Water-based ink, ink cartridge, and inkjet recording method

Abstract

To provide an aqueous ink for inkjet capable of recording an image excellent in scratch resistance and glossiness, an ink cartridge using the aqueous ink, and an inkjet recording method.SOLUTION: The aqueous ink for inkjet contains a coloring material and a plurality of resins (a first resin and a second resin) different from the coloring material. The first resin is resin particles formed of a first polyester resin. The second resin is at least one of (i) a block copolymer containing an A block having no acid group and a B block having an acid group, and (ii) a second polyester resin having a sulfonic acid group. The ink cartridge uses the aqueous ink. The inkjet recording method records an image on a recording medium by discharging the aqueous ink from a recording head of an inkjet system.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, it has become possible to easily and inexpensively record images with high definition and high gloss as realized by silver halide photography and offset printing using an inkjet recording apparatus.

[0003] As one of the inks capable of recording an image with excellent gloss, there is a dye ink containing a dye as a coloring material. By using the dye ink, it is possible to record a high-quality image with reduced granularity. However, the image recorded with the dye ink has a problem of poor fastness due to the decomposition of the dye. For this reason, in recent years, a pigment ink containing a pigment as a coloring material has come to be used. As a pigment ink capable of improving the fixing property of the pigment to the recording medium, for example, an aqueous ink for inkjet containing polyester-based resin particles has been proposed (Patent Document 1). Further, an aqueous dispersion containing polyester-based colored resin fine particles and an ink using the same have been proposed (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventors examined the aqueous inks proposed in Patent Documents 1 and 2. As a result, it has been found that it is difficult to record an image that satisfies both the rubbing resistance and the gloss at the levels required in recent years.

[0006] Accordingly, an object of the present invention is to provide an aqueous ink for inkjet that can record an image excellent in rubbing resistance and glossiness. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using this aqueous ink.

Means for Solving the Problems

[0007] That is, according to the present invention, there is provided an aqueous ink for inkjet containing a coloring material and a plurality of resins different from the coloring material, wherein the plurality of resins include a first resin and a second resin, the first resin is resin particles formed of a first polyester resin, and the second resin is at least one of (i) a block copolymer including a block A having no acid group and a block B having an acid group, and (ii) a second polyester resin having a sulfonic acid group. (d) the first polyester resin is composed of units derived from a polyhydric alcohol and units derived from a polyvalent carboxylic acid, does not have a sulfonic acid group, the number average molecular weight of the first polyester resin is 3,000 or more and 30,000 or less, the number average molecular weight of the second resin is 3,000 or more and 20,000 or less, the acid value of the block copolymer is 50 mgKOH / g or more and 200 mgKOH / g or less; (e) the second polyester resin is composed of units derived from a polyhydric alcohol and units derived from a polyvalent carboxylic acid, further has a carboxylic acid group, the amount of sulfonic acid groups in the second polyester resin is 0.08 times or more and 0.50 times or less in terms of the molar ratio to the amount of carboxylic acid groups in the second polyester resin, the acid value of the second polyester resin is 2 mgKOH / g or more and 30 mgKOH / g or less; and (f) the content (% by mass) of the first resin is 4.0 times or more and 100.0 times or less in terms of the mass ratio to the content (% by mass) of the second resin An aqueous ink characterized by the above is provided.

Effects of the Invention

[0008] According to the present invention, it is possible to provide an aqueous ink for inkjet that can record an image excellent in rubbing resistance and glossiness. Further, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method using this aqueous ink.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] The preferred embodiments of the present invention are described below to explain the present invention in further detail. When the compound is a salt in the present invention, although the salt dissociates into ions in the ink, for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet may be simply described as "ink". Physical property values are values at normal temperature (25 °C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified. "Unit" means a unit structure corresponding to one monomer unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are described, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

[0011] The polyester resin is usually composed of a unit derived from a polyhydric alcohol and a unit derived from a polyvalent carboxylic acid. A structure containing an ester bond (-COO-) composed of a unit derived from a polyhydric alcohol and a unit derived from a polyvalent carboxylic acid is also referred to as an "ester unit".

[0012] The oxygen atom constituting the carbonyl group of the ester bond is polarized to δ - Since a general recording medium used in the inkjet recording method is neutral to acidic, there are hydrogen atoms polarized to δ + When an ink containing resin particles formed of a polyester resin is applied to the recording medium, the oxygen atom polarized to δ - of the polyester resin and the hydrogen atom polarized to δ + of the recording medium attract each other, making it easier for the recording medium and the resin particles to adhere. Furthermore, the molecular chain of the polyester resin having a carboxylic acid group becomes entangled in a state formed by hydrogen bonds generated between a plurality of carboxylic acid groups on the recording medium. Then, due to the adhesion between the recording medium and the resin particles and the entanglement of the molecular chains of the polyester resin, the scratch resistance of the image is exhibited.

[0013] The inventors have studied ways to increase the hydrophilicity of resin particles formed from a first polyester resin as the first resin (hereinafter also simply referred to as "resin particles") in order to improve the smoothness of the recorded image by suppressing the aggregation of the resin particles. Specifically, it was predicted that by controlling the hydrophilicity of the surface of the resin particles, rapid aggregation of the resin particles could be suppressed. However, it was found that even when the hydrophilicity of the resin particles was increased, the glossiness of the recorded image might not improve. Therefore, as a result of further study, it was found that by incorporating a second resin described below into the ink together with the resin particles, it is possible to record an image with improved glossiness without impairing the rub resistance. This second resin is at least one of (i) a block copolymer containing a block A having no acid group and a block B having an acid group, and (ii) a second polyester resin having a sulfonic acid group.

[0014] As a method of increasing the hydrophilicity of the polyester resin forming the resin particles, there is a method of incorporating an acid group into the molecular chain of the polyester. However, according to this method, the water solubility of the polyester resin increases and it becomes difficult to maintain the shape of the resin particles. For this reason, the polyester resin gradually dissolves in the aqueous ink, and the viscosity of the ink increases. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, and macro irregularities occur on the image surface, so the glossiness of the image does not improve.

[0015] In contrast, the ink of the present invention contains a second resin together with resin particles formed of a first polyester resin as the first resin. The second resin is at least one of (i) a block copolymer including an A block having no acid group and a B block having an acid group, and (ii) a second polyester resin having a sulfonic acid group. When a block copolymer is used as the second resin, the resin particles and the A block can be physically adsorbed by hydrophobic interaction. Further, the acid group in the B block of the block copolymer can impart hydrophilicity to the resin particles while maintaining the shape of the particles. When a second polyester resin is used as the second resin, the first polyester resin and the second polyester resin are physically adsorbed by hydrophobic interaction. In addition, the sulfonic acid group of the second polyester resin causes the resin particles to have hydrophilicity while maintaining the shape as particles. Thereby, it becomes possible to suppress rapid aggregation of the resin particles, and even microscopic irregularities on the image surface are reduced, so that the glossiness of the image can be improved. In order to efficiently exhibit this effect, the first resin and the second resin need to be different from the colorant, that is, to exist separately from the colorant.

[0016] <Ink> The ink of the present invention is an aqueous ink for inkjet containing a colorant and a plurality of resins (a first resin and a second resin) different from the colorant. The first resin is resin particles formed of a first polyester resin. The second resin is at least one of (i) a block copolymer including an A block having no acid group and a B block having an acid group, and (ii) a second polyester resin having a sulfonic acid group. Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail.

[0017] (Colorant) The ink contains a coloring material. This coloring material is different from both the first resin and the second resin. That is, the coloring material is neither dispersed in at least one of the first resin and the second resin, nor encapsulated in the first resin or the second resin. In other words, in the ink, the coloring material is distinguished from the first resin and the second resin, and they exist separately.

[0018] Examples of the coloring material include pigments and dyes. Among them, it is preferable to use a pigment. Different from a dye, a pigment exists in a particulate state in the ink. Therefore, an image recorded with an ink containing a pigment as the coloring material tends to have a reduced abrasion resistance. However, by containing the aforementioned first resin, even when a pigment is used as the coloring material, a reduction in the abrasion resistance of the image can be effectively suppressed. Also, when an ink containing a dye as the coloring material is used, the problem of abrasion resistance is less likely to occur than in the case of pigment ink. However, by containing the aforementioned first resin, it is easy to enhance the fastness while improving the glossiness without impairing the abrasion resistance. The content (% by mass) of the coloring material in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0019] Specific examples of the pigment include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, and perinone. Among the pigments, it is preferable to use carbon black and organic pigments.

[0020] Examples of pigment dispersion methods include resin-dispersed pigments using a resin as a dispersant, self-dispersing pigments in which a hydrophilic group is bonded to the particle surface of the pigment, and the like. Further examples include resin-bonded pigments in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, and microcapsule pigments in which the surface of the pigment particles is coated with a resin or the like. Among these, it is preferable to use a resin-dispersed pigment in which a resin as a dispersant is physically adsorbed on the particle surface of the pigment, rather than a resin-bonded pigment or a microcapsule pigment.

[0021] As the resin dispersant for dispersing the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of an anionic group. As the resin dispersant, it is preferable to use a water-soluble resin. This resin dispersant is a resin different from both the first resin and the second resin.

[0022] Examples of the resin dispersant include acrylic resins and urethane resins. Among these, acrylic resins are preferable, and acrylic resins composed of units derived from (meth)acrylic acid and (meth)acrylic acid esters are more preferable.

[0023] As the acrylic resin, those having a hydrophilic unit and a hydrophobic unit as constituent units are preferable. Among these, resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and (meth)acrylic acid ester are preferable. In particular, resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of the monomers styrene and α-methylstyrene are preferable. Since these resins easily cause an interaction with the pigment, they can be suitably used as a resin dispersant for dispersing the pigment.

[0024] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit having no hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylate monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and the like.

[0025] As the self-dispersing pigment, those in which an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group is bonded directly or via another atomic group (-R-) to the particle surface of the pigment can be used. The anionic group may be in either the acid form or the salt form, and in the case of the salt form, it may be in a state where a part thereof is dissociated or a state where all of it is dissociated. When the anionic group is in the salt form, examples of the cation serving as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; an ether group, and the like. Further, a group formed by combining these groups may also be used.

