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

Abstract

To provide an inkjet recording method excellent in suction recovery properties and ink discharge stability.SOLUTION: Using an ink jet recording apparatus including a recording head including an ejection orifice for ejecting an aqueous ink, a pressure chamber communicating with the ejection orifice, an ejection device disposed in the pressure chamber and generating energy for ejecting the aqueous ink from the ejection orifice, a liquid storage chamber capable of supplying the aqueous ink to the pressure chamber, a decompression chamber disposed adjacent to the liquid storage chamber and configured to be capable of decompressing the inside thereof, and a gas permeable membrane having a thickness of 0. 01mm or more disposed at a boundary between the liquid storage chamber and the decompression chamber, An ink jet recording method includes applying an aqueous ink ejected from an ejection orifice to a recording medium to record an image. The surface tension γ I (mN / m) of the aqueous ink at 25 °C. and the surface energy γ m (mN / m) of the gas-permeable membrane satisfy the relationship of the following formula (1). Γ I - γ m ≤ 11 (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 methods make it possible to record images such as photographs and documents on various recording media. Various inks have been proposed depending on the intended use, such as inks suitable for recording photographic quality images on glossy paper and inks suitable for recording documents on plain paper.

[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] If the amount of bubbles that have infiltrated the print head increases after the printing device has been left unused for a certain period of time, a suction recovery process is performed to recover the print head by sucking the bubbles together with the ink through the ejection ports. If a large amount of bubbles has been mixed in, the suction recovery process must be performed multiple times. Because a large amount of ink is sucked in during the suction recovery process, the amount of ink that is not used for printing increases as the number of processes and the amount of ink sucked in each process increase. This reduces the amount of images (number of sheets) that can be printed with a certain amount of ink, resulting in a problem of reduced productivity.

[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 cycles, 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, and bubbles that flow into the ejection section in excess of the allowable amount can cause ejection defects. Furthermore, the device proposed in Patent Document 3 is unable to adequately degas, resulting in ejection defects. Furthermore, even when the transparent partition wall proposed in Patent Document 4 is used, the bubble discharge effect is insufficient, resulting in ejection defects. Therefore, it was found that in order to restore the print head to a state where normal ejection is possible, it is necessary to increase the number of suction cycles or the amount of ink to be sucked.

[0008] Therefore, an object of the present invention is to provide an inkjet recording method that is excellent in suction recovery property and ink ejection stability. Another object of the present invention is to provide an inkjet recording apparatus and a water-based ink that are used in the 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 the liquid storage chamber and configured to be able to decompress the interior thereof, and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, and recording an image by applying the aqueous ink ejected from the ejection port to a recording medium, wherein the surface tension γ of the aqueous ink at 25°C is i (mN / m) and the surface energy γ of the gas-permeable membrane m (mN / m) satisfies the relationship of the following formula (1): gamma i -γ m ≦11 (1) [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inkjet recording method that is excellent in suction recovery property and ink ejection stability, and also to provide an inkjet recording apparatus and a water-based ink that are used in the inkjet recording method. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective 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 the ejection characteristics of aqueous ink from a print head when an image is printed on a recording medium using an inkjet printing apparatus. Specifically, an inkjet printing apparatus was prepared, equipped with a print head including a liquid storage chamber, a pressure reduction chamber adjacent to the liquid storage chamber, capable of reducing the pressure inside the chamber, and a gas-permeable membrane located at the boundary between the liquid storage chamber and the pressure reduction chamber. To simulate the condition after a certain period of use, the liquid storage chamber was filled with the maximum amount of air that could be trapped and left for five days. The pressure reduction chamber was then reduced, and the air in the liquid storage chamber was transferred to the pressure reduction chamber via the gas-permeable membrane. Then, a standard suction recovery operation was performed, in which air was sucked from the ejection orifices, to check the ink ejection characteristics. The results revealed that ejection failures, such as ejection failures and irregular ejection, occurred, resulting in degraded ink ejection characteristics. Close observation of the ink flow path of the ejection orifice where the irregular ejection occurred, revealed the presence of bubbles in the ink flow path connected to the ejection orifice. This indicates that the bubbles were not sufficiently removed by reducing the pressure or by performing standard suction recovery operations.

