Aqueous inkjet ink set for impermeable substrates, image recording method, and recorded image product

Abstract

Provided is an aqueous inkjet ink set for impermeable substrates that satisfies expressions (1) to (5), wherein: Ak, Ac, Am, and Ay are the respective amounts, in μL, of a pretreatment liquid that need to be added to 20 mL of each of black ink, cyan ink, magenta ink, and yellow ink to make the viscosities at 25°C of the inks after addition of the pretreatment liquid greater than 15 mPa·s; μk, μc, μm, and μy are the respective highest viscosities, in mPa·s, at 25°C reached by the inks after addition of the pretreatment liquid; Amin and Amax are, respectively, the lowest value and the highest value among Ak, Ac, Am, and Ay; and μmin and μmax are, respectively, the lowest value and the highest value among μk, μc, μm, and μy.

Description

Aqueous Inkjet Ink Set for Non-Permeable Substrate, Image Recording Method, and Image Record

[0001] The present disclosure relates to an ink set comprising a pretreatment liquid and an inkjet ink, an image recording method, and an image record.

[0002] Digital printing, unlike conventional plate printing, does not require a plate-making film or plate-making, and thus cost reduction and speed increase can be achieved.

[0003] In an inkjet printing method, which is a type of digital printing, droplets of inkjet ink are directly ejected onto a recording medium from very fine nozzles and adhered thereto to obtain characters and images (hereinafter collectively also referred to as "printed matter"). The inkjet printing method has advantages such as low noise of the apparatus used, good operability, and easy colorization, and is widely used as an output device in offices and homes. In addition, due to the improvement of inkjet technology, it is also used in industrial applications.

[0004] Conventionally, inks used in the inkjet printing method for industrial applications were solvent inks or ultraviolet (UV) curable inks. However, in recent years, due to considerations such as safety, health, and environment, the demand for aqueous inks has been increasing.

[0005] Aqueous inks used in the inkjet printing method (hereinafter also simply referred to as "for inkjet") have conventionally been for plain paper or special paper (for example, photographic glossy paper). That is, while water is the main component, water-soluble organic solvents such as glycerin are added to control the wettability and drying property with respect to the recording medium. When a pattern of characters or images is printed on the above recording medium using an inkjet aqueous ink (hereinafter also referred to as "aqueous inkjet ink", "aqueous ink", or simply "ink") composed of these liquid components, the liquid components penetrate into the recording medium, dry, and fix.

[0006] Recording media for inkjet printing include not only highly permeable materials such as plain paper, specialty paper, high-quality paper, and recycled paper, but also low-permeability materials such as coated paper, art paper, and lightly coated paper, as well as non-permeable materials such as film substrates. Until now, usable image quality has been achieved using water-based inkjet inks on highly permeable and low-permeability recording media. In contrast, when printing on non-permeable recording media such as film substrates, the ink droplets do not penetrate the recording media at all after landing, so drying by penetration hardly occurs, and as a result the droplets merge together, resulting in color bleeding and color unevenness (a state of uneven color in areas that should be the same color), and the image quality is impaired.

[0007] As a countermeasure to the above-mentioned problems, a pretreatment process involving the application of a pretreatment solution to impermeable recording media is known. Specifically, this process involves intentionally inducing aggregation of solid components (pigments and / or resins) present in the aqueous inkjet ink, or increasing the viscosity of the aqueous inkjet ink, thereby preventing color bleeding and unevenness between droplets of aqueous inkjet ink, and improving image quality.

[0008] However, even when a pretreatment solution is applied to the substrate as described above, it is difficult to satisfy image quality requirements for all inks when recording an image using multiple inks of different hues. Therefore, various studies are being conducted to further improve image quality in ink sets of pretreatment solutions and inkjet inks used when recording images on non-permeable substrates.

[0009] For example, Japanese Patent Publication No. 2018-35295 describes an inkjet ink set comprising a first ink containing an infrared absorbent and water, and a second ink containing an infrared absorbent and water, wherein the value of coefficient a in the relationship between the viscosity and evaporation rate of the ink differs from that of the first ink by 1.5 times or more.

[0010] When recording images by layering two or more inks with different hues, differences in the aggregation rates between the inks could sometimes cause cracking in the recorded image for some colors, or result in a decrease in image clarity or color mixing between colors.

[0011] This disclosure has been made in view of these circumstances, and one embodiment of this disclosure aims to solve the problem of providing an aqueous inkjet ink set for a non-permeable substrate that suppresses cracking of recorded images, has excellent image clarity, and suppresses color mixing between colors. Another embodiment of this disclosure aims to solve the problem of providing an image recording method and an image recording material using the above-mentioned aqueous inkjet ink set for a non-permeable substrate.

[0012] This disclosure includes the following embodiments: <1> A pretreatment solution containing a flocculant; a black ink containing water, black pigment, pigment dispersion resin, and binder resin; a cyan ink containing water, cyan pigment, pigment dispersion resin, and binder resin; a magenta ink containing water, magenta pigment, pigment dispersion resin, and binder resin; and a yellow ink containing water, yellow pigment, pigment dispersion resin, and binder resin, wherein the viscosity of the black ink, cyan ink, magenta ink, and yellow ink at 25°C is 3.5 mPa·s to 8.0 mPa·s, and the amount of pretreatment solution required to add the pretreatment solution to 20 mL each of the black ink, cyan ink, magenta ink, and yellow ink so that the viscosity of each ink at 25°C after addition exceeds 15 mPa·s is Ak, Ac, Am, and Ay, respectively, in units of μL. A water-based inkjet ink set for non-permeable substrates that satisfies the following equations (1) to (5), where the maximum viscosity of each ink after addition at 25°C is given in units of mPa·s as μk, μc, μm, and μy, with Amin being the minimum value and Amax being the maximum value among Ak, Ac, Am, and Ay, and μmin being the minimum value and μmax being the maximum value among μk, μc, μm, and μy: Amin≧500 …(1) Amax≦3000 …(2) Amax / Amin≦2 …(3) μmin≧200 …(4) μmax≦2000 …(5) <2> The water-based inkjet ink set for non-permeable substrates according to <1>, wherein the flocculant comprises at least one selected from the group consisting of polyvalent metal compounds, organic acids, and water-soluble cationic polymers. <3> An aqueous inkjet ink set for non-permeable substrates as described in <1> or <2>, wherein the mass ratio of the coagulant contained in the pretreatment solution is F, and the mass ratios of the binder resin contained in the black ink, cyan ink, magenta ink, and yellow ink are Pk, Pc, Pm, and Py, respectively, satisfy the following formulas (6) to (9).0.5 ≤ Pk / F ≤ 2.0 …(6) 0.5 ≤ Pc / F ≤ 2.0 …(7) 0.5 ≤ Pm / F ≤ 2.0 …(8) 0.5 ≤ Py / F ≤ 2.0 …(9) <4> An aqueous inkjet ink set for a non-permeable substrate according to any one of <1> to <3>, wherein the binder resin contains resin particles, and the resin particles are particles containing a resin, which is at least one selected from the group consisting of acrylic resin, polyester resin, and urethane resin. <5> An aqueous inkjet ink set for a non-permeable substrate according to any one of <1> to <4>, wherein the pretreatment liquid further contains resin particles, and the resin particles are at least one selected from the group consisting of particles containing acrylic resin, particles containing polyester resin, particles containing urethane resin, and composite particles containing acrylic resin and polyester resin. <6> An image recording method comprising: using the aqueous inkjet ink set for non-permeable substrates described in any one of <1> to <5>, applying a pretreatment solution to a non-permeable substrate to form a pretreatment layer; and applying black ink, cyan ink, magenta ink, and yellow ink to at least a portion of the pretreatment layer using an inkjet recording method to record an image. <7> An image recording material comprising: an impermeable substrate, a pretreatment layer disposed on the non-permeable substrate and containing non-volatile components of the pretreatment solution, and an ink layer disposed on at least a portion of the pretreatment layer and containing non-volatile components of black ink, cyan ink, magenta ink, and yellow ink, comprising the aqueous inkjet ink set for non-permeable substrates described in any one of <1> to <5>.

