Inkjet recording method and inkjet recording apparatus

Abstract

To provide an inkjet recording method in which ink dischargeability hardly deteriorates although a cumulative discharge frequency increases, when using a miniaturized inkjet recording apparatus comprising a recording head with a mechanism for heating aqueous ink.SOLUTION: An inkjet recording method includes a step for recording an image by applying aqueous ink to a recording medium by using an inkjet recording apparatus comprising aqueous ink containing a pigment and resin particles, an ink storage part, and a recording head in which a discharge port is formed for discharging the aqueous ink according to an action of heat energy. The ink storage part is a housing formed of thermoplastic resin, and the recording head is bonded thereto without interposing another member. The recording head includes heating means for heating the aqueous ink in the recording head, and an amount (μmol / g) of an anionic group in the resin particles is smaller than an amount (μmol / g) of an anionic group in the pigment.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus. [Background technology]

[0002] In recent years, the demand for home inkjet recording devices has increased due to an increase in remote work from home. In addition, there is a demand for inkjet recording devices to be further miniaturized for home use. In order to miniaturize inkjet recording devices, miniaturization of the recording head and ink storage unit is essential. For example, there is an inkjet recording device equipped with a miniaturized recording unit that integrates the ink storage unit and the recording head.

[0003] From the viewpoint of enabling a more compact design, such inkjet recording devices employ a recording head that ejects ink by the action of thermal energy. Also, by providing ejection port rows that eject ink of multiple colors on the same recording element substrate, the recording head can be made smaller. Furthermore, the recording unit is made smaller by bonding the recording head to the ink storage section without using any other members. The ink storage section is made of a thermoplastic resin to reduce the weight of the recording unit and to reduce the rigidity required for the carriage section, thereby making the device smaller.

[0004] On the other hand, there are inkjet recording devices equipped with a recording head having a mechanism for heating the ink therein. In such recording devices, the ink heating mechanism keeps the temperature of the ink in the recording head at a moderate temperature, suppressing the variation in the volume of the ink droplets ejected and suppressing the occurrence of image unevenness. If the ink temperature is about to exceed a predetermined upper limit during recording, the recording operation is started after waiting for the recording head temperature to drop, or the recording operation is stopped. If the temperature of the recording head rises excessively, bubbles may be generated in the ink. The generated bubbles may cause the ink to fail to eject, resulting in missing images and causing the recording head or recording device to break down.

[0005] In addition, the output of business documents is increasing as a home use of a miniaturized inkjet recording device. In inkjet recording devices used for such purposes, water-based pigment inks containing pigments as coloring materials are widely used to record images with excellent color development. Since pigments are insoluble in water, they exist in a dispersed state in water-based inks. When water-based pigment inks are discharged from a recording head that applies thermal energy to discharge ink, the dispersion state of the pigments becomes unstable, and scorch may adhere to the heater that generates the thermal energy. When scorch accumulates on the heater, the thermal energy applied to the ink decreases, and the ink dischargeability decreases. For this reason, the ink dischargeability changes depending on the cumulative number of times that ink is discharged from the discharge port. That is, the ink dischargeability from a discharge port with a small cumulative number of discharges is good, while the ink dischargeability from a discharge port with a large cumulative number of discharges is poor, and such a difference leads to the occurrence of image unevenness. Therefore, even if the cumulative number of discharges differs for each discharge port, it is required that the ink dischargeability does not change.

[0006] For example, a water-based ink has been proposed in which a water-soluble resin is added to stabilize the ink ejection properties and the pigment dispersibility, and a specific surfactant is further added to remove scorch marks on the heater (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-143803 Summary of the Invention [Problem to be solved by the invention]

[0008] The present inventors used a compact inkjet recording device having the above-mentioned configuration to evaluate the ejection properties of the ink proposed in Patent Document 1. As a result, it was found that the ejection properties of the ink from some ejection ports decreased with an increase in the cumulative number of ejections.

[0009] The inventors also prepared a print head that does not have a mechanism for heating the ink, a print head that uses energy other than thermal energy, a print head that is integrated with an ink storage section, and a print head that has a heat sink between the ink storage section and the print head. Using inkjet recording devices each equipped with these print heads, the ejection properties of the ink proposed in Patent Document 1 were evaluated. As a result, unlike the case where the aforementioned inkjet recording device corresponding to miniaturization was used, the ejection properties of the ink from the ejection port did not decrease even when the cumulative number of ejections increased.

[0010] Therefore, an object of the present invention is to provide an inkjet recording method in which the ink ejection properties are not likely to deteriorate even if the cumulative number of ejections increases when a compact inkjet recording device equipped with a recording head having a mechanism for heating the water-based ink is used. Another object of the present invention is to provide an inkjet recording device used in this inkjet recording method. [Means for solving the problem]

[0011] That is, according to the present invention, there is provided an inkjet recording method comprising a step of applying the water-based ink ejected from the ejection port to a recording medium to record an image using an inkjet recording device comprising an aqueous ink containing a pigment and resin particles, an ink storage section for storing the aqueous ink, and a recording head formed with an ejection port for ejecting the aqueous ink supplied from the ink storage section by the action of thermal energy, wherein the ink storage section is a housing formed of a thermoplastic resin, and the recording head is bonded to the ink storage section without any intervening member, the recording head has a heating means for heating the aqueous ink in the recording head, and the amount of anionic groups (μmol / g) of the resin particles is less than the amount of anionic groups (μmol / g) of the pigment. Effect of the Invention

[0012] According to the present invention, it is possible to provide an inkjet recording method in which the ink ejection properties are not easily deteriorated even if the cumulative number of ejections increases when a compact inkjet recording device equipped with a recording head having a mechanism for heating the water-based ink is used. Also, according to the present invention, it is possible to provide an inkjet recording device used in this inkjet recording method. [Brief description of the drawings]

[0013] [Figure 1] 1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. [Diagram 2] 1 is a perspective view showing a schematic internal structure of an inkjet recording apparatus according to an embodiment of the present invention; [Diagram 3] 1A and 1B are diagrams illustrating an example of a recording unit, in which FIG. 1A is a perspective view and FIG. 1B is a perspective view in an exploded state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0015] A recording head that ejects ink by the action of thermal energy is usually temperature-adjusted based on the temperature read by a sensor attached to the recording head. For cost reasons, this sensor is not provided for all ejection ports, and only a few are provided for each recording head. In addition, if the recording head is directly attached to the ink storage section, which is a housing made of thermoplastic resin, without a heat sink or the like, heat is likely to be trapped after recording, and the temperature of the recording head as a whole is difficult to drop. For this reason, temperature variations are likely to occur between the ejection ports that have been used and the ejection ports that have not been used. In particular, heat is likely to be trapped in the center of the recording head, and the temperature is difficult to drop, so that even if the temperature of the ejection port near the sensor has dropped, the temperature of the other ejection ports may not have dropped. If the temperature of the recording head is adjusted in such a state, the ejection ports whose temperature has not dropped will be in an overheated state, and the dispersion state of the pigment in the ink will become unstable. If thermal energy is applied to ink containing a pigment whose dispersion state has become unstable, scorching will easily adhere to the heater. As a result, it is believed that the ejection performance of the ink decreases according to the cumulative number of times the ink is ejected from the ejection port.

