inkjet ink

Abstract

We provide inkjet inks that can achieve both high image quality and stable pigment dispersion. [Solution] The inkjet ink contains a pigment, a pigment dispersion resin, a surfactant represented by general formula (1), a diol having 3 to 5 carbon atoms, and water. The mass ratio of the pigment dispersion resin to the pigment is 0.5 to 1.1. TIFF2026059557000013.tif28164 (In general formula (1), x, y, and z are integers determined such that the ratio of the number-average molecular weight of the propylene oxide chain alone in the surfactant to the number-average molecular weight of the surfactant is between 0.85 and 0.91.)

Description

Technical Field

[0001] The present invention relates to an ink for inkjet.

Background Art

[0002] Patent Documents 1 and 2 disclose inks for inkjet for recording an image on a recording medium such as paper. An ink for inkjet is required to form a high-quality image without unevenness on the recording medium. On the other hand, an ink for inkjet is also required to have high dispersion stability for maintaining the dispersed state of the pigment in the solvent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, an ink for inkjet requires a certain degree of wet spreading property on the recording medium in order to form an image without unevenness on the recording medium. That is, in an ink for inkjet, in order to achieve both the quality of the image and the dispersion stability of the pigment, the behavior of the pigment that is contradictory between on the recording medium and in the solvent is required.

[0005] In view of the above circumstances, an object of the present invention is to provide an ink for inkjet capable of achieving both the quality of the image and the dispersion stability of the pigment.

Means for Solving the Problems

[0006] To achieve the above objective, an inkjet ink according to one embodiment of the present invention contains a pigment, a pigment dispersion resin, a surfactant represented by general formula (1), a diol having 3 to 5 carbon atoms, and water. The mass ratio of the pigment dispersion resin to the pigment is 0.5 to 1.1. [ka] (In general formula (1), x, y, and z are integers determined such that the ratio of the number-average molecular weight of the propylene oxide chain alone in the surfactant to the number-average molecular weight of the surfactant is between 0.85 and 0.91.)

[0007] In this inkjet ink, the wettability on the recording medium can be improved by increasing the proportion of the propylene oxide chain, which is the hydrophobic segment, in the surfactant represented by general formula (1). As a result, this inkjet ink makes it easier to ensure wettability on the recording medium even when using a water-soluble humectant with relatively low hydrophobicity. Specifically, in this inkjet ink, sufficient wettability on the recording medium can be ensured by setting the number of carbon atoms in the diol used as the water-soluble humectant to 3 or more. On the other hand, in this inkjet ink, high dispersion stability of the pigment in the solvent is achieved by keeping the number of carbon atoms in the diol used as a water-soluble humectant to 5 or less, while incorporating a large amount of pigment-dispersing resin. Furthermore, in this inkjet ink, the ethylene oxide chain, which is the hydrophilic segment of the surfactant represented by general formula (1), contributes to improving the dispersion stability of the pigment in the solvent. As a result, high dispersion stability of the pigment in the solvent is achieved in this inkjet ink. In this way, this inkjet ink makes it possible to achieve both high image quality and stable pigment dispersion.

[0008] The number-average molecular weight of the above surfactant may be 1,900 or more and 3,000 or less. The log Kow of the above diol may be between -1.6 and 0.6. [Effects of the Invention]

[0009] As described above, the present invention can provide an inkjet ink that can achieve both image quality and pigment dispersion stability. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below.

[0011] [Ink composition] (Schematic configuration) An inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "ink") contains a pigment a, a pigment dispersion resin b, a surfactant c, a water-soluble humectant d, and water. The ink according to this embodiment is a water-based ink that is ejected from the recording head of an inkjet recording device onto a recording medium to record an image on the recording medium. The recording medium on which the image is recorded with the ink according to this embodiment is made of fibers such as cellulose fibers, and examples include plain paper, copy paper, recycled paper, thin paper, and thick paper.

[0012] In the ink according to this embodiment, the synergistic effect of the combination of pigment dispersion resin b, surfactant c, and water-soluble humectant d makes it possible to achieve both the quality of the image formed on the recording medium and the dispersion stability of pigment a in the solvent. The details of each component of the ink according to this embodiment will be described below.

