JP7195776B2 - Inkjet recording method and inkjet recording apparatus - Google Patents

Description

The present invention relates to an inkjet recording method and an inkjet recording apparatus.

In recent years, inkjet recording methods have made it possible to record high-definition, high-color images similar to those achieved by silver halide photography and offset printing, and the demand for ink reliability has become more stringent. ing.

In the inkjet recording method, methods for ejecting ink from a recording head include a method using mechanical energy and a method using thermal energy. In the thermal method in which ink is ejected from the printhead by the action of thermal energy, the heater (electrothermal conversion element) of the printhead is exposed to high temperatures. In addition to this, the heater is subjected to multiple physical effects such as impact due to cavitation due to foaming of the ink and contraction of the bubbles, and chemical effects due to the ink. In order to protect the heater from these effects, the heater portion of the ink flow path is provided with a protective layer. When the ink is repeatedly ejected, the components in the ink are heated to a high temperature, changing to a substance that is difficult to dissolve or disperse, and this causes a phenomenon that the substance adheres to the surface of the protective layer. This substance is the so-called "kogation". When kogation adheres and accumulates on the protective layer, the thermal energy applied to the heater is not sufficiently transmitted to the ink, and as a result, the thermal energy applied to the ink is reduced, which affects ejection performance. The decrease in ejection performance caused in this manner causes image unevenness.

In response to such problems, countermeasures against kogation have been studied so far. First, there is a proposal regarding a recording head provided with means for removing adhered kogation (see Patent Document 1). In Patent Document 1, an upper protective layer as a surface layer portion of the protective layer is formed of a metal such as iridium, and the upper protective layer is used as an electrode to cause an electrochemical reaction to elute the upper protective layer, thereby dissolving the upper protective layer into the heater section. It is disclosed to remove the deposited kogation. On the other hand, there is also a proposal regarding a recording head provided with a means for suppressing the adhesion of kogation (see Patent Document 2). This recording head is similar to the recording head described in Japanese Patent Application Laid-Open No. 2002-200014 in that the protective layer is used as an electrode, but the concept of kogation is different. Specifically, in Patent Document 2, by charging the protective layer to the same polarity side as the component in the ink that can cause burnt deposits, voltage control is performed to cause electrical repulsion, thereby eliminating substances that cause burnt deposits. It is disclosed to inhibit adhesion.

JP 2008-105364 A JP 2009-051146 A

As a result of studies by the present inventors, it has been confirmed that a certain degree of effect can be obtained by controlling the voltage of the recording head with reference to the description of Japanese Patent Laid-Open No. 2002-300021 and suppressing the adhesion of kogation. However, it has been found that as the number of times of ink ejection increases, the ejection performance gradually deteriorates, affecting the image.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an inkjet recording method and an inkjet recording apparatus capable of suppressing deterioration in ejection performance when voltage control of a recording head is performed.

The above object is solved by the present invention described below. That is, the ink jet recording method according to the present invention includes a heater for ejecting ink arranged in an ink channel communicating with an ejection port, a heater arranged at a position corresponding to the heater, and the heater and the ink channel. a recording head having a first protective layer that blocks contact with ink inside, and a second protective layer that corresponds to the heater and is arranged at a position that contacts the ink and is formed of a metal material; Using an ink jet recording apparatus equipped with means for applying a voltage with the second protective layer as a cathode and a portion conducting through the ink as an anode, ink is ejected from the recording head to form a recording medium wherein the ink contains a component having an anionic group and a soluble metal ion having a standard electrode potential exceeding 0 V, and the content of the metal ion ( % by mass) is 0.1 ppm or more and 15.0 ppm or less based on the total mass of the ink.

According to the present invention, it is possible to provide an inkjet recording method and an inkjet recording apparatus capable of suppressing deterioration in ejection performance when performing voltage control of the recording head.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of main parts of the inkjet recording apparatus and (b) is a perspective view of a head cartridge; 4 is a plan view schematically showing the vicinity of heaters of the printing element substrate; FIG. FIG. 3 is a cross-sectional view schematically showing a state in which the recording element substrate is cut perpendicularly along line XY in FIG. 2; 2 is a block diagram showing an example of the control configuration of the inkjet recording apparatus; FIG. FIG. 4 is a schematic diagram showing an example of a voltage control procedure;

The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing the salt." Ink jet ink is sometimes simply referred to as "ink". Physical properties are values at room temperature (25° C.) unless otherwise specified.

In the case of a thermal method in which ink is ejected from a print head by the action of thermal energy, the print head has a plurality of ejection openings, an ink flow path communicating with the ejection openings, and a heater that generates thermal energy for ejecting ink. . An electrothermal conversion element as a heater has a heating resistor and electrodes for supplying power thereto. By covering the heaters with the protective layer having electrical insulation, the insulation between the heaters corresponding to the plurality of ejection ports is ensured.

Japanese Patent Application Laid-Open No. 2002-200000 discloses that the adhesion of substances that cause burnt deposits is suppressed by performing voltage control so that the protective layer of the heater is charged to the same polarity side as the components in the ink. However, it was found that even if voltage control was performed, the ejection performance gradually deteriorated as the number of ejections increased. As a result of examining the cause of this problem, the present inventors have found that the ejectability is deteriorated due to the substance adhering to the "counter electrode" during voltage control.

The counter electrode is an electrode paired with the "heater-side electrode", and is charged oppositely (positively) to components having anionic groups such as dyes, resin dispersants, and resin particles. Therefore, although the component having an anionic group is separated from the negatively charged heater-side electrode, it is attracted to the counter electrode and gradually adheres to the counter electrode. This phenomenon is also recognized in the invention described in Patent Document 2, and as a countermeasure, it is said that it is effective to use a polar substance in which ionic hydrophilic groups and nonionic hydrophilic groups coexist in the molecule. However, even if this polar substance is used, it becomes impossible to prevent the component having an anionic group from adhering to the counter electrode as the number of ejections increases.

If a substance adheres to the counter electrode, it becomes difficult to perform voltage control between the paired heater-side electrode. As a result, the potential applied to the heater-side electrode is also lowered, and the electrical repulsive force between the heater-side electrode and the component having an anionic group is reduced. In addition, there is also an effect due to energy for ejection. In a state in which energy for ejection is not applied to the ink in the flow path of the print head, if voltage control is performed, the heater-side electrode and the component having an anionic group electrically repel each other. As a result, the component having an anionic group is prevented from adhering to the heater-side electrode, and the counter ion exists at an energetically stable position with respect to the component having an anionic group, thereby stabilizing the dispersed state. be kept. After that, when energy for ejection is applied to the ink in the flow path of the recording head, the counter ions are repelled from the vicinity of the component having an anionic group under the influence of physical or chemical action. Such a situation may occur. As a result, part of the component having an anionic group became unstable in dispersion state, eventually becoming burnt deposits and adhering to the heater.

