JP2011189706A - Image forming device, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device carrying out image forming while achieving uniformization of the grade of coagulation when coagulating components corresponding to inks in recording liquids by applying a voltage to the recording liquids while the recording liquids discharged from nozzles temporarily bridges between the nozzles and an intermediate transferring member; and to provide a method for forming images using the same. <P>SOLUTION: The image forming apparatus uses: intermediate transferring member 37 fed with the electroconductive recording liquids discharged from heads 61Y, 61M, 61C, 61BK (hereinafter referred to as "heads 61") and causing coagulation action by the application of a voltage; a voltage applying unit 33 for applying the voltage between the heads 61 and the intermediate transferring member 37 so as to coagulate the electroconductive recording liquids discharged from the heads 61 and temporarily bridging between the heads 61 and the intermediate transferring member 37; and a voltage applying controller 40 for controlling the voltage applied by the voltage applying unit 33 when applying the voltage according to the interval between the heads 61 and the intermediate transferring member 37. <P>COPYRIGHT: (C)2011,JPO&INPIT

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, it has been equipped with a head that ejects droplets of recording liquid such as ink from a plurality of minute nozzles by a movable actuator method typified by a piezo method, a heated film boiling method typified by a thermal method, etc. 2. Description of the Related Art An inkjet image forming apparatus such as an inkjet printer is known (see, for example, [Patent Document 1] to [Patent Document 7]).

  In the inkjet system, in a configuration in which a recording liquid is directly discharged from a head to a recording material such as recording paper (see, for example, [Patent Document 1] to [Patent Document 5]), the head and the recording material are close to each other. Paper dust, dust, etc. adhering to the recording material are likely to adhere to the nozzle. 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. As a measure for avoiding such a problem, priority is given to ejection stability from the nozzle, and it is common to use a recording liquid having a low viscosity, for example, containing a large amount of water, but the viscosity is low. The recording liquid is likely to bleed when landing on the recording material. Various techniques have been proposed that take measures against such bleeding in a configuration in which recording liquid is directly discharged from a head onto a recording material such as recording paper (see, for example, [Patent Document 2] to [Patent Document 5]). Neither is sufficient.

  Therefore, 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 6). (See Patent Document 7).

  Further, in the image forming apparatus provided with the intermediate transfer member as described above, there is provided an image forming apparatus 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 reduce bleeding. It has been proposed (for example, see [Patent Document 6]). 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 member, there has also been proposed an image forming apparatus in which a powder that absorbs recording liquid is previously deposited on an intermediate transfer member in order to reduce bleeding (for example, [Patent Documents] 7]).

  However, such an image forming apparatus has problems such as an increase in cost due to supply of processing liquid or powder, a decrease in image forming speed due to time required for application or reaction of processing liquid or powder, complication of an apparatus, and an increase in size. is there. In addition, there is a possibility that the intermediate transfer member is corroded particularly in the configuration in which the treatment liquid is applied, and in the configuration in which the powder is applied, the recording liquid is ejected from the head because the powder easily adheres to the nozzle. However, it is necessary to solve these problems while ensuring the discharge performance of the recording liquid from the head.

  In this regard, the applicant applied an application to the ink in the recording liquid by applying a voltage to the recording liquid in a state where the recording liquid discharged from the nozzle temporarily bridges between the nozzle and the intermediate transfer member. A technique for aggregating corresponding components has been proposed, and according to this technique, such a problem can be solved.

  However, in such a technique, simply by applying such a voltage, if the gap between the nozzle and the intermediate transfer member changes, the degree of aggregation can change, resulting in a change in image quality. obtain. Such fluctuation is caused by, for example, position fluctuation due to driving of the intermediate transfer member.

  In the present invention, when the recording liquid discharged from the nozzle temporarily bridges between the nozzle and the intermediate transfer member, a voltage is applied to the recording liquid to aggregate the components corresponding to the ink in the recording liquid. It is an object of the present invention to provide an image forming apparatus that forms an image while making the degree of aggregation uniform, and an image forming method using the image forming apparatus.

