LIQUID EJECTION APPARATUS AND CONTROL METHOD

Abstract

To provide a technology which suppresses unevenness with a lower control load as compared with a conventional technology.SOLUTION: A liquid discharge device includes: a liquid discharge head having a conversion element which generates energy necessary to discharge liquid, a first protection layer which blocks contact between the conversion element and the liquid, a second protection layer which functions as a first electrode by covering a part of the first protection layer, a second electrode which is electrically connected to the first electrode through the liquid, and a discharge port which discharges the liquid; and control means which controls so that a potential difference between the first electrode and the second electrode in printing becomes a predetermined value by changing a potential of at least one of the first electrode and the second electrode. The control means sets the potential difference on the basis of at least either a state or a structure of the liquid discharge head.SELECTED DRAWING: Figure 19

Description

[Technical field]

[0001] The present disclosure relates to a liquid ejection device having a liquid ejection head that ejects liquid such as ink. [Background technology]

[0002] Inkjet printing methods include those that use electrothermal conversion elements (hereafter referred to as "heaters") with heat resistors to heat the ink and cause bubbles to form. In printheads that use heaters, depending on the nozzle condition based on temperature, ink scorching, etc., there is a risk that the ejection speed may differ from the speed intended by the designer. Therefore, a method is required to correct the ejection speed according to the condition of the printhead.

[0003] To address the above problem, Patent Document 1 proposes a method of increasing the ejection speed compared to the case of using a single pulse by dividing the heating pulse applied to the heater into a first drive pulse and a second drive pulse. In this method, a superheated liquid layer is formed by the first drive pulse, and after a sufficient thickness of the superheated liquid layer is ensured, rapid heating is performed by the second drive pulse, thereby increasing the foaming energy while ensuring foaming stability.

[0004] Patent Document 2 also discloses that in the recording head of a recording device, an upper protective layer covering the part heated by the heater functions as one electrode, and a counter electrode is provided that is connected to this electrode via a liquid. This recording device has a potential control means that forms an electric field between the upper protective layer electrode and the counter electrode, and during normal printing, the potential of the counter electrode is made relatively higher than that of the upper protective layer electrode. This prevents ink colorants and resins that are negatively charged and cause scorching from approaching the heater, making it difficult for scorching to occur, and thus reducing unevenness. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-246899 A [Patent Document 2] JP 2019-38127 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in order to further improve the image quality, the technology of the above patent documents faces the problem of increasing the control load. The reason for this is that the ink droplets ejected when forming a high-definition image become smaller, so the number of droplets required increases and the number of heat pulses driven per unit time increases. Therefore, when multiple drive pulses are used as in Patent Document 1, each drive pulse needs to be optimally modulated, which increases the control load.

[0007] In view of the above, an object of one embodiment of the present invention is to provide a technique for suppressing unevenness that imposes a lower control load than conventional techniques. [Means for solving the problem]

[0008] One embodiment of the present invention is a liquid ejection device having a liquid ejection head having a conversion element for generating energy required to eject liquid, a first protective layer that blocks contact between the conversion element and the liquid, a second protective layer that covers part of the first protective layer and functions as a first electrode, a second electrode that is electrically connected to the first electrode via the liquid, and an ejection port from which the liquid is ejected, and a control means that controls the potential difference between the first electrode and the second electrode during printing to a predetermined value by changing the potential of at least one of the first electrode and the second electrode, wherein the control means sets the potential difference based on at least one of the state and configuration of the liquid ejection head. Effect of the Invention

[0009] According to one embodiment of the present invention, it is possible to provide a technique for suppressing unevenness that requires a lower control load than conventional techniques. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a recording apparatus; [Diagram 2] Schematic diagram showing the first circulation path [Diagram 3] Schematic diagram showing the second circulation path [Figure 4] A perspective view of a liquid ejection head [Diagram 5] An exploded perspective view of a liquid ejection head [Figure 6] A diagram showing a flow path member [Figure 7] FIG. 1 shows the connection relationship of flow paths in a flow path member. [Figure 8] 8 is a cross-sectional view taken along line VIII-VIII of FIG. [Figure 9] FIG. 2 shows the dispensing module. [Figure 10] FIG. 1 shows a structure of a recording element substrate. [Figure 11] FIG. 11 is a perspective view showing the structure of the recording element substrate and the cover member taken along the cross-sectional line XI-XI in FIG. [Figure 12] FIG. 2 is a partially enlarged plan view showing an adjacent portion of the recording element substrate; [Figure 13] A diagram modeling the communication between the liquid ejection head and the main body. [Figure 14] The total heating time is divided into two parts, and the discharge speed is measured when the divided parts are changed in various ways. [Figure 15] FIG. 1 is a diagram showing a structure of a heat application portion in a recording element substrate; [Figure 16] FIG. 1 is a diagram for explaining electric field control. [Figure 17] Graph showing the relationship between ΔV and discharge speed [Figure 18] A diagram showing the relationship between the number of ejections and the ejection speed when ΔV is constant or fluctuating. [Figure 19] Sequence diagram of a series of processes related to adjusting ΔV based on dot count [Figure 20]FIG. 1 shows wiring on a recording element substrate. [Figure 21] A graph showing the relationship between temperature and discharge speed [Figure 22] A diagram showing a table for changing ΔV [Diagram 23] A sequence diagram of a series of processes related to adjusting ΔV based on temperature and dot count [Figure 24] A diagram showing a table for changing ΔV [Diagram 25] A sequence diagram of a series of processes related to adjusting ΔV based on temperature, duty, and dot count. [Figure 26] FIG. 13 is a diagram showing the relationship between the elapsed time and the ejection speed when the ink ejection that had been continued is temporarily stopped. [Figure 27] A diagram showing a table for changing ΔV [Figure 28] A diagram showing the relationship between ΔV and discharge speed DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a recording device employing an inkjet recording method will be described as an example of the present disclosure. The recording device may be, for example, a single-function printer having only a recording function, or a multifunction printer having multiple functions such as a recording function, a FAX function, and a scanner function. The recording device may also be a manufacturing device for manufacturing color filters, electronic devices, optical devices, microstructures, and the like, using a predetermined recording method.

[0012] In the following description, "recording" refers not only to the formation of meaningful information such as characters and figures, but also to both meaningful and insignificant information. Furthermore, it also broadly refers to the formation of images, patterns, structures, etc. on a recording medium, or the processing of a medium, regardless of whether they are manifested in a way that humans can perceive visually.

[0013] In addition, "recording medium" refers not only to paper used in general recording devices, but also to anything that can accept ink, such as cloth, plastic film, metal plate, glass, ceramics, resin, wood, and leather.

[0014] Furthermore, the term "ink" should be interpreted broadly in the same manner as the definition of "recording" above. Therefore, it refers to a liquid that can be applied onto a recording medium to form an image, design, pattern, etc., or to process the recording medium, or to process the ink (for example, to solidify or insolubilize the coloring material in the ink applied to the recording medium).

[0015] Furthermore, unless otherwise specified, the term "recording element" (sometimes called "nozzle") refers collectively to an ink ejection port, a liquid path connected to the ink ejection port, and an element that generates the energy used to eject ink.

[0016] [First embodiment] Although this embodiment relates to an inkjet recording apparatus in a form in which liquid such as ink is circulated between a tank and a liquid ejection head, other forms are also possible. For example, instead of circulating the ink, two tanks may be provided on the upstream side and downstream side of the liquid ejection head, and the ink may flow from one tank to the other tank to cause the ink to flow in the pressure chamber.

[0017] The liquid ejection head according to the present embodiment is a so-called line type head having a length corresponding to the width of the recording medium, but the present embodiment can also be applied to a so-called serial type liquid ejection head that performs printing while scanning the recording medium. An example of a serial type liquid ejection head is a configuration in which one black ink recording element board and one color ink recording element board are mounted, but the present embodiment is not limited to this. Specifically, a short line head shorter than the width of the recording medium may be created by arranging several recording element boards so that the ejection nozzle rows overlap in the ejection port nozzle row direction, and the recording medium may be scanned with the line head.

