an amount of 0.001 to 3 wt.%, more preferably 0.01 to 1.0 wt.%, based on the total weight of the ink.

[0097] One or more photothermal processing agents are preferably present in an amount ranging from 0.1 to 10 wt.% based on the total weight of the ink.

[0098] B.2. Overprint Varnish The varnish, as part of the liquid ink set according to the present invention, is used to protect inkjet printed images from wet and dry friction, scratches, and solvents. Therefore, the varnish contains water and resin particles.

[0099] The varnish included in the liquid set according to the present invention may contain wax. The wax may improve the durability of the printed image. In general, any suitable wax may be used in the varnish composition. Suitable waxes are described in §B.1.

[0100] resin particles Examples of resin particles that can be included in varnish include well-known resins such as urethane-based resins, acrylic resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, and vinyl chloride-based resins. Vinyl chloride-based resins include vinyl chloride copolymers (such as vinyl chloride-vinyl acetate copolymers). These resins can be used individually or in combination of two or more.

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

[0102] Commercially available urethane-based resins may be used, such as SUPER FLEX 460, 460s, 840, E-4000 (trade names, manufactured by DKS Co., Ltd.), RESAMINE D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (trade names, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), TAKELAC WS-6021, W-512-A-6 (trade names, manufactured by Mitsui Chemicals Polyurethanes INC.), SUNCURE 2710 (trade name, manufactured by LUBRIZOL Corporation), and Permalin UA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.).

[0103] Acrylic resin is a general term for polymers obtained by polymerizing at least acrylic monomers (such as (meth)acrylic acid and (meth)acrylate). Examples include (meth)acrylic resins obtained from acrylic monomers, and copolymers of acrylic monomers with monomers other than acrylic monomers (e.g., vinyl-based monomers such as styrene). Acrylamide and acrylonitrile can also be used as acrylic monomers. Acrylic resins can be non-reactive or self-crosslinkable. Commercially available products can be used as resin emulsions using acrylic resin as a raw material. Examples include FK-854 (trade name, manufactured by CHIRIKA Co., Ltd.), Mowinyl952B, 718A (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), NipolLX852, and LX874 (trade name, manufactured by ZEON Corporation).

[0104] Examples of styrene-acrylic resins include poly(styrene-alkyl acrylate), polystyrene-1,3-diene, poly(styrene-alkyl methacrylate), poly(styrene-alkyl acrylate-acrylic acid), poly(styrene-1,3-diene-acrylic acid), poly(styrene-alkyl methacrylate-acrylic acid), poly(styrene-alkyl acrylate-acrylonitrile-acrylic acid), and poly(styrene-1,3-diene-acrylonitrile-acrylic acid). Other examples include poly(styrene-propyl acrylate), poly(styrene-butyl acrylate), poly(styrene-butadiene-acrylic acid), poly(styrene-butadiene-methacrylic acid), poly(styrene-butadiene-acrylonitrile-acrylic acid), poly(styrene-butyl acrylate-acrylic acid), poly(styrene-butyl acrylate-methacrylic acid), poly(styrene-butyl acrylate-acrylononitrile), and poly(styrene-butyl acrylate-acrylononitrile-acrylic acid). Commercial styrene-acrylic resins include Neocryl D2101 (Covestro) and Bonron PS001 and Bonron PS002 (Mitsui).

[0105] Other suitable resins include Esajet acrylic latex supplied by Lamberti (such as Esajet AC20, Esajet AC22, Esajet AC29, Esajet AC31, and Esajet AC03).

[0106] The varnish contains resin in an amount of 1 wt.% to 30 wt.% relative to the total mass of the liquid. When the resin content in the varnish is within the aforementioned range, the effect of improving the friction resistance of the image tends to be better. More preferably, the varnish contains resin in an amount of 3 wt.% to 15 wt.% relative to the weight of the liquid. Most preferably, the varnish contains resin in an amount of 5 wt.% to 12 wt.% relative to the weight of the liquid.

