Aqueous ink, ink cartridge, and inkjet recording method

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

[Technical Field]

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

[0002] Traditionally, inkjet printers have been widely used as small home printers, and in recent years, their use has expanded to offices and commercial printing. In fields such as offices and commercial printing, there is a demand for the ability to record images with higher scratch resistance compared to small home printers.

[0003] For example, an aqueous inkjet ink containing polyester resin particles has been proposed as an ink that can improve the fixation of colorants to recording media (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-125555 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present inventors investigated the aqueous ink proposed in Patent Document 1. As a result, it was found that it is difficult to record images that achieve both chemical resistance, such as alcohol abrasion resistance, and image quality at the level required in recent years. Chemical resistance (alcohol abrasion resistance) refers to the property that solvent marks or peeling do not easily occur on the image even under harsh conditions where external force is applied to the part of the image to which a solvent that can dissolve the image layer or recording medium is attached. Image quality refers to a property that is an indicator of the sharpness of the image when an image is projected onto the image; if the image quality is low, the image appears blurry, and if the image quality is high, the image appears sharp.

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

Means for Solving the Problems

[0007] That is, according to the present invention, there is provided an aqueous ink for inkjet containing coloring material particles and resin particles, wherein the resin particles are formed of a crystalline polyester resin having a carboxylic acid group, and the cumulative 50% particle diameter (D 50C ) of the volume-based particle size distribution of the coloring material particles and the cumulative 50% particle diameter (D 50R ) of the volume-based particle size distribution of the resin particles, and the difference (D 50C -D 50R ) is 10 nm or more. An aqueous ink is provided.

Effects of the Invention

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

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. [Figure 2] It is a view 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 a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

Modes for Carrying Out the Invention

[0010] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based ink for inkjet printers may be simply referred to as "ink." Unless otherwise specified, physical properties are given at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). Also, unless otherwise specified, "unit" refers to the unit structure corresponding to one monomer. When "(meth)acrylic acid" or "(meth)acrylate" is written, it refers to "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0011] The present inventors investigated an ink containing resin particles (hereinafter also simply referred to as "resin particles") formed from a crystalline polyester resin having carboxylic acid groups, in order to improve the chemical resistance of images, such as resistance to alcohol abrasion. It is presumed that polyester resins having carboxylic acid groups form a strong film on the recording medium as the molecular chains of the resin become entangled due to hydrogen bonding between the carboxylic acid groups. Furthermore, it is thought that when an ink containing resin particles formed from crystalline polyester resin is applied to a recording medium, the crystalline polyester resins can come into close proximity to each other even among multiple resin particles, allowing the growth of a crystalline structure. It is thought that the resulting crystalline structure causes the polyester resins to come into close proximity, forming a polyester resin film, which suppresses the penetration of chemicals such as alcohol into the image layer and exhibits chemical resistance.

[0012] However, investigations revealed that even when resin particles formed from crystalline polyester resin having carboxylic acid groups were used, the chemical resistance of the recorded images did not always improve. Furthermore, it was found that the growth of the crystal structure of the crystalline polyester resin tended to cause surface irregularities in the image, leading to a decrease in image clarity. As a result of further investigations, the inventors discovered that by satisfying the following requirements (i) and (ii), it was possible to improve the chemical resistance of images without reducing image clarity, leading to the present invention. (i) It contains coloring material particles and resin particles formed of a crystalline polyester resin having a carboxylic acid group. (ii) The difference (D 50C ) between the cumulative 50% particle diameter (D 50R ) of the coloring material particles based on volume and the cumulative 50% particle diameter (D 50C ) of the resin particles based on volume is 10 nm or more. ) is 10 nm or more.

[0013] Both the coloring material particles and the resin particles continue to perform Brownian motion within the ink droplets. The movement range of the particles depends on their particle diameter, and the smaller the particle diameter, the wider the movement range. Therefore, the probability of the presence of smaller particles increases near the interface of the ink droplets applied to the recording medium. When the requirement of (ii) is satisfied, after the liquid medium in the ink penetrates or evaporates and decreases, more resin particles will exist near the surface of the recorded image compared to the inside of the image layer. Since the resin particles are formed of a crystalline polyester resin having a carboxylic acid group, in addition to the hydrogen bonds between the carboxylic acid groups, a crystalline film is formed near the surface of the image so as to cover the coloring material particles due to the growth of the crystal structure accompanying the proximity of the crystalline polyester resins. Since the crystalline film is formed by the dense arrangement of the molecules of the crystalline polyester resin, it is possible to suppress the penetration of drugs such as alcohol into the image layer, and the chemical resistance of the image is improved.

[0014] "D 50C -D 50R " is less than 10 nm, the coloring material particles are unevenly present near the surface of the image, drugs such as alcohol easily penetrate into the image layer, and the chemical resistance of the image does not improve. Also, there is a bias in the distribution of the resin particles near the surface of the image, and crystal growth is likely to occur in the portions where many resin particles are present. Therefore, since the light reflection state changes between the portion where many resin particles are present and the portion where many coloring material particles are present, the imageability of the image does not improve.

[0015] <Ink> ​The ink of the present invention is an aqueous inkjet ink containing colorant particles and resin particles. The resin particles are formed from a crystalline polyester resin having a carboxylic acid group. The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

[0016] (Resin particles) The ink contains resin particles (hereinafter sometimes simply referred to as "resin particles") formed from a crystalline polyester resin having carboxylic acid groups. The resin particles are dispersed in the ink, i.e., they exist in the ink in the form of a resin emulsion. Preferably, the resin particles are dispersed by the action of the carboxylic acid groups they possess (self-dispersing type), rather than being dispersed by components such as surfactants or resins (emulsified type). The resin particles do not need to contain colorants. The proportion (mass%) of crystalline polyester resin in the resin forming the resin particles is preferably 50.00% by mass or more, and more preferably 100.00% by mass, based on the total mass of the resin. In other words, it is preferable that the resin particles are substantially formed solely from crystalline polyester resin. The content (mass%) of resin particles in the ink is preferably 0.01% by mass or more and 10.00% by mass or less, and more preferably 0.02% by mass or more and 5.00% by mass or less, based on the total mass of the ink.

[0017] In this invention, "resin particles" refers to resins that exist in an insoluble state in the aqueous medium constituting the ink. More specifically, it refers to resins that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. On the other hand, "water-soluble resin" refers to resins that exist in a dissolved state in the aqueous medium constituting the ink. More specifically, it refers to resins that can exist in the aqueous medium in a state in which particles whose particle size can not be measured by dynamic light scattering are not formed. If resin particles are expressed in contrast to "water-soluble resin," they become "water-dispersible resin (water-insoluble resin)."

