Liquid discharge head and liquid discharge method

Abstract

To provide discharge stability during long continuous discharging while suppressing generation of a satellite by shortening a tail length.SOLUTION: This liquid discharge head comprises: an element that generates thermal energy for discharging liquid; a pressure chamber provided with the element; an outlet through which the liquid is discharged; and an outlet through which the outlet and the pressure chamber communicate with each other. Bubbles are generated in the pressure chamber by the thermal energy, the generated bubbles enter the inside of the outlet, and the liquid is discharged through the outlet by a pressure of the bubbles. The bubbles communicate with the atmosphere, and the liquid is discharged through the outlet in a state where at least some of the bubbles which have entered the inside of the outlet have speed components toward the surface of the pressure chamber provided with the element and a state before the liquid discharged through the outlet is pulled into the pressure chamber due to shrinkage of the bubbles to come into contact with the surface of the pressure chamber provided with the element.SELECTED DRAWING: Figure 18

Description

[Technical field]

[0001] The present invention relates to a liquid ejection head and a liquid ejection method. [Background technology]

[0002] A liquid ejection method using a liquid ejection head, such as an inkjet head, includes a thermal method in which heat is applied to a liquid (such as ink) to cause film boiling, and the resulting bubbling force is utilized. A liquid ejection head used in a thermal method has a pressure chamber for applying the force to eject the liquid, a heat generating resistor element (heater) provided in the pressure chamber, a flow path for supplying liquid to the pressure chamber, and an element substrate on which a supply port for supplying liquid to the flow path is formed. The liquid is ejected from the ejection port of the element substrate by the energy generated by the heat generating resistor element.

[0003] When liquid is discharged by the above-mentioned thermal liquid discharge head, the discharged liquid becomes a columnar shape including a main droplet and a long, thin trailing portion (hereinafter also referred to as a tail) that extends so as to connect to the rear of the main droplet. This trailing portion is separated from the main droplet by the surface tension of the liquid while the droplet is flying, and becomes a minute droplet (a secondary droplet, a satellite). This satellite may land at a position on the recording medium that is shifted from the main droplet, causing a decrease in image quality. Furthermore, the particularly minute satellite does not reach the recording medium, and becomes a floating droplet (hereinafter also referred to as a mist). The mist may soil a liquid discharge device such as an inkjet printer, and the dirt from the liquid discharge device may be transferred to the recording medium, soiling the recording medium.

[0004] As a means for preventing degradation of image quality due to such satellites, Patent Document 1 discloses the configuration of a liquid ejection head capable of shortening the tail length of liquid droplets. In a liquid ejection head provided with a protrusion at the ejection port, air bubbles are generated in a pressure chamber by thermal energy, and the generated air bubbles enter the inside of the ejection port, and liquid is ejected from the ejection port due to the pressure of the air bubbles. It is described that the air bubbles that have entered the inside of the ejection port communicate with the atmosphere outside the ejection port, thereby shortening the tail length of the liquid droplets and suppressing satellites. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-124600 A Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of the inventors' investigations, they found a new problem that the tail of the droplets is easily unstable in the configuration of the liquid ejection head and the liquid ejection method disclosed in the above-mentioned Patent Document 1. It was found that if ejection is performed continuously for a long time without performing a recovery operation such as wiping the vicinity of the ejection port with a wiper, foreign matter may accumulate near the ejection port, causing a large deviation in the landing position of the ejected droplets. Therefore, an object of the present invention is to provide a liquid ejection head and a liquid ejection method that shorten the tail length to suppress the occurrence of satellites and have ejection stability during long-term continuous ejection. [Means for solving the problem]

[0007] The present invention, which solves the above-mentioned problems, is a liquid ejection head comprising an element that generates thermal energy for ejecting liquid, a pressure chamber containing said element, an ejection port from which liquid is ejected, and an ejection port portion connecting said ejection port and said pressure chamber, wherein bubbles are generated in said pressure chamber by the thermal energy, the generated bubbles enter the interior of said ejection port portion, and liquid is ejected from said ejection port by the pressure of the bubbles, and wherein the liquid ejection head is configured such that, when at least a part of the bubbles that have entered the interior of the ejection port portion has a velocity component directed toward a surface of said pressure chamber containing said element, and before the liquid ejected from the ejection port is drawn into the pressure chamber by the contraction of the bubble and comes into contact with the surface of the pressure chamber containing the element, the bubbles communicate with the atmosphere and liquid is ejected from the ejection port. It is. Effect of the Invention

[0008] According to the present invention, it is possible to provide a liquid ejection head and a liquid ejection method that have ejection stability during long-term continuous ejection while reducing the tail length and suppressing the occurrence of satellites. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a liquid ejection apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a conceptual diagram showing a control system according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram showing a liquid circulation path according to an embodiment of the present invention. [Figure 4] 1 is a perspective view showing a liquid ejection head according to an embodiment of the present invention. [Diagram 5] FIG. 2 is an exploded perspective view of the liquid ejection head according to the embodiment of the present invention. [Figure 6] FIG. 2 is a plan view of the flow path member according to the embodiment of the present invention. [Figure 7] 1A and 1B are a perspective view and a cross-sectional view of a flow path member according to an embodiment of the present invention. [Figure 8] 1A and 1B are a perspective view and an exploded perspective view of a dispensing module according to an embodiment of the present invention; [Figure 9] FIG. 2 is a plan view of an element substrate according to the embodiment of the present invention. [Figure 10] 2 is a cross-sectional view of an element substrate according to an embodiment of the present invention. [Figure 11] 3A and 3B are schematic diagrams illustrating a temperature adjusting means of the element substrate according to the embodiment of the present invention. [Figure 12] 4 is a partial enlarged plan view of an adjacent portion of an element substrate according to the embodiment of the present invention. FIG. [Figure 13] 2A and 2B are a plan view and a cross-sectional view showing the inside of a liquid ejection head according to an embodiment of the present invention. [Figure 14] FIG. 2 is an enlarged plan view of the vicinity of an ejection port of a liquid ejection head according to an embodiment of the present invention. [Figure 15] 1A to 1C are schematic diagrams showing a transitional process of the ejection phenomenon in Comparative Example 1. [Figure 16] 1A to 1C are schematic diagrams showing a transitional process of the ejection phenomenon in Comparative Example 1. [Figure 17] 13 is a schematic diagram showing a transitional process of the ejection phenomenon in Comparative Example 2. FIG. [Figure 18] 5A to 5C are schematic diagrams illustrating a transitional process of a discharge phenomenon in an embodiment of the present invention. [Figure 19] FIG. 11 is a diagram showing the relationship between the time from the start of foaming and the volume of bubbles in the transitional process of the discharge phenomenon in an embodiment of the present invention. [Figure 20] 11 is a diagram showing the relationship between the distance OH from the bottom surface of the pressure chamber to the ejection port and the time Tth-Tfall from when the size of the bubble reaches a maximum until it communicates with the atmosphere. [Figure 21] 13 is a diagram showing the distance OH from the bottom surface of the pressure chamber to the ejection port, and the time Tfall-Tth from when the bubble communicates with the atmosphere until the tail falls onto the recording element. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the following description does not limit the scope of the present invention. As an example, in this embodiment, a thermal method is adopted in which a heat generating element generates bubbles to eject liquid. However, the present invention can also be applied to a liquid ejection head that employs a piezo method using a piezoelectric element as an energy generating element for ejecting liquid, or other various liquid ejection methods. The liquid ejection head of the present invention and a liquid ejection device equipped with the liquid ejection head can be applied to devices such as inkjet printers, copiers, facsimiles with communication systems, and word processors with printer units. Furthermore, they can be applied to industrial recording devices that are combined in a composite manner with various processing devices. For example, they can also be used for applications such as biochip production, electronic circuit printing, and semiconductor substrate production.

