Inkjet ink, ink set, and inkjet recording method

Abstract

This inkjet ink contains water, a pigment, a polymer dispersant having at least one of a crosslinked structure and a block copolymer structure, and silicone-based resin particles. There are also provided an ink set including the inkjet ink, and an inkjet recording method using the inkjet ink.

Description

Inkjet ink, ink set, and inkjet recording method

[0001] This disclosure relates to inkjet inks, ink sets, and inkjet recording methods.

[0002] Various studies have been conducted regarding image recording using inkjet inks. For example, Patent Document 1 describes the following image recording method, which can record images that are excellent in granularity (i.e., suppression of graininess), resolution, and scratch resistance, and that suppress 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, for image recording using inkjet inks, there are cases where it is necessary to further improve the ejection stability of the inkjet ink and the image blocking resistance (i.e., the ability to suppress blocking). For example, in high-speed inkjet recording methods (for example, inkjet recording methods in which inkjet ink is applied to a substrate being transported at a transport speed of 200 m / min or more; the same applies hereinafter), it is necessary to improve the ejection stability of the inkjet ink 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.

[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 ink that is excellent in ejection stability and resistance to blocking of the recorded image, an ink set containing this inkjet ink, and an inkjet recording method that applies the inkjet ink to a substrate being transported at a transport speed of 200 m / min or more, while providing an inkjet recording method that is excellent in resistance to blocking of the recorded image and ejection stability of the inkjet ink.

[0006] This disclosure includes the following embodiments: <1> An inkjet ink comprising water, a pigment, a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure, and silicone resin particles. <2> The inkjet ink according to <1>, wherein the glass transition temperature of the silicone resin particles is 80°C or higher. <3> The inkjet ink according to <1> or <2>, wherein the content of silicone resin particles is 3% to 30% by mass with respect to the total solid content of the inkjet ink. <4> The inkjet ink according to any one of <1> to <3>, further comprising non-silicone resin particles having a glass transition temperature of 80°C or higher. <5> The inkjet ink according to any one of <1> to <4>, further comprising an organic solvent, wherein the organic solvent comprises at least one selected from the group consisting of an alkanediol having 4 or fewer carbon atoms, a monoalkylene glycol monoalkyl ether, and a 1,2-alkanediol having 5 or more carbon atoms. <6> The inkjet ink according to any one of <1> to <5>, further comprising an organic solvent, wherein the organic solvent comprises propylene glycol and at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monobutyl ether, and diethylene glycol monoethyl ether. <7> The inkjet ink according to any one of <1> to <6>, further comprising wax particles. <8> The inkjet ink according to any one of <1> to <7>, further comprising a nonionic surfactant, wherein the nonionic surfactant comprises an acetylene-based surfactant and a silicone-based surfactant. <9> The inkjet ink according to <8>, wherein the acetylene-based surfactant comprises an acetylene-based surfactant having an HLB value of 6 or less. <10> The inkjet ink according to <8> or <9>, wherein the nonionic surfactant further comprises a polyoxyethylene alkyl ether. <11> An inkjet ink according to any one of <1> to <10>, wherein 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.<12> An inkjet ink used as an ink in an inkjet recording method that includes applying ink to a substrate being transported at a transport speed of 200 m / min or more by an inkjet method to record an image. <13> The inkjet ink according to <12>, wherein the substrate is roll paper. <14> An ink set comprising cyan ink, magenta ink, yellow ink, and black ink, wherein at least one of the cyan ink, magenta ink, yellow ink, and black ink is the inkjet ink according to any one of <1> to <13>. <15> An ink set comprising the inkjet ink according to any one of <1> to <13>, and a pretreatment liquid containing water and a coagulant. <16> An inkjet recording method that includes applying the inkjet ink according to any one of <1> to <13> to a substrate being transported at a transport speed of 200 m / min or more by an inkjet method to record an image.

[0007] According to one embodiment of the present disclosure, an inkjet ink having excellent ejection stability and resistance to blocking of the recorded image, an ink set containing this inkjet ink, and an inkjet recording method that applies the inkjet ink to a substrate being transported at a transport speed of 200 m / min or more, while having excellent resistance to blocking of the recorded image and ejection stability of the inkjet ink are provided.

[0008] This figure conceptually illustrates an example of an inkjet recording apparatus used in the inkjet recording method of this disclosure.

[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 Ink] The inkjet ink of this disclosure (hereinafter also simply referred to as "ink") contains water, a pigment, a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure, and silicone resin particles.

[0012] The inks of this disclosure exhibit excellent ejection stability and resistance to blocking of recorded images. The improvement in ink ejection stability is thought to be due to improved pigment dispersibility achieved by using a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure as a dispersant for the pigments in the ink. The improvement in image resistance is thought to be due to the inclusion of silicone resin particles in the ink.

[0013] Generally, high-speed inkjet recording methods (for example, inkjet recording methods that apply inkjet ink to a substrate (e.g., roll paper) being transported at a transport speed of 200 m / min or more, particularly 240 m / min or more) require improved inkjet ink ejection stability. Furthermore, high-speed inkjet recording methods (especially high-speed inkjet recording methods using roll paper) tend to result in shorter drying times, making image blocking more likely. Therefore, there is a need to further improve image blocking resistance. When the ink of this disclosure is used in a high-speed inkjet recording method (for example, an inkjet recording method that applies inkjet ink to a substrate (e.g., roll paper) being transported at a transport speed of 200 m / min or more, particularly 240 m / min or more), the effects of improving ink ejection stability and improving the blocking resistance of the recorded image are more effectively demonstrated.

[0014] The inks described in this disclosure are explained in more detail below.

[0015] <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.

[0016] <Pigments> The inks of this disclosure contain at least one pigment.

[0017] 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.

[0018] 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.

[0019] Examples of pigments from a hue perspective include cyan pigment, magenta pigment, yellow pigment, black pigment, and white pigment.

[0020] The pigment content relative to the total amount of ink is preferably 1% to 10% by mass, more preferably 1.5% to 10% by mass, and even more preferably 2% to 8% by mass, from the viewpoint of image color density and ink ejection performance.

[0021] <Polymer Dispersant> The ink of this disclosure contains at least one polymer dispersant having at least one of a crosslinked structure and a block copolymer structure (hereinafter also referred to as the "specific dispersant").

[0022] Specific dispersants have the function of dispersing pigments in ink by interacting with them (e.g., by adsorption). Specifically, for example, in ink, it is thought that the specific dispersant adsorbs onto the pigment (e.g., coats the pigment) and forms dispersed particles.

[0023] The specific dispersant has at least one of a crosslinked structure and a block copolymer structure. This improves the ink ejection stability. This is thought to be because, because the specific dispersant has at least one of a crosslinked structure and a block copolymer structure, the specific dispersant adsorbed on the pigment (for example, coating the pigment) in the ink is less likely to detach from the pigment, and as a result, the dispersion stability of the pigment is improved.