[0013] According to one embodiment of the present disclosure, an aqueous inkjet ink set for a non-permeable substrate is provided that suppresses cracking of recorded images, provides excellent image clarity, and suppresses color mixing between colors. According to another embodiment of the present disclosure, an image recording method and an image recording material using the above-mentioned aqueous inkjet ink set for a non-permeable substrate are provided.

[0014] This diagram conceptually shows the character images used to evaluate image quality in the embodiment.

[0015] The aqueous inkjet ink set for non-penetrating substrates, the image recording method, and the image recording material of this disclosure will be described in detail below.

[0016] In this specification, a numerical range indicated using "~" means a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in 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.

[0017] 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" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0018] In this specification, "image" refers to the entire film formed by applying the pretreatment solution and ink in that order, and "image recording" refers to the formation of an image (i.e., a film). Furthermore, the concept of "image" in this specification also includes solid images.

[0019] In this specification, "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate. Similarly, "(meth)acrylic" is a concept that encompasses both acrylic and methacrylic.

[0020] The aqueous inkjet ink set for non-permeable substrates of this disclosure (hereinafter also simply referred to as "ink set") comprises a pretreatment liquid containing a flocculant, a black ink containing water, black pigment, pigment dispersion resin, and binder resin, a cyan ink containing water, cyan pigment, pigment dispersion resin, and binder resin, a magenta ink containing water, magenta pigment, pigment dispersion resin, and binder resin, and a yellow ink containing water, yellow pigment, pigment dispersion resin, and binder resin, wherein the viscosity of the black ink, cyan ink, magenta ink, and yellow ink at 25°C is 3.5 mPa·s to 8.0 mPa·s. When a pretreatment solution is added to 20 mL each of black ink, cyan ink, magenta ink, and yellow ink, and the amount of pretreatment solution required for the viscosity of each ink at 25°C to exceed 15 mPa·s after addition is Ak, Ac, Am, and Ay, respectively, in units of μL, and the maximum viscosity of each ink at 25°C after addition is μk, μc, μm, and μy, respectively, in units of mPa·s, and the minimum value among Ak, Ac, Am, and Ay is Amin and the maximum value is Amax, and the minimum value among μk, μc, μm, and μy is μmin and the maximum value is μmax, then the following equations (1) to (5) are satisfied. Amin ≥ 500 …(1) Amax ≤ 3000 …(2) Amax / Amin ≤ 2 …(3) μmin ≥ 200 …(4) μmax ≤ 2000 …(5)

[0021] According to the ink set disclosed herein, cracking of recorded images is suppressed, image clarity is excellent, and color mixing between colors is suppressed. The reasons for these effects are presumed to be as follows.

[0022] The pretreatment solution contains a coagulant. When ink is applied to a substrate treated with the pretreatment solution, the components of the ink (e.g., pigment dispersant, binder resin, etc.) coagulate due to the coagulant. Cracks may appear in the recorded image, which is thought to be due to uneven coagulation. This uneven coagulation often occurs when the ink coagulates too quickly. On the other hand, if the coagulation is too slow, the ink will not fix properly, resulting in reduced image clarity and color mixing.

[0023] When recording images by layering two or more inks with different hues, if there is too much difference in the viscosity (coagulation rate) of each ink using the pretreatment solution, cracking may occur only in inks that tend to coagulate with the same pretreatment solution, or conversely, the image clarity may deteriorate or inter-color mixing (bleeding) may occur only in inks that do not coagulate easily, making it impossible to obtain excellent image quality with all inks simultaneously.

[0024] The inventors focused on the viscosity increase rate (aggregation rate) of each ink in relation to the pretreatment solution for two or more inks with different hues. Specifically, when a pretreatment solution is added to 20 mL each of black, cyan, magenta, and yellow ink, the amount of pretreatment solution required for the viscosity of each ink at 25°C after addition to exceed 15 mPa·s is Ak, Ac, Am, and Ay, respectively, in units of μL. The maximum viscosity achieved by each ink at 25°C after addition is μk, μc, μm, and μy, respectively, in units of mPa·s. Among Ak, Ac, Am, and Ay, the minimum value is Amin and the maximum value is Amax. Among μk, μc, μm, and μy, the minimum value is μmin and the maximum value is μmax. By controlling the minimum amount of pretreatment solution required for thickening to "Amin ≥ 500" and the maximum maximum viscosity to "μmax ≤ 2000", it was found that image cracking due to excessive ink aggregation can be suppressed. Furthermore, we found that by controlling the maximum amount of pre-treatment solution required for thickening to "Amax ≤ 3000" and the minimum value of the maximum achievable viscosity to "μmin ≥ 200", it is possible to suppress the deterioration of image sharpness and inter-color mixing (bleeding) due to insufficient ink aggregation. Moreover, by setting "Amax / Amin ≤ 2" and reducing the difference in aggregation speed between each ink, we found that excellent image quality can be obtained simultaneously without image cracking, loss of image sharpness, or inter-color mixing occurring with all inks.

[0025] The amounts of pretreatment solution Ak, Ac, Am, and Ay required for each ink to have a viscosity of over 15 mPa·s at 25°C after addition, and the maximum achievable viscosities μk, μc, μm, and μy of each ink at 25°C after addition, are calculated as follows: First, 20 mL each of black ink, cyan ink, magenta ink, and yellow ink are placed in separate containers, and the initial viscosity of each ink at 25°C is measured using an E-type viscometer. After measuring the initial viscosity, the E-type viscometer is removed from the ink, and 200 μL of pretreatment solution is added dropwise using a micropipette. The viscosity of the ink is measured again using the E-type viscometer, and after measurement, the E-type viscometer is removed from the ink. This process is repeated, and the amount of pretreatment solution added when the viscosity exceeds 15 mPa·s is defined as Ak, Ac, Am, and Ay, and the maximum achievable viscosities of the ink are defined as μk, μc, μm, and μy. After the ink viscosity reaches its highest point, the viscosity decreases as aggregates of pigment or resin in the ink settle.

[0026] Ak, Ac, Am, and Ay are preferably 500 to 3000, more preferably 550 to 2500, and particularly preferably 600 to 2000. Amin is preferably 500 to 2000, more preferably 550 to 1700, and particularly preferably 600 to 1400. Amax is preferably 600 to 3000, more preferably 650 to 2500, and particularly preferably 700 to 2000.

[0027] μk, μc, μm, and μy are preferably 200 to 2000, more preferably 200 to 1800, and particularly preferably 200 to 1600. μmin is preferably 200 to 1500, more preferably 200 to 1250, and particularly preferably 200 to 1000. μmax is preferably 300 to 2000, more preferably 400 to 1800, and particularly preferably 400 to 1600.

[0028] Amax / Amin is preferably 1.0 to 2.0, more preferably 1.0 to 1.8, and particularly preferably 1.0 to 1.5.

[0029] μmax / μmin is preferably 1.0 to 4.0, more preferably 1.0 to 3.0, and particularly preferably 1.0 to 2.0.

[0030] <Ink> The ink set provided in this disclosure includes black ink, cyan ink, magenta ink, and yellow ink.

[0031] (Pigments) The inks included in the ink set of this disclosure include pigments. The pigments included in the inks may be one type or two or more types.

[0032] The pigment may be either commercially available organic or inorganic pigments. Examples of pigments include those described in "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and Japanese Patent Publication No. 2002-12607, 2002-188025, 2003-26978, and 2003-342503.

[0033] Furthermore, the pigment may be a water-insoluble pigment that can be dispersed in water by a dispersant, or it may be a self-dispersing pigment. A self-dispersing pigment is a pigment that can be dispersed in water without the use of a dispersant. A self-dispersing pigment is a compound in which at least one hydrophilic group selected from the group consisting of carbonyl groups, hydroxyl groups, carboxyl groups, sulfo groups, phosphate groups, and salts thereof is chemically bonded to the surface of the pigment, either directly or via other groups.

[0034] Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Examples of azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments. Examples of polycyclic pigments include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments. Examples of dye chelates include basic dye-type chelates and acid dye-type chelates.

[0035] Examples of inorganic pigments include titanium dioxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chromium yellow, and carbon black.

[0036] From the viewpoint of image density and ink ejection performance, the pigment content in the ink 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.

[0037] (Water) The ink in the ink set of this disclosure contains water. The water content is not particularly limited, but is, for example, 40% to 70% by mass.