[0018] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, the liquid containing the resin to be judged is diluted with pure water to prepare a sample with a resin content of approximately 1.0%. Then, the particle size of the resin in the sample is measured by dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if no particles with a particle size are measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0.

[0019] As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, product name "NanoTrac WAVE II-Q," manufactured by MicroTrac-Bell) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those mentioned above.

[0020] For resins other than crystalline polyester resins (such as resin dispersants and other resins), the definition of whether or not they are resin particles is the same as described above. For other resins, it is possible to determine whether they are resin particles or water-soluble resins using the same method as described above. However, for the sake of convenience, for other resins, it may be possible to determine whether they are resin particles or water-soluble resins using a liquid containing the resin neutralized with an alkali (such as sodium hydroxide or potassium hydroxide) with an acid value equivalent to that of the resin (resin content: 10% by mass), or a liquid obtained by appropriately diluting it.

[0021] [Crystalline polyester resin] The crystalline polyester resin that forms the resin particles has carboxylic acid groups. That is, crystalline polyester resin is a resin that has units containing carboxylic acid groups. Unreacted hydroxyl groups or carboxylic acid groups are present at the ends of the crystalline polyester resin. If carboxylic acid groups are not present at the ends of the crystalline polyester resin, then carboxylic acid groups are present in other parts of the resin. By utilizing the interactions between the carboxylic acid groups of crystalline polyester resin, the chemical resistance of recorded images can be improved.

[0022] Polyester resins can be broadly classified into crystalline polyester resins and amorphous polyester resins. Crystalline polyester resins are polyester resins that have a melting point. The melting point of a polyester resin refers to the melting peak temperature (temperature of the endothermic peak due to melting) measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121:1987. In this invention, a melting peak is determined to exist (i.e., it is a crystalline polyester resin) if the amount of endothermic energy obtained from the integral value of the peak is 20 J / g or more.

[0023] Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. A structure containing an ester bond (-COO-) composed of a unit derived from a polyhydric alcohol and a unit derived from a polyhydric carboxylic acid is also referred to as an "ester unit."

[0024] [Polyhydric alcohols] Polyhydric alcohols that form units constituting crystalline polyester resins through reactions include dihydric to tetrahydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. In addition, oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols.

[0025] It is preferable to use polyhydric alcohols in which the hydrocarbon portion is saturated. Resin particles formed from polyester resins synthesized using polyhydric alcohols in which the hydrocarbon portion is unsaturated (sometimes referred to as unsaturated polyhydric alcohols) have a high refractive index, which may slightly reduce the image resolution. The proportion of units derived from unsaturated polyhydric alcohols to the total polyhydric alcohol units constituting the crystalline polyester resin is preferably 50 mol% or less, preferably 10 mol% or less, and particularly preferably 0 mol%.

[0026] As the polyhydric alcohol, polyhydric alcohols having aliphatic groups can be preferably used. Among these, those with 4 or more carbon atoms are preferred, those with 6 or more carbon atoms are more preferred, those with 12 or fewer carbon atoms are preferred, and those with 8 or fewer carbon atoms are even more preferred. Furthermore, those in a linear hydrocarbon chain are preferred. Furthermore, those with hydroxyl groups at both ends of the hydrocarbon chain are preferred. It is preferable to use divalent or trivalent polyhydric alcohols because it is easy to adjust the weight-average molecular weight of the polyester resin. In particular, it is preferable to use divalent polyhydric alcohols. Among these, it is preferable to use polyhydric alcohols having linear aliphatic groups because it further improves the crystallinity of the crystalline polyester resin and further enhances its chemical resistance. Two or more polyhydric alcohols, including polyhydric alcohols having linear aliphatic groups, can also be used in combination. Specifically, it is preferable that the proportion of units derived from the above-mentioned preferred polyhydric alcohols to the units derived from the polyhydric alcohols having aliphatic groups that constitute the crystalline polyester resin is 50 mol% or more. Furthermore, it is even more preferable that the proportion of the above units is 100 mol%.

[0027] [Polyhydric carboxylic acids] Polycarboxylic acids that form units constituting polyester resins through reactions include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acid structures include polycarboxylic acids with aliphatic groups, polycarboxylic acids with aromatic groups, and nitrogen-containing polycarboxylic acids. Examples of polycarboxylic 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; and tetravalent carboxylic acids such as ethylenediaminetetraacetic acid. Furthermore, oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polycarboxylic acids.

[0028] It is preferable to use polycarboxylic acids in which the hydrocarbon portion is saturated. Resin particles formed from polyester resins synthesized using polycarboxylic acids in which the hydrocarbon portion is unsaturated (sometimes referred to as unsaturated polycarboxylic acids) have a high refractive index, which may slightly reduce the image resolution. The proportion of units derived from unsaturated polycarboxylic acids to the total polycarboxylic acid units constituting the crystalline polyester resin is preferably 50 mol% or less, preferably 10 mol% or less, and particularly preferably 0 mol%.

[0029] As the polycarboxylic acid, polycarboxylic acids having aliphatic groups can be preferably used. Among these, those with 4 or more carbon atoms are preferred, those with 6 or more carbon atoms are more preferred, those with 12 or fewer carbon atoms are preferred, and those with 8 or fewer carbon atoms are even more preferred. This carbon number does not include the carbon atoms constituting the carboxylic acid group. It is also preferable to use those with a saturated hydrocarbon portion. Furthermore, it is preferable that the hydrocarbon portion is linear. Furthermore, it is preferable that the carboxylic acid group is at both ends of the hydrocarbon chain. It is preferable to use divalent or trivalent polycarboxylic acids 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 divalent polycarboxylic acids. Among these, it is preferable to use polycarboxylic acids having linear aliphatic groups because it further improves the crystallinity of the crystalline polyester resin and further enhances its chemical resistance. Two or more polycarboxylic acids, including polycarboxylic acids having linear aliphatic groups, can also be used in combination. Specifically, it is preferable that the proportion of units derived from the above-mentioned preferred polycarboxylic acids having aliphatic groups in the units derived from the polycarboxylic acid having aliphatic groups constituting the crystalline polyester resin is 50 mol% or more. Furthermore, it is even more preferable that the proportion of the above units be 100 mol%.

