JP4854276B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by discharging a recording liquid.

  As an image forming apparatus such as a printer, a facsimile, a copying apparatus, and a multifunction machine of these, for example, an ink jet recording apparatus is known. The ink jet recording apparatus is a recording medium such as recording paper (hereinafter referred to as “paper”) from the recording head, but the material is not limited to paper, and is also referred to as recording medium, transfer paper, transfer material, recording material, and the like. Recording is performed by ejecting ink droplets as recording liquid droplets (image formation, printing, printing, printing, etc. are also synonymous), and high-definition images are recorded at high speed. Therefore, there are advantages that the running cost is low, the noise is low, and it is easy to record a color image using multi-color ink.

  In general, the properties required for recording liquids (inks) for ink jet recording include colorant, image density, and bleeding for achieving high image quality, and the stability of dissolution or dispersion of the colorant in the ink for achieving reliability. Water resistance, light resistance, etc. to ensure the storage stability of recorded images, such as stability, storage stability, ejection stability, etc., and quick drying of ink to achieve high speed, etc. Various attempts have been made so far to satisfy the requirements. For example, as an ink colorant, dye ink was mainly used at first because of its good color development and high reliability. However, recently, recorded images have light resistance and water resistance. Therefore, an ink composition using a pigment such as carbon black is being used.

  On the other hand, in order to achieve high image quality and high-speed printing, ink droplets have recently been trending down, and the nozzle diameter is also in the direction of decreasing the diameter.

  Therefore, it is quite difficult to ensure ejection stability when a pigment is used as a colorant and a recording head with a reduced nozzle diameter is used, and many attempts have been made so far to achieve compatibility with other ink characteristics. However, the current situation is that no sufficient measures have been taken.

With respect to conventional recording liquids, in order to improve the reliability of the image forming apparatus, the direction in which the increase in viscosity is suppressed as much as possible has been studied. For example, Patent Document 1 discloses that the change in viscosity when the ink is concentrated twice is within 10 times and the change in particle diameter is within 3 times, and Patent Document 2 describes the residual after evaporation of the volatile components in the ink. Ink whose liquid is a liquid and whose viscosity is within 10 times the initial viscosity is disclosed in Patent Document 3 in which the ink viscosity when evaporated in a 60 ° C. environment is 600 times or less of the viscosity before evaporation. In Japanese Patent Application Laid-Open No. H10-228707, a high-viscosity ink (5 to 15 mPa · s) is necessary to ensure high image quality, and the initial evaporation rate is adjusted to ensure reliability, and It is described that a specific compound is added as a viscosity modifier for adjusting the viscosity.
JP 2002-337449 A JP 2000-095983 A Japanese Patent Laid-Open No. 9-111166 JP 2001-262025 A

  However, it is difficult to form a high-quality image on plain paper with the ink of Patent Document 1, and the ink of Patent Document 2 is a dye ink, and although the reliability is high, the image quality on plain paper is still insufficient. The ink of Patent Document 3 is also a dye ink, and by adding a water-soluble polymer, the ink reliability and the durability of the image quality are balanced, but there remains a problem in water resistance, and Patent Document In the ink No. 4, there is no disclosure about the stability of the particle size of the pigment to be used. Therefore, although it is said that there is reliability after being left for 24 hours, depending on the configuration of the head to be ejected and the size of the nozzle diameter, it is left for a longer period of time. The ink formulation is inferior in reliability.

  As described above, in order to ensure high-speed and high-quality printing quality, it is necessary to use high-viscosity ink. However, it is difficult to ensure the reliability of high-viscosity ink, and it is difficult to use it. It's real.

Accordingly, the present applicant includes at least a colorant, a wetting agent, and a permeability improver that are dispersed in water, and the rate of increase in viscosity (mPa · s /%) accompanying water evaporation is up to a water evaporation rate of 30% with respect to the total weight of the ink. It is proposed to use an ink that has a point that the viscosity increase rate exceeds 50 between 1.0 and 1.0 and a water evaporation rate of 30 to 45%.
JP 2005-170035 A

  By prescribing the recording liquid (ink) in this way, nozzle clogging does not occur even when left for a long time, and high image quality and high-speed printing on plain paper can be achieved. This recording liquid is easy to maintain and recover, because even if the recording liquid in the nozzle is dried and thickened, it cannot be ejected from the nozzle, so the pigment does not become coarse particles and nozzle clogging occurs. It has the advantage that it can be easily recovered by operation.

  On the other hand, in an ink jet recording apparatus, a maintenance and recovery mechanism for maintaining and recovering the reliability of the recording head is indispensable. In this maintenance and recovery mechanism, foreign matter such as thickened or dried ink, dust, or dust adheres to the outer surface of the nozzle of the head, causing the nozzle to become clogged, or to generate an air damper phenomenon due to generation of bubbles inside the nozzle. In order to prevent the occurrence of normal discharge due to the occurrence of the above, a cap (cap member) that seals the nozzle surface of the recording head is provided. Furthermore, the operation of sucking ink filled in the head from the nozzle by a suction means such as a suction pump communicating with the cap (head suction or nozzle suction), by a wiper blade using an elastic member such as rubber A wiping operation on the head surface, an idle ejection operation (or also referred to as a preliminary ejection operation) for ejecting ink so as not to contribute to image formation, and ejecting thickened ink or mixed color ink in the nozzle hole and in the vicinity of the entrance. In combination, the operation of removing bubbles, thickened ink, adhering dust, etc. in the liquid chamber and maintaining a state where stable droplet discharge can be performed is performed.

Regarding the recovery operation by such a maintenance recovery mechanism, Patent Document 6 predicts the state of bubbles inside the recording head from the number of printed sheets, and performs preliminary ejection based on the standing time after printing and the count value of the number of printed sheets. It is described to change the number of drops when doing.
JP 09-193415 A

  By the way, as described above, it contains at least a colorant and a wetting agent that are dispersed in water, and the water evaporation rate increases rapidly between 30 to 45% of the initial weight ratio (viscosity increase rate (mPa · s /%)). In the case of using a recording liquid formulated so as to exceed 50), the nozzle omission (discharge failure) that occurs when the nozzle is clogged with dye precipitates or pigment solids that have become unstable in dispersion, Although a remarkable improvement effect has been confirmed, a new problem has been clarified that can not occur in the conventional recording liquid because of its evaporation rate-viscosity characteristics.

  That is, the phenomenon that the recording liquid adhering and remaining in the suction cap by performing a maintenance and recovery operation such as cleaning deprives moisture from the nozzles of the head and causes defective ejection has become apparent.

