Cleaning method and ink ejection device

Abstract

The present invention provides an ink ejection device capable of performing cleaning and a method for thoroughly removing burnt-on residue regardless of the degree of residue buildup. [Solution] A cleaning method for removing burnt residue accumulated on the upper protective layer, comprising a burnt residue removal step in which the upper protective layer is used as the anode electrode and a portion of the upper protective layer that can conduct electricity through the ink is used as the cathode electrode, and a voltage is applied to remove burnt residue accumulated on the surface of the upper protective layer, wherein the burnt residue removal step is performed under a first condition in which a voltage is applied for a first time, and then under a second condition in which a voltage is applied for a second time longer than the first time.

Description

Technical Field

[0001] The present disclosure relates to a cleaning method and an ink ejection device.

Background Art

[0002] Among the recording methods adopted by recording devices such as multifunction printers, the inkjet recording method is a non-impact recording method and is widely adopted because it enables low-noise, high-density, and high-speed recording. An ink ejection device includes a mechanism for driving a carrier on which an inkjet head is mounted, a transport mechanism for transporting a recording medium such as recording paper, and a control configuration for controlling these. In this specification, the inkjet head is also referred to as an "ink ejection head (head)".

[0003] As a method for generating energy for ejecting ink from the ejection port of an ink ejection head, there is a method of generating foaming by heating the ink with an electrothermal conversion unit having a heating resistor (hereinafter also referred to as a "heater"). The ink used for the ink ejection head often contains dyes or pigments as coloring agents. In the method of ejecting ink using the electrothermal conversion unit, there is a risk of so-called coking, in which the coloring material thermally decomposes and deposits on the heater surface as inorganic or organic substances. Since coking is a factor that hinders heat conduction from the heater to the ink, it causes a decrease in the ejection speed of the ejected ink, and for example, fine lines due to landing position deviation, character distortion, color change, etc. occur.

[0004] In response to this problem, Patent Document 1 proposes a head having an upper protective layer disposed such that electrical connection is possible to form an electrode that causes an electrochemical reaction with ink in a region including the heat acting portion of the heater. In such a head, it is possible to remove the coking deposited together with the metal forming the upper protective layer by eluting the surface of the upper protective layer as an anode by an electrochemical reaction.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-105364 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in Patent Document 1, when the removal of burnt residue is performed repeatedly, the burnt residue removal process is carried out under the same conditions, which may lead to gradually insufficient removal of the burnt residue. This is because if the burnt residue cannot be completely removed in a single removal process, the amount of burnt residue accumulating on the heater will gradually increase. In such cases, the surface condition of the heater may change, potentially resulting in insufficient heat being transferred to the ink. For example, if the heater is an element that generates energy to eject ink from the ejection port, there is a concern that a decrease in ejection speed may prevent stable ejection from being achieved.

[0007] In view of the above-mentioned problems, this disclosure aims to provide a cleaning method that sufficiently removes burnt residue regardless of the state of burnt residue accumulation, and an ink ejection device capable of performing this method. [Means for solving the problem]

[0008] The cleaning method of the present disclosure is a cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, which comprises an electrothermal conversion unit disposed in an ink channel communicating with an ink ejection port for ejecting ink, an insulating protective layer for blocking contact between the electrothermal conversion unit and the ink in the ink channel, and an upper protective layer covering a portion of the protective layer that is heated by the electrothermal conversion unit, the method comprising a burnt residue removal step in which the upper protective layer is used as the anode electrode and a portion of the upper protective layer that is conductive to the upper protective layer via the ink is used as the cathode electrode, and the burnt residue removal step is performed by applying a voltage to remove burnt residue accumulated on the surface of the upper protective layer, characterized in that the burnt residue removal step is performed under a first condition in which the voltage is applied for a first time, and then under a second condition in which the voltage is applied for a second time longer than the first time. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an ink ejection device that can perform cleaning and a method for removing burnt residue sufficiently, regardless of the state of burnt residue accumulation. [Brief explanation of the drawing]

[0010] [Figure 1] Diagram showing the schematic configuration of the recording device. [Figure 2] Schematic diagram showing the first circulation path. [Figure 3] Schematic diagram showing the second circulation path. [Figure 4] Perspective view of the ink ejection head [Figure 5] Disassembled perspective view of the ink ejection head. [Figure 6] Diagram showing the flow channel component. [Figure 7] Diagram showing the connection relationships of flow channels within a flow channel member. [Figure 8] Cross-sectional view along section VIII-VIII in Figure 7 [Figure 9] Diagram showing the discharge module [Figure 10] Diagram showing the structure of the recording element substrate. [Figure 11]Perspective view showing the structure of the recording element substrate and the lid member in the sectional line XI-XI of FIG. 10 [Figure 12] Plan view showing a partially enlarged adjacent portion of the recording element substrate [Figure 13] Diagram showing the structure of the heat acting portion in the recording element substrate[[ID=…]] [Figure 14] Diagram showing the transition of the ejection speed in the conventional example [Figure 15] Diagram showing the transition of the ejection speed in this embodiment [Figure 16] Diagram modeling the communication between the head and the main body, and between the ink cartridge and the main body [Figure 17] Flowchart of a recording method including a cinder removal process [Embodiments for Carrying Out the Invention]

[0011] Hereinafter, embodiments 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 disclosure. 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 recording while scanning the recording medium. Examples of the configuration of the serial type liquid ejection device include a configuration in which one recording element substrate for black ink and one recording element substrate for color ink are each mounted. However, the present disclosure is not limited to this form, and a short line head shorter than the width of the recording medium, in which a plurality of recording element substrates are arranged such that the ejection ports overlap in the ejection port row direction, may be created and scanned with respect to the recording medium. Further, the recording device of the present embodiment is a circulation type inkjet recording device that circulates a liquid such as ink between a tank and the liquid ejection device, but a non-circulation type may also be used.

[0012] (First Embodiment) (Inkjet Recording Device) Figure 1 shows a schematic configuration of a liquid ejection device according to this embodiment, specifically an ink ejection device 1000 (hereinafter also referred to as a recording device) that ejects ink for recording. The recording device has a transport unit 1 that transports a recording medium 2 and a line-type ink ejection head 3 arranged substantially perpendicular to the transport direction of the recording medium, and is a line-type device that performs continuous recording in one pass while transporting the recording medium 2 continuously or intermittently. The recording medium 2 is not limited to cut paper, but may also be continuous roll paper. The ink ejection head 3 is capable of full-color printing using CMYK (cyan, magenta, yellow, black) inks. In the ink ejection head 3, a liquid supply means that constitutes a supply path for supplying ink to the ink ejection head, a main tank, and a buffer tank are fluidly connected (see Figure 2). In addition, an electrical control unit that transmits power and ejection control signals to the ink ejection head 3 is electrically connected to the ink ejection head 3. The liquid path and electrical signal path within the ink ejection head 3 will be described later.

[0013] (First Circulation Pathway) Figure 2 is a schematic diagram showing a first circulation path as one form of the circulation path applied to the recording device according to this embodiment. As shown in Figure 2, the ink ejection head 3 is fluidically connected to the first circulation pump (high pressure side) 1001, the first circulation pump (low pressure side) 1002, and the buffer tank 1003, etc. Note that in Figure 2, for the sake of simplicity, only the path through which one color of CMYK ink flows is shown, but in reality, circulation paths for four colors are provided in the ink ejection head 3 and the recording device body.

