Water-based ink, ink cartridge, and ink-jet 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 a water-based ink, an ink cartridge, and an inkjet recording method. [Background technology]

[0002] In recent years, there has been an increase in the number of opportunities to record images on large-format recording media, such as posters and advertisements, using inkjet recording devices capable of recording large-format images. Such images require durability, such as lightfastness, so that they can withstand display, and therefore inks containing pigments as coloring materials (pigment inks) are widely used.

[0003] When using an inkjet recording device capable of recording large-format images, the image may come into contact with a basket (a component made of cloth or other material that holds the recorded image) immediately after recording. Furthermore, the image may be moved by multiple people immediately after recording, so the image is required to have scratch resistance even immediately after recording.

[0004] Furthermore, when recording large-format images, multiple images are recorded at once, and therefore printing speeds are increasing. In order to improve printing speeds, it is important that the ink applied to the recording medium quickly penetrates into the interior of the recording medium and does not overflow onto the surface of the recording medium. In other words, inks with good permeability into the recording medium are required.

[0005] Various proposals have been made to solve the above-mentioned problems. For example, an ink containing a wax emulsion and latex particles having a specific glass transition temperature (Tg) that can record images with improved scratch resistance has been proposed (Patent Document 1). Also, an inkjet ink containing a phosphate ester compound that is used in combination with a pretreatment liquid has been proposed (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2015 / 0225586 [Patent Document 2] Japanese Patent Publication No. 2022-14128 Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have investigated the characteristics of images recorded with the ink proposed in Patent Document 1. As a result, they found that while the abrasion resistance of the images was good, the level of beading resistance was insufficient. Analysis of the image surface revealed that the abrasion resistance of the images was reduced because the penetration of the ink into the recording medium was reduced due to the sealing action of wax and latex particles in the ink applied to the recording medium.

[0008] Therefore, an object of the present invention is to provide a water-based inkjet ink that is capable of recording images with less noticeable beading and excellent abrasion resistance. Another object of the present invention is to provide an ink cartridge and an inkjet recording method that use this water-based ink. [Means for solving the problem]

[0009] That is, according to the present invention, there is provided an aqueous inkjet ink 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 phosphates and polyoxyethylene alkenyl ether phosphates, the polyether-modified silicone surfactant contains ethylene oxide groups, and the number of moles of ethylene oxide groups added in the polyether-modified silicone surfactant is equal to or greater than the number of moles of ethylene oxide groups added in the phosphate ester. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a water-based inkjet ink that is capable of recording images with less noticeable beading and excellent abrasion resistance. Furthermore, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method that use this water-based ink. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating an embodiment of an ink cartridge of the present invention. [Figure 2] 1A and 1B are diagrams schematically illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which FIG. 1A is a perspective view of the main part of the inkjet recording apparatus, and FIG. 1B is a perspective view of a head cartridge. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the aqueous ink as dissociated ions, but for convenience it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Unless otherwise specified, physical property values ​​are those at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (relative humidity 50%).

[0013] Unless otherwise specified, the term "unit" refers to a unit structure corresponding to one monomer. When written as "(meth)acrylic acid" or "(meth)acrylate", it means "acrylic acid, methacrylic acid" or "acrylate, methacrylate", respectively.

[0014] The present inventors have investigated inks containing various waxes, urethane resins, etc., in order to record images that are both beading-resistant and scratch-resistant. However, because waxes and urethane resins are polymeric materials, they have been found to tend to reduce beading resistance due to factors such as a filling effect and an increase in the viscosity of the ink.

[0015] Therefore, the present inventors investigated inks containing silicone surfactants to improve the abrasion resistance of images by reducing the surface energy. As a result, they found that adding a silicone surfactant improved the abrasion resistance of images. However, they also found that adding a silicone surfactant made ink droplets more likely to repel each other, resulting in localized areas where ink droplets were joined together or where no ink droplets were present, i.e., uneven shading, making beading more likely to occur.

