Liquid ejecting head and method for ejecting liquid

Abstract

The present disclosure relates to a liquid ejecting head including: a liquid chamber having an element that generates thermal energy; a discharge port for the liquid; a nozzle communicating between the discharge port and the liquid chamber; and a liquid supply path and a liquid collection path communicating with the liquid chamber on opposite sides. The thermal energy forms bubbles in the liquid chamber, and the formed bubbles enter the nozzle to eject liquid under the pressure of the bubbles. In a state in which at least a portion of the bubble in the nozzle has a velocity component toward a surface having the element of the liquid chamber and before a liquid to be ejected is dragged into the liquid chamber by contraction of the bubble to come into contact with the surface of the liquid chamber, the liquid to be ejected is injected into the liquid chamber. The bubbles communicate with the atmosphere, and the liquid is ejected through the discharge port. The present disclosure also relates to a method for ejecting a liquid.

Description

Technical Field

[0001] The present disclosure relates to a liquid ejection head and a method for ejecting liquid. Background Art

[0002] A typical example of a method for ejecting liquid adopted in a liquid ejection head such as an inkjet head is a thermal ejection method, which involves applying heat to a liquid (e.g., ink) to perform film boiling, and ejecting the liquid by using a bubbling force caused by the film boiling. The liquid ejection head used for the thermal ejection method includes: a pressure chamber that provides a force for ejecting the liquid; a heating resistor (heater) in the pressure chamber; a channel through which the liquid is supplied to the pressure chamber; and an element substrate having a supply port through which the liquid is supplied to the channel. The liquid is ejected through a discharge port in the element substrate by the energy generated by the heating resistor.

[0003] When the above-mentioned thermal liquid injection head sprays liquid, the sprayed liquid is columnar, having a main droplet and an elongated tail (hereinafter referred to as the tail) extending from the rear of the main droplet. The tail is separated from the main droplet due to the surface tension of the liquid during the flight of the droplet and becomes fine droplets (sub-droplets, satellite droplets). The satellite droplets may fall on the recording medium at a position far away from the main droplet, reducing the image quality. Among the satellite droplets, particularly fine satellite droplets do not reach the recording medium, but become floating droplets (hereinafter referred to as mist). The mist may dirty the liquid injection device, such as an inkjet printer, and the dirt on the liquid injection device may be transferred to the recording medium, dirtying the recording medium.

[0004] Japanese Patent Laid-Open No. 2017-124600 discloses a structure of a liquid ejection head that can shorten the tail of a droplet to prevent image quality degradation caused by satellite droplets. In a liquid ejection head having a protrusion in a discharge port, heat energy generates bubbles in a pressure chamber, and the generated bubbles enter the nozzle and force the liquid to be ejected through the outlet under the pressure of the bubbles. It is described that a structure that allows bubbles entering the nozzle to communicate with the atmosphere at a position outside the discharge port shortens the tail of the droplet and thereby reduces satellite droplets.

[0005] The study found a new problem that the tail of the droplet tends to be unstable in the configuration of the liquid ejection head and the method for ejecting liquid disclosed in Japanese Patent Laid-Open No. 2017-124600. It has been found that if long-term continuous ejection is performed without any recovery action (such as an action of wiping the area near the discharge port with a wiper), foreign matter may accumulate near the discharge port, causing the landing position of the ejected droplet to deviate significantly. Summary of the invention

[0006] The present disclosure provides a liquid ejection head and a method for ejecting liquid, which has ejection stability during long-term continuous ejection while reducing the generation of satellite droplets by shortening the tail. The present disclosure, which solves the above-mentioned problems, provides a liquid ejection head, including: a liquid chamber, the liquid chamber having an element that generates thermal energy for ejecting liquid; a discharge port, liquid is ejected through the discharge port; a nozzle, the nozzle is connected between the discharge port and the liquid chamber; a liquid supply path, the liquid supply path is connected to the liquid chamber, and liquid is supplied to the liquid chamber through the liquid supply path; and a liquid collection path, the liquid collection path is connected to the liquid chamber on the side of the liquid chamber opposite to the liquid supply path, and liquid is collected through the liquid collection path. The thermal energy forms bubbles in the liquid chamber, and the formed bubbles enter the nozzle to eject liquid through the discharge port under the pressure of the bubbles. In a state in which at least a portion of the bubble in the nozzle has a velocity component toward the surface of the liquid chamber having the element and before the liquid to be ejected through the discharge port is dragged into the liquid chamber by contraction of the bubble and contacts the surface of the liquid chamber, the bubble is connected to the atmosphere and the liquid is ejected through the discharge port.

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

[0008] Figure 1 is a view showing a liquid ejection apparatus according to one or more aspects of the present disclosure.

[0009] Figure 2 is a conceptual diagram of a control system according to one or more aspects of the present disclosure.

[0010] Figure 3 is a schematic diagram illustrating a liquid circulation path according to one or more aspects of the present disclosure.

[0011] Figure 4A and Figure 4B is a perspective view showing a liquid ejection head according to one or more aspects of the present disclosure.

[0012] Figure 5 is an exploded perspective view of a liquid ejection head according to one or more aspects of the present disclosure.

[0013] FIG. 6A to FIG. 6D is a plan view of a channel member according to one or more aspects of the present disclosure.

[0014] Fig. 7Ais a perspective view of a channel member according to one or more aspects of the present disclosure, and Figure 7B is a cross-sectional view of a channel member.

[0015] Fig. 8A is a perspective view of a jetting module according to one or more aspects of the present disclosure, and Figure 8B is an exploded perspective view of the injection module.

[0016] 9A to 9C is a plan view of a component substrate according to one or more aspects of the present disclosure.

[0017] Fig.10 is a cross-sectional perspective view of a component substrate according to one or more aspects of the present disclosure.

[0018] Fig.11A and Fig. 11B is a schematic diagram illustrating a temperature control unit included in an element substrate according to one or more aspects of the present disclosure.

[0019] Fig.12 is a partially enlarged plan view showing adjacent portions of an element substrate according to one or more aspects of the present disclosure.

[0020] Fig.13A is a plan view showing the interior of a liquid ejection head according to one or more aspects of the present disclosure, and Fig. 13B is a cross-sectional view showing the interior of the liquid ejecting head.

[0021] Fig.14A and Fig. 14B is an enlarged plan view of a region including a discharge port of a liquid ejection head according to one or more aspects of the present disclosure.

[0022] FIG. 15A to FIG. 15D is a schematic diagram showing a transient injection process in Comparative Example 1.

[0023] FIG. 16A to FIG. 16D is a schematic diagram showing a transient injection process in Comparative Example 1.

[0024] 17A to 17H is a schematic diagram showing a transient injection process in Comparative Example 2.

[0025] FIG. 18A to FIG. 18G is a schematic diagram illustrating a transient injection process according to one or more aspects of the present disclosure.

[0026] Fig.19 is a graph indicating the relationship between the time elapsed from the start of bubble generation and the volume of the bubble during transient injection according to one or more aspects of the present disclosure.

[0027] Fig. 20is the distance OH between the bottom of the pressure chamber and the discharge port and the time T from when the bubble size reaches its maximum until the bubble is connected to the atmosphere th -T max A diagram of the relationship between .

[0028] Fig.21 is the distance OH between the bottom of the pressure chamber and the exhaust port and the time T from when the bubble is connected to the atmosphere until the tail falls on the substrate fall -T th A diagram of the relationship between . DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the following description should not be construed as limiting the scope of the present disclosure. The liquid ejection head of the present disclosure and the liquid ejection device including the liquid ejection head can be applied to devices such as inkjet printers, copiers, fax machines with communication systems, and word processors with printer parts. They can also be applied to industrial recording devices used in combination with various processing devices. For example, they can be used to produce biochips, printed electronic circuits, and semiconductor substrates.

