Inkjet recording method and inkjet recording device

Abstract

This inkjet recording method includes unwinding paper from a paper roll and continuously conveying the paper at a speed of 160 m / minute while recording an image by applying, heating and drying ink, cooling the image, and winding the paper up, in this sequence, wherein: the ink contains water, a pigment, a polymer dispersant having a crosslinked structure, and resin particles; and the weighted average value of the glass transition temperature of the resin particles and the polymer dispersant having the crosslinked structure is at least 15°C higher than the surface temperature T1 of the image at the time of winding.

Description

Inkjet recording method and inkjet recording apparatus

[0001] This disclosure relates to an inkjet recording method and an inkjet recording apparatus.

[0002] Various studies have been conducted on inkjet recording methods, which are image recording methods that apply ink using an inkjet method. For example, Patent Document 1 describes the following image recording method as an image recording method that can record images with excellent granularity (i.e., suppression of graininess), resolution, and scratch resistance, and with suppressed inter-color bleeding. The image recording method described in Patent Document 1 includes the steps of: applying first ink and second ink, which have different hues, in order to a recording medium transported at a transport speed of 40 m / min or more and 300 m / min or less, using an inkjet method, under the condition that the resolution in the direction perpendicular to the transport direction of the recording medium is 1200 dpi or more; and recording an image by heating and drying the applied first ink and second ink; in the image recording step, when the difference in the arrival time between the first ink and the second ink is T1 seconds, and the time from the time when the last droplet of the second ink arrives until the droplet is heated and dried is T2 seconds, T1 is 0.020 or more and 1.2 or less, and T2 is 2.0 or less; each of the first ink and the second ink contains water, an organic solvent, a surfactant, and wax particles; the organic solvent includes solvent type A which has a specific structure and a ClogP value of -0.60 or more and 2.70 or less; The image recording method comprises an acetylene-based surfactant (A), a polyoxyethylene alkyl ether-based surfactant (B) having an HLB value of 4.0 to 18.0, and a polyether-modified silicone-based surfactant (C).

[0003] Patent Document 1: International Publication No. 2023 / 171302

[0004] However, there are cases where it is necessary to further improve the ink ejection stability and image blocking resistance (i.e., the ability to suppress blocking) of inkjet recording methods. For example, in high-speed inkjet recording methods (specifically, inkjet recording methods that apply ink to paper being transported at a transport speed of 160 m / min or more; the same applies hereinafter), it is necessary to further improve the ink ejection stability from the inkjet head. Also, in high-speed inkjet recording methods, the drying time is shorter, so it is necessary to further improve the image blocking resistance (i.e., to further suppress image blocking; the same applies hereinafter).

[0005] This disclosure has been made in view of these circumstances. One embodiment of this disclosure aims to solve the problem of providing an inkjet recording method that is excellent in blocking resistance of the recorded image and ink ejection stability, and an inkjet recording apparatus for carrying out the above inkjet recording method.

[0006] This disclosure includes the following embodiments: <1> An inkjet recording method comprising: feeding paper from a roll of paper and transporting it continuously, applying ink to the continuously transported paper using an inkjet method, recording an image by heating and drying the applied ink, cooling the image, and after cooling, winding up the paper on which the image is recorded, wherein the ink contains water, pigment, a polymer dispersant having a cross-linked structure, and resin particles, the pigment content relative to the total amount of ink is 4% by mass or more, and the value X represented by the following formula (X) is 15 or more. Value X = ((Tgd × D + Tgp × P) / (D + P)) - T1 ... Equation (X) In Equation (X), Tgd is the glass transition temperature (°C) of the crosslinked polymer dispersant, D is the mass %) of the crosslinked polymer dispersant relative to the total amount of ink, Tgp is the glass transition temperature (°C) of the resin particles, P is the mass %) of the resin particles relative to the total amount of ink, and T1 is the surface temperature of the image at the time of winding (°C). <2> The inkjet recording method according to <1>, wherein the crosslinked polymer dispersant contains at least one structural unit A selected from the group consisting of structural units derived from alkyl (meth)acrylate having 12 to 24 carbon atoms in the alkyl group, structural units derived from styrene, and structural units derived from benzyl (meth)acrylate, the content of structural unit A is 30% to 70% by mass with respect to the total amount of the crosslinked polymer dispersant, and the degree of crosslinking of the crosslinked polymer dispersant is 30% or more and less than 80%. <3> The inkjet recording method according to <1> or <2>, further comprising wax particles. <4> The inkjet recording method according to any one of <1> to <3>, wherein the image is cooled by a cooling roller. <5> The inkjet recording method according to any one of <1> to <4>, wherein the tension when the paper on which the image is recorded is wound is 100N to 500N. <6> An inkjet recording method described in any one of <1> to <5>, wherein the value Y represented by the following formula (Y) is 0.05 or greater. Value Y = Value X / S1 ... Formula (Y) In formula (Y), S1 is the tension when the paper on which the image is recorded is wound, and Value X is the value X represented by formula (X).<7> The inkjet recording method according to any one of <1> to <6>, wherein the ink further contains a nonionic surfactant, and the nonionic surfactant comprises a silicone-based surfactant and an acetylene-based surfactant having an HLB value of 8 or less. <8> The inkjet recording method according to any one of <1> to <7>, wherein the ink further contains an organic solvent, and the organic solvent comprises at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, 1,2-hexanediol, diethylene glycol monoethyl ether, and diethylene glycol monoisopropyl ether, and propylene glycol. <9> The inkjet recording method according to any one of <1> to <8>, wherein the ink does not contain an organic solvent with a boiling point of 250°C or higher, or if it does contain such an organic solvent, the content of such organic solvent with a boiling point of 250°C or higher relative to the total amount of ink is 6% by mass or less. <10> The inkjet recording method according to any one of <1> to <9>, wherein the content of the organic solvent relative to the total amount of ink is 20% to 28% by mass. <11> The inkjet recording method according to any one of <1> to <10>, wherein the paper transport speed is 200 m / min or more. <12> The inkjet recording method according to any one of <1> to <11>, comprising applying a pretreatment liquid to the paper after the paper has been fed out of the roll paper and before ink has been applied to the paper. <13> The inkjet recording method according to <12>, wherein the pretreatment liquid contains water, a coagulant, and a surfactant. <14> An inkjet recording apparatus for carrying out the inkjet recording method described in any one of <1> to <13>, comprising: a feeding device for feeding paper from a roll of paper; a transport mechanism for continuously transporting the paper fed from the roll of paper; an inkjet head for applying ink to the continuously transported paper; a heating and drying device for heating and drying the applied ink; a cooling device for cooling the heated and dried ink to obtain an image; and a winding device for winding up the paper on which the image is recorded, wherein the paper transport speed is 160 m / min or more, and the value X represented by formula (X) is 15 or more.

[0007] According to one embodiment of the present disclosure, an inkjet recording method is provided that is excellent in terms of blocking resistance of the recorded image and ink ejection stability, as well as an inkjet recording apparatus for carrying out the above inkjet recording method.

[0008] This is a schematic diagram showing an example of an inkjet recording apparatus for implementing the inkjet recording method disclosed herein.

[0009] In this specification, numerical ranges indicated using "~" mean a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the value shown in the example. In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition if there are multiple substances corresponding to each component in the composition, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0010] In this specification, “image” means any film formed by applying ink, and “image recording” means the formation of an image (i.e., a film). The concept of “image” in this specification also includes solid images. In this specification, “(meth)acryloyl group” is a concept that includes both acryloyl group and methacryloyl, “(meth)acrylate” is a concept that includes both acrylate and methacrylate, and “(meth)acrylic” is a concept that includes both acrylic and methacrylic. In this specification, the term “dispersant” simply means a polymeric dispersant, and the term “solvent” simply means an organic solvent.

[0011] [Inkjet Recording Method] The inkjet recording method of this disclosure includes: feeding paper from a roll of paper and transporting it continuously, applying ink to the continuously transported paper using an inkjet method, recording an image by heating and drying the applied ink, cooling the recorded image, and after cooling, winding up the paper on which the image is recorded, wherein the ink contains water, pigment, a polymer dispersant having a cross-linked structure, and resin particles, the pigment content relative to the total amount of ink is 4% by mass or more, the paper transport speed is 160 m / min or more, and the value X represented by the following formula (X) is 15 or more.

[0012] Value X = ((Tgd × D + Tgp × P) / (D + P)) - T1 ... Equation (X) In Equation (X), Tgd is the glass transition temperature (°C) of the crosslinked polymer dispersant, D is the mass %) of the crosslinked polymer dispersant relative to the total amount of ink, Tgp is the glass transition temperature (°C) of the resin particles, P is the mass %) of the resin particles relative to the total amount of ink, and T1 is the surface temperature of the image at the time of winding (°C).

[0013] The inkjet recording method of this disclosure offers excellent blocking resistance and ink ejection stability for the recorded image.

[0014] The effect of improving the blocking resistance of images by the inkjet recording method of this disclosure (i.e., the effect of suppressing image blocking) is obtained when the value X, expressed by the above formula (X), is 15 or more. Here, "((Tgd × D + Tgp × P) / (D + P))" in formula (X) is the weighted average value of the glass transition temperature (Tg) of the cross-linked polymer dispersant (hereinafter also referred to as "cross-linked dispersant") and resin particles contained in the ink. That is, a value X of 15 or more means that the weighted average value of the glass transition temperature (Tg) is 15°C or more higher than the surface temperature of the image at the time of winding. In other words, it means that the image is cooled so that the surface temperature of the image at the time of winding is 15°C or more lower than the weighted average value of the glass transition temperature (Tg). As a result, blocking of the image after winding of the paper is suppressed (i.e., the blocking resistance of the image is improved).

[0015] The effect of improving ink ejection stability by the inkjet recording method of this disclosure is thought to be due to the improved dispersibility of the pigment as a result of the polymer dispersant in the ink having a cross-linked structure.

[0016] The inkjet recording method described herein will be explained in more detail below.

[0017] [Roll Paper] In the inkjet recording method of this disclosure, paper is fed from a roll of paper, and an image is recorded on the continuously transported paper while the fed paper is continuously transported. There are no particular restrictions on the roll paper as long as it is paper wound in a roll shape. Commercially available products may be used as the roll paper. Examples of commercially available products include the gloss coated paper "OK ​​Topcoat 104" manufactured by Oji Paper Co., Ltd.

[0018] [Paper transport speed] The inkjet recording method of this disclosure performs ink application, heating and drying, image cooling, and paper winding in this order while continuously transporting paper by feeding it from a roll. According to the inkjet recording method of this disclosure, even when high-speed image recording is performed (for example, when the paper transport speed is 160 m / min or more), the blocking resistance of the image and the ejection stability of the ink can be improved. The paper transport speed may be 160 m / min or more, or 200 m / min or more. The paper transport speed may be 260 m / min or less, or 250 m / min or less. The paper transport speed may fluctuate from the time the paper is fed out until it is wound up. In this case, the paper transport speed is the average running speed of the paper from the time the paper is fed out until it is wound up.

[0019] [Ink] In the inkjet recording method of this disclosure, ink is applied to continuously transported paper using an inkjet method, and an image is recorded by heating and drying the applied ink. The ink used in the inkjet recording method of this disclosure will be described below.

[0020] <Water> The ink of this disclosure contains water. The water content is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total amount of ink. The upper limit of the water content depends on the amounts of other components. The upper limits of the water content relative to the total amount of ink are, for example, 90% by mass and 80% by mass.

[0021] <Pigments> The inks of this disclosure contain at least one pigment.

[0022] There are no particular restrictions on the pigment, and either organic or inorganic pigments may be used. Examples of pigments include those described in publicly available literature such as "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, Japanese Patent Publication No. 2002-12607, Japanese Patent Publication No. 2002-188025, Japanese Patent Publication No. 2003-26978, Japanese Patent Publication No. 2003-342503, and Japanese Patent Publication No. 2015-193729.

[0023] Examples of pigments include polycyclic pigments such as azo lake pigments, azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments; and inorganic pigments such as titanium dioxide, iron oxide-based pigments, and carbon black-based pigments. Preferably, the pigment is an azo pigment, phthalocyanine pigment, anthraquinone pigment, quinacridone pigment, or carbon black pigment. Regarding pigments, reference may be made to known documents such as Japanese Patent Publication No. 5404669 as appropriate.

[0024] Examples of pigments from a hue perspective include cyan pigment, magenta pigment, yellow pigment, black pigment, and white pigment.

[0025] The pigment content relative to the total amount of ink is 4% by mass or more, from the viewpoint of image color density. Generally, a higher pigment content is detrimental to ink ejection stability, but the inkjet recording method of this disclosure exhibits excellent ink ejection stability despite having a pigment content of 4% by mass or more. The pigment content relative to the total amount of ink is preferably 4% by mass to 10% by mass, more preferably 4% by mass to 8% by mass.

