Ink jet recording apparatus, discharge failure suppression method, and program

Abstract

To provide an inkjet recording apparatus capable of suppressing a discharge failure of a nozzle caused by ozone, a discharge failure suppression method, and a program.SOLUTION: An inkjet recording apparatus 1 includes an image forming apparatus 20 that forms an image by discharging ink from the nozzles N of an inkjet head 241 onto a recording medium P, and a control unit 50 that acquires information on degree of denaturation of the ink in the nozzles N and controls discharge operation of discharging the ink from the nozzles N in accordance with the acquired information.SELECTED DRAWING: Figure 8A

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording apparatus, a method for suppressing ejection defects, and a program. [Background technology]

[0002] 2. Description of the Related Art Conventionally, inkjet recording devices are known that form images by ejecting ink onto a recording medium from nozzles formed on a nozzle surface of an inkjet head.

[0003] In such inkjet recording devices, if foreign matter adheres to the nozzles, ejection defects can occur. Therefore, for example, Patent Document 1 describes an inkjet recording device that removes foreign matter by wiping the nozzle surface with a wiping blade.

[0004] Furthermore, one example of foreign matter that adheres to the nozzles is an organic acid salt formed when ozone generated inside the device reacts with ink. For example, Patent Document 2 describes an inkjet recording device that extends the time that the web is in contact with the nozzle surface during wiping maintenance, depending on the amount of ozone generated inside the device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-205625 [Patent Document 2] Patent Publication No. 2021-084226 Summary of the Invention [Problem to be solved by the invention]

[0006] However, foreign matter that causes ejection defects is not limited to being generated on the nozzle surface. Figure 9 is a graph showing the relationship between the number of standby days since the last image formation and the number of defective nozzles that have developed ejection defects, depending on the amount of ozone inside the device. In Figure 9, the horizontal axis shows the number of standby days, and the vertical axis shows the cumulative number of defective nozzles that have developed. Figure 9 shows that when ozone is generated inside the device, foreign matter will develop over time in nozzles that are not ejecting ink, causing them to become defective nozzles.

[0007] This phenomenon occurs when ink remaining in the nozzle is degraded by ozone, becoming foreign matter that adheres to the inside of the nozzle. Therefore, the inventions of Patent Documents 1 and 2, which wipe the nozzle surface, cannot prevent the degeneration of ink inside the nozzle and the occurrence of ejection defects.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an inkjet recording apparatus, a method for suppressing ejection defects, and a program for suppressing ejection defects in nozzles caused by ozone. [Means for solving the problem]

[0009] In order to solve the above problems, the invention described in claim 1 is an inkjet recording apparatus, an image forming apparatus that forms an image by ejecting ink from nozzles of an inkjet head onto a recording medium; an acquisition unit that acquires information related to the degree of modification of the ink in the nozzle; The ink ejection device further includes a control unit that controls a discharge operation for discharging the modified ink from the nozzles in accordance with the information acquired by the acquisition unit.

[0010] The invention described in claim 2 is the inkjet recording apparatus described in claim 1, an ink absorber that contacts the nozzle surface and absorbs the modified ink; As the discharging operation, the control unit controls the negative pressure in the nozzle to a second value that is smaller than a first value during image formation, and brings the nozzle surface into contact with the ink absorber.

[0011] The invention described in claim 3 is the inkjet recording apparatus described in claim 2, As the discharge operation, the control unit controls the negative pressure in the nozzle to a third value smaller than the second value and then to the second value, thereby bringing the nozzle surface into contact with the ink absorber.

[0012] The invention described in claim 4 is the inkjet recording apparatus described in claim 1, The control unit performs a discharge process of discharging the modified ink from the nozzle.

[0013] The invention described in claim 5 is the inkjet recording apparatus described in claim 1, the acquisition unit acquires the timing at which each of the plurality of nozzles last ejected ink; The control unit executes the discharge operation when the time since the nozzle last ejected ink exceeds a predetermined threshold.

[0014] The invention described in claim 6 is the inkjet recording apparatus according to any one of claims 1 to 4, the acquisition unit acquires an estimated value of the amount of ozone in the device; The control unit executes the cleaning operation before the estimated value exceeds a predetermined value.

[0015] The invention described in claim 7 is the inkjet recording apparatus described in claim 6, The acquisition unit acquires the estimated value based on an output value and a driving time of an ozone generation source.

[0016] The invention described in claim 8 is the inkjet recording apparatus described in claim 7, The source of the ozone is an ionizer that neutralizes the recording medium.

[0017] The invention described in claim 9 is the inkjet recording apparatus described in claim 8, The acquisition unit acquires the output value of the ionizer based on the type of recording medium or the temperature and humidity inside the device.

[0018] The invention described in claim 10 is the inkjet recording apparatus described in claim 8, The acquisition unit acquires an output value of the ionizer based on the amount of charge on the recording medium.

[0019] The invention described in claim 11 is the inkjet recording apparatus described in claim 7, The source of the ozone is a fixing unit that irradiates the recording medium with energy rays.

[0020] The invention described in claim 12 is the inkjet recording apparatus described in claim 11, the image forming device forms an image based on image data, The acquisition unit acquires an output value of the fixing unit based on the image data.