Based on the phenomenon described above, the present inventors have investigated a technique for more reliably suppressing the adhesion of substances to each electrode. As a result, by further adding "a soluble metal ion having a standard electrode potential exceeding 0 V" to the ink containing a component having an anionic group, when the voltage control of the recording head is performed, the ejection performance is improved. It was found that the decrease in the Hereinafter, "a soluble metal ion having a standard electrode potential exceeding 0 V" may be referred to as a "soluble metal ion".

The present inventors presume that the reason why the soluble metal ions can suppress the deterioration of the ejection property is as follows. Hereinafter, as the component having an anionic group, a pigment dispersed with a resin dispersant having an anionic group (resin-dispersed pigment) will be described as an example. Of course, not only resin-dispersed pigments, but also "components having an anionic group" that can be used in water-based inkjet inks can be said to have the same effect as resin-dispersed pigments.

First, the phenomenon in the counter electrode will be explained. It was confirmed that the use of ink containing soluble metal ions in voltage control reduces the adhesion of substances to the counter electrode. This is believed to be due to the following reasons. In the absence of soluble metal ions in the ink, the resin-dispersed pigment adhering to the counter electrode has no counter ions in the vicinity, that is, the anionic group is not ion-dissociated (acid form). Hydrophilicity is low. On the other hand, when soluble metal ions are present in the ink, the metal ions have a standard electrode potential of more than 0V, and thus have a lower ionization tendency than hydrogen atoms having a standard electrode potential of 0V. Therefore, soluble metal ions cannot remain in an ionic state, and stabilize their existence state by converting hydrogen atoms that constitute an acid-type anionic group into hydrogen ions. As a result, the anionic group of the acid-type resin dispersant is dissociated again, and the ions electrically repel the heater-side electrode, making it difficult to adhere to the counter electrode.

Next, the phenomenon in the heater-side electrode will be explained. As described above, when the adhesion of the resin-dispersed pigment to the counter electrode is suppressed by the presence of soluble metal ions in the ink, the applied voltage is efficiently converted into potential. In addition to this, the soluble metal ions act to protect the heater-side electrode. In the vicinity of the heater of the print head, after the ink bubbles during ejection, new ink is supplied (refilled) to the vicinity of the heater as the bubbles shrink. As described above, when energy for ejection is applied to the ink in the print head, counter ions are ejected from the vicinity of the resin-dispersed pigment under the influence of physical or chemical action. may become. As a result, part of the resin-dispersed pigment becomes unstable in its dispersed state, and eventually becomes burnt deposits and adheres to the heater. Here, the soluble metal ions have a charge opposite to that of the heater-side electrode, and their molecular weight is sufficiently small compared to components having major anionic groups, such as coloring materials and resins in the ink. Molecular size is compact. Due to these characteristics, the soluble metal ions in the ink migrate to the vicinity of the heater-side electrode during refilling, and act to protect the heater-side electrode. Therefore, it is considered that even if the resin-dispersed pigment whose dispersed state was unstable existed, adhesion to the heater-side electrode could be suppressed.

A soluble metal ion having a standard electrode potential of less than 0 V has a higher ionization tendency than a hydrogen atom, and does not have the above-described effect, so it is not possible to suppress the deterioration of ejection properties. In addition, even if soluble metal ions having a standard electrode potential of more than 0 V are present in the ink, if the amount is too small, the component having an anionic group attached to the counter electrode cannot be completely removed, thereby suppressing deterioration in ejection performance. It is not possible. On the other hand, if it is too large, it will also adhere to the heater-side electrode and lower the electrical repulsive force, so it is not possible to suppress the deterioration of the ejection performance. Therefore, the content (ppm) of the metal ions in the ink should be 0.1 ppm or more and 15.0 ppm or less based on the total mass of the ink.

<Inkjet recording method, inkjet recording apparatus>
The inkjet recording method of the present invention is a method for recording an image on a recording medium by ejecting water-based ink from an inkjet recording head. As a method of ejecting ink, a method of applying thermal energy to the ink is used.

FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. is. The inkjet recording apparatus is provided with transport means (not shown) for transporting the recording medium 500 and a carriage shaft 400 . A head cartridge 200 can be mounted on the carriage shaft 400 . The head cartridge 200 has the recording head 100 (100a and 100b), and is configured so that the ink cartridge 300 is set therein. While the head cartridge 200 is conveyed along the carriage shaft 400 in the main scanning direction, ink (not shown) is ejected from the printheads 100 (100a and 100b) toward the print medium 500 . An image is recorded on the recording medium 500 by conveying the recording medium 500 in the sub-scanning direction by conveying means (not shown).

(recording head)
[Recording element substrate]
FIG. 2 is a plan view schematically showing the vicinity of the heaters of the recording element substrate. FIG. 3 is a cross-sectional view schematically showing a state in which the recording element substrate is cut perpendicularly along line XY in FIG.

The configuration of the recording element substrate 101 of the recording head 100 will be described. The recording element substrate 101 is composed of a silicon substrate 102 , a heat storage layer 103 , a heating resistor layer 104 and an electric wiring layer 105 . The heat storage layer 103 is made of a material such as a silicon thermal oxide film, a silicon oxide film, or a silicon nitride film. The electric wiring layer 105 is a wiring made of a metal material such as aluminum, aluminum-silicon, aluminum-copper. The heat generating portion 104a as a heater (electrothermal conversion element) is formed by removing a portion of the electric wiring layer 105 to form a gap and exposing the heat generating resistor layer 104 in that portion. The electric wiring layer 105 is connected to a drive element circuit (not shown) or an external power supply terminal (not shown) to receive power supply from the outside. In the illustrated example, an electric wiring layer 105 is arranged as a layer adjacent to the heating resistor layer 104 . However, the configuration is not limited to this configuration, and a configuration in which the electric wiring layer 105 is formed as a layer adjacent to the silicon substrate 102 or the heat storage layer 103, a part thereof is partially removed as a gap, and the heating resistor layer 104 is arranged. good too.