[0038] (Pigment-dispersing resin) The ink in the ink set of this disclosure includes a pigment-dispersing resin. In this disclosure, a pigment-dispersing resin is a resin that has the function of dispersing pigments.

[0039] The form of the pigment dispersion resin is not particularly limited and may be a random resin, a block resin, or a graft resin. The pigment dispersion resin may also be a resin having a crosslinked structure.

[0040] (Binder Resin) The ink in the ink set of this disclosure contains a binder resin. In this disclosure, "binder resin" is a resin used to fix an image onto a substrate. Pigment dispersion resin and binder resin can be distinguished by centrifuging the ink. Specifically, the resin contained in the precipitate obtained by centrifuging the ink is determined to be the pigment dispersion resin. On the other hand, the resin contained in the supernatant obtained by centrifuging the ink is determined to be the binder resin. Here, centrifugation is performed using a centrifuge (Himac CS-150FNX) at a rotation speed of 40,000 rpm (revolutions per minute) for 60 minutes.

[0041] The resin is preferably at least one selected from the group consisting of acrylic resin, polyester resin, and urethane resin. This further improves the adhesion of the image, the scratch resistance of the image, and the drying speed of the image.

[0042] In this disclosure, "acrylic resin" means a polymer (homopolymer or copolymer) of raw material monomers containing at least one selected from the group consisting of acrylic acid, derivatives of acrylic acid (e.g., acrylic acid esters), methacrylic acid, and derivatives of methacrylic acid (e.g., methacrylic acid esters). In this disclosure, "polyester resin" means a polymer compound containing ester bonds in its main chain. Examples of polyester resins include polycondensates of polycarboxylic acids (e.g., dicarboxylic acids) and polyalcohols (e.g., diols). In this disclosure, "urethane resin" means a polymer compound containing urethane bonds in its main chain.

[0043] The weight average molecular weight (Mw) of the acrylic resin is preferably from 3,000 to 100,000, more preferably from 5,000 to 80,000, and still more preferably from 8,000 to 60,000. The weight average molecular weight (Mw) of the polyester resin is preferably from 3,000 to 200,000, more preferably from 4,000 to 150,000, and still more preferably from 5,000 to 100,000. The weight average molecular weight (Mw) of the urethane resin is preferably from 3,000 to 500,000, more preferably from 4,000 to 300,000, and still more preferably from 5,000 to 200,000.

[0044] In the present disclosure, unless otherwise specified, the weight average molecular weight (Mw) means a value measured by gel permeation chromatography (GPC). The measurement by gel permeation chromatography (GPC) is performed using HLC (registered trademark)-8020GPC (Tosoh Corporation) as the measuring device, three TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID × 15 cm, Tosoh Corporation) columns, and tetrahydrofuran (THF) as the eluent. The measurement conditions are as follows: the sample concentration is 0.45% by mass, the flow rate is 0.35 ml / min, the sample injection volume is 10 μL, the measurement temperature is 40°C, and the measurement is performed using an RI detector. The calibration curve is prepared from eight samples of "Standard Sample TSK standard, polystyrene" of Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0045] In the ink set of the present disclosure, it is preferable that the binder resins contained in each ink are of the same type. Specifically, when the binder resin is a polymer, it is preferable that the types of the structural units constituting the polymer are the same in the binder resins contained in each ink. Further, when the binder resin is a commercially available product, it is preferable that the binder resins contained in each ink are the same. When the binder resins contained in each ink are of the same type, the difference in the aggregation rate between the inks can be made smaller, and cracking of the image, deterioration of the sharpness of the image, and color mixing between colors can be more suppressed.

[0046] From the viewpoint of further improving the adhesion and abrasion resistance of the image, the binder resin preferably contains at least one kind of resin particles. When the binder resin contains resin particles, the proportion of the resin particles in the binder resin is preferably more than 50% by mass, more preferably 60% by mass or more, and still more preferably 80% by mass or more.

[0047] (Resin particles) When the ink contains resin particles, the adhesion between the layer derived from the pretreatment liquid and the layer derived from the ink is enhanced in the recorded image. As a result, the adhesion between the image (that is, the image including the layer derived from the pretreatment liquid and the layer derived from the ink) and the non-permeable substrate is improved, and the strength of the layer derived from the ink is increased. As a result, the abrasion resistance of the image is improved. Further, when the resin particles in the ink come into contact with the aggregating agent in the pretreatment liquid on the non-permeable substrate, the resin particles in the ink aggregate or become unstable in dispersion, thereby thickening the ink. As a result, the image quality is improved and the speed of image recording is increased.

[0048] From the viewpoint of further improving the adhesion of the image, the resin particles contained in the ink are preferably particles containing at least one resin selected from the group consisting of an acrylic resin, a polyester resin, and a urethane resin.

[0049] As the acrylic resin particles, acrylic resin particles which are self-dispersible resin particles are also preferable. Examples of the self-dispersible resin particles include the self-dispersible polymer particles described in paragraphs 0062 to 0076 of JP-A-2016-188345.

[0050] The glass transition temperature (Tgi) of the resin particles contained in the ink is not particularly limited, but from the viewpoint of the manufacturing suitability of the resin particles, it is preferably 150°C or lower, more preferably 130°C or lower. There is no particular limitation on the lower limit of Tgi, but it is, for example, 50°C, preferably 80°C.

[0051] Further, the volume average particle diameter (Pi) of the resin particles contained in the ink is preferably 1 nm to 200 nm, more preferably 3 nm to 200 nm, and still more preferably 5 nm to 50 nm.

[0052] The resin in the resin particles contained in the ink preferably has an anionic group in its structure. The anionic group is not particularly limited, but it is preferably a carboxyl group or a sulfo group, and more preferably a sulfo group. The amount of the anionic group is not particularly limited, but it is preferably 0.001 mol to 1.0 mol per 100 g of resin, and more preferably 0.01 mol to 0.5 mol.

[0053] The resin particle content relative to the total amount of ink is preferably 1% to 25% by mass, more preferably 2% to 20% by mass, and even more preferably 3% to 15% by mass.

[0054] (Water-soluble solvents) The ink preferably contains at least one water-soluble solvent. This allows for the suppression of ink drying or the moistening of the ink. The water-soluble solvents that can be contained in the ink may be used, for example, as drying inhibitors to prevent the ink from adhering and drying at the ink outlet of a spray nozzle, forming aggregates and causing clogging. From the viewpoint of suppressing drying and moistening, the water-soluble solvent contained in the ink is preferably a water-soluble solvent with a vapor pressure lower than that of water. Furthermore, the boiling point of the water-soluble solvent at 1 atmosphere (1013.25 hPa) is preferably 80°C to 300°C, and more preferably 120°C to 250°C.

[0055] The drying inhibitor is preferably a water-soluble solvent with a vapor pressure lower than that of water. Specific examples of such water-soluble solvents include polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, acetylene glycol derivatives, glycerin, and trimethylolpropane. Of these, polyhydric alcohols such as propylene glycol, glycerin, and diethylene glycol are preferred as drying inhibitors. The drying inhibitor may be used alone or in combination of two or more. The content of the drying inhibitor is preferably in the range of 10% to 50% by mass relative to the total amount of ink.

[0056] In addition to the above, water-soluble solvents may also be used to adjust the viscosity of the ink. Specific examples of water-soluble solvents that can be used to adjust viscosity include alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol), polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), glycol derivatives (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene This includes ethylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amines (e.g., ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine), and other polar solvents (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone). In this case, the water-soluble solvent may be used alone or in combination of two or more.

[0057] (Other Additives) The ink may contain other components besides those listed above. Examples of other components include known additives such as anti-fading agents, emulsifying stabilizers, penetration enhancers, UV absorbers, preservatives, fungicides, pH adjusters, surface tension adjusters, defoamers, viscosity adjusters, dispersion stabilizers, rust inhibitors, and chelating agents.

[0058] (Physical Properties) The pH of the ink is preferably 7 to 10, and more preferably 7.5 to 9.5, from the viewpoint of improving ejection stability. The pH is measured at 25°C using a pH meter, for example, using a pH meter (model number "HM-31") manufactured by Toa DKK Co., Ltd.