[0021] The invention described in claim 13 is the inkjet recording apparatus described in claim 6, The acquisition unit acquires the estimated value from an ozone sensor that detects the ozone concentration in the drawn air.

[0022] The invention described in claim 14 is the inkjet recording apparatus according to any one of claims 1 to 4, The ink is a UV ink.

[0023] The invention described in claim 15 is an image forming apparatus that records an image by ejecting ink from nozzles of an inkjet head onto a conveyed recording medium based on image data; a cleaning unit that cleans the inkjet head, an acquisition step of acquiring information relating to the degree of modification of the ink in the nozzle; and a removal step of controlling the cleaning operation by the cleaning unit in accordance with the results obtained in the obtaining step to remove the modified ink from inside the nozzles.

[0024] The invention described in claim 16 is a program, an image forming apparatus that records an image by ejecting ink from nozzles of an inkjet head onto a conveyed recording medium based on image data; a cleaning unit that cleans the inkjet head; an acquisition unit that acquires information related to the degree of modification of the ink in the nozzle; The cleaning operation by the cleaning unit is controlled in accordance with the results obtained by the obtaining unit, and the cleaning unit functions as a removal unit that removes modified ink from inside the nozzles. [Effects of the Invention]

[0025] According to the present invention, ejection defects in nozzles caused by ozone can be suppressed. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a side cross-sectional view of an inkjet recording apparatus. [Figure 2] FIG. 1 is a block diagram of an inkjet recording apparatus. [Figure 3] FIG. 2 is a bottom view showing the configuration of the head unit. [Figure 4] FIG. 10 is a diagram showing a carriage that moves in the width direction. [Figure 5] 10A and 10B are diagrams illustrating a movable range of the carriage in the width direction. [Figure 6A] FIG. 10 is a cross-sectional view of the cleaning unit during the discharging process. [Figure 6B] FIG. 10 is a cross-sectional view of the cleaning unit during a scraping operation. [Figure 7] 10 is a flowchart of an image forming process and an overflow process. [Figure 8A] FIG. 10 is an enlarged view of the nozzle surface near the nozzle during the overflow process. [Figure 8B] FIG. 10 is an enlarged view of the nozzle surface near the nozzle during the liquid absorption process after the overflow process. [Figure 9] 10 is a graph showing the relationship between the number of days in standby mode and the number of defective nozzles depending on the amount of ozone. DETAILED DESCRIPTION OF THE INVENTION

[0027] An inkjet recording apparatus according to an embodiment of the present invention will be described in detail below with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In the following description, components having the same functions and configurations will be given the same reference numerals and their description will be omitted.

[0028] [Overall configuration of inkjet recording device] Fig. 1 is a side cross-sectional view showing a schematic configuration of an inkjet recording apparatus 1. Fig. 2 is a block diagram showing a functional configuration of the inkjet recording apparatus 1. The inkjet recording apparatus 1 includes a paper feed device 10, an image forming device 20, a paper discharge device 30, a cleaning unit 40, and a control unit 50.

[0029] Under the control of the control unit 50, the inkjet recording device 1 forms an image by ejecting ink using the image forming device 20 onto the recording medium P conveyed from the paper feeder 10, and then ejects the recording medium P to the paper ejection device 30. Also, under the control of the control unit 50, the inkjet recording device 1 cleans the inkjet head 24a (see FIG. 3) of the image forming device 20 using the cleaning unit 40.

[0030] In the following description, the X direction, Y direction, and Z direction are the directions shown in Fig. 1. In addition, in the following description, the X direction, Y direction, and Z direction are also referred to as the width direction, conveyance direction, and height direction, respectively.

[0031] (Paper feeder) The paper feeding device 10 includes a paper feeding tray 11 and a paper feeding section 12. The paper feeding tray 11 stores recording media P. The paper feeding section 12 conveys the recording media P to the image forming device 20 under the control of the control section 50.

[0032] The recording medium P is not limited to paper such as plain paper or coated paper. Various media can be used as the recording medium P, such as fabric, polyester, and synthetic fiber, as long as the ink that lands on the surface can be fixed thereto. Also, while Fig. 1 shows an example of the paper feed device 10 having one paper feed tray 11, the present invention is not limited to this, and the paper feed device 10 may have multiple paper feed trays 11 that store multiple types of recording media P, respectively.

[0033] (Image forming device) {Body} Image forming apparatus 20 includes multiple types of cylinders 21 for transporting recording medium P. In this embodiment, the multiple types of cylinders 21 include A cylinder 21a, A cylinder hold-down roller 21b, recording medium hold-down roller 21c, and triple cylinder 21d. Cylinders 21 sandwich recording medium P to transport recording medium P in the transport direction.

[0034] The image forming apparatus 20 also includes a surface potential meter 22, an ionizer 23, a head unit 24, a fixing unit 25, an ozone sensor 26, a thermo-hygrometer 27, and a transport roller .

[0035] {Surface electrometer} The surface electrometer 22 is provided upstream in the transport direction from the ionizer 23. The surface electrometer 22 detects the surface potential of the recording medium P. The surface potential of the recording medium P detected by the surface electrometer 22 is sent to the control unit 50.

