JP2006187893A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when recording liquids with colors having different physical properties are used, inferiority of delivering of the recording liquids caused by drying can not be prevented from occurring, and as a result, decrease in printing speed is brought by changing a timing for performing a maintenance operation on each color. <P>SOLUTION: A lapse of time from releasing capping, or a lapse of time from the preceding empty delivering operation is measured. When the lapse of time reaches a predetermined setting time T, on a head 34k delivering a black (K) ink, a head 34c delivering a cyan (C) ink, a head 34m delivering a magenta (M) ink, and a head 34y delivering a yellow (Y) ink, maintenance operations corresponding to physical properties of the inks of colors used are respectively performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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. In other words, recording is performed by ejecting ink droplets, which are droplets of recording liquid (image formation, printing, printing, printing, etc. are also synonymous).

  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 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 Combining the wiping operation on the head surface and the empty ejection operation that discharges ink so that it does not contribute to image formation and discharges thickened ink and mixed color ink in the nozzle hole and near the entrance, etc. An operation of removing thickened ink, adhering dust, etc., and maintaining a state where stable droplet discharge can be performed is performed.

As a conventional ink jet recording apparatus, as described in Patent Document 1, a cap member for capping the print head to prevent ink drying at the nozzle, and an elapsed time from the previous maintenance operation are measured, Further, the capping time during which the print head is capped by the cap member is a predetermined value obtained by measuring the elapsed time measuring means for measuring the capping time to be shorter than the actual time and the measured value by the elapsed time measuring means. It is known to have a maintenance means for performing a maintenance operation at the time, thereby reducing the ink consumption with respect to the number of print data and reliably preventing clogging.
Japanese Patent No. 3481042

In addition, as described in Patent Document 2, the ink consumption amount in the ink jet recording apparatus includes a suction amount detection unit, a discharge amount detection unit, and an ink remaining amount calculation unit. The amount of ink sucked by the suction pump from the nozzle of the recording head is detected at the initial stage when the cartridge is replaced and when the function of the recording head is restored, and the discharge amount detecting means detects the amount of ink discharged during printing and the nozzle of the recording head. Ink amount is detected when purging ink from the nozzles of the recording head in order to maintain the normal state, and the ink remaining amount calculation means sucks from the total ink filling amount of the cartridge or the previously calculated ink remaining amount. A device that calculates the remaining ink amount in the cartridge by subtracting the suction amount detected by the amount detection unit and the discharge amount detected by the discharge amount detection unit is known.
JP 2001-260375 A

  As described above, in an image forming apparatus such as an ink jet recording apparatus, since a pigment-based recording liquid has been used in particular, the physical properties of the recording liquids for each color are different, and as a result, all the drying conditions are all different. The color recording liquid is not the same. For this reason, even if a nozzle that ejects a recording liquid of a certain color is normal, the nozzle that ejects a recording liquid of another color may be clogged, resulting in ejection failure (ejection failure, ejection bend, etc.).

  In this case, as in the ink jet recording apparatus described in Patent Document 1, the timing for performing the maintenance operation for each color can be varied. However, if the timing for performing the maintenance operation for each color is different, the maintenance operation is performed each time. As a result, printing is stopped, which causes a problem that the printing speed is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that can reliably prevent ejection failure due to drying of a recording liquid even when recording liquids of different colors are used. .

  In order to solve the above-described problem, an image forming apparatus according to the present invention includes a unit that measures an elapsed time from the previous maintenance operation, and a nozzle row or a head for each color when the elapsed time reaches a predetermined time. And a means for performing a maintenance operation in accordance with the physical properties of the recording liquid.

  Here, the maintenance operation is preferably an idle discharge operation for discharging droplets that do not contribute to image formation. Moreover, it is preferable that the number of empty ejection droplets during the maintenance operation is set for each color recording liquid. Further, it is preferable that the maintenance operation is an idle discharge operation for discharging droplets that do not contribute to image formation during printing. Furthermore, the maintenance operation is preferably performed at the same timing for the nozzle rows or heads of the recording liquids of the respective colors.

  According to the image forming apparatus of the present invention, the means for measuring the elapsed time from the previous maintenance operation, and the physical properties of the recording liquid for each nozzle row or head of each color when the elapsed time reaches a predetermined time. Therefore, even when recording liquids having different physical properties are used, ejection failure due to drying of the recording liquid can be reliably prevented.

