JP2009042667A - Liquid developing device and image forming apparatus mounted with tha same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developing device for which space saving is achieved without separately providing a cleaning member on a supply roller surface and time and labor for maintenance is eliminated, and in which toner particles are prevented from accumulating on or adhering to the cell bottoms of the surface of the supply roller and appropriate image quality can be maintained. <P>SOLUTION: The liquid developing device 10 includes: an anilox roller 13 which supplies a liquid developer 18 to a developing roller 12; and a doctor roller 15 made of a conductive material and disposed in contact with the anilox roller 13. Using a bias voltage application means 19, the bias voltage of polarity reverse to the charging polarity of toner is applied. Thus, the liquid developer 18 in each of the cells 13c on the surface of the anilox roller 13 is subjected to doctoring in a contact area with the doctor roller 15, and an accurately specified quantity of liquid developer remains. Simultaneously, toner particles T in the cells 13c are attracted to the doctor roller 15 charged to the polarity reverse to the charging polarity by the action of a bias voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid developing device applicable to an image forming apparatus represented by a copying machine or a printer. The present invention also relates to an image forming apparatus equipped with the liquid developing device.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a photosensitive drum is widely used as an image carrier. A general image forming operation using the photosensitive drum is as follows. The surface of the photosensitive drum is uniformly charged with a predetermined potential by a charging device, and by irradiating the LED light or the like of the exposure device there, the potential is partially attenuated to form an electrostatic latent image of an original image. Is done. By developing the electrostatic latent image with a developing device, a toner image is formed on the surface of the photosensitive drum. The toner image is transferred onto the sheet when the sheet is inserted into a transfer region formed by bringing the photosensitive drum and the transfer member into contact with or in close proximity to each other.

  As a method for developing an electrostatic latent image, there are a dry development method and a wet development method. Among these, in the wet development method, a liquid developer is used. The liquid developer is adjusted so that toner particles are dispersed at a high concentration in an insulating liquid, that is, a carrier liquid which is an electrically neutral solvent. The wet image forming apparatus is equipped with a liquid developing device, and the electrostatic latent image formed on the photosensitive drum is supplied by a liquid developer supplied from a developing roller which is a developer carrying member of the liquid developing device. develop.

  Conventionally, an anilox roller is used as a supply roller for supplying the liquid developer to the developing roller for the purpose of forming a uniform thin layer of the liquid developer on the surface of the developing roller. The anilox roller is particularly widely known as a liquid ink supply roller in a printing technique such as flexographic printing, and a large number of fine concave cells are provided on the outer peripheral surface thereof.

  The liquid developer drawn up from the developer tank and delivered to the anilox roller is held in each cell on the surface of the anilox roller and conveyed to the surface of the development roller. At this time, the surface of the anilox roller is doctored with a doctor blade as a regulating member, so that a liquid developer having a precisely defined amount of liquid remains in each cell, and this liquid developer is supplied to the surface of the development roller. A uniform thin layer is formed.

  In the liquid developer supply process as described above, solid matter such as toner particles settled in the cell of the anilox roller may be accumulated and fixed to the cell bottom. In such a situation, an appropriate thin layer of liquid developer cannot be formed on the surface of the developing roller, which may adversely affect image quality. Therefore, special care must be taken not to deposit solids such as toner particles in the cells of the anilox roller. In order to deal with such problems, in general, operators or the like regularly inspect and perform maintenance such as cleaning the anilox roller cell as necessary to maintain the cell state properly. Yes.

However, such maintenance is time consuming, and toner particles and the like are deposited on the cells until the maintenance, so that the image quality may gradually deteriorate. In order to solve these problems, a method for removing foreign matters mixed in the liquid developer has been proposed, and an example thereof can be seen in Patent Document 1. The liquid developing device described in Patent Document 1 is provided with brush-like foreign matter removing means so as to come into contact with the surface of an application roller (anilox roller), and removes foreign matters such as dust and paper dust mixed in the liquid developer. I am doing so.
JP 2002-72695 A (page 4-5, FIG. 2)

  As in the liquid developing device described in Patent Document 1, it is possible to prevent toner particles from staying at the bottom of the cell by using a brush-like foreign substance removing means that contacts the surface of the anilox roller. It is possible to prevent the accumulation and sticking of particles. However, in this configuration, a foreign matter removing means must be provided as a member that contacts the anilox roller, separately from the regulating member such as a doctor blade. As described above, if the regulating member and the foreign matter removing unit are provided separately, it is necessary to secure a wide space in the liquid developing device, which may increase the size of the liquid developing device and the size of the image forming apparatus. . Further, if the regulating member and the foreign matter removing means are provided separately, the number of parts increases and the manufacturing process also increases.

  The present invention has been made in view of the above points, and an increase in the number of parts can be achieved without separately providing a cleaning member for cleaning the surface of a supply roller for supplying a liquid developer to a developer carrying member. Preventing toner particles from depositing and sticking to the bottom of the cell on the surface of the supply roller without taking time for maintenance by utilizing the characteristics of the toner particles in the liquid developer. An object of the present invention is to provide a liquid developing apparatus capable of maintaining an appropriate image quality. It is another object of the present invention to provide a high-performance image forming apparatus equipped with such a liquid developing device.

  In order to solve the above problems, the present invention provides an image carrier, a developer carrier for supplying a liquid developer in which toner is dispersed in an insulating liquid to the image carrier, and a liquid on the developer carrier. In a liquid developing device including a supply roller for supplying a developer, a roller-shaped regulating member made of a conductive material provided in contact with the supply roller is opposite to the charged polarity of toner by a bias voltage applying unit. The bias voltage was applied.

  In the liquid developing apparatus having the above-described configuration, the supply roller has a conductive material inside and a surface formed of an insulating material, and the bias voltage applying unit applies a bias voltage having the same polarity as the charging polarity of the toner. It was decided to be applied.

  In the liquid developing apparatus having the above-described configuration, the insulating material on the surface of the supply roller is made of ceramic.

  In the liquid developing device having the above configuration, the bias voltage applied to the roller-shaped regulating member by the bias voltage applying unit may cause the liquid developer passing between the roller-shaped regulating member and the supply roller to be transferred to the toner image. This was done when used for formation.

  In the liquid developing device having the above-described configuration, when the liquid developer passing between the roller-shaped regulating member and the supply roller is not used for forming a toner image, the roller-shaped regulating member is formed by the bias voltage applying unit. In addition, it is possible to apply a bias voltage having the same polarity as the charging polarity of the toner and higher than the absolute value of the bias voltage of the supply roller.

  In the liquid developing device having the above-described configuration, the roller-like regulating member has a surface made of an elastic material.

  In the present invention, the liquid developing device is mounted on the image forming apparatus.

  According to the configuration of the present invention, the image carrier, the developer carrier that supplies the image carrier with the liquid developer in which the toner is dispersed in the insulating liquid, and the supply that supplies the liquid developer to the developer carrier. In a liquid developing apparatus including a roller, a bias voltage having a polarity opposite to the toner charging polarity is applied to a roller-shaped regulating member made of a conductive material in contact with the supply roller by a bias voltage applying unit. Therefore, the liquid developer delivered from the pumping roller into each cell on the surface of the supply roller is doctored at the contact portion with the roller-shaped regulating member, and the liquid volume precisely defined in each cell. At the same time, the toner particles in the liquid developer are attracted to the roller-shaped regulating member charged in the opposite polarity to the charged polarity of the toner particles in the cell due to the action of the bias voltage, and are collected on the surface layer. That.

  As a result, in the cell, a high-concentration liquid developer layer having a high toner particle content is formed on the surface layer, and a low-concentration liquid development having a low toner particle content is formed in the lower layer, which is the cell bottom. An agent layer is formed. Accordingly, the developer carrier is supplied with a high-concentration liquid developer layer formed on the surface layer of the cell of the supply roller, and the thin layer of liquid developer formed on the surface of the developer carrier is a normal liquid. Contains toner particles at a higher concentration than the developer. As a result, in the transport path of the liquid developer up to the supply roller or the liquid developing device, it is sufficient to transport the liquid developer having a lower concentration than the liquid developer actually used for development, that is, a low viscosity. There is no need to take measures against poor fluidity due to high viscosity, and a simple configuration can be achieved.

  Then, a large amount of toner particles in each cell of the supply roller are attracted to the cell surface layer and supplied to the surface of the developer carrying member, so that the liquid developer remaining at the bottom of the cell thereafter has almost no toner particles. It is possible not to remain. Therefore, it is possible to prevent toner particles from being deposited and adhered to the cell bottom portion on the surface of the supply roller, so that maintenance for the purpose of cleaning the cell is not required and the life of the supply roller can be extended. In this way, without providing a separate cleaning member for cleaning the surface of the supply roller, it is possible to prevent an increase in the number of components and save space, and the cell of the supply roller regardless of the usage time and frequency of use. Can be maintained in a favorable state with respect to development, and a liquid developing apparatus capable of maintaining appropriate image quality over a long period of time can be provided.

  The supply roller has a conductive material inside and an insulating material on the surface, and the bias voltage applying means applies a bias voltage having the same polarity as the toner charging polarity. Applying a bias voltage to the conductive material inside the supply roller while maintaining insulation from the developer carrier and the roller-shaped regulating member, generates a potential difference with respect to the developer carrier and the roller-shaped regulating member. Can do. Therefore, each bias voltage can be controlled independently, and the degree of freedom of control can be increased. In other words, the toner in the liquid developer is adjusted by appropriately adjusting the bias voltage applied to the developer carrying member, the roller-shaped regulating member, and the supply roller with respect to the charged toner particles individually or relatively. The behavior of the particles can be freely controlled. As a result, by utilizing the characteristics of the toner particles in the liquid developer, it is possible to prevent toner particles from accumulating and sticking to the cell bottom of the supply roller surface, and to further improve the effect of maintaining proper image quality. become.

  In addition, since the insulating material on the surface of the supply roller is made of ceramic, in addition to being able to form a precise cell due to its material characteristics, a supply roller with improved durability and solvent resistance is provided. Obtainable. Thereby, it is possible to form a thin layer of a liquid developer with high concentration and high accuracy on the surface of the developer carrying member stably over a long period of time. Therefore, it is possible to obtain a liquid developing apparatus that requires less labor for maintenance, has a long life, and can maintain an appropriate image quality for a long period of time.

