Ink set, inkjet recording method, print medium, and print medium set

Abstract

To provide an ink set, an inkjet printing method, a printing media, and a printing media set capable of providing a printed image that is extremely excellent in bleeding between colors, further does not deteriorate the bleeding between colors irrespective of a storage period.SOLUTION: An ink set containing a first ink composition containing water, a first coloring agent, a first silicone surfactant, and a first nonionic surfactant; and a second ink composition containing water, a second coloring agent, a second silicone surfactant and a second nonionic surfactant, and is applied onto a first image formed using the first ink composition to form a second image is provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set, an inkjet printing method, a print medium, and a print media set. [Background technology]

[0002] Among various color printing methods, inkjet printing, one of the most representative methods, generates small droplets of ink and deposits them on a printing medium such as paper to print. In recent years, demand for inkjet printers for industrial use has increased, and there is a demand for inks that can be used to print on a variety of printing media.

[0003] Among printing media, inks that wet and spread well on non-ink-absorbent media and poorly ink-absorbent media (hereinafter sometimes referred to as "non-ink-absorbent or poorly ink-absorbent media") are in demand. Good wet and spreadability on media means that a larger area can be colored using the same amount of ink droplets (in other words, the ink dot diameter becomes larger), thereby reducing ink consumption. However, non-ink-absorbent or poorly ink-absorbent media are media that have poor ink absorption. As a result, ink does not soak into the media easily, and compared to ink-absorbent media, the ink wets and spreads poorly, generally resulting in smaller ink dot diameters. For this reason, improvements are needed.

[0004] Furthermore, print quality requires minimal graininess. Inks containing water-insoluble colorants are in a non-uniform state (not in a solution state, but in a dispersion state). When solid printing is performed on print media using such non-uniform ink, the printed image may appear to have scattered grains of varying shades, resulting in an inconsistent image. Such printed images are evaluated as having "graininess" and are one of the factors that significantly degrade print quality. For this reason, there is a strong demand for inks that produce printed images with minimal graininess. For example, Patent Documents 1 to 3 disclose ink compositions that combine specific organic solvents and surfactants, and disclose inks that have good wetting and spreading properties for non- or poorly ink-absorbing media.

[0005] Furthermore, when performing color printing, an ink set consisting of multiple colors is used. It is known that when performing color printing using such an ink set, bleeding between the first and second colors can occur when the landing positions of a first color ink and a second color ink are adjacent to each other on the printing medium. This "inter-color bleeding" is one of the factors that significantly deteriorates print quality. Therefore, there is a demand for eliminating this inter-color bleeding, and ink sets that solve this problem have been proposed.

[0006] Patent Document 4 discloses an ink containing a polyalkoxylate of an acetylene glycol surfactant in order to eliminate this inter-color bleeding, and proposes an ink that can produce high-quality images without color unevenness or inter-color bleeding for non-ink or poorly ink-absorbing media. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-044188 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-139004 [Patent Document 3] International Publication No. 2011 / 136000 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-136573 Summary of the Invention [Problem to be solved by the invention]

[0008] However, it has been found that the problem of inter-color bleeding involves more complex factors. That is, in the early stages of printing, printing can be performed using a combination of a first color ink composition and a second color ink composition, both of which have been manufactured only recently (in other words, both are new). Therefore, by selecting and using an ink set that takes inter-color bleeding into consideration, high-quality printing without inter-color bleeding can be performed.

[0009] However, as printing continues, the consumption of each ink composition varies depending on the color of the ink composition. Therefore, when an ink composition with a high consumption rate runs out, it is replaced with a new ink composition. On the other hand, an ink composition with a low consumption rate continues to be used until the ink composition initially used runs out. As a result, new and old ink compositions are used in combination. There may be a difference of several months to a year in the shelf life before use between an ink composition with a high consumption rate and an ink composition with a low consumption rate. When printing is performed using ink compositions with different shelf lives in combination, there may be no significant change in the storage stability (various physical properties such as ejection performance, average particle size, viscosity, and pH) of the ink compositions themselves, but inter-color bleeding may worsen, resulting in a deterioration in print quality. A solution to this problem is desired.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide an ink set that makes it possible to provide printed images that have extremely good inter-color bleeding and that do not deteriorate over storage periods, an inkjet recording method that uses the ink set, a printing medium, and a printing media set. [Means for solving the problem]

[0011] As a result of extensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by the inventions described in the following [1] to

[12] , and have completed the present invention.

[0012] That is, the present invention relates to the following [1] to

[12] . [1] A first ink composition containing water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; a second ink composition containing water, a second colorant, a second silicone surfactant, and a second nonionic surfactant, and applied onto a first image formed using the first ink composition to form a second image, The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): [ka] (In the formula, a is an integer of 1 to 80, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, and R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1, the content of the first nonionic surfactant is A2, the content of the second silicone surfactant is B1, and the content of the second nonionic surfactant is B2, 0.10 ≦(B1-A1)+(B2-A2)≦ 0.95 Meet the ink set. [2] The ink set according to [1], wherein in the formula (1), m and n are each independently an integer of 1 to 30. [3] The ink set according to [1] or [2], wherein one or both of the first ink composition and the second ink composition further contain a binder. [4] The ink set according to [3], wherein the binder contains at least one selected from waxes and (meth)acrylic acid-based polymers. [5] The ink set according to [4], wherein the wax is one or more selected from the group consisting of polyalkylene wax, polyalkylene oxide wax, and paraffin wax. [6] The ink set according to [4] or [5], wherein the wax is an oxidized polyethylene wax. [7] The ink set according to any one of [1] to [6], wherein the first nonionic surfactant and the second nonionic surfactant have an HLB value of 6.0 or greater. [8] An inkjet recording method using the ink set according to any one of [1] to [7], ejecting droplets of the first ink composition onto a print medium to form a first image; and a step of ejecting droplets of the second ink composition and depositing them onto the print medium on which the first image has been formed, thereby forming a second image. [9] A printing medium in which a second image is formed by applying the second ink composition onto a first image formed by applying the first ink composition contained in the ink set according to any one of [1] to [7].

[10] An ink-media set comprising the ink set according to any one of [1] to [7] and a print medium.

