Ink jet recording method, ink jet recording apparatus, and aqueous ink

Abstract

To provide an inkjet recording method excellent in suction recoverability and ink discharge stability even when using ink containing wax for recording an image excellent in scratch resistance.SOLUTION: Using an ink jet recording apparatus including a recording head including an ejection orifice configured to eject an aqueous ink, a pressure chamber communicating with the ejection orifice, an ejection element disposed in the pressure chamber and configured to generate energy for ejecting the aqueous ink from the ejection orifice, a liquid storage chamber configured to supply the aqueous ink to the pressure chamber, a depressurization chamber disposed above and adjacent to the liquid storage chamber in a vertical direction and configured to depressurize an inside thereof, and a gas permeable membrane disposed at a boundary between the liquid storage chamber and the depressurization chamber, An ink jet recording method includes applying an aqueous ink ejected from an ejection orifice to a recording medium to record an image. A melting point Tw (°C) of the wax particles in the aqueous ink and a maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy a relationship of the following Expression (1). Tw-Ti ≥ 10 (1) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and a water-based ink. [Background technology]

[0002] Inkjet recording devices can record high-resolution images such as photographs, documents, and posters by ejecting ink from the nozzles of a recording head and applying it to a recording medium. In recent years, the images to be recorded are required to have properties such as abrasion resistance in addition to high resolution. In order to record images with improved abrasion resistance, inks containing wax are used.

[0003] When using an inkjet recording device, bubbles may be trapped in the ink flow path when replacing the ink container, such as an ink cartridge or ink container bag, or when replacing the recording head. If these bubbles enter the pressure chamber of the recording head, the pressure required to eject the ink may be insufficient, affecting the ink ejection performance. Furthermore, if bubbles remain in the ink flow path of the recording head, they may expand due to changes in the external environment, such as an increase in the temperature of the installation environment, which could lead to ink leakage. Therefore, to ensure stable use of the recording device and recording head, it is preferable to configure the recording head so that bubbles that have entered the interior can be expelled to the exterior.

[0004] When the amount of bubbles that have invaded the interior of the print head increases, a suction recovery process is performed, in which the bubbles are sucked out along with the ink through the ejection ports to restore the print head to its original state. If the amount of bubbles increases due to continuous use of the printing apparatus or after it has been left unused for a long period of time, the suction recovery process must be performed multiple times. However, the suction recovery process results in downtime during which printing cannot be performed, which reduces the amount (number) of images that can be printed in a certain period of time and leads to reduced productivity, so it is best to avoid this process as much as possible.

[0005] As a technology for dealing with bubbles, a recording device has been proposed that incorporates a degassing unit equipped with a hollow fiber module and a filter that captures bubbles in the path that supplies ink from the ink storage unit to the recording head (Patent Documents 1 and 2). Meanwhile, a recording device has been proposed that incorporates a degassing unit that includes a partition formed from a hollow fiber membrane inside the recording head (Patent Document 3). Furthermore, recognizing the issue that using a membrane would result in insufficient strength, a liquid ejection device has been proposed that uses a permeable partition wall molded integrally with the liquid storage chamber instead of a membrane, and that reduces the pressure in the gas recovery unit to recover the gas (Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-058544 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-223980 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-173428 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-173961 Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have studied the characteristics of the devices proposed in Patent Documents 1 to 4. While the device proposed in Patent Document 1 can restore the state of a print head after a certain period of inactivity with a small number of suction operations, it suffers from the drawback of a complex configuration and a large device size. Furthermore, the device proposed in Patent Document 2 is unable to adequately capture bubbles, resulting in ejection defects due to bubbles that flow into the ejection section in excess of the allowable amount. Furthermore, the device proposed in Patent Document 3 is unable to adequately degas the ink, resulting in ejection defects. In particular, it has been found that when ink containing wax is used in the liquid ejection device proposed in Patent Document 3, the bubble discharge effect is insufficient, making ejection defects more likely to occur. Furthermore, even when the transparent partition wall proposed in Patent Document 4 is used, the bubble discharge effect is insufficient, resulting in ejection defects.

[0008] Therefore, an object of the present invention is to provide an inkjet recording method that has excellent suction recovery properties and ink ejection stability, even when using ink containing wax to record images with excellent abrasion resistance. Another object of the present invention is to provide an inkjet recording apparatus and a water-based ink for use in this inkjet recording method. [Means for solving the problem]

[0009] That is, according to the present invention, there is provided an inkjet recording method using an inkjet recording device equipped with a recording head comprising: an ejection port for ejecting aqueous ink, a pressure chamber communicating with the ejection port, an ejection element disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection port, a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber, a decompression chamber disposed adjacent to and vertically above the liquid storage chamber and configured to be able to decompress the interior thereof, and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, and applying the aqueous ink ejected from the ejection port to a recording medium to record an image, wherein the aqueous ink contains wax particles, the specific gravity of the wax particles being smaller than the specific gravity of the aqueous ink, and the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1) [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inkjet recording method that exhibits excellent suction recovery and ink ejection stability even when using an ink containing wax to record an image with excellent abrasion resistance. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus and a water-based ink for use in this inkjet recording method. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 1B] 1 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of a recording unit. [Figure 3] FIG. 3 is a schematic diagram illustrating an example of a flow path of an ink supply unit. [Figure 4] FIG. 10 is a schematic diagram illustrating an example of a bubble removal and decompression operation. [Figure 5] FIG. 2 is an exploded perspective view showing an example of a recording head. [Figure 6] FIG. 2 is a vertical cross-sectional view showing an example of a circulation path. [Figure 7] FIG. 2 is a schematic diagram showing an example of a bubble removal unit. [Figure 8] FIG. 2 is a diagram schematically illustrating a first configuration example of an ink path. [Figure 9] FIG. 10 is a diagram schematically illustrating a first modified example of a circulation path. [Figure 10] FIG. 10 is a diagram schematically illustrating a second configuration example of an ink path. [Figure 11] FIG. 10 is a diagram schematically illustrating a second modified example of the circulation path. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Unless otherwise specified, physical property values ​​are values ​​at room temperature (25°C) and normal pressure (1 atmosphere). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0013] The inventors investigated why the bubble discharge effect was insufficient when using ink containing wax. Specifically, they analyzed a print head in which the bubble discharge effect was insufficient. As a result, they found that wax adhered to the gas-permeable membrane, clogging the membrane's fine pores and resulting in insufficient bubble discharge. Furthermore, they found that bubble discharge problems due to wax clogging occur only in limited circumstances and are more likely to occur when the device is restarted after a long period of inactivity.

[0014] The inventors speculate as follows about the reason why bubble discharge problems tend to occur when the device is restarted after a long period of inactivity. Generally, wax, which is commonly used in aqueous inks due to its low cost, easy availability, and stable properties, has a specific gravity of less than 1.00, while the specific gravity of aqueous inks is greater than 1.00. That is, the specific gravity of wax particles is lower than that of aqueous inks. Therefore, wax particles in ink that has been left stationary for a long period of time rise to the surface of the ink. Furthermore, the liquid components in the ink tend to evaporate easily in the liquid storage chamber, causing the wax that has risen to the surface of the ink that has been left stationary in the liquid storage chamber to concentrate. If the device is restarted in this state, the wax is likely to melt and adhere due to the temperature increase caused by continuous operation of the device, clogging the fine pores in the gas-permeable membrane. In other words, bubble discharge problems are a problem that arises specifically when wax particles, which have a specific gravity lower than that of aqueous inks, are used.

[0015] Next, the inventors controlled the ink temperature, which increased with use, to be below the melting point of the wax in order to prevent wax fusion. However, this did not sufficiently prevent clogging of the fine pores in the gas-permeable membrane. It is generally believed that wax begins to fuse when the ink temperature approaches the wax's melting point. Furthermore, concentrated wax is more likely to fuse due to the close interparticle distance, and is thought to begin fusing at temperatures lower than its melting point. The inventors positioned a decompression chamber vertically above the liquid storage chamber, and when reducing pressure through the gas-permeable membrane to expel bubbles, controlled the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber to satisfy the relationship shown in formula (1) below. They discovered that this prevented clogging of the fine pores in the gas-permeable membrane due to wax fusion and improved ink ejection stability, leading to the present invention. Tw-Ti≧10 (1)

[0016] By satisfying the relationship of the above formula (1), the fusion of the wax is suppressed and bubbles can be expelled. If the decompression chamber is located to the side of the liquid storage chamber in the vertical direction, when an ink containing wax is used, it is not possible to improve the bubble expulsion efficiency and obtain ejection stability even if the relationship of specific gravity and temperature is adjusted.

[0017] <Inkjet recording method, inkjet recording apparatus, and water-based ink> The inkjet recording method of the present invention uses an inkjet recording device equipped with a predetermined recording head, and records an image by applying aqueous ink ejected from the ejection orifices of the recording head to a recording medium. The recording head includes an ejection orifice for ejecting the aqueous ink, a pressure chamber communicating with the ejection orifice, an ejection element, a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber, a decompression chamber, and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber. The ejection element is disposed in the pressure chamber and generates energy for ejecting the aqueous ink from the ejection orifice. The decompression chamber is disposed adjacent to and vertically above the liquid storage chamber and is configured to be able to decompress its interior. The aqueous ink contains wax particles, and the specific gravity of the wax particles is smaller than that of the aqueous ink. The melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1)

[0018] The inkjet recording apparatus of the present invention is an inkjet recording apparatus equipped with a predetermined recording head. The recording head includes an ejection port for ejecting aqueous ink, a pressure chamber communicating with the ejection port, an ejection element, a liquid storage chamber capable of supplying aqueous ink to the pressure chamber, a decompression chamber, and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber. The ejection element is disposed in the pressure chamber and generates energy for ejecting the aqueous ink from the ejection port. The decompression chamber is disposed adjacent to and vertically above the liquid storage chamber and is configured to be able to decompress its interior. The aqueous ink contains wax particles, and the specific gravity of the wax particles is smaller than that of the aqueous ink. The melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1)

[0019] Furthermore, the aqueous ink of the present invention is an ink for use in an inkjet recording method using an inkjet recording device equipped with a predetermined recording head, in which the aqueous ink is ejected from the ejection orifices of the recording head and applied to a recording medium to record an image. The recording head includes an ejection orifice for ejecting the aqueous ink, a pressure chamber communicating with the ejection orifice, an ejection element, a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber, a decompression chamber, and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber. The ejection element is disposed in the pressure chamber and generates energy for ejecting the aqueous ink from the ejection orifice. The decompression chamber is disposed adjacent to and vertically above the liquid storage chamber and is configured to be able to decompress its interior. The aqueous ink contains wax particles, and the specific gravity of the wax particles is smaller than that of the aqueous ink. The melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1)

[0020] (Inkjet recording device) FIG. 1A is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus according to the present invention. FIG. 1B is a side view schematically illustrating an embodiment of an inkjet recording apparatus according to the present invention. As shown in FIGS. 1A and 1B, the recording apparatus according to this embodiment includes an inkjet recording head 1 that ejects ink. Examples of the recording head include a recording head that ejects ink by the action of mechanical energy and a recording head that ejects ink by the action of thermal energy. Of these, a recording head that ejects ink by the action of thermal energy is preferred. A recording head that ejects ink by the action of thermal energy is a thermal recording head that applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element, thereby ejecting the ink from the ejection orifices. This thermal recording head preferably includes a mechanism (temperature control mechanism) that heats the aqueous ink to a predetermined temperature before it is ejected from the recording head and applied to the recording medium. If a temperature control mechanism is included, the heating temperature of the ink ejected from the recording head is preferably 35°C or higher and 70°C or lower.

[0021] [Heating process] The recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink has been applied. Heating the recording medium to which the ink has been applied can promote drying and increase the strength of the image. Examples of means for heating the recording medium include known heating means such as heaters, air blowing means using air blowers such as dryers, and combinations of these. Examples of heat treatment methods include a method of applying heat from the opposite side (back side) of the recording surface (ink-applied surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used.