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 ink cartridges 10k, 10c, 10m, and 10y are configured to be loaded side by side in a vertical state.

  The front cover 6 is entirely transparent so that the plurality of ink cartridges 10k, 10c, 10m, and 10y loaded in the cartridge loading unit 4 can be visually recognized from the outside with the front cover 6 closed. It is formed of a translucent member. In addition, if the ink cartridges 10k, 10c, 10m, and 10y can be visually recognized from the outside, a part of the ink cartridges 10k, 10c, 10m, and 10y may be formed of a transparent or translucent member.

  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 the respective colors. A remaining amount display portion 11k, 11c, 11m, 11y of each color for displaying the near end and the end is arranged (referred to as “remaining amount display portion 11” when colors are not distinguished). 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 this 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 carriage 33 is slidably held in the main scanning direction by a guide rod 31 which is a guide member horizontally mounted on the left and right side plates 21A and 21B constituting the frame 21, and a stay 32. Move and scan in the direction indicated by the arrow (carriage main scanning direction).

  As described above, the carriage 33 includes heads 34k and 34c including four droplet ejection heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). , 34m, 34y (referred to as "recording head 34" as a whole) are arranged in a direction crossing the main scanning direction with the nozzle surface 34a on which a plurality of ink discharge ports (nozzles) are formed, and the ink discharge direction is directed downward. Wearing. Here, the recording head is composed of a plurality of heads that eject recording liquids of different colors, but the recording head is composed of one or a plurality of heads having nozzle rows that eject recording liquids of different colors. In this case, “each recording liquid head of each color” in the following description may be read as “nozzle row of recording liquid of each color”.

  As an inkjet head constituting the recording head 34, 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.

  A driver IC is mounted on the recording head 34 and is connected to a control unit (not shown) via a harness (flexible print cable) 22.

  In addition, the carriage 33 is equipped with a sub tank 35 for each color for supplying ink of each color to the recording head 34. As described above, each color sub-tank 35 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 36 of each color. The cartridge loading 4 is provided with a supply pump unit 24 for feeding ink in the ink cartridge 10, and the ink supply tube 36 is engaged with the rear plate 21 </ b> C constituting the frame 21 in the middle of turning. It is held by a stop member 25.

  On the other hand, as a paper feeding unit for feeding the papers 42 stacked on the paper stacking unit (pressure plate) 41 of the paper feeding tray 2, a half-moon roller (feeding) that separates and feeds the papers 42 one by one from the paper stacking unit 41. A separation pad 44 made of a material having a large friction coefficient is provided facing the paper roller 43) and the paper feed roller 43, and the separation pad 44 is urged toward the paper feed roller 43 side.

  In order to feed the paper 42 fed from the paper feeding unit to the lower side of the recording head 34, a guide member 45 for guiding the paper 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 34.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 so as to circulate in the belt transport direction (sub-scanning direction). 56 is charged (charged).

  The transport belt 51 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of the conveyance belt 51 having a one-layer structure, the entire layer is formed of an insulating material because it is in contact with the paper 42 and the charging row 56. In the case of the transport belt 51 having a multi-layer structure, the side that contacts the paper 42 and the charging roller 56 is preferably formed of an insulating layer, and the side that does not contact the paper 42 and the charging roller 56 is preferably formed of a conductive layer. .

As an insulating material for forming the single-layered conveying belt 51 and an insulating material for forming the insulating layer of the multilayered conveying belt 51, for example, conductive with resin or elastomer such as PET, PEI, PVDF, PC, ETFE, PTFE, etc. It is preferable that the material does not contain a control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. Further, as a material for forming the conductive layer of the transport belt 51 having a multi-layer structure, it is preferable that the resin or elastomer contains carbon so that the volume resistivity is 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 56 is disposed so as to come into contact with an insulating layer (in the case of a multilayer belt) forming the surface layer of the conveyor belt 51, and to rotate following the rotation of the conveyor belt 51, and to apply pressure to both ends of the shaft. It is over. The charging roller 26 is formed of a conductive member having a volume resistivity of 10 ⁶ to 10 ⁹ Ω / □. As will be described later, a positive / negative AC bias (high voltage) of 2 kV, for example, is applied to the charging roller 26 from an AC bias supply unit (high voltage power source) 315. The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  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 34. 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 transport belt 51 rotates in the belt transport direction of FIG. 3 when the transport roller 52 is rotationally driven via a drive belt by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying 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. Here, the height from between the paper discharge roller 62 and the paper discharge roller 63 to the paper discharge tray 3 is increased to some extent in order to increase the amount that can be stored in the paper discharge tray 3.

