Ink set, inkjet recording method, ink medium set, and printing medium

Abstract

The present invention provides an ink set, which includes a first ink composition for forming a first image and a second ink composition for forming a second image on the first image. The first ink composition contains a colorant, A1% by mass of a surfactant, A2% by mass of a hydrophobic organic solvent, and water. The second ink composition contains a colorant, B1% by mass of a surfactant, B2% by mass of a hydrophobic organic solvent, and water. The surfactant is a specific silicone-based surfactant. The water-octanol partition coefficient of the hydrophobic organic solvent is 2.00 or more and less than 3.50. The ink set satisfies the condition of the following formula: 0.05 ≤ [0.5×(B1 - A1) + (B2 - A2)] ≤ 0.70. In addition, an inkjet recording method using the ink set, an ink-medium set including the ink set and a printing medium, and a printing medium printed using the ink set are provided.

Description

Technical Field

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

[0002] As one of the representative methods among various color recording methods, the recording method based on an inkjet printer (inkjet recording method) is a method of generating small droplets of ink and attaching them to a printing medium such as paper to perform printing. In recent years, with the increasing demand for industrial use, inks that can be printed on various printing media have been required.

[0003] Among printing media, for ink non-absorbent media and ink poorly absorbent media (hereinafter, also referred to as "ink non- / poorly absorbent media"), inks with good wetting spread on the media are urgently desired. This is because if the wetting spread on the media is good, the area that can be colored becomes larger when using the same amount of ink droplets (in other words, the dot diameter of the ink becomes larger), and the consumption of ink can be suppressed. However, compared with ink absorbent media, the wetting spread of ink on ink non- / poorly absorbent media is poor, so the dot diameter of the ink generally tends to become smaller. Therefore, improvement of the wetting spread of the ink is required, and inks for solving this problem have also been proposed. For example, in Patent Documents 1 to 3, inks having improved wetting spread for ink non- / poorly absorbent media by combining specific organic solvents and surfactants are disclosed.

[0004] In addition, when performing color printing, an ink set containing multiple colors is used. It is known that when performing color printing using such an ink set, since the landing position of the ink of the first color and the landing position of the ink of the second color are adjacent on the printing medium, bleeding may occur between the colors of the first color and the second color. This bleeding between colors is one of the important factors that significantly deteriorate the printing quality. Therefore, elimination of this bleeding between colors is required, and inks for solving this problem have also been proposed. For example, Patent Document 4 discloses an ink containing a polyalkoxylate of an alkynediol-based surfactant, which can obtain a high-quality image without color unevenness and bleeding between colors even in ink non- / poorly absorbent media.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-044188

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-139004

[0009] Patent Document 3: International Publication No. 2011 / 136000

[0010] Patent Document 4: Japanese Patent Application Laid-Open No. 2012-136573 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, as a result of research by the inventors of the present application, it has been found that the problem of bleeding between colors includes the following complex and important factors.

[0013] In the initial stage of printing, printing can be performed using both the first color ink and the second color ink, both of which are fresh (in other words, both are newly manufactured). Therefore, by selecting and using an ink set that takes into account bleeding between colors, high-quality printing can be performed in which bleeding between colors is suppressed.

[0014] However, if printing is continued, the consumption amounts of the respective inks gradually differ depending on the type of ink color. Therefore, the ink with a large consumption amount is replaced with new ink at the point in time when the ink runs out. On the other hand, the ink with a small consumption amount continues to be used as it is until the initially used ink runs out. As a result, new ink and old ink will be used together. For the ink with a large consumption amount and the ink with a small consumption amount, there is sometimes a difference of several months to about one year in the storage period until use. If printing is performed using inks with different storage periods, even if there is no significant change in the storage stability (various physical property values such as ejection property, average particle diameter, viscosity, pH, etc.) of each ink itself, bleeding between colors sometimes deteriorates and the print quality decreases.

[0015] The present invention has been made in view of the above circumstances, and an object thereof is to provide an ink set that is less likely to cause bleeding between colors regardless of the storage period of each ink composition, an inkjet recording method using the ink set, an ink medium set including the ink set and a printing medium, and a printing medium printed using the ink set.

[0016] Means for Solving the Problems

[0017] Specific means for solving the above problems include the following embodiments.

[0018] [1] An ink set, comprising:

[0019] a first ink composition containing a first colorant, a first surfactant, a first hydrophobic organic solvent, and water; and

[0020] a second ink composition containing a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, the second ink composition being applied to a first image formed using the first ink composition to form a second image,

[0021] Each of the aforementioned first surfactant and the aforementioned second surfactant is independently a silicone surfactant represented by the following formula (1).

[0022] [Chemical formula 1]

[0023]

[0024] (In the formula, R 1 and R 2 are each independently a hydrogen atom, a hydroxyl 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 from 2 to 100, and o + p is from 0 to 80.)

[0025] The water - octanol partition coefficient of the aforementioned first hydrophobic organic solvent and the aforementioned second hydrophobic organic solvent is 2.00 or more and less than 3.50.

[0026] When the content rate of the aforementioned first surfactant in the aforementioned first ink composition is set as A1 (mass %), the content rate of the aforementioned first hydrophobic organic solvent is set as A2 (mass %), the content rate of the aforementioned second surfactant in the aforementioned second ink composition is set as B1 (mass %), and the content rate of the aforementioned second hydrophobic organic solvent is set as B2 (mass %), the condition represented by the following formula (2) is satisfied.

[0027] 0.05 ≤ [0.5×(B1 - A1)+(B2 - A2)] ≤ 0.70 ···(2)

[0028] [2] The ink set according to [1], wherein in the aforementioned formula (1), m and n are each independently an integer from 1 to 30.

[0029] [3] The ink set according to [1] or [2], wherein one or both of the aforementioned first ink composition and the aforementioned second ink composition contain a binder.

[0030] [4] The ink set according to [3], wherein the aforementioned binder is at least one selected from wax and (meth)acrylic polymers.

[0031] [5] The ink set according to [4], wherein the aforementioned wax is at least one selected from polyalkylene wax, oxidized polyalkylene wax, and paraffin wax.

[0032] [6] The ink set according to [4] or [5], wherein the aforementioned wax is oxidized polyethylene wax.

[0033] [7] An inkjet recording method that uses the ink set according to any one of [1] to [6], the inkjet recording method including the following steps:

[0034] A step of ejecting droplets of the first ink composition and attaching the droplets to a printing medium to form a first image; and

[0035] A step of ejecting droplets of the second ink composition and attaching the droplets to the printing medium on which the first image is formed to form a second image.

[0036] [8] An ink medium set that includes the ink set according to any one of [1] to [6] and a printing medium.

[0037] [9] A printing medium, wherein a second image is formed by applying the second ink composition included in the ink set on the first image formed by applying the first ink composition included in the ink set according to any one of [1] to [6].

[0038]

[10] An ink composition that is the ink composition for forming the first image and is used together with the ink composition for forming the second image applied to the first image.

[0039] The ink composition for forming the first image contains a first colorant, a first surfactant, a first hydrophobic organic solvent, and water.

[0040] The ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water.