[0036] {Ionizer} The ionizer 23 is provided upstream in the transport direction from the head unit 24. Under the control of the control unit 50, the ionizer 23 blows an ion wind toward the recording medium P in an amount corresponding to the measurement result of the surface electrometer 22, thereby neutralizing the recording medium P.

[0037] If the recording medium P is charged, the ink repels the ink, making it easier for ink mist to adhere to the nozzle surface 241a (see FIG. 3). If the head unit 24 forms an image while ink mist remains on the nozzle surface 241a, image quality will be reduced due to deflected or missing droplets. In this embodiment, the recording medium P is neutralized by the ionizer 23, thereby reducing this risk.

[0038] {Head Unit} The head unit 24 forms an image on the recording medium P conveyed by the triple cylinder 21d. In this embodiment, the head unit 24 includes a plurality of inkjet heads 241, a head driving unit 242, and a carriage 24a.

[0039] Head unit 24 is positioned so that its nozzle openings are spaced a predetermined distance from the transport surface of triple-sized cylinder 21d. Head unit 24 supplies a drive signal to inkjet head 241 via head driver 242 at appropriate timing according to the rotation of triple-sized cylinder 21d, which holds recording medium P. Upon receiving the drive signal, inkjet head 241 ejects ink onto recording medium P from nozzle surface 241a, which is an ink ejection surface facing the transport surface of triple-sized cylinder 21d, to record an image.

[0040] In this embodiment, four head units 24 corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively, are arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transport direction.

[0041] Inkjet head 3 is a bottom view of the entire head unit 24, seen from the side facing the transport surface of the triple cylinder 21d. The head unit 24 of this embodiment is equipped with 16 inkjet heads 241. Each inkjet head 241 has a nozzle row made up of nozzles N arranged in the width direction on its nozzle surface 241a, which is its bottom surface. In addition, the nozzle surface 241a of the inkjet head 241 is coated with a water-repellent film, which is an organic film made of, for example, a fluorine-based resin.

[0042] The arrangement direction of the nozzles N in each inkjet head 241 is not limited to the width direction, but may be a direction intersecting the transport direction at an angle other than a right angle. Furthermore, the number of inkjet heads 241 provided in the head unit 24 is not limited to 16. The number of inkjet heads 241 may be changed as appropriate depending on the recording width of the image, etc.

[0043] <Head module> The 16 inkjet heads 241 are combined in pairs to form eight head modules 241M. The nozzle rows of each head module 241M are adjusted in the width direction so that the nozzle positions in the width direction do not overlap.

[0044] Each head module 241M fits into an opening provided in a support plate at the bottom of the carriage 24a. Each head module 241M is supported by the support plate with the nozzle surface 241a of the inkjet head 241 exposed from the bottom surface of the support plate. The eight head modules 241M are arranged in a staggered pattern to form a line head so that the range in which ink can be ejected from the nozzles N is continuously connected in the width direction.

[0045] The widthwise arrangement range of the nozzles N included in head unit 24 covers the width of the image recording area of ​​recording medium P transported by triple cylinder 21d. Head unit 24 is used in a fixed position when recording an image. Head unit 24 records an image by a single pass method by sequentially ejecting ink at predetermined intervals to different positions in the transport direction as recording medium P is transported.

[0046] The head unit 24 may record an image by a multi-pass method in which the nozzles N are arranged in a widthwise range that is shorter than the width of the image recording area and ink is ejected sequentially while moving in the widthwise direction.

[0047] The ink ejection mechanism for ejecting ink from each nozzle N is not particularly limited, but a piezo-type mechanism using a piezoelectric element can be used. Known piezo-type ink ejection mechanisms include shear mode and vent mode. A shear mode ink ejection mechanism ejects ink by varying the pressure of the ink in the pressure chamber by generating a shear mode type displacement in a piezoelectric element provided on the wall surface of a pressure chamber communicating with the nozzle N. A vent mode ink ejection mechanism ejects ink by varying the pressure of the ink in the pressure chamber by deforming a piezoelectric element fixed to a diaphragm that forms the wall surface of the pressure chamber.

[0048] The ink used to record images by the head unit 24 changes phase between a gel state and a sol state depending on, for example, the temperature. A gel state is a form of solid, and a sol state is a form of liquid. An example of such an ink composition is a composition primarily composed of a polymerizable compound and a photopolymerization initiator to which a few percent of a gelling agent has been added. When gel-state ink is heated and the temperature is increased, the viscosity begins to decrease significantly once the ink's inherent sol-state temperature (e.g., around 70°C) is exceeded, causing the ink to change phase to a sol-state. On the other hand, when the temperature of sol-state ink is decreased, the viscosity begins to increase significantly once the ink's inherent gel-state temperature (e.g., around 50°C) is reached, causing the ink to change phase to a gel-state.

[0049] The head unit 24 has an ink heating section (not shown) that heats the ink before it is supplied to the inkjet head 241 and the ink that has been supplied to the inkjet head 241. The inkjet head 241 ejects the ink that has been heated by the ink heating section and turned into a sol from the nozzles N. The ink that has been ejected from the nozzles N and landed on the recording medium P is cooled and quickly changes phase to a gel state.

[0050] The ink used in this embodiment is UV ink that hardens when exposed to ultraviolet light. That is, the ink used in this embodiment is cooled and gelled on the recording medium P, and then hardened by exposure to ultraviolet light in the fixing unit 25, thereby being fixed on the recording medium P.

