JP2012103545A - Developing device, image forming apparatus and method for forming image - Google Patents

Abstract

A liquid developer carried on a developer carrying member is adjusted to a suitable charged state.
A developing device according to the present invention includes a developer carrying body that carries a liquid developer containing toner and a carrier liquid and is applied with a developing bias, and a liquid developer carried on the developer carrying body. The charging unit 22 for charging the first developer, the first potential which is the potential of the developer carrier 20 at a position where the liquid developer is not carried, and the position where the liquid developer is carried and charged by the charging unit 22. The potential measurement unit 23 that measures the second potential, which is the potential of the developer carrier 20, and the difference between the first potential and the second potