JP2018109129A - Aqueous ink, ink cartridge, and ink jet recording method - Google Patents

Abstract

An image having excellent storage stability, scratch resistance and marker resistance can be recorded on plain paper, and an image excellent in scratch resistance can be recorded on glossy paper. An ink jet ink, an ink cartridge using the ink, and an ink jet recording method are provided. An aqueous inkjet ink containing a pigment, an acrylic resin, and a urethane resin. The urethane resin is a resin having a crosslinked structure having units derived from polyisocyanate, polycarbonate polyol, and polyol having an acid group. In addition, an ink cartridge and an ink jet recording method using the water-based ink are provided. [Selection figure] None

Description

  The present invention relates to an aqueous ink, an ink cartridge, and an ink jet recording method.

  In recent years, inkjet recording apparatuses and inkjet water-based inks used therein have been required to satisfy various performances simultaneously in order to meet a wide range of user needs. For example, the ink is required to have excellent reliability such as storage stability. Furthermore, images with excellent scratch resistance can be recorded on various recording media such as plain paper and glossy paper, and images with excellent marker resistance can be recorded on recording media such as plain paper. Is required.

  In order to satisfy at least one of the above requirements, for example, a pigment ink containing a urethane resin having a cross-linked structure in which intramolecular cross-linking is proposed (Patent Documents 1 to 3).

Special table 2007-522285 Special table 2011-507994 gazette JP 2011-144354 A

  The present inventors evaluated the storage stability of an ink containing a urethane resin having a crosslinked structure proposed in Patent Documents 1 to 3, and the scratch resistance and marker resistance of a recorded image. As a result, it has been found that an image having excellent scratch resistance and marker resistance can be recorded on plain paper.

  However, when the inks proposed in Patent Documents 1 and 2 are stored for a long time, the scratch resistance and marker resistance of images recorded on plain paper tend to decrease, that is, the ink storage stability is insufficient. I found out that Further, the image recorded on plain paper using the ink of Patent Document 3 had good scratch resistance and marker resistance. However, it was found that the storage stability of the ink was insufficient and the scratch resistance of the image recorded on the glossy paper was insufficient.

  Therefore, an object of the present invention is to record an image having excellent storage stability, scratch resistance and marker resistance on plain paper, and to provide an image having excellent scratch resistance on glossy paper. An object of the present invention is to provide an ink-jet aqueous ink that can be recorded. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the water-based ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, a water-based inkjet ink containing a pigment, an acrylic resin, and a urethane resin, wherein the urethane resin is derived from each of a polyisocyanate, a polycarbonate polyol, and a polyol having an acid group. There is provided a water-based ink having a unit and a resin having a crosslinked structure.

  According to the present invention, an image having excellent storage stability, scratch resistance and marker resistance can be recorded on plain paper, and an image excellent in scratch resistance can be recorded on glossy paper. It is possible to provide an aqueous inkjet ink. In addition, according to the present invention, an ink cartridge and an ink jet recording method using this water-based ink can be provided.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but is expressed as “contains a salt” for convenience. In addition, water-based ink for inkjet may be simply referred to as “ink”. Further, the physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  Urethane resin refers to a resin synthesized using (poly) isocyanate in a broad sense. A urethane resin generally used for water-based inks for inkjet is synthesized using a polyisocyanate and a component (polyol or polyamine) that reacts with the polyisocyanate, and a crosslinking agent or a chain extender is also used as necessary. Urethane resins synthesized using such components are mainly composed of two segments, a hard segment and a soft segment.

  The hard segment is composed of units derived from a compound having a relatively low molecular weight, such as polyisocyanate, polyamine or polyol having an acid group, and a crosslinking agent or chain extender. Since the hard segment has many urethane bonds, and the hard segment portion tends to be dense due to hydrogen bonds between the urethane bonds, the hard segment mainly contributes to the strength of the urethane resin. On the other hand, the soft segment is composed of units derived from a compound having a relatively large molecular weight, such as a polyol having no acid group. Since the soft segment is less dense than the hard segment, the soft segment mainly contributes to the flexibility of the urethane resin.

  A film formed of a urethane resin (hereinafter also referred to as “urethane resin film”) has a microphase separation structure formed by a hard segment and a soft segment, and thus has both strength and flexibility and exhibits high elasticity. Such characteristics of the urethane resin film are closely related to the development of the scratch resistance of the image.

  As described above, when a conventional ink containing a urethane resin having a crosslinked structure is stored for a long time, the scratch resistance and marker resistance of an image recorded on plain paper are deteriorated, that is, the storage stability of the ink is insufficient. Met. The present inventors presume the reason why such a phenomenon occurs as follows. The urethane resin having a cross-linked structure blended in conventional inks is easily decomposed due to dissolved oxygen in the ink and the action of heat and light from the outside, and the unit derived from the polyol having no acid group is easily decomposed. As a result, the molecular weight of the urethane resin decreases. Therefore, it is considered that the scratch resistance and marker resistance of the image are lowered when the ink after being stored for a long time is used. In particular, when an ink containing a urethane resin in which a unit derived from a polyol having no acid group is a unit derived from a polyester polyol or a polyether polyol is stored for a long period of time, the scratch resistance and marker resistance of the image are remarkable. To drop.

