JP2014008736A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus forming images by applying recording liquid to an intermediate transfer body through a head and forming images while uniformizing blurring suppression actions suppressing blurring without adding process liquid or powder other than the recording liquid or suppressing blurring by ensuring electrolysis of the recording liquid without using a high voltage or a large amount of electrolytes, and to provide an image forming method.SOLUTION: An image forming apparatus includes: an intermediate transfer body 37 having an electrically conductive surface on which electrically conductive recording liquid discharged from a nozzle 61b of heads 61Y, M, C, BK (hereinafter referred to as head 61) is applied in accordance with a driving signal; voltage application means 33 applying voltage between the intermediate transfer body 37 and the head 61 so as to electrolyze the recording liquid discharged from the head 61 and bridging a gap between the head 61 and the intermediate transfer body 37; and discharge control means 40 generating a driving signal in such a manner that amounts of current flowing in the recording liquid in the state are equal to one another according to the interval between the nozzle 61b and the intermediate transfer body 37.

Description

  The present invention relates to an inkjet image forming apparatus that forms an image by applying a recording liquid such as ink to an intermediate transfer member with a head, and an image forming method using the same.

  Conventionally, a head that discharges recording liquid such as ink from a plurality of minute nozzles by using a movable actuator system typified by a piezo system, a heating film boiling system typified by a thermal system, etc. 1] and [Patent Document 2]), and an inkjet image forming apparatus such as an ink jet printer that performs ink jet recording is known (see, for example, [Patent Document 3] to [Patent Document 6]).

  In the inkjet system, in the configuration in which the recording liquid is directly discharged from the head to the recording material such as recording paper, the head and the recording material are close to each other, so paper dust, dust, etc. adhering to the recording material is applied to the nozzle. Easy to adhere. When paper dust or the like adheres to the nozzle, the flying direction of droplets ejected from the nozzle is disturbed, or the nozzle is blocked, resulting in a reduction in image quality and reliability. In order to avoid such a problem, priority is given to the ejection stability from the nozzles, and it is common to use a recording liquid having a low viscosity. However, a recording liquid having a low viscosity is applied to the recording material. Bleeding is likely to occur when landing.

  In view of this, an image forming apparatus that includes an intermediate transfer member that carries the recording liquid discharged from the head, forms an image on the intermediate transfer member, and then transfers the image to a recording material has been proposed (for example, Patent Document 3). To [Patent Document 6].

  Further, in the image forming apparatus provided with the intermediate transfer member as described above, an image forming device including a processing liquid applying unit that applies a processing liquid for changing the pH of the recording liquid to the intermediate transfer member in order to further reduce bleeding. Has been proposed (see, for example, [Patent Document 3]). In this image forming apparatus, in the recording liquid, at least a pigment and polymer fine particles are dispersed in a medium composed of water and a water-soluble solvent, and the pigment and polymer fine particles are aggregated by changing pH.

  In addition, in an image forming apparatus provided with an intermediate transfer body, an image forming apparatus is proposed in which a powder that absorbs a recording liquid is previously deposited on the intermediate transfer body in order to reduce bleeding (for example, [Patent Documents] 4]).

  Further, in an image forming apparatus provided with an intermediate transfer body, as a countermeasure against bleeding, a bridge of a liquid column of conductive recording liquid is temporarily formed between the nozzle and the intermediate transfer body, and is included in the bridge of the liquid column. An image forming apparatus that applies a potential so that water is electrolyzed has been proposed (see, for example, [Patent Document 5] and [Patent Document 6]).

  However, an image forming apparatus (see, for example, [Patent Document 3] and [Patent Document 4]) that applies a processing liquid or powder to the intermediate transfer member has a problem that the printing speed decreases due to the processing liquid or powder being applied There is a problem that the apparatus becomes large. In particular, in the configuration in which the powder is applied, the powder tends to adhere to the nozzle and the discharge performance of the recording liquid from the head tends to decrease. It is necessary to solve the problem while ensuring the discharge performance.

  On the other hand, an image forming apparatus of a type that performs electrolysis by temporarily forming a bridge of a liquid column of conductive recording liquid between a nozzle and an intermediate transfer member and applying a voltage (for example, [Patent Document 5] ] And [Patent Document 6]), there is an advantage that no processing liquid or powder other than the recording liquid is required.

  However, in this type of image forming apparatus, simply by applying such a voltage, when the gap between the nozzle and the intermediate transfer body changes, the amount of current flowing through the recording liquid changes. Thus, since the degree of suppression or prevention of bleeding can change, image quality fluctuations and the like can occur. The change in the gap between the nozzle and the intermediate transfer member is caused by, for example, a change in position due to the driving of the intermediate transfer member.

  In this regard, there has been proposed an image forming apparatus that controls the value of the voltage applied between the nozzle and the intermediate transfer body in accordance with the change in the gap between the nozzle and the intermediate transfer body (for example, [Patent Reference 6]).

  However, in the configuration for controlling the value of the voltage applied between the nozzle and the intermediate transfer member, for example, the same voltage is applied to each of the recording liquid ejected from a plurality of nozzles. In this case, when there is a gap variation along the nozzle arrangement direction, a deviation occurs in the amount of current flowing in the recording liquid, and a difference occurs in the degree of bleeding in each of the recording liquids. Therefore, in such a configuration, it cannot be said that the variation of the gap between the nozzle and the intermediate transfer member is sufficiently dealt with.

  Therefore, the recording liquid discharged from the nozzle is temporarily bridged between the nozzle and the intermediate transfer member, and voltage is applied to the recording liquid so as to suppress or prevent the recording liquid from spreading. It is an object of the present invention to provide an image forming apparatus and an image forming method for forming an image.

  The present invention relates to an image forming apparatus for forming an image by applying a recording liquid to an intermediate transfer member with a head, which suppresses bleeding without applying a treatment liquid or powder other than the recording liquid, and also provides a high voltage. The object is to provide an image forming apparatus and an image forming method for forming an image while achieving uniform blurring suppression action, such as ensuring electrolysis of the recording liquid and suppressing blurring without using a large amount of electrolyte. And

  In order to achieve the above object, the present invention provides a head including a nozzle that discharges a conductive recording liquid in accordance with a drive signal, and a conductive recording liquid discharged by the head, and at least the surface is conductive. Between the intermediate transfer member and the head for electrolyzing the conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member. A voltage applying means for applying a voltage; a transfer means for transferring an image carried on the intermediate transfer member by a conductive recording liquid to a recording material; and for discharging the conductive recording liquid from the nozzle. Discharge control means for generating a drive signal, and the discharge control means applies the voltage to the drive signal by the voltage application means according to the interval between the nozzle and the intermediate transfer member. In an image forming apparatus amount of current flowing through the conductive recording liquid of the state can produces to be equal to each other.

  The present invention provides a head having a nozzle for discharging a conductive recording liquid in response to a drive signal, an intermediate transfer body having at least a surface conductive, to which the conductive recording liquid discharged by the head is applied, Voltage for applying voltage between the intermediate transfer member and the head for electrolyzing the conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member An application unit; a transfer unit that transfers an image carried on the intermediate transfer member to the recording material by a conductive recording liquid; and a discharge control that generates the drive signal to discharge the conductive recording liquid from the nozzle. And the discharge control means outputs the drive signal when the voltage is applied by the voltage application means according to the interval between the nozzle and the intermediate transfer member. Record Since the image forming apparatus generates the currents flowing in the liquid so that they are equal to each other, a processing liquid or powder other than the conductive recording liquid is applied while ensuring the discharge performance of the conductive recording liquid from the head. At the very least, regardless of the distance between the nozzle and the intermediate transfer member, the recording liquid is discharged so that the amount of current flowing through the conductive recording liquid at the time of bridge formation is equal to each other, so that bleeding is highly suppressed and high voltage is applied. In addition, the electrolysis of the conductive recording liquid can be ensured without using a large amount of electrolyte, and bleeding can be suppressed, reducing running costs and saving resources, and enabling high-quality image formation. An image forming apparatus can be provided.

1 is a schematic front view according to an embodiment of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic diagram illustrating a state in which conductive recording liquid is applied from a head to an intermediate transfer member in the image forming apparatus illustrated in FIG. 1. It is a control block diagram regarding the control means, head, and voltage application means shown in FIG. FIG. 2 is a conceptual diagram illustrating a state where pigments in a conductive recording liquid discharged from a head in the image forming apparatus illustrated in FIG. 1 are aggregated via protons. FIG. 2 is a conceptual diagram showing a state of a liquid column by a conductive recording liquid formed between a cathode and an anode in the image forming apparatus shown in FIG. FIG. 5 is a conceptual diagram for explaining a state where the position of the meniscus is located outside the nozzle while the recording liquid is temporarily bridged between the head and the intermediate transfer member. Correlation diagram schematically showing a correlation between the distance between the head, the intermediate transfer member, and the energization amount that is an integrated value of the current flowing in the recording liquid in a state where the head and the intermediate transfer member are temporarily bridged. It is. It is a conceptual diagram which shows the production | generation aspect of the 1st drive signal by a discharge control means, and a 2nd drive signal. Correlation diagram schematically showing the correlation between the voltage of the second drive signal and the energization amount that is the integrated value of the current flowing in the recording liquid in a state where the head and the intermediate transfer member are temporarily bridged. It is. By adjusting the voltage of the second drive signal in accordance with the distance between the head and the intermediate transfer body, or adjusting the distance between the first drive signal and the second drive signal, the head and the intermediate transfer FIG. 6 is a conceptual diagram showing that an energization amount that is an integrated value of a current flowing in a recording liquid in a state where the body is temporarily bridged is made uniform. A correlation between an interval between the first drive signal and the second drive signal and an energization amount that is an integrated value of a current flowing through the recording liquid in a state where the head and the intermediate transfer member are temporarily bridged is obtained. It is the correlation figure shown roughly. FIG. 3 is a schematic view corresponding to FIG. 2 of another configuration example of the image forming apparatus to which the present invention is applied. FIG. 13 is a control block diagram corresponding to FIG. 3 of the image forming apparatus shown in FIG. 12. FIG. 4 is a conceptual diagram showing that there is a correlation between an interval between a head and an intermediate transfer member and a maximum current value flowing through a conductive recording liquid discharged from the head. FIG. 4 is a conceptual diagram showing that there is a correlation between an interval between a head and an intermediate transfer member and an amount of energized charge flowing in a conductive recording liquid discharged from the head. FIG. 4 is a conceptual diagram showing that there is a correlation between an interval between a head and an intermediate transfer member and an energization start time of a current flowing in a conductive recording liquid discharged from the head. FIG. 4 is a conceptual diagram showing that there is a correlation between an interval between a head and an intermediate transfer member and an energization duration time of a current flowing through a conductive recording liquid discharged from the head. FIG. 4 is a schematic view corresponding to FIG. 2 of another configuration example of an image forming apparatus to which the present invention is applied. FIG. 19 is a control block diagram corresponding to FIG. 3 of the image forming apparatus shown in FIG. 18. FIG. 3 is a conceptual diagram showing a state in which pigments in a conductive recording liquid discharged from a head in an image forming apparatus having a metal intermediate transfer member surface aggregated via protons and metal cations. FIG. 2 is a schematic front view illustrating a configuration example of an image forming apparatus having a transfer image carrier having an elastic surface in an image forming apparatus having a metal intermediate transfer body surface.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a printer as an inkjet printer, and can perform full-color image formation. The image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside.

  The image forming apparatus 100 can form an image on a sheet-like recording medium using not only plain paper generally used for copying, but also OHP sheets, cardboard, cardboard, cardboard, and envelopes. It is. The image forming apparatus 100 is a single-sided image forming apparatus that can form an image on one side of a transfer sheet S that is a recording medium as a recording medium that is a recording medium. It may be an image forming apparatus.