[0030] The liquid ejection device of the present embodiment has a configuration in which a liquid (such as ink) circulates between a tank and a liquid ejection head, but may have a different configuration. For example, in the absence of liquid circulation, the liquid ejection device may have two tanks at the upstream and downstream sides of the liquid ejection head. The flow of liquid from one tank to another causes the flow of liquid in the pressure chamber. The present embodiment is a line head (page width head) having a length corresponding to the width of a recording medium. However, the present disclosure may also be applicable to a serial liquid ejection head that performs recording while moving over a recording medium. The serial liquid ejection head may have a configuration including an element substrate for black ink and an element substrate for color ink, but this should not be construed as restrictive. The short line head may include a plurality of element substrates arranged so that the discharge ports overlap each other in the discharge port arrangement direction to have a length shorter than the width of the recording medium, and the line head may be moved over the recording medium.

[0031] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0032] First embodiment

[0033] Overall structure of the equipment

[0034] Figure 1An example of a liquid ejection device of the present embodiment is shown. The liquid ejection device of the present embodiment is a liquid ejection device 1000 (hereinafter may be simply referred to as device 1000) in the form of an inkjet printer, which records a color image on a recording medium 3 by ejecting yellow (Y), magenta (M), cyan (C), and black (Bk) inks. In the drawings, the X direction is a conveying direction of the recording medium 3, the Y direction is a width direction of the recording medium, and the Z direction is a direction intersecting the X and Y directions and is a direction in which liquid is ejected.

[0035] Figure 1 The apparatus 1000 including the liquid ejection head 1 is shown, and the liquid ejection head is configured to apply ink directly to the recording medium 3 conveyed in the X direction. The recording medium 3 is placed on the conveying part 2 and conveyed in the X direction at a predetermined speed under the four liquid ejection heads 1 (1Y, 1M, 1C, 1Bk) ejecting different inks. Figure 1 , four liquid ejection heads 1Bk, 1C, 1M and 1Y are arranged in this order in the X direction, and black, cyan, magenta and yellow inks are applied in this order onto a recording medium 3. In each of the liquid ejection heads 1, ink discharge ports through which ink is ejected are arranged in the Y direction.

[0036] exist Figure 1 In the figure, the cut sheet is illustrated as the recording medium 3, but the recording medium 3 may be a continuous roll of paper. The recording medium is not limited to paper, but may be a film, for example.

[0037] In the liquid ejection apparatus of the present embodiment, one liquid ejection head ejects ink of a single color, but one liquid ejection head may eject ink of a plurality of colors. Alternatively, the liquid ejection head may eject liquid other than ink, such as a reaction liquid and an external application agent.

[0038] Figure 2 5 is a block diagram showing a control configuration of the liquid ejection apparatus 1000. The controller 500 includes a CPU and other components, and controls the entire liquid ejection apparatus 1000 according to a program and various parameters stored in a ROM 501 while using a RAM 502 as a work area. The controller 500 performs predetermined image processing on image data sent from an externally connected host device 600 according to the program and parameters stored in the ROM 501 to generate ejection data for ejection from the liquid ejection head 1. The liquid ejection head 1 is then driven according to the ejection data to eject ink at a predetermined frequency.

[0039] During the ejection operation of the liquid ejection head 1, the controller 500 drives the conveying motor 503 to convey the recording medium 3 in the X direction at a speed corresponding to the driving frequency. Thus, an image according to image data sent from the host device 600 is recorded on the recording medium 3. The ROM 501 rewritably stores, for each of the liquid ejection heads 1, information related to the area of ​​the discharge port that can be used for ejection from the liquid ejection head 1.

[0040] Liquid circulation path

[0041] Figure 3 The liquid circulation path in the liquid ejecting apparatus of the present embodiment is schematically shown. The liquid ejecting head 1 is connected to a first circulation pump 1002, a buffer tank 1003, and other components so as to allow the liquid to circulate. Figure 3 Only the ink flow path in the liquid ejection head for one color of ink is shown. However, the apparatus 1000 has a circulation path corresponding to the type of liquid to be ejected, such as ink.

[0042] The buffer tank 1003 as a sub-tank connected to the main tank 1006 has an atmosphere communication hole (not shown) that communicates between the inside and outside of the tank, allowing bubbles in the ink to be discharged to the outside. The buffer tank 1003 is also connected to a refill pump 1005. When the liquid in the liquid ejection head 1 is consumed due to the ejection (discharge) of ink for recording or suction recovery (which requires ejection of ink through the discharge port of the liquid ejection head), the refill pump 1005 transfers the consumed amount of ink from the main tank 1006 to the buffer tank 1003.

[0043] The first circulation pump 1002 has a function of extracting liquid from the liquid connection portion 111 of the liquid ejection head 1 and delivering it to the buffer tank 1003. When the liquid ejection head 1 is driven, the first circulation pump 1002 causes ink to flow through the common collection channel 212 in a constant amount.

[0044] The negative pressure control unit 230 is located on the path between the second circulation pump 1004 and the liquid injection unit 300. The negative pressure control unit 230 is configured to maintain the pressure downstream of the negative pressure control unit 230 (on the side adjacent to the liquid injection unit 300) at a preset constant pressure even when the flow rate of the circulation system fluctuates due to the recorded load difference.

[0045] like Figure 3 As shown, the negative pressure control unit 230 has two pressure regulators set to have different regulated pressures. Of the two pressure regulators, one pressure regulator (negative pressure control unit 230H, in Figure 3 H in the figure) and a pressure regulator (negative pressure control unit 230L, in which the pressure is set at a relatively low pressure. Figure 3The liquid ejecting unit 300 is connected to the common supply channel 211 and the common collecting channel 212 of the liquid ejecting unit 300 via the liquid supply unit 220. The liquid ejecting unit 300 has a separate supply channel 213a and a separate collecting channel 213b that are connected to the element substrate 10, and the element substrate has a common supply channel 211, a collecting channel 212, and a discharge port. The element substrate will be described in detail later. Since the separate channel 213 is connected to the common supply channel 211 and the common collecting channel 212, the liquid pumped by the second circulation pump 1004 partially flows from the common supply channel 211 to the common collecting channel 212 (represented by L) through the internal channel of the element substrate 10. Figure 3 This is due to the fact that there is a pressure difference between the pressure regulator H connected to the common supply channel 211 and the pressure regulator L connected to the common collection channel 212, and the first circulation pump 1002 is connected only to the common collection channel 212.

[0046] In this way, the liquid ejection unit 300 has a liquid flow through the common collecting channel 212 and a liquid flow from the common supply channel 211 to the common collecting channel 212 through the element substrate 10. The flow from the common supply channel 211 to the common collecting channel 212 allows the heat generated in each element substrate 10 to be released to the outside of the element substrate 10. This configuration also allows the ink to flow through unused discharge ports and pressure chambers during recording by the liquid ejection head 1, thereby reducing the thickening of the ink in these areas. This configuration also allows the thickened ink and foreign matter in the ink to be discharged into the common collecting channel 212. Therefore, the liquid ejection head 1 according to the present embodiment can perform high-speed and high-quality recording.