  In addition, since the bias voltage is applied to the roller-shaped regulating member by the bias voltage applying means when the liquid developer passing between the roller-shaped regulating member and the supply roller is used for forming a toner image, During the startup of the liquid developing device, the liquid developer passing between the roller-shaped regulating member and the supply roller is transferred to the supply roller having the liquid developer on the surface even during a period other than the time of image formation. Only when it is used for formation, by applying a bias voltage having a polarity opposite to that of toner particles to the roller-shaped regulating member and to the supply roller having the same polarity as that of toner particles, the effect of collecting the toner particles in the liquid developer on the surface layer is enhanced. be able to. Therefore, when the liquid developer passing between the roller-shaped regulating member and the supply roller is used for forming a toner image, a high concentration liquid is prevented while preventing toner particles from accumulating and sticking to the cells on the surface of the supply roller. A developer can be obtained.

  Further, when the liquid developer passing between the roller-shaped regulating member and the supply roller is not used for forming a toner image, the bias voltage applying unit causes the roller-shaped regulating member to have the same polarity as the toner charging polarity. In addition, since it is possible to apply a bias voltage higher than the absolute value of the bias voltage of the supply roller, the toner particles in the liquid developer are in contrast to the liquid developer adhering to the roller-like regulating member. Moves to the supply roller side in order to move to the lower bias voltage due to the difference between the bias voltage applied to the roller-shaped regulating member and the supply roller. As a result, the toner particles adhering to the roller-like regulating member are removed, and the effect of maintaining proper image quality can be enhanced.

  The above-described operation is performed when the liquid developer passing between the roller-shaped regulating member and the supply roller is not used for forming a toner image. In such a period, the toner particles adhering to the roller-shaped regulating member can be removed. Therefore, it is not necessary to provide a special period for that purpose, and it is possible to prevent a series of image forming operations from being obstructed, and to prevent the user's convenience from being impaired.

  Further, since the surface of the roller-like regulating member is made of an elastic material, for example, the surface of the supply roller is wavy, or the roller-like regulating member is inclined with respect to the supply roller. Even if they are in contact, appropriate doctoring along the surface of the supply roller can be performed. As a result, a liquid developer having a precisely defined liquid amount remains in each cell on the surface of the supply roller. Therefore, by utilizing the characteristics of the toner particles in the liquid developer, it is possible to further improve the effect of maintaining proper image quality while preventing the toner particles from being deposited and fixed on the cell bottom of the supply roller surface. It becomes possible.

  In the present invention, since the liquid developing device is mounted on the image forming apparatus, a cleaning member for cleaning the surface of the supply roller for supplying the liquid developer to the developer carrying member is not separately provided. The increase in the number of parts, space saving, and the characteristics of the toner particles in the liquid developer are used to deposit toner particles on the bottom of the cell on the surface of the supply roller without troublesome maintenance. It is possible to obtain a high-performance image forming apparatus that can prevent sticking and can maintain appropriate image quality.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, an outline of an image forming operation of an image forming apparatus equipped with a liquid developing device according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1 is a schematic vertical sectional front view of the image forming apparatus, and FIG. 2 is a partially enlarged vertical sectional view of the image forming unit shown in FIG. This image forming apparatus is a so-called tandem type color printing type printer that transfers a toner image onto a sheet using an intermediate transfer belt.

  The printer 100 in FIG. 1 includes a paper feeding unit 1, a vertical conveyance path 2, a registration roller pair 3, a belt conveyance unit 4, a first image forming unit 5B, a second image forming unit 5M, and a third image forming unit 5C. , A fourth image forming unit 5Y, a secondary transfer unit 6, a fixing unit 7, a discharge conveyance path 8, a discharge tray 9, and the like.

  The printer 100 configured as described above performs the following image forming process. The paper P is fed upward from the paper feed cassette 1 a of the paper feed unit 1 provided at the lower part of the main body through the vertical conveyance path 2 by the pickup roller 1 b, and to the secondary transfer unit 6 through the registration roller pair 3. Be transported.

  Above the paper feed unit 1, the intermediate transfer belt 43 using the intermediate transfer member in the form of an endless belt is fed in the direction of the arrow in FIG. 1 by the drive roller 41, and the image forming units 5Y, 5C, 5M, and 5B. Thus, the toner images of the respective colors of yellow, cyan, magenta, and black formed on the respective photosensitive drums 51 that are image carriers are sequentially transferred, and a color image is formed on the surface of the intermediate transfer belt 43.

  The color image formed here is secondarily transferred by the secondary transfer unit 6 from the intermediate transfer belt 43 to the paper P conveyed from the paper feed cassette 1a, and a color image is formed on the paper P. The

  Thereafter, the paper P on which the unfixed color image is transferred is separated from the intermediate transfer belt 43 and conveyed to the fixing unit 7. Then, at the fixing nip portion formed by the pressure contact between the fixing roller 7a and the pressure roller 7b, the heat amount necessary for fixing is supplied to the paper P, and the color image is fixed. Finally, the sheet P is discharged to the discharge tray 9 through the discharge conveyance path 8 after being subjected to fixing processing by the fixing unit 7. The fixing roller 7a includes a heater (not shown), and this heater is controlled so as to generate a predetermined temperature necessary for fixing.

