Aqueous ink, nk cartridge, and inkjet recording method

Abstract

To provide an aqueous ink for inkjet capable of recording an image without noticeable beading and with excellent abrasion resistance.SOLUTION: There is provided an aqueous ink for inkjet which contains a pigment, a polyether-modified silicone-based surfactant, a phosphoric acid ester, and calcium ions. The phosphoric acid ester is at least one selected from the group consisting of a polyoxyethylene alkyl ether phosphate and a polyoxyethylene alkenyl ether phosphate, the polyether-modified silicone-based surfactant contains an ethylene oxide group and the addition molar number of ethylene oxide groups of the polyether-modified silicone surfactant is larger than the addition molar number of ethylene oxide groups of the phosphoric acid ester.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method.

Background Art

[0002] In recent years, the opportunity to record images on large-format recording media such as posters and advertisements using an inkjet recording apparatus capable of recording large-format images has increased. For such images, since fastness such as light resistance capable of withstanding posting is required, an ink containing a pigment as a coloring material (pigment ink) is widely used.

[0003] When using an inkjet recording apparatus capable of recording large-format images, the image immediately after recording may touch a basket (a member composed of a cloth or the like for receiving the recorded matter). In addition, since the image immediately after recording may be moved by a plurality of people's hands, the image immediately after recording is also required to have rub resistance.

[0004] In addition, when recording large-format images, a plurality of images are recorded at once, so the printing speed is increasing. In order to improve the printing speed, it is important that the ink applied to the recording medium quickly penetrates into the recording medium and the ink does not overflow on the surface of the recording medium. That is, an ink with good penetrability into the recording medium is required.

[0005] To solve the above problems, various proposals have been made so far. For example, an ink containing a wax emulsion and latex particles having a specific glass transition point (Tg) and capable of recording an image with improved rub resistance has been proposed (Patent Document 1). In addition, an ink for inkjet containing a phosphate ester compound and used in combination with a pretreatment liquid has been proposed (Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] The inventors of the present invention examined the characteristics of an image recorded with the ink proposed in Patent Document 1. As a result, it was found that while the image had good erasability, the level of bead resistance was insufficient. Analysis of the image surface revealed that the erasability of the image decreased because the penetration of the ink into the recording medium decreased due to the blocking effect of wax and latex particles in the ink applied to the recording medium.

[0008] Therefore, an object of the present invention is to provide an aqueous ink for inkjet that can record an image with inconspicuous beading and excellent erasability. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Means for Solving the Problems]

[0009] That is, according to the present invention, there is provided an aqueous ink for inkjet containing a pigment, a polyether-modified silicone-based surfactant, a phosphate ester, and calcium ions, wherein the phosphate ester is at least one selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate, the polyether-modified silicone-based surfactant contains an ethylene oxide group, and the number of moles of ethylene oxide groups added to the polyether-modified silicone-based surfactant is equal to or more than the number of moles of ethylene oxide groups added to the phosphate ester. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous ink for inkjet that can record an image with inconspicuous beading and excellent rubbing resistance. Further, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Brief Description of Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in more detail by giving preferred embodiments. In the present invention, when the compound is a salt, the salt dissociates into ions and exists in the aqueous ink, but for convenience, it is expressed as "containing a salt". Further, the aqueous ink for inkjet may be simply described as "ink". Physical property values are values at normal temperature (25°C), normal pressure (1 atm = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified.

[0013] Unless otherwise specified, "unit" means a unit structure corresponding to one monomer. When "(meth)acrylic acid" and "(meth)acrylate" are described, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

[0014] The present inventors studied inks to which various waxes, urethane resins, etc. were added in order to record an image in which bead resistance and rubbing resistance were compatible. However, since waxes and urethane resins are polymer materials, it was found that the bead resistance is likely to decrease due to plugging action and an increase in the viscosity of the ink.

[0015] Therefore, the present inventors studied an ink added with a silicone-based surfactant in order to improve the rub resistance of an image by reducing the surface energy. As a result, the rub resistance of the image was improved by adding the silicone-based surfactant. On the other hand, it was found that the ink droplets became more likely to bounce off each other, resulting in locally connected or non-existent ink droplet portions, that is, shading occurred and beading was likely to occur.

[0016] As a result of further studies, the present inventors have found that by using an ink that satisfies the following requirements (i) and (ii), it is possible to record an image that achieves both bead resistance and rub resistance, leading to the present invention. (i) It contains a pigment, a polyether-modified silicone-based surfactant, a phosphate ester (at least one selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate), and calcium ions. (ii) The added molar number of ethylene oxide groups of the polyether-modified silicone-based surfactant is equal to or more than the added molar number of ethylene oxide groups of the phosphate ester.

