JP5333278B2 - Image forming apparatus and nozzle discharge state detection method - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material by forming an image on an intermediate transfer body by an inkjet method and transfers the image to the recording material, and a nozzle discharge state detection method.

Inkjet systems include a movable actuator system represented by the piezo system and a heated film boiling system represented by the thermal system. All of these inks form droplets of ink through micro nozzles and record paper or the like according to image information. This is an image forming technique for attaching to a medium.
Such an ink jet system is expanding its application range to printers, facsimiles, copiers, and the like because of the simplicity of the apparatus configuration compared to the electrophotographic system. It is also expected to develop into new fields such as electrical circuit formation and biotechnology applications.
In an inkjet image forming apparatus, the main part of the image forming engine is composed of a recording head, ink, and recording paper, and the recording paper is conveyed in an area close to the recording head. Easy to adhere.
As a result, the flying direction of the droplets ejected from the nozzle is disturbed or the nozzle is blocked, resulting in a reduction in image quality and reliability. In general, ink having a low viscosity is used with priority given to ejectability from the nozzles, but ink bleeding tends to occur when landing on recording paper.

Therefore, in order to reduce paper dust adhesion etc., avoid the configuration where the nozzle and the recording medium face each other directly, discharge the ink from the recording head to form an ink image on the intermediate transfer body, and then transfer to the recording medium It has been known.
In Patent Document 1, a treatment liquid application unit that applies a treatment liquid for changing the pH of ink to the intermediate transfer member, an ink application unit that applies ink onto the treatment liquid, and an intermediate transfer member are formed. An image forming apparatus including a transfer unit that transfers an image to a recording medium is disclosed. In the ink, at least a pigment and polymer fine particles are dispersed in a medium composed of water and a conductive solvent, and the pigment and polymer fine particles are aggregated by changing pH.

On the other hand, as a method for preventing deterioration in image quality, there is a known method for detecting a nozzle that has caused a discharge failure, thereby quickly recovering the nozzle or sending information to the control unit of the recording head. It is possible to take measures such as substituting with a normal nozzle.
In Patent Document 2, an optical sensor including a light emitting unit that emits light and a light receiving unit that receives light emitted from the light emitting unit is provided, and light reflected from the discharge liquid emitted from the light emitting unit is received by the light receiving unit. A method is disclosed in which light is received and the presence or absence of ejection failure is detected based on the difference in the amount of light.

However, in the image forming apparatus described in Patent Document 1, since the processing liquid must be applied to agglomerate the pigment contained in the ink, the processing liquid application configuration increases the size and cost of the apparatus and increases the processing cost. There was a problem that a decrease in printing speed was unavoidable due to the presence of the liquid application step.
In the detection configuration described in Patent Document 2, since the light emitting means and the light receiving means are necessary, there is a problem that the apparatus is increased in size and cost.

  The present invention has been made in view of the above problems, and without using consumables other than ink, such as reaction liquid and processing liquid, at high speed on plain paper generally used as a recording material, and image density. Inkjet system that can obtain high-quality images with high feathering, bleeding, and beading, and can detect the nozzle discharge state with a simple and low-cost configuration and quickly perform nozzle recovery processing The main object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, the present invention eliminates the problem of bleeding by causing the recording liquid (conductive ink) to agglomerate by electrolysis on the intermediate transfer member, and also provides a voltage as an energy source for electrolysis. The nozzle discharge state is detected by using discharge light generated secondary by application.

  Specifically, in the first aspect of the present invention, the conductive ink is ejected from the nozzles of the recording head on the intermediate transfer body according to the image signal, and the image on the intermediate transfer body is transferred to the recording material. The intermediate transfer member has a conductive surface, and the shape of the conductive ink ejected from the nozzle during image formation is between the nozzle and the surface of the intermediate transfer member. A liquid column capable of temporarily bridging, a voltage applying means for applying a voltage between the nozzle and the surface of the intermediate transfer member, and a discharge emitted from the vicinity of the liquid column of the conductive ink. And a light receiving means for receiving light.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of light receiving elements constituting the light receiving means are arranged along a longitudinal direction of the recording head.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the light receiving unit includes a moving mechanism that is movable along a longitudinal direction of the recording head.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus includes a deflecting unit that guides the light generated by the discharge to the light receiving unit.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the deflecting unit includes a moving mechanism that is movable along a longitudinal direction of the recording head.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, a discharge state from the nozzle is determined based on a light reception signal from the light receiving unit, and the nozzle Control means is provided for executing normalization processing when necessary, or notifying that normalization processing is necessary.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the control unit changes a voltage applied by the voltage applying unit according to a difference in conductivity depending on a type of the conductive ink. It is characterized by that.