[0016] As a result of further investigation, the present inventors discovered that by creating an ink that satisfies the following requirements (i) and (ii), it is possible to record an image that has both beading resistance and abrasion resistance, and thus arrived at the present invention. (i) Contains a pigment, a polyether-modified silicone surfactant, a phosphate ester (at least one selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether), and calcium ions. (ii) The number of moles of ethylene oxide groups added in the polyether-modified silicone surfactant is equal to or greater than the number of moles of ethylene oxide groups added in the phosphate ester.

[0017] The present inventors speculate as follows about the mechanism by which the above-described effects are obtained. Calcium ions are stabilized in the ink by oxygen atoms in the ether bonds that make up the polyoxyethylene chains of the polyether-modified silicone surfactant, polyoxyethylene alkyl ether phosphate, and polyoxyethylene alkenyl ether phosphate. Furthermore, satisfying the above requirement (ii) makes it easier for calcium ions to exist around the polyether-modified silicone surfactant, which has a relatively large number of oxygen atoms. Hereinafter, "polyoxyethylene alkyl ether phosphate" and "polyoxyethylene alkenyl ether phosphate" will also be collectively referred to as "polyoxyethylene alkyl ether phosphate."

[0018] When the ink is applied to a recording medium, as the water evaporates, the phosphate groups in the polyoxyethylene alkyl ether phosphate bond with calcium ions to form calcium phosphate, accelerating solid-liquid separation and promoting penetration of the ink into the recording medium. Furthermore, as described above, the presence of calcium ions around the polyether-modified silicone surfactant allows the polyether-modified silicone surfactant and polyoxyethylene alkyl ether phosphate to be present near the surface of the ink droplets. This makes it possible to suppress the decrease in surface energy that occurs when the silicone surfactant is simply added, suppressing ink droplets from repelling each other and improving beading resistance without impairing ink penetration.

[0019] Furthermore, due to the solid-liquid separation promoted by the formation of calcium phosphate, alkyl groups of polyoxyethylene alkyl ether phosphate present near the surface of the ink droplets interact hydrophobically with each other. As a result, some of the polyoxyethylene alkyl ether phosphates self-assemble, and the carbon chains exhibit slipperiness, which is thought to result in improved abrasion resistance that could not be achieved by simply adding a silicone surfactant.

[0020] If the ink does not contain a polyether-modified silicone surfactant, the surface energy of the printed image is not reduced, and the effect of improving abrasion resistance is not achieved. Furthermore, 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 tend to exist around the polyoxyethylene alkyl ether phosphate. As a result, the polyoxyethylene alkyl ether phosphate cannot exist around the polyether-modified silicone surfactant when water evaporates, and the decrease in surface energy associated with the silicone surfactant cannot be suppressed. As a result, the effect of improving beading resistance is not achieved.

[0021] <Ink> The ink of the present invention is an aqueous inkjet ink 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 phosphates and polyoxyethylene alkenyl ether phosphates. The polyether-modified silicone surfactant contains ethylene oxide groups, and the number of moles of ethylene oxide groups added in the polyether-modified silicone surfactant is equal to or greater than the number of moles of ethylene oxide groups added in the phosphate ester. The ink of the present invention does not need to be used in combination with a liquid that reacts or thickens when they come into contact with each other (for example, a reaction liquid containing a component that reacts with the ink). The components that make up the ink and the physical properties of the ink are described below.

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

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

[0024] The average particle size (average primary particle size) of the pigment is preferably 10 nm or more and 300 nm or less. If the average particle size of the pigment is less than 10 nm, the interaction between the primary particles becomes strong, and the storage stability of the ink may not be sufficiently obtained. On the other hand, if the average particle size of the pigment is more than 300 nm, the saturation and gloss of the image may not be sufficient. In this specification, the "average particle size" refers to the cumulative 50% particle size (median diameter; D) of the particle size distribution based on volume. 50 ) means

[0025] Examples of pigment dispersion methods include resin-dispersed pigments, which use a resin as a dispersant, and self-dispersed pigments, in which hydrophilic groups are bonded to the pigment particle surface. Other examples include resin-bonded pigments, in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microencapsulated pigments, in which the pigment particle surface is coated or encapsulated with a resin. It is also possible to use pigments with different dispersion methods in combination. When using a resin-dispersed pigment, the pigment content (mass%) in the ink is preferably 0.30 to 10.0 times the mass ratio of the resin dispersant content (mass%).