[11] An ink composition for forming a first image, which is used together with an ink composition for forming a second image by being applied onto a first image, comprising: the ink composition for forming the first image contains water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; the ink composition for forming the second image contains water, a second colorant, a second silicone surfactant, and a second nonionic surfactant; The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): [ka] (In the formula, a is an integer of 1 to 80, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, and R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1, the content of the first nonionic surfactant is A2, the content of the second silicone surfactant is B1, and the content of the second nonionic surfactant is B2, 0.10 ≦(B1-A1)+(B2-A2)≦ 0.95 Ink composition that satisfies the above requirements.

[12] An ink composition for forming a second image, which is used together with an ink composition for forming a first image on which a second image is formed, the ink composition for forming the first image contains water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; the ink composition for forming the second image contains water, a second colorant, a second silicone surfactant, and a second nonionic surfactant; The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): [ka] (In the formula, a is an integer of 1 to 80, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, and R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1, the content of the first nonionic surfactant is A2, the content of the second silicone surfactant is B1, and the content of the second nonionic surfactant is B2, 0.10 ≦(B1-A1)+(B2-A2)≦ 0.95 Ink composition that satisfies the above requirements. [Effects of the Invention]

[0013] The present invention can provide an ink set, an inkjet printing method, a printing medium, and a printing medium set that can provide printed images that have extremely good intercolor bleeding and that do not deteriorate over storage periods. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Ink set> The ink set according to the present invention comprises a first ink composition containing water, a first colorant, a first silicone surfactant, and a first nonionic surfactant, and a second ink composition containing water, a second colorant, a second silicone surfactant, and a second nonionic surfactant, and which is applied onto a first image formed using the first ink composition to form a second image.

[0015] [First ink composition] The first ink composition contains water, a first colorant, a first silicone surfactant, and a first nonionic surfactant, and optionally further contains other components, such as a dispersant and an ink preparation agent.

[0016] (First Colorant) The first colorant is not particularly limited as long as it is a water-insoluble colorant. In the specification and claims of this application, a water-insoluble colorant refers to a colorant whose solubility in 1 liter of water at 25°C is typically 5 g or less, preferably 3 g or less, more preferably 1 g or less, and even more preferably 0.5 g or less. The lower limit of the solubility includes 0 g. Hereinafter, unless otherwise specified, a "water-insoluble colorant" will also be simply referred to as a "colorant." Examples of colorants that can be used include known pigments, disperse dyes, solvent dyes, and water-insoluble resins colored with colorants such as dyes and pigments. The colorant is preferably a pigment. Examples of pigments include inorganic pigments, organic pigments, and extender pigments.

[0017] Examples of inorganic pigments include carbon black, titanium oxide, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides. Preferred carbon blacks for use in black inks include thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon; the Monarch series, Regal series, and Mogul series manufactured by Cabot Corporation; the ColorBlack series, Printex series, SPECIALBLACK series, and Nerox series manufactured by Orion Engineered Carbons; and the MA series, MCF series, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, and No. 2300 manufactured by Mitsubishi Chemical Corporation.

[0018] Examples of organic pigments include various pigments such as azo, diazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone. Specific examples of organic pigments include yellows such as CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 180, 185, 193, 199, 202, and 213; and CI Pigment Red. Reds such as 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, and 272; Blues such as CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, and 80; Violets such as CI Pigment Violet 19, 23, 29, 37, 38, and 50; Oranges such as CI Pigment Orange 13, 16, 68, 69, 71, and 73; Greens such as CI Pigment Green 7, 36, and 54; and CI Pigment Examples of pigments include various black colors such as Black 1.

[0019] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. Extender pigments are often used in combination with other colorants.

[0020] The disperse dye may be any known disperse dye, and among them, dyes selected from CI Disperses are preferred. Specific examples thereof include yellows such as CI Dispers Yellow 9, 23, 33, 42, 49, 54, 58, 60, 64, 66, 71, 76, 79, 83, 86, 90, 93, 99, 114, 116, 119, 122, 126, 149, 160, 163, 165, 180, 183, 186, 198, 200, 211, 224, 226, 227, 231, and 237; reds such as CI Dispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, and 283; and CI Dispers Orange. Examples of disperse dyes include oranges such as 9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, and 97; violets such as CI Disperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, and 79:1; and blues such as CI Disperse Blue 27, 56, 60, 79:1, 87, 143, 165, 165:1, 165:2, 181, 185, 197, 202, 225, 257, 266, 267, 281, 341, 353, 354, 358, 364, 365, and 368.

[0021] The content of the colorant relative to the total mass of the ink composition is usually 1 to 30%, preferably 1 to 10%, and more preferably 2 to 7%. Herein, in the specification and claims of the present application, "%" and "parts" are written on a mass basis unless otherwise specified. The average particle size of the colorant is usually 50 nm to 250 nm, and preferably 60 nm to 200 nm. In the specification and claims of this application, the average particle size refers to the particle size at 50% of the integrated value in the particle size distribution determined by a laser diffraction / scattering method.

[0022] A dispersant is preferably used to disperse a water-insoluble colorant in the ink composition. The dispersant is not particularly limited, and known dispersants can be used. Polymer dispersants such as resins are generally used as dispersants. Examples of such resins include polymers derived from polyvinyl alcohol, cellulose derivatives, polyethylene oxide, polypropylene oxide, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoesters, maleic acid, maleic acid monoesters, fumaric acid, fumaric acid monoesters, vinyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, ionic monomers such as α,β-unsaturated monomers of sulfonated vinylnaphthalene, styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, and N-butoxymethylacrylamide.

[0023] Examples of resins used as dispersants include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from the group consisting of styrene and its derivatives, vinylnaphthalene and its derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, faric acid and its derivatives, vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and derivatives thereof. Examples of such copolymers include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, (meth)acrylic acid ester-(meth)acrylic acid copolymers, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers, and styrene-maleic acid copolymers. Among these, styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymer are preferred; styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer are more preferred; (meth)acrylic acid ester-(meth)acrylic acid copolymer is even more preferred; and methacrylic acid ester-methacrylic acid copolymer is particularly preferred. In the specification and claims of this application, the term "(meth)acrylic acid" is used to mean both "acrylic acid" and "methacrylic acid." Similarly, "(meth)acrylate" means both methacrylate and acrylate. Examples of types of copolymers include block copolymers, random copolymers, and graft copolymers, and / or salts thereof.

[0024] Resins used as dispersants can be synthesized or commercially available, such as styrene-acrylic copolymers such as JONCRYL 62, 67, 68, 678, and 687 (manufactured by BASF), Movinyl S-100A (modified vinyl acetate copolymer manufactured by Japan Coating Resins), and Jurymer AT-210 (polyacrylic acid ester copolymer manufactured by Toagosei Co., Ltd.). Preferred examples of copolymers obtained by synthesis include the AB block polymers disclosed in WO 2013 / 115071.