The first protective layer 106 is formed of a material such as silicon oxide or silicon nitride, and is provided adjacent to the heating portion 104a and the heating resistor layer 104 with the electrical wiring layer 105 partially interposed therebetween. In addition, the first protective layer 106 functions as an insulating layer that blocks contact between the heat generating portion 104a and the ink in the ink flow path.

The second protective layer 107 is the outermost layer that contacts the ink in the ink flow path. A region of the second protective layer 107 that is located on the ink flow path side of the heat generating portion 104 a and applies the heat generated by the heat generating portion 104 a to the ink hits the heater 108 . The second protective layer 107 protects the heater 108 from chemical impact and physical impact (cavitation) caused by heat generation of the heat generating portion 104a, and also functions as an electrode. In order to achieve both of these characteristics, the second protective layer 107 made of a metal material is used.

A protective layer that is strong against physical effects such as impact due to cavitation and chemical effects due to ink is preferable. For this reason, it is preferable to use at least one metal material selected from the group consisting of iridium, ruthenium, tantalum, and materials containing at least one of these metal elements as the material forming the protective layer. Among them, it is more preferable to use at least one metal material selected from the group consisting of iridium, ruthenium, and materials containing at least one of iridium and ruthenium. Materials containing at least one of the above metal elements include alloys of these and other metals. In the case of an alloy, the higher the proportion of the metal element, the more likely the protective layer will be resistant to physical and chemical action. Preferably iridium, ruthenium and tantalum are used rather than alloys. It is difficult to form a strong oxide film even when heated, and the potential can be generated more uniformly. Therefore, from the viewpoint of facilitating removal of the component having an anionic group attached to the electrode, it is particularly preferable to use iridium and ruthenium. preferable. In addition, the surface of the second protective layer is heated to about 300 to 600° C. by the heat generated by the heater 108, but even in the air where oxygen is richer than in the ink, iridium can be heated up to 800° C. as an oxide film. It is more preferable to use iridium because it does not form

As the second protective layer 107, at least one metal material selected from the group consisting of iridium, ruthenium, tantalum, and materials containing at least one of these metal elements can be used. The material has poor adhesion. Therefore, the adhesion layer 109 is arranged between the first protective layer 106 and the second protective layer 107 to improve the adhesion of the second protective layer 107 to the first protective layer 106 . The adhesion layer 109 is formed using a conductive material.

The second protective layer 107 is inserted through the through hole 110 and electrically connected to the electrical wiring layer 105 via the adhesion layer 109 . The electric wiring layer 105 extends to the edge of the recording element substrate 101, and its tip serves as an external electrode 111 for electrical connection with the outside.

A flow path forming member 112 is bonded to the recording element substrate 101 having the above configuration. The flow path forming member 112 has an ejection port 113 at a position corresponding to the heater 108 , and ink flows from an ink supply port (not shown) provided penetrating the recording element substrate 101 to the ejection port 113 via the heater 108 . Form a flow path.

[Voltage control]
A method of performing voltage control in the recording head described above will be described. The second protective layer 107 is composed of two regions: a region (heater-side region) 107a including the heater 108 formed at a position corresponding to the heat-generating portion 104a, and a region (counter-electrode-side region) 107b. , electrical connections are made to the respective regions. When there is no ink in the ink flow path, no electrical connection is made between the heater side region 107a and the counter electrode side region 107b. However, the ink used in the present invention contains components having anionic groups and electrolytes including soluble metal ions. Therefore, when the ink flow path is filled with ink, the heater-side region 107a and the counter-electrode-side portion 107b, which is a portion that conducts through the ink, become conductive through the ink.

In this state, when a voltage is applied with the heater side region 107a as a cathode and the counter electrode side region 107b as an anode, a potential difference is generated between these electrodes. Components having anionic groups generate electrical repulsion against the heater-side region 107a, and soluble metal ions generate electrical repulsion against the counter-electrode-side region 107b. , the distribution state of each component changes. Since the heater-side region 107a is negatively charged, the component having an anionic group moves away from the vicinity of the heater 108 due to electrical repulsion, making it difficult for the component to adhere to the heater, thereby suppressing deterioration in ejection performance. Since the counter-electrode-side region 107b is positively charged, the component having an anionic group moves toward it, and part of it temporarily adheres to the counter-electrode-side region 107b. However, soluble metal ions present in the vicinity thereof can remove components having anionic groups. In this way, the behaviors of the heater side region 107a and the counter electrode side region 107b are combined to suppress deterioration of ejection performance when voltage control of the print head is performed.

[Configuration of control system]
FIG. 4 is a block diagram showing an example of the control configuration of the inkjet printing apparatus shown in FIG. A controller 1200 is a main control unit, executes the procedure shown in FIG. A CPU 1201 takes the form of a microcomputer or the like, and controls each part of the printing apparatus according to a control program and predetermined data stored in a ROM 1202 and corresponding to the procedure of FIG. 5, which will be described later. Examples of the data include the driving conditions of the recording head, such as the shape and driving time of the driving pulse applied to the heat generating portion 104a, as well as the voltage applied to the second protective layer 107 and its duration. The EEPROM 1203 holds predetermined data when the device is powered off. The RAM 1205 is provided with an area for developing image data, an area for work, and the like. A gate array 1204 controls the supply of print data to the print head 100 and controls data transfer between the interface 1100 , CPU 1201 and RAM 1205 . The host device 1000 is a supply source of image data, and may be a computer that generates and processes image data related to printing, or a reader unit that reads images. Image data, other commands, status signals, etc. are sent to and received from controller 1200 via interface 1100 .

A carriage motor 1301 conveys a carriage on which a head cartridge 200 having a print head 100 is mounted, in the main scanning direction, and a motor driver 1304 drives the carriage. A conveying motor 1302 conveys the recording medium 500, and a motor driver 1305 drives it. A recovery system motor 1303 operates suction recovery means such as a cap covering the ejection port of the print head 100 and a pump for suction recovery, and a motor driver 1306 drives this. A head driver 1307 drives the print head 100 .