  Next, a configuration around the image forming unit 5 that is a main component of the printer 100 will be described in detail. Around the image forming unit 5, a belt conveyance unit 4, first to fourth image forming units 5 </ b> B, 5 </ b> M, 5 </ b> C, 5 </ b> Y on which a liquid developing device is mounted, and an intermediate transfer cleaning unit 45 are provided. .

  The belt conveyance unit 4 includes a driving roller 41, a driven roller 42, and an endless intermediate transfer belt 43 that is stretched between the two rollers. The intermediate transfer belt 43 is maintained at an appropriate tension by a tension roller 44. In this state, the driving roller 41 receives the driving force from a driving motor (not shown), and the outer peripheral speed of the photosensitive drum 51 in each image forming unit 5 and the outer peripheral speed of the intermediate transfer belt 43 of the belt conveying unit 4. However, it is designed to be driven at a constant speed.

  The first to fourth image forming units 5B, 5M, 5C, and 5Y are arranged side by side below the belt conveyance unit 4. Arrangements of the respective image forming units 5 are for yellow (5Y), cyan (5C), magenta (5M), and black (5B) in order from the upstream side in the sheet conveyance direction. Therefore, in the first to fourth image forming units 5B, 5M, 5C, and 5Y, the same reference numerals are given to portions that are the same as the configuration of the image forming unit 5 used in the following description. In the following description, the identification symbols “B”, “M”, “C”, and “Y” are omitted unless particularly limited.

  As shown in FIG. 2, the image forming unit 5 includes a photosensitive drum 51 as an image carrier, a main charging device 52, an exposure device 53, a liquid developing device 10, a primary transfer unit 54, a cleaning device 55, and a charge removal lamp 59. The unit is assembled into a housing made of resin or the like to form one unit and is attached to the printer 100 main body.

  The photosensitive drum 51 uses an amorphous silicon drum and is charged by the main charging device 52 so that the dark potential at the developing position becomes a predetermined potential. An electrostatic latent image is formed on the surface of the photosensitive drum 51 by the exposure device 53 irradiating the charged surface of the photosensitive drum 51 with light corresponding to image information. Note that the exposure device 53 may use LPH (LED PRINT HEAD) or LSU (laser scanning unit).

  The developer tank 11 of the liquid developing device 10 stores a liquid developer 18 composed of toner particles and a carrier that is an insulating liquid. The liquid developer 18 is adjusted so that toner particles are dispersed at a high concentration in a carrier liquid that is a nonpolar, ie, electrically neutral, solvent such as silicone oil. The toner particles contain a colorant, a resin (binder) and, if necessary, a charge control agent. The resin (binder) is adsorbed on the colorant, is well dispersed in the carrier liquid, and applies a positive or negative charge to the adsorbed colorant. In this embodiment, the toner particles are positively charged by a resin (binder). As the carrier liquid, an isoparaffin solvent (for example, Isopar G (manufactured by Exxon)), a higher fatty acid ester, silicon oil, or the like can be used.

  By supplying the liquid developer 18 from the developing roller 12 to the electrostatic latent image of the portion irradiated with light from the photosensitive drum 51, the toner image is developed on the photosensitive drum 51.

  The dark potential of the photosensitive drum 51 is set to plus 300V, the developing bias is set to plus 200V, and the post-exposure potential is set to plus 20V. The difference between the developing bias and the post-exposure potential is a so-called contrast potential. That is, the dark potential corresponds to the white portion of the image, and the post-exposure potential corresponds to the black portion of the image. The toner image obtained by developing the electrostatic latent image formed as described above is transferred to the intermediate transfer belt 43 of the belt conveyance unit 4 at the nip with the primary transfer unit 54. The primary transfer means 54 uses a transfer roller in this embodiment, and a bias voltage in which a voltage having a polarity opposite to the surface potential of the photosensitive drum 51 is set in a range of minus 100 to minus 1000 V is applied. It has become.

  Residual toner particles that have not been transferred onto the photosensitive drum 51 are removed by the cleaning roller 56 and the cleaning blade 57 of the cleaning device 55, and are sent toward the discharge screw 58 in accordance with the action of gravity and the rotation of the cleaning roller 56. Then, it is conveyed to the outside of the housing by the discharge screw 58. The neutralizing lamp 59 irradiates the photosensitive drum 51 with neutralizing light such as an LED (light emitting diode), thereby removing the charged charges on the surface thereof and preparing for the charging process in the next image forming operation. The potential setting in image formation can be selected to an optimum value according to the characteristics of the photosensitive drum 51, the characteristics of the toner particles, the environment, and the like.

  Based on the image forming method of the image forming unit 5 described above, the printer 100 displays images corresponding to black, magenta, cyan, and yellow in the first to fourth image forming units 5B, 5M, 5C, and 5Y. By developing on the photosensitive drum 51 and sequentially repeating the transfer on the intermediate transfer belt 43 without transfer, one color image is formed.

  As shown in FIG. 1, the intermediate transfer cleaning unit 45 includes an intermediate transfer cleaning roller 45a and an intermediate transfer cleaning blade 45b. The intermediate transfer cleaning roller 45 a is in pressure contact with the intermediate transfer belt 43 and is rotated in the same direction as the rotation direction of the intermediate transfer belt 43. The intermediate transfer cleaning blade 45b contacts the intermediate transfer belt 43 on the downstream side from the position of the intermediate transfer cleaning roller 45a in the moving direction of the intermediate transfer belt 43, thereby removing the transfer residual toner on the intermediate transfer belt 43. Scratch off.