[0107] The varnish may contain a surfactant. Preferred surfactants are described in §B.1.3, but polyethersiloxane surfactants are preferred.

[0108] The varnish may further comprise a water-soluble polymer selected from the group consisting of linear PPO-PEO copolymers and arylethylphenyl polyglycol ethers described in unpublished patent application EP23161106.2A.

[0109] The varnish may further contain a crosslinking agent. Any water-soluble or water-dispersible crosslinking agent may be used, but preferably the crosslinking agent is a carbodiimide, such as that described in unpublished patent application EP23164057.4A.

[0110] C. Recording Method C.1. Method of applying pretreatment solution The pretreatment solution according to the present invention is suitable for treating different substrates, absorbent substrates, and non-absorbent substrates. The substrate has an absorbed water content of at least 10 g / m² after a contact time of 60 seconds. 2 Materials are characterized as absorbent if they meet certain criteria. Absorbent substrates include paper, cardboard, plain cardboard, corrugated cardboard, packaging board, folding board, wood, ceramic, stone, leather, and fabric. Non-absorbent substrates include metal, glass, polypropylene, polyvinyl chloride, PET, PMMA, polycarbonate, polyamide, polystyrene, or copolymers thereof.

[0111] The pretreatment liquid is particularly suitable for coating or spraying onto paper for packaging applications, more preferably onto absorbent substrates (such as cardboard, paper wire, corrugated cardboard, packaging board, folded board, and paper). The paper may be single-layer or multi-layer paper.

[0112] The paper may be brown kraft paper, white top paper, or bleached board. The paper may be manufactured from chemicals, wood, or recycled fibers. For example, the paper may be a liner for printing on a page-width web press and can be processed into corrugated boxes. In this embodiment, the liner paper may be used as a double-sided liner, either processed directly in a corrugator or laminated onto a double-sided liner after lamination. The paper may also be a board used for boxes or other packaging applications.

[0113] All well-known conventional methods can be used to coat or impregnate the substrate with the pretreatment solution. Examples of methods include air knife coating, blade coating, roll coating, gravure coating, and spraying. More preferably, the pretreatment solution is applied by a spraying method.

[0114] Subsequently, the pretreatment solution is applied using an inkjet head or a valve jet head. This pretreatment solution application method is preferably image-dependent, and has the advantage that the amount of pretreatment solution required is substantially less than that required by other application methods. The jet head makes it possible to apply the pretreatment solution to the substrate area on which the image is to be printed. Suitable inkjet head systems for applying the pretreatment solution are the piezo type, continuous type, thermal print head type, Memjet type, valve jet type, or through-flow head described in C.2.

[0115] After applying the pretreatment solution to the substrate, the liquid is preferably at least partially dried so that a precoat layer is formed before the image is printed on the treated substrate.

[0116] The substrate to which the pretreatment solution has been applied is dried and optionally subjected to heat treatment, and then subjected to an ink ejection step of a colorant-containing ink onto the formed precoat layer. Examples of heating processes include, but are not limited to, heat pressing, steam treatment under atmospheric pressure, high-pressure steam treatment, and THERMOFIX. Any heat source can be used for the heating process, for example, an infrared lamp may be used.

[0117] In another preferred embodiment of the present invention, the pretreatment solution is substantially dried before the image is printed by the aqueous ink ejection step.

[0118] C.2. Ink ejection and drying After applying a pretreatment solution to the substrate, an aqueous inkjet ink, as part of the ink set according to the present invention, is applied to obtain a printed image, preferably at least on the area to which the pretreatment solution has been applied. The inkjet ink contains a colorant, and more preferably a pigment. A preferred method for applying the aqueous inkjet ink is by an ink ejection method.

