Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide an aqueous ink for inkjet which is capable of recording an image excellent in glossiness and scratch resistance and has excellent intermittent discharge stability.SOLUTION: The aqueous ink for inkjet contains a pigment, a water-soluble urethane resin, a polyethylene wax, a water-soluble organic solvent, and polyethylene glycol. The water-soluble organic solvent contains at least one selected from the group consisting of glycols and glycol ethers having a vapor pressure at 20°C of 1.0 Pa or more and a polarity term δP of Hansen solubility parameters of 10.0 MPa1 / 2 or less. The polyethylene glycol has a number average molecular weight of 200 or more.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, inkjet recording methods have made it possible to record high-resolution images with excellent gloss, similar to those achieved by silver halide photography and offset printing. Coloring materials used in inks include dyes and pigments. Among these, pigments are widely used as coloring materials because they can record images with excellent fastness, such as gas resistance, light resistance, and water resistance.

[0003] In images recorded on glossy paper using ink containing a dye as a colorant (dye ink), the dye dissolves in a molecular state in the aqueous medium and is absorbed into the fixing layer, making the image surface scratch-resistant. On the other hand, in images recorded on glossy paper using ink containing a pigment as a colorant (pigment ink), the pigment is not absorbed into the fixing layer and is fixed to the surface of the glossy paper, making the image surface scratched by rubbing. For this reason, improving the scratch resistance of recorded images is a challenge for pigment inks. Furthermore, in commercial and industrial printing, scratch resistance immediately after recording is required in environments where the image is touched immediately after recording, such as high-speed recording and label applications.

[0004] For example, Patent Document 1 proposes an ink that combines gloss and abrasion resistance by containing a water-soluble urethane resin and wax particles, while Patent Documents 2 and 3 describe inks that contain a water-soluble urethane resin and wax particles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-202419 [Patent Document 2] Japanese Patent Publication No. 2023-060416 [Patent Document 3] Patent Publication No. 2021-070239 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the investigations of the present inventors, it was found that the images recorded with the ink proposed in Patent Document 1 had good abrasion resistance after storage at room temperature for 24 hours, but had poor abrasion resistance immediately after recording. On the other hand, the images recorded with the inks described in Patent Documents 2 and 3 had a certain degree of abrasion resistance immediately after recording, but this was not sufficient, and the "intermittent ejection stability" was also poor.

[0007] Intermittent ejection refers to ejection without a recovery operation of the print head after a prolonged period of time in which ink is not ejected from the ejection ports of an inkjet print head. In such a case, moisture in the ink evaporates from the ejection ports, causing the ink to thicken and adhere to the nozzles. If an attempt is then made to eject ink from the ejection ports again without a recovery operation, the first ejection of ink may become unstable, or ink may not be ejected at all, making the image more susceptible to distortion. In this specification, this state is referred to as having low "intermittent ejection stability."

[0008] Therefore, an object of the present invention is to provide a water-based inkjet ink that is capable of recording images with excellent gloss and abrasion resistance and that has excellent intermittent ejection stability. 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 water-soluble urethane resin, a polyethylene wax, a water-soluble organic solvent, and polyethylene glycol, wherein the water-soluble organic solvent has a vapor pressure of 1.0 Pa or more at 20° C. and a polarity term δ of the Hansen solubility parameter P is 10.0 MPa 1 / 2 The present invention provides an aqueous ink comprising at least one polyethylene glycol selected from the group consisting of glycols and glycol ethers, wherein the polyethylene glycol has a number average molecular weight of 200 or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inkjet water-based ink that is capable of recording images with excellent gloss and abrasion resistance and has excellent intermittent ejection stability. 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 ink dissociated into ions, but for convenience it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. In this specification, "(meth)acrylic acid" means "acrylic acid, methacrylic acid." In this specification, the term "unit" constituting a resin means a repeating unit derived from one monomer.

[0013] Inks containing water-soluble urethane resin and polyethylene wax can record images with excellent gloss and abrasion resistance. However, the inventors' studies have found that the abrasion resistance and intermittent ejection stability of images immediately after recording differ depending on the type of water-soluble organic solvent contained in the ink. The inventors focused on two parameters as characteristics of the water-soluble organic solvent that affect these performances. One was the vapor pressure of the water-soluble organic solvent from the perspective of volatility. Water-soluble organic solvents with high vapor pressure are highly volatile and easily evaporate even immediately after recording, and can therefore have a certain effect on the abrasion resistance of images immediately after recording.

[0014] The second is the polarity term δ of the Hansen solubility parameters of water-soluble organic solvents from the viewpoint of polarity. P (Hereinafter, simply “polar term δ P "). In pigment dispersions, pigments are dispersed in water by making the surface of the pigment hydrophilic. Therefore, pigment dispersions are made using highly polar water-soluble organic solvents, i.e., the polarity term δ of the Hansen solubility parameters P It has high affinity with water-soluble organic solvents with high solubility. The polarity term δ of the Hansen solubility parameters P When the ink contains a highly soluble water-soluble organic solvent, even if the water evaporates from the ink near the ejection orifice and the concentration of the water-soluble organic solvent increases, the pigment is likely to maintain a dispersed state because of the high affinity between the water-soluble organic solvent and the pigment dispersion liquid.

[0015] On the other hand, the pigment dispersion is made of a water-soluble organic solvent with low polarity, i.e., the polarity term δ P It has low affinity with water-soluble organic solvents with low solubility. The polarity term δ of the Hansen solubility parameter P When an ink contains a water-soluble organic solvent with a low water content, evaporation of water from the ink near the ejection orifices increases the concentration of the water-soluble organic solvent, making it difficult to maintain the pigment dispersion due to the low affinity between the water-soluble organic solvent and the pigment dispersion. As a result, the pigment dispersion is encouraged to move away from the ejection orifices, where the affinity is higher and the water concentration is higher. This phenomenon reduces the pigment concentration, thereby reducing the viscosity of the ink and improving intermittent ejection stability, even if the ink is not ejected from the ejection orifices for a long period of time.