[Voltage control procedure]
A procedure for voltage control will be described. FIG. 5 is a schematic diagram showing an example of a voltage control procedure. When a recording instruction is issued from the host device 1000 or the like, the following procedure is started. First, image data to be printed is received from the host device 1000, and the image data is developed as data suitable for the printing device (step S1). Next, a potential difference is generated between the heater side region 107a and the counter electrode side region 107b of the second protective layer 107 in the recording head 100 (step S2). At this time, a voltage is applied from the voltage applying means of the recording apparatus through the recording element substrate 101 of the recording head 100, with the heater side region 107a of the second protective layer 107 as the cathode and the counter electrode side region 107b as the anode. start being applied. After that, recording is started by ejecting ink (step S3). After the recording is finished (step S4), the voltage application between the heater-side region 107a and the counter-electrode-side region 107b of the second protective layer 107 is stopped, and the potential difference between them is released. (Step S5). In the present embodiment, the printing operation by ejecting ink includes not only the period during which the printhead is performing printing by ejecting ink, but also the period from when the print start command is received until the ejection of ink is completed.

Voltage control is performed to suppress adhesion of substances that cause burnt deposits to the heater. Therefore, it is preferable to continuously perform voltage control for a certain period of time before and after the timing of ink ejection based on print data, preliminary ejection data, and the like. At this time, the period during which the voltage control is continued may be appropriately set in consideration of power consumption and the like. Considering that voltage control is performed in the presence of aqueous ink containing an electrolyte, it is preferable to apply a voltage of about 0.1 to 4 V that does not cause electrolysis of water. It is preferable to apply a voltage of about 4V.

The application of the voltage with the heater-side region 107a of the second protective layer 107 as the cathode and the counter-electrode-side region 107b as the anode is performed so that these electrodes have the above-described relationship of cathode and anode. You can do it. The control at this time includes the following methods. (1) Using the heater-side region 107a as a ground, apply a positive potential to the counter-electrode-side region 107b. (2) A negative potential is applied to the heater side region 107a, and the opposing electrode side region 107b is grounded. (3) A potential is applied to both the heater side region 107a and the counter electrode side region 107b. Among them, the method (1) is preferable in the present invention.

<Aqueous ink>
The ink used in the ink jet recording method and the ink jet recording apparatus of the present invention is a water-based ink for ink jet containing a component having an anionic group and a soluble metal ion having a standard electrode potential exceeding 0V. Furthermore, the content (ppm) of soluble metal ions having a standard electrode potential exceeding 0 V in the ink must be 0.1 ppm or more and 15.0 ppm or less based on the total mass of the ink. Each component constituting the ink and physical properties of the ink will be described in detail below.

(Component having an anionic group)
The component having an anionic group is not particularly limited as long as it is included in this definition. Specifically, coloring materials having anionic groups such as dyes and self-dispersing pigments; resins having anionic groups such as water-soluble resins and resin particles; additives having anionic groups such as surfactants and pH adjusters agents and the like. At least one of these components is usually present in the ink if it is an aqueous ink for inkjet. Among them, coloring materials such as self-dispersing pigments having anionic groups and resins having anionic groups are more preferable, and resins having anionic groups are particularly preferable. Since these components are "solids", they tend to become burnt deposits and adhere to the heater.

The content (% by mass) of the component having an anionic group in the ink varies depending on the number of anionic groups possessed by the component and the application, but should be 20.00% by mass or less based on the total mass of the ink. is preferred. If the content exceeds 20.0% by mass, the amount of the component having an anionic group present in the ink increases, and the frequency of adhesion to the counter electrode increases, so that it may not be possible to sufficiently suppress the deterioration of the ejection performance. be. The content (% by mass) of the component having an anionic group in the ink is preferably 0.10% by mass or more based on the total mass of the ink. The above content means the total content when a component having a plurality of anionic groups is used.

(colorant)
A pigment or a dye can be used as the coloring material. The content (% by mass) of the coloring material in the ink is preferably 0.50% by mass or more and 15.00% by mass or less, and 1.00% by mass or more and 10.00% by mass, based on the total mass of the ink. The following are more preferable.

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole and dioxazine.

As a method of dispersing the pigment, a resin-dispersed pigment using a resin as a dispersing agent, or a self-dispersing pigment having a hydrophilic group bonded to the particle surface of the pigment can be used. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of a pigment particle, or a microcapsule pigment in which the surface of a pigment particle is coated with a resin or the like can be used. As the "component having an anionic group", a resin-dispersed pigment using a resin having an anionic group as a dispersant, or a self-dispersing pigment having an anionic hydrophilic group can be used.

As the resin dispersant, it is preferable to use a resin having an anionic group that disperses the pigment in an aqueous medium by the action of the anionic group. As the resin dispersant, it is preferable to use a resin as described later, more preferably a water-soluble resin. The content (% by mass) of the pigment is preferably 0.3 times or more and 10.0 times or less in mass ratio (pigment/resin dispersant ) to the content (% by mass) of the resin dispersant.

As the self-dispersing pigment, those in which an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group is bonded directly or via another atomic group (-R-) to the particle surface of the pigment is used. be able to. Anionic groups may be in either acid or salt form. When it is in a salt form, it may be in a partially dissociated state or in a completely dissociated state. When the anionic group is in the salt form, cations that serve as counter ions include alkali metal cations; ammonium; organic ammonium; and the like. Further, specific examples of other atomic groups (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene groups and naphthylene groups; carbonyl groups; imino groups; a sulfonyl group; an ester group; and an ether group. Moreover, it is good also as a group which combined these groups.

As the dye, it is preferable to use one having an anionic group. Specific examples of dyes include dyes such as azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone.

Among the coloring materials described above, it is preferable to use a compound having a copper phthalocyanine skeleton. As a compound having a copper phthalocyanine skeleton, C.I. I. Pigment Blue 15:3, C.I. I. Pigment Blue 15:4; C.I. I. Dyes such as Direct Blue 199 are included.

(resin)
The ink can contain a resin. The resin content (% by mass) in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the ink. is more preferable.

The resin can be contained in the ink for the following reasons: (i) it stabilizes the dispersed state of the pigment, that is, it serves as the above-mentioned resin dispersant or its auxiliary, and (ii) it improves various characteristics of the recorded image. can. At this time, as the resin to be contained in the ink for reasons such as (i) and (ii) above, a resin having an anionic group, which is a "component having an anionic group", can be used. Forms of the resin include block copolymers, random copolymers, graft copolymers, combinations thereof, and the like. Moreover, the resin may be dissolved in the aqueous medium as a water-soluble resin, or may be dispersed as resin particles in the aqueous medium. The resin particles do not need to contain a coloring material.