  The ink of the present invention contains a urethane resin having a cross-linked structure (cross-linked urethane resin) having units derived from polycarbonate polyol. The cross-linked urethane resin usually has a carbonate bond, a urethane bond, and a urea bond in its molecular structure. The oxygen atom in the carbonate bond strongly interacts with the hydrogen atom in the urethane bond and the urea bond through the hydrogen bond. Moreover, since the cross-linked urethane resin has a three-dimensional network structure, a strong interaction due to hydrogen bonding works three-dimensionally, and decomposition due to hydrolysis of a unit derived from a polyol having no acid group hardly occurs. Therefore, it is considered that the storage stability of the ink is improved by blending the crosslinked urethane resin.

  The cross-linked urethane resin is excellent in flexibility and has high binding properties with cellulose fibers. For this reason, even if it is plain paper in which a pigment and resin are easy to sink, if ink containing a cross-linked urethane resin is used, an image with improved scratch resistance and marker resistance can be recorded. However, the strength of the urethane resin film formed of the crosslinked urethane resin tends to be lower than the strength of the film formed of the acrylic resin. Therefore, when ink containing a crosslinked urethane resin is applied to glossy paper, most of the pigment and resin in the ink remain on the surface of the glossy paper, but the scratch resistance of the recorded image becomes insufficient.

  Based on the above and characteristics of the crosslinked urethane resin and acrylic resin, in order to achieve both the scratch resistance and marker resistance of images recorded on plain paper and the scratch resistance of images recorded on glossy paper, It is conceivable to include an acrylic resin in the ink. However, since general urethane resins and acrylic resins have low compatibility, it may be difficult to simultaneously improve the image characteristics required for various recording media even if these resins are blended in ink. Many.

  On the other hand, the ink of the present invention contains a highly compatible crosslinked urethane resin and acrylic resin. For this reason, if the ink of the present invention is used, the scratch resistance and marker resistance of an image recorded on plain paper can be made compatible with the scratch resistance of an image recorded on glossy paper. The present inventors presume the reason why such an effect is obtained as follows.

  Since a crosslinked urethane resin having a unit derived from a polycarbonate polyol usually has a carbonate bond, a urethane bond, and a urea bond in its molecular structure, a strong intermolecular interaction due to a hydrogen bond works three-dimensionally. On the other hand, since the acrylic resin has a carbonyl bond in its molecular structure, the oxygen atom of the carbonyl bond interacts with the hydrogen atom of the urethane bond and urea bond in the cross-linked urethane resin by the hydrogen bond, so the compatibility is high. Rise. For this reason, the acrylic resin is easily taken into the strong intermolecular interaction of the crosslinked urethane resin. As a result, it is considered that an image having the flexibility of the crosslinked urethane resin and the strength of the acrylic resin can be recorded on plain paper and glossy paper.

<Ink>
The ink of the present invention is an ink-jet aqueous ink containing a pigment, an acrylic resin, and a urethane resin. The urethane resin is a resin having a crosslinked structure having units derived from polyisocyanate, polycarbonate polyol, and polyol having an acid group. Hereafter, each component which comprises the ink of this invention is demonstrated in detail.

(Urethane resin)
As described above, the urethane resin generally used for inkjet ink is synthesized using at least a polyisocyanate and a component (polyol or polyamine) that reacts with the polyisocyanate, and if necessary, a crosslinking agent or a chain extender. Is also used. The urethane resin used in the ink of the present invention has units derived from each of polyisocyanate, polycarbonate polyol, and polyol having an acid group. The urethane resin is a resin having a crosslinked structure (crosslinked urethane resin). The “unit” of the urethane resin in the present invention means a repeating unit derived from one monomer. Hereafter, each monomer used as the unit which comprises a urethane resin is demonstrated.

[Polyisocyanate]
Polyisocyanate is a compound having two or more isocyanate groups in its molecular structure. As the polyisocyanate, aliphatic polyisocyanate, aromatic polyisocyanate and the like can be used. The proportion (mol%) of the unit derived from polyisocyanate in the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less, and preferably 20.0 mol% or more and 60.0 mol% or less. More preferably it is.

  Aliphatic polyisocyanates include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1 , 5-diisocyanate, polyisocyanate having a chain structure such as 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, Polypropylene having a cyclic structure such as methylcyclohexylene diisocyanate and 1,3-bis (isocyanatomethyl) cyclohexane Or the like can be mentioned cyanate.

  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. Examples include isocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α ′, α′-tetramethylxylylene diisocyanate. .

  Among these polyisocyanates, aliphatic polyisocyanates are preferably used, aliphatic polyisocyanates having a cyclic structure are more preferably used, and isophorone diisocyanate is particularly preferably used.

  Moreover, in order to set it as the urethane resin which has a crosslinked structure, the polyisocyanate (3 or more functional polyisocyanate) which has 3 or more isocyanate groups can be used. Examples of the trifunctional or higher polyisocyanate include various polyisocyanates such as isocyanurate type polyisocyanate, adduct type polyisocyanate, and biuret type polyisocyanate. When a trifunctional or higher polyisocyanate is used, the content of units derived from the trifunctional or higher polyisocyanate in the urethane resin is 5.0% by mass or more and 90.0% based on the units derived from all the polyisocyanates. It is preferable that it is below mass%. If the content of the unit derived from the trifunctional or higher polyisocyanate is less than 5.0% by mass, the effect of improving the scratch resistance and marker resistance of the image may be lowered. On the other hand, when the content of the unit derived from the trifunctional or higher polyisocyanate is more than 90.0% by mass, the urethane resin film becomes tough and the flexibility tends to be lowered. For this reason, the effect of improving the scratch resistance and marker resistance of the image may be lowered, and the ink ejection stability may be easily lowered.

[Polycarbonate polyol]
Polycarbonate polyol is a polyol having a carbonate bond in its molecular structure. As the polycarbonate polyol serving as a unit constituting the urethane resin for water-based ink, those having no acid group are widely used.