[0016] The present inventors have conducted extensive research using the above two points as criteria for selecting water-soluble organic solvents, and have evaluated the gloss and abrasion resistance of images, as well as the intermittent ejection stability of inks for each of the solvents. As a result, the specific vapor pressure and polarity term δ P It has been found that the desired ink can be obtained by using at least one water-soluble organic solvent selected from the group consisting of glycols and glycol ethers having the formula: and polyethylene glycol having a number average molecular weight of 200 or more. That is, the water-soluble organic solvent has a vapor pressure of 1.0 Pa or more at 20°C and a polar term δ of the Hansen solubility parameter P is 10.0 MPa 1 / 2 At least one selected from the group consisting of glycols and glycol ethers is used, which has the following specific vapor pressure and polarity term δ P By using a glycol and / or glycol ether having the formula (I) and a polyethylene glycol having a number average molecular weight of 200 or more, an ink having excellent intermittent ejection stability and capable of recording images with excellent gloss and abrasion resistance can be obtained.

[0017] Next, a detailed study will be explained. First, the vapor pressure at 20°C is 1.0 Pa or more and the polarity term δ of the Hansen solubility parameter is P is 10.0 MPa 1 / 2It has been found that the use of the following water-soluble organic solvents can improve the scratch resistance of images immediately after printing and the intermittent ejection stability to a certain extent. However, the vapor pressure is 1.0 Pa or more, and the polarity term δ of the Hansen solubility parameters is P is 10.0 MPa 1 / 2 Even if the water-soluble organic solvent is below the above range, other than glycol and glycol ether, neither the scratch resistance nor the intermittent ejection stability reaches the required level.

[0018] Therefore, the present inventors investigated whether excessive evaporation at the ejection port could be suppressed by using a water-soluble organic solvent with a relatively low vapor pressure in combination with polyethylene glycol in order to improve the intermittent ejection stability. As a result, it was found that using polyethylene glycol as a water-soluble organic solvent with a relatively low vapor pressure is effective. That is, polyethylene glycol and a water-soluble organic solvent with a vapor pressure of 1.0 Pa or more at 20°C and a polarity term δ P is 10.0 MPa 1 / 2 It was found that intermittent ejection stability was improved in inks that used the following glycols and / or glycol ethers in combination. Further investigation revealed that the use of polyethylene glycols with a number average molecular weight of 200 or more significantly improved intermittent ejection stability while also significantly improving the scratch resistance of images immediately after printing.

[0019] As described above, in order to record an image with excellent gloss and abrasion resistance, the ink contains a water-soluble urethane resin and a polyethylene wax. Furthermore, the ink has a vapor pressure of 1.0 Pa or more at 20° C. and a polarity term δ P is 10.0 MPa 1 / 2 The ink contains glycol and / or glycol ether having the following structure and polyethylene glycol having a number average molecular weight of at least 200. The inventors of the present invention speculate as follows about the reason why the ink maintains the glossiness of the image while achieving both abrasion resistance immediately after recording and intermittent ejection stability.

[0020] Polyethylene glycol easily interacts with glycols and glycol ethers, which have similar CO bonds, and is thought to keep glycols and glycol ethers, which have high vapor pressures, within the ink system, thereby suppressing evaporation from the ejection port. Furthermore, the polar term δ of the Hansen solubility parameter P It is believed that glycols and glycol ethers with low viscosity effectively promote the movement of the pigment dispersion liquid in a direction away from the ejection orifice, preventing an increase in the viscosity of the ink and providing sufficient intermittent ejection stability.

[0021] On the other hand, even when polyethylene glycol with a low vapor pressure is contained in the ink, it has been found that the abrasion resistance immediately after recording is good as long as the number-average molecular weight is 200 or more. The reason why the use of polyethylene glycol with a low vapor pressure improves abrasion resistance immediately after recording is unclear, but the inventors speculate as follows: It is believed that water evaporates from an image recorded on a recording medium using the ink, and hydrophilic groups of the water-soluble urethane resin, such as urethane bonds or polyol moieties, form associations with the ether bonds of the polyethylene glycol through hydrogen bonding. The formation of associations reduces the polarity of the water-soluble urethane resin, which is believed to strengthen the interaction between the water-soluble urethane resin with reduced polarity and the low-polarity polyethylene wax. The associations of the low-polarity polyethylene glycol and the water-soluble urethane resin and the polyethylene wax are then concentrated on the surface of the image, forming a strong film, which is believed to sufficiently improve abrasion resistance immediately after recording. It is also believed that the interaction between polyethylene glycol and glycol ethers is weakened by forming associations with the water-soluble urethane resin. Because the conditions at the ejection port are different, glycols and glycol ethers with high vapor pressure tend to evaporate easily even immediately after printing, which is thought to improve abrasion resistance immediately after printing. However, if the number-average molecular weight of polyethylene glycol is less than 200, abrasion resistance immediately after printing decreases. This is thought to be because polyethylene glycol with a number-average molecular weight of less than 200 penetrates the recording medium, preventing the above-mentioned effect from being achieved.

[0022] <Ink> The aqueous inkjet ink of the present invention contains a pigment, a water-soluble urethane resin, a polyethylene wax, a water-soluble organic solvent, and polyethylene glycol. Each component constituting the ink will be described in detail below.

[0023] (colorant) The colorant contained in the ink is a pigment, and the content (mass %) of the colorant in the aqueous ink is preferably 0.10% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink.

[0024] Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, imidazolone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, etc. One type of pigment may be used alone, or two or more types may be used in combination.

[0025] As a pigment dispersion method, resin-dispersed pigments using a resin as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface can be used. Also usable are 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 with a resin or the like. It is also possible to use a combination of these pigments with different dispersion methods. Of these, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface.

[0026] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of anionic groups. As the resin dispersant, a resin having anionic groups can be used, and it is preferable to use a resin such as those described below, especially a water-soluble resin. The content (mass %) of the pigment in the aqueous ink is preferably 0.3 to 10.0 times the content (mass %) of the resin dispersant.

[0027] The self-dispersing pigment may be one in which an anionic group is bonded to the surface of the pigment particle directly or via another atomic group (-R-). Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Furthermore, a group that is a combination of these groups may also be used.

[0028] Examples of the anionic group mentioned in the description of the resin dispersant and the self-dispersing pigment include a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group. The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium.