  More specifically, the maintenance / recovery mechanism includes a suction cap for capping the nozzle surface of the recording head and sucking and discharging the recording liquid from the nozzle as described above. The recording liquid discharged and remaining in the suction cap is dried according to the installation environment of the ink jet recording apparatus, and when the recording head is capped with the suction cap in such a state, the recording liquid is in a dry state. On the contrary, a certain recording liquid deprives moisture from the recording liquid in the nozzle, and the recording liquid in the nozzle of the recording head deprives moisture, causing a sudden increase in viscosity, resulting in a thickening of the recording liquid in the nozzle. This causes clogging and discharge failure.

  Then, when a maintenance / recovery mechanism is adopted in which the suction cap is shared by a plurality of recording heads and the other recording heads are moisturizing caps (protective caps), the recording heads are capped with the suction caps. Since the degree of drying of the recording liquid in the nozzle is different between the recording head capped with the moisture retention cap and before the printing operation, the recording liquid is discharged before the printing operation (a certain amount of recording liquid is discharged from the nozzle to the non-printing area). Even if a recovery operation such as (operation) is performed, there is a problem that an appropriate recovery operation cannot be performed on the recording head capped with the suction cap.

  The present invention has been made in view of the above-described problems, and effectively prevents ejection failure due to moisture absorption of the recording liquid in the nozzle by the residual recording liquid in the suction cap without wasteful recording liquid consumption. An object is to provide an image forming apparatus.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of recording heads having nozzles for discharging recording liquid droplets, a moisture retaining cap for preventing drying of the nozzle surface of the recording head, and a moisture retaining cap, and the nozzle surface of the recording head is capped. In an image forming apparatus comprising a maintenance recovery mechanism including a suction cap for sucking a recording liquid from the nozzle in a state, and forming an image on a recording medium by discharging droplets from the nozzle of the recording head.
Control means for controlling a recovery operation for the recording head,
The control means includes
The elapsed time after performing the recovery operation by the idle ejection for ejecting the droplets that are not involved in the recording last for all the recording heads is a predetermined predetermined value in which the residual recording liquid in the suction cap becomes dry of until passage of time, the row Align the recovery operation in the same recovery condition for a recording head is capped by the recording head and the suction cap to be capped by the moisturizing cap,
After the predetermined time has elapsed, the recovery condition of the recovery operation for the recording head capped by the suction cap is made stronger than the recovery condition of the recovery operation for the recording head capped by the moisturizing cap. It was set as the structure which performs operation | movement .

The image forming apparatus according to the present invention includes a control unit that controls a recovery operation for the recording head, and the control unit performs a recovery operation by idle discharge that discharges droplets that are not involved in recording for all the recording heads at the end. The elapsed recording time after capping is capped with a recording head and a suction cap that are capped with a moisturizing cap until the predetermined recording time in which the residual recording liquid in the suction cap becomes dry has elapsed. that line Align the recovery operation in the same recovery condition for the recording head, after the lapse of a predetermined time, a recovery condition of the recovery operation for the recording head is capped by the suction cap, the recording head is capped with the cap moisturizing since a configuration in which to perform the recovery operation in the more powerful than the recovery condition of the recovery operation, and the the moisture cap and the coercive moisturizing If the suction cap is equipped with a moisturizing cap, the recovery operation can be performed under appropriate recovery conditions for the recording head capped with the suction cap, and suction can be performed without wasteful recording liquid consumption. It is possible to effectively prevent ejection failure due to moisture absorption of the recording liquid in the nozzle due to the residual recording liquid in the cap.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory perspective view of the image forming apparatus as an example of the image forming apparatus according to the present invention as viewed from the front side.
The image forming apparatus includes an apparatus main body 1, a paper feed tray 2 for loading paper loaded in the apparatus main body 1, and a sheet on which an image is recorded (formed) by being detachably mounted on the apparatus main body 1. A paper discharge tray 3 for stocking is provided. Further, a cartridge loading for loading an ink cartridge that protrudes from the front surface to the front side of the apparatus main body 1 and is lower than the upper surface is provided at one end side of the front surface of the apparatus main body 1 (side of the paper supply / discharge tray section) The cartridge loading unit 4 has an operation / display unit 5 provided with operation buttons and a display.

  The cartridge loading unit 4 includes a plurality of recording liquid cartridges that contain recording liquids (inks) of different colors, for example, black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink. Ink cartridges 10k, 10c, 10m, and 10y (referred to as “ink cartridge 10” when colors are not distinguished) are inserted from the front side to the rear side of the apparatus main body 1 and can be loaded. A front cover (cartridge cover) 6 that is opened when the ink cartridge 10 is attached or detached is provided on the front side of the unit 4 so as to be openable and closable.

  Further, the operation / display unit 5 has the remaining amounts of the ink cartridges 10k, 10c, 10m, and 10y of each color at the arrangement positions corresponding to the mounting positions (arrangement positions) of the ink cartridges 10k, 10c, 10m, and 10y of each color. The remaining amount display portions 11k, 11c, 11m, and 11y for each color for displaying the near end and the end are arranged. Further, the operation / display unit 5 is also provided with a power button 12, a paper feed / print resume button 13, and a cancel button 14.

Next, the mechanism of the image forming apparatus will be described with reference to FIGS. FIG. 2 is a schematic configuration diagram for explaining the overall configuration of the mechanism unit, and FIG. 3 is a plan view for explaining a main part of the mechanism unit.
A guide rod 21, which is a guide member placed horizontally between left and right side plates (not shown), and a stay 22 hold the carriage 23 slidably in the main scanning direction, and is driven between the driving pulley 25 and the driven pulley 26 by the main scanning motor 24. 3 moves and scans in the direction indicated by the arrow (carriage scanning direction: main scanning direction) in FIG.

  The carriage 23 has recording heads 31k, 31c, 31m, and 31y (distinguishable) composed of droplet ejection heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). If not, it is referred to as “recording head 31”). A plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward.

  As an ink jet head constituting the recording head 31, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. It is possible to use a shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like provided as pressure generating means for generating a pressure for discharging a droplet. In addition, the inkjet head has a configuration in which a plurality of nozzle rows are arranged and a plurality of nozzle rows are arranged, and droplets of the same color are ejected from each nozzle row. Also good.

  The carriage 23 is equipped with a sub tank 32 for each color for supplying each color ink to the recording head 31. Each color sub-tank 32 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 4 via the ink supply tube of each color.

  On the other hand, as a sheet feeding unit that is a feeding unit for feeding the sheets 42 stacked on the sheet stacking unit (pressure plate) 41 of the sheet feeding tray 2, the sheets 42 are separated and fed one by one from the sheet stacking unit 41. A half paddle (feed roller) 43 and a separation pad 44 made of a material having a large friction coefficient are provided opposite to the half-moon roller (sheet feed roller) 43, and the separation pad 44 is urged toward the sheet feed roller 43 side.

