Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide aqueous ink for inkjet which can record an image excellent in scratch resistance and image clarity.SOLUTION: Aqueous ink for inkjet contains resin particles. The resin particles contain (i) resin particles α formed of a first resin and resin particles β formed of a second resin, wherein the first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a (meth)acrylic acid, and the second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group, and a unit derived from a (meth)acrylic acid.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] Conventionally, inkjet recording devices have been widely used as small home printers, and in recent years, they have also been deployed for use in offices and commercial printing. In fields such as offices and commercial printing, it is required to be able to record an image having higher rub resistance than that of a small home printer or the like.

[0003] In order to record an image with improved rub resistance and adhesion on a recording medium, for example, an ink containing resin particles having a core-shell structure has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Under the situation where the application fields of inkjet recording devices are expanding to the commercial printing field and the office printing field, the required level for the rub resistance of images is increasing. Furthermore, the required level for image performance such as imageability is also increasing further. The present inventors examined the ink proposed in Patent Document 1. As a result, it was found that even when using the ink proposed in Patent Document 1, it is difficult to record an image that satisfies the high levels of rub resistance and imageability required in the commercial printing field and the office printing field.

[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 imageability. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Means for Solving the Problems

[0007] That is, according to the present invention, there is provided an aqueous ink for inkjet containing resin particles, wherein the resin particles include (i) resin particles α formed of a first resin and resin particles β formed of a second resin, or (ii) resin particles γ formed of a first resin and a second resin, the first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the following general formula (1), and the second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the following general formula (2).

[0008] TIFF2025095570000001.tif52170(In the general formulas (1) and (2), R1 and R2 each independently represent an alkyl group having the same number of carbon atoms n, one is a branched or cyclic alkyl group having n carbon atoms, and the other is a linear alkyl group having n carbon atoms. X represents a hydrogen atom or a methyl group)

Effects of the Invention

[0009] 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 imageability. Further, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

[0011] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt dissociates into ions and exists in the aqueous ink. For convenience, it is expressed as "containing a salt". Further, the aqueous ink for inkjet may be simply referred to as "ink". Physical property values are values at normal temperature (25 ° C), normal pressure (1 atm = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified.

[0012] Unless otherwise specified, "unit" means a unit structure corresponding to one monomer. When "(meth) acrylic acid" or "(meth) acrylate" is described, it means "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively. The resin particles mean the whole including all components other than the resin such as the initiator used in the production of the resin particles and the resin used other than the main component resin (the resin having the largest proportion). Examples of the non-absorbent recording medium include plastic films formed of polymer compounds such as polyethylene, polyethylene terephthalate (PET) having transparency, polypropylene, polyolefin, and vinyl chloride; films obtained by vapor-depositing a metal such as aluminum on these plastic films; and the like.

[0013] The inventors studied an ink containing resin particles having a carboxylic acid group or a sulfonic acid group in order to record an image excellent in abrasion resistance and imageability. The carboxylic acid group in the resin particles forms a hydrogen bond when recording an image. Therefore, when using an ink containing resin particles having a carboxylic acid group, the cohesive force increases with the formation of a hydrogen bond, so that the abrasion resistance of the recorded image can be improved. However, when the solvent in the ink evaporates or penetrates, the resin particles approach each other and tend to aggregate, so that irregularities occur on the surface of the recorded image and the imageability of the image decreases.

[0014] On the other hand, in the case of resin particles having a sulfonic acid group, even when the solvent in the ink evaporates or penetrates and the resin particles approach each other, they do not aggregate and form a film slowly, so that the imageability of the recorded image can be improved. However, the hydrophilic site derived from the sulfonic acid group tends to remain on the surface of the image, and the evaporation of moisture is hindered by this hydrophilic site, so that the abrasion resistance of the image decreases. From the above, it has been found that it is difficult to achieve both the abrasion resistance and the imageability of the recorded image only by adjusting the amounts of the carboxylic acid group and the sulfonic acid group in the resin particles.

[0015] As a result of further studies, the inventors have found that (i) resin particles α formed of a first resin and resin particles β formed of a second resin, or (ii) resin particles γ formed of a first resin and a second resin are contained. And as a result, it has been found that an image excellent in abrasion resistance and imageability can be recorded, and the present invention has been achieved. · First resin: A copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the following general formula (1) · Second resin: A copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the following general formula (2)

[0016] TIFF2025095570000002.tif52170(In general formulas (1) and (2), R1 and R2 each independently represent an alkyl group having the same number of carbon atoms n, one is a branched or cyclic alkyl group having n carbon atoms, and the other is a linear alkyl group having n carbon atoms. X represents a hydrogen atom or a methyl group)

[0017] By using the resin particles having the above configuration, it is possible to achieve both the abrasion resistance and the imageability of the image. One of the first resin and the second resin is a copolymer containing units with low mobility derived from a compound having a branched or cyclic alkyl group. This unit is considered to form a domain and act like a filler in the image after film formation. Therefore, by using a copolymer containing this unit, the abrasion resistance of the recorded image can be improved without increasing the cohesiveness due to the carboxylic acid group.