[0014] The buffer tank 1003, which is connected to the main tank 1006 and functions as a sub-tank, has an air vent (not shown) that connects the inside and outside of the tank, allowing air bubbles in the ink to be discharged to the outside. The buffer tank 1003 is also connected to the replenishment pump 1005. When ink is consumed by the ink ejection head 3, the replenishment pump 1005 transfers the consumed ink from the main tank 1006 to the buffer tank 1003. Ink is consumed by the ink ejection head 3 when ink is ejected (discharged) from the ejection port of the ink ejection head, for example, when recording by ejecting ink or when suction recovery occurs.

[0015] The two first circulation pumps 1001 and 1002 are responsible for drawing ink from the liquid connection part 111 of the ink ejection head 3 and flowing it to the buffer tank 1003. A positive displacement pump with a quantitative liquid delivery capacity is preferred as the first circulation pump. Specifically, this could be a tube pump, gear pump, diaphragm pump, syringe pump, etc., but it can also be used in a configuration where a constant flow rate is ensured by placing a general constant flow valve or relief valve at the pump outlet. When the ink ejection head 3 is driven, a certain amount of ink flows through the common supply channel 211 and the common recovery channel 212, respectively, 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 to a level that does not affect the recording image quality due to the temperature difference between each recording element substrate 10 within the ink ejection head 3. However, if the flow rate is set too high, the negative pressure difference between each recording element substrate 10 becomes too large due to the pressure loss in the flow path within the liquid ejection unit 300, resulting in uneven image density. Therefore, it is preferable to set the flow rate while taking into account the temperature difference and negative pressure difference between each recording element substrate 10.

[0016] The negative pressure control unit 230 is located in the middle of the path connecting the second circulation pump 1004 and the liquid discharge 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., on the liquid discharge unit 300 side) at a preset constant pressure, even when the flow rate of the circulation system fluctuates due to differences in the recording duty cycle. Any mechanism can be used as the two pressure adjustment mechanisms that constitute the negative pressure control unit 230, as long as it can control the pressure downstream of itself within a certain range of fluctuations around a desired set pressure. For example, a mechanism similar to a so-called "pressure reducing regulator" can be adopted. When a pressure reducing regulator is used, as shown in Figure 2, 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. This suppresses the effect of the hydrostatic pressure on the ink discharge head 3 of the buffer tank 1003, thereby increasing the flexibility of the layout of the buffer tank 1003 in the recording device 1000. The second circulation pump 1004 can be any pump that has a head pressure above a certain level within the range of ink circulation flow rate used when driving the ink ejection head 3, and can be a turbo pump or positive displacement pump, etc. Specifically, a diaphragm pump is applicable. Alternatively, instead of the second circulation pump 1004, a head tank positioned with a certain head difference relative to the negative pressure control unit 230 can also be used.

[0017] As shown in Figure 2, the negative pressure control unit 230 is equipped with two pressure adjustment mechanisms, each with a different control pressure set. Of the two negative pressure adjustment mechanisms, the one with the relatively higher pressure setting (labeled H in Figure 2) is connected to the common supply channel 211 in the liquid discharge unit 300 via the liquid supply unit 220. The one with the relatively lower pressure setting (labeled L in Figure 2) is connected to the common recovery channel 212 via the liquid supply unit 220.

[0018] The liquid discharge unit 300 is provided with a common supply channel 211, a common recovery channel 212, and individual supply channels 213a and individual recovery channels 213b that communicate with each recording element substrate 10. Since the individual supply channels 213a and 213b communicate with the common supply channel 211 and the common recovery channel 212, a flow occurs in which some of the ink flows from the common supply channel 211 through the internal channels of the recording element substrate 10 to the common recovery channel 212 (arrow in Figure 2). This is because a pressure adjustment mechanism H is connected to the common supply channel 211 and a pressure adjustment mechanism L is connected to the common recovery channel 212, resulting in a pressure difference between the two common channels.

[0019] In this way, the liquid ejection unit 300 flows ink through the common supply channel 211 and the common recovery channel 212, respectively, while generating a flow that allows some of the ink to pass through each recording element substrate 10. As a result, the heat generated in each recording element substrate 10 can be discharged to the outside of the recording element substrate 10 by the flow in the common supply channel 211 and the common recovery channel 212. Furthermore, with this configuration, ink flow can be generated even in the ejection port and pressure chamber that are not recording when the ink ejection head 3 is performing recording, thereby suppressing ink viscosity in those areas. In addition, the viscous ink and foreign matter in the ink can be discharged into the common recovery channel 212. As a result, the ink ejection head 3 of this embodiment enables high-speed, high-quality recording.

[0020] (Second circulation pathway) Figure 3 is a schematic diagram showing a second circulation path, which differs 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.

[0021] First, the two pressure adjustment mechanisms constituting the negative pressure control unit 230 both have a mechanism (a mechanism component that functions similarly to a so-called "back pressure regulator") that controls the pressure upstream of the negative pressure control unit 230 within a certain range of fluctuations centered on a desired set pressure. In addition, 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 located upstream of the ink ejection head, and the negative pressure control unit 230 is located downstream of the ink ejection head.

[0022] The negative pressure control unit 230 in the second circulation path operates so that even if the flow rate fluctuates due to changes in the recording duty cycle when recording is performed by the ink ejection head 3, the pressure fluctuation on its upstream side (i.e., the liquid ejection unit 300 side) remains within a certain range. The pressure fluctuation is kept within a certain range, for example, centered around a preset pressure. As shown in Figure 3, it is preferable to pressurize the downstream side of the negative pressure control unit 230 via the liquid supply unit 220 using the second circulation pump 1004. This suppresses the influence of the buffer tank 1003's hydrostatic pressure on the ink ejection head 3, thereby increasing the flexibility of the layout of the buffer tank 1003 in the recording device 1000. Alternatively, instead of the second circulation pump 1004, a hydrostatic tank positioned with a predetermined hydrostatic head difference relative to the negative pressure control unit 230 may be used.

[0023] Similar to the first circulation path, the negative pressure control unit 230 shown in Figure 3 is equipped with two pressure adjustment mechanisms, each with a different control pressure set. Of the two negative pressure adjustment mechanisms, the one with the relatively higher pressure setting (labeled H in Figure 3) is connected to the common supply channel 211 in the liquid discharge unit 300 via the liquid supply unit 220. The one with the relatively lower pressure setting (labeled L in Figure 3) is connected to the common recovery channel 212 via the liquid supply unit 220.

[0024] Two negative pressure adjustment mechanisms ensure that the pressure in the common supply channel 211 is relatively higher than the pressure in the common recovery channel 212. This configuration generates an ink flow from the common supply channel 211 through the individual channels 213 and the internal channels of each recording element substrate 10 to the common recovery channel 212 (arrows in Figure 3). Thus, the second circulation path provides the same ink flow conditions within the liquid ejection unit 300 as the first circulation path, but with two advantages that differ from the first circulation path.