[0030] [Combinations of polyhydric alcohols and polyhydric carboxylic acids] A polyester resin composed of units derived from diols having hydroxyl groups at both ends of a linear saturated hydrocarbon group, and units derived from dicarboxylic acids having a carboxylic acid group at each end of a linear saturated hydrocarbon group, is preferred. In such a polyester resin, the hydrocarbon groups of the diol and dicarboxylic acid interact easily, and crystallinity tends to be increased. The ratio of the total units derived from the diol and the polycarboxylic acid to the total units derived from the polyhydric alcohol that constitute the crystalline polyester resin is preferably as follows: that is, it is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 100 mol%. Resin particles formed from a crystalline polyester resin with a high ratio of the above can suppress the decrease in crystallinity due to hydration in the aqueous medium that constitutes the aqueous ink, and the chemical resistance of the recorded image can be further improved.

[0031] [Physical properties of resin particles] [Melting point of crystalline polyester resin] The melting point of the crystalline polyester resin is preferably between 50°C and 140°C. If the melting point is below 50°C, the resin particles may not remain near the surface of the image but flow and fall into the gaps of the colorant, making it difficult to form a crystalline film near the surface of the image, which may reduce the effect of improving chemical resistance. On the other hand, if the melting point is above 140°C, crystal growth is difficult even when resin particles are in close proximity to each other, and the shape of the resin particles is maintained, making it easier for light to scatter, which may reduce the effect of improving image quality. The "melting peak temperature" obtained by differential scanning calorimetry (DSC) in accordance with JIS K 7121:1987 is defined as the melting point of the crystalline polyester resin. The melting point of the crystalline polyester resin is preferably between 50°C and 100°C.

[0032] [Acid value of crystalline polyester resins] The acid value of the crystalline polyester resin is preferably between 10 mg KOH / g and 50 mg KOH / g. If the acid value is less than 10 mg KOH / g, the amount of carboxylic acid groups is somewhat small, making it easy for multiple resin particles to aggregate. Light scattering is more likely to occur in the aggregated areas, which may reduce the effect of improving image quality. On the other hand, if the acid value is greater than 50 mg KOH / g, the amount of carboxylic acid groups is somewhat large, which may slightly increase the hydrophilicity of the resin particles. As a result, the amount of carboxylic acid groups present near the surface of the image also increases, slowing down the penetration or evaporation of the liquid medium in the ink, which may cause unevenness in the image and reduce the effect of improving image quality. The acid value of the crystalline polyester resin forming the resin particles is more preferably between 15 mg KOH / g and 25 mg KOH / g. The acid value of the crystalline polyester resin can be measured by neutralization titration using a potential difference.

[0033] The acid value of crystalline polyester resin can be adjusted by changing the ratio of the polyhydric alcohol and polycarboxylic acid used as raw materials. For example, when synthesizing crystalline polyester resin using a diol and a dicarboxylic acid as raw materials, if the diol and dicarboxylic acid are used in equimolar amounts, there is a high probability that one end of the molecular chain of the synthesized crystalline polyester resin will be a hydroxyl group and the other end will be a carboxylic acid group. The acid value can be adjusted by changing the ratio of the amount of carboxylic acid groups (y moles) of the polycarboxylic acid to the amount of hydroxyl groups (x moles) of the polyhydric alcohol. In other words, even if the amount of polyhydric alcohol (x moles) is greater than the amount of polycarboxylic acid (y moles) (y / x < 1), it is possible to synthesize crystalline polyester having acid groups. Since the acid value can be easily adjusted, it is preferable that y / x is 0.8 times or more, and preferably 1.4 times or less.

[0034] [Weight-average molecular weight of crystalline polyester resins] The weight-average molecular weight of the crystalline polyester resin is preferably between 10,000 and 70,000, and more preferably between 15,000 and 30,000. The weight-average molecular weight of the crystalline polyester resin is a polystyrene equivalent value measured by gel permeation chromatography.

[0035] [Particle size of resin particles] Cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles 50R ) is preferably 5 nm to 30 nm. 50R If the thickness is less than 5 nm, the thickness of the crystalline film formed near the surface of the image by the resin particles becomes thinner, which can make it easier for chemicals such as alcohol to penetrate the image layer, potentially reducing the effect of improving the image's chemical resistance. On the other hand, D 50R If the particle size is greater than 30 nm, resin particles may overlap near the surface of the image, and crystal growth may form seemingly larger particles, which can cause light scattering and reduce the effect of improving image quality. Cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles 50R ) is more preferably 15 nm to 25 nm. Also, the cumulative 90% particle size (D) of the volume-based particle size distribution of the resin particles is also preferable. 90R ) is preferably between 10 nm and 60 nm.

[0036] Cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles 50R ) is the cumulative 90% particle size (D) of the volume-based particle size distribution of resin particles. 90R The ratio to is preferably 0.6 times or more. If the above ratio is less than 0.6 times, coarse particles are more likely to be present, light is more likely to scatter, and the effect of improving image quality may decrease. The above ratio is preferably 0.8 times or less.

[0037] Cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles 50R ) and cumulative 90% particle size (D 90R) refers to the diameters of particles that, when integrated from the smallest particle diameter side, account for 50% and 90% of the total volume of the measured particles in the particle diameter integration curve, respectively. 50R and D 90R All of these can be measured by dynamic light scattering under the same conditions as the method described above for determining whether or not they are "resin particles."

[0038] [Method for manufacturing resin particles] Resin particles can be produced, for example, by atomizing a synthesized crystalline polyester resin. Crystalline polyester resin can also be synthesized by reacting a polyhydric alcohol and a polycarboxylic acid (esterification reaction). It is preferable to use an esterification catalyst during the esterification reaction. Examples of esterification catalysts include metal compounds such as tin compounds, titanium compounds, antimony compounds, and germanium compounds. The amount of esterification catalyst is preferably 100 ppm to 5000 ppm, based on the total amount of the polyhydric alcohol and polycarboxylic acid. If necessary, the molecular weight of the resulting crystalline polyester resin can be adjusted by adding either the polyhydric alcohol or polycarboxylic acid to the reaction system and performing a transesterification reaction to cleave some of the ester bonds.

[0039] By adjusting the amount of raw materials used in the esterification reaction so that the number of carboxylic acid groups of the polycarboxylic acid exceeds the number of hydroxyl groups of the polyhydric alcohol, a crystalline polyester resin containing carboxylic acid groups can be obtained. Alternatively, a crystalline polyester resin containing carboxylic acid groups can also be obtained by using a polyhydric carboxylic acid in the transesterification reaction.

[0040] 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 between 180°C and 260°C. The reaction time during the esterification reaction is preferably between 1 hour and 5 hours.

