JP2017167255A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fixing liquid from adhering to an outer peripheral surface of a nozzle for spraying a fixing liquid.SOLUTION: A fixing device 7 includes: a fixing head 71 having a housing part 73 for housing a fixing liquid L inside and a nozzle N communicating with the housing part 73 to spray a developer image on a recording sheet with the fixing liquid L; potential difference forming parts (a first electrode 74 and a second electrode 72) for forming a potential difference between the fixing liquid L in the nozzle N and a recording sheet transported at a position separated from the nozzle N; pressure applying means (pressure applying device 75) for applying pressure to the fixing liquid; and a control part 100 for controlling an electric voltage applied to the potential difference forming parts and pressure applied to the fixing liquid L. The control part 100 applies an electric voltage to the potential difference forming parts while applying pressure to the fixing liquid L, when spraying with the fixing liquid L is performed, and performs voltage reduction processing for reducing an electric voltage applied to the fixing liquid L after starting pressure reduction processing for reducing pressure applied to the fixing liquid L, when spraying with the fixing liquid L is stopped.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus is known that includes a fixing device that melts toner by heating a transferred toner image to fix the toner on a sheet. The fixing device has a heating element such as a halogen heater or a ceramic heater to melt the toner. The melted toner is pressed against the paper and fixed on the paper. Such a fixing device is widely used because it has a high fixing speed and good image quality. However, an image forming apparatus using such a heat fixing type fixing device consumes a large amount of power because it heats toner, and thus is not suitable for power saving of the image forming apparatus.

  In order to solve the above problems, there is an image forming apparatus including a fixing device that fixes a toner image on a sheet by applying a fixing solution for dissolving or swelling the toner to the toner on the sheet. This fixing device does not require a heat treatment for melting the toner as in the heat fixing method, has low power consumption, and is excellent in power saving. As a method for applying a fixing solution to a toner image, a method of applying a fixing solution to a toner image by electrostatic spraying is known (see Patent Document 1).

JP 2009-69256 A

  By the way, in the fixing method using electrostatic spraying, when spraying of the fixer from the nozzle spraying the fixer is stopped, if the fixer adheres to the outer peripheral surface of the nozzle and remains, normal spraying is started at the start of the next spraying. May not be able to do.

  Therefore, an object of the present invention is to suppress the fixing liquid from adhering to the outer peripheral surface of a nozzle that sprays the fixing liquid.

In order to solve the above-described problem, a fixing device according to the present invention sprays the fixing solution toward a developer image on a recording sheet in communication with the storage portion that stores the fixing solution therein and the storage portion. A potential difference forming unit for forming a potential difference between a fixing head having a nozzle, the fixing liquid in the nozzle, and a recording sheet conveyed at a position away from the nozzle; and a fixing liquid at a tip of the nozzle A pressure applying unit that applies pressure to the fixing solution, and a control unit that controls a voltage applied to the potential difference forming unit and a pressure applied to the fixing solution.
When stopping the spraying of the fixing solution, the control unit starts a pressure reduction process for controlling the pressure applying unit so as to reduce the pressure applied to the fixing solution, and then applies the applied pressure to the fixing solution. The voltage reduction process for controlling the potential difference forming unit is performed so that the voltage to be reduced is lower than the voltage at the start of the pressure reduction process.

  According to this configuration, when the spraying of the fixing solution is stopped, the pressure applied to the fixing solution is reduced before the voltage is reduced, so that the amount of the fixing solution fed to the nozzle tip by the pressure is reduced. After the pressure is lowered, the spraying is continued while the volume of the Taylor cone-shaped fixer formed by applying the voltage gradually decreases. This reduces the amount of fixer remaining at the tip of the nozzle, so that even if the surface shape of the fixer that had become a Taylor cone shape changes to a spherical shape after the voltage drop, , It is possible to prevent the fixing liquid from adhering to the outer peripheral surface of the nozzle.

  Further, in the above-described configuration, the control unit determines whether or not spraying of the fixing liquid has stopped after starting the pressure decreasing process, and performs the voltage decreasing process when determining that spraying has stopped. It may be configured to do.

  According to this, since the voltage application is continued until the spraying of the fixing solution is stopped, the volume of the Taylor cone-shaped fixing solution can be made extremely small.

  Further, in the configuration described above, the control unit determines whether or not the current flowing through the potential difference forming unit has become a predetermined value or less, and determines that spraying has stopped when the current has decreased to a predetermined value or less. It may be configured.

  According to this, it is possible to satisfactorily determine whether to stop spraying based on the current flowing through the potential difference forming unit.

  Further, in the above-described configuration, the control unit determines whether or not a predetermined time has elapsed after performing the pressure reduction process, and determines that spraying has stopped when it is determined that the predetermined time has elapsed. It may be configured.

  According to this, the control can be simplified by determining the stop of the spray based on the elapsed time from the start of the pressure reduction process.

  In the above-described configuration, the control unit may be configured to make the pressure equal to or less than the meniscus pressure resistance in the pressure reduction process.

  In the above configuration, the control unit may be configured to start the pressure reduction process before the upstream end of the image of the last page in the print job passes through the fixing liquid spray region. .

  According to this, the fixer sprayed after the pressure reduction process can be effectively used.

  In the above-described configuration, the control unit may be configured to perform the pressure reduction process after the upstream end of the image of the last page in the print job passes through the spray region of the fixing liquid.