[0059] The viscosity of the ink is preferably 0.5 mPa·s to 30 mPa·s, more preferably 2 mPa·s to 20 mPa·s, even more preferably 2 mPa·s to 15 mPa·s, and particularly preferably 3 mPa·s to 10 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, using a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0060] The surface tension of the ink is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 30 mN / m to 45 mN / m. The surface tension is measured at 25°C using a surface tension meter, for example, by the plate method using an automatic surface tension meter (product name "CBVP-Z") manufactured by Kyowa Interface Science Co., Ltd.

[0061] <Pretreatment solution> (Flocculant) The pretreatment solution contains a flocculant. Preferably, the flocculant contains at least one selected from the group consisting of polyvalent metal compounds, organic acids, and water-soluble cationic polymers.

[0062] The presence of a coagulant in the pretreatment solution can improve ink viscosity, thereby enhancing image quality.

[0063] - Organic Acids - Examples of organic acids include organic compounds that have an acidic group.

[0064] Examples of acidic groups include phosphoric acid groups, phosphonic acid groups, phosphinic acid groups, sulfate groups, sulfonic acid groups, sulfinic acid groups, and carboxyl groups.

[0065] In particular, from the viewpoint of ink aggregation rate, the acidic group is preferably a phosphoric acid group or a carboxyl group, and more preferably a carboxyl group.

[0066] It is preferable that at least a portion of the acidic group is dissociated in the pretreatment solution.

[0067] Examples of organic compounds having a carboxyl group include (meth)acrylic acid, poly(meth)acrylic acid, acetic acid, formic acid, benzoic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, succinic acid, glutaric acid, pimelic acid, adipic acid, fumaric acid, citric acid, tartaric acid, phthalic 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, and nicotinic acid.

[0068] In particular, from the viewpoint of ink aggregation rate, the organic compound having a carboxyl group is preferably a divalent or higher carboxylic acid (hereinafter also referred to as a polyvalent carboxylic acid), and more preferably a dicarboxylic acid.

[0069] Specifically, the polycarboxylic acid is preferably malonic acid, malic acid, maleic acid, succinic acid, glutaric acid, pimelic acid, adipic acid, fumaric acid, tartaric acid, 4-methylphthalic acid, or citric acid, and more preferably malonic acid, malic acid, tartaric acid, succinic acid, glutaric acid, pimelic acid, adipic acid, or citric acid.

[0070] The organic acid is preferably one with a low pKa (for example, 1.0 to 5.0). This reduces the dispersion stability of particles such as pigments and resin particles in ink, which are dispersed and stabilized by weakly acidic functional groups such as carboxyl groups, by bringing them into contact with an organic acid with an even lower pKa.

[0071] The organic acid is preferably low in pKa, highly soluble in water, and has a valency of 2 or higher. Furthermore, it is more preferable that the organic acid has 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.

[0072] -Polyvalent Metal Compounds- Examples of polyvalent metal compounds include salts of alkaline earth metals in Group 2 of the periodic table (e.g., magnesium, calcium), transition metals in Group 3 of the periodic table (e.g., lanthanum), metals in Group 13 of the periodic table (e.g., aluminum), and lanthanides (e.g., neodymium).

[0073] These metal salts are preferably salts, nitrates, chlorides, or thiocyanates of organic acids, as described later.

[0074] In particular, the polyvalent metal compound is preferably a calcium or magnesium salt of an organic acid (e.g., formic acid, acetic acid, benzoic acid, etc.); a calcium or magnesium salt of nitric acid; calcium chloride, magnesium chloride, or a calcium or magnesium salt of thiocyanate.

[0075] 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.

[0076] -Water-soluble cationic polymers- Examples of water-soluble cationic polymers include polyallylamine, polyallylamine derivatives, poly-2-hydroxypropyldimethylammonium chloride, poly(diallyldimethylammonium chloride), etc. For water-soluble cationic polymers, refer to the descriptions in publicly available documents such as Japanese Patent Application Publication No. 2011-042150 (especially paragraph 0156) and Japanese Patent Application Publication No. 2007-98610 (especially paragraphs 0096 to 0108) as appropriate. Examples of commercially available water-soluble cationic polymers include Sharol® DC-303P and Sharol DC-902P (both manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Catiomaster® PD-7 and Catiomaster PD-30 (both manufactured by Yokkaichi Gosei Co., Ltd.), and Unisense FPA100L (manufactured by Senka Co., Ltd.).

[0077] The pretreatment solution may contain only one type of coagulant, or it may contain two or more types.

[0078] The coagulant content 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, based on the total amount of the pretreatment solution.

[0079] When the mass ratio of the coagulant contained in the pretreatment solution is F, and the mass ratios of the binder resin contained in the black ink, cyan ink, magenta ink, and yellow ink are Pk, Pc, Pm, and Py, the values ​​of Pk / F, Pc / F, Pm / F, and Py / F are preferably 0.3 to 3.0, more preferably 0.4 to 2.5, particularly preferably 0.5 to 2.0, and most preferably 0.5 to 3.0.

[0080] (Resin particles) The pretreatment solution preferably contains resin particles. The resin particles may contain only one type of resin or two or more types of resin. The resins contained in the resin particles are preferably water-insoluble resins.

[0081] In this disclosure, "water-insoluble" in a water-insoluble resin refers to the property that its solubility in 100 g of water at 25°C is less than 1.0 g (more preferably less than 0.5 g).

[0082] Examples of resins constituting the resin particles include acrylic resin, polyester resin, and urethane resin. Preferably, the resin particles are at least one selected from the group consisting of particles containing acrylic resin, particles containing polyester resin, particles containing urethane resin, and composite particles containing acrylic resin and polyester resin.

[0083] In this disclosure, a composite particle containing an acrylic resin and a polyester resin means a particle that contains both an acrylic resin and a polyester resin within a single particle. The total proportion of the acrylic resin and polyester resin in the composite particle is preferably 90% by mass or more.

[0084] There are no particular limitations on the specific form of the composite particle described above (i.e., a particle containing both acrylic resin and polyester resin). Specific examples of the composite particle include a form in which the polymer chains of the acrylic resin and the polymer chains of the polyester resin are intertwined with each other.

[0085] Examples of methods for producing the above-mentioned composite particles include: mixing an aqueous dispersion of polyester resin with an aqueous dispersion of acrylic resin having a glycidyl group; polymerizing (homopolymerizing or copolymerizing) at least one radical polymerizable unsaturated monomer having a glycidyl group in an aqueous dispersion of polyester resin; copolymerizing a radical polymerizable unsaturated monomer having a glycidyl group with another radical polymerizable unsaturated monomer in an aqueous dispersion of polyester resin; and so on. For more information on methods for producing the above-mentioned composite particles, please refer to publicly available documents such as Japanese Patent Application Publication No. 2010-143955.

[0086] In this disclosure, when preparing a pretreatment solution containing composite particles, a commercially available aqueous dispersion of composite particles may be used as a raw material. Examples of aqueous dispersions of composite particles include PESRESIN TF13-BP, PESRESIN A615GE, and PESRESIN A613GE (all manufactured by Takamatsu Oil & Fat Co., Ltd.).

[0087] The resin particles contained in the pretreatment solution preferably include the composite particles mentioned above. The ratio of the composite particles (i.e., composite particles containing acrylic resin and polyester resin) to the resin particles contained in the pretreatment solution is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0088] Furthermore, the glass transition temperature (Tgp) of the resin particles contained in the pretreatment solution is preferably 0°C or higher (i.e., satisfying 0°C ≤ Tgp), more preferably 10°C or higher, even more preferably 20°C or higher, and even more preferably 30°C or higher, from the viewpoint of suitability for manufacturing the resin particles. The upper limit of Tgp is preferably 150°C, and more preferably 100°C, from the viewpoint of further improving image adhesion.

[0089] (Water) The pretreatment solution contains water. The water content is not particularly limited, and is, for example, 50% to 90% by mass.

[0090] (Other components) The pretreatment solution may contain surfactants and other components other than water, as needed. Other components that may be contained in the pretreatment solution include known additives such as organic solvents, defoamers, solid wetting agents, colloidal silica, inorganic salts, anti-fading agents, emulsifying stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, fungicides, pH adjusters, viscosity adjusters, rust inhibitors, chelating agents, and water-soluble polymer compounds (for example, water-soluble polymer compounds described in paragraphs 0026 to 0080 of Japanese Patent Application Publication No. 2013-001854).