  In order to feed the sheet 42 fed from the sheet feeding unit to the lower side of the recording head 31, a guide member 45 for guiding the sheet 42, a counter roller 46, a transport guide member 47, and a tip pressure roller. And a holding belt 48 which is a conveying means for electrostatically attracting the fed paper 42 and conveying it at a position facing the recording head 31.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 and circulate in the belt transport direction (sub-scanning direction). This transport belt 51 is, for example, a surface layer that is a sheet adsorbing surface formed of a pure resin material having a thickness of about 40 μm that is not subjected to resistance control, such as ETFE pure material, and resistance control by carbon with the same material as this surface layer. And a back layer (medium resistance layer, ground layer).

  A charging roller 56 is provided as charging means for charging the surface of the conveyor belt 51. The charging roller 56 is disposed so as to come into contact with the surface layer of the conveyor belt 51 and to be rotated by the rotation of the conveyor belt 51, and applies a predetermined pressing force to both ends of the shaft as a pressing force. The transport roller 52 also functions as an earth roller, and is in contact with the middle resistance layer (back layer) of the transport belt 51 and is grounded.

  In addition, a guide member 57 is disposed on the back side of the conveyance belt 51 so as to correspond to a printing area by the recording head 31. The guide member 57 has an upper surface that protrudes toward the recording head 35 from the tangent line of two rollers (the conveyance roller 52 and the tension roller 53) that support the conveyance belt 51, thereby maintaining high-precision flatness of the conveyance belt 51. Like to do.

  The conveyance belt 51 rotates in the belt conveyance direction (sub-scanning direction) in FIG. 3 when the conveyance roller 52 is rotationally driven by the sub-scanning motor 58 via the drive belt 59 and the pulley 60.

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 31, a separation claw 61 for separating the paper 42 from the conveyance belt 51, a paper discharge roller 62, and a paper discharge roller 63 are provided. The paper discharge tray 3 is provided below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the conveyance belt 51, reverses it, and feeds it again between the counter roller 46 and the conveyance belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, as shown in FIG. 3, a maintenance / recovery mechanism 81 including a recovery means for maintaining and recovering the nozzle state of the recording head 31 is arranged in the non-printing area on one side of the carriage 23 in the scanning direction. Yes.

  The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a to 82d (hereinafter referred to as “caps 82” when not distinguished from each other) for capping the nozzle surfaces of the recording head 31, and nozzle surfaces. A wiper blade 83 that is a blade member for wiping the ink, and an empty discharge receiver 84 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing. Here, the cap 82a is a sucking and moisturizing cap (hereinafter referred to as "suction cap"), and the other caps 82b to 82d are moisturizing caps.

  Further, in the non-printing area on the other side of the carriage 23 in the scanning direction, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 88 is arranged, and the idle discharge receiver 88 is provided with openings 89 a to 89 d along the nozzle row direction of the recording head 31.

  In the ink jet recording apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide 45, and the transport belt 51 and the counter roller 46, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the tip pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive voltage and a negative output are alternately repeated from the AC bias supply unit to the charging roller 56 by a control unit (not shown), that is, an alternating voltage is applied, and the conveying belt 51 alternates. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. When the paper 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 51.

  Therefore, by driving the recording head 31 according to the image signal while moving the carriage 23, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3.

  During printing (recording) standby, the carriage 23 is moved to the maintenance / recovery mechanism 81 side, the recording head 31 is capped by the cap 82, and the nozzles are kept in a wet state to prevent ejection failure due to ink drying. . Further, the recording liquid is sucked from the nozzle by a suction pump (not shown) with the recording head 31 capped by the cap 82 (referred to as “nozzle suction” or “head suction”), and the thickened recording liquid and bubbles are discharged. Perform recovery action. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 31 is maintained.

  Next, an example of a droplet discharge head constituting the recording head in this image forming apparatus will be described with reference to FIGS. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the head, and FIG. 5 is a cross-sectional explanatory view of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  The droplet discharge head includes a flow channel plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by nickel electroforming, for example, bonded to the lower surface of the flow channel plate 101, and a flow plate. A nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and a nozzle communication path 105, a liquid chamber 106, and a liquid chamber, which are channels through which the nozzles 104 that discharge liquid droplets (ink droplets) communicate with each other. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to 106 is formed.

  In addition, two rows (only one row is shown in FIG. 6) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support.

  Further, an FPC cable 126 for connecting to a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, Although a recess or a hole serving as the liquid chamber 106 is formed, the invention is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the support post 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer. The surface of the nozzle plate 103 is the nozzle surface 31a described above.

  The piezoelectric element 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121 alternately. In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the droplet discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, the ink flows into the liquid chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the direction of the nozzle 104 to change the volume of the liquid chamber 106. / By contracting the volume, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected (jetted) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. The recording liquid is filled in 106. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (drawing-pushing), and striking or pushing can be performed depending on the direction of the drive waveform.

Next, an outline of the maintenance / recovery mechanism 81 will be described with reference to FIG. This figure is a schematic explanatory view showing the maintenance and recovery mechanism partially expanded.
As described above, the maintenance / recovery mechanism 81 includes a cap holder 201A including a holding mechanism for holding the suction and moisturizing cap 82a and the moisturizing cap 82b, and a holding mechanism for holding the moisturizing cap 82c and the moisturizing cap 82d. , A blade holder 203 that holds a wiper blade 83 that is a blade made of an elastic body for cleaning (wiping) the nozzle surface 31a of the recording head 31, and a liquid that does not contribute to printing from the recording head 31. An empty discharge receiver 84 for performing an empty discharge operation (preliminary discharge operation) for discharging droplets is disposed.

  Here, a tubing pump (suction pump) 211 serving as a suction means is connected to the suction and moisture retention cap 82a closest to the print area via a flexible tube 210. Therefore, when performing the maintenance recovery operation of the recording head 31, the recording head 31 performing the recovery operation is selectively moved to a position where it can be capped by the cap 82a. The suction and moisturizing cap 82a is provided with a moisturizing member (not shown) to increase the threshold, which will be described later, when performing the maintenance / recovery operation according to the present invention. The printing standby time associated with wasteful consumption of the recording liquid and recovery operation can be shortened.

  A cam shaft 213 rotatably supported by the frame 212 is disposed below the cap holders 201A and 201B, and cap cams 214A and 214B for raising and lowering the cap holders 201A and 201B are disposed on the cam shaft 213. And a wiper cam 215 for moving the blade holder 203 up and down.