  According to this, for example, when the image density of the upstream portion of the image of the last page is high and a large amount of fixing solution is required (when the amount of fixing solution corresponding to the volume of the Taylor cone is insufficient), the upstream of the image The side portion can be fixed satisfactorily.

  In the above-described configuration, the control unit may be configured to start the pressure reduction process and then perform the voltage reduction process when the recording sheet is jammed.

  According to this, even when the recording sheet is jammed, it is possible to suppress the fixing liquid from adhering to the outer peripheral surface of the nozzle.

  In the above configuration, the pressure applying unit may include a pump that pressurizes the gas in the fixing head.

  In the above-described configuration, the control unit may be configured to keep the voltage constant from the start of the pressure reduction process to the start of the voltage reduction process.

  Further, in the above-described configuration, the electric field forming unit may include a first electrode that comes into contact with the fixing liquid in the housing unit, and a second electrode that is disposed at a distance from the nozzle.

  According to the present invention, it is possible to suppress the fixing liquid from adhering to the outer peripheral surface of the nozzle that sprays the fixing liquid.

1 is a diagram illustrating a laser printer including a fixing device according to an embodiment of the present invention. It is a figure which shows a fixing device in detail. FIG. 4 is a perspective view (a) of the fixing head as viewed obliquely from above and a perspective view (b) of the first fixing head as viewed from obliquely below. FIG. 6 is a bottom view of the fixing head as viewed from below. It is a flowchart which shows operation | movement of a control part. FIGS. 5A to 5C are views illustrating the state of the fixing liquid in the vicinity of the nozzle tip when the spraying of the fixing liquid is stopped. 10 is a flowchart illustrating an operation of a control unit according to Modification 1. 10 is a flowchart illustrating an operation of a control unit according to Modification 2.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, the overall configuration of the laser printer will be described, and then the features of the present invention will be described in detail.

  In the following description, directions will be described in the directions shown in FIG. That is, in FIG. 1, the right side toward the paper surface is “front side”, the left side toward the paper surface is “rear side”, the back side toward the paper surface is “right side”, and the front side toward the paper surface is “left side”. To do. In addition, the vertical direction toward the page is defined as the “vertical direction”.

  As shown in FIG. 1, a laser printer 1 includes a main body housing 2, a feeder unit 3 for feeding a sheet SH as an example of a recording sheet, and an image forming unit 4 for forming an image on the sheet SH. And.

  The feeder unit 3 includes a paper feed tray 31 that is detachably attached to the lower part of the main body housing 2 and a paper feed mechanism 32 that feeds the paper SH in the paper feed tray 31 toward the image forming unit 4. ing. The paper feed mechanism 32 includes a paper feed roller 32A, a separation roller 32B, a separation pad 32C, a paper dust removing roller 32D, and a registration roller 32E. The registration roller 32E is a roller that aligns the leading end position of the paper SH, and can be appropriately stopped and rotated by the control unit 100 described later.

  The image forming unit 4 is accommodated in the main body housing 2 and mainly includes a scanner unit 5, a process cartridge 6, a transfer roller TR, and a fixing device 7.

  The scanner unit 5 is provided in an upper part in the main body housing 2 and includes a laser light emitting unit, a polygon mirror, a lens, a reflecting mirror, and the like (not shown). In the scanner unit 5, a laser beam is irradiated on the surface of a photosensitive drum 61 described later by high-speed scanning.

  The process cartridge 6 can be attached to and detached from the main body housing 2. The process cartridge 6 includes a photosensitive drum 61 on which an electrostatic latent image is formed, a charger (not shown), a toner storage unit 62 that stores toner as an example of a developer, and a toner in the toner storage unit 62. A supply roller 63 and a developing roller 64 for supplying to 61 are provided.

  In the process cartridge 6, a charger (not shown) uniformly charges the surface of the rotating photosensitive drum 61. The scanner unit 5 emits a laser beam to the surface of the photosensitive drum 61 to expose the surface of the photosensitive drum 61, thereby forming an electrostatic latent image based on the image data on the surface of the photosensitive drum 61.

  Next, the rotationally driven developing roller 64 supplies toner to the electrostatic latent image on the photosensitive drum 61 to form a toner image on the surface of the photosensitive drum 61. Thereafter, the toner image carried on the surface of the photosensitive drum 61 is attracted to the transfer roller TR and transferred onto the paper SH when the paper SH is conveyed between the photosensitive drum 61 and the transfer roller TR.

  The fixing device 7 is a device that fixes the toner image on the paper SH by supplying the charged fixing liquid L to the toner image on the paper SH by electrostatic spraying. The configuration of the fixing device 7 will be described in detail later.

  On the downstream side of the fixing device 7, a pair of downstream-side transport rollers Rd for sandwiching and transporting the paper SH discharged from the fixing device 7 to the downstream side is provided. The paper SH transported by the downstream transport roller Rd is transported to the paper discharge roller R and is discharged onto the paper discharge tray 21 from the paper discharge roller R.

Next, the configuration of the fixing device 7 will be described in detail.
As shown in FIG. 2, the fixing device 7 includes a fixing head 71 for spraying the fixing liquid L toward the toner image on the paper SH, and a second electrode 72 that supports the paper SH under the fixing head 71. A pressurizing device 75 as an example of a pressure applying unit, a fixer cartridge 76, a tank 77, and a control unit 100 are provided.