  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 for maintaining and recovering the nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction.

  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 34, 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 suction and moisture retention cap, and the other caps 82b to 82d are moisture retention caps.

  Then, the waste liquid of the recording liquid generated by the maintenance / recovery operation by the maintenance / recovery mechanism 81, the ink discharged to the cap 82, the ink attached to the wiper blade 83 and removed by the wiper cleaner 85, and the idle ejection to the idle ejection receiver 94. The discharged ink is discharged and stored in the waste liquid tank 100 of FIG.

  Further, as shown in FIG. 3, in the non-printing area on the other side in the scanning direction of the carriage 33, idle ejection is performed to eject droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An empty discharge receiver 88 for receiving the droplets at the time is disposed, and the empty discharge receiver 88 is provided with an opening 89 along the nozzle row direction of the recording head 34.

  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 short side of the liquid chamber (arrangement direction of nozzles).

  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 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 22 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 34a 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 (pulling-pushing), and it is also possible to perform striking or pushing depending on the direction to which the driving waveform is given.

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 34a of the recording head 34, and a liquid that does not contribute to printing from the recording head 34. 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 34, the recording head 34 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 camshaft 213, the motor gear 221 rotates on the motor shaft 221a and the pump gear 223 provided on the pump shaft 211a of the tubing pump 211 is meshed with the pump gear 213. 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 in the forward direction, 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. As the cam shaft 213 rotates, the cap cams 214A and 214B and the wiper cam 215 are raised and lowered at predetermined timings, respectively.

  When cleaning the nozzle surface 34 a of the recording head 34, the wiper blade 83 is raised and the nozzle surface 34 a is wiped by moving the recording head 34 relative to the wiper blade 83.

  In this image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding tray 2, and the sheets 42 fed substantially vertically upward are guided by the guide 45, and are conveyed to the conveyor belt 51 and the counter. It is sandwiched between the rollers 46 and conveyed, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the leading end pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive output and a negative output are alternately repeated from the AC bias supply unit 315 of the control unit, which will be described later, to the charging roller 56 alternately, that is, an alternating voltage is applied and the conveying belt 51 alternates. That is, a pattern in which plus and minus are alternately charged in a band shape with a predetermined width is formed 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 34 according to the image signal while moving the carriage 33, 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.

  Further, during printing (recording) standby, the carriage 33 is moved to the maintenance / recovery mechanism 81 side, and the recording head 34 is capped by the cap 82 to prevent ejection failure due to ink drying by keeping the nozzle in a wet state. . Further, the recording liquid is sucked from the nozzle by a suction pump (not shown) while the recording head 34 is 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. Also, an idle ejection operation as a maintenance operation according to the present invention for ejecting ink not related to the recording before the start of recording or during the recording is performed. Thereby, the stable ejection performance of the recording head 34 is maintained.

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 inlet 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.

  Each ink of the above production example has a viscosity increase rate (mPa · s /%) accompanying water evaporation of 1.0 or less up to a water evaporation rate of 30% with respect to the total weight of the ink, and a water evaporation rate of 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, 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 300 temporarily stores a CPU 301 that also functions as a aging unit and a maintenance unit according to the present invention that controls the entire apparatus, a ROM 302 that stores programs executed by the CPU 301 and other fixed data, and image data. A RAM 303, a non-volatile memory (NVRAM) 304 for holding data while the apparatus is powered off, image processing for performing various signal processing and rearrangement on image data, and other control of the entire apparatus ASIC 305 for processing the input / output signals.

  The control unit 300 also includes an I / F 306 for transmitting and receiving data and signals to and from the host side, and a drive waveform generation unit 307 that generates a drive waveform for driving and controlling the pressure generating means of the recording head 34. , A head driver 308, a main scanning motor driving unit 311 for driving the main scanning motor 310, a sub scanning motor driving unit 313 for driving the sub scanning motor 312, and an AC for supplying an AC bias to the charging roller 56. A bias supply unit 315, a maintenance / recovery mechanism drive unit 317 for driving the motor 221 of the maintenance / recovery mechanism 81, an encoder 321 that outputs a detection signal corresponding to the amount and speed of movement of the conveyor belt 51, environmental temperature and environment Detection signals from the environmental sensor 322 for detecting humidity (only environmental humidity may be used) and detection signals from various sensors (not shown). It has a such as I / O318 to force. The control unit 300 is connected to an operation / display unit 5 for inputting and displaying information necessary for the apparatus.