The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7, wherein the conductive ink contains water as a solvent, and the pigment is dispersed by an anionic dispersant. The intermediate transfer member functions as an anode when a voltage is applied by the voltage applying unit.
The invention according to claim 9 is the image forming apparatus according to claim 8, wherein the surface of the intermediate transfer member is made of metal.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the conductive ink includes water as a solvent, and the pigment is dispersed by a cationic dispersant. The intermediate transfer member functions as a cathode when a voltage is applied by the voltage applying means.

According to an eleventh aspect of the present invention, conductive ink is ejected from a nozzle of a recording head in accordance with an image signal onto an intermediate transfer member having a conductive surface, and the image on the intermediate transfer member is used as a recording material. An image forming apparatus for transferring and recording, wherein a voltage is applied between the nozzle and the surface of the intermediate transfer member during image formation, and the liquid column of the conductive ink discharged from the nozzle is connected to the nozzle. In the nozzle discharge detection method in an image forming apparatus that temporarily bridges the surface of the intermediate transfer member, light received by a discharge emitted from the vicinity of a liquid column of the conductive ink is received by a light receiving unit. To do.
According to a twelfth aspect of the present invention, in the nozzle discharge state detecting method according to the eleventh aspect, the light receiving means is composed of a plurality of light receiving elements arranged along the longitudinal direction of the recording head. And
A thirteenth aspect of the invention is the nozzle discharge state detection method according to the twelfth aspect of the invention, wherein the light receiving means is moved to change the nozzle position to be detected.
According to a fourteenth aspect of the present invention, in the nozzle discharge state detecting method according to the eleventh aspect, light generated by the discharge is deflected by a deflecting unit and guided to the light receiving unit.
According to a fifteenth aspect of the present invention, in the nozzle discharge state detecting method according to the fourteenth aspect, the nozzle position to be detected is changed by moving the deflecting unit.

According to the present invention, it is possible to cause an aggregating action due to electrolysis of conductive ink on the intermediate transfer member, so that it is possible to produce a plain paper without increasing consumables such as reaction liquid and processing liquid as in the prior art. It becomes possible to obtain a high-quality image with less beading, feathering and bleeding. Further, since the intermediate transfer method is used, it is possible to reduce nozzle clogging of the recording head due to paper dust, and it is possible to obtain a highly reliable image.
In addition, by detecting light emission due to secondary discharge caused by voltage application with the light receiving element, it is possible to detect nozzle discharge defects without providing light emitting means, and it is possible to reduce the size and cost of the discharge defect detection configuration. realizable.
Further, when the amount of light emission of the discharge is much larger than the normal reference, it can also serve as a safety device by stopping the image formation.

In the configuration in which the light receiving elements constituting the light receiving means are arranged along the longitudinal direction of the recording head, the ejection failure can be detected for all the nozzles simultaneously.
In the configuration in which the light receiving means is equipped with a moving mechanism that can move along the nozzle row direction, even if there is only one light receiving element, it is possible to detect ejection failure for all nozzles, thus realizing low cost. it can.
In the configuration in which the discharge light is guided to the light receiving means by the deflecting means, it is not necessary to move the light receiving element, so that it is possible to detect the ejection failure with high accuracy and simplicity.
In a configuration in which the conductive ink contains water as a solvent, the pigment is dispersed by an anionic dispersant, and the intermediate transfer member functions as an anode when a voltage is applied by a voltage applying unit, a highly versatile conductive material is used. High-quality image formation and ejection failure detection can be performed using an ink.

