JP2023084668A - Aqueous ink, ink cartridge, and inkjet recording method - Google Patents

Abstract

To provide an aqueous ink for inkjet capable of recording images excellent in chemical resistance and image clarity, and to provide an ink cartridge and an inkjet recording method using the aqueous ink.SOLUTION: An aqueous ink for inkjet contains coloring material particles and resin particles. The resin particle is formed from a crystalline polyester resin having a carboxylic acid group. A difference (D50C-D50R) between a cumulative 50% particle diameter (D50C) in a particle size distribution of volume reference of the coloring material particles, and a cumulative 50% particle diameter (D50R) in a particle size distribution of volume reference of the resin particles is 10 nm or more. An ink cartridge and an inkjet recording method using the aqueous ink are also provided.SELECTED DRAWING: None

Description

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

2. Description of the Related Art Conventionally, inkjet recording apparatuses have been widely used as compact printers for home use, and in recent years, they have come to be used in offices and commercial printing. In the field of office and commercial printing, it is required to be able to record images with higher scratch resistance than small printers for home use.

For example, a water-based inkjet ink containing polyester-based resin particles has been proposed as an ink that can improve the fixability of a coloring material to a recording medium (Patent Document 1).

JP 2014-125555 A

The present inventors examined the water-based ink proposed in Patent Document 1. As a result, it has been found that it is difficult to record an image having both chemical resistance, typified by alcohol rub resistance, and image clarity at the levels required in recent years. Chemical resistance (alcohol scratch resistance) means that even under severe conditions such as applying an external force to the area where a solvent capable of dissolving the image layer or recording medium adheres to the image, the image does not show solvent marks or come off. means the property that is unlikely to occur. In addition, image clarity refers to the property of being an index that indicates the sharpness of an image when projected onto an image. appear.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a water-based inkjet ink capable of recording images with excellent chemical resistance and image clarity. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using this water-based ink.

That is, according to the present invention, there is provided an aqueous ink for inkjet containing colorant particles and resin particles, wherein the resin particles are formed of a crystalline polyester resin having a carboxylic acid group, and the volume of the colorant particles is The difference (D _50C −D _50R ) between the cumulative 50% particle diameter (D _50C ) of the reference particle size distribution and the cumulative 50% particle diameter (D _50R ) of the volume-based particle size distribution of the resin particles is 10 nm or more. A water-based ink is provided characterized by:

According to the present invention, it is possible to provide a water-based inkjet ink capable of recording images with excellent chemical resistance and image clarity. Further, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method using this water-based ink.

1 is a cross-sectional view schematically showing one embodiment of an ink cartridge of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of main parts of the inkjet recording apparatus and (b) is a perspective view of a head cartridge;

The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing the salt." In addition, water-based ink for inkjet is sometimes simply referred to as "ink". Unless otherwise specified, physical property values are values at normal temperature (25° C.), normal pressure (1 atm=101,325 Pa), and normal humidity (50% relative humidity). In addition, "unit" means a unit structure corresponding to one monomer, unless otherwise specified. When describing "(meth)acrylic acid" and "(meth)acrylate", they represent "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

In order to improve the chemical resistance of images such as alcohol abrasion resistance, the present inventors have incorporated resin particles (hereinafter also simply referred to as "resin particles") formed of a crystalline polyester resin having a carboxylic acid group. We examined the ink to be used. A polyester resin having a carboxylic acid group is presumed to form a strong film on a recording medium because the molecular chains of the resin are entangled by hydrogen bonding between the carboxylic acid groups. Furthermore, it is thought that when an ink containing resin particles formed of a crystalline polyester resin is applied to a recording medium, the crystalline polyester resins can be brought closer to each other even among a plurality of resin particles, allowing the crystal structure to grow. be done. It is believed that due to the formed crystal structure, the polyester resin film is formed by closely adjoining the polyester resins, thereby suppressing the permeation of chemicals such as alcohol into the image layer and exhibiting chemical resistance.

However, as a result of investigation, it has been found that the use of resin particles formed of a crystalline polyester resin having carboxylic acid groups may not improve the chemical resistance of recorded images. In addition, it has been found that as the crystal structure of the crystalline polyester resin grows, the surface of the image tends to become uneven, and the image clarity of the image decreases. As a result of further studies, the present inventors found that by satisfying the following requirements (i) and (ii), the chemical resistance of the image can be improved without deteriorating the image clarity. reached.
(i) Colorant particles and resin particles formed of a crystalline polyester resin having a carboxylic acid group are contained.
(ii) the _difference (D _{50C −D 50R} ) is greater than or equal to 10 nm.

Both the colorant particles and the resin particles continue to undergo Brownian motion within the ink droplets. The motion range of a particle depends on its particle size, and the smaller the particle size, the wider the motion range. Therefore, the probability of existence of smaller particles increases in the vicinity of the interface of the ink droplet applied to the recording medium. When the above requirement (ii) is satisfied, after the liquid medium in the ink permeates or evaporates and decreases, there are more resin particles in the vicinity of the surface of the recorded image than in the interior of the image layer. It will be done. Since the resin particles are formed of a crystalline polyester resin having carboxylic acid groups, the colorant particles are covered by hydrogen bonding between carboxylic acid groups and growth of the crystal structure accompanying the proximity of the crystalline polyester resins. Thus, a crystalline film is formed near the surface of the image. Since the crystalline film is formed by densely arranging the molecules of the crystalline polyester resin, it is possible to suppress the permeation of chemicals such as alcohol into the image layer, thereby improving the chemical resistance of the image.

When "D _50C -D _50R " is less than 10 nm, the coloring material particles are unevenly present near the surface of the image, and chemicals such as alcohol easily penetrate into the image layer, and the chemical resistance of the image is not improved. . Moreover, the distribution of the resin particles is uneven in the vicinity of the surface of the image, and crystal growth tends to occur in portions where a large amount of resin particles are present. For this reason, the reflection state of light differs between the portion where many resin particles are present and the portion where many colorant particles are present, and the image clarity of the image is not improved.

<Ink>
The ink of the present invention is a water-based inkjet ink containing colorant particles and resin particles. The resin particles are made of a crystalline polyester resin having carboxylic acid groups. The components constituting the ink of the present invention and physical properties of the ink will be described in detail below.

(resin particles)
The ink contains resin particles (hereinafter sometimes simply referred to as “resin particles”) formed of a crystalline polyester resin having carboxylic acid groups. The resin particles exist in the ink in a state of being dispersed in the ink, that is, in the form of a resin emulsion. The resin particles are preferably dispersed by the action of the carboxylic acid groups of the resin particles (self-dispersion type) rather than dispersed by components such as surfactants and resins (emulsification type). The resin particles do not need to contain a coloring material. The ratio (% by mass) of the crystalline polyester resin in the resin forming the resin particles is preferably 50.00% by mass or more, more preferably 100.00% by mass, based on the total mass of the resin. preferable. That is, it is preferable that the resin particles are substantially formed only of the crystalline polyester resin. The content (% by mass) of the resin particles in the ink is preferably 0.01% by mass or more and 10.00% by mass or less, and 0.02% by mass or more and 5.00% by mass, based on the total mass of the ink. More preferably:

In the present invention, the term "resin particles" means a resin that exists in an undissolved state in the aqueous medium that constitutes the ink. More specifically, it means a resin that can exist in an aqueous medium in the form of particles whose particle diameter can be measured by a dynamic light scattering method. On the other hand, "water-soluble resin" means a resin dissolved in an aqueous medium that constitutes ink. More specifically, it means a resin that can exist in an aqueous medium without forming particles whose particle size can be measured by a dynamic light scattering method. When the resin particles are expressed as being paired with the "water-soluble resin", it becomes a "water-dispersible resin (water-insoluble resin)".