[0011] In this embodiment, the liquid ejection device is configured to circulate the liquid such as ink between a tank and a liquid ejection head, but other configurations are also possible. For example, the liquid may be moved in a pressure chamber by providing two tanks on the upstream side and downstream side of the liquid ejection head and flowing the liquid from one tank to the other tank without circulating the liquid. In addition, the present embodiment is a so-called line type (page wide type) head having a length corresponding to the width of the recording medium, but the present invention can also be applied to a so-called serial type liquid ejection head that performs recording while scanning the recording medium. An example of a serial type liquid ejection head is a configuration in which one element substrate for black ink and one element substrate for color ink are mounted, but the present invention is not limited to this. A short line head shorter than the width of the recording medium may be created by arranging several element substrates so that the ejection ports overlap in the ejection port row direction, and the recording medium is scanned with the line head.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] (First embodiment) <Overall configuration of the device> 1 is a diagram showing an example of a liquid ejection device in this embodiment. The liquid ejection device in this embodiment is a liquid ejection device 1000 (hereinafter, simply referred to as device 1000) serving as an inkjet printer that records a color image on a recording medium 3 by ejecting yellow (Y), magenta (M), cyan (C), and black (Bk) inks. In the figure, the X direction is the transport direction of the recording medium 3, the Y direction is the width direction of the recording medium, and the Z direction is the direction intersecting the X and Y directions and is the direction in which liquid is ejected.

[0014] Fig. 1 shows an apparatus 1000 in which a liquid ejection head 1 applies ink directly to a recording medium 3 transported in the X direction. The recording medium 3 is mounted on a transport section 2 and transported in the X direction at a predetermined speed below four liquid ejection heads 1 (1Y, 1M, 1C, 1Bk) that eject different inks. In Fig. 1, the four liquid ejection heads 1 are arranged in the X direction in the order of 1Bk, 1Y, 1M, 1C, and inks are applied to the recording medium 3 in the order of black, cyan, magenta, and yellow. Each liquid ejection head 1 has a plurality of ejection openings arranged in the Y direction for ejecting ink.

[0015] 1 shows cut paper as the recording medium 3, the recording medium 3 may be continuous paper supplied from a roll of paper. The recording medium is not limited to paper, and may be, for example, a film.

[0016] In the present embodiment, the liquid ejection device has been described as having a configuration in which one liquid ejection head ejects ink of a single color, but one liquid ejection head may be configured to eject ink of multiple colors, or may be configured to eject liquid other than ink, such as a reaction liquid or an overcoat agent.

[0017] 2 is a block diagram for explaining the control configuration of the liquid ejection device 1000. The control unit 500 is composed of a CPU and the like, and controls the entire liquid ejection device 1000 while using a RAM 502 as a work area in accordance with programs and various parameters stored in a ROM 501. The control unit 500 performs predetermined image processing on image data received from an externally connected host device 600 in accordance with the programs and parameters stored in the ROM 501, and generates ejection data that can be ejected by the liquid ejection head 3. Then, the liquid ejection head 3 is driven in accordance with this ejection data, causing it to eject ink at a predetermined frequency.

[0018] During the ejection operation by the liquid ejection head 3, the control unit 500 drives the transport motor 503 to transport the recording medium 2 in the X direction at a speed corresponding to the drive frequency. As a result, an image is recorded on the recording medium 2 according to the image data received from the host device 600. Information on the use areas of the ejection ports used for ejection in the liquid ejection head 3 is stored in the ROM 501 in a rewritable manner for each liquid ejection head 3.

[0019] <Liquid circulation path> 3 is a schematic diagram showing the circulation paths of liquid in the liquid ejection device of this embodiment, and shows the liquid ejection head 3 fluidly connected to a first circulation pump 1002, a buffer tank 1003, etc. Note that, although Fig. 3 only shows the path through which ink flows in the liquid ejection head corresponding to one color of ink, the device main body 1000 is provided with circulation paths corresponding to the type of liquid, such as ink, to be ejected.

[0020] The buffer tank 1003, which serves as a sub-tank and is connected to the main tank 1006, has an air communication port (not shown) that communicates between the inside of the tank and the outside, and is capable of discharging air bubbles in the ink to the outside. The buffer tank 1003 is also connected to a refill pump 1005. When liquid is consumed in the liquid discharge head 3 by discharging (discharging) ink from the discharge ports of the liquid discharge head for recording by discharging ink or for suction recovery, the refill pump 1005 transfers the amount of consumed ink from the main tank 1006 to the buffer tank 1003.

[0021] The first circulation pump 1002 has a role of drawing liquid from the liquid connection portion 111 of the liquid ejection head 3 and flowing it to the buffer tank 1003. When the liquid ejection head 3 is driven, a constant amount of ink flows inside the common recovery channel 212 by the first circulation pump 1002.

[0022] The negative pressure control unit 230 is provided between the second circulation pump 1004 and the liquid ejection unit 300. Even if the flow rate of the circulation system varies due to a difference in the duty of recording, the negative pressure control unit 230 has a function of operating to maintain the pressure downstream (the liquid ejection unit 300 side) at a preset constant pressure.

[0023] As shown in Fig. 3, the negative pressure control unit 230 includes two pressure adjustment mechanisms, and different control pressures are set for each pressure adjustment mechanism. Of the two pressure adjustment mechanisms, the relatively high pressure setting side (indicated as H in Fig. 3) and the relatively low pressure side (indicated as L in Fig. 3) are connected to the common supply flow channel 211 and the common recovery flow channel 212 in the liquid ejection unit 300 via the liquid supply unit 220, respectively. The liquid ejection unit 300 is provided with the common supply flow channel 211, the common recovery flow channel 212, and individual supply flow channels 213a and individual recovery flow channels 214a that communicate with each element substrate. Since the individual flow channel 213 communicates with the common supply flow channel 211 and the common recovery flow channel 212, a part of the liquid flown by the second circulation pump 1004 flows from the common supply flow channel 211 through the internal flow channel of the element substrate 10 to the common recovery flow channel 212 (arrow in Fig. 3). This is because a pressure difference is provided between the pressure adjustment mechanism H connected to the common supply flow path 211 and the pressure adjustment mechanism L connected to the common recovery flow path 212, and the first circulation pump 1002 is connected only to the common recovery flow path 212.

[0024] In this way, in the liquid ejection unit 300, a liquid flow that passes through the common recovery flow path 212 and a flow that passes through each element substrate 10 from the common supply flow path 211 to the common recovery flow path 212 are generated. Therefore, heat generated in each element substrate 10 can be discharged to the outside of the element substrate 10 by the flow from the common supply flow path 211 to the common recovery flow path 212. Furthermore, with this configuration, when recording is being performed by the liquid ejection head 3, an ink flow can be generated even in ejection ports and pressure chambers that are not performing recording, so that thickening of the ink in those areas can be suppressed. Also, thickened ink and foreign matter in the ink can be discharged to the common recovery flow path 212. Therefore, the liquid ejection head 3 of this embodiment is capable of high-speed, high-quality recording.