[0014] When ejecting ink after a recording device has been left unused for a certain period of time, a suction recovery process is required to remove bubbles that have formed in the ink in the ink flow path from the liquid storage chamber to the ejection orifices. However, if air is trapped in the liquid storage chamber, the suction recovery process can cause bubbles to flow into the ink flow path. While it is possible to prevent bubbles from flowing into the ink flow path by performing the suction recovery process more frequently, this reduces productivity per unit time because no printing can be performed during the suction recovery process. Therefore, a pressure reduction chamber is located adjacent to the liquid storage chamber via a gas-permeable membrane with a thickness of 0.10 mm or more. By depressurizing the pressure reduction chamber, the air trapped in the liquid storage chamber is transferred to the pressure reduction chamber via the gas-permeable membrane. As a result, bubbles in the ink in the ink flow path from the liquid storage chamber to the ejection orifices can be removed with minimal suction recovery operations. If the thickness of the gas-permeable membrane is less than 0.01 mm, the membrane will not be strong enough to reduce the pressure sufficiently, making it impossible to fully remove bubbles from the ink in the ink flow path and improving the ink ejection stability.

[0015] By reducing the pressure in the liquid storage chamber through a gas-permeable membrane with a thickness of 0.01 mm or more, bubbles accumulated in the liquid storage chamber burst, removing the air. It is known that the smaller the bubble, the higher the internal pressure. Smaller bubbles with higher internal pressure burst and are removed more efficiently under reduced pressure. The inventors' investigations revealed that increasing the wettability of the ink with the gas-permeable membrane is effective in generating such small bubbles, leading to the present invention. To efficiently remove bubbles, it is preferable to reduce the surface tension of the ink and increase the surface energy of the gas-permeable membrane. Specifically, the surface tension γ of the ink at 25°C is i (mN / m) and the surface energy of the gas-permeable membrane γ m (mN / m) is designed to satisfy the relationship of the following formula (1). gamma i -γ m ≦11 (1)

[0016] It is generally known that the lower the surface tension of a liquid, the more easily it will wet an object. It is also known that the higher the surface energy of a solid, the more easily it will wet a liquid. Therefore, by selecting inks that are mutually wettable and a gas-permeable membrane with a thickness of 0.01 mm or more, it is possible to effectively remove bubbles in the ink within the ink flow path, improving ink ejection stability.

[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 comprises 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 having a thickness of 0.01 mm or more and 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 the liquid storage chamber and is configured to be able to decompress its interior. The surface tension γ of the aqueous ink at 25°C is i (mN / m) and the surface energy of the gas-permeable membrane γ m (mN / m) satisfies the relationship of the following formula (1). gamma i -γ m ≦11 (1)

[0018] The inkjet recording apparatus of the present invention is an inkjet recording apparatus equipped with a predetermined recording head. The recording head comprises 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 having a thickness of 0.01 mm or more and disposed at the boundary between the liquid storage chamber and the decompression chamber. The ejection element is disposed in the pressure chamber and is a part that generates energy for ejecting aqueous ink from the ejection port. The decompression chamber is disposed adjacent to the liquid storage chamber and is configured to be able to decompress its interior. The surface tension γ of the aqueous ink at 25°C is i (mN / m) and the surface energy of the gas-permeable membrane γ m (mN / m) satisfies the relationship of the following formula (1). gamma i -γ m ≦11 (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 comprises 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 having a thickness of 0.01 mm or more and disposed at the boundary between the liquid storage chamber and the decompression chamber. The ejection element is disposed in the pressure chamber and is a component that generates energy for ejecting the aqueous ink from the ejection orifice. The decompression chamber is disposed adjacent to the liquid storage chamber and is configured to be able to decompress its interior. The surface tension γ of the aqueous ink at 25°C is i (mN / m) and the surface energy of the gas-permeable membrane γ m (mN / m) satisfies the relationship of the following formula (1). gamma i -γ m ≦11 (1)

