Liquid ejection device and control method

Abstract

To provide a technique for obtaining stable ejection characteristics. A different potential difference ΔVa is used as the potential difference between an electrode 121 and a counter electrode 129 during liquid ejection between a brand new liquid ejection head and a liquid ejection head that has undergone a kogation removal operation.

Description

[Technical Field]

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

[0002] In a recording device that ejects liquid such as ink from a liquid ejection head, one method of generating energy for ejecting the liquid is to heat the ink with a heating resistor (hereinafter also referred to as "heater") to cause it to foam and be ejected. In such a method of ejecting ink by heating with a heater, the ink may be scorched on the surface of the heater due to the heater heating the ink, which may change the ink ejection speed.

[0003] The inks used in such recording devices are often dye-based or pigment-based, and many of these colorants are insoluble or poorly soluble in water. These insoluble or poorly soluble colorants are thought to be one of the causes of scorching.

[0004] When there is almost no scorching on the heater surface, if ink that burns easily as described above is ejected, scorching will occur on the heater surface where there was no scorching. As a result, the way heat is transferred to the ink changes, and it is known that the ejection characteristics change (the ejection speed decreases).

[0005] Patent Document 1 proposes a fluid ejection device in which first and second electrodes are arranged to generate an electric field in the liquid chamber of the liquid ejection head. By generating an electric field in the liquid chamber, charged particles that cause kogation are separated from the heater surface, suppressing the occurrence of kogation during ejection from the liquid ejection head substrate and improving the durability of the liquid ejection head substrate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-38127 Summary of the Invention [Problem to be solved by the invention]

[0007] Meanwhile, a known method for removing kogation from a heater involves an electrochemical reaction with ink to dissolve the heater surface and remove the kogation (hereinafter referred to as a kogation removal process). However, for example, the surface condition of the heater when the liquid ejection head is first used is not the same as that of the heater surface after the kogation removal process. Therefore, as in Patent Document 1, even if ejection is performed under the same conditions to suppress the occurrence of kogation regardless of the state of the liquid ejection head, the ejection characteristics may still differ.

[0008] Therefore, the present invention provides a technique that can obtain stable ejection characteristics regardless of the state of the liquid ejection head. [Means for solving the problem]

[0009] Therefore, the liquid ejection device of the present invention is a liquid ejection device that can be equipped with an ejection means having a heating resistor that generates energy for ejecting liquid by generating heat when electricity is applied, a first electrode provided in a protective part that covers and protects the heating resistor, and a second electrode that can be electrically connected to the first electrode via a liquid, and is equipped with a control means that controls the equipped ejection means, and the control means is capable of performing a kogane removal process that applies a voltage between the first electrode and the second electrode to dissolve the surface of the first electrode into the liquid and remove accumulated kogane, and is characterized in that the potential difference applied between the first electrode and the second electrode during the liquid ejection operation of the ejection means is different between when the ejection means has performed the kogane removal process and when the ejection means has not performed the kogane removal process. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a technique that can obtain stable ejection characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a liquid ejection device. [Figure 2] FIG. 1 is a block diagram showing the configuration of a recording device. [Figure 3] FIG. 2 is a schematic diagram showing a first circulation path as one form of a circulation path. [Figure 4] FIG. 4 is a schematic diagram showing a second circulation path. [Figure 5] FIG. [Figure 6] FIG. 2 is an exploded perspective view of each part or unit that constitutes the recording medium. [Figure 7] 3 is a diagram showing the front and back surfaces of the first to third flow path members. FIG. [Figure 8] 10 is a perspective view of the first flow path member as seen from the surface on which the discharge module is mounted. FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] FIG. 2 is a perspective view showing a discharge module. [Figure 11] FIG. 2 is a plan view of a recording element substrate. [Figure 12] FIG. 2 is a perspective view showing a cross section of a recording element substrate and a cover member. [Figure 13] FIG. 4 is a partially enlarged plan view showing an adjacent portion of the recording element substrate. [Figure 14] FIG. 3 is a diagram showing the vicinity of a heat application portion on a recording element substrate. [Figure 15] 1A and 1B are schematic diagrams illustrating kogation suppression treatment for negatively charged particles. [Figure 16] 10 is a graph showing the relationship between the discharge speed and the potential difference. [Figure 17] 1A and 1B are schematic diagrams illustrating kogation suppression treatment for positively charged particles. DETAILED DESCRIPTION OF THE INVENTION

[0012] A first embodiment of the present invention will be described below with reference to the drawings.

[0013] FIG. 1 is a diagram showing a schematic configuration of a liquid ejection apparatus (hereinafter also referred to as a recording apparatus) 1000 according to this embodiment. The recording apparatus 1000 is a line-type recording apparatus having 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. The recording apparatus 1000 is a line-type recording apparatus that performs continuous recording in one pass while continuously or intermittently conveying multiple recording media 2. The recording media 2 are not limited to cut paper, but may also be continuous roll paper. The liquid ejection head 3 is capable of full-color printing using CMYK (cyan, magenta, yellow, and black) liquid inks. Each liquid ejection head 3 may correspond to one color, or may correspond to multiple colors. The liquid ejection head 3 is replaceably attached to the recording apparatus 1000. As described below, the liquid ejection head 3 is fluidly connected to a liquid supply unit that constitutes a supply path for supplying ink to the liquid ejection head, an ink cartridge 1006 serving as a main tank, and a buffer tank 1003 (see FIG. 3). In addition, an electrical control unit that transmits power and ejection control signals to the liquid ejection head 3 is electrically connected to the liquid ejection head 3. The liquid paths and electrical signal paths within the liquid ejection head 3 will be described later. The recording apparatus 1000 circulates ink through the liquid ejection head 3.

[0014] 2 is a block diagram showing the configuration of a recording apparatus 1000. The recording apparatus 1000 includes a control unit 30 having a CPU 30a such as a microprocessor and a RAM 30b that is used as a work area for the CPU 30a and stores various data such as recording data and registration adjustment values. The control unit 30 includes a ROM 30c that stores the control program for the CPU 30a and various data. The recording apparatus 1100 also includes an interface 31, an operation panel 32, and drivers 35 and 36. The driver 35 drives and controls a motor 34 for driving the transport rollers, circulation pumps 1001, 1002, and 1004 of the ink supply flow path, and a refill pump 1005, while the driver 36 drives the liquid ejection head 3.

