Resin-containing pretreatment liquid for inkjet printing and recording method

Abstract

An aqueous pretreatment liquid for inkjet printing comprises resin particles having an average diameter of 1 [mu] m or less and comprising a first polymer and a second polymer, and a fixing agent, the first polymer is a polymer selected from the group consisting of polyureas, polyurethanes, polyamides, polyesters, polycarbonates, polysulfonamides, polyamides, polysulfonamides, melamine-based polymers, silica-based sol-gel polymers, and combinations thereof, and the second polymer is a polyoxyalkylene graft polymer obtained by polycondensation or addition polymerization, the polyoxyalkylene graft has a number average chain length of 20 or more oxyalkylene units. The pre-treatment liquid is useful for inkjet printing on packaging materials such as cardboard or corrugated cardboard.

Description

Technical Field

[0001] The present invention relates to a pretreatment liquid containing resin particles, which is used for inkjet printing, especially for inkjet printing on corrugated paper packaging and corrugated cardboard. Background Art

[0002] Today, the field of digital pre-printing for corrugated paper packaging, folding cardboard, and the liner of corrugated cardboard is growing. Pre-printing with a primer or pretreatment liquid improves the image quality of the image printed by inkjet printing on the pretreatment liquid. The possibility of applying the pretreatment liquid only to the parts that will carry the image makes it possible to reduce the consumption of the pretreatment liquid composition. Since the presence of the pretreatment liquid has a negative impact on the adhesion of the adhesive, it is also beneficial not to apply the pretreatment liquid to the parts of the packaging material that must be glued.

[0003] To obtain a high-quality image, the pretreatment liquid is a composition that can receive ink and fix the colorant in the ink to a greater extent than the substrate untreated with the pretreatment liquid. In particular, the pretreatment liquid can fix the colorant at or near the surface of the substrate, so that the optical density and color gamut of the printed image can be improved compared to the porous substrate untreated with the pretreatment liquid.

[0004] The colorant in the aqueous inkjet ink for inkjet printing can be a dye or a pigment. Pigment-based inks have the advantage that the lightfastness of the provided images is higher than that of dye-based inks. To bond the pigment to the substrate, a reactive binder technology has preferably been introduced into the ink as well as the pretreatment liquid. Several methods have been disclosed in the patent literature.

[0005] WO2014 / 039306A discloses a pretreatment for digital printing on a substrate, which contains an aqueous cationic polyurethane dispersion, a coagulating acid, and a reactive crosslinking moiety.

[0006] US2009 / 0226678 discloses an ink set containing a fixing liquid and a reactant for fixing the pigment of the inkjet ink. The fixing liquid contains polymer fine particles synthesized from (meth)acrylic acid alkyl esters and / or (meth)acrylic acid cycloalkyl esters, and the reactant is a blocked isocyanate, an oxazoline-containing polymer, or a polycarbodiimide.

[0007] WO2018 / 138069 discloses a pretreatment liquid containing capsules composed of a polymer shell surrounding a core, and the core contains one or more chemical reactants capable of forming a reaction product when heat and / or radiation is applied. The shell is stabilized by a cationic dispersion group connected to the shell by means of a copolymerizable surfactant. The chemical reactant is preferably a blocked isocyanate.

[0008] Introducing chemical reactants and reactive binders into aqueous liquids suitable for inkjet printing presents shelf-life stability issues, health, and safety issues due to the reactivity of the chemical reactants, especially when in contact with food.

[0009] Furthermore, a dispersing group that is solely a cationic group provides only moderate storage stability in the presence of cationic fixatives of pretreatment liquids such as polyvalent metal salts or water-soluble polymers.

[0010] Latex-based methods have been disclosed in the patent literature (see WO2018 / 114314A, US 2013 / 0245157A1, and EP3275949A1), which have adhesive capabilities to meet some of the requirements for physical properties for several applications. However, latex-based inkjet inks generally do not simultaneously improve the water resistance and rub resistance of printed images on low-absorbency substrates such as corrugated cardboard, liner paper, folding cardboard, etc. In addition, latex-based inkjet inks have a tendency to form films in the nozzles of the print head and the ink supply, which results in reliability issues during printing. In industrial applications, system reliability and especially jetting reliability are crucial. Therefore, there is still a need for more optimized resin technology.

[0011] Polymerizable polymers having reactive functional groups such as in US2019 / 0023922 are known to be reactive towards typical shell monomers such as isocyanates used in interfacial polymerization, especially starting from a moderately basic pH. This reactivity towards shell monomers limits the encapsulation range of these polymers based on interfacial polymerization, which is a concern for industrialization and scalability. The industrialization range of core-shell particles is crucial for avoiding production losses that result in significant economic and ecological losses.

[0012] Therefore, there is still a need for resin technology for inkjet printing applications that combines on the one hand excellent physical properties and jetting reliability in the final application and on the other hand reliable industrialization. Summary of the Invention

[0013] The object of the present invention is to provide a solution to the above problems. This object has been achieved by providing an aqueous pretreatment liquid for inkjet printing containing resin particles as defined in claim 1.

[0014] A further object of the present invention is to provide a liquid set for inkjet printing as defined in claim 9, which contains an aqueous inkjet ink and a pretreatment liquid.

[0015] A further object of the present invention is to provide a method for preparing the above-mentioned capsules as defined in claim 13.

[0016] Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention. Specific embodiments of the present invention are also defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1: Pattern for inkjet printing during evaluation of the image quality of the image obtained with the pretreatment composition. The pattern contains a solid area and negative text with different sizes ranging from 1 pt to 16 pt. DETAILED DESCRIPTION

[0018] A. Pretreatment liquid A.1. Resin Particles

[0019] The object of the present invention is achieved by an aqueous pretreatment liquid which comprises a fixing agent and resin particles with an average particle size of 1 μm or less. The resin particles comprise a first polymer and a second polymer, and the second polymer is a polyoxyalkylene graft polymer obtained by polycondensation or addition polymerization. The polyoxyalkylene graft has a number-average chain length of 20 or more oxyalkylene units. Preferably, the first polymer is different from the second polymer.

[0020] The presence of the polyoxyalkylene graft with at least 20 units gives the resin particles increased colloidal stability due to the steric repulsion of the particles, resulting in improved storage stability of the pretreatment liquid. In a preferred embodiment, the first polymer comprises a cationic dispersing group, such as a quaternary ammonium group, which gives the resin particles additional electrostatic stability.

[0021] A.1.1. First Polymer

[0022] The resin particles in the pretreatment liquid for inkjet printing according to the present invention comprise a first polymer, including polyurea, polyurethane, polyester, polycarbonate, polyamide, polyacrylate, polyvinyl ether, polyvinyl ester, polysulfonamide, melamine-based polymers, silica-based sol-gel polymers such as those in US603149B1, or mixtures thereof, where polyurea and polyurethane are particularly preferred, and polyurea is most preferred.

[0023] The colloidal stability of the resin particles in the carrier of the pretreatment liquid according to the present invention can be further improved by incorporating a dispersing group covalently bonded to the first polymer and / or by using a dispersant or surfactant preferably added during or after the formation of the capsules.

[0024] The incorporation of the dispersion group covalently bonded to the first polymer is preferably carried out by reacting with a compound containing at least two functional groups capable of reacting with primary and secondary amines. The primary and secondary amines are from a compound containing a dispersion group (such as a quaternary ammonium group). The presence of the primary and secondary amines makes the compound a polyamine crosslinking agent.

[0025] The first polymer in the resin particles according to the present invention can preferably be obtained by reacting a polyamine crosslinking agent containing at least two primary or secondary amines and a quaternary ammonium group with a compound containing at least two functional groups capable of reacting with the primary and secondary amines of the crosslinking agent. Preferably, the functional group is an epoxide, isocyanate, β-ketoester, β-ketoamide, acid anhydride, 1,3-diketone, chloroformate, sulfonyl chloride, acyl halide, enol ester, oxalate or aziridine, most preferably isocyanate. Other preferred functional groups are acyl halide, chloroformate, enol ester, oxalate, N-hydroxysuccinimide active ester, tert-butyl carbamate / boc anhydride, and other active esters.

[0026] Examples of active ester chemicals are described in Miklos Bodanszky's Major Methods of Peptide Bond Formation, Chapter 3 - Active Esters in Peptide Synthesis, The Peptides: Analysis, Synthesis, Biology, 1979, pages 105 - 196. Some examples of useful reagents are: adipoyl chloride (CAS No. 111 - 50 - 2), phthaloyl chloride (CAS No. 88 - 95 - 9), dibenzoyl dichloride (CAS No. 7535 - 15 - 1), 3,3′-[[2,2 - bis[(3 - chloro - 3 - oxopropoxy)methyl]-1,3 - propanediyl]bis(oxy)]bis[propanoyl chloride] (CAS No. 132491 - 88 - 4), 3,3′-[[2 - [(3 - chloro - 3 - oxopropoxy)methyl]-2 - ethyl - 1,3 - propanediyl]bis(oxy)]bis(propanoyl chloride) (CAS No. 78799 - 44 - 7), 2,4,6 - trioxo - 1,3,5 - triazine - 1,3,5(2H,4H,6H)-tropanoyl chloride (CAS No. 33919 - 40 - 3), tricyclo[3.3.1.13.7]decane - 1,3,5 - tricarbonyl trichloride (CAS No. 753025 - 22 - 8), bis(chloroformyl)oxy diethylene ester (CAS No. 106 - 75 - 2), 1,4 - butanediol bis(chloroformate) (CAS No. 2157 - 16 - 6), trimethylolpropane tris(chloroformate) (CAS No. 14031 - 47 - 1). Polymer curing agents having active ester groups are also commercially available from, for example, Dai Nippon Ink & Chemicals, such as Epiclon EXB 9451 (CAS No. 931106 - 68 - 2) and Epiclon HPC 8000 - 65T (CAS No. 1352138 - 02 - 3). Active ester - based initiators for preparing (co)polymers having active ester groups capable of reacting with polyamine curing agents have structures described, for example, in Patent JP2001206946. Copolymers of active ester - functionalized monomers such as: NHS - PEO8 - maleimide (CAS No. 289888 - 73 - 9). Condensation copolymers of diglycolyl chloride (CAS No. 21062 - 20 - 4). Copolymers of sulfonyl chloride monomers such as: 2 - propene sulfonyl chloride and p - styrene sulfonyl chloride.

[0027] Different chemical substances can be used as suitable polyisocyanates. Preferably, a polyamine comprising at least two primary or secondary amines, as well as quaternary ammonium groups, is reacted with an isocyanato-based resin soluble in an organic solvent (such as a polyisocyanate (such as a structure based on biuret, urethane or isocyanurate trimers)). In order to obtain good reactivity and crosslink density, biuret-functionalized polyisocyanates are preferred, such as Desmodur N3200 or Desmodur N75BA.

[0028] The chemistry of the polyisocyanate has a significant impact on particle formation during high-shear processing and interfacial polymerization. The type of polyisocyanate used affects, for example, the reactivity towards the polyamine, solubility and viscosity in the organic solvent. Suitable polyisocyanates are monomeric isocyanates, biuret structures, urethiones, urethanes, isocyanurate trimers, isocyanate adducts or (partially) modified polyisocyanates.