  The proportion (mol%) of the unit derived from the polycarbonate polyol of the urethane resin is preferably 10.0 mol% or more and 80.0 mol% or less, and preferably 20.0 mol% or more and 60.0 mol% or less. More preferably it is. Moreover, it is preferable that the ratio (mol%) of the unit derived from polycarbonate polyol which occupies for the total amount of the unit derived from polyol which a urethane resin has is as follows. That is, it is preferably 1.0 mol% or more and 100.0 mol% or less, more preferably 5.0 mol% or more and 50.0 mol% or less, and 10.0 mol% or more and 30.0 mol% or less. It is particularly preferred that

  As the polycarbonate polyol, a polycarbonate polyol produced by a known method can be used. Examples of the polycarbonate polyol include alkanediol-based polycarbonate diols such as polyhexamethylene carbonate diol. Moreover, polycarbonate diol obtained by making carbonates, such as alkylene carbonate, diaryl carbonate, and dialkyl carbonate, phosgene, and aliphatic diol, etc. can be mentioned. As the polycarbonate polyol, those having no acid group are preferably used.

  The polystyrene-converted weight average molecular weight of the polycarbonate polyol, measured by gel permeation chromatography (GPC), is preferably 1,000 or more and 4,000 or less. When the weight average molecular weight of the polycarbonate polyol is less than 1,000, the flexibility of the urethane resin film is lowered, and the effect of improving the scratch resistance and marker resistance of the image may be lowered. On the other hand, when the weight average molecular weight of the polycarbonate polyol is more than 4,000, the flexibility of the urethane resin film becomes too high, and the effect of improving the scratch resistance and marker resistance of the image may be lowered.

[Polyols having acid groups]
The polyol having an acid group is a polyol having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group in its molecular structure. The acid group is preferably a carboxylic acid group. The polyol having an acid group preferably has 1 to 7 carbon atoms. When a polyol having an acid group having 8 or more carbon atoms is used, a urethane resin having an acid group in the soft segment tends to be obtained. When such a urethane resin is used, the balance between the strength and flexibility of the formed urethane resin film tends to be lost, and the effect of improving the scratch resistance and marker resistance may be reduced. Examples of the polyol having an acid group include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid. Among these, it is preferable to use at least one of dimethylolpropionic acid and dimethylolbutanoic acid.

  The ratio (mol%) of the unit derived from the polyol having an acid group in the total amount of the unit derived from the polyol in the urethane resin is preferably as follows. That is, it exceeds 0.0 mol% and is preferably 100.0 mol% or less, more preferably 30.0 mol% or more and 90.0 mol% or less, further preferably 50.0 mol% or more and 90.0 mol% or less. It is particularly preferable that the amount is not more than mol%.

[Crosslinking agent]
A urethane resin having a crosslinked structure is a resin having a three-dimensional network structure formed by a three-dimensional progression of a urethanization reaction in its molecular structure. Usually, a crosslinking agent is used in the synthesis of the prepolymer. The cross-linked urethane resin has, for example, a unit derived from a compound (cross-linking agent) having three or more reactive functional groups. As the crosslinking agent, trifunctional or higher functional polyisocyanate, trifunctional or higher functional polyol, trifunctional or higher functional polyamine, and the like can be used.

  Examples of the trifunctional or higher functional polyol include the above-described trifunctional or higher functional polyisocyanate. Examples thereof include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, pentaerythritol, polyoxypropylenetriol, and a compound obtained by adding glycol to polyether polyol. Examples of the trifunctional or higher polyamine include bishexamethylenetriamine, trimethylolmelamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

  Among these cross-linking agents, it is preferable to use a triamine or higher polyamine because of its excellent reactivity during the urethanization reaction. When a tri- or higher functional polyisocyanate or a tri- or higher functional polyol is used, a urethane bond is generated three-dimensionally to form a crosslinked structure. On the other hand, when a triamine or higher polyamine is used, a urea bond is generated three-dimensionally to form a crosslinked structure. Of the trifunctional or higher polyamines, diethylenetriamine and triethylenetetramine are preferable. Diethylenetriamine and triethylenetetramine are preferable because the reaction efficiency with the isocyanate group is high and a moderately flexible crosslinked structure is formed.

  A three-dimensional structure formed by hydrogen bonds generated between urethane bonds or between a urethane bond and a hydroxyl group of a polyol is not included in the crosslinked structure in the present invention. Further, the urethane resin obtained by the two-component reaction type crosslinking reaction is included in the urethane resin in the present invention as long as it is added to the ink after the crosslinking reaction. On the other hand, the three-dimensional structure formed by the crosslinking reaction after application to the recording medium is not included in the crosslinked structure in the present invention.

[Chain extender]
When synthesizing the urethane resin, a chain extender can be used. The chain extender is used when performing a chain extension reaction on a prepolymer synthesized in advance. That is, the chain extender is a compound that reacts with a residual isocyanate group that has not formed a urethane bond among the units derived from the polyisocyanate constituting the prepolymer. Basically, the chain extender can be appropriately selected from water, polyisocyanate, polyamine, polyol and the like as mentioned above. As the chain extender, those capable of crosslinking the urethane resin can also be used.

  Chain extenders include trimethylolmelamine and its derivatives, dimethylolurea and its derivatives, dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine, ethylenediamine, propylenediamine, diethylenetriamine, hexylenediamine, triethylene Polyamines such as tetramine, bishexamethylenetriamine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine and hydrazine, polyamines such as polyamide polyamine and polyethylene polyimine; ethylene glycol, propylene glycol 1,3-propanediol, 1,3-butanediol, 1,4-butanediol 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, Mention may be made of polyols such as 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, glycerin, trimethylolpropane, pentaerythritol. it can.