[0025] The acid value of the dispersant is usually 90 to 200 mgKOH / g, preferably 100 to 150 mgKOH / g, and more preferably 100 to 120 mgKOH / g. The mass average molecular weight of the dispersant is usually 10,000 to 60,000, preferably 10,000 to 40,000, more preferably 15,000 to 30,000, and even more preferably 20,000 to 25,000. The PDI (mass average molecular weight / number average molecular weight) of the dispersant is about 1.29 to 1.49. By setting the PDI within this range, the dispersibility and storage stability of the ink composition can be improved.

[0026] Examples of neutralizing agents used to dissolve a colorant dispersion prepared using a block copolymer in water include ammonia, alkali metal hydroxides, alkaline earth metal hydroxides, aliphatic amine compounds, and alkanolamine compounds. Ammonia and alkali metal hydroxides are preferred, with ammonia being particularly preferred. The amount of neutralizing agent used is not particularly limited. As a guideline, the degree of neutralization is typically 30 to 300%, more preferably 50 to 200%, with 100% neutralization being defined as neutralization with the theoretical equivalent of the acid value of the dispersant.

[0027] The resin as the dispersant can be used either in a state where it is mixed with the colorant, or in a state where a part or all of the surface of the colorant is coated with the resin as the dispersant, or both of these states can be used in combination. The ink composition is preferably prepared by preparing a dispersion containing a water-insoluble colorant and a resin as a dispersant, and then mixing it with other components. A known method can be used to prepare the dispersion. One example is the phase inversion emulsification method. Specifically, a resin as a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizer is added to prepare an emulsion. A colorant is then added to the resulting emulsion, followed by a dispersion treatment. The organic solvent and a portion of the water are removed from the resulting solution by vacuum distillation, yielding the desired dispersion. The dispersion treatment can be carried out using, for example, a sand mill (bead mill), a roll mill, a ball mill, a paint shaker, an ultrasonic disperser, a microfluidizer, etc. When using a sand mill, for example, beads with a particle diameter of about 0.01 mm to 1 mm are used, and the dispersion treatment can be carried out by appropriately setting the bead packing rate. The dispersion obtained as described above can be subjected to filtration and / or centrifugation, etc. This operation allows the particle diameter of the particles contained in the dispersion to be uniform. If foaming occurs during the preparation of the dispersion, a very small amount of a known antifoaming agent such as a silicone-based or acetylene glycol-based agent can be added. Other methods for preparing the dispersion liquid include acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, and spray drying. Of these, acid precipitation and interfacial polymerization are preferred.

[0028] The average particle size (D50) of the colorant dispersion in the dispersion is usually 300 nm or less, preferably 30 to 280 nm, more preferably 40 to 270 nm, and even more preferably 50 to 250 nm. Furthermore, D90 is usually 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less. The lower limit is preferably 100 nm. D10 is usually 10 nm or more, preferably 20 nm or more, and more preferably 30 nm or more, with the upper limit being 100 nm. By ensuring that the particle size of the colorant in the dispersion is within the above range, the storage stability of the ink is ensured, and the ink is ejected stably without clogging the inkjet head nozzles. Here, the average particle size (D50) is the particle size at which the cumulative particle size distribution from the small particle size side in the particle size distribution obtained by the laser diffraction / scattering method is 50%, D10 is the particle size at which the cumulative particle size distribution from the small particle size side is 10%, and D90 is the particle size at which the cumulative particle size distribution from the small particle size side is 90%.

[0029] (First silicone surfactant) It is important for ink compositions to have sufficient wettability on non-ink-absorbent or poorly ink-absorbent media. To achieve this, surfactants are commonly used. Various surfactants, including silicone-based, fluorine-based, and acetylene-based surfactants, are widely known for their wettability, depending on the application. Among these, silicone-based surfactants excel in their ability to provide wettability. However, the present inventors have observed that when printing inks with different storage periods, intercolor bleeding worsens depending on the structure of each silicone-based surfactant, even though the storage stability of the inks themselves (various physical properties such as ejection performance, average particle size, viscosity, and pH) remains unchanged. According to the Journal of the Japan Society of Color Materials, Vol. 74, No. 1, pp. 34-38 (by Koji Sakuta), it has been confirmed that silicone-based surfactants generally decompose over time during long-term storage. From this, it is inferred that silicone-based surfactants with specific structures lose their ability to control intercolor bleeding due to structural decomposition.

[0030] The present inventors have investigated the relationship between the structure of a silicone surfactant and changes in inter-color bleeding over time, and have found that by using a silicone surfactant represented by the following formula (1) as the first surfactant, it is possible to provide a set of ink compositions that can produce printed images that do not deteriorate in inter-color bleeding, regardless of whether the storage periods of the two ink compositions are the same or different. The reason why changes in inter-color bleeding over time can be suppressed is not clear, but it is thought that this is because by using a silicone surfactant represented by formula (1), even if the structure decomposes over time, most of the structural portion consisting of the hydrophobic part of the siloxane structure (-Si-O-) and the hydrophilic part consisting of an ethyleneoxy group and a propyleneoxy group is maintained, so that the function as a surfactant is not impaired. [ka]

[0031] In formula (1), a is an integer of 1 to 80, preferably 2 to 40. x and y each independently represent an integer of 1 to 4, preferably 1 to 3. m and n each independently represent an integer of 1 to 50, preferably 2 to 40, and more preferably 4 to 20. o and p each independently represent an integer of 0 to 40, preferably 0 to 20, and more preferably 0 to 10. m+n is 2-100, preferably 4-80, and more preferably 8-40. o+p is 0 to 80, preferably 0 to 40, and more preferably 0 to 20. R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group, and are preferably a hydrogen atom.