[0029] Examples of modified polyisocyanates are hydrophilic isocyanates, such as polyether-modified polyisocyanates, such as Bayhydur 3100, Bayhydur 305, Bayhydur XP2451 / 1. The type of isocyanate present in the polyisocyanate is also important for the adhesion properties of the pretreatment composition to the substrate and the physical properties of the topcoat varnish. Hexamethylene diisocyanate (HDI) provides higher flexibility than isophorone diisocyanate (IPDI).

[0030] Polyisocyanates based on mixtures of monomeric isocyanates (such as a mixture of HDI and IPDI) can be used to obtain optimized properties. The polyisocyanate can be based on the following monomeric isocyanates: isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 2,4,4'-trimethyl-1,6-hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI) and diphenylmethane diisocyanate (MDI). Modified polyisocyanates can also be used. Examples are reaction products with alcohols such as TMP (= trimethylolpropane) or alcohol-terminated polymers.

[0031] Other suitable isocyanate-containing compounds are copolymers based on isocyanate group monomers prepared by free radical copolymerization. The copolymerization can be carried out in an organic solvent used for preparing the lipophilic phase. Suitable monomers for preparing isocyanate group-functionalized copolymers by addition polymerization are, for example, isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 3-isocyanatopropyl acrylate, and 1-(1-isocyanato-1-methylethyl)-3-isopropenylbenzene (TMI monomer Allnex). A copolymer of methyl methacrylate and 1-(1-isocyanato-1-methylethyl)-3-isopropenylbenzene can be obtained in ethyl acetate and can thus be used for preparing the resin particle dispersions of the present invention.

[0032] In another preferred embodiment, the compound reacting with a polyamine comprising at least two primary or secondary amines, and a quaternary ammonium group is a resin containing epoxy groups. Examples are epoxy resins based on bisphenol A diglycidyl ether, copolymers of epoxy-functionalized monomers such as glycidyl methacrylate (GMA), glycidyl acrylate, allyl glycidyl ether, 4-vinylcyclohexene oxide, or methyl (3,4-epoxycyclohexyl) acrylate, and epoxidized oils such as epoxidized soybean oil.

[0033] In another embodiment of the present invention, the compound reacting with a polyamine comprising at least two primary or secondary amines, and a quaternary ammonium group is a polyaziridine. Suitable polyaziridines are NeoAdd Pax 521 supplied by Covestro (i.e., an 80% solution in ethyl acetate) and the polyaziridine described in the patent application WO 2020 / 020714 of DSM IP Assets B.V.

[0034] In another embodiment of the present invention, the compound reacting with the polyamine comprising at least two primary or secondary amines and a quaternary ammonium group is an alkoxysilane-functionalized polymer, such as a copolymer of SiliXan Lab1039M1 (50% in butyl acetate) supplied by SiliXan GmbH and a silane monomer.Suitable silane monomers are 3-(trimethoxysilyl)propyl methacrylate supplied under the trade names Dynasilan MEMO (Evonik), Geniosil GF31 (Momentive), KBM-503 (Shin Etsu Silicones); vinyltrimethoxysilane, Geniosil XL10 (Momentive), acryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, 3-acryloxypropyltriethoxysilane, methacryloxypropyltriisopropoxysilane, (ethylacryloxymethyl)trimethoxysilane, methacryloxymethyltriethoxysilane, 3-[tris(2-methoxyethoxy)silyl]propyl 2-methyl-2-propenoate, 4-oxo-4-[[3-(triethoxysilyl)propyl]amino]-2-butenoic acid, 2-methyl-N-[3-(triethoxysilyl)propyl]-2-propenamide, N-[3-(trimethoxysilyl)propyl]-2-propenamide, (3-acryloxypropyl)methyldimethoxysilane, 3-(diethoxymethylsilyl)propyl 2-propenoate, (dimethoxymethylsilyl)methyl ester, vinyltriethoxysilane, vinylmethyldimethoxysilane, vinyltriisopropoxysilane, vinylmethyldiethoxysilane, 1,3-divinyl-1,1,3,3-tetraethoxydisiloxane, (vinyldiethoxysilyl)benzene, 3-(trimethoxysilyl)-2-propen-1-yl 2-methyl-2-propenoate, 1,3-divinyl-1,1,3,3-tetramethoxydisiloxane, 1-vinyl-4-(trimethoxysilyl)benzene, 1-vinyl-4-(triethoxysilyl)benzene, 1-(diethoxymethylsilyl)-4-vinylbenzene, (acryloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane, 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione, (2Z)-4-oxo-4-[[3-(triethoxysilyl)propyl]amino]-2-butenoic acid, N-2-propen-1-yl-N-[3-(triethoxysilyl)propyl]-2-propen-1-amine, 4-oxo-4-[[3-(triethoxysilyl)propyl]amino]-2-butenoic acid, 4-[[3-(trimethoxysilyl)propyl]amino]butyl 2-propenoate, 9,9-diethoxy-4-oxo-3,10-dioxa-5-aza-9-siladodecan-1-yl 2-propenoate, (2Z)-4-[[3-(diethoxymethylsilyl)propyl]amino]-4-oxo-2-butenoic acid.

[0035] In another embodiment of the present invention, the compound reacting with a polyamine containing at least two primary or secondary amines and a quaternary ammonium group may be a resin having acrylate groups or acrylamide groups and capable of reacting via Michael addition. Such resins can be prepared by modifying a hydroxyl-functionalized polymer with isocyanatoethyl acrylate or by modifying a maleic anhydride copolymer with a hydroxyl-functionalized acrylate such as hydroxybutyl acrylate.

[0036] In another embodiment of the present invention, the compound reacting with a polyamine containing at least two primary or secondary amines and a quaternary ammonium group may be a copolymer of maleic anhydride. Typical anhydride monomers are maleic anhydride, but copolymers of other anhydride monomers such as itaconic anhydride or crotonic anhydride may also be used.

[0037] In another embodiment of the present invention, the compound reacting with a polyamine containing at least two primary or secondary amines and a quaternary ammonium group may be a copolymer with a monomer having an active methylene group, such as β-keto esters, β-keto amides, acid anhydrides, or 1,3-diketones, for example diacetone acrylamide or 2-(acetoacetoxy)ethyl methacrylate.

[0038] Preferably, the first polymer is crosslinked by reacting a polyamine crosslinker containing at least 2 primary amine groups or secondary amine groups and a group selected from quaternary ammonium groups and tertiary amine groups with a compound containing two functional groups capable of reacting with the crosslinker. Preferably, the polyamine crosslinker contains at least 2 primary amine groups or secondary amine groups and a quaternary ammonium group. The presence of the quaternary ammonium group ensures a permanent cationic charge independent of the pH value of the liquid in which the resin particles of the present invention are incorporated.

[0039] Preferably, the functional groups are selected from epoxides, isocyanates, β-keto esters, β-keto amides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates, and aziridines. The reaction preferably occurs at the interface formed by the lipophilic phase and the aqueous phase. In this case, the reaction is an interfacial polymerization reaction.

[0040] Preferred polyamine crosslinkers are according to Formulas I and II.

[0041]

[0042] Wherein

[0043] R1, R2, R3, R4, and R5 are independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkaryl, and substituted or unsubstituted aryl or heteroaryl

[0044] L, L1 and L2 independently represent divalent linking groups having no more than 15 carbon atoms

[0045] A represents a structural moiety containing at least two functional groups selected from primary or secondary amines, and A1 and A2 independently represent structural moieties containing at least one functional group selected from primary or secondary amines

[0046] X - is a counterion for compensating the positive charge of the quaternary ammonium group.

[0047] More preferably, the linking groups L, L1 and L2 are according to formula III, IV or V:

[0048]

[0049] wherein Q is O or NH, and R is an alkyl or substituted alkyl.

[0050]

[0051] wherein R1 = H, substituted or unsubstituted alkyl, and R2 = substituted or unsubstituted alkyl

[0052] -----CH2-R1-----

[0053] Formula V

[0054] wherein

[0055] R1 is a substituted or unsubstituted alkyl

[0056] The dashed lines in formulas III, IV and V represent the bonding of the linking groups in the structures of formulas I and II.

[0057] A preferred method for producing resin particles to be used in the pretreatment liquid according to the present invention is by interfacial polymerization (see below). Interfacial polymerization requires an oil phase to be emulsified in a continuous aqueous phase, or vice versa. Preferably, the oil phase is obtained by using an organic solvent that is substantially immiscible with water and dissolving a second polymer together with a compound containing two functional groups capable of reacting with a primary or secondary amine. The functional groups are preferably epoxides, isocyanates, β-keto esters, β-keto amides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates or aziridines.

[0058] Preferably, a polyamine containing at least two primary or secondary amines and a quaternary ammonium group is added to the aqueous phase.

[0059] After or during emulsification of the lipophilic phase in the aqueous phase, a polyamine comprising at least two primary or secondary amines, and a quaternary ammonium group can react at the interface between the lipophilic and aqueous phases with a compound comprising at least two functional groups capable of reacting with the primary or secondary amines of the crosslinking agent to form a first polymer in the resin particles. Preferably, the functional groups are epoxides, isocyanates, β-keto esters, β-keto amides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates or aziridines.

[0060] In most cases, a crosslinked polymer shell that partially or completely surrounds the dispersed phase is obtained. The resin particles of the present invention also include particles that do not have a separate dispersed phase, but have a polymer shell with a crosslinking degree gradient that is higher at the surface than inside the particle.

[0061] In a more preferred embodiment, the lipophilic phase comprises a polyisocyanate together with a second polymer, and the aqueous phase contains a cationic polyamine comprising at least two primary or secondary amines, and a quaternary ammonium group. Urea bonds are formed when these two compounds react.

[0062] By reacting a polyamine having primary and secondary amine groups with a reagent having a cationic group, except for alkylation reactions in which the secondary amine groups react faster, in most cases the primary amine groups will react first. In any case, the resulting polyamine crosslinking agent will thus have a lower reactivity towards a compound comprising at least two functional groups capable of reacting with the primary and secondary amines of the crosslinking agent in an interfacial reaction. This enables the addition of the polyamine crosslinking agent during the dispersion step without an overly rapid reaction. Since the cationic crosslinking agent also provides electrostatic stabilization to the obtained resin particles, a large amount of surfactant is not required to stabilize the particles during the preparation step. This reduces foam formation during the preparation of the particles.

[0063] It is not easy to obtain a polyamine crosslinking agent comprising at least two primary or secondary amines, and a quaternary ammonium group. Typical polyamines to be used in the preparation of a polyamine crosslinking agent comprising at least two primary or secondary amines, and a quaternary ammonium group are listed in Table 1:

[0064] Table 1: Polyamines that can be used as reagents for preparing polyamine crosslinking agents.

