LIQUID EJECTION APPARATUS AND CONTROL METHOD

Abstract

To suppress damage to a heater material to thereby speedily complete aging.SOLUTION: According to one embodiment of the present invention, a liquid ejection device is provided, having a liquid ejection head and control means. The liquid ejection head has: a heat generating element; a first protective layer blocking contact between the heat generating element and liquid; a second protective layer covering a part 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 ejecting the liquid. The control means performs control of changing potential of at least one of the first electrode and the second electrode, thereby setting potential difference between the first electrode and the second electrode to a predetermined value at each of aging and printing times, wherein the liquid ejection device satisfies an inequality ΔVa≠ΔVp when the potential different at the aging time is denoted as ΔVa, and a potential difference at the printing time is denoted as ΔVp.SELECTED DRAWING: Figure 14

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] Among the recording methods employed by recording devices such as multifunction printers, the inkjet recording method is a non-impact recording method that is widely adopted because it allows low noise, high density, and high speed recording. An inkjet recording device has a mechanism for driving a carrier that carries an inkjet head, a transport mechanism for transporting a recording medium such as recording paper, and a control configuration for controlling these. In this specification, an inkjet head is simply referred to as a "(recording) head." Also, a head that ejects liquid such as ink is referred to as a "liquid ejection head."

[0003] Methods of generating energy to eject ink from the nozzles of a print head include a method of pressurizing ink using electromechanical conversion elements such as piezoelectric elements, a method of using the pressure of air bubbles by generating bubbles through heat generated by irradiating electromagnetic waves such as lasers, etc., and a method of generating bubbles by heating the ink with an electrothermal conversion element (hereafter referred to as "heater") having a heating resistor.

[0004] In a recording head using this heater, the ink is heated by the heater, causing the ink to burn onto the surface, which can cause a large change in the ejection speed. Many of the inks used in such recording heads are dye- or pigment-based inks, and many of these inks are insoluble or poorly soluble in water. For this reason, it is said that the ejection characteristics are easily changed because insoluble or poorly soluble substances burn onto the heater.

[0005] Incidentally, when the head is mounted and there is almost no scorching on the surface of the heater, it is known that if an ink that is prone to scorching as described above is ejected, scorching occurs on the heater, resulting in a large change in the initial ejection characteristics (for example, the ejection speed decreases). This change in the initial ejection characteristics may cause image problems, such as the appearance of thin lines, distorted characters, and changes in color due to the deviation of the landing position.

[0006] To address this problem, Patent Document 1 proposes performing a preliminary ink ejection process (hereinafter also referred to as aging) that does not contribute to recording on the paper surface before recording on the paper surface. Aging causes a certain amount of ink to be koged on the heater surface, making the koged surface uniform (bringing the koged surface adhesion and desorption to a nearly equilibrium state), stabilizing the heater surface, and suppressing changes in the initial ejection characteristics.

[0007] Furthermore, Patent Document 2 proposes a head having an upper protective layer arranged in an area including the thermal action portion of the heater so as to be electrically connectable to serve as an electrode for causing an electrochemical reaction with the ink.

[0008] Furthermore, Patent Document 3 proposes a liquid ejection head having an upper protective layer that covers the portion heated by the heater, and an opposing electrode that uses the upper protective layer as one of the electrodes and is connected to the electrode via liquid. The liquid ejection head of Patent Document 3 has a potential control means that generates an electric field between the upper protective layer electrode and the opposing electrode, and during normal printing, the potential of the opposing electrode is relatively higher than the potential of the upper protective layer electrode, thereby making it difficult for kogation to adhere to the upper protective layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2014-131867 A [Patent Document 2] JP 2008-105364 A [Patent Document 3] JP 2019-38127 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, the above-mentioned patent document has the following problem. To explain in detail, problems occur when a pulse with a larger voltage value than that normally applied during recording or the like is applied to the recording element for a longer time than is normally applied in order to accelerate aging. In this case, excessive energy is applied to the heater material to which electricity is applied, which may damage the heater material and shorten its lifespan.