[0024] Furthermore, specific dispersants may also contribute to improving the blocking resistance of images. This is thought to be because the glass transition temperature (Tg) of the specific dispersant is improved due to the presence of at least one of a crosslinked structure and a block copolymer structure.

[0025] For specific dispersants (polymeric dispersants having at least one of a crosslinked structure and a block copolymer structure), refer to the descriptions in publicly available documents such as International Publication No. 2022 / 239625 and International Publication No. 2013 / 115071 as appropriate.

[0026] 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.

[0027] 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".

[0028] Acrylic resin is preferred as the resin constituting the specific dispersant. In this disclosure, acrylic resin means a resin containing at least one of structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylic acid esters.

[0029] The weight-average molecular weight (Mw) of the specific dispersant is preferably 3,000 to 100,000, more preferably 4,000 to 80,000, and even more preferably 5,000 to 60,000.

[0030] The specific dispersant preferably contains structural units having an adsorption group and structural units having anionic groups.

[0031] A structural unit having an anionic group is a structural unit that contributes to dispersibility. The polymer 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, with a carboxy group being 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.

[0032] In the present disclosure, a structural unit derived from Compound A (for example, (meth)acrylic acid) means a structural unit formed by polymerization of Compound A (for example, (meth)acrylic acid).

[0033] 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. The adsorptive group preferably contains 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 more preferably contains 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 a (meth)acrylate having an adsorptive group.

[0034] - Crosslinked Dispersant - For the specific dispersant having a crosslinked structure (hereinafter also referred to as a crosslinked dispersant), for example, the description in International Publication No. WO 2022 / 239625 can be referred to.

[0035] The crosslinking dispersant is not particularly limited as long as it is a polymer compound having at least one crosslinking structure within its molecule. The crosslinking 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 neutralizing bases include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; organic amines such as dimethylethanolamine and diisopropylethylamine; and so on. 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 the crosslinking agent, the uncrosslinked dispersant may be neutralized with a neutralizing base, then an acid may be added to adjust the degree of neutralization, and then crosslinked with the crosslinking agent. Examples of acids include hydrochloric acid, acetic acid, citric acid, malonic acid, boric acid, maleic acid, and so on. The degree of neutralization (%) of the uncrosslinked dispersant after adjustment with acid is preferably 20 to 80, more preferably 30 to 70.

[0036] The uncrosslinked dispersant is preferably a water-soluble polymer compound.

[0037] In this disclosure, "water-soluble" in "water-soluble polymer dispersant" means the property of dissolving 1 g or more in 100 g of water at 25°C. Preferably, "water-soluble" means dissolving 3 g or more (more preferably 10 g or more) in 100 g of water at 25°C.

[0038] Furthermore, even if an uncrosslinked polymer dispersant is water-soluble, a polymer dispersant with a crosslinked structure (i.e., a crosslinked dispersant) is not necessarily water-soluble.

[0039] Examples of uncrosslinked dispersants include polyvinyl, polyurethane, and polyester. Among these, polyvinyl is preferred as the uncrosslinked polymer.

[0040] 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 polymer is preferably a polymer containing a carboxyl group.

[0041] 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.

[0042] Examples of monomers containing a carboxyl group include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 polymer.

[0048] 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 polymer.

[0049] 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).

[0050] 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).

[0051] The content of (meth)acrylate structural units having a benzene ring is preferably 10% to 60% by mass, and more preferably 10% to 40% by mass, based on the total amount of the polymer (i.e., uncrosslinked polymer or crosslinked polymer).

[0052] 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.

[0053] 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 polymer (i.e., uncrosslinked polymer or crosslinked polymer).

[0054] 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 to the total uncrosslinked dispersant or crosslinked dispersant is preferably 10% by mass or less, more preferably 1% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass.

[0055] 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.

[0056] 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.

[0057] 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 uncrosslinked polymer.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Among these, the preferred epoxy compounds with two or more functions are polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether.

[0062] 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).

[0063] The molar ratio of the reaction sites in the crosslinking agent (e.g., epoxy groups) to the reaction sites in the uncrosslinked polymer (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.

[0064] The degree of crosslinking of the crosslinking dispersant is preferably 10% to 70%, more preferably 20% to 60%, 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).

[0065] -Block Dispersants- For specific dispersants having a block copolymer structure (hereinafter also referred to as "block dispersants"), see, for example, the description in International Publication No. 2022 / 239625. That is, a block dispersant may contain structural units derived from a hydrophobic monomer and structural units derived from a monomer containing an anionic group (hereinafter referred to as "anionic group-containing monomer").

[0066] The structural units derived from hydrophobic monomers contained in the block dispersant may be one type or two or more types. The structural units derived from anionic group-containing monomers contained in the block polymer may be one type or two or more types.

[0067] Structural units derived from hydrophobic monomers include ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure, and (meth)acrylates having an alkyl group with 1 to 20 carbon atoms.

[0068] 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 70% to 90% by mass, relative to the total amount of the blocking dispersant.

[0069] From the viewpoint of adsorption with pigments, the hydrophobic monomer preferably contains an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure, more preferably contains an ethylenically unsaturated compound having an alicyclic structure, and even more preferably contains an ethylenically unsaturated compound having an alicyclic structure with 6 or more carbon atoms.

[0070] The content of structural units derived from ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure is preferably 10% to 90% by mass, more preferably 20% to 80% by mass, even more preferably 30% to 70% by mass, and still more preferably 30% to 60% by mass, based on the total amount of the block polymer.

[0071] The structural units derived from hydrophobic monomers may also preferably include (meth)acrylates having an alkyl group with 1 to 20 carbon atoms. The alkyl group may be linear or branched.

[0072] Examples of (meth)acrylates having an alkyl group with 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate.

[0073] The content of structural units derived from (meth)acrylate having an alkyl group with 1 to 20 carbon atoms is preferably 10% to 90% by mass, more preferably 20% to 80% by mass, even more preferably 30% to 70% by mass, and particularly preferably 40% to 60% by mass, based on the total amount of the blocking dispersant.

[0074] In structural units derived from anionic group-containing monomers, examples of anionic groups include carboxyl groups, salts of carboxyl groups, sulfo groups, salts of sulfo groups, phosphate groups, salts of phosphate groups, phosphonic acid groups, and salts of phosphonic acid groups.

[0075] Counterions in salts include alkali metal ions such as sodium ions, potassium ions, and lithium ions; alkaline earth metal ions such as calcium ions and magnesium ions; and ammonium ions.

[0076] In particular, the anionic group is preferably a carboxyl group or a salt of a carboxyl group. Examples of anionic group-containing monomers include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid. In particular, the anionic group-containing monomer is preferably (meth)acrylic acid.