[0018] <Inkjet recording device> FIG. 1 shows a schematic configuration of a liquid ejection device according to the present embodiment, specifically, an inkjet recording device 1000 (hereinafter also referred to as a recording device) that performs recording by ejecting ink. The recording device 1000 is a line-type recording device that has a conveying unit 1 that conveys a recording medium 2 and a line-type liquid ejection head 3 arranged approximately perpendicular to the conveying direction of the recording medium, and performs continuous recording in one pass while conveying multiple recording media 2 continuously or intermittently. The recording medium 2 is not limited to cut paper, but may be continuous roll paper. The liquid ejection head 3 is capable of full-color printing with CMYK (cyan, magenta, yellow, black) inks. In the liquid ejection head 3, a liquid supplying means that constitutes a supply path that supplies ink to the liquid ejection head, as described later, is fluidly connected to a main tank and a buffer tank (see FIG. 2). In addition, an electric control unit that transmits power and an ejection control signal to the liquid ejection head 3 is electrically connected to the liquid ejection head 3. The liquid path and the electric signal path in the liquid ejection head 3 will be described later.

[0019] <First circulation route> Fig. 2 is a schematic diagram showing a first circulation path as one form of the circulation path applied to the recording apparatus according to this embodiment. As shown in Fig. 2, the liquid ejection head 3 is fluidly connected to a first circulation pump (high pressure side) 1001, a first circulation pump (low pressure side) 1002, a buffer tank 1003, and the like. Note that in Fig. 2, for the sake of simplicity, only a path through which one color of ink out of CMYK ink flows is shown, but in reality, circulation paths for four colors are provided in the liquid ejection head 3 and the recording apparatus body.

[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 connects the inside of the tank to 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 ink is consumed by the liquid ejection head 3, the refill pump 1005 transfers the amount of ink consumed from the main tank 1006 to the buffer tank 1003. The ink is consumed by the liquid ejection head 3, for example, when ink is ejected (discharged) from the ejection ports of the liquid ejection head, such as for recording by ejecting ink or for suction recovery.

[0021] The two first circulation pumps 1001 and 1002 have a role of drawing ink from the liquid connection part 111 of the liquid ejection head 3 and flowing it to the buffer tank 1003. The first circulation pump is preferably a volumetric pump having a quantitative liquid delivery capacity. Specific examples include a tube pump, a gear pump, a diaphragm pump, a syringe pump, etc., but it can also be used in a form in which a general constant flow valve or a relief valve is arranged at the pump outlet to ensure a constant flow rate. When the liquid ejection head 3 is driven, a certain amount of ink flows in the common supply flow path 211 and the common recovery flow path 212 by the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002. It is preferable to set this flow rate at a flow rate at which the temperature difference between each recording element substrate 10 in the liquid ejection head 3 does not affect the recording image quality. However, if a flow rate is set too large, the negative pressure difference becomes too large in each recording element substrate 10 due to the influence of pressure loss in the flow path in the liquid ejection unit 300, resulting in uneven density of the image. For this reason, it is preferable to set the flow rate while taking into consideration the temperature difference and negative pressure difference between the recording element substrates 10.

[0022] The negative pressure control unit 230 is provided in the middle of the path connecting the second circulation pump 1004 and the liquid ejection unit 300. Therefore, the negative pressure control unit 230 has a function of operating to maintain the pressure downstream of the negative pressure control unit 230 (i.e., the liquid ejection unit 300 side) at a preset constant pressure even when the flow rate of the circulation system fluctuates due to the difference in duty for recording. As the two pressure adjustment mechanisms constituting the negative pressure control unit 230, any mechanism may be used as long as it can control the pressure downstream of itself to fluctuate within a certain range centered on a desired set pressure. As an example, a mechanism similar to a so-called "pressure reducing regulator" can be adopted. When a pressure reducing regulator is used, it is preferable to pressurize the upstream side of the negative pressure control unit 230 via the liquid supply unit 220 by the second circulation pump 1004, as shown in FIG. 2. In this way, the effect of the head pressure of the buffer tank 1003 on the liquid ejection head 3 can be suppressed, so that the degree of freedom of layout of the buffer tank 1003 in the recording apparatus 1000 can be increased. The second circulation pump 1004 may be any pump having a head pressure equal to or greater than a certain pressure within the range of the ink circulation flow rate used when driving the liquid ejection head 3, and may be a turbo pump, a positive displacement pump, or the like. Specifically, a diaphragm pump or the like may be used. Also, instead of the second circulation pump 1004, for example, a head tank disposed with a certain head difference relative to the negative pressure control unit 230 may be used.

[0023] 2, the negative pressure control unit 230 includes two pressure adjustment mechanisms, each set to a different control pressure. Of the two negative pressure adjustment mechanisms, the one set to a relatively high pressure (indicated as H in FIG. 2) is connected to a common supply flow path 211 in the liquid ejection unit 300 via the liquid supply unit 220. Moreover, the one set to a relatively low pressure (indicated as L in FIG. 2) is connected to a common recovery flow path 212 via the liquid supply unit 220.

[0024] The liquid ejection unit 300 is provided with a common supply flow path 211, a common recovery flow path 212, and individual supply flow paths 213a and individual recovery flow paths 213b that communicate with each recording element substrate 10. Since the individual supply flow paths 213a and 213b communicate with the common supply flow path 211 and the common recovery flow path 212, a flow (arrow in FIG. 2) occurs in which a portion of the ink flows from the common supply flow path 211 through the internal flow path of the recording element substrate 10 to the common recovery flow path 212. The reason for this is that a pressure adjustment mechanism H is connected to the common supply flow path 211, and a pressure adjustment mechanism L is connected to the common recovery flow path 212, causing a pressure difference between the two common flow paths.

[0025] In this way, in the liquid ejection unit 300, while ink flows to pass through the common supply flow path 211 and the common recovery flow path 212, a flow occurs in which part of the ink passes through each recording element substrate 10. Therefore, heat generated in each recording element substrate 10 can be discharged to the outside of the recording element substrate 10 by the flow through the common supply flow path 211 and the common recovery flow path 212. In addition, with this configuration, when recording is being performed by the liquid ejection head 3, 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.

[0026] <Second circulation route> 3 is a schematic diagram showing a second circulation path, which is different from the first circulation path described above, among the circulation paths applied to the recording device according to this embodiment. The main differences from the first circulation path are as follows.

[0027] First, each of the two pressure adjustment mechanisms constituting the negative pressure control unit 230 has a mechanism (a mechanical component having the same function as a so-called "back pressure regulator") that controls the pressure upstream of the negative pressure control unit 230 within a certain range centered on a desired set pressure. Also, the second circulation pump 1004 acts as a negative pressure source that reduces the pressure downstream of the negative pressure control unit 230. Furthermore, the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002 are disposed upstream of the liquid ejection head, and the negative pressure control unit 230 is disposed downstream of the liquid ejection head.

[0028] The negative pressure control unit 230 in the second circulation path operates so that the pressure fluctuation on the upstream side (i.e., the liquid ejection unit 300 side) of itself is within a certain range even if the flow rate fluctuates due to a change in the printing duty when printing is performed by the liquid ejection head 3. The pressure fluctuation is, for example, within a certain range centered on a preset pressure. As shown in FIG. 3, it is preferable to pressurize the downstream side of the negative pressure control unit 230 via the liquid supply unit 220 by the second circulation pump 1004. In this way, the influence of the head pressure of the buffer tank 1003 on the liquid ejection head 3 can be suppressed, so that the degree of freedom in the layout of the buffer tank 1003 in the recording apparatus 1000 can be increased. Note that, instead of the second circulation pump 1004, for example, a head tank arranged with a predetermined head difference with respect to the negative pressure control unit 230 may be applied.

[0029] 3 includes two pressure adjustment mechanisms, each of which is set to a different control pressure. Of the two negative pressure adjustment mechanisms, the one set to a relatively high pressure (indicated as H in FIG. 3) is connected to a common supply flow path 211 in the liquid ejection unit 300 via the liquid supply unit 220. The one set to a relatively low pressure (indicated as L in FIG. 3) is connected to a common recovery flow path 212 via the liquid supply unit 220.

[0030] The two negative pressure adjustment mechanisms make the pressure in the common supply flow path 211 relatively higher than the pressure in the common recovery flow path 212. With this configuration, an ink flow is generated that flows from the common supply flow path 211 through the individual flow paths 213 and the internal flow paths of each recording element substrate 10 to the common recovery flow path 212 (arrow in FIG. 3). In this way, with the second circulation path, an ink flow state similar to that of the first circulation path is obtained within the liquid ejection unit 300, but there are two advantages that are different from the first circulation path.