[0013] (Pigment a) The ink according to this embodiment contains pigment a as a coloring agent, from the viewpoint of improving the ability to prevent color mixing and the water resistance of images recorded on a recording medium. Pigment a may be either an inorganic pigment or an organic pigment. In addition, if necessary, these may be used in combination with an extender pigment.

[0014] Specific examples of inorganic pigments usable in the ink according to this embodiment include, for example, carbon black and metal oxides, with carbon black being particularly preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0015] Specific examples of organic pigments that can be used in the ink according to this embodiment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0016] In the ink according to this embodiment, the hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred chromatic pigments include CI pigment yellow, CI pigment red, CI pigment orange, CI pigment violet, CI pigment blue, and CI pigment green. In the ink according to this embodiment, one or more selected from these chromatic pigments can be used as pigment a.

[0017] (Pigment-dispersed resin b) The ink according to this embodiment contains pigment dispersion resin b, which is a fine particle of resin, as a dispersant to improve the dispersibility of pigment a in the solvent by adsorbing onto the surface of pigment a. Suitable pigment dispersion resin b for the ink according to this embodiment include, for example, benzyl methacrylate / methacrylic acid copolymer, benzyl methacrylate / acrylic acid copolymer, styrene / methacrylic acid copolymer, styrene / acrylic acid copolymer, and urethane resin, among which benzyl methacrylate / methacrylic acid copolymer is preferred.

[0018] The molecular weight of the pigment dispersion resin b is preferably on the order of tens of thousands. In the pigment dispersion resin b, from the viewpoints of improving the dispersibility of the pigment a in the solvent, reducing the particle size, and improving the color development and coloring power by the pigment a, the acid value is preferably 150 mgKOH / g or more. On the other hand, in the pigment dispersion resin b, from the viewpoint of improving the storage stability of the ink, the acid value is preferably 300 mgKOH / g or less.

[0019] In the ink according to this embodiment, in order to obtain high dispersion stability of the pigment a in the solvent, the mass ratio of the pigment dispersion resin b to the pigment a is 0.5 or more. Further, in the ink according to this embodiment, in order to ensure sufficient dispersion stability, the mass ratio of the pigment dispersion resin b to the pigment a is 1.1 or less.

[0020] (Surfactant c) In the ink according to this embodiment, a surfactant c represented by the following general formula (1) is used. The surfactant c has a propylene oxide chain (PO chain) constituting the central part and ethylene oxide chains (EO chains) arranged on both sides of the PO chain.

[0021] [Chemical formula] (In the general formula (1), x, y, and z are integers determined such that the ratio of the number average molecular weight of only the PO chain in the surfactant c to the number average molecular weight of the surfactant c (hereinafter, also simply referred to as "the ratio of the PO chain") is 0.85 or more and 0.91 or less.)

[0022] In the ink according to this embodiment, by setting the ratio of the PO chain in the surfactant c to 0.85 or more, increasing the ratio of the PO chain which is a hydrophobic segment, and making the surfactant c have a relatively high hydrophobic structure, the wetting spreadability on the recording medium can be improved. Also, in the surfactant c, by keeping the ratio of the PO chain which is a hydrophobic segment at 0.91 or less, the solubility in water can be ensured. Further, in the ink according to this embodiment, the EO chain which is a hydrophilic segment in the surfactant c contributes to improving the dispersion stability of the pigment a in the solvent.

[0023] Furthermore, in the ink according to this embodiment, it is preferable that the number-average molecular weight of surfactant c is 1900 or more in order to obtain high wettability. Also, in the ink according to this embodiment, it is preferable that the number-average molecular weight of surfactant c is 3000 or less in order to obtain high dispersion stability.

[0024] In the ink according to this embodiment, it is preferable that the content of surfactant c is 0.5% by mass or more in order to fully obtain the effect of surfactant c. Furthermore, in the ink according to this embodiment, it is preferable that the content of surfactant c is 1.1% by mass or less in order to obtain high dispersion stability. In this embodiment, the number average molecular weight is measured using gel filtration chromatography (HLC-8020GPC manufactured by Tosoh Corporation) under the following conditions. • Column: TSKgel SuperMultiporeHZ-H manufactured by Tosoh Corporation (semi-micro column with 4.6mm I.D. x 15cm) • Number of columns: 3 • Eluent: Tetrahydrofuran ·Flow rate: 0.35mL / min • Sample injection volume: 10 μL ·Measurement temperature: 40℃ • Detector: IR detector The calibration curve is created by selecting seven types of TSKgel standard polystyrene manufactured by Tosoh Corporation—F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000—along with n-propylbenzene.