[0077] The content of structural units derived from anionic group-containing monomers is preferably 1% to 30% by mass, more preferably 2% to 25% by mass, and even more preferably 3% to 20% by mass, relative to the total amount of the blocking dispersant.

[0078] Whether or not a polymer compound contained in an ink is a block copolymer can be determined, for example, by the following method. First, the polymer compound is separated from the ink using a separation method such as solvent extraction. The separated polymer compound is then analyzed using various analytical methods such as nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and thermal analysis, and its physical properties, such as the glass transition temperature, are measured to comprehensively determine whether or not it is a polymer compound.

[0079] The weight-average molecular weight (Mw) of the blocking dispersant is not particularly limited, but from the viewpoint of pigment dispersibility, it is preferably 3,000 to 100,000, more preferably 5,000 to 80,000, and even more preferably 10,000 to 60,000.

[0080] For the block dispersant, the description in International Publication No. WO 2013 / 115071 can also be referred to. That is, the block dispersant is, for example, an A-B block polymer (A and B each mean a polymer obtained by polymerizing different monomers), wherein the monomer constituting the A block is one or more monomers represented by the following formula (3), and the monomer constituting the B block may be benzyl methacrylate and / or benzyl acrylate. The block dispersant of this embodiment is obtained, for example, by copolymerization via living radical polymerization using either a mixture of an organic tellurium compound represented by the following formula (1) and an organic ditellurium compound represented by the following formula (2) as a polymerization initiator, or a mixture of an organic tellurium compound represented by the following formula (1), an azo-based polymerization initiator, and an organic ditellurium compound represented by the following formula (2).

[0081]

[0082] In formula (1), R １ represents a C1-C8 alkyl group, an aryl group, a substituted aryl group, or an aromatic heterocyclic group. R ２ and R ３ represent a hydrogen atom or a C1-C8 alkyl group. R ４ represents an aryl group, a substituted aryl group, an aromatic heterocyclic group, an acyl group, an amide group, an oxycarbonyl group, or a cyano group. In formula (2), R １ has the same definition as R １ in formula (1). In formula (3), R ５ represents a hydrogen atom or an alkyl group which may have a branch having 4 carbon atoms, and R ６ represents a hydrogen atom or a methyl group.

[0083] The acid value of the block dispersant according to the above embodiment may be 90 mgKOH / g to 200 mgKOH / g. The weight average molecular weight of the block dispersant according to the above embodiment may be 10,000 to 60,000. In the block dispersant according to the above embodiment, the monomer forming the A block is, in the above formula (3), a monomer in which R ５ is a hydrogen atom and R ６ is a methyl group, and a monomer in which R ５ is an n-butyl group and R ６The monomers may be two different monomers, each having a methyl group.

[0084] The mixing ratio of the pigment to the specific dispersant (i.e., a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure) 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.

[0085] <Silicone-based resin particles> The ink of this disclosure contains at least one type of silicone-based resin particle. This provides an effect of preventing image blocking.

[0086] The silicone resin that forms the silicone resin particles contains a silicone structure (i.e., an organopolysiloxane structure). Preferably, the silicone resin is a silicone acrylic resin containing a silicone structure and at least one of structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylic acid esters. For silicone resin particles, see, for example, Japanese Patent Application Publication No. 2018-30957.

[0087] The glass transition temperature of the silicone resin particles (i.e., the glass transition temperature of the silicone resin in the silicone resin particles) is preferably -20°C, more preferably 0°C or higher, even more preferably 20°C or higher, even more preferably 50°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher, from the viewpoint of further improving the blocking resistance of the image. There is no particular upper limit to the glass transition temperature of the silicone resin particles, but examples include 150°C, 130°C, 120°C, etc.

[0088] In this disclosure, the glass transition temperature of a resin refers to the value measured using differential scanning calorimetry (DSC). The specific measurement of the glass transition temperature is carried out in accordance with the method described in JIS K 7121 (1987) or JIS K 6240 (2011). The glass transition temperature in this disclosure is the extrapolation glass transition onset temperature (hereinafter sometimes referred to as Tig). The method for measuring the glass transition temperature will be described in more detail. When determining the glass transition temperature, the resin is held at a temperature approximately 50°C lower than the expected glass transition temperature until the apparatus stabilizes, and then heated at a heating rate of 20°C / min to a temperature approximately 30°C higher than the temperature at which the glass transition ends, and a differential thermal analysis (DTA) curve or DSC curve is created. The extrapolation glass transition onset temperature (Tig), i.e., the glass transition temperature in this disclosure, is determined as the temperature at the intersection of a straight line drawn by extending the low-temperature baseline of the DTA curve or DSC curve toward the high-temperature side, and a tangent line drawn at the point where the slope of the curve representing the stepwise transition portion of the glass transition is maximum.

[0089] When an ink contains two or more types of silicone resin particles, the glass transition temperature (Tg) of the silicone resin particles in the ink represents the weighted average of the glass transition temperatures of the individual silicone resin particles.

[0090] The weight-average molecular weight (Mw) of the silicone resin in the silicone resin particles is not particularly limited, but is preferably 10,000 to 1,000,000, more preferably 20,000 to 200,000, and even more preferably 30,000 to 150,000.

[0091] The content of silicone resin particles relative to the total solid content of the ink is preferably 2% to 32% by mass, more preferably 3% to 30% by mass, even more preferably 4% to 25% by mass, and even more preferably 5% to 20% by mass. When the content of silicone resin particles is 2% by mass or more, the image blocking resistance is further improved. When the content of silicone resin particles is 32% by mass or less, the ink ejection stability is further improved.

[0092] In this disclosure, the total solids content of the ink means the total amount of ink excluding the solvent (i.e., water and, if present, organic solvents).

[0093] <Non-silicone resin particles> The ink of this disclosure may contain at least one type of non-silicone resin particle. Here, non-silicone resin particles mean resin particles that do not contain a silicone structure. Examples of non-silicone resin particles include acrylic resin particles, polyurethane resin particles, polyester resin particles, polyolefin resin particles, and the like.

[0094] For non-silicone 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.

[0095] The glass transition temperature (Tg) of non-silicone resin particles is preferably -20°C, more preferably 0°C or higher, even more preferably 20°C or higher, even more preferably 50°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher, from the viewpoint of further improving the blocking resistance of images. There is no particular upper limit to the glass transition temperature of non-silicone resin particles, but examples include 150°C, 130°C, 120°C, etc.

[0096] The weight-average molecular weight (Mw) of the non-silicone resin in the non-silicone resin particles is not particularly limited, but is preferably 10,000 to 1,000,000, more preferably 20,000 to 200,000, and even more preferably 30,000 to 150,000.

[0097] <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, and even more preferably 15% to 35% by mass, based on the total amount of ink.