[0031] The first advantage is that, in the second circulation path, the negative pressure control unit 230 is disposed downstream of the liquid ejection head 3, so there is little concern that dust or foreign matter generated from the negative pressure control unit 230 will flow into the head. The second advantage is that, in the second circulation path, the maximum flow rate required to supply liquid from the buffer tank 1003 to the liquid ejection head 3 is smaller than that in the first circulation path. The reason is as follows. The total flow rate in the common supply flow path 211 and the common recovery flow path 212 when circulating during standby for recording is defined as A. The value of A is defined as the minimum flow rate required to keep the temperature difference in the liquid ejection unit 300 within a desired range when adjusting the temperature of the liquid ejection head 3 during standby for recording. The ejection flow rate when ink is ejected from all ejection ports of the liquid ejection unit 300 (during full ejection) is defined as F. In this case, in the case of the first circulation path (Figure 2), the set flow rate of the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002 is A, so the maximum amount of liquid supplied to the liquid ejection head 3 required for full ejection is A+F.

[0032] On the other hand, in the case of the second circulation path (FIG. 3), the amount of liquid supplied to the liquid ejection head 3 required during standby for printing is flow rate A. The amount of liquid supplied to the liquid ejection head 3 required during full ejection is flow rate F. Then, in the case of the second circulation path, the total value of the set flow rates of the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002, i.e., the maximum value of the required supply flow rate, is the larger value of A or F. Therefore, as long as the liquid ejection unit 300 of the same configuration is used, the maximum value of the required supply flow rate (A or F) in the second circulation path is always smaller than the maximum value of the required supply flow rate (A+F) in the first circulation path. Therefore, in the case of the second circulation path, the degree of freedom of the applicable circulation pump is increased. For example, it is possible to use a low-cost circulation pump with a simple configuration, and to reduce the load on a cooler (not shown) installed in the main body side path, which is advantageous in that the cost of the main body of the recording device can be reduced. This advantage is greater for a line head with a relatively large value of A or F, and is more beneficial for a line head with a long longitudinal length among line heads.

[0033] However, the first circulation path has some advantages over the second circulation path. To be more specific, in the second circulation path, the flow rate flowing through the liquid ejection unit 300 during standby for printing is maximized, so that the lower the printing duty, the higher the negative pressure applied to each nozzle. For this reason, particularly when the flow path width (length in the direction perpendicular to the ink flow direction) of the common supply flow path 211 and the common recovery flow path 212 is reduced to reduce the head width (length in the short direction of the liquid ejection head), a high negative pressure is applied to the nozzle in a low-duty image in which unevenness is easily visible. There is a risk that the effect of satellite droplets will be large due to the application of such high negative pressure. On the other hand, in the case of the first circulation path, the timing at which a high negative pressure is applied to the nozzle is when a high-duty image is formed, so that even if satellites are generated, they are difficult to see, and there is an advantage that the effect on the printed image is small. A preferable selection can be made between the two circulation paths in light of the specifications (ejection flow rate F, minimum circulation flow rate A, and flow path resistance within the head) of the liquid ejection head and the printing apparatus main body.

[0034] <Configuration of Liquid Ejection Head> The configuration of the liquid ejection head 3 according to the first embodiment will be described. Fig. 4(a) and Fig. 4(b) are perspective views of the liquid ejection head 3 according to this embodiment. The liquid ejection head 3 is a line-type liquid ejection head in which 15 recording element substrates 10 capable of ejecting ink of four colors, C / M / Y / K, are arranged in a straight line (arranged in-line). As shown in Fig. 4(a), the liquid ejection head 3 has a signal input terminal 91 and a power supply terminal 92 electrically connected to each recording element substrate 10 via a flexible wiring substrate 40 and an electric wiring substrate 90. The signal input terminal 91 and the power supply terminal 92 are electrically connected to a control unit of the recording apparatus 1000, an ejection drive signal is supplied to the recording element substrate 10 via the signal input terminal 91, and power required for ejection is supplied to the recording element substrate 10 via the power supply terminal 92.

[0035] By consolidating the wiring by the electric circuit in the electric wiring board 90, the number of signal output terminals 91 and power supply terminals 92 can be reduced compared to the number of recording element boards 10. This reduces the number of electrical connections that need to be removed when assembling the liquid ejection head 3 to the recording device 1000 or replacing the liquid ejection head. As shown in FIG. 4B, the liquid connection parts 111 provided at both ends of the liquid ejection head 3 are connected to the liquid supply system of the recording device 1000. As a result, the four colors of ink, CMYK, are supplied from the supply system of the recording device 1000 to the liquid ejection head 3, and the ink that has passed through the liquid ejection head 3 is collected by the supply system of the recording device 1000. In this way, the ink of each color can circulate through the path of the recording device 1000 and the path of the liquid ejection head 3.

[0036] 5 shows an exploded perspective view of each part or unit constituting the liquid ejection head 3. 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 (FIGS. 2 and 3), and inside the liquid supply unit 220, filters 221 (FIGS. 2 and 3) for each color are provided which communicate with the openings of the liquid connection part 111 in order to remove foreign matter from the ink being supplied. Each of the two liquid supply units 220 is provided with filters 221 for two colors. The ink that passes through the filters 221 is supplied to negative pressure control units 230 arranged on the supply unit 220 corresponding to each color.

[0037] The negative pressure control unit 230 is a unit consisting of pressure adjustment valves for each color. The negative pressure control unit 230 greatly attenuates the pressure loss change in the supply system of the recording device 1000 (the supply system upstream of the liquid ejection head 3) caused by the fluctuation of the ink flow rate by the action of valves and spring members provided inside each negative pressure control unit. Therefore, the negative pressure control unit 230 can stabilize the negative pressure change downstream of the pressure control unit (the liquid ejection unit 300 side) within a certain range. As described in FIG. 2, two pressure adjustment valves are built into the negative pressure control unit 230 for each color. These pressure adjustment valves are set to different control pressures, and the high pressure side communicates with the common supply flow path 211 in the liquid ejection unit 300, and the low pressure side communicates with the common recovery flow path 212 via the liquid supply unit 220.

[0038] 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 3. 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 has a role of correcting warping and deformation of the liquid discharge unit 300 and ensuring the relative positional accuracy of the multiple recording element boards 10, thereby suppressing streaks and unevenness in the recorded matter. For this reason, the liquid discharge unit support part 81 preferably has sufficient rigidity, and is preferably made of a metal material such as SUS or aluminum, or a ceramic such as alumina. The liquid discharge unit support part 81 is provided with openings 83 and 84 into which the joint rubber 100 is inserted. The ink supplied from the liquid supply unit 220 is led to the third flow path member 70 constituting the liquid discharge unit 300 via the joint rubber.

[0039] The liquid ejection unit 300 has a plurality of ejection modules 200 and a flow path member 210, and a cover member 130 is attached to the surface of the liquid ejection unit 300 on the recording medium side. Here, as shown in FIG. 5, the cover member 130 is a member having a frame-shaped surface with a long opening 131, and the recording element substrate 10 and the sealant 110 (FIG. 9) included in the ejection module 200 are exposed from the opening 131. The frame portion around the opening 131 functions as a contact surface of a cap member that caps the liquid ejection head 3 during standby for recording. For this reason, it is preferable to apply an adhesive, sealant, filler, or the like along the periphery of the opening 131 to fill in unevenness and gaps on the ejection port surface of the liquid ejection unit 300, so that a closed space is formed when capping.

[0040] Next, the configuration of the flow path member 210 included in the liquid ejection unit 300 will be described. As shown in Fig. 5, the flow path member 210 is formed by laminating a first flow path member 50, a second flow path member 60, and a third flow path member 70. The flow path member 210 distributes ink supplied from the liquid supply unit 220 to each ejection module 200, and returns ink circulating from the ejection modules 200 to the liquid supply unit 220. The flow path member 210 is fixed to the liquid ejection unit support part 81 with screws, which suppresses warping and deformation of the flow path member 210.

