Inkjet ink set and inkjet recording method

Abstract

To provide an ink set or the like that can form an image that achieves both friction resistance and black color reproduction. [Solution] An inkjet ink set comprising a first inkjet ink and a second inkjet ink, wherein the first inkjet ink contains a first pigment containing a black pigment, a first binder resin containing anionic acrylic resin particles, an organic solvent, and water, the content of the first pigment is 3% by mass or more of the total amount of the first inkjet ink, the content of the anionic acrylic resin particles is 3% by mass or more of the total amount of the first inkjet ink, and the anionic acrylic resin particles are the only resin particles with the highest content among the first binder resin, and the second inkjet ink contains a second pigment containing a blue pigment, a second binder resin containing anionic urethane resin particles, an organic solvent, and water, the content of the second pigment is 3% by mass or more of the total amount of the second inkjet ink, the content of the anionic urethane resin particles is 5% by mass or more of the total amount of the second inkjet ink, and the anionic urethane resin particles are the only resin particles with the highest content among the second binder resin.

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink set and an inkjet recording method. [Background technology]

[0002] Inkjet recording methods, which enable the recording of high-resolution images with relatively simple equipment, are undergoing rapid development in various fields. Within this context, various studies are being conducted on the friction fastness of the formed images. For example, Patent Document 1 discloses a technique for improving friction fastness by applying a colorant-free coating liquid on top of a pigment-containing aqueous ink. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-088510 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in the technology disclosed in Patent Document 1, the brightness of the image tends to increase with the coating solution, making it difficult to obtain a black image with a high OD (optical density) value. Therefore, there is a need for a technology that can form an image that is both friction-resistant and black-colored. [Means for solving the problem]

[0005] The ink set of the present invention comprises a first inkjet ink and a second inkjet ink, wherein the first inkjet ink contains a first pigment containing a black pigment, a first binder resin containing anionic acrylic resin particles, an organic solvent, and water, with the first pigment content being 3% by mass or more of the total amount of the first inkjet ink, the anionic acrylic resin particle content being 3% by mass or more of the total amount of the first inkjet ink, and the anionic acrylic resin particles being the only resin particles with the highest content among the first binder resin, and the second inkjet ink contains a second pigment containing a blue pigment, a second binder resin containing anionic urethane resin particles, an organic solvent, and water, with the second pigment content being 3% by mass or more of the total amount of the second inkjet ink, the anionic urethane resin particle content being 5% by mass or more of the total amount of the second inkjet ink, and the anionic urethane resin particles being the only resin particles with the highest content among the second binder resin.

[0006] The inkjet recording method of the present invention comprises a first ink deposition step of using the above-mentioned inkjet ink set to eject a first inkjet ink by an inkjet method and adhere it to a recording medium, and a second ink deposition step of ejecting a second inkjet ink by an inkjet method and adhering it to a recording medium, wherein the first ink deposition step and the second ink deposition step are performed on the same area on the recording medium. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows an example of a serial-type inkjet recording device. [Figure 2] This table shows the results of the examples. [Figure 3] This table shows the results of the examples. [Modes for carrying out the invention]

[0008] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention. In the drawings, the same reference numerals are given to the same elements, and overlapping descriptions are omitted. In addition, unless otherwise specified, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0009] In the present embodiment, "inkjet ink" is also simply referred to as "ink". For example, "inkjet ink set" is also referred to as "ink set", "first inkjet ink" is also referred to as "first ink", and "second inkjet ink" is also referred to as "second ink".

[0010] 1. Inkjet ink set The ink set of the present embodiment includes a first ink and a second ink. The first ink contains a first pigment including a black pigment, a first binder resin including anionic acrylic resin particles, an organic solvent, and water. The content of the first pigment is 3% by mass or more based on the total amount of the first ink. The content of the anionic acrylic resin particles is 3% by mass or more based on the total amount of the first ink. The anionic acrylic resin particles are the only resin particles with the highest content among the first binder resin. The second ink contains a second pigment including a blue pigment, a second binder resin including anionic urethane resin particles, an organic solvent, and water. The content of the second pigment is 3% by mass or more based on the total amount of the second ink. The content of the anionic urethane resin particles is 5% by mass or more based on the total amount of the second ink. The anionic urethane resin particles are the only resin particles with the highest content among the second binder resin.

[0011] Because urethane resins tend to aggregate relatively easily, they tend to improve the frictional fastness of the resulting coating. On the other hand, because urethane resins tend to shrink easily, they tend to reduce the smoothness of the resulting coating. As a result, light passing through the coating is easily scattered, which is a factor in reducing black color development. For these reasons, it is difficult to achieve both frictional fastness and black color development when using urethane resin alone.