[0041] The first surfactant and the second surfactant are each independently a silicone-based surfactant represented by the following formula (1).

[0042] [Chemical formula 2]

[0043]

[0044] (In the formula, R 1 and R 2 are each independently a hydrogen atom, a hydroxyl 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 from 2 to 100, and o + p is from 0 to 80.)

[0045] The water-octanol partition coefficient of the first hydrophobic organic solvent and the second organic solvent is 2.00 or more and less than 3.50.

[0046] When the content rate of the first surfactant in the ink composition for forming the first image is A1 (mass %), the content rate of the first hydrophobic organic solvent is A2 (mass %), the content rate of the second surfactant in the ink composition for forming the second image is B1 (mass %), and the content rate of the second hydrophobic organic solvent is B2 (mass %), the conditions represented by the following formula (2) are satisfied.

[0047] 0.05 ≤ [0.5×(B1 - A1) + (B2 - A2)] ≤ 0.70 ··· (2)

[0048]

[11] An ink composition, which is an ink composition for forming the second image and is used together with the ink composition for forming the first image on which the second image is formed above.

[0049] The ink composition for forming the first image contains a first colorant, a first surfactant, a first hydrophobic organic solvent, and water.

[0050] The ink composition for forming the second image contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water.

[0051] The first surfactant and the second surfactant are each independently a silicone surfactant represented by the following formula (1).

[0052] [Chemical formula 3]

[0053]

[0054] (In the formula, R 1 and R 2 are each independently a hydrogen atom, a hydroxyl 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.)

[0055] The water - octanol partition coefficient of the first hydrophobic organic solvent and the second organic solvent is 2.00 or more and less than 3.50.

[0056] When the content rate of the first surfactant in the ink composition for forming the first image is A1 (mass %), the content rate of the first hydrophobic organic solvent is A2 (mass %), the content rate of the second surfactant in the ink composition for forming the second image is B1 (mass %), and the content rate of the second hydrophobic organic solvent is B2 (mass %), the conditions represented by the following formula (2) are satisfied.

[0057] 0.05 ≤ [0.5×(B1 - A1) + (B2 - A2)] ≤ 0.70 ··· (2)

[0058] Advantages of the Invention

[0059] According to the present invention, there can be provided an ink set in which bleeding between colors is less likely to occur regardless of the storage period of each ink composition, an inkjet recording method using the ink set, an ink medium set including the ink set and a printing medium, and a printing medium printed using the ink set. Detailed Embodiments

[0060] Hereinafter, detailed description will be given of specific embodiments to which the present invention is applied.

[0061] In this specification, "C.I." means "Color Index".

[0062] In addition, in this specification, the term "(meth)acrylo-" means both "acrylo-" and "methacrylo-". Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate", and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl".

[0063] <Ink Set>

[0064] The ink set according to the present embodiment includes: 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, the second ink composition being applied to a first image formed using the first ink composition to form a second image.

[0065] <First Ink Composition>

[0066] 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 the other components include a dispersant and an ink conditioner. Hereinafter, the components contained in the first ink composition will be described in detail. It should be noted that each of the components described below may be used alone or in combination of two or more.

[0067] [First Colorant]

[0068] As the first colorant, a water-insoluble colorant can be used. The so-called water-insoluble colorant refers to a colorant having a solubility in water at 25 °C of usually 5 g / L or less, preferably 3 g / L or less, more preferably 1 g / L or less, and further preferably 0.5 g / L or less. The lower limit of the solubility includes 0 g / L.

[0069] As the first colorant, for example, known pigments, disperse dyes, solvent dyes, and water-insoluble resins colored with dyes, pigments, etc. can be used. Among them, pigments are preferred.

[0070] Examples of the pigment include inorganic pigments, organic pigments, extender pigments, etc.

[0071] Examples of the inorganic pigment include carbon black, metal oxides, metal hydroxides, metal sulfides, metal ferrocyanides, metal chlorides, etc. When the first ink composition is a black ink composition and the first colorant is an inorganic pigment, as the inorganic pigment, carbon black such as thermal cracking carbon black, acetylene black, oil furnace carbon black, gas furnace carbon black, lamp black, gas black, channel carbon black, etc. is preferred. Specific examples of the carbon black include, for example, the Raven series manufactured by Columbia Carbon Co., Ltd.; 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 Co., Ltd.; 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; and so on.

[0072] As organic pigments, for example, various pigments such as azo, bisazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, violanthrone, thioindigo, anthraquinone, and quinophthalone can be cited. As specific examples of organic pigments, for example, C.I. 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, 213, etc. yellow pigments; C.I. Pigment Red 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, 272, etc. red pigments; C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80, etc. blue pigments; C.I. Pigment Violet 19, 23, 29, 37, 38, 50, etc. purple pigments; C.I. Pigment Orange 13, 16, 68, 69, 71, 73, etc. orange pigments; C.I. Pigment Green 7, 36, 54, etc. green pigments; C.I. Pigment Black 1, etc. black pigments; and so on.

[0073] As extender pigments, for example, silica, calcium carbonate, talc, clay, barium sulfate, silica white, etc. can be cited. Most of these extender pigments are used in combination with other colorants.

[0074] As the disperse dye, it is preferably a dye selected from C.I. Disperse Dyes (C.I.Dispers). As specific examples thereof, for example, C.I. Disperse 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, 237 and other yellow dyes can be cited; C.I. Disperse Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283 and other red dyes; C.I. Disperse Orange 9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97 and other orange dyes; C.I. Disperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1 and other purple dyes; C.I. 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, 368 and other blue dyes; and so on.

[0075] As the solvent dye, it is preferably a dye selected from C.I. Solvent Dyes (C.I.Solvent), for example.

[0076] The average particle diameter (D50) of the first colorant is usually 50 to 250 nm, preferably 60 to 200 nm. Here, the average particle diameter (D50) refers to the particle diameter 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 becomes 50%.

[0077] With respect to the total mass of the first ink composition, the content rate 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.

[0078] [Dispersant]

[0079] In order to disperse the first colorant, the first ink composition preferably contains a dispersant. As the dispersant, there is no particular limitation, and known dispersants such as polymer dispersants can be used. As the polymer dispersant, for example, copolymers composed of at least two monomers selected from the following monomers (preferably at least one of them is a hydrophilic monomer) can be cited: 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; fumaric acid and its derivatives; vinyl acetate, vinyl alcohol, vinyl pyrrolidone, acrylamide, and their derivatives; and so on. As such copolymers, for example, styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylate copolymers, (meth)acrylate-(meth)acrylic acid copolymers, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers, styrene-maleic acid copolymers, etc. can be cited. Among them, styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylate copolymers, and (meth)acrylate-(meth)acrylic acid copolymers are preferred, (meth)acrylate-(meth)acrylic acid copolymers are more preferred, and methyl acrylate-methyl acrylic acid copolymers are further preferred. As the types of copolymers, for example, block copolymers, random copolymers, and graft copolymers can be cited. These copolymers can also be in the form of salts.

[0080] The dispersant can be obtained in the form of a commercial product or synthesized.