[0015] The recording data received by the recording device 1000 is stored in RAM 30b of the control unit 30. In accordance with the recording data stored in RAM 30b, the control unit 30 outputs ON / OFF signals to the driver 35 for driving the motor 34 and outputs ejection signals and the like to the driver 36, thereby forming an image on the recording medium. The control unit 30 also outputs a signal to the driver 35 for driving the circulation pump 1002 in accordance with a control sequence described below, thereby controlling the circulation pump 1002.

[0016] Fig. 3 is a schematic diagram showing a first circulation path as one form of circulation path applied to the recording apparatus according to this embodiment. As shown in Fig. 3, the liquid ejection head 3 is fluidly connected to two first circulation pumps 1001 (high pressure side) and 1002 (low pressure side), a buffer tank 1003, etc. Note that, for the sake of simplicity, Fig. 3 shows only the path through which one color of ink out of CMYK ink flows, but in reality, circulation paths for all four colors are provided in the liquid ejection head 3 and the recording apparatus main body.

[0017] The recording device 1000 is mountable with an ink cartridge 1006 that contains ink, and has a buffer tank 1003 that serves as a sub-tank connected to the ink cartridge 1006. The buffer tank 1003 has an air vent (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 replenishment pump 1005. When ink is consumed in the liquid ejection head 3, the replenishment pump 1005 transfers the consumed ink from the ink cartridge 1006 to the buffer tank 1003. Ink is consumed in 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.

[0018] The two first circulation pumps 1001 and 1002 draw ink from the liquid connection 111 of the liquid ejection head 3 and send it to the buffer tank 1003. The first circulation pumps 1001 and 1002 are preferably positive displacement pumps with a constant liquid delivery capacity. Specific examples include tube pumps, gear pumps, diaphragm pumps, and syringe pumps. However, pumps that ensure a constant flow rate by arranging a general constant flow valve or relief valve at the pump outlet can also be used. When the liquid ejection head 3 is driven, the first circulation pump (high-pressure side) 1001 and the first circulation pump (low-pressure side) 1002 cause a certain amount of ink to flow through the common supply flow path 211 and the common recovery flow path 212, respectively. This flow rate is preferably set to a level at which the temperature difference between the recording element substrates 10 in the liquid ejection head 3 does not affect the image quality of the recording. However, if the flow rate is set too high, the negative pressure difference between the recording element substrates 10 will become too large due to the influence of pressure loss in the flow paths within the liquid ejection unit 300, resulting in uneven density in 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.

[0019] The negative pressure control unit 230 is provided in the path connecting the second circulation pump 1004 and the liquid ejection unit 300. Therefore, the negative pressure control unit 230 has the function of maintaining 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 in the circulation system fluctuates due to differences in printing duties. The two pressure adjustment mechanisms constituting the negative pressure control unit 230 may be any mechanism capable of controlling the pressure downstream of the negative pressure control unit 230 within a certain range centered on a desired set pressure. As an example, a mechanism similar to a so-called "pressure reducing regulator" may be employed. 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 using the second circulation pump 1004, as shown in FIG. 3 . This configuration suppresses the effect of head pressure on the liquid ejection head 3 in the buffer tank 1003, thereby increasing the flexibility of the layout of the buffer tank 1003 in the recording apparatus 1000. 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 ink circulation flow rate used when driving the liquid ejection head 3, such as a turbo pump or a positive displacement pump. 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.

[0020] 3, the negative pressure control unit 230 has 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. 3) is connected to a common supply flow path 211 in the liquid ejection unit 300 via the liquid supply unit 220. Furthermore, 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.

[0021] 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 214b that communicate with each recording element substrate 10. Because the individual supply flow paths 213a and individual recovery flow paths 214b communicate with the common supply flow path 211 and the common recovery flow path 212, a flow (arrow in FIG. 3) occurs in which a portion of the ink flows from the common supply flow path 211 through the internal flow paths 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.

[0022] In this way, in the liquid ejection unit 300, ink flows through the common supply flow path 211 and the common recovery flow path 212, while a portion of the ink flows through each recording element substrate 10. This allows heat generated in each recording element substrate 10 to be discharged to the outside of the recording element substrate 10 via the flow through the common supply flow path 211 and the common recovery flow path 212. Furthermore, with this configuration, while recording is being performed using the liquid ejection head 3, ink can also flow through ejection ports and pressure chambers that are not performing recording, thereby suppressing thickening of the ink in those areas. Furthermore, thickened ink and foreign matter in the ink can be discharged to the common recovery flow path 212. This allows the liquid ejection head 3 of this embodiment to perform high-speed, high-quality recording.

[0023] 4 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 apparatus 1000 according to this embodiment. The main differences from the first circulation path are as follows.

[0024] 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 3, and the negative pressure control unit 230 is disposed downstream of the liquid ejection head 3.

[0025] The negative pressure control unit 230 in the second circulation path operates to keep pressure fluctuations upstream of itself (i.e., the liquid ejection unit 300 side) within a certain range, even if fluctuations in flow rate occur due to changes in the printing duty when printing is performed by the liquid ejection head 3. The pressure fluctuations are kept within a certain range, for example, centered around a preset pressure. As shown in FIG. 4, it is preferable to use the second circulation pump 1004 to pressurize the downstream side of the negative pressure control unit 230 via the liquid supply unit 220. This reduces the effect of the head pressure of the buffer tank 1003 on the liquid ejection head 3, thereby increasing the flexibility in layout of the buffer tank 1003 in the printing apparatus 1000. Note that instead of the second circulation pump 1004, for example, a head tank arranged with a predetermined head difference relative to the negative pressure control unit 230 may be used.

[0026] 4 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. 4) is connected to the 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. 4) is connected to the common recovery flow path 212 via the liquid supply unit 220.

[0027] 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 occurs from the common supply flow path 211 through the individual supply flow paths 213 and the internal flow paths of each recording element substrate 10 to the common recovery flow path 212 (arrows in FIG. 4). In this way, the second circulation path achieves an ink flow state similar to that of the first circulation path within the liquid ejection unit 300, but has two advantages different from the first circulation path.

[0028] 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 less concern about dust or foreign matter generated by the negative pressure control unit 230 flowing into the liquid ejection head 3. 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 lower than in the case of the first circulation path. The reason for this is as follows. The sum of the flow rates 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 within 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 of the 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 (see Figure 3), 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.