[0016] In the case of a so-called piezo type recording head, which ejects ink by deformation of a piezo element, scorching does not occur, so there is no deterioration in ink ejection due to scorching. Also, when using a recording unit with improved heat dissipation, such as by placing a metal heat sink between the ink storage unit and the recording head, heat is less likely to build up in the ejection port and the ink does not overheat, so the ink ejection is less likely to deteriorate.

[0017] The present inventors have conducted various studies to suppress the deterioration of ink ejection properties even when the cumulative number of ejections increases when an image is recorded using a compact inkjet recording device having the following configurations (i) to (iii). As a result, they have found that by using an ink in which the amount of anionic groups in the resin particles (μmol / g) is less than the amount of anionic groups in the pigment (μmol / g), it is possible to suppress the accumulation of kogation on the heater and suppress the deterioration of ink ejection properties. (i) The ink jet recording device comprises an ink containing a pigment and resin particles, an ink storage section for storing the ink, and a recording head having an ejection port formed therein for ejecting the ink supplied from the ink storage section by the action of thermal energy. (ii) The ink container is a housing made of a thermoplastic resin, and the recording head is bonded to the ink container without any other member therebetween. (iii) The recording head has a mechanism for heating the ink inside the recording head.

[0018] Like the pigment, the dispersion state of the resin particles also becomes unstable when the ink is overheated. When thermal energy is applied to ink containing resin particles in an unstable dispersion state to eject the ink, the heat of the heater makes it easier for the resin particles to adhere to the heater. Here, if the amount of anionic groups of the resin particles is less than the amount of anionic groups of the pigment, the resin particles are more likely to be burned, and the burnt particles derived from the resin particles adhere to the heater before the burnt particles derived from the pigment. The burnt particles derived from the resin particles that adhere to the heater are easily detached by the thermal energy of the heater, and an equilibrium state between attachment and detachment is reached. Therefore, even if the burnt particles derived from the pigment adhere to the burnt particles derived from the resin particles, the burnt particles derived from the pigment are easily detached together with the burnt particles derived from the resin particles, so that the accumulation of the burnt particles on the heater is suppressed. As a result, it is considered that the deterioration of the ejectability of the ink is suppressed even when the cumulative number of ejections increases. In other words, it is considered that the resin particles play a role in preventing the pigment from being directly burnt on the heater and protecting the heater. If the amount of anionic groups in the resin particles is equal to or greater than the amount of anionic groups in the pigment, the pigment will burn preferentially, and the burnt material derived from the pigment will adhere to the heater first, making it impossible to suppress a decrease in the ejection performance of the ink.

[0019] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention is a recording method using an inkjet recording device including an ink, an ink storage section for storing the ink, and a recording head. The ink contains pigment and resin particles. The recording head is a member having an ejection port formed therein for ejecting the ink supplied from the ink storage section by the action of thermal energy. The inkjet recording method of the present invention includes a step of applying the ink ejected from the ejection port to a recording medium to record an image. The ink storage section is a housing formed of a thermoplastic resin, and the recording head is bonded to the ink storage section without any other member being interposed therebetween. The recording head has a mechanism for heating the ink in the recording head. The amount of anionic groups (μmol / g) of the resin particles in the ink is less than the amount of anionic groups (μmol / g) of the pigment in the ink.

[0020] The inkjet recording device of the present invention includes an ink, an ink storage section that stores the ink, and a recording head. The ink contains pigment and resin particles. The recording head is a member having an ejection port that ejects ink supplied from the ink storage section by the action of thermal energy. The ink storage section is a housing made of a thermoplastic resin, and the recording head is attached to the ink storage section without any other member being interposed. The recording head has a mechanism for heating the ink in the recording head. The amount of anionic groups of the resin particles in the ink (μmol / g) is less than the amount of anionic groups of the pigment in the ink (μmol / g).

[0021] (Inkjet recording device) Fig. 1 is a perspective view showing a schematic diagram of an embodiment of an inkjet recording apparatus of the present invention. As shown in Fig. 1, an inkjet recording apparatus 70 of this embodiment has an exterior 71 and a cover member 72 provided on the upper surface of the exterior 71. The cover member 72 is a member that can be opened and closed in the vertical direction, and by opening it in the upward direction, the inside of the inkjet recording apparatus 70, which has a substantially rectangular parallelepiped shape, can be seen.

[0022] FIG. 2 is a perspective view showing a schematic internal structure of an embodiment of an inkjet recording device of the present invention. A recording unit 8 in which a recording head and an ink storage unit are integrally formed is configured to be mountable on a carriage (support member) 81, and is mounted on the carriage by connecting to a joint (not shown) provided on the upper part of the carriage 81. The recording unit 8 is connected to a tube 82 which is a flexible member, and the other end of the tube 82 is connected to a main tank (second ink storage unit) 73 which is a second ink storage unit. When the recording unit 8 is mounted on the carriage 81, the recording head 11 (FIG. 3) communicates with the main tank 73 via the joint and the tube 82. The inkjet recording device 70 of this embodiment is a serial scan type recording device, and the carriage 81 is guided by a guide shaft so as to be freely movable in the main scanning direction. The carriage 81 reciprocates in the main scanning direction by a driving force transmission mechanism such as a carriage motor and a belt which transmits the driving force of the carriage motor (both not shown).

[0023] FIG. 3 is a diagram showing an example of a recording unit, where (a) is a perspective view and (b) is a perspective view in an exploded state. The recording unit 8 shown in FIG. 3 has an ink storage section 10, which is a housing made of a thermoplastic resin, and a recording head 11. The recording head 11 is attached to the ink storage section 10 without any other member such as a heat sink. The ink storage section 10 is lightweight because it is a housing made of a thermoplastic resin. Furthermore, the recording head 11 is attached to the ink storage section 10 without any other member such as a heat sink, so the entire recording unit 8 is small and lightweight. By using such a recording unit 8, the entire inkjet recording device can be made small and lightweight. The heat sink can be made of a material such as a metal oxide such as alumina.

[0024] The recording head 11 is provided with a plurality of ejection ports for ejecting ink, energy generating elements for generating thermal energy for ejecting ink, and the like. The energy generating elements can be driven, for example, by power supplied through an electric wiring member 14. The energy generating elements are elements that generate thermal energy, and the ink can be ejected from the ejection ports by the action of the generated thermal energy.

[0025] The recording head 11 has an ejection port surface in which multiple ejection port arrays each consisting of multiple ejection ports are arranged on the same recording element substrate. By arranging multiple ejection port arrays on the same recording element substrate, it is possible to eject multiple inks with one recording unit, and the entire inkjet recording device can be made smaller. It is preferable that the multiple ejection port arrays are arranged in a direction (sub-scanning direction) perpendicular to the reciprocating movement direction (main scanning direction) of the recording unit. Furthermore, by configuring the ejection port array with multiple ejection ports, the area that can be printed when the recording unit moves becomes wider, and therefore the printing speed can be increased.

[0026] Sponge-like ink absorbers 12a to 12c are stored in the ink storage section 10. Filters 13a to 13c are disposed below the ink storage section 10 in the direction of gravity. By utilizing the capillary force of the sponge-like ink absorbers 12a to 12c to generate negative pressure, it is possible to prevent ink from leaking from the ejection orifices. Furthermore, by disposing the filters 13a to 13c, it is possible to prevent fine foreign matter such as dust from entering the ejection orifices.

[0027] The recording head has a heating means for heating the ink in the recording head. The heating means may be any means capable of heating the ink in the recording head to a temperature higher than the recording environment temperature such as room temperature (25°C). Examples of such heating means include a heater for adjusting the ink temperature arranged in contact with the recording head, and a heater for ink ejection. To heat the ink using a heater for ink ejection, for example, a current that does not eject the ink may be repeatedly passed through the heater. It is preferable to heat the ink using the heating means so that the temperature of the ink in the recording head is 30°C or higher and 60°C or lower.

[0028] The inkjet recording device preferably further includes a second ink storage unit such as a main tank having a larger capacity than the ink storage unit (first ink storage unit) such as a subtank, and a tube through which ink flows between the second ink storage unit and the ink storage unit. Considering the usage mode in remote work at home, it is important to reduce the frequency of replacing the ink cartridge as well as to reduce the size of the device. For this reason, by further providing a second ink storage unit such as a main tank, it is possible to reduce the frequency of ink replacement while avoiding an increase in the size of the device body. Hereinafter, an inkjet recording device in which only a first ink storage unit such as a subtank bonded to a recording head is provided as an ink storage unit is also referred to as a "first device configuration". In addition, an inkjet recording device in which a second ink storage unit such as a main tank having a larger capacity than the subtank is further provided as an ink storage unit is also referred to as a "second device configuration".

[0029] In the case of the second device configuration, the frequency of ink replacement is reduced compared to the first device configuration, so the period during which the ink is held in a stationary state in the main tank is longer. In addition, in the case of pigment ink, the pigment is more likely to settle if the period during which the ink is held in a stationary state is longer. The decrease in ejection performance due to ink adhesion occurs due to the ink drying in the flow path and the pigment coagulating, so the greater the pigment content of the ink used, the more pronounced the ink is. Depending on the usage conditions, the adhesion recovery of the second device configuration is often inferior to that of the first device configuration. Furthermore, if there is a difference in adhesion recovery between inks, the difference becomes greater. For this reason, generally, the second device configuration is prone to problems such as an even greater amount of waste ink compared to the first device configuration. In contrast, in the inkjet recording method of the present invention, the difference in adhesion recovery between the inks used is small, so it is possible to reduce the amount of waste ink even when the second device configuration is used, and it is possible to achieve both a reduction in the frequency of ink replacement and a reduction in the amount of waste ink.

[0030] (Water-based ink) The inkjet recording method of the present invention includes a step of recording an image by applying the ink containing a pigment and resin particles to a recording medium by ejecting the ink from an ejection orifice.

[0031] [Colorant] A pigment is used as the coloring material of the ink. The amount of anionic groups of the pigment (μmol / g) must be greater than the amount of anionic groups of the resin particles (μmol / g). The anionic groups of the pigment correspond to the pigment dispersion method described below. For example, in the case of a dispersion method using a resin, it refers to the amount of anionic groups of the resin, and is expressed as the value of micromoles of anionic groups per unit mass of the total of the pigment and the resin dispersant. In addition, in the case of a self-dispersion method, it refers to the amount of anionic groups bonded to the pigment particle surface directly or via other atomic groups, and is expressed as the value of micromoles of anionic groups per unit mass of the self-dispersion pigment. The content (mass%) of the pigment 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.

[0032] Examples of the pigment include inorganic pigments such as carbon black; and organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, imidazolone pigments, diketopyrrolopyrrole pigments, and dioxazine pigments. Carbon black has a very high decomposition temperature and good heat resistance, so it is likely to be strongly burnt on the heater, and once burnt, it is difficult to peel off from the heater. In contrast, organic pigments have low heat resistance, so even if they are burnt on the heater, they are relatively easy to peel off. For this reason, the ejection properties of inks containing carbon black as a pigment are generally likely to decrease. However, in the inkjet recording method of the present invention, the burnt particles derived from the resin particles adhere to the heater before the burnt particles derived from the pigment, thereby protecting the heater. For this reason, even if an ink containing carbon black as a pigment is used, the decrease in the ejection properties of the ink can be effectively suppressed.

[0033] Examples of pigment dispersion methods include resin-dispersed pigments that use a resin (resin dispersant) as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface. In addition, resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microcapsule pigments in which the pigment particle surface is coated with a resin or the like can be used. Among these, "resin-dispersed pigments" that are dispersed by a resin dispersant physically adsorbed on the pigment particle surface, and "self-dispersed pigments" in which anionic groups are bonded to the pigment particle surface directly or via other atomic groups are particularly preferred.

[0034] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of anionic groups. As the resin dispersant, a water-soluble resin described below can be used. When a resin-dispersed pigment is used, the content (mass%) of the pigment in the ink is preferably 0.2 times or more and 10.0 times or less in mass ratio to the content (mass%) of the resin dispersant.

[0035] As the self-dispersing pigment, an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group can be used, which is bonded to the particle surface of the pigment directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. In addition, it may be a group that is a combination of these groups.

[0036] The amount of anionic groups in the pigment (μmol / g) is preferably 150 μmol / g or more, more preferably 180 μmol / g or more. If the amount of anionic groups in the pigment is less than 150 μmol / g, the pigment becomes unstable in dispersion and is prone to aggregation when heated. Therefore, even if resin particles with a smaller amount of anionic groups are present, the pigment may burn before the resin particles, and the pigment may be easily burned on the heater, which may reduce the effect of suppressing the decrease in the ink ejection performance. The upper limit of the amount of anionic groups in the pigment is preferably 230 μmol / g or less. If the pigment is a resin-dispersed pigment, the amount of anionic groups in the pigment can be adjusted by the mass ratio of the pigment to the resin dispersant, the acid value of the resin dispersant, etc. If the pigment is a self-dispersed pigment, the amount of anionic groups can be adjusted by the density of the anionic groups.

[0037] This section describes a method for confirming the amount of anionic groups in a pigment for an ink that contains a water-soluble resin other than the resin dispersant in addition to a water-soluble resin (resin dispersant) for dispersing the pigment. The ink is concentrated or diluted to prepare a liquid with a solid content (pigment, water-soluble resin, resin particles, etc.) of about 10% by mass. This liquid is centrifuged at 12,000 rpm for one hour. This separates the liquid layer into one containing the water-soluble organic solvent and resin that does not contribute to dispersion, and one containing the pigment, which are then collected separately. The water-soluble resin that is primarily contained in the solid layer containing the pigment is the resin dispersant, and the resin that is primarily contained in the liquid layer is the water-soluble resin that does not contribute to the dispersion of the pigment.