[0041] 6(a) to 6(f) are diagrams showing the front and back surfaces of the first to third flow path members. FIG. 6(a) shows the surface of the first flow path member 50 on which the discharge module 200 is mounted, and FIG. 6(f) shows the surface of the third flow path member 70 on which the liquid discharge unit support part 81 is abutted. The first flow path member 50 and the second flow path member 60 are joined so that the surface shown in FIG. 6(b) and the surface shown in FIG. 6(c), which are the abutment surfaces of the respective flow path members, face each other. The second flow path member and the third flow path member are joined so that the surface shown in FIG. 6(d) and the surface shown in FIG. 6(e), which are the abutment surfaces of the respective flow path members, face each other. By joining the second flow path member 60 and the third flow path member 70, eight common flow paths extending in the longitudinal direction of the flow path members are formed by the common flow path grooves 62 and the common flow path grooves 71 formed in the respective flow path members. 7, a set of a common supply flow path 211 and a common recovery flow path 212 is formed for each color in the flow path member 210. The communication port 72 of the third flow path member 70 communicates with each hole of the joint rubber 100, and is fluidically connected to the liquid supply unit 220. A plurality of communication ports 61 are formed in the bottom surface of the common flow path groove 62 of the second flow path member 60, and communicates with one end of the individual flow path groove 52 of the first flow path member 50. A communication port 51 is formed in the other end of the individual flow path groove 52 of the first flow path member 50, and is fluidically connected to a plurality of ejection modules 200 via the communication port 51. The individual flow path groove 52 makes it possible to aggregate the flow paths toward the center side of the flow path member.

[0042] The first to third flow path members are preferably made of a material that is resistant to corrosion by liquids and has a low linear expansion coefficient. Suitable materials include alumina, LCP (liquid crystal polymer), PPS (polyphenyl sulfide), and PSF (polysulfone) as a base material, and composite materials (resin materials) with inorganic fillers such as silica particles and fibers added thereto. The flow path member 210 can be formed by stacking three flow path members and bonding them to each other. They may be bonded, or when a resin composite material is selected as the material, a joining method by welding may be used.

[0043] Next, the connection relationship of each flow path in the flow path member 210 will be described with reference to Fig. 7. Fig. 7 is a perspective view showing a flow path in the flow path member 210 formed by joining the first to third flow path members, partially enlarged from the surface side of the first flow path member 50 on which the ejection module 200 is mounted. The flow path member 210 is provided with common supply flow paths 211 (211a, 211b, 211c, 211d) and common recovery flow paths 212 (212a, 212b, 212c, 212d) that extend in the longitudinal direction of the liquid ejection head 3 for each color. A plurality of individual supply flow paths (213a, 213b, 213c, 213d) formed by the individual flow path grooves 52 are connected to the common supply flow path 211 for each color via a communication port 61. Furthermore, a plurality of individual recovery flow paths (214a, 214b, 214c, 214d) formed by the individual flow path grooves 52 are connected to the common recovery flow path 212 of each color via the communication port 61. With this flow path configuration, ink can be collected from each common supply flow path 211 via the individual supply flow paths 213 to the recording element substrate 10 located at the center of the flow path member. Also, ink can be recovered from the recording element substrate 10 via the individual recovery flow paths 214 to each common recovery flow path 212.

[0044] 8 is a diagram showing a cross section taken along line EE in FIG. 7. As shown in this figure, each of the individual recovery flow paths (214a, 214c) communicates with the ejection module 200 via the communication port 51. Although only the individual recovery flow paths (214a, 214c) are shown in FIG. 8, in another cross section, the individual supply flow paths 213 communicate with the ejection module 200 as shown in FIG. 7. A flow path is formed in the support member 30 and the recording element substrate 10 included in each ejection module 200 to supply ink from the first flow path member 50 to the recording element 15 (FIG. 10) provided on the recording element substrate 10. In addition, a flow path is formed in the support member 30 and the recording element substrate 10 to recover (circulate) a part or all of the ink supplied to the recording element 15 to the first flow path member 50. Here, the common supply flow path 211 of each color is connected to the negative pressure control unit 230 (high pressure side) of the corresponding color via the liquid supply unit 220, and the common recovery flow path 212 is connected to the negative pressure control unit 230 (low pressure side) via the liquid supply unit 220. This negative pressure control unit 230 generates a pressure difference between the common supply flow path 211 and the common recovery flow path 212. For this reason, in the liquid ejection head of this embodiment in which the flow paths are connected as shown in Figures 7 and 8, a flow is generated for each color that flows in the order of the common supply flow path 211 -> the individual supply flow path 213a -> the recording element substrate 10 -> the individual recovery flow path 213b -> the common recovery flow path 212.

[0045] <Discharge module> FIG. 9(a) shows a perspective view of one discharge module 200, and FIG. 9(b) shows an exploded view thereof. In the manufacturing method of the discharge module 200, first, the recording element substrate 10 and the flexible wiring substrate 40 are bonded onto the support member 30 in which the liquid communication port 31 is provided in advance. Then, the terminal 16 on the recording 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 flexible wiring substrate 40 opposite the recording 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 recording element substrate 10 and is also a flow path member for fluidly communicating the recording 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 joined to the recording element substrate with sufficiently high reliability. For example, alumina or a resin material is preferable as the material.

[0046] <Structure of the recording element substrate> The configuration of the recording element substrate 10 in this embodiment will be described. FIG. 10(a) shows a plan view of the surface of the recording element substrate 10 on which the ejection ports 13 are formed, FIG. 10(b) shows an enlarged view of the portion indicated by Xb in FIG. 10(a), and FIG. 10(c) shows a plan view of the back surface of FIG. 10(a). FIG. 11 is a perspective view showing a cross section of the recording element substrate 10 and the cover member 20 taken along the cross section line XI-XI shown in FIG. 10(a). As shown in FIG. 10(a), four ejection port arrays corresponding to the ink colors are formed in the ejection port forming member 12 of the recording element substrate 10. Hereinafter, the direction in which the ejection port arrays in which the multiple ejection ports 13 are arranged extend will be referred to as the "ejection port array direction."

[0047] As shown in FIG. 10(b), a recording element 15, which is a heating element for foaming ink with thermal energy, is disposed at a position corresponding to each ejection port 13. A pressure chamber 23 in which the recording element 15 is disposed is partitioned by a partition wall 22. The recording element 15 is electrically connected to a terminal 16 in FIG. 10(a) by an electric wiring (not shown) provided on the recording element substrate 10. The recording element 15 generates heat based on a pulse signal input from a control circuit of the recording device 1000 via an electric wiring substrate 90 (FIG. 5) and a flexible wiring substrate 40 (FIG. 9) to boil the ink. The ink is ejected from the ejection port 13 by the force of foaming caused by this boiling. As shown in FIG. 10(b), 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. The liquid supply path 18 and the liquid recovery path 19 are flow paths extending in the direction of the ejection port array provided on the recording element substrate 10, and communicate with the ejection ports 13 via the supply path 17a and the recovery path 17b, respectively.

[0048] As shown in FIG. 10(c) and FIG. 11, a sheet-like cover member 20 is laminated on the back surface of the recording element substrate 10 on which the ejection ports 13 are formed, and the cover member 20 is provided with a plurality of openings 21 communicating with the liquid supply path 18 and the liquid recovery path 19 described later. In this embodiment, three openings 21 are provided on the cover member 20 for each liquid supply path 18, and two openings 21 are provided on each liquid recovery path 19. As shown in FIG. 10(b), each opening 21 of the cover member 20 communicates with a plurality of communication ports 51 shown in FIG. 7 and the like. As shown in FIG. 11, the cover member 20 functions as a cover that forms a part of the walls of the liquid supply path 18 and the liquid recovery path 19 formed on the substrate 11 of the recording element substrate 10. The cover member 20 is preferably a material having sufficient corrosion resistance against ink, and from the viewpoint of preventing color mixing, high accuracy is required for the opening shape and opening position of the opening 21. For this reason, it is preferable to use a photosensitive resin material or a silicon plate as the material for the lid member 20, and to provide the openings 21 by a photolithography process. In this way, the lid member changes the pitch of the flow path by the openings 21, and considering the pressure loss, it is preferable that the thickness is thin and that the lid member is made of a film-like material.

