Image recording method

Abstract

The image recording method of the present invention includes: a process of preparing an ink containing water and a white pigment; and a process of imparting the ink to a substrate by ejecting the ink from an inkjet head at a droplet volume of 1.0 pL or more, immersing the ejection surface of the ink in the inkjet head in the ink in a vertically upright state for 2 seconds, then taking the ejection surface out of the ink while maintaining the state, and then leaving the ejection surface for 1 minute while maintaining the state, in which case the ratio of the area of ​​the region to which the ink is attached in the ejection surface is less than 40% by area.

Description

Technical Field

[0001] The present invention relates to an image recording method. Background Art

[0002] Various studies have been conducted on image recording methods.

[0003] For example, Patent Document 1 discloses a particle capable of forming a particle structure in which structural color can be observed, and comprising:

[0004] core; and

[0005] The shell portion is formed of polydopamine or a derivative thereof and has a thickness of 1.0 nm to 10.0 nm.

[0006] The extinction coefficient with respect to light having a wavelength of 380 nm to 780 nm inclusive is 0.1 or less, and the refractive index with respect to light having a wavelength of 380 nm to 780 nm inclusive is 1.7 or more.

[0007] Patent Document 1 also discloses an ink containing the above-mentioned particles and a method of recording an image by an inkjet method using the above-mentioned ink.

[0008] Patent Document 2 discloses an aqueous inkjet ink comprising at least water, titanium oxide, a pigment dispersant, and an organic solvent, wherein the aqueous inkjet ink has excellent printability or jetting stability on a substrate with low absorption and excellent ink properties such as storage stability, sedimentation, and hiding power as a pigment, and the aqueous inkjet ink is characterized in that:

[0009] The titanium oxide is obtained by treating the surface of the pigment with an organic compound.

[0010] Furthermore, the amount of alkali on the surface of the titanium oxide pigment is 28 μmol / g or more.

[0011] Furthermore, the pigment dispersant is an acidic dispersant having an acid value of 5 mgKOH / g or more and 150 mgKOH / g or less.

[0012] Furthermore, at least one or more organic solvents having a boiling point of 200° C. to 265° C. and a surface tension of 20 mN / m to 30 mN / m are contained as the organic solvent.

[0013] Patent Document 1: Japanese Patent Application Publication No. 2018-2929

[0014] Patent Document 2: Japanese Patent Application Publication No. 2015-124348 Summary of the invention

[0015] Technical issues to be solved by the invention

[0016] However, in the image recording method using ink, there is a need to further improve the continuous ejection property of the ink and the concealability of the image.

[0017] An object of one aspect of the present invention is to provide an image recording method that is excellent in continuous ink ejection performance and image concealment performance.

[0018] Means for solving technical problems

[0019] Specific methods for solving the problem include the following.

[0020] <1> A method for recording an image, comprising:

[0021] The process of preparing ink containing water and white pigment; and

[0022] The step of applying ink to a substrate by ejecting ink from an inkjet head in a droplet volume of 1.0 pL or more,

[0023] The ejection surface of the ink in the inkjet head is immersed in the ink for 2 seconds in a vertically upright state, and then the ejection surface is taken out of the ink while maintaining the above state, and then the ejection surface is left for 1 minute while maintaining the above state. In this case, the ratio of the area of ​​the region to which the ink is attached in the ejection surface is less than 40 area %.

[0024] <2> according to <1> The image recording method described above is characterized in that the area ratio of the region to which the ink is attached on the ejection surface is 15 area % or less.

[0025] <3> according to <1> or <2> The image recording method, wherein:

[0026] The ink further contains a solvent S1, which is a water-soluble organic solvent having a contact angle of 85° or less with respect to the ejection surface.

[0027] The content of the solvent S1 is 0.1% by mass to 10% by mass based on the total amount of the ink.

[0028] <4> according to <3> The image recording method described above, wherein the solvent S1 contains a water-soluble organic solvent having a contact angle of 80° or less with respect to the ejection surface.

[0029] <5> according to <4> In the above-mentioned image recording method, the solvent S1 contains a water-soluble organic solvent having a contact angle of 75° or less with respect to the ejection surface.

[0030] <6> according to <3> to <5> The image recording method described in any one of the above, wherein the solvent S1 contains an alkylene glycol monoalkyl ether.

[0031] <7> according to <3> to <6> The image recording method described in any one of the above, wherein the solvent S1 contains at least one selected from the group X consisting of ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether.

[0032] <8> according to <7> The image recording method, wherein the solvent S1 contains at least two selected from group X.

[0033] <9> according to <1> to <8> The image recording method according to any one of the preceding claims, wherein the content of the water-soluble organic solvent having a boiling point of 220° C. or higher in the ink is 5% by mass or less.

[0034] <10> according to <1> to <9> The image recording method as described in any one of the preceding claims, wherein:

[0035] The ink also contains a polymer dispersant,

[0036] The polymer dispersant contains a block polymer or a polymer having a cross-linked structure.

[0037] <11> according to <1> to <10> The image recording method according to any one of the preceding claims, wherein a standard deviation of a volume-based particle size distribution of dispersed particles containing a white pigment in the ink is 140 nm or less.

[0038] <12> according to <1> to <11> The image recording method described in any one of the above, wherein the substrate is a non-permeable substrate.

[0039] <13> according to <1> to <12> The image recording method described in any one of the above aspects, wherein the step of applying the ink is a step of applying the ink to the substrate by a one-pass method.

[0040] <14> according to <1> to <13> The image recording method described in any one of the above, wherein the diameter of a nozzle hole for ejecting ink in the inkjet head is 20 μm or less.

[0041] Effects of the Invention

[0042] According to one aspect of the present invention, there is provided an image recording method which is excellent in the continuous ejection property of ink and the concealability of the image. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a black character image used for evaluation of the concealment property of an image in the example. DETAILED DESCRIPTION

[0044] In the present invention, a numerical range expressed using "to" indicates a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0045] In the present invention, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition represents the total amount of the plurality of substances present in the composition unless otherwise specified.

[0046] In the numerical ranges described stepwise in the present invention, the upper limit or lower limit described in a certain numerical range may be replaced by the upper limit or lower limit of another numerical range described stepwise, or may be replaced by the value shown in the Examples.

[0047] In the present invention, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0048] In the present invention, a combination of preferred embodiments is a more preferred embodiment.

[0049] In the present invention, "image" means the entire film formed by applying ink, and "image recording" means the formation of the film.

[0050] The concept of "image" in the present invention also includes a solid image.

[0051] [Image recording method]

[0052] The image recording method of the present invention comprises:

[0053] A step of preparing ink containing water and a white pigment (hereinafter also referred to as an "ink preparation step"); and

[0054] A step of applying ink to a substrate by ejecting ink from an inkjet head in a droplet volume of 1.0 pL (picoliter) or more (hereinafter also referred to as "ink applying step"),

[0055] The ejection surface of the ink in the inkjet head is immersed in the ink for 2 seconds in a vertically upright state, then the ejection surface is taken out from the ink while maintaining the above state, and then the ejection surface is left for 1 minute while maintaining the above state (hereinafter, the operation so far is also referred to as the "repellency test"). In this case, the ratio of the area of ​​the region to which the ink is attached in the ejection surface (hereinafter, also referred to as the "ink adhesion rate after the repellency test") is less than 40 area%.

[0056] The image recording method of the present invention is excellent in the continuous ejection property of ink and the concealability of the image.

[0057] The reason why this effect is achieved is presumed as follows.

[0058] In the image recording method of the present invention, by satisfying both the requirement that the ink contains a white pigment and the ink droplet amount is 1.0 pL or more, the concealability of the image is improved.

[0059] Here, the concealment of an image is one of the properties of an image, and refers to the property of using the image to conceal a substrate on which the image is recorded (for example, an impermeable substrate, a color image recorded on an impermeable substrate, etc.).

[0060] However, it was found that if the ink droplet amount is 1.0 pL or more, the continuous jetting property of the ink sometimes decreases. This is believed to be because, as the ink droplet amount (i.e., the volume of the droplet) increases, the ink easily overflows from the nozzle hole (i.e., the nozzle) in the inkjet head, and the overflowed ink easily adheres to the ejection surface (i.e., the nozzle surface) in the inkjet head. In other words, it is believed that the ink attached to the ejection surface easily causes the ink to eject poorly (e.g., ejection bending, etc.), and thus the continuous jetting property of the ink is easily reduced.

[0061] Regarding the above-mentioned problem when the ink droplet volume is 1.0 pL or more, in the image recording method of the present invention, the ink adhesion rate after the dispersibility test is 40 area % or less. Thus, when the ink is attached to the ejection surface of the inkjet head, the dispersibility of the ink from the ejection surface (that is, the ease of removing the ink from the ejection surface) is improved. As a result, even though the ink droplet volume is 1.0 pL or more, the continuous ejection property of the ink can be suppressed from decreasing.

[0062] The reason why the image recording method of the present invention is excellent in the continuous ejection property of the ink and the concealment property of the image is presumably as described above.

[0063] <Ink Adhesion Rate after Dispersibility Test>

[0064] In the present invention, the dispersibility test refers to the following operation: immersing the ejection surface of the ink in the inkjet head in the ink in a vertically upright state for 2 seconds, then taking the above ejection surface out of the ink while maintaining the above state, and then leaving the above ejection surface for 1 minute while maintaining the above state.

[0065] Here, the state in which the ejection surface is vertically erected means a state in which the normal direction of the ejection surface (that is, the direction perpendicular to the ejection surface) is in the horizontal direction.

[0066] In the present invention, the ink adhesion rate (area %) after the repellency test is a value related to the repellency (ease of removability) of the ink from the ejection surface.

[0067] When the ink has excellent repellency, the ink drips from the ejection surface after the repellency test due to gravity, and as a result, the area to which the ink adheres becomes smaller, and the ink adhesion rate after the repellency test decreases.

[0068] In the case where the repellency of the ink is poor, the area on the ejection surface to which the ink is always attached after the repellency test becomes larger, and the ink adhesion rate after the repellency test increases.

[0069] The ink adhesion rate (area %) after the repellency test was measured as follows.

[0070] A photograph of the ejection surface in the inkjet head after the repellency test (ie, after the above-mentioned standing for 1 minute) was taken, and the obtained photograph was subjected to binarization processing.

[0071] The binarization process is performed using, for example, image analysis software "ImageJ" manufactured by the National Institutes of Health (NIH) of the United States.

[0072] The obtained binary image was used to determine the ratio (area %) of the area of ​​the region where the ink adhered to the area of ​​the entire ejection surface immersed in the ink, and this ratio was used as the ink adhesion rate (area %) after the repellency test.

[0073] In the present invention, the ink adhesion rate after the dispersibility test is less than 40 area %. Thus, the dispersibility of the ink from the ejection surface is excellent to some extent, so the occurrence of ejection failure caused by the ink adhering to the ejection surface can be suppressed, and as a result, the continuous ejection of the ink is improved.

[0074] From the viewpoint of further improving the continuous ejection property of the ink, the ink adhesion rate after the repellency test is preferably 15 area % or less.

[0075] The lower limit of the ink adhesion rate after the repellency test is not particularly limited, and may be 0 area % or may exceed 0 area % (for example, 1 area %, 5 area % or the like).

[0076] Hereinafter, each step that may be included in the image recording method of the present invention will be described.

[0077] <Ink preparation process>

[0078] The ink preparation step is a step of preparing ink containing water and a white pigment.

[0079] The ink preparation step may be a step of manufacturing ink or a step of simply preparing ink manufactured in advance.

[0080] The ink prepared in this step will be described below.

[0081] (white pigment)

[0082] The ink contains at least one white pigment.

[0083] As white pigment, there is no particular limitation, and known white pigments can be used, for example, inorganic pigment particles such as titanium dioxide particles (TiO2), zinc oxide particles, barium sulfate particles, silicon oxide particles, aluminum oxide particles, magnesium oxide particles, calcium silicate particles, calcium carbonate particles, kaolin particles, talc particles, colloidal silica particles, etc. can be cited. In addition, hollow resin particles can also be cited as white pigment.