In the present invention, the resin being water-soluble means that the resin does not form particles whose particle size can be measured by a dynamic light scattering method when the resin is neutralized with an acid value and an equimolar amount of alkali. It is assumed that Whether or not the resin is water-soluble can be determined according to the method described below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an acid value equivalent alkali (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10-fold (by volume) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by the dynamic light scattering method, if particles having the particle size are not measured, it can be determined that the resin is water-soluble. The measurement conditions at this time can be set to, for example, SetZero: 30 seconds, the number of measurements: 3, and the measurement time: 180 seconds. As the particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, trade name “UPA-EX150” manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and measurement conditions are not limited to those described above.

In the case of a water-soluble resin, the acid value of the resin is preferably 250 mgKOH/g or less, more preferably 100 mgKOH/g or more and 250 mgKOH/g or less. Moreover, in the case of resin particles, the acid value of the resin is preferably 5 mgKOH/g or more and 100 mgKOH/g or less. In the case of resin particles, the amount of acid groups introduced is preferably 250 μmol/g or less, more preferably 120 μmol/g or more and 250 μmol/g or less. Resin particles generally have a small amount of acid groups introduced. ' is preferred. When the acid value of the water-soluble resin is more than 250 mgKOH/g, or when the amount of acid groups introduced into the resin particles is more than 250 μmol/g, it may not be possible to sufficiently suppress the decrease in dischargeability. This is because when the resin adheres to the counter electrode, there are too many anionic groups in the resin, making it difficult for the dissociation of ions by the soluble metal ions to occur efficiently.

The weight average molecular weight of the resin is preferably from 3,000 to 15,000 in the case of the water-soluble resin, and from 1,000 to 2,000,000 in the case of the resin particles. The volume average particle diameter of the resin particles measured by the dynamic light scattering method (measurement conditions are the same as above) is preferably 50 nm or more and 500 nm or less.

Examples of resins include acrylic resins, urethane resins, and olefin resins. Among them, acrylic resins and urethane resins are preferable.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as structural units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester-based monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene is preferred. Since these resins easily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

A hydrophilic unit is a unit having a hydrophilic group such as an anionic group. A hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having hydrophilic groups include acidic monomers having carboxylic acid groups such as (meth)acrylic acid, itaconic acid, maleic acid and fumaric acid, and anions such as anhydrides and salts of these acidic monomers. organic monomers, and the like. Examples of cations constituting salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium and organic ammonium. A hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. A hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; methyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylic acid 2 - (meth)acrylic acid ester monomers such as ethylhexyl.

As the urethane-based resin, for example, one obtained by reacting polyisocyanate and polyol can be used. Moreover, what made the chain extension agent further react may be used. Examples of olefinic resins include polyethylene and polypropylene.

(Soluble metal ions whose standard electrode potential is greater than 0 V)
The ink contains soluble metal ions with a standard electrode potential greater than 0V. The standard electrode potential is a single electrode potential of a metal or the like, and is a value expressed in units of V (volt) with the potential of the standard hydrogen electrode as a reference (0 volt), quantifying the so-called "ionization tendency". It is what I did. The standard electrode potential of a metal is in principle defined as the value of the metal itself, and is described, for example, in "Chemical Handbook, Basic Edition, Revised 5th Edition" (edited by The Chemical Society of Japan, Maruzen Co., Ltd.).

Examples of metals having a standard electrode potential of over 0 V at 25° C. include gold, platinum, iridium, silver, mercury, copper, and ruthenium. For metals whose standard electrode potential is less than 0 V (e.g., lead, tin, nickel, cobalt, iron, zinc, aluminum, etc.), even if the soluble metal ions are present in the ink, There is no effect of suppressing the adhesion of , and the deterioration of ejection properties cannot be suppressed. Among metals having a standard electrode potential exceeding 0 V, metals different from the main components (iridium, ruthenium, etc.) constituting the second protective layer of the recording head are preferred, and copper and silver are particularly preferred. These soluble metal ions are more likely to stably exist in the water-based ink than other metals, so that the deterioration of the ejection performance can be more effectively suppressed.

Also, metals with a standard electrode potential exceeding 0 V must exist in the ink in the form of soluble ions. "Soluble" means that it can exist in a dissolved state in ink. Whether or not metal ions having a standard electrode potential exceeding 0 V in the ink are “soluble” can be confirmed, for example, as follows. Excess acid is added to the ink to precipitate the components, and the precipitate and supernatant liquid are separated by centrifugation or the like. This supernatant liquid can be analyzed by inductively coupled plasma atomic emission spectrometry or the like to determine the presence, type, and content of metals. Since it can be said that the masses of metal and its ions are substantially equivalent, the content of metal ions is a value calculated as the content of "metal" for convenience.

In the case of inks containing particulate matter such as pigments and resin particles, the addition of excess acid may be omitted and the supernatant liquid obtained by centrifugation may be analyzed. In any case, if the metal ion is "soluble", it will be present in the liquid component even if acid is added or centrifugation is performed. can be confirmed. The above confirmation may be performed using an intermediate material used when preparing the ink, such as a pigment dispersion, an aqueous dye solution, or a liquid containing a resin.

The content (ppm) of soluble metal ions with a standard electrode potential exceeding 0 V in the ink should be 0.1 ppm or more and 15.0 ppm or less based on the total mass of the ink. If the content is less than 0.1 ppm or more than 15.0 ppm, as described above, it is not possible to suppress the deterioration of ejection properties. Also, a metal having a standard electrode potential of more than 0 V usually becomes a multivalent metal ion. For this reason, when it coexists with a component having an anionic group in the ink, an ionic reaction may occur and the storage stability of the ink tends to decrease. Specifically, the content (ppm) of soluble metal ions having a standard electrode potential exceeding 0 V in the ink is preferably 0.1 ppm or more and 10.0 ppm or less based on the total mass of the ink.

In particular, the soluble metal ions having a standard electrode potential exceeding 0 V in the ink are copper and silver, and their content (ppm) is 1.0 ppm or more and 10.0 ppm or less based on the total mass of the ink. is preferably When these conditions are satisfied, it is possible to more effectively suppress deterioration of ejection properties. This content means the total content when copper and silver are used together.