[0081] As dispersants that can be obtained in the form of commercial products, for example, Joncyrl 62, 67, 68, 678, 687 (styrene-acrylic acid copolymers manufactured by BASF); Mowinyl S-100A (modified vinyl acetate copolymers manufactured by Japan Coating Resin Corporation); Jurymer AT-210 (polyacrylate copolymers manufactured by Toagosei Co., Ltd.); and so on can be cited.

[0082] As a dispersant obtained by synthesis, for example, an A-B block polymer disclosed in International Publication No. 2013 / 115071 can be cited. The monomers constituting the A block of the A-B block polymer disclosed in International Publication No. 2013 / 115071 are at least one monomer selected from (meth)acrylic acid and linear or branched C4 alkyl (meth)acrylate, preferably at least one monomer selected from methacrylic acid and n-butyl methacrylate, and more preferably these two monomers are used in combination. In addition, the monomers constituting the B block of the A-B block polymer disclosed in International Publication No. 2013 / 115071 are at least one monomer selected from benzyl methacrylate and benzyl acrylate, and preferably benzyl methacrylate. As a specific example of the A-B block polymer, block copolymers disclosed in Synthesis Examples 3 to 8 of International Publication No. 2013 / 115071 can be cited.

[0083] 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.

[0084] In order to uniformly disperse the dispersant in water, a neutralizing agent can be used. As the neutralizing agent, for example, ammonia, hydroxides of alkali metals, hydroxides of alkaline earth metals, aliphatic amine compounds, alkanolamine compounds, etc. can be cited. Among them, ammonia and hydroxides of alkali metals are preferred, and ammonia is more preferred. As a standard for the amount of the neutralizing agent, when neutralization is carried out with the theoretical equivalent amount of the acid value of the dispersant, it is set as 100% neutralization degree, and usually it is 30 to 300% neutralization degree, preferably 50 to 200% neutralization degree.

[0085] The weight-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 further preferably 20,000 to 25,000. The weight-average molecular weight of the dispersant can be measured by gel permeation chromatography (GPC method). Specifically, HLC-8320GPC (manufactured by TOSOH Corporation) can be used as the GPC device, two TSK gel Super MultIpore HZ-H (manufactured by TOSOH Corporation, inner diameter 4.6 mm × 15 cm) can be used as columns, tetrahydrofuran can be used as the eluent, and TSK Standard (manufactured by TOSOH Corporation) can be used as the standard sample for measurement.

[0086] The PDI (weight-average molecular weight / number-average molecular weight) of the dispersant is preferably about 1.29 to 1.49. By setting it within the above range, the dispersibility and storage stability of the first ink composition tend to be improved.

[0087] The dispersant can be used in a state of being mixed with the first colorant. Additionally, it can also be used in a state where a part or all of the surface of the first colorant is coated with the dispersant. Or, these two states can also be used in combination.

[0088] The ratio of the total mass of the dispersant to the total mass of the first colorant is generally 0.01 to 1.0, preferably 0.05 to 0.6, and more preferably 0.1 to 0.5.

[0089] [First surfactant]

[0090] It is important that the ink composition has sufficient wettability on the ink non-absorbing / difficult-to-absorb medium. To impart wettability, surfactants are usually used. As surfactants for imparting wettability, various surfactants such as silicone-based, fluorine-based, and acetylene-based surfactants are well-known according to the use. Among them, for silicone-based surfactants, their ability to impart wettability is excellent. However, as a result of the research by the inventors of the present application, it has been found that when printing with ink compositions having different storage periods in combination, depending on the structure of the silicone-based surfactant, even if the storage stability (various physical property values such as ejection property, average particle size, viscosity, pH, etc.) of each ink composition does not change significantly, color bleeding between colors deteriorates. It is known that generally silicone-based surfactants decompose over time due to long-term storage (see Koji Sakuta, Journal of the Society of Dyers and Colourists, 2001, Vol. 74, No. 1, p. 34 - 38, etc.). From this, it is speculated that in silicone-based surfactants having a specific structure, the ability to adjust color bleeding between colors is lost due to structural decomposition.

[0091] The inventors of the present application studied the relationship between the structure of the silicone-based surfactant and the change in color bleeding over time, and found that by using the silicone-based surfactant represented by the following formula (1), color bleeding between colors is less likely to occur regardless of whether the storage periods of the two ink compositions are the same or different. The reason for suppressing the change in color bleeding over time is not clear, but it is speculated that the reason is that by using the silicone-based surfactant represented by formula (1), even if the structure decomposes over time, the structural parts of the hydrophobic part containing a siloxane structure (-Si-O-) and the hydrophilic part composed of ethyleneoxy and propyleneoxy are mostly maintained, and the function as a surfactant is not impaired.

[0092] [Chemical formula 4]

[0093]

[0094] In the above formula (1), R 1 and R 2 are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, preferably a hydroxyl group.

[0095] In the above formula (1), a is an integer from 1 to 80, preferably from 2 to 40, more preferably from 5 to 34. x and y are each independently an integer from 1 to 4, preferably an integer from 1 to 3. m and n are each independently an integer from 1 to 50, preferably an integer from 1 to 40, more preferably an integer from 1 to 30, further preferably an integer from 4 to 20, and particularly preferably an integer from 5 to 12. o and p are each independently an integer from 0 to 40, preferably an integer from 0 to 20, more preferably an integer from 0 to 10, further preferably an integer from 0 to 5. m + n is from 2 to 100, preferably from 4 to 80, more preferably from 8 to 40, further preferably from 10 to 25. o + p is from 0 to 80, preferably from 0 to 40, more preferably from 0 to 20, further preferably from 0 to 10.

[0096] The silicone surfactant represented by the above formula (1) can be obtained in the form of a commercial product or synthesized.

[0097] Examples of commercial products of the silicone surfactant represented by the above formula (1) include Silwet CoatOSil 2812, Silwet CoatOSil 2816, Silwet CoatOSil 3500, and Silwet CoatOSil 3505 manufactured by Momentive Performance Materials Inc.; BYK-331, BYK-333, BYK-UV3500 manufactured by BYK-Chemie GmbH, the general grade of BYK-New Product 1 and the cyclic siloxane-reduced grade of BYK-New Product 2 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); Tego Glide 410, Tego Glide 432, Tego Glide 435, Tego Glide 440, and Tego Glide 450 manufactured by Evonik Degussa GmbH; Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.; and so on.

[0098] The silicone surfactant represented by the above formula (1) can also be synthesized, for example, by a hydrosilylation reaction using a platinum catalyst with polyethylene glycol having an allyl group at one end and polydimethylsiloxane containing hydrogen groups at both ends as materials.

[0099] The content rate of the silicone surfactant represented by the above formula (1) is generally 0.01 to 3% by mass, preferably 0.05 to 2% by mass, and more preferably 0.1 to 1% by mass with respect to the total mass of the first ink composition.