[0022] To improve the abrasion resistance of the image, the heating temperature of the recording medium to which the ink has been applied is preferably 50° C. or higher and 90° C. or lower. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined in advance depending on the type of ink and recording medium.

[0023] In the recording device shown in FIGS. 1A and 1B, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 1 reciprocates in the main scanning direction B. The recording medium P to which ink has been applied can be heated by the heater 25. Specific examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 onto the recording medium P. The heater cover 26 also serves as a member for protecting the heater 25. The recording medium P to which ink has been applied and ejected from the recording head 1 is taken up by a take-up spool 27 to form a roll-shaped taken-up medium 24.

[0024] [Recording Media] Any recording medium may be used. For example, recording media having ink absorption (permeability) such as recording media without a coating layer, such as plain paper, uncoated paper, and synthetic paper; and recording media with a coating layer, such as recording paper, glossy paper, and art paper; can be used. Also, recording media without permeability, such as films or sheets made of resin materials such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET), can be used.

[0025] [Recording Department] Fig. 2 is a diagram schematically illustrating an example of a recording unit, and is an enlarged view of the recording head of the recording unit and its surroundings. First, the general configuration of the recording unit 50 will be described with reference to Fig. 2. Fig. 2(a) is a perspective view schematically illustrating the recording unit 50 on which the recording head 1 can be mounted. The recording unit 50 constitutes a serial inkjet recording device that performs recording on a recording medium P by ejecting ink while scanning the recording head 1.

[0026] The recording head 1 is mounted on a carriage 60. The carriage 60 moves back and forth along a guide shaft 51 in the main scanning direction (X direction). The recording medium P is transported in a sub-scanning direction (Y direction) that intersects (in this example, orthogonal to) the main scanning direction by upstream transport rollers 55 and 56 and downstream transport rollers 57 and 58. In each of the figures referred to below, the Z direction indicates the vertical direction and intersects (in this example, orthogonal to) the XY plane defined by the X and Y directions. The recording head 1 is configured to be detachable from and attachable to the carriage 60 by the user.

[0027] The recording head 1 is configured to include a circulation unit 54 (see FIG. 5) and a discharge unit 3 (see FIG. 5), which will be described later. The specific configuration will be described later, but the discharge unit 3 is provided with a plurality of discharge ports and energy generating elements (hereinafter referred to as discharge elements) that generate discharge energy for discharging ink from each discharge port.

[0028] The recording unit 50 is also provided with an ink storage unit 2, which is an ink supply source, and an ink supply unit 400. The ink stored in the ink storage unit 2 is supplied to the recording head 1 by the ink supply unit 400 via a first supply path 111 and a second supply path 112. Gas such as bubbles generated in the recording head 1 is also discharged to the outside of the recording head 1 by the ink supply unit 400 via a third air flow path 113.

[0029] The recording unit 50 records a predetermined image on the recording medium P by repeating a recording scan in which the recording head 1 mounted on the carriage 60 moves in the main scanning direction while ejecting ink to perform recording, and a transport operation in which the recording medium P is transported in the sub-scanning direction. The recording head 1 is capable of ejecting four types of ink: black (K), cyan (C), magenta (M), and yellow (Y), and is capable of recording a full-color image using these inks. However, the inks that can be ejected from the recording head 1 are not limited to the above four types of ink. The present disclosure is also applicable to recording heads that eject other types of ink. In other words, the types and number of inks ejected from the recording head are not limited. For example, the type of ink ejected from the recording head may be one type, or two or more types. In addition, ink that does not contain a colorant (clear ink) or a reaction liquid containing a reactant that reacts with the ink may also be used as the ink.

[0030] The recording unit 50 is also provided with a control unit 100 and a cap member (not shown) capable of covering the ejection port surface of the recording head 1 on which the ejection ports are formed. The cap member is provided at a position in the recording unit 50 that is offset in the X direction from the conveyance path of the recording medium P. The cap member covers the ejection port surface of the recording head 1 when not in recording operation, and is used to prevent ink near the ejection ports from drying, to protect the recording head, and to suck ink from the ejection ports. Signals output from the control unit 100 are sent to the recording head 1 and the like via signal lines 109.

[0031] FIG. 2B is a block diagram showing the control system of the recording unit 50. The control unit 100 of the recording unit 50 includes a CPU 103, a RAM 102, a ROM 101, a head driver 1A, motor drivers 104A and 105A, and pump drivers 404A and 500A. The CPU 103 functions as a control unit that controls the operation of each component of the recording unit 50 based on programs, such as processing procedures, stored in the ROM 101. The RAM 102 is used as a work area when the CPU 103 executes processing. The CPU 103 receives image data from a host device 900 external to the recording unit 50, controls the head driver 1A, and controls the driving of the ejection elements provided in the ejection unit 3. The CPU 103 also controls the drivers of various actuators provided in the recording unit. For example, the CPU 103 controls a motor driver 104A that drives a conveyance motor 104 for conveying the recording medium P. The CPU 103 controls a motor driver 105A that drives a carriage motor 105 to move the carriage 60. The CPU 103 controls a pump driver 500A that drives a circulation pump 500. The CPU 103 controls a pump driver 404A that drives a one-way pump 404, which will be described later. In addition, signals output from various sensors such as a volume sensor, a pressure sensor 409, and a liquid sensor 416 are input to the control unit 100. Although FIG. 2(b) shows a form in which processing is performed upon receiving image data from the host device 900, processing may also be performed by the printing unit 50 without relying on data from the host device 900.

[0032] [Ink supply unit] FIG. 3 is a schematic diagram showing an example of a flow path of the ink supply unit. The ink supply unit 400 shown in FIG. 3 has an intermediate container 401 that temporarily stores ink supplied through a first supply path 111 from an ink container 2 that is detachably attached to the recording unit 50. A first check valve 222 is provided in the first supply path 111, and the first check valve 222 prevents ink from flowing back from the intermediate container 401 to the ink container 2. At least one surface of the intermediate container 401 is formed by a flexible film 402, which allows the volume of the intermediate container 401 to be changed. A volume sensor (not shown) is provided in the intermediate container 401. The volume sensor can detect the volume of the intermediate container 401 by measuring the displacement of the flexible film 402. The amount of ink in the intermediate container 401 can be estimated from the volume of the intermediate container 401 detected by the volume sensor. The amount of ink in the intermediate storage section 401 may be estimated from the volume of the intermediate storage section 401 detected by a volume sensor and the amount of ink consumed by forming an image on a recording medium, suctioning ink from the cap member, etc.

[0033] The intermediate storage section 401 is in contact with a pressure chamber filled with air via a flexible membrane 402. Hereinafter, the pressure chamber of the intermediate storage section 401 will be referred to as an intermediate pressure chamber 403. The pressure of the ink stored in the intermediate storage section 401 can be changed by changing the pressure of the gas (air) in the intermediate pressure chamber 403. The ink stored in the intermediate storage section 401 is supplied to the print head 1 through a second supply path 112 connected to the intermediate storage section 401 and the filter 110 of the print head 1. A second check valve 223 is provided in the second supply path 112, and the second check valve 223 prevents the ink from flowing back from the print head 1 to the intermediate storage section 401. The ink supply section 400 has a one-way pump 404 driven by a pump driver 404A. The one-way pump 404 is configured using, for example, a diaphragm pump, and is capable of unidirectionally drawing in and discharging air when driven by the pump driver 404A.

[0034] The intermediate pressure chamber 403 and the suction side of the one-way pump 404 are connected via a first air flow path 414. A first on-off valve 408 is provided in the first air flow path 414, and opening and closing the first on-off valve 408 makes it possible to switch between open and closed states of the first air flow path 414. A first branch air flow path 418 is provided in the first air flow path 414, branching between the first on-off valve 408 and the one-way pump 404 and having one end connected to the atmosphere. A third on-off valve 407 is provided in the first branch air flow path 418, and opening and closing the third on-off valve 407 makes it possible to switch between sealing the suction side of the one-way pump 404 and opening it to the atmosphere.

[0035] The intermediate pressure chamber 403 and the ejection side of the one-way pump 404 are connected via a second air flow path 415. A second on-off valve 405 is provided in the second air flow path 415, and opening and closing the second air flow path 415 allows the second air flow path 415 to be switched between open and closed. A second branch air flow path 419 is provided in the second air flow path 415, branching between the second on-off valve 405 and the one-way pump 404 and having one end connected to the atmosphere. A fourth on-off valve 406 is provided in the second branch air flow path 419, and opening and closing the fourth on-off valve 406 allows the ejection side of the one-way pump 404 to be switched between closed and open to the atmosphere. A liquid sensor 416 is provided at the end of the second branch air flow path 419 that is open to the atmosphere. The liquid sensor 416 is capable of detecting ink that has entered the air flow path. A pressure sensor 409 is provided at a position communicating with the intermediate pressure chamber 403. The pressure sensor 409 can detect the pressure of the gas (air) in the intermediate pressure chamber 403. The one-way pump 404 and the decompression chamber 760 of the bubble removal unit 770 in the recording head 1 are connected via a third air flow path 113. A third check valve 213 is provided in the third air flow path 113, and the third check valve 213 regulates the backflow of the gas (air) from the ink supply unit 400 to the decompression chamber 760. In Fig. 3, reference numerals 121, 151, and 152 indicate a first valve chamber, a second valve chamber, and a second pressure control chamber, respectively.

[0036] In order to record an image on the recording medium P, the ink supply unit 400 mainly performs four operations (pressurizing the pressure chamber, maintaining the pressure, replenishing the ink, and depressurizing the bubble removal). Based on the detection results of a volume sensor (not shown) and a pressure sensor 409, the CPU 103 controls the one-way pump 404 and the first to fourth opening / closing valves, thereby performing the pressurizing the pressure chamber, maintaining the pressure, replenishing the ink, and depressurizing the bubble removal.

[0037] [Bubble removal and decompression operation] FIG. 4 is a schematic diagram illustrating an example of a bubble removal decompression operation. The bubble removal decompression operation is an operation for reducing the pressure in the decompression chamber 760. The speed at which gas moves from the bubble reservoir chamber 520 of the bubble removal unit 770 in the recording head 1 to the decompression chamber 760 through the gas-permeable membrane 710 is proportional to the difference between the pressure in the bubble reservoir chamber 520 and the pressure in the decompression chamber 760. For this reason, it is preferable to maintain the pressure in the decompression chamber 760 at a low pressure. The third check valve 213 provided in the third air flow path 113 restricts the inflow of gas from the third air flow path 113 to the decompression chamber 760. However, the inflow of gas from the bubble reservoir chamber 520 through the gas-permeable membrane 710 and the inflow of gas that slightly permeates the components that make up the decompression chamber 760 gradually increases the pressure in the decompression chamber 760 over time. When the pressure in the decompression chamber 760 gradually increases over time, a bubble removal decompression operation is required to reduce the pressure in the decompression chamber 760. If it is estimated that the pressure in the decompression chamber 760 exceeds a predetermined pressure based on the time elapsed since the previous bubble removal decompression operation, the ink supply unit 400 performs the bubble removal decompression operation. During the bubble removal decompression operation, the ink supply unit 400 drives the one-way pump 404 to reduce the pressure in the decompression chamber 760 while keeping the first on-off valve 408 in a closed state, the second on-off valve 405 in a closed state, the third on-off valve 407 in a closed state, and the fourth on-off valve 406 in an open state. If a predetermined time has elapsed since the one-way pump 404 was driven and it is estimated that the pressure in the decompression chamber 760 has dropped below the predetermined pressure, the ink supply unit 400 stops driving the one-way pump 404. During this time, the first on-off valve 408 and the second on-off valve 405 are closed, so the gas pressure in the intermediate pressure chamber 403 is maintained at a positive pressure. After the bubble removal and decompression operation, even if the pressure in the intermediate pressure chamber 403 and the first to third airflow paths fluctuates due to the aforementioned pressure chamber pressurization operation, pressure maintenance operation, ink replenishing operation, etc., the pressure in the decompression chamber 760 is maintained at a low pressure (negative pressure) because the third check valve 213 is closed. For example, in situations where bubbles are likely to be generated, such as at the start of initial use or after cleaning, the frequency of the bubble removal and decompression operation may be increased. The frequency of the bubble removal and decompression operation may be reduced as time passes at the start of initial use or after cleaning.Furthermore, the frequency of the debubbling and decompression operation may be changed depending on the temperature, the state of use, and the like.