The fixing liquid L can be used by dispersing a solute that dissolves toner in a solvent having a high dielectric constant in order to perform electrostatic spraying well and perform fixing. Safe water can be used as a solvent having a high dielectric constant. That is, in this embodiment, the toner is dissolved by a so-called oil-in-water emulsion in which a solute that dissolves the toner is dispersed in water. That is, a fixing solution in which a solute insoluble or hardly soluble in water as a solvent is dispersed in water is used. Solutes include aliphatic monocarboxylic acid esters such as ethyl laurate, butyl laurate, isopropyl laurate, ethyl myristate, butyl myristate, isopropyl myristate, ethyl palmitate, butyl palmitate, isopropyl palmitate, fat As an aliphatic dicarboxylic acid ester system, diethyl succinate, dibutyl succinate, as an aliphatic tricarboxylic acid ester system, o acetyl citrate triethyl, o acetyl tributyl citrate, as an aliphatic dicarboxylic acid dialkoxyalkyl system as diethoxyethyl succinate, Ethylene carbonate and propylene carbonate can be used as dibutoxyethyl succinate and carbonate ester. These solutes have a function of softening the toner.
In addition, a surfactant may be added in order to form an emulsion satisfactorily. As the surfactant, an anionic surfactant, a cationic surfactant, or a nonionic surfactant can be used. Examples of anionic surfactants include higher fatty acid salts such as sodium laurate, alkylaryl sulfonates such as sodium dodecylbenzene sulfonate, alkyl sulfate salts such as sodium dodecyl sulfate, and polyethoxyethylene lauryl ether sodium sulfate. Polyoxyethylene alkylaryl ether sulfate salts such as oxyethylene alkyl ether sulfate salts and sodium polyoxyethylene nonylphenyl ether sulfate can be used. As the cationic surfactant, aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts can be used. Nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonylphenyl ether, sorbitan higher fatty acid esters such as sorbitan monolaurate, Use polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate, and sucrose fatty acid esters such as sucrose laurate. Can do.

  As shown in FIG. 3A, the fixing head 71 includes a first fixing head 71A, a second fixing head 71B, a third fixing head 71C, a fourth fixing head 71D, and a fifth fixing that are arranged in a staggered manner in the width direction. It has a head 71E. The first fixing head 71A, the third fixing head 71C, and the fifth fixing head 71E are arranged at substantially the same position in the front-rear direction, that is, the conveyance direction of the sheet SH, and are spaced apart in the left-right direction, that is, the width direction of the sheet SH. Has been placed. The second fixing head 71B is arranged on the upstream side of the first fixing head 71A and the third fixing head 71C in the transport direction, and the central portion in the width direction is between the first fixing head 71A and the third fixing head 71C in the width direction. Arranged between. The fourth fixing head 71D is arranged on the upstream side of the third fixing head 71C and the fifth fixing head 71E in the transport direction, and the center portion in the width direction is the third fixing head 71C and the fifth fixing head 71E in the width direction. Arranged between.

  The first fixing head 71A includes an accommodating portion 73 that accommodates the fixing liquid L therein, a plurality of nozzles N that communicate with the accommodating portion 73 and spray the fixing liquid L toward the toner image, the inside of the accommodating portion 73, and the respective portions. And a first electrode 74 for applying a voltage to the fixing liquid L in the nozzle N. The other fixing heads 71B to 71E have substantially the same configuration as the first fixing head 71A. Therefore, the members constituting the other fixing heads 71B to 71E are the members constituting the first fixing head 71A. The same reference numerals are given and the description is omitted as appropriate. That is, each of the fixing heads 71A to 71E (each accommodating portion 73) has the same shape and is configured separately. Further, the same number of nozzles N are provided in the same arrangement in each accommodating portion 73.

  The accommodating portion 73 is a rectangular insulating container that is long in the width direction, and includes an upper wall 73A, a front wall 73B, a rear wall 73C, a left wall 73D, a right wall 73E, and a lower wall 73F. As shown in FIG. 3B, the plurality of nozzles N in the fixing heads 71 </ b> A to 71 </ b> E protrude downward from the lower wall 73 </ b> F of the accommodating portion 73, and the diameter gradually decreases toward the lower side. ing. The plurality of nozzles N are arranged in the width direction and are arranged in the transport direction.

  Specifically, the plurality of nozzles N constitute a first staggered array group U1 and a second staggered array group U2 arranged in the transport direction. As shown in FIG. 4, the first staggered array group U1 includes a plurality of first nozzles N1 arranged at a constant interval in the width direction and a plurality of first nozzles N1 arranged at a constant interval in the width direction. The first nozzle N1 and the second nozzle N2 are alternately arranged on one side and the other side in the transport direction from one side in the width direction to the other side.

  Further, each second nozzle N2 is disposed between the two first nozzles N1 in the width direction. The shape connecting two first nozzles N1 adjacent in the width direction and the second nozzle N2 disposed between the two first nozzles N1 is an equilateral triangle or an isosceles triangle. In addition, the shape connecting two second nozzles N2 adjacent in the width direction and the first nozzle N1 disposed between the two second nozzles N2 is also an equilateral triangle or an isosceles triangle.

  The second staggered array group U2 has the same structure as the first staggered array group U1. In this embodiment, the nozzle pitch (the shortest distance between the outer diameters of adjacent nozzles) may be set in the range of 1 mm or more and 14 mm or less.