  The image forming apparatus 100 ejects a recording liquid, which is a conductive recording liquid as ink of that color, capable of forming an image as an image corresponding to each color separated into yellow, magenta, cyan, and black. The recording heads 61 </ b> Y, 61 </ b> M, 61 </ b> C, and 61 </ b> BK are recording heads that are ink heads as recording liquid discharge bodies.

  The heads 61Y, 61M, 61C, and 61BK are disposed at positions facing the outer peripheral surface of the intermediate transfer body 37 that is an intermediate transfer drum disposed at a substantially central portion of the main body 99 of the image forming apparatus 100. The heads 61Y, 61M, 61C, 61BK are arranged in this order from the upstream side in the A1 direction, which is the moving direction of the intermediate transfer body 37 and is the clockwise direction in FIG. In the drawing, Y, M, C, and BK added after the numerals of the reference numerals indicate members for yellow, magenta, cyan, and black.

  The heads 61Y, 61M, 61C, and 61BK are respectively ink ejection devices 60Y, 60M, which are recording liquid ejection devices for forming yellow (Y), magenta (M), cyan (C), and black (BK) images. It is provided in 60C and 60BK. Each of the heads 61Y, 61M, 61C, and 61BK is provided in the ink ejection devices 60Y, 60M, 60C, and 60BK in such a manner that a plurality of the heads 61Y, 61M, 61C, and 61BK are arranged in parallel in the direction perpendicular to the paper surface of FIG.

  The intermediate transfer body 37 is rotated in the A1 direction and is recorded in yellow, magenta, cyan, and black from the heads 61Y, 61M, 61C, and 61BK in an area facing the heads 61Y, 61M, 61C, and 61BK. The liquids are ejected and applied in such a manner that they are sequentially superimposed, and an image is formed on the surface. As described above, the image forming apparatus 100 has a tandem structure in which the heads 61Y, 61M, 61C, and 61BK are opposed to the intermediate transfer member 37 and are arranged in parallel in the A1 direction.

  The recording liquid is ejected or applied to the intermediate transfer member 37 by the heads 61Y, 61M, 61C, 61BK upstream of the A1 direction so that the image areas of yellow, magenta, cyan, and black are overlapped at the same position on the intermediate transfer member 37. The timing is shifted from the side toward the downstream side.

  The image forming apparatus 100 includes ink discharge devices 60Y, 60M, 60C, and 60BK that are provided with heads 61Y, 61M, 61C, and 61BK, and an intermediate transfer member 37 that is transferred as the intermediate transfer member 37 rotates in the A1 direction. A transport unit 10 serving as a paper transport unit for transporting the paper S, and a feeding unit that can load a large number of transfer sheets S and feeds only the top transfer sheet S among the stacked transfer sheets S toward the transport unit 10. It has a paper unit 20 and a paper discharge tray 25 on which a large number of printed transfer papers S that have been transported by the transport unit 10 can be stacked.

  In the image forming apparatus 100, as shown in FIG. 2B, the liquid column of the recording liquid immediately after being ejected from the heads 61Y, 61M, 61C, 61BK is changed to the heads 61Y, 61M, 61C, 61BK, the intermediate transfer body 37, The electrode oxidation reaction is performed inside the recording liquid in such a liquid column so that a potential difference is formed between the intermediate transfer member 37 and the heads 61Y, 61M, 61C, 61BK in a state where the space between the intermediate transfer body 37 and the head 61Y, 61M, 61C, 61BK. Alternatively, an energizing means 33 as a voltage applying means for energizing the recording liquid in a state where the current component resulting from the electrode reduction reaction is applied and promoting the aggregation of the pigment or the thickening of the recording liquid as described later is provided. Have.

  As shown in FIG. 1, the image forming apparatus 100 also removes the recording liquid remaining on the intermediate transfer body 37 from the intermediate transfer body 37 after the recording liquid is transferred to the transfer paper S. A cleaning unit 34 as a cleaning unit for cleaning, a carriage 50 as a head support that integrally supports the heads 61Y, 61M, 61C, and 61BK, a CPU that controls the overall operation of the image forming apparatus 100, a memory, and the like And a control unit 40 as control means.

  Although not shown, the image forming apparatus 100 detects a phase of the intermediate transfer body 37 with respect to the reference point by detecting a predetermined reference point of the intermediate transfer body 37 in the A1 direction. It has an encoder as phase detection means.

  In addition to the intermediate transfer member 37, the transport unit 10 is disposed so as to face the intermediate transfer member 37, and when the transfer sheet S passes through the transfer unit 31 that is an area between the transfer unit S and the intermediate transfer member 37. The transfer means 64 for transferring the image of the recording liquid carried thereon onto the transfer paper S and the transfer paper S fed from the paper supply unit 20 are guided to the transfer unit 31 and passed through the transfer unit 31. A guide plate 39 that guides the transfer sheet S to the paper discharge table 25, and a motor or the like as a driving unit (not shown) that rotationally drives the intermediate transfer body 37 in the A1 direction. As described above, the image forming apparatus 100 is an indirect image forming apparatus that indirectly forms an image on the transfer sheet S using the intermediate transfer body 37.

  The transfer unit 64 includes a transfer roller 38 that rotates following the intermediate transfer member 37. The transfer roller 38 may include a heater for fixing the image transferred onto the transfer paper S to the transfer paper S. Further, the transport unit 10 may include a fixing roller as a fixing unit for fixing the image transferred from the intermediate transfer body 37 to the transfer sheet S by the transfer roller 38 on the transfer sheet S.

  As shown in FIG. 2, the intermediate transfer member 37 includes a support 37a made of aluminum, which is a conductive substrate, and a surface layer 37b made of silicone rubber formed on the support 37a. The material of the support 37a is not limited to aluminum, and may be formed of a metal such as an aluminum alloy, copper, or stainless steel as long as it has mechanical strength. The material of the surface layer 37b is not limited to silicone rubber. For the advantage of high releasability of the recording liquid, any elastic material having low surface energy and high followability to the transfer paper S may be used. You may form with rubber | gum, fluororubber, nitrile butadiene rubber, etc.

The surface layer 37b is a conductive rubber in which metal fine particles such as carbon, platinum, and gold as a conductive agent are dispersed and mixed in the rubber material in order to impart conductivity to the intermediate transfer member 37. It has become. However, when the number of conductive fine particles is increased, the conductivity is improved, but since there is a trade-off relationship in which the releasability is lowered, adjustment is necessary as appropriate. As will be described later, in order to form a desired potential difference in the liquid column of the recording liquid temporarily bridged by the heads 61Y, 61M, 61C, 61BK and the intermediate transfer body 37, the volume resistivity of the conductive rubber is 10 ^3. It is preferably less than Ω · cm, and preferably smaller than the volume resistivity of the recording liquid.

  The thickness of the surface layer 37b is preferably about 0.1 to 1 mm, and preferably 0.2 to 0.6 mm. However, the surface layer 37 b is not an essential component, and only the support 37 a may be used as the intermediate transfer member 37. Further, the intermediate transfer body 37 is not in a drum shape, but may be in an endless belt shape or in a sheet shape if possible.

  As shown in FIG. 1, the paper feeding unit 20 transports only the uppermost transfer paper S among the paper feed tray 21 on which a large number of transfer papers S can be stacked and the transfer paper S stacked on the paper feed tray 21. The sheet feeding roller 22 fed toward the unit 10, the casing 23 supporting the sheet feeding tray 21 and the sheet feeding roller 22, and the sheet feeding roller 22 are ejected from the recording liquid in the heads 61Y, 61M, 61C, 61BK. It has a motor or the like as a driving means (not shown) that rotates and feeds the transfer paper S so as to match the timing.

  The carriage 50 can be replaced with a new one when the heads 61Y, 61M, 61C, 61BK are deteriorated, and in order to facilitate maintenance, the heads 61Y, 61M, 61C, 61BK can be replaced. And can be attached to and detached from the main body 99. Each of the heads 61Y, 61M, 61C, 61BK can be independently attached to and detached from the main body 99 so that it can be replaced with a new one when deterioration or the like occurs and for easy maintenance. ing. This facilitates replacement work and maintenance work.

  The ink discharge devices 60Y, 60M, 60C, and 60BK have substantially the same configuration with respect to the other points although the colors of the recording liquid to be used are different. Each of the ink ejection devices 60Y, 60M, 60C, and 60BK includes a plurality of heads 61Y, 61M, 61C, and 61BK that are arranged in the main scanning direction. The ink ejection devices 60Y, 60M, 60C, and 60BK, and the image forming apparatus 100 are heads. It is a fixed full line type.

  The ink ejection devices 60Y, 60M, 60C, and 60BK are ink cartridges 81Y, 81M, and 81C that are recording liquid cartridges as main tanks that store the recording liquids of the corresponding colors supplied to the plurality of heads 61Y, 61M, 61C, and 61BK. , 81BK, a pump (not shown) as a supply pump for pumping and feeding the recording liquid stored in the ink cartridges 81Y, 81M, 81C, 81BK toward the heads 61Y, 61M, 61C, 61BK, and a pump Is a distributor as an ink supply unit that is a recording liquid supply unit that distributes and supplies the recording liquid supplied from the ink cartridges 81Y, 81M, 81C, and 81BK to the heads 61Y, 61M, 61C, and 61BK. With distributor tank

  The ink ejection devices 60Y, 60M, 60C, and 60BK are also inks (not shown) as ink amount detection means that are recording liquid amount detection means for detecting the recording liquid amount in order to detect a shortage of the recording liquid amount in the distributor tank. An amount detection sensor, a pipe (not shown) that forms a feeding path for the recording liquid between the ink cartridges 81Y, 81M, 81C, 81BK and the distributor tank together with a pump; a distributor tank and each head 61Y, 61M, 61C; And a pipe (not shown) that forms a recording liquid feeding path between the unit and 61BK.

  The ink cartridges 81Y, 81M, 81C, 81BK are replaced with new ones when the internal recording liquid is consumed and the remaining amount is low or no longer used, and in order to facilitate maintenance. 99 is removable.

  The operation of the pump is controlled by the control unit 40. Specifically, on the condition that the ink amount detection sensor detects the shortage of the recording liquid amount in the distributor tank, it is driven until this shortage is not detected, and the recording in the ink cartridges 81Y, 81M, 81C, 81BK is performed. Supply liquid to distributor tank. In this respect, the control unit 40 functions as an ink supply control unit that is a recording liquid supply control unit. The control unit 40 controls the driving of the image forming apparatus 100 even when not specifically described.

  The recording liquid contains at least a colorant corresponding to yellow, magenta, cyan, and black, an anionic dispersant that is a dispersant for the colorant, and a solvent. Due to the colorant and the dispersant, the ink component of the recording liquid has an anionic group. The solvent contains water from the viewpoint of safety and the conductivity from the viewpoint of causing electrolysis to be described later, and the recording liquid is a water-soluble recording liquid that is a conductive ink and a water-soluble ink. The recording liquid is desirably alkaline from the viewpoint of storage stability.

The pigment that is a colorant used in the recording liquid is not particularly limited, but as a pigment for orange or yellow, C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. And CI Pigment Yellow 185.
Further, as a pigment for red or magenta, C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.
Further, as a pigment for green or cyan, C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.
Further, as a pigment for black, C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.
The content of the pigment in the recording liquid is usually 0.1 to 40% by mass, preferably 1 to 30% by mass, and more preferably 2 to 20% by mass.

  In order to electrolyze the water in the recording liquid as described later, it is necessary to add an electrolyte component for increasing the ionic conductivity of the recording liquid. As electrolyte components to be added to the recording solution, sodium chloride, potassium chloride, lithium chloride, rubidium chloride, sodium bromide, sodium iodide, sodium sulfate, sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, potassium sulfate, sodium nitrate, sulfite Inorganic alkali metal salts such as sodium nitrate, potassium nitrate, sodium phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, potassium acetate, sodium oxalate, sodium citrate, sodium hydrogen citrate, potassium citrate, potassium hydrogen citrate Organic alkali metal salts such as ammonium chloride, ammonium nitrate, ammonium sulfate, tetramethylammonium chloride, tetramethylammonium nitrate, and organic ammonium salts such as choline chloride .