[0018] Also, the other resin of the first resin and the second resin is a copolymer containing units with high mobility derived from a compound having a linear alkyl group. Since this unit is linear and has few steric hindrances, it is considered to act so as to fill the gaps between the particles during image formation. Therefore, by using a copolymer containing this unit, the unevenness on the surface of the image can be suppressed and the imageability of the recorded image can be improved without increasing the sulfonic acid group. When a branched or cyclic alkyl group and a linear alkyl group are present in the same copolymer (resin), these units in a structural isomer relationship inhibit each other, and the effects of improving abrasion resistance and imageability cannot be obtained. Therefore, the branched or cyclic alkyl group and the linear alkyl group need to be present in different resins respectively. And the first resin and the second resin may be contained in the same resin particles or in different resin particles respectively.

[0019] In general formulas (1) and (2), the number of carbon atoms n of the alkyl groups represented by R1 and R2 is the same. By using resin particles γ formed of two types of resins (first resin and second resin) each having an alkyl group with the same number of carbon atoms n, an image can be recorded while suppressing phase separation between the domains formed by the units in one resin and the other resin. Similarly, in the resin particles α formed of the first resin and the resin particles β formed of the second resin, an image can be recorded while suppressing phase separation between the domains formed by the units in one resin and the other resin. As a result, the imageability of the recorded image can be improved.

[0020] <Ink> The ink of the present invention is an aqueous ink for inkjet containing resin particles, and the resin particles include (i) resin particles α formed of a first resin and resin particles β formed of a second resin, or (ii) resin particles γ formed of a first resin and a second resin. The first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the following general formula (1). The second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the following general formula (2). Hereinafter, each component constituting the ink and the physical properties of the ink will be described.

[0021] TIFF2025095570000003.tif52170(In general formulas (1) and (2), R1 and R2 each independently represent an alkyl group having the same number of carbon atoms n, one is a branched or cyclic alkyl group having n carbon atoms, and the other is a linear alkyl group having n carbon atoms. X represents a hydrogen atom or a methyl group)

[0022] (Resin particles) The ink of the present invention contains resin particles. The content (mass %) of the resin particles in the ink is preferably 1.0 mass % or more and 20.0 mass % or less, more preferably 3.0 mass % or more and 15.0 mass % or less, based on the total mass of the ink. The "resin particles" in this specification means a resin that exists in a state where it is not dissolved in the aqueous medium constituting the ink. More specifically, it means a resin that can exist in the aqueous medium in a state where particles with a particle size measurable by the dynamic light scattering method are formed. On the other hand, the "water-soluble resin" means a resin that exists in a state where it is dissolved in the aqueous medium constituting the ink. More specifically, it means a resin that can exist in the aqueous medium in a state where particles with a particle size measurable by the dynamic light scattering method are not formed. When expressing the resin particles as a pair with the "water-soluble resin", it becomes "water-dispersible resin (water-insoluble resin)".

[0023] Whether a certain resin is a "resin particle" or not can be determined according to the method shown below. First, prepare a liquid (resin solid content: 10 mass %) containing a resin neutralized with an alkali equivalent to the acid value (such as sodium hydroxide, potassium hydroxide). Next, dilute the prepared liquid 100 times (by volume) with pure water to prepare a sample solution. Then, when measuring the particle size of the resin in the sample solution by the dynamic light scattering method, if particles having a particle size are measured, it can be determined that the resin is a "resin particle". As a particle size distribution measuring device by the dynamic light scattering method, a particle size analyzer (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) can be used. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: true sphere, refractive index: 1.59. Of course, the particle size distribution measuring device used, the measurement conditions, etc. are not limited to the above. Measuring the particle size using the neutralized resin is to confirm that particles are formed even when it is sufficiently neutralized and it is more difficult to form particles. Even under such conditions, a resin having the shape of particles exists in the form of particles in the aqueous ink.

[0024] The resin particles γ preferably have a core-shell structure in which a core polymer (core polymer) is coated with another polymer (shell polymer). That is, it is preferably resin particles having a core-shell structure including a core polymer and a shell polymer. In that case, it is preferable that the first resin described later is the shell polymer and the second resin described later is the core polymer. By using resin particles having such a structure, the mapping property of the image can be further improved. Further, the carboxylic acid groups (μmol / g) present in the resin particles γ are preferably 200 μmol / g or more and 500 μmol / g or less, and more preferably 200 μmol / g or more and 400 μmol / g or less. This value represents the density (in micromoles) of the carboxylic acid groups present in the resin particles per unit mass of the resin particles. If the carboxylic acid groups present in the resin particles γ are less than 200 μmol / g, sufficient ejection stability cannot be obtained, and as a result, the amount of the resin particles to be applied is reduced, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. On the other hand, if the carboxylic acid groups present in the resin particles γ exceed 500 μmol / g, the aggregability of the resin particles becomes too high, and the effect of improving the mapping property of the image may not be sufficiently obtained. The density of the carboxylic acid groups present in the resin particles can be calculated, for example, by identifying the types of monomers present in the resin particles by py-GC / MS, dissolving the resin particles in an appropriate solvent, 13 and measuring the molar ratio of the monomers by 13C-NMR.

