Inkjet ink composition, ink set, and recording method

Abstract

To provide an inkjet ink composition with improved clogging recovery, intermittent and stacking properties, an ink set, and a recording method.SOLUTION: An inkjet ink composition, which is a water-based ink, contains a self-dispersible pigment, inorganic oxide particles, and a polyethylene glycol represented by the following general formula (I), the ink composition containing at least one metal ion selected from the group consisting of a potassium ion, a sodium ion, and a lithium ion. HO-(CH2-CH2-O-)n-H (I), where n represents an integer of 3 to 9.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink composition, an ink set, and a 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. In particular, inkjet recording using water-based inks on plain paper with high-speed continuous inkjet printers is prone to the problem of curling, which reduces stackability. To suppress such curling, inkjet ink compositions containing inorganic oxide particles such as silica particles are being investigated. For example, Patent Document 1 discloses an inkjet recording ink containing colloidal silica with the aim of providing an inkjet recording ink that can improve stackability. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-007444 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, inks using self-dispersing pigments and inorganic oxide particles exhibited poor clogging recovery. [Means for solving the problem]

[0005] The inkjet ink composition of the present invention comprises a self-dispersing 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. This is an inkjet ink composition, which is a water-based ink. HO-(CH2-CH2-O-) n -H ··· (I) (In the formula, n is an integer between 3 and 9.)

[0006] The ink set of the present invention comprises a first ink composition which is the above-described inkjet ink composition, and a second ink composition which is a water-based inkjet ink composition.

[0007] The recording method of the present invention is a recording method that includes an ejection step of ejecting the above-mentioned inkjet ink composition from an inkjet head and adhering it to a recording medium. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of a recording device used in the recording method of this embodiment. [Modes for carrying out the invention]

[0009] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the drawings, the same elements will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Moreover, the dimensional ratios in the drawings are not limited to those shown.

[0010] 1. Inkjet ink composition The inkjet ink composition according to this embodiment (hereinafter also simply referred to as "ink composition") is an aqueous inkjet ink composition comprising a self-dispersing pigment, inorganic oxide particles, and polyethylene glycol represented by the following general formula (I), and containing one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. Furthermore, the inkjet ink composition of this embodiment may contain other components as needed. HO-(CH2-CH2-O-) n -H ··· (I) (In the formula, n is an integer between 3 and 9.)

[0011] Conventionally, inkjet recording using water-based inks on plain paper has the problem of curling, which tends to reduce stackability. Therefore, inkjet ink compositions containing inorganic oxide particles such as silica particles have been investigated with the aim of suppressing curling and improving stackability. Stackability refers to whether the edges of the recording media can be aligned and neatly stacked when they are discharged into the printer's output tray and stacked in large numbers after recording. If curling occurs in the recording media after recording, stackability deteriorates.

[0012] However, it has become clear that in inks containing such inorganic oxide particles, foreign matter is particularly likely to occur in the ink when the pigment is a self-dispersing pigment. Furthermore, the inventors of this invention conducted a thorough investigation into the cause and found the following: When inorganic oxide particles and a self-dispersing pigment are included, and one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions are also included, the dispersion stability becomes unstable and the clogging recovery performance deteriorates. The metal ions may also be counterions of the inorganic oxide particles or the self-dispersing pigment.

[0013] In particular, when a certain ink composition contains inorganic oxide particles and a self-dispersing pigment, and also 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 its clogging recovery performance deteriorates. Specifically, when the self-dispersing pigment and inorganic oxide particles contained in a certain ink have different metal ions as counterions to the self-dispersing pigment and the inorganic oxide particles, the ink composition will contain two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. These different metal ions then mix in the ink, causing the dispersion stability to become unstable.

[0014] Alternatively, if a certain ink composition contains inorganic oxide particles and a self-dispersing pigment, and contains one metal ion selected from the group consisting of potassium ions, sodium ions, and lithium ions, and another ink composition used for recording in conjunction with that ink composition contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, but different from the metal ions contained in the ink composition, the dispersion stability of the ink composition becomes unstable, causing clogging and deterioration of ejection stability. In this case as well, each metal ion may be a counterion of the self-dispersing pigment or inorganic oxide particles contained in one of the inks.

[0015] In these cases, dispersion instability causes self-dispersing pigments and inorganic oxide particles to aggregate, becoming coarse particles and thus constituting foreign matter. In particular, it has been found that when either the self-dispersing pigment or the inorganic oxide particles becomes dispersion unstable, the other is also involved, forming a composite foreign matter consisting of self-dispersing pigments and inorganic oxide particles, which tends to reduce clogging recovery and intermittency during inkjet recording.

[0016] Therefore, the inkjet ink composition of the present embodiment contains inorganic oxide particles, thereby improving the stacking property. In addition, by containing a predetermined metal ion and a predetermined polyethylene glycol, it is possible to suppress composite foreign matter of the self-dispersible pigment and the metal ion, and improve the clogging recovery property and intermittency.

[0017] The relationship between the polyethylene glycol and the metal ion is not particularly limited. For example, it is considered that when the polyethylene glycol having a predetermined molecular weight coordinates to the predetermined metal ion, the interaction between the self-dispersible pigment and the metal ion that leads to the formation of composite foreign matter is inactivated. The mechanism by which the generation of composite foreign matter is suppressed is not limited to the above.

[0018] Hereinafter, the components, ink sets, and recording methods of the inkjet ink composition according to the present embodiment will be described in detail.