[0098] If the ink of this disclosure contains an organic solvent, it is more preferable that the organic solvent includes an alkanediol having 4 or fewer carbon atoms, and at least one selected from the group consisting of monoalkylene glycol monoalkyl ethers and 1,2-alkanediols having 5 or more carbon atoms. In this case, the total amount of the alkanediol having 4 or fewer carbon atoms, and at least one selected from the group consisting of monoalkylene glycol monoalkyl ethers and 1,2-alkanediols having 5 or more carbon atoms is preferably 5% to 50% by mass, more preferably 10% to 40% by mass, and even more preferably 15% to 35% by mass, based on the total amount of ink.

[0099] Examples of alkanediols having four or fewer carbon atoms include ethylene glycol, propylene glycol (also known as 1,2-propanediol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. Propylene glycol is particularly preferred among alkanediols having four or fewer carbon atoms.

[0100] Examples of monoalkylene glycol monoalkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-t-butyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and the like.

[0101] Examples of 1,2-alkanediols having five or more carbon atoms include 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol, and the like.

[0102] The organic solvent preferably contains propylene glycol and at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monobutyl ether, and diethylene glycol monoethyl ether. In this case, the total amount of propylene glycol and at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monobutyl ether, and diethylene glycol monoethyl ether is preferably 5% to 50% by mass, more preferably 10% to 40% by mass, and even more preferably 15% to 35% by mass, based on the total amount of ink.

[0103] The organic solvent may include other solvent species besides the preferred solvent species described above. Examples of other solvent species include diethylene glycol monoethyl ether, triethylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, glycerin, and the like.

[0104] <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.

[0105] 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.

[0106] Examples of waxes that make up wax particles include natural waxes and synthetic waxes.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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, from the viewpoint of image resolution.

[0112] <Surfactants> The inks of this disclosure may contain at least one surfactant. Nonionic surfactants are preferred as the surfactant.

[0113] From the viewpoint of further improving image blocking resistance, the nonionic surfactant preferably includes acetylene-based surfactants and silicone-based surfactants.

[0114] (Acetylene-based surfactants) As acetylene-based surfactants, compounds represented by the following formula (A1) are preferred.

[0115]

[0116] 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 R ３ 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.

[0117] 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).

[0118] The acetylene-based surfactant preferably includes an acetylene-based surfactant having an HLB value of 3.0 to 9.0 (preferably 3.5 to 9.0). When the acetylene-based surfactant includes an acetylene-based surfactant with an HLB value of 3.0 or higher, the image resolution is further improved. When the acetylene-based surfactant includes an acetylene-based surfactant with an HLB value of 9.0 or lower, the image granularity is further improved.

[0119] Commercially available acetylene-based surfactants may be used. Examples of commercially available acetylene-based surfactants include those manufactured by Nisshin Chemical Co., Ltd. Examples of acetylene-based surfactants manufactured by Nisshin Chemical include Surfinol 104 (HLB value 4.0), Surfinol 420 (HLB value 4.0), Surfinol 440 (HLB value 8.0), Surfinol SE (HLB value 6.0), Surfinol SE-F (HLB value 6.0), Surfinol 61 (HLB value 6.0), Surfinol 82 (HLB value 4.0), Surfinol DF110D (HLB value 3.0), Dynol 604 (HLB value 8.0), Dynol 607 (HLB value 8.0), Surfinol 2502 (HLB value 8.0), Surfinol TG (HLB value 9.0), Orphin E1004 (HLB value: 7.0-9.0), Orphin E1010 (HLB value: 13.5), and others.

[0120] From the viewpoint of further improving the image blocking resistance, it is preferable that the acetylene-based surfactant includes an acetylene-based surfactant having an HLB value of 6 or less (more preferably 3 to 6).

[0121] The content of acetylene-based surfactant (for example, acetylene-based surfactant with an HLB value of 6 or less) relative to the total amount of ink is preferably 0.05% to 2.5% by mass, more preferably 0.1% to 2.0% by mass, and even more preferably 0.2% to 1.5% by mass, from the viewpoint of improving the blocking resistance of the image.

[0122] (Silicone-based surfactants) As silicone-based surfactants, compounds represented by the following formula (C1) are preferred.

[0123]

[0124] In formula (C1), R １ Each of these independently represents an alkyl group or hydroxyl group having 1 to 3 carbon atoms, R ２ R represents an alkanediyl group with 2 to 5 carbon atoms. ３∫ represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a hydroxyl group. PO represents a propylene oxy group, and EO represents an ethylene oxy group. a, b, m, and n represent the average number of moles added for each unit, where a is 0 to 10, b is 1 to 50, m is 1 to 500, and n is 1 to 50.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] (Polyoxyethylene alkyl ether) From the viewpoint of further improving the blocking resistance of images, it is preferable that the nonionic surfactant further contains polyoxyethylene alkyl ether.

[0131] As the polyoxyethylene alkyl ether, the compound represented by the following formula (B1) is preferred.

[0132]

[0133] In formula (B1), R １ represents a hydrocarbon group, and a represents an integer from 1 to 60.

[0134] 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.

[0135] 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.

[0136] As the polyoxyethylene alkyl ether, a polyoxyethylene alkyl ether with an HLB value of 4 to 18 is preferred.

[0137] 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.

[0138] <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.

[0139] 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.

[0140] 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.

[0141] <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.

[0142] 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.

[0143] <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.

[0144] <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.

[0145] 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 "BP100" is used as the bubble pressure type dynamic surface tension meter.

[0146] -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.

[0147] In this disclosure, static surface tension refers to the value measured by the Wilhelmy method using a platinum plate. In the embodiments described later, an automatic surface tension meter "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. is used as the static surface tension meter.

[0148] 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.

[0149] - 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.

[0150] -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.

[0151] [Inkjet Recording Method] The ink of this disclosure is particularly suitable for use in the inkjet recording method of this embodiment described below.

[0152] The inkjet recording method of this embodiment includes recording an image by applying the aforementioned inks to a substrate being transported at a transport speed of 200 m / min or more (preferably 240 m / min or more) using an inkjet method.

[0153] As mentioned above, in general, high-speed inkjet recording methods (for example, inkjet recording methods that apply inkjet ink to a substrate being transported at a transport speed of 200 m / min or more) tend to result in image blocking due to the short drying time. However, since the inkjet recording method of this disclosure uses the ink described above, it can effectively suppress image blocking (i.e., it has excellent image blocking resistance) even though it is a high-speed inkjet recording method (for example, an inkjet recording method that applies inkjet ink to a substrate being transported at a transport speed of 200 m / min or more). It also has excellent ink ejection stability, which is required in high-speed inkjet recording methods.

[0154] The inkjet recording method of this embodiment will be described in detail below.