  In order to achieve the above object, the invention described in claim 1 is provided with a head including a nozzle for discharging a conductive recording liquid that generates an aggregating action when a voltage is applied, and a conductive recording liquid discharged by the head. An intermediate transfer member, and the head and the intermediate transfer member for causing an aggregating action on the conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member. Voltage application means for applying a voltage between them, and voltage application control means for controlling the voltage applied by the voltage application means when applying the voltage according to the interval between the nozzle and the intermediate transfer member; In an image forming apparatus.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus further includes an interval storage unit that stores the interval measured in advance, and the voltage application control unit is stored in the interval storage unit. The control is performed according to the interval.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus further includes an interval measuring unit that measures the interval, and the voltage application control unit sets the interval measured by the interval measuring unit. The control is performed accordingly.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the interval measuring unit measures the interval by measuring a surface position of the intermediate transfer member with respect to the nozzle.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect of the invention, the distance measuring unit is configured so that the nozzle discharges the conductive recording liquid in the relative movement direction of the nozzle and the intermediate transfer member. Is also provided integrally with the head so as to measure the distance by measuring the surface position on the upstream side.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth aspects, the interval measuring unit measures an energization state between the head and the intermediate transfer member. The interval is measured.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the distance measuring means is a maximum when the conductive recording liquid in the state is energized between the head and the intermediate transfer member. The current value, the amount of charge that flows between the head and the intermediate transfer member when the conductive recording liquid in the state is energized, and the conductive recording liquid becomes the state from the start of driving of the head. Energization start time until energization starts between the intermediate transfer member and the intermediate transfer member, and the conductive recording liquid is in the state after the energization starts between the head and the intermediate transfer member. The interval is measured by measuring at least one of the energization durations until the state is canceled as the energized state.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the control according to the interval measured by the measurement of the energization time is performed so that the state is formed after the measurement. It is carried out when forming.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the sixth to eighth aspects, the voltage application unit performs measurement based on the measurement of the energization time and the interval measured by the measurement. The voltage to be determined is determined during maintenance.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the sixth to ninth aspects, the energized state is applied to the conductive recording liquid in the state by the voltage applying unit. It is characterized by forming.

  According to an eleventh aspect of the present invention, there is provided an image forming method for forming an image using the image forming apparatus according to any one of the first to tenth aspects.

  The present invention includes a head having a nozzle that discharges a conductive recording liquid that generates an aggregating action when a voltage is applied thereto, an intermediate transfer member to which the conductive recording liquid discharged by the head is applied, and a discharge from the head. Voltage applying means for applying a voltage between the head and the intermediate transfer member for causing an aggregating action in the conductive recording liquid in a state where the head and the intermediate transfer member are temporarily bridged And a voltage application control unit that controls a voltage applied by the voltage application unit when the voltage application is performed according to an interval between the nozzle and the intermediate transfer member. Regardless of the distance from the intermediate transfer member, the recording liquid discharged from the nozzle temporarily applies a voltage to the recording liquid in a state where the nozzle and the intermediate transfer member are bridged. The degree of aggregation at the time of performing the aggregation of the corresponding components can be equalized, it is possible to provide an image forming apparatus which can enhance image quality by reducing this by bleeding.

  If it has interval storage means for storing the interval measured in advance, and the voltage application control means performs the control according to the interval stored in the interval storage means, the cost can be reduced. However, the recording liquid discharged from the nozzle is temporarily bridged between the nozzle and the intermediate transfer member regardless of the interval between the nozzle and the intermediate transfer member, and a voltage is applied to the recording liquid to apply ink to the recording liquid. It is possible to provide an image forming apparatus capable of making the degree of aggregation when the corresponding components are aggregated uniform, thereby reducing bleeding and improving the image quality.

  If it has interval measuring means for measuring the interval, and the voltage application control means performs the control according to the interval measured by the interval measuring means, the interval measured by the interval measuring means is obtained. By performing the control used, a voltage is applied to the recording liquid while the recording liquid ejected from the nozzle temporarily bridges between the nozzle and the intermediate transfer member regardless of the distance between the nozzle and the intermediate transfer member. It is possible to provide an image forming apparatus capable of uniformizing the degree of aggregation when the components corresponding to the ink in the recording liquid are aggregated, thereby reducing bleeding and improving the image quality. .

  If the distance measuring means measures the distance by measuring the surface position of the intermediate transfer member with respect to the nozzle, the distance measuring means can measure the distance with a relatively high accuracy. By performing the control using the determined interval, the recording liquid discharged from the nozzle is temporarily bridged between the nozzle and the intermediate transfer member regardless of the interval between the nozzle and the intermediate transfer member. Image formation that can make the degree of aggregation more uniform when applying a voltage and aggregating the components corresponding to the ink in the recording liquid, thereby achieving high image quality with highly reduced bleeding An apparatus can be provided.

  The interval measuring unit 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. If it is provided integrally with the head, the interval can be measured by the interval measuring means with higher accuracy, and the nozzle and the intermediate transfer member can be controlled by performing control using the measured interval. Regardless of the distance between the nozzle and the intermediate transfer member, the recording liquid discharged from the nozzle temporarily applies a voltage to the recording liquid to aggregate the components corresponding to the ink in the recording liquid. It is possible to provide an image forming apparatus capable of further uniforming the degree of aggregation at the time, thereby further reducing bleeding and improving image quality.

  If the distance measuring unit measures the distance by measuring the energization state between the head and the intermediate transfer member, the distance measuring unit can change with time with relatively high accuracy while suppressing cost. It is possible to measure the interval while eliminating the influence of the recording liquid, and by performing control using the measured interval, the recording liquid discharged from the nozzle is not affected by the interval between the nozzle and the intermediate transfer member. When a voltage is applied to the recording liquid in a state where it is temporarily bridged between the intermediate transfer member and the intermediate transfer member, the degree of aggregation when the components corresponding to the ink in the recording liquid are aggregated can be made more uniform. As a result, it is possible to provide an image forming apparatus capable of highly reducing blur and achieving high image quality.