[0038] [Resin particles] The ink contains resin particles having an anionic group. Examples of the anionic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. In this specification, the term "resin particles" refers to a resin that does not dissolve in the aqueous medium constituting the ink, specifically, a resin that can exist in the aqueous medium in a state in which particles whose particle diameter can be measured by dynamic light scattering are formed. On the other hand, the term "water-soluble resin" refers to a resin that can dissolve in the aqueous medium constituting the ink, specifically, a resin that can exist in the aqueous medium in a state in which particles whose particle diameter can be measured by dynamic light scattering are not formed. The term "resin particles" can also be referred to as "water-dispersible resin (water-insoluble resin)".

[0039] Whether or not a certain resin is a "resin particle" can be determined according to the following method. First, a liquid containing the resin to be determined (resin content: 10% by mass) is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with ion-exchanged water to prepare a sample. Then, when the particle size of the resin in the sample is measured by dynamic light scattering, if a particle having a particle size is measured, the particle is determined to be a "resin particle" (water-dispersible resin). On the other hand, if a particle having a particle size is not measured, the resin is determined not to be a "resin particle" (it is a "water-soluble resin"). The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. As a particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method (for example, the product name "Nanotrac UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and the measurement conditions are not limited to those described above.

[0040] The amount of anionic groups in the resin particles (μmol / g) is less than the amount of anionic groups in the pigment (μmol / g), which allows the kogation derived from the resin particles to adhere to the heater before the kogation derived from the pigment, thereby protecting the heater and preventing the kogation derived from the pigment from adhering directly to the heater.

[0041] The amount of anionic groups in the resin particles (μmol / g) is preferably 80 μmol / g or more and 140 μmol / g or less, and more preferably 90 μmol / g or more and 130 μmol / g or less. If the amount of anionic groups in the resin particles is less than 80 μmol / g, the dispersion state of the resin particles becomes unstable and they tend to aggregate when the temperature rises excessively. For this reason, kogation may adhere and accumulate at places in the ejection port other than the heater, and the effect of suppressing the deterioration of the ejection properties of the ink may be reduced. On the other hand, if the amount of anionic groups in the resin particles is more than 140 μmol / g, the dispersion state of the resin particles becomes excessively stable, and kogation derived from the resin particles is less likely to adhere to the heater, so the effect of suppressing the deterioration of the ejection properties of the ink may be reduced.

[0042] The amount of anionic groups in both the pigment and the resin particles can be calculated from the surface charge amount measured by colloid titration. In the examples described below, an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500) was used to measure the surface charge amount of the pigment and the resin particles by colloid titration using potential difference. More specifically, the pigment and the resin particles were each diluted about 300 times (by mass) with pure water, and then the pH was adjusted to about 10 with potassium hydroxide as necessary, and potentiometric titration was performed using 5 mmol / L methyl glycol chitosan as a titration reagent. It is of course possible to measure the amount of anionic groups using pigment and resin particles extracted from ink by an appropriate method.

[0043] The glass transition temperature (Tg (°C)) of the resin particles is preferably higher than the temperature of the ink when the ink in the recording head is heated by the heating means. If the glass transition temperature of the resin particles is lower than the temperature of the heated ink, the resin particles may be more likely to dissolve in the ink, and the ejection properties may be more likely to decrease. The glass transition temperature (Tg (°C)) of the resin particles is preferably equal to or lower than the temperature of the ink when the ink in the recording head is heated by the heating means + 40°C. If the glass transition temperature of the resin particles is excessively higher than the temperature of the heated ink, the dispersibility of the resin particles becomes stable and scorch adhesion to the heater becomes difficult, which may reduce the effect of suppressing the decrease in the ejection properties of the ink.

[0044] The glass transition temperature (Tg (°C)) of the resin particles can be measured using a differential scanning calorimeter (DSC). Specifically, the resin particles are first dried at 60°C, and 2 mg of the dried product is sealed in an aluminum container. Then, the glass transition temperature (Tg (°C)) of the resin particles can be measured using a differential scanning calorimeter (DSC, product name "Q1000", manufactured by TA instruments) for this dried product. The temperature program for measuring the glass transition temperature may be, for example, the following procedures (1) and (2). (1) Heat to 200°C at 10°C / min, then cool from 200°C to -50°C at 5°C / min. (2) Next, a thermal analysis is performed while increasing the temperature from -50°C to 200°C at a rate of 10°C / min.

[0045] The content (mass%) of the resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 1.5% by mass or more and 8.0% by mass or less, based on the total mass of the ink. The content (mass%) of the resin particles in the aqueous ink is preferably 0.4 times or more in terms of mass ratio to the content (mass%) of the pigment. If the mass ratio is less than 0.4 times, the heater cannot be protected even by the burnt particles derived from the resin particles, and the burnt particles derived from the pigment may easily adhere to the heater. For this reason, the effect of suppressing the decrease in the ejection property of the ink may decrease. The upper limit of the mass ratio is not particularly limited, but is preferably 1.0 times or less. Examples of the resin particles include acrylic resin particles, polyolefin resin particles, urethane resin particles, and polyester resin particles. Among them, acrylic resin particles are particularly preferred.

[0046] [Water-soluble resin] The ink may contain a water-soluble resin. The content (mass%) of the water-soluble resin in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. The water-soluble resin may be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) to improve various properties of the recorded image. Examples of the form of the water-soluble resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Examples of the water-soluble resin include acrylic resins, urethane resins, and olefin resins.

[0047] When carbon black is used as the pigment, the ink preferably contains a water-soluble resin having a unit derived from styrene. Since styrene strongly interacts with carbon black, the water-soluble resin having a unit derived from styrene is adsorbed to the carbon black and can stabilize the dispersibility of the carbon black. As a result, the heater is less likely to become burnt due to the pigment, and the decrease in the ejection performance can be further suppressed. The ratio (mass%) of the unit derived from styrene in the water-soluble resin is preferably 10.0 mass% or more. If the ratio of the unit derived from styrene is less than 10.0 mass%, the effect of stabilizing the dispersibility of the pigment is weakened, and the effect of suppressing the decrease in the ejection performance of the ink may decrease. The ratio (mass%) of the unit derived from styrene in the water-soluble resin is preferably 50.0 mass% or less, more preferably 30.0 mass% or less.

[0048] [Resin composition] Preferred constituent units of the resin particles and water-soluble resin will be described. In this specification, "acrylic resin" refers to a resin having at least a unit derived from an acrylic monomer such as (meth)acrylic acid or (meth)acrylate. In the following description, "(meth)acrylic" means "acrylic" and "methacrylic", and "(meth)acrylate" means "acrylate" and "methacrylate".

[0049] [Acrylic resin] The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as constituent units. The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

[0050] The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and the like.

[0051] [Urethane resin] The urethane resin can be obtained, for example, by reacting polyisocyanate with a component that reacts therewith (polyol or polyamine). In addition, the urethane resin may be further reacted with a crosslinking agent or a chain extender. In particular, the ink preferably contains a water-soluble urethane resin having a urea bond. When thermal energy generated by a heater is applied to a water-soluble urethane resin having a urea bond, amines are generated and the pH of the ink increases locally. When the pH of the ink increases, the dispersibility of the pigment is stabilized, and scorch originating from the pigment is less likely to adhere to the heater, further improving the effect of suppressing the decrease in the ejection properties of the ink.