[0019] 1.1. Self-dispersible pigment In the present embodiment, the self-dispersible pigment is a pigment that can be dispersed in an aqueous medium without a dispersant. Examples of such self-dispersible pigments include pigments in which hydrophilic functional groups or the like are directly introduced onto the pigment surface by performing physical and / or chemical surface treatment and dispersed in a solvent. The self-dispersible pigment is distinguished from the resin-dispersed pigment dispersed in a solvent using a dispersant.

[0020] Pigments used in such self-dispersing pigments are not particularly limited, but examples include organic pigments such as azo pigments (e.g., azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), nitro pigments, nitroso pigments, and aniline black; inorganic pigments such as carbon black (e.g., furnace black, thermal lamp black, acetylene black, channel black, etc.), metal oxides, metal sulfides, and metal chlorides; and extender pigments such as silica, calcium carbonate, and talc. Pigments may be used individually or in combination of two or more.

[0021] Among these, it is preferable to include one or more selected from the group consisting of carbon black and organic pigments. This tends to result in better image quality. Inks containing these pigments can be black ink or chromatic ink. Examples of chromatic inks include cyan ink, magenta ink, and yellow ink, as well as orange ink, red ink, and blue ink. Black ink is often used for recording text, and inks with particularly good color development are useful.

[0022] Here, conventionally known methods can be used for surface treatment of the pigment, and such methods are not particularly limited, but examples include methods of ozone treatment, alkaline treatment, or other chemical reactions applied to the pigment surface to introduce hydrophilic functional groups through chemical reactions. Examples of hydrophilic functional groups to be introduced include carboxyl groups, phosphate groups, and sulfo groups.

[0023] Self-dispersing pigments may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions as counterions. While there are no particular limitations on the method for preparing the counterions of self-dispersing pigments, examples include preparing the alkali metal salt used in the preparation of the self-dispersing pigment.

[0024] Furthermore, the volume-average particle size D of self-dispersing pigments 50 The volume average particle diameter is preferably 40 to 250 nm, more preferably 80 to 210 nm, and even more preferably 100 to 170 nm. 110 to 150 nm is particularly preferred. A volume average particle diameter below the above tends to result in superior intermittency and clogging recovery, while a volume average particle diameter above the above tends to result in superior image quality.

[0025] Volume-average particle diameter D 50 This can be measured using a particle size distribution analyzer that employs dynamic light scattering as its measurement principle. An example of such a particle size distribution analyzer is the "Zeta Potential, Particle Size, and Molecular Weight Measurement System ELSZ2000ZS" (product name) manufactured by Otsuka Electronics Co., Ltd., which employs a homodyne optical system as its frequency analysis method. In this specification, "average particle diameter" refers to the average particle diameter based on the number of particles, unless otherwise specified.

[0026] The content of the self-dispersing pigment is preferably 4.0 to 12% by mass, more preferably 6.0 to 10% by mass, and even more preferably 6.0 to 8.0% by mass, relative to the total amount of the inkjet ink composition. A self-dispersing pigment content of 4.0% by mass or more tends to result in superior image quality.

[0027] 1.2. Inorganic oxide particles The inorganic oxide particles are not particularly limited as long as they can be dispersed in water, but examples include metal oxides such as silica, alumina, titania, zirconia, 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 composites thereof. The inorganic oxide particles may also form salts. Furthermore, the inorganic oxide particles may be used alone or in combination of two or more types. The inorganic oxide particles only need to contain at least an inorganic oxide within the particle. Preferably, the particles are made of inorganic oxides.

[0028] 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. The method for preparing the counterions of the inorganic oxide particles is not particularly limited, but examples include preparing the alkali metal salt used when preparing the inorganic oxide particles.

[0029] Preferably, it contains one or more selected from the group consisting of silica, alumina, zirconia, titania, and ceria, and more preferably contains silica. This makes it possible to further suppress curling in inkjet recording using a water-based inkjet ink composition, and tends to result in excellent stackability.

[0030] Volume-average particle diameter D of inorganic oxide particles 50The volume average particle diameter D of inorganic oxide particles is preferably 100 nm or less, more preferably 5 to 90 nm. Furthermore, it is preferably 10 to 80 nm, more preferably 20 to 70 nm, even more preferably 30 to 80 nm, and even more preferably 40 to 60 nm. 50 However, being below the above limits tends to result in superior intermittency and clogging recovery, and the volume average particle diameter D of inorganic oxide particles 50 However, exceeding the above specifications tends to result in superior image quality. The method for measuring the volume-average particle diameter is the same as described above.

[0031] The inorganic oxide particle content 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 amount of the inkjet ink composition. When the inorganic oxide particle content is 0.5% by mass or more, the stacking performance tends to be excellent, and when the inorganic oxide particle content is 8.0% by mass or less, the clogging recovery performance tends to be excellent.

[0032] 1.3. Metal Ions 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. Furthermore, the metal ions preferably include metal ions derived from at least one counterion among self-dispersing pigments and inorganic oxide particles.

[0033] In this embodiment, a counterion refers to an ion that is electrically paired with a self-dispersing pigment and / or inorganic oxide particles when the self-dispersing pigment and / or inorganic oxide particles form a salt. It also refers to an ion that was electrically paired with the self-dispersing pigment and / or inorganic oxide particles when they were forming a salt.