[0032] The content of the silicone surfactant represented by formula (1) in the ink composition is usually 0.01 to 3%, preferably 0.05 to 2%, more preferably 0.1 to 1%. Specific examples of commercially available silicone surfactants represented by formula (1) include Silwet CoatOSil 2812, Silwet CoatOSil 2816, Silwet CoatOSil 3500, and Silwet CoatOSil 3500 manufactured by Momentive Performance Materials. 3505, BYK-Chemie BYK-331, BYK-333, BYK-UV3500, BYK-New Product 1 General Grade and BYK-New Product 2 Cyclic Siloxane Reduced Grade described in the document published on June 22, 2020 (URL: https: / / www.byk.com / ja / company-news / media / news / detail / japanese-news-20200622-new-silicone-surface-modifier-for-aqueous-systems), Tegoglide 410, Tegoglide 432, Tegoglide 435, Tegoglide 440, and Tegoglide 450 manufactured by Evonik Degussa, and Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd. The silicone surfactant represented by formula (1) can be synthesized by a platinum-catalyzed hydrosilylation reaction using polyethylene glycol with an allyl group at one end and polydimethylsiloxane containing hydrogen groups at both ends.

[0033] (First nonionic surfactant) The first nonionic surfactant is a nonionic surfactant other than a silicone surfactant, having an HLB value of 6.0 or more but less than 12.0. The HLB value of the nonionic surfactant is preferably 6.5 to 11.0, more preferably 7.0 to 10.0. By setting the partition coefficient within this range, it is possible to further improve inter-color bleeding, which is insufficient when using a silicone surfactant alone. In the specification and claims of this application, the "HLB value" refers to the value calculated by the HLB value calculation method shown on p. 324 and following of "Surfactant Handbook" (edited by Nishiichiro et al., Sangyo Tosho Co., Ltd., 1960) (see "Surfactant Handbook" (edited by Nishiichiro et al., Sangyo Tosho Co., Ltd., 1960, p. 324).

[0034] [How to calculate HLB value] A solution is obtained by dissolving 0.5 g of a nonionic surfactant in 5 mL of ethanol. The resulting solution is stirred at 25°C, and a 2% by weight aqueous phenol solution is added dropwise to the solution. The endpoint is when the solution becomes cloudy. When the amount of 2% by weight aqueous phenol solution required to reach the endpoint is Q (mL), the HLB value is calculated using the following formula, and the result is rounded to one decimal place to obtain the HLB value. HLB value = 0.89×Q+1.11

[0035] The first nonionic surfactant is preferably a nonionic surfactant represented by the following formula (2). [ka] In formula (2), R 3represents a linear or branched hydrocarbon group having 6 to 20 carbon atoms. The linear or branched hydrocarbon group is preferably a linear alkyl group or a branched alkyl group. The branched alkyl group is preferably a branched alkyl group in which an alkyl group is substituted on the 1st or 2nd carbon atom. The linear alkyl group may have a substituent at its terminal, and the substituent is, for example, a benzyl group or a naphthyl group. When the linear alkyl group and the branched alkyl group have a substituent, the total number of carbon atoms is 6 to 20. s represents the number of propyleneoxy groups, and t represents the number of ethyleneoxy groups, where s is 1 to 20 and t is 0 to 5.

[0036] Examples of nonionic surfactants having an HLB value within the above range include Newcol 2303 (7.9) and Newcol NT-3 (6.3) manufactured by Nippon Nyukazai Co., Ltd., GENAPOL EP2564 (7.4) and GENAPOL EP2584 (8.2) manufactured by Clariant, Lutensol XL40 (8.1) and Lutensol FT XL70 (11.1) manufactured by BASF, BYK DYNWET 800N (8.1) and BYK-LP X 7113 (9.9) manufactured by BYK-Chemie, and TEGO Wet500 (6.5), TEGO Wet505 (8.2), and TEGO Wet510 (9.1) manufactured by EVONIC.

[0037] The content of the first nonionic surfactant in the first ink composition is 0.01 to 2%, preferably 0.05 to 1.5%, and more preferably 0.1 to 1% by mass.

[0038] (Ink preparation agent) Examples of ink preparation agents include binders, penetrants, viscosity adjusters, surfactants other than silicone surfactants, preservatives, antifungal agents, pH adjusters, chelating agents, rust inhibitors, water-soluble ultraviolet absorbers, and antioxidants. The total content of ink preparation agents excluding binders, penetrants, and viscosity modifiers is usually about 0 to 30%, preferably about 0.1 to 20%, and more preferably about 0.5 to 10%, based on the total mass of the ink composition.

[0039] (a) Binder The binder is preferably at least one selected from waxes and (meth)acrylic acid-based polymers. By including a binder in the ink composition, the scratch resistance of the printed image can be improved. The binder is preferably included in the form of an emulsion, and an aqueous emulsion is more preferred. The average particle size of the binder is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head. When the ink composition contains a binder, the content of the binder relative to the total mass of the ink composition, calculated as solid content, is usually 0.1 to 14%, preferably 0.5 to 12%, more preferably 2 to 10%, and even more preferably 3 to 8%. Such a content can improve the scratch resistance of the printed image.

[0040] As the wax, natural wax and synthetic wax can be used. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; plant-based waxes such as carnauba wax and candelilla wax; and emulsions of animal and plant-based waxes such as beeswax and lanolin dispersed in an aqueous medium. Examples of synthetic waxes include polyalkylene waxes (preferably poly C2-C4 alkylene waxes), oxidized polyalkylene waxes (preferably poly C2-C4 alkylene waxes), and paraffin waxes. Among these, one or more waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, and oxidized polyethylene wax is more preferred. Commercially available wax emulsions include, for example, CERAFLOUR 925, 929, 950, and 991 manufactured by BYK-Chemie; AQUACER 498, 515, 526, 531, 537, 539, 552, and 1547; AQUAMAT 208, 263, and 272; and MINERPOL 221 manufactured by Mitsui Chemicals, Inc.; Mitsui Hiwax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, and NP505 manufactured by Mitsui Chemicals, Inc.; and KUE-100 and 11 manufactured by Sanyo Chemical Co., Ltd. Among these, AQUACER 515, 531, 537, 539, and 1547 are preferred, and AQUACER 515, 531, 537, and 1547 are more preferred.