[0065]

[0066]

[0067] The above-mentioned polyamines can react with cationic epoxides, such as glycidyltrimethylammonium chloride, i.e., CAS No. 3033-77-0 (e.g., GMAC supplied by Sachem). Other suitable epoxides are glycidyldimethyldodecylammonium chloride, glycidyltriethylammonium chloride, glycidyldimethyloctylammonium chloride, N,N-dimethyl-N-(phenylmethyl)-oxiranemethylammonium chloride, (2,3-epoxypropyl)tris(2-hydroxyethyl)ammonium chloride, N,N-dimethyl-N-(oxiranylmethyl)-oxiranemethylammonium chloride, α,α′-[[octadecyl(oxiranylmethyl)imino]bis(2,1-ethanediyl)]bis[ω-hydroxy-poly(oxy-1,2-ethanediyl) chloride], N,N,N-trimethyl-oxiranepropylammonium bromide, N-ethyl-N,N-bis(2-hydroxyethyl)-oxiranemethylammonium chloride.

[0068] For example, the reaction of TETA with 1 equivalent of GMAC will produce a product mixture. The primary amine groups will react faster than the secondary amine groups. Preferably, GMAC is slowly added to TETA to facilitate obtaining more monofunctionalized polyamines (e.g., of formula V) than the bis(GMAC) adduct (e.g., of formula VI). The reaction of PA-1 with GMAC produces products according to formulas VI and VII.

[0069]

[0070]

[0071] After the polyamine is modified, the polyamine should still have unreacted NH or NH2 groups to be reactive towards compounds containing at least two functional groups such as epoxides, isocyanates, β-ketoesters, β-ketamides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates or aziridines.

[0072] As an alternative to the reaction with GMAC is the reaction with 3-chloro-2-hydroxypropyltrimethylammonium chloride (e.g., using Reagens 65 supplied by Sachem) (CAS No. 3327-22-8).

[0073] Compared to the reaction with GMAC, similar reaction products are formed, but there is an additional 1 equivalent of HCl, which will protonate one of the other amine groups of the polyamine. Another difference is that the alkylation with a halide (e.g., Reagens 65) is more reactive towards the secondary amine group than towards the primary amine group. However, the alkylation reaction with a reagent (e.g., Reagens 65) is more reactive towards the secondary and tertiary amine groups, and one can prepare a crosslinker with more than one quaternary amine group, for example, by reacting TREN (tris(2-aminoethyl)amine) with Reagens 65 (3-chloro-2-hydroxypropyltrimethylammonium chloride). See Formula VIII.

[0074]

[0075] The reaction of TETA with Reagens 65 gives a product according to Formula IX:

[0076]

[0077] In addition to using the epoxy-amine reaction for modifying polyamines, one can also use the Michael addition reaction. The reaction of TETA with a cationic acrylate (Q = O) or acrylamide (Q = NH) gives a product according to Formula X:

[0078]

[0079] where

[0080] Q represents O or NH

[0081] R8, R9, and R10 are substituted or unsubstituted alkyl, aryl, alkylaryl

[0082] K is a linking group.

[0083] Examples of cationic acrylamides or acrylates that can be used are listed in Table 2.

[0084] Table 2: Cationic Acrylamide / Acrylate

[0085]

[0086]

[0087] One can increase the cationic charge density of the polyamine crosslinker by modifying the polyamine with more than 1 equivalent of a cationic reagent. Another way to increase the charge density is by lowering the pH before, during, or after the preparation of the resin particle dispersion, in order to facilitate the formation of more quaternary amines due to protonation.

[0088] Instead of reacting a cationic reagent with a polyamine, one can also react a reagent having a tertiary amine group (such as those listed in Table 3).

[0089] Table 3: Acrylates and acrylamides containing a tertiary amine group

[0090]

[0091] The product (such as dimethylaminopropylacrylamide) can also be quaternized with a reagent (such as 3-chloro-2-hydroxypropyltrimethylammonium chloride) in order to obtain a product with a higher charge density: 2-hydroxy-N,N,N,N′,N′-pentamethyl-N′-[3-[(1-oxo-2-propenyl)amino]propyl]-1,3-propanediammonium dichloride (CAS No. 110226-36-3).

[0092] In addition to cationic reagents, zwitterionic reagents can also react with polyamines, such as N-(2-carboxyethyl)-N,N-dimethyl-3-[(1-oxo-2-propenyl)amino]-1-propanaminium (inner salt) (CAS No. 79704-35-1).

[0093] Another type of reaction that can be used to prepare polyamines containing at least two primary or secondary amines and quaternary ammonium groups is the imine-forming reaction of an aldehyde with a polyamine, such as using 2-(dimethylamino)acetaldehyde (CAS No. 52334-92-6); or a derivative of 2-(dimethylamino)acetaldehyde, such as the reaction product with Reagens 65.

[0094] Cationic polyamine crosslinkers can be derived from protonated tertiary amines. Polyamines having secondary and primary amines can also become cationic at low pH, but are less preferred if the pH of the sprayable liquid is 5 or higher. These can be obtained by modification of conventional polyamines such as: spermidine, diethylenetriamine, N,N′-bis(2-aminoethyl)-1,3-propanediamine, triethylenetetramine, tetraethylenepentamine, N,N′-bis(3-aminopropyl)ethylenediamine, pentaethylenehexamine, bis(hexamethylene)triamine, bis(3-aminopropyl)amine, bis(3-aminopropyl)methylamine, bis(2-aminoethyl)methylamine, tris(2-aminoethyl)amine, tris(3-aminopropyl)amine.

[0095] In order to modify the polyamines mentioned above, one can use, for example, the Michael addition reaction with the following reagents: such as N-[3-(dimethylamino)propyl]acrylamide, dimethylaminoethyl acrylate, N-[2-(dimethylamino)ethyl]acrylamide, 3-(dimethylamino)propyl acrylate.

[0096] The above-mentioned polyamines can also be modified by an epoxyamine reaction using the following reagents: for example, N,N-dimethylethanolamine and N,N-dimethyl-2-(2-aminoethyl)amine.

[0097] A.1.2. Second polymer

[0098] The second polymer in the resin particles of the pretreatment liquid according to the present invention is a polyalkylene oxide graft polymer that can be prepared by polycondensation or addition polymerization. The second polymer having a polyalkylene oxide graft is preferably selected from polyurethanes and their copolymers, acrylates and their copolymers, polyesters and their copolymers, styrenics and their copolymers, polyvinylamides and their copolymers, polyolefins and their copolymers, polyvinyl alcohol derivatives and their copolymers, polyacetals and their copolymers, polyethers and their copolymers, polyamides and their copolymers, polyimides and their copolymers, polyimines and their copolymers, polycarbonates and their copolymers, polyvinyl chlorides and their copolymers, polyvinylidene chlorides and their copolymers, polyamic acids and their copolymers, polysaccharides and their derivatives, celluloses and their derivatives, and combinations thereof. Derivatives of polysaccharides and celluloses are esters and ethers as disclosed in https: / / en.wikipedia.org / wiki / Cellulose They include cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), nitrocellulose (nitrocellulose), cellulose sulfate, methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose.

[0099] The polyalkylene oxide graft in the second polymer has a number average chain length of 20 or more alkylene oxide units. More preferably, the polyalkylene oxide graft is a polyethylene oxide graft having a number average chain length of 20 or more ethylene oxide (EO) units. Polyurethanes and polyacrylates are particularly preferred. More preferably, polyurethanes and polyacrylates, wherein the polyalkylene oxide graft is a polyethylene oxide graft having a number average chain length of 20 EO units.

[0100] In a preferred method for producing the resin particles, the second polymer is mixed with a monomer such as polyisocyanate before the high-shear treatment of the interfacial polymerization. Additionally, the second polymer should preferably be soluble in an organic solvent that forms the oil phase in the interfacial polymerization (see §A.1.4.) or should at least have a segment that is soluble or swellable in the organic solvent.

[0101] The presence of a hydrophilic segment, such as the presence of a polyalkylene oxide chain (e.g., a polyethylene oxide chain) in a graft copolymer in the second polymer, appears to further contribute to obtaining resin particles with a particle size of less than 500 nm, even less than 200 nm.

[0102] When the second polymer is polyurethane, the incorporation of the polyalkylene oxide graft can be achieved by copolymerization of a polyether diol. When the second polymer is a polyacrylate, the incorporation of the hydrophilic graft can be achieved by a graft copolymer of methacryloyl-terminated polyethylene glycol. Examples are polyethylene glycol-functionalized polyacrylate copolymers such as Byk LPG21241; or polyethylene glycol-based block copolymers that are sufficiently soluble in the organic phase (ethyl acetate). Such graft copolymers or block copolymers thus contain, in addition to the water-compatible polyether chains, segments that are insoluble in water (such as polyester, polyacrylate, polyurethane).

[0103] Suitable polyether diols in the present invention are Ymer N90 or Tegomer D 3403, i.e., α-[2,2-bis(hydroxymethyl)butyl]-ω-methoxy-poly(oxy-1,2-ethanediyl). These diols can be prepared from trimethylolpropane oxetane (TMPO). Fock, J.; 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 describes a possible synthesis procedure. In general, other polyether 1,2-diols or polyether 1,3-diols can also be used.

[0104] It has been observed that the length of the polyalkylene oxide chain incorporated into the second polymer determines the colloidal stability of the resin particles of the present invention in the pretreatment liquid formulation. Shorter polyether chains (such as for Ymer N180 or Ymer N120) are less preferred than longer polyether chains (such as for Ymer N90).

[0105] Suitable polyurethanes as the second polymer can be obtained by polymerization of a diisocyanate or polyisocyanate with a diol. Typical diisocyanates can be selected from isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 2,4,4'-trimethyl-1,6-hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI), and diphenylmethane diisocyanate (MDI).

[0106] The diol can be a low molecular weight compound, but oligomeric diols are particularly preferred. Typical oligomeric diols can be selected from polyester polyols, polyether polyols, polyamide polyols, polyacrylate polyols, polycarbonate polyols, and polyolefin polyols.

[0107] To prepare a suitable polyacrylate graft copolymer, acrylate monomers are copolymerized with a macromonomer containing a polyalkylene oxide, such as methoxypolyethylene glycol monomethacrylate (CAS registration number 26915-72-0), for example Bisomer S20W, Visiomer MPEG 2005MAW, or Visiomer MPEG 5005MAW. Other suitable macromonomers are: methoxypolyethylene glycol acrylate (CAS registration number 32171-39-4), polyethylene glycol monoacrylate (CAS registration number 26403-58-7), polyethylene glycol acrylate (CAS registration number 26915-72-0), polyethylene glycol monomethacrylate (CAS registration number 25736-86-1), polyethylene glycol maleimide (CAS registration number 58914-60-6), and N-polyethylene glycol acrylamide (CAS registration number 39839-67-3). In the case where the macromonomer is supplied in water, the water is removed, for example, by freeze drying or distillation, before the copolymerization in an organic solvent.

[0108] Suitable acrylates as the second polymer are obtained by polymerization of monomers selected from: ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl acrylate, lauryl methacrylate, cetyl acrylate, cetyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isopropyl acrylate, isopropyl methacrylate, and copolymers of acrylic or methacrylic monomers with monomers selected from: α-methylstyrene, vinyl acetate, vinyl versatate, butadiene, isoprene, acrylonitrile, methacrylonitrile, styrene, p-methylstyrene, tert-butylstyrene, butyl vinyl ether, hydroxybutyl vinyl ether, and ethylene.

