Water-based ink, ink cartridge, inkjet recording method, and method for manufacturing water-based ink.

Abstract

To provide aqueous ink for inkjet which enables recording of a yellow image excellent in color development property and light resistance.SOLUTION: Aqueous ink for inkjet contains a pigment and a resin dispersant for dispersing a pigment. The pigment contains C.I. pigment yellow 74 and C.I. pigment yellow 138, a volume-based cumulative 50%-particle size of particle size distribution of the C.I. pigment yellow 138 is 85 nm or less, and a ratio of the volume-based cumulative 50%-particle size of particle size distribution of the C.I. pigment yellow 138 to the volume-based cumulative 50%-particle size of particle size distribution of the C.I. pigment yellow 74 is 0.72 times or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to water-based ink and ink cartridges. ,stomach Inkjet recording method , and method for manufacturing aqueous inks Regarding. [Background technology]

[0002] In recent years, there has been a growing demand for improved lightfastness of images recorded using inkjet recording methods. As a result, the use of pigment inks, which contain pigments as colorants, is increasing as they can record images with superior lightfastness. However, compared to dye-based inks, which contain dyes as colorants, pigment inks can sometimes produce images with inferior color reproduction. Therefore, there is a need for pigment inks that can record images with both excellent lightfastness and color reproduction. In particular, yellow inks containing yellow pigments present challenges in achieving both lightfastness and color reproduction in the resulting images.

[0003] To address the above-mentioned challenges, for example, an ink has been proposed that uses CI Pigment Yellow 138 and CI Pigment Yellow 74 in combination to achieve both lightfastness and color development in images (Patent Document 1). Furthermore, an ink has been proposed that contains CI Pigment Yellow 74, CI Pigment Yellow 128, and multiple resins that disperse these pigments, enabling the recording of images with improved lightfastness, color development, and gloss (Patent Document 2). Additionally, an ink has been proposed that contains CI Pigment Yellow 74, CI Pigment Yellow 128, a specific surfactant, and a specific organic solvent, enabling the recording of images with improved lightfastness, color development, and gloss (Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-099917 [Patent Document 2] Japanese Patent Publication No. 2011-174044 [Patent Document 3] Japanese Patent Publication No. 2012-072359 [Overview of the project] [Problems that the invention aims to solve]

[0005] Using the inks proposed in Patent Documents 1 to 3, it was possible to record images with improved color development compared to using inks containing CI Pigment Yellow 138 or CI Pigment Yellow 128 alone as a colorant. However, the color development of images recorded with the inks proposed in Patent Documents 1 to 3 was not as good as that of images recorded with inks containing only CI Pigment Yellow 74 as a colorant. Furthermore, when CI Pigment Yellow 138 and CI Pigment Yellow 74 were used together, the lightfastness of the image sometimes decreased compared to when each pigment was used alone.

[0006] Therefore, an object of the present invention is to provide an aqueous inkjet ink capable of recording yellow images with excellent color development and lightfastness. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided an aqueous ink for inkjet containing a pigment and a resin dispersant for dispersing the pigment, wherein the pigment includes C.I. Pigment Yellow 74 and C.I. Pigment Yellow 138, the cumulative 50% particle size based on volume-based particle size distribution of the C.I. Pigment Yellow 138 is 85 nm or less, the ratio of the cumulative 50% particle size based on volume-based particle size distribution of the C.I. Pigment Yellow 138 to the cumulative 50% particle size based on volume-based particle size distribution of the C.I. Pigment Yellow 74 is 0.72 times or less, the resin dispersant is physically adsorbed on the particle surfaces of the C.I. Pigment Yellow 74 and the C.I. Pigment Yellow 138 respectively, and disperses the C.I. Pigment Yellow 74 and the C.I. Pigment Yellow 138 in the aqueous ink respectively, and the acid value of the resin dispersant is 115 mgKOH / g or more 350mgKOH / g or less , and the aqueous ink is characterized by comprising a resin having a unit derived from at least one monomer selected from the group consisting of acrylic acid and methacrylic acid. Effects of the Invention

[0008] According to the present invention, an aqueous ink for inkjet capable of recording a yellow image excellent in color developability and light resistance can be provided. Further, according to the present invention, an ink cartridge using the aqueous ink and an inkjet recording method can be provided. Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically showing one embodiment of the ink cartridge of the present invention. [Figure 2] FIG. 2 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, wherein (a) is a perspective view of a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. Mode for Carrying Out the Invention

[0010] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based inkjet ink may be simply referred to as "ink." Unless otherwise specified, physical properties are values ​​at room temperature (25°C). "CI" is an abbreviation for "color index."