The soluble metal ions include free metal ions, complex ions, etc., and may be hydrates. Specific examples of copper, silver, and platinum include the following. Examples of soluble copper ions include free copper ions, tetraamminecopper(II) ions, bis(ethylenediamine)copper(II) ions, ethylenediaminetetraacetic acid-copper(II) ions, and tetracyanocopper(I) ions. be done. Examples of soluble silver ions include free silver ions and diammine silver (I) ions. Examples of soluble platinum ions include free platinum ions, tetraammineplatinum (II) hydroxide, [PtCl ₄ ][Pt(NH ₃ ) ₄ ] (tetraammineplatinum (II) tetrachloroplatinic acid (II)), and the like. is mentioned.

(chelating agent)
The ink preferably contains a chelating agent. Among them, it is preferable to use an alkanolamine having two or more hydroxy groups. Alkanolamine having two or more hydroxy groups forms a complex with a soluble metal ion having a standard electrode potential of more than 0 V, thereby suppressing adhesion of the metal ion to the heater-side electrode. can be more effectively suppressed.

Examples of alkanolamines having two or more hydroxy groups include compounds represented by N(H) _x (R—OH) _y . In the formula, R represents an alkylene group, x is 0 or 1, y is 2 or 3, and x+y is 3. The alkylene group of R preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms.

Alkanolamines having two or more hydroxy groups include, for example, dialkanolamines such as diethanolamine; trialkanolamines such as triethanolamine and tripropanolamine.

The content (% by mass) of the alkanolamine having two or more hydroxy groups in the ink is preferably 0.30% by mass or more and 1.00% by mass or less based on the total mass of the ink. If the content is less than 0.30%, the amount of alkanolamine is too small from the viewpoint of the balance with the soluble metal ions, and the decrease in ejection properties may not be sufficiently suppressed. If the content is more than 1.00% by mass, the intermolecular interaction tends to be strong, making it difficult to form a complex with soluble metal ions. .

Chelating agents commonly used in water-based inkjet inks include acidic compounds such as polyvalent carboxylic acids and phosphates. Since these compounds have an anionic group unlike the alkanolamine, they may be easily attracted to the counter electrode when voltage control is performed. Therefore, as the chelating agent, it is preferable to use an alkanolamine having two or more hydroxy groups rather than using an acidic compound.

(aqueous medium)
The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water or ion-exchanged water. The water content (% by mass) in the ink is preferably 50.00% by mass or more and 95.00% by mass or less based on the total mass of the ink. Also, the content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds, and the like, which can be used for inkjet inks, can be used.

(Other additives)
In addition to the above ingredients, various other agents such as antifoaming agents, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, antiseptics, anti-mold agents, antioxidants, and anti-reduction agents may be added to the ink. may contain additives.

(Physical properties of ink)
The inks described above are water-based inks applicable to the inkjet system. 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. Also, 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, more preferably 8.0 or more and 9.5 or less.

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

<Preparation of resin aqueous solution>
(Resin 1)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) having an acid value of 120 mgKOH/g and a weight average molecular weight of 8,000 was prepared by a conventional method. 40.0 parts of resin 1 is neutralized with potassium hydroxide having an equimolar acid value, and an appropriate amount of pure water is added to prepare an aqueous solution of resin 1 having a resin (solid content) content of 40.0%. was prepared.

(Resin 2)
Resin 1 was changed to a styrene-ethyl acrylate-acrylic acid copolymer (resin 2) synthesized by a conventional method and having an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000. Except for this, an aqueous solution of resin 2 having a resin (solid content) content of 40.0% was prepared in the same manner as the aqueous solution of resin 1 described above.

(Resin 3)
Resin 1 was changed to a styrene-ethyl acrylate-acrylic acid copolymer (resin 3) synthesized by a conventional method and having an acid value of 250 mgKOH/g and a weight average molecular weight of 8,000. Except for this, an aqueous solution of resin 3 having a resin (solid content) content of 40.0% was prepared in the same manner as the aqueous solution of resin 1 described above.

(Resin 4)
Resin 1 was changed to a styrene-ethyl acrylate-acrylic acid copolymer (resin 4) synthesized by a conventional method and having an acid value of 260 mgKOH/g and a weight average molecular weight of 8,000. Except for this, an aqueous solution of resin 4 having a resin (solid content) content of 40.0% was prepared in the same manner as the aqueous solution of resin 1 described above.

(Resin 5)
Resin 1 was changed to a benzyl methacrylate-methacrylic acid copolymer (resin 5) synthesized by a conventional method and having an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000. Except for this, an aqueous solution of resin 5 having a resin (solid content) content of 40.0% was prepared in the same manner as the aqueous solution of resin 1 described above.

(Resin 6)
240.0 parts of polytetramethylene glycol having a number average molecular weight of 1,000, 282.0 parts of isophorone diisocyanate, and 0 parts of dibutyltin dilaurate were added to a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet, and condenser. .007 parts were added. After reacting at a temperature of 100° C. for 5 hours in a nitrogen gas atmosphere, the temperature was cooled to 65° C. or lower. 118.0 parts of dimethylolpropionic acid, 447.8 parts of neopentyl glycol and 150.0 parts of methyl ethyl ketone were added and reacted at a temperature of 80°C. After that, the temperature was cooled to 40° C., and 20.0 parts of methanol was added to terminate the reaction. Next, an appropriate amount of pure water was added, and a necessary amount of 10.0% potassium hydroxide aqueous solution was added to neutralize the resin while stirring with a homomixer. Thereafter, methyl ethyl ketone and unreacted methanol are distilled off under heating and reduced pressure to contain resin 6 having an acid value of 55 mgKOH/g and a weight average molecular weight of 15,000, and the resin (solid content) content is 40.0%. An aqueous solution of resin 6 was prepared.

<Preparation of aqueous dispersion of resin particles>
(Resin particle 1)
18.0 parts of butyl methacrylate, 0.18 parts of methacrylic acid, a polymerization initiator (2,2′-azobis(2-methylbutyl 2.0 parts of lonitrile)) and 2.0 parts of n-hexadecane were added. Nitrogen gas was introduced into the reaction system and stirred for 0.5 hours. 78.0 parts of a 6.0% aqueous solution of an emulsifier (trade name “NIKKOL BC15”, manufactured by Nikko Chemicals) was added dropwise to the reaction system and stirred for 0.5 hour to obtain a mixture. After emulsifying the mixture by irradiating it with ultrasonic waves for 3 hours using an ultrasonic irradiator, a polymerization reaction was carried out at 80° C. for 4 hours in a nitrogen atmosphere. After cooling the reaction system to 25° C., it was filtered, and an appropriate amount of pure water was added to prepare an aqueous dispersion of resin particles 1 having a resin particle (solid content) content of 40.0%. The amount of acid groups introduced into Resin Particle 1 was 120 μmol/g.

