Inkjet ink and image recording method

Abstract

Provided are: an inkjet ink which contains water, a pigment, and at least one among resin particles and wax particles, has a pH of 7.2-11, and satisfies the expression (X) below; and an image recording method. In the expression (X), ORPi represents the redox potential of the inkjet ink in mV as measured under the apparatus condition in which the redox potential of water at pH 6.2 is 310 mV, and pHi represents the pH of the inkjet ink.　(X): ORPi-[285-59×(pHi-6.2)]≥0

Description

[Technical Field]

[0001] The present disclosure relates to inkjet inks and image recording methods. [Background technology]

[0002] Conventionally, various studies have been conducted on image recording using the inkjet method (i.e., image recording by ejecting ink from a recording head in an inkjet recording device and applying it onto a recording medium), and on the ink used for this image recording (hereinafter also referred to as "inkjet ink").

[0003] For example, Japanese Patent Application Laid-Open No. 2015-063574 describes an ink that, when used in an inkjet recording apparatus equipped with a recording head having a protective layer and a resin member that comes into contact with the ink, is less likely to reduce the thickness of the protective layer and less likely to deteriorate the resin member. An ink for use in an inkjet recording apparatus having a recording head (i.e., an inkjet head) in which at least a part of a member that comes into contact with the ink is formed of at least one material selected from the group consisting of silicon, silicon oxide, silicon nitride, and silicon carbide, and a resin member that comes into contact with the ink, An ink containing a pigment, soluble copper ions, and a specific compound containing a bipyridine structure is disclosed.

[0004] In addition, Japanese Patent Application Laid-Open No. 2003-165936 describes an inkjet ink that has excellent dispersion and dissolution stability without causing changes in the size of ink droplets or the ejection speed of ink droplets, ejection defects, etc., as follows: An ink used in an inkjet printer in which at least a part of a member that comes into contact with the ink is formed of silicon, glass, or a film of these with any of an oxide, nitride, metal, or organic compound provided thereon, Aqueous ink with a zeta potential between the component and the colorant of 0 to -50 mV at pH 6.5 to 11.5 has been disclosed.

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2016-044236 describes an ink that contains a resin that is effective in increasing the robustness of the recorded image, while suppressing the elution of silicon compounds from the recording head (i.e., inkjet head), has good ejection stability and storage stability, and is capable of recording images with high optical density, as follows: An ink for use in an ink jet recording method in which a recording head is used, at least a part of a member that comes into contact with the ink being made of silicon or a silicon compound, and the ink is ejected from the recording head to record an image on a recording medium, An ink containing a self-dispersing pigment having a phosphonic acid group bonded to the particle surface directly or via another atomic group, a resin having an anionic group, and a specific compound having an amino group. has been disclosed.

[0006] Furthermore, Japanese Patent Application Laid-Open No. 2011-063000 describes an image forming method that can suppress deterioration of head components (particularly head plates and ink flow paths) when forming images using an inkjet head having an ink circulation system, and can stably form high-resolution images over a long period of time. an ink jet head including a plurality of droplet ejection elements, a common flow path communicating with the plurality of droplet ejection elements via a supply path, and a common circulation path communicating with the plurality of droplet ejection elements via a return path, the ink composition being supplied from the common flow path to the plurality of droplet ejection elements, and an ink circulation device for circulating the ink composition in the common circulation path; Formation method has been disclosed.

[0007] Furthermore, Japanese Patent Application Laid-Open No. 2011-111527 describes an aqueous ink composition that has excellent long-term ejection properties and can suppress deformation of inkjet head members and a decrease in liquid repellency, as follows: An aqueous ink composition comprising a colorant containing at least one of an azo pigment having a specific structure, a tautomer thereof, and a salt and hydrate thereof, a dispersant, and colloidal silica. has been disclosed. Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, when an alkaline inkjet ink (for example, pH 7.2 or higher) and an inkjet head containing silicon in the ink flow path wall are used and the inkjet ink is ejected from the inkjet head to record an image, the alkaline inkjet ink may etch the ink flow path wall containing silicon. From the viewpoint of ejection properties of inkjet ink, it is sometimes required to suppress etching of the ink flow path walls.

[0009] An object of one aspect of the present disclosure is to provide an inkjet ink that is ejected from an inkjet head having an ink flow path wall containing silicon, and that can suppress etching of the ink flow path wall, and an image recording method using the inkjet ink. [Means for solving the problem]

[0010] Specific means for solving the problems include the following aspects. <1> An inkjet ink ejected from an inkjet head containing silicon in an ink flow path wall, Contains water, a pigment, and at least one of resin particles and wax particles, pH is 7.2 to 11, Satisfy the following inequality (X): Inkjet ink. ORPi-[285-59×(pHi-6.2)]≧0 … Inequality (X) In inequality (X), ORPi represents the oxidation-reduction potential of the inkjet ink in mV, measured under instrument conditions such that the oxidation-reduction potential of water at pH 6.2 is 310 mV, and pHi represents the pH of the inkjet ink. <2> Further, containing an oxidizing agent, <1> The inkjet ink according to claim 1. <3> The oxidizing agent comprises at least one selected from the group consisting of hydrogen peroxide and peroxide; <2> The inkjet ink according to claim 1. <4> The oxidizing agent comprises at least one selected from the group consisting of hydrogen peroxide, peracetic acid, sodium percarbonate, and hydrogen peroxide urea; <2> or <3> The inkjet ink according to claim 1. <5> The mass ratio of the content of the oxidizing agent to the total content of the resin particles and the wax particles is 0. 0.02% to 6% by weight, <2> ~ <4> 10. The ink-jet ink according to any one of the preceding items. <6> Further, containing colloidal silica, <1> ~ <5> 10. The ink-jet ink according to any one of the preceding items. <7> Further, an organic solvent having a ClogP value of 1.0 to 3.5 is contained. <1> ~ <6> 10. The ink-jet ink according to any one of the preceding items. <8> The organic solvent having a ClogP value of 1.0 to 3.5 is at least one selected from the group consisting of compounds represented by the following formula 1 and compounds represented by the following formula 2: <7> The inkjet ink according to claim 1.

[0011] [ka]

[0012] In Formula 1 or Formula 2, R 1 each independently represents a hydrogen atom or a methyl group, R 2 each independently represents a linear or branched hydrocarbon group having 4 to 9 carbon atoms or an aryl group having 6 to 10 carbon atoms; and n represents an integer of 1 to 3.

[0013] <9> Further, the dispersant is contained, and the dispersant is crosslinked. <1> ~ <8> 10. The ink-jet ink according to any one of the preceding items. <10> The resin particles contain a resin containing a structural unit represented by the following formula 3: <1> ~ <9> 10. The ink-jet ink according to any one of the preceding items.

[0014] [ka]

[0015] In formula 3, R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X 1 represents a divalent linking group, Y 1 represents an anionic group, and X 1 and Y 1 Among these, the atom farthest from the main chain is 4 to 27 atoms away from the main chain.

[0016] <11> Furthermore, it contains cellulose nanofibers, <1> ~ <10> 10. The ink-jet ink according to any one of the preceding items. <12> The average fiber width of the cellulose nanofiber is 1 nm or more and 10 nm or less. <11> The inkjet ink according to claim 1. <13> The average fiber length of the cellulose nanofiber is 10 nm or more and 1000 nm or less. <11> or <12> The inkjet ink according to claim 1. <14> The cellulose nanofiber is a TEMPO-oxidized cellulose nanofiber. <11> ~ <13> 10. The ink-jet ink according to any one of the preceding items. <15> The ratio of cellulose nanofibers to the total content of resin particles and wax particles The mass ratio of the content is 1.00 mass% to 10.00 mass%. <11> ~ <14> 10. The ink-jet ink according to any one of the preceding items. <16> The content of cellulose nanofibers is 0.01% by mass to 1.00% by mass relative to the total amount of the inkjet ink. <11> ~ <15> 10. The ink-jet ink according to any one of the preceding items. <17> The viscosity measured at 30°C and 100 rpm is 3.8 mPa·s to 6.0 mPa·s. <11> ~ <16> 10. The ink-jet ink according to any one of the preceding items.

[0017] <18> On the recording medium <1> ~ <17> 2. An image recording method, comprising a step of applying the ink-jet ink according to any one of the above items 1 to an ink flow path wall by ejection from an ink-jet head containing silicon. [Effects of the Invention]

[0018] According to one aspect of the present disclosure, there is provided an inkjet ink that is ejected from an inkjet head containing silicon in an ink flow path wall, and that can suppress etching of the ink flow path wall, and an image recording method using the inkjet ink. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced by the upper or lower limit value of another numerical range described in stages, or may be replaced by a value shown in an example. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In the present disclosure, combinations of preferred aspects are more preferred aspects. In the present disclosure, "(meth)acrylic" is a concept that encompasses both acrylic and methacrylic, and "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate.

[0020] [Inkjet ink] The inkjet ink (hereinafter also simply referred to as "ink") of the present disclosure is An inkjet ink ejected from an inkjet head having an ink flow path wall containing silicon (Si), Contains water, a pigment, and at least one of resin particles and wax particles (hereinafter also referred to as "resin particles and / or wax particles"); pH is 7.2 to 11, The following inequality (X) is satisfied.

[0021] ORPi-[285-59×(pHi-6.2)]≧0 … Inequality (X) In inequality (X), ORP represents the oxidation-reduction potential of the inkjet ink in mV, measured under instrument conditions such that the oxidation-reduction potential of water at pH 6.2 is 310 mV, and pH represents the pH of the inkjet ink.

[0022] As mentioned above, conventional alkaline inkjet inks (e.g., pH 7.2 or higher) When an inkjet head having an ink flow path wall containing silicon is used and the inkjet ink is ejected from the inkjet head to record an image, the ink flow path wall containing silicon may be etched by the alkaline inkjet ink. If the ink flow path walls are etched, the ink ejection performance from the inkjet head may be impaired, so it is desirable to suppress etching of the ink flow path walls.

[0023] Although the ink of the present disclosure is an alkaline ink, it can suppress etching of the ink flow path walls containing silicon in the inkjet head. In particular, the inks of the present disclosure include: The ink contains at least one of resin particles and wax particles; and The ink satisfies inequality (X) (i.e., the ink's oxidation-reduction potential ORPi is 285-59 x (pHi-6.2) or greater). This can suppress etching of the ink flow path walls containing silicon in the inkjet head. The reason why such an effect is achieved is presumed to be as follows.

[0024] In the ink of the present disclosure, the ink satisfies inequality (X), which is thought to promote the formation of an oxide film (i.e., a silicon oxide film) on the surface of the ink flow path wall, which contains silicon, and which protects the ink flow path wall and thereby suppresses etching of the ink flow path wall. Furthermore, in the ink of the present disclosure, the resin particles and / or wax particles in the ink function as a buffer material, which prevents the ink flow path walls from being polished by the pigments in the ink, and as a result, it is believed that etching caused by polishing scratches on the ink flow path walls is suppressed.

[0025] <ph> The pH of the ink of the present disclosure (ie, pHi in inequality (X)) is 7.2 to 11. That is, the ink of the present disclosure is an alkaline ink. As mentioned above, conventional alkaline inks can cause etching of the ink flow path walls, but the ink of the present disclosure solves the problem of etching of the ink flow path walls.

[0026] An ink pH of 7.2 to 11 is advantageous in terms of storage stability of the ink. The pH of the ink is preferably 7.5 to 10, and more preferably 8.0 to 9.5.

[0027] In the present disclosure, pH refers to a value measured at a temperature of 25°C using a pH meter (for example, product name "WM-50EG" manufactured by Toa DDK Corporation).

[0028] <Inequalities (X)> The ink of the present disclosure satisfies the following inequality (X):

[0029] ORPi-[285-59×(pHi-6.2)]≧0 … Inequality (X) In inequality (X), ORPi represents the oxidation-reduction potential of the inkjet ink in mV, measured under instrument conditions such that the oxidation-reduction potential of water at pH 6.2 is 310 mV, and pHi represents the pH of the inkjet ink.

[0030] The ORPi in the present disclosure is measured using an oxidation-reduction potential measuring device (e.g., OPR Tester manufactured by EUTECH) calibrated so that the oxidation-reduction potential of water at pH 6.2 is 310 mV. 10) means the value measured using

[0031] There are no particular limitations on the specific method for making the ink satisfy inequality (X). For example, by adjusting the types and amounts of the components contained in the ink, the ink can be adjusted so as to satisfy inequality (X).