  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 to start the energization between the head and the intermediate transfer member until the conductive recording liquid is released from the state If the interval is measured by measuring the energized state, a comparison is made while measuring costs by measuring at least one of the maximum current value, charge amount, energization start time, and energization duration time. It is possible to measure the interval while eliminating the influence of changes over time by the interval measuring means with high accuracy, and by performing control using the measured interval, regardless of the interval between the nozzle and the intermediate transfer member The degree of aggregation when the recording liquid ejected from the nozzle temporarily aggregates between the nozzle and the intermediate transfer member to apply a voltage to the recording liquid and aggregate the components corresponding to the ink in the recording liquid. Accordingly, it is possible to provide an image forming apparatus that can be made more uniform and can thereby achieve high image quality by highly reducing bleeding.

  If the control according to the interval measured by measuring the energization time is performed when the state is formed and the image is formed after the measurement, relatively high accuracy is achieved while suppressing costs. In addition, it is possible to measure the interval while eliminating the influence of the change over time by the interval measuring means, and by performing control using the measured interval after the measurement, the interval between the nozzle and the intermediate transfer member can be adjusted. Regardless of the aggregation of the recording liquid discharged from the nozzle, the voltage corresponding to the ink in the recording liquid is aggregated by applying a voltage to the recording liquid in a state where the nozzle and the intermediate transfer member are temporarily bridged. Thus, it is possible to provide an image forming apparatus that can make the degree more uniform, thereby reducing blurring and improving the image quality.

  If the measurement of the energization time and the determination of the voltage to be applied by the voltage application means performed based on the interval measured by this measurement are performed during maintenance, such measurement and determination are performed in advance of image formation. As a result, it is possible to perform the measurement without reducing the productivity of image formation, and it is possible to measure the interval while eliminating the influence of the change with time by the interval measurement means with relatively high accuracy while suppressing the cost. By performing control using the measured interval, the recording liquid discharged from the nozzle is recorded in a state where the nozzle and the intermediate transfer member are temporarily bridged regardless of the interval between the nozzle and the intermediate transfer member. It is possible to make the degree of aggregation more uniform when applying a voltage to the liquid and aggregating the component corresponding to the ink in the recording liquid, thereby reducing bleeding. It is possible to improve image quality by.

  If the energized state is formed by applying a voltage to the conductive recording liquid in the state by the voltage applying means, the recording liquid ejected from the nozzle temporarily moves between the nozzle and the intermediate transfer member. When the voltage corresponding to the ink in the recording liquid is aggregated by applying a voltage to the recording liquid in a bridged state, the interval is measured by the interval measuring means, thereby suppressing the cost relatively quickly and relatively accurately. In addition, it is possible to measure the interval while eliminating the influence of the change over time by the interval measuring means, and by performing control using the measured interval, the interval is measured regardless of the interval between the nozzle and the intermediate transfer member. It is possible to provide an image forming apparatus capable of making the degree of aggregation when performing aggregation more uniform, thereby reducing blurring and improving the image quality.

  Since the present invention is in an image forming method for forming an image using such an image forming apparatus, the recording liquid ejected from the nozzle is interposed between the nozzle and the intermediate transfer member regardless of the interval between the nozzle and the intermediate transfer member. A voltage is applied to the recording liquid in a temporarily bridged state, and the degree of aggregation can be made uniform when the components corresponding to the ink in the recording liquid are aggregated. An image forming method capable of achieving the above can be provided.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a conceptual diagram illustrating a more specific configuration of a head, an intermediate transfer member, and a voltage application unit illustrated in FIG. 1. It is a control block diagram regarding the head and voltage application means shown in FIG. 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. 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. 6 is a conceptual diagram showing that the current waveform flowing in the conductive recording liquid ejected from the head differs according to the distance between the head and the intermediate transfer member. FIG. 4 is a conceptual diagram showing that there is a correlation between the distance between the head and the intermediate transfer member, the voltage, and the current value. FIG. 3 is a conceptual diagram corresponding to FIG. 2 of another configuration example of the image forming apparatus to which the present invention is applied. FIG. 10 is a control block diagram corresponding to FIG. 3 of the image forming apparatus shown in FIG. 9. 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. 3 is a conceptual diagram corresponding to FIG. 2 of another configuration example of an image forming apparatus to which the present invention is applied. FIG. 16 is a control block diagram corresponding to FIG. 3 of the image forming apparatus shown in FIG. 15.

  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 ink jet printer and can perform full-color image formation. The image forming apparatus 100 performs image forming processing based on a print signal that is an image signal corresponding to image information received from the outside.

  The image forming apparatus 100 forms an image on a sheet-like recording medium that is a medium, such as plain paper generally used for copying, OHP sheets, cardboard, cardboard, cardboard, and envelopes. It is possible. 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 as recording heads are ink heads as liquid ejecting heads that are recording liquid ejection 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 as an intermediate transfer member disposed at a substantially central portion of the main body 99 of the image forming apparatus 100. Has been. 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.