[0084] From the viewpoint of concealability of an image, the white pigment particularly preferably contains titanium dioxide particles.

[0085] Titanium dioxide particles are particles with a large refractive index, and therefore, if the white pigment contains titanium dioxide particles, the concealability of the image is further improved.

[0086] Examples of the titanium dioxide particles include anatase-type titanium dioxide particles, rutile-type titanium dioxide particles, and brookite-type titanium dioxide particles. From the viewpoint of the refractive index, rutile-type titanium dioxide particles are preferred.

[0087] Furthermore, rutile titanium dioxide particles have a weaker photocatalytic effect than anatase titanium dioxide particles and brookite titanium dioxide particles, and therefore have an advantage of having less influence on the resin in the ink, the resin base material, and the like.

[0088] When the white pigment contains titanium dioxide particles, the white pigment may contain white pigments other than titanium dioxide particles (for example, inorganic pigment particles).

[0089] When the white pigment contains titanium dioxide particles, the proportion of the titanium dioxide particles in the total amount of the white pigment is preferably 20% by mass or more, more preferably 50% by mass or more, and more preferably 80% by mass or more. The upper limit of the proportion of the titanium dioxide particles in the total amount of the white pigment is not particularly limited, as long as it is 100% by mass or less.

[0090] From the viewpoint of further improving the hiding property of an image, the average primary particle size of the white pigment is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more.

[0091] Furthermore, the average primary particle size of the white pigment is preferably 400 nm or less, and more preferably 300 nm or less, from the viewpoint of dispersion stability of the ink (for example, ejection stability when the ink is used as an inkjet ink).

[0092] In the present invention, the average primary particle size of the white pigment is a value measured using a transmission electron microscope (TEM). The measurement can be performed using a transmission electron microscope 1200EX manufactured by JEOL Ltd.

[0093] Specifically, a 1,000-fold diluted ink was dropped onto a Cu200 mesh (manufactured by JEOL Ltd.) with a carbon film attached thereto and dried. Then, the circle equivalent diameters of 300 independent non-overlapping white pigments were measured from an image magnified 100,000 times by TEM, and the measured values ​​were averaged to determine the average particle size.

[0094] Furthermore, from the viewpoint of image concealability, the refractive index of the white pigment is preferably 2.0 or more.

[0095] In the present invention, unless otherwise specified, the "refractive index" refers to a value measured by an ellipsometer at a temperature of 23° C. using visible light with a wavelength of 550 nm.

[0096] The content of the white pigment in the ink is preferably 1 to 20% by mass, more preferably 3 to 20% by mass, further preferably 5 to 20% by mass, further preferably 6 to 20% by mass, further preferably 7 to 15% by mass, relative to the total amount of the ink.

[0097] When the content of the white pigment in the ink is 1% by mass or more relative to the total amount of the ink, the concealability of the image is further improved.

[0098] When the content of the white pigment in the ink is 20% by mass or less relative to the total amount of the ink, the continuous ejection property of the ink is further improved.

[0099] (Standard deviation of volume-based particle size distribution of dispersed particles containing white pigment)

[0100] In the present invention, the standard deviation of the volume-based particle size distribution of dispersed particles containing the white pigment in the ink is preferably 160 nm or less, more preferably 150 nm or less, further preferably 140 nm or less, and further preferably 130 nm or less.

[0101] When the standard deviation is 160 nm or less, the ratio of coarse particles in the ink is reduced, and as a result, the continuous ejection property of the ink is further improved.

[0102] In the present invention, the standard deviation of the volume-based particle size distribution of dispersed particles containing a white pigment in the ink is measured by a dynamic light scattering method using an ink diluted 1,000 times. As a measuring device, for example, a particle size distribution measuring device "NANOTRAC UPA-EX150" manufactured by Nikkiso Co., Ltd. is used.

[0103] When the ink contains a polymer dispersant described later, the dispersed particles containing the white pigment are considered to be dispersed particles containing the white pigment and the polymer dispersant that interacts with the surface of the white pigment.

[0104] (Polymer Dispersant)

[0105] The ink preferably contains at least one polymeric dispersant.

[0106] The polymer dispersant has a function of dispersing the white pigment in the ink. Therefore, when the ink contains the polymer dispersant, the dispersibility of the white pigment in the ink is further improved.

[0107] In the case where the ink contains a polymer dispersant, it is considered that the ink contains dispersed particles containing a white pigment and a polymer dispersant that interacts with (eg, adsorbs) the white pigment.

[0108] In the present invention, the "polymer" refers to a compound having a weight average molecular weight (Mw) of 1,000 or more.

[0109] In the present invention, the weight average molecular weight (Mw) indicates a value measured by gel permeation chromatography (GPC).

[0110] When the measurement is performed by gel permeation chromatography (GPC), HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) is used as a measuring device, three TSKgel (registered trademark) Super MultiporeHZ-H (4.6 mmID×15 cm, manufactured by Tosoh Corporation) are used as columns, and THF (tetrahydrofuran) is used as an eluent. In addition, the measurement is performed using an RI detector, wherein the sample concentration is set to 0.45% by mass, the flow rate is set to 0.35 ml / min, the sample injection volume is set to 10 μL, and the measurement temperature is set to 40°C. The calibration curve is prepared based on eight samples of "TSK standard, polystyrene (polystyrene)" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000" and "n-propylbenzene".

[0111] As the polymer dispersant, a known polymer dispersant can be used without particular limitation.

[0112] As the polymer dispersant, for example, those described in known documents such as paragraphs 0080 to 0096 of JP-A-2016-145312 and paragraphs 0078 to 0108 of International Publication No. 2013 / 180074 can be used.

[0113] As the polymer dispersant, acrylic resin is preferred.

[0114] In the present invention, acrylic resin refers to a polymer (homopolymer or copolymer) containing at least one raw material monomer selected from the group consisting of acrylic acid, acrylic acid derivatives (eg, acrylic esters, etc.), methacrylic acid and methacrylic acid derivatives (eg, methacrylic esters, etc.).

[0115] The weight average molecular weight (Mw) of the polymer dispersant is preferably 3,000 to 100,000, more preferably 4,000 to 80,000, and even more preferably 5,000 to 60,000.

[0116] The polymer dispersant preferably contains a structural unit having an adsorptive group and a structural unit having an anionic group.

[0117] The structural unit having an anionic group is a structural unit that contributes to dispersibility.

[0118] The polymer dispersant may contain only one type of structural unit having an anionic group, or may contain two or more types of structural units having anionic groups.

[0119] Examples of the anionic group include an acid group and a salt thereof.

[0120] Examples of the acid group include a carboxyl group, a sulfone group, a phosphoric acid group, and a phosphonic acid group. Among them, a carboxyl group is preferred.

[0121] As the salt of the acid group, an alkali metal salt is preferred, and a sodium salt or a potassium salt is more preferred.

[0122] 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 preferred.

[0123] In the present invention, the structural unit derived from the compound A (eg, (meth)acrylic acid) means a structural unit formed by polymerizing the compound A (eg, (meth)acrylic acid).

[0124] The adsorbent group in the structural unit having an adsorbent group has a function of adsorbing to the white pigment.

[0125] The polymer dispersant may contain only one type of structural unit having an adsorptive group, or may contain two or more types of structural units having an adsorptive group.

[0126] 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.

[0127] The structural unit having an adsorptive group is preferably a structural unit derived from a (meth)acrylate having an adsorptive group.

[0128] The polymer dispersant may be a random polymer (ie, a random copolymer), a block polymer (ie, a block copolymer), or a polymer having a cross-linked structure.

[0129] The polymer dispersant preferably contains a block polymer or a polymer having a cross-linked structure. In this case, the polymer dispersant may contain both a block polymer and a polymer having a cross-linked structure.

[0130] When the polymer dispersant contains a block polymer or a polymer having a cross-linked structure, the continuous jetting property of the ink is further improved. This is believed to be because, when the polymer dispersant contains a block polymer or a polymer having a cross-linked structure, the interaction between the polymer dispersant and the white pigment in the ink is further improved, and the generation of free polymer dispersant can be further suppressed. As a result, the viscosity increase of the ink caused by the free polymer dispersant can be suppressed.

[0131] From the viewpoint of further improving the continuous ejection properties of the ink, the polymer dispersant more preferably contains a block polymer.

[0132] -Block Polymers-

[0133] The block polymer preferably contains:

[0134] Structural units derived from hydrophobic monomers; and

[0135] A structural unit derived from a monomer containing an anionic group (hereinafter referred to as "anionic group-containing monomer").

[0136] The structural unit derived from the hydrophobic monomer contained in the block polymer may be only one kind or two or more kinds.

[0137] The structural unit derived from the anionic group-containing monomer contained in the block polymer may be only one kind or two or more kinds.

[0138] Examples of the structural unit derived from the hydrophobic monomer include:

[0139] Olefinic unsaturated compounds having an aromatic ring structure or an alicyclic structure; and

[0140] (Meth)acrylate having an alkyl group having 1 to 20 carbon atoms.

[0141] The content of the structural unit derived from the hydrophobic monomer is preferably 35 to 95% by mass, more preferably 50 to 95% by mass, and further preferably 70 to 90% by mass, based on the total amount of the block polymer.

[0142] From the viewpoint of adsorption to the white pigment, the hydrophobic monomer preferably contains an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure.

[0143] The structural unit derived from an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure is preferably at least one selected from the group consisting of structural units represented by the following formulae (A) to (F).

[0144] [Chemical formula 1]

[0145]

[0146] In formula (A) to formula (F), R 5 R each independently represents a hydrogen atom or a methyl group. 6 Each independently represents an alkyl group, an alkenyl group or an alkynyl group. m is an integer of 0 to 5. n is an integer of 0 to 11. 5 It represents a divalent group which is one selected from the first group consisting of an alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- and -C(=O)-, a divalent group consisting of a combination of two or more selected from the first group, or a single bond.

[0147] In formula (A) to formula (F), R 6 Each independently represents an alkyl group, an alkenyl group or an alkynyl group.

[0148] The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and further preferably a methyl group or an ethyl group.

[0149] The alkenyl group is preferably an alkenyl group having 2 to 10 carbon atoms, more preferably an alkenyl group having 2 to 4 carbon atoms, and further preferably an alkenyl group having 2 or 3 carbon atoms.

[0150] The alkynyl group is preferably an alkynyl group having 2 to 10 carbon atoms, more preferably an alkynyl group having 2 to 4 carbon atoms, and further preferably an alkynyl group having 2 or 3 carbon atoms.

[0151] And, R 6 It may be an unsubstituted group or a group substituted by a substituent. 6 When the moiety is substituted with a substituent, examples of the substituent include a halogen atom (eg, a chlorine atom, a bromine atom, etc.) and an alkyl group (eg, a methyl group, an ethyl group, etc.).

[0152] In formula (A) and formula (B), m represents a substituent on the benzene ring (R6 ) quantity.

[0153] m is an integer of 0 to 5, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, and further preferably 0 or 1.

[0154] In formula (C), n represents a substituent on the cyclohexane ring (R 6 ) quantity.

[0155] n is an integer of 0 to 11, preferably an integer of 0 to 6, more preferably an integer of 0 to 2, and further preferably 0 or 1.

[0156] In formula (A) to formula (F), L 5 It represents a divalent group which is one selected from the first group consisting of an alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- and -C(=O)-, a divalent group consisting of a combination of two or more selected from the first group, or a single bond.

[0157] L 5 The alkylene group having 1 to 18 carbon atoms may be linear, branched, and / or cyclic.

[0158] L 5 The alkylene group having 1 to 18 carbon atoms preferably has 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 or 2 carbon atoms.

[0159] Examples of the arylene group having 6 to 18 carbon atoms include a phenylene group, a naphthylene group, and a tolylene group.

[0160] L 5 The arylene group having 6 to 18 carbon atoms preferably has 6 to 12 carbon atoms, more preferably 6 to 10 carbon atoms.