[0025] (Water-soluble humectant d) In the ink according to this embodiment, the wettability on the recording medium can be improved by the action of the surfactant c described above, so there is little need to use a highly hydrophobic solvent as the water-soluble humectant d. For this reason, in the ink according to this embodiment, the dispersion stability of pigment a in the solvent is less likely to be impaired by the influence of the water-soluble humectant d.

[0026] In the ink according to this embodiment, a diol with 3 to 5 carbon atoms is used as the water-soluble humectant d. In the ink according to this embodiment, by setting the number of carbon atoms of the diol used as the water-soluble humectant d to 3 or more, high wettability and spreadability on the recording medium can be obtained. Furthermore, in the ink according to this embodiment, by keeping the number of carbon atoms of the diol used as the water-soluble humectant d to 5 or less, dispersion stability in the solvent can be ensured.

[0027] Examples of diols with 3 carbon atoms include propylene glycol and 1,3-propanediol. Examples of diols with 4 carbon atoms include 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 2,3-butanediol. Examples of diols with 5 carbon atoms include 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2,5-pentanediol, and 3,4-pentanediol.

[0028] Furthermore, in the ink according to this embodiment, it is preferable that the log Kow of the water-soluble humectant d is -1.6 or higher from the viewpoint of ensuring wettability on the recording medium. Also, in the water-soluble humectant d, it is preferable that the log Kow is 0.7 or lower from the viewpoint of ensuring solubility in water. log Kow is the water / octanol coefficient. The value of log Kow in this invention is the value calculated from the Hansen solubility parameter software "HSPiP".

[0029] In the ink according to this embodiment, it is preferable that the content of the water-soluble humectant d is 30% by mass or more in order to fully obtain the effect of the water-soluble humectant d. Furthermore, in the ink according to this embodiment, it is preferable that the content of the water-soluble humectant d is 60% by mass or less in order to obtain high discharge performance.

[0030] (water) In the ink according to this embodiment, for example, ion-exchanged water, purified water, or distilled water can be used as water. In the ink according to this embodiment, from the viewpoint of drying properties and ejection reliability, it is preferable that the water content is 30% by mass or more and 60% by mass or less.

[0031] (Other ingredients) The ink according to this embodiment may contain other components as needed. For example, the ink according to this embodiment may contain various additives as needed, such as penetrating agents, dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents.

[0032] [Examples] In Examples 1 to 3 of the present invention, inks were prepared and evaluated.

[0033] (Ink evaluation) First, we will explain the evaluation method for the inks common to Examples 1 to 3. The inks prepared in Examples 1 to 3 were evaluated for wetting spreadability and dispersion stability.

[0034] • Method for evaluating wetting spread For the evaluation of wetting spreadability, an inkjet recording device (line type, manufactured by Kyocera Document Solutions Inc.) was used as the test machine, and copy paper (Mondi "Color Copy A4 90g / m²") was used as the recording medium. 2 The following was used: The test machine was set to drive voltage so that the amount of ink ejected from one recording head was 11 pL, and an image of 10 straight lines (one-dot lines) was formed on the recording medium.

[0035] For each of the 10 straight lines that appeared as an image on a recording medium that had been dried overnight after the image was formed, the line width was measured using an optical microscope (Nikon Corporation "MM-800" application measurement (line measurement)), and the average line width of the 10 straight lines was used as the evaluation value for the wetting spreadability of each ink. For wetting spreadability, inks with an evaluation value of 75 μm or more were considered acceptable, and inks with an evaluation value of less than 75 μm were considered unacceptable.