[0011] To obtain an ink capable of recording images with excellent color development, it is preferable to use CI Pigment Yellow 74, which has high color development characteristics in terms of molecular structure and hue angle. However, CI Pigment Yellow 74 is an organic pigment that is easily degraded by light because it has azo bonds in its molecular structure that are easily broken by light. Therefore, the inventors attempted to achieve both color development and lightfastness by using CI Pigment Yellow 138, which has a molecular structure that is less susceptible to degradation by light and has excellent lightfastness, in combination with CI Pigment Yellow 74. As a result, it was found that, as expected, the color development of the resulting image decreased when CI Pigment Yellow 138 and CI Pigment Yellow 74 were used together compared to when CI Pigment Yellow 74 was used alone. However, it was found that the lightfastness of the resulting image actually decreased when these pigments were used together compared to when CI Pigment Yellow 74 or CI Pigment Yellow 138 were used alone.

[0012] The density of CI Pigment Yellow 74 is 1.44 g / cm³. 3 It is approximately [amount]. On the other hand, the density of CI Pigment Yellow 138 is 1.85 g / cm³. 3This is the extent of the issue. Therefore, when particle sizes are equivalent, on a recording medium coated with ink, many of the CI Pigment Yellow 138 particles have a greater settling velocity than the CI Pigment Yellow 74 particles. Furthermore, when using a general-purpose resin dispersant in an inkjet water-based ink, the adsorption force of the resin dispersant to CI Pigment Yellow 74 is weaker than that of the resin dispersant to CI Pigment Yellow 138. Therefore, the resin dispersant that dispersed the CI Pigment Yellow 74 is easily pulled down and settles by the CI Pigment Yellow 138. Consequently, when CI Pigment Yellow 138 and CI Pigment Yellow 74 are used together, compared to when CI Pigment Yellow 74 is used alone, the amount of resin dispersant remaining near the surface of the recorded image is considered to be less. And when the amount of resin dispersant remaining near the surface is small, the lightfastness of the image decreases. For the reasons described above, it is considered that the lightfastness of the image is reduced when CI Pigment Yellow 74 or CI Pigment Yellow 138 are used together, compared to when CI Pigment Yellow 74 or CI Pigment Yellow 138 are used alone.

[0013] The inventors further investigated the particle size of CI Pigment Yellow 138. As a result, they found that light resistance is improved when the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is set to 0.72 times or less the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74. According to Stokes' formula for calculating the settling velocity from particle size and density, the density difference of the particles is 0.41 g / cm³. 3The sedimentation rates of C.I. Pigment Yellow 138 and C.I. Pigment Yellow 74 can be estimated at this level. If the particle size of C.I. Pigment Yellow 138 having a higher density is about 0.72 times the particle size of C.I. Pigment Yellow 74 having a lower density, the sedimentation rates of these two pigments are equal. Accordingly, the cumulative 50% particle size based on volume particle size distribution of C.I. Pigment Yellow 138, expressed as a ratio to the cumulative 50% particle size based on volume particle size distribution of C.I. Pigment Yellow 74, is set to 0.72 times or less. This makes it easy for the sedimentation rate of C.I. Pigment Yellow 138 to decrease, and makes it difficult for the sedimentation rate of C.I. Pigment Yellow 138 to exceed the sedimentation rate of C.I. Pigment Yellow 74.