[0025] [First Resin] The resin particles include (i) resin particles α formed of the first resin and resin particles β formed of the second resin, or (ii) resin particles γ formed of the first resin and the second resin particles. Among them, it is preferable to contain resin particles formed of the first resin and the second resin. The first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the general formula (1).

[0026] TIFF2025095570000004.tif26170

[0027] In the general formula (1), R1 is an alkyl group, and among them, a linear alkyl group is preferably used. Examples of the linear alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. The n (number of carbon atoms) of R1 is preferably 3 or more and 12 or less, and more preferably 3 or more and 8 or less.

[0028] The first resin is a resin having a carboxylic acid group and a sulfonic acid group as acid groups. The proportion (mass%) of the unit derived from the compound represented by the general formula (1) in the first resin is preferably 30.0 mass% or more and 90.0 mass% or less, and more preferably 60.0 mass% or more and 90.0 mass% or less, based on the total mass of the first resin. When the proportion of the unit derived from the compound represented by the general formula (1) is less than 30.0 mass%, the effect of improving the rubbing resistance of the image may not be sufficiently obtained. On the other hand, when the proportion of the unit derived from the compound represented by the general formula (1) is 90.0 mass% or more, the content of the unit contributing to the cohesiveness relatively decreases, and the effect of improving the imageability of the image may not be sufficiently obtained.

[0029] The carboxylic acid group present in the first resin is preferably the same as the carboxylic acid group present in the resin particles. That is, the second resin preferably does not substantially contain a carboxylic acid group. The carboxylic acid group (μmol / g) present in the first resin is preferably 200 μmol / g or more and 500 μmol / g or less, and more preferably 200 μmol / g or more and 400 μmol / g or less.

[0030] When the resin particles have a core-shell structure with the first resin as the shell polymer, the anionic groups present on the particle surface of these resin particles (resin particles γ) are derived from the carboxylic acid groups and sulfonic acid groups in the first resin. In this case, the anionic groups (μmol / g) present on the particle surface of the resin particles γ are preferably 100 μmol / g or more and 300 μmol / g or less, and more preferably 130 μmol / g or more and 270 μmol / g or less. By using the resin particles within the above range, the abrasion resistance can be further improved. And the proportion (%) of the carboxylic acid groups in the anionic groups (μmol / g) present on the particle surface of the resin particles γ is preferably 50.0% or more and 85.0% or less, and more preferably 60.0% or more and 75.0% or less. If the proportion is less than 50.0%, the cohesive force becomes insufficient, and the effect of improving the abrasion resistance of the image may not be sufficiently obtained. On the other hand, if the proportion exceeds 85.0%, the effects of improving the abrasion resistance and imageability of the image may not be sufficiently obtained. This value represents the density (in micromol units) of the anionic groups present on the particle surface of the resin particles per unit mass of the resin particles. The density of the anionic groups present on the particle surface can be measured by dissociating all the anionic groups present on the particle surface of the resin particles, for example, by setting the pH to 12 or more.

[0031] In the resin particles γ, the content (% by mass) of the first resin is preferably 0.10 times or more and 0.60 times or less, more preferably 0.20 times or more and 0.50 times or less, in terms of the mass ratio to the content (% by mass) of the second resin described below. When the mass ratio is less than 0.10 times, the resin that fills the domains and the gaps between the particles becomes relatively small, and the effect of improving the image mapping property may not be sufficiently obtained. On the other hand, when the mass ratio exceeds 0.60 times, the formation of domains becomes insufficient, the role as a filler cannot be sufficiently exerted, and the effect of improving the rubbing resistance of the image may not be sufficiently obtained. Similarly, the content (% by mass) of the resin particles α formed of the first resin is preferably 0.10 times or more and 0.60 times or less, more preferably 0.20 times or more and 0.50 times or less, in terms of the mass ratio to the content (% by mass) of the resin particles β formed of the second resin.

[0032] [Second resin] The second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the general formula (2). In the general formula (2), R2 needs to be an alkyl group, and among them, a branched or cyclic alkyl group is preferable. With the above configuration, the rubbing resistance of the image can be further improved. The number of carbon atoms n of R2 is the same as the number of carbon atoms of R1. Examples of the monomer of the general formula (2) having a branched alkyl group include isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, and the like. Examples of the monomer of the general formula (2) having a cyclic alkyl group include cyclohexyl methacrylate, isobornyl methacrylate, and the like.