[0025] The first advantage is that in the second circulation path, the negative pressure control unit 230 is located downstream of the ink ejection head 3, so there is less concern about dust and foreign matter generated from the negative pressure control unit 230 flowing into the head. The second advantage is that in the second circulation path, the maximum required flow rate from the buffer tank 1003 to the ink ejection head 3 is less than in the first circulation path. The reason for this is as follows: Let A be the sum of the flow rates in the common supply channel 211 and the common recovery channel 212 when circulation is in operation during recording standby. The value of A is defined as the minimum flow rate required to bring the temperature difference within the liquid ejection unit 300 within the desired range when adjusting the temperature of the ink ejection head 3 during recording standby. Also, let F be defined as the ejection flow rate when ink is ejected from all ejection ports of the liquid ejection unit 300 (full ejection). In the case of the first circulation path (Figure 2), the set flow rates of the first circulation pump (high pressure side) 1001 and the first circulation pump (low pressure side) 1002 become A, so the maximum amount of liquid supplied to the ink ejection head 3 required when all ink is ejected is A + F.

[0026] On the other hand, in the case of the second circulation path (Figure 3), the amount of liquid supplied to the ink ejection head 3 required when recording is in standby mode is flow rate A. The amount of liquid supplied to the ink ejection head 3 required when full ejection is performed is flow rate F. In this case, 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 configuration is used, the maximum required supply amount (A or F) in the second circulation path will always be smaller than the maximum required supply flow rate (A + F) in the first circulation path. Consequently, in the case of the second circulation path, the degree of freedom in the applicable circulation pump increases. For example, it is possible to use a simple and low-cost circulation pump, or reduce the load on the cooler (not shown) installed in the main unit-side path, which has the advantage of reducing the cost of the recording device itself. This advantage becomes greater for line heads where the value of A or F is relatively large, and is more beneficial for line heads with a long longitudinal length.

[0027] However, the first circulation path has advantages over the second circulation path. Specifically, in the second circulation path, the flow rate within the liquid ejection unit 300 is maximum when recording is in standby mode. Therefore, the lower the recording duty cycle, the higher the negative pressure applied to each nozzle. For this reason, especially 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 and the head width (length in the short side direction of the ink ejection head) is reduced, high negative pressure is applied to the nozzles in low-duty images where unevenness is easily visible. Due to this high negative pressure application, there is a risk that the effect of satellite droplets will be greater. On the other hand, in the case of the first circulation path, the timing of high negative pressure being applied to the nozzles is when high-duty images are formed. Therefore, even if satellite droplets occur, they are less likely to be visible, and the effect on the recorded image is small. The two circulation paths can be preferred in light of the specifications of the ink ejection head and the recording device body (ejection flow rate F, minimum circulation flow rate A, and flow resistance inside the head).

[0028] (Ink ejection head configuration) The configuration of the ink ejection head 3 according to the first embodiment will now be described. Figures 4(a) and 4(b) are perspective views of the ink ejection head 3 according to this embodiment. The ink ejection head 3 is a line-type ink ejection head in which 15 recording element substrates 10 capable of ejecting four colors of ink (C / M / Y / K) from a single recording element substrate 10 are arranged in a straight line (inline). As shown in Figure 4(a), the ink ejection head 3 has a signal input terminal 91 and a power supply terminal 92 that are electrically connected to each recording element substrate 10 via a flexible wiring board 40 and an electrical wiring board 90. The signal input terminal 91 and the power supply terminal 92 are electrically connected to the control unit of the recording device 1000, and an ejection drive signal is supplied to the recording element substrate 10 via the signal input terminal 91, and the power required for ejection is supplied to the recording element substrate 10 via the power supply terminal 92.

[0029] By consolidating the wiring using the electrical circuits within the electrical 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 ink ejection head 3 to the recording device 1000 or when replacing the ink ejection head. As shown in Figure 4(b), the liquid connection parts 111 provided at both ends of the ink ejection head 3 are connected to the liquid supply system of the recording device 1000. As a result, CMYK four-color inks are supplied from the supply system of the recording device 1000 to the ink ejection head 3, and the ink that has passed through the ink ejection head 3 is recovered to the supply system of the recording device 1000. In this way, the ink of each color can circulate via the path of the recording device 1000 and the path of the ink ejection head 3.

[0030] Figure 5 shows an exploded perspective view of each component or unit that makes up the ink ejection head 3. The liquid ejection unit 300, the liquid supply unit 220, and the electrical wiring board 90 are mounted on the housing 80. The liquid supply unit 220 is provided with a liquid connection part 111 (Figures 2 and 3), and inside the liquid supply unit 220, there are color-specific filters 221 (Figures 2 and 3) that communicate with each opening of the liquid connection part 111 in order to remove foreign matter from the supplied ink. Each of the two liquid supply units 220 is provided with filters 221 for two colors. The ink that has passed through the filters 221 is supplied to a negative pressure control unit 230 located on the supply unit 220, corresponding to each color.

[0031] The negative pressure control unit 230 is a unit consisting of pressure regulating valves for each color. Through the action of valves, spring members, etc., provided inside each unit, the negative pressure control unit 230 significantly reduces pressure loss changes in the supply system of the recording device 1000 (the supply system upstream of the ink ejection head 3) that occur due to fluctuations in ink flow rate. As a result, the negative pressure control unit 230 can stabilize negative pressure changes downstream of the pressure control unit (on the liquid ejection unit 300 side) within a certain range. Each color negative pressure control unit 230 contains two pressure regulating valves for each color, as described in Figure 2. These pressure regulating valves are set to different control pressures, and the high-pressure side is connected to the common supply passage 211 in the liquid ejection unit 300, and the low-pressure side is connected to the common recovery passage 212, via the liquid supply unit 220.

[0032] The housing 80 consists of a liquid ejection unit support section 81 and an electrical wiring board support section 82, supporting the liquid ejection unit 300 and the electrical wiring board 90, and ensuring the rigidity of the ink ejection head 3. The electrical wiring board support section 82 is for supporting the electrical wiring board 90 and is fixed to the liquid ejection unit support section 81 by screws. The liquid ejection unit support section 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 the recorded material. For this reason, the liquid ejection unit support section 81 preferably has sufficient rigidity, and suitable materials include metal materials such as SUS or aluminum, or ceramics such as alumina. The liquid ejection unit support section 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 guided through the joint rubber to the third flow path member 70 that constitutes the liquid ejection unit 300.

[0033] 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 side of the liquid ejection unit 300 that is on the recording medium side. Here, as shown in Figure 5, the cover member 130 is a member having a frame-like surface with a long opening 131, and the recording element substrate 10 and sealing material 110 (Figure 9) included in the ejection module 200 are exposed through the opening 131. The frame portion around the opening 131 functions as a contact surface for a cap member that caps the ink ejection head 3 when it is in standby mode for recording. For this reason, it is preferable to apply an adhesive, sealing material, filler, etc. along the perimeter of the opening 131 to fill in any irregularities or gaps on the ejection port surface of the liquid ejection unit 300 so that a closed space is formed when the cap is applied.

[0034] Next, the configuration of the flow channel member 210 included in the liquid discharge unit 300 will be described. As shown in Figure 5, the flow channel member 210 is made up of a stack of a first flow channel member 50, a second flow channel member 60, and a third flow channel member 70. The flow channel member 210 distributes the ink supplied from the liquid supply unit 220 to each discharge module 200, and returns the ink circulating from the discharge module 200 back to the liquid supply unit 220. The flow channel member 210 is fixed to the liquid discharge unit support part 81 with screws, thereby suppressing warping and deformation of the flow channel member 210.