[0038] [Recording head] FIG. 5 is an exploded perspective view showing an example of a recording head. The basic configuration of a recording head will be described below, focusing on FIG. 5 and referring to FIG. 2 as appropriate. Here, an example including a circulation unit is shown, but the circulation unit is not necessary. As shown in FIG. 5, the recording head 1 includes a circulation unit 54 and an ejection unit 3 for ejecting ink supplied from the circulation unit 54 onto a recording medium P. The recording head 1 is fixedly supported on a carriage 60 of the recording section 50 by positioning means and electrical contacts (not shown) provided on the carriage 60. The recording head 1 ejects ink while moving together with the carriage 60 in the main scanning direction (X direction) shown in FIG. 2, and performs recording on the recording medium P.

[0039] A second support member 7 having an opening 7a through which the ejection module 300 is inserted is adhesively fixed to one surface of the first support member 4. The second support member 7 holds an electrical wiring member 5 electrically connected to the ejection module 300. The electrical wiring member 5 applies an electrical signal to the ejection module 300 for ejecting ink. The electrical connection between the ejection module 300 and the electrical wiring member 5 is sealed with a sealant (not shown) to protect it from corrosion by ink and external impacts. An electrical contact substrate 6 is thermocompression-bonded to an end 5a of the electrical wiring member 5 using an anisotropic conductive film (not shown) or the like, thereby electrically connecting the electrical wiring member 5 and the electrical contact substrate 6. The electrical contact substrate 6 has an external signal input terminal (not shown) for receiving an electrical signal from the recording unit 50.

[0040] As shown in FIG. 2, the ink supply unit 400, which is connected to the ink storage unit 2 serving as an ink supply source, is provided with a first supply path 111 and a second supply path 112. A main body-side connecting member is provided at the end of the second supply path 112. When the recording head 1 is mounted on the recording unit 50, the main body-side connecting member provided at the end of the second supply path 112 is detachably connected to a head-side connecting member 800 provided on the head housing 53 of the recording head 1. This forms ink supply paths (the first supply path 111 and the second supply path 112) that run from the ink storage unit 2 to the recording head 1 via the ink supply unit 400. Since the recording head 1 uses four types of ink, four sets of ink storage units 2, first supply paths 111, second supply paths 112, and circulation units 54 are provided corresponding to the four types of ink, and four independent ink supply paths corresponding to the four inks are formed. In this way, the recording unit 50 is provided with an ink supply system to which ink is supplied from the ink storage unit 2 provided outside the recording head 1.

[0041] [Configuration of the defoaming unit] FIG. 7 is a schematic diagram showing an example of a bubble removal unit. FIG. 7(a) is a cross-sectional view of a bubble removal unit 770. FIG. 7(b) is a schematic diagram of a deformation suppression member 720 in the bubble removal unit 770. The second bubble removal unit 770B has the same configuration as the first bubble removal unit 770A. The second foam reservoir chamber 520B has the same configuration as the first foam reservoir chamber 520A. Hereinafter, the first bubble removal unit 770A and the second bubble removal unit 770B may be collectively referred to as the bubble removal unit 770. Furthermore, the first foam reservoir chamber 520A and the second foam reservoir chamber 520B may be collectively referred to as the foam reservoir chamber 520. 7(a), the bubble removal unit 770 (first bubble removal unit 770A and second bubble removal unit 770B) has a foam reservoir chamber 520 (first foam reservoir chamber 520A and second foam reservoir chamber 520B) and a decompression chamber 760. The bubble removal unit 770 also has a gas-permeable membrane 710, a deformation suppression member 720, a first communication port 751 for communicating the foam reservoir chamber 520 with the ink flow path or liquid chamber, and a second communication port 761 for communicating the decompression chamber 760 with the ink supply unit 400.

[0042] The bubble removal units 770 (first bubble removal unit 770A and second bubble removal unit 770B) are connected to the ink supply unit 400 provided in the main body of the recording unit 50, and are depressurized by the operation of the ink supply unit 400. Furthermore, a third check valve 213 (FIGS. 3 and 4) is provided between the bubble removal unit 770 and the ink supply unit 400, and the depressurized state is maintained even when the recording unit 50 is not operating, thereby enabling the bubble removal operation. The third check valves 213 may be provided at the branched portions of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B. The third check valves 213 may also be provided at the combined portion of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B.

[0043] FIG. 6 is a vertical cross-sectional view showing an example of a circulation path. As shown in FIG. 6(a), a first bubble removal unit 770A is provided vertically above the supply flow path 130, and a second bubble removal unit 770B is provided vertically above the first recovery flow path 140. One bubble removal unit 770 (first bubble removal unit 770A) may be provided only for the supply flow path 130. The bubble removal unit 770 may also be provided vertically above the ink storage section 2, first supply path 111, second supply path 112, third supply path 910, filter 110, pump inlet flow path 170, pump outlet flow path 180, bypass flow path 160, and pressure chamber 12. Note that the present invention does not include a configuration in which the first bubble reservoir 520A is connected to a side surface of the supply flow path 130 and the first bubble removal unit 770A extends laterally from the first bubble reservoir 520A, as shown in FIG. 6(b). If the pressure reduction chamber is located to the side of the liquid storage chamber in the vertical direction, when ink containing wax is used, the bubble removal efficiency does not improve even if the specific gravity and temperature relationship are adjusted, and the ejection stability cannot be improved.

[0044] A pressure chamber 12, a common supply flow path 18, and a common recovery flow path 19 are formed for each of the multiple ejection ports 13 that make up the ejection port array. The first pressure adjustment means 120 includes a first valve chamber 121 and a first pressure control chamber 122. The second pressure adjustment means 150 includes a second valve chamber 151 and a second pressure control chamber 152. The first pressure adjustment means 120 is configured to control a pressure that is relatively higher than that of the second pressure adjustment means 150. The first valve chamber 121 communicates with the first pressure control chamber 122 via a communication port 191A that can be opened and closed by a valve 190A shown in FIG. 6. A valve shaft 190s that is inserted into the communication port 191A protrudes from the center of the valve 190. By pressing this valve shaft 190s against the biasing force of a valve spring 200, the valve 190 moves away from a partition wall (not shown), allowing ink to flow through the communication port 191. The second valve chamber 151 communicates with the second pressure control chamber 152 via a communication port 191B that is opened and closed by a valve 190B shown in Figure 6. A pressure adjustment spring 220 serving as a biasing member is provided between the pressure plate 210 and a partition wall (not shown). The biasing force of the pressure adjustment spring 220 biases the pressure plate 210 and the flexible member 230 in a direction that increases the internal volume of the first pressure control chamber 122. Furthermore, when the pressure in the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 displace against the pressure of the pressure adjustment spring 220 in a direction that decreases the internal volume of the first pressure control chamber 122.

[0045] [Gas permeable membrane] As shown in FIG. 7( a), the gas-permeable membrane 710 is provided in the housing of the circulation unit 54 that forms the foam reservoir chamber 520 so as to separate the foam reservoir chamber 520 from the decompression chamber 760. Hereinafter, the housing of the circulation unit 54 that forms the foam reservoir chamber 520 will be referred to as the unit housing 540. The gas-permeable membrane 710 is bonded to the unit housing 540 by a bonding method such as thermal welding, ultrasonic welding, or laser welding. Any bonding method such as thermal welding, ultrasonic welding, or laser welding can be used as long as the foam reservoir chamber 520 is sealed so that the ink does not leak into the decompression chamber 760.

[0046] The gas-permeable membrane 710 is preferably a flexible member and flat. The gas-permeable membrane 710 is formed from a material having a free volume or pores large enough to allow air, a gas mixture containing oxygen gas, nitrogen gas, and the like, specifically oxygen molecules, nitrogen molecules, and mixtures of these molecules (hereinafter collectively referred to as "gas") to pass through. When using a gas-permeable membrane formed from a material with pores, the pores only need to have a pore diameter large enough to allow gas to pass through without allowing ink to pass through. For example, the pore diameter is preferably 100 nm or less, and preferably 0.01 nm or more. The gas-permeable membrane 710 is preferably made of a resin. Specific examples of the material for the gas-permeable membrane 710 include polypropylene (PP), polyethylene (PE), polymethylpentene (TPX), and polytetrafluoroethylene (PTFE). To improve bubble removal efficiency, the material for the gas-permeable membrane 710 preferably has high gas permeability. Furthermore, the material of gas-permeable membrane 710 is required to be easily bonded to unit housing 540 by heat welding and not to tear or peel off. The material of gas-permeable membrane 710 is required to be reliable as a liquid-contacting material. Thus, it is preferable to select the material of gas-permeable membrane 710 from the viewpoints of gas permeability, manufacturing method (productivity), and reliability. The material of the gas-permeable membrane is preferably polypropylene or polyethylene, and more preferably polypropylene, because these have excellent gas permeability and can further improve discharge stability.

[0047] The foam that flows into the foam reservoir chamber 520 includes initial foam (approximately 0.2 mL) remaining after initial filling at the start of initial use, replacement foam (approximately 0.015 mL per month) that flows into the storage compartment during normal use, and permeated foam (approximately 0.001 mL / day) that permeates from the outside. To deal with these foams, it is preferable to perform the defoaming operation at a permeation rate of 0.01 mL / day or more. As specified in JIS K7126-1, the gas permeation rate through the gas-permeable membrane 710 can be verified using a pressure sensor method. The pressure sensor method measures gas permeability by maintaining a vacuum on one side (the low-pressure side) separated by a test piece, introducing a test gas into the other side (the high-pressure side), and measuring the increase in pressure on the low-pressure side. The pressure sensor method allows the gas permeability coefficient to be calculated from the gas permeability and the thickness of the test piece. In the pressure sensor method, the gas permeation rate through the gas-permeable membrane can be verified by measuring the gas permeability using a test piece as the gas-permeable membrane. Ink is filled into the recording head 1 by suction, the bubbles in the bubble reservoir chamber 520 are brought into contact with the entire gas-permeable membrane 710, and the gas pressure in the decompression chamber 760 is maintained at a negative pressure of about 50 kPa by the ink supply unit 400, and the recording head 1 is left in an environment of room temperature (25°C) and normal pressure (1 atmosphere). During this series of operations, the amount of bubbles in the bubble reservoir chamber 520 is measured over time using computer tomography (CT) or the like, making it possible to verify the amount of bubbles (gas) passing through the gas-permeable membrane 710.

[0048] Because the gas-permeable membrane 710 is welded to the unit housing 540 to seal the bubble reservoir chamber 520, the material of the gas-permeable membrane 710 is preferably one that ensures high reliability in welding the gas-permeable membrane 710 and as a liquid-contacting material. To achieve a bubble permeation rate of 0.01 mL / day or more, the thickness of the gas-permeable membrane 710 is preferably 0.10 mm or less, more preferably less than 0.10 mm, and particularly preferably 0.09 mm or less. A thickness of 0.10 mm or less allows bubbles to be easily removed, further improving ejection stability. Furthermore, the thickness of the gas-permeable membrane 710 is preferably 0.01 mm or more. A thickness of 0.01 mm or more provides sufficient strength for the gas-permeable membrane to efficiently remove bubbles, further improving ejection stability.