[0100] [First hydrophobic organic solvent]

[0101] 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 making the water-octanol partition coefficient within this range, the effect of suppressing bleeding between colors, which is insufficient in the case of the silicone surfactant alone, can be further improved. In this specification, the so-called "water-octanol partition coefficient" refers to the ClogP value calculated using ChemDraw Professional ver.16.0 manufactured by Perkin Elmer. The number of decimal places of the value calculated in this way is not necessarily fixed. Therefore, in this specification, the third decimal place is rounded off and the value is recorded to the second decimal place. In addition, when the calculated value has two decimal places, the value is directly recorded. In addition, when the calculated value does not have two decimal places, the values of each digit up to the second decimal place are regarded as "zero" and all are recorded to the second decimal place. Hereinafter, the "water-octanol partition coefficient" may sometimes be referred to as the "ClogP value".

[0102] Examples of the organic solvent 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 ketone (2.71), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (2.74), 2-ethyl-1-hexanol (2.81), 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), diethylene glycol monobutyl ether adipate (3.49), etc. It should be noted that the values in parentheses are ClogP values.

[0103] The content rate of the first hydrophobic organic solvent is generally 0.01 to 2% by mass, preferably 0.05 to 1.5% by mass, and more preferably 0.1 to 1% by mass with respect to the total mass of the first ink composition.

[0104] [Water]

[0105] The first ink composition contains the above components and, if necessary, an ink conditioner, with the balance being water. As the water, ion-exchanged water, distilled water, or the like with few impurities (such as metal ions) is preferred.

[0106] [Ink conditioner]

[0107] The first ink composition may contain an ink conditioner in addition to the above components. As the ink conditioner, for example, binders, penetrants, viscosity regulators, surfactants other than silicone-based surfactants, preservatives, fungicides, pH regulators, chelating agents, rust inhibitors, water-soluble ultraviolet absorbers, antioxidants, etc. can be cited.

[0108] With respect to the total mass of the first ink composition, the total content rate of the ink conditioner other than the binder, penetrant, and viscosity regulator is usually 0 to 30% by mass, preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass.

[0109] (Binder)

[0110] As the binder, at least one selected from waxes and (meth)acrylic acid-based polymers is preferred. By including a binder in the ink composition, the abrasion resistance of the printed image can be improved. The binder is preferably added in the form of an emulsion, more preferably in the form of an aqueous emulsion.

[0111] As the wax, natural waxes and synthetic waxes can be used. As the natural wax, for example, emulsions obtained by dispersing the following waxes in an aqueous medium can be cited: 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; animal and plant-based waxes such as beeswax and lanolin; and so on. As the synthetic wax, for example, polyalkylene waxes (preferably poly C2-C4 alkylene waxes), oxidized polyalkylene waxes (preferably oxidized poly C2-C4 alkylene waxes), paraffin wax, etc. can be cited. Among them, at least one selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax is preferred, and oxidized polyethylene wax is more preferred.

[0112] As commercially available wax emulsions, for example, CERAFLOUR 925, 929, 950, 991, AQUACER 498, 515, 526, 531, 537, 539, 552, 1547, AQUAMAT 208, 263, 272 manufactured by BYK-Chemie; MINERPOL221, etc.; Mitsui Hi-WAX NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, NP505, etc. manufactured by Mitsui Chemicals, Inc.; KUE-100, 11 manufactured by Sanyo Chemical Industries, Ltd.; and so on. Among them, AQUACER515, 531, 537, 539, 1547 are preferred, and AQUACER 515, 531, 537, 1547 are more preferred.

[0113] The (meth)acrylic polymer as the binder is a polymer different from the above-mentioned dispersant. The (meth)acrylic polymer is preferably a polymer composed of four monomers: C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate.

[0114] The alkyl part of the C1-C4 alkyl methacrylate can 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 further preferred.

[0115] The alkyl part of the C6-C10 alkyl acrylate can be linear or branched, and is 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 further preferred.

[0116] The proportions of the four monomers, namely C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate, in the (meth)acrylic polymer are usually 40 to 60% by mass, 38 to 58% by mass, 1 to 10% by mass, and 1 to 5% by mass, preferably 45 to 55% by mass, 52 to 42% by mass, 2 to 4% by mass, and 1 to 3% by mass, and it is preferably set within these ranges so that the total is 100% by mass.

[0117] The acid value of the (meth)acrylic polymer is usually -10 to 35 mgKOH / g, preferably -5 to 30 mgKOH / g, and more preferably 0 to 25 mgKOH / g.

[0118] The glass transition temperature (Tg) of the (meth)acrylic polymer is usually -20 to 30 °C, preferably -15 to 25 °C, more preferably -10 to 20 °C.

[0119] In order to prevent clogging of the inkjet head, the average particle size of the binder is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm.

[0120] When the first ink composition contains a binder, its content (content based on the solid component) is usually 0.1 to 14% by mass, preferably 0.5 to 12% by mass, more preferably 2 to 10% by mass, and further preferably 3 to 8% by mass, relative to the total mass of the first ink composition.

[0121] (Penetrant)

[0122] As the penetrant, an organic solvent selected from glycol ethers and C4-C9 alkane diols and having a ClogP value of 0.00 or more and less than 2.00 is preferred. By including a penetrant in the ink composition, the ink tends to wet and spread on the non- or poorly absorbent medium, and the drying property of the ink becomes good.

[0123] Examples of penetrants having 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), isopropoxyethanol (0.09), diethylene glycol ethyl methyl ether (0.13), dipropylene glycol dimethyl ether (0.36), 3-methoxy-3-methyl-1-butanol (0.42), butyltriglycol (0.49), diethylene glycol diethyl ether (0.52), 1,2-hexanediol (0.53), diethylene glycol mono-isobutyl ether (0.54), propylpropylene glycol (0.62), butyldiglycol (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 values in parentheses are the ClogP values.

[0124] When the first ink composition contains a penetrant, its content is usually 0.1 to 30% by mass, preferably 0.2 to 20% by mass, more preferably 0.5 to 10% by mass, further preferably 2 to 8% by mass, and particularly preferably 4 to 6% by mass, relative to the total mass of the first ink composition.

[0125] (Viscosity regulator)

[0126] The first ink composition may further contain a viscosity regulator. In the case of industrial inkjet printers, based on the specifications of the mounted print head (the nozzle for ejecting ink), the viscosity range of the ink composition that can usually be ejected has been determined. Therefore, a viscosity regulator can be added to the first ink composition to adjust its viscosity to an appropriate range.

[0127] As the viscosity regulator, any substance that can adjust the viscosity of the ink composition is acceptable and there is no particular limitation, and known substances can be used. As specific examples thereof, for example, water-soluble organic solvents (excluding the organic solvents cited as the above penetrants), saccharides, etc. can be cited. Among them, water-soluble organic solvents having a ClogP value of usually less than 0.00, preferably -0.05 or less, 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, usually -4.00 or more, preferably -3.00 or more, more preferably -2.00 or more, and further preferably -1.50 or more.

[0128] As water-soluble organic solvents having a ClogP value less than 0.00, for example, 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-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), glycerol (-1.54), diglycerol (-2.96), Glycereth-3 (-3.49) and Glycereth-20 (-5.42) manufactured by Aoki Oil & Fat Co., Ltd., etc. It should be noted that the values in parentheses are ClogP values.