[0020] (Inkjet recording device) FIG. 1 is a perspective view schematically illustrating one embodiment of an inkjet recording apparatus according to the present invention. As shown in FIG. 1, a feeding unit 20 of a recording apparatus 1000 can hold multiple recording media, and feeds the recording media using a feeding roller (not shown). The recording media may be cut sheets of paper cut to a predetermined size, or rolled paper. The recording media fed by the feeding unit 20 are transported in the Y direction (transport direction) by a transport unit including a transport roller, and move to a recording position opposite a recording head that ejects ink. A carriage 60 carries a recording head 1, and is driven by a carriage motor 4 to reciprocate along a guide shaft 3 via a timing belt 2 in the X direction (main scanning direction) that intersects with the Y direction.

[0021] After an image for a unit area is recorded by the movement of the carriage 60 in the X direction and the ink ejection operation of the print head 1, the print medium is transported in the Y direction by the transport unit. The unit area can be arbitrarily set, such as the arrangement width of the nozzle array arranged along the Y direction in the print head 1, "one band" that can be recorded with one movement of the print head 1 in the X direction, or "one pixel" corresponding to the print head resolution. In the serial method, an image can be recorded over the entire print medium by a printing operation that repeats the ink ejection operation for one band and intermittent transport operation of the print medium. In this embodiment, the X direction and the Y direction are orthogonal.

[0022] [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.

[0023] [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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] [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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] [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.

[0036] [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.

[0037] 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.

[0038] 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.

[0039] [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.

[0040] 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.

[0041] FIG. 6 is a vertical cross-sectional view showing an example of a circulation path. As shown in FIG. 6(a), the first bubble removal unit 770A is provided vertically above the supply flow path 130, and the second bubble removal unit 770B is provided vertically above the first recovery flow path 140, but this is not limited to this. 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 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 pump inlet flow path 170, the pump outlet flow path 180, the bypass flow path 160, and the pressure chamber 12. As shown in FIG. 6(b), the first bubble storage chamber 520A may be connected to a side surface of the supply flow path 130, and the first bubble removal unit 770A may be formed to extend laterally from the first bubble storage chamber 520A. The second foam reservoir chamber 520B may be connected to a side surface of the first recovery channel 140, and the second foam removal unit 770B may be formed extending laterally from the second foam reservoir chamber 520B. As long as the configuration is capable of capturing bubbles and bringing them into contact with the gas-permeable membrane 710, the foam reservoir chamber 520 may be connected to a side surface of a communication part other than the supply channel 130 and the first recovery channel 140, and the foam removal unit 770 may be formed extending laterally from the foam reservoir chamber 520. In other words, the bubble removal unit 770 may be formed extending horizontally from the foam reservoir chamber 520, rather than vertically above the foam reservoir chamber 520. From the viewpoint of bubble removal efficiency, it is preferable that the decompression chamber be located adjacent to and vertically above the liquid storage chamber.

[0042] 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.

[0043] [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.

[0044] 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.

[0045] Surface energy γ of the gas-permeable membrane 710 m The surface energy γ of the gas-permeable membrane is preferably 24 mN / m or more, more preferably 29 mN / m or more, and is preferably 40 mN / m or less. m If the surface energy γ of the gas-permeable membrane is less than 24 mN / m, the wettability of the ink to the gas-permeable membrane may be slightly reduced, and the bubble-removal property may be reduced, which may reduce the effect of improving the ink ejection stability. mcan be measured using a dyne pen (for example, "Dyne Pen" manufactured by Arcotest GmbH) conforming to ISO 8296, DIN 53364, ASTM 2587, and JIS K 6768. The dyne pen used to measure the surface energy of a gas-permeable membrane is not limited to this. Furthermore, as long as the surface energy can be measured, the method for measuring the surface energy of a gas-permeable membrane is not limited to the method using a dyne pen.