[0109] The weight average molecular weight (M w ) of the second polymer is preferably between 500 g / mol and 400,000 g / mol, more preferably between 1000 g / mol and 100,000 g / mol, and most preferably between 2000 g / mol and 50,000 g / mol.

[0110] A.1.3. Resin Particle Properties

[0111] The resin particles to be used in the pretreatment liquid are preferably jet - sprayable, with an average particle size not exceeding 1 μm as determined by dynamic laser diffraction. The nozzle diameter of an ink - jet printing head is typically 20 - 35 μm. Reliable ink - jet printing is possible if the average particle size of the capsules is one - fifth of the nozzle diameter. An average particle size not exceeding 1 μm allows jet - spraying through a jet - head with a minimum nozzle diameter of 20 μm. In a more preferred embodiment, the average particle size of the capsules is one - tenth of the nozzle diameter. Thus, preferably, the average particle size is 0.05 - 1 μm. When the average particle size of the particles is less than 1 μm, excellent resolution and dispersion stability over time are obtained.

[0112] Based on the total weight of the pretreatment liquid, the amount of resin particles present in the liquid is preferably not more than 45 wt.%, and preferably between 1 wt.% and 25 wt.%. It has been observed that jet - spraying is not always reliable when it exceeds 30 wt.%.

[0113] A.1.4. Preparation of resin particles

[0114] Both chemical and physical methods can be used to prepare the resin particles in the pretreatment liquid according to the present invention. Suitable methodologies include complex coacervation, liposome formation, spray - drying, and polymerization methods.

[0115] In the present invention, polymerization methods are preferably used because they allow the highest control in designing the resin particles. More preferably, interfacial polymerization is used to prepare the resin particles of the present invention. This technique is well - known and has been reviewed by Zhang Y. and Rochefort D. (Journal of Microencapsulation, 29(7), 636 - 649(2012)) and Salitin (in Encapsulation Nanotechnologies, Vikas Mittal (editor), Chapter 5, 137 - 173

[0116] (Scrivener Publishing LLC(2013)).

[0117] In interfacial polymerization (e.g., interfacial polycondensation), two reactants meet at the interface of the emulsion droplets and react rapidly.

[0118] Generally speaking, interfacial polymerization requires an emulsion of a lipophilic phase in a continuous aqueous phase or vice versa. The lipophilic phase is preferably obtained by using an organic solvent that is substantially immiscible with water. Each phase contains at least one dissolved reagent (the first ' monomer '), which is capable of reacting with another reagent (the second ' monomer ') dissolved in the other phase to form a first polymer of resin particles. When polymerized, a first polymer is formed that is insoluble in either the aqueous phase or the lipophilic phase. As a result, the formed polymer has a tendency to precipitate at the interface between the lipophilic phase and the aqueous phase. In some cases, a partial or complete shell is formed around the dispersed phase containing the second polymer, and the shell grows during further polymerization. The particles according to the invention are preferably prepared from a lipophilic emulsion in a continuous aqueous phase.

[0119] In a preferred embodiment of the invention, interfacial polymerization is carried out and a first polymer is formed at the interface (see A.1.1.). A compound preferably containing at least two functional groups capable of reacting with a primary amine or a secondary amine or water is used. The functional group is preferably an epoxide, isocyanate, β - ketoester, β - ketoamide, acid anhydride, 1,3 - dione, chloroformate, sulfonyl chloride, acyl halide, enol ester, oxalate or aziridine, most preferably an isocyanate. The compound is preferably present in the lipophilic phase. The compound reacts with a reagent such as water or a cross - linker in the aqueous phase. The cross - linker is preferably a polyamine containing a primary amine group and a secondary amine group together with a quaternary ammonium group. A polyamine is preferred, however polyols show a much slower reaction rate. Alternatively, the polyamine cross - linker can be omitted because water can react with the isocyanate moiety and can form an amine. This in - situ formed amine can then further react with additional isocyanate moieties present in the polyisocyanate. Thus, a cross - linked first polymer can be obtained even without adding a polyamine cross - linker.

[0120] In addition, the concentration of the polyisocyanate, the added second polymer, and especially the ratio of the water - immiscible solvent phase / aqueous phase determine the size of the lipophilic droplets during high - shear treatment. The amount of isocyanate groups in the polyisocyanate, their reactivity, and the concentration of the reagent (preferably the polyamine cross - linker) in the aqueous phase determine the cross - link density of the first polymer in the resin particles.

[0121] The type of solvent for forming the lipophilic phase in interfacial polymerization is important for obtaining an industrially scalable process. Organic solvents with low boiling points that can be easily removed, such as ethyl acetate or dichloromethane, are preferably used. Preferably, the boiling point of the organic solvent is lower than that of water.

[0122] The type of polyisocyanate has a significant impact on resin particle formation. Suitable polyisocyanates can be monomeric isocyanates, biuret structures, urethiones, urethanes, isocyanurate trimers, isocyanate adducts or (partially) modified polyisocyanates.

[0123] Examples of modified polyisocyanates are hydrophilic isocyanates, such as polyether-modified polyisocyanates, such as Bayhudur 3100, Bayhydur 305, Bayhydur XP2451 / 1.

[0124] The reactivity of isocyanates depends on the structure. Aromatic isocyanates are more reactive than aliphatic isocyanates. The reactivity is further reduced by steric hindrance in the isocyanate group. The structure of the polyisocyanate will also determine the final mechanical properties of the shell. Polyisocyanates having many sp 3 hybridized carbon atoms in their structure will produce a more flexible shell than polyisocyanates having a small number of sp 3 carbon atoms.

[0125] Ionic polyisocyanates (such as Bayhydur XP2547 or Bayhydur XP2700) can also be used, but are less preferred due to reduced solubility in organic solvents such as ethyl acetate.

[0126] Optimized properties, such as dispersibility in water and reactivity with amines, can be obtained using polyisocyanates based on mixtures of monomeric isocyanates. The use of mixtures of HDI and IPDI in polyisocyanates is quite common. Polyisocyanates can be based on the following monomeric isocyanates: isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 2,4,4'-trimethyl-1,6-hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), toluene diisocyanate (TDI), xylene diisocyanate (XDI), and diphenylmethane diisocyanate (MDI).

[0127] When highly reactive reagents (water, crosslinking agents such as polyamines, etc.) are used in the aqueous phase to form the first polymer, it may be preferred to first emulsify the lipophilic phase to small droplet sizes with high shear, and thus add the crosslinking agent (such as polyamine) to the emulsion to prevent premature polymerization. When the monomer has low reactivity, the monomer can be added before the emulsification step.

[0128] Modified polyisocyanates are also suitable for preparing the resin particles of the present invention. Examples are reaction products of diisocyanates or polyisocyanates with alcohols (such as TMP = trimethylolpropane) or alcohol-terminated polymers (such as monoalkoxy-terminated polyethylene glycol).

[0129] In a particularly preferred embodiment, the first polymer consists of a polyurea or a combination thereof with a polyurethane. In a further preferred embodiment, a solvent that is substantially immiscible with water is used in the dispersion step and removed by solvent stripping before or after shell formation. In a particularly preferred embodiment, the water-immiscible solvent has a boiling point below 100 °C at atmospheric pressure. Esters and ketones are particularly preferred as the water-immiscible solvents.

[0130] A solvent that is substantially immiscible with water is an organic solvent that has low miscibility in water. Low miscibility is defined as any water-solvent combination that forms a two-phase system when mixed in a one-to-one volume ratio at 20 °C.

[0131] A preferred organic solvent is ethyl acetate because it also has a low flammability hazard compared to other organic solvents.

[0132] A preferred method for producing the resin particles as part of the pretreatment liquid according to the invention consists in preferably preparing an aqueous dispersion of the resin particles by means of interfacial polymerization. This method for preparing the dispersion of the particles according to the invention preferably comprises the following steps:

[0133] a) Preparing a second polymer according to the invention in a solvent that is substantially immiscible with water, for example to form a non-aqueous solution;

[0134] b) Adding to the non-aqueous solution of the second polymer a compound containing at least two functional groups capable of reacting with the primary and secondary amines of the crosslinking agent, the functional groups being epoxides, isocyanates, β-keto esters, β-keto amides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates or aziridines, most preferably isocyanates;

[0135] c) Preparing an aqueous solution of an emulsifier and optionally a crosslinking agent for forming the first polymer;

[0136] d) Emulsifying the non-aqueous solution in the aqueous solution at high shear or vice versa;

[0137] e) Optionally stripping the organic solvent from the mixture of the aqueous solution and the non-aqueous solution; and

[0138] f) Forming the first polymer by interfacial polymerization of the first components and thus forming a dispersion of resin particles. This occurs spontaneously or can be initiated by increasing the temperature, adding a catalyst or by UV irradiation.

[0139] The initiation of the interfacial polymerization mostly occurs spontaneously at room temperature and thus does not require initiation.

[0140] The resin particle dispersion can then be completed to a pretreatment liquid formulation by adding, for example, water, a humectant, a surfactant, a solvent, etc.

[0141] For various reasons, one or more organic solvents may be added. For example, it may be advantageous to add a small amount of an organic solvent to improve the solubility of the compound in the pretreatment liquid to be prepared, to obtain better penetration in the porous substrate or to prevent rapid drying at the nozzles of the inkjet head. Preferred water-soluble organic solvents are polyols (such as ethylene glycol, glycerol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,2,4-butanetriol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,5-pentanediol, 1,2-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol and 2-methyl-1,3-propanediol), N-hydroxyethyl-pyrrolidone, N-butyl-pyrrolidone, amines (such as ethanolamine and 2-(dimethylamino)ethanol), monohydric alcohols (such as methanol, ethanol and butanol), alkyl ethers of polyols (such as diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether), 2,2'-thiodiethanol, amides (such as N,N-dimethylformamide), heterocycles (such as 2-pyrrolidone and N-methyl-2-pyrrolidone) and acetonitrile.

[0142] A.2. Fixative

[0143] The aqueous pretreatment composition according to the invention comprises a fixative. The fixative is used to crash, precipitate or destabilize the ink colorants and thus to fix them to the substrate. This results in improved image quality (less bleeding, less coalescence).

[0144] The fixative is preferably a water-soluble polyvalent metal salt or a cationic polymer.

[0145] Polyvalent metal salts may be present in the pretreatment composition to improve the inkjet printing quality. Generally, the polyvalent metal salt can be any water-soluble polyvalent metal salt. In a specific example, the polyvalent metal salt may include calcium chloride (CaCl2), magnesium chloride (MgCl2), magnesium sulfate (MgSO4), aluminum chloride (AlCl3), calcium nitrate (Ca(NO3)2), magnesium nitrate (Mg(NO3)2), magnesium acetate (Mg(CH3COO)2), zinc acetate (Zn(CH3COO)2), calcium propionate (Ca(C2H5COO)2) or a combination thereof. In a further example, the polyvalent metal salt may comprise a metal cation selected from calcium, copper, nickel, magnesium, zinc, barium, iron, aluminum, chromium or another polyvalent metal.