[0033] The proportion (mass %) of the unit derived from the compound represented by the general formula (2) in the second resin is preferably 50.0 mass % or more and 97.0 mass % or less, more preferably 60.0 mass % or more and 97.0 mass % or less, based on the total mass of the second resin. When the content of the unit derived from the compound represented by the general formula (2) is less than 50.0 mass %, the sites with low motility are likely to spread when an image is formed. As a result, the formed domain becomes small and the role as a filler becomes weak, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. On the other hand, when the content of the unit derived from the compound represented by the general formula (2) exceeds 97.0 mass %, the content of the unit derived from the second monomer having a sulfonic acid group relatively decreases. The unit derived from the second monomer having a sulfonic acid group has a function of maintaining the dispersibility of the resin particles while maintaining the electrostatic repulsion. Therefore, when the content of the unit derived from the second monomer having a sulfonic acid group relatively decreases, the dispersibility of the resin particles becomes unstable and the resin particles may easily aggregate. As a result, unevenness is likely to occur in the image, and the effect of improving the imageability of the image may not be sufficiently obtained.

[0034] The second resin is preferably a copolymer substantially free of units derived from monomers having a carboxylic acid group. That is, the acid groups in the second resin are preferably only sulfonic acid groups. When the second resin has a carboxylic acid group, the dispersibility of the resin particles may become unstable and the resin particles may easily aggregate. As a result, unevenness is likely to occur in the image, and the effect of improving the imageability of the image may not be sufficiently obtained.

[0035] [Monomer] The monomers constituting each unit of the copolymer which is the first resin are a monomer having a carboxylic acid group, a first monomer having a sulfonic acid group, and a compound represented by the general formula (1). The monomers constituting each unit of the copolymer which is the second resin are a second monomer having a sulfonic acid group, and a compound represented by the following general formula (2). Hereinafter, the details of the monomers constituting each unit will be described.

[0036] Examples of the monomer having a carboxylic acid group include (meth)acrylic acid and itaconic acid. Both the compound represented by the general formula (1) and the compound represented by the general formula (2) are (meth)acrylate esters. Examples of the (meth)acrylate esters include propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Among them, from the viewpoints of easy adjustment of properties such as the glass transition point of the obtained resin particles and properties of the formed image, it is preferable to use a (meth)acrylate having an alkyl group with 3 to 12 carbon atoms.

[0037] A polymerizable surfactant can also be used as a monomer. The polymerizable surfactant has a hydrophilic group, a hydrophobic group, and a radically polymerizable functional group in its molecule. Examples of the hydrophilic group include a sulfate ester group, a phosphate ester group, a carboxylic acid group, an alkylene oxide group (ethylene oxide group, propylene oxide group), a hydroxy group, and a pyrrolidone group. Examples of the hydrophobic group include an aliphatic alkyl group having 2 to 20 carbon atoms and an aromatic group. Examples of the radically polymerizable functional group include an acrylic group, a methacrylic group, an allyl group, a methallyloxy group, and a propenyl group.

[0038] The first monomer and the second monomer having a sulfonic acid group are each preferably a compound represented by the following general formula (3). R3O-(EO) n -SO3M ···(3) (In the general formula (3), R3 represents a hydrophobic group having a radically polymerizable functional group, EO represents an ethylene oxide group, n is 1 or more and 30 or less, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

[0039] In addition, a polymerizable surfactant can be used as the first monomer and the second monomer having a sulfonic acid group. Here, as the polymerizable surfactant, a commercially available one or a synthesized one may be used. Among them, it is preferable to use a polyoxyethylene alkyl ether sulfate ester salt having a sulfonic acid group as the polymerizable surfactant.

[0040] In addition, aromatic vinyls such as styrene, 4-methylstyrene, and 1-vinylnaphthalene can be used as monomers. Furthermore, alkenes having 1 to 22 carbon atoms; (meth)acrylic acid; and the like can be used as monomers.

[0041] [Method for producing resin particles] The resin particles can be produced according to a known method. Specifically, the resin particles can be produced by methods such as an emulsion polymerization method, a pre-emulsion polymerization method, a seed polymerization method, and a phase inversion emulsification method.

[0042] For example, first, a first step of emulsion-polymerizing a monomer that forms a unit constituting the second resin to obtain a liquid containing the second resin that forms a core is carried out. Next, by carrying out a second step of adding and polymerizing a monomer that forms a unit constituting the first resin to the liquid obtained in the first step, resin particles having a core-shell structure can be produced. Note that both the first step and the second step are preferably carried out in an aqueous liquid medium.

[0043] [Colorant] The ink may further contain a colorant. As the colorant, a dye or a pigment can be used. The content (% by mass) of the colorant 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.

[0044] Examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone. Examples of pigments include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine.

[0045] Examples of pigment dispersion methods include resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which a hydrophilic group is bonded to the surface of pigment particles. Further, resin-bonded pigments in which an organic group containing a resin is chemically bonded to the surface of pigment particles, microcapsule pigments in which the surface of pigment particles is coated or encapsulated with a resin, etc. can be used. It is also possible to use pigments with different dispersion methods in combination.