[0026] When the ink contains a pigment, the content (% by mass) of the first resin in the ink is preferably 0.5 times or more and 3.0 times or less in terms of the mass ratio (times) to the content (% by mass) of the pigment. If the above ratio is less than 0.5 times, there is too little first resin relative to the pigment, and the degree of improvement in the rub resistance of the image may be low. On the other hand, if the above ratio exceeds 3.0 times, there is too much first resin that is softer than the pigment. For this reason, the image is likely to be deformed by rubbing, and the degree of improvement in the rub resistance of the image may be low.

[0027] As the dye, it is preferable to use one having an anionic group. Specific examples of the dye include dyes such as azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone.

[0028] (Plural resins: first resin and second resin) The ink contains a plurality of resins (the first resin and the second resin described later). The content (% by mass) of the first resin in the ink is preferably 4.0 times or more and 100.0 times or less in terms of the mass ratio to the content (% by mass) of the second resin. If the above mass ratio is less than 4.0 times, the amount of the second resin relative to the amount of the first resin becomes excessive, so the second resins that do not physically adsorb to the first resin are likely to associate in the ink to form micelles. Then, as the aqueous medium evaporates from the ink droplets and concentrates, or penetrates into the recording medium, the micelles aggregate and the first resin may also aggregate. As a result, unevenness of the resin is likely to occur in the recorded image, and the degree of improvement in glossiness may be low. On the other hand, if the above mass ratio exceeds 100.0 times, the amount of the second resin relative to the amount of the first resin becomes extremely small. For this reason, the leveling property between the dots of the ink applied to the recording medium deteriorates, macro irregularities are likely to occur on the image surface, and the degree of improvement in glossiness may be low.

[0029] (First resin) The first resin is resin particles formed of a first polyester resin. The first polyester resin preferably has no sulfonic acid group. The content (mass %) of the first resin in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink. The resin particles as the first resin are present in the ink in a dispersed state, i.e., in the form of a resin emulsion. The resin particles preferably do not encapsulate a colorant. The proportion (mass %) of the first polyester resin in the resin forming the resin particles is preferably 80.0 mass % or more, more preferably 90.0 mass % or more, based on the total mass of the resin. Also, the proportion (mass %) of the first polyester resin may be 100.0 mass % based on the total mass of the resin, and is more preferably 99.5 mass % or less. That is, the resin particles as the first resin are preferably substantially formed only of the first polyester resin, except for a light-resistant agent (details will be described later) that may be encapsulated in the resin particles.

[0030] The "resin particles" refer to a resin that is insoluble in the aqueous medium constituting the ink. Specifically, it means a resin that can exist in the aqueous medium in a state where particles having a particle diameter measurable by the dynamic light scattering method are formed. On the other hand, the "water-soluble resin" refers to a resin that can be dissolved in the aqueous medium constituting the ink. Specifically, it means a resin that can exist in the aqueous medium in a state where particles having a particle diameter measurable by the dynamic light scattering method are not formed. The "resin particles" can also be referred to as "water-dispersible resin (water-insoluble resin)".

[0031] Whether the resin is "resin particles" can be determined according to the method shown below. First, prepare a liquid containing the resin to be determined (resin solid content: 10% by mass). Next, dilute the prepared liquid 10-fold (volume basis) with ion-exchanged water to prepare a sample. Then, when measuring the particle size of the resin in the sample by the dynamic light scattering method, if particles having a particle size are measured, it is determined that the particles are "resin particles" (water-dispersible resin). On the other hand, if particles having a particle size are not measured, it is determined that the resin is not "resin particles" (it is a "water-soluble resin"). The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: true spherical, refractive index: 1.59. As the particle size distribution measuring device, a particle size analyzer by the dynamic light scattering method (for example, trade name "NanoTrack UPA-EX150", manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device, measurement conditions, etc. are not limited to the above.

[0032] Regarding resins other than the first resin (other resins such as resin dispersants and the second resin, etc.), it is also determined whether they are resin particles according to the above method. However, for the sake of simplicity in determination, for other resins, it is preferable to use a liquid containing a resin neutralized with an alkali equivalent to the acid value (sodium hydroxide, potassium hydroxide, etc.) (resin content: 10% by mass).

[0033] 〔Constituent Materials of Polyester Resin〕 The resin particles as the first resin are formed by the first polyester resin. At the ends of the polyester resin, unreacted hydroxy groups or carboxylic acid groups are present. The polyester resin is usually composed of units derived from polyhydric alcohols and units derived from polyvalent carboxylic acids. The total of the proportion (mass%) of the units derived from polyhydric alcohols and the proportion (mass%) of the units derived from polyvalent carboxylic acids in the first polyester resin is preferably 90.0% by mass or more. This total is more preferably 95.0% by mass or more, and may be 100.0% by mass.

[0034] [Polyhydric alcohol] Examples of the polyhydric alcohol include dihydric to tetrahydric alcohols. Examples of the polyhydric alcohol include polyhydric alcohols having an aliphatic group, polyhydric alcohols having an aromatic group, sugar alcohols, and the like. Examples of the polyhydric alcohol include, for example, dihydric alcohols such as ethylene glycol [1,2-ethanediol], neopentyl glycol [2,2-dimethyl-1,3-propanediol], 1,3-propanediol, 1,4-butanediol, benzenediol, 2,2-bis(4-hydroxyphenyl)propane [bisphenol A]; trihydric alcohols such as glycerin, trimethylolethane, trimethylolpropane; tetrahydric alcohols such as pentaerythritol; and the like. As the polyhydric alcohol, an oligomer (a low molecular weight polymer having a molecular weight of 1,000 or less) can also be used. The proportion (mass%) of the unit derived from the polyhydric alcohol in the first polyester resin is preferably 40.0 mass% or more and 60.0 mass% or less.

[0035] It is preferable to use a dihydric alcohol or a trihydric alcohol because it is easy to adjust the number average molecular weight of the obtained first polyester resin. From the viewpoint of enhancing the interaction with the second resin, it is preferable to use a polyhydric alcohol having an aromatic group as the polyhydric alcohol. Among them, it is preferable to use bisphenol A. Further, a polyhydric alcohol having an aromatic group and a polyhydric alcohol having an aliphatic group may be used in combination. As the polyhydric alcohol having an aliphatic group, a polyhydric alcohol having a linear or branched aliphatic group having 1 to 6 carbon atoms is preferable. Among them, ethylene glycol, neopentyl glycol, and glycerin are preferable.

[0036] [Polycarboxylic acid] Examples of the polyvalent carboxylic acid include divalent to tetravalent polyvalent carboxylic acids. Examples of the polyvalent carboxylic acid include polyvalent carboxylic acids having an aliphatic group, polyvalent carboxylic acids having an aromatic group, nitrogen-containing polyvalent carboxylic acids, and the like. Examples of the polyvalent carboxylic acid include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; tetravalent carboxylic acids such as ethylenediaminetetraacetic acid; and the like. As the polyvalent carboxylic acid, an oligomer (a low molecular weight polymer having a molecular weight of 1,000 or less) can also be used. The proportion (mass %) of the unit derived from the polyvalent carboxylic acid in the first polyester resin is preferably 40.0 mass % or more and 60.0 mass % or less.

[0037] [Preferred constituent materials] It is preferable to use a divalent carboxylic acid or a trivalent carboxylic acid because it is easy to adjust the number average molecular weight and acid value of the obtained first polyester resin. From the viewpoint of enhancing the interaction with the second resin, it is preferable to use a polyvalent carboxylic acid having an aromatic group as the polyhydric alcohol. Among them, it is preferable to use adipic acid, terephthalic acid, isophthalic acid, and trimellitic acid.

[0038] A polyester resin containing a unit derived from a low molecular weight polyhydric alcohol and a unit derived from a low molecular weight polyvalent carboxylic acid has a higher proportion of ester bonds contained in the molecular chain compared to a polyester resin containing a unit derived from a high molecular weight raw material. Therefore, it is preferable to use the first polyester resin containing a unit derived from a low molecular weight polyhydric alcohol and a unit derived from a low molecular weight polyvalent carboxylic acid because an image with more excellent scratch resistance can be recorded. Therefore, the molecular weight of the polyhydric alcohol is preferably 50 or more and 300 or less. Further, the molecular weight of the polyvalent carboxylic acid is preferably 100 or more and 300 or less.

[0039] It is preferable that both the valences of the polyhydric alcohol and the polyvalent carboxylic acid are divalent or trivalent. When the valences of the polyhydric alcohol and the polyvalent carboxylic acid are tetravalent or higher, the resulting first polyester resin has many branches and tends to have a three-dimensionally complex structure. Since the molecular chains of such a first polyester resin are unlikely to be entangled on the recording medium, the degree of improvement in scratch resistance may be low.

[0040] The first polyester resin preferably contains a unit derived from an aromatic compound. Examples of the aromatic compound include a polyhydric alcohol having an aromatic group and a polyvalent carboxylic acid having an aromatic group. By including a unit (a unit having an aromatic group) derived from an aromatic compound, a first polyester resin that interacts more strongly with the second resin can be obtained. In addition, the molecular chains of the first polyester resin containing a unit derived from an aromatic compound are more likely to be entangled on the recording medium due to the hydrophobic interaction between the aromatic groups, so the scratch resistance of the image can be further improved. The proportion (mass %) of the unit derived from the aromatic compound in the first polyester resin is preferably 25.0 mass % or more and 50.0 mass % or less based on the total mass of the first polyester resin. The proportion (mass %) of the unit having no aromatic group in the first polyester resin is preferably 50.0 mass % or more and 75.0 mass % or less based on the total mass of the first polyester resin.