Whether or not a certain resin corresponds to "resin particles" can be determined according to the method shown below. First, a liquid containing a resin to be determined is diluted with pure water to prepare a sample having a resin content of about 1.0%. Then, when the particle diameter of the resin in the sample is measured by a dynamic light scattering method, if particles having a particle diameter are measured, the resin is a "resin particle" (i.e., a "water-dispersible resin" Yes). On the other hand, if particles having a particle size are not measured, the resin is determined not to be "resin particles" (that is, to be "water-soluble resin"). The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 10, measurement time: 120 seconds, shape: spherical, refractive index: 1.5, density: 1.0.

As the particle size distribution analyzer, a particle size analyzer using a dynamic light scattering method (for example, trade name “Nanotrack WAVE II-Q” manufactured by Microtrack Bell) can be used. Of course, the particle size distribution measuring device and measurement conditions to be used are not limited to those described above.

For resins other than crystalline polyester resins (other resins such as resin dispersants), whether or not they are resin particles is defined in the same manner as above. Other resins can also be determined whether they are resin particles or water-soluble resins by the same method as described above. However, in order to make the judgment simply, for other resins, a liquid containing a resin neutralized with an alkali equivalent to its acid value (sodium hydroxide, potassium hydroxide, etc.) (resin content: 10% by mass) Alternatively, it may be determined using a liquid diluted appropriately.

[Crystalline polyester resin]
The crystalline polyester resin forming the resin particles has carboxylic acid groups. That is, a crystalline polyester resin is a resin having a unit having a carboxylic acid group. An unreacted hydroxy group or carboxylic acid group exists at the terminal of the crystalline polyester resin. When the terminal of the crystalline polyester resin does not have a carboxylic acid group, the carboxylic acid group exists in a portion other than the terminal. By utilizing the interaction between the carboxylic acid groups of the crystalline polyester resin, the chemical resistance of the image to be recorded can be improved.

Polyester resins can be broadly classified into crystalline polyester resins and amorphous polyester resins. A crystalline polyester resin is a polyester resin that has a melting point. The melting point of the polyester resin means the melting peak temperature (endothermic peak temperature due to melting) measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121:1987. In the present invention, it is determined that a melting peak exists (that is, the resin is a crystalline polyester resin) when the endothermic value obtained from the integrated value of the peak is 20 J/g or more.

A polyester resin is usually composed of a unit derived from a polyhydric alcohol and a unit derived from a polycarboxylic acid. A structure containing an ester bond (—COO—) composed of a unit derived from a polyhydric alcohol and a unit derived from a polycarboxylic acid is also referred to as an “ester unit”.

[Polyhydric alcohol]
Dihydric to tetrahydric polyhydric alcohols can be mentioned as the polyhydric alcohol that becomes a unit derived from the polyhydric alcohol that constitutes the crystalline polyester resin by reaction. Examples of polyhydric alcohols include polyhydric alcohols having an aliphatic group, polyhydric alcohols having an aromatic group, and sugar alcohols. Polyhydric alcohols include ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzene diols, dihydric alcohols such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane and trimethylolpropane; tetrahydric alcohols such as pentaerythritol; can be mentioned. Oligomers (low-molecular-weight polymers having a molecular weight of 1,000 or less) can also be used as polyhydric alcohols.

As the polyhydric alcohol, it is preferable to use one having a saturated hydrocarbon portion. A resin particle formed from a polyester resin synthesized using a polyhydric alcohol whose hydrocarbon portion is unsaturated (sometimes referred to as an unsaturated polyhydric alcohol) has a high refractive index and poor image clarity. may decrease slightly. The ratio of the units derived from the unsaturated polyhydric alcohol to the units derived from the polyhydric alcohol constituting the crystalline polyester resin is preferably 50 mol% or less, preferably 10 mol% or less. , 0 mol %.

As the polyhydric alcohol, a polyhydric alcohol having an aliphatic group can be preferably used. Among them, those having 4 or more carbon atoms are preferable, those having 6 or more carbon atoms are more preferable, those having 12 or less carbon atoms are preferable, and those having 8 or less carbon atoms are more preferable. Moreover, it is preferable that the hydrocarbon moiety is linear. Moreover, it is preferable to have hydroxyl groups at both ends of the hydrocarbon chain. It is preferable to use a dihydric or trihydric polyhydric alcohol because the weight average molecular weight of the polyester resin can be easily adjusted. In particular, it is preferable to use a dihydric polyhydric alcohol. Among them, it is preferable to use a polyhydric alcohol having a linear aliphatic group, since the crystallinity of the crystalline polyester resin is further improved and the chemical resistance of the image is further enhanced. Two or more kinds of polyhydric alcohols including polyhydric alcohols having linear aliphatic groups can also be used in combination. Specifically, the ratio of the units derived from the polyhydric alcohol having an aliphatic group as described above to the units derived from the polyhydric alcohol having an aliphatic group, which constitute the crystalline polyester resin, is 50. It is preferably mol % or more. Further, it is more preferable that the proportion of the above units is 100 mol %.

[Polyvalent carboxylic acid]
Divalent to tetravalent polyvalent carboxylic acids can be mentioned as the polyvalent carboxylic acid that becomes a unit derived from the polyvalent carboxylic acid that constitutes the polyester resin by reaction. Examples of the structure of the polycarboxylic acid include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, and nitrogen-containing polycarboxylic acids. Examples of polyvalent carboxylic acids include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; tetravalent acids such as ethylenediaminetetraacetic acid. Carboxylic acids etc. can be mentioned. Oligomers (low-molecular-weight polymers having a molecular weight of 1,000 or less) can also be used as polyvalent carboxylic acids.

As the polyvalent carboxylic acid, it is preferable to use one having a saturated hydrocarbon portion. A resin particle formed from a polyester resin synthesized using a polyvalent carboxylic acid having an unsaturated hydrocarbon portion (sometimes referred to as an unsaturated polyvalent carboxylic acid) has a large refractive index, resulting in poor image quality. Image clarity may be slightly reduced. The ratio of the units derived from the unsaturated polycarboxylic acid to the units derived from the polycarboxylic acid constituting the crystalline polyester resin is preferably 50 mol% or less, and 10 mol% or less. is preferred, and 0 mol % is particularly preferred.

As polyvalent carboxylic acid, polyvalent carboxylic acid having an aliphatic group can be preferably used. Among them, those having 4 or more carbon atoms are preferable, those having 6 or more carbon atoms are more preferable, those having 12 or less carbon atoms are preferable, and those having 8 or less carbon atoms are more preferable. This carbon number does not include the carbon atoms that constitute the carboxylic acid group. Also, it is preferable to use one having a saturated hydrocarbon portion. Moreover, it is preferable that the hydrocarbon moiety is linear. Moreover, those having carboxylic acid groups at both ends of the hydrocarbon chain are preferred. It is preferable to use divalent or trivalent polyvalent carboxylic acid because it is easy to adjust the weight average molecular weight and acid value of the polyester resin. In particular, it is preferable to use a divalent polyvalent carboxylic acid. Among them, it is preferable to use a polyvalent carboxylic acid having a linear aliphatic group, since the crystallinity of the crystalline polyester resin is further improved and the chemical resistance of the image is further enhanced. Two or more polyvalent carboxylic acids including a polyvalent carboxylic acid having a linear aliphatic group can also be used in combination. Specifically, the ratio of units derived from a polycarboxylic acid having an aliphatic group as described above to the units derived from a polycarboxylic acid having an aliphatic group, which constitutes the crystalline polyester resin, is It is preferably 50 mol % or more. Further, it is more preferable that the proportion of the above units is 100 mol %.