[0029] (Water-soluble urethane resin) The ink contains a water-soluble urethane resin. In this specification, the term "water-soluble resin" refers to a resin that exists in an aqueous medium in a state where, when neutralized with an alkali equivalent to its acid value, it does not form particles whose particle size can be measured by dynamic light scattering. Whether a resin is water-soluble or not can be determined according to the following method. First, a liquid (resin solids content: 10% by mass) containing the resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles having the particle size are measured, the resin can be determined to be water-soluble. The measurement conditions can be, for example, as follows: [Measurement conditions] SetZero: 30 seconds Number of measurements: 3 Measurement time: 180 seconds The particle size distribution measuring device may be a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150" manufactured by Nikkiso). Of course, the particle size distribution measuring device used and the measurement conditions are not limited to those described above. If the ink does not contain a water-soluble urethane resin but instead contains a form in which the urethane resin exists in an aqueous medium in a state of particle size, such as a urethane resin emulsion (urethane resin particles), the gloss of the image will decrease.

[0030] The content (mass%) of the water-soluble urethane resin in the aqueous ink is preferably 0.10% by mass or more and 15.00% by mass or less, based on the total mass of the ink. The content (mass%) of the water-soluble urethane resin is more preferably 0.50% by mass or more and 10.00% by mass or less, and even more preferably 0.50% by mass or more and 3.00% by mass or less. The content of the water-soluble urethane resin refers to the content in one type of ink. By keeping the content of the water-soluble urethane resin in the ink within the above range, the glossiness of the image can be further improved.

[0031] The water-soluble urethane resin preferably contains at least one unit selected from the group consisting of a unit derived from polyethylene glycol and a unit derived from polypropylene glycol. When the water-soluble urethane resin contains the unit, the interaction with the polyethylene glycol in the ink becomes stronger, and the scratch resistance of the image immediately after recording can be further improved. Polyethylene glycol and polypropylene glycol can be used as a polyol without an acid group, as described below, in the synthesis of the water-soluble urethane resin.

[0032] The water-soluble urethane resin may be a water-soluble acrylic urethane resin containing a unit derived from (meth)acrylic acid and / or a unit derived from a (meth)acrylic acid alkyl ester. In this specification, the term "water-soluble urethane resin" also encompasses water-soluble acrylic urethane resin. However, it is preferable that the water-soluble urethane resin does not contain either a unit derived from (meth)acrylic acid or a unit derived from a (meth)acrylic acid alkyl ester. The absence of the above-mentioned acrylic units in the water-soluble urethane resin increases the polarity of the water-soluble urethane resin, which tends to strengthen the interaction with polyethylene glycol in the ink, further improving the scratch resistance of the image immediately after recording. Urethane resins containing a unit derived from (meth)acrylic acid and / or a unit derived from a (meth)acrylic acid alkyl ester are referred to as acrylic urethane resins.

[0033] The water-soluble urethane resin can be obtained, for example, by reacting a polyisocyanate with a component that reacts therewith (such as a polyol or a polyamine). Furthermore, the water-soluble urethane resin may be further reacted with a crosslinking agent or a chain extender. The water-soluble urethane resin is preferably a water-soluble urethane resin containing units derived from a polyisocyanate, a polyol having no acid groups, and a polyol having acid groups.

[0034] Polyisocyanates are compounds having two or more isocyanate groups in their molecular structure. Examples of polyisocyanates include aliphatic polyisocyanates and aromatic polyisocyanates, and one or more of these can be used.

[0035] Specific examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure (alicyclic polyisocyanates) such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane. For the synthesis of the water-soluble urethane resin, one or more of the above-mentioned aliphatic polyisocyanates can be used.

[0036] Specific examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate. One or more of the above aromatic polyisocyanates can be used to synthesize the water-soluble urethane resin. Among the above polyisocyanates, aliphatic polyisocyanates are preferred, alicyclic polyisocyanates are more preferred, and isophorone diisocyanate is even more preferred.

[0037] Polyol is a compound having two or more hydroxyl groups in its molecular structure. Examples of polyols include polyols without acid groups, such as polyether polyols, polyester polyols, and polycarbonate polyols; and polyols with acid groups. One or more of the above polyols can be used to synthesize the water-soluble urethane resin.

[0038] Examples of polyether polyols include addition polymers of alkylene oxides and polyols, glycols such as (poly)alkylene glycol, etc. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, α-olefin oxide, etc. Examples of polyols to be addition polymerized with alkylene oxide include diols such as 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 4,4-dihydroxyphenylpropane, 4,4-dihydroxyphenylmethane, hydrogenated bisphenol A, dimethylolurea and derivatives thereof; and triols such as glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, trimethylolmelamine and derivatives thereof, and polyoxypropylenetriol. Examples of glycols include (poly)alkylene glycols such as tetramethylene glycol, hexamethylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, (poly)tetramethylene glycol, and neopentyl glycol; and ethylene glycol-propylene glycol copolymers. The water-soluble urethane resin can be synthesized using one or more of the above polyether polyols. Among the above polyether polyols, polyethylene glycol and polypropylene glycol are preferred.

[0039] Examples of polyester polyols include acid esters. Examples of acid components constituting acid esters include aromatic dicarboxylic acids such as phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; alicyclic dicarboxylic acids such as hydrogenated products of these aromatic dicarboxylic acids; and aliphatic dicarboxylic acids such as malonic acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkylsuccinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid. Anhydrides, salts, and derivatives (alkyl esters, acid halides) of these compounds can also be used as acid components. Examples of components that form esters with the acid components include polyols such as diols and triols; and glycols such as (poly)alkylene glycols. Examples of polyols and glycols include those exemplified as components constituting the polyether polyols. For the synthesis of the water-soluble urethane resin, one or more of the above polyester polyols can be used.

[0040] The polycarbonate polyol can be a polycarbonate polyol produced by a known method. Specific examples include alkanediol-based polycarbonate diols such as polyhexamethylene carbonate diol. Other examples include polycarbonate diols obtained by reacting a carbonate component such as alkylene carbonate, diaryl carbonate, or dialkyl carbonate, or phosgene with an aliphatic diol. One or more of the above polycarbonate polyols can be used to synthesize the water-soluble urethane resin.

