Inkjet recording method

Abstract

The present invention provides an inkjet recording method which comprises an ink application step in which an ink that contains water is applied onto an impermeable base material by means of an inkjet method. In the ink application step, the ink is applied onto the impermeable base material under such a condition that the polarity of static electricity of an impermeable base material surface, to which the ink is to be applied, and the polarity of the zeta potential of the ink are opposite to each other.

Description

Technical Field

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

Background Art

[0002] Conventionally, various studies have been made on inkjet recording methods. For example, Patent Document 1 discloses an inkjet recording medium and an inkjet recording method excellent in image density and ink fixing properties, in which the surface zeta potential at pH 7 of the recording surface of an inkjet recording medium having at least one ink absorption layer on a support is +5 mV or more and +30 mV or less, and an inkjet recording method of recording on this inkjet recording medium with a recording liquid having a negative zeta potential.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-291237

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, Patent Document 1 discloses an inkjet recording method for recording an image on a recording medium including an ink absorption layer. However, through the studies by the present inventors, when a non-permeable base material as a recording medium is used instead of a recording medium including an ink absorption layer, and an ink containing water is used to record an image on this non-permeable base material by an inkjet method, it has been found that image quality deterioration is likely to occur due to a decrease in ink droplet ejection accuracy and / or a deviation in ink droplet ejection timing. Here, a decrease in ink droplet ejection accuracy means a decrease in the positional accuracy of the point where the ink reaches the non-permeable base material, and a deviation in ink droplet ejection timing means a deviation of the timing when the ink reaches the non-permeable base material from the ideal timing.

[0005] An object of one aspect of this disclosure is to provide an inkjet recording method that uses water-containing ink to record an image on a non-permeable substrate in which a decrease in the accuracy of ink droplet application and / or a decrease in image quality caused by a deviation in droplet application timing is suppressed. [Means for solving the problem]

[0006] This disclosure includes the following aspects: <1> The process includes an ink application step in which a water-containing ink is applied to a non-permeable substrate by an inkjet method. The ink application step involves applying the ink onto the non-permeable substrate under the condition that the electrostatic polarity of the surface of the non-permeable substrate to which the ink is applied and the polarity of the zeta potential of the ink are opposite. Inkjet recording method. <2> The ink application step involves applying the ink onto the non-permeable substrate under the condition that the difference [AB], which is the difference between A and B, is between 30 and 110, where A is the electrostatic charge on the surface of the non-permeable substrate to which the ink is applied, and B is the zeta potential of the ink. <1> The inkjet recording method described above. <3> The ink application step involves applying the ink onto the non-permeable substrate under the condition that the difference [AB] is 45 to 70. <2> The inkjet recording method described above. <4> The zeta potential of the aforementioned ink is -80mV to -30mV. <1> ~ <3> The inkjet recording method described in one of the following documents. <5> The electrostatic charge on the surface of the non-permeable substrate to which the ink is applied is 10kV to 30kV. <1> ~ <4> The inkjet recording method described in one of the following documents. <6> The non-permeable substrate is a resin substrate. <1> ~ <5> The inkjet recording method described in one of the following documents. <7> The process further includes a pretreatment liquid application step in which a pretreatment liquid containing water and a coagulant is applied to the non-permeable substrate prior to the ink application step, The ink application step involves applying the ink onto the area on the non-permeable substrate to which the pretreatment liquid has been applied. <1> ~ <6> The inkjet recording method described in one of the following documents. <8> An ink set is used that includes at least one colored ink containing water and a coloring pigment, and at least one white ink containing water and a white pigment. The ink application step involves applying at least one colored ink and at least one white ink to the same surface of the non-permeable substrate by an inkjet method, satisfying the following conditions a1, a2, and a3. <1> ~ <7> The inkjet recording method described in one of the following documents. Condition a1: The polarity of the zeta potential of all inks, including at least one colored ink and at least one white ink, is the same. Condition a2: The electrostatic polarity of the same surface of the non-permeable substrate is opposite to the polarity of the zeta potential of the entire ink. Condition a3: When the electrostatic charge on the same surface of the non-permeable substrate is AkV, and the zeta potential of each of the at least one colored ink and the at least one white ink is BmV, the difference [AB] obtained by subtracting B from A for all inks satisfies the condition that it is between 30 and 110. <9> Of the differences [AB] for each of the at least one colored ink and the at least one white ink, the difference [AB] for the ink that is applied last is the largest. <8> The inkjet recording method described above. <10> In the above-mentioned at least one colored ink and at least one white ink, when n is an integer of 2 or more, the difference [AB] for the nth ink in the application order is equal to or greater than the difference [AB] for the (n-1)th ink in the application order, and the difference [AB] for the last ink applied is greater than the difference [AB] for the first ink applied. <8> or <9> The inkjet recording method described above. [Effects of the Invention]

[0007] According to one aspect of this disclosure, an inkjet recording method is provided that uses water-containing ink to record an image on a non-permeable substrate in which a decrease in the accuracy of ink droplet application and / or a decrease in image quality caused by a deviation in droplet application timing is suppressed. [Modes for carrying out the invention]

[0008] In this specification, a numerical range indicated using "~" means a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in the numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0009] In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that the intended purpose of the process is achieved.

[0010] In this specification, "image" means all films formed by ink, and "image recording" means the formation of an image (i.e., a film). Also, the concept of "image" in this specification includes solid images.

[0011] In this specification, "colored ink" means ink of a color other than white, and "colored pigment" means pigment of a color other than white. The concept of colored ink includes black ink, and the concept of colored pigment includes black pigment.

[0012] In this specification, "(meth)acrylate" is a concept that includes both acrylate and methacrylate. "(meth)acrylic" is a concept that includes both acrylic and methacrylic. "Alkylene glycol" is a concept that includes both monoalkylene glycol and polyalkylene glycol. "Alkylene glycol alkyl ether" is a concept that includes monoalkylene glycol monoalkyl ether, monoalkylene glycol polyalkyl ether, polyalkylene glycol monoalkyl ether, and polyalkylene glycol polyalkyl ether.

[0013] 〔Inkjet recording method〕 The inkjet recording method of the present disclosure (hereinafter, also simply referred to as "recording method") includes an ink application step of applying an ink containing water onto a non-permeable substrate by an inkjet method, and in the ink application step, the ink is applied onto the non-permeable substrate under the condition that the polarity of the static electricity on the surface of the non-permeable substrate to which the ink is applied is opposite to the polarity of the zeta potential of the ink. The recording method of the present disclosure may include other steps as necessary.

[0014] According to the recording method of this disclosure, an image is obtained by applying the water-containing ink onto an impermeable substrate. In the obtained image, a decrease in image quality caused by a decrease in the accuracy of ink droplet application (i.e., a decrease in the positional accuracy of the point where the ink reaches the impermeable substrate) and / or a deviation in droplet timing (i.e., a deviation from the ideal timing of when the ink reaches the impermeable substrate) is suppressed. The reason why the ink droplet accuracy is suppressed by the recording method of this disclosure is thought to be that the electrostatic polarity of the surface of the non-permeable substrate to which the ink is applied and the polarity of the ink's zeta potential are opposite, creating an attractive force between the surface of the non-permeable substrate to which the ink is applied and the ink. This attractive force improves the straightness of the ink, and as a result, the ink droplet accuracy is improved. Furthermore, it is believed that the aforementioned attractive force also contributes to the effect of suppressing the timing discrepancy of droplet application.

[0015] The following describes each step of the recording method described herein.

[0016] <Ink application process> The ink application process is a process of applying water-containing ink to a non-permeable substrate by an inkjet method, wherein the polarity of the electrostatic charge on the surface of the non-permeable substrate to which the ink is applied and the polarity of the zeta potential of the ink are opposite.

[0017] (Non-permeable base material) In the ink application process, the above ink is applied to a non-permeable substrate. In this disclosure, a non-permeable substrate refers to a substrate whose water absorption rate (mass%) (24hr.) is less than 0.2 according to the ASTM D570 test method. There are no particular restrictions on the non-permeable substrate, but a resin substrate is preferred. There are no particular restrictions on the resin substrate; for example, a thermoplastic resin substrate can be used. Examples of resin substrates include thermoplastic resins molded into sheet or film shapes. As the resin substrate, a substrate containing polypropylene, polyethylene terephthalate, nylon, polyethylene, or polyimide is preferred.

[0018] The resin substrate may be a transparent resin substrate. Here, "transparent" means that the transmittance of visible light with wavelengths of 400 nm to 700 nm is 80% or higher (preferably 90% or higher). In an embodiment as described in Example 201 below, where a colored ink having a hue other than white (preferably a chromatic color or black; for example, cyan, magenta, yellow, black, etc.) and a white ink having a white hue are applied in this order to an impermeable substrate, if the impermeable substrate is a transparent resin substrate, the colored image with a white image as the background can be viewed through the impermeable substrate from the non-image-recording side of the impermeable substrate (i.e., the side where no image is recorded). The resin substrate may be colored.

[0019] The shape of the resin substrate is not particularly limited, but it is preferably a sheet-shaped resin substrate, and more preferably a sheet-shaped resin substrate that can be formed into a roll by winding, from the viewpoint of productivity of the recording medium. The thickness of the resin substrate is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0020] The resin substrate may be surface-treated to improve its surface energy. Surface treatments include, but are not limited to, corona treatment, plasma treatment, flame treatment, heat treatment, abrasion treatment, light irradiation treatment (UV treatment), and fire treatment.

[0021] (ink) In the ink application process, an ink containing water is applied to a non-permeable substrate.

[0022] -water- Ink contains water. The water content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of ink. The upper limit of the water content depends on the amounts of other components, but is preferably 90% by mass or less, and more preferably 80% by mass or less, relative to the total amount of ink.

[0023] -Pigment- The ink may contain at least one pigment. There are no particular restrictions on the pigment; both organic and inorganic pigments are acceptable.

[0024] Examples of organic pigments include azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates, nitro pigments, nitroso pigments, aniline black, and the like. Examples of inorganic pigments include white inorganic pigments, iron oxide, barium yellow, cadmium red, chromium yellow, and carbon black. Preferred embodiments of white inorganic pigments will be described later. Examples of pigments include those described in paragraphs 0096 to 0100 of Japanese Patent Publication No. 2009-241586.

[0025] An ink containing a chromatic pigment or a black pigment can be used, for example, as a colored ink (e.g., cyan ink, magenta ink, yellow ink, black ink, etc.).

[0026] An ink comprising a white pigment (for example, a white inorganic pigment) can be used, for example, as a white ink (hereinafter also referred to as "white ink"). Examples of white inorganic pigments include titanium dioxide (TiO2), barium sulfate, calcium carbonate, aluminum hydroxide, silica, zinc oxide, zinc sulfide, mica, talc, and pearl. Among the white inorganic pigments, titanium dioxide, barium sulfate, calcium carbonate, or zinc oxide are preferred, with titanium dioxide being more preferred.

[0027] The average primary particle size of white inorganic pigments is, for example, 150 nm to 400 nm. When the average primary particle diameter is 150 nm or larger, the opacity is further improved. Here, opacity refers to the property of covering and concealing the underlying surface with an image (e.g., a white image). When the average primary particle diameter is 400 nm or less, the ink ejection performance is further improved. The average primary particle size of the white inorganic pigment is preferably 250 nm to 350 nm, and more preferably 250 nm to 300 nm.

[0028] The average primary particle size of white inorganic pigments is measured using a transmission electron microscope (TEM). A JEOL Ltd. 1200EX transmission electron microscope can be used for this measurement. Specifically, a Cu200 mesh (manufactured by JEOL Ltd.) with a carbon film attached is dropped with ink diluted 1,000 times and dried. Then, the circular equivalent diameter of 300 independent, non-overlapping particles is measured from an image magnified 100,000 times using TEM, and the average of the obtained measurements is defined as the average primary particle diameter.