  In order to rotationally drive the tubing pump 211 and the cam shaft 213, the motor gear 222 provided on the motor shaft 221a is rotated with the pump gear 223 provided on the pump shaft 211a of the tubing pump 211, and the pump gear is further rotated. An intermediate gear 226 with a one-way clutch 227 is meshed with an intermediate gear 224 integral with the intermediate gear 225, and the intermediate gear 228 coaxial with the intermediate gear 226 is fixed to the camshaft 213 via the intermediate gear 229. The cam gear 230 is engaged.

  In the maintenance / recovery mechanism 81, when the motor 221 rotates forward, the motor gear 222, the intermediate gear 224, the pump gear 223, the intermediate gears 225 and 226 rotate, and the shaft 211a of the tubing pump 211 rotates to rotate the tubing pump 211. Is activated to suck the inside of the suction cap 82a (this operation is referred to as “in-cap suction” or “head suction”). Since the other gears 228 and thereafter are blocked by the one-way clutch 227, they do not rotate (activate).

  Further, since the one-way clutch 227 is connected by the reverse rotation of the motor 221, the rotation of the motor 221 is transferred to the cam gear 230 via the motor gear 222, the intermediate gear 224, the pump gear 223, the intermediate gears 225, 226, 228, and 229. As a result, the cam shaft 213 rotates. At this time, the tubing pump 211 has a structure that does not operate by reversing the pump shaft 211a. With the rotation of the cam shaft 213, the cap cams 214A and 214B and the wiper cam 215 are raised and lowered at predetermined timings, respectively.

  When cleaning the nozzle surface 31 a of the recording head 31, the wiper blade 83 is raised and the recording head 31 is moved relative to the wiper blade 83 to wipe the nozzle surface 31 a.

Next, an adjustment example of ink (recording liquid, hereinafter referred to as “main ink”) used in the image forming apparatus will be described. However, the present invention is not limited to this.
<Production Example 1 ink>
(Black ink)
KM-9036 (Toyo Ink) (self-dispersing pigment) 50% by weight
Glycerin 10% by weight
1,3-butanediol 15% by weight
2-ethyl-1,3-hexanediol 2% by weight
2-pyrrolidone 2% by weight
Surfactant (1-9) 1% by weight
Silicone defoamer KS508 (Shin-Etsu Chemical) 0.1% by weight
Residual amount of ion-exchanged water An ink composition having the above formulation was prepared and sufficiently stirred at room temperature, and then filtered through a membrane filter having an average pore diameter of 1.2 μm to obtain an ink of Production Example 1.

<Production Example 2 ink>
(Preparation of polymer solution A)
After sufficiently replacing nitrogen gas in the 1 L flask equipped with a mechanical stirrer, thermometer, nitrogen gas introduction tube, reflux tube and dropping funnel, 11.2 g of styrene, 2.8 g of acrylic acid, 12.0 g of lauryl methacrylate, Polyethylene glycol methacrylate 4.0 g, styrene macromer 4.0 g and mercaptoethanol 0.4 g were mixed and heated to 65 ° C. Next, 100.8 g of styrene, 25.2 g of acrylic acid, 108.0 g of lauryl methacrylate, 36.0 g of polyethylene glycol methacrylate, 60.0 g of hydroxylethyl methacrylate, 36.0 g of styrene macromer, 3.6 g of mercaptoethanol, azobismethylvaleronitrile A mixed solution of 2.4 g and methyl ethyl ketone 18 g was dropped into the flask over 2.5 hours. After dropping, a mixed solution of 0.8 g of azobismethylvaleronitrile and 18 g of methyl ethyl ketone was dropped into the flask over 0.5 hours. After aging at 65 ° C. for 1 hour, 0.8 g of azobismethylvaleronitrile was added and further aging was performed for 1 hour. After completion of the reaction, 364 g of methyl ethyl ketone was added to the flask to obtain 800 g of a polymer solution having a concentration of 50%. A part of this polymer solution was dried and measured by gel permeation chromatography (standard: polystyrene, solvent: tetrahydrofuran). The weight average molecular weight was 15000.

(Preparation of pigment-containing polymer fine particle aqueous dispersion)
28 g of polymer solution A and C.I. I. 26 g of Pigment Yellow 97, 13.6 g of a 1 mol / L potassium hydroxide aqueous solution, 20 g of methyl ethyl ketone and 13.6 g of ion-exchanged water were sufficiently stirred, and then kneaded using a roll mill. The obtained paste was put into 200 g of ion-exchanged water and sufficiently stirred, and then methyl ethyl ketone and water were distilled off using an evaporator to obtain an aqueous dispersion of yellow polymer fine particles.
(Yellow ink)
Yellow polymer fine particle dispersion 40% by weight
Glycerin 8% by weight
1,3-butanediol 20% by weight
2,2,4-Trimethyl-1,3-pentanediol 2% by weight
Surfactant (1-8) 1.5% by weight
Silicone defoamer KS508 (manufactured by Shin-Etsu Chemical Co., Ltd.) 0.1% by weight
Residual amount of ion-exchanged water An ink composition having the above formulation was prepared and sufficiently stirred at room temperature, followed by filtration through a membrane filter having an average pore diameter of 1.2 μm to obtain an ink of Production Example 2.

<Production Example 3 ink>
(Preparation of pigment-containing polymer fine particle aqueous dispersion)
The pigment type is C.I. I. An aqueous dispersion of magenta polymer fine particles was obtained in the same manner except that the pigment red 122 was used.
(Magenta ink)
Dispersion of magenta polymer fine particles 50% by weight
Glycerin 10% by weight
1,3-butanediol 18% by weight
2,2,4-Trimethyl-1,3-pentanediol 2% by weight
Surfactant (1-8) 1.5% by weight
Silicone defoamer KS508 (manufactured by Shin-Etsu Chemical Co., Ltd.) 0.1% by weight
Residual amount of ion-exchanged water An ink composition having the above formulation was prepared and sufficiently stirred at room temperature, and then filtered through a membrane filter having an average pore size of 1.2 μm to obtain an ink of Production Example 3.

<Production Example 4 ink>
(Preparation of pigment-containing polymer fine particle aqueous dispersion)
The pigment type is C.I. I. An aqueous dispersion of cyan polymer fine particles was obtained in the same manner except that the pigment blue was changed to 15: 3.
(Cyan ink)
Cyan polymer fine particle dispersion 40% by weight
Glycerin 8% by weight
1,3-butanediol 20% by weight
2,2,4-Trimethyl-1,3-pentanediol 2% by weight
Surfactant (1-8) 1.5% by weight
Silicone defoamer KS508 (manufactured by Shin-Etsu Chemical Co., Ltd.) 0.1% by weight
Residual amount of ion-exchanged water An ink composition having the above formulation was prepared and sufficiently stirred at room temperature, and then filtered through a membrane filter having an average pore size of 1.2 μm to obtain an ink of Production Example 4.

