Liquid ejecting head and liquid ejecting apparatus

Abstract

The invention relates to a liquid ejecting head and a liquid ejecting apparatus. A liquid ejecting head includes: an ejection port portion having an ejection port configured to eject a liquid in an ejection direction; a pressure chamber in which an energy generating element for ejecting the liquid from the ejection port is included; a supply channel configured to supply a liquid to the pressure chamber; a collection channel configured to collect the liquid from the pressure chamber; and a pump configured to flow the liquid in the collection channel into the supply channel, where Fratio is 1.0 or more and 1.4 or less.

Description

Technical Field

[0001] The present disclosure relates to a liquid ejection head and a liquid ejection apparatus having the same. Background Art

[0002] A circulation type liquid ejecting apparatus is known in which liquid is circulated between a liquid ejecting head (hereinafter also referred to as a "head") and a liquid storage portion (hereinafter also referred to as a "tank") to discharge bubbles in a channel and reduce thickening of ink near an ejection port. In some circulation type liquid ejecting apparatuses, a pump outside the head (a pump provided in a main body, etc.) is used to circulate the liquid between the liquid ejecting head and the main body, or a pump provided in the liquid ejecting head (a pump inside the head) is used to circulate the liquid in the liquid ejecting head.

[0003] There is a liquid ejection device that circulates ink in a liquid ejection head by installing a piezoelectric circulation pump (hereinafter also referred to as a "piezoelectric pump") as a pump inside the head (Japanese Patent Laid-Open No. 2014-195932, Japanese Patent Laid-Open No. 2019-059046, etc.). In Japanese Patent Laid-Open No. 2014-195932, ink supplied from the circulation pump to the pressure control mechanism is supplied to the pressure chamber through the ink supply channel, and un-ejected ink is collected to the circulation pump through the ink collection channel. The liquid circulator in Japanese Patent Laid-Open No. 2019-059046 has: an upstream channel and a downstream channel as a circulation path, the circulation path connecting a tank for storing liquid to be supplied to the head to the liquid ejection head; a bypass for connecting the upstream channel and the downstream channel without passing through the head; and a pressure detection section for detecting the bypass pressure. Summary of the invention

[0004] In order to solve the above-mentioned problems, the present disclosure provides a liquid ejection head, which includes: an ejection port portion, the ejection port portion having an ejection port configured to eject liquid along an ejection direction at a first end portion; a pressure chamber, the pressure chamber including an energy generating element, the energy generating element configured to generate energy required to eject liquid from the ejection port, and the pressure chamber is connected to the ejection port portion at a second end portion opposite to the first end portion; a supply channel, the supply channel configured to supply liquid to the pressure chamber; a collection channel, the collection channel configured to collect liquid from the pressure chamber; and a pump, the pump configured to make the liquid in the collection channel flow into the supply channel, wherein F represented by the following formula ratio 1.0 or more and 1.4 or less:

[0005] F ratio =1.619×(H -0.34 P -0.66 W)-0.1569 ×log(U x / U v ) -0.2560

[0006] Wherein, W [μm] represents the length of the ejection port in the flow direction of the liquid in the pressure chamber, P [μm] represents the length of the ejection port portion in the ejection direction of the liquid ejected from the ejection port, H [μm] represents the height of the pressure chamber on the upstream side in the flow direction of the liquid in the pressure chamber, and U v [m / s] represents the evaporation rate in the jet orifice, and U x [m / s] indicates the flow rate of the liquid flowing through the pressure chamber.

[0007] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A and Figure 1B It is an explanatory diagram of a liquid ejecting device.

[0009] Figure 2 is an exploded perspective view of a liquid ejecting head.

[0010] Figure 3A is a vertical cross-sectional view of a liquid ejecting head, Figure 3B is an enlarged cross-sectional view of the injection module.

[0011] Figure 4 is a schematic appearance diagram of a cycle unit.

[0012] Figure 5 is a vertical cross-section of the circulation path.

[0013] Figure 6 is a schematic block diagram of the cycle path.

[0014] 7A to 7C is a cross-sectional view of an example of a pressure control unit.

[0015] Fig. 8A and Figure 8B is an external perspective view of the circulation pump.

[0016] Fig. 9 yes Fig. 8A sectional view of the circulation pump shown in FIG. 1 taken along line IX-IX.

[0017] FIG. 10A to FIG. 10E It is an explanatory diagram of the ink flow in the liquid ejecting head.

[0018] Fig.11A and Fig. 11Bis a schematic diagram of the circulation path in the injection unit.

[0019] Fig.12 is a view of the opening plate.

[0020] Fig.13 is a view of the ejection element substrate.

[0021] FIG. 14A to FIG. 14C is a cross-sectional view of the ink flow in the ejection unit.

[0022] Fig.15A and Fig. 15B This is a cross-sectional view near the injection port.

[0023] Fig.16A and Fig. 16B It is a cross-sectional view of a comparative example near the injection port.

[0024] Fig.17 is a view of a comparative example of an ejection element substrate.

[0025] Fig.18A and Fig.18B is a view of the channel configuration of the liquid ejecting head.

[0026] Fig.19 It is a diagram showing a connection state between a main body portion of a liquid ejecting apparatus and a liquid ejecting head.

[0027] FIG. 20A to FIG. 20C It is a schematic diagram of the vicinity of the ejection port of the liquid ejecting head.

[0028] Fig.21 Schematic diagram of the state of the circulation flow through the liquid ejecting head.

[0029] Fig. 22 is a graph showing the relationship between the liquid ejecting head in flow pattern A and the liquid ejecting head in flow pattern B.

[0030] FIG. 23A to FIG. 23D Schematic diagram of the state of the circulation flow through the liquid ejecting head.

[0031] Fig.24 It is a graph showing the results of judging the flow state in the liquid ejecting head having various supply channel shapes.

[0032] FIG. 25A to FIG. 25E is a view of the effect of circulation flow rate.

[0033] Fig.26 It is a contour plot of the concentration ratio. DETAILED DESCRIPTION

[0034] When the pump is set in the head, the size of the pump should be considered. This is described in more detail below. In order to achieve the above-mentioned circulation effect (discharging bubbles, inhibiting ink thickening, etc.), as a pump capacity, it is necessary to ensure a circulation flow that exhibits the effect. However, simply increasing the circulation flow requires a larger pump. In particular, in a piezoelectric pump, the pump capacity depends on the displacement of the piezoelectric element, and the size of the piezoelectric element needs to be increased, resulting in an increase in the size of the piezoelectric pump. At this time, the pump size allowed by the design of the pump inside the head is smaller than the pump size allowed by the design of the pump outside the head (such as the pump in the main body). Therefore, in order to set the pump inside the head, it is required to design the pump as small as possible by clarifying the circulation flow to achieve the circulation effect and clarifying the minimum pump capacity required for the circulation flow, rather than designing a pump that unnecessarily increases the circulation flow (thus increasing the pump size).

[0035] However, in the liquid ejection apparatus described in Japanese Patent Application Publication No. 2014-195932 and Japanese Patent Application Publication No. 2019-059046, the circulation flow rate and size of the piezoelectric pump in the head are not considered. More specifically, the flow rate of the piezoelectric pump is not even described, and when the circulation flow rate needs to be increased, the size of the pump may need to be increased.

[0036] In view of the above circumstances, the present disclosure provides a liquid ejection head and a liquid ejection apparatus which can effectively achieve a circulation effect without increasing the size of a pump provided inside the head.

[0037] One or more embodiments of the present disclosure are described in detail below in conjunction with the accompanying drawings. The following embodiments do not limit the matters of the present disclosure, and all combinations of the features described in the embodiments are not necessarily required for the solutions of the present disclosure. The same constituent elements are represented by the same figure marks. Although in the present embodiment, the example of a thermal system that uses an electrothermal conversion element to generate bubbles and thereby eject liquid is described as an ejection element for ejecting liquid, the present disclosure is not limited to this. The present disclosure can also be applied to a liquid ejection head that uses an ejection method that uses a piezoelectric element (piezo) to eject liquid or another ejection method. In addition, the pump, pressure control unit, etc. described below are not limited to the contents described in the embodiments and the accompanying drawings. In the following description, the basic configuration of the present disclosure is first described, and then the features of the present disclosure are described.

[0038] <Liquid Jetting Equipment>

[0039] Figure 1A and Figure 1B is an illustration of a liquid ejection device. Figure 1A This is an enlarged view of the liquid ejection head of the liquid ejection device and its vicinity. Figure 1A A schematic configuration of a liquid ejecting apparatus 50 according to the present embodiment is described. Figure 1Ais a schematic perspective view of a liquid ejecting apparatus including a liquid ejecting head 1. A liquid ejecting apparatus 50 according to the present embodiment constitutes a tandem inkjet recording apparatus that ejects ink as liquid for recording on a recording medium P while the liquid ejecting head 1 moves.

[0040] The liquid ejection head 1 is mounted on a carriage 60. The carriage 60 reciprocates in the main scanning direction (in the X direction) along the guide shaft 51. The recording medium P is transported by transport rollers 55, 56, 57 and 58 along a sub-scanning direction (Y direction) that intersects (orthogonally in this example) the main scanning direction. In each of the drawings mentioned below, the Z direction represents a vertical direction and intersects (orthogonally in this example) an XY plane defined by the X direction and the Y direction. The liquid ejection head 1 is configured to be detachable from and attached to the carriage 60 by a user.

[0041] The liquid ejection head 1 includes a circulation unit 54 and an ejection unit 3 (see Figure 2 Although a specific configuration is described later, the ejection unit 3 includes a plurality of ejection ports and an energy generating element (hereinafter referred to as an ejection element) that generates ejection energy required to eject liquid from each ejection port.

[0042] The liquid ejecting apparatus 50 includes an ink tank 2 as an ink supply source and an external pump 21. The ink stored in the ink tank 2 is supplied to the circulation unit 54 through the ink supply tube 59 by the driving force of the external pump 21.

[0043] The liquid ejection device 50 forms a predetermined image on the recording medium P by repeating the printing scan and the conveying operation of conveying the recording medium P along the sub-scanning direction, and the liquid ejection head 1 installed on the carriage 60 ejects the ink for recording while moving along the main scanning direction in the printing scan. The liquid ejection head 1 in the present embodiment can eject four kinds of ink, that is, black (B), cyan (C), magenta (M) and yellow (Y), and these inks can be used to record a full-color image. However, the ink that can be ejected from the liquid ejection head 1 is not limited to the above four kinds of ink. The present disclosure is also applicable to liquid ejection heads that eject other types of ink. Therefore, the liquid ejection head can eject any type and amount of ink.

[0044] The liquid ejection device 50 includes a cap member (not shown) at a position deviated from the conveying path of the recording medium P in the X direction. The cap member may cover the ejection port surface where the ejection port of the liquid ejection head is formed. The cap member covers the ejection port surface of the liquid ejection head 1 during non-printing operation and is used to prevent the ejection port from drying or to protect the ejection port, for an ink suction operation of sucking ink from the ejection port, or for other purposes.

[0045] although Figure 1AThe liquid ejection head 1 in the embodiment includes four circulation units 54 corresponding to the four ink types, but the liquid ejection head 1 only needs to include the circulation unit 54 corresponding to the type of liquid to be ejected. In addition, a plurality of circulation units 54 may be provided for the same type of liquid. In other words, the liquid ejection head 1 may be configured to include one or more circulation units. Instead of circulating all four inks, only at least one ink may be circulated.

[0046] Figure 1B 1 is a block diagram of a control system of the liquid ejecting device 50. The CPU 103 is used as a control unit that controls the operation of each unit of the liquid ejecting device 50 based on a program such as a process stored in the ROM 101. The RAM 102 is used as a work area when the CPU 103 performs processing, etc. The CPU 103 receives image data from a host device 400 outside the liquid ejecting device 50, controls the head driver 1A, and controls the drive of the ejection element in the ejection unit 3. The CPU 103 also controls the drivers of various actuators in the liquid ejecting device. For example, the CPU 103 controls a motor driver 105A of a carriage motor 105 for moving the carriage 60, a motor driver 104A of a conveying motor 104 for conveying the recording medium P, and the like. The CPU 103 also controls a pump driver 500A for driving the circulation pump 500 described later, a pump driver 21A for the external pump 21, and the like. Although Figure 1B The process performed upon receiving image data from the host device 400 is shown, but the liquid ejection device 50 may perform the process without data from the host device 400 .

[0047] <Basic Configuration of Liquid Ejecting Head>

[0048] Figure 2 is an exploded perspective view of the liquid ejecting head 1 according to the present embodiment. Figure 3A yes Figure 2 The liquid ejecting head 1 is shown in a cross-sectional view taken along line IIIA-IIIA. Figure 3A is an overall vertical cross-sectional view of the liquid ejecting head 1, Figure 3B yes Figure 3A The enlarged view of the injection module is shown below. Figure 2 and Figure 3A as well as Figure 3B , a basic configuration of a liquid ejecting head 1 according to the present embodiment will be described with reference to FIG. 1 as appropriate.

[0049] like Figure 2As shown in FIG. 1 , 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 according to the present embodiment is fixed to and supported by the carriage 60 using a positioning unit and an electrical contact (not shown) provided in the carriage 60 of the liquid ejection apparatus 50. The liquid ejection head 1 ejects ink for recording on the recording medium P while moving along the main scanning direction (X direction) shown in FIG. 1 together with the carriage 60.

[0050] The external pump 21 connected to the ink tank 2 used as an ink supply source is provided with an ink supply tube 59 (see FIG. 1 ). A liquid connector (not shown) is provided at the end of the ink supply tube 59. When the liquid ejection head 1 is mounted on the liquid ejection device 50, the liquid connector provided at the end of the ink supply tube 59 is airtightly connected to the liquid connector insertion groove 53a, which is a liquid inlet provided in the head housing 53 of the liquid ejection head 1. This forms an ink supply channel from the ink tank 2 to the liquid ejection head 1 through the external pump 21. In this embodiment, four kinds of ink are used, four groups of ink tanks 2, external pumps 21, ink supply tubes 59 and circulation units 54 for various inks are provided, and four ink supply channels for various inks are independently formed. Therefore, the liquid ejection device 50 according to the present embodiment includes an ink supply system to supply ink from the ink tank 2 outside the liquid ejection head 1 to the ink supply system. The liquid ejection device 50 according to the present embodiment is not provided with an ink collection system for collecting ink in the liquid ejection head 1 to the ink tank 2. Therefore, the liquid ejection head 1 has a liquid connector insertion groove 53a for connecting the ink supply tube 59 of the ink tank 2, but does not have a connector insertion groove for connecting a tube for collecting ink in the liquid ejection head 1 into the ink tank 2. The liquid connector insertion groove 53a is provided for each ink.

