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

Abstract

The present invention provides an ink set which comprises a first ink composition that contains a coloring agent, a surfactant in an amount of A1 mass%, a hydrophobic organic solvent in an amount of A2 mass%, and water, the first ink composition being used for the purpose of forming a first image, and a second ink composition that contains a coloring agent, a surfactant in an amount of B1 mass%, a hydrophobic organic solvent in an amount of B2 mass%, and water, the second ink composition being used for the purpose of forming a second image on the first image, wherein: the surfactant is a specific silicone-based surfactant; the octanol / water partition coefficient of the hydrophobic organic solvent is not less than 2.00 but less than 3.50; and the following formula 0.05 ≤ (0.5 × (B1 - A1) + (B2 -A2)) ≤ 0.70 is satisfied. The present invention also provides: an inkjet recording method which uses this ink set; an ink medium set which comprises this ink set and a printing medium; and a printing medium on which a print is made with use of this ink set.

Description

[Technical Field]

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

[0002] Among various color recording methods, the recording method using an inkjet printer (inkjet recording method), which is one of the most representative methods, generates small droplets of ink and deposits them on a printing medium such as paper to perform printing. In recent years, demand for inks 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 print media, inks with good wetting and spreading properties are desired for non-ink-absorbent media and poorly ink-absorbent media (hereinafter also referred to as "non-ink-absorbent / poorly ink-absorbent media"). Good wetting and spreading properties on media allow for a larger area to be colored using the same amount of ink droplets (in other words, larger ink dot diameters), thereby reducing ink consumption. However, ink wetting and spreading properties on non-ink-absorbent / poorly ink-absorbent media are poorer than ink-absorbent media, so ink dot diameters generally tend to be smaller. Therefore, improved ink wetting and spreading properties are required, and inks that address this issue have been proposed. For example, Patent Documents 1 to 3 disclose inks with improved wetting and spreading properties for non-ink-absorbent / poorly ink-absorbent media by combining specific organic solvents and surfactants.

[0004] 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 may 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 bleeding between colors is one of the factors that significantly deteriorates print quality. Therefore, there is a demand for eliminating this bleeding between colors, and inks that solve this problem have been proposed. For example, Patent Document 4 discloses an ink that contains a polyalkoxylate of an acetylene glycol-based surfactant and that can produce high-quality images without color unevenness or bleeding between colors, even on non-ink-absorbent or poorly ink-absorbing media. [Prior art documents] [Patent documents]

[0005] [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]

[0006] However, the inventors have investigated the issue of inter-color bleeding and found that it involves the following complex factors.

[0007] In the early stages of printing, printing can be performed using a combination of a first color ink and a second color ink, 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 with reduced inter-color bleeding can be performed.

[0008] However, as printing continues, the consumption of each ink varies depending on the type of ink. For this reason, inks with high consumption are replaced with new ink when they run out. Meanwhile, inks with low consumption continue to be used until the ink originally used runs out. As a result, new inks and old inks are used together. There can be a difference of several months to a year between inks with high consumption and inks with low consumption in terms of their shelf life before use. When printing using inks with different shelf lives together, inter-color bleeding can worsen, resulting in a deterioration in print quality, even though there is no significant change in the storage stability of the inks themselves (various physical properties such as ejection performance, average particle size, viscosity, and pH).

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ink set that is less likely to cause inter-color bleeding regardless of the storage period of each ink composition, an inkjet recording method that uses the ink set, an ink media set that includes the ink set and a print media, and a print media printed using the ink set. [Means for solving the problem]

[0010] Specific means for solving the above problems include the following embodiments. [1] A first ink composition containing a first colorant, a first surfactant, a first hydrophobic organic solvent, and water; a second ink composition containing a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, and applied onto the first image formed using the first ink composition to form a second image; and An ink set comprising: The first surfactant and the second surfactant each independently represent the following formula (1): [ka] (In the formula, R 1 and R 2are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; 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; and o+p is 0 to 80. It is a silicone surfactant represented by the water-octanol partition coefficients of the first hydrophobic organic solvent and the second hydrophobic organic solvent are 2.00 or more and less than 3.50; When the content of the first surfactant in the first ink composition is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the second ink composition is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70···(2) An ink set that satisfies the conditions expressed by

[0011] [2] The ink set according to [1], wherein in the formula (1), m and n each independently represent an integer of 1 to 30.

[0012] [3] The ink set according to [1] or [2], wherein one or both of the first ink composition and the second ink composition contain a binder.

[0013] [4] The ink set according to [3], wherein the binder is at least one selected from waxes and (meth)acrylic polymers.

[0014] [5] The ink set according to [4], wherein the wax is at least one selected from the group consisting of polyalkylene wax, polyalkylene oxide wax, and paraffin wax.

[0015] [6] The ink set according to [4] or [5], wherein the wax is an oxidized polyethylene wax.

[0016] [7] An inkjet recording method using the ink set according to any one of [1] to [6], ejecting droplets of the first ink composition and depositing the droplets on a print medium to form a first image; ejecting droplets of the second ink composition and depositing the droplets on the print medium on which the first image has been formed to form a second image; An inkjet recording method comprising:

[0017] [8] An ink-media set comprising the ink set according to any one of [1] to [6] and a print medium.

[0018] [9] A printing medium in which a first image is formed by applying the first ink composition provided in the ink set according to any one of [1] to [6], and a second image is formed by applying the second ink composition provided in the ink set.