[0161] L 5 The "divalent group formed by combining two or more types selected from the first group" is preferably a divalent group formed by combining at least one of an alkylene group having 1 to 18 carbon atoms and an arylene group having 6 to 18 carbon atoms and at least one of -O-, -NH-, -S- and -C(=O)-, and is particularly preferably the following group (AO5) or the following group (AO6).

[0162] [Chemical formula 2]

[0163]

[0164] In the group (AO5), R 1A and R 2AEach independently represents a hydrogen atom or a methyl group, n represents an integer of 1 to 8 (preferably an integer of 1 to 4, more preferably 1 or 2), *1 represents a bonding position to a carbonyl carbon atom, and *2 represents a bonding position to a non-carbonyl carbon atom.

[0165] In R 1A and R 2A When one of is a methyl group, the other is preferably a hydrogen atom.

[0166] In the group (AO6), L 6 represents an alkylene group having 1 to 8 carbon atoms (preferably 1 to 4, more preferably 1 or 2), *1 represents a bonding position to a carbonyl carbon atom, and *2 represents a bonding position to a non-carbonyl carbon atom.

[0167] L 5 It is preferably a single bond, -O-, group (AO5) or group (AO6), more preferably a single bond or -O-, and further preferably -O-.

[0168] Specific examples of the structural unit represented by formula (A) are shown below, but the structural unit represented by formula (A) is not limited to the following specific examples.

[0169] [Chemical formula 3]

[0170]

[0171] Specific examples of the structural unit represented by formula (B) are shown below, but the structural unit represented by formula (B) is not limited to the following specific examples.

[0172] [Chemical formula 4]

[0173]

[0174] Specific examples of the structural unit represented by formula (C) are shown below, but the structural unit represented by formula (C) is not limited to the following specific examples.

[0175] [Chemical formula 5]

[0176]

[0177] Specific examples of the structural unit represented by formula (D) are shown below, but the structural unit represented by formula (D) is not limited to the following specific examples.

[0178] [Chemical formula 6]

[0179]

[0180] Specific examples of the structural unit represented by formula (E) are shown below, but the structural unit represented by formula (E) is not limited to the following specific examples.

[0181] [Chemical formula 7]

[0182]

[0183] Specific examples of the structural unit represented by formula (F) are shown below, but the structural unit represented by formula (F) is not limited to the following specific examples.

[0184] [Chemical formula 8]

[0185]

[0186] The content of the structural unit derived from the ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, further preferably 30 to 70% by mass, and further preferably 30 to 60% by mass, based on the total amount of the block polymer.

[0187] The structural unit derived from the hydrophobic monomer also preferably contains a (meth)acrylate having an alkyl group having 1 to 20 carbon atoms.

[0188] The alkyl group may be either linear or branched.

[0189] Examples of the (meth)acrylate having an alkyl group having 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.

[0190] The content of the structural unit derived from the (meth)acrylate having an alkyl group having 1 to 20 carbon atoms is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, further preferably 30 to 70% by mass, and further preferably 40 to 60% by mass, based on the total amount of the block polymer.

[0191] Examples of the anionic group in the structural unit derived from the anionic group-containing monomer include a carboxyl group, a carboxyl salt, a sulfonic group, a sulfonic group salt, a phosphoric acid group, a phosphoric acid salt, a phosphonic acid group, and a phosphonic acid salt.

[0192] Examples of the counter ion in the salt include:

[0193] Alkali metal ions such as sodium ions, potassium ions, and lithium ions;

[0194] Alkaline earth metal ions such as calcium ions and magnesium ions;

[0195] Ammonium ion.

[0196] Among them, the anionic group is preferably a carboxyl group or a salt of a carboxyl group. Examples of the anionic group-containing monomer include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0197] Among them, the anionic group-containing monomer is preferably (meth)acrylic acid.

[0198] The content of the structural unit derived from the anionic group-containing monomer is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, and further preferably 3 to 20% by mass, based on the total amount of the block polymer.

[0199] Furthermore, from the viewpoint of suppressing cracks in the recorded image and improving the image quality of the recorded image, the acid value of the block polymer is preferably 8 mgKOH / g to 300 mgKOH / g, more preferably 20 mgKOH / g to 250 mgKOH / g, further preferably 80 mgKOH / g to 200 mgKOH / g, and particularly preferably 100 mgKOH / g to 150 mgKOH / g. If the acid value of the block polymer is 20 mgKOH / g or more, the image quality of the recorded image is more excellent. Furthermore, if the acid value of the block polymer is 250 mgKOH / g or less, the cracks of the recorded image can be further suppressed.

[0200] The weight average molecular weight (Mw) of the block polymer is not particularly limited, but is preferably 3,000 to 100,000, more preferably 4,000 to 80,000, and even more preferably 5,000 to 60,000 from the viewpoint of pigment dispersibility.

[0201] -Polymer with cross-linked structure-

[0202] The polymer having a cross-linked structure is not particularly limited as long as it has at least one cross-linked structure in the molecule.

[0203] The polymer having a crosslinked structure (hereinafter also referred to as a "crosslinked polymer") is formed by, for example, crosslinking an uncrosslinked polymer with a crosslinking agent.

[0204] The uncrosslinked polymer is preferably a water-soluble polymer.

[0205] In the present invention, "water-soluble" means a property that the amount of a compound that dissolves in 100 g of distilled water at 25°C is 1 g or more.

[0206] The “water solubility” preferably means that the amount of the compound to be dissolved in distilled water at 25° C. is 2 g or more, more preferably 5 g or more, and still more preferably 10 g or more.

[0207] Examples of the uncrosslinked polymer include polyethylene compounds, polyurethanes, and polyesters. Among them, the uncrosslinked polymer is preferably a polyethylene compound.

[0208] The uncrosslinked polymer is preferably a polymer having a functional group that can be crosslinked by a crosslinking agent. Examples of the crosslinkable functional group include a carboxyl group or a salt thereof, an isocyanate group, and an epoxy group.

[0209] Among them, from the viewpoint of improving the dispersibility of the white pigment, the cross-linkable functional group is preferably a carboxyl group or a salt thereof, and particularly preferably a carboxyl group. That is, the uncross-linked polymer is preferably a polymer containing a carboxyl group.

[0210] The uncrosslinked polymer is preferably a copolymer containing a structural unit derived from a monomer containing a carboxyl group (hereinafter referred to as a "carboxyl-containing monomer"). The structural unit derived from the carboxyl-containing monomer contained in the copolymer may be only one type or two or more types. The copolymer may be a random copolymer or a block copolymer, but is preferably a random copolymer.

[0211] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0212] From the viewpoint of crosslinking property and dispersibility, the carboxyl group-containing monomer is preferably (meth)acrylic acid or β-carboxyethyl acrylate, and more preferably (meth)acrylic acid.

[0213] The content of the structural unit derived from the carboxyl group-containing monomer that can be contained in the uncrosslinked polymer is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, and further preferably 3 to 20% by mass based on the total amount of the block polymer.

[0214] The uncrosslinked polymer preferably contains a structural unit derived from a hydrophobic monomer in addition to the structural unit derived from the carboxyl group-containing monomer.

[0215] The structural unit derived from the hydrophobic monomer may be of only one kind or of two or more kinds.

[0216] Examples of the structural unit derived from the hydrophobic monomer that may be contained in the uncrosslinked polymer include:

[0217] Structural units derived from ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure; and

[0218] A structural unit derived from a (meth)acrylate having an alkyl group having 1 to 20 carbon atoms.

[0219] Preferred aspects of these structural units that may be contained in the uncrosslinked polymer are the same as preferred aspects of these structural units that may be contained in the block polymer.

[0220] The content of the structural unit derived from the hydrophobic monomer in the uncrosslinked polymer is preferably 35 to 95% by mass, more preferably 50 to 95% by mass, and even more preferably 70 to 90% by mass based on the total amount of the uncrosslinked polymer.

[0221] Likewise, the content of the structural unit derived from the hydrophobic monomer in the cross-linked polymer is preferably 35 to 95% by mass, more preferably 50 to 95% by mass, and even more preferably 70 to 90% by mass, based on the total amount of the cross-linked polymer.

[0222] As structural units derived from hydrophobic monomers, the uncrosslinked polymer and the crosslinked polymer may each contain:

[0223] A (meth)acrylate structural unit having a benzene ring; and

[0224] A (meth)acrylate structural unit having an alkyl group having 12 or more carbon atoms.

[0225] The content of the (meth)acrylate structural unit having a benzene ring is preferably 20% by mass to 60% by mass based on the total amount of the polymer (ie, the uncrosslinked polymer or the crosslinked polymer).

[0226] The content of the (meth)acrylate structural unit having an alkyl group having 12 or more carbon atoms is preferably 10% by mass to 40% by mass based on the total amount of the polymer (ie, the uncrosslinked polymer or the crosslinked polymer).

[0227] From the viewpoint of pigment dispersibility, the acid value of the uncrosslinked polymer is preferably 67 mgKOH / g to 200 mgKOH / g, and more preferably 67 mgKOH / g to 150 mgKOH / g. In the present invention, the acid value is a value measured by the method described in JIS K0070:1992.

[0228] Furthermore, from the viewpoint of suppressing cracks in the recorded image and improving the image quality of the recorded image, the acid value of the cross-linked polymer is preferably 35 mgKOH / g to 185 mgKOH / g, more preferably 50 mgKOH / g to 150 mgKOH / g, and even more preferably 80 mgKOH / g to 130 mgKOH / g. If the acid value of the cross-linked polymer is 50 mgKOH / g or more, the image quality of the recorded image is more excellent. Furthermore, if the acid value of the cross-linked polymer is 150 mgKOH / g or less, cracks in the recorded image can be further suppressed.

[0229] The weight average molecular weight (Mw) of the uncrosslinked polymer is not particularly limited, but is preferably 3,000 to 100,000, more preferably 4,000 to 80,000, further preferably 5,000 to 60,000, and further preferably 10,000 to 60,000 from the viewpoint of pigment dispersibility.

[0230] The preferred range of the weight average molecular weight (Mw) of the cross-linked polymer is also the same as the preferred range of the weight average molecular weight (Mw) of the non-cross-linked polymer.

[0231] The crosslinking agent used when crosslinking the uncrosslinked polymer is preferably a compound having two or more reaction sites with the uncrosslinked polymer (for example, a polymer having a carboxyl group). The crosslinking agent may be used alone or in combination of two or more.

[0232] A preferred combination of a crosslinking agent and an uncrosslinked polymer is a combination of a compound having two or more epoxy groups (i.e., an epoxy compound having two or more functions) and a polymer having a carboxyl group. In this combination, a crosslinked structure is formed by the reaction of the epoxy group and the carboxyl group. The formation of the crosslinked structure using a crosslinking agent is preferably performed after the pigment is dispersed by the uncrosslinked polymer.

[0233] Examples of the bifunctional or higher-functional epoxy compound 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.

[0234] Among them, the bifunctional or higher-functional epoxy compound is preferably polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether.

[0235] The cross-linking agent may be a commercially available product.

[0236] As a commercially available product, Denacol EX-321, EX-821, EX-830, EX-850, and EX-851 (made by Nagase ChemteX Corporation) are mentioned, for example.

[0237] From the viewpoint of the crosslinking reaction rate and the dispersion stability after crosslinking, the molar ratio of the reactive site in the crosslinking agent (e.g., epoxy group) to the reactive site in the uncrosslinked polymer (e.g., carboxyl group) 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.

[0238] (water)

[0239] The ink contains water.

[0240] The content of water is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and further preferably 60% by mass or more, based on the total amount of the ink.

[0241] The upper limit of the water content is appropriately determined according to the contents of other components. Examples of the upper limit of the water content include 90% by mass and 80% by mass.

[0242] (Water-soluble organic solvent)

[0243] The ink preferably contains at least one water-soluble organic solvent.

[0244] The content of the water-soluble organic solvent is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 15% by mass to 30% by mass, based on the total amount of the ink.

[0245] -Solvent S1-

[0246] The ink preferably contains at least one solvent S1 described below.