[0051] exist Figure 3A 54B represents a black ink circulation unit, 54C represents a cyan ink circulation unit, 54M represents a magenta ink circulation unit, and 54Y represents a yellow ink circulation unit. The configuration of each circulation unit is almost the same. When the circulation units are not particularly distinguished in this embodiment, each circulation unit is referred to as a circulation unit 54.

[0052] exist Figure 2 and Figure 3A In the embodiment, the spraying unit 3 includes two spraying modules 300, a first support member 4, a second support member 7, an electrical wiring member (wire tape) 5 and an electrical contact substrate 6. Figure 3BAs shown, each ejection module 300 includes a silicon substrate 310 having a thickness of 0.5 mm to 1 mm and a plurality of ejection elements 15 located on one surface of the silicon substrate 310. Each ejection element 15 in this embodiment is composed of an electrothermal conversion element (heater) that generates heat energy as ejection energy required for ejecting liquid. Power is supplied to each ejection element 15 via electrical wiring formed on the silicon substrate 310 by film forming technology.

[0053] The ejection port forming member 320 is formed on the front surface ( Figure 3B The ejection port forming member 320 has a plurality of pressure chambers 12 corresponding to the plurality of ejection elements 15 and a plurality of ejection ports 13 for ejecting ink formed by photolithography. In addition, the silicon substrate 310 has a common supply channel 18 and a common collection channel 19. The silicon substrate 310 also has a supply connection channel 323 that connects the common supply channel 18 with each pressure chamber 12 and a collection connection channel 324 that connects the common collection channel 19 with each pressure chamber 12. In the present embodiment, one ejection module 300 is configured to eject two kinds of ink. Therefore, in Figure 3A Of the two jet modules shown, the jet module 300 on the left side of the figure jets black ink and cyan ink, and the jet module 300 on the right side of the figure jets magenta ink and yellow ink. This combination is an example, and any combination of inks may be used. One jet module may be configured to jet one ink, or may be configured to jet three or more inks. The two jet modules 300 do not have to jet the same type of ink. One jet module 300 may be provided, or three or more jet modules 300 may be provided. In addition, Figure 3A and Figure 3B In the example shown, two ejection port arrays extending in the Y direction are formed for ink of one color. A pressure chamber 12, a common supply channel 18, and a common collecting channel 19 are formed for each of the plurality of ejection ports 13 constituting each ejection port array.

[0054] On the back side of the silicon substrate 310 ( Figure 3B The ink supply port and the ink collection port described later are formed on the upper surface of the ink supply channel 48. The ink supply port supplies ink from the ink supply channel 48 to the plurality of common supply channels 18, and the ink collection port collects ink from the plurality of common collection channels 19 to the ink collection channel 49.

[0055] The ink supply port and the ink collection port refer to openings for supplying and collecting ink during the ink circulation in the forward direction described later. Therefore, during the ink circulation in the forward direction, ink is supplied from the ink supply port to each common supply channel 18 and collected from each common collection channel 19 to the ink collection port. The ink may also circulate in the reverse direction. In this case, ink is supplied from the above-mentioned ink collection port to the common collection channel 19, and collected from the common supply channel 18 to the ink supply port.

[0056] like Figure 3A As shown, the rear surface ( Figure 3A The upper surface of the first support member 4 is attached and fixed to one surface ( Figure 3A The first supporting member 4 has an ink supply channel 48 and an ink collection channel 49 extending from one surface thereof to the other surface thereof. One opening of the ink supply channel 48 is connected to the ink supply port in the silicon substrate 310, and one opening of the ink collection channel 49 is connected to the ink collection port in the silicon substrate 310. The ink supply channel 48 and the ink collection channel 49 are independently provided for each ink.

[0057] There is an opening 7a (see Figure 2 ) is attached and fixed to one surface of the first supporting member 4 ( Figure 3A The second support member 7 holds the electrical wiring member 5 electrically connected to the jetting module 300. The electrical wiring member 5 is a member for applying an electrical signal for jetting ink to the jetting module 300. The electrical connection portion between the jetting module 300 and the electrical wiring member 5 is sealed with a sealant (not shown) and is protected from ink corrosion and external impact.

[0058] The end portion 5a (see FIG. 1 ) of the electric wiring member 5 is formed by using an anisotropic conductive film (not shown). Figure 2 ) is thermocompression bonded to the electric contact substrate 6, and the electric wiring member 5 is electrically connected to the electric contact substrate 6. The electric contact substrate 6 has an external signal input terminal (not shown) for receiving an electric signal from the liquid ejection device 50.

[0059] In addition, a joint member 8 ( Figure 3A ). The joint member 8 has a supply port 88 and a collection port 89 for each ink. The supply port 88 and the collection port 89 allow the ink supply channel 48 and the ink collection channel 49 of the first support member 4 to communicate with the channel formed in the circulation unit 54. Figure 3A In the embodiment, the supply port 88B and the collection port 89B are provided for black ink, the supply port 88C and the collection port 89C are provided for cyan ink, the supply port 88M and the collection port 89M are provided for magenta ink, and the supply port 88Y and the collection port 89Y are provided for yellow ink.

[0060] The opening at one end portion of each of the ink supply channel 48 and the ink collection channel 49 of the first support member 4 has a small opening area corresponding to the ink supply port and the ink collection port of the silicon substrate 310. On the other hand, the shape of the opening at the other end portion of each of the ink supply channel 48 and the ink collection channel 49 of the first support member 4 is expanded to the same opening area as the large opening area of ​​the joint member 8 of the channel assembled to the circulation unit 54. Such a configuration can reduce the increase in channel resistance to the ink collected from each collection channel. The shape of the opening at one end portion and the other end portion of each of the ink supply channel 48 and the ink collection channel 49 is not limited to these examples.

[0061] In the liquid ejection head 1 having the above-described configuration, the ink supplied to the circulation unit 54 flows from the ink supply port of each ejection module 300 into the common supply channel 18 through the supply port 88 of the joint member 8 and the ink supply channel 48 of the first support member 4. Subsequently, the ink flows from the common supply channel 18 into the pressure chamber 12 through the supply connection channel 323, and the ink flowing into the pressure chamber is partially ejected from the ejection port 13 under the action of the drive of the ejection element 15. The residual ink that has not been ejected flows from the pressure chamber 12 through the collection connection channel 324, the common collection channel 19, and the ink collection port into the ink collection channel 49 of the first support member 4. The ink that has flowed into the ink collection channel 49 then flows into the circulation unit 54 through the collection port 89 of the joint member 8 and is collected.

[0062] <Components of the Circulation Unit>

[0063] Figure 4 5 is a schematic external view of a circulation unit 54 for one ink applied to the recording device of this embodiment. In addition to the circulation pump 500, the circulation unit 54 may further include a filter 110, a first pressure control unit 120 and a second pressure control unit 150. Figure 5 and Figure 6 As shown, these constituent elements are connected in each channel and constitute a circulation path for supplying ink to and collecting ink from ejection modules 300 in liquid ejection head 1 .

[0064] <Circulation Path in Liquid Ejecting Head>

[0065] Figure 5 1 is a schematic vertical sectional view of a circulation path of one ink (one color ink) in the liquid ejection head 1. In order to more clearly describe the circulation path, the Figure 5 The relative positions of the various configurations (the first pressure control unit 120, the second pressure control unit 150, the circulation pump 500, etc.) in the embodiment of the present invention are shown in FIG. Fig.19 The relative positions of different configurations. Figure 6 yes Figure 5 A schematic block diagram of the cycle path is shown. Figure 5 and Figure 6 As shown, the first pressure control unit 120 includes a first valve chamber 121 and a first pressure control chamber 122. The second pressure control unit 150 includes a second valve chamber 151 and a second pressure control chamber 152. The first pressure control unit 120 is configured to have a higher control pressure than the second pressure control unit 150. In this embodiment, the two pressure control units 120 and 150 are used to circulate in a circulation path within a certain pressure range. The ink flows through the pressure chamber 12 (the ejection element 15) at a flow rate corresponding to the pressure difference between the first pressure control unit 120 and the second pressure control unit 150. hereinafter refer to Figure 5 and Figure 6 Description is made of a circulation path and an ink flow in the circulation path in the liquid ejection head 1. Arrows in the figure indicate the flow direction of the ink.

[0066] First, the connection state of each constituent element in the liquid ejecting head 1 is described.

[0067] The ink tank 2 ( Figure 6 ) is connected to the circulation unit 54 through the ink supply tube 59 (FIG. 1). The filter 110 is provided in the ink channel (inflow channel) located on the upstream side of the circulation unit 54. The ink supply channel (inflow channel) located on the downstream side of the filter 110 is connected to the first valve chamber 121 of the first pressure control unit 120. The first valve chamber 121 is connected to the first pressure control chamber 122 through the communication port 191A, and the communication port can be used to Figure 5 The valve 190A shown opens and closes. The inflow channel is a channel through which liquid in the ink tank 2 outside the liquid ejection head 1 flows into the liquid ejection head 1 to be supplied to the pressure chamber 12.

[0068] The first pressure control chamber 122 is connected to the supply channel 130, the bypass 160 and the pump outlet channel 180 of the circulation pump 500. The supply channel 130 is connected to the common supply channel 18 through the ink supply port provided in the jetting module 300. The bypass 160 is connected to the second valve chamber 151 provided in the second pressure control unit 150. Figure 5 The valve 190B shown opens and closes the communication port 191B to connect the second valve chamber 151 to the second pressure control chamber 152. Figure 5 and Figure 6In the example shown, one end of the bypass 160 is connected to the first pressure control chamber 122 of the first pressure control unit 120, and the other end of the bypass 160 is connected to the second valve chamber 151 of the second pressure control unit 150. One end of the bypass 160 may be connected to the supply passage 130, and the other end of the bypass 160 may be connected to the second valve chamber 151.

[0069] The second pressure control chamber 152 is connected to the collecting channel 140. The collecting channel 140 is connected to the common collecting channel 19 through the ink collecting port provided in the jetting module 300. In addition, the second pressure control chamber 152 is connected to the circulation pump 500 through the pump inlet channel 170. Figure 5 , 170a represents an inlet port of the pump inlet passage 170.

[0070] Next, the ink flow in the liquid ejection head 1 having the above-described configuration will be described. Figure 6 As shown, the ink in the ink tank 2 is pressurized by the external pump 21 in the liquid ejecting apparatus 50 and supplied to the circulation unit 54 of the liquid ejecting head 1 as a positive-pressure ink flow.

[0071] The ink supplied to the circulation unit 54 flows through the filter 110 to remove foreign matter such as dust and bubbles, and then flows into the first valve chamber 121 in the first pressure control unit 120. Although the pressure of the ink is reduced due to the pressure drop during the passage through the filter 110, the ink pressure at this stage is still in a positive pressure state. When the valve 190A is in an open state, the ink flowing into the first valve chamber 121 flows into the first pressure control chamber 122 through the communication port 191A. The pressure drop during the passage through the communication port 191A changes the pressure of the ink flowing into the first pressure control chamber 122 from positive pressure to negative pressure.

[0072] Next, the ink flow in the circulation path is described. The circulation pump 500 operates so that the ink sucked from the pump inlet channel 170 located on the upstream side is sent to the pump outlet channel 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 channel 130 and the bypass 160 together with the ink delivered from the pump outlet channel 180. Although the details will be described later, in this embodiment, a piezoelectric diaphragm pump is used as a circulation pump capable of feeding liquid, and the piezoelectric diaphragm pump includes a piezoelectric element attached to a diaphragm as a driving source. The piezoelectric diaphragm pump feeds liquid by inputting a driving voltage to the piezoelectric element to change the pump chamber volume and cause a pressure change to cause the two check valves to move alternately.

[0073] The ink flowing into the supply channel 130 flows from the ink supply port of the ejection module 300 into the pressure chamber 12 through the common supply channel 18, and the ink is partially ejected from the ejection port 13 under the driving (heating) action of the ejection element 15. In addition, the residual ink that is not ejected flows through the pressure chamber 12 and the common collection channel 19, and then flows into the collection channel 140 connected to the ejection module 300. The ink flowing into the collection channel 140 flows into the second pressure control chamber 152 of the second pressure control unit 150.

[0074] On the other hand, the ink flowing into the bypass 160 from the first pressure control chamber 122 flows into the second valve chamber 151, and then flows into the second pressure control chamber 152 through the communication port 191B. The ink flowing into the second pressure control chamber 152 through the bypass 160 and the ink collected from the collection channel 140 are sucked into the circulation pump 500 through the pump inlet channel 170 under the driving action of the circulation pump 500. The ink sucked into the circulation pump 500 is then transported to the pump outlet channel 180 and flows into the first pressure control chamber 122 again. Subsequently, the ink flowing into the second pressure control chamber 152 from the first pressure control chamber 122 through the supply channel 130 and the jetting module 300 and the ink flowing into the second pressure control chamber 152 through the bypass 160 flow into the circulation pump 500. Then, the ink is transported from the circulation pump 500 to the first pressure control chamber 122. In this way, the ink circulates in the circulation path.

[0075] As described above, in the present embodiment, the circulation pump 500 can circulate the liquid along the circulation path in the liquid ejection head 1. This can suppress the thickening of the ink and the accumulation of the precipitated components in the coloring matter of the ink in the ejection module 300, and maintain the fluidity of the ink in the ejection module 300 and the ejection characteristics in the ejection port in a good state.

[0076] The circulation path in this embodiment is completed in the liquid ejection head 1 and can therefore be much shorter than the path between the ink tank 2 outside the liquid ejection head 1 and the liquid ejection head 1. Therefore, the ink can be circulated with a smaller circulation pump.

[0077] In addition, the connection channel between the liquid ejection head 1 and the ink tank 2 is only a channel for supplying ink. Therefore, a channel for collecting ink from the liquid ejection head 1 to the ink tank 2 is not required. Therefore, in order to connect the ink tank 2 and the liquid ejection head 1, only the ink supply tube is sufficient, and the ink collection tube is not required. Therefore, the liquid ejection device 50 can have a simple internal structure with a reduced number of tubes, and the size of the entire device can be reduced. In addition, the reduction in the number of tubes can also reduce the fluctuation of the ink pressure caused by the tube oscillation accompanying the main scan using the liquid ejection head 1. The tube oscillation during the main scan using the liquid ejection head 1 causes a driving load on the carriage motor that drives the carriage 60. Therefore, the reduction in the number of tubes can lead to a reduction in the driving load on the carriage motor and a simplification of the main scanning mechanism including the carriage motor, etc. In addition, since it is not necessary to collect ink from the liquid ejection head to the ink tank, the size of the external pump 21 can be reduced. Therefore, the present embodiment can reduce the size of the liquid ejection device 50 and reduce the cost of the liquid ejection device.