[0026] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use a resin that can disperse the pigment in the aqueous medium by the action of anionic groups. 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 hydrophilic monomers 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 cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

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

[0029] Examples of self-dispersing pigments include pigments in which anionic groups are bonded to the particle surface directly or via other atomic groups. Examples of the anionic groups include carboxylic acid groups, sulfonic acid groups, phosphate groups, and phosphonic acid groups. Examples of counter ions of the anionic groups include cations such as hydrogen atoms, alkali metals, ammonium, and organic ammonium groups. The other atomic groups function as spacers between the pigment particle surface and the anionic groups, and preferably have a molecular weight of 1,000 or less. Examples of the other atomic groups include alkylene groups having approximately 1 to 6 carbon atoms, arylene groups such as phenylene groups and naphthylene groups, ester groups, imino groups, amide groups, sulfonyl groups, and ether groups.

[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 side chain hydrocarbon groups and terminal hydrocarbon groups of silicone oil is substituted with a polyether group. Examples of polyether groups include polyoxyethylene groups, polyoxypropylene groups, and polyoxyalkylene groups in which oxyethylene groups (EO) and oxypropylene groups (PO) are attached in a block or random manner. Compounds in which polyether groups are grafted onto a silicone main chain and compounds in which silicone and polyether groups are bonded in a block manner can also 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 to stabilize the calcium ions.

[0031] The content (mass %) of the polyether-modified silicone surfactant in the ink is preferably 0.1% by mass or more and 1.0% by mass or less, based on the total mass of the ink. Furthermore, the number of moles of ethylene oxide groups added to the polyether-modified silicone surfactant is preferably three or more moles greater than the number of moles of ethylene oxide groups added to the phosphate ester, as described below. 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 the polyoxyethylene alkyl ether phosphate and calcium ions is more likely to occur around the polyether-modified silicone surfactant, allowing both to be more uniformly oriented on the surface of the ink droplets, further improving the scratch resistance of the image.

[0032] The number of moles of ethylene oxide groups added in the polyether-modified silicone surfactant is preferably 7 to 15, and more preferably 7 to 14. If the number of moles of ethylene oxide groups added is less than 7, the number of oxygen atoms in the ether bond is small, which may result in an insufficient calcium ion stabilization effect. As a result, solid-liquid separation between the polyoxyethylene alkyl ether phosphate and calcium ions is difficult to occur, and the ink penetration into the recording medium may be reduced, resulting in an insufficient improvement in beading resistance. On the other hand, if the number of moles of ethylene oxide groups added in the polyether-modified silicone surfactant is more than 15, the water solubility of the polyether-modified silicone surfactant may be excessively high. This may result in the polyether-modified silicone surfactant being less likely to orient at the interface of the ink droplets, resulting in an insufficient improvement in abrasion resistance.

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

[0034] TIFF0007802903000001.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] TIFF0007802903000002.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] TIFF0007802903000003.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 general formula (2), R4 in general formula (3), and R6 in 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 general formula (2), R3 in general formula (3), and R5 in 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. Of these, a methyl group is particularly preferable.

[0038] Among these, the polyether-modified silicone surfactant is preferably a compound represented by general formula (2). Because compounds represented by general formula (2) have oxyethylene groups in their side chains, the oxyethylene groups have a higher degree of freedom than compounds having oxyethylene groups in their main chains, making them more likely to capture calcium ions. Therefore, when a compound represented by general formula (2) is used, polyoxyethylene alkyl ether phosphate is more likely to react around the compound. This allows the polyether-modified silicone surfactant and polyoxyethylene alkyl ether phosphate to be more uniformly oriented on the surface of the ink droplets, further improving the scratch resistance of the image. In general formula (2), m+n is preferably 3 or more and 10 or less. Furthermore, m is preferably 2 or more and 8 or less, and n is preferably 1 or 2, and more preferably 1.

[0039] The compound represented by 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 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). Furthermore, the compound represented by 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] TIFF0007802903000004.tif26170 (in the general formula (A), m and n each independently have the same meaning as m and n in the general formula (2))

[0041] TIFF0007802903000005.tif18170 (in the general formula (B), R 11 represents an alkenyl group, and R2, a, and b have the same meanings as R2, a, and b in general formula (2).