[0146] Polymeric cationic polymers suitable as fixatives in pretreatment compositions contain guanidinium or fully quaternized ammonium functional groups, such as quaternized polyamine copolymers. Generally, the weight average molecular weight (Mw) of the cationic polymer is such that the viscosity at 25 °C as measured on a Brookfield viscometer is less than 25 cP. Typically, the Mw is less than 500,000 and, in one aspect, less than 50,000.

[0147] Suitable types of cationic polymers that can be used include, but are not limited to, quaternized polyamines, dicyandiamide polycations, diallyldimethylammonium chloride copolymers, quaternized dimethylaminoethyl (meth)acrylate polymers, quaternized vinylimidazole polymers, alkylguanidine polymers, alkoxylated polyethyleneimines, and mixtures thereof.

[0148] A.3. Carrier

[0149] The aqueous medium of the pretreatment liquid contains water, but may preferably contain one or more water-soluble organic solvents. Suitable solvents that can be incorporated into the pretreatment liquid are described in §A.1.

[0150] A.4. Wax

[0151] The pretreatment composition according to the present invention may contain wax. The wax can improve the durability of the ink and the pretreatment packaging during corrugation. Generally, any suitable wax can be used in the pretreatment composition. Thus, the wax can be polyethylene wax, petroleum wax, paraffin wax, carnauba wax, polypropylene wax, crystalline wax and microcrystalline wax, amide wax (oleamide, stearamide, erucamide, cyclic amide, etc.), and combinations thereof. In one aspect of the present invention, the wax can be high-density polyethylene wax. In another aspect, the wax can be micronized polypropylene wax, such as Mju:Wax 4810 available from Cerona GmbH.

[0152] Examples of polyethylene waxes include high-density polyethylene (HDPE) waxes having a density range of about 0.93 g / mL - 0.97 g / mL.

[0153] Examples of modified paraffin wax particles include paraffin waxes that have been modified (e.g., via emulsification) to improve solubility in water. The modified paraffin wax can be surface-modified, chemically-modified, etc.

[0154] Some specific examples of waxes that can be used include those of the JONCRYL Wax series (e.g., JONCRYL Wax 22, JONCRYL Wax 26, and JONCRYL Wax 120 available from BASF Corp.), those of the AQUACER series (e.g., AQUACER 498, AQUACER 501, AQUACER 505, AQUACER 513, AQUACER 530, AQUACER

[0155] 531, AQUACER 535, AQUACER 537, AQUACER 539, and AQUACER 552 available from BYK - Gardner (Columbia, Md.)), and Liquilube 404E from Lubrizol.

[0156] The wax can have i) a high melting temperature T and / or ii) a small average particle size. In one instance, the wax can have a high T, e.g., a T equal to or higher than about 100 °C. In one instance, the T of the wax can range from about 100 °C to about 150 °C. In another instance, the T of the wax can range from about 110 °C to about 135 °C. Further, the average particle size of the wax can range from 0.03 μm to 15 μm (in terms of the effective diameter, assuming that individual wax particles are not perfectly spherical). In another instance, the average particle size of the wax particles can be 0.05 μm to 10 μm, more preferably 0.09 μm to 0.50 μm (D50). If the particle size exceeds these upper limits, jetting reliability problems of the pre - coating composition may occur.

[0157] Based on the total solid weight of the pretreatment composition, the amount of wax present in the pretreatment liquid can range from 3 - 25 wt.%, more preferably 5 - 20 wt.%.

[0158] A.5. Additives

[0159] The pretreatment liquid according to the present invention may also contain a humectant. The humectant is preferably incorporated into the pretreatment liquid, especially when the liquid has to be applied by jetting techniques such as inkjet or valve jetting. The humectant prevents nozzle clogging. This prevention is attributed to the ability of the humectant to slow down the evaporation rate of the inkjet ink (especially the water in the liquid). The humectant is preferably an organic solvent with a boiling point higher than that of water. Suitable humectants include triacetin, N - methyl - 2 - pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl ureas, alkyl thioureas, dialkyl ureas, and dialkyl thioureas; diols, including ethylene glycol, propylene glycol, glycerol, butylene glycol, pentylene glycol, and hexylene glycol; dihydric alcohols, including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, tetraethylene glycol, and their mixtures and derivatives. The preferred humectant is glycerol.

[0160] Based on the total weight of the pretreatment liquid, the humectant is preferably added to the pretreatment liquid formulation in an amount of 0.1-20 wt.%.

[0161] The pretreatment liquid may contain a surfactant. Any known surfactant can be used, but preferably a diol surfactant and / or an acetylenic alcohol surfactant and / or a polysiloxane surfactant is used. The use of an acetylenic diol surfactant and / or an acetylenic alcohol surfactant and / or a polysiloxane surfactant further reduces bleeding to improve the printing quality, and also improves the drying properties in printing to allow high-speed printing.

[0162] The acetylenic diol surfactant and / or the acetylenic alcohol surfactant is preferably one or more selected from the following: 2,4,7,9-tetramethyl-5-decyn-4,7-diol, an alkylene oxide adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4-dimethyl-5-decyn-4-ol, and an alkylene oxide adduct of 2,4-dimethyl-5-decyn-4-ol. These are available from, for example, Air Products (GB) or Nissin Chemical Industry, such as Olfine (registered trademark), such as Olfine E1010, 104 series; and Surfynol (registered trademark) E series, such as 465 and Surfynol 61.

[0163] B. Liquid set containing pretreatment liquid and aqueous inkjet ink

[0164] The liquid set according to the present invention comprises a pretreatment (liquid) as described in §A and an aqueous inkjet ink comprising at least an aqueous medium and a colorant.

[0165] B.1. Aqueous inkjet ink

[0166] The aqueous inkjet ink as part of the liquid set according to the present invention comprises at least a) an aqueous medium; and b) a colorant, and the colorant is preferably a pigment. The aqueous medium of the ink contains water, but may contain one or more water-soluble organic solvents.

[0167] In a preferred embodiment of the present invention, the aqueous inkjet ink comprises a resin and / or a wax. Suitable waxes are described in §A.4.

[0168] The aqueous inkjet ink may further comprise a surfactant, a humectant, a biocide, a resin, and a thickener as additives.

[0169] B.2.1. Pigment

[0170] The pigments in the aqueous inkjet ink in the liquid set according to the present invention can be black, white, cyan, magenta, yellow, red, orange, purple, blue, green, brown, mixtures thereof, etc. The color pigments can be selected from those disclosed by HERBST, Willy et al. in Industrial Organic Pigments, Production, Properties, Applications, 3rd Edition, Wiley-VCH, 2004, ISBN 3527305769.

[0171] Suitable pigments are disclosed in paragraphs

[0128] -

[0138] of WO 2008 / 074548.

[0172] The pigment particles are dispersed in the aqueous medium using a polymeric dispersant, a surfactant, or a combination thereof. Self-dispersing pigments can be used. The latter prevent the interaction of the polymeric dispersant with the dispersing groups of the binder or capsules that may be contained in the inkjet ink (see below).

[0173] A self-dispersing pigment is a pigment having covalently bonded anionic hydrophilic groups or salt-forming groups on its surface, which allow the pigment to be dispersed in the aqueous medium without using a surfactant or a resin.

[0174] Techniques for preparing self-dispersing pigments are well known. For example, EP1220879A discloses pigments suitable for inkjet inks, which are linked to a) at least one steric group and b) at least one organic ionic group and at least one amphiphilic counterion, where the amphiphilic counterion has a charge opposite to the charge of the organic ionic group. EP906371A also discloses suitable surface-modified colored pigments having linked hydrophilic organic groups containing one or more ionic groups or ionizable groups. Suitable commercially available self-dispersing color pigments are, for example, CAB-O-JET from CABOT TM Inkjet colorant.

[0175] The pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet printing device (especially at the ejection nozzle). It is also desirable to use small particles to maximize the color intensity and slow down sedimentation.

[0176] The average pigment particle size is preferably between 0.050 μm and 1 μm, more preferably between 0.070 μm and 0.300 μm, and particularly preferably between 0.080 μm and 0.200 μm. Most preferably, the number-average pigment particle size is not greater than 0.150 μm. The average particle size of the pigment particles is measured using a Brookhaven Instruments Particle Sizer BI90plus based on the principle of dynamic light scattering.

[0177] Table 2 in

[0116] of WO 2008 / 074548 gives suitable white pigments. The white pigment is preferably a pigment having a refractive index greater than 1.60. The white pigments can be used singly or in combination. It is preferred to use titanium dioxide as the pigment having a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in

[0117] and

[0118] of WO 2008 / 074548.

[0178] Suitable polymeric dispersants are copolymers of two monomers, but they can contain three, four, five or even more monomers. The properties of the polymeric dispersant depend on both the nature of the monomers and their distribution in the polymer. The copolymeric dispersant preferably has the following polymer compositions:

[0179] ● Statistically polymerized monomers (e.g., monomers A and B polymerized into ABBAABAB);

[0180] ● Alternatingly polymerized monomers (e.g., monomers A and B polymerized into ABABABAB);

[0181] ● Gradient polymerized monomers (e.g., monomers A and B polymerized into

[0182] AAABAABBABBB);

[0183] ● Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB), where the block lengths of each block (2, 3, 4, 5 or even more) are important for the dispersing ability of the polymeric dispersant;

[0184] ● Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and

[0185] ● Mixed forms of these polymers, such as block gradient copolymers.

[0186] Suitable dispersants are DISPERBYK dispersants available from BYK CHEMIE TM dispersants, JONCRYL TM dispersants available from BASF and SOLSPERSE TM dispersants available from Lubrizol. A detailed list of non-polymeric dispersants and some polymeric dispersants is disclosed in McCutcheon. Functional Materials (North American Edition) Glen Rock, N.J.: Manufacturing Confectioner Publishing Co., 1990, pages 110 - 129.

[0187] The number average molecular weight Mn of the polymeric dispersant is preferably between 500 and 30,000, more preferably between 1,500 and 10,000.

[0188] The weight average molecular weight Mw of the polymeric dispersant is preferably less than 100,000, more preferably less than 50,000 and most preferably less than 30,000.

[0189] The pigment is preferably present in the range of 0.01 - 15% by weight, more preferably in the range of 0.05 - 10% by weight, and most preferably in the range of 0.1 - 5% by weight, each based on the total weight of the inkjet ink. For white inkjet inks, the amount of white pigment present, by weight of the inkjet ink, is preferably 3% - 40%, and more preferably 5% - 35%. An amount less than 3% by weight does not achieve sufficient coverage.

[0190] In a preferred embodiment of the present invention, the aqueous ink comprises a pigment encapsulated by a crosslinked polymeric shell. Encapsulating the pigment provides a printed image with improved physical properties with respect to a pigment dispersed by an uncrosslinked polymer, such physical properties as water resistance and dry rub resistance.

[0191] Suitable encapsulated pigments are provided by Lubrizol as Diamond HSDX - dispersions and by Fujifilm as RxD pigment dispersions (such as APD1000 and APD400 premium dispersions).