[0029] The pigment content is preferably 1% to 20% by mass, more preferably 1% to 15% by mass, and even more preferably 1% to 10% by mass, relative to the total amount of ink.

[0030] -resin- The ink may contain at least one type of resin. There are no particular restrictions on the resin, but preferably it is an acrylic resin, polyester resin, polyurethane resin, or polyolefin resin.

[0031] The resin content relative to the total amount of ink is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, even more preferably 2% to 15% by mass, and even more preferably 2% to 10% by mass.

[0032] Examples of resins include pigment dispersion resins for dispersing pigments, and resin particles, which are particles made of resin.

[0033] -Pigment-dispersed resin- The resin may include a pigment dispersant resin as a pigment dispersant. If the resin contains a pigment dispersion resin, the ink contains a resin-coated pigment having a structure in which at least a portion of the surface of the pigment is coated with the pigment dispersion resin. A water-insoluble resin is preferred as the pigment dispersion resin.

[0034] The pigment dispersion resin is preferably an acrylic resin. Examples of pigment dispersion resins include those described in International Publication No. 2013 / 180074, Japanese Patent Publication No. 5863600, Japanese Unexamined Patent Publication No. 2018-28080, Japanese Unexamined Patent Publication No. 2017-149906, and Japanese Unexamined Patent Publication No. 2016-193981. Pigment dispersion resins are also referred to as "resin dispersants," etc. Furthermore, as a combination of pigment and pigment dispersion resin, a resin-coated pigment in which the pigment is coated with a crosslinked water-soluble resin, as described in, for example, Japanese Patent Publication No. 5404669, may be used. In this case, the resin-coated pigment can be prepared, for example, by using an acrylic resin having a carboxyl group as the water-soluble resin and a bifunctional or more epoxy compound as the crosslinking agent.

[0035] From the viewpoint of adsorption to pigments, the pigment dispersion resin preferably contains an alicyclic structure or an aromatic cyclic structure, and more preferably contains an aromatic cyclic structure. As for the alicyclic structure, an alicyclic hydrocarbon structure having 5 to 10 carbon atoms is preferred, and a cyclohexane ring structure, dicyclopentanyl ring structure, dicyclopentenyl ring structure, norbornane ring structure, isobornane ring structure, norbornene ring structure, isobornene ring structure, or adamantane ring structure is preferred. The aromatic ring structure is preferably a naphthalene ring or a benzene ring, with a benzene ring being more preferred. The amount of alicyclic or aromatic ring structure is preferably 0.01 mol to 1.5 mol per 100 g of resin contained in the resin particles, and more preferably 0.1 mol to 1 mol.

[0036] From the viewpoint of pigment dispersion performance, it is preferable that the pigment dispersion resin has ionic groups in its structure. The ionic group may be an anionic group or a cationic group, but an anionic group is preferred. The anionic group is not particularly limited, but a carboxyl group, a salt of a carboxyl group, a sulfo group, or a salt of a sulfo group is preferred.

[0037] From the viewpoint of pigment dispersibility and storage stability, the acid value of the pigment dispersion resin is preferably 30 mg KOH / g to 300 mg KOH / g, more preferably 30 mg KOH / g to 200 mg KOH / g, and even more preferably 50 mg KOH / g to 200 mg KOH / g. Here, the acid value is defined as the mass (mg) of KOH required to completely neutralize 1 g of resin, and is measured by the method described in the JIS standard (JIS K 0070, 1992).

[0038] The weight-average molecular weight (Mw) of the pigment-dispersed resin is preferably 30,000 or more, more preferably 30,000 to 150,000, even more preferably 30,000 to 100,000, and even more preferably 30,000 to 80,000.

[0039] When the resin contains a pigment dispersion resin, the content of the pigment dispersion resin is preferably 1% to 25% by mass, more preferably 1% to 20% by mass, even more preferably 1% to 15% by mass, and even more preferably 1% to 10% by mass, based on the total amount of ink.

[0040] When the resin contains a pigment-dispersing resin, the ratio of the pigment-dispersing resin (D) to the pigment (P) (i.e., the D / P ratio) is preferably 0.05 to 3, more preferably 0.05 to 2, even more preferably 0.05 to 1, and even more preferably 0.05 to 0.7.

[0041] Known dispersion devices can be used to disperse pigments, including, for example, ball mills, sand mills, bead mills, roll mills, jet mills, paint shakers, attritors, ultrasonic dispersers, and dispersers.

[0042] The form of the pigment dispersion resin is not particularly limited and may be a random polymer, a block polymer, or a graft polymer, or it may be a polymer having a crosslinked structure. The pigment dispersion resin is preferably a polymer or block polymer having a crosslinked structure. The following describes preferred embodiments of polymers having a crosslinked structure and block polymers, which are preferred pigment dispersion resins.

[0043] In this disclosure, "polymer" refers to a compound with a weight-average molecular weight of 1000 or more.

[0044] In this disclosure, weight-average molecular weight refers to the value measured by gel permeation chromatography (GPC). The GPC measurement is performed using an HLC®-8020GPC (manufactured by Tosoh Corporation) as the measuring instrument, with three TSKgel® Super Multipore HZ-H columns (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation), and THF (tetrahydrofuran) as the eluent. The measurement is performed with a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C, using an RI detector. A calibration curve is prepared from eight samples of Tosoh Corporation's "Standard Samples TSK standard, polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0045] --Polymers with cross-linked structures-- A polymer having a cross-linked structure is not particularly limited as long as it has at least one cross-linked structure within its molecule.

[0046] Whether or not the polymers contained in the ink have a cross-linked structure can be determined, for example, by the following method. First, the polymers are separated from the ink using a separation method such as solvent extraction. The separated polymers can then be analyzed using various analytical methods such as nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and thermal analysis to comprehensively determine whether or not they have a cross-linked structure.

[0047] A polymer having a crosslinked structure (hereinafter also referred to as "crosslinked polymer") is formed, for example, by crosslinking an uncrosslinked polymer (hereinafter also referred to as "uncrosslinked polymer") with a crosslinking agent. The uncrosslinked polymer is preferably a water-soluble polymer.

[0048] In this disclosure, "water-soluble" means the property of dissolving 1 g or more in 100 g of water at 25°C. Preferably, "water-soluble" means dissolving 3 g or more (more preferably 10 g or more) in 100 g of water at 25°C.

[0049] Furthermore, even if an uncrosslinked polymer is water-soluble, the crosslinked polymer is not necessarily water-soluble.

[0050] Examples of uncrosslinked polymers include vinyl resins, acrylic resins, urethane resins, and polyester resins. Among these, acrylic resin is preferred as the uncrosslinked polymer.

[0051] The uncrosslinked polymer is preferably a polymer having functional groups that can be crosslinked by a crosslinking agent. Examples of crosslinkable functional groups include carboxyl groups or their salts, isocyanate groups, and epoxy groups. Among these, from the viewpoint of improving the dispersibility of the pigment, the crosslinkable functional group is preferably a carboxyl group or its salt, and a carboxyl group is particularly preferred. In other words, the uncrosslinked polymer is preferably a polymer containing carboxyl groups.

[0052] The uncrosslinked polymer is preferably a copolymer containing structural units derived from monomers containing carboxyl groups (hereinafter referred to as "carboxyl group-containing monomers"). The copolymer may contain only one type of structural unit derived from carboxyl group-containing monomers, or two or more types. The copolymer may be a random copolymer or a block copolymer, but it is preferably a random copolymer.

[0053] Examples of monomers containing a carboxyl group include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0054] The carboxyl group-containing monomer is preferably (meth)acrylic acid or β-carboxyethyl acrylate, with (meth)acrylic acid being more preferred, from the viewpoint of crosslinkability and dispersibility.

[0055] The content of structural units derived from carboxyl group-containing monomers is preferably 5% to 40% by mass, more preferably 10% to 35% by mass, and even more preferably 10% to 30% by mass, based on the total amount of the uncrosslinked polymer.

[0056] The uncrosslinked polymer preferably contains structural units derived from hydrophobic monomers in addition to structural units derived from carboxyl group-containing monomers. The copolymer may contain only one type of structural unit derived from hydrophobic monomers, or two or more types.

[0057] Examples of hydrophobic monomers include (meth)acrylates having alkyl groups with 1 to 20 carbon atoms, (meth)acrylates having aromatic rings (e.g., benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc.), styrene, and styrene derivatives.

[0058] The content of structural units derived from hydrophobic monomers is preferably 60% to 95% by mass, more preferably 65% ​​to 90% by mass, and even more preferably 70% to 90% by mass, relative to the total amount of the uncrosslinked polymer.

[0059] The uncrosslinked polymer is preferably a random copolymer comprising structural units derived from a carboxyl group-containing monomer and at least one of structural units derived from (meth)acrylate having an alkyl group with 1 to 20 carbon atoms and structural units derived from (meth)acrylate having an aromatic ring; more preferably a random copolymer comprising structural units derived from (meth)acrylic acid and structural units derived from (meth)acrylate having an aromatic ring; and even more preferably a copolymer comprising structural units derived from (meth)acrylic acid and structural units derived from benzyl (meth)acrylate.

[0060] The weight-average molecular weight (Mw) of the uncrosslinked polymer is not particularly limited, but from the viewpoint of the dispersibility of the white pigment, it is preferably 3,000 to 300,000, more preferably 5,000 to 200,000, and even more preferably 7,000 to 100,000.

[0061] The preferred range for the weight-average molecular weight of the crosslinked polymer is the same as the preferred range for the weight-average molecular weight of the uncrosslinked polymer.

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

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

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

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

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

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

[0068] --Block Polymer-- A block polymer, also known as a block copolymer, is a copolymer in which at least two polymers are bonded together within the molecule.

[0069] The block polymer preferably contains structural units derived from hydrophobic monomers and structural units derived from monomers containing anionic groups (hereinafter referred to as "anionic group-containing monomers").

[0070] The structural units derived from hydrophobic monomers contained in the block polymer may be one type or two or more types. The structural units derived from anionic group-containing monomers contained in the block polymer may be one type or two or more types.

[0071] Structural units derived from hydrophobic monomers include ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure, and (meth)acrylates having an alkyl group with 1 to 20 carbon atoms.

[0072] The content of structural units derived from hydrophobic monomers is preferably 35% to 95% by mass, more preferably 50% to 95% by mass, and even more preferably 70% to 90% by mass, relative to the total amount of the block polymer.

[0073] From the viewpoint of adsorption with pigments, the hydrophobic monomer preferably contains an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure, more preferably contains an ethylenically unsaturated compound having an alicyclic structure, and even more preferably contains an ethylenically unsaturated compound having an alicyclic structure with 6 or more carbon atoms.

[0074] The content of structural units derived from ethylenically unsaturated compounds having an aromatic ring structure or an alicyclic structure is preferably 10% to 90% by mass, more preferably 20% to 80% by mass, even more preferably 30% to 70% by mass, and still more preferably 30% to 60% by mass, based on the total amount of the block polymer.

[0075] The structural units derived from hydrophobic monomers may also preferably include (meth)acrylates having an alkyl group with 1 to 20 carbon atoms. The alkyl group may be linear or branched.

[0076] Examples of (meth)acrylates having an alkyl group with 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate.

[0077] The content of structural units derived from (meth)acrylates having an alkyl group with 1 to 20 carbon atoms is preferably 10% to 90% by mass, more preferably 20% to 80% by mass, even more preferably 30% to 70% by mass, and particularly preferably 40% to 60% by mass, based on the total amount of the block polymer.

[0078] In structural units derived from anionic group-containing monomers, examples of anionic groups include carboxyl groups, salts of carboxyl groups, sulfo groups, salts of sulfo groups, phosphate groups, salts of phosphate groups, phosphonic acid groups, and salts of phosphonic acid groups.