  Next, the configuration of the liquid developing device 10 mounted on the printer 100 according to the above configuration will be described in detail with reference to FIG.

  As shown in FIG. 2, the liquid developing apparatus 10 according to this embodiment includes a developer tank 11 that stores a liquid developer 18. Inside the liquid developing device 10, there are a developing roller 12, an anilox roller 13 as a supply roller, a pumping roller 14, a doctor roller 15 as a roller-shaped regulating member, a cleaning blade 16, and a pair of stirring screws 17a and 17b. And are provided. The developing roller 12, the anilox roller 13, the pumping roller 14, the doctor roller 15, and the stirring screws 17a and 17b are rotationally driven by a driving unit including a common gear train.

  A liquid developer 18 is stored in the developer tank 11, and stirring screws 17 a and 17 b are provided so as to be immersed in the liquid developer 18. The draw-up roller 14 is provided in the developer tank 11 so that a part of the roller is immersed in the liquid developer 18, and an anilox roller 13 as a supply roller is provided above the draw-up roller 14. A developing roller 12 is provided above the anilox roller 13.

  The doctor roller 15, which is a roller-shaped regulating member, contacts the anilox roller 13 in parallel to the axial direction of the anilox roller 13 on the upstream side in the rotation direction of the anilox roller 13 with respect to the contact point between the developing roller 12 and the anilox roller 13. It is provided in contact. The doctor roller 15 thins the liquid developer 18 supplied to the roller surface of the anilox roller 13. The photosensitive drum 51 is outside the liquid developing device 10 and is in contact with the developing roller 12.

  The cleaning blade 16 is arranged on the downstream side in the rotation direction of the developing roller 12 with respect to the contact portion between the photosensitive drum 51 and the developing roller 12 so that one end of the blade contacts the developing roller 12 with a counter. The cleaning blade 16 removes the liquid developer 18 remaining on the developing roller 12 after development.

  Next, an operation process of the liquid developing device 10 will be described.

  In FIG. 2, as described above, the liquid developer 18 contains toner particles (particle size: about 1 μm) made of a fine resin having a positive charge in a nonpolar insulating liquid made of silicon oil or the like as a carrier. Dispersed and turbid. The liquid developer 18 stored in the developer tank 11 is stirred by the stirring screws 17a and 17b, and the toner particles are dispersed so as to be uniform in the liquid.

  The liquid developer 18 is sequentially attached to the surface of the immersed roller by the rotation of the pumping roller 14 that is partially immersed in the liquid developer 18 and pumped up. Then, it is sequentially applied to the roller surface of the anilox roller 73 that rotates in synchronization through the nip portion between the anilox roller 13 and the pumping roller 14.

  The liquid developer 18 applied to the anilox roller 13 is made into a uniform thin layer by the doctor roller 15, abuts against the anilox roller 13, and is applied as a thin film layer to the roller surface of the developing roller 12 that rotates synchronously. . Thereafter, the electrostatic latent image is supplied to the photosensitive drum 51, and the toner image is developed on the photosensitive drum 51.

  Next, cleaning of the toner compaction, the anilox roller 13 and the doctor roller 15 by applying a bias voltage to the doctor roller 15 which is a roller-shaped regulating member and the anilox roller 13 which is a supply roller, which is a characteristic part of the present invention, will be described. .

  First, the structure of this characteristic part will be described with reference to FIG. 3 in addition to FIG. FIG. 3 is a partial enlarged cross-sectional view showing the state of the liquid developer at the contact portions of the anilox roller 13 and the doctor roller 15.

  As shown in FIG. 3, the anilox roller 13 is a roller in which a large number of precise fine concave cells 13c are regularly engraved on the entire outer peripheral surface. The liquid developer 18 is supplied from the scooping roller 14 to each cell 13c. The surface layer 13a having the cells 13c of the anilox roller 13 is made of ceramic which is an insulating material, and the roller interior 13b is made of a conductive material. The cell 13c is composed of a single continuous groove, and is inclined at an angle of 45 degrees with respect to the axial direction of the anilox roller 13 and is engraved in a spiral shape. The depth of the deepest part of the cell 13c is about 30 μm, the width of the groove is about 100 μm, and the distance between the grooves is about 25 μm.

  The ceramic of the surface layer 13a is formed by firing and spraying a metal oxide such as chromium oxide on the surface of the roller interior 13b. The layer thickness is 100 to 200 μm. After the outer peripheral surface of the surface layer 13a is polished, the cells 13c are precisely formed on the surface by a laser. The conductive material of the roller interior 13b is composed of free-cutting steel (SUM material).

  As shown in FIG. 2, the bias voltage applying means 19 is connected to the conductive material inside the roller 13b, and the bias voltage of a set value (plus 200V) is applied to the anilox roller according to the request of the control means 20. 13 is applied. Since the surface layer 13a of the anilox roller 13 is ceramic, which is an insulating material, even if a bias voltage is applied to the developing roller 12 and the doctor roller 15 that are in contact with the anilox roller 13, the potential difference is not generated. Can be maintained.

