Inkjet ink composition, ink set, and recording method

Abstract

The present invention provides an inkjet ink composition, an ink set, and a recording method, which are excellent in clogging recovery, intermittence, and stacking. An inkjet ink composition comprising a self-dispersible pigment, inorganic oxide particles, and polyethylene glycol represented by the following general formula (I), and comprising one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, and the inkjet ink composition is an aqueous ink, HO-(CH2-CH2-O-) n -H...(I), wherein n represents an integer of 3 to 9.

Description

Technical Field

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

[0002] Inkjet recording methods, which enable the recording of high-definition images using relatively simple equipment, have seen rapid development in various fields. However, in particular, when using high-speed continuous inkjet printers with aqueous inks on plain paper, curling can occur, which can reduce stacking properties. To prevent this curling, inkjet ink compositions containing inorganic oxide particles, such as silica particles, have been studied. For example, Patent Document 1 discloses an inkjet recording ink containing colloidal silica to provide an inkjet recording ink that improves stacking properties.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-007444

[0004] However, inks using self-dispersible pigments and inorganic oxide particles have poor clogging recovery properties. Summary of the Invention

[0005] The inkjet ink composition of the present invention is an inkjet ink composition comprising a self-dispersible pigment, inorganic oxide particles, and polyethylene glycol represented by the following general formula (I), and comprising one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The inkjet ink composition is an aqueous ink.

[0006] HO-(CH2-CH2-O-) n -H……(I)

[0007] (In the formula, n represents an integer from 3 to 9.)

[0008] The ink set of the present invention comprises a first ink composition and a second ink composition. The first ink composition is the above-mentioned inkjet ink composition, and the second ink composition is an aqueous inkjet ink composition.

[0009] The recording method of the present invention includes a discharge step of discharging the inkjet ink composition from an inkjet head and causing it to adhere to a recording medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a diagram showing an example of a recording device used in the recording method of this embodiment.

[0011] Description of Reference Numerals

[0012] 10: Recording device; 11: Conveying path; 12: Paper feed section; 14: Conveying section; 16: Belt conveying section; 18: Recording section; 20: Fd discharge section; 22: Fd loading section; 24: Reversing path section; 26: Fu discharge section; 28: Fu loading section; 30: Paper feed tray; 32: Paper feed roller; 34: Conveying drive roller; 36: Conveying driven roller; 38: First roller; 40: Second roller; 42: An endless belt; 42a: Upper section of the endless belt; 44: Support body; 46: Head bracket; 48: Inkjet head; 50: First branch section; 52: Reversing path; 54: Second branch section; 56: Discharge roller pair; 64: Discharge drive roller; 68: Drive shaft; 76: Loading surface; 78: Conveyor section; 80: First force member; 82: Second force member; 84, 86: Support shafts; P: Recording medium. DETAILED DESCRIPTION

[0013] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the accompanying drawings as needed, but the present invention is not limited thereto and various modifications can be made without departing from the scope of the present invention. It should be noted that the same elements are given the same symbols in the accompanying drawings, and repeated descriptions are omitted. In addition, unless otherwise specified, the positional relationships such as up and down and left and right are based on the positional relationships shown in the drawings. In addition, the dimensional ratios in the drawings are not limited to the ratios shown in the drawings.

[0014] 1. Inkjet ink composition

[0015] The inkjet ink composition according to this embodiment (hereinafter also referred to as the "ink composition") is an aqueous ink comprising a self-dispersible pigment, inorganic oxide particles, and polyethylene glycol represented by the following general formula (I), and containing at least one metal ion selected from the group consisting of potassium ions, sodium ions, and lithium ions. The inkjet ink composition according to this embodiment may further comprise other components as needed.

[0016] HO-(CH2-CH2-O-) n -H……(I)

[0017] (In the formula, n represents an integer from 3 to 9.)

[0018] In the past, when using water-based ink for inkjet recording on plain paper, there was a problem that curling easily occurred and stacking property was reduced. Therefore, in order to suppress the generation of curling and improve stacking property, inkjet ink compositions containing inorganic oxide particles such as silica particles have been studied. Stacking property refers to whether the recording medium after recording can be neatly stacked in a manner that the end positions of the recording medium are aligned when the recording medium is discharged onto the paper output tray of the printer and multiple sheets are stacked in an overlapping manner. When the recording medium after recording produces curling, the stacking property deteriorates.

[0019] However, it is known that, for such inks containing inorganic oxide particles, especially when the pigment is a self-dispersible pigment, foreign matter is easily generated in the ink. Furthermore, the present inventors have conducted in-depth research on this cause and found the following: When containing inorganic oxide particles and a self-dispersible pigment, and containing one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, dispersion stability becomes unstable and clogging recovery deteriorates. The metal ions may be counterions of the inorganic oxide particles or the self-dispersible pigment.

[0020] In particular, when an ink composition contains inorganic oxide particles and a self-dispersible pigment, and contains two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, the dispersion stability of the ink composition becomes unstable and the clogging recovery property deteriorates. In particular, when the self-dispersible pigment and the inorganic oxide particles contained in the ink have different metal ions as the counter ions of the self-dispersible pigment and the inorganic oxide particles, the ink composition contains two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. Furthermore, these different metal ions mix in the ink, causing the dispersion stability to become unstable.

[0021] Alternatively, if an ink composition contains inorganic oxide particles and a self-dispersible pigment, and contains a metal ion selected from the group consisting of potassium, sodium, and lithium ions, and another ink composition used for recording as a set with the ink composition contains one or more metal ions selected from the group consisting of potassium, sodium, and lithium ions that are different from the metal ions contained in the ink composition, the dispersion stability of the ink composition may become unstable, causing clogging or poor ejection stability. In this case, each metal ion may serve as a counter ion for the self-dispersible pigment or inorganic oxide particles contained in either ink.

[0022] In these cases, due to unstable dispersion, the self-dispersible pigment or inorganic oxide particles aggregate into coarse particles and become foreign matter. In particular, it is known that when one of the self-dispersible pigment and inorganic oxide particles becomes unstable in dispersion, it can entrain the other, forming a composite foreign matter composed of the self-dispersible pigment and inorganic oxide particles. This can easily reduce clogging recovery and intermittency during inkjet recording.