[0025] <Configuration of Liquid Ejection Head> 4(a) and 4(b) are perspective views of the liquid ejection head 1 according to the present embodiment. The liquid ejection head 1 is a line-type liquid ejection head in which 17 element substrates 10 capable of ejecting ink are arranged in a straight line (arranged in-line). As shown in FIG. 4(a) and FIG. 4(b), the liquid ejection head 1 includes each element substrate 10, a signal input terminal 91 and a power supply terminal 92 electrically connected via an electric wiring board (flexible wiring board) 40 and an electric wiring board 90. The signal input terminal 91 and the power supply terminal 92 are electrically connected to a control unit of the device 1000, and supply the ejection drive signal and the power required for ejection to the element substrate 10, respectively. By consolidating the wiring by the electric circuit in the electric wiring board 90, the number of signal output terminals 91 and the power supply terminals 92 can be made smaller than the number of element substrates 10. This reduces the number of electrical connections that need to be removed when assembling the liquid ejection head 1 to the device 1000 or when replacing the liquid ejection head 1. 4(a), a liquid connection part 111 provided on one side of the liquid ejection head 1 is connected to a liquid supply system of the device 1000. This allows ink to be supplied from the supply system of the device 1000 to the liquid ejection head 1, and ink that has passed through the liquid ejection head 1 is collected by the supply system of the device 1000. In this way, ink can be circulated via the path of the device 1000 and the path of the liquid ejection head 1.

[0026] FIG. 5 shows an exploded perspective view of each part or unit constituting the liquid ejection head 1. The liquid ejection unit 300, the liquid supply unit 220, and the electric wiring board 90 are attached to the housing 80. The liquid supply unit 220 is provided with a liquid connection part 111, and the liquid supply unit 220 is provided with a filter 221 (FIG. 5) communicating with each opening of the liquid connection part 111 in order to remove foreign matter from the ink being supplied. The liquid that has passed through the filter 221 is supplied to the negative pressure control unit 230 arranged on the liquid supply unit 220. The negative pressure control unit 230 is a unit consisting of a pressure adjustment valve, and the valves and spring members provided therein greatly attenuate the pressure loss change in the supply system of the device 1000 (the supply system upstream of the liquid ejection head 1) that occurs with the fluctuation of the liquid flow rate. This makes it possible to stabilize the negative pressure change downstream of the negative pressure control unit 230 (the liquid ejection unit 300 side) within a certain range. Two pressure regulating valves are built into the negative pressure control unit 230, each set to a different control pressure, and the high pressure side is connected to the common supply flow path 211 in the liquid ejection unit 300, and the low pressure side is connected to the common recovery flow path 212 via the liquid supply unit 220.

[0027] The housing 80 is composed of a liquid discharge unit support part 81 and an electric wiring board support part 82, and supports the liquid discharge unit 300 and the electric wiring board 90 while ensuring the rigidity of the liquid discharge head 1. The electric wiring board support part 82 is for supporting the electric wiring board 90, and is fixed to the liquid discharge unit support part 81 by screwing. The liquid discharge unit support part 81 is provided with openings 83 and 84 into which a joint rubber 100 is inserted. The liquid supplied from the liquid supply unit 220 is led via the joint rubber 100 to the second flow path member 60 constituting the liquid discharge unit 300.

[0028] Next, the configuration of the flow path member 210 included in the liquid discharge unit 300 will be described. As shown in FIG. 5, in the flow path member 210, a first flow path member 50 and a second flow path member 60 are laminated. A plurality of discharge modules 200 are bonded to the bonding surface of the first flow path member 50 with an adhesive (not shown). The flow path member 210 is a flow path member for distributing liquid supplied from the liquid supply unit 220 to each discharge module 200 and returning liquid flowing out from the discharge module 200 to the liquid supply unit 220. In addition, the flow path member 210 is fixed to the liquid discharge unit support part 81 by screws, which suppresses warping and deformation of the flow path member 210.

[0029] FIG. 6 is a diagram for explaining a detailed configuration of the flow path member 210. FIG. 6(a) shows the support member 30 provided on the surface of the first flow path member 50 on which the discharge module 200 is mounted, and FIG. 6(b) shows the contact surface of the first flow path member 50 with the support member 30. FIG. 6(c) shows a cross-sectional view of the first flow path member 50 on a surface perpendicular to the Z direction and near the center in the Z direction, and FIG. 6(d) shows the surface of the second flow path member 60 on the side that contacts the liquid discharge unit support part 81. Note that FIGS. 6(a) to 6(c) are views seen from the discharge module 200 side, and FIG. 6(d) is a view seen from the liquid discharge unit support part 81 side.

[0030] A plurality of support members 30 arranged in the Y direction are disposed on the surface of the first flow path member 50 opposite to the second flow path member 60, and one element substrate 10 is disposed on each support member 30. By adjusting the number of arranged discharge modules 200, it is possible to configure liquid discharge heads 3 of various sizes.

[0031] 6(a), the support member 30 has, on its surface in contact with the element substrate 10, a support member communication port 31 that is fluidly connected to the element substrate 10 and serves as the individual supply flow paths 213a and the individual recovery flow paths 213b described above in Fig. 3. As shown in Fig. 6(b), the support member communication port 31 is fluidly connected to the common supply flow path 211 or the common recovery flow path 212 via a communication port 51 provided in the flow path member 50.

[0032] 6(c), in a middle layer near the center in the Z direction of the first flow path member 50, common flow path grooves 61 and 62 which become the common supply flow path 211 and the common recovery flow path 212 described in FIGS. 3(a) and 3(b) extend in the Y direction. As shown in FIG. 6(d), at both ends or one end of the common flow path grooves 61 and 62, a common communication port 63 which is fluidly connected to the liquid supply unit 220 is formed.

[0033] Figures 7(a) and (b) are a perspective view and a cross-sectional view for explaining a flow path structure formed inside the liquid discharge unit 300. Figure 7(a) is an enlarged perspective view of the flow path member 210 as viewed from the Z direction, and Figure 7(b) is a cross-sectional view taken along line VII-VII in Figure 7(a).

[0034] The element substrate 10 of the ejection module 200 is placed on the communication port 51 of the first flow path member 50 via the support member 30. In FIG. 7(b), only the communication port 51 corresponding to the common supply flow path 211 is illustrated, but in another cross section, the common recovery flow path 212 and the communication port 51 are communicated with each other as shown in FIG. 6. In the support member 30 and the element substrate 10 included in each ejection module 200, a flow path is formed for supplying ink from the first flow path member 50 to the heating resistor element 15 (see FIG. 9) provided on the element substrate 10. In addition, in the support member 30 and the element substrate 10, a flow path is formed for recovering (circulating) a part or all of the liquid supplied to the heating resistor element 15 to the first flow path member 50.

[0035] As described above, the common supply flow path 211 is connected to the relatively high pressure negative pressure control unit 230H, and the common recovery flow path 212 is connected to the relatively low pressure negative pressure control unit 230L. An ink supply path is formed that supplies ink to a flow path formed in the element substrate 10 through the common communication port 63 (see FIG. 6), the common supply flow path 211, and the support member communication port 31. Similarly, an ink recovery path is formed from the flow path in the element substrate 10 through the support member communication port 31, the communication port 51, the common recovery flow path 212, and the common communication port 63 (see FIG. 7). While the ink is circulated in this manner, an ejection operation according to the ejection data is performed in the element substrate 10, and the ink that is not consumed by the ejection operation among the ink supplied through the ink supply path is recovered by the ink recovery path.