[0011] In addition, in a head that has an opposing electrode and performs potential control to prevent kogation from adhering to the heater surface, when there is almost no kogation on the heater surface, there is a problem that the ejection characteristics are difficult to change and aging takes time. The increase in aging time leads to an increase in downtime and waste ink.

[0012] In view of the above problems, an object of the present disclosure is to suppress damage to the heater material and quickly complete aging. [Means for solving the problem]

[0013] One embodiment of the present invention relates to a liquid ejection head having a heating element for generating energy required for ejecting liquid, a first protective layer for blocking contact between the heating 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, and a liquid ejection head that changes the potential of at least one of the first electrode and the second electrode to adjust the potential between the first electrode and the second electrode during aging and during printing. and a control means for controlling the potential difference to a predetermined value, wherein when the potential of the first electrode during aging is Vah, the potential of the second electrode is Vac, the potential difference between the potential Vah of the first electrode and the potential Vac of the second electrode is ΔVa (=Vac-Vah), the potential of the first electrode during printing is Vph, the potential of the second electrode is Vpc, and the potential difference between the potential Vph of the first electrode and the potential Vpc of the second electrode is ΔVp (=Vpc-Vph), ΔVa ≠ ΔVp is satisfied. Effect of the Invention

[0014] According to one embodiment of the present invention, it is possible to suppress damage to the heater material and quickly complete the aging process. [Brief description of the drawings]

[0015] [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 is a diagram showing the 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] FIG. 1 is a diagram showing a structure of a heat application portion in a recording element substrate; [Figure 14] An explanatory diagram of the burn prevention process when negatively charged particles are the main cause of burnt food. [Figure 15] An explanatory diagram of the burn prevention process when positively charged particles are the main cause of burnt food. [Figure 16] Relationship between number of shots and speed [Figure 17] Relationship between ΔV and amount of kogation on heater upper protective layer in the first embodiment [Figure 18] Relationship between ΔV and amount of kogation on heater upper protective layer in the second embodiment [Figure 19] Relationship between ΔV and amount of kogation on heater upper protective layer in the third embodiment [Figure 20] A diagram modeling the communication between the liquid ejection head and the main body. [Figure 21] Flowchart of processing in the first embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. However, the following description does not unnecessarily limit the scope of the present invention. In the following description, a liquid ejection device having a so-called line-type head having a length corresponding to the width of the recording medium is exemplified, but the idea of ​​the present disclosure can also be applied to a so-called serial-type liquid ejection device that performs printing while scanning the recording medium. An example of the configuration of the serial-type liquid ejection device is a configuration in which one black ink recording element board and one color ink recording element board are mounted. However, the present disclosure is not limited to this form, and 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 openings overlap in the ejection opening row direction, and the recording medium may be scanned with the line head. In addition, the recording device of this embodiment is a circulation-type inkjet recording device in which liquid such as ink is circulated between a tank and the liquid ejection device, but it may also be a non-circulation-type form.

[0017] [First embodiment] <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.

[0018] <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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] <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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] <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.

[0034] 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.

[0035] 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.

[0036] The negative pressure control unit 230 is a unit consisting of a pressure adjustment valve 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 on the upstream side of the liquid ejection head 3) caused by the fluctuation of the ink flow rate by the action of the 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 8 is a diagram showing a cross section taken along line VIII-VIII in FIG. 7. As shown in this figure, each individual recovery flow path (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. In the support member 30 and the recording element substrate 10 included in each ejection module 200, a flow path is formed for supplying ink from the first flow path member 50 to the recording element 15 (FIG. 10) provided on the recording element substrate 10. In addition, in the support member 30 and the recording element substrate 10, a flow path is formed for recovering (circulating) 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.

[0044] <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.

[0045] <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."

[0046] 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.

[0047] 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.