[0023] Therefore, the inkjet ink composition of this embodiment improves stacking properties by containing inorganic oxide particles. In addition, by containing predetermined metal ions and predetermined polyethylene glycol, it can suppress the formation of complex foreign matter between the self-dispersible pigment and the metal ions, thereby improving clogging recovery and intermittency.

[0024] The relationship between polyethylene glycol and metal ions is not particularly limited. For example, it is believed that the coordination of polyethylene glycol of a predetermined molecular weight with a predetermined metal ion can deactivate the interaction between the self-dispersible pigment and the metal ion that leads to the formation of complex foreign matter. It should be noted that the mechanism of action for suppressing the formation of complex foreign matter is not limited to the above.

[0025] Hereinafter, the components of the inkjet ink composition, the ink set, the recording method, and the like according to this embodiment will be described in detail.

[0026] 1.1. Self-dispersible pigments

[0027] In this embodiment, a self-dispersible pigment refers to a pigment that can be dispersed in a dispersant or an aqueous medium. Examples of such self-dispersible pigments include pigments that are dispersed in a solvent by directly introducing hydrophilic functional groups or the like onto the pigment surface through physical and / or chemical surface treatment. It should be noted that self-dispersible pigments are distinguished from resin-dispersible pigments that are dispersed in a solvent using a dispersant.

[0028] Pigments used for such self-dispersible pigments are not particularly limited, and examples thereof include azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments), polycyclic pigments (such as phthalocyanine pigments, perylene pigments, pyrene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), organic pigments such as nitro pigments, nitroso pigments, and aniline black; inorganic pigments such as carbon black (such as furnace black, thermal lamp black, acetylene black, and channel black); metal oxides, metal sulfides, and metal chlorides; and extender pigments such as silica, calcium carbonate, and talc. The pigments may be used alone or in combination of two or more.

[0029] Among them, it is preferred to contain one or more selected from the group consisting of carbon black and organic pigments. This tends to result in better image quality. The ink containing these pigments can be black ink or color ink. Examples of color inks include cyan ink, magenta ink, yellow ink, etc., and also include orange ink, red ink, blue ink, etc. Black ink is often used for recording text, and inks with excellent color rendering properties are particularly useful.

[0030] Here, as a method for performing surface treatment of the pigment, conventionally known methods can be used, and such methods are not particularly limited. Examples thereof include ozone treatment of the pigment surface, alkali treatment of the pigment surface, or other chemical reactions to introduce hydrophilic functional groups by chemical reaction. Examples of the hydrophilic functional groups introduced include carboxyl groups, phosphoric acid groups, and sulfonic acid groups.

[0031] The self-dispersible pigment may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions as counterions. The method for adjusting the counterions of the self-dispersible pigment is not particularly limited, and examples thereof include methods for adjusting the alkali metal salt used in preparing the self-dispersible pigment.

[0032] In addition, the volume average particle size D of the self-dispersible pigment 50 The particle size is preferably 40 to 250 nm, more preferably 80 to 210 nm, and even more preferably 100 to 170 nm. It is particularly preferably 110 to 150 nm. When the volume average particle size is below these values, intermittent performance and clogging recovery tend to be more excellent, while when the volume average particle size is above these values, image quality tends to be excellent.

[0033] Volume average particle size D 50 The particle size distribution can be measured using a particle size analyzer that uses a dynamic light scattering method as its measurement principle. Examples of such particle size distribution analyzers include the "Zeta Potential, Particle Size, and Molecular Weight Measurement System ELSZ2000ZS" (trade name) manufactured by Otsuka Electronics Co., Ltd., which uses a homodyne optical system as its frequency analysis method. It should be noted that, in this specification, unless otherwise specified, "average particle size" refers to the average particle size based on the number of particles.

[0034] The content of the self-dispersible pigment relative to the total mass of the inkjet ink composition is preferably 4.0 to 12 mass%, more preferably 6.0 to 10 mass%, and even more preferably 6.0 to 8.0 mass%. A self-dispersible pigment content of 4.0 mass% or greater tends to result in excellent image quality.

[0035] 1.2. Inorganic oxide particles

[0036] As inorganic oxide particles, there are no particular limitations as long as they can be dispersed in water. Examples include metal oxides such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, antimony oxide, tin oxide, tantalum oxide, zinc oxide, cerium oxide, lead oxide, and indium oxide; metal nitrides such as silicon nitride, titanium nitride, and aluminum nitride; metal carbides such as silicon carbide and titanium carbide; metal sulfides such as zinc sulfide; metal carbonates such as calcium carbonate and magnesium carbonate; metal sulfates such as calcium sulfate and magnesium sulfate; metal silicates such as calcium silicate and magnesium silicate; metal phosphates such as calcium phosphate; metal borates such as aluminum borate and magnesium borate, and complexes thereof. The inorganic oxide particles may form salts. Inorganic oxide particles may be used alone or in combination of two or more. Any inorganic oxide particle containing at least an inorganic oxide is sufficient. Particles formed from an inorganic oxide are preferred.

[0037] The inorganic oxide particles may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions as counterions. There are no particular limitations on the method for adjusting the counterions in the inorganic oxide particles, and examples thereof include methods for adjusting the alkali metal salt used in preparing the inorganic oxide particles.

[0038] Among them, it is preferred to include one or more selected from the group consisting of silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, and cerium oxide, and more preferably silicon oxide. This can further suppress the occurrence of curling in inkjet recording using the aqueous inkjet ink composition, and tends to have excellent stacking properties.

[0039] Volume average particle size D of inorganic oxide particles 50 It is preferably 100 nm or less, more preferably 5 to 90 nm. It is also preferably 10 to 80 nm, more preferably 20 to 70 nm, further preferably 30 to 80 nm, and further preferably 40 to 60 nm. The volume average particle size D of the inorganic oxide particles is determined by the volume average particle size D of the inorganic oxide particles. 50 If the value is less than the above value, intermittency and clogging recovery tend to be more excellent. 50 The above value or more tends to result in better image quality. The method for measuring the volume average particle size is the same as described above.