[0032] The value of "ORPi-[285-59×(pHi-6.2)]" is greater than or equal to 0, as shown in the inequality (X). The value of "ORPi-[285-59×(pHi-6.2)]" is preferably 5.0 or more, and more preferably 10 or more, from the viewpoint of further suppressing etching of the ink flow path walls. There is no particular upper limit to the value of "ORPi-[285-59×(pHi-6.2)]", but an example of the upper limit is 30.

[0033] <Inkjet head> The inks of the present disclosure are ejected from inkjet heads having ink flow channel walls that include silicon. In the inkjet head, the ink flow path walls are preferably formed of a silicon-containing material. There are no particular limitations on such inkjet heads, but reference can be made as appropriate to inkjet heads described in publicly known documents such as JP 2015-063574 A, JP 2003-165936 A, JP 2016-044236 A, JP 2011-063000 A, JP 2011-111527 A, and Japanese Patent No. 4902711.

[0034] <Water> The inks of the present disclosure contain water. The water content relative to the total amount of the ink of the present disclosure is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more. The upper limit of the water content relative to the total amount of the ink of the present disclosure depends on the amounts of other components, but is, for example, 99 mass %, 90 mass %, 80 mass %, etc.

[0035] <Pigments> The inks of the present disclosure contain pigments. The type of pigment is not particularly limited, and may be either an organic pigment or an inorganic pigment. Examples of pigments include those described in "Encyclopedia of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and JP-A Nos. 2002-12607, 2002-188025, 2003-26978, and 2003-342503.

[0036] From the viewpoint of ink ejection properties, the content of the pigment is preferably 0.5% by mass to 15% by mass, and more preferably 1% by mass to 10% by mass, relative to the total amount of the ink.

[0037] <Resin particles and / or wax particles> The ink of the present disclosure contains resin particles and / or wax particles. When the ink of the present disclosure contains resin particles, the resin particles may be of one type or two or more types. Furthermore, when the ink of the present disclosure contains resin particles, the resin particles may be dispersed in the ink using a dispersant for resin particles. When the ink of the present disclosure contains wax particles, the wax particles contained may be of only one type or of two or more types. When the ink of the present disclosure contains wax particles, the wax particles contained are dispersed in the ink by a dispersant for wax particles. It may also be used.

[0038] The total content of resin particles and wax particles in the ink of the present disclosure is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and even more preferably 1.5% by mass to 8% by mass, relative to the total amount of ink.

[0039] (resin particles) The resin particles contain a resin and may contain a core material other than a resin, but are preferably resin particles consisting only of a resin.

[0040] -Structural unit (c1)- The resin particles preferably contain a resin containing a structural unit represented by the following formula 3 (hereinafter also referred to as "structural unit (c1)").

[0041] [ka]

[0042] In formula 3, R 3 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X 1 represents a divalent linking group, Y 1 represents an anionic group, and X 1 and Y 1 Among these, the atom farthest from the main chain is 4 to 27 atoms away from the main chain. When the distance of the atom farthest from the main chain is 4 atoms or more from the main chain, the hydrophobicity of the structural unit c1 increases, and the hydrophobicity of the resin particle as a whole increases. As a result, after the ink droplets land on the recording medium, the resin particles contained in the ink droplets are easily fixed on the recording medium, and landing interference is suppressed. Therefore, it is believed that the use of the ink of the present disclosure will result in an image with excellent graininess. Furthermore, because the resin particles as a whole are highly hydrophobic, the resin particles are less likely to swell, and the ink according to the present disclosure is believed to have excellent ejection properties. On the other hand, when the distance of the atom farthest from the main chain is 27 atoms or less from the main chain, the hydrophobicity of the resin particle as a whole is not too high, and it is thought that the ejection property is excellent. Also, from the viewpoint of availability of raw materials and suitability for production, it is preferable that the distance of the atom farthest from the main chain of X1 and Y1 is 27 atoms or less from the main chain.

[0043] In formula 3, R 3 is preferably a hydrogen atom or a methyl group.

[0044] In formula 3, X 1 is -C(=O)O-, -C(=O)NR 4 -, a group selected from the group consisting of an alkylene group and an arylene group, or a divalent group formed by combining two or more groups selected from these groups, and -C(=O)O-, -C(=O)NR 4 It is more preferably a group selected from the group consisting of -, alkylene groups having 6 to 22 carbon atoms, and arylene groups having 6 to 20 carbon atoms, or a divalent group formed by combining two or more groups selected from these groups.

[0045] X 1 is -C(=O)O- or -C(=O)NR 4 -, R in Formula 3 3 and a carbon atom to which -C(=O)O- or -C(=O)NR 4 -carbon atom in (R 4 It is preferable that the carbon atom is directly bonded to the carbon atom (excluding the carbon atom contained in

[0046] R 4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.

[0047] In formula 3, Y 1 is preferably -C(=O)OM, -S(=O)2OM, or -OP(=O)(OM)2, and more preferably -C(=O)OM.

[0048] M represents a hydrogen atom, an alkali metal, or a quaternary ammonium. M may be bonded or dissociated. From the viewpoint of dispersion stability of the resin particles in the ink, M is preferably an alkali metal. Examples of alkali metals include sodium and potassium. Resin particles in which M is an alkali metal may be, for example, Y 1 In the process of synthesizing resin particles using a monomer in which the substituent is -C(=O)OH, hydrogen atoms are substituted with alkali metal bicarbonate, alkali metal carbonate, sodium hydroxide, potassium hydroxide, etc.

[0049] In formula 3, X 1 and Y 1 Among these, the atom farthest from the main chain is preferably 10 to 23 atoms away from the main chain, and more preferably 12 to 20 atoms away from the main chain, from the viewpoints of improving the ink ejection properties and obtaining an image with excellent granularity.

[0050] The structural unit c1 is preferably a structural unit represented by the following formula 4 or 5, and more preferably a structural unit represented by formula 4.

[0051] [ka]

[0052] In Formula 4 or Formula 5, R 3 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; A 1 each independently represents a single bond, —C(═O)O—, or —C(═O)NR 4 - represents R 4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and L 1 each independently represents a divalent linking group having 6 to 22 carbon atoms; Y 1 represents an anionic group, and L 1 and Y 1 Among these, the atom farthest from the main chain is 4 to 27 atoms away from the main chain.

[0053] In Formula 4 or Formula 5, R 3 is R in the above formula 3 3 The same applies to the preferred embodiments.

[0054] In formula 4, A 1 is -C(=O)O- or -C(=O)NR 4 In formula 5, A is preferably 1 is preferably a single bond.

[0055] In Formula 4 or Formula 5, -C(=O)O- or -C(=O)NR 4 The direction of the - bond is particularly Non-limiting examples include -C(=O)O- or -C(=O)NR 4 and the carbon atom in Formula 4 or Formula 5 3 is preferably directly bonded to the carbon atom to which is bonded.

[0056] R 4 is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.

[0057] In formula 4, L 1 L preferably represents an alkylene group having 6 to 22 carbon atoms. The alkylene group may be linear or branched, but is preferably linear from the viewpoint of ink ejection properties. 1 is preferably an alkylene group having 8 to 22 carbon atoms, more preferably an alkylene group having 8 to 16 carbon atoms, and even more preferably an alkylene group having 10 to 12 carbon atoms.

[0058] In formula 5, L 1 is preferably a divalent linking group having 6 to 20 carbon atoms. The divalent linking group is not particularly limited, but from the viewpoint of synthetic suitability, -C(=O)NR 4 -(CH2) n - or -C(=O)O-(CH2) n - is preferred, and -C(=O)NR 4 -(CH2) n It is more preferable that R 4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. Furthermore, n represents an integer of 5 to 18, more preferably 7 to 15, and even more preferably 10 to 12.

[0059] In Formula 4 or Formula 5, Y 1 are each independently preferably -C(=O)OM, -S(=O)2OM, or -OP(=O)(OM)2, and more preferably -C(=O)OM.

[0060] M represents a hydrogen atom, an alkali metal, or a quaternary ammonium. M may be bonded or dissociated. From the viewpoint of dispersion stability of the resin particles in the ink, M is preferably an alkali metal. Examples of alkali metals include sodium and potassium.

[0061] In Formula 4 or Formula 5, L 1 and Y 1 Among these, the atom farthest from the main chain is preferably 10 to 23 atoms away from the main chain, and more preferably 12 to 20 atoms away from the main chain, from the viewpoints of improving the ink ejection properties and obtaining an image with excellent granularity.

[0062] Preferred specific examples of the structural unit c1 are shown below, but the structural unit c1 is not limited to these examples. In the specific examples, n represents the number of repetitions, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0063] [ka]

[0064] The content of the structural unit c1 is 1% by mass to 20% by mass relative to the total mass of the resin, and from the viewpoint of ink ejection performance, it is preferably 1.5% by mass to 18% by mass, and more preferably 2% by mass to 12% by mass.

[0065] In the present disclosure, the resin may contain only one type of structural unit c1, or may contain two or more types. When the resin contains two or more types of structural unit c1, the above content refers to the total content of the two or more types of structural unit c1.

[0066] The structural unit c1 is derived from a monomer containing an anionic group, and has a relatively long side chain, resulting in high hydrophobicity. Increasing the hydrophobicity of the structural unit derived from the anionic group-containing monomer increases the hydrophobicity of the resin particle as a whole. As a result, after the ink droplets land on a recording medium, the resin particles contained in the ink droplets quickly settle, suppressing landing interference. Therefore, it is believed that the use of the ink of the present disclosure will result in images with excellent graininess. Furthermore, because the resin particles as a whole are highly hydrophobic, the resin particles are less likely to swell, and the ink of the present disclosure is believed to have excellent ejection properties.

[0067] In the present disclosure, the content of the structural unit c1 is 1% by mass to 20% by mass relative to the total mass of the resin, but the type of structural unit other than the structural unit c1 is not particularly limited. In general, it is believed that the physical properties of the entire resin change depending on the type of each structural unit constituting the resin. However, the present inventors have found that the structural unit c1 is a structural unit derived from a monomer containing an anionic group. As a result, it has been found that the ink ejection properties are improved and images with excellent graininess can be obtained, as described above.

[0068] -Structural unit c2- The resin preferably further contains, as a structural unit other than the structural unit c1, a structural unit c2 (hereinafter also simply referred to as "structural unit c2") derived from an ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure.

[0069] Examples of the ring contained in the structural unit c2 include a benzene ring, a naphthalene ring, an anthracene ring, and an aliphatic hydrocarbon ring having 5 to 20 carbon atoms. Among these, the ring contained in the structural unit c2 is preferably a benzene ring or an aliphatic hydrocarbon ring having 6 to 10 carbon atoms. These rings may have a substituent on the ring.

[0070] The ethylenically unsaturated compound having an aromatic ring structure or an alicyclic structure is preferably an ethylenically unsaturated compound having an ethylenically unsaturated group at the compound terminal, more preferably styrene, styrene having a substituent, a (meth)acrylate compound, or a (meth)acrylamide compound, and even more preferably styrene, styrene having a substituent, or a (meth)acrylate compound.

[0071] From the viewpoint of improving the scratch resistance of the resulting image, the structural unit c2 is preferably at least one selected from the group consisting of structural units represented by the following formulae A to F. Furthermore, from the viewpoint of further improving the ejection properties of the ink, the structural unit c2 more preferably includes a structural unit represented by the following formula A.

[0072] [ka]

[0073] In formulas A to F, R 11 and R 12 R each independently represents a hydrogen atom or a methyl group. 13 each independently represents a linear or branched alkyl group having 1 to 10 carbon atoms. Each n independently represents an integer of 0 to 5. L 2 each independently represents a divalent group selected from the group consisting of an alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S-, and -C(=O)-, a divalent group formed by combining two or more groups selected from these groups, or a single bond.

[0074] In formula A, R 11 is preferably a hydrogen atom. In formulas B to F, R 12 is preferably a methyl group. In formulas A to C, R 13 are each independently preferably a linear or branched alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group. In Formulae A to C, n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0. In formula B, L 2 is preferably a divalent linking group containing at least -O- or -NH- at the bonding site to the carbon atom bonded to the carbonyl group described in formula B, more preferably a divalent linking group containing at least -O- or -NH- at the bonding site to the carbon atom bonded to the carbonyl group and containing a linear or branched alkylene group having 1 to 18 carbon atoms and optionally having a ring structure, further preferably -OCH2- or -NHCH2-, and particularly preferably -OCH2-. In formulas C to E, L 2 is preferably a divalent linking group containing at least -O- or -NH- at the bonding site to the carbon atom bonded to the carbonyl group described in Formulae C to F, more preferably -O- or -NH-, and even more preferably -O-.