[0155] <Substrate> The substrate used in the inkjet recording method of this embodiment is not particularly limited, and examples include so-called coated paper used in general offset printing. Coated paper is made by applying a coating material to the surface of a generally untreated high-quality paper, neutral paper, etc., which is mainly composed of cellulose, to provide a coating layer.

[0156] Coated paper may be one that is generally available on the market. For example, general-purpose coated paper for printing can be used as the coated paper. Specifically, examples include coated papers (A2, B2) such as "OK Topcoat+" from Oji Paper Co., Ltd., "Aurora Coat" and "U-Light" from Nippon Paper Industries Co., Ltd., and art paper (A1) such as "Tokuryo Art" from Mitsubishi Paper Mills Ltd.

[0157] In order to more effectively demonstrate the image blocking resistance effect of the inks disclosed herein, roll paper is preferred as the substrate. Examples of roll paper include the gloss-coated paper "OK ​​Topcoat 104" (manufactured by Oji Paper Co., Ltd.).

[0158] <Substrate transport speed> In the inkjet recording method of this embodiment, the substrate transport speed is 200 m / min or more. This enables high-speed inkjet recording.

[0159] The conveying speed of the substrate should be 200 m / min or more (preferably 240 m / min or more), and may be constant or not. The upper limit of the conveying speed of the substrate is, for example, 300 m / min.

[0160] <Ink Application by Inkjet Method> In the inkjet recording method of this disclosure, an image is recorded by applying the aforementioned ink of this disclosure to a transported substrate by an inkjet method. The ink application by the inkjet method is performed by ejecting ink from an inkjet head.

[0161] 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.

[0162] From the viewpoint of obtaining a high-resolution image, the amount of ink droplets is preferably 1 pL (picoliters) to 10 pL, and more preferably 1.5 pL to 6 pL.

[0163] <Other Operations> The inkjet recording method of this disclosure may include other operations besides applying ink. Other operations include, for example, preheating the substrate and drying the ink-coated substrate.

[0164] Hereinafter, an example of an inkjet recording apparatus used in the inkjet recording method of this disclosure will be described with reference to the drawings.

[0165] 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.

[0166] Figure 1 is a conceptual diagram showing an inkjet recording apparatus 100, which is an example of an inkjet recording apparatus used in the inkjet recording method of this disclosure.

[0167] As shown in Figure 1, the inkjet recording device 100 includes an ink application unit 101 that includes a first inkjet head 111A for ejecting a first ink, a second inkjet head 111B for ejecting a second ink, a third inkjet head 111C for ejecting a third ink, and a fourth inkjet head 111D for ejecting a fourth ink, applied to continuous paper 110 as a substrate. Here, at least one of the first to fourth inks is the ink of this disclosure. Alternatively, at least two of the first to fourth inks may be inks from the ink set of this disclosure described later.

[0168] The ink application unit 101 is configured, for example, with four full-line inkjet heads 111A, 111B, 111C, and 111D arranged in order from the upstream side in the transport direction of the continuous paper 110. Each of the inkjet heads 111A, 111B, 111C, and 111D applies, for example, black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink to the continuous paper 110. However, the types and number of colors are not limited to these.

[0169] A preferred full-line inkjet head used here is a non-recirculating head. This type of inkjet head is available from Kyocera. A second preferred full-line inkjet head has an ink circulation channel in the ink supply system. This channel allows fresh ink to be ejected and can be part of the ink supply system or part of a specially developed channel that runs behind the nozzle plate. The ink supply system preferably runs behind the nozzle plate to allow for the use of more ink without impairing the restart / standby behavior. This type of inkjet head is available from Fujifilm Dimatix and Kyocera.

[0170] The ink ejected from each inkjet head contains a pigment and an organic solvent. The details of the first and second inks are as described above.

[0171] The continuous sheet of paper 110 is fed out from the main winding roller 102 and sent by the transport roller 112 of the transport unit 103 onto the transport guide member 113 which is positioned opposite the ink application unit 101, and is transported (moved) guided by the transport guide member 113.

[0172] The continuous sheet of paper 110, to which ink has been applied by the ink application unit 101, is sent by the discharge roller 118 through a heating and drying device (not shown) and wound onto the winding roller 105.

[0173] Furthermore, the inkjet recording device may be equipped with a preheating and drying device for preheating the substrate, and a substrate inversion device for applying ink to both sides of the substrate. In addition, a heating device may be provided for applying radiant heating to the ink-coated substrate. "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).

[0174] Furthermore, a pretreatment liquid application unit may be provided upstream of the ink application unit 101 to apply a pretreatment liquid containing water and a coagulant to the surface of the substrate to which the ink will be applied before the ink is applied. This can further improve the resolution of the image.

[0175] <Ink Set> The ink set of this disclosure includes a plurality of inkjet inks, including the ink of this disclosure as described above. Because the ink set of this disclosure includes the ink of this disclosure, it provides the effects of the ink of this disclosure (i.e., improved image blocking resistance and improved ink ejection stability).

[0176] A first example of the ink set of the present disclosure includes a cyan ink, a magenta ink, a yellow ink, and a black ink, wherein at least one of the cyan ink, magenta ink, yellow ink, and black ink is the ink of the present disclosure as described above.

[0177] A second example of the ink set of this disclosure includes the aforementioned ink of this disclosure and a pretreatment solution containing water and a coagulant. According to this example, a more detailed image can be recorded.

[0178] For pretreatment solutions containing water and coagulants, refer to publicly available documents such as International Publication No. 2019 / 004485 and International Publication No. 2019 / 163581 as appropriate.

[0179] 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.

[0180] 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.

[0181] Examples of the ink sets of this disclosure include a combination of the first and second examples (i.e., an embodiment including cyan ink, magenta ink, yellow ink, and black ink, and including a pretreatment solution).

[0182] 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.

[0183] [Preparation of Pigment Dispersion P1 Containing Pigment and Crosslinking Dispersant P1] A pigment dispersion P1 containing a pigment and a crosslinking dispersant P1 which is a polymer dispersant (acrylic resin) having a crosslinked structure is prepared as follows.

[0184] <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 of the following composition (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.

[0185] - Composition of raw material monomers - Methacrylic acid: 37 parts by mass Stearyl methacrylate: 36.5 parts by mass Phenoxydiethylene glycol acrylate: 24 parts by mass Methyl methacrylate: 2.5 parts by mass

[0186] <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).

[0187] The acid value AV1 (mgKOH / g) of dispersant A after neutralization is 241 mgKOH / g. Note that the acid value is calculated by comparing the unneutralized acid group (-COOH group) with the neutralized acid group (-COOH group). － Since it is related to the total amount with the base, the acid value does not change due to neutralization. Therefore, the acid value AV1 (mgKOH / g) of dispersant A after neutralization is the same as the acid value (mgKOH / g) of uncrosslinked dispersant N.