[0129] With respect to the total mass of the first ink composition, the content rate of the viscosity regulator is usually 0 to 55% by mass, preferably 5 to 40% by mass, more preferably 10 to 30% by mass.

[0130] (Surfactants other than silicone-based surfactants)

[0131] As surfactants, anionic, cationic, amphoteric, and fluorine-based surfactants can be cited.

[0132] As anionic surfactants, for example, alkylsulfonocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acyl amino acids or their salts, N-acyl methyl taurates, polyoxyalkylene ether sulfates of alkyl sulfates, phosphate esters of polyoxyethylene alkyl ethers of alkyl sulfates, rosin soaps, castor oil sulfate esters, lauryl sulfate esters, alkylphenol-type phosphate esters, alkyl-type phosphate esters, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, dioctyl sulfosuccinates, etc. can be cited.

[0133] As cationic surfactants, for example, 2-vinylpyridine derivatives, poly-4-vinylpyridine derivatives, etc. can be cited.

[0134] As amphoteric surfactants, for example, lauryldimethylaminoacetate betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid amide propyldimethylaminoacetate betaine, polyoctyl polyaminoethyl glycine, imidazoline derivatives, etc. can be cited.

[0135] As fluorine-based surfactants, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid-based compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain, etc. can be cited.

[0136] When the first ink composition contains a surfactant other than a silicone-based surfactant, its content is usually 0.1 to 2.0% by mass relative to the total mass of the first ink composition.

[0137] (Preservatives)

[0138] As preservatives, for example, organic sulfur-based, organic nitrogen-sulfur-based, organic halogen-based, haloarylsulfone-based, iodopropargyl-based, haloalkylthio-based, nitrile-based, pyridine-based, 8-hydroxyquinoline-based, benzothiazole-based, isothiazoline-based, dithiol-based, pyridine oxide-based, nitropropane-based, organotin-based, phenol-based, quaternary ammonium salt-based, triazine-based, thiazine-based, acyl aniline-based, adamantane-based, dithiocarbamate-based, brominated indanone-based, benzyl bromoacetate-based, inorganic salt-based and other compounds can be cited. Specific examples of commercially available products of preservatives can be cited such as Proxel GXL(S), XL-2(S) manufactured by LONZA Co., Ltd.

[0139] (Mildew-proof agents)

[0140] As a mildew-proof agent, for example, sodium dehydroacetate, sodium benzoate, sodium 1-oxide pyrithione, ethyl p-hydroxybenzoate, 1,2-benzisothiazolin-3-one, and their salts, etc. can be cited.

[0141] (pH adjuster)

[0142] As a pH adjuster, any substance can be used as long as it can adjust the pH of the prepared ink composition to 5 to 11 without causing adverse effects. As specific examples thereof, for example, alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (ammonia water); carbonates of alkali metals such as lithium carbonate, sodium carbonate, sodium bicarbonate, and potassium carbonate; alkali metal salts of organic acids such as sodium silicate and potassium acetate; inorganic bases such as disodium phosphate; and so on.

[0143] (Chelating agent)

[0144] As a chelating agent, for example, sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethyl ethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uracildiacetate, etc. can be cited.

[0145] (Rust inhibitor)

[0146] As a rust inhibitor, for example, acid sulfite, sodium thiosulfate, ammonium mercaptoacetate, diisopropylammonium nitrite, pentaerythritol tetranitrate, dicyclohexylammonium nitrite, etc. can be cited.

[0147] (Water-soluble ultraviolet absorber)

[0148] As a water-soluble ultraviolet absorber, for example, sulfonated benzophenone-based compounds, benzotriazole-based compounds, salicylic acid-based compounds, cinnamic acid-based compounds, triazine-based compounds, etc. can be cited.

[0149] (Antioxidant)

[0150] As an antioxidant, various organic-based and metal complex-based anti-fading agents can be used. As the organic-based anti-fading agents, for example, hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, etc. can be cited.

[0151] [Preparation method of ink composition, etc.]

[0152] The first ink composition is preferably prepared by mixing with other components after preparing a dispersion liquid containing the first colorant and a dispersant.

[0153] As a method for preparing a dispersion, there may be mentioned a phase inversion emulsification method, an acid precipitation method, an interfacial polymerization method, an in-situ polymerization method, a liquid-phase curing film method, a coagulation (phase separation) method, a liquid drying method, a melt dispersion cooling method, an air suspension coating method, a spray drying method, etc. Among them, the phase inversion emulsification method, the acid precipitation method, and the interfacial polymerization method are preferred, and the phase inversion emulsification method is more preferred.

[0154] In the case of preparing a dispersion by the phase inversion emulsification method, 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. From the liquid obtained as described above, the organic solvent and a part of water are distilled off under reduced pressure, whereby the target dispersion can be obtained.

[0155] The dispersion treatment can be carried out using a sand mill (bead mill), a roll mill, a ball mill, a paint shaker, an ultrasonic disperser, a microfluidic homogenizer, etc. For example, when using a sand mill, beads having a particle size of about 0.01 to 1 mm can be used, and the filling rate of the beads can be appropriately set to carry out the dispersion treatment. Operations such as filtration and centrifugation can be performed on the dispersion obtained as described above, whereby the particle sizes of the particles contained in the dispersion are made uniform. When foaming occurs in the preparation of the dispersion, a very small amount of a known antifoaming agent such as a silicone-based or alkynediol-based antifoaming agent can be added.

[0156] 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 further preferably 50 to 250 nm. In addition, 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 making the particle size of the first colorant in the dispersion within the range described above, there is a tendency to ensure the storage stability of the ink composition and to stably eject the ink without clogging the nozzles of the inkjet head. 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 becomes 50%, D90 is the particle size at which the cumulative particle size distribution from the small particle size side becomes 90%, and D10 is the particle size at which the cumulative particle size distribution from the small particle size side becomes 10%.

[0157] The pH of the first ink composition at 25°C is generally 7 to 11, preferably 8 to 10. The surface tension of the first ink composition at 25°C is generally 10 to 50 mN / m, preferably 20 to 40 mN / m. The viscosity of the first ink composition at 25°C is generally 2 to 30 mPa·s, preferably 3 to 20 mPa·s. The pH, surface tension, and viscosity of the first ink composition can be adjusted using a pH regulator, a surfactant, a viscosity regulator, etc.

[0158] The first ink composition can be used in various printing processes. For example, the first ink composition is suitable for writing instruments, various printing, information printing, dyeing, etc., and is preferably used for inkjet printing.

[0159] <Second Ink Composition>

[0160] The second ink composition contains a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, and may also contain other components. As other components, for example, a dispersant and an ink conditioner can be cited.

[0161] As the second colorant, the second surfactant, the second hydrophobic organic solvent, and other components, the same substances as those in the first ink composition can be used. In addition, the content rate of each component can also be set to the preferred range described for the first ink composition.

[0162] The second colorant is preferably a color different from the first colorant. This is because when the first colorant and the second colorant are different to the extent that they can be visually recognized, color bleeding is easily observed. 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 purple.