[0042] TIFF0007802903000006.tif28170 (in the general formula (C), p has the same meaning as p in the general formula (3))

[0043] TIFF0007802903000007.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 general formula (3).

[0044] TIFF0007802903000008.tif25170 (in the general formula (E), q has the same meaning as q in the general formula (4))

[0045] TIFF0007802903000009.tif19170 (in the general formula (F), R 51 and R 61 represents an alkenyl group, and e and f have the same meanings as e and f in general formula (4).

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

[0047] In general formula (B), R 11 is a group that becomes R1 in general formula (2) by addition reaction between a compound represented by general formula (A) and a compound represented by general formula (B). 41 is a group that becomes R4 in general formula (3) by addition reaction between a compound represented by general formula (C) and a compound represented by general formula (D). 51 and R 61 are groups that become R5 and R6 in general formula (4) by addition reaction between a compound represented by general formula (E) and a compound represented by general formula (F), respectively. 11 , R in general formula (D) 41 and R in general formula (F)51 and R 61 The alkenyl group represented by the formula (I) 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 phosphate ester selected from the group consisting of polyoxyethylene alkyl ether phosphate and polyoxyethylene alkenyl ether phosphate. Polyoxyethylene alkyl ether phosphate is a phosphate ester of polyoxyethylene alkyl ether. 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 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 phosphate ester in the ink is preferably 0.10 to 10.0 times the content (mass %) of the polyether-modified silicone surfactant. If the mass ratio is less than 0.10, it is difficult to suppress the reduction in surface energy caused by the polyether-modified silicone surfactant, and ink droplets are likely to join together locally, resulting in uneven shading, and the beading resistance may not be sufficiently improved. On the other hand, if the mass ratio is more than 10.0, it may be difficult to uniformly orient the polyoxyethylene alkyl ether phosphate and polyether-modified silicone surfactant near the surface of the ink droplets, and the abrasion resistance may not be sufficiently improved. The mass ratio is more preferably 1.0 to 7.0 times.

[0050] The content (mass %) of the phosphate ester in the ink is preferably 25 to 10,000 times the mass of the calcium ion content (mass %). A mass ratio of 50 to 9,000 times is more preferable, and a mass ratio of 300 to 8,000 times is particularly preferable. If the mass ratio is less than 25 times, the cohesive force of the polyoxyethylene alkyl ether phosphate increases upon water evaporation, resulting in insufficient ink penetration into the recording medium and insufficient improvement in beading resistance. On the other hand, if the mass ratio is more than 10,000 times, the polyoxyethylene alkyl ether phosphate may not be able to sufficiently promote solid-liquid separation, resulting in insufficient improvement in beading resistance and abrasion resistance.

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

[0052] TIFF0007802903000010.tif27170 (in the general formula (1), R A represents an alkyl or alkenyl group having 12 to 18 carbon atoms, and x represents an integer of 3 to 10.

[0053] In general formula (1), R A If the number of carbon atoms in the alkyl or alkenyl group represented by the formula (1) is less than 12, the carbon chains may not easily form hydrophobic interactions with each other. As a result, self-assembly of the polyoxyethylene alkyl ether phosphate may not easily occur, and the effect of improving the abrasion resistance may not be sufficiently obtained. A If the number of carbon atoms in the alkyl or alkenyl group represented by R exceeds 18, the water solubility of the polyoxyethylene alkyl ether phosphate decreases. As a result, the polyoxyethylene alkyl ether phosphates tend to aggregate with each other as the water evaporates, which reduces the permeability of the ink into the recording medium and may prevent a sufficient improvement in beading resistance. A When multiple compounds having different numbers of carbon atoms in the alkyl or alkenyl groups represented by AThe average number of carbon atoms in the alkyl group may be 12 or more and 18 or less.