  Since a polyvalent metal salt having a valence of 2 or more impairs the solubility or dispersibility of a colorant, an ABA type amphiphilic polymer, or the like, a monovalent metal salt is preferable. In particular, it is preferable to add a quaternary ammonium salt as an electrolyte component. This is because the quaternary ammonium ions are dispersed in charge by an alkyl group bonded to the central element, and the interaction with the colorant, the ABA type amphiphilic polymer, etc. is small and stable. In addition, quaternary ammonium ions hardly form a cluster with water and rarely deprive water of hydration necessary for dissolution or dispersion of a colorant, an ABA type amphiphilic polymer, or the like. The electrical conductivity per unit molecular weight (molar ionic conductivity) is high for compounds having a small molecular weight, and among the quaternary ammonium salts, tetramethylammonium salts are particularly preferred. Counter ions include chloride ions, nitrate ions, sulfate ions, etc., but chloride ions may cause an electrode reaction at the anode to generate chlorine. Therefore, inactive nitrate ions and sulfate ions are preferable.

The anionic dispersant preferably includes a polymer type dispersant such as a polymer dispersant or a low molecular type dispersant such as a surfactant.
Examples of polymer type dispersants having an anionic group include polyacrylic acid and salts thereof, polymethacrylic acid and salts thereof, acrylic acid-acrylonitrile copolymers and salts thereof, and acrylic acid-alkyl acrylate copolymers. And its salt, styrene-acrylic acid copolymer and its salt, styrene-methacrylic acid copolymer and its salt, styrene-acrylic acid-alkyl acrylate copolymer and its salt, styrene-methacrylic acid-alkyl acrylate Ester copolymer and salt thereof, styrene-α methylstyrene-acrylic acid copolymer and salt thereof, styrene-α methylstyrene-acrylic acid copolymer-alkyl acrylate copolymer and salt thereof, styrene-maleic acid Copolymers and salts thereof, vinyl naphthalene-male Inacid copolymer and salt thereof, vinyl acetate-ethylene copolymer and salt thereof, vinyl acetate-crotonic acid copolymer and salt thereof, vinyl acetate-acrylic acid copolymer and salt thereof, β naphthalenesulfonic acid formalin condensate , Etc.

  Since these anionic polymers react with hydrogen ions generated by electrolysis of water and aggregate, they are preferable in terms of aggregation than the self-dispersing pigment alone. Further, since these anionic polymers have a colorant adhesion function, there is an advantage of improving the transfer rate from the intermediate transfer body 37 to the transfer paper S in the transfer process.

  Specific examples of the low molecular weight type dispersant having an anionic group include oleic acid and its salt, lauric acid and its salt, behenic acid and its salt, stearic acid and its salt, and such fatty acid and its salt. Salts, dodecylsulfonic acid and salts thereof, decylsulfonic acid and salts thereof, and alkylsulfuric acid and salts thereof, alkyl sulfate ertels such as lauryl sulfate and oleyl sulfate, dodecylbenzenesulfonic acid and salts thereof, lauryl Benzenesulfonic acid and its salts, and such alkylbenzenesulfonic acid and its salts, dioctylsulfosuccinic acid and its salts, dihexylsulfosuccinic acid and its salts, and such dialkylsulfosuccinic acid and its salts, naphthylsulfonic acid and Its salts, naphthylcarboxylic acid and Salts thereof, such aromatic anionic surfactants, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl ether sulfonates, fluorinated alkyl carboxylic acids and salts thereof, Examples thereof include dispersants using fluorine-based anionic surfactants such as fluorinated alkyl sulfonic acids and salts thereof.

  The recording liquid uses water as a main liquid medium. In order to make the recording liquid have desired physical properties or to prevent clogging of the nozzle 61c due to the drying of the recording liquid, a water-soluble organic solvent described below is used as a humectant component. It is preferable to use as.

  Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, and 1,4-butanediol. 1,5-pentanediol, 1,6-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, 1,2,4-butanetriol, 1, Polyhydric alcohols such as 2,3-butanetriol and petriol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethyl Polyhydric alcohol alkyl ethers such as ethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, N-methyl-2 -Pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, nitrogen-containing heterocyclic compounds such as ε-caprolactam, formamide, N-methylformamide, N, N-dimethylformamide, etc. Amides, monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine and other amines, dimethyl sulfoxide, sulfolane , Sulfur-containing compounds such as thiodiethanol, propylene carbonate, ethylene carbonate, γ-butyrolactone, and the like, and two or more of them may be used in combination.

  In addition, as other moisturizing components, sugar alcohols such as sorbitol, polysaccharides such as hyaluronic acid, polymers such as polyethylene glycol, and natural moisturizing components such as urea, lactic acid, citrate, and amino acids can be used. is there. These solvents are used alone or in combination with water. Although there is no restriction | limiting in particular in content of these water-soluble organic solvents, Preferably it is 1-60 weight% of the whole ink, More preferably, it uses in the range of 10-40 weight%.

  The recording liquid comprises an ABA type amphiphilic polymer composed of a hydrophobic A segment and a hydrophilic B segment, and a carboxylic acid surfactant that dissolves or disperses the ABA type amphiphilic polymer in the aqueous solvent. It is desirable to include.

  Any of the following can be applied as the hydrophobic A segment of the ABA type amphiphilic polymer, that is, the hydrophobic A block. Examples thereof include dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl and the like, which are linear alkyl groups having 12 or more carbon atoms. Examples of the branched alkyl group include 2-decyl dodecyl, 2-dodecyl dodecyl, 2-decyl hexadecyl, and the like. In addition, the aromatic-containing alkyl group includes phenylalkyl, diphenylalkyl, triphenylalkyl, naphthylalkyl, dinaphthylalkyl, trinaphthylalkyl, anthracenylalkyl, and a phenyl group in which the benzene ring is a branched alkyl group. Examples of dialkylphenylalkyl, trialkylphenylalkyl, and cyclic alkyl group-containing compounds include cyclohexylalkyl, dialkylcyclohexylalkyl, trialkylcyclohexylalkyl, cyclopentylalkyl, dialkylcyclopentylalkyl, and trialkylcyclopentylalkyl. As described above, the hydrophobic A block preferably includes at least one of a linear alkyl group, a branched alkyl group, a cyclic alkyl group, and a phenyl group.

  Further, it may be a block polymer made of a hydrophobic monomer. Examples thereof include styrene polymers, alkyl acrylate polymers, alkyl methacrylate polymers, acrylamide alkyl polymers, and methacrylamide alkyl polymers.

  Any hydrophilic B segment of the ABA-type amphiphilic polymer, that is, hydrophilic B block, can be used as long as it has an affinity for an aqueous solvent. In order to increase the viscosity of the ink composition by physical crosslinking by hydrophobic association in an aqueous solvent, the hydrophilic B block needs to have a sufficiently long chain length (larger) than the hydrophobic A block. Examples thereof include those having 100-mer or more such as ethylene oxide polymer and propylene oxide polymer containing linear polyethylene oxide. The hydrophilic B block may have a 4-Arms structure or a 6-Arms structure containing a multi-branched polyethylene oxide having a branched hydrophilic portion. Arms means hydrophobic A block. Thus, it is desirable that the hydrophilic B block contains at least one of linear polyethylene oxide and multi-branched polyethylene oxide.

As described above, the ABA type amphiphilic polymer is desirably an _An B type amphiphilic polymer having three or more hydrophobic A blocks. This is because hydrophobic association between the hydrophobic A segments is likely to occur, and the viscosity responsiveness to pH change is improved. The “ABA type” in the ABA type amphiphilic polymer means a structure in which a hydrophilic B block and a plurality of hydrophobic A blocks are bonded around a hydrophilic B block.

Other examples of the hydrophilic B block include vinyl alcohol polymers, vinyl ether polymers, vinyl pyrrolidone polymers, acrylamide polymers, methacrylamide polymers, and derivatives thereof. Also, it may be ionic, acrylate polymer, methacrylate polymer, alkyl quaternary ammonium salt polymer, alkyl quaternary ammonium salt polymer, acrylamide alkyl quaternary ammonium salt polymer, Examples thereof include styrene sulfonate polymer. In addition, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starch derivatives such as methyl starch, ethyl starch, hydroxyethyl starch, carboxymethyl starch, alginic acid derivatives such as propylene glycol alginate, gelatin, casein, albumin, collagen, etc. And derivatives of plant polymers such as guar gum, locust bean gum, quince seed gum and carrageenan, and derivatives of microbial polymers such as xanthan gum, dextran, hyaluronic acid, pullulan and curdlan.
The chemical bond between the hydrophobic A block and the hydrophilic B block may be any as long as it is stable, and examples thereof include an ether bond, a urethane bond, an amide bond, and an ester bond.

  Any carboxylic acid surfactant that dissolves or disperses the ABA-type amphiphilic polymer in an aqueous solvent may be used as long as it is composed of a hydrophobic alkyl moiety and a carboxylate. As such, sodium caproate, potassium caproate, sodium caprylate, potassium caprylate, sodium caprate, potassium caprate, sodium laurate, potassium laurate, sodium myristate, potassium myristate, sodium palmitate, Fatty acid salts such as potassium palmitate, sodium stearate, potassium stearate and the like can be mentioned. In addition to the monocarboxylic acid as described above, it may be a dicarboxylate or a tricarboxylate.

  As will be described later, the viscosity of the aqueous ink composition constituting the recording liquid changes depending on the pH. However, the change in pH of the recording liquid in this embodiment means that protons are supplied to the ink composition. means. PKa is a measure of the pH at which a carboxylate ion, which is a weak acid salt, is protonated. The pKa of the fatty acid salt is preferably about pKa: 7-9 and higher.

  There is no particular limitation on the average weight molecular weight of the ABA type amphiphilic polymer, but it is preferable that the molecular weight is small in view of ink jet discharge property in a completely dissolved or dispersed state with a carboxylic acid surfactant or the like. Considering the strength of the thickened state, it is preferable that the molecular weight of the polymer is large. Therefore, the thing of the range of 10,000 or more and 100,000 or less is preferable. Moreover, 20,000 or more and 50,000 or less are more preferable. The number of repeats of the polymer portion is preferably from 100 to 1000 mer. The concentration of the polymer in the ink composition is preferably in the range of 0.1% by weight to 10% by weight, and more preferably 0.5% by weight to 5% by weight.

  The viscosity of the recording liquid during ejection is 1 to 20 mPa · s, preferably 2 to 8 mPa · s. The recording liquid has a viscosity increase at least 10 times, preferably 100 times, more preferably 1000 times or more of the time of ejection due to thickening due to pH change after landing, which will be described later, and becomes a gel state. In addition, the preferable range of physical properties of the recording liquid is a surface tension of 10 to 60 mN / m, preferably 20 to 50 mN / m, and an electrical conductivity of 0.01 to 3 S / m, preferably 0.02 to 1 S / m. is there.

  As shown in FIG. 2, each of the heads 61Y, 61M, 61C, 61BK includes a conductive nozzle plate 61a disposed on the recording liquid discharge side facing downward in the drawing and a nozzle 61b formed on the nozzle plate 61a. And an ink chamber 61c as a liquid chamber supplied with the recording liquid from the distributor tank and filled with the recording liquid.

  As shown in FIG. 3, each of the heads 61Y, 61M, 61C, and 61BK also includes a piezoelectric element 61d that is an ink ejection unit serving as a recording liquid ejection unit that ejects the recording liquid in the ink chamber 61c from the nozzle 61b, and a piezoelectric element. A head driving circuit 61e as a head driving means for driving 61d.

  The nozzle plate 61a, the nozzle 61b, the ink chamber 61c, and the piezoelectric element 61d are provided as a set, and each of the heads 61Y, 61M, 61C, and 61BK is provided in large numbers. Is illustrated. One head driving circuit 61e is provided for each of the heads 61Y, 61M, 61C, 61BK.