[0034] Furthermore, the inkjet ink composition of this embodiment may 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 metal ions derived from the counterions of the self-dispersing pigment described above, and metal ions that differ from those metal ions and are derived from counterions of inorganic oxide particles.

[0035] Of the metal ions, potassium ions are preferred because they provide superior image quality. Sodium ions or lithium ions are also preferred because they offer superior clogging recovery and other advantages, with sodium ions being more preferred. Among these, the metal ions more preferably include potassium ions derived from counterions of self-dispersing pigments, sodium ions derived from counterions of inorganic oxide particles, and lithium ions derived from counterions of inorganic oxide particles, and the metal ions more preferably include potassium ions derived from counterions of self-dispersing pigments and sodium ions derived from counterions of inorganic oxide particles. This tends to result in superior image quality and clogging recovery.

[0036] Furthermore, the inkjet ink composition of this embodiment may be used for recording together with other inkjet ink compositions that are water-based inks. In that case, the other inkjet ink composition may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. In that case, the other inkjet ink composition may contain one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, which are different from the metal ions contained in the inkjet ink composition.

[0037] When two or more ink compositions containing different metal ions are used in combination and ejected from the nozzles of the same inkjet head, there are inevitably opportunities for the two ink compositions to come into contact with each other due to contact between adjacent nozzles, contact caused by flying ink mist, contact caused by wiping during cleaning, etc. If ions from one ink mix with the other ink due to such contact, it can cause dispersion breakdown, potentially leading to the formation of composite foreign matter, for example, a mixture of self-dispersing pigments and inorganic oxide particles.

[0038] However, because the ink composition of this embodiment has the above-described structure, it is less likely to generate complex foreign matter, making it suitable for use in combination with other ink compositions containing different metal ions. Specifically, when used in combination with other ink compositions, the inkjet ink composition of this embodiment tends to be less likely to generate complex foreign matter, even if there is contact between adjacent nozzles of their respective pigment inks, contact due to the airborne ink mist, or contact due to wiping during cleaning, and exhibits excellent clogging recovery and intermittent properties.

[0039] 1.4. Polyethylene glycol The polyethylene glycol in this embodiment is polyethylene glycol represented by the following general formula (I). In this embodiment, by containing polyethylene glycol represented by the following general formula (I) in the ink, the generation of foreign matter originating from self-dispersing pigments, inorganic oxide particles, and metal ions is suppressed, resulting in excellent clogging recovery and intermittent properties. It also exhibits excellent discharge stability.

[0040] In particular, by using polyethylene glycol represented by the following general formula (I) with a chain length corresponding to the ionic radius, it is thought that ions can be appropriately encapsulated and the generation of composite foreign matter can be suppressed, but this is not limited to this. The polyethylene glycol of this embodiment may be used alone or two or more types may be used in combination. HO-(CH2-CH2-O-) n -H ··· (I) (In the formula, n is an integer between 3 and 9.)

[0041] In this embodiment, if the metal ion includes potassium ions, preferably n is any integer represented by 4 to 9, more preferably n is any integer represented by 5 to 9, and even more preferably n is any integer represented by 6 to 8. The inclusion of potassium ions in the metal ion tends to result in superior image quality. Furthermore, because n is within the above range, the polyethylene glycol can reduce the generation of complex foreign matter derived from potassium ions, and tends to exhibit superior clogging recovery and intermittent performance.

[0042] In this embodiment, if the metal ions include sodium ions, preferably n is any integer from 3 to 9, more preferably n is any integer from 3 to 7, and even more preferably n is any 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 intermittent properties.

[0043] In this embodiment, if the metal ion includes lithium ions, then preferably n is any integer represented from 3 to 9, more preferably n is any integer represented from 3 to 7, and even more preferably n is any integer represented from 3 to 5.

[0044] The polyethylene glycol content is preferably 0.5 to 10.0% by mass relative to the total amount of the inkjet ink composition. More preferably, it is 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% by mass or more tends to result in excellent clogging recovery, while a polyethylene glycol content below the above tends to result in excellent intermittent performance.

[0045] The polyethylene glycol content is preferably 5.0 to 75% by mass, relative to the total amount of the self-dispersing pigment and the inorganic oxide particles. More preferably 5.0 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass.

[0046] 1.5. Water-soluble fixing resin The inkjet ink composition of this embodiment preferably further comprises a water-soluble fixing resin. Compared to resin emulsions and the like, water-soluble fixing resins tend to introduce fewer counterions into the inkjet ink composition, thus reducing the generation of complex foreign matter, and tend to exhibit superior clogging recovery and intermittent properties.

[0047] A water-soluble fixing resin is a resin that is both water-soluble and a fixing resin. A water-soluble resin is a resin that, at room temperature, dissolves in water rather than in a dispersed form such as a resin emulsion. It is also a resin that dissolves in ink rather than in a dispersed form such as a resin emulsion. A fixing resin is a resin that enhances the adhesion of ink to a recording medium.

[0048] Such water-soluble fixing resins are not particularly limited, but examples include urethane resins, acrylic resins, fluorene resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, ethylene vinyl acetate resins, etc., with urethane resins being preferred among them. The fixing resin may be used alone or in combination of two or more types.

[0049] The content of the water-soluble fixing resin is preferably 0.01 to 1.0% by mass relative to the total amount of the inkjet ink composition. More preferably it is 0.05 to 0.5% by mass, more preferably 0.02 to 0.3% by mass, even more 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 more tends to result in excellent resistance to line markers, while a water-soluble fixing resin content below the above tends to result in excellent intermittent performance.