[0163] The content rates of the first surfactant and the first hydrophobic organic solvent in the first ink composition, and the content rates 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 rate of the first surfactant in the first ink composition is set as A1 (mass%), the content rate of the first hydrophobic organic solvent is set as A2 (mass%), the content rate of the second surfactant in the second ink composition is set as B1 (mass%), and the content rate of the second hydrophobic organic solvent is set as B2 (mass%), the condition represented by the following formula (2) must be satisfied.

[0164] 0.05 ≤ [0.5×(B1 - A1) + (B2 - A2)] ≤ 0.70 ··· (2)

[0165] The value of [0.5×(B1 - A1)+(B2 - A2)] is preferably in the range of 0.10 to 0.65, more preferably in the range of 0.20 to 0.60.

[0166] In the above formula (2), the coefficient is determined according to the degree of influence on bleeding between colors. Specifically, compared with the surfactant, the low molecular weight hydrophobic organic solvent greatly contributes to bleeding between colors. Therefore, the difference in the content rate of the surfactant (B1 - A1) is multiplied by 0.5 as the coefficient. By satisfying the conditions of the formula (2), bleeding between colors can be suppressed, thereby achieving good printing image quality. It has been confirmed that when the value of [0.5×(B1 - A1)+(B2 - A2)] is outside the above range, the balance of hydrophilicity and hydrophobicity at the ink interface of the first ink composition and the second ink composition collapses, and thus bleeding between colors deteriorates. For example, it has been confirmed that when the value of [0.5×(B1 - A1)+(B2 - A2)] is less than 0.05, bleeding of the first ink composition into the second ink composition occurs. On the other hand, when the value of [0.5×(B1 - A1)+(B2 - A2)] is greater than 0.70, bleeding of the second ink composition into the first ink composition occurs.

[0167] It should be noted that the phenomenon that bleeding between colors can be suppressed when the conditions of the above formula (2) are satisfied only occurs when the organosilicon surfactant represented by the above formula (1) is used in the first and second ink compositions. The reason is not yet clear. It is speculated that when printing two different colors of ink continuously, if the balance of the ink interface tension between the two colors collapses, the color will bleed into the other. It is considered that at the ink interface, the surfactant and the hydrophobic organic solvent are oriented, and thus are greatly affected by them. On the other hand, since the ink ejection based on inkjet printing is achieved by the vibration of the piezoelectric element of the inkjet head, until just after the ink lands, it is also affected by the vibration caused by the driving of the inkjet head, etc. Therefore, it is considered that just after the ink lands, first, the low molecular weight hydrophobic organic solvent that is relatively easy to be oriented at the interface is oriented, and then the surfactant is oriented at the interface. It is speculated that the difference in the timing of this orientation contributes to the suppression of bleeding between colors. In addition, compared with the general surfactant in which the hydrophilic group and the hydrophobic group are separated at both ends, the organosilicon surfactant represented by the above formula (1) has a structure in which hydrophilic groups are present at its characteristic two ends. Therefore, it is speculated that the timing of its orientation to the ink interface is late. It is considered that because the timing of orientation is late, the influence on the ink interface just after the ink lands becomes smaller. It is considered that since the above formula (2) uses the coefficient corresponding to the organosilicon surfactant represented by the above formula (1), the above relational expression is not satisfied in the case of other types of surfactants.

[0168] According to the ink set related to the present embodiment, regardless of the storage period of each ink composition, a printed image with extremely little color bleeding can be achieved. In addition, the ink set related to the present embodiment has good wetting and spreading on an ink non- or poorly absorbent medium, and a printed image with extremely little granularity can be obtained. The ink set related to the present embodiment is extremely useful in various printing applications, especially inkjet printing.

[0169] 《Ink Medium Set》

[0170] The ink medium set related to the present embodiment includes the above-mentioned ink set related to the present embodiment and a printing medium.

[0171] Examples of the printing medium include paper, film, fiber, cloth (such as cellulose, nylon, wool, etc.), leather, a substrate for a color filter, and the like. These printing media can be generally classified into printing media having an ink receiving layer and printing media not having an ink receiving layer. The ink set related to the present embodiment can be applied to any printing medium, but is suitably used for printing media not having an ink receiving layer.

[0172] Printing media having an ink receiving layer are generally referred to as inkjet special paper, inkjet special film, glossy paper, and the like. Examples of representative commercially available products thereof include professional photo paper, super photo paper, glossy Gold, and matte photo paper manufactured by Canon Inc.; photo paper CRISPIA (high gloss), photo paper (glossy), and matte photo paper manufactured by Seiko Epson Corp.; high-quality photo paper (glossy) manufactured by Hewlett-Packard Japan, Ltd.; and Picture Color Photo Retouch Pro manufactured by FUJI FILM Co., Ltd.; and so on.

[0173] Examples of printing media not having an ink receiving layer include various papers such as art paper and coated paper used in intaglio printing and offset printing; cast-coated paper used in label printing; and the like. When using a printing medium not having an ink receiving layer, an operation of performing surface modification treatment on the printing medium is also preferably performed for the purpose of improving the fixing property of the colorant and the like. Examples of the surface modification treatment include known methods such as corona discharge treatment, plasma treatment, and flame treatment.

[0174] 《Inkjet Recording Method and Printing Medium》

[0175] The inkjet recording method related to the present embodiment is an inkjet recording method using the above-mentioned ink set related to the present embodiment, and includes the following steps: a step of ejecting droplets of a first ink composition and attaching the droplets to a printing medium to form a first image; and a step of ejecting droplets of a second ink composition and attaching the droplets to the printing medium on which the first image is formed to form a second image. The step of forming the first image and the step of forming the second image are performed by an inkjet method.

[0176] In addition, the printing medium according to the present embodiment is obtained by applying a second ink composition on a first image formed by applying a first ink composition.

[0177] As the inkjet method, a known method can be adopted. Specific examples of the inkjet method include, for example, a charge control method, a drop-on-demand (pressure pulse) method, an acoustic inkjet method, a thermal inkjet method, and the like. In addition, the inkjet method also includes the following methods: a method of improving the image quality by ejecting a large amount of an ink composition having a low content rate of a colorant in a small volume; a method of improving the image quality by using a plurality of ink compositions having substantially the same hue and different content rates of a colorant; a method of improving the fixing property of a colorant by using a colorless and transparent ink; and the like.

[0178] When printing on a printing medium, for example, a container (ink tank) containing ink is loaded into a predetermined position of an inkjet printer, and printing is performed on the printing medium by the above-described printing method. It should be noted that by loading containers containing inks of respective colors into predetermined positions of an inkjet printer and performing printing on a printing medium by the above-described printing method, full-color printing can also be achieved.

[0179] Regarding all of the above, combinations of preferred options are more preferred, and combinations of more preferred options are further preferred. The same applies to combinations of a preferred option and a more preferred option, combinations of a more preferred option and a further preferred option, and the like.

[0180] Examples

[0181] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited by the following examples.

[0182] In the examples, unless otherwise specified, "parts" means parts by mass and "%" means mass%. In the examples, when it is necessary to quantify the solid content of the colorant in the dispersion, MS-70 manufactured by A&D Co., Ltd. is used, and the value is calculated as a conversion value of only the colorant by the dry weight method.