  The nozzle plate 61a is provided in each of the heads 61Y, 61M, 61C, 61BK, and is common to all the nozzles 61b in each of the heads 61Y, 61M, 61C, 61BK.

  Although detailed illustration is omitted, the nozzle plate 61 a includes a conductive substrate and a water repellent film formed on the surface of the substrate facing the intermediate transfer body 37. The water-repellent film may be formed by applying a fluorine-based water repellent or a silicon-based water repellent, or may be formed by plating a fluorine-based polymer or a fluorine-metal compound eutectoid, Any film having water repellency is not particularly limited. The nozzle plate 61a includes a surface on the ink chamber 61c side as an interface forming portion that forms an interface with the recording liquid in the ink chamber 61c, and functions as a cathode as will be described later.

  The entire nozzle plate 61a may be conductive, or may be a member in which only the surface on the ink chamber 61c side is subjected to conductive treatment, or an intermediate member between the conductive member disposed on the ink chamber 61c side. You may comprise by the insulating member arrange | positioned by the transfer body 37 side.

  Since the conductive portion of the nozzle plate 61a is provided as a cathode as will be described later, it does not have to be made of a material having resistance to metal elution, and if it is made of a highly conductive material such as metal or carbon. Good.

  The nozzle plate 61 a is set so that the gap with the intermediate transfer member 37 is 50 to 200 μm. If the gap is less than 50 μm, it may be difficult to maintain the gap between the intermediate transfer member 37, which is a rotating body, and the nozzle plate 61a. If the gap exceeds 200 μm, the liquid injection described later may be performed. This is because it may be difficult to form a bridge. However, if the gap can be maintained, there is no particular problem even if it is less than 50 μm, and even if it is 200 μm or more, there is no problem if a stable liquid column bridge is formed.

  The piezoelectric element 61d is an actuator for causing the recording liquid to be ejected from each nozzle 61b as droplets and landed on the transfer paper S. The piezoelectric element 61d discharges the recording liquid from the nozzle 61b in accordance with a drive signal that is a voltage pulse applied to the piezoelectric element 61d under the control of the control unit 40.

  The piezoelectric element 61d is provided as a pressure applying unit that discharges the recording liquid by applying pressure to the ink chamber 61c. This pressure applying means may be a movable actuator of another type which is a shape deforming element type, such as a piezo type, instead of the piezoelectric element 61d. The ink discharge means may be a heating means that discharges the recording liquid from the nozzle 61b by a heater method such as a thermal method, and discharges the recording liquid by film boiling due to heating.

  The energizing unit 33 turns on / off the power source 33a that forms a predetermined voltage difference between the nozzle plate 61a and the intermediate transfer member 37 and serves as a power supply unit as a liquid column application power source with a variable output voltage. And a power switch 33b. The energizing means 33 also has an electric circuit (not shown) in which the power source 33a is connected to the support 37a and the nozzle plate 61a.

  With this electric circuit, the power source 33a has an anode connected to the support 37a and a cathode connected to the nozzle plate 61a. Therefore, the energizing unit 33 includes the intermediate transfer member 37 as an anode and the nozzle plate 61a as a cathode. In this way, the power source 33a maintains a predetermined potential difference between the nozzle plate 61a and the intermediate transfer member 37.

  The heads 61Y, 61M, 61C, 61BK and the energizing means 33 provided in each of the heads 61Y, 61M, 61C, 61BK constitute recording head devices 35Y, 35M, 35C, 35BK.

As shown in FIG. 1, the cleaning means 34 is constituted by a cleaning blade as a cleaning member formed of rubber as an elastic body, which is in contact with the intermediate transfer body 37 in a so-called counter contact manner. . The cleaning unit 34 may include a cleaning roller as a cleaning member together with the cleaning blade.
When the encoder detects the reference point of the intermediate transfer member 37, the encoder inputs a signal to that effect to the control unit 40.

  As shown in FIG. 3, the control unit 40 includes a print signal receiving unit 40a that receives an external print signal, and a head 61Y based on an input image that constitutes the print signal received by the print signal receiving unit 40a. Control of the voltage applied by the recording liquid discharge control means 40b as the ink discharge control means, which is a discharge control means for generating a predetermined drive signal for driving 61M, 61C, 61BK and inputting it to the head drive circuit 61e, and the energization means 33 The liquid column application voltage control means 40c is provided as voltage application control means for controlling the power supply 33a via the power switch 33b.

  The control unit 40 also includes a head drive voltage control table 40d for generating a drive signal to be input to the head drive circuit 61e in the recording liquid discharge control means 40b, and the gap between the nozzle plate 61a and the intermediate transfer body 37, in other words, the nozzle 61b. And a dimension measurement value storage means 40e as an interval storage means for storing intermediate transfer member dimension measurement values including a gap between the intermediate transfer member 37 and the intermediate transfer member 37.

  The print signal receiving unit 40 a is realized as a function of the I / O interface of the control unit 40. The recording liquid discharge control means 40b and the liquid column application voltage control means 40c are realized as a function of the CPU of the control unit 40. The head drive voltage control table 40d is realized as one function of the memory of the control unit 40. The dimension measurement value storage means 40e is realized as one function of the memory of the control unit 40.

  The print signal receiving unit 40a receives image information to be formed in the image forming apparatus 100 as a print signal from an external apparatus such as a PC externally connected to the image forming apparatus 100.

  The recording liquid discharge control means 40b generates a voltage pulse, which is a head drive waveform as a head drive signal for driving the piezoelectric element 61d, with a predetermined signal waveform by the head drive circuit 61e, and drives each of the piezoelectric elements 61d. Input as pulse and apply. For this purpose, the recording liquid discharge control means 40b generates a predetermined drive signal to be input to the head drive circuit 61e as described later.

  Therefore, each head 61Y, 61M, 61C, 61BK, specifically each nozzle 61b provided in each head 61Y, 61M, 61C, 61BK, records according to the drive signal generated by the recording liquid discharge control means 40b. The liquid is discharged.

  The liquid column application voltage control means 40c controls the voltage application timing and application time by the power source 33a. The liquid column application voltage control unit 40c also functions as a voltage changing unit that changes the voltage of the power source 33a.

  The recording liquid discharge control means 40b and the liquid column application voltage control means 40c are not realized as one function of the control unit 40, but may be provided in each of the recording head devices 35Y, 35M, 35C, and 35BK, for example. .

  The head drive voltage control table 40d is referred to by the recording liquid discharge control means 40b when generating a drive signal to be input to the head drive circuit 61e in the recording liquid discharge control means 40b.

  The intermediate transfer member dimension measurement value stored in the dimension measurement value storage unit 40e is a gap between the nozzle 61b and the intermediate transfer body 37, which is measured in advance as a characteristic value of the image forming apparatus 100 before shipment of the image forming apparatus 100. And data on the accuracy of this gap.

  The control unit 40 generates a paper feed signal as a media transport signal that drives a motor that rotationally drives the paper feed roller 22, and inputs the generated paper feed signal to the motor to drive the motor to rotate.

  The control unit 40 generates an intermediate transfer drive signal for driving a motor that rotationally drives the intermediate transfer body 37 and inputs the generated intermediate transfer drive signal to the motor to rotationally drive the motor. Since the control unit 40 receives a signal indicating that the reference point has been detected from the encoder, the control unit 40 manages and grasps the phase of the intermediate transfer body 37, that is, the rotational posture, by associating this signal with the intermediate transfer drive signal. .

  In the image forming apparatus 100 having such a configuration, the intermediate transfer body 37 rotates in the A1 direction while facing the heads 61Y, 61M, 61C, 61BK in response to the input of a predetermined signal indicating the start of image formation. In the process, the yellow, magenta, cyan, and black recording liquids are transferred from the heads 61Y, 61M, 61C, and 61BK so that the image areas of the respective colors of yellow, magenta, cyan, and black overlap with the same position on the intermediate transfer body 37. The images are ejected in such a manner that they are sequentially overlapped from the upstream side toward the downstream side in the A1 direction, and an image is temporarily carried on the intermediate transfer member 37.

At this time, the energizing unit 33 is driven by the control unit 40 as the voltage application control unit, and a voltage is applied between the support 37a and the nozzle plate 61a from the power source 33a.
In this state, the recording liquid is applied from the heads 61Y, 61M, 61C, 61BK onto the intermediate transfer body 37. At that time, first, the heads 61Y, 61M, 61C, 61BK are used as shown in FIG. As shown in FIG. 2B, the recording liquid forming a meniscus in the nozzle 61b moves toward the intermediate transfer body 37 as shown in FIG. 2B, and the recording liquid is recorded between the nozzle 61b and the intermediate transfer body 37. A bridge of a liquid column made of liquid is temporarily formed, and then, as shown in FIG. 2C, the bridge of the liquid column made of recording liquid is divided so as to be carried on the intermediate transfer body 37, and the intermediate transfer. An image of the recording liquid is formed on the body 37.

In the state where the liquid injection bridge made of the recording liquid is formed as shown in FIG. 2B, the colorant component in the recording liquid is subjected to an aggregating action by the energizing means 33. Specifically, the voltage application of the energizing means 33 causes the following electrode reactions to occur in the nozzle plate 61a serving as the cathode and the intermediate transfer member 37 serving as the anode, respectively, and the water contained in the bridge of the liquid column of the recording liquid. Electrolyzed.
^{_{Cathode: 4H 2 O + 4e - →}} 2H 2 + 4OH - ··· reaction formula (1)
_{^{Anode: 2H 2 O → 4H + +}} O 2 + 4e - ··· reaction formula (2)

  As a result, the water contained in the bridge of the liquid column of the recording liquid is oxidized on the surface of the intermediate transfer member 37 functioning as the anode to generate protons (H +). Therefore, as shown in FIG. The pigment P dispersed by D aggregates via protons. Alternatively, when an ABA type amphiphilic polymer and a carboxylic acid surfactant are included, the carboxylic acid surfactant is protonated to bond the hydrophobic groups of the ABA type amphiphilic polymer to each other. Liquid thickening occurs. The thickening of the recording liquid brings about an action of gelling the recording liquid.

  Thereby, the occurrence of bleeding between adjacent dots is suppressed, and a high-definition image is formed. In addition, there is an advantage that clogging of the nozzle 61b is prevented by such voltage application. The time for forming such a bridge can be controlled by the peak voltage and pulse width of the electromagnetic pulse applied to the piezoelectric element 61d.

Here, the bridge of the liquid column formed between the cathode and the anode will be described with reference to FIG. Inside the bridge B of the liquid column, cations and anions move in the vicinity of the cathode C and the anode A, respectively. As a result, the surface of the cathode C and the anode A, the electric double layer E _C and E _A respectively is formed, the charging speed of the electric double layer E _C and E _A is the conductivity of the bridge B of the liquid column, recording It is almost determined by the concentration of ions contained in the liquid. At this time, when the voltage of the electric double layer E _A reaches several V, Faraday current flows water is electrolyzed. As a result, on the surface of the anode A, water is oxidized to generate protons, and aggregation of the pigment dispersed by the anionic dispersant or thickening of the recording liquid occurs. That is, at the moment when such a bridge is formed, ions that cause an aggregation action of the pigment are efficiently generated in the bridge, so that the pigment is aggregated simultaneously with the landing of the recording liquid on the intermediate transfer body 37. As a result, pigment bleeding does not occur between adjacent recording liquid dots, and a very high-definition solute image is formed.

As described above, the energizing means 33 includes the intermediate transfer body 37 and the heads 61Y, 61M, 61C, 61BK, specifically the nozzle plate 61a for electrolyzing the recording liquid forming the bridge B of the liquid column. It is the structure for performing the voltage application between.
This voltage application is controlled by the control unit 40 functioning as a voltage application control means and a voltage changing means in order to control the amount of current flowing through the recording liquid by this voltage application.