[0036] <Configuration of the discharge module> FIG. 8(a) is a perspective view showing one discharge module 200, and FIG. 8(b) is an exploded view thereof. In the manufacturing method of the discharge module 200, first, the element substrate 10 and the flexible wiring substrate 40 are bonded onto the support member 30 in which the support member communication port 31 is provided in advance. Then, the terminal 16 on the element substrate 10 and the terminal 41 on the flexible wiring substrate 40 are electrically connected by wire bonding, and then the wire bonding portion (electrical connection portion) is covered and sealed with a sealant 110. The terminal 42 on the opposite side of the flexible wiring substrate 40 from the element substrate 10 is electrically connected to the connection terminal 93 (see FIG. 5) of the electrical wiring substrate 90. The support member 30 is a support for supporting the element substrate 10 and is also a flow path member for fluidly communicating the element substrate 10 and the flow path member 210, so it is preferable that the support member 30 has a high flatness and can be bonded to the element substrate with sufficiently high reliability. For example, alumina or a resin material is preferable as the material.

[0037] <Configuration of element substrate> The configuration of the element substrate 10 in this embodiment will be described. Fig. 9(a) shows a plan view of the surface of the element substrate 10 on which the ejection ports 13 are formed, Fig. 9(b) shows an enlarged view of a portion indicated by A in Fig. 9(a), and Fig. 9(c) shows a plan view of the back surface of Fig. 9(a). Fig. 10 is a cross-sectional perspective view of the element substrate 10 taken along line XX in Fig. 9(a). Hereinafter, the direction in which an ejection port array in which a plurality of ejection ports 13 are arranged extends is referred to as the "ejection port array direction".

[0038] As shown in FIG. 9B, a heating resistor element 15, which is a heating element (pressure generating element) for foaming the liquid by utilizing the thermal energy generated by the liquid, is disposed at a position corresponding to each ejection port 13. A pressure chamber 23 in which the heating resistor element 15 is disposed is partitioned by a partition wall 22. The heating resistor element 15 is electrically connected to a terminal 16 by an electric wiring (not shown) provided on the element substrate 10. The heating resistor element 15 generates heat based on a pulse signal input from a control circuit of the liquid ejection device 1000 via an electric wiring substrate 90 (see FIG. 5) and a flexible wiring substrate 40 (see FIG. 8) to boil the liquid. The liquid is ejected from the ejection port 13 by the force of foaming caused by the boiling. As shown in FIG. 9B, a liquid supply path 18 extends on one side along each ejection port row, and a liquid recovery path 19 extends on the other side along each ejection port row. The liquid supply path 18 and the liquid recovery path 19 are flow paths extending in the ejection port array direction provided in the element substrate 10, and communicate with the ejection ports 13 via the supply ports 17a and the recovery ports 17b, respectively. Figures 9(a) to 9(c) show an element substrate 10 having 16 ejection port arrays as an example.

[0039] As shown in FIG. 9(c) and FIG. 10, a sheet-like cover plate 20 is laminated on the back surface of the element substrate 10, opposite to the surface on which the ejection ports 13 are formed. As shown in FIG. 9(c), the cover plate 20 is provided with a plurality of openings 21 communicating with the liquid supply passage 18 and the liquid recovery passage 19, which will be described later. In this embodiment, the cover plate 20 is provided with four supply openings 21a for one liquid supply passage 18 and three recovery openings 21b for one liquid recovery passage 19, but the number of openings is not limited to this. As shown in FIG. 9(b), each opening 21 in the cover plate 20 communicates with the communication port 51 shown in FIG. 7(a). The cover plate 20 is preferably made of a material having sufficient corrosion resistance against liquid, and high accuracy is required for the opening shape and opening position of the opening 21 so that ink is supplied to the pressure chamber. For this reason, it is preferable to use a photosensitive resin material or a silicon plate as the material of the cover plate 20, and provide the openings 21 by photolithography technology. In this manner, the cover plate 20 changes the pitch of the flow paths by the openings 21, and the cover plate is desirably made of a film-like material having a thickness of about 30 to 600 μm from the viewpoints of pressure loss, strength, and workability.

[0040] Next, the flow of liquid in the element substrate 10 will be described. In FIG. 10, a configuration in which four rows of ejection ports are formed in the ejection port forming member 12 in the element substrate 10 is shown, but the number of ejection port rows is not limited to four and can be appropriately selected. The element substrate 10 is formed by laminating a substrate 11 made of silicon and an ejection port forming member 12 made of a photosensitive resin, and a cover plate 20 is bonded to the back surface of the substrate 11. The cover plate 20 functions as a lid that forms part of the walls of the liquid supply path 18 and the liquid recovery path 19 formed in the substrate 11 of the element substrate 10. In the element substrate 10, a heating resistor element 15 is formed on one surface side of the substrate 11 (see FIG. 9), and a groove that constitutes the liquid supply path 18 and the liquid recovery path 19 extending along the ejection port rows is formed on the back surface side. The liquid supply path 18 and the liquid recovery path 19 formed by the substrate 11 and the cover plate 20 are connected to a common supply path 211 and a common recovery path 212 in the flow path member 210, respectively (see FIG. 7), and a pressure difference is generated between the liquid supply path 18 and the liquid recovery path 19. This pressure difference generates a circulation flow C in which the liquid in the liquid supply path 18 provided in the substrate 11 flows to the liquid recovery path 19 via the supply port 17a, the pressure chamber 23, and the recovery port 17b (flow indicated by the arrow C in FIG. 10). This flow allows the thickened ink, bubbles, foreign matter, and the like generated by evaporation from the ejection port 13 to be collected in the liquid recovery path 19 in the ejection port 13 and the pressure chamber 23 that are not performing the ejection operation. In addition, it is possible to suppress the ink in the ejection port 13 and the pressure chamber 23 from becoming thicker and the concentration of the coloring material from increasing. As shown in Figure 7, the liquid recovered to the liquid recovery path 19 is recovered in the order of the opening 21 in the cover plate 20 and the support member communication port 31 of the support member 30, the communication port 51 of the first flow path member 50, and the common recovery flow path 212, and is then recovered to the supply path of the liquid ejection device 1000.

[0041] That is, the liquid supplied from the liquid discharge device main body to the liquid discharge head 3 flows in the following order, and is supplied and recovered. The liquid first flows into the inside of the liquid discharge head 3 from the liquid connection portion 111 of the liquid supply unit 220. Then, the liquid is supplied in this order to the joint rubber 100, the common communication port 63 provided in the second flow path member, the common flow path groove 61 and the communication port 51 provided in the first flow path member. After that, the liquid is supplied to the pressure chamber 23 via the support member communication port 31 provided in the support member 30, the opening 21 provided in the cover plate 20, the liquid supply path 18 and the supply port 17a provided in the substrate 11. Of the liquid supplied to the pressure chamber 23, the liquid that is not discharged from the discharge port 13 flows in this order through the recovery port 17b and the liquid recovery path 19 provided in the substrate 11, the opening 21 provided in the cover plate 20, and the support member communication port 31 provided in the support member 30. Thereafter, the liquid flows in sequence through the communication port 51 and the common flow path 62 provided in the first flow path member, the common communication port 63 provided in the second flow path member, and the joint rubber 100. Then, the liquid flows from the liquid connection part 111 provided in the liquid supply unit to the outside of the liquid ejection head 3. In the form of the circulation path shown in FIG. 3, the liquid that flows in from the liquid connection part 111 is supplied to the joint rubber 100 after passing through the negative pressure control unit 230.