  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. 4B, the liquid column by 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, and the like. The electrode oxidation reaction is performed inside the recording liquid in the liquid column state so that a potential difference is formed between the intermediate transfer body 37 and the heads 61Y, 61M, 61C, 61BK in a state where the space between the intermediate transfer body 37 and the head 61Y is changed. Alternatively, it has energization means 33 as voltage application means for energizing the recording liquid in a state where the current component resulting from the electrode reduction reaction is applied and promoting aggregation of the colorant contained in the recording liquid as described later.

  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 means 34 as a cleaning means that is an initialization means for cleaning and initializing the surface of the intermediate transfer body 37; a carriage 50 as a head support that integrally supports the heads 61Y, 61M, 61C, 61BK; A CPU (not shown) for controlling the overall operation of the image forming apparatus 100, a memory constituted by a RAM and a ROM, and a control unit 40 serving as a control means that is a microcomputer including an I / O interface and the like.

  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 in an adhesive transfer mode, and the transfer paper S fed from the paper supply unit 20 are held and conveyed toward the transfer unit 31. At the same time, a roller pair 39 that constitutes a conveying unit that holds the transfer sheet S that has passed through the transfer unit 31 and conveys the transfer sheet S toward the paper discharge table 25, and a motor as a driving unit (not shown) that rotationally drives the roller pair 39. And a motor or the like as a driving means (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 means 64 includes a transfer roller 38 that rotates following the intermediate transfer body 37, and a spring (not shown) as pressure means that presses the transfer roller 38 against the intermediate transfer body 37 and causes the transfer roller 38 to function as a pressure roller. The transfer paper S is conveyed under pressure between the intermediate transfer member 37 and the transfer roller 38. Although not shown, the transfer roller 38 has a metal cored bar and a 5 mm thick rubber layer provided on the surface of the cored bar as a surface layer for securing the transfer force of the transfer paper S. is doing. The transfer roller 38 may include a heater for fixing the image transferred onto the transfer paper S to the transfer paper 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, increasing the number of conductive fine particles improves the conductivity, but a trade-off relationship that lowers the releasability, so 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 most preferably smaller than the volume resistivity of the recording liquid, particularly in the state of the liquid column shown in FIG.

  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 A distributor tank (not shown) that is a distributor as an ink supply unit that is a recording liquid supply unit that supplies the recording liquid supplied from the ink cartridges 81Y, 81M, 81C, and 81BK to the heads 61Y, 61M, 61C, and 61BK. have.

  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.

  Examples of the anionic dispersant include, but are not limited to, fatty acid salt, alkyl sulfate ester salt, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, poly Examples thereof include oxyethylene alkyl sulfate esters, and two or more of them may be used in combination.

From the viewpoint of transferability, the recording liquid preferably further contains a resin having an anionic group in which a carboxyl group, a sulfonic acid group, a phosphonic acid group or the like is neutralized with a base.
The recording liquid may further contain a solvent soluble in water. Solvents that are soluble in water are not particularly limited, but are polyvalent such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, and glycerin. Alcohols: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, ethylene oxide adduct of diglycerin Polyhydric alcohol derivatives such as pyrrolidone, N-methyl-2-pyrrolidone, Nitrogen-containing solvents such as hexylpyrrolidone and triethanolamine; alcohols such as ethanol, isopropyl alcohol, butyl alcohol, and benzyl alcohol; sulfur-containing solvents such as thiodiethanol, thiodiglycerol, sulfolane, and dimethyl sulfoxide; propylene carbonate, ethylene carbonate, and the like These may be used in combination of two or more.

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

  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, there is no particular problem even if the gap is less than 50 μm as long as the gap can be maintained.

  The piezoelectric element 61d is an actuator for forming recording liquid droplets from each nozzle 61b to be discharged and landed on the transfer paper S. The piezoelectric element 61d discharges the recording liquid from the nozzle 61b in accordance with a voltage pulse applied by control by the control unit 40. It is designed to discharge. The actuator of the ink discharge means is a movable actuator of another type which is a shape deforming element type, such as a piezo type, instead of the piezoelectric element 61d as a pressure applying means for discharging the recording liquid by applying pressure to the ink chamber 61c. There may be. 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 energization means 33 forms a predetermined voltage difference between the nozzle plate 61a and the intermediate transfer body 37, and includes a power supply 33a as a power supply means as a liquid column application power supply with a variable output voltage, and the power supply 33a as a support 37a. An electric circuit (not shown) connected to the nozzle plate 61a and a power switch 33b for turning on / off the power source 33a are provided.

  The power source 33a has an anode connected to the support 37a and a cathode connected to the nozzle plate 61a by an electric circuit. 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.

  In this embodiment, the voltage from the power source 33a is applied between the nozzle plate 61a and the intermediate transfer member 37. However, an electrode is disposed in the ink chamber 61c, and the electrode and the intermediate transfer member 37 are connected to each other. It is good also as a structure applied in between. When it is set as the structure which applies a voltage to the nozzle plate 61a like this form, it is preferable that the electroconductive part to which the power supply 33a of the nozzle plate 61a is connected has high electroconductivity.