[0079] Counterions in salts include alkali metal ions such as sodium ions, potassium ions, and lithium ions; alkaline earth metal ions such as calcium ions and magnesium ions; and ammonium ions.

[0080] In particular, the anionic group is preferably a carboxyl group or a salt of a carboxyl group. Examples of anionic group-containing monomers include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid. In particular, the anionic group-containing monomer is preferably (meth)acrylic acid.

[0081] The content of structural units derived from anionic group-containing monomers is preferably 1% to 30% by mass, more preferably 2% to 25% by mass, and even more preferably 3% to 20% by mass, based on the total amount of the block polymer.

[0082] Whether or not the polymer contained in the ink is a block polymer can be determined, for example, by the following method. First, the polymer is separated from the ink using a separation method such as solvent extraction. The separated polymer is then analyzed using various analytical methods such as nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and thermal analysis, and its physical properties, such as the glass transition temperature, are measured to comprehensively determine whether or not it is a block polymer.

[0083] The weight-average molecular weight (Mw) of the block polymer is not particularly limited, but from the viewpoint of pigment dispersibility, it is preferably 3,000 to 100,000, more preferably 5,000 to 80,000, and even more preferably 10,000 to 60,000.

[0084] -Resin particles- The resin may contain resin particles. Here, the resin particles are distinguished from the pigment-dispersed resins mentioned earlier in that they are particles made of resin. Water-insoluble resins are preferred as the resins that make up the resin particles.

[0085] There are no particular restrictions on the glass transition temperature of the resin particles (i.e., the glass transition temperature of the resin in the resin particles). From the viewpoint of further improving image intensity, 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. From the viewpoint of suitability for manufacturing resin particles, the glass transition temperature (Tg) of the resin particles is preferably 150°C or lower, and more preferably 130°C or lower.

[0086] Preferably, the resin particles are particles made of acrylic resin (hereinafter also referred to as acrylic resin particles), particles made of styrene-acrylic resin (hereinafter also referred to as styrene-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).

[0087] Self-dispersible resin particles are preferred as the resin particles. Examples of self-dispersing resin particles include self-dispersing polymer particles described in paragraphs 0062 to 0076 of Japanese Patent Publication No. 2016-188345 and paragraphs 0109 to 0140 of International Publication No. 2013 / 180074.

[0088] 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. The weight-average molecular weight is measured by gel permeation chromatography (GPC). Details of GPC are as previously described.

[0089] 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.

[0090] If the ink contains resin particles, the content of resin particles relative to the total amount of ink is preferably 1% to 25% by mass, more preferably 2% to 20% by mass, even more preferably 2% to 15% by mass, and still more preferably 2% to 10% by mass.

[0091] -Water-soluble organic solvents with a boiling point below 220°C- The ink preferably contains at least one water-soluble organic solvent with a boiling point of less than 220°C. This improves the lamination strength of image recordings. In this disclosure, boiling point means boiling point at 1 atmosphere (101325 Pa).

[0092] Examples of water-soluble organic solvents with a boiling point below 220°C include 1,2-propanediol (also known as propylene glycol) (boiling point 188°C), 1,3-propanediol (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), and propylene glycol monopropyl ether (boiling point 124°C). Examples include 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), and dipropylene glycol dimethyl ether (boiling point 175°C).

[0093] When the ink contains a water-soluble organic solvent with a boiling point of less than 220°C, the content of the water-soluble organic solvent with a boiling point of less than 220°C is preferably 1% to 50% by mass, more preferably 5% to 40% by mass, even more preferably 10% to 40% by mass, and even more preferably 15% to 35% by mass, based on the total amount of ink.

[0094] -Organic solvents with a boiling point of 220°C or higher- The content of organic solvents with a boiling point of 220°C or higher (hereinafter also referred to as "high-boiling point solvents") in the ink is preferably 5% by mass or less. This further improves the lamination strength and image adhesion of the image recording material. Here, "the content of organic solvents with a boiling point of 220°C or higher in the ink is 5% by mass or less" means that the ink does not contain organic solvents with a boiling point of 220°C or higher (i.e., the content of organic solvents with a boiling point of 220°C or higher in the ink is 0% by mass), or, if it does contain such solvents, the content of organic solvents with a boiling point of 220°C or higher is 5% by mass or less of the total amount of ink. The content of organic solvents with a boiling point of 220°C or higher in the ink is more preferably 3% by mass or less, even more preferably 2% by mass or less, even more preferably 1% by mass or less, and even more preferably 0% by mass.

[0095] Examples of organic solvents with 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), triethylene glycol monomethyl ether (boiling point 248°C), and the like.

[0096] - Surfactants - The ink may contain at least one surfactant. Examples of surfactants include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants.

[0097] A preferred surfactant is an acetylene glycol-based surfactant, which is a type of nonionic surfactant. As an acetylene glycol-based surfactant, for example, an acetylene glycol-based surfactant described in paragraphs 0070-0080 of International Publication No. 2017 / 149917 can be used. Examples of acetylene glycol-based surfactants include Polyalkylene oxide adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (preferably polyethylene oxide adduct), Polyalkylene oxide adduct of 3,6-dimethyl-4-octin-3,6-diol (preferably polyethylene oxide adduct), Polyalkylene oxide adduct of 2,5,8,11-tetramethyl-6-dodecine-5,8-diol (preferably polyethylene oxide adduct), Polyalkylene oxide adduct of 2,5-dimethyl-3-hexyn-2,5-diol (preferably polyethylene oxide adduct) These are some examples. Commercially available acetylene glycol-based surfactants include the Surfinol series (e.g., Surfinol 420, Surfinol 440, Surfinol 465, Surfinol 485), Olfin series (e.g., Olfin E1010, Olfin E1020), and Dynol series (e.g., Dynol 604) manufactured by Air Products Co., Ltd. or Nisshin Chemical Industry Co., Ltd.; and Acetyleneol, etc., manufactured by Kawaken Fine Chemical Co., Ltd. Commercially available acetylene glycol-based surfactants are also supplied by companies such as Dow Chemical and General Aniline.

[0098] Examples of surfactants include the compounds listed as surfactants on pages 37-38 of Japanese Patent Publication No. 59-157636 and in Research Disclosure No. 308119 (1989). Other examples include fluorine (alkyl fluoride) surfactants and silicone surfactants described in Japanese Patent Publication Nos. 2003-322926, 2004-325707, and 2004-309806.

[0099] If the ink contains a surfactant, the amount of surfactant in the ink is adjusted appropriately, taking into account the surface tension of the ink. The surfactant content in the ink is preferably 0.01% to 5% by mass, more preferably 0.05% to 3% by mass, and even more preferably 0.1% to 2% by mass, based on the total amount of ink.

[0100] -Other ingredients- The ink may contain other components besides those listed above. Other known additives include, for example, silicate compounds (e.g., silicate compounds described in paragraphs 0058-0075 of Japanese Patent No. 5430316), urea, urea derivatives, waxes, colorfastness inhibitors, emulsifying stabilizers, penetration enhancers, UV absorbers, preservatives, fungicides, pH adjusters, defoamers, viscosity modifiers, dispersion stabilizers, and chelating agents.

[0101] -Desired physical properties of ink- The viscosity of the ink (at 25°C) 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 preferably 2.5 mPa·s or more and less than 10 mPa·s.

[0102] The surface tension of the ink (at 25°C) is preferably 25 mN / m to 50 mN / m, more preferably 30 mN / m to 45 mN / m, and even more preferably 30 mN / m to 40 mN / m.

[0103] 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. The pH of the ink at 25°C is measured using a commercially available pH meter.

[0104] (Ink application) In the ink application process, the above-mentioned ink is applied to a non-permeable substrate by an inkjet method (i.e., by ejection from an inkjet head). There are no particular restrictions on the ink ejection method in the inkjet method, and any known method may be used, such as a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into an acoustic beam and irradiates the ink to eject the ink using the radiation pressure, and a thermal inkjet (bubble jet®) method that heats the ink to form bubbles and utilizes the resulting pressure. As an inkjet method, in particular, the method described in Japanese Patent Publication No. 54-59936, in which the ink, when subjected to thermal energy, undergoes a rapid volume change, and the force resulting from this state change causes the ink to be ejected from the nozzle, can be effectively utilized. As an inkjet method, the method described in paragraphs 0093 to 0105 of Japanese Patent Publication No. 2003-306623 can also be applied.

[0105] Ink application using the inkjet method is performed by ejecting ink from the nozzles of the inkjet head. Inkjet head systems include the shuttle system, which uses a short serial head to scan the recording medium in the width direction while recording, and the line system, which uses a line head in which recording elements are arranged to cover the entire width of one side of the recording medium. In the line method, image recording can be performed across the entire surface of the recording medium by scanning it in a direction intersecting the arrangement direction of the recording elements. The line method eliminates the need for a transport system such as a carriage that scans the short head, which is required in the shuttle method. Furthermore, compared to the shuttle method, the line method eliminates the need for complex scanning control of the carriage movement and the recording medium, as only the recording medium moves. For this reason, the line method enables faster image recording compared to the shuttle method.

[0106] Ink is preferably applied using an inkjet head with a resolution of 300 dpi or higher (more preferably 600 dpi, and even more preferably 800 dpi). Here, dpi is an abbreviation for dots per inch, and 1 inch is equal to 2.54 cm.

[0107] From the viewpoint of obtaining a high-resolution image, the amount of ink droplets ejected from the nozzles of the inkjet head is preferably 1 pL (picoliters) to 10 pL, and more preferably 1.5 pL to 6 pL. Furthermore, from the perspective of improving image uniformity and the continuity of continuous tonal gradations, it is also effective to dispense a combination of appropriate amounts of different liquids.

[0108] The recording method of this disclosure may include a step of preheating a non-permeable substrate before the ink application step. In this case, the ink application step involves applying ink to the preheated non-permeable substrate. The heating temperature for preheating can be set as appropriate, but it is preferable to set the temperature of the non-permeable substrate to 20°C to 50°C, and more preferably to 25°C to 40°C.

[0109] The ink application process may involve applying two or more inks to a non-permeable substrate. Preferably, the two or more inks consist of two or more colors, preferably two or more inks selected from the group consisting of at least one colored ink and at least one white ink, and more preferably two or more inks that are a combination of at least one colored ink and at least one white ink.

[0110] In this disclosure, "colored ink" means an ink having a hue other than white (e.g., chromatic colors and black) (e.g., cyan ink, magenta ink, yellow ink, and black ink).

[0111] In the ink application process, when two or more inks are sequentially applied to a non-permeable substrate, Alternatively, an n-color ink (where n is an integer of 1 or more; the same applies hereinafter) applied to a non-permeable substrate may be heated and dried, and then an (n+1)-color ink may be applied on top of the heated and dried n-color inks. The nth color ink applied to the non-permeable substrate may be applied to the nth color ink without heating and drying it.

[0112] (Static electricity of non-permeable substrates and zeta potential of ink) The ink application process involves applying ink to a non-permeable substrate under the condition that the electrostatic polarity of the surface on which the ink is applied and the polarity of the zeta potential of the ink are opposite. The combination of the polarity of the static electricity and the polarity of the zeta potential may be either a combination where the polarity of the static electricity is positive (+) and the polarity of the zeta potential is negative (-), or a combination where the polarity of the static electricity is negative (-) and the polarity of the zeta potential is positive (+). However, from the viewpoint of further suppressing the deterioration of image quality, the combination where the polarity of the static electricity is positive (+) and the polarity of the zeta potential is negative (-) is preferred.