[0078] <Pump flow rate>

[0079] Generally, the purpose of the circulation flow in the channel may be (i) to discharge bubbles, (ii) to suppress precipitation, and (iii) to suppress ink concentration due to evaporation at the ejection port. In particular, the circulation flow rate is increased so that the effect of (iii) suppressing ink concentration due to evaporation at the ejection port is more effective than (i) and (ii). In addition, it is known that this depends largely on the structure of the ejection port portion.

[0080] Therefore, when the circulation flow rate increases, in a configuration where the pump is located outside the head (e.g., a pump in the main body), this problem is less obvious. In contrast, a pump or pressure control mechanism inside the head, such as in the present disclosure, tends to make this problem more obvious. Therefore, it is necessary to design the pump as small as possible by clarifying the relationship between the circulation flow rate to achieve the circulation effect and the configuration of the injection port portion, rather than designing a pump that unnecessarily increases the circulation flow rate (which increases the size of the pump).

[0081] The relationship between the circulation effect and the circulation flow rate according to the configuration of the injection port portion will be explained below.

[0082] Description of the jet

[0083] FIG. 20A to FIG. 20C is a schematic diagram showing in detail the vicinity of an ejection outlet of a liquid ejection head that ejects liquid such as ink in this embodiment. Fig. 20A is a plan view viewed along the ejection direction of droplets ejected from the ejection port, Fig. 20B It is along Fig. 20A A cross-sectional view taken along lines XXB, XXC-XXB, XXC, and Fig. 20C is along Fig. 20AA cross-sectional perspective view taken along lines XXB, XXC-XXB, XXC.

[0084] exist FIG. 20A to FIG. 20C In the embodiment, the liquid ejection head includes an ejection port 1011 for ejecting liquid and an ejection element 1014 formed in a pressure chamber 1013 and generating energy required for ejecting liquid. Ink is supplied from one end to the other end in the pressure chamber, and the ejection port is formed in a region between one end and the other end of the pressure chamber. An ink meniscus is formed in the ejection port, and an ejection port interface is formed at the interface between the ink and the atmosphere. In the present embodiment, an electrothermal conversion element (heater) driven as an ejection element generates bubbles in the liquid and ejects the liquid from the ejection port. The ejection element is not limited to a heater and may be an energy generating element, such as a piezoelectric element. The liquid ejection head includes a supply connection channel 323 and a collection connection channel 324 as a through hole extending in a direction intersecting the pressure chamber. In addition, the supply connection channel 323 is connected to a common supply channel 1015 (inflow opening), which serves as a liquid inlet leading to the liquid ejection head from the outside, and the collection connection channel 324 is connected to a common collection channel 1016 (outflow opening), which is a liquid outlet from the liquid ejection head to the outside. Therefore, the liquid ejection head has a liquid path that supplies liquid in the order of a common supply channel (inflow opening), a supply connection channel, a pressure chamber / ejection port, a collection connection channel, and a common collection channel (outflow opening). In the present embodiment, as described later, a so-called circulation path is formed in which the liquid flowing out from the common collection channel (outflow opening) to the outside of the liquid ejection head flows into the common supply channel of the liquid ejection head again, and a circulation flow 1017 is formed in the liquid ejection head. In the present embodiment, while the ink flows in the pressure chamber, the ejection element is driven to eject droplets from the ejection port. The speed of the circulation flow flowing through the pressure chamber is, for example, about 0.1 mm / s to 100 mm / s, and even if the ejection operation is performed while the ink is flowing, there is almost no effect on the landing accuracy, etc.

[0085] exist Fig. 20B , an ejection element 1014 is formed in an element substrate 1018 made of silicon (Si), and an ejection port 1011 for ejecting liquid and an ejection port portion 1012 for communicating the ejection port with a pressure chamber are formed in an orifice plate 1019. In other words, the ejection port is an opening portion formed on the front surface (the surface on the side from which droplets are ejected) of the orifice plate, and the ejection port portion is a tubular portion connecting the ejection port and the pressure chamber.

[0086] The relationship between P, W and H

[0087] Next, the relationship among the height of the pressure chamber, the thickness of the orifice plate, and the length of the ejection ports in the liquid ejection head according to the present embodiment and a method of supplying ink in the liquid ejection head are described below.

[0088] like Fig. 20B As shown, in the communicating portion between the pressure chamber and the ejection port portion, the pressure chamber height on the upstream side in the liquid flow direction in the pressure chamber is defined as H, and the length of the ejection port portion in the ejection direction in which the liquid is ejected from the ejection port is defined as P. Furthermore, the length of the ejection port portion 1012 in the flow direction of the liquid in the pressure chamber is defined as W. In the present embodiment, the range of H is 3 μm to 30 μm, the range of P is 3 μm to 30 μm, and the range of W is 6 μm to 30 μm.

[0089] Fig.21 The state of the circulating flow flowing through the liquid ejection head in the steady state in the ejection port 1011, the ejection port portion 1012 and the pressure chamber 1013 is shown. The length of the vector in this figure does not represent the velocity magnitude, but is constant for all velocity values. Fig.21 The arrow indicates that when 1.26×10 -4 Ink flow when ml / min of ink flows from the supply connection channel 323 into the pressure chamber in the liquid ejection head, where H is 14 μm, P is 5 μm, and W is 12.4 μm.

[0090] The present embodiment is configured as follows to suppress the ink from staying in the ejection port 13 and the ejection port portion 1012, wherein the coloring matter concentration of the ink changes due to the evaporation of the ink from the ejection port. More specifically, as Fig.21 As shown, the liquid ejection head according to the present embodiment has a circulation flow, wherein the circulation flow of the ink flowing through the pressure chamber flows into the ejection port portion 1012, reaches the vicinity of the ejection port interface, and then returns to the pressure chamber through the ejection port portion 1012. The ink returned to the pressure chamber flows out from the common collecting channel to the outside of the liquid ejection head through the collecting connection channel. In this way, a flow is formed in which the circulation flow enters the interior of the ejection port portion, reaches the meniscus position in the ejection port (near the meniscus interface), and then returns to the pressure chamber again. This enables not only the ink that is easily evaporated in the ejection port portion but also the ink that is particularly easily evaporated near the ejection port interface to flow out to the pressure chamber without staying in the ejection port portion.

[0091] The circulation flow in this embodiment is characterized by having a flow direction of the ink in the pressure chamber (from the center to the center of the ejection port) at least in the central portion near the ejection port interface (the central portion of the ejection port). Fig.21 The velocity component on the left side to the right side of the axis (hereinafter referred to as the positive velocity component). In this specification, Fig.21As shown in FIG. 1 , the flow pattern in which the circulating flow has a positive velocity component at least in the central portion of the injection port interface is referred to as flow pattern A. As described below, Fig. 23B and Fig.23D In the comparative example shown, there is a negative velocity component (in the center portion of the injection port interface) opposite to the positive velocity component. Fig. 23B The flow pattern in the direction from right to left in the image is called flow pattern B.

[0092] The inventors' research revealed that the liquid ejection head in the flow pattern A in the present embodiment satisfies the following formula to suppress the ink having the coloring matter concentration changed by evaporation from staying in the ejection port. More specifically, the pressure chamber height H (the pressure chamber height near the upstream side of the portion where the pressure chamber and the ejection port portion communicate with each other), the ejection port length P, and the ejection port width W in FIG. 20 satisfy the following relational expression (1):

[0093] H -0.34 ×P -0.66 ×W>1.7 (1)

[0094] The left side of the relational expression (1) is referred to as the determination value J. The inventors' research has shown that a liquid ejecting head satisfying the relational expression (1) has the following characteristics: Fig.21 The liquid ejecting head in the flow pattern A and flow pattern B shown does not satisfy the relational expression (1). Figure 22 to Figure 24 Describe the relational expression (1).

[0095] Fig. 22 The relationship between the liquid ejecting head in flow pattern A and the liquid ejecting head in flow pattern B is shown. Fig. 22 In FIG. 1 , the horizontal axis represents the ratio of P to H (P / H), and the vertical axis represents the ratio of W to P (W / P). In the figure, TH represents a threshold line, and the threshold line satisfies the following relationship (2):

[0096]

[0097] It has been found that the relationship between H, P and W is Fig. 22 The liquid ejection head above the threshold line of the graph of has flow pattern A, and the liquid ejection head below the threshold line has flow pattern B. Therefore, the liquid ejection head satisfying the following relational expression (3) has flow pattern A.

[0098]

[0099] Relational expression (3) is converted into relational expression (1). Therefore, a head (a head whose determination value J is 1.7 or more) in which the relationship between H, P, and W satisfies relational expression (1) has flow pattern A.

[0100] Reference FIG. 23A to FIG. 23D and Fig.24 To test the above relationship. FIG. 23A to FIG. 23D Each liquid ejecting head is Fig. 22 An example of the state of the circulation flow near the ejection port portion of the liquid ejection head in the areas above and below the middle threshold line. Fig.24 The results of determining whether the flow pattern is flow pattern A or flow pattern B by examining the flow state in the liquid ejection head having various supply channel shapes are shown. Fig.24 In FIG. 1 , solid circles represent liquid ejecting heads in flow pattern A, and cross marks represent liquid ejecting heads in flow pattern B. FIG.

[0101] Fig.23A A liquid ejection head having H of 3 μm, P of 9 μm, and W of 12 μm is shown, and the judgment value J on the left side of the relational expression (1) is 1.93, which is greater than 1.7. It is found that the actual circulation flow has the following characteristics: Fig.23A The flow pattern A is shown. This corresponds to Fig.24 Next, Fig. 23B A liquid ejection head with H of 8 μm, P of 9 μm, and W of 12 μm is shown, and the judgment value is 1.39, which is less than 1.7. The actual circulation flow has a flow pattern B. This corresponds to Fig.24 Point B in . Fig.23C A liquid ejection head with H of 6 μm, P of 6 μm, and W of 12 μm is shown, and the judgment value is 2.0, which is greater than 1.7. The actual circulation flow has a flow pattern A. This corresponds to Fig.24 Finally, Fig.23D A liquid ejection head with H of 6 μm, P of 6 μm, and W of 6 μm is shown, and the determination value is 1.0, which is less than 1.7. The actual circulation flow has a flow pattern B. This corresponds to Fig.24 Point D in.

[0102] In this way, it is possible to Fig. 22The threshold line in is used as a boundary to separate the liquid ejection head in flow mode A from the liquid ejection head in flow mode B. More specifically, the liquid ejection head whose judgment value J of the relational expression (1) is greater than 1.7 has flow mode A, and the circulating flow has a positive velocity component at least in the central part of the ejection port interface. The conditions of P, W and H have a dominant influence on whether the circulating flow in the ejection port is flow mode A or flow mode B. Other conditions, such as the flow rate of the circulating flow 1017, the viscosity of the ink, the width of the ejection port in the direction perpendicular to the flow direction of the circulating flow (the length of the ejection port in the direction orthogonal to W), have much less influence than P, W and H. Therefore, the flow rate and viscosity of the circulating flow of the ink can be appropriately determined according to the required specifications of the liquid ejection head (inkjet recording device) and the environmental conditions of the use of the liquid ejection head. When environmental changes, etc. increase the amount of ink evaporated from the ejection port during use, the flow rate of the circulating flow can be appropriately increased to make it have flow mode A. The liquid ejection head in flow mode B cannot have flow mode A no matter how the flow rate is increased. In other words, flow pattern A or flow pattern B is not mainly determined by the flow rate of ink or the viscosity of ink, but by the conditions of H, P, and W of the liquid ejection head. In addition, among various liquid ejection heads of flow pattern A, especially a liquid ejection head having H of 20 μm or less, P of 20 μm or less, and W of 30 μm or less can form an image with higher resolution.

[0103] Relationship between judgment value J, ambient temperature / humidity and circulation flow rate

[0104] The following describes the relationship between the judgment value J and the concentration due to the change in evaporation rate or the change in circulation flow rate related to the ambient temperature / humidity. The concentration index is expressed by the average concentration in the injection port length P. The concentration at the pressure chamber height H is independent of the flow patterns A and B, and even a small circulation flow causes advection, making the influence small. Therefore, it is considered that the average value in the injection port length P is good.

[0105] In order to clarify the relationship between the circulation flow rate and the evaporation at the nozzle interface, in addition to the flow pattern (P, W, H conditions), a simple prediction formula was formed using the following dimensionless number regression equation.

[0106] F ratio =a1×(H -0.34 P -0.66 W) a2 ×log(U x / U v ) a3

[0107] F ratio : Ratio of initial viscosity to viscosity after concentration

[0108] U x: Flow rate of the liquid flowing through the pressure chamber

[0109] U v : Evaporation rate in the nozzle

[0110] In the above characteristics, the second item on the right side is an index representing the strength of the flow pattern by a dimensionless number representing the judgment value J. The third item on the right side is an index representing the strength of the circulation flow by the dimensionless logarithmic ratio of the circulation flow velocity at the injection port interface to the evaporation velocity. The left side is an index representing the degree of concentration by the dimensionless ratio of the initial viscosity to the viscosity after concentration. Therefore, the relational expression shows that the concentration ratio is proportional to the strength of the flow pattern and the strength of the circulation flow. In addition, a1, a2, and a3 are coefficients calculated by the least squares method, and the coefficients are calculated according to the levels described later, and as described below, a1=1.619, a2=-0.1569, and a3=-0.2560.

[0111] F ratio =1.619×(H -0.34 P -0.66 W) -0.1569 ×log(U x / U v ) -0.2560

[0112] The prediction formula is limited to the following level values.

[0113] -Pressure chamber height H = 14μm, 12μm, 9μm, 6μm, 4μm (five levels)

[0114] - Injection port length P = 11 μm, 9 μm, 6 μm, 4 μm (four levels)

[0115] - Temperature = 25℃, 40℃, 55℃ (three levels)

[0116] -Humidity = 50% (one level)

[0117] -Injection port diameter = Φ16 (one level)

[0118] -Circulation flow rate = 1mm / s, 10mm / s, 30mm / s (three levels)

[0119] The concentration ratio is calculated for a total of 180 levels. The range of the judgment value J in these numerical ranges corresponds to 1.2 to 3.6, and the range of the ratio of the circulation flow rate / evaporation rate corresponds to 4 to 1300 (0.65 to 3.09 in the logarithmic expression). The non-logarithmic expression differs greatly from the typical range of the judgment value J, while the logarithmic expression provides a uniform weight for each dimensionless number. For an ink composed of two components, a volatile component (such as water) and a non-volatile component (such as a solvent), the evaporation, advection, and diffusion phenomena are numerically calculated, and the concentration ratio is approximated by a regression line using the viscosity change rate from the initial stage relative to the average value in the ejection port length P.

