JP2020132689A - Ink for inkjet ink, and method for manufacturing ink for inkjet ink - Google Patents

Abstract

To provide ink for inkjet capable of forming an image which is excellent in storage stability, has high image density and is excellent in scratch resistance on a recording medium.SOLUTION: Ink for inkjet contains resin-containing particles containing at least a polyester resin, and an aqueous medium. At least a part of the resin-containing particles is first resin-containing particles having a first feature. The first feature is such that each of the first resin-containing particles further contain at least one coloring agent particle in addition to the polyester resin, and at least one coloring agent particle is positioned inside the first resin-containing particles without being exposed to the surface of the first resin-containing particles. An area ratio of the first resin-containing particles to the area of the resin-containing particles in a cross section photographic image of the resin-containing particles is 90% or more. A coloring agent inclusion concentration is 15% or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inkjet ink and a method for producing an inkjet ink.

An image is formed on a recording medium by ejecting ink for inkjet from a recording head of an inkjet recording device. Various studies have been made to improve the abrasion resistance of the image formed on the recording medium. For example, Patent Document 1 describes an aqueous ink composition containing at least an aqueous medium and resin fine particles. The resin of the resin fine particles is an acrylic resin having a structural unit having a specific structure.

JP-A-2016-069583

The water-based ink composition described in Patent Document 1 contains resin fine particles of acrylic resin. An image formed on a recording medium using such a water-based ink composition has been found to be insufficient in terms of abrasion resistance by the study of the present inventor. Further, it has been found by the study of the present inventor that such an aqueous ink composition has low dispersibility of resin fine particles and is insufficient in terms of storage stability.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet ink capable of forming an image having excellent storage stability, high image density, and excellent abrasion resistance on a recording medium. That is. Another object of the present invention is to provide a method for producing such an inkjet ink.

The inkjet ink according to the present invention contains resin-containing particles containing at least a polyester resin and an aqueous medium. At least a part of the resin-containing particles is the first resin-containing particles having the first characteristic. The first feature is that each of the first resin-containing particles further contains at least one colorant particle in addition to the polyester resin, and each of the at least one colorant particle is the first resin-containing particle. This is a feature that is located inside the first resin-containing particles without being exposed on the surface of the first resin. The area ratio of the first resin-containing particles to the area of the resin-containing particles in the cross-sectional image of the resin-containing particles is 90% or more. The concentration of the intrinsic colorant represented by the formula (1) is 15% or more.

_{C 20 = (M R / M} INK) × (A 1 / A 10) × (A 20 / A 1) × 100 ··· (1)

In the formula (1), C ₂₀ represents the concentration of the intrinsic colorant. M _INK represents the mass of the above-mentioned inkjet ink. M _R represents a mass of the polyester resin contained in the inkjet ink. A ₁₀ represents the area of the resin-containing particles in the cross-sectional image. A ₁ represents the area of the first resin-containing particles in the cross-sectional image. A ₂₀ represents the area of the colorant particles located inside the first resin-containing particles in the cross-sectional image.

The method for producing an inkjet ink according to the present invention is the method for producing an inkjet ink already described. The method for producing an inkjet ink according to the present invention includes a resin-containing particle forming step and a mixing step. In the resin-containing particle forming step, the resin is formed by adding an aqueous phase to an oil phase containing the polyester resin, the colorant particles, and a base, and emulsifying the oil phase and the aqueous phase. Form containing particles. In the mixing step, the resin-containing particles and the aqueous medium are mixed.

The inkjet ink according to the present invention and the inkjet ink produced by the production method according to the present invention can form an image having excellent storage stability, high image density, and excellent scratch resistance on a recording medium.

It is sectional drawing which shows the resin-containing particle and colorant particle contained in the ink which concerns on embodiment of this invention. It is a figure for demonstrating phase inversion emulsification.

An embodiment of the present invention will be described. First, terms used in the present specification will be described.

The glass transition point (Tg) is a value measured according to "JIS (Japanese Industrial Standards) K7121-2012" using a differential scanning calorimeter ("DSC-6220" manufactured by Seiko Instruments Inc.) unless otherwise specified. Is. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured by the differential scanning calorimeter, the inflection point due to the glass transition (baseline extrapolation line and falling line extrapolation line) The temperature (onset temperature) at the intersection with) corresponds to the glass transition point.

The softening point (Tm) is a value measured using a high-grade flow tester (“CFT-500D” manufactured by Shimadzu Corporation) unless otherwise specified. In the S-curve (horizontal axis: temperature, vertical axis: stroke) measured by the heightened flow tester, the temperature of "(baseline stroke value + maximum stroke value) / 2" corresponds to the softening point.

Unless otherwise specified, the acid value is "JIS (Japanese Industrial Standard) K0070-1992 (test method for acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponified product of chemical products)". It is a value measured according to.

Unless otherwise specified, the volume median diameter (D ₅₀ ) of the particles (for example, resin-containing particles and pigment particles) is a laser diffraction / scattering type particle size distribution measuring device (“LA-950” manufactured by HORIBA, Ltd.). It is a value measured using. The terms used in the present specification have been described above.

<Ink for Ink>
Next, with reference to FIG. 1, the inkjet ink (hereinafter, referred to as ink) 100 of the present embodiment will be described. FIG. 1 shows a cross section of the resin-containing particles 10 and the colorant particles 20 contained in the ink 100. The ink 100 contains the resin-containing particles 10 and an aqueous medium. The ink 100 is a water-based ink containing a water-based medium. The ink 100 further contains the colorant particles 20.

The resin-containing particles 10 contain at least a polyester resin. The polyester resin fixes well to the recording medium as compared with other resins (for example, acrylic resin and styrene acrylic resin). When an image is formed on a recording medium using the ink 100, the resin-containing particles 10 containing a polyester resin are satisfactorily fixed on the recording medium. Therefore, when the resin-containing particles 10 contain the polyester resin, an image having excellent abrasion resistance can be formed on the recording medium.

Further, when the resin-containing particles 10 contain the polyester resin, the dispersibility of the resin-containing particles 10 in the ink 100 is enhanced, and the storage stability of the ink 100 is improved.

(First feature)
The resin-containing particles 10 include the first resin-containing particles 1 having the first characteristic. The first feature is that each of the first resin-containing particles 1 further contains at least one colorant particle 20 in addition to the polyester resin, and each of the at least one colorant particle 20 is the first resin-containing particle 1. It is a feature that it is located inside the first resin-containing particles 1 without being exposed on the surface.

Examples of the first resin-containing particles 1 having the first characteristic include the first resin-containing particles 1A and the first resin-containing particles 1B. The first resin-containing particles 1A contain a plurality of colorant particles 20. All of the plurality of colorant particles 20 (all of the plurality of colorant particles 20) are located inside the first resin-containing particles 1A without being exposed on the surface of the first resin-containing particles 1A. On the other hand, the first resin-containing particles 1B contains one colorant particle 20. One colorant particle 20 is located inside the first resin-containing particle 1B without being exposed on the surface of the first resin-containing particle 1B. Hereinafter, when it is not necessary to distinguish between the "first resin-containing particles 1A" and the "first resin-containing particles 1B", the first resin-containing particles 1A and 1B are comprehensively referred to as "first resin-containing particles 1". ".

The resin-containing particles 10 may further contain resin-containing particles 10 other than the first resin-containing particles 1 that do not have the first characteristic. Examples of the resin-containing particles 10 other than the first resin-containing particles 1 that do not have the first characteristic include the second resin-containing particles 2 and the third resin-containing particles 3. The second resin-containing particles 2 further contain a plurality of colorant particles 20 in addition to the polyester resin. However, at least one of the plurality of colorant particles 20 is exposed on the surface of the second resin-containing particles 2. Therefore, the second resin-containing particles 2 do not have the first feature. Further, the third resin-containing particles 3 contain the polyester resin, but do not contain the colorant particles 20. Therefore, the third resin-containing particles 3 do not have the first feature.