  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 fluoro rubber as an elastic body, which is in contact with the intermediate transfer body 37 in a so-called counter contact manner. Yes. The cleaning unit 34 may include a cleaning roller as a cleaning member together with the cleaning blade.

  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. In order to control the voltage applied by the recording liquid discharge control means 40b as the ink discharge control means that generates a predetermined head drive signal for driving 61M, 61C, 61BK and inputs it to the head drive circuit 61e, and the energization means 33 Liquid column application voltage control means 40c as voltage application control means for controlling the power supply 33a via the power switch 33b.

  The control unit 40 also includes a liquid column application voltage control table 40d for determining the voltage application mode of the power source 33a by the liquid column application voltage control means 40c, 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 40a is realized as one function of the I / O interface of the control unit 40, and the recording liquid discharge control unit 40b and the liquid column application voltage control unit 40c are one function of the CPU of the control unit 40. The liquid column application voltage control table 40d is stored in the memory of the control unit 40 and is realized as a function of this memory, and the dimension measurement value storage means 40e is provided in the control unit 40. This is realized as a function of the memory.

  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.

  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 liquid column application voltage control table 40d receives the intermediate transfer member dimension measurement value stored in the dimension measurement value storage means 40e by the liquid column application voltage control means 40c when determining the application voltage of the power source 33a. The output value of the applied voltage of the power source 33a corresponding to the measured value of the intermediate transfer member dimension is input to the liquid column applied voltage control means 40c.

  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 media transport signal that drives a motor that rotationally drives the roller pair 39, and inputs the generated media transport signal to the motor to rotationally drive the motor. 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. The control unit 40 generates a paper feed 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.

  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 member 37. At that time, first, the heads 61Y, 61M, 61C, 61BK are used as shown in FIG. The recording liquid that forms a meniscus in the nozzle 61b in the initial state moves while being columnar toward the intermediate transfer member 37 as shown in FIG. 4A by applying a drive pulse to the piezoelectric element 61d. Start. Thus, in a state where a liquid column is being formed between the nozzle 61b and the intermediate transfer member 37, the recording liquid moves to the intermediate transfer member 37 and faces the intermediate transfer member 37 of the nozzle plate 61a. A very small amount of induced current flows between the surface and the intermediate transfer member 37, but this current is very weak.

  Next, as shown in FIG. 4B, the tip of the columnar recording liquid that has moved toward the intermediate transfer member 37 is deposited on the surface of the intermediate transfer member 37, and between the nozzle 61b and the intermediate transfer member 37, A bridge of the liquid column made of the recording liquid is temporarily formed. When this bridge-shaped liquid column is formed, that is, when such liquid landing occurs, a large current starts to flow between the nozzle plate 61a and the intermediate transfer body 37 at the same time.

  After that, as shown in FIG. 4C, the bridge of the liquid column made of the recording liquid is divided to be carried on the intermediate transfer body 37, and an image of the recording liquid is formed on the intermediate transfer body 37. Such division occurs in the vicinity of the nozzle 61b. However, before the division, the bridge-like liquid column becomes narrower, so that the electrical resistance increases and the amount of current flowing between the nozzle plate 61a and the intermediate transfer body 37 decreases. Then, when the liquid column is finally divided, the energizing current stops.

The above is the process when the recording liquid is ejected from the nozzle 61b.
The amount and size of the recording liquid droplets adhering to the intermediate transfer member 37 in the state shown in FIG. 4C are generated by the head drive circuit 61e according to the density of the image to be formed. It can be adjusted by the waveform of the drive pulse input to the piezoelectric element 61d. For example, the image density can be adjusted by increasing the size of the liquid droplets in order from the highest image density. The head drive circuit 61e can control the discharge mode of the recording liquid from the nozzle 61b under such a plurality of discharge conditions.

In the state where the liquid injection bridge made of the recording liquid as shown in FIG. 4B is formed, the colorant component in the recording liquid is subjected to 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 +), and as shown in FIG. The pigment P dispersed by D aggregates via protons. 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.

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 the pigment dispersed by the anionic dispersant is aggregated. 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.

  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.

  The state where the bridge B of the liquid column is formed is observed with a high-speed camera. From this observation, after the voltage pulse is input to the piezoelectric element 61d by the control unit 40 functioning as the ink discharge control means, the timing at which the recording liquid is discharged from the nozzle 61b, and the intermediate transfer body 37 after the recording liquid is discharged. The timing until the bridge B is formed and the duration of the bridge can be measured in units of μsec for each nozzle 61b.

