JP2007225951A - Liquid developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developing device which saves trouble for maintenance while saving space by decreasing the number of components and can form a fine image of high picture quality, wherein a supply roller is mounted with a means serving as both a cleaning means of cleaning a cell and a compaction means of compacting toner particles in a developing solution without individually providing the cleaning means and compaction means. <P>SOLUTION: In the liquid developing device including a photoreceptor drum 51, a developing roller 12 which supplies a developing solution 18 having toner particles dispersed in insulating liquid to the photoreceptor drum 51, and an anilox roller 13 which supplies the developing solution 18 to the developing roller 12, a bias potential applying means applies a bias potential having the opposite polarity from the developing solution 18 to a doctor blade 15 provided in contact with the anilox roller 13 and made of a conductive material to form a thin layer of the developing solution 18 on a surface of the developing roller 12 to high concentration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid developing device employed in a copying machine, a facsimile machine, a printer, and the like, and a wet image forming apparatus equipped with the liquid developing device.

  Photosensitive drums are widely used in electrophotographic image forming apparatuses such as copying machines and printers. A general image forming process 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 and an electrostatic latent image of the original image is formed. It is formed. The toner image is developed by developing the electrostatic latent image with a developing device.

  In a wet image forming apparatus, a liquid developing device is mounted as a developing device, and an electrostatic latent image formed on a photosensitive drum as an image carrier is used as a liquid developer supplied from the liquid developing device. Develop with the developer.

  In the liquid developing device, the developer stored in the developer tank is pumped up by a pump-up roller, thinned by a supply roller, applied to the developing roller as a thin layer, and supplied to the photosensitive drum. The

  Conventionally, an anilox roller is used as a supply roller for the purpose of forming a uniform thin layer of the developer. The anilox roller is a roller having a precise cell engraved on its surface, and the developer supplied by the pumping roller is stored in the cell and conveyed to the developing roller. At this time, the surface of the anilox roller is doctored by a doctor blade as a regulating blade, so that for each cell, a precisely defined liquid amount remains in the cell and is applied to the developing roller, and a thin layer of the developer is formed. It comes to form.

  In this process, a problem that solid matter such as settled toner particles accumulates in the cell of the anilox roller and sticks to the cell bottom frequently occurs. In such a situation, an appropriate developer thin layer is not formed on the developing roller, which may adversely affect the image quality of the formed image. Therefore, in the liquid developing device, care must be taken not to deposit toner or the like in the cells of the anilox roller. In order to deal with such problems, in general, an operator or the like regularly inspects and, if necessary, performs maintenance such as cleaning the anilox roller cell to change the state of the anilox roller cell. Maintained properly.

  However, such maintenance takes time and the accumulation of toner or the like on the cells proceeds until the maintenance, and there is a risk that the image quality is gradually deteriorated. In order to improve such a problem, for example, there is an anilox roller provided with foreign matter removing means for removing foreign matter mixed in the developer (for example, Patent Document 1).

On the other hand, in order to obtain a fine image, it is important to collect high-concentration toner particles (toner compaction) on the surface layer of a thin developer layer formed on the developing roller. As this compaction means, generally, a developing roller is applied by applying a potential of the same polarity to the developing solution by a charging unit provided on the developing roller to a thin layer of the developing solution formed on the developing roller. In many cases, toner particles are gathered on the surface. In addition to this, for example, there is an apparatus in which an intermediate roller is provided between a supply roller and a developing roller, and a charging unit is installed on the intermediate roller (for example, Patent Document 2).
JP 2002-72695 PR JP-A-9-211994

  The above-described cleaning of the cell of the anilox roller and the compaction of the toner particles are indispensable for stably performing high-quality image formation. In the conventional example, a cleaning unit is provided for cleaning the cell of the anilox roller, and a toner compaction processing unit such as a charging unit is provided for compaction of the toner particles. Methods for providing units have been devised and practiced.

  However, if these are provided separately, a large space is required in the liquid developing apparatus, and they are located close to each other, so that design restrictions are increased.