At least a part of the resin-containing particles 10 (for example, the first resin-containing particles 1, the second resin-containing particles 2, and the third resin-containing particles 3) is the first resin-containing particles 1 having the first characteristic. .. The resin-containing particles 10 contain only the first resin-containing particles 1 and include resin-containing particles 10 other than the first resin-containing particles 1 (for example, the second resin-containing particles 2 and the third resin-containing particles 3). It does not have to be. That is, all of the resin-containing particles 10 may be the first resin-containing particles 1. Alternatively, the resin-containing particles 10 further include resin-containing particles 10 other than the first resin-containing particles 1 (for example, the second resin-containing particles 2 and the third resin-containing particles 3) in addition to the first resin-containing particles 1. It may be included. That is, a part of the resin-containing particles 10 may be the first resin-containing particles 1. The colorant particles 20 (colorant particles 20 not contained in the resin-containing particles 10) that are not coated with the polyester resin may be contained in the ink 100.

The colorant particles 20 containing the colorant are difficult to disperse with respect to the aqueous medium contained in the ink 100. Therefore, the colorant particles 20 that are not coated with the polyester resin tend to be difficult to disperse in the aqueous medium. Further, the second resin-containing particles 2 in which the colorant particles 20 are exposed on the surface also tend to be difficult to disperse in the aqueous medium. On the other hand, the first resin-containing particles 1 in which at least one colorant particles 20 are located inside without being exposed on the surface are well dispersed in the aqueous medium. Therefore, when at least a part of the resin-containing particles 10 is the first resin-containing particles 1, the dispersibility of the resin-containing particles 10 in the ink 100 is enhanced. As a result, the storage stability of the ink 100 can be improved.

Further, as already described, the polyester resin is well fixed to the recording medium. The entire surface of the first resin-containing particles 1 in which at least one colorant particle 20 is located inside without being exposed on the surface is made of polyester resin. Therefore, when an image is formed on a recording medium using the ink 100, the first resin-containing particles 1 are particularly well fixed on the recording medium. Therefore, since at least a part of the resin-containing particles 10 is the first resin-containing particles 1, the ink 100 can be satisfactorily fixed on the recording medium, and an image having excellent abrasion resistance can be formed on the recording medium. Can be done.

Whether the resin-containing particles 10 have a first characteristic, for example, by the method described in <the first measurement of the area ratio R ₁ of the resin-containing particles 1> embodiments described later, be confirmed.

For example, in the resin-containing particle forming step described later, the first resin-containing particles having the first characteristic are obtained by adding the polyester resin and the colorant particles 20 to the oil phase OIL (see FIG. 2) and performing phase inversion emulsification. 1 can be produced.

(Area ratio of first resin-containing particles R ₁ )
The area ratio of the first resin-containing particles 1 to the area of the resin-containing particles 10 in the cross-sectional image of the resin-containing particles 10 is 90% or more. Hereinafter, "the area ratio of the first resin-containing particles 1 to the area of the resin-containing particles 10 in the cross-sectional photographed image of the resin-containing particles 10" may be described as "the area ratio R _{1 of} the first resin-containing particles ₁ ". is there. The area of the resin-containing particles 10 in the cross-sectional image of the resin-containing particles 10 is the area of each of the resin-containing particles 10 (for example, the first resin-containing particles 1, the second resin-containing particles 2, and the third resin-containing particles 3). Is the total of. The area of the first resin-containing particles 1 in the cross-sectional image of the resin-containing particles 10 is the total area of each of the first resin-containing particles 1.

As the area ratio R ₁ of the first resin-containing particles 1 is higher, the first resin-containing particles 1 content of the resin-containing particles 10 is increased. As described above, the first resin-containing particles 1 in which at least one colorant particle 20 is located inside without being exposed to the surface are well dispersed in the aqueous medium. Therefore, when the area ratio R _{1 of} the first resin-containing particles 1 is 90% or more, the number of the first resin-containing particles 1 that are well dispersed in the aqueous medium increases, and the storage stability of the ink 100 is improved. it can. Further, as already described, when an image is formed on a recording medium using the ink 100, the first resin-containing particles 1 whose entire surface is made of polyester resin are satisfactorily fixed to the recording medium. Therefore, when the area ratio R _{1 of} the first resin-containing particles 1 is 90% or more, the number of the first resin-containing particles 1 satisfactorily fixed on the recording medium increases, and an image having excellent abrasion resistance is recorded. Can be formed on a medium.

To improve the storage stability of the ink 100, in order to form a recording medium an image having excellent scratch resistance, it is preferable area ratio R ₁ of the first resin-containing particles 1 is not less than 94%. The upper limit of the area ratio _{R 1} of the first resin-containing particles 1 is, for example, 100% or less.

The area ratio R ₁ of the first resin-containing particles 1 can be measured, for example, by the method described in <Measurement of the area ratio R ₁ of the first resin-containing particles 1> in Examples described later.

The area ratio R ₁ of the first resin-containing particles 1 can be adjusted, for example, by changing the concentration of the polyester resin in the oil phase OIL in the resin-containing particle forming step described later. Higher the concentration of the polyester resin in the oil phase OIL increases, the area ratio R ₁ of the first resin-containing particles 1 increases. In order to adjust the area ratio R ₁ of the first resin-containing particles 1 to a predetermined range, that the concentration of the polyester resin in the oil phase OIL, is preferably at least 20 wt%, at least 30 wt% It is more preferably 33% or more, and particularly preferably 33% or more. The upper limit of the concentration of the polyester resin in the oil phase OIL is not particularly limited, but is, for example, 40% by mass.

(Internal colorant concentration)
The intrinsic colorant concentration C ₂₀ represented by the following formula (1) is 15% or more.
_{C 20 = (M R / M} INK) × (A 1 / A 10) × (A 20 / A 1) × 100 ··· (1)

In formula (1), C ₂₀ represents the concentration of the intrinsic colorant. M _INK represents the mass of the ink 100. M _R represents the mass of the polyester resin contained in the ink 100. A ₁₀ represents the area of the resin-containing particles 10 in the cross-sectional photographed image of the resin-containing particles 10. A ₁ represents the area of the first resin-containing particles 1 in the cross-sectional image of the resin-containing particles 10. A ₂₀ represents the area of the colorant particles 20 located inside the first resin-containing particles 1 in the cross-sectional image of the resin-containing particles 10.

The intrinsic colorant concentration C ₂₀ has a correlation with the content of the colorant particles 20 located inside the first resin-containing particles 1 with respect to the mass _MINK of the ink 100. The colorant particles 20 that are not coated with the polyester resin are difficult to disperse in the aqueous medium and tend to settle in the ink 100. Further, the second resin-containing particles 2 in which the colorant particles 20 are exposed on the surface are also difficult to disperse in the aqueous medium and tend to settle in the ink 100. On the other hand, the first resin-containing particles 1 in which at least one colorant particles 20 are located inside without being exposed on the surface are well dispersed in the aqueous medium. The first resin-containing particles 1 dispersed in the ink 100 without settling are ejected from the recording head of the inkjet recording device. Then, an image is formed on the recording medium by the colorant particles 20 located inside the first resin-containing particles 1. Therefore, the higher the intrinsic colorant concentration C ₂₀ (15% or more) that correlates with the content of the colorant particles 20 located inside the first resin-containing particles 1, the higher the image density is. It can be formed on a recording medium.

In order to form an image having a high image density on a recording medium, the intrinsic colorant concentration C ₂₀ is preferably 17% or more. The upper limit of the intrinsic colorant concentration C ₂₀ is not particularly limited, but is, for example, 30% or less.

The intrinsic colorant concentration C ₂₀ can be measured, for example, by the method described in <Measurement of the intrinsic colorant concentration C ₂₀ > of Examples described later.