[0017] Regarding the mechanism by which the above effects are obtained, the present inventors speculate as follows. Calcium ions are stabilized in the ink by oxygen atoms in the ether bonds that constitute the polyoxyethylene chains of the polyether-modified silicone-based surfactant, polyoxyethylene alkyl ether phosphate, and polyoxyethylene alkenyl ether phosphate. Also, by satisfying the requirement (ii) above, it becomes possible to easily make calcium ions exist around the polyether-modified silicone-based surfactant having relatively many oxygen atoms. Hereinafter, "polyoxyethylene alkyl ether phosphate" and "polyoxyethylene alkenyl ether phosphate" are also collectively referred to as "polyoxyethylene alkyl ether phosphate".

[0018] When ink is applied to a recording medium, as moisture evaporates, the phosphate groups in polyoxyethylene alkyl ether phosphate bind with calcium ions to form calcium phosphate, which promotes solid-liquid separation and allows the ink to penetrate further into the recording medium. Also, as described above, since calcium ions are present around the polyether-modified silicone surfactant, it is possible to place the polyether-modified silicone surfactant and polyoxyethylene alkyl ether phosphate near the surface of the ink droplet. This makes it possible to suppress the decrease in surface energy that occurs when the silicone surfactant is simply added, suppress the repulsion between ink droplets, and improve the anti-beading property without impairing the ink's permeability.

[0019] Also, due to the solid-liquid separation promoted by the formation of calcium phosphate described above, the alkyl groups of polyoxyethylene alkyl ether phosphate present near the surface of the ink droplet interact hydrophobically with each other. As a result, part of the polyoxyethylene alkyl ether phosphate self-organizes, and the slipperiness between the carbon chains is exhibited, so it is considered that an effect of improving the abrasion resistance, which could not be obtained when the silicone surfactant was simply added, can be obtained.

[0020] If the ink does not contain a polyether-modified silicone surfactant, the surface energy of the recorded image is not easily reduced, so the effect of improving the abrasion resistance cannot be obtained. Also, assume that the number of moles of ethylene oxide groups added to the polyether-modified silicone surfactant is less than the number of moles of ethylene oxide groups added to the polyoxyethylene alkyl ether phosphate. In this case, calcium ions are likely to be present around the polyoxyethylene alkyl ether phosphate. Therefore, when moisture evaporates, polyoxyethylene alkyl ether phosphate cannot be present around the polyether-modified silicone surfactant, and the decrease in surface energy associated with the silicone surfactant cannot be suppressed. As a result, the effect of improving the anti-beading property cannot be obtained.

[0021] <Ink> The ink of the present invention is an aqueous ink for inkjet containing a pigment, a polyether-modified silicone surfactant, a phosphate ester, and calcium ions. The phosphate ester is at least one selected from the group consisting of polyoxyethylene alkyl ether phosphoric acid and polyoxyethylene alkenyl ether phosphoric acid. The polyether-modified silicone surfactant contains an ethylene oxide group, and the added molar number of the ethylene oxide group of the polyether-modified silicone surfactant is equal to or more than the added molar number of the ethylene oxide group of the phosphate ester. The ink of the present invention does not need to be used in combination with a liquid that causes reaction or thickening when in contact with each other (for example, a reaction liquid containing a component that reacts with the ink). Hereinafter, each component constituting the ink and the physical properties of the ink will be described.

[0022] (Pigment) The ink contains a pigment as a coloring material. The content (mass%) of the pigment in the ink is preferably 0.1 mass% or more and 15.0 mass% or less, more preferably 1.0 mass% or more and 10.0 mass% or less, based on the total mass of the ink.

[0023] Examples of the pigment include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, and perinone.

[0024] The average particle diameter (average primary particle diameter) of the pigment is preferably 10 nm or more and 300 nm or less. If the average particle diameter of the pigment is less than 10 nm, the interaction between primary particles becomes strong, and the storage stability of the ink may not be sufficiently obtained. On the other hand, if the average particle diameter of the pigment exceeds 300 nm, the color density and glossiness of the image may not be sufficiently obtained. The "average particle diameter" in this specification means the cumulative 50% particle diameter (median diameter; D 50 ) on a volume basis.

[0025] Examples of pigment dispersion methods include resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which a hydrophilic group is bonded to the particle surface of the pigment. Further, resin-bonded pigments in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, microcapsule pigments in which the surface of the pigment particles is coated or encapsulated with a resin, etc. can be used. It is also possible to use pigments with different dispersion methods in combination. When using a resin-dispersed pigment, the content (mass %) of the pigment in the ink is preferably 0.30 times or more and 10.0 times or less in terms of the mass ratio to the content (mass %) of the resin dispersant.

[0026] As the resin dispersant for dispersing the pigment in an aqueous medium, it is preferable to use a resin capable of dispersing the pigment in the aqueous medium by the action of an anionic group. Examples of the resin dispersant include acrylic resins, urethane resins, and olefin resins. Among them, acrylic resins composed of hydrophilic units and hydrophobic units are more preferable.

