Inkjet recording method

Abstract

To provide an inkjet recording method which can enhance redispersibility of ink containing titanic oxide to improve stability of discharging ink.SOLUTION: In an inkjet recording method, a liquid discharging head discharges ink. The ink contains titanic oxide, in which sedimentation-speed based on a Stokes equation is 1.0×10-11 m / s or more. The liquid discharging head has: a discharge port; a pressure chamber; an energy generating element for discharging the ink; an upstream-side flow passage for supplying liquid to the pressure chamber; a downstream-side flow passage communicated with the pressure chamber; and a pump, communicated with the upstream-side flow passage and the downstream-side flow passage, which forms a circulation path through which the ink circulates through the upstream-side flow passage, the pressure chamber, the downstream-side flow passage and the upstream-side flow passage in this order. When maximum cross sectional areas of the circulation path is defined as S[mm2] and a flow rate of the ink in the circulation path is defined as Q[mL / s], a ratio Q / S is larger than the sedimentation-speed of the ink.SELECTED DRAWING: Figure 20

Description

[Technical field]

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

[0002] In recent years, inkjet recording devices have come to be widely used when printing advertisements and exhibits using recording media such as paper and resin film. For example, in order to express clear color images even on transparent recording media, white ink is used in addition to black and basic color inks (hereinafter, these may be collectively referred to as color inks). Specifically, a recording method is used in which white ink is applied in advance to a location on a transparent recording medium including an area where an image is to be recorded to perform base treatment, and color inks are applied on top of that, or each ink is applied in the reverse order (so-called back printing).

[0003] Titanium oxide is widely used as a coloring material for white ink because it is low cost and has excellent properties required for white ink, such as whiteness and hiding power. However, titanium oxide has a problem that it is prone to settling. Therefore, in the past, methods have been considered for improving the dispersion stability by surface-treating titanium oxide from the viewpoint of suppressing the settling of titanium oxide in white ink. For example, Patent Document 1 proposes a method for producing a dried titanium dioxide product in which titanium oxide is surface-treated with silica, and then further surface-treated with a silane coupling agent and dried, thereby covalently bonding a part of the silane coupling agent to the surface of titanium oxide particles.

[0004] Furthermore, Patent Document 2 proposes an ink containing titanium oxide that has been surface-treated with alumina, a monovalent metal salt, and fine alumina particles.

[0005] That is, in Patent Documents 1 and 2, attempts are made to use a white ink in which the settling of titanium oxide is suppressed, thereby achieving stable ejection of the white ink and suppressing the occurrence of image unevenness in the recorded image. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2017-521348 [Patent Document 2] International Publication No. 2018 / 190848 Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have devised a method for achieving stable ink ejection in an inkjet recording method using inks such as white inks that contain titanium oxide, which is prone to settling, by using titanium oxide particles with good redispersibility, rather than constructing the ink so as to suppress the settling of titanium oxide, and then by constructing a liquid ejection head so that the ink will be redispersed even if it settles.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an ink jet recording method which enhances the redispersibility of ink containing titanium oxide and improves the ejection stability of the ink. [Means for solving the problem]

[0009] The present invention for solving the above-mentioned problems is an inkjet recording method in which ink is discharged from a liquid discharge head, the ink contains titanium oxide and has a sedimentation velocity based on Stokes' law of 1.0×10 -11 m / s or more, the liquid ejection head includes an ejection port for ejecting the ink, a pressure chamber for supplying the ink to the ejection port, an energy generating element for generating energy for ejecting the ink, an upstream flow path for supplying liquid to the pressure chamber, a downstream flow path communicating with the pressure chamber, and a pump communicating with the upstream flow path and the downstream flow path, forming a circulation path through which the ink circulates in the order of the upstream flow path, the pressure chamber, the downstream flow path and the upstream flow path, and a maximum cross-sectional area of ​​the circulation path is S [mm 2a flow rate of the ink in the circulation path being Q [mL / s], Q / S is greater than the settling velocity of the ink. Effect of the Invention

[0010] According to the present invention, it is possible to provide an ink jet recording method in which the ejection stability of ink containing titanium oxide is improved. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a liquid ejection device. [Diagram 2] FIG. 1 is an exploded perspective view of a liquid ejection head; [Diagram 3] 2A and 2B are a longitudinal section of a liquid ejection head and an enlarged cross-sectional view of an ejection module. [Figure 4] FIG. 1 is a schematic view showing the appearance of a circulation unit; [Diagram 5] FIG. [Figure 6] FIG. 4 is a block diagram showing a schematic diagram of a circulation path. [Figure 7] FIG. 4 is a cross-sectional view showing an example of a pressure adjusting means. [Figure 8] FIG. 2 is an external perspective view of a circulation pump. [Figure 9] 9 is a cross-sectional view of the circulating pump shown in FIG. 8(a) taken along line IX-IX. [Figure 10] 3A and 3B are diagrams illustrating the flow of ink in a liquid ejection head. [Figure 11] FIG. 4 is a schematic diagram showing a circulation path in the discharge unit. [Figure 12] FIG. 3 shows an aperture plate 330. [Figure 13] FIG. 2 is a diagram showing a discharge element substrate. [Figure 14] 5A and 5B are cross-sectional views showing the ink flow in the ejection unit. [Figure 15] FIG. 4 is a cross-sectional view showing the vicinity of a discharge port. [Figure 16] FIG. 11 is a cross-sectional view showing a comparative example near the ejection port. [Figure 17] 11A and 11B are diagrams showing a comparative example of a discharge element substrate. [Figure 18] FIG. 2 is a diagram showing a flow path configuration of a liquid ejection head. [Figure 19] 2A and 2B are diagrams illustrating a connection state between a main body of the liquid ejection device and a liquid ejection head. [Figure 20] FIG. 2 is a diagram showing an ink circulation system. [Figure 21] FIG. 2 is a diagram showing an ink circulation system. [Figure 22] FIG. 4 is a cross-sectional view of a connection portion between the circulation unit and the discharge unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Inkjet recording method> The inkjet recording method of the present invention is a method in which an ink, which will be described later, is discharged from an inkjet recording head to record an image on a recording medium.

[0013] The recording medium is not particularly limited, but a transparent or colored recording medium can be used. The recording medium may also be a poorly absorbing medium (non-absorbent medium) that has low absorbency of the liquid medium, such as a resin film. Multi-pass recording is preferable in which ink is applied to a unit area of ​​the recording medium by multiple relative scans of the recording head and the recording medium. In particular, it is preferable to apply white ink and color ink to the unit area by different relative scans. This increases the time until the inks come into contact with each other, making it easier to suppress mixing. The unit area can be set as any area, such as one pixel or one band.

[0014] The present inventors first investigated a method for improving the redispersibility of ink containing titanium oxide when it settles. As a result of the investigations by the present inventors, it was found that in order to improve the redispersibility of the ink, the settling velocity based on the Stokes' law (terminal velocity when settling) needs to be 1.0×10 -11It was found that the settling velocity must be at least m / s. The settling velocity based on Stokes' law means the speed at which the resistance and buoyancy acting on the particle in an upward direction are balanced with the gravity acting on the particle in a downward direction, resulting in uniform motion.

[0015] However, when such ink with high redispersibility is used, the titanium oxide itself in the ink is likely to settle. Therefore, if the flow rate of the ink flow generated by circulation is equal to or higher than the settling rate of the ink, the redispersion of the ink is promoted. To achieve stable ejection from the ejection port 13, it is desirable that ink in which the titanium oxide particles are sufficiently dispersed flows into the pressure chamber. Therefore, in the present invention, the liquid ejection head has a mechanism for circulating the ink in a circulation path in the head, and the ink in the circulation path is encouraged to be redispersed by the circulation flow, thereby allowing ink with a uniform pigment concentration to flow into the pressure chamber, improving the ejection stability of the ink.

[0016] The circulation of ink in a liquid ejection head will be described with reference to FIG. 5. FIG. 5 is a cross-sectional view showing the vicinity of an ejection port 13 in one example of a liquid ejection head of the present invention described later. The liquid ejection head 1 shown in FIG. 5 includes an ejection port 13 for ejecting the reaction liquid, a pressure chamber 12 including an ejection element 15 that generates energy for ejecting the reaction liquid, and a common supply flow path 18 (upstream flow path) and a common recovery flow path 19 (downstream flow path) that communicate between the ejection port 13 and the ejection element 15 and through which the reaction liquid flows. The reaction liquid flows between the ejection port 13 and the ejection element 15 to the common supply flow path 18 and the common recovery flow path 19 (in the direction of the arrow in FIG. 5). Furthermore, the liquid ejection head 1 includes a pump 500 configured to cause the liquid in the common recovery flow path 19 to flow into the common supply flow path 18. As a result, a circulation path is formed in the liquid ejection head 1 in which the ink circulates through the common supply flow path 18, the pressure chamber 12, the common recovery flow path 19, and the common supply flow path 18 in this order.

[0017] In order to promote the redispersion of titanium oxide by the ink flow, it is sufficient that the ink flow is faster than the settling velocity of titanium oxide particles, even in the place in the circulation path where the flow velocity is the slowest. The flow velocity acting on titanium oxide particles in the ink due to circulation is calculated by the circulation flow rate Q [mL / min] and the maximum cross-sectional area S [mm 2 It is expressed as Q / S, where Q / S is greater than the settling velocity. It is thought that redispersion is promoted.

[0018] Here, the cross-sectional area of ​​the circulation path is the area of ​​the surface perpendicular to the flow direction of the liquid. If the maximum cross-sectional area S is large, the circulation flow rate Q required for redispersion of the ink will be large. Therefore, the maximum cross-sectional area is set to 500 mm 2 It is preferable that the length is less than 350 mm. 2 It is more preferable that:

[0019] (1)Liquid discharge device Hereinafter, a preferred embodiment of the present disclosure will be described in detail with reference to the attached drawings with respect to a liquid ejection device (inkjet recording device) that can be used in the inkjet recording method of the present invention. Note that the following embodiment does not limit the subject matter of the present disclosure, and not all combinations of features described in the present embodiment are necessarily essential to the solution of the present disclosure. Note that the same components are given the same reference numbers. In this embodiment, an example is described in which a thermal method is adopted in which an electrothermal conversion element is used to generate bubbles to eject liquid as an ejection element for ejecting liquid, but this is not limited thereto. The present invention can also be applied to a liquid ejection head that employs an ejection method that ejects liquid using a piezoelectric element (piezo) or another ejection method. Furthermore, the pump and pressure adjustment means described below are not limited to the configurations themselves described in the embodiment and drawings.

[0020] <Liquid discharge device> Fig. 1 is a diagram for explaining a liquid ejection device, and is an enlarged view of a liquid ejection head of the liquid ejection device and its surroundings. First, a schematic configuration of a liquid ejection device 50 in this embodiment will be described with reference to Fig. 1. Fig. 1(a) is a perspective view that shows a liquid ejection device that uses a liquid ejection head 1. The liquid ejection device 50 in this embodiment constitutes a serial type inkjet recording device that performs recording on a recording medium P by ejecting ink as a liquid while scanning the liquid ejection head 1.

[0021] The liquid ejection head 1 is mounted on a carriage 60. The carriage 60 reciprocates along a guide shaft 51 in a main scanning direction (X direction). The recording medium P is transported in a sub-scanning direction (Y direction) that intersects (orthogonal in this example) the main scanning direction by transport rollers 55, 56, 57, and 58. That is, the liquid ejection head 1 is configured to eject liquid while scanning in a direction perpendicular to the transport direction of the recording medium to which ink is applied. In each of the figures referred to below, the Z direction indicates the vertical direction and intersects (orthogonal in this example) the XY plane defined by the X and Y directions. The liquid ejection head 1 is configured to be removable and attachable to the carriage 60 by the user.

[0022] The liquid ejection head 1 includes a circulation unit 54 and an ejection unit 3 (see FIG. 2) described later. The specific configuration will be described later, but the ejection unit 3 is provided with a plurality of ejection ports and energy generating elements (hereinafter referred to as ejection elements) that generate ejection energy for ejecting liquid from each ejection port.

[0023] The liquid ejection device 50 is also provided with an ink tank 2 (liquid storage section) which is an ink supply source, and an external pump 21, and the ink stored in the ink tank 2 is supplied to the circulation unit 54 via an ink supply tube 59 by the driving force of the external pump 21.

[0024] The liquid ejection device 50 repeats a recording scan in which the liquid ejection 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, thereby forming a predetermined image on the recording medium P. The liquid ejection head 1 in this embodiment is configured to be capable of ejecting four types of ink including ink containing titanium oxide. However, the configuration of the inkjet recording device in the present invention is not limited to one that ejects four types of liquid. For example, a configuration that can eject black (K), cyan (C), magenta (M), yellow (Y), and white (W) ink can be exemplified, and in this case, a full-color image can be recorded using these inks. However, the ink that can be ejected from the liquid ejection head 1 is not limited to the above five types of ink. The present disclosure is also applicable to liquid ejection heads for ejecting other types of ink, reaction liquids other than ink, and the like. In other words, the types and number of liquids ejected from the liquid ejection head are not limited.

[0025] Furthermore, the liquid ejection device 50 is provided with a cap member (not shown) capable of covering the ejection port surface on which the ejection ports of the liquid ejection head are formed, at a position offset in the X direction from the transport path of the recording medium P. The cap member covers the ejection port surface of the liquid ejection head 1 during non-recording operations, and is used to prevent and protect the ejection ports from drying, and to suck ink from the ejection ports, etc.