[0049] Next, the flow of ink in the recording element substrate 10 will be described. FIG. 11 is a perspective view showing a cross section of the recording element substrate 10 and the cover member 20 taken along the cross section line XI-XI in FIG. 10(a). The recording element substrate 10 is formed by laminating a substrate 11 made of Si and an ejection port forming member 12 made of a photosensitive resin, and a cover member 20 is bonded to the rear surface of the substrate 11. A recording element 15 is formed on one surface of the substrate 11 (FIG. 10), and grooves that form a liquid supply path 18 and a liquid recovery path 19 that extend along the ejection port row are formed on the rear surface of the substrate 11. The liquid supply path 18 and the liquid recovery path 19 formed by the substrate 11 and the cover member 20 are connected to a common supply path 211 and a common recovery path 212 in a path member 210, respectively, and a pressure difference is generated between the liquid supply path 18 and the liquid recovery path 19. When ink is discharged from the multiple discharge ports 13 of the liquid discharge head 3 to perform recording, the ink flow in the liquid supply path 18 provided in the substrate 11 becomes the flow indicated by the arrow C in FIG. 11 due to this pressure difference in the discharge ports not performing the discharge operation. That is, the ink flows to the liquid recovery path 19 via the supply port 17a, the pressure chamber 23, and the recovery port 17b. This flow allows the ink, bubbles, foreign matter, and the like that are caused by evaporation from the discharge port 13 in the discharge port 13 and the pressure chamber 23 where recording is paused to be recovered to the liquid recovery path 19. Also, the increase in the viscosity of the ink in the discharge port 13 and the pressure chamber 23 can be suppressed. The ink recovered to the liquid recovery path 19 is recovered in the order of the communication port 51 in the flow path member 210, the individual recovery flow path 214, and the common recovery flow path 212 through the opening 21 of the cover member 20 and the liquid communication port 31 of the support member 30 (see FIG. 9(b)). This ink is finally recovered to the supply path of the recording device 1000.

[0050] That is, the ink supplied from the recording apparatus body to the liquid ejection head 3 flows, is supplied, and is recovered in the following order. The ink first flows into the liquid ejection head 3 from the liquid connection portion 111 of the liquid supply unit 220. The ink is then supplied in the order of the joint rubber 100, the communication port 72 and the common flow channel 71 provided in the third flow channel member, the common flow channel 62 and the communication port 61 provided in the second flow channel member, and the individual flow channel 52 and the communication port 51 provided in the first flow channel member. Thereafter, the ink is supplied to the pressure chamber 23 via the liquid communication port 31 provided in the support member 30, the opening 21 provided in the cover member, the liquid supply path 18 and the supply port 17a provided in the substrate 11, in that order. Of the ink supplied to the pressure chamber 23, the ink that is not ejected from the ejection port 13 flows in the order of the recovery port 17b and the liquid recovery path 19 provided in the substrate 11, the opening 21 provided in the cover member, and the liquid communication port 31 provided in the support member 30. Thereafter, the ink flows through the communication port 51 and the individual flow channel 52 provided in the first flow channel member, the communication port 61 and the common flow channel 62 provided in the second flow channel member, the common flow channel 71 and the communication port 72 provided in the third flow channel member 70, and the joint rubber 100 in this order. Furthermore, the ink flows from the liquid connection portion 111 provided in the liquid supply unit to the outside of the liquid ejection head 3. In the form of the first circulation path shown in FIG. 2, the ink flowing in from the liquid connection portion 111 is supplied to the joint rubber 100 after passing through the negative pressure control unit 230. In the form of the second circulation path shown in FIG. 3, the ink collected from the pressure chamber 23 passes through the joint rubber 100, and then flows from the liquid connection portion 111 to the outside of the liquid ejection head via the negative pressure control unit 230.

[0051] 2 and 3, not all of the ink flowing in from one end of the common supply flow path 211 of the liquid ejection unit 300 is supplied to the pressure chamber 23 via the individual supply flow path 213a. Some ink flows from the other end of the common supply flow path 211 to the liquid supply unit 220 without flowing into the individual supply flow path 213a. In this way, by providing a path that does not pass through the recording element substrate 10, even in the case of the recording element substrate 10 having a fine flow path with a large flow resistance as in this embodiment, it is possible to suppress the backflow of the circulating flow of the ink. In this way, in the liquid ejection head of this embodiment, the viscosity of the ink in the pressure chamber or in the vicinity of the ejection port can be suppressed, so that deviation from the normal direction of ejection and non-ejection can be suppressed, and as a result, high-quality printing can be performed.

[0052] <Positional relationship between recording element substrates> FIG. 12 is a partially enlarged plan view showing adjacent portions of the recording element substrates in two adjacent ejection modules. As shown in FIG. 10(a) and the like, in this embodiment, a recording element substrate having a shape of a parallelogram is used. As shown in FIG. 12, each ejection port array (14a to 14d) in which the ejection ports 13 in each recording element substrate 10 are arranged so as to be inclined at a certain angle with respect to the conveying direction of the recording medium. As a result, the ejection port arrays in the adjacent portions of the recording element substrates 10 overlap with at least one ejection port in the conveying direction of the recording medium. In FIG. 12, two ejection ports on line D are in an overlapping relationship with each other. With this arrangement, even if the position of the recording 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. Even when a plurality of recording element substrates 10 are arranged in a straight line (inline) instead of in a staggered arrangement, the configuration shown in FIG. 12 can be used. This makes it possible to suppress an increase in the length of the liquid ejection head in the transport direction of the recording medium, while taking measures against black streaks and white spots at the joints between the recording element substrates 10. Note that, although the main plane of the recording element substrate is a parallelogram here, this embodiment is not limited to this, and the configuration of this embodiment can be preferably applied even when a recording element substrate having a rectangular, trapezoidal, or other shape is used.

[0053] <Communication control between liquid ejection head and main body> Hereinafter, communication control between the liquid ejection head and the main body according to this embodiment will be described with reference to Fig. 13. Fig. 13 is a diagram modeling communication between the liquid ejection head and the main body. The main body board built into the main body of the recording device 1000 has a CPU, ROM, RAM, etc. This main body board receives temperature information on each recording element board 10 from the liquid ejection head 3, and transmits control signals for driving each recording element board 10 to the electric wiring board 90 of the liquid ejection head 3 based on the received temperature information.

[0054] This control signal includes various information such as temperature information, as well as information on the pulse to be applied to each heating element (called pulse information). For example, in Patent Document 1, the pulse information includes the transmission timing T1 and pulse width Pw1 for the first pulse signal, and the transmission timing T2 and pulse width Pw2 for the second pulse signal. In contrast, in this embodiment, the pulse information is only the transmission timing T1 and pulse width Pw1 for the first pulse signal, and the amount of data processing is small even if voltage information is added separately to the control information. This makes it possible to reduce the processing load.

[0055] <Pulse width of the pulse signal and the ink droplet ejection speed> In this embodiment, when the ink is bubbled by the heating element to eject the ink from the ejection port, a total heating time of 0.5 microseconds or less is expected to be more effective. When foaming the ink, the shorter the heating time, i.e., the greater the heat flux, the more stable the foaming and the smaller the variation in ejection speed. In particular, for ink with a high solid content, a pulse signal with a shorter pulse width is preferable since foaming is easily inhibited. However, the greater the heat flux and the shorter the heating time, the slower the ejection speed becomes.

[0056] 14 is a graph of the ejection speed when the total heating time is divided into two and the divided time is changed in various ways, as in Patent Document 1, with black dots indicating data when the total heating time is 0.2 microseconds and white dots indicating data when the total heating time is 0.3 microseconds. Comparing the 0.2 microsecond data with the 0.3 microsecond data, the ejection speed modulation width is small when the total heating time is 0.2 microseconds, and there is a possibility that the ejection speed modulation is insufficient.

[0057] In this embodiment, as described below, by shortening the total overheating time and driving the recording elements with adjustment of the potential difference ΔV based on the state and configuration of the liquid ejection head (recording element substrate), it is possible to correct the ejection speed while suppressing the fluctuation of ejection. Here, the state of the liquid ejection head includes the amount of kogation on the recording element substrate, the temperature of the element substrate, and the adsorption state of the ink components, as described below, and the configuration of the liquid ejection head includes the dimensions of the ejection openings of the recording element substrate, as described below.

[0058] <Structure of heat application part in recording element substrate> The structure of the heat application part in the recording element substrate according to this embodiment will be described below with reference to Fig. 15. Fig. 15(a) is a plan view showing an enlarged schematic view of the vicinity of the heat application part in the recording element substrate 10. Fig. 15(b) is a cross-sectional view taken along dashed line XVb-XVb in Fig. 15(a).