  The present invention has been made in view of the above points, and in the supply roller, cleaning is performed without separately providing a cleaning means for cleaning the cells and a toner compaction processing means for compacting the toner particles in the developer. The present invention provides a liquid developing device that is equipped with a means that serves both as a means and a toner compaction processing means, reduces the number of parts, realizes space saving, requires less maintenance, and can form a fine high-quality image. Objective.

  In order to solve the above problems, the invention described in claim 1 is directed to an image carrier, a developer carrier that supplies a liquid developer in which toner particles are dispersed in an insulating liquid, and a developer. In a liquid developing device including a supply roller for supplying a liquid developer to the agent carrier, the liquid developer and the regulation blade made of a conductive material provided in contact with the supply roller are A bias potential having a reverse polarity was applied.

  According to a second aspect of the present invention, the supply roller has a conductive material inside the roller and a ceramic surface, and the bias potential applying means applies a bias potential having the same polarity as the liquid developer. It was decided to apply.

  According to a third aspect of the present invention, the bias potential applying means applies a bias potential having the same polarity as that of the liquid developer and lower than the absolute value of the bias potential of the supply roller to the regulating blade. The liquid developer deposited on the blade was cleaned.

  According to a fourth aspect of the present invention, application of a bias potential having a polarity opposite to that of the liquid developer to the regulating blade by the bias potential applying means is performed during development of the toner image.

  According to a fifth aspect of the present invention, the cleaning of the liquid developer deposited on the regulating blade is performed when the toner image is not developed.

  In the invention according to claim 6, the material of the regulating blade has elasticity.

  According to a seventh aspect of the present invention, the image forming apparatus includes the liquid developing device according to any one of the first to sixth aspects.

  According to the configuration of the first aspect of the present invention, an image carrier, a developer carrier that supplies the image carrier with a liquid developer in which toner particles are dispersed in an insulating liquid, and a liquid that is applied to the developer carrier. In a liquid developing device including a supply roller for supplying a developer, a bias potential having a polarity opposite to that of the liquid developer is applied to a regulating blade made of a conductive material provided in contact with the supply roller by a bias potential applying unit. It was decided to apply.

  Therefore, for example, assuming that the charging polarity of the toner particles in the liquid developer is positive (+), a bias potential applying means such as a charging device or the like controls the negative (−) bias potential that is opposite in polarity to the toner particles. When applied to the developer, the developer supplied from the pumping roller into each cell applied to the surface of the supply roller is doctored at the contact portion with the regulating blade, and the amount of liquid precisely defined for each cell. At the same time, the toner particles in the developer are attracted to the regulating blade charged to the opposite polarity and are collected on the surface layer in the developer in the cell by the action of the bias potential (toner compaction process). ).

  Therefore, in the cell, a high-concentration developer layer having a high toner particle content is formed on the surface layer portion, and a low-concentration developer layer having a low toner particle content is formed in the lower layer, which is the cell bottom. It is formed. Since the high-concentration developer layer formed on the surface layer of the cell of the supply roller is supplied to the developing roller, the thin layer of the developer formed on the developing roller is a toner having a higher concentration than that of a normal developer. Contains particles. Then, by supplying a high-concentration developer to the photosensitive drum and performing image formation, a high-density fine high-quality image can be formed.

  On the other hand, the toner particles in the developer in each cell of the supply roller are attracted to the regulating blade charged to the opposite polarity and are collected on the surface layer, so that many toner particles in the cell are attracted to the cell surface layer. Since the toner is supplied to the developing roller, toner particles hardly remain in the developer remaining at the cell bottom after that.

  Therefore, since toner particles do not accumulate on the cell bottom portion of the supply roller, maintenance for the purpose of cleaning the cell becomes unnecessary, and the life of the supply roller can be extended. In addition, this configuration can maintain the cell state of the supply roller appropriately regardless of the usage time and frequency of use, so there is no risk of image quality deterioration and high-quality images can be stably formed over a long period of time. .

  According to a second aspect of the present invention, the supply roller has a conductive material inside the roller and a ceramic surface, and the bias potential applying means biases the same polarity as the liquid developer. An electric potential was applied.