[0042] The liquid ejection head of this embodiment further has a temperature adjustment mechanism in the element substrate 10. FIG. 11 is a schematic diagram showing how each element substrate 10 is divided into a plurality of areas for temperature adjustment. A temperature sensor 301 and an individually controllable sub-heater 302 are provided for each area, and the control unit 500 (see FIG. 2) adjusts the temperature based on the temperature (target temperature) set for each area using the temperature sensor 301 and the sub-heater 302. That is, the control unit 500 drives the sub-heater 302 only in the area where the temperature detected by the temperature sensor 301 is equal to or lower than the target temperature. By setting the target temperature of the element substrate 10 to a relatively high temperature, the viscosity of the ink can be reduced, and ejection and circulation can be performed favorably. By performing such temperature control, the temperature variation within the element substrate 10 and the temperature variation between the plurality of element substrates 10 are suppressed within a predetermined range. This reduces the variation in the ejection amount caused by the temperature variation, and suppresses density unevenness in the printed image. The target temperature of the element substrate 10 is preferably set to a temperature equal to or higher than the equilibrium temperature of the element substrate 10 when all the heating resistor elements 15 are driven at the highest expected driving frequency. A diode sensor, an aluminum sensor, or the like can be used as the temperature sensor 301. In addition, the heating resistor element 15, which is a heating element, can also be used as a heating means for the element substrate 10. Specifically, the element substrate 10 may be heated by applying a voltage to the heating resistor element 15 that does not cause bubbling. For example, the heating resistor element 15 may be used as a heating means instead of the sub-heater 302, or the sub-heater 302 and the heating resistor element 15 may be used in combination.

[0043] <Positional relationship between element substrates> FIG. 12 is a partially enlarged plan view showing adjacent portions of element substrates in two adjacent ejection modules. As shown in FIG. 9, in this embodiment, an element substrate having an outer shape of a substantially parallelogram is used. As shown in FIG. 12, each ejection port row (14a to 14d) in which the ejection ports 13 in each element substrate 10 are arranged so as to be inclined at a certain angle with respect to the transport direction of the recording medium. As a result, the ejection ports in the adjacent portions of the element substrates 10 overlap at least one ejection port in the transport direction of the recording medium. In FIG. 12, two ejection ports on line D overlap each other. With this arrangement, even if the position of the element substrate 10 is slightly deviated from the predetermined position, black stripes and white spots in the recorded image can be made less noticeable by driving control of the overlapping ejection ports. 12, it is possible to prevent black streaks and white spots at the joints between the element substrates 10 while suppressing an increase in the length of the liquid ejection head 3 in the transport direction of the recording medium. Note that, although the main plane of the element substrate 10 is a parallelogram in this embodiment, the present invention is not limited to this, and the configuration of the present invention can be preferably applied even when an element substrate having a rectangular, trapezoidal, or other shape is used.

[0044] <Liquid flow near the pressure chamber> 13(a) and 13(b) show the inside of the liquid ejection head, where FIG. 13(a) is a plan view (perspective view) showing the heating resistor element and the flow path, and FIG. 13(b) is a cross-sectional view taken along line XIIIb-XIIIb in FIG. 13(a). Between the substrate 11 and the ejection port forming member 12 of the element substrate 10, a plurality of pressure chambers 23 each having an ejection port 13, and an inlet flow path 24a and an outlet flow path 24b communicating with each pressure chamber 23 are provided. The pressure chambers 23 are partitioned by a wall member 26. The substrate 11 is configured so that a circulating flow C is formed in which the liquid in the liquid supply path 18 flows to the liquid recovery path 19 via the supply port 17a, the inlet flow path 24a, the pressure chamber 23, the outlet flow path 24b, and the recovery port 17b. The speed of the circulating flow C in the pressure chamber is preferably, for example, 1.0 mm / s or more and 250 mm / s or less, and is a speed that has little effect on the landing accuracy even when the ejection operation is performed in a state in which the liquid is flowing. 13(b), the discharge port 13 is an opening located at the end of a cylindrical discharge port portion 25 formed in the discharge port forming member 12, and the discharge port portion 25 connects the discharge port 13 to the pressure chamber 23. The direction in which liquid is discharged from the discharge port 13 (the up-down direction in FIG. 13(b)) is referred to as the "discharge direction", and the flow direction of the liquid in the pressure chamber 23 (the left-right direction in FIG. 13(b)) is simply referred to as the "flow direction".

[0045] In the following description, an example is given in which the liquid to be ejected is ink with a non-volatile solvent concentration of 10 wt% to 20 wt%, a pigment concentration of 3 wt% to 10 wt%, a solids concentration of 10 wt% to 30 wt%, and a viscosity of 0.003 Pa·s to 0.006 Pa·s. Here, the solids concentration refers to the concentration of the pigment, resin, wax, etc. contained in the ink. Note that the conditions of the liquid applicable to the liquid ejection head and liquid ejection method of the present invention are not limited to those mentioned above.

[0046] The plurality of supply ports 17a form a supply port row, and the plurality of recovery ports 17b form a recovery port row. An ejection port row in which a plurality of ejection ports 13 are arranged is formed between the supply port row and the recovery port row. In this embodiment, as described above, a pressure difference is provided between the liquid supply path 18 and the liquid recovery path 19. Due to this pressure difference, ink is introduced from the supply port 17a through the inlet flow path 24a into the pressure chamber 23, and a circulating flow C is generated in which ink flows from the outlet flow path 24b to the recovery port 17b.

[0047] A heating resistor element 15 that generates thermal energy is provided on the bottom surface of the pressure chamber 23 facing the ejection port 13. An ejection port portion (nozzle) 25 penetrates the ejection port forming member 12 at a position facing the pressure chamber 23. The outer end of the ejection port portion 25, i.e., the end opposite the heating resistor element 15, forms the ejection port 13 from which ink is ejected. The ejection port portion 25 or the ejection port 13 is provided at a position facing the heating resistor element 15. In this specification, the ejection port 13 is an opening located on the outer surface of the ejection port forming member 12 facing the recording medium, and the ejection port portion 25 is a portion that communicates between the ejection port 13 and the pressure chamber 23 and means a through hole that penetrates the ejection port forming member 12.

[0048] As shown in Fig. 13, this embodiment does not have a filter such as a columnar structure that is often provided in the flow path of a liquid ejection head to prevent foreign matter such as dust from entering the pressure chamber. In this case, the flow resistance in the flow path can be reduced, and the refill performance of the ink can be improved, which is preferable because it provides effects such as increasing the ejection frequency. In the present invention, as described later, foreign matter can be trapped by the flow path in the ejection port forming member, which has a relatively low height, so a filter can be eliminated.

[0049] <Outlet shape> FIG. 14(a) is a plan view showing the shape of the discharge port in this embodiment, and FIG. 14(b) is a plan view showing another example of the shape of the discharge port. As shown in FIG. 14(a), in this embodiment, two protrusions 27 are provided on both sides of a straight line L passing through the center F of the discharge port 13, with the same shape, so as to protrude toward the center F. This provides the effect of shortening the tail of the discharged droplet. To be more specific, the meniscus of the ink formed between the protrusions 27 is more easily maintained than the meniscus in other parts. For this reason, the tail of the droplet extending from the discharge port 13 can be cut off at an earlier timing, and the generation of mist, which is a minute droplet generated accompanying the main droplet, can be suppressed. Note that in FIGS. 1 to 13, the discharge port 13 may be depicted without the protrusions 27. If the interval 28 between the protrusions 27 is wide, the tail of the discharged droplets becomes longer and small satellites are more likely to occur, so the interval 28 is desirably 7.0 μm or less, and more desirably 5.0 μm or less. On the other hand, if the interval is too narrow, it may be difficult to form the protrusions or the discharged droplets may be separated into two, so the interval 28 is desirably 2.0 μm or more. In other words, the interval 28 is desirably 2.0 μm or more and 7.0 μm or less, and more desirably 2.0 μm or more and 5.0 μm or less. In this embodiment, the interval 28 is set to 3.0 μm as an example.