[0012] On the other hand, acrylic resin has high transparency and good film-forming properties, which tends to improve the smoothness of the resulting coating. Therefore, it is possible to obtain a coating that does not scatter light easily using acrylic resin. In addition, acrylic resin is relatively less prone to aggregation, which promotes the wetting and spreading of ink, and tends to improve the ink's filling ability on recording media. As described above, because acrylic resin can form a coating with low scattering and good filling ability, it tends to produce images with higher black color development compared to urethane resin. On the other hand, because acrylic resin is less prone to aggregation, the resulting coating tends to have lower friction fastness compared to urethane resin. For these reasons, it is difficult to achieve both friction fastness and high black color development even when using acrylic resin alone.

[0013] Furthermore, even when using both urethane resin and acrylic resin in a single ink, it is difficult to achieve both friction fastness and black color development. This is presumably because when urethane resin and acrylic resin are contained in roughly equal amounts in a single ink, the two resins tend to be uniformly mixed within the ink film, causing their respective properties to cancel each other out. Additionally, including both urethane resin and acrylic resin in a single ink leads to problems with the ink's storage stability.

[0014] In contrast, in this embodiment, a first ink containing the largest amount of anionic acrylic resin particles as the binder resin and a second ink containing the largest amount of anionic urethane resin particles as the binder resin are used as a set. With this configuration, this embodiment can form an image that achieves both friction fastness and black color development. The reason for this is presumed to be as follows: When a coating film is formed by the first ink, which is rich in acrylic resin, and the second ink, which is rich in urethane resin, the acrylic resin and urethane resin will exist in a relatively independent state within the coating film. As a result, the acrylic resin and urethane resin do not mix too much, so their performance is less likely to cancel each other out, thus achieving both friction fastness and black color development. It should be noted that this effect mechanism is a hypothesis, and the effect mechanism of this embodiment is not limited to this.

[0015] Furthermore, the ink set in this embodiment preferably consists of a first ink, which is black ink, and a second ink, which is blue ink. This tends to improve the black color reproduction when the first and second inks are used together.

[0016] The ink set of this embodiment is not particularly limited, but it is preferably for textile printing. Because fabrics tend to have high ink permeability, it is difficult to achieve both friction fastness and black color development. However, with the ink set of this embodiment, it is possible to achieve both friction fastness and black color development even when printing on fabrics.

[0017] 1.1. First inkjet ink The first ink contains a first pigment containing a black pigment, a first binder resin containing anionic acrylic resin particles, an organic solvent, and water. The first ink is preferably a black ink from the viewpoint of improving the black color development of the image. In this embodiment, "black ink" refers to the L in the Lab color space of a printed image obtained by a predetermined printing method. * is 50 or less, a * is 10 or less, and b *This refers to items where the value is 10 or less. The prescribed printing method is as follows: An inkjet printer is used to eject ink onto the fabric. The print resolution is 1440 x 720 dpi, the ink dot density is 22 ng / dot, and the ink application density is 22.8 mg / inch. 2 The fabric on which the image is recorded is dried at 160°C for 3 minutes to obtain a printed image.

[0018] 1.1.1. First Pigment The first pigment contains a black pigment. The first pigment may also contain pigments other than the black pigment. However, since the first ink is preferably a black ink, it is preferable that the first pigment does not contain pigments other than the black pigment. If the first pigment contains pigments other than the black pigment, it is preferable that the black pigment is the pigment that is present in the largest single content within the first pigment.

[0019] Examples of black pigments include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, or metals such as copper oxide and iron oxide (CI Pigment Black 11), and organic pigments such as aniline black (CI Pigment Black 1). Among these, carbon black is preferred as the black pigment. Carbon black has a relatively low specific gravity and does not easily settle in ink.

[0020] The black pigment may be self-dispersing or resin-dispersible, but it is preferable to be self-dispersing. Self-dispersing black pigments tend to improve the black color development of images compared to resin-dispersible black pigments. In this embodiment, "self-dispersing" means that the pigment disperses on its own without the presence of a dispersant. In contrast, "resin-dispersible" means that the pigment is dispersed by a resin dispersant. In this embodiment, the resin dispersant used to disperse the pigment does not fall under the category of "binder resin". The black pigment is particularly preferably self-dispersing carbon black.

[0021] The content of the first pigment is 3% by mass or more, preferably 4% by mass or more, and 5% by mass or more, relative to the total amount of the first ink. This tends to further improve the black color development of the image. The content of the first pigment is preferably 10% by mass or less, and 8% by mass or less, relative to the total amount of the first ink.

[0022] 1.1.2. First Binder Resin The first binder resin contains anionic acrylic resin particles as the only resin particles present in the largest quantity within the first binder resin. "The only resin particles present in the largest quantity within the first binder resin" can also be rephrased as "the resin particles present in the largest quantity by themselves within the first binder resin." In other words, the first binder resin may contain resin particles other than anionic acrylic resin particles, but the content of these other resin particles is less than that of anionic acrylic resin particles.

[0023] If the ink contains 50 parts by mass of anionic acrylic resin particles and 50 parts by mass of resin particles other than anionic acrylic resin particles in 100 parts by mass of binder resin, then there will be two resin particles with the highest content, and there will be no "single resin particle with the highest content," so it will be determined that the above requirement is not met.