[0026] 1(a) shows an example in which the liquid ejection head 1 is provided with four circulation units 54 corresponding to the four types of ink, but it is sufficient that the liquid ejection head 1 is provided with a circulation unit 54 corresponding to the type of liquid to be ejected. Also, multiple circulation units 54 may be provided for the same type of liquid. In other words, the liquid ejection head 1 can be configured to include one or more circulation units. It is also possible to have a configuration in which only at least one ink containing titanium oxide is circulated, rather than circulating all four types of ink.

[0027] FIG. 1B is a block diagram showing a control system of the liquid ejection device 50. The CPU 103 functions as a control means for controlling the operation of each part of the liquid ejection device 50 based on a program such as a processing procedure 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 400 outside the liquid ejection device 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 liquid ejection device. For example, the CPU 103 controls a motor driver 105A of a carriage motor 105 for moving the carriage 60, and a motor driver 104A of a conveying motor 104 for conveying the recording medium P. The CPU 103 also controls a pump driver 500A for driving a circulation pump 500 described later, a pump driver 21A of an external pump 21, and the like. Although FIG. 1B shows a form in which processing is performed upon receiving image data from the host device 400, processing may be performed by the liquid ejection device 50 independently of data from the host device 400.

[0028] <Basic configuration of liquid ejection head> Fig. 2 is an exploded perspective view of the liquid ejection head 1 of this embodiment. Fig. 3 is a cross-sectional view of the liquid ejection head 1 shown in Fig. 2 taken along line IIIa-IIIa. Fig. 3(a) is an overall vertical cross-sectional view of the liquid ejection head 1, and Fig. 3(b) is an enlarged view of the ejection module 300 shown in Fig. 3(a). The basic configuration of the liquid ejection head 1 of this embodiment will be described below mainly with reference to Fig. 2 and Fig. 3, and also with reference to Fig. 1 as appropriate.

[0029] 2, the liquid ejection 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 liquid ejection head 1 in this embodiment is fixedly supported on a carriage 60 of the liquid ejection device 50 by positioning means and electrical contacts (not shown) provided on the carriage 60. The liquid ejection head 1 ejects ink while moving together with the carriage 60 in the main scanning direction (X direction) shown in FIG. 1, and performs recording on the recording medium P.

[0030] An ink supply tube 59 is provided on the external pump 21 connected to the ink tank 2 serving as the ink supply source (see FIG. 1). A liquid connector (not shown) is provided on the tip of the ink supply tube 59. When the liquid ejection head 1 is mounted on the liquid ejection device 50, the liquid connector provided on the tip of the ink supply tube 59 is airtightly connected to a liquid connector insertion port 53a, which is a liquid inlet port provided on a head housing 53 of the liquid ejection head 1. This forms an ink supply path from the ink tank 2 to the liquid ejection head 1 via the external pump 21. In this embodiment, since four types of ink are used, four sets of the ink tank 2, the external pump 21, the ink supply tube 59, and the circulation unit 54 are provided corresponding to each ink, and four ink supply paths corresponding to each ink are independently formed. In this way, the liquid ejection device 50 of this embodiment is provided with an ink supply system to which ink is supplied from the ink tank 2 provided outside the liquid ejection head 1. Note that the liquid ejection device 50 of this embodiment is not provided with an ink recovery system that recovers the ink in the liquid ejection head 1 to the ink tank 2. Therefore, the liquid ejection head 1 is provided with a liquid connector insertion port 53a for connecting an ink supply tube 59 of the ink tank 2, but is not provided with a connector insertion port for connecting a tube for recovering ink from the liquid ejection head 1 to the ink tank 2. A liquid connector insertion port 53a is provided for each ink.

[0031] In Fig. 3, 54A indicates a circulation unit for the first ink, 54B indicates a circulation unit for the second ink, 54C indicates a circulation unit for the third ink, and 54D indicates a circulation unit for the fourth ink. When at least one of these inks (first, second, third, and fourth inks) contains titanium oxide, the present invention can be suitably used. Each circulation unit has a substantially similar configuration, and in this embodiment, when there is no particular need to distinguish between the circulation units, they are all referred to as circulation unit 54.

[0032] 2 and 3(a), the discharge unit 3 includes two discharge modules 300, a first support member 4, a second support member 7, an electric wiring member (electric wiring tape) 5, and an electric contact substrate 6. As shown in FIG. 3(b), the discharge module 300 includes a silicon substrate 310 having a thickness of 0.5 to 1 mm, and a plurality of discharge elements 15 provided on one side of the silicon substrate 310. In this embodiment, the discharge elements 15 are configured by electrothermal conversion elements (heaters) that generate thermal energy as discharge energy for discharging liquid. Electric power is supplied to each discharge element 15 via electric wiring formed on the silicon substrate 310 by a film formation technique.

[0033] Moreover, an ejection port forming member 320 is formed on the surface (lower surface in FIG. 3(b)) of the silicon substrate 310. In the ejection port forming member 320, a plurality of pressure chambers 12 corresponding to a plurality of ejection elements 15 and a plurality of ejection ports 13 for ejecting ink are formed by photolithography. Furthermore, a common supply flow path 18 and a common recovery flow path 19 are formed in the silicon substrate 310. In addition, in the silicon substrate 310, a supply connection flow path 323 that communicates the common supply flow path 18 with each pressure chamber 12, and a recovery connection flow path 324 that communicates the common recovery flow path 19 with each pressure chamber 12 are formed. In this embodiment, one ejection module 300 is configured to eject two types of ink. That is, of the two ejection modules shown in FIG. 3(a), the ejection module 300 located on the left side of the figure ejects the first ink and the second ink, and the ejection module 300 located on the right side of the figure ejects the third ink and the fourth ink. Note that this combination is an example, and any combination of inks may be used. One ejection module may be configured to eject one type of ink, or may be configured to eject three or more types of ink. The two ejection modules 300 do not have to eject the same number of types of ink. One ejection module 300 may be provided, or may be configured to include three or more ejection modules 300. Furthermore, in the example shown in FIG. 3, two ejection port arrays extending in the Y direction are formed for one type of ink. 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 constitute each ejection port array.

[0034] An ink supply port and an ink recovery port, which will be described later, are formed on the back surface (upper surface in FIG. 3(b)) of the silicon substrate 310. The ink supply port supplies ink from an ink supply flow path 48 to the multiple common supply flow paths 18, and the ink recovery port recovers ink from the multiple common recovery flow paths 19 to an ink recovery flow path 49.

[0035] The ink supply port and ink recovery port referred to here refer to openings that supply and recover ink during forward ink circulation, which will be described later. That is, during forward ink circulation, ink is supplied from the ink supply port to each common supply flow path 18, and ink is recovered from each common recovery flow path 19 to the ink recovery port. However, there are also cases where ink circulation is performed in the reverse direction. In this case, ink is supplied from the ink recovery port described above to the common recovery flow path 19, and ink is recovered from the common supply flow path 18 to the ink supply port.

[0036] As shown in FIG. 3(a), the back surface (upper surface in FIG. 3(a)) of the ejection module 300 is adhesively fixed to one surface (lower surface in FIG. 3(a)) of the first support member 4. An ink supply flow path 48 and an ink recovery flow path 49 are formed in the first support member 4, penetrating from one surface to the other surface. One opening of the ink supply flow path 48 communicates with the ink supply port in the silicon substrate 310, and one opening of the ink recovery flow path 49 communicates with the ink recovery port in the silicon substrate 310. The ink supply flow path 48 and the ink recovery flow path 49 are provided independently for each type of ink.

[0037] A second support member 7 having an opening 7a (see FIG. 2) through which the ejection module 300 is inserted is adhesively fixed to one surface of the first support member 4 (the upper surface in FIG. 3(a)). The second support member 7 holds an electrical wiring member 5 that is electrically connected to the ejection module 300. The electrical wiring member 5 is a member for applying an electrical signal to the ejection module 300 to eject ink. The electrical connection portion between the ejection module 300 and the electrical wiring member 5 is sealed with a sealant (not shown) and is protected from corrosion by ink and external impacts.

[0038] Furthermore, an electrical contact board 6 is thermocompression bonded to an end 5a (see FIG. 2) of the electrical wiring member 5 using an anisotropic conductive film (not shown), and the electrical wiring member 5 and the electrical contact board 6 are electrically connected. The electrical contact board 6 has an external signal input terminal (not shown) for receiving an electrical signal from the liquid ejection device 50.

[0039] Furthermore, a joint member 8 (FIG. 3(a)) is provided between the first support member 4 and the circulation unit 54. A supply port 88 and a recovery port 89 are formed in the joint member 8 for each type of ink. The supply port 88 and the recovery port 89 communicate the ink supply flow path 48 and the ink recovery flow path 49 of the first support member 4 with the flow paths formed in the circulation unit 54. In FIG. 3(a), the supply port 88A and the recovery port 89A correspond to the first ink, and the supply port 88B and the recovery port 89B correspond to the second ink. Furthermore, the supply port 88C and the recovery port 89C correspond to the third ink, and the supply port 88D and the recovery port 89D correspond to the fourth reaction liquid.

[0040] The openings at one end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 of the first support member 4 have a small opening area that matches the ink supply port and the ink recovery port in the silicon substrate 310. In contrast, the openings at the other end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 of the first support member 4 have a shape that is expanded to the same opening area as the large opening area of ​​the joint member 8 formed to match the flow passage of the circulation unit 54. By adopting such a configuration, it is possible to suppress an increase in flow passage resistance to the ink collected from each recovery flow passage. However, the shapes of the openings at one end and the other end of each of the ink supply flow passage 48 and the ink recovery flow passage 49 are not limited to the above example.

[0041] In the liquid ejection head 1 having the above configuration, ink supplied to the circulation unit 54 passes through the supply port 88 of the joint member 8 and the ink supply flow path 48 of the first support member 4, and flows from the ink supply port of the ejection module 300 into the common supply flow path 18. The ink then flows from the common supply flow path 18 into the pressure chamber 12 via the supply connection flow path 323, and a portion of the ink that has flowed into the pressure chamber is ejected from the ejection port 13 by driving the ejection element 15. The remaining ink that has not been ejected passes from the pressure chamber 12 through the recovery connection flow path 324 and the common recovery flow path 19, and flows from the ink recovery port into the ink recovery flow path 49 of the first support member 4. The ink that has flowed into the ink recovery flow path 49 then flows into the circulation unit 54 via the recovery port 89 of the joint member 8, and is recovered.

[0042] <Components of the circulation unit> 4 is a schematic external view of one circulation unit 54 corresponding to one type of ink applied to the recording apparatus of this embodiment. In addition to the circulation pump 500, the circulation unit 54 preferably has a filter 110, a first pressure adjustment means 120, and a second pressure adjustment means 150. These components are connected by respective flow paths as shown in FIGS. 5 and 6, and constitute a circulation path that supplies and recovers ink to and from the ejection module 300 in the liquid ejection head 1.

[0043] <Circulation path inside the liquid ejection head> FIG. 5 is a vertical cross-sectional view showing a circulation path of one type of ink (one color ink) in the liquid ejection head 1. In order to explain the circulation path more clearly, the relative positions of each component (first pressure adjustment means 120, second pressure adjustment means 150, circulation pump 500, etc.) in FIG. 5 are simplified. Therefore, the relative positions of each component are different from the configuration in FIG. 19 described later. FIG. 6 is a block diagram showing the circulation path shown in FIG. 5. As shown in FIG. 5 and FIG. 6, 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 have a relatively higher control pressure than the second pressure adjustment means 150. In this embodiment, the two pressure adjustment means 120 and 150 are used to achieve circulation within a certain pressure range in the circulation path. Also, the ink is configured to flow through the pressure chamber 12 (ejection element 15) at a flow rate according to the pressure difference between the first pressure adjustment means 120 and the second pressure adjustment means 150. Below, the circulation path in the liquid ejection head 1 and the flow of ink within the circulation path will be described with reference to Figures 5 and 6. Note that the arrows in each figure indicate the direction of ink flow.

[0044] First, the connection state of each component of the liquid ejection head 1 will be described.

[0045] An external pump 21 that sends ink contained in an ink tank 2 (FIG. 6) provided outside the liquid ejection head 1 to the liquid ejection head 1 is connected to a circulation unit 54 via an ink supply tube 59 (FIG. 1). A filter 110 is provided in an ink flow path (inflow flow path) located upstream of the circulation unit 54. An ink supply path (inflow flow path) located downstream of the filter 110 is connected to a first valve chamber 121 of a first pressure adjustment means 120. The first valve chamber 121 communicates with a first pressure control chamber 122 via a communication port 191A that can be opened and closed by a valve 190A shown in FIG. 5. The inflow flow path is a flow path through which liquid in an ink tank 2 provided outside the liquid ejection head 1 flows into the liquid ejection head 1 to be supplied to the pressure chamber 12.

[0046] The first pressure control chamber 122 is connected to the supply flow path 130, the bypass flow path 160, and the pump outlet flow path 180 of the circulation pump 500. The supply flow path 130 is connected to the common supply flow path 18 via the ink supply port provided in the ejection module 300. The bypass flow path 160 is connected to a second valve chamber 151 provided in the second pressure adjustment means 150. The second valve chamber 151 is connected to the second pressure control chamber 152 via a communication port 191B that is opened and closed by a valve 190B shown in FIG. 5. Note that FIGS. 5 and 6 show an example in which one end of the bypass flow path 160 is connected to the first pressure control chamber 122 of the first pressure adjustment means 120, and the other end of the bypass flow path 160 is connected to the second valve chamber 151 of the second pressure adjustment means 150. Note that one end of the bypass flow path 160 may be connected to the supply flow path 130, and the other end of the bypass flow path may be connected to the second valve chamber 151.

[0047] The second pressure control chamber 152 is connected to the recovery flow path 140. The recovery flow path 140 is connected to the common recovery flow path 19 via the ink recovery port provided in the ejection module 300. Furthermore, the second pressure control chamber 152 is connected to the circulation pump 500 via a pump inlet flow path 170. In addition, in FIG. 5, 170a indicates the inlet of the pump inlet flow path 170.