Endogenous colorant concentration C _20, for example, is added in the resin-containing particles forming process to be described later, by changing the mass M ₂₀ of the colorant particles 20 mass M _R of the polyester resin can be adjusted. Higher the ratio _M 20 / _{M R} of the mass _{M 20} of the colorant particles 20 with respect to the mass _{M R} of the polyester resin is high, inherent coloring agent concentration _{C 20} increases. A ratio _M 20 / _{M R} of the mass _{M 20} of the colorant particles 20 with respect to the mass _{M R} of the polyester resin is preferably 0.8 or more, more preferably 0.9 or more, 1.0 or more It is more preferable to have. The upper limit of the ratio _M 20 / _{M R} of the mass _{M 20} of the colorant particles 20 with respect to the mass _{M R} of the polyester resin is not particularly limited, for example, 1.5 or less.

It is preferable that the first resin-containing particles 1 are dispersed in the ink 100 without the dispersant being contained in the ink 100. As described above, the entire surface of the first resin-containing particles 1 in which at least one colorant particle 20 is located inside without being exposed to the surface is made of polyester resin. Carboxy group of the polyester resin (-COOH group) is, -COO in an aqueous medium ^- a group. Plurality of -COO the first surface of the resin-containing particles 1 ^- since that group is present, the first resin-containing particles 1 in an aqueous medium can be self-dispersing. Therefore, even when the ink 100 does not contain a dispersant, the first resin-containing particles 1 can be satisfactorily dispersed in the ink 100. Since the ink 100 does not contain a dispersant, the viscosity of the ink 100 is less likely to decrease, and an image with less bleeding can be formed on the recording medium. Further, since the ink 100 does not contain a dispersant, an odor is less likely to be generated when the ink 100 is fixed to the recording medium by heating. For example, the ink 100 preferably does not contain a surfactant described later as a dispersant. Further, for example, it is preferable that the ink 100 does not contain a dispersant other than a surfactant (for example, a polymer dispersant such as gum arabic and methyl cellulose) as a dispersant.

The acid value of the polyester resin contained in the resin-containing particles 10 is preferably 20 mgKOH / g or more and 200 mgKOH / g or less, and more preferably 30 mgKOH / g or more and 80 mgKOH / g or less. When the acid value of the polyester resin falls within this range, -COO present in the first surface of the resin-containing particles 1 ^- the number of groups can be ensured, even if the dispersing agent in the ink 100 is not contained, The first resin-containing particles 1 can be well dispersed in the ink 100. Further, when the acid value of the polyester resin is within such a range, the polyester resin has an appropriate affinity for the aqueous phase W (see FIG. 2) at the time of phase inversion emulsification described later. Therefore, the phase inversion emulsification can be suitably promoted.

(Resin-containing particles)
As already described, the resin-containing particles 10 contain at least a polyester resin. Hereinafter, the polyester resin contained in the resin-containing particles 10 will be described.

The polyester resin is obtained by polycondensing at least one alcohol monomer and at least one carboxylic acid monomer. The polyester resin is a polymer of at least one alcohol monomer and at least one carboxylic acid monomer.

Examples of alcohol monomers include diol monomers, bisphenol monomers, and trihydric or higher alcohol monomers.

Examples of diol monomers include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4-diol. , 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

Examples of bisphenol monomers include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct (eg, 2 mol of bisphenol A ethylene oxide adduct), and bisphenol A propylene oxide adduct (eg, 2 mol of bisphenol A propylene oxide adduct). Additives).

Examples of trihydric or higher alcohol monomers include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol. , 1,2,5-pentantriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-triol Hydroxylmethylbenzene can be mentioned.

Examples of the carboxylic acid monomer include a divalent carboxylic acid monomer and a trivalent or higher carboxylic acid monomer.

Examples of divalent carboxylic acid monomers include maleic acid, fumaric acid, citraconic acid, succinic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, 5-sulfoisophthalic acid, sodium 5-sulfoisophthalate, cyclohexanedicarboxylic acid. , Adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, alkylsuccinic acid, and alkenylsuccinic acid. Examples of alkyl succinic acid include n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, and isododecyl succinic acid. Examples of alkenyl succinic acid include n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, and isododecenyl succinic acid.

Examples of trivalent or higher valent carboxylic acid monomers include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2. , 4-Butantricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxy-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxy) methane , 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empole trimeric acid.

Only one kind of alcohol monomer may be used, or two or more kinds may be used. Only one kind of carboxylic acid monomer may be used, or two or more kinds may be used. Further, the carboxylic acid monomer may be derivatized into an ester-forming derivative and used. Examples of ester-forming derivatives include acid halides, acid anhydrides, and alkyl (eg, alkyls having 1 to 6 carbon atoms) esters.

The polyester resin is preferably a polymer of at least one type (for example, two types) of bisphenol monomer and at least one type (for example, two types) of divalent carboxylic acid monomer. The polyester resin has at least one (for example, two) bisphenol A alkylene oxide adduct, at least one (for example, one) benzenedicarboxylic acid, and at least one (for example, one). More preferably, it is a polymer with an alkane substituted with a carboxy group. The polyester resin contains at least one (for example, two) bisphenol A alkylene oxide adduct having 1 to 6 carbon atoms, at least one (for example, one) benzenedicarboxylic acid, and at least one (for example). For example, it is more preferably a polymer with an alkane having 1 or more and 6 or less carbon atoms substituted with two carboxy groups of (1 type). The polyester resin is more preferably a polymer of a bisphenol A ethylene oxide adduct, a bisphenol A propylene oxide adduct, terephthalic acid, and adipic acid. The polyester resin is particularly preferably a polymer of a bisphenol A ethylene oxide 2 mol adduct, a bisphenol A propylene oxide 2 mol adduct, terephthalic acid, and adipic acid.

The glass transition point of the polyester resin is preferably 30 ° C. or higher and 80 ° C. or lower, more preferably 40 ° C. or higher and 60 ° C. or lower, and particularly preferably 50 ° C. or lower.

The softening point of the polyester resin is preferably 60 ° C. or higher and 130 ° C. or lower, more preferably 80 ° C. or higher and 120 ° C. or lower, further preferably 90 ° C. or higher and 110 ° C. or lower, and 100 ° C. Is particularly preferable.

The content of the polyester resin is preferably 15 parts by mass or more and 200 parts by mass or less, more preferably 50 parts by mass or more and 150 parts by mass or less, and 80 parts by mass with respect to 100 parts by mass of the colorant particles 20. It is more preferable that the amount is 120 parts by mass or more. When the content of the polyester resin is 15 parts by mass or more, strike-through is unlikely to occur in the recording medium after image formation. On the other hand, when the content of the polyester resin is 200 parts by mass or less, a desired image density can be easily obtained.

The number average primary particle diameter of the resin-containing particles 10 is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less, and further preferably 30 nm or more and 50 nm or less. When the number average primary particle diameter of the resin-containing particles 10 is within such a range, the colorant particles 20 are likely to be located inside the resin-containing particles 10, and the first resin-containing particles 1 having the first characteristic are preferably used. Obtainable.

(Colorant particles)
The colorant particles 20 contain a colorant. The colorant particles 20 preferably contain a water-insoluble colorant, and more preferably contain only the water-insoluble colorant. When the colorant particles 20 contain a water-insoluble colorant, the affinity of the colorant particles 20 for the aqueous medium is lowered, and the colorant particles 20 are located inside the resin-containing particles 10 in the phase inversion emulsion described later. It will be easier. Examples of such a water-insoluble colorant include pigments and oil-soluble dyes.

Examples of the pigment include a yellow pigment, an orange pigment, a red pigment, a blue pigment, a purple pigment, and a black pigment. Examples of the yellow pigment include C.I. I. Pigment Yellow 74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193. Examples of the orange pigment include C.I. I. Pigment Orange 34, 36, 43, 61, 63, and 71. Examples of the red pigment include C.I. I. Pigment Red 122, and 202. Quinacridone magenta (PR122) may be used as the red pigment. Examples of the blue pigment include C.I. I. Pigment Blue 15 and 15: 3. Examples of the purple pigment include C.I. I. Pigment Violet 19, 23, and 33. Examples of the black pigment include C.I. I. Pigment Black 7 and carbon black can be mentioned. As the pigment, a black pigment is preferable, and carbon black is more preferable. The colorant particles 20 preferably contain a black pigment, more preferably carbon black, and particularly preferably only carbon black.