[0024] Examples of acrylic resins that make up acrylic resin particles include resins obtained by polymerizing (meth)acrylic monomers such as (meth)acrylic acid and (meth)acrylic acid esters, and resins obtained by copolymerizing (meth)acrylic monomers with other monomers.

[0025] Acrylic resin particles tend to have improved dispersion stability due to their anionic nature. Anionic acrylic resin particles have, for example, carboxyl groups, sulfo groups, hydroxyl groups, etc.

[0026] The content of anionic acrylic resin particles is 3% by mass or more, preferably 4% by mass or more, and 5% by mass or more, relative to the total amount of the first ink. This tends to further improve the friction fastness of the image. Alternatively, the content of anionic acrylic resin particles is preferably 12% by mass or less, preferably 10% by mass or less, and 8% by mass or less, relative to the total amount of the first ink. This tends to further improve the black color development of the image.

[0027] The content of the first binder resin is preferably 12% by mass or less, 10% by mass or less, and 8% by mass or less, relative to the total amount of the first ink. This tends to further improve ejection stability and black color development of the image. Alternatively, the content of the first binder resin is preferably 3% by mass or more, 4% by mass or more, and 5% by mass or more, relative to the total amount of the first ink. This tends to further improve the friction fastness of the image.

[0028] The total content of the first pigment and the first binder resin is preferably 17% by mass or less, 15% by mass or less, and 13% by mass or less, relative to the total amount of the first ink. This tends to further improve ejection stability. Alternatively, the total content of the first pigment and the first binder resin is preferably 6% by mass or more, 8% by mass or more, and 10% by mass or more, relative to the total amount of the first ink. This tends to further improve the friction fastness of the image.

[0029] 1.1.3. Organic Solvents The first ink contains an organic solvent. Examples of organic solvents include glycerin; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and Examples include glycol monoethers such as propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and triethylene glycol monomethyl ether; nitrogen-containing solvents such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone; and alcohols such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol.

[0030] Among these, glycerin or glycols are preferred as the organic solvent, and glycerin or triethylene glycol is more preferred. The organic solvent may be used alone or in combination of two or more.

[0031] The content of the organic solvent is preferably 5.0 to 30% by mass, 10 to 25% by mass, and 15 to 20% by mass, relative to the total amount of the first ink. Having the organic solvent content within these ranges tends to improve storage stability and mechanical stability.

[0032] 1.1.4.Water The first ink contains water. The water content is preferably 55-85% by mass, 60-80% by mass, or 65-75% by mass, relative to the total amount of the first ink.

[0033] 1.1.5. pH adjusters The first ink may contain a pH adjuster. Examples of pH adjusters include inorganic acids (e.g., sulfuric acid, hydrochloric acid, nitric acid, etc.), inorganic bases (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), organic bases (e.g., triethanolamine, diethanolamine, monoethanolamine, trippropanolamine), and organic acids (e.g., adipic acid, citric acid, succinic acid, etc.). The inclusion of a pH adjuster tends to improve dispersion stability. The pH adjuster may be used alone or in a mixture of two or more.

[0034] The pH adjusting agent content is preferably 0.01 to 1.5% by mass, 0.05 to 1.0% by mass, and 0.1 to 0.75% by mass, relative to the total amount of the first ink. When the pH adjusting agent content is within the above range, dispersion stability tends to be further improved.

[0035] 1.1.6. Surfactants The first ink may contain a surfactant. The surfactant is not particularly limited, but examples include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. The surfactant may be used alone or in combination of two or more types.

[0036] The acetylene glycol-based surfactant is not particularly limited, but preferably one or more selected from, for example, 2,4,7,9-tetramethyl-5-decine-4,7-diol and its alkylene oxide adduct, and 2,4-dimethyl-5-decine-4-ol and its alkylene oxide adduct. Commercially available acetylene glycol-based surfactants are not particularly limited, but examples include Olfin E1010 and D-10PG (manufactured by Nisshin Chemical Industry Co., Ltd.).

[0037] Examples of fluorinated surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds.

[0038] Examples of silicone-based surfactants include polysiloxane compounds and polyether-modified organosiloxanes.

[0039] The HLB (Hydrophile-Lipophile Balance) value of the surfactant is preferably 10 or higher, more preferably 10 to 18, and even more preferably 12 to 16. Having the HLB value of the surfactant within this range tends to improve the storage stability and mechanical stability of the ink. The HLB value as used herein is defined by the Griffin method.

[0040] Among these, acetylene glycol-based surfactants are preferred, and acetylene glycol-based surfactants with an HLB value of 10 or higher are more preferred. By using such surfactants, the storage stability and mechanical stability of the ink are further improved, and the penetration of the ink into the recording medium is suppressed, which tends to further improve the black color reproduction of images.