[0050] 1.6.1.Water The ink composition of this embodiment is a water-based ink. A water-based ink is an ink that contains water as the main solvent component. The water content in the water-based ink is preferably 40% by mass or more, more preferably 45 to 98% by mass, relative to the total amount of ink. Furthermore, it is preferably 50% by mass or more and 80% by mass or less, and more preferably 65% ​​by mass or more and 75% by mass or less. When the ink is a water-based ink, the inclusion of inorganic oxide particles can provide excellent stackability.

[0051] 1.6.2. Organic Solvents The organic solvent in this embodiment is not particularly limited, but examples 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, and tripropylene glycol, and glycerin; 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 preferred, and glycerin is preferred. The organic solvent may be used alone or in combination of two or more types.

[0052] 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.

[0053] 1.7. Lactam compounds The lactam compound is not particularly limited as long as it is an organic solvent or a compound fixed at room temperature, but examples include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 3-methoxy-2-pyrrolidone, 3-acetoxy-2-pyrrolidone, 4-pentanelactam, and ε-caprolactam, among which ε-caprolactam is preferred. Inkjet ink compositions containing lactam compounds tend to be less prone to the generation of complex foreign matter and tend to have excellent clogging recovery and intermittent properties.

[0054] 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 amount of the ink composition. A lactam compound content of 1.0% by mass or more tends to result in excellent intermittent properties. Lactam compounds that are liquid at room temperature are also organic solvents.

[0055] 1.8. Surfactants The ink composition of this embodiment may further contain a surfactant. The surfactant may be used alone or in combination of two or more. Such surfactants are not particularly limited, but examples include acetylene glycol-based surfactants, silicone-based surfactants, and fluorine-based surfactants. The surfactant may be used alone or in combination of two or more.

[0056] Examples of acetylene glycol-based surfactants include, but are not limited to, 2,4,7,9-tetramethyl-5-decine-4,7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol, 2,4-dimethyl-5-decine-4-ol, and alkylene oxide adducts of 2,4-dimethyl-5-decine-4-ol.

[0057] Silicone-based surfactants are not particularly limited, but examples include polysiloxane compounds and polyether-modified organosiloxanes.

[0058] Examples of fluorinated surfactants are not particularly limited, but include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds.

[0059] The surfactant content 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.

[0060] 1.9. Other Ingredients 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, but examples include solubilizers, viscosity modifiers, pH adjusters, antioxidants, preservatives, fungicides, corrosion inhibitors, chelating agents and other additives for capturing metal ions that affect dispersion, and organic solvents other than those mentioned above.

[0061] 2. Ink Set The ink set of this embodiment comprises a first ink composition, which is the inkjet ink composition according to the embodiment described above, and a second ink composition, which is a water-based inkjet ink composition. Furthermore, the ink set of this embodiment can use one or more ink compositions as the first ink composition and / or the second ink composition. The ink set is a set of two or more ink compositions used for recording. Each ink composition in the ink set may be housed in a separate ink container, or in separate compartments of an integrated ink container.

[0062] Not only when the metal ions that act as counterions for the self-dispersing pigment and inorganic oxide particles contained in a single pigment ink are different, but also when 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 adjacent nozzles of each pigment ink, contact due to the airborne ink mist, contact due to wiping during cleaning, etc., which can reduce long-term ejection stability.

[0063] In addition, it has become clear that in flushing boxes, caps, and wastewater tanks, the metal ions that are counterions in the self-dispersing pigments mentioned above are mixed with the metal ions that are counterions in different inorganic oxide particles, resulting in the generation of complex foreign matter, which can easily cause blockages in wastewater tanks and wastewater flow paths.

[0064] Therefore, in this embodiment, the inkjet ink composition included in the ink set contains inorganic oxide particles to improve stackability, and the inkjet ink composition contains predetermined metal ions and predetermined polyethylene glycol to suppress the formation of complex foreign matter of self-dispersing pigments and metal ions, thereby providing an ink set with excellent clogging recovery and intermittent performance.

[0065] The second ink composition described above is not particularly limited as long as it is a water-based pigment ink; conventionally known pigment inks can be used.

[0066] Furthermore, the second ink composition may or may not contain the self-dispersing pigment, inorganic oxide particles, polyethylene glycol, water-soluble fixing resin, organic solvent, lactam compound, surfactant, and other components of this embodiment.

[0067] The second ink composition contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, and may contain different types of metal ions than those contained in the first ink composition. In this case as well, the ink set of this embodiment tends to have excellent long-term ejection stability.

[0068] The second ink composition may contain at least one of a self-dispersing pigment and inorganic oxide particles. In this case, one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, which are different from the metal ions contained in the first ink composition, may be counterions of the self-dispersing pigment or inorganic oxide particles contained in the second ink composition. If the second ink composition contains a self-dispersing pigment and inorganic oxide particles, it is preferable that the second ink composition contains the aforementioned polyethylene glycol.

[0069] 3. Inkjet recording method The inkjet recording method of this embodiment includes an ejection step of ejecting the inkjet ink composition from an inkjet head and adhering it to a recording medium. The ejection step may also include an ejection step of ejecting each ink composition of the ink set from the inkjet head and adhering it to the recording medium. The inkjet recording method may further include a transport step of transporting the recording medium. The ejection step and the transport step may be performed simultaneously or alternately.