[0050] Also, if the tip (center F side) of the protrusion 27 is thick, the discharged droplet may be divided by the protrusion 27 and split into two droplets. Therefore, the width 271 of the tip of the protrusion 27 is preferably 4.0 μm or less, and in this embodiment, it is set to 2.0 μm as an example. In addition, when the tip of the protrusion is rounded as in this embodiment shown in FIG. 14(a), the length of the line segment divided at the intersection point between the line L at the tip of the protrusion and two lines extending from the two long sides of the protrusion, as shown by the dotted line in the figure, can be considered as the width 271 of the tip. In addition, in order to increase the strength of the protrusion 27, it is preferable that the width 272 of the base of the protrusion 27 is formed thicker than the tip 271, and in this embodiment, it is set to 4.0 μm as an example. In addition, when the shape of the outlet 13 at the base 272 is curved as in this embodiment shown in Fig. 14(a), the length of the line segment divided by the intersection of two lines extending from the two long sides of the protrusion and the outer periphery when the outlet 13 is a circle, as shown by the dotted lines in the figure, can be considered as the width 272 of the base. Thus, from the viewpoint of droplet formation, the protrusion 27 is preferably shaped so that its width narrows from the base to the tip, and the protrusion may have an arc shape as shown in Fig. 14(b).

[0051] Moreover, it is desirable that the two protrusions 27 extend in a direction substantially parallel to the transport direction (X direction) of the recording medium 2. Since the protrusions 27 have a great influence on the ejection of droplets, when there is a slight manufacturing variation in the shape of the two protrusions, the droplets fly in a direction shifted toward one of the protrusions, resulting in a landing position shift. In general, the landing position shift in the ejection port arrangement direction (Y direction) is easier to see on an image than the landing position shift in the recording medium direction (X direction). Therefore, by making the direction of the protrusions substantially parallel to the transport direction of the recording medium 2, the deviation in the ejection port arrangement direction can be suppressed, and the effect of maintaining good printing can be obtained. It is also desirable that the protrusions 27 extend along the flow direction of the liquid in the vicinity of the pressure chamber. In other words, it is desirable that the straight line L on which the protrusions are located forms an angle of 45 degrees or less with respect to the flow path axis connecting the liquid supply path 18 and the liquid recovery path 19, or connecting the inlet flow path 24a and the outlet flow path 24b.

[0052] In this embodiment, two protrusions 27 extend toward the center F of the ejection port, but droplet formation is maintained well even if there is only one protrusion 27. In this case, however, the landing position may be significantly shifted in a direction where there is no protrusion 27, reducing the stability of the landing position, so it is more preferable that two protrusions 27 extend toward the ejection port center F. Also, the present invention can be suitably used even in liquid ejection heads whose ejection ports do not have protrusions 27.

[0053] Furthermore, in order to aim to achieve good image quality with stable ejection quality, it is desirable that the landing dot size of the droplets on the recording medium 2 is relatively small and highly precise. Therefore, in the liquid ejection head of this embodiment, the ejection volume is set to be relatively small at 2.0 ng.

[0054] <Detailed explanation of the liquid ejection process> First, the problem to be solved by the present invention will be described with reference to comparative examples shown in Figs. 15 and 16. Fig. 15 is a schematic diagram showing a transitional process of liquid ejection in comparative example 1 of the present invention, and corresponds to an enlarged portion of part E in Fig. 13(b). The ejection port 13 has the shape shown in Fig. 14(a), and the protrusions 27 are shown by dotted lines. In comparative example 1, the thickness H1 of the ejection port forming member 12 shown in Fig. 15(a) is 4.5 µm, and the height H2 of the inlet flow path 24a (height to the ejection port part 25 of the pressure chamber) is 5.0 µm. Furthermore, the protrusion interval 28 is 3.0 µm, and the opening area of ​​the ejection port 13 is approximately 310 µm. 2 The discharge volume is about 2 ng at a discharge speed of about 10 m / s. Note that the discharge speed is the speed at which the liquid is discharged from the discharge port 13.

[0055] Ink is supplied to the pressure chamber 23 from the inlet flow path 24a (FIG. 15(a)). When ink is discharged, the heat generating resistor element 15 is driven to generate thermal energy, and the ink near the heat generating resistor element 15 is heated to generate a bubble B (FIG. 15(b)). The pressure of the bubble B in the initial stage of generation is very high, and the bubble B pushes the ink between the bubble B and the discharge port 13 toward the discharge port 13 (see the arrow in FIG. 15(b)). The bubble B grows and enters the discharge port portion 25, so that the discharged ink droplet in the process of being discharged and the ink in the flow path (pressure chamber) are separated by the bubble B (FIG. 15(c)). In this comparative example 1, the discharge port 13 has a protrusion 27, and H1 and H2 are relatively short, so that the bubble B communicates with the atmosphere before the volume of the bubble B starts to decrease after it grows. As a result, bubble B does not retract the tail when it contracts, and the tail length becomes shorter, making it difficult for the main droplet and satellite to separate during flight (Figure 15(d)).

[0056] However, since the bubble B does not pull in the tail when it contracts as described above, the tail may become unstable due to various disturbances, such as fine bubbles or aggregates in the ink pulling the tail with a circulating flow, causing the tail to bend. FIG. 16 is a schematic diagram showing a transitional process of liquid ejection when the tail is unstable in Comparative Example 1. When the tail becomes unstable due to disturbances (FIG. 16(c)), the tail may touch the protrusion 27 (FIG. 16(d)). In this way, when the tail touches an unexpected part of the face, the ink may ride up on the protrusion and be left behind as a foreign matter, and the foreign matter may adhere to the face. In this case, if the nozzle face is continuously ejected for a long time without cleaning, the foreign matter may cause the ejection to be disturbed and the landing position to be significantly shifted. Such adhesion of foreign matter to the face is likely to occur when the ink has a high solid content concentration, such as in this embodiment, in which the ink has a solid content concentration of 10 wt% or more and 30 wt% or less.

[0057] Next, comparative example 2 will be described. FIG. 17 is a schematic diagram showing a transitional process of liquid ejection in comparative example 1 of the present invention, and corresponds to the enlarged portion E in FIG. 13(b). The projections 27 of the ejection port 13 are shown by dotted lines. The ejection port 13 has the shape shown in FIG. 14(a), and the projections 27 are shown by dotted lines. In comparative example 2, H1 shown in FIG. 17(a) is 6.0 μm, and H2 is 16 μm, and the distance (ejection port height) OH from the bottom surface of the pressure chamber to the ejection port 13 is longer than in comparative example 1. The distance OH is equal to the sum of H1, which is the thickness of the ejection port forming member 12 or the height of the ejection port portion 25, and H2, which is the height of the inlet flow path 24a in the direction perpendicular to the surface on which the heating resistor element 15 of the pressure chamber 23 is provided. The projection interval is 3.0 μm, and the area of ​​the ejection opening portion is about 166 μm. 2 The ejection speed is about 10 m / s and the ejection volume is about 2 ng.