[0247] The solvent S1 is a water-soluble organic solvent having a contact angle of 85° or less with respect to the ejection surface (ie, nozzle surface) in the inkjet head.

[0248] When the ink contains the solvent S1, it is easier to achieve an ink adhesion rate of 40 area % or less after the repellency test, and as a result, the continuous ejection property of the ink is further improved.

[0249] This effect is considered to be obtained because, when the ink contains the solvent S1 that is easily compatible with the ejection surface, the solvent S1 in the ink attached to the ejection surface is easily oriented toward the ejection surface, resulting in improved dispersibility of the ink from the ejection surface.

[0250] Here, the contact angle refers to the contact angle measured 1 minute after the solvent droplet comes into contact with the ejection surface, measured according to the method described in JIS R3257: 1999. The solvent droplet volume was set to 2 μL.

[0251] As a measuring apparatus, for example, a contact angle meter DropMaster DM700 (manufactured by Kyowa Interface Science Co., Ltd.) is used.

[0252] The content of the solvent S1 is preferably 0.1% by mass to 10% by mass based on the total amount of the ink.

[0253] This makes it easier to reduce the ink adhesion rate after the repellency test, and as a result, the continuous ejection property of the ink is further improved.

[0254] The lower limit of the content of the solvent S1 relative to the total amount of the ink is more preferably 0.5% by mass, and further preferably 1% by mass.

[0255] The upper limit of the content of the solvent S1 is more preferably 8% by mass, and further preferably 5% by mass, relative to the total amount of the ink.

[0256] As the solvent S1, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, triethylene glycol monobutyl ether, tripropylene glycol, 2-ethyl-1-hexanol, 1-pentanol, 1-hexanol, 1-octanol, 1,2-hexanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-3-methyl-1-butyl acetate, 3-methyl-1,3-butanediol, 2-dimethylaminoethanol, 2-amino-2-methyl-1-propanol, etc.

[0257] The solvent S1 preferably contains at least one water-soluble organic solvent (hereinafter, also referred to as "solvent S1A") having a contact angle of 80° or less with respect to the ejection surface.

[0258] The ratio of the solvent S1A in the solvent S1 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0259] As the solvent S1A, for example, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether, triethylene glycol monobutyl ether, 2-ethyl-1-hexanol, 1-pentanol, 1-hexanol, 1-octanol, 1,2-hexanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-3-methyl-1-butyl acetate, 2-dimethylaminoethanol, etc.

[0260] The solvent S1 preferably contains at least one water-soluble organic solvent (hereinafter, also referred to as "solvent S1B") having a contact angle of 75° or less with respect to the ejection surface.

[0261] The contact angle of solvent S1B is preferably less than 75°.

[0262] The ratio of the solvent S1B in the solvent S1 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0263] Examples of the solvent S1B include ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, 1-pentanol, 1-hexanol, 1-octanol, 1,2-hexanediol, 3-methoxy-3-methyl-1-butyl acetate, and 2-dimethylaminoethanol.

[0264] The solvent S1 preferably contains at least one alkylene glycol monoalkyl ether.

[0265] The ratio of the alkylene glycol monoalkyl ether in the solvent S1 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0266] As alkylene glycol monoalkyl ether,

[0267] Preferably ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether or triethylene glycol monobutyl ether,

[0268] More preferably, as the solvent S1A, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monomethyl ether or triethylene glycol monobutyl ether is used.

[0269] Further preferred as the solvent S1B is ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether or dipropylene glycol monomethyl ether.

[0270] From the viewpoint of further reducing the ink adhesion rate after the repellency test and further improving the continuous jetting property of the ink, the solvent S1 preferably contains at least one selected from the group X including ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether, and more preferably contains at least two selected from the above group X.

[0271] Examples of the preferred combination of the two include a combination of propylene glycol monopropyl ether and dipropylene glycol monomethyl ether, and a combination of ethylene glycol monobutyl ether and propylene glycol monoethyl ether.

[0272] -Water-soluble organic solvents with a boiling point below 220°C-

[0273] The ink may contain at least one water-soluble organic solvent having a boiling point below 220°C.

[0274] This further improves the drying properties of the ink (that is, the drying properties of the recorded image).

[0275] In the present invention, the boiling point means the boiling point at 1 atmosphere (101,325 Pa).

[0276] The water-soluble organic solvent having a boiling point lower than 220° C. may or may not correspond to the solvent S1.

[0277] Examples of water-soluble organic solvents with a boiling point lower than 220° C. include 1,2-propylene glycol (also called propylene glycol; PG) (boiling point 188° C.), 1,3-propylene glycol (boiling point 213° C.), propylene glycol monomethyl ether (boiling point 121° C.), ethylene glycol (boiling point 197° C.), ethylene glycol monomethyl ether (boiling point 124° C.), propylene glycol monoethyl ether (boiling point 133° C.), ethylene glycol monoethyl ether (boiling point 135° C.), propylene glycol monomethyl ether (boiling point 136° C.), propylene glycol monoethyl ether (boiling point 137 ... Alcohol monopropyl ether (boiling point 149°C), ethylene glycol monopropyl ether (boiling point 151°C), propylene glycol monobutyl ether (boiling point 170°C), ethylene glycol monobutyl ether (boiling point 171°C), 2-ethyl-1-hexanol (boiling point 187°C), dipropylene glycol monomethyl ether (boiling point 188°C), diethylene glycol dimethyl ether (boiling point 162°C), diethylene glycol diethyl ether (boiling point 188°C), dipropylene glycol dimethyl ether (boiling point 175°C), etc.

[0278] When the ink contains a water-soluble organic solvent having a boiling point lower than 220°C, the content of the water-soluble organic solvent having a boiling point lower than 220°C is preferably 1% to 50% by mass, more preferably 5% to 40% by mass, further preferably 10% to 40% by mass, further preferably 15% to 35% by mass, relative to the total amount of the ink.

[0279] -Water-soluble organic solvents with a boiling point of 220°C or above-

[0280] The content of the water-soluble organic solvent having a boiling point of 220° C. or higher (hereinafter also referred to as “high boiling point solvent”) in the ink is preferably 5% by mass or less. This further improves the drying properties of the ink (ie, the drying properties of the recorded image).

[0281] Here, "the content of water-soluble organic solvents having a boiling point of 220°C or higher in the ink is 5 mass % or lower" means that the ink does not contain a water-soluble organic solvent having a boiling point of 220°C or higher (i.e., the content of water-soluble organic solvents having a boiling point of 220°C or higher in the ink is 0 mass %), or, even if it contains a water-soluble organic solvent having a boiling point of 220°C or higher, the content of the water-soluble organic solvent having a boiling point of 220°C or higher is 5 mass % or lower relative to the total amount of the ink.

[0282] The content of the water-soluble organic solvent having a boiling point of 220° C. or higher in the ink is more preferably 3% by mass or less, further preferably 2% by mass or less, further preferably 1% by mass or less, and further preferably 0% by mass.

[0283] Examples of the water-soluble organic solvent having a boiling point of 220° C. or higher include glycerin (boiling point 290° C.), 1,2-hexanediol (HDO) (boiling point 223° C.), diethylene glycol (boiling point 245° C.), diethylene glycol monobutyl ether (boiling point 230° C.), triethylene glycol (boiling point 285° C.), dipropylene glycol (boiling point 232° C.), tripropylene glycol (boiling point 267° C.), trimethylolpropane (boiling point 295° C.), 2-pyrrolidone (boiling point 245° C.), tripropylene glycol monomethyl ether (boiling point 243° C.), and triethylene glycol monomethyl ether (boiling point 248° C.).

[0284] (resin particles)

[0285] The ink preferably contains at least one type of resin particles.

[0286] When the ink contains resin particles, the adhesion of the recorded image is further improved.

[0287] Here, the resin particles are different from the polymer dispersant in that they are particles composed of resin.

[0288] As the resin constituting the resin particles, a water-insoluble resin is preferred.

[0289] When the ink contains resin particles, the viscosity of the ink can be further suppressed compared to when the ink contains the same mass of water-soluble resin. As a result, when the ink is used as an inkjet ink, the ejection property of the ink from the inkjet head (hereinafter also referred to as "the ejection property of the ink") is further improved.

[0290] The definition and preferred range of "water-soluble" are as described above.

[0291] “Water-insoluble” means a property that the amount of a substance that dissolves in 100 g of distilled water at 25° C. is less than 1 g.

[0292] The glass transition temperature of the resin particles (that is, the glass transition temperature of the resin in the resin particles) is not particularly limited.

[0293] From the viewpoint of further improving the strength of the image, the glass transition temperature (Tg) of the resin particles is preferably 20° C. or higher, more preferably 50° C. or higher, and even more preferably 80° C. or higher.

[0294] From the viewpoint of the production suitability of the resin particles, the glass transition temperature (Tg) of the resin particles is preferably 200° C. or lower, more preferably 150° C. or lower, and further preferably 130° C. or lower.

[0295] The resin particles are preferably particles made of acrylic resin (hereinafter also referred to as acrylic resin particles), particles made of polyester resin (hereinafter also referred to as polyester resin particles), particles made of polyurethane resin (hereinafter also referred to as polyurethane resin particles), or particles made of polyolefin resin (hereinafter also referred to as polyolefin resin particles).

[0296] In the present invention, the polyester resin refers to a polymer compound having an ester bond in the main chain. Examples of the polyester resin include polycondensates of polycarboxylic acids (eg, dicarboxylic acids) and polyols (eg, diols).

[0297] In the present invention, polyolefin resin refers to a polymer (homopolymer or copolymer) of a raw material monomer containing olefin. As polyolefin resin, there are polymers of one olefin, copolymers of two or more olefins, copolymers of one or more olefins and one or more other monomers, etc. As olefin, α-olefin having 2 to 30 carbon atoms can be cited.

[0298] In the present invention, the polyurethane resin refers to a polymer compound including a urethane bond.

[0299] From the viewpoint of further improving the adhesion and abrasion resistance of the image, the resin particles contained in the ink preferably contain acrylic resin particles.

[0300] When the resin particles contained in the ink include acrylic resin particles, the ratio of the acrylic resin particles in the resin particles contained in the ink is preferably 60 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more.

[0301] When the ratio of the acrylic resin particles in the resin particles contained in the ink is 60% by mass or more, the adhesion of the image is further improved.

[0302] As the resin particles, self-dispersible resin particles are preferred.

[0303] Examples of the self-dispersible resin particles include self-dispersible polymer particles described in paragraphs 0062 to 0076 of JP-A-2016-188345 and paragraphs 0109 to 0140 of International Publication No. 2013 / 180074.

[0304] The resin in the resin particles preferably contains an alicyclic structure or an aromatic ring structure, and more preferably contains an alicyclic structure.

[0305] The alicyclic structure is preferably an alicyclic hydrocarbon structure having 5 to 10 carbon atoms, and preferably a cyclohexane ring structure, a dicyclopentyl ring structure, a dicyclopentenyl ring structure, a norbornane ring structure, an isobornane ring structure, a norbornene ring structure, an isobornene ring structure or an adamantane ring structure.

[0306] As the aromatic ring structure, a naphthalene ring or a benzene ring is preferred, and a benzene ring is more preferred.

[0307] The amount of the alicyclic structure or the aromatic ring structure is, for example, preferably 0.01 mol to 1.5 mol, more preferably 0.1 mol to 1 mol per 100 g of the resin in the resin particles.

[0308] From the viewpoint of further improving the water dispersibility of the resin particles, the resin in the resin particles preferably has an ionic group in its structure.

[0309] The ionic group may be an anionic group or a cationic group, but an anionic group is preferred.

[0310] The anionic group is not particularly limited, but is preferably a carboxyl group, a carboxyl salt, a sulfonyl group, or a sulfonyl salt.