[0048] Next, a description will be given of the flow of ink in the liquid ejection head 1 having the above configuration. As shown in Fig. 6, the ink stored in the ink tank 2 is pressurized by an external pump 21 provided in the liquid ejection device 50, and is supplied to the circulation unit 54 of the liquid ejection head 1 as a positive pressure ink flow.

[0049] The ink supplied to the circulation unit 54 passes through the filter 110 to remove foreign matter such as dust and air bubbles, and then flows into the first valve chamber 121 provided in the first pressure adjustment means 120. The ink pressure decreases due to pressure loss when passing through the filter 110, but the ink pressure at this stage is positive. The ink that has flowed into the first valve chamber 121 then passes through the communication port 191A and flows into the first pressure control chamber 122 when the valve 190A is in the open state. Due to the pressure loss when passing through the communication port 191A, the ink that has flowed into the first pressure control chamber 122 switches from positive pressure to negative pressure.

[0050] Next, the flow of ink in the circulation path will be described. The circulation pump 500 operates to pump ink sucked from the pump inlet flow path 170 on the upstream side to the pump outlet flow path 180 on the downstream side. Therefore, when the pump is driven, the ink supplied to the first pressure control chamber 122 flows into the supply flow path 130 and the bypass flow path 160 together with the ink sent from the pump outlet flow path 180. Note that, although details will be described later, in this embodiment, a piezoelectric diaphragm pump using a piezoelectric element attached to a diaphragm as a driving source is used as a circulation pump capable of sending liquid. The piezoelectric diaphragm pump is a pump that changes the volume of the pump chamber by inputting a driving voltage to a piezoelectric element, and sends liquid by alternately moving two check valves due to pressure fluctuations.

[0051] The ink that has flowed into the supply flow channel 130 flows from the ink supply port of the ejection module 300 through the common supply flow channel 18 into the pressure chamber 12, and some of the ink is ejected from the ejection port 13 by driving (heat generation) the ejection element 15. The remaining ink that has not been used for ejection flows through the pressure chamber 12, passes through the common recovery flow channel 19, and then flows into the recovery flow channel 140 connected to the ejection module 300. The ink that has flowed into the recovery flow channel 140 flows into the second pressure control chamber 152 of the second pressure adjustment means 150.

[0052] On the other hand, the ink that has flowed from the first pressure control chamber 122 into the bypass flow path 160 flows into the second valve chamber 151, and then passes through the communication port 191B and flows into the second pressure control chamber 152. The ink that has flowed into the second pressure control chamber 152 via the bypass flow path 160 and the ink that has been recovered from the recovery flow path 140 are sucked into the circulation pump 500 via the pump inlet flow path 170 by the operation of the circulation pump 500. Then, the ink that has been sucked into the circulation pump 500 is sent to the pump outlet flow path 180 and flows into the first pressure control chamber 122 again. Thereafter, the ink that has flowed into the second pressure control chamber 152 from the first pressure control chamber 122 via the supply flow path 130 through the ejection module 300 and the ink that has flowed into the second pressure control chamber 152 via the bypass flow path 160 flows into the circulation pump 500. Then, the ink is sent from the circulation pump 500 to the first pressure control chamber 122. In this manner, the ink is circulated in the circulation path.

[0053] As described above, in this embodiment, the circulation pump 500 can circulate the liquid along the circulation path formed in the liquid ejection head 1. This makes it possible to suppress thickening of the ink in the ejection module 300 and accumulation of sedimentation components of the ink color material, and makes it possible to maintain good ink fluidity in the ejection module 300 and ejection characteristics at the ejection ports.

[0054] Furthermore, since the circulation path in this embodiment is configured to be completed within the liquid ejection head 1, the length of the circulation path can be significantly shortened compared to when ink is circulated between the ink tank 2 provided outside the liquid ejection head and the liquid ejection head 1. This makes it possible to circulate the ink using a small circulation pump such as a piezoelectric pump.

[0055] Furthermore, the connection flow path between the liquid ejection head 1 and the ink tank 2 is configured to include only a flow path for supplying ink. In other words, a configuration is adopted in which a flow path for recovering ink from the liquid ejection head 1 to the ink tank 2 is not required. Therefore, only a tube for supplying ink is required to connect the ink tank 2 and the liquid ejection head 1, and no tube for recovering ink is required. Therefore, the inside of the liquid ejection device 50 can be simplified with a reduced number of tubes, and the entire device can be made compact. Furthermore, by reducing the number of tubes, it is possible to reduce the pressure fluctuation of the ink caused by the oscillation of the tubes accompanying the main scanning of the liquid ejection head 1. In addition, the oscillation of the tubes during the main scanning of the liquid ejection head 1 becomes a driving load of the carriage motor that drives the carriage 60. Therefore, by reducing the number of tubes, the driving load of the carriage motor is reduced, and it is possible to simplify the main scanning mechanism including the carriage motor and the like. Furthermore, since it is not necessary to recover ink from the liquid ejection head to the ink tank, the external pump 21 can also be made compact. In this way, according to this embodiment, the liquid ejection device 50 can be configured to be circulatory, while achieving miniaturization and cost reduction.

[0056] The flow rate at which the reaction solution is circulated (circulation flow rate) is preferably 1.0 mL / min or more and 10.0 mL / min or less, more preferably 2.0 mL / min or more and 10.0 mL / min or less, and even more preferably 2.0 mL / min or more and 5.0 mL / min or less.

[0057] <Pressure Adjustment Means> FIG. 7 is a diagram showing an example of a pressure adjustment means. The configuration and operation of the pressure adjustment means (first pressure adjustment means 120, second pressure adjustment means 150) built into the above-mentioned liquid ejection head 1 will be described in more detail with reference to FIG. 7. The first pressure adjustment means 120 and the second pressure adjustment means 150 have substantially the same configuration. For this reason, the following description will be given taking the first pressure adjustment means 120 as an example, and the second pressure adjustment means 150 will only be described with the reference numerals of the parts corresponding to the first pressure adjustment means in FIG. 7. In the case of the second pressure adjustment means 150, the first valve chamber 121 described below will be read as the second valve chamber 151, and the first pressure control chamber 122 will be read as the second pressure control chamber 152.

[0058] The first pressure adjustment means 120 has a first valve chamber 121 and a first pressure control chamber 122 formed in a cylindrical housing 125. The first valve chamber 121 and the first pressure control chamber 122 are separated by a partition wall 123 provided in the cylindrical housing 125. However, the first valve chamber 121 communicates with the first pressure control chamber 122 through a communication port 191 formed in the partition wall 123. The first valve chamber 121 is provided with a valve 190 that switches between communication and blocking between the first valve chamber 121 and the first pressure control chamber 122 at the communication port 191. The valve 190 is held in a position facing the communication port 191 by a valve spring 200, and has a configuration that allows it to come into close contact with the partition wall 123 by the biasing force of the valve spring 200. When the valve 190 comes into close contact with the partition wall 123, the flow of ink through the communication port 191 is blocked. In order to increase the close contact with the partition wall 123, it is preferable that the portion of the valve 190 that comes into contact with the partition wall 123 is made of an elastic material. A valve shaft 190a that is inserted into the communication port 191 protrudes from the center of the valve 190. By pressing this valve shaft 190a against the biasing force of a valve spring 200, the valve 190 moves away from the partition wall 123, allowing ink to flow through the communication port 191. Hereinafter, the state in which the valve 190 blocks the flow of ink through the communication port 191 will be referred to as the "closed state", and the state in which ink can flow through the communication port 191 will be referred to as the "open state".

[0059] The opening of the cylindrical housing 125 is closed by the flexible member 230 and the pressure plate 210. The first pressure control chamber 122 is formed by the flexible member 230, the pressure plate 210, the peripheral wall of the housing 125, and the partition wall 123. The pressure plate 210 is configured to be displaceable in accordance with the displacement of the flexible member 230. The materials of the pressure plate 210 and the flexible member 230 are not particularly limited, but for example, the pressure plate 210 can be configured from a resin molded part, and the flexible member 230 can be configured from a resin film. In this case, the pressure plate 210 can be fixed to the flexible member 230 by thermal welding.

[0060] A pressure adjustment spring 220 (biasing member) is provided between the pressure plate 210 and the partition wall 123. The pressure plate 210 and the flexible member 230 are biased by the biasing force of the pressure adjustment spring 220 in a direction in which the internal volume of the first pressure control chamber 122 expands, as shown in FIG. 7(a). When the pressure in the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 are displaced in a direction in which the internal volume of the first pressure control chamber 122 decreases against the pressure of the pressure adjustment spring 220. When the internal volume of the first pressure control chamber 122 decreases to a certain amount, the pressure plate 210 abuts against the valve shaft 190a of the valve 190. When the internal volume of the first pressure control chamber 122 further decreases thereafter, the valve 190 moves together with the valve shaft 190a against the biasing force of the valve spring 200, and moves away from the partition wall 123. As a result, the communication port 191 is in an open state (the state shown in FIG. 7(b)).

[0061] In this embodiment, the connection in the circulation path is set so that the pressure in the first valve chamber 121 when the communication port 191 is in the open state is higher than the pressure in the first pressure control chamber 122. As a result, when the communication port 191 is in the open state, ink flows from the first valve chamber 121 to the first pressure control chamber 122. This ink flow causes the flexible member 230 and the pressure plate 210 to be displaced in a direction in which the internal volume of the first pressure control chamber 122 increases. As a result, the pressure plate 210 moves away from the valve shaft 190a of the valve 190, and the valve 190 is brought into close contact with the partition wall 123 by the biasing force of the valve spring 200, and the communication port 191 is in the closed state (the state of FIG. 7(c)).

[0062] In this manner, in the first pressure adjustment means 120 of this embodiment, when the pressure in the first pressure control chamber 122 decreases to a certain pressure or below (for example, when the negative pressure becomes stronger), ink flows in from the first valve chamber 121 via the communication port 191. This prevents the pressure in the first pressure control chamber 122 from decreasing any further. Therefore, the pressure in the first pressure control chamber 122 is controlled to be kept within a certain range.

[0063] Next, the pressure in the first pressure control chamber 122 will be described in more detail.

[0064] Consider a state in which the flexible member 230 and the pressure plate 210 are displaced in response to the pressure in the first pressure control chamber 122 as described above, and the pressure plate 210 comes into contact with the valve shaft 190a, opening the communication port 191 (the state shown in FIG. 7(b)). At this time, the relationship of the forces acting on the pressure plate 210 is expressed by the following equation 1.

[0065] P2×S2+F2+(P1-P2)×S1+F1=0...Equation 1 Furthermore, rearranging Equation 1 for P2 gives P2 = -(F1 + F2 + P1 × S1) / (S2-S1) Equation 2.

[0066] P1: Pressure (gauge pressure) of the first valve chamber 121 P2: Pressure (gauge pressure) of the first pressure control chamber 122 F1: Valve spring force 200 F2: Spring force of the pressure adjusting spring 220 S1: Pressure receiving area of ​​valve 190 S2: Pressure receiving area of ​​the pressure plate 210 Here, the spring force F1 of the valve spring 200 and the spring force F2 of the pressure adjustment spring 220 are positive (leftward in FIG. 7) in the direction pressing the valve 190 and the pressure plate 210. In addition, the pressure P1 in the first valve chamber 121 and the pressure P2 in the first pressure control chamber 122 are configured so that P1 satisfies the relationship P1≧P2.

[0067] The pressure P2 in the first pressure control chamber 122 when the communication port 191 is open is determined by formula 2, and when the communication port 191 is open, due to the relationship P1≧P2, ink flows from the first valve chamber 121 into the first pressure control chamber 122. As a result, the pressure P2 in the first pressure control chamber 122 does not decrease any further, and P2 is maintained within a certain pressure range.

[0068] On the other hand, as shown in FIG. 7(c), when the pressure plate 210 is not in contact with the valve shaft 190a and the communication port 191 is closed, the relationship of the forces acting on the pressure plate 210 is expressed by Equation 3.

[0069] P3×S3+F3=0...Equation 3 Now, rearrange Equation 3 for P3 as follows: P3 = -F3 / S3...Equation 4.

[0070] F3: The spring force of the pressure adjusting spring 220 when the pressure plate 210 and the valve shaft 190a are not in contact with each other P3: pressure (gauge pressure) in the first pressure control chamber 122 when the pressure plate 210 and the valve shaft 190a are not in contact with each other S3: The pressure-receiving area of ​​the pressure plate 210 when the pressure plate 210 and the valve 190 are not in contact with each other Here, FIG. 7(c) shows a state in which the pressure plate 210 and the flexible member 230 are displaced to the right side of the figure to the limit of their displacement. The pressure P3 in the first pressure control chamber 122, the spring force F3 of the pressure adjustment spring 220, and the pressure receiving area S3 of the pressure plate 210 change according to the amount of displacement while the pressure plate 210 and the flexible member 230 are displaced to the state of FIG. 7(c). Specifically, when the pressure plate 210 and the flexible member 230 are in the right direction in FIG. 7 compared to FIG. 7(c), the pressure receiving area S3 of the pressure plate 210 becomes smaller, and the spring force F3 of the pressure adjustment spring 220 becomes larger. As a result, the pressure P3 in the first pressure control chamber 122 becomes smaller according to the relationship of Equation 4. Therefore, according to Equation 2 and Equation 4, the pressure in the first pressure control chamber 122 gradually increases from the state of FIG. 7(b) to the state of FIG. 7(c) (i.e., the negative pressure becomes weaker and approaches the positive pressure side). That is, from a state in which the communication port 191 is open, the pressure plate 210 and the flexible member 230 gradually displace to the left, and the pressure in the first pressure control chamber 122 gradually increases until the internal volume of the first pressure control chamber 122 finally reaches its limit of displacement. In other words, the negative pressure weakens.