[0051] <carriage> The carriage 24a carries multiple inkjet heads 241. The carriages 24a are provided so that they can move individually in the width direction. FIG. 4 is a diagram showing the carriage 24a moving in the width direction. FIG. 5 is a diagram showing the range of movement of the carriage 24a in the width direction. The carriage 24a moves in the width direction between the image recording position and the discharge maintenance position by a carriage movement unit 62, which will be described later, as shown in FIGS. 4 and 5.

[0052] The image recording position is the position where the nozzle surface 241a faces the transport surface of the triple cylinder 21d, and is the position of the carriage 24a when ink is ejected onto the recording medium P on the transport surface 21a to record an image.

[0053] The discharge maintenance position is a position where the nozzle surface 241a faces the ink receiving unit 41 of the cleaning unit 40, which will be described later. The discharge maintenance position is also the position of the carriage 24a when a discharge operation is performed to discharge ink from the nozzles N of the inkjet head 241. The discharge maintenance position is also a standby position where the carriage 24 is located except during image formation processing. The carriage 24a can be moved to the discharge maintenance position by lifting the carriage 24a from the image recording position and then moving it in the +X direction.

[0054] In the discharging operation, the control unit 50, as in the case of recording an image, varies the pressure of the ink in the pressure chamber communicating with the nozzle N to discharge the ink from the nozzle N. The discharging operation includes two processes: a discharge process and an overflow process. The discharging operation will be described in detail later.

[0055] <Head drive unit> The head driving unit 242 supplies a driving signal that deforms the piezoelectric element in accordance with the image data at an appropriate timing to the inkjet head 241. By this control, the head driving unit 242 causes the nozzle N of the inkjet head 241 to eject an amount of ink that corresponds to the pixel value of the image data.

[0056] {Fixing part} Returning to FIG. 1, the fixing unit 25 is provided downstream of the head unit 24 in the transport direction. The fixing unit 25 fixes the image formed on the recording medium P by the head unit 24. The fixing unit 25 is, for example, an energy beam irradiation unit. Specifically, the fixing unit 25 includes a light-emitting unit arranged across the width of the transport surface of the triple cylinder 21d. Under the control of the control unit 50, the light-emitting unit irradiates the transported paper P with energy beams such as ultraviolet rays. This hardens and fixes the ink on the recording medium P.

[0057] {Ozone sensor} The ozone sensor 26 has, for example, a pair of electrodes connected to a thin film conductor and a voltage applied between the electrodes. The ozone sensor 26 detects the ozone concentration in the air based on a change in resistance value that accompanies a change in electrical conductivity when ozone gas comes into contact with the thin film conductor, and sends the result to the control unit 50. Note that the ozone sensor 26 is not limited to the above configuration as long as it can measure the amount of ozone inside the image forming apparatus 20.

[0058] {Thermo-hygrometer} The thermo-hygrometer 27 includes a thermometer that measures the temperature and a hygrometer that measures the humidity inside the image forming apparatus 20. The thermo-hygrometer 27 transmits the measurement results to the control unit 50.

[0059] {Transport roller} Conveying roller 28 is provided downstream in the conveying direction from fixing unit 25. Conveying roller 28 conveys recording medium P, which has passed through head unit 24 and fixing unit 25 and been handed over from triple cylinder 21d, to paper discharge device 30.

[0060] (Paper output device) The paper discharge device 30 holds the recording medium P discharged from the image forming device 20 until the user collects it. The paper discharge device 30 includes a plate-shaped paper discharge tray 31. Note that the paper discharge device 30 may include multiple paper discharge trays 31, similar to the paper feed device 10. In this configuration, the paper discharge device 30 appropriately controls the storage destination of the recording medium P in accordance with instructions from the control unit 50 according to the image formation conditions of the image forming device 20.

[0061] (Cleaning section) The cleaning unit 40 prevents ejection defects by cleaning the nozzle surface 241a and the nozzles N of the inkjet head 241. The cleaning unit 40 is provided on the width direction side of the image forming device 20. The cleaning unit 40 includes an ink receiving unit 41, a scraping member 42, and an ink storage unit 43. The cleaning unit 40 also includes an ink absorber 44 that is separate from the ink receiving unit 41, the scraping member 42, and the ink storage unit 43.

[0062] {Ink receiving part} 6A is a cross-sectional view of cleaning unit 40 during discharge maintenance. Ink receiving unit 41 includes ink tub 411 having an inclined surface inclined relative to the horizontal plane. Ink tub 411 receives the ink discharged from nozzle N on the inclined surface. The material of ink tub 411 can be, for example, aluminum, but is not limited to this.

[0063] In this embodiment, a case where one ink tub 411 is provided in common for the four carriages 24a is illustrated, but this is not limiting. That is, a configuration in which one ink tub 411 is provided separately for each carriage 24a may also be used.

[0064] An outlet 411a into which ink flowing down the inclined surface flows is provided at the bottom of ink tub 411. Ink that drops (lands) on the inclined surface flows downward along the inclined surface due to gravity and flows into outlet 411a.