[0027] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit having no hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylate monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0028] The urethane resin can be obtained, for example, by reacting a polyisocyanate and a polyol. Further, it may be a product obtained by further reacting a chain extender. Examples of the olefin resin include polyethylene and polypropylene.

[0029] Examples of the self-dispersing pigment include those in which an anionic group is directly bonded to the particle surface of the pigment or via another atomic group. Examples of the anionic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Examples of the counter ion of the anionic group include cations such as a hydrogen atom, an alkali metal, ammonium, and organic ammonium. The other atomic group is a group having a function as a spacer between the particle surface of the pigment and the anionic group, and preferably has a molecular weight of 1,000 or less. Examples of the other atomic group include an alkylene group having about 1 to 6 carbon atoms, an arylene group such as a phenylene group and a naphthylene group, an ester group, an imino group, an amide group, a sulfonyl group, and an ether group.

[0030] (Polyether-modified silicone surfactant) The polyether-modified silicone surfactant has a structure in which at least one hydrocarbon group selected from the group consisting of the hydrocarbon group in the side chain and the terminal hydrocarbon group of the silicone oil is substituted with a polyether group. Examples of the polyether group include a polyoxyethylene group, a polyoxypropylene group, and a polyoxyalkylene group in which an oxyethylene group (EO) and an oxypropylene group (PO) are added in a block or random manner. Further, a compound in which a polyether group is grafted to the silicone main chain, a compound in which a silicone and a polyether group are bonded in a block manner, etc. can be used. The polyether-modified silicone surfactant contained in the ink of the present invention has an oxyethylene group (ethylene oxide group: EO) in its molecule in order to stabilize the aforementioned calcium ions.

[0031] The content (mass %) of the polyether-modified silicone surfactant in the ink is preferably 0.1 mass % or more and 1.0 mass % or less based on the total mass of the ink. Further, the added molar number of ethylene oxide groups of the polyether-modified silicone surfactant is preferably 3 or more greater than the added molar number of ethylene oxide groups of the phosphate ester described later. Thus, when the ethylene oxide chain (EO chain) of the polyether-modified silicone surfactant is sufficiently long, calcium ions are more likely to be present around the polyether-modified silicone surfactant in the ink. As a result, the reaction between polyoxyethylene alkyl ether phosphate and calcium ions is likely to occur around the polyether-modified silicone surfactant, and both are more uniformly oriented on the surface of the ink droplet, and the scratch resistance of the image can be further improved.

[0032] The added molar number of ethylene oxide groups of the polyether-modified silicone surfactant is preferably 7 or more and 15 or less, and more preferably 7 or more and 14 or less. When the added molar number of ethylene oxide groups is less than 7, since the number of oxygen atoms in the ether bond is small, the effect of stabilizing calcium ions may not be sufficiently obtained. As a result, solid-liquid separation due to polyoxyethylene alkyl ether phosphate and calcium ions is less likely to occur, and the permeability of the ink into the recording medium may decrease, and the effect of improving the bead resistance may not be sufficiently obtained. On the other hand, when the added molar number of ethylene oxide groups of the polyether-modified silicone surfactant exceeds 15, the water solubility of the polyether-modified silicone surfactant may become excessively high. As a result, the polyether-modified silicone surfactant may be less likely to be oriented at the interface of the ink droplet, and the effect of improving the scratch resistance may not be sufficiently obtained.

[0033] Examples of the polyether-modified silicone surfactant include compounds represented by the following general formulas (2) to (4).

[0034] TIFF2025100447000001.tif30170(In the general formula (2), R1 represents an alkylene group, R2 represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, a represents an integer of 1 or more, and b represents an integer of 0 or more)

[0035] TIFF2025100447000002.tif28170(In the general formula (3), R3 represents a hydrogen atom or an alkyl group, R4 represents an alkylene group, p represents an integer of 1 or more, c represents an integer of 1 or more, and d represents an integer of 0 or more)

[0036] TIFF2025100447000003.tif26170(In the general formula (4), R5 represents a hydrogen atom or an alkyl group, R6 represents an alkylene group, q and r each independently represent an integer of 1 or more, e represents an integer of 1 or more, and f represents an integer of 0 or more)

[0037] The alkylene group represented by R1 in the general formula (2), R4 in the general formula (3), and R6 in the general formula (4) is preferably an alkylene group having 2 to 6 carbon atoms. As this alkylene group, an ethylene group or a propylene group is more preferable, and a propylene group is even more preferable. The alkyl group represented by R2 in the general formula (2), R3 in the general formula (3), and R5 in the general formula (4) is preferably an alkyl group having 1 to 6 carbon atoms, and a methyl group, an ethyl group, or a propyl group is even more preferable. Among them, a methyl group is particularly preferable.