It is the perspective view and block diagram which show the structure which detects the nozzle discharge state which concerns on the 1st Embodiment of this invention. 1 is a schematic configuration diagram of an image forming apparatus. FIG. 4A is a diagram illustrating a mechanism for forming an ink image on an intermediate transfer member, FIG. 4A is a diagram illustrating a state in which ink forms a meniscus at a nozzle, and FIG. 4B is a diagram illustrating a liquid column of ejected ink between the nozzle and the intermediate transfer member. FIG. 6C is a diagram showing a state where the transfer body is bridged, and FIG. 10C is a diagram showing a state where ink droplets are separated and attached as an image on the intermediate transfer body. It is a schematic diagram which shows the state which the pigment disperse | distributed with the anionic dispersing agent aggregated through the proton. It is a schematic diagram which shows the state which the pigment disperse | distributed with the anionic dispersing agent aggregated through the proton and the metal cation. It is a schematic diagram showing a bridge of a liquid column formed between a cathode (nozzle plate) and an anode (intermediate transfer member). It is the perspective view and block diagram which show the structure which detects the nozzle discharge state in 2nd Embodiment. It is the perspective view and block diagram which show the structure which detects the nozzle discharge state in 3rd Embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 to 6 show a first embodiment.
First, an outline of the configuration of the image forming apparatus (inkjet printer) according to the present embodiment will be described with reference to FIG. The image forming apparatus 100 includes recording heads (hereinafter simply referred to as “heads”) 61Y, 61M, 61C, which can form images as images corresponding to colors separated into yellow, magenta, cyan, and black, respectively. It has 61BK. These heads serve as recording liquid discharge bodies or ink heads that discharge conductive ink as the recording liquid of each color.
The heads 61Y, 61M, 61C, 61BK are disposed at positions facing the outer peripheral surface of the intermediate transfer drum 37 serving as an intermediate transfer member 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 drum 37 and is the clockwise direction in FIG. In the drawing, Y, M, C, and BK added after the numerals of the respective symbols 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, 61BK is provided in the ink ejection devices 60Y, 60M, 60C, 60BK in such a manner that a plurality of the heads 61Y, 61M, 61C, 61BK are arranged in parallel so that their longitudinal directions extend in a direction perpendicular to the paper surface of FIG. It has been.
The intermediate transfer drum 37 is rotated in the A1 direction, and records 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 drum 37 and are arranged in parallel in the A1 direction.

The recording liquid is discharged or applied to the intermediate transfer drum 37 by the heads 61Y, 61M, 61C, and 61BK, so that the image areas of yellow, magenta, cyan, and black are overlapped at the same position on the intermediate transfer drum 37. The timing is shifted from the side toward the downstream side.
The image forming apparatus 100 includes the ink discharge devices 60Y, 60M, 60C, and 60BK that include the heads 61Y, 61M, 61C, and 61BK, and the intermediate transfer drum 37 that includes the intermediate transfer drum 37. A transport unit 10 as a paper transport unit for transporting a transfer sheet S as a medium, and a large number of transfer sheets S can be stacked, and only the uppermost transfer sheet S among the stacked transfer sheets S is directed toward the transport unit 10. It has a paper feed unit 20 for feeding, and a paper discharge tray 25 on which a large number of image-formed transfer papers S that have been transported by the transport unit 10 can be stacked.

As shown in FIG. 3B, the image forming apparatus 100 also includes a liquid column made of a recording liquid immediately after being ejected from the heads 61Y, 61M, 61C, 61BK, the heads 61Y, 61M, 61C, 61BK, the intermediate transfer drum 37, and the like. Are temporarily bridged (connected) between the intermediate transfer drum 37 and the heads 61Y, 61M, 61C, 61BK so that a potential difference is formed between the recording liquids in the liquid column state. A voltage application means 33 is provided for energizing the current component resulting from the electrode oxidation reaction or electrode reduction reaction to promote aggregation of the colorant contained in the recording liquid in such a state as described later.
As shown in FIG. 2, the image forming apparatus 100 also removes the recording liquid remaining on the intermediate transfer drum 37 from the intermediate transfer drum 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 Including control means (not shown).