[0075] Specific examples of the structural unit represented by formula A are shown below, but the structural unit represented by formula A is not limited to the following specific examples.

[0076] [ka]

[0077] Specific examples of the structural unit represented by formula B are shown below, but the structural unit represented by formula B is not limited to the following specific examples.

[0078] [ka]

[0079] Specific examples of the structural unit represented by formula C are shown below, but the structural unit represented by formula C is not limited to the following specific examples.

[0080] [ka]

[0081] Specific examples of the structural unit represented by formula D are shown below, but the structural unit represented by formula D is not limited to the following specific examples.

[0082] [ka]

[0083] Specific examples of the structural unit represented by formula E are shown below, but the structural unit represented by formula E is not limited to the following specific examples.

[0084] [ka]

[0085] Specific examples of the structural unit represented by formula F are shown below, but the structural unit represented by formula F is not limited to the following specific examples.

[0086] [ka]

[0087] From the viewpoint of improving the ejection properties of the ink, the content of the structural unit c2 is preferably 5% by mass to 90% by mass, and more preferably 10% by mass to 50% by mass, relative to the total mass of the resin.

[0088] The resin may contain only one type of structural unit c2, or may contain two or more types. When the resin contains two or more types of structural unit c2, the above content refers to the total content of the two or more types of structural unit c2.

[0089] -Other structural units c3- The resin may contain a structural unit c3 (hereinafter simply referred to as "structural unit c3") other than the structural unit c1 and the structural unit c2.

[0090] The structural unit c3 is not particularly limited, but is preferably a structural unit derived from a (meth)acrylamide compound or a (meth)acrylate compound, more preferably a structural unit derived from a (meth)acrylate compound. In addition, the structural unit c3 preferably does not contain an anionic group.

[0091] The structural unit c3 is preferably a structural unit derived from an alkyl(meth)acrylate compound in which the alkyl group has a carbon number of 1 to 10. The alkyl group may be linear or branched, or may have a cyclic structure.

[0092] The resin may or may not contain the structural unit c3. When the resin contains the structural unit c3, the content of the structural unit c3 is preferably 10% by mass to 90% by mass, and more preferably 30% by mass to 85% by mass, based on the total mass of the resin, from the viewpoint of improving the ejection properties of the ink. It is more preferable that the content is 50% by mass to 80% by mass, and even more preferable that the content is 50% by mass to 80% by mass.

[0093] The resin may contain only one type of structural unit c3, or may contain two or more types. When the resin contains two or more types of structural unit c3, the above content refers to the total content of the two or more types of structural unit c3.

[0094] (Characteristics of resin particles) From the viewpoint of dispersibility of the resin particles, the content of the anionic group in the resin contained in the resin particles relative to the total mass of the resin is preferably 0.05 mmol / g to 0.7 mmol / g, and more preferably 0.1 mmol / g to 0.4 mmol / g.

[0095] The weight average molecular weight (Mw) of the resin is preferably 10,000 to 1,000,000, and more preferably 20,000 to 500,000.

[0096] In this disclosure, unless otherwise specified, the weight-average molecular weight (Mw) refers to a value measured by gel permeation chromatography (GPC). Measurements by gel permeation chromatography (GPC) were performed using an HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) as a measuring device, three TSKgel (registered trademark) Super Multipore HZ-H columns (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation), and THF (tetrahydrofuran) as an eluent. Measurements were performed using an RI detector at a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C. The calibration curve is prepared from eight samples of "TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0097] The glass transition temperature (Tg) of the resin is preferably from 30°C to 120°C, more preferably from 50°C to 100°C, and even more preferably from 70°C to 100°C, from the viewpoint of improving the scratch resistance of the image.

[0098] The glass transition temperature (Tg) is the measured Tg obtained by actual measurement. The measured Tg is measured under normal measurement conditions using a differential scanning calorimeter, such as a differential scanning calorimeter manufactured by SII Nanotechnology (product name "EXSTAR6220"), however, if measurement is difficult due to material decomposition or other reasons, the calculated Tg calculated using the following formula is used. The calculated Tg is the value calculated using the following formula 1. 1 / Tg=Σ(Xi / Tgi) …(1) Here, the polymer to be calculated is assumed to be a copolymer of n types of monomer components, i = 1 to n. Xi is the mass fraction of the i-th monomer (ΣXi = 1), and Tgi is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum from i = 1 to n. The glass transition temperature of the homopolymer of each monomer (Tgi) is calculated from Polymer Handbook (3rd Edition) (J. Brandrup, The value given by E.H. Immergut (Wiley-Interscience, 1989) is used.

[0099] From the viewpoint of ink ejection properties, the volume average particle size of the resin particles is preferably 1 nm to 200 nm, more preferably 5 nm to 100 nm, and most preferably 10 nm to 50 nm.

[0100] The volume average particle size is measured by a particle size distribution measuring device using light scattering, for example, a particle size distribution measuring device manufactured by Nikkiso Co., Ltd. (product name "Microtrac UPA (registered trademark) EX150"). do.

[0101] -Method of manufacturing resin particles- The method for producing resin particles is not particularly limited, but emulsion polymerization is preferred. Emulsion polymerization is a method in which an emulsion is prepared by adding a monomer, a polymerization initiator, an emulsifier, and, if necessary, additives such as a chain transfer agent to an aqueous medium (e.g., water), and then polymerizing the resulting emulsion. When emulsion polymerization is applied to the preparation of resin particles, the monomer forming the structural unit c1 also functions as an emulsifier. Therefore, it is not necessary to add an emulsifier separately from the monomer forming the structural unit c1. However, a known emulsifier may be added separately as long as it does not impair the ink ejection properties and image quality.

[0102] The polymerization initiator used in the method for producing resin particles is not particularly limited, and examples thereof include inorganic persulfates (e.g., potassium persulfate, sodium persulfate, ammonium persulfate, etc.), azo initiators (e.g., 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], etc.), organic peroxides (e.g., t-butyl peroxypivalate, t-butyl hydroperoxide, etc.), and salts thereof. Only one type of polymerization initiator may be used, or two or more types may be used in combination. Among these, the polymerization initiator is preferably an azo initiator or an organic peroxide.

[0103] The amount of the polymerization initiator used is preferably 0.01% by mass to 2% by mass, and more preferably 0.2% by mass to 1% by mass, based on the total mass of the monomers.

[0104] Examples of chain transfer agents used in the method for producing resin particles include known compounds such as carbon tetrahalides, dimers of styrenes, dimers of (meth)acrylic esters, mercaptans, sulfides, etc. Among these, the chain transfer agent is preferably a dimer of styrenes or a mercaptan as described in JP-A-5-17510.

[0105] The resin particles are preferably dispersed in the ink. The resin particles are preferably self-dispersing resin particles. The self-dispersing resin particles are resin particles made of a water-insoluble resin that can be dispersed in an aqueous medium due to functional groups (e.g., anionic groups) possessed by the resin itself when dispersed by a phase inversion emulsification method in the absence of a surfactant.

[0106] The dispersed state includes both an emulsified state (emulsion) in which the water-insoluble resin is dispersed in a liquid state in an aqueous medium, and a dispersed state (suspension) in which the water-insoluble resin is dispersed in a solid state in an aqueous medium.

[0107] Moreover, "water-insoluble" means that the amount dissolved in 100 parts by mass of water at 25°C is 5.0 parts by mass or less.

[0108] The resin particles do not function as a dispersant for the pigment, and are present in the ink in the form of particles, and are therefore distinguishable from the dispersant used in the present disclosure.

[0109] From the viewpoint of the storage stability of the ink and the abrasion resistance of the resulting image, the content of the resin particles is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and even more preferably 1.5% by mass to 8% by mass, relative to the total mass of the ink.

[0110] Specific examples of resins contained in the resin particles are shown below, but the present disclosure is not limited thereto. In the specific examples below, n represents the number of repetitions, and the mass % indicates the content of each structural unit. The resin particles are preferably resin particles made of the resins shown in the following specific examples. In addition, although the following specific examples all describe anionic groups in an acid state, some or all of the acids may be in the form of salts.

[0111] [ka]

[0112] [ka]

[0113] [ka]

[0114] [ka]

[0115] When the ink of the present disclosure contains resin particles, the ink of the present disclosure may be prepared using a commercially available resin emulsion (i.e., an aqueous dispersion of resin particles). Examples of commercially available resin emulsions include A-810 (Sansui Co., Ltd.), A-995 (Sansui Co., Ltd.), Hi-Loss-X NE-2186 (Seiko PMC Corporation), Hi-Loss-X TE-1048 (Seiko PMC Corporation), Saivinol SK-202 (Saiden Chemical Co., Ltd.), TOCRYL W-1048 (Toyochem), WC-M-1217 (Arakawa Chemical Co., Ltd.), WC-M-1219 (Arakawa Chemical Co., Ltd.), N985(A)-1 (E-Tech Co., Ltd.), Neocryl A-1105 (DSM coating resin), Acrylit SE-810A, Acrylit SE-953A-2, Acrylit SE-1658F, Acrylit SE-2974F, Acrylit SE-2978F (Taisei Fine Chemical), and Luckstar 7132-C. (DIC), ST200 (Nippon Shokubai), Movinyl 972 (Japan Coating Resin Co., Ltd.), etc.

[0116] (wax particles) The inks of the present disclosure may contain wax particles.

[0117] The melting point of the wax constituting the wax particles is preferably 40°C or higher and 140°C or lower, more preferably 45°C or higher and 100°C or lower, and even more preferably 50°C or higher and 95°C or lower.

[0118] The wax constituting the wax particles may include natural wax and synthetic wax.

[0119] Natural waxes include petroleum-based waxes, vegetable-based waxes, and animal and vegetable-based waxes. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Examples of vegetable waxes include carnauba wax, candelilla wax, rice wax, and Japan wax. Examples of animal and vegetable waxes include lanolin and beeswax.

[0120] Examples of synthetic waxes include synthetic hydrocarbon waxes and modified waxes. Examples of synthetic hydrocarbon waxes include polyethylene wax and Fischer-Tropsch wax. Modified waxes include paraffin wax derivatives, montan wax derivatives, microcrystalline wax derivatives, and derivatives thereof.

[0121] As the wax constituting the wax particles, carnauba wax is particularly preferred from the viewpoint of further improving the abrasion resistance of the image.

[0122] Commercially available wax particles include Cellosol 524, Trasol CN, Trasol PF60, Polylon L-787, Polylon P-502 (all manufactured by Chukyo Yushi Co., Ltd.), ITOHWAX E-210 (manufactured by Ito Oil Mills Co., Ltd.), Nopcoat PEM17 (manufactured by San Nopco Ltd.), and AQUACER 515 (manufactured by BYK Japan Co., Ltd.). Further, examples of the wax particles include Ester A described in paragraph 0254 of JP-A No. 2011-162692. Among these, carnauba waxes are Cellosol 524 and Trasol CN.

[0123] For other preferred forms of wax particles (such as organic solvents and dispersion stabilizers that can be used when dispersing wax particles), the descriptions in paragraphs 0154 to 0170 of JP-A No. 2011-162692 can be appropriately referred to.

[0124] <Oxidizing agent> The inks of the present disclosure preferably contain at least one oxidizing agent. This makes it possible to further suppress etching of the ink flow path walls.

[0125] The oxidizing agent may be at least one selected from the group consisting of hydrogen peroxide and peroxides. Examples of peroxides include peracetic acid, sodium percarbonate, and urea hydrogen peroxide.

[0126] The oxidizing agent preferably contains at least one selected from the group consisting of hydrogen peroxide, peracetic acid, sodium percarbonate, and urea hydrogen peroxide. This makes it possible to further suppress etching of the ink flow path walls.