[0065] {Scraping member} A blade-shaped scraping member 42 is attached to the upper end of the side wall on the -X direction side of the ink tub 411. A total of four scraping members 42 are provided, one for each carriage 24a. However, this is not limiting, and a configuration in which one common scraping member 42 is provided for all four carriages 24a may also be used.

[0066] The length of the scraping member 42 in the transport direction is longer than the length of the nozzle surface 241a in the transport direction. The material of the scraping member 42 is not particularly limited, but may be, for example, various resins or metals. The scraping member 42 scrapes off and removes ink that has been discharged from the nozzles N and adhered to the nozzle surface 241a during discharge maintenance.

[0067] 6B is a diagram showing a cross section of the cleaning unit during the ink scraping operation by the scraping member 42. The upper tip of the scraping member 42 in the height direction is positioned so that it does not come into contact with the nozzle surface 241a but does come into contact with ink adhering to the nozzle surface 241a when the carriage 24a moves in the −X direction from the discharge maintenance position.

[0068] 6B, when the nozzle surface 241a moves in the −X direction together with the carriage 24a, the tip of the scraping member 42 approaches the nozzle surface 241a. Then, the ink scraped from the nozzle surface 241a flows from the tip of the scraping member 42 to the side surface. In other words, the scraping member 42 scrapes the ink off the nozzle surface 241a without coming into contact with the nozzle surface 241a.

[0069] A tray 421 is attached to the lower end of the scraping member 42. The tray 421 adjusts the drip position of the scraped ink. That is, the tray 421 allows the scraped ink scraped by the scraping member 42 to drip to a predetermined drip position and flow into the discharge port 411a.

[0070] {Ink storage section} As shown in FIGS. 6A and 6B, outlet 411a of ink tub 411 is connected to ink storage unit 43. Ink storage unit 43 stores the ink that has been received by ink tub 411 and flowed into outlet 411a. An ink amount detection unit 431 is provided at the bottom of ink storage unit 43. Ink amount detection unit 431 detects the amount of ink stored in ink storage unit 43 and sends the detected amount to control unit 50. Ink amount detection unit 431 is, for example, a load cell that detects the weight of the stored ink. Ink amount detection unit 431 is not limited to a load cell, and may be, for example, a liquid level sensor that detects the height of the ink liquid surface.

[0071] (ink absorber) The ink absorber 44 is disposed in a position where it comes into contact with the nozzle surface 241a when the carriage 24a returns from the discharge maintenance position to the recording position. By coming into contact with the nozzle surface 241a, the ink absorber 44 absorbs and removes from the nozzle surface 241a any ink that remains on the nozzle surface 241a without being scraped off by the scraping member 42. The material of the ink absorber 44 is not particularly limited, but may be, for example, a cloth or a sponge.

[0072] A detailed description of the method for cleaning the nozzle surface 241a and the nozzles N by the cleaning unit 40 will be given later.

[0073] (Control unit) 2, the control unit 50 is a processor that controls the overall operation of the inkjet recording apparatus 1. The control unit 50 includes a CPU (Central Processing Unit) 51, a RAM (Random Access Memory) 52, a ROM (Read Only Memory) 53, a storage unit 54, and the like.

[0074] {CPU} The CPU 51 reads out various control programs and setting data stored in the ROM 53, stores them in the RAM 52, and executes the programs to perform various arithmetic processing.

[0075] {RAM} The RAM 52 provides a working memory space for the CPU 51 and stores temporary data. The RAM 52 may include a non-volatile memory.

[0076] {ROM} The ROM 53 stores various control programs and setting data executed by the CPU 51. Note that the ROM 53 may be replaced by a rewritable nonvolatile memory such as a flash memory.

[0077] {Storage section} The storage unit 54 stores print jobs input from an external device via the communication unit 64 and image data of images to be recorded related to the print jobs. For example, an HDD (Hard Disk Drive) is used as the storage unit 54. Alternatively, a DRAM (Dynamic Random Access Memory) or the like may be used in combination with the storage unit 54.

[0078] <Transport drive unit> The transport drive unit 61 supplies a drive signal to the drive motor of the triple-sized cylinder 21d based on a control signal supplied from the control unit 50. Through this control, the transport drive unit 61 rotates the triple-sized cylinder 21d at a predetermined speed and timing. Furthermore, based on the control signal supplied from the control unit 50, the transport drive unit 61 supplies a drive signal to a motor for operating the medium supply unit 12, the transfer unit 22, and the delivery unit 26. Through this control, the transport drive unit 61 supplies the recording medium P to the triple-sized cylinder 21d and ejects it from the triple-sized cylinder 21d.

[0079] <Carriage moving part> The carriage moving unit 62 outputs drive signals to the motors and brakes of the moving mechanism that moves the carriage 24a up and down in the height direction or moves it in the width direction under the control of the control unit 50. Through this control, the carriage moving unit 62 moves the carriage 24a between the above-mentioned recording position and the discharge maintenance position.

[0080] {Operation display section} The operation display unit 63 displays the status of the inkjet recording apparatus 1, an operation menu, etc. in response to a control signal from the control unit 50. The operation display unit 63 also accepts user operations and outputs them to the control unit 50. The operation display unit 63 includes, for example, a liquid crystal display unit in which a touch sensor as an operation accepting means is provided superimposed on a display screen as a display means.