[Method for determining whether or not the urethane resin has a crosslinked structure]
Whether or not the urethane resin has a crosslinked structure can be determined by measuring the gel fraction of tetrahydrofuran of the target urethane resin. The gel fraction of the urethane resin means a mass ratio of a portion (gel) remaining without being dissolved when the urethane resin is dissolved in a specific solvent. The crosslinked structure part contained in the urethane resin does not dissolve in the solvent and remains as a gel. That is, the gel fraction is a physical property value serving as an index representing the degree of crosslinking, which is measured from the solvent solubility of the filmed urethane resin. For this reason, the higher the degree of crosslinking and the greater the content of the crosslinked structure, the higher the gel fraction. In the present invention, the gel fraction of the urethane resin is measured according to the method shown below, and it is determined whether or not the urethane resin has a crosslinked structure.

  The urethane resin is immersed in tetrahydrofuran and left at 23 ° C. for 24 hours. Then, if the mass of the film that did not dissolve in tetrahydrofuran (weighing value: A) was measured and divided by the mass of the film before soaking (weighing value: B), the gel fraction of tetrahydrofuran ((A / B) × 100 (%)) can be calculated. In this invention, if this gel fraction is 50 mass% or more, it will judge that it is a urethane resin which has a crosslinked structure. The upper limit of the gel fraction is 100% by mass. As a sample used in the measurement of the gel fraction, it is preferable to use a film obtained by extracting a urethane resin from ink in advance by solvent extraction or the like and drying it.

[Synthesis method and analysis method of urethane resin]
The urethane resin can be synthesized according to a conventional general method for synthesizing a urethane resin. For example, a urethane resin can be synthesized according to the method shown below. The polyisocyanate, the polycarbonate polyol, and the polyol having an acid group are reacted in an equivalent ratio such that the isocyanate group becomes excessive in the presence or absence of an organic solvent having a boiling point of 100 ° C. or less. Thereby, a prepolymer having an isocyanate group at the molecular end is synthesized. Subsequently, acid groups such as carboxylic acid groups and sulfonic acid groups in the synthesized prepolymer are neutralized using a neutralizing agent. After that, the prepolymer neutralized with acid groups is poured into a liquid containing a chain extender, reacted, and then the organic solvent remaining in the system is removed as necessary to obtain a urethane resin. Can do.

  Examples of neutralizers include alkanolamines such as N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, and triethanolamine; inorganic bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia Organic bases such as trimethylamine and triethylamine can be used. Especially, it is preferable to use the neutralizing agent containing alkali metals, such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. When the acid group in the prepolymer is neutralized with a neutralizing agent containing an alkali metal, the ink ejection stability can be improved as compared with the case of neutralizing with a neutralizing agent such as amines. The neutralizing agent is preferably used in an amount of 0.5 to 1.0 mol, more preferably 0.8 to 1.0 mol, per 1 mol of acid groups in the prepolymer. When the use amount of the neutralizing agent is out of the above range, the workability may be deteriorated because the liquid containing the urethane resin becomes unstable or the viscosity increases.

  When synthesizing a urethane resin having a crosslinked structure, an organic solvent can be used as necessary. Examples of the organic solvent include ketones such as methyl ethyl ketone and acetone; esters such as methyl acetate and ethyl acetate; acetonitrile and tetrahydrofuran. These organic solvents can be used alone or in combination of two or more. The boiling point of the organic solvent is preferably 100 ° C. or lower, which is the boiling point of water. If an organic solvent having a boiling point of more than 100 ° C. is used, the organic solvent tends to remain in the liquid containing the urethane resin finally obtained, and thus it may be necessary to remove the remaining organic solvent by reducing the pressure.

  The physical properties such as the composition, molecular weight, and acid value of the urethane resin can be measured according to a conventionally known method. Specifically, the physical property value of the urethane resin can be measured by analyzing a sediment and a supernatant obtained by centrifuging the ink. Since the pigment is insoluble in an organic solvent, the urethane resin can be separated from the pigment by solvent extraction. Although the urethane resin can be analyzed even in the ink state, analysis of the urethane resin extracted from the ink is preferable because the measurement accuracy can be improved. Specifically, the supernatant obtained by centrifuging the ink at 80,000 rpm is analyzed using a Fourier transform infrared spectrophotometer (FT-IR). Thereby, the kind of polyisocyanate and the kind of polycarbonate polyol can be analyzed from the absorption wavelength peculiar to a urethane bond. Further, the supernatant obtained by centrifuging the ink is acidified with hydrochloric acid or the like, and then dried, the acid precipitated product is dissolved in chloroform or the like and analyzed by nuclear magnetic resonance (NMR). Thereby, the molecular weight of the polycarbonate polyol can be analyzed.

  The acid value of the urethane resin can be measured by a titration method. In examples described later, a urethane resin dissolved in tetrahydrofuran is prepared as a measurement sample. The acid value of the urethane resin can be measured by potentiometric titration with potassium hydroxide ethanol titrant using an automatic potentiometric titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.). The weight average molecular weight of the urethane resin can be measured by GPC. GPC measurement conditions are as follows.