[0019]

[10] 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 a first colorant, a first surfactant, a first hydrophobic organic solvent, and water. the ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water; The first surfactant and the second surfactant each independently represent the following formula (1): [ka] (In the formula, R 1 and R 2are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; 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; and o+p is 0 to 80. It is a silicone surfactant represented by The first hydrophobic organic solvent and the second hydrophobic organic solvent Hydrophobic the water-octanol partition coefficient of the organic solvent is 2.00 or more and less than 3.50, When the content of the first surfactant in the ink composition for forming the first image is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the ink composition for forming the second image is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70···(2) An ink composition that satisfies the condition expressed by

[0020]

[11] 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 a first colorant, a first surfactant, a first hydrophobic organic solvent, and water. the ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water; The first surfactant and the second surfactant each independently represent the following formula (1): [ka] (In the formula, R 1 and R 2are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; 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; and o+p is 0 to 80. It is a silicone surfactant represented by The first hydrophobic organic solvent and the second hydrophobic organic solvent Hydrophobic the water-octanol partition coefficient of the organic solvent is 2.00 or more and less than 3.50, When the content of the first surfactant in the ink composition for forming the first image is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the ink composition for forming the second image is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70···(2) An ink composition that satisfies the condition expressed by [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an ink set that is resistant to inter-color bleeding regardless of the storage period of each ink composition, an inkjet recording method that uses the ink set, an ink media set that includes the ink set and a print media, and a print media printed using the ink set. DETAILED DESCRIPTION OF THE INVENTION

[0022] Specific embodiments to which the present invention is applied will be described in detail below. As used herein, "CI" means "Color Index." In addition, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate," and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl."

[0023] <Ink set> The ink set according to this embodiment comprises a first ink composition containing a first colorant, a first surfactant, a first hydrophobic organic solvent, and water, and a second ink composition containing a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, and which is applied onto a first image formed using the first ink composition to form a second image.

[0024] <First ink composition> The first ink composition contains a first colorant, a first surfactant, a first hydrophobic organic solvent, and water, and may further contain other components. Examples of other components include a dispersant and an ink preparation agent. The components contained in the first ink composition are described in detail below. Note that each of the components described below may be used alone or in combination of two or more.

[0025] [First colorant] The first colorant is a water-insoluble colorant. The water-insoluble colorant generally has a solubility in water at 25°C of 5 g / L or less, preferably 3 g / L or less, more preferably 1 g / L or less, and even more preferably 0.5 g / L or less. The lower limit of the solubility includes 0 g / L.

[0026] As the first colorant, for example, a known pigment, disperse dye, solvent dye, or water-insoluble resin colored with a colorant such as a dye or pigment can be used. Among these, a pigment is preferred.

[0027] Examples of pigments include inorganic pigments, organic pigments, and extender pigments.

[0028] Examples of inorganic pigments include carbon black, metal oxides, metal hydroxides, metal sulfides, metal ferrocyanides, and metal chlorides. When the first ink composition is a black ink composition and the first colorant is an inorganic pigment, preferred examples of the inorganic pigment include carbon blacks such as 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.

[0029] 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 yellow pigments 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. Red pigments 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; blue pigments 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; violet pigments such as CI Pigment Violet 19, 23, 29, 37, 38, and 50; orange pigments such as CI Pigment Orange 13, 16, 68, 69, 71, and 73; and CI Pigment Green green pigments such as CI Pigment Black 1; and the like.

[0030] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, white carbon, etc. These extender pigments are often used in combination with other colorants.

[0031] As disperse dyes, dyes selected from CI Dispers are preferred. Specific examples thereof include yellow dyes 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; red dyes 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. Orange dyes 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; violet dyes such as CI Disperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, and 79:1; blue dyes 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; and the like.

[0032] As the solvent dye, for example, a dye selected from C1Solvent is preferred.

[0033] The first colorant has an average particle size (D50) of usually 50 to 250 nm, preferably 60 to 200 nm. Here, the average particle size (D50) means the particle size at which the cumulative particle size distribution from the small particle size side in the particle size distribution determined by a laser diffraction / scattering method is 50%.

[0034] The content of the first colorant is usually 1 to 30% by mass, preferably 1 to 10% by mass, and more preferably 2 to 7% by mass, relative to the total mass of the first ink composition.

[0035] [Dispersant] The first ink composition preferably contains a dispersant to disperse the first colorant. The dispersant is not particularly limited, and known dispersants such as polymeric dispersants can be used. Examples of polymeric 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; (meth)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 their derivatives. 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, and (meth)acrylic acid ester-(meth)acrylic acid copolymer are preferred, (meth)acrylic acid ester-(meth)acrylic acid copolymer is more preferred, and methacrylic acid ester-methacrylic acid copolymer is even more preferred. Examples of the copolymer include block copolymers, random copolymers, and graft copolymers. These copolymers may be in the form of a salt.

[0036] Dispersants can be commercially available or synthesized.

[0037] Examples of commercially available dispersants include Joncyrl 62, 67, 68, 678, and 687 (styrene-acrylic copolymers manufactured by BASF); Movinyl S-100A (modified vinyl acetate copolymer manufactured by Japan Coating Resins Co., Ltd.); and Jurymer AT-210 (polyacrylic acid ester copolymer manufactured by Toa Gosei Co., Ltd.).

[0038] Examples of dispersants obtained by synthesis include the AB block polymer disclosed in WO 2013 / 115071. The monomer constituting the A block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from (meth)acrylic acid and linear or branched C4 alkyl (meth)acrylates, preferably at least one monomer selected from methacrylic acid and n-butyl methacrylate, and more preferably a combination of these two monomers. Furthermore, the monomer constituting the B block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from benzyl methacrylate and benzyl acrylate, preferably benzyl methacrylate. Specific examples of AB block polymers include the block copolymers disclosed in Synthesis Examples 3 to 8 of WO 2013 / 115071.

[0039] 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.