[0038] Among them, the polyether-modified silicone surfactant is preferably a compound represented by the general formula (2). Since the compound represented by the general formula (2) has an oxyethylene group in the side chain, the degree of freedom of the oxyethylene group is higher than that of a compound having an oxyethylene group in the main chain, and it is easy to capture calcium ions. Therefore, when the compound represented by the general formula (2) is used, polyoxyethylene alkyl ether phosphate is likely to react around this compound. As a result, the polyether-modified silicone surfactant and polyoxyethylene alkyl ether phosphate are more uniformly oriented on the surface of the ink droplet, and the scratch resistance of the image can be further improved. In the general formula (2), m + n is preferably 3 or more and 10 or less. Further, m is preferably 2 or more and 8 or less, n is preferably 1 or 2, and more preferably 1.

[0039] The compound represented by the general formula (2) can be obtained, for example, by an addition reaction between a compound represented by the following general formula (A) and a compound represented by the following general formula (B). The compound represented by the general formula (3) can be obtained, for example, by an addition reaction between a compound represented by the following general formula (C) and a compound represented by the following general formula (D). Further, the compound represented by the general formula (4) can be obtained, for example, by an addition reaction between a compound represented by the following general formula (E) and a compound represented by the following general formula (F).

[0040] TIFF2025100447000004.tif26170 (In the general formula (A), m and n are each independently synonymous with m and n in the general formula (2))

[0041] TIFF2025100447000005.tif18170 (In the general formula (B), R 11 represents an alkenyl group, and R2, a, and b are synonymous with R2, a, and b in the general formula (2))

[0042] TIFF2025100447000006.tif28170 (In the general formula (C), p is synonymous with p in the general formula (3))

[0043] TIFF2025100447000007.tif18170 (In the general formula (D), R 41 represents an alkenyl group, and R3, c, and d have the same meanings as R3, c, and d in the general formula (3).)

[0044] TIFF2025100447000008.tif25170 (In the general formula (E), q has the same meaning as q in the general formula (4).)

[0045] TIFF2025100447000009.tif19170 (In the general formula (F), R 51 and R 61 represent an alkenyl group, and e and f have the same meanings as e and f in the general formula (4).)

[0046] The compound represented by the general formula (A) is a polysiloxane compound having n hydrogen atoms bonded to n Si in the general formula (A). The compound represented by the general formula (C) and the compound represented by the general formula (E) are both polysiloxane compounds having hydrogen atoms at both ends. Also, the compound represented by the general formula (B), the compound represented by the general formula (D), and the compound represented by the general formula (F) are all polyoxyalkylene compounds having ethylene oxide units or propylene oxide units.

[0047] In the general formula (B), R 11 is a group that becomes R1 in the general formula (2) by the addition reaction between the compound represented by the general formula (A) and the compound represented by the general formula (B). In the general formula (D), R 41 is a group that becomes R4 in the general formula (3) by the addition reaction between the compound represented by the general formula (C) and the compound represented by the general formula (D). R 51 and R 61 in the general formula (F) are groups that become R5 and R6 in the general formula (4), respectively, by the addition reaction between the compound represented by the general formula (E) and the compound represented by the general formula (F). R 11 in the general formula (B), R 41 in the general formula (D), and R51 and R 61 The alkenyl group represented by 61 is preferably an alkenyl group having 2 to 6 carbon atoms, and more preferably an allyl group.

[0048] (Phosphate ester) The aqueous ink of the present invention contains at least one selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate as the phosphate ester. Polyoxyethylene alkyl ether phosphate is a phosphate ester of polyoxyethylene alkyl ether. Further, polyoxyethylene alkenyl ether phosphate is a phosphate ester of polyoxyethylene alkenyl ether. Polyoxyethylene alkyl ether and polyoxyethylene alkenyl ether can be obtained, for example, by addition polymerization of ethylene oxide to a higher alcohol. The content (mass%) of the above phosphate ester in the ink is preferably 0.10 mass% or more and 1.0 mass% or less based on the total mass of the ink.

[0049] The content (mass%) of the above phosphate ester in the ink is preferably 0.10 times or more and 10.0 times or less in terms of the mass ratio to the content (mass%) of the polyether-modified silicone-based surfactant. When the above mass ratio is less than 0.10 times, it is difficult to suppress the decrease in surface energy by the polyether-modified silicone-based surfactant, and ink droplets are likely to be locally connected to cause shading, and the effect of improving the bead resistance may not be sufficiently obtained. On the other hand, when the above mass ratio exceeds 10.0 times, it may be difficult for polyoxyethylene alkyl ether phosphate and the polyether-modified silicone-based surfactant to be uniformly oriented near the surface of the ink droplets, and the effect of improving the rubbing resistance may not be sufficiently obtained. The above mass ratio is more preferably 1.0 times or more and 7.0 times or less.