[0058] As in Comparative Example 1, the heating resistor element 15 is driven to generate thermal energy, which heats the ink near the heating resistor element 15 and generates a bubble B (FIG. 17(b)). As the bubble B grows, the ink in the discharge port 25 is pushed toward the discharge port 13 (FIG. 17(c)). As the bubble B grows, the internal pressure of the bubble B changes suddenly from a positive pressure to a negative pressure lower than the atmospheric pressure (FIG. 17(d)). The negative pressure draws the rear end of the droplet toward the heating resistor element 15, and the tail length increases (FIG. 17(e)). The bubble B starts to shrink, and the tail of the liquid (the rear end of the droplet) is pulled and falls into the discharge port. In Comparative Example 2, the OH is longer than in Comparative Example 1, so it takes longer for the bubble to communicate with the atmosphere, and the tail is pulled for a relatively long time (FIG. 17(f)). As a result, the droplets are ejected with a long tail (Fig. 17(g)), and they may separate into a main droplet and a satellite droplet during flight (Fig. 17(h)), which may affect the recording accuracy.

[0059] Next, an embodiment of the present invention will be described. Figure 18 is a schematic diagram showing a transitional process of liquid ejection in this embodiment, and corresponds to an enlarged portion of part E in Figure 13(b). The protrusions 27 of the ejection port 13 are shown by dotted lines. In this embodiment, as an example, H1 shown in Figure 18(a) is 6.0 μm, H2 is 8.5 μm, and OH is longer than in Comparative Example 1 and shorter than in Comparative Example 2. The projection interval is 3.0 μm, and the area of ​​the ejection opening is approximately 200 μm. 2 The discharge volume is about 2 ng at a discharge speed of about 10 m / s. As in Comparative Examples 1 and 2, the heating resistor element 15 is driven to generate thermal energy, which heats the ink near the heating resistor element 15 and generates a bubble B (FIG. 18(b)). As a result, the ink between the bubble B and the discharge port 13 is pushed toward the discharge port 13 (see the arrow in FIG. 18(b)), and the ink at the discharge port portion 25 is pushed toward the discharge port 13 (FIG. 18(c)). The volume of the bubble B increases, and the bubble B enters the discharge port portion 25, causing the discharged ink droplet in the process of being discharged and the ink in the flow path to be separated by the bubble B (FIG. 18(c)).

[0060] In this embodiment, in which OH is longer than that of Comparative Example 1, the rear end of the discharged ink droplet moves toward the heating resistor element 15 side as the bubble B shrinks after it grows to its maximum volume (FIG. 18(d)). At this time, at least a part of the bubble B that has entered the inside of the discharge port has a velocity component moving toward the surface of the pressure chamber equipped with the heating resistor element 15. The tail of the ink droplet is pulled toward the heating resistor element 15 by the contraction of the bubble B, so that the tail is generated stably. This suppresses the contact of the tail with the discharge port 13 and the protrusion 27. Therefore, adhesion of foreign matter to the discharge port 13 and the protrusion is suppressed, and stable continuous discharge can be performed even if the nozzle face surface is not cleaned for a long time. The tail extends as the bubble B shrinks, but since OH is shorter than that of Example 2, the rear end of the droplet, which is the tail, communicates with the atmosphere at a relatively early timing before contacting the surface (bottom surface) of the pressure chamber equipped with the element 15 (see FIG. 17(f)) (FIG. 18(e)). This makes it possible to perform ejection while suppressing satellites (FIG. 18(g)).

[0061] As described above, when OH is short as in Comparative Example 1, the tail length is short and the occurrence of satellites is suppressed, but the tail becomes unstable, which may lead to ejection failure during long-term continuous ejection. On the other hand, when OH is long as in Comparative Example 2, the tail stability increases and stability during long-term continuous ejection is maintained, but the tail length becomes long, which deteriorates droplet formation and makes satellites more likely to occur. Here, the thickness H1 of the ejection port forming member 12 and the height H2 of the inlet flow path 24a (height of the pressure chamber) with respect to the stability of the tail will be described in detail.

[0062] FIG. 19 shows the size of the bubble in the transitional process of the discharge phenomenon in the present embodiment shown in FIG. 18. The horizontal axis indicates the time after the generation of bubble B (see FIG. 18), and the vertical axis indicates the volume of bubble B. Bubble B generated by thermal energy increases in volume immediately after the bubble is generated due to its inertial force. In this embodiment, the volume of the bubble reaches a maximum about 1 μs after the bubble starts to bubble. After that, bubble B starts to shrink due to the negative pressure of the bubble, and in this embodiment, the bubble is connected to the atmosphere about 2 μs after the bubble starts to bubble. The tail retraction by the bubble is more stable when the bubble B is connected to the atmosphere after it shrinks, as in this embodiment, than when the bubble B is connected to the atmosphere before it starts to shrink, as in Comparative Example 1. For this reason, when discharging droplets, it is desirable for bubble B to be connected to the atmosphere after a sufficient amount of time has passed since the volume reaches a maximum. The time from the start of bubble generation until the volume of the bubble reaches a maximum is called T max The time from the start of foaming until the bubbles are in communication with the atmosphere is T th Then, T th -T max is preferably sufficiently large.

[0063] Figure 20 shows the relationship between OH and T th -T max The conditions other than the OH height at each point are the same, the projection interval of the discharge port 13 is 3.0 μm, the discharge speed is about 10 m / s, and the discharge volume is about 2 ng. As can be seen from FIG. 20, T th -T maxFrom this, it can be said that it is preferable for the OH to be 13 μm or more in order to ensure a sufficient time from when the bubble volume reaches its maximum until it communicates with the atmosphere.

[0064] After the bubble communicates with the atmosphere, the tail is then drawn into the discharge port 25 by the bubble and crashes onto the substrate 11 (FIG. 18(f)). In this embodiment, the tail crashes about 3 μs after the bubble is generated (see FIG. 19), meaning that the crash occurs after the bubble communicates with the atmosphere. According to this embodiment, communicating with the atmosphere before the tail crashes is desirable because it shortens the time the tail is pulled, thereby suppressing an increase in the tail length and suppressing the generation of satellites. The time at which the tail crashes is referred to as T fall Then, T fall -T th is preferably 0 or greater.

[0065] Figure 21 shows the relationship between OH and T fall -T th As in FIG. 20, the conditions other than the OH height at each point are the same, the projection interval of the discharge port 13 is 3.0 μm, the discharge speed is about 10 m / s, and the discharge volume is about 2 ng. As can be seen from FIG. 21, T fall -T th was nearly 0 when OH was around 16 μm. From this, it can be said that it is preferable that OH is 16 μm or less.

[0066] Also, if the value of H1 is too small, the strength of the protrusions decreases and they become more likely to break, so it is desirable that the value be 4 μm or more. Also, if the value of H1 is too large, the effect of suppressing thickening near the ejection port due to circulation becomes smaller, so it is desirable that the value be around 10 μm or less. Also, if the value of H2 is too small, it becomes difficult to supply ink to the ejection port, so it is desirable that the value be around 5 μm or more.