  Therefore, the surface of the supply roller is made of the ceramic while the roller surface of the supply roller is made of ceramic capable of forming a precise cell, and a thin layer with high accuracy of the developer can be formed on the development roller surface. It is possible to create a potential difference between the regulating blade and the developing roller by applying a bias potential to the conductive material inside the supply roller while maintaining the insulating property with the regulating blade and the developing roller in an insulated state. Therefore, since each bias potential can be controlled independently, the degree of freedom of control is increased. That is, the behavior of the toner particles in the developer can be freely controlled by appropriately adjusting the bias potential applied to the roller or blade appropriately or individually with respect to the charged toner particles. .

  According to the invention of claim 3, the bias potential applying means applies a bias potential having the same polarity as the liquid developer and lower than the absolute value of the bias potential of the supply roller to the regulating blade, The liquid developer deposited on the regulating blade was cleaned.

  Therefore, for example, during standby, the developer attached and deposited on the regulating blade is repelled by the repulsive force from the regulating blade to which a bias potential having the same polarity as the toner particles in the developer is applied. At this time, since the bias potential applied to the regulating blade is lower than the absolute value of the bias potential of the supply roller, the repulsive force by the supply roller is larger than the repulsive force by the regulating blade. Particles can be prevented from adhering to the supply roller.

  Therefore, the developer adhering to the regulating blade is removed without adhering to the supply roller, and the regulating blade can be kept in a good state for a long time.

  According to the fourth aspect of the present invention, the bias potential having a polarity opposite to that of the liquid developer is applied to the regulating blade by the bias potential applying means when the toner image is developed.

  Therefore, when the toner image is developed in the supply roller to which the developer is supplied even during start-up and other than during image formation, a bias potential having a polarity opposite to that of the toner particles is applied to the regulating blade or the same polarity as that of the toner particles is applied to the supply roller. By applying the toner particles, the toner particles in the developer are collected on the surface layer. At this time, since the toner particles at the bottom of the cell of the supply roller are similarly attracted to the surface layer, the toner particles do not accumulate at the cell bottom of the supply roller.

  Therefore, the thin layer of the developer formed on the developing roller by the supply roller contains toner particles having a higher concentration than the developer stored in the developer tank, so that a high-density accurate image can be obtained. Can be formed.

  Further, since toner particles do not accumulate on the cell bottom of the supply roller, maintenance is not required and a high-quality image can be stably formed.

  Further, since unnecessary toner compaction processing is not performed when the toner image is not developed, there is an advantage that power can be saved and the reusability of the collected developer can be improved.

  According to the fifth aspect of the present invention, the cleaning of the liquid developer deposited on the regulation blade is performed when the toner image is not developed.

  Therefore, when developing the toner image on the photosensitive drum, the toner particles adhere to the regulating blade that attracted the toner particles by applying a bias potential having a polarity opposite to that of the toner particles, but the toner image is developed on the photosensitive drum. According to the method described in claim 3, the toner particles adhering to the regulating blade can be removed and cleaned by applying a bias potential to the supply roller and the regulating blade, respectively.

  Therefore, the cleaning of the liquid developer deposited on the regulating blade is performed during a standby time when the toner image is not developed. Therefore, no special time is required for cleaning, which impairs the convenience for the user. There is nothing.

  According to the invention described in claim 6, the material of the regulating blade is elastic.

  Thus, a flexible regulating blade made of a conductive material can be doctored along the surface of the supply roller, so that for each cell a precisely defined liquid volume remains in the cell. At this time, by applying a bias potential having a polarity opposite to that of the toner particles to the regulating blade, the toner particles in the developer of the cell are attracted to the surface layer, and a thin layer of the developer having a high concentration and an appropriate amount is developed on the developing roller. Can be formed. Therefore, it is possible to form a fine high-quality image.

  According to a seventh aspect of the present invention, the image forming apparatus includes the liquid developing device according to any one of the first to sixth aspects.