[0035] Figures 6(a) to 6(f) show the front and back surfaces of the first to third flow channel members. Figure 6(a) shows the side of the first flow channel member 50 on which the discharge module 200 is mounted, and Figure 6(f) shows the side of the third flow channel member 70 that abuts against the liquid discharge unit support 81. The first flow channel member 50 and the second flow channel member 60 are joined so that the abutment surfaces of each flow channel member, shown in Figure 6(b) and Figure 6(c), face each other. The second flow channel member and the third flow channel member are joined so that the abutment surfaces of each flow channel member, shown in Figure 6(d) and Figure 6(e), face each other. By joining the second flow channel member 60 and the third flow channel member 70, eight common flow channels extending in the longitudinal direction of the flow channel members are formed by the common flow channel grooves 62 and 71 formed in each flow channel member. As a result, as shown in Figure 7, sets of common supply channels 211 and common recovery channels 212 are formed within the channel member 210 for each color. The communication ports 72 of the third channel member 70 communicate with each hole in the joint rubber 100 and are in fluidic communication with the liquid supply unit 220. Multiple communication ports 61 are formed on the bottom surface of the common channel groove 62 of the second channel member 60 and communicate with one end of the individual channel groove 52 of the first channel member 50. A communication port 51 is formed at the other end of the individual channel groove 52 of the first channel member 50 and is in fluidic communication with multiple discharge modules 200 via the communication port 51. This individual channel groove 52 makes it possible to concentrate the channels toward the center of the channel member.

[0036] The first to third flow channel members are preferably made of a material that is corrosion-resistant to liquids and has a low coefficient of thermal expansion. Suitable materials include, for example, alumina, LCP (liquid crystal polymer), PPS (polyphenyl sulfide), and PSF (polysulfone) as the base material, to which inorganic fillers such as silica fine particles or fibers are added (resin materials). As for the method of forming the flow channel members 210, the three flow channel members may be laminated and bonded to each other, or if a resin composite resin material is selected as the material, a welding method may be used for joining.

[0037] Next, the connection relationships of each flow path within the flow path member 210 will be explained using Figure 7. Figure 7 is a perspective view of the flow paths within the flow path member 210, which is formed by joining the first to third flow path members, with a portion enlarged from the 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 ink ejection head 3 for each color. Multiple 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 a communication port 61. Furthermore, multiple individual recovery channels (214a, 214b, 214c, 214d) formed by individual channel grooves 52 are connected to the common recovery channel 212 for each color via a communication port 61. With this channel configuration, ink can be concentrated from each common supply channel 211 through the individual supply channels 213 to the recording element substrate 10 located in the center of the channel member. Ink can also be recovered from the recording element substrate 10 to each common recovery channel 212 via the individual recovery channels 214.

[0038] Figure 8 shows a cross-section along line VIII-VIII in Figure 7. As shown in this figure, each individual recovery channel (214a, 214c) communicates with the discharge module 200 via a communication port 51. Although only the individual recovery channels (214a, 214c) are shown in Figure 8, in another cross-section, the individual supply channel 213 and the discharge module 200 are in communication, as shown in Figure 7. Each discharge module 200 has a support member 30 and a recording element substrate 10, both of which have channels formed to supply ink from the first channel member 50 to the recording element 15 (Figure 10) provided on the recording element substrate 10. The support member 30 and the recording element substrate 10 also have channels formed to recover (recirculate) some or all of the ink supplied to the recording element 15 back to the first channel member 50. Here, the common supply channel 211 for each color is connected via the corresponding color negative pressure control unit 230 (high pressure side) and liquid supply unit 220, and the common recovery channel 212 is connected via the negative pressure control unit 230 (low pressure side) and liquid supply unit 220. The negative pressure control unit 230 creates a differential pressure (pressure difference) between the common supply channel 211 and the common recovery channel 212. As a result, in the ink ejection head of this embodiment, where each channel is connected as shown in Figures 7 and 8, a flow occurs for each color in the following order: common supply channel 211 ~ individual supply channel 213a ~ recording element substrate 10 ~ individual recovery channel 213b ~ common recovery channel 212.

[0039] (Discharge module) Figure 9(a) shows a perspective view of one discharge module 200, and Figure 9(b) shows an exploded view thereof. As for the manufacturing method of the discharge module 200, first, the recording element substrate 10 and the flexible wiring board 40 are bonded to a support member 30 which is provided with a liquid communication port 31 in advance. Then, the terminals 16 on the recording element substrate 10 and the terminals 41 on the flexible wiring board 40 are electrically connected by wire bonding, and then the wire bonding portion (electrical connection portion) is covered and sealed with a sealing material 110. The terminal 42 on the side of the flexible wiring board 40 opposite to the recording element substrate 10 is electrically connected to the connection terminal 93 (see Figure 5) of the electrical wiring board 90. The support member 30 is a support body that supports the recording element substrate 10 and a flow channel member that fluidly communicates the recording element substrate 10 and the flow channel member 210, so it is preferable that it has high flatness and can be bonded to the recording element substrate with sufficiently high reliability. As for the material, alumina or resin material is preferred.

[0040] (Structure of the recording element substrate) The configuration of the recording element substrate 10 in this embodiment will now be described. Figure 10(a) shows a plan view of the side of the recording element substrate 10 on which the ejection ports 13 are formed, Figure 10(b) shows an enlarged view of the portion indicated by Xb in Figure 10(a), and Figure 10(c) shows a plan view of the back surface of Figure 10(a). Figure 11 is a perspective view showing a cross-section of the recording element substrate 10 and the lid member 20 along the cross-sectional line XI-XI shown in Figure 10(a). As shown in Figure 10(a), four rows of ejection ports corresponding to each ink color are formed on the ejection port forming member 12 of the recording element substrate 10. Hereafter, the direction in which the rows of ejection ports in which the multiple ejection ports 13 are arranged extend will be referred to as the "ejection port row direction."

[0041] As shown in Figure 10(b), recording elements 15, which are heating elements for foaming the ink using thermal energy, are positioned at the location corresponding to each discharge port 13. A partition wall 22 separates a pressure chamber 23 containing the recording elements 15. The recording elements 15 are electrically connected to the terminals 16 in Figure 10(a) by electrical wiring (not shown) provided on the recording element substrate 10. The recording elements 15 generate heat and boil the ink based on pulse signals input from the control circuit of the recording device 1000 via the electrical wiring board 90 (Figure 5) and the flexible wiring board 40 (Figure 9). The force of foaming caused by this boiling ejects the ink from the discharge port 13. As shown in Figure 10(b), a liquid supply path 18 extends along one side of each row of discharge ports, and a liquid recovery path 19 extends along the other side. The liquid supply path 18 and the liquid recovery path 19 are flow paths extending in the direction of the discharge port row provided on the recording element substrate 10, and are in communication with the discharge port 13 via the supply port 17a and the recovery port 17b, respectively.

[0042] As shown in Figures 10(c) and 11, a sheet-like lid member 20 is laminated on the back surface of the recording element substrate 10 where the ejection port 13 is formed. The lid member 20 is provided with multiple openings 21 that communicate with the liquid supply passage 18 and the liquid recovery passage 19, which will be described later. In this embodiment, three openings 21 are provided in the lid member 20 for each liquid supply passage 18, and two openings 21 are provided for each liquid recovery passage 19. As shown in Figure 10(b), each opening 21 of the lid member 20 communicates with a plurality of communication ports 51 shown in Figure 7, etc. As shown in Figure 11, the lid member 20 functions as a lid that forms part of the walls of the liquid supply passage 18 and the liquid recovery passage 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 viewpoint of preventing color mixing, high precision is required in the shape and position of the openings 21. Therefore, it is preferable to use a photosensitive resin material or a silicon plate as the material for the lid member 20 and to create the opening 21 by a photolithography process. In this way, the lid member changes the pitch of the flow path by the opening 21, and considering the pressure loss, it is desirable that the thickness be thin and that it be composed of a film-like material.