[0029] On the other hand, in the case of the second circulation path (see FIG. 4), the amount of liquid required to be supplied to the liquid ejection head 3 during standby for printing is flow rate A. The amount of liquid required to be supplied to the liquid ejection head 3 during full ejection is flow rate F. Therefore, in the case of the second circulation path, the sum 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 required supply flow rate, is the larger of A or F. Therefore, as long as the same liquid ejection unit 300 is used, the maximum required supply flow rate (A or F) in the second circulation path is always smaller than the maximum required supply flow rate (A + F) in the first circulation path. Therefore, the second circulation path offers greater flexibility in the type of circulation pump that can be applied. This allows, for example, the use of a simple, low-cost circulation pump and the reduction of the load on a cooler (not shown) installed in the main body path, resulting in the advantage of reducing the cost of the recording apparatus main body. This advantage is greater for line heads with a relatively large value of A or F, and is more beneficial for line heads with a longer longitudinal length.

[0030] However, the first circulation path has some advantages over the second circulation path. Specifically, in the second circulation path, the flow rate through the liquid ejection unit 300 is at its maximum during standby for printing. Therefore, the lower the printing duty, the higher the negative pressure applied to each ejection port. Therefore, particularly when the flow path widths (lengths perpendicular to the ink flow direction) of the common supply flow path 211 and the common recovery flow path 212 are reduced and the head width (lengths in the shorter direction of the liquid ejection head) is reduced, high negative pressures are applied to the ejection ports in low-duty images where unevenness is easily visible. The application of such high negative pressures may increase the impact of satellite droplets. On the other hand, in the case of the first circulation path, high negative pressures are applied to the ejection ports during high-duty image formation. Therefore, even if satellite droplets are generated, they are less visible, and the impact on the printed image is minimal. A preferable selection can be made between the two circulation paths in light of the specifications of the liquid ejection head and the recording apparatus main body (ejection flow rate F, minimum circulation flow rate A, and flow path resistance within the head).

[0031] Figures 5(a) and 5(b) are perspective views of the liquid ejection head 3. Below, in Figures 5 to 13, a configuration in which one liquid ejection head ejects four colors of ink will be described. As shown in Figure 5(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 electrical 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, and 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.

[0032] By consolidating the wiring using the electrical circuit within the electrical wiring board 90, the number of signal input terminals 91 and power supply terminals 92 can be reduced compared to the number of recording element substrates 10. This reduces the number of electrical connections that need to be removed when assembling the liquid ejection head 3 to the recording apparatus 1000 or when replacing the liquid ejection head 3. As shown in FIG. 5B, liquid connections 111 provided at both ends of the liquid ejection head 3 are connected to the liquid supply system of the recording apparatus 1000. This allows four colors of ink, CMYK, to be supplied from the supply system of the recording apparatus 1000 to the liquid ejection head 3, and the ink that has passed through the liquid ejection head 3 is collected back into the supply system of the recording apparatus 1000. In this way, each color of ink can circulate via the paths in the recording apparatus 1000 and the paths in the liquid ejection head 3.

[0033] FIG. 6 is an exploded perspective view of each component or unit that constitutes the liquid ejection head 3. A liquid ejection unit 300, a liquid supply unit 220, and an electric wiring board 90 are attached to a housing 80. A liquid connection part 111 (see FIGS. 3 and 4) is provided in the liquid supply unit 220, and filters 221 (see FIG. 4) for each color are provided inside the liquid supply unit 220 and communicate with the openings of the liquid connection part 111 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 that are arranged on the liquid supply unit 220 corresponding to each color.

[0034] The negative pressure control unit 230 is a unit consisting of pressure adjustment valves for each color. The negative pressure control unit 230 significantly attenuates changes in pressure loss within the supply system of the recording apparatus 1000 (the supply system upstream of the liquid ejection head 3) that occur due to fluctuations in the ink flow rate through the action of valves, spring members, and the like provided within each unit. Therefore, the negative pressure control unit 230 can stabilize negative pressure changes downstream of the pressure control unit (the liquid ejection unit 300 side) within a certain range. As shown in FIG. 3, each negative pressure control unit 230 for each color contains two pressure adjustment valves. These pressure adjustment valves are set to different control pressures, and their high-pressure sides communicate with the common supply flow path 211 in the liquid ejection unit 300, and their low-pressure sides communicate with the common recovery flow path 212 via the liquid supply unit 220.

[0035] The housing 80 is composed of a liquid ejection unit support portion 81 and an electric wiring board support portion 82. It supports the liquid ejection unit 300 and the electric wiring board 90 while ensuring the rigidity of the liquid ejection head 3. The electric wiring board support portion 82 supports the electric wiring board 90 and is fixed to the liquid ejection unit support portion 81 with screws. The liquid ejection unit support portion 81 corrects warping and deformation of the liquid ejection unit 300 and ensures the relative positional accuracy of the multiple recording element substrates 10, thereby suppressing streaks and unevenness in printed materials. Therefore, the liquid ejection unit support portion 81 preferably has sufficient rigidity and is preferably made of a metal material such as stainless steel or aluminum, or a ceramic such as alumina. The liquid ejection unit support portion 81 has openings 83 and 84 through which the joint rubber 100 is inserted. Ink supplied from the liquid supply unit 220 is guided via the joint rubber to the third flow path member 70 constituting the liquid ejection unit 300.

[0036] 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 recording medium side surface of the liquid ejection unit 300. Here, as shown in FIG. 6, the cover member 130 is a member having a frame-like surface with a long opening 131 provided therein, and the recording element substrate 10 and sealant 110 (see FIG. 10) included in the ejection module 200 are exposed through the opening 131. The frame portion around the opening 131 functions as an abutment surface for a cap member that caps the liquid ejection head 3 when the liquid ejection unit 300 is on standby for recording. For this reason, it is preferable to apply an adhesive, sealant, filler, or the like around the periphery of the opening 131 to fill in any irregularities or gaps on the ejection port surface of the liquid ejection unit 300, thereby forming a closed space when the liquid ejection unit 300 is capped.

[0037] Next, the configuration of the flow path member 210 included in the liquid ejection unit 300 will be described. As shown in Fig. 6, 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 prevents the flow path member 210 from warping or deforming.