[0113] From the viewpoint of further suppressing the degradation of image quality, it is preferable that the ink application process is carried out under the condition that the difference [AB], which is the value obtained by subtracting B from A when the electrostatic charge on the surface of the non-permeable substrate to which the ink is applied is AkV and the zeta potential of the ink is BmV, is between 30 and 110 (i.e., +30 to +110). When the difference [AB] is 30 or greater, the degradation of image quality caused by a decrease in ink droplet accuracy is particularly suppressed. From the viewpoint of this effect, the difference [AB] is more preferably 40 or greater, and even more preferably 45 or greater. When the difference [AB] is 110 or less, the degradation of image quality caused by the timing difference of ink droplet application is particularly suppressed. From the viewpoint of this effect, the difference [AB] is more preferably 90 or less, and even more preferably 70 or less.

[0114] From the viewpoint of further suppressing the degradation of image quality, it is preferable that the ink application process be carried out under conditions where the difference [AB] is 45 to 70, and the ink is applied to a non-permeable substrate.

[0115] The zeta potential ("B" (in mV)) of the ink is preferably -80mV to -10mV, more preferably -80mV to -20mV, and even more preferably -80mV to -30mV. When the zeta potential of the ink is -80mV or higher, it is easier to achieve a difference [AB] of 110 or less. When the zeta potential of the ink is -20mV or less, it is easier to achieve a difference [AB] of 30 or more.

[0116] The zeta potential of ink can be adjusted by controlling the types of components contained in the ink, the ink's composition, and other factors. The zeta potential of the ink can be adjusted, for example, by adjusting the acid value and / or degree of neutralization of the pigment dispersant contained in the ink, the acid value and / or degree of neutralization of the resin particles contained in the ink, the acid value and / or degree of neutralization of the water-soluble resin contained in the ink, etc.

[0117] In this disclosure, the zeta potential of the ink refers to the value measured using a Malvern ZETASIZER NANO-ZS. Specifically, the zeta potential of the ink in this disclosure is measured using a ZETASIZER NANO-ZS after diluting the ink 1000 times with ultrapure water, shaking it in a shaker for 30 seconds.

[0118] The electrostatic charge ("A" (in kV)) of the surface to which the ink of the non-permeable substrate is applied is preferably 0kV to 50kV (i.e., 0kV to +50kV), more preferably 5kV to 40kV, and even more preferably 10kV to 30kV. When the electrostatic charge on the surface to which the ink of a non-permeable substrate is applied is 0kV or higher, it is easier to achieve a difference [AB] of 30 or higher. When the electrostatic charge on the surface to which the ink of a non-permeable substrate is applied is 50kV or less, it is easier to achieve a difference [AB] of 110 or less.

[0119] In this disclosure, the amount of static electricity on the surface of a non-permeable substrate to which the ink is applied means the value measured using a KEYENCE SK-H050 electrostatic meter. Specifically, using the electrostatic measuring instrument described above, the electrostatic potential is measured in Far (wide range mode) from a position 10 cm away from the surface to which the ink of the non-permeable substrate is applied, and the obtained electrostatic potential is taken as the electrostatic charge of the surface to which the ink of the non-permeable substrate is applied.

[0120] The amount of static electricity on the surface to which the ink of a non-penetrating substrate is applied can be adjusted, for example, by an ionizer, an anti-static brush, or an anti-static sheet.

[0121] (Ink heating and drying) In the ink application process, the ink applied to the non-permeable substrate may be heated and dried. Means for performing heating and drying include known heating means such as infrared heaters, known blowing means such as dryers, and means that combine two or more of these means. Methods for heat drying include, for example, A method of applying warm air or hot air to a surface of a non-penetrating substrate to which ink has been applied. A method of applying heat to a non-permeable substrate from the side to which the ink is applied and / or the side opposite to the side to which the ink is applied, using an infrared heater or the like. A method that combines these multiple methods, These are some examples. 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. There is no particular upper limit to the heating temperature, but an upper limit of, for example, 100°C is possible, and 90°C is preferred. There are no particular restrictions on the heating and drying time, but 3 to 60 seconds is preferred, 5 to 30 seconds is more preferred, and 5 to 20 seconds is particularly preferred.

[0122] <Aspects of using an ink set> The recording method of this disclosure may use two or more ink sets containing water. For example, the recording method of this disclosure may use an ink set comprising at least one colored ink containing water and a coloring pigment (hereinafter also simply referred to as "colored ink") and at least one white ink containing water and a white pigment (hereinafter also simply referred to as "white ink"). The ink set containing colored ink and white ink may further include the aforementioned pretreatment solution.

[0123] In the recording method of this disclosure, when an ink set including a colored ink and a white ink is used, the ink application step involves applying the colored ink and the white ink to the same surface of a non-permeable substrate by an inkjet method, satisfying the following conditions a1, a2, and a3. Condition a1: The polarity of the zeta potential of all inks, including at least one colored ink and at least one white ink, is the same. Condition a2: The electrostatic polarity of the same surface of the non-permeable substrate is opposite to the polarity of the zeta potential of the entire ink. Condition a3: When the electrostatic charge on the same surface of the non-permeable substrate is AkV, and the zeta potential of each of the at least one colored ink and the at least one white ink is BmV, the difference [AB] obtained by subtracting B from A for all inks satisfies the condition that it is between 30 and 110.

[0124] In the recording method of this disclosure, when an ink set including colored ink and white ink is used, an image derived from these inks can be obtained. In this case, a decrease in droplet accuracy and a deviation in droplet timing are suppressed for each of these inks. As a result, a decrease in droplet accuracy and / or a decrease in image quality caused by droplet timing (e.g., the occurrence of streaks) is suppressed in the obtained image.

[0125] In the recording method of this disclosure, when an ink set including a colored ink and a white ink is used, it is preferable that the difference [AB] for the last ink applied is the largest among the differences [AB] for each of the colored ink and the white ink. This more effectively suppresses the decrease in ink droplet accuracy and / or the decrease in image quality caused by the timing of droplet application (e.g., the appearance of streaks) in the resulting image. The reason this effect is achieved is likely because the precision and timing of the final ink application have the greatest impact on the image quality of the resulting image.

[0126] In the recording method of this disclosure, when an ink set including colored ink and white ink is used, it is preferable that, when n is an integer of 2 or more, the difference [AB] for the nth ink in the application order is equal to or greater than the difference [AB] for the (n-1)th ink in the application order, and the difference [AB] for the last ink applied is greater than the difference [AB] for the first ink applied. This more effectively suppresses the decrease in ink droplet accuracy and / or the decrease in image quality caused by the timing of droplet application (e.g., the appearance of streaks) in the resulting image. The reason this effect is achieved is thought to be that the influence of ink on the image quality of the resulting image increases as the order in which the ink is applied progresses.

[0127] In the recording method of this disclosure, when an ink set including colored ink and white ink is used, in the ink application step, for example, the colored ink and white ink are applied in this order. That is, the white ink is applied last. In this embodiment, for example, a transparent substrate is used as the impermeable substrate, and a colored image (i.e., a chromatic image or a black image; for example, a pattern image such as characters or figures) is recorded on the impermeable substrate using colored ink. Then, a white image (e.g., a solid color image) is recorded on the impermeable substrate on which the colored image is recorded, so as to cover the colored image. In this case, when observed from the non-image-recorded side of the impermeable substrate (i.e., the side where no image is recorded), the colored image with the white image as the background can be seen through the impermeable substrate. On the other hand, when observed from the image-recorded side of the impermeable substrate (i.e., the side where an image is recorded), the colored image and the impermeable substrate are obscured by the white image created by the white ink, making it difficult to see the colored image and the impermeable substrate.

[0128] <Pretreatment solution application process> The recording method of this disclosure may further include a pretreatment liquid application step of applying a pretreatment liquid containing water and a coagulant to a non-permeable substrate before the ink application step. In this case, the ink application process involves applying ink to an area on a non-permeable substrate that has been treated with a pretreatment solution. According to this embodiment, by coagulating the components in the ink with a coagulant, an image with superior image quality can be obtained.

[0129] If the recording method of this disclosure includes a pretreatment liquid application step, the static electricity and amount of static electricity of the "ink-applied surface of the non-permeable substrate" in the ink application step mean the static electricity and amount of static electricity of the area on the non-permeable substrate to which the pretreatment liquid has been applied.

[0130] (Pretreatment solution) The pretreatment solution contains water and a coagulant.

[0131] -water- The pretreatment solution contains water. The water content is preferably 50% by mass or more, and more preferably 60% by mass or more, relative to the total amount of the pretreatment solution. The upper limit of the water content depends on the amounts of other components, but is preferably 90% by mass or less of the total amount of the pretreatment solution.

[0132] -Agglutinant- The pretreatment solution is prepared by adding a flocculant, which is at least one selected from the group consisting of organic acids, organic acid salts, polyvalent metal compounds, and metal complexes. A coagulant is a component that causes the components in ink (for example, resin) to coagulate.

[0133] -Organic acid- Examples of organic acids include organic compounds that have an acidic group. Examples of acidic groups include phosphate groups, phosphonic acid groups, phosphinic acid groups, sulfate groups, sulfonic acid groups, sulfinic acid groups, and carboxyl groups. From the viewpoint of the ink aggregation rate, the above-mentioned acidic group is preferably a phosphoric acid group or a carboxyl group, and more preferably a carboxyl group. Furthermore, it is preferable that at least a portion of the above-mentioned acidic group is dissociated in the pretreatment solution.

[0134] Preferred organic compounds having a carboxyl group include polyacrylic acid, acetic acid, formic acid, benzoic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, phthalic acid, adipic acid, pimelic acid, 4-methylphthalic acid, lactic acid, pyrrolidone carboxylic acid, pyrrone carboxylic acid, pyrrole carboxylic acid, furanic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, pimelic acid, and the like. These compounds may be used individually or in combination of two or more.

[0135] As for organic compounds having a carboxyl group, divalent or higher carboxylic acids (hereinafter also referred to as polyvalent carboxylic acids) are preferred from the viewpoint of ink aggregation rate. As for polycarboxylic acids, Dicarboxylic acids or tricarboxylic acids are preferred. Glutaric acid, malonic acid, succinic acid, adipic acid, pimelic acid, malic acid, maleic acid, fumaric acid, tartaric acid, or citric acid are more preferably used. Glutaric acid, malonic acid, succinic acid, adipic acid, pimelic acid, malic acid, fumaric acid, tartaric acid, or citric acid are more preferably used. Glutaric acid, malonic acid, succinic acid, adipic acid, or pimelic acid are more preferred.

[0136] Organic acids are preferably those with a low pKa (e.g., 1.0 to 5.0). This allows for a reduction in the dispersion stability of particles such as pigments and polymer particles in inks, which are dispersed and stabilized by weakly acidic functional groups such as carboxyl groups, by bringing them into contact with organic acidic compounds with lower pKa values.

[0137] The organic acid is preferably a divalent or trivalent acidic substance that has a low pKa, high solubility in water, and a valency of 2 or higher, and more preferably has a high buffering capacity in a pH range lower than the pKa of the functional group (e.g., carboxyl group) that disperses and stabilizes the particles in the ink.

[0138] -Organic acid salt- Examples of organic acid salts include the salts of the organic acids exemplified above. Examples of organic acid salts include those containing alkaline earth metals from Group 2 of the periodic table (e.g., magnesium, calcium), transition metals from Group 3 of the periodic table (e.g., lanthanum), cations from Group 13 of the periodic table (e.g., aluminum), and lanthanides (e.g., neodymium). As for organic acid salts, organic acid salts containing alkaline earth metals are preferred, and organic acid salts containing calcium (e.g., calcium lactate, calcium acetate, etc.) or organic acid salts containing magnesium (e.g., magnesium lactate, magnesium acetate, etc.) are preferred.