[0043] Next, the flow of ink within the recording element substrate 10 will be described. Figure 11 is a perspective view showing a cross-section of the recording element substrate 10 and the lid member 20 along the cross-sectional line XI-XI in Figure 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 photosensitive resin, with the lid member 20 bonded to the back surface of the substrate 11. A recording element 15 is formed on one side of the substrate 11 (Figure 10), and grooves constituting a liquid supply passage 18 and a liquid recovery passage 19 extending along the row of ejection ports are formed on the back surface. The liquid supply passage 18 and the liquid recovery passage 19 formed by the substrate 11 and the lid member 20 are connected to a common supply passage 211 and a common recovery passage 212 in the flow path member 210, respectively, and a differential pressure is generated between the liquid supply passage 18 and the liquid recovery passage 19. When ink is ejected from multiple ejection ports 13 of the ink ejection head 3 and recording is being performed, the differential pressure at the ejection ports that are not currently ejecting causes the ink flow in the liquid supply passage 18 provided in the substrate 11 to follow the flow shown by arrow C in Figure 11. That is, the ink flows to the liquid recovery passage 19 via the supply port 17a, pressure chamber 23, and recovery port 17b. This flow allows thickened ink, bubbles, and foreign matter generated by evaporation from the ejection ports 13 and pressure chamber 23 to be recovered into the liquid recovery passage 19. It also suppresses the thickening of the ink in the ejection ports 13 and pressure chamber 23. The ink recovered into the liquid recovery passage 19 is then recovered in the following order: through the opening 21 of the lid member 20 and the liquid communication port 31 of the support member 30 (see Figure 9(b)), to the communication port 51 in the flow path member 210, the individual recovery passage 214, and the common recovery passage 212. This ink is ultimately recovered into the supply path of the recording device 1000.

[0044] In other words, the ink supplied from the recording device body to the ink ejection head 3 flows, is supplied, and is recovered in the following order. First, the ink flows into the inside of the ink ejection head 3 from the liquid connection part 111 of the liquid supply unit 220. The ink is then supplied in the following order: through the joint rubber 100, the communication port 72 and common flow channel groove 71 provided in the third flow channel member, the common flow channel groove 62 and communication port 61 provided in the second flow channel member, and the individual flow channel groove 52 and communication port 51 provided in the first flow channel member. After that, it is supplied to the pressure chamber 23 in the following order: through the liquid communication port 31 provided in the support member 30, the opening 21 provided in the lid member, and the liquid supply passage 18 and supply port 17a provided in the substrate 11. Of the ink supplied to the pressure chamber 23, the ink that is not ejected from the ejection port 13 flows in the following order: through the recovery port 17b and liquid recovery passage 19 provided in the substrate 11, the opening 21 provided in the lid member, and the liquid communication port 31 provided in the support member 30. Subsequently, the ink flows sequentially through the communication port 51 and individual flow channel grooves 52 provided in the first flow channel member, the communication port 61 and common flow channel groove 62 provided in the second flow channel member, the common flow channel groove 71 and communication port 72 provided in the third flow channel member 70, and the joint rubber 100. Furthermore, ink flows from the liquid connection part 111 provided in the liquid supply unit to the outside of the ink ejection head 3. In the configuration of the first circulation path shown in Figure 2, the ink flowing in from the liquid connection part 111 is supplied to the joint rubber 100 after passing through the negative pressure control unit 230. In the configuration of the second circulation path shown in Figure 3, the ink recovered from the pressure chamber 23 passes through the joint rubber 100 and then flows from the liquid connection part 111 to the outside of the ink ejection head via the negative pressure control unit 230.

[0045] Furthermore, as shown in Figures 2 and 3, not all ink flowing in from one end of the common supply channel 211 of the liquid ejection unit 300 is supplied to the pressure chamber 23 via the individual supply channel 213a. Some ink flows to the liquid supply unit 220 from the other end of the common supply channel 211 without flowing into the individual supply channel 213a. By providing a path through which the ink flows without passing through the recording element substrate 10, even when the recording element substrate 10 has fine channels with high flow resistance, as in this embodiment, backflow of the circulating ink can be suppressed. In this way, the ink ejection head of this embodiment can suppress the viscosity of the ink in the pressure chamber and near the ejection port, thereby suppressing deviations from the normal direction of ejection and non-ejection, and as a result, high-quality recording can be achieved.

[0046] (Positional relationship between recording element substrates) Figure 12 is a plan view showing a partially enlarged view of the adjacent portion of the recording element substrate in two adjacent ejection modules. As shown in Figure 10(a), etc., this embodiment uses a substantially parallelogram-shaped recording element substrate. As shown in Figure 12, each ejection port row (14a to 14d) in which the ejection ports 13 of each recording element substrate 10 are arranged is tilted at a certain angle with respect to the transport direction of the recording medium. As a result, at least one ejection port in the ejection port row at the adjacent portion of the recording element substrates 10 overlaps in the transport direction of the recording medium. In Figure 12, the two ejection ports on line D overlap each other. With this arrangement, even if the position of the recording element substrate 10 is slightly shifted from a predetermined position, the drive control of the overlapping ejection ports can make black streaks and white spots in the recorded image less noticeable. Even when multiple recording element substrates 10 are arranged in a straight line (inline) instead of in a staggered arrangement, the configuration shown in Figure 12 can be achieved. This makes it possible to suppress the increase in the length of the transport direction of the recording medium in the ink ejection head while preventing black streaks and white gaps at the connections between the recording element substrates 10. In this embodiment, the main plane of the recording element substrate is a parallelogram, but this embodiment is not limited to this, and the configuration of this embodiment can be preferably applied even when a recording element substrate of a rectangular, trapezoidal, or other shape is used.

[0047] (Structure of the thermal action area in the recording element substrate) The structure of the thermal area in the recording element substrate according to this embodiment will be described below with reference to Figure 13. Figure 13(a) is a schematic, enlarged plan view showing the area near the thermal area in the recording element substrate 10. Figure 13(b) is a cross-sectional view taken along the dashed line XIIIb-XIIIb in Figure 13(a).

[0048] In the ink ejection head, a liquid ejection recording substrate is formed by laminating multiple layers on a silicon substrate 121. In this embodiment, a heat storage layer formed of a thermal oxide film, SiO film, SiN film, etc. is placed on the substrate 121. A heat-generating resistor 126, which is an electrothermal conversion unit, is placed on the heat storage layer, and an electrode wiring layer (not shown) formed of a metallic material such as Al, Al-Si, or Al-Cu is connected to the heat-generating resistor 126 via a tungsten plug 128. As shown in Figure 13(b), an insulating protective layer 127 is placed on the heat-generating resistor 126 to block contact between the heat-generating resistor, which is an electrothermal conversion unit, and the ink in the ink channel. The insulating protective layer 127 is an insulating layer provided on top of the heat-generating resistor 126 so as to cover it. The insulating protective layer 127 is formed of an SiO film, SiN film, etc. The electrothermal conversion unit is located in the ink channel that communicates with the ink ejection port.