  Further, two fixing heads (for example, the first fixing head 71A and the second fixing head 71B) that are adjacent in the width direction are arranged so that the storage portions 73 overlap each other when viewed from the transport direction. Specifically, the minimum pitch (for example, the pitch between the first nozzle N1 and the second nozzle N2) in the width direction of the plurality of nozzles N in a predetermined fixing head (for example, the first fixing head 71A) is Da. Yes. On the other hand, a fixing head adjacent to one side of the predetermined fixing head from the nozzle N on the most one side in the width direction of the predetermined fixing head (for example, the leftmost first nozzle N1 of the first fixing head 71A). For example, the distance Db to the nozzle N on the other side in the width direction of the second fixing head 71B) (for example, the first nozzle N1 on the right side of the second fixing head 71B) is smaller than the minimum pitch Da.

  That is, the fixing areas A1 to A5 (areas where the fixing liquid L is sprayed on the paper SH by the nozzles N of the fixing heads 71A to 71E) set for the fixing heads 71A to 71E are viewed from the transport direction. The fixing heads 71A to 71E are arranged so as to overlap each other. In the present embodiment, the fixing areas A1 to A5 of the fixing heads 71A to 71E will be described as having the same shape, size, and position as the lower surface of the housing portion 73 for convenience.

  More specifically, the first fixing area A1, which is an area where the fixing liquid L is sprayed from the first fixing head 71A, is conveyed to the second fixing area A2, which is an area where the fixing liquid L is sprayed from the second fixing head 71B. Overlapping from the direction. The fifth fixing area A5, which is an area where the fixing liquid L is sprayed from the fifth fixing head 71E, is viewed from the transport direction in the fourth fixing area A4 where the fixing liquid L is sprayed from the fourth fixing head 71D. overlapping.

  The third fixing area A3, which is an area where the fixing liquid L is sprayed from the third fixing head 71C, overlaps the second fixing area A2 and the fourth fixing area A4 when viewed from the transport direction. By arranging the fixing heads 71A to 71E in this way, it is possible to suppress the occurrence of a region where the fixing liquid L is not sprayed between the fixing heads 71A to 71E.

  The first fixing head 71 </ b> A is a head for spraying the fixing liquid L onto the narrowest first sheet SH <b> 1 among a plurality of types of sheets SH that can be printed by the laser printer 1. It is formed with a width smaller than the width of the paper SH1. The first fixing head 71A is disposed on the inner side in the left-right direction than the left and right ends of the first sheet SH1. Specifically, the first fixing area A1 of the first fixing head 71A is formed to have a size that is equal to or larger than the width of the image forming area that is an area on which the image of the first sheet SH1 is formed. They are arranged so that the entire width of the image forming area falls within the width of the area A1.

  In the present embodiment, as shown in FIG. 4, the sheets SH1 to SH5 having different sheet widths are conveyed with the left end as a reference. Specifically, a guide member (not shown) that contacts the left end of each sheet SH1 to SH5 and guides the left end in the main body housing 2 is provided.

  The second fixing head 71B is adjacent to the right side (one side in the width direction) of the first fixing head 71A, and is on the left side of the right end of the second sheet SH2 that is wider than the first sheet SH1 ( It is arranged on the other side. Specifically, the right end of the second fixing area A2 of the second fixing head 71B is disposed at the same position as the right end of the image forming area of the second sheet SH2 or at a position on the right side of the right end. Note that the left end of the image forming area of the second sheet SH2 is substantially the same position as the left end of the image forming area of the first sheet SH1. As described above, by arranging the first fixing head 71A and the second fixing head 71B, the first fixing head 71A and the second fixing head 71B can fix the fixing liquid L to the image forming area of the second sheet SH2. Can be sprayed.

  The third fixing head 71C is adjacent to the right side of the second fixing head 71B, and is disposed on the left side of the right end of the third sheet SH3 that is wider than the second sheet SH2. Specifically, the right end of the third fixing area A3 of the third fixing head 71C is disposed at the same position as the right end of the image forming area of the third sheet SH3 or at a position on the right side of the right end. Note that the left end of the image forming area of the third sheet SH3 is substantially the same position as the left end of the image forming area of the first sheet SH1. As described above, the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C are arranged, so that the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C are the third fixing head. The fixer L can be sprayed onto the image forming area of the sheet SH3.

  The fourth fixing head 71D is adjacent to the right side of the third fixing head 71C, and is disposed on the left side of the right end of the fourth sheet SH4 that is wider than the third sheet SH3. Specifically, the right end of the fourth fixing area A4 of the fourth fixing head 71D is disposed at the same position as the right end of the image forming area of the fourth sheet SH4 or at a position on the right side of the right end. Note that the left end of the image forming area of the fourth sheet SH4 is substantially the same position as the left end of the image forming area of the first sheet SH1. As described above, the fixing heads 71A to 71D are arranged so that the fixing heads 71A to 71D can spray the fixing liquid L onto the image forming area of the fourth sheet SH4.

  The fifth fixing head 71E is adjacent to the right side of the fourth fixing head 71D, and is disposed on the left side of the right end portion of the fifth sheet SH5 wider than the fourth sheet SH4. Specifically, the right end of the fifth fixing area A5 of the fifth fixing head 71E is disposed at the same position as the right end of the image forming area of the fifth sheet SH5 or at the right side of the right end. Note that the left end of the image forming area of the fifth sheet SH5 is substantially the same position as the left end of the image forming area of the first sheet SH1. As described above, the fixing heads 71A to 71E are arranged so that the fixing heads 71A to 71E can spray the fixing liquid L onto the image forming area of the fifth sheet SH5.