[0119] The preferred inkjet head for ejecting pre-treatment liquids in a printing system is a piezo-type inkjet head. Piezo-type inkjet ejection is based on the operation of a piezo-type ceramic transducer when voltage is applied to it. The application of voltage changes the shape of the piezo-type ceramic transducer in the print head, creating a void, which is then filled with aqueous inkjet ink. When the voltage is removed again, the ceramic expands and returns to its original shape, causing droplets of pre-treatment liquid to be ejected from the inkjet head. However, ink ejection according to the present invention is not limited to piezo-type inkjet printing. Other inkjet print heads can also be used, and these inkjet print heads include various types (continuous, thermal, Memjet, and valvejet, etc.).

[0120] In a preferred embodiment, the printing system is configured to recirculate the aqueous ink before printing. Inkjet heads particularly useful for printing aqueous inkjet inks of the liquid set of the present invention are derived from systems that include ink recirculation within the head, such as through-flow heads disclosed in WO2006 / 030235A2 and WO2006 / 064036A1. Inkjet heads of this type are very suitable for incorporation into printing systems that include through-flow printheads having one or more nozzles for ejecting droplets of pretreatment liquid and / or aqueous ink. An ink circulation system for supplying and circulating pretreatment liquid and / or ink through the printhead includes an ink tank for containing pretreatment liquid and / or ink, a supply buffer tank for receiving pretreatment liquid and / or ink from a main tank and supplying the ink to the through-flow printhead, and a recovery manifold for receiving pretreatment liquid and / or ink from the through-flow printhead and returning the pretreatment liquid and / or ink to the main ink tank via a pump.

[0121] After an image is formed by applying an aqueous inkjet ink onto at least a portion of a pretreatment solution or precoat layer, the image is dried.

[0122] The drying step of the image can be carried out by applying airflow and / or heat. The heating step must be carried out by using a heat source. Examples include forced air heating, radiant heating (IR irradiation (NIR irradiation, CIR irradiation, and SWI), forced air heating, radiant heating (IR irradiation, NIR irradiation, and SWI), forced air heating, radiant heating (IR irradiation, NIR irradiation, and NIR irradiation), and SWI Examples include apparatus for conductive heating, high-frequency drying, and microwave drying (including R irradiation).

[0123] Examples of heating processes include, but are not limited to, heat pressing, steam treatment under atmospheric pressure, high-pressure steam treatment, and THERMOFIX. Any heat source can be used for the heating process, for example, an infrared lamp.

[0124] C.3. Application of Varnish After the image obtained by printing with aqueous inkjet ink has dried at least partially, a varnish constituting part of the liquid set according to the present invention is applied over at least part of the image.

[0125] In one embodiment of the present invention, the varnish is applied to a non-image area, more specifically, to a non-image area containing a pretreatment solution or a pre-coat layer.

[0126] All well-known conventional methods can be used to coat or print varnish onto at least a portion of an image. Examples of methods include air knife coating, blade coating, roll coating, gravure coating, and spraying. The advantage of these coating or printing methods is that a thick varnish layer can be obtained in a single pass on the recording medium, ensuring sufficient abrasion resistance of the image.

[0127] The varnish is preferably applied via a spraying technique that allows for selective application of the varnish onto the image. This varnish composition application method, being preferably image-dependent, has the advantage of requiring substantially less varnish material than other application methods. Suitable spraying heads for spraying the varnish are the same as those described in §C.2.

[0128] Finally, the applied varnish is dried according to one of the above methods for drying the pretreatment solution or water-based inkjet ink.