[0052] Polyisocyanates are compounds that have two or more isocyanate groups in their molecular structure. Examples of polyisocyanates that can be used include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of the aliphatic polyisocyanate include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0053] Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0054] A polyol is a compound having two or more hydroxyl groups in its molecular structure. Examples of the polyol include polyols having no acid group and polyols having an acid group.

[0055] Examples of polyols without an acid group include long-chain polyols having a number average molecular weight of about 450 to 4,000, such as polyether polyols, polyester polyols, and polycarbonate polyols. Examples of polyols with an acid group include polyols containing an acid group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group in their molecular structure. Among these, it is preferable to use a urethane resin synthesized by further using a polyol with an acid group, such as dimethylolpropionic acid or dimethylolbutanoic acid, in addition to a polyol without an acid group.

[0056] Examples of polyamines include monoamines having multiple hydroxyl groups, such as dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, and dibutanolmethylamine; bifunctional polyamines, such as ethylenediamine, propylenediamine, hexylenediamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, and hydrazine; trifunctional or higher polyamines, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamidepolyamine, and polyethylenepolyimine; etc. For convenience, compounds having multiple hydroxyl groups and one "amino group, imino group" are also listed as "polyamines".

[0057] Generally, a crosslinking agent is used when synthesizing a prepolymer. A chain extender is used when extending the chain of a prepolymer that has been previously synthesized. The crosslinking agent and the chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. according to the purpose of crosslinking or chain extension. A compound capable of crosslinking a urethane resin can also be used as the chain extender.

[0058] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The ink preferably contains a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 40.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks such as alcohols, glycols, glycol ethers, and nitrogen-containing compounds can be used. The water-soluble organic solvent is preferably one that has a vapor pressure at 25°C lower than that of water. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink, and more preferably 15.0 mass% or more and 30.0 mass% or less.

[0059] The mass average value of the relative dielectric constant of the water-soluble organic solvent in the ink is preferably 34.0 or more. When a large amount of water-soluble organic solvent with a relatively high relative dielectric constant is present, the dispersibility of the pigment is stabilized, and scorch caused by the pigment is less likely to adhere to the heater. When the mass average value of the relative dielectric constant of the water-soluble organic solvent in the ink is less than 34.0, the dispersibility of the pigment may become somewhat unstable, and the effect of suppressing the deterioration of the ink ejection performance may decrease. There is no particular limit to the upper limit of the mass average value of the relative dielectric constant of the water-soluble organic solvent in the ink, but it is preferably 38.0 or less.

[0060] The mass average value of the relative dielectric constant of the water-soluble organic solvent in the ink can be calculated by the following formula (A) for an ink containing, for example, 15.0 mass % of a water-soluble organic solvent with a relative dielectric constant of 40.0 and 10.0 mass % of a water-soluble organic solvent with a relative dielectric constant of 20.0. Note that the relative dielectric constant of water is not taken into consideration when calculating the mass average value of the relative dielectric constant of the water-soluble organic solvent in the ink. This is because the water-soluble organic solvents generally used in aqueous inks used in small inkjet recording devices have a lower vapor pressure than water, and when the ink solidifies near the ejection orifice, the evaporation of water has progressed sufficiently, and most of the liquid medium is water-soluble organic solvent. (40.0×15.0+20.0×10.0) / (15.0+10.0)=32.0 (A)

[0061] The relative dielectric constant of a water-soluble organic solvent can be measured using a dielectric constant meter (for example, trade name "BI-870" manufactured by BROOKHAVEN INSTRUMENTS CORPORATION) at a frequency of 10 kHz. The relative dielectric constant of a water-soluble organic solvent that is solid at 25°C is a value calculated from the relative dielectric constant of a 50% by mass aqueous solution by the following formula (1). Usually, a "water-soluble organic solvent" is a liquid, but in the present invention, for the sake of convenience, those that are solid at 25°C (room temperature) are also included in the water-soluble organic solvent. ε sol =2ε 50% -ε water (1) ε sol : Dielectric constant of solid water-soluble organic solvent at 25℃ ε 50% : Relative dielectric constant of a 50% by mass aqueous solution of a solid water-soluble organic solvent at 25°C ε water : relative dielectric constant of water

[0062] Examples of water-soluble organic solvents that are generally used in aqueous inks and are solid at 25°C include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number-average molecular weight of 1,000. The reason for determining the relative dielectric constant of a water-soluble organic solvent that is solid at 25°C from the relative dielectric constant of a 50% by mass aqueous solution is as follows. Among water-soluble organic solvents that are solid at 25°C and can be used as components of aqueous inks, it is difficult to prepare a high-concentration aqueous solution of more than 50% by mass. On the other hand, in a low-concentration aqueous solution of 10% by mass or less, the relative dielectric constant of water becomes dominant, and it is not possible to obtain a reliable (effective) relative dielectric constant value of the water-soluble organic solvent. As a result of the inventors' investigation, it was found that the aqueous solution to be measured can be prepared from almost all of the water-soluble organic solvents that are solid at 25°C and can be used in inks, and the relative dielectric constant to be determined is consistent with the effect of the present invention. For these reasons, it was decided to use a 50% by mass aqueous solution. For water-soluble organic solvents that are solid at 25°C and cannot be prepared as a 50% aqueous solution due to their low solubility in water, use an aqueous solution of the saturated concentration and use the above ε sol For convenience, the value of the relative dielectric constant calculated in accordance with the case of determining

[0063] Specific examples of water-soluble organic solvents include the following (the numbers in parentheses indicate the relative dielectric constant at 25°C): monohydric alcohols having 1 to 4 carbon atoms, such as methanol (33.1), ethanol (23.8), n-propanol (12.0), isopropanol (18.3), n-butanol, sec-butanol, and tert-butanol. Dihydric alcohols such as 1,2-propanediol (28.8), 1,2-butanediol (22.2), 1,3-butanediol (30.0), 1,4-butanediol (31.1), 1,5-pentanediol (27.0), 1,2-hexanediol (14.8), 1,6-hexanediol (7.1), 2-methyl-1,3-propanediol (28.3), 3-methyl-1,3-butanediol (24.0), 3-methyl-1,5-pentanediol (23.9), 2-ethyl-1,3-hexanediol (18.5), etc. Polyhydric alcohols such as 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7), trimethylolethane, etc. Alkylene glycols such as ethylene glycol (40.4), diethylene glycol (31.7), triethylene glycol (22.7), tetraethylene glycol (20.8), dipropylene glycol (19.7), butylene glycol, hexylene glycol, thiodiglycol, etc. Glycol ethers such as ethylene glycol monobutyl ether (9.4), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether (11.0), triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8), tetraethylene glycol monobutyl ether (9.4), propylene glycol monomethyl ether (12.4), tripropylene glycol monomethyl ether (8.5), etc. Polyalkylene glycols having a number average molecular weight of 200 to 1,000 such as polyethylene glycol having a number average molecular weight of 200 (18.9), polyethylene glycol having a number average molecular weight of 600 (11.5), polyethylene glycol having a number average molecular weight of 1,000 (4.6), polypropylene glycol, etc.Nitrogen-containing compounds such as 2-pyrrolidone (28.0), N-methyl-2-pyrrolidone (32.0), 1-(2-hydroxyethyl)-2-pyrrolidone (37.6), 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine, 1-(hydroxymethyl)-5,5-dimethylhydantoin (23.7), 1,3-bis(2-hydroxyethyl)-5,5-dimethylhydantoin (16.0), urea (110.3), ethyleneurea (49.7), and triethanolamine (31.9). Sulfur-containing compounds such as dimethyl sulfoxide (48.9) and bis(2-hydroxyethylsulfone). As the water-soluble organic solvent to be contained in the ink, it is preferable to use one having a relative dielectric constant of 3.0 or more, 120.0 or less, and a vapor pressure at 25°C lower than that of water.