[0041] The polyol having an acid group is a polyol containing an acid group in its structure. Examples of the acid group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. The acid group may also be in the form of a salt. Examples of cations constituting the salt include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The acid group is preferably a carboxylic acid group. Examples of polyols having a carboxylic acid group include dimethylol acetic acid, dimethylol propionic acid, dimethylol butanoic acid, and dimethylol butyric acid. One or more of the above polyols having an acid group can be used to synthesize the water-soluble urethane resin. Among the polyols having an acid group, dimethylol propionic acid is preferred.

[0042] Examples of polyamines include monoamines having multiple hydroxy groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; and trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine. One or more of the above polyamines can be used to synthesize water-soluble urethane resins. For convenience, compounds having multiple hydroxy groups and one "amino group or imino group" are also listed as "polyamines."

[0043] When synthesizing a water-soluble urethane resin, a crosslinking agent or a chain extender can also be used. Typically, a crosslinking agent is used when synthesizing a prepolymer, and a chain extender is used when carrying out a chain extension reaction on a pre-synthesized prepolymer. Basically, the crosslinking agent or chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. depending on the purpose, such as crosslinking or chain extension. A chain extender that can crosslink the water-soluble urethane resin can also be used.

[0044] (Polyethylene wax) The ink contains polyethylene wax. By including polyethylene wax in the ink, it is possible to record an image that is highly flexible and has excellent abrasion resistance. In this specification, the polyethylene wax may be a composition containing components other than polyethylene wax, or may be polyethylene wax itself. One type of polyethylene wax may be used alone, or two or more types may be used in combination.

[0045] The content (mass %) of polyethylene wax in the aqueous ink is preferably 0.05% by mass or more and 5.00% by mass or less, based on the total mass of the ink. Having a polyethylene wax content of 0.05% by mass or more in the ink tends to further improve the scratch resistance of the image. On the other hand, having a polyethylene wax content of 5.00% by mass or less in the ink tends to further improve the intermittent ejection stability of the ink.

[0046] The melting point of the polyethylene wax is preferably from 50° C. to 200° C., more preferably from 70° C. to 180° C., and even more preferably from 90° C. to 180° C. The melting point of the polyethylene wax can be measured by a differential scanning calorimeter (DSC).

[0047] In the ink, the polyethylene wax is preferably dispersed in the form of particles (wax particles). The particle diameter (nm) at 50% cumulative concentration in the volume-based particle size distribution of the polyethylene wax is preferably 10 nm or more and 200 nm or less, more preferably 30 nm or more and 150 nm or less, and even more preferably 30 nm or more and 100 nm or less. The particle diameter (D 50 ) can be determined by dynamic light scattering. The particle size at 50% of the cumulative volume of the particle size distribution is the diameter of the particle that is 50% of the total volume of the measured particles when integrated from the small particle size side in the particle size integration curve.

[0048] In order to disperse the polyethylene wax in the ink, the ink may contain a dispersant for dispersing the polyethylene wax. Examples of dispersants for polyethylene wax include surfactants; resins having hydrophilic groups such as sulfonic acid groups or carboxylic acid groups; and the like. Examples of resins having hydrophilic groups include resins to which hydrophilic groups are graft-bonded; and resins having units derived from both a monomer having hydrophilic properties and a monomer having hydrophobic moieties. One type of dispersant for polyethylene wax may be used alone, or two or more types may be used in combination.

[0049] Surfactants that can be used as dispersants for polyethylene wax include anionic surfactants and nonionic surfactants. Examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Specific examples include alkylbenzene sulfonates, polyoxyethylene alkyl ether sulfates, and polyoxyethylene alkyl ether sulfonates. Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether; and ethylene oxide adducts of acetylene glycol. Examples of resins having hydrophilic groups that can be used as dispersants for polyethylene wax include acrylic resins having units derived from (meth)acrylic acid, such as ethylene-acrylic acid copolymers.

[0050] (Water-soluble organic solvent) The ink contains a water-soluble organic solvent. The water-soluble organic solvent includes at least one selected from the group consisting of glycols and glycol ethers. The glycols and glycol ethers have a vapor pressure of 1.0 Pa or more at 20°C and a polarity term δ of the Hansen solubility parameter. P is 10.0 MPa 1 / 2 Use the following:

[0051] The total content (% by mass) of the glycols and glycol ethers in the aqueous ink is preferably 0.50% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 12.00% by mass or less, based on the total mass of the ink. When the total content of the glycols and glycol ethers in the ink is 1.00% by mass or more, the effect of moving the pigment dispersion away from the ejection orifice is likely to be enhanced, and intermittent ejection stability is likely to be further improved. On the other hand, when the total content of the glycols and glycol ethers in the ink is 12.00% by mass or less, the scratch resistance of the image immediately after printing is likely to be further improved.

[0052] The vapor pressure of the glycol and glycol ether at 20°C is 1.0 Pa or more, and preferably 3.0 Pa or more. If the vapor pressure of the glycol and glycol ether at 20°C is less than 1.0 Pa, the water-soluble organic solvent does not completely volatilize immediately after recording, resulting in a decrease in the abrasion resistance of the image immediately after recording. If the vapor pressure of the glycol and glycol ether at 20°C is 3.0 Pa or more, the abrasion resistance of the image immediately after recording is likely to be further improved. Furthermore, the vapor pressure of the glycol and glycol ether at 20°C is preferably 30.0 Pa or less, and more preferably 10.0 Pa or less. If the vapor pressure of the glycol and glycol ether at 20°C is 30.0 Pa or less, or even 10.0 Pa or less, the volatilization of the water-soluble organic solvent near the ejection orifice is suppressed to some extent, and intermittent ejection stability is likely to be further improved. The vapor pressure (Pa) at 20°C can be a value measured by a static method.

[0053] The polar term δ of the Hansen solubility parameters of the above glycols and glycol ethers P is 10.0 MPa 1 / 2 The polar term δ of the Hansen solubility parameters of glycols and glycol ethers is as follows: P is 10.0 MPa 1 / 2 If the solubility exceeds δ, the effect of moving the pigment dispersion liquid away from the ejection port is insufficient, the viscosity of the ink near the ejection port increases, and the intermittent ejection stability decreases. P is 9.5 MPa 1 / 2 Preferably, it is 9.0 MPa or less. 1 / 2 It is more preferable that the polarity term δ of the Hansen solubility parameters of glycols and glycol ethers is less than or equal to 1. P There is no particular restriction on the lower limit of the polar term δ P is 4.0 MPa 1 / 2 It is preferable that the polarity term δ is equal to or greater than δ. P is 4.0 MPa 1 / 2By satisfying the above conditions, the solubility of glycol and glycol ether in water is improved, and the intermittent ejection stability can be further improved.