  Returning to FIG. 2, the first electrode 74 is an electrode for generating an electric field at the tip of each nozzle N by applying a voltage to the fixing liquid L in the container 73. The first electrode 74 is provided so as to penetrate the upper wall 73A of the housing portion 73 from the top to the bottom, and the lower end portion is disposed in the fixing liquid L in the housing portion 73 so as to come into contact with the fixing liquid L, and Is connected to the control unit 100 having the voltage application unit 120. The voltage applied to the first electrode 74 is preferably 1 kV to 10 kV.

  A pressure device 75 is connected to each of the fixing heads 71A to 71E. The pressurizing device 75 is a device that applies pressure to the fixing liquid L in each of the fixing heads 71A to 71E, and includes a pump 75A that pressurizes the air in each of the fixing heads 71A to 71E, and air from within each of the fixing heads 71A to 71E. And a pressure reducing valve 75B for reducing the pressure by releasing the air. Further, each of the fixing heads 71A to 71E is provided with a pressure sensor SP (only one is shown) for detecting the pressure of the fixing liquid L in each of the fixing heads 71A to 71E.

  The second electrode 72 is an electrode for contacting the paper SH to form a potential difference between the fixing liquid L in the nozzle N and the paper SH, and from the tip of each nozzle N of each fixing head 71A to 71E. The fixing heads 71A to 71E are arranged below the fixing heads so as to be separated from each other by a predetermined distance. Here, the predetermined distance is a distance larger than the thickness of the paper SH, and is set to a distance at which electrostatic spraying can be suitably performed by experiments or simulations.

  The second electrode 72 is grounded. The second electrode 72 is not necessarily grounded. For example, a voltage smaller than the voltage applied to the first electrode 74 may be applied to the second electrode 72. The second electrode 72 forms an electric field with the tip of the nozzle N.

  When a voltage is applied to the first electrode 74, an electric field is formed in the space near the tip of the nozzle N. The second electrode 72 forms an electric field with the fixing liquid L at the tip of the nozzle N because the fixing liquid L is supplied toward the tip of the nozzle N by the pressure device 75. Then, at the tip of the nozzle N, the fixing liquid L is pulled by an electric field, so that a so-called Taylor cone is formed. Fine droplets are generated by tearing the fixing liquid L from the tip of the Taylor cone.

  The droplet-shaped fixing liquid L sprayed from the nozzle N is positively charged. On the other hand, the sheet SH is substantially in a zero potential state. For this reason, the droplet-like fixing liquid L flies toward the sheet SH by the Coulomb force, and adheres to the sheet SH and the toner image.

  The first current sensor SB is a sensor that indirectly detects the current flowing through the fixing liquid L by detecting the current flowing through the first electrode 74, and is provided corresponding to each first electrode 74. The first current sensor SB detects a current flowing through the first electrode 74 when the fixing liquid L is sprayed from the nozzle N onto the paper SH, and outputs the detected value to the control unit 100. Here, even when a voltage is applied to the first electrode 74, when the fixing liquid L is not sprayed from the nozzle N, no current flows through the first electrode 74, and the fixing liquid L is sprayed from the nozzle N. That is, when the charged fixing liquid L moves from the nozzle N to the paper SH, a current flows through the first electrode 74.

  The second current sensor SA is a sensor that detects a current flowing through the second electrode 72. The second current sensor SA detects a current flowing through the second electrode 72 when the fixing liquid L is sprayed from the nozzle N onto the paper SH, and outputs the detected value to the control unit 100. Here, even when a voltage is applied to the first electrode 74, when the fixing liquid L is not sprayed from the nozzle N, no current flows through the second electrode 72, and the fixing liquid L is sprayed from the nozzle N. That is, when the charged fixer L moves from the nozzle N to the paper SH, a current flows through the second electrode 72.

  The first electrode 74 and the second electrode 72 configured in this way form a potential difference for forming a potential difference between the fixing liquid L in the nozzle N and the paper SH transported at a position away from the nozzle N. Has become a department.

  The fixer cartridge 76 is a cartridge filled with the fixer L and is configured to be detachable from the main body housing 2. The fixer cartridge 76 is connected to the tank 77 via a pipe 76A. The pipe 76A may be provided with a hydraulic pump for supplying the fixing liquid L from the fixing liquid cartridge 76 to the tank 77, a switching valve for switching supply / stop of the fixing liquid L, and the like.

  The tank 77 is provided in the main body housing 2 and is connected to the accommodating portion 73 of each of the fixing heads 71A to 71E via a plurality of pipes 77A. Each pipe 77A is provided with a hydraulic pump for supplying the fixing liquid L from the tank 77 to the fixing heads 71A to 71E, and a valve 77B for switching supply / stop of the fixing liquid L. The valve 77B is made of an insulating member.

  The control unit 100 includes a storage unit 110 made of RAM, ROM, etc., a voltage application unit 120 that applies a voltage to the first electrode 74, a CPU, an input / output circuit, and the like. The control unit 100 has a function of performing control of the pressurizing device 75 and control of the voltage applied to the first electrode 74 based on image data input from the outside and signals from the sensors SP, SA, and SB. have. Specifically, the control unit 100 individually controls the voltage applied to the fixing liquid L in each of the fixing heads 71A to 71E and the pressure applied to the fixing liquid L in each of the fixing heads 71A to 71E for each fixing head. It is configured as follows.

  Specifically, when spraying the fixing liquid L, the control unit 100 sets the pressure P applied to the fixing liquid L to the first pressure P1, and sets the voltage V applied to each first electrode 74 to the image data. It controls so that it may control based on the target spray amount (rho) calculated | required based on. Here, the target spray amount ρ is a target value of the fixing liquid L sprayed per unit area of the paper SH, and is set to a larger spray amount as the image density is higher. Further, the first pressure P1 is appropriately set by, for example, experiments or simulations.