[0041] [Light stabilizer] It is preferable to encapsulate a light stabilizer in the resin particles. The state where the resin particles encapsulate the light stabilizer means a state where the light stabilizer exists inside the three-dimensional structure formed by the entanglement of the polyester resins. Examples of the light stabilizer include benzotriazoles, thioethers, triazines, benzoates, benzophenones, polyphenols, carotenoids, sulfides, hindered amines, and the like. By using the resin particles encapsulating the light stabilizer, the light resistance of the recorded image can be enhanced. The proportion (mass %) of the light stabilizer in the resin particles is preferably 0.5 mass % or more and 25.0 mass % or less based on the total mass of the resin particles. As a method for encapsulating the light stabilizer in the resin particles, a method similar to the method for producing the resin particles described below can be mentioned, except that the light stabilizer is dissolved in an organic solvent together with the first polyester resin.

[0042] 〔Physical properties of the first resin (resin particles and first polyester resin)〕 [Amount of carboxylic acid groups present on the particle surface of the resin particles] The amount of carboxylic acid groups present on the particle surface of the resin particles is preferably 30 μmol / g or more and 110 μmol / g or less. In the resin particles formed from a polyester resin having carboxylic acid groups, at least a part of the carboxylic acid groups tend to be present in a state incorporated into the interior of the particles, so it is advisable to consider the amount of carboxylic acid groups exposed on the particle surface. If the amount of carboxylic acid groups present on the particle surface of the resin particles is less than 30 μmol / g, the charge repulsion occurring between the plurality of carboxylic acid groups is weak, and the resin particles may rapidly aggregate due to concentration by evaporation of the aqueous medium from the ink droplets or penetration into the recording medium. As a result, microscopic irregularities are likely to occur on the surface of the recorded image, and the degree of improvement in glossiness may be low. On the other hand, if the amount of carboxylic acid groups present on the particle surface of the resin particles exceeds 110 μmol / g, the hydrophilicity of the resin particles is too high, so the first polyester resin forming the resin particles may gradually dissolve in the ink and the viscosity of the ink may increase. As a result, the leveling property between the dots of the ink applied to the recording medium deteriorates, macroscopic irregularities are likely to occur on the image surface, and the degree of improvement in glossiness may be low. The amount of carboxylic acid groups present on the particle surface of the resin particles can be measured by colloid titration using a potential difference. The amount of acid groups other than carboxylic acid groups, such as sulfonic acid groups, present on the particle surface of the resin particles is preferably 5 μmol / g or less, and more preferably 0 μmol / g.

[0043] [Acid value of the first polyester resin] The acid value of the first polyester resin is preferably 2 mgKOH / g or more and 30 mgKOH / g or less. When the acid value of the first polyester resin is less than 2 mgKOH / g, since the amount of carboxylic acid groups is too small, resin particles may rapidly aggregate due to concentration by evaporation of the aqueous medium from the ink droplets or penetration into the recording medium. As a result, micro unevenness is likely to occur on the surface of the recorded image, and the degree of improvement in glossiness may be low. On the other hand, when the acid value of the first polyester resin exceeds 30 mgKOH / g, since the amount of carboxylic acid groups is too large, the first polyester resin may gradually dissolve in the ink and the viscosity of the ink may increase. As a result, the leveling property between the dots of the ink applied to the recording medium deteriorates, macro unevenness is likely to occur on the image surface, and the degree of improvement in glossiness may be low. The acid value of the first polyester resin can be measured by neutralization titration using a potential difference. The acid value X (mgKOH / g) and the amount of carboxylic acid groups Y (μmol / g) can be converted by the formula: "X = Y × 56.1 / 1,000".

[0044] [Number average molecular weight of the first polyester resin] The number average molecular weight of the first polyester resin is preferably 3,000 or more and 30,000 or less. When the number average molecular weight of the first polyester resin is 3,000 less than that, the molecular chains are too short to entangle easily, so the degree of improvement in abrasion resistance may be low. On the other hand, when the number average molecular weight of the first polyester resin exceeds 30,000, the molecular chains are too long to move easily and are difficult to entangle. For this reason, the degree of improvement in abrasion resistance may be low. The number average molecular weight of the first polyester resin is a value in terms of polystyrene measured by gel permeation chromatography.

[0045] [Glass transition temperature of resin particles] The glass transition temperature of the resin particles is preferably 40°C or higher and 120°C or lower. The glass transition temperature is the temperature at which the resin particles begin to change from a glassy state to a viscous state, and is a physical property value that indicates the ease of softening of the resin particles. The higher the glass transition temperature of the resin particles, the more likely they are to exist in a hard state near room temperature (25°C). The harder the resin particles, the less likely they are to be deformed by external forces. Therefore, by using resin particles with a high glass transition temperature, the strength of the resin layer formed on the recording medium by the first polyester resin can be improved, and the scratch resistance of the recorded image can be further enhanced. The glass transition temperature of the resin particles can be measured using a thermal analyzer such as a differential scanning calorimeter (DSC).

[0046] [Particle size of resin particles] The volume-based cumulative 50% particle size (D 50 ) of the resin particles is preferably 50 nm or more and 200 nm or less. When considering a certain amount of resin particles, the specific surface area increases as the particle size decreases, and the specific surface area decreases as the particle size increases. If the D 50 of the resin particles is less than 50 nm, the specific surface area of the resin particles is large, the contact opportunity between the resin particles increases, and the concentration due to the evaporation of the aqueous medium from the ink droplets easily causes the resin particles to rapidly aggregate by penetrating into the recording medium. As a result, micro unevenness is likely to occur on the surface of the recorded image, and the degree of improvement in glossiness may be low. On the other hand, if the D 50 of the resin particles exceeds 200 nm, the dispersion state of the resin particles becomes unstable, and it may be difficult to uniformly form ink dots on the recording medium. As a result, macro unevenness is likely to occur on the image surface, and the degree of improvement in glossiness may be low. The volume-based cumulative 90% particle size (D 90 ) of the resin particles is preferably 70 nm or more and 280 nm or less.

[0047] The volume-based cumulative 50% particle size (D 50 ) of the resin particles is the volume-based cumulative 90% particle size (D 90The ratio (times) to is preferably 0.6 times or more and 0.8 times or less. If the above ratio is less than 0.6 times, the particle size distribution of the resin particles will be wide, and there will be many resin particles with significantly different particle sizes. When resin particles with large particle sizes collide with resin particles with small particle sizes, the resin particles tend to aggregate due to so-called heteroaggregation. As a result, microscopic irregularities are likely to occur on the surface of the recorded image, and the degree of improvement in gloss may be low. The cumulative 50% particle size (D 50 ) and the cumulative 90% particle size (D 90 ) of the resin particles are the diameters of the particles that reach 50% or 90% when integrated from the small particle size side based on the total volume of the measured particles in the particle size integration curve. The D 50 and D 90 of the resin particles can be measured by the dynamic light scattering method under the same conditions as the determination method of "whether the resin is resin particles" described above.

[0048] 〔Manufacturing method of resin particles〕 The resin particles can be manufactured, for example, by synthesizing a first polyester resin and then granulating it. The first polyester resin can be obtained, for example, by reacting a polyhydric alcohol and a polyvalent carboxylic acid (esterification reaction). If necessary, a so-called transesterification reaction can be performed by adding either the polyhydric alcohol or the polyvalent carboxylic acid to cleave a part of the ester bonds, and the molecular weight of the obtained first polyester resin can be adjusted. The polyvalent carboxylic acid used when synthesizing the polyester resin may be in the salt form (preferably an alkali metal salt form such as a sodium salt) or in the ester form (preferably an alkyl ester form).

[0049] For example, by adjusting the usage amount of the raw materials so that the number of moles of the carboxylic acid groups of the polyvalent carboxylic acid is more than the number of moles of the hydroxy groups of the polyhydric alcohol, the amount of carboxylic acid groups of the obtained first polyester resin can be adjusted. Also, by adding a polyvalent carboxylic acid during the transesterification reaction, the amount of carboxylic acid groups of the obtained first polyester resin can be adjusted.

[0050] The esterification reaction is carried out in an inert gas atmosphere such as nitrogen gas. The reaction temperature during the esterification reaction is preferably 180 to 260°C. The reaction time of the esterification reaction is preferably 2.5 to 10 hours, and more preferably 4 to 6 hours.

[0051] During the esterification reaction, the inside of the reaction system may be depressurized, and the water generated in the esterification reaction may be discharged out of the system to promote the esterification (dehydration condensation) reaction. The reaction under reduced pressure is carried out in an inert gas atmosphere such as nitrogen gas following the esterification reaction. The reaction temperature under reduced pressure is preferably 220 to 280°C. The reaction time under reduced pressure is preferably 2.5 to 10 hours, and more preferably 4 to 6 hours. The degree of vacuum is preferably 1 Pa or more and 130 Pa or less. However, if the degree of vacuum is too low, the reaction efficiency may decrease or the number average molecular weight of the first polyester resin may become small, so it is preferably adjusted according to the desired reaction conditions. It is preferable to gradually reduce the pressure over a period of about 60 to 180 minutes until it reaches 130 Pa or less from atmospheric pressure (101,325 Pa).

[0052] The transesterification reaction is carried out by adding either a polyhydric alcohol or a polycarboxylic acid to cleave a part of the ester bond and adjust the molecular weight of the first polyester resin. Since it is easy to balance the number average molecular weight and acid value of the first polyester resin, it is preferable to carry out the transesterification reaction by adding a polycarboxylic acid having 3 or more valences (among them, at least one of trimellitic acid and trimellitic anhydride is preferable).

[0053] The transesterification reaction is also carried out under an inert gas atmosphere such as nitrogen gas following the esterification reaction. The reaction temperature during the transesterification reaction is preferably 180 to 260 °C. The reaction time of the transesterification reaction is preferably 1 to 5 hours. The transesterification reaction can be carried out in the presence of a catalyst and a heat stabilizer. Examples of the catalyst include zinc acetate, antimony trioxide, tetra-n-butyl titanate, n-butylhydroxyoxytin, etc. The amount of catalyst used (mol) is 1×10 -1 mol to 20×10 -4 mol per 1 mol of the polyhydric alcohol or polycarboxylic acid used in the transesterification reaction, which is preferable. Examples of the heat stabilizer include acids such as phosphoric acid and acid esters such as triethyl phosphate.