[0129] D.1. Material All materials used in the following examples are readily available from standard suppliers (such as Aldrich Chemical Co. (Belgium) and Acros (Belgium)) unless otherwise specified. When used, water is demineralized water (DI water). Proxel is a 5 wt.% aqueous solution of 1,2-benzoisothiazolin 3-one, available as Proxel® K supplied by YDS CHEMICALS NV. Surfynol 104PG50 is a 50 wt.% solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol in propylene glycol supplied by Evonik. Printrite DP379 is a 30 wt.% aqueous dispersion of polyether-based polyurethane supplied by Lubrizol. Aquacer530 is an aqueous dispersion supplied by BYK containing 32 wt.% of oxidized HDPE wax. Kauropal K933 is a nonionic oxirane, mono(2-propylheptyl) ether supplied by BASF. Pluronic PE10500 is a 100 wt.% ethylene oxide and propylene oxide block copolymer supplied by BASF, with an EO content of 50% and a Mw of 6500. Tego Foamex822 is a polyethersiloxane copolymer supplied by Evonik. Mg(NO3)2,6H2O is magnesium nitrate hexahydrate supplied by the Merck Group. PG is propylene glycol supplied by Merck. ·HC327(HPMA) is Changzhou Wujin Honggunang This is hydrolyzed poly(maleic acid) supplied by Chemical Co Ltd, with a Mw of 300 g / mol or more and a calculated acid value of 967 mg KOH / g polymer. SMA 3000H is poly(styrene-co-maleic anhydride) supplied from Aurorium, with a manganese content of 3500 g / mol, a manganese content of 8500 g / mol, and a calculated acid value of 346 mg KOH / g. ZEMAC E10 is poly(ethylene-co-maleic anhydride) supplied from Aurorium, with a Mw of 10,000 g / mol and a calculated acid value of 779 mg KOH / g. ZEMAC E60 is poly(ethylene-co-maleic anhydride) supplied from Aurorium, with a Mw of 60,000 g / mol and a calculated acid value of 779 mg KOH / g. Itaconix DSP5K is a linear polyitaconic acid partially neutralized with a sodium salt supplied from Itaconix, with a calculated acid value of 863 mg KOH / g. ITACONIX® DSP 2K® is a linear polyitaconic acid partially neutralized with a sodium salt supplied by Itaconix, with an acid value of 863 mg KOH / g. Sokalan CP12S is a 50% solution of poly(acrylic acid-co-maleic acid) supplied by BASF, with a molar mass of 3000 g / mol and a calculated acid value of 826 mg KOH / g. KOH 30PCT is a 30% solution of potassium hydroxide supplied by VWR. PAA-1800 is a polyacrylic acid supplied by Sigma-Aldrich, with a molecular weight (Mw) of 1800 g / mol. PAA-30000 is a 25% polyacrylic acid solution supplied by BASF, its trade name is ALCOTAC CB9, and its Mw is 30,000 g / mol. Ultralube GA1042 is supplied by Keim additec surface GmbH and obtained via Grolman Benelux BV. BYK3450 is a polyethersiloxane supplied by BYK-Chemie GmbH. The HSD X1 series cyan dispersion is a cyan pigment dispersion supplied by Lubrizol. The HSD X1 series magenta dispersion is a magenta pigment dispersion supplied by Lubrizol. The HSD Y1 series yellow dispersion is a yellow pigment dispersion supplied by Lubrizol.

[0130] D.2. Evaluation Method D.2.1. Sample Preparation Coated Ensocoat liner (Stora Enzo https: / / www.storaenso.com / en / products / paperboard-materials / folding-cartons / ensocoat Using a 4μm spiral bar on a homogeneous bleached sulfate board coated with ) The sample was prepared by coating it with a pretreatment solution. The coated liner was dried in an oven at 60°C for 2 minutes.

[0131] To obtain an image with a cyan color, cyan water-based inkjet ink was ejected onto a coated liner using a Samba G3L printhead with a resolution of 1200 dpi x 1200 dpi and a droplet size of approximately 4.5 pL. To obtain an image with a magenta color, magenta water-based inkjet ink was ejected onto a coated liner using a Samba G5L printhead with a resolution of 800 dpi x 1200 dpi and a droplet size of approximately 8 pL.

[0132] The printed image was dried in an oven at 60°C for 5 minutes. Figure 1 shows the printed pattern.

[0133] To obtain an image with a composite color (green), a solid area of ​​yellow ink was first printed onto a coated liner, and then the image shown in Figure 1 was printed on the yellow area using cyan ink. Both inks were printed in single-pass mode using a Ricoh Gen5S inkjet head with a resolution of 1200 dpi x 1200 dpi and a droplet size of approximately 6 pL.