Apparatus: Alliance GPC 2695 (manufactured by Waters)
Column: 4-column column of Shodex KF-806M (Showa Denko)
・ Mobile phase: Tetrahydrofuran (special grade)
・ Flow rate: 1.0 mL / min
・ Oven temperature: 40.0 ℃
-Sample solution injection volume: 0.1 mL
・ Detector: RI (refractive index)
Polystyrene standard sample: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weight: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000 , 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580)

  The content (% by mass) of the urethane resin in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and 0.5% by mass or more and 3.0% by mass based on the total mass of the ink. More preferably, it is as follows. The content (mass%) of the urethane resin in the ink is a mass ratio to the content (mass%) of the pigment, and is preferably 0.10 times or more and 0.90 times or less. If the mass ratio is less than 0.10 times, the effect of improving the scratch resistance and marker resistance of an image recorded on plain paper and the effect of improving the scratch resistance of an image recorded on glossy paper may be reduced. is there. On the other hand, if the mass ratio is more than 0.90 times, the ink sticking resistance may be lowered.

  The weight average molecular weight in terms of polystyrene of the urethane resin measured by GPC is preferably 10,000 or more and 100,000 or less. Moreover, it is preferable that the acid value of a urethane resin is less than 60 mgKOH / g. When the urethane resin has an acid value of 60 mgKOH / g or more, the hydrophilicity of the urethane resin is high, so the effect of improving the marker resistance of an image recorded on plain paper and the effect of improving the storage stability of the ink are reduced. There is. The acid value of the urethane resin is preferably 59 mgKOH / g or less, more preferably 55 mgKOH / g or less, and preferably 30 mgKOH / g or more.

(Pigment)
The ink of the present invention contains a pigment such as an inorganic pigment or an organic pigment as a color material. Examples of the inorganic pigment include carbon black, calcium carbonate, and titanium oxide. Examples of the organic pigment include azo, phthalocyanine, quinacdrine and the like. In addition, for purposes such as toning, a dye may be used in combination as a coloring material. The content (% by mass) of the pigment in the ink is preferably 0.5% by mass or more and 10.0% by mass or less, and 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. More preferably.

  When the pigments are classified by the dispersion method, there can be mentioned resin-dispersed pigments using a resin dispersant, self-dispersed pigments that do not require a resin dispersant, and the like. Any dispersion system pigment can be used in the ink of the present invention. In particular, it is preferable to employ a method of dispersing the pigment using a resin such as a resin-dispersed pigment, a resin-bonded self-dispersed pigment, or a microcapsule pigment. When the pigment dispersed by the resin is used, the adsorption amount of the acrylic resin and the urethane resin with respect to the pigment can be kept higher than when the self-dispersing pigment is used. For this reason, it is possible to further improve the scratch resistance of an image recorded on glossy paper.

[Method for determining whether pigment is dispersed by resin]
Whether or not the pigment is dispersed by the resin can be determined by the following method. The liquid prepared by concentrating or diluting the ink so that the total solid content is about 10% by mass is centrifuged at 12,000 rpm for 1 hour to recover the precipitated components including the pigment. The liquid layer contains a water-soluble organic solvent, a resin that does not contribute to pigment dispersion, and the like. And when resin is contained in the sedimentation component, it can be judged that the pigment was disperse | distributed with resin. Note that the resin contained as a main component in the sediment component is a resin that contributes to the dispersion of the pigment, and the resin contained as a main component in the liquid layer is a resin that does not contribute to the dispersion of the pigment. be able to.

(acrylic resin)
The ink of the present invention contains an acrylic resin. As the acrylic resin, a resin having a hydrophilic unit and a hydrophobic unit as constituent units is preferable, and the hydrophobic unit preferably has an aromatic group. “(Meth) acryl” in the present invention means acrylic and methacrylic.

  The hydrophilic unit is formed by polymerizing a monomer having a hydrophilic group. Examples of the monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth) acrylic acid, itaconic acid, maleic acid and fumaric acid; ethyl (meth) acrylic acid-2-phosphonate Acidic monomers having phosphonic acid groups; anionic monomers such as anhydrides and salts of these acidic monomers; (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid-3-hydroxypropyl Monomers having a hydroxy group such as; monomers having an ethylene oxide group such as methoxy (mono, di, tri, poly) ethylene glycol (meth) acrylate, and the like. Examples of the cation constituting the salt of the anionic monomer include lithium ion, sodium ion, potassium ion, ammonium ion, and organic ammonium ion.

  The hydrophobic unit is formed by polymerizing a monomer having a hydrophobic group. Monomers having a hydrophobic group include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; ethyl (meth) acrylate, methyl (meth) acrylate, (iso) propyl ( Examples thereof include a monomer having an aliphatic group such as (meth) acrylate, (n-, iso-, t-) butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate. The acrylic resin may be any of a random copolymer, a block copolymer, and a graft copolymer.

  The acrylic resin can be used as a resin dispersant for dispersing the pigment or as an additive component that is not a resin dispersant. In particular, an acrylic resin is preferably used as a resin dispersant for dispersing the pigment. Among them, it is preferable to use an acrylic resin as a resin dispersant having a unit having an aromatic group to disperse a pigment because the scratch resistance of an image recorded on glossy paper can be further improved. About the point from which such an effect is acquired, the present inventors are estimating as follows. Since the acrylic resin having a unit having an aromatic group has a highly hydrophobic structural portion in the molecule, the acrylic resin has a hydrophobic interaction with a highly hydrophobic pigment and easily adsorbs to the pigment particle surface. In addition, since the acrylic resin is highly compatible with the crosslinked urethane resin, not only the acrylic resin but also the urethane resin is likely to be adsorbed on the pigment particle surface. Therefore, when an acrylic resin having a unit having an aromatic group is used as a resin dispersant, the adsorption amount of the urethane resin and the acrylic resin to the pigment is kept high, and the image is fixed in a state where the pigment and the resin are well blended. be able to. For this reason, it is considered that the pigment layer composed of the pigment and the resin becomes flexible and tough, and the scratch resistance of the image recorded on the glossy paper can be further improved.