[0054] The synthesized first polyester resin is preferably used in the next step of pelletization after being made into an appropriate form by pressurization, pulverization, etc. The resin particles formed from the first polyester resin are preferably pelletized so as to be in the state of a dispersion liquid (liquid containing resin particles) dispersed in an aqueous liquid medium for use as a constituent component of the aqueous ink. The aqueous liquid medium is mainly composed of water such as deionized water, ion-exchanged water, distilled water, etc., and contains a water-soluble organic solvent as necessary. The water content in the aqueous liquid medium is preferably 50% by mass or more, and it is also preferable to use water that does not contain a water-soluble organic solvent.

[0055] Examples of the method for pelletizing the first polyester resin to form resin particles include a dispersion method, a phase inversion (emulsification) method, etc. Examples of the dispersion method include the methods (1) and (2) shown below. (1) A method of adding a solution obtained by dissolving the first polyester resin in an organic solvent to an aqueous liquid medium to disperse the first polyester resin (2) A method of dissolving the first polyester resin in an organic solvent, then adding and mixing an aqueous liquid medium to disperse the first polyester resin

[0056] As the phase inversion (emulsification) method, for example, a method can be mentioned in which an aqueous liquid medium is added to a solution obtained by dissolving a first polyester resin in an organic solvent, and the first polyester resin is precipitated in the form of particles in the process of phase inversion from a solvent system to an aqueous system. In either the dispersion method or the phase inversion (emulsification) method, it is preferable to adjust the particle diameter of the obtained resin particles by using a known disperser or the like and subjecting them to atomization while applying an appropriate shearing force. Since the amount of carboxylic acid groups present on the particle surface can be accurately adjusted, it is preferable to produce resin particles by the phase inversion (emulsification) method. Hereinafter, a method for producing resin particles by the phase inversion (emulsification) method will be described.

[0057] A resin solution is prepared by dissolving a first polyester resin in an organic solvent capable of dissolving the first polyester resin. Examples of the organic solvent include ethers such as tetrahydrofuran and dibutyl ether; ketones such as acetone and methyl ethyl ketone; and alcohols such as isopropanol. If only an organic solvent with low water solubility and immiscible in any proportion (such as methyl ethyl ketone) is used, it may be difficult to adjust the amount of carboxylic acid groups present on the particle surface within a predetermined range. Therefore, as the organic solvent, it is preferable to use ethers such as tetrahydrofuran that can be miscible with water in any proportion. Ethers such as tetrahydrofuran are also preferable in terms of their excellent solubility in the first polyester resin. If the concentration of the first polyester resin in the resin solution is dilute, it may be difficult to adjust the amount of carboxylic acid groups present on the particle surface within a predetermined range. Therefore, the content (mass%) of the first polyester resin in the resin solution is preferably 20.0 mass% or more and 80.0 mass% or less, and more preferably 30.0 mass% or more and 50.0 mass% or less.

[0058] Next, an aqueous liquid medium is gradually added to the prepared resin solution to precipitate resin particles. Since the dispersed state of the resin particles can be stably maintained, it is preferable to add a base before or during the addition of the aqueous liquid medium. Examples of the base include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, and ammonia. The base is preferably added in an aqueous solution state. Cations exist in the system to which the base is added. In an attempt to neutralize this cation, the carboxylic acid groups of the first polyester resin are granulated in a state where they are located on the particle surface, and resin particles having carboxylic acid groups on the particle surface are formed. That is, by adjusting the amount of the base in the system, the amount of carboxylic acid groups present on the particle surface of the resin particles can be accurately adjusted. For example, if the amount of the base in the system is large, the amount of carboxylic acid groups on the particle surface of the obtained resin particles also increases. On the other hand, if the amount of the base in the system is small, the amount of carboxylic acid groups on the particle surface of the obtained resin particles also decreases.

[0059] The amount of the base to be added can be controlled by the neutralization rate (mol%) based on the acid value of the first polyester resin. As the addition amount of the aqueous liquid medium increases, the initially transparent resin solution gradually becomes turbid and emulsifies, and resin particles are formed. The particle diameter and particle size distribution of the obtained resin particles can be controlled by the content of the first polyester resin in the resin solution, the addition rate of the aqueous liquid medium, the shear force applied during dispersion, and the like.

[0060] The emulsion containing the resin particles is depressurized to distill off the organic solvent, and if necessary, it is filtered through a filter (stainless steel mesh) with an appropriate pore size to remove coarse particles. Then, by adding water to adjust the content of the resin particles, a liquid containing the resin particles (aqueous dispersion of the resin particles) can be prepared. From the viewpoint of ink productivity, the content (mass%) of the resin particles in the liquid containing the resin particles is preferably 10.0 mass% or more and 50.0 mass% or less, and more preferably 20.0 mass% or more and 45.0 mass% or less.

[0061] 〔Analysis of Resin Particles〕 Regarding the composition of the first polyester resin constituting the resin particles, for example, it can be analyzed by the method shown below. First, a sample is prepared by dissolving the resin particles in an organic solvent such as tetrahydrofuran that can dissolve the resin particles. The resin particles to be dissolved in the organic solvent may be in the state of an aqueous dispersion or in a dry state. By analyzing the prepared sample by analytical methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), the types and ratios of the units (monomers) constituting the resin can be known. Also, by analyzing the resin particles by pyrolysis gas chromatography, the units (monomers) constituting the resin can be detected. When insoluble matter that does not dissolve in the organic solvent occurs during sample preparation, the generated insoluble matter can also be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. Incidentally, the second polyester resin described later can also be analyzed by the same method as the first polyester resin.

[0062] (Second Resin) The second resin is at least one of (i) a block copolymer containing an A block having no acid group and a B block having an acid group, and (ii) a second polyester resin having a sulfonic acid group. The content (% by mass) of the second resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 2.0% by mass or less, based on the total mass of the ink. The block copolymer and the second polyester resin as the second resin may be present in the ink in a dissolved state or in a dispersed state. When the second resin is present in the ink in a dispersed state, that is, when it is resin particles, it is preferably one that does not encapsulate the colorant. Among them, the block copolymer is preferably present in the ink in a dispersed state, that is, present in the ink in the form of micelles. Also, the second polyester resin is a water-soluble resin and is preferably present in the ink in a dissolved state. From the viewpoint of ejection characteristics, as the second resin, the block copolymer is more preferable than the second polyester resin.

[0063] (Second Resin (i): Block Copolymer) 〔Constituent Materials of Block Copolymer〕 The block copolymer as the second resin contains an A block having no acid group and a B block having an acid group. The presence or absence of an acid group in the block can be adjusted by whether or not a known monomer having an acid group is used in the process of synthesizing each block. Each block can be formed of known monomers. Each block may be a homopolymer formed of only units derived from a single monomer, or may be a copolymer containing units derived from a plurality of monomers. Each block may contain a plurality of segments. Specifically, the block copolymer may be a so-called A-B block copolymer consisting of only one A block and one B block. Further, it may be a block copolymer containing an A block composed of two segments A and a B block composed of one segment B. Further, it may be a block copolymer containing an A block composed of one segment A and a B block composed of two segments B.

[0064] 〔A Block〕 The A block is a hydrophobic polymer block composed of units having no acid group. Segment A can be formed by (co)polymerizing one or more known monomers having no acid group.

[0065] Examples of the monomer for forming the A block include monomers having an aromatic group such as styrene, vinyltoluene, α-methylstyrene, benzyl (meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; (meth)acrylic acid esters having substituents such as amino groups (monomers having an aliphatic group) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dimethylaminoethyl (meth)acrylate; (meth)acrylic acid derivatives such as (meth)acrylonitrile, (meth)acrylamide; and the like.

[0066] When the interaction between the resin particles and the block copolymer is weak, the block copolymer may desorb from the resin particles in the ink, and the viscosity of the ink may easily increase. As a result, the leveling property between the dots of the ink applied to the recording medium deteriorates, macro unevenness is likely to occur on the image surface, and the degree of improvement in glossiness may be low. Therefore, from the viewpoint of enhancing the interaction between the resin particles and the block copolymer, it is preferable that the A block contains a unit derived from a monomer having an aromatic group. As the monomer having an aromatic group, styrene and benzyl (meth)acrylate are preferable.

[0067] [B block] The B block is a hydrophilic polymer block composed of units having an acid group. The B block can be formed by (co)polymerizing one or more known monomers including a monomer having an acid group. The segment B is preferably a copolymer containing two or more types of units, and more preferably a random copolymer.

[0068] As the monomer having an acid group, a monomer having a carboxylic acid group is preferable, and (meth)acrylic acid is more preferable. As a unit derived from a monomer for constituting the B block, a unit derived from a monomer having no acid group can be further used. Examples of the monomer having no acid group include the same ones as those exemplified as the monomer for forming the aforementioned A block. As the monomer that becomes a unit for forming the B block by polymerization, in addition to (meth)acrylic acid, it is preferable to include a monomer having no acid group. This monomer having no acid group preferably includes (meth)acrylate.

[0069] [Physical properties of block copolymer] [Acid value of block copolymer] The acid value of the block copolymer is preferably 50 mgKOH / g or more and 200 mgKOH / g or less. When the acid value of the block copolymer is less than 50 mgKOH / g, since the amount of acid groups is too small, the block copolymers in the ink tend to associate with each other to form micelles. Then, with the evaporation of the aqueous medium from the ink droplets and the penetration into the recording medium, the micelles aggregate, and the resin particles may also aggregate. As a result, unevenness of the resin is likely to occur in the recorded image, and the degree of improvement in gloss may be low. On the other hand, when the acid value of the block copolymer exceeds 200 mgKOH / g, since the amount of carboxylic acid groups is too large, the block copolymer spreads in the ink, and the viscosity of the ink may increase. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, macro unevenness is likely to occur on the image surface, and the degree of improvement in gloss may be low. The acid value of the block copolymer can be measured by neutralization titration using a potential difference. The acid value X (mgKOH / g) and the amount of carboxylic acid groups Y (μmol / g) can be converted by the formula: "X = Y × 56.1 / 1,000".