[0040] The content of the inorganic oxide particles is preferably 0.5 to 8.0% by mass, more preferably 1.0 to 6.0% by mass, and even more preferably 2.0 to 4.0% by mass relative to the total mass of the inkjet ink composition. When the content of the inorganic oxide particles is 0.5% by mass or greater, stacking properties tend to be excellent, while when the content of the inorganic oxide particles is 8.0% by mass or less, clogging recovery properties tend to be excellent.

[0041] Metal ions

[0042] The inkjet ink composition of this embodiment contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The metal ions preferably contain metal ions derived from counter ions of at least one of the self-dispersible pigment and the inorganic oxide particles.

[0043] Here, in this embodiment, the counter ion refers to an ion that is electrically paired when the self-dispersible pigment and / or inorganic oxide particles form a salt. Furthermore, when the self-dispersible pigment and / or inorganic oxide particles already form a salt, the counter ion refers to an ion that is electrically paired.

[0044] The inkjet ink composition of this embodiment may also contain two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. These two or more metal ions preferably include a metal ion derived from the counter ion of the self-dispersible pigment and a metal ion different from the metal ion and derived from the counter ion of the inorganic oxide particles.

[0045] Among the metal ions, potassium ions are preferred from the perspective of better image quality, while sodium ions or lithium ions are preferred from the perspective of better clogging recovery, and sodium ions are more preferred.

[0046] Among them, the metal ions more preferably include one or more metal ions selected from the group consisting of potassium ions, which are counter ions derived from the self-dispersible pigment, sodium ions, which are counter ions derived from the inorganic oxide particles, and lithium ions, which are counter ions derived from the inorganic oxide particles. The metal ions further preferably include potassium ions, which are counter ions derived from the self-dispersible pigment, and sodium ions, which are counter ions derived from the inorganic oxide particles. This tends to result in excellent image quality and clogging recovery.

[0047] The inkjet ink composition of this embodiment can be used for recording together with another inkjet ink composition that is an aqueous ink. In this case, the other inkjet ink composition can contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. Furthermore, in this case, the other inkjet ink composition can contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions that are different from the metal ions contained in the inkjet ink composition.

[0048] When two or more ink compositions containing different metal ions are used together and ejected from the nozzles of the same inkjet head, there are many opportunities for contact between the two ink compositions due to contact between the pigment inks of adjacent nozzles, contact caused by ink mist dispersion, contact caused by wiping during cleaning, and other factors. When ions from one ink mix with the other ink due to such contact, this can disrupt dispersion, potentially resulting in the formation of composite foreign matter composed of self-dispersible pigments and inorganic oxide particles.

[0049] However, the ink composition of this embodiment, due to its aforementioned structure, is less likely to generate complex foreign matter, making it suitable for use with other ink compositions containing different metal ions. Specifically, when used in combination with other ink compositions, the inkjet ink composition of this embodiment is less likely to generate complex foreign matter, even when there is contact between adjacent nozzles, contact caused by ink mist dispersion, or contact caused by wiping during cleaning. It also tends to exhibit excellent clogging recovery and intermittency.

[0050] 1.4. Polyethylene glycol

[0051] The polyethylene glycol in this embodiment is represented by the following general formula (I). In this embodiment, the inclusion of polyethylene glycol in the ink suppresses the generation of foreign matter originating from self-dispersible pigments, inorganic oxide particles, and metal ions, resulting in excellent clogging recovery and intermittent properties. This also results in excellent discharge stability.

[0052] In particular, as a polyethylene glycol represented by the following general formula (I), by using a polyethylene glycol with a chain length corresponding to the ionic radius, it is believed that ions can be appropriately included and the generation of complex foreign matter can be suppressed, but the present invention is not limited thereto. The polyethylene glycol of this embodiment can be used alone or in combination of two or more.

[0053] HO-(CH2-CH2-O-) n -H……(I)

[0054] (In the formula, n represents an integer from 3 to 9.)

[0055] In the present embodiment, when the metal ion includes potassium ions, n preferably represents an integer from 4 to 9, more preferably from 5 to 9, and even more preferably from 6 to 8. When the metal ion includes potassium ions, image quality tends to be excellent. Furthermore, when n is within the above range, the polyethylene glycol can reduce the generation of complex foreign matter derived from potassium ions, tending to have excellent clogging recovery and intermittency.

[0056] When the metal ions in the present embodiment include sodium ions, n preferably represents an integer from 3 to 9, more preferably represents an integer from 3 to 7, and even more preferably represents an integer from 4 to 6. As a result, the polyethylene glycol can reduce the generation of complex foreign matter derived from sodium ions, and tends to have excellent clogging recovery and intermittency.

[0057] When the metal ions in the present embodiment include lithium ions, n preferably represents an integer of 3 to 9, more preferably represents an integer of 3 to 7, and even more preferably represents an integer of 3 to 5.

[0058] The polyethylene glycol content is preferably 0.5 to 10.0% by mass relative to the total weight of the inkjet ink composition. Furthermore, it is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass. A polyethylene glycol content of 0.5% or greater tends to improve clogging recovery properties, while a polyethylene glycol content below this value tends to improve intermittency.

[0059] The polyethylene glycol content is preferably 5.0 to 75% by mass, more preferably 5.0 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass, relative to the total amount of the self-dispersible pigment and the inorganic oxide particles.

[0060] 1.5. Water-soluble fixing resin

[0061] The inkjet ink composition of this embodiment preferably further includes a water-soluble fixing resin. Compared to resin emulsions, water-soluble fixing resins introduce fewer counterions into the inkjet ink composition, thus tending to be less likely to form complex foreign matter and exhibiting excellent clogging recovery and intermittency.

[0062] A water-soluble fixing resin is a water-soluble resin that also functions as a fixing resin. A water-soluble resin is a resin that is dissolved in water at room temperature, not dispersed like a resin emulsion. Furthermore, a water-soluble resin is a resin that is dissolved in ink, not dispersed like a resin emulsion. Fixing resins improve the fixability of ink to the recording medium.