[0071] <Circulation pump> Next, the configuration and operation of the circulation pump 500 built into the above-mentioned liquid ejection head 1 will be described in detail with reference to FIGS.

[0072] FIG. 8 is an external perspective view of the circulation pump 500. FIG. 8(a) is an external perspective view showing the front side of the circulation pump 500, and FIG. 8(b) is an external perspective view showing the rear side of the circulation pump 500. The outer shell of the circulation pump 500 is composed of a pump housing 505 and a cover 507 fixed to the pump housing 505. The pump housing 505 is composed of a housing body 505a and a flow path connecting member 505b adhesively fixed to the outer surface of the housing body 505a. The housing body 505a and the flow path connecting member 505b each have a pair of through holes communicating with each other at two different positions. The pair of through holes provided at one position forms a pump supply hole 501, and the pair of through holes provided at the other position forms a pump discharge hole 502. The pump supply hole 501 is connected to the pump inlet flow path 170 connected to the second pressure control chamber 152, and the pump discharge hole 502 is connected to the pump outlet flow path 180 connected to the first pressure control chamber 122. Ink supplied from pump supply hole 501 passes through a pump chamber 503 (see FIG. 9) described below, and is discharged from pump discharge hole 502.

[0073] FIG. 9 is a cross-sectional view of the circulating pump 500 shown in FIG. 8(a) taken along line IX-IX. A diaphragm 506 is joined to the inner surface of a pump housing 505, and a pump chamber 503 is formed between the diaphragm 506 and a recess formed on the inner surface of the pump housing 505. The pump chamber 503 communicates with a pump supply hole 501 and a pump discharge hole 502 formed in the pump housing 505. A check valve 504a is provided in the middle of the pump supply hole 501, and a check valve 504b is provided in the middle of the pump discharge hole 502. Specifically, the check valve 504a is arranged so that a part of the check valve 504a can move leftward in the figure in a space 512a formed in the middle of the pump supply hole 501. A part of the check valve 504b is arranged so that it can move rightward in the figure in a space 512b formed in the middle of the pump discharge hole 502.

[0074] When diaphragm 506 is displaced to increase the volume of pump chamber 503 and reduce the pressure in pump chamber 503, check valve 504a moves away from the opening of pump supply hole 501 in space 512a (i.e., moves to the left in the figure). When check valve 504a moves away from the opening of pump supply hole 501 in space 512a, the check valve 504a enters an open state that allows the flow of ink through pump supply hole 501. When diaphragm 506 is displaced to decrease the volume of pump chamber 503 and reduce the pressure in pump chamber 503, check valve 504a comes into close contact with the wall surface surrounding the opening of pump supply hole 501. As a result, the check valve 504a enters a closed state that blocks the flow of ink through pump supply hole 501.

[0075] On the other hand, when the pump chamber 503 is depressurized, the check valve 504b comes into close contact with the wall surface surrounding the opening of the pump housing 505 and enters a closed state in which it blocks the flow of ink through the pump discharge hole 502. When the pump chamber 503 is pressurized, the check valve 504b moves away from the opening of the pump housing 505 toward the space 512b (i.e., moves to the right in the figure), allowing the flow of ink through the pump discharge hole 502.

[0076] The material of each of the check valves 504a and 504b may be any material that can deform in response to the pressure in the pump chamber 503, and may be, for example, an elastic member such as EPDM or elastomer, or a film or thin plate such as polypropylene, but is not limited to these.

[0077] As described above, pump chamber 503 is formed by joining pump housing 505 and diaphragm 506. Therefore, the pressure in pump chamber 503 changes as diaphragm 506 deforms. For example, when diaphragm 506 is displaced toward pump housing 505 (displaced to the right in the figure) and the volume of pump chamber 503 decreases, the pressure in pump chamber 503 increases. As a result, check valve 504b arranged opposite pump discharge hole 502 opens, and ink in pump chamber 503 is discharged. At this time, check valve 504a arranged opposite pump supply hole 501 is in close contact with the wall surface surrounding pump supply hole 501, so that the backflow of ink from pump chamber 503 to pump supply hole 501 is suppressed.

[0078] Conversely, when the diaphragm 506 is displaced in the direction in which the pump chamber 503 expands, the pressure in the pump chamber 503 decreases. As a result, the check valve 504a arranged opposite the pump supply hole 501 opens, and ink is supplied to the pump chamber 503. At this time, the check valve 504b arranged at the pump discharge hole 502 comes into close contact with the wall surface surrounding the opening formed in the pump housing 505 and closes the opening. As a result, the backflow of ink from the pump discharge hole 502 to the pump chamber 503 is suppressed.

[0079] In this way, in the circulation pump 500, the diaphragm 506 deforms, changing the pressure in the pump chamber 503, thereby sucking in and discharging ink. At this time, if bubbles get into the pump chamber 503, even if the diaphragm 506 is displaced, the bubbles expand and contract, reducing the pressure change in the pump chamber 503 and decreasing the amount of liquid delivered. Therefore, the pump chamber 503 is arranged parallel to gravity to make it easier for bubbles that get into the pump chamber 503 to gather above the pump chamber 503, and the pump discharge hole 502 is arranged above the center of the pump chamber 503. This makes it possible to improve the discharge of bubbles in the pump and stabilize the flow rate.

[0080] <Ink flow inside the liquid ejection head> FIG. 10 is a diagram for explaining the flow of ink in the liquid ejection head. The circulation of ink in the liquid ejection head 1 will be explained with reference to FIG. 10. In order to more clearly explain the ink circulation path, the relative positions of each component (first pressure adjustment means 120, second pressure adjustment means 150, circulation pump 500, etc.) in FIG. 10 are simplified. Therefore, the relative positions of each component are different from the configuration in FIG. 19 described later. FIG. 10(a) is a schematic diagram showing the flow of ink when a recording operation is performed by ejecting ink from the ejection port 13. Note that the arrows in the figure indicate the flow of ink. In this embodiment, when a recording operation is performed, both the external pump 21 and the circulation pump 500 start to be driven. Note that the external pump 21 and the circulation pump 500 may be driven when no recording operation is performed. In addition, the external pump 21 and the circulation pump 500 do not need to be driven in conjunction with each other, and may be driven independently.

[0081] During the recording operation, the circulation pump 500 is ON (driven), and the ink flowing out from the first pressure control chamber 122 flows into the supply flow path 130 and the bypass flow path 160. The ink that flows into the supply flow path 130 passes through the ejection module 300, then flows into the recovery flow path 140, and is then supplied to the second pressure control chamber 152.

[0082] On the other hand, the ink that has flowed into the bypass flow path 160 from the first pressure control chamber 122 flows into the second pressure control chamber 152 via the second valve chamber 151. The ink that has flowed into the second pressure control chamber 152 passes through the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180, and then flows into the first pressure control chamber 122 again. At this time, the control pressure by the first valve chamber 121 is set higher than the control pressure of the first pressure control chamber 122 based on the relationship of the above-mentioned formula 2. Therefore, the ink in the first pressure control chamber 122 is supplied to the ejection module 300 again via the supply flow path 130 without flowing into the first valve chamber 121. The ink that has flowed into the ejection module 300 flows into the first pressure control chamber 122 again via the recovery flow path 140, the second pressure control chamber 152, the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180. In this manner, the ink circulation that is completed within the liquid ejection head 1 is performed.

[0083] In the above-described ink circulation, the amount of ink circulating (flow rate) in the ejection module 300 is determined by the difference in the control pressure between the first pressure control chamber 122 and the second pressure control chamber 152. This pressure difference is set so as to provide a circulation amount that can suppress thickening of the ink near the ejection port in the ejection module 300. In the circulation unit 54 that is compatible with ink containing titanium oxide, the circulation flow rate Q [mL / min] and the maximum cross-sectional area S [mm 2] is set so that Q / S, which is expressed by the formula [1], is greater than the settling velocity of titanium oxide. In addition, the ink consumed by recording is supplied from the ink tank 2 to the first pressure control chamber 122 via the filter 110 and the first valve chamber 121. The mechanism by which the consumed ink is supplied will be described in detail. By reducing the ink from the circulation path by the amount of ink consumed by recording, the pressure in the first pressure control chamber is reduced, and as a result, the ink in the first pressure control chamber 122 is also reduced. As the ink in the first pressure control chamber 122 is reduced, the internal volume of the first pressure control chamber 122 is reduced. Due to this reduction in the internal volume of the first pressure control chamber 122, the communication port 191A is opened, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. A pressure loss occurs in the supplied ink when it passes from the first valve chamber 121 to the communication port 191A, and the ink flows into the first pressure control chamber 122, switching the positive pressure ink to a negative pressure state. Then, as ink flows into the first pressure control chamber 122 from the first valve chamber 121, the pressure in the first pressure control chamber increases, increasing the internal volume of the first pressure control chamber and closing the communication port 191A. In this way, the communication port 191A alternates between an open state and a closed state depending on the consumption of ink. Furthermore, when ink is not consumed, the communication port 191A is maintained in a closed state.

[0084] FIG. 10B is a schematic diagram showing the flow of ink immediately after the recording operation is completed and the circulation pump 500 is turned off (stopped). When the recording operation is completed and the circulation pump 500 is turned off, the pressures of the first pressure control chamber 122 and the second pressure control chamber 152 are both at the control pressure during the recording operation. Therefore, the ink moves as shown in FIG. 10B according to the pressure difference between the pressures of the first pressure control chamber 122 and the second pressure control chamber 152. Specifically, the ink continues to flow from the first pressure control chamber 122 to the ejection module 300 via the supply flow path 130, and then to the second pressure control chamber 152 via the recovery flow path 140. The ink also continues to flow from the first pressure control chamber 122 to the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151.

[0085] The amount of ink that has moved from the first pressure control chamber 122 to the second pressure control chamber 152 by these ink flows is supplied to the first pressure control chamber 122 from the ink tank 2 via the filter 110 and the first valve chamber 121. Therefore, the content volume in the first pressure control chamber 122 is kept constant. From the relationship of the above-mentioned formula 2, when the content volume in the first pressure control chamber 122 is constant, the spring force F1 of the valve spring 200, the spring force F2 of the pressure adjustment spring 220, the pressure receiving area S1 of the valve 190, and the pressure receiving area S2 of the pressure plate 210 are kept constant. Therefore, the pressure in the first pressure control chamber 122 is determined according to the change in the pressure (gauge pressure) P1 in the first valve chamber 121. Therefore, when there is no change in the pressure P1 in the first valve chamber 121, the pressure P2 in the first pressure control chamber 122 is kept at the same pressure as the control pressure during the recording operation.

[0086] On the other hand, the pressure of the second pressure control chamber 152 changes over time according to the change in the content volume caused by the inflow of ink from the first pressure control chamber 122. Specifically, from the state of FIG. 10(b) until the communication port 191 is closed and the second valve chamber 151 and the second pressure control chamber 152 are not in communication with each other as shown in FIG. 10(c), the pressure of the second pressure control chamber 152 changes according to the formula 2. Thereafter, the pressure plate 210 and the valve shaft 190a are not in contact with each other and the communication port 191 is closed. Then, as shown in FIG. 10(d), ink flows from the recovery passage 140 into the second pressure control chamber 152. This ink inflow displaces the pressure plate 210 and the flexible member 230, and the pressure of the second pressure control chamber 152 changes according to the formula 4 until the internal volume of the second pressure control chamber 152 reaches its maximum. That is, it rises.

[0087] 10(c), no ink flows from the first pressure control chamber 122 to the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151. Therefore, after the ink in the first pressure control chamber 122 is supplied to the ejection module 300 via the supply flow path 130, only a flow occurs to reach the second pressure control chamber 152 via the recovery flow path 140. As described above, the movement of ink from the first pressure control chamber 122 to the second pressure control chamber 152 occurs according to the pressure difference between the pressure in the first pressure control chamber 122 and the pressure in the second pressure control chamber 152. Therefore, when the pressure in the second pressure control chamber 152 becomes equal to the pressure in the first pressure control chamber 122, the movement of ink stops.

[0088] In addition, in a state where the pressure in the second pressure control chamber 152 is equal to the pressure in the first pressure control chamber 122, the second pressure control chamber 152 expands to a state shown in FIG. 10(d). When the second pressure control chamber 152 expands as shown in FIG. 10(d), a storage portion capable of storing ink is formed in the second pressure control chamber 152. Note that the time from when the circulation pump 500 is stopped to when the state shown in FIG. 10(d) is transitioned to is about 1 to 2 minutes, although this time may vary depending on the shape and size of the flow path and the properties of the ink. When the circulation pump 500 is driven from the state shown in FIG. 10(d) where ink is stored in the storage portion, the ink in the storage portion is supplied to the first pressure control chamber 122 by the circulation pump 500. As a result, the amount of ink in the first pressure control chamber 122 increases as shown in FIG. 10(e), and the flexible member 230 and the pressure plate 210 are displaced in the expansion direction. Then, when the circulation pump 500 continues to be driven, the state inside the circulation path changes as shown in FIG. 10(a).

[0089] 10(a) is an example of the ink circulation during the printing operation, but as described above, the ink may be circulated without the printing operation. Even in this case, the ink flows as shown in FIGS. 10(a) to 10(e) according to the driving and stopping of the circulation pump 500.