[0050] The content (mass %) of the phosphate ester in the ink is preferably 25 times or more and 10,000 times or less in terms of the mass ratio to the content (mass %) of calcium ions. Among them, it is more preferably 50 times or more and 9,000 times or less, and particularly preferably 300 times or more and 8,000 times or less. When the above mass ratio is less than 25 times, the cohesive force of polyoxyethylene alkyl ether phosphate during water evaporation becomes high, the permeability of the ink into the recording medium cannot be sufficiently obtained, and the effect of improving the bead resistance may not be sufficiently obtained. On the other hand, when the above mass ratio exceeds 10,000 times, the promoting effect of solid-liquid separation by polyoxyethylene alkyl ether phosphate cannot be sufficiently obtained, and the effects of improving the bead resistance and abrasion resistance may not be sufficiently obtained.

[0051] The phosphate ester is preferably a compound represented by the following general formula (1).

[0052] TIFF2025100447000010.tif27170 (In the general formula (1), R A represents an alkyl group or alkenyl group having 12 to 18 carbon atoms, and x represents an integer of 3 to 10)

[0053] In the general formula (1), when the number of carbon atoms of the alkyl group or alkenyl group represented by R A is less than 12, the hydrophobic interaction between carbon chains may become difficult. As a result, the self-organization of polyoxyethylene alkyl ether phosphate may be difficult to occur, and the effect of improving the abrasion resistance may not be sufficiently obtained. On the other hand, in the general formula (1), when the number of carbon atoms of the alkyl group or alkenyl group represented by R A exceeds 18, the water solubility of polyoxyethylene alkyl ether phosphate decreases. As a result, polyoxyethylene alkyl ether phosphates tend to aggregate with each other as water evaporates, the permeability of the ink into the recording medium decreases, and the effect of improving the bead resistance may not be sufficiently obtained. When a plurality of compounds having different numbers of carbon atoms of the alkyl group or alkenyl group represented by R A are included, R in these compounds AThe average number of carbon atoms may be 12 or more and 18 or less.

[0054] In the general formula (1), if the number of moles of ethylene oxide groups represented by x is less than 3, the water solubility of polyoxyethylene alkyl ether phosphate decreases. As a result, as water evaporates, polyoxyethylene alkyl ether phosphates tend to aggregate with each other, the permeability of the ink into the recording medium decreases, and the effect of improving the bead resistance may not be sufficiently obtained. On the other hand, in the general formula (1), if the number of moles of ethylene oxide groups represented by x exceeds 10, the water solubility of polyoxyethylene alkyl ether phosphate is high, and thus the reactivity with calcium ions may decrease. As a result, the effect of promoting solid-liquid separation may not be sufficiently obtained, and the effect of improving the bead resistance may not be sufficiently obtained.

[0055] (Calcium ions) The ink contains calcium ions, which are polyvalent metal ions. Calcium ions have good reactivity with polyether-modified silicone surfactants compared to other metal ions. Therefore, when calcium ions are contained in the ink, as water evaporates, calcium ions react with the polyether-modified silicone surfactant, and solid-liquid separation is promoted. The content (mass%) of calcium ions in the ink is preferably 0.0001 mass% or more and 0.006 mass% or less based on the total mass of the ink.

[0056] By adding a metal salt capable of generating calcium ions to the ink, calcium ions can be present in the ink. As counterions that form a metal salt together with calcium ions, Cl - , Br - , I - , ClO - , ClO2 - , ClO3 - , ClO4 - , NO2 - , NO3 - , SO4 2- , CO3 2- , PO4 3- , HPO42- and H2PO4 - and other inorganic anions; HCO3 - and HCOO - , (COO - )2, COOH(COO - ), CH3COO - , C2H4(COO - )2, C6H5CO - , C6H4(COO - )2 and CH3SO4 - and other organic anions; can be mentioned.

[0057] The metal salt may be used in the form of a hydrate. Calcium ions may also be present in the ink due to contamination from components of the ink such as pigments, resins, and water-soluble organic solvents, or elution from members in contact with the ink. The content of calcium ions in the ink can be measured by a measuring method such as ICP emission spectrometry.

[0058] (aqueous medium) The ink of the present invention is an aqueous ink containing an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion-exchanged water) as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those that can be used in inks for inkjet, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

[0059] The ink preferably further contains 1-(2-hydroxyethyl)-2-pyrrolidone, which is a nitrogen-containing compound. 1-(2-hydroxyethyl)-2-pyrrolidone is a type of polar solvent having a hydroxyethyl group in its molecule. By containing 1-(2-hydroxyethyl)-2-pyrrolidone, the wettability of the ink on the surface of the recording medium can be improved. Further, the hydroxy group in the molecule of 1-(2-hydroxyethyl)-2-pyrrolidone has a high affinity for polyether-modified silicone surfactants and polyoxyethylene alkyl ether phosphates. Therefore, by containing 1-(2-hydroxyethyl)-2-pyrrolidone, the penetrability of the ink into the recording medium can be further improved, and the bead resistance of the recorded image can be further improved.