[Combination of Polyhydric Alcohol and Polycarboxylic Acid]
Composed of a diol-derived unit having a hydroxy group at both ends of a straight-chain saturated hydrocarbon group and a dicarboxylic acid-derived unit having a carboxylic acid group at each end of the straight-chain saturated hydrocarbon group polyester resins are preferred. In such a polyester resin, the hydrocarbon groups of the diol and the dicarboxylic acid are likely to interact with each other, and the crystallinity is likely to be enhanced. The ratio of the total of the units derived from the diol and the units derived from the polycarboxylic acid to the total of the units derived from the polyhydric alcohol and the units derived from the dicarboxylic acid, which constitute the crystalline polyester resin, is as follows. It is preferable to That is, it is preferably 50 mol % or more, more preferably 70 mol % or more, and particularly preferably 100 mol %. The resin particles formed of the crystalline polyester resin having a high proportion as described above suppress the decrease in crystallinity due to hydration in the aqueous medium that constitutes the aqueous ink, and further improve the chemical resistance of the image to be recorded. can be done.

[Physical properties of resin particles]
[Melting point of crystalline polyester resin]
The melting point of the crystalline polyester resin is preferably 50°C or higher and 140°C or lower. If the melting point is lower than 50° C., the resin particles may not remain in the vicinity of the surface of the image and flow, and may flow down into the gaps between the coloring materials, making it difficult to form a crystalline film in the vicinity of the surface of the image. improvement effect may decrease. On the other hand, if the melting point is higher than 140° C., crystal growth is difficult even if the resin particles are close to each other, and the shape of the resin particles is maintained as it is, light is easily scattered, and the effect of improving image clarity is reduced. There is The "melting peak temperature" obtained by differential scanning calorimetry (DSC) according to JIS K 7121:1987 is taken as the melting point of the crystalline polyester resin. The melting point of the crystalline polyester resin is preferably from 50°C to 100°C.

[Acid value of crystalline polyester resin]
The acid value of the crystalline polyester resin is preferably 10 mgKOH/g or more and 50 mgKOH/g or less. When the acid value is less than 10 mgKOH/g, the amount of carboxylic acid groups is slightly small, so that a plurality of resin particles tend to aggregate, and the aggregated portions tend to scatter light, reducing the effect of improving image clarity. sometimes. On the other hand, if the acid value is more than 50 mgKOH/g, the hydrophilicity of the resin particles may be slightly increased due to the slightly large amount of carboxylic acid groups. As a result, the amount of carboxylic acid groups present in the vicinity of the surface of the image also increases, slowing the penetration or evaporation of the liquid medium in the ink, causing unevenness in the image and possibly reducing the effect of improving image clarity. . More preferably, the acid value of the crystalline polyester resin forming the resin particles is 15 mgKOH/g or more and 25 mgKOH/g or less. The acid value of the crystalline polyester resin can be measured by neutralization titration using a potential difference.

The acid value of the crystalline polyester resin can be adjusted by adjusting the ratio of the raw material polyhydric alcohol and polyhydric carboxylic acid. For example, when synthesizing a crystalline polyester resin using a diol and a dicarboxylic acid as raw materials, if the diol and the dicarboxylic acid are used in equimolar amounts, one end of the molecular chain of the synthesized crystalline polyester resin is a hydroxy group, and the other end is a hydroxyl group. is likely to be a carboxylic acid group. The acid value can be adjusted by changing the ratio of the amount (y mol) of the carboxylic acid group of the polyhydric carboxylic acid to the amount (x mol) of the hydroxy group of the polyhydric alcohol. That is, even if the amount of polyhydric alcohol (x mol) is greater than the amount of polycarboxylic acid (y mol) (y/x<1), it is possible to synthesize a crystalline polyester having an acid group. . Since the acid value can be easily adjusted, y/x is preferably 0.8 times or more and preferably 1.4 times or less.

[Weight Average Molecular Weight of Crystalline Polyester Resin]
The weight average molecular weight of the crystalline polyester resin is preferably 10,000 or more and 70,000 or less, more preferably 15,000 or more and 30,000 or less. The weight average molecular weight of the crystalline polyester resin is a polystyrene-equivalent value measured by gel permeation chromatography.

[Particle size of resin particles]
The cumulative 50% particle diameter (D _50R ) of the volume-based particle size distribution of the resin particles is preferably 5 nm or more and 30 nm or less. If the _D50R is less than 5 nm, the thickness of the crystalline film formed in the vicinity of the surface of the image by the resin particles becomes thin, and chemicals such as alcohol may easily permeate the image layer, resulting in poor image quality. The effect of improving chemical resistance may decrease. On the other hand, if the D _50R is more than 30 nm, the resin particles may overlap each other near the surface of the image, and apparently large particles may be formed due to crystal growth, which facilitates light scattering and improves image clarity. may decrease. The cumulative 50% particle diameter (D _50R ) of the volume-based particle size distribution of the resin particles is more preferably 15 nm or more and 25 nm or less. In addition, the cumulative 90% particle diameter (D _90R ) of the volume-based particle size distribution of the resin particles is preferably 10 nm or more and 60 nm or less.

The cumulative 50% particle diameter (D _50R ) of the volume-based particle size distribution of the resin particles is a ratio of the cumulative 90% particle diameter (D _90R ) of the volume-based particle size distribution of the resin particles, and is 0.6 times or more. is preferred. If the above ratio is less than 0.6 times, coarse particles tend to exist, light tends to scatter, and the effect of improving image clarity may decrease. The above ratio is preferably 0.8 times or less.

The cumulative 50% particle size (D _50R ) and the cumulative 90% particle size (D _90R ) of the volume-based particle size distribution of the resin particles are the small particle size based on the total volume of the measured particles in the particle size integration curve. Means the diameter of the particles that, when integrated from the side, are 50% and 90%, respectively. Both the D _50R and D _90R of the resin particles can be measured by the dynamic light scattering method under the same conditions as the method for judging "whether or not they correspond to the resin particles" described above.

[Method for producing resin particles]
Resin particles can be produced, for example, by granulating a synthesized crystalline polyester resin. Also, the crystalline polyester resin can be synthesized by reacting (esterification reaction) a polyhydric alcohol and a polycarboxylic acid. It is preferable to use an esterification catalyst during the esterification reaction. Esterification catalysts can include metal compounds such as tin compounds, titanium compounds, antimony compounds, and germanium compounds. The amount of the esterification catalyst is preferably 100 ppm or more and 5000 ppm or less based on the total amount of the polyhydric alcohol and the polyhydric carboxylic acid. If necessary, either a polyhydric alcohol or a polyhydric carboxylic acid is added to the reaction system, and a transesterification reaction is performed to break a part of the ester bond, thereby adjusting the molecular weight of the resulting crystalline polyester resin. be able to.