[0036] • Method for evaluating dispersion stability In evaluating dispersion stability, the particle size of the pigment dispersion, a composite in which pigment dispersion resin b is adsorbed onto pigment a, was measured before and after drying. In the drying process, 10 g of ink was placed in an iBoy container, and the solvent components were evaporated until the amount of ink in the iBoy container reached 6 g. The ratio of the change in particle size of the pigment dispersion before and after drying to the particle size of the pigment dispersion before drying was calculated. The calculated ratio was used as the evaluation value for the dispersion stability of each ink. The evaluation value for the dispersion stability of each ink was evaluated according to the following criteria A and B. For dispersion stability, inks with an evaluation of A were considered passable, and inks with an evaluation of B were considered failing. A (good): 10% or less B (Bad): More than 10%

[0037] (Example 1) In Example 1, ink samples 1 to 10 were prepared. To prepare ink samples 1 to 10 according to Example 1, a pigment dispersion was first prepared in which pigment a was dispersed in water. The pigment dispersion was prepared by blending pigment a, pigment dispersion resin b, sodium hydroxide, Olphine® E1010, and water in the amounts shown in Table 1.

[0038] [Table 1]

[0039] Sodium hydroxide was added as a neutralizing agent to neutralize pigment dispersion resin b. Olfin® E1010 was added as a dispersant to improve the dispersibility of pigment a in the solvent, and is a nonionic surfactant manufactured by Nisshin Chemical Industry Co., Ltd. In all of the ink samples 1 to 10 of Example 1, pigment a was pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351"), and deionized water was used as the water.

[0040] The pigment dispersion was prepared by mixing the above components using a wet dispersion method with a media-type wet disperser. Examples of media-type wet dispersers include wet dispersers (more specifically, the "NanoGlenMill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries, Ltd., and the "DinoMill" manufactured by Shinmaru Enterprises, Ltd.).

[0041] In wet dispersion using a media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were set in the vessel, and the discharge rate was controlled to 200-600 g / min to adjust the average particle size of the pigment dispersion, in which the dispersant adhered to pigment a dispersed in water, to 90-110 nm. The particle size distribution of the pigment dispersion was measured using a Zetasizer Nano manufactured by Sysmex Corporation, with the pigment dispersion diluted 300 times with deionized water.

[0042] Next, samples 1 to 10 of the ink according to Example 1 were prepared. Each sample 1 to 10 was prepared by blending the above-mentioned pigment dispersion, surfactant c, water-soluble humectant d, triethylene glycol monobutyl ether, and water in the amounts shown in Table 2. In all samples 1 to 10, benzyl methacrylate (BzMMA) / methacrylic acid (MAA) copolymer (BzMMA: 64% by mass, MAA: 36% by mass, acid value: 160 mg KOH / g) was used as the pigment dispersion resin b, and 1,3-propanediol was used as the water-soluble humectant d. Triethylene glycol monobutyl ether was added as a viscosity modifier.

[0043] [Table 2]

[0044] In preparing ink samples 1 to 10 for Example 1, the components shown in Table 2 were added sequentially while stirring the solvent with a stirrer. Furthermore, foreign matter, debris, and coarse particles were removed by filtering each ink after stirring using a filter with a pore size of φ5 μm.

[0045] In samples 1 to 10 of the ink according to Example 1, various different surfactants c were used. Specifically, in sample 1, Sanyo Chemical Industries, Ltd.'s "Newpol PE-61" was used as surfactant c. In sample 2, Sanyo Chemical Industries, Ltd.'s "Newpol PE-71" was used as surfactant c. In sample 3, ADEKA Corporation's "ADEKA Pluronic L-31" was used as surfactant c. In sample 4, ADEKA Corporation's "ADEKA Pluronic L-61" was used as surfactant c. In sample 5, ADEKA Corporation's "ADEKA Pluronic L-81" was used as surfactant c. In sample 6, Sanyo Chemical Industries, Ltd.'s "Newpol PE-62" was used as surfactant c. In sample 7, Sanyo Chemical Industries, Ltd.'s "Newpol PE-34" was used as surfactant c. In sample 8, Sanyo Chemical Industries, Ltd.'s "Newpol PE-64" was used as surfactant c. In sample 9, Sanyo Chemical Industries, Ltd.'s "Newpol PE-74" was used as surfactant c. In Sample 10, polypropylene glycol was used as surfactant c.