[0060] (Other components) In addition to the above-described components, the ink may contain water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethylene urea. Further, the ink may contain various additives such as surfactants other than the above-described polyether-modified silicone surfactants and phosphate esters, pH adjusters, defoamers, rust preventives, preservatives, fungicides, antioxidants, anti-reducing agents, and chelating agents, as needed.

[0061] (Physical properties of the ink) The ink of the present invention is an aqueous ink applicable to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, more preferably 1.0 mPa·s or more and 5.0 mPa·s or less, and particularly preferably 1.0 mPa·s or more and 3.0 mPa·s or less. Further, the surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, more preferably 20 mN / m or more and 60 mN / m or less, and particularly preferably 30 mN / m or more and 50 mN / m or less. The pH of the ink at 25°C is preferably 5.0 or more and 10.0 or less, and more preferably 7.0 or more and 9.5 or less.

[0062] <Ink cartridge> The ink cartridge of the present invention includes ink and an ink storage unit that stores this ink. And the ink stored in this ink storage unit is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge serves as an ink storage unit for storing ink. The ink storage unit is composed of an ink storage chamber 14 and an absorber storage chamber 16, and these communicate with each other through a communication port 18. Further, the absorber storage chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may be in a form that does not have an ink storage chamber for storing liquid ink and holds the entire amount of the stored ink by the absorber. Further, the ink storage unit may be in a form that does not have an absorber and stores the entire amount of the ink in a liquid state. Furthermore, it may be an ink cartridge configured to have an ink storage unit and a recording head.

[0063] <Inkjet recording method> The inkjet recording method of the present invention is a method of discharging the aqueous ink of the present invention described above from an inkjet recording head and recording an image on a recording medium. Examples of the method of discharging the ink include a method of imparting mechanical energy to the ink and a method of imparting thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of discharging the ink by imparting thermal energy to the ink. Except for using the ink of the present invention, the steps of the inkjet recording method may be those known in the art.

[0064] Figure 2 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention. (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40 and is configured such that an ink cartridge 42 can be set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is discharged from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by the conveying means (not shown).

[0065] As the recording medium, it is preferable to use permeable paper such as plain paper and recording media having a coating layer (glossy paper, art paper, etc.). Among them, it is particularly preferable to use a recording medium having a coating layer that allows at least a part of the pigment in the ink to be present on the surface or in the vicinity thereof. The recording medium can be appropriately selected according to the purpose of use of the recorded matter on which the image is recorded. For example, glossy paper suitable for recording an image having a photographic image quality gloss, or art paper that takes advantage of the texture of the base material (such as drawing paper texture, canvas texture, Japanese paper texture, etc.) to express paintings, photos, and graphic images according to preference can be used. Among them, it is preferable to use so-called glossy paper in which the surface of the coating layer exhibits glossiness.

Examples

[0066] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Regarding the amounts of components, “parts” and “%” are based on mass unless otherwise specified. Note that 1 ppm is synonymous with 0.0001%.

[0067] <Preparation of Pigment Dispersion> Each component shown in Table 1 (unit: parts) and 85 parts of 0.3 mm zirconia beads were placed in a batch vertical sand mill (manufactured by Imex), dispersed for 3 hours while cooling with water, and then centrifuged to remove non-dispersed matter containing coarse particles. Next, pressure filtration was performed using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare pigment dispersions 1 to 8. The aqueous solution of resin 1 used as the dispersant was prepared as follows. A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) having an acid value of 170 mgKOH / g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 was neutralized with potassium hydroxide in an equimolar amount to its acid value, and an appropriate amount of pure water was added to obtain an aqueous solution of resin 1 having a resin (solid content) content of 20.0%. The details of each component in Table 1 are shown below. · Carbon black (trade name “Black Pearls 880”, manufactured by Cabot) · C.I. Pigment Blue 15:3 (trade name "Hostaperm Blue B2G", manufactured by Hoechst) · Magenta solid solution pigment (solid solution of C.I. Pigment Red 202 and C.I. Pigment Violet 19, trade name "Sunfast Magenta D4500J", manufactured by Sankyo Chemical) · C.I. Pigment Yellow 74 (trade name "Fast Yellow 011", manufactured by Dainichi Seika Kogyo) · C.I. Pigment Red 254 (trade name "Irgalite Red L3630", manufactured by BASF) · C.I. Pigment Orange 43 (trade name "Novoperm Orange GRL", manufactured by Clariant) · C.I. Pigment Green 7 (trade name "Fastogen Green S", manufactured by DIC) · C.I. Pigment Blue 23 (trade name "Hostaperm Violet RLSP", manufactured by Clariant)

[0068] TIFF2025100447000011.tif89170

[0069] <Preparation of Phosphate Esters> Using aliphatic alcohol ethoxylate as a raw material, polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate were produced according to the method shown below.