[0139] -Polyvalent metal compounds- Examples of polyvalent metal compounds include salts (excluding organic salts) containing at least one selected from the group consisting of alkaline earth metals of Group 2 of the periodic table (e.g., magnesium, calcium), transition metals of Group 3 of the periodic table (e.g., lanthanum), cations from Group 13 of the periodic table (e.g., aluminum), and lanthanides (e.g., neodymium). Suitable polyvalent metal compounds include nitrates, chlorides, or thiocyanates. Particularly preferred polyvalent metal compounds are calcium or magnesium salts of nitric acid, calcium chloride, magnesium chloride, or calcium or magnesium salts of thiocyanate. It is preferable that the polyvalent metal compound dissociates into polyvalent metal ions and counterions in the pretreatment solution, at least a portion of which is present.

[0140] -Metal complex- As for the metal complex, a metal complex containing at least one element selected from the group consisting of zirconium, aluminum, and titanium is preferred. As for the metal complex, a metal complex comprising at least one selected from the group consisting of acetate, acetylacetonate, methylacetoacetate, ethylacetoacetate, octylene glycolate, butoxyacetylacetonate, lactate, lactate ammonium salt, and triethanolamine as a ligand is preferred.

[0141] Various metal complexes are commercially available, and in this disclosure, commercially available metal complexes may be used. In addition, various organic ligands, in particular various polydentate ligands that can form metal chelate catalysts, are commercially available. Therefore, metal complexes prepared by combining commercially available organic ligands with metals may also be used.

[0142] There are no particular restrictions on the amount of flocculant contained. From the viewpoint of ink aggregation rate, the content of the coagulant relative to the total amount of pretreatment solution is preferably 0.1% to 40% by mass, more preferably 0.1% to 30% by mass, even more preferably 1% to 20% by mass, and particularly preferably 1% to 10% by mass.

[0143] -resin- The pretreatment solution preferably contains at least one type of resin. Examples of resins include acrylic resin, polyester resin, polyolefin resin, polyurethane resin, polyurea resin, polyamide resin, polycarbonate resin, and polystyrene resin. The pretreatment solution preferably contains at least one type of resin particle, which is made of resin.

[0144] When preparing the pretreatment solution, commercially available aqueous dispersions of resin particles may be used. Commercially available aqueous dispersions of resin particles include Pesresin A124GP, Pesresin A645GH, Pesresin A615GE, Pesresin A520 (all manufactured by Takamatsu Oil & Fat Co., Ltd.), Eastek1100, Eastek1200 (both manufactured by Eastman Chemical Co., Ltd.), Pluscoat RZ570, Pluscoat Z687, Pluscoat Z565, Pluscoat RZ570, Pluscoat Z690 (all manufactured by Go-o Chemical Industry Co., Ltd.), Byronal MD1200 (manufactured by Toyobo Co., Ltd.), EM57DOC (manufactured by Daicel Finechem Co., Ltd.), Superflex M500 (Daiichi Kogyo Seiyaku Co., Ltd.), and others.

[0145] If the pretreatment solution contains resin particles, the content of resin particles relative to the total amount of the pretreatment solution is preferably 0.5% to 30% by mass, more preferably 1% to 20% by mass, and particularly preferably 1% to 15% by mass.

[0146] -Water-soluble organic solvent- The pretreatment solution may contain at least one water-soluble organic solvent. Any known water-soluble organic solvent can be used without any particular restrictions. Examples of water-soluble organic solvents include those similar to those that can be contained in ink.

[0147] If the pretreatment solution contains a water-soluble organic solvent, the content of the water-soluble organic solvent relative to the total amount of the pretreatment solution is preferably 0.5% to 30% by mass, more preferably 1% to 20% by mass, and particularly preferably 1% to 15% by mass.

[0148] -Other ingredients- The pretreatment solution may contain other components not listed above, if necessary. Other components that may be contained in the pretreatment solution include known additives such as surfactants, solid wetting agents, silicate compounds (e.g., colloidal silica), inorganic salts, anti-fading agents, emulsifying stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, antifungal agents, pH adjusters, viscosity adjusters, rust inhibitors, chelating agents, and water-soluble polymer compounds other than water-soluble cationic polymers (e.g., water-soluble polymer compounds described in paragraphs 0026 to 0080 of Japanese Patent Application Publication No. 2013-001854). Other components that may be included in the pretreatment solution can also be seen from the components that may be included in the first ink, as described later.

[0149] <Other processes> The recording method of this disclosure may include other steps besides those described above. Other steps include, for example, laminating a laminating substrate onto an image recorded on an impermeable substrate. By laminating the laminating substrate onto the image recorded on the impermeable substrate, the image is effectively protected.

[0150] A resin substrate is preferred as the base material for lamination. The resin substrate is not particularly limited, but examples include a substrate made of a thermoplastic resin. Examples of resin substrates include substrates made by molding thermoplastic resin into a sheet. The resin substrate preferably contains polypropylene, polyethylene terephthalate, nylon, polyethylene, or polyimide.

[0151] The shape of the resin substrate is not particularly limited, but a sheet-like resin substrate is preferred. The thickness of the resin substrate is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0152] The laminating substrate may be laminated directly onto the side of the image recording material on which the image is placed, or it may be laminated via another layer (e.g., an adhesive layer).

[0153] When laminating a laminating substrate directly onto the side of the image recording material on which the image is placed, the lamination can be carried out by known methods such as heat bonding or heat fusion.

[0154] Furthermore, when laminating a laminate substrate to the side of the image recording object on which the image is placed, the lamination can be carried out, for example, by applying adhesive to the side of the image recording object on which the image is recorded, then placing the laminate substrate on top, and then bonding the image recording object and the laminate substrate together. Furthermore, when laminating the image recording material on the side where the image is placed via an adhesive layer, lamination can also be carried out by methods such as extrusion lamination (i.e., sandwich lamination).

[0155] In the embodiment in which the image recording material described above is laminated to the side on which the image is placed via an adhesive layer, the adhesive layer preferably contains an isocyanate compound. When the adhesive layer contains an isocyanate compound, the adhesion between this adhesive layer and the image ink-derived layer is improved, thereby increasing the lamination strength. [Examples]

[0156] The following are examples of the embodiments of this disclosure, but this disclosure is not limited to the following embodiments. The pH value was measured at 25°C using a pH meter (model: WM-50EG, manufactured by Toa DDK Co., Ltd.).

[0157] [Examples 1-10, Comparative Examples 1-3] Examples 1-10 and Comparative Examples 1-3 are examples and comparative examples that record images in a single color of cyan. The details are explained below.

[0158] <Preparation of pretreatment solution> The following components were mixed to prepare a pretreatment solution.

[0159] -Composition of pretreatment solution- • Glutaric acid [coagulant] …6.1% by mass • Propylene glycol [solvent] …5.0% by mass • Orphine E1010 (manufactured by Nisshin Chemical Co., Ltd.) [Surfactant] …0.5% by mass • Superflex M500 (Daiichi Kogyo Seiyaku) [Aqueous dispersion of urethane resin particles] …7.0% by mass • Triisopropanolamine [pH adjuster] …0.2% by mass • BYK024 (BYK Corporation) [Antifoaming agent] …0.01% by mass ·Ultra pure water ...the remaining amount is 100% by mass of the entire pretreatment solution.

[0160] <Preparation of cyan ink> (Synthesis of pigment dispersant P1) 965 g of dipropylene glycol was added to a 5000 mL three-necked flask equipped with a stirrer and a condenser, and the mixture was heated to 85°C under a nitrogen atmosphere. Solution I was obtained by dissolving 640 g of benzyl methacrylate, 340 g of methacrylic acid, and 19.94 g of 2-mercaptopropionic acid in 370.28 g of dipropylene glycol, Solution II, obtained by dissolving 17.69 g of t-butylperoxy-2-ethylhexanoate (product name "Perbutyl O", manufactured by NOF Corporation) in 221.17 g of dipropylene glycol, Each of these was prepared. Solution I was added dropwise to the three-necked flask over 4 hours, and solution II over 5 hours. After the dropwise addition was complete, the reaction was allowed to continue for another 2 hours. The disappearance of monomers was 1 Confirmed by 1H-NMR. The resulting reaction solution was heated to 70°C, and 248.02 g of a 50% potassium hydroxide aqueous solution was added. Then, 107.48 g of dipropylene glycol and 75.52 g of pure water were added and the mixture was stirred to obtain a 37% random polymer solution. This random polymer was used as the pigment dispersant P1. The structural units that make up the obtained random polymer 1 The results were confirmed by 1H-NMR. The weight-average molecular weight (Mw) was also determined by GPC. The weight-average molecular weight (Mw) of the obtained pigment dispersant P1 was 8400, and the acid value was 221.7 mgKOH / g.

[0161] (Preparation of low-acid value cyanide pigment solution) 150 parts by mass of pigment dispersant P1 was dissolved in water to prepare a polymer aqueous solution with a concentration of pigment dispersant P1 of approximately 25% by mass. 180 parts by mass of this 25% by mass polymer aqueous solution was mixed with 90 parts by mass of cyanide pigment PB15:3 (manufactured by Dainichi Seika) and 171.9 parts by mass of water to obtain a mixture. Potassium hydroxide aqueous solution was added to the resulting mixture to adjust the pH to 8.7 after neutralization. Next, the neutralized mixture was subjected to a dispersion treatment for 3 hours using a bead mill (bead diameter: 0.1 mmφ, zirconia beads). This yielded a cyanide pigment dispersion (uncrosslinked dispersion) in which the cyanide pigment was dispersed by the pigment dispersant P1. Water was added to this cyanide pigment dispersion to prepare an uncrosslinked dispersion C1 (pigment concentration 15% by mass). Next, to 136 parts by mass of the uncrosslinked dispersion (C1), 3.77 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 41.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) were added as crosslinking agents, and the mixture was reacted at 70°C for 6 hours, after which it was cooled to 25°C. As a result, a cyanide pigment dispersion (crosslinked dispersion) was obtained in which the pigment dispersant P1 was crosslinked and the cyanide pigment was dispersed by the pigment dispersant P1a. Here, the pigment dispersant P1a is a polymer in which the uncrosslinked polymer, the pigment dispersant P1, has been crosslinked by the crosslinking agent. Next, deionized water was added to the cross-linked dispersion to achieve a pigment concentration of 15% by mass. The resulting liquid was ultrafiltered through an ultrafiltration apparatus (cross-flow type ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (pore size: 0.1 μm) at a flow rate of 600 mL per minute. At this time, the liquid temperature was adjusted to 25°C, and ultrafiltration was performed eight times, with each ultrafiltration cycle being 1x the volume of the charged liquid. Deionized water was added to the resulting liquid to achieve a pigment concentration of 15% by mass. This yielded a low-acid-value cyanide pigment dispersion. The acid value of the pigment dispersant P1a (low-acid-value cross-linked polymer) contained in the low-acid-value cyanide pigment dispersion was 75 mgKOH / g.

[0162] (Dispersion of moderately acidic cyanide pigment) A medium-acid value cyanide pigment dispersion was prepared in the same manner as the preparation of the low-acid value cyanide pigment solution described above, except that the amounts of 3.77 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 41.2 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), which were added to 136 parts by mass of the uncrosslinked dispersion (C1), were changed to 3.00 parts by mass of trimethylolpropane polyglycidyl ether and 32.8 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass). The acid value of the pigment dispersant P1b (specifically, a polymer in which pigment dispersant P1 is crosslinked by a crosslinking agent) contained in the medium-acid value cyanide pigment dispersion was 105 mgKOH / g.

[0163] (High acid value cyanide pigment dispersion) A high-acid-value cyanide pigment dispersion was prepared in the same manner as the preparation of the low-acid-value cyanide pigment solution described above, except that the amounts of 3.77 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 41.2 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), which were added to 136 parts by mass of the uncrosslinked dispersion (C1), were changed to 0.94 parts by mass of trimethylolpropane polyglycidyl ether and 10.3 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass). The acid value of the pigment dispersant P1b (specifically, a polymer in which pigment dispersant P1 is crosslinked by a crosslinking agent) contained in the high acid value cyanide pigment dispersion was 185 mgKOH / g.