  The time from the formation of the bridge B of the liquid column to the separation is usually several microseconds to several tens of microseconds, and the conductivity of the recording liquid is usually several tens mS / m to several hundreds mS / second. m. For this reason, in order to form an image of the recording liquid on the intermediate transfer member 37, the voltage applied by the energizing means 33 is 1.23 V, which is the theoretical decomposition voltage of water, or a number that is a general condition for electrolysis of water. V to several tens of volts is insufficient, and it is preferably several tens of volts to several hundreds of volts.

  In synchronization with the timing at which the leading edge of the image carried on the intermediate transfer body 37 reaches the transfer unit 31, a single sheet of transfer paper S fed from the paper supply unit 20 is supplied to the transfer unit 31, and the transfer roller 38. , The image carried on the intermediate transfer body 37 is transferred to the transfer sheet S passing through the transfer unit 31, and an image is formed on the surface of the transfer sheet S. The transfer sheet S on which the image is formed is guided to the paper discharge tray 25 and stacked on the paper discharge tray 25.

  When the image is transferred onto the transfer paper S in this way, the aggregated and thickened recording liquid is transferred onto the transfer paper S. Accordingly, an image is formed by the recording liquid that has been agglomerated and thickened by the above-described agglomeration and thickening action, thereby preventing or suppressing feathering and bleeding even when the transfer paper S is plain paper. High-speed image formation with high image density and high image quality is possible.

  In order to perform high-speed image formation, since the recording liquid needs to be quick-drying, the recording liquid generally has high absorbability to the transfer paper S. In this case, the recording liquid is deep in the transfer paper S. Penetrating to the surface and causing so-called offset, making it unsuitable for double-sided image formation. However, the aggregating / thickening action reduces the absorbability of the recording liquid onto the transfer paper S, so that the set-off is prevented or suppressed, and is suitable for double-sided image formation. Furthermore, since the absorbability of the recording liquid to the transfer paper S is reduced, deformation of the transfer paper S such as cockling and curling is suppressed or prevented, and thereby the transfer paper S carrying an image is conveyed. The handling of the transfer sheet S is facilitated, for example, the property is improved and jamming is prevented or suppressed.

  Almost no components due to the recording liquid remain on the intermediate transfer member 37 that has passed through the transfer unit 31 due to the transfer in the transfer unit 31, but the intermediate transfer member 37 is subjected to cleaning by the cleaning unit 34, thereby recording. Liquid offset is highly prevented or suppressed, and even when image formation is repeatedly performed, background contamination due to offset is prevented or suppressed, image deterioration and deterioration of the intermediate transfer body 37 are suppressed or prevented, and the time is good. Image formation can be performed.

  In the image forming apparatus 100 as described above, in order to perform good image formation in which bleeding is suppressed or prevented by the above-described aggregation / thickening action, the recording liquid generated on the surface of the intermediate transfer member 37 by the reaction formula (2). It is necessary that the amount of protons per unit volume is sufficiently ensured to perform such good image formation. The amount of such protons is increased by promoting the electrolysis represented by the reaction formula (2).

  Here, the amount of protons generated is determined by the integral value of the current I flowing in the recording liquid in a state where the heads 61Y, 61M, 61C, 61BK and the intermediate transfer body 37 are temporarily bridged per unit time. The current I is determined by the following (a) and (b).

(A) The recording liquid is applied between the intermediate transfer member 37 and the heads 61Y, 61M, 61C, 61BK, specifically, a liquid column that bridges between the nozzle plate 61a by the energizing means 33. Here, the current I at a certain time is proportional to this voltage.

(B) Electric resistance of recording liquid The current I at a certain time is inversely proportional to the electric resistance of the recording liquid. The value R of the electrical resistance is determined by the electrical conductivity σ of the recording liquid and the shape of the liquid column of the recording liquid, and is represented by the following equation (A). In the formula (A), r (x) represents the radius of the liquid column at the position x when the discharge direction of the recording liquid is taken on the x-axis, as shown in FIG.

Considering the shape of the liquid column of the recording liquid, generally, the recording liquid discharged from the nozzle has a thick tip and a cylindrical shape. I am interrupted.
For this reason, when such a voltage is constant, the current flowing through the recording liquid forming the liquid column is greatest at the moment of landing, and decreases as the liquid column becomes narrower as time passes.

  On the other hand, in the above-described process when the recording liquid is ejected from the nozzle 61b, the recording liquid discharged from the nozzle 61b reaches the intermediate transfer body 37 as the gap between the nozzle 61b and the intermediate transfer body 37 becomes narrower. The time until is shortened. For this reason, the energization start time of the current becomes earlier, and the formation time of the bridge of the liquid column made of the recording liquid becomes longer even if the volume of the ejected recording liquid is constant, and the nozzle plate 61a passes through the liquid column. Energizing time of the current flowing between the intermediate transfer member 37 and the intermediate transfer member 37 becomes longer. Further, if the volume of the ejected recording liquid is constant, the electric resistance of the recording liquid decreases because the thickness of the liquid column tends to increase as the gap becomes narrower.

  On the contrary, when the gap is widened, the time until the recording liquid discharged from the nozzle 61 b reaches the intermediate transfer member 37 becomes longer. Therefore, the energization start time of such current is delayed, and if the volume of the ejected recording liquid is constant, the time for forming the bridge of the liquid column made of the recording liquid is shortened, and the nozzle plate 61a is connected to the nozzle plate 61a via the liquid column. The energization time of the current flowing between the intermediate transfer member 37 is shortened. Further, if the volume of the recording liquid to be ejected is constant, the electric resistance of the recording liquid increases because the liquid column tends to become thinner as the gap becomes wider.

Therefore, if the applied voltage and the volume of the recording liquid to be ejected are constant, the current supply mode changes depending on the size of the gap.
Specifically, the energization amount, which is the amount of current per volume of the recording liquid that flows through the recording liquid while the bridge of the liquid column is formed, increases as the gap becomes smaller as shown in FIG. As the gap increases, it decreases. The amount of current and the amount of energization mean the sum of the currents flowing through the recording liquid while the liquid column bridge is formed, in other words, the integrated value.

  In addition, as described above, the recording liquid exhibits aggregating action and gelling action due to thickening when a voltage is applied. Since these actions correspond to the energization amounts, if the applied voltage and the volume of the ejected recording liquid are constant, these actions change when the gap size changes.

  That is, if the applied voltage and the volume of the recording liquid to be ejected are constant, as the gap is narrow and the energization amount is increased, the aggregation and gelling action of the recording liquid due to thickening increases, the gap is wide, and the energization amount is large. As the amount decreases, the aggregation and gelling action of the recording liquid due to thickening decreases. For this reason, when the applied voltage and the volume of the ejected recording liquid are constant, the image quality is affected by the size of the gap.

  However, the gap varies depending on the accuracy of the intermediate transfer body 37 itself or the parts supporting it. For example, when the intermediate transfer member 37 is eccentric, the gap fluctuates when the intermediate transfer member 37 rotates, and it is extremely difficult to completely eliminate such a gap change.

  Therefore, if the voltage applied by the power source 33a is constant and the volume of the ejected recording liquid is constant, the gap varies with the rotation of the intermediate transfer member 37 when the intermediate transfer member 37 rotates. Along with this, changes occur in the aggregating action and gelling action of the recording liquid, and the image quality changes.

  Here, considering the control of the voltage applied by the power source 33a, in this case, the same voltage is applied to each of the recording liquid ejected from the plurality of nozzles 61b. Therefore, when there is a gap variation along the arrangement direction of the nozzles 61b, a deviation occurs in the energization amount flowing through the recording liquid, and a difference occurs in the degree of bleeding and the degree of gelation in each of the recording liquids. Even if the number of nozzles 61b is singular, the phase of the intermediate transfer member 37 carrying the recording liquid discharged from the nozzle 61b is not always constant, and therefore a gap fluctuation occurs as the intermediate transfer member 37 rotates. As a result, the image quality changes.

  Therefore, in the image forming apparatus 100, the recording liquid discharge control unit 40b generates a drive signal for driving the heads 61Y, 61M, 61C, 61BK in accordance with the gap. That is, in the recording liquid discharge control unit 40b, when the voltage application for causing the above-described electrolysis to occur in the recording liquid column is performed by the energizing unit 33, the energization amounts flowing in the recording liquid column become equal to each other. As described above, the drive signal is generated according to the gap.

  The targets for which the energization amounts are equal to each other are the recording liquid ejected from different nozzles 61b and formed with a liquid column between the intermediate transfer member 37 and the intermediate transfer member 37 ejected from the same nozzle 61b. Is a recording liquid in a state in which a liquid column is formed. Therefore, the recording liquid discharge control means 40b generates the drive signals for driving the heads 61Y, 61M, 61C, 61BK so that the energization amounts for the nozzles 61b are equal to each other. In response to this, the recording liquid is discharged each time. Incidentally, if the number of nozzles 61b is singular, the generation of a drive signal for driving the head so that the energization amounts for the nozzles 61b are equal to each other is generated for the nozzles 61b according to the gaps. This is performed each time the recording liquid is discharged.

  In order to make the current amounts equal to each other, the recording liquid discharge control means 40b uses the drive signal so that the meniscus is positioned outside the nozzle 61b while the liquid column state of the recording liquid is formed. As such, each nozzle 61b is generated individually. The position of the meniscus is located outside the nozzle 61b means that the position of the meniscus is located outside the nozzle plate 61a or the heads 61Y, 61M, 61C, 61BK.

  Here, as shown in FIG. 6, the position of the meniscus is x in the central part of the meniscus formed in the nozzle 61b in a hemispherical shape by the recording liquid when considered excluding the liquid column portion of the recording liquid. Refers to the position that will be the tip in the direction. This position is the position of the tip portion in the x direction of the recording liquid that is cylindrical on the downstream side in the x direction with respect to the meniscus. Therefore, the state where the position of the meniscus in the state where the recording liquid is bridged is located outside the nozzle 61b indicates that the recording liquid is protruding from the entire nozzle 61b.

  However, the position of the meniscus does not always need to be outside the nozzle 61b while the bridge of the liquid column is formed, and the meniscus need only be located outside the nozzle 61b for a part of the time.

  By setting the meniscus in this way, the electric resistance of the entire liquid column of the recording liquid obtained by adding the liquid column portion of the recording liquid, that is, the recording liquid shown in FIG. The rate is reduced in the comparison over time. As a result, the amount of electrolysis per unit volume of the recording liquid increases as a whole, thereby increasing the energization amount. This energization amount is equivalent to the amount of protons per unit volume of the recording liquid.

  If the amount of such protons is sufficient without using a driving signal such that the position of the meniscus at the time of bridge formation is outside the nozzle 61b, the voltage to be applied by the energizing means 33 can be obtained using such a driving signal. Can be lowered. That is, in such a case, the voltage to be applied by the energizing means 33 may be lowered by using a drive signal that causes the meniscus position at the time of bridge formation to be outside the nozzle 61b.

  If this voltage is lowered, the required power due to the voltage applied by the energizing means 33 is suppressed and the scattering of the recording liquid due to the discharge of the recording liquid is suppressed or prevented, so that a better image formation can be performed. In such a case, instead of lowering the voltage to be applied by the energizing means 33, and in addition to this, the amount of electrolyte contained in the recording liquid may be reduced. Cost reduction and resource saving are possible.

  Examples of specific drive signals for equalizing the amounts of current flowing in the liquid column of the recording liquid when the voltage application for causing the above-described electrolysis in the liquid column of the recording liquid is performed by the energizing means 33 As shown in FIG. This drive signal realizes the shape of the liquid column in which the meniscus position at the time of bridge formation is outside the nozzle 61b. This drive signal is generated by the recording liquid discharge control means 40b in a state adjusted according to the gap between the nozzle 61b and the intermediate transfer member 37 as will be described later.

  The drive signal generated by the recording liquid discharge control means 40b is as follows, as shown in FIG. That is, the drive signal is formed as a first drive signal as a first drive pulse with a first signal waveform and as a second drive pulse with a second signal waveform formed at a predetermined time interval. And a second drive signal.