[0064] [Surfactants] The ink preferably further contains a surfactant. In addition, it is particularly preferable that the ink contains a surfactant having a cloud point. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. In particular, it is preferable to use nonionic surfactants such as acetylene glycol surfactants and polyoxyethylene alkyl ethers. The content (mass %) of the surfactant 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.

[0065] [Other ingredients] The ink may further contain various additives, as necessary, such as an antifoaming agent, a pH adjuster, a viscosity adjuster, an antirust agent, an antiseptic, an antifungal agent, an antioxidant, an antireducing agent, etc. These additives and the above-mentioned surfactants are not included in the calculation of the relative dielectric constant.

[0066] [Ink properties] The ink is a water-based ink applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. In addition, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less. EXAMPLES

[0067] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0068] <Preparation of pigment dispersion> (Pigment dispersion 1) A solution of 5.0 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5°C, and 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added in this state. The container containing this solution was placed in an ice bath, and while stirring to maintain the temperature of the solution below 10°C, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of water at 5°C was added. After stirring for 15 minutes, the specific surface area was 250 m 2 6.0 g of carbon black with a DBP oil absorption of 140 mL / 100 g was added under stirring. The mixture was further stirred for 15 minutes to obtain a slurry. The obtained slurry was filtered with filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), and the particles were thoroughly washed with water and dried in an oven at 110 °C. Thereafter, sodium ions were replaced with potassium ions by ion exchange to obtain a self-dispersing pigment in which -C6H3-(COOK)2 groups were bonded to the pigment particle surface. An appropriate amount of water was added to adjust the pigment content, and a pigment dispersion 1 with a pigment content of 15.0% was obtained. The amount of anionic groups in the self-dispersing pigment was 200 μmol / g.

[0069] (Pigment dispersion 2) A styrene-acrylic acid copolymer with an acid value of 90 mgKOH / g and a weight average molecular weight of 10,000 was neutralized with a 10% aqueous potassium hydroxide solution. 15.0 parts of carbon black (trade name "Printex85", manufactured by Orion Engineered Carbons), 4.5 parts of neutralized styrene-acrylic acid copolymer (solid content), and 80.5 parts of ion-exchanged water were mixed to obtain a mixture. The mixture obtained was dispersed for 1 hour using a sand grinder, and then centrifuged to remove coarse particles. The mixture was then filtered under pressure using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to obtain pigment dispersion 2 in which carbon black was dispersed in water by resin. The pigment content in pigment dispersion 2 was 15.0%, and the resin dispersant content was 4.5%. The amount of anionic groups in the pigment was 200 μmol / g.

[0070] (Pigment dispersion 3) Pigment dispersion 3 was obtained in the same manner as pigment dispersion 2, except that the amount of neutralized styrene-acrylic acid copolymer (solid content) was changed to 3.8 parts and the amount of ion-exchanged water was changed to 81.2 parts. The pigment content in pigment dispersion 3 was 15.0%, and the resin dispersant content was 3.8%. The amount of anionic groups in the pigment was 150 μmol / g.

[0071] (Pigment Dispersion 4) Pigment dispersion 4 was obtained in the same manner as pigment dispersion 2, except that the amount of neutralized styrene-acrylic acid copolymer (solid content) was changed to 5.2 parts and the amount of ion-exchanged water was changed to 79.8 parts. The pigment content in pigment dispersion 4 was 15.0%, and the resin dispersant content was 5.2%. The amount of anionic groups in the pigment was 230 μmol / g.

[0072] (Pigment Dispersion 5) Pigment Dispersion 5 was obtained in the same manner as Pigment Dispersion 1 described above, except that CI Pigment Blue 15:3 was used instead of carbon black. Pigment Dispersion 5 contained a self-dispersing pigment in which a phthalic acid group with a sodium ion as a counter ion was bonded to the pigment particle surface, and the pigment content was 15.0%. The amount of anionic groups in the self-dispersing pigment was 200 μmol / g.

[0073] (Pigment Dispersion 6) Pigment dispersion 6 was obtained in the same manner as in Pigment Dispersion 2, except that CI Pigment Blue 15:3 was used instead of carbon black. The pigment content in Pigment Dispersion 6 was 15.0%, and the resin dispersant content was 4.5%. The amount of anionic groups in the pigment was 200 μmol / g.

[0074] (Pigment Dispersion 7) Pigment dispersion 7 was obtained in the same manner as in Pigment Dispersion 2, except that CI Pigment Red 122 was used instead of carbon black. The pigment content in Pigment Dispersion 7 was 15.0%, and the resin dispersant content was 4.5%. The amount of anionic groups in the pigment was 200 μmol / g.

[0075] (Pigment Dispersion 8) Pigment dispersion 8 was obtained in the same manner as in Pigment Dispersion 2, except that CI Pigment Yellow 74 was used instead of carbon black. The pigment content in Pigment Dispersion 8 was 15.0%, and the resin dispersant content was 4.5%. The amount of anionic groups in the pigment was 200 μmol / g.

[0076] (Pigment Dispersion 9) Except for changing the amount of 4-amino-1,2-benzenedicarboxylic acid to 0.5 g, the same procedure as for the above-mentioned Pigment Dispersion 1 was repeated to obtain Pigment Dispersion 9 having a pigment content of 15.0%. The amount of anionic groups in the self-dispersing pigment was 67 μmol / g.

[0077] (Pigment Dispersion 10) Pigment dispersion 10 was obtained in the same manner as in Pigment Dispersion 2, except that the amount of neutralized styrene-acrylic acid copolymer (solid content) was changed to 2.0 parts and the amount of ion-exchanged water was changed to 83.0 parts. The pigment content in Pigment Dispersion 10 was 15.0%, and the resin dispersant content was 2.0%. The amount of anionic groups in the pigment was 89 μmol / g.

[0078] (Pigment Dispersion 11) A styrene-ethyl acrylate-methacrylic acid copolymer having an acid value of 400 mgKOH / g and a weight average molecular weight of 6,000 was neutralized with a 10% aqueous potassium hydroxide solution. 24.0 parts of carbon black (trade name "Mogul L", manufactured by Cabot), 8.0 parts of neutralized styrene-ethyl acrylate-methacrylic acid copolymer (solid content), and 68.0 parts of ion-exchanged water were mixed to obtain a mixture. Pigment dispersion 11 was obtained in the same manner as in the above-mentioned pigment dispersion 2, except that this mixture was used. The pigment content in pigment dispersion 11 was 24.0%, and the resin dispersant content was 8.0%. The amount of anionic groups in the pigment was 750 μmol / g.