In addition to the intermediate transfer drum 37, the transport unit 10 is disposed so as to face the intermediate transfer drum 37, and when the transfer sheet S passes through a transfer unit 31 that is an area between the transfer unit 37 and the intermediate transfer drum 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 drum 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 drum 37.
The transfer unit 64 includes a transfer roller 38 that rotates following the intermediate transfer drum 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 drum 37 to the transfer paper S by the transfer roller 38 on the transfer paper S.

As shown in FIG. 3, the intermediate transfer drum 37 has 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 drum 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 due to the recording liquid in which the heads 61Y, 61M, 61C, 61BK and the intermediate transfer drum 37 are temporarily bridged, the volume resistivity of the conductive rubber is 1 ×. It is preferably less than 10 ³ 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 drum 37. Further, the intermediate transfer drum 37 is not a drum, but may be an endless belt, or a sheet if possible.
As shown in FIG. 2, 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 replaced with a main body 99 (strictly speaking, in order to be able to be replaced with a new one when deterioration or the like occurs, and to facilitate maintenance. It is detachable from the carriage 50. 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, 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 by a pump. Not have distributor tank and .

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 means 2 described later. 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 2 functions as an ink supply control unit that is a recording liquid supply control unit. The control unit controls the drive 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 viewpoint of conductivity for causing electrolysis described later, and the recording liquid is a conductive 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 salts, alkyl sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensates, 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. 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. 3, 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 supplied with the recording liquid from the distributor tank and filled with the recording liquid, and an ink discharge means (not shown) for discharging the recording liquid in the ink chamber 61c from the nozzle 61b.
The nozzle 61b, the ink chamber 61c, and the ink discharge means are one set, and each head 61Y, 61M, 61C, 61BK is provided in large numbers, but only one of them is shown in the figure. Yes.
The entire nozzle plate 61a is conductive. The nozzle plate 61a includes the 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. Further, a water repellent film may be provided on the surface of the nozzle plate 61a. The water-repellent film may be a film coated with a fluorine-based water repellent or a silicon-based water repellent, or may be plated with a fluorine-based polymer or a fluorine-metal compound eutectoid. It is not limited.

The nozzle plate 61a is not limited to a conductive material as a whole, and may be a member in which only the surface on the ink chamber 61c side is subjected to a conductive treatment, or an intermediate member between a conductive member disposed on the ink chamber 61c side. You may comprise by the insulating member arrange | positioned at the transfer drum 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 61a is set so that the gap with the intermediate transfer drum 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 drum 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 ink ejecting means has a piezoelectric element as an actuator for ejecting the recording liquid from the nozzle 61b as droplets and landing on the transfer paper S, and the recording liquid is ejected from the nozzle 61b in accordance with a voltage pulse applied to the piezoelectric element. It is designed to discharge.
The actuator of the ink discharge means may be a movable actuator of another method that is a shape deformation element method such as a piezo method, or the recording liquid is discharged from the nozzle 61b by a heater method such as a thermal method. Also good.

The voltage application means 33 includes a power supply 33a, an electric circuit (not shown) in which the power supply 33a is connected to the support 37a and the nozzle plate 61a, and voltage application control means for controlling the voltage application timing and application time of the power supply 33a. Have. The control means 2 also serves as the voltage application control means. The control means as the voltage application control means also functions as a voltage changing means for changing the voltage of the power source 33a.
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 voltage applying unit 33 includes the intermediate transfer drum 37 as an anode and the nozzle plate 61a as a cathode.

As shown in FIG. 2, the cleaning means 34 is configured by a cleaning blade as a cleaning member formed of rubber as an elastic body, which is in contact with the intermediate transfer drum 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.
In the image forming apparatus 100 having such a configuration, the intermediate transfer drum 37 rotates in the A1 direction while facing the heads 61Y, 61M, 61C, 61BK in response to the input of a predetermined signal to start image formation. In the process, the recording liquids of yellow, magenta, cyan, and black are transferred from the heads 61Y, 61M, 61C, and 61BK so that the image areas of yellow, magenta, cyan, and black are overlapped at the same position on the intermediate transfer drum 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 drum 37.