[0026] <Polymer Dispersant> The ink of this disclosure contains at least one polymer dispersant having a crosslinked structure (hereinafter also referred to as "crosslinked dispersant").

[0027] Crosslinking dispersants have the function of dispersing pigments in ink by interacting with them (e.g., by adsorption). Specifically, for example, in ink, crosslinking dispersants are thought to adsorb to pigments (e.g., coat the pigments) and form dispersed particles.

[0028] The crosslinking dispersant has a crosslinked structure. This improves the ink ejection stability. This is thought to be because, due to the crosslinked structure of the crosslinking dispersant, the crosslinking dispersant adsorbed to the pigment (for example, coating the pigment) in the ink is less likely to detach from the pigment, resulting in improved dispersion stability of the pigment.

[0029] Furthermore, crosslinking dispersants can also contribute to improving the blocking resistance of images. This is thought to be because the crosslinking structure of the dispersant improves its glass transition temperature (Tg).

[0030] Regarding crosslinking dispersants, you can refer to the descriptions in publicly available documents, such as International Publication No. 2022 / 239625, as appropriate.

[0031] In this disclosure, "polymer" means a compound having a weight-average molecular weight (Mw) of 1000 or more. In this disclosure, "polymer" and "resin" are synonymous.

[0032] In this disclosure, weight-average molecular weight (Mw) refers to the value measured by gel permeation chromatography (GPC). The GPC measurement is performed using an HLC®-8020GPC (manufactured by Tosoh Corporation) as the measuring instrument, with three TSKgel® Super Multipore HZ-H columns (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation) and THF (tetrahydrofuran) as the eluent. The measurement is performed with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μL, and a measurement temperature of 40°C, using an RI detector. The calibration curve will be prepared from eight samples of "Standard Samples TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0033] As the resin constituting the crosslinked dispersant, acrylic resins are preferable. In the present disclosure, an acrylic resin means a resin containing at least one of a structural unit derived from (meth)acrylic acid and a structural unit derived from (meth)acrylic acid ester.

[0034] The weight average molecular weight (Mw) of the crosslinked dispersant is preferably from 3,000 to 100,000, more preferably from 4,000 to 80,000, still more preferably from 5,000 to 60,000.

[0035] It is preferable that the crosslinked dispersant contains a structural unit having an adsorptive group and a structural unit having an anionic group.

[0036] A structural unit having an anionic group is a structural unit that contributes to dispersibility. The crosslinked dispersant may contain only one type of structural unit having an anionic group, or may contain two or more types thereof. Examples of the anionic group include an acid group and salts thereof. Examples of the acid group include a carboxy group, a sulfo group, a phosphoric acid group, a phosphonic acid group, and the like, and a carboxy group is particularly preferable. As the salt of an acid group, an alkali metal salt is preferable, and a sodium salt or a potassium salt is more preferable. As the structural unit having an anionic group, at least one of a structural unit derived from (meth)acrylic acid and a structural unit derived from a salt of (meth)acrylic acid is preferable.

[0037] In the present disclosure, a structural unit derived from a compound A (e.g., (meth)acrylic acid) means a structural unit formed by polymerization of the compound A (e.g., (meth)acrylic acid).

[0038] The adsorptive group in the structural unit having an adsorptive group has a function of adsorbing to a pigment. The polymer dispersant may contain only one type of structural unit having an adsorptive group, or may contain two or more types thereof. It is preferable that the adsorptive group includes at least one selected from the group consisting of an aromatic ring structure, an alicyclic structure, and an alkyl group having 6 or more carbon atoms, and it is more preferable that the adsorptive group includes at least one selected from the group consisting of an aromatic ring structure and an alicyclic structure. The structural unit having an adsorptive group is preferably a structural unit derived from (meth)acrylate having an adsorptive group.

[0039] The crosslinked dispersant is not particularly limited as long as it is a polymer compound having at least one crosslinked structure in the molecule. The crosslinked dispersant is formed, for example, by crosslinking an uncrosslinked dispersant (i.e., an uncrosslinked polymer compound) with a crosslinking agent. Here, if necessary, the uncrosslinked dispersant may be neutralized with a neutralizing base before crosslinking with the crosslinking agent. Examples of the neutralizing base include: alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; organic amines such as dimethylethanolamine and diisopropylethylamine; and the like. The degree of neutralization (%) of the uncrosslinked dispersant after neutralization with the neutralizing base is preferably 40 to 95, more preferably 50 to 90. Furthermore, before crosslinking with a crosslinking agent, the uncrosslinked dispersant may be neutralized with a neutralizing base, then an acid is added to adjust the degree of neutralization, followed by crosslinking with the crosslinking agent. Examples of the acid include hydrochloric acid, acetic acid, citric acid, malonic acid, boric acid, maleic acid, and the like. The degree of neutralization (%) of the uncrosslinked dispersant after adjustment of the degree of neutralization with an acid is preferably 20 to 80, more preferably 30 to 70.

[0040] The uncrosslinked dispersant is preferably a water-soluble polymer compound.

[0041] In the present disclosure, "water-soluble" in "water-soluble polymer dispersant" means the property of dissolving in an amount of 1 g or more in 100 g of water at 25°C. "Water-soluble" is preferably the property of dissolving in an amount of 3 g or more (more preferably 10 g or more) in 100 g of water at 25°C.

[0042] It should be noted that even if the uncrosslinked polymer dispersant is water-soluble, the polymer dispersant having a crosslinked structure (i.e., the crosslinked dispersant) is not necessarily water-soluble.

[0043] Examples of the uncrosslinked dispersant include polyvinyl, polyurethane and polyester. Among these, the uncrosslinked dispersant is preferably polyvinyl.

[0044] The uncrosslinked dispersant is preferably a polymer compound having a functional group that can be crosslinked by the crosslinking agent. Examples of crosslinkable functional groups include carboxyl groups or their salts, isocyanate groups, and epoxy groups. Among these, from the viewpoint of improving the dispersibility of titanium dioxide particles, the crosslinkable functional group is preferably a carboxyl group or its salt, and a carboxyl group is particularly preferred. In other words, the uncrosslinked dispersant is preferably a dispersant containing a carboxyl group.

[0045] The uncrosslinked dispersant is preferably a copolymer containing structural units derived from monomers containing carboxyl groups (hereinafter referred to as "carboxyl group-containing monomers"). The copolymer may contain only one type of structural unit derived from carboxyl group-containing monomers, or two or more types. The copolymer may be a random copolymer or a block copolymer, but a random copolymer is preferred.

[0046] Examples of monomers containing a carboxyl group include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0047] The carboxyl group-containing monomer is preferably (meth)acrylic acid or β-carboxyethyl acrylate, and more preferably (meth)acrylic acid, from the viewpoint of crosslinkability and dispersibility.

[0048] The content of structural units derived from carboxyl group-containing monomers that may be contained in the uncrosslinked dispersant is preferably 5% to 70% by mass, more preferably 10% to 60% by mass, and even more preferably 20% to 50% by mass, based on the total amount of the uncrosslinked dispersant.

[0049] The uncrosslinked dispersant preferably contains structural units derived from hydrophobic monomers in addition to structural units derived from carboxyl group-containing monomers. The structural units derived from hydrophobic monomers may be one type or two or more types.

[0050] Structural units derived from hydrophobic monomers that may be included in uncrosslinked dispersants include structural units derived from ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure, and structural units derived from (meth)acrylates having an alkyl group.

[0051] In the uncrosslinked dispersant, the content of structural units derived from hydrophobic monomers is preferably 35% to 95% by mass, more preferably 50% to 95% by mass, and even more preferably 50% to 90% by mass, based on the total amount of the uncrosslinked dispersant.

[0052] Similarly, the content of structural units derived from hydrophobic monomers in the crosslinking dispersant is preferably 35% to 95% by mass, more preferably 50% to 95% by mass, and even more preferably 50% to 90% by mass, based on the total amount of the crosslinking dispersant.

[0053] The uncrosslinked dispersant and the crosslinked dispersant may each contain, as structural units derived from hydrophobic monomers, (meth)acrylate structural units having a benzene ring and (meth)acrylate structural units having an alkyl group having 10 or more carbon atoms (preferably 10 to 30).

[0054] Examples of (meth)acrylates having a benzene ring for forming a (meth)acrylate structural unit having a benzene ring include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxyethylene glycol (meth)acrylate, and phenoxy polyethylene glycol (meth)acrylate (the number of repeating units in polyethylene glycol is preferably 2 to 4, more preferably 2 to 3).

[0055] The content of (meth)acrylate constituent units having a benzene ring is preferably 10% to 60% by mass, and more preferably 10% to 40% by mass, relative to the total amount of the dispersant (i.e., uncrosslinked dispersant or crosslinked dispersant).

[0056] Examples of (meth)acrylates having an alkyl group with 10 or more carbon atoms (preferably 10 to 30 carbon atoms) for forming a (meth)acrylate structural unit having an alkyl group with 10 or more carbon atoms (preferably 10 to 30 carbon atoms) include stearyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, and the like.

[0057] The content of (meth)acrylate constituent units having an alkyl group with 10 or more carbon atoms is preferably 10% to 60% by mass, and more preferably 20% to 50% by mass, based on the total amount of the dispersant (i.e., uncrosslinked dispersant or crosslinked dispersant).

[0058] The uncrosslinked dispersant and the crosslinked dispersant may each contain structural units derived from methyl (meth)acrylate. When the uncrosslinked dispersant or the crosslinked dispersant contains structural units derived from methyl (meth)acrylate, the proportion of structural units derived from methyl (meth)acrylate in the total uncrosslinked dispersant or the crosslinked dispersant is preferably 30% by mass or less, more preferably 5% to 30% by mass, and more preferably 5% to 25% by mass.

[0059] The acid value (unit: mgKOH / g) of the uncrosslinked dispersant is preferably 100 to 350, more preferably 150 to 330, and even more preferably 150 to 300. The acid value of the crosslinked dispersant is preferably 100 to 300, more preferably 100 to 250.

[0060] The weight-average molecular weight (Mw) of the uncrosslinked dispersant is not particularly limited, but from the viewpoint of pigment dispersibility, it is preferably 3,000 to 100,000, more preferably 4,000 to 80,000, even more preferably 5,000 to 60,000, and still more preferably 10,000 to 60,000.

[0061] The preferred range for the weight-average molecular weight (Mw) of the crosslinking dispersant is the same as the preferred range for the weight-average molecular weight (Mw) of the uncrosslinking dispersant.

[0062] The crosslinking agent used when crosslinking an uncrosslinked dispersant is preferably a compound having two or more reaction sites with the uncrosslinked dispersant (for example, a polymer compound having a carboxyl group). One type of crosslinking agent may be used, or two or more types may be used.

[0063] A preferred combination of a crosslinking agent and an uncrosslinked dispersant is a compound having two or more epoxy groups (i.e., a bifunctional or more epoxy compound) and a polymer compound having a carboxyl group. In this combination, a crosslinked structure is formed by the reaction between the epoxy groups and the carboxyl groups. It is preferable that the formation of the crosslinked structure by the crosslinking agent is carried out after the pigment has been dispersed by the uncrosslinked dispersant.

[0064] Examples of bifunctional or more epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

[0065] Among these, the preferred epoxy compounds with two or more functions are polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether.

[0066] The crosslinking agent may be a commercially available product. Examples of commercially available products include Denacol EX-321, EX-821, EX-830, EX-850, and EX-851 (manufactured by Nagase ChemteX Corporation).

[0067] The molar ratio of the reaction sites in the crosslinking agent (e.g., epoxy groups) to the reaction sites in the uncrosslinked dispersant (e.g., carboxyl groups) is preferably 1:1.1 to 1:10, more preferably 1:1.1 to 1:5, and even more preferably 1:1.1 to 1:3, from the viewpoint of crosslinking reaction rate and dispersion stability after crosslinking.

[0068] From the viewpoint of further improving the ink discharge stability, the degree of crosslinking of the crosslinking dispersant is preferably 30% or more and less than 80%, more preferably 30% to 70%, and even more preferably 30% to 50%. The degree of crosslinking of the crosslinking dispersant is determined by the following formula. The degree of crosslinking is determined by NMR analysis. Degree of crosslinking (%) = (Number of acid groups that formed a crosslinked structure) / (Number of unneutralized acid groups + Number of neutralized acid groups + Number of acid groups that formed a crosslinked structure) × 100 Here, the acid groups that formed a crosslinked structure refer to the crosslinked structure derived from the acid groups formed by the reaction of the acid groups with the crosslinking agent, and the neutralized acid groups refer to the salts of the acid groups formed by the reaction of the acid groups with a neutralizing base (for example, -COONa groups).