[0063] Such water-soluble fixing resins are not particularly limited, and examples thereof include urethane resins, acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, and ethylene-vinyl acetate resins. Among them, urethane resins are preferred. The fixing resins may be used alone or in combination of two or more.

[0064] The content of the water-soluble fixing resin is preferably 0.01 to 1.0% by mass relative to the total mass of the inkjet ink composition. Furthermore, it is preferably 0.05 to 0.5% by mass, more preferably 0.02 to 0.3% by mass, further preferably 0.03 to 0.3% by mass, and even more preferably 0.05 to 0.2% by mass. A water-soluble fixing resin content of 0.01% by mass or greater tends to result in excellent marker pen resistance, while a water-soluble fixing resin content below this value tends to result in excellent intermittent properties.

[0065] 1.6.1. Water

[0066] The ink composition of this embodiment is a water-based ink. A water-based ink is an ink containing water as its primary solvent component. The water content of the water-based ink is preferably 40% by mass or greater, more preferably 45% to 98% by mass, relative to the total ink volume. Furthermore, it is preferably 50% by mass or greater and 80% by mass or less, and more preferably 65% ​​by mass or greater and 75% by mass or less. When the ink is a water-based ink, the inclusion of inorganic oxide particles can enhance stacking properties.

[0067] 1.6.2. Organic solvents

[0068] The organic solvent in this embodiment is not particularly limited, and examples thereof include lower alcohols such as methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and 2-methyl-2-propanol; polyols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and glycerol; and glycol ethers such as triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monopropyl ether. Among these, polyols are preferably included, and glycerol is more preferably included. The organic solvent may be used alone or in combination of two or more.

[0069] The content of the organic solvent is preferably 5.0 to 25% by mass, more preferably 7.5 to 20% by mass, and even more preferably 10 to 15% by mass, relative to the total amount of the ink composition.

[0070] 1.7. Lactam compounds

[0071] The lactam compound is not particularly limited as long as it is an organic solvent or a compound that is fixed at room temperature. Examples include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 3-methoxy-2-pyrrolidone, 3-acetoxy-2-pyrrolidone, 4-valerolactam, and ε-caprolactam. ε-caprolactam is preferred. The inclusion of a lactam compound in the inkjet ink composition tends to reduce the formation of complex foreign matter and exhibits excellent clogging recovery and intermittency.

[0072] The content of the lactam compound is preferably 1.0 to 8.0% by mass, more preferably 1.5 to 6.0% by mass, and even more preferably 2.0 to 4.0% by mass relative to the total mass of the ink composition. A lactam compound content of 1.0% or greater tends to improve intermittent properties. Lactam compounds that are liquid at room temperature are also organic solvents.

[0073] 1.8. Surfactants

[0074] The ink composition of this embodiment may further contain a surfactant. Surfactants may be used alone or in combination of two or more. Such surfactants are not particularly limited, and examples include acetylene glycol surfactants, silicone surfactants, and fluorine-containing surfactants. Surfactants may be used alone or in combination of two or more.

[0075] The acetylene glycol surfactant is not particularly limited, and examples thereof include 2,4,7,9-tetramethyl-5-decyn-4,7-diol, an alkylene oxide adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4-dimethyl-5-decyn-4-ol, and an alkylene oxide adduct of 2,4-dimethyl-5-decyn-4-ol.

[0076] The silicone-based surfactant is not particularly limited, and examples thereof include polysiloxane-based compounds and polyether-modified silicones.

[0077] The fluorinated surfactant is not particularly limited, and examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxides.

[0078] The content of the surfactant is preferably 0.1 to 2.0% by mass, more preferably 0.6 to 1.6% by mass, and even more preferably 0.9 to 1.2% by mass, relative to the total amount of the ink composition.

[0079] 1.9. Other ingredients

[0080] The inkjet ink composition of this embodiment may contain, in addition to the above-mentioned components, one or more known components that can be used in conventional inkjet ink compositions. Such known components are not particularly limited, and examples thereof include cosolvents, viscosity modifiers, pH modifiers, antioxidants, preservatives, mildew inhibitors, corrosion inhibitors, other additives such as chelating agents for capturing metal ions that affect dispersion, and organic solvents other than the above-mentioned organic solvents.

[0081] 2. Ink set

[0082] The ink set of this embodiment comprises a first ink composition and a second ink composition. The first ink composition is the inkjet ink composition described above in this embodiment, and the second ink composition is an aqueous inkjet ink composition. Furthermore, the ink set of this embodiment can use one or more ink compositions as the first and second ink compositions. An ink set is a set of two or more ink compositions used for recording. Each ink composition in an ink set can be housed in a separate ink container or in separate compartments of an integrated ink container.

[0083] This is not limited to the case where the metal ions that serve as counter ions of the self-dispersible pigment and inorganic oxide particles contained in a single pigment ink are different. In the case where two or more pigment inks used for recording as an ink set each contain different metal ions, complex foreign matter may be generated due to contact between the pigment inks between adjacent nozzles, contact caused by the scattering of ink mist, contact caused by wiping during cleaning, etc., and long-term ejection stability may be reduced.

[0084] In addition, it is known that in the flushing box, cover and waste liquid tank, etc., complex foreign matter is produced due to the mixing of the metal ions that serve as counter ions of the self-dispersible pigment as described above and the metal ions that serve as counter ions of the inorganic oxide particles, which are different from them, and blockage is likely to occur in the waste liquid tank or the waste liquid flow path.

[0085] Therefore, in this embodiment, the inkjet ink composition included in the ink set contains inorganic oxide particles, which improves stacking properties. At the same time, the inkjet ink composition contains specified metal ions and specified polyethylene glycol, which can suppress the formation of complex foreign substances between self-dispersible pigments and metal ions, and can provide an ink set with excellent clogging recovery and intermittency.

[0086] The second ink composition is not particularly limited as long as it is a water-based pigment ink, and conventionally known pigment inks can be used.

[0087] The second ink composition may or may not contain the self-dispersible pigment of this embodiment, inorganic oxide particles, the aforementioned polyethylene glycol, a water-soluble fixing resin, an organic solvent, a lactam compound, a surfactant, and other components.