[0164] (Preparation of cyan inks C1-C3) Each component of the composition listed below was mixed to prepare cyan inks C1 to C3. The cyanide pigment dispersion in the following composition is: In cyan ink C1, the above-mentioned medium acid value cyan pigment dispersion is used. In cyan ink C2, the low acid value cyan pigment dispersion described above is used. In the case of cyan ink C3, the high acid value cyan pigment dispersion described above was used.

[0165] -Composition of Cyan Ink C1~C3- • Cyan pigment dispersion (pigment is CI Pigment Blue 15:3) ...4.0% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount of ink will be 100% by mass.

[0166] <Preparation of non-permeable substrate> Three types of non-permeable substrates (hereinafter also simply referred to as "substrates") were prepared. • PET substrate… Polyethylene terephthalate substrate (product name "FE2001", manufactured by Futamura Chemical Co., Ltd., thickness 12 μm, width 100 mm, length 240 mm) • OPP substrate… Biaxially oriented polypropylene substrate (Futamura Co., Ltd. FOR-AQ (20μm)) • Nylon substrate… Unitika Corporation Emblem ON 15μm.

[0167] <Preparation of the image recording device> An image recording device was prepared that included a transport mechanism for transporting the substrate, and, in the order of the upstream side in the transport direction of the substrate (hereinafter also simply referred to as the "upstream side"), a wire bar coater for applying pretreatment liquid, and six inkjet heads (hereinafter also simply referred to as "heads") for applying ink. The six heads are arranged along the direction in which the substrate is transported. Hereafter, the heads will be referred to as the 1st head, 2nd head, 3rd head, 4th head, 5th head, and 6th head, starting from the upstream head.

[0168] Each head was a 1200 dpi / 20-inch wide piezo full-line head. Here, dpi stands for dots per inch. Each head is a line head in which nozzles are arranged perpendicular to the substrate transport direction (i.e., in the width direction of the substrate). For each of the above-mentioned heads, I used the Samba G3L (manufactured by FUJIFILM DIMATIX).

[0169] <Image recording (cyan monochrome)> The above substrate was surface-treated by applying corona discharge to a corona treatment machine (TEC-4AX, Corona Surface Modification Evaluation Device, manufactured by Kasuga Electric Co., Ltd.) under the conditions of a discharge gap of 1 mm, 100 W, and 4 m / min. The surface-treated substrate, the pretreatment solution, and the cyan ink (any of cyan inks C1 to C3; see Table 1 for details) were set in the image recording device described above. The cyan ink was set to be ejected from the second head. The cyan ink used was degassed through a degassing filter and temperature-controlled to 30°C. The substrate was moved at a constant speed of 50 m / min while the pretreatment solution was applied to the substrate using a wire bar coater. The amount of pretreatment solution applied is 1.5 g / m². 2 That's what I decided. Here, the mass of pretreatment solution applied is the value obtained by dividing the applied mass of pretreatment solution by the area of ​​the region to which the pretreatment solution was applied. At the point where the application of the pretreatment solution was completed, drying of the pretreatment solution using a dryer was started 2 seconds after the completion of the application to that point. The pretreatment solution was dried at 60°C for 3 seconds. As measured with a Karl Fischer moisture meter, the residual water content was 0.01 g / m². 2 The results were as follows:

[0170] Next, air was blown onto the surface of the substrate to which the pretreatment solution had been applied, using an ionizer (Keyence SJ-L005M) placed 10 cm away from the surface, under conditions of air pressure of 0.05 MPa and air flow rate of 96 L / min. The amount of static electricity was adjusted by adjusting the air pressure and air flow rate. Table 1 shows the electrostatic charge A (in kV) of the substrate after the above adjustments (specifically, the surface of the substrate to which the pretreatment solution was applied).

[0171] While the substrate, whose electrostatic charge level had been adjusted, was moved at a constant speed of 50 m / min, cyan ink (any of cyan inks C1 to C3; see Table 1 for details) was ejected from the second head onto the surface of the substrate that had been treated with the pretreatment solution, creating a solid image. At this time, the ink droplet size was 2.1 ng, the duty cycle was 100%, and the ejection frequency was 39.37 kHz.

[0172] Next, the cyan ink applied to the substrate was subjected to infrared (IR) drying using an infrared (IR) irradiation device (PLC-328, manufactured by Noritake Co., Ltd.) 2 seconds after the ink application was completed, under conditions that the surface temperature of the ink reached 75°C. Subsequently, a dryer was used to perform hot air drying with 80°C hot air for 20 seconds to obtain a solid cyan image. Based on the above, an image recording material comprising a substrate and a solid cyan image provided on the substrate was obtained.

[0173] <Image quality evaluation> The following image quality evaluations were performed on solid cyan images in image recordings. The results are shown in Table 1.

[0174] (droplet ejection accuracy) In the solid cyan image, streaks (specifically, dark and white streaks) along the transport direction were identified, and the image quality resulting from droplet accuracy in the direction perpendicular to the transport direction (i.e., the direction in which the nozzles are arranged) was evaluated according to the following evaluation criteria.

[0175] -Evaluation Criteria for Droplet Placement Accuracy- AA: No dark or white streaks were observed. A: The total number of dark and white streaks is between 1 and 4. B: The total number of dark and white streaks is 4 or more but less than 8. C: The total number of dark and white streaks is 8 or more but less than 15. D: The total number of dark and white streaks is 15 or more.

[0176] (Drip timing) In the solid cyan image, we identified droplet timing discrepancies, which are dot misalignments in the transport direction, and evaluated the image quality caused by droplet timing according to the following evaluation criteria.

[0177] -Evaluation Criteria for Droplet Timing- A: Droplet timing deviation is less than 1 dot. B: Droplet timing deviation is between 1 and 3 dots. C: Droplet timing deviation is between 3 and 5 dots. D: Droplet timing discrepancy of 5 dots or more.

[0178] [Table 1]

[0179] As shown in Table 1, in Examples 1 to 10, where ink was applied to a non-permeable substrate under the condition that the electrostatic polarity of the surface to which the ink was applied and the polarity of the ink's zeta potential were opposite, the resulting images showed suppression of reduced ink droplet accuracy and reduced image quality due to timing discrepancies in droplet application. In contrast, in Comparative Examples 1-3, where ink was applied to a non-permeable substrate under the condition that the electrostatic polarity of the surface to which the ink was applied was the same as the polarity of the zeta potential of the ink, the resulting images showed a decrease in ink droplet accuracy and / or a decrease in image quality due to a timing discrepancy in droplet application.

[0180] In Examples 1-10, when the difference [AB], which is the value obtained by subtracting the zeta potential B (unit mV) of the ink from the electrostatic charge A (unit kV) of the surface of the non-permeable substrate to which the ink is applied, was 30-110, the deterioration in image quality caused by the decrease in ink droplet accuracy was more suppressed compared to Example 4, when the difference [AB] was less than 30.

[0181] Of Examples 1 and 2, Example 2, where the above difference [AB] was 45 or more, showed a more suppressed reduction in image quality caused by a decrease in ink droplet accuracy. Of Examples 3 and 5, Example 3, where the above difference [AB] was 70 or less, showed that the degradation of image quality caused by the timing difference in ink droplet application was more suppressed.

[0182] [Examples 101-106] Examples 101 to 106 are examples of recording a white monochrome image. The details are explained below.

[0183] <Preparation of pretreatment solution> The following components were mixed to prepare a pretreatment solution.

[0184] -Composition of pretreatment solution- • Glutaric acid [coagulant] …6.1% by mass • Propylene glycol [solvent] …5.0% by mass • Orphine E1010 (manufactured by Nisshin Chemical Co., Ltd.) [Surfactant] …0.5% by mass • Superflex M500 (Daiichi Kogyo Seiyaku) [Aqueous dispersion of urethane resin particles] …7.0 mass% ·Ultra-pure water …The remaining amount that makes up 100 mass% of the entire pretreatment liquid

[0185] <Preparation of White Ink> (Synthesis of Pigment Dispersant (Block Polymer) for Low Acid-Value White Pigment Dispersion) Referring to Synthesis Example 8 of JP-A-2015-83688, block polymer 1 was synthesized as a pigment dispersant for a low acid-value white pigment dispersion. Details are shown below. Into a reaction apparatus of 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 initiation 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 (7.9 parts by mass), and 2-t-butyl-4,6-dimethylphenol (0.7 parts by mass; catalyst) were added and stirred while flowing nitrogen. Next, the temperature of the mixture in the reaction apparatus (reaction temperature) was raised to 70°C and polymerized for 3 hours to obtain a polymerization solution A containing an MMA / AA / CHMA copolymer. After 3 hours, a part of the above polymerization solution A was sampled and the solid content was measured. As a result, it was 42.0 mass%, and it was confirmed that most of the monomers had polymerized. Also, when the molecular weight of the MMA / AA / CHMA copolymer was measured by GPC, the weight average molecular weight (Mn) was 7,500. The acid value of this MMA / AA / CHMA copolymer was 101.0 mgKOH / g.

[0186] Next, a mixture of benzyl methacrylate (BzMA) (35.2 parts by mass; monomer) and V-65 (0.3 parts by mass; radical initiator) was added to the above polymerization solution A, and polymerization was carried out at 70 °C for 3 hours to obtain a polymerization solution B containing block polymer 1 as a pigment dispersant for a low acid value white pigment dispersion. Here, block polymer 1 is a block polymer containing an A block that is an MMA / AA / CHMA copolymer and a B block that is a BzMA homopolymer. When the solid content of the obtained polymerization solution B was measured, it was 43.2% by mass, and it was confirmed that most of the monomers had polymerized. Also, the Mw of block polymer 1 was 8,500, and the acid value was 89.3 mgKOH / g.

[0187] (Preparation of Low Acid Value White Pigment Dispersion) The above block polymer 1 (136.4 parts by mass), butyl carbitol (163.6 parts by mass), and C.I. Pigment White 6 (trade name "JR-405", titanium dioxide particles, manufactured by Tayca Corporation) (450 parts by mass) as a white pigment were blended and stirred with a disper. Next, the white pigment was sufficiently dispersed using a horizontal media disperser to obtain an oily pigment dispersion. The average particle diameter of the white pigment dispersed in the oily pigment dispersion was 290 nm. The viscosity of the oily pigment dispersion was 86.3 m3Pa·s. Next, while stirring the above oily pigment dispersion (700 parts by mass) using a disper, a mixed solution composed of potassium hydroxide (4.0 parts by mass) and water (341 parts by mass) was gradually added thereto for neutralization. Then, the white pigment was sufficiently dispersed using a horizontal media disperser to obtain a pigment dispersion. Next, ultrafiltration was performed on the obtained pigment dispersion using an ultrafiltration device (crossflow type ultrafilter (UF), manufactured by Sartorius) by flowing ion-exchanged water at a flow rate of 600 mL per minute for 1 minute. The liquid temperature was maintained at 25 °C, and ultrafiltration was performed 10 times with one time being one-fold the volume of the charged liquid. Ion-exchanged water was added to obtain a low acid value white pigment dispersion having a white pigment concentration of 45% by mass and a block polymer concentration of 3.7% by mass.

[0188] (Preparation of a medium-acid value white pigment dispersion) -Synthesis of pigment dispersant P1- A pigment dispersant P1 (uncrosslinked polymer) similar to the pigment dispersant P1 used in the preparation of each cyanide pigment dispersion described above was synthesized.