[0134] The printed image was dried in the oven at 60°C for 5 minutes.

[0135] D.2.2 Image Quality The print quality was evaluated by visually analyzing the following characteristics: 1) ink spread, and 2) ink fixation.

[0136] Ink Spread: The ink should completely cover the solid areas in the printed image. Lack of ink spread is demonstrated by the appearance of white lines within the solid areas. The solid areas were visually observed and evaluated by assigning a score from 0 (good ink spread, complete coverage) to 3 (poor ink spread, more than 20 visible white lines within the solid area).

[0137] Ink Fixation: The ink should uniformly and densely cover the solid areas in the printed image. Lack of ink fixation is demonstrated by the appearance of uneven patterns within the solid areas. Ink fixation was evaluated by visually observing the solid areas and assigning scores from 0 (good ink fixation, uniform coverage) to 3 (poor ink fixation, strong unevenness observed).

[0138] D.2.3. Pretreatment solution recirculation test A recirculation test is performed to test the suitability of the pretreatment solution to be used in a printhead equipped with a recirculating ink system. To perform the recirculation test, the device continuously delivers 3.5 to 4 liters of pretreatment solution through a 10 μm filter mesh at a constant flow rate of 1.0 to 1.3 L / min at a temperature of 32°C. The pressure of the pretreatment solution before and after the filter mesh is monitored throughout the entire test period. The pressure loss across the filter is calculated according to the following formula. Pressure loss = Pressure (before entering the filter) - Pressure (after leaving the filter) Over time, an increase in pressure loss may indicate clogging of the filter mesh. A suitable pretreatment solution will result in a pressure loss increase of less than 15% after 10,000 minutes of recirculation.

[0139] C.3. Preparation of aqueous pretreatment solution C.3.1 Preparation of aqueous pretreatment solution containing resin particles A comparative pretreatment solution and the pretreatment solution of the present invention were prepared by mixing the components shown in Table 1. Weight percentages are relative to the total weight of the pretreatment solution. The raw materials were used in their supplied state without any additional processing. [Table 1] [Table 2]

[0140] C.3.2 Preparation of aqueous pretreatment solution free of resin particles A comparative pretreatment solution and the pretreatment solution of the present invention were prepared by mixing the components shown in Table 2. Weight percentages are relative to the total weight of the pretreatment solution. The raw materials were used in their supplied state without any additional processing. [Table 3] [Table 4]

[0141] C.4. Preparation of water-based inkjet inks Aqueous inks INVINK-1 to INVINK-5 were prepared by adding the components listed in Table 3 to the receiving material. All components listed in Table 3 are expressed in wt.% based on the total weight of the ink. Water was added to complete the ink to achieve the desired pigment concentration.

[0142] Water-based inks INVINK-1 to INVINK-3 were prepared by first diluting the wax and then adding the other components listed in Table 3. [Table 5]

[0143] C.5. Results of the image quality evaluation Table 4 shows the performance of pretreatment solutions containing resin particles on the image quality of inkjet printed images using INV-INK-1 (the results obtained in §D.2.1 were evaluated as described in §D.2.2) (with the exception of INV-PL-3, which was used in combination with INV-INK-3). [Table 6] *: Performance of INV-PL-3 in relation to the image quality of inkjet printed images using INV-INK-3.

[0144] Table 5 shows the performance of resin particle-free pretreatment solutions on the image quality of inkjet printed images using INV-INK-2 (the results obtained in §D.2.1 were evaluated as described in §D.2.2). [Table 7]

[0145] Table 6 shows the performance of resin particle-free pretreatment solutions on the image quality of inkjet printed images with a composite color (green) using INV-INK-4 and INV-INK-5 (the results obtained in §D.2.1 were evaluated as described in §D.2.2). [Table 8]

[0146] From Tables 4, 5, and 6, it can be concluded that the pretreatment solution according to the present invention was able to improve the image quality of the image printed on the liner.