[0069] The crosslinking dispersant contains structural unit A, which is at least one selected from the group consisting of structural units derived from alkyl (meth)acrylate having 12 to 24 carbon atoms in the alkyl group, structural units derived from styrene, and structural units derived from benzyl (meth)acrylate, from the viewpoint of further improving the ink discharge stability, and the content of structural unit A is preferably 20% to 80% by mass (more preferably 25% to 75% by mass, and even more preferably 30% to 70% by mass) of the total amount of the polymer dispersant having a crosslinking structure.

[0070] Specific examples of alkyl (meth)acrylates having an alkyl group with 12 to 24 carbon atoms can be appropriately referenced from the specific examples of (meth)acrylates having an alkyl group with 10 or more carbon atoms (preferably 10 to 30 carbon atoms) mentioned above.

[0071] From the viewpoint of further improving the ink ejection stability, it is particularly preferable that the crosslinking dispersant satisfies the aforementioned preferred degree of crosslinking within a preferred range of the content of structural unit A.

[0072] The glass transition temperature (Tgd) of the crosslinking dispersant is preferably 30°C to 130°C, more preferably 40°C to 120°C, and even more preferably 50°C to 100°C.

[0073] In this disclosure, the glass transition temperature (Tg) of the crosslinking dispersant, Tgd, and the glass transition temperature (Tg) of the resin particles described later, Tgp, are both calculated using the following formula (1): 1 / Tg = Σ(Xi / Tgi) ... Formula (1) Here, the resin to be calculated is assumed to be a copolymer of n raw material monomers from i=1 to n. Xi is the weight fraction of the i-th monomer (ΣXi=1), and Tgi is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. Σ means the sum from i=1 to n. The values ​​of the homopolymer glass transition temperature (Tgi) of each monomer are taken from the Polymer Handbook (3rd Edition) (by J. Brandrup and E.H. Immergut (Wiley-Interscience, 1989)).

[0074] The glass transition temperature (Tgd) of a crosslinking dispersant is calculated by centrifuging the ink, analyzing the copolymer composition of the crosslinking dispersant in the precipitate (i.e., pigment particles containing the pigment and crosslinking dispersant), and then weighting the Tg of the homopolymers of the raw material monomers of the crosslinking dispersant based on the obtained copolymer composition.

[0075] The mixing ratio of the pigment to the crosslinking dispersant is preferably 1:0.02 to 1:2 by mass, more preferably 1:0.03 to 1:1.5, and even more preferably 1:0.04 to 1:1.

[0076] The content of the crosslinking dispersant relative to the total amount of ink (mass%) (D in formula (X)) is preferably 0.5% to 5% by mass, more preferably 1% to 4% by mass, and even more preferably 1% to 3% by mass.

[0077] <Resin Particles> The ink in this disclosure contains at least one type of resin particle. This improves the film-forming properties and strength of the image, and improves the blocking resistance of the image (i.e., image blocking is suppressed). The resin particles contain resin and may also contain core materials other than resin, but it is preferable that the resin particles consist only of resin.

[0078] The resin particles are preferably made of acrylic resin, polyester resin, polyurethane resin, or polyolefin resin, and are more preferably made of acrylic resin.

[0079] For resin particles, you may refer to, for example, paragraphs 0038 to 0114 of International Publication No. 2021 / 192720, paragraphs 0109 to 0120 of Japanese Patent Publication No. 2015-25076, etc.

[0080] The glass transition temperature (Tg) of the resin particles, Tgp, is preferably 50°C to 150°C, more preferably 60°C to 100°C, and even more preferably 60°C to 90°C. As mentioned above, Tgp is the calculated Tg.

[0081] The glass transition temperature (Tg) of resin particles, Tgp, is calculated by centrifuging the ink, analyzing the copolymer composition of the resin particles contained in the supernatant, and then taking a weighted average of the Tg of the homopolymers of the raw material monomers of the resin particles based on the obtained copolymer composition.

[0082] The content of resin particles (by mass) relative to the total amount of ink (P in formula (X)) is preferably 0.5% to 10% by mass, more preferably 1% to 7% by mass, and even more preferably 1.5% to 5% by mass.

[0083] Furthermore, if the ink contains resin particles, the mass ratio of resin particles to wax particles is preferably in the range of 1:5 to 5:1 (solid content ratio). When the mass ratio is within this range, the scratch resistance of the image is superior.

[0084] The first ink, if it contains resin particles, may be prepared using a commercially available resin emulsion (i.e., an aqueous dispersion of resin particles). Examples of commercially available resin emulsions include A-810 (Sansui Co., Ltd.), A-995 (Sansui Co., Ltd.), Hyros-X NE-2186 (Seiko PMC Co., Ltd.), Hyros-X TE-1048 (Seiko PMC Co., Ltd.), Saibinol SK-202 (Saiden Chemical Co., Ltd.), TOCRYL W-1048 (Toyo Chem), WC-M-1217 (Arakawa Chemical), WC-M-1219 (Arakawa Chemical), N985(A)-1 (E-Tech Co., Ltd.), Neocryl A-1105 (DSM coating resin), Acrit SE-810A, Acrit SE-953A-2, Acrit SE-1658F, Acrit SE-2974F, Acrit SE-2978F (Taisei Fine Chemical), and Luxstar. Examples include 7132-C (DIC), ST200 (Nippon Shokubai), and Movinyl 972 (Japan Coating Resin Co., Ltd.).

[0085] <Organic Solvents> The inks of this disclosure preferably contain at least one organic solvent from the viewpoint of further improving the ink discharge stability. In this case, the content of the organic solvent is preferably 5% to 50% by mass, more preferably 10% to 40% by mass, even more preferably 15% to 35% by mass, and even more preferably 20% to 28% by mass, based on the total amount of ink. When the content of the organic solvent relative to the total amount of ink is 5% by mass or more, the ink discharge stability is further improved. When the content of the organic solvent relative to the total amount of ink is 50% by mass or less, the image blocking resistance is further improved.

[0086] As the organic solvent, a water-soluble organic solvent is preferred. Here, "water-soluble" in "water-soluble organic solvent" means that it dissolves in 1 g or more (preferably 3 g or more, more preferably 5 g or more) of water at 25°C.

[0087] As the organic solvent, an organic solvent with a boiling point of less than 250°C is preferred. In this disclosure, boiling point means the boiling point at 1 atmosphere (101325 Pa).

[0088] Organic solvents with a boiling point below 250°C include: alkanediols (polyhydric alcohols) such as ethylene glycol, propylene glycol (also known as 1,2-propanediol (PG)), 1,2-hexanediol (1,2-HDO), and hexylene glycol (also known as 2-methyl-2,4-pentanediol); sugar alcohols; and alkyl alcohols with 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, and isopropanol. Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether (EGmHE), ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether (DEGmEE), diethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether (DEGmiPE), ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl ether Examples include glycol ethers such as tyl-1-methoxybutanol, propylene glycol monomethyl ether (PGmME), propylene glycol monoethyl ether, propylene glycol monobutyl ether (PGmBE), propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, triethylene glycol monobutyl ether (TEGmBE), and tripropylene glycol monomethyl ether. These organic solvents with a boiling point of less than 250°C can be used individually or in combination of two or more.

[0089] From the viewpoint of further improving the ink ejection stability, the organic solvent in the ink preferably contains at least one selected from the group consisting of ethylene glycol monohexyl ether (EGmHE), propylene glycol monomethyl ether (PGmME), propylene glycol monobutyl ether (PGmBE), 1,2-hexanediol (1,2-HDO), diethylene glycol monoethyl ether (DEGmEE), and diethylene glycol monoisopropyl ether (DEGmiPE), and propylene glycol (PG). The preferred range for the total amount of these preferred organic solvents can be applied to the preferred range for the content of the organic solvents described above.

[0090] From the viewpoint of further suppressing image blocking, the ink preferably does not contain organic solvents with a boiling point of 250°C or higher, or, if it does contain such solvents, the content of organic solvents with a boiling point of 250°C or higher relative to the total amount of ink is preferably 6% by mass or less.

[0091] Examples of organic solvents with a boiling point of 250°C or higher include glycerin, diethylene glycol dibutyl ether, triethylene glycol, triethylene glycol butyl methyl ether, tripropylene glycol, tetraethylene glycol dimethyl ether, 1,2,6-hexanetriol, trimethylolpropane, and compounds represented by the following structural formula (S).

[0092]

[0093] In structural formula (S), t, u, and v each independently represent integers of 1 or greater, satisfying t + u + v = 3 to 15, and AO represents ethylene oxy (EO) or propylene oxy (PO). (AO) ｔ (AO) ｕ , and (AO) ｖ Each AO in this context may be the same or different.

[0094] The range of t + u + v is preferably 3 to 12, and more preferably 3 to 10. Propylene oxy is preferred as the AO.

[0095] A commercially available example of the compound represented by structural formula (S) is Sannix® GP250 manufactured by Sanyo Chemical Industries, Ltd.

[0096] Generally, organic solvents with a boiling point of 250°C or higher are sometimes included in the ink of sheet-fed inkjet recording methods from the viewpoint of suppressing paper curling, etc. Since the inkjet recording method of this disclosure is not a sheet-fed method but a so-called roll-to-roll method, as mentioned above, it is preferable to reduce (or not include) organic solvents with a boiling point of 250°C or higher in the ink in order to suppress image blocking after winding.

[0097] <Wax Particles> The ink of this disclosure preferably contains at least one type of wax particle from the viewpoint of further improving the blocking resistance of the image.

[0098] As the wax particles, any known wax particles can be used without particular limitation. For preferred forms of wax particles, refer to paragraphs 0154 to 0170 of Japanese Patent Application Publication No. 2011-162692.

[0099] Examples of waxes that make up wax particles include natural waxes and synthetic waxes.

[0100] Natural waxes include petroleum-based waxes, plant-based waxes, and animal / plant-based waxes. Petroleum-based waxes include paraffin wax, microcrystalline wax, and petrolatum. Plant-based waxes include carnauba wax, candelilla wax, rice wax, and wood wax. Animal / plant-based waxes include lanolin and beeswax.

[0101] Examples of synthetic waxes include synthetic hydrocarbon waxes and modified waxes. Examples of synthetic hydrocarbon waxes include polyethylene wax and Fischer-Trobusch wax. Examples of modified waxes include paraffin wax derivatives, montan wax derivatives, microcrystalline wax derivatives, and derivatives thereof.

[0102] From the viewpoint of further improving the image blocking resistance, the wax particles preferably contain at least one selected from the group consisting of paraffin wax, polyethylene wax, and carnauba wax, and more preferably contain polyethylene wax.

[0103] Examples of commercially available wax particles include: Cellosol 524, Trasol CN, Trasol PF60, Polylon L-787, Polylon P-502 (all manufactured by Chukyo Oils Co., Ltd.); Hi-Tec E6314 (manufactured by Toho Chemical Industry Co., Ltd.); ITOHWAX E-210 (manufactured by Ito Oil Co., Ltd.); Nopcoat PEM17 (manufactured by Sunnopco Corporation); AQUACER 515, AQUACER 1039 (both manufactured by BYK Corporation); and others. Ester A described in paragraph 0254 of Japanese Patent Publication No. 2011-162692 can also be used as a wax particle.

[0104] If the ink of this disclosure contains wax particles, the content of wax particles relative to the total amount of ink is preferably 0.01% to 20% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.5% to 5% by mass.

[0105] <Surfactants> The inks of this disclosure may contain at least one surfactant. Nonionic surfactants are preferred as the surfactant.

[0106] From the viewpoint of further improving image blocking resistance, the nonionic surfactant preferably includes an acetylene-based surfactant (preferably an acetylene-based surfactant with an HLB value of 8 or less) and a silicone-based surfactant.

[0107] (Acetylene-based surfactants) As acetylene-based surfactants, compounds represented by the following formula (A1) are preferred.

[0108]

[0109] In formula (A1), R １ and R ４ Each of these independently represents an alkyl group having 3 to 10 carbon atoms, R ２ and R３ Each of these independently represents either a methyl group or an ethyl group. a, b, c, and d represent the average number of moles added for each unit, ranging from 0 to 50.

[0110] Suitable examples of acetylene-based surfactants include, for example: acetylene glycol selected from the group consisting of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 2,5,6,11-tetramethyl-6-dodecine-5,8-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecine-5,8-diol; and ethylene oxide adducts of the above acetylene glycols. Acetylene-based surfactants can be synthesized, for example, by reacting acetylene with a ketone or aldehyde corresponding to the desired acetylene glycol. Acetylene-based surfactants can be obtained, for example, by the methods described on pages 94-107 of "New Introduction to Surfactants" (Revised Edition) by Takehiko Fujimoto (published by Sanyo Chemical Industries, Ltd., 1992).