[0188] <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.

[0189] -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

[0190] <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%.

[0191] <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 P1 (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

[0192] The acid value AV2 (mgKOH / g) of the crosslinking dispersant P1 is 169 mgKOH / g, as shown in Table 1. In crosslinking, the unneutralized acid group (-COOH group) and the neutralized acid group (-COOH group) in the polymer dispersant are crosslinked.－ A cross-linked structure is formed in the polymer dispersant by the reaction between at least one of the acid groups and the epoxy group of the cross-linking agent (specifically, the epoxy group in the structure of the glycidyl group). In this way, at least one of the unneutralized acid groups and the neutralized acid group is consumed to form the cross-linked structure, so the acid value of the polymer dispersant decreases due to cross-linking. Therefore, the acid value AV2 (mgKOH / g) of the cross-linked dispersant P1 is, in principle, lower than the acid value AV1 (mgKOH / g) of the neutralized dispersant A.

[0193] Furthermore, the degree of crosslinking of the crosslinking dispersant P1, represented by the following formula, is 30%. 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.

[0194] <Centrifugation and Filtration of Pigment Dispersion> 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 magenta pigment concentration becomes 15% by mass to obtain a pigment dispersion P1 containing magenta pigment and crosslinking dispersant P1.

[0195] [Preparation of Pigment Dispersion P2 (Used in Example 41) Containing Pigment and Crosslinking Dispersant P2] A pigment dispersion P2 containing a pigment and a crosslinking dispersant P2, which is a polymer dispersant having a crosslinked structure, is prepared in the same manner as the preparation of pigment dispersion P1 described above, except that the acid value of the crosslinking dispersant P1 is changed as shown in Table 5 to form the crosslinking dispersant P2. The acid value of the crosslinking dispersant is changed by adjusting the composition of the raw material monomers.

[0196] [Synthesis of Pigment Dispersion B1 (Used in Example 35) Containing Pigment and Block Dispersant B1] A pigment dispersion B1 containing a pigment and a block dispersant B1 which is a polymeric dispersant (acrylic resin) having a block copolymer structure is prepared as follows.

[0197] <Synthesis of Block Dispersant B1> Block dispersant B1, which is an acrylic resin having a block copolymer structure, is synthesized according to paragraphs 0110-0112 of International Publication No. 2013 / 115071 (Synthesis Example 3 "Synthesis of Block Copolymer A"). Details are shown below.

[0198] (Synthesis of ethyl-2-methyl-2-n-butylteranyl-propionate (hereinafter referred to as "BTEE")) 6.38 g (50 mmol) of metallic tellurium (trade name: Tellurium (-40 mesh), Aldrich) is suspended in 50 ml of THF. 34.4 mL (55 mmol) of n-butyllithium (Aldrich, 1.6 M hexane solution) is slowly added dropwise to the resulting suspension at room temperature (for 10 minutes). The resulting reaction solution is stirred until all metallic tellurium has disappeared (for 20 minutes). Next, 10.7 g (55 mmol) of ethyl-2-bromo-isobutyrate is added at room temperature and the mixture is stirred for 2 hours. After the reaction is complete, the solvent is concentrated under reduced pressure, followed by vacuum distillation to obtain 8.98 g (yield 59.5%) of BTEE, which is a yellow oily substance.

[0199] (Synthesis of Dibutylditerlide (hereinafter referred to as "DBDT")) 3.19 g (25 mmol) of metallic tellurium (trade name: Tellurium (-40 mesh), Aldrich) is suspended in 25 mL of THF. 17.2 mL (27.5 mmol) of n-butyllithium (Aldrich, 1.6 M hexane solution) is slowly added to the resulting suspension at 0°C (for 10 minutes). The resulting reaction solution is stirred until all metallic tellurium is completely gone (for 10 minutes). Next, 20 mL of ammonium chloride solution is added at room temperature and the mixture is stirred for 1 hour. After the reaction is complete, the organic layer is separated and the aqueous layer is extracted three times with diethyl ether. The collected organic layer is dried over anhydrous sodium sulfate and concentrated under reduced pressure to obtain 4.41 g (11.93 mmol: 95% yield) of a blackish-purple oily substance, which is DBDT.

[0200] (Synthesis of Block Dispersant B1) In a nitrogen-purged glove box, 90 g (511 mmol) of benzyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.), 2.00 g (6.67 mmol) of BTEE (i.e., ethyl-2-methyl-2-n-butylteranyl propionate), 1.22 g (3.33 mmol) of DBDT (i.e., dibutyl diterlide), 0.33 g (2.00 mmol) of 2,2'-azobis-isobutyronitrile (trade name: AIBN, manufactured by Otsuka Chemical Co., Ltd., hereinafter referred to as "AIBN"), and 90 g of methoxypropanol were charged into a flask equipped with a stirrer, and the mixture was reacted at 60°C for 16 hours. The polymerization rate was 99.6%, Mw was 16,200, and PDI was 1.41. To the resulting solution, 45 g (317 mmol) of butyl methacrylate (Tokyo Chemical Industries, Ltd.), 25 g (290 mmol) of methacrylic acid (Tokyo Chemical Industries, Ltd.), 0.22 g (1.33 mmol) of AIBN, and 70 g of methoxypropanol were added, and the mixture was reacted at 60°C for 22 hours. The polymerization rate was 99.1%. After the reaction was complete, the reaction solution was poured into 5 L of heptane, and the precipitate was filtered by suction and dried to obtain 38.2 g (86% yield) of a white powdery block dispersant B1. The acid value was 104. Mw and PDI were measured after methyl esterification of the carboxylic acid component in the block copolymer. Mw was 24300 and PDI was 1.49.

[0201] <Preparation of Pigment Dispersion B1> After pre-dispersing the mixture of the following composition to a uniform state, a 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 Pigment Dispersion B1 in which magenta pigment is dispersed by the blocking dispersant B1.

[0202] -Composition- Pigment Red 122 (Magenta pigment, which is a quinacridone pigment) ... 120.0 parts by mass Block Dispersant B1 ... 120.0 parts by mass MFTG ... 6.0 parts by mass Water ... 230.0 parts by mass

[0203] [Preparation of Pigment Dispersion N1 (Used in Comparative Example 1) Containing Pigment and Uncrosslinked Dispersant N1] 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 a pigment dispersion B1 in which magenta pigment is dispersed by the blocking dispersant B1.

[0204] -Composition- • Pigment Red 122 (Magenta pigment, which is a quinacridone pigment) ... 120.0 parts by mass • MFTG solution of uncrosslinked dispersant N1 (30% solids by mass concentration) ... 120.0 parts by mass • MFTG ... 6.0 parts by mass • Water ... 230.0 parts by mass

[0205] The MFTG solution of the uncrosslinked dispersant N1 is prepared in the same manner as the MFTG solution of the neutralized dispersant A (30% solids by mass concentration) described above, except that the composition of the raw material monomers is adjusted so that the acid value of the dispersant is 145 mg KOH / g.