  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 to the transfer paper S in this way, the recording liquid containing the aggregation component is transferred to the transfer paper S. Therefore, by forming an image with the colorant aggregated by the above-described aggregation action, even when the transfer paper S is plain paper, high image density can be achieved at high speed while preventing or suppressing feathering and bleeding. High-quality image formation 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, since the aggregating action reduces the absorbability of the recording liquid onto the transfer paper S, such a set-off is prevented or suppressed, which 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 the above-described process when the recording liquid is ejected from the nozzle 61b, the recording liquid discharged from the nozzle 61b as the gap between the nozzle 61b and the intermediate transfer body 37 becomes narrower. The time until the ink reaches the intermediate transfer member 37 is shortened, the current application start time is shortened, and the formation time of the bridge of the liquid column made of the recording liquid is lengthened, and the nozzle plate passes through the liquid column. The energization time of the current flowing between 61a and the intermediate transfer member 37 becomes longer. That is, the energization mode of the current changes depending on the size of the gap. Further, as described above, since the recording liquid causes an aggregating action when a voltage is applied, if the gap size changes, the aggregating action also changes, which affects the image quality. Further, the gap fluctuates when the intermediate transfer body 37 is rotated, for example, when the intermediate transfer body 37 is eccentric due to the accuracy of the intermediate transfer body 37 itself or the parts that support the gap. It is extremely difficult to completely eliminate such gap fluctuations. Therefore, if the voltage applied by the power source 33a is constant, the gap varies with the rotation of the intermediate transfer member 37 when the intermediate transfer member 37 rotates, and this causes a change in the aggregating action of the recording liquid. The image quality will change.

  Here, in FIG. 7, when the recording liquid is discharged from the nozzle 61b to the intermediate transfer member 37 in a state where a voltage is applied between the nozzle plate 61a and the intermediate transfer member 37 by the power source 33a, the nozzle plate 61a and the intermediate transfer member. 37 shows the result of measuring the amount of current flowing between the current and the current flow rate. In the figure, the time on the horizontal axis indicates the time from the start of input of the drive pulse to the piezoelectric element 61d.

  In the measurement, the applied voltage from the power source 33a is the same, and the gap between the nozzle plate 61a and the intermediate transfer member 37 is small, medium, and large, and the total is four conditions when the gap is large and the applied voltage is increased. I went there. When the gap is small, medium, and large, the gap is assumed to be about 100 μm, about 200 μm, and about 300 μm, respectively.

From this figure, it can be considered that when the gap is widened, a constricted shape is formed which narrows the liquid column, the resistance value of the liquid column becomes high, and the current hardly flows. Therefore, when the dimensional accuracy and the flare accuracy of the intermediate transfer member 37 are poor, the gap increases and decreases, so that even when the recording liquid is discharged from the same nozzle 61b, the rotation direction of the intermediate transfer member 37, in other words, in the phase. The current value of liquid column energization changes depending on the discharge position.
Further, it can be seen from the figure that even when the gap is large, it is possible to increase the maximum current value to the same level as when the gap is small by increasing the applied voltage.

  From the above, even when there is a change in the gap, if the voltage value applied by the power source 33a is changed in accordance with the change in the gap, the current value of the liquid column state recording liquid is controlled to be uniform. It can be seen that the image quality can be made uniform.

  FIG. 8 shows the fluctuation of the gap in one rotation period T of the intermediate transfer member 37, the applied voltage value when the applied voltage value is controlled in accordance with this fluctuation, and the current value flowing through the recording liquid in the liquid column state. The conceptual diagram which showed the time change of is shown.

  In the figure, the applied voltage is obtained by calculating the applied voltage value using the liquid column applied voltage control table 40d in accordance with the variation of the gap. The liquid column applied voltage control table 40d measures and determines the relationship between applied voltages corresponding to the gaps in advance. That is, the liquid column applied voltage control table 40d is created so that the applied voltage is determined so that the current value becomes constant in accordance with the variation of the gap. The change in the shape of the liquid column of the recording liquid due to the change in the gap is not easily proportional because it is affected by the characteristic value such as viscosity related to the behavior of the recording liquid. Therefore, the liquid column application voltage control table 40d is created in consideration of the characteristic value and environment of the recording liquid.

  This figure shows that the current applied to the liquid column of the recording liquid becomes uniform by controlling the voltage applied between the nozzle plate 61a and the intermediate transfer member 37 by the power source 33a. This confirms the measurement results shown in FIG.

  Based on the above, in the image forming apparatus 100 according to the present embodiment, intermediate transfer as intermediate transfer member dimension data including fluctuations in the gap between the nozzle 61b and the intermediate transfer body 37, which is measured in advance, in the dimension measurement value storage unit 40e. The member dimension measurement value is stored in association with the phase of the intermediate transfer body 37 with the reference point determined for the intermediate transfer body 37 as a reference. At the time of image formation, the control unit 40 manages and grasps the phase of the intermediate transfer body 37, that is, the rotation posture in association with the driving of the intermediate transfer body 37, and adjusts the intermediate transfer member dimension measurement value to the phase. The liquid column application voltage control means 40c reads out from the dimension measurement value storage means 40e, determines the voltage value to be applied by the power source 33a by the liquid column application voltage control table 40d, and at the determined voltage value, the nozzle plate 61a by the power source 33a. A voltage is applied between the intermediate transfer member 37 and the piezoelectric element 61 is driven in synchronization with the voltage application timing to discharge the recording liquid from the nozzle 61b. Thus, the timing at which the recording liquid is ejected from the nozzle 61b and the timing at which the voltage is applied between the nozzle plate 61a and the intermediate transfer member 37 by the power source 33a are always synchronized and matched. However, strictly speaking, this synchronization is achieved at the timing when the recording liquid is ejected from the nozzle 61 b and the liquid column of the recording liquid forms a bridge between the nozzle 61 b and the intermediate transfer body 37. As described above, this timing can be measured by measuring in advance by observation with a high-speed camera.