[0070] [Number-average molecular weight of block copolymer] The number-average molecular weight of the block copolymer is preferably 3,000 or more and 20,000 or less. When the number-average molecular weight of the block copolymer is less than 3,000, the molecular chains of the block copolymer are less likely to entangle with the molecular chains of other resins, so the degree of improvement in abrasion resistance may be low. On the other hand, when the number-average molecular weight of the block copolymer exceeds 20,000, the viscosity of the ink may increase. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, macro unevenness is likely to occur on the image surface, and the degree of improvement in gloss may be low. The number-average molecular weight of the block copolymer is a value in terms of polystyrene measured by gel permeation chromatography.

[0071] 〈Number-average molecular weight of A block / Number-average molecular weight of block copolymer〉 The number average molecular weight of block A is preferably 0.30 times or more and 0.80 times or less the number average molecular weight of the block copolymer. When the above ratio is less than 0.30 times, the proportion of block A having no acid group is small and the proportion of block B having an acid group is large, so the interaction between the resin particles and the block copolymer becomes weak. As a result, the block copolymer may desorb from the resin particles in the ink, increasing the viscosity of the ink. As a result, the leveling property between the dots of the ink applied to the recording medium deteriorates, macro unevenness is likely to occur on the image surface, and the degree of gloss improvement may be low. On the other hand, when the above ratio exceeds 0.80 times, the proportion of block A having no acid group is large and the proportion of block B having an acid group is small, so the block copolymers are likely to associate with each other in the ink to form micelles. Then, the micelles aggregate due to the concentration by evaporation of the aqueous medium from the ink droplets and penetration into the recording medium, and the resin particles may also aggregate. As a result, unevenness of the resin is likely to occur in the recorded image, and the degree of gloss improvement may be low.

[0072] [Glass transition temperature of block copolymer] The glass transition temperature of the block copolymer is preferably 40°C or higher and 120°C or lower. The glass transition temperature is the temperature at which the block copolymer begins to change from a glassy state to a viscous state, and is a physical property value indicating the ease of softening of the block copolymer. The higher the glass transition temperature of the block copolymer, the more likely it is to exist in a hard state near room temperature (25°C). The harder the block copolymer, the more difficult it is to deform by an external force. Therefore, by using a block copolymer with a high glass transition temperature, the strength of the resin layer formed on the recording medium by the first polyester resin can be improved, and the scratch resistance of the recorded image can be further enhanced. The glass transition temperature of the block copolymer can be measured using a thermal analyzer such as a differential scanning calorimeter (DSC).

[0073] [Method for producing block copolymer] The block copolymer can be produced by various living polymerization methods such as, for example, living radical polymerization method, living anion polymerization method, and living cation polymerization method. Among them, producing the block copolymer by the living radical polymerization method is preferable because it is easy to be compatible with general-purpose monomers (especially monomers having an aromatic group, (meth)acrylic acid esters, etc.) for the copolymer contained in the aqueous ink for inkjet. Examples of the living radical polymerization method include NMP method, ATRP method, RAFT method, TERP method, SBRP method, BIRP method, CMRP method, RTCP method, etc.

[0074] In the living radical polymerization method, the polymerization rate of the first block is calculated from the concentration of the residual monomer measured by dry solid content or gas chromatography, and when the consumption of the monomer is confirmed, the monomer constituting the second block is added to proceed with the polymerization reaction. Thereby, a diblock copolymer in which the first block and the second block are bonded can be obtained. Further, by repeating the above operation a plurality of times, a block copolymer in which blocks composed of a plurality of segments are bonded can be obtained.

[0075] 〔Analysis of block copolymer〕 Regarding the composition of the block copolymer, for example, it can be analyzed by the method shown below. First, a sample is prepared by dissolving the block copolymer in an organic solvent such as tetrahydrofuran that can dissolve the block copolymer. The block copolymer to be dissolved in the organic solvent may be in the state of an aqueous solution or an aqueous dispersion, or may be in a dry state, but a dry state is preferred. By analyzing the prepared sample by an analytical method such as nuclear magnetic resonance (NMR) spectroscopy or matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), the types and ratios of the units (monomers) constituting the resin can be known. Also, by analyzing the block copolymer by pyrolysis gas chromatography, the units (monomers) constituting the resin can be detected. When insoluble matter that does not dissolve in the organic solvent occurs during sample preparation, the generated insoluble matter can also be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. Whether the resin has block properties can be determined from the confirmation of the continuity of the units in matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS).

[0076] (Second Resin (ii): Second Polyester Resin) [Constituent Materials of the Second Polyester Resin] The second polyester resin having a sulfonic acid group as the second resin is a polyester resin composed of units derived from polyhydric alcohols and units derived from polyvalent carboxylic acids, into which a sulfonic acid group is incorporated. Preferably, a polyester resin containing units derived from a polyvalent carboxylic acid having a sulfonic acid group can be used. Hereinafter, unless otherwise specified, the "polyvalent carboxylic acid" used as a raw material for the second polyester resin is shown as including both "a polyvalent carboxylic acid having no sulfonic acid group" and "a polyvalent carboxylic acid having a sulfonic acid group". The total of the ratio (mass%) of the units derived from polyhydric alcohols and the ratio (mass%) of the units derived from polyvalent carboxylic acids in the second polyester resin is preferably 90.0 mass% or more. This total is more preferably 95.0 mass% or more, and may be 100.0 mass%.

[0077] [Polyhydric alcohol] Examples of the polyhydric alcohol include the same ones as those exemplified as the polyhydric alcohol for forming the aforementioned first polyester resin. The proportion (mass%) of the unit derived from the polyhydric alcohol in the second polyester resin is preferably 40.0 mass% or more and 60.0 mass% or less.

[0078] [Polycarboxylic acid having no sulfonic acid group] Examples of the polycarboxylic acid having no sulfonic acid group include the same ones as those exemplified as the polycarboxylic acid for forming the aforementioned first polyester resin. The proportion (mass%) of the unit derived from the polycarboxylic acid having no sulfonic acid group in the second polyester resin is preferably 10.0 mass% or more and 55.0 mass% or less.

[0079] [Polycarboxylic acid having a sulfonic acid group] Examples of the polycarboxylic acid having a sulfonic acid group include polycarboxylic acids having 2 to 4 valences. Examples of the polycarboxylic acid having a sulfonic acid group include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, nitrogen-containing polycarboxylic acids, and the like. Examples of the polycarboxylic acid having a sulfonic acid group include, for example, sulfosuccinic acid, 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and the like. As the polycarboxylic acid, an oligomer (a low molecular weight polymer having a molecular weight of 1,000 or less) can also be used. Further, when the second polyester resin is produced by a transesterification reaction, an esterified product can also be used as the polycarboxylic acid. The proportion (mass%) of the unit derived from the polycarboxylic acid having a sulfonic acid group in the second polyester resin is preferably 1.0 mass% or more and 40.0 mass% or less.

[0080] [Preferred constituent materials] Preferred constituent materials include the same materials as those exemplified as the preferred constituent materials for forming the aforementioned first polyester resin. Since the second polyester resin is preferably a water-soluble resin that exists in the ink in a dissolved state, different from the first resin, it is preferable that the second polyester resin has higher hydrophilicity than the first polyester resin.

[0081] It is preferable to use a divalent carboxylic acid or a trivalent carboxylic acid because it is easy to adjust the number average molecular weight and acid value of the resulting second polyester resin. From the viewpoint of enhancing the interaction with the first resin, it is preferable to use a polyhydric carboxylic acid having an aromatic group as the polyhydric alcohol having a sulfonic acid group. That is, it is preferable that the second polyester resin contains a unit derived from an aromatic compound. Examples of the aromatic compound include a polyhydric alcohol having an aromatic group and a polyhydric carboxylic acid having an aromatic group (and a sulfonic acid group). As the polyhydric carboxylic acid having an aromatic group (and a sulfonic acid group), it is preferable to use terephthalic acid, isophthalic acid, trimellitic acid, 5-sulfoisophthalic acid, sulfoterephthalic acid, or 4-sulfophthalic acid. The proportion (mass%) of the unit derived from the aromatic compound in the second polyester resin is preferably 25.0 mass% or more and 50.0 mass% or less based on the total mass of the second polyester resin. The proportion (mass%) of the unit having no aromatic group in the second polyester resin is preferably 50.0 mass% or more and 75.0 mass% or less based on the total mass of the second polyester resin.

[0082] 〔Physical properties of the second polyester resin〕 [Amount of sulfonic acid group / Amount of carboxylic acid group] The second polyester resin further has a carboxylic acid group, and the amount of sulfonic acid groups in the second polyester resin is preferably 0.08 times or more and 0.50 times or less in terms of the molar ratio to the amount of carboxylic acid groups in the second polyester resin. If the above ratio is less than 0.08 times, the proportion of sulfonic acid groups that dissociate into ions and cause electrical repulsion in the aqueous ink is small, so the second polyester resins in the ink tend to associate with each other to form micelles. Then, as the aqueous medium evaporates from the ink droplets and concentrates, or penetrates into the recording medium, the micelles aggregate, and the first resin may also aggregate. As a result, unevenness of the resin is likely to occur in the recorded image, and the degree of improvement in glossiness may be low. On the other hand, if the above ratio exceeds 0.50 times, the proportion of sulfonic acid groups is too large, so the interaction between the first resin and the second polyester resin becomes weak. As a result, the second polyester resin may desorb from the first resin in the ink, causing the viscosity of the ink to increase. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, macro unevenness is likely to occur on the image surface, and the degree of improvement in glossiness may be low.