(Resin particles 2)
Resin particles having a resin particle (solid content) content of 40.0% were prepared in the same manner as for the aqueous dispersion of resin particles 1 described above, except that the amount of methacrylic acid used was changed to 0.35 parts. An aqueous dispersion of 2 was prepared. The amount of acid groups introduced into resin particles 2 was 150 μmol/g.

(Resin particles 3)
Resin particles having a resin particle (solid content) content of 40.0% were prepared in the same manner as for the aqueous dispersion of resin particles 1 described above, except that the amount of methacrylic acid used was changed to 0.54 parts. An aqueous dispersion of 3 was prepared. The amount of acid groups introduced into resin particles 3 was 250 μmol/g.

(Resin particle 4)
Resin particles having a resin particle (solid content) content of 40.0% were prepared in the same manner as the aqueous dispersion of resin particles 1 described above, except that the amount of methacrylic acid used was changed to 0.60 parts. An aqueous dispersion of 4 was prepared. The amount of acid groups introduced into resin particles 4 was 270 μmol/g.

<Resin analysis conditions>
The acid value of the resin and the amount of acid group introduced were measured and calculated by potentiometric titration with a potassium hydroxide/ethanol titrant using an automatic potentiometric titrator. The weight average molecular weight (converted to polystyrene) of the resin was measured by gel permeation chromatography. Further, whether or not the resin was water-soluble was confirmed according to the method shown below. First, a liquid containing resin was diluted with pure water to prepare a sample having a resin (solid content) content of 1.0%. Next, when the particle size of the resin in the prepared sample was measured by the dynamic light scattering method, the resin was judged to be water-soluble when no particles having the particle size were measured. The measurement conditions at this time are shown below. As a particle size distribution analyzer, a particle size analyzer (trade name “UPA-EX150” manufactured by Nikkiso Co., Ltd.) using dynamic light scattering method was used.

[Measurement condition]
- SetZero: 30 seconds - Number of measurements: 3 - Measurement time: 180 seconds.

The particle diameters of the synthesized resin particles 1 to 4 could be measured by the method described above. On the other hand, the particle diameters of the resins other than the resin particles 1 to 4 could not be measured, confirming that they were water-soluble resins.

<Preparation of liquid containing coloring material>
Each of the liquids prepared as follows was passed through a column filled with a chelate exchange resin five times to remove polyvalent metal ions, and then used for ink preparation. When the content of polyvalent metal ions in the liquid containing the coloring material passed through the column was measured by the method described later, no soluble metal ions with a standard electrode potential exceeding 0 V were detected.

The method for measuring the content of metal ions is as follows. First, in the case of the pigment dispersion, the pigment dispersion was centrifuged at 12,000 rpm for 1 hour, and then the supernatant liquid other than the precipitate was collected. This liquid was analyzed for the content of metal ions by inductively coupled plasma emission spectrometry (trade name: "ICP-OES720", manufactured by Agilent Technologies). In the case of an aqueous dye solution, an excess of acid was added to the aqueous dye solution to precipitate the dye, followed by centrifugation at 12,000 rpm for 1 hour to collect the supernatant liquid other than the precipitate. Thereafter, the content of metal ions was analyzed in the same manner as for the pigment dispersion.

(Pigment dispersion liquids 1 to 4 and 6 to 9)
A mixture of components (unit: %) shown in the upper part of Table 1 was placed in a batch-type vertical sand mill (manufactured by Imex) filled with 200 parts of zirconia beads with a diameter of 0.3 mm, and dispersed for 5 hours while cooling with water. After that, centrifugation was performed to remove coarse particles. Further, pressure filtration was performed with a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm to obtain each pigment dispersion. The lower part of Table 1 shows the pigment and resin contents in the pigment dispersion.

(Pigment dispersion liquid 5)
A pigment dispersion having a pigment content of 10.0% by adding an appropriate amount of pure water to a commercially available pigment dispersion containing a self-dispersing pigment (trade name “Cab-o-jet 300” manufactured by Cabot). Got 5. The pigment in pigment dispersion 5 is C.I. I. Pigment Blue 15:4.

(Aqueous dye solution)
After dissolving a dye (CI Direct Blue 199) in pure water, excess acid was added to precipitate the dye. The precipitated dye was separated by filtration to obtain a wet cake of the dye whose anionic group was an acid form. The resulting wet cake was added to pure water, and an aqueous solution of sodium hydroxide in an amount equimolar to the anionic groups of the dye was added to neutralize the anionic groups and dissolve the dye. Further, an appropriate amount of pure water was added to obtain a dye aqueous solution 1 having a dye content of 10.0%.

<Preparation of metal ion aqueous solution>
Copper nitrate, silver nitrate, tetraammineplatinum (II) hydroxide, and iron nitrate were each dissolved in an appropriate amount of pure water to prepare an aqueous solution of each metal ion having a soluble metal ion content of 100 ppm.

<Ink preparation>
Each component (unit: %) shown in the upper part of Tables 2 to 4 was mixed, thoroughly stirred, and filtered under pressure through a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm to prepare each ink. Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals, and Proxel GXL(S) is a preservative manufactured by Lonza. The “polar substance” used in the preparation of ink 53 is polyoxyethylene (n=10) phosphate ester choline salt described in Patent Document 2. In the lower part of Tables 2 to 4, the content of soluble metal ions with a standard electrode potential exceeding 0 V (specific soluble metal ions (ppm)) and the content of coloring materials (coloring materials ( %)), the content of water-soluble resin (water-soluble resin (%)), and the content of resin particles (resin particles (%)).

<Fabrication of recording head>
A recording head having the configuration shown in FIG. 2 was manufactured. As the constituent materials of the second protective layer 107, recording head 1: iridium, recording head 2: ruthenium, and recording head 3: tantalum were used. The manufacturing method described in Patent Document 1 was referred to in manufacturing the recording head.

<Evaluation>
The inks and recording heads obtained above were used in the combinations shown in Table 5, and the following evaluations were performed using an inkjet recording apparatus having the configuration shown in FIG. In this embodiment, the print duty of a solid image printed under the condition of applying 8 droplets of 4 ng ink to a unit area of 1/600 inch×1/600 inch is defined as 100%. In the present invention, in the following evaluation criteria for each item, "AA", "A", and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. Table 5 shows the evaluation results.