  Therefore, the liquid developing device prevents toner particles from accumulating on the bottom of each cell of the supply roller, and the regulating blade is properly cleaned, and the toner particles in the developer are compacted. It is possible to provide an image forming apparatus that stably forms a high-quality image over a long period of time and requires less maintenance.

  Hereinafter, a wet image forming apparatus according to the present invention will be described with reference to FIGS. As an example of the wet image forming apparatus according to the present invention, a tandem color image forming apparatus is given as an example. First, an image forming process will be described with reference to FIG. 1 and FIG. explain. FIG. 1 is a schematic vertical sectional view showing a schematic structure of a printer 100 as a tandem type color image forming apparatus. FIG. 2 is a schematic vertical sectional side view of the image forming means 5 shown in FIG.

  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 sheet P is conveyed from the sheet feeding cassette 1 a of the sheet feeding unit 1 to the vertical conveyance path 2 by the pickup roller 1 b and is conveyed to the secondary transfer unit 6 through the registration roller pair 3.

  In the image forming unit 50, the intermediate transfer belt 43 is fed in the direction of the arrow by the drive roller 41, and is formed on each photosensitive drum 51 as an image carrier in the image forming units 5Y, 5C, 5M, and 5B. The yellow, cyan, magenta, and black toner images are sequentially transferred, and a color image is formed on 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 nip portion formed by the pressure contact between the fixing roller 7a and the pressure roller 7b, a heat amount necessary for fixing is supplied to the paper P, and a 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, the configuration of the image forming unit 50, which is a main component of the printer 100, will be described in detail. The image forming unit 50 includes a belt conveyance unit 4, first to fourth image forming units 5B, 5M, 5C, and 5Y including a liquid developing device, and an intermediate transfer cleaning unit 45.

  The belt conveyance unit 4 includes a driving roller 41, a driven roller 42, and an endless intermediate transfer belt 43 that is stretched over 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 and the outer peripheral speed of the intermediate transfer belt 43 of the belt conveying unit 4 are set. It is driven so as to have a constant speed.

  The first to fourth image forming units 5 </ b> B, 5 </ b> M, 5 </ b> C, and 5 </ b> Y are arranged below the belt conveyance unit 4. Arrangements of the respective image forming units are for yellow (Y), cyan (C), magenta (M), and black (B) in order from the upstream in the paper conveyance direction, and all of the units (image forming apparatuses) having substantially the same configuration. Means 5). 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, 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 eliminating lamp 59. Are assembled into a single unit, and attached to the apparatus main body (not shown).

  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 when the exposure device 53 irradiates light according to image information onto the surface of the charged photosensitive drum 51. Note that the exposure device 53 may use LPH (LED PRINT HEAD) or LSU (laser scanning unit).

  A developer tank 11 in the liquid developing device 10 stores a developer 18 composed of toner particles and a carrier which is an insulating liquid. The developer 18 is adjusted so that toner particles are dispersed at a high concentration in a carrier liquid which 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 charged to a positive potential (+) by the 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 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 +300 V, the developing bias is set to +200 V, and the post-exposure potential is set to +20 V. 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 conveying unit 4 at the nip with the primary transfer unit 54. In the present embodiment, the primary transfer unit 54 uses a transfer roller, and a voltage having a polarity opposite to the surface potential of the photosensitive drum 51 is set in a range of −100 to −1000 V and applied. ing.

  The toner particles that have not been transferred on the photosensitive drum 51 are scraped off by the rubber blade 57 of the cleaning device 55, and are neutralized by the neutralizing lamp 59 in order to lower the residual potential on the surface of the photosensitive drum 51 and make it uniform. Prepare for the next series of processes. The potential setting in image formation can be selected as an optimum value according to the characteristics of the photosensitive drum 51, the characteristics of the toner particles, the environment, and the like. The printer 100 uses the first to fourth image forming units 5B, 5M, 5C, and 5Y to display images corresponding to black, magenta, cyan, and yellow on the basis of the method of the image forming unit 5 described above. By developing on 51 and sequentially repeating on the intermediate transfer belt 43 and transferring without deviation, 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 abuts against 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 developer 18. Inside the liquid developing device 10, a developing roller 12, an anilox roller 13, a pumping roller 14, a doctor blade 15, a cleaning blade 16, and a pair of stirring screws 17 a and 17 b are provided. The anilox roller 13, the pumping roller 14, and the stirring screws 17a and 17b are rotationally driven by a driving means including a gear train and the like.