[0081] {Communications Department} The communication unit 64 is a communication interface that controls communication operations with external devices. The communication interface may include one or more devices compatible with various communication protocols, such as a LAN board or LAN card. The communication unit 64 acquires image data to be recorded from the external device under the control of the control unit 50. The communication unit 64 also transmits status information and the like to the external device.

[0082] {bus} The bus 65 is a path that electrically connects the above components and allows signals to be exchanged between them.

[0083] [Image formation processing, overflow processing] The image forming process including the ejection process and the overflow process performed by the image forming device 20 in the inkjet recording apparatus 1 described above will be described with reference to the flowchart of FIG.

[0084] The control unit 50 drives the ionizer 23 (step S101). The control unit 50 forms an image on the recording medium P fed from the paper feeder 10 using the image forming device 20 (step S102). The control unit 50 continues image formation for a predetermined time (step S103). When the predetermined time has elapsed (step S103; Yes), the control unit 50 stops image formation (step S104). Then, the control unit 50 causes the carriage moving unit 62 to move the carriage 24a to the discharge maintenance position. The control unit 50 also causes the head driving unit 242 to execute a discharge process that deforms the piezoelectric elements to discharge ink from all the nozzles N (step S105).

[0085] By performing this type of ejection process at predetermined time intervals, even if the ink inside the nozzle N is denatured by ozone, the denatured ink is ejected outside the nozzle N, reducing the concentration of the denatured ink inside the nozzle N. Therefore, it is possible to prevent foreign matter from forming inside a nozzle N that has not ejected ink for a long time, causing the nozzle to become defective.

[0086] The predetermined time is determined, for example, according to the amount of ozone inside the image forming device 20. For example, when the amount of ozone inside the image forming device 20 is large, the ink inside the nozzles N is more likely to be altered by the ozone. Therefore, when the amount of ozone inside the image forming device 20 is large, the control unit 50 shortens the predetermined time (by shortening the interval between performing the discharge process) to prevent the nozzles from becoming defective.

[0087] On the other hand, when the amount of ozone in the image forming apparatus 20 is small, the ink in the nozzles N is less likely to be altered by the ozone. Therefore, when the amount of ozone in the image forming apparatus 20 is small, the control unit 50 lengthens the predetermined time (by lengthening the interval between discharge processing) to suppress a decrease in productivity.

[0088] The control unit 50 can obtain the amount of ozone in the image forming apparatus 20, for example, from the ozone sensor 26. Alternatively, the control unit 50 can obtain the amount of ozone in the image forming apparatus 20 based on the output value and driving time of the ionizer 23 and the fixing unit 25, which are ozone generation sources.

[0089] More specifically, the control unit 50 can calculate the output value of the ionizer 23 based on, for example, the type of recording medium P and the measured values ​​of the surface electrometer 22 or the thermo-hygrometer 27. The control unit 50 can also calculate the output value of the fixing unit 25 based on, for example, image data including the coverage of the image formed in step S102.

[0090] Furthermore, although the ejection process is performed after the carriage 24a is moved to the ejection maintenance position, the present invention is not limited to this and may be performed outside the image formation area of ​​the recording medium P, for example.

[0091] The control unit 50 determines whether the print job has ended (step S106). If the print job has not ended (step S106; No), the process proceeds to step S102 and continues the image forming process. If the print job has ended (step S106; Yes), the control unit 50 determines whether a predetermined condition is met (step S107).

[0092] The predetermined condition is, for example, whether the amount of ozone in the image forming apparatus 20 is equal to or greater than a predetermined value. Alternatively, the predetermined condition is whether a predetermined time has elapsed since the previous overflow process was performed.

[0093] If the predetermined condition is not met (step S107; No), the process stops driving the inkjet recording apparatus 1. On the other hand, if the predetermined condition is met (step S107; Yes), the process executes overflow processing.

[0094] [Overflow processing] In the overflow process, the control unit 50 first controls the carriage movement unit 62 to move the carriage 24a to the discharge maintenance position (step S201). Then, the head drive unit 242 controls the negative pressure in the nozzles N to a third value Pp that is smaller than the first value Pi during image formation, thereby performing a purge process that causes the ink to overflow onto the nozzle surface 241a (step S202). This control dissolves or peels off the modified ink adhering to the nozzle surface 241a, as shown in FIG. 8A. Furthermore, the modified ink in the nozzles N overflows onto the nozzle surface 241a.

[0095] After a predetermined time has elapsed (step S203; Yes), the control unit 50 controls the head driving unit 242 to control the negative pressure inside the nozzle N to a second value Pm that is smaller than the first value Pi and larger than the third value Pp (step S204). After controlling the negative pressure inside the nozzle N, the control unit 50 controls the carriage moving unit 62 to press the nozzle surface 241a against the ink absorber 44 for a predetermined time to absorb the ink (step S205).

[0096] In step S205, because the negative pressure inside the nozzle N is set to the second value Pm in step S204, the ink absorber 44 can absorb the liquid with the meniscus lowered, as shown in Fig. 8B. Therefore, the modified ink that overflowed in step S202 and the modified ink that has dissolved or peeled off from the nozzle surface 241a can be reliably absorbed by the ink absorber 44.