Examples of the oil-soluble dye include C.I. I. Solvent yellow (2, 6, 14, 15, 19, and 21) can be mentioned.

The content of the colorant particles 20 in the ink 100 is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 15% by mass or less. When the content of the colorant particles 20 in the ink 100 is 5% by mass or more, an image having a desired image density can be easily obtained. When the content of the colorant particles 20 in the ink 100 is 30% by mass or less, the fluidity of the ink 100 and the permeability of the ink 100 to the recording medium can be easily ensured.

The number average primary particle size of the colorant particles 20 is preferably smaller than the number average primary particle size of the resin-containing particles 10. With such colorant particles 20, the colorant particles 20 are likely to be located inside the resin-containing particles 10, and the first resin-containing particles 1 having the first characteristic can be preferably obtained.

The number average primary particle diameter of the colorant particles 20 is preferably 5 nm or more and 100 nm or less, more preferably 5 nm or more and 30 nm or less, and further preferably 10 nm or more and 20 nm or less. When the number average primary particle diameter of the colorant particles 20 is within such a range, the colorant particles 20 are likely to be located inside the resin-containing particles 10, and the first resin-containing particles 1 having the first characteristic are preferably used. Obtainable. Further, when the number average primary particle diameter of the colorant particles 20 is within such a range, the color density, hue, and stability of the ink 100 are improved.

(Aqueous medium)
The aqueous medium is a medium containing water as a main component. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include water or a mixed solution of water and a polar solvent. Examples of polar solvents contained in aqueous media include methanol, ethanol, and methyl ethyl ketone. The content of water in the aqueous medium is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 100% by mass. .. The aqueous medium is preferably water, more preferably ion-exchanged water.

The content of the aqueous medium in the ink 100 is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and 20% by mass or more and 30% by mass or less. Is more preferable. When the content of the aqueous medium in the ink 100 is within such a range, the ink 100 having an appropriate viscosity can be provided.

The ink 100 may further contain at least one of a surfactant, a dissolution stabilizer, a moisturizer, a penetrant, and a viscosity modifier, if necessary. Hereinafter, surfactants, dissolution stabilizers, moisturizers, penetrants, and viscosity modifiers will be described.

(Surfactant)
Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, and surfactants having a betaine structure. Examples of the anionic surfactant include sodium lauryl sulfate and potassium lauryl sulfate. Nonionic surfactants include, for example, acetylenediol ethylene oxide adducts. However, as already described, it is preferable that the ink 100 does not contain such a surfactant.

(Dissolution stabilizer)
When the ink 100 contains a dissolution stabilizer, the components contained in the ink 100 are easily compatible with each other, and the dissolved state of the ink 100 can be stabilized. The dissolution stabilizer is preferably at least one of 2-pyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolidone. The dissolution stabilizer is more preferably 2-pyrrolidone. The content of the dissolution stabilizer in the ink 100 is preferably 0.1% by mass or more and 20.0% by mass or less, more preferably 0.1% by mass or more and 15.0% by mass or less, and further preferably 0. .1% by mass or more and 1.0% by mass or less.

(Moisturizer)
If the ink 100 contains a moisturizer, volatilization of liquid components from the ink 100 can be suppressed. The moisturizer is preferably at least one of polyalkylene glycols, alkylene glycols, and glycerin. The polyalkylene glycols are preferably polyethylene glycol or polypropylene glycol. The alkylene glycols include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol (that is, 1,3-propanediol), triethylene glycol, tripropylene glycol, 1,2,6-hexanetriol. , Thiodiglycol, 1,3-butanediol, or 1,5-pentanediol is preferred. The moisturizer is more preferably at least one of alkylene glycols and glycerin, and even more preferably at least one of 1,3-propanediol and glycerin. The content of the moisturizer in the ink 100 is preferably 2.0% by mass or more and 30.0% by mass or less, and more preferably 5.0% by mass or more and 25.0% by mass or less.

(Penetrating agent)
If the ink 100 contains a penetrant, the permeability of the ink 100 to the recording medium is improved. The penetrant is preferably 1,2-hexylene glycol, 1,2-octanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, It is at least one of triethylene glycol monobutyl ether and diethylene glycol monobutyl ether. The penetrant is more preferably at least one of 1,2-octanediol and triethylene glycol monobutyl ether. The content of the penetrant in the ink 100 is preferably 0.5% by mass or more and 20.0% by mass or less, and more preferably 10.0% by mass or more and 20.0% by mass or less.

(Viscosity modifier)
Examples of the viscosity modifier include N-methyldiethanolamine. N-Methyldiethanolamine is a compound having a relatively high boiling point among organic amine compounds. Therefore, by including N-methyldiethanolamine in the ink 100, the viscosity of the ink 100 at the time of drying can be lowered.

<Ink manufacturing method>
Next, the method for producing the ink 100 of the present embodiment will be described. An example of the method for producing the ink 100 of the present embodiment includes a resin-containing particle forming step and a mixing step. The method for producing the ink 100 of the present embodiment may further include a polyester resin preparation step.

(Polyester resin preparation process)
In the polyester resin preparation step, the polyester resin is prepared. Specifically, in the presence of a polymerization catalyst, the alcohol monomer and the carboxylic acid monomer are polycondensed to obtain a polyester resin. Examples of the polymerization catalyst include tin (II) 2-ethylhexanoate. The reaction temperature is preferably 100 ° C. or higher and 300 ° C. or lower, and more preferably 200 ° C. or higher and 250 ° C. or lower. The polycondensation reaction may be carried out in an inert gas atmosphere (for example, a nitrogen atmosphere). The polycondensation reaction may be carried out in a reduced pressure atmosphere.

Next, the resin-containing particle forming step will be described with reference to FIG. FIG. 2 is a diagram for explaining phase inversion emulsification. In the resin-containing particle forming step, the aqueous phase W is added to the oil phase OIL to emulsify the oil phase OIL and the aqueous phase W. The resin-containing particles 10 are formed by phase inversion emulsification.

As shown in FIG. 2, the phase inversion emulsification proceeds through the states of the first liquid phase 31, the second liquid phase 32, and the third liquid phase 33. The first liquid phase 31 is an oil phase OIL. The oil phase OIL contains a polyester resin, colorant particles 20, and a base. The oil phase OIL may further contain a polar solvent (eg, methyl ethyl ketone).

Then, when the aqueous phase W is added to the oil phase OIL, the first liquid phase 31 changes to the second liquid phase 32. The aqueous phase W contains at least an aqueous medium. The second liquid phase 32 includes an oil phase OIL and an aqueous phase W. In the second liquid phase 32, the oil phase OIL is a continuous phase and the aqueous phase W is a dispersed phase. In the second liquid phase 32, the aqueous phase W in a droplet state is dispersed in the oil phase OIL. The second liquid phase 32 is a liquid phase of a water-in-oi1 (W / O) type emulsion.

Then, by inversion emulsifying the second liquid phase 32, the second liquid phase 32 changes to the third liquid phase 33. The third liquid phase 33 includes an oil phase OIL and an aqueous phase W. In the third liquid phase 33, the aqueous phase W is a continuous phase and the oil phase OIL is a dispersed phase. In the third liquid phase 33, the oil phase OIL in a droplet state is dispersed in the aqueous phase W. The third liquid phase 33 is a liquid phase of an oi1-in-water (O / W) type emulsion.

Inversion emulsification is caused, for example, by stirring the oil phase OIL and the aqueous phase W with a stirrer in the presence of a base. By stirring, the continuous phase is changed from the oil phase OIL to the aqueous phase W. In this way, the second liquid phase 32 changes to the third liquid phase 33. The oil phase OIL in the liquid drop state in the third liquid phase 33 becomes the resin-containing particles 10.