[0120] Generally, the degree of concentration ratio due to volatilization depends on the components of the ink composition and has different results. However, flow pattern A has a circulating flow within the jet port length P and is slightly affected by the ink composition. In particular, when the judgment value J in flow pattern A increases, its influence becomes extremely small. Therefore, it is considered that the component difference of the ink composition is negligible this time. In addition, since the concentration phenomenon caused by evaporation progresses over time, it is difficult to define a stable state. However, due to the circulating flow within the jet port length P in flow pattern A, the concentration phenomenon progresses only in a partial area of ​​the jet port groove where advection is difficult to occur. However, when the concentration ratio of the jet port length P is assumed, its influence is limited to a very small microscopic part, and considering the concentration phenomenon of the second order, a stable state has generally been confirmed.

[0121] Several examples calculated as described above are compared (see Figure 25).

[0122] 1) H = 14 μm, P = 11 μm, temperature = 40 °C, U x =1mm / s, J=1.34, F ratio =1.54( Fig.25A )

[0123] 2) H = 14 μm, P = 11 μm, temperature = 40 °C, U x =30mm / s, J=1.34, F ratio =1.22( Fig.25B )

[0124] 3) H = 14 μm, P = 4 μm, temperature = 40 °C, U x =1mm / s, J=2.61, F ratio =1.38( Fig.25C )

[0125] 4) H = 14 μm, P = 4 μm, temperature = 40 °C, U x =30mm / s, J=2.61, F ratio=1.10( Fig.25D )

[0126] 5) H = 14 μm, P = 4 μm, temperature = 25 °C, U x =1mm / s, J=2.61, F ratio =1.23( Fig.25E )

[0127] Fig.25A and Fig.25B The effect of the circulation flow rate on flow pattern B is shown. It can be seen that even if the circulation flow rate is increased by 30 times in flow pattern B, the effect of reducing the concentration ratio is small because the circulation flow is not easy to flow to the injection port interface. On the other hand, Fig.25C and 25D The effect of the circulation flow rate on flow pattern A is shown. It can be seen that increasing the circulation flow rate by 30 times in flow pattern A has a great effect on reducing the concentration ratio because the circulation flow flows to the injection port interface. Fig.25D The circulation velocity is increased, but Fig.25E Lowering the temperature can reduce the evaporation rate. Even if the circulation flow rate is 1mm / s, it can increase the ratio of the circulation flow rate to the evaporation rate and enhance the effect of reducing the concentration ratio.

[0128] Fig.26 The response surface for these levels is shown and is an isoline diagram for the concentration ratio, wherein the horizontal axis represents the judgment value J and the vertical axis represents the logarithmic ratio of the circulation flow rate / evaporation rate. When the judgment value J is high, it is found that the concentration ratio is suppressed even if the circulation flow rate is low. This shows that in flow pattern A, the effect of increasing the flow rate is greater. On the other hand, in flow pattern A, the concentration ratio can be reduced even at low flow rates. In contrast, in flow pattern B, even if the flow rate is increased, the effect is small, and it is difficult to make the concentration ratio close to the concentration ratio in flow pattern A. Therefore, it can be understood that in flow pattern B, it is difficult to reduce the pump flow while reducing the concentration ratio. Therefore, it is ideal that the judgment value J is greater than 1.7. However, even in a configuration where the judgment value J is less than 1.7, the pump flow rate can be reduced by reducing the evaporation rate (for example, by reducing the temperature, increasing the humidity, increasing the injection port diameter, etc.). Therefore, flow pattern B can also be adopted.

[0129] In order to estimate the pump flow rate required this time, first, the judgment value J can be calculated by determining the pressure chamber height H, the injection port length P, and the injection port diameter W. On the other hand, strictly speaking, the evaporation rate U v Ideally it is determined using Fick's diffusion equation relating diffusion, but can be calculated using the following formula and a predictive formula can be used to determine the necessary circulation flow rate.

[0130]

[0131] U v : Evaporation rate per unit area [m / s]

[0132] a: coefficient 0.0101

[0133] r: injection port radius [m] (corresponding to W / 2)

[0134] D: Diffusion coefficient [m 2 / s]

[0135] S: injection port area [m 2 ]

[0136] P: atmospheric pressure [Pa]

[0137] Ps: saturated vapor pressure [Pa]

[0138] Pa: Water vapor pressure in the environment [Pa]

[0139] Using humidity H[%], Pa and Ps have the following relationship.

[0140]

[0141] In this formula, the evaporation rate U can be simply calculated by determining the nozzle diameter W and the ambient temperature / humidity used. v From this, the target concentration ratio F can be determined ratio The corresponding circulation flow rate U x .

[0142] In addition, when the required flow rate at the injection port can be calculated, the pump flow rate Q [m 3 / s].

[0143] Q=U x ×S×N

[0144] S: cross-sectional area [m 2 ]

[0145] N: Number of injection ports [-]

[0146] The cross-sectional area S is the cross-sectional area of ​​the upstream passage of the pressure chamber near the upstream side where the pressure chamber and the injection port portion communicate with each other, that is, the cross-sectional area corresponds to the height H of the pressure chamber.

[0147] From the value of Q, it can be verified whether the pressure control mechanism required to achieve the pump flow rate and flow rate has a size and value suitable for the target, and it can be judged whether the size is allowable. Therefore, for multiple injection ports, by using the pump flow rate Q [m 3 / s], cross-sectional area S[m 2] and the number of injection ports N are expressed by the following formula U x [m / s].

[0148] U x =Q / (S×N)

[0149] Generally speaking, at low solid density (when the degree of thickening during evaporation is small), at the concentration ratio F ratio When F is less than 1.4, the circulation effect can be obtained. However, at high solid density (when the degree of thickening during evaporation is large), the concentration ratio F ratio In addition, for inks that are easy to solidify (in which the concentration phenomenon affects only a part of the ejection port groove), for example, latex inks or high-concentration pigment inks with reduced water content (water content ≤ 60 wt %, pigment concentration ≥ 8 wt %), the concentration ratio F ratio It can be 1.2 or less.

[0150] Therefore, in order to suppress the concentration of ink due to evaporation at the injection port, under the same environment, the flow pattern corresponds to flow pattern A in which the judgment value J is greater than 1.7, and as the value increases, the circulation flow rate can be reduced. This reduces the size of the pump and the pressure control mechanism in the injection head. This enables miniaturized design. On the other hand, when the judgment value J is small in flow pattern A, the circulation flow rate should be increased. Therefore, it is necessary to verify whether the pump and the pressure control mechanism are applicable. In some cases, it is necessary to increase the judgment value J by reconsidering the injection configuration or to reduce the evaporation rate by reconsidering the temperature and humidity to prevent the size of the pump from increasing. On the other hand, for the judgment value J in flow pattern B, it can be seen that even increasing the circulation flow rate has little effect on reducing the concentration ratio. In this case, it is necessary to reduce the evaporation rate by lowering the temperature, increasing the humidity, increasing the injection port diameter, etc., thereby reducing the required circulation flow rate and reducing the pump flow rate.

[0151] <Pressure Control Unit>

[0152] 7A to 7C An example of a pressure control unit is shown. 7A to 7C , the configuration and operation of the pressure control units (the first pressure control unit 120 and the second pressure control unit 150) incorporated in the liquid ejection head 1 are described in more detail. The first pressure control unit 120 and the second pressure control unit 150 have substantially the same configuration. Therefore, the following description will be made taking the first pressure control unit 120 as an example, and for the second pressure control unit 150, only the configurations related to the first pressure control unit 120 and the second pressure control unit 150 will be described. 7A to 7C For the second pressure control unit 150 , the first valve chamber 121 described below is understood as the second valve chamber 151 , and the first pressure control chamber 122 is understood as the second pressure control chamber 152 .

[0153] The first pressure control unit 120 includes 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 from each other by a partition 123 provided in the cylindrical housing 125. However, the first valve chamber 121 is communicated with the first pressure control chamber 122 via a communication port 191 formed in the partition 123. The first valve chamber 121 includes a valve 190 that switches communication and isolation between the first valve chamber 121 and the first pressure control chamber 122 in the communication port 191. The valve 190 is held at a position facing the communication port 191 by a valve spring 200, and is configured to be in close contact with the partition 123 under the urging force of the valve spring 200. The valve 190 is in close contact with the partition 123 and interrupts the flow of ink in the communication port 191. In order to enhance the close contact with the partition 123, the contact portion of the valve 190 with the partition 123 may be formed by an elastic member. A valve shaft 190a to be inserted into the communication port 191 extends in the central portion of the valve 190. The valve shaft 190a can be pressed against the urging force of the valve spring 200 to separate the valve 190 from the partition 123 and transfer ink through the communication port 191. The state in which the valve 190 interrupts the flow of ink in the communication port 191 is hereinafter referred to as a "closed state", and the state in which ink can flow in the communication port 191 is hereinafter referred to as an "open state".

[0154] The opening portion of the cylindrical housing 125 is closed by the flexible member 230 and the pressing plate 210. The first pressure control chamber 122 is formed by the flexible member 230, the pressing plate 210, the peripheral wall of the housing 125 and the partition 123. The pressing plate 210 is configured to be displaced with the displacement of the flexible member 230. The pressing plate 210 and the flexible member 230 can be made of any material. For example, the pressing plate 210 can be composed of a molded plastic part, and the flexible member 230 can be composed of a resin film. In this case, the pressing plate 210 can be fixed to the flexible member 230 by thermal fusion.

[0155] The pressure control spring 220 (urging member) is provided between the pressure plate 210 and the partition 123. Fig. 7AAs shown, the pushing force of the pressure control spring 220 pushes the pressure plate 210 and the flexible member 230 in the direction of increasing the internal volume of the first pressure control chamber 122. When the internal pressure of the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 are displaced in the direction of decreasing the internal volume of the first pressure control chamber 122 against the pressure of the pressure control 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. Subsequently, when the internal volume of the first pressure control chamber 122 further decreases, the valve 190 moves together with the valve shaft 190a against the pushing force of the valve spring 200 and separates from the partition 123. This causes the communication port 191 to be in an open state ( Figure 7B status in ).

[0156] In the present embodiment, in the open state of the communication port 191, the connection in the circulation path is configured so that the first valve chamber 121 has a higher pressure than the first pressure control chamber 122. Therefore, in the open state of the communication port 191, ink flows from the first valve chamber 121 into the first pressure control chamber 122. The inflow of ink causes the flexible member 230 and the pressure plate 210 to shift in the direction in which the internal volume of the first pressure control chamber 122 increases. Therefore, the pressure plate 210 is separated from the valve shaft 190a of the valve 190, and the valve 190 is in close contact with the partition 123 due to the urging force of the valve spring 200, resulting in the communication port 191 being in a closed state ( Figure 7C status in ).

[0157] As described above, in the first pressure regulating unit 120 of the present embodiment, when the internal pressure of the first pressure control chamber 122 decreases below a certain pressure (for example, when the negative pressure is strengthened), the ink flows from the first valve chamber 121 through the communication port 191. Therefore, the pressure of the first pressure control chamber 122 does not decrease further. Therefore, the first pressure control chamber 122 is controlled to have a pressure within a certain range.

[0158] Next, the pressure of the first pressure control chamber 122 is described in more detail.

[0159] The following describes the open state of the communication port 191 ( Figure 7B In this state, the relationship between the forces acting on the pressure plate 210 is expressed by the following formula 1, wherein the flexible member 230 and the pressure plate 210 are displaced according to the pressure of the first pressure control chamber 122 as described above, and the pressure plate 210 abuts against the valve shaft 190a.

[0160] P2×S2+F2+(P1-P2) ×S1+F1=0 Formula 1

[0161] Formula 1 is transformed into P2

[0162] P2=-(F1+F2+P1×S1) / (S2-S1) Formula 2

[0163] P1: Pressure of the first valve chamber 121 (gauge pressure)

[0164] P2: Pressure of the first pressure control chamber 122 (gauge pressure)

[0165] F1: Spring force of valve spring 200

[0166] F2: Spring force of pressure control spring 220

[0167] S1: Pressure area of ​​valve 190

[0168] S2: The pressure area of ​​the pressure plate 210

[0169] The direction in which the spring force F1 of the valve spring 200 and the spring force F2 of the pressure control spring 220 push the valve 190 and the pressure plate 210 is defined as positive ( Figures 7A to 7C The pressure P1 of the first valve chamber 121 and the pressure P2 of the first pressure control chamber 122 are configured to have a relationship of P1 ≥ P2.

[0170] The pressure P2 of the first pressure control chamber 122 in the open state of the communication port 191 is determined using Formula 2. In the open state of the communication port 191, due to the relationship of P1 ≥ P2, ink flows from the first valve chamber 121 into the first pressure control chamber 122. Therefore, the pressure P2 of the first pressure control chamber 122 does not further decrease but remains within a certain range.

[0171] On the other hand, Figure 7C As shown, when the pressure plate 210 does not abut against the valve shaft 190a and the communication port 191 is in a closed state, the relationship between the forces acting on the pressure plate 210 is expressed by Formula 3.

[0172] P3×S3+F3=0 Formula 3

[0173] Formula 3 is transformed into P3

[0174] P3=-F3 / S3 Formula 4

[0175] F3: Spring force of the pressure control spring 220 when the pressure plate 210 does not abut against the valve shaft 190a

[0176] P3: Pressure (gauge pressure) of the first pressure control chamber 122 when the pressure plate 210 does not abut against the valve shaft 190a

[0177] S3: The pressure area of ​​the pressure plate 210 when the pressure plate 210 does not abut against the valve 190

[0178] Figure 7CThe pressure plate 210 and the flexible member 230 are shown to be displaced to the left to the limit of displacement. The pressure P3 of the first pressure control chamber 122, the spring force F3 of the pressure control spring 220, and the pressure area S3 of the pressure plate 210 increase with the increase of the pressure P3. Figure 7C More specifically, when the pressing plate 210 and the flexible member 230 are located at Figure 7C When the pressure plate 210 is on the right side in FIG. 1 , the pressure plate 210 has a smaller pressure area S3, and the pressure control spring 220 has a larger spring force F3. Therefore, the pressure P3 of the first pressure control chamber 122 decreases according to the relationship of Formula 4. Therefore, according to Formulas 2 and 4, when Figure 7B The status changes to Figure 7C During the state of the first pressure control chamber 122, the pressure of the first pressure control chamber 122 gradually increases (that is, the negative pressure is enhanced to a value close to the positive pressure side). Therefore, starting from the open state of the communication port 191, the pressure plate 210 and the flexible member 230 gradually shift to the left, and the pressure of the first pressure control chamber 122 gradually increases until the internal volume of the first pressure control chamber 122 finally reaches the displaceable limit. Therefore, the negative pressure is enhanced.