[0046] The SP value of the resin used as the material of the gas permeable membrane 710 is 5.0 (cal / cm 3 ) 1 / 2 More than 15.0(cal / cm 3 ) 1 / 2 It is preferable that the viscosity is 5.0 (cal / cm 3 ) 1 / 2 More than 10.0(cal / cm 3 ) 1 / 2 If the SP value of the resin constituting the gas-permeable membrane is outside the above range, the wettability of the ink to the gas-permeable membrane may be slightly reduced, and the bubble-removal ability may be reduced, which may reduce the effect of improving the ink ejection 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 of the test piece using the 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 is highly reliable in welding the gas-permeable membrane 710 and as a liquid-contacting material. Furthermore, because bubbles are removed by decompression, the gas-permeable membrane 710 must be strong enough to withstand decompression. Therefore, the thickness of the gas-permeable membrane 710 must be 0.01 mm or greater. Meanwhile, to achieve a bubble permeation rate of 0.01 mL / day or greater, 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. Having a thickness of 0.10 mm or less facilitates bubble removal, further improving discharge 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 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.

[0056] [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.

[0057] 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.

[0058] 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.

[0059] 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 bubble 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.

[0060] [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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] [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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 bubble 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.

[0070] [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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] (ink) The ink used in the recording method of the present invention has a surface tension γ i (mN / m) and the surface energy of the gas-permeable membrane γ m (mN / m) satisfies the relationship of the following formula (1): Each component used in the ink will be described in detail below. gamma i -γ m ≦11 (1)

[0077] [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.

[0078] 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.

[0079] Pigment dispersion methods include resin-dispersed pigments that use a resin as a dispersant and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface. 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, can also be used. It is also possible to combine pigments with different dispersion methods. In particular, rather than resin-bonded pigments or microencapsulated pigments, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed to the pigment particle surface, or self-dispersed pigments in which anionic groups are bonded to the pigment particle surface directly or via another atomic group (-R-).

[0080] 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.

[0081] 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.

[0082] The dye preferably has an anionic group. Specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. A single dye may be used, or two or more dyes may be used in combination. The colorant is preferably a pigment, and more preferably a resin-dispersed pigment in which a resin serving as a dispersant is physically adsorbed onto the surface of the pigment particles, or a self-dispersed pigment in which an anionic group is bonded to the surface of the pigment particles directly or via another atomic group (-R-).

[0083] [resin] The ink can contain a resin. By using an ink containing a resin, it is possible to record an image with improved scratch resistance. Resins can be added to the ink (i) to stabilize the dispersion state of the pigment, i.e., as a resin dispersant or its auxiliary, and (ii) to improve various properties of the recorded image.

[0084] The content (mass %) of the resin in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the ink. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. One type of resin may be used alone, or two or more types may be used in combination.

[0085] [Resin Composition] Examples of the 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] [Resin properties] 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.

[0090] The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 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. 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 3,000,000 or less, more preferably 100,000 or more and 3,000,000 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 cumulative 50% particle diameter of resin particles is the diameter of the particles that is 50% when integrated from the small particle diameter side based on the total volume of the measured particles in a particle diameter integration curve. The volume-based cumulative 50% particle diameter of resin particles can be measured using the dynamic light scattering particle size analyzer and measurement conditions described above. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, more preferably 50°C or more and 100°C or less. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain a colorant.

[0091] [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.

[0092] When the ink contains a water-soluble organic solvent, the ejection stability can be further improved. Therefore, the average SP value of the water-soluble organic solvent in the ink is 15.0 (cal / cm 3 ) 1 / 2 The average SP value of the water-soluble organic solvent in the ink is preferably 8.0 (cal / cm 3 ) 1 / 2 More preferably, it is 12.0 (cal / cm 3 ) 1 / 2More preferably, it is equal to or greater than this.

[0093] When the material of the gas-permeable membrane is resin, the ejection stability can be further improved. Therefore, the difference between the average SP value of the water-soluble organic solvent in the ink and the SP value of the resin that constitutes the gas-permeable membrane is 6.5 (cal / cm 3 ) 1 / 2 It is preferable that the viscosity is 6.0 (cal / cm 3 ) 1 / 2 It is more preferable that the viscosity is 3.0 (cal / cm 3 ) 1 / 2 More preferably, it is equal to or greater than this.