[0041] The (meth)acrylic acid-based polymer used as the binder is a polymer different from the dispersant described above. The (meth)acrylic acid-based polymer is preferably a (meth)acrylic acid-based polymer composed of four types of monomers: C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate. The C1-C4 alkyl methacrylate preferably has a linear or branched alkyl moiety, more preferably a linear alkyl moiety. The C1-C4 alkyl methacrylate is preferably a C1-C3 alkyl methacrylate, more preferably a C1-C2 alkyl methacrylate, and even more preferably methyl methacrylate. The C6-C10 alkyl acrylate preferably has a linear or branched alkyl moiety, more preferably a branched alkyl moiety. The C6-C10 alkyl acrylate is preferably a C7-C9 alkyl acrylate, more preferably a C8 alkyl acrylate, and even more preferably 2-ethylhexyl acrylate. The contents of the four monomers, C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate, in the (meth)acrylic acid-based polymer are typically 40-60%, 38-58%, 1-10%, and 1-5%, respectively, by mass, and preferably 45-55%, 52-42%, 2-4%, and 1-3%, and it is preferable that the total of these monomer contents be 100%. The acid value (unit: mgKOH / g) of the (meth)acrylic acid-based polymer is usually -10 to 35, preferably -5 to 30, and more preferably 0 to 25. The glass transition temperature (Tg) of the (meth)acrylic acid polymer is usually from -20 to 30°C, preferably from -15 to 25°C, and more preferably from -10 to 20°C.

[0042] (b) Penetrant The ink composition may further contain at least one organic solvent selected from glycol ethers and C4-C9 alkanediols, each having a water-octanol partition coefficient of 0.00 or more and less than 2.00, as a penetrant, which tends to improve the ink's wetting, spreading, and drying properties on non- or poorly ink-absorbing media. Examples of penetrants having a Clog P within the above numerical range include 1,2-pentanediol (-0.00), ethylene glycol monoallyl ether (0.03), isopropyl alcohol (0.07), isopropyl glycol (0.09), diethylene glycol ethyl methyl ether (0.13), dipropylene glycol dimethyl ether (0.36), 3-methoxy-3-methyl-1-butanol (0.42), butyl triglycol (0.49), diethylene glycol diethyl ether (0.52), 1,2-hexanediol (0.53), diethylene glycol monoisobutyl ether (0.54), propyl propylene glycol (0.62), butyl diglycol (0.67), and dipropylene glycol. n-propyl ether (0.75), 2,2-diethyl-1,3-propanediol (0.82), 2,2,4-trimethyl-1,3-pentanediol (1.00), 2-ethyl-1,3-hexanediol (1.26), 1,2-octanediol (1.58), and hexyl diglycol (1.72). The total content of these in the total mass of the ink composition is usually 0.1 to 30%, preferably 0.2 to 20%, more preferably 0.5 to 10%, even more preferably 2 to 8%, and particularly preferably 4 to 6%.

[0043] (c) Viscosity modifier The ink composition may further contain a viscosity modifier. Industrial inkjet printers usually have a predetermined viscosity range for the ink that can be ejected based on the specifications of the printer head (the head that ejects the ink) installed in the printer. Therefore, a viscosity modifier can be added to the ink to adjust the viscosity to an appropriate range. The viscosity adjuster is not particularly limited as long as it can adjust the viscosity of the ink, and known substances can be used. Specific examples include water-soluble organic solvents (excluding the "organic solvents" listed above as penetrants), sugars, and the like. Among these, water-soluble organic solvents with a ClogP value typically less than 0.00, preferably -0.05 or less, and more preferably -0.08 or less, are preferred. The lower limit of the ClogP value of the water-soluble organic solvent is not particularly limited, but is typically -4.00 or greater, preferably -3.00 or greater, more preferably -2.00 or greater, and even more preferably -1.50 or greater. Examples of such water-soluble organic solvents include 2-methyl-2,4-pentanediol (-0.02), tripropylene glycol monomethyl ether (-0.03), isopropyl diglycol (-0.08), dipropylene glycol monomethyl ether (-0.16), ethanol (-0.24), 3-methyl-1,5-pentanediol (-0.24), diethylene glycol dimethyl ether (-0.26), propylene glycol monomethyl ether (-0.30), 3-methyl-1,3-butanediol (-0.33), trimethylolpropane (-0.39), N-methyl-2-pyrrolidone (-0.40), 1,2-butanediol (-0.53), 3-ethyl-3-hydroxymethyl ether (-0.53), methylpropane ... Examples include thyloxetane (-0.58), 1,5-pentanediol (-0.64), 2-methyl-1,3-propanediol (-0.64), dipropylene glycol (-0.69), 1,3-butanediol (-0.73), methyl diglycol (-0.78), methyl triglycol (-0.96), 2-pyrrolidone (-0.97), propylene glycol (-1.06), 1,4-butanediol (-1.16), diethylene glycol (-1.30), ethylene glycol (-1.37), triethylene glycol (-1.48), glycerin (-1.54), diglycerin (-2.96), Aoki Oil & Fat Industries' Glycereth-3 (-3.49), and Glycereth-20 (-5.42). The total content of the water-soluble organic solvent is usually about 0% to 55%, preferably about 5% to 40%, and more preferably about 10% to 30%.

[0044] (d) Preservatives Examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloarylsulfone compounds, iodopropargyl compounds, haloalkylthio compounds, nitrile compounds, pyridine compounds, 8-oxyquinolines, benzothiazole compounds, isothiazolinone compounds, dithiols, pyridine oxide compounds, nitropropane compounds, organic tin compounds, phenol compounds, quaternary ammonium salt compounds, triazine compounds, thiazine compounds, anilides, adamantane compounds, dithiocarbamates, brominated indanone compounds, benzyl bromoacetate compounds, and inorganic salt compounds. Specific examples of commercially available preservatives include Proxel GXL(S) and XL-2(S) manufactured by Arch Chemicals.

[0045] (e) Antifungal agents Examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, and 1,2-benzisothiazolin-3-one and salts thereof.

[0046] (f) pH adjuster Any substance can be used as the pH adjuster as long as it does not adversely affect the ink composition to be prepared and can adjust the pH to 5 to 11. Specific examples include alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (aqueous ammonia); alkali metal carbonates such as lithium carbonate, sodium carbonate, sodium bicarbonate, and potassium carbonate; alkali metal salts of organic acids such as sodium silicate and potassium acetate; and inorganic bases such as disodium phosphate.

[0047] (g) Chelating agents Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0048] (h) Rust inhibitor Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0049] (i) Water-soluble ultraviolet absorber Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0050] (j) antioxidants Examples of the antioxidant include various organic and metal complex anti-fading agents, such as hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles.

[0051] [water] The first ink composition contains the above-mentioned components and, if necessary, ink preparation agents, with the remainder being water. The water used in the ink is preferably ion-exchanged water, distilled water, or the like, which has a low content of impurities such as metal ions.