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

  The doctor blade 15 is in contact with the upper part of the anilox roller 13 and upstream of the developing roller 12 in the rotational direction of the anilox roller 13 in the axial direction of the anilox roller 13. The developer 18 supplied to the roller surface is thinned. 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 disposed above the developing roller 12 and on the downstream side in the rotation direction of the developing roller 12 with respect to the photosensitive drum 51, and one end of the blade is disposed in the axial direction with respect to the developing roller 12. The developing solution 18 remaining on the developing roller 12 after development is removed by contacting the counter.

  Next, an operation process of the liquid developing device 10 will be described. In FIG. 2, as described above, the 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 developer 18 stored in the developer tank 11 is agitated by the agitating screws 17a and 17b, and the toner particles are dispersed so as to be uniform in the solution.

  As the pumping roller 14 that is partially immersed in the developer 18 rotates, the developer 18 is sequentially attached to the surface of the immersed roller 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 developer 18 applied to the anilox roller 13 is made into a uniform thin layer by the doctor blade 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 blade 15 by applying a bias potential to the doctor blade 15 as the regulating blade and the anilox roller 13 as the supply roller, which is a characteristic part of the present invention, will be described.

  First, the structure of the characteristic portion will be described with reference to FIG. 3 in addition to FIG. FIG. 3 is a partially enlarged cross-sectional view showing the state of the developer at the contact portion between the anilox roller 13 and the doctor blade 15 as supply rollers.

  As shown in FIG. 3, the anilox roller 13 is a roller in which a large number of fine precise concave cells are regularly engraved on the entire surface, and a developer 18 is supplied to each cell from the pumping roller 14 in the previous stage. It is like that. The surface layer 13a having the cells of the anilox roller 13 is made of ceramic, and the roller interior 13b is made of a conductive material. A bias potential applying means such as a charger is connected to the conductive material inside the roller 13b, and a bias potential having a set value is applied to the anilox roller in accordance with a request from the control means. ing. Since the surface layer of the anilox roller 13 is an insulating ceramic, even if a bias potential is applied to the developing roller 12 or the doctor blade that is in contact with the anilox roller 13, it does not conduct, so the potential difference is reduced. Can be maintained.

  The doctor blade 15 is a plate-like member made of a flexible resin or metal having elasticity having conductivity, and its longitudinal direction is parallel to the axis of the anilox roller 13, and as shown in FIG. On the other hand, the contact surface approaches the upstream side in the rotation direction of the anilox roller 13 from the upstream side to the downstream side in the rotation direction of the anilox roller 13, and the end portion abuts the roller surface so as to form a pressure nip. Is provided. A bias potential applying means such as a charger is connected to the doctor blade 15, and a bias potential having a set value is applied to the doctor blade 15 in accordance with a request from the control means or the like.

  Next, the operation and effect of the above configuration will be described. First, operations and effects during development of a toner image will be described.

  In the liquid developing device 10, the developer 18 stored in the developer tank 11 is immersed in the developer 18 and is attached to the roller surface of the rotating pumping roller 14, and is the same as the pumping roller 14 rotates. At a linear velocity, the surface is 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 this time, each cell of the anilox roller 13 in contact with the pumping roller 14 and supplied with the developer 18 is filled with the developer 18.

  Thereafter, each cell filled with the developer 18 reaches the contact portion with the doctor blade 15 as the anilox roller 13 rotates.