At this time, the voltage application means 33 is driven by the control means 2 as the voltage application control means, 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 drum 37. At this time, first, the heads 61Y, 61M, 61C, 61BK are used as shown in FIG. As shown in FIG. 3B, the recording liquid forming a meniscus in the nozzle 61b moves toward the intermediate transfer drum 37 as shown in FIG. 3B, and the recording liquid is recorded between the nozzle 61c and the intermediate transfer drum 37. A bridge of liquid columns made of liquid is temporarily formed.
Next, as shown in FIG. 3C, the bridge of the liquid column made of the recording liquid is divided so that it is carried on the intermediate transfer drum 37, and an image of the recording liquid is formed on the intermediate transfer drum 37.

In the state shown in FIG. 3B in which the liquid injection bridge made of the recording liquid is formed, the color application component in the recording liquid is subjected to an aggregating action by the voltage application means 33.
Specifically, by the voltage application of the voltage application means 33, the following electrode reactions occur in the nozzle plate 61a as the cathode and the intermediate transfer drum 37 as the anode, respectively, and the water contained in the bridge of the liquid column of the recording liquid. Is electrolyzed.
Cathode: 4H2O + 4e- → 2H2 + 4OH -... Reaction formula (1)
Anode: 2H2O → 4H ++ O2 + 4e−... Reaction formula (2)
As a result, water contained in the bridge of the liquid column of the recording liquid is oxidized on the surface of the intermediate transfer drum 37 functioning as an anode to generate protons (H ⁺ ). The pigment P dispersed by the agent D aggregates via protons.
As a result, the occurrence of bleeding between adjacent dots is suppressed without applying a treatment liquid or the like as in Patent Document 1, 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.

In addition, when using the electroconductive support body 37a in which the electroconductive layer 37b is not formed as an intermediate transfer drum instead of the intermediate transfer drum 37, a metal is made with water on the surface of the electroconductive support body 37a functioning as an anode. Can be oxidized. As a result, a metal cation excellent in the effect of aggregating the pigment is produced together with the proton, so that the pigment dispersed by the anionic dispersant D via the proton and the metal cation (M ^{n +} ) as shown in FIG. P can be aggregated.
Further, instead of agglomerating the pigment dispersed by the anionic dispersant via protons generated on the surface of the intermediate transfer drum 37 functioning as the anode, the pigment dispersed by the cationic dispersant is replaced by the cathode. The particles may be aggregated through hydroxide ions generated on the surface of the intermediate transfer drum 37 functioning as

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 electric double layers EC and EA are formed on the surfaces of the cathode C and the anode A, respectively. The charge rates of the electric double layers EC and EA are included in the conductivity of the bridge B of the liquid column and the recording liquid. It is almost determined by the concentration of ions. At this time, when the voltage of the electric double layer EA reaches several volts, water is electrolyzed and a Faraday current flows. 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 aggregation of the pigment is performed simultaneously with the landing of the recording liquid onto the intermediate transfer drum 37. As a result, pigment bleeding does not occur between adjacent recording liquid dots, and a very high-definition solute image is formed.

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. Therefore, in order to form an image of the recording liquid on the intermediate transfer drum 37, the voltage applied by the voltage applying unit 33 is a theoretical water decomposition voltage of 1.23 V or a general water electrolysis condition. Several tens to several tens of volts are insufficient, and several tens to several hundreds of volts are preferable.
In synchronization with the timing at which the leading edge of the image carried on the intermediate transfer drum 37 reaches the transfer unit 31, one 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 drum 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 component due to the recording liquid remains on the intermediate transfer drum 37 that has passed through the transfer unit 31 due to the transfer in the transfer unit 31, but the intermediate transfer drum 37 is subjected to cleaning by the cleaning unit 34, thereby recording. Liquid offset is highly prevented or suppressed, and even if image formation is repeatedly performed, background contamination due to offset is prevented or suppressed, and image deterioration and deterioration of the intermediate transfer drum 37 are suppressed or prevented. Image formation can be performed.