  In each ink of the above production example, the rate of increase in viscosity (mPa · s /%) accompanying water evaporation is 1.0 or less up to a water evaporation rate of 30% with respect to the total weight of the ink, and the water evaporation rate is 30 to 45%. The average particle diameter of the colorant in the ink at a point where the viscosity increase rate exceeds 50 and the viscosity increase rate exceeds 50 is less than 5 times the initial average particle diameter, and 0 It was confirmed to be 8 μm or less.

  By using such a recording liquid, as described above, nozzle clogging does not occur even when left for a long period of time, and high image quality and high-speed printing on plain paper can be achieved. Moreover, even if the recording liquid in the nozzle is dried and thickened and cannot be discharged from the nozzle, the recording liquid does not cause the nozzle to clog due to coarse particles of the pigment. It has an advantage that it can be easily recovered by the maintenance recovery operation.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit controls the entire image forming apparatus. The main control unit 301 configured by a microcomputer also serving as a control unit related to the recovery operation according to the present invention, and the printing configured by the microcomputer that controls the printing control. And a control unit 302.

  Then, the main control unit 301 uses the main scanning motor 24 and the sub-scanning motor 58 as described above in order to form an image on the paper 42 based on the print processing information input from the communication circuit 300. Drive control is performed via the drive circuit 303 and the sub-scanning motor 304, and control such as sending print data to the print control unit 302 is performed.

  The main control unit 301 receives a detection signal from a carriage position detection circuit 305 that detects the position of the carriage 23, and the main control unit 301 controls the movement position and movement speed of the carriage 23 based on the detection signal. To do. The carriage position detection circuit 305 detects the position of the carriage 23 by, for example, reading and counting the number of slits of an encoder sheet arranged in the scanning direction of the carriage 23 with a photosensor mounted on the carriage 23. The main scanning motor drive circuit 303 rotates the main scanning motor 24 according to the carriage movement amount input from the main control unit 301 to move the carriage 23 to a predetermined position at a predetermined speed.

  Further, the main control unit 301 receives a detection signal from a conveyance amount detection circuit 306 that detects the movement amount of the conveyance belt 51, and the main control unit 301 moves the movement amount and movement speed of the conveyance belt 51 based on the detection signal. To control. The conveyance amount detection circuit 306 detects the conveyance amount by, for example, reading and counting the number of slits of the rotary encoder sheet attached to the rotation shaft of the conveyance roller 52 with a photo sensor. The sub-scanning motor driving circuit 304 rotates the sub-scanning motor 58 in accordance with the conveyance amount input from the main control unit 301 to rotate the conveyance roller 52 to move the conveyance belt 51 to a predetermined position at a predetermined speed. Move with.

  The main control unit 301 rotates the sheet feeding roller 43 once by giving a sheet feeding roller driving command to the sheet feeding roller driving circuit 307. The main control unit 301 rotationally drives the motor 221 of the maintenance / recovery mechanism 81 via the maintenance / recovery mechanism drive motor drive circuit 308, thereby raising and lowering the cap 82, raising and lowering the wiper blade 83, and the suction pump 211 as described above. Drive.

  The main control unit 301 drives and controls an ink supply motor for driving the pump of the supply unit via the ink supply motor drive circuit 311, and ink is supplied from the ink cartridge 10 loaded in the cartridge loading unit 4 to the sub tank 32. Replenish supply. At this time, the main control unit 301 controls replenishment supply based on a detection signal from the sub tank full tank sensor 312 that detects that the sub tank 32 is full.

  Further, the main control unit 301 takes in information stored in the nonvolatile memory 316 which is a storage unit provided in each ink cartridge 10 mounted on the cartridge loading unit 4 through the cartridge communication circuit 314, and performs a necessary process. And stored in a non-volatile memory (for example, EEPROM) 315 which is a main body storage means.

  Further, the main control unit 301 receives a detection signal from an environmental sensor 313 that detects environmental temperature and environmental humidity.

  The print control unit 302 generates pressure for discharging droplets of the recording head 31 based on the signal from the main control unit 301 and the carriage position and conveyance amount from the carriage position detection circuit 305 and the conveyance amount detection circuit 306. Data for driving the means is generated, and the above-mentioned image data is transferred to the head drive circuit 310 as serial data, and the transfer clock and latch signal necessary for transferring the image data and confirming the transfer, drop control, etc. In addition to outputting a signal (mask signal) etc. to the head drive circuit 310, it comprises a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM. Drive waveform generation means and drive waveform selection means to be given to the head driver, one drive pulse (drive signal) or a plurality of drive parameters. Scan to generate a composed drive waveform (drive signal) to the head drive circuit 310.

  The head drive circuit 310 selectively selects a drive signal constituting a drive waveform supplied from the print control unit 302 based on image data corresponding to one row of the print head 31 that is input serially. The recording head 31 is driven by applying it to a driving element (for example, a piezoelectric element as described above) that generates energy for discharging the ink. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets (large dots), medium droplets (medium dots), and small droplets (small dots) can be distinguished. it can.

Next, an example of the print control unit 302 and the head drive circuit (head driver) 310 will be described with reference to FIG.
As described above, the print control unit 302 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle and outputs the drive waveform, and a print image. And a data transfer unit 402 for outputting a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The droplet control signals M0 to M3 are 2-bit signals for instructing opening / closing of an analog switch 415, which will be described later in the head driving circuit 310, for each droplet, and are selected according to the printing cycle of the common driving waveform. The state transitions to the H level (ON) in the power waveform, and the state transitions to the L level (OFF) when not selected.

  The headed drive circuit 310 receives a transfer clock (shift clock) and serial image data (gradation data: 2 bits / CH) from the data transfer unit 402, and latches each register value of the shift register 411. The latch circuit 412 for latching, the decoder 413 for decoding the gradation data and the control signals M0 to M3 and outputting the result, and the logic level voltage signal of the decoder 413 to a level at which the analog switch 415 can operate. A level shifter 414 for conversion and an analog switch 415 that is turned on / off (opened / closed) by the output of the decoder 413 provided via the level shifter 414 are provided.

  The analog switch 415 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 401 is input thereto. Accordingly, when the analog switch 415 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals M0 to M3 by the decoder 413, a required drive signal constituting the common drive waveform can be obtained. Passing (selected) is applied to the piezoelectric element 121.