[0083] [Acid value of the second polyester resin] The acid value of the second polyester resin is preferably 2 mgKOH / g or more and 30 mgKOH / g or less. When the acid value of the second polyester resin is less than 2 mgKOH / g, since the amount of acid groups is too small, the resin particles may rapidly aggregate due to the evaporation of the aqueous medium from the ink droplets and penetration into the recording medium. As a result, microscopic irregularities are likely to occur on the surface of the recorded image, and the degree of improvement in gloss may be low. On the other hand, when the acid value of the second polyester resin exceeds 30 mgKOH / g, since the amount of acid groups is too large, the second polyester resin may gradually dissolve in the ink, causing the viscosity of the ink to increase. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, macroscopic irregularities are likely to occur on the image surface, and the degree of improvement in gloss may be low. The acid value of the second polyester resin can be measured by neutralization titration using a potential difference. The acid value X (mgKOH / g) and the amount of acid groups Y (μmol / g) can be converted by the formula: "X = Y × 56.1 / 1,000".

[0084] [Number average molecular weight of the second polyester resin] The number average molecular weight of the second polyester resin is preferably 5,000 or more and 40,000 or less. When the number average molecular weight of the second polyester resin is less than 5,000, the molecular chains of the second polyester resin are less likely to entangle with the molecular chains of other resins, so the degree of improvement in abrasion resistance may be low. On the other hand, when the number average molecular weight of the second polyester resin exceeds 20,000, the viscosity of the ink may increase. As a result, the leveling property between the dots of the ink applied to the recording medium decreases, macroscopic irregularities are likely to occur on the image surface, and the degree of improvement in gloss may be low. The number average molecular weight of the second polyester resin is a value in terms of polystyrene measured by gel permeation chromatography.

[0085] [Glass transition temperature of the second polyester resin] The glass transition temperature of the second polyester resin is preferably 40°C or higher and 120°C or lower. The glass transition temperature is the temperature at which the second polyester resin begins to change from a glassy state to a viscous state, and is a physical property value that indicates the ease of softening of the second polyester resin. The higher the glass transition temperature of the second polyester resin, the more likely it is to exist in a hard state near room temperature (25°C). The harder the second polyester resin, the more difficult it is to deform by an external force. Therefore, by using a second polyester resin with a high glass transition temperature, the strength of the resin layer formed on the recording medium by the first polyester resin can be improved, and the scratch resistance of the recorded image can be further enhanced. The glass transition temperature of the second polyester resin can be measured using a thermal analyzer such as a differential scanning calorimeter (DSC).

[0086] 〔Method for producing the second polyester resin〕 Unlike the first resin, the second polyester resin is preferably a water-soluble resin that exists in the ink in a dissolved state. As a method for producing the second polyester resin, a method similar to the method for producing the first resin and the methods exemplified as post-treatment can be mentioned, except that it is made into a water-soluble resin. Specifically, by replacing at least a part of the polyvalent carboxylic acid with a polyvalent carboxylic acid having a sulfonic acid group, a second polyester resin having a sulfonic acid group can be synthesized.

[0087] (Aqueous medium) The ink of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink can contain an aqueous medium that is water or a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water or ion-exchanged water. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. Also, the content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inks for inkjet such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds, etc. can be used.

[0088] (Other components) In addition to the above components, the ink may contain water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane; urea derivatives like urea and ethylene urea; etc. Further, the ink may contain various additives such as surfactants, pH adjusters, defoamers, rust preventives, preservatives, fungicides, antioxidants, anti-reduction agents, and chelating agents as required. When a surfactant is contained, the content (mass%) of the surfactant in the ink is preferably 0.1 mass% or more and 5.0 mass% or less, and more preferably 0.1 mass% or more and 2.0 mass% or less based on the total mass of the ink.

[0089] (Physical properties of the ink) The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, more preferably 1.0 mPa·s or more and 5.0 mPa·s or less, and particularly preferably 1.0 mPa·s or more and 3.0 mPa·s or less. The surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, more preferably 20 mN / m or more and 60 mN / m or less, and particularly preferably 30 mN / m or more and 50 mN / m or less. The pH of the ink at 25°C is preferably 5.0 or more and 10.0 or less, and more preferably 7.0 or more and 9.5 or less.

[0090] <Ink cartridge> The ink cartridge of the present invention includes ink and an ink storage unit for storing the ink. The ink stored in the ink storage unit is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage unit for storing ink. The ink storage unit is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other through a communication port 18. Further, the absorber storage chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may not have an ink storage chamber for storing liquid ink, and may be in a form in which the entire amount of the stored ink is held by the absorber. Further, the ink storage unit may not have an absorber and may be in a form in which the entire amount of the ink is stored in a liquid state. Furthermore, it may be an ink cartridge configured to have an ink storage unit and a recording head.

[0091] <Inkjet recording method> The inkjet recording method of the present invention is a method of discharging the aqueous ink of the present invention described above from an inkjet recording head and recording an image on a recording medium. Examples of the method of discharging the ink include a method of 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 adopt a method of applying thermal energy to the ink to discharge the ink. Except for using the ink of the present invention, the steps of the inkjet recording method may be known ones. After applying the ink to the recording medium to record an image, a step of heating the image (ink) may be carried out. The heating temperature at this time can be appropriately set so as to be a temperature equal to or higher than the glass transition temperature of the resin particles constituting the image. The upper limit of the temperature is not particularly limited, but it is preferably 120°C or lower.

[0092] Figure 2 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention. (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40 and is configured such that an ink cartridge 42 can be set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is discharged from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by a conveying means (not shown), and an image is recorded on the recording medium 32. As the recording medium 32, for example, it is preferable to use a recording medium having no coating layer such as plain paper, or a recording medium having a coating layer such as glossy paper, matte paper, or printed book paper. Examples of the base material of these recording media include paper, film, and plastic.

Examples

[0093] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples in any way as long as the gist thereof is not exceeded. Regarding the amounts of components, "parts" and "%" are based on mass unless otherwise specified.

[0094] <Measurement method of physical property values> (Amount of carboxylic acid groups on the particle surface of resin particles) A liquid containing resin particles was used as a sample, and the amount of carboxylic acid groups on the particle surface of the resin particles was measured by colloidal titration using the potential difference. For the colloidal titration, an automatic potentiometric titrator (trade name "AT510", manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a streaming potential titration unit (trade name "PCD-500", manufactured by Kyoto Electronics Industry Co., Ltd.) was used. As the titration reagent, a 0.005 mol / L methyl glycol chitosan solution was used.

[0095] (Acid value of resin) The acid values of the polyester resin and the block copolymer were measured according to the following procedure. The resin (polyester resin or block copolymer) was separated from the liquid containing the resin and washed with 1.0 mol / L hydrochloric acid and water. The washed resin was added to 60 mL of a liquid obtained by mixing water and tetrahydrofuran at a mass ratio of 1:6, and the resin was dissolved at 25 °C to prepare a sample. The prepared sample was subjected to neutralization titration to measure the acid value of the resin. For the neutralization titration, an automatic potentiometric titrator (trade name "AT510", manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a composite glass electrode (trade name "C-171", manufactured by Kyoto Electronics Industry Co., Ltd.) was used. As the titration reagent, a 0.5 mol / L potassium hydroxide ethanol solution was used.

[0096] (Number average molecular weight of resin) The number average molecular weight of the resin and the number average molecular weight of the A block of the block copolymer were measured according to the following procedure. The polyester resin, A block or block copolymer was added to tetrahydrofuran, and after dissolving the resin over 24 hours at 25°C, the sample was prepared by filtering through a membrane filter. The resin content in the sample was adjusted to be approximately 0.3%. For the prepared sample, analysis by gel permeation chromatography was performed according to the conditions shown below, and the number average molecular weight was calculated using a molecular weight calibration curve prepared using a standard polystyrene resin. As the standard polystyrene resin, products with the trade names "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500" (manufactured by Tosoh Corporation) were used. · HPLC apparatus: Product name "2695 Separations Module" (manufactured by Waters) · Differential refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) · Column: Four-connected column with the product name "GPC KF-806M" (manufactured by Showa Denko) · Eluent: Tetrahydrofuran · Flow rate: 1.0 mL / min · Oven temperature: 40°C · Sample injection volume: 100 μL

[0097] (Glass transition temperature of the first resin) 2 mg of resin particles obtained by drying the liquid containing resin particles at 60°C was placed in an aluminum container and sealed to prepare a sample for measurement. For the prepared sample, using a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments), a heating curve was created by performing thermal analysis according to the temperature program shown below. The temperature at the intersection of the straight line extended to the high temperature side through two points in the low temperature side curve and the tangent line drawn at the point where the gradient of the stepped change part in the curve is maximum in the heating curve (horizontal axis: temperature, vertical axis: heat quantity) was defined as the "glass transition temperature of the resin particles". [Temperature program]: (1) Heat the temperature at a rate of 10 °C / min up to 200 °C (2) Cool the temperature at a rate of 5 °C / min from 200 °C to -50 °C (3) Heat the temperature at a rate of 10 °C / min from -50 °C to 200 °C

[0098] (Judgment on whether the resin is resin particles, particle size) The liquid containing the resin was diluted with ion-exchanged water to prepare a sample with a resin content of about 1.0%. For this sample, using a particle size distribution meter by dynamic light scattering method, according to the measurement conditions shown below, the particle size (cumulative 50% particle size D based on volume 50 of the resin particles, and the same 90% particle size D 90 ) was measured. As the particle size distribution meter, the product named "NanoTrack WAVEII-Q" (manufactured by Microtrac·BEL) was used. When particles having a particle size were measured by this measurement method, the resin was judged to be "resin particles" (it is a "water-dispersible resin"). On the other hand, when particles having a particle size were not measured by this measurement method, the resin was judged not to be "resin particles" (it is a "water-soluble resin"). [Measurement conditions]: ·SetZero: 30s ·Number of measurements: 3 times ·Measurement time: 180 seconds ·Shape: True spherical ·Refractive index: 1.6 ·Density: 1.0

[0099] (Viscosity of the ink) An apparatus with a rotor (1°34’×R24) attached was prepared for an E-type viscometer (product name "RE80-L", manufactured by Toki Sangyo Co., Ltd.) that circulates antifreeze through a tube in a thermostatic bath set at 25 °C. Using this apparatus, the viscosity of the ink was measured.