[0041] During the esterification reaction, the reaction system may be depressurized to remove the water produced by the reaction, thereby accelerating the esterification (dehydration condensation) reaction. Under reduced pressure, the reaction is carried out under an inert gas atmosphere such as nitrogen gas, following the esterification reaction. The reaction temperature under reduced pressure is preferably 220°C to 280°C. The reaction time under reduced pressure is preferably 0.5 hours to 5 hours, and more preferably 1 hour to 3 hours. The degree of reduced pressure (vacuum) is preferably 1 Pa to 130 Pa, and more preferably 1 Pa to 50 Pa. However, if the degree of reduced pressure is too low, the reaction efficiency will decrease, or the weight-average molecular weight of the resulting crystalline polyester resin will be small, so it is preferable to adjust it according to the reaction conditions. It is preferable to gradually reduce the pressure from atmospheric pressure (101,325 Pa) to 130 Pa or less over a period of about 0.1 to 3 hours.

[0042] Transesterification reactions are carried out by adding either a polyhydric alcohol or a polyhydric carboxylic acid to the reaction system to cleave some of the ester bonds, thereby adjusting the molecular weight of the resulting crystalline polyester resin or, more specifically, to have carboxylic acid groups at the ends of the molecular chains. From the viewpoint of efficiently obtaining crystalline polyester resins containing carboxylic acid groups, it is preferable to carry out the transesterification reaction using a polyhydric carboxylic acid.

[0043] The synthesized crystalline polyester resin is preferably used in the next step of particle formation after being processed into an appropriate form by pressurization and pulverization. Since the resin particles formed from the crystalline polyester resin are used as components of aqueous ink, it is preferable that they be dispersed in an aqueous liquid medium. The aqueous liquid medium mainly consists of water, such as deionized water, ion-exchanged water, and distilled water, and may contain a water-soluble organic solvent as needed. The water content (mass%) in the aqueous liquid medium is preferably 50% by mass or more, and it is also preferable to use a liquid medium that substantially does not contain a water-soluble organic solvent (i.e., water).

[0044] Methods for forming resin particles by atomizing crystalline polyester resin include, for example, dispersion methods and phase inversion (emulsification) methods. Dispersion methods include the methods shown in (1) and (2) below. (1) A method of dispersing crystalline polyester resin by adding a solution obtained by dissolving crystalline polyester resin in an organic solvent to an aqueous liquid medium. (2) A method of dispersing the crystalline polyester resin by adding it to an organic solvent and then adding and mixing an aqueous liquid medium.

[0045] Phase inversion (emulsification) methods include a method in which a polyester resin is dissolved in an organic solvent, and an aqueous liquid medium is added to the resulting solution to induce a phase inversion from a solvent system to an aqueous system, thereby precipitating the polyester resin in the form of particles. In either method, it is preferable to use a known disperser and adjust the particle size of the resulting resin particles by pulverizing the resin while applying appropriate shear force.

[0046] Since the particle size of the resulting resin particles can be precisely controlled, it is preferable to manufacture resin particles by the phase inversion (emulsification) method. The method for manufacturing resin particles by the phase inversion (emulsification) method will be described below.

[0047] First, a resin solution is obtained by dissolving a crystalline polyester resin in an organic solvent. Examples of organic solvents include ethers such as tetrahydrofuran and dibutyl ether; ketones such as acetone and methyl ethyl ketone; and alcohols such as isopropanol. If only organic solvents with low water solubility and poor miscibility with water in any proportion (such as methyl ethyl ketone) are used, it may be difficult to precisely adjust the particle size. For this reason, it is preferable to use ethers such as tetrahydrofuran, which can be miscible with water in any proportion, as the organic solvent. Ethers such as tetrahydrofuran are also preferable because they have excellent solubility for crystalline polyester resins.

[0048] To uniformly dissolve the crystalline polyester resin, it is preferable to dissolve the crystalline polyester resin in an organic solvent while heating it. However, it is preferable to heat it to a temperature lower than the boiling point of the organic solvent being used for dissolution. If the concentration of crystalline polyester resin in the resin solution is dilute, it may be difficult to control the particle size distribution. For this reason, the content (mass%) of 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.

[0049] 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 in order to maintain a stable dispersion state of the resin particles. As the base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or ammonia can be used, and it is preferable to add them in the form of an aqueous solution. The amount of base to be added can be controlled by the neutralization rate (mol%) based on the acid value corresponding to all 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 aqueous liquid medium added increases, the resin solution, which was initially transparent, becomes cloudy and emulsifies, and resin particles are formed. By adjusting the content of crystalline polyester resin in the resin solution, the neutralization rate, and the shear force applied during dispersion, the particle size and particle size distribution of the obtained resin particles can be controlled.

[0050] The resulting emulsion is subjected to reduced pressure to remove the organic solvent by distillation, and if necessary, it is filtered using a filter of appropriate pore size (stainless steel mesh) to remove coarse particles. Next, water is added to adjust the resin particle content, thereby preparing a liquid containing resin particles (aqueous dispersion of resin particles). The water used to adjust the content is preferably deionized water, ion-exchanged water, or distilled water. From the viewpoint of ink productivity, the resin particle content (mass%) in the liquid containing resin particles is preferably 5.0% by mass or more and 30.0% by mass or less, and more preferably 15.0% by mass or more and 30.0% by mass or less.

[0051] [Compositional analysis of resin particles] The crystalline polyester resin that constitutes resin particles can be determined, for example, by the following methods. First, a sample is prepared by dissolving the resin particles in an organic solvent capable of dissolving resin particles, such as tetrahydrofuran. The resin particles used may be in an aqueous dispersion or in a dry state. The prepared sample is analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS), etc. This allows for the determination of the types and proportions of units (monomers) that constitute the resin. Alternatively, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that constitute the resin. If insoluble matter that does not dissolve in the 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. Furthermore, crystalline properties can be determined by performing differential scanning calorimetry (DSC) on a dried sample and confirming that it has a melting peak temperature (melting point).

[0052] (Coloring material particles) As the colorant for the ink, particulate colorant particles are used. Colorants that can dissolve in ink as molecules, such as water-soluble dyes, are much smaller in size than resin particles. Therefore, non-particulate colorants have a higher probability of being present near the interface of the ink droplet, and more colorants are present near the surface of the recorded image compared to within the image layer. Non-particulate colorants tend to dissolve easily in chemicals such as alcohol, and therefore cannot improve the chemical resistance of the image.

[0053] The colorant particles are pigments or dyes, and are contained in the ink in a dispersed state as particles with a particle size. The content (mass%) of colorant particles in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0054] Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, isoindolinone pigments, and imidazolon pigments.