Next, an example of a drive waveform preferable when using the ink as described above will be described with reference to FIGS.
As shown in FIG. 8, the drive waveform generation unit 401 is fair in one print cycle (one drive cycle) with a waveform element falling from the reference potential Ve and a waveform element rising from the state after the fall. A drive signal (drive waveform) composed of eight drive pulses P1 to P8 is generated and output. On the other hand, the driving pulse to be used is selected by the droplet control signals M0 to M3 from the data transfer unit 402.

  Here, the waveform element in which the potential V of the drive pulse falls from the reference potential Ve is a drawing waveform element in which the piezoelectric element 121 contracts and the volume of the pressurized liquid chamber 106 expands. Further, the waveform element that rises from the state after the fall is a pressurizing waveform element that causes the piezoelectric element 121 to expand and the volume of the pressurized liquid chamber 106 to contract.

  Then, when forming a small droplet (small dot) by the droplet control signals M0 to M3 from the data transfer unit 402, the drive pulse P1 is selected as shown in FIG. 10A to form a medium droplet (medium dot). When driving, the driving pulses P4 to P6 are selected as shown in FIG. 4B, and when forming large droplets (large dots), the driving pulses P2 to P8 are selected as shown in FIG. In this case (when the meniscus is vibrated without droplet ejection), the fine drive pulse P2 is selected and applied to the piezoelectric element 121 of the recording head 31 as shown in FIG.

  When forming a medium droplet, the first droplet is ejected by the drive pulse P4, the second droplet is ejected by the drive pulse P5, and the third droplet is ejected by the drive pulse P6. At this time, if the natural vibration period of the pressure chamber (liquid chamber 106) is Tc, the interval between the ejection timings of the drive pulses P4 and P5 is preferably 2Tc ± 0.5 μs. Since the drive pulses P4 and P5 are configured by simple strike waveform elements, if the drive pulse P6 is also set to the same simple strike waveform element, the ink droplet velocity becomes too large, and the landing positions of other droplet types are affected. There is a risk of shifting. Therefore, the drive pulse P6 reduces the pull-in voltage (decreasing the falling potential) to reduce the meniscus pull-in and suppress the ink drop speed of the third drop. However, the startup voltage is not reduced in order to increase the necessary ink droplet volume.

  That is, in the drawing waveform element of the final drive pulse among the plurality of drive pulses, by reducing the drawing voltage relatively, the droplet discharge speed by the final drive pulse is relatively reduced, and the landing position is set to other droplets. It can be combined with the seed as much as possible.

  The fine drive pulse P2 is a drive waveform that vibrates the meniscus without ejecting ink droplets in order to prevent drying of the meniscus of the nozzle. This fine driving pulse P2 is applied to the recording head 7 in the non-printing area. In addition, by using the drive pulse P2 which is the fine drive waveform as one of the drive pulses constituting the large droplet, it is possible to achieve a shortened (higher speed) drive cycle.

  Furthermore, by setting the interval between the ejection timings of the fine drive pulse P2 and the drive pulse P3 within the range of the natural vibration period Tc ± 0.5 μs, the volume of ink droplets ejected by the drive pulse P3 can be increased. In other words, by superimposing the expansion of the pressurized liquid chamber 6 by the drive pulse P3 on the pressure vibration of the pressurized liquid chamber 106 by the vibration cycle generated by the fine drive pulse P2, the droplet volume of the droplet that can be ejected by the drive pulse P3 is driven. It can be made larger than when applying P3 alone.

  Since the required drive waveform varies depending on the viscosity of the ink, in this image forming apparatus, as shown in FIG. 11, the drive waveform when the ink viscosity is 5 mPa · s, and the same when the viscosity is 10 mPa · s. A drive waveform, similarly a drive waveform at 20 mPa · s, is prepared, and the ink viscosity is determined from the temperature detected by the temperature sensor, and the drive waveform to be used is selected.

  That is, when the ink viscosity is small, the voltage of the drive pulse is relatively small, and when the ink viscosity is large, the voltage of the drive pulse is relatively large. The volume can be discharged substantially constant. Further, the driving pulse 2 can vibrate the meniscus without ejecting ink droplets by selecting the peak value according to the ink viscosity.

  By using a drive waveform composed of such drive pulses, it is possible to control the time until each large, medium, and small droplet lands on the paper, and the ejection start time differs for each large, medium, and small droplet. In addition, each drop can be landed at substantially the same position.

Next, the hygroscopic effect of the ink remaining in the cap will be described with reference to FIG.
During the head recovery operation by the maintenance / recovery mechanism 81, as described above, the nozzle surface 31a of the recording head 31 is capped with the suction cap 82a and the ink is sucked and discharged from the nozzle 104, and then the dirt on the surface of the nozzle surface 31a is discharged. Wiping is performed with the wiped blade 83 together with the ink that has been scraped off and cleaned.

  Although the ink discharged into the suction cap 82a by this recovery operation is discharged by the suction by the suction pump 211, all the ink cannot be removed from the suction cap 82a. The ink remaining in the cap 82a gradually increases by repeating such an operation.

  As a result, as shown in FIG. 12A, the residual ink 500 in the suction cap 82a gradually becomes dry, and as shown in FIG. 12B, the dry residual ink 500 adheres. If the nozzle surface 31a of the recording head 31 is capped by the suction cap 82a, the dried residual ink 500 absorbs moisture from the ink in the nozzle 104 of the recording head 31, and the nozzle 104 The ink inside absorbs moisture and thickens.

  When ink having increased viscosity is generated in the nozzle 104 of the recording head 31 in this way, the ejection direction is bent or ejection becomes impossible during ejection of droplets, leading to deterioration in print quality.

Next, the relationship between the elapsed time from the capping of the recording head and the change in viscosity near the nozzle surface of the recording head will be described with reference to FIG.
Recording liquid in the vicinity of the nozzles of the recording head 31 with respect to the lapse of time from the time when the recovery operation by idle ejection is performed to all the recording heads 31 until the next idle ejection before printing is performed thereafter. The viscosity changes as shown in the figure. In the recovery operation for individual recording heads such as head suction, a recording head that is not recovered at that timing is generated. Therefore, it is not suitable to use this individual recovery operation as a base point.

  In FIG. 13, the recording head 31 is not capped until time point C0. At this time, the recording head 31k capped by the suction cap 82a and the recording head 31c capped by the moisture retention cap 82b are as follows. There is no difference in the viscosity change of the recording liquid in the vicinity of the nozzle. Since the recording heads 31m and 31y capped by the moisturizing caps 82c and 82d are the same, the description thereof is omitted here.