[0100] ><Synthesis of resin particles formed of the first resin: polyester resin> (Polyester resin) A mixture of the components (unit: part) shown in the item of "esterification reaction" in Table 1 was placed in a reaction vessel installed in an autoclave, and heated at 220 °C for 4 hours to carry out an esterification reaction. Next, the temperature was raised to 240 °C, and the pressure was reduced to 13 Pa over 90 minutes. After maintaining the reduced pressure state of 240 °C and 13 Pa for 5 hours to continue the esterification (dehydration condensation) reaction, nitrogen gas was introduced to return to normal pressure. After the temperature was lowered to 220 °C, a catalyst (tetra-n-butyl titanate) and the components (unit: part) shown in the item of "transesterification reaction" in Table 1 were added, and heated at 220 °C for 2 hours to carry out a transesterification reaction. The usage amount (mol) of the catalyst was "3×10 -4 × total usage amount (mol) of polycarboxylic acid". Then, nitrogen gas was introduced to make it a pressurized state, and a sheet-shaped resin was taken out. After the taken-out resin was cooled to 25 °C, it was pulverized using a crusher to obtain a polyester resin. The properties of the obtained polyester resin are shown in Table 1. The meanings of the abbreviations of each component in Table 1 are shown below. ·EG: Ethylene glycol ·NPG: Neopentyl glycol ·BPA: Bisphenol A ·GLY: Glycerin ·tPA: Terephthalic acid ·iPA: Isophthalic acid ·BTA: Trimellitic acid ·HAD: Adipic acid

[0101] TIFF0007699934000001.tif112170

[0102] <Manufacture of the First Resin> (First Resins 1 to 30) A stirrer (product name: "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was set in a beaker with a volume of 2 L. The polyester resin, organic solvent, and light stabilizer of the types and amounts used (unit: g) shown in Table 2-1 were placed in this beaker, and stirred at 25 °C to dissolve the components. Next, an aqueous 5% sodium hydroxide solution in an amount corresponding to the neutralization rate (mol%) based on the acid value of the polyester resin was added, and stirred for 30 minutes. Further, while stirring at 10 °C and the stirring speed shown in Table 2-1, 900 g of ion-exchanged water was added dropwise at a rate of 20 mL / min. Thereafter, the temperature was raised to 60 °C, and the organic solvent and part of the water were distilled off under reduced pressure. The beaker was placed in a water bath, and heat treatment was carried out by stirring at 85 °C for the heat treatment time shown in Table 2-1. After filtering the content through a 150-mesh wire mesh, an appropriate amount of ion-exchanged water was added to obtain a liquid containing each first resin with a resin particle content of 25.0%. The characteristics of the obtained liquid containing the first resin and the first resin are shown in Table 2-2. In Table 2-2, "amount of carboxylic acid groups (μmol / g)" indicates the amount of carboxylic acid groups present on the particle surface of the resin particles. The meanings of the types of light stabilizers and abbreviations of organic solvents in Table 2-1 are shown below. · Light stabilizer 1: Benzotriazole-based light stabilizer (product name: "ADEKA STAB LA-31RG", manufactured by ADEKA) · Light stabilizer 2: Thioether-based light stabilizer (product name: "ADEKA STAB AO-503", manufactured by ADEKA) · Light stabilizer 3: Triazine-based light stabilizer (product name: "ADEKA STAB LA-46", manufactured by ADEKA) · Light stabilizer 4: Benzophenone-based light stabilizer (product name: "ADEKA STAB 1413", manufactured by ADEKA) · Light stabilizer 5: Hindered amine-based light stabilizer (product name: "ADEKA STAB LA-63P", manufactured by ADEKA) · THF: Tetrahydrofuran · MEK: Methyl ethyl ketone · IPA: Isopropanol

[0103] TIFF0007699934000002.tif205170

[0104] TIFF0007699934000003.tif204170

[0105] (First Resin C1) 0.2 parts of potassium persulfate and 79.4 parts of ion-exchanged water were placed in a four-necked flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, and nitrogen gas was introduced. Also, 19.7 parts of butyl methacrylate, 0.4 parts of methacrylic acid, and 0.3 parts of a reactive surfactant (trade name "Aqualon KH-05", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were mixed to obtain a mixture. The obtained mixture was added dropwise into the four-necked flask with stirring over 1 hour, and then reacted at 80 °C for 2 hours. After cooling the content to 25 °C, potassium hydroxide and an appropriate amount of ion-exchanged water were added to adjust the pH of the liquid to 8.5. Thus, a liquid containing the first resin C1 with a resin particle content of 25.0% was obtained.

[0106] (First Resin C2) According to the description of "Production Example 34" in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-88552), an "aqueous dispersion of graft polymer G6" was prepared. It was adjusted so that the resin particle content was 25.0% to obtain a liquid containing the first resin C2. This resin is composed of a polyester resin as the main chain and an addition polymerization resin as the side chain, and does not have a sulfonic acid group.

[0107] (First Resin C3) According to the description of Japanese Unexamined Patent Application Publication No. 08-269310, "non-spherical particles C1" were prepared. It was adjusted so that the resin particle content was 25.0% to obtain a liquid containing the first resin C3. These resin particles are formed of a polyester resin having no sulfonic acid group.

[0108] <Production of the Second Resin> (Second Resins 1 - 22: Block Copolymers) The inside of a four-necked flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was purged with nitrogen. Into this flask were placed 100.0 parts of methyl ethyl ketone, the monomers shown in "Segment A1" in Table 3 (unit: parts), a RAFT agent (cumyl dithiobenzoate, unit: parts), and a polymerization initiator (azobisisobutyronitrile, unit: parts). After purging with nitrogen at 25 °C for 30 minutes, the temperature was raised to 75 °C to initiate the reaction. The solution was withdrawn at regular intervals, and the polymerization rate was calculated by measuring the dry solid content in the solution. Also, using a part of the withdrawn solution, the number average molecular weight of the product was measured.

[0109] After confirming that the polymerization rate reached 95% or more, the monomer shown in "Segment A2" in Table 3 (unit: parts) was added and the reaction was further continued. Next, after confirming that the polymerization rate reached 95% or more, the monomers shown in "Segment B1" and "Segment B2" in Table 3 (unit: parts) were sequentially added and the reaction was further continued. After confirming that the final polymerization rate reached 98%, 50.0 parts of methyl ethyl ketone was added, and the flask was cooled to stop the reaction. The reaction solution was added to a large amount of methanol, and the resulting precipitate was vacuum dried at 40 °C for 24 hours to obtain a second resin. All of the obtained second resins 1 to 22 were water-soluble resins. Potassium hydroxide at 0.9 times the molar ratio to the acid value of the resin and an appropriate amount of ion-exchanged water were added to obtain a liquid containing each second resin with a second resin content of 10.0%. The acid value, number average molecular weight (Mn), number average molecular weight of block A (MnA), number average molecular weight of block B (MnB), and number average molecular weight of block A / number average molecular weight (MnA / Mn) of the obtained second resin are shown in Table 4. The meanings of the abbreviations of each component in Table 3 are shown below. · BzMA: Benzyl methacrylate · St: Styrene · MMA: Methyl methacrylate · HEMA: 2-Hydroxyethyl methacrylate · MAA: Methacrylic acid · nBMA: n-Butyl methacrylate

[0110] TIFF0007699934000004.tif153170

[0111] TIFF0007699934000005.tif154170

[0112] (2nd Resin 23 - 40: 2nd Polyester Resin) A mixture of the components shown in Table 5 (unit: g) and 0.1 part of a catalyst (potassium titanium oxalate) was placed in a reaction vessel installed in an autoclave. After heating to 200 °C with stirring under a nitrogen atmosphere, the temperature was gradually raised to 260 °C over 4 hours to carry out an esterification reaction and a transesterification reaction. Next, the pressure was reduced to 67 Pa over 90 minutes. After continuing the transesterification reaction while maintaining a reduced pressure state of 250 °C and 67 Pa for the condensation time shown in Table 5, nitrogen gas was introduced to return to normal pressure. Then, it was cooled to 25 °C to obtain the 2nd resin. All of the obtained 2nd resins 23 - 40 were water-soluble resins. An appropriate amount of ion-exchanged water was added to 10.0 g of the obtained 2nd resin, and it was stirred at 80 - 95 °C for 2 hours to dissolve the 2nd resin in water, obtaining a liquid containing each 2nd resin with a 2nd resin content of 10.0%. The properties of the obtained 2nd polyester resin are shown in Table 6. The meanings of the abbreviations of each component in Table 5 are shown below. ·EG: Ethylene Glycol ·16HD: 1,6 - Hexanediol ·NPG: Neopentyl Glycol ·14BD: 1,4 - Butanediol ·DMT: Dimethyl Terephthalate ·DMI: Dimethyl Isophthalate ·BTA: Trimellitic Acid ·DMA: Dimethyl Adipate ·5SIPM: Sodium 5 - Sulfonate Dimethyl Isophthalate ·STPM: Sodium Sulfonate Dimethyl Terephthalate ·4SIPM: Sodium 4 - Sulfonate Dimethyl Isophthalate ·SSM: Sodium Sulfonate Dimethyl Succinate

[0113] TIFF0007699934000006.tif129170

[0114] TIFF0007699934000007.tif129170

[0115] (Second Resin C1) Joncryl 683 (trade name, manufactured by BASF, acid value 160 mgKOH / g, number average molecular weight 3,500), which is an acrylic resin, was prepared. To this acrylic resin, potassium hydroxide in a molar ratio of 0.9 times the acid value and an appropriate amount of ion-exchanged water were added to obtain a liquid containing Second Resin C1 with a content of the second resin of 10.0%. This resin is a random copolymer having an aromatic group.

[0116] (Second Resin C2) According to the description in JP-A-08-269310, "Colored polyester fine particles B1" were prepared. An appropriate amount of ion-exchanged water was added to obtain a liquid containing Second Resin C2 with a content of the second resin of 10.0%. This resin is one in which a colorant (oil-soluble dye) is encapsulated in resin particles formed of a polyester resin having a sulfonic acid group.