[0311] As the resin in the resin particles,

[0312] More preferably, it is an acrylic resin containing at least one selected from the group consisting of benzyl (meth)acrylate units, phenoxyethyl (meth)acrylate units, and (meth)acrylate units containing an alicyclic structure, and a (meth)acrylic acid unit,

[0313] More preferably, the acrylic resin contains at least one selected from the group consisting of a benzyl (meth)acrylate unit, a phenoxyethyl (meth)acrylate unit, and a (meth)acrylate unit containing an alicyclic structure, a (meth)acrylic acid unit, and an alkyl (meth)acrylate unit containing an alkyl group having 1 to 4 carbon atoms.

[0314] The (meth)acrylate containing an alicyclic structure is preferably at least one selected from the group consisting of an alkyl (meth)acrylate having a cycloalkyl group having 3 to 10 carbon atoms (e.g., cyclohexyl (meth)acrylate), isobornyl (meth)acrylate, adamantyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0315] More preferably, it is at least one selected from the group consisting of isobornyl (meth)acrylate, adamantyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0316] The acid value of the resin in the resin particles is preferably 25 to 100 mgKOH / g, more preferably 30 to 90 mgKOH / g, and even more preferably 35 to 80 mgKOH / g, from the viewpoint of self-dispersibility and cohesiveness during image recording.

[0317] The molecular weight of the resin in the resin particles is preferably 1,000 to 300,000, more preferably 2,000 to 200,000, and even more preferably 5,000 to 100,000 in terms of weight average molecular weight.

[0318] The weight average molecular weight is determined by gel permeation chromatography (GPC). The details of GPC are as described above.

[0319] The volume average particle size of the resin particles is preferably 1 nm to 200 nm, more preferably 3 nm to 200 nm, and even more preferably 5 nm to 50 nm.

[0320] When the ink contains resin particles, the content of the resin particles is preferably 1% to 25% by mass, more preferably 2% to 20% by mass, further preferably 2% to 15% by mass, and further preferably 2% to 10% by mass, relative to the total amount of the ink.

[0321] (Surfactant)

[0322] The ink may contain at least one surfactant.

[0323] Examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants.

[0324] As a preferable surfactant, an acetylene glycol-based surfactant which is a kind of nonionic surfactant can be mentioned.

[0325] As the acetylene glycol-based surfactant, for example, the acetylene glycol-based surfactants described in paragraphs 0070 to 0080 of International Publication No. 2017 / 149917 can be used.

[0326] Examples of acetylene glycol-based surfactants include polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 3,6-dimethyl-4-octyne-3,6-diol, polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (preferably polyethylene oxide adducts), and polyalkylene oxide adducts (preferably polyethylene oxide adducts) of 2,5-dimethyl-3-hexyne-2,5-diol.

[0327] Commercially available products of acetylene glycol-based surfactants include: Surfynol series (e.g., Surfynol 420, Surfynol 440, Surfynol 465, Surfynol 485), Olfine series (e.g., Olfine E1010, Olfine E1020), Dynol series (e.g., Dyno 1604), etc. manufactured by Air Products Ltd. or Nissin Chemical Co., Ltd.; ACETY LENOL manufactured by Kawaken Fine Chemicals Co., Ltd., etc.

[0328] Commercial products of acetylene glycol-based surfactants are also provided by The Dow Chemical Company, General Aniline & Film Corp., and the like.

[0329] The surfactant also preferably contains a fluorine-based surfactant.

[0330] Examples of commercially available fluorine-based surfactants include Capstone FS-63, Capstone FS-61 (manufactured by DuPont de Nemours, Inc.), Ftergent 100, Ftergent 110, Ftergent 150 (manufactured by NEO S COMPANY LIMITED), and CHEMGUARD S-760P (manufactured by Chemguard Inc.).

[0331] As surfactants, there are also compounds listed as surfactants in JP-A-59-157636, pages 37 to 38, and Research Disclosure No. 308119 (1989). In addition, there are fluorine-based (fluoroalkyl-based) surfactants and silicone-based surfactants described in JP-A-2003-322926, JP-A-2004-325707, and JP-A-2004-309806.

[0332] When the ink contains a surfactant, the content of the surfactant in the ink may be appropriately adjusted in consideration of the surface tension of the ink.

[0333] The content of the surfactant in the ink is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 3% by mass, and even more preferably 0.1% by mass to 2% by mass, based on the total amount of the ink.

[0334] (Other ingredients)

[0335] The ink may contain other components besides the above components.

[0336] Examples of other components include known additives such as silicic acid compounds (e.g., colloidal silica), urea, urea derivatives, wax, anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, mildew inhibitors, pH adjusters, defoaming agents, viscosity adjusters, dispersion stabilizers, and chelating agents.

[0337] (Preferred physical properties of ink)

[0338] The viscosity of the ink is preferably 1.2 mPa·s or more and 15.0 mPa·s or less, more preferably 2 mPa·s or more and less than 13 mPa·s, and even more preferably 2.5 mPa·s or more and less than 10 mPa·s.

[0339] The viscosity is a value measured at 25°C using a viscometer.

[0340] As the viscometer, for example, VISCOMETER TV-22 type viscometer (manufactured by Toki Sangyo Co., Ltd.) can be used.

[0341] The surface tension of the ink is preferably 25 mN / m or more and 40 mN / m or less, and more preferably 27 mN / m or more and 37 mN / m or less.

[0342] The surface tension is a value measured at a temperature of 25°C.

[0343] The surface tension can be measured using, for example, Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[0344] From the viewpoint of dispersion stability, the pH of the ink at 25° C. is preferably pH 6 to 11, more preferably pH 7 to 10, and even more preferably pH 7 to 9.

[0345] The pH of the ink at 25° C. was measured using a commercially available pH meter.

[0346] <Ink application process>

[0347] The ink applying step is a step of applying the ink onto the substrate by ejecting the ink from the inkjet head in a droplet amount of 1.0 pL or more.

[0348] (Base material)

[0349] The substrate is not particularly limited, and a known substrate can be used.

[0350] Examples of the substrate include paper substrates, paper substrates laminated with resins (e.g., polyethylene, polypropylene, polystyrene, etc.), resin substrates, metal plates (e.g., plates of metals such as aluminum, zinc, and copper), paper substrates laminated or vapor-deposited with the above metals, and resin substrates laminated or vapor-deposited with the above metals.

[0351] Furthermore, as the substrate, a textile substrate can also be mentioned.

[0352] As raw materials for textile substrates, there can be mentioned: natural fibers such as cotton, silk, linen, and wool; chemical fibers such as viscose rayon and lyocell; synthetic fibers such as polyester, polyamide, and acrylic; a mixture of at least two selected from the group consisting of natural fibers, chemical fibers, and synthetic fibers, etc. As textile substrates, textile substrates described in paragraphs

[0039] to

[0042] of International Publication No. 2015 / 158592 can also be used.

[0353] As the substrate, a non-permeable substrate is preferred.

[0354] The non-permeable substrate refers to a substrate having a water absorption rate (mass %, 24 hr.) of less than 0.2 in the ASTM test method ASTM D570.

[0355] The impermeable substrate is not particularly limited, but is preferably a resin substrate.

[0356] The resin substrate is not particularly limited, and examples thereof include thermoplastic resin substrates.

[0357] Examples of the resin substrate include a substrate obtained by molding a thermoplastic resin into a sheet or film shape.

[0358] As the resin substrate, a substrate containing polypropylene, polyethylene terephthalate, nylon, polyethylene or polyimide is preferred.

[0359] The resin substrate may be a transparent resin substrate or a colored resin substrate.

[0360] Here, the term "transparent" means that the transmittance of visible light having a wavelength of 400 nm to 700 nm is 80% or more (preferably 90% or more).

[0361] The shape of the resin substrate is not particularly limited, but a sheet-shaped resin substrate is preferred, and a sheet-shaped resin substrate that can be wound into a roll is more preferred.

[0362] The thickness of the resin substrate is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm.

[0363] From the viewpoint of increasing the surface energy, the resin substrate may be surface treated.

[0364] Examples of the surface treatment include corona treatment, plasma treatment, heat treatment, abrasion treatment, light irradiation treatment (UV treatment), and flame treatment, but the surface treatment is not limited to these.

[0365] (Inkjet Head)

[0366] From the viewpoint of obtaining an image with excellent concealment properties, the amount of ink droplets ejected from the nozzles of the inkjet head is 1.0 pL (picoliter) or more.

[0367] The droplet amount of the ink is preferably 1.5 pL or more.

[0368] The upper limit of the ink droplet amount is preferably 10 pL, more preferably 6 pL.

[0369] In the inkjet head, the diameter of the nozzle hole (ie, nozzle diameter) for ejecting ink is preferably 20 μm or less.

[0370] By setting the diameter of the nozzle hole to 20 μm or less, a finer image can be recorded.

[0371] Also, generally, when the diameter of the nozzle hole is 20 μm or less, the continuous ejection property of the ink tends to be easily reduced. However, in the image recording method of the present invention, even when the diameter of the nozzle hole is 20 μm or less, excellent continuous ejection property can be achieved.

[0372] The diameter of the nozzle hole is more preferably 18 μm.

[0373] The lower limit of the diameter of the nozzle hole is not particularly limited, and examples of the lower limit include 10 μm, 11 μm, and 12 μm.

[0374] The resolution of the inkjet head is preferably 300 dpi or higher, more preferably 600 dpi, and further preferably 800 dpi.

[0375] Among them, dpi is the abbreviation of dot per inch, and 1inch is 2.54cm.

[0376] As a method of ejecting ink from an inkjet head, for example, a charge control method that utilizes electrostatic attraction to eject ink, a drop-on-demand inkjet method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam and irradiates the beam onto the ink to eject the ink using radiation pressure, a thermal inkjet (Bubble Jet (registered trademark)) method that heats the ink to form bubbles and utilizes the generated pressure, etc.

[0377] Furthermore, as a method of ejecting ink from an inkjet head, for example, the following method described in Japanese Patent Application Laid-Open No. 54-59936 can be applied: the ink undergoes a rapid volume change due to thermal energy, and the ink is ejected from the nozzle using the force generated by the state change.

[0378] Furthermore, as a method of ejecting ink from an inkjet head, the method described in paragraphs 0093 to 0105 of Japanese Patent Application Laid-Open No. 2003-306623 may also be applied.

[0379] As the inkjet head, for example, an inkjet head having a plurality of nozzle holes and having a liquid-repellent film provided on the ejection surface can be used.

[0380] Regarding this type of inkjet head, for example, reference may be made to known documents such as Japanese Patent No. 5775485.

[0381] The liquid-repellent film in the inkjet head preferably contains a fluorine compound, more preferably contains a fluoroalkyl-containing compound, and further preferably contains a perfluoroalkyl ether.

[0382] The thickness of the liquid-repellent film is not particularly limited, but is preferably 0.2 nm to 30 nm, and more preferably 0.4 nm to 20 nm.

[0383] As the inkjet head, a commercially available product can be used.

[0384] Examples of commercially available products include an inkjet head “KM1800i” manufactured by KONICA MINOLTA, Inc., an inkjet head “KJ4A-AA” manufactured by KY OCERA Corporation, and an inkjet head “Samba G3L” manufactured by FUJIFILM Dimatix, Inc.

[0385] (How to apply ink)

[0386] The ink application method may be a single-pass method or a scanning method. However, from the viewpoint of image recording speed, the single-pass method is preferred.

[0387] Here, the one-way method is as follows: a line head having nozzles arranged corresponding to the entire area of ​​one side of a substrate is used as an inkjet head, and the line head is fixedly arranged, and ink is applied to the transported substrate while the substrate is transported in a direction intersecting the arrangement direction of the nozzles of the line head.

[0388] On the other hand, the scanning method is a method in which a short-length stripe serial head is used as an inkjet head and ink is applied so that the short-length stripe serial head scans the substrate.

[0389] Generally, in image recording (ie, application of ink) by a one-pass method, excellent continuous ejection performance is required.

[0390] According to the image recording method of the present invention, the above-mentioned requirements for image recording in a one-pass method can be met.

[0391] In the ink application step, the ink applied to the substrate can be dried by heating to obtain an image.

[0392] As a mechanism for performing heating and drying, a known heating mechanism such as a heater, a known air blowing mechanism such as a dryer, and a combination of these mechanisms are mentioned.