Based on FIG. 1, the structure which detects the nozzle discharge state in this embodiment is demonstrated concretely.
When the recording liquid is ejected from the nozzle 61 in a state where a voltage is applied between the nozzle 61 and the intermediate transfer drum 37 by the voltage application means 33, a liquid injection bridge made of the recording liquid is formed. Discharge occurs near the column.
The conditions under which the discharge occurs include various factors such as the conductivity of the recording liquid, the shape of the discharged recording liquid, the material of the nozzle 61 and the intermediate transfer drum 37, and the gap between the nozzle 61 and the intermediate transfer drum 37, in addition to the applied voltage. Since it is involved, it cannot be generally stated, but it is desirable that the applied voltage be 300 V or higher in order to cause discharge in all ejections.
If an excessively strong discharge occurs, the surface of the nozzle 61 and the intermediate transfer drum 37 may be destroyed and the image may be deteriorated. Therefore, the applied voltage is more preferably 300 to 500V.

The discharge light 70 generated for each nozzle is detected by the light receiving means 71. The light receiving means 71 has a configuration in which a plurality of light receiving elements are regularly arranged in an array along the longitudinal direction of the recording head.
When the light receiving element detects the discharge light 70 from the detection target nozzle, the control means 2 considers that the recording liquid is normally discharged from the nozzle, and conversely, if the discharge light 70 cannot be detected, the discharge failure is detected. And the nozzle cleaning means 5 such as wiping is driven to perform nozzle normalization processing (recovery processing).
The control unit 2 may display a message indicating that normalization processing is necessary via the liquid crystal display unit of the operation panel 3, and the operator may operate the nozzle cleaning unit or replace the nozzle based on this.
If the discharge light 70 cannot be detected again for the same nozzle after the normalization process, the control means 2 displays that the nozzle needs to be replaced.

A discharge threshold may be provided for the detection level (light reception amount range) of the discharge light 70 received by the light receiving element to make a detailed determination of ejection failure.
In addition, when the ink type is set by the operation panel 3 or the like, or when the ink type is automatically detected, the control means 2 stores the “conductivity and applied voltage depending on the ink type” stored in advance in a memory such as a ROM. The corresponding applied voltage may be selected from the data table, and the applied voltage may be changed by controlling the voltage applying means.
In this embodiment, the discharge light generated when the droplet bridge is formed is received, but this may be detected by intentionally emitting light from the nozzle.

A second embodiment will be described with reference to FIG. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, description of the configuration and functions already described is omitted, and only the main part will be described (the same applies to other embodiments below).
In the present embodiment, the light receiving means 71 has one light receiving element, and the light receiving means 71 can be moved by the light receiving means moving mechanism 6.
The control means 2 drives the light receiving means moving mechanism 6 to move the light receiving means 71 so as to correspond to the nozzles to be detected by the light receiving element.
As the light receiving means moving mechanism 6, for example, a screw feed mechanism, a timing belt drive mechanism, a pinion / rack mechanism, or the like can be adopted, and table control may be performed using a home position sensor and a stepping motor as a drive source.
In the present embodiment, the number of light receiving elements of the light receiving means 71 is one, but the light receiving means 71 having a plurality of light receiving elements may be moved to simultaneously check a plurality of nozzles.
Which nozzle is detected is determined by the position of the light receiving means 71. The movement of the light receiving means 71 is not limited to the example shown here (linear movement), and for example, a method of changing the detection location by rotating the light receiving means 71 may be used.

A third embodiment will be described with reference to FIG.
In this embodiment, the light receiving means 71 having one light receiving element is fixed in position, and the discharge light 70 is guided to the light receiving means 71 by a polygon mirror 72 as a deflecting means.
The polygon mirror 72 can be moved (rotated) by a polygon motor 7 as mirror moving means. The rotation angle of the polygon mirror 72 is detected by the rotation angle detector 8. Which nozzle is detected by the light receiving element is determined by the rotation angle of the polygon mirror 72.
The deflecting means is not limited to the polygon mirror but may be other types of mirrors such as a plane mirror, and the moving means is not limited to rotation but may be a spatial movement along the nozzle row direction.
In addition, this invention is not limited to the above Example, Other forms may be sufficient.