[0014] Furthermore, it has been found that using C.I. Pigment Yellow 138, which has a cumulative 50% particle size based on volume particle size distribution of 85 nm or less, in combination with C.I. Pigment Yellow 74 can improve the color developing property of an image (chroma C * ) as compared with the case where C.I. Pigment Yellow 74 is used alone. Reducing the particle size of C.I. Pigment Yellow 138 can suppress the absorption of light on the long-wavelength side, so a * in the CIELab color system has a larger absolute value, and chroma C * (= (a * ) 2 + (b * ) 2} 1 / 2 ) increases, which is considered to improve the color developing property.

[0015] <Ink> The ink of the present invention is an aqueous inkjet ink containing a pigment and a resin dispersant for dispersing the pigment. The pigment includes CI Pigment Yellow 74 and CI Pigment Yellow 138. The cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 85 nm or less. Furthermore, the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 0.72 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74. The ink of the present invention does not need to be curable by active energy rays, and therefore does not need to contain monomers having polymerizable groups. The details of the ink of the present invention will be described below.

[0016] (Pigment) The pigments include CI Pigment Yellow 74 and CI Pigment Yellow 138. These pigments are dispersed in the ink by a resin dispersant. In other words, the pigments used in the ink of the present invention are resin-dispersed pigments dispersed in the ink by the action of a resin used as a resin dispersant.

[0017] The cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 85 nm or less. Furthermore, the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is preferably between 30 nm and 60 nm, and more preferably between 40 nm and 60 nm. By setting the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 within the above range, the color reproduction of the recorded image can be further improved. Additionally, the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74 is preferably between 50 nm and 145 nm.

[0018] The cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 0.72 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74. Furthermore, it is preferable that the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 0.50 times or more and 0.72 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74. By keeping the ratio of the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74 within the above range, the lightfastness of the recorded image can be further improved.

[0019] The cumulative 90% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is preferably 3.00 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138. Furthermore, it is even more preferable that the above ratio is between 1.50 and 2.50 times. If the above ratio exceeds 3.00 times, the proportion of particles in CI Pigment Yellow 138 that have a sedimentation velocity exceeding that of CI Pigment Yellow 74 will increase, which may slightly reduce the effect of improving the lightfastness and color development of the image. The cumulative 90% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is preferably between 50 nm and 100 nm.

[0020] The cumulative 50% particle size (D50) and cumulative 90% particle size (D90) of volume-based particle size distributions for pigments such as CI Pigment Yellow 74 and CI Pigment Yellow 138 can both be measured using a dynamic light scattering particle size analyzer.

[0021] The content of CI Pigment Yellow 74 in the ink (mass%) is preferably 0.1% to 8.0% by mass, based on the total mass of the ink. The content of CI Pigment Yellow 138 in the ink (mass%) is also preferably 0.1% to 8.0% by mass, based on the total mass of the ink. The ink may further contain other pigments besides CI Pigment Yellow 74 and CI Pigment Yellow 138. The total pigment content in the ink (mass%) is preferably 1.0% to 10.0% by mass, based on the total mass of the ink. Furthermore, the content of CI Pigment Yellow 138 in the ink (mass%) is preferably 0.1 to 10.0 times, and more preferably 1.0 to 5.0 times, in terms of mass ratio to the content of CI Pigment Yellow 74 (mass%). If the above mass ratio is less than 0.1 times, the effect of improving the lightfastness and color development of the image may be slightly reduced. On the other hand, if the above mass ratio is more than 10.0 times, then compared to CI Pigment Yellow 74, b * The effect of CI Pigment Yellow 138, which has a small value, becomes more pronounced. * A decrease in this value may slightly reduce the effect of improving the color reproduction of the image.

[0022] (Resin dispersant) The ink contains a resin dispersant that disperses the pigment within the ink. As the resin dispersant, a general resin used in water-based pigment inks for inkjet printing can be used. Among these, acrylic resin is preferred. Besides resin dispersants that physically adsorb onto the surface of pigment particles to disperse the pigment in the ink, other examples of resin dispersants include those chemically bonded to the surface of pigment particles and microcapsule-type resin dispersants that coat the surface of pigment particles.