[0094] The SP value (δ: solubility parameter) in this specification is a value calculated by the Fedors method based on the following formula (A) (unit: (cal / cm 3 ) 1 / 2 ) when converting to the SI unit system, use "(cal / cm 3 ) 1 / 2 =2.046×10 3 (J / m 3 ) 1 / 2 " relationship can be used. ΔE vap and V can be determined by referring to the description in, for example, Coating Times No. 193 (1992). δ = (ΔE vap / V) 1 / 2 (A) (In the formula (A), ΔE vap represents the molar heat of vaporization of the compound (cal / mol), and V is the molar volume of the compound at 25°C (cm 3 / mol)

[0095] Water-based inkjet inks typically contain multiple types of water-soluble organic solvents. For this reason, it is appropriate to consider the SP value of the water-soluble organic solvents in the ink in terms of the concept of an "average SP value." The average SP value is the value calculated for each water-soluble organic solvent by multiplying the SP value specific to that water-soluble organic solvent by the proportion (mass %) of that water-soluble organic solvent in the total amount of water-soluble organic solvents in the ink, and then adding up the results. When the ink contains only one type of water-soluble organic solvent, the SP value of that water-soluble organic solvent is the "average SP value."

[0096] For example, in the case of "Ink 1" prepared in the "Examples" described below, the composition of the water-soluble organic solvents (total 20.0 parts by mass) is as follows: The numbers in parentheses are the SP values ​​(units omitted) of each water-soluble organic solvent. The average SP value of the water-soluble organic solvents in this "Ink 1" can be calculated using the following formula (B): Glycerin (16.4): 10.00 parts by weight (% by weight) Polyethylene glycol (10.5) with a number average molecular weight of 600: 10.00 parts by mass (mass%) Average SP value = (16.4 × 10.00 / 20.00) + (10.5 × 10.00 / 20.00) = 13.5 (B)

[0097] The SP value of a general-purpose water-soluble organic solvent in water-based inkjet inks, measured by the Fedors method, is expressed in units of (cal / cm 3 ) 1 / 2The following are abbreviated: Glycerin (16.4), 1,3-propanediol (16.1), trimethylolpropane (15.9), 1,4-butanediol (15.0), diethylene glycol (15.0), ethylene glycol (14.8), 1,3-butanediol (14.8), 2-methyl-1,3-propanediol (14.8), 1,2,6-hexanetriol (14.5), urea (14.4), ethyleneurea (14.2), 1,5-pentanediol (14.2), triethanolamine (13.7), methanol (13.8), triethylene glycol (13.6), 1,6-hexanediol (13.5), 3-methyl-1,5-pentanediol (13.4), tetraethylene glycol (12.8), polyethylene glycol with a number average molecular weight of 200 (12.8), 2-pyrrolidone (12.6), ethanol (12.6), 1,2-pentanediol (12.2), ethylene glycol monomethyl ether (12.0), n-propanol (11.8), 1,2-hexanediol (11.8), isopropanol (11.6), N-methyl-2-pyrrolidone (11.5), ethylene glycol monoethyl ether (12.0), 1,3-dimethyl-2-imidazolidinone (11.4), n-butanol (11.3), diethylene glycol monomethyl ether (11.2), 2-butanol (11.1), isobutanol (11.1), diethylene glycol monoethyl ether (10.9), tert-butanol (10.9), triethylene glycol monoethyl ether (10.6), poly(ethylene glycol) with a number average molecular weight of 600. Ethylene glycol (10.5), diethylene glycol monobutyl ether (10.5), triethylene glycol monobutyl ether (10.3), tetraethylene glycol monobutyl ether (10.2), polyethylene glycol with a number average molecular weight of 1,000 (10.1), acetone (9.1), methyl ethyl ketone (9.0), tetraethylene glycol dimethyl ether (8.5), triethylene glycol butyl methyl ether (8.4), ethylene glycol dimethyl ether (7.6). The SP value of the water-soluble organic solvent is 5.0 (cal / cm 3 ) 1 / 2 More than 15.0(cal / cm 3 )1 / 2 It is preferable that:

[0098] The water-soluble organic solvent is preferably a compound having an alkylene oxide structure. Furthermore, the ink preferably contains a nonionic surfactant in addition to the compound having an alkylene oxide structure as the water-soluble organic solvent. Compounds having an alkylene oxide structure have a high affinity with hydroxy groups and nonionic surfactants having an alkylene oxide structure. Therefore, when a nonionic surfactant and a compound having an alkylene oxide structure are used in combination, the two are compatible with each other, further improving the wettability of the ink to the gas-permeable membrane and further improving ejection stability. Examples of alkylene oxide structures include ethylene oxide (-CH2-CH2-O-) and propylene oxide (-CH2-CH(CH3)-O-), with ethylene oxide being particularly preferred.