[0055] As pigment-based colorant particles, resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with a resin can be used. Among these, it is preferable to use self-dispersing pigments or resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the surface of the pigment particles, rather than resin-bonded pigments or microcapsule pigments, and it is even more preferable to use the aforementioned resin-dispersed pigments. As the dispersant for resin-dispersed pigments, it is even more preferable to use a water-soluble resin rather than a water-insoluble resin.

[0056] Self-dispersing pigments include those in which anionic groups are directly or via other atomic groups bonded to the surface of the pigment particles. Examples of anionic groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups. Examples of counterions to the anionic groups include hydrogen atoms, alkali metals, ammonium, and cations such as organic ammonium. The other atomic groups are groups that function as spacers between the surface of the pigment particles and the ionic groups, and it is preferable that their molecular weight is 1,000 or less. Examples of other atomic groups include alkylene groups with about 1 to 6 carbon atoms, arylene groups such as phenylene groups and naphthylene groups, ester groups, imino groups, amide groups, sulfonyl groups, and ether groups. Alternatively, groups may be combinations of these groups.

[0057] For dispersing pigments in an aqueous medium, it is preferable to use a resin that can disperse pigments in the aqueous medium through the action of anionic groups. Examples of resin dispersants include acrylic resins and urethane resins. Among these, acrylic resins are preferred, and acrylic resins having hydrophilic units and hydrophobic units as constituent units are even more preferred. In particular, acrylic resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from monomers having aliphatic or aromatic groups are preferred.

[0058] Hydrophilic units are units that have hydrophilic groups such as anionic groups, hydroxyl groups, and ethylene oxide groups. Hydrophilic units can be formed, for example, by polymerizing monomers that have hydrophilic groups. Specific examples of monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups such as (meth)acrylic acid; anionic monomers such as anhydrides and salts of these acidic monomers; monomers having hydroxyl groups such as 2-hydroxyethyl (meth)acrylate; and monomers having ethylene oxide groups such as methoxypolyethylene glycol (meth)acrylate. Cationic ions that constitute salts of acidic monomers include lithium, sodium, potassium, ammonium, and organic ammonium ions.

[0059] A hydrophobic unit is a unit that does not have hydrophilic groups such as anionic groups, hydroxyl groups, or ethylene oxide groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups. Specific examples of hydrophobic monomers include monomers having aromatic groups such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and monomers having aliphatic groups such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso-)propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0060] Specific examples of dyes include oil-soluble dyes, disperse dyes, reactive dyes, direct dyes, acid dyes, and basic dyes. Among these, oil-soluble dyes, disperse dyes, and basic dyes are preferred. Dyes that do not dissolve in the aqueous medium that constitutes aqueous ink can be suitably used as colorant particles by dispersing them with a resin dispersant or by dyeing them onto resin particles. Among such dyes, oil-soluble dyes, disperse dyes, and basic dyes are also preferred. When using dyes as colorants, it is preferable to use resin particles dyed with dyes.

[0061] As a resin dispersant for dispersing dyes in an aqueous medium, one can be selected and used from the same types as those listed as resin dispersants for pigments. Resin particles dyed with dye can be obtained as an aqueous dispersion of dye-dyed resin particles by dissolving the resin and dye in an organic solvent, emulsifying it with water, and then removing the organic solvent. Alternatively, an aqueous dispersion of dye-dyed resin particles can be obtained by adding a dye to an aqueous dispersion of resin particles obtained by emulsion polymerization of various monomers, heating it, and pressurizing it as needed.

[0062] Whether or not resin particles are stained with dye can be determined according to the following method. Here, we will describe a method for extracting and analyzing resin particles from ink, but resin particles extracted from aqueous dispersions, etc., can be analyzed in the same way. First, resin particles are separated from the ink containing resin particles by density gradient centrifugation. Density gradient centrifugation includes density gradient sedimentation velocity method and density gradient sedimentation equilibrium method. In the density gradient sedimentation velocity method, resin particles can be separated and extracted based on the difference in sedimentation coefficient. In the density gradient sedimentation equilibrium method, resin particles can be separated and extracted based on the difference in density. After drying the obtained dispersion of resin particles, a solution is prepared using an organic solvent capable of dissolving dyes, additives, and resins. Components in the prepared solution are separated by preparative gel permeation chromatography (GPC), preparative high-performance liquid chromatography (HPLC), and column chromatography, and the dyes, additives, and resins are separated. The separated dyes, additives, and resins are analyzed using analytical methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). This allows for the identification of the types of dyes and additives, as well as the types and proportions of the constituent units (monomers) of the resins. Furthermore, by analyzing the separated resins using pyrolysis gas chromatography, monomers produced during depolymerization can be directly detected.

[0063] [Physical properties of colorant particles] [Particle size of colorant particles] The cumulative 50% particle size (D) of the volume-based particle size distribution of colorant particles. 50C ) is preferably 40 nm to 150 nm. 50C If the wavelength is less than 40 nm, the colorant particles placed near the surface of the image may become unevenly distributed, making it easier for the chemical to penetrate the image layer, which may reduce the effectiveness of improving chemical resistance. On the other hand, D 50C If the particle size is greater than 150 nm, irregularities originating from the pigment particles near the surface of the image may become somewhat noticeable, light scattering may increase, and the effect of improving image clarity may decrease. Cumulative 50% particle size (D) of the volume-based particle size distribution of pigment particles 50C) is preferably 80 nm to 120 nm. D of the colorant particles 50C This can be measured by dynamic light scattering using a sample containing approximately 1.0% colorant particles, under the same conditions as the method described above for determining whether or not it corresponds to "resin particles."

[0064] [Difference in particle size between colorant particles and resin particles] The cumulative 50% particle size (D) of the volume-based particle size distribution of colorant particles. 50C ) and the cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles. 50R ) difference (D 50C -D 50R ) is 10nm or larger. 50C -D 50R By setting the value to 10nm or more, the chemical resistance of the image can be improved without reducing the image quality. 50C -D 50R " is preferably 150nm or less, and more preferably 100nm or less. 50C -D 50R If the wavelength exceeds 150 nm, resin particles can easily penetrate the gaps between colorant particles formed by the ink applied to the recording medium, making it difficult for resin particles to be positioned near the surface of the image. As a result, chemicals can easily penetrate the image layer, which may reduce the effect of improving the image's chemical resistance. The effect of improving image quality may also be reduced.