[0189] -Preparation of a medium-acid value white pigment solution- A polymer solution was prepared by dissolving pigment dispersant P1 (150 parts by mass) in water, resulting in a concentration of pigment dispersant P1 of 25% by mass. 96 parts by mass of the above polymer solution, 300 parts by mass of CI Pigment White 6 (product name "JR-405", titanium dioxide particles, manufactured by Teika Co., Ltd.), a white pigment, and 270 parts by mass of water were mixed to obtain a mixture. Potassium hydroxide aqueous solution was added to the obtained mixture to adjust the pH to 8.7 after neutralization. Next, the neutralized mixture was subjected to a dispersion treatment for 3 hours using a bead mill (bead diameter: 0.1 mmφ, zirconia beads). This yielded a white pigment dispersion (uncrosslinked dispersion) PD1 in which the white pigment was dispersed by the pigment dispersant P1. Next, the obtained white pigment dispersion (uncrosslinked dispersion) PD1 was subjected to ultrafiltration using an ultrafiltration apparatus (cross-flow ultrafilter (UF), manufactured by Sartorius) by flowing deionized water at a flow rate of 600 mL per minute. The liquid temperature was maintained at 25°C, and ultrafiltration was performed three times, with each pass representing 1x the volume of the liquid charged. Deionized water was added to the liquid after ultrafiltration to obtain a dispersion with a white pigment concentration of 45% by mass and a pigment dispersant P1 concentration of 3.6% by mass.

[0190] To 136 parts by mass of the ultrafiltration-resolved dispersion, 1.35 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 14.5 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) were added as crosslinking agents. The mixture was reacted at 70°C for 6 hours and then cooled to 25°C. This crosslinked the pigment dispersant P1 in the dispersion to form a crosslinked polymer dispersant, pigment dispersant P1a, and obtained a white pigment dispersion (crosslinked dispersion) in which the white pigment was dispersed by the crosslinked polymer dispersant L1, pigment dispersant P1a. To the obtained cross-linked dispersion, deionized water was added to achieve a pigment concentration of 15% by mass. The cross-linked dispersion with added deionized water was ultrafiltered through an ultrafiltration apparatus (cross-flow type ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (micropore size: 0.1 μm) at a flow rate of 600 mL per minute. At this time, the liquid temperature was adjusted to 25°C, and ultrafiltration was performed three times, with each ultrafiltration being one volume-fold increase of the initial liquid. Next, deionized water was added to achieve a white pigment concentration of 45% by mass. This yielded a medium-acid value white pigment dispersion. The acid value of pigment dispersant P1a contained in the medium-acid value white pigment dispersion was 144 mgKOH / g. The concentration of pigment dispersant P1a was 3.6% by mass. Pigment dispersant P1a is a crosslinked polymer formed by crosslinking pigment dispersant P1, which is an uncrosslinked polymer, with polyethylene glycol diglycidyl ether as a crosslinking agent.

[0191] (Preparation of a high-acid value white pigment dispersion) A high-acid-value white pigment dispersion was prepared in the same manner as the preparation of the medium-acid-value white pigment solution described above, except that the amounts of 1.35 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 14.5 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), which were added to 136 parts by mass of the ultrafiltration-resolved dispersion, were changed to 0.63 parts by mass of trimethylolpropane polyglycidyl ether and 7.25 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), respectively. The acid value of the pigment dispersant P1b (specifically, a polymer in which pigment dispersant P1 is crosslinked by a crosslinking agent) contained in the high acid value white pigment dispersion was 185 mgKOH / g.

[0192] (Preparation of white inks W1-W3) White inks W1 to W3 were prepared by mixing each component of the composition listed below. The white pigment dispersion in the following composition is: In white ink W1, the above-mentioned medium-acid value white pigment dispersion is used. In White Ink W2, the low acid value white pigment dispersion described above is used. In the case of White Ink W3, the aforementioned high-acid-value white pigment dispersion was used.

[0193] -Composition of White Ink W1~W3- • White pigment dispersion ... 14% by mass (as pigment content) • Propylene glycol (water-soluble organic solvent) …30% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) … 1% by mass Neocryl A-1105 (Acrylic polymer resin particle dispersion) (Manufactured by DSM Corporation) ... 5.0% by mass (as resin particle content) • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass · BYK3450 (silicone surfactant manufactured by BYK) … 1.0% by mass · PVP K15 (polyvinylpyrrolidone K15) … 0.15% by mass · ST-XS (colloidal silica dispersion) (manufactured by Nissan Chemical Industries, Ltd.) … 0.05% by mass as the content of colloidal silica particles · Water … The balance to make up 100% by mass in total

[0194] <Preparation of Substrate and Image Recording Apparatus> The substrate used in Example 1 (i.e., non-permeable substrate) and the same substrate and image recording apparatus as those in Example 1 were prepared respectively.

[0195] <Image Recording (White Monochrome)> Instead of the cyan ink set to be ejected from the second head, white ink (any one of White Inks W1 to W3. For details, refer to Table 2) set to be ejected from the fifth head was used, and the same operations as those in the image recording in Example 1 were performed except that the ink droplet amount was changed to 4.0 ng, and an image recording product including a substrate and a white solid image provided on the substrate was obtained.

[0196] <Evaluation of Image Quality> Regarding the white solid image in the image recording product, the same evaluation as that of the cyan solid image in Example 1 was performed for the image quality. The results are shown in Table 2.

[0197]

Table 2

[0198] As shown in Table 2, in Examples 101 to 106, where ink was applied to a non-permeable substrate under conditions where the electrostatic polarity of the surface to which the ink was applied and the polarity of the ink's zeta potential were opposite, the resulting images showed suppression of both reduced ink droplet accuracy and reduced image quality due to timing discrepancies, similar to Examples 1 to 10.

[0199] [Examples 201-209] Examples 201-209 describe the recording of multilayer images using an ink set comprising a pretreatment solution, a colored ink (specifically, at least one of black ink, cyan ink, magenta ink, and yellow ink), and white ink. Details are described below.

[0200] <Preparation of pretreatment solution> A pretreatment solution similar to the one prepared in Example 101 was prepared.

[0201] <Preparing the cyan ink> The aforementioned cyan inks C1 and C2 were prepared.

[0202] <Preparing the white ink> I prepared the aforementioned white ink W1.

[0203] <Preparing the black ink> (Synthesis of pigment dispersant P1) A pigment dispersant P1 (uncrosslinked polymer) similar to the pigment dispersant P1 used in the preparation of each cyanide pigment dispersion described above was synthesized.

[0204] (Preparation of black pigment dispersion) 150 parts by mass of pigment dispersant P1 was dissolved in water to prepare a polymer aqueous solution with a concentration of pigment dispersant P1 of approximately 25% by mass. 180 parts by mass of this 25% by mass polymer aqueous solution was mixed with 110.0 parts by mass of carbon black pigment FW182 (manufactured by Orion) and 240.0 parts by mass of water to obtain a mixture. Potassium hydroxide aqueous solution was added to the resulting mixture to adjust the pH to 8.7 after neutralization. Next, the neutralized mixture was subjected to a dispersion treatment for 3 hours using a bead mill (bead diameter: 0.1 mmφ, zirconia beads). This yielded a black pigment dispersion (uncrosslinked dispersion) in which the black pigment was dispersed by the pigment dispersant P1. Water was added to the black pigment dispersion to prepare an uncrosslinked dispersion K1 (pigment concentration 15% by mass). Next, to 136 parts by mass of the uncrosslinked dispersion (K1), 2.40 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 26.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) were added as crosslinking agents, and the mixture was reacted at 70°C for 6 hours, after which it was cooled to 25°C. As a result, a black pigment dispersion (crosslinked dispersion) was obtained in which the pigment dispersant P1 was crosslinked and the black pigment was dispersed by the pigment dispersant P1a. Here, the pigment dispersant P1a is a polymer in which the uncrosslinked polymer, the pigment dispersant P1, has been crosslinked by the crosslinking agent. Next, deionized water was added to the cross-linked dispersion to achieve a pigment concentration of 15% by mass. The resulting liquid was ultrafiltered through an ultrafiltration apparatus (cross-flow type ultrafilter (UF), manufactured by Sartorius) equipped with a polyethersulfone (PESU) membrane (pore size: 0.1 μm) at a flow rate of 600 mL per minute. At this time, the liquid temperature was adjusted to 25°C, and ultrafiltration was performed eight times, with each ultrafiltration cycle being 1x the volume of the initially charged liquid. Deionized water was then added to the resulting liquid to achieve a pigment concentration of 15% by mass. This yielded a black pigment dispersion. The acid value of the pigment dispersant P1a (cross-linked polymer) contained in the black pigment dispersion was 105 mgKOH / g.

[0205] (Preparation of Black Ink K1) Black ink K1 was prepared by mixing the components of the following composition.

[0206] -Composition of Black Ink K1- • The above black pigment dispersion ...5.0% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic polymer resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount totals 100% by mass.

[0207] <Preparing the magenta ink> (Preparation of PR-122 dispersion) The operation involves "mixing 180 parts by mass of a 25% by mass polymer aqueous solution, 110.0 parts by mass of FW182 (manufactured by Orion), which is a carbon black pigment, and 240.0 parts by mass of water." "180 parts by mass of a 25% by mass polymer aqueous solution and PR-122 (pigment) which is a magenta pigment The procedure was changed to "mixing 90 parts by mass of Menthol Red 122 (FUJI Fast Red (registered trademark), manufactured by Fuji Pigment Co., Ltd.) with 171.9 parts by mass of water," and, The procedure involves adding 2.40 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 26.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) as crosslinking agents. The procedure was changed to "add 3.00 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) as a crosslinking agent, and 32.8 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass)." The PR-122 dispersion was prepared in the same manner as the black pigment dispersion described above, except for the following: The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the PR-122 dispersion was 105 mgKOH / g.

[0208] (Preparation of PR-254 dispersion A) PR-254 dispersion A was obtained in the same manner as the preparation of PR-122 dispersion, except that PR-122 was replaced with the same mass portion of PR-254 (Pigment Red 254). The acid value of the pigment dispersant P1a (crosslinked polymer) contained in PR-254 dispersion A was 105 mg KOH / g.

[0209] (Preparation of PR-150 dispersion) A PR-150 dispersion was obtained in the same manner as the PR-122 dispersion, except that PR-122 was replaced with the same mass portion of PR-150 (Pigment Red 150). The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the PR-150 dispersion was 105 mgKOH / g.

[0210] (Preparation of PR-254 dispersion B) PR-254 dispersion B was prepared in the same manner as the preparation of PR-254 dispersion A described above, except that the amounts of 3.00 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 32.8 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), which were added to 136 parts by mass of the uncrosslinked dispersion, were changed to 0.94 parts by mass of trimethylolpropane polyglycidyl ether and 10.3 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass), respectively. The acid value of the pigment dispersant P1b (specifically, a polymer in which the pigment dispersant P1 is crosslinked by a crosslinking agent) contained in PR-254 dispersion B was 185 mgKOH / g.

[0211] (Preparation of magenta ink M1) Magenta ink M1 was prepared by mixing the components of the following composition.

[0212] -Composition of Magenta Ink M1- • The above PR-122 dispersion ...4.5% by mass as pigment content • PR-254 dispersion A ...1.5% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic polymer resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount totals 100% by mass.

[0213] (Preparation of magenta ink M2) Magenta ink M2 was prepared by mixing the components of the following composition.

[0214] -Composition of Magenta Ink M2- • The above PR-122 dispersion ...4.5% by mass as pigment content • PR-254 dispersion B ...1.5% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic polymer resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount totals 100% by mass.

[0215] (Preparation of Magenta Ink M3) Magenta ink M3 was prepared by mixing the components of the following composition.

[0216] -Composition of Magenta Ink M3- • The above PR-122 dispersion ...4.5% by mass as pigment content • The above PR-150 dispersion ...1.5% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic polymer resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount totals 100% by mass.