  Even if the recording head 31 is capped at the time point C0, the above-described suction is performed within a relatively short elapsed time from when the recovery operation by idle ejection is performed on all the recording heads 31 until the time T0 elapses. Since the effect of moisture absorption by residual ink adhering to the cap 82a is small, the viscosity of the recording liquid in the vicinity of the nozzles of the recording head 31k capped by the suction cap 82a and the recording head 31c capped by the moisture retaining cap 82b is reduced. This is almost the same as the change, and the temperature and humidity state in the cap 82 is not different from the outside air, so that it is possible to perform a recovery operation by idle ejection under the same recovery condition as the recovery condition before printing.

  When the elapsed time exceeds the time T0, a moisture absorbing action is caused by the residual ink adhering to the suction cap 82a, so that the recording head 31k capped by the suction cap 82a has an ink viscosity in the vicinity of the nozzle. The increase is significant. On the other hand, the moisture retention cap 82b does not absorb moisture, and therefore only increases in viscosity due to environmental conditions (temperature and humidity). Therefore, in the recording head 31c capped with the moisture retention cap 82b, the vicinity of the nozzles is present. The increase in ink viscosity is gradual.

  Here, if the limit of the viscosity that can be recovered by the idle ejection operation determined by the performance of the recording head (for example, the strength of the drive waveform that can be applied for idle ejection) is the “pre-printing idle ejection recovery limit viscosity”, the viscosity suddenly increases. In the recording head 31k capped by the suction cap 82a that causes the rise, the ink viscosity in the vicinity of the nozzle exceeds the pre-printing empty discharge recovery limit viscosity when the time T1 exceeding the time T0 has elapsed.

  On the other hand, in the recording head 31c capped by the moisturizing cap 82b whose viscosity increase is relatively gradual, the ink viscosity in the vicinity of the nozzle reaches the pre-printing empty discharge recovery limit when the time T2 exceeding the time T1 has elapsed. The viscosity will be exceeded.

A first example of the recovery operation process will be described with reference to FIGS.
As described above, the standing time (elapsed time) T from the time point when the recovery operation by idle ejection is performed on all the recording heads 31 is measured, and this recovery operation processing is entered before the printing operation. T is read and it is determined whether or not the time T0 or less (T ≦ T0).

  At this time, if the standing time T is equal to or shorter than the time T0, as described above, the recording head 31k capped by the suction cap 82a and the recording heads 31c, 31d, 31y capped by the moisture retaining caps 82b to 82d are as follows. There is almost no change in viscosity near the nozzle. Accordingly, the recording head 31k capped by the suction cap 82a performs the idle ejection recovery operation in which the number of droplets A is idle, and similarly, the recording heads 31c, 31d, and 31y capped by the moisture retaining caps 82b to 82d. Also, an idle ejection recovery operation is performed in which idle ejection is performed for the number of drops A (denoted as “A droplet” in the figure, the same applies hereinafter). The number A of drops is the same as the ejection recovery operation condition by the idle ejection during the printing operation, but may be different.

  That is, when all the print heads are within the first predetermined time (the above-described time T0) after the discharge recovery operation by the last empty discharge is performed, the recording head is capped with the moisturizing cap. By performing the recovery operation under the same recovery conditions (here, the same number of empty ejected droplets) for both the recording head and the recording head capped with the suction cap, unnecessary recording liquid consumption is prevented.

  The recovery condition in this case is a recovery condition that uses a relatively small amount of recording liquid, such as an ejection recovery condition due to idle ejection during a printing operation, thereby facilitating idle ejection control and reducing recording liquid consumption. The discharge performance can be maintained, and the printing process time can be shortened to enable high-speed printing.

  On the other hand, if the standing time T exceeds the time T0 (if T> T0, however, it is not more than the time T1 in FIG. 13), the recording liquid viscosity near the nozzles of the recording head 31 is the time T0. As described above, the recording head 31k capped with the suction cap 82a has a significantly increased viscosity, whereas the recording head 31c capped with the moisture retention caps 82b to 82d, The increase in the viscosity in the vicinity of the nozzles 31d and 31y is relatively small.

  Therefore, the recording head 31k capped by the suction cap 82a performs the idle ejection recovery operation in which the number of droplets B is idle, and the recording heads 31c, 31d, and 31y capped by the moisture retaining caps 82b to 82d. Performs an idle ejection recovery operation in which idle ejection is performed by the number of drops C smaller than the number of drops B. Note that the number of drops A <the number of drops C <the number of drops B is in a relationship.

  In other words, when all the print heads have elapsed since the last discharge recovery operation by idle discharge exceeds a first predetermined time (the above time T0), the print heads capped with the moisture retention cap. And the recording head capped with the suction cap, the recovery operation is performed under different recovery conditions (here, the number of empty ejection droplets is different). As a result, it is possible to reliably recover the performance of the recording head capped with the suction cap without consuming unnecessary recording liquid and eliminating the influence of the dehumidifying action due to the residual recording liquid in the suction cap. Can do.

  Here, as the different recovery conditions, the number of idle ejection droplets is varied here, but the same effect can be obtained even if the strength of the ejection waveform of idle ejection is varied. For example, when the drive waveform corresponding to the viscosity is provided as described above, the drive waveform for relatively high viscosity is used for the print head capped with the suction cap, and the print head is capped with the moisturizing cap. Can be made different by using a relatively low-viscosity driving waveform, or using a driving waveform for ejecting large droplets and a driving waveform for ejecting a middle enemy.

Therefore, a second example of the recovery operation process will be described with reference to FIGS.
As described above, the standing time (elapsed time) T from the time point when the recovery operation by idle ejection is performed on all the recording heads 31 is measured, and this recovery operation processing is entered before the printing operation. T is read and it is determined whether or not the time T0 or less (T ≦ T0).

  At this time, if the standing time T is equal to or shorter than the time T0, as described above, the recording head 31k capped by the suction cap 82a and the recording heads 31c, 31d, 31y capped by the moisture retaining caps 82b to 82d are as follows. There is almost no change in viscosity near the nozzle. Accordingly, the recording head 31k capped by the suction cap 82a performs the idle ejection recovery operation in which the number of droplets A is idle, and similarly, the recording heads 31c, 31d, and 31y capped by the moisture retaining caps 82b to 82d. Also, the idle ejection recovery operation is performed in which the idle ejection is performed by the number A of drops. The number A of drops is the same as the ejection recovery operation condition by the idle ejection during the printing operation, but may be different.

  On the other hand, if the leaving time T exceeds the time T0 (T> T0), it is determined whether or not the leaving time T is equal to or less than the time T1 (T0 <T ≦ T1).

  At this time, when the standing time T is equal to or shorter than the time T1 (T0 <T ≦ T1), as described above, the idle ejection recovery is performed in which the recording head 31k capped by the suction cap 82a performs idle ejection by the number B of drops. On the other hand, the recording heads 31c, 31d, and 31y capped by the moisture retention caps 82b to 82d perform the idle ejection recovery operation in which idle ejection is performed by the number of drops C smaller than the number of drops B. Note that the number of drops A <the number of drops C <the number of drops B is in a relationship.