[0065] [Mass ratio of colorant particles to resin particles] The content (mass%) of colorant particles in the ink is preferably 1.0 to 100.0 times the mass ratio of the resin particle content (mass%). If the above mass ratio is less than 1.0, the resin particle content is slightly high, which may hinder the fixation of the colorant particles to the recording medium. As a result, when stress is applied to the image along with the chemical, the image may easily peel off from the recording medium. On the other hand, if the above mass ratio is greater than 100.0 times, the resin particle content is slightly low, which may result in a slightly smaller amount of resin particles positioned near the surface of the image. As a result, the chemical may penetrate the image layer more easily, and the effect of improving the chemical resistance of the image may decrease.

[0066] (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. Deionized water (ion-exchanged water) is preferably used as the water. The water content (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 solvent usable for inkjet inks, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The water-soluble organic solvent content (mass%) 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 water-soluble organic solvent content is outside the above range, the reliability of the inkjet aqueous ink, such as its adhesion resistance, may decrease.

[0067] (Other ingredients) In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives such as surfactants, pH adjusters, defoamers, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, and chelating agents. When surfactants are used, the surfactant content (mass%) in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the ink.

[0068] The ink may further contain other resins in addition to resin particles formed from crystalline polyester resin. These other resins may include resin dispersants for dispersing pigments. It is preferable to use a water-soluble resin as the other resin. Examples of water-soluble resins include block copolymers, random copolymers, graft copolymers, and combinations thereof. Examples of water-soluble resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred.

[0069] (Ink properties) The ink of the present invention is an aqueous ink for use in inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 10.0 mPa·s, more preferably 1.0 mPa·s to 5.0 mPa·s, and particularly preferably 1.0 mPa·s to 3.0 mPa·s. The surface tension of the ink at 25°C is preferably 10 mN / m to 60 mN / m, more preferably 20 mN / m to 60 mN / m, and particularly preferably 30 mN / m to 50 mN / m. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5.

[0070] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0071] <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 aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0072] Figure 2 is a schematic diagram 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 the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a 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 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32.

[0073] Any recording medium can be used as the recording medium to be recorded using the ink of the present invention. Recording media with ink absorption properties can be used, such as recording media without a coating layer, such as plain paper, and recording media with a coating layer, such as glossy paper or matte paper. In addition, recording media with low ink absorption or no ink absorption properties, such as printing paper, coated paper, resin sheets, and resin films, can be used. The ink of the present invention can be suitably used for applications in which images are recorded by directly applying ink to such recording media. [Examples]

[0074] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0075] <Method for measuring physical properties> (Melting point of crystalline polyester resin) Resin particles formed from 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 the measurement sample. The melting peak temperature measured using a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments) in accordance with JIS K 7121:1987 was defined as the "melting point". A melting peak was determined to have been obtained when the endothermic amount obtained from the integral value of the peak was 20 J / g or more, and this melting peak temperature was defined as the "melting point".

[0076] (Acid value of crystalline polyester resin) Resin particles formed from crystalline polyester resin were precipitated using a 1.0 mol / L hydrochloric acid aqueous solution, thoroughly washed with water, and dried at 60°C. The resulting dried material was added to 50 mL of tetrahydrofuran at 50°C and dissolved, then 5 mL of water was added and the mixture was cooled to room temperature to obtain the measurement sample. The acid value of the polyester resin was measured by neutralization titration of the obtained measurement sample. For neutralization titration, a potentiometric automatic titrator (product name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a composite glass electrode (product name "C-171", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) was used. A 0.5 mol / L potassium hydroxide ethanol solution was used as the titration reagent.

[0077] (Weight-average molecular weight of crystalline polyester resin) Resin particles formed from 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 material was added to tetrahydrofuran, and the crystalline polyester resin was dissolved at 25°C for 24 hours. The mixture was then filtered through a membrane filter to obtain the measurement sample. The resin content in the measurement sample was adjusted to approximately 0.3%. The prepared measurement sample was analyzed by gel permeation chromatography according to the conditions shown below, and the weight-average molecular weight was calculated using a molecular weight calibration curve created using standard polystyrene resin. The standard polystyrene resin used was "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500" (manufactured by Tosoh Corporation). • HPLC system: Product name "2695 Separations Module" (manufactured by Waters) • Differential refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) • Column: 4-row column of product name "GPC KF-806M" (manufactured by Showa Denko) • Eluent: Tetrahydrofuran ·Flow rate: 1.0mL / min Oven temperature: 40℃ • Sample injection volume: 100 μL

[0078] (Determination of whether the sample is a particle or not, particle size) The liquid containing the sample was diluted with pure water to obtain a measurement sample with a sample content of approximately 1.0%. Then, the particle size (D) of the resin particles in the measurement sample was measured using a particle size analyzer. 50R , D 90R ) and the particle size (D 50CThe particle size was measured. The measurement conditions are as follows. A particle size analyzer using the dynamic light scattering method (product name "NanoTrac WAVE II-Q", manufactured by MicroTrac-Bel) was used as the particle size analyzer. If particles with a particle size were measured using the above method, the sample was determined to be "particles" ("aqueous dispersion"), and if particles with a particle size were not measured, the sample was determined not to be "particles" ("aqueous solution"). [Measurement conditions] SetZero: 30 seconds Number of measurements: 10 Measurement time: 120 seconds Shape: true spherical Refractive index: 1.5 Density: 1.0

[0079] <Synthesis of polyester resin> A reaction vessel equipped with a stirrer, condenser, and thermometer was prepared. A mixture of polyhydric alcohols and polyhydric carboxylic acids of the types and amounts (in parts) shown in Table 1 was placed in this reaction vessel. Furthermore, tetra-n-butyl titanate was added as a catalyst in an amount equal to 200 ppm based on the total amount of polyhydric alcohols and polyhydric carboxylic acids, and the temperature was raised to 240°C over 4 hours to carry out the esterification reaction. After reducing the pressure in the system to 26 Pa over 20 minutes, the reduced pressure state of 240°C and 26 Pa was maintained for the reaction time shown in Table 1 to polymerize a resin with a weight-average molecular weight of 25,000. After returning to 25°C and atmospheric pressure, the contents were crushed with a crusher to obtain polyester resin. The physical properties of the obtained polyester resin are shown in Table 1. Of the obtained polyester resins, polyester resins 1-15 and 17, which have melting points, are crystalline polyester resins, and polyester resin 16, which does not have a melting point, is an amorphous polyester resin. The meaning of the abbreviations for 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: Dodecane dioxide SEA: Sebaciate • ADA: Adipic acid SUA: succinic acid tPA: Terephthalic acid iPA: Isophthalic acid

[0080] TIFF2023084668000001.tif128170

[0081] <Manufacturing of resin particles> (Resin particles 1-23, 25) A 2L beaker equipped with a stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was prepared. The types of polyester resins shown in Table 2 were dissolved in tetrahydrofuran heated to 45°C, and 300 parts of resin solutions of the concentrations shown in Table 2 were prepared and placed in the beaker. A 5% potassium hydroxide aqueous solution in an amount corresponding to the neutralization rate shown in Table 2, based on the acid value of the polyester resin, was added and stirred for 30 minutes. Under conditions of 45°C, 300 parts of deionized water were added dropwise at a rate of 20 mL / min while stirring at the rotation speed shown in Table 2. After removing the organic solvent and some water by reducing the pressure, the contents of the beaker were filtered using a 150-mesh wire mesh (a filter in which 150 stainless steel wires are woven vertically and horizontally in a 1-inch square). An appropriate amount of deionized water was added to adjust the resin particle content, and a liquid containing each resin particle with a resin particle content of 25.0% was obtained.