[0049] [Bubble chamber] FIG. 6 is a vertical cross-sectional view showing an example of a circulation path. As shown in FIG. 6(a), the first bubble reservoir chamber 520A is provided vertically above the supply flow path 130 so as to communicate with the supply flow path 130 via the first communication port 751. The second bubble reservoir chamber 520B is provided vertically above the first recovery flow path 140 so as to communicate with the first recovery flow path 140 via the first communication port 751. This allows bubbles mixed into the ink in the first pressure adjustment unit 120, the second pressure adjustment unit 150, the supply flow path 130, and the first recovery flow path 140 due to circulation and ejection operations to be captured in the bubble reservoir chamber 520 and removed from the ink by a bubble removal operation. Examples of bubbles mixed into the ink include upstream bubbles that enter the print head due to replacement of the ink storage unit 2, elution bubbles that occur in the print head due to environmental changes, and unexpected bubbles that occur in the print head unexpectedly. The types of bubbles that can be removed by the bubble removal operation are not limited to these. If the amount of bubbles is large enough to be captured in the bubble reservoir 520 and to ensure a sufficient bubble removal speed, the bubbles mixed in the ink can be discharged to the outside of the recording head 1.

[0050] Examples of materials for unit housing 540 that forms foam reservoir chamber 520 include polypropylene (PP) and polyethylene (PE). In addition to the viewpoints of reliability of welding of gas-permeable membrane 710 and ease of handling, polypropylene is preferably used as the material for unit housing 540, as it can further improve discharge stability.

[0051] [Decompression chamber] As shown in FIG. 7( a), the decompression chamber 760 has an opening in which the gas-permeable membrane 710 is disposed, an opening facing the opening for welding the gas-permeable membrane 710, and a second communication port 761. The decompression chamber 760 is surrounded by the unit housing 540, the gas-permeable membrane 710, and the cover member 730. The second communication port 761 penetrates the side of the unit housing 540 and connects the decompression chamber 760 to the degassing flow path. The opening for welding the gas-permeable membrane 710 is sealed by bonding a separate cover member 730 to the unit housing 540. Examples of methods for bonding the cover member 730 include thermal welding, ultrasonic welding, and laser welding. Examples of materials for the cover member 730 include polypropylene (PP) and polyethylene (PE). From the viewpoint of reliability of welding of cover member 730 and ease of handling, it is preferable that the material of cover member 730 is the same as the material of unit housing 540 that forms foam reservoir chamber 520 .

[0052] [Principle of defoaming] During the bubble removal operation, the pressure in decompression chamber 760 is reduced, and the difference in pressure between the bubbles in bubble reservoir chamber 520 and the gas pressure in decompression chamber 760 causes the bubbles to permeate through gas-permeable membrane 710. The amount of permeation during the bubble removal operation is expressed by the following formula (X): In formula (X), Q represents the gas permeation amount, P represents the permeability coefficient, p represents the degree of vacuum (gauge pressure), S represents the bubble contact area, t represents time, and L represents the thickness of gas-permeable membrane 710. Q=P×p×S×t / L (X)

[0053] The gas permeation rate, represented by Q, is the amount of gas contained in bubbles that permeates during the bubble removal operation. The permeability coefficient, represented by P, is a value determined by the material properties of the gas-permeable membrane 710 and represents the basic speed of the bubble removal operation. The pressure reduction rate, represented by p, is the degree of pressure reduction (gauge pressure) of the pressure reduction chamber 760. The bubble contact area, represented by S, is the area of ​​contact between the bubbles and the gas-permeable membrane 710. The value represented by L is the thickness of the gas-permeable membrane 710. The higher the pressure reduction rate, the greater the amount of bubble permeation. To ensure a sufficient amount of bubble permeation to process bubbles generated during normal use and further improve discharge stability, it is preferable to set the pressure reduction rate to 10 kPa or more. It is preferable that the pressure reduction rate be 70 kPa or less.

[0054] The operation of the bubble removal unit has been described using an example in which the bubble removal unit 770 (first bubble removal unit 770A and second bubble removal unit 770B) has a bubble reservoir chamber 520 (first bubble reservoir chamber 520A and second bubble reservoir chamber 520B), but this is not limiting. A liquid reservoir chamber capable of storing ink may be provided between the pressure chamber 12 and the decompression chamber 760, and bubbles may be stored in part of the liquid reservoir chamber. In this case, a gas-permeable membrane is disposed at a position connected to the liquid reservoir chamber, and the decompression chamber is adjacent to the liquid reservoir chamber via the gas-permeable membrane.

[0055] The maximum temperature Ti (°C) of the ink in the liquid storage chamber can be controlled, for example, by a heater disposed in the recording head. The temperature of the ink in the liquid storage chamber can also be measured, for example, by a temperature sensor disposed inside the liquid storage chamber. In order to further improve ejection stability, it is preferable that the maximum temperature Ti (°C) of the ink in the liquid storage chamber be set to 30°C or higher and 50°C or lower.

[0056] The configuration of the circulation path is not limited to the configuration described above. Below, as other configurations of the circulation path, a first configuration example and a second configuration example of the ink path, and various modified examples of the circulation path will be described.

[0057] [First example of ink path configuration] 8 is a diagram schematically illustrating a first configuration example of the ink path. The first configuration example of the ink path is an example in which the second pressure adjustment means 150, second foam reservoir chamber 520B, circulation pump 500, bypass flow path 160, and first recovery flow path 140 in FIG. 6 are not arranged. In the first configuration example of the ink path, ink is not circulated, and ink supplied from the second supply path 112 flows in this order through the first pressure adjustment means 120, supply flow path 130, and pressure chamber 12, and is ejected from the ejection port 13. The pressures of the first pressure control chamber 122, supply flow path 130, and pressure chamber 12 are controlled by the first pressure adjustment means 120, thereby achieving stable ink ejection.

[0058] The first bubble reservoir 520A is provided vertically above the supply flow path 130 so as to communicate with the supply flow path 130, and the first bubble removal unit 770A is formed to extend vertically above the first bubble reservoir 520A. This allows bubbles that have become mixed into the ink in the first pressure adjustment means 120 or the supply flow path 130 due to circulation or ejection operations to be captured in the first bubble reservoir 520A and then removed from the ink by the bubble removal operation. Bubbles that may become mixed into the ink include, but are not limited to, the aforementioned upstream bubbles, eluted bubbles, and unexpected bubbles. It is possible to remove from the ink a quantity of bubbles that can be captured in the bubble reservoir 520 and that can achieve a sufficient bubble removal speed. This significantly reduces the possibility of bubbles entering the ink flow path that communicates with the ejection port 13.

[0059] The first bubble removal unit 770A communicates with the ink supply unit 400 in the main body of the recording unit 50, and is depressurized by the operation of the ink supply unit 400. Furthermore, a third check valve 213 is provided between the bubble removal unit 770 and the ink supply unit 400, and the depressurized state is maintained even if the main body of the recording unit 50 is not constantly operating, thereby enabling the bubble removal operation. The third check valve 213 may be provided in the third air flow path 113 between the first bubble removal unit 770A and the ink supply unit 400.

[0060] Two or more foam reservoir chambers 520 and two or more bubble removal units 770 may be provided. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not need to be provided in the supply flow path 130. For example, the foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the ink storage section 2, the first supply path 111, the second supply path 112, the third supply path 910, the filter 110, the pressure chamber 12, or the like. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not necessarily need to be provided vertically above the communication portions of the supply flow path 130 or the like. As long as the configuration allows bubbles to be captured and brought into contact with the gas-permeable membrane, the foam reservoir chamber 520 may be connected to a side surface of the communication portion, and the bubble removal unit 770 may be formed to extend laterally from the foam reservoir chamber 520. This also applies to the case where the foam reservoir chamber 520 and the foam removal unit 770 are provided in multiple portions of the communication part other than the supply flow path 130 and the first recovery flow path 140.

[0061] [First variation of circulation route] Fig. 9 is a diagram showing a first modified example of the circulation path. Fig. 9 shows the circulation path when circulation is performed without ejection. The first modified example of the circulation path is an example in which the second pressure adjustment means 150 in Fig. 6 is not provided, and the bypass flow path 160 and the first recovery flow path 140 are directly connected.

[0062] In the first modified example of the circulation path, the flow path resistance of the ink flow path through the bypass flow path 160 to the first recovery flow path 140 is R1, and the flow path resistance of the ink flow path from the supply flow path 130 to the first recovery flow path 140 through the ejection module 300 is R2. Since the flow rate of ink flowing through each flow path is inversely proportional to the flow path resistance, the ratio of the ink flow rate through the bypass flow path 160 to the ink flow rate through the ejection module 300 is R2 to R1. According to this relationship, the flow path resistances are set to achieve a circulation amount that can suppress ink thickening near the ejection ports 13 in the ejection module 300. In other words, the flow path resistances are set so that the flow velocity of ink in the pressure chamber 12 is equal to or greater than a predetermined flow velocity. The flow path resistance R1 of the flow path through the bypass flow path 160 is controlled by changing the cross-sectional area or length of the flow path, providing a throttle in the flow path, or the like.

[0063] The first foam reservoir chamber 520A is provided vertically above the supply flow path 130 so as to communicate with the supply flow path 130, and the first bubble removal unit 770A is formed to extend vertically above the first foam reservoir chamber 520A. The second foam reservoir chamber 520B is provided vertically above the first recovery flow path 140 so as to communicate with the first recovery flow path 140, and the second bubble removal unit 770B is formed to extend vertically above the second foam reservoir chamber 520B. As a result, bubbles that have become mixed into the ink in the first pressure adjustment means 120, the supply flow path 130, the first recovery flow path 140, etc. due to circulation and discharge operations can be captured in the foam reservoir chamber 520 and then removed from the ink by the bubble removal operation. Bubbles that get mixed into the ink include, but are not limited to, the aforementioned upstream bubbles, eluted bubbles, and unexpected bubbles. It is possible to discharge from the ink an amount of bubbles that can be captured in the bubble reservoir chamber 520 and that can provide a sufficient bubble removal speed. This makes it possible to greatly reduce the possibility of bubbles entering the ink flow path that communicates with the ejection port 13.

[0064] The first bubble removal unit 770A and the second bubble removal unit 770B are connected to the ink supply unit 400 in the main body of the recording unit 50, and are depressurized by the operation of the ink supply unit 400. Furthermore, a third check valve 213 is provided between the bubble removal unit 770 and the ink supply unit 400, so that the depressurized state can be maintained even when the main body of the recording unit 50 is not constantly operating, thereby enabling the bubble removal operation. The third check valves 213 may be provided in the branched portions of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B, respectively. The third check valves 213 may also be provided in the combined portion of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B.

[0065] The foam reservoir chamber 520 and the bubble removal unit 770 do not have to be provided in both the supply flow path 130 and the first recovery flow path 140; they may be provided only in the supply flow path 130 or only in the first recovery flow path 140. Furthermore, three or more foam reservoir chambers 520 and bubble removal units 770 may be provided. The foam reservoir chambers 520 and bubble removal units 770 do not have to be provided in the supply flow path 130 and the first recovery flow path 140. For example, the foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the ink storage section 2, the first supply path 111, the second supply path 112, and the third supply path 910. The foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the filter 110, the pump outlet flow path 180, the bypass flow path 160, and the pressure chamber 12. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not necessarily need to be provided vertically above a communication part such as the supply flow path 130. As long as the configuration is such that bubbles can be captured and brought into contact with the gas-permeable membrane, the foam reservoir chamber 520 may be connected to the side of the communication part, and the bubble removal unit 770 may be formed extending to the side of the foam reservoir chamber 520. This also applies when the foam reservoir chamber 520 and the bubble removal unit 770 are provided in multiple parts of the communication part other than the supply flow path 130 and the first recovery flow path 140.