[0041] The surfactant content is preferably 0.3 to 2.5% by mass and 0.5 to 2.0% by mass relative to the total amount of the first ink. When the surfactant content is within the above range, the black color development of the image, as well as the storage stability and mechanical stability of the ink tend to improve.

[0042] 1.1.7. Other Ingredients The first ink may also contain other components besides those mentioned above, such as chelating agents, softeners, solubilizers, viscosity modifiers, ultraviolet absorbers, antioxidants, corrosion inhibitors, etc.

[0043] 1.1.8. pH The pH of the first ink at 25°C is preferably 8 to 11, 8.1 to 10, and 8.2 to 9. The acrylic resin particles contained in the first ink are anionic, and the pigment may also be anionic. When the pH is 8 or higher, these anionic components are less likely to aggregate, which tends to improve ejection stability. When the pH is 11 or lower, the anionic components are less likely to redisperse after film formation, which tends to improve the friction fastness of the image.

[0044] 1.2. Second inkjet ink The second ink contains a second pigment containing a blue pigment, a second binder resin containing anionic urethane resin particles, an organic solvent, and water. The second ink is preferably a blue ink from the viewpoint of improving the black color development of the image. "Blue ink" refers to an ink that, when diluted with water and subjected to spectral measurement, has a maximum absorption wavelength in the visible light region of 350 to 800 nm that falls within the range of 550 to 650 nm, and does not fall under the definition of "black ink" described above.

[0045] 1.2.1. Second Pigment The second pigment contains a blue pigment. The second pigment may contain pigments other than the blue pigment, but it is preferable that it does not contain pigments other than the blue pigment. If the second pigment contains pigments other than the blue pigment, it is preferable that the blue pigment is the pigment that is present in the largest amount by itself among the second pigments.

[0046] Examples of blue pigments include CIPigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66. Among these, it is preferable that the blue pigment contains CIPigment Blue 15:3.

[0047] The blue pigment may be self-dispersible or resin-dispersible, but resin-dispersible is preferred. Resin-dispersible blue pigments tend to improve the friction fastness of images compared to self-dispersible blue pigments.

[0048] The content of the second pigment is 3% by mass or more, preferably 3.5% by mass or more, and 4% by mass or more, relative to the total amount of the second ink. This tends to further improve the black color development of the image. The content of the second pigment is preferably 10% by mass or less, and 8% by mass or less, relative to the total amount of the second ink.

[0049] 1.2.2. Second Binder Resin The second binder resin contains anionic urethane resin particles as the only resin particle with the highest content within the second binder resin. "The only resin particle with the highest content within the second binder resin" can also be rephrased as "the resin particle with the highest content by itself within the second binder resin." In other words, the second binder resin may contain resin particles other than anionic urethane resin particles, but the content of these other resin particles is lower than that of anionic urethane resin particles.

[0050] If the ink contains 50 parts by mass of anionic urethane resin particles and 50 parts by mass of resin particles other than anionic urethane resin particles in 100 parts by mass of binder resin, then there will be two resin particles with the highest content, and there will be no "single resin particle with the highest content," so it will be determined that the above requirement is not met.

[0051] The urethane resin that constitutes the urethane resin particles is not particularly limited as long as it is a resin that has urethane bonds in its molecule. Examples of urethane resins include polyether-type urethane resins containing ether bonds in the main chain, polyester-type urethane resins containing ester bonds in the main chain, and polycarbonate-type urethane resins containing carbonate bonds in the main chain.

[0052] Urethane resin particles tend to have improved dispersion stability due to their anionic nature. Anionic urethane resin particles have, for example, carboxyl groups, sulfo groups, hydroxyl groups, etc.

[0053] The content of anionic urethane resin particles is 5% by mass or more relative to the total amount of the second ink. This tends to further improve the friction fastness of the image. Furthermore, the content of anionic urethane resin particles is preferably 12% by mass or less, 10% by mass or less, or 8% by mass or less relative to the total amount of the second ink. This tends to further improve the black color development of the image.

[0054] The content of the second binder resin is preferably 12% by mass or less, 10% by mass or less, and 8% by mass or less, relative to the total amount of the second ink. This tends to further improve ejection stability and black color development of the image. Alternatively, the content of the second binder resin is 5% by mass or more, relative to the total amount of the second ink.

[0055] The total content of the second pigment and the second binder resin is preferably 15% by mass or less, 13% by mass or less, 11% by mass or less, and 10% by mass or less, relative to the total amount of the second ink. This tends to further improve ejection stability. The total content of the second pigment and the second binder resin is preferably 6% by mass or more, 7% by mass or more, and 8% by mass or more, relative to the total amount of the second ink. This tends to further improve the black color development and friction fastness of the image.

[0056] 1.2.3. Organic Solvents The second ink contains an organic solvent. Examples of organic solvents contained in the second ink are the same as those contained in the first ink. The organic solvent contained in the second ink may be the same as or different from the organic solvent contained in the first ink.