[0090] Here, if the circulation pump 500 is stopped for a long period of time (for example, when the power supply to the main body is turned off), it is considered that the titanium oxide particles in the ink will not be redispersed and will settle. In addition, it is considered that the ink concentration will increase or the ink will become thicker due to the ink evaporation from the discharge port 13, and the negative pressure inside the head will decrease due to the air penetrating the liquid discharge head housing. If the recording operation is performed in this state, the quality of the recorded image may decrease. Therefore, it is preferable to perform a suction and discharge process in which the ink in the discharge port is refreshed and the ink discharge performance is maintained and restored by sucking and discharging the thickened ink and air bubbles together with the ink from the discharge port 13 of the liquid discharge head 1 using the above-mentioned cap member or the like. This suction and discharge process sucks and discharges the settled ink, thereby eliminating the settling in the liquid discharge head.

[0091] As described above, the first pressure adjustment means 120 and the second pressure adjustment means 150 in this embodiment have a configuration in which the flexible member 230 and the pressure plate 210 are displaced by receiving the pressure inside the liquid ejection head 1. In terms of negative pressure design, a pressure receiving area with a certain degree of width is necessary, and accordingly, the volumes of the first pressure control chamber 122 and the second pressure control chamber 152 are larger than other parts in the circulation path, and are parts of the liquid ejection head where ink is likely to settle. In this case, it is considered that the settled ink (titanium oxide particles) inhibits the displacement of the flexible member 230 and the pressure plate 210, making it impossible to maintain an appropriate negative pressure.

[0092] Therefore, it is preferable that the portions (250, 260, 280, 240, and 270 in FIG. 10) in which the pressure control chambers (first pressure control chamber 122 and second pressure control chamber 152) communicate with other flow paths in the circulation path are disposed vertically below the pressure control chambers. This makes it possible to effectively discharge the settled ink in the pressure control chambers to the outside of the liquid ejection head during the suction and discharge process. The ink is sucked from the ejection port 13 by the suction and discharge process, and an ink flow toward the ejection port 13 is generated in the supply flow path 130 and the recovery flow path 140. The ink in the pressure control chambers is discharged from the ejection port 13 through the supply flow path 130 and the recovery flow path 140. That is, it is preferable to dispose the portion (hole) communicating with the supply flow path 130 or the recovery flow path 140 at a position in the pressure control chamber of the pressure control means where the ink is likely to settle, and this makes it possible for the settled ink to easily flow into the supply flow path 130 or the recovery flow path 140 and be sucked and discharged from the ejection port 13. In FIG. 10, the connection portion 250 of the first pressure control chamber 122 with the supply passage 130 and the connection portion 270 of the second pressure control chamber 152 with the recovery passage 140 are both located vertically below their respective pressure control chambers (the first pressure control chamber and the second pressure control chamber).

[0093] Furthermore, a connection portion 260 between the first pressure control chamber 122 and the bypass flow path 160, and a connection portion 280 between the first pressure control chamber 122 and the pump outlet flow path 180 are also disposed vertically below the first pressure control chamber 122, and a connection portion 240 between the second pressure control chamber 152 and the pump inlet flow path 170 is also disposed vertically below the second pressure control chamber 152. This is preferable because it is possible to eliminate bag-shaped stagnation regions in the pressure control chambers in the circulation path, which can cause ink to settle and make it difficult to circulate, and which become blind spots in the circulation flow.

[0094] In the above description, "vertically below the pressure control chamber" means within half the length of the pressure control chamber from below in the vertical direction, when the liquid ejection head is in the position during recording, and more preferably within ¼ of the length of the pressure control chamber from below in the vertical direction.

[0095] Furthermore, it is more preferable that the flow paths in the discharge unit 3 have a structure that makes it easy to discharge ink that has settled in the circulation path from the discharge port 13 to the outside, and it is preferable that the wall surfaces of the flow paths 301 and 302 are perpendicular or inclined to the vertical direction at the connection portion between the circulation unit 54 and the discharge unit 3. That is, it is more preferable that the wall surfaces of the flow paths in the discharge unit 54 that are in fluid communication with the circulation unit 54 are perpendicular or inclined to the vertical direction at the portion where the discharge unit 3 and the circulation unit 54 are fluidly connected to each other. This makes it possible to obtain an effect that the ink components that have settled in the circulation unit 54 are drawn into the supply flow path 130 or the recovery flow path 140 at the connection portions between the supply port 88 and the support member supply port 211, and between the recovery port 89 and the support member supply port 212, and are easily discharged from the discharge port 13. Fig. 22 is a cross-sectional view of another example of the liquid ejection head 1, where Fig. 22(a) is a cross-sectional view showing a connection portion between the circulation unit 54 and the ejection unit 3 on the liquid supply side, and Fig. 22(b) is a cross-sectional view showing a connection portion between the circulation unit 54 and the ejection unit 3 on the liquid recovery side. Fig. 22 shows a configuration in which the wall surfaces of the flow paths 301 and 302 at the connection portion between the circulation unit 54 and the ejection unit 3 are perpendicular or inclined with respect to the vertical direction.

[0096] As described above, in this embodiment, the communication port 191B in the second pressure adjustment means 150 is in an open state when the circulation pump 500 is driven to circulate the ink, and is in a closed state when the circulation of the ink stops, but this is not limited to the above example. The control pressure may be set so that the communication port 191B in the second pressure adjustment means 150 is in a closed state even when the circulation pump 500 is driven to circulate the ink. Hereinafter, the role of the bypass flow path 160 will be specifically described.

[0097] The bypass flow path 160 connecting the first pressure adjustment means 120 and the second pressure adjustment means 150 is provided to prevent the negative pressure generated in the circulation path from being affected by the discharge module 300 when the negative pressure exceeds a predetermined value. The bypass flow path 160 is also provided to supply ink to the pressure chamber 12 from both sides of the supply flow path 130 and the recovery flow path 140.

[0098] First, an example will be described in which the bypass flow path 160 is provided to prevent the negative pressure from being influenced by the discharge module 300 when the negative pressure becomes stronger than a preset value. For example, the ink characteristics (e.g., viscosity) may change due to a change in the environmental temperature. When the ink viscosity changes, the pressure loss in the circulation path also changes. For example, when the ink viscosity decreases, the pressure loss in the circulation path decreases. As a result, the flow rate of the circulation pump 500 driven at a constant drive amount increases, and the flow rate through the discharge module 300 increases. On the other hand, since the discharge module 300 is kept at a constant temperature by a temperature adjustment mechanism (not shown), the viscosity of the ink in the discharge module 300 is maintained constant even if the environmental temperature changes. While the viscosity of the ink in the discharge module 300 does not change, the flow rate of the ink flowing through the discharge module 300 increases, and the negative pressure in the discharge module 300 is strengthened due to flow resistance. In this way, if the negative pressure in the discharge module 300 becomes stronger than the default value, the meniscus of the discharge port 13 may be destroyed, and external air may be drawn into the circulation path, preventing normal discharge. Even if the meniscus is not destroyed, the negative pressure in the pressure chamber 12 may become stronger than the default value, affecting discharge.

[0099] For this reason, in this embodiment, the bypass flow path 160 is formed in the circulation path. By providing the bypass flow path 160, when the negative pressure becomes stronger than a preset value, ink also flows through the bypass flow path 160, so that the pressure of the ejection module 300 can be kept constant. Therefore, for example, the communication port 191B in the second pressure adjustment means 150 may be configured with a control pressure that maintains the closed state even when the circulation pump 500 is being driven. Then, the control pressure in the second pressure adjustment means may be set so that the communication port 191 in the second pressure adjustment means 150 is in an open state when the negative pressure becomes stronger than a preset value. In other words, if the meniscus does not collapse even when the flow rate of the pump is changed due to a viscosity change such as an environmental change, or if a predetermined negative pressure is maintained, the communication port 191B may be in a closed state when the circulation pump 500 is driven.

[0100] Next, an example will be described in which the bypass flow path 160 is provided to supply ink to the pressure chamber 12 from both the supply flow path 130 and the recovery flow path 140. Pressure fluctuations in the circulation path can also be caused by the ejection operation of the ejection element 15. This is because a force that draws ink into the pressure chamber is generated by the ejection operation.

[0101] Hereinafter, it will be explained that when high duty recording is continued, the ink supplied to the pressure chamber 12 is supplied to both the supply flow path 130 side and the recovery flow path 140 side. Note that the definition of duty can change depending on various conditions, but here, the state in which one 4pl ink droplet is recorded on a 1200dpi grid is treated as 100%. High duty recording is, for example, recording performed at a duty of 100%.

[0102] If recording at a high duty continues, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow path 140 decreases. On the other hand, since the circulation pump 500 causes a constant amount of ink to flow out, the balance between the inflow and outflow in the second pressure control chamber 152 is lost, the ink in the second pressure control chamber 152 decreases, the negative pressure in the second pressure control chamber 152 becomes stronger, and the second pressure control chamber 152 shrinks. Then, as the negative pressure in the second pressure control chamber 152 becomes stronger, the inflow amount of ink flowing into the second pressure control chamber 152 through the bypass flow path 160 increases, and the second pressure control chamber 152 becomes stable with the outflow and inflow balanced. As a result, the negative pressure in the second pressure control chamber 152 becomes stronger according to the duty. Furthermore, as described above, when the circulation pump 500 is driven, in a configuration in which the communication port 191B is in a closed state, the communication port 191B opens depending on the duty, and ink flows from the bypass flow path 160 into the second pressure control chamber 152.

[0103] Then, when recording at an even higher duty is continued, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow passage 140 decreases, and instead the amount of ink flowing into the second pressure control chamber 152 from the communication port 191B via the bypass flow passage 160 increases. If this state progresses further, the amount of ink flowing from the pressure chamber 12 into the second pressure control chamber 152 through the recovery flow passage 140 becomes zero, and all ink flowing out to the circulation pump 500 becomes ink flowing in from the communication port 191B. If this state progresses further, ink now flows back from the second pressure control chamber 152 into the pressure chamber 12 through the recovery flow passage 140. In this state, the ink flowing out from the second pressure control chamber 152 to the circulation pump 500 and the ink flowing out to the pressure chamber 12 flow into the second pressure control chamber 152 from the communication port 191B through the bypass flow passage 160. In this case, the pressure chamber 12 is filled with ink from the supply flow passage 130 and ink from the recovery flow passage 140, and is ejected.

[0104] Incidentally, this backflow of ink occurring when the printing duty is high is a phenomenon that occurs due to the provision of the bypass flow path 160. Also, in the above, an example has been described in which the communication port 191B in the second pressure adjustment means is opened in response to the backflow of ink, but backflow of ink may also occur when the communication port 191B in the second pressure adjustment means is in an open state. Also, even in a configuration that does not include a second pressure adjustment means, the provision of the bypass flow path 160 may cause the above-mentioned backflow of ink.

[0105] <Configuration of the discharge unit> FIG. 11 is a schematic diagram showing a circulation path for one color of ink in the discharge unit 3 of this embodiment. FIG. 11(a) is an exploded perspective view of the discharge unit 3 seen from the first support member 4 side, and FIG. 11(b) is an exploded perspective view of the discharge unit 3 seen from the discharge module 300 side. Note that the arrows indicated by IN and OUT in the figure indicate the flow of ink, and the flow of ink for only one color will be described, but the other colors flow in the same manner. Also, in FIG. 11, the second support member 7 and the electric wiring member 5 are omitted, and are also omitted in the following description of the configuration of the discharge unit. Also, the first support member 4 in FIG. 11(a) shows a cross section taken along line XI-XI in FIG. 3. The discharge module 300 includes a discharge element substrate 340 and an aperture plate 330. FIG. 12 is a diagram showing the aperture plate 330, and FIG. 13 is a diagram showing the discharge element substrate 340.

[0106] Ink is supplied to the discharge unit 3 from the circulation unit 54 via a joint member 8 (see FIG. 3). The ink path from when the ink passes through the joint member 8 until when the ink returns to the joint member 8 will be described. Note that the joint member 8 will be omitted from the following drawings.

[0107] The ejection module 300 includes an ejection element substrate 340, which is a silicon substrate 310, and an aperture plate 330, and further includes an ejection port forming member 320. The ejection element substrate 340, the aperture plate 330, and the ejection port forming member 320 are overlapped and joined together so that the ink flow paths communicate with each other to form the ejection module 300, which is supported by a first support member 4. The ejection module 300 is supported by the first support member 4 to form an ejection unit 3. The ejection element substrate 340 includes an ejection port forming member 320, which includes a plurality of ejection port rows in which a plurality of ejection ports 13 are arranged in a row, and ejects a portion of the ink supplied through the ink flow path in the ejection module 300 from the ejection port 13. Ink that is not ejected is collected through the ink flow path in the ejection module 300.

[0108] As shown in Figs. 11 and 12, the opening plate 330 has a plurality of arranged ink supply ports 311 and a plurality of arranged ink recovery ports 312. As shown in Figs. 13 and 14, the ejection element substrate 340 has a plurality of arranged supply connection channels 323 and a plurality of arranged recovery connection channels 324. The ejection element substrate 340 further has a common supply channel 18 communicating with the plurality of supply connection channels 323 and a common recovery channel 19 communicating with the plurality of recovery connection channels 324. The ink flow channels in the ejection unit 3 are formed by communicating an ink supply channel 48 and an ink recovery channel 49 (see Fig. 3) provided in the first support member 4 with a flow channel provided in the ejection module 300. The support member supply port 211 is a cross-sectional opening that forms the ink supply channel 48, and the support member recovery port 212 is a cross-sectional opening that forms the ink recovery channel 49.