  As described above, the doctor roller 15 is in contact with the anilox roller 13 in parallel with the axial direction of the anilox roller 13 on the upstream side of the rotation direction of the anilox roller 13 with respect to the contact point between the developing roller 12 and the anilox roller 13. (See FIG. 2). As shown in FIG. 3, the doctor roller 15 is pressed against the anilox roller 13 so that a contact nip portion N is formed at a contact point with the anilox roller 13. The doctor roller 15 rotates so that the surface at the contact point with the anilox roller 13 moves in a direction different from the moving direction of the anilox roller 13 surface.

  The doctor roller 15 is configured by providing a conductive roller, which is an elastic material, on the surface of a metal roller or a metal core material. The conductive rubber is constituted by blending carbon with urethane rubber or blending epichlorohydrin with nitrile rubber (NBR), and the thickness thereof is 0.5 to 1.0 mm. In order to reduce the frictional resistance of the surface, a coating such as a urethane coat or a fluororesin coat may be applied or a PFA (polytetrafluoroethylene) tube may be attached.

  As shown in FIG. 2, a bias voltage applying unit 19 is connected to the doctor roller 15, and a bias voltage having a set value is applied according to a request from the control unit 20. A cleaning roller (not shown) is provided for cleaning the surface of the doctor roller 15.

  Next, the operation and effect of the above configuration will be described. First, operations and effects when the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is used for forming a toner image will be described.

  In the liquid developing device 10, the liquid developer 18 stored in the developer tank 11 is immersed in the liquid developer 18 and is attached to the roller surface of the rotating pumping roller 14. These are sequentially supplied to the surface of the anilox roller 13 through a contact portion with the anilox roller 13 rotating in the reverse direction at the same linear velocity. At this time, each cell 13 c of the anilox roller 13 that is in contact with the pumping roller 14 and supplied with the liquid developer 18 is filled with the liquid developer 18.

  Each cell 13c filled with the liquid developer 18 thereafter reaches the contact nip portion N with the doctor roller 15 as the anilox roller 13 rotates.

  As shown in FIG. 3, in front of the doctor roller 15, the liquid developer 18 supplied to the anilox roller 13 does not stay in each cell 13c but adheres to the entire roller surface, resulting in an excessive state. Yes. Since the contact nip portion N of the elastic doctor roller 15 is in close contact with the surface of the anilox roller 13, the liquid developer 18 on the anilox roller 13 reaching the portion is in the cell 13c. Except for the accumulated one, it remains in front of the contact nip N with the doctor roller 15 and is returned to the developer tank 11 (see FIG. 2). After passing through the doctor roller 15 contact nip N by such doctoring by the doctor roller 15, the excess liquid developer 18 adhering to the surface of the anilox roller 13 is removed, and each cell 13c is filled with the liquid. Will leave the liquid developer 18 in an approximately precisely defined amount.

  When the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is used for the formation of a toner image, the doctor roller 15 is supplied with a liquid developer by a bias voltage applying means 19 that receives a request from the control means 20. A bias voltage (minus 300V) having a charge polarity (plus) of 18 toner particles and a polarity opposite to (minus) is applied. As a result, the liquid developer 18 in the cell 13c is adjusted to a specified amount, and at the same time, the toner particles T dispersed in the liquid developer 18 in the cell 13c are removed from the surface of the doctor roller 15 to which a bias voltage is applied. (Refer to toner compaction phenomenon, FIG. 3).

  Therefore, in the liquid developer 18 in the cell 13c, a layer of the high-concentration liquid developer 18 having a high content of toner particles T is formed on the surface layer portion in the vicinity of the doctor roller 15, and is the bottom of the cell 13c. In the lower layer, a low-concentration liquid developer 18 layer having a low content of toner particles T is formed.

  Then, the layer of the high-concentration liquid developer 18 formed on the surface layer portion of the cell 13c reaches the contact portion with the developing roller 12 while maintaining this state, and the roller of the developing roller 12 here. Then, a thin layer of the liquid developer 18 is formed on the surface of the developing roller 12.

  Generally, the amount of liquid developer 18 transferred from the anilox roller 13 to the developing roller 12 is about 30 to 60% of the cell capacity, and all the liquid developer 18 in the cell 13c is transferred to the developing roller 12. Never do. Therefore, by forming a layer of the high-concentration liquid developer 18 on the surface layer of the cell of the anilox roller 13, a larger amount of the high-concentration liquid developer 18 is transferred to the development roller 12, and the low concentration at the bottom of the cell 13c is reduced. The liquid developer 18 having a concentration remains.

  Therefore, the thin layer of the liquid developer 18 formed on the developing roller 12 has a higher concentration of the liquid developer 18 containing more toner particles T than the liquid developer 18 stored in the developer tank 11. Become a thin layer. The thin layer of the high-concentration liquid developer 18 formed on the developing roller 12 is supplied to the photosensitive drum 51 to develop the electrostatic latent image.

  Thus, since the liquid developer 18 used when forming the toner image using the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 has a high toner concentration, the liquid supplied to the liquid developing device 11 is used. As the developer 18, a liquid developer 18 having a lower concentration than the liquid developer 18 actually used for development can be used. When the concentration of the liquid developer 18 is low, the viscosity is lowered, so that handling becomes easy, and it is possible to adopt a simple transport path configuration for the liquid developer 18.