[0183] <Preparation Example 1: Preparation of Dispersion Dp1 of Colorant>

[0184] An additional experiment was conducted on Synthesis Example 3 of International Publication No. 2013 / 115071 to obtain a block copolymer (Block Copolymer A). The acid value of the obtained block copolymer was 105 mgKOH / g, and the weight-average molecular weight was 25,000. 4.8 parts of the obtained block copolymer was dissolved in 20 parts of 2-butanone to form a uniform solution. A liquid obtained by dissolving sodium hydroxide (0.35 part) in water (58.8 parts) was added to this liquid, and the mixture was stirred for 1 hour to obtain an emulsion. C.I. Pigment Blue 15:4 (hereinafter referred to as "PB15:4".) (16 parts) was added to this emulsion, and the mixture was subjected to dispersion treatment in a sand mill at 1500 rpm for 15 hours to obtain a liquid. After adding water (100 parts) dropwise to the obtained liquid, the liquid was filtered to obtain a filtrate. From the obtained filtrate, 2-butanone and a part of water were distilled off under reduced pressure using an evaporator to obtain a cyan dispersion having a coloring agent content of 12.0%. The obtained dispersion was designated as "Dp1".

[0185] <Preparation Example 2: Preparation of Dispersion Dp2 of Colorant>

[0186] Except for using C.I. Pigment Yellow 74 (hereinafter referred to as "PY74".) instead of PB15:4, the same operations as in Preparation Example 1 were carried out to obtain a yellow dispersion having a coloring agent content of 12.0%. The obtained dispersion was designated as "Dp2".

[0187] <Synthesis Example 1: Synthesis of Organosilicon Surfactant B>

[0188] To a solution of hexaethylene glycol allyl methyl ether (7.0 g) in tetrahydrofuran (20 mL) was added hexadecamethyloctasiloxane (5.8 g) and chloroplatinic acid (0.1 mL), and the mixture was maintained at 65 °C for 24 hours with stirring to carry out the reaction. After the reaction was completed, the solvent was distilled off under reduced pressure using an evaporator to obtain organosilicon surfactant B. The obtained organosilicon surfactant B was the surfactant in which R 1 and R 2 were hydroxyl groups, a = 6, x = 2, y = 2, m = 7, n = 7, o = 0, p = 0.

[0189] <Preparation of Ink Compositions C1 - C18 and Y1 - Y20>

[0190] The dispersion liquids Dp1 and Dp2 were mixed with the respective components described in Tables 1 to 4 below, and then filtered using a membrane filter with a pore size of 3 μm (cellulose mixed ester type membrane filter manufactured by Advantec), whereby ink compositions C1 to C18 and Y1 to Y20 for evaluation tests were obtained. The content ratios of the colorants were adjusted so as to be 4.5% with respect to the total mass of the ink compositions. The ink compositions C1 to C18 described in Tables 1 and 2 are all cyan inks. In addition, the ink compositions Y1 to Y20 described in Tables 3 and 4 are all yellow inks. The numerical values in Tables 1 to 4 represent the parts of the respective components.

[0191] [Table 1]

[0192] Ingredient C1 C2 C3 C4 C5 C6 C7 C8 C9 Dp1 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 PG 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 1,2-HD 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 TEA 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 TG450 0.5 0.5 0.5 1.0 1.0 0.5 SAG005 0.5 Surfactant A 0.5 Surfactant B BYK349 TW270 CS-12 0.8 1.0 1.4 0.8 1.4 0.8 0.0 0.8 0.8 DBDG 1,2-ND EGmHE CS-16 1,2-DD Aquacer 515 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 Water 22.0 21.8 21.4 21.5 20.9 22.5 22.8 22.0 22.0 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0193] [Table 2]

[0194] Ingredient C10 C11 C12 C13 C14 C15 C16 C17 C18 Dp1 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 PG 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 1,2-HD 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 TEA 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 TG450 0.5 0.5 0.5 0.5 0.5 0.5 SAG005 Surfactant A Surfactant B 0.5 BYK349 0.5 TW270 0.5 CS-12 0.8 0.8 0.8 DBDG 0.8 1,2-ND 0.8 EGmHE 0.8 0.8 CS-16 0.8 1,2-DD 0.8 Aquacer 515 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 Water 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0195] [Table 3]

[0196] Ingredient Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10 Dp2 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 PG 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 1,2-HD 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 TEA 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 TG450 0.5 0.5 1.0 1.0 0.0 0.8 SAG005 0.5 Surfactant A 0.5 Surfactant B 0.5 BYK349 0.5 TW270 CS-12 0.8 1.4 0.8 1.4 1.4 0.8 1.4 1.4 1.4 DBDG 1,2-ND EGmHE CS-16 1,2-DD Aquacer 515 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 Water 22.0 21.4 21.5 20.9 21.9 22.5 22.0 21.4 21.4 21.4 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0197] [Table 4]

[0198] Ingredient Y11 Y12 Y13 Y14 Y15 Y16 Y17 Y18 Y19 Y20 Dp2 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 37.5 PG 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 1,2-HD 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 TEA 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 TG450 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 SAG005 Surfactant A Surfactant B BYK349 TW270 0.5 CS-12 1.4 1.5 0.9 1.55 DBDG 1.4 1,2-ND 1.4 EGmHE 1.4 1.4 CS-16 1.4 1,2-DD 1.4 Aquacer 515 5.7 5.7 5.7 5.7 5.7 Water 21.4 21.4 21.4 21.4 21.4 98.5 99.2 98.6 98.5 98.6 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

[0199] Details of the respective components in Tables 1 to 4 are as described below.

[0200] (Dispersion liquid)

[0201] · Dp1: Dispersion liquid Dp1 obtained in Production Example 1

[0202] · Dp2: Dispersion liquid Dp2 obtained in Production Example 2

[0203] (Viscosity regulator)

[0204] · PG: Propylene glycol

[0205] (Penetrant)

[0206] · 1,2-HD: 1,2-Hexanediol

[0207] (pH regulator)

[0208] · TEA: Triethanolamine

[0209] (Silicone-based surfactant)

[0210] · TG450: TEGO Glide 450

[0211] · SAG005: Silface SAG005

[0212] · Surfactant A: BYK - New Product 1 general grade described in the materials published on June 22, 2020

[0213] · Surfactant B: Surfactant B obtained in Synthesis Example 1

[0214] · TW270: TEGO wet 270

[0215] (Hydrophobic organic solvent)

[0216] · CS - 12: 2,2,4 - trimethyl - 1,3 - pentanediol monoisobutyrate (ClogP value: 2.74)

[0217] · DBDG: Dibutyl diglycol (ClogP value: 2.63)

[0218] · 1,2 - ND: 1,2 - nonanediol (ClogP value: 2.11)

[0219] · EGmHE: Ethylene glycol monohexyl ether (ClogP value: 1.90)

[0220] · CS - 16: 2,2,4 - trimethyl - 1,3 - pentanediol diisobutyrate (ClogP value: 4.49)

[0221] · 1,2 - DD: 1,2 - dodecanediol (ClogP value: 3.70)

[0222] <Examples 1 - 12 and Comparative Examples 1 - 13>

[0223] After storing the ink compositions C1 - C18 and Y1 - Y20 prepared as described above at room temperature for 4 weeks, they were combined as the first ink composition and the second ink composition as shown in Tables 5 - 8 below to prepare the ink sets of Examples 1 - 12 and Comparative Examples 1 - 13.