[0048] 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 with increased viscosity caused by evaporation from the discharge port 13, bubbles, foreign matter, etc., to be recovered to the liquid recovery path 19 in the discharge port 13 and the pressure chamber 23 where recording is paused. In addition, the increase in 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.

[0049] 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.

[0050] 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.

[0051] <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.

[0052] <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. 13. Fig. 13(a) is a plan view showing an enlarged schematic view of the heat application part and its vicinity in the recording element substrate 10. Fig. 13(b) is a cross-sectional view taken along dashed line XIIIb-XIIIb in Fig. 13(a).

[0053] In the liquid ejection head, a plurality of layers are laminated on a base 121 made of silicon to form a liquid ejection recording substrate. In this embodiment, a heat storage layer formed of a thermal oxide film, a SiO film, a SiN film, or the like is disposed on the base 121. A heating resistor 126 is disposed on the heat storage layer, and an electrode wiring layer (not shown) as wiring formed 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. 13(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 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.

[0054] A protective layer for blocking contact with liquid is disposed on the insulating protective layer 127. This protective layer is made up of a lower protective layer 125, an upper protective layer 124 (second protective layer), and an adhesive protective layer 123, and protects the surface of the heating resistor 126 from chemical and physical shocks caused by heat generation by the heating resistor 126.

[0055] 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). The protective layers made of these materials are conductive. A protective layer 122 is disposed on the adhesive protective layer 123 for improving liquid resistance and adhesion to the ejection port forming member 12. The protective layer 122 is made of SiC. The upper protective layer 124 is made of a material that contains a metal that dissolves due to an electrochemical reaction and does not form an oxide film that prevents dissolution by heating.

[0056] 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.

[0057] 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.

[0058] In this embodiment, a burn prevention process is performed to prevent burnt particles from accumulating 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, forming an electric field through the liquid in the liquid chamber 132. 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 particles from accumulating on the upper protective layer 124 on the heating resistor 126 during printing. This burnt prevention 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 on 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.

[0059] 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. 14. In Fig. 14(a), an electrode 121 of the upper protective layer and a counter electrode 129 are disposed in a liquid chamber 132, 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.

[0060] 14(b) shows a state in which a voltage is applied so that the potential of the electrode 121 of the upper protective layer is relatively lower than the potential of the counter electrode 129, and for example, the potential difference between the electrode 121 and the counter electrode 129 is about 0.5 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, causing the surface of the electrode 121 to dissolve into the liquid, and therefore it is preferable to set the potential difference to a level that does not dissolve the electrode 121. In other words, in this embodiment, when the potential difference between the electrode 121 and the counter electrode 129 during printing is ΔVp and the potential difference between the electrode 121 and the counter electrode 129 during aging is ΔVa, it is preferable to satisfy the following formula.

[0061]

number

[0062]

number

[0063] 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 negatively charged particles 141 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.

[0064] Fig. 14(d) is a schematic diagram showing an enlargement of the vicinity of the upper protective layer shown in Fig. 14(b). A negatively charged particle 141 is repelled by a repulsive force 143 from the surface of the electrode 121 of the upper protective layer along the electric field lines of the electric field 140 formed in the liquid.

[0065] Due to the above mechanism, in this embodiment, when the potential of the counter electrode is Vc and the potential of the upper protective layer electrode of the heater is Vh, the larger the potential difference ΔV (=Vc-Vh), the more the negatively charged particles 141 that cause kogation are repelled, and the amount of kogation decreases. The relationship between ΔV and the amount of kogation in this embodiment is as shown in FIG.

[0066] However, in the above head configuration, if initial aging is performed with a potential difference between the electrode 121 of the upper protective layer, which is less susceptible to kogation, and the counter electrode 129, as in the case of printing, the upper protective layer 124 is less susceptible to kogation and the ink ejection characteristics are less likely to change. Therefore, in this case, the initial aging takes a long time, which results in problems such as increased downtime and increased waste ink.