[0047] Structure of liquid ejecting head

[0048] Figure 4A and Figure 4B 1 is a perspective view showing a liquid ejection head 1 according to the present embodiment. The liquid ejection head 1 is a line type liquid ejection head having 17 element substrates 10 capable of ejecting ink and arranged in a straight line (arranged in a row). Figure 4A and Figure 4B As shown, the liquid ejection head 1 has an element substrate 10, a signal input terminal 91 and a power terminal 92, which are electrically connected via an electrical wiring board (flexible wiring board) 40 and an electrical wiring board 90. The signal input terminal 91 and the power terminal 92 electrically connected to the controller of the device 1000 provide an ejection drive signal and the power required for ejection to the element substrate 10, respectively. The merging of wiring through the circuit of the electrical wiring board 90 can make the number of signal input terminals 91 and power terminals 92 smaller than the number of element substrates 10. This reduces the number of electrical connection units that must be removed when the liquid ejection head 1 is attached to the device 1000 or when the liquid ejection head 1 is replaced. As Figure 4A As shown, the liquid connection portion 111 at one end of the liquid ejection head 1 is connected to the 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 to be collected from the liquid ejection head 1 to the supply system of the device 1000. Thus, ink can circulate through the path of the device 1000 and the path of the liquid ejection head 1.

[0049] Figure 5 1 is an exploded perspective view of the components or units of the liquid ejection head 1. The liquid ejection unit 300, the liquid supply unit 220, and the electrical wiring board 90 are attached to the housing 80. The liquid supply unit 220 has a liquid connecting portion 111, and a filter 221 ( Figure 3 ), which is connected to the opening of the liquid connection part 111 to remove foreign matter in the supplied ink. The liquid passing through the filter 221 flows to the negative pressure control unit 230 on the liquid supply unit 220. The negative pressure control unit 230 includes a unit having a pressure regulating valve, and utilizes the action of the valve, spring member, etc. in each of these units to significantly reduce the pressure loss variation in the supply system of the device 1000 (the upstream supply system of the liquid ejection head 1), which may occur with the change in the flow rate of the liquid.

[0050] This can stabilize the negative pressure change of the area downstream of the negative pressure control unit 230 (the side adjacent to the liquid injection unit 300) within a predetermined range. The negative pressure control unit 230 has two built-in pressure regulating valves set at different control pressures. The pressure regulating valve set at a higher pressure and the pressure regulating valve set at a lower pressure are respectively connected to the common supply channel 211 and the common collection channel 212 of the liquid injection unit 300 via the liquid supply unit 220.

[0051] The housing 80 has a liquid ejection unit support 81 and an electrical wiring board support 82 for supporting the liquid ejection unit 300 and the electrical wiring board 90 and enhancing the rigidity of the liquid ejection head 1. The electrical wiring board support 82 supporting the electrical wiring board 90 is fixed to the liquid ejection unit support 81 with screws. The liquid ejection unit support 81 has openings 83 and 84 for receiving the bonding rubber 100. The liquid supplied from the liquid supply unit 220 is introduced into the second channel member 60 included in the liquid ejection unit 300 through the bonding rubber 100.

[0052] Next, the configuration of the channel member 210 included in the liquid ejecting unit 300 will be described. Figure 5As shown, the channel member 210 is a stack of the first channel member 50 and the second channel member 60. A plurality of jetting modules 200 are bonded to the bonding surface of the first channel member 50 by an adhesive (not shown). The channel member 210 distributes the liquid supplied from the liquid supply unit 220 to the jetting modules 200, and returns the liquid flowing out of the jetting modules 200 to the liquid supply unit 220. The channel member 210 is fixed to the liquid jetting unit support 81 with screws, reducing warping and deformation of the channel member 210.

[0053] FIG. 6A to FIG. 6D 2 is a view showing a detailed configuration of the channel member 210 . Fig. 6A The support member 30 is shown arranged on a surface of the first channel member 50 on which the injection module 200 is mounted. Figure 6B The surface of the first channel member 50 that is in contact with the support member 30 is shown. Figure 6C : is a cross-sectional view of the first passage member 50 taken in a direction perpendicular to the Z direction at a position around the center in the Z direction. Fig.6D The surface of the second channel member 60 that is in contact with the liquid ejection unit support 81 is shown. FIG. 6A to FIG. 6C This is a view viewed from one side of the injection module 200. Fig.6D It is a view viewed from the liquid ejection unit support member 81 side.

[0054] The first channel member 50 has a plurality of support members 30 arranged in the Y direction on a surface away from the second channel member 60, and each support member 30 has one element substrate 10. Liquid ejection heads 1 of various sizes can be produced by adjusting the number of ejection modules 200.

[0055] like Fig. 6A As shown, the support member 30 has a communication hole 31 in the surface in contact with the element substrate 10. The hole 31 is connected to the element substrate 10 to allow liquid circulation and becomes the reference numeral 31 in the above reference numeral 31. Figure 3 The separate supply channel 213a and the separate collection channel 213b described above are shown in FIG. Figure 6B As shown, the communication hole 31 is connected to the common supply channel 211 or the common collection channel 212 through the communication hole 51 in the channel member 50 to allow liquid circulation.

[0056] like Figure 6C As shown, in the middle layer around the center of the first channel member 50 along the Z direction, the reference Figure 3 The common channel grooves 61 and 62 of the common supply channel 211 and the common collection channel 212 described above extend along the Y direction. Fig.6DAs shown, the common channel grooves 61 and 62 each have a common communication hole 63 at each end or one end that communicates with the liquid supply unit 220 to allow liquid circulation.

[0057] Fig. 7A and Figure 7B 3 and 4 are a perspective view and a cross-sectional view respectively showing the configuration of a channel formed in the liquid ejecting unit 300 . Fig. 7A is an enlarged perspective view of the channel member 210 viewed along the Z direction, and Figure 7B is along Fig. 7A A cross-sectional view taken along line VIIB-VIIB in FIG.

[0058] The element substrate 10 of the injection module 200 is placed on the communication hole 51 of the first channel member 50, wherein the support member 30 is located between the element substrate 10 and the communication hole 51. Figure 7B 6, only the communication hole 51 for the common supply channel 211 is shown, but in another cross section, the common collection channel 212 is communicated with the communication hole 51, as shown in FIG6. The support member 30 and the element substrate 10 included in each of the ejection modules 200 have a channel for supplying ink from the first channel member 50 to the heat generating resistor 15 (see FIG9) on the element substrate 10. In addition, the support member 30 and the element substrate 10 have a channel to collect (reflow) some or all of the liquid supplied to the heat generating resistor 15 into the first channel member 50.

[0059] As described above, the common supply channel 211 is connected to the negative pressure control unit 230H set to a relatively high pressure, and the common collection channel 212 is connected to the negative pressure control unit 230L set to a relatively low pressure. This forms an ink supply path extending through the common communication hole 63 (see FIG. 6 ), the common supply channel 211, and the communication hole 31, and ink is supplied to the channel in the element substrate 10 through this ink supply path. Similarly, this forms an ink collection path extending from the channel in the element substrate 10 and having the communication hole 31, the communication hole 51, the common collection channel 212, and the common communication hole 63 (see FIG. 6 ). Fig.6D ). While the ink circulates in this manner, an ejection action is performed in the element substrate 10 according to the ejection data. Of the ink supplied through the ink supply path, the ink not used by the ejection operation is collected through the ink collection path.