[0023] Acrylic resins can be obtained by copolymerizing hydrophilic monomers or hydrophobic monomers. Examples of hydrophilic monomers include acid monomers, salts of acid monomers, and compounds having nonionic hydrophilic groups (such as hydroxyl groups and amide groups). Examples of acid monomers and salts of acid monomers include unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, itaconic acid, and fumaric acid; their derivatives; and their salts. Examples of salts include salts of alkali metals such as lithium, sodium, and potassium; ammonium salts; and organic ammonium salts. Among these, (meth)acrylic acid and salts of (meth)acrylic acid are preferred. Sodium salts and potassium salts are also preferred as salts.

[0024] Furthermore, examples of compounds having nonionic hydrophilic groups include hydroxyalkyl (meth)acrylate esters such as 2-hydroxyethyl (meth)acrylate and 3-methyl-5-hydroxypentyl (meth)acrylate; mono(meth)acrylate esters of polyhydric alcohols such as ethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; (meth)acrylate esters to which ethylene oxide has been added, such as methoxyethylene glycol (meth)acrylate, alkoxypolyalkylene glycol (meth)acrylate, and 2-phenoxyethylene glycol (meth)acrylate; and (meth)acrylamide compounds such as methyl (meth)acrylamide and ethyl (meth)acrylamide.

[0025] Examples of hydrophobic monomers include α,β-ethylenically unsaturated compounds having an aryl group and alkyl (meth)acrylates. Examples of α,β-ethylenically unsaturated compounds having an aryl group include aromatic vinyl compounds such as styrene and α-methylstyrene; and ester compounds synthesized from α,β-ethylenically unsaturated carboxylic acids and alkyl alcohols having an aryl group, such as benzyl (meth)acrylate and 2-phenoxyethyl (meth)acrylate. Among these, styrene and α-methylstyrene are preferred.

[0026] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and tricyclodecanedimethanol di(meth)acrylate. The acrylic resin may be in any of the following forms: random copolymer, block copolymer, graft copolymer, or gradient copolymer.

[0027] The content (by mass) of the resin dispersant in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, based on the total mass of the ink. The weight-average molecular weight of the resin used as the resin dispersant is preferably 1,000 or more and 30,000 or less, and more preferably 3,000 or more and 15,000 or less. In this specification, "weight-average molecular weight of the resin" means the value on a polystyrene basis measured by gel permeation chromatography (GPC).

[0028] The resin dispersant preferably contains resin A for dispersing CI pigment yellow 74 and resin B for dispersing CI pigment yellow 138. The weight-average molecular weight of resin B is preferably 1.0 times or more, more preferably 1.0 to 1.5 times, and particularly preferably 1.1 to 1.5 times, relative to the weight-average molecular weight of resin A. If the above ratio is less than 1.0 times, the resins will not entangle with each other as much, and CI pigment yellow 138 will more easily penetrate the gaps between CI pigment yellow 74 on the recording medium. As a result, pigment yellow 138 will be more easily positioned near the surface of the recording medium, which may slightly reduce the effect of improving the color development and lightfastness of the image. Resins A and B may be the same or different. The same resin means that the composition and physical properties are the same, and different resins mean that at least one of the composition and physical properties is different.

[0029] The acid value of the resin is preferably 120 mgKOH / g or more and 350 mgKOH / g or less. The acid value (mgKOH / g) of resin B that disperses CI Pigment Yellow 138 is preferably 1.0 times or more in ratio to the acid value (mgKOH / g) of resin A that disperses CI Pigment Yellow 74. Furthermore, the above ratio is more preferably 1.0 times or more and 1.5 times or less, and even more preferably 1.1 times or more and 1.5 times or less. Assume that the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 138 is 0.72 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of CI Pigment Yellow 74. In this case, the surface area per unit mass is larger for CI Pigment Yellow 138 than for CI Pigment Yellow 74. Therefore, if the above ratio is less than 1.0, the amount of charge per unit surface area will be smaller for CI Pigment Yellow 138, resulting in slightly weaker charge repulsion. Consequently, CI Pigment Yellow 138 will more easily penetrate the gaps between CI Pigment Yellow 74 on the recording medium, and Pigment Yellow 138 will be more likely to be positioned near the surface of the recording medium. This may slightly reduce the effect of improving the color reproduction and lightfastness of the image.