[0054] In general formula (1), if the number of moles of ethylene oxide groups added, represented by x, is less than 3, the water solubility of the polyoxyethylene alkyl ether phosphate decreases. As a result, polyoxyethylene alkyl ether phosphates tend to aggregate with each other as water evaporates, reducing the ink's penetration into the recording medium and potentially preventing a sufficient improvement in beading resistance. On the other hand, if the number of moles of ethylene oxide groups added, represented by x, is more than 10, the polyoxyethylene alkyl ether phosphate has high water solubility, which may reduce its reactivity with calcium ions. As a result, the solid-liquid separation is not sufficiently promoted, and the beading resistance may not be sufficiently improved.

[0055] (Calcium ions) The ink contains calcium ions, which are polyvalent metal ions. Compared to other metal ions, calcium ions have a higher reactivity with polyether-modified silicone surfactants. Therefore, when calcium ions are contained in the ink, the polyether-modified silicone surfactant reacts with the calcium ions as water evaporates, promoting solid-liquid separation. The content (mass %) of calcium ions in the ink is preferably 0.0001% to 0.006% by mass, based on the total mass of the ink.

[0056] By blending a metal salt capable of generating calcium ions into the ink, calcium ions can be present in the ink. Counter ions that form metal salts with calcium ions include Cl. - , Br - , I - , ClO - , ClO2 - , ClO3 - , ClO4 - , NO2 - , NO3 - , SO4 2- , CO3 2- , PO4 3- , HPO42- , and H2PO4 - Inorganic anions such as HCO3 - , H.C.O.O. - , (COO - )2, COOH(COO - ), CH3COO - , C2H4(COO - )2, C6H5CO - , C6H4(COO - )2 and CH3SO4 - and other organic anions.

[0057] The metal salt may be used in the form of a hydrate. Calcium ions may be present in the ink due to contamination from ink constituent materials such as pigments, resins, and water-soluble organic solvents, or leaching from components with which the ink comes into contact. The calcium ion content in the ink can be measured by a measurement method such as ICP atomic emission spectroscopy.

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

[0059] The ink preferably further contains 1-(2-hydroxyethyl)-2-pyrrolidone, a nitrogen-containing compound. 1-(2-hydroxyethyl)-2-pyrrolidone is a polar solvent containing a hydroxyethyl group in its molecule. The inclusion of 1-(2-hydroxyethyl)-2-pyrrolidone can improve the wetting of the ink onto the recording medium surface. Furthermore, the hydroxy group in the 1-(2-hydroxyethyl)-2-pyrrolidone molecule has a high affinity for polyether-modified silicone surfactants and polyoxyethylene alkyl ether phosphates. Therefore, the inclusion of 1-(2-hydroxyethyl)-2-pyrrolidone can further improve the ink's penetration into the recording medium and the beading resistance of the recorded image.

[0060] (Other ingredients) In addition to the components described above, the ink may contain, as necessary, 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 ethyleneurea. Furthermore, the ink may contain, as necessary, various additives such as surfactants other than the above-mentioned polyether-modified silicone surfactants and phosphate esters, pH adjusters, antifoaming agents, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, and chelating agents.

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

[0062] <Ink cartridges> The ink cartridge of the present invention includes ink and an ink storage section that stores the ink. The ink stored in the ink storage section is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically illustrating one embodiment of the ink cartridge of the present invention. As shown in FIG. 1, the bottom of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The interior of the ink cartridge serves as an ink storage section for storing the ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are connected to each other via a communication port 18. The absorber storage chamber 16 is also connected to the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 contains absorbers 22 and 24 that retain the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, but may instead use an absorber to hold all of the ink stored therein. Alternatively, the ink storage section may not have an absorber and may store all of the ink in a liquid state. Furthermore, the ink cartridge may be configured to have an ink storage section and a recording head.

[0063] <Inkjet recording method> The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods for ejecting the ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to employ a method of ejecting the ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be any known method.

[0064] FIG. 2 is a diagram schematically illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main components of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting a recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured to accommodate an ink cartridge 42. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. An image is then recorded on the recording medium 32 by transporting the recording medium 32 in the sub-scanning direction by a transport means (not shown).