6 Light receiving means moving mechanism as moving mechanism 7 Polygon motor as moving mechanism 33 Voltage applying means 37 Intermediate transfer drum as intermediate transfer body 61Y, 61M, 61C, 61BK Recording head 61b Nozzle 71 Light receiving means 72 Polygon mirror as deflecting means B Liquid column S Transfer paper as recording material

JP 2008-62397 A JP 2006-123203 A

Claims (15)

In an image forming apparatus of a type in which conductive ink is ejected from a nozzle of a recording head in accordance with an image signal onto an intermediate transfer member, and an image on the intermediate transfer member is transferred to a recording material.
The intermediate transfer member has a conductive surface, and the shape of the conductive ink discharged from the nozzle during image formation may temporarily bridge between the nozzle and the surface of the intermediate transfer member. Possible liquid column,
Voltage applying means for applying a voltage between the nozzle and the surface of the intermediate transfer member;
An image forming apparatus comprising: a light receiving unit configured to receive light generated by a discharge emitted from a vicinity of the liquid column of the conductive ink. The image forming apparatus according to claim 1.
An image forming apparatus, wherein a plurality of light receiving elements constituting the light receiving means are arranged along a longitudinal direction of the recording head. The image forming apparatus according to claim 1, wherein
An image forming apparatus, wherein the light receiving means includes a moving mechanism that is movable along a longitudinal direction of the recording head. The image forming apparatus according to claim 1.
An image forming apparatus comprising: a deflecting unit that guides light generated by the discharge to the light receiving unit. The image forming apparatus according to claim 4.
An image forming apparatus, wherein the deflection unit includes a moving mechanism that is movable along a longitudinal direction of the recording head. The image forming apparatus according to any one of claims 1 to 5,
Control means for determining a discharge state from the nozzle based on a light reception signal from the light receiving means, and executing the normalization process when the nozzle normalization process is necessary or notifying that the normalization process is necessary An image forming apparatus comprising: The image forming apparatus according to claim 6.
The image forming apparatus according to claim 1, wherein the control unit changes a voltage applied by the voltage applying unit according to a difference in conductivity depending on a type of the conductive ink. The image forming apparatus according to any one of claims 1 to 7,
The conductive ink contains water as a solvent, the pigment is dispersed by an anionic dispersant,
The image forming apparatus, wherein the intermediate transfer member functions as an anode when a voltage is applied by the voltage applying unit. The image forming apparatus according to claim 8.
An image forming apparatus, wherein the surface of the intermediate transfer member is made of metal. The image forming apparatus according to any one of claims 1 to 7,
The conductive ink contains water as a solvent, the pigment is dispersed by a cationic dispersant,
The image forming apparatus, wherein the intermediate transfer member functions as a cathode when a voltage is applied by the voltage applying unit. An image forming apparatus that discharges conductive ink onto an intermediate transfer member having a conductive surface from a nozzle of a recording head according to an image signal, and transfers the image on the intermediate transfer member onto a recording material for recording. In forming an image, a voltage is applied between the nozzle and the surface of the intermediate transfer member, and the liquid column of the conductive ink discharged from the nozzle is between the nozzle and the surface of the intermediate transfer member. In the nozzle discharge state detection method in the image forming apparatus that temporarily bridges
A nozzle discharge state detecting method, wherein light received by a discharge emitted from the vicinity of a liquid column of the conductive ink is received by a light receiving means. In the nozzle discharge state detection method according to claim 11,
A nozzle discharge state detection method, wherein the light receiving means is composed of a plurality of light receiving elements arranged along the longitudinal direction of the recording head. In the nozzle discharge state detection method according to claim 12,
A nozzle discharge state detection method comprising: moving the light receiving means to change a nozzle position to be detected. In the nozzle discharge state detection method according to claim 11,
A method for detecting a nozzle discharge state, wherein the discharge light is deflected by a deflecting unit and guided to the light receiving unit. In the nozzle discharge state detection method according to claim 14,
A nozzle discharge state detection method, wherein the nozzle position to be detected is changed by moving the deflection means.

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