[0046] (Other resins) The ink may further contain a resin other than the above resin particles (other resins). The other resin can be added to the ink (i) to stabilize the dispersion state of the pigment, i.e., as a resin dispersant or its auxiliary. Also, (ii) it can be added to the ink to improve various properties of the recorded image. Examples of the form of the other resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Further, the other resin may be a water-soluble resin that can be dissolved in an aqueous medium, or resin particles that are dispersed in an aqueous medium. The other resin is preferably a water-soluble resin.

[0047] Examples of water-soluble resins include acrylic resins different from the above resins (other acrylic resins), urethane resins, etc. Among them, other acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

[0048] As other acrylic resins, those having a hydrophilic unit and a hydrophobic unit as constituent units are preferred. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid, a hydrophobic unit derived from at least one selected from the group consisting of a monomer having an aromatic ring, and a (meth)acrylate monomer is preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferred. Since these resins are likely to interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0049] 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.

[0050] The urethane resin can be obtained, for example, by reacting a polyisocyanate and a polyol. Further, it may be a product obtained by further reacting a chain extender. Examples of the olefin resin include polyethylene and polypropylene.

[0051] (aqueous medium) The ink of the present invention is an aqueous ink containing an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion-exchanged water) as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inks for inkjet, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

[0052] (Other components) In addition to the above-described components, the ink may contain water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethyleneurea, as required. Further, the ink may contain various additives such as surfactants, pH adjusters, defoamers, rust preventives, antiseptics, fungicides, antioxidants, anti-reduction agents, and chelating agents, as required.

[0053] (Physical properties of the ink) The ink of the present invention is an aqueous ink applicable to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, more preferably 1.0 mPa·s or more and 5.0 mPa·s or less, and particularly preferably 1.0 mPa·s or more and 3.0 mPa·s or less. Also, 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.

[0054] <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. A liquid ink 20 is stored in the ink storage chamber 14, and absorbers 22 and 24 for holding the ink in an impregnated state are stored in the absorber storage chamber 16. The ink storage unit may be in a form that does not have an ink storage chamber for storing liquid ink and holds the entire amount of the stored ink by the absorber. Further, the ink storage unit may be in a form that does not have an absorber and stores the entire amount of the ink in a liquid state. Furthermore, it may be an ink cartridge configured to have an ink storage unit and a recording head.

[0055] <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.

[0056] 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 ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown).

Example

[0057] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Regarding the amounts of components, “parts” and “%” are based on mass unless otherwise specified.

[0058] <Method for Measuring Physical Property Values> (Anionic Groups Present on the Particle Surface of Resin Particles) An appropriate amount of 1 mol / L potassium hydroxide aqueous solution was added to 250 g of a dilution solution in which the resin particle content was 0.10%, and the solution adjusted to pH 12 or higher was used as a sample. Colloid titration was performed on this sample to measure the amount of anionic groups (acid groups) on the particle surface of the resin particles. For colloid titration, a streaming potential detection unit (trade name “PCD-500”, manufactured by Kyoto Electronics Industry Co., Ltd.) was connected to an automatic potentiometric titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.) and used. As the measurement sample and the titration reagent, an N / 200 methyl glycol chitosan titration solution (manufactured by Fujifilm Wako Pure Chemical Corporation) was used. The anionic group At present on the particle surface of the resin particles was calculated by the following formula. At = (Drop volume [mL] × F × 500) / (250 × 0.10 / 100) F: Titer of methyl glycol chitosan

[0059] (Ratio of carboxylic acid groups among the anionic groups present on the particle surface of the resin particles) A sample was prepared by adding 12 g of a buffer solution with a pH of 2.6 to 238 g of a dilution solution in which the resin particle content was 0.10%. The anionic groups (derived from sulfonic acid groups) As present on the particle surface of the resin particles were measured by the above measurement method. The ratio Ac (%) of carboxylic acid groups among the anionic groups present on the particle surface of the resin particles was calculated by the following formula. Ac (%) = 100 × (At - As) / At

[0060] <Production of aqueous dispersion of resin particles> (Aqueous dispersion of resin particles 1) A reaction vessel equipped with a dropping device, a thermometer, a water-cooled reflux condenser, and a stirrer was prepared and filled with 400 parts of ion-exchanged water. To this reaction vessel, 80.0 parts of a monomer mixture containing 76.8 parts of isobutyl methacrylate and 3.20 parts of a reactive surfactant (trade name "Aquaron KH-05", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were added. After heating the contents to 75°C under a nitrogen atmosphere while stirring, 0.2 part of potassium persulfate was added. Polymerization was carried out at this temperature for 1 hour to obtain a liquid containing resin particles formed of the second resin.