[0099] Although the term "water-soluble organic solvent" generally refers to a liquid, in the present invention, compounds that are solid at 25° C. (room temperature) are also included in the water-soluble organic solvent. Examples of water-soluble organic solvents that are generally used in aqueous inks and are solid at 25° C. include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number-average molecular weight of 1,000.

[0100] [Surfactants] The ink preferably contains a surfactant. Examples of surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. Among these, the use of a nonionic surfactant with an HLB value of 12 or less is preferred because it can further increase the wettability of the ink to the gas-permeable membrane and further improve the ejection stability.

[0101] Examples of nonionic surfactants include hydrocarbon-based nonionic surfactants, fluorine-based nonionic surfactants, and silicone-based nonionic surfactants. Among these, hydrocarbon-based nonionic surfactants are preferred, and acetylene glycol-based surfactants are even more preferred because they can further improve ejection stability. The "HLB value" of a surfactant in this specification is a value determined by the Griffin method and is calculated based on the formula: HLB value = 20 × (formula weight of hydrophilic groups in the surfactant) / (molecular weight of the surfactant). The HLB value determined by the Griffin method is a physical property value that represents the degree of hydrophilicity and lipophilicity of a surfactant, and takes a value from 0 to 20. The smaller the HLB value, the higher the lipophilicity, and the higher the HLB value, the higher the hydrophilicity. The HLB value of a surfactant is preferably 4 or higher.

[0102] The content (mass %) of the surfactant in the ink is preferably 0.10 mass % or more and 5.00 mass % or less, and more preferably 0.30 mass % or more and 1.50 mass % or less, based on the total mass of the ink. Two or more types of surfactants may be added to the ink. Adding surfactants with different properties can further improve the wettability of the ink to the gas-permeable membrane.

[0103] [Other ingredients] The ink may contain various other components (additives) as needed. Examples of other components include various additives such as antifoaming agents, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents. In the present invention, these additives (including surfactants) are not included in the calculation of the SP value because their content is small and their impact on the effects of the present invention is relatively small.

[0104] [Ink properties] Surface tension γ of ink at 25°C i The surface tension γ of the ink is preferably 40 mN / m or less, and more preferably 25 mN / m or more and 35 mN / m or less. iIf the surface tension γ of the ink exceeds 40 mN / m, the ink may have poor wettability to the gas-permeable membrane, which may lead to poor bubble-removal properties, and the ink may not be as effective in improving its ejection stability. Furthermore, the closer the surface tension value of the ink is to the surface energy value of the gas-permeable membrane, the better the ink will be wettability to the gas-permeable membrane, and the more improved the bubble-removal properties will be. In this specification, the surface tension γ of the ink is i (mN / m) is the "static surface tension" measured by the plate method at a temperature of 25° C. The surface tension of the ink can be adjusted using, for example, a surfactant or a water-soluble organic solvent.

[0105] The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The viscosity of the ink at 25°C can be measured using a rotational viscometer. The pH of the ink at 25°C is preferably 7.0 or more and 9.0 or less. The pH of the ink can be measured using a general pH meter equipped with a glass electrode or the like. [Example]

[0106] 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.

[0107] <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%.

[0108] (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%.

[0109] (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%.

[0110] (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%.

[0111] (Pigment dispersion 5) An aqueous dispersion containing a self-dispersing pigment in which benzenecarboxylic acid groups are bonded to the particle surfaces of carbon black (product name "Cab-O-Jet 300", manufactured by Cabot) was used as pigment dispersion 5. The pigment content in pigment dispersion 5 was 15.00%.