(Aqueous medium)
The ink of the present invention is preferably an aqueous ink containing at least water as an aqueous medium. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.0% by mass or more and 90.0% by mass or less, preferably 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the ink. More preferably.

  The aqueous medium can further contain a water-soluble organic solvent. As the water-soluble organic solvent, monohydric alcohol, polyhydric alcohol, (poly) alkylene glycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

(Other additives)
In addition to the above-described components, the ink of the present invention is water-soluble at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. An organic compound may be contained. Furthermore, in the ink of the present invention, a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, and You may contain various additives, such as water-soluble resin.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage portion for storing ink. The ink storage portion is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other via a communication port 18. The absorber housing chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may have a form in which the entire amount of ink stored is held by an absorber without having an ink storage chamber for storing liquid ink. Further, the ink storage portion may have a form that does not have an absorber and stores the entire amount of ink in a liquid state. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by discharging the ink of the present invention described above from an ink jet recording head. Examples of the method for ejecting ink include a method for imparting mechanical energy to the ink and a method for imparting thermal energy to the ink. In the present invention, it is particularly preferable to employ a method in which thermal energy is applied to the ink and the ink is ejected. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

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

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
A styrene-acrylic acid copolymer having an acid value of 140 mgKOH / g and a weight average molecular weight of 10,000 was neutralized with a 10% aqueous potassium hydroxide solution. Mixing 10.0 parts of carbon black with a specific surface area of 220 m ² / g, DBP oil absorption of 105 mL / 100 g, 5.0 parts of neutralized styrene-acrylic acid copolymer (solid content), and 85.0 parts of water A mixture was obtained. The mixture obtained using a sand grinder was dispersed for 1 hour and then centrifuged to remove coarse particles. A pigment dispersion 1 containing carbon black in a state of being dispersed in water by a resin (styrene-acrylic acid copolymer) was obtained by pressure filtration through a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm. . The pigment dispersion 1 obtained had a pigment (carbon black) content of 10.0% and a resin content of 5.0%.

(Pigment dispersion 2)
The pigment is C.I. I. Pigment dispersion 2 was obtained in the same procedure as in the case of pigment dispersion 1 except that the pigment blue was changed to 15: 3. The content of the pigment in the obtained pigment dispersion 2 was 10.0%, and the content of the resin was 5.0%.

(Pigment dispersion 3)
The pigment is C.I. I. A pigment dispersion 3 was obtained in the same procedure as in the case of the pigment dispersion 1 except that the pigment red 122 was used. The content of the pigment in the obtained pigment dispersion 3 was 10.0%, and the content of the resin was 5.0%.

(Pigment dispersion 4)
The pigment is C.I. I. A pigment dispersion 4 was obtained in the same procedure as in the case of the pigment dispersion 1 except that the pigment yellow 74 was used. The pigment content in the obtained pigment dispersion 4 was 10.0%, and the resin content was 5.0%.

(Pigment dispersion 5)
A reaction vessel equipped with a stirrer, a thermometer, a reflux tube, and a dropping funnel was prepared, and the inside of the vessel was purged with nitrogen. In this reaction vessel, 20.0 parts of styrene, 5.0 parts of 2-ethylhexyl methacrylate, 15.0 parts of butyl methacrylate, 10.0 parts of lauryl methacrylate, 2.0 parts of methacrylic acid, and 0.3 part of t-dodecyl mercaptan And heated to 70 ° C. Meanwhile, 150.0 parts of styrene, 15.0 parts of acrylic acid, 50.0 parts of butyl methacrylate, 1.0 part of t-dodecyl mercaptan, 20.0 of methyl ethyl ketone, and 1.0 part of azobisisobutyronitrile are added to the dropping funnel. Put in. The contents of the dropping funnel were dropped into the reaction vessel over 4 hours to cause a polymerization reaction, and then methyl ethyl ketone was added to obtain a liquid containing 40.0% resin.

50.0 parts of the obtained liquid, 40.0 parts of carbon black, 100.0 parts of 0.1 mol / L potassium hydroxide aqueous solution, and 30.0 parts of methyl ethyl ketone were mixed and stirred for 30 minutes using a homogenizer. Carbon black having a specific surface area of 220 m ² / g and DBP oil absorption of 105 mL / 100 g was used. After stirring, 300 parts of ion-exchanged water was added and further stirred for 1 hour. The whole amount of methyl ethyl ketone and a part of water were distilled off using a rotary evaporator, and then neutralized by adding an aqueous potassium hydroxide solution. After adding an appropriate amount of ion-exchanged water to adjust the concentration, centrifugal treatment was performed to remove coarse particles. The pigment dispersion 5 was obtained by pressure filtration with a microfilter (manufactured by Fuji Film) having a pore size of 3.0 μm. The pigment dispersion 5 obtained had a pigment content of 10.0% and a resin content of 5.0%.