[0179] <Circulation Pump>

[0180] Next, refer to Fig. 8A and Figure 8B as well as Fig. 9 , the configuration and operation of the circulation pump 500 incorporated in the liquid ejection head 1 are described in detail.

[0181] Fig. 8A and 8B is an external perspective view of the circulation pump 500 . Fig. 8A is an external perspective view of the front side of the circulation pump 500, Figure 8B 501 is an external perspective view of 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 channel connecting member 505b attached to and fixed to the outer surface of the housing body 505a. Each of the housing body 505a and the channel connecting member 505b has a pair of through holes connected to each other at two different positions. A pair of through holes at one position forms a pump supply hole 501, and a pair of through holes at another position forms a pump discharge hole 502. The pump supply hole 501 is connected to the pump inlet channel 170 connected to the second pressure control chamber 152, and the pump discharge hole 502 is connected to the pump outlet channel 180 connected to the first pressure control chamber 122. The ink supplied from the pump supply hole 501 passes through the pump chamber 503 described later (see Fig. 9 ) and discharged from the pump discharge hole 502.

[0182] Fig. 9 yes Fig. 8A1 is a cross-sectional view of the circulation pump 500 taken along line IX-IX. The diaphragm 506 is bonded to the inner surface of the pump housing 505, and the pump chamber 503 is formed between the diaphragm 506 and the recessed portion formed in the inner surface of the pump housing 505. The pump chamber 503 is connected to the pump supply hole 501 and the pump discharge hole 502 formed in the pump housing 505. The check valve 504a is provided in the middle part of the pump supply hole 501, and the check valve 504b is provided in the middle part of the pump discharge hole 502.

[0183] More specifically, the check valve 504a is arranged so that a part thereof can move leftward in the figure in a space 512a formed in a middle portion of the pump supply hole 501. The check valve 504b is arranged so that a part thereof can move rightward in the figure in a space 512b formed in a middle portion of the pump discharge hole 502.

[0184] When the diaphragm 506 is displaced to increase the volume of the pump chamber 503 and depressurize the pump chamber 503, the check valve 504a is separated from the opening of the pump supply hole 501 in the space 512a (i.e., moved to the left in the figure). When the check valve 504a is separated from the opening of the pump supply hole 501 in the space 512a, ink can flow through the pump supply hole 501 in the open state. When the diaphragm 506 is displaced to reduce the volume of the pump chamber 503 and pressurize the pump chamber 503, the check valve 504a is in close contact with the wall around the opening of the pump supply hole 501. Therefore, in the closed state, the flow of ink through the pump supply hole 501 is interrupted.

[0185] On the other hand, when the pump chamber 503 is depressurized, the check valve 504b is in close contact with the wall around the opening of the pump housing 505, and the ink flow in the pump discharge hole 502 is interrupted in the closed state. When the pump chamber 503 is pressurized, the check valve 504b is separated from the opening of the pump housing 505 and moves toward the space 512b (i.e., moves to the right in the figure), thereby allowing ink to flow through the pump discharge hole 502.

[0186] The check valves 504a and 504b may be made of any material that can be deformed according to the internal pressure of the pump chamber 503, and may be made of, for example, an elastic member such as EPDM rubber or elastomer, a polypropylene film or sheet, etc. However, the present disclosure is not limited thereto.

[0187] As described above, the pump chamber 503 is formed by bonding the pump housing 505 and the diaphragm 506 together. Therefore, the deformation of the diaphragm 506 causes the pressure of the pump chamber 503 to change. For example, the displacement of the diaphragm 506 to the pump housing 505 side (toward the right in the figure) reduces the volume of the pump chamber 503 and increases the internal pressure of the pump chamber 503. This opens the check valve 504b facing the pump discharge hole 502, and the ink is discharged from the pump chamber 503. At this time, the check valve 504a facing the pump supply hole 501 is in close contact with the wall around the pump supply hole 501 and suppresses the ink from flowing back from the pump chamber 503 to the pump supply hole 501.

[0188] On the contrary, the diaphragm 506 displaced in the direction in which the pump chamber 503 expands reduces the pressure of the pump chamber 503. This opens the check valve 504a facing the pump supply hole 501, and ink is supplied to the pump chamber 503. At this time, the check valve 504b in the pump discharge hole 502 is in close contact with the wall around the opening formed in the pump housing 505 and closes the opening. This suppresses the ink from flowing back from the pump discharge hole 502 to the pump chamber 503.

[0189] Therefore, in the circulation pump 500, the diaphragm 506 is deformed to change the internal pressure of the pump chamber 503, thereby sucking and discharging ink. At this time, if bubbles are mixed into the pump chamber 503, even if the diaphragm 506 is displaced, the expansion and contraction of the bubbles will reduce the change of the internal pressure of the pump chamber 503 and reduce the liquid feed rate. Therefore, the pump chamber 503 is arranged parallel to gravity, so that the bubbles mixed into the pump chamber 503 are easily collected in the upper part of the pump chamber 503, and the pump discharge hole 502 is arranged above the center of the pump chamber 503. This can improve the discharge performance of the bubbles in the pump and stabilize the flow rate.

[0190] <Ink Flow in Liquid Ejection Head>

[0191] FIG. 10A to FIG. 10E 2 is an explanatory diagram of the ink flow in the liquid ejection head. FIG. 10A to FIG. 10E The ink circulation in the liquid ejection head 1 is described. In order to more clearly describe the ink circulation path, the ink circulation path is simplified. FIG. 10A to FIG. 10E The relative position of each configuration (first pressure control unit 120, second pressure control unit 150, circulation pump 500, etc.) in FIG. Therefore, the relative position of each configuration is different from that described later. Fig.19 The configuration is different. Fig. 10A The ink flow during the recording operation of ejecting ink from the ejection port 13 is schematically illustrated. The arrows in the figure represent the ink flow. In the present embodiment, for the recording operation, both the external pump 21 and the circulation pump 500 begin to be driven. The external pump 21 and the circulation pump 500 can be driven independently of the recording operation. The external pump 21 and the circulation pump 500 do not have to be driven in conjunction with each other, but can be driven separately and independently.

[0192] During the recording operation, the circulation pump 500 is in the on state (driving state), and the ink flowing out of the first pressure control chamber 122 flows into the supply channel 130 and the bypass 160. The ink flowing into the supply channel 130 passes through the ejection module 300, flows into the collection channel 140, and is then supplied to the second pressure control chamber 152.

[0193] On the other hand, the ink flowing into the bypass 160 from the first pressure control chamber 122 flows into the second pressure control chamber 152 through the second valve chamber 151. The ink flowing into the second pressure control chamber 152 passes through the pump inlet channel 170, the circulation pump 500, and the pump outlet channel 180, and then flows into the first pressure control chamber 122 again. At this time, according to the relationship of Formula 2, the control pressure of the first valve chamber 121 is set to be higher than the control pressure of the first pressure control chamber 122. Therefore, the ink in the first pressure control chamber 122 is supplied to the ejection module 300 again through the supply channel 130 without flowing into the first valve chamber 121. The ink flowing into the ejection module 300 flows into the first pressure control chamber 122 again through the collection channel 140, the second pressure control chamber 152, the pump inlet channel 170, the circulation pump 500, and the pump outlet channel 180. In this way, the ink circulation is completed in the liquid ejection head 1.

[0194] In the ink circulation, the circulation amount (flow rate) of the ink in the jet module 300 depends on the control pressure difference between the first pressure control chamber 122 and the second pressure control chamber 152. The pressure difference is determined so that the ink can be suppressed from thickening near the jet port in the jet module 300 at the circulation amount. The ink consumed by recording is supplied from the ink tank 2 to the first pressure control chamber 122 through the filter 110 and the first valve chamber 121. The mechanism for supplying the consumed ink is described in detail below. The reduction in the amount of ink consumed by recording in the circulation path causes the internal pressure of the first pressure control chamber 122 to decrease and the amount of ink in the first pressure control chamber 122 to decrease. The reduction in the amount of ink in the first pressure control chamber 122 causes the internal volume of the first pressure control chamber 122 to decrease. Since the internal volume of the first pressure control chamber 122 is reduced, the communication port 191A is opened, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. The ink supplied from the first valve chamber 121 through the communication port 191A causes a pressure drop, and the ink flowing into the first pressure control chamber 122 switches the positive pressure to a negative pressure. The ink flowing from the first valve chamber 121 into the first pressure control chamber 122 increases the internal pressure of the first pressure control chamber 122, thereby increasing the internal volume of the first pressure control chamber 122, thereby closing the communication port 191A. In this way, the communication port 191A repeats an open state and a closed state according to the consumption of ink. When the ink is not consumed, the communication port 191A remains in a closed state.

[0195] Fig. 10BThe ink flow immediately after the recording operation is completed and the circulation pump 500 is turned off (in a stopped state) is schematically shown. When the recording operation is completed and the circulation pump 500 is turned off, the pressure of the first pressure control chamber 122 and the pressure of the second pressure control chamber 152 are both the control pressures during the recording operation. Fig. 10B As shown, the ink moves according to the pressure difference between the pressure of the first pressure control chamber 122 and the pressure of the second pressure control chamber 152. More specifically, the ink is supplied from the first pressure control chamber 122 to the jetting module 300 through the supply channel 130, and then flows to the second pressure control chamber 152 through the collection channel 140. Subsequently, the ink flows from the first pressure control chamber 122 to the second pressure control chamber 152 through the bypass 160 and the second valve chamber 151.

[0196] The amount of ink moved from the first pressure control chamber 122 to the second pressure control chamber 152 by these ink flows is supplied from the ink tank 2 to the first pressure control chamber 122 through the filter 110 and the first valve chamber 121. Therefore, the internal content of the first pressure control chamber 122 is kept constant. When the internal content of the first pressure control chamber 122 is constant, the spring force F1 of the valve spring 200, the spring force F2 of the pressure control spring 220, the pressure area S1 of the valve 190, and the pressure area S2 of the pressure plate 210 are kept constant according to Formula 2. Therefore, the pressure of the first pressure control chamber 122 depends on the change of the pressure (gauge pressure) P1 of the first valve chamber 121. Therefore, when the pressure P1 of the first valve chamber 121 is unchanged, the pressure P2 of the first pressure control chamber 122 is kept at the same level as the control pressure during the recording operation.

[0197] On the other hand, the pressure of the second pressure control chamber 152 changes with time according to the change in the internal content volume accompanying the inflow of ink from the first pressure control chamber 122. More specifically, Fig. 10B The status shown is Fig. 10C The communication port 191 shown is closed and the second valve chamber 151 and the second pressure control chamber 152 are not connected to each other, and the pressure of the second pressure control chamber 152 changes according to Formula 2. Then, the pressure plate 210 and the valve shaft 190a enter a non-contact state, and the communication port 191 enters a closed state. Fig. 10D As shown, ink then flows from the collection channel 140 into the second pressure control chamber 152. The pressure plate 210 and the flexible member 230 are displaced by the inflow of ink, and the pressure of the second pressure control chamber 152 changes according to Formula 4 until the internal volume of the second pressure control chamber 152 reaches a maximum value. Therefore, it increases.

[0198] exist Fig. 10CIn the state of the first pressure control chamber 122, the ink does not flow from the first pressure control chamber 122 to the second pressure control chamber 152 through the bypass 160 and the second valve chamber 151. Therefore, the ink in the first pressure control chamber 122 supplied to the jetting module 300 through the supply channel 130 flows only to the second pressure control chamber 152 through the collecting channel 140. As described above, the movement of the ink from the first pressure control chamber 122 to the second pressure control chamber 152 occurs according to the pressure difference between the internal pressure of the first pressure control chamber 122 and the internal pressure of the second pressure control chamber 152. Therefore, when the second pressure control chamber 152 has the same internal pressure as the first pressure control chamber 122, the movement of the ink stops.

[0199] In a state where the second pressure control chamber 152 has the same internal pressure as the first pressure control chamber 122, the second pressure control chamber 152 expands to Fig. 10D When the second pressure control chamber 152 is Fig. 10D When the ink is expanded as shown, a storage portion capable of storing ink is formed in the second pressure control chamber 152. Fig. 10D The transition time to the state of may vary with the shape and size of the channel and the characteristics of the ink and ranges from about 1 minute to 2 minutes. Fig. 10D When the circulation pump 500 is driven in the state where the ink is stored in the storage portion, the circulation pump 500 supplies the ink from the storage portion to the first pressure control chamber 122. Fig. 10E As shown in FIG. 1 , this increases the amount of ink in the first pressure control chamber 122 and causes the flexible member 230 and the pressure plate 210 to shift in the expansion direction. When the circulation pump 500 is continuously driven, the state in the circulation path is as follows: Fig. 10A Changes shown.

[0200] In the above description, although Fig. 10A The example in the recording operation is described, but as described above, the ink can be circulated in the absence of the recording operation. Even in this case, the ink is circulated according to the driving and stopping of the circulation pump 500. FIG. 10A to FIG. 10E Flow shown.

[0201] As described above, in the present embodiment, the communication port 191B in the second pressure control unit 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 ink circulation stops. However, the present disclosure is not limited thereto. The control pressure may be set so that the communication port 191B in the second pressure control unit 150 is in a closed state even when the circulation pump 500 is driven to circulate the ink. This point is described in more detail together with the function of the bypass 160.

[0202] For example, a bypass 160 is provided to connect the first pressure control unit 120 and the second pressure control unit 150, so that a negative pressure in the circulation path stronger than a predetermined value will not affect the jetting module 300. The bypass 160 is also provided to supply ink to the pressure chamber 12 from both sides of the supply channel 130 and the collection channel 140.