[0054] The vapor pressure at 20°C is 1.0 Pa or more and the polarity term δ of the Hansen solubility parameter P is 10.0 MPa 1 / 2 Examples of glycols with a viscosity of 1.5 Pa or less include 1,2-butanediol (2.7 Pa / 9.0 MPa) 1 / 2 ), 1,3-butanediol (8.0Pa / 8.1MPa 1 / 2 ), 1,2-pentanediol (1.5Pa / 7.8MPa 1 / 2 ), 1,3-pentanediol (1.3Pa / 8.2MPa 1 / 2 In addition, the vapor pressure at 20°C is 1.0 Pa or more and the polarity term δ of the Hansen solubility parameter is P is 10.0 MPa 1 / 2 Examples of glycol ethers that are below the viscosity limit include ethylene glycol monobutyl ether (100.0 Pa / 5.1 MPa) 1 / 2 ), diethylene glycol monomethyl ether (30.0 Pa / 7.8 MPa 1 / 2 ), diethylene glycol monoethyl ether (13.0 Pa / 9.2 MPa 1 / 2 ), diethylene glycol monobutyl ether (3.0Pa / 7.0MPa 1 / 2 ), triethylene glycol monomethyl ether (10.0Pa / 7.6MPa 1 / 2 The numbers in parentheses for each glycol and glycol ether are (vapor pressure at 20°C / polar term δ of Hansen solubility parameter) P )

[0055] Water-soluble organic solvents that do not fall under the above glycol and glycol ether categories include ethylene glycol (6.5 Pa / 11.0 MPa 1 / 2 ), 1,2-propanediol (10.6Pa / 10.4MPa 1 / 2 ), 1,4-butanediol (1.0Pa / 11.0MPa1 / 2 ), 1,2-hexanediol (0.6Pa / 7.1MPa 1 / 2 ), 1,6-hexanediol (less than 0.1 Pa / 8.4 MPa 1 / 2 ), triethylene glycol monoethyl ether (0.3Pa / 7.1MPa 1 / 2 ), glycerin (less than 0.1 Pa / 11.3 MPa) 1 / 2 ), 3-chloroaniline (9.0Pa / 7.3MPa 1 / 2 ), triethanolamine (1.3Pa / 7.6MPa 1 / 2 ), phenethyl alcohol (8.0Pa / 5.6MPa 1 / 2 ), and n-octanol (8.7 Pa / 5.0 MPa 1 / 2 The numbers in parentheses for each water-soluble organic solvent are (vapor pressure at 20°C / polar term δ of Hansen solubility parameter) P ) The above glycols and glycol ethers do not include polyethylene glycol.

[0056] (Polyethylene glycol) The ink contains polyethylene glycol having a number-average molecular weight of 200 or more. The number-average molecular weight of the polyethylene glycol is preferably 600 or more. When the number-average molecular weight of the polyethylene glycol is 600 or more, the polyethylene glycol is less likely to penetrate into the recording medium, which further increases the scratch resistance of the image immediately after recording. On the other hand, the number-average molecular weight of the polyethylene glycol is preferably 3,000 or less, and more preferably 2,000 or less. When the number-average molecular weight of the polyethylene glycol is 3,000 or less, or even 2,000 or less, an excessive increase in the viscosity of the ink is suppressed, which further increases the intermittent ejection stability.

[0057] The number-average molecular weight of polyethylene glycol can be measured and calculated according to the following procedure. 1 g of polyethylene glycol to be measured (weighed to the nearest 0.1 mg) is placed in 25 mL of phthalic anhydride pyridine solution accurately weighed in a stoppered flask, the stopper is then attached, and the flask is heated in a boiling water bath for 2 hours, then allowed to cool to room temperature. Then, 50 mL of 0.5 mol / L aqueous sodium hydroxide (weighed accurately) and 10 drops of phenolphthalein titration solution are placed in the flask. The liquid in the flask is titrated with 0.5 mol / L aqueous sodium hydroxide, and the endpoint is the point at which the liquid remains red for 15 seconds. The number-average molecular weight of polyethylene glycol can be calculated according to the following formula from the titer M (mL) obtained and the titer R (mL) obtained from a blank test conducted in the same manner as above, except without polyethylene glycol: Number average molecular weight = {(amount of polyethylene glycol (g)) × 4,000} / {(MR) × 0.5 (mol / L)}

[0058] The content (% by mass) of polyethylene glycol in the aqueous ink is preferably 1.0 times or less in mass ratio to the total content (% by mass) of the glycol and glycol ether described above. When the ratio of the content of polyethylene glycol to the total content of glycol and glycol ether is 1.0 times or less, the volatilization of glycol and glycol ether immediately after recording is less likely to be hindered, and the scratch resistance of the image immediately after recording is likely to be further improved.

[0059] The content (mass %) of polyethylene glycol in the ink is preferably 0.10 mass % or more and 10.00 mass % or less, and more preferably 0.50 mass % or more and 5.00 mass % or less, based on the total mass of the ink.

[0060] (aqueous medium) The ink is an aqueous ink containing at least water as the aqueous medium. The ink may further contain water-soluble organic solvents (other water-soluble organic solvents) other than the glycols and glycol ethers described above as the aqueous medium. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the aqueous ink is preferably 50.00% to 95.00% by mass, based on the total mass of the ink. Furthermore, any of the other water-soluble organic solvents commonly used in inks can be used. Examples include alcohols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. The water-soluble organic solvent content (mass %) in the aqueous ink is preferably 3.00% to 48.00% by mass, based on the total mass of the ink. This water-soluble organic solvent content includes the glycols and glycol ethers described above.

[0061] (Other ingredients) In addition to the components described above, the ink may contain various additives as needed, such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, evaporation accelerators, chelating agents, and other polymers. The ink may also contain coloring materials such as dyes, but typically does not need to contain such coloring materials.

[0062] (Ink properties) Since the ink is a water-based ink used in inkjet printing, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C, measured by the plate method, is preferably 20 mN / m or more and 60 mN / m or less, and more preferably 25 mN / m or more and 45 mN / m or less. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, and more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 10.0 or less.