[0059] The recording element substrate of the liquid ejection head is formed by stacking a plurality of layers on a base body made of silicon. In this embodiment, a heat storage layer made of a thermal oxide film, a SiO film, a SiN film, or the like is disposed on the base body. A heating resistor 126 is disposed on the heat storage layer, and an electrode wiring layer (not shown) as wiring made of a metal material such as Al, Al-Si, or Al-Cu is connected to the heating resistor 126 via a tungsten plug 128. As shown in FIG. 15(b), an insulating protective layer 127 (first protective layer) is disposed on the heating resistor 126. The insulating protective layer 127 is an insulating layer disposed on the upper side of the heating resistor 126 so as to cover the heating resistor 126. The insulating protective layer 127 is formed of a SiO film, a SiN film, or the like.

[0060] A protective layer for blocking contact with liquid is disposed on the insulating protective layer 127. This protective layer includes a lower protective layer 125, an upper protective layer 124 (second protective layer), and an adhesive protective layer 123. In this embodiment, the lower protective layer 125 and the upper protective layer 124 are provided on the heating resistor 126, and protect the surface of the heating resistor 126 from chemical and physical shocks caused by heat generation by the heating resistor 126.

[0061] In this embodiment, the lower protective layer 125 is made of tantalum (Ta), the upper protective layer 124 is made of iridium (Ir), and the adhesive protective layer 123 is made of tantalum (Ta). In addition, the protective layers made of these materials have electrical conductivity. A protective layer 122 is disposed on the adhesive protective layer 123 as a liquid-resistant layer for improving adhesion with the ejection port forming member 12. The protective layer 122 is made of SiC.

[0062] When liquid is discharged, the upper part of the upper protective layer 124 is in contact with the liquid, and the temperature of the liquid rises instantaneously at the upper part, causing bubbles, which then disappear, creating a harsh environment in which cavitation occurs. For this reason, in this embodiment, the upper protective layer 124 made of an iridium material, which has high corrosion resistance and reliability, is formed at a position corresponding to the heating resistor 126 and is in contact with the liquid.

[0063] In this embodiment, an ink circulation configuration is adopted in which liquid is supplied from the supply port 17a inside the pressure chamber 23 and the liquid is recovered to the recovery port 17b. Therefore, during printing, the liquid flows over the heating resistor 126 from the supply port 17a on the upstream side to the recovery port 17b on the downstream side.

[0064] In this embodiment, a burn prevention process is performed to prevent burnt deposits on the upper protective layer 124 on the heating resistor 126 during printing. To explain in detail, the upper protective layer 124 has an electrode 121 (first electrode) directly above the heating resistor 126, and an opposing electrode 129 (second electrode) corresponding to the electrode 121 is provided to form an electric field through the liquid in the liquid chamber. This causes negatively charged particles such as pigments in the liquid to be repelled from the surface of the upper protective layer 124 on the heating resistor 126. In this way, the presence rate of negatively charged particles such as pigments near the surface of the upper protective layer 124 is reduced, thereby preventing burnt deposits from depositing on the upper protective layer 124 on the heating resistor 126 during printing. This burnt deposit prevention process takes into consideration the phenomenon that occurs when coloring materials, additives, etc. contained in the liquid are decomposed at the molecular level by high-temperature heating, converted into hardly soluble substances, and physically adsorbed onto the upper protective layer. When the upper protective layer 124 is heated to a high temperature, reducing the presence rate of coloring materials, additives, etc. that cause scorching in the vicinity of the surface of the upper protective layer 124 on the heating resistor 126 leads to suppression of scorching.

[0065] The mechanism of electric field control (also called potential control or potential difference control) used in this embodiment will be described below with reference to Fig. 16. In Fig. 16(a), an electrode 121 of the upper protective layer and a counter electrode 129 are arranged in a bubble-forming chamber, which is filled with liquid. The liquid contains particles 141 such as a pigment that are negatively charged, and the particles 141 are dispersed approximately uniformly in the liquid.

[0066] FIG. 16(b) shows a state in which a voltage is applied so that the voltage of the electrode 121 of the upper protective layer is relatively lower than that of the counter electrode 129. For example, the potential difference between the electrode 121 and the counter electrode 129 is about 0.2 to 2.5 V. This is because, when the upper protective layer 124 is made of iridium, if the potential difference between the two electrodes exceeds 2.5 V, an electrochemical reaction occurs between the electrode 121 and the liquid, and the surface of the electrode 121 dissolves into the liquid, so it is preferable to set the potential difference to a level that does not dissolve the electrode 121. That is, at this time, an electric field 140 is formed between the electrode 121 of the upper protective layer and the counter electrode 129 via the liquid, but no current flows. Since the electrode 121 of the upper protective layer has a negative potential relative to the counter electrode 129, the particles 141 charged to a negative potential are repelled from the surface of the electrode 121 of the upper protective layer, and the presence rate of the particles 141 in the vicinity of the surface of the electrode 121 of the upper protective layer decreases.

[0067] Fig. 16(c) is a schematic diagram showing an enlargement of the vicinity of the upper protective layer 11 shown in Fig. 16(b). The negatively charged particles 141 are repelled by a repulsive force 143 from the surface of the upper protective layer 11 along the electric field lines of the electric field 140 formed in the liquid. In other words, the larger the potential difference ΔV (=Vc-Vh) when the potential of the counter electrode is Vc and the potential of the upper protective layer electrode of the heater is Vh, the more the negatively charged particles 141 are repelled. On the other hand, the positively charged particles approach the heater. In this embodiment, the negative charge is a factor that inhibits foaming, and the larger ΔV is, the higher the foaming temperature and the faster the discharge speed.

[0068] Figure 17 shows the relationship between ΔV and the ejection speed, specifically, the measurement results of the ejection speed when ΔV is changed in increments of 0.5 V. In this example, Vh was fixed at 0 V, and measurements were taken while varying Vc. As shown in Figure 17, it is possible to change the ejection speed v by changing ΔV. According to the mechanism introduced here, when the ejection speed changes due to external factors, it is possible to correct the ejection speed by changing ΔV, thereby suppressing printing unevenness.

[0069] In this embodiment, in order to prevent the discharge speed from changing due to the burnt surface of the heater, resulting in uneven printing, the discharge speed is corrected by changing ΔV. In particular, when multiple chips (recording element substrates) are mounted on a liquid discharge head as in this embodiment, if the number of discharges differs between the chips, the discharge speed and discharge amount of each chip will change, which may result in unevenness between the chips. Here, burnt surface of the heater refers to ink denaturation caused by the heater surface becoming hot during discharge, and the resulting components being deposited on the surface.

[0070] 18 shows the change in ejection speed due to the mechanism of this embodiment. Specifically, the solid line shows the relationship between the ejection speed and the number of ejections when ΔV is reset each time (twice), and the dashed line shows the relationship between the ejection speed and the number of ejections when ΔV is not reset.

[0071] Burnt ink on the heater surface inhibits foaming. Therefore, when ΔV is constant, the droplet ejection speed decreases as the number of ejections increases, as shown in Figure 18. Therefore, while the ejection speed of the tip used for printing decreases, the ejection speed of the tip not used for printing does not decrease. As a result, differences in the ejection speed between the tips occur, causing unevenness.

[0072] Therefore, in this embodiment, the potential difference ΔV (=Vc-Vh) in the tip is adjusted according to the amount of kogation. This makes it possible to print while maintaining the ejection speed of all tips within a specified range. The potential difference ΔV can be adjusted by changing the potential of at least one of the electrode 121 and the counter electrode 129. Note that the amount of kogation is preferably managed using the number of ejections (so-called dot count).

[0073] <Adjustment of potential difference ΔV based on dot count> 19A is a sequence diagram of a series of processes related to the adjustment of the potential difference ΔV based on the dot count according to this embodiment. In this example, the initial value of the potential of the upper protective layer electrode is set to 0.0 V, and the initial value of the potential of the opposing electrode is set to about 1.9 V. These initial values ​​differ for each type of ink, and from the viewpoint of durability, the most durable voltage is set.

[0074] In step S1901, the recording device 1000 performs printing. Note that hereinafter, "step S~" will be abbreviated to "S~".

[0075] After printing in S1901 is completed, in S1902, the CPU of the recording device 1000 performs dot counting for each chip to determine the number of shots for each chip. Then, for all chips other than the chip with the largest number of ink droplets, the CPU derives the difference in the number of shots between each chip and the chip with the largest number of ink droplets, and determines for each chip whether the derived difference in the number of shots is equal to or greater than a predetermined threshold value.