[0052] The pH of the first ink composition is usually 7 to 11, and preferably 8 to 10. The surface tension of the ink composition is usually 10 to 50 mN / m, and preferably 20 to 40 mN / m. The viscosity of the ink composition is usually 2 to 30 mPa·s, and preferably 3 to 20 mPa·s. The pH and surface tension of the ink composition can be adjusted by using a pH adjuster, a surfactant, a water-soluble organic solvent, and the like.

[0053] The first ink composition can be used in various printing applications, such as writing instruments, various printing applications, information printing, and textile printing, and is particularly preferably used in inkjet printing.

[0054] [Second ink composition] The second ink composition contains water, a second colorant, a second silicone surfactant, and a second nonionic surfactant, and optionally further contains other components. Examples of the other components include dispersants, water-soluble organic solvents, and ink preparation agents. The water, second colorant, second silicone surfactant, second nonionic surfactant, and other components may be the same as those in the first ink composition. The content of each component in the second ink composition may also be within the preferred ranges described for the first ink composition. The preferred ranges for the pH, surface tension, and viscosity of the second ink composition are the same as those for the first ink composition. The second colorant is preferably a different color from the first colorant. This is because inter-color bleeding is likely to be observed when the first and second colorants are visually distinct from each other.

[0055] The contents of the first silicone surfactant and the first nonionic surfactant in the first ink composition and the contents of the second silicone surfactant and the second nonionic surfactant in the second ink composition are determined to have a specific relationship. That is, when the content of the first silicone surfactant is A1, the content of the first nonionic surfactant is A2, the content of the second silicone surfactant is B1, and the content of the second nonionic surfactant is B2, 0.10 ≦(B1-A1)+(B2-A2)≦ 0.95 Make sure to satisfy the following. In the above relational expression, the coefficients are determined according to the degree of influence on inter-color bleeding. Satisfying this formula suppresses intercolor bleeding and achieves good print quality. It has been confirmed that if the value of this formula is outside the range, the hydrophilic-hydrophobic balance at the ink interface between the first ink composition and the second ink composition is disrupted, resulting in worsening intercolor bleeding. It has been confirmed that if the value of this formula is less than 0.10, the first ink composition bleeds into the second ink composition, while if the value of this formula is greater than 0.95, the second ink composition bleeds into the first ink composition. While the reason for this is unclear, it is speculated that when two different colors of ink are printed consecutively, if the balance of interfacial tension between the two inks is disrupted, one color bleeds into the other. It is speculated that this is due to the significant influence of surfactants and hydrophobic organic solvents oriented at the ink interface. The inventors have also discovered that the phenomenon of reduced intercolor bleeding when the above formula is satisfied only occurs when the first and second ink compositions contain a silicone surfactant represented by formula (1).

[0056] The ink set according to the present invention can realize printed images that exhibit extremely good inter-color bleeding and that do not deteriorate over storage periods. Furthermore, the ink set according to the present invention exhibits good wetting and spreading properties on non-ink-absorbent or poorly ink-absorbent media, resulting in printed images with extremely little graininess. The ink set according to the present invention is extremely useful for various printing applications, particularly inkjet printing.

[0057] <Inkjet recording method> An inkjet recording method is an inkjet recording method using the above ink set, and includes the steps of ejecting droplets of a first ink composition and depositing them onto a print medium to form a first image, and ejecting droplets of a second ink composition and depositing them onto the print medium on which the first image has been formed to form a second image. The steps of forming the first image and forming the second image can be carried out using an inkjet system.

[0058] Any known inkjet method can be used, including, for example, a charge control method, a drop-on-demand (pressure pulse) method, an acoustic inkjet method, and a thermal inkjet method. Inkjet methods also include a method for improving image quality by ejecting a large number of small volumes of ink containing a small amount of colorant, a method for improving image quality by using multiple inks that are essentially the same hue but have different concentrations of colorant, and a method for improving the fixability of colorant by using colorless, transparent ink.

[0059] <Print Media> The printing medium refers to a material to which the ink compositions of the ink set can be adhered. Examples of printing media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and color filter substrates. Print media can be broadly divided into those with and without an ink-receiving layer. The ink set described above can be applied to either type of print media, but is particularly suitable for use with print media that do not have an ink-receiving layer. Printing media having an ink-receiving layer are usually called inkjet paper, inkjet film, glossy paper, etc. Representative commercially available examples include Professional Photo Paper, Super Photo Paper, Gloss Gold, and Matte Photo Paper manufactured by Canon Inc.; Crispia (high gloss) photo paper, glossy photo paper, and matte photo paper manufactured by Seiko Epson Corporation; Advanced Photo Paper (glossy) manufactured by Hewlett-Packard Japan; and Gasai Photo Finishing Pro manufactured by Fujifilm Corporation. Examples of printing media that do not have an ink-receiving layer include various types of paper, such as coated paper and art paper, used in applications such as gravure printing and offset printing; and cast-coated paper, used in label printing. When using printing media that do not have an ink-receiving layer, it is preferable to subject the printing media to a surface modification treatment in order to improve the fixation of colorants, etc. Examples of surface modification treatments include known methods such as corona discharge treatment, plasma treatment, and flame treatment.

[0060] <Ink media set> The ink media set is a set that includes the ink set of the present invention and a printing medium.

[0061] For all of the above items, combinations of preferred items are more preferred, and combinations of more preferred items are even more preferred. The same applies to combinations of preferred items and more preferred items, and combinations of more preferred items and even more preferred items. Unless otherwise specified, all of the above-mentioned components can be used singly or in combination of two or more. [Example]

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. In the examples, when it was necessary to measure the content (solids) of colorant contained in various liquids, it was calculated as a converted value of only the colorant by the dry weight method using an MS-70 manufactured by A&D Co., Ltd.

[0063] [Preparation Example 1 of Colorant Dispersion (Dp1)] A block copolymer (block copolymer A) was obtained by reproducing Synthesis Example 3 of WO 2013 / 115071. The obtained block copolymer (4.8 parts) was dissolved in 20 parts of 2-butanone to obtain a homogeneous solution. A solution of sodium hydroxide (0.35 parts) dissolved in water (58.8 parts) was added to this solution and stirred for 1 hour to obtain a liquid. CI Pigment Blue 15:4 (hereinafter referred to as "PB15:4", 16 parts) was added to this solution and dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. Water (100 parts) was added dropwise to the obtained liquid, and the liquid was filtered to obtain a filtrate. 2-butanone and a portion of the water were distilled off from the obtained filtrate under reduced pressure using an evaporator to obtain a cyan dispersion with a colorant content of 12.0%. The obtained dispersion is designated "Dp1."