[0065] As the recording medium, it is preferable to use permeable paper such as plain paper or a recording medium having a coating layer (glossy paper or art paper). In particular, it is preferable to use a recording medium having a coating layer that allows at least a portion of the pigment in the ink to be present on or near the surface. The recording medium can be appropriately selected depending on the intended use of the recorded image. For example, glossy paper suitable for recording images with a glossy appearance of photographic quality, or art paper that makes use of the texture of the substrate (such as drawing paper, canvas, or Japanese paper) to express paintings, photographs, and graphic images as desired, can be used. In particular, it is preferable to use so-called glossy paper, in which the surface of the coating layer exhibits gloss. [Example]

[0066] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the invention. Regarding the amount of a component, "parts" and "%" are based on mass unless otherwise specified. 1 ppm is equivalent to 0.0001%.

[0067] <Preparation of pigment dispersion> The components (unit: parts) listed in Table 1 and 85 parts of 0.3 mm zirconia beads were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 3 hours with water cooling. The dispersion was then centrifuged to remove undispersed material, including coarse particles. The dispersion was then pressure-filtered through a 3.0 μm pore cellulose acetate filter (manufactured by Advantec) to prepare pigment dispersions 1 to 8. An aqueous solution of Resin 1, used as a dispersant, was prepared as follows: A styrene-ethyl acrylate-acrylic acid copolymer (Resin 1) with an acid value of 170 mg KOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of Resin 1 were neutralized with potassium hydroxide in an amount equal to the acid value, and an appropriate amount of pure water was added to obtain an aqueous solution of Resin 1 with a resin (solids) content of 20.0%. Details of each component in Table 1 are provided below. Carbon black (product name "Black Pearls 880", manufactured by Cabot) CI Pigment Blue 15:3 (product name "Hostapalm Blue B2G", manufactured by Heubach) Magenta solid solution pigment (a solid solution of CI Pigment Red 202 and CI Pigment Violet 19, product name "Synthesia Magenta D4500J", manufactured by Sun Chemical) CI Pigment Yellow 74 (product name "Fast Yellow 011", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) CI Pigment Red 254 (product name "Irgazin Red L3630", manufactured by BASF) CI Pigment Orange 43 (product name "Novopalm Orange GRL", manufactured by Clariant) CI Pigment Green 7 (product name "Fastgen Green S", manufactured by DIC) CI Pigment Blue 23 (product name "Host Palm Violet RLSP", manufactured by Clariant)

[0068] TIFF0007802903000011.tif89170

[0069] <Preparing phosphate ester> Using an 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] Strong phosphoric acid (manufactured by Rasa Industries) and N,N-dimethylformamide were placed in a flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, and stirred at 60°C. After dropping in an aliphatic alcohol ethoxylate, the mixture was heated to 80°C and reacted for 12 hours. Saturated saline was then added, and the mixture was stirred at 60°C for 12 hours to hydrolyze the pyrophosphate ester, yielding a phosphate ester surfactant, polyoxyethylene alkyl ether phosphate or polyoxyethylene alkenyl ether phosphate. The types of phosphate esters are shown in Table 2. For phosphate esters 3 to 5, the average number of carbon atoms in the alkyl group is shown.

[0071] TIFF0007802903000012.tif115170

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

[0073] TIFF0007802903000013.tif76170

[0074] (Surfactant 9) The polysiloxane compound and polyoxyalkylene compound shown below were placed in a glass vessel equipped with a thermometer and a stirring means. 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 surfactant having a structure represented by general formula (3). Here, the polysiloxane compound used was a compound represented by general formula (C) (p=8). The polyoxyalkylene compound used was 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 which p = 8, c = 11, d = 0, R3 = methyl group, and R4 = propylene group in general formula (3).