[0063] <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.

[0064] <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.

[0065] The inkjet recording method of the present invention preferably uses an inkjet recording apparatus equipped with a recording head having ejection ports for ejecting ink and a heating means for heating the recording head. A specific example of the heating means is preferably a means for heating the recording head by applying a pulse (short pulse) to an electrothermal converter that is not strong enough to eject ink. The temperature of the recording head is preferably adjusted to 60°C or less. Heating the recording head to a temperature of 60°C or less appropriately suppresses the volatilization of the water-soluble organic solvent in the ink, further improving intermittent ejection stability. When the recording head is heated, the temperature of the recording head is preferably 30°C or higher.

[0066] 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).

[0067] The recording medium is not particularly limited, and for example, a recording medium for inkjet recording having a coating layer (ink receiving layer) (glossy paper, matte paper, etc.) or a recording medium without a coating layer (plain paper, etc.) can be used. [Example]

[0068] 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 the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0069] <Synthesis of urethane resin> (Water-soluble urethane resin 1) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux condenser was prepared. 41.7 parts of isophorone diisocyanate, 40.1 parts of polypropylene glycol (number average molecular weight 2,000), 13.2 parts of dimethylolpropionic acid, and 200.0 parts of methyl ethyl ketone were placed in the four-neck flask. These were then reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Next, 0.6 parts of ethylenediamine, 2.0 parts of methanol, 2.4 parts of dimethylolpropionic acid, and 100.0 parts of methyl ethyl ketone were added. The residual isocyanate group percentage was confirmed by FT-IR, and the reaction was continued at 80°C until the desired residual percentage was reached, yielding a reaction solution. The resulting reaction solution was cooled to 40°C, and then ion-exchanged water was added. A potassium hydroxide aqueous solution was added while stirring at high speed with a homomixer to obtain a liquid. Methyl ethyl ketone was distilled off from the resulting liquid by heating under reduced pressure, to obtain an aqueous solution of water-soluble urethane resin 1 with a urethane resin (solid content) content of 20.0%.

[0070] (Water-soluble urethane resin 2) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux condenser was prepared. 41.7 parts of isophorone diisocyanate, 40.1 parts of polycarbonate diol (number average molecular weight 2,000), 13.2 parts of dimethylolpropionic acid, and 200.0 parts of methyl ethyl ketone were placed in the four-neck flask. These were then reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Next, 0.6 parts of ethylenediamine, 2.0 parts of methanol, 2.4 parts of dimethylolpropionic acid, and 100.0 parts of methyl ethyl ketone were added. The residual isocyanate group percentage was confirmed by FT-IR, and the reaction was continued at 80°C until the desired residual percentage was reached, yielding a reaction solution. The resulting reaction solution was cooled to 40°C, and then ion-exchanged water was added. A potassium hydroxide aqueous solution was added while stirring at high speed with a homomixer to obtain a liquid. Methyl ethyl ketone was distilled off from the resulting liquid by heating under reduced pressure, to obtain an aqueous solution of water-soluble urethane resin 2 having a urethane resin (solid content) content of 20.0%.

[0071] (Water-soluble urethane resin 3) Synthesis was performed using polypropylene glycol (number average molecular weight 2,000) instead of polycarbonate polyol C-2090, with reference to "Synthesis Example 9: Synthesis of Water-Soluble Acrylic Urethane Resin (B-1)" described in Patent Document 2. This resulted in an aqueous solution (solid content: 25%) of water-soluble acrylic urethane resin, water-soluble urethane resin 3.

[0072] (Water-soluble urethane resin 4) "Water-soluble acrylic urethane resin (B-2)" was synthesized with reference to "Synthesis Example 10: Synthesis of water-soluble acrylic urethane resin (B-2)" described in Patent Document 2. As a result, an aqueous solution (solid content: 25%) of water-soluble acrylic urethane resin, water-soluble urethane resin 4, was obtained.

[0073] (urethane resin emulsion) A commercially available aqueous dispersion containing urethane resin particles having a predetermined particle size (trade name "Superflex 170", manufactured by Daiichi Kogyo Seiyaku, resin (solid content) 33.0%) was used as the urethane resin emulsion.

[0074] <Preparation of polyethylene wax> (Synthesis of ethylene-acrylic resin) A 500 mL four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was prepared. 100.0 parts of polyethylene and 100.0 parts of diethylene glycol monoethyl ether acetate were placed in this four-neck flask. Under a nitrogen atmosphere, the mixture was melted in an oil bath maintained at 180°C, and the temperature of the oil bath was adjusted with stirring so that the temperature inside the system reached 170°C. While stirring, 10.0 parts of benzyl acrylate, 5.0 parts of acrylic acid, and 0.4 parts of di-t-butyl peroxide were added. The system was maintained at 170°C and allowed to react for 30 minutes, after which the same amounts of benzyl acrylate, acrylic acid, and di-t-butyl peroxide were added. Similarly, benzyl acrylate, acrylic acid, and di-t-butyl peroxide were added five times every 30 minutes. The temperature in the system was lowered to 50°C, and the pressure in the flask was reduced using an aspirator for 1 hour to remove the solvent, unreacted monomer, di-t-butyl peroxide, and decomposition products of di-t-butyl peroxide. After aging for 2 hours, the ethylene glycol monobutyl ether was distilled off under reduced pressure to obtain a resin. To the obtained resin, potassium hydroxide in an amount equimolar to the acid value of the resin and an appropriate amount of ion-exchanged water were added, and the mixture was heated to 80°C to dissolve. This yielded a liquid containing ethylene-acrylic resin with an ethylene-acrylic resin (solids) content of 20.0%.

[0075] (Polyethylene wax dispersion 1) A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was prepared. 225 g of ion-exchanged water and 50 g of polyethylene wax were placed in the four-necked flask, and the mixture was melted and stirred while maintaining the temperature at 90 to 95°C. 25 g of the liquid containing the ethylene-acrylic resin obtained above was added, and while maintaining the temperature at 90 to 95°C, an ultrasonic homogenizer was used to measure the cumulative 50% particle diameter (D) of the volume-based particle size distribution. 50After the dispersion treatment was continued until the particle size reached 100 nm, the mixture was cooled to room temperature to obtain a dispersion. Ion-exchanged water was added to the obtained dispersion to adjust the solid content to 10.0%, thereby obtaining polyethylene wax dispersion 1.