[0030] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may further contain a water-soluble organic solvent as an aqueous medium. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. Any of the water-soluble organic solvents commonly used in inks can be used as the water-soluble organic solvent. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The water-soluble organic solvent content (mass%) in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

[0031] (Other additives) In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea. Furthermore, the ink may also contain, as necessary, various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins.

[0032] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0033] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0034] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32. [Examples]

[0035] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0036] <Preparation of resin (resin dispersant)> Each monomer was polymerized according to a conventional method to achieve the composition ratio (mass ratio) of the units shown in Table 1, and each resin was synthesized. Each resin was neutralized with a 10.0% potassium hydroxide aqueous solution to obtain a solution containing each resin in an amount equal to its acid value. The acid values ​​of the resins are shown in Table 1. The acid values ​​of the resins were measured by potentiometric titration with potassium hydroxide ethanol titrant using a potentiometric automatic titrator. The meaning of the abbreviations in Table 1 is shown below. St: Styrene nBA: n-butyl acrylate BzA: Benzyl acrylate BzMA: Benzyl methacrylate AA: Acrylic acid • MAA: Methacrylic acid

[0037] TIFF0007919846000001.tif144170

[0038] <Preparation of Pigment Dispersion> To achieve a PB ratio (mass ratio of pigment to resin (solids)) of 10:3, 16 parts of each pigment, a liquid containing the types of resins shown in Tables 2-4, and ion-exchanged water (total 100.0 parts) were mixed and dispersed for 2 hours using a batch-type vertical sand mill. The pigments used were CI Pigment Yellow 74 (PY74), CI Pigment Yellow 138 (PY138), and CI Pigment Yellow 128 (PY128). After removing coarse particles by centrifugation, the mixture was pressure-filtered through a 3.0 μm pore size microfilter (manufactured by Fujifilm) to obtain pigment dispersions with a pigment content of 16.0%. The cumulative 50% particle size (D50) of the volume-based particle size distribution of the pigments in the obtained pigment dispersions was then measured. A D50 B D50 C Tables 2-4 show the cumulative 90% particle size (D90) of the pigment in the pigment dispersion containing PY138, based on volume. B The results are shown in Table 3. The particle size of the pigments in the pigment dispersion was measured using a dynamic light scattering nanoparticle size analyzer (product name "Nanotrac WaveII-EX150," manufactured by Microtrac-Bell). The meanings of the abbreviations in Tables 2-4 are as follows. D50 A : Volume-based particle size distribution of CI Pigment Yellow 74, cumulative 50% particle size D50 B : Volume-based particle size distribution of CI Pigment Yellow 138, cumulative 50% particle size ·D90 B : Volume-based particle size distribution of CI Pigment Yellow 138, cumulative 90% particle size D50 C : Volume-based particle size distribution of CI Pigment Yellow 128, cumulative 50% particle size

[0039] TIFF0007919846000002.tif107170

[0040] TIFF0007919846000003.tif174170

[0041] TIFF0007919846000004.tif55170

[0042] <Ink preparation> The following types and quantities of each component were mixed and thoroughly stirred, then the ink was prepared by pressure filtration through a 0.45 μm pore size microfilter (manufactured by Fujifilm). The characteristics of the prepared ink are shown in Table 5. In Table 5, "C A " is "the amount of resin A that disperses CI Pigment Yellow 74", "C B " represents the content of resin B that disperses CI Pigment Yellow 138. In Table 5, "Mw A " is "the weight-average molecular weight of resin A that disperses CI Pigment Yellow 74", "Mw B " and " mean "the weight-average molecular weight of resin B that disperses CI Pigment Yellow 138". A " is "the acid value of resin A that disperses CI Pigment Yellow 74", "An B " represents the acid value of resin B that disperses CI Pigment Yellow 138. • Pigment dispersion shown in Table 5: Usage amount (%) shown in Table 5 Glycerin: 10.0% Triethylene glycol: 5.0% • Acetyleneol E100: 1.0% • Ion-exchanged water: Remaining volume (%) when the total amount of components reaches 100.0%