During the esterification reaction, the amount of raw materials used is adjusted so that the number of moles of the carboxylic acid group of the polyhydric carboxylic acid is greater than the number of moles of the hydroxy group of the polyhydric alcohol, thereby removing the carboxylic acid group. It is possible to obtain a crystalline polyester resin having A crystalline polyester resin having carboxylic acid groups can also be obtained by using a polyvalent carboxylic acid in the transesterification reaction.

The esterification reaction is preferably carried out under an inert gas atmosphere such as nitrogen gas. The reaction temperature during the esterification reaction is preferably 180° C. or higher and 260° C. or lower. The reaction time during the esterification reaction is preferably from 1 hour to 5 hours.

During the esterification reaction, the pressure in the reaction system may be reduced to discharge water produced by the reaction out of the system to promote the esterification (dehydration condensation) reaction. Under reduced pressure, the esterification reaction is followed by reaction under an inert gas atmosphere such as nitrogen gas. The reaction temperature under reduced pressure is preferably 220° C. or higher and 280° C. or lower. The reaction time under reduced pressure is preferably 0.5 hours or more and 5 hours or less, more preferably 1 hour or more and 3 hours or less. The degree of pressure reduction (degree of vacuum) is preferably 1 Pa or more and 130 Pa or less, more preferably 1 Pa or more and 50 Pa or less. However, if the degree of pressure reduction is too low, the reaction efficiency will decrease and the weight-average molecular weight of the resulting crystalline polyester resin will decrease. It is preferable to reduce the pressure gradually from the atmospheric pressure (101,325 Pa) to 130 Pa or less over a period of about 0.1 to 3 hours.

In the transesterification reaction, either a polyhydric alcohol or a polycarboxylic acid is added to the reaction system, and some of the ester bonds are cut to adjust the molecular weight of the resulting crystalline polyester resin, or mainly the molecular chain. This is done in order to have a carboxylic acid group present at the end of the From the viewpoint of efficiently obtaining a crystalline polyester resin having a carboxylic acid group, it is preferable to carry out the transesterification reaction using a polyvalent carboxylic acid.

It is preferable to use the synthesized crystalline polyester resin in the next step of granulating it after making it into an appropriate form by pressurization and pulverization. Since the resin particles formed of the crystalline polyester resin are used as a constituent component of the water-based ink, they are preferably dispersed in a water-based liquid medium to form a dispersion. The aqueous liquid medium contains water such as deionized water, ion-exchanged water, and distilled water as a main component, and may contain a water-soluble organic solvent if necessary. The content (% by mass) of water in the aqueous liquid medium is preferably 50% by mass or more, and it is also preferred to use a liquid medium (that is, water) that does not substantially contain a water-soluble organic solvent.

Examples of methods for forming resin particles by granulating a crystalline polyester resin include a dispersion method and a phase inversion (emulsification) method. Dispersion methods include methods (1) and (2) shown below.
(1) A method in which a solution obtained by dissolving a crystalline polyester resin in an organic solvent is added to an aqueous liquid medium to disperse the crystalline polyester resin. (2) A crystalline polyester resin is added to an organic solvent, and further A method of adding and mixing an aqueous liquid medium to disperse the crystalline polyester resin.

As a phase inversion (emulsification) method, an aqueous liquid medium is added to a solution obtained by dissolving a polyester resin in an organic solvent, and the polyester resin is precipitated in the form of particles during the phase inversion from the solvent system to the aqueous system. There are methods. In any method, it is preferable to adjust the particle size of the obtained resin particles by using a known dispersing machine to form particles while applying an appropriate shearing force.

It is preferable to produce resin particles by a phase inversion (emulsification) method because the particle size of the resulting resin particles can be adjusted with high accuracy. A method for producing resin particles by a phase inversion (emulsification) method will be described below.

First, a crystalline polyester resin is dissolved in an organic solvent to obtain a resin solution. Examples of organic solvents include ethers such as tetrahydrofuran and dibutyl ether; ketones such as acetone and methyl ethyl ketone; alcohols such as isopropanol; If only an organic solvent (such as methyl ethyl ketone) that has low water solubility and is difficult to mix with water at an arbitrary ratio is used, it may be difficult to adjust the particle size with high accuracy. Therefore, as the organic solvent, it is preferable to use ethers such as tetrahydrofuran, which are miscible with water at any ratio. Ethers such as tetrahydrofuran are also preferable in terms of excellent solubility of the crystalline polyester resin.

In order to dissolve the crystalline polyester resin uniformly, it is preferable to dissolve the crystalline polyester resin in the organic solvent while heating. However, it is preferable to heat to a temperature lower than the boiling point of the organic solvent to be dissolved. If the concentration of the crystalline polyester resin in the resin solution is too low, it may become difficult to control the particle size distribution. Therefore, the content (% by mass) of the crystalline polyester resin in the resin solution is preferably 10.0% by mass or more and 60.0% by mass or less, and more preferably 20.0% by mass or more and 40.0% by mass or less. It is more preferable that

Next, an aqueous liquid medium is gradually added to the obtained resin solution to precipitate resin particles. It is preferable to add a base before or during the addition of the aqueous liquid medium, since the dispersed state of the resin particles can be stably maintained. As the base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and the like can be used, and both are preferably added in the form of an aqueous solution. The amount of the base to be added can be controlled by the neutralization rate (mol %) based on the acid value corresponding to all the carboxylic acid groups in the crystalline polyester resin. The neutralization rate is preferably 70 mol % or more and 100 mol % or less. As the amount of the aqueous liquid medium added increases, the initially transparent resin solution becomes cloudy and emulsified to form resin particles. By adjusting the content of the crystalline polyester resin in the resin solution, the neutralization rate, the shearing force applied during dispersion, and the like, the particle size and particle size distribution of the resulting resin particles can be controlled.

The obtained emulsion is depressurized to distill off the organic solvent, and if necessary, filtered through a filter (stainless mesh) having an appropriate pore size to remove coarse particles. Then, by adding water to adjust the content of resin particles, a liquid containing resin particles (aqueous dispersion of resin particles) can be prepared. The water used for adjusting the content is preferably deionized water, ion-exchanged water, or distilled water. From the viewpoint of ink productivity, the resin particle content (% by mass) in the liquid containing resin particles is preferably 5.0% by mass or more and 30.0% by mass or less, and is preferably 15.0% by mass or more. It is more preferably 30.0% by mass or less.

[Composition analysis of resin particles]
Whether the resin constituting the resin particles is a crystalline polyester resin can be determined, for example, by the following method. First, a sample is prepared by dissolving the resin particles in an organic solvent capable of dissolving the resin particles, such as tetrahydrofuran. The resin particles to be used may be in the form of an aqueous dispersion or in a dried form. The prepared samples are analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), or the like. This makes it possible to know the types and proportions of the units (monomers) that constitute the resin. Also, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that constitute the resin. When an insoluble matter that does not dissolve in an organic solvent is generated during sample preparation, the resulting insoluble matter can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that constitute the resin. Further, by confirming that the dried sample has a melting peak temperature (melting point) by performing differential scanning calorimetry (DSC), it can be determined that the sample is crystalline.

(colorant particles)
Colorant particles, which are particulate colorants, are used as the colorant of the ink. A colorant such as a water-soluble dye that can be dissolved in ink as a molecule is much smaller in size than resin particles. Therefore, non-particulate coloring materials have a higher probability of being present near the interface of ink droplets, and more coloring materials are present near the surface of an image to be recorded than inside the image layer. Non-particulate coloring materials tend to dissolve in chemicals such as alcohol, and cannot improve the chemical resistance of images.