[0066] [Second example of ink path configuration] FIG. 10 is a schematic diagram illustrating a second configuration example of the ink path. The second configuration example of the ink path is an example in which the first pressure adjustment unit 120, the second pressure adjustment unit 150, the second foam reservoir chamber 520B, the circulation pump 500, the bypass flow path 160, and the first recovery flow path 140 shown in FIG. 6 are not provided. The second configuration example of the ink path is an example in which a third pressure adjustment unit 902 communicating with the second supply path 112 is provided instead of the first pressure adjustment unit 120, the second pressure adjustment unit 150, and the like. In the second configuration example of the ink path, ink is not circulated. Instead, ink supplied from the second supply path 112 flows through the supply flow path 130 and the pressure chamber 12, and is ejected from the ejection port 13. The pressures of the second supply path 112, the third supply path 910, the supply flow path 130, and the pressure chamber 12 are controlled by the third pressure adjustment unit 902, thereby achieving stable ink ejection.

[0067] The third pressure adjustment means 902 is disposed outside the print head 1 and communicates with the third supply path 910 of the print head 1 via the second supply path 112. As the third pressure adjustment means 902, for example, a water head method utilizing a water head difference can be mentioned, but any method can be applied. This modified example can be applied to ink supply methods such as an ink cartridge method in which an ink cartridge is replaced when the ink contained in the ink storage section is consumed, or a so-called CISS method (continuous ink supply method) in which ink is injected from an inlet.

[0068] The first bubble reservoir 520A is provided vertically above the supply flow path 130 so as to communicate with the supply flow path 130, and the first bubble removal unit 770A is formed to extend vertically above the first bubble reservoir 520A. This allows bubbles that have become mixed into the ink in the supply flow path 130 or elsewhere due to circulation or ejection operations to be captured in the first bubble reservoir 520A and then removed from the ink by the bubble removal operation. Bubbles that become mixed into the ink include, but are not limited to, the aforementioned upstream bubbles, eluted bubbles, and unexpected bubbles. It is possible to remove from the ink a quantity of bubbles that can be captured in the bubble reservoir 520 and that can achieve a sufficient bubble removal speed. This significantly reduces the possibility of bubbles entering the ink flow path that communicates with the ejection port 13.

[0069] The first bubble removal unit 770A communicates with the ink supply unit 400 in the main body of the recording unit 50, and is depressurized by the operation of the ink supply unit 400. Furthermore, a third check valve 213 is provided between the bubble removal unit 770 and the ink supply unit 400, and the depressurized state is maintained even if the main body of the recording unit 50 is not constantly operating, thereby enabling the bubble removal operation. The third check valve 213 may be provided in the third air flow path 113 between the first bubble removal unit 770A and the ink supply unit 400.

[0070] Two or more foam reservoir chambers 520 and two or more bubble removal units 770 may be provided. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not need to be provided in the supply flow path 130. For example, the foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the ink storage section 2, the first supply path 111, the second supply path 112, the third supply path 910, the filter 110, the pressure chamber 12, or the like. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not necessarily need to be provided vertically above the communication portions of the supply flow path 130 or the like. As long as the configuration allows bubbles to be captured and brought into contact with the gas-permeable membrane, the foam reservoir chamber 520 may be connected to a side surface of the communication portion, and the bubble removal unit 770 may be formed to extend laterally from the foam reservoir chamber 520. This also applies to the case where the foam reservoir chamber 520 and the foam removal unit 770 are provided in multiple portions of the communication part other than the supply flow path 130 and the first recovery flow path 140.

[0071] [Second variation of the circulation route] Fig. 11 is a diagram schematically illustrating a second modified circulation path. Fig. 11 shows the circulation path when circulation is performed without ejection. The second modified circulation path is an example in which the first pressure adjustment means 120 and second pressure adjustment means 150 in Fig. 6 are not provided, and the bypass flow path 160 and the first recovery flow path 140 are directly connected.

[0072] In the second variation of the circulation path, the flow path resistance of the ink flow path through the bypass flow path 160 to the first recovery flow path 140 is R1, and the flow path resistance of the ink flow path from the supply flow path 130 to the first recovery flow path 140 through the ejection module 300 is R2. Since the flow rate of ink flowing through each flow path is inversely proportional to the flow path resistance, the ratio of the ink flow rate through the bypass flow path 160 to the ink flow rate through the ejection module 300 is R2 to R1. According to this relationship, the flow path resistances are set to achieve a circulation amount that can suppress ink thickening near the ejection ports 13 in the ejection module 300. In other words, the flow path resistances are set so that the flow velocity of ink in the pressure chamber 12 is equal to or greater than a predetermined flow velocity. The flow path resistance R1 of the flow path through the bypass flow path 160 is controlled by changing the cross-sectional area or length of the flow path, providing a throttle in the flow path, or the like.

[0073] The third pressure adjustment means 902 is disposed outside the print head 1 and communicates with the third supply path 910 of the print head 1 via the second supply path 112. As the third pressure adjustment means 902, for example, a head system utilizing a head difference can be used, but either system can be applied. This modification can be applied to both the ink cartridge system described above and ink supply systems such as the CISS system.

[0074] The first foam reservoir chamber 520A is provided vertically above the supply flow path 130 so as to communicate with the supply flow path 130, and the first bubble removal unit 770A is formed to extend vertically above the first foam reservoir chamber 520A. The second foam reservoir chamber 520B is provided vertically above the first recovery flow path 140 so as to communicate with the first recovery flow path 140, and the second bubble removal unit 770B is formed to extend vertically above the second foam reservoir chamber 520B. As a result, bubbles that have become mixed into the ink in the supply flow path 130, the first recovery flow path 140, the pump inlet flow path 170, the pump outlet flow path 180, etc. due to the circulation and discharge operations can be captured in the foam reservoir chamber 520 and then removed from the ink by the bubble removal operation. Bubbles that get mixed into the ink include, but are not limited to, the aforementioned upstream bubbles, eluted bubbles, and unexpected bubbles. It is possible to discharge from the ink an amount of bubbles that can be captured in the bubble reservoir chamber 520 and that can provide a sufficient bubble removal speed. This makes it possible to greatly reduce the possibility of bubbles entering the ink flow path that communicates with the ejection port 13.

[0075] The first bubble removal unit 770A and the second bubble removal unit 770B are connected to the ink supply unit 400 in the main body of the recording unit 50, and are depressurized by the operation of the ink supply unit 400. Furthermore, a third check valve 213 is provided between the bubble removal unit 770 and the ink supply unit 400, so that the depressurized state can be maintained even when the main body of the recording unit 50 is not constantly operating, thereby enabling the bubble removal operation. The third check valves 213 may be provided in the branched portions of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B, respectively. The third check valves 213 may also be provided in the combined portion of the third air flow path 113 between the ink supply unit 400 and the first bubble removal unit 770A and the second bubble removal unit 770B.

[0076] The foam reservoir chamber 520 and the bubble removal unit 770 do not have to be provided in both the supply flow path 130 and the first recovery flow path 140; they may be provided only in the supply flow path 130 or only in the first recovery flow path 140. Furthermore, three or more foam reservoir chambers 520 and bubble removal units 770 may be provided. The foam reservoir chambers 520 and bubble removal units 770 do not have to be provided in the supply flow path 130 and the first recovery flow path 140. For example, the foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the ink storage section 2, the first supply path 111, the second supply path 112, and the third supply path 910. The foam reservoir chamber 520 and the bubble removal unit 770 may be provided vertically above the filter 110, the pump inlet flow path 170, the pump outlet flow path 180, the bypass flow path 160, and the pressure chamber 12. Furthermore, the foam reservoir chamber 520 and the bubble removal unit 770 do not necessarily need to be provided vertically above a communication part such as the supply flow path 130. As long as the configuration is such that bubbles can be captured and brought into contact with the gas-permeable membrane, the foam reservoir chamber 520 may be connected to the side of the communication part, and the bubble removal unit 770 may be formed extending to the side of the foam reservoir chamber 520. This also applies when the foam reservoir chamber 520 and the bubble removal unit 770 are provided in multiple parts of the communication part other than the supply flow path 130 and the first recovery flow path 140.

[0077] (ink) The ink used in the recording method of the present invention is an aqueous inkjet ink containing wax particles. The specific gravity of the wax particles is smaller than that of the ink, and the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the ink in the liquid storage chamber satisfy the relationship shown in formula (1) below. Each component of the ink will be described in detail below. Tw-Ti≧10 (1)

[0078] [Colorant] The ink preferably contains a colorant. Pigments or dyes can be used as the colorant. The content (mass %) of the colorant in the ink is preferably 0.50 mass % or more and 15.00 mass % or less, and more preferably 1.00 mass % or more and 10.00 mass % or less, based on the total mass of the ink.

[0079] 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, dioxazine, etc. One type of pigment may be used alone, or two or more types may be used in combination.

[0080] As a pigment dispersion method, resin-dispersed pigments using a resin as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface can be used. Also usable are resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microencapsulated pigments in which the pigment particle surface is coated with a resin or the like. It is also possible to use a combination of these pigments with different dispersion methods. In particular, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microencapsulated pigments.

[0081] 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 resin having anionic groups can be used, and it is preferable to use a resin such as those described below, especially a water-soluble resin. The content (mass %) of the pigment in the ink is preferably 0.3 to 10.0 times the content (mass %) of the resin dispersant.

[0082] Self-dispersing pigments can be used in which an anionic group such as a carboxylic acid group, sulfonic acid group, or phosphonic acid group is bonded to the surface of the pigment particle directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Furthermore, combinations of these groups may also be used.

[0083] The dye preferably has an anionic group. Specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. The dye may be used alone or in combination of two or more. The colorant is more preferably a resin-dispersed pigment in which a resin serving as a dispersant is physically adsorbed onto the surface of pigment particles, or a self-dispersed pigment in which an anionic group is bonded to the surface of pigment particles directly or via another atomic group (-R-).

[0084] The ink preferably contains a pigment. By containing a pigment, it is easier to physically inhibit and suppress wax fusion, making it easier to remove bubbles and further improving ejection stability. Furthermore, since the wax fusion suppression effect is more easily achieved, making it easier to remove bubbles and further improving ejection stability, it is preferable that the pigment content (mass %) in the ink be 1.0 times or more in mass ratio to the wax particle content (mass %). The mass ratio is preferably 10.0 times or less, and more preferably 5.0 times or less.

[0085] [Resin particles] The ink preferably contains resin particles different from the wax particles, which physically inhibits and makes it easier to suppress the fusion of the wax, making it easier to remove bubbles and further improving the ejection stability.

[0086] Examples of resins constituting the resin particles include acrylic resins, urethane resins, olefin resins, and polyester resins. Of these, acrylic resins are preferred. The content (mass%) of resin particles in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink. The content (mass%) of resin particles in the ink is preferably 1.5 times or more, more preferably 1.7 times or more, and preferably 10.0 times or less, the mass ratio of the pigment content (mass%). The resin particles are present in the ink in a dispersed state, i.e., in the form of a resin emulsion.

[0087] In this specification, "resin particles" refers to a resin that does not dissolve in the aqueous medium that constitutes the ink, and specifically refers to a resin that can exist in the aqueous medium in the form of particles whose particle diameter can be measured by dynamic light scattering. On the other hand, "water-soluble resin" refers to a resin that can dissolve in the aqueous medium that constitutes the ink, and specifically refers to a resin that can exist in the aqueous medium in the form of particles whose particle diameter cannot be measured by dynamic light scattering. "Resin particles" can also be referred to as "water-dispersible resin (water-insoluble resin)."

[0088] The acid value of the resin constituting the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 2,000,000 or less. The volume-based cumulative 50% particle diameter (D 50) is preferably 50 nm or more and 500 nm or less. The volume-based 50% cumulative particle diameter of resin particles is the diameter of particles that is 50% of the total volume of measured particles when integrated from the small particle diameter side in a particle diameter integration curve. The volume-based 50% cumulative particle diameter of resin particles can be measured using a dynamic light scattering particle size analyzer and measurement conditions described below. The resin particles do not need to contain a colorant.

[0089] The content (mass %) of resin particles in the ink is preferably 4.0 times or more the content (mass %) of wax particles. By setting the mass ratio as described above, the effect of suppressing wax fusion can be further enhanced. The mass ratio is preferably 30.0 times or less.