[0203] First, an example is described in which the bypass 160 is set so that a negative pressure stronger than a predetermined value does not affect the jetting module 300. For example, a change in ambient temperature may change the characteristics of the ink (e.g., viscosity). A change in the viscosity of the ink also changes the pressure drop in the circulation path. For example, a decrease in the viscosity of the ink may result in a decrease in the pressure drop in the circulation path. This increases the flow rate of the circulation pump 500 driven at a constant drive amount and increases the flow rate through the jetting module 300. On the other hand, the jetting module 300 maintains a constant temperature through a temperature control mechanism (not shown) and therefore the ink in the jetting module 300 has a constant viscosity even at different ambient temperatures. Although the viscosity of the ink in the jetting module 300 does not change, the increase in the flow rate of the ink flowing through the jetting module 300 increases the negative pressure in the jetting module 300 due to flow resistance. Therefore, a negative pressure stronger than a predetermined value in the jetting module 300 may destroy the meniscus in the jetting port 13, bring external air into the circulation path, and prevent normal jetting. Even if the meniscus is not destroyed, a negative pressure stronger than a predetermined value in the pressure chamber 12 may also affect the jetting.

[0204] Therefore, in the present embodiment, a bypass 160 is formed in the circulation path. In the presence of the bypass 160, when the negative pressure is stronger than a predetermined value, the ink also flows through the bypass 160, and the pressure of the jetting module 300 can be kept constant. Therefore, for example, the communication port 191B in the second pressure control unit 150 can have such a control pressure that the closed state can be maintained even when the circulation pump 500 is driven. In addition, the control pressure of the second pressure control unit can be set so that the communication port 191 in the second pressure control unit 150 is in an open state under a negative pressure stronger than a predetermined value. Therefore, as long as the meniscus is not destroyed or the predetermined negative pressure is maintained even when the flow rate of the pump is changed due to viscosity changes caused by environmental changes, etc., the communication port 191B can also be in a closed state when the circulation pump 500 is driven.

[0205] In the next example, a bypass 160 is provided to supply ink to the pressure chamber 12 from both the supply channel 130 and the collection channel 140. The ejection operation of the ejection element 15 also causes pressure fluctuations in the circulation path. This is because the ejection operation generates a force that draws ink into the pressure chamber.

[0206] The following describes the supply of ink to the pressure chamber 12 from both sides of the supply channel 130 and the collection channel 140 during continuous high duty cycle recording. Although the definition of duty cycle may vary due to various conditions, recording one ink drop of 4 pl on a 1200 dpi grid is considered to be 100% here. For example, high duty cycle recording refers to recording at a duty cycle of 100%.

[0207] Continuous high duty cycle recording reduces the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152. On the other hand, the circulation pump 500 implements ink outflow at a constant amount. This destroys the balance between inflow and outflow in the second pressure control chamber 152, reduces the amount of ink in the second pressure control chamber 152, reduces the internal negative pressure of the second pressure control chamber 152, and shrinks the second pressure control chamber 152. The reduction in the internal negative pressure of the second pressure control chamber 152 increases the ink flowing into the second pressure control chamber 152 through the bypass 160 and stabilizes the second pressure control chamber 152 in a state of outflow and inflow balance. Therefore, as a result, the internal negative pressure in the second pressure control chamber 152 is reduced according to the duty cycle. In addition, as described above, in the closed state of the communication port 191B when the circulation pump 500 is driven, the communication port 191B is in an open state according to the duty cycle, and ink flows into the second pressure control chamber 152 from the bypass 160.

[0208] The continuous high duty cycle recording reduces the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152, and conversely increases the amount of ink flowing from the communication port 191B into the second pressure control chamber 152 through the bypass 160. When this state further develops, the amount of ink flowing from the pressure chamber 12 through the collecting channel 140 into the second pressure control chamber 152 becomes zero, and all the ink flowing out to the circulation pump 500 is the ink flowing out from the communication port 191B. When this state further develops, the ink flows back from the second pressure control chamber 152 into the pressure chamber 12 through the collecting channel 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 160. In this case, the ink in the supply channel 130 and the ink in the collecting channel 140 fill the pressure chamber 12 and are ejected.

[0209] The ink backflow under the high recording duty cycle condition is a phenomenon caused by the bypass 160. Although the communication port 191B in the second pressure regulating unit enters the open state in response to the ink backflow in the above example, the ink backflow may also occur when the communication port 191B in the second pressure regulating unit is in the open state. Even without the second pressure regulating unit, the bypass 160 may cause the ink backflow.

[0210] <Configuration of injection unit>

[0211] Fig.11A and Fig. 11B : is a schematic diagram of a circulation path for ink of one color in the ejection unit 3 of the present embodiment. Fig.11A is an exploded perspective view of the injection unit 3 as viewed from the first support member 4 side, Fig. 11B 3 is an exploded perspective view of the ejection unit 3 viewed from the ejection module 300 side. The arrows indicated by the in and out in the figure indicate the ink flow. The ink flow is described only for one color, but the flow of the other color is the same. In addition, Fig.11A and Fig. 11B The second supporting member 7 and the electric wiring member 5 are not shown and the configuration of the ejection unit is also not shown. Fig.11A The first support member 4 is shown along Figure 3A The ejection module 300 includes an ejection element substrate 340 and an opening plate 330 . Fig.12 is a view of the opening plate 330 . Fig.13 is a view of the ejection element substrate 340.

[0212] The ink is supplied from the circulation unit 54 to the ejection unit 3 (see FIG. 3 ) through the joint member 8. The following describes the ink path after the ink passes through the joint member 8 and returns to the joint member 8. In the following drawings, the joint member 8 is not shown.

[0213] The jet module 300 includes a jet element substrate 340 and an opening plate 330 constituting a silicon substrate 310, and also includes a jet port forming member 320. The jet element substrate 340, the opening plate 330, and the jet port forming member 320 are stacked and bonded to each other so that the channels of various inks are connected to each other to constitute the jet module 300, and are supported by the first supporting member 4. The jet module 300 is supported by the first supporting member 4 and constitutes the jet unit 3. The jet element substrate 340 includes a jet port forming member 320. The jet port forming member 320 includes a plurality of jet port arrays, each of which is constituted by a plurality of jet ports 13, and the jet port forming member ejects a portion of the ink supplied through the ink channel in the jet module 300 from the jet ports 13. The ink that is not ejected is collected by the ink channel in the jet module 300.

[0214] like Fig.11A and Fig. 11B as well as Fig.12 As shown, the opening plate 330 includes a plurality of arranged ink supply ports 311 and a plurality of arranged ink collection ports 312. Fig.13 and FIG. 14A to FIG. 14CAs shown, the ejection element substrate 340 includes a plurality of arranged supply connection channels 323 and a plurality of arranged collection connection channels 324. In addition, the ejection element substrate 340 includes a common supply channel 18 communicating with the plurality of supply connection channels 323 and a common collection channel 19 communicating with the plurality of collection connection channels 324. The ink channel in the ejection unit 3 is formed by connecting the ink supply channel 48 or the ink collection channel 49 (see FIG. 3) provided in the first support member 4 with the channel provided in the ejection module 300. The support member supply port 211 is a cross-sectional opening forming the ink supply channel 48, and the support member collection port 212 is a cross-sectional opening forming the ink collection channel 49.

[0215] The ink supplied to the ejection unit 3 is supplied from the circulation unit 54 (see Figure 3A ) side is supplied to the ink supply channel 48 of the first supporting member 4 (see Figure 3A The ink flowing through the support member supply port 211 in the ink supply channel 48 passes through the ink supply channel 48 (see Figure 3A ) and the ink supply port 311 of the opening plate 330 are supplied to the common supply channel 18 of the ejection element substrate 340 and enter the supply connection channel 323. These constitute the channel on the supply side. Subsequently, the ink passes through the pressure chamber 12 (see Figure 3B ) flows into the collection connection channel 324 on the collection side. The flow of ink in the pressure chamber 12 will be described in detail later.

[0216] In the channel on the collection side, the ink in the collection connection channel 324 flows into the common collection channel 19. Subsequently, the ink flows from the common collection channel 19 to the ink collection channel 49 of the first support member 4 through the ink collection port 312 of the opening plate 330 and is collected in the circulation unit 54 through the support member collection port 212.

[0217] The area of ​​the opening plate 330 without the ink supply port 311 or the ink collection port 312 corresponds to the area of ​​the first support member 4 for separating the support member supply port 211 and the support member collection port 212. The first support member 4 also has no opening in this area. This area is used as a bonding area for bonding the jetting module 300 and the first support member 4 together.

[0218] exist Fig.12 In the opening plate 330 shown, a plurality of arrays are arranged along the Y direction, each array is composed of a plurality of openings arranged along the X direction, and the openings for supply (in) and the openings for collection (out) are alternately arranged along the Y direction and offset by half a pitch in the X direction. Fig.13In the ejection element substrate 340 shown, the common supply channel 18 connected to the plurality of supply connection channels 323 arranged along the Y direction and the common collection channel 19 connected to the plurality of collection connection channels 324 arranged along the Y direction are alternately arranged along the X direction. The common supply channel 18 and the common collection channel 19 are divided for each ink, and the number of the common supply channels 18 and the number of the common collection channels 19 to be arranged are determined according to the number of ejection port arrays of each color. The number of the supply connection channels 323 and the collection connection channels 324 to be arranged also corresponds to the number of ejection ports 13. It is not necessary to require a one-to-one correspondence, and one supply connection channel 323 and one collection connection channel 324 may be provided for a plurality of ejection ports 13.

[0219] The opening plate 330 and the ejection element substrate 340 are stacked and bonded to each other so that the channels of each ink communicate with each other to constitute the ejection module 300, and are supported by the first support member 4, thereby forming ink channels including the supply channel and the collection channel as described above.

[0220] FIG. 14A to FIG. 14C is a cross-sectional view of ink flows in different parts of the ejection unit 3 . Fig.14A Shown along Fig.11A XIVA-XIVA of FIG. 4 and shows a cross section of a portion where the ink supply channel 48 and the ink supply port 311 communicate with each other in the ejection unit 3 . Fig. 14B Shown along Fig.11A XIVB-XIVB is a cross section taken along the line XIVB-XIVB and shows a cross section of a portion where the ink collection channel 49 and the ink collection port 312 communicate with each other in the ejection unit 3. Fig. 14C Shown along Fig.11A XIVC-XIVC is a cross section taken along the line XIVC-XIVC and shows a cross section of a portion where the ink supply port 311 and the ink collection port 312 are not in communication with the channel of the first supporting member 4 .

[0221] In the supply channel for supplying ink, as Fig.14A As shown, ink is supplied from a portion where the ink supply channel 48 of the first support member 4 overlaps and communicates with the ink supply port 311 of the opening plate 330. In the collection channel for collecting ink, as shown in FIG. Fig. 14B As shown, ink is collected from the portion where the ink collection channel 49 of the first support member 4 overlaps and communicates with the ink collection port 312 of the opening plate 330. Fig. 14C As shown, in the ejection unit 3, the opening plate 330 has an area without an opening. In such an area, ink is not supplied and collected between the ejection element substrate 340 and the first support member 4. Fig.14A As shown, ink is supplied in the area where the ink supply port 311 is provided, and as shown in FIG. Fig. 14BAs shown, ink is collected in the area where the ink collecting port 312 is provided. Although the configuration including the opening plate 330 is described as an example in the present embodiment, a configuration without the opening plate 330 may be adopted. For example, channels corresponding to the ink supply channel 48 and the ink collecting channel 49 may be formed in the first supporting member 4, and the ejection element substrate 340 may be bonded to the first supporting member 4.

[0222] Fig.15A and Fig. 15B It is a cross-sectional view of the vicinity of the injection port 13 in the injection module 300 . Fig.16A and Fig. 16B is a cross-sectional view of an injection module as a comparative example, the injection module including a common supply channel 18 and a common collection channel 19 extending along the X direction. Fig.15A and Fig. 15B as well as Fig.16A and Fig. 16B The thick arrows in the common supply channel 18 and the common collecting channel 19 in FIG. 3 represent the oscillation of the ink in the embodiment using the tandem type liquid ejecting device 50. The ink supplied to the pressure chamber 12 through the common supply channel 18 and the supply connection channel 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 collected from the pressure chamber 12 to the common collecting channel 19 through the collecting connection channel 324 as a collecting channel.

[0223] In the embodiment using the tandem type liquid ejection apparatus 50, when ejecting such circulating ink, the oscillation of the ink in the ink channel due to the main scanning using the liquid ejection head 1 seriously affects the ejection of the ink. More specifically, the influence of the ink oscillation in the ink channel may appear as a difference in the ink ejection amount or a deviation in the ejection direction. Fig.16A and Fig. 16B As shown in FIG. 1 , when the common supply channel 18 and the common collecting channel 19 have a wider cross-sectional shape in the X direction (i.e., the main scanning direction), the ink in the common supply channel 18 and the common collecting channel 19 may be subjected to the inertial force in the main scanning direction and undergo greater oscillation. Therefore, the oscillation of the ink may affect the ejection of the ink from the ejection port 13. The common supply channel 18 and the common collecting channel 19 extending in the X direction may cause the distance between colors to increase and the printing efficiency to decrease.

[0224] Therefore, the common supply channel 18 and the common collection channel 19 in this embodiment are both Fig.15A and 15BIn the cross section shown, it extends in the Y direction and also extends in the Z direction perpendicular to the X direction, which is the main scanning direction. Such a configuration can reduce the channel width of each of the common supply channel 18 and the common collection channel 19 in the main scanning direction. Reducing the channel width of each of the common supply channel 18 and the common collection channel 19 in the main scanning direction weakens the ink oscillation caused by the inertial force (thick black arrow in the figure) acting on the ink in the common supply channel 18 and the common collection channel 19 in the direction opposite to the main scanning direction during the main scanning. This can reduce the impact of ink oscillation on ink ejection. In addition, the common supply channel 18 and the common collection channel 19 extending in the Z direction increase the cross-sectional area and reduce the channel pressure drop.

[0225] Although the channel width of each of the common supply channel 18 and the common collection channel 19 in the main scanning direction is reduced as described above to weaken the ink oscillation in the common supply channel 18 and the common collection channel 19 during the main scanning, the oscillation is not completely eliminated. Therefore, in the present embodiment, in order to reduce the ejection difference of different types of inks that may still be caused by the weakened oscillation, the common supply channel 18 and the common collection channel 19 are arranged at a position overlapping along the X direction.

[0226] As described above, in the present embodiment, the supply connection channel 323 and the collection connection channel 324 are provided for the ejection ports 13 and are arranged in a corresponding relationship in parallel along the X direction, with the ejection ports 13 interposed therebetween. Therefore, when there is a portion where the common supply channel 18 and the common collection channel 19 do not overlap each other in the X direction and the corresponding relationship between the supply connection channel 323 and the collection connection channel 324 in the X direction is broken, this affects the flow and ejection of the ink in the pressure chamber 12 in the X direction. When the influence of ink oscillation is added, the ejection of the ink in each ejection port may be further affected.