[0040] A neutralizing agent may be used to uniformly disperse the dispersant in water. Examples of neutralizing agents include ammonia, alkali metal hydroxides, alkaline earth metal hydroxides, aliphatic amine compounds, and alkanolamine compounds. Among these, ammonia and alkali metal hydroxides are preferred, and ammonia is more preferred. The amount of neutralizing agent used is typically 30 to 300% neutralization, preferably 50 to 200%, with 100% neutralization being defined as neutralization with the theoretical equivalent of the acid value of the dispersant.

[0041] 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 mass-average molecular weight of the dispersant can be measured by gel permeation chromatography (GPC). Specifically, the measurement can be performed using an HLC-8320GPC (manufactured by Tosoh Corporation) as the GPC device, two TSK gel Super Multipore HZ-H columns (manufactured by Tosoh Corporation, inner diameter 4.6 mm × 15 cm), tetrahydrofuran as the eluent, and TSK Standard (manufactured by Tosoh Corporation) as the standard sample.

[0042] The PDI (mass average molecular weight / number average molecular weight) of the dispersant is preferably about 1.29 to 1.49. By setting the PDI within this range, the dispersibility and storage stability of the first ink composition tend to be improved.

[0043] The dispersant can be used in a state where it is mixed with the first colorant, or in a state where the surface of the first colorant is partially or entirely coated with the dispersant, or both of these states can be used in combination.

[0044] The ratio of the total mass of the dispersant to the total mass of the first colorant is usually 0.01 to 1.0, preferably 0.05 to 0.6, and more preferably 0.1 to 0.5.

[0045] [First 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 used to provide wettability, depending on the application. Silicone-based surfactants, among others, are particularly well-known for their ability to provide wettability. However, the inventors' investigations revealed that when printing ink compositions with different storage periods are used together, intercolor bleeding worsens depending on the structure of the silicone-based surfactant, even though there is no significant change in the storage stability of each ink composition (various physical properties such as ejection performance, average particle size, viscosity, and pH). Silicone-based surfactants are generally known to decompose over time during long-term storage (see, for example, Koji Sakuta, Journal of the Japan Society of Color Materials, 2001, Vol. 74, No. 1, pp. 34-38). From this, it is inferred that silicone-based surfactants with specific structures lose their ability to control intercolor bleeding due to structural decomposition.

[0046] 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), inter-color bleeding is less likely to occur, regardless of whether the storage periods of the two ink compositions are the same or different. Although the reason why changes in inter-color bleeding over time can be suppressed is not clear, it is presumed that 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 ethyleneoxy groups and propyleneoxy groups is maintained, and the function as a surfactant is not impaired.

[0047] [ka]

[0048] In the above formula (1), R 1 and R 2are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, and are preferably a hydroxy group.

[0049] In the above formula (1), a is an integer of 1 to 80, preferably 2 to 40, and more preferably 5 to 34. x and y are each independently an integer of 1 to 4, preferably an integer of 1 to 3. m and n are each independently an integer of 1 to 50, preferably an integer of 1 to 40, more preferably an integer of 1 to 30, even more preferably an integer of 4 to 20, and particularly preferably an integer of 5 to 12. o and p are each independently an integer of 0 to 40, preferably an integer of 0 to 20, more preferably an integer of 0 to 10, and even more preferably an integer of 0 to 5. m+n is 2 to 100, preferably 4 to 80, more preferably 8 to 40, and even more preferably 10 to 25. o+p is 0 to 80, preferably 0 to 40, more preferably 0 to 20, and even more preferably 0 to 10.

[0050] The silicone surfactant represented by the above formula (1) can be obtained as a commercial product or can be synthesized.

[0051] Commercially available silicone surfactants represented by the formula (1) include, for example, Silwet CoatOSil 2812, Silwet CoatOSil 2816, Silwet CoatOSil 3500, and Silwet CoatOSil 3505 manufactured by Momentive Performance Materials; BYK-331, BYK-333, BYK-UV3500 manufactured by BYK-Chemie; 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); and Tego Glide 410, Tego Glide 432, and Tego Glide manufactured by Evonik Degussa. 435, Tego Glide 440, and Tego Glide 450; Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.; and the like.

[0052] The silicone surfactant represented by the above formula (1) can also be synthesized, for example, by subjecting polyethylene glycol having an allyl group at one end and polydimethylsiloxane having hydrogen groups at both ends to a hydrosilylation reaction using a platinum catalyst.

[0053] The content of the silicone surfactant represented by the above formula (1) is usually 0.01 to 3 mass %, preferably 0.05 to 2 mass %, and more preferably 0.1 to 1 mass %, relative to the total mass of the first ink composition.

[0054] [First hydrophobic organic solvent] The water-octanol partition coefficient of the first hydrophobic organic solvent is 2.00 or more and less than 3.50, preferably 2.40 to 3.00. By setting the water-octanol partition coefficient within this range, it is possible to further improve the effect of suppressing inter-color bleeding, which is insufficient when using a silicone surfactant alone. In this specification, the "water-octanol partition coefficient" refers to the ClogP value calculated using ChemDraw Professional ver. 16.0 manufactured by PerkinElmer. The number of decimal places calculated in this manner is not consistent. Therefore, in this specification, the value is rounded to two decimal places and reported to two decimal places. Furthermore, when the calculated value has two decimal places, the value is reported as is. Furthermore, when the calculated value does not have two decimal places, the values ​​up to the second decimal place are considered to be "zero," and all values ​​are reported to two decimal places. Hereinafter, the "water-octanol partition coefficient" may be referred to as the "ClogP value."