[0088] The second ink composition may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, different from the metal ions contained in the first ink composition. Even in this case, the ink set of this embodiment tends to have excellent long-term ejection stability.

[0089] The second ink composition may contain at least one of a self-dispersible pigment and inorganic oxide particles. In this case, the metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, different from the metal ions contained in the first ink composition, contained in the second ink composition may serve as counterions for the self-dispersible pigment or inorganic oxide particles contained in the second ink composition. When the second ink composition contains a self-dispersible pigment and inorganic oxide particles, the second ink composition preferably contains the aforementioned polyethylene glycol.

[0090] 3. Inkjet recording method

[0091] The inkjet recording method of this embodiment includes a discharge step of discharging the inkjet ink composition from an inkjet head and depositing it onto a recording medium. The discharge step may include a discharge step of discharging each ink composition contained in the ink set from the inkjet head and depositing it onto the recording medium. The inkjet recording method may further include a transport step of transporting the recording medium. The discharge step and the transport step may be performed simultaneously or alternately.

[0092] 3.1. Spraying process

[0093] In the ejection process, ink is ejected from an inkjet head and deposited onto a recording medium. More specifically, the pressure generating unit within the inkjet head is driven, causing the ink, which is filled within the pressure generating chamber of the inkjet head, to be ejected from the nozzles. This ejection method is also known as the inkjet method.

[0094] Examples of the inkjet head used in the discharge step include a line inkjet head that performs recording in a line manner and a serial inkjet head that performs recording in a serial manner.

[0095] In a line-type inkjet printer using a line inkjet head, for example, an inkjet head having a width greater than the recording width of the recording medium is fixed to a recording device. The recording medium is then moved in a sub-scanning direction (the direction in which the recording medium is transported), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0096] In a serial-type printing method using a serial inkjet head, for example, the inkjet head is mounted on a carriage that is movable along the width of the recording medium. The carriage is moved in the main scanning direction (the width of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0097] 3.2. Conveying process

[0098] During the transport process, the recording medium is conveyed along a predetermined direction within the recording device. More specifically, a conveyor roller or belt installed within the recording device is used to transport the recording medium from the paper feed section to the paper discharge section. During this transport process, ink ejected from the inkjet head adheres to the recording medium, forming a recorded object. Transport can be performed continuously or intermittently.

[0099] 3.3. Recording Media

[0100] The recording medium used in this embodiment is not particularly limited, and examples thereof include absorbent and non-absorbent recording media. Absorbent recording media are susceptible to problems such as curling. Therefore, the use of inorganic oxide particles can suppress curling and is effective for the inkjet ink composition of this embodiment, which has excellent clogging recovery properties.

[0101] There are no particular restrictions on the absorptive recording medium, and examples thereof include ordinary paper such as electronic photographic paper having high permeability to the inkjet ink composition, inkjet paper (inkjet-specific paper having an ink-absorbing layer composed of silicon oxide particles or aluminum oxide particles, or an ink-absorbing layer composed of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP), and art paper, coated paper, and cast-coated paper used for conventional offset printing having relatively low ink permeability.

[0102] The non-absorbent recording medium is not particularly limited, and examples thereof include: films or plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; or metal plates or plastic films produced by vapor deposition of these various metals, or alloy plates such as stainless steel and brass; recording media obtained by gluing (coating) a film of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane onto a paper substrate, etc.

[0103] 4. Inkjet recording device

[0104] The recording device of this embodiment includes an inkjet head having nozzles for ejecting an inkjet ink composition onto a recording medium, and a transport unit for transporting the recording medium. The inkjet head includes a pressure chamber for supplying ink and nozzles for ejecting ink. The transport unit is comprised of a transport roller or a transport belt disposed within the recording device.

[0105] Below, refer to Figure 1 An example of a recording device according to this embodiment will be described. Figure 1 In the XYZ coordinate system shown in , the X direction indicates the longitudinal direction of the recording medium, the Y direction indicates the width direction of the recording medium in the conveyance path in the recording apparatus, and the Z direction indicates the apparatus height direction.

[0106] The recording device 10 is, for example, a line inkjet printer capable of high-speed and high-density printing. The recording device 10 includes a paper feed unit 12 for storing a recording medium P, such as paper, a conveyor unit 14, a belt conveyor unit 16, a recording unit 18, an Fd (face down) discharge unit 20 as a "discharge unit," an Fd (face down) placement unit 22 as a "placement unit," a reversing path unit 24 as a "reversing conveying mechanism," a Fu (face up) discharge unit 26, and a Fu (face up) placement unit 28.

[0107] The paper feed unit 12 is disposed at the lower portion of the recording apparatus 10 . The paper feed unit 12 includes a paper feed tray 30 that stores recording media P and a paper feed roller 32 that feeds the recording media P stored in the paper feed tray 30 to the transport path 11 .

[0108] The recording medium P stored in the paper feed tray 30 is fed to the conveyor unit 14 along the conveyance path 11 by the paper feed roller 32. The conveyor unit 14 includes a conveyance drive roller 34 and a conveyance driven roller 36. The conveyance drive roller 34 is rotationally driven by a drive source (not shown). In the conveyor unit 14, the recording medium P is sandwiched (held between) the conveyance drive roller 34 and the conveyance driven roller 36 and conveyed to the belt conveyor unit 16 located downstream of the conveyance path 11.

[0109] The belt conveying section 16 includes a first roller 38 located on the upstream side of the conveying path 11, a second roller 40 located on the downstream side, an endless belt 42 rotatably mounted on the first roller 38 and the second roller 40, and a support body 44 supporting the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0110] The endless belt 42 is driven by the first roller 38 or the second roller 40 driven by a driving source (not shown) so as to move from the +X direction to the −X direction in the upper section 42a. Therefore, the recording medium P conveyed from the conveying section 14 is further conveyed downstream in the conveying path 11 by the belt conveying section 16.