  In addition, when the spraying of the fixing liquid L is stopped, the control unit 100 starts the pressure reduction process for reducing the pressure P applied to the fixing liquid L and then sets the voltage to the voltage at the start of the pressure reduction process. It is configured to perform a voltage reduction process that lowers the voltage. Specifically, in the voltage reduction process, the control unit 100 stops the voltage application to each first electrode 74 to reduce the voltage to 0V. The control unit 100 also generates an error when the fixing spray process is completed (that is, when the fixing liquid L is sprayed on the image on the most upstream side of the last page in the print job) or during printing control. In such a case, it is determined to stop the spraying of the fixing liquid L.

  Here, as an error, for example, when the paper SH is jammed in the transport path in the laser printer 1, or when a cover for opening and closing the opening for exchanging the process cartridge 6 is opened during printing control. Is mentioned. Further, as the error determination, for example, the jam of the paper SH may be determined based on a signal from a paper passing sensor (not shown) arranged in the transport path, or a diagram for detecting opening and closing of the cover. Based on a signal from an open / close detection sensor (not shown), it may be determined whether the cover is open during printing control.

  When it is determined that the spraying of the fixing liquid L is stopped, the control unit 100 sets the voltage V applied to the fixing liquid L to the predetermined voltage Va and starts the pressure reduction process. Here, the predetermined voltage Va is a value within the range of the voltage used in the fixing control, and is appropriately determined by experiment, simulation, or the like. Further, the control unit 100 maintains the voltage V at the predetermined voltage Va from when it is determined to stop the spraying of the fixing liquid L until the voltage reduction process is started.

  In the pressure reduction process, the control unit 100 changes the pressure P applied to the fixing liquid L from the first pressure P1 to the second pressure P2 that is lower than the first pressure P1. Here, the second pressure P2 is a value within a range of 0 ≦ P2 <P1, and is appropriately determined by experiments, simulations, or the like so as to be a pressure equal to or lower than the meniscus pressure resistance.

Here, the meniscus pressure resistance refers to the maximum pressure at which the fixing liquid L can be held in the nozzle N in a state where no voltage is applied to the fixing liquid L, and is expressed by the following equation (1). .
Pm = (4 · σ · cos θ) / d (1)
Pm: Meniscus pressure resistance σ: Surface tension of fixer L θ: Contact angle d: Inner diameter (diameter) of nozzle N

  That is, when a voltage larger than the meniscus pressure resistance is applied to the fixing liquid L in a state where no voltage is applied to the fixing liquid L, the fixing liquid L leaks from the tip of the nozzle N, and the pressure applied to the fixing liquid L is changed to the meniscus pressure resistance. Assuming the following, the fixing liquid L is held in the nozzle N.

  After starting the pressure reduction process, the control unit 100 determines whether or not the spraying of the fixing liquid L has stopped, and performs the voltage reduction process when determining that the spraying has stopped. Specifically, the control unit 100 determines whether or not the current A detected by the second current sensor SA has become a predetermined value Ath or less, and determines that spraying has stopped when the current A has become the predetermined value Ath or less. To do.

  Next, the operation of the control unit 100 will be described in detail with reference to FIG. The control unit 100 executes the process shown in FIG. 5 for each of the fixing heads 71A to 71E. In the following, the control of the first fixing head 71A will be described as a representative.

  As shown in FIG. 5, the control unit 100 first determines whether or not there is a print command (S1). If it is determined in step S1 that there is no print command (No), the control unit 100 ends this control.

  If it is determined in step S1 that there is a print command (Yes), the control unit 100 sets the target spray amount ρ based on the image corresponding to the first fixing head 71A based on the print data (S2). After step S2, the control unit 100 sets the pressure P applied to the fixing liquid L in the first fixing head 71A to the first pressure P1 (S3).

  After step S3, the control unit 100 sets the voltage V to be applied to the first electrode 74 based on the target spray amount ρ, and applies the voltage V to the first electrode 74, so that the first fixing head 71A A fixing spray process for spraying the fixing liquid L on the image of the sheet SH is executed (S4). After step S4, the control unit 100 determines whether or not the fixing spray process has been completed (S5).

  If it is determined in step S5 that the fixing spray process has not ended (No), the control unit 100 determines whether an error has occurred (S6). If it is determined in step S6 that no error has occurred (No), the control unit 100 returns to the process of step S4.

  If it is determined in step S5 that the fixing spray process has been completed (Yes), or if it is determined in step S6 that an error has occurred (Yes), the control unit 100 stops the spraying of the fixing liquid L. Then, the voltage V applied to the first electrode 74 is set to a predetermined voltage Va (S7). After step S7, the control unit 100 opens the pressure reducing valve 75B of the pressurizing device 75 (S8), and starts the pressure reduction process.

  After step S8, the control unit 100 determines whether or not the pressure P of the fixing liquid L in the first fixing head 71A is equal to or lower than the second pressure P2 based on the signal from the pressure sensor SP (S9). . In step S9, the control unit 100 proceeds to the processing of step S11 when P> P2 (No), and closes the pressure reducing valve 75B (S10) when P ≦ P2 (Yes), The lowering process is terminated.