[0055] Examples of organic solvents having a ClogP value of 2.00 or more and less than 3.50 include 1,2-nonanediol (2.11), 2-propylheptane-1,3-diol (2.31), ethylene glycol monoheptyl ether (2.43), ethylene glycol diisobutyl ether (2.55), dibutyl diglycol (2.63), 1,2-decanediol (2.64), 2-[2-(2-ethylhexyloxy)ethoxy]ethanol (2.65), diisobutyl Examples include ethylene glycol dibutyl ether (2.81), 2,6-dimethyl-4-heptanol (2.99), 3,5,5-trimethyl-1-hexanol (3.08), 2-butoxyethyl benzoate (3.43), and diethylene glycol monobutyl ether adipate (3.49). The values ​​in parentheses are ClogP values.

[0056] The content of the first hydrophobic organic solvent is usually 0.01 to 2 mass %, preferably 0.05 to 1.5 mass %, and more preferably 0.1 to 1 mass %, relative to the total mass of the first ink composition.

[0057] [water] The first ink composition contains the above-mentioned components and, if necessary, ink preparation agents, with the remainder being water. As the water, ion-exchanged water, distilled water, or the like with a low content of impurities (such as metal ions) is preferred.

[0058] [Ink preparation agents] In addition to the above components, the first ink composition may further contain ink preparation agents, such as binders, penetrants, viscosity modifiers, surfactants other than silicone surfactants, preservatives, antifungal agents, pH adjusters, chelating agents, rust inhibitors, water-soluble ultraviolet absorbers, and antioxidants.

[0059] The total content of ink preparation agents excluding the binder, penetrant, and viscosity modifier is typically 0 to 30% by mass, preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass, relative to the total mass of the first ink composition.

[0060] (binder) The binder is preferably at least one selected from wax and (meth)acrylic polymer. By adding a binder to the ink composition, the scratch resistance of the printed image can be improved. The binder is preferably added as an emulsion, more preferably as an aqueous emulsion.

[0061] The wax may be natural or synthetic. Examples of natural waxes include emulsions of petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; vegetable waxes such as carnauba wax and candelilla wax; and animal and vegetable waxes such as beeswax and lanolin, dispersed in an aqueous medium. Examples of synthetic waxes include polyalkylene waxes (preferably poly C2-C4 alkylene wax), oxidized polyalkylene waxes (preferably poly C2-C4 alkylene wax), and paraffin wax. Among these, at least one selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax is preferred, with oxidized polyethylene wax being more preferred.

[0062] Commercially available wax emulsions include, for example, CERAFLOUR 925, 929, 950, 991, AQUACER 498, 515, 526, 531, 537, 539, 552, 1547, AQUAMAT 208, 263, 272, MINERPOL 221, etc., manufactured by BYK-Chemie Co., Ltd.; MITSUI HIWAX NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, NP505, etc., manufactured by Mitsui Chemicals, Inc.; and KUE-100 and 11, manufactured by Sanyo Chemical Industry Co., Ltd. Among these, AQUACER 515, 531, 537, 539, and 1547 are preferred, with AQUACER 515, 531, 537, and 1547 being more preferred.

[0063] The (meth)acrylic polymer used as the binder is a polymer different from the dispersant described above. The (meth)acrylic polymer is preferably a polymer composed of four types of monomers: C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate.

[0064] The alkyl moiety of the C1-C4 alkyl methacrylate may be linear or branched, and is preferably linear. As the C1-C4 alkyl methacrylate, C1-C3 alkyl methacrylate is preferred, C1-C2 alkyl methacrylate is more preferred, and methyl methacrylate is even more preferred.

[0065] The alkyl moiety of the C6-C10 alkyl acrylate may be linear or branched, preferably branched. As the C6-C10 alkyl acrylate, C7-C9 alkyl acrylate is preferred, C8 alkyl acrylate is more preferred, and 2-ethylhexyl acrylate is even more preferred.

[0066] The proportions of the four monomers, C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate, in the (meth)acrylic polymer are typically 40 to 60 mass%, 38 to 58 mass%, 1 to 10 mass%, and 1 to 5 mass%, respectively, and preferably 45 to 55 mass%, 52 to 42 mass%, 2 to 4 mass%, and 1 to 3 mass%, and it is preferable for the total to be 100 mass% within these ranges.

[0067] The acid value of the (meth)acrylic polymer is usually from −10 to 35 mgKOH / g, preferably from −5 to 30 mgKOH / g, and more preferably from 0 to 25 mgKOH / g.

[0068] The glass transition temperature (Tg) of the (meth)acrylic polymer is usually from -20 to 30°C, preferably from -15 to 25°C, and more preferably from -10 to 20°C.

[0069] The average particle size of the binder is preferably 50 nm to 5 μm, and more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head.

[0070] When the first ink composition contains a binder, the content (content as solid content) of the binder is usually 0.1 to 14 mass %, preferably 0.5 to 12 mass %, more preferably 2 to 10 mass %, and even more preferably 3 to 8 mass %, relative to the total mass of the first ink composition.

[0071] (penetrating agent) The penetrant is preferably an organic solvent selected from glycol ethers and C4-C9 alkanediols, and having a ClogP value of 0.00 or more and less than 2.00. By including a penetrant in the ink composition, the ink tends to wet and spread well on non- or poorly ink-absorbing media, and the ink tends to dry well.

[0072] Examples of penetrants with a ClogP value of 0.00 or more and less than 2.00 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 triglyceride (0.49), diethylene glycol diethyl ether (0.52), ...0), isopropyl alcohol (0.00), isopropyl glycol (0.00), diethylene glycol diethyl ether (0.52), 1,2-pentanediol (0.00), isopropyl alcohol (0.00), isopropyl alcohol (0.00), isopropyl alcohol (0.00), isopropyl alcohol (0.00 ,2-hexanediol (0.53), diethylene glycol monoisobutyl ether (0.54), propyl propylene glycol (0.62), butyl diglycol (0.67), 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), hexyl diglycol (1.72), etc. The numbers in parentheses are ClogP values.