[0049] A protective layer is placed on the insulating protective layer 127 to block contact with liquid. This protective layer includes a lower protective layer 125, an upper protective layer 124, and an adhesion protective layer 123, and protects the surface of the heating resistor 126 from chemical and physical shocks caused by the heating of the heating resistor 126. The upper protective layer 124 is formed in a position that covers at least the portion heated by the electrothermal conversion unit.

[0050] 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 adhesion protective layer 123 is made of tantalum (Ta). Furthermore, the protective layers formed from these materials are electrically conductive. A protective layer 122 is placed on the adhesion protective layer 123 for liquid resistance and to improve adhesion with the discharge port forming member 12. The protective layer 122 is made of SiC. The upper protective layer 124 is preferably made of a material that contains a metal that dissolves by electrochemical reaction and does not form an oxide film that prevents dissolution by heating, and is preferably made of a material containing Ir or Ru.

[0051] When liquid is discharged, the upper part of the upper protective layer 124 is in contact with the liquid, and the liquid temperature rises instantaneously at this upper part, causing foaming, defoaming, and cavitation to occur in a harsh environment. Therefore, in this embodiment, the upper protective layer 124, which is made of a highly corrosion-resistant and reliable iridium material, is formed at a position corresponding to the heat-generating resistor 126 and is in contact with the liquid.

[0052] In this embodiment, an ink circulation configuration is employed in which liquid is supplied from the supply port 17a within the pressure chamber 23 and recovered to the recovery port 17b. Therefore, during printing, liquid flows on the heating resistor 126 from the upstream supply port 17a to the downstream recovery port 17b.

[0053] (Cleaning method) First, let's explain the principle of charring and how to clean it. In the ink ejection head, the heat from the electric heat conversion unit (heater) acts on the ink in the pressure chamber 23, causing the ink to be ejected from the ejection port. Since the ink ejection head ejects ink many times, the electric heat conversion unit is heated many times. As a result, components in the ink accumulate on the upper protective layer due to the heating, causing what is known as charring. When charring occurs, heat conduction from the electric heat conversion unit to the ink is hindered, causing a decrease in the ink ejection speed from the ink ejection head.

[0054] A charring removal process is performed as a cleaning method to remove charring that accumulates on the upper protective layer. The charring removal process is carried out by applying a voltage to the upper protective layer 124, using the area directly above the electrothermal conversion section as the anode electrode and the area that can conduct electricity to the upper protective layer 124 via ink as the cathode electrode, thereby inducing an electrochemical reaction. At this time, the metal forming the upper protective layer 124 dissolves into the ink at the anode, so the charring accumulated on the surface of the upper protective layer 124 is removed along with the metal. Once the charring is removed, the decrease in ink ejection speed that was caused by the accumulation of charring is restored.

[0055] However, in conventional burnt-on charring removal processes, as the heat generated by the electric heat conversion unit is repeated, it becomes impossible to completely remove the charred charring in a single process, and there is a risk that the amount of charred charring will gradually increase. Figure 14 shows the change in discharge speed according to the number of times the electric heat conversion unit is driven, i.e., the number of pulses applied to drive the electric heat conversion unit, when the burnt-on charring removal process is performed under predetermined conditions. Hereinafter, the number of pulses applied refers to the number of times the electric heat conversion unit is driven. After burnt-on charring removal is performed in process (a) under the first condition, and then burnt-on charring removal is performed in process (b) under the first condition, the discharge speed has not recovered to the level immediately after burnt-on charring removal in process (a). In such cases, as the number of pulses applied increases, the discharge speed gradually decreases, and when burnt-on charring removal is performed in (c) under the first condition, the discharge speed reaches the lower limit of the allowable discharge speed range. Then, immediately before burnt-on charring removal is performed in processes (d) and (e), the discharge speed falls below the lower limit of the allowable discharge speed range, resulting in deterioration of the recording quality due to the decrease in discharge speed. This decrease in discharge rate due to the accumulation of burnt residue can occur because the conditions for the burnt residue removal process are always constant under the first condition.

[0056] Next, the burnt residue removal process in this embodiment will be explained using Figure 15. In this embodiment, the burnt residue removal in steps (a) and (b) is the same as in conventional burnt residue removal. However, in (c), when the discharge speed reaches the allowable range, the burnt residue removal process is performed under a second condition, which makes it easier to remove burnt residue than under the first condition. This suppresses the risk of the discharge speed falling below the lower limit of the allowable range, even immediately before steps (d) and (e), thereby suppressing a decrease in recording quality. In this embodiment, the burnt residue removal process under the second condition is performed when the discharge speed reaches the lower limit of the allowable range, but this is not the only option; it is sufficient to perform the burnt residue removal process under the second condition after the burnt residue removal process under the first condition.

[0057] Next, we will explain the second condition, which makes it easier to remove burnt-on residue than the first condition. The second condition is not particularly limited as long as it makes it easier to remove burnt-on residue than the first condition, but examples include the duration of voltage application in the burnt-on residue removal process, the magnitude of the applied voltage, and the number of pulses applied between burnt-on residue removal processes. We will explain specific examples of each.

[0058] The burnt residue removal process can be performed under a first condition in which voltage is applied for a first period of time, and then under a second condition in which voltage is applied for a second period of time longer than the first period. This makes it easier to remove burnt residue under the second condition than under the first condition, and suppresses a decrease in ejection speed. The first and second periods are preferably 30 seconds to 150 seconds in order to remove burnt residue while suppressing excessive dissolution of the upper protective layer. The first and second periods may be applied by repeatedly applying voltage for short periods of time discontinuously, or by continuously applying voltage over the first and second periods. For inks that are less prone to a decrease in ejection speed, extending the voltage application time makes it easier to uniformly remove burnt residue accumulated on the upper protective layer. On the other hand, for inks that are more prone to a decrease in ejection speed, it is preferable to shorten the voltage application time.

[0059] Furthermore, the burnt-on residue removal process can be performed under a first condition where a first voltage is applied, and then under a second condition where a second voltage greater than the first voltage is applied. When the applied voltage is higher, the amount of the upper protective layer that dissolves due to the electrochemical reaction increases. Therefore, burnt-on residue is easier to remove under the second condition than under the first condition, and a decrease in the ejection speed can be suppressed. If the applied voltage is too high, the upper protective layer will dissolve excessively, so it is preferable to set the voltage while considering the balance between burnt-on residue removal and the deterioration of the upper protective layer's function. Specifically, it is preferable that the first and second voltages be between 3V and 5V. Note that depending on the type of ink, increasing the applied voltage may generate positive ions, which may aggregate and cause adhesion. Therefore, it is preferable to increase the voltage for ink types that are less prone to adhesion, and to adjust the first and second times for ink types that are prone to adhesion.

[0060] Furthermore, the burnt-on residue removal process can be performed under a first condition, where it is performed every time a pulse to drive the electric heat conversion unit is applied a first number of times, and then under a second condition, where it is performed every time a second number of pulses are applied, which is fewer than the first number of pulses. In this way, by reducing the interval (number of pulse applications) between the accumulation of burnt residue and the burnt-on residue removal process, the burnt-on residue removal process can be performed more frequently, keeping the discharge speed within an acceptable range. As mentioned above, the upper protective layer dissolves when the burnt-on residue removal process is performed, which may reduce the function of the upper protective layer. Therefore, it is preferable to set the first and second number of pulse applications considering the balance between the number of pulses applied before the burnt-on residue removal process and the reduction in the function of the upper protective layer. Specifically, the first and second number of pulse applications should be 2.5 × 10⁻⁶. 8 6 x 10 times or more 9 It is preferable that the number of times is less than or equal to 1.