  On the other hand, if the leaving time T is not less than the time T1, that is, if it exceeds the time T1 (if T> T1), the leaving time T is less than the time T2 (T1 <T ≦ T2). It is determined whether or not.

  At this time, if the standing time T is equal to or less than the time T2 (T1 <T ≦ T2), as described above, the recording head 31k capped by the suction cap 82a exceeds the idle ejection recovery limit viscosity, and the idle ejection is performed. Since it cannot be recovered simply by performing the suction, the suction pump 211 is operated in a state where the recording head 81k is capped by the suction cap 82a, and the suction recovery operation by the nozzle suction for sucking the recording liquid from the nozzle of the recording head 31k is performed. On the other hand, since the recording heads 31c, 31d, and 31y capped by the moisture retaining caps 82b to 82d have not yet exceeded the empty discharge recovery limit viscosity, the empty discharge recovery operation is performed in which empty discharge is performed by the number of drops D. The number of drops D may be the same as or different from the number of drops B.

  That is, here, the idle ejection operation and the suction recovery operation are different recovery conditions for the recording head capped with the moisture retention cap and the recording head capped with the suction cap. As a result, the recording head capped with the moisturizing cap can be completed with only the idle ejection operation, and the recording head capped with the suction cap can be reliably recovered by suction while suppressing wasteful consumption of the recording liquid. Recovery can be performed by eliminating the influence of the dehumidifying effect of the residual recording liquid in the suction cap.

  On the other hand, if the leaving time T is not less than the time T2, that is, if the leaving time T exceeds the time T2 (T> T2), as described above, capping is performed by the suction cap 82a. The recording head 31k performs suction recovery, and the recording heads 31c, 31d, and 31y capped by the moisture retaining caps 82b to 82d also exceed the empty discharge recovery limit viscosity. Therefore, the recording heads 31c are sequentially used by using the suction cap 82a. , 31d and 31y are suction-recovered.

  By performing the above treatment, there are a recording head capped with a suction cap and a recording head capped with a moisturizing cap, and in particular, at least a colorant, a wetting agent, and a permeability improver that are dispersed in water. The viscosity increase rate (mPa · s /%) accompanying water evaporation is 1.0 or less up to a water evaporation rate of 30% with respect to the total weight of the recording liquid, and the viscosity is between 30 and 45%. Even when a recording liquid configured to have a rate of increase exceeding 50 is used, it is possible to reliably recover the recording head moisturized by the suction cap while suppressing wasteful recording liquid consumption. It is possible to suppress degradation of image quality.

  In this case, the average particle diameter of the colorant in the recording liquid when the viscosity increase rate exceeds 50 is not more than 5 times the initial average particle diameter and not more than 0.8 μm. Even with the prescribed recording liquid, the same effect can be obtained, and by using such a recording liquid, high-speed and high-quality recording on plain paper can be performed. Of course, the present invention is not limited to the case where such a recording liquid is used, and similar effects can be obtained when a recording liquid that generates a hygroscopic action as described above is used.

  In the above-described embodiment, an example in which there is one suction cap has been described. In short, however, the maintenance has one or more moisture retention caps less than the number of recording heads and one or more suction caps also serving as moisture retention. If a recovery mechanism is provided, the same applies. Further, the threshold time to be compared with the elapsed time (for example, the above-described times T0, T1, and T2) can be changed according to environmental conditions (temperature and humidity, particularly high temperature and low humidity, normal temperature and normal humidity, low temperature and low humidity, etc.).

  In each of the above embodiments, the printer configuration has been described as the image forming apparatus according to the present invention. However, the present invention is not limited to this, and can be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. Further, the present invention can be applied to an image forming apparatus using a recording liquid or a fixing processing liquid that is a liquid other than ink.

1 is a perspective view illustrating an example of an image forming apparatus according to the present invention as viewed from the front side. 2 is a configuration diagram illustrating an outline of a mechanism unit of the image forming apparatus. FIG. It is principal part plane explanatory drawing of the mechanism part. FIG. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a droplet discharge head constituting the recording head of the image forming apparatus. It is sectional explanatory drawing along the liquid chamber transversal direction of the head. FIG. 3 is a development schematic explanatory view of a maintenance / recovery mechanism of the image forming apparatus. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. It is a block diagram which shows an example of the printing control part of the control part. It is explanatory drawing which shows an example of the drive waveform produced | generated and output by the drive waveform production | generation part of the same printing control part. It is explanatory drawing explaining each drive signal of the small droplet, medium droplet, large droplet, and fine drive selected from the same drive waveform. It is explanatory drawing explaining the drive waveform according to the recording liquid viscosity. It is explanatory drawing with which it uses for description of the hygroscopic effect | action by the ink in a cap. It is explanatory drawing explaining an example of the elapsed time after capping about a recording head capped with a suction cap and a moisturizing cap and a viscosity change near the nozzle. It is a flowchart which shows an example of the recovery operation which the same control part performs. It is explanatory drawing of the relationship between elapsed time and recovery conditions similarly. It is a flowchart which shows an example of the recovery operation which the same control part performs. It is explanatory drawing of the relationship between elapsed time and recovery conditions similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ink cartridge 23 ... Carriage 31 ... Recording head 32 ... Sub tank 51 ... Conveyance belt 81 ... Maintenance recovery mechanism 82a ... Suction cap 82b-82d ... Moisturizing cap 300 ... Control part 313 ... Environmental sensor

Claims (1)

A plurality of recording heads having nozzles for discharging recording liquid droplets, a moisture retaining cap for preventing drying of the nozzle surface of the recording head, and a moisture retaining cap, and the nozzle surface of the recording head is capped. In an image forming apparatus comprising a maintenance recovery mechanism including a suction cap for sucking a recording liquid from the nozzle in a state, and forming an image on a recording medium by discharging droplets from the nozzle of the recording head.
Control means for controlling a recovery operation for the recording head,
The control means includes
The elapsed time after performing the recovery operation by the idle ejection for ejecting the droplets that are not involved in the recording last for all the recording heads is a predetermined predetermined value in which the residual recording liquid in the suction cap becomes dry of until passage of time, the row Align the recovery operation in the same recovery condition for a recording head is capped by the recording head and the suction cap to be capped by the moisturizing cap,
After the predetermined time has elapsed, the recovery condition of the recovery operation for the recording head capped by the suction cap is made stronger than the recovery condition of the recovery operation for the recording head capped by the moisturizing cap. An image forming apparatus characterized in that an operation is performed .

Images