[0217] <Preparing the yellow ink> (Preparation of yellow pigment dispersion) The operation involves "mixing 180 parts by mass of a 25% by mass polymer aqueous solution, 110.0 parts by mass of FW182 (manufactured by Orion), which is a carbon black pigment, and 240.0 parts by mass of water." The procedure was changed to "mixing 180 parts by mass of a 25% by mass polymer aqueous solution, 75 parts by mass of the yellow pigment PY-74 (Pigment Yellow 74) (FUJI Fast Red (registered trademark), manufactured by Fuji Pigment Co., Ltd.), and 140 parts by mass of water," and, The procedure involves adding 2.40 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) and 26.2 parts by mass of an aqueous boric acid solution (boric acid concentration: 4% by mass) as crosslinking agents. The procedure was changed to "add 3.60 parts by mass of trimethylolpropane polyglycidyl ether (product name "Denacol EX-321", manufactured by Nagase ChemteX Corporation) as a crosslinking agent, and 39.4 parts by mass of boric acid aqueous solution (boric acid concentration: 4% by mass)." A yellow pigment dispersion was prepared in the same manner as the black pigment dispersion described above, except for the following: The acid value of the pigment dispersant P1a (crosslinked polymer) contained in the yellow pigment dispersion was 105 mgKOH / g.

[0218] (Preparation of yellow ink Y1) Yellow ink Y1 was prepared by mixing the components of the following composition.

[0219] -Composition of Yellow Ink Y1- • The above yellow pigment dispersion ...4.0% by mass as pigment content • The above PR-150 dispersion ...1.5% by mass as pigment content • Propylene glycol (water-soluble organic solvent) …30.0% by mass • Propylene glycol monomethyl ether (water-soluble organic solvent) …1.0% by mass Neocryl A-1105 (Acrylic resin particle dispersion) (Manufactured by DSM Corporation) ...5.0% by mass as resin particle content • Orphine E1010 (an acetylene glycol-based surfactant manufactured by Nisshin Chemical Industry Co., Ltd.) …1.0% by mass • BYK3450 (a silicone-based surfactant manufactured by BYK) …1.0% by mass • PVPK15 (Polyvinylpyrrolidone K15) …0.15% by mass • ST-XS (Colloidal Silica Dispersion) (Manufactured by Nissan Chemical Corporation) ...Colloidal silica particle content: 0.05% by mass ·water ...The remaining amount totals 100% by mass.

[0220] <Preparation of substrate and image recording device> A substrate (i.e., a non-permeable substrate) and image recording device similar to those used in Example 1 were prepared.

[0221] <Image recording (multilayer image)> Image recording (multilayer image) was performed in the same manner as in Example 1 (cyan monochromatic image), except for the following points.

[0222] -Differences from the image recording (cyan monochromatic) in Example 1- Each ink was set up so that the respective inks shown in Table 3 were ejected from the first through sixth print heads. A "-" in the Ink No. column of Table 3 indicates that the corresponding ink was not used. The operation involves applying cyan ink in a solid image pattern onto a surface of a substrate to which a pretreatment solution has been applied after the electrostatic charge has been adjusted. The process involves sequentially applying each ink shown in Table 3 to the surface of the substrate to which the pretreatment solution has been applied after the electrostatic charge has been adjusted, creating a solid image. I changed it to this. The ink application amounts were 4.0 ng for white ink and 2.1 ng for the other inks. The duty cycles for each ink application are shown in Table 3. Each ink was applied so that it overlapped on the same area.

[0223] Next, the outermost layer of ink applied to the substrate (i.e., the last applied ink) was subjected to infrared (IR) drying using an infrared (IR) irradiation device (PLC-328, manufactured by Noritake Co., Ltd.) 2 seconds after the completion of the application of the last applied ink, under conditions that the surface temperature of the ink reached 75°C. Subsequently, a dryer was used to perform hot air drying with 80°C hot air for 20 seconds to obtain a multi-layer solid image. As described above, an image recording material comprising a substrate and a multilayer solid image provided on the substrate was obtained. In all embodiments, the outermost layer of the multilayer solid image is a white image derived from white ink W1.

[0224] <Image quality evaluation> The above-mentioned image recording material was placed on the black area of ​​an opacity test paper (JIS compliant) manufactured by TP Giken Co., Ltd., with the image recording surface of the image recording material (i.e., the surface of the substrate) in contact with the black area. In this state, the multilayer image of the image recording was visually observed from the outermost white layer, and streaks (specifically, dark streaks and white streaks) were confirmed. Based on the results of the verification, the image quality was evaluated according to the following evaluation criteria. The streaks in this multilayer image are defects resulting from reduced droplet accuracy and / or timing discrepancies in droplet placement.

[0225] -Criteria for evaluating image quality- AA: The total number of dark and white streaks is between 0 and 5. A: The total number of dark and white streaks is between 5 and 10. B: The total number of dark and white streaks is 10 or more but less than 20. C: The total number of dark and white streaks is 20 or more but less than 30. D: The total number of dark and white streaks is 30 or more. The results are shown in Table 3.

[0226] [Table 3]

[0227] As shown in Table 3, in Examples 201 to 209, which used an ink set containing at least one colored ink (i.e., at least one of black ink K1, cyan inks C1 to C2, magenta inks M1 to M3, and yellow ink Y1) and at least one white ink (i.e., white ink W1), and applied these inks to a substrate while satisfying the following conditions a1, a2, and a3, a decrease in droplet accuracy and / or a decrease in image quality (i.e., streaks) caused by a deviation in droplet timing were suppressed. Condition a1: The polarity of the zeta potential of all inks, including at least one colored ink and at least one white ink, is the same. Condition a2: The electrostatic polarity of the same surface of the non-permeable substrate is opposite to the polarity of the zeta potential of the entire ink. Condition a3: When the electrostatic charge on the same surface of a non-permeable substrate is AkV, and the zeta potential of at least one colored ink and at least one white ink is BmV, the difference [AB] obtained by subtracting B from A for all inks satisfies the condition that it is between 30 and 110.

[0228] The results from Examples 201-209 show that when the difference [AB] for the last ink applied is the largest (Examples 201, 202, 205, 206, 208, and 209), the degradation of image quality is more suppressed.

[0229] [Examples 1A to 10A] In Examples 1 to 10, the same procedure was followed as in Examples 1 to 10, except that the pretreatment solution was not applied. As a result, the same effects as in Examples 1 to 10 were obtained.

[0230] [Examples 1B-10B, 101B-106B, 201B-209B] In Examples 1-10, 101-106, and 201-209, the same procedure as in Examples 1-10, 101-106, and 201-209 was followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "0.6% by mass of glutaric acid, 5.0% by mass of adipic acid, and 0.5% by mass of succinic acid". As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0231] [Examples 1C-10C, 101C-106C, 201C-209C] In each of Examples 1-10, 101-106, and 201-209, the same procedure as in Examples 1-10, 101-106, and 201-209 was followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "0.6% by mass of glutaric acid, 5.0% by mass of adipic acid, and 0.5% by mass of succinic acid," and the acrylic resin particles in the ink were replaced with the same amount of styrene-acrylic resin particles (using "Neocryl A-1109" manufactured by DSM as the resin particle dispersion). As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0232] [Examples 1D-10D, 101D-106D, 201D-209D] In Examples 1-10, 101-106, and 201-209, the same procedure as in Examples 1-10, 101-106, and 201-209 was followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "5.0% by mass of calcium formate and 3.0% by mass of calcium lactate". As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0233] [Examples 1E-10E, 101E-106E, 201E-209E] In Examples 1-10, 101-106, and 201-209, the same procedures as in Examples 1-10, 101-106, and 201-209 were followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "5.0% by mass of calcium formate and 3.0% by mass of calcium lactate," and the acrylic resin in the ink was replaced with the same amount of styrene acrylic resin (Neocryl A-1109, manufactured by DSM). As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0234] [Examples 1F-10F, 101F-106F, 201F-209F] In each of Examples 1-10, 101-106, and 201-209, the same procedure as in Examples 1-10, 101-106, and 201-209 was followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "5.0% by mass of calcium formate and 3.0% by mass of calcium lactate," and the acrylic resin particles in the ink were replaced with the same amount of urethane resin particles (using "Superflex 460" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. as the resin particle dispersion). As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0235] [Examples 1G-10G, 101G-106G, 201G-209G] In each of Examples 1-10, 101-106, and 201-209, the same procedure as in Examples 1-10, 101-106, and 201-209 was followed, except that "6.1% by mass of glutaric acid" in the composition of the pretreatment solution was replaced with "0.6% by mass of glutaric acid, 5.0% by mass of adipic acid, and 0.5% by mass of succinic acid," and the acrylic resin particles in the ink were replaced with the same amount of urethane resin particles (using "Superflex 460" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. as the resin particle dispersion). As a result, the same effects as in Examples 1-10, 101-106, and 201-209 were obtained.

[0236] The disclosure of Japanese Patent Application No. 2021-191601, filed on 25 November 2021, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. The process includes an ink application step in which a water-containing ink is applied to a non-permeable substrate by an inkjet method. The ink application step involves applying the ink onto the non-permeable substrate under the condition that the electrostatic polarity of the surface of the non-permeable substrate to which the ink is applied and the polarity of the zeta potential of the ink are opposite. Inkjet recording method.

2. The ink application step involves applying the ink onto the non-permeable substrate under the condition that the difference [A-B], which is the value obtained by subtracting B from A when the electrostatic charge of the surface of the non-permeable substrate to which the ink is applied is AkV and the zeta potential of the ink is BmV, is between 30 and 110. The inkjet recording method according to claim 1.

3. The ink application step involves applying the ink onto the non-permeable substrate under the condition that the difference [A-B] is 45 to 70. The inkjet recording method according to claim 2.

4. The zeta potential of the aforementioned ink is -80 mV to -30 mV. The inkjet recording method according to claim 1 or claim 2.

5. The electrostatic charge on the surface of the non-permeable substrate to which the ink is applied is 10 kV to 30 kV. The inkjet recording method according to claim 1 or claim 2.

6. The non-permeable substrate is a resin substrate. The inkjet recording method according to claim 1 or claim 2.

7. The process further includes a pretreatment liquid application step in which a pretreatment liquid containing water and a coagulant is applied to the non-permeable substrate prior to the ink application step, The ink application step involves applying the ink onto the area on the non-permeable substrate to which the pretreatment liquid has been applied. The inkjet recording method according to claim 1 or claim 2.

8. An ink set is used that includes at least one colored ink containing water and a coloring pigment, and at least one white ink containing water and a white pigment. The ink application step involves applying at least one colored ink and at least one white ink to the same surface of the non-permeable substrate by an inkjet method, satisfying the following conditions a1, a2, and a3. The inkjet recording method according to claim 1 or claim 2. Condition a1: The polarity of the zeta potential of all inks, including at least one colored ink and at least one white ink, is the same. Condition a2: The electrostatic polarity of the same surface of the non-permeable substrate is opposite to the polarity of the zeta potential of the entire ink. Condition a3: When the electrostatic charge on the same surface of the non-permeable substrate is AkV, and the zeta potential of each of the at least one colored ink and the at least one white ink is BmV, the difference [A-B] obtained by subtracting B from A for all inks satisfies the condition that it is between 30 and 110.

9. Of the differences [A-B] for each of the at least one colored ink and the at least one white ink, the difference [A-B] for the ink that is applied last is the largest. The inkjet recording method according to claim 8.

10. In the above-mentioned at least one colored ink and at least one white ink, when n is an integer of 2 or more, the difference [A-B] for the nth ink in the application order is equal to or greater than the difference [A-B] for the (n-1)th ink in the application order, and the difference [A-B] for the last ink applied is greater than the difference [A-B] for the first ink applied. The inkjet recording method according to claim 8.

11. Used in the inkjet recording method described in Claim 7, The system includes a transport mechanism for transporting the non-permeable substrate, The following components are arranged in this order, starting from the upstream side in the transport direction of the non-permeable substrate: a wire bar coater for applying the pretreatment liquid, and an inkjet head for applying the ink. Inkjet image recording device.

Images