[0067] This embodiment provides a method for solving such a problem. To explain in detail, when the potential difference during printing is ΔVp and the potential difference during aging is ΔVa, the conditions ΔVp≧0 and ΔVa<ΔVp are satisfied as shown in Fig. 14(b) and Fig. 14(c). Here, ΔVp=potential Vpc of the opposing electrode during printing-potential Vph of the upper protective layer electrode of the heater during printing, and ΔVa=potential Vac of the opposing electrode during aging-potential Vah of the upper protective layer electrode of the heater during aging. By adopting ΔVa (smaller than ΔVp) as the potential difference during aging, kogation is more likely to occur on the upper protective layer of the heater than when ΔVp is adopted (see Fig. 17).

[0068] According to the above method, during aging, the presence rate of negatively charged particles near the surface of the upper protective layer 124 of the heater is higher than during printing, so the upper protective layer 124 is more likely to burn. This makes it possible to reduce the number of times the heating resistor 126 is driven until the resistance value of the heating resistor 126 stabilizes, and shortens the aging period (the time until the ejection speed stabilizes). In this regard, FIG. 14(c) shows the case where ΔVa<0. In this way, by setting ΔVa<0 during aging, negatively charged particles are attracted to the surface of the upper protective layer 124, making it more likely to burn, and therefore the aging period can be further shortened.

[0069] Here, FIG. 16 is referred to. FIG. 16(a) is a diagram showing the initial change in the ejection speed when aging is performed by adopting the same potential difference ΔVp (ΔVp>0, specifically +0.5 to 2.5V) as during printing for the potential difference between the potential of the upper protective layer electrode of the heater and the potential of the counter electrode. Note that the initial change in the ejection speed here refers to a drop in the ejection speed of about 5 to 10% compared to before aging when the number of ejections during aging is about 1×10^7. In contrast, FIG. 16(b) is a diagram showing the change in the ejection speed when a potential difference ΔVa (ΔVa<ΔVp) smaller than the potential difference during printing is adopted for the potential difference between the potential of the upper protective layer electrode of the heater and the potential of the counter electrode during aging, and ΔVp is adopted during subsequent printing.

[0070] As shown in FIG. 16(a), if the same potential difference as during printing is used during aging, the heater does not burn quickly, so the number of ejections required until the ejection speed settles increases, and the aging period becomes longer. In contrast, as shown in FIG. 16(b), if a potential difference ΔVa (ΔVa<ΔVp) smaller than the potential difference during printing is used during aging, the initial ejection speed change can be performed quickly. Therefore, the number of ejections required until aging is completed can be reduced, the time until aging is completed can be shortened, the shortening of the life of the heating resistor 126 can be suppressed, and downtime and the amount of waste ink can be reduced. In addition, since the potential difference is set to ΔVp during printing after aging, the heater returns to a state that is less likely to burn when the printing period is long, and image deterioration can be suppressed without changing the ejection speed. Incidentally, the initial change in ejection speed at the potential difference ΔVa during aging refers to, for example, a steep drop in the ejection speed of about 5 to 10% from before aging when the number of aging ejections is about 5×10^6.

[0071] In this embodiment, the potential difference ΔV between the potential of the upper protective layer electrode of the heater and the potential of the counter electrode may be changed by changing either the potential of the upper protective layer electrode of the heater or the potential of the counter electrode, or by changing both of them. However, in the case where the potential difference ΔV can be changed by changing the potential of either one of the electrodes, the circuit configuration can be simplified, which is advantageous in terms of cost.

[0072] Also, the opportunity to age the upper protective layer of the heater includes a case where the recording device is in a brand new state with no discharge history, and a case where kogation has accumulated on the upper protective layer after the recording device has been used and kogation removal has been performed. Here, kogation removal is performed by applying a voltage between the electrode 121 of the upper protective layer and the counter electrode 129 via a liquid, causing an electrochemical reaction between the electrode 121 and the liquid, and dissolving the material that constitutes the upper protective layer into the liquid, thereby removing the kogation that has adhered to the upper protective layer. For example, when iridium is used for the upper protective layer, kogation removal can be performed by setting the potential of the upper protective layer to +2.5V or more higher than the potential of the counter electrode.