[0192] B.2.2. Carrier

[0193] The aqueous ink according to the present invention comprises water as a carrier. The aqueous carrier may further comprise one or more water - soluble organic solvents.

[0194] For various reasons, one or more organic solvents may be added. For example, it may be advantageous to add a small amount of an organic solvent to improve the dissolution of the compounds in the ink composition to be prepared or to prevent the rapid drying of the ink at the nozzles of the inkjet head. Examples of useful water - soluble organic solvents can be found in §A.1.4.

[0195] B.2.3. Resin

[0196] The inkjet ink composition according to the present invention may comprise a resin suspension. Resins are generally added to inkjet ink formulations to achieve good adhesion of the pigment to the substrate. The resin is preferably a polymer, and suitable resins can be acrylic - based resins, polyurethane resins or waxes.

[0197] With respect to the total weight of the inkjet ink according to the present invention, the concentration of resin in the ink is at least 1 wt.%, and preferably less than 30 wt.%, more preferably less than 20 wt.%.

[0198] The ink-jet ink composition according to the present invention may contain capsules. Capsules (more preferably nanocapsules) are generally incorporated into ink-jet ink formulations to encapsulate colorants (US2009227711A, JP2004075759) or to encapsulate crosslinkable reactive components. Particularly useful are the nanocapsules disclosed in WO2015158649 [0037-0110]: the nanocapsules have a polymer shell surrounding a core containing reactive chemicals. The shell material includes polyureas, polyurethanes, polyesters, polycarbonates, polyamides, melamine-based polymers, and mixtures thereof, with polyureas and polyurethanes being particularly preferred. Other particularly useful nanocapsules are disclosed in WO2016165970 [0051-0138]: the nanocapsules are self-dispersing and contain a dispersing group covalently coupled to the shell polymer. The core of the nanocapsules in WO2015158649 [0037-0110] and WO2016165970 [0051-0138] contains reactive chemicals capable of forming reaction products upon application of heat and / or light, allowing for the treatment of a wide variety of substrates. Other suitable reactive chemicals are those activated upon radiation as described in WO2015158649 [0068-0110].

[0199] Based on the total weight of the ink-jet ink, the amount of resin present in the ink is preferably not more than 30 wt.%, preferably between 5 wt.% and 25 wt.%. It has been observed that jetting is not always so reliable above 30 wt.%.

[0200] B.2.4. Additives

[0201] The ink composition may contain surfactants. Any known surfactant may be used, but preferably diol surfactants and / or acetylenic alcohol surfactants and / or polysiloxane surfactants are used. The use of acetylenic diol surfactants and / or acetylenic alcohol surfactants and / or polysiloxane surfactants improves the drying properties in printing to allow for high-speed printing.

[0202] The acetylenic diol surfactant and / or the acetylenic alcohol surfactant is preferably one or more selected from the following: 2,4,7,9 - tetramethyl - 5 - decyne - 4,7 - diol, an alkylene oxide adduct of 2,4,7,9 - tetramethyl - 5 - decyne - 4,7 - diol, 2,4 - dimethyl - 5 - decyne - 4 - ol, and an alkylene oxide adduct of 2,4 - dimethyl - 5 - decyne - 4 - ol. These are available from Nissin Chemical Industry, for example, as Olfine (registered trademark) E series, such as Olfine E1010; or as Surfynol (registered trademark), 104, Surfynol 465, and Surfynol 61 available from Evonik (formerly Air Products (GB)).

[0203] A biocide can be added to the ink composition to prevent unwanted microbial growth that may occur over time. The biocide can be used alone or in combination. Biocides suitable for the ink - jet inks of the present invention include sodium dehydroacetate, 2 - phenoxyethanol, sodium benzoate, sodium pyridinethion - 1 - oxide, ethyl p - hydroxybenzoate, and 1,2 - benzisothiazolin - 3 - one and its salts.

[0204] Preferred biocides are Proxel TM GXL and Proxel TM Ultra5, and Bronidox available from Cognis TM .

[0205] The biocide is preferably added to the aqueous medium in an amount of 0.001 - 3 wt.%, more preferably 0.01 - 1.0 wt.%, each based on the total weight of the liquid.

[0206] C. Inkjet printing method

[0207] The ink - jet recording method including the pretreatment liquid according to the present invention is suitable for preparing an image on a substrate (such as a substrate intended for packaging applications).

[0208] The substrate in the ink - jet recording method can be porous, such as textiles, paper, and leather. Porous substrates include paper, cardboard, white - lined chipboard, corrugated cardboard, packaging cardboard, folding cardboard, wood, ceramics, stone, leather, and textiles. The paper can be a single layer in a multi - layer paper.

[0209] The paper can be brown kraft paper, white top paper, or bleached paperboard. The paper can be made from chemical fibers, wood fibers, or recycled fibers. As an example, the paper can be a liner intended to be printed on a web press and converted into a corrugated box. In this regard, the liner can be used as a double-sided liner and can be directly converted in a corrugator or laminated to a double-sided liner after corrugation. The paper can also be paperboard for boxes and other packaging applications.

[0210] The pretreatment liquid according to the present invention is also used for printing on non-absorbent substrates such as polyethylene, polypropylene, polycarbonate, polyvinyl chloride; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polylactide (PLA), polymethyl methacrylate, or polyimide.

[0211] The substrate can be transparent, translucent, or opaque. Preferred opaque substrates include so-called synthetic papers such as Synaps from Agfa-Gevaert TM grade, which is an opaque polyester paper sheet with a density of 1.10 g / cm 3 or greater.

[0212] C.1. Method of applying the pretreatment liquid

[0213] The pretreatment liquid according to the present invention is suitable for treating different substrates: porous substrates and non-porous substrates. Treatment with the pretreatment liquid according to the present invention provides fixation of the colorants of the ink that is jetted onto the applied pretreatment composition to form a printed image. This fixation strongly limits bleeding, increases the sharpness of the image, provides good spreading of the inkjet ink, and increases the water resistance and solvent resistance of the printed image.

[0214] All well-known conventional methods can be used to coat or impregnate the substrate with the pretreatment composition. Examples of such methods include air knife coating, knife coating, roll coating, flexographic coating, gravure coating, and spraying. More preferably, the pretreatment composition is applied by means of a jetting technique such as inkjet technology. Then, preferably, an inkjet head or a valve jet head is used to apply the pretreatment composition.

[0215] This means of applying the pretreatment composition preferably according to the image has the following advantages: the amount of the pretreatment composition required is significantly lower than that using a coating method. This reduces the material cost and the time required to dry the applied amount of the pretreatment composition. Since the resin particles do not form a film in the inkjet head nozzles and the supply device, high jetting reliability of the pretreatment liquid is obtained.

[0216] Suitable inkjet head types for applying the pretreatment composition are piezoelectric type, continuous type, thermal print head type, Memjet type, or valve jet type.

[0217] After applying the pretreatment liquid to the substrate, it is preferred to at least partially dry the liquid and then print an image onto the treated substrate.

[0218] Before the subsequent inkjet step with ink containing a colorant, the substrate to which the pretreatment composition has been applied can be (partially) dried and optionally subjected to a heat treatment. The drying step can be carried out in air, but the heating step must be carried out by using a heat source; examples include equipment for forced air heating, radiant heating (such as IR radiation, including NIR radiation, CIR radiation, and SWIR radiation), conduction heating, high-frequency drying, and microwave drying. Examples of heat treatment include but are not limited to hot pressing, atmospheric steaming, high-pressure steaming, and THERMOFIX. Any heat source can be used for the heat treatment, for example, using an infrared lamp.

[0219] In another preferred embodiment of the present invention, the pretreatment composition is substantially undried before printing an image by means of the ejection of an aqueous inkjet step.

[0220] C.2. Inkjet & Drying

[0221] After applying the pretreatment composition to the substrate, an aqueous inkjet ink containing a colorant is applied to the substrate, preferably to the part on which the pretreatment composition has been applied. The colorant is preferably a pigment. The preferred method of applying the aqueous inkjet ink is by means of inkjet technology.

[0222] A preferred inkjet head for ejecting the pretreatment composition and the inkjet ink is a piezoelectric inkjet head. Piezoelectric inkjet ejection is based on the movement of a piezoelectric ceramic transducer when a voltage is applied to it. The application of the voltage changes the shape of the piezoelectric ceramic transducer in the print head, creating a void that is then filled with the pretreatment composition. When the voltage is removed again, the ceramic expands to its original shape, ejecting ink droplets from the inkjet head.

[0223] The ejection of the aqueous inkjet ink is not limited to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as continuous type, thermal print head type, Memjet type heads, and valve jet type.

[0224] Examples of the heat treatment for drying the inkjet ink according to the present invention are listed in §C.1. The drying step preferably results in a temperature of the printed image below 150°C.

[0225] D. Examples

[0226] D.1. Materials

[0227] Unless otherwise specified, all materials used in the following examples are readily available from standard sources such as Sigma - Aldrich (Belgium) and Acros (Belgium). The water used is deionized water.

[0228] Dynacoll 7150 is a polyester polyol containing terephthalate units and isophthalate units supplied by Evonik

[0229] Ymer N90 is a 1,3 - diol polyether from Perstorp, and each graft has an average number of 26 EO units

[0230] Ymer N120 is a 1,3 - diol polyether from Perstorp, and each graft has an average number of 20 EO units

[0231] Ymer N180 is a 1,3 - diol polyether from Perstorp, and each graft has an average number of 10 EO units

[0232] Reaxis C708 is a bismuth - based catalyst supplied by Reaxis BV

[0233] Reagens 65 is a 65% aqueous solution of 3 - chloro - 2 - hydroxypropyltrimethylammonium chloride supplied by Sachem

[0234] GMAC is a 72% solution of glycidyltrimethylammonium chloride supplied by Sachem

[0235] CROSS - 1 is a cationic cross - linker and is prepared as follows: In a 500 ml round - bottom flask, 30.417 g of tris(2 - aminoethyl)amine is diluted with 68.10 g of water. The resulting solution is cooled to 5 °C. The Reagens 65 solution is slowly added to the TREN solution over a period of 20 minutes. The reaction mixture is stirred using a magnetic stirrer during the addition. After the addition is complete, the reaction mixture is stirred at 5 °C for an additional 30 minutes and then heated to 70 °C. The reaction mixture is then heated for 24 hours and then cooled to room temperature. The prepared CROSS1 shows a solid content of 32.7 wt.% after drying at 140 °C for 45 minutes.

[0236] CROSS-2 is a cationic crosslinking agent prepared as follows: In a 120 ml reactor, 7.83 g of bis(3-aminopropyl)methylamine and 36.53 g of water were added. The amine solution was cooled to 15 °C. Then 15.6 g of Reagens 65 was slowly added within 30 minutes. The reaction mixture was continuously stirred during the 30 minutes and then the reaction mixture was heated to 70 °C and heated overnight for 24 hours. After that, the reaction mixture was cooled to room temperature and the concentration was determined (dried at 140 °C for 45 minutes). The solid content was 31.4%.