[0070] 3.1.Discharge process In the ejection process, ink is ejected from the inkjet head and deposited onto the recording medium. More specifically, a pressure generating mechanism located within the inkjet head is driven to eject the ink filled in the pressure generating chamber of the inkjet head from the nozzle. This ejection method is also called the inkjet method.

[0071] Inkjet heads used in the ejection process include line heads that record using a line method and serial heads that record using a serial method.

[0072] In a line-type system using a line head, for example, an inkjet head with a width greater than the recording width of the recording medium is fixed to the recording device. The recording medium is then moved along the 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.

[0073] In a serial method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved along the main scanning direction (the width direction 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.

[0074] 3.2. Conveying Process In the transport process, the recording medium is transported in a predetermined direction within the recording device. More specifically, the recording medium is transported from the paper feed section to the paper discharge section of the recording device using transport rollers and transport belts provided within the recording device. During this transport process, ink ejected from the inkjet head adheres to the recording medium, forming a recorded material. Transport may be performed continuously or intermittently.

[0075] 3.3 Recording media The recording medium used in this embodiment is not particularly limited, but examples include absorbent or non-absorbent recording media. Among these, absorbent recording media are prone to problems such as curling, so the inkjet ink composition of this embodiment, which can suppress the occurrence of curling using inorganic oxide particles and has excellent clogging recovery properties, is effective.

[0076] Absorbent recording media are not particularly limited, but examples include plain paper such as electrophotographic paper with high permeability to inkjet ink compositions, inkjet paper (inkjet-specific paper equipped with an ink-absorbing layer composed of silica particles or alumina particles, or an ink-absorbing layer composed of hydrophilic polymers such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), and art paper, coated paper, and cast paper used in general offset printing, which have relatively low ink permeability.

[0077] Examples of non-absorbent recording media include, but are not limited to, films and 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; metal plates or plastic films made by vapor deposition of these metals; plates of alloys such as stainless steel and brass; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are bonded (coated) to a paper substrate.

[0078] 4. Inkjet recording device The recording device of this embodiment comprises an inkjet head having a nozzle for ejecting an inkjet ink composition onto a recording medium, and a transport means for transporting the recording medium. The inkjet head comprises a pressure chamber to which ink is supplied and a nozzle for ejecting ink. The transport means consists of transport rollers and a transport belt provided within the recording device.

[0079] Hereinafter, an example of a recording device according to this embodiment will be described with reference to Figure 1. In Figure 1, the XYZ coordinate system is such that the X direction represents the length direction of the recording medium, the Y direction represents the width direction of the recording medium in the transport path within the recording device, and the Z direction represents the height direction of the device.

[0080] As an example, the recording device 10 is a line-type inkjet printer capable of high-speed and high-density printing. The recording device 10 includes a feeding unit 12 for storing a recording medium P such as paper, a transport unit 14, a belt transport unit 16, a recording unit 18, an Fd (face down) ejection unit 20 as an "ejection unit", an Fd (face down) placement unit 22 as a "placement unit", an inversion path unit 24 as an "inversion transport mechanism", a Fu (face up) ejection unit 26, and a Fu (face up) placement unit 28.

[0081] The feeding unit 12 is located at the bottom of the recording device 10. The feeding unit 12 includes a feeding tray 30 for storing recording media P and a feeding roller 32 for sending the recording media P stored in the feeding tray 30 to the transport path 11.

[0082] The recording medium P stored in the feeding tray 30 is fed along the transport path 11 to the transport unit 14 by the feeding roller 32. The transport unit 14 is equipped with a transport drive roller 34 and a transport driven roller 36. The transport drive roller 34 is rotationally driven by a drive source (not shown). In the transport unit 14, the recording medium P is nipped between the transport drive roller 34 and the transport driven roller 36 and transported to the belt transport unit 16 located downstream of the transport path 11.

[0083] The belt conveying unit 16 includes a first roller 38 located upstream in the conveying path 11, a second roller 40 located downstream, an endless belt 42 rotatably mounted on the first roller 38 and the second roller 40, and a support 44 that supports the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0084] The endless belt 42 is driven by a first roller 38 or a second roller 40, driven by a drive source (not shown), to move in the upper section 42a from the +X direction to the -X direction. As a result, the recording medium P conveyed from the conveying section 14 is further conveyed downstream of the conveying path 11 in the belt conveying section 16.

[0085] The recording unit 18 comprises a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. The recording unit 18 may also be a serial-type unit in which the inkjet head is mounted on a carriage that reciprocates in the Y-axis direction. The inkjet head 48 is positioned to face the upper section 42a of an endless belt 42 supported by a support 44. When the recording medium P is transported along the upper section 42a of the endless belt 42, the inkjet head 48 ejects ink toward the recording medium P and performs recording. While recording is taking place, the recording medium P is transported downstream of the transport path 11 by the belt transport unit 16.

[0086] A "line-type inkjet head" is a head used in a recording device where the nozzle area, formed in a direction intersecting the transport direction of the recording medium P, is provided to cover the entire intersecting direction of the recording medium P, and an image is formed by fixing either the head or the recording medium P and moving the other. However, the nozzle area in the intersecting direction of the line head does not necessarily have to cover the entire intersecting direction of all recording mediums P supported by the recording device.