[0070] Concentrated phosphoric acid (manufactured by Rasa Industries) and N,N-dimethylformamide were placed in a flask equipped with a stirrer, a nitrogen inlet tube, a reflux condenser, and a thermometer, and stirred at 60 °C. After dropping aliphatic alcohol ethoxylate, the temperature was raised to 80 °C and reacted for 12 hours. Then, saturated brine was added and stirred at 60 °C for 12 hours to hydrolyze the pyrophosphate ester, obtaining polyoxyethylene alkyl ether phosphate or polyoxyethylene alkenyl ether phosphate, which is a phosphate ester type surfactant. The types of phosphate esters are shown in Table 2. For phosphate esters 3 to 5, the average value of the carbon number of the alkyl group is described.

[0071] TIFF2025100447000012.tif115170

[0072] <Production of polyether-modified silicone-based surfactant> (Surfactants 1 - 8) A glass container equipped with a thermometer and stirring means was charged with the following polysiloxane compound and polyoxyalkylene compound. Then, an addition reaction was carried out in the presence of a platinum catalyst to obtain Surfactants 1 - 8 respectively. These surfactants are polyether-modified silicone-based surfactants having a structure represented by General Formula (2). Here, as the polysiloxane compound, a compound represented by General Formula (A) (m = 3 or 5, n = 1) was used. As the polyoxyalkylene compound, a compound represented by General Formula (B) (a, b, R 11 , and R2 are the numbers or structures shown in Table 3) was used. The types of the obtained polyether-modified silicone-based surfactants are shown in Table 3. In Table 3, m, n, a, b, R2, and R1 respectively represent m, n, a, b, R2, and R1 in General Formula (2).

[0073] TIFF2025100447000013.tif76170

[0074] (Surfactant 9) A glass container equipped with a thermometer and stirring means was charged with the following polysiloxane compound and polyoxyalkylene compound. Then, an addition reaction was carried out in the presence of a platinum catalyst to obtain Surfactant 9. Surfactant 9 is a polyether-modified silicone-based surfactant having a structure represented by General Formula (3). Here, as the polysiloxane compound, a compound represented by General Formula (C) (p = 8) was used. As the polyoxyalkylene compound, a compound represented by General Formula (D) (c = 11, d = 0, R 41 = allyl group, R3 = methyl group) was used. The obtained Surfactant 9 is a compound in General Formula (3) with p = 8, c = 11, d = 0, R3 = methyl group, and R4 = propylene group.

[0075] <Preparation of Ink> (Examples 1 to 35, Comparative Examples 1 to 7) Each component (unit: %) shown in the upper rows of Tables 4-1 to 4-4 was mixed and thoroughly stirred, and then each ink was prepared by pressure filtration through a cellulose acetate filter (manufactured by Advantec) with a pore size of 0.8 μm. The calcium ion (Ca 2+ ) content in the ink was adjusted using Ca(NO3)2·4H2O. The calcium ion (Ca 2+ ) content in the ink was measured using an ICP emission spectroscopic analyzer (trade name "SPS5100", manufactured by SII Nanotechnology Inc.). The characteristics of the obtained inks are shown in the lower rows of Tables 4-1 to 4-4. Also, the details of the materials in Tables 4-1 to 4-4 are shown below. · Aqueous solution of Resin 2: A styrene-ethyl acrylate-acrylic acid copolymer (Resin 2) with an acid value of 160 mg KOH / g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of Resin 2 was neutralized with potassium hydroxide in an equimolar amount to its acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of Resin 2 with a resin (solid content) content of 20.0% for use. · Proxel GXL: A preservative (manufactured by Arch Chemicals) · Capstone FS3100 (perfluoroalkyl ethylene oxide adduct, manufactured by Chemours)

[0076] TIFF2025100447000014.tif253170

[0077] TIFF2025100447000015.tif253170

[0078] TIFF2025100447000016.tif250170

[0079] TIFF2025100447000017.tif255159

[0080] (Comparative Example 9) Ink was prepared with reference to the description of "Inkjet Component I-9" in Patent Document 2. Specifically, ink was prepared using a resin-dispersed pigment of Pigment Blue 15:3, a phosphate ester type anionic surfactant (polyoxypropylene alkyl ether phosphate salt), and a silicone-based surfactant (BYK-333). As the silicone-based surfactant, the product named "BYK-333" (manufactured by BYK Chemie Japan) was used. The content of calcium ions (Ca 2+ ) adjusted using Ca(NO3)2·4H2O was 2 ppm.