[0038] 7(a) to 7(f) are diagrams showing the front and back surfaces of the first to third flow path members. FIG. 7(a) shows the surface of the first flow path member 50 on which the discharge module 200 is mounted, and FIG. 7(f) shows the surface of the third flow path member 70 that abuts against the liquid discharge unit support 81. The first flow path member 50 and the second flow path member 60 are joined so that the abutting surfaces of the respective flow path members, that is, the surface shown in FIG. 7(b), and the surface shown in FIG. 7(c), face each other. The second flow path member and the third flow path member are joined so that the abutting surfaces of the respective flow path members, that is, the surface shown in FIG. 7(d), and the surface shown in FIG. 7(e), 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 within the flow path member 210. The communication ports 72 of the third flow path member 70 communicate with each hole of the joint rubber 100, and are fluidly 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 are fluidly connected to one end of the individual flow path grooves 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 fluidly connected to a plurality of discharge modules 200 via the communication ports 51. The individual flow path grooves 52 make it possible to aggregate the flow paths toward the center of the flow path member.

[0039] 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 a composite material (resin material) containing inorganic fillers such as silica particles and fibers. The flow path member 210 may be formed by laminating three flow path members and bonding them together, or by welding when a resin composite resin material is selected as the material.

[0040] 8 is a partially enlarged perspective view of the flow paths in a flow path member 210 formed by joining the first to third flow path members, viewed from the side of the first flow path member 50 on which the ejection module 200 is mounted. The connection relationship of each flow path in the flow path member 210 will be described below. 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 individual flow path grooves 52 are connected to the common supply flow path 211 for each color via communication ports 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 for each color via the communication ports 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 in the center of the flow path member 210. Furthermore, ink can be recovered from the recording element substrate 10 via the individual recovery flow paths 214 to each common recovery flow path 212.

[0041] 9 is a cross-sectional view taken along line IX-IX in FIG. 8. As shown in this figure, each of the individual recovery channels (214a, 214c) communicates with the ejection module 200 via the communication port 51. While only the individual recovery channels (214a, 214c) are shown in FIG. 9, in another cross-section, the individual supply channels 213 communicate with the ejection module 200 as shown in FIG. 8. A channel is formed in the support member 33 and the recording element substrate 10 included in each ejection module 200 to supply ink from the first channel member 50 to the recording elements 15 (see FIG. 11(b)) provided on the recording element substrate 10. A channel is also formed in the support member 33 and the recording element substrate 10 to recover (return) some or all of the ink supplied to the recording elements 15 to the first channel member 50. Here, the common supply flow path 211 for 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 differential pressure (pressure difference) between the common supply flow path 211 and the common recovery flow path 212. For this reason, within the liquid ejection head in which the flow paths are connected as shown in Figures 8 and 9, a flow is generated for each color that flows in the order of the common supply flow path 211 -> individual supply flow path 213a -> recording element substrate 10 -> individual recovery flow path 214b -> common recovery flow path 212.

[0042] FIG. 10(a) is a perspective view showing one ejection module 200, and FIG. 10(b) is an exploded view of the ejection module 200. The manufacturing method of the ejection module 200 involves first adhering the recording element substrate 10 and the flexible wiring substrate 40 to a support member 33, which is provided with a liquid communication port 37. Then, the terminals 16 on the recording element substrate 10 are electrically connected to the terminals 41 on the flexible wiring substrate 40 by wire bonding, and then the wire-bonded portion (electrical connection portion) is covered and sealed with a sealant 110. The terminals 42 on the flexible wiring substrate 40 on the side opposite the recording element substrate 10 are electrically connected to the connection terminals 93 (see FIG. 6) on the electrical wiring substrate 90. The support member 33 is a support that supports the recording element substrate 10 and also a flow path member that fluidly connects the recording element substrate 10 and the flow path member 210. Therefore, it is preferable that the support member 33 has high flatness and can be bonded to the recording element substrate with sufficiently high reliability. Examples of the material for the support member 33 include alumina and resin.

[0043] Fig. 11(a) is a plan view of the surface of the recording element substrate 10 on which the ejection ports 13 are formed, Fig. 11(b) is an enlarged view of the portion indicated by Xb in Fig. 11(a), and Fig. 11(c) is a plan view of the back surface of Fig. 10(a). Fig. 12 is a perspective view showing a cross section of the recording element substrate 10 and the cover member 20 taken along the cross-sectional line XII-XII shown in Fig. 11(a). The configuration of the recording element substrate 10 will be described below.

[0044] 11(a), four ejection port arrays corresponding to the respective ink colors are formed in the ejection port forming member 12 of the recording element substrate 10. Note that 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."

[0045] As shown in FIG. 11(b), a recording element 15, which is a heating element for causing bubbles in the ink using thermal energy, is disposed at a position corresponding to each ejection port 13. A partition 22 defines a pressure chamber 23, inside which the recording element 15 is disposed. The recording element 15 is electrically connected to the terminal 16 shown in FIG. 11(a) by electrical wiring (not shown) provided on the recording element substrate 10. The recording element 15 generates heat and boils the ink based on a pulse signal input from the control circuit of the recording device 1000 via the electrical wiring substrate 90 (FIG. 5) and the flexible wiring substrate 40 (see FIG. 10(b)). The bubbling force caused by this boiling causes the ink to be ejected from the ejection port 13. As shown in FIG. 12(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 that extend 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 port 17a and the recovery port 17b, respectively.

[0046] As shown in FIGS. 11(b) and 12, a sheet-like lid member 20 is laminated on the back surface of the recording element substrate 10 opposite the surface on which the ejection ports 13 are formed. The lid member 20 is provided with a plurality of openings 21 that communicate with the liquid supply channels 18 and liquid recovery channels 19, which will be described later. Three openings 21 are provided in the lid member 20 for each liquid supply channel 18, and two openings 21 are provided in the lid member 20 for each liquid recovery channel 19. As shown in FIG. 11(c), each opening 21 in the lid member 20 communicates with a plurality of communication ports 51 shown in FIG. 8 and other figures. As shown in FIG. 12, the lid member 20 functions as a lid that forms part of the walls of the liquid supply channels 18 and liquid recovery channels 19 formed in the substrate 11 of the recording element substrate 10. The lid member 20 is preferably made of a material that has sufficient corrosion resistance to ink, and from the standpoint of preventing color mixing, high precision is required for the shape and position of the openings 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 form the openings 21 by a photolithography process. In this way, the lid member changes the pitch of the flow paths by the openings 21, and in consideration of pressure loss, it is desirable that the lid member be thin and made of a film-like material.