[0087] Furthermore, a first branching section 50 is provided downstream of the transport path 11 of the belt transport section 16. The first branching section 50 is configured to switch between a transport path 11 that transports the recording medium P to the Fd discharge section 20 or the Fu discharge section 26, and an inversion path 52 of an inversion path section 24 that inverts the recording surface of the recording medium P and transports the recording medium P back to the recording section 18. When the recording medium P is transported after being switched to the inversion path 52 by the first branching section 50, the recording surface is inverted during the transport process in the inversion path 52, and it is transported back to the recording section 18 so that the side opposite to the original recording surface faces the inkjet head 48.

[0088] A second branching section 54 is provided downstream of the first branching section 50 along the transport path 11. The second branching section 54 is configured to switch the transport direction of the recording medium P so as to transport the recording medium P toward the Fd discharge section 20 or toward the Fu discharge section 26.

[0089] The recording medium P transported toward the Fd discharge section 20 at the second branching section 54 is discharged from the Fd discharge section 20 and placed on the Fd mounting section 22. At this time, the recording surface of the recording medium P is placed facing the Fd mounting section 22. The recording medium P transported toward the Fu discharge section 26 at the second branching section 54 is discharged from the Fu discharge section 26 and placed on the Fu mounting section 28. At this time, the recording surface of the recording medium P is placed facing away from the Fu mounting section 28.

[0090] Although the above describes an example using a line-type inkjet head, the recording device according to this embodiment may also be a printer using a serial-type inkjet head (serial printer). In a serial printer, printing is performed by moving the inkjet head in a direction intersecting the transport direction while the recording medium is transported in the transport direction.

[0091] When the recording apparatus uses a line-type inkjet head, a high recording speed is preferable. However, ink mist is likely to be generated from the nozzles of the inkjet head, and this embodiment is particularly useful for obtaining excellent long-term discharge stability.

Example

[0092] Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited in any way by the following examples.

[0093] 1. Inkjet ink composition 1.1. Preparation of inkjet ink composition The components were placed in a mixing tank to obtain the composition described in Tables 1 to 2, mixed and stirred, and further filtered through a 5-μm membrane filter to obtain the inkjet ink compositions of each example. Note that the numerical values of each component shown in the tables represent mass% unless otherwise specified. Also, in the tables, the numerical values of the self-dispersible pigment, resin-dispersed pigment, inorganic oxide particles, water-soluble fixing resin, and lactam-based compound represent mass% of the solid content.

[0094]

Table 1

[0095]

Table 2

[0096] The abbreviations and details of the product components used in Tables 1 to 2 are as follows. <Self-dispersible pigment> · Self-dispersible pigment 1: Prepared as follows. Carbon black was pulverized, mixed with water, and the mixture was subjected to ozone treatment. The ozone treatment was performed for 6 hours with the ozone concentration of the mixture being 5.5 to 6.0 wt%. After the treatment, potassium hydroxide was added to this mixture. Further, a crushing process was performed. Volume average particle diameter D 50A self-dispersing carbon black pigment with a wavelength of 110 nm and containing potassium as a counterion was obtained. • Self-dispersing pigment 2: Prepared as follows. In the preparation of self-dispersing pigment 1, the volume-average particle size D was determined in the same manner, except that sodium hydroxide was used instead of potassium hydroxide. 50 A self-dispersing carbon black pigment with a wavelength of 110 nm and containing sodium as a counterion was obtained. • Self-dispersing pigment 3: Prepared as follows. In the preparation of self-dispersing pigment 1, the volume-average particle size D was determined in the same manner, except that lithium hydroxide was used instead of potassium hydroxide. 50 The wavelength is 110 nm, and a self-dispersing carbon black pigment having lithium as a counterion was obtained. • Self-dispersing pigment 4: Cabojet250C, manufactured by Cabot Japan, is a self-dispersing copper phthalocyanine pigment that contains sodium as a counterion. <Resin-dispersed pigments> • Resin-dispersed pigment 1: Prepared as follows. Carbon black powder was pulverized and mixed with a styrene-acrylic resin dispersant (YS-1274, manufactured by Seikoh PMC) in a mass ratio of 3:1 in water. The mixture was then stirred using a bead mill to obtain a resin-dispersed pigment. The volume-average particle size was 110 nm. <Inorganic oxide particles> • Colloidal silica 1 (particle size: 80nm): "Cataloid SI-80P" manufactured by JGC Catalysts & Chemicals Co., Ltd. • Colloidal silica 2 (particle size: 45 nm): "Cataloid SI-45" manufactured by JGC Catalysts & Chemicals Co., Ltd. • Colloidal silica 3 (particle size: 11nm): "Cataloid SI-30" manufactured by JGC Catalysts & Chemicals Co., Ltd. All of them were colloidal silica with sodium as the counterion. <Water-soluble fixing resin> • Water-soluble fixing resin 1: Prepared as follows. A four-necked flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube was prepared. 41.7 parts by mass of isophorone diisocyanate, 40.1 parts by mass of polypropylene glycol (number average molecular weight 2,000), 13.2 parts by mass of dimethylolpropionic acid, and 200.0 parts by mass of methyl ethyl ketone were added to this four-necked flask and reacted at 80°C for 6 hours under a nitrogen gas 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 remaining percentage of isocyanate groups was confirmed by FT-IR, and the reaction was continued at 80°C until the desired percentage was reached to obtain the reaction solution. After cooling the obtained reaction solution to 40°C, ion-exchanged water was added, and potassium hydroxide aqueous solution was added while rapidly stirring with a homomixer to obtain a liquid. Methyl ethyl ketone was removed from the obtained liquid by heating and reducing the pressure to obtain a water-soluble fixing resin with a urethane resin (solids) content of 20.0%. <Polyethylene glycol> • PEG1 (n=4~9): Toho Polyethylene Glycol 400 manufactured by Toho Chemical Industry Co., Ltd. • PEG2 (n=3~7): "Toho Polyethylene Glycol 300" manufactured by Toho Chemical Industry Co., Ltd. • PEG3 (n=3~5): "Toho Polyethylene Glycol 200" manufactured by Toho Chemical Industry Co., Ltd. • PEG4 (n=2): "Diethylene glycol" • PEG5 (n=10~15): Polyethylene glycol with n=10 or more was purified by fractionating "Toho Polyethylene Glycol 600" manufactured by Toho Chemical Industry Co., Ltd. <Lactam compounds> • ε-caprolactam <Organic solvents> Glycerin Triethylene glycol monobutyl ether <Surfactants> • Acetylene glycol-based surfactant: Olfin E1010 (product name manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant)