[0046] Table 3 shows the number-average molecular weight of surfactant c, the number-average molecular weight of the PO chain, and the ratio of PO chains used in samples 1 to 10, as well as the evaluation results for wettability and dispersion stability for samples 1 to 10. Samples 1 to 4 all received good evaluation results for both wettability and dispersion stability. On the other hand, samples 5 to 9, which had a low ratio of PO chains in surfactant c, all failed to meet the wettability standard. This is thought to be because the hydrophobicity of surfactant c was too low in samples 5 to 9, resulting in insufficient wettability. Furthermore, in sample 10, where surfactant c consisted only of PO chains, surfactant c did not dissolve in the solvent, making evaluation impossible. This is thought to be because the hydrophobicity was too high in sample 10, resulting in insufficient solubility in water.

[0047] [Table 3]

[0048] (Example 2) In Example 2, ink samples 11 to 15 were prepared. To prepare ink samples 11 to 15 according to Example 2, a pigment dispersion was first prepared in which pigment a was dispersed in water. The pigment dispersion was prepared by blending pigment a, pigment dispersion resin b, sodium hydroxide, Olphine® E1010, and water in the amounts shown in Table 4. The amount of pigment dispersion resin b was determined for each sample 11 to 15 according to its ratio to pigment a.

[0049] [Table 4]

[0050] Sodium hydroxide was added as a neutralizing agent to neutralize pigment dispersion resin b. Olfin® E1010 was added as a dispersant to improve the dispersibility of pigment a in the solvent, and is a nonionic surfactant manufactured by Nisshin Chemical Industry Co., Ltd. In all of the ink samples 11 to 15 of Example 2, pigment a was pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351"), and deionized water was used as the water.

[0051] The pigment dispersion was prepared by mixing the above components using a wet dispersion method with a media-type wet disperser. Examples of media-type wet dispersers include wet dispersers (more specifically, the "NanoGlenMill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries, Ltd., and the "DinoMill" manufactured by Shinmaru Enterprises, Ltd.).

[0052] In wet dispersion using a media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were set in the vessel, and the discharge rate was controlled to 200-600 g / min to adjust the average particle size of the pigment dispersion, in which the dispersant adhered to pigment a dispersed in water, to 90-110 nm. The particle size distribution of the pigment dispersion was measured using a Zetasizer Nano manufactured by Sysmex Corporation, with the pigment dispersion diluted 300 times with deionized water.

[0053] Next, samples 11 to 15 of the ink according to Example 2 were prepared. Each sample 11 to 15 was prepared by blending the above-mentioned pigment dispersion, surfactant c, water-soluble humectant d, triethylene glycol monobutyl ether, and water in the quantities shown in Table 5. In all samples 11 to 15, benzyl methacrylate (BzMMA) / methacrylic acid (MAA) copolymer (BzMMA: 64% by mass, MAA: 36% by mass, acid value: 160 mg KOH / g) was used as the pigment dispersion resin b, "ADEKA Pluronic L-61" manufactured by ADEKA Corporation was used as the surfactant c, and 1,3-propanediol was used as the water-soluble humectant d. Triethylene glycol monobutyl ether was added as a viscosity modifier.

[0054] [Table 5]

[0055] In preparing ink samples 11-15 for Example 2, the components shown in Table 5 were added sequentially while stirring the solvent with a stirrer. Furthermore, foreign matter, debris, and coarse particles were removed by filtering each ink after stirring using a filter with a pore size of φ5 μm.

[0056] In samples 11-15 of the ink according to Example 2, the mass ratio of pigment dispersion resin b to pigment a was varied by adjusting the amount of pigment dispersion resin b used.

[0057] Table 6 shows the mass ratio of pigment dispersion resin b to pigment a in samples 11-15, as well as the evaluation results for wettability and dispersion stability for samples 11-15. Samples 12-15 all showed good evaluation results for both wettability and dispersion stability. On the other hand, sample 11, which had a low mass ratio of pigment dispersion resin b to pigment a, failed both evaluations for wettability and dispersion stability. This is thought to be because the effect of pigment dispersion resin b was not fully obtained in sample 11.

[0058] [Table 6]

[0059] (Example 3) In Example 3, ink samples 16 to 23 were prepared. To prepare ink samples 16 to 23 according to Example 3, a pigment dispersion was first prepared in which pigment a was dispersed in water. The pigment dispersion was prepared by blending pigment a, pigment dispersion resin b, sodium hydroxide, Olphine® E1010, and water in the amounts shown in Table 7.