  After step S10 or when determining No in step S9, the control unit 100 determines whether or not the current A detected by the second current sensor SA has become equal to or less than a predetermined value Ath (S11). In step S11, the control unit 100 returns to the process of step S9 when A> Ath (No), and executes a voltage reduction process for setting the voltage V to 0 when A ≦ Ath (Yes). After (S12), this control is finished. In step S12, when the pressure reducing valve 75B is open, the control unit 100 also performs control to close the pressure reducing valve 75B.

Next, the state of the fixing liquid L near the tip of the nozzle N when the spraying of the fixing liquid L is stopped will be described with reference to FIGS.
As shown in FIG. 6A, in the fixing spray process, a conical fixing liquid L, that is, a Taylor cone, is formed at the tip of the nozzle N, and the fixing liquid L having a target spray amount ρ is supplied from the tip of the Taylor cone. Sprayed. When the fixing spray process is completed and the pressure reduction process is started, the amount of the fixing liquid L fed to the tip of the nozzle N gradually decreases, and as shown in FIG. Volume gradually decreases.

  Thereafter, when spraying from the Taylor cone stops and the control unit 100 stops applying the voltage V to the fixer L, as shown in FIG. The surface shape changes to a spherical shape. At this time, since the volume of the Taylor cone is reduced by the spraying of the fixing liquid L from the end of the fixing spraying process until the application of the voltage V is stopped, the fixing liquid L remaining at the tip of the nozzle N is reduced. Since the amount (the amount of the fixer L positioned below the tip of the nozzle N) is small, the fixer L remaining at the tip of the nozzle N does not wrap around the outer peripheral surface of the nozzle N and enters the nozzle N. Retained.

According to the above, the following effects can be obtained in the present embodiment.
After the fixing spray process is finished, the pressure drop process is performed and then the voltage drop process is performed, so that the fixer L can be prevented from flowing from the tip of the nozzle N to the outer peripheral surface of the nozzle N. It is possible to suppress the fixing liquid L from adhering to the surface.

  Since the voltage application (V = Va) is continued until the spraying of the fixing liquid L is stopped after the fixing spraying process is finished, the volume of the Taylor cone-shaped fixing liquid L can be extremely reduced.

  Since the stop of spraying of the fixing liquid L is determined based on the current A detected by the second current sensor SA, it is possible to satisfactorily determine the stop of spraying.

  Even when an error occurs such as when the paper SH is jammed, the pressure reduction process and the voltage reduction process are performed, so that the fixing liquid L can be prevented from adhering to the outer peripheral surface of the nozzle N even when an error occurs.

  In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below. In the following description, the same reference numerals are given to members having substantially the same structure as in the above embodiment, and the description thereof is omitted.

  In the embodiment, the determination of stopping the spraying of the fixing liquid L is determined based on the current A detected by the second current sensor SA, but the present invention is not limited to this. For example, the voltage detected by the voltage sensor The stoppage of spraying may be determined based on the above. Specifically, a resistance connected to the wiring connected to the second electrode 72 and a voltage sensor that detects a voltage applied to the resistance are provided, and by determining whether or not the voltage detected by the voltage sensor has become a predetermined value or less, It may be determined whether or not the current value has become a predetermined value or less (spraying has stopped).

  Moreover, you may judge the stop of spraying by the time after performing a pressure reduction process. Specifically, for example, a process of step S21 shown in FIG. 7 may be provided instead of step S11 of FIG.

  Specifically, in step S21, the control unit 100 determines whether or not a predetermined time has elapsed after starting the pressure reduction process (after executing step S8). When the control unit 100 determines in step S21 that the predetermined time has not elapsed (No), the control unit 100 returns to the process of step S9, and when it is determined that the predetermined time has elapsed (Yes), It is determined that spraying has stopped, and the process proceeds to step S12.

  According to this aspect, since the stop of the spray is determined based on the elapsed time from the start of the pressure reduction process, the control can be simplified as compared with the embodiment.

  In the above-described embodiment, the pressure lowering process is always performed after the fixing spraying process is finished, that is, after the upstream end of the image of the last page in the print job passes through the fixing areas A1 to A5 (spraying areas) of the fixing liquid L. However, the present invention is not limited to this. For example, the control unit 100 may be configured to start the pressure reduction process before the upstream end of the image of the last page in the print job passes through the fixing regions A1 to A5 of the fixing liquid L.

  Specifically, as shown in FIG. 8, new steps S31 and S32 may be provided for the flowchart of FIG. The process of step S31 is provided between step S4 and step S5.

  In step S31, the control unit 100 determines that the target spray amount ρr set for the most upstream image Gr (an image having the same size as the fixing areas A1 to A5) arranged at the most upstream of the last page in the print job is a predetermined value. It is determined whether or not it is larger than the threshold value ρth. Here, the threshold value ρth is appropriately set by experiment, simulation, or the like as a value corresponding to the amount of the fixing liquid L sprayed between Step S7 and Step S12.

  If ρr> ρth in Step S31 (Yes), the control unit 100 determines that the most upstream image Gr cannot be fixed satisfactorily with the amount of the fixing liquid L sprayed between Step S7 and Step S12. The process proceeds to step S5. That is, when the image density of the most upstream image Gr is high and a large amount of the fixing solution L is necessary for fixing the most upstream image Gr (when the amount of the fixing solution L corresponding to the volume of the Taylor cone is insufficient), step S5 is performed. Since the fixing liquid L corresponding to the target spray amount ρr is sprayed on the most upstream image Gr by shifting to the process of step S4 and then the process of step S4, the most upstream image Gr is fixed well. Can do.