[0111] The acetylene-based surfactant preferably includes an acetylene-based surfactant having an HLB value of 9 or less (preferably 8 or less). The lower limit of the HLB value of the acetylene-based surfactant is preferably 3.

[0112] As the acetylene-based surfactant, a commercially available product may be used. Examples of commercially available acetylene-based surfactants include acetylene-based surfactants manufactured by Nissin Chemical Industry. Examples of the acetylene-based surfactants manufactured by Nissin Chemical Industry include Surfynol 104 (HLB value: 4.0), Surfynol 420 (HLB value: 4.0), Surfynol 440 (HLB value: 8.0), Surfynol SE (HLB value: 6.0), Surfynol SE-F (HLB value: 6.0), Surfynol 61 (HLB value: 6.0), Surfynol 82 (HLB value: 4.0), Surfynol DF110D (HLB value: 3.0), Dynol 604 (HLB value: 8.0), Dynol 607 (HLB value: 8.0), Surfynol 2502 (HLB value: 8.0), Surfynol TG (HLB value: 9.0), Olfine E1004 (HLB value: 7.0 to 9.0), Olfine E1010 (HLB value: 13.5), and the like.

[0113] The content of the acetylene-based surfactant (for example, an acetylene-based surfactant having an HLB value of 8 or less) relative to the total mass of the ink is preferably 0.05% by mass to 2.5% by mass, more preferably 0.1% by mass to 2.0% by mass, and still more preferably 0.2% by mass to 1.5% by mass, from the viewpoint of improving the blocking resistance of an image.

[0114] (Silicone-based Surfactant) As the silicone-based surfactant, a compound represented by the following formula (C1) is preferable.

[0115]

[0116] In formula (C1), R １ each independently represents an alkyl group having 1 to 3 carbon atoms or a hydroxy group, R ２ represents an alkanediyl group having 2 to 5 carbon atoms, R ３ represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a hydroxy group, PO represents a propyleneoxy group, and EO represents an ethyleneoxy group. a, b, m and n each represent the average number of added moles of each unit, a is 0 to 10, b is 1 to 50, m is 1 to 500, and n is 1 to 50.

[0117] In formula (C1), the arrangement of PO and EO may be a block copolymer arrangement or a random copolymer arrangement. In formula (C1), the arrangement of the structural unit denoted by the subscript m and the structural unit denoted by the subscript n may be a block copolymer arrangement or a random copolymer arrangement.

[0118] R １ R is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. ２ It is preferably an alkanediyl group having 3 or 4 carbon atoms, and more preferably a trimethylene group. ３ It is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.

[0119] It is more preferable that a is 0, b is 1 to 15, m is 1 to 10, and n is 1 to 5. Furthermore, it is even more preferable that a is 0, b is 3 to 10, m is 1 to 3, and n is 1 to 3.

[0120] Commercially available silicone-based surfactants may be used. Examples of commercially available silicone-based surfactants include BYK-302, BYK-307, BYK-331, BYK-333, BYK-345, BYK-347, BYK-348, BYK-349, BYK-378, BYK-3400, BYK-3450, BYK-3451, BYK-3455, and BYK-3760 (all manufactured by BYK Corporation). Examples include KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-644, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020 (all manufactured by Evonik), etc.

[0121] The content of the silicone-based surfactant relative to the total amount of ink is preferably 0.01% to 2.0% by mass, and more preferably 0.01% to 1.0% by mass.

[0122] (Polyoxyethylene alkyl ether) From the viewpoint of further improving the image blocking resistance, it is preferable that the nonionic surfactant further contains a polyoxyethylene alkyl ether.

[0123] As the polyoxyethylene alkyl ether, the compound represented by the following formula (B1) is preferred.

[0124]

[0125] In formula (B1), R １ represents a hydrocarbon group, and a represents an integer from 1 to 60.

[0126] R in equation (B1) １ The hydrocarbon group represented by may be either a straight chain or a branched chain. In formula (B1) R １ The number of carbon atoms in the hydrocarbon group represented is preferably 6 to 24, and more preferably 10 to 20.

[0127] A commercially available surfactant (B) may be used. Examples of commercially available surfactants (B) include: Emulgen 102KG, Emulgen 103, Emulgen 104P, Emulgen 105, Emulgen 106, Emulgen 108, Emulgen 109P, Emulgen 1108, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 210P, Emulgen 220, Emulgen 306P, Emulgen 320P, Emulgen 350, Emulgen 404, Emulgen 408, Emulgen 409P, Emulgen 420, Emulgen 430, Emulgen 705, Emulgen 707, Emulgen 709, Emulgen 1118S-70 (all manufactured by Kao Corporation); Naroacty ID-40, Naroacty ID-60, Naroacty ID-70, Naroacty CL-40, Naroacty CL-50, Naroacty CL-70, Naroacty CL-85, Naroacty CL-95, Naroacty CL-100, Naroacty CL-120, Naroacty CL-140, Naroacty CL-160, Naroacty CL-200, Sunnonic DE-70, Sunnonic FN-80, Sunnonic FN-100, Sunnonic FN-140, Sunnonic SS-30, Sunnonic SS-50, Sunnonic SS-70, Sunnonic SS-90, Sunnonic SS-120, Sedran FF-180, Sedran FF-200, Sedran FF -210, Cedran FF-220, Cedran SF-506, Emarumin FL-80, Emarumin FL-100, Emarumin HL-100, Emarumin NL-70, Emarumin NL-80, Emarumin NL-90, Emarumin NL-100, Emarumin NL-110, Emarumin 40S, Emarumin 40, Emarumin 50, Emarumin 60, Emarumin Examples include Emulmin 70, Emulmin 110, Emulmin 140, Emulmin 180, Emulmin 200, Emulmin 240, Emulmin CC-100, Emulmin CC-130, Emulmin CC-150, Emulmin CC-200, Emulmin CC-290, Emulmin CO-50, Emulmin CO-100, Emulmin CO-200 (all manufactured by Sanyo Chemical Industries, Ltd.); and others.

[0128] As the polyoxyethylene alkyl ether, a polyoxyethylene alkyl ether with an HLB value of 4 to 18 is preferred.

[0129] The polyoxyethylene alkyl ether content relative to the total amount of ink is preferably 0.01% to 2.0% by mass, more preferably 0.01% to 1.0% by mass.

[0130] <Inorganic Silicon Compounds> The inks of this disclosure may contain at least one inorganic silicon compound, preferably colloidal silica or an alkali metal silicate, and more preferably colloidal silica, from the viewpoint of further improving the ejection stability of the ink.

[0131] Colloidal silica is preferably a colloid consisting of fine particles of an inorganic oxide containing silicon with an average particle size of several hundred nm or less. Colloidal silica contains silicon dioxide (including its hydrate) as the main component and may also contain aluminates (such as sodium aluminate and potassium aluminate) as minor components. Colloidal silica may also contain inorganic salts such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonium hydroxide, as well as organic salts such as tetramethylammonium hydroxide. These inorganic and organic salts act, for example, as colloidal stabilizers. For more information on colloidal silica, refer to paragraphs 0043 to 0050 of Japanese Patent Application Publication No. 2011-202117 as appropriate. Furthermore, the ink of this disclosure may, if necessary, contain alkali metal silicates in place of colloidal silica, or in addition to colloidal silica. For alkali metal silicates, refer to paragraphs 0052 to 0056 of Japanese Patent Publication No. 2011-202117 as appropriate.

[0132] If the ink of this disclosure contains colloidal silica, the colloidal silica content is preferably 0.0001% to 10% by mass, more preferably 0.01% to 3% by mass, even more preferably 0.02% to 0.5% by mass, and particularly preferably 0.03% to 0.3% by mass, based on the total amount of ink.

[0133] <Urea> The ink of this disclosure may contain urea from the viewpoint of further improving the ink ejection stability. Because urea has high moisturizing properties, it effectively suppresses the drying or solidification of the ink as a solid wetting agent.

[0134] The urea content in the ink of this disclosure is preferably 0.1% to 10% by mass, more preferably 0.2% to 5% by mass, and even more preferably 0.3% to 3% by mass.

[0135] <Other Components> The inks of this disclosure may contain other components besides those described above, as necessary. Examples of other components include inorganic salts, anti-fading agents, emulsifying stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, fungicides, pH adjusters, defoamers, viscosity modifiers, dispersion stabilizers, rust inhibitors, chelating agents, water-soluble polymer compounds, and the like.

[0136] <Physical Properties of Ink> -Dynamic Surface Tension- From the viewpoint of further improving the image blocking resistance, the dynamic surface tension of the ink disclosed herein is preferably 26 mN / m to 37 mN / m, more preferably 26 mN / m to 33 mN / m, at 20 ms.

[0137] The dynamic surface tension at 20 ms is close to the dynamic surface tension at the moment the ink droplet lands on the substrate. In this disclosure, the dynamic surface tension at 20 ms refers to the value measured using a bubble pressure type dynamic surface tension meter. In the embodiments described later, KRUSS's "BD100" is used as the bubble pressure type dynamic surface tension meter.

[0138] -Static Surface Tension- The ink of this disclosure preferably has a static surface tension of 23 mN / m to 30 mN / m, from the viewpoint of further improving the image blocking resistance.

[0139] In the ink of this disclosure, from the viewpoint of further improving the image blocking resistance, it is particularly preferable that the static surface tension is 23 mN / m to 30 mN / m and the dynamic surface tension at 20 ms is 26 mN / m to 33 mN / m.

[0140] - Viscosity - The viscosity of the ink is preferably 1.2 mPa·s to 15.0 mPa·s, more preferably 2.0 mPa·s to 13.0 mPa·s, and even more preferably 2.5 mPa·s to 10.0 mPa·s. The viscosity of the ink is measured at a temperature of 30°C using a rotational viscometer, for example, a product named "VISCOMETER TV-22" manufactured by Toki Sangyo Co., Ltd.

[0141] -pH- The pH of the ink is preferably 6.0 to 11.0, more preferably 7.0 to 10.0, and even more preferably 7.0 to 9.5, from the viewpoint of the storage stability of the ink. The pH of the ink is measured at a temperature of 25°C using a pH meter, for example, a product named "WM-50EG" manufactured by Toa DKK Co., Ltd.

[0142] [Ink Application] In the inkjet recording method of this disclosure, the aforementioned ink is applied to the continuously transported paper using an inkjet method. Ink application by the inkjet method is performed by ejecting ink from an inkjet head.

[0143] Examples of inkjet methods include charge control methods that use electrostatic attraction to eject ink, drop-on-demand methods (pressure pulse methods) that use the vibration pressure of a piezoelectric element, acoustic inkjet methods that convert electrical signals into acoustic beams and irradiate ink to eject ink using radiation pressure, and thermal inkjet (BubbleJet®) methods that heat ink to form bubbles and utilize the resulting pressure.

[0144] For use in an inkjet printing system, a line head is preferred, in which recording elements are arranged to cover the entire area of ​​one side of the substrate.

[0145] In inkjet systems using line heads, patterns can be formed across the entire surface of the substrate by scanning it in a direction intersecting the arrangement direction of the recording elements, eliminating the need for transport systems such as carriages that scan short heads. Furthermore, in inkjet systems using line heads, complex scanning control between carriage movement and substrate is unnecessary, and only the substrate moves, resulting in faster recording speeds compared to shuttle systems that scan short heads.

[0146] The amount of ink droplets ejected from the inkjet head is preferably 1 pL (picoliters) to 100 pL, more preferably 1.5 pL to 80 pL, and even more preferably 1.8 pL to 50 pL.

[0147] Ink ejection is preferably performed using an inkjet head having a resolution of 300 dpi or higher (more preferably 600 dpi or higher, and even more preferably 800 dpi or higher). Here, dpi is an abbreviation for dots per inch, and 1 inch is equal to 2.54 cm.

[0148] In the inkjet recording method of this disclosure, multiple inks may be applied to continuously transported paper using an inkjet method. In this case, at least one of the multiple inks is the ink described above in this disclosure. Examples of the multiple inks include two or more selected from the group consisting of cyan ink, magenta ink, yellow ink, black ink, and white ink.

[0149] As an example of the order in which multiple inks are applied, one example is to alternately apply ink with a high pigment content relative to the total ink volume and ink with a low pigment content relative to the total ink volume. This reduces blocking and graininess (i.e., roughness) in images of third-order or higher colors recorded with three or more inks. In detail, by alternately applying ink with a high pigment content relative to the total ink volume and ink with a low pigment content relative to the total ink volume, the impact interference between the ink applied first and the ink applied later is reduced, reducing dot movement due to this impact interference, and as a result, the phenomenon of locally high ink volume is suppressed, and as a result, blocking and graininess in images of third-order or higher colors are reduced. As a more specific example of the application order, one could apply the following in this order: the first ink with a high pigment content relative to the total ink volume (e.g., 6% by mass or more), the second ink with a low pigment content relative to the total ink volume (e.g., 4% by mass or more but less than 6% by mass), the third ink with a high pigment content relative to the total ink volume (e.g., 5.5% by mass or more), and the fourth ink with a low pigment content relative to the total ink volume (e.g., 5% by mass or more but less than 5.5% by mass).