[0117] <Preparation of Pigment Dispersion> (Pigment Dispersion 1) A batch vertical sand mill (manufactured by Aimax) filled with 200 parts of zirconia beads with a diameter of 0.3 mm was charged with a mixture of 10.0 parts of pigment, 20.0 parts of a liquid containing resin, and 70.0 parts of ion-exchanged water, and dispersed for 5 hours. As the pigment, C.I. Pigment Yellow 74 (trade name "Hansa yellow 5GX 01 LV 3344", manufactured by Clariant) was used. As the liquid containing resin, an aqueous solution with a resin content of 30.0% was used, which was prepared by dissolving a water-soluble resin in water containing potassium hydroxide in an equimolar amount to its acid value. As the water-soluble resin, a styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 167 mgKOH / g and a weight-average molecular weight of 10,000 was used. The mixture was centrifuged to remove coarse particles and then pressure-filtered through a microfilter with a pore size of 3.0 μm (manufactured by Fujifilm) to obtain Pigment Dispersion 1. The pigment content in Pigment Dispersion 1 was 10.0%, and the resin content was 6.0%.

[0118] (Pigment Dispersion 2) 5.0 g of concentrated hydrochloric acid was dissolved in 5.5 g of water, and the solution was cooled to 5°C. In this state, 1.6 g of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath, and while stirring to keep the solution temperature below 10°C, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of ion-exchanged water at 5°C was added. After stirring for 15 minutes, 6.0 g of carbon black (trade name "NIPex 170IQ", manufactured by Orion Engineered Carbons) was added with stirring, and further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (trade name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and dried in an oven at 110°C. Then, the counterions were replaced from sodium ions to potassium ions by an ion exchange method to obtain a self-dispersing pigment with -C6H3-(COOK)2 groups bonded to the particle surface of the carbon black. An appropriate amount of ion-exchanged water was added to adjust the pigment content, and Pigment Dispersion 2 with a pigment content of 10.0% was obtained.

[0119] <Preparation of Ink> The following components were mixed and stirred well, and then pressure-filtered through a microfilter with a pore size of 2.5 μm to prepare the ink. "Acetylenol E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The characteristics of the prepared ink are shown in Tables 7-1 to 7-3. · Color materials of the types shown in Tables 7-1 to 7-3: The usage amounts (%) shown in Tables 7-1 to 7-3 · Liquid containing the first resin of the types shown in Tables 7-1 to 7-3: The amount (%) that becomes the content R of the first resin shown in Tables 7-1 to 7-3 · Liquid containing the second resin of the types shown in Tables 7-1 to 7-3: The amount (%) that becomes the content Q (%) of the second resin shown in Tables 7-1 to 7-3 · Glycerin: 5.0% · Triethylene glycol: 10.0% · Acetylenol E100: 0.1% · Ion-exchanged water: The remaining amount (%) such that the total of the components becomes 100.0%

[0120] TIFF0007699934000008.tif249170

[0121] TIFF0007699934000009.tif232170

[0122] TIFF0007699934000010.tif233170

[0123] <Evaluation> Each of the inks obtained above was filled into an ink cartridge and mounted on an inkjet recording apparatus (trade name "PIXUS iP3100", manufactured by Canon) that discharges the ink from a recording head by the action of thermal energy. In this example, the recording duty of a solid image recorded under the condition of applying 1 ink droplet of 5 pL per droplet to a unit area of 1 / 1,200 inch × 1 / 1,200 inch was defined as 100%. In the present invention, based on the evaluation criteria of the following items, "A" and "B" were set as acceptable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Table 8.

[0124] (Scratch resistance) Using the above inkjet recording apparatus, a solid image of 200 mm × 200 mm with a recording duty of 100% was recorded on a recording medium (trade name "Aurora Coat", manufactured by Nippon Paper Industries). After drying the image at 25°C for 24 hours, it was heated at 100°C for 1 hour using a heating oven. For the obtained image, a friction test was conducted under the condition of 10 reciprocations with a load of 500 g using a Gakushin type testing machine (trade name "Wear Resistance Tester", manufactured by Imoto Seisakusho) that can perform measurements according to JIS L 0849:2013. The image after the friction test was visually confirmed, and the rub resistance of the image was evaluated according to the evaluation criteria shown below. A: There were no rubbing marks on the image. B: There were rubbing marks on the image, but the recording medium was not visible. C: There were rubbing marks on the image, and the recording medium was visible.

[0125] (Glossiness) Using the above inkjet recording apparatus, a solid image of 2 cm × 2 cm with a recording duty of 100% was recorded on a recording medium (trade name "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon). After drying the image at 25°C for 24 hours, using two fluorescent lamps arranged in parallel at an interval of 10 cm as an observation light source, the light of the fluorescent lamps was irradiated onto the image from a distance of 2 m at an angle of 45 degrees (illumination angle 45 degrees). The shape of the fluorescent lamp reflected on the image was visually confirmed from an angle of 45 degrees (observation angle 45 degrees), and the glossiness of the image was evaluated according to the evaluation criteria shown below. A: The boundary between the two reflected fluorescent lamps was distinguishable, and no blurring was observed at the edge. B: The boundary between the two reflected fluorescent lamps was distinguishable, but slight blurring was observed at the edge. C: The boundary between the two reflected fluorescent lamps was not distinguishable.

[0126] TIFF0007699934000011.tif234170

[0127] (Lightfastness) Using each of the inks of Examples 1 and 14 to 18, the above inkjet recording apparatus was used to record a solid image of 2 cm × 2 cm with a recording duty of 100% on a recording medium (trade name "Canon Photo Paper, Glossy Gold GL-101", manufactured by Canon). After drying the image at 25°C for 24 hours, L * , a * , and b * were measured. Next, a xenon weather meter (trade name "Atlas Weatherometer Ci4000", manufactured by Suga Test Instruments Co., Ltd.) was used to irradiate the image with xenon light. The irradiation conditions were an irradiation intensity of 0.39 W / m 2 , a black panel temperature of 63°C, a relative humidity of 70%, and an irradiation time of 100 hours. After irradiation with xenon light, L * , a * , b * of the image were measured. L * , a * , b * of the image before xenon light irradiation were designated as "L1 * ", "a1 * ", "b1 * ", and L * , a * , b * of the image after irradiation were designated as "L2 * ", "a2 * ", "b2 * ". From the measured values, the color difference ΔE = {(L1 * - L2 * ) 2 + (a1 * - a2 * ) 2 + (b1 * - b2 * ) 2} 1 / 2 was calculated. It can be determined that the smaller the value of ΔE, the less likely it is to fade by light. When the ΔE calculated in this way was compared, it was confirmed that in Examples 14 to 18, ΔE was smaller than that in Example 1, and the light resistance was good.

Claims

1. An aqueous ink for inkjet containing a coloring material and a plurality of resins different from the coloring material, wherein the plurality of resins include a first resin and a second resin, the first resin is resin particles formed of a first polyester resin, the second resin is at least one of (i) a block copolymer containing a block A having no acid group and a block B having an acid group, and (ii) a second polyester resin having a sulfonic acid group, the first polyester resin is composed of a unit derived from a polyhydric alcohol and a unit derived from a polyvalent carboxylic acid, and has no sulfonic acid group, the number average molecular weight of the first polyester resin is 3,000 or more and 30,000 or less, the number average molecular weight of the second resin is 3,000 or more and 20,000 or less, the acid value of the block copolymer is 50 mgKOH / g or more and 200 mgKOH / g or less, the second polyester resin is composed of a unit derived from a polyhydric alcohol and a unit derived from a polyvalent carboxylic acid, and further has a carboxylic acid group, and the amount of the sulfonic acid group of the second polyester resin is 0.08 times or more and 0.50 times or less in terms of the molar ratio to the amount of the carboxylic acid group of the second polyester resin, the acid value of the second polyester resin is 2 mgKOH / g or more and 30 mgKOH / g or less, An aqueous ink, characterized in that the content (% by mass) of the first resin is 4.0 times or more and 100.0 times or less in terms of the mass ratio to the content (% by mass) of the second resin.

2. The aqueous ink according to Claim 1, wherein the acid value of the first polyester resin is 2 mgKOH / g or more and 30 mgKOH / g or less.

3. The aqueous ink according to Claim 1 or 2, wherein the first polyester resin contains a unit derived from an aromatic compound.

4. The aqueous ink according to any one of Claims 1 to 3, wherein the second resin contains a unit derived from an aromatic compound.

5. The aqueous ink according to any one of Claims 1 to 4, wherein the number average molecular weight of the block A of the block copolymer is 0.30 times or more and 0.80 times or less in terms of the ratio to the number average molecular weight of the block copolymer.

6. The aqueous ink according to any one of Claims 1 to 5, wherein the content (% by mass) of the first resin is 0.1% by mass or more and 15.0% by mass or less based on the total mass of the ink.

7. The aqueous ink according to any one of claims 1 to 6, wherein the content (mass%) of the second resin is 0.1 mass% or more and 5.0 mass% or less based on the total mass of the ink.

8. The aqueous ink according to any one of claims 1 to 7, wherein the second resin is a block copolymer containing an A block having no acid group and a B block having an acid group.

9. The aqueous ink according to any one of claims 1 to 8, wherein the content (mass%) of the colorant is 0.1 mass% or more and 15.0 mass% or less based on the total mass of the ink.

10. The aqueous ink according to any one of claims 1 to 9, wherein the colorant is a pigment.

11. The aqueous ink according to claim 10, wherein the content (mass%) of the first resin is 0.5 times or more and 3.0 times or less in terms of the mass ratio to the content (mass%) of the pigment.

12. The aqueous ink according to claim 10 or 11, wherein the pigment is dispersed by a resin dispersant which is a resin different from both the first resin and the second resin.

13. An ink cartridge comprising ink and an ink containing portion for containing the ink, The ink cartridge characterized in that the ink is the aqueous ink according to any one of claims 1 to 12.

14. An inkjet recording method for ejecting ink from an inkjet recording head and recording an image on a recording medium, The inkjet recording method characterized in that the ink is the aqueous ink according to any one of claims 1 to 12.

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