[0067] In addition, the preferable OH height explained with reference to Figs. 19 to 21 is that the projection interval of the discharge port 13 is 3.0 µm and the area of ​​the discharge opening portion is about 200 µm. 2The above is based on the results of a simulation performed under conditions of a discharge speed of about 10 m / s and a discharge volume of about 2 ng. However, the above-mentioned preferable OH height is not limited to the above-mentioned conditions in this embodiment. The discharge behavior of droplets is mainly influenced by the discharge speed and the viscosity of the liquid, so that the preferable OH height (13 μm or more and 16 μm or less) can be suitably used as long as at least the discharge speed and the viscosity of the liquid are within the ranges shown in this specification. Specifically, the viscosity of the liquid for which the preferable OH height can be suitably used is 0.002 Pa·s or more and 0.010 Pa·s or less (2 cP or more and 10 cP or less) at 25° C., and the discharge speed is 7.0 m / s or more and 12 m / s or less.

[0068] As mentioned above, droplet formation is affected not only by the OH length mentioned above, but also by the ink droplet ejection speed. If the ejection speed is too fast, the tip of the main droplet will be ejected before the tail, and the tail will tend to break off and become a satellite. For this reason, an ejection speed of 12 m / s or less is desirable.

[0069] In addition, in a liquid ejection head having a protrusion 27 at the ejection port 13 as in the present invention, compared to a liquid ejection head not having a protrusion at the ejection port, the ink viscosity near the ejection port increases due to evaporation of moisture near the ejection port, and ejection defects are more likely to occur. This is because an ejection port having a protrusion has a longer perimeter than a circular nozzle, and the resistance when ejecting liquid from the ejection port 13 is large. In particular, in inkjet printers used in commercial and industrial fields that require better droplet formation, ink with a high solid content is used from the viewpoint of image robustness and color development, and ejection defects due to ink concentration caused by evaporation of moisture in the ink may become more noticeable. Ink concentration can be suppressed by increasing the ejection speed, but as described above, if the ejection speed is too fast, the tail is easily torn off and satellites are easily generated. Therefore, in the liquid ejection head of this embodiment, an inlet flow path 24a and an outlet flow path 24b are provided for the pressure chamber, and a differential pressure is applied between them to circulate the ink inside the pressure chamber (see Figures 13(a) and (b)). As a result, even if the moisture in the vicinity of the ejection port 13 evaporates, fresh unevaporated ink is supplied from the inlet flow path 24a, so that stable ejection can be achieved without excessively increasing the ejection speed. Note that the means for circulating the liquid may be a circulation configuration other than differential pressure, such as a configuration using a pump.

[0070] In addition, it is desirable that the inlet flow path 24a and the outlet flow path 24b have the same magnitude of flow resistance. The bubbles generated by thermal energy spread not only in the liquid discharge direction but also in the directions of the inlet flow path 24a and the outlet flow path 24b (see Figs. 18(b) and (c)). In this case, if the difference in flow resistance between the inlet flow path 24a and the outlet flow path 24b is large, the generated bubbles will spread asymmetrically inside the flow path. In this case, the tail will also be generated asymmetrically, and when the tail contracts and tries to merge with the main droplet, the axis may shift, which may deteriorate the formation of droplets that can be successfully merged. In order to reduce the difference in flow resistance between the inlet flow path 24a and the outlet flow path 24b, it is desirable that the flow path heights of the inlet flow path 24a and the outlet flow path 24b in the liquid discharge direction are the same. [Explanation of symbols]

[0071] 3 Liquid ejection head 10 Element substrate 13 Outlet 18 Liquid supply path 19 Liquid recovery passage 23 Pressure Chamber 25 Discharge port 27 Protrusion

Claims

1. a pressure chamber including an element that generates thermal energy for discharging a liquid; an ejection port that ejects the liquid; and an ejection port portion that communicates between the ejection port and the pressure chamber, a liquid ejection head in which air bubbles are generated in the pressure chamber by the thermal energy, the generated air bubbles enter the inside of the ejection port, and liquid is ejected from the ejection port by the pressure of the air bubbles, A liquid ejection head configured such that, when at least a portion of the bubble that has entered the interior of the ejection outlet portion has a velocity component directed toward the surface of the pressure chamber in which the element is contained, and before the liquid ejected from the ejection outlet is drawn into the pressure chamber by the contraction of the bubble and comes into contact with the surface of the pressure chamber in which the element is contained, the bubble communicates with the atmosphere and liquid is ejected from the ejection outlet.

2. 2. The liquid ejection head according to claim 1, wherein the distance between the ejection port and the surface of the pressure chamber including the element is 13 [mu]m or more.

3. 2. The liquid ejection head according to claim 1, wherein the distance between the ejection port and the surface of the pressure chamber including the element is 16 [mu]m or less.

4. a pressure chamber including an element configured to generate thermal energy utilized for discharging liquid, the element being provided therein, a discharge port for discharging liquid, and a discharge port portion communicating the discharge port with the pressure chamber; a liquid ejection head in which air bubbles are generated in the pressure chamber by the thermal energy, the generated air bubbles enter the inside of the ejection port, and liquid is ejected from the ejection port by the pressure of the air bubbles, A liquid ejection head, wherein the distance between the ejection port and a surface of the pressure chamber including the element is 13 μm or more and 16 μm or less.

5. The liquid ejection head according to claim 1 , wherein the ejection port has at least one protrusion protruding toward the center of the ejection port.

6. The liquid ejection head according to claim 5 , further comprising two protrusions located on a straight line passing through the center and provided on both sides of the center.

7. 7. The liquid ejection head according to claim 6, wherein the distance between the tips of the two protrusions provided in one ejection port is not less than 2.0 [mu]m and not more than 5.0 [mu]m.

8. The liquid ejection head according to claim 6 , wherein the width of the protrusion is configured to decrease toward the center of the ejection port.

9. 5. A liquid ejection head according to claim 1, further comprising: a liquid supply passage communicating with the pressure chamber and supplying liquid to the pressure chamber; and a liquid recovery passage communicating with the pressure chamber on the opposite side of the pressure chamber to the liquid supply passage and recovering the liquid.

10. The outlet has two projections protruding toward a center of the outlet, The two protrusions are located on a straight line passing through the center and are provided on both sides of the center, 10. The liquid ejection head according to claim 9, wherein the straight line forms an angle of 45 degrees or less with respect to a flow path axis connecting the liquid supply path and the liquid recovery path.

11. The liquid ejection head according to claim 9 , wherein the liquid inside the pressure chamber is circulated between the pressure chamber and an outside thereof.

12. 5. The liquid ejection head according to claim 1, wherein the ejection speed of the liquid ejected from the ejection port is 7.0 m / s or more and 12 m / s or less.

13. A liquid ejection method using a liquid ejection head having an element that generates thermal energy for ejecting liquid, a pressure chamber having the element, an ejection port through which liquid is ejected, and an ejection port portion that communicates between the ejection port and the pressure chamber, comprising: generating bubbles in the liquid in the pressure chamber by the element; Allowing the generated air bubbles to enter the inside of the discharge port portion; and and discharging the liquid from the discharge port by pressure of the generated air bubbles, A liquid ejection method, wherein when the bubble contracts, the bubble communicates with the atmosphere before the liquid ejected from the ejection port is drawn into the pressure chamber by the contraction of the bubble and comes into contact with the surface of the pressure chamber containing the element.

14. The liquid ejection method according to claim 13, wherein the viscosity of the liquid ejected from the ejection port is equal to or greater than 0.002 Pa·s and equal to or less than 0.010 Pa·s.

Images