[0043] TIFF0007919846000005.tif224170

[0044] <Rating> An inkjet recording device (product name "PIXUS PRO-10S", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy was prepared. Ink cartridges filled with each of the prepared inks were set in the inkjet recording device. Using this inkjet recording device, a 14-level solid image was recorded on glossy paper (product name "Canon Photo Paper Gloss Gold GL-101", manufactured by Canon) with the recording duty cycle varied in 10% increments from 10% to 140%. In this embodiment, an image recorded under the conditions of a resolution of 600 dpi x 600 dpi and applying 8 drops of 3.8 ng of ink to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as having a recording duty cycle of 100%. In the evaluation criteria for each evaluation item shown below, "C" was defined as an unacceptable level, "B" as an acceptable level, and "A" as an excellent level. The evaluation results are shown in Table 6.

[0045] (Color development) After recording images and allowing the resulting recordings to air dry for 24 hours, a spectrophotometer (product name "Spectrolino", manufactured by Gretag Macbeth) was used to measure the L values ​​of the CIELab color system for each recording duty cycle. * a * , and b * The value of was measured. And the saturation C * ={(a * ) 2 +(b * ) 2} 1 / 2 The values ​​were calculated, and the color reproduction of the images was evaluated according to the evaluation criteria shown below. A:C * The value was 110 or higher. B:C * The value was between 100 and 110. C:C * The value was less than 100.

[0046] (Lightfastness) The recorded images were allowed to air dry for 24 hours. Next, a spectrophotometer (product name "Spectrolino," manufactured by Gretag Macbeth) was used to measure the spectral sensitivity characteristics of the images for each recording duty cycle, and the recording with the image closest to an optical density of 1.0 was identified. The spectral sensitivity characteristics described above represent the optical density of the yellow component as defined by "ISO Status A." The identified recordings were placed in a lightfastness tester (product name "Xenon Weathermeter X75SC," manufactured by Suga Test Instruments). Then, xenon light with a wavelength of 340 nm was irradiated at an intensity of 0.39 W / (m²). 2 The images were irradiated for 200 hours under the conditions of (nm), black panel temperature 63°C, and relative humidity 70%. After the optical density of the images was measured again, the "optical density retention rate (%)" was calculated using the following formula (1), and the lightfastness of the images was evaluated according to the evaluation criteria shown below. Optical density residual rate (%) = {(Optical density after irradiation) / (Optical density before irradiation)} × 100 ... (1) A: The optical density retention rate was 85% or higher. B: The optical density retention rate was 70% or more but less than 85%. C: Optical density retention rate was less than 70%.

[0047] TIFF0007919846000006.tif187170

Claims

1. An aqueous inkjet ink containing a pigment and a resin dispersant for dispersing the pigment, The aforementioned pigment comprises C.I. Pigment Yellow 74 and C.I. Pigment Yellow 138. The cumulative 50% particle size of the volume-based particle size distribution of the aforementioned C.I. Pigment Yellow 138 is 85 nm or less. The cumulative 50% particle size of the volume-based particle size distribution of C.I. Pigment Yellow 138 is 0.72 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of C.I. Pigment Yellow 74. The resin dispersant is physically adsorbed onto the particle surfaces of the C.I. Pigment Yellow 74 and the C.I. Pigment Yellow 138, respectively, and disperses the C.I. Pigment Yellow 74 and the C.I. Pigment Yellow 138 in the aqueous ink, respectively. The aqueous ink is characterized in that the resin dispersant contains a resin having a unit derived from at least one monomer selected from the group consisting of acrylic acid and methacrylic acid, the acid value of which is 115 mg KOH / g or more and 350 mg KOH / g or less.