  On the other hand, since the toner compaction due to the bias voltage of the doctor roller 15 in contact with the liquid developer 18 having a low concentration that remains on the bottom of the cell 13c of the anilox roller 13 has hardly any toner particles T remaining therein, It is possible to prevent the toner particles T from being settled and deposited and fixed on the cell bottom.

  Therefore, the maintenance for the purpose of cleaning the cell 13c of the anilox roller 13 which has been conventionally required becomes unnecessary, and the maintenance management becomes easy. In other words, even if the cleaning is not performed regularly, the toner particles T are always kept clean in the cells 13c without being deposited, so that the state of the cells 13c is properly maintained regardless of the frequency of use. Thus, a thin layer of the appropriate liquid developer 18 is stably formed on the developing roller 12, and the image quality can be kept good. Further, since no mechanical means is used for cleaning the anilox roller 13, deterioration of the roller surface is suppressed, and the life of the anilox roller 13 can be extended.

  In this way, the anilox roller 13 as the supply roller is not provided with a separate cleaning member for cleaning its surface, thereby preventing an increase in the number of parts and saving space, regardless of the usage time and usage frequency. Thus, it is possible to provide the liquid developing device 10 that can maintain the cell 13c of the anilox roller 13 in a good state with respect to development and can maintain appropriate image quality for a long period of time.

  Further, the anilox roller 13 has an inner portion 13b made of a conductive material and a surface 13a made of an insulating material, and a bias voltage having the same polarity as the charging polarity of the toner is applied by the bias voltage applying means 19, so that development is possible. A potential difference is generated between the developing roller 12 and the doctor roller 15 by applying a bias voltage to the conductive material inside the roller 13b of the anilox roller 13 while maintaining insulation with the roller 12 and the doctor roller 15. Can do. Therefore, each bias voltage can be controlled independently, and the degree of freedom of control can be increased. That is, by adjusting the bias voltage applied to the developing roller 12, the doctor roller 15, and the anilox roller 13 with respect to the charged toner particles T individually or relatively appropriately, The behavior of the toner particles T can be freely controlled. As a result, the characteristics of the toner particles T in the liquid developer 18 are used to prevent the toner particles T from being deposited and fixed on the bottom of the cell 13c on the surface of the anilox roller 13 and to maintain an appropriate image quality. It becomes possible to improve.

  Further, since the insulating material of the surface layer 13a of the anilox roller 13 is made of ceramic, an anilox roller having improved durability and solvent resistance in addition to the ability to form a precise cell 13c due to its material characteristics. 13 can be obtained. As a result, it is possible to form a thin layer of the liquid developer 18 with a high concentration and high accuracy on the surface of the developing roller 12 stably over a long period of time. Therefore, it is possible to obtain the liquid developing apparatus 10 that does not require labor for maintenance, extends the life, and can maintain an appropriate image quality for a long period of time.

  The bias voltage applying means 19 applies a bias voltage having a polarity opposite to the charging polarity of the toner to the doctor roller 15 so that the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 forms a toner image. Since it is performed at the time of use, it is passing between the doctor roller 15 and the anilox roller 13 with respect to the anilox roller 13 in which the liquid developer 18 exists on the surface even during a period other than the time of image formation during the startup of the liquid developing device 10 The liquid developer 18 is applied to the doctor roller 15 by applying a bias voltage having a polarity opposite to that of the toner particles T and to the anilox roller 13 only when the liquid developer 18 is used for forming a toner image. The effect of collecting the toner particles T in 18 on the surface layer can be enhanced. Therefore, when the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is used for the formation of a toner image, while preventing the toner particles T from being deposited and fixed on the cells 13c on the surface of the anilox roller 13, A high-concentration liquid developer 18 can be obtained.

  Next, operations and effects when the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is not used for forming a toner image will be described.

  When the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is used for forming a toner image, the doctor roller 15 is opposite to the charged polarity (plus) of the toner particles T in the liquid developer 18. A polarity (minus) bias voltage was applied to play the role of attracting the toner particles T in the liquid developer on the anilox roller 13. At this time, a part of the attracted toner particles T was absorbed by the doctor roller 15. Will adhere to the surface of the.

  The bias voltage applying means 19 that has received a request from the control means 20 applies a bias voltage having the same polarity as the charged polarity (plus) of the toner particles T to the anilox roller 13 during printing standby or between paper sheets where image formation is not performed. Further, it is possible to apply a bias voltage (plus 400 V) which is the same polarity as the charging polarity (plus) of the toner particles T and higher than the bias voltage of the anilox roller 13 to the doctor roller 15. Since the surface of the anilox roller 13 is made of ceramic which is an insulating member, the potential difference from the doctor roller 15 in contact with the anilox roller 13 is properly maintained.

  At this time, the toner particles T adhering to the doctor roller 15 in the toner compaction process or the like try to move to the lower bias voltage due to the difference in the bias voltage applied to the doctor roller 15 and the anilox roller 13. Move to the 13th side. Then, the toner particles T peeled from the doctor roller 15 continue to flow downstream together with the liquid developer 18 supplied from the developer tank 11.

  In this way, the toner particles T adhering to the doctor roller 15 are removed, and the effect of maintaining an appropriate image quality can be enhanced.