[0047] Next, the flow of ink within the recording element substrate 10 will be described. As shown in Figure 12, the recording element substrate 10 is formed by laminating a substrate 11 made of Si and an ejection port forming member 12 made of photosensitive resin, and a lid member 20 is bonded to the back surface of the substrate 11. Recording elements 15 are formed on one surface of the substrate 11 (see Figure 11(b)), and grooves that form liquid supply paths 18 and liquid recovery paths 19 that extend along the ejection port array are formed on the back surface. The liquid supply paths 18 and liquid recovery paths 19 formed by the substrate 11 and the lid 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.

[0048] When ink is ejected from the multiple ejection ports 13 of the liquid ejection head 3 to perform printing, the differential pressure causes the ink flow in the liquid supply path 18 provided in the substrate 11 to follow the flow indicated by arrow C in FIG. 12 at ejection ports that are not performing the ejection 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, which has increased in viscosity due to evaporation from the ejection ports 13 and the pressure chamber 23 that are not performing printing, as well as bubbles and foreign matter, to be recovered to the liquid recovery path 19. This flow also makes it possible to suppress the increase in viscosity of the ink in the ejection ports 13 and the pressure chamber 23. The ink recovered to the liquid recovery path 19 passes through the opening 21 of the cover member 20 and the liquid communication port 37 of the support member 33 (see FIG. 10(b)), and is then recovered to the communication port 51 in the flow path member 210, the individual recovery path 214, and the common recovery path 212 in that order. This ink is ultimately recovered to the supply path of the recording device 1000.

[0049] In other words, ink supplied from the recording apparatus main body to the liquid ejection head 3 flows, and is supplied and 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 this order, to the joint rubber 100, the communication port 72 and common flow path groove 71 provided in the third flow path member, the common flow path groove 62 and communication port 61 provided in the second flow path member, and the individual flow path grooves 52 and communication port 51 provided in the first flow path member. The ink is then supplied to the pressure chambers 23 via the liquid communication port 37 provided in the support member 33, the opening 21 provided in the cover member, and the liquid supply path 18 and supply port 17a provided in the substrate 11. Of the ink supplied to the pressure chambers 23, the ink that is not ejected from the ejection port 13 flows, in this order, through the recovery port 17b and liquid recovery path 19 provided in the substrate 11, the opening 21 provided in the cover member, and the liquid communication port 37 provided in the support member 33. The ink then flows sequentially through the communication ports 51 and individual flow channel grooves 52 provided in the first flow channel member, the communication ports 61 and common flow channel groove 62 provided in the second flow channel member, the common flow channel groove 71 and communication ports 72 provided in the third flow channel member 70, and the joint rubber 100. The ink then flows from the liquid connection portion 111 provided in the liquid supply unit to the outside of the liquid ejection head 3. In the configuration of the first circulation path shown in FIG. 3, the ink that flows in from the liquid connection portion 111 passes through the negative pressure control unit 230 and is then supplied to the joint rubber 100. In the configuration of the second circulation path shown in FIG. 3, the ink recovered 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] 3 and 4, not all of the ink that flows in from one end of the common supply flow path 211 of the liquid ejection unit 300 is supplied to the pressure chambers 23 via the individual supply flow paths 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 paths 213a. In this way, by providing a flow path that does not pass through the recording element substrate 10, it is possible to prevent backflow of the circulating flow of ink, even in the case of a recording element substrate 10 that has fine flow paths with high flow resistance. In this way, the liquid ejection head 3 can prevent the viscosity of the ink in the pressure chambers and in the vicinity of the ejection ports from increasing, thereby preventing deviations from the normal ejection direction and ejection failures, thereby enabling high-quality printing.

[0051] FIG. 13 is a partially enlarged plan view showing the adjacent portions of the recording element substrates 10 in two adjacent ejection modules. As shown in FIG. 11(a) and other figures, the recording element substrates 10 are generally parallelogram-shaped. As shown in FIG. 13, each of the ejection port arrays (14a-14d) in which the ejection ports 13 are arranged in each of the recording element substrates 10 is arranged at a fixed angle with respect to the recording medium transport direction. As a result, the ejection port arrays in the adjacent portions of the recording element substrates 10 overlap in the recording medium transport direction, with at least one ejection port overlapping with the recording medium transport direction. In FIG. 13, two ejection ports on line D overlap with each other. With this arrangement, even if the position of the recording element substrate 10 is slightly shifted from the predetermined position, drive control of the overlapping ejection ports can make black stripes and white gaps in the recorded image less noticeable. The configuration shown in FIG. 13 can also be achieved when multiple recording element substrates 10 are arranged in a straight line (inline) rather than in a staggered arrangement. This makes it possible to prevent black streaks and white spots at the joints between the recording element substrates 10 while suppressing an increase in the length of the liquid ejection head 3 in the recording medium transport direction. Note that although the main plane of the recording element substrate 10 is a parallelogram here, this is not limitative, and the configuration can be preferably applied even when a recording element substrate having a rectangular, trapezoidal, or other shape is used.

[0052] Fig. 14(a) is an enlarged plan view schematically showing the vicinity of the thermal application portion in the recording element substrate 10, and Fig. 14(b) is a cross-sectional view taken along the dashed dotted line XIVb-XIVb in Fig. 14(a). The structure of the thermal application portion in the recording element substrate according to this embodiment will be described below.

[0053] In the liquid ejection head 3, a recording substrate is formed by stacking multiple layers on a base (not shown) made of silicon. In this embodiment, a heat storage layer (not shown) made of a thermal oxide film, SiO film, SiN film, or the like is disposed on the base. A heating resistor 126 is disposed on the heat storage layer, and an electrode wiring layer (not shown in FIG. 4(b)) serving 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. The heating resistor 126 generates heat when current is applied via the electrode wiring layer (not shown). The heat generated by the heating resistor 126 causes film boiling in the ink in the bubble-forming chamber 14, causing ink to be ejected from the ejection orifice 13 and recording on a recording medium.

[0054] 14(b), the heating resistor 126 is covered with an insulating protective layer 127. The insulating protective layer 127 is an insulating layer that is also provided 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 an SiO film, a SiN film, or the like.