  The control unit 300 receives print data and the like from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera, via the cable or the network, via the I / F 316.

  The CPU 301 reads and analyzes the print data in the reception buffer included in the I / F 306, performs necessary image processing, data rearrangement processing, and the like in the ASIC 305, and corresponds to one line of the recording head 34. Image data (dot pattern data) is sent as serial data to the head driver 308 in synchronization with the clock signal, and a latch signal and a control signal are sent to the head driver 308 at a predetermined timing.

  The CPU 301 reads and analyzes the print data in the reception buffer included in the I / F 306, performs necessary image processing, data rearrangement processing, and the like in the ASIC 305, and transfers the image data to the head driver 308. The generation of dot pattern data for image output may be performed by storing font data in the ROM 302, for example, or image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  The drive waveform generation unit 307 includes a D / A converter that performs D / A conversion on the drive waveform pattern data, and includes a single drive pulse (drive signal) or a plurality of drive pulses (drive signal). The waveform is output to the head driver 308.

  The head driver 308 selectively records drive pulses constituting a drive waveform supplied from the drive waveform generator 307 based on image data (dot pattern data) corresponding to one line of the recording head 34 input serially. The recording head 34 is driven by being applied to the pressure generating means of the head 34.

  Further, the control unit 300 controls the charging pattern (applied charge amount) on the conveyance belt 51 by performing ON / OFF control of the AC bias supplied from the AC bias supply unit 315 to the charging roller 56.

Accordingly, processing (maintenance control processing) related to the maintenance operation by the control unit 300 according to the present invention will be described with reference to FIG.
First, when there is a printing command, printing is started after the capping of the recording head 34 by the cap 82 is released. And the measurement of the elapsed time from the capping release is started, and the elapsed time is calculated. This elapsed time may be measured by storing the time when capping is canceled and calculating the elapsed time by obtaining a deviation from the current time, or by setting a timer that times up every time a preset set time elapses. If used, the timer is set and started.

  Here, when the elapsed time reaches a preset time T (when the deviation reaches the preset time T, the timer of the preset time T has expired, etc.), black (K) ink is ejected. For the head 34k, the head 34c that discharges cyan (C) ink, the head 34m that discharges magenta (M) ink, and the head 34y that discharges yellow (Y) ink, the recording liquid (ink) of the color used respectively. Perform maintenance operations according to the physical properties of the machine. Here, as a maintenance operation, an empty discharge operation for discharging droplets that do not contribute to image formation is performed, and the number of empty discharge droplets is set for each color recording liquid as described later in accordance with the physical properties of the recording liquid (ink). Perform maintenance operations.

  This idle discharge operation during printing is performed at the same timing for the recording liquid heads 34k, 34c, 34m, and 34y of the respective colors by performing idle discharge to the opening of the idle discharge receiver 88. In this way, by periodically performing idle ejection during printing, it is possible to prevent non-ejection (ejection failure) due to ink drying for nozzles that are not used during continuous printing. In this case, since the number of times of maintenance increases and the printing speed decreases when the idle ejection is performed separately for each color head, the maintenance operation is performed at the same timing for all color heads. The overall maintenance operation time is shortened.

  Then, the printing is resumed after the maintenance operation, and the measurement of the elapsed time from the idle ejection operation (the elapsed time from the previous maintenance operation) is started. The measurement of the elapsed time is the same as the measurement of the elapsed time from the capping release described above. Each time the print heads 34k, 34c, 34m, and 34y are used, as described above, every time the elapsed time from the previous idle discharge reaches the set time T until the end of printing. A maintenance operation (empty ejection operation) corresponding to the physical properties of the color recording liquid (ink) is performed.

  In this way, by measuring the elapsed time from the previous maintenance operation, and performing the maintenance operation according to the physical properties of the recording liquid for each color recording liquid head when the elapsed time reaches a predetermined time, Even when recording liquids having different physical properties are used, an optimum maintenance operation corresponding to the recording liquid can be performed, and ejection failure due to drying of the recording liquid can be reliably prevented.

  More specifically, FIGS. 9A and 9B show a maintenance interval (period: elapsed time from the previous maintenance operation) for the heads 34k and 34c that discharge black (K) ink and cyan (C) ink. ), The number of empty ejection droplets, and the clogging prevention effect (ejection failure prevention effect).