  As shown in FIG. 3, in front of the doctor blade 15, the developer 18 supplied to the anilox roller 13 does not stay in each cell but adheres to the entire roller surface and is in an excessive state. Since the pressure contact nip portion of the elastic doctor blade 15 is in close contact with the surface of the anilox roller 13, the developer 18 on the anilox roller 13 reaching the portion is accumulated in the cell. Is left before the pressure-contact nip with the doctor blade 15 and returned to the developer tank 11. Therefore, after passing through the doctor blade 15 pressure nip portion, the excess developer 18 adhering to the surface of the anilox roller 13 is removed, and in each cell, an amount of developer 18 that is defined approximately accurately is obtained. Remains.

  At the time of developing the toner image, the control means applies a bias potential having a polarity (−) opposite to the charging polarity (+) of the toner particles of the developer 18 to the doctor blade 15 by a bias potential applying means such as a charger. Since the developer 18 in the cell is adjusted to a specified amount, the toner particles dispersed in the developer 18 in the cell are applied to the surface of the doctor blade 15 to which a bias potential is applied. (Toner compaction described above).

  Therefore, in the developer 18 in the cell, a high-concentration developer 18 layer having a high toner particle content is formed in the surface layer portion near the doctor blade 15, and the toner layer is formed in the lower layer as the cell bottom portion. A layer of a low concentration developer 18 having a low particle content is formed.

  The layer of the high-concentration developer 18 formed on the surface layer portion of the cell reaches the abutting portion with the developing roller 12 while maintaining this state, and on the roller surface of the developing roller 12 here. As a result of the transfer, a thin layer of the developer 18 is formed on the surface of the developing roller 12.

  Generally, the amount of the 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 developer 18 in the cell is transferred to the developing roller 12. Absent. Therefore, by forming a layer of the high-concentration developer 18 on the surface layer of the cell of the anilox roller 13, more of the high-concentration developer 18 is transferred to the development roller 12, and the low-density development at the bottom of the cell. Liquid 18 will remain.

  Therefore, the thin layer of the developer 18 formed on the developing roller 12 has a smaller amount of carrier liquid than the developer 18 stored in the developer tank 11 and a high concentration development containing a lot of toner particles. A thin layer of liquid 18 is formed. The thin layer of the high-concentration developer 18 formed on the developing roller 12 is supplied to the photosensitive drum 51 to develop the electrostatic latent image.

  The image formed in this manner has a high toner density of the developer 18 used for developing the toner image, so that it becomes a high-definition and high-density image, which greatly contributes to improving the image quality of the formed image.

  On the other hand, because toner compaction due to the bias potential of the abutting doctor blade 15 causes almost no toner particles to remain in the low concentration developer 18 remaining at the cell bottom of the anilox roller 13, the toner particles in the developer 18. Does not settle and deposit on the cell bottom.

  Therefore, the cell portion of the anilox roller 13 that is conventionally required is not required to be cleaned, and the maintenance management is facilitated. That is, even if it is not regularly cleaned, the toner particles do not accumulate in the cell and are always kept clean, so that the cell state is maintained and stable regardless of the frequency of use. Thus, a suitable thin layer of the developer 18 is 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.

  Further, since unnecessary toner compaction processing is not performed when the toner image is not developed, there is an advantage that power saving is possible and reusability of the collected developer 18 is improved.

  Next, operations and effects in the interval between sheets when the toner image is not developed will be described. As described above, at the time of printing, the doctor blade 15 is applied with a bias potential having the opposite polarity (−) to the charging polarity (+) of the toner particles in the developer 18, and is in the developer on the anilox roller 13. However, at this time, some of the attracted toner particles adhere to the surface of the doctor blade 15.

  A bias potential having the same polarity as the charging polarity (+) of the toner particles is applied to the anilox roller 13 by the bias potential applying means between the sheets on which image formation is not performed, such as during printing standby, and the doctor blade 15 is also charged. Is controlled by the control means so that a bias potential having the same polarity as the charging polarity (+) of the toner particles and lower than the bias potential of the anilox roller 13 is applied. Since the surface of the anilox roller 13 is made of ceramic that is an insulator, the potential difference with the doctor blade 15 that abuts is maintained appropriately.