(Pigment dispersion 6)
An n-butyl acrylate-acrylic acid copolymer having an acid value of 140 mgKOH / g and a weight average molecular weight of 10,000 was neutralized with a 10% aqueous potassium hydroxide solution. Mixing 10.0 parts of carbon black with a specific surface area of 220 m ² / g, DBP oil absorption of 105 mL / 100 g, 5.0 parts of neutralized styrene-acrylic acid copolymer (solid content), and 70.0 parts of water A mixture was obtained. The mixture obtained using a sand grinder was dispersed for 1 hour and then centrifuged to remove coarse particles. Pigment dispersion 6 containing carbon black in a state of being pressure-filtered with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm and dispersed in water with a resin (n-butyl acrylate-acrylic acid copolymer) Got. The pigment content of the obtained pigment dispersion 6 was 10.0%, and the resin content was 5.0%.

(Pigment dispersion 7)
A solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added. A container containing this solution was placed in an ice bath and cooled to 10 ° C. or lower, and a solution obtained by dissolving 1.8 g of sodium nitrite in 9 g of water at 5 ° C. was added. After stirring for 15 minutes, 6.0 g of carbon black having a specific surface area of 220 m ² / g and DBP oil absorption of 105 mL / 100 g was added with stirring, and further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered with a filter paper (trade name “filter paper for standard No. 2”, manufactured by Advantech), and the obtained particles were sufficiently washed with water. The washed particles were dried in an oven at 110 ° C. to obtain a self-dispersing pigment. Water was added to the obtained self-dispersing pigment so that the pigment content was 10.0%, and the self-dispersing pigment was dispersed. As a result, a pigment dispersion containing a self-dispersing pigment having —C ₆ H ₃ — (COONa) ₂ groups bonded to the surface of carbon black particles was obtained. Next, sodium ion was replaced with potassium ion by an ion exchange method to obtain pigment dispersion 7 containing a self-dispersed pigment in which —C ₆ H ₃ — (COOK) ₂ groups were bonded to the surface of carbon black particles. The pigment content of Pigment Dispersion Liquid 7 was 10.0%.

<Synthesis of urethane resin>
After the polyol having no acid group of the type and amount shown in Table 1 was dissolved in methyl ethyl ketone, the polyisocyanate of the type and amount shown in Table 1 and the polyol having an acid group were added and reacted at 75 ° C. for 1 hour. A prepolymer solution was obtained. The obtained prepolymer solution is cooled to 60 ° C., an aqueous potassium hydroxide solution is added to neutralize carboxylic acid groups, and then cooled to 40 ° C., ion-exchanged water is added, and the mixture is stirred and homogenized with a homomixer. It was. The types and amounts of crosslinking agents and chain extenders shown in Table 1 were added and reacted at 30 ° C. for 12 hours. After the isocyanate group was no longer confirmed by FT-IR, the mixture was heated under reduced pressure to distill off methyl ethyl ketone to obtain a liquid containing a urethane resin having a weight average molecular weight of 30,000. Content of the urethane resin in each obtained liquid was 20.0%. Table 1 shows the synthesis conditions and characteristics of the urethane resin. Moreover, the detail of each component in Table 1 is shown below.

IPDI: Isophorone diisocyanate Desmodur N3400: Hexamethylene diisocyanate dimer 40.0% and trimer 60.0% blend (from Bayer)
PPG2000: Polypropylene glycol (number average molecular weight: 2,000)
PTMG2000: polytetramethylene glycol (number average molecular weight: 2,000)
PC2000: polycarbonate diol (number average molecular weight: 2,000)
PC1000: polycarbonate diol (number average molecular weight: 1,000)
PC500: Polycarbonate diol (number average molecular weight: 500)
PES2000: Polyester polyol (Number average molecular weight: 2,000)
TMP: trimethylolpropane DMPA: dimethylolpropionic acid DETA: diethylenetriamine TETA: triethylenetetraamine BHTA: bishexamethylenetriamine EDA: ethylenediamine

<Preparation of liquid containing acrylic resin>
A styrene-acrylic acid copolymer having an acid value of 140 mgKOH / g and a weight average molecular weight of 10,000 is neutralized with a 10% aqueous potassium hydroxide solution to obtain a liquid containing an acrylic resin having a resin content of 20.0%. It was.

<Preparation of ink>
After mixing each component (unit:%) shown in Tables 2-1 to 2-3 and stirring sufficiently, pressure filtration is performed with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each ink. did. “Acetyleneol E100” in Tables 2-1 to 2-3 is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals.

<Evaluation>
Each evaluation shown below was performed using each prepared ink. For the evaluation, an ink jet recording apparatus (trade name “PIXUS iP3100”, manufactured by Canon Inc.) that discharges ink from the recording head by the action of thermal energy was used. In this embodiment, the recording duty of a solid image recorded under the condition that one ink droplet having a mass per droplet of 28 ng ± 10% is applied to a unit area of 1/600 inch × 1/600 inch is 100. It is defined as%. The recording conditions were a temperature of 23 ° C. and a relative humidity of 55%. In the present invention, “AA”, “A”, and “B” are acceptable levels and “C” is not acceptable in the evaluation criteria for the following evaluation items. The evaluation results are shown in Table 3.

(Abrasion resistance on plain paper)
Using the inkjet recording apparatus described above, a solid image of 1.0 inch × 0.5 inch having a recording duty of 100% was recorded on plain paper (trade name “PPC paper GF-500”, manufactured by Canon). A record was obtained. 10 minutes and 1 day after recording, a sillbon paper and a weight having a surface pressure of 40 g / cm ² were placed on the solid image, and the solid image and the sylbon paper were rubbed together. After removing the sylbon paper and the weight, the state of the non-recorded portion was visually checked, and the scratch resistance was evaluated according to the following evaluation criteria.
AA: After 10 minutes, there was no stain on the non-recording area.
A: The non-recorded portion was slightly stained after 10 minutes, but the non-recorded portion was not stained after 1 day.
B: After 10 minutes, the non-recorded portion was stained but at a level that was not noticeable, and after 1 day, the non-recorded portion was not stained.
C: The non-recorded portion was stained after 10 minutes and 1 day.