[0060] The structure of the injection module

[0061] Fig. 8A is a perspective view showing one injection module 200, and Figure 8B: is an exploded view of the injection module 200. In order to manufacture the injection module 200, the element substrate 10 and the flexible wiring board 40 are first bonded to the support member 30, which has the pre-formed communication hole 31. Then, the terminal 16 on the element substrate 10 and the terminal 41 on the flexible wiring board 40 are electrically connected to each other by wire bonding, and then the wire bonding portion (electrical connection portion) is covered and sealed by the sealant 110. The terminal 42 on the side of the flexible wiring board 40 away from the element substrate 10 is electrically connected to the connection terminal 93 ( Figure 5 ). The support member 30 as a support for the element substrate 10 also serves as a channel member communicating between the element substrate 10 and the channel member 210 to allow liquid circulation, and thus can be a member having high flatness and can be bonded to the element substrate with sufficiently high reliability. For example, the support member 30 can be formed of alumina or a resin material.

[0062] Component substrate structure

[0063] The configuration of the element substrate 10 according to the present embodiment will be described. Fig.9A is a plan view showing a surface of the element substrate 10 having the discharge port 13, Fig. 9B Shows Fig.9A is an enlarged view of the portion indicated by IXB in FIG. 1 , and Fig. 9C is shown with Fig.9A A plan view of the surface opposite the surface shown. Fig.10 It is along Fig.9A 1 is a cross-sectional perspective view of the element substrate 10 taken along line XX in FIG. 10. Hereinafter, the direction in which the array of the discharge ports 13 extends is referred to as a discharge port array direction.

[0064] like Fig. 9B As shown, a heating resistor 15 is arranged at a position corresponding to the discharge port 13, and the heating resistor is a heating element (pressure generating element) configured to generate bubbles in the liquid by using heat energy. The partition wall 22 defines pressure chambers (liquid chambers) 23, each of which accommodates a heating resistor 15. The heating resistor 15 is electrically connected to the terminal 16 through an electric wire (not shown) on the element substrate 10. The heating resistor 15 is based on the electrical wiring board 90 (see Figure 5 ) and the flexible wiring board 40 (see FIG. 8 ) generate heat by a pulse signal input from the control circuit of the liquid ejection device 1000 to boil the liquid. The liquid is ejected through the discharge port 13 by the bubbling force caused by boiling. Fig. 9BAs shown, the liquid supply path 18 and the liquid collection path 19 extend along each discharge port array, wherein the discharge port array is located between the liquid supply path 18 and the liquid collection path 19. The liquid supply path 18 and the liquid collection path 19 are channels extending in the element substrate 10 along the discharge port array direction, and are connected to the discharge port 13 via the supply port 17a and the collection port 17b, respectively.

[0065] exist 9A to 9C In the example shown, the element substrate 10 has an array of 16 discharge ports.

[0066] like Fig. 9C and Fig.10 As shown, the cover plate 20 having a sheet shape is arranged on the surface of the element substrate 10 opposite to the surface having the discharge port 13. Fig. 9C As shown, the cover plate 20 has a plurality of openings 21 communicating with the liquid supply path 18 and the liquid collection path 19, which will be described later. In the present embodiment, the cover plate 20 has four supply openings 21a for one liquid supply path 18 and three collection openings 21b for one liquid collection path 19. However, the number of openings should not be limited to this. Fig. 9B As shown, the opening 21 in the cover plate 20 is Fig. 7A The corresponding communicating holes 51 shown are connected. The cover plate 20 can be formed of a material having sufficiently high corrosion resistance to the liquid, and the opening 21 needs to have high shape accuracy and high positioning accuracy so that the ink is supplied to the pressure chamber. Therefore, the cover plate 20 can be formed of a photosensitive resin material or a silicon plate, and the opening 21 can be formed by photolithography. The cover plate 20 can change the channel spacing by using the opening 21. Considering the pressure loss, strength and processability, the cover plate can be formed of a film-like member with a thickness of about 30 to 600 μm.

[0067] Next, the flow of the liquid in the element substrate 10 will be described. Fig.10, the discharge port forming member 12 of the element substrate 10 has four discharge port arrays. However, the number of discharge port arrays should not be limited to four, and can be appropriately selected. The element substrate 10 is a stack of a substrate 11 formed of silicon and a discharge port forming member 12 formed of a photosensitive resin. A cover plate 20 is bonded to the rear surface of the substrate 11. The cover plate 20 serves as a cover, which forms a part of the wall of the liquid supply path 18 and the liquid collection path 19 in the substrate 11 of the element substrate 10. The element substrate 10 has a heating resistor 15 on the surface of the substrate 11 (see FIG. 9), and has a groove constituting a liquid supply path 18 and a liquid collection path 19 extending along the discharge port array on the other surface. The liquid supply path 18 and the liquid collection path 19 defined by the substrate 11 and the cover plate 20 are respectively connected to a common supply channel 211 and a common collection channel 212 in the channel member 210 (see FIG. 7). There is a pressure difference between the liquid supply path 18 and the liquid collection path 19. This pressure difference forms a circulation flow C in which the liquid in the liquid supply path 18 in the substrate 11 flows to the liquid collection path 19 ( Fig.10 The flow shown by the arrow C in FIG. 1 ). This flow allows the thickened ink, foam and foreign matter generated by evaporation to be collected from the discharge port 13 to the liquid collection path 19 in the discharge port 13 and the pressure chamber 23 that are not in the ejection operation. This flow also reduces the thickening of the ink in the discharge port 13 and the pressure chamber 23, and reduces the increase in the density of the coloring material. As shown in FIG. 7 , the liquid collected in the liquid collection path 19 flows through the opening 21 in the cover plate 20 and the connecting hole 31 in the support member 30 in the following order through the connecting hole 31 in the support member 30 and the connecting hole 51 in the first channel member 50 to reach the common collection channel 212, and then the liquid is collected in the supply path of the liquid ejection device 1000.

[0068] In other words, the liquid supplied from the main body of the liquid ejection device to the liquid ejection head 1 flows in the following order for supply and collection. First, the liquid flows into the liquid ejection head 1 from the liquid connection portion 111 of the liquid supply unit 220. Then, the liquid sequentially flows through the joint rubber 100, the common communication hole 63 in the second channel member, and the common channel groove 61 and the communication hole 51 in the first channel member. Then, the liquid sequentially flows through the communication hole 31 in the support member 30, the opening 21 in the cover plate 20, and the liquid supply path 18 and the supply port 17a in the substrate 11 to reach the pressure chamber 23. Some of the liquid in the pressure chamber 23 that is not ejected through the discharge port 13 sequentially flows through the collection port 17b and the liquid collection path 19 in the substrate 11, the opening 21 in the cover plate 20, and the communication hole 31 in the support member 30. Then, the liquid sequentially flows through the communication hole 51 and the common channel 62 in the first channel member, the common communication hole 63 in the second channel member, and the joint rubber 100. The liquid then flows to the outside of the liquid ejection head 1 through the liquid connecting portion 111 in the liquid supply unit.

[0069] exist Figure 3 In the circulation path shown, the liquid entering from the liquid connection portion 111 flows into the joint rubber 100 through the negative pressure control unit 230 .

[0070] The liquid ejecting head of the present embodiment further includes a temperature control unit on the element substrate 10 . Fig.11A and Fig. 11B is a schematic diagram showing how each element substrate 10 is divided into a plurality of areas for temperature control.