As already mentioned, the oil phase OIL contains the polyester resin and the colorant particles 20. The affinity of the polyester resin for the aqueous medium is higher than the affinity of the colorant particles 20 for the aqueous medium. Therefore, at the time of phase inversion, the polyester resin is located near the surface of the oil phase OIL in the droplet state, which is in contact with the aqueous phase W containing the aqueous medium. On the other hand, the colorant particles 20 having low affinity for the aqueous medium are located inside the oil phase OIL in the liquid drop state. Therefore, the resin-containing particles 10 corresponding to the oil phase OIL in the liquid drop state tend to have the first characteristic. As described above, the resin-containing particles 10 in which at least a part of the resin-containing particles 10 is the first resin-containing particles 1 having the first characteristic can be obtained by phase inversion emulsification.

In order to preferably proceed with phase inversion emulsification, the base is preferably an amine substituted with 1 or more and 3 or less hydroxyalkyl groups, and the number of carbon atoms of 1 or more and 3 or less is 1 or more and 6 or less. It is more preferably an amine substituted with a hydroxyalkyl group of, and particularly preferably a triethanolamine. An amine substituted with a hydroxyalkyl group having 1 or more and 3 or less carbon atoms and having 1 or more and 6 or less carbon atoms is represented by the general formula "N (-R _1- OH) _n (-H) _3-n ". In this general formula, R ₁ represents an alkylene group having 1 or more and 6 or less carbon atoms, and n represents an integer of 1 or more and 3 or less. R ₁ preferably represents an alkylene group having 1 or more and 3 or less carbon atoms, and more preferably represents −CH _2- CH ₂ − groups. The content of the base in the oil phase OIL is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 1.0% by mass or more and 3.0% by mass or less.

(Mixing process)
In the mixing step, the resin-containing particles 10 and the aqueous medium are mixed. By mixing, the ink 100 of the present embodiment is obtained. The resin-containing particles 10 may be mixed with a further aqueous medium in the state of latex in which the resin-containing particles 10 are dispersed in the aqueous medium. For mixing, for example, a stirrer (for example, "Three One Motor (registered trademark) BL-600" manufactured by Shinto Kagaku Co., Ltd.) is used. In addition to the resin-containing particles 10 and the aqueous medium, other ink components may be further mixed. Examples of other ink components include at least one of a surfactant, a dissolution stabilizer, a moisturizer, a penetrant, and a viscosity modifier.

However, in the production of the ink 100, it is preferable that a dispersant (for example, a surfactant and a dispersant other than the surfactant) is not used. As described above, the first resin-containing particles 1 can be dispersed in the ink 100 even when the ink 100 does not contain the dispersant. For example, it is preferable that no dispersant (for example, a surfactant and a dispersant other than the surfactant) is used in the resin-containing particle forming step. Further, for example, it is preferable that no dispersant (for example, a surfactant and a dispersant other than the surfactant) is used in the mixing step. After mixing, filtration is performed if necessary. In this way, the ink 100 is obtained. The method for producing the ink 100 of the present embodiment has been described above.

Next, examples of the present invention will be described. In the evaluation in which an error occurs, a considerable number of measured values in which the error is sufficiently small are obtained, and the arithmetic mean of the obtained measured values is used as the evaluation value.

[Ink preparation]
The inks (IA1) according to the examples and the inks (IB1) to (IB5) according to the comparative examples were prepared. The configurations of the ink (IA1) and the inks (IB1) to (IB5) are shown in Table 1 described later.

<Preparation of polyester resin PES>
Polyester resin PES was prepared for use in the preparation of the inks (IA1), (IB1), (IB2), and (IB5). Specifically, as a monomer for synthesizing the polyester resin PES, 100 g of a bisphenol A ethylene oxide 2 mol adduct, 100 g of a bisphenol A propylene oxide 2 mol adduct, 50 g of terephthalic acid, and 30 g of adipic acid are used in a volume of 10 L. It was placed in a four-necked flask. A thermometer, a stirrer (stainless steel stirrer), a flow-down condenser (heat exchanger), and a nitrogen introduction tube were installed in the flask. Nitrogen gas was introduced into the flask through the nitrogen introduction pipe to create a nitrogen atmosphere in the flask. Subsequently, the temperature of the flask contents was raised to 235 ° C. while stirring the flask contents in a nitrogen atmosphere. The flask contents were stirred at a temperature of 235 ° C. under a nitrogen atmosphere until all the monomers (bisphenol A ethylene oxide 2 mol adduct, bisphenol A propylene oxide 2 mol adduct, terephthalic acid, and adipic acid) were dissolved. Then, 54 g of tin (II) 2-ethylhexanoate was added into the flask, and the pressure inside the flask was reduced. Under the conditions of a reduced pressure atmosphere (absolute pressure: 8 kPa) and a temperature of 235 ° C., the contents of the flask were polycondensed until the glass transition point of the reaction product reached 50 ° C. and the softening point reached 100 ° C. In this way, a polyester resin PES was obtained. The obtained polyester resin PES had a glass transition point of 50 ° C., a softening point of 100 ° C., and an acid value of 40 mgKOH / g.

<Preparation of styrene acrylic resin SA>
A styrene acrylic resin SA for use in the preparation of the inks (IB3) and (IB4) was prepared. Specifically, 20 parts by mass of styrene, 5 parts by mass of 2-ethylhexyl methacrylate, 15 parts by mass of butyl methacrylate, 10 parts by mass of lauryl methacrylate, 2 parts by mass of methacrylic acid, and 0.3 parts by mass of t-dodecyl mercaptan are placed in a reaction vessel. It was. The reaction vessel was equipped with a stirrer, a thermometer, a reflux tube, a dropping funnel, and a nitrogen introduction tube. Nitrogen gas was introduced into the reaction vessel through the nitrogen introduction pipe to create a nitrogen atmosphere in the reaction vessel. Next, 150 parts by mass of styrene, 15 parts by mass of acrylic acid, 50 parts by mass of butyl methacrylate, 1 part by mass of t-dodecyl mercaptan, 20 parts by mass of methyl ethyl ketone, and 1 part by mass of azobisisobutyronitrile were placed in the dropping funnel. The liquid in the dropping funnel was dropped into the reaction vessel over 4 hours while stirring the contents of the reaction vessel under the conditions of a nitrogen gas atmosphere and a temperature of 70 ° C. In this way, the contents of the reaction vessel were polymerized. Next, methyl ethyl ketone was added to the reaction vessel so that the solid content concentration was 60% by mass to obtain a dispersion of styrene acrylic resin SA.

<Preparation of ink (IA1)>
(Resin-containing particle forming step)
A solution was obtained by dissolving 100 g of polyester resin PES in 100 g of methyl ethyl ketone. 100 g of carbon black (“MONARCH® 880” manufactured by Cabot Corporation) was added to the solution and stirred to prepare an oil phase. Next, 20 g of methyl ethyl ketone was added to 200 g of ion-exchanged water and stirred to prepare an aqueous phase. Next, 7 g of triethanolamine was added to the oil phase, and the oil phase was stirred using a stirrer (“RW20” manufactured by IKA) under the condition of a rotation speed of 500 rpm. While continuing to stir the oil phase, an aqueous phase was added to the oil phase to emulsify the phase. In this way, a phase inversion emulsion was obtained. Next, using a rotary evaporator, the methyl ethyl ketone was gradually evaporated from the phase-integrated emulsion, taking care not to cause bumping, and the phase-inverted emulsion was concentrated. In this way, latex (LA1) of resin-containing particles (specifically, polyester resin-containing particles containing colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LA1) was 1% by mass or less. The solid content concentration of latex (LA1) was 60% by mass.