[0393] As methods for heating and drying the ink, for example, there can be cited a method of heating the substrate from the side opposite to the surface to which the ink is applied using a heater, a method of blowing warm air or hot air toward the surface to which the ink is applied, a method of heating the substrate from the surface to which the ink is applied or the side opposite to the surface to which the ink is applied using an infrared heater, a method of combining a plurality of these methods, and the like.

[0394] The heating temperature during heat drying is preferably 55° C. or higher, more preferably 60° C. or higher, and particularly preferably 65° C. or higher. The upper limit of the heating temperature is not particularly limited, and the upper limit may be, for example, 100° C., and preferably 90° C.

[0395] The heating and drying time of the ink is not particularly limited, but is preferably 3 seconds to 60 seconds, more preferably 5 seconds to 60 seconds, and particularly preferably 10 seconds to 45 seconds.

[0396] Furthermore, the substrate may be heated in advance before applying the ink.

[0397] The heating temperature can be appropriately set, but the temperature of the substrate is preferably 20°C to 50°C, more preferably 25°C to 40°C.

[0398] <Other Processes>

[0399] The image recording method of the present invention may include other steps besides the ink preparation step and the ink application step.

[0400] As another step, there can be mentioned a pre-treatment liquid applying step of applying a pre-treatment liquid containing a coagulant and water to the substrate, which is provided before the ink applying step.

[0401] When the image recording method of the present invention includes the pre-treatment liquid applying step, in the ink applying step, the ink is applied to the region on the substrate to which the pre-treatment liquid is applied.

[0402] Regarding the pretreatment liquid imparting step, reference may be made to known documents such as International Publication No. 2019 / 004485 and International Publication No. 2019 / 163581 as appropriate.

[0403] The coagulant contained in the pretreatment liquid is preferably at least one selected from the group consisting of a polyvalent metal compound, an organic acid, a metal complex, and a cationic polymer, and more preferably contains an organic acid.

[0404] The application of the pretreatment liquid in the pretreatment liquid application step can be performed by applying a known application method such as a coating method, an inkjet recording method, or a dipping method.

[0405] Examples of the coating method include known coating methods using a bar coater, an extrusion die coater, an air knife coater, a blade coater, a rod coater, a knife coater, an extrusion coater, a reverse roll coater, and the like.

[0406] In the pretreatment liquid application step, the pretreatment liquid applied to the substrate may be heated and dried.

[0407] The preferred method and conditions for heat drying are the same as the preferred method and conditions for heat drying of the ink that can be performed in the ink application step.

[0408] 〔Pigment dispersion〕

[0409] Hereinafter, a pigment dispersion according to another embodiment of the present invention (hereinafter also referred to as “pigment dispersion X”) will be described.

[0410] Pigment dispersion X contains:

[0411] water;

[0412] White pigment;

[0413] polymeric dispersants; and

[0414] A water-soluble organic solvent (X) which is an alkylene glycol monoalkyl ether.

[0415] The pigment dispersion X is preferably an ink.

[0416] According to the pigment dispersion X, the same effects as those of the image recording method of the present invention can be exerted.

[0417] Also, the pigment dispersion X can be preferably used as ink in the image recording method of the present invention.

[0418] Preferred embodiments of the pigment dispersion X are the same as the preferred embodiments of the ink described in the section "ink preparation step" in the image recording method of the present invention.

[0419] One preferred embodiment of the pigment dispersion X is a pigment dispersion containing the following substances:

[0420] water;

[0421] white pigment, containing titanium dioxide particles;

[0422] Polymer dispersants containing block polymers or polymers having a cross-linked structure; and

[0423] The water-soluble organic solvent (X) is at least one selected from the group consisting of ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether.

[0424] The content of the water-soluble organic solvent (X) relative to the total amount of the pigment dispersion X is preferably 0.1% by mass to 10% by mass.

[0425] Thereby, the continuous ejection property when the pigment dispersion X is used as ink is further improved.

[0426] The lower limit of the content of the water-soluble organic solvent (X) relative to the total amount of the pigment dispersion X is more preferably 0.5% by mass, and further preferably 1% by mass.

[0427] The upper limit of the content of the water-soluble organic solvent (X) relative to the total amount of the pigment dispersion X is more preferably 8% by mass.

[0428] The pigment dispersion X preferably contains at least one water-soluble organic solvent having a boiling point lower than 220°C.

[0429] Thereby, the drying property when the pigment dispersion X is used as ink (that is, the drying property of the recorded image) is further improved.

[0430] The water-soluble organic solvent having a boiling point lower than 220° C. may or may not correspond to the water-soluble organic solvent (X).

[0431] Specific examples of the water-soluble organic solvent having a boiling point of less than 220° C. are shown in the section “ink preparation step” in the above-mentioned image recording method of the present invention.

[0432] The preferred range of the content of the water-soluble organic solvent having a boiling point lower than 220°C relative to the total amount of the pigment dispersion X is the same as the preferred range of the content of the water-soluble organic solvent having a boiling point lower than 220°C relative to the total amount of the ink shown in the above-mentioned "Ink preparation process" item.

[0433] The preferred range of the content of the water-soluble organic solvent with a boiling point of 220°C or above relative to the total amount of the pigment dispersion X is also the same as the preferred range of the content of the water-soluble organic solvent with a boiling point of 220°C or above relative to the total amount of the ink shown in the above-mentioned "Ink preparation process" item.

[0434] Example

[0435] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0436] Hereinafter, unless otherwise specified, "water" means deionized water.

[0437] [Example 1]

[0438] <Synthesis of polymer dispersant (block polymer 1)>

[0439] Block polymer 1 was synthesized as a polymer dispersant with reference to Synthesis Example 8 of JP-A-2015-83688. The details are shown below.

[0440] Into a reaction apparatus having a 1 L separable flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet tube, diethylene glycol dimethyl ether (266 parts by mass; polymerization solvent), 2-iodo-2-cyanopropane (6.2 parts by mass; polymerization initiator compound), methyl methacrylate (MMA) (120 parts by mass; monomer), acrylic acid (AA) (28.8 parts by mass; monomer), cyclohexyl methacrylate (CHMA) (67.2 parts by mass; monomer), azobisdimethylisovaleronitrile (hereinafter, abbreviated as “V-65”; radical generator) (7.9 parts by mass) and 2-tert-butyl-4,6-dimethylphenol (0.7 parts by mass; catalyst) were added, and the mixture was stirred while flowing nitrogen gas.

[0441] Next, the temperature of the mixture in the reaction apparatus (reaction temperature) was raised to 70° C., and polymerization was performed for 3 hours to obtain a polymerization solution A containing an MMA / AA / CHMA copolymer.

[0442] After 3 hours, a part of the polymerization solution A was sampled and the solid content was measured. The result was 42.0% by mass, confirming that most of the monomers had been polymerized.

[0443] Furthermore, the molecular weight of the MMA / AA / CHMA copolymer was measured by GPC, and as a result, the weight average molecular weight (Mw) was 7,500.

[0444] The acid value of the MMA / AA / CHMA copolymer was 101.0 mgKOH / g.

[0445] Next, a mixture of benzyl methacrylate (BzMA) (35.2 parts by mass; monomer) and V-65 (0.3 parts by mass; radical generator) was added to the above polymerization solution A, and polymerization was performed at 70° C. for 3 hours to obtain a polymerization solution B containing block polymer 1 as a polymer dispersant.

[0446] Here, block polymer 1 is a block polymer including an A block (MMA / AA / CHMA copolymer) and a B block (BzMA homopolymer).

[0447] The solid content of the obtained polymerization solution B was measured and found to be 43.2% by mass, confirming that most of the monomers had been polymerized.

[0448] Furthermore, the Mw of the block polymer 1 was 8,500.

[0449] The acid value of the block polymer 1 was 89.3 mgKOH / g.

[0450] <Preparation of White Pigment Dispersion>

[0451] The above-mentioned polymerization solution B, white pigment 1 (titanium dioxide pigment "R-930" manufactured by ISHIHARA SANGYO KAISHA, LTD.) and water were mixed to prepare a mixture consisting of white pigment 1 (20 parts by mass), block polymer 1 as a polymer dispersant (18.5 parts by mass in terms of solid content) and water (61.5 parts by mass).

[0452] use The obtained mixture was dispersed for 4 hours using zirconia beads and a paint conditioner, and then coarse particles were removed by filtration to obtain a white pigment paste.

[0453] To 100 parts by mass of the obtained white pigment paste were added 28% by mass ammonia water (2.4 parts) and water (3.6 parts by mass), and the mixture was stirred with a high-speed disperser to obtain a white pigment dispersion (white pigment concentration: 50.1% by mass, solid content: 52.6% by mass).

[0454] <Preparation of Dispersion of Resin Particles P1>

[0455] A dispersion of resin particles P1, which is one of the components in the ink, was prepared. The details are shown below.

[0456] 560.0 g of methyl ethyl ketone was placed in a 2-liter three-necked flask (reaction vessel) equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen inlet tube, and the temperature was raised to 87° C. Next, while maintaining the reflux state in the reaction vessel (hereinafter, the reflux state was maintained until the reaction was completed), a mixed solution consisting of 220.4 g of methyl methacrylate, 301.6 g of isobornyl methacrylate, 58.0 g of methacrylic acid, 108 g of methyl ethyl ketone, and 2.32 g of "V-601" (polymerization initiator manufactured by FUJIFILM Wako Pure Chemical Corporation; 2,2'-azobis(2-methylpropionic acid) dimethyl ester) was added dropwise at a constant rate to the methyl ethyl ketone in the reaction vessel in such a manner that the addition was completed within 2 hours. After the addition was completed, the mixture was stirred for 1 hour, and then the following step (1) was performed on the solution after stirring for 1 hour.

[0457] Step (1) ... A solution consisting of 1.16 g of "V-601" and 6.4 g of methyl ethyl ketone was added, and the mixture was stirred for 2 hours.

[0458] Next, the operation of step (1) was repeated four times, and then a solution consisting of 1.16 g of "V-601" and 6.4 g of methyl ethyl ketone was further added, and stirring was continued for 3 hours (the operation up to this point is regarded as "reaction").

[0459] After the reaction was completed, the temperature of the solution was lowered to 65° C., 163.0 g of isopropyl alcohol was added, and the mixture was cooled naturally to obtain a polymerization solution (solid content concentration: 41.0% by mass) containing a copolymer.

[0460] Next, 317.3 g of the obtained polymerization solution was weighed, and 46.4 g of isopropyl alcohol, 1.65 g of a 20% by mass aqueous maleic anhydride solution (equivalent to 0.3% by mass in terms of maleic acid relative to the water-soluble acidic compound and the copolymer) and 40.77 g of a 2 mol / L aqueous sodium hydroxide (NaOH) solution were added thereto, and the temperature of the liquid in the reaction container was raised to 70°C.

[0461] Next, 380 g of distilled water was added dropwise to the liquid heated to 70° C. at a rate of 10 mL / min to perform water dispersion (dispersion step).

[0462] Then, the temperature of the liquid in the reaction container was maintained at 70° C. for 1.5 hours under reduced pressure, thereby distilling off a total of 287.0 g of isopropyl alcohol, methyl ethyl ketone, and distilled water (solvent removal step). 0.278 g of PROXEL GXL (S) (manufactured by Arch Chemicals Japan, Inc.) (440 mass ppm in terms of benzisothiazoline-3-one relative to the polymer solid content) was added to the obtained liquid.

[0463] The obtained liquid was filtered through a 1 μm filter and the filtrate was recovered to obtain an aqueous dispersion of resin particles P1 composed of a copolymer of methyl methacrylate / isobornyl methacrylate / methacrylic acid / sodium methacrylate (=70 / 20 / 5 / 5 [mass ratio]) (non-volatile content concentration 23.2 mass %). The volume average particle size of the resin particles P1 was 5.0 nm, and the weight average molecular weight (Mw) of the resin particles P1 was 60,000.