[0227] Therefore, the common supply channel 18 and the common collecting channel 19 arranged at overlapping positions along the X direction have almost the same ink oscillation during the main scan at any position in the Y direction where the ejection ports 13 are arranged. This prevents a large change in the pressure difference between the common supply channel 18 side and the common collecting channel 19 side in the pressure chamber 12 and allows stable ejection.

[0228] In a certain type of liquid ejection head that circulates ink, a channel for supplying ink to the liquid ejection head and a channel for collecting ink are the same. However, in the present embodiment, a common supply channel 18 and a common collecting channel 19 are different. The supply connection channel 323 and the pressure chamber 12 are communicated with each other, the pressure chamber 12 and the collecting connection channel 324 are communicated with each other, and ink is ejected from the ejection port 13 of the pressure chamber 12. Therefore, the pressure chamber 12, which is a path connecting the supply connection channel 323 and the collecting connection channel 324, has the ejection port 13. Therefore, the pressure chamber 12 has an ink flow from the supply connection channel 323 to the collecting connection channel 324, and the ink in the pressure chamber 12 is effectively circulated. Although the ink in the pressure chamber 12 may be affected by the evaporation of the ink from the ejection port 13, the ink that is effectively circulated in the pressure chamber 12 can maintain its fresh state.

[0229] Since the two channels of the common supply channel 18 and the common collection channel 19 are connected to the pressure chamber 12, ink can be supplied from the two channels when it is necessary to eject at a high flow rate. Therefore, compared with a configuration having only one channel for supplying and collecting ink, the present embodiment has the advantage that not only circulation can be effectively implemented, but also ejection at a high flow rate can be implemented.

[0230] The influence of ink oscillation can be reduced by arranging the common supply channel 18 and the common collection channel 19 at positions close to each other in the X direction. The distance between the channels may desirably be in the range of 75 μm to 100 μm.

[0231] Fig.17 3 is a view of an ejection element substrate 340 as a comparative example. Fig.17 323 and the collection connection channel 324 are not shown. After receiving the heat energy from the ejection element 15 in the pressure chamber 12, the ink flowing into the common collection channel 19 has a higher temperature than the ink in the common supply channel 18. Fig.17 As shown in the α portion within the dot-dash line in , a portion of the ejection element substrate 340 in the X direction has only the common collecting channel 19. In this case, the portion may be locally heated, causing a temperature change in the ejection module 300 and affecting ejection.

[0232] Ink having a lower temperature than that in the common collecting channel 19 flows through the common supply channel 18. Therefore, when the common supply channel 18 and the common collecting channel 19 are adjacent to each other, in the vicinity thereof, the temperatures of the common supply channel 18 and the common collecting channel 19 partially offset each other without significantly increasing. Therefore, the common supply channel 18 and the common collecting channel 19 may have almost the same length, exist at a position overlapping in the X direction, and be adjacent to each other.

[0233] Fig.18A and 18B 2 shows the channel configuration of the liquid ejection head 1 for three color inks of cyan (C), magenta (M) and yellow (Y). Fig.18A As shown in FIG. 1 , the liquid ejection head 1 has a circulation channel for each ink. The pressure chamber 12 is arranged along the X direction which is the main scanning direction of the liquid ejection head 1. Fig.18B As shown, the common supply channel 18 and the common collecting channel 19 are arranged along the ejection port array of the ejection ports 13 and extend along the Y direction, wherein the ejection port array is interposed between the common supply channel 18 and the common collecting channel 19 .

[0234] <Connection between Main Body and Liquid Ejecting Head>

[0235] Fig.19 2 is a schematic diagram showing in more detail the connection state between the ink tank 2, the external pump 21 and the liquid ejection head 1 in the main body part of the liquid ejection device 50 according to the present embodiment, and the arrangement of the circulation pump and the like. In the liquid ejection device 50 according to the present embodiment, in the event of a malfunction of the liquid ejection head 1, the liquid ejection head 1 can be easily replaced alone. More specifically, a liquid connection portion 700 is provided, which can easily implement connection and disconnection between the ink supply tube 59 connected to the external pump 21 and the liquid ejection head 1. Thus, only the liquid ejection head 1 can be easily attached to and detached from the liquid ejection device 50.

[0236] like Fig.19 As shown, the liquid connection portion 700 includes a liquid connection member insertion groove 53a protruding from the head housing 53 of the liquid ejection head 1 and a cylindrical liquid connection member 59a into which the liquid connection member insertion groove 53a can be inserted. The liquid connection member insertion groove 53a is fluidically connected to an ink supply channel (inflow channel) formed in the liquid ejection head 1 and is connected to the first pressure control unit 120 via a filter 110. The liquid connection member 59a is provided at the end of an ink supply tube 59 connected to an external pump 21 that pressurizes and feeds ink from the ink tank 2 to the liquid ejection head 1.

[0237] As mentioned above, in Fig.19 In the liquid ejection head 1 shown, the liquid connection part 700 allows easy attachment, removal and replacement of the liquid ejection head 1. However, when the sealing performance between the liquid connection member insertion groove 53a and the liquid connection member 59a deteriorates, the ink fed by the external pump 21 under pressure may leak from the liquid connection part 700. The leaked ink attached to the circulation pump 500 and the like may cause a malfunction in the electrical system. Therefore, in the present embodiment, the circulation pump and the like are provided as described below.

[0238] <Layout of circulation pump, etc.>

[0239] like Fig.19 As shown, in the present embodiment, the circulation pump 500 is arranged above the liquid connection part 700 in the direction of gravity to prevent the ink leaking from the liquid connection part 700 from adhering to the circulation pump 500. More specifically, the circulation pump 500 is arranged above the liquid connection member insertion groove 53a as the liquid inlet of the liquid jet head 1 in the direction of gravity. In addition, the circulation pump 500 is arranged not to contact with the member constituting the liquid connection part 700. Therefore, even if ink leaks from the liquid connection part 700, the ink will flow horizontally along the opening direction of the liquid connection member 59a or flow downward in the direction of gravity and is unlikely to reach the circulation pump 500 located above in the direction of gravity. In addition, the circulation pump 500 is arranged at a position away from the liquid connection part 700, and therefore the ink is unlikely to reach the circulation pump 500 along the member.

[0240] Furthermore, an electrical connection portion 515 electrically connecting the circulation pump 500 to the electrical contact substrate 6 via the flexible wiring member 514 is provided above the liquid connection portion 700 in the gravity direction. This can reduce the possibility of electrical failure caused by ink from the liquid connection portion 700.

[0241] In this embodiment, the head housing 53 has the wall portion 52 b which blocks the ink even if the ink is ejected from the opening 59 b of the liquid connecting portion 700 and reduces the possibility of the ink reaching the circulation pump 500 or the electrical connecting portion 515 .

[0242] [Image recording method]

[0243] In the present disclosure, the image recording method includes a method of ejecting ink described later from a liquid ejection head to record an image on a recording medium described later. In particular, in the inkjet recording method, ink can be ejected from an inkjet liquid ejection head (inkjet recording head) to record an image.

[0244] (1) Recording medium

[0245] The recording medium may be, but is not limited to, a transparent or colored recording medium. The recording medium may be a poorly absorptive medium (non-absorbable medium) having poor absorption capacity for liquid media, such as a resin film. The ink may be applied to a unit area of ​​the recording medium by multiple recordings in which the recording head and the recording medium are relatively moved multiple times. In particular, white ink and color ink may be applied to the unit area by different relative scans. This increases the time interval between ink contacts and easily suppresses mixing. The unit area may be set to an arbitrary area, such as a pixel or a band.

[0246] (2) Ink

[0247] The ink that can be ejected from the liquid ejection head of the present disclosure will be described in detail below with reference to the embodiments. In the following description, with respect to the salt compound, although the salt in the ink is dissociated into ions, it is expressed as "containing salt" for convenience. Titanium oxide or titanium oxide particles can be referred to as "pigment". Aqueous ink for inkjet recording can be referred to as "ink". Unless otherwise specified, physical properties are determined at room temperature (25°C). For recording images using white ink, white ink can be used as a background color treatment for color ink. In this case, the image can be recorded by applying a color ink (black ink, cyan ink, magenta ink, yellow ink, etc.) so that it overlaps at least a portion of the area to which white ink has been applied. It can also be used for reverse color printing, that is, applying white ink so that it overlaps at least a portion of the area to which color ink has been applied.

[0248] <Water-based ink and method for producing water-based ink>

[0249] In the present disclosure, a white ink containing titanium oxide as a white pigment can be used as ink. In the present disclosure, the ink is not necessarily a so-called "curable ink". Therefore, in the present disclosure, the ink does not necessarily contain a compound, such as a polymerizable monomer that can be polymerized by external energy (such as heat or light). The components constituting the ink according to the present disclosure, the physical properties of the ink, the method for producing the ink, etc. are described in detail below.

[0250] Coloring matter

[0251] The ink contains titanium oxide as a coloring substance (pigment). The titanium oxide may be titanium oxide particles surface-treated with a specific inorganic oxide. Therefore, the ink may contain titanium oxide particles whose surfaces are coated with a specific inorganic oxide. The titanium oxide particle content (mass %) of the ink is preferably greater than 0.10 mass % and less than 20.00 mass % of the total mass of the ink. The titanium oxide particle content (mass %) of the ink is more preferably greater than 1.00 mass % and less than 20.00 mass % of the total mass of the ink. The titanium oxide particle content (mass %) of the ink is particularly preferably greater than 1.00 mass % and less than 15.00 mass % of the total mass of the ink.

[0252] Titanium oxide is a white pigment and has three crystal forms: rutile, anatase, and brookite. In particular, rutile titanium oxide can be used. Titanium oxide can be industrially produced by a sulfuric acid method or a chlorine method, and the titanium oxide used in the present disclosure can be produced by any method.

[0253] The titanium oxide particles preferably have a cumulative 50% particle size based on volume of 200 nm or more and 500 nm or less (hereinafter also referred to as the average particle size). In particular, the titanium oxide particles more preferably have a cumulative 50% particle size based on volume of 200 nm or more and 400 nm or less. The cumulative 50% particle size (D50) based on volume of the titanium oxide particles is the particle diameter at the integral value of 50% of the total volume of the particles measured from the minimum particle size in the cumulative particle size curve. The D50 of the titanium oxide particles can be measured under conditions such as SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: non-spherical, and refractive index: 2.60. A particle size analyzer using a dynamic light scattering method can be used as a particle size distribution analyzer. Of course, the measurement conditions, etc. are not limited to the above.

[0254] Titanium oxide can be surface treated with alumina and silica. Surface treatment is expected to reduce photocatalytic activity and improve dispersibility. The term "alumina" as used herein is a general term for oxides of aluminum (e.g., aluminum oxide). The term "silica" as used herein is a general term for silicon dioxide or a substance composed of silicon dioxide. Most of the alumina and silica coating the titanium oxide are in the form of silicon dioxide and alumina.

[0255] The titanium oxide content (mass %) of the titanium oxide particles is preferably 90.00 mass % or more of the total mass of the titanium oxide particles. The titanium oxide content (mass %) of the titanium oxide particles is preferably 98.50 mass % or less of the total mass of the titanium oxide particles. In terms of mass ratio, the aluminum oxide content (mass %) of the titanium oxide particles needs to be 0.50 times or more and 1.00 times or less of the silica content (mass %). A mass ratio of less than 0.50 times or greater than 1.00 times results in a lower jetting stability of the ink. The silica content (mass %) of the titanium oxide particles is preferably 1.00 mass % or more and 4.00 mass % or less of the total mass of the titanium oxide particles. A silica content (mass %) of less than 1.00 mass % may result in insufficient affinity of the compound represented by the general formula (1), and the jetting stability of the ink may become insufficient. A silica content (mass %) of more than 4.00 mass % may result in a large amount of the compound represented by the general formula (1) being adsorbed on the titanium oxide particles even when the surface treatment is performed with aluminum oxide and may result in insufficient ink ejection stability. The aluminum oxide content (mass %) of the titanium oxide particles is preferably 0.50 mass % or more and 4.00 mass % or less of the total mass of the titanium oxide particles.

[0256] The content of aluminum oxide and silica of the titanium oxide particles, i.e., the coating amount of aluminum oxide and silica, can be measured, for example, by quantitatively analyzing the aluminum element and the silicon element using inductively coupled plasma (ICP) emission spectrometry. In this case, the content can be calculated by assuming that all atoms covering the surface are oxides and converting the obtained values ​​of aluminum and silicon into their oxides (i.e., aluminum oxide and silica). In terms of mass ratio, the aluminum element content (mass %) of the titanium oxide particles determined by inductively coupled plasma emission spectrometry is 0.57 times or more and 1.13 times or less of the silicon element content (mass %). When this value is converted into its oxide (i.e., aluminum oxide and silica), in terms of mass ratio, the aluminum oxide content (mass %) of the titanium oxide particles is 0.50 times or more and 1.00 times or less of the silica content (mass %).

[0257] The surface treatment method of titanium oxide can be wet treatment, dry treatment, etc. 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 proportion of the surface treatment agent can be appropriately changed to adjust to the desired characteristics. In addition to alumina and silica, surface treatment can also use inorganic oxides such as zinc oxide or zirconium oxide or organic substances such as polyols without losing the advantages of the present disclosure.

[0258] The ink may contain pigments other than titanium oxide without losing the advantages of the present disclosure. In this case, inks of colors other than white ink may be used. The content (mass %) of other pigments in the ink is preferably 0.10 mass % or more and 5.00 mass % or less of the total mass of the ink, more preferably 0.10 mass % or more and 1.00 mass % or less.

[0259] Compounds represented by the general formula (1)

[0260] The ink may contain a compound represented by the following general formula (1) as a dispersant for dispersing titanium oxide particles. The amount (mass %) of the compound represented by the 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, of the total mass of the ink.

[0261]

[0262] (In the general formula (1), R1, R2 and R3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. R4 each independently represents a hydrocarbylene group having 2 to 4 carbon atoms. X represents a single bond or a hydrocarbylene group having 1 to 6 carbon atoms. The range of n is 6 to 24. The range of a is 1 to 3, the range of b is 0 to 2, and a+b=3).

[0263] In the general formula (1), R1, R2 and R3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. The hydrocarbon group having 1 to 4 carbon atoms may be a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group. In particular, from the perspective of easy hydrolysis, a methyl group may be used. When R1, R2 and R3 each independently represent a hydrocarbon group having more than 4 carbon atoms, it is difficult to form a silanol group by hydrolysis, and affinity with the titanium oxide particles cannot be obtained. Therefore, the titanium oxide particles cannot be stably dispersed, and the jetting stability of the ink cannot be obtained. The range of a representing the number of R1O is 1 to 3, the range of b representing the number of R2 is 0 to 2, and a+b=3. In particular, a is preferably 3, and b is preferably 0, that is, all three substituents on the silicon atom may be R1O.