[0097] 1.2. Evaluation Method for Inkjet Ink Compositions 1.2.1. Clogging recovery The ink cartridge of a modified Seiko Epson LX-10050MF (line inkjet printer) was filled with the ink composition prepared as described above, and a test pattern was recorded on a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m²) under the pattern conditions of adhesion amount 6 ng / dpi and recording resolution 600 x 1200 dpi. 2 The data was recorded on paper with a thickness of 88 μm. After confirming that ink could be ejected from all nozzles, the inkjet head was left in a 35°C environment for one day with the cap misaligned from the position of the cap on the printer and the head uncapped. After this period, the inkjet head was cleaned by suctioning the ink from the nozzles once, and the number of nozzles that could not eject ink was counted. The clogging recovery performance was then evaluated according to the evaluation criteria below. The evaluation results are shown in Tables 1 and 2. [Evaluation Criteria] A: There are no nozzles with dispensing problems. B: The number of nozzles with poor dispensing performance is 1% or less of all nozzles. C: The number of nozzles with poor dispensing performance is between 1% and 3% of all nozzles. D: The number of nozzles with poor dispensing performance exceeds 3% of all nozzles.

[0098] 1.2.2. Intermittent Under the above pattern conditions, recording was performed continuously for 6 hours, and the nozzles were inspected every hour during the recording, including at the end of the recording, to check for any nozzles with ejection problems. If ink did not eject or if the ink flight was bent even once, it was considered an ejection problem, and the intermittency was evaluated according to the evaluation criteria below. The evaluation results are shown in Tables 1 and 2. [Evaluation Criteria] A: There are no nozzles with poor dispensing performance. B: The number of nozzles with poor dispensing performance is 1% or less of all nozzles. C: The number of nozzles with poor dispensing performance exceeds 1% of all nozzles.

[0099] 1.2.3. Image Quality (OD Value) The image quality (OD value) of the test patterns of the recorded materials obtained above was measured using a colorimeter (Xrite i1, manufactured by Xrite), and the image quality (OD value) was evaluated according to the evaluation criteria below. The evaluation results are shown in Tables 1 and 2. [Evaluation Criteria] A: The OD value is 1 or greater. B: The OD value is less than 1 but greater than or equal to 0.95. The C:OD value is less than 0.95.

[0100] 1.2.4. Stackability The above 20 recording media were continuously recorded under the above pattern conditions, and the stackability of the recorded material continuously ejected from the ejection section of the inkjet recording device was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 and 2. [Evaluation Criteria] A: Twenty sheets of paper are placed in the output tray, and the edges of the sheets are aligned without any misalignment, allowing them to be stapled. B: Twenty sheets of paper are in the output tray, but their edges are misaligned and not properly aligned. C: 20 sheets of paper are sticking out of the output tray and do not fit inside.

[0101] 1.2.5. Resistance to line markers The test patterns of the recordings obtained above were marked with a line marker (ZEBRA's "OPTEX CARE WKCR1-Y (yellow)" highlighter) and their resistance to the line marker was evaluated according to the evaluation criteria below. The evaluation results are shown in Tables 1 and 2. [Evaluation Criteria] A: The printed area does not smudge even when highlighted with a highlighter. B: When the printed area is colored with a highlighter, some bleeding is observed. C: When the printed area is colored with a highlighter, the bleeding is clearly noticeable.

[0102] 2. Ink set evaluation 2.1. Ink Set Preparation Ink set 1 was prepared by combining ink 1 and ink 9 as shown in Table 3.

[0103] Next, ink set 2 was prepared by combining ink 1 and an inkjet ink composition obtained by removing polyethylene glycol from ink 9 (hereinafter referred to as ink 9-2) so as shown in Table 3.

[0104] [Table 3]

[0105] 2.2. Ink Set Evaluation Method The ink cartridges of a modified Seiko Epson LX-10050MF (line inkjet printer) were each filled with the ink sets prepared as described above, so that the two ink compositions in the ink sets were ejected from adjacent nozzle rows.

[0106] <Clogging recovery> Using the recording device described above, each ink composition was evaluated using either one or the other of the two ink compositions in the same manner as described above for its clogging recovery properties.

[0107] <Long-term discharge stability> The above recording device was used to record a test pattern using two inks simultaneously. The adhesion conditions were 6 ng / dpi per ink and a recording resolution of 300 x 600 dpi, with both inks applied to the test pattern. The test pattern was recorded on a recording medium (A4 size Xerox P paper, Fuji Xerox copy paper, basis weight 64 g / m²). 2 The data was recorded on paper with a thickness of 88 μm and recorded continuously for 10 hours.