[0150] [Heat Drying] In the inkjet recording method of this disclosure, an image is recorded by heat drying the ink applied to paper that is being continuously transported. The heat drying temperature is preferably 80°C to 200°C, more preferably 100°C to 170°C, and even more preferably 120°C to 140°C. The heat drying time is preferably 0.3 seconds to 6.0 seconds, more preferably 0.5 seconds to 3.0 seconds, and even more preferably 0.5 seconds to 2.5 seconds.

[0151] The heating means for heating and drying are not particularly limited. Examples of heating means include a heat drum, hot air, infrared lamp, hot oven, hot plate, etc. Two or more of these heating means may be used in combination.

[0152] [Cooling] In the inkjet recording method of this disclosure, the image recorded as described above is cooled. Cooling is performed so that the value X is 15 or more (i.e., so that the surface temperature T1 of the image at the time of winding is 15°C or more lower than the weighted average value of the Tg of the crosslinking dispersant and resin particles). This suppresses blocking of the image after the paper is wound.

[0153] The cooling means for cooling the image are not particularly limited. Examples of cooling means include cooling rollers, cooling air blowers, etc. Two or more of these cooling means may be used in combination.

[0154] The cooling means preferably includes a cooling roller. In this case, the image is cooled by bringing the image recording surface and / or non-image recording surface of the paper into contact with the cooling roller. This efficiently reduces the surface temperature T1 of the image during winding, making it easy to adjust the value X to 15 or higher.

[0155] The surface temperature T1 of the image during winding is preferably 15°C to 50°C, more preferably 20°C to 50°C, and even more preferably 25°C to 40°C.

[0156] The surface temperature T1 of the image during winding is measured by a non-contact thermometer at a position downstream of the image cooling unit 22 and within 500 mm of the winding section.

[0157] [Winding] In the inkjet recording method of this disclosure, after the image has cooled, the paper on which the image is recorded is wound up. Winding can be performed using a conventional winding device in a conventional roll-to-roll system.

[0158] [Tension during winding (Tension S1)] In the inkjet recording method of this disclosure, the tension (hereinafter also referred to as tension S1) during winding of the paper on which the image is recorded is preferably 100N to 600N, more preferably 100N to 550N, and even more preferably 100N to 500N. When tension S1 is 600N or less, image blocking is further suppressed.

[0159] The tension S1 may be adjusted by adjusting the paper winding speed, by providing a tension adjustment device within the apparatus and adjusting it using the tension adjustment device, or by a combination of these methods. The tension adjustment device can be installed, for example, between a cooling unit that cools the image and a winding unit that winds the paper. An example of a tension adjustment device is a dancer roller.

[0160] [Value (X)] In the inkjet recording method of this disclosure, the value (X) represented by formula (X) is 15 or greater, as described above. This suppresses image blocking.

[0161] Value X = ((Tgd × D + Tgp × P) / (D + P)) - T1 ... Equation (X) In Equation (X), Tgd is the glass transition temperature (°C) of the crosslinked polymer dispersant, D is the mass %) of the crosslinked polymer dispersant relative to the total amount of ink, Tgp is the glass transition temperature (°C) of the resin particles, P is the mass %) of the resin particles relative to the total amount of ink, and T1 is the surface temperature of the image at the time of winding (°C).

[0162] The preferred ranges for Tgd, Tgp, D, P, and T1 in equation (X) are as described above.

[0163] In equation (X), "((Tgd × D + Tgp × P) / (D + P))" is the weighted average value of the glass transition temperatures (Tg) of the crosslinking dispersant and resin particles contained in the ink.

[0164] From the viewpoint of further suppressing image blocking, the value (X) is preferably 18 or higher, more preferably 20 or higher, even more preferably 24 or higher, and even more preferably 30 or higher. There is no particular upper limit to the value (X), but examples of upper limits include 60 and 55.

[0165] [Value (Y)] In the inkjet recording method of this disclosure, from the viewpoint of further suppressing image blocking, it is preferable that the value (Y) represented by the following formula (Y) is 0.05 or more.

[0166] Value Y = Value X / Tension S1 ... Equation (Y) In Equation (Y), S1 is the tension when the paper on which the image is recorded is wound up, and Value X is the value X expressed by Equation (X).

[0167] The preferred ranges for the value X and tension S1 in equation (Y) are as described above.

[0168] From the viewpoint of further suppressing image blocking, the value (Y) is preferably 0.06 or higher, more preferably 0.08 or higher, and even more preferably 0.10 or higher. There is no particular upper limit to the value (Y), but examples of upper limits include 0.25 and 0.20.

[0169] [Application of pre-treatment solution] The inkjet recording method of this disclosure may include applying a pre-treatment solution to the paper after the paper has been fed from the roll and before ink has been applied to the paper. This further improves the resolution of the image.

[0170] The pretreatment solution preferably contains water, a flocculant, and a surfactant.

[0171] For pretreatment solutions containing water, a coagulant, and a surfactant, refer to publicly available documents such as International Publication No. 2019 / 004485 and International Publication No. 2019 / 163581 as appropriate.

[0172] The flocculant contained in the pretreatment solution is preferably at least one selected from the group consisting of polyvalent metal compounds, organic acids, metal complexes, and cationic polymers, and more preferably contains an organic acid.

[0173] Examples of surfactants contained in the pretreatment solution include nonionic surfactants similar to those found in the ink mentioned above.

[0174] The pretreatment solution can be applied using known application methods such as coating, inkjet recording, or immersion. Examples of coating methods include known coating methods using bar coaters, extrusion die coaters, air doctor coaters, blade coaters, rod coaters, knife coaters, squeeze coaters, and reverse roll coaters.

[0175] [Inkjet Recording Apparatus] The inkjet recording method of this disclosure can be carried out, for example, using the following inkjet recording apparatus A. Inkjet recording apparatus A comprises: a feeding device for feeding paper from a roll of paper; a transport mechanism for continuously transporting the paper fed from the roll of paper; an inkjet head for applying ink to the continuously transported paper; a heating and drying device for heating and drying the applied ink; a cooling device for cooling the heated and dried ink to obtain an image; and a winding device for winding up the paper on which the image is recorded. The paper transport speed is 160 m / min or more, and the value X represented by formula (X) is 15 or more.

[0176] The inkjet recording device A may also include other elements such as a device for adjusting the tension of the paper, a device for applying a pretreatment solution, etc.

[0177] A specific example of inkjet recording device A is an inkjet recording device for continuous form paper, which is an example of roll paper. For information on inkjet recording devices for continuous form paper, refer to prior art such as Japanese Patent Application Publication No. 2019-59804 (e.g., paragraphs 0085 to 0104).

[0178] The following describes a specific example of an inkjet recording device A, specifically an inkjet recording device for continuous paper, with reference to the drawings.

[0179] In the drawings and descriptions herein, substantially identical elements (e.g., parts or components) may be denoted by the same reference numeral, and redundant descriptions may be omitted.

[0180] Figure 1 is a conceptual diagram of an inkjet recording device 10, which is an example of an inkjet recording device A. As shown in Figure 1, the inkjet recording device 10 is a recording device equipped with an inkjet head 122 that ejects ink onto paper P fed from a roll of paper 14B. The inkjet recording device 10 records an image by ejecting ink onto paper P.

[0181] Specifically, the inkjet recording device 10 includes, for example, an image recording unit 12 that records an image on paper P unwound from a roll of paper 14B. The inkjet recording device 10 also includes a supply unit 14 that unwounds paper P from the roll of paper 14B and supplies it to the image recording unit 12, and a buffer unit 16 that adjusts the transport speed of the paper P supplied from the supply unit 14 to the image recording unit 12. The buffer unit 16 is located between the image recording unit 12 and the supply unit 14. The inkjet recording device 10 also includes, for example, a winding unit 18 that winds up the paper P discharged from the image recording unit 12, and a buffer unit 20 that adjusts the transport speed of the paper P discharged from the image recording unit 12 to the winding unit 18. The buffer unit 20 is located between the image recording unit 12 and the winding unit 18. The inkjet recording device 10 also includes a cooling unit 22 located between the image recording unit 12 and the buffer unit 20 that cools the paper P discharged from the image recording unit 12.

[0182] The image recording unit 12 includes, for example, a roll member (not shown) that guides the paper P along the transport path 124 of the paper P, and an inkjet head 122 that records an image by ejecting ink (ink droplets) onto the paper P being transported along the transport path 124 of the paper P. The inkjet head 122 is, for example, a long recording head in which the effective recording area (the area where the nozzles for ejecting ink are arranged) is greater than or equal to the width of the paper P (the length in the direction intersecting (e.g., perpendicular to) the transport direction of the paper P).

[0183] The inkjet head 122 may be a so-called thermal type that ejects ink droplets by heat, or a so-called piezo type that ejects ink droplets by pressure, and known types are used. The inkjet head 122 includes, for example, an inkjet head 122K that ejects ink onto paper P to record a K (black) color image, an inkjet head 122C that records a C (cyan) color image, an inkjet head 122M that records an M (magenta) color image, and an inkjet head 122Y that records a Y (yellow) color image. The inkjet heads 122K, 122C, 122M, and 122Y are arranged in this order along the transport direction of paper P (hereinafter also simply referred to as the "transport direction") from upstream to downstream, facing the paper P.

[0184] The inkjet heads 122K, 122C, 122M, and 122Y are connected to the respective color ink cartridges 123K, 123C, 123M, and 123Y, which are attached to and detached from the inkjet recording device 10, via supply pipes (not shown), and the ink cartridges 123 supply ink of each color to the respective inkjet heads 122.

[0185] The inkjet head 122 is not limited to a configuration in which four inkjet heads 122 corresponding to each of the four colors mentioned above are arranged. Depending on the purpose, it may also be a configuration in which four or more inkjet heads 122 corresponding to four or more colors, including other intermediate colors, are arranged.

[0186] Downstream of the inkjet head 122 in the paper transport direction, a drying drum 126 (an example of a heating and drying device) is arranged, which, for example, has the back side of the paper P wrapped around it and rotates in contact with the transported paper P to dry the image (ink) on the paper P. A heating source (e.g., halogen heater, etc.: not shown) is built into the drying drum 126. The drying drum 126 dries the image (ink) on the paper P by heating from the heating source. A hot air blower 128 (an example of a drying device) is arranged around the drying drum 126 to dry the image (ink) on the paper P. The hot air from this hot air blower 128 dries the image (ink) on the paper P wrapped around the drying drum 126. Downstream of the inkjet head 122 in the paper transport direction, other drying devices such as a near-infrared heater (not shown) or a laser irradiation device may be arranged to dry the image (ink) on the paper P. Other drying devices, such as near-infrared heaters and laser irradiation devices, are provided in place of at least one of the drying drum 126 and the hot air blower 128, or in addition to the drying drum 126 and the hot air blower 128.

[0187] The buffer unit 16, for example, has a first pass roller 16A, a dancer roller 16B, and a second pass roller 16C arranged along the paper transport direction. The dancer roller 16B moves up and down in Figure 1 to adjust the tension of the paper P being transported to the image recording unit 12 and adjust the transport speed of the paper P.

[0188] In the winding unit 18, the paper P on which the image is recorded is wound up. The wound-up paper is indicated by the reference numeral 18A.

[0189] The buffer unit 20, for example, has a first pass roller 20A, a dancer roller 20B, and a second pass roller 20C arranged along the paper transport direction. The dancer roller 20B moves up and down in Figure 1 to adjust the tension of the paper P discharged to the winding unit 18 and to adjust the transport speed of the paper P.

[0190] The cooling unit 22 is equipped with multiple cooling rollers 22A. When cooling an image using multiple cooling rollers 22A, the image recorded on the paper P is cooled by bringing the image recording surface and / or non-image recording surface of the paper P into contact with the multiple cooling rollers 22A during transport. Note that the number of cooling rollers may be one. Further downstream of the multiple cooling rollers 22A in the cooling unit 22, multiple cooling air blowers 22B are arranged. When cooling an image using multiple cooling air blowers 22B, the image on the paper P is cooled by blowing cold air from the cooling air blowers 22B onto the image recording surface of the paper P. Note that the number of cooling air blowers may be one. The cooling rollers 22A are equipped with a mechanism that allows for temperature adjustment. By setting the temperature of the cooling rollers 22A to room temperature, it is possible to transport the paper without substantially performing cooling by the cooling rollers 22A (cooling off). Furthermore, the cooling blower 22B is equipped with an on / off mechanism that switches between a state in which air is blown (cooling in operation (on) state) and a state in which air is not blown (cooling not in operation (off) state).