  In the above embodiment, the voltage applied by the power source 33a is controlled in accordance with the known gap between the nozzle 61b and the intermediate transfer member 37 stored in the dimension measurement value storage means 40e. As shown in FIG. 3, the image forming apparatus 100 includes a gap measuring sensor 36 as an interval measuring unit that measures the gap, and controls the voltage according to the gap measured by the gap measuring sensor 36. May be.

  As shown in FIG. 9, the gap measurement sensor 36 is provided integrally with each of the heads 61Y, 61M, 61C, 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. In order to measure the surface position of 37, the heads 61Y, 61M, 61C and 61BK are integrally provided on the upstream side of the nozzle 61b in the rotational direction. This is because the gap measurement sensor 36 measures the gap and determines the voltage value to be applied by the power source 33a until the voltage is applied between the nozzle plate 61a and the intermediate transfer body 37 with the determined voltage value. Considering the time lag, the gap at the position upstream of the recording liquid landing position on the intermediate transfer member 37 in the rotational direction is measured in advance from the recording liquid discharge timing, and the voltage application timing and the discharge timing are measured. This is to synchronize the 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. 10, with the provision of the gap measurement sensor 36, the control unit 40 includes a gap measurement value input unit 40f instead of the dimension measurement value storage means 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 liquid column application voltage control means 40c. It is done in association. Thereafter, a voltage value to be applied by the power source 33a is determined by the liquid column application voltage control table 40d, and a voltage is applied between the nozzle plate 61a and the intermediate transfer member 37 by the power source 33a with the determined voltage value. Operations such as driving the piezoelectric element 61 in synchronism with the application timing and discharging the recording liquid from the nozzle 61b are the same as in the above-described embodiment.

  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 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 faster. In addition, the gap is substantially measured by measuring the energized state by taking advantage of the fact that the formation time of the bridge of the liquid column made of the recording liquid becomes long.

  With reference to FIGS. 11 to 14, 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. 11 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. 12 shows the amount of charge that flows between the nozzle 61b and the intermediate transfer member 37 when the recording liquid in a state where the nozzle 61b and the intermediate transfer member 37 are bridged is energized, and the nozzle 61b and the intermediate transfer member. 37 shows the relationship with the gap distance.

  FIG. 13 shows the state from when the driving of the heads 61Y, 61M, 61C, and 61BK starts until the recording liquid bridges between the nozzle 61b and the intermediate transfer member 37 and energization between the nozzle 61b and the intermediate transfer member 37 starts. And the gap distance between the nozzle 61b and the intermediate transfer member 37 is shown.

  FIG. 14 shows a state in which the nozzle 61b and the intermediate transfer body 37 are bridged, and after the energization is started between the nozzle 61b and the intermediate transfer body 37, the state where the recording liquid is applied is canceled and the energization is interrupted. 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 energization current amount in FIG. 11, the charge amount in FIG. 12, the energization start time in FIG. There is a clear correlation between the energization duration in FIG. 14 and the gap distance. That is, the energization current value, the charge amount, and the time change, which are energization feature amounts, have a 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. 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 and the amount of charge flowing between the nozzle plate 61a and the intermediate transfer member 37 via the liquid column are increased. growing. 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.

  The gap distance can be calculated by means of calculating the gap distance based on a coefficient fitted with a polynomial or the like from a result measured in advance, or by creating a lookup table from the result measured in advance and referring to the table. A means for calculating the distance can be employed.

  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.

  15 and 16 include an ammeter 33c as an interval measuring unit that measures the gap between the nozzle 61b and the intermediate transfer body 37 by measuring the energization state between the nozzle plate 61a and the intermediate transfer body 37. An example configuration is shown.

  As shown in FIG. 15, 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 nozzle 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. 16, with the provision of the ammeter 33c, the control unit 40 replaces the dimension measurement value storage means 40e shown in FIG. 3 and the gap measurement value input unit 40f shown in FIG. There is provided a current value input unit 40g for inputting the liquid column energization current amount from the ammeter 33c as an energization feature amount measurement signal including information on the above-described 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 liquid column applied voltage control unit 40c. This input is performed in association with the phase of the intermediate transfer member 37. The liquid column application voltage control table 40d is provided with the above-described fitting coefficient and lookup table, and the liquid column application voltage control table 40d determines the voltage value applied by the power source 33a. Based on the fitting coefficient and the lookup table. At this time, it is applied by the power source 33a 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. The voltage value to be determined is determined.

  A voltage is applied between the nozzle plate 61a and the intermediate transfer body 37 by the power source 33a with the determined voltage value, and the piezoelectric element 61 is driven in synchronization with the voltage application timing to discharge the recording liquid from the nozzle 61b. These operations are the same as in the above-described embodiment.