[0090] [Water-soluble resin] The ink preferably contains a water-soluble resin with an acid value of 100 mgKOH / g or more. By incorporating a water-soluble resin with an acid value of 100 mgKOH / g or more, the wax fusion suppression effect can be further enhanced, bubbles can be more easily removed, and ejection stability can be further improved. It is believed that the water-soluble resin with a certain degree of ionicity is adsorbed onto the surface of the wax particles, making the surface of the wax particles more hydrophilic, thereby further enhancing the wax fusion suppression effect. The acid value of the water-soluble resin is preferably 200 mgKOH / g or less, and more preferably 150 mgKOH / g or less. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

[0091] The content (mass %) of the water-soluble resin in the ink is preferably 0.10% by mass or more and 10.00% by mass or less, and more preferably 0.50% by mass or more and 5.00% by mass or less, based on the total mass of the ink. Examples of the form of the water-soluble resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. One type of resin may be used alone, or two or more types may be used in combination.

[0092] [Resin Composition] Examples of the water-soluble resin include acrylic resins, urethane resins, olefin resins, and polyester resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

[0093] The acrylic resin is preferably one having a hydrophilic unit and a hydrophobic unit as constituent units. Among these, 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 preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a styrene and an α-methylstyrene monomer is preferred. These resins are likely to interact with pigments, and can therefore be suitably used as resin dispersants for dispersing pigments.

[0094] 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. Specific examples of hydrophilic monomers 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 cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having 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; and (meth)acrylic acid ester monomers, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0095] Urethane resins can be obtained, for example, by reacting polyisocyanate with polyol. Furthermore, they may be obtained by further reacting a chain extender. Examples of olefin resins include polyethylene and polypropylene. Polyester resins can be obtained, for example, by dehydration condensation of polycarboxylic acid with polyol.

[0096] [Properties of water-soluble resin] As used herein, the term "water-soluble resin" means that when the resin is neutralized with an alkali equivalent to its acid value, it exists in an aqueous medium in a state in which it does not form particles whose particle size can be measured by dynamic light scattering. Whether a resin is water-soluble or not can be determined according to the following method. First, a liquid (resin solids content: 10% by mass) containing the resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles having the particle size are measured, the resin can be determined to be water-soluble. The measurement conditions can be, for example, Set Zero: 30 seconds, measurement count: 3, and measurement time: 180 seconds. Furthermore, a particle size distribution measuring device such as a particle size analyzer using dynamic light scattering (e.g., the "UPA-EX150" product, manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and measuring conditions to be used are not limited to those described above.

[0097] [Wax particles] The ink contains wax particles formed from wax. By using an ink containing wax particles, it is possible to record an image with improved abrasion resistance. The wax in this specification may be a composition containing components other than wax, or may be wax itself. The wax particles may be dispersed using a dispersant such as a surfactant or resin. One type of wax may be used alone, or two or more types may be used in combination. The content (mass %) of wax particles in the ink is preferably 0.50% by mass or more and 2.00% by mass or less, based on the total mass of the ink. If the content of wax particles is less than 0.50% by mass, the effect of improving the abrasion resistance of the image may be reduced. On the other hand, if the content of wax particles is more than 2.00% by mass, the wax may be easily concentrated, making it difficult for bubbles to escape, and the effect of further improving ejection stability may not be sufficiently achieved.

[0098] In a narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but excludes oils and fats. In a broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the present invention, any wax in the broad sense can be used without particular limitation. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends thereof (blended waxes), and modified products thereof (modified waxes).

[0099] Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); plant waxes such as Japan wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). Blended waxes are mixtures of the above waxes. Modified waxes are those obtained by modifying the above waxes through oxidation, hydrogenation, alcohol modification, acrylic modification, urethane modification, or other such processes. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended versions thereof. Among these, a blend of multiple types of wax is more preferred, and a blend of petroleum wax and synthetic wax is particularly preferred.

[0100] The wax particles are preferably particles formed from a wax containing oxidized wax. Because the surfaces of wax particles formed from oxidized wax are more hydrophilic, the use of wax particles formed from oxidized wax can further enhance the effect of suppressing fusion, facilitate the release of bubbles, and further improve discharge stability.

[0101] The melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the ink in the liquid storage chamber satisfy the relationship of the following formula (1). Preferably, the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the ink in the liquid storage chamber satisfy the relationship of the following formula (2). When Tw (°C) and Ti (°C) satisfy the relationship of the following formula (2), the effect of suppressing fusion of the wax particles can be further enhanced, bubbles can be easily removed, and ejection stability can be further improved. Tw-Ti is preferably 70 (°C) or less, and more preferably 60 (°C) or less. Tw-Ti≧10 (1) Tw-Ti≧30 (2)

[0102] The wax particles are preferably solid at room temperature (25°C). The melting point Tw (°C) of the wax particles is preferably 80°C or higher, since this can further enhance the fusion suppression effect, facilitate the release of bubbles, and further improve discharge stability. The melting point Tw (°C) of the wax particles is preferably 120°C or lower, and more preferably 100°C or lower. The melting point of the wax particles can be measured in accordance with the test method described in 5.3.1 (Melting Point Test Method) of JIS K2235:1991 (Petroleum Wax). For microcrystalline wax, petrolatum, and mixtures of multiple waxes, more accurate measurements can be achieved by using the test method described in 5.3.2. The melting point of the wax particles is easily affected by properties such as the molecular weight of the wax (the higher the molecular weight, the higher the melting point), molecular structure (linear chains have a high melting point, branched structures have a lower melting point), crystallinity (the higher the crystallinity), and density (the higher the crystallinity). Therefore, by controlling these properties, wax particles with the desired melting point can be obtained. The melting point of the wax particles in the ink can be measured, for example, by ultracentrifuging the ink, separating out the wax particles, washing and drying them, and then following the test method described above.

[0103] The cumulative 50% particle diameter (D 50 ) is preferably 150 nm or more, since this can further enhance the fusion suppression effect, facilitate the escape of bubbles, and further improve discharge stability. The volume-based cumulative 50% particle diameter of the wax particles can be measured in the same manner as in the case of the volume-based cumulative 50% particle diameter of the resin particles described above. If the volume-based cumulative 50% particle diameter of the wax particles is less than 150 nm, the fusion suppression effect of the wax particles may be slightly reduced. The volume-based cumulative 50% particle diameter (D 50 The cumulative 50% particle diameter (D) of the wax particles based on the volume is preferably 250 nm or less, and more preferably 200 nm or less. 50 ) can be measured by dynamic light scattering, and the measurement conditions and equipment can be the same as those used in the measurement method for the resin described above.

[0104] The specific gravity of the wax particles is smaller than that of the ink. The difference between the specific gravity of the wax particles and that of the ink is preferably 0.15 or less, more preferably greater than 0.00 and 0.10 or greater. By keeping the difference between the specific gravity of the wax particles and that of the ink within the above range, the wax particles are less likely to concentrate, bubbles are more easily removed, and ejection stability is further improved. The specific gravity of the wax particles is preferably 0.85 or more, and more preferably 1.10 or less, more preferably 1.00 or less, and particularly preferably 0.95 or less. The specific gravity of the ink is preferably 1.00 or more, preferably 1.01 or more, and more preferably 1.10 or less, and more preferably 1.05 or less. In this specification, specific gravity is measured in accordance with "JIS K0061: Method for Measuring Density and Specific Gravity of Chemical Products." The "true specific gravity" is used to refer to the specific gravity of the wax particles. The true specific gravity of the wax particles can be measured using a pycnometer or the like. The specific gravity of the ink can be measured in accordance with the hydrometer method specified in "JIS Z8804 Method for measuring density and specific gravity of liquids."

[0105] [Aqueous medium] The ink used in the recording method of the present invention is an aqueous ink containing at least water as the aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the aqueous ink is preferably 50.00% to 95.00% by mass based on the total mass of the ink. Furthermore, the water-soluble organic solvent content (mass %) in the aqueous ink is preferably 2.00% to 40.00% by mass based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. The water-soluble organic solvents may be used alone or in combination of two or more.

[0106] The ink also has a vapor pressure of 2.7 x 10 -2 It is preferable that the ink contains a first water-soluble organic solvent having a vapor pressure of 2.7×10 kPa or less. By containing a first water-soluble organic solvent having a low vapor pressure, it is possible to further prevent the concentration of wax particles due to evaporation of the liquid components in the liquid storage chamber, making it easier to remove bubbles and further improving the ejection stability. -2 A specific example of a water-soluble organic solvent with a pressure of less than 1.0 kPa is triethanolamine (1.0 × 10 -6 kPa), 2-pyrrolidone (3.9 × 10 -3 kPa), 1-(2-hydroxyethyl)-2-pyrrolidone (2.0 × 10 -5 kPa), trimethylolpropane (2.1 × 10 -5 kPa), glycerin (3.3 × 10 -5 kPa), triethylene glycol (3.6 × 10 -5 kPa), 1,6-hexanediol (9.2 × 10 -4 kPa), diethylene glycol monobutyl ether (1.7 × 10 -3 kPa), 1,2-hexanediol (2.6 × 10 -3 kPa), 1,2-butanediol (2.0 × 10 -2 kPa), 1,2-propanediol (2.7 × 10 -2 kPa), and 1,3-propanediol (4.6 × 10 -3 The vapor pressure of the first water-soluble organic solvent is 1.0 × 10 -35 It is preferable that the pressure is at least 100 kPa.

[0107] Furthermore, the organic solvent preferably has a dielectric constant of 22.0 or higher. Organic solvents with a dielectric constant of 20 or higher tend to maintain a stable wax dispersion, thereby more effectively suppressing wax fusion, facilitating bubble removal, and further improving ejection stability. The first water-soluble organic solvent preferably has a dielectric constant of 35.0 or lower. Specific examples of water-soluble organic solvents with a dielectric constant of 20.0 or higher include triethanolamine (31.9), 2-pyrrolidone (28.0), 1-(2-hydroxyethyl)-2-pyrrolidone (37.6), trimethylolpropane (33.7), glycerin (42.3), triethylene glycol (22.7), 1,2-butanediol (22.2), 2,3-butanediol (23.9), 1,2-propanediol (28.8), and 1,3-propanediol (34.9). The first water-soluble organic solvent preferably has a relative dielectric constant of 200.0 or less, more preferably 50.0 or less.

[0108] The "vapor pressure" in this specification is a value at 25°C and 1 atmosphere. Various literature values ​​and, for compounds not described in literature, calculated values ​​using a calculation tool (for example, product name "CAS SciFinder" manufactured by the Japan Chemical Information Association) can be used.

[0109] Furthermore, the "dielectric constant" in this specification can be measured, for example, using a dielectric constant meter (for example, trade name "BI-870" manufactured by BROOKHAVEN INSTRUMENTS CORPORATION) at a frequency of 10 kHz. The dielectric constant of a water-soluble organic solvent that is solid at 25°C is determined by measuring the dielectric constant of a 50% by mass aqueous solution and calculating the value from the following formula (1). Usually, the term "water-soluble organic solvent" refers to a liquid, but in the present invention, water-soluble organic solvents also include those that are solid at 25°C. ε sol =2ε 50% -ε water ···(1) ε sol : Dielectric constant of solid water-soluble organic solvent at 25℃ ε50% : 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

[0110] Examples of water-soluble organic solvents commonly used in aqueous inks that 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 dielectric constant of a water-soluble organic solvent that is solid at 25°C from the 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 aqueous solutions with high concentrations exceeding 50% by mass. On the other hand, in aqueous solutions with low concentrations of 10% by mass or less, the dielectric constant of water dominates, making it impossible to obtain a reliable (effective) dielectric constant value for the water-soluble organic solvent. Therefore, the inventors conducted research and found that aqueous solutions to be measured can be prepared using almost all water-soluble organic solvents that are solid at 25°C and can be used in inks, and that the dielectric constants obtained are consistent with the effects of the present invention. For these reasons, we 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% by mass aqueous solution due to their low solubility in water, use an aqueous solution of saturated concentration and use the above ε sol For convenience, the value of the relative permittivity calculated in accordance with the case of determining the relative permittivity will be used.