(Mixing process)
45.0 parts by mass of latex (LA1), 5.0 parts by mass of triethylene glycol monobutyl ether, 0.5 parts by mass of 2-pyrrolidone, and 0.7 parts by mass of N-methyldiethanolamine (boiling point). : 247 ° C.), 8.0 parts by mass of 1,2-octanediol, 5.0 parts by mass of glycerin, and 10.0 parts by mass of 1,3-propanediol were charged into the reaction vessel. Ion-exchanged water was added to the reaction vessel so that the total amount of the contents of the reaction vessel was 100.0 parts by mass. The contents in the reaction vessel were stirred under the condition of a rotation speed of 400 rpm using a stirrer (“Three One Motor BL-600” manufactured by Shinto Kagaku Co., Ltd.). The obtained liquid was filtered using a filter (pore diameter: 5 μm). In this way, the ink (IA1) was obtained.

<Preparation of ink (IB1)>
(Resin-containing particle forming step)
An oil phase was prepared by dissolving 150 g of polyester resin PES in 100 g of methyl ethyl ketone. No carbon black was added to the oil phase. Next, 20 g of methyl ethyl ketone was added to 200 g of ion-exchanged water and stirred to prepare an aqueous phase. 7 g of triethanolamine was added to the oil phase, and the oil phase was stirred. While continuing to stir the oil phase, an aqueous phase was added to the oil phase to emulsify the phase. In this way, a phase inversion emulsion was obtained. Next, using a rotary evaporator, the methyl ethyl ketone was gradually evaporated from the phase-integrated emulsion, taking care not to cause bumping, and the phase-inverted emulsion was concentrated. In this way, latex (LB1) of resin-containing particles (specifically, polyester resin-containing particles that do not contain colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LB1) was 1% by mass or less. The solid content concentration of latex (LB1) was 40% by mass.

Then, using a paint shaker, 40.0 parts by mass of carbon black (“MONARCH® 880” manufactured by Cabot Corporation), 100.0 parts by mass of latex (LB1), and zirconia beads (diameter: 0. 5 mm) 50.0 parts by mass was shaken for 6 hours. Carbon black was crushed by shaking. Zirconia beads were removed from the contents of the paint shaker to obtain a mixed solution (MB1) of latex (LB1) and colorant particles. The solid content concentration of the mixed solution (MB1) was 60% by mass.

(Mixing process)
The ink (IB1) mixing step was performed in the same manner as the ink (IA1) mixing step, except that the latex (LA1) was changed to the mixed solution (MB1). In this way, the ink (IB1) was obtained.

<Preparation of ink (IB2)>
(Resin-containing particle forming step)
Ink in the same manner as the resin-containing particle forming step of the ink (IA1), except that the amount of polyester resin PES added was changed from 100 g to 125 g and the amount of carbon black added was changed from 100 g to 75 g. The resin-containing particle forming step of (IB2) was performed. In this way, latex (LB2) of resin-containing particles (specifically, polyester resin-containing particles containing colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LB2) was 1% by mass or less. The solid content concentration of latex (LB2) was 60% by mass.

(Mixing process)
The ink (IB2) mixing step was performed in the same manner as the ink (IA1) mixing step, except that the latex (LA1) was changed to latex (LB2). In this way, the ink (IB2) was obtained.

<Preparation of ink (IB3)>
(Resin-containing particle forming step)
40 parts by mass of dispersion of styrene acrylic resin SA, 30 parts by mass of carbon black ("MONARCH (registered trademark) 880" manufactured by Cabot Corporation), 70 parts by mass of aqueous sodium hydroxide solution (concentration: 0.1 mol / L), and 30 parts of methyl ethyl ketone. The parts by mass were stirred for 30 minutes using a homogenizer. 100 parts by mass of ion-exchanged water was added to the stirred liquid, and the mixture was further stirred for 1 hour to obtain a liquid. Using a rotary evaporator, methyl ethyl ketone and a part of water were distilled off from the obtained liquid to obtain a concentrated liquid. The pH of the concentrated solution was adjusted to 9 using an aqueous sodium hydroxide solution (concentration: 0.1 mol / L). Then, the concentrated solution was filtered using a membrane filter (pore size: 0.3 μm). In this way, latex (LB3) of resin-containing particles (specifically, styrene acrylic resin-containing particles containing colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LB3) was 1% by mass or less. The solid content concentration of latex (LB3) was 60% by mass.

(Mixing process)
The ink (IB3) mixing step was performed in the same manner as the ink (IA1) mixing step, except that the latex (LA1) was changed to latex (LB3). In this way, the ink (IB3) was obtained.

<Preparation of ink (IB4)>
(Resin-containing particle forming step)
A dispersion of styrene acrylic resin SA (solid content: 150 g) was dissolved in 100 g of methyl ethyl ketone to prepare an oil phase. No carbon black was added to the oil phase. Next, 20 g of methyl ethyl ketone was added to 200 g of ion-exchanged water and stirred to prepare an aqueous phase. 7 g of triethanolamine was added to the oil phase, and the oil phase was stirred. While continuing to stir the oil phase, an aqueous phase was added to the oil phase to emulsify the phase. In this way, a phase inversion emulsion was obtained. Next, using a rotary evaporator, the methyl ethyl ketone was gradually evaporated from the phase-integrated emulsion, taking care not to cause bumping, and the phase-inverted emulsion was concentrated. In this way, latex (LB4) of resin-containing particles (specifically, styrene acrylic resin-containing particles containing no colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LB4) was 1% by mass or less. The solid content concentration of latex (LB4) was 40% by mass.

Then, using a paint shaker, 40.0 parts by mass of carbon black (“MONARCH® 880” manufactured by Cabot Corporation), 100.0 parts by mass of latex (LB4), and zirconia beads (diameter: 0. 5 mm) 50.0 parts by mass was shaken for 6 hours. Carbon black was crushed by shaking. Zirconia beads were removed from the contents of the paint shaker to obtain a mixed solution (MB4) of latex (LB4) and colorant particles. The solid content concentration of the mixed solution (MB4) was 60% by mass.

(Mixing process)
The ink (IB4) mixing step was performed in the same manner as the ink (IA1) mixing step, except that the latex (LA1) was changed to the mixed solution (MB4). In this way, the ink (IB4) was obtained.

<Preparation of ink (IB5)>
(Resin-containing particle forming step)
Resin-containing particle forming step of ink (IA1) except that the addition amount of polyester resin PES was changed from 100 g to 50 g and the addition amount of methyl ethyl ketone for preparing an oil phase was changed from 100 g to 150 g. The resin-containing particle forming step of the ink (IB5) was carried out in the same manner as in the above. In this way, latex (LB5) of resin-containing particles (specifically, polyester resin-containing particles containing colorant particles) was obtained. The concentration of methyl ethyl ketone contained in the latex (LB5) was 1% by mass or less. The solid content concentration of latex (LB5) was 60% by mass.

(Mixing process)
The ink (IB5) mixing step was performed in the same manner as the ink (IA1) mixing step, except that the latex (LA1) was changed to latex (LB5). In this way, the ink (IB5) was obtained.

[Measuring method]
<First measurement of the area ratio _{R 1} of the resin-containing particles 1>
Referring again to FIG. 1, illustrating a first method for measuring the area ratio R ₁ of the resin-containing particles 1. First, the ink 100 (more specifically, the ink (IA1)) was dried using a vacuum dryer set at 40 ° C. to obtain a dried product of the ink 100. After the dried product of ink 100 was dispersed in a photocurable adhesive (“Aronix (registered trademark) LCR D-800” manufactured by Toagosei Co., Ltd.), the obtained dispersion was allowed to be dispersed in an atmosphere at a temperature of 40 ° C. for 2 days. It was cured to obtain a cured product. Using an ultramicrotome equipped with a diamond knife (“EM UC6” manufactured by Leica Microsystems, Inc.), the obtained cured product was cut out to obtain a flaky sample. The cross section of the flaky sample was photographed using a field emission transmission electron microscope (TEM, "JEM-2100F" manufactured by Nippon Denshi Co., Ltd.) under the conditions of an acceleration voltage of 30 kV and a magnification of 30,000 times. A TEM photograph of the contained particles 10 was obtained. A TEM photograph of 500 resin-containing particles 10 was taken.