[0057] The content of the organic solvent is preferably 5.0 to 30% by mass, 10 to 25% by mass, and 15 to 20% by mass, relative to the total amount of the second ink. Having the organic solvent content within these ranges tends to improve storage stability and mechanical stability.

[0058] 1.2.4.Water The second ink contains water. The water content is preferably 55-85% by mass, 60-80% by mass, or 65-75% by mass, relative to the total amount of the second ink.

[0059] 1.2.5. pH adjusters The second ink may contain a pH adjuster. Examples of pH adjusters that the second ink may contain are the same as those that the first ink may contain. The pH adjuster in the second ink may be the same as or different from the pH adjuster in the first ink.

[0060] The pH adjusting agent content is preferably 0.01 to 1.5% by mass, 0.05 to 1.0% by mass, and 0.1 to 0.75% by mass, relative to the total amount of the second ink. When the pH adjusting agent content is within the above range, dispersion stability tends to be further improved.

[0061] 1.2.6. Surfactants The second ink may contain a surfactant. Examples of surfactants that the second ink may contain are the same as those that the first ink may contain. The surfactant contained in the second ink may be the same as or different from the surfactant contained in the first ink.

[0062] The surfactant content is preferably 0.3 to 2.5% by mass and 0.5 to 2.0% by mass relative to the total amount of the second ink. When the surfactant content is within the above range, the black color development of the image, as well as the storage stability and mechanical stability of the ink tend to improve.

[0063] 1.2.7. Other Ingredients The second ink may contain other components besides those mentioned above, such as chelating agents, softeners, solubilizers, viscosity modifiers, ultraviolet absorbers, antioxidants, corrosion inhibitors, etc.

[0064] 1.2.8. pH The pH of the second ink at 25°C is preferably 8 to 11, 8.2 to 10, and 8.4 to 9.5. The urethane resin particles contained in the second ink are anionic, and the pigment may also be anionic. When the pH is 8 or higher, these anionic components are less likely to aggregate, which tends to improve ejection stability. When the pH is 11 or lower, the anionic components are less likely to redisperse after film formation, which tends to improve the friction fastness of the image.

[0065] 1.3. Method of manufacturing ink The first and second inks can be manufactured, for example, by mixing the components in any order and removing impurities, foreign matter, etc., by filtration or other methods as needed. A method of mixing the components is to sequentially add each component to a container equipped with a stirring device such as a mechanical stirrer or magnetic stirrer, and then stir and mix them. Examples of filtration methods include centrifugal filtration and filter filtration.

[0066] 2. Inkjet recording method The inkjet recording method of this embodiment uses the above-described ink set and performs the first ink application step and the second ink application step on the same area on the recording medium. The first ink application step is the step of ejecting the first ink by the inkjet method and adhering it to the recording medium. The second ink application step is the step of ejecting the second ink by the inkjet method and adhering it to the recording medium. By performing the first and second ink application steps on the same area on the recording medium, the urethane resin and the acrylic resin exist in a relatively independent state within the coating film. As a result, the urethane resin and the acrylic resin do not mix excessively, so their performance is less likely to cancel each other out, thus achieving both friction fastness and black color development.

[0067] The recording medium is not particularly limited, but a fabric is preferred. Since fabrics tend to have high ink permeability, it is difficult to achieve both friction fastness and black color development. However, with the ink set of the present embodiment, both friction fastness and black color development can be achieved even when the recording medium is a fabric. The fibers constituting the fabric are not particularly limited, and examples thereof include natural fibers or synthetic fibers such as silk, cotton, wool, nylon, polyester, and rayon.

[0068] The ink adhesion amount in the first ink adhesion step is preferably 13 mg / inch 2 or more, more preferably 15 mg / inch 2 or more, and even more preferably 17 mg / inch 2 or more, and still more preferably 19 mg / inch 2 or more. The ink adhesion amount in the first ink adhesion step is preferably 40 mg / inch 2 or less, more preferably 35 mg / inch 2 or less, even more preferably 30 mg / inch 2 or less, and still more preferably 25 mg / inch 2 or less.

[0069] Further, the ink adhesion amount in the second ink adhesion step is preferably 6 mg / inch 2 or more, more preferably 8 mg / inch 2 or more, even more preferably 10 mg / inch 2 or more, still more preferably 12 mg / inch 2 or more, and even still more preferably 13 mg / inch 2 or more. The ink adhesion amount in the second ink adhesion step is preferably 30 mg / inch 2 or less, more preferably 25 mg / inch 2 or less, even more preferably 20 mg / inch 2 or less, and still more preferably 15 mg / inch 2 or less.

[0070] When the ink adhesion amount in the first ink adhesion step and the ink adhesion amount in the second ink adhesion step are within the above ranges, both the friction fastness and black color development of the image tend to be improved.

[0071] The sum of the ink adhesion amount in the first ink adhesion step and the ink adhesion amount in the second ink adhesion step is preferably 20 to 50 mg / inch. 2 Therefore, 26-40 mg / inch 2 Therefore, 30-40 mg / inch 2 This tends to improve both the frictional fastness and black color reproduction of the image.