[0073] Furthermore, this also includes a case where the burnt state of the upper layer of the heater of the target nozzle is relatively less than the burnt state of the nozzles around the target nozzle. Note that the state of the recording device is different between a new product with no ejection history and a state after kogation removal has been performed during use, and therefore the amount of kogation on the upper protective layer of the heater often differs between these states. Therefore, a different ΔVa can be used when there is no ejection history and when kogation removal has been performed.

[0074] In addition, the amount of kogation during aging is preferably controlled using the number of ejections (also called dot count).

[0075] As a method for determining whether aging has been properly performed, for example, an image of uniform density is printed as a test and the density of the output is checked. This density checking means may be a density sensor provided in the recording device body, or a visual check.

[0076] <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. 20. Fig. 20 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.

[0077] <Process flow> Reference is now made to FIG. 21. FIG. 21 is a flow chart showing an example of the flow of a series of processes in this embodiment. In this series of processes, aging is performed on a liquid ejection head of a brand new recording device that has no ejection history, and printing is performed after the aging. Thereafter, when the number of ejections reaches a predetermined threshold, kogation removal is performed on the upper protective layer of the heater, and then aging is performed again. Each step will be described in detail below.

[0078] When a brand new liquid ejection head with no ejection history is attached to the recording apparatus body, in step S2101, the CPU of the recording apparatus 1000 sets the potential of the upper protective layer electrode of the heater to Vah and the potential of the counter electrode to Vac so as to achieve an optimal potential difference ΔVa for initial aging. Note that hereinafter, "Step S~" will be abbreviated to "S~".

[0079] In S2102, the CPU of the recording device 1000 performs aging.

[0080] In S2103, the CPU of the recording apparatus 1000 judges whether kogation has been properly applied to the upper protective layer of the heater. If the judgment result in this step is true, the process proceeds to S2104, whereas if the judgment result is false, the process returns to S2101. Note that in this step, as described above, the measured density is obtained by checking the density of the output obtained by test printing, and a judgment is made as to whether the measured density is within a predetermined range. In other words, if the measured density is within the predetermined range, it is considered that kogation has been properly applied.

[0081] In S2104, the CPU of the printing apparatus 1000 sets the potential of the upper protective layer electrode of the heater to Vph and the potential of the counter electrode to Vpc so that the potential difference is ΔVp suitable for printing.

[0082] In S2105, the CPU of the recording device 1000 performs print processing.

[0083] In S2106, the CPU of the recording apparatus 1000 judges whether the number of ejections is greater than a predetermined threshold (Nd). If the judgment result in this step is true, it is assumed that the amount of kogation on the upper protective layer of the heater has exceeded the allowable value, and the process proceeds to S2107. On the other hand, if the judgment result in this step is false, the process returns to S2105, and printing continues with the same settings.

[0084] In S2107, the CPU of the recording apparatus 1000 performs kogation removal.

[0085] After the kogation removal in S2107, the kogation on the upper protective layer of the heater is removed and there is almost no kogation, so the process proceeds to S2101 and S2102. That is, aging is carried out again. As described above, the value of the potential difference ΔVa during the second and subsequent aging processes may be different from that during the initial aging process for a new head with no ejection history.

[0086] It is necessary to pay attention to how the potential difference ΔVa during aging is changed to the potential difference ΔVp during printing. To explain in more detail, a sudden change in potential can cause a sudden change in the way the kogation of the upper protective layer of the heater occurs (for example, the kogation that occurred during aging can suddenly come off), which can change the ejection characteristics and cause problems such as image unevenness. Therefore, in order to prevent such problems, it is preferable to gradually bring ΔVa closer to ΔVp as the number of ejections increases during aging.