(Marker resistance on plain paper)
Using the ink jet recording apparatus, a vertical ruled line having a thickness of 1/10 inch was recorded on plain paper (trade name “PPC paper GF-500”, manufactured by Canon) to obtain a recorded matter. After 5 minutes and 1 day from the recording, the vertical ruled line was marked with a yellow line marker (trade name “OPTEX2”, manufactured by Zebra), and immediately after that, the non-recorded portion of the recorded matter was marked. The state of the marker pen tip and the non-recorded portion was confirmed visually, and the marker resistance was evaluated according to the following evaluation criteria.
AA: After 5 minutes and 1 day, the pen tip was not soiled, and the non-recording area was not soiled.
A: The pen tip was slightly stained after 5 minutes, but the non-recorded portion was hardly stained. After one day, the pen tip was not soiled, and the non-recording area was not soiled.
B: After 5 minutes and 1 day, the pen tip was slightly stained, but the non-recorded area was hardly stained.
C: After 5 minutes and 1 day, the pen tip was dirty, and the non-recording area was also dirty.

(Abrasion resistance on glossy paper)
Using the ink jet recording apparatus described above, a solid image of 1.0 inch × 0.5 inch having a recording duty of 100% on glossy paper (trade name “Photo Paper / Glossy Gold GL-101”, manufactured by Canon) Recordings were obtained. 10 minutes and 1 day after recording, a sillbon paper and a weight having a surface pressure of 40 g / cm ² were placed on the solid image, and the solid image and the sylbon paper were rubbed together. After removing the sylbon paper and the weight, the state of the non-recorded portion was visually checked, and the scratch resistance was evaluated according to the following evaluation criteria.
AA: After 10 minutes, there was no stain on the non-recording area.
A: The non-recorded portion was slightly stained after 10 minutes, but the non-recorded portion was not stained after 1 day.
B: After 10 minutes, the non-recorded portion was stained but at a level that was not noticeable, and after 1 day, the non-recorded portion was not stained.
C: The non-recorded portion was stained after 10 minutes and 1 day.

(Storage stability)
Using the ink jet recording apparatus, a vertical ruled line having a thickness of 1/10 inch was recorded on plain paper (trade name “PPC paper GF-500”, manufactured by Canon) to obtain a recorded matter. 5 minutes after recording, immediately after marking with a yellow line marker (product name “OPTEX2”, made by Zebra) on the vertical ruled line, further marking is performed on the non-recording part, and the marker pen tip and non-recording part The state of dirt was confirmed visually (referred to as “before storage”). Further, in the same manner as described above, except that the ink after storage at 60 ° C. for 90 days was used, the state of the marker pen tip and the non-recorded portion was visually confirmed (referred to as “after storage”). The storage conditions of the ink were evaluated according to the following evaluation criteria by comparing the state of the stain on the pen tip and the non-recorded portion of the marker before storage and after storage. The increase in the degree of soiling due to storage correlates with the degree of molecular weight reduction due to the decomposition of the urethane resin.
AA: Before and after storage, the marker pen tip and the non-recorded portion were in the same dirt state.
A: The pen tip and the non-recording portion of the marker were more dirty after storage than before storage, but the difference was slight.
B: Compared with before storage, the pen tip and the non-recording portion of the marker were more dirty after storage, and the difference was recognized visually.
C: Compared with before storage, the pen tip and the non-recording portion of the marker were more dirty after storage, and the difference could be clearly recognized visually.

(Sticking resistance)
After mounting an ink cartridge filled with ink on the head cartridge of the above-described ink jet recording apparatus, a nozzle check pattern was recorded, and it was confirmed that ink was discharged from all of the discharge ports. Thereafter, the head cartridge was removed from the apparatus and placed in a constant temperature bath at 35 ° C. and a relative humidity of 10% for 1 week. The head cartridge was mounted on the apparatus, and the nozzle check pattern was recorded on coated paper (trade name “high quality exclusive paper”, manufactured by Canon). The discharge state of the ink from the discharge port was visually confirmed, and the sticking resistance was evaluated according to the following evaluation criteria.
A: Ink was ejected from all ejection ports.
B: There were ejection ports that could not eject ink normally, but there were less than 10.
C: There were 10 or more ejection ports from which ink could not be ejected normally.

Claims (8)

An ink-jet aqueous ink containing a pigment, an acrylic resin, and a urethane resin,
A water-based ink, wherein the urethane resin is a resin having a crosslinked structure having units derived from a polyisocyanate, a polycarbonate polyol, and a polyol having an acid group.   The water-based ink according to claim 1, wherein the acrylic resin is a resin dispersant for dispersing the pigment having a unit having an aromatic group.   The water-based ink according to claim 1 or 2, wherein the urethane resin is a resin having a cross-linked structure cross-linked by a triamine or higher polyamine.   The water-based ink according to claim 3, wherein the polyamine is at least one of diethylenetriamine and triethylenetetramine.   The content (mass%) of the urethane resin is a mass ratio with respect to the content (mass%) of the pigment, and is 0.10 times or more and 0.90 times or less. Water-based ink.   The water-based ink according to any one of claims 1 to 5, wherein an acid value of the urethane resin is less than 60 mgKOH / g. An ink cartridge comprising ink and an ink containing portion for containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 6. An inkjet recording method for recording an image on a recording medium by discharging ink from an inkjet recording head,
An ink jet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 6.

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