[0079] <Preparation of Water-Soluble Acrylic Resin> The types and amounts of monomers shown in Table 1 were copolymerized in a conventional manner to synthesize water-soluble acrylic resins 1 to 5. After neutralizing the carboxylic acid groups in the resins with potassium hydroxide in an amount equimolar to the acid value, an appropriate amount of pure water was added to obtain aqueous solutions of acrylic resins 1 to 5 with a resin content of 20.00%. The meanings of the abbreviations in Table 1 are as follows: St: styrene MMA: Methyl methacrylate ·AA: Acrylic acid

[0080] TIFF2024174841000001.tif55170

[0081] <Preparation of Water-Soluble Urethane Resin> A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was prepared. The types and amounts of polyisocyanate, polyol, and 300.0 parts of methyl ethyl ketone shown in Table 2 were placed in this four-neck flask. Then, the mixture was reacted at 80°C for 6 hours under a nitrogen gas atmosphere. Next, the amount of polyamine shown in Table 2 was added, and the mixture was reacted at 80°C to obtain a reaction liquid. After the reaction liquid obtained was cooled to 40°C, ion-exchanged water was added, and an aqueous potassium hydroxide solution was added while stirring at high speed with a homomixer to obtain a liquid. Methyl ethyl ketone was distilled off from the liquid obtained by heating and reducing the pressure, and aqueous solutions of urethane resins 1 and 2 with a urethane resin (solid content) content of 20.0% were obtained. The properties of the urethane resins are shown in Table 2. The content (mol%) of urethane bonds in the total of urethane bonds and urea bonds in the urethane resin was: 13 The abbreviations in Table 2 are as follows: IPDI: Isophorone diisocyanate PPG: Polypropylene glycol (number average molecular weight: 1,000) DMPA: Dimethylolpropionic acid EDA: Ethylenediamine

[0082] TIFF2024174841000002.tif34170

[0083] <Synthesis of resin particles> (Resin particles 1) A solution was prepared by mixing 79.4 parts of ion-exchanged water and 0.2 parts of potassium persulfate. An emulsion was prepared by mixing 16.7 parts of butyl methacrylate, 0.4 parts of methacrylic acid, 3.0 parts of ethylene glycol dimethacrylate, and 0.3 parts of a reactive surfactant (trade name "Aqualon KH-05", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). Under a nitrogen atmosphere, the prepared emulsion was dropped into the above solution over 1 hour, and a polymerization reaction was carried out while stirring at 80°C, and then the solution was stirred for 2 hours. After cooling to room temperature, ion-exchanged water and an aqueous potassium hydroxide solution were added to obtain an aqueous dispersion of resin particles 1 with a pH of 8.5. The content of resin particles in the obtained dispersion was 15.0%. The amount of anionic groups in resin particles 1 was 108 μmol / g, and the glass transition temperature of resin particles 1 was 74°C.

[0084] (Resin particles 2) Except for changing the amount of methacrylic acid to 0.3 parts, an aqueous dispersion of resin particles 2 was obtained in the same manner as resin particles 1. The content of resin particles in the obtained dispersion was 15.0%. The amount of anionic groups in resin particles 2 was 80 μmol / g, and the glass transition temperature of resin particles 1 was 74° C.

[0085] (Resin particles 3) Except for changing the amount of methacrylic acid to 0.5 parts, an aqueous dispersion of resin particles 3 was obtained in the same manner as resin particles 1. The content of resin particles in the obtained dispersion was 15.0%. The amount of anionic groups in resin particles 3 was 140 μmol / g, and the glass transition temperature of resin particles 3 was 74° C.

[0086] (Resin particles 4) A mixture of 90 parts of neopentyl glycol, 10 parts of bisphenol A, 50 parts of terephthalic acid, 50 parts of isophthalic acid, and 7.6 parts of trimellitic acid was placed in a reaction vessel installed in an autoclave, and heated at 220 ° C for 4 hours to carry out an esterification reaction. The temperature was then raised to 240 ° C, and the pressure in the autoclave was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued by maintaining the reduced pressure of 240 ° C and 13 Pa for 5 hours, and then nitrogen gas was introduced into the autoclave to return to normal pressure. The temperature in the reaction vessel was lowered to 220 ° C, and a catalyst (tetra-n-butyl titanate) and 2.4 parts of trimellitic acid were added, and the mixture was heated at 220 ° C for 2 hours to carry out an ester exchange reaction. The amount (mol) of the catalyst used was 3 × 10 -4 × the total amount (mol) of polyvalent carboxylic acid used. Nitrogen gas was then introduced into the autoclave to create a pressurized state, and a sheet-like resin was taken out. The resin taken out was cooled to 25°C and then crushed in a crusher to obtain a polyester resin.

[0087] A stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was set in a beaker with a volume of 2 L. 210 g of polyester resin and methyl ethyl ketone (MEK) were placed in this beaker and stirred at 30° C. to dissolve the polyester resin. Next, a 5% aqueous potassium hydroxide solution was added in an amount corresponding to a neutralization rate (mol%) based on the acid value corresponding to all acid groups of the polyester resin, and stirred for 30 minutes. 500 g of deionized water was dropped at a rate of 20 mL / min while stirring at 30° C. Then, the temperature was raised to 60° C. to distill off MEK, and further, a part of the water was also distilled off. After cooling to 25° C., the mixture was filtered through a 150 mesh wire net and the solid concentration was adjusted to 15% with deionized water to obtain an aqueous dispersion of resin particles 4. The amount of anionic groups in resin particles 4 was 125 μmol / g, and the glass transition temperature of resin particles 4 was 64° C.

[0088] (Resin particles 5) A 1L separable flask equipped with a stirrer, a thermometer, and a reflux tube was prepared. 100g of polycarbonate-based polymer polyol, 4.2g of 2,2-bis(hydroxymethyl)propionic acid, 41g of 4,4'-dicyclohexylmethane diisocyanate, 2.2g of triethylamine, and 80g of acetone were placed in the flask while introducing nitrogen. As the polycarbonate-based polymer polyol, a product named "T-5650E" (manufactured by Asahi Kasei Chemicals) was used. After adding one drop of catalyst (tin(II) di(2-ethylhexanoate)), the temperature was raised and refluxed for 3 to 15 hours. After lowering the temperature to 40°C and maintaining it, water was slowly added while stirring at a speed of 300 rpm to form fine particles, and the mixture was heated and stirred for 30 minutes. 1.2g of diethylenetriamine was added and heated and stirred for 3 to 6 hours, and the organic solvent was removed to obtain an aqueous dispersion of resin particles 5. The content of resin particles in the obtained aqueous dispersion of resin particles 5 was 15%. The amount of anionic groups in resin particles 5 was 125 μmol / g, and the glass transition temperature of resin particles 5 was 64° C.