[0127] The mass ratio of the oxidizing agent content to the total content of the resin particles and wax particles is preferably 0.02 mass% to 6 mass%, more preferably 0.05 mass% to 4 mass%, and even more preferably 0.1 mass% to 2 mass%. When the content of the oxidizing agent relative to the total content of the resin particles and wax particles is 0.02 mass % or more, etching of the ink flow path walls is further suppressed. When the content of the oxidizing agent relative to the total content of the resin particles and wax particles is 6% by mass or less, the stability of the ink is further improved.

[0128] The mass ratio of the oxidizing agent content to the total amount of ink is preferably 0.001 mass % to 1 mass %, and more preferably 0.01 mass % to 0.1 mass %. When the content of the oxidizing agent relative to the total amount of ink is 0.001 mass % or more, etching of the ink flow path wall is further suppressed. When the content of the oxidizing agent relative to the total amount of the ink is 1 mass % or less, the stability of the ink is further improved.

[0129] <Colloidal silica> The ink of the present disclosure preferably contains at least one type of colloidal silica. This further suppresses etching of the ink flow path walls.

[0130] Colloidal silica is a colloid made up of fine particles of inorganic oxides containing silicon. Colloidal silica contains silicon dioxide (including its hydrate) as a major component, and may contain aluminate as a minor component. Aluminates that may be included as minor components include sodium aluminate and potassium aluminate. Colloidal silica may also contain inorganic salts such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonium hydroxide, and organic salts such as tetramethylammonium hydroxide, etc. These inorganic salts and organic salts act, for example, as colloid stabilizers.

[0131] The dispersion medium for colloidal silica is not particularly limited, and may be any of water, an organic solvent, and a mixture thereof. The organic solvent may be either a water-soluble organic solvent or a water-insoluble organic solvent, but is preferably a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include methanol, ethanol, isopropyl alcohol, and n-propanol.

[0132] There are no particular limitations on the method for producing colloidal silica, and it can be produced by a commonly used method. For example, aerosil synthesis by thermal decomposition of silicon tetrachloride or production from water glass can be used. Alternatively, it can be produced by a liquid phase synthesis method such as hydrolysis of alkoxide (see, for example, "Sen-i to Kogyo," Vol. 60, No. 7 (2004) p. 376).

[0133] The volume average particle size of the colloidal silica may satisfy a particle size ratio [colloidal silica / titanium dioxide particles] of 0.04 or less. From the viewpoint of more effectively suppressing wear and deterioration of the inkjet head, the volume average particle diameter of the colloidal silica is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 25 nm or less, and still more preferably 20 nm or less. The lower limit of the volume average particle size of the colloidal silica is, for example, 1 nm or 3 nm.

[0134] The volume average particle size of the colloidal silica is determined by dynamic light scattering. As an apparatus for measuring the volume average particle size by dynamic light scattering, for example, Nanotrac UPA manufactured by Microtrac Co., Ltd. is used.

[0135] The shape of the colloidal silica is not particularly limited as long as it does not impair the ink ejection performance. For example, it may be spherical, elongated, needle-like, or bead-like. Among these, a spherical shape is preferred from the viewpoint of ink ejection performance.

[0136] The colloidal silica may be manufactured or commercially available. Specific examples of commercially available products include: Ludox AM, Ludox AS, Ludox LS, Ludox TM, Ludox HS, etc. (all manufactured by EI Du Pont de Nemouvs & Co.); Snowtex S, Snowtex XS, Snowtex 20, Snowtex 30, Snowtex 40, Snowtex N, Snowtex C, Snowtex O, etc. (all manufactured by Nissan Chemical Industries, Ltd.); Syton C-30, SytonZOO, etc. (all manufactured by Mons anto Co); Nalcoag-1060, Nalcoag-ID21~64 (all manufactured by Nalco Chem Co); Methanol sol, IPA sol, MEK sol, and toluene sol (all manufactured by Fuso Chemical Co., Ltd.); Cataloid-S, Cataloid-F120, Cataloid SI-350 , Cataloid SI-500, Cataloid SI-30, Cataloid S-20L, Cataloid S-20H, Cataloid S-30L, Catal oid S-30H, Cataloid SI-40, OSCAL-1432 (isopropyl alcohol sol), etc. (all manufactured by JGC Catalysts and Chemicals); Adelite (manufactured by Asahi Denka Co., Ltd.); etc. Other examples of the beaded colloidal silica include those commercially available under the trade names Snowtex ST-UP, Snowtex PS-S, Snowtex PS-M, Snowtex ST-OUP, Snowtex PS-SO, and Snowtex PS-MO (all manufactured by Nissan Chemical Industries, Ltd.).

[0137] From the viewpoint of further suppressing etching of the ink flow path walls, the solid content of colloidal silica is preferably 0.01% by mass to 5% by mass, more preferably 0.01% by mass to 2% by mass, and even more preferably 0.01% by mass to 1% by mass, relative to the total amount of ink.

[0138] <Organic solvents> From the viewpoint of ink ejection properties, the ink of the present disclosure preferably contains an organic solvent.

[0139] From the viewpoint of ink ejection properties, the content of the organic solvent is preferably 2.5% by mass or more relative to the total amount of the ink. The upper limit of the organic solvent content is not particularly limited, but from the viewpoint of ink drying properties, it is preferably 30% by mass.

[0140] The organic solvent is preferably an organic solvent having a ClogP value of 1.0 to 3.5. When the ClogP value of the organic solvent is 1.0 or more, the hydrophobicity is not too low, which is preferable from the viewpoint of suppressing interference of ink landing and improving the graininess of the image. When the ClogP value of the organic solvent is 3.5 or less, the hydrophobicity is not too high, and therefore the ejection property is excellent.

[0141] The organic solvents include: At least one compound selected from the group consisting of compounds represented by the following formula 1 and compounds represented by formula 2 is preferred: More preferred is an organic solvent that is at least one of the above and has a ClogP value of 1.0 to 3.5.

[0142] [ka]

[0143] In Formula 1 or Formula 2, R 1 each independently represents a hydrogen atom or a methyl group, R 2 each independently represents a linear or branched hydrocarbon group having 4 to 9 carbon atoms or an aryl group having 6 to 10 carbon atoms; and n represents an integer of 1 to 3.

[0144] In formula 1, R 1 is preferably a hydrogen atom from the viewpoint of reducing the surface tension of the ink.

[0145] In formula 1, n is preferably 1 or 2 from the viewpoint of reducing the surface tension of the ink.

[0146] In Formula 1 and Formula 2, R 2 Examples of the linear or branched hydrocarbon group having 4 to 9 carbon atoms represented by the formula (I) include an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, and a 2-ethylhexyl group.

[0147] In Formula 1 and Formula 2, R 2 Examples of the aryl group having 6 to 10 carbon atoms represented by the formula (I) include a phenyl group, a p-toluyl group, an m-toluyl group, a 2,6-dimethylphenyl group, a 4-t-butylphenyl group, a 4-methoxyphenyl group, a 4-butoxyphenyl group, a 2-chlorophenyl group, and a naphthyl group.

[0148] Examples of organic solvents represented by Formula 1 or Formula 2 and having a ClogP value of 1.0 to 3.5 include: Ethylene glycol monopentyl ether, ethylene glycol monohexyl ether, ethylene glycol monoheptyl ether, ethylene glycol monooctyl ether ethylene glycol monoalkyl ethers such as ethylene glycol monononyl ether and ethylene glycol mono-2-ethylhexyl ether; diethylene glycol monoalkyl ethers such as diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, diethylene glycol monooctyl ether, diethylene glycol monononyl ether, and diethylene glycol mono-2-ethylhexyl ether; triethylene glycol monoalkyl ethers such as triethylene glycol monopentyl ether, triethylene glycol monohexyl ether, triethylene glycol monoheptyl ether, triethylene glycol monooctyl ether, triethylene glycol monononyl ether, and triethylene glycol mono-2-ethylhexyl ether; propylene glycol monoalkyl ethers such as propylene glycol monobutyl ether, propylene glycol monopentyl ether, propylene glycol monohexyl ether, propylene glycol monoheptyl ether, propylene glycol monooctyl ether, and propylene glycol mono-2-ethylhexyl ether; dipropylene glycol monoalkyl ethers such as dipropylene glycol monobutyl ether, dipropylene glycol monopentyl ether, dipropylene glycol monohexyl ether, dipropylene glycol monoheptyl ether, dipropylene glycol monooctyl ether, and dipropylene glycol mono-2-ethylhexyl ether; Tripropylene glycol monoalkyl ethers such as tripropylene glycol monobutyl ether, tripropylene glycol monopentyl ether, tripropylene glycol monohexyl ether, tripropylene glycol monoheptyl ether, tripropylene glycol monooctyl ether, and tripropylene glycol mono-2-ethylhexyl ether; and Examples of the alkanediol include 1,2-heptanediol, 1,2-octanediol, 1,2-nonanediol, and 1,2-decanediol.

[0149] Among them, organic solvents that can be contained in the ink include: Preferably, the alkyl group is an ethylene glycol monoalkyl ether, a diethylene glycol monoalkyl ether, or an alkanediol; Ethylene glycol monohexyl ether, diethylene glycol monohexyl ether (hexyldiglycol), diethylene glycol mono-2-ethylhexyl ether or 1,2-octanediol It is more preferable that:

[0150] Further, examples of organic solvents that can be contained in the ink of the present disclosure include the solvents described in paragraphs 0142 to 0154 of JP-A No. 2015-180710.

[0151] <Dispersant> The inks of the present disclosure may contain at least one dispersant. In the present disclosure, a dispersant has the function of dispersing a pigment. The dispersant adsorbs to the surface of the pigment and coats at least a portion of the surface of the pigment, making the pigment more easily dispersible in a dispersion medium (e.g., water, a mixture of water and an organic solvent, etc.).

[0152] From the viewpoint of improving the ejection properties of the ink, the dispersant is preferably crosslinked. It is believed that the dispersant is present in the ink by being partially adsorbed onto the surface of the pigment and partially desorbed from the surface of the pigment. When the dispersant is crosslinked, it is thought that the dispersant is less likely to be released from the surface of the pigment, thereby improving the ejection properties of the ink.

[0153] Whether or not a dispersant is crosslinked can be determined, for example, by the following method. After centrifuging the ink at 10,000 rpm for 30 minutes, the settled pigment dispersion is extracted with a highly polar organic solvent, and the components are analyzed by spectroscopy or nuclear magnetic resonance (NMR) to identify the dispersant structure and the content ratio of the constituent monomers. The highly polar organic solvent used here is selected appropriately depending on the type of polymer to be extracted.

[0154] From the viewpoint of dispersion stability of the ink, the dispersant is preferably a polymer. The structure of the dispersant is not particularly limited, and may be any of a random polymer, a block polymer, and a graft polymer.

[0155] More preferably, the dispersant is a crosslinked polymer (hereinafter also referred to as a "crosslinked polymer"). A crosslinked polymer is formed, for example, by crosslinking an uncrosslinked polymer with a crosslinking agent. In this case, it is preferable to first prepare a pigment dispersion containing an uncrosslinked polymer and a pigment, and then crosslink the uncrosslinked polymer in the uncrosslinked pigment dispersion with a crosslinking agent to form a crosslinked polymer (i.e., obtain a pigment dispersion containing a crosslinked polymer and a pigment). The uncrosslinked polymer is preferably a water-soluble polymer.

[0156] In the present disclosure, the term "water-soluble" in "water-soluble polymer" means that the polymer dissolves in distilled water at 25° C. to a degree of 2% by mass or more. The water-soluble resin preferably dissolves in distilled water at 25° C. to a degree of 5% by mass or more, and more preferably to a degree of 10% by mass or more.

[0157] Examples of the uncrosslinked polymer include polyvinyl, polyurethane, and polyester. Among them, the uncrosslinked polymer is preferably polyvinyl.

[0158] The uncrosslinked polymer is preferably a polymer having a functional group that can be crosslinked by a crosslinking agent. Examples of the crosslinkable functional group include a carboxy group or a salt thereof, an isocyanate group, and an epoxy group. Among these, from the viewpoint of improving the dispersibility of the pigment, the crosslinkable functional group is preferably a carboxy group or a salt thereof, and more preferably a carboxy group.

[0159] The polymer having a carboxy group is preferably a copolymer containing a structural unit derived from a monomer containing a carboxy group (hereinafter referred to as a "carboxy group-containing monomer"). The structural unit derived from the carboxy group-containing monomer contained in the copolymer may be of one type only, or may be of two or more types. The copolymer may be a random copolymer or a block copolymer.