[0061] 20 parts of ion-exchanged water, 17.0 parts of n-butyl methacrylate, 1.04 parts of a reactive surfactant (trade name "Aquaron KH-05", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 1.96 parts of methacrylic acid were mixed to obtain an emulsion. The inside of the reaction vessel containing the dispersion containing the resin particles formed of the second resin obtained above was heated to 85°C, and the obtained emulsion was dropped over 1 hour and then polymerized with stirring for 2 hours. After cooling to room temperature, potassium hydroxide was added to adjust the pH to the range of 8.0 to 8.5. Filtration was carried out through a 1-μm filter to obtain an aqueous dispersion of resin particles 1 having a core-shell structure with a shell formed of the first resin and a core formed of the second resin. The content of the resin particles in the obtained aqueous dispersion was 20.0%.

[0062] (Aqueous dispersion of resin particles 2 to 21 and 23 to 38) An aqueous dispersion of resin particles 2 to 21 and 23 to 38 with a resin particle content of 20.0% was obtained in the same manner as in the case of the aqueous dispersion of resin particles 1 described above, except that the composition shown in Tables 1-1 to 1-4 (unit: part) and the reaction temperature during the first resin polymerization were used.

[0063] (Aqueous dispersion of resin particles 22) A reaction vessel equipped with a dropping device, a thermometer, a water-cooled reflux condenser, and a stirrer was prepared, and 200 parts of ion-exchanged water was put therein. To this reaction vessel, 70.0 parts of a monomer mixture containing 67.0 parts of iso-butyl methacrylate and 3.0 parts of a reactive surfactant (trade name "Aquaron KH-05", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was further added. After raising the temperature of the contents to 75°C under a nitrogen atmosphere while stirring, 0.2 part of potassium persulfate was added. Polymerization was carried out at this temperature for 1 hour to obtain a liquid containing resin particles formed of the second resin.

[0064] Also, another reaction vessel equipped with a dropping device, a thermometer, a water-cooled reflux condenser, and a stirrer was prepared, and 50 parts of ion-exchanged water was put therein. To this reaction vessel, 30.0 parts of a monomer mixture containing 25.0 parts of n-butyl methacrylate, 3.0 parts of a reactive surfactant (trade name "Aquaron KH-05", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 2.0 parts of methacrylic acid was further added. After raising the temperature of the contents to 75°C under a nitrogen atmosphere while stirring, 0.1 part of potassium persulfate was added. Polymerization was carried out at this temperature for 1 hour to obtain a liquid containing resin particles formed of the first resin.

[0065] After mixing the two obtained liquids, potassium hydroxide was added to adjust the pH to the range of 8.0 to 8.5. Filtration was performed with a 1-μm filter to obtain an aqueous dispersion containing two types of resin particles (corresponding to resin particles α and resin particles β) having no core-shell structure. The total content of the resin particles in the obtained aqueous dispersion was 20.0%. The mass ratio of the content of the resin particles formed of the first resin to the content of the resin particles formed of the second resin was 3:7. Also, in Tables 1-1 to 1-4, C, At, As, and Ac describe the values for the resin particles formed of the first resin.

[0066] The details of the product names in Tables 1-1 to 1-4 are shown below. In Tables 1-1 to 1-4, isobutyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, and 2-ethylhexyl acrylate are monomers corresponding to the compounds represented by General Formula (2). n-butyl methacrylate, n-hexyl methacrylate, and n-octyl acrylate are monomers corresponding to the compounds represented by General Formula (1). Methacrylic acid is a monomer having a carboxylic acid group, and Aqualon KH-05, Adeka Resoap SR-20, and Ereminol JS-20 are monomers having a sulfonic acid group. Furthermore, Aqualon KH-05 and Adeka Resoap SR-20 are monomers corresponding to the compounds represented by General Formula (3). · Aqualon KH-05: Reactive surfactant, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. · Adeka Resoap SR-20: Reactive surfactant, manufactured by ADEKA · Ereminol JS-20: Reactive surfactant, manufactured by Sanyo Chemical Industries, Ltd.

[0067] (Carboxylic acid groups present in the resin particles) The carboxylic acid groups C present in the resin particles were calculated by the following formula. Carboxylic acid groups C (μmol / g) = {(M2 + M1) / 86.09} × 10,000 M2: Amount of methacrylic acid used in the second resin (parts) M1: Amount of methacrylic acid used in the first resin (parts)

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[0072] <Preparation of Pigment Dispersion Liquid> (Pigment Dispersion Liquid 1) A styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 150 mg KOH / g and a weight average molecular weight of 8,000 was neutralized with a 10% aqueous potassium hydroxide solution to obtain an aqueous resin solution with a resin content of 20.0%. 30.0 parts of the obtained aqueous resin solution, 20.0 parts of a pigment (carbon black), and 50.0 parts of ion-exchanged water were mixed to obtain a mixture. The obtained mixture was placed in a batch vertical sand mill (manufactured by Imex) filled with 200 parts of zirconia beads with a particle size of 0.3 mm and subjected to a dispersion treatment for 5 hours. After removing coarse particles by centrifugal separation, it was pressure-filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare Pigment Dispersion Liquid 1 with a pigment content of 20.0% and a resin dispersant (resin) content of 6.0%.