[0091] (Physical Properties) The pH of the pretreatment solution is preferably 0.1 to 4.5, and more preferably 0.2 to 4.0, from the viewpoint of the ink aggregation rate. The pH is measured at 25°C using a pH meter, for example, using a pH meter (model number "HM-31") manufactured by Toa DKK Co., Ltd.

[0092] The viscosity of the pretreatment solution is preferably 0.5 mPa·s to 10 mPa·s, and more preferably 1 mPa·s to 5 mPa·s, from the viewpoint of the ink aggregation rate. The viscosity is measured using a viscometer at 25°C. For example, the viscosity is measured using a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0093] The surface tension of the pretreatment solution is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 30 mN / m to 45 mN / m. The surface tension is measured at a temperature of 25°C. The surface tension is measured by the plate method using, for example, an automatic surface tension meter (product name "CBVP-Z") manufactured by Kyowa Interface Science Co., Ltd.

[0094] (Applications) The pretreatment liquid included in the ink set of this disclosure is for use with inkjet inks. That is, the pretreatment liquid included in the ink set of this disclosure is a liquid used to be applied to a substrate in advance before applying inkjet ink to the substrate.

[0095] In particular, the pretreatment solution included in the ink set of this disclosure is preferably used for image recording on an impermeable substrate. An image is recorded by applying the pretreatment solution and the ink in that order to the impermeable substrate.

[0096] - Non-permeable Substrate - In this disclosure, non-permeability in a non-permeable substrate means that the water absorption rate over 24 hours, as measured in accordance with ASTM D570-98 (2018), is 2.5% or less. Here, the unit of water absorption rate, "%", is on a mass basis. The above water absorption rate is preferably 1.0% or less, and more preferably 0.5% or less.

[0097] Examples of materials for non-permeable substrates include glass, metals (e.g., aluminum, zinc, copper, etc.), and resins (e.g., polyvinyl chloride, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, nylon, acrylic resin, etc.).

[0098] The material of the non-permeable substrate is preferably a resin. In other words, the non-permeable substrate is preferably a resin substrate.

[0099] In particular, from the standpoint of versatility, the material of the non-permeable substrate is preferably polypropylene, polyethylene, polyethylene terephthalate, nylon, acrylic resin, or polyvinyl chloride.

[0100] The shape of the non-permeable substrate is preferably in the form of a sheet (film) or a plate. Examples of non-permeable substrates having such shapes include glass plates, metal plates, resin sheets (resin films), paper laminated with plastic, paper laminated or vapor-deposited with metal, and plastic sheets (plastic films) laminated or vapor-deposited with metal.

[0101] Examples of non-permeable resin substrates include resin sheets (resin films), specifically, flexible packaging materials for packaging food and other products, and panels for floor guidance in mass retail stores.

[0102] In addition to sheet-like (film-like) or plate-like non-permeable substrates, examples of non-permeable substrates include textiles and nonwoven fabrics formed from non-permeable fibers.

[0103] The thickness of the non-permeable substrate is preferably 0.1 μm to 1,000 μm, more preferably 0.1 μm to 800 μm, and even more preferably 1 μm to 500 μm.

[0104] Impermeable substrates may be subjected to hydrophilic treatment. Examples of hydrophilic treatments include, but are not limited to, corona treatment, plasma treatment, heat treatment, abrasion treatment, light irradiation treatment (e.g., UV treatment), and flame treatment. Corona treatment can be performed, for example, using a corona master (product name "PS-10S", manufactured by Shinko Electric Instruments Co., Ltd.). The conditions for corona treatment should be appropriately selected depending on the type of impermeable substrate.

[0105] The non-permeable substrate may be a transparent non-permeable substrate. Here, transparency means that the transmittance of visible light with wavelengths of 400 nm to 700 nm is 80% or more (preferably 90% or more). When the non-permeable substrate is a transparent non-permeable substrate, the image is easily visible through the non-permeable substrate from the non-image recording side of the non-permeable substrate. For example, when the non-permeable substrate is a transparent non-permeable substrate, and an image is recorded on the non-permeable substrate by applying a pre-treatment liquid, a colored ink, and a white ink in this order, the colored image (e.g., a pattern image such as characters or figures) with a white image (e.g., a solid image) as the background is easily visible through the non-permeable substrate from the non-image recording side of the non-permeable substrate.

[0106] [Image Recording Method] The image recording method of the present disclosure includes the steps of: applying a pretreatment liquid to a non-permeable substrate using the ink set of the present disclosure to form a pretreatment layer (hereinafter also referred to as the "pretreatment liquid application step"); and applying black ink, cyan ink, magenta ink, and yellow ink to at least a portion of the pretreatment layer using an inkjet recording method to record an image (hereinafter also referred to as the "image recording step").

[0107] (Pretreatment liquid application step) In the pretreatment liquid application step, the pretreatment liquid is applied to the non-permeable substrate. Details of the non-permeable substrate are as described above. The method of applying the pretreatment liquid is not particularly limited and known methods such as coating, immersion, and inkjet recording can be used.

[0108] Known coating methods include those using bar coaters, extrusion die coaters, air doctor coaters, blade coaters, rod coaters, knife coaters, squeeze coaters, reverse roll coaters, and the like.

[0109] There are no particular restrictions on the ink ejection method in an inkjet recording system. 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, irradiates the ink with it, and ejects the ink using the radiation pressure, or a thermal inkjet (bubble jet®) method that heats the ink to form bubbles and utilizes the resulting pressure. When a pretreatment solution is applied in an inkjet recording system, the pretreatment solution can be filled into the ink tank of the inkjet recording device instead of the ink.

[0110] As an inkjet recording method, the method described in Japanese Patent Publication No. 54-59936 is particularly effective, as it involves the ink undergoing a rapid volume change due to the action of thermal energy, and the force resulting from this state change ejects the ink from the nozzle. As an inkjet recording method, the method described in paragraphs 0093 to 0105 of Japanese Patent Publication No. 2003-306623 can also be applied.

[0111] The application of a pretreatment solution to a non-permeable substrate using an inkjet recording method is performed by ejecting the pretreatment solution from the nozzle of the inkjet head.

[0112] 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.

[0113] 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.

[0114] The pretreatment solution is preferably applied using an inkjet head having a resolution of 300 dpi or higher (more preferably 600 dpi or higher, and even more preferably 800 dpi or higher). Here, dpi is an abbreviation for dots per inch, and 1 inch is equal to 2.54 cm.

[0115] From the viewpoint of obtaining high-resolution images, the amount of pre-treatment liquid 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.

[0116] (Image Recording Process) In the image recording process, each ink is applied to at least a portion of the impermeable substrate (i.e., the pre-treatment layer) to which the pre-treatment solution has been applied, using an inkjet recording method to record an image. Details of the inkjet recording method are the same as those for the inkjet recording method in the method of applying the pre-treatment solution.

[0117] (Other steps) The image recording method of the present disclosure may include other steps other than the pretreatment solution application step and the image recording step.

[0118] After applying the pretreatment solution, the pretreatment solution applied to the non-permeable substrate may be heated and dried. Means for heating and drying the pretreatment solution include known heating means such as heaters, known blowing means such as dryers, and means combining these.

[0119] Methods for heating and drying the pretreatment solution include, for example, applying heat with a heater from the side opposite to the side of the non-permeable substrate to which the pretreatment solution has been applied; applying warm air or hot air to the side of the non-permeable substrate to which the pretreatment solution has been applied; applying heat with an infrared heater from the side of the non-permeable substrate to which the pretreatment solution has been applied or from the side opposite to the side to which the pretreatment solution has been applied; and methods combining several of these.

[0120] The heating temperature during the heat drying of the pretreatment solution is preferably 35°C or higher, and more preferably 40°C or higher. There is no particular upper limit to the heating temperature, but 100°C is preferred, 90°C is more preferred, and 70°C is even more preferred.

[0121] The heating and drying time is not particularly limited, but is preferably 0.5 to 60 seconds, more preferably 0.5 to 20 seconds, and even more preferably 0.5 to 10 seconds.

[0122] [Image Recording Material] The image recording material of the present disclosure uses the ink set of the present disclosure and comprises a non-permeable substrate, a pre-treatment layer disposed on the non-permeable substrate and containing a non-volatile component of a pre-treatment solution, and an ink layer disposed on at least a portion of the pre-treatment layer and containing a non-volatile component of each ink.