[0111] [Other ingredients] The ink may contain various other components (additives) as needed, such as antifoaming agents, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents.

[0112] [Ink properties] The ink is a water-based ink used in inkjet printing. Therefore, from the perspective of reliability, it is preferable to appropriately control its physical properties. The ink's viscosity at 25°C is preferably 3.0 mPa·s or more and 8.0 mPa·s or less. If the ink viscosity is less than 3.0 mPa·s, the wax tends to thicken, making it difficult for bubbles to escape, and the effect of further improving ejection stability may not be fully achieved. On the other hand, if the ink viscosity exceeds 8.0 mPa·s, the movement of bubbles slows, reducing the effectiveness of bubble removal, and the effect of further improving ejection stability may not be fully achieved. The ink viscosity at 25°C can be measured using a rotational viscometer. The ink viscosity can be adjusted using, for example, a water-soluble organic solvent, a resin, or a surfactant.

[0113] The surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The surface tension of the ink at 25°C can be measured by a plate method or the like. 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. The pH of the ink can be measured using a general pH meter equipped with a glass electrode or the like. [Example]

[0114] 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 as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0115] <Preparation of pigment dispersion> (Pigment dispersion 1) 15.0 parts of pigment, 15.0 parts of a resin dispersant solution, and 70.0 parts of water were mixed and dispersed in a sand grinder for 1 hour. The mixture was then centrifuged to remove undispersed material, including coarse particles. Carbon black (trade name "Printex 85" manufactured by Orion Engineered Carbons) was used as the pigment. The resin dispersant solution was prepared by neutralizing a styrene-acrylic acid copolymer with a 10% potassium hydroxide solution in an amount equimolar to the acid value, followed by the addition of an appropriate amount of ion-exchanged water to obtain an aqueous solution with a resin (solids) content of 20.0%. The acid value of the styrene-acrylic acid copolymer was 150 mg KOH / g and its weight-average molecular weight was 8,000. After pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm), an appropriate amount of ion-exchanged water was added to prepare Pigment Dispersion 1. The pigment content in Pigment Dispersion 1 was 15.00%, and the resin content was 3.00%.

[0116] (Pigment dispersion 2) Pigment Dispersion Liquid 2 was obtained in the same manner as for Pigment Dispersion Liquid 1, except that CI Pigment Blue 15:3 was used as the pigment. The pigment content in the obtained Pigment Dispersion Liquid 2 was 15.00%, and the resin content was 3.00%.

[0117] (Pigment dispersion 3) Pigment Dispersion Liquid 3 was obtained in the same manner as for the above-described Pigment Dispersion Liquid 1, except that CI Pigment Red 122 was used as the pigment. The pigment content in the obtained Pigment Dispersion Liquid 3 was 15.00%, and the resin content was 3.00%.

[0118] (Pigment dispersion 4) Pigment Dispersion Liquid 4 was obtained in the same manner as for Pigment Dispersion Liquid 1, except that CI Pigment Yellow 74 was used as the pigment. The pigment content in the obtained Pigment Dispersion Liquid 4 was 15.00%, and the resin content was 3.00%.

[0119] (Pigment dispersion 5) A self-dispersing pigment (product name "Cab-O-Jet 300" manufactured by Cabot Corporation) in which benzenecarboxylic acid groups are bonded to the surface of carbon black particles was prepared. The prepared self-dispersing pigment was diluted with water and thoroughly stirred to obtain Pigment Dispersion 5 with a pigment content of 15.00%.

[0120] <Preparation of aqueous dispersion of wax particles> The components (unit: parts) shown in Table 1 were mixed with pure water, and the wax was dispersed while adjusting the temperature and pressure as appropriate. An appropriate amount of pure water was added to adjust the concentration, and aqueous dispersions 1 to 10 of wax particles were prepared, each with a total content of wax particles and dispersant of 35.00%. Details of "Waxes 1 to 8" in Table 1 are shown below. Polyoxyethylene cetyl ether (10 moles of ethylene oxide units added) was used as the dispersant. Potassium hydroxide was used as the neutralizing agent. The bottom row of Table 1 shows the cumulative 50% particle diameter (D 50 The cumulative 50% particle diameter (D 50 ) was measured using a dynamic light scattering particle size analyzer (product name "UPA-EX150", manufactured by Nikkiso) under the following conditions: Set Zero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Wax 1: Oxidized polyethylene wax (melting point: 90°C, specific gravity: 0.90) Wax 2: Oxidized polyethylene wax (melting point: 61°C, specific gravity: 0.90) Wax 3: Oxidized polyethylene wax (melting point: 78°C, specific gravity: 0.90) Wax 4: Oxidized polyethylene wax (melting point: 80°C, specific gravity: 0.90) Wax 5: Oxidized polyethylene wax (melting point: 100°C, specific gravity: 0.90) Wax 6: Polyethylene wax (melting point: 90°C, specific gravity: 0.90) Wax 7: Fischer-Tropsch wax (melting point: 73°C, specific gravity: 0.90) Wax 8: Polytetrafluoroethylene wax (melting point: 110°C, specific gravity: 1.05)

[0121] TIFF2026025897000001.tif97170

[0122] <Preparation of resin particles> (Resin particles 1) 1,160 mL of water was placed in a reaction vessel and heated to 90°C. An initiator solution was prepared by dissolving 1.39 g of polymerization initiator (potassium persulfate) in 160 mL of water. 32 mL of the initiator solution was added to the reaction vessel and stirred. A monomer emulsion was prepared by mixing 159.4 mL of water, 183 g of styrene, 80 g of benzyl acrylate, 1.5 g of methacrylic acid, 1.6 g of isooctylthioglycolate chain transfer agent, and 9.98 g of a 30% aqueous solution of anionic surfactant. The anionic surfactant used was Rhodafac RS 710 (manufactured by Rhodia Novecare). The prepared monomer emulsion and 129.4 g of the initiator solution were simultaneously added dropwise to the reaction vessel over 30 minutes and stirred. After stirring at 90°C for 3 hours, the mixture was cooled to 2.5°C to obtain a latex solution. The pH was adjusted to 8.5 by adding a 50% aqueous potassium hydroxide solution, and then the mixture was cooled to ambient temperature. After filtering through a 200-mesh filter, the concentration was adjusted by adding deionized water to obtain an aqueous dispersion of resin particles 1, with a resin particle content of 40.00% made of acrylic resin.

[0123] (Resin particles 2) A four-neck flask equipped with a stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 74.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate and mixed. An emulsion was prepared by mixing 24.0 parts of ethyl methacrylate, 1.5 parts of methacrylic acid, and 0.3 parts of a reactive surfactant. The reactive surfactant used was "ADEKA REASOAP ER20" (Adeka, nonionic surfactant). The emulsion was added dropwise to the four-neck flask under a nitrogen atmosphere over 1 hour, and a polymerization reaction was carried out for 2 hours at 80°C with stirring. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide in an amount equimolar to the acid value of the resin particles were added to obtain an aqueous dispersion of resin particles 2 with a resin particle content of 40.0%.

[0124] (Resin particles 3) A reaction vessel installed in an autoclave was charged with 60.0 parts of ethylene glycol, 40.0 parts of neopentyl glycol, 54.5 parts of terephthalic acid, and 54.5 parts of isophthalic acid, and the mixture was heated at 220°C for 4 hours to carry out an esterification reaction. The temperature was raised to 240°C, and the pressure inside 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, after which nitrogen gas was introduced into the autoclave to return the pressure to normal (1 atm). After the temperature inside the reaction vessel was lowered to 220°C, a catalyst (tetra-n-butyl titanate) and 1.0 part of trimellitic acid were added, and the mixture was heated at 220°C for 2 hours to carry out a transesterification reaction. The amount of catalyst used (mol) was 3 x 10 -4 × (total amount (mol) of polycarboxylic acids used). Nitrogen gas was then introduced into the autoclave to create a pressurized state, and a sheet-like resin was taken out. The taken-out resin was cooled to 25°C and then crushed in a crusher to obtain a polyester resin.

[0125] A stirrer (product name: "Tornado Stirrer Standard SM-104" manufactured by AS ONE) was placed in a 2 L beaker. 200 g of the above polyester resin and methyl ethyl ketone (MEK) were placed in the beaker and stirred at 30°C to dissolve the polyester. 15.9 g of a 5% aqueous potassium hydroxide solution was added and stirred for 30 minutes. 500 g of deionized water was added dropwise at a rate of 20 mL / min while stirring at 30°C. After heating to 60°C, the MEK was distilled off, and then some of the water was also distilled off. After cooling to 25°C, the mixture was filtered through a 150-mesh wire mesh (a filter with 150 stainless steel wires woven vertically and horizontally in a 1-inch square). Deionized water was added to adjust the concentration, yielding an aqueous dispersion of resin particles 3 containing 40.00% polyester resin particles.

[0126] <Preparation of water-soluble resin> A four-neck flask equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser was charged with 100.0 parts of ethylene glycol monobutyl ether. Nitrogen gas was then introduced into the flask, and the temperature was raised to 110°C while stirring. A monomer solution was prepared by dissolving the monomer mixture of the types and amounts shown in Table 2 and 1.3 parts of a polymerization initiator (t-butyl peroxide) in ethylene glycol monobutyl ether. The prepared monomer solution was added dropwise to the flask over 3 hours. After stirring for 2 hours, the ethylene glycol monobutyl ether was removed under reduced pressure to obtain water-soluble resins 1 to 4 (all solids). The obtained water-soluble resins 1 to 4 were neutralized with potassium hydroxide in an amount 1.0 times (molar ratio) the acid value of each resin. An appropriate amount of ion-exchanged water was then added and dissolved at 80°C to obtain aqueous solutions of water-soluble resins 1 to 4 with a resin content of 15.00%.

[0127] TIFF2026025897000002.tif55170

[0128] <Ink Preparation> The components (unit: %) shown in the middle of Tables 3-1 to 3-5 were mixed, thoroughly stirred, and then pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec) to prepare each ink. The physical properties of each ink prepared are shown in the bottom of Tables 3-1 to 3-5. In Tables 3-1 to 3-5, "Acetylenol E100" is the trade name for an ethylene oxide adduct of acetylene glycol (a nonionic surfactant, manufactured by Kawaken Fine Chemicals). The specific gravity of the ink was measured in accordance with the hydrometer-based specific gravity measurement method specified in "JIS Z8804 Method for Determining the Density and Specific Gravity of Liquids." The viscosity of the ink was measured using an E-type viscometer (trade name "RE-85L," manufactured by Toki Sangyo Co., Ltd.).

[0129] TIFF2026025897000003.tif156170

[0130] TIFF2026025897000004.tif157170

[0131] TIFF2026025897000005.tif157170

[0132] TIFF2026025897000006.tif155170

[0133] TIFF2026025897000007.tif182170

[0134] <Recording head> Recording heads with the configurations shown in Table 4 were manufactured. The abbreviations in Table 4 are PP: polypropylene, PE: polyethylene, FEP: fluorinated ethylene hexafluoropropylene copolymer, and PS: polystyrene. A recording head in which the pressure reduction chamber was positioned vertically above the liquid storage chamber (FIG. 6(a)), and a recording head in which the pressure reduction chamber was positioned to the side of the liquid storage chamber (FIG. 6(b)) are indicated as "top" and "side," respectively, in the "Position of pressure reduction chamber relative to liquid storage chamber" column in Table 4.