  In the example shown in FIG. 6A, the first drive signal is generated by the recording liquid ejected from the nozzle 61b, and the heads 61Y, 61M, 61C, 61BK, specifically the nozzle plate 61a and the intermediate transfer member 37. Is generated to form a bridge between the two. The second drive signal is generated in order to additionally discharge the recording liquid from the nozzle 61b in such a state formed by the first drive signal.

  In the example shown in FIG. 6A, the second drive signal supplies the recording liquid to the portion where the liquid column is narrow in the vicinity of the nozzle 61b, to alleviate the decrease in the diameter of the liquid column. And input to the piezoelectric element 61d. That is, the second drive signal relaxes the decrease in the current flowing through the liquid column of the recording liquid by the voltage applied by the energizing means 33, in other words, the electrolysis represented by the reaction formula (2) is maintained. It is generated for the purpose of doing so and input to the piezoelectric element 61d.

  In the example shown in FIG. 2A, the interval between the first drive waveform and the second drive waveform, that is, the time interval from the input of the first drive signal to the input of the second drive signal is It is set so that the electrolysis is efficiently maintained by the additional discharge of the recording liquid. That is, the shape of the liquid column of the recording liquid is set so as to maintain a shape that maintains the efficiency of electrolysis.

  However, if the recording liquid discharged from the nozzle 61b by the second drive signal lands on the intermediate transfer body 37, the volume of the recording liquid carried on the intermediate transfer body 37, that is, the electrolysis, causes aggregation / thickening. This increases the volume of the recording liquid to be acted on. In this case, eventually, it is necessary to supply as much electric power as the coagulation / thickening action increase, and a large increase in the amount of protons per unit volume of the recording liquid cannot be expected.

  Accordingly, the recording liquid discharge control means 40b paraphrases the second drive signal in the example shown in FIG. 7A so that the amount of additional recording liquid discharged from the nozzle 61b returns to the nozzle 61b. Then, the amount of recording liquid additionally discharged from the nozzle 61 b is generated so as not to land on the intermediate transfer body 37.

  However, the second drive signal in the example shown in FIG. 5A is required to be generated so that the total amount of the recording liquid additionally discharged from the nozzle 61b returns to the nozzle 61b side strictly. However, it is sufficient that the amount of protons generated per unit volume of the recording liquid is ensured.

  In addition, compared with the case where only the first drive signal is used, when the first drive signal and the second drive signal are used, there is the following tendency. That is, in such a case, as long as the recording liquid additionally discharged by the second drive waveform does not land on the intermediate transfer body 37, the stronger the second drive signal, the more landed on the intermediate transfer body 37 and the upper surface of the intermediate transfer body 37. There is a tendency that the amount of the remaining recording liquid slightly decreases. This is considered to be because a part of the recording liquid ejected by the first drive waveform is dragged toward the nozzle 61b when the additionally ejected recording liquid returns to the nozzle 61b.

  The time interval from the input of the first drive signal to the input of the second drive signal is such that the shape of the liquid column of the recording liquid is maintained in a shape that maintains the efficiency of electrolysis. From the viewpoint, it is also set by corresponding to the vibration cycle of the meniscus in the nozzle 61b.

  Explaining this point, the phase of the residual vibration of the meniscus in the recording liquid ejected by the first driving signal and the phase of the second driving signal, that is, the phase of the recording liquid additionally ejected by the second driving signal are described. If they match, it looks like this: That is, the recording liquid is efficiently supplied to the portion near the nozzle 61b where the liquid column is narrowed.

  Accordingly, the recording liquid discharge control means 40b is set so that the interval between the first drive signal and the second drive signal is an integral multiple of the vibration period. And satisfy | filling the conditions regarding this vibration period will also satisfy | fill the conditions regarding this viewpoint, ie, the conditions regarding liquid column shape maintenance.

  As for the condition related to the vibration cycle, the interval between the first drive signal and the second drive signal may be set so as to coincide with the vibration cycle in order to satisfactorily satisfy the condition related to the liquid column shape maintenance. preferable. This is because it is preferable to supply the recording liquid by the second drive signal before the liquid column becomes too thin, in other words, to replenish the liquid column in order to maintain the shape of the liquid column satisfactorily.

  The condition relating to the vibration cycle does not require that the interval between the first drive signal and the second drive signal is completely coincident with the meniscus vibration cycle itself or an integral multiple thereof, and may be shifted to some extent. . This is because even if the vibration period itself or an integer multiple thereof deviates by about ± 20%, a sufficient amount of protons generated per unit volume of the recording liquid may be secured. Therefore, a sufficient amount of protons generated per unit volume of the recording liquid can be secured to set the interval between the first drive signal and the second drive signal so as to coincide with the vibration period or an integral multiple thereof. Including deviations in the range of

The drive signal may be generated not only in the manner shown in FIG. 8A but also in the manner shown in FIG. 8B to FIG.
In the example shown in FIGS. 7B and 7C, the second drive signal is generated so as not to reduce the pressure in the nozzle 61b immediately after the first drive signal. In the example shown in (d), the recording liquid is supplied to the portion where the liquid column is narrowed by using the reaction to act only to reduce the pressure in the nozzle 61b immediately after the first drive signal. Thus, the second drive signal is generated.

  Note that in FIGS. 1A to 1D, the intervals between the first drive signal and the second drive signal correspond to each other between the first drive signal and the second drive signal. It is said that the time interval of the location.

  Further, the drive signal that causes the meniscus position at the time of bridge formation to be outside the nozzle 61b is the difference between the first drive signal and the second drive signal shown in FIGS. It is not limited to the combination.

  That is, the drive signal may be generated in any waveform as long as the amount of protons per unit volume of the recording liquid increases by setting the meniscus position at the time of bridge formation outside the nozzle 61b. Setting the position of the meniscus at the time of bridge formation outside the nozzle 61b reduces the electrical resistivity of the liquid column of the recording liquid over time, and increases the amount of electrolysis per unit volume of the recording liquid as a whole. It is to be.

As long as the amount of protons per unit volume of the recording liquid increases in this way, the drive signal may be generated in any waveform.
Note that the second drive signal may be generated and used in a plurality of times within a range that satisfies the above conditions.

  As described above, if the shape of the liquid column at the time of bridge formation is controlled by controlling the drive signal, the amount of energization is controlled, and variation in the amount of electrolysis is suppressed. By performing this control in consideration of the gap between the nozzle 61b and the intermediate transfer member 37, it is possible to make the energization amounts of the recording liquids of the respective liquid columns equal to each other.

  As another method for suppressing variation in the amount of electrolysis caused by the gap between the nozzle 61b and the intermediate transfer member 37, the following method can be considered. That is, a method of changing the voltage applied between the intermediate transfer member 37 and the heads 61Y, 61M, 61C, 61BK by the energizing means 33 in correspondence with the gap, a method of controlling the position of the head in correspondence with the gap, etc. It is.

  However, these methods are controls performed on all the nozzles 61b in the same head. Therefore, as already described with respect to the former method, since the fluctuation of the gap actually differs for each nozzle 61b, it is difficult to eliminate variation in the amount of electrolysis for each nozzle 61b only by these controls.

  On the other hand, if a method for controlling the shape of the liquid column at the time of bridge formation is used as in this embodiment, the variation in the amount of electrolysis due to the variation in the gap that differs for each nozzle 61b, that is, the variation in the energization amount. Suppression is done. As a result, the degree of bleeding and the degree of gelation are made uniform in each of the recording liquids, and image formation with good and constant image quality is performed.

  Since the volume of the recording liquid to which the voltage is applied by the power source 33a increases due to the additional discharge of the recording liquid, if the value of the voltage applied by the power source 33a is constant, the amount of protons to be generated decreases, and the aggregating action, gel It is thought that the degree of conversion will decrease.

  However, as described above, when the recording liquid is additionally ejected, the diameter of the liquid column is increased, the electrical resistance is decreased, and the amount of protons generated as a whole is increased. Protons are easily generated in the recording liquid in the vicinity of the surface of the intermediate transfer member 37 among the recording liquids forming the liquid column. The protons that contribute to image quality by causing aggregation and gelation are protons in the vicinity of the surface.

  Therefore, by adjusting the drive signals of the heads 61Y, 61M, 61C, and 61BK according to the gap between the nozzle 61b and the intermediate transfer member 37, the degree of bleeding and gelation of each of the recording liquid ejected from each nozzle 61b are adjusted. The image quality is made uniform, and image formation with good and constant image quality is performed.

  There are various methods for controlling the drive signal to suppress the variation in the energization amount. For example, as shown in FIG. 8, when a drive signal having a first drive signal and a second drive signal is used, the magnitude of the second drive signal is set for the recording liquid of each liquid column. There is a method of setting the energization amounts to be equal to each other.

  Here, FIG. 9 is a schematic diagram showing how the energization amount changes when the magnitude of the second drive signal, that is, the voltage is changed. From the figure, it can be seen that the energization amount increases as the magnitude of the second drive signal increases. This is because the liquid column near the nozzle becomes thicker as the magnitude of the second drive signal increases.

  Therefore, the magnitude of the second drive signal may be increased as the gap is increased, and the magnitude of the second drive signal may be decreased as the gap is decreased. However, as already described, if the second drive signal is too large, the recording liquid does not return to the nozzle 61b, and the energization amount becomes small.

  Therefore, the shape of the meniscus at the time of bridge formation is controlled by controlling the drive signal in such a range that the amount of recording liquid additionally discharged from the nozzle 61b returns to the nozzle 61b, and the energization amount is controlled in a certain range. It becomes possible to do.

  FIG. 10A shows a gap variation accompanying the rotation of the intermediate transfer member 37 in the period T of one rotation of the intermediate transfer member 37, and the magnitude of the second drive signal controlled in synchronization with this variation. The relationship of the time change of the applied voltage value of a 2nd drive signal and the energization amount of the recording liquid of a liquid column state is shown. This applied voltage value corresponds to the height of the drive voltage of the second drive waveform shown in FIG.

  In FIG. 10A, the applied voltage value of the second drive signal is set for the second drive signal using the head drive voltage control table 40d by the recording liquid discharge control means 40b in accordance with the gap fluctuation. It is calculated as a drive voltage value. The head drive voltage control table 40d stores an applied voltage value corresponding to the drive signal including the second drive signal, which is determined in advance corresponding to the size of the gap in order to equalize the energization amount. .

  That is, the applied voltage value is determined and the head drive voltage control table 40d is created so that the energization amount becomes constant according to the fluctuation of the gap. In determining the applied voltage value, the applied voltage value of the second drive signal for obtaining a constant energization amount capable of obtaining a sufficient proton amount for various gaps is measured.

  The change in the liquid column shape of the recording liquid due to the change in the gap is influenced by the characteristic value such as viscosity related to the behavior of the recording liquid. Therefore, the head drive voltage control table 40d for the second drive signal is created in consideration of the characteristic value and environment of the recording liquid.

  This figure shows that as a result of controlling the second drive voltage in accordance with the gap variation, the energization amount of the liquid column of the recording liquid becomes uniform regardless of the gap variation. As described above, when the magnitude of the second drive signal is controlled in accordance with the width of the gap in synchronization with the gap fluctuation, the energization amount becomes equal.

As another method for making the energization amounts equal to each other, there is a method of controlling the interval between the first drive signal and the second drive signal. That is, this interval is a method of setting the energization amounts for the recording liquids of the respective liquid columns to be equal to each other.
FIG. 11 is a schematic diagram showing how the energization amount changes when the interval according to FIG. 11 is changed.

  As already described, when the interval matches the phase of the residual vibration of the meniscus, the energization amount takes a peak value. In the figure, two peaks are observed, and the maximum values are shown at two locations. On the other hand, in the vicinity of the minimum value between the peak and the peak, the effect of increasing the energization amount by using the second drive signal in addition to the first drive signal is small. This is clear from the fact that the minimum value and the energization amount when the second drive signal is not used, which are also shown in FIG.