  In this example, in the case of the black ink head 34k, when the maintenance interval is set to 15 [μsec] or 20 [μsec], if the number of empty ejected droplets is set to 20 or 40 droplets, ejection failure due to drying can be reliably ensured. Cannot be removed ("x" in the figure). On the other hand, in the case of the cyan ink head 34c, when the maintenance interval is set to 15 [μsec] or 20 [μsec], even if the number of empty ejected drops is set to 20 drops or 40 drops, it is caused by drying. Discharge defects can be reliably removed (marked with “◯” in the figure).

  In other words, setting the same number of empty ejected droplets regardless of the physical properties of the ink (recording liquid) causes non-ejection (ejection failure) with ink that is particularly easy to dry, and wastes too much ink with ink that is difficult to dry. Will be. That is, even if the number of empty ejected droplets is optimal for a certain ink, the number of empty ejected droplets is not necessarily optimal for other inks.

  Therefore, in order to make it possible to set and change the number of empty ejection droplets according to the physical properties of the ink, as shown in FIG. 10, a table is provided for determining the number of empty ejection droplets for each color ink (stored in the ROM 202 or the like). For ink that is easy to dry, the ink can be ejected in an appropriate state at all times by performing the idle ejection of the number of drops corresponding to the state of the ink. This increases the number of empty ejected droplets for inks that are easy to dry, and reduces the number of empty ejected droplets for inks that are difficult to dry to improve image quality without waste and reliable maintenance. ing.

  In this case, since the degree of ink drying varies depending on the environmental temperature, the environmental temperature is divided into a plurality of steps as shown in FIG. 10, and the number of ejected droplets and the cycle are determined for each step. Thus, in the example of this table, the number of empty ejection drops K1 to K8 for black ink, the number of empty ejection drops C1 to C8 for cyan ink, the number of empty ejection drops M1 to M8 for magenta ink, and the number of empty ejection drops for yellow ink. The number of ejected droplets Y1 to Y8 and the period T are defined as T1 to T8.

  In the idle discharge operation in the maintenance control process described above, the corresponding temperature compensation step period T is set based on the detection result (environmental temperature) of the environmental sensor 322, and the corresponding empty for each color recording liquid head. Empty ejection is performed with the number of ejected droplets.

  In 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 flowchart with which it uses for description of the maintenance control which the same control part performs. It is explanatory drawing explaining an example of the relationship between the kind of recording liquid, the frequency | count of idle discharge, a period, and the drying prevention effect. It is explanatory drawing explaining an example of the table used for the maintenance control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ink cartridge 33 ... Carriage 34k, 34c, 34m, 34y ... Head 35 ... Sub tank 51 ... Conveyance belt 52 ... Conveyance roller 53 ... Follower roller 56 ... Charging roller 81 ... Maintenance recovery mechanism 82a ... Suction and moisture retention caps 82b-82d DESCRIPTION OF SYMBOLS ... Moisturizing cap 83 ... Wiper blade 84 ... Empty discharge receptacle 88 ... Empty discharge receptacle 300 ... Control part 315 ... AC bias supply part 317 ... Maintenance recovery mechanism drive part 322 ... Environmental sensor

Claims (5)

  A recording head composed of a plurality of nozzle rows or a plurality of heads for discharging recording liquid droplets of different colors, and means for performing a maintenance operation for maintaining or recovering the droplet discharging state of the recording head In the image forming apparatus that forms an image on a recording medium by discharging droplets from the nozzles of the recording head, means for measuring an elapsed time from the previous maintenance operation, and the elapsed time is a predetermined time An image forming apparatus comprising: means for performing a maintenance operation corresponding to the physical properties of the recording liquid for each nozzle row or head of each color.   2. The image forming apparatus according to claim 1, wherein the maintenance operation is an idle ejection operation for ejecting liquid droplets that do not contribute to image formation.   The image forming apparatus according to claim 2, wherein the number of empty ejected droplets during the maintenance operation is set for each color recording liquid.   4. The image forming apparatus according to claim 1, wherein the maintenance operation is an idle ejection operation for ejecting liquid droplets that do not contribute to image formation during printing. 5. The image forming apparatus according to claim 1, wherein the maintenance operation is performed at the same timing for the nozzle rows or the heads of the recording liquids of the respective colors.

Images