  However, since the control based on the determined voltage value cannot be performed for the discharge of the recording liquid used to determine the voltage value due to a delay in the control process, the control is performed once for the intermediate transfer member 37. To do later. That is, for controlling the applied voltage value by the power source 33a each time the recording liquid is ejected, the liquid column energization current amount measured before one rotation of the intermediate transfer body 37 is used. 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 applied voltage value by the power source 33a by the liquid column applied voltage control table 40d. Therefore, in the liquid column application voltage control table 40d, a fitting coefficient and a lookup table are prepared for such voltage values. Note that for the first image formation immediately after receiving the print signal, that is, the first image formation, voltage is applied by the power source 33a using the value measured during maintenance such as pre-printing idle discharge. In order to measure such a gap, the current state of the bridge of the liquid column made of the recording liquid between the nozzle plate 61a and the intermediate transfer member 37, which is generated when the recording liquid agglomerates, is generated. Even when the heads 61Y, 61M, 61C, and 61BK undergo positional fluctuations over time, the gap is accurately measured, and the determination of the voltage value and control based on the gap are performed with high accuracy at a relatively low cost. Is called.

  Here, the control unit 40 is discharged from the heads 61Y, 61M, 61C, 61BK, the intermediate transfer body 37, and the heads 61Y, 61M, 61C, 61BK, as described above, into the memory. In order to apply a voltage between the head heads 61Y, 61M, 61C, 61BK and the intermediate transfer member 37 for causing an aggregating action in the recording liquid temporarily bridged between 61BK and the intermediate transfer member 37. Current supply means 33, and a control unit 40 or liquid column application voltage control means for controlling the voltage applied by the current supply means 33 or the power source 33a when applying such voltage according to the interval between the nozzle 61b and the intermediate transfer body 37. 40c and an image forming program for executing an image forming method for forming an image using the computer 40c. In this regard, the control unit 40 or the memory functions as an image forming program storage unit. Such an image forming program includes not only a memory provided in the control unit 40 but also a semiconductor medium (for example, ROM, non-volatile memory), an optical medium (for example, DVD, MO, MD, CD-R, etc.), a magnetic medium. (For example, a hard disk, a magnetic tape, a flexible disk, etc.) It can be stored in other storage media. When such an image forming program is stored in such a memory or other storage medium, the computer reading that stores the image forming program Configure possible recording media.

  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 through 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, and other types of image forming apparatuses, that is, the head, in the main scanning direction of the medium, specifically, for example, on the paper surface in FIG. It may be a shuttle type movable in the vertical direction, and may be a copying machine, a facsimile alone, or a complex machine such as these, a multifunction machine such as a monochrome machine related thereto, or other image formation used for forming an electric circuit. It may be an image forming apparatus used to form a predetermined image in the apparatus or biotechnology field. 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 member 40, 40c Voltage application control unit 40e Interval storage unit 61b Nozzle 61Y, 61M, 61C, 61BK Head 100 Image forming apparatus

JP 11-320855 A JP 2000-117959 A Japanese Patent Application Laid-Open No. 11-207946 Japanese Patent Laid-Open No. 11-028810 Japanese Patent No. 3612949 JP 2008-62397 A Japanese Patent Laid-Open No. 11-188858

Claims (11)

A head provided with a nozzle for discharging a conductive recording liquid that generates an aggregating action by application of a voltage;
An intermediate transfer member to which the conductive recording liquid discharged by the head is applied;
A voltage is applied between the head and the intermediate transfer member to cause a cohesive action in the conductive recording liquid discharged from the head and temporarily bridging between the head and the intermediate transfer member. Voltage applying means for,
An image forming apparatus comprising: a voltage application control unit that controls a voltage applied by the voltage application unit when the voltage application is performed in accordance with an interval between the nozzle and the intermediate transfer member. The image forming apparatus according to claim 1.
Having interval storage means for storing the interval measured in advance;
The image forming apparatus, wherein the voltage application control unit performs the control according to the interval stored in the interval storage unit. The image forming apparatus according to claim 1 or 2,
Having interval measuring means for measuring the interval;
The image forming apparatus, wherein the voltage application control unit performs the control according to the interval measured by the interval measurement unit. The image forming apparatus according to claim 3.
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 4.
The interval measuring unit 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 3 to 5,
The image forming apparatus, wherein the interval measuring unit measures the interval by measuring an energization state between the head and the intermediate transfer member. The image forming apparatus according to claim 6.
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 to start the energization 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 6 or 7,
An image forming apparatus, wherein the control according to the interval measured by measuring the energization time 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 6 to 8,
An image forming apparatus, wherein the measurement of the energization time and the determination of the voltage to be applied by the voltage applying means performed based on the interval measured by the measurement are performed during maintenance. The image forming apparatus according to any one of claims 6 to 9,
The image forming apparatus, wherein the energized state is formed by applying a voltage to the conductive recording liquid in the state by the voltage applying unit.   An image forming method for forming an image using the image forming apparatus according to claim 1.

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