[0111] The recording unit 18 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. It should be noted that the recording unit 18 may also be a serial-type recording unit in which the inkjet head is mounted on a carriage that reciprocates along the Y-axis. The inkjet head 48 is positioned opposite the upper section 42a of the endless belt 42 supported by the support body 44. While the recording medium P is being conveyed in the upper section 42a of the endless belt 42, the inkjet head 48 ejects ink onto the recording medium P to perform recording. While recording is being performed, the recording medium P is conveyed downstream of the conveyance path 11 by the belt conveyor 16.

[0112] It should be noted that a "line inkjet head" refers to an inkjet head used in a recording device in which the nozzle area formed in a direction intersecting the conveyance direction of the recording medium P is arranged so as to cover the entire intersecting direction of the recording medium P. A recording device forms a recorded image by fixing either the inkjet head or the recording medium P while the other is moved. It should be noted that the nozzle area in the intersecting direction of the line inkjet head may not cover the entire intersecting direction of all recording media P used by the recording device.

[0113] A first branching portion 50 is provided downstream of the conveyance path 11 of the belt conveyor 16. The first branching portion 50 is configured to switch between the conveyance path 11, which conveys the recording medium P to the Fd discharge unit 20 or the Fu discharge unit 26, and the reversing path 52 of the reversing path portion 24, which reverses the recording surface of the recording medium P and re-conveys the recording medium P to the recording unit 18. It should be noted that the recording medium P, which is switched to the reversing path 52 by the first branching portion 50 and conveyed, has its recording surface reversed during conveyance in the reversing path 52, and is re-conveyed to the recording unit 18 with the surface opposite to the original recording surface facing the inkjet head 48.

[0114] A second branching portion 54 is further provided downstream of the first branching portion 50 along the conveying path 11 . The second branching portion 54 is configured to switch the conveying direction of the recording medium P to either the Fd discharge portion 20 or the Fu discharge portion 26 .

[0115] The recording medium P conveyed to the Fd discharge section 20 by the second branch section 54 is discharged from the Fd discharge section 20 and placed on the Fd placement section 22. At this time, the recording surface of the recording medium P is placed so as to face the Fd placement section 22. Furthermore, the recording medium P conveyed to the Fu discharge section 26 by the second branch section 54 is discharged from the Fu discharge section 26 and placed on the Fu placement section 28. At this time, the recording surface of the recording medium P is placed so as to face the side opposite to the Fu placement section 28.

[0116] It should be noted that, while the above description uses an example of a line-type inkjet head, the recording device of this embodiment may also be a printer using a serial-type inkjet head (serial printer). In a serial-type printer, printing is performed by moving the inkjet head in a direction intersecting the conveying direction while the recording medium is conveyed along the conveying direction.

[0117] When the recording apparatus uses a line inkjet head, a high recording speed is preferred, but ink mist is easily generated from the nozzles of the inkjet head. Therefore, this embodiment is particularly useful for obtaining excellent long-term ejection stability.

[0118] Example

[0119] Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. However, the present invention is not limited in any way by the following Examples.

[0120] 1. Inkjet ink composition

[0121] 1.1. Preparation of inkjet ink composition

[0122] The components were added to a mixing tank to obtain the compositions listed in Tables 1 and 2, mixed and stirred, and then filtered through a 5 μm membrane filter to obtain the respective inkjet ink compositions. It should be noted that, unless otherwise stated, the numerical values ​​for each component shown in each example in the tables represent mass %. In addition, the numerical values ​​for self-dispersible pigments, resin-dispersible pigments, inorganic oxide particles, water-soluble fixing resins, and lactam compounds in the tables represent the mass % of solids.

[0123] [Table 1]

[0124]

[0125] [Table 2]

[0126]

[0127] The abbreviations used in Tables 1 and 2 and the details of the product ingredients are as follows.

[0128] Self-dispersible pigments

[0129] Self-dispersible pigment 1: prepared as follows.

[0130] The carbon black is pulverized, mixed with water, and the mixture is ozonated. The ozone treatment is performed for 6 hours at an ozone concentration of 5.5 to 6.0 wt%. After the treatment, potassium hydroxide is added to the mixture. The pulverization process is then continued.

[0131] The volume average particle size D 50 A self-dispersible carbon black pigment with a diameter of 110 nm and potassium as the counter ion.

[0132] Self-dispersible pigment 2: prepared as follows.

[0133] The same operation was carried out except that sodium hydroxide was used instead of potassium hydroxide in the preparation of the self-dispersible pigment 1 to obtain a volume average particle size D 50 A self-dispersible carbon black pigment with a diameter of 110 nm and sodium as the counter ion.

[0134] Self-dispersible pigment 3: prepared as follows.

[0135] The same operation was carried out except that lithium hydroxide was used instead of potassium hydroxide in the preparation of the self-dispersible pigment 1 to obtain a volume average particle size D 50 A self-dispersible carbon black pigment with a diameter of 110 nm and lithium as a counter ion.

[0136] Self-dispersible pigment 4: “Cabojet 250C” manufactured by Cabot Japan Co., Ltd., a self-dispersible copper phthalocyanine pigment having sodium as a counter ion.

[0137] Resin dispersed pigments

[0138] Resin-dispersed pigment 1: prepared as follows.

[0139] Carbon black powder was pulverized and mixed with a styrene-acrylic resin dispersant resin ("YS-1274" manufactured by Seikyo PMC) in water at a mass ratio of 3:1. The mixture was then stirred using a bead mill to obtain a resin-dispersed pigment. The volume average particle size was 110 nm.

[0140] Inorganic oxide particles

[0141] Colloidal silica 1 (particle size: 80 nm): Cataloid SI-80P manufactured by JGC Catalysts & Chemicals Co., Ltd.

[0142] Colloidal silica 2 (particle size: 45 nm): Cataloid SI-45 manufactured by JGC Catalysts & Chemicals

[0143] Colloidal silica 3 (particle size: 11 nm): Cataloid SI-30 manufactured by JGC Catalysts & Chemicals

[0144] Both are colloidal silica with sodium as the counter ion.

[0145] Water-soluble fixing resin

[0146] Water-soluble fixing resin 1: prepared as follows.