[0071] Each zone has a temperature sensor 301 and an individually controllable sub-heater 302. The controller 500 (see Figure 2) The temperature is adjusted using the temperature sensor 301 and the sub-heater 302 according to the temperature (target temperature) set for each area. In other words, the controller 500 drives the sub-heater 302 only in the area where the temperature detected by the temperature sensor 301 is lower than the target temperature. The target temperature of the element substrate 10 can be set to a slightly higher temperature to reduce the viscosity of the ink, which allows better ejection operation and circulation. Such temperature control keeps the temperature variation in the element substrate 10 and the temperature variation between the element substrates 10 within a predetermined range. This reduces the variation in the ejection amount caused by the temperature variation, thereby reducing the density unevenness in the recorded image. The target temperature of the element substrate 10 can be set to a temperature equal to or greater than the equilibrium temperature of the element substrate 10 when all the heating resistors 15 are driven at the highest expected driving frequency. Examples of the temperature sensor 301 include a diode sensor and an aluminum sensor. As a heater for the element substrate 10, a heating resistor 15 as a heating element can also be used. Specifically, a voltage low enough not to generate bubbles can be applied to the element substrate 10, thereby heating the heating resistor 15. For example, as the heater, the heat generating resistor 15 may be used instead of the sub-heater 302 , or the sub-heater 302 and the heat generating resistor 15 may be used together.

[0072] Positional relationship between component substrates

[0073] Fig.12 is a partially enlarged plan view showing adjacent portions of the element substrates of two adjacent injection modules. Fig.9A As shown in FIG. 1 , in this embodiment, the element substrate has a substantially parallelogram shape. Fig.12 As shown, the discharge port arrays (14a to 14d) each including the discharge port 13 of the element substrate 10 are inclined at a certain angle relative to the conveying direction of the recording medium. With this configuration, the discharge port arrays of adjacent element substrates 10 each have at least one discharge port that overlaps with the discharge port of the adjacent element substrate 10 in the conveying direction of the recording medium. Fig.12 , the two discharge ports on the D line overlap each other. This arrangement makes it possible to make black bars or white dots in the recorded image less noticeable by controlling the ejection of the overlapping discharge ports even when the element substrate 10 is positioned slightly away from the predetermined position. In other words, the element substrates 10 can be arranged in a straight line (inline) instead of a staggered arrangement to reduce the increase in the length of the liquid ejection head 1 in the conveying direction of the recording medium 3. In this case, Fig.12The illustrated configuration can prevent black stripes or white spots at the junctions between the element substrates 10 while reducing the increase in the length of the liquid ejection head 1 in the conveying direction of the recording medium. In the present embodiment, the principal plane of the element substrate 10 is a parallelogram, but the present disclosure should not be limited thereto. Even when the element substrate has other shapes such as a rectangular shape and a trapezoidal shape, the configuration of the present disclosure is applicable.

[0074] Liquid flow near the pressure chamber

[0075] Fig.13A and Fig. 13B The interior of the liquid ejection head is shown. Fig.13A is a plan view (perspective view) showing a heat generating resistor and a channel. Fig. 13B It is along Fig.13A A sectional view taken along line XIIIB-XIIIB in FIG. Between the substrate 11 of the element substrate 10 and the discharge port forming member 12, there are a plurality of pressure chambers 23 and inlet channels 24a and outlet channels 24b connected to the corresponding pressure chambers 23, each pressure chamber having a discharge port 13. The pressure chambers 23 are separated from each other by walls 26. The substrate 11 is configured to generate a circulating flow C, in which the liquid in the liquid supply path 18 flows to the liquid collection path 19 through the supply port 17a, the inlet channel 24a, the pressure chamber 23, the outlet channel 24b and the collection port 17b. The speed of the circulating flow C in the pressure chamber is, for example, greater than or equal to 1.0 mm / s and less than or equal to 250 mm / s, which has little effect on the landing accuracy even if the injection operation is performed while the liquid is flowing. As Fig. 13B As shown, the discharge port 13 is an opening at the end of a cylindrical nozzle 25 of the discharge port forming member 12. The nozzle 25 communicates between the discharge port 13 and the pressure chamber 23. The direction in which the liquid is ejected through the discharge port 13 ( Fig. 13B The vertical direction in the pressure chamber 23 is referred to as the ejection direction, and the direction in which the liquid flows in the pressure chamber 23 ( Fig. 13B The left and right direction in the figure is referred to as the flow direction.

[0076] In the following example, the liquid to be ejected is ink, whose non-volatile solvent concentration is greater than or equal to 10% by weight and less than or equal to 20% by weight, pigment concentration is greater than or equal to 3% by weight and less than or equal to 10% by weight, solid component concentration is greater than or equal to 10% by weight and less than or equal to 30% by weight, and viscosity is greater than or equal to 0.003Pa·s and less than or equal to 0.006Pa·s. Here, solid component concentration refers to the concentration of pigment, resin and wax in ink. The conditions of the liquid applicable to the liquid ejection head and the method for ejecting liquid of the present disclosure should not be limited to the above.

[0077] The supply ports 17a form a supply port array, and the collection ports 17b form a collection port array. The exhaust port array in which the exhaust ports 13 are arranged is located between the supply port array and the collection port array.

[0078] In this embodiment, as described above, there is a pressure difference between the liquid supply path 18 and the liquid collection path 19. The pressure difference generates a circulation flow C in which ink flows from the supply port 17a to the pressure chamber 23 through the inlet channel 24a and flows to the collection port 17b through the outlet channel 24b.

[0079] The heat generating resistor 15 that generates heat energy is disposed on the bottom of the pressure chamber 23 facing the discharge port (outlet) 13. The nozzle (outlet portion) 25 extends through the discharge port forming member 12 at a position facing the pressure chamber 23. The outer end of the nozzle 25, that is, the end away from the heat generating resistor 15, is the ejection port 13 through which the ink is ejected. The nozzle 25 or the discharge port 13 is positioned to face the heat generating resistor 15. In this specification, the discharge port 13 is an opening in the outer surface of the discharge port forming member 12 facing the recording medium, and the nozzle 25 is a portion that communicates between the discharge port 13 and the pressure chamber 23, that is, a through hole extending through the discharge port forming member 12.

[0080] like Fig. 13B As shown, the present embodiment does not have a filter, such as a filter having a columnar shape, which is usually arranged in the channel of the liquid ejection head to prevent foreign matter such as dust from entering the pressure chamber. In this configuration, the flow resistance in the channel is smaller, and thus the ink refilling performance is improved, thereby bringing advantages such as increased ejection frequency. In the present disclosure, the filter can be omitted because foreign matter can be captured by the channel (inlet channel 24a) having a relatively low height in the discharge port forming member, as described below.

[0081] Shape of discharge port

[0082] Fig.14A is a plan view showing the shape of the discharge port of this embodiment, and Fig. 14B FIG. 2 is a plan view showing another example of the shape of the discharge port. Fig.14A As shown, in the present embodiment, two protrusions 27 having the same shape are located on opposite sides of the center F on a straight line L extending through the center F of the discharge port 13 so as to protrude toward the center F. This shape can provide an effect of shortening the tail of the ejected droplet. Specifically, the meniscus of ink formed between the protrusions 27 is easier to retain than the meniscus in other areas. This allows the tail of the droplet extending from the discharge port 13 to be cut off at an earlier time, suppressing the generation of mist (i.e., tiny droplets generated together with the main droplet). Figure 1 to Figure 13, the discharge port 13 is shown without the protrusion 27. If the distance 28 between the protrusions 27 becomes larger, the tail of the sprayed droplet becomes longer, and small satellite droplets are more likely to be produced. Therefore, the distance 28 is preferably 7.0 μm or less, and more preferably 5.0 μm or less. However, if the distance 28 is too small, the formation of the protrusion may be difficult, or the sprayed droplet may be divided into two parts, so the distance 28 may be 2.0 μm or more. In other words, the distance 28 is preferably greater than or equal to 2.0 μm and less than or equal to 7.0 μm, and more preferably greater than or equal to 2.0 μm and less than or equal to 5.0 μm. In the example of the present embodiment, the distance 28 is 3.0 μm.