[0191] Next, the operation of the inkjet recording device 10 (inkjet recording method) will be described. In the inkjet recording device 10, first, the supply unit 14 feeds paper P from the roll paper 14B, and the fed paper P is transported to the image recording unit 12 through the buffer unit 16. Next, in the image recording unit 12, ink is ejected from the inkjet head 122 and applied to the paper P. After that, the drying drum 126 dries the image (ink) on the paper P from the back side of the paper P (the side opposite to the recording surface). Then, the hot air blower 128 dries the ink (image) ejected onto the paper P from the front side of the paper P (the recording surface). In other words, the drying drum 126 and the hot air blower 128 dry the ink ejected onto the paper P. This obtains an image. Next, the cooling unit 22 cools the image recorded on the paper P. Next, the paper P with the recorded image is wound up in the winding unit 18 through the buffer unit 16, and wound paper 18A is obtained. Image blocking is suppressed when the rolled-up paper 18A is unrolled.

[0192] Furthermore, the inkjet recording device may be equipped with a preheating and drying device for preheating the paper P, and a substrate inversion device for applying ink to both sides of the paper P. In addition, a heating device may be provided for applying radiant heating to the paper P to which the ink has been applied. "Radiant heating" means the propagation of thermal energy through space or a medium, and an example of this is the flow of electromagnetic waves (electromagnetic radiation).

[0193] Furthermore, a pretreatment solution application unit may be provided upstream of the inkjet head 122 to apply a pretreatment solution containing water, a coagulant, and a surfactant to the surface of the paper P to which the ink will be applied, before the ink is applied. This can further improve the detail of the image.

[0194] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure. Hereinafter, the term "dispersant" simply means a polymeric dispersant, and the term "solvent" simply means an organic solvent.

[0195] [Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1] A pigment dispersion D1 containing a pigment and a crosslinking dispersant D1 which is a polymer dispersant (acrylic resin) having a crosslinked structure is produced as follows.

[0196] <Synthesis of Uncrosslinked Dispersant N> In a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 153.5 parts by mass of tripropylene glycol monomethyl ether (product name "MFTG", manufactured by Nippon Emulsifier Co., Ltd.) as the reaction solvent is charged, and then the inside of the reaction vessel is replaced with nitrogen gas. Next, the inside of the reaction vessel is heated to 85°C, and a mixture of MFTG (76.8 parts by mass) as the reaction solvent, raw material monomers having the composition of C18MA / PDEGA / MAA / MMA (details shown below) (totaling 100 parts by mass), and V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (3.0 parts by mass) as a polymerization initiator is added dropwise over 3 hours to carry out the polymerization reaction. After the dropwise addition is complete, the reaction is continued at 85°C for another 3 hours to complete the polymerization and obtain a solution containing uncrosslinked dispersant N. The weight-average molecular weight of uncrosslinked dispersant N is 32600.

[0197] - Composition of raw material monomers - Stearyl methacrylate (C18MA) (Tg of homopolymer = 38°C) ... 36 parts by mass Phenoxydiethylene glycol acrylate (PDEGA) (Tg of homopolymer = -12°C) ... 15 parts by mass Methacrylic acid (MAA) (Tg of homopolymer = 228°C) ... 31 parts by mass Methyl methacrylate (MMA) (Tg of homopolymer = 105°C) ... 18 parts by mass

[0198] <Neutralization of Uncrosslinked Dispersant N> After cooling the solution containing the uncrosslinked dispersant N to room temperature, an aqueous solution of NaOH, which is an aqueous solution of a neutralizing base, is added to neutralize 80 mol% of the carboxyl groups in the uncrosslinked dispersant N. This yields a solution containing neutralized dispersant A (i.e., a polymeric dispersant obtained by neutralizing the uncrosslinked dispersant N) with a neutralization degree ND1 of 80%. The solid content concentration in the obtained solution is adjusted to 30% by mass to obtain an MFTG solution of neutralized dispersant A (30% by mass solid content concentration).

[0199] <Preparation of Uncrosslinked Dispersion A> After pre-dispersing the mixture of the following composition to a uniform state, dispersion treatment is performed for 3 hours using a bead mill (Star Mill manufactured by Ashizawa Finetex Co., Ltd., bead diameter: 0.3 mmφ, zirconia beads). This yields Uncrosslinked Dispersion A, in which magenta pigment is dispersed by neutralization-dispersant A.

[0200] -Composition- • Pigment Red 122 (Magenta pigment, which is a quinacridone pigment) ... 120.0 parts by mass • MFTG solution of neutralized dispersant A (30% solid content concentration) ... 120.0 parts by mass • MFTG ... 6.0 parts by mass • Water ... 230.0 parts by mass

[0201] <Acid Addition> Uncrosslinked dispersion A is diluted with deionized water to obtain a diluted solution of uncrosslinked dispersion A, with a pigment concentration of 15% by mass. While stirring the obtained diluted solution of uncrosslinked dispersion A (500 parts by mass), a mixture of 1 mol / L hydrochloric acid aqueous solution (19.4 parts by mass) and ultrapure water (225.2 parts by mass) is added over 5 minutes to reduce the degree of neutralization of the post-neutralization dispersant A in the diluted solution of uncrosslinked dispersion A from 80% to 60%, and then the mixture is stirred with a magnetic stirrer for 60 minutes. This yields an uncrosslinked dispersion B in which magenta pigment is dispersed by post-neutralization dispersant B (i.e., a polymer dispersant obtained by reducing the degree of neutralization of post-neutralization dispersant A to 60%), which has a neutralization degree ND2 of 60%.

[0202] <Crosslinking> Next, the mixture with the following composition is reacted at 70°C for 6 hours and then cooled to 25°C to crosslink the neutralized dispersant B in the uncrosslinked dispersion B with the crosslinking agent, thereby obtaining a crosslinked dispersion (i.e., a pigment dispersion) containing crosslinked dispersant D1 (i.e., a polymer dispersant obtained by crosslinking the neutralized dispersant B) and magenta pigment. -Composition- Uncrosslinked dispersion B ... 744.6 parts by mass "Denacol EX-321" (manufactured by Nagase ChemteX Corporation) (trimethylolpropane polyglycidyl ether; crosslinking agent) ... 5.4 parts by mass

[0203] Furthermore, the degree of crosslinking of the crosslinking dispersant D1, represented by the following formula, is 40%. Degree of crosslinking (%) = (Number of acid groups that formed a crosslinked structure) / (Number of unneutralized acid groups + Number of neutralized acid groups + Number of acid groups that formed a crosslinked structure) × 100 The degree of crosslinking is determined by NMR analysis.

[0204] <Centrifugation and Filtration of Pigment Dispersion (Production of Pigment Dispersion D1)> The crosslinked dispersion (i.e., pigment dispersion) obtained above is centrifuged at 7000 G for 20 minutes in a centrifuge to remove coarse particles. Next, the centrifuged crosslinked dispersion is filtered through a LABO-PURE filter (0.5 μm) manufactured by Loki to further remove coarse particles. Next, the filtered crosslinked dispersion is ultrafiltered by flowing it at a flow rate of 600 mL per minute through an ultrafiltration apparatus (cross-flow type ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (micropore size: 0.1 μm). At this time, the liquid temperature is adjusted to 25°C, and ultrafiltration is performed 10 times, with each ultrafiltration being one times the volume ratio of the charged liquid. After that, ion-exchanged water is added so that the concentration of magenta pigment becomes 15% by mass to obtain pigment dispersion D1 containing magenta pigment and crosslinking dispersant D1.

[0205] The glass transition temperature (Tgd) of the crosslinking dispersant D1 is shown in Tables 1 to 4. Tgd is calculated by centrifuging the ink described later, analyzing the copolymer composition of the crosslinking dispersant D1 in the precipitate (i.e., pigment particles containing the pigment and crosslinking dispersant D1), and then taking a weighted average of the Tg of the homopolymers of each raw material monomer based on the obtained copolymer composition.

[0206] Here, centrifugation is performed using a Himac CS-150FNS centrifuge at a rotation speed of 40,000 rpm (revolutions per minute) for 60 minutes. For the analysis of the precipitate, the precipitate is treated with THF (tetrahydrofuran) to dissolve the crosslinking dispersant D1, and the resulting solution is analyzed by GC-MASS and NMR. The amount of crosslinking dispersant in the ink is determined by drying the precipitate as described above, measuring the solid content, and subtracting the pigment concentration in the precipitate (Note: This pigment concentration is quantified by spectral absorption measurement) from the obtained solid content.

[0207] [Production of Pigment Dispersion D2 Containing Pigment and Crosslinking Dispersant D2] Except for changing the composition of the raw material monomers at the synthesis stage of the uncrosslinked dispersant N to the composition of C18MA / PDEGA / AA (details shown below), the production of pigment dispersion D2 containing pigment and crosslinking dispersant D2 is carried out in the same manner as in "Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1". -Composition of raw material monomers- Stearyl methacrylate (C18MA) ... 36 parts by mass Phenoxydiethylene glycol acrylate (PDEGA) ... 33 parts by mass Acrylic acid (AA) (Tg of homopolymer = 106°C) ... 31 parts by mass

[0208] [Production of Pigment Dispersion D3 Containing Pigment and Crosslinking Dispersant D3] The production of Pigment Dispersion D3 containing Pigment and Crosslinking Dispersant D3 is carried out in the same manner as in "Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1," except that the composition of the raw material monomers at the stage of synthesis of the uncrosslinked dispersant N is changed to the composition of C18MA / IBOMA / MAA (details are shown below). -Composition of Raw Material Monomers- Stearyl methacrylate (C18MA) ... 36 parts by mass Isobornyl methacrylate (IBOMA) (Tg of homopolymer = 180°C) ... 33 parts by mass Methacrylic acid (MAA) ... 31 parts by mass

[0209] [Production of Pigment Dispersion D4 Containing Pigment and Crosslinking Dispersant D4] Pigment dispersion D4 containing pigment and crosslinking dispersant D4 is produced in the same manner as in "Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1," except that the composition of the raw material monomers at the stage of synthesis of uncrosslinked dispersant N is changed to the composition of St / αMeSt / AA (details are shown below). -Composition of raw material monomers- Styrene (St) (Tg of homopolymer = 100°C) ... 64 parts by mass α-Methylstyrene (αMeSt) (Tg of homopolymer = 102°C) ... 5 parts by mass Acrylic acid (AA) (Tg of homopolymer = 106°C) ... 31 parts by mass

[0210] [Production of Pigment Dispersion D5 Containing Pigment and Crosslinking Dispersant D5] The production of Pigment Dispersion D5 containing Pigment and Crosslinking Dispersant D5 is carried out in the same manner as in "Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1," except that the composition of the raw material monomers at the stage of synthesis of the uncrosslinked dispersant N is changed to the composition of BzMA / MAA / MMA (details are shown below). -Composition of raw material monomers- ・Benzyl methacrylate (BzMA) (Tg of homopolymer = 54°C) ... 30 parts by mass ・Methacrylic acid (MAA) ... 25 parts by mass ・Methyl methacrylate (MMA) ... 45 parts by mass

[0211] [Production of Pigment Dispersion D6 Containing Pigment and Crosslinking Dispersant D6] Except for changing the composition of the raw material monomers at the stage of synthesis of the uncrosslinked dispersant N to the composition of BzMA / MAA (details shown below), the pigment dispersion D6 containing the pigment and crosslinking dispersant D6 is produced in the same manner as in "Production of Pigment Dispersion D1 Containing Pigment and Crosslinking Dispersant D1". -Composition of Raw Material Monomers- ・Benzyl methacrylate (BzMA) ... 72 parts by mass ・Methacrylic acid (MAA) ... 28 parts by mass

[0212] [Production of Pigment Dispersion N1 Containing Pigment and Uncrosslinked Dispersant N1] The pigment dispersion N1 containing pigment and uncrosslinked dispersant N1 is produced in the same manner as "Production of Pigment Dispersion D1 Containing Pigment and Crosslinked Dispersant D1," except that the composition of the raw material monomers at the stage of synthesis of uncrosslinked dispersant N is changed to the composition of C18MA / PDEGA / AA (details shown below), and the acid addition and crosslinking operations (i.e., operations after obtaining uncrosslinked dispersion A) are omitted. -Composition of Raw Material Monomers- Stearyl methacrylate (C18MA) ... 36 parts by mass Phenoxydiethylene glycol acrylate (PDEGA) ... 33 parts by mass Acrylic acid (AA) ... 31 parts by mass

[0213] [Examples 1-32, Comparative Examples 1-4] <Ink Preparation> The components shown in Tables 1-4 and water are mixed and stirred with a magnetic stirrer for 60 minutes. The mixture is then filtered through a LABO-PURE filter (0.5 μm) manufactured by Loki to obtain magenta ink having the composition shown in Tables 1-4. Any of the pigment dispersions D1-D6 or pigment dispersion N1 is used as the source of the pigments and dispersants in Tables 1-4.