[0237] SURF1 is a reaction product of glycidyltrimethylammonium chloride and dodecylamine. This copolymerizable cationic surfactant was prepared as follows: 10.024 g of 98% dodecylamine was added to a 100 ml round-bottom flask, stirred using a magnetic stirrer, and 30 g of water was added. Then 11.433 g of GMAC was added. After stirring at room temperature for 48 hours, a clear solution was obtained. The solid content was determined by drying at 140 °C for 45 minutes, i.e., the solid content in water = 35.6%

[0238] SR552 is a methoxy-terminated polyethylene glycol monomethacrylate from Arkema, which has an average number of 11 EO units

[0239] Wako V601 is dimethyl 2,2'-azobis(isobutyrate) supplied by FujiFilm Wako Chemicals Europe GmbH

[0240] Bisomer S20W is a methoxy-terminated polyethylene glycol monomethacrylate from GEO Specialty Chemicals UK Ltd and pre-freeze-dried to remove water, and each graft has an average number of 45 EO units

[0241] Desmodur N3200 is an HDI-based polyisocyanurate supplied by Covestro

[0242] Vestanat IPDI is isophorone diisocyanate supplied by Evonik

[0243] Ultralube GA 1042 is a 35 wt.% HDPE wax dispersion from KEIM-ADDITEC SURFACE GMBH

[0244] Surfynol 104PG50 is a 50 wt.% solution of 2,4,7,9-tetramethyl-5-decyn-4,7-diol in propylene glycol from Evonik

[0245] Kauropal K933 is 100% non-ionic ethylene oxide, mono(2-propylheptyl) ether from BASF

[0246] Tego Foamex 822 is a 20% defoamer from Evonik Industries AG, which contains an emulsion of polyether siloxane copolymer in water

[0247] Proxel is available as Proxel TM K is a 5 wt.% aqueous solution of 1,2-benzisothiazolin-3-one from YDS CHEMICALS NV

[0248] Aquacer 530 is an aqueous dispersion from BYK containing 32 wt.% oxidized HDPE wax

[0249] Synperonic PE P105 is a PEO / PPO copolymer dispersant from Croda, with an average Mw of 6500 g / mol and a PPO / PEO weight ratio of approximately 1.00

[0250] HSDCX1 is a 19.7 wt.% pigment blue 15:3 dispersion encapsulated in water from Lubrizol Corporation

[0251] Mg(NO3)2.6H2O is magnesium nitrate hexahydrate from Merck Group

[0252] PD is 1,2-propanediol manufactured by Dow Chemical D.2. Measurement methods

[0253] D.2.1. Storage stability of resin particle dispersions

[0254] The freshly prepared resin particle dispersion is measured by a Malvern Zetasizer. Both the average particle size and the polydispersity index (PDI) are recorded. Subsequently, the resin particle dispersion is visually observed over a period of several days at room temperature to determine the stability of the dispersion. A stable resin particle dispersion is indicated by an optically uniform appearance of the liquid. Instability of the dispersion is indicated by visual cues such as sedimentation or creaming.

[0255] D.2.2. Image quality of images printed onto a pretreated substrate

[0256] The pretreatment liquid is applied to the coated corrugated liner XLHD MMX-Liner HD (180 g / m from MM Karton using a 4 μm spiral rod 2)Above. The coated backing paper was dried in an oven at 60 °C for 2 minutes to obtain a pretreated backing paper.

[0257] The inkjet ink was ejected onto the pretreated backing paper by means of an ImageXpert JetXpert with GIS printhead drive electronics for a FujiFilm Dimatix Samba printhead (Samba G3L), where the droplet volume was between 5.4 - 6.5 pl, at 32 °C at a voltage between 19.5 - 23.5 V, and the ejection frequency was 7.8 kHz. The printed image was dried in an oven at 60 °C for 2 minutes. The pattern of the printed matter is as shown.

[0258] The image quality of the printed matter was evaluated by visually analyzing the following three properties: 1) ink spreading; 2) ink fixation; and 3) image sharpness.

[0259] Ink spreading: The ink should completely cover the solid areas in the printed image. The lack of ink spreading is indicated by the appearance of white lines in the solid areas. It was evaluated by visually observing the solid areas and giving a score from 0 (excellent ink spreading, complete coverage) to 3 (poor ink spreading, more than 20 white lines visible in the solid areas).

[0260] Ink fixation: The ink should cover the solid areas in the printed image evenly and densely. The lack of ink fixation is indicated by the appearance of non-uniform patterns in the solid areas. Ink fixation was evaluated by visually observing the solid areas and giving a score from 0 (excellent ink fixation, uniform coverage) to 3 (poor ink fixation, strong non-uniformity observable).

[0261] Image sharpness: Fine text should be legible. The lack of image sharpness is indicated by the disappearance of the negative text. Image sharpness was evaluated by visually observing the negative text and giving a score from 0 (excellent image sharpness, 6pt clearly legible) to 3 (poor image sharpness, 16pt partially or completely covered by ink).

[0262] D.3. Preparation of the resin particle dispersion D.3.1. Preparation of the second polymer (polyurethane resin)

[0263] PU-1 solution

[0264] The PU-1 solution was prepared through the following steps. 2171 g of Dynacoll 7150 was dissolved in 2951 g of ethyl acetate at 45 °C in a 12 L double-jacketed glass reactor. 542.8 g of Ymer N90 dissolved in 856.2 g of ethyl acetate was added to the Dynacol solution. Since Ymer N90 is a wax, it was preheated at 90 °C to facilitate becoming a liquid and being more easily handled. After the Ymer was added to the ethyl acetate solution, it was allowed to cool to room temperature. A catalyst solution was prepared by diluting 20.30 g of Reaxis C708 in 182.7 g of ethyl acetate. The polyol solution was transferred to a 12 L double-jacketed glass reactor equipped with a coil condenser and an overhead stirrer. The reactor was flushed with nitrogen and a slow nitrogen flow was maintained during stirring and reaction. Subsequently, the catalyst was added dropwise via a feed funnel with a pressure equalizing arm. The oil bath was heated to 75 °C. After about 1 hour, the reaction mixture reached a constant temperature of about 68 °C. Subsequently, 275.8 g of Vestanat IPDI was added via a feed funnel with a pressure equalizing arm over 90 minutes. Then the oil bath was set at 70 °C and the reaction was allowed to proceed overnight for about 19 hours. After the reaction overnight, the oil bath was placed at 75 °C again for 30 minutes and then cooled to room temperature. The solid content was 45.21% as determined by drying at 85 °C for 2 hours.

[0265] PU-3 solution

[0266] The PU-3 solution was prepared through the following steps. 111.16 g of Dynacoll 7150 was dissolved in 200.45 g of ethyl acetate at 45 °C in a 500 ml Erlenmeyer flask. 27.79 g of Ymer N180 was added to the Dynacol solution. A catalyst solution was prepared by diluting 1.07 g of Reaxis C708 in 9.6 g of ethyl acetate. The polyol solution was transferred to a 500 ml three-necked round-bottom flask equipped with a coil condenser and an overhead stirrer. The flask was flushed with nitrogen and a slow nitrogen flow was maintained during stirring and reaction. Subsequently, the catalyst was added dropwise via a feed funnel with a pressure equalizing arm. The oil bath was heated to 75 °C. After about 1 hour, the reaction mixture reached a constant temperature of about 68 °C. Subsequently, 19.07 g of Vestanat IPDI was added via a feed funnel with a pressure equalizing arm over 110 minutes. Then the oil bath was set at 70 °C and the reaction was allowed to proceed overnight for about 19 hours. After the reaction overnight, the oil bath was placed at 75 °C again for 30 minutes and then cooled to room temperature. The solid content was 46.04% as determined by drying at 85 °C for 2 hours.

[0267] PU-4 solution

[0268] The PU-4 solution was prepared in the same manner as PU-3, but using 227.49 g of Dynacoll 7150 and 56.87 g of Ymer N120 instead of Ymer N180, which were dissolved in 402.83 g of ethyl acetate in a 1000 ml Erlenmeyer at 45 °C, and a catalyst solution prepared by diluting 2.14 g of Reaxis C708 in 19.34 g of ethyl acetate. The solid content was 43.0%.

[0269] D.3.2. Preparation of the second polymer (polyacrylic resin)

[0270] PMMA-1 solution

[0271] In a three-necked round-bottom flask, 42 g of methyl methacrylate was added, and then 59.97 g of ethyl acetate was added. In a 250 g beaker, 10.5 g of SR552 and 29.98 g of ethyl acetate were dissolved at 40 °C. The SR552 solution was added to the round-bottom flask. Then the round-bottom flask was flushed with nitrogen for 10 minutes. 2.10 g of 98% 1-dodecanethiol was added to the reaction mixture. Then 1.09 g of Wako V601 was dissolved in 4.36 g of ethyl acetate and added. The reaction mixture was heated to 68 °C and the nitrogen flush was stopped after 4 hours. The reaction mixture was stirred overnight for 16 hours and then cooled to room temperature. The obtained solid content was 42.48%. The molecular weight was measured by GPC, i.e., Mw = 14542 g / mol, and the polydispersity index was 1.31.

[0272] PMMA-3 solution

[0273] PMMA-3 was prepared in the same manner as PMMA-1, but using Bisomer S20W instead of SR552.

[0274] D.3.3. Preparation of the resin particle dispersion

[0275] CM-1

[0276] Preparation of the inventive resin particle dispersion CM-1 via interfacial polymerization. The lipophilic phase was prepared by mixing 58.51 g of ethyl acetate, 16.24 g of Desmodur N3200 and 35.92 g of PU-1 solution. The aqueous phase was prepared by mixing 4.84 g of dodecyltrimethylammonium chloride, 6.51 g of CROSS1 and 84.93 g of water. The aqueous phase was placed in a plastic bottle with a wide mouth and placed in an ice bath for 10 minutes. The organic phase was also placed in an ice bath for 10 minutes and then added. The organic phase was added to the aqueous phase. The organic phase was emulsified in the aqueous phase using an Ultraturrax device at 18000 RPM for 5 minutes. Ethyl acetate was evaporated on a rotary evaporator until the weight was 145 g. The temperature was set to 40 °C and ethyl acetate was removed under reduced pressure. Evaporation was started at a pressure of 200 mbar and the pressure was gradually reduced until 40 mbar. When too much water was evaporated, the water was compensated by adding until a total of 145 g. The round-bottom flask was placed in an oil bath at 40 °C and heated to 60 °C within 30 minutes. Then the dispersion was kept at 60 °C overnight for 16 hours and then cooled to room temperature. The resulting resin particle dispersion CM-1 had a solids content of 30.79 wt.%. The average particle size was 169.4 nm (measured by a Malvern particle size analyzer), the PDI was 0.10 and there was no measurable particle fraction with a particle size exceeding 1 μm.

[0277] CM-3

[0278] The comparative resin particle dispersion CM-3 was prepared in the same manner as CM-1, but using a lipophilic phase prepared by mixing 57.94 g of ethyl acetate, 16.50 g of Desmodur N3200 and 35.84 g of PU-3 solution, and an aqueous phase prepared by mixing 4.90 g of dodecyltrimethylammonium chloride, 3.3 g of CROSS1 and 86.06 g of water. The resulting resin particle dispersion CM-3 had a solids content of 28.03 wt.%. The average particle size was 838.40 nm (measured by a Malvern particle size analyzer), the PDI was 0.79, and there was a significant amount of particle fraction with a particle size exceeding 1 μm.