Subsequently, by analyzing the cross-sectional image of the resin-containing particles 10 in the photographed TEM photograph using image analysis software (“WinROOF” manufactured by Mitani Shoji Co., Ltd.), each of the 500 resin-containing particles 10 was analyzed. The area was measured. The total area of the 500 resin-containing particles 10 was defined as the area A ₁₀ of the resin-containing particles 10. In addition, it was confirmed whether or not the resin-containing particles 10 had the first characteristic by analyzing the cross-sectional photographed image of the resin-containing particles 10 in the photographed TEM photograph. The resin contained in the resin-containing particles 10 and the colorant particles 20 can be distinguished by the presence or absence of coloring in the cross-sectional image. Then, the area of each of the first resin-containing particles 1 having the first characteristic was measured among the 500 resin-containing particles 10. The total area of the measured first resin-containing particles 1 was defined as the area A _{1 of} the first resin-containing particles 1.

From the measured area A _{10 of} the resin-containing particles 10 and the area A _{1 of} the first resin-containing particles 1 of the resin-containing particles 10, the area ratio R _{1 of} the first resin-containing particles 1 (2) according to the following formula (2). Unit:%) was calculated.
R ₁ = (A ₁ / A ₁₀ ) x 100 ... (2)

In the formula (2), R ₁ represents the area ratio R ₁ of the first resin-containing particles 1. A ₁₀ represents the area of the resin-containing particles 10 in the cross-sectional photographed image of the resin-containing particles 10. A ₁ represents the area of the first resin-containing particles 1 in the cross-sectional image of the resin-containing particles 10.

For each of the inks (IB1) to (IB5), the area ratio R1 of the first resin-containing particles ₁ was calculated by the same method as that for the inks (IA1). The first calculation result of the area ratio R ₁ of the resin-containing particles 1 are shown in Table 1.

<Measurement of intrinsic colorant concentration C ₂₀ >
Hereinafter, a method for measuring the intrinsic colorant concentration C ₂₀ will be described with reference to FIG. 1. First, the intrinsic colorant concentration C ₂₀ was measured with respect to the ink 100 (more specifically, the ink (IA1)) by the following method.

First, the mass _{M INK} of the ink 100 in the formula (1) described in embodiment, and resin (specifically, a polyester resin) contained in the ink 100 was measured mass _{M R} of. Specifically, a resin (specifically, a polyester resin) was extracted from 30 g of ink 100 at 40 ° C. using 50 mL of tetrahydrofuran. The extract was distilled off under reduced pressure to obtain a tetrahydrofuran extract. Mass tetrahydrofuran extract (unit: g) of measured (specifically, polyester resin) resin contained in the ink 100 and the mass M _R of. Further, the mass (30 g) of the ink 100 used for extraction was _{defined as} the mass _{MINK of the} ink 100.

Next, in the cross-sectional image of the resin-containing particles 10, the area A ₁₀ of the resin-containing particles ₁₀ , the area A ₁ of the first resin-containing particles 1, and the colorant particles 20 located inside the first resin-containing particles 1. Area A ₂₀ was measured. Specifically, the area A ₁₀ of the resin-containing particles 10 and the area A ₁ of the first resin-containing particles ₁ were measured by the same method as in the above <Measurement of the area ratio R ₁ of the first resin-containing particles 1>. Furthermore, by analyzing the cross-sectional imaging images of the resin-containing particles 10 of the TEM in the photograph taken by the <first measurement of the area ratio R ₁ of the resin-containing particles 1>, among 500 pieces of the resin-containing particles 10, first The area of each of the colorant particles 20 located inside the characteristic first resin-containing particles 1 was measured. The total area of the colorant particles 20 located inside the first resin-containing particles 1 was taken as the area A ₂₀ of the colorant particles 20 located inside the first resin-containing particles 1. Of the 500 resin-containing particles 10, the area of the colorant particles 20 contained in the resin-containing particles 10 having no first feature (for example, the second resin-containing particles 2) is not measured.

Measured mass _{M INK,} mass _{M R,} the area _{A 10,} from the area _{A 1,} and the area _{A 20,} wherein described in Embodiment (1), i.e., _{"C 20 = (M R / M} INK) × (A 1 The intrinsic colorant concentration C ₂₀ (unit:%) was calculated according to "/ A ₁₀ ) x (A ₂₀ / A ₁ ) x 100".

For each of the inks (IB1) to (IB5), the intrinsic colorant concentration C ₂₀ was calculated in the same manner as for the ink (IA1). Incidentally, in the ink (I-B3) and (I-B4), (specifically, styrene-acrylic resins) resin mass was a mass _{M R.} The calculation results of the intrinsic colorant concentration C ₂₀ are shown in Table 1. As described above, the method for measuring the intrinsic colorant concentration C ₂₀ has been described with reference to FIG.

[Evaluation method]
<Image density>
The evaluation machine used to evaluate the image density was an inkjet recording device (a prototype evaluation machine manufactured by Kyocera Document Solutions Co., Ltd.). As the recording head provided in the evaluation machine, a recording head for "Gel Jet Printer IPSiO GX5000" manufactured by Ricoh Corporation was used. This recording head had a resolution of 1200 × 1200 dpi and a droplet amount of 3.5 pL, and was a line-type recording head.

The recording head of the evaluator was filled with ink (more specifically, any of ink (IA1) and (IB1) to (IB5)). The ejection conditions of the recording head were adjusted so that the volume of ink ejected from the recording head was 11 pL per ink drop. In an environment with a temperature of 25 ° C and a relative humidity of 60% RH, a solid image (size: length 10 cm and width 10 cm) was printed on plain paper (A4 size PPC paper, "C ² " manufactured by Fuji Xerox Co., Ltd.) using an evaluation machine. , Printing rate: 100%) was formed. The plain paper on which the image was formed was allowed to stand for 24 hours in an environment of a temperature of 25 ° C. and a relative humidity of 60% RH. After standing still, the image densities at 10 points in the same image were measured using a reflection densitometer (“RD-19” sold by Sakata Inx Engineering Co., Ltd.). The average value of the measured image densities at 10 points was used as the ID value. The image density of each ink was evaluated from the obtained ID values according to the following criteria. The evaluation results of the image density are shown in Table 1.

(Evaluation criteria for image density)
Evaluation A (good): The ID value was 1.30 or more.
Evaluation B (defective): The ID value was less than 1.30.

<Storage stability>
First, the rate of change in the viscosity of the ink before and after storage was measured. Inks at 25 ° C. (more specifically, inks (IA1) and (IB1) to (I-), in accordance with the method described in "JIS Z 8803: 2011 (Method for measuring liquid viscosity)". The viscosity of each) of B5) was measured. In this way, the viscosity before storage was determined. Next, the ink was placed in a container, and the container was stored in an oven at a set temperature of 60 ° C. for one month. The container was removed from the oven and allowed to stand until the temperature inside the container returned to 25 ° C. Then, the viscosity of the ink at 25 ° C. was measured according to the method described in "JIS Z 8803: 2011 (Method for measuring viscosity of liquid)". In this way, the viscosity after storage was determined. Then, the rate of change in the viscosity of the ink (unit:%) before and after storage was determined using the following formula. The two "|" in the formula indicate that the calculated value is an absolute value.
Viscosity change rate = | 100 x [(viscosity after storage)-(viscosity before storage)] / (viscosity before storage) |