[0072] The ratio of the amount of ink applied in the first ink application step to the amount of ink applied in the second ink application step is preferably 1.0 to 2.5, 1.1 to 2.3, 1.2 to 2.2, or 1.3 to 1.8.

[0073] It is preferable that the amount of ink applied in the first ink application step is greater than the amount of ink applied in the second ink application step. This tends to further improve the black color reproduction of the image.

[0074] The first ink application process and the second ink application process may be performed multiple times on the same area of ​​the recording medium, or only once. Furthermore, the first ink application process and the second ink application process may be performed simultaneously, or in any order, for example, alternately.

[0075] In the inkjet recording method, inks other than the first or second ink, or processing liquids, may be used, as long as the effects of the present invention are not hindered. The processing liquids are, for example, pre-treatment liquids, coating liquids, etc.

[0076] 3. Inkjet recording device The inkjet recording device used in the inkjet recording method is not particularly limited and may be, for example, a serial type or a line type. A serial type is one in which a head unit is mounted on a carriage that moves in the main scanning direction (horizontal direction, width direction of the recording medium), and droplets are ejected from nozzles onto the recording medium as the carriage moves. A line type is one in which the head is fixed, and the recording medium is moved along the sub-scanning direction (vertical direction, transport direction of the recording medium), and droplets are ejected from the nozzles of the head in conjunction with this movement.

[0077] Figure 1 is a perspective view showing an example of a serial inkjet recording device. The inkjet recording device 10 illustrated in Figure 1 comprises a transport unit 120 and a recording unit 130. The transport unit 120 has feed rollers that transport the recording medium F in the sub-scanning direction T2, transporting the recording medium F to the recording unit 130 and ejecting the recording medium F after recording. The recording unit 130 comprises a carriage 134 and a carriage moving mechanism 135 that moves the carriage 134 in the main scanning directions S1 and S2. The carriage 134 is equipped with an inkjet head 131. The inkjet head 131 has nozzles that eject ink onto the recording medium F. As the carriage 134 moves, the inkjet head 131 moves in the main scanning directions S1 and S2 (main scan, pass). The inkjet head 131 ejects ink onto the recording medium F while moving in the main scanning directions S1 and S2. In the serial inkjet recording device 10, image formation is performed in multiple passes (multi-pass). Between passes, the recording medium F is transported (sub-scanning). In a serial-type inkjet recording device 10, for example, main scanning and sub-scanning are performed alternately. [Examples]

[0078] The present invention will be described more specifically below with reference to examples and comparative examples. The present invention is not limited in any way by the following examples.

[0079] 1. Preparation of pigment dispersion 1.1 Preparation of Self-Dispersing Black Pigment Dispersion 500g of raw carbon black powder prepared by the furnace method (primary particle size = 18nm, BET specific surface area = 180m²) 2 A solution containing self-dispersing carbon black was added to 3750g of deionized water (186mL / g, DBP absorption rate = 186mL / 100g) and heated to 45°C while stirring with a dissolver. Then, while grinding with a sand mill using 0.8mm diameter zirconia beads, 30000g of an aqueous solution of sodium hypochlorite (effective chlorine concentration = 12%) was added dropwise at 45°C for 3.5 hours. Grinding was continued with the sand mill for 30 minutes to obtain a treatment solution containing self-dispersing carbon black. This treatment solution was filtered through a 400-mesh wire mesh to separate the zirconia beads and unreacted carbon black from the treatment solution. A 5% aqueous solution of potassium hydroxide was added to the separated treatment solution to adjust the pH to 7.5. Desalting and purification were performed using an ultrafiltration membrane until the conductivity of the solution was 1.5mS / cm. Further desalting and purification were performed using an electrodialysis machine until the conductivity of the solution was 1.0mS / cm. The solution was concentrated until the concentration of self-dispersing carbon black reached 17% by mass. This concentrate was subjected to a centrifuge to remove coarse particles and filtered through a 0.6 μm filter. Deionized water was added to the resulting filtrate, and the solution was diluted and dispersed until the concentration of self-dispersing carbon black reached 15% by mass to obtain a self-dispersing black pigment dispersion.

[0080] 1.2. Preparation of resin-dispersed black pigment dispersion To 15 parts by mass of carbon black, 10 parts by mass of ammonium salt of styrene-acrylic acid copolymer (weight-average molecular weight 10,000) as a dispersant polymer component and 55 parts by mass of ion-exchanged water were added and thoroughly mixed. Then, this mixture was dispersed in a sand mill (manufactured by Yaskawa Corporation) with glass beads (1.7 mm in diameter, 1.5 times the amount of the mixture) for 2 hours. After dispersion, the glass beads were removed to obtain a resin-dispersed black pigment dispersion containing resin-dispersed carbon black.