[0214] Tables 1 to 4 are explained below. The "%" in each component column represents the content (mass %) relative to the total amount of ink. However, if the abbreviation of the aqueous dispersion containing the corresponding component (e.g., resin particles P1, E6314, etc.) is listed in each component column, the "%" represents the content (mass %) of the solids in the aqueous dispersion (i.e., the corresponding component) relative to the total amount of ink. A "-" in each component column means that the corresponding component is not contained. In the ink, the components other than those shown in Tables 1 to 4 (i.e., the remainder) are water.

[0215] The details of each component in Tables 1 to 4 (including components included in Example 2 and later) are as follows.

[0216] - Pigments - Pigment: Pigment Red 122 (Magenta Pigment) - Dispersants - Crosslinked Dispersant D1: Crosslinked dispersant D1 in the aforementioned pigment dispersion D1 Crosslinked Dispersant D2: Crosslinked dispersant D2 in the aforementioned pigment dispersion D2 Crosslinked Dispersant D3: Crosslinked dispersant D3 in the aforementioned pigment dispersion D3 Crosslinked Dispersant D4: Crosslinked dispersant D4 in the aforementioned pigment dispersion D4 Crosslinked Dispersant D5: Crosslinked dispersant D5 in the aforementioned pigment dispersion D5 Crosslinked Dispersant D6: Crosslinked dispersant D6 in the aforementioned pigment dispersion D6 Uncrosslinked Dispersant N1: Uncrosslinked dispersant N1 in the aforementioned pigment dispersion N1

[0217] - Organic solvents (boiling point (BP) less than 250°C) - PG ... Propylene glycol EGmHE ... Ethylene glycol monohexyl ether PGmBE ... Propylene glycol monobutyl ether 1,2-HDO ... 1,2-Hexanediol DEGmEE ... Diethylene glycol monoethyl ether DEGmiPE ... Diethylene glycol monoisopropyl ether TEGmBE ... Triethylene glycol monobutyl ether

[0218] - Organic solvents (boiling point (BP) 250°C or higher) - Glycerin... Glycerin GP-250... Sanyo Chemical Industries' "Sannix GP-250" PEG200... Polyethylene glycol 200 (manufactured by Fujifilm Wako Pure Chemical Industries)

[0219] - Resin particles (glass transition temperature (Tgp) is as shown in Tables 1 to 4) - Resin particle P1... an aqueous dispersion of acrylic resin particles prepared by the following method. --Method for preparing resin particle P1 -- In a three-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, water (250 g), 12-methacrylamide dodecanoic acid (6.7 g), potassium bicarbonate (0.17 g), and isopropanol (20 g) are charged and heated to 85°C under a nitrogen atmosphere. A mixed solution consisting of 4,4'-azobis(4-cyanovaleric acid) (radical polymerization initiator, product name "V-501", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (0.11 g), potassium bicarbonate (0.08 g), and water (9 g) is added and stirred for 10 minutes. Next, a monomer solution consisting of styrene (14 g), benzyl methacrylate (14 g), methyl methacrylate (48 g), butyl methacrylate (3.3 g), and hydroxyethyl methacrylate (14 g) is added dropwise to the three-necked flask at a constant rate so that the addition is completed in 3 hours. Furthermore, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) is added in two portions: immediately after the start of the addition of the monomer solution and 1.5 hours after the start of the addition of the monomer solution. After the addition of the monomer solution is completed, the mixture is stirred for 1 hour. Subsequently, the mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) is added to the resulting reaction mixture, and the mixture is stirred for a further 3 hours. The resulting reaction mixture is filtered through a 50 μm mesh to obtain an aqueous dispersion of resin particles P1.・PDX-7692… Joncryl PDX-7692, an aqueous dispersion of styrene-acrylic copolymer particles manufactured by BASF. ・PDX-7780… Joncryl PDX-7780, an aqueous dispersion of styrene-acrylic copolymer particles manufactured by BASF. *Tgp is calculated by centrifuging the ink described below, analyzing the copolymer composition of the resin particles in the supernatant, and taking a weighted average of the Tg of the homopolymers of each raw material monomer based on the copolymer composition described above. The centrifugation and analysis methods for measuring Tgp are the same as those for measuring Tgd described above.

[0220] - Wax Particles - ・E6314 … High-tech E6314, a polyethylene wax aqueous dispersion manufactured by Toho Chemical Industry Co., Ltd.

[0221] - Surfactants (HLB values ​​are shown in Tables 1 to 4) - Surfinol 104: Acetylene-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd. - Orphine E1010: Acetylene-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd. - BYK345: Silicone-based surfactant manufactured by BYK - Emulgen 103: Surfactant manufactured by Kao Corporation (polyoxyethylene (3) lauryl ether)

[0222] <Preparation of Inkjet Recording Device> As the inkjet recording device, an inkjet recording device having the configuration of the recording device 10 (Figure 1) described above is prepared. The inkjet recording device used in this embodiment comprises, in order from the upstream side in the paper transport direction of the paper P, a supply unit 14 that unwinds the paper P from the roll paper 14B (i.e., the paper P wound in a roll) and supplies it to the image recording unit 12, a transport mechanism that continuously transports the paper P unwinds from the roll paper 14B, an image recording unit 12 including an inkjet head 122 that applies ink to the continuously transported paper P, a drying drum 126 and a hot air blower 128 that heat and dry the applied ink, a cooling unit 22 for cooling the heated and dried ink to obtain an image, a buffer unit 16 that adjusts the tension of the paper P on which the image is recorded and adjusts the transport speed, and a take-up roll 18A that winds up the paper P on which the image is recorded. Here, the cooling unit 22 comprises, in order from the upstream side in the direction of transport of the paper P, a cooling roller 22A and a cooling cold air device 22B.

[0223] The transport speed of paper P shall be as shown in Tables 1 to 4.

[0224] The specifications for the inkjet head are as follows: • Fujifilm Dimatix SAMBA head will be used. • Inkjet head temperature: 32°C • Inkjet head resolution: 1200 dpi x 600 dpi • Ink droplet size: 3.5 pL • Environment around the inkjet head: Temperature 25°C ± 1°C, relative humidity 25°C ± 5%

[0225] The temperature for heating and drying by the drying drum 126 and the hot air blower 128 is 130°C. The cooling unit 22 includes a cooling roller 22A and a cooling blower 22B. For each embodiment and each comparative example, the on / off settings for the cooling roller 22A and the cooling blower 22B are set (in Tables 1 to 4, "Y" means cooling on (i.e., cooling is performed), and "-" means cooling off (i.e., cooling is not performed. Room temperature (20°C))). In each embodiment, the cooling unit 22 cools the image so that the value X represented by formula (X) is 15 or more. In other words, in each embodiment, the cooling unit 22 cools the image so that the weighted average value of the glass transition temperatures of the resin particles and the polymer dispersant having a cross-linked structure (i.e., "((Tgd × D + Tgp × P) / (D + P))" in formula (X) is 15°C or more higher than the surface temperature T1 of the image at the time of winding.

[0226] Value X = ((Tgd × D + Tgp × P) / (D + P)) - T1 ... Equation (X) In Equation (X), Tgd is the glass transition temperature (°C) of the crosslinked polymer dispersant, D is the mass %) of the crosslinked polymer dispersant relative to the total amount of ink, Tgp is the glass transition temperature (°C) of the resin particles, P is the mass %) of the resin particles relative to the total amount of ink, and T1 is the surface temperature (°C) of the image at the time of winding.

[0227] The surface temperature T1 of the image during winding is measured using a non-contact thermometer (Infrared Thermometer AD-5619 manufactured by A&D Company Limited) at a position downstream of the image cooling unit 22 and within 500 mm of the winding section.

[0228] The tension S1 of the paper during winding should be adjusted to the values ​​shown in Tables 1 to 4.

[0229] <Maintenance procedure for the nozzle surface of the inkjet head> Before inkjet recording in the evaluation described below, the nozzle surface of the inkjet head shall be cleaned with the following maintenance fluid. After cleaning, the residue of the maintenance fluid shall be removed with a rubber wiper blade. After removal, the nozzle surface shall be wiped with a cleaning cloth (Toray's "Toraysee") soaked in the following maintenance fluid. -Preparation of maintenance fluid- The components with the following composition shall be mixed and stirred in a stirrer for 1 hour, and then filtered through a 5 μm filter manufactured by Pall to obtain the maintenance fluid. --Composition of Maintenance Fluid-- • Diethylene glycol … 25% by mass • Diethylene glycol monobutyl ether … 5% by mass • Isopropyl alcohol … 2% by mass • Nitric acid … 0.01% by mass • Trishydroxymethylaminomethane … 0.1% by mass • Takesurf D-1715-N (manufactured by Takemoto Oil & Fat Co., Ltd.) … 1.5% by mass • NIKKOL PBC-31 (manufactured by Nikko Chemicals Co., Ltd.) … 1.5% by mass • Ion-exchanged water … 64.89% by mass

[0230] <Evaluation> Inkjet recording was performed using the inkjet recording device described above under the conditions described above, and the following evaluation was carried out. The results are shown in Tables 1 to 4.

[0231] (Image Blocking Resistance) Using the above inkjet recording method, paper is unwound from a roll, and an image with a halftone density of 100% is recorded on both sides of a 200m length of the unwound paper. The paper on which this image is recorded (hereinafter also referred to as the image recording) is then wound up. The wound image recording is unwound, and at a point approximately 100m from the end of the winding (i.e., midway through the 200m length of the image), the sound of peeling due to unwinding is checked, and a 100mm x 100mm area in the image is observed. The image blocking resistance is then evaluated according to the evaluation criteria below. In the evaluation criteria below, the rank with the best image blocking resistance is AA.

[0232] - Criteria for evaluating image blocking resistance - AA: No peeling sound is heard due to unwinding, and no white spots due to image defects are observed. A: Peeling sound is sometimes heard due to unwinding, but no white spots due to image defects are observed. B: Peeling sound is continuously heard due to unwinding, but no white spots due to image defects are observed. C: White spots due to image defects are observed (less than 5 in a 100mm x 100mm observation area). D: White spots due to image defects are observed (5 or more in a 100mm x 100mm observation area).

[0233] (Ink ejection stability) In the image used to evaluate the blocking resistance of the image, a 100 mm x 100 mm area in the last recorded portion of a 200 m length of paper (i.e., approximately 200 m away from the first recorded portion of the image) was visually inspected to check for streaks caused by poor ink ejection, and the ink ejection stability was evaluated according to the evaluation criteria below. In the evaluation criteria below, the rank of AA is the best for ink ejection stability.

[0234] - Criteria for evaluating ink ejection stability - AA: 0 streaks caused by poor ink ejection. A: 1 or more but less than 4 streaks caused by poor ink ejection. B: 4 or more but less than 8 streaks caused by poor ink ejection. C: 8 or more but less than 15 streaks caused by poor ink ejection. D: 15 or more streaks caused by poor ink ejection.

[0235]

[0236]

[0237]

[0238]

[0239] As shown in Tables 1 to 4, inkjet recording in each example using an ink containing a crosslinking dispersant (i.e., a polymer dispersant having a crosslinked structure) and resin particles, where the value X is 15 or higher (i.e., the weighted average value of the glass transition temperatures of the crosslinking dispersant and resin particles is 15°C or higher than the surface temperature of the image at winding), exhibits excellent ink ejection stability and excellent resistance to blocking of the recorded image (i.e., image blocking is suppressed). In contrast, in Comparative Example 1, where the polymer dispersant in the ink does not have a crosslinked structure, the ink ejection stability decreases. Also, in Comparative Example 3, where the ink does not contain resin particles, the resistance to blocking of the image decreases (i.e., image blocking occurs). Furthermore, in Comparative Examples 2 and 4, where the ink contains resin particles but the value X is less than 15, the resistance to blocking of the image decreases (i.e., image blocking occurs).

[0240] The results from Examples 9 to 11 show that when the content of structural unit A in the crosslinking dispersant is 30% to 70% by mass relative to the total amount of the crosslinking dispersant (Example 10), the ink ejection stability is further improved.

[0241] The results from Examples 1 and 7 show that when the ink contains wax particles (Example 1), the image blocking resistance is further improved (i.e., image blocking is further suppressed).

[0242] From the results of Examples 1 and 2, it can be seen that in Example 1, where the heated and dried ink is cooled by a cooling roller, the image's resistance to blocking is further improved.