[0082] (Resin particles 24) 30% by mass resin solution, prepared by dissolving polyester resin 16 (crystalline polyester without carboxylic acid groups) in tetrahydrofuran heated to 45°C, was placed in a 2L beaker. Then, 9 parts of surfactant (product name "Emal 0", manufactured by Kao Corporation) were added and the mixture was stirred for 30 minutes. Next, 300 parts of deionized water heated to 45°C were added. Using an ultrasonic irradiator (product name "S-150D Digital Sonifire", manufactured by Branson Corporation), the mixture was emulsified under the conditions of 50W, 20kHz, and 30 minutes, after which the organic solvent and some water were removed by distillation 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 vertically and horizontally per 1-inch square). 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.

[0083] The cumulative 50% particle size (D) of the resin particles in the liquid containing each of the obtained resin particles, based on volume. 50R (nm), and volume-based cumulative 90% particle size (D 90R ) for the cumulative 50% particle size (D) based on volume. 50R The ratio value of (D 50R / D 90R The (times) are shown in Table 2.

[0084] TIFF2023084668000002.tif197170

[0085] <Manufacturing of colorant particles> (Coloring material particles 1, 2, 6~13) A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 zirconia beads with a diameter of 0.3 mm was filled with a mixture of 10.0 parts of the colorants of the types shown in Table 3, 20.0 parts of a resin-containing liquid, and 70.0 parts of deionized water, and dispersed for the dispersion time shown in Table 3. As the resin-containing liquid, an aqueous solution with a resin content of 30.0% was used, obtained by dissolving a water-soluble resin in an aqueous potassium hydroxide solution equimolar to its acid value. This water-soluble resin is a styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 167 mgKOH / g and a weight-average molecular weight of 10,000. After removing coarse particles by centrifugation, the mixture was pressure-filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. The concentration was adjusted by adding an appropriate amount of deionized water to obtain liquids 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: CI Pigment Yellow 74 (Product name "Hansa yellow 5GX 01 LV 3344", manufactured by Clariant)

[0086] (Coloring material particles 3) 5.0 g of concentrated hydrochloric acid was dissolved in 5.5 g of water and the solution was cooled to 5°C. 1.6 g of 4-aminophthalic acid was then added to this solution. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C. A solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of ion-exchanged water at 5°C was added. After stirring for 15 minutes, 6.0 g of carbon black (product name "NIPex90", manufactured by Orion Engineered Carbons) was added under stirring. The mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and the mixture was dried in an oven at 110°C. Subsequently, sodium ions were replaced with potassium ions by ion exchange to obtain a liquid containing self-dispersing pigment, which is a colorant particle in which two -C6H3-(COOK) groups are bonded to the surface of the carbon black particles. An appropriate amount of deionized water was added to adjust the content of the colorant particles, and a liquid containing colorant particles 3 with a colorant particle (self-dispersing pigment) content of 10.0% was obtained.

[0087] (colorant particles 4) A 2L beaker equipped with a stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was prepared. 300 parts of a 30% tetrahydrofuran solution of styrene-ethyl acrylate-acrylonitrile-acrylic acid copolymer with an acid value of 60 mg KOH / g and a weight-average molecular weight of 10,000, and 9 parts of CI Basic Red 1 were added to this beaker and stirred for 30 minutes. Next, an amount equivalent to 50 mol% of the copolymer's acid value, consisting of a 5% sodium hydroxide aqueous solution, was added and stirred for 30 minutes. While stirring, 300 parts of deionized water were added dropwise at a rate of 20 mL / min. After removing the organic solvent and some water by reducing the pressure, the contents of the beaker were filtered using a 150-mesh wire mesh (a filter with 150 stainless steel wires woven vertically and horizontally per 1-inch square). An appropriate amount of deionized water was added to adjust the concentration, and a liquid containing 10.0% colorant particles (resin particles dyed with dye) was obtained, which contained 4 colorant particles.

[0088] (color material particles 5) 300 parts of a 30% methyl ethyl ketone solution of a styrene-ethyl acrylate-acrylonitrile-acrylic acid copolymer with an acid value of 60 mg KOH / g and a weight-average molecular weight of 10,000 were placed in a 2 L beaker. 9 parts of CI Basic Red 1 and a mixture of 300 parts of 5% sodium hydroxide aqueous solution and deionized water, in an amount equivalent to 50 mol% based on the acid value of the copolymer, were added. Emulsification was performed using an ultrasonic irradiator (product name "S-150D Digital Sonifier", manufactured by Branson) at 50 W, 20 kHz, and for 30 minutes, after which the organic solvent and some water were removed by distillation under reduced pressure. The contents of the beaker were filtered using a 150-mesh wire mesh (a filter with 150 stainless steel wires woven vertically and horizontally per 1 inch square). The concentration was adjusted by adding an appropriate amount of deionized water to obtain a liquid containing 10.0% colorant particles (dye dispersed by resin) and colorant particles 5.

[0089] The cumulative 50% particle size (D) of the volume-based particle size distribution of the colorant particles in the liquid containing the obtained colorant particles. 50C ) are shown in Table 3.