[0083] If the front end (close to the center F) of the protrusion 27 is thicker, the ejected droplet can be divided into two droplets by the protrusion 27. In view of this, the protrusion 27 can have a front end width 271 of 4.0 μm or less. In the example of the present embodiment, the front end width 271 is 2.0 μm. Fig.14A In the embodiment shown, the protrusion may have a rounded front end. In this case, Fig.14A As shown by the dotted line in FIG. 2 , the front end width 271 can be considered to be the length of the segment between the line extending orthogonally to the straight line L at the front end of the protrusion and the intersection of the line and the two lines extending from the long sides of the protrusion. In addition, the protrusion 27 may have a base width 272 that is larger than the front end width 271 to increase the strength of the protrusion 27. In the example of the present embodiment, the base width 272 is 4.0 μm. Fig.14A In the embodiment shown, the discharge port 13 may have a curved base at the bottom of the protrusion 27. In this case, as shown by the dotted line in the figure, the base width 272 can be considered as the length of the segment between the outer circumference line of the circular discharge port 13 and the intersection of the line and the two lines extending from the long sides of the protrusion. As described above, from the perspective of droplet formation, the protrusion 27 may have a shape that tapers from the base to the front end, such as Fig. 14B The arc shape shown.

[0084] The two protrusions 27 can extend in a direction substantially parallel to the conveying direction (X direction) of the recording medium 3. Since the protrusions 27 have a very large influence on the droplet ejection, a slight manufacturing difference in the shape of the two protrusions can cause the droplet to fly away in the direction toward one of the protrusions, deviating from the landing position. Generally, the deviation of the landing position in the discharge port array direction (Y direction) is more obvious in the image than the deviation in the conveying direction (X direction) of the recording medium. Therefore, the protrusion direction of the protrusion is made substantially parallel to the conveying direction of the recording medium 3 to reduce the deviation in the discharge port array direction and maintain high-quality printing. The protrusion 27 can extend in the direction of the liquid flow in the area around the pressure chamber. In other words, the straight line L in which the protrusion is located can form an angle of 45 degrees or less relative to the flow path axis connecting the liquid supply path 18 and the liquid collection path 19 or connecting the inlet channel 24a and the outlet channel 24b.

[0085] The present embodiment includes two protrusions 27 extending toward the center F of the discharge port. However, reliable droplet formation may also be achieved by only one protrusion 27. However, in this case, the droplet may deviate toward a position without the protrusion 27, reducing the stability of the landing position. Therefore, the two protrusions 27 may extend toward the center F of the discharge port. The present disclosure may also be applicable to a liquid ejection head having a discharge port without the protrusion 27.

[0086] Furthermore, in order to achieve high image quality with stable ejection quality, the droplets landing on the recording medium 3 may have a relatively small size and high definition. Therefore, in the liquid ejection head of this embodiment, the ejection amount is set to a relatively small amount of 2.0 ng.

[0087] Detailed description of the liquid injection process

[0088] First, refer to FIG. 15A to FIG. 15D and FIG. 16A to FIG. 16D The comparative example in illustrates the problem of the present disclosure. FIG. 15A to FIG. 15D is a schematic diagram showing a transient liquid ejection process in Comparative Example 1 of the present disclosure, and corresponds to Fig. 13B The discharge port 13 has Fig.14A The shape shown in FIG. 1 is shown in FIG. 1 , and the protrusion 27 is indicated by a dotted line. Fig.15A The discharge port forming member 12 shown has a thickness H1 of 4.5 μm, and the inlet passage 24a has a height H2 of 5.0 μm (the height to the nozzle 25 of the pressure chamber). The distance 28 of the protrusion is 3.0 μm, and the opening area of ​​the discharge port 13 is about 310 μm. 2 , and the ejection amount is about 2 ng at an ejection rate of about 10 m / s. The ejection rate is a rate at which the liquid is ejected through the discharge port 13 .

[0089] Ink is supplied from the inlet passage 24a to the pressure chamber 23 ( Fig.15A ). In order to eject ink, the heating resistor 15 is first driven to generate heat energy, which heats the ink around the heating resistor 15 and forms bubbles B ( Fig. 15B ).

[0090] The pressure of the newly formed bubble B is high, so that the bubble B pushes the ink between the bubble B and the discharge port 13 toward the discharge port 13 (see Fig. 15B When the bubble B grows and enters the nozzle 25, the bubble B separates the ink droplet in the ejection process from the ink in the channel (pressure chamber) ( Fig. 15C ). In Comparative Example 1 in which the discharge port 13 has the protrusion 27 and relatively short H1 and H2, the bubble B communicates with the atmosphere before the volume of the bubble B, which has fully grown, begins to decrease. In this case, the bubble B does not drag a tail during contraction. This shortens the tail length and makes it difficult for the satellite droplet to separate from the main droplet during flight ( Fig.15D ).

[0091] However, as described above, since the bubble B does not drag the tail during contraction, the tail may be unstable due to various disturbances. For example, fine bubbles or accumulations in the ink may drag the tail in the circulation flow and cause the tail to bend. FIG. 16A to FIG. 16D is a schematic diagram showing the transient liquid injection process in Comparative Example 1, in which the tail is unstable. If the tail is unstable due to interference ( Fig. 16C ), the tail may hit the protrusion 27 ( Fig.16D ). If the tail contacts an unexpected portion of the face surface, the ink may be positioned and retained on the protrusion and become a foreign matter. The foreign matter may adhere to it. In this case, if the jetting continues for a long time without cleaning the nozzle face surface, the foreign matter may interfere with the jetting, resulting in a significant deviation of the landing position. When the solid component concentration of the ink is high, as in the present embodiment, where the solid component concentration of the ink is greater than or equal to 10% by weight and less than or equal to 30% by weight, it is more likely that foreign matter will adhere to the face surface.

[0092] Next, Comparative Example 2 will be described. 17A to 17H is a schematic diagram showing a transient liquid injection process in Comparative Example 2 of the present disclosure, and corresponds to Fig. 13B The projection 27 of the discharge port 13 is indicated by a dotted line. The discharge port 13 has Fig.14A The shape shown in FIG. 1 is shown in FIG. 1 , and the protrusion 27 is indicated by a dotted line. In Comparative Example 2, Fig.17AH1 and H2 shown in are 6.0 μm and 16 μm, respectively. The distance (nozzle height) OH between the bottom of the pressure chamber and the discharge port 13 in Comparative Example 2 is longer than that in Comparative Example 1. The distance OH is equal to the sum of H1 and H2, H1 is the thickness of the discharge port forming member 12 or the height of the nozzle 25, and H2 is the height of the inlet channel 24a in the direction perpendicular to the surface of the pressure chamber 23 having the heat generating resistor 15. The distance of the protrusion is 3.0 μm, and the area of ​​the discharge port opening is about 166 μm 2 , and the injection amount is about 2ng at an injection speed of about 10m / s.

[0093] As in Comparative Example 1, the heat generating resistor 15 is driven to generate heat energy, which heats the ink around the heat generating resistor 15 and forms the bubble B ( Fig. 17B As the bubble B grows, the ink in the nozzle 25 is pushed toward the discharge port 13 ( Fig. 17C ).