[0123] The preferred embodiments of each component in the image recording material are as described above. In this disclosure, non-volatile components mean components other than volatile components such as water and organic solvents. Non-volatile components of the pretreatment liquid are, for example, flocculants. Non-volatile components of the ink are, for example, pigments, pigment dispersion resins, and binder resins.

[0124] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0125] <Preparation of pretreatment solution> Prepare pretreatment solutions P1 to P8 by mixing the resin particles, flocculant, and surfactant listed in Table 1 with an organic solvent, defoamer, other components, and water.

[0126] The details of each component listed in Table 1 are as follows, and the values ​​are in mass percent. Note that in Table 1, the amount of each component is the amount as solid content. If the solid content concentration is not 100% by mass, the amount of water included is included in the "Water" item. For "Water," the amount of remaining water that makes up 100% by mass of the entire pretreatment solution is used.

[0127] (Aqueous dispersion of resin particles) ・Pesresin TF-13BP...Aqueous dispersion of composite particles containing acrylic resin and polyester resin, manufactured by Takamatsu Oil & Fat Co., Ltd. ・Aqueous dispersion of acrylic resin particle 1...Aqueous dispersion of acrylic resin 1 prepared as follows ・Aqueous dispersion of acrylic resin particle 2...Aqueous dispersion of acrylic resin 2 prepared as follows ・Hi-Tec E-6400...Aqueous dispersion of acrylic resin, manufactured by Toho Chemical Industry Co., Ltd. ・Aqueous dispersion of urethane resin particle 3...Aqueous dispersion of urethane resin A prepared as follows

[0128] - Preparation of aqueous dispersion of acrylic resin particles 1 - In a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 124 parts of deionized water and 1.2 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's Latemul E-150) as an emulsifier are charged. Meanwhile, another mixing vessel equipped with a stirrer is prepared, and 2 parts of acrylic acid, 38 parts of n-butyl acrylate, 60 parts of butyl methacrylate, 64 parts of deionized water, and 0.8 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's Latemul E-150) as an emulsifier are added in sequence, then stirred and mixed to form an emulsion.

[0129] Eight parts of the above emulsion are taken and added to the above reaction vessel. After addition, the internal temperature is raised to 80°C and the inside of the vessel is thoroughly purged with nitrogen. Then, four parts of a 5% aqueous solution of potassium persulfate and eight parts of a 1% by mass aqueous solution of anhydrous sodium bisulfite are added to start the polymerization reaction. After the polymerization reaction has started, while maintaining the internal temperature at 80°C, the remaining emulsion prepared above, along with 1.2 parts of a 5% aqueous solution of potassium persulfate and 2.5 parts of a 1% by mass aqueous solution of anhydrous sodium bisulfite are added dropwise over 1.5 hours. After the dropwise addition is complete, stirring is continued for another 2 hours, and then the mixture is cooled until the internal temperature drops below 30°C. Dimethylaminoethanol is then added to adjust the pH of the contents to 8.5, and then ion-exchanged water is added to adjust the solid content to 30%, thereby obtaining an aqueous dispersion of (meth)acrylic resin particles 1 (solid content 30%) with an acid value of 15.6 (mg KOH / g) and a Tg of -5.9 (°C).

[0130] - Preparation of aqueous dispersion of acrylic resin particles 2 - In a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 124 parts of deionized water and 1.2 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's Latemul E-150) as an emulsifier are charged. Meanwhile, another mixing vessel equipped with a stirrer is prepared, and 2 parts of acrylic acid, 70 parts of methyl methacrylate, 28 parts of butyl methacrylate, 64 parts of deionized water, and 0.8 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's Latemul E-150) as an emulsifier are added in sequence, and then stirred to form an emulsion.

[0131] Eight parts of the above emulsion are taken and added to the above reaction vessel. After addition, the internal temperature is raised to 80°C and the inside of the vessel is thoroughly purged with nitrogen. Then, four parts of a 5% aqueous solution of potassium persulfate and eight parts of a 1% by mass aqueous solution of anhydrous sodium bisulfite are added to start the polymerization reaction. After the polymerization reaction has started, while maintaining the internal temperature at 80°C, the remaining emulsion prepared above, along with 1.2 parts of a 5% aqueous solution of potassium persulfate and 2.5 parts of a 1% by mass aqueous solution of anhydrous sodium bisulfite are added dropwise over 1.5 hours. After the dropwise addition is complete, stirring is continued for a further 2 hours, and then the mixture is cooled until the internal temperature drops below 30°C. Dimethylaminoethanol is then added to adjust the pH of the contents to 8.5, and then ion-exchanged water is added to adjust the solid content to 30% by mass, thereby obtaining an aqueous dispersion of (meth)acrylic resin particles 2 (solid content 30%) with an acid value of 15.6 (mg KOH / g) and a Tg of 76.6 (°C).

[0132] -Preparation of aqueous dispersion of urethane resin particles 3- In a simple pressurized reaction apparatus equipped with a stirrer and a heating device, 35.9 parts by mass of tricyclo[5.2.1.0(2,6)]decandimethanol as a polycyclic aliphatic diol, 4.5 parts by mass of 2,2-dimethylolpropionic acid as a polyol component having a carboxyl group, 37.4 parts by mass of 4,4-diphenylmethane diisocyanate as an aromatic polyisocyanate component, 22.1 parts by mass of isophorone diisocyanate as an aliphatic isocyanate, and 54 parts by mass of methyl ethyl ketone as an organic solvent for the reaction are charged and stirred at 70°C for 12 hours to carry out the urethane reaction to produce a methyl ethyl ketone solution of urethane prepolymer (P1) having an isocyanate group. Next, 2.9 parts by mass of triethylamine is added as a neutralizing agent to the methyl ethyl ketone solution of the obtained urethane prepolymer (P1) and homogenized. Then, 176 parts by mass of ion-exchanged water as an aqueous medium is added while stirring at 200 rpm to disperse the polyurethane prepolymer in water. The resulting dispersion is heated to 50°C and stirred for 4 hours to carry out a chain extension reaction by amino groups formed by the reaction of water with isocyanate groups. The mixture is then heated under reduced pressure to 60°C to distill off the methyl ethyl ketone. After that, water is added to adjust the solid content concentration to 30% by mass to obtain an aqueous dispersion of urethane resin 3. The urethane resin 3 exists as resin particles in the aqueous dispersion.

[0133] (Coagulants) ・Adipic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Glutaric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Magnesium lactate trihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Calcium formate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Calcium lactate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0134] (Water-soluble organic solvent) ・2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0135] (Other ingredients) ・Orphine E-1010: Ethylene oxide adduct of acetylene glycol (manufactured by Nisshin Chemical Industry Co., Ltd.) ・Surfinol 440: Ethylene oxide adduct of acetylene glycol (manufactured by Nisshin Chemical Industry Co., Ltd.) ・Newpol PE-75: Pluronic nonionic surfactant obtained by adding ethylene oxide to polypropylene glycol (manufactured by Sanyo Chemical Industries, Ltd.) ・Triisopropanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Potassium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・Polyethylene glycol 20000 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ・BYK-024: Antifoaming agent (manufactured by BYK) ・Proxel GXL: Preservative (manufactured by Abyssia)

[0136]

[0137] <Ink Preparation>

[0138] Each component shown in Tables 2 and 3 was mixed to the content (mass %) indicated in each table. Coarse particles were removed from the mixture using a 1 μm filter to prepare each ink. K-1 to K-6 are black inks, C-1 to C-6 are cyan inks, M-1 to M-6 are magenta inks, and Y-1 to Y-6 are yellow inks.

[0139] Details of each component listed in Tables 2 and 3 are as follows. Note that in Tables 2 and 3, the amounts of each component are given as solid content. If the solid content concentration is not 100% by mass, the amounts of water and organic solvents included are included in the "Water" and "Organic Solvent" sections, respectively.