[0224] <(A) Evaluation of initial color bleeding>

[0225] (1) Preparation of Test Piece 1

[0226] Using the ink sets of Examples 1 to 12 and Comparative Examples 1 to 13, a linear image (second image) with a line width of 1.0 mm was printed at 100% of the second ink composition in a manner overlapping a solid image (first image) of 100% of the first ink composition to obtain a printed image. During printing, a printing apparatus equipped with two KJ4B inkjet heads manufactured by KYOCERA Corporation was used, and printing was performed under the conditions of a frequency of 10 kHz and binary (medium droplet) in the order of the first ink composition and the second ink composition, using "OK Topcoat+" manufactured by Oji Paper Co., Ltd. as the printing medium. The two inkjet heads were provided in the printing apparatus in the order of the first ink composition and the second ink composition from the upstream side in the feeding direction of the printing medium. At this time, the interval between the inkjet heads filled with the first ink composition and the second ink composition was set to 90 mm. The obtained 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 Test Piece 1 was measured. In the measurement of the line width, a printing image evaluation apparatus PIAS-II manufactured by QEA Corporation was used.

[0227] (2) Preparation of Test Piece 2

[0228] Using the ink sets of Examples 1 to 12 and Comparative Examples 1 to 13, a solid image (second image) of 100% of the second ink composition was printed in a manner overlapping a linear image (first image) of 100% of the first ink composition with a line width of 1.0 mm to obtain a printed image. The printing apparatus, printing conditions, and printing medium were the same as those in the above (1). The obtained printed image was dried in the same manner as in the above (1) to obtain Test Piece 2. Then, the line width of the first image observed through the second image of Test Piece 2 was measured.

[0229] (3) Evaluation

[0230] The ratio (%) of the line width was calculated according to the following formula and evaluated according to the following four-grade evaluation criteria. When the ratio of the line width is small, it means that bleeding between colors is suppressed. The evaluation results are shown in Tables 5 to 8 below.

[0231] Ratio of line width (%) = 100 × (measured value of line width - 1.0 mm) / 1.0 mm

[0232] - Evaluation Criteria -

[0233] A: Ratio is 25% or less

[0234] B: Ratio is 26 - 50%

[0235] C: Ratio is 51 - 100%

[0236] D: Ratio is 101% or more

[0237] [Table 5]

[0238]

[0239] [Table 6]

[0240]

[0241] [Table 7]

[0242]

[0243] [Table 8]

[0244]

[0245] [Examples 13 to 24 and Comparative Examples 14 to 26]

[0246] The first ink composition in Tables 9 to 12 was stored in a constant temperature bath at 60°C for 4 weeks to conduct an accelerated test. The second ink composition was not subjected to the accelerated test and was stored at room temperature for 4 weeks. The accelerated test of storing at 60°C for 4 weeks is equivalent to storing at 25°C for 1 year. The first ink composition that had undergone the accelerated test and the second ink composition that had been stored at room temperature were combined as shown in Tables 9 to 12 to prepare the ink sets of Examples 13 to 24 and Comparative Examples 14 to 26.

[0247] [(B) Evaluation of Color Bleeding after Accelerated Test]

[0248] (1) Preparation of Test Piece 3

[0249] Using the ink sets of Examples 13 to 24 and Comparative Examples 13 to 26, a straight-line image (second image) with a line width of 1.0 mm was printed in an amount of 100% of the second ink composition in such a manner as to overlap a solid image (first image) of 100% of the first ink composition to obtain a printed image. The printing apparatus, printing conditions, and printing medium were the same as those in (1) of the above (A). The obtained printed image was dried under an IR heater set at 100°C for 3 seconds to obtain Test Piece 3. Then, the line width of the second image formed on the first image of Test Piece 3 was measured.

[0250] (2) Evaluation

[0251] The ratio (%) of the line width was calculated according to the following formula and evaluated according to the following four-grade evaluation criteria. When the ratio of the line width is small, it means that color bleeding is suppressed regardless of the storage period. The evaluation results are shown in Tables 9 to 12 below.

[0252] Ratio (%) of line width = 100 × {Measured value of line width - (Measured value of line width obtained in (1) of (A) above)} / (Measured value of line width obtained in (1) of (A) above)

[0253] - Evaluation criteria -

[0254] A: Ratio is 25% or less

[0255] B: Ratio is 26 - 50%

[0256] C: Ratio is 51 - 100%

[0257] D: Ratio is 101% or more

[0258] [Table 9]

[0259]

[0260] [Table 10]

[0261]

[0262] [Table 11]

[0263]

[0264] [Table 12]

[0265]

[0266] As shown in Tables 5 and 6 above, the ink sets of Examples 1 to 12 suppressed bleeding between colors to 25% or less. From this, it was confirmed that for the ink sets of Examples 1 to 12, the storage period after preparing the first and second ink compositions was short, and in a fresh state, the performance of suppressing bleeding between colors was excellent. In addition, as shown in Tables 9 and 10 above, the ink sets of Examples 13 to 24 also suppressed bleeding between colors to 25%. From this, it was confirmed that for the ink sets of Examples 13 to 24, even when the storage periods of the first and second ink compositions were different, the deterioration of bleeding between colors was reduced.

[0267] On the other hand, as shown in Tables 7, 8, 11, and 12 above, it was confirmed that for the ink sets of Comparative Examples 1 to 26, in at least one of the cases where the storage periods were the same and the cases where the storage periods were different, the evaluation of bleeding between colors was inferior to that of the Examples.

Claims

1. An ink set, comprising: 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, wherein the second ink composition is applied onto a first image formed using the first ink composition to form a second image, wherein the first surfactant and the second surfactant are each independently a silicone surfactant represented by the following formula (1), [Chemical formula 1] In formula (1), R 1 and R 2 are each independently a hydrogen atom, a hydroxyl 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 from 2 to 100, and o + p is from 0 to 80; 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 ratio of the first surfactant in the first ink composition is A1 (mass %), the content ratio of the first hydrophobic organic solvent is A2 (mass %), the content ratio of the second surfactant in the second ink composition is B1 (mass %), and the content ratio of the second hydrophobic organic solvent is B2 (mass %), the following condition represented by formula (2) is satisfied, 0.05 ≤ [0.5×(B1 - A1) + (B2 - A2)] ≤ 0.70 ··· (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. 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 wax and (meth)acrylic polymers.

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

6. The ink set according to claim 4 or 5, wherein, the wax is oxidized polyethylene wax.

7. An inkjet recording method using the ink set according to any one of claims 1 to 6, the inkjet recording method including the following steps: a step of ejecting droplets of the first ink composition and attaching the droplets to a printing medium to form a first image; and a step of ejecting droplets of the second ink composition and attaching the droplets to the printing medium on which the first image is formed to form a second image.

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

Images