[0073] (Pigment Dispersion Liquid 2) Except for changing the pigment to C.I. Pigment Blue 15:3, Pigment Dispersion Liquid 2 with a pigment content of 20.0% and a resin dispersant (resin) content of 6.0% was prepared in the same procedure as Pigment Dispersion Liquid 1 described above.

[0074] (Pigment Dispersion Liquid 3) Except for changing the pigment to C.I. Pigment Red 122, Pigment Dispersion Liquid 3 with a pigment content of 20.0% and a resin dispersant (resin) content of 6.0% was prepared in the same procedure as Pigment Dispersion Liquid 1 described above.

[0075] (Pigment Dispersion Liquid 4) Except for changing the pigment to C.I. Pigment Yellow 74, Pigment Dispersion Liquid 4 with a pigment content of 20.0% and a resin dispersant (resin) content of 6.0% was prepared in the same procedure as Pigment Dispersion Liquid 1 described above.

[0076] <Preparation of Ink> The components shown in Tables 2-1 to 2-4 (unit: parts) were mixed and stirred well, and then each ink was prepared by pressure filtration through a microfilter with a pore size of 3.0 μm (manufactured by Fujifilm). Acetylenol E100 is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals Co., Ltd.

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[0081] <Evaluation> Each prepared ink was filled into an ink cartridge and mounted on an inkjet recording apparatus (trade name "PIXUS iP3100", manufactured by Canon) that discharges 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%. Using this inkjet recording apparatus, solid images of 200 mm × 200 mm with a recording duty of 100% were recorded on a corona-discharged PET film. As the corona-discharged PET film, a product named "E5100" (manufactured by Toyobo, thickness 12 μm) cut into A4 size was used. In the present invention, according to the evaluation criteria of each evaluation item shown below, "A" was set as an excellent level, "B" as an acceptable level, and "C" as an unacceptable level. The evaluation results are shown in Table 3.

[0082] (Scratch resistance) After leaving the recorded solid image for one day, a friction test was conducted in accordance with JIS L 0849:2013 using a Gakushin-type testing machine (trade name "Wear Resistance Tester", manufactured by Imoto Seisakusho). Specifically, the friction test was carried out under the condition of 10 reciprocations with a load of 500 g. The image after the friction test was visually confirmed, and the scratch resistance of the image was evaluated according to the evaluation criteria shown below. A: There were no scratch marks on the image. B: There were scratch marks on the image, but the surface of the recording medium was not visible. C: There were scratch marks on the image, and the surface of the recording medium was visible.

[0083] (Image reproducibility) Using the above inkjet recording apparatus, a 2 cm × 2 cm solid image 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 recorded image at 25°C for 24 hours, two fluorescent lamps arranged in parallel at 10 cm intervals were used to irradiate the image with light at an angle of 45 degrees from a distance of 2 m (illumination angle 45 degrees). The shape of the fluorescent lamps projected onto the image was visually confirmed from an angle of 45 degrees (observation angle 45 degrees), and the image reproducibility of the image was evaluated according to the evaluation criteria shown below. A: The boundary between the two projected fluorescent lamps was distinguishable, and no blurring was observed at the edges. B: The boundary between the two projected fluorescent lamps was distinguishable, but blurring was observed at the edges. C: The boundary between the two projected fluorescent lamps was indistinguishable.

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[0085] The evaluation result of the scratch resistance of Example 35 was the same "B" as that of Example 39, but Example 39 was superior.

[0086] Note that the disclosure of this embodiment includes the following configurations and methods. (Configuration 1) An aqueous ink for inkjet containing resin particles, The resin particles contain (i) resin particles α formed of a first resin and resin particles β formed of a second resin, or (ii) resin particles γ formed of the first resin and the second resin, The first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the following general formula (1), The second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the following general formula (2), and the aqueous ink is characterized by this.

[0087] TIFF2025095570000014.tif52170(In the general formulas (1) and (2), R1 and R2 each independently represent an alkyl group having the same number of carbon atoms n, one is a branched or cyclic alkyl group having n carbon atoms, and the other is a linear alkyl group having n carbon atoms. X represents a hydrogen atom or a methyl group)