[0089] <Method for measuring the amount of anionic groups> The amount of anionic groups in both the pigment and resin particles was measured using an automatic potentiometric titrator equipped with a streaming potential titration unit (PCD-500). Specifically, the amount of anionic groups was measured by potentiometric titration using 5 mmol / L methyl glycol chitosan as the titration reagent. The automatic potentiometric titrator used was an "AT-510" (manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0090] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in Tables 3-1 to 3-3, thoroughly stirring, and then filtering under pressure through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. In Tables 3-1 to 3-3, "Acetylenol E60" is the trade name of a nonionic surfactant (manufactured by Kawaken Fine Chemicals). In Tables 3-1 to 3-3, "Surfactant SF-1" is a surfactant described in Patent Document 1, and is a surfactant that is a C 16 H 33It is a compound represented by the formula -N-{(CH2CH2O)8-H}2. In Tables 3-1 to 3-3, the numbers in parentheses attached to the water-soluble organic solvents indicate the relative dielectric constant.

[0091] In addition, the following inks were used to simulate a recording method using an inkjet recording device of the second device configuration having a main tank. That is, the ink used to evaluate the second device configuration had a composition simulating a state in which the solid content (pigment, water-soluble resin, resin particles) was concentrated by 20% compared to the ink used to evaluate the first device configuration. In other words, the content of the solid content was set high in advance. On the other hand, in Examples 25 and 26 and Comparative Examples 3 and 6, inks of compositions that did not simulate a concentrated state were used for evaluation in order to simulate a recording method using an inkjet recording device of the first device configuration.

[0092] TIFF2024174841000003.tif153170

[0093] TIFF2024174841000004.tif153170

[0094] TIFF2024174841000005.tif154170

[0095] <Recording unit> (Recording Unit 1) A recording unit with the product name "PIXUS TS5330S" (manufactured by Canon) was prepared. This recording unit 1 is equipped with a recording head in which ejection ports that eject ink by the action of thermal energy are formed. The ink storage section is a housing made of thermoplastic resin, and the recording head is bonded to the ink storage section without any other members in between. The recording head of the recording device equipped with this recording unit is provided with a mechanism for heating the ink in the recording head, and sensors for measuring the temperature of the ink in the recording head are attached to two points on both ends of the recording head.

[0096] (Recording Unit 2) A recording unit with the product name "GX6030" (manufactured by Canon) was prepared. This recording unit 2 has the same configuration as the above-mentioned recording unit 1, except that the recording head is attached to the ink storage section via a heat sink.

[0097] <Inkjet recording device> An inkjet recording device (product name "PIXUS TS5330S", manufactured by Canon) was modified as follows to prepare recording devices 1 and 2. The recording device 1 is an inkjet recording device of the "first device configuration" type that omits the main tank (73 in Figs. 1 and 2) placed inside the device. This recording device is a product named "PIXUS TS5330S" that incorporates the recording unit prepared above as a sub-tank on the carriage. The recording device 2 is an inkjet recording device of the “second device configuration” type, which is a product name “PIXUS TS5330S” equipped with a main tank (73 in Figs. 1 and 2) and incorporates the recording unit prepared above as a sub-tank on the carriage.

[0098] <Evaluation> The ink dischargeability was evaluated by discharging ink heated to the ink temperature (°C) shown in Table 4 using the combination of ink, recording unit, and recording device shown in Table 4. Specifically, a constant driving voltage was applied to the recording head, and the state of the ink discharged from the discharge port was photographed by a CCD camera from a direction perpendicular to the ink discharge direction (horizontal direction), and the discharge speed was calculated. At this time, the strobe light emission interval and the photographing interval were synchronized, and the strobe was caused to emit light at very short intervals. During this time, a driving voltage for discharge was applied, and at the point when a predetermined time had elapsed from that point, the distance (μm) between the surface of the recording head where the discharge port was provided and the center of gravity of the discharged ink droplet was obtained from the photographing data. Then, the discharge speed (m / s) was calculated from the obtained distance (μm) and the strobe light emission interval (μsec), and the ink dischargeability was evaluated according to the evaluation criteria shown below. The results are shown in Table 4. The discharge speed was measured for three discharge ports, and the average was taken as the measured value. The ink was continuously ejected at an ejection frequency of 15,000 Hz, and the difference between the initial ejection speed and the ejection speed after 160 minutes of ejection was compared for evaluation. Note that in Comparative Example 6 and Reference Examples 4 and 5, the ink was ejected without heating. In the evaluation criteria for each item shown below, "AA", "A" and "B" were considered acceptable levels, and "C" and "D" were considered unacceptable levels. AA: The difference in discharge speed was 0.5 m / s or less. A: The difference in discharge speed was more than 0.5 m / s and less than 1.0 m / s. B: The difference in discharge speed was more than 1.0 m / s and 2.0 m / s or less. C: The difference in discharge speed was more than 2.0 m / s and 3.0 m / s or less. D: The difference in discharge speed was more than 3.0 m / s.

[0099] TIFF2024174841000006.tif149170

Claims

1. using an inkjet recording device including an aqueous ink containing a pigment and resin particles, an ink storage unit for storing the aqueous ink, and a recording head having an ejection port for ejecting the aqueous ink supplied from the ink storage unit by the action of thermal energy, An inkjet recording method comprising a step of applying the water-based ink ejected from the ejection orifice to a recording medium to record an image, the ink container is a housing made of a thermoplastic resin, and the recording head is bonded to the ink container without any other member therebetween; the recording head has a heating means for heating the water-based ink in the recording head, The ink-jet recording method according to claim 1, wherein the amount (μmol / g) of the anionic group in the resin particles is smaller than the amount (μmol / g) of the anionic group in the pigment.

2. 2. The ink-jet recording method according to claim 1, wherein the pigment is carbon black.

3. The ink-jet recording method according to claim 1 , wherein the water-based ink further contains a water-soluble resin having a unit derived from styrene.

4. The ink jet recording method according to claim 3, wherein the proportion (mass %) of the units derived from the styrene in the water-soluble resin is 10.0 mass % or more.

5. The ink jet recording method according to claim 1 , wherein the water-based ink further contains a water-soluble urethane resin having a urea bond.

6. the water-based ink further contains a water-soluble organic solvent, 2. The ink jet recording method according to claim 1, wherein the water-soluble organic solvent has a mass average relative dielectric constant of 34.0 or more.

7. The inkjet recording method according to claim 1 , wherein a content (mass %) of the resin particles in the aqueous ink is 0.4 times or more in mass ratio to a content (mass %) of the pigment.

8. 2. The ink jet recording method according to claim 1, wherein the glass transition temperature (° C.) of the resin particles is higher than a temperature (° C.) of the water-based ink heated by the heating means in the recording head.

9. 9. The inkjet recording method according to claim 1, further comprising: a second ink containing section having a larger capacity than the ink containing section; and a tube through which the water-based ink circulates between the second ink containing section and the ink containing section.

10. An inkjet recording apparatus comprising: an aqueous ink containing a pigment and resin particles; an ink storage section that stores the aqueous ink; and a recording head having an ejection port that ejects the aqueous ink supplied from the ink storage section by the action of thermal energy, the ink container is a housing made of a thermoplastic resin, and the recording head is bonded to the ink container without any other member therebetween; the recording head has a mechanism for heating the water-based ink in the recording head, an amount (μmol / g) of anionic groups in the resin particles being smaller than an amount (μmol / g) of anionic groups in the pigment;

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