[0160] Examples of carboxy group-containing monomers include (meth)acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, and crotonic acid.

[0161] From the viewpoint of crosslinkability and dispersibility, the carboxy group-containing monomer is preferably (meth)acrylic acid or β-carboxyethyl acrylate, and more preferably (meth)acrylic acid.

[0162] The copolymer preferably contains structural units derived from hydrophobic monomers in addition to structural units derived from carboxyl group-containing monomers. The structural units derived from hydrophobic monomers contained in the copolymer may be of one type or two or more types.

[0163] Examples of the hydrophobic monomer include (meth)acrylates having an alkyl group with 1 to 20 carbon atoms and (meth)acrylates having an aromatic ring.

[0164] The polymer having a carboxy group is preferably a copolymer containing a structural unit derived from a carboxy group-containing monomer and at least one selected from the group consisting of a structural unit derived from a (meth)acrylate having an alkyl group with 1 to 20 carbon atoms and a structural unit derived from a (meth)acrylate having an aromatic ring, more preferably a copolymer containing a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylate having an aromatic ring, and particularly preferably a copolymer containing a structural unit derived from (meth)acrylic acid and a structural unit derived from benzyl (meth)acrylate.

[0165] The acid value of the uncrosslinked polymer is preferably from 67 mgKOH / g to 200 mgKOH / g, more preferably from 67 mgKOH / g to 150 mgKOH / g, from the viewpoint of pigment dispersibility.

[0166] Moreover, the acid value of the crosslinked polymer is preferably 55 mgKOH / g to 100 mgKOH / g from the viewpoint of pigment dispersibility.

[0167] The weight average molecular weight (Mw) of the uncrosslinked polymer is not particularly limited, but from the viewpoint of pigment dispersibility, it is preferably 3,000 to 100,000, more preferably 5,000 to 80,000, and even more preferably 10,000 to 60,000.

[0168] The preferred range of the weight average molecular weight of the crosslinked polymer is the same as the preferred range of the weight average molecular weight of the uncrosslinked polymer.

[0169] The crosslinking agent used to crosslink the uncrosslinked polymer is preferably a compound having two or more reactive sites with the uncrosslinked polymer (e.g., a polymer having a carboxy group). Only one type of crosslinking agent may be used, or two or more types may be used.

[0170] A preferred combination of a crosslinking agent and an uncrosslinked polymer is a combination of a compound having two or more epoxy groups (i.e., a bifunctional or higher epoxy compound) and a polymer having a carboxy group. In this combination, a crosslinked structure is formed by reaction between the epoxy group and the carboxy group. This results in a crosslinked polymer. The formation of a crosslinked structure by the crosslinking agent is preferably carried out after the pigment has been dispersed by the uncrosslinked polymer.

[0171] Examples of difunctional or higher functional epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

[0172] Among these, the difunctional or higher epoxy compound is preferably polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether.

[0173] The crosslinking agent may be a commercially available product. Commercially available products include, for example, Denacol EX-321, EX-821, EX-830, EX-850 and EX-851 (manufactured by Nagase ChemteX Corporation).

[0174] The molar ratio of reactive sites (e.g., epoxy groups) in the crosslinking agent to reactive sites (e.g., carboxy groups) in the uncrosslinked polymer is preferably 1:1.1 to 1:10, more preferably 1:1.1 to 1:5, and even more preferably 1:1.1 to 1:3, from the viewpoints of the crosslinking reaction rate and dispersion stability after crosslinking.

[0175] The mixing ratio of the pigment to the dispersant is preferably 1:0.06 to 1:3, more preferably 1:0.125 to 1:2, and even more preferably 1:0.125 to 1:1.5, on a mass basis.

[0176] <Silicone surfactants> The inks of the present disclosure may contain at least one silicone surfactant. The silicone surfactant is preferably a compound having a polysiloxane structure in its molecule. When the ink contains a silicone surfactant, the ink ejection properties are improved. This is thought to be because when the ink contains a silicone surfactant, the ink is less likely to adhere to the nozzles from which the ink is ejected.

[0177] Examples of silicone surfactants include compounds in which an organic group is introduced into a part of dimethylpolysiloxane. The organic group is introduced into a side chain, one end, both ends, or both the side chain and the end of the dimethylpolysiloxane.

[0178] Examples of dimethylpolysiloxanes into which an organic group has been introduced include modified silicone compounds such as amine-modified silicones, alcohol-modified silicones, polyether-modified silicones, and long-chain alkyl-modified silicones. Among these, from the viewpoint of improving the ejection properties of the ink, the silicone surfactant is preferably a polyether-modified silicone.

[0179] The silicone surfactant is preferably a compound having a molecular weight of 200 to 2000 and a structure represented by the following formula 4.

[0180] [ka]

[0181] In formula 4, R 4 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and x, y, and z each independently represent an integer of 1 or more. * represents the bonding position to other structures in the molecule.

[0182] In formula 4, R 4 is preferably a hydrogen atom or a methyl group.

[0183] The molecular weight of the silicone surfactant is 200 to 2000, and preferably 400 to 1800. A silicone surfactant with a molecular weight of 200 to 2000 is easily oriented at the interface, improving the ejection properties.

[0184] The content of the silicone surfactant is preferably 0.03% to 0.8% by mass, more preferably 0.04% to 0.5% by mass, and even more preferably 0.05% to 0.3% by mass, relative to the total mass of the ink.

[0185] <Acetylene glycol surfactant> The ink of the present disclosure may contain at least one acetylene glycol surfactant. The acetylene glycol surfactant may be an acetylene glycol surfactant represented by the following formula 6.

[0186] [ka]

[0187] In formula 6, R 52 , R 53 , R 54 , and R 55 Y each independently represents a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 8 carbon atoms. 2 and Y 3 each independently represents an alkylene group having 2 to 6 carbon atoms; x and y represent the average number of moles added; and 1≦x +y≦85.

[0188] R 52 and R 54 Examples of the linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms represented by the formula (R) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a 2-butyl group, a t-butyl group, a hexyl group, a cyclohexyl group, and an octyl group. 52 and R 54 When R represents a cyclic alkyl group, the alkyl group preferably has 3 to 8 carbon atoms. 52 and R 54 is an alkyl group having 1 to 3 carbon atoms. A group is preferred, and a methyl group is most preferred.

[0189] R 53 and R 55 Examples of the linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms represented by the formula (R) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a 2-butyl group, a t-butyl group, a hexyl group, a cyclohexyl group, and an octyl group. 53 and R 55 When R represents a cyclic alkyl group, the alkyl group preferably has 3 to 8 carbon atoms. 53 and R 55 is preferably a linear, branched, or cyclic alkyl group having 3 to 8 carbon atoms, and is particularly preferably an isobutyl group.

[0190] The sum of x and y is 1 to 85 (1≦x+y≦85), and is preferably 3 to 50. It is preferable that the sum of x and y is 3 to 30, and it is even more preferable that the sum of x and y is 3 or more, and the solubility is further improved and the cloud point is higher. This further suppresses separation, precipitation, etc. when the moisturizing liquid is heated to 30°C or higher. On the other hand, when the sum of x and y is 30 or less, the effect of lowering the surface tension and improving the wettability is more effectively manifested. This further improves the ejection properties of the ejected ink when the ink filled with the moisturizing liquid is ejected.

[0191] Y 2 and Y 3 are each independently preferably an alkylene group having 2 to 4 carbon atoms, An alkylene group having 2 or 3 carbon atoms is more preferred, and an alkylene group having 2 carbon atoms (ethylene group) is particularly preferred. That is, among the compounds represented by formula 6, acetylene glycol represented by the following formula 7 is preferred. Coal-based surfactants are more preferred.

[0192] [ka]

[0193] In Equation 7, R 52 , R 53 , R 54 , R 55 , x, and y are R in Equation 6 52 , R 53 , R 54 , R 55 , x, and y have the same meanings, and the preferred ranges thereof are also the same.

[0194] The acetylene glycol surfactant represented by formula 6 includes alkylene oxide adducts (preferably 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 2,5-dimethyl-3-hexyne-2,5-diol, etc. In particular, the acetylene glycol surfactant represented by formula 6 is an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Preferably, it is an ethylene oxide adduct (3≦x+y≦30, preferably 5≦x+y≦30).

[0195] The acetylene glycol surfactant represented by formula 6 may be a commercially available product. Commercially available products include the Surfynol series (e.g., Surfynol 420, Surfynol 440, Surfynol 465, and Surfynol 485), the Olfine series (e.g., Olfine E1010 and Olfine E1020), and the Dynol series (e.g., Dynol 604), all manufactured by Air Products Co., Ltd. or Nissin Chemical Industry Co., Ltd., and Acetylenol manufactured by Kawaken Fine Chemicals Co., Ltd. Furthermore, commercially available products are also provided by The Dow Chemical Company, General Aniline Company, etc.

[0196] The content of the acetylene glycol surfactant is preferably 0.03% to 5% by mass, more preferably 0.04% to 4% by mass, and even more preferably 0.05% to 3% by mass, relative to the total amount of the ink.

[0197] <Cellulose nanofiber> The ink of the present disclosure preferably contains at least one type of cellulose nanofiber. By including cellulose nanofibers in the ink of the present disclosure, the viscosity of the ink can be effectively increased, which is expected to improve the ink ejection properties.

[0198] Cellulose nanofibers are nanocellulose extracted from cellulose sources (e.g., wood). Methods for extracting cellulose nanofibers include, for example, mechanical treatment (for example, pulverization treatment using a bead mill) and chemical treatment (for example, TEMPO-catalyzed oxidation treatment, carboxymethylation treatment, cationization treatment, etc.).

[0199] The cellulose nanofibers that can be contained in the ink of the present disclosure can improve the filterability of the ink (i.e., the ability to inhibit clogging of the filter when the ink passes through the filter; the same applies hereinafter). From the viewpoint of further improving the above, it is preferable that the composition contains TEMPO-oxidized cellulose nanofibers (i.e., nanocellulose extracted by TEMPO-catalyzed oxidation treatment). Here, TEMPO means 2,2,6,6-tetramethyl-1-piperidine-oxy radical.

[0200] As the cellulose nanofibers, commercially available products may be used. Commercially available cellulose nanofibers include: "LeoCrysta" (registered trademark) manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; "Cellenpia" (registered trademark) manufactured by Nippon Paper Industries Co., Ltd.; Sugino Machine's IMa-10002, BMa-10002, WMa-10002, AMa-10002, FMa-10002; "ELEX" manufactured by Daio Paper Corporation; "Aurovisco" (registered trademark) manufactured by Oji Paper Co., Ltd.; etc.

[0201] The average fiber width of the cellulose nanofibers is preferably 1 nm or more and 20 nm or less, more preferably 1 nm or more and 10 nm or less. When the average fiber width of the cellulose nanofibers is 20 nm or less, the filterability of the ink is further improved. In the present disclosure, the average fiber width of cellulose nanofibers is determined by measuring the fiber widths of 10 cellulose nanofibers by scanning electron microscope observation and then calculating the arithmetic mean of the measured fiber widths of the 10 fibers.

[0202] The average fiber length of the cellulose nanofibers is preferably 10 nm or more and 1000 nm or less, more preferably 100 nm or more and 900 nm or less, even more preferably 100 nm or more and 600 nm or less, and even more preferably 200 nm or more and 400 nm or less. When the average fiber length of the cellulose nanofibers is 1000 nm or less, the filterability of the ink is further improved. In the present disclosure, the average fiber length of cellulose nanofibers is determined by measuring the fiber lengths of 10 cellulose nanofibers by scanning electron microscope observation and then calculating the arithmetic mean of the measured fiber lengths of the 10 fibers.

[0203] The average aspect ratio of the cellulose nanofibers is preferably 100 or more and 400 or less, more preferably 100 or more and 300 or less, from the viewpoint of further improving the effect of increasing the viscosity of the ink and the filterability of the ink. In the present disclosure, the average aspect ratio of cellulose nanofibers is determined by measuring the aspect ratios (i.e., ratio [fiber length / fiber width]) of 10 cellulose nanofibers by scanning electron microscope observation and then calculating the arithmetic average of the measured aspect ratios for the 10 fibers.