[0147] Prepare a four-necked flask with a stirrer, a thermometer, a nitrogen inlet tube and a reflux tube. To the four-necked flask, 41.7 parts by mass of isophorone diisocyanate, 40.1 parts by mass of polypropylene glycol (number average molecular weight 2000), 13.2 parts by mass of dimethylolpropionic acid and 200.0 parts by mass of methyl ethyl ketone were added, and the mixture was reacted at 80°C for 6 hours under a nitrogen atmosphere. Next, 0.6 parts by mass of ethylenediamine, 2.0 parts by mass of methanol, 2.4 parts by mass of dimethylolpropionic acid and 100.0 parts by mass of methyl ethyl ketone were added. The residual rate of the isocyanate group was confirmed by FT-IR, and the reaction was carried out at 80°C until the desired residual rate was reached, thereby obtaining a reaction solution. The obtained reaction solution was cooled to 40°C, ion-exchanged water was then added, and a potassium hydroxide aqueous solution was added while stirring at high speed using a homomixer to obtain a liquid. The obtained liquid was heated and decompressed to distill off methyl ethyl ketone, thereby obtaining a water-soluble fixing resin having a urethane resin (solid content) content of 20.0%.

[0148] polyethylene glycol

[0149] PEG1 (n=4-9): "TOHO Polyethylene Glycol 400" manufactured by Toho Chemical Industry Co., Ltd.

[0150] PEG2 (n=3-7): "TOHO Polyethylene Glycol 300" manufactured by Toho Chemical Industry Co., Ltd.

[0151] PEG3 (n=3-5): "TOHO Polyethylene Glycol 200" manufactured by Toho Chemical Industry Co., Ltd.

[0152] PEG4 (n=2): "Diethylene glycol"

[0153] PEG5 (n=10 to 15): Polyethylene glycol with n=10 or more was purified by fractionating "TOHO Polyethylene Glycol 600" manufactured by Toho Chemical Industry Co., Ltd.

[0154] Lactam compounds

[0155] ·ε-caprolactam

[0156] organic solvents

[0157] ·glycerin

[0158] Triethylene glycol monobutyl ether

[0159] surfactants

[0160] Acetylene glycol surfactant: OLFINE E1010 (manufactured by Nissin Chemical Industry Co., Ltd., trade name, acetylene glycol surfactant)

[0161] 1.2. Evaluation Method of Inkjet Ink Composition

[0162] 1.2.1. Blockage recovery

[0163] The ink composition prepared as described above was filled into an ink cartridge of a modified LX-10050MF (line inkjet printer) manufactured by Seiko Epson, and printed on a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m2) under the conditions of an adhesion amount of 6 ng / dpi and a recording resolution of 600×1200 dpi. 2A test pattern was recorded on a paper sheet (88 μm thick). After confirming that ink could be ejected from all nozzles, the inkjet head was removed from the printer's cap and left uncapped at 35°C for one day. After this period, the ink within the nozzles was aspirated once as a cleaning step, and the number of nozzles with poor ejection (i.e., unable to eject ink) was counted. Clogging recovery was also evaluated using the following criteria. The results are shown in Tables 1 and 2.

[0164] Evaluation Criteria

[0165] A: There are no nozzles with defective discharge.

[0166] B: The number of nozzles with poor ejection is 1% or less of all nozzles.

[0167] C: The number of nozzles with ejection failure is greater than 1% and less than 3% of all nozzles.

[0168] D: The number of nozzles with poor ejection is greater than 3% of all nozzles.

[0169] 1.2.2. Intermittent

[0170] Recording was performed continuously for 6 hours under the above patterning conditions. Nozzles were inspected every hour during recording, including at the end of the recording cycle, to check for any nozzle failures. Failures were considered as no ink discharge or when the ink jet was bent after at least one ejection. Intermittency was evaluated using the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0171] Evaluation Criteria

[0172] A: There are no nozzles with defective discharge.

[0173] B: The number of nozzles with poor ejection is 1% or less of all nozzles.

[0174] C: The number of nozzles with poor ejection is greater than 1% of all nozzles.

[0175] 1.2.3. Image quality (OD value)

[0176] The image quality (OD value) of the test pattern of the recorded material obtained above was measured using a colorimeter (Xrite i1, manufactured by Xrite Corporation) and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0177] Evaluation Criteria

[0178] A: OD value is 1 or more.

[0179] B: OD value is less than 1 and 0.95 or more.

[0180] C: OD value is less than 0.95.

[0181] 1.2.4. Stackability

[0182] Recording was continuously performed on 20 sheets of the above recording medium under the above pattern conditions, and the recorded products were continuously discharged to the discharge unit of the inkjet recording apparatus. The stacking properties were evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0183] Evaluation Criteria

[0184] A: 20 recorded sheets are stored in the paper output tray, and the ends of the recorded sheets are neatly aligned as if they were stapled together.

[0185] B: 20 ​​recorded papers are stored in the paper discharge tray, but the ends are displaced and misaligned.

[0186] C: 20 recorded sheets flew out of the paper output tray without being collected.

[0187] 1.2.5. Marker pen resistance

[0188] The test pattern of the recorded material obtained above was marked with a marker pen (a fluorescent pen "OPTEXCARE WKCR1-Y (yellow)" manufactured by ZEBRA), and the marker pen resistance was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0189] Evaluation Criteria

[0190] A: The printed part does not bleed even when painted with a marker.

[0191] B: Slight bleeding was observed on the printed portion when painted with a marker.

[0192] C: The printed part bleeds clearly when painted with a marker.

[0193] 2. Evaluation of ink set

[0194] 2.1. Preparation of ink set

[0195] Ink 1 and ink 9 were combined to form the combination shown in Table 3 to prepare ink set 1.

[0196] Next, Ink Set 2 was prepared by combining Ink 1 with an inkjet ink composition obtained by removing polyethylene glycol from Ink 9 (hereinafter referred to as Ink 9-2) to obtain the combination shown in Table 3.