Further, in the portion surrounded by an ellipse in the figure, the energization amount decreases as the interval between the first drive signal and the second drive signal increases. This indicates that the amount of electrolysis decreases when the interval between the first drive signal and the second drive signal increases in such a portion.
Therefore, by using this relationship and controlling the distance between the first drive signal and the second drive signal within a range surrounded by an ellipse, it is possible to control the energization amount to be constant.

  FIG. 10B shows a gap variation accompanying the rotation of the intermediate transfer member 37 in one rotation period T of the intermediate transfer member 37, and the first drive signal and the second drive signal in synchronization with the change. The relationship of the time change of this space | interval when controlling a space | interval and the energization amount of the recording liquid of a liquid column state is shown. This interval corresponds to the interval shown in FIG.

  In FIG. 10B, the interval is calculated by the recording liquid discharge control means 40b using the head drive voltage control table 40d according to the gap fluctuation. The head drive voltage control table 40d stores such intervals determined in advance corresponding to the size of the gap in order to equalize the energization amount.

  That is, according to the change in the gap, the interval is determined so that the energization amount is constant, and the head drive voltage control table 40d is created. In determining such an interval, such an interval for obtaining a constant energization amount capable of obtaining a sufficient proton amount is measured for various gaps.

  The change in the liquid column shape of the recording liquid due to the change in the gap is influenced by the characteristic value such as viscosity related to the behavior of the recording liquid. Therefore, the head drive voltage control table 40d for the interval is created in consideration of the characteristic value and environment of the recording liquid.

  This figure shows that as a result of controlling the interval corresponding to the gap variation, the energization amount of the liquid column of the recording liquid becomes uniform regardless of the gap variation. Thus, if the length of the interval is controlled in accordance with the width of the gap in synchronization with the gap fluctuation, the energization amount becomes equal.

  As described above, two examples of the adjustment of the drive signal for equalizing the energization amount according to the variation of the gap are given. The following is a case where the former method of controlling the voltage of the second drive signal is applied. Will be explained. Note that the interval between the first drive signal and the second drive signal may be controlled instead of or together with the control of the voltage of the second drive signal, or another control method may be used alone or You may use it with an appropriate combination with this method.

  Based on the above, in the image forming apparatus 100 according to the present embodiment, the intermediate transfer member 37 is determined as the intermediate transfer member dimension measurement value as the intermediate transfer member dimension data measured in advance in the dimension measurement value storage unit 40e. The reference point is stored in association with the phase of the intermediate transfer member 37. The intermediate transfer member dimension measurement value includes a change in the gap between the nozzle 61 b and the intermediate transfer member 37.

  At the time of image formation, the control unit 40 grasps the phase of the intermediate transfer body 37 based on the input from the encoder, and the recording liquid discharge control means 40b determines the intermediate transfer member dimension measurement value in accordance with the phase. Read from the dimension measurement value storage means 40e.

  The recording liquid discharge control means 40b reads out the intermediate transfer member dimension measurement value and refers to the head drive voltage control table 40d, and reads out the intermediate transfer member dimension read out of the drive signals stored in the head drive voltage control table 40d. Select the drive signal corresponding to the measured value. In this way, the recording liquid discharge control means 40b determines a drive signal, in particular, the second drive signal, in which the energization amount of the recording liquid in the liquid column is constant regardless of the gap between the nozzle 61b and the intermediate transfer member 37. And generate.

  The recording liquid discharge control means 40b inputs the generated drive signal to the head drive circuit 61e. As a result, the head drive circuit 61e inputs a voltage pulse to the piezoelectric element 61d to drive the heads 61Y, 61M, 61C, 61B, and ejects the recording liquid from the nozzle 61b.

  On the other hand, the liquid column application voltage control means 40c drives the power switch 33b so as to include the timing at which the liquid column of the recording liquid is formed, and a voltage is applied between the nozzle plate 61a and the intermediate transfer member 37 by the power source 33a. Apply. While this voltage application is being performed, a liquid column is formed between the nozzle 61 b and the intermediate transfer member 37.

  The voltage value applied by the power source 33a is controlled by the liquid column application voltage control means 40c, but the voltage value may be constant or may be changed according to the phase of the intermediate transfer member 37. When changing the voltage value of the power supply 33a, the gap fluctuations related to all the nozzles 61b in the same head are separated from those that are not, the former is the control of the power supply 33a, the latter is the control of the voltage of the second drive pulse, etc. It is better to distribute the drive signal control.

  In the above-described embodiment, the magnitude of the second drive signal is controlled according to the known gap between the nozzle 61b and the intermediate transfer member 37 stored in the dimension measurement value storage unit 40e. However, as shown in FIGS. 12 and 13, the image forming apparatus 100 includes a gap measurement sensor 36 as an interval measurement unit that measures the gap, and a second measurement is performed according to the gap measured by the gap measurement sensor 36. Control of the drive signal including the drive signal may be performed.

  As shown in FIG. 12, the gap measurement sensor 36 is provided integrally with each of the heads 61Y, 61M, 61C, and 61BK. The gap measurement sensor 36 is an optical sensor that measures the gap by measuring the surface position of the intermediate transfer body 37 with respect to the nozzle 61b. Since the gap measuring sensor 36 is provided integrally with the heads 61Y, 61M, 61C, 61BK, even if the positions of the heads 61Y, 61M, 61C, 61BK change over time or due to vibrations, the gap is accurate. Is measured.

  The gap measurement sensor 36 is located upstream of the position where the nozzle 61b discharges the recording liquid in the rotational direction of the intermediate transfer body 37, which is the relative movement direction of the nozzle 61b and the intermediate transfer body 37, that is, the intermediate transfer body on the left side in FIG. The surface position of 37 is measured. Therefore, the gap measuring sensor 36 is integrally provided in each of the heads 61Y, 61M, 61C, 61BK on the upstream side of the nozzle 61b in the rotational direction.

  This is because a time lag from when the gap measurement sensor 36 measures the gap to determine a drive signal including the second drive signal and to apply a voltage to the piezoelectric element 61d according to the determined drive signal is considered. Is. Therefore, the gap at the position upstream of the recording liquid landing position on the intermediate transfer body 37 in the rotational direction is measured in advance from the recording liquid discharge timing.

  To what extent the gap measurement position is positioned upstream in the rotational direction relative to the liquid deposition position is the time lag, that is, the gap measurement sensor 36, the control unit 40, the recording head devices 35Y, 35M, 35C, 35BK, etc. Responsiveness, processing speed, etc.

  As shown in FIG. 13, the control unit 40 includes a gap measurement value input unit 40f instead of the dimension measurement value storage unit 40e shown in FIG. The gap measurement value input unit 40 f is realized as a function of the I / O interface of the control unit 40.

  The gap measurement value input unit 40f inputs the gap between the nozzle 61b and the intermediate transfer body 37, which is input from the gap measurement sensor 36, to the recording liquid discharge control means 40b. This input is associated with the phase of the intermediate transfer body 37. Done. Thereafter, the recording liquid discharge control means 40b determines a drive signal including the second drive signal with reference to the head drive voltage control table 40d. The operation of applying a voltage to the piezoelectric element 61d in accordance with the determined drive signal and ejecting the recording liquid from the nozzle 61b is the same as that described above.

  As described above, since the gap is measured and controlled in real time, even when the heads 61Y, 61M, 61C, and 61BK undergo positional fluctuations over time, the gap is accurately grasped, and the voltage value is determined. Determination and control based on the determination are performed with high accuracy.

  The gap measuring means does not directly detect the gap optically like the gap measuring sensor 36, but substantially measures by measuring the energization state between the nozzle plate 61a and the intermediate transfer body 37. It may be.

  For example, as the gap between the nozzle 61b and the intermediate transfer body 37 becomes narrower, the time until the recording liquid ejected from the nozzle 61b reaches the intermediate transfer body 37 becomes shorter, and the current application start time becomes faster. Is used. Further, as the gap between the nozzle 61b and the intermediate transfer body 37 becomes narrower, the time until the recording liquid discharged from the nozzle 61b reaches the intermediate transfer body 37 is shortened, and a bridge of liquid columns made of the recording liquid is formed. Take advantage of the increased time. Therefore, the gap is substantially measured by measuring the energized state using at least one of these.

  With reference to FIGS. 14 to 17, it will be described that the gap between the nozzle 61 b and the intermediate transfer body 37 is measured by measuring the energization state between the nozzle plate 61 a and the intermediate transfer body 37.

  FIG. 14 shows the relationship between the maximum current value when the recording liquid in a state where the nozzle 61 b and the intermediate transfer body 37 are bridged is energized and the gap distance between the nozzle 61 b and the intermediate transfer body 37. .

  FIG. 15 shows the amount of electric charge that flows between the nozzle 61b and the intermediate transfer body 37 when the recording liquid in a state where the nozzle 61b and the intermediate transfer body 37 are bridged, and the nozzle 61b and the intermediate transfer body 37. The relationship with the gap distance with the body 37 is shown. This energized charge amount is an integrated value of the current amount and is equivalent to the energized amount.

  FIG. 16 shows the state from when the driving of the heads 61Y, 61M, 61C, 61BK is started until the recording liquid bridges between the nozzle 61b and the intermediate transfer body 37 and energization between the nozzle 61b and the intermediate transfer body 37 starts. And the gap distance between the nozzle 61b and the intermediate transfer member 37 is shown.

  FIG. 17 shows a state in which the nozzle 61b and the intermediate transfer body 37 are bridged, and after the energization starts between the nozzle 61b and the intermediate transfer body 37, the state where the recording liquid is applied is canceled and the energization is cut off. The relationship between the energization continuation time and the gap distance between the nozzle 61b and the intermediate transfer member 37 is shown.

  In each of these figures, the points indicated by black circles indicate data obtained as a result of experiments, and straight lines or curves indicate results obtained by fitting such data using polynomials or the like. As is clear from these figures, the energization feature amount indicating the energization state between the nozzle plate 61a and the intermediate transfer body 37, that is, the maximum current value in FIG. 14, the energization charge amount in FIG. 15, and the energization start time in FIG. There is a clear correlation between the energization duration in FIG. 17 and the gap distance.

  That is, the maximum current value, the energized charge amount, and the time change which are energization feature amounts have dependency on the gap distance. For example, as the gap between the nozzle 61b and the intermediate transfer member 37 becomes narrower, the time until the recording liquid ejected from the nozzle 61b reaches the intermediate transfer member 37 becomes shorter, and the current application start time becomes shorter. Along with this, the energization continuation time, which is the formation time of the bridge of the liquid column made of the recording liquid, becomes longer, and the maximum current value of the current flowing between the nozzle plate 61a and the intermediate transfer body 37 via the liquid column, Energized charge amount increases. Therefore, it is possible to calculate the gap distance by measuring and extracting at least one energization feature amount among the maximum current value, energization charge amount, energization start time, and energization duration time.

  For the calculation of the gap distance, it is possible to employ means for calculating the gap distance based on a coefficient fitted with a polynomial or the like from the result of measurement in advance. Further, instead of this means, or together with this means, a means for calculating a gap distance by creating a lookup table from a result obtained by measuring in advance and referring to the table can be adopted.

  Further, as described above, since the ejection state of the recording liquid from the nozzle 61b differs depending on the signal of the head drive circuit 61e, that is, the drive pulse, fitting coefficients and lookup tables are prepared for a plurality of ejection conditions. More preferred. In order to calculate the gap distance more accurately, an average value may be adopted by calculating the gap distance from a plurality of energization feature amounts.

  18 and 19, an ammeter 33c is provided as an interval measuring means for measuring a gap between the nozzle 61b and the intermediate transfer body 37 by measuring a current-carrying state between the nozzle plate 61a and the intermediate transfer body 37. An example configuration is shown.

  As shown in FIG. 18, the ammeter 33c is provided in each of the heads 61Y, 61M, 61C, and 61BK. In order to measure the gap between the nozzle 61b and the intermediate transfer body 37, the ammeter plate 61a and the intermediate transfer The current between the body 37 is measured as the amount of liquid column energization current.