[0243] The results from Examples 1 and 23 show that the image blocking resistance is improved when the tension (S1) during winding of the paper on which the image is recorded is between 100N and 500N (Example 1), compared to when the tension is greater than 500N (Example 23).

[0244] From the results of Examples 2 and 22, it can be seen that when the value Y (= value X / S1) is 0.05 or higher (Example 2), the image's blocking resistance is further improved.

[0245] The results from Examples 1, 20, and 21 show that when the ink contains a nonionic surfactant, and the nonionic surfactant includes a silicone-based surfactant and an acetylene-based surfactant with an HLB value of 8 or less (Example 1), the image blocking resistance is further improved.

[0246] From the results of Examples 1 and 12-18, it can be seen that when the ink contains an organic solvent, and the organic solvent is at least one selected from the group consisting of ethylene glycol monohexyl ether (EGmHE), propylene glycol monomethyl ether (PGmME), propylene glycol monobutyl ether (PGmBE), 1,2-hexanediol (1,2-HDO), diethylene glycol monoethyl ether (DEGmEE), and diethylene glycol monoisopropyl ether (DEGmiPE), and propylene glycol (PG) (Examples 1 and 13-17), the ink ejection stability is further improved.

[0247] From the results of Examples 1 and 26-30, it can be seen that the image blocking resistance is further improved when the ink does not contain a high-boiling point solvent (i.e., an organic solvent with a boiling point of 250°C or higher) (Example 1), or when it does contain one, compared to when the content of the high-boiling point solvent relative to the total amount of ink is 6% by mass or less (Examples 27-30), or when the content of the high-boiling point solvent relative to the total amount of ink is more than 6% by mass (Example 26).

[0248] The results from Examples 1 and 32 show that the image blocking resistance is further improved when the organic solvent content relative to the total amount of ink is 20% to 28% by mass (Example 1) compared to when the organic solvent content relative to the total amount of ink is more than 28% by mass (Example 32). The results from Examples 1 and 31 show that the ink ejection stability is further improved when the organic solvent content relative to the total amount of ink is 20% to 28% by mass (Example 1) compared to when the organic solvent content relative to the total amount of ink is less than 20% by mass (Example 31).

[0249] The results from Examples 1, 24, and 25 show that when the paper transport speed is 200 m / min or higher (Examples 24 and 25), the conditions for image blocking become more stringent.

[0250] Although the above examples show the use of magenta ink as the ink of the present disclosure, the same effects as in the above examples can be obtained when using other inks as the ink of the present disclosure (for example, cyan ink, yellow ink, black ink, white ink, orange ink, green ink, violet ink, or magenta ink with a different pigment type) instead of (or in addition to) magenta ink as the ink of the present disclosure, and / or when the aforementioned pretreatment solution (i.e., a pretreatment solution containing water, a coagulant, and a surfactant) is applied before applying the ink of the present disclosure. In addition to Pigment Red 122 (single, pigment content 6.0% by mass) in the above-mentioned ink, other magenta pigments in magenta ink include, for example, a mixture of Pigment Red 122 (pigment content, for example, 5.0% by mass) and Pigment Red 150 (pigment content, for example, 1.0% by mass), a mixture of Pigment Red 122 (pigment content, for example, 5.0% by mass) and Pigment Red 254 (pigment content, for example, 1.0% by mass), a mixture of Pigment Red 122 (pigment content, for example, 5.0% by mass) and Pigment Violet 19 (pigment content, for example, 1.0% by mass), a mixture of Pigment Red 122 (pigment content, for example, 4.0% by mass), Pigment Red 150 (pigment content, for example, 1.0% by mass), and Pigment Violet 19 (pigment content, for example, 1.0% by mass), Examples include a mixture of Pigment Red 122 (pigment content of, for example, 4.0% by mass), Pigment Red 254 (pigment content of, for example, 1.0% by mass), and Pigment Violet 19 (pigment content of, for example, 1.0% by mass). Examples of cyan pigments in cyan ink include Pigment Blue 15:3, Pigment Blue 15:4, etc. Examples of yellow pigments in yellow ink include Pigment Yellow 14, Pigment Yellow 74, Pigment Yellow 110, Pigment Yellow 155, etc. Examples of black pigments in black ink include Pigment Black 7, etc. Examples of white pigments in white ink include Pigment White 6, etc.

[0251] [Example 101] (Evaluation of blocking resistance of quaternary color image 1) Prepare the ink from Example 1 (pigment content 6.0% by mass) as magenta ink 1. Manufacture cyan ink 1 (pigment content 6.0% by mass) in the same manner as the ink from Example 1, except that pigment red 122, which is a magenta pigment, is replaced with pigment blue 15:3, which is a cyan pigment. Manufacture yellow ink 1 (pigment content 6.0% by mass) in the same manner as the ink from Example 1, except that pigment red 122, which is a magenta pigment, is replaced with pigment yellow 74, which is a yellow pigment. Manufacture black ink 1 (pigment content 6.0% by mass) in the same manner as the ink from Example 1, except that pigment red 122, which is a magenta pigment, is replaced with pigment black 7, which is a black pigment. In this example, instead of recording an image with 100% halftone coverage using the inks of Example 1, the following images were recorded in the same order to obtain the quaternary color image 1: an image with 30% halftone coverage using black ink 1 (pigment content 6.0% by mass), an image with 30% halftone coverage using cyan ink 1 (pigment content 6.0% by mass), an image with 30% halftone coverage using magenta ink 1 (pigment content 6.0% by mass), and an image with 30% halftone coverage using yellow ink 1 (pigment content 6.0% by mass). The evaluation was the same as the blocking resistance evaluation in Example 1. As a result, the blocking resistance of the quaternary color image 1 was determined to be "B" according to the evaluation criteria described above.

[0252] [Example 102] (Evaluation of blocking resistance of quaternary color image 2) Black ink 2 is obtained in the same manner as black ink 1, except that the pigment content is changed to 6.6% by mass and the amount of crosslinking dispersant is changed to an amount equivalent to 30% by mass relative to the pigment content. Cyan ink 2 is obtained in the same manner as cyan ink 1, except that the pigment content is changed to 4.5% by mass and the amount of crosslinking dispersant is changed to an amount equivalent to 30% by mass relative to the pigment content. Magenta ink 2 is obtained in the same manner as magenta ink 1, except that the pigment content is changed to 5.8% by mass and the amount of crosslinking dispersant is changed to an amount equivalent to 30% by mass relative to the pigment content. Yellow ink 2 is obtained in the same manner as yellow ink 1, except that the pigment content is changed to 5.1% by mass and the amount of crosslinking dispersant is changed to an amount equivalent to 30% by mass relative to the pigment content. In this example, instead of recording an image with 100% halftone coverage using the inks of Example 1, the following images were recorded in the same order to obtain the quaternary color image 2: an image with 30% halftone coverage using black ink 2 (pigment content 6.6 mass%), an image with 30% halftone coverage using cyan ink 2 (pigment content 4.5 mass%), an image with 30% halftone coverage using magenta ink 2 (pigment content 5.8 mass%), and an image with 30% halftone coverage using yellow ink 2 (pigment content 5.1 mass%). The evaluation was the same as the blocking resistance evaluation in Example 1. As a result, the blocking resistance of the quaternary color image 2 was found to be "A" according to the evaluation criteria described above.

[0253] [Example 103] (Evaluation of blocking resistance of quaternary color image 3) Magenta ink 3 (pigment content 6.0% by mass) is manufactured in the same manner as the ink in Example 1, except that pigment red 122 (pigment content 6.0% by mass) is replaced with a mixture of pigment red 122 (pigment content 5.0% by mass) and pigment red 150 (pigment content 1.0% by mass). Black ink 2, cyan ink 2, and yellow ink 2 are prepared in the same manner as in Example 102. In this example, instead of recording an image with 100% halftone coverage using the inks of Example 1, the following images were recorded in the same order to obtain the quaternary color image 3: an image with 30% halftone coverage using black ink 2 (pigment content 6.6 mass%), an image with 30% halftone coverage using cyan ink 2 (pigment content 4.5 mass%), an image with 30% halftone coverage using magenta ink 3 (pigment content 6.0 mass%), and an image with 30% halftone coverage using yellow ink 2 (pigment content 5.1 mass%). The evaluation of blocking resistance was the same as in Example 1. As a result, the blocking resistance of the quaternary color image 3 was found to be "A" according to the evaluation criteria described above.

[0254] As shown in Examples 101 to 103, when applying four inks to obtain a quaternary color image, it can be seen that the blocking resistance of the image is further improved when the first ink has a high pigment content relative to the total ink amount (e.g., 6% by mass or more), the second ink has a low pigment content relative to the total ink amount (e.g., 4% by mass or more and less than 6% by mass), the third ink has a high pigment content relative to the total ink amount (e.g., 5.5% by mass or more), and the fourth ink has a low pigment content relative to the total ink amount (e.g., 5% by mass or more and less than 5.5% by mass) in this order (Examples 102 and 103).

[0255] The disclosure of Japanese Patent Application No. 2025-054586, filed on 27 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. An inkjet recording method comprising: feeding paper from a roll and transporting it continuously; applying ink to the continuously transported paper using an inkjet method; recording an image by heating and drying the applied ink; cooling the image; and, after cooling, winding up the paper on which the image is recorded, wherein the ink contains water, pigment, a polymer dispersant having a cross-linked structure, and resin particles, the pigment content relative to the total amount of ink is 4% by mass or more, and the value X represented by the following formula (X) is 15 or more. Value X = ((Tgd × D + Tgp × P) / (D + P)) - T1 ... Equation (X) In Equation (X), Tgd is the glass transition temperature (°C) of the polymer dispersant having a crosslinked structure, D is the content (mass%) of the polymer dispersant having a crosslinked structure relative to the total amount of ink, Tgp is the glass transition temperature (°C) of the resin particles, P is the content (mass%) of the resin particles relative to the total amount of ink, and T1 is the surface temperature (°C) of the image at the time of winding.

2. The inkjet recording method according to claim 1, wherein the polymer dispersant having a crosslinked structure contains at least one structural unit A selected from the group consisting of structural units derived from alkyl (meth)acrylate having 12 to 24 carbon atoms in the alkyl group, structural units derived from styrene, and structural units derived from benzyl (meth)acrylate, the content of structural unit A is 30% to 70% by mass with respect to the total amount of the polymer dispersant having a crosslinked structure, and the degree of crosslinking of the polymer dispersant having a crosslinked structure is 30% or more and less than 80%.

3. The inkjet recording method according to claim 1, further comprising wax particles.

4. The inkjet recording method according to claim 1, wherein the cooling of the image is performed by a cooling roller.

5. The inkjet recording method according to claim 1, wherein the tension when winding up the paper on which the image is recorded is 100 N to 500 N.

6. The inkjet recording method according to claim 1, wherein the value Y, represented by the following formula (Y), is 0.05 or greater. Value Y = Value X / S1 ... Formula (Y) In formula (Y), S1 is the tension when the paper on which the image is recorded is wound up, and Value X is the value X represented by the above formula (X).

7. The inkjet recording method according to claim 1, wherein the ink further contains a nonionic surfactant, and the nonionic surfactant comprises a silicone-based surfactant and an acetylene-based surfactant having an HLB value of 8 or less.

8. The inkjet recording method according to claim 1, wherein the ink further contains an organic solvent, the organic solvent comprising at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, 1,2-hexanediol, diethylene glycol monoethyl ether, and diethylene glycol monoisopropyl ether, and propylene glycol.

9. The inkjet recording method according to claim 1, wherein the ink does not contain an organic solvent with a boiling point of 250°C or higher, or if it does contain such an organic solvent, the amount of such solvent relative to the total amount of the ink is 6% by mass or less.

10. The inkjet recording method according to claim 1, wherein the content of the organic solvent relative to the total amount of the ink is 20% by mass to 28% by mass.

11. The inkjet recording method according to claim 1, wherein the paper transport speed is 200 m / min or more.

12. The inkjet recording method according to claim 1, comprising applying a pretreatment liquid to the paper after the paper has been unwound from the roll paper and before the ink has been applied to the paper.

13. The inkjet recording method according to claim 12, wherein the pretreatment solution contains water, a coagulant, and a surfactant.

14. An inkjet recording apparatus for carrying out the inkjet recording method described in claim 1, comprising: a feeding device for feeding paper from a roll of paper; a transport mechanism for continuously transporting the paper fed from the roll of paper; an inkjet head for applying ink onto the continuously transported paper; a heating and drying device for heating and drying the applied ink; a cooling device for cooling the heated and dried ink to obtain an image; and a winding device for winding up the paper on which the image is recorded, wherein the transport speed of the paper is 160 m / min or more, and the value X represented by formula (X) is 15 or more.

Images