[0147] C.6. Evaluation of the recirculation behavior of the pretreatment solution The recirculation behavior of pretreatment solutions COMP-PL-2 and INV-PL-3 was tested for recirculation according to §D.2.3. After 10,000 minutes of recirculation, the wax-containing pretreatment solution COMP-PL-2 showed an increase in pressure loss of more than 15%. The pretreatment solutions of the present invention showed no increase in pressure loss throughout the 10,000 minutes of recirculation.

[0148] It can be concluded that the pretreatment solution of the present invention, when combined with aqueous inkjet ink, exhibits excellent image quality while simultaneously not causing filter clogging when used in a recirculating inkjet head.

Claims

1. An aqueous pretreatment solution for inkjet recording comprising a polyvalent metal salt and a carboxylic acid-containing polymer or a salt thereof or a carboxylic acid anhydride-containing polymer, wherein the polymer has an acid value of 950 mg KOH / g of polymer or less.

2. The aqueous pretreatment solution according to claim 1, wherein the polymer has a molecular weight of 5000 g / mol or more, and the molecular weight is measured relative to a polyethylene standard via a GPC method using a general calibration using a polyethylene glycol standard.

3. An aqueous pretreatment solution according to any of the prior claims, further containing a water-soluble organic solvent.

4. The polymer has an acid value of 346 mg KOH / g polymer or more and 950 mg KOH / g polymer or less.

5. An aqueous pretreatment solution according to any of the prior claims, further containing resin particles, wherein the resin is selected from the group consisting of poly(urethane) and its copolymer, acrylic and its copolymer, poly(ester), poly(styrene) and its copolymer, poly(vinylamide) and its copolymer, poly(vinyl alcohol) derivatives and their copolymer, poly(acetal) and its copolymer, poly(ether) and its copolymer, poly(vinyl ether) and its copolymer, polyvinyl(ester) and its copolymer, poly(imide) and its copolymer, poly(imine) and its copolymer, polycarbonate and its copolymer, poly(vinyl chloride) and its copolymer, poly(vinylidene chloride) and its copolymer, poly(amidic acid) and its copolymer, poly(saccharide) and its derivative, and cellulose and its derivative.

6. An aqueous pretreatment solution according to any of the prior claims, further comprising a nonionic dispersant which is a PPO / PEO copolymer, an arylethylphenyl polyglycol ether, or a fatty acid derivative having an EO / PO moiety.

7. An ink set for inkjet recording, wherein the set comprises an aqueous pretreatment solution and an aqueous ink, the pretreatment solution comprising a polyvalent metal salt and a carboxylic acid-containing polymer or a salt thereof or a carboxylic acid anhydride-containing polymer, the polymer having an acid value of 400 mg KOH / g of polymer or more and 950 mg KOH / g of polymer or less, and the aqueous ink comprising a colorant and a water-soluble organic solvent.

8. The inkjet recording ink set according to claim 7, wherein the colorant is a pigment.

9. The ink set for inkjet recording according to claims 7 to 8, wherein the aqueous inkjet ink contains resin particles.

10. The ink set for inkjet recording according to claims 7 to 9, wherein the set further comprises an aqueous varnish containing resin particles, the resin being selected from the group consisting of urethane-based resins, acrylic resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, vinyl chloride-based resins, and waxes.

11. a) A step of applying the pretreatment solution described in claims 1 to 6 to a substrate, b) Optionally, a step of drying the applied pretreatment solution at least partially, c) A step of spraying an aqueous inkjet ink containing a colorant onto the applied pretreatment liquid, d) A step of applying heat to dry the applied pretreatment liquid and the ejected inkjet ink, A recording method that includes this.

12. The recording method according to claim 11, wherein the application of the pretreatment liquid is carried out by an inkjet head, and the liquid is recirculated within the head or liquid supply system of the inkjet head.

13. The recording method according to claims 11 to 12, wherein a varnish is applied during or after the ejection of the aqueous inkjet ink, and the varnish comprises water and resin particles.

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