  As shown in FIG. 19, with the provision of the ammeter 33c, the control unit 40 replaces the dimension measurement value storage unit 40e shown in FIG. 3 and the gap measurement value input unit 40f shown in FIG. A current value input unit 40g is provided. The current value input unit 40g receives the liquid column energization current amount from the ammeter 33c as an energization feature amount measurement signal including information on the above energization feature amount. The current value input unit 40g is realized as one function of the I / O interface of the control unit 40.

  The current value input unit 40g inputs the liquid column energization current amount input from the ammeter 33c to the recording liquid discharge control means 40b. This input is performed in association with the phase of the intermediate transfer member 37. In the head drive voltage control table 40d, the above-described fitting coefficient and lookup table are prepared. Determination of the drive signal including the second drive signal by the recording liquid discharge control means 40b using the head drive voltage control table 40d uses such a fitting coefficient and a lookup table based on the liquid column energization current amount. Done. At this time, the second drive is performed using at least one of the above-described energization feature amounts indicating the energization state between the nozzle plate 61a and the intermediate transfer body 37, which is included in the liquid column energization current amount. A drive signal including the signal is determined.

The operation of applying a voltage to the piezoelectric element 61d in accordance with the determined drive signal and discharging the recording liquid from the nozzle 61b is the same as in the above-described embodiment.
However, the control based on the determined drive signal cannot be performed for the ejection of the recording liquid used to determine the voltage value due to a delay in the control process.

  Therefore, the generation of the drive signal corresponding to the gap substantially measured based on the measured liquid column energization current amount and the control using the generated drive signal are specifically performed when the subsequent image formation is performed. This is performed when an image is formed by discharging the recording liquid after one rotation of the intermediate transfer member 37. That is, a driving signal is generated each time the recording liquid is ejected, and the control using the generated driving signal uses the liquid column energization current amount measured before one rotation of the intermediate transfer body 37.

  For this reason, the voltage value applied by the power source 33a before one rotation of the intermediate transfer body 37 is also used for determining the drive signal including the second drive signal by the head drive voltage control table 40d. Therefore, in the head drive voltage control table 40d, a fitting coefficient and a lookup table are prepared for such voltage values.

  In this way, the gap is generated by utilizing the energized state of the bridge of the liquid column made of the recording liquid between the nozzle plate 61a and the intermediate transfer body 37, which is generated when the recording liquid is agglomerated and gelled. Therefore, even when the heads 61Y, 61M, 61C, and 61BK change their position over time, the gap is accurately measured, and the determination of the voltage value and the control based on the gap are relatively low cost. It is done with high accuracy.

  Note that for the first image formation immediately after receiving the print signal, that is, the first image formation, the gap measurement is performed using the liquid column energization current measured during maintenance such as pre-printing idle discharge. Then, a drive signal is generated based on this gap, and a voltage is applied using the generated drive signal during subsequent image formation.

Here, in the configuration in which the intermediate transfer body 37 is not provided with the surface layer 37b and is composed of the support body 37a, the support body 37a functions as an anode as described above. In this case, it is possible to oxidize the support body 37a which is a metal together with water on the surface of the support body 37a. When the support 37a, which is a metal, is oxidized, a metal cation excellent in aggregating the colorant is generated. Therefore, as shown in FIG. 20, an anionic property is obtained via the proton and the metal cation (M ^{n +} ). The pigment P dispersed by the dispersant D is aggregated, and the cohesion is increased.

  In such a configuration, as shown in FIG. 21, the transfer means 64 transfers not only the transfer roller 38 but also the image formed on the intermediate transfer body 37 and temporarily supports it as an elastic layer on the surface. It is desirable to provide an intermediate transfer drum 63 as a transfer image carrier having a rubber layer 63a. The intermediate transfer drum 63 is rotated with the intermediate transfer member 37, and the transfer roller 38 is rotated with the intermediate transfer drum 63. Since the surface of the intermediate transfer drum 63 is an elastic body, the transfer of the image from the intermediate transfer body 37 made of metal and having a high surface hardness is performed well, and the transferability is improved.

  The intermediate transfer drum 63 has a rubber layer 63a and a base 63b covered with the rubber layer 63a. Although it does not specifically limit as a material which comprises the base | substrate 63b, Metals, such as aluminum, an aluminum alloy, copper, and stainless steel, are mentioned. Although it does not specifically limit as a material which comprises the rubber layer 63a, Silicone rubber, urethane rubber, fluorine rubber, etc. are mentioned.

  Here, the control unit 40 records in the memory the recording liquid ejected by the heads 61Y, 61M, 61C, 61BK and the heads 61Y, 61M, 61C, 61BK provided with the nozzles 61b that eject the recording liquid in accordance with the drive signal. The intermediate transfer member 37 having at least the surface conductive and the heads 61Y, 61M, 61C, 61BK discharged from the heads 61Y, 61M, 61C, 61BK and the intermediate transfer member 37 are temporarily bridged. Energized means 33 for applying a voltage between the intermediate transfer body 37 for electrolyzing the recording liquid in the state and the heads 61Y, 61M, 61C, 61BK, and carried on the intermediate transfer body 37 by the recording liquid Transfer means 64 for transferring the image to the transfer paper S and drive signals for discharging the recording liquid from the nozzles 61Y, 61M, 61C, 61BK The control unit 40 that functions as a discharge control unit that generates the control signal and the control unit 40 that functions as a discharge control unit sends the drive signal according to the interval between the nozzles 61Y, 61M, 61C, 61BK and the intermediate transfer member 37. An image forming program for executing an image forming method for generating the current amounts flowing in the recording liquid in such a state when the voltage application is performed by the energizing unit 33 is stored.

  In this regard, the control unit 40 or the memory functions as an image forming program storage unit. Such an image forming program can be stored not only in the memory provided in the control unit 40 but also in, for example, the following storage medium. That is, a storage medium such as a semiconductor medium (for example, ROM, nonvolatile memory, etc.), an optical medium (for example, DVD, MO, MD, CD-R, etc.), a magnetic medium (for example, hard disk, magnetic tape, flexible disk, etc.) It is. When such an image forming program is stored, such a memory, a storage medium, and the like constitute a computer-readable recording medium that stores the image forming program.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

For example, the pigment in the conductive recording liquid may be dispersed by a cationic dispersant and aggregated via hydroxide ions generated on the surface of the intermediate transfer member functioning as a cathode.
The intermediate transfer member does not need to be conductive as a whole, and at least the surface may be conductive.

  The image forming apparatus to which the present invention is applied is not limited to the above-described type of image forming apparatus, but may be other types of image forming apparatuses, that is, a shuttle type with respect to the head, or a copying machine or a facsimile alone. Alternatively, these multifunction peripherals, multifunction peripherals such as monochrome machines related thereto, other image forming apparatuses used for forming electric circuits, and image forming apparatuses used for forming predetermined images in the biotechnology field may be used. . The number of heads is increased or decreased according to the application of the image forming apparatus, and may be one or plural.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

33 Voltage application unit 33c Interval measurement unit 36 Interval measurement unit 37 Intermediate transfer body 40, 40b Discharge control unit 40e Interval storage unit 61b Nozzle 61Y, 61M, 61C, 61BK Head 64 Transfer unit 100 Image forming apparatus S Recording material

JP-A-01-130949 Japanese Patent No. 2724141 JP 2008-62397 A Japanese Patent Laid-Open No. 11-188858 JP 2010-188665 A JP 2011-189706 A

Claims (15)

A head including a nozzle for discharging a conductive recording liquid in response to a drive signal;
An intermediate transfer body having at least a surface conductive, to which the conductive recording liquid discharged by the head is applied,
For applying a voltage between the intermediate transfer member and the head for electrolyzing a conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member. Voltage applying means;
Transfer means for transferring an image carried on the intermediate transfer member by a conductive recording liquid to a recording material;
Discharge control means for generating the drive signal to discharge conductive recording liquid from the nozzle,
The ejection control unit is configured to apply the drive signal to the conductive recording liquid in the state when the voltage is applied by the voltage application unit according to the interval between the nozzle and the intermediate transfer member. An image forming apparatus that generates images so that they are equal to each other. The image forming apparatus according to claim 1.
The ejection control means generates the drive signal so that the meniscus is positioned outside the nozzle while the state is formed in order to make the current amounts equal to each other. Image forming apparatus. The image forming apparatus according to claim 1 or 2,
In order to make the current amounts equal to each other, the discharge control means includes a first drive signal for forming the state as the drive signal, and the nozzle in the state formed by the first drive signal. Generating a second drive signal for additionally discharging conductive recording liquid from the image forming apparatus. The image forming apparatus according to claim 3.
The image forming apparatus, wherein the ejection control unit sets the magnitude of a second drive signal so that the current amounts are equal to each other. The image forming apparatus according to claim 3 or 4, wherein:
The image forming apparatus, wherein the ejection control unit sets an interval between the first drive signal and the second drive signal so that the current amounts are equal to each other. The image forming apparatus according to any one of claims 1 to 5,
Having interval storage means for storing the interval measured in advance;
The image forming apparatus, wherein the ejection control unit generates the drive signal in accordance with the interval stored in the interval storage unit. The image forming apparatus according to any one of claims 1 to 5,
Having interval measuring means for measuring the interval;
The image forming apparatus, wherein the ejection control unit generates the drive signal according to the interval measured by the interval measurement unit. The image forming apparatus according to claim 7.
The image forming apparatus, wherein the interval measuring unit measures the interval by measuring a surface position of the intermediate transfer member with respect to the nozzle. The image forming apparatus according to claim 8.
The interval measuring means measures the interval by measuring the surface position upstream of the position where the nozzle discharges the conductive recording liquid in the relative movement direction of the nozzle and the intermediate transfer member. The image forming apparatus is provided integrally with the head. The image forming apparatus according to any one of claims 7 to 9,
The image forming apparatus, wherein the interval measuring unit measures the interval by measuring an energized state between the head and the intermediate transfer member. The image forming apparatus according to claim 10.
The interval measuring means has a maximum current value when the conductive recording liquid in the state is energized between the head and the intermediate transfer member, and when the conductive recording liquid in the state is energized, The amount of charge flowing between the head and the intermediate transfer member, the energization start time from the start of driving the head until the conductive recording liquid is in the state and energization is started between the head and the intermediate transfer member; At least one of the energization continuation time from when the conductive recording liquid is in the state until energization is started between the head and the intermediate transfer member until the conductive recording liquid is released from the state An image forming apparatus, wherein the interval is measured by measuring as an energized state. The image forming apparatus according to claim 10 or 11,
The image forming apparatus according to claim 1, wherein the generation of the driving signal according to the interval measured by measuring the energized state is performed when the state is formed and image formation is performed after the measurement. The image forming apparatus according to any one of claims 10 to 12,
An image forming apparatus characterized in that the measurement of the energized state and the generation of the drive signal performed by the discharge control means performed based on the interval measured by the measurement are performed during maintenance. The image forming apparatus according to any one of claims 1 to 13,
A plurality of the nozzles are provided, and the discharge control unit generates the drive signal individually for each nozzle so that the amount of current flowing through the conductive recording liquid in the state for each nozzle is equal to each other. An image forming apparatus. A head including a nozzle for discharging a conductive recording liquid in response to a drive signal;
An intermediate transfer body having at least a surface conductive, to which the conductive recording liquid discharged by the head is applied,
For applying a voltage between the intermediate transfer member and the head for electrolyzing a conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member. Voltage applying means;
Transfer means for transferring an image carried on the intermediate transfer member by a conductive recording liquid to a recording material;
Using discharge control means for generating the drive signal to discharge the conductive recording liquid from the nozzle,
The amount of current that flows through the conductive recording liquid in the state when the voltage is applied by the voltage application unit according to the interval between the nozzle and the intermediate transfer member by the ejection control unit. An image forming method for generating the images so as to be equal to each other.

Images