[0109] Ink supplied to the ejection unit 3 is supplied from the circulation unit 54 (see FIG. 3(a)) side to the ink supply flow path 48 (see FIG. 3(a)) of the first support member 4. The ink flowing through the support member supply port 211 in the ink supply flow path 48 is supplied to the common supply flow path 18 of the ejection element substrate 340 via the ink supply flow path 48 (see FIG. 3(a)) and the ink supply port 311 of the opening plate 330, and enters the supply connection flow path 323. This is the supply side flow path. After that, the ink flows through the pressure chamber 12 (see FIG. 3(b)) of the ejection port forming member 320 to the recovery connection flow path 324 of the recovery side flow path. The flow of ink in the pressure chamber 12 will be described in detail later.

[0110] In the recovery side flow path, the ink that has entered the recovery connection flow path 324 flows into the common recovery flow path 19. Thereafter, the ink flows from the common recovery flow path 19 through the ink recovery port 312 of the opening plate 330 to the ink recovery flow path 49 of the first support member 4, and then through the support member recovery port 212 to be recovered in the circulation unit 54.

[0111] The area of ​​the opening plate 330 without the ink supply port 311 or the ink recovery port 312 corresponds to the area for separating the support member supply port 211 and the support member recovery port 212 in the first support member 4. Moreover, this area does not have an opening in the first support member 4 either. Such an area is used as an adhesion area when the ejection module 300 and the first support member 4 are adhered to each other.

[0112] In FIG. 12, the aperture plate 330 has a plurality of rows of apertures arranged in the X direction, and the supply (IN) apertures and the recovery (OUT) apertures are arranged alternately in the Y direction so as to be shifted by half a pitch in the X direction. In FIG. 13, the ejection element substrate 340 has a common supply flow path 18 communicating with a plurality of supply connection flow paths 323 arranged in the Y direction, and a common recovery flow path 19 communicating with a plurality of recovery connection flow paths 324 arranged in the Y direction, arranged alternately in the X direction. The common supply flow paths 18 and the common recovery flow path 19 are separated for each type of ink, and the number of common supply flow paths 18 and common recovery flow paths 19 is determined according to the number of ejection port rows of each color. In addition, the supply connection flow paths 323 and the recovery connection flow paths 324 are also arranged in the number corresponding to the ejection ports 13. It is not necessarily required that there is a one-to-one correspondence, and one supply connection flow path 323 and one recovery connection flow path 324 may correspond to a plurality of ejection ports 13.

[0113] Such an opening plate 330 and an ejection element substrate 340 are overlapped and joined so that the flow paths of each ink are connected to form an ejection module 300, and by being supported by the first support member 4, an ink flow path having a supply flow path and a recovery flow path as described above is formed.

[0114] Fig. 14(a) to (c) are cross-sectional views showing ink flows in different parts of the discharge unit 3. Fig. 14(a) is a cross-section shown by XIVa-XIVa in Fig. 11(a) and shows a cross-section of a part where the ink supply flow path 48 and the ink supply port 311 in the discharge unit 3 communicate with each other. Fig. 14(b) is a cross-section shown by XIVb-XIVb in Fig. 11(a) and shows a cross-section of a part where the ink recovery flow path 49 and the ink recovery port 312 in the discharge unit 3 communicate with each other. Fig. 14(c) is a cross-section shown by XIVc-XIVc in Fig. 11(a) and shows a cross-section of a part where the ink supply port 311 and the ink recovery port 312 do not communicate with the flow path of the first support member 4.

[0115] In the supply flow path for supplying ink, as shown in FIG. 14(a), ink is supplied from a portion where the ink supply flow path 48 of the first support member 4 and the ink supply port 311 of the opening plate 330 overlap and communicate with each other. In the recovery flow path for recovering ink, as shown in FIG. 14(b), ink is recovered from a portion where the ink recovery flow path 49 of the first support member 4 and the ink recovery port 312 of the opening plate 330 overlap and communicate with each other. In addition, as shown in FIG. 14(c), in the ejection unit 3, there is also a region where the opening plate 330 does not have an opening. In such a region, ink is not supplied or recovered between the ejection element substrate 340 and the first support member 4. As shown in FIG. 14(a), ink is supplied in a region where the ink supply port 311 is provided, and as shown in FIG. 14(b), ink is recovered in a region where the ink recovery port 312 is provided. In the present embodiment, the configuration using the opening plate 330 has been described as an example, but a configuration without using the opening plate 330 may be used. For example, a configuration may be used in which flow paths corresponding to the ink supply flow path 48 and the ink recovery flow path 49 are formed in the first support member 4, and the ejection element substrate 340 is joined to the first support member 4.

[0116] 15(a) and (b) are cross-sectional views showing the vicinity of the ejection port 13 in the ejection module 300, and FIG. 16 is a cross-sectional view showing an ejection module having a configuration in which the common supply flow path 18 and the common recovery flow path 19 are expanded in the X direction as a comparative example. Note that the thick arrows shown in the common supply flow path 18 and the common recovery flow path 19 in FIG. 15 and FIG. 16 indicate the oscillation of ink in a configuration in which a serial type liquid ejection device 50 is used. The ink supplied to the pressure chamber 12 via the common supply flow path 18 and the supply connection flow path 323 is ejected from the ejection port 13 by driving the ejection element 15. When the ejection element 15 is not driven, the ink is recovered from the pressure chamber 12 to the common recovery flow path 19 via the recovery connection flow path 324, which is a recovery flow path.

[0117] In the case of using the serial type liquid ejection device 50, when ejecting ink from the circulating ink, the ejection of the ink is influenced by the ink oscillation in the ink flow path caused by the main scanning of the liquid ejection head 1. Specifically, the influence of the ink oscillation in the ink flow path may appear as a difference in the amount of ink ejected or a deviation in the ejection direction. As shown in FIG. 16, when the common supply flow path 18 and the common recovery flow path 19 have a cross-sectional shape that is wide in the X direction, which is the main scanning direction, the ink in the common supply flow path 18 and the common recovery flow path 19 is easily subjected to an inertial force in the main scanning direction, and the ink is greatly oscillated. As a result, there is a risk that the ink oscillation will affect the ejection of the ink from the ejection port 13. In addition, if the common supply flow path 18 and the common recovery flow path 19 are widened in the X direction, the distance between the colors will be increased, which may reduce the printing efficiency.

[0118] Therefore, the common supply flow path 18 and the common recovery flow path 19 of this embodiment extend in the Y direction in the cross section shown in FIG. 15, but are also configured to extend in the Z direction perpendicular to the X direction, which is the main scanning direction. With this configuration, the width of each flow path in the main scanning direction of the common supply flow path 18 and the common recovery flow path 19 can be reduced. By reducing the width of each flow path in the main scanning direction of the common supply flow path 18 and the common recovery flow path 19, the ink oscillation caused by the inertial force (indicated by the thick black arrow in the figure) acting on the ink in the common supply flow path 18 and the common recovery flow path 19 in the opposite direction to the main scanning direction during the main scanning is reduced. This makes it possible to suppress the effect of the ink oscillation on the ink ejection. In addition, the cross-sectional area is increased by extending the common supply flow path 18 and the common recovery flow path 19 in the Z direction, thereby reducing the flow path pressure loss.

[0119] As described above, by reducing the width of each of the common supply flow path 18 and the common recovery flow path 19 in the main scanning direction, the oscillation of ink in the common supply flow path 18 and the common recovery flow path 19 during main scanning is reduced, but the oscillation is not eliminated. Therefore, in order to suppress the occurrence of differences in ejection for each ink type that may still occur even with the reduced oscillation, in this embodiment, the common supply flow path 18 and the common recovery flow path 19 are configured to be disposed at positions that overlap with each other in the X direction.

[0120] As described above, in this embodiment, the supply connection flow path 323 and the recovery connection flow path 324 are provided corresponding to the ejection port 13, and the supply connection flow path 323 and the recovery connection flow path 324 are arranged side by side in the X direction with the ejection port 13 in between. Therefore, there are portions where the common supply flow path 18 and the common recovery flow path 19 do not overlap in the X direction, and if the corresponding relationship in the X direction between the supply connection flow path 323 and the recovery connection flow path 324 is lost, it will affect the flow and ejection of ink in the X direction in the pressure chamber 12. If the influence of ink fluctuation is added to this, it may further affect the ejection of ink from each ejection port.

[0121] Therefore, by arranging the common supply flow path 18 and the common recovery flow path 19 at positions where they overlap in the X direction, the ink oscillation during main scanning in the common supply flow path 18 and the common recovery flow path 19 becomes approximately equal at any position in the Y direction where the ejection ports 13 are arranged. As a result, the pressure difference between the common supply flow path 18 side and the common recovery flow path 19 side generated in the pressure chamber 12 does not vary greatly, and stable ejection can be performed.

[0122] In addition, in some liquid ejection heads that circulate ink, the flow path that supplies ink to the liquid ejection head and the flow path that recovers ink are configured as the same flow path, but in this embodiment, the common supply flow path 18 and the common recovery flow path 19 are configured as separate flow paths. The supply connection flow path 323 and the pressure chamber 12 are connected to each other, and the pressure chamber 12 and the recovery connection flow path 324 are connected to each other, and ink is ejected from the ejection port 13 of the pressure chamber 12. In other words, the pressure chamber 12, which is a path that connects the supply connection flow path 323 and the recovery connection flow path 324, is configured to have the ejection port 13. Therefore, an ink flow that flows from the supply connection flow path 323 side to the recovery connection flow path 324 side is generated in the pressure chamber 12, and the ink in the pressure chamber 12 is efficiently circulated. By efficiently circulating the ink in the pressure chamber 12, the ink in the pressure chamber 12, which is easily affected by the evaporation of ink from the ejection port 13, can be kept fresh.

[0123] Furthermore, since the two flow paths, the common supply flow path 18 and the common recovery flow path 19, are connected to the pressure chamber 12, if it becomes necessary to eject ink at a high flow rate, it is possible to supply ink from both flow paths. In other words, compared to a configuration in which ink supply and recovery are configured using only one flow path, the configuration of this embodiment has the advantage of not only being able to circulate ink efficiently, but also being able to handle ejection at a high flow rate.

[0124] Furthermore, the common supply flow path 18 and the common recovery flow path 19 are less susceptible to the influence of ink fluctuations when they are disposed close to each other in the X direction. It is preferable that the distance between the flow paths is 75 μm to 100 μm.

[0125] Fig. 17 is a diagram showing an ejection element substrate 340 as a comparative example. Note that in Fig. 17, the supply connection flow path 323 and the recovery connection flow path 324 are omitted. Since ink that has received thermal energy from the ejection elements 15 in the pressure chambers 12 flows into the common recovery flow path 19, ink with a relatively high temperature flows compared to the temperature of the ink in the common supply flow path 18. At this time, in the comparative example, there is a portion in the X direction of the ejection element substrate 340 where only the common recovery flow path 19 exists, such as the α portion surrounded by the dashed line in Fig. 17. In this case, the temperature locally increases in that portion, causing temperature unevenness in the ejection module 300, which may affect ejection.

[0126] In the common supply flow path 18, ink flows that is at a relatively low temperature relative to the common recovery flow path 19. Therefore, when the common supply flow path 18 and the common recovery flow path 19 are adjacent to each other, the temperatures in the common supply flow path 18 and the common recovery flow path 19 are partially offset in the vicinity thereof, suppressing a rise in temperature. Therefore, it is preferable that the common supply flow path 18 and the common recovery flow path 19 are adjacent to each other and have approximately the same length, and are positioned so as to overlap each other in the X direction.

[0127] 18(a) and (b) are diagrams showing the flow path configuration of a liquid ejection head 1 compatible with three types of ink. As shown in FIG. 18(a), the liquid ejection head 1 is provided with a circulation flow path for each type of ink. The pressure chambers 12 are provided along the X direction, which is the main scanning direction of the liquid ejection head 1. As shown in FIG. 18(b), the common supply flow path 18 and the common recovery flow path 19 are provided along the ejection port row in which the ejection ports 13 are arranged, and extend in the Y direction so as to sandwich the ejection port row between the common supply flow path 18 and the common recovery flow path 19.

[0128] <Connection between the main body and the liquid ejection head> 19 is a schematic diagram showing in more detail the connection state between the ink tank 2 and external pump 21 provided in the main body of the liquid ejection device 50 of this embodiment and the liquid ejection head 1, and the arrangement of the circulation pump, etc. The liquid ejection device 50 of this embodiment is configured so that when a problem occurs in the liquid ejection head 1, only the liquid ejection head 1 can be easily replaced. Specifically, it has a liquid connection part 700 that can easily connect and disconnect the ink supply tube 59 connected to the external pump 21 and the liquid ejection head 1. This makes it possible to easily attach and detach only the liquid ejection head 1 to and from the liquid ejection device 50.

[0129] 19, the liquid connection part 700 has a liquid connector insertion port 53a protruding from the head housing 53 of the liquid ejection head 1, and a cylindrical liquid connector 59a into which the liquid connector insertion port 53a can be inserted. The liquid connector insertion port 53a is fluidly connected to an ink supply flow path (inflow flow path) formed in the liquid ejection head 1, and is connected to the first pressure adjustment means 120 via the above-mentioned filter 110. In addition, the liquid connector 59a is provided at the tip of an ink supply tube 59 connected to an external pump 21 that pressurizes and supplies ink from the ink tank 2 to the liquid ejection head 1.

[0130] 19, the liquid ejection head 1 can be easily attached, detached, and replaced by the liquid connection part 700. However, if the sealing performance between the liquid connector insertion port 53a and the liquid connector 59a is reduced, there is a risk that ink supplied under pressure by the external pump 21 will leak from the liquid connection part 700. If the leaked ink adheres to the circulation pump 500 or the like, a malfunction may occur in the electrical system. Therefore, in this embodiment, the circulation pump and the like are arranged as follows.