[0055] Three protective layers are disposed on the insulating protective layer 127 to prevent the insulating protective layer 127 from coming into contact with liquid. The three protective layers include a lower protective layer 125, an upper protective layer 124, and an adhesive protective layer 123, and protect the surface of the heating resistor 126 from chemical and physical shocks caused by heat generation by the heating resistor 126.

[0056] 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). Protective layers made of these materials are electrically conductive. An adhesive protective layer 122 is disposed on the adhesive protective layer 123 to provide liquid resistance and improve adhesion to the ejection port forming member 12. The adhesive protective layer 122 is formed of SiC. The adhesive protective layer 122 is not disposed in the position corresponding to the heating resistor 126, and the upper protective layer 124 is exposed within the pressure chamber 23, providing a protective portion for the heating resistor 126. This region is the thermally active portion during ejection. The upper protective layer 124 is formed of a material that contains a metal that dissolves due to an electrochemical reaction and does not form an oxide film that prevents dissolution when heated.

[0057] The upper protective layer 124 of the heat application part is in contact with the liquid, and when the liquid is discharged, the temperature of the liquid rises instantaneously, causing bubbles to form, which then disappear, resulting in cavitation. For this reason, in this embodiment, the upper protective layer 124, which is made of a highly corrosion-resistant and reliable iridium material, is arranged in a position that comes into contact with the liquid.

[0058] In this embodiment, an ink circulation configuration is adopted in which liquid is supplied from the supply port 17a and recovered to the recovery port 17b inside the pressure chamber 23. Therefore, during printing, the liquid flows over the heating resistor 126 in a direction from the supply port 17a on the upstream side to the recovery port 17b on the downstream side.

[0059] In this embodiment, in addition to the conventional kogation removal process, a kogation prevention process is performed to prevent kogation from accumulating on the upper protective layer 124 on the heating resistor 126. This kogation prevention process can be performed during liquid ejection.

[0060] Burning occurs when particles in the ink are heated by the heating resistor 126 during ejection, and as ejection is repeated, they accumulate on the surface of the upper protective layer 124, which acts as a heat source during ejection. The particles in the ink that cause burning are electrically charged, but the polarity of the charge differs depending on the type of particle. Generally, colorants such as pigments in ink particles tend to be negatively charged, while metal particles and the like tend to be positively charged. In other words, the polarity of the charge of the particles that cause burning differs depending on the type of particle contained in the ink.

[0061] The following description will be given taking as an example a recording apparatus 1000 that ejects ink containing a negatively charged pigment. To explain the kogation prevention process in this embodiment in detail, the portion of the upper protective layer 124 directly above the heating resistor 126 is used as a negative electrode 121, and a region of the upper protective layer 124 located away from the electrode 121 is used as a positive electrode 129. The electrodes 121 and 129 are configured to be electrically conductive via a liquid. As a result, particles such as negatively charged pigment are repelled by the negative electrode 121, reducing their presence rate near the electrode 121. As a result, kogation that accumulates on the electrode 121 during recording can be reduced. In this way, the presence rate of colorants, additives, and the like that cause kogation near the surface of the upper protective layer 124 above the heating resistor 126 can be reduced, thereby reducing the occurrence of kogation.

[0062] Fig. 15 is a schematic diagram showing a kogation suppression process when negatively charged particles are the dominant cause of kogation in the bubbling chamber 14. The mechanism of potential control used in this embodiment will be described below with reference to Fig. 15. As shown in Fig. 15(a), an electrode 121 and a counter electrode 129 are disposed in the bubbling chamber 14, and the bubbling chamber 14 is filled with liquid (ink). The liquid contains particles 141 such as a pigment that are negatively charged, and the particles 141 are dispersed approximately uniformly in the liquid.

[0063] FIG. 15(b) shows a state in which a voltage is applied so that the potential of the electrode 121 is relatively lower than the potential of the counter electrode 129. The potential difference between the electrode 121 and the counter electrode 129 is preferably in the range of 0.5 V to 2.5 V. At this time, an electric field 140 is formed between the electrode 121 and the counter electrode 129 through the liquid, but no current flows. Because the electrode 121 has a negative potential relative to the counter electrode 129, negatively charged particles 141 are repelled by the electrode 121, and the presence rate of particles 141 near the surface of the electrode 121 decreases. FIG. 15(c) is a schematic enlarged view of the vicinity of the electrode 121 shown in FIG. 15(b). The negatively charged particles 141 are subjected to a repulsive force 143 along the electric field lines of the electric field 140 formed in the liquid, and move away from the electrode 121.

[0064] When the potential of the counter electrode 129 is Vc and the potential of the electrode 121 on the heating resistor 126 (heater) side is Vh, the larger the potential difference ΔV (=Vc-Vh), the larger the repulsive force against the particles 141. In other words, the presence rate of negatively charged particles 141, which are the source of kogation, in the vicinity of the electrode 121 decreases as the potential difference ΔV increases, and the amount of kogation accumulation is suppressed.

[0065] FIG. 16 is a graph showing the relationship between the discharge speed and the potential difference ΔV. The discharge speed is inversely proportional to the amount of kogation that accumulates on the electrode 121, and the faster the discharge speed, the less kogation there is. From the graph in FIG. 16, the relationship between the potential difference ΔV and the discharge speed in this embodiment can be used to learn the relationship between the potential difference ΔV and the amount of kogation on the electrode 121. From FIG. 16, it can be seen that the larger the potential difference ΔV, the faster the discharge speed, and the larger the potential difference ΔV, the less kogation there is.

[0066] Up to this point, an example of ejecting ink containing negatively charged pigment has been described, but when ejecting ink containing positively charged particles, a voltage can be applied so that electrode 121 is the positive electrode and counter electrode 129 is the negative electrode. This reduces the presence rate of particles 141 that become the source of kogation near electrode 121, thereby suppressing the occurrence of kogation.

[0067] 17 is a schematic diagram showing a kogation suppression process when positively charged particles are the dominant cause of kogation in the bubbling chamber 14. As shown in FIG. 17(a), an electrode 121 and a counter electrode 129 are arranged in the bubbling chamber 14, and the bubbling chamber 14 is filled with a liquid (ink). The liquid contains positively charged particles 141 such as pigments, and when no voltage is applied between the electrodes, the particles 141 are dispersed approximately uniformly in the liquid.