[0088] (Configuration 2) The aqueous ink according to Configuration 1, wherein in the general formula (2), R2 is a branched or cyclic alkyl group. (Configuration 3) The aqueous ink according to any one of Configuration 1 or 2, wherein the acid group in the second resin is only a sulfonic acid group. (Configuration 4) The aqueous ink according to any one of Configuration 1 to 3, wherein the ratio (mass%) of the unit derived from the compound represented by the general formula (1) in the first resin is 30.0 mass% or more and 90.0 mass% or less based on the total mass of the first resin. (Configuration 5) The aqueous ink according to any one of Configuration 1 to 4, wherein the ratio (mass%) of the unit derived from the compound represented by the general formula (2) in the second resin is 50.0 mass% or more and 97.0 mass% or less based on the total mass of the second resin. (Configuration 6) The aqueous ink according to any one of Configuration 1 to 5, wherein in the resin particles γ, the content (mass%) of the first resin is 0.10 times or more and 0.60 times or less the mass ratio to the content (mass%) of the second resin. (Configuration 7) The aqueous ink according to any one of Configurations 1 to 6, wherein the first monomer and the second monomer are each independently a compound represented by the following general formula (3). R3O-(EO) n -SO3M ···(3) (In the general formula (3), R3 represents a hydrophobic group having a radically polymerizable functional group, EO represents an ethylene oxide group, n is 1 or more and 30 or less, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.) (Configuration 8) The resin particles γ have a core-shell structure including a core polymer and a shell polymer, The aqueous ink according to any one of Configurations 1 to 7, wherein the first resin is the shell polymer and the second resin is the core polymer. (Configuration 9) The aqueous ink according to Configuration 8, wherein the carboxylic acid groups (μmol / g) present in the resin particles γ are 200 μmol / g or more and 500 μmol / g or less. (Configuration 10) The aqueous ink according to Configuration 8 or 9, wherein the anionic groups (μmol / g) present on the particle surface of the resin particles γ are 100 μmol / g or more and 300 μmol / g or less. (Configuration 11) The aqueous ink according to any one of Configurations 8 to 10, wherein the ratio (%) of the carboxylic acid groups to the anionic groups (μmol / g) present on the particle surface of the resin particles γ is 50.0% or more and 85.0% or less. (Configuration 12) An ink cartridge including ink and an ink storage unit for storing the ink, The ink cartridge is characterized in that the ink is the aqueous ink according to any one of Configurations 1 to 11. (Method 1) An inkjet recording method of ejecting ink from an inkjet recording head to record an image on a recording medium, The inkjet recording method is characterized in that the ink is the aqueous ink according to any one of Configurations 1 to 11.

Claims

1. An aqueous ink for inkjet containing resin particles, wherein the resin particles include (i) resin particles α formed of a first resin and resin particles β formed of a second resin, or (ii) resin particles γ formed of a first resin and a second resin, the first resin is a copolymer containing a unit derived from a monomer having a carboxylic acid group, a unit derived from a first monomer having a sulfonic acid group, and a unit derived from a compound represented by the following general formula (1), the second resin is a copolymer containing a unit derived from a second monomer having a sulfonic acid group and a unit derived from a compound represented by the following general formula (2), characterized in that it is an aqueous ink. (In the general formulas (1) and (2), R １ and R ２ each independently represents an alkyl group having the same number of carbon atoms n, one is a branched or cyclic alkyl group having n carbon atoms, and the other is a linear alkyl group having n carbon atoms. X represents a hydrogen atom or a methyl group)

2. In the general formula (2), R ２ The aqueous ink according to claim 1, wherein ２ is a branched or cyclic alkyl group.

3. The aqueous ink according to claim 1, wherein the acid group in the second resin is only a sulfonic acid group.

4. The aqueous ink according to claim 1, wherein the proportion (mass%) of the unit derived from the compound represented by the general formula (1) in the first resin is 30.0 mass% or more and 90.0 mass% or less based on the total mass of the first resin.

5. The aqueous ink according to claim 1, wherein the proportion (mass%) of the unit derived from the compound represented by the general formula (2) in the second resin is 50.0 mass% or more and 97.0 mass% or less based on the total mass of the second resin.

6. The aqueous ink according to claim 1, wherein in the resin particles γ, the content (mass%) of the first resin is 0.10 times or more and 0.60 times or less in terms of mass ratio with respect to the content (mass%) of the second resin.

7. The aqueous ink according to claim 1, wherein the first monomer and the second monomer are each independently a compound represented by the following general formula (3). R ３ O-(EO) ｎ -SO ３ M...(3) (In the general formula (3), R ３ represents a hydrophobic group having a radically polymerizable functional group, EO represents an ethylene oxide group, n is an integer of 1 or more and 30 or less, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

8. The resin particles γ have a core-shell structure including a core polymer and a shell polymer, the first resin is the shell polymer, and the second resin is the core polymer, according to claim 1 of the aqueous ink.

9. The aqueous ink according to claim 8, wherein the carboxylic acid groups (μmol / g) present in the resin particles γ are 200 μmol / g or more and 500 μmol / g or less.

10. The aqueous ink according to claim 8, wherein the anionic groups (μmol / g) present on the particle surface of the resin particles γ are 100 μmol / g or more and 300 μmol / g or less.

11. The water-based ink according to claim 8, wherein the ratio (%) of the carboxylic acid group to the anionic groups (μmol / g) present on the particle surface of the resin particles γ is 50.0% or more and 85.0% or less.

12. An ink cartridge comprising an ink and an ink storage section for storing the ink, wherein the ink is the water-based ink according to any one of claims 1 to 11.

13. An inkjet recording method for ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is the water-based ink according to any one of claims 1 to 11.

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