[0279] CM-4

[0280] The inventive resin particle dispersion CM-4 was prepared in the same manner as CM-1, but using a lipophilic phase prepared by mixing 57.09 g of ethyl acetate, 16.50 g of Desmodur N3200, and 36.50 g of a PU-1 solution, and an aqueous phase prepared by mixing 4.90 g of dodecyltrimethylammonium chloride, 3.44 g of CROSS2, and 85.92 g of water. The resulting resin particle dispersion CM-4 had a solids content of 27.67 wt.%. The average particle size was 159.1 nm (measured by a Malvern particle size analyzer), the PDI was 0.14, and there was no measurable particle fraction with a particle size exceeding 1 μm.

[0281] CM-6

[0282] The comparative resin particle dispersion CM-6 was prepared in the same manner as CM-1, but using a lipophilic phase prepared by mixing 57.92 g of ethyl acetate, 16.50 g of Desmodur N3200, and 35.84 g of a PU-3 solution, and an aqueous phase prepared by mixing 4.90 g of dodecyltrimethylammonium chloride, 3.55 g of CROSS2, and 85.8 g of water. The resulting resin particle dispersion CM-6 had a solids content of 26.00 wt.%. The average particle size was 880.50 nm (measured by a Malvern particle size analyzer), the PDI was 0.90, and there was a large particle fraction with a particle size exceeding 1 μm.

[0283] CM-7

[0284] The comparative resin particle dispersion CM-7 was prepared via interfacial polymerization. The lipophilic phase was prepared by mixing 60.19 g of ethyl acetate, 17.989 g of Desmodur N3200, and 41.821 g of a PU-4 solution. The aqueous phase was prepared by mixing 15.001 g of SURF-1, 3.43 g of CROSS2, and 83.82 g of water. The lipophilic ethyl acetate phase was placed in a plastic bottle with a wide mouth and placed in an ice bath and cooled for 10 minutes. The aqueous phase, which was also cooled in the ice bath during the 10 minutes, was added to the lipophilic phase. The emulsification and polymerization reaction of the aqueous phase were carried out in the same manner as described in CM-1. The resulting resin particle dispersion CM-7 had a solids content of 33.92 wt.%. The average particle size was 247.40 nm (measured by a Malvern particle size analyzer), the PDI was 0.44, and there was a large particle fraction with a particle size exceeding 1 μm.

[0285] CM-9

[0286] A comparative resin particle dispersion CM-9 was prepared in the same manner as CM-1, but using a lipophilic phase prepared by mixing 59.90 g of ethyl acetate, 16.50 g of Desmodur N3200, and 39.29 g of PMMA-1 solution, and an aqueous phase prepared by mixing 4.9 g of dodecyltrimethylammonium chloride, 6.51 g of CROSS1, and 78.31 g of water.

[0287] Before placing the round-bottom flask in an oil bath at 40 °C, it was observed that the resin particle dispersion was completely flocculated and partially settled to the bottom. A stable dispersion could not be obtained.

[0288] CM-11

[0289] An inventive resin particle dispersion CM-11 was prepared in the same manner as CM-1, but using a lipophilic phase prepared by mixing 55.07 g of ethyl acetate, 16.50 g of Desmodur N3200, and 44.12 g of PMMA-3 solution, and preparing the aqueous phase by mixing 4.90 g of dodecyltrimethylammonium chloride, 6.51 g of CROSS1, and 78.31 g of water. The resulting resin particle dispersion CM-11 had a solids content of 23.96 wt.%. The average particle size was 169.80 nm (measured by a Malvern particle size analyzer), the PDI was 0.26, and there were no measurable particles with a particle size exceeding 1 μm.

[0290] The storage stability of the obtained resin particle dispersions, evaluated as described in §D.2.1., is summarized in Table 4.

[0291] Table 4: Properties of Comparative and Inventive Resin Particle Dispersions

[0292]

[0293] As can be seen from Table 4, when the average number of EO units of the second polymer is 20 or more, the resin particle dispersion is stable. Among them, the resin particle dispersion CM-7 in which the cationic dispersion group is introduced via a copolymerizable surfactant, as described in WO2018 / 138069A, indeed shows a large fraction of particles with a particle size exceeding 1 μm.

[0294] D.4. Pretreatment Liquid and Preparation of Aqueous Inkjet Ink

[0295] D.4.1. Pretreatment Liquid

[0296] The pretreatment composition is prepared by mixing the ingredients given in Table 5. The weight percentages are based on the total weight of the pretreatment composition. The raw materials are used as supplied without any further treatment. The CM-3 resin particle dispersion and the CM-6 resin particle dispersion are not suitable for the preparation of the pretreatment liquid due to their instability.

[0297] Table 5: Composition of the inventive pretreatment liquid

[0298]

[0299]

[0300] A white opaque liquid is obtained. The pretreatment liquids are subjected to an accelerated aging test by heating them in an oven for several weeks. Both the pretreatment liquid PL 1 and the pretreatment liquid PL 3 are stable for 2 weeks at 45 °C, as demonstrated by an increase in the average particle size after aging of less than 40% compared to the fresh formulation.

[0301] Among these two pretreatment liquids, PL 1 shows the best results in the accelerated aging test by being stable for 4 weeks at 60 °C.

[0302] D.4.2. Aqueous inkjet ink

[0303] An aqueous cyan ink is prepared by diluting the wax dispersion with the other ink components according to Table 6 (each component is expressed as wt.% based on the total weight of the ink). Water is added to bring the ink to the desired pigment concentration.

[0304] Table 6: Composition of the aqueous inkjet ink

[0305] INV-INK1 Ultralube GA 1042 1.43 PD 42.0 n-butanol 2.95 Surfynol 104PG50 0.4 Proxel 0.2 HSDCX1 13.16 Deionized water To achieve 100%

[0306] D.5. Evaluation of image quality

[0307] The performance of different pretreatment compositions on the inkjet printed image, as described in §D.2.2., is listed in Table 7.

[0308] Compared to the inkjet printed image without the pretreatment liquid, the pretreatment liquid according to the present invention can improve the image quality of the image printed on the backing paper by significantly better ink spreading and ink fixation.

[0309] Table 7: Evaluation of the image quality of the printed image

[0310] Pretreatment composition Without PL PL 1 PL 3 Ink spreading 1 0 0 Ink fixation 3 0 0 Image sharpness 0 0 0

Claims

1. An aqueous pretreatment liquid for inkjet printing, comprising resin particles and a fixing agent, the resin particles having an average diameter of 1 μm or less as measured by dynamic light scattering, and comprising a first polymer and a second polymer, the first polymer being a polymer selected from the following: polyurea, polyurethane, polyamide, polyester, polycarbonate, polysulfonamide, polyacrylate, polyvinyl ether, polyvinyl ester, polyamide, polysulfonamide, melamine-based polymers, silica-based sol-gel polymers, and combinations thereof, the second polymer being a polyalkylene oxide graft polymer obtained by polycondensation or addition polymerization, the polyalkylene oxide graft having a number-average chain length of 20 or more alkylene oxide units.

2. The aqueous pretreatment liquid according to claim 1, wherein the second polymer is a polyalkylene oxide graft polymer selected from the following: polyurethane and its copolymers, acrylics and their copolymers, polyester and its copolymers, polystyrenes and their copolymers, polyvinylamide and its copolymers, polyolefins and their copolymers, polyvinyl alcohol derivatives and their copolymers, polyacetals and their copolymers, polyethers and their copolymers, polyamides and their copolymers, polyimides and their copolymers, polyimines and their copolymers, polycarbonates and their copolymers, polyvinyl chloride and its copolymers, polyvinylidene chloride and its copolymers, polyamic acid and its copolymers, polysaccharides and their derivatives, cellulose and its derivatives, and combinations thereof.

3. The aqueous pretreatment liquid according to any one of the preceding claims, wherein the second polymer is polyethylene oxide-grafted-polyurethane or polyethylene oxide-grafted-polyacrylate.

4. The aqueous pretreatment liquid according to any one of the preceding claims, wherein the first polymer is crosslinked by a crosslinking agent comprising at least two primary or secondary amines and at least one quaternary ammonium group.

5. The aqueous pretreatment liquid according to claim 4, wherein the crosslinking agent comprises two quaternary ammonium groups.

6. The pretreatment liquid according to any one of the preceding claims, further comprising a water-soluble organic solvent.

7. The pretreatment liquid according to any one of the preceding claims, further comprising wax.

8. The pretreatment composition according to any one of the preceding claims, wherein the amount of the resin particles is 1 wt.% - 45 wt.%, and the fixing agent is a polyvalent metal salt.

9. A liquid set for inkjet printing, comprising the aqueous pretreatment liquid as defined in claims 1 to 8 and an aqueous inkjet ink comprising a colorant.

10. The liquid set according to claim 9, wherein the aqueous inkjet ink comprises a water-soluble organic solvent, and the colorant is a pigment.

11. The liquid set according to claims 9 to 10, wherein the aqueous inkjet ink comprises wax.

12. The liquid set according to claims 10 to 11, wherein the pigment is at least partially encapsulated by a polymer.

13. A method for preparing resin particles having an average diameter of 1 μm or less and comprising a first polymer and a second polymer, wherein the first polymer is a polymer selected from the group consisting of: polyureas, polyurethanes, polyamides, polyesters, polycarbonates, polysulfonamides, polyacrylates, polyvinyl ethers, polyvinyl esters, polyamides, polysulfonamides, melamine-based polymers, silica-based sol-gel polymers, and combinations thereof, and the first polymer is crosslinked by a crosslinking agent comprising at least two primary or secondary amines and at least one quaternary ammonium group, and the second polymer is a polyalkylene oxide graft polymer obtained by polycondensation or addition polymerization, and the polyalkylene oxide graft has a number-average chain length of 20 or more alkylene oxide units, and the method comprises the following steps: a) preparing a first solution by dissolving the second polymer and a compound having at least two functional groups capable of reacting with primary and secondary amines in a solvent that is substantially immiscible with water; and b) preparing a second solution by dissolving an emulsifier and a crosslinking agent comprising at least two primary or secondary amines and at least one quaternary ammonium group in water; and c) emulsifying the first solution in the second solution or vice versa; and d) optionally evaporating the solvent that is substantially immiscible with water; and e) initiating the formation of the first polymer by interfacial polymerization.

14. The method for preparing resin particles according to claim 13, wherein the functional groups are epoxides, isocyanates, β-keto esters, β-keto amides, acid anhydrides, 1,3-diketones, chloroformates, sulfonyl chlorides, acyl halides, enol esters, oxalates or aziridines.

15. An inkjet printing method, comprising the following steps: a) applying a pretreatment liquid as defined in claims 1 to 8 to a substrate; and b) optionally drying at least a part of the applied pretreatment liquid so as to obtain a pretreated substrate; and c) jetting an aqueous inkjet ink containing a colorant onto the applied pretreatment liquid or the pretreated substrate; and d) applying heat to dry the jetted aqueous inkjet ink.

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