[0061] In the above explanation, the conditions for the burnt-on grime removal process were changed by modifying the time the voltage is applied, the magnitude of the applied voltage, and the number of pulses applied between burnt-on grime removal processes. However, the burnt-on grime removal process may be performed by changing only two conditions. Furthermore, three or more conditions may be changed. By setting the second set of conditions by changing multiple conditions from the first set of conditions, it is possible to accurately perform burnt-on grime removal that is appropriate for the state of grime accumulation.

[0062] Next, we will explain the timing of the burnt-on residue removal process. As mentioned above, the burnt-on residue removal process removes the burnt residue by dissolving the upper protective layer. Therefore, performing the burnt-on residue removal process excessively may lead to a decrease in the function of the upper protective layer. For this reason, it is preferable to perform the burnt-on residue removal process at a time when the ejection characteristics, such as the ejection speed, change. For example, if the ink ejection speed slows down by 2 m / s, image degradation such as uneven density and misaligned lines is likely to occur. In other words, it is preferable to perform the burnt-on residue removal process every time the ink ejection speed slows down by 2 m / s from the normal state. However, it is difficult to accurately measure the ink ejection speed and perform the burnt-on residue removal process accordingly. Therefore, the present disclosers have found that it is preferable to perform the burnt-on residue removal process based on the number of pulses applied to drive the electrothermal conversion unit, based on the idea that the decrease in ejection speed due to the accumulation of burnt residue is based on the number of pulses applied to drive the electrothermal conversion unit. In other words, it is preferable to switch the burnt-on residue removal process from the first condition to the second condition when the number of pulses applied to drive the electrothermal conversion unit exceeds a threshold.

[0063] Furthermore, after switching the burnt-on grime removal process conditions from the first condition to the second condition, it is also possible to switch back to the first condition. This allows the burnt-on grime removal process to be performed under the second condition, which is more efficient for removing burnt-on grime, only when necessary. In addition, although the above explanation has listed the first and second conditions as examples, the burnt-on grime removal process may be performed under three or more conditions, not just two. Even in that case, by performing the burnt-on grime removal process under the conditions that are more efficient for removing burnt-on grime later, sufficient burnt-on grime can be removed regardless of the extent of the grime buildup.

[0064] (Communication control between the ink ejection head and the ink ejection device body) The communication control between the ink ejection head and the ink ejection device body according to this embodiment will be described below with reference to Figure 16. Figure 16 is a diagram that models the communication between the head and the body, and between the ink cartridge and the body.

[0065] The main circuit board built into the main body of the ink ejection device 1000 includes a CPU 500, ROM 501, RAM 502, etc. This main circuit board receives temperature information from the head 3 on each recording element board 10 and transmits control signals to the electrical wiring board 90 of the head 3 to drive each electrical heat conversion unit based on the received temperature information. The head is equipped with a temperature sensor 301 and a sub-heater 302 for preheating the ink before heating the ink with the energy that generates the pressure for ejecting ink from the head.

[0066] To perform the burnt-on residue removal process according to this embodiment, the ink ejection device preferably includes a counting means for counting the number of times a pulse is applied to drive the electrothermal conversion unit, and an identification means for determining whether the number of applied pulses is above a threshold. The counting means and the identification means may be any configuration of the main substrate as described above, and the counting means and the identification means may be the same configuration.

[0067] (Processing for removing burnt-on food) Next, the image recording flow including the burnt-on residue removal process according to this embodiment will be described. Figure 17 shows a flowchart of the image recording process. First, in S2101, ink is ejected from the ink ejection head to print on the recording medium. At this time, the number of times a pulse is applied to the electric heat conversion unit to eject the ink is counted by the counting means. Next, in S2102, it is determined that the conditions for performing the burnt-on residue removal process have been met. If this result is false (NO), the process returns to S2101 and is repeated until the result is true (YES). If the result of S2102 is true (YES), in S2103, the identification means identifies whether the number of times a pulse has been applied to drive the electric heat conversion unit is above a threshold. At this time, the number of times a pulse has been applied is counted by the counting means. If the identification result of S2103 is false (NO), in S2104(a), the burnt-on residue removal process is performed under the first condition. On the other hand, if the identification result of S2103 is true (YES), then in S2104(b), the burn removal process is performed under the second condition, which makes it easier to remove burn marks than under the first condition. Next, after the processes of S2104(a) and S2104(b), S2105 determines whether to terminate printing. If S2105 is false (NO), the process returns to S2101. On the other hand, if S2105 is true (YES), the image recording is terminated.

[0068] (Other embodiments) As a cleaning method for removing burnt residue, one electrode may be used on the upper protective layer 124 of the heater, directly above the heating resistor 126, and the other electrode may be used as ground, or a counter electrode 129 (Figure 13) may be provided.

[0069] In the first embodiment, an element that generates energy for ejecting ink was used as the electrothermal conversion unit, but an element that generates pressure for the ink to circulate within the ink channel may also be used. Even if an element that generates pressure for the ink to circulate within the ink channel is used, an upper protective layer 124 is provided directly above it, and the accumulation of charring on the upper protective layer may make it difficult for the heat from the electrothermal conversion unit to act on the ink. For this reason, the cleaning method in this disclosure is preferred.

[0070] Furthermore, other electrical heat conversion units may include a sub-heater 302 (Figure 16) provided in the head. Burnt residue accumulated on the upper protective layer of the sub-heater 302 can also be removed by the Kel cleaning method of this disclosure.

[0071] Based on the above, according to this disclosure, burnt char can be sufficiently removed regardless of the state of charring accumulation.

[0072] To summarize this disclosure, it includes the following methods and structure:

[0073] (Method 1) An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on residue removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that is electrically conductive through the ink is used as the cathode electrode, and a voltage is applied to remove burnt residue accumulated on the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under a first condition in which a voltage is applied for a first time period, and then under a second condition in which a voltage is applied for a second time period longer than the first time period.

[0074] (Method 2) An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that can conduct electricity through the ink is used as the cathode electrode, and a voltage is applied to dissolve the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under first conditions in which a first voltage is applied, and then under second conditions in which a second voltage greater than the first voltage is applied.

[0075] (Method 3) An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that can conduct electricity through the ink is used as the cathode electrode, and a voltage is applied to dissolve the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under a first condition in which a pulse that drives the electric heat conversion unit is applied a first number of times, and then performed under a second condition in which the pulse is applied a second number of times, which is fewer than the first number of times.

[0076] (Method 4) A cleaning method according to any one of methods 1 to 3, wherein when the number of pulses applied to drive the electric heat conversion unit exceeds a threshold, the conditions for the burnt-on grease removal process are switched from the first conditions to the second conditions.

[0077] (Method 5) The first condition is that a first voltage is applied, The cleaning method according to any one of methods 1 to 4, wherein the second condition is to apply a second voltage greater than the first voltage.