[0081] 1.3. Preparation of resin-dispersed cyanide pigment dispersion A resin-dispersed cyanide pigment dispersion was obtained using the same method as described above for the preparation of the resin-dispersed black pigment dispersion, except that CIPigment Blue 15:3 was used instead of carbon black.

[0082] 1.4. Preparation of resin-dispersed yellow pigment dispersion A resin-dispersed yellow pigment dispersion was obtained using the same method as described above for the preparation of the resin-dispersed black pigment dispersion, except that CIPigment Yellow 180 was used instead of carbon black.

[0083] 1.5. Preparation of resin-dispersed magenta pigment dispersion A resin-dispersed magenta pigment dispersion was obtained using the same method as described above for the preparation of the resin-dispersed black pigment dispersion, except that CIPigment Red 122 was used instead of carbon black.

[0084] 2. Preparation of binder resin dispersion 2.1 Preparation of urethane-based binder resin dispersion In a four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, 322.2 g of polytetramethylene ether glycol with a number-average molecular weight of 1000, 19.7 g of 2,2-dimethylolbutanoic acid, 16.9 g of 1,4-butanediol, 137.9 g of hexamethylene diisocyanate, and 344.0 g of methyl ethyl ketone were charged and reacted at 80°C for 6 hours under a nitrogen gas atmosphere. The mixture was then cooled to 60°C, 12.5 g of triethylamine was added, and the mixture was mixed at this temperature for 30 minutes. The resulting prepolymer was mixed with 1146.7 g of deionized water and stirred for 2 hours. Subsequently, the methyl ethyl ketone was removed under reduced pressure at 40°C. This yielded a urethane binder resin dispersion containing anionic urethane resin particles having carboxyl groups as acidic groups. The solid content concentration in the obtained dispersion was 30% by mass.

[0085] 2.2 Preparation of acrylic binder resin dispersion In a reaction vessel equipped with a stirrer, reflux condenser, dropper, and thermometer, 2600g of deionized water and 0.5g of sodium lauryl sulfate were charged, and the temperature was raised to 70°C while stirring and purging with nitrogen. Maintaining the internal temperature at 70°C, 4g of potassium persulfate was added as a polymerization initiator. After dissolution, an emulsion prepared in advance by adding 300g of deionized water, 0.5g of sodium lauryl sulfate, 2g of acrylamide, 180g of methyl methacrylate, 25g of butyl acrylate, and 2g of methacrylic acid under stirring was continuously added dropwise to the reaction solution over 3 hours. After the addition was complete, the mixture was allowed to mature for 1 hour. After the maturation was complete, an emulsion prepared in advance by adding 500g of deionized water, 1.5g of sodium lauryl sulfate, 30g of acrylamide, 1200g of styrene, 200g of 2-ethylhexyl methacrylate, and 30g of methacrylic acid under stirring was continuously added dropwise to the reaction solution over 4 hours. After the addition was complete, the mixture was allowed to mature for 3 hours. The resulting aqueous emulsion was cooled to room temperature, and then deionized water and sodium hydroxide solution were added to adjust the solid content to 30% by mass and the pH to 8. This yielded an acrylic binder resin dispersion containing anionic acrylic resin particles having carboxyl groups as acidic groups.

[0086] 3. Ink preparation Each material was mixed according to the composition shown in the table in Figure 2, and thoroughly stirred to obtain inks 1 to 15. The composition of the pigment dispersions listed in the table in Figure 2 is the pigment equivalent value. The composition of the binder resin dispersions listed in the table in Figure 2 is the binder resin equivalent value. The units of the compositions listed in the table in Figure 2 are in mass%, and the total composition is 100.0 mass%. Olfin E1010 and Olfin D-10PG are both acetylene glycol-based surfactants manufactured by Nisshin Chemical Industry Co., Ltd.

[0087] 4. Measurement of the ink's maximum absorption wavelength For each ink, the maximum absorption wavelength was measured using a spectrophotometer (Hitachi High-Tech Science Co., Ltd. "U-39000H" model) diluted with pure water at a dilution ratio that resulted in a maximum absorption of 1 in the 350-800 nm range. The measurement results are shown in the table in Figure 2.

[0088] 5. Measuring the pH of the ink For each ink, the pH was measured at 25°C using a desktop pH meter (model number: F-72, manufacturer: HORIBA). The measurement results are shown in the table in Figure 2.

[0089] 6. Inkjet recording (textile printing) The inks prepared above were filled into cartridges of an inkjet printer (Seiko Epson, product name "PX-G930"). Using this printer, pre-treated cotton (Fortex, product name "COT-PT", 100% cotton, basis weight 130 g / m²) was used. 2 The ink prepared above was ejected from the print head in the same pass to record a solid image. The print resolution was 1440 x 720 dpi. The ink density was 22 ng / dot. The ink combinations and the amount of each ink applied were as shown in the table in Figure 3 for each of Examples 1-5 and Comparative Examples 1-12. The fabric on which the image was recorded was dried at 160°C for 3 minutes to obtain a printed product.