[0073] When the first ink composition contains a penetrant, the content thereof is usually 0.1 to 30 mass %, preferably 0.2 to 20 mass %, more preferably 0.5 to 10 mass %, even more preferably 2 to 8 mass %, and particularly preferably 4 to 6 mass %, relative to the total mass of the first ink composition.

[0074] (Viscosity modifier) The first ink composition may further contain a viscosity modifier. The viscosity range of the ink composition that can be ejected from an industrial inkjet printer is usually determined 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 first ink composition to adjust its viscosity to an appropriate range.

[0075] The viscosity adjuster is not particularly limited as long as it can adjust the viscosity of the ink composition, and known substances can be used. Specific examples include water-soluble organic solvents (excluding the organic solvents listed above as penetrants) and sugars. Among these, water-soluble organic solvents with a ClogP value of 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 more, preferably -3.00 or more, more preferably -2.00 or more, and even more preferably -1.50 or more.

[0076] Examples of water-soluble organic solvents with a ClogP value of less than 0.00 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-hydroxybenzoate (-0.53), and 2-methyl-2-benzoate (-0.53). Examples of suitable hydroxymethyloxetane include hydroxymethyloxetane (-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), and glycereth-3 (-3.49) and glycereth-20 (-5.42) manufactured by Aoki Oil & Fat Industries Co., Ltd. The numbers in parentheses are ClogP values.

[0077] The content of the viscosity modifier is usually 0 to 55% by mass, preferably 5 to 40% by mass, and more preferably 10 to 30% by mass, relative to the total mass of the first ink composition.

[0078] (Surfactants other than silicone surfactants) The surfactants include anionic, cationic, amphoteric and fluorine-based surfactants.

[0079] Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acylamino acids or salts thereof, N-acylmethyl taurines, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosin acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, alkyl phosphates, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, and dioctyl sulfosuccinates.

[0080] Examples of cationic surfactants include 2-vinylpyridine derivatives and poly(4-vinylpyridine) derivatives.

[0081] Examples of amphoteric surfactants include lauryl dimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, polyoctyl polyaminoethyl glycine, and imidazoline derivatives.

[0082] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains.

[0083] When the first ink composition contains a surfactant other than a silicone surfactant, the content thereof is usually 0.1 to 2.0% by mass relative to the total mass of the first ink composition.

[0084] (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, inorganic salt compounds, etc. Specific examples of commercially available preservatives include Proxel GXL(S) and XL-2(S) manufactured by Lonza.

[0085] (Anti-mold agent) Examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, and 1,2-benzisothiazolin-3-one, as well as salts thereof.

[0086] (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.

[0087] (chelating agent) Examples of the chelating agent include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0088] (rust inhibitor) Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0089] (Water-soluble UV absorber) Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0090] (antioxidant) As the antioxidant, various organic and metal complex anti-fading agents can be used, such as hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles.

[0091] [Method of preparing ink composition, etc.] The first ink composition is preferably prepared by preparing a dispersion containing the first colorant and a dispersant, and then mixing it with other components.

[0092] Methods for preparing the dispersion include phase inversion emulsification, acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, spray drying, etc. Among these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred, and phase inversion emulsification is more preferred.

[0093] When preparing a dispersion by phase inversion emulsification, for example, a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizing agent is added to prepare an emulsion. A first colorant is added to the obtained emulsion, and a dispersion treatment is performed. The organic solvent and a portion of the water are distilled off under reduced pressure from the obtained liquid to obtain the desired dispersion.

[0094] Dispersion treatment can be carried out using a sand mill (bead mill), roll mill, ball mill, paint shaker, ultrasonic disperser, microfluidizer, etc. For example, when using a sand mill, beads with a particle size of about 0.01 to 1 mm can be used, and the bead packing rate can be appropriately set to carry out dispersion treatment. The particle size of the particles contained in the dispersion can be made uniform by subjecting the dispersion obtained as described above to operations such as filtration and centrifugation. If foaming occurs during preparation of the dispersion, a trace amount of a known silicone-based, acetylene glycol-based, or other antifoaming agent can be added.

[0095] The average particle size (D50) of the first colorant 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 of D90 is preferably 100 nm. D10 is usually 10 nm or more, preferably 20 nm or more, and more preferably 30 nm or more. The upper limit of D10 is preferably 100 nm. By ensuring that the particle size of the first colorant in the dispersion is within the above range, the storage stability of the ink composition is ensured, and the ink tends to be 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 determined by the laser diffraction / scattering method is 50%, D90 is the particle size at which the cumulative particle size distribution from the small particle size side is 90%, and D10 is the particle size at which the cumulative particle size distribution from the small particle size side is 10%.

[0096] The pH of the first ink composition at 25°C is usually 7 to 11, and preferably 8 to 10. The surface tension of the first ink composition at 25°C is usually 10 to 50 mN / m, and preferably 20 to 40 mN / m. The viscosity of the first ink composition at 25°C is usually 2 to 30 mPa·s, and preferably 3 to 20 mPa·s. The pH, surface tension, and viscosity of the first ink composition can be adjusted with a pH adjuster, a surfactant, a viscosity adjuster, etc.

[0097] The first ink composition can be used in various printing processes. For example, the first ink composition is suitable for writing instruments, various types of printing, information printing, textile printing, etc., and is preferably used in inkjet printing.

[0098] <Second ink composition> The second ink composition contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, and may further contain other components, such as a dispersant and an ink preparation agent.