[0097] After a predetermined time has elapsed (step S206; Yes), the control unit 50 causes the carriage movement unit 62 to move the carriage 24a away from the ink absorber 44 (step S207). The control unit 50 controls the negative pressure in the nozzle N to a fourth value Pb greater than the first value Pi by the head drive unit 242, thereby drawing ink into the nozzle N (step S208).

[0098] The control unit 50 causes the carriage moving unit 62 to press the carriage 24a against the ink absorber 44 again (step S209). This control ensures that the ink on the nozzle surface 241a that was not completely collected in step S205 can be wiped off.

[0099] After a predetermined time, the control unit 50 causes the carriage moving unit 62 to move the carriage 24a to the standby position above the ink receiving unit 41 (step S210), and ends the overflow process. [Example]

[0100] Next, the results of evaluation of preferred configurations of the present invention through various tests will be described. The present invention will be specifically described below using examples, but the present invention is not limited to these examples.

[0101] [Test 1. Conditions that make non-discharge nozzles prone to become defective nozzles] In an inkjet recording apparatus 1 such as that shown in Figure 1, continuous printing was performed by controlling so that only the K head unit 24 was ejected. After continuous printing, the nozzle surface 241a was wiped and then the inkjet recording apparatus 1 was turned off. Three days later, a predetermined impact position detection chart was printed on the M head unit 24 from which the adjacent Y and C head units 24 were not ejecting ink, and the amount of misalignment of the impact position of each nozzle N was measured. Nozzles N with an impact position misalignment of 21 μm or more were counted as defective nozzles.

[0102] In this series of steps, the conditions for continuous printing were varied and the number of defective nozzles that occurred was counted to verify the conditions under which defective nozzles are likely to occur. The continuous printing conditions that were varied were the type of recording medium P, the temperature and humidity of the inkjet recording device 1, the image coverage, the continuous printing time, the ON / OFF state of the ionizer 23 that generates ozone, and the frequency of the spit-out process during printing. The evaluation was also carried out with an A rating if the number of defective nozzles that occurred was less than 10, a C rating if it was 50 or more, and a B rating if it was 10 or more but less than 50.

[0103] The results of the tests are shown in Table I.

[0104] [Table 1]

[0105] The results in Table I show that the likelihood of defective nozzles occurring varies depending on the type of recording medium P. Specifically, when the recording medium P is PFA (thermoplastic resin), defective nozzles are more likely to occur than when the recording medium P has an OK top coat. This is because PFA is easily charged, which increases the output of the ionizer 23 and increases the amount of ozone inside the image forming apparatus 20.

[0106] It can also be seen that the likelihood of defective nozzles occurring varies depending on the environment (temperature and humidity) inside the image forming apparatus 20. Specifically, when the temperature and humidity inside the image forming apparatus 20 are low, defective nozzles are more likely to occur. This is because the recording medium P is more likely to become charged, which in turn increases the amount of ozone inside the image forming apparatus 20. Furthermore, when the humidity inside the inkjet recording apparatus 1 is particularly low, ozone is less likely to be deactivated, and the ozone from the recording medium P passes into the nozzles N.

[0107] It can also be seen that the likelihood of defective nozzles occurring varies depending on the image coverage. Specifically, when the image coverage is high, defective nozzles are more likely to occur. This is because the irradiation amount of the fixing unit 25 increases, and the amount of ozone inside the image forming apparatus 20 also increases.

[0108] It can also be seen that the likelihood of defective nozzles occurring varies depending on the continuous printing time. Specifically, the longer the continuous printing time, the more likely defective nozzles are to occur. This is because the driving time of the ionizer 23 also becomes longer, increasing the amount of ozone inside the image forming device 20.

[0109] It can also be seen that the likelihood of defective nozzles occurring varies depending on the frequency with which the ejection process is performed. Specifically, when the ejection process is performed less frequently (or not at all), defective nozzles are more likely to occur. This is because the proportion of denatured ink in the nozzles N is more likely to increase, making it easier for foreign matter to form.

[0110] From the above, for example, when the recording medium P is PFA, when the image forming device 20 is in a low temperature and low humidity environment, when a high coverage image is formed, or when the continuous printing time is long, it is preferable to increase the frequency of the discharge process or the overflow process.

[0111] It can also be seen that even if the output of the ozone generation source is off, ozone is generated inside the image forming apparatus 20 under conditions that result in a large amount of ozone being generated.

[0112] [Test 2. Effect of overflow treatment] In an inkjet recording apparatus 1 such as that shown in Figure 1, continuous printing was performed by controlling the head units 24 that ejected Y, C, and K inks to eject only. After the continuous printing, maintenance was performed by adjusting the negative pressure in the nozzles N from -0.5 kPa (normal) to wipe the nozzle surfaces 241a, and then the inkjet recording apparatus 1 was turned off. Then, three days later, the number of defective nozzles in the M head unit 24 from which the adjacent Y and C head units 24 had ejected ink was counted.

[0113] In this series of steps, the number of defective nozzles that occurred was evaluated by changing the continuous printing time and the operation of the negative pressure inside nozzle N. The operation of the negative pressure inside nozzle N was performed in the following ways: no operation (remaining at -0.5 kPa), 0 kPa, and 0.5 kPa → 0 kPa (overflow processing).

[0114] The results of the tests are shown in Table II.