2. The aqueous ink according to claim 1, wherein the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 30 nm or more and 60 nm or less.

3. The aqueous ink according to claim 1 or 2, wherein the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 40 nm or more and 60 nm or less.

4. The aqueous ink according to any one of claims 1 to 3, wherein the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 0.50 times or more in ratio to the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 74.

5. The aqueous ink according to any one of claims 1 to 4, wherein the content (mass%) of C.I. Pigment Yellow 138 is 0.1 times or more and 10.0 times or less in mass ratio to the content (mass%) of C.I. Pigment Yellow 74.

6. The aqueous ink according to any one of claims 1 to 5, wherein the content (mass%) of C.I. Pigment Yellow 138 is 1.0 times or more and 5.0 times or less in mass ratio to the content (mass%) of C.I. Pigment Yellow 74.

7. The aqueous ink according to any one of claims 1 to 6, wherein the cumulative 90% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 3.00 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138.

8. The aqueous ink according to any one of claims 1 to 7, wherein the cumulative 90% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 1.50 times or more and 2.50 times or less in ratio to the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138.

9. The aqueous ink according to any one of claims 1 to 8, wherein the cumulative 50% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 30 nm or more and 60 nm or less.

10. The aqueous ink according to any one of claims 1 to 9, wherein the cumulative 90% particle size of the volume-based particle size distribution of the C.I. Pigment Yellow 138 is 50 nm or more and 100 nm or less.

11. The aqueous ink according to any one of claims 1 to 10, wherein the content (by mass) of the C.I. Pigment Yellow 74 is 0.1% by mass or more and 8.0% by mass or less, based on the total mass of the ink.

12. The aqueous ink according to any one of claims 1 to 11, wherein the content (by mass) of the C.I. Pigment Yellow 138 is 0.1% by mass or more and 8.0% by mass or less, based on the total mass of the ink.

13. The aqueous ink according to any one of claims 1 to 12, wherein the acid value (mgKOH / g) of the resin is 264 mgKOH / g or less.

14. The aqueous ink according to any one of claims 1 to 13, wherein the weight-average molecular weight of the resin is 6,000 or more and 32,000 or less.

15. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in any one of claims 1 to 14.

16. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of claims 1 to 14.

17. A method for producing an aqueous inkjet ink according to any one of claims 1 to 14, The process involves dispersing the aforementioned C.I. Pigment Yellow 74, the resin dispersant, and water to obtain a first pigment dispersion, A step of dispersing the aforementioned C.I. Pigment Yellow 138, the resin dispersant, and water to obtain a second pigment dispersion, A step of preparing the aqueous ink by mixing the first pigment dispersion and the second pigment dispersion, A method for producing aqueous ink, characterized by having the following features.

18. The resin dispersant used in the step of obtaining the first pigment dispersion comprises resin A for dispersing the C.I. Pigment Yellow 74. The resin dispersant used in the step of obtaining the second pigment dispersion contains resin B which disperses the C.I. Pigment Yellow 138, The method for producing an aqueous ink according to claim 17, wherein the weight-average molecular weight of resin B is 1.0 times or more in ratio to the weight-average molecular weight of resin A.

19. The method for producing an aqueous ink according to claim 18, wherein the weight-average molecular weight of resin B is 1.50 times or less in ratio to the weight-average molecular weight of resin A.

20. The method for producing aqueous ink according to claim 18 or 19, wherein the acid value (mgKOH / g) of resin B is 1.0 times or more in ratio to the acid value (mgKOH / g) of resin A.

21. The method for producing an aqueous ink according to claim 20, wherein the acid value (mgKOH / g) of resin B is 1.5 times or less in ratio to the acid value (mgKOH / g) of resin A.

22. A method for producing aqueous ink according to any one of claims 18 to 21, wherein the acid value (mgKOH / g) of resin A and resin B is 264 mgKOH / g or less, respectively.

23. A method for producing an aqueous ink according to any one of claims 18 to 22, wherein the weight-average molecular weights of resin A and resin B are each 6,000 or more and 32,000 or less.

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