[0068] FIG. 17(b) shows a state in which a voltage is applied so that the potential of the electrode 121 is relatively higher than the potential of the counter electrode 129. For example, the potential difference (absolute value) between the electrode 121 and the counter electrode 129 is in the range of 0.5 V to 2.5 V. At this time, an electric field 140 is formed between the electrode 121 and the counter electrode 129 via the liquid. Because the electrode 121 has a positive potential relative to the counter electrode 129, the positively charged particles 141 are repelled by the electrode 121, and the presence rate of the particles 141 near the surface of the electrode 121 decreases. Hereinafter, in this specification, the process of generating a potential difference between the electrode 121 and the counter electrode 129 and separating the charged particles from the electrode 121 side is referred to as the kogation suppression process. The mechanism of such a kogation suppression process is described, for example, in Patent Document 1.

[0069] Furthermore, by controlling the potential within the liquid ejection head, a kogation removal operation can be performed to remove kogation accumulated on the electrode 121. Here, the kogation removal operation is an operation of applying (giving) a voltage so that the electrode 121 acts as the anode and the counter electrode 129 acts as the cathode. This electrochemically dissolves the electrode 121 in the liquid, removing the kogation along with the protective film, thereby refreshing the surface of the electrode 121 to an almost brand new state. The timing of the kogation removal operation can be managed by, for example, counting the number of ejections since the previous kogation removal operation was performed.

[0070] However, the condition of the heater electrode in a brand new liquid ejection head before kogation removal is not exactly the same as that of the heater electrode in a liquid ejection head after kogation removal has been performed. Generally, the heater electrode surface is contaminated during the manufacturing process, so the heater electrode surface in a brand new state is dirty. On the other hand, the surface of the electrode 121 after kogation removal is not contaminated because the upper protective layer 124 is dissolved to perform the kogation removal operation, and is therefore less dirty than in a brand new state.

[0071] Therefore, in a brand new liquid ejection head in which the surface of the electrode 121 is dirty, the accumulation of burnt material during the ejection operation becomes unstable, and there is a risk that stable ejection characteristics cannot be obtained.

[0072] Therefore, in this embodiment, the potential difference ΔVa between the electrode 121 and the counter electrode 129 during ejection is made different between a brand new liquid ejection head and a liquid ejection head that has undergone a kogane removal operation. Specifically, a kogane suppression process is performed using a larger potential difference in the brand new liquid ejection head than in the liquid ejection head that has undergone a kogane removal operation. For example, the potential difference ΔVa1 between the electrode 121 and the counter electrode 129 in the liquid ejection head that has undergone a kogane removal operation is set to a value in the range of 0.5 V to 2.4 V. The potential difference ΔVa2 between the electrode 121 and the counter electrode 129 in the brand new liquid ejection head is set to a value in the range of 0.5 V to 2.5 V and smaller than the potential difference ΔVa1. This strengthens the repulsive force from the electrode 121 to the charged particles in the brand new liquid ejection head, thereby reducing the presence rate of charged particles near the electrode 121. As a result, it is possible to achieve ejection characteristics similar to those of a liquid ejection head that has undergone a kogane removal operation, even in the brand new liquid ejection head.

[0073] It is desirable to optimize the liquid ejection head potential control conditions for the electrode 121 and the counter electrode 129 depending on the ink. That is, since the polarity of charge differs depending on the type of particles in the ink, it is desirable to apply voltage with the polarity of the electrode 121 and the counter electrode 129 changed depending on the type of particle. Furthermore, even if the polarity is the same, the number of particles contained in the ink varies depending on the ink, so the potential difference may be adjusted depending on the number of particles (colorant concentration).

[0074] In this embodiment, the potential difference ΔVa between the potential of the electrode 121 and the potential of the counter electrode 129 may be changed by changing the potential of either the electrode 121 or the counter electrode 129, or by changing both. However, a configuration in which the potential difference ΔVa can be changed by changing the potential of one of the electrodes is advantageous in terms of cost because it simplifies the circuit configuration. Alternatively, one electrode may be fixed to GND, and the other electrode may be changed depending on the conditions.

[0075] In this way, the potential difference between the electrode 121 and the counter electrode 129 in the kogation suppression process during ejection is made different between a brand new liquid ejection head and a liquid ejection head that has undergone a kogation removal operation. This allows for stable ejection operations regardless of the state of the liquid ejection head.

[0076] (Second embodiment) The second embodiment of the present invention will be described below. Note that the basic configuration of this embodiment is the same as that of the first embodiment, so the following will describe the characteristic configuration.

[0077] In the first embodiment, the surface of the electrode 121 after the kogation removal operation is less contaminated than when it is new, and therefore less prone to kogation. However, there are cases where kogation remains on the surface of the electrode 121 after the kogation removal operation. In this case, there is a risk that the discharge characteristics may be more unstable than when it is new.

[0078] In consideration of this situation, in this embodiment, the liquid ejection head after the kogation removal operation is subjected to the kogation suppression process under the potential control condition of a larger potential difference ΔVa2 than that of a new liquid ejection head. This makes it possible to achieve ejection characteristics similar to those of a new liquid ejection head, even in a liquid ejection head with remaining kogation.

[0079] Whether or not kogation remains on the surface of the electrode 121 after the kogation removal operation can be confirmed by ejecting a small number of times so that the amount of kogation does not affect the ejection speed, and examining the ejection characteristics (e.g., ejection speed). Therefore, after examining the ejection characteristics by ejecting a small number of times so that the amount of kogation does not affect the ejection speed, ejection can be performed while performing kogation suppression processing under potential control according to the degree of kogation removal.

[0080] The disclosure of this embodiment includes the following configurations and methods.

[0081] (Configuration 1) a heating resistor that generates heat when energized to generate energy for ejecting liquid; a first electrode provided on a protection part that covers and protects the heating resistor; a second electrode that is electrically connected to the first electrode via a liquid; A liquid ejection device comprising a control means for controlling the attached ejection means, The control means By applying a voltage between the first electrode and the second electrode, a kogane removal process can be performed in which the surface of the first electrode is dissolved in a liquid to remove kogane that has accumulated on the surface, A liquid ejection device characterized in that the potential difference applied between the first electrode and the second electrode during the liquid ejection operation of the ejection means is different depending on whether the ejection means has performed the kogane removal process or not.