[0087] In order to further accelerate the change in ejection due to aging, a pulse with a voltage value larger than that of a normal voltage pulse during recording, etc. may be applied to the extent that the heater material is not damaged. Also, during aging, a pulse may be applied for a longer period of time than the normal pulse application period.

[0088] In addition, the liquid ejection head in this embodiment is a head that prints four colors of ink, CMYK (cyan, magenta, yellow, black), but aging is not required for colors that do not burn easily. Also, since there are colors that burn easily and colors that do not burn easily, the values ​​of ΔVa and ΔVp for each ink color are not uniform, and each ink color may have a different combination of values.

[0089] [Second embodiment] <Structure of heat application part in recording element substrate> The second embodiment is an embodiment for dealing with a case where the amount of kogation on the upper protective layer of the heater has a minimum value in the relationship to 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, as shown in Fig. 18. In the following explanation, the differences from the first embodiment will be mainly explained, and explanations of the same contents as in the first embodiment will be omitted as appropriate.

[0090] As described in the first embodiment, since most of the particles that cause kogation are negatively charged, the more negative the potential of the upper protective layer electrode of the heater, the less likely the negatively charged particles 141 are to approach the periphery of the heater and burn. Nevertheless, as shown in Fig. 18, one of the reasons why the amount of kogation on the upper protective layer of the heater has an extreme value is thought to be the accumulation of kogation on the counter electrode side.

[0091] In other words, the more negative the potential of the upper protective layer electrode of the heater is made, the more positive the potential of the opposing electrode becomes, so that the negatively charged particles 141 tend to approach the opposing electrode and tend to burn on the opposing electrode. As a result, the opposing electrode and the ink are insulated due to the deposits on the opposing electrode, the electric field gradually approaches zero, and the potential control becomes ineffective, so that the amount of kogation increases when ΔV is increased. For these reasons, it is believed that the amount of kogation has a minimum value, as shown in Figure 18.

[0092] In view of the above, the present embodiment is characterized in that the potential difference is ΔVp≧0, ΔVa>ΔVp.

[0093] More specifically, it is preferable that the potential difference ΔVp between the potential of the opposing electrode and the potential of the upper protective layer electrode of the heater during printing is a value that causes little kogation to accumulate even after long-term use, that is, a value at which the amount of kogation is minimized.On the other hand, it is preferable that the potential difference ΔVa between the potential of the opposing electrode and the potential of the upper protective layer electrode of the heater during aging is a value larger than the value of ΔVp at which the amount of kogation is minimized (ΔVa>ΔVp).

[0094] [Third embodiment] <Structure of heat application part in recording element substrate> The third embodiment is an embodiment for dealing with a case where the amount of kogation in the upper protective layer of the heater increases monotonically in relation to 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, as shown in Fig. 19. In the following explanation, the differences from the first embodiment will be mainly explained, and explanations of the same contents as in the first embodiment will be omitted as appropriate.

[0095] As described in the first embodiment, most particles that cause kogation are negatively charged, but in rare cases, they may be positively charged. In this case, as shown in Figures 15(a) and 15(b), the more negative the potential of the upper protective layer electrode of the heater, the more likely the positively charged particles are to approach the upper protective layer of the heater and burn on the upper protective layer of the heater.

[0096] In view of the above, the present embodiment is characterized in that the potential difference is ΔVp<0 and ΔVa>ΔVp.

[0097] More specifically, the potential difference ΔVp between the potential of the opposing electrode and the potential of the upper protective layer electrode of the heater during printing is preferably set as small as possible, i.e., ΔVp<0, so that the accumulation of kogation is reduced when the electrode is used for a long period of time. On the other hand, the potential difference ΔVa between the potential of the opposing electrode and the potential of the upper protective layer electrode of the heater during aging is preferably set to a value larger than the value of ΔVp at which kogation is unlikely to occur (preferably ΔVa>ΔVp). Note that, although FIG. 15(c) shows the case where ΔVa>0, ΔVa≦0 may also be satisfied.