[0112] <Preparing surfactant> The types of surfactants shown in Table 1 were prepared.

[0113] TIFF2026025898000001.tif76170

[0114] <Ink Preparation> The components (unit: %) shown in the middle of Tables 2-1 to 2-3 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each ink. In Tables 2-1 to 2-3, the values ​​in parentheses next to the water-soluble organic solvents are the SP values ​​(cal / cm) of the water-soluble organic solvents. 3 ) 1 / 2 The physical properties of each ink prepared are shown in the lower part of Tables 2-1 to 2-3.

[0115] TIFF2026025898000002.tif152170

[0116] TIFF2026025898000003.tif167170

[0117] TIFF2026025898000004.tif168170

[0118] <Recording head> A recording head was manufactured with the configuration shown in Table 3. The abbreviations in Table 3 are: PP: polypropylene, FEP: fluorinated ethylene hexafluoropropylene copolymer, PE: polyethylene, and PS: polystyrene.

[0119] TIFF2026025898000005.tif134170

[0120] <Evaluation> An inkjet recording device (trade name "GX6030," manufactured by Canon) incorporating the type of recording head shown in Table 4 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 prepared ink was filled into an ink cartridge, and the ink cartridge was set in the inkjet recording device so as to provide the combination of recording head and ink shown in Table 4, and the following items were evaluated. In the present invention, the evaluation criteria for each item below were "AA," "A," and "B," with "C" being an acceptable level and "AA" being an unacceptable level. The evaluation results are shown in Table 4.

[0121] In Comparative Example 4, 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.

[0122] (Discharge stability) To simulate the condition after a certain period of storage, 0.3 mL of air was injected into the liquid storage chamber. The volume of the bubble storage chamber in the liquid storage chamber was 0.5 mL. The vacuum chamber was depressurized for five days at the vacuum level shown in Table 4, and the air in the liquid storage chamber was transferred to the vacuum chamber through the gas-permeable membrane. After that, the printer driver performed the normal suction recovery operation to expel bubbles from the nozzles, and then 200 solid images with a print duty of 100% were printed on the entire surface of an A4-sized recording medium. When depressurization was not performed, the same procedure was used for evaluation, except that 0.3 mL of air was injected into the liquid storage chamber and the device was left to stand for five days. Plain paper (product name "CS-068 A4" manufactured by Canon) was used as the recording medium. The printed images were visually inspected, and the ink ejection stability was evaluated according to the following evaluation criteria. AA: The percentage of the area where non-ejection occurred was 0%. A: The percentage of the area where non-ejection occurred was more than 0% and less than 5%. B: The proportion of the area where non-ejection occurred was 5% or more and less than 10%. C: The proportion of the area where non-ejection occurred was 10% or more.

[0123] (Suction recovery) After filling the ink using the same procedure as in the evaluation of ejection stability, five days later, the cycle of normal suction from the ejection port and printing a solid image with a printing duty of 100% on the entire surface of an A4-sized recording medium was repeated until a smooth image was printed. Plain paper (product name "CS-068 A4", manufactured by Canon) was used as the recording medium. Suction recovery was then evaluated according to the following evaluation criteria. A: A single suction operation eliminated the distortion of the solid image and prevented non-discharge. C: After two or more suction operations, the solid image was cleared and no ejection failures occurred.

[0124] TIFF2026025898000006.tif255155

[0125] Reference Example 1 was excellent in ejection stability and suction recovery, but the device was large in size.