[0081] <Evaluation> Each prepared ink was filled into an ink cartridge and mounted on an inkjet recording apparatus (product name "PIXUS PRO-10S", manufactured by Canon) that discharges ink from a recording head by the action of thermal energy. In this example, a solid image recording duty was defined as 100% under the condition of recording at a resolution of 600 dpi × 600 dpi and applying 8 ink droplets of 3.5 ng per droplet to a unit area of 1 / 600 inch × 1 / 600 inch. Also, in this apparatus, multi-pass recording can be performed in which the application of ink to a unit area of the recording medium is divided into a plurality of relative scans of the recording head and the recording medium. For example, when recording is performed in 4 passes, it means that the application of ink to a unit area of the recording medium is divided into 4 relative scans of the recording head and the recording medium. The unit area can be set as an arbitrary area such as 1 pixel or 1 band. In the present invention, according to the evaluation criteria of each item shown below, "A" and "B" are acceptable levels, and "C" is an unacceptable level. The evaluation results are shown in Table 5.

[0082] (Beading resistance) Using the above inkjet recording apparatus, six solid images with a recording duty in the range of 100 to 150% in 10% increments were recorded on glossy paper (product name "Canon Photo Paper Glossy Pro Platinum Grade PT-101", manufactured by Canon) in 4 passes. The recorded solid images were observed, and the beading resistance was evaluated according to the evaluation criteria shown below. A: In the area with a recording duty of 100 - 150%, no beading phenomenon could be confirmed visually or even when magnified 10 times, and the image was uniform. B: In the area with a recording duty of 100 - 150%, the beading phenomenon could not be confirmed visually, but it was confirmed when magnified 10 times. C: In the area with a recording duty of 100 - 150%, the beading phenomenon was confirmed visually.

[0083] (Abrasion resistance) Using the above inkjet recording apparatus, 15 solid images with a recording duty in the range of 10 - 150% in 10% increments were recorded on glossy paper (product name "Canon Photo Paper Glossy Gold GL - 101", manufactured by Canon) in 8 passes. After 5 minutes from the recording, a rubbing test was conducted on the surface of the solid image by dragging it 3 cm with a polycarbonate card having a thickness of 0.76 mm. The test conditions were an angle of 30°, a load of 0.7 kgf, and a speed of 3 cm / second. The state of the image after the rubbing test was visually confirmed, and the abrasion resistance of the image was evaluated according to the following evaluation criteria. A: No traces of rubbing could be confirmed visually from the front for all 15 images. B: Traces of rubbing could be visually confirmed for some images, but the substrate of the recording medium was not visible. C: Traces of rubbing could be visually confirmed for some images, and the white background of the recording medium was visible.

[0084] TIFF2025100447000018.tif182170

[0085] The evaluation result of the abrasion resistance of Example 27 was the same "B" as that of Example 26 and Example 38, but Example 26 and Example 38 were superior.

Claims

1. An aqueous ink for inkjet containing a pigment, a polyether-modified silicone surfactant, a phosphate ester, and calcium ions, wherein the phosphate ester is at least one selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate, the polyether-modified silicone surfactant contains an ethylene oxide group, and the number of moles of added ethylene oxide groups of the polyether-modified silicone surfactant is equal to or more than the number of moles of added ethylene oxide groups of the phosphate ester. An aqueous ink characterized by this.

2. The aqueous ink according to claim 1, wherein the content (% by mass) of the phosphate ester is 0.10 times or more and 10.0 times or less in terms of mass ratio to the content (% by mass) of the polyether-modified silicone surfactant.

3. The aqueous ink according to claim 1, wherein the content (% by mass) of the phosphate ester is 25 times or more and 10,000 times or less in terms of mass ratio to the content (% by mass) of the calcium ions.

4. The aqueous ink according to claim 1, wherein the number of moles of added ethylene oxide groups of the polyether-modified silicone surfactant is 3 or more more than the number of moles of added ethylene oxide groups of the phosphate ester.

5. The aqueous ink according to claim 1, wherein the number of moles of added ethylene oxide groups of the polyether-modified silicone surfactant is 7 or more and 15 or less.

6. The aqueous ink according to claim 1, wherein the phosphate ester is a compound represented by the following general formula (1). (In the general formula (1), R Ａ represents an alkyl group or an alkenyl group having 12 to 18 carbon atoms, and x represents an integer of 3 to 10).

7. The aqueous ink according to claim 1, wherein the polyether-modified silicone surfactant is a compound represented by the following general formula (2). (In the general formula (2), R １ represents an alkylene group, R ２ represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or more, a represents an integer of 1 or more, and b represents an integer of 0 or more).

8. Furthermore, the aqueous ink according to claim 1, which contains 1-(2-hydroxyethyl)-2-pyrrolidone.

9. An ink cartridge including an ink and an ink storage unit for storing the ink, wherein the ink is the aqueous ink according to any one of claims 1 to 8. An ink cartridge characterized by this.

10. An inkjet recording method for ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is the aqueous ink according to any one of claims 1 to 8. An inkjet recording method characterized by this.

Images