[0060] [Table 7]

[0061] Sodium hydroxide was added as a neutralizing agent to neutralize pigment dispersion resin b. Olfin® E1010 was added as a dispersant to improve the dispersibility of pigment a in the solvent, and is a nonionic surfactant manufactured by Nisshin Chemical Industry Co., Ltd. In all of the ink samples 16 to 23 of Example 3, pigment a was pigment blue 15:3 (Toyo Color Co., Ltd. "Lionol Blue FG-7351"), and deionized water was used as the water.

[0062] The pigment dispersion was prepared by mixing the above components using a wet dispersion method with a media-type wet disperser. Examples of media-type wet dispersers include wet dispersers (more specifically, the "NanoGlenMill" manufactured by Asada Iron Works Co., Ltd., the "MSC Mill" manufactured by Nippon Coke Industries, Ltd., and the "DinoMill" manufactured by Shinmaru Enterprises, Ltd.).

[0063] In wet dispersion using a media-type wet disperser, media (zirconia beads with a diameter of 0.5 mm) were set in the vessel, and the discharge rate was controlled to 200-600 g / min to adjust the average particle size of the pigment dispersion, in which the dispersant adhered to pigment a dispersed in water, to 90-110 nm. The particle size distribution of the pigment dispersion was measured using a Zetasizer Nano manufactured by Sysmex Corporation, with the pigment dispersion diluted 300 times with deionized water.

[0064] Next, samples 16 to 23 of the ink according to Example 3 were prepared. Each sample 16 to 23 was prepared by blending the above-mentioned pigment dispersion, surfactant c, water-soluble humectant d, triethylene glycol monobutyl ether, and water in the amounts shown in Table 8. In all samples 16 to 23, benzyl methacrylate (BzMMA) / methacrylic acid (MAA) copolymer (BzMMA: 64% by mass, MAA: 36% by mass, acid value: 160 mg KOH / g) was used as the pigment dispersion resin b, and "ADEKA Pluronic L-61" manufactured by ADEKA Corporation was used as the surfactant c. In addition, triethylene glycol monobutyl ether was added as a viscosity modifier.

[0065] [Table 8]

[0066] In preparing ink samples 16-23 for Example 3, the components shown in Table 5 were added sequentially while stirring the solvent with a stirrer. Furthermore, foreign matter, debris, and coarse particles were removed by filtering each ink after stirring using a filter with a pore size of φ5 μm.

[0067] In the ink samples 16-23 of Example 3, various different water-soluble humectants d were used.

[0068] Table 9 shows the material names and log Kow values ​​of the water-soluble humectant d used in samples 16-23, as well as the evaluation results for wettability and dispersion stability for samples 16-23. Samples 18-22, in which water-soluble humectant d has 3 carbon atoms, all showed good evaluation results for both wettability and dispersion stability. On the other hand, sample 16, in which water-soluble humectant d is a triol, and sample 17, in which water-soluble humectant d has 2 carbon atoms, failed to meet the wettability standards. This is thought to be because the hydrophobicity of water-soluble humectant d was too low in samples 16 and 17, resulting in insufficient wettability. Furthermore, sample 23, in which water-soluble humectant d has 6 carbon atoms, failed to meet the dispersion stability standards. This is thought to be because the hydrophobicity of water-soluble humectant d was too high, causing aggregation of pigment a.

[0069] [Table 9]

Claims

1. Pigments and Pigment dispersion resin and A surfactant represented by general formula (1), Diols with 3 to 5 carbon atoms, It contains water, The mass ratio of the pigment dispersion resin to the pigment is 0.5 or more and 1.1 or less. Inkjet ink. 【Chemistry 1】 (In general formula (1), x, y, and z are integers determined such that the ratio of the number-average molecular weight of the propylene oxide chain alone in the surfactant to the number-average molecular weight of the surfactant is between 0.85 and 0.91.)

2. An inkjet ink according to claim 1, The number-average molecular weight of the surfactant is 1,900 or more and 3,000 or less. Inkjet ink.

3. An inkjet ink according to claim 1 or 2, The log Kow of the aforementioned diol is between -1.6 and 0.

6. Inkjet ink.

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