[0204] The mass ratio of the cellulose nanofiber content to the total content of the resin particles and wax particles is preferably 1.00 mass% to 10.00 mass%, more preferably 2.00 mass% to 8.00 mass%, and even more preferably 3.00 mass% to 6.00 mass%. When the content of cellulose nanofibers relative to the total content of resin particles and wax particles is 1.00 mass % or more, the viscosity of the ink can be increased more effectively. When the content of cellulose nanofibers relative to the total content of resin particles and wax particles is 10.00 mass %, the filter suitability of the ink can be further improved.

[0205] The mass ratio of the cellulose nanofiber content to the total amount of ink is preferably 0.01 mass % to 1.00 mass %, more preferably 0.03 mass % to 0.50 mass %, and even more preferably 0.05 mass % to 0.40 mass %. When the content of cellulose nanofibers relative to the total amount of ink is 0.01 mass % or more, the viscosity of the ink can be increased more effectively. When the content of cellulose nanofibers relative to the total amount of ink is 1.00 mass % or less, the filter suitability of the ink can be further improved.

[0206] <Other ingredients> The ink of the present disclosure may contain other components in addition to the components described above. Other components include surfactants other than silicone surfactants and acetylene glycol surfactants. Other components include preservatives, ultraviolet absorbers, anti-fading agents, antifungals, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents (e.g., the antifoaming agents described in paragraph 0159 of JP-A 2015-180710), viscosity modifiers, dispersion stabilizers, chelating agents, solid wetting agents (e.g., urea), and water-soluble polymers (e.g., the water-soluble polymers described in paragraph 0139 of JP-A 2015-180710).

[0207] <Ink properties> (dynamic surface tension) The ink of the present disclosure preferably has a dynamic surface tension of 35 mN / m or less at 10 milliseconds. This improves the quality of images printed with the ink. This is thought to be because the dynamic surface tension at 10 milliseconds is 35 mN / m or less, which reduces the surface tension of the ink, suppresses impact interference, and improves the wetting and spreading properties of the ink. Although there are no particular restrictions on the lower limit of the dynamic surface tension at 10 milliseconds, it is preferably 15 mN / m from the viewpoint of ink storage stability.

[0208] In this disclosure, the dynamic surface tension at 10 milliseconds is measured by the maximum bubble pressure method in an environment of 23°C and 55% relative humidity. The dynamic surface tension at 10 milliseconds is measured using, for example, a bubble pressure type dynamic surface tensiometer (product name "BP100", manufactured by KRUSS). The dynamic surface tension at 10 milliseconds is the surface tension calculated from the maximum bubble pressure when bubbles are continuously ejected from a probe tube inserted into ink and the time from when a new interface is generated at the tip of the probe tube (0 milliseconds) to when the maximum bubble pressure is reached is 10 milliseconds.

[0209] The dynamic surface tension of ink ejected from a nozzle begins to decrease the moment it is ejected and continues to decrease after it lands on the recording medium, eventually converging to the static surface tension of the ink. The rate of decrease in dynamic surface tension is greatest immediately after ejection and gradually decreases as time passes. Therefore, if ink droplet A lands on a recording medium and then ink droplet B lands on the recording medium, the dynamic surface tension of ink droplet A will be lower than that of ink droplet B at the time ink droplet B lands. If the dynamic surface tensions of the two ink droplets are different, interference is likely to occur between the ink droplet A that lands first and the ink droplet B that lands later. Specifically, ink droplet A, which has a relatively low dynamic surface tension, is attracted to ink droplet B, which has a relatively high dynamic surface tension, resulting in uneven image density. However, uneven density results in a rough image, which in turn results in poor image graininess.

[0210] The dynamic surface tension at 10 milliseconds is the dynamic surface tension at the moment when the ink droplet hits the recording medium. This is the closest value. If the dynamic surface tension at 10 milliseconds is 35 mN / m or less, the ink droplets spread out on the recording medium, suppressing impact interference. This reduces unevenness in image density and allows for the production of images with excellent graininess.

[0211] (viscosity) In the ink of the present disclosure, the viscosity measured at 30°C and 100 revolutions per minute (rpm) is preferably from 1.2 mPa·s to 15.0 mPa·s, more preferably from 2.0 mPa·s to 13.0 mPa·s or less, even more preferably from 2.5 mPa·s to 10.0 mPa·s or less, and even more preferably from 3.8 mPa·s to 6.0 mPa·s, from the viewpoint of ink ejection properties.

[0212] The viscosity is measured using a rotational viscometer. As the rotational viscometer, for example, "VISCOMETER TV-22" (manufactured by TOKI SANGYO CO., LTD) is used.

[0213] [Image Recording Method] The image recording method of the present disclosure includes a step of applying the ink of the present disclosure described above onto a recording medium by ejecting it from an inkjet head containing silicon onto the ink flow path walls (hereinafter also referred to as the "ink application step"). The image recording method of the present disclosure uses the ink of the present disclosure and the inkjet head, and therefore, the image recording method of the present disclosure can suppress etching of the ink flow path walls containing silicon in the inkjet head.

[0214] The image recording method of the present disclosure may, as needed, a step of drying the water and organic solvent contained in the ink applied onto the recording medium (hereinafter also referred to as the "ink drying step"); A process of melting and fixing the resin particles contained in the ink (hereinafter also referred to as the "thermal fixing process"); Other steps such as the above may also be included.

[0215] The image recording method of the present disclosure is preferably a method of recording an image by directly applying the ink of the present disclosure onto a recording medium, that is, the image recording method of the present disclosure is preferably a so-called one-liquid system.

[0216] <Ink application process> In the ink application step, the ink of the present disclosure is applied onto a recording medium by being ejected from an inkjet head having ink flow path walls containing silicon, thereby recording an image using the ink of the present disclosure.

[0217] The recording medium is not particularly limited, and examples thereof include coated paper used in general offset printing. Coated paper is a type of paper in which a coating material is applied to the surface of cellulose-based high-quality paper, neutral paper, or the like that is generally not surface-treated, to form a coating layer.

[0218] Coated paper is commercially available, and examples of coated paper include coated papers (A2, B2) such as "OK Top Coat+" manufactured by Oji Paper Co., Ltd., and "Aurora Coat" and "U-Lite" manufactured by Nippon Paper Industries Co., Ltd., and art papers (A1) such as "Tokubishi Art" manufactured by Mitsubishi Paper Mills, Ltd.

[0219] The ink is ejected and applied to the recording medium using a normal ink jet recording method. This can be done. Examples of inkjet recording methods include: A charge control method that uses electrostatic attraction to eject ink. Drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, An acoustic inkjet method in which an electrical signal is converted into an acoustic beam, which is irradiated onto the ink and ejects the ink using radiation pressure; and Thermal inkjet method: Heats ink to form bubbles, which then generate pressure. Examples include:

[0220] Generally, image recording methods using inkjet recording devices include a shuttle scan method (also called a "serial head method"), which uses a short serial head to record images, and a single pass method (also called a "line head method"), which uses a line head in which recording elements are arranged to cover the entire width of the recording medium to record images. In the shuttle scan method, an image is recorded while scanning a serial head in the width direction of a recording medium. In contrast, the single-pass method allows for image recording over the entire surface of a recording medium by scanning the recording medium in a direction perpendicular to the direction in which the recording elements are arranged. Therefore, unlike the shuttle scan method, the single-pass method does not require a transport system such as a carriage for scanning the serial head. Furthermore, the single-pass method does not require complex scanning control of the carriage movement and the recording medium, and only the recording medium moves, allowing for faster recording speeds compared to the shuttle scan method.

[0221] From the viewpoint of maintaining image quality, the volume of ink droplets ejected from the inkjet head is preferably 1 pL (picoliter) to 10 pL, and more preferably 1.5 pL to 6 pL. Note that the volume of ink droplets ejected at one time from one nozzle by the inkjet recording method.

[0222] When the inkjet head has a nozzle surface on which nozzles that eject ink are arranged, the inkjet head may have a moisture retention cap that covers the nozzle surface and forms a moisture retention space between the nozzle surface and the nozzle surface. A moisture retention liquid can be stored inside the moisture retention cap to increase the humidity of the moisture retention space.

[0223] The moisturizing liquid may contain an acetylene glycol surfactant, water, and a preservative.

[0224] <Ink drying process> The image recording method of the present disclosure may include an ink drying step as needed. The ink drying step is a step of drying the water and organic solvent contained in the ink applied onto the recording medium. The heating means is not particularly limited as long as it can dry the water and organic solvent contained in the ink, and examples thereof include a heat drum, hot air, an infrared lamp, a heat oven, and a heat plate. The heating temperature and heating time are adjusted appropriately depending on the contents of water and organic solvent contained in the ink.

[0225] <Heat fixing process> The image recording method of the present disclosure may, if necessary, include a heat fixing step after the ink application step. The thermal fixing step is a step of melting and fixing resin particles contained in the ink. The thermal fixing step fixes the image on the recording medium, thereby improving the scratch resistance of the image. For example, the thermal fixing step is described in paragraphs 0112 to 0113 of JP-A-2010-221415. 20. The heat fixing step described in 20 can be employed.

[0226] <Processing liquid application step> The image recording method of the present disclosure may include a treatment liquid application step of applying a treatment liquid containing water and a flocculant to the surface of the recording medium onto which the ink is to be applied, prior to the ink application step. In this case, in the ink application step, the ink of the present disclosure is applied onto the area of ​​the recording medium onto which the treatment liquid has been applied. This is advantageous in terms of the quality (for example, definition) of the resulting image, since the components in the ink can be aggregated by the aggregating agent in the treatment liquid that has been applied in advance.

[0227] (Processing liquid) For details about the treatment liquid, refer to the description in paragraphs 0176 to 0198 of JP-A No. 2015-180710. From the viewpoint of the ink aggregation rate, the pH of the treatment liquid at 25° C. is preferably 0.1 to 4.0, and more preferably 0.2 to 2.0.

[0228] The treatment liquid contains water. The content of water relative to the total amount of the treatment liquid is preferably 50% by mass or more, and more preferably 60% by mass or more. The upper limit of the water content relative to the total amount of the treatment liquid is, for example, 90 mass % or 80 mass %, although it depends on the amounts of other components such as the coagulant.

[0229] The treatment liquid contains a flocculant. The treatment liquid preferably contains at least one acidic compound as a flocculant. As the acidic compound used as the flocculant, either an organic acidic compound or an inorganic acidic compound may be used, and two or more organic acidic compounds and inorganic acidic compounds may be used in combination.

[0230] The organic acidic compound includes an organic compound having an acidic group. Examples of the acidic group include a phosphate group, a phosphonate group, a phosphinate group, a sulfate group, a sulfonic acid group, a sulfinic acid group, and a carboxy group. Of these, a phosphate group or a carboxy group is preferred, and a carboxy group is more preferred.

[0231] Preferred organic compounds having a carboxy group (organic carboxylic acids) include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, phthalic acid, 4-methylphthalic acid, lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, or derivatives of these compounds, or salts thereof (e.g., polyvalent metal salts), etc. These compounds may be used alone or in combination of two or more. The organic carboxylic acid is preferably a divalent or higher carboxylic acid (hereinafter also referred to as a polycarboxylic acid), more preferably at least one selected from the group consisting of malonic acid, malic acid, maleic acid, succinic acid, glutaric acid, fumaric acid, tartaric acid, 4-methylphthalic acid, and citric acid, and particularly preferably at least one selected from the group consisting of malonic acid, malic acid, tartaric acid, and citric acid.

[0232] Examples of inorganic acidic compounds include phosphoric acid, nitric acid, nitrous acid, sulfuric acid, and hydrochloric acid, with phosphoric acid being particularly preferred.

[0233] There is no particular limit to the total amount of acidic compounds contained in the treatment liquid, but from the viewpoint of the ink coagulation speed, Therefore, the content is preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass. The content ratio of the organic acidic compound to the inorganic acidic compound is preferably 5 mol% to 50 mol%, more preferably 10 mol% to 40 mol%, and even more preferably 15 mol% to 35 mol%, in terms of the inorganic acidic compound content relative to the organic acidic compound content.

[0234] The treatment liquid may contain other flocculating components such as polyvalent metal salts and cationic polymers as the flocculant instead of or in addition to the acidic compound. As for the polyvalent metal salt and cationic polymer, for example, the polyvalent metal salts and cationic polymers described in paragraphs 0155 to 0156 of JP-A No. 2011-042150 can be used.