[0076] For the chips for which the result of the determination in S1902 is true, the process proceeds to S1903. On the other hand, for the chips for which the result of the determination in S1902 is false, the process returns to S1901, and the next printing is performed with the same settings. The predetermined threshold value used in S1902 is called the set number of shots Nd.

[0077] In S1903, the CPU of the recording apparatus 1000 resets the voltage of the opposing electrode for all chips for which the most recent determination in S1902 was true. Specifically, a value obtained by subtracting 0.1 V from the current value is set. The CPU of the recording apparatus 1000 then resets the dot count for all chips, and sets the dot count value (also called the number of ejections) to zero. Note that, although the predetermined subtraction amount is set to 0.1 V here, the predetermined subtraction amount is not limited to 0.1 V, and any value may be used.

[0078] In this series of processes, the potential difference in the other chips is adjusted in accordance with the decrease in the ejection speed of the chip that ejects the most ink droplets, thereby making it possible to equalize the ejection speeds between the chips and prevent a decrease in print quality.

[0079] In addition, the liquid ejection head of this embodiment is a liquid ejection head that prints four colors of ink, CMYK, and the initial value of the potential of the opposing electrode and the set number of dot counts Nd may be the same for each ink color, or different values ​​may be used.

[0080] The potential difference ΔV may be common to all ink colors, or may be set for each ink color. FIG. 20(a) shows a board with common wiring so that the potential difference ΔV is the same for all columns, and FIG. 20(b) shows a board with wiring for each column. When the structure shown in FIG. 20(a) is adopted, the chip can be made smaller. On the other hand, when the structure shown in FIG. 20(b) is adopted, a wiring is assigned to each ink color, so that an appropriate ΔV can be set for each ink color. For example, for ink colors that burn easily, the set number of shots Nd is reduced and the speed is adjusted finely. This improves the print quality.

[0081] [Second embodiment] In this embodiment, the change in ejection speed caused by the change in head temperature is dealt with using the same mechanism as in the first embodiment. Note that in the following explanation of each embodiment, differences from the previous embodiment will be mainly explained, and explanations of the same contents as the previous embodiment will be omitted as appropriate.

[0082] In an inkjet recording device that uses thermal energy to eject ink droplets, the higher the temperature, the higher the ejection speed. Figure 21 shows an example of the change in ejection speed when the temperature is actually changed. Since the ejection speed can change due to temperature changes in this way, it is required to print while keeping the temperature constant. However, in an inkjet recording device that performs high-speed printing, the temperature changes due to various factors such as temperature changes caused by the head, such as temperature rise due to ejection of ink droplets and cooling due to ink supply, cooling due to air flow for feeding the paper, and temperature rise of the main body to evaporate the ink at high speed. For this reason, it is required to print while correcting the ejection speed that changes due to temperature changes of the recording head.

[0083] This embodiment is characterized in that the temperature is measured by a temperature sensor such as a diode mounted in the head, and printing is performed while adjusting the potential difference based on the measured temperature. FIG. 22 shows an example of a table (called a ΔV change table) in which each value of the potential difference ΔV is stored. This ΔV change table stores each value of the potential difference ΔV that is used for updating when the temperature acquired as a result of measurement by the temperature sensor has changed from a reference set temperature (called a reference temperature). The "potential control reference value" in FIG. 22 is the reference value of the potential difference ΔV that is set when the first embodiment is applied, and in this example, four values ​​(0.5, 1.0, 1.5, 2.0) are assumed as the potential control reference value. Note that the specific values ​​stored in this table differ depending on the type of ink.

[0084] For example, if the reference temperature is set to 40° C., the potential control reference value is set to 1.0 V, and the temperature sensor measures a temperature of 42° C., then the corrected potential difference ΔV (=Vc-Vh) can be set to 0.7 V.

[0085] FIG. 23 is a sequence diagram of a series of processes relating to ΔV adjustment based on temperature and dot count according to this embodiment.

[0086] In this example, the initial value of the potential of the upper protective layer electrode is set to 0.0V, and the initial value of the potential of the counter electrode is set to about 0.2 to 0.5V.

[0087] 23, in this embodiment, in S2301 before printing, the CPU of the recording device 1000 measures the temperature using a temperature sensor mounted on the recording device 1000, and derives the difference between the temperature acquired by the temperature measurement and a reference temperature. Then, the CPU of the recording device 1000 determines the value of ΔV corresponding to this difference by referring to the ΔV change table shown in FIG. 22, and resets the voltage of the counter electrode to the determined value.

[0088] S1901 to S1903 after S2301 are the same as those in the first embodiment (see FIG. 19(a)). Note that, although the temperature measurement is performed before printing as an example here, it may be performed during printing.

[0089] As described above, according to this embodiment, it is possible to correct the ejection speed in response to temperature changes.

[0090] [Third embodiment] In this embodiment, when using a mechanism similar to that of the first or second embodiment, the potential control reference value is corrected based on the temperature change caused by ejection. In an inkjet recording device that ejects ink droplets using thermal energy, the temperature in the vicinity of the ejection port increases as the number of ink droplets ejected simultaneously increases. Since the temperature changes (rises) rapidly as ink is ejected, it is preferable to estimate the temperature change in advance based on the print data and correct the ejection speed in advance.

[0091] An example of estimating temperature change based on print data according to this embodiment will be described below. As an example, a form of estimating temperature rise based on the number of simultaneous ejections in an ejection port array will be described. When the number of simultaneous ejections is calculated for each ejection port array, the potential control reference value is corrected based on the ratio of the number of ejection ports in the ejection port array that are ejecting (hereinafter referred to as duty).

[0092] Fig. 24 shows an example of a ΔV change table according to this embodiment. This ΔV change table holds the value of the potential difference ΔV corresponding to each duty value (0 to 100%). The potential control reference value as the reference voltage (potential difference) here is a voltage value calculated by the first or second embodiment, and in Fig. 24, four values ​​(0.5, 1.0, 1.5, 2.0) are assumed.

[0093] Here, a specific example of how to use the ΔV change table will be described. For example, if an ejection port array is formed of 100 ejection ports and the number of simultaneous ejections is 80, the duty will be 80%. In this case, if the potential control reference value is 1V, ΔV can be set to 0.8V using the table in FIG.

[0094] FIG. 25 is a sequence diagram of a series of processes relating to ΔV adjustment based on temperature, duty, and dot count according to this embodiment.

[0095] In S2501, the CPU of the printing apparatus 1000 measures the temperature using a temperature sensor mounted on the printing apparatus 1000.

[0096] In S2502, the CPU of the recording apparatus 1000 calculates the duty based on the print data.

[0097] In S2503, the CPU of the recording apparatus 1000 derives the difference between the temperature acquired in the most recent S2501 and the reference temperature. Then, as in the second embodiment, the CPU of the recording apparatus 1000 derives a ΔV value (defined as a first correction value) corresponding to this difference by referring to the ΔV change table shown in FIG. 22. Then, the CPU of the recording apparatus 1000 further derives a ΔV value (defined as a second correction value) corresponding to the derived first correction value by referring to the ΔV change table shown in FIG. 24. Finally, the CPU of the recording apparatus 1000 resets the voltage of the opposing electrode to the second correction value.

[0098] S1901 to S1903 after S2503 are similar to those in the first embodiment (see FIG. 19(a)).

[0099] As described above, according to this embodiment, the electrode potential is set according to the temperature change near the ejection port by changing ΔV based on the duty. This makes it possible to correct the ejection speed according to the sudden temperature change caused by printing near the ejection port, thereby improving the print quality. Note that, as described above, in this embodiment, the number of simultaneous ejections in the ejection port array is calculated, but the number of simultaneous ejections may be calculated for the entire chip or the entire head, or the ejection port array may be divided into multiple blocks and the number of simultaneous ejections may be calculated for each block.

[0100] [Fourth embodiment] This embodiment is characterized in that when ink droplets are continuously ejected, the potential difference ΔV is set according to the number of ejections. The reason for setting ΔV according to the number of ejections in this way is that, as shown in FIG. 26, the ejection speed of ink droplets when ink droplets are continuously ejected is fast at the beginning and gradually slows down, and it is necessary to deal with this. Also, as shown in FIG. 26, when the ejection is stopped for a while, the ejection speed temporarily increases again, but if the ejection is continued, it decreases over time. This is thought to be due to the fact that ink components are adsorbed at the ejection port and the interface with the upper protective film when not ejecting, making the bubbling unstable. To solve this problem, in this embodiment, the potential difference ΔV is set according to the number of continuous ejections.