[0464] <Preparation of white ink>

[0465] A white ink having the following composition was prepared using the white pigment dispersion, the dispersion of the resin particles P1, the solvent S1 described below, the other water-soluble organic solvent described below, the surfactant described below, and water.

[0466] - Composition of white ink -

[0467] White pigment 1

[0468] ...12% by mass

[0469] Block polymers as polymeric dispersants 1

[0470] ...0.6% by mass

[0471] Propylene glycol monopropyl ether (PGmPE) (Solvent S1)

[0472] ...1.5% by mass

[0473] Ethylene glycol monobutyl ether (EGmBE) (Solvent S1)

[0474] ...0.5% by mass

[0475] Propylene glycol (PG) (other water-soluble organic solvents)

[0476] ...25% by mass

[0477] Resin particles P1

[0478] ...5% by mass

[0479] Surfactants

[0480] ...Olfine E1010 (Nissin Chemical Co., Ltd. acetylene glycol surfactant) 0.5 mass%

[0481] ·water

[0482] ...the remainder to make 100% by mass

[0483] <Image Record>

[0484] Using the above ink, an image was recorded as follows using a biaxially stretched polypropylene (OPP) film (thickness 40 μm, surface treatment: corona discharge treatment, manufactured by FUTAMURA CHEMICAL CO., LTD.) as a substrate (impermeable substrate).

[0485] (1) Recording method

[0486] The ink was ejected from the inkjet head using an inkjet recording device having a conveying system for conveying a substrate and the following inkjet head, and the ink was applied to the corona discharge treated surface of the substrate in the form of a solid image. The ink applied to the substrate was dried at 80° C. for 30 seconds, thereby obtaining a solid image as a white image. The ink was dried by placing the substrate to which the ink was applied on a hot plate.

[0487] In this manner, an image recorded material including a substrate and a solid image disposed on the substrate is obtained.

[0488] (2) Recording conditions

[0489] Inkjet head: an inkjet head "Samba G3L" manufactured by FUJIFILM Dimatix, Inc., which is a 1200 dpi / 20 inch width piezoelectric full line head. The diameter of the nozzle holes in this inkjet head is 20 μm or less.

[0490] Ink droplet volume: 1.8pL

[0491] Drive frequency: 30kHz (substrate conveying speed: 635mm / sec)

[0492] Ink application method: one-way method

[0493] <Measurement and Evaluation>

[0494] The following measurements and evaluations were performed.

[0495] The results are shown in Table 1.

[0496] (Contact angle of each solvent with respect to the ejection surface of the inkjet head)

[0497] Regarding each solvent (for example, solvent S1) used in preparing the ink, the contact angle of each solvent with respect to the ejection surface of the inkjet head was measured in advance.

[0498] The contact angle is measured by the above-mentioned method using a contact angle meter DropMaster DM700 (manufactured by Kyowa Interface Science Co., Ltd.).

[0499] (Determination of ink adhesion rate after repellency test)

[0500] The above ink and the above inkjet head were used to perform a repellency test according to the above method, and the ink adhesion rate after the repellency test was measured.

[0501] (Measurement of average primary particle size of white pigment)

[0502] The above ink was used to measure the average primary particle size of the white pigment in the ink by the above method. As TEM, a transmission electron microscope 1200EX manufactured by JEOL Ltd. was used.

[0503] (Measurement of Standard Deviation of Volume-Based Particle Size Distribution of Dispersed Particles Containing White Pigment)

[0504] The standard deviation of the volume-based particle size distribution of dispersed particles containing the white pigment in the ink was measured by the above method using the above ink. As a measuring device, a particle size distribution measuring device "NANOTRAC UPA-EX150" manufactured by Nikkiso Co., Ltd. was used.

[0505] (Continuous jet)

[0506] The ink was continuously ejected from the inkjet head in a 1200 dpi mode for 5 minutes, and the number of locations where ejection failure (for example, ejection bending) occurred during this operation was evaluated.

[0507] The evaluation was performed six times or more, and based on the obtained results, the ejectability of the ink was evaluated according to the following evaluation criteria.

[0508] In the following evaluation criteria, the most excellent grade in continuous ejection property of ink is "AA".

[0509] -Evaluation criteria for continuous jetting of ink-

[0510] AA: No ejection failure occurred in any of the 6 evaluations.

[0511] A: Only one ejection failure occurred in one evaluation, and no ejection failure occurred in five evaluations.

[0512] B: Only one ejection failure occurred in each of the two evaluations, and no ejection failure occurred in the four evaluations.

[0513] C: Ejection failure occurred only at one point in each of the three evaluations, and no ejection failure occurred in the three evaluations.

[0514] D: corresponds to at least one of the following: only one ejection failure occurred in each of four or more evaluations and two ejection failures occurred in each of one or more evaluations.

[0515] (Dryness)

[0516] The logarithmic decrement (%) when the temperature of the solid image (hereinafter also referred to as "sample temperature") was increased from room temperature to 150° C. at a heating rate of 6.0° C. / min was measured for the solid image 5 minutes after the solid image was recorded (i.e., 30 seconds drying at 80° C.) using a pendulum viscoelasticity tester (Rigid pendulum physical property tester "RPT-3000W" manufactured by A&D Company, Limited). Based on the obtained results, the drying property of the image was evaluated according to the following evaluation criteria.

[0517] In the following evaluation criteria, the image with the most excellent drying property was rated as “A”.

[0518] -Evaluation criteria for image drying-

[0519] A: The logarithmic attenuation at a sample temperature of 80°C is less than 4%.

[0520] B: The logarithmic decrement at a sample temperature of 80° C. is 4% or more and less than 6%.

[0521] C: The logarithmic decrement at a sample temperature of 80° C. is 6% or more and less than 10%.

[0522] D: The logarithmic decrement at a sample temperature of 80° C. is 10% or more and less than 15%.

[0523] E: The logarithmic decrement at a sample temperature of 80° C. is 15% or more.

[0524] (Concealment)

[0525] The concealability of the solid image of the above-mentioned image recorded matter was evaluated as follows.

[0526] Separately from the above image recording, black character images (4 in total) of 2pt (dot), 4pt, 6pt and 8pt in size were recorded on the above OPP substrate using commercially available black inkjet ink to obtain a substrate with black character images. The 4 black character images were set as Figure 1 Black character image shown.

[0527] The image recording material and the substrate with the black character image were overlapped in a direction that the non-image recording surface (surface without the recorded image) of each other was in contact with each other to form a laminate. The obtained laminate was covered on a 30W fluorescent lamp in a manner that the solid image was facing the evaluator side, and it was confirmed whether the details of each black character image could be visually recognized through the solid image, and the concealment of the solid image was evaluated according to the following evaluation criteria. At this time, the distance between the evaluator's eyes and the laminate was set to 20cm, and the distance from the laminate to the fluorescent lamp was set to 2m.

[0528] In the following evaluation criteria, the level with the best concealment of a solid image is "A".

[0529] -Evaluation criteria for concealment-

[0530] A: Details of black character images of 2 pt, 4 pt, 6 pt, and 8 pt cannot be visually recognized.

[0531] B: The details of the black character image of 8 pt were visually recognized, but the details of the black character images of 2 pt, 4 pt, and 6 pt were not visually recognized.

[0532] C: Details of the black character images of 6 pt and 8 pt were visually recognized, but details of the black character images of 2 pt and 4 pt were not visually recognized.

[0533] D: Details of the black character images of 4 pt, 6 pt, and 8 pt were visually recognized, but details of the black character image of 2 pt were not visually recognized.

[0534] E: Details of the black character images of 2 pt, 4 pt, 6 pt, and 8 pt are visually recognized.

[0535] [Examples 2, 6 to 12 and 15]

[0536] As shown in Table 1, the same operation as in Example 1 was performed except that the combination of the type and content of the solvent S1 was changed.

[0537] The results are shown in Table 1.

[0538] The abbreviations of the solvents in Table 1 have the following meanings.

[0539] EGmBE…ethylene glycol monobutyl ether

[0540] PGmPE…propylene glycol monopropyl ether

[0541] PGmME…propylene glycol monomethyl ether

[0542] ·DPGmME…Dipropylene glycol monomethyl ether

[0543] ·DEGmEE…Diethylene glycol monoethyl ether

[0544] ·TPG…Tripropylene glycol

[0545] ·1-Hex…1-Hexanol

[0546] EG…ethylene glycol

[0547] PG…propylene glycol

[0548] [Example 3]

[0549] The same operation as in Example 1 was carried out except that the inkjet head was changed to an inkjet head "KJ4A-AA" manufactured by KYOCERA Corporation.

[0550] The results are shown in Table 1.

[0551] [Examples 4 and 5]

[0552] The same operation as in Example 1 was carried out except for the following points. The results are shown in Table 1.

[0553] - Differences from Example 1 -

[0554] The white pigment 1 (titanium dioxide pigment "R-930" manufactured by ISHIHARA SANGYO KAISHA, LTD.) was replaced with the following white pigment 2 or the following white pigment 3.

[0555] White pigment 2…Titanium dioxide pigment “CR-60” manufactured by ISHIHARA SANGYO KAISHA, LTD.

[0556] White pigment 3…Titanium dioxide pigment “PF690” manufactured by ISHIHARA SANGYO KAISHA, LTD.

[0557] In Example 4, in the preparation of the white pigment dispersion, Zirconia beads changed to Zirconia beads were added and the dispersion time was changed from 4 hours to 5 hours.

[0558] [Example 13]

[0559] The same operation as in Example 1 was carried out except that the white pigment dispersion using the block polymer 1 as the polymer dispersant was changed to the white pigment dispersion using the random polymer 1 as the polymer dispersant.

[0560] The results are shown in Table 1.

[0561] The following describes a method for synthesizing the random polymer 1 as a polymer dispersant and a method for preparing a white pigment dispersion using the random polymer 1.

[0562] <Synthesis of Random Polymer 1 (Polymer Dispersant)>

[0563] A solution I in which 234 g of benzyl methacrylate, 120 g of stearyl methacrylate, 84 g of methacrylic acid, 162 g of hydroxyethyl methacrylate and 3.93 g of 2-mercaptopropionic acid were mixed and a solution II in which 6.2 g of tert-butyl peroxy-2-ethylhexanoate (PERBUTYL O manufactured by NOFCORPORATION) was dissolved in 115 g of dipropylene glycol was prepared.

[0564] 605 g of dipropylene glycol was added to a three-necked flask equipped with a stirrer and a cooling tube, and heated to 85° C. in a nitrogen atmosphere. The solution I was added dropwise thereto over 4 hours, and the solution II was added dropwise thereto over 5 hours.

[0565] After the dropwise addition was completed, the mixture was allowed to react for a further 2 hours, and then the temperature was raised to 95°C and heated and stirred for 3 hours to allow all unreacted monomers to react. 1 H-NMR confirmed the disappearance of the monomer.

[0566] The obtained reaction solution was heated to 70°C, 74 g of dimethylaminoethanol was added as an amine compound, and then 764 g of propylene glycol was added and stirred to obtain a solution of random polymer 1 having a weight average molecular weight (Mw) of 30,000 and an acid value of 112 mgKOH / g (solid content: 30% by mass).

[0567] pass 1 The constituent components of the obtained polymer were confirmed by H-NMR.

[0568] <Preparation of White Pigment Dispersion>

[0569] 150 parts by mass of random polymer 1 was dissolved in water, and the pH after neutralization was adjusted to 9 using an aqueous potassium hydroxide solution to adjust the concentration of random polymer 1 to about 25% by mass, thereby obtaining an aqueous solution of random polymer 1.

[0570] The components were mixed in the following white pigment dispersion, and the dispersion was prepared using LABSTAR Mini LMZ015 (manufactured by Ashizawa Finetech Ltd., bead diameter: , zirconia beads, rotation speed: 10 m / sec) was subjected to a dispersion treatment for 1.5 hours to obtain a white pigment dispersion (white pigment concentration: 48% by mass, solid content concentration: 50% by mass).