Next, the rate of change in the particle size of the particles contained in the ink before and after storage was measured. The particles contained in the ink were, for example, resin-containing particles and colorant particles. Use a particle size distribution measuring device (“LA-950” manufactured by HORIBA, Ltd.) to apply ink (more specifically, ink (IA1) and (IB1) to (IB5), respectively). The volume median diameter of the contained particles was determined. In this way, the volume median diameter of the particles contained in the ink before storage was determined. Next, the ink was placed in a container, and the container was stored in an oven at a set temperature of 60 ° C. for one month. The container was removed from the oven and allowed to stand until the temperature inside the container returned to 25 ° C. Then, using a particle size distribution measuring device (“LA-950” manufactured by HORIBA, Ltd.), the medium volume diameter of the particles contained in the ink was determined. In this way, the volume median diameter of the particles contained in the ink after storage was determined. Then, the rate of change (unit:%) of the volume median diameter of the particles contained in the ink before and after storage was determined using the following formula. The two "|" in the formula indicate that the calculated value is an absolute value.
Rate of change of medium volume diameter = | 100 x [(medium volume diameter after storage)-(medium volume diameter before storage)] / (medium volume diameter before storage) |

The storage stability of each ink was evaluated from the rate of change in the viscosity of the ink before and after storage and the rate of change in the volume median diameter of the particles contained in the ink before and after storage according to the following criteria. The evaluation results of storage stability are shown in Table 1. As the precipitation and aggregation of particles in the ink are caused during storage, the rate of change in the viscosity of the ink before and after storage and the rate of change in the volume median diameter of the particles contained in the ink before and after storage tend to increase. It is in.

(Evaluation criteria for storage stability)
Evaluation A (good): Both the rate of change in viscosity and the rate of change in medium volume diameter were 5% or less.
Evaluation B (normal): At least one of the rate of change in viscosity and the rate of change in medium volume diameter was more than 5% and 10% or less.
Evaluation C (defective): At least one of the rate of change in viscosity and the rate of change in medium volume diameter was more than 10%.

<Abrasion resistance>
The evaluation machine used to evaluate the abrasion resistance was an inkjet recording device (a prototype evaluation machine manufactured by Kyocera Document Solutions Co., Ltd.). As the recording head provided in the evaluation machine, a recording head for "Gel Jet Printer IPSiO GX5000" manufactured by Ricoh Corporation was used. This recording head had a resolution of 1200 × 1200 dpi and a droplet amount of 3.5 pL, and was a line-type recording head. This recording head was installed obliquely with respect to the transport direction of the recording medium.

Next, two sheets of art paper (“Tokuryo Art Double-sided N” manufactured by Mitsubishi Paper Mills Limited) were prepared. Hereinafter, one of the two art papers will be referred to as art paper A, and the other will be referred to as art paper B. First, the surface of art paper A was treated. Specifically, art paper A was fixed on the stage. While moving the stage at a speed of 500 mm / sec, the treatment liquid (“OK Top Coat” manufactured by Oji Paper Co., Ltd.) was applied to the art paper A on the stage using a wire bar coater. The coating amount was adjusted so that the coating amount of the treatment liquid was 1.7 g / m ² . The art paper A coated with the treatment liquid was dried at 50 ° C. for 2 seconds. The art paper B was not surface-treated.

Next, the recording head of the evaluation machine was filled with ink (more specifically, any of ink (IA1) and (IB1) to (IB5)). A solid image was formed on art paper A using an evaluation machine. Immediately after image formation, the art paper A was placed on a hot plate set at 60 ° C. so that the image formation surface was on top. Then, using a dryer, the image-forming surface of the art paper A was dried with warm air at 120 ° C. for 10 seconds.

Next, the art paper B was wrapped around a paperweight (weight: 470 g, size: 15 mm × 30 mm × 120 mm). A paperweight wrapped with art paper B was placed on the image forming surface of art paper A. The area (contact area) in which the art paper A and the art paper B contact was 150 mm ² . The image forming surface of art paper A was rubbed 10 times back and forth using a paperweight wrapped with art paper B. The art paper B was visually observed to confirm the color transfer from the image formed on the art paper A. Then, the scratch resistance of the ink was evaluated according to the following criteria. The evaluation results of abrasion resistance are shown in Table 1.

(Evaluation criteria for abrasion resistance)
Evaluation A (good): No color transfer from art paper A to art paper B was confirmed.
Evaluation B (normal): A slight color transfer was confirmed from art paper A to art paper B.
Evaluation C (defective): Clear color transfer was confirmed from art paper A to art paper B.

The meanings of each term in Table 1 are as follows. “Resin” refers to a resin contained in the resin-containing particles. "Polyester" indicates polyester resin PES. "Styrene acrylic" indicates styrene acrylic resin SA. "Area ratio R _1" represents an area ratio R ₁ of the first resin-containing particles 1. "Concentration C ₂₀ " indicates the intrinsic colorant concentration C ₂₀ .

As shown in Table 1, the ink (IA1) contained resin-containing particles containing at least a polyester resin. As determined from the first value of the area ratio R ₁ of the resin-containing particles 1 having a first feature, at least a portion of the resin-containing particles had a first feature. The area ratio _{R 1} of the first resin-containing particles 1 was 90% or more. The intrinsic colorant concentration C ₂₀ was 15% or more. As shown in Table 1, the evaluation of the image density, the evaluation of the storage stability, and the evaluation of the abrasion resistance using the ink (IA1) were all evaluated as A. From this, it was shown that if the ink (IA1) is used, an image having excellent storage stability, high image density, and excellent abrasion resistance can be formed on the recording medium.

The ink according to the present invention and the ink produced by the production method according to the present invention can be used, for example, in an inkjet printer.

1, 1A, 1B: 1st resin-containing particles 2: 2nd resin-containing particles 3: 3rd resin-containing particles 10: Resin-containing particles 20: Colorant particles 31: 1st liquid phase 32: 2nd liquid phase 33: 1st 3 liquid phase 100: ink OIL: oil phase W: aqueous phase

Claims (8)

It contains resin-containing particles containing at least a polyester resin and an aqueous medium,
At least a part of the resin-containing particles is the first resin-containing particles having the first characteristic.
The first feature is that each of the first resin-containing particles further contains at least one colorant particle in addition to the polyester resin, and each of the at least one colorant particle is the first resin-containing particle. It is a feature that is located inside the first resin-containing particles without being exposed on the surface of the first resin.
The area ratio of the first resin-containing particles to the area of the resin-containing particles in the cross-sectional image of the resin-containing particles is 90% or more.
An inkjet ink having an intrinsic colorant concentration represented by the following formula (1) of 15% or more.
_{C 20 = (M R / M} INK) × (A 1 / A 10) × (A 20 / A 1) × 100 ··· (1)
(In the above formula (1),
C ₂₀ represents the concentration of the intrinsic colorant.
M _INK represents the mass of the above-mentioned inkjet ink.
M _R represents the mass of the polyester resin contained in the inkjet ink,
A ₁₀ represents the area of the resin-containing particles in the cross-sectional image.
A ₁ represents the area of the first resin-containing particles in the cross-sectional image.
A ₂₀ represents the area of the colorant particles located inside the first resin-containing particles in the cross-sectional image. ) The inkjet ink according to claim 1, wherein the first resin-containing particles are dispersed without containing a dispersant. The ink for inkjet according to claim 1 or 2, wherein the polyester resin is a polymer of a bisphenol A ethylene oxide adduct, a bisphenol A propylene oxide adduct, terephthalic acid, and adipic acid. The inkjet ink according to any one of claims 1 to 3, wherein the colorant particles contain a water-insoluble colorant. The inkjet ink according to any one of claims 1 to 4, wherein the colorant particles contain carbon black. Resin-containing particles that form the resin-containing particles by adding an aqueous phase to an oil phase containing the polyester resin, the colorant particles, and a base, and inversion emulsifying the oil phase and the aqueous phase. The formation process and
The method for producing an ink for an inkjet according to any one of claims 1 to 5, further comprising a mixing step of mixing the resin-containing particles and the aqueous medium. The method for producing an ink for an inkjet according to claim 6, wherein the base is an amine substituted with 1 or more and 3 or less hydroxyalkyl groups. The method for producing an inkjet ink according to claim 6 or 7, wherein no dispersant is used.

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