[0099] The second colorant, second surfactant, second hydrophobic organic solvent, and other components may be the same as those in the first ink composition, and the content of each component may be within the preferred range described for the first ink composition.

[0100] 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 colorant and the second colorant are different enough to be visually distinguishable. The first colorant and the second colorant are preferably two different colors selected from the group consisting of cyan, magenta, yellow, black, green, orange, red, and violet.

[0101] The contents of the first surfactant and the first hydrophobic organic solvent in the first ink composition and the contents of the second surfactant and the second hydrophobic organic solvent in the second ink composition must satisfy a specific relationship. More specifically, when the content of the first surfactant in the first ink composition is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), and the content of the second surfactant in the second ink composition is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2) is satisfied: 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70···(2) It is necessary to satisfy the condition expressed by the following formula: The value of [0.5×(B1−A1)+(B2−A2)] is preferably within the range of 0.10 to 0.65, and more preferably within the range of 0.20 to 0.60.

[0102] In the above formula (2), the coefficient is determined according to the degree of influence on intercolor bleeding. Specifically, because low-molecular-weight hydrophobic organic solvents contribute more significantly to intercolor bleeding than surfactants, the difference in surfactant content (B1-A1) is multiplied by a coefficient of 0.5. By satisfying the conditions of this formula (2), it is possible to suppress intercolor bleeding and achieve good print image quality. It has been confirmed that if the value of [0.5 x (B1-A1) + (B2-A2)] is outside the above 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. For example, it has been confirmed that when the value of [0.5×(B1−A1)+(B2−A2)] is smaller than 0.05, the first ink composition bleeds into the second ink composition, whereas when the value of [0.5×(B1−A1)+(B2−A2)] is larger than 0.70, the second ink composition bleeds into the first ink composition.

[0103] The phenomenon of suppressing intercolor bleeding when the condition of formula (2) is satisfied only occurs when the first and second ink compositions contain the silicone surfactant represented by formula (1). While the reason for this is unclear, it is presumed that when two different color inks are printed consecutively, the imbalance in the interfacial tension between the two inks causes one color to bleed into the other. Because surfactants and hydrophobic organic solvents are oriented at the ink interface, they are thought to have a significant effect. Meanwhile, ink ejection in inkjet printing is driven by the vibration of the piezoelectric element in the inkjet head, and therefore, the ink is also affected by vibrations caused by the operation of the inkjet head until immediately after ink landing. Therefore, immediately after ink landing, the low-molecular-weight hydrophobic organic solvent, which is more likely to orient at the interface, is presumed to orient first, followed by the surfactant. It is presumed that the difference in the timing of this orientation contributes to the suppression of intercolor bleeding. Furthermore, compared to typical surfactants, which have hydrophilic and hydrophobic groups at both ends, silicone surfactants expressed by the above formula (1) have a characteristic structure with hydrophilic groups at both ends, which is presumably why the timing of their orientation to the ink interface is delayed. The delayed timing of orientation is thought to reduce the impact on the ink interface immediately after ink impact. Because the above formula (2) uses coefficients tailored to the silicone surfactant expressed by the above formula (1), it is thought that other types of surfactants would not satisfy the above relationship.

[0104] The ink set according to this embodiment can produce printed images with extremely little inter-color bleeding, regardless of the storage period of each ink composition. Furthermore, the ink set according to this embodiment exhibits good wetting and spreading properties on non- or poorly ink-absorbent media, enabling the production of printed images with extremely little graininess. The ink set according to this embodiment is extremely useful for various printing applications, particularly inkjet printing applications.

[0105] <Ink media set> The ink media set according to this embodiment includes the ink set according to this embodiment described above and a print medium.

[0106] Examples of print media include paper, film, fibers and fabrics (cellulose, nylon, wool, etc.), leather, and color filter substrates. These print media can be broadly divided into those with and without an ink-receiving layer. The ink set according to this embodiment can be applied to any print media, but is preferably used for print media that do not have an ink-receiving layer.

[0107] 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, Glossy 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 (gloss) manufactured by Hewlett-Packard Japan, Ltd.; and Gasai Photo Finishing Pro manufactured by Fujifilm Corporation.

[0108] 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 also 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.

[0109] <Inkjet recording method and printing medium> The inkjet recording method according to this embodiment is an inkjet recording method using the ink set according to this embodiment described above, and includes the steps of ejecting droplets of a first ink composition and depositing the droplets onto a print medium to form a first image, and ejecting droplets of a second ink composition and depositing the droplets 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 are carried out using an inkjet system.

[0110] Furthermore, the print medium according to this embodiment has a first image formed by applying a first ink composition, and a second image formed by applying a second ink composition onto the first image.

[0111] As the inkjet method, a known method can be employed. Specific examples of inkjet methods include 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 of improving image quality by ejecting a large number of ink compositions with a low colorant content in a small volume; a method of improving image quality by using multiple ink compositions with substantially the same hue but different colorant contents; and a method of improving colorant fixation by using a colorless, transparent ink.

[0112] When printing on a print medium, for example, a container containing ink (ink tank) is loaded into a predetermined position of an inkjet printer, and printing is performed on the print medium using the above printing method. Note that full-color printing can also be achieved by loading containers containing ink of each color into a predetermined position of the inkjet printer and printing on the print medium using the above printing method.

[0113] For all of the above, 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. [Example]

[0114] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0115] In the examples, unless otherwise specified, "parts" means parts by mass and "%" means % by mass. In the examples, when quantitative determination of the solid content of the colorant in the dispersion was required, it was calculated as a value converted to the colorant only by the dry weight method using an MS-70 manufactured by A&D Co., Ltd.