[0076] (Polyethylene wax dispersion 2) A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was prepared. 225 g of ion-exchanged water and 50 g of polyethylene wax were placed in the four-necked flask, and the mixture was melted and stirred while maintaining the temperature at 90 to 95°C. 25 g of the liquid containing the ethylene-acrylic resin obtained above was added, and while maintaining the temperature at 90 to 95°C, an ultrasonic homogenizer was used to measure the cumulative 50% particle diameter (D) of the volume-based particle size distribution. 50 After the dispersion treatment was continued until the particle size reached 30 nm, the mixture was cooled to room temperature to obtain a dispersion. Ion-exchanged water was added to the obtained dispersion to adjust the solid content to 10.0%, thereby obtaining polyethylene wax dispersion 2.

[0077] [Cumulative 50% particle size of volume-based particle size distribution of wax particles] The properties of the obtained polyethylene wax dispersions 1 and 2, and the product name "AQUACER 515" (aqueous dispersion of polyethylene wax manufactured by BYK-Chemie) are shown in Table 1. The cumulative 50% particle diameter (D 50 ) was measured by the following method. A sample of wax particle dispersion diluted with pure water was measured using a particle size analyzer (trade name "Microtrac WAVE" manufactured by Microtrac Bell) using the dynamic light scattering method to measure the cumulative 50% particle diameter (D 50 The measurement conditions were: Set Zero: 30 seconds, number of measurements: 3, measurement time: 120 seconds, shape: spherical, refractive index: 1.59.

[0078] TIFF2025164716000001.tif37170

[0079] <Preparation of pigment dispersion> (Pigment dispersion 1) A mixture was obtained by mixing 10.0 parts of CI Pigment Blue 15:3 (trade name "Hostaperm Blue B2G" manufactured by Clariant), 20.0 parts of a resin dispersant solution, and 70.0 parts of ion-exchanged water. The resin dispersant solution was a 20.0% resin (solids) solution obtained by neutralizing a styrene-acrylic acid copolymer with an acid value of 120 mg KOH / g with a 10.0% sodium hydroxide solution. The resulting mixture was placed in a batch-type vertical sand mill (manufactured by Imex), filled with 85 parts of 0.3 mm zirconia beads, and dispersed for 3 hours while cooling with water. The mixture was then centrifuged to remove undispersed material, including coarse particles. The mixture was then pressure-filtered using a 1.2 μm pore-size cellulose acetate filter (manufactured by Advantec) to prepare Pigment Dispersion 1, which had a pigment (solids) content of 10.0% and a resin content of 4.0%.

[0080] (Pigment dispersion 2) Pigment Dispersion 2 was prepared in the same manner as in the preparation of Pigment Dispersion 1, except that the CI Pigment Blue 15:3 used in Pigment Dispersion 1 was changed to carbon black (trade name "MCF88B", manufactured by Mitsubishi Chemical Corporation). The pigment content (solid content) in Pigment Dispersion 2 was 10.0%, and the resin content was 4.0%.

[0081] (Pigment dispersion 3) The CI Pigment Blue 15:3 used in Pigment Dispersion 1 was changed to a solid solution of CI Pigment Red 202 and CI Pigment Violet 19 (product name "Cinquasia Magenta D 4500 J", manufactured by SunChemical). Except for this, Pigment Dispersion 3 was prepared in the same manner as in the preparation of Pigment Dispersion 1 described above. The pigment content (solid content) in Pigment Dispersion 3 was 10.0%, and the resin content was 4.0%.

[0082] (Pigment dispersion 4) Pigment Dispersion 4 was prepared in the same manner as in the preparation of Pigment Dispersion 1, except that the CI Pigment Blue 15:3 used in Pigment Dispersion 1 was changed to CI Pigment Yellow 74 (trade name "Hansa yellow 5GX-W", manufactured by Heabach). The pigment content (solid content) in Pigment Dispersion 4 was 10.0%, and the resin content was 4.0%.

[0083] (Pigment dispersion 5) Pigment dispersion 5 was prepared in the same manner as in the preparation of pigment dispersion 1, except that the styrene-acrylic acid copolymer with an acid value of 120 mgKOH / g used in pigment dispersion 1 was changed to a styrene-acrylic acid copolymer with an acid value of 180 mgKOH / g. The pigment content (solid content) in pigment dispersion 5 was 10.0%, and the resin content was 4.0%.

[0084] (Pigment dispersion 6) A cyan pigment dispersion, Pigment Dispersion 6, was prepared with reference to the "Production of Cyan Pigment Dispersion" described in Patent Document 2. The pigment content (solid content) in Pigment Dispersion 6 was 15.0%, and the resin content was 3.0%.

[0085] <Ink Preparation> Each ink was prepared by mixing the components (unit: mass %) shown in the middle of Table 2 (Table 2-1 to Table 2-6), thoroughly stirring, and then filtering under pressure using a polypropylene filter (manufactured by Advantec Co., Ltd.) with a pore size of 1.0 μm. For the "pigment dispersion" and "aqueous solution of water-soluble urethane resin" shown in the middle of Table 2, the pigment dispersion and aqueous solution of water-soluble urethane resin of the type (number) shown in the top of Table 2 were used, respectively. The properties of the inks are shown in the bottom of Table 2.

[0086] In the lower part of Table 2, "Vapor pressure (Pa) of specific glycol or glycol ether at 20°C" and "Polar term δ of specific glycol or glycol ether" are P (MPa 1 / 2 )" has a vapor pressure of 1.0 Pa or more at 20°C and the polarity term δ of the Hansen solubility parameter P is 10.0 MPa 1 / 2Only glycols and glycol ethers that fall within the range are listed, and those that fall outside the range or are not glycols or glycol ethers are marked with "-". In addition, the "total content (%) of specific glycols and glycol ethers" is defined as those whose vapor pressure at 20°C is 1.0 Pa or more and whose polarity term δ of the Hansen solubility parameter is 1.0 Pa or more. P is 10.0 MPa 1 / 2 The total content of glycol and glycol ether is as follows. The pH of each prepared ink was adjusted using a 0.5 N aqueous sulfuric acid solution so that it was within the range of 8.5 to 9.0. Note that the ink of Example 1 and the ink of Example 3 have the same composition, but the evaluation conditions for intermittent ejection stability, which will be described later, were changed between Examples 1 and 3.