  At this time, the toner particles attached to the doctor blade 15 in the toner compaction process or the like are repelled by the bias potential applied to the doctor blade 15 and are peeled off from the surface of the doctor blade 15. At this time, since the bias potential higher than that of the doctor blade 15 is applied to the anilox roller 13 in contact with the doctor blade 15, the peeled toner particles have a larger repulsive force from the anilox roller 13. In response, it does not adhere to the anilox roller 13.

  Therefore, the toner particles peeled off from the doctor blade 15 continue to flow downstream together with the developer 18 supplied from the developer tank 11.

  In this way, the toner particles in the developer adhering to the doctor blade 15 at the time of printing are cleaned at a predetermined timing or at regular intervals between papers during standby or the like, so that the toner residue on the doctor blade 15 The surface state of the doctor blade 15 is always properly maintained.

  Cleaning of the residual toner accumulated on the doctor blade 15 is performed during a standby time when the toner image is not developed, so that no special time is required for cleaning. Similarly to the cleaning of the anilox roller 13, since the image forming apparatus itself performs cleaning, maintenance by the operator is unnecessary, so that it is not necessary to provide maintenance / inspection time, and the convenience for the user is improved.

  In addition, there is no problem in forming a thin layer of the developer in the developing roller 12 due to the residual toner accumulated on the doctor blade 15 or causing toner contamination. A high-quality image can be formed.

  With the above configuration, the bias potential of the anilox roller 13 and the doctor blade 15 is appropriately controlled according to the printing situation, so that the size of the liquid developing device 10 can be increased without providing a dedicated unit for cleaning or toner compaction. The anilox roller 13 and the doctor blade 15 can be properly cleaned and a thin layer of the high-concentration developer 18 can be appropriately formed on the developing roller 12 while maintaining the thickness. However, it is possible to provide a liquid developing device that contributes to fine high-quality images with less maintenance work.

  Further, by mounting the liquid developing apparatus 10 according to the present invention on a liquid developing apparatus such as the printer 100, the labor required for cleaning the anilox roller 13 and the doctor blade 15 which have been required up to now can be saved, and a separate unit or the like is provided. Accordingly, it is possible to provide an image forming apparatus that performs toner compaction during printing, stably forms fine high-quality images over a long period of time, and requires less maintenance and management.

  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.

A tandem type color image forming apparatus equipped with a liquid developing apparatus according to the present invention. 3 is a schematic vertical sectional side view of the image forming means 5. FIG. The partial expanded sectional view which shows the mode of the developing solution in the pressure nip part of an anilox roller and a doctor blade.

Explanation of symbols

5 Image forming means (5Y, 5C, 5M, 5B)
DESCRIPTION OF SYMBOLS 10 Liquid developing device 11 Developer tank 12 Developing roller (developer carrier)
13 Anilox roller (supply roller)
15 Doctor blade (regulated blade)
18 Developer (liquid developer)
51 Photosensitive drum (image carrier)
100 printer (image forming apparatus)

Claims (7)

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 supply roller for supplying the liquid developer to the developer carrier. In a liquid developing device,
A liquid developing apparatus, wherein a bias potential having a polarity opposite to that of the liquid developer is applied by a bias potential applying unit to a regulating blade 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 thereof is made of ceramic, and a bias potential having the same polarity as that of the liquid developer is applied by the bias potential applying unit. Liquid developing device.   By applying a bias potential having the same polarity as the liquid developer and lower than the absolute value of the bias potential of the supply roller to the regulating blade by the bias potential applying means, the liquid developer deposited on the regulating blade is removed. The liquid developing device according to claim 2, wherein the liquid developing device is cleaned.   The application of a bias potential having a polarity opposite to that of the liquid developer to the regulating blade by the bias potential applying unit is performed at the time of developing a toner image. Liquid developing device.   The liquid developing device according to claim 4, wherein cleaning of the liquid developer deposited on the regulating blade is performed when the toner image is not developed.   The liquid developing device according to claim 1, wherein a material of the regulating blade is elastic.   An image forming apparatus comprising the liquid developing device according to claim 1.

Images