The colorant particles are colorant particles using a pigment or a dye, and are contained in the ink in a dispersed state as particles having a particle size. The content (% by mass) of the colorant particles in the ink is preferably 0.1% by mass or more and 15.0% by mass or less based on the total mass of the ink, and is preferably 1.0% by mass or more and 10.0% by mass. More preferably:

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; organic pigments such as pigments;

As the colorant particles using a pigment, a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment in which a hydrophilic group is bonded to the particle surface of the pigment, or the like can be used. Moreover, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, or a microcapsule pigment in which the particle surface of the pigment is coated with a resin or the like can be used. Among them, it is preferable to use a self-dispersed pigment or a resin-dispersed pigment in which a resin as a dispersant is physically adsorbed on the particle surface of the pigment instead of a resin-bonded pigment or a microcapsule pigment, and the resin-dispersed pigment is preferably used. is more preferred. As a dispersant for the resin-dispersed pigment, it is more preferable to use a water-soluble resin rather than a water-insoluble resin.

Examples of self-dispersing pigments include pigments in which an anionic group is bonded directly or via another atomic group to the particle surface of the pigment. Examples of anionic groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups. Counter ions for anionic groups include cations such as hydrogen atoms, alkali metals, ammonium, and organic ammonium. The other atomic group is a group having a spacer function between the pigment particle surface and the ionic group, and preferably has a molecular weight of 1,000 or less. Other atomic groups include an alkylene group having about 1 to 6 carbon atoms, an arylene group such as a phenylene group and a naphthylene group, an ester group, an imino group, an amide group, a sulfonyl group, an ether group, and the like. Moreover, the group which combined these groups may be sufficient.

As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use a resin capable of dispersing the pigment in the aqueous medium by the action of an anionic group. Examples of resin dispersants include acrylic resins and urethane resins. Among them, acrylic resins are preferable, and acrylic resins having a hydrophilic unit and a hydrophobic unit as constituent units are more preferable. In particular, an acrylic resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from a monomer having an aliphatic group or an aromatic group is preferred.

A hydrophilic unit is a unit having a hydrophilic group such as an anionic group, a hydroxy group, or an ethylene oxide group. A hydrophilic unit can be formed, for example, by polymerizing a monomer having a hydrophilic group. Specific examples of monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid; anionic monomers such as anhydrides and salts of these acidic monomers; 2-hydroxyethyl (meth)acrylate hydroxy group-containing monomers such as methoxypolyethylene glycol (meth)acrylate and other ethylene oxide group-containing monomers; and the like. Examples of cations constituting salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium and organic ammonium.

A hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group, a hydroxy group, or an ethylene oxide group. A hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group. Specific examples of hydrophobic monomers include monomers having aromatic groups such as styrene, α-methylstyrene, and benzyl (meth)acrylate; ethyl (meth)acrylate, methyl (meth)acrylate, (iso-)propyl (meth) Monomers having an aliphatic group such as acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate;

Specific examples of dyes include oil-soluble dyes, disperse dyes, reactive dyes, direct dyes, acid dyes, and basic dyes. Among them, oil-soluble dyes, disperse dyes, and basic dyes are preferred. A dye insoluble in an aqueous medium that constitutes a water-based ink can be suitably used as colorant particles using a dye by dispersing it with a resin dispersant or dyeing resin particles. Oil-soluble dyes, disperse dyes, and basic dyes are also preferable as such dyes. When a dye is used as the coloring material, it is preferable to use resin particles dyed with the dye.

The resin dispersant for dispersing the dye in the aqueous medium can be selected from the same resin dispersants as the pigment dispersant. The resin particles dyed with the dye are prepared by dissolving the resin and the dye in an organic solvent, emulsifying the mixture with water or the like, and then removing the organic solvent to obtain the resin particles dyed with the dye. can be obtained as an aqueous dispersion of Alternatively, a dye is added to an aqueous dispersion of resin particles obtained by emulsion polymerization of various monomers, and the mixture is heated and, if necessary, pressurized to obtain an aqueous dispersion of resin particles dyed with the dye. can also

Whether or not the resin particles are dyed with a dye can be determined according to the method described below. Here, a method of extracting and analyzing resin particles from ink will be described, but resin particles extracted from an aqueous dispersion or the like can also be analyzed in the same manner. First, the resin particles are separated from the ink containing the resin particles by density gradient centrifugation. Density gradient centrifugation includes a density gradient sedimentation velocity method and a density gradient sedimentation equilibrium method. In the density gradient sedimentation velocity method, resin particles can be separated and extracted according to the difference in sedimentation coefficient. In the density gradient sedimentation equilibrium method, resin particles can be separated and extracted according to density differences. After drying the resulting dispersion of resin particles, a solution is prepared using an organic solvent capable of dissolving a dye, an additive, and a resin. Components in a prepared solution are separated by preparative gel permeation chromatography (GPC), preparative high performance liquid chromatography (HPLC), column chromatography, or the like, and dyes, additives, resins, and the like are separated. The separated dyes, additives, and resins are analyzed by analytical methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). This makes it possible to know the types of dyes and additives, and the types and ratios of constituent units (monomers) of the resin. Furthermore, by analyzing the fractionated resin by pyrolysis gas chromatography, the monomers generated by depolymerization can be directly detected.

[Physical properties of colorant particles]
[Particle size of colorant particles]
The cumulative 50% particle size (D _50C ) of the volume-based particle size distribution of the colorant particles is preferably 40 nm or more and 150 nm or less. If the _D50C is less than 40 nm, the colorant particles arranged near the surface of the image may be biased, and the chemical may easily permeate the image layer, and the effect of improving the chemical resistance may decrease. . On the other hand, if the _D50C is more than 150 nm, unevenness derived from the colorant particles in the vicinity of the surface of the image may be slightly conspicuous, light may be easily scattered, and the image clarity improvement effect of the image may be reduced. The cumulative 50% particle size (D _50C ) of the volume-based particle size distribution of the colorant particles is preferably 80 nm or more and 120 nm or less. D _50C of the colorant particles is determined by using a sample having a colorant particle content of about 1.0%, and applying dynamic light under the same conditions as the method for determining whether or not it corresponds to the resin particles described above. It can be measured by a scattering method.

[Difference in Particle Size Between Colorant Particles and Resin Particles]
The difference (D _50C −D _50R ) between the cumulative 50% particle diameter (D 50C ) of the volume-based particle size distribution of the colorant particles and the cumulative 50% particle diameter (D _50R ) of the volume-based particle size distribution of the resin _particles is , 10 nm or more. By setting “D _50C -D _50R ” to 10 nm or more, the chemical resistance of the image can be improved without lowering the image clarity. “D _50C -D _50R ” is preferably 150 nm or less, more preferably 100 nm or less. When "D _50C -D _50R " is more than 150 nm, the resin particles tend to enter the gaps between the colorant particles formed by the ink applied to the recording medium, and the resin particles are less likely to be arranged near the surface of the image. Sometimes. As a result, the chemical easily permeates into the image layer, and the effect of improving the chemical resistance of the image may be reduced. In addition, the effect of improving image clarity may also decrease.

[Mass ratio of colorant particles and resin particles]
The content (% by mass) of the colorant particles in the ink is preferably 1.0 to 100.0 times the content (% by mass) of the resin particles as a mass ratio. If the above mass ratio is less than 1.0 times, the content of the resin particles is rather large, and the resin particles may tend to hinder the fixing of the coloring material particles to the recording medium. Therefore, when stress is applied to the image together with the chemical, the image may easily peel off from the recording medium. On the other hand, when the mass ratio is more than 100.0 times, the content of the resin particles is slightly small, so the amount of the resin particles arranged in the vicinity of the surface of the image may be slightly small. Therefore, the chemical easily permeates into the image layer, and the effect of improving the chemical resistance of the image may be reduced.

(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 water. The water content (% by mass) 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 one that can be used for inkjet ink, 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. If the content of the water-soluble organic solvent is outside the above range, the reliability of the water-based ink for inkjet, such as anti-sticking property, may deteriorate.

(other ingredients)
In addition to the components described above, the ink may optionally contain water-soluble organic compounds that are solid at 25° C., such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. may contain. Furthermore, various additives such as surfactants, pH adjusters, antifoaming agents, rust inhibitors, preservatives, antifungal agents, antioxidants, anti-reduction agents, and chelating agents may be added to the ink as necessary. agents may be included. When a surfactant is used, the content (% by mass) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink. More preferably, it is at least 2.0% by mass and no more than 2.0% by mass.

The ink may further contain other resins in addition to the resin particles formed of the crystalline polyester resin. Other resins include resin dispersants for dispersing pigments. As other resins, it is preferable to use water-soluble resins. Forms of the water-soluble resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Examples of water-soluble resins include acrylic resins, urethane resins, and olefin resins. Among them, acrylic resins and urethane resins are preferable.

(Physical properties of ink)
The ink of the present invention is a water-based ink suitable for inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the 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 1.0 mPa·s. It is particularly preferable that the viscosity is 3.0 mPa·s or more. 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 30 mN/m or more and 50 mN/m or less. is particularly preferred. The pH of the ink at 25° C. is preferably from 5.0 to 10.0, more preferably from 7.0 to 9.5.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink containing portion that contains the ink. The ink contained in this ink container is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing one embodiment of the ink cartridge of the present invention. As shown in FIG. 1, the bottom surface of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The interior of the ink cartridge serves as an ink containing portion for containing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16 which communicate with each other through a communication port 18 . Also, the absorber storage chamber 16 communicates with the ink supply port 12 . The ink containing chamber 14 contains liquid ink 20 , and the absorber containing chamber 16 contains absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may have a configuration in which the absorber retains the total amount of the stored ink without having an ink storage chamber for storing liquid ink. Further, the ink containing portion may have a form in which the ink is contained in a liquid state without having an absorber. Further, the ink cartridge may be configured to have an ink containing portion and a recording head.

<Inkjet recording method>
The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the above-described water-based ink of the present invention from an inkjet recording head. Methods for ejecting ink include a method in which mechanical energy is applied to ink and a method in which thermal energy is applied to ink. In the present invention, it is particularly preferable to adopt a method of applying thermal energy to the ink to eject the ink. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

FIG. 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 a head cartridge. is. The inkjet recording apparatus is provided with transport means (not shown) for transporting 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 has recording heads 38 and 40, and is constructed so that an ink cartridge 42 is set therein. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32 . An image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by conveying means (not shown).

Any recording medium may be used as a target recording medium using the ink of the present invention. Ink-absorbing recording media such as recording media without a coat layer such as plain paper and recording media with a coat layer such as glossy paper and matte paper can be used. In addition, recording media such as printed paper, coated paper, resin sheets, and resin films with low or no ink absorbability can be used. The ink of the present invention can be suitably used for recording images by directly applying ink to such recording media.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as the gist thereof is not exceeded. "Parts" and "%" regarding component amounts are based on mass unless otherwise specified.

<Method for measuring physical properties>
(Melting point of crystalline polyester resin)
Resin particles formed of a crystalline polyester resin were precipitated using a 1.0 mol/L hydrochloric acid aqueous solution, thoroughly washed with water, and dried at 60° C. to obtain a measurement sample. Using a differential scanning calorimeter (trade name “Q1000”, manufactured by TA Instruments), the melting peak temperature measured according to JIS K 7121:1987 was defined as “melting point”. When the endothermic value obtained from the integrated value of the peak was 20 J/g or more, it was judged that a melting peak was obtained, and this melting peak temperature was taken as the "melting point".

(Acid value of crystalline polyester resin)
Resin particles formed of a crystalline polyester resin were precipitated using a 1.0 mol/L hydrochloric acid aqueous solution, thoroughly washed with water, and then dried at 60°C. After adding and dissolving the obtained dried product in 50 mL of tetrahydrofuran at 50° C., 5 mL of water was added and the solution was cooled to room temperature to obtain a measurement sample. The resulting measurement sample was subjected to neutralization titration to measure the acid value of the polyester resin. For the neutralization titration, an automatic potentiometric titrator (trade name: "AT510", manufactured by Kyoto Electronics Industry) equipped with a composite glass electrode (trade name: "C-171", manufactured by Kyoto Electronics Industry) was used. A 0.5 mol/L potassium hydroxide ethanol solution was used as a titration reagent.

(Weight average molecular weight of crystalline polyester resin)
Resin particles formed of a crystalline polyester resin were precipitated using a 1.0 mol/L hydrochloric acid aqueous solution, thoroughly washed with water, and then dried at 60°C. The resulting dried product was added to tetrahydrofuran, and the crystalline polyester resin was dissolved at 25° C. for 24 hours, followed by filtration through a membrane filter to obtain a measurement sample. The resin content in the measurement sample was adjusted to about 0.3%. The prepared measurement sample was analyzed by gel permeation chromatography under the conditions shown below, and the weight average molecular weight was calculated using a molecular weight calibration curve created using a standard polystyrene resin. As the standard polystyrene resin, the product name "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F- 2, F-1, A-5000, A-2500, A-1000, A-500” (manufactured by Tosoh).
・ HPLC device: trade name “2695 Separations Module” (manufactured by Waters)
・ Differential refractive index (RI) detector: trade name “2414 detector” (manufactured by Waters)
・Column: Quadruple column with the trade name “GPC KF-806M” (manufactured by Showa Denko)
・Eluent: tetrahydrofuran ・Flow rate: 1.0 mL/min
・Oven temperature: 40℃
・Sample injection volume: 100 μL

(Determination of whether the sample is particles, particle size)
A sample-containing liquid was diluted with pure water to obtain a measurement sample in which the sample content was adjusted to about 1.0%. Then, the particle diameters (D _50R , D _90R ) of the resin particles and the particle diameter (D _50C ) of the colorant particles in the measurement sample were measured using a particle size measuring device. The measurement conditions at this time are shown below. As a particle size measuring device, a particle size distribution meter (trade name “Nanotrack WAVE II-Q”, manufactured by Microtrack Bell) using a dynamic light scattering method was used. By the above method, when particles having a particle size are measured, the sample is determined to be "particles"("aqueousdispersion"), and when particles having a particle size are not measured, the The sample was judged not to be "particulate" (it was an "aqueous solution").
[Measurement condition]
SetZero: 30 seconds Number of measurements: 10 Measurement time: 120 seconds Shape: spherical Refractive index: 1.5
Density: 1.0

<Synthesis of polyester resin>
A reaction vessel equipped with a stirrer, condenser, and thermometer was provided. A mixture of a polyhydric alcohol and a polyhydric carboxylic acid of the type and amount (unit: part) shown in Table 1 was put into this reaction vessel. Furthermore, after adding tetra-n-butyl titanate in an amount of 200 ppm based on the total amount of polyhydric alcohol and polycarboxylic acid as a catalyst, the temperature was raised to 240 ° C. over 4 hours to carry out an esterification reaction. rice field. After reducing the pressure in the system to 26 Pa over 20 minutes, the pressure was maintained at 240° C. and 26 Pa for the reaction time shown in Table 1 to polymerize a resin having a weight average molecular weight of 25,000. After returning to 25° C. and atmospheric pressure, the content was pulverized with a crusher to obtain a polyester resin. Table 1 shows the physical properties of the obtained polyester resin. Among the obtained polyester resins, polyester resins 1 to 15 and 17 having melting points are crystalline polyester resins, and polyester resin 16 having no melting point is amorphous polyester resin. The meaning of the abbreviation of each component in Table 1 is shown below.
・DDD: 1,12-dodecanediol ・DD: 1,10-decanediol ・HD: 1,6-hexanediol ・BD: 1,4-butanediol ・NPG: neopentyl glycol ・DDA: dodecanedioic acid ・SEA : sebacic acid ADA: adipic acid SUA: succinic acid tPA: terephthalic acid iPA: isophthalic acid

<Production of resin particles>
(Resin particles 1 to 23, 25)
A beaker with a volume of 2 L in which a stirrer (trade name “Tornado Stirrer Standard SM-104”, manufactured by AS ONE) was set was prepared. The types of polyester resins shown in Table 2 were dissolved in tetrahydrofuran heated to 45° C. to prepare 300 parts of a resin solution having the concentration shown in Table 2 and placed in a beaker. A 5% potassium hydroxide aqueous solution was added in an amount corresponding to the neutralization rate shown in Table 2 based on the acid value of the polyester resin, and stirred for 30 minutes. Under the condition of 45° C., 300 parts of deionized water was added dropwise at a rate of 20 mL/min while stirring at the rotational speed shown in Table 2. After distilling off the organic solvent and part of the water under reduced pressure, the contents of the beaker were filtered using a 150-mesh wire mesh (a filter in which 150 stainless steel wires are woven into each length and width in a 1-inch square). An appropriate amount of deionized water was added to adjust the content of the resin particles to obtain a liquid containing resin particles with a resin particle content of 25.0%.

(Resin particles 24)
300 parts of a 30% by mass resin solution prepared by dissolving polyester resin 16 (a crystalline polyester having no carboxylic acid group) in tetrahydrofuran heated to 45° C. was placed in a 2 L beaker, and then a surfactant was added. (trade name “Emal 0”, manufactured by Kao) was added and stirred for 30 minutes. Further, 300 parts of deionized water heated to 45° C. was added. Using an ultrasonic irradiator (trade name “S-150D Digital Sonifier”, manufactured by Branson), emulsification was performed under the conditions of 50 W, 20 kHz, and 30 minutes, and then the pressure was reduced to distill off the organic solvent and part of the water. . The contents of the beaker were filtered using a 150-mesh wire mesh (a 1-inch square filter with 150 stainless steel wires woven into each length and width). An appropriate amount of deionized water was added to adjust the resin particle content, and a liquid containing resin particles 24 with a resin particle content of 25.0% was obtained.

The volume-based cumulative 50% particle diameter (D _50R (nm)) and the volume-based cumulative 90% particle diameter (D _90R ) of the resin particles in the liquid containing the obtained resin particles. Table 2 shows the ratio value (D _50R /D _90R (times)) of the % particle size (D _50R ).

<Production of colorant particles>
(Colorant particles 1, 2, 6 to 13)
A batch-type vertical sand mill (manufactured by Aimex) filled with 200 parts of zirconia beads with a diameter of 0.3 mm is charged with 10.0 parts of a coloring material of the type shown in Table 3, 20.0 parts of a resin-containing liquid, and 70 parts of ion-exchanged water. 0.0 part of the mixture was added and dispersed for the dispersion time shown in Table 3. As the resin-containing liquid, an aqueous solution having a resin content of 30.0%, which is obtained by dissolving a water-soluble resin in an aqueous potassium hydroxide solution having an equimolar acid value, was used. This water-soluble resin is a styrene-ethyl acrylate-acrylic acid copolymer having an acid value of 167 mgKOH/g and a weight average molecular weight of 10,000. After removing coarse particles by centrifugation, pressure filtration was performed with a microfilter (manufactured by FUJIFILM Corporation) having a pore size of 3.0 μm. An appropriate amount of deionized water was added to adjust the concentration to obtain a liquid containing each colorant particle (resin-dispersed pigment) with a content of 10.0%. The meaning of each component in Table 3 is shown below.
・NIPex90: Carbon black (manufactured by Orion Engineered Carbons)
・5GX01: C.I. I. Pigment Yellow 74 (trade name “Hansa yellow 5GX 01 LV 3344”, manufactured by Clariant)

(Colorant particles 3)
5.0 g of concentrated hydrochloric acid was dissolved in 5.5 g of water, the solution was cooled to 5° C., and 1.6 g of 4-aminophthalic acid was added in this state. The container containing this solution was placed in an ice bath, and while stirring to keep the temperature of the solution below 10°C, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of deionized water at 5°C was prepared. added. After stirring for 15 minutes, 6.0 g of carbon black (trade name “NIPex90”, manufactured by Orion Engineered Carbons) was added with stirring. Stirred for an additional 15 minutes to obtain a slurry. The resulting slurry was filtered through a filter paper (trade name “Standard Filter Paper No. 2”, manufactured by Advantech), and the particles were thoroughly washed with water and dried in an oven at 110°C. After that, sodium ions were replaced with potassium ions by an ion exchange method to obtain a liquid containing a self-dispersing pigment, which is colorant particles in which —C ₆ H ₃ —(COOK) ₂ groups are bonded to the surface of carbon black particles. . An appropriate amount of deionized water was added to adjust the content of the colorant particles, thereby obtaining a liquid containing colorant particles 3 with a content of colorant particles (self-dispersing pigment) of 10.0%.

(Colorant particles 4)
A beaker with a volume of 2 L in which a stirrer (trade name “Tornado Stirrer Standard SM-104”, manufactured by AS ONE) was set was prepared. Into this beaker were added 300 parts of a 30% tetrahydrofuran solution of a styrene-ethyl acrylate-acrylonitrile-acrylic acid copolymer having an acid value of 60 mg KOH/g and a weight average molecular weight of 10,000, and C.I. I. 9 parts of Basic Red 1 was added and stirred for 30 minutes. Then, based on the acid value of the copolymer, a 5% sodium hydroxide aqueous solution was added in an amount corresponding to 50 mol % and stirred for 30 minutes. 300 parts of deionized water was added dropwise at a rate of 20 mL/min while stirring. After the organic solvent and part of the water were distilled off under reduced pressure, the contents of the beaker were filtered using a 150-mesh wire mesh (a 1-inch square filter in which 150 stainless steel wires were woven in each direction). An appropriate amount of deionized water was added to adjust the concentration to obtain a liquid containing colorant particles 4 in which the content of colorant particles (resin particles dyed with a dye) was 10.0%.