[0064] [Preparation Example 2 of Colorant Dispersion (Dp2)] A yellow dispersion with a colorant content of 12.0% was obtained in the same manner as in Preparation Example 1, except that 16 parts of CI Pigment Yellow 74 (hereinafter referred to as "PY74") was used instead of PB15:4. The obtained dispersion was designated "Dp2".

[0065] [Synthesis example of silicone surfactant B] To a 20 mL solution of 7.0 g of hexaethylene glycol allyl methyl ether in tetrahydrofuran, 5.8 g of hexadecamethyloctasiloxane and 0.1 mL of chloroplatinic acid were added, and the mixture was stirred and held at 65°C for 24 hours to react. After the reaction was complete, the solvent was removed by rotary evaporation to obtain a silicone surfactant. The obtained silicone surfactant has the formula (1), where a = 6, x = 2, y = 2, m = 7, n = 7, o = 0, p = 0, and R 1 and R 2 is a hydroxy group.

[0066] [How to calculate HLB value] The HLB value of a compound was calculated as follows. An example of calculating L 40 is given below. 500 mg of "Lutensol XL 40," a compound represented by formula (1), was dissolved in 10 mL of ethanol under stirring to obtain a solution that was visually transparent. A 25 mL burette was used to dropwise add a 2% aqueous phenol solution to this solution. As the 2% aqueous phenol solution was added, the liquid in the beaker became cloudy and did not return to transparency. The amount of 2% aqueous phenol solution added at this time, Q, was 7.8 mL. Using "Q = 7.8," the HLB value was calculated using formula (2) above (HLB value = 0.89 × 7.8 + 1.11 = 8.052), and the HLB value of the compound represented by formula (1) was calculated to be 8.1 by rounding to the nearest tenth. The HLB values ​​of the compounds listed in Table 1 were calculated in the same manner as for Lutensol XL 40.

[0067] [Preparation example of ink composition] Dispersions Dp1 and Dp2 were mixed with the components listed in Tables 1 and 2 below, and then filtered through a 3 μm membrane filter (a cellulose mixed ester type membrane filter manufactured by Advantec Co., Ltd.) to obtain ink compositions C1 to 16 and Y1 to 15 for evaluation tests. The colorant content of each ink was adjusted to 4.5% relative to the total mass of the ink composition. Ink compositions C1 to 16 listed in Table 1 are all cyan inks. Ink compositions Y1 to 15 listed in Table 2 are all yellow inks.

[0068] [Table 1] [Table 2]

[0069] Details of the components in Tables 1 and 2 are as follows: Dp1: Dispersant 1 obtained in Preparation Example 1 Dp2: Dispersant 2 obtained in Preparation Example 1 PG: Propylene glycol 1,2-HD: 1,2-hexanediol TEA: Triethanolamine TG450: TEGO Glide 450 SAG005: Silface SAG005 Surfactant A: BYK New Product 1 general grade as described in the publication dated June 22, 2020 Surfactant B: Surfactant B obtained in the synthesis example XL40: Lutensol XL40 (HLB=8.1) ·EP2564:GENAPOL EP2564(HLB=7.4) TW510: TEGO Wet510 (HLB=9.1) NT-3: Nucol NT-3 (HLB=6.3) ·EP12030:SOFTANOL EP12030(HLB=4.5) ·XL70:Lutensol XL70(HLB=11.1) ·XL100:Lutensol XL100(HLB=14.3)

[0070] [Examples 1 to 11 and Comparative Examples 1 to 11] The ink compositions C1 to C18 and Y1 to 18 prepared as described above were each stored at room temperature for 4 weeks, and then combined as the first ink composition and the second ink composition as shown in Tables 3 and 4 to prepare the ink sets of Examples 1 to 11 and Comparative Examples 1 to 11.

[0071] [(A) Evaluation of intercolor bleeding (initial stage)] (1) Preparation of test piece 1 Using the ink sets of Examples 1 to 11 and Comparative Examples 1 to 11, a single linear image (second image) of 100% second ink composition with a line width of 1.0 mm was printed on top of a solid image (first image) of 100% first ink composition, resulting in a printed image. Printing was performed using a printing tool equipped with two KJ4B inkjet heads manufactured by Kyocera Corporation, in the order of the first ink composition and the second ink composition, under conditions of a frequency of 10 kHz and binary (medium droplet) printing, using "OK Topcoat+" manufactured by Oji Paper Co., Ltd. as the printing medium. The two inkjet heads were installed in a print evaluation device, with the first ink composition and the second ink composition being printed from the upstream side in the feed direction of the printing medium. The distance between the inkjet heads filled with the first ink composition and the second ink composition was set to 90 mm. The resulting printed image was dried for 3 seconds under an IR heater set at 100°C to obtain test piece 1. The line width of the second image formed on the first image of the test piece was measured using a print image evaluation device PIAS-II manufactured by QEA. (2) Preparation of test piece 2 Using the ink sets of Examples 1 to 11 and Comparative Examples 1 to 11, a solid image (second image) made of 100% of the second ink composition was printed so as to overlap a linear image (first image) made of 100% of the first ink composition and having a line width of 1.0 mm, thereby obtaining a printed image. The printing apparatus, conditions, and printing media used were the same as in (1). The obtained printed image was dried in the same manner as in (1), to obtain test piece 2. The line width of the first image observed through the second image on test piece 2 was measured. (3) Evaluation The line width ratio was calculated by dividing the measured line width by the line width of 1.0 mm, and evaluated using the following four-level evaluation criteria. The smaller the line width ratio, the better the performance in preventing intercolor bleeding. The evaluation results are shown in Tables 3 and 4 below. [Evaluation criteria] D: Ratio 101% or more C: Ratio 51~100% B: Ratio 26~50% A: Ratio 25% or less

[0072] [Table 3] [Table 4]

[0073] [Examples 12 to 22 and Comparative Examples 12 to 22] An accelerated test was performed on the first ink composition in Tables 5 and 6 by storing it in a thermostatic chamber at 60°C for four weeks. The second ink composition was stored at room temperature for four weeks without being subjected to an accelerated test. The accelerated test of storing it at 60°C for four weeks is equivalent to storing it at 25°C for one year. The first ink composition that had been subjected to the accelerated test and the second ink composition that had been stored at room temperature were combined as shown in Tables 5 and 6 to prepare ink sets of Examples 9 to 16 and Comparative Examples 12 to 22.