[0116] <Preparation Example 1: Preparation of Colorant Dispersion Dp1> A block copolymer (Block Copolymer A) was obtained by reproducing Synthesis Example 3 of WO 2013 / 115071. The acid value of the obtained block copolymer was 105 mgKOH / g and the mass average molecular weight was 25,000. 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 an emulsion. CI Pigment Blue 15:4 (hereinafter referred to as "PB15:4") (16 parts) was added to this emulsion, and the mixture was 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 using an evaporator under reduced pressure to obtain a cyan dispersion with a colorant content of 12.0%. The resulting dispersion is designated as "Dp1."

[0117] <Preparation Example 2: Preparation 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 CI Pigment Yellow 74 (hereinafter referred to as "PY74") was used instead of PB15:4. The obtained dispersion was designated "Dp2".

[0118] <Synthesis Example 1: Synthesis of Silicone Surfactant B> Hexadecamethyloctasiloxane (5.8 g) and chloroplatinic acid (0.1 mL) were added to a tetrahydrofuran solution (20 mL) containing hexaethylene glycol allyl methyl ether (7.0 g), and the mixture was stirred at 65°C for 24 hours to allow the reaction to proceed. After the reaction was complete, the solvent was removed under reduced pressure using an evaporator to obtain silicone surfactant B. The obtained silicone surfactant B was a compound represented by the formula (1) above, where R 1 and R 2 is a hydroxy group, and a=6, x=2, y=2, m=7, n=7, o=0, and p=0.

[0119] <Preparation of Ink Compositions C1 to C18 and Y1 to Y20> Dispersions Dp1 and Dp2 were mixed with the components listed in Tables 1 to 4 below, and then filtered through a membrane filter with a pore size of 3 μm (a cellulose mixed ester type membrane filter manufactured by Advantec Co., Ltd.) to obtain ink compositions C1 to C18 and Y1 to Y20 for evaluation tests. The colorant content relative to the total mass of the ink composition was adjusted to 4.5% in all cases. Ink compositions C1 to C18 listed in Tables 1 and 2 are all cyan inks. Ink compositions Y1 to Y20 listed in Tables 3 and 4 are all yellow inks. The numbers in Tables 1 to 4 indicate the number of parts of each component.

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] [Table 4]

[0124] Details of each component in Tables 1 to 4 are as follows. (dispersion) Dp1: Dispersion Dp1 obtained in Preparation Example 1 Dp2: Dispersion Dp2 obtained in Preparation Example 2 (Viscosity modifier) PG: Propylene glycol (penetrating agent) 1,2-HD: 1,2-hexanediol (pH adjuster) TEA: Triethanolamine (Silicone surfactant) 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 Synthesis Example 1 TW270: TEGO wet 270 (hydrophobic organic solvent) CS-12: 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (ClogP value: 2.74) DBDG: Dibutyldiglycol (ClogP value: 2.63) 1,2-ND: 1,2-nonanediol (ClogP value: 2.11) EGmHE: Ethylene glycol monohexyl ether (ClogP value: 1.90) CS-16: 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (ClogP value: 4.49) 1,2-DD: 1,2-dodecanediol (ClogP value: 3.70)

[0125] <Examples 1 to 12 and Comparative Examples 1 to 13> The ink compositions C1 to C18 and Y1 to Y20 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 5 to 8 below to prepare the ink sets of Examples 1 to 12 and Comparative Examples 1 to 13.

[0126] <(A) Evaluation of initial inter-color bleeding> (1) Preparation of test piece 1 Using the ink sets of Examples 1 to 12 and Comparative Examples 1 to 13, a single linear image (second image) was printed with 100% second ink composition and a line width of 1.0 mm, overlapping a solid image (first image) with 100% first ink composition, to obtain a printed image. Printing was performed using a printing device equipped with two KJ4B inkjet heads manufactured by Kyocera Corporation, printing the first ink composition and then 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 equipped on the printing device in the order of the first ink composition and the second ink composition, 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. Then, the line width of the second image formed on the first image of the test piece 1 was measured. A print image evaluation device PIAS-II manufactured by QEA was used to measure the line width.

[0127] (2) Preparation of test piece 2 Using the ink sets of Examples 1 to 12 and Comparative Examples 1 to 13, a solid image (second image) containing 100% of the second ink composition was printed so as to overlap a linear image (first image) containing 100% of the first ink composition and having a line width of 1.0 mm, thereby obtaining a printed image. The printing device, printing conditions, and printing media were the same as those described in (1) above. The obtained printed image was dried in the same manner as described in (1) above to obtain test piece 2. The line width of the first image observed through the second image on test piece 2 was then measured.

[0128] (3) Evaluation The line width ratio (%) was calculated according to the following formula and evaluated according to the following four-level evaluation criteria. A smaller line width ratio means that inter-color bleeding is more suppressed. The evaluation results are shown in Tables 5 to 8 below. Line width ratio (%) = 100 x (measured line width - 1.0 mm) / 1.0 mm -Evaluation criteria- A: Ratio 25% or less B: Ratio 26~50% C: Ratio 51~100% D: Ratio 101% or more

[0129] [Table 5]

[0130] [Table 6]

[0131] [Table 7]

[0132] [Table 8]

[0133] [Examples 13 to 24 and Comparative Examples 14 to 26] An accelerated test was performed on the first ink compositions in Tables 9 to 12 by storing them in a thermostatic chamber at 60°C for four weeks. The second ink compositions were stored at room temperature for four weeks without undergoing an accelerated test. The accelerated test of storing them at 60°C for four weeks corresponds to storage at 25°C for one year. The first ink compositions that had been subjected to the accelerated test and the second ink compositions that had been stored at room temperature were combined as shown in Tables 9 to 12 to prepare ink sets of Examples 13 to 24 and Comparative Examples 14 to 26.