[0098] [Other embodiments] In the above embodiment, the potential difference between the upper protective layer electrode of the heater and the potential of the opposing electrode is set to ΔVa during aging and ΔVp during printing, but the potential of each electrode may be set arbitrarily. That is, the potential of the upper protective layer electrode of the heater may be fixed (Vah=Vph). Or, the potential of the opposing electrode may be fixed (Vac=Vpc).

[0099] Moreover, all of the values ​​of Vac, Vah, Vpc, and Vph may be 0 or greater.

[0100] 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 third embodiments may be used in appropriate combination. [Explanation of symbols]

[0101] 3 Liquid ejection head 10. Recording element board 121 Electrode 129 Counter Electrode

Claims

1. a liquid ejection head having a heat generating element for generating energy required for ejecting liquid, a first protective layer for blocking contact between the heat generating 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 aging and during printing by changing a potential of at least one of the first electrode and the second electrode; A liquid ejection device having The potential of the first electrode during aging is Vah, the potential of the second electrode is Vac, and the potential difference between the potential Vah of the first electrode and the potential Vac of the second electrode is ΔVa (=Vac−Vah), When the potential of the first electrode during printing is Vph, the potential of the second electrode is Vpc, and the potential difference between the potential Vph of the first electrode and the potential Vpc of the second electrode is ΔVp (=Vpc−Vph), Satisfying formula (1), A liquid ejection device comprising: ΔVa≠ΔVp...Formula (1)

2. 2. The liquid ejection device according to claim 1, wherein the following formula (2) is satisfied: ΔVa<ΔVp...Formula (2)

3. 3. The liquid ejection device according to claim 1, wherein the following formula (3) is satisfied: ΔVp≧0...Formula (3)

4. 2. The liquid ejection device according to claim 1, wherein the following formula (4) is satisfied: ΔVa>ΔVp...Formula (4)

5. 5. The liquid ejection device according to claim 4, wherein the following formula (5) is satisfied: ΔVp≧0...Formula (5)

6. 5. The liquid ejection device according to claim 4, wherein the following formula (6) is satisfied: ΔVp<0 Equation (6)

7. 7. The liquid ejection device according to claim 6, wherein the following formula (7) is satisfied: ΔVa≦0...Formula (7)

8. 7. The liquid ejection device according to claim 6, wherein the following formula (8) is satisfied: ΔVa>0...Formula (8)

9. 9. The liquid ejection device according to claim 1, wherein the following formula (9) is satisfied: Vah=Vph...Formula (9)

10. 8. The liquid ejection device according to claim 1, wherein the following formula (10) is satisfied: Vac=Vpc...Formula (10)

11. the second protective layer is made of a material that contains a metal that dissolves by an electrochemical reaction and does not form an oxide film that prevents dissolution by heating; 11. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

12. 12. The liquid ejection device according to claim 1, wherein the following formulas (11) and (12) are satisfied: |ΔVa|≦2.5V...Formula (11) |ΔVp|≦2.5 V ... Equation (12)

13. All of the values ​​of Vac, Vah, Vpc, and Vph are equal to or greater than 0; 13. The liquid ejection device according to claim 1, wherein the liquid ejection device is a liquid ejection device.

14. The aging is performed after kogation removal is performed.

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

15. The method further includes a determination unit that determines whether or not to perform kogation removal after printing based on the number of ejections.

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

16. a liquid ejection head having a heat generating element for generating energy required for ejecting liquid, a first protective layer for blocking contact between the heat generating 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 aging and 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 potential of the first electrode during aging is Vah, the potential of the second electrode is Vac, and the potential difference between the potential Vah of the first electrode and the potential Vac of the second electrode is ΔVa (=Vac−Vah), When the potential of the first electrode during printing is Vph, the potential of the second electrode is Vpc, and the potential difference between the potential Vph of the first electrode and the potential Vpc of the second electrode is ΔVp (=Vpc−Vph), Satisfying formula (13), A control method comprising: ΔVa≠ΔVp...Formula (13)

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