[0115] [Table 2]

[0116] As noted in Table I, when the continuous printing time is long, the driving time of the ionizer 23 becomes longer, making it more likely that a defective nozzle will occur. When the continuous printing time is short and the concentration of the modified ink in nozzle N is low, simply changing the negative pressure in nozzle N from a first value (-0.5 kPa) to a second value (0 kPa) smaller than the first value is sufficient to cause the modified ink in nozzle N to overflow. On the other hand, when the continuous printing time is long and the concentration of the modified ink in nozzle N is high, it is clear that the modified ink in nozzle N will not overflow sufficiently unless the negative pressure in nozzle N is changed from the first value to a third value (0.5 kPa) smaller than the second value, and then changed back to the second value.

[0117] [Effects of the embodiment] As described above, the inkjet recording apparatus 1 according to this embodiment includes an image forming device 20 that ejects ink from the nozzles N of the inkjet head 241 onto a recording medium P to record an image. The inkjet recording apparatus 1 also includes a control unit 50 that functions as an acquisition unit that acquires information related to the degree of modification of the ink in the nozzles N. The control unit 50 then controls the cleaning operation of the cleaning unit 40 in accordance with the acquired information to remove the modified ink from the inkjet head 241. This configuration can reliably suppress ejection defects caused by ozone.

[0118] Although the above describes an example in which a hard disk or a semiconductor nonvolatile memory is used as a computer-readable medium for the program according to the present invention, the present invention is not limited to this example. Other computer-readable media include portable recording media such as CD-ROMs. Furthermore, a carrier wave can also be used as a medium for providing the program data according to the present invention via a communication line. [Explanation of symbols]

[0119] 1. Inkjet recording device 20 Image forming device 23 Ionizer 241 Inkjet head 241a Nozzle surface 25 Fixing section 26 Ozone Sensor 40 Cleaning Section 41 Ink receiving section 44 Ink absorber 50 Control unit (acquisition unit) P Recording medium N nozzle

Claims

1. an image forming apparatus that forms an image by ejecting ink from nozzles of an inkjet head onto a recording medium; an acquisition unit that acquires information related to the degree of modification of the ink in the nozzle; An inkjet recording apparatus comprising: a control unit that controls a discharge operation for discharging modified ink from the nozzles in accordance with the information acquired by the acquisition unit.

2. an ink absorber that contacts the nozzle surface and absorbs the modified ink; The inkjet recording apparatus according to claim 1 , wherein the control unit controls the negative pressure in the nozzle to a second value smaller than the first value during image formation as the discharge operation, thereby bringing the nozzle surface into contact with the ink absorber.

3. The inkjet recording device according to claim 2, wherein the control unit controls the negative pressure in the nozzle to a third value smaller than the second value and then to the second value as the discharge operation, thereby bringing the nozzle surface into contact with the ink absorber.

4. The inkjet recording apparatus according to claim 1 , wherein the control unit performs a discharge process of discharging the modified ink from the nozzles as the discharge operation.

5. the acquisition unit acquires the timing at which each of the plurality of nozzles last ejected ink; The inkjet recording apparatus according to claim 1 , wherein the control unit executes the discharging operation when the time since the nozzle last ejected ink exceeds a predetermined threshold value.

6. the acquisition unit acquires an estimated value of the amount of ozone in the device; The inkjet recording apparatus according to claim 1 , wherein the control unit executes the discharging operation when the estimated value exceeds a predetermined value.

7. The inkjet recording apparatus according to claim 6 , wherein the acquisition unit acquires the estimated value based on an output value and a driving time of an ozone generating source.

8. 8. The inkjet recording apparatus according to claim 7, wherein the ozone generating source is an ionizer that neutralizes the recording medium.

9. The inkjet recording apparatus according to claim 8 , wherein the acquisition unit acquires the output value of the ionizer based on the type of recording medium or the temperature and humidity inside the apparatus.

10. The inkjet recording apparatus according to claim 8 , wherein the acquisition unit acquires the output value of the ionizer based on the amount of charge on the recording medium.

11. 8. The inkjet recording apparatus according to claim 7, wherein the ozone generation source is a fixing unit that irradiates the recording medium with energy rays.

12. the image forming device forms an image based on image data, The inkjet recording apparatus according to claim 11 , wherein the acquisition unit acquires the output value of the fixing unit based on the image data.

13. The inkjet recording apparatus according to claim 6 , wherein the acquisition unit acquires the estimated value from an ozone sensor that detects the ozone concentration in the sucked air.

14. 5. The inkjet recording apparatus according to claim 1, wherein the ink is a UV ink.

15. 1. A method for suppressing ejection defects in an inkjet recording apparatus having an image forming apparatus that records an image by ejecting ink from nozzles of an inkjet head onto a recording medium, comprising: an acquisition step of acquiring information relating to the degree of modification of the ink in the nozzle; a discharging step of discharging ink from the nozzles in accordance with the information acquired in the acquiring step.

16. A computer for an inkjet recording device that includes an image forming device that records an image by ejecting ink from the nozzles of an inkjet head onto a recording medium, an acquisition unit that acquires information related to the degree of modification of the ink in the nozzle; a program that functions as a control unit that controls a discharge operation that causes ink to be discharged from the nozzles in accordance with the information acquired by the acquisition unit;

Images