[0078] (Method 6) The first condition is that the burnt-on charring step is executed each time a pulse is applied to drive the electric heat conversion unit a first number of times. The cleaning method according to any one of methods 1 to 5, wherein the second condition is that the burnt-on charring step is performed each time the pulse is applied a second number of times, which is less than the first number of times.

[0079] (Method 7) The first condition is that the burnt-on residue removal process is performed by applying a first voltage each time a pulse that drives the electric heat conversion unit is applied a first number of times. The cleaning method according to any one of methods 1 to 6, wherein the second condition is that the burnt-on residue removal step is performed by applying a second voltage greater than the first voltage each time the pulse is applied a second number of times, which is fewer than the first number of times.

[0080] (Method 8) The cleaning method according to any one of methods 1 to 7, wherein the upper protective layer is made of a material that does not form an oxide film that prevents the dissolution of the upper protective layer by heating of the electrothermal conversion unit.

[0081] (Method 9) The cleaning method according to any one of methods 1 to 8, wherein the upper protective layer is formed of a material containing Ir or Ru.

[0082] (Method 10) The cleaning method according to Method 1, wherein the first time and the second time are 30 seconds or more and 150 seconds or less.

[0083] (Method 11) The cleaning method according to method 2, 5, or 7, wherein the first voltage and the second voltage are 3V or more and 5V or less.

[0084] (Method 12) The first number of times and the second number of times are 2.5 × 10 8 6 x 10 times or more 9 The cleaning method described in Method 3, 6, or 7, which is performed no more than twice.

[0085] (Method 13) The cleaning method according to any one of methods 1 to 12, wherein the electric heat conversion unit is an element that generates energy for ejecting ink from the ejection port.

[0086] (Method 14) The cleaning method according to any one of methods 1 to 13, wherein the electric heat conversion unit is an element that generates pressure for the ink to circulate within the ink flow path.

[0087] (Composition 1) An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized by having a changing means for switching the voltage applied for the electrochemical reaction from a first voltage to a second voltage greater than the first voltage when the identification result by the identification means is greater than or equal to a threshold.

[0088] (Configuration 2) An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized by having a changing means for switching the time for which voltage is applied for the electrochemical reaction from a first time to a second time that is longer than the first time, when the identification result by the identification means is greater than or equal to a threshold.

[0089] (Composition 3) An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized in that, when the identification result by the identification means is greater than or equal to a threshold, the electrochemical reaction is switched from a first condition in which the reaction is performed each time the pulse is applied a first number of times, to a second condition in which the reaction is performed each time the pulse is applied a second number of times, which is greater than the first number of times. [Explanation of symbols]

[0090] 13 Ink ejection port 23 Ink channel 124 Upper protective layer 126 Electric Heat Conversion Unit (Heater) 127 Insulating protective layer

Claims

1. An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on residue removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that is electrically conductive through the ink is used as the cathode electrode, and a voltage is applied to remove burnt residue accumulated on the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under a first condition in which a voltage is applied for a first time period, and then under a second condition in which a voltage is applied for a second time period longer than the first time period.

2. An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that can conduct electricity through the ink is used as the cathode electrode, and a voltage is applied to dissolve the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under first conditions in which a first voltage is applied, and then under second conditions in which a second voltage greater than the first voltage is applied.

3. An electric heat conversion unit is located within the ink channel that communicates with the ink ejection port, An insulating protective layer for blocking contact between the electric heat conversion unit and the ink in the ink channel, The upper protective layer covers the portion of the protective layer that is heated by the electric heat conversion unit, A cleaning method for removing burnt residue accumulated on the upper protective layer of an inkjet head, comprising: The process includes a burnt-on removal step in which the upper protective layer is used as the anode electrode, and a portion of the upper protective layer that can conduct electricity through the ink is used as the cathode electrode, and a voltage is applied to dissolve the surface of the upper protective layer. The cleaning method is characterized in that the burnt-on residue removal step is performed under a first condition in which a pulse that drives the electric heat conversion unit is applied a first number of times, and then performed under a second condition in which the pulse is applied a second number of times, which is fewer than the first number of times.

4. The cleaning method according to any one of claims 1 to 3, wherein when the number of pulses applied to drive the electric heat conversion unit exceeds a threshold, the conditions for the burnt-on grease removal process are switched from the first conditions to the second conditions.

5. The first condition is that a first voltage is applied, The cleaning method according to claim 1 or 3, wherein the second condition is to apply a second voltage greater than the first voltage.

6. The first condition is that the burnt-on charring process is executed each time a pulse is applied to drive the electric heat conversion unit a first number of times. The cleaning method according to claim 1 or 2, wherein the second condition is that the burnt-on residue removal step is performed each time the pulse is applied a second number of times, which is less than the first number of times.

7. The first condition is that the burnt-on charring process is performed by applying a first voltage each time a pulse that drives the electric heat conversion unit is applied a first number of times. The cleaning method according to claim 1, wherein the second condition is that the burnt-on residue removal step is performed by applying a second voltage greater than the first voltage each time the pulse is applied a second number of times, which is fewer than the first number of times.

8. The cleaning method according to any one of claims 1 to 3, wherein the upper protective layer is made of a material that does not form an oxide film that prevents the dissolution of the upper protective layer by heating of the electrothermal conversion unit.

9. The cleaning method according to any one of claims 1 to 3, wherein the upper protective layer is formed of a material containing Ir or Ru.

10. The cleaning method according to claim 1, wherein the first time and the second time are 30 seconds or more and 150 seconds or less.

11. The cleaning method according to claim 2, wherein the first voltage and the second voltage are 3V or more and 5V or less.

12. The first number of times and the second number of times are 2.5 × 10 ８ 6 x 10 times or more ９ The cleaning method according to claim 3, wherein the number of times is less than or equal to 3.

13. The cleaning method according to any one of claims 1 to 3, wherein the electric heat conversion unit is an element that generates energy for ejecting ink from the ejection port.

14. The cleaning method according to any one of claims 1 to 3, wherein the electric heat conversion unit is an element that generates pressure for the ink to circulate within the ink flow path.

15. An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized by having a changing means for switching the voltage applied for the electrochemical reaction from a first voltage to a second voltage greater than the first voltage when the identification result by the identification means is greater than or equal to a threshold.

16. An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized by having a changing means for switching the time for which voltage is applied for the electrochemical reaction from a first time to a second time that is longer than the first time, when the identification result by the identification means is greater than or equal to a threshold.

17. An inkjet head comprising: an ink ejection port for ejecting ink; an electrothermal conversion unit disposed in an ink channel communicating with the ejection port; an insulating protective layer for preventing contact between the electrothermal conversion unit and the ink in the ink channel; and an upper protective layer covering the portion of the protective layer heated by the electrothermal conversion unit. A counting means for counting the number of times a pulse is applied to drive the aforementioned electric heat conversion unit, An identification means for determining whether the number of times the application has been performed is equal to or greater than a threshold, An ink ejection device comprising, The upper protective layer is used as the anode electrode, and the portion that can conduct electricity to the upper protective layer via the ink is used as the cathode electrode, making it possible to dissolve the surface of the upper protective layer by an electrochemical reaction. An ink ejection device characterized in that, when the identification result by the identification means is greater than or equal to a threshold, the electrochemical reaction is switched from a first condition in which the reaction is performed each time the pulse is applied a first number of times, to a second condition in which the reaction is performed each time the pulse is applied a second number of times, which is greater than the first number of times.

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