Ink was filled into the ink flow path of the recording head. As a result, the heater-side region 107a of the second protective layer serving as a cathode and the counter-electrode-side region 107b of the second protective layer serving as an anode were electrically connected. In this state, the external electrode 111 connected to the counter-electrode-side region 107b of the second protective layer is controlled by voltage control to negatively charge the heater-side region 107a of the second protective layer and to positively charge the counter-electrode-side region 107b. A DC voltage of +2 V was applied to the side (step S2).

A voltage for ejecting ink was applied to the heating portion 104a while maintaining the voltage control state (step S3). Specifically, a driving pulse having a voltage of 20 V and a pulse width of 1.5 μsec was applied to the heat generating portion 104a 1.5×10 ⁸ times at a frequency of 0.5 kHz to eject ink. This ejection assumes the number of ejections at a level at which burnt deposits would occur on the heater if ink containing no soluble metal ions with a standard electrode potential exceeding 0 V was used and voltage control was not performed.

After that, a solid image of 5 cm×5 cm with a recording duty of 100% was recorded on a recording medium (trade name “Canon Photo Paper Glossy Gold”, manufactured by Canon), and this was designated as “solid image 1”. Further, under the same conditions as above, a driving pulse was applied to the heating portion 2.5×10 ⁷ times to eject ink, and then a solid image of 5 cm×5 cm with a print duty of 100% was printed. The cycle was repeated to obtain a solid image 2 and a solid image 3. After the solid image 3 was completely recorded (step S4), the voltage control was stopped (step S5). However, in Reference Examples 1 to 4, voltage control was not performed in any of the above procedures.

The solid images 1 to 3 thus obtained were visually checked for unevenness, and the ejection property was evaluated according to the evaluation criteria shown below.
AA: No unevenness occurred in any of solid images 1 to 3 A: No unevenness occurred in solid images 1 and 2, but unevenness occurred in solid image 3 B: Solid image 1 There was no unevenness in solid images 2 and 3, but unevenness occurred in solid images 2 and 3. C: All of solid images 1 to 3 had unevenness.

Claims (20)

a heater for ejecting ink, disposed in an ink flow path communicating with the ejection port;
a first protective layer disposed at a position corresponding to the heater and blocking contact between the heater and the ink in the ink flow path;
a recording head having a second protective layer that corresponds to the heater and is arranged at a position in contact with the ink and made of a metal material;
Means for applying a voltage with the second protective layer as a cathode and a portion conducting through the ink as an anode;
An inkjet recording method for recording an image on a recording medium by ejecting ink from the recording head using an inkjet recording apparatus comprising
The ink contains a component having an anionic group and a soluble metal ion having a standard electrode potential of more than 0 V, and the content (ppm) of the metal ion is 0 based on the total mass of the ink. An ink jet recording method characterized in that the water-based ink is 1 ppm or more and 15.0 ppm or less. 2. The inkjet recording method according to claim 1, wherein the metal ions are at least one of copper ions and silver ions. 2. The ink jet recording method according to claim 1, wherein the metal ions are copper ions. 3. The inkjet recording method according to claim 2, wherein the content (ppm) of at least one of the copper ions and the silver ions is 1.0 ppm or more and 10.0 ppm or less based on the total mass of the ink. 5. Any one of claims 1 to 4, wherein the content (% by mass) of the component having an anionic group in the ink is 0.10% by mass or more and 20.00% by mass or less based on the total mass of the ink. The ink jet recording method according to the item. The ink jet recording method according to any one of claims 1 to 5, wherein the component having an anionic group is a resin having an anionic group. 7. The inkjet recording method according to claim 6, wherein the resin having an anionic group is at least one of an acrylic resin and a urethane resin. The component having an anionic group is at least one of (i) a water-soluble resin having an acid value of 250 mgKOH/g or less and (ii) resin particles having an acid group introduction amount of 250 μmol/g or less. 8. The inkjet recording method according to any one of 1 to 7. 9. The inkjet recording method according to claim 8 , wherein the component having an anionic group contains (i) a water-soluble resin having an acid value of 250 mgKOH/g or less. 9. The inkjet recording method according to claim 8 , wherein the component having an anionic group contains (ii) resin particles in which the amount of acid groups introduced is 250 μmol/g or less. The inkjet recording method according to any one of claims 1 to 10, wherein the ink contains an alkanolamine having two or more hydroxy groups. 12. The method according to claim 11, wherein the content (% by mass) of the alkanolamine having two or more hydroxy groups in the ink is 0.30% by mass or more and 1.00% by mass or less based on the total mass of the ink. Inkjet recording method. 13. The inkjet recording method according to any one of claims 1 to 12, wherein the ink contains a compound having a copper phthalocyanine skeleton. 14. The method according to any one of claims 1 to 13, wherein the second protective layer is made of at least one metal material selected from the group consisting of iridium, ruthenium, and materials containing at least one of iridium and ruthenium. The ink jet recording method described. 15. The inkjet recording method according to claim 14, wherein the metal material forming the second protective layer contains the iridium. 16. Any one of claims 1 to 15, wherein the ink contains a compound having a copper phthalocyanine skeleton, the metal ions are copper ions, and the metal material forming the second protective layer contains iridium. 2. The inkjet recording method according to item 1 or 2. 17. The inkjet recording method according to any one of claims 1 to 16, wherein the amount of voltage applied is 0.1 V or more and 4 V or less. 18. The inkjet recording method according to any one of claims 1 to 17, wherein the amount of voltage applied is 1 V or more and 4 V or less. 19. The inkjet recording method according to any one of claims 1 to 18, wherein the ink is ejected from the recording head while the voltage is maintained. a heater for ejecting ink, disposed in an ink flow path communicating with the ejection port;
a first protective layer disposed at a position corresponding to the heater and blocking contact between the heater and the ink in the ink flow path;
a recording head having a second protective layer that corresponds to the heater and is arranged at a position in contact with the ink and made of a metal material;
An inkjet recording device comprising
The ink contains a component having an anionic group and a soluble metal ion having a standard electrode potential of more than 0 V, and the content (ppm) of the metal ion is 0 based on the total mass of the ink. .1 ppm or more and 15.0 ppm or less water-based ink,
An ink jet recording apparatus, comprising means for applying a voltage having the second protective layer as a cathode and a portion conducting through the ink as an anode.

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