[0131] <Location of circulating pumps, etc.> As shown in FIG. 19, in this embodiment, in order to prevent ink leaking from the liquid connection part 700 from adhering to the circulation pump 500, the circulation pump 500 is disposed above the liquid connection part 700 in the direction of gravity. In other words, the circulation pump 500 is disposed above the liquid connector insertion port 53a, which is the liquid inlet port of the liquid ejection head 1, in the direction of gravity. Furthermore, the circulation pump 500 is disposed at a position where it is not in contact with the members constituting the liquid connection part 700. As a result, even if ink leaks from the liquid connection part 700, the ink flows in the horizontal direction, which is the opening direction of the liquid connector 59a, or downward in the direction of gravity, so that it is possible to prevent the ink from reaching the circulation pump 500, which is located above in the direction of gravity. In addition, since the circulation pump 500 is disposed at a position away from the liquid connection part 700, the possibility that the ink will reach the circulation pump 500 by running down the members is also reduced.

[0132] Furthermore, the electrical connection part 515, which electrically connects the circulation pump 500 and the electrical contact board 6 via a flexible wiring member 514, is provided above the liquid connection part 700 in the direction of gravity. This makes it possible to reduce the possibility of electrical trouble caused by ink from the liquid connection part 700.

[0133] Furthermore, in this embodiment, since the wall portion 52b of the head housing 53 is provided, even if ink is ejected from the opening 59b of the liquid connection portion 700, the ink can be blocked, reducing the possibility of the ink reaching the circulation pump 500 or the electrical connection portion 515.

[0134] 20 shows the ink circulation system of this embodiment. In this embodiment, ink is pressurized and supplied from the ink tank 2 to the liquid ejection head 1 via the liquid connection part 700 using an external pump 21. The external pump 21 draws ink from the ink tank 2 and pressurizes and supplies the ink to the liquid ejection head 1.

[0135] A flow path 591 is provided between the external pump 21 and the liquid connection part 700 so as to run parallel to the ink supply tube 59. A second external pump 22 is provided in the flow path 591, and the ink is configured to circulate in a range including the downstream of the external pump (first external pump) 21 to the carriage 60. This makes it possible to agitate the ink in flow paths other than the liquid ejection head 1 of the liquid ejection device 50.

[0136] Here, an ink circulation system of a comparative example is shown in FIG. 21. First, ink is sent from the ink tank 2 to the sub tank 25 by using the external pump 21. After that, the ink is circulated (agitated) between the sub tank 25 and the liquid ejection head 1 and the entire flow path between them by the supply pump 23 and the recovery pump 24. In this case, since it is necessary to move the ink from the sub tank 25 to the liquid ejection head 1 and throughout the entire liquid ejection device 50, the supply pump 23 and the recovery pump 24 require a relatively higher capacity than the pump of this embodiment. In addition, since two types of connection parts, a liquid connection part 700a for supply and a liquid connection part 700b for discharge, are required for the liquid ejection head 1, the size of the liquid ejection head 1 tends to be large. Furthermore, since the recovery pump 24 and the ejection unit 3 are directly fluidically connected, the pulsation of the recovery pump 24 is easily transmitted to the ejection unit 3, which may cause a deterioration in the quality of the recorded image. In addition, in the serial type liquid ejection head 1, since both the ink supply tube 59 and the ink recovery tube 591 oscillate due to scanning, the pressure change due to the oscillation of the ink recovery tube is easily transmitted to the liquid ejection unit 3, which may cause a deterioration in the quality of the recorded image. The effect of the present invention can be sufficiently obtained even in an ink circulation system and an ink ejection method using a liquid ejection device that does not have the flow path 591 and the second external pump 22 shown in FIG. 20. Also, the flow path 591 and the second external pump 22 may be applied only to the ink circulation system for the ink containing titanium oxide. In this case, it is possible to suppress an excessive increase in the manufacturing cost of the device and an increase in the size of the device while obtaining a better effect of suppressing the settling of the ink containing titanium oxide. Also, the total volume of the ink flowing in one circulation path including the circulation pump 500 in the liquid ejection head 1 is preferably 30 mL or less, more preferably 15 mL or less. Also, it is preferably 5 mL or more. That is, the volume of the liquid flowing in the circulation path is preferably 5 mL or more and 30 mL or less, more preferably 5 mL or more and 15 mL or less.

[0137] As described above, with an ink circulation system as shown in FIG. 20, it is possible to realize both a compact liquid ejection device and an improvement in the quality of the recorded image.

[0138] (2) Ink Hereinafter, the ink that can be used in the inkjet recording method of the present invention will be described in detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing salt". Titanium oxide and titanium oxide particles may be simply referred to as "pigment". In addition, water-based ink for inkjet may be simply referred to as "ink". Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. In addition, when recording an image with white ink, white ink may be used as a base treatment for color ink. In that case, color ink (ink such as black, cyan, magenta, yellow, etc.) may be applied so as to overlap at least a part of the area where the white ink is applied, and an image may be recorded. In addition, it can also be used for back printing in which white ink is applied so as to overlap at least a part of the area where the color ink is applied.

[0139] <Water-based ink and method of manufacturing water-based ink> The ink of the present invention is an ink containing titanium oxide. This ink is preferably a white ink because titanium oxide is a white pigment. However, the present invention can be suitably used for inks other than white as long as they contain titanium oxide. In addition, the ink of the present invention does not need to be a so-called "curable ink". Therefore, the ink of the present invention does not need to contain a compound such as a polymerizable monomer that can be polymerized by the addition of external energy such as heat or light. The components constituting the ink of the present invention, the physical properties of the ink, the production method, etc. will be described in detail below.

[0140] (Colorant) The ink contains titanium oxide as a coloring material (pigment). The titanium oxide may be titanium oxide particles that have been surface-treated with a specific inorganic oxide. In other words, the ink may contain titanium oxide particles that are titanium oxide whose surfaces are coated with a specific inorganic oxide. The content (mass%) of titanium oxide particles in the ink is preferably 0.10% by mass or more and 20.00% by mass or less based on the total mass of the ink. The content (mass%) of titanium oxide particles in the ink is more preferably 1.00% by mass or more and 20.00% by mass or less based on the total mass of the ink. Furthermore, in the present invention, the redispersibility of the ink is improved by the configuration of the liquid ejection device, so that the content (mass%) of titanium oxide particles in the ink is easily increased, and is particularly preferably 5.00% by mass or more and 20.00% by mass or less based on the total mass of the ink.

[0141] Titanium oxide is a white pigment, and has three crystal forms: rutile, anatase, and brookite. Among them, rutile titanium oxide is preferred. Titanium oxide can be industrially produced by the sulfuric acid method and the chlorine method, and the titanium oxide used in the present invention may be produced by either method.

[0142] The volume-based cumulative 50% particle diameter (hereinafter also referred to as the average particle diameter) of the titanium oxide particles is preferably 200 nm or more and 500 nm or less. In particular, the volume-based cumulative 50% particle diameter of the titanium oxide particles is more preferably 200 nm or more and 400 nm or less. The volume-based cumulative 50% particle diameter (D50) of the titanium oxide particles is the diameter of the particle that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in a particle diameter integration curve. The D50 of the titanium oxide particles can be measured under the following conditions, for example: SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: non-spherical, refractive index: 2.60. A particle size analyzer using a dynamic light scattering method can be used as the particle size distribution measuring device. Of course, the measurement conditions are not limited to those described above.

[0143] Titanium oxide that has been surface-treated with alumina and silica may be used. The surface treatment is expected to suppress photocatalytic activity and improve dispersibility. In this specification, "alumina" is a general term for oxides of aluminum such as aluminum oxide. In this specification, "silica" is a general term for silicon dioxide or a substance composed of silicon dioxide. Most of the alumina and silica that coat titanium oxide are present in the form of silicon dioxide and aluminum oxide.

[0144] The ratio (mass%) of titanium oxide in the titanium oxide particles is preferably 90.00% by mass or more based on the total mass of the titanium oxide particles. The ratio (mass%) of titanium oxide in the titanium oxide particles is preferably 98.50% by mass or less based on the total mass of the titanium oxide particles. The ratio (mass%) of alumina in the titanium oxide particles must be 0.50 times or more and 1.00 times or less in mass ratio to the ratio (mass%) of silica. If the mass ratio is less than 0.50 times or more than 1.00 times, the ink ejection stability cannot be obtained. The ratio (mass%) of silica in the titanium oxide particles is preferably 1.00% by mass or more and 4.00% by mass or less based on the total mass of the titanium oxide particles. If the ratio (mass%) of silica is less than 1.00% by mass, the affinity with the compound represented by general formula (1) cannot be obtained sufficiently, and the ink ejection stability may not be obtained sufficiently. If the proportion (mass%) of silica exceeds 4.00% by mass, the amount of the compound represented by general formula (1) adsorbed to the titanium oxide particles cannot be suppressed even if the titanium oxide particles are surface-treated with alumina, and sufficient ink ejection stability may not be obtained. The proportion (mass%) of alumina in the titanium oxide particles is preferably 0.50% by mass or more and 4.00% by mass or less based on the total mass of the titanium oxide particles.

[0145] The proportion of alumina and silica in titanium oxide particles, i.e., the amount of alumina and silica coating, can be measured by, for example, quantitative analysis of aluminum and silicon elements by inductively coupled plasma (ICP) emission spectrometry. In this case, it is assumed that all atoms coating the surface are oxides, and the obtained values ​​of aluminum and silicon can be calculated by converting them to their oxides, i.e., alumina and silica. The proportion (mass%) of aluminum element in titanium oxide particles obtained by inductively coupled plasma emission spectrometry is 0.57 times or more and 1.13 times or less in mass ratio to the proportion (mass%) of silicon element. When this value is converted to its oxides, i.e., alumina and silica, the proportion (mass%) of alumina in titanium oxide particles is 0.50 times or more and 1.00 times or less in mass ratio to the proportion (mass%) of silica.

[0146] Surface treatment methods for titanium oxide include wet treatment and dry treatment. For example, titanium oxide can be dispersed in a liquid medium and then reacted with a surface treatment agent such as sodium aluminate or sodium silicate to perform surface treatment, and the desired characteristics can be achieved by appropriately changing the ratio of these surface treatment agents. In addition to alumina and silica, inorganic oxides such as zinc oxide and zirconia, and organic substances such as polyols can also be used for surface treatment, as long as the effects of the present invention are not impaired.

[0147] As long as the effect of the present invention is not impaired, the ink may contain other pigments besides titanium oxide. In this case, the ink may be of a color other than white ink. The content (mass %) of the other pigments in the ink is preferably 0.10 mass % or more and 5.00 mass % or less, and more preferably 0.10 mass % or more and 1.00 mass % or less, based on the total mass of the ink.

[0148] (Compound represented by general formula (1)) The ink preferably contains a compound represented by the following general formula (1) as a dispersant for dispersing titanium oxide particles: The content (mass %) of the compound represented by general formula (1) in the ink is preferably 0.01 mass % or more and 1.00 mass % or less, and more preferably 0.02 mass % or more and 0.50 mass % or less, based on the total mass of the ink.

[0149] [ka]

[0150] (In general formula (1), R1, R2, and R3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Each R4 is independently an alkylene group having 2 to 4 carbon atoms. X is a single bond or an alkylene group having 1 to 6 carbon atoms. n is 6 to 24. a is 1 to 3, b is 0 to 2, and a+b=3.) In the general formula (1), R1, R2, and R3 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and an n-butyl group. Among them, a methyl group is preferable from the viewpoint of ease of hydrolysis. If R1, R2, and R3 are each an alkyl group having more than 4 carbon atoms, it becomes difficult to form a silanol group by hydrolysis, and affinity with titanium oxide particles is not obtained. Therefore, the titanium oxide particles cannot be stably dispersed, and the ink ejection stability is not obtained. a, which represents the number of R1O, is 1 to 3, and b, which represents the number of R2, is 0 to 2, and a+b=3. Among them, it is preferable that a is 3 and b is 0, that is, all three substituents of the silicon atom are R1O.

[0151] In the general formula (1), R4 is independently an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, an n-propylene group, an i-propylene group, and an n-butylene group. Among them, an ethylene group is preferable. The number of OR4, that is, n (average value) representing the number of alkylene oxide groups, is 6 to 24. When n is less than 6, the length of the alkylene oxide chain is too short, so that the repulsive force due to steric hindrance is not sufficiently obtained, and the ink ejection stability is not obtained. When n is more than 24, the length of the alkylene oxide chain is too long, so that the hydrophilicity is increased and the ink is easily liberated in the aqueous medium. Therefore, the affinity with the surface hydroxyl group of the titanium oxide particles is not sufficiently obtained, and the aggregation of the titanium oxide particles cannot be suppressed. Therefore, the titanium oxide particles cannot be stably dispersed, and the ink ejection stability is not obtained.

[0152] In the general formula (1), X is a single bond or an alkylene group having 1 to 6 carbon atoms. When X is a single bond, it means that the silicon atom and OR4 are directly bonded. Examples of the alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, an n-propylene group, an i-propylene group, an n-butylene group, an n-pentylene group, and an n-hexylene group. Of these, an n-propylene group is preferable. When X is an alkylene group having more than 6 carbon atoms, the hydrophobicity of the compound represented by the general formula (1) becomes too high, so that the titanium oxide particles cannot be stably dispersed, and the ink ejection stability cannot be obtained.

[0153] The compound represented by general formula (1), which is a dispersant for titanium oxide particles, is preferably a compound represented by the following general formula (2). The compound represented by general formula (2) has three OR1s bonded to silicon atoms, so that a part of it can be hydrolyzed in an aqueous medium to form three hydroxyl groups bonded to silicon atoms, thereby increasing the portion having affinity with titanium oxide particles. In addition, the compound represented by the following general formula (2) has a repeating structure of ethylene oxide groups. Therefore, the ethylene oxide chains can be appropriately extended in an aqueous medium, and a repulsive force due to steric hindrance can be obtained.