[0206] [Examples 1-43, Comparative Examples 1-2] <Ink Preparation> The components shown in Tables 1-5 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 1-5. Pigment dispersion P1, pigment dispersion P2, block pigment dispersion P1, or pigment dispersion N1 are used as the source of pigment and dispersant in Tables 1-5.

[0207] Tables 1 to 5 are explained below. The "%" in each component column represents the content (mass %) relative to the total ink volume. However, if the abbreviation of the aqueous dispersion containing the corresponding component (e.g., XS, E370, 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 ink volume. 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 5 (i.e., the remainder) are water.

[0208] The details of each component in Table 1 (including components included in Example 2 and later) are as follows.

[0209] - Pigments - Pigment: Pigment Red 122 (Magenta Pigment) - Dispersants - Crosslinked Dispersant P1: Crosslinked dispersant P1 in the aforementioned pigment dispersion P1 Crosslinked Dispersant P2: Crosslinked dispersant P2 in the aforementioned pigment dispersion P2 Uncrosslinked Dispersant N1: Crosslinked dispersant N1 in the aforementioned pigment dispersion N1 Blocked Dispersant B1: Blocked dispersant B1 in the aforementioned pigment dispersion B1

[0210] - Organic Solvents - PG ... Propylene glycol 1,2-BDO ... 1,2-Butanediol EGmHE ... Ethylene glycol monohexyl ether PGmBE ... Propylene glycol monobutyl ether DEGmEE ... Diethylene glycol monoethyl ether 1,2-HDO ... 1,2-Hexanediol TEGMBE ... Triethylene glycol monobutyl ether DEGmiPE ... Diethylene glycol monoisopropyl ether PGmME ... Propylene glycol monomethyl ether PGmPE ... Propylene glycol monopropyl ether

[0211] - Inorganic Silicon Compounds - ・XS … Snowtex XS, a colloidal silica dispersion manufactured by Nissan Chemical Corporation.

[0212] -Silicone resin particles (Tg of silicone resin is as shown in Tables 1 to 5)- ・E370 …Aqueous dispersion of silicone resin particles (specifically, silicone-acrylic copolymer particles) manufactured by Nisshin Chemical Industry Co., Ltd., "Charine E370" ・M7110 …Aqueous dispersion of silicone resin particles (specifically, silicone-acrylic copolymer particles) manufactured by Japan Coating Resin Co., Ltd., "Movinyl 7110" ・FE502 …Aqueous dispersion of silicone resin particles (specifically, silicone-acrylic copolymer particles) manufactured by Nisshin Chemical Industry Co., Ltd., "Charine FE502" ・E371 …Aqueous dispersion of silicone resin particles (specifically, silicone-acrylic copolymer particles) manufactured by Nisshin Chemical Industry Co., Ltd., "Charine E371" ・E790 …Aqueous dispersion of silicone resin particles (specifically, silicone-acrylic copolymer particles) manufactured by Nisshin Chemical Industry Co., Ltd., "Charine E790"

[0213] - Non-silicone resin particles (Tg of non-silicone resin is as shown in Tables 1 to 5) - Resin particle A... Aqueous dispersion of acrylic resin particles as non-silicone resin particles prepared by the following method --Method for preparing aqueous dispersion of resin particle A-- 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 the temperature is raised to 85°C under a nitrogen stream. 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 A. The Tg of resin particles A is 97°C.・PDX-7667 … Aqueous dispersion of non-silicone resin particles (specifically, styrene-acrylic copolymer particles) manufactured by BASF, "Joncryl PDX-7667" ・PDX-7692 … Aqueous dispersion of non-silicone resin particles (specifically, styrene-acrylic copolymer particles) manufactured by BASF, "Joncryl PDX-7692" ・PDX-7780 … Aqueous dispersion of non-silicone resin particles (specifically, styrene-acrylic copolymer particles) manufactured by BASF, "Joncryl PDX-7780" ・M972 … Aqueous dispersion of non-silicone resin particles (specifically, styrene-acrylic copolymer particles) manufactured by Japan Coating Resin, "Movinyl 972" ・A-2092 … Aqueous dispersion of non-silicone resin particles (specifically, styrene-acrylic copolymer particles) manufactured by Covestro, "Neocryl A-2092"・SF130… "Superflex 130," an aqueous dispersion of non-silicone resin particles (specifically, urethane resin particles) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. ・Resin particles B… An aqueous dispersion of acrylic resin particles as non-silicone resin particles prepared by the following method --Method for preparing resin particles B-- 293 g of methyl ethyl ketone is placed in a 2-liter three-necked flask (hereinafter also referred to as the "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, and the temperature is raised to 80°C. Next, while maintaining the temperature inside the reaction vessel at 80°C, a mixed solution consisting of 90.0 g of methyl methacrylate (manufactured by Mitsubishi Gas Chemical Co., Ltd.), 139.4 g of isobornyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 25.5 g of methacrylic acid (manufactured by Mitsubishi Gas Chemical Co., Ltd.), 48 g of methyl ethyl ketone, and 1.25 g of "V-601" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., polymerization initiator) is added dropwise at a constant rate so that the addition is completed in 2 hours. After the addition is complete, (1) a solution of 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone is added and the mixture is stirred for another 2 hours. Then, step (1) is repeated four times, and a solution of 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone is added and the mixture is stirred for 3 hours. As a result, a polymer solution is obtained, which is a solution of methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 35 / 55 / 10 [mass ratio]) copolymer.The weight-average molecular weight (Mw) of the copolymer in the polymer solution is 72,000. Next, 588.2 g of the polymer solution is weighed into a reaction vessel, 165 g of isopropanol and 120.8 ml of 1 mol / L sodium hydroxide (NaOH) aqueous solution are added, and the temperature in the reaction vessel is raised to 80°C. Next, 718.0 g of distilled water is added dropwise to the reaction vessel at a rate of 20 ml / min to disperse the mixture in water. After that, the temperature in the reaction vessel is maintained at 80°C for 2 hours, 85°C for 2 hours, and 90°C for 2 hours under atmospheric pressure, and then the pressure in the reaction vessel is reduced, and a total of 913.7 g of isopropanol, methyl ethyl ketone, and distilled water is removed by distillation. The resulting mixture is filtered through a 50 μm mesh to obtain an aqueous dispersion of resin particles B (solid content concentration 23.2% by mass). The Tg of resin particles B is 150°C.

[0214] - Wax Particles - ・E6314 … Polyethylene wax aqueous dispersion "Hi-Tec E6314" manufactured by Toho Chemical Industry Co., Ltd. ・A1039 … Paraffin wax aqueous dispersion "Aquacer 1039" manufactured by BYK Co., Ltd.