[0075] <Ink Preparation> (Examples 1 to 35, Comparative Examples 1 to 7) The components (unit: %) shown in the upper part of Tables 4-1 to 4-4 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 0.8 μm to prepare each ink. 2+ The content of calcium ions (Ca) in the ink was adjusted using Ca(NO3)2·4H2O. 2+ The content of ) was measured using an ICP optical emission spectrometer (product name "SPS5100", manufactured by SII Nano Technology). The properties of the obtained inks are shown in the lower part of Tables 4-1 to 4-4. The details of the materials in Tables 4-1 to 4-4 are shown below. Resin 2 aqueous solution: A styrene-ethyl acrylate-acrylic acid copolymer (Resin 2) with an acid value of 160 mgKOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of Resin 2 were neutralized with potassium hydroxide in an amount equal to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of Resin 2 with a resin (solids) content of 20.0%. Proxel GXL: Preservative (manufactured by Arch Chemicals) Capstone FS3100 (perfluoroalkyl ethylene oxide adduct, manufactured by Chemours)

[0076] TIFF0007802903000014.tif253170

[0077] TIFF0007802903000015.tif253170

[0078] TIFF0007802903000016.tif250170

[0079] TIFF0007802903000017.tif255159

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

[0081] <Evaluation> Each ink was filled into an ink cartridge and installed in an inkjet recording device (trade name "PIXUS PRO-10S," manufactured by Canon) that ejects ink from a recording head using thermal energy. In this example, the recording duty of a solid image recorded at a resolution of 600 dpi x 600 dpi under conditions in which eight ink droplets of 3.5 ng per droplet were deposited in a unit area of ​​1 / 600 inch x 1 / 600 inch was defined as 100%. This device also supports multi-pass recording, in which ink deposition to a unit area on the recording medium is divided into multiple relative scans of the recording head and the recording medium. For example, four-pass recording means that ink deposition to a unit area on the recording medium was divided into four relative scans of the recording head and the recording medium. A unit area can be defined as any area, such as one pixel or one band. In this invention, the following evaluation criteria for each item were used: "A" and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 5.

[0082] (Beading resistance) Using the inkjet recording device described above, six types of solid images were recorded in four passes on glossy paper (product name "Canon Photo Paper Glossy Pro Platinum Grade PT-101", manufactured by Canon) with a recording duty ranging from 100 to 150% in 10% increments. The recorded solid images were observed, and beading resistance was evaluated according to the following evaluation criteria. A: In the range of 100 to 150% recording duty, no beading phenomenon was observed visually or even at 10x magnification, and the image was uniform. B: In the region of 100 to 150% recording duty, the beading phenomenon was not visible to the naked eye, but was confirmed when magnified 10 times. C: In the region of 100 to 150% recording duty, beading was visually confirmed.

[0083] (Abrasion resistance) Using the inkjet recording device described above, 15 solid images were recorded in 8 passes on glossy paper (Canon Photo Paper Gloss Gold GL-101, manufactured by Canon) with a recording duty ranging from 10 to 150% in 10% increments. Five minutes after recording, a scratch test was performed in which the surface of the solid image was dragged 3 cm with a 0.76 mm thick polycarbonate card. The test conditions were an angle of 30°, a load of 0.7 kgf, and a speed of 3 cm / sec. The condition of the image after the scratch test was visually inspected, and the scratch resistance of the image was evaluated according to the following evaluation criteria. A: Even when visually inspecting all 15 images from the front, no traces of scraping could be seen. B: Scraping marks could be visually confirmed in some images, but the underlying surface of the recording medium was not visible. C: Scraping marks were visible in some images, and the white background of the recording medium was visible.

[0084] TIFF0007802903000018.tif182170

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

Claims

1. A water-based inkjet ink 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 phosphates and polyoxyethylene alkenyl ether phosphates, the polyether-modified silicone surfactant contains an ethylene oxide group, The aqueous ink is characterized in that the number of moles of ethylene oxide groups added to the polyether-modified silicone surfactant is equal to or greater than the number of moles of ethylene oxide groups added to the phosphate ester.

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

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

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

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

6. 2. 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 or alkenyl group having 12 to 18 carbon atoms, and x represents an integer of 3 to 10.

7. 2. 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, and R ２ represents a hydrogen atom or an alkyl group, m and n each independently represent an integer of 1 or greater, a represents an integer of 1 or greater, and b represents an integer of 0 or greater.

8. 2. The aqueous ink according to claim 1, further comprising 1-(2-hydroxyethyl)-2-pyrrolidone.

9. An ink cartridge comprising ink and an ink storage section for storing the ink, 9. An ink cartridge, wherein the ink is the aqueous ink according to claim 1.

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

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