[0264] In the general formula (1), R4 each independently represents an alkylene group having 2 to 4 carbon atoms. The alkylene group having 2 to 4 carbon atoms may be vinyl, n-propylene, isopropylene and n-butylene. In particular, vinyl may be used. The number of OR4, i.e., the range of n (average value) representing the number of epoxy hydrocarbon groups, is 6 to 24. n is less than 6, resulting in insufficient repulsive force generated by steric hindrance and insufficient ink jetting stability due to the short length of the epoxy hydrocarbon chain. n is greater than 24, resulting in too long a length of the epoxy hydrocarbon chain, thus increasing hydrophilicity and being easily released in an aqueous medium. This results in insufficient affinity of the surface hydroxyl groups of the titanium oxide particles and causes aggregation of the titanium oxide particles. Therefore, the titanium oxide particles cannot be stably dispersed and the ink jetting stability cannot be obtained.

[0265] In the general formula (1), X represents a single bond or an alkylene group having 1 to 6 carbon atoms. When X represents a single bond, it means that the silicon atom is directly bonded to OR4. The alkylene group having 1 to 6 carbon atoms may be a methylene group, a vinyl group, a n-propenyl group, an isopropenyl group, a n-butenyl group, a n-pentenyl group, a n-hexenyl group, etc. In particular, a n-propenyl group may be used. When X represents an alkylene group having more than 6 carbon atoms, the hydrophobicity of the compound represented by the general formula (1) becomes too high, the titanium oxide particles cannot be stably dispersed, and the ink cannot have jetting stability.

[0266] The compound represented by the general formula (1) as a dispersant for titanium oxide particles can be a compound represented by the following general formula (2). Since it has three OR1s bonded to the silicon atom, the compound represented by the general formula (2) can be partially hydrolyzed in an aqueous medium and form three hydroxyl groups bonded to the silicon atom, thereby increasing the portion having affinity for titanium oxide particles. The compound represented by the following general formula (2) has a repeating structure of ethylene oxide. Therefore, the ethylene oxide chain is moderately elongated in an aqueous medium, and a repulsive force due to steric hindrance can be obtained.

[0267]

[0268] (In the general formula (2), R1 and R3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. m ranges from 8 to 24).

[0269] In terms of mass ratio, the amount (mass %) of the compound represented by the general formula (1) in the ink is preferably 0.002 times or more and 0.10 times or less of the content (mass %) of the titanium oxide particles. A mass ratio of less than 0.002 times may result in a poor stable dispersion effect of the titanium oxide particles, and the ink may have insufficient jetting stability. A mass ratio greater than 0.10 times tends to result in an excessively high proportion of the compound represented by the general formula (1), and condensation (self-condensation) occurs between the molecules of the compound represented by the general formula (1). This may result in the compound represented by the general formula (1) being consumed and unable to act as a dispersant, the effect of stabilizing the dispersion of the titanium oxide particles is weakened, and the ink has insufficient jetting stability.

[0270] The compound represented by the general formula (1) is hydrogen bonded to the surface hydroxyl groups of the titanium oxide particles and it can be considered that part of it forms a covalent bond through a dehydration reaction. However, in the present disclosure, the compound represented by the general formula (1) can disperse the titanium oxide particles without forming a covalent bond with the titanium oxide particles. Therefore, 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 covalently bonded compound represented by the general formula (1). Based on the research results of the inventors, it was found that the amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles is too much, resulting in a decrease in the jetting stability of the ink. The reason is as follows. Generally, in a liquid medium with a high dielectric constant (such as water), electrostatic attraction is unlikely to work and the titanium oxide particles move freely without significant environmental influences. However, when the compound represented by the general formula (1) is covalently bonded to the titanium oxide particles, the hydrophilic part (OR4 part) of the structure of the general formula (1) forms a hydrogen bond with the water molecule and may therefore affect the movement of the titanium oxide particles. Therefore, in the case where the liquid is deformed by instantaneous pressure (such as inkjet ejection), the characteristics as described above appear as differences in ejection characteristics. Therefore, in terms of mass ratio, the amount (mass %) of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles is preferably less than 0.001 times the content (mass %) of the titanium oxide particles. A mass ratio greater than 0.001 times may result in insufficient ejection stability of the ink. The mass ratio may be 0.000 times. The amount of the compound represented by the general formula (1) covalently bonded to the titanium oxide particles can be calculated by methods such as thermogravimetric analysis.

[0271] Resin

[0272] The ink may contain a resin. The resin may be an acrylic resin, a polyurethane resin, and a urea resin. In particular, an acrylic resin may be used. The resin content (mass %) of the ink is preferably 1.00 mass % or more and 25.00 mass % or less of the total mass of the ink, more preferably 3.00 mass % or more and 15.00 mass % or less. In particular, 5.00 mass % or more and 15.00 mass % or less is particularly preferred.

[0273] The ink may contain resin to improve various characteristics of the image to be recorded, such as scratch resistance and hiding power. The resin may be a block copolymer, a random copolymer, a graft copolymer, or a combination thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or a resin particle dispersed in an aqueous medium. The resin particles do not need to contain a coloring matter.

[0274] In this specification, the phrase "the resin is water-soluble" means that when the resin is neutralized with an amount of alkali equivalent to the acid value, the resin exists in an aqueous medium without forming particles whose particle size can be measured by a dynamic light scattering method. Whether the resin is water-soluble can be judged by the following method. First, a liquid containing a resin (resin solid content: 10% by mass) neutralized with an alkali equivalent to the acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Subsequently, the prepared liquid is diluted 10 times (based on volume) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles with a particle size are observed, it can be judged that the resin is water-soluble. For example, the measurement conditions are SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As a particle size distribution analyzer, a particle size analyzer applying a dynamic light scattering method (for example, trade name: "UPA-EX150", manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution analyzer used, the measurement conditions, etc. are not limited to the above.

[0275] 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. The acid value of the resin particles (if present) 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 polystyrene equivalent molecular weight measured by gel permeation chromatography (GPC).

[0276] Aqueous medium

[0277] The ink is an aqueous ink containing water as an aqueous medium. The ink may contain water or an aqueous medium, wherein the aqueous medium is a mixed solvent of water and a water-soluble organic solvent. The water may be deionized water (ion exchange water). The water content (mass %) of the ink is preferably 50.00 mass % or more and 95.00 mass % or less of the total mass of the ink.

[0278] There is no particular limitation on the water-soluble organic solvent, as long as the solvent is water-soluble (for example, the solvent can be dissolved in water in any proportion at 25°C). More specifically, monohydric or dihydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. The water-soluble organic solvent content (mass %) of the ink is preferably 3.00 mass % or more and 50.00 mass % or less of the total mass of the ink, and more preferably 10.00 mass % or more and 40.00 mass % or less of the total mass of the ink. A water-soluble organic solvent content (mass %) of less than 3.00 mass % can cause the ink to solidify in the inkjet recording device and can cause insufficient anti-stickiness. A water-soluble organic solvent content (mass %) greater than 50.00 mass % can cause ink supply failure.

[0279] Other additives

[0280] In addition to the above-mentioned additives, the ink may also contain other additives as needed, such as surfactants, pH regulators, corrosion inhibitors, preservatives, mildew inhibitors, antioxidants, reduction inhibitors, evaporation promoters and / or chelating agents. In particular, the ink may contain a surfactant. The surfactant content (mass %) in the ink is preferably more than 0.10 mass % and less than 5.00 mass % of the total mass of the ink, more preferably more than 0.10 mass % and less than 2.00 mass % of the total mass of the ink. The surfactant may be an anionic surfactant, a cationic surfactant or a nonionic surfactant. In particular, the nonionic surfactant may be used to adjust the various physical properties of the ink, and the nonionic surfactant has a low affinity for titanium oxide particles and can produce an effect even if the amount used is small.

[0281] Physical properties of ink

[0282] The ink is an ink applied to an inkjet system and its physical properties can be appropriately adjusted for the inkjet system. The surface tension of the ink at 25°C is preferably 10mN / m or more and 60mN / m or less, more preferably 20mN / m or more and 40mN / 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 the present disclosure, the viscosity of the white ink at 25°C is preferably 1.0mPa·s or more and 10.0mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.0 or less. When the pH of the ink is within the above range, the compound represented by the general formula (1) hydrolyzes and produces a silanol group, thereby effectively showing a weak affinity for titanium oxide particles. The pH of the ink can be measured using an ordinary pH meter equipped with a glass electrode.

[0283] Ink production method

[0284] In the present disclosure, the method for producing ink includes the step of mixing a dispersion of titanium oxide particles with other ink components. The dispersion of titanium oxide particles is a dispersion of titanium oxide particles produced by the production method described later. Other ink components may be water, a water-soluble organic solvent, a resin to be further added, the above-mentioned "other additives", etc. For example, the ink can be produced by stirring the dispersion of titanium oxide particles and other ink components in a suitable container. Conditions such as stirring speed, temperature and time can be appropriately determined according to the desired conditions. In addition, another known production process may also be combined.

[0285] The present disclosure can provide a liquid ejection head and a liquid ejection apparatus that can effectively achieve a circulation effect.

[0286] Although the present invention has been described with reference to one or more embodiments, it should be understood that the present invention is not limited to the disclosed embodiments. The above embodiments may be implemented individually, or as a combination of multiple elements or features thereof when necessary or when a combination of elements or features from various embodiments is beneficial in a single embodiment. The scope of the appended claims should be given the broadest interpretation so as to cover all such modifications and equivalent structures and functions that are obvious or apparent to those skilled in the art.

Claims

1. A liquid ejection head, comprising: an ejection port portion having, at the first end portion, an ejection port configured to eject the liquid along an ejection direction; a pressure chamber including an energy generating element therein, the energy generating element being configured to generate energy required to eject the liquid from the ejection port, and the pressure chamber being in communication with the ejection port portion at a second end portion opposite to the first end portion; a supply channel configured to supply liquid to the pressure chamber; a collection channel configured to collect liquid from the pressure chamber; and a pump configured to cause the liquid in the collection channel to flow into the supply channel, Among them, F is expressed by the following formula ratio 1.0 or more and 1.4 or less: F ratio =1.619×(H -0.34 Q -0.66 w) -0.1569 ×log(U x / U v ) -0.2560 Wherein, W [μm] represents the length of the ejection port in the flow direction of the liquid in the pressure chamber, P [μm] represents the length of the ejection port portion in the ejection direction of the liquid ejected from the ejection port, H [μm] represents the height of the pressure chamber on the upstream side in the flow direction of the liquid in the pressure chamber, and U [μm] represents the height of the pressure chamber on the upstream side in the flow direction of the liquid in the pressure chamber. v [m / s] represents the evaporation rate in the jet orifice, and U x [m / s] indicates the flow rate of the liquid flowing through the pressure chamber.

2. The liquid ejecting head according to claim 1, wherein: F ratio It is 1.0 or more and 1.3 or less.

3. The liquid ejecting head according to claim 1, wherein: F ratio It is 1.0 or more and 1.2 or less.

4. The liquid ejecting head according to claim 1, comprising: a plurality of said injection ports, Among them, U x [m / s] is expressed by the following formula, U x =Q / (S×N) Among them, Q[m 3 / s] represents the flow rate of the pump, S[m 2 ] represents the cross-sectional area corresponding to the height H of the pressure chamber, and N represents the number of the injection ports.

5. The liquid ejection head according to claim 1, wherein the liquid ejection head further satisfies the following formula: H -0.34 ×P -0.66 ×W>1.7 6 . The liquid ejection head according to claim 1 , further comprising a first pressure regulating unit configured to regulate the pressure of the liquid in the supply channel.

7. The liquid ejecting head according to claim 6, wherein: The first pressure regulating unit includes a first valve chamber, a first pressure control chamber, a first opening allowing the first valve chamber and the first pressure control chamber to communicate with each other, and a first valve configured to open and close the first opening.

8. The liquid ejecting head according to claim 7, wherein: The first pressure control chamber includes a first pressure plate, which has a surface partially formed by a first flexible member configured to be displaceable and can be displaced in conjunction with the first flexible member, the first pressure control chamber includes a first pushing member, the first pushing member pushes the first pressure plate in a direction in which the first pressure control chamber has an increased volume, and the first pressure control chamber is configured to be able to open and close the first valve according to the displacement of the first pressure plate and the first flexible member. 9 . The liquid ejection head according to claim 8 , further comprising a channel configured to supply liquid to the first pressure regulating unit from the outside. 10 . The liquid ejection head according to claim 6 , further comprising a second pressure regulating unit configured to regulate the pressure of the liquid in the collection channel. 11 . The liquid ejection head according to claim 1 , comprising a bypass that allows the supply channel and the collection channel to communicate with each other without passing through the pressure chamber.

12. The liquid ejecting head according to claim 1, wherein The pump is a piezoelectric pump.

13. The liquid ejecting head according to claim 1, wherein The liquid is ink.

14. The liquid ejecting head according to claim 13, wherein: The ink is a white ink containing titanium oxide.

15. A liquid ejecting device comprising a liquid ejecting head, the liquid ejecting head comprising: an ejection port portion having, at the first end portion, an ejection port configured to eject the liquid along an ejection direction; a pressure chamber including an energy generating element therein, the energy generating element being configured to generate energy required to eject the liquid from the ejection port, and the pressure chamber being in communication with the ejection port portion at a second end portion opposite to the first end portion; a supply channel configured to supply liquid to the pressure chamber; a collection channel configured to collect liquid from the pressure chamber; and a pump configured to cause the liquid in the collection channel to flow into the supply channel, Among them, F is expressed by the following formula ratio 1.0 or more and 1.4 or less: F ratio =1.619×(H -0.34 Q -0.66 w) -0.1569 ×log(U x / U v ) -0.2560 Wherein, W [μm] represents the length of the ejection port in the flow direction of the liquid in the pressure chamber, P [μm] represents the length of the ejection port portion in the ejection direction of the liquid ejected from the ejection port, H [μm] represents the height of the pressure chamber on the upstream side in the flow direction of the liquid in the pressure chamber, and U [μm] represents the height of the pressure chamber on the upstream side in the flow direction of the liquid in the pressure chamber. v [m / s] represents the evaporation rate in the jet orifice, and U x [m / s] indicates the flow rate of the liquid flowing through the pressure chamber.

Images