[0235] -Water-soluble polymer compounds- The treatment liquid preferably contains at least one water-soluble polymer compound. The water-soluble polymer compound is not particularly limited, and known water-soluble polymer compounds such as polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, and polyethylene glycol can be used. Furthermore, the water-soluble polymer compound may preferably be a specific polymer compound described below or the water-soluble polymer compounds described in paragraphs 0026 to 0080 of JP-A No. 2013-001854.

[0236] There are no particular limitations on the weight-average molecular weight of the water-soluble polymer compound, but it can be, for example, 10,000 to 100,000, preferably 20,000 to 80,000, and more preferably 30,000 to 80,000.

[0237] Furthermore, the content of the water-soluble polymer compound in the treatment liquid of the present invention is not particularly limited, but is preferably 0.1% by mass to 10% by mass, more preferably 0.1% by mass to 4% by mass, even more preferably 0.1% by mass to 2% by mass, and particularly preferably 0.1% by mass to 1% by mass, relative to the total amount of the treatment liquid. A content of 0.1% by mass or more can further promote the spreading of ink droplets, and a content of 10% by mass or less can further suppress thickening of the treatment liquid.Furthermore, a content of 10% by mass or less can further suppress uneven application of the treatment liquid due to bubbles in the treatment liquid.

[0238] The water-soluble polymer compound is preferably a polymer compound (hereinafter also referred to as a "specific polymer compound") containing a hydrophilic structural unit having an ionic group (preferably an anionic group), which can further promote the spreading of ink droplets applied to a recording medium and further suppress roughness in the image. Examples of the ionic group in the specific polymer compound include a carboxyl group, a sulfonic acid group, a phosphate group, a boronic acid group, an amino group, an ammonium group, or a salt thereof. Among these, a carboxyl group, a sulfonic acid group, a phosphate group, or a salt thereof is preferred, a carboxyl group, a sulfonic acid group, or a salt thereof is more preferred, and a sulfonic acid group or a salt thereof is even more preferred. As the hydrophilic structural unit having an ionic group (preferably an anionic group), a structural unit derived from a (meth)acrylamide compound having an ionic group (preferably an anionic group) is preferred. The content of the hydrophilic structural unit having an ionic group (preferably an anionic group) in the water-soluble polymer compound can be, for example, 10% by mass to 100% by mass, preferably 10% by mass to 90% by mass, more preferably 10% by mass to 70% by mass, and even more preferably 10% by mass to 50% by mass, based on the total mass of the water-soluble polymer compound. It is preferable that the content is 20% by mass to 40% by mass.

[0239] The specific polymer compound more preferably contains at least one hydrophobic structural unit in addition to at least one hydrophilic structural unit having an ionic group (preferably an anionic group, particularly preferably a sulfonic acid group) as described above. By containing a hydrophobic structural unit, the specific polymer compound is more likely to be present on the surface of the treatment liquid, which further promotes the spreading of ink droplets applied to the recording medium and further suppresses roughness in the image. The hydrophobic structural unit is preferably a structural unit derived from a (meth)acrylic acid ester (preferably an alkyl ester of (meth)acrylic acid having 1 to 4 carbon atoms).

[0240] The content of the hydrophobic structural unit in the specific polymer compound can be, for example, 10% by mass to 90% by mass, preferably 30% by mass to 90% by mass, more preferably 50% by mass to 90% by mass, and particularly preferably 60% by mass to 80% by mass, based on the total mass of the specific polymer compound.

[0241] -Water-soluble organic solvent- The treatment liquid preferably contains at least one water-soluble organic solvent. The water-soluble organic solvent is not particularly limited as long as it dissolves 5 g or more in 100 g of water at 20° C. Specifically, the water-soluble organic solvents that can be contained in the ink composition described below can also be used in the treatment liquid. Among these, from the viewpoint of suppressing curling, polyalkylene glycol or a derivative thereof is preferred, and at least one selected from diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, dipropylene glycol, tripropylene glycol monoalkyl ether, polyoxypropylene glyceryl ether, and polyoxyethylene polyoxypropylene glycol is more preferred.

[0242] From the viewpoint of coatability, the content of the water-soluble organic solvent in the treatment liquid is preferably 3% by mass to 20% by mass, and more preferably 5% by mass to 15% by mass, based on the total amount of the treatment liquid.

[0243] -Surfactants- The treatment liquid may contain at least one surfactant. The surfactant can be used as a surface tension adjuster. Examples of the surface tension adjuster include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants. Among these, nonionic surfactants and anionic surfactants are preferred from the viewpoint of the aggregation rate of the ink composition.

[0244] Examples of surfactants include the compounds listed as surfactants on pages 37-38 of JP-A-59-157636 and Research Disclosure No. 308119 (1989).Other examples include fluorine (alkyl fluoride) surfactants and silicone surfactants described in JP-A-2003-322926, JP-A-2004-325707, and JP-A-2004-309806.

[0245] The treatment liquid may contain other components. For other components that may be contained in the treatment liquid, reference can be made to the other components of the ink described above, as appropriate. [Example]

[0246] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples. Hereinafter, "parts" are based on mass. In Tables 1 to 4, "weight percentage (%)" means "mass %."

[0247] In the examples, the volume average particle size was measured using a particle size distribution measuring device manufactured by Nikkiso Co., Ltd. (product name: "Microtrac UPA (registered trademark) EX150").

[0248] The weight average molecular weight was measured using a measuring device HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) and a column TSKgel (registered trademark) Super Multipore Three HZ-H columns (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation) were used, and THF (tetrahydrofuran) was used as the eluent. Measurements were performed using an RI detector with a sample concentration of 0.45% by mass, a flow rate of 0.35 mL / min, a sample injection volume of 10 μL, and a measurement temperature of 40°C. Calibration curves were prepared using eight samples of "TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40," "F-20," "F-4," "F-1," "A-5000," "A-2500," "A-1000," and "n-propylbenzene."

[0249] The glass transition temperature was measured using a differential scanning calorimeter (product name "EXSTAR6220") manufactured by SII NanoTechnology, Inc.

[0250] The dynamic surface tension at 10 milliseconds was measured using a bubble pressure dynamic surface tensiometer (product name "BP100", manufactured by KRUSS).

[0251] [Preparation of Resin Particles] <Preparation of Resin Particles C-29> Resin particles C-29, among the specific examples of resin particles described above, were prepared as follows. A three-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with water (250 g), 12-methacrylamidodecanoic acid (6.7 g), potassium bicarbonate (0.17 g), and isopropanol (20 g), and the temperature was raised to 85°C under a nitrogen stream. A mixed solution consisting of 4,4'-azobis(4-cyanovaleric acid) (radical polymerization initiator, product name "V-501", Fujifilm Wako Pure Chemical Industries, Ltd.) (0.11 g), potassium bicarbonate (0.08 g), and water (9 g) was added to the flask and stirred for 10 minutes. Next, a monomer solution consisting of styrene (14 g), benzyl methacrylate (14 g), methyl methacrylate (48 g), butyl methacrylate (3.3 g), and hydroxyethyl methacrylate (14 g) was added dropwise to the three-neck flask at a constant rate so that the addition was completed within 3 hours. Furthermore, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added in two portions: immediately after the start of the monomer solution addition and 1.5 hours after the start of the monomer solution addition. After the monomer solution addition was completed, the mixture was stirred for 1 hour. Subsequently, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added to the resulting reaction mixture and stirred for an additional 3 hours. The resulting reaction mixture was filtered through a 50 μm mesh to obtain an aqueous dispersion of resin particles C-29.

[0252] <Preparation of Resin Particles C-30, C-23, and C-24> In preparing resin particles C-29, the type and amount of monomer used were appropriately changed to prepare aqueous dispersions of resin particles C-30, C-23, and C-24, which are specific examples of resin particles described above.

[0253] <Resin particle D> An aqueous dispersion of resin particles D was obtained with reference to paragraphs 0240 and 0241 of JP 2015-180710 A. The resin in resin particle D is a methyl methacrylate unit / isobornyl methacrylate It is a copolymer of methacrylic acid units, methacrylic acid units, and sodium methacrylate units (=70 / 20 / 5 / 5 [mass ratio]).

[0254] Preparation of pigment dispersion with cross-linked dispersant As a pigment dispersion in which the dispersant is crosslinked (specifically, a crosslinked polymer), Projet Cyan APD1000 (manufactured by FUJIFILM Imaging Colorants, cyan pigment dispersion, pigment concentration in pigment dispersion: 12% by mass) was prepared.

[0255] Preparation of pigment dispersion with non-crosslinked dispersant As a pigment dispersion in which the dispersant is not cross-linked, FUJI SP BLUE 6633 (manufactured by Fuji Pigment Co., Ltd., cyan pigment dispersion, pigment concentration in pigment dispersion: 17% by mass) was prepared.

[0256] [Examples 1 to 27, Comparative Examples 1 to 4] <Ink Preparation> The active ingredients of the inks shown in Tables 1 to 3 were mixed with water, and coarse particles were removed from the resulting mixture to obtain inks. The total amount of the active ingredients of the inks shown in Tables 1 to 3 and the amount of water is 100 parts by mass. Details of the following components in Tables 1 to 3 are as follows:

[0257] Sannix GP250: Polyoxypropylated glycerin manufactured by Sanyo Chemical Industries, Ltd. PEG200: Polyethylene glycol 200 manufactured by Sanyo Chemical Industries, Ltd. PVP K-15: Polyvinylpyrrolidone manufactured by Ashland Snowtex XS: Colloidal silica manufactured by Nissan Chemical Industries, Ltd. Movinyl 972: Aqueous dispersion of styrene / acrylic resin particles manufactured by Japan Coating Resin Co., Ltd. - Trasol CN: Wax particles manufactured by Chukyo Yushi Co., Ltd. Cellosol 524D: Wax particles manufactured by Chukyo Yushi Co., Ltd. Hitec-E6314: Wax particles manufactured by Toho Chemical Industry Co., Ltd. BYK-347: A silicone surfactant manufactured by BYK BYK-024: A silicone surfactant manufactured by BYK Olfine E1010: Acetylene glycol surfactant manufactured by Nissin Chemical Industry Co., Ltd. Olfine E1020: Acetylene glycol surfactant manufactured by Nissin Chemical Industry Co., Ltd.

[0258] <Ink measurement> The pH and oxidation-reduction potential of the inks of the examples and comparative examples were measured and designated as pHi and ORPi, respectively. Using these values, the value of the left side of inequality (X) was calculated. The results are shown in Tables 1 to 3.

[0259] Furthermore, the dynamic surface tension at 10 milliseconds was measured for the inks of the examples and comparative examples. The results are shown in Tables 1 to 3.

[0260] <Preparation of Processing Solution 1 and Processing Solution 2> The components of the following compositions were mixed to obtain treatment liquid 1 and treatment liquid 2, respectively.

[0261] -Composition of treatment solution 1- ·DEGmBE (Diethylene glycol monobutyl ether) …6.0% by mass Malonic acid …5.6% by mass Malic acid …3.83% by mass ·Phosphoric acid 85% by mass aqueous solution …3.37% by mass The following water-soluble polymer 1 (in the following water-soluble polymer 1, the numbers to the bottom right of each structural unit represent the mass ratio (mass%), and Mw represents the weight-average molecular weight.) …0.4% by mass Antifoaming agent (TSA manufactured by Momentive Performance Materials Japan, LLC) 739 (15%); emulsion type silicone defoamer) ... 0.0083% by mass of silicone oil Benzotriazole …1.0% by mass Teika Power BN2070M (surfactant manufactured by Teika) ...0.42% by mass of active ingredient Ion-exchanged water ...Remaining amount that totals 100% by mass

[0262] [ka]

[0263] -Composition of treatment solution 2- ·DEGmBE (Diethylene glycol monobutyl ether) …7.2% by mass Malonic acid …11.2% by mass Malic acid …7.66% by mass ·Phosphoric acid 85% by mass aqueous solution …6.73% by mass The above water-soluble polymer 1 …0.8% by mass Antifoaming agent (TSA manufactured by Momentive Performance Materials Japan, LLC) 739 (15%); emulsion type silicone defoamer) ... 0.01% by mass of silicone oil Benzotriazole …1.2% by mass Teika Power BN2070M ...0.5% by mass of active ingredient Ion-exchanged water ...Remaining amount that totals 100% by mass

[0264] <Image recording> Coated paper (product name "OK Topcoat+", manufactured by Oji Paper Co., Ltd.) was used as the recording medium, the treatment liquid 1 was used as the treatment liquid, and the inks of each example or each comparative example were used as the ink, and an image was recorded using a Jet Press 750S (manufactured by Fujifilm Corporation) as the inkjet recording device. The treatment liquid was applied as a preconditioner to the surface of the recording medium onto which the ink was to be applied, before the ink was applied. The ink was applied to the surface of the recording medium on which the treatment liquid had been applied. The ink image resolution was 1200 dpi x 1200 dpi, and the image recording speed was 3600 sph. Here, dpi stands for dot per inch, and sph stands for sheet per hour.