[0108] Nozzle cleaning was performed every hour during recording, including at the end of continuous recording, by wiping the nozzle surface with a wiper. After recording, the nozzles were inspected to check for any nozzles with ejection problems. If ink did not eject or if any deviation in the ink flight after ejection was observed even once, it was considered an ejection problem, and the long-term ejection stability of each nozzle ejecting each ink composition was evaluated according to the evaluation criteria below. The evaluation results are shown below and in Table 3. [Evaluation Criteria] A: There are no nozzles with poor dispensing performance. B: The number of nozzles with poor dispensing performance is 1% or less of all nozzles. C: The number of nozzles with poor dispensing performance exceeds 1% of all nozzles.

[0109] 3. Evaluation Results A comparison of the inks 1-20 of the examples with the inks H1-H4 of the comparative examples revealed that the ink composition according to this embodiment is superior to the ink compositions of comparative examples H1-H4, which do not satisfy the constituent requirements of the ink composition, in terms of clogging recovery, intermittency, and stackability.

[0110] Evaluation of the ink sets revealed that ink 9-2, which did not contain two different metal ions or a specific polyethylene glycol, exhibited poor long-term ejection stability when used in combination with ink 1 for recording. Furthermore, foreign matter was observed around the nozzle of ink 9-2 after the long-term ejection stability test. In contrast, ink 9, which did not contain two different metal ions and did contain a specific polyethylene glycol, exhibited superior long-term ejection stability even when used in combination with ink 1 for recording. [Explanation of Symbols]

[0111] 10 Recording device, 11 Transport path, 12 Feeding section, 14 Transport section, 16 Belt transport section, 18 Recording section, 20 Fd discharge section, 22 Fd mounting section, 24 Reversal path section, 26 Fu discharge section, 28 Fu mounting section, 30 Feeding tray, 32 Feeding roller, 34 Transport drive roller, 36 Transport driven roller, 38 First roller, 40 Second roller, 42 Endless belt, 42a Upper section of endless belt, 44 Support, 46 Head holder, 48 Inkjet head, 50 First branch section, 52 Reversal path, 54 Second branch section, 56 Discharge roller pair, 64 Discharge drive roller, 68 Drive shaft, 76 Mounting surface, 78 Convex section, 80 First biasing member, 82 Second biasing member, 84, 86 Support shaft, P Recording medium

Claims

1. The invention comprises a first ink composition which is a water-based inkjet ink composition, and a second ink composition which is a water-based inkjet ink composition. The first ink composition comprises a self-dispersing pigment, silica which is an inorganic oxide particle, and polyethylene glycol represented by the following general formula (I), The first ink composition contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The self-dispersing pigment is a pigment dispersed without the use of a dispersant, and comprises one or more selected from the group consisting of carbon black and organic pigments. The second ink composition contains one or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions, and is of a different type from the metal ions contained in the first ink composition. The silica content is 0.5 to 8.0% by mass relative to the total amount of the first ink composition. The content of the self-dispersing pigment is 4.0 to 12.0% by mass relative to the total amount of the first ink composition. The polyethylene glycol content is 0.5 to 10% by mass relative to the total amount of the first ink composition. Ink set. HO-(CH) 2 -CH 2 -O-)n-H ・・・ (I) (In the formula, n is an integer between 3 and 9.)

2. The first ink composition contains two or more metal ions selected from the group consisting of potassium ions, sodium ions, and lithium ions. The ink set according to claim 1.

3. The self-dispersing pigment is a pigment in which hydrophilic functional groups are introduced and dispersed on the pigment surface by physical and / or chemical surface treatment. The ink set according to claim 1 or 2.

4. The metal ion in the first ink composition contains potassium ions, The polyethylene glycol includes n, where n is an integer represented by 4 to 9. The ink set according to any one of claims 1 to 3.

5. The metal ion in the first ink composition includes a sodium ion. The polyethylene glycol comprising n being an integer represented by 3 to 9, The ink set according to any one of claims 1 to 4.

6. The metal ion in the first ink composition includes a lithium ion. The polyethylene glycol comprising n being an integer represented by 3 to 9, The ink set according to any one of claims 1 to 5.

7. The polyethylene glycol content is 1.0 to 5.0% by mass relative to the total amount of the first ink composition. The ink set according to any one of claims 1 to 6.

8. Volume average particle size D of the self-dispersing pigment 50 However, the range is 40-250 nm. The ink set according to any one of claims 1 to 7.

9. The silica content is 0.5 to 6.0% by mass relative to the total amount of the first ink composition. The ink set according to any one of claims 1 to 8.

10. The volume-average particle size D of the silica 50 However, it is less than 100 nm. The ink set according to any one of claims 1 to 9.

11. The second ink composition contains a pigment, The ink set according to any one of claims 1 to 10.

12. The first ink composition further comprises a water-soluble fixing resin. The ink set according to any one of claims 1 to 11.

13. The content of the self-dispersing pigment is 4.0 to 10% by mass relative to the total amount of the first ink composition. The ink set according to any one of claims 1 to 12.

14. The invention includes an ejection step of ejecting the first ink composition and the second ink composition provided in any one of claims 1 to 13 from an inkjet head and adhering them to a recording medium, Recording method.

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