[0134] [(B) Evaluation of inter-color bleeding after accelerated testing] (1) Preparation of test piece 3 Using the ink sets of Examples 13 to 24 and Comparative Examples 13 to 26, a single linear image (second image) was printed with 100% of the second ink composition and a line width of 1.0 mm, overlapping a solid image (first image) with 100% of the first ink composition, to obtain a printed image. The printing device, printing conditions, and printing media were the same as those 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. The line width of the second image formed on the first image of test piece 3 was then measured.

[0135] (2) Evaluation The line width ratio (%) was calculated according to the formula below and evaluated according to the following four-level evaluation criteria. A smaller line width ratio means that inter-color bleeding is more suppressed regardless of the storage period. The evaluation results are shown in Tables 9 to 12 below. Line width ratio (%) = 100 × {measured line width - (measured line width obtained in (A)(1) above)} / (measured line width obtained in (A)(1) above) -Evaluation criteria- A: Ratio 25% or less B: Ratio 26~50% C: Ratio 51~100% D: Ratio 101% or more

[0136] [Table 9]

[0137] [Table 10]

[0138] [Table 11]

[0139] [Table 12]

[0140] As shown in Tables 5 and 6 above, the ink sets of Examples 1 to 12 suppressed intercolor bleeding to 25% or less. This confirmed that the ink sets of Examples 1 to 12 had a short storage period after the preparation of the first and second ink compositions, and were excellent in suppressing intercolor bleeding even when fresh. Furthermore, as shown in Tables 9 and 10 above, the ink sets of Examples 13 to 24 also suppressed intercolor bleeding to 25%. This confirmed that the ink sets of Examples 13 to 24 reduced the deterioration of intercolor bleeding even when the storage periods of the first and second ink compositions were different.

[0141] On the other hand, as shown in Tables 7, 8, 11, and 12 above, it was confirmed that the ink sets of Comparative Examples 1 to 26 were inferior to the Examples in the evaluation of inter-color bleeding when the storage periods were the same or different.

Claims

1. a first ink composition containing a first colorant, a first surfactant, a first hydrophobic organic solvent, and water; a second ink composition containing a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, the second ink composition being applied onto the first image formed using the first ink composition to form a second image; and An ink set comprising: The first surfactant and the second surfactant each independently represent the following formula (1): 【Chemistry 1】 (In the formula, R １ and R ２ are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; a is an integer from 1 to 80; x and y are each independently an integer from 1 to 4; m and n are each independently an integer from 1 to 50; o and p are each independently an integer from 0 to 40; m+n is 2 to 100; and o+p is 0 to 80. It is a silicone surfactant represented by the first hydrophobic organic solvent and the second hydrophobic organic solvent have water-octanol partition coefficients of 2.00 or more and less than 3.50; When the content of the first surfactant in the first ink composition is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the second ink composition is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70...(2) An ink set that satisfies the conditions expressed by

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

3. The ink set according to claim 1 or 2, wherein one or both of the first ink composition and the second ink composition contain a binder.

4. The ink set according to claim 3 , wherein the binder is at least one selected from the group consisting of wax and (meth)acrylic polymers.

5. The ink set according to claim 4, wherein the wax is at least one selected from the group consisting of polyalkylene wax, polyalkylene oxide wax, and paraffin wax.

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

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

8. An ink-media set comprising the ink set according to any one of claims 1 to 6 and a print medium.

9. A printing medium on which a first image is formed by applying the first ink composition provided in the ink set according to any one of claims 1 to 6, and a second image is formed by applying the second ink composition provided in the ink set.

10. An ink composition for forming a first image, which is used together with an ink composition applied onto a first image to form a second image, the ink composition comprising: The ink composition for forming the first image contains a first colorant, a first surfactant, a first hydrophobic organic solvent, and water. the ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water; The first surfactant and the second surfactant each independently represent the following formula (1): 【Chemistry 2】 (In the formula, R １ and R ２ are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; a is an integer from 1 to 80; x and y are each independently an integer from 1 to 4; m and n are each independently an integer from 1 to 50; o and p are each independently an integer from 0 to 40; m+n is 2 to 100; and o+p is 0 to 80. It is a silicone surfactant represented by the first hydrophobic organic solvent and the second hydrophobic organic solvent have water-octanol partition coefficients of 2.00 or more and less than 3.50; When the content of the first surfactant in the ink composition for forming the first image is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the ink composition for forming the second image is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70...(2) An ink composition that satisfies the condition expressed by

11. 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 a first colorant, a first surfactant, a first hydrophobic organic solvent, and water. the ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water; The first surfactant and the second surfactant each independently represent the following formula (1): 【Transformation 3】 (In the formula, R １ and R ２ are each independently a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms; a is an integer from 1 to 80; x and y are each independently an integer from 1 to 4; m and n are each independently an integer from 1 to 50; o and p are each independently an integer from 0 to 40; m+n is 2 to 100; and o+p is 0 to 80. It is a silicone surfactant represented by the first hydrophobic organic solvent and the second hydrophobic organic solvent have water-octanol partition coefficients of 2.00 or more and less than 3.50; When the content of the first surfactant in the ink composition for forming the first image is A1 (mass%), the content of the first hydrophobic organic solvent is A2 (mass%), the content of the second surfactant in the ink composition for forming the second image is B1 (mass%), and the content of the second hydrophobic organic solvent is B2 (mass%), the following formula (2): 0.05≦[0.5×(B1-A1)+(B2-A2)]≦0.70...(2) An ink composition that satisfies the condition expressed by

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