  The operation as described above is performed when the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is not used for the formation of a toner image. The toner particles T adhering to the roller 15 can be removed. Therefore, it is not necessary to provide a special period for that purpose, and it is possible to prevent a series of image forming operations from being obstructed, and to prevent the user's convenience from being impaired.

  When the liquid developer 18 passing between the doctor roller 15 and the anilox roller 13 is not used for forming a toner image, the polarity is the same as the charging polarity (plus) of the toner particles T to the doctor roller 15. The bias voltage higher than the bias voltage of the anilox roller 13 is preferably kept for a short time (for example, 2 seconds) in order to prevent excessive toner movement to the anilox roller 13 side. Further, when the liquid developing device 10 is driven for a relatively long time (for example, 3 minutes) without forming a toner image, such as when the printer 100 is started, the charging polarity (plus) of the toner particles T to the doctor roller 15 is positive. ) And a bias voltage higher than the bias voltage of the anilox roller 13 and a bias voltage having a polarity opposite to the charging polarity of the toner are alternately applied (for example, every 2 seconds), thereby an anilox roller. It is possible to prevent toner from adhering to both 13 and the doctor roller 15.

  In addition, there is no problem in forming a thin layer of the liquid developer 18 on the developing roller 12 due to the residual toner accumulated on the doctor roller 15, and no toner contamination occurs. As a result, a high-quality image can be formed.

  Further, since the surface of the doctor roller 15 roller-shaped regulating member is made of an elastic material, for example, undulation is generated on the surface of the anilox roller 13 or the doctor roller 15 is inclined with respect to the anilox roller 13. Even if they are in contact with each other, appropriate doctoring along the surface of the anilox roller 13 can be performed. As a result, the liquid developer 18 having a precisely defined amount of liquid remains in each cell 13c on the surface of the anilox roller 13. Therefore, the characteristics of the toner particles T in the liquid developer 18 are used to prevent the toner particles T from being deposited and fixed on the bottom of the cell 13c on the surface of the anilox roller 13 and to maintain an appropriate image quality. Further improvement is possible.

  In the present invention, since the liquid developing device 10 is mounted on the printer 100 as an image forming apparatus, a cleaning member for cleaning the surface of the anilox roller 13 that supplies the liquid developer 18 to the developing roller 12 is separately provided. Without being provided, the number of parts can be prevented from increasing, space saving can be achieved, and the characteristics of the toner particles T in the liquid developer 18 can be used to save maintenance, and the bottom of the cell 13c on the surface of the anilox roller 13 can be saved. Therefore, it is possible to obtain a high-performance printer 100 that can prevent toner particles T from being deposited and fixed on the toner and can maintain proper image quality.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the above-described embodiment, the printer 100 is an image forming apparatus for color printing including the endless intermediate transfer belt 43 as an intermediate transfer body, but uses only black toner without using the intermediate transfer body. It may be an image forming apparatus for monochrome printing.

  The present invention can be used in a liquid developing device applicable to an image forming apparatus using a liquid developer supply roller such as an anilox roller.

1 is a schematic vertical sectional front view of a printer which is an image forming apparatus equipped with a liquid developing device according to an embodiment of the present invention. FIG. 2 is a partially enlarged vertical cross-sectional view illustrating the periphery of an image forming unit of the printer of FIG. 1. FIG. 3 is a partially enlarged cross-sectional view illustrating a state of a liquid developer at a contact nip portion of an anilox roller and a doctor roller in FIG. 2.

Explanation of symbols

5 Image forming section (5Y, 5C, 5M, 5B)
DESCRIPTION OF SYMBOLS 10 Liquid developing device 11 Developer tank 12 Developing roller (developer carrier)
13 Anilox roller (supply roller)
13a Surface layer 13b Inside roller 13c Cell 15 Doctor roller (roller-shaped regulating member)
18 Liquid developer (liquid developer)
19 Bias applying means 51 Photosensitive drum (image carrier)
100 printer (image forming apparatus)

Claims (7)

A liquid comprising: an image carrier; a developer carrier that supplies a liquid developer in which toner is dispersed in an insulating liquid to the image carrier; and a supply roller that supplies the liquid developer to the developer carrier. In the developing device,
A liquid developing device, wherein a bias voltage applying means applies a bias voltage having a polarity opposite to that of toner to a roller-shaped regulating member made of a conductive material provided in contact with the supply roller.   2. The supply roller according to claim 1, wherein the inside of the supply roller is made of a conductive material and the surface is made of an insulating material, and a bias voltage having the same polarity as the charging polarity of the toner is applied by the bias voltage applying means. 2. A liquid developing device according to 1.   The liquid developing device according to claim 2, wherein the insulating material on the surface of the supply roller is made of ceramic.   The bias voltage is applied to the roller-shaped regulating member by the bias voltage applying means when the liquid developer passing between the roller-shaped regulating member and the supply roller is used for forming a toner image. The liquid developing device according to claim 1.   When the liquid developer passing between the roller-shaped regulating member and the supply roller is not used for forming a toner image, the bias voltage applying unit causes the roller-shaped regulating member to have the same polarity as the toner charging polarity, 5. The liquid developing device according to claim 2, wherein a bias voltage higher than an absolute value of a bias voltage of the supply roller can be applied.   The liquid developing device according to claim 1, wherein a surface of the roller-shaped regulating member is made of an elastic material.   An image forming apparatus comprising the liquid developing device according to claim 1.

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