[0074] [(B) Evaluation of intercolor bleeding after accelerated testing] (1) Preparation of test piece 3 Using the ink sets of Examples 12 to 22 and Comparative Examples 12 to 22, a single linear image (second image) containing 100% of the second ink composition and having a line width of 1.0 mm was printed on top of a solid image (first image) containing 100% of the first ink composition, thereby obtaining a printed image. The printing apparatus, conditions, and printing media used were the same as those described in (A)(1) above. The resulting printed image was dried for 3 seconds under an IR heater set at 100°C to obtain test piece 3.

[0075] (2) Evaluation The line width of the second image formed on the first image of test piece 3 was measured. The line width measurement value obtained was divided by the line width of the second image of test piece 1 obtained in (A)(1) to calculate the line width ratio, which was then evaluated using the following four-level evaluation criteria. A smaller line width ratio indicates that intercolor bleeding does not worsen regardless of the storage period, and therefore indicates excellent intercolor bleeding performance. The evaluation results are shown in Tables 5 and 6 below. [Evaluation criteria] D: Ratio 101% or more C: Ratio 51~100% B: Ratio 26~50% A: Ratio 25% or less

[0076] [Table 5] [Table 6]

[0077] As is clear from Tables 5 and 6 above, the ink sets of Examples 1 to 11 suppressed intercolor bleeding to 25% or less. Therefore, the ink sets of Examples 1 to 11 were shown to have excellent performance in suppressing intercolor bleeding even when the ink compositions were fresh and had a short storage period after preparation. Furthermore, the results shown in Table 5 also showed that the intercolor bleeding of the ink sets of Examples 12 to 22 was suppressed to 25%. This confirmed that the ink sets of Examples 12 to 22 reduced the deterioration of intercolor bleeding even when the storage periods of the ink compositions contained in the ink sets were different. The results in Tables 3 to 6 confirm that the ink sets of Examples 1 to 22 had excellent performance in that they had low inter-color bleeding whether the storage periods of the ink compositions were the same or different, whereas the ink sets of Comparative Examples 1 to 22 had poor evaluations of inter-color bleeding in at least one of the cases where the storage periods were the same and where the storage periods were different. [Industrial Applicability]

[0078] The present invention provides an ink set having two ink compositions that can provide printed images that exhibit extremely good intercolor bleeding and that do not deteriorate over storage periods, as well as an inkjet printing method, print medium, and print media set that use the ink set. The ink set of the present invention is extremely useful for various printing applications, particularly inkjet printing applications.

Claims

1. a first ink composition containing water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; a second ink composition containing water, a second colorant, a second silicone surfactant, and a second nonionic surfactant, and applied onto a first image formed using the first ink composition to form a second image, The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): 【Chemistry 1】 (wherein a is an integer of 1 to 40, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, R １ and R ２ are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1 (mass%), the content of the first nonionic surfactant is A2 (mass%), the content of the second silicone surfactant is B1 (mass%), and the content of the second nonionic surfactant is B2 (mass%), 0.10≦(B1-A1)+(B2-A2)≦0.95 Fulfilling one or both of the first ink composition and the second ink composition further contain a binder, the binder contains at least one kind selected from a wax and a (meth)acrylic acid-based polymer, and a content of the binder relative to the total mass of the ink compositions is 0.1 to 8% in terms of solid content.

2. 2. The ink set according to claim 1, wherein in formula (1), m and n are each independently an integer of 1 to 30.

3. 2. The ink set according to claim 1, wherein the wax is at least one selected from the group consisting of polyalkylene wax, polyalkylene oxide wax, and paraffin wax.

4. 4. The ink set according to claim 1, wherein the wax is an oxidized polyethylene wax.

5. 5. The ink set according to claim 1, wherein the first nonionic surfactant and the second nonionic surfactant have an HLB value of 6.0 or more.

6. An inkjet recording method using the ink set according to any one of claims 1 to 5, ejecting droplets of the first ink composition onto a print medium to form a first image; ejecting droplets of the second ink composition onto the print medium on which the first image has been formed, thereby forming a second image; An inkjet recording method comprising:

7. A printing medium on which a second image is formed by applying the second ink composition onto a first image formed by applying the first ink composition contained in the ink set according to any one of claims 1 to 5.

8. An ink-media set comprising the ink set according to any one of claims 1 to 5 and a printing medium.

9. An ink composition for forming a first image, which is used together with an ink composition for forming a second image by being applied onto a first image, comprising: the ink composition for forming the first image contains water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; the ink composition for forming the second image contains water, a second colorant, a second silicone surfactant, and a second nonionic surfactant; The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): 【Chemistry 2】 (wherein a is an integer of 1 to 40, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, R １ and R ２ are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1 (mass%), the content of the first nonionic surfactant is A2 (mass%), the content of the second silicone surfactant is B1 (mass%), and the content of the second nonionic surfactant is B2 (mass%), 0.10≦(B1-A1)+(B2-A2)≦0.95 Fulfilling One or both of the first ink composition and the second ink composition further contain a binder, the binder containing at least one selected from the group consisting of wax and a (meth)acrylic acid-based polymer, and a content of the binder relative to the total mass of the ink composition in terms of solid content of 0.1 to 8%.

10. An ink composition for forming a second image, which is used together with an ink composition for forming a first image on which a second image is formed, the ink composition for forming the first image contains water, a first colorant, a first silicone surfactant, and a first nonionic surfactant; the ink composition for forming the second image contains water, a second colorant, a second silicone surfactant, and a second nonionic surfactant; The first silicone surfactant and the second silicone surfactant each independently represent the following formula (1): 【Transformation 3】 (wherein a is an integer of 1 to 40, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, m+n is 2 to 100, o+p is 0 to 80, R １ and R ２ are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a (meth)acrylic group. It is a silicone surfactant represented by the first nonionic surfactant and the second nonionic surfactant are nonionic surfactants other than silicone surfactants and have an HLB value of 6.0 or more and less than 12.0; When the content of the first silicone surfactant is A1 (mass%), the content of the first nonionic surfactant is A2 (mass%), the content of the second silicone surfactant is B1 (mass%), and the content of the second nonionic surfactant is B2 (mass%), 0.10≦(B1-A1)+(B2-A2)≦0.95 Fulfilling One or both of the first ink composition and the second ink composition further contain a binder, the binder containing at least one selected from the group consisting of wax and a (meth)acrylic acid-based polymer, and a content of the binder relative to the total mass of the ink composition in terms of solid content of 0.1 to 8%.

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