[0265] <Evaluation> Using the inks of the examples and comparative examples, an evaluation was carried out to assess the inhibition of etching of the ink flow path walls containing silicon. The evaluation results are shown in Tables 1 to 3. The evaluation method is as follows.

[0266] <Etching-resistance of silicon-containing ink flow path walls> An evaluation sample of an ink flow path wall containing silicon in an inkjet head was prepared as follows. A 1 cm x 1 cm chip of silicon substrate (research high-purity silicon wafer 6-P-25, model number 2-960-59) was prepared. Kapton tape was attached to part of this chip (i.e., silicon substrate), leaving an exposed silicon area that would come into contact with ink and a masked area to which Kapton tape was attached. This was used as an evaluation sample.

[0267] The ink of each Example and Comparative Example was placed in a container with a lid, and the evaluation sample was then immersed in the ink. A stirrer tip had been placed in the container with a lid in advance, and the evaluation sample was immersed in the ink while the ink was being stirred. The lidded container containing the ink and the evaluation sample was placed in an evaluation furnace set at 60°C, and left to stand for 8 days while stirring with a stirrer. After the lapse of time, the evaluation sample was taken out of the container, washed and dried, and then the masking tape was removed. The step height of the exposed silicon portion relative to the masked portion (i.e., the step height caused by etching) was measured using a step height measuring instrument (Surfcorder SE-500A manufactured by Kosaka Laboratory Co., Ltd.). Based on the step, the etching suppression of the ink flow path wall containing silicon was evaluated according to the following evaluation criteria. In the following evaluation criteria, the higher the score, the better the etching suppression of the ink flow path wall containing silicon (that is, the more etching is suppressed).

[0268] -Evaluation criteria- 5...No etching steps were detected. 4.5 ... Steps due to etching were detected, but were less than 0.2 μm. 4... The step caused by etching was 0.2 μm or more and less than 0.5 μm. 3.5: The step caused by etching was 0.5 μm or more and less than 1.0 μm. 3...The step caused by etching was 1.0 μm or more and less than 2.0 μm. 2...The step caused by etching was 2.0 μm or more and less than 3.0 μm. 1...The step caused by etching was 3.0 μm or more.

[0269] <Image density maintenance> To evaluate the etching suppression ability of the ink flow path walls, the image density maintenance ability was evaluated as follows. When etching of the ink flow path walls progresses, ink ejection failure from the inkjet head becomes more likely to occur, and image density fluctuations become more likely to occur (i.e., image density maintenance ability becomes more likely to decrease). First, the ink was loaded into the inkjet recording device shown in the "Image Recording" operation above, and a solid image was recorded within 3 hours after loading. The density of the resulting solid image was measured using a densitometer (FD-5, manufactured by Konica Minolta), and the result was designated as the "initial density." Next, the ink was left in the inkjet recording apparatus for 3 days, and then a solid image was recorded in the same manner as above, and the density of the solid image was measured. The result was designated as "density after 3 days." The ratio (%) of the concentration after 3 days to the initial concentration was calculated as the concentration maintenance rate. Based on the obtained density fluctuation rate, the density maintenance of the image was evaluated according to the following evaluation criteria. In the following evaluation criteria, rank A indicates that the image density maintenance is most suppressed.

[0270] -Evaluation criteria- A: The concentration retention rate was 95% or more. B: The concentration maintenance rate was 70% or more but less than 95%. C: The concentration retention rate was less than 70%.

[0271] [Table 1]

[0272] [Table 2]

[0273] [Table 3]

[0274] As shown in Tables 1 to 3, in Examples 1 to 27, which contained water, pigment, and at least one of resin particles and wax particles, had a pH (i.e., pHi in inequality (X)) of 7.2 to 11, and satisfied inequality (X), i.e., "ORPi-[285-59×(pHi-6.2)]≧0," etching of the ink flow path walls containing silicon was suppressed. In contrast to this, in Comparative Examples 1 to 4, which do not satisfy inequality (X), the ability to suppress etching of the ink flow path wall containing silicon was insufficient.

[0275] From the results of Examples 1 to 3, when the ink contains an oxidizing agent (Example 1), the etching It can be seen that the suppression is further improved.

[0276] The results of Examples 2 and 3 show that when the ink contains colloidal silica (Example 2), the etching suppression is further improved.

[0277] Next, the evaluation was performed in the same manner as described above, except that the recording medium was changed to coated paper manufactured by Sappi (product name "FLO Gloss Text"), and the results obtained were the same as those of the evaluation described above (i.e., the results shown in Tables 1 to 3). In addition, the evaluation was performed in the same manner as described above, except that the recording medium was changed to coated paper manufactured by LECTA (product name "Condat Gloss"), and the results obtained were the same as those of the evaluation described above (i.e., the results shown in Tables 1 to 3). Furthermore, when the evaluation was carried out in the same manner as described above except that the treatment liquid was changed to treatment liquid 2, the same results as those of the evaluation described above (i.e., the results shown in Tables 1 to 3) were obtained. In addition, the evaluation was performed in the same manner as described above, except that the image recording speed was changed to 5400 sph, no processing liquid was used, and the resolution was changed to 1200 dpi x 600 dpi.The results obtained were similar to those of the evaluation described above (i.e., the results shown in Tables 1 to 3).

[0278] Example 101 The same procedures as in Example 24 were carried out, except that the viscosity of the ink and the filter suitability of the ink were measured as described below. That is, the composition of the ink in Example 101 is the same as the composition of the ink in Example 24. The results are shown in Table 4.

[0279] <Ink viscosity measurement> The viscosity (mPa·s) of the ink composition was measured using a rotational viscometer "VISCOMETER TV-22" (manufactured by TOKI SANGYO CO., LTD) at 30° C. and 100 rpm (revolutions per minute).

[0280] <Evaluation of ink filter suitability> An Isopore membrane filter (manufactured by Merck Millipore Ltd.) with a pore size of 2 μm was placed in a syringe, and tubes that would serve as ink flow paths were connected to both ends of the syringe. Ink was supplied to a tube connected to one end of the syringe, and the ink was pushed out with a pressure of 75 kPa so that the ink would pass through the Isopore membrane filter in the syringe. The amount of ink passing through (g) was measured for 100 seconds from the start of ink extrusion. Based on the measurement results, the filter suitability of the ink was evaluated according to the following evaluation criteria. In the following evaluation criteria, the most excellent rank for ink filter suitability is "5".

[0281] -Evaluation criteria for ink filter suitability- 5...The amount of ink passing through was 80g or more. 4... The amount of ink passing through was 60g or more but less than 80g. 3...The amount of ink passing through was 40g or more but less than 60g. 2...The amount of ink passing through was 20g or more but less than 40g. 1...The amount of ink passing through was less than 20g.

[0282] Examples 102 to 107 The same procedure as in Example 101 was carried out, except that the active ingredients of the ink were changed as shown in Table 4. The results are shown in Table 4.

[0283] In the inks of Examples 102 to 107, the type and amount (% by mass of the total ink) of cellulose nanofibers shown in Table 4 was added to the ink of Example 101. Here, Cellenpia TC-02X, Cellenpia TC-01A, and Cellenpia CS-01 are all cellulose nanofibers manufactured by Nippon Paper Industries Co., Ltd. Among these cellulose nanofibers, Cellenpia TC-02X and Cellenpia TC-01A are TEMPO-oxidized cellulose nanofibers. Cellenpia TC-02X had an average fiber diameter of 3.5 nm and an average fiber length of 350 nm. Cellenpia TC-01A had an average fiber diameter of 3.5 nm and an average fiber length of 750 nm. Cellenpia CS-01 had an average fiber diameter of 13.5 nm and an average fiber length of 1500 nm or more.

[0284] [Table 4]

[0285] As shown in Table 4, in Examples 101 to 107, similar to Examples 1 to 27, etching of the ink flow path walls containing silicon was suppressed. Among Examples 101 to 107, in Examples 102 to 107 in which the ink contained cellulose nanofibers, the ink viscosity was effectively increased, which is expected to further improve the ink ejection properties.

[0286] The results of Examples 102 to 104 show that when the cellulose nanofibers contain TEMPO-oxidized cellulose nanofibers (Examples 102 and 103), the filterability of the ink is further improved.

[0287] The disclosures of Japanese Patent Application No. 2021-157230, filed on September 27, 2021, and Japanese Patent Application No. 2022-050285, filed on March 25, 2022, are incorporated herein by reference in their entireties. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.< / ph>

Claims

1. An inkjet ink ejected from an inkjet head containing silicon in an ink flow path wall, Contains water, a pigment, an oxidizing agent, and at least one of resin particles and wax particles, pH is 7.2 to 11, a mass ratio of the content of the oxidizing agent to the total content of the resin particles and the wax particles is 0.02 mass% to 6 mass%; Satisfy the following inequality (X): Inkjet ink. ORPi-[285-59×(pHi-6.2)]≧0... Inequality (X) In inequality (X), ORPi represents the oxidation-reduction potential of the inkjet ink in mV, measured under instrument conditions such that the oxidation-reduction potential of water at pH 6.2 is 310 mV, and pHi represents the pH of the inkjet ink.

2. The ink-jet ink of claim 1 , wherein the oxidizing agent comprises at least one selected from the group consisting of hydrogen peroxide and peroxides.

3. The ink-jet ink of claim 1 , wherein the oxidizing agent comprises at least one selected from the group consisting of hydrogen peroxide, peracetic acid, sodium percarbonate, and urea hydrogen peroxide.

4. The ink-jet ink of claim 1 , further comprising colloidal silica.

5. 2. The ink-jet ink according to claim 1, further comprising an organic solvent having a ClogP value of 1.0 to 3.

5.

6. 6. The ink-jet ink according to claim 5, wherein the organic solvent having a ClogP value of 1.0 to 3.5 is at least one selected from the group consisting of compounds represented by the following formula 1 and compounds represented by the following formula 2: 【Chemistry 1】 In Formula 1 or Formula 2, R １ each independently represents a hydrogen atom or a methyl group, R ２ each independently represents a linear or branched hydrocarbon group having 4 to 9 carbon atoms or an aryl group having 6 to 10 carbon atoms; and n represents an integer of 1 to 3.

7. The ink-jet ink of claim 1 further comprising a dispersant, wherein the dispersant is crosslinked.

8. The ink-jet ink according to claim 1 , wherein the resin particles contain a resin containing a structural unit represented by the following formula 3: 【Chemistry 2】 In formula 3, R ３ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; X １ represents a divalent linking group, Y １ represents an anionic group, and X １ and Y １ Among these, the atom farthest from the main chain is 4 to 27 atoms away from the main chain.

9. The inkjet ink according to claim 1 , further comprising cellulose nanofibers.

10. The inkjet ink according to claim 9, wherein the cellulose nanofibers have an average fiber width of 1 nm or more and 10 nm or less.

11. The inkjet ink according to claim 9, wherein the cellulose nanofibers have an average fiber length of 10 nm or more and 1000 nm or less.

12. The inkjet ink of claim 9 , wherein the cellulose nanofibers comprise TEMPO-oxidized cellulose nanofibers.

13. 10. The inkjet ink according to claim 9, wherein the mass ratio of the content of the cellulose nanofibers to the total content of the resin particles and the wax particles is 1.00% by mass to 10.00% by mass.

14. The inkjet ink according to claim 9, wherein the content of the cellulose nanofibers is 0.01% by mass to 1.00% by mass relative to the total amount of the inkjet ink.

15. 10. The ink-jet ink according to claim 9, wherein the viscosity measured at 30° C. and 100 rpm is 3.8 mPa·s to 6.0 mPa·s.

16. An image recording method, comprising a step of applying the ink-jet ink according to any one of claims 1 to 15 onto a recording medium by ejecting it from an ink-jet head having an ink flow path wall containing silicon.

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