[0197] [Table 3]

[0198]

[0199] 2.2. Evaluation method of ink set

[0200] The ink cartridges of a modified LX-10050MF (line inkjet printer) manufactured by Seiko Epson were filled with the ink sets prepared as described above, and the two ink compositions in the ink sets were ejected from adjacent nozzle rows.

[0201] Blockage recovery

[0202] Only one of the two ink compositions or only the other was used in the above-mentioned recording apparatus, and each ink composition was evaluated in the same manner as the above-mentioned clogging recovery property.

[0203] Long-term spray stability

[0204] In the recording device, a test pattern was recorded using two inks simultaneously. The two inks were deposited on the test pattern under the following conditions: a deposition rate of 6 ng / dpi for each ink and a recording resolution of 300 × 600 dpi. The recording medium (A4-sized Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m2) was used. 2 , paper thickness 88 μm) and record the test pattern continuously for 10 hours.

[0205] Nozzle cleaning was performed every hour during recording, including at the end of continuous recording. Nozzles were inspected after recording to confirm any ejection failures. Failures were defined as no ink ejection or observed ink jet deflection after at least one ejection. Long-term ejection stability was evaluated for nozzles ejecting various ink compositions using the following evaluation criteria. The evaluation results are shown below and in Table 3.

[0206] Evaluation Criteria

[0207] A: There are no nozzles with defective discharge.

[0208] B: The number of nozzles with poor ejection is 1% or less of all nozzles.

[0209] C: The number of nozzles with poor ejection is greater than 1% of all nozzles.

[0210] 3. Evaluation results

[0211] A comparison of Example Inks 1 to 20 with Comparative Example Inks H1 to H4 reveals that the ink composition according to this embodiment is superior in terms of clogging recovery, intermittency, and stacking properties, compared to the ink compositions according to Comparative Example Inks H1 to H4, which do not meet the constituent requirements of the ink composition.

[0212] Evaluation of the ink set revealed that Ink 9-2, which does not contain two different metal ions and a specific polyethylene glycol, exhibited poor long-term ejection stability when used in a recording set with Ink 1. It should be noted that, after long-term ejection stability testing, foreign matter was observed around the nozzles of Ink 9-2. In contrast, Ink 9, which contains two different metal ions and a specific polyethylene glycol, also exhibited excellent long-term ejection stability when used in a recording set with Ink 1.

Claims

1. An inkjet ink composition, characterized in that The inkjet ink composition comprises a self-dispersible pigment, inorganic oxide particles, and polyethylene glycol represented by the following general formula (I), and contains two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The self-dispersible pigment is a pigment that has a hydrophilic functional group introduced by a chemical reaction and is dispersed in an aqueous solvent without a dispersant. The two or more metal ions include counter ions of the inorganic oxide particles and counter ions of the self-dispersible pigment, The two or more metal ions include potassium ions, The inkjet ink composition is a water-based ink, HO-(CH2-CH2-O-) n -H……(I), In the formula, n represents an integer from 5 to 9.

2. The inkjet ink composition according to claim 1, wherein The hydrophilic functional group is any one of a carboxyl group, a phosphoric acid group, and a sulfonic acid group.

3. The inkjet ink composition according to claim 1, wherein The inkjet ink composition includes the polyethylene glycol, wherein n represents an integer of 5 to 8.

4. The inkjet ink composition according to claim 1, wherein The metal ions further include sodium ions.

5. The inkjet ink composition according to claim 1, wherein The metal ions further include lithium ions.

6. The inkjet ink composition according to claim 1, wherein The content of the polyethylene glycol is 1.0 to 5.0% by mass relative to the total amount of the inkjet ink composition.

7. The inkjet ink composition according to claim 1, wherein The volume average particle size D of the self-dispersible pigment 50 40~250nm.

8. The inkjet ink composition according to claim 1, wherein The content of the inorganic oxide particles is 0.5 to 8.0% by mass relative to the total amount of the inkjet ink composition.

9. The inkjet ink composition according to claim 1, wherein The volume average particle size D of the inorganic oxide particles 50 It is less than 100nm.

10. The inkjet ink composition according to claim 1, wherein The self-dispersible pigment includes one or more selected from the group consisting of carbon black and organic pigments.

11. The inkjet ink composition according to claim 1, wherein The inorganic oxide particles include one or more selected from the group consisting of silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, and cerium oxide.

12. The inkjet ink composition according to claim 1, wherein The inkjet ink composition further includes a water-soluble fixing resin.

13. The inkjet ink composition according to claim 1, wherein The content of the self-dispersible pigment is 1.0 to 10% by mass relative to the total amount of the inkjet ink composition.

14. An ink set, characterized in that: comprising a first ink composition and a second ink composition, The first ink composition and the second ink composition are aqueous inkjet inks, The first ink composition comprises: a self-dispersible pigment; inorganic oxide particles; and polyethylene glycol represented by the following general formula (I), and contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The self-dispersible pigment is a pigment that has a hydrophilic functional group introduced by a chemical reaction and is dispersed in an aqueous solvent without a dispersant. The one or more metal ions comprise counter ions of the inorganic oxide particles, The second ink composition includes a self-dispersible pigment and one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, and different from the metal ions contained in the first ink composition. This self-dispersible pigment is a pigment that has hydrophilic functional groups introduced through a chemical reaction and is dispersed in an aqueous solvent without the need for a dispersant. The one or more metal ions comprise a counter ion of the self-dispersible pigment, Any one of the metal ions contained in the first ink composition and the metal ions contained in the second ink composition comprises potassium ions, HO-(CH2-CH2-O-) n -H……(I), In the formula, n represents an integer from 5 to 9.

15. An ink set, characterized in that: The ink set comprises a first ink composition and a second ink composition, wherein the first ink composition is the inkjet ink composition according to any one of claims 1 to 13, and the second ink composition is an aqueous inkjet ink composition.

16. The ink set according to claim 15, wherein: The second ink composition contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, the type of which is different from the metal ions contained in the first ink composition.

17. A recording method, characterized in that: The recording method includes a discharge step of discharging the inkjet ink composition according to any one of claims 1 to 13 or the ink set comprising the first ink composition and the second ink composition according to claim 14 from an inkjet head and causing the ink to adhere to a recording medium.

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