(Colorant particles 5)
300 parts of a 30% methyl ethyl ketone solution of a styrene-ethyl acrylate-acrylonitrile-acrylic acid copolymer having an acid value of 60 mgKOH/g and a weight average molecular weight of 10,000 was placed in a 2 L beaker. C. I. 9 parts of Basic Red 1 and a mixture of 5% aqueous sodium hydroxide solution and 300 parts of deionized water in an amount corresponding to 50 mol % based on the acid value of the copolymer were added. Using an ultrasonic irradiator (trade name “S-150D Digital Sonifier”, manufactured by Branson), emulsification was performed under the conditions of 50 W, 20 kHz, and 30 minutes, and then the pressure was reduced to distill off the organic solvent and part of the water. . The contents of the beaker were filtered using a 150-mesh wire mesh (a 1-inch square filter with 150 stainless steel wires woven into each length and width). An appropriate amount of deionized water was added to adjust the concentration to obtain a liquid containing colorant particles 5 with a colorant particle (dye dispersed by resin) content of 10.0%.

Table 3 shows the cumulative 50% particle size (D _50C ) of the volume-based particle size distribution of the colorant particles in the liquid containing the obtained colorant particles.

<Ink preparation>
(Examples 1 to 39, Comparative Examples 1 to 5)
After each component shown below was mixed and sufficiently stirred, the mixture was pressure-filtered through a microfilter with a pore size of 2.5 μm to prepare an ink. Among the components shown below, "acetylenol E100" is a trade name of a nonionic surfactant (manufactured by Kawaken Fine Chemicals). Physical properties of the ink are shown in Tables 4-1 and 4-2.
・Liquid containing resin particles: Amount corresponding to content R (%) of resin particles shown in Tables 4-1 and 4-2 ・Liquid containing colorant particles: Colorant particles shown in Tables 4-1 and 4-2 Content C (%) of Glycerin: 5.00%
・Triethylene glycol: 10.00%
・Acetylenol E100: 0.10%
・Ion-exchanged water: Remaining amount (%) when the total of components is 100.00%

(Comparative Example 6)
"Pigment-containing polymer particles" and "Em4-1" described in JP-A-2014-125555 were prepared. Then, each component shown below was mixed, thoroughly stirred, and pressure-filtered through a microfilter having a pore size of 2.5 μm to prepare an ink. Physical properties of the ink are shown in Table 4-2.
・Em4-1: 0.40%
・Pigment-containing polymer particles: 4.00%
・Glycerin: 5.00%
・Triethylene glycol: 10.00%
・Acetylenol E100: 0.10%
・Ion-exchanged water: Remaining amount (%) when the total of components becomes 100.00%

<Evaluation>
In the present invention, in the evaluation criteria for each item shown below, "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. In addition, when a clear difference is observed even within the same evaluation criteria, relatively inferior among "A" is "A ^- ", and relatively inferior among "B" is " ^B- ”. Table 5 shows the evaluation results.

(Chemical resistance)
Each of the prepared inks was filled in an ink cartridge, and mounted in an inkjet recording apparatus (trade name “PIXUS iP3100” manufactured by Canon Inc.) that ejects ink from a recording head by the action of thermal energy. In this embodiment, the print duty of a solid image printed under the condition that one ink droplet of 5 pL is applied to a unit area of 1/1,200 inch×1/1,200 inch is defined as 100%. do. Using this inkjet recording apparatus, a solid image of 200 mm×200 mm with a recording duty of 100% was recorded on a recording medium (trade name “Aurora Coat”, manufactured by Nippon Paper Industries). After the recorded image was dried at 25° C. for 24 hours, it was heated at 100° C. for 5 minutes using a heating oven. After the temperature of the image after heating was returned to 25° C., 0.1 g of a 70% ethanol aqueous solution was placed on the image, and after 1 minute had passed, the image was wiped off with a cellulose nonwoven fabric, and the chemical resistance of the image was evaluated according to the evaluation criteria shown below.
A: There was no trace of droplets on the image.
B: The area ratio of the exposed recording medium to the area to which droplets adhered was less than 5%.
C: The area ratio of the exposed recording medium to the area to which droplets adhered was 5% or more.

(image clarity)
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) using the inkjet recording apparatus described above. After the recorded image was dried at 25° C. for 24 hours, the image was illuminated at an angle of 45° from a distance of 2 m using two fluorescent lamps arranged side by side at an interval of 10 cm (illumination angle 45° ). The shape of the fluorescent lamp projected on the image was visually confirmed from an angle of 45 degrees (observation angle of 45 degrees), and the image clarity of the image was evaluated according to the evaluation criteria shown below.
A: The boundary between the two projected fluorescent lamps was recognized, and no blurring was observed on the edge.
B: The boundary between the two projected fluorescent lamps was recognized, but the edges were slightly blurred.
C: The boundary between the two projected fluorescent lamps was not recognized.

Note that the disclosure of the present embodiment includes the following configurations.
(Configuration 1) A water-based inkjet ink containing colorant particles and resin particles,
The resin particles are formed of a crystalline polyester resin having a carboxylic acid group,
The difference between the cumulative 50% particle size (D _50C ) of the volume-based particle size distribution of the colorant particles and the cumulative 50% particle size (D _50R ) of the volume-based particle size distribution of the resin particles (D _50C −D _50R ) is 10 nm or more.
(Arrangement 2) The water-based ink according to Arrangement 1, wherein the D _50C -D _50R is 150 nm or less.
(Structure 3) The water-based ink according to Structure 1 or 2, wherein the D _50C -D _50R is 100 nm or less.
(Structure 4) The water-based ink according to any one of Structures 1 to 3, wherein the _D50R is 5 nm or more and 30 nm or less.
(Configuration 5) Any one of Configurations 1 to 4, wherein the D _50R is a ratio of the cumulative 90% particle diameter (D _90R ) of the volume-based particle size distribution of the resin particles to 0.6 times or more. water-based ink.
(Arrangement 6) Any one of Arrangements 1 to 5, wherein the content (% by mass) of the colorant particles is 1.0 to 100.0 times the content (% by mass) of the resin particles as a mass ratio. 1. The water-based ink according to 1.
(Arrangement 7) An ink cartridge comprising ink and an ink containing portion containing the ink,
7. An ink cartridge, wherein the ink is the water-based ink according to any one of Structures 1 to 6.
(Arrangement 8) An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head,
An inkjet recording method, wherein the ink is the water-based ink according to any one of Structures 1 to 6.

Claims (8)

A water-based inkjet ink containing colorant particles and resin particles,
The resin particles are formed of a crystalline polyester resin having a carboxylic acid group,
The difference between the cumulative 50% particle size (D _50C ) of the volume-based particle size distribution of the colorant particles and the cumulative 50% particle size (D _50R ) of the volume-based particle size distribution of the resin particles (D _50C −D _50R ) is 10 nm or more. The water-based ink according to claim 1, wherein the D _50C -D _50R is 150 nm or less. The water-based ink according to claim 1, wherein the D _50C -D _50R is 100 nm or less. The water-based ink according to any one of claims 1 to 3, wherein the _D50R is 5 nm or more and 30 nm or less. The water-based ink according to any one of claims 1 to 3, wherein the _D50R is a ratio of the cumulative 90% particle diameter ( _D90R ) of the volume-based particle size distribution of the resin particles to be 0.6 times or more. . 4. Any one of claims 1 to 3, wherein the content (% by mass) of the colorant particles is 1.0 times or more and 100.0 times or less as a mass ratio with respect to the content (% by mass) of the resin particles. The water-based ink described in . An ink cartridge comprising ink and an ink containing portion containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 3. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head,
An inkjet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 3.

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