[0087] The values ​​in parentheses for the water-soluble organic solvents in Table 2 are calculated by dividing the vapor pressure at 20°C by the polarity term δ of the Hansen solubility parameter. P ), and the number in parentheses for polyethylene glycol represents the number-average molecular weight measured by the aforementioned measurement method. Furthermore, "AST499" shown in Table 2 is the trade name of an acrylic resin emulsion (40% solids) (manufactured by Daicel Miraize). "Acetylenol E100" is the trade name of a nonionic acetylene glycol surfactant (manufactured by Kawaken Fine Chemicals). "Surfynol 104" is the trade name of a nonionic acetylene glycol surfactant (manufactured by Nissin Chemical Industry). "TEGO Wet280" is the trade name of a siloxane surfactant (manufactured by Evonik). "BYK348" is the trade name of a silicone surfactant (manufactured by BYK), and "Proxel GXL" is the trade name of a preservative (manufactured by Arch Chemicals).

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[0094] <Evaluation> Each ink obtained above was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS PRO-10S", a modified Canon model) equipped with a recording head that ejects ink using thermal energy. An image recorded under conditions in which 30 ng of ink droplets are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as having a recording duty of 100%. In this evaluation, the following evaluation criteria for each item were used: "AA", "A", "B", "B1", and "B2" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 3 (Table 3-1 and Table 3-2).

[0095] (glossiness) Using the inkjet recording device described above, a pattern containing a 5 cm x 5 cm solid image at 100% recording duty was recorded on a recording medium (product name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon) to obtain a recorded image. Two fluorescent lamps spaced 10 cm apart were used as the observation light source, and the fluorescent lamps were projected onto the recorded image from a distance of 2 m. The shape of the fluorescent lamps projected onto the image was visually confirmed under conditions of an illumination angle of 45 degrees and an observation angle of 45 degrees, and the glossiness of the image was evaluated according to the evaluation criteria shown below. A: Two fluorescent lights were clearly projected onto the image, or the edges were slightly blurred. C: I couldn't see the boundary between the two projected fluorescent lights.

[0096] (Abrasion resistance immediately after recording) Using the inkjet recording device described above, a pattern containing a 5 cm x 5 cm solid image with a recording duty of 100% was recorded on a recording medium (product name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon) to obtain a recorded product. 10 minutes after recording, the image was lightly rubbed with a fingernail and visually observed to evaluate the scratch resistance of the image immediately after recording. A: The image was not damaged. B: The image was scratched, but the underlying material was not exposed. C: The image was scratched and the base was exposed.

[0097] (Intermittent discharge stability) Using the inkjet recording device described above, a solid image was recorded with a recording duty of 100%. Fifty images were recorded under the condition that cleaning was performed once for each image recorded. In other words, 50 cleanings were performed. Glossy paper (Canon Photo Paper Glossy Gold GL-101, manufactured by Canon) was used as the recording medium. Recording conditions were a temperature of 15°C and a relative humidity of 10%. After recording 50 images (50 cleanings), the recording head was left for 20 seconds with the cap covering the nozzles removed. Subsequently, without cleaning, 5-point, 8-point, and 10-point characters were recorded. When the recording head was heated (with short pulse heating), the electrothermal transducer was driven to heat the recording head to 40°C to a temperature that prevented ink from being ejected, and then the image was recorded. On the other hand, when the recording head was not heated (without short pulse heating), the recording head was not heated (kept warm). The recorded characters were visually inspected, and the intermittent ejection stability was evaluated according to the following evaluation criteria. The smaller the letters, the more difficult they become to read due to blurring. AA: None of the letters were blurred. A: There was slight blurring on all the letters, but the 5-point, 8-point, and 10-point letters were legible. B1: All characters were slightly faded, and the 5-point characters were unreadable, but the 8-point and 10-point characters were readable. B2: All characters were slightly faded, and the 5-point and 8-point characters were unreadable, but the 10-point characters were readable. C: There was a lot of blurring in all the letters, and the 5-point, 8-point, and 10-point letters were illegible.

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Claims

1. A water-based inkjet ink containing a pigment, a water-soluble urethane resin, a polyethylene wax, a water-soluble organic solvent, and polyethylene glycol, The water-soluble organic solvent has a vapor pressure of 1.0 Pa or more at 20° C. and a polarity term δ of the Hansen solubility parameter Ｐ is 10.0 MPa １／２ At least one selected from the group consisting of glycols and glycol ethers, The water-based ink is characterized in that the number average molecular weight of the polyethylene glycol is 200 or more.

2. 2. The aqueous ink according to claim 1, wherein the water-soluble urethane resin contains at least one unit selected from the group consisting of a unit derived from polyethylene glycol and a unit derived from polypropylene glycol.

3. 2. The water-based ink according to claim 1, wherein the water-soluble urethane resin does not contain any unit derived from (meth)acrylic acid or any unit derived from a (meth)acrylic acid alkyl ester.

4. 2. The aqueous ink according to claim 1, wherein the total content (% by mass) of the glycol and the glycol ether in the aqueous ink is 1.00% by mass or more and 12.00% by mass or less, based on the total mass of the ink.

5. 2. The aqueous ink according to claim 1, wherein the glycol and the glycol ether have a vapor pressure of 3.0 Pa or more at 20[deg.] C.

6. 2. The aqueous ink according to claim 1, wherein the glycol and the glycol ether have a vapor pressure of 30.0 Pa or less at 20[deg.] C.

7. 2. The aqueous ink according to claim 1, wherein the glycol and the glycol ether have a vapor pressure of 10.0 Pa or less at 20[deg.] C.

8. 2. The aqueous ink according to claim 1, wherein the polyethylene glycol has a number average molecular weight of 600 or more.

9. 2. The aqueous ink according to claim 1, wherein the content (mass %) of the polyethylene glycol in the aqueous ink is 1.0 times or less in mass ratio to the total content (mass %) of the glycol and the glycol ether.

10. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge, wherein the ink is the aqueous ink according to any one of claims 1 to 9.

11. 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 9.

Images