[0571] - Composition of white pigment dispersion -

[0572] Aqueous solution of random polymer 1: 54 parts by mass

[0573] White pigment 1 (Titanium dioxide pigment "R-930" manufactured by ISHIHARA SANGYO KAISHA, LTD.): 500 parts by mass

[0574] Propylene glycol: 100 parts by mass

[0575] Water: The balance is 1000 parts by mass

[0576] [Example 14]

[0577] The same operation as in Example 1 was performed except that the white pigment dispersion using the block polymer 1 as the polymer dispersant was changed to the white pigment dispersion CL using the crosslinked polymer 1 as the polymer dispersant.

[0578] The results are shown in Table 1.

[0579] The white pigment dispersion CL using the crosslinked polymer 1 as a polymer dispersant was prepared with reference to the synthesis examples (paragraphs 0071, 0072, and 0075) of Japanese Patent Application Laid-Open No. 2009-190379. The details are shown below.

[0580] <Synthesis of Uncrosslinked Water-Soluble Polymer 1 (Polymer Dispersant)>

[0581] Dipropylene glycol (198 g) was added to a 2000 ml three-necked flask equipped with a stirrer and a cooling tube, and the mixture was heated to 85° C. under a nitrogen atmosphere.

[0582] A solution I in which benzyl methacrylate (135 g), stearyl methacrylate (90 g), methacrylic acid (75 g) and 2-mercaptopropionic acid (5.7 g) were dissolved in dipropylene glycol (114 g) and a solution II in which 4.5 g of tert-butyl peroxy-2-ethylhexanoate (PERBUTYL O manufactured by NOF CORPORATION) was dissolved in 152 g of dipropylene glycol were prepared.

[0583] To the three-necked flask, solution I was added dropwise over 4 hours, and solution II was added dropwise over 5 hours.

[0584] After the addition was completed, the mixture was allowed to react for a further 2 hours, and then the temperature was raised to 95°C and heated and stirred for 3 hours to allow all unreacted monomers to react. 1 H-NMR confirmed the disappearance of the monomer.

[0585] The obtained reaction solution was heated to 70° C., and after adding 82.9 g of a 50 mass % KOH aqueous solution, 833 g of pure water was added and stirred to obtain a 20 mass % solution of the uncrosslinked water-soluble polymer 1.

[0586] The solvent was removed under reduced pressure to obtain an uncrosslinked water-soluble polymer 1 with a Mw of 8000.

[0587] <Preparation of White Pigment Dispersion Liquid N Using Uncrosslinked Water-Soluble Polymer 1>

[0588] Water-soluble polymer 1 (150 parts by mass) was dissolved in water, and then the pH after neutralization was adjusted to 10.1 using an aqueous potassium hydroxide solution to adjust the concentration of water-soluble polymer 1 to 30.6% by mass, thereby obtaining an aqueous solution of water-soluble polymer 1.

[0589] White pigment 1 (titanium dioxide pigment "R-930" manufactured by ISHIHARA SANGYO KAISHA, LTD.) (300 parts by mass) and water (362 parts by mass) were mixed with an aqueous solution of water-soluble polymer 1 (147 parts by mass) and the mixture was pulverized using a bead mill ( The mixture was dispersed in zirconia beads for 3 hours to obtain a white pigment dispersion N (white pigment concentration: 50% by mass, solid content concentration: 52.5% by mass) using the uncrosslinked water-soluble polymer 1.

[0590] <Preparation of White Pigment Dispersion Liquid CL Using Crosslinked Polymer 1>

[0591] Polyethylene glycol diglycidyl ether (0.35 parts by mass) was added as a crosslinking agent to white pigment dispersion N (70 parts by mass), and the mixture was reacted at 50° C. for 6.5 hours, followed by cooling to 25° C., thereby obtaining a white pigment dispersion CL (white pigment concentration 50% by mass, solid content concentration 52.5% by mass) using crosslinked polymer 1.

[0592] The cross-linked polymer 1 is a polymer having a cross-linked structure in which the water-soluble polymer 1 is cross-linked with polyethylene glycol diglycidyl ether as a cross-linking agent.

[0593] [Comparative Example 1]

[0594] The same operation as in Example 1 was performed except that the solvent S1 having a contact angle of 85° or less with respect to the ejection surface was changed to ethylene glycol (EG) (comparative solvent) having a contact angle of more than 85° with respect to the ejection surface.

[0595] The results are shown in Table 1.

[0596] The ink adhesion rate after the repellency test was 45 area %.

[0597] [Comparative Example 2]

[0598] The same operation as in Example 1 was performed except that the amount of ink droplets ejected from the inkjet head was changed to 0.8 pL.

[0599] The results are shown in Table 1.

[0600]

[0601] As shown in Table 1, the inks of Examples 1 to 15, in which the droplet amount of ink ejected from the inkjet head was 1.0 pL or more and the ink adhesion rate after the repellency test was 40 area % or less, were excellent in continuous ejection and concealment.

[0602] On the other hand, in Comparative Example 1 in which the adhesion rate of the ink after the repellency test exceeded 40 area %, the continuous ejection property of the ink was reduced.

[0603] Furthermore, in Comparative Example 2 in which the amount of ink droplets ejected from the inkjet head was less than 1.0 pL, although the continuous ejection property of the ink was good, the concealment property was reduced.

[0604] Among Examples 1 to 3 and 6, the inks of Examples 1 to 3, in which the adhesion rate of the ink after the repellency test was 15 area % or less, were more excellent in continuous ejection properties.

[0605] In Examples 8 to 10, the content of solvent S1 (i.e., a water-soluble organic solvent having a contact angle of 85° or less with respect to the ejection surface) in the ink is 0.1 mass % to 10 mass % relative to the total amount of the ink. The ink of Example 9 has better continuous ejection properties.

[0606] Among Examples 11 and 12, the ink of Example 11, in which the solvent S1 in the ink contained a water-soluble organic solvent having a contact angle with the ejection surface of 80° or less, was more excellent in continuous ejection properties.

[0607] In Examples 7 and 11, the ink of Example 7, in which the solvent S1 in the ink contained a water-soluble organic solvent having a contact angle of 75° or less with respect to the ejection surface, had more excellent continuous ejection properties.

[0608] Among Examples 1 to 4, 6, and 7, the inks of Examples 1 to 4 containing at least two kinds of solvents S1 were more excellent in continuous ejection properties.

[0609] Among Examples 1, 2, 13 and 14, the inks of Examples 1, 2 and 14 in which the polymer dispersant contained a block polymer or a crosslinked polymer had more excellent continuous jetting properties.

[0610] Among Examples 1 to 5, the inks of Examples 1 to 4 in which the standard deviation of the volume-based particle size distribution of the dispersed particles in the ink was 140 nm or less were more excellent in continuous ejection properties.

[0611] [Examples 101 to 115 and Comparative Examples 101 and 102]

[0612] As Examples 101 to 115 and Comparative Examples 101 and 102, in image recording, a pretreatment liquid having the following composition is applied to a substrate in the form of a solid image and dried, and ink is applied to the area on the substrate to which the pretreatment liquid is applied to record the image. Except for this, the same operations as in Examples 1 to 15 and Comparative Examples 1 and 2 are performed.

[0613] As a result, in Examples 101 to 115 and Comparative Examples 101 and 102, the same results as those of Examples 1 to 15 and Comparative Examples 1 and 2 were obtained, respectively.

[0614] - Composition of pretreatment solution -

[0615] Eastek (registered trademark) 1100 (manufactured by Eastman Chemical Company) [Polyester resin particles]

[0616] ...10% by mass based on the amount of resin particles (solid content)

[0617] Glutaric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation)〔Flocculant〕

[0618] ...4.1% by mass

[0619] ·Propylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation) [Water-soluble organic solvent]

[0620] ...10% by mass

[0621] ·water

[0622] ...the remainder is 100% by mass

[0623] The method of applying and drying the pretreatment liquid is as follows.

[0624] The pretreatment liquid was applied to the substrate using a wire bar coater. The amount of pretreatment liquid applied (i.e., converted to per 1 m 2 The area of ​​the given gram) is set to 1.5g / m 2 .

[0625] At the part where the application of the pretreatment liquid was completed, drying of the pretreatment liquid was started using a dryer at 50° C. 1.5 seconds after the application of the pretreatment liquid to the part was completed, and drying was completed 3.5 seconds after the application of the pretreatment liquid was completed. The drying time at this time was 2 seconds.

[0626] In Examples 101 to 115 and Comparative Examples 101 and 102, as described above, ink was applied to the region where the pre-treatment liquid was applied and dried, and an image was recorded.

[0627] [Examples 201 to 215 and Comparative Examples 201 and 202]

[0628] As Examples 201 to 215 and Comparative Examples 201 and 202, in image recording, a pretreatment liquid having the following composition is applied to a substrate in the form of a solid image and dried, and ink is applied to the area on the substrate to which the pretreatment liquid is applied to record the image. Except for this, the same operations as in Examples 1 to 15 and Comparative Examples 1 and 2 are performed.

[0629] As a result, in Examples 201 to 215 and Comparative Examples 201 and 202, the same results as those of Examples 1 to 15 and Comparative Examples 1 and 2 were obtained, respectively.

[0630] In addition, the application and drying of the pretreatment liquid were carried out by the same method as the application and drying of the pretreatment liquid in Example 101.

[0631] - Composition of pretreatment solution -

[0632] Eastek (registered trademark) 1100 (manufactured by Eastman Chemical Company) [Polyester resin particles]

[0633] ...10% by mass based on the amount of resin particles (solid content)

[0634] Aluminum sulfate

[0635] ...2.7% by mass

[0636] ·Propylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation) [Water-soluble organic solvent]

[0637] ...10% by mass

[0638] ·water

[0639] ...the remainder is 100% by mass

[0640] The entire contents of Japanese Patent Application No. 2020-078680 filed on April 27, 2020 are incorporated herein by reference.

[0641] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, patent application, and technical standard was specifically and individually incorporated by reference.

Claims

1. An image recording method comprising the following steps: A step of preparing ink containing water, white pigment and solvent S1; and The step of applying the ink to a substrate by ejecting the ink from an inkjet head in a droplet amount of 1.0 pL or more, The ejection surface of the ink in the inkjet head is immersed in the ink for 2 seconds in a vertically upright state, then the ejection surface is taken out of the ink while maintaining the state, and then the ejection surface is left for 1 minute while maintaining the state, in which case, the area ratio of the region to which the ink is attached in the ejection surface is 40% by area or less, The solvent S1 is a water-soluble organic solvent having a contact angle of 85° or less with respect to the ejection surface. The solvent S1 contains at least two selected from the group X consisting of ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether.

2. The image recording method according to claim 1, wherein: The area ratio of the region to which the ink is attached on the ejection surface is 15 area % or less.

3. The image recording method according to claim 1 or 2, wherein: The content of the solvent S1 is 0.1 mass % to 10 mass % based on the total amount of the ink.

4. The image recording method according to claim 1, wherein: The solvent S1 includes a water-soluble organic solvent having a contact angle of 80° or less with respect to the ejection surface.

5. The image recording method according to claim 4, wherein: The solvent S1 includes a water-soluble organic solvent having a contact angle of 75° or less with respect to the ejection surface.

6. The image recording method according to claim 1 or 2, wherein: The content of the water-soluble organic solvent having a boiling point of 220° C. or higher in the ink is 5% by mass or less.

7. The image recording method according to claim 1 or 2, wherein: The ink also contains a polymer dispersant, The polymer dispersant contains a block polymer or a polymer having a cross-linked structure.

8. The image recording method according to claim 1 or 2, wherein: The standard deviation of the volume-based particle size distribution of dispersed particles containing the white pigment in the ink is 140 nm or less.

9. The image recording method according to claim 1 or 2, wherein: The substrate is a non-permeable substrate.

10. The image recording method according to claim 1 or 2, wherein: The step of applying the ink is a step of applying the ink to the substrate in a one-pass method.

11. The image recording method according to claim 1 or 2, wherein: In the inkjet head, a diameter of a nozzle hole for ejecting the ink is 20 μm or less.

Images