[0090] 7.L * a * , and b * Measurement L in the Lab color space of the obtained printed image * a * , and b * The following was measured. As a result, the ink in each example containing the black pigment dispersion was L * is 50 or less, a * is 10 or less, and b * The value was 10 or less. In contrast, the inks in each example that did not contain black pigment dispersion were L * a * , and b * At least one of the above was not within the specified range.

[0091] 8. Evaluation 8.1. Black color development (optical density of black) The optical density (OD, Status E) of the black in the printed image of the prepared textile was measured and further evaluated according to the following criteria. This allowed us to evaluate the black color development performance. A: The OD of black in the printed image is 1.60 or higher. B: The OD of black in the printed image is between 1.56 and 1.60. C: The OD of black in the printed image is between 1.52 and 1.56. D: The OD of black in the printed image is less than 1.52.

[0092] 8.2. Friction fastness (wet friction fastness) The printed material prepared as described above was rubbed 10 times with a load of 9N using a cotton cloth (white cotton cloth) that had been wetted with pure water to approximately 100% moisture, using a clock meter (FI-306, manufactured by Tester Sangyo Co., Ltd.) on the image of the printed material. After that, the optical density of black (OD, Status E) was measured using a colorimeter (FD-7, manufactured by Konica Minolta Corporation) in the ink-contaminated areas of the rubbed cloth, and further evaluation was performed according to the following criteria. This evaluated the friction fastness. A: The OD of the black area in the contaminated region is 0.5 or less. B: The OD of the black area in the contaminated zone is greater than 0.5 and less than or equal to 0.6. C: Black OD in the contaminated area is greater than 0.6

[0093] 9. Evaluation Results The evaluation results are shown in the table in Figure 3. From these results, it can be seen that the ink set of this embodiment can form images that have both friction fastness and black color development. [Explanation of symbols]

[0094] 10... Inkjet recording device, 120... Transport unit, 130... Recording unit, 131... Inkjet head, 134... Carriage, 135... Carriage movement mechanism, F... Recording medium, S1, S2... Main scanning direction, T2... Sub-scanning direction.

Claims

1. Including a first inkjet ink and a second inkjet ink, The first inkjet ink contains a first pigment containing a black pigment, a first binder resin containing anionic acrylic resin particles, an organic solvent, and water. The content of the first pigment is 3% by mass or more relative to the total amount of the first inkjet ink. The content of the anionic acrylic resin particles is 3% by mass or more relative to the total amount of the first inkjet ink. The anionic acrylic resin particles are the only resin particles that are present in the largest quantity among the first binder resins. The second inkjet ink contains a second pigment containing a blue pigment, a second binder resin containing anionic urethane resin particles, an organic solvent, and water. The content of the second pigment is 3% by mass or more relative to the total amount of the second inkjet ink. The content of the anionic urethane resin particles is 5% by mass or more relative to the total amount of the second inkjet ink. The anionic urethane resin particles are the only resin particles that are present in the largest quantity among the second binder resins. Inkjet ink set.

2. The pH of the first inkjet ink at 25°C is 8 to 11. The pH of the second inkjet ink at 25°C is 8 to 11. The inkjet ink set according to claim 1.

3. The content of the first binder resin is 10% by mass or less relative to the total amount of the first inkjet ink. The content of the second binder resin is 10% by mass or less relative to the total amount of the second inkjet ink. The inkjet ink set according to claim 1.

4. The blue pigment comprises C.I. Pigment Blue 15:

3. The inkjet ink set according to claim 1.

5. The total content of the first pigment and the first binder resin is 13% by mass or less relative to the total amount of the first inkjet ink. The total content of the second pigment and the second binder resin is 13% by mass or less relative to the total amount of the second inkjet ink. The inkjet ink set according to claim 1.

6. It is for printing. The inkjet ink set according to claim 1.

7. The aforementioned black pigment is self-dispersing carbon black. The inkjet ink set according to claim 1.

8. The aforementioned blue pigment is a resin-dispersed pigment. The inkjet ink set according to claim 1.

9. Using the inkjet ink set described in any one of claims 1 to 8, A first ink deposition step involves ejecting the first inkjet ink by an inkjet method and depositing it onto a recording medium, The process includes a second ink application step, in which the second inkjet ink is ejected by an inkjet method and attached to the recording medium, The first ink application step and the second ink application step are performed on the same area on the recording medium. Inkjet recording method.

10. The amount of ink applied in the first ink application step is 13 mg / inch. 2 That's all. The amount of ink applied in the second ink application step is 13 mg / inch. 2 That's all. The sum of the amount of ink applied in the first ink application step and the amount of ink applied in the second ink application step is 26 to 40 mg / inch. 2 That is, The inkjet recording method according to claim 9.

11. The amount of ink applied in the first ink application step is greater than the amount of ink applied in the second ink application step. The inkjet recording method according to claim 9.

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