[0140] (Pigment Dispersions) Prepare the following pigment dispersions as black pigment dispersion, cyan pigment dispersion, magenta pigment dispersion, and yellow pigment dispersion. All of these pigment dispersions are dispersions in which the pigments of each color are dispersed by a cross-linked polymer. • Black pigment dispersion 1: PRO-JET APD4000 Black, pigment concentration 15.0% by mass, manufactured by FUJIFILM Imaging Colorants. • Black pigment dispersion 2: Pigment dispersion prepared using pigment dispersion resin 1 manufactured according to the manufacturing example described below. • PRO-JET APD1000 Cyan: Cyan pigment dispersion, pigment concentration 14.0% by mass, manufactured by FUJIFILM Imaging Colorants. • Cyan pigment dispersion 2: Pigment dispersion prepared using pigment dispersion resin 1 manufactured according to the manufacturing example described below. • Magenta pigment dispersion 1: PRO-JET APD4000 Magenta: Magenta pigment dispersion, pigment concentration 18.5% by mass (manufactured by FUJIFILM Imaging Colorants). - Magenta pigment dispersion 2: PRO-JET APD1000RED, pigment concentration 16.0% by mass (manufactured by FUJIFILM Imaging Colorants) - Magenta pigment dispersion 3: Pigment dispersion prepared using pigment dispersion resin 1 manufactured according to the manufacturing example described below - PRO-JET APD1000Yellow-TP: Yellow pigment dispersion, pigment concentration 15.4% by mass (manufactured by FUJIFILM Imaging Colorants)

[0141] <Preparation of Black Pigment Dispersion 2> (Example of preparation of Pigment Dispersion Resin 1) 95 parts of butanol are charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture is purged with nitrogen gas. After heating the reaction vessel to 110°C, a mixture of 45 parts of polymerizable monomer styrene, 30 parts of acrylic acid, 25 parts of lauryl methacrylate, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) is added dropwise over 2 hours to carry out the polymerization reaction. After the dropwise addition is complete, the reaction is continued at 110°C for 3 hours, then 0.6 parts of V-601 are added, and the reaction is continued at 110°C for another hour. After that, the reaction vessel is cooled to room temperature, then dimethylaminoethanol is added to completely neutralize the acid groups of the product, and then 100 parts of water are added to make it aqueous. Then, the reaction vessel is heated to over 100°C, and the butanol is removed by distillation by azeotropic distillation of the butanol with water, while the solid content is adjusted to 30%, thereby obtaining an aqueous solution of pigment dispersion resin 1 (solid content 30%). The acid value of pigment dispersion resin 1 is 233.6 mg KOH / g.

[0142] (Preparation of Black Pigment Dispersion 2) 15 parts of carbon black (PrinteX85, manufactured by Orion Engineered Carbons), 10 parts of an aqueous solution of pigment dispersion resin 1 (30% solids), and 75 parts of water are added to a mixing container equipped with a stirrer and premixed for 1 hour. Then, the mixture is circulated and dispersed using a Dynomill (manufactured by Shinmaru Enterprises, 0.6 L volume) filled with 1800 g of 0.5 mm diameter zirconia beads to produce the black pigment dispersion.

[0143] <Preparation of Cyan Pigment Dispersion 2, Magenta Pigment Dispersion 3, and Yellow Pigment Dispersion 2> Cyan pigment dispersion 2, magenta pigment dispersion 3, and yellow pigment dispersion 2 are obtained by the same method as for the black pigment dispersion described above, except that the following pigments are used as pigments. ・Cyan: LIONOL BLUE 7358G (C.I. Pigment Blue 15:3) manufactured by Toyo Color Co., Ltd. ・Magenta: FASTGEN SUPER MAGENTA RG (C.I. Pigment Red 122) manufactured by DIC Corporation ・Yellow: LIONOL YELLOW TT1405G (C.I. Pigment Yellow 14) manufactured by Toyo Color Co., Ltd.

[0144] (Organic solvents) ・Propylene glycol (manufactured by ADEKA Corporation) ・Diethylene glycol monobutyl ether (manufactured by KH Neochem Co., Ltd., trade name "Butysenol 20P") ・3-Methoxy-3-methyl-1-butanol (manufactured by Fujifilm Wako Pure Chemical Industries Ltd.) ・Propylene glycol monomethyl ether (manufactured by Nippon Emulsifier Co., Ltd.)

[0145] (Aqueous dispersion of resin particles) ・Neocryl A1091: Styrene-acrylic polymer resin fine particle dispersion (manufactured by Covestro) ・Evaphanol HA-55: Polycarbonate-urethane polymer resin fine particle dispersion (manufactured by Nikka Chemical Co., Ltd.)

[0146] (Aqueous solution of resin) ・Resin 1: Aqueous solution of binder resin 28 manufactured by the method described in the examples of Japanese Patent Publication No. 2020-180178

[0147] (Other ingredients) ・Orphine E-1010: Ethylene oxide adduct of acetylene glycol (manufactured by Nisshin Chemical Industry Co., Ltd.) ・Surfinol 465: Ethylene oxide adduct of acetylene glycol (manufactured by Nisshin Chemical Industry Co., Ltd.) ・BYK 3450: Silicone-based surfactant (manufactured by BYK) ・TEGO Wet 280: Silicone-based surfactant (manufactured by Evonik Industries) ・PVP K-15: Polyvinylpyrrolidone (average molecular weight 10,000, manufactured by Ashland) ・Snowtex XS: Colloidal silica (manufactured by Nissan Chemical Corporation) ・Urea: Manufactured by Nissan Chemical Corporation

[0148]

[0149]

[0150] <Image Recording> A polyester film (product name "FE2301", manufactured by Futamura Chemical Co., Ltd., thickness 12 μm, width 100 mm, length 240 mm) is prepared as a non-permeable substrate (hereinafter also simply referred to as "substrate").

[0151] A transport mechanism for transporting the substrate and an image recording device are prepared, which includes, in this order from the upstream side in the transport direction of the substrate, a wire bar coater for applying pretreatment liquid, a first inkjet head for applying black ink, a second inkjet head for applying cyan ink, a third inkjet head for applying magenta ink, and a fourth inkjet head for applying yellow ink.

[0152] The first, second, third, and fourth inkjet heads are all 1200 dpi / 20-inch wide piezo full line heads. Here, dpi is an abbreviation for dots per inch.

[0153] The first, second, third, and fourth inkjet heads are all arranged in a line head configuration, with the heads aligned perpendicular to the substrate transport direction (i.e., in the width direction of the substrate). Each of the above inkjet heads is a Samba® G3L (manufactured by FUJIFILM DIMATIX).

[0154] The substrate, pretreatment solution, black ink, cyan ink, magenta ink, and yellow ink are set in the image recording device described above.

[0155] The pretreatment solution, black ink, cyan ink, magenta ink, and yellow ink listed in Table 3 are applied to the substrate in this order to create an image recording. The specific method is as follows.

[0156] (Preparation of Image Recording Material 1) While moving the substrate at a constant speed of 50 m / min, the pretreatment solution is applied to the substrate using a wire bar coater. The amount of pretreatment solution applied is 2.0 g / m ２ Let's assume that.

[0157] One second after the application of the pretreatment solution is completed, the pretreatment solution is dried by applying 60°C hot air at a wind speed of 22 m / s for 3 seconds using a dryer, thereby forming a pretreatment solution layer on the substrate.

[0158] A substrate with a pre-treated liquid layer formed on it is moved at a constant speed of 50 m / min while black ink is ejected from the first inkjet head onto the surface of the pre-treated liquid layer. Immediately after recording the cut-out character images shown in Figure 1 within the solid black ink image with font sizes of 5pt, 6pt, 7pt, and 8pt, the recording medium is placed on a 50°C hot plate with the image recording surface facing upwards, and immediately dried with 120°C hot air using a dryer for 15 seconds to produce the image recording material 1. The same process was followed for printing the cut-out character images shown in Figure 1 with cyan ink, magenta ink, and yellow ink. The ejection conditions for each ink were the same: resolution of 1200 dpi × 1200 dpi and ejection frequency of 39.37 kHz.

[0159] (Preparation of Image Recording Material 2) While moving the substrate at a constant speed of 50 m / min, the pretreatment solution is applied to the substrate using a wire bar coater. The amount of pretreatment solution applied is 2.0 g / m ２ Let's assume that.

[0160] One second after the application of the pretreatment solution is completed, the pretreatment solution is dried by applying 60°C hot air at a wind speed of 22 m / s for 3 seconds using a dryer, thereby forming a pretreatment solution layer on the substrate.