[0215] - Surfactants (HLB values ​​are shown in Tables 1 to 5) - Surfinol 104: Acetylene-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd. 1.0% by mass - Orphine E1010: Acetylene-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd. 1.0% by mass - BYK345: Silicone-based surfactant manufactured by BYK - Emulgen 120: Surfactant manufactured by Kao Corporation (polyoxyethylene (12) lauryl ether) - Emulgen 103: Surfactant manufactured by Kao Corporation (polyoxyethylene (3) lauryl ether)

[0216] <Inkjet Recording> A SAMBA G3L head manufactured by Fujifilm Dimatix is ​​prepared as the inkjet head, and the above ink is loaded into the storage tank connected to the inkjet head. The inkjet head and storage tank are set in the inkjet recording device. OK Topcoat 104 (manufactured by Oji Paper Co., Ltd.), a gloss-coated roll paper, is used as the substrate, and while the substrate is being transported, ink is applied from the inkjet head onto the transported substrate to perform image recording (i.e., inkjet recording). The inkjet recording device used in this embodiment includes a substrate inversion device for performing image recording on both sides of the substrate. The detailed conditions for inkjet recording are as follows.

[0217] <Inkjet Recording Conditions> ・Substrate transport mechanism: Roll to roll ・Inkjet head temperature: 32°C ・Inkjet head resolution: 1200 dpi x 600 dpi ・Ink droplet size: 3.5 pL ・Environment around inkjet head: Temperature 25°C ± 1°C, relative humidity 25°C ± 5% ・Substrate transport speed: 240 m / min ・Substrate tension during transport: 60 N

[0218] <Evaluation> The inkjet recording described above was performed, and the following evaluation was conducted. The results are shown in Tables 1 to 5.

[0219] (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.

[0220] - 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).

[0221] (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.

[0222] - 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.

[0223]

[0224]

[0225]

[0226]

[0227]

[0228] As shown in Tables 1 to 5, each example using an ink containing water, a pigment, a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure, and silicone resin particles exhibits superior ejection stability compared to Comparative Example 1, which uses an ink containing a polymeric dispersant without a crosslinked structure. Furthermore, each example exhibits superior image blocking resistance compared to Comparative Example 2, which uses an ink without silicone resin particles.

[0229] The results from Examples 5, 8, and 9 show that when the glass transition temperature of the silicone resin particles is 80°C or higher (Example 5), the image blocking resistance is further improved.

[0230] The results from Examples 5, 10, and 11 show that when the content of silicone resin particles is 3% by mass or more relative to the total solid content of the ink (Examples 5 and 10), the image blocking resistance is further improved. The results from Examples 4 and 5 show that when the content of silicone resin particles is 30% by mass or less relative to the total solid content of the ink (Example 5), the ink ejection stability is further improved.

[0231] The results from Examples 1 and 5 show that when the ink contains non-silicone resin particles with a glass transition temperature of 80°C or higher (Example 5), the image blocking resistance is further improved.

[0232] The results from Examples 21 to 30 show that when the organic solvent in the ink contains an alkanediol with 4 or fewer carbon atoms (specifically propylene glycol) and at least one selected from the group consisting of monoalkylene glycol monoalkyl ethers and 1,2-alkanediols with 5 or more carbon atoms (specifically at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monobutyl ether, and diethylene glycol monoethyl ether) (Examples 21, 22, and 28-30), the ink ejection stability is further improved.

[0233] From the results of Examples 5 and 15-18 (Example 5 is the example without wax particles), and Examples 21, 23, and 33-35 (Examples 21 and 23 are the examples without wax particles), it can be seen that when the ink contains wax particles (Examples 15-18, 33-35), the blocking resistance is further improved.

[0234] The results from Examples 37 to 40 show that when the ink contains an acetylene-based surfactant with an HLB value of 6 or less (Examples 37, 39, and 40), the image's blocking resistance is further improved.

[0235] Although the above examples show the use of magenta ink as the ink of the present disclosure, if other inks (for example, cyan ink, yellow ink, or black ink) are used as the ink of the present disclosure in place of or in addition to magenta ink, the same effects as those in the above examples can be obtained even if the aforementioned pretreatment solution is applied before applying the ink of the present disclosure.

[0236] The disclosure of Japanese Patent Application No. 2025-054585, 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 ink comprising water, a pigment, a polymeric dispersant having at least one of a crosslinked structure and a block copolymer structure, and silicone resin particles.

2. The inkjet ink according to claim 1, wherein the glass transition temperature of the silicone resin particles is 80°C or higher.

3. The inkjet ink according to claim 1, wherein the content of the silicone resin particles is 3% by mass to 30% by mass with respect to the total solid content of the inkjet ink.

4. The inkjet ink according to claim 1, further comprising non-silicone resin particles having a glass transition temperature of 80°C or higher.

5. The inkjet ink according to claim 1, further comprising an organic solvent, wherein the organic solvent comprises at least one selected from the group consisting of an alkanediol having 4 or fewer carbon atoms, a monoalkylene glycol monoalkyl ether, and a 1,2-alkanediol having 5 or more carbon atoms.

6. The inkjet ink according to claim 1, further comprising an organic solvent, wherein the organic solvent comprises propylene glycol and at least one selected from the group consisting of ethylene glycol monohexyl ether, propylene glycol monobutyl ether, and diethylene glycol monoethyl ether.

7. The inkjet ink according to claim 1, further comprising wax particles.

8. The inkjet ink according to claim 1, further comprising a nonionic surfactant, wherein the nonionic surfactant comprises an acetylene-based surfactant and a silicone-based surfactant.

9. The inkjet ink according to claim 8, wherein the acetylene-based surfactant comprises an acetylene-based surfactant having an HLB value of 6 or less.

10. The inkjet ink according to claim 8, wherein the nonionic surfactant further comprises a polyoxyethylene alkyl ether.

11. The inkjet ink according to claim 1, wherein 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.

12. The inkjet ink according to claim 1, used as the ink in an inkjet recording method that includes applying ink to a substrate being transported at a transport speed of 200 m / min or more by an inkjet method to record an image.

13. The inkjet ink according to claim 12, wherein the substrate is roll paper.

14. An ink set comprising cyan ink, magenta ink, yellow ink, and black ink, wherein at least one of the cyan ink, magenta ink, yellow ink, and black ink is an inkjet ink according to any one of claims 1 to 13.

15. An ink set comprising an inkjet ink according to any one of claims 1 to 13, and a pretreatment solution containing water and a coagulant.

16. An inkjet recording method comprising applying an inkjet ink described in any one of claims 1 to 13 to a substrate being transported at a transport speed of 200 m / min or more by an inkjet method to record an image.

Images