[0090] TIFF2023084668000003.tif116170

[0091] <Ink preparation> (Examples 1-39, Comparative Examples 1-5) The following components were mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size microfilter to prepare the ink. Of the components listed below, "Acetylenel E100" is a trade name for a nonionic surfactant (manufactured by Kawaken Fine Chemicals). The physical properties of the ink are shown in Tables 4-1 and 4-2. • Liquids containing resin particles: The amount of resin particles R(%) shown in Tables 4-1 and 4-2. • Liquid containing colorant particles: The amount of colorant particles C(%) shown in Tables 4-1 and 4-2. Glycerin: 5.00% Triethylene glycol: 10.00% • Acetyleneol E100: 0.10% • Ion-exchanged water: Remaining volume (%) where the total amount of components is 100.00%

[0092] (Comparative Example 6) The "pigment-containing polymer particles" and "Em4-1" described in Japanese Patent Publication No. 2014-125555 were prepared. Then, the following components were mixed and thoroughly stirred, and the mixture was pressure filtered through a microfilter with a pore size of 2.5 μm to prepare the ink. The 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% • Acetyleneol E100: 0.10% • Ion-exchanged water: Remaining volume (%) when the total amount of components reaches 100.00%

[0093] TIFF2023084668000004.tif191170

[0094] TIFF2023084668000005.tif196170

[0095] <Rating> In this invention, "A" and "B" are considered acceptable levels in the evaluation criteria for each item shown below, and "C" is considered an unacceptable level. Furthermore, even within the same evaluation criteria, if a clear difference is observed, those that are relatively inferior among those rated "A" are rated "A - " and among those "B", those that are relatively inferior are designated as "B - The evaluation results are shown in Table 5.

[0096] (chemical resistance) Each prepared ink was filled into an ink cartridge and mounted on an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from the recording head using thermal energy. In this example, a recording duty cycle of 100% was defined as a solid image recorded under the condition that one drop of ink with a concentration of 5 pL per drop is applied to a unit area of ​​1 / 1,200 inch × 1 / 1,200 inch. Using this inkjet recording device, a 200 mm × 200 mm solid image with a recording duty cycle of 100% was recorded on a recording medium (product name "Aurora Coat", manufactured by Nippon Paper Industries). After drying the recorded image at 25°C for 24 hours, it was heated in a heated oven at 100°C for 5 minutes. After the temperature of the heated image returned to 25°C, 0.1 g of 70% ethanol aqueous solution was placed on it, and after 1 minute, it was wiped off with a cellulose nonwoven cloth, and the chemical resistance of the image was evaluated according to the evaluation criteria shown below. A: There were no traces of liquid droplets on the image. B: The area ratio of the exposed recording medium to the area where the droplets were attached was less than 5%. C: The ratio of the exposed recording medium area to the area where the droplets were attached was 5% or more.

[0097] (Mapping property) Using the inkjet recording device described above, a 2cm x 2cm solid image with a 100% recording duty cycle was recorded on a recording medium (product name "Canon Photo Paper Gloss Gold GL-101", manufactured by Canon). After drying the recorded image at 25°C for 24 hours, two fluorescent lamps placed in parallel 10cm apart were used to illuminate the image from a distance of 2m at a 45-degree angle (illumination angle 45 degrees). The shape of the fluorescent lamps projected onto the image was visually confirmed from a 45-degree angle (observation angle 45 degrees), and the image quality was evaluated according to the evaluation criteria shown below. A: The boundary between the two projected fluorescent lights was clear, and no blurring was observed at the edges. B: The boundary between the two projected fluorescent lights was discernible, but a slight blurring was observed at the edges. C: I couldn't see the boundary between the two projected fluorescent lights.

[0098] TIFF2023084668000006.tif170170

[0099] Furthermore, the disclosure of this embodiment includes the following configuration. (Composition 1) An aqueous inkjet ink containing colorant particles and resin particles, The resin particles are formed from a crystalline polyester resin having a carboxylic acid group. The cumulative 50% particle size (D) of the volume-based particle size distribution of the aforementioned colorant particles 50C ) and the cumulative 50% particle size (D) of the volume-based particle size distribution of the resin particles. 50R ) difference (D 50C -D 50R A water-based ink characterized by having a n-cell size of 10 nm or larger. (Configuration 2) D 50C -D 50R However, the water-based ink described in Configuration 1 has a wavelength of 150 nm or less. (Configuration 3) D 50C -D 50R However, the aqueous ink described in configuration 1 or 2 is 100 nm or less. (Configuration 4) D 50R However, the aqueous ink described in any one of items 1 to 3, wherein the wavelength is between 5 nm and 30 nm. (Configuration 5) D 50R However, the cumulative 90% particle size (D) of the volume-based particle size distribution of the aforementioned resin particles 90R A water-based ink according to any one of items 1 to 4, wherein the ratio to ) is 0.6 times or more. (Configuration 6) An aqueous ink according to any one of Configurations 1 to 5, wherein the content (mass%) of the colorant particles is 1.0 times or more and 100.0 times or less by mass ratio to the content (mass%) of the resin particles. (Configuration 7) An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is an aqueous ink according to any one of the items 1 to 6 of the configuration. (Configuration 8) An inkjet recording method that ejects ink from an inkjet recording head to record an image on a recording medium, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of the items 1 to 6.

Claims

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 particle diameter of the colorant particles at cumulative 50% of the particle size distribution based on the volume (D ５０Ｃ ) and the cumulative 50% particle diameter (D ５０Ｒ ) and the difference (D ５０Ｃ -D ５０Ｒ ) is 10 nm or more.

2. The above D ５０Ｃ -D ５０Ｒ The aqueous ink according to claim 1, wherein the average particle diameter is 150 nm or less.

3. The above D ５０Ｃ -D ５０Ｒ The aqueous ink according to claim 1, wherein the average particle size is 100 nm or less.

4. An aqueous ink as described in claim 1, wherein the weight average molecular weight of the crystalline polyester resin is 15,000 or more and 30,000 or less.

5. An aqueous ink as described in claim 1, wherein the content (mass %) of the resin particles is 0.01 mass % or more and 10.00 mass % or less, based on the total mass of the ink.

6. An aqueous ink as described in claim 1, wherein the content (mass %) of the resin particles is 0.02 mass % or more and 5.00 mass % or less, based on the total mass of the ink.

7. An aqueous ink as described in claim 1, wherein the acid value of the crystalline polyester resin is 15 mg KOH / g or more and 25 mg KOH / g or less.

8. The above D ５０Ｒ The aqueous ink according to any one of claims 1 to 7, wherein the average particle size is 5 nm or more and 30 nm or less.

9. The above D ５０Ｒ is the cumulative 90% particle diameter (D ９０Ｒ 8. The aqueous ink according to claim 1, wherein the ratio of the amount of the water-soluble polymer to the amount of the water-soluble polymer is 0.6 times or more.

10. The aqueous ink according to claim 9, wherein the ratio of D 50R to D 90R is 0.8 or less.

11. 8. The aqueous ink according to claim 1, wherein the content (mass %) of the colorant particles is 1.0 to 100.0 times the content (mass %) of the resin particles in terms of mass ratio.

12. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge, wherein the ink is the aqueous ink according to any one of claims 1 to 7.

13. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, An ink-jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 7.

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