[0161] A substrate with a pre-treated liquid layer is moved at a constant speed of 50 m / min, and a first ink is ejected from the first inkjet head to record a line pattern image with a width of 500 μm at 100% duty cycle. Next, cyan ink is ejected from the second inkjet head to record a solid image at 100% duty cycle, overlapping the line pattern image. Immediately after recording the solid image, the recording medium is placed on a 50°C hot plate with the image recording surface facing upwards, and immediately dried with 120°C hot air using a dryer for 15 seconds to produce image recording material 2 (K-C). Image recording material 2 (K-C) has a solid image of cyan ink recorded on top of a line pattern image of black ink.

[0162] In the same manner as described above, image recording 2 (K-M) is created in which a solid magenta ink image is recorded on a black ink line pattern image; image recording 2 (K-Y) is created in which a solid yellow ink image is recorded on a black ink line pattern image; image recording 2 (C-M) is created in which a solid magenta ink image is recorded on a cyan ink line pattern image; image recording 2 (Y-C) is created in which a yellow ink line pattern image is recorded on a cyan ink solid image; and image recording 2 (M-Y) is created in which a solid yellow ink image is recorded on a magenta ink line pattern image.

[0163] Image recordings 1 and 2 are used to evaluate image cracking, image clarity, and inter-color mixing. The evaluation method is as follows. The evaluation results are shown in Tables 4 to 7.

[0164]

[0165]

[0166]

[0167]

[0168] <Image Crack Evaluation> In image recording 1, the solid image area was observed with the naked eye and with an optical microscope (magnification 60x). The evaluation criteria are as follows: Evaluations A and B are acceptable for practical purposes. A: No image cracks are visible to the naked eye, and no image cracks are visible with an optical microscope. B: No image cracks are visible to the naked eye, but slight image cracks are visible with an optical microscope. C: Slight image cracks are visible to the naked eye. D: Image cracks are clearly visible to the naked eye.

[0169] <Image Clarity> In image recording 1, the cutout text images shown in Figure 1 were observed with the naked eye and under an optical microscope (60x magnification) in order from font size 5pt to 8pt. The evaluation criteria are as follows: A, B, and C ratings indicate no practical problems. A: Font size 5pt can be read clearly. B: Font size 5pt cannot be read clearly, but font size 6pt can be read clearly. C: Font sizes 5pt and 6pt cannot be read clearly, but font size 7pt can be read clearly. D: Font sizes 5pt, 6pt, and 7pt cannot be read clearly, but font size 8pt can be read clearly. E: Font size 8pt cannot be read clearly.

[0170] <Inter-color mixing> Image recordings 2 (K-C), in which a solid cyan ink image was recorded on a black ink line pattern image, image recording 2 (K-M), in which a solid magenta ink image was recorded on a black ink line pattern image, image recording 2 (K-Y), in which a solid yellow ink image was recorded on a black ink line pattern image, image recording 2 (C-M), in which a solid magenta ink image was recorded on a cyan ink line pattern image, image recording 2 (Y-C), and image recording 2 (M-Y), in which a line pattern image of yellow ink was recorded on a solid magenta ink image, were observed with an optical microscope. The width of the overlapping area was measured at 10 locations and the average value was calculated. Inter-color mixing was evaluated based on the width of the overlapping area. The evaluation criteria are as follows: Ranks A, B, and C are at a level that does not pose a practical problem. A: The width is less than 700 μm. B: Width is 700 μm or more and less than 800 μm. C: Width is 800 μm or more and less than 900 μm. D: Width is 900 μm or more and less than 1000 μm. E: Width is 1000 μm or more.

[0171] As shown in Tables 4 and 5, in Examples 1 to 6, all of equations (1) to (5) were satisfied, so image cracking was suppressed, image clarity was excellent, and color mixing between colors was suppressed.

[0172] On the other hand, in Comparative Example 3, it was found that image cracking could not be suppressed because formula (1) was not satisfied. Also, in Comparative Example 4, it was found that the image clarity was poor and color mixing could not be suppressed because formula (2) was not satisfied. Comparative Examples 5 and 6, which used the same ink set, did not satisfy formula (3). As a result, in Comparative Example 5, where the cohesive force of the pretreatment solution was strong, image cracking could not be suppressed due to the ink that was prone to coagulation, and in Comparative Example 6, where the cohesive force of the pretreatment solution was weak, image clarity was poor due to the ink that was not prone to coagulation, and color mixing could not be suppressed. On the other hand, in Comparative Example 1, it was found that image cracking could not be suppressed because formula (4) was not satisfied. Also, in Comparative Example 2, it was found that the image clarity was poor and color mixing could not be suppressed because formula (5) was not satisfied.

[0173] Furthermore, the disclosures of Japanese Patent Application No. 2024-208697, filed on November 29, 2024, and Japanese Patent Application No. 2025-088356, filed on May 27, 2025, are incorporated herein by reference in their entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if the incorporation of each individual document, patent application, and technical standard were specifically and individually noted.

Claims

1. A pretreatment solution containing a flocculant; a black ink containing water, black pigment, pigment dispersion resin, and binder resin; a cyan ink containing water, cyan pigment, pigment dispersion resin, and binder resin; a magenta ink containing water, magenta pigment, pigment dispersion resin, and binder resin; and a yellow ink containing water, yellow pigment, pigment dispersion resin, and binder resin, wherein the viscosity of the black ink, cyan ink, magenta ink, and yellow ink at 25°C is 3.5 mPa·s to 8.0 mPa·s; the amount of pretreatment solution required to add the pretreatment solution to 20 mL each of the black ink, cyan ink, magenta ink, and yellow ink so that the viscosity of each ink at 25°C after addition exceeds 15 mPa·s is Ak, Ac, Am, and Ay, respectively, in units of μL. A water-based inkjet ink set for non-permeable substrates that satisfies the following equations (1) to (5), where the maximum viscosity of each ink after addition at 25°C is given in units of mPa·s as μk, μc, μm, and μy, with Amin being the minimum value and Amax being the maximum value among Ak, Ac, Am, and Ay, and μmin being the minimum value and μmax being the maximum value among μk, μc, μm, and μy: Amin ≥ 500 …(1) Amax ≤ 3000 …(2) Amax / Amin ≤ 2 …(3) μmin ≥ 200 …(4) μmax ≤ 2000 …(5) 2. The aqueous inkjet ink set for a non-permeable substrate according to claim 1, wherein the flocculant comprises at least one selected from the group consisting of polyvalent metal compounds, organic acids, and water-soluble cationic polymers.

3. The aqueous inkjet ink set for a non-permeable substrate according to claim 1, wherein the mass ratio of the coagulant contained in the pretreatment liquid is F, and the mass ratios of the binder resin contained in the black ink, cyan ink, magenta ink, and yellow ink are Pk, Pc, Pm, and Py, respectively, satisfying the following formulas (6) to (9): 0.5 ≤ Pk / F ≤ 2.0 …(6) 0.5 ≤ Pc / F ≤ 2.0 …(7) 0.5 ≤ Pm / F ≤ 2.0 …(8) 0.5 ≤ Py / F ≤ 2.0 …(9) 4. The aqueous inkjet ink set for a non-permeable substrate according to claim 1, wherein the binder resin contains resin particles, and the resin particles are particles containing a resin selected from the group consisting of acrylic resin, polyester resin, and urethane resin.

5. The aqueous inkjet ink set for a non-permeable substrate according to claim 1, wherein the pretreatment liquid further comprises resin particles, and the resin particles are at least one selected from the group consisting of particles containing acrylic resin, particles containing polyester resin, particles containing urethane resin, and composite particles containing acrylic resin and polyester resin.

6. An image recording method comprising: using the aqueous inkjet ink set for a non-permeable substrate described in any one of claims 1 to 5, and comprising the steps of: applying the pretreatment liquid to a non-permeable substrate to form a pretreatment layer; and applying the black ink, the cyan ink, the magenta ink, and the yellow ink to at least a portion of the pretreatment layer using an inkjet recording method to record an image.

7. An image recording material comprising: an impermeable substrate; a pretreatment layer disposed on the impermeable substrate and containing a non-volatile component of the pretreatment solution; and an ink layer disposed on at least a portion of the pretreatment layer and containing a non-volatile component of the black ink, the cyan ink, the magenta ink, and the yellow ink.

Images