[0154] [ka]

[0155] (In general formula (2), R1 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m is an integer of 8 to 24.) The content (mass%) of the compound represented by general formula (1) in the ink is preferably 0.002 times or more and 0.10 times or less in mass ratio to the content (mass%) of titanium oxide particles. If the mass ratio is less than 0.002 times, the effect of stably dispersing titanium oxide particles is weakened, and the ink ejection stability may not be sufficiently obtained. If the mass ratio is more than 0.10 times, the proportion of the compound represented by general formula (1) becomes too high, and condensation (self-condensation) between molecules of the compound represented by general formula (1) is likely to occur. Therefore, the compound represented by general formula (1) is consumed without acting as a dispersant, and the effect of stably dispersing titanium oxide particles is weakened, and the ink ejection stability may not be sufficiently obtained.

[0156] The compound represented by the general formula (1) forms hydrogen bonds with the surface hydroxyl groups of the titanium oxide particles, but some of them are thought to form covalent bonds through a dehydration reaction. However, in the present invention, the compound represented by the general formula (1) can disperse the titanium oxide particles even if it does not form a covalent bond with the titanium oxide particles. In other words, the amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles is very small and can be ignored. Therefore, the content of the titanium oxide particles does not include the compound represented by the general formula (1) covalently bonded. As a result of the investigation by the present inventors, it was found that if the amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles is too large, the ejection stability of the ink decreases. The reasons for this are considered to be as follows. In general, in a liquid medium with a high dielectric constant such as water, electrostatic attraction is less likely to work, so that the titanium oxide particles move freely without being affected much by the surrounding environment. However, when the compound represented by the general formula (1) forms a covalent bond with the titanium oxide particles, the hydrophilic portion (OR4 portion) of the structure of the general formula (1) forms a hydrogen bond with the water molecules, which may affect the movement of the titanium oxide particles. Therefore, in a situation where the liquid is deformed by instantaneous pressure, such as during inkjet ejection, the above characteristics appear as differences in ejection characteristics. For this reason, the amount (mass%) of the compound represented by general formula (1) covalently bonded to the titanium oxide particles is preferably 0.001 or less in mass ratio to the titanium oxide particle content (mass%). If the mass ratio exceeds 0.001, the ink ejection stability may not be sufficient. The mass ratio may be 0.000. The amount of the compound represented by general formula (1) covalently bonded to the titanium oxide particles can be calculated by thermogravimetric analysis or the like.

[0157] (wax particles) In the present invention, the ink may contain wax particles. The wax may be a composition containing components other than wax, or may be the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a resin.

[0158] In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends thereof (blended waxes), and modified products thereof (modified waxes).

[0159] Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among them, a blend of multiple types of wax is more preferable, and a blend of petroleum wax and synthetic wax is particularly preferable.

[0160] The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or more and 120°C or less, more preferably 50°C or more and 100°C or less. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if it is linear, and the lower the melting point if it is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, a wax having a desired melting point can be obtained.

[0161] (resin) The ink may contain a resin. Examples of the resin include acrylic resin, urethane resin, and urea resin. Of these, acrylic resin is preferred. The content (mass%) of the resin in the ink is preferably 1.00% by mass or more and 25.00% by mass or less, and more preferably 3.00% by mass or more and 15.00% by mass or less, based on the total mass of the ink. Of these, the content of 5.00% by mass or more and 15.00% by mass or less is particularly preferred.

[0162] The resin can be contained in the ink for the purpose of improving various properties of the recorded image, such as abrasion resistance and hiding power. Examples of the form of the resin 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. The resin particles do not need to encapsulate a coloring material.

[0163] In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which it does not form particles whose particle size can be measured by a dynamic light scattering method. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a 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 (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if particles having a particle size are not measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

[0164] The acid value of the water-soluble resin is preferably 80 mgKOH / g or more and 250 mgKOH / g or less, more preferably 100 mgKOH / g or more and 200 mgKOH / g or less. When resin particles are used, the acid value is preferably 0 mgKOH / g or more and 50 mgKOH / g or less. The weight average molecular weight of the resin is preferably 1,000 or more and 30,000 or less, more preferably 5,000 or more and 15,000 or less. The weight average molecular weight of the resin is a value measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0165] (aqueous medium) The ink is an aqueous ink containing water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water (ion-exchanged water). The content (mass %) of water in the ink is preferably 50.00 mass % or more and 95.00 mass % or less based on the total mass of the ink.

[0166] The water-soluble organic solvent is not particularly limited as long as it is water-soluble (preferably, dissolves in water at any ratio at 25°C). Specifically, monohydric or polyhydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, and more preferably 10.00% by mass or more and 40.00% by mass or less, based on the total mass of the ink. If the content (mass%) of the water-soluble organic solvent is less than 3.00% by mass, the ink may be stuck in the inkjet recording device, and sufficient sticking resistance may not be obtained. If the content (mass%) of the water-soluble organic solvent is more than 50.00% by mass, poor ink supply may occur.

[0167] (Other additives) In addition to the above additives, the ink may contain various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, and chelating agents, as necessary. Among these, it is preferable that the ink contains a surfactant. The content (mass%) of the surfactant in the ink is preferably 0.10% by mass or more and 5.00% by mass or less, and more preferably 0.10% by mass or more and 2.00% by mass or less, based on the total mass of the ink. Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferable because they have low affinity with titanium oxide particles and are effective in small amounts, since they are used to adjust various physical properties of the ink.

[0168] (Ink properties) Since the ink is applied to the inkjet method, it is preferable to appropriately control the physical properties of the ink. The surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, and more preferably 20 mN / m or more and 40 mN / m or less. The surface tension of the ink can be adjusted by appropriately determining the type and content of the surfactant in the ink. In addition, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.0 or less. If the pH of the ink is within the above range, the generation of silanol groups due to hydrolysis of the compound represented by general formula (1) proceeds, and the weak affinity between the titanium oxide particles and the compound represented by general formula (1) is effectively exerted. The pH of the ink can be measured with a general pH meter equipped with a glass electrode or the like. EXAMPLES

[0169] 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 in any way as long as it does not deviate from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified. In addition, a dispersion of titanium oxide particles is referred to as a "pigment dispersion."

[0170] <Preparation of titanium dioxide> Commercially available rutile-type titanium oxide particles that had been surface-treated in advance were used. The cumulative 50% particle diameter (D 50 ) was measured using a particle size analyzer using the dynamic light scattering method (product name "Nanotrac WaveII-EX150", manufactured by Microtrack Bell). The properties of each titanium oxide particle are shown in Table 1.

[0171] [Table 1]

[0172] <Preparation of pigment dispersion> (Pigment dispersion 1) A styrene-methyl methacrylate-methacrylic acid copolymer (resin 1) with an acid value of 150 mgKOH / g and a weight average molecular weight of 10,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equivalent to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. 40.0 parts of titanium oxide particles 1, 40.0 parts of the aqueous solution of resin 1, and ion-exchanged water with a total of 100.0 parts of the components were mixed and pre-dispersed using a homogenizer. Then, using 0.5 mm zirconia beads, a dispersion treatment (main dispersion) was performed for 12 hours at 25°C using a paint shaker. The zirconia beads were filtered off, and an appropriate amount of ion-exchanged water was added as necessary to prepare a pigment dispersion 1 with a titanium oxide particle content of 40.0% and a resin dispersant (resin 1) content of 8.0%.

[0173] (Pigment dispersion 2) Pigment dispersion 2 was prepared in the same manner as pigment dispersion 1, except that the pigment was changed to titanium oxide particles 2. The titanium oxide particles content was 40.0% and the resin dispersant (resin 1) content was 8.0%.

[0174] <Ink Preparation> 25.0 parts of Pigment Dispersion Liquid 1 and the following components were mixed and stirred. The mixture was then filtered under pressure using a membrane filter (manufactured by Sartorius) with a pore size of 5.0 μm to prepare Ink 1. Ink 2 was prepared in the same manner as Ink 1, except that Pigment Dispersion Liquid 2 was used instead of Pigment Dispersion Liquid 1.

[0175] The details of each mixed component are given below. Acrylic resin particles (product name "Vinyblan 2685", manufactured by Nissin Chemical Industry Co., Ltd., resin particle content: 30%): 20.0 parts Diethylene glycol: 10.0 parts Diethylene glycol isobutyl ether: 10.0 parts Fluorosurfactant (product name "Capstone FS-3100", manufactured by Chemours): 1.0 part -Ion-exchanged water: 34.0 parts.

[0176] Viscosity (Pa s) and density of liquid components of inks 1 and 2 (g / cm 3 ) are 8 Pa s and 1.16 g / cm 3 Using these values, the settling velocity of each ink was calculated, and the settling velocity of ink 1 was 1.2×10 -11 The settling velocity of ink 2 was 8.5×10 -12 m / s.

[0177] The settling velocity was calculated using the following formula (Stokes' equation): where ν is the settling velocity, D is the particle diameter of titanium oxide, and ρ p is the density of titanium oxide particles, ρ f is the density of ion-exchanged water, g is the acceleration due to gravity, and η is the viscosity of ion-exchanged water.

[0178]

number

[0179] <Liquid ejection head> (Head 1) The liquid ejection head shown in Figs. 2 to 5 was prepared as the head 1. The maximum cross-sectional area S of the circulation path in the head 1 was 300 mm 2 It was.

[0180] <Evaluation> Ink 1 was set in an inkjet recording device equipped with head 1, and the ink was discharged in an environment of a temperature of 25° C. and a relative humidity of 50%. The circulation flow rate Q was 4.0 mL / min. That is, Q / S was 2.2×10 ―6 As a result, it was confirmed that the effects of the present invention can be obtained sufficiently. [Explanation of symbols]

[0181] 1 Liquid ejection head 12 Pressure Chamber 15 Discharge element 130 Supply Channel 140 Recovery channel 500 Circulation Pump

Claims

1. An inkjet recording method in which ink is ejected from a liquid ejection head, The aforementioned ink contains titanium dioxide and has a sedimentation velocity of 1.0 × 10⁻⁶ according to Stokes' equation. －１１ m / s or greater, The aforementioned liquid dispensing head is An outlet for ejecting the aforementioned ink, A pressure chamber for supplying the ink to the discharge port, An energy generating element for generating the energy to eject the aforementioned ink, An upstream flow path for supplying liquid to the pressure chamber, A downstream flow path communicating with the pressure chamber, A pump that communicates with the upstream channel and the downstream channel, and forms a circulation path through which the ink circulates in the order of the upstream channel, the pressure chamber, the downstream channel, and the upstream channel, Includes, The maximum cross-sectional area of ​​the aforementioned circulation path is S [mm²] ２ An inkjet recording method wherein, when the flow rate of the ink in the circulation path is Q [mL / min], Q / S is greater than the sedimentation velocity of the ink.

2. The inkjet recording method according to claim 1, wherein the flow rate Q is the flow rate of the pump.

3. The inkjet recording method according to claim 1, wherein the flow rate Q is 2.0 mL / min or more and 10 mL / min or less.

4. The inkjet recording method according to claim 1, wherein the volume of the ink flowing in the circulation path is 5 mL or more and 30 mL or less.

5. The inkjet recording method according to claim 1, wherein the liquid ejection head is configured to eject liquid while scanning in a direction perpendicular to the transport direction of the recording medium to which the ink is applied.

6. The inkjet recording method according to claim 1, wherein the liquid discharge head further comprises a first pressure adjustment means configured to adjust the pressure of the liquid in the upstream flow path.

7. The inkjet recording method according to claim 6, wherein the first pressure adjustment means comprises a first valve chamber, a first pressure control chamber, a first opening that connects the first valve chamber and the first pressure control chamber, and a first valve configured to open and close the first opening.

8. The inkjet recording method according to claim 7, wherein the first pressure control chamber has a portion of its surface formed by a first flexible member configured to be displaceable, a first pressure plate that is displaceable in conjunction with the first flexible member, and a first biasing member that biases the first pressure plate in a direction that increases the volume of the first pressure control chamber, and the first valve is configured to be opened and closed according to the displacement of the first pressure plate and the first flexible member.

9. The inkjet recording method according to claim 1, wherein the liquid discharge head further comprises a second pressure adjustment means configured to adjust the pressure of the liquid in the downstream flow path.

10. The inkjet recording method according to claim 9, wherein the second pressure adjustment means comprises a second valve chamber, a second pressure control chamber, a second opening that connects the second valve chamber and the second pressure control chamber, and a second valve configured to open and close the second opening.

11. The inkjet recording method according to claim 7, wherein the first communication port, through which the first pressure control chamber communicates with the upstream flow path, is located vertically below the first pressure control chamber.

12. The inkjet recording method according to claim 10, wherein the second communication port, through which the second pressure control chamber communicates with the downstream flow path, is located vertically below the first pressure control chamber.

13. The aforementioned liquid dispensing head is Discharge unit including the element substrate, The system includes the pump and a circulation unit configured to circulate liquid between the pump and the discharge unit, The inkjet recording method according to claim 1, wherein, in the portion where the discharge unit and the circulation unit are fluidly connected, the wall surface of the flow path in the discharge unit that is in fluid communication with the circulation unit is perpendicular or inclined with respect to the vertical direction.

14. The inkjet recording method according to claim 1, comprising a liquid storage unit configured to supply the ink to the ejection head and connected to the ejection head via a tube.

15. The inkjet recording method according to claim 1, wherein the pump is a piezoelectric pump.

16. The inkjet recording method according to claim 1, wherein the concentration of titanium dioxide in the ink is 5.00% by mass or more and 20.00% by mass or less.

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