[0135] TIFF2026025897000008.tif142170

[0136] <Evaluation> An inkjet recording device (product name "GX6030," manufactured by Canon) incorporating the types of recording heads shown in Tables 5-1 and 5-2 was prepared. In this example, the recording duty of a solid image recorded under the condition that two ink droplets with a mass of 11.7 ng ± 10% per droplet were deposited in a unit area of ​​1 / 600 inch x 1 / 600 inch was defined as 100%. Each ink prepared was filled into an ink cartridge, and the ink cartridge was set in the inkjet recording device so as to have the combination of recording head and ink shown in Tables 5-1 and 5-2, and the following items were evaluated. In the present invention, the following evaluation criteria for each item were used: "AA," "A," and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Tables 5-1 and 5-2.

[0137] In Comparative Example 5, an inkjet recording device was used in which a degassing unit equipped with a hollow fiber module was provided in the path for supplying ink from the ink storage unit to the recording head, with reference to the description in Patent Document 1. Furthermore, in Reference Example 1, an inkjet recording device was used in which a filter for capturing bubbles was provided in the path for supplying ink from the ink storage unit to the recording head, with reference to the description in Patent Document 2. In Reference Example 2, an inkjet recording device was used in which a degassing unit including a partition formed of a hollow fiber membrane was provided inside the recording head, with reference to the description in Patent Document 3. In Reference Example 3, an inkjet recording device was used in which a permeable partition wall with a thickness of 1.00 mm was provided inside the recording head instead of a gas-permeable membrane, with reference to the description in Patent Document 4.

[0138] (Discharge stability) To simulate the condition after a certain period of use, 0.3 mL of air was injected into the liquid reservoir. The volume of the bubble reservoir in the liquid reservoir was 0.5 mL. The maximum ink temperature Ti (°C) in the liquid reservoir was controlled to the temperature shown in Tables 5-1 and 5-2 using a heater installed in the recording head. The pressure reduction chamber was depressurized at the pressure reduction levels shown in Tables 5-1 and 5-2 for 10 days, and the air in the liquid reservoir was transferred to the depressurization chamber through the gas-permeable membrane. Then, to simulate the condition after a certain period of use, 0.3 mL of air was injected into the liquid reservoir, and 100 15 cm x 25 cm solid images were printed on A4-sized recording media. When depressurization was not performed, the same procedure was used, except that the maximum ink temperature Ti (°C) in the liquid reservoir was set to the temperature shown in Tables 5-1 and 5-2 and the device was left stationary for 10 days. The recording medium used was glossy paper (product name "Photo Paper Glossy Gold A4" manufactured by Canon). After that, a nozzle check pattern was recorded on the GX6030, and the recorded nozzle check pattern was visually inspected to evaluate the ink ejection stability according to the following evaluation criteria. AA: The number of ejection ports that failed to eject was 5 or less. A: The number of non-discharging orifices was 6 or more and 10 or less. B: The number of non-discharging orifices was 11 or more and 15 or less. C: The number of non-ejecting outlets was 16 or more.

[0139] (Abrasion resistance) A friction test was conducted using a friction resistance tester (product name "AB-301", manufactured by Tester Sangyo), which is a friction tester II (Gakushin type) conforming to JIS L 0849. Specifically, a friction test was conducted on the surface of the solid image recorded in the above-mentioned ejection stability evaluation, using a white rubbing cloth (cotton) specified in JIS L 0803, by rubbing it back and forth 5 times and 10 times at a load of 500 g. The image after the friction test was visually inspected, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below. A: No scraping was observed in either the image after 5 strokes or the image after 10 strokes. B: Scraping was observed in the image after 10 reciprocal passes, but no scraping was observed in the image after 5 reciprocal passes. C: Scraping was observed on the image after five reciprocal passes.

[0140] (Suction recovery) Five days after the ink was refilled, the printer driver performed the normal suction recovery operation. A nozzle check pattern was then recorded on the recording medium. Glossy paper (product name "Photo Paper Gloss Gold A4", manufactured by Canon) was used as the recording medium. The recorded nozzle check pattern was visually inspected, and the suction recovery was evaluated according to the following evaluation criteria. A: The number of non-discharging orifices was 15 or less. C: The number of non-ejecting outlets was 16 or more.

[0141] TIFF2026025897000009.tif255163

[0142] TIFF2026025897000010.tif255168

[0143] Reference Example 1 was excellent in ejection stability and suction recovery, but the device was large in size.

[0144] The disclosure of this embodiment includes the following methods and configurations. (Method 1) An inkjet recording method using an inkjet recording device equipped with a recording head including: an ejection port for ejecting aqueous ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection port; a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, the method comprising: applying the aqueous ink ejected from the ejection port to a recording medium to record an image, the water-based ink contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; An inkjet recording method, characterized in that the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the water-based ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1) (Method 2) The inkjet recording method according to Method 1, wherein the water-based ink further contains a pigment. (Method 3) The inkjet recording method according to Method 1 or 2, wherein the water-based ink further contains resin particles different from the wax particles. (Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the difference between the specific gravity of the wax particles and the specific gravity of the water-based ink is 0.15 or less. (Method 5) The inkjet recording method according to any one of Methods 1 to 4, wherein the viscosity of the aqueous ink is 3.0 mPa·s or more and 8.0 mPa·s or less. (Method 6) The inkjet recording method according to any one of Methods 1 to 5, wherein the melting point Tw (°C) of the wax particles is 80°C or higher. (Method 7) The inkjet recording method according to any one of Methods 1 to 6, wherein the wax particles have a volume-based cumulative 50% particle diameter of 150 nm or more. (Method 8) The inkjet recording method according to any one of Methods 1 to 7, wherein the wax particles are particles formed of a wax containing oxidized wax. (Method 9) The inkjet recording method according to any one of Methods 1 to 8, wherein the water-based ink further contains a water-soluble resin having an acid value of 100 mgKOH / g or more. (Method 10) The inkjet recording method according to Method 2, wherein the content (mass %) of the pigment in the aqueous ink is 1.0 times or more the mass ratio of the content (mass %) of the wax particles. (Method 11) The inkjet recording method according to Method 3, wherein the content (mass %) of the resin particles in the aqueous ink is 4.0 times or more the mass ratio of the content (mass %) of the wax particles. (Method 12) The inkjet recording method according to any one of Methods 1 to 11, wherein the content (mass %) of the wax particles in the aqueous ink is 0.50 mass % or more and 2.00 mass % or less, based on the total mass of the aqueous ink. (Method 13) The water-based ink further has a vapor pressure of 2.7 × 10 -2 13. The inkjet recording method according to any one of Methods 1 to 12, further comprising a first water-soluble organic solvent having a viscosity of 100 kPa or less. (Method 14) The inkjet recording method according to Method 13, wherein the first water-soluble organic solvent has a relative dielectric constant of 22.0 or more. (Method 15) The inkjet recording method according to any one of Methods 1 to 14, wherein the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (2): Tw-Tr≧30 (2) (Method 16) The inkjet recording method according to any one of Methods 1 to 15, wherein the gas-permeable membrane has a thickness of 0.01 mm or more. (Method 17) The inkjet recording method according to any one of Methods 1 to 16, wherein the gas-permeable membrane has a thickness of 0.10 mm or less. (Method 18) The inkjet recording method according to any one of Methods 1 to 17, wherein the material of the gas-permeable membrane is polypropylene. (Method 19) The inkjet recording method according to any one of Methods 1 to 18, wherein the degree of vacuum in the vacuum chamber is 10 kPa or more. (Configuration 1) An inkjet recording device comprising a recording head including: an ejection port for ejecting aqueous ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection port; a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, the water-based ink contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; An inkjet recording apparatus, characterized in that the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the water-based ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1) (Configuration 2) A water-based ink for use in an inkjet recording method, which uses an inkjet recording device equipped with a recording head comprising: an ejection port for ejecting the water-based ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the water-based ink from the ejection port; a liquid storage chamber capable of supplying the water-based ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, and which records an image by applying the water-based ink ejected from the ejection port to a recording medium, Contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; A water-based ink characterized in that the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the water-based ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10 (1)

Claims

1. an inkjet recording method using an inkjet recording device equipped with a recording head including: an ejection port for ejecting aqueous ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection port; a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber, the decompression chamber being configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at a boundary between the liquid storage chamber and the decompression chamber, the method comprising: applying the aqueous ink ejected from the ejection port to a recording medium to record an image, the water-based ink contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; an inkjet recording method, wherein the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (1): Tw-Ti≧10...(1)

2. The inkjet recording method according to claim 1 , wherein the water-based ink further contains a pigment.

3. 2. The ink jet recording method according to claim 1, wherein the water-based ink further contains resin particles different from the wax particles.

4. 2. The ink jet recording method according to claim 1, wherein the difference between the specific gravity of the wax particles and the specific gravity of the water-based ink is 0.15 or less.

5. 2. The ink jet recording method according to claim 1, wherein the viscosity of the aqueous ink is 3.0 mPa.s or more and 8.0 mPa.s or less.

6. 2. The ink jet recording method according to claim 1, wherein the wax particles have a melting point Tw (° C.) of 80° C. or higher.

7. 2. The ink jet recording method according to claim 1, wherein the wax particles have a volume-based cumulative 50% particle diameter of 150 nm or more.

8. 2. The ink jet recording method according to claim 1, wherein the wax particles are particles formed of a wax containing oxidized wax.

9. 2. The ink jet recording method according to claim 1, wherein the water-based ink further contains a water-soluble resin having an acid value of 100 mgKOH / g or more.

10. The inkjet recording method according to claim 2, wherein the content (% by mass) of the pigment in the aqueous ink is 1.0 times or more the content (% by mass) of the wax particles in terms of a mass ratio.

11. The inkjet recording method according to claim 3, wherein the content (% by mass) of the resin particles in the aqueous ink is 4.0 times or more the content (% by mass) of the wax particles.

12. 2. The inkjet recording method according to claim 1, wherein the content (% by mass) of the wax particles in the aqueous ink is 0.50% by mass or more and 2.00% by mass or less based on the total mass of the ink.

13. The water-based ink further has a vapor pressure of 2.7×10 －２ 2. The ink jet recording method according to claim 1, further comprising a first water-soluble organic solvent having a viscosity of 100 kPa or less.

14. 14. The ink jet recording method according to claim 13, wherein the first water-soluble organic solvent has a relative dielectric constant of 22.0 or more.

15. 2. The inkjet recording method according to claim 1, wherein the melting point Tw (° C.) of the wax particles and the maximum temperature Ti (° C.) of the aqueous ink in the liquid storage chamber satisfy the relationship of the following formula (2). Tw-Ti≧30...(2)

16. 16. The ink jet recording method according to claim 1, wherein the gas-permeable membrane has a thickness of 0.01 mm or more.

17. 16. The ink jet recording method according to claim 1, wherein the gas-permeable membrane has a thickness of 0.10 mm or less.

18. 16. The ink jet recording method according to claim 1, wherein the gas-permeable membrane is made of polypropylene.

19. 16. The inkjet recording method according to claim 1, wherein the degree of vacuum in the vacuum chamber is 10 kPa or more.

20. an inkjet recording device equipped with a recording head including: an ejection port for ejecting aqueous ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection port; a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber, the decompression chamber being configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, the water-based ink contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; an ink jet recording apparatus, characterized in that the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the water-based ink in the liquid storage chamber satisfy the relationship of the following formula (1): Tw-Ti≧10...(1)

21. an ink jet recording device including a recording head including: an ejection port for ejecting the water-based ink; a pressure chamber communicating with the ejection port; an ejection element disposed in the pressure chamber and generating energy for ejecting the water-based ink from the ejection port; a liquid storage chamber capable of supplying the water-based ink to the pressure chamber; a decompression chamber disposed adjacent to and vertically above the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane disposed at the boundary between the liquid storage chamber and the decompression chamber, wherein the water-based ink is applied to a recording medium to record an image, Contains wax particles, the wax particles have a specific gravity smaller than that of the water-based ink; A water-based ink characterized in that the melting point Tw (°C) of the wax particles and the maximum temperature Ti (°C) of the water-based ink in the liquid storage chamber satisfy the relationship of the following formula (1). Tw-Ti≧10...(1)

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