[0126] 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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, wherein the ink is ejected from the ejection port and applied to a recording medium to record an image, The surface tension γ of the water-based ink at 25°C i (mN / m) and the surface energy γ of the gas-permeable membrane m (mN / m) satisfies the relationship of the following formula (1): gamma i -γ m ≦11 (1) (Method 2) Surface tension γ of the water-based ink at 25°C i 2. The inkjet recording method according to claim 1, wherein the surface tension is 40 mN / m or less. (Method 3) The water-based ink contains a water-soluble organic solvent, The average SP value of the water-soluble organic solvent is 15.0 (cal / cm 3 ) 1 / 2 3. The inkjet recording method according to Method 1 or 2, wherein: (Method 4) The material of the gas-permeable membrane is a resin, The difference between the average SP value of the water-soluble organic solvent and the SP value of the resin is 6.5 (cal / cm 3 ) 1 / 2 The inkjet recording method according to Method 3, which is as follows: (Method 5) The aqueous ink contains a surfactant, 5. The inkjet recording method according to any one of Methods 1 to 4, wherein the surfactant has an HLB value of 12 or less. (Method 6) The inkjet recording method according to Method 5, wherein the surfactant is an acetylene glycol surfactant. (Method 7) The inkjet recording method according to any one of Methods 3 to 6, wherein the water-soluble organic solvent contains a compound having an alkylene oxide structure. (Method 8) The inkjet recording method according to any one of Methods 1 to 7, wherein the gas-permeable membrane has a thickness of 0.10 mm or less. (Method 9) The inkjet recording method according to any one of Methods 1 to 8, wherein the material of the gas-permeable membrane is polypropylene or polyethylene. (Method 10) The inkjet recording method according to any one of Methods 1 to 9, wherein the material of the gas-permeable membrane is polypropylene. (Method 11) The inkjet recording method according to any one of Methods 1 to 10, 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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, The surface tension γ of the water-based ink at 25°C i (mN / m) and the surface energy γ of the gas-permeable membrane m (mN / m) satisfies the relationship of the following formula (1): gamma i -γ m ≦11 (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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, and which comprises: The surface tension γ of the water-based ink at 25°C i (mN / m) and the surface energy γ of the gas-permeable membrane m (mN / m) satisfies the relationship of the following formula (1): gamma i -γ m ≦11 (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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more 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 surface tension γ of the water-based ink at 25°C ｉ (mN / m) and the surface energy γ of the gas-permeable membrane ｍ (mN / m) satisfies the relationship of the following formula (1): c ｉ -c ｍ ≦11・・・(1)

2. The surface tension γ of the water-based ink at 25°C ｉ 2. The ink jet recording method according to claim 1, wherein the surface tension is 40 mN / m or less.

3. the water-based ink contains a water-soluble organic solvent, The average SP value of the water-soluble organic solvent is 15.0 (cal / cm ３ ) １／２ 2. The ink jet recording method according to claim 1, wherein:

4. the gas-permeable membrane is made of a resin; The difference between the average SP value of the water-soluble organic solvent and the SP value of the resin is 6.5 (cal / cm ３ ) １／２ The ink jet recording method according to claim 3, wherein the ink jet recording method is as follows:

5. the aqueous ink contains a surfactant, 2. The ink jet recording method according to claim 1, wherein the HLB value of the surfactant is 12 or less.

6. 6. The ink jet recording method according to claim 5, wherein the surfactant is an acetylene glycol surfactant.

7. 4. The ink jet recording method according to claim 3, wherein the water-soluble organic solvent contains a compound having an alkylene oxide structure.

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

9. 8. The ink jet recording method according to claim 1, wherein the gas-permeable membrane is made of polypropylene or polyethylene.

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

11. 8. The ink jet recording method according to claim 1, wherein the degree of vacuum in the vacuum chamber is 10 kPa or more.

12. 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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, The surface tension γ of the water-based ink at 25°C ｉ (mN / m) and the surface energy γ of the gas-permeable membrane ｍ (mN / m) satisfies the relationship of the following formula (1): c ｉ -c ｍ ≦11・・・(1)

13. an ink jet recording device including 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 the liquid storage chamber and configured to be able to decompress the interior thereof; and a gas-permeable membrane having a thickness of 0.01 mm or more disposed at the boundary between the liquid storage chamber and the decompression chamber, the water-based ink being ejected from the ejection port and being used in an ink jet recording method for recording an image by applying the water-based ink ejected from the ejection port to a recording medium, The surface tension γ of the water-based ink at 25°C ｉ (mN / m) and the surface energy γ of the gas-permeable membrane ｍ (mN / m) satisfies the relationship of the following formula (1): c ｉ -c ｍ ≦11・・・(1)

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