[0082] (Configuration 2) The liquid ejection device described in configuration 1, wherein the control means, during the liquid ejection operation of the ejection means, reduces the potential difference applied between the first electrode and the second electrode if the ejection means has performed the kogane removal process before compared to when the ejection means has not performed the kogane removal process.

[0083] (Configuration 3) A liquid ejection device described in configuration 1 or 2, wherein the potential difference is in the range of 0.5V to 2.4V when the ejection means has performed the kogane removal process, and the potential difference is in the range of 0.5V to 2.5V when the ejection means has not performed the kogane removal process.

[0084] (Configuration 4) 4. The liquid ejection device according to any one of configurations 1 to 3, wherein the control means sets the polarities of the first electrode and the second electrode in accordance with the type of liquid.

[0085] (Configuration 5) 5. The liquid ejection device according to configuration 4, wherein the control means applies a voltage to the first electrode so as to make the first electrode a negative electrode when the liquid contains negatively charged particles.

[0086] (Configuration 6) 5. The liquid ejection device according to configuration 4, wherein the control means applies a voltage to the first electrode so as to make the first electrode a positive electrode when the liquid contains positively charged particles.

[0087] (Configuration 7) 7. The liquid ejection device according to any one of configurations 1 to 6, wherein the control means varies the potential difference between the first electrode and the second electrode depending on the type of liquid.

[0088] (Configuration 8) The liquid ejection device described in configuration 1, wherein the control means increases the potential difference applied between the first electrode and the second electrode when the ejection means has performed the kogane removal process compared to when the ejection means has not performed the kogane removal process.

[0089] The liquid ejection device described in configuration 1, wherein the control means makes the potential of the first electrode different when the ejection means has performed the kogane removal process and when the ejection means has not performed the kogane removal process, and makes the potential of the second electrode the same value.

[0090] (Method 1) a heating resistor that generates heat when energized to generate energy for ejecting liquid; a first electrode provided on a protection part that covers and protects the heating resistor; a second electrode that is electrically connected to the first electrode via a liquid; a kogane removal step of applying a voltage between the first electrode and the second electrode to dissolve the surface of the first electrode in a liquid and remove kogane that has accumulated on the surface of the first electrode; A control method for a liquid ejection device, characterized in that the potential difference applied between the first electrode and the second electrode during the liquid ejection operation of the ejection means is made different between when the ejection means has performed the kogane removal process and when the ejection means has not performed the kogane removal process.

[0091] (Method 2) A method for controlling a liquid ejection device according to Method 1, in which the polarities of the first electrode and the second electrode are matched to the type of liquid to eject the liquid.

[0092] (Method 3) The method for controlling a liquid ejection device according to Method 2, wherein when the liquid contains negatively charged particles, a voltage is applied so that the first electrode becomes a negative electrode.

[0093] (Method 4) The method for controlling a liquid ejection device according to Method 2, wherein when the liquid contains positively charged particles, a voltage is applied so that the first electrode becomes a positive electrode. [Explanation of symbols]

[0094] 123 Adhesion protective layer 121 Electrode 124 Upper protective layer 129 Counter Electrode 141 particles 1000 liquid dispensing device

Claims

1. a heating resistor that generates heat when energized to generate energy for ejecting liquid; a first electrode provided on a protection part that covers and protects the heating resistor; a second electrode that is electrically connected to the first electrode via a liquid; A liquid ejection device comprising a control means for controlling the attached ejection means, The control means A kogane removal process can be performed by applying a voltage between the first electrode and the second electrode to dissolve the surface of the first electrode in a liquid and remove kogane that has accumulated on the surface of the first electrode, A liquid ejection device characterized in that the potential difference applied between the first electrode and the second electrode during the liquid ejection operation of the ejection means is different depending on whether the ejection means has performed the kogane removal process or not.

2. The liquid ejection device described in claim 1, wherein the control means, during the liquid ejection operation of the ejection means, reduces the potential difference applied between the first electrode and the second electrode when the ejection means has performed the kogane removal process compared to when the ejection means has not performed the kogane removal process.

3. A liquid ejection device as described in claim 1, wherein the potential difference is in the range of 0.5V to 2.4V when the ejection means has performed the kogane removal process, and the potential difference is in the range of 0.5V to 2.5V when the ejection means has not performed the kogane removal process.

4. 2. The liquid ejection device according to claim 1, wherein the control means sets the polarities of the first electrode and the second electrode in accordance with the type of liquid.

5. 5. The liquid ejection apparatus according to claim 4, wherein the control means applies a voltage to the first electrode so as to make the first electrode a negative electrode when the liquid contains negatively charged particles.

6. 5. The liquid ejection apparatus according to claim 4, wherein the control means applies a voltage to the first electrode so that the first electrode becomes a positive electrode when the liquid contains positively charged particles.

7. 2. The liquid ejection device according to claim 1, wherein the control means varies the potential difference between the first electrode and the second electrode depending on the type of liquid.

8. The liquid ejection device described in claim 1, wherein the control means applies a larger potential difference between the first electrode and the second electrode when the ejection means has performed the kogane removal process than when the ejection means has not performed the kogane removal process.

9. The liquid ejection device described in claim 1, wherein the control means changes the potential of the first electrode between when the ejection means has performed the kogane removal process and when the ejection means has not performed the kogane removal process, and sets the potential of the second electrode to the same value.

10. a heating resistor that generates heat when energized to generate energy for ejecting liquid; a first electrode provided on a protection part that covers and protects the heating resistor; a second electrode that is electrically connected to the first electrode via a liquid; a kogane removal step of applying a voltage between the first electrode and the second electrode to dissolve the surface of the first electrode in a liquid and remove kogane that has accumulated on the surface of the first electrode; A control method for a liquid ejection device, characterized in that the potential difference applied between the first electrode and the second electrode during the liquid ejection operation of the ejection means is made different between when the ejection means has performed the kogane removal process and when the ejection means has not performed the kogane removal process.

11. The method for controlling a liquid ejection device according to claim 10, wherein the polarities of the first electrode and the second electrode are matched to the type of liquid to eject the liquid.

12. The method for controlling a liquid ejection device according to claim 11, wherein, when the liquid contains negatively charged particles, a voltage is applied so that the first electrode becomes a negative electrode.

13. The method for controlling a liquid ejection device according to claim 11, wherein, when the liquid contains positively charged particles, a voltage is applied so that the first electrode becomes a positive electrode.

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