  When ρr ≦ ρth in Step S31 (No), the control unit 100 determines that the most upstream image Gr can be sufficiently fixed by the amount of the fixing liquid L sprayed between Step S7 and Step S12, and the most. It is determined whether or not the upstream image Gr has reached the spray area (for example, the fixing area A1) (S32). When it is determined in step S32 that the most upstream image Gr has not reached the spray region (No), the control unit 100 returns to the process of step S4.

  When it is determined in step S32 that the most upstream image Gr has reached the spray region (Yes), the control unit 100 proceeds to the process of step S7. Thereby, before the most upstream image Gr passes through the spray region, the processing from step S7 is executed, so that the fixing liquid L sprayed between steps S7 to S12 is used for fixing the most upstream image Gr. The fixing liquid L can be effectively used.

  In the said embodiment, although the 1st electrode 74 was arrange | positioned inside the accommodating part 73, this invention is not limited to this, For example, a nozzle and an accommodating part are formed with electroconductive members, such as a metal, and a nozzle or an accommodating part A voltage may be applied to. In this case, the nozzle or the container to which the voltage is applied functions as the first electrode. Further, in this case, when the plurality of conductive accommodating portions are separated from each other or an insulating member is provided between the accommodating portions, the movement of electric charges between the accommodating portions is blocked. Good. Alternatively, the housing portion may be formed of a non-conductive member such as resin, the nozzle may be formed of a conductive member such as metal, and a voltage may be applied to the nozzle. In this case, the nozzle functions as the first electrode.

  In the above embodiment, the present invention is applied to the laser printer 1. However, the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

  In the embodiment, the recording sheet is exemplified by the paper SH such as thick paper, postcard, and thin paper. However, the present invention is not limited to this, and may be, for example, an OHP sheet.

  In the above-described embodiment, the pressurizing device 75 having the pump 75A and the pressure reducing valve 75B is exemplified as the pressure applying means for applying pressure to the fixing liquid in the storage unit. However, the present invention is not limited to this, and for example, the water head difference A device for pressurizing or depressurizing the liquid in each head using the above may be used.

  In the above embodiment, for convenience of explanation, the fixing areas A1 to A5 have the same shape, size, and position as the lower surface of the housing portion 73. However, the present invention is not limited to this, and the fixing region is formed from the lower surface of the housing portion. May be small or large. In other words, the fixing area may be defined by the width in the front-rear direction and the left-right direction of the fixing liquid sprayed on the paper.

  In the above embodiment, the voltage is lowered to 0 in the voltage drop process, but the present invention is not limited to this, and in the voltage drop process, the voltage is smaller than the voltage at the start of the pressure drop process. , It may be lowered to a value larger than 0. In other words, in the voltage reduction process, the voltage may be reduced to a value smaller than the minimum value of the current range used in the fixing spray process and larger than 0.

7 Fixing Device 71 Fixing Head 72 Second Electrode 73 Housing Unit 74 First Electrode 75 Pressurizing Device 100 Controlling Unit L Fixing Liquid N Nozzle SH Paper

Claims (11)

An accommodating portion for accommodating a fixing solution therein; and a fixing head having a nozzle that communicates with the accommodating portion and sprays the fixing solution toward a developer image on a recording sheet;
A potential difference forming unit for forming a potential difference between the fixing liquid in the nozzle and a recording sheet conveyed at a position away from the nozzle;
A pressure applying means for applying pressure to the fixing solution in order to supply the fixing solution to the tip of the nozzle;
A control unit that controls a voltage applied to the potential difference forming unit and a pressure applied to the fixing solution;
When stopping the spraying of the fixing solution, the control unit starts a pressure reduction process for controlling the pressure applying unit so as to reduce the pressure applied to the fixing solution, and then applies the applied pressure to the fixing solution. And a voltage lowering process for controlling the potential difference forming unit so as to lower the voltage to be lower than a voltage at the start of the pressure lowering process.   The control unit determines whether or not spraying of the fixing liquid has stopped after starting the pressure reduction process, and performs the voltage reduction process when it is determined that spraying has stopped. Item 4. The fixing device according to Item 1.   The control unit determines whether or not a current flowing through the potential difference forming unit is a predetermined value or less, and determines that spraying is stopped when the current is a predetermined value or less. The fixing device according to 1.   The control unit determines whether or not a predetermined time has elapsed since the pressure reduction process, and determines that spraying has stopped when it is determined that the predetermined time has elapsed. The fixing device according to 1.   5. The fixing device according to claim 1, wherein the control unit sets the pressure to a meniscus withstand pressure or less in the pressure reduction process. 6.   6. The control unit according to claim 1, wherein the control unit starts the pressure reduction process before an upstream end of an image of a final page in the print job passes through the spray region of the fixing liquid. The fixing device according to Item 1.   6. The control unit according to claim 1, wherein the control unit performs the pressure reduction processing after an upstream end of an image of a final page in a print job passes through the spray region of the fixing liquid. The fixing device according to Item.   8. The fixing device according to claim 1, wherein when the recording sheet is jammed, the control unit starts the pressure lowering process and then performs the voltage lowering process. 9. .   The fixing device according to claim 1, wherein the pressure applying unit includes a pump that pressurizes a gas in the fixing head.   9. The control unit according to claim 1, wherein the control unit keeps the voltage constant during a period from the start of the pressure reduction process to the start of the voltage reduction process. Fixing device. The electric field forming part is
A first electrode in contact with the fixer in the housing;
A second electrode disposed at a distance from the nozzle;
The fixing device according to claim 1, further comprising:

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