[0094] As bubble B grows, the internal pressure of bubble B suddenly changes from positive pressure to negative pressure, which is lower than atmospheric pressure ( Fig.17D The negative pressure drags the trailing edge of the droplet toward the heating resistor 15 and lengthens the tail ( Fig.17E ). The bubble B starts to shrink, and the shrinkage drags a portion of the liquid that becomes the tail (the trailing edge of the droplet) into the discharge port. In Comparative Example 2, the distance OH is longer than that in Comparative Example 1, and therefore it takes a longer time for the bubble to communicate with the atmosphere. The tail remains dragged for a relatively long time ( Fig.17F ). In this case, the droplet is ejected while having a long tail length ( Figure 17G ), and the droplets may be separated into main droplets and satellite droplets during flight ( Fig.17H ), thus affecting the recording accuracy.

[0095] Next, embodiments of the present disclosure will be described. FIG. 18A to FIG. 18G is a schematic diagram showing the instantaneous liquid injection process in this embodiment, and corresponds to Fig. 13B The projection 27 of the discharge port 13 is indicated by a dotted line. In the example of this embodiment, Fig.18A H1 and H2 shown in are 6.0 μm and 8.5 μm, respectively, and OH is longer than that in Comparative Example 1 and shorter than that in Comparative Example 2. The distance of the protrusion is 3.0 μm, and the area of ​​the discharge port opening is about 200 μm 2 , and the ejection amount is about 2ng at an ejection rate of about 10m / s. Similar to Comparative Examples 1 and 2, the heat generating resistor 15 is driven to generate heat energy, which heats the ink around the heat generating resistor 15 and forms bubbles B ( Fig.18BThis pushes the ink between the bubble B and the discharge port 13 toward the discharge port 13 (see Fig.18B ), and then pushes the ink in the nozzle 25 toward the discharge port 13 ( Fig.18C When the volume of the bubble B increases and the bubble B enters the nozzle 25, the bubble B separates the ink droplet in the ejection process from the ink in the channel B ( Fig.18C ).

[0096] In the present embodiment in which the distance OH is longer than that in Comparative Example 1, as the bubble B having grown to its maximum volume shrinks, the trailing edge of the ejected ink droplet moves toward the heat generating resistor 15 ( Fig.18D ). At this time, at least a portion of the bubble B that has entered the nozzle has a velocity component toward the surface of the pressure chamber having the heating resistor 15. The contraction of the bubble B drags the tail of the ink droplet toward the heating resistor 15, thereby generating a stable tail. This reduces the contact of the tail with the discharge port 13 and the protrusion 27, for example.

[0097] Therefore, foreign matter is less likely to adhere to the discharge port 13 and the protrusion, and therefore ejection can be stably continued even if the nozzle face surface is not cleaned for a long time. Although the tail elongates as the bubble B contracts, the bubble is connected to the atmosphere at a relatively early time before the rear edge (as the portion that will become the tail of the droplet) contacts the surface (bottom) of the pressure chamber having the heat generating resistor 15 ( Fig.18E ), because the distance OH is shorter than that in Comparative Example 2. This enables ejection with fewer satellite droplets ( Figure 18G ).

[0098] As described above, when OH is short as in Comparative Example 1, the tail length is short, and thus the generation of satellite droplets is suppressed. However, the stability of the tail is lost, and thus injection defects are likely to occur during long-term continuous injection. On the contrary, when OH is long as in Comparative Example 2, the stability of the tail is increased, and stability is maintained during long-term continuous injection. However, the tail may be very long, which may destroy the formation of droplets and easily lead to the generation of satellite droplets. Here, the thickness H1 of the discharge port forming member 12 and the height H2 of the inlet channel 24a (the height of the pressure chamber) are explained in detail from the perspective of the stability of the tail.

[0099] Fig.19 Shows FIG. 18A to FIG. 18GThe size of the bubble during the transient injection process in the present embodiment is shown. The horizontal axis represents the time that has passed since the bubble B starts to be generated (see Figure 18). The vertical axis represents the volume of the bubble B. The bubble B formed by thermal energy increases in volume immediately after generation due to its inertia. In the present embodiment, the volume of the bubble reaches its maximum value at about 1μs from the start of bubble generation. Then, due to the negative pressure of the bubble, the bubble B begins to shrink, and in the present embodiment, the bubble is connected to the atmosphere at about 2μs from the start of bubble generation. Compared with when the bubble B is connected to the atmosphere before starting to shrink in Comparative Example 1, when the bubble B is connected to the atmosphere after shrinking as in the present embodiment, the tail is dragged more stably by the bubble. As can be seen from the above, when ejecting droplets, the bubble B can be connected to the atmosphere after a sufficiently long time has passed since the bubble B reached its maximum volume. T th -T max The value of can be large enough, where T max is the time from the start of bubble generation until the bubble volume reaches its maximum value, and T th It is the time from the generation of bubbles until the bubbles connect to the atmosphere.

[0100] Fig. 20 Indicates OH and T th -T max The conditions other than the height OH are the same at each point. The distance of the protrusion of the discharge port 13 is 3.0 μm, the injection rate is about 10 m / s, and the injection amount is about 2 ng. Fig. 20 It can be seen that when OH exceeds 13 μm, T th -T max This suggests that the OH may be 13 μm or larger to ensure that there is sufficient time from the time the bubble volume reaches its maximum value until the bubble communicates with the atmosphere.

[0101] After the bubble is connected to the atmosphere, the tail is then dragged into the nozzle 25 by the bubble and falls on the substrate 11 ( Fig.18F In this embodiment, the tail falls about 3 μs after the bubble is generated (see Fig.19 ), which is later than the time when the bubble is connected to the atmosphere. According to this embodiment, the bubble is connected to the atmosphere before the tail falls, which takes a shorter time to drag the tail. Therefore, the increase in the tail length is reduced, and the generation of satellite droplets can be reduced. fall -T th Can be greater than or equal to 0, where T fall is the time during which the tail falls.

[0102] Fig.21 Indicates OH and T fall -T th The relationship between Fig. 20As shown, the conditions other than OH are the same at each point. The distance of the protrusion of the discharge port 13 is 3.0 μm, the injection rate is about 10 m / s, and the injection amount is about 2 ng. Fig.21 It can be seen that when OH is about 16 μm, T fall -T th Almost 0. This indicates that OH can be 16 μm or less.

[0103] If H1 is too small, the protrusion will have low strength and break easily. Therefore, H1 may be 4 μm or more. If H1 is too large, thickening near the discharge port is less suppressed by circulation. Therefore, H1 may be about 10 μm or less. If H2 is too small, it will be difficult to supply ink to the discharge port. Therefore, H2 may be about 5 μm or more.

[0104] refer to Figures 19 to 21 The height OH described is based on the simulation results performed under the following conditions: the distance of the protrusion of the discharge port 13 is 3.0 μm, and the area of ​​the ejection port is about 200 μm. 2 , the injection rate is about 10m / s, and the injection amount is about 2ng. However, the above-mentioned height OH should not be limited to the height under the above-mentioned conditions of this embodiment. Because the droplet injection behavior is mainly affected by the injection rate and viscosity of the liquid, as long as the injection rate and viscosity of the liquid are at least within the range specified in this specification, the height OH (greater than or equal to 13μm and less than or equal to 16μm) can be adopted. Specifically, when the height OH is adopted, the viscosity of the liquid is greater than or equal to 0.002Pa·s and less than or equal to 0.010Pa·s (greater than or equal to 2cP and less than or equal to 10cP) at 25°C, and the injection rate is greater than or equal to 7.0m / s and less than or equal to 12m / s.

[0105] As described above, the formation of the droplet is affected not only by the length of the OH, but also by the ejection rate of the ink droplet. If the ejection rate is too high, the front end of the main droplet is ejected much earlier than the tail, and the tail tends to fall off and become a satellite droplet. In view of this, the ejection rate can be 12m / s or lower.

[0106] In the liquid ejection head having a protrusion 27 in the discharge port 13 of the present disclosure, as the moisture near the discharge port evaporates, the viscosity of the ink near the discharge port increases, and therefore the present liquid ejection head is more susceptible to ejection defects than a liquid ejection head having no protrusion in the discharge port. This is due to the fact that the discharge port having a protrusion has a longer circumference than a circular nozzle and generates greater resistance when the liquid is ejected through the discharge port 13. In particular, inkjet printers used in commercial and industrial fields that require better droplet formation use inks with a high solid component concentration in view of image fastness and color reproducibility, and in some cases, ejection defects associated with the thickening of the ink caused by the evaporation of moisture in the ink become more apparent. The thickening of the ink can be prevented by increasing the ejection rate. However, if the ejection rate is too high, the tail tends to fall off and become a satellite droplet as described above. In view of the above, in the liquid ejection head of the present embodiment, the inlet channel 24a and the outlet channel 24b are provided for the pressure chamber, and the ink in the pressure chamber can be circulated by the pressure difference between the inlet channel 24a and the outlet channel 24b (see Fig.13A and Fig. 13B As a result, even if the water near the discharge port 13 evaporates, fresh ink that has not evaporated is supplied from the inlet channel 24a, enabling stable ejection without excessively increasing the ejection rate. The liquid may be circulated by using other circulation configurations than the pressure difference configuration, such as a pump-based configuration.

[0107] The inlet channel 24a and the outlet channel 24b may have the same magnitude of flow resistance. The bubbles formed by the heat energy not only diffuse in the liquid ejection direction, but also diffuse toward the inlet channel 24a and the outlet channel 24b (see Fig.18B and Fig.18C ). If the difference in flow resistance between the inlet channel 24a and the outlet channel 24b is large, the generated bubbles will diffuse into the channel asymmetrically. In this case, the tail may be formed asymmetrically, and therefore, when the tail shrinks to merge with the main droplet, the axis may be offset, thereby adversely affecting the droplet formation to be achieved by successful merger. In order to reduce the difference in flow resistance between the inlet channel 24a and the outlet channel 24b, the inlet channel 24a and the outlet channel 24b may have the same height in the liquid ejection direction.

[0108] The present disclosure can provide a liquid ejection head having ejection stability during long-term continuous ejection while suppressing generation of satellite droplets by shortening the tail length, and can also provide a method for ejecting liquid.

[0109] Although the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A liquid ejection head, comprising: a liquid chamber having an element for generating thermal energy for ejecting the liquid; a discharge port through which liquid is ejected; a nozzle communicating between the discharge port and the liquid chamber; a liquid supply path, the liquid supply path being in communication with the liquid chamber and through which liquid is supplied to the liquid chamber; as well as a liquid collecting path communicating with the liquid chamber on a side of the liquid chamber opposite to the liquid supply path and through which liquid is collected, wherein The heat energy forms bubbles in the liquid chamber, and the formed bubbles enter the nozzle to eject the liquid through the discharge port under the pressure of the bubbles, and In a state in which at least a portion of the bubble in the nozzle has a velocity component toward the surface of the liquid chamber having the element and before the liquid to be ejected through the discharge port is dragged into the liquid chamber by contraction of the bubble and contacts the surface of the liquid chamber, the bubble is connected to the atmosphere and the liquid is ejected through the discharge port.

2. The liquid ejecting head according to claim 1, wherein: The distance between the discharge port and the surface of the liquid chamber having the element is 13 μm or more.

3. The liquid ejecting head according to claim 1, wherein: The distance between the discharge port and the surface of the liquid chamber having the element is 16 μm or less.

4. A liquid ejection head, comprising: a liquid chamber having an element for generating thermal energy for ejecting the liquid; a discharge port through which liquid is ejected; a nozzle communicating between the discharge port and the liquid chamber; a liquid supply path, the liquid supply path being in communication with the liquid chamber and through which liquid is supplied to the liquid chamber; as well as a liquid collecting path communicating with the liquid chamber on a side of the liquid chamber opposite to the liquid supply path and through which liquid is collected, wherein The heat energy forms bubbles in the liquid chamber, and the formed bubbles enter the nozzle to eject the liquid through the discharge port under the pressure of the bubbles, and A distance between the discharge port and a surface of the liquid chamber having the element is greater than or equal to 13 μm and less than or equal to 16 μm.

5. The liquid ejecting head according to claim 1 or 4, wherein: The discharge port has at least one protrusion protruding toward a center of the discharge port.

6. The liquid ejecting head according to claim 5, wherein: The discharge port has two protrusions that are located on a straight line extending through the center of the discharge port and that protrude toward the center on opposite sides of the center.

7. The liquid ejecting head according to claim 6, wherein: A distance between the two protrusions of the discharge port is greater than or equal to 2.0 μm and less than or equal to 5.0 μm.

8. The liquid ejecting head according to claim 6, wherein: The width of the protrusion decreases toward the center of the injection port.

9. The liquid ejecting head according to claim 1 or 4, wherein: The discharge port has two protrusions protruding toward the center of the discharge port, The two protrusions are located on a straight line extending through the center of the discharge port and are located on opposite sides of the center, and The straight line forms an angle of 45 degrees or less with respect to an axis of a flow path connecting the liquid supply path and the liquid collection path.

10. The liquid ejecting head according to claim 1 or 4, wherein: The liquid circulates between the inside and the outside of the liquid chamber.

11. The liquid ejecting head according to claim 1 or 4, wherein: The liquid is ejected through the discharge port at a rate of 7.0 m / s or more and 12 m / s or less.

12. A method for ejecting a liquid by using a liquid ejecting head, the liquid ejecting head comprising: a liquid chamber having an element for generating thermal energy for ejecting the liquid; a discharge port through which liquid is ejected; a nozzle communicating between the discharge port and the liquid chamber; a liquid supply path communicating with the liquid chamber and through which liquid is supplied to the liquid chamber; and a liquid collecting path, the liquid collecting path communicating with the liquid chamber on a side of the liquid chamber opposite to the liquid supply path, and collecting liquid through the liquid collecting path, the method comprising: generating bubbles in the liquid in the liquid chamber by using the element; moving the generated bubbles into the nozzle; and The liquid is ejected through the discharge port under the pressure of the generated bubbles, wherein The bubble communicates with the atmosphere when the bubble contracts and before liquid is dragged into the liquid chamber by the contraction of the bubble to come into contact with the surface of the liquid chamber having the element.

13. The method for spraying a liquid according to claim 12, wherein: The viscosity of the liquid ejected through the discharge port is greater than or equal to 0.002 Pa·s and less than or equal to 0.010 Pa·s.

14. The method for spraying a liquid according to claim 12, wherein: The solid content concentration of the liquid ejected through the discharge port is 10 wt % or more and 30 wt % or less.

15. The method for spraying a liquid according to claim 12, wherein: The liquid circulates between the inside and the outside of the liquid chamber.

16. The method for spraying a liquid according to claim 12, wherein: The liquid is ejected through the discharge port at a rate of 7.0 m / s or more and 12 m / s or less.

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