[0101] Fig. 27 shows an example of a ΔV change table according to this embodiment. This ΔV change table holds corrected potential difference ΔV values ​​corresponding to each value of the number of continuous ejections (10 to 500). Note that the number of continuous ejections according to this embodiment refers to the number of ink droplets that are continuously ejected after a predetermined rest time (specifically, about 0.1 seconds) has passed. Also, the potential control reference value as the reference voltage (potential difference) in this embodiment is a voltage value calculated by the first to third embodiments, and in the example of Fig. 27, four values ​​(0.5, 1.0, 1.5, 1.9) are assumed.

[0102] Here, a specific example of how to use the ΔV changing table will be described. For example, when the number of continuous ejections is 100 and the potential control reference value is 1V, ΔV can be set to 0.85V using the table in FIG.

[0103] In the ΔV setting sequence according to this embodiment, the number of continuous ejections and the pause time are calculated based on the print data before printing (see FIG. 25) as in the third embodiment. Then, based on the calculated number of continuous ejections and the pause time, a corrected ΔV is derived using a ΔV changing table as shown in FIG. 27, and the voltage of the opposing electrode is set according to the derived corrected ΔV.

[0104] As described above, in this embodiment, ΔV is changed based on the number of continuous ejections, which makes it possible to set the electrode potential according to the adsorption state of the ink components, thereby improving the print quality.

[0105] [Fifth embodiment] This embodiment is characterized by providing an inter-chip potential difference based on the dimensions of the ejection port that ejects ink. The ejection speed can change depending on the dimensions of the ejection port, and the dimensions can vary within the manufacturing tolerances. The larger the diameter of the ejection port, the greater the amount of liquid ejected, and therefore the slower the ejection speed. Therefore, it is necessary to correct the ejection speed based on the dimensions of the ejection port.

[0106] The discharge speed correction according to this embodiment can be performed by directly measuring the discharge dimensions and discharge speed during inspection when the recording device 1000 is shipped. Alternatively, it can be performed by printing a predetermined ruled line pattern and estimating the discharge speed difference between the chips based on the output result. By providing a potential difference so as to correct the discharge speed difference between the chips, printing can be performed while correcting the discharge speed that varies due to the dimensional deviation between the chips.

[0107] [Sixth embodiment] This embodiment is applied to the case where the discharge speed monotonically decreases as the potential difference ΔV (=Vc-Vh) between the potential Vc of the counter electrode and the potential Vh of the upper protective layer electrode of the heater increases (FIG. 28). As described in the first embodiment, particles that inhibit foaming are generally negatively charged, but in rare cases, they may be positively charged. In such a case, the more positive the potential of the upper protective layer electrode of the heater is made relative to the counter electrode, the more likely the positively charged particles will be attracted to the upper protective layer, and the discharge speed will decrease.

[0108] Therefore, in this embodiment, when the discharge speed is increased, the potential difference ΔV (=Vc-Vh) between the potential Vc of the opposing electrode and the potential Vh of the upper protective layer electrode of the heater is set to be small, and when the discharge speed is decreased, the potential difference ΔV is set to be large. In addition, in making such settings, the voltage may be determined by estimating the amount of kogation using dot count as in the first embodiment, or the voltage may be determined using temperature as in the second embodiment.

[0109] 19B shows an example of a sequence using the same dot count as in the first embodiment. In this example, the initial value of the potential of the upper protective layer electrode is set to 0.0V, and the initial value of the potential of the counter electrode is set to −0.2V.

[0110] In S1901, the recording device 1000 performs printing.

[0111] After printing in S1901 is completed, in S1902, the CPU of the recording device 1000 performs dot counting for each chip to determine the number of ejections for each chip. Then, for all chips other than the chip with the largest number of ink droplets ejected, the CPU derives the difference in the number of ejections between each chip and the chip with the largest number of ink droplets ejected, and determines for each chip whether the derived difference in the number of ejections is equal to or greater than a predetermined threshold value.

[0112] For the chips for which the result of the determination in S1902 is true, the process proceeds to S1904. On the other hand, for the chips for which the result of the determination in S1902 is false, the process returns to S1901, and the next printing is performed with the same settings. The predetermined threshold value used in S1902 is called the set number of shots Nd.

[0113] In S1904, the CPU of the printing apparatus 1000 resets the voltage of the counter electrode for all chips for which the most recent determination in S1902 was true. Specifically, a value is set by adding 0.1 V to the current value. The CPU of the printing apparatus 1000 then resets the dot count for all chips, setting the dot count value to zero. Note that although the predetermined amount of addition is set to 0.1 V here, the predetermined amount of addition is not limited to 0.1 V and any value may be used.

[0114] According to this embodiment, even when using ink in which foaming inhibition occurs due to positive charge, it is possible to adjust the ejection speed based on the dot count in the same manner as in the first embodiment.

[0115] [Other embodiments] The present invention can also be realized by supplying a program for realizing one or more functions of the above-mentioned embodiments to a system or device via a network or a storage medium, and having one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) for realizing one or more functions. The contents of the first to sixth embodiments may be used in appropriate combination. [Explanation of symbols]

[0116] 3 Liquid ejection head 10 Recording element board 11 electrodes 129 Counter Electrode

Claims

1. a liquid ejection head having a conversion element for generating energy required for ejecting liquid, a first protective layer for blocking contact between the conversion element and the liquid, a second protective layer for covering a portion of the first protective layer and functioning as a first electrode, a second electrode electrically connected to the first electrode via the liquid, and an ejection port for ejecting the liquid; a control means for controlling a potential difference between the first electrode and the second electrode to a predetermined value during printing by changing a potential of at least one of the first electrode and the second electrode; A liquid ejection device having the control unit sets the potential difference based on at least one of a state and a configuration of the liquid ejection head. A liquid ejection device comprising:

2. The control means is capable of resetting the potential difference during printing. The liquid ejection device according to claim 1 .

3. The first electrode is a portion of the second protective layer directly above the conversion element. The liquid ejection device according to claim 2 .

4. the liquid ejection head includes a plurality of element substrates each including the conversion element, the first protective layer, the second protective layer, the second electrode, and the ejection port; the control means is capable of setting the potential difference for each of the element substrates.

4. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

5. a counting means for counting the number of ejections of the liquid for each of the element substrates; a calculation means for calculating a difference in the number of ejections between each of the element substrates other than the element substrate having the largest number of ejections and the element substrate having the largest number of ejections; a determination means for determining whether the difference in the number of ejections is equal to or greater than a predetermined threshold value for all element substrates other than the element substrate with the largest number of ejections; Further comprising 5. The liquid ejection device according to claim 4.

6. For an element substrate for which the determination result by the determination means is true, the control means sets a value obtained by subtracting a current value from the potential of the second electrode.

6. The liquid ejection device according to claim 5.

7. For an element substrate for which the determination result by the determination means is true, the control means sets a value obtained by adding a current value to the potential of the second electrode.

6. The liquid ejection device according to claim 5.

8. Further comprising a measuring means for measuring a temperature, the control means sets the potential difference based on a difference between a reference temperature and the temperature acquired by the measurement means.

8. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

9. the control means sets the potential difference based on a duty of print data.

9. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

10. the control means sets the potential difference based on the number of continuous ejections of the droplets of the liquid.

10. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

11. the control means sets the potential difference based on a dimension of the ejection port.

11. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

12. The first protective layer is insulating. The liquid ejection device according to any one of claims 1 to 11.

13. the liquid is ink, the control means performs the control for each ink color, 13. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

14. a liquid ejection head having a conversion element for generating energy required for ejecting liquid, a first protective layer for blocking contact between the conversion element and the liquid, a second protective layer for covering a portion of the first protective layer and functioning as a first electrode, a second electrode electrically connected to the first electrode via the liquid, and an ejection port for ejecting the liquid; a control means for controlling a potential difference between the first electrode and the second electrode to a predetermined value during printing by changing a potential of at least one of the first electrode and the second electrode; A method for controlling a liquid ejection device comprising: the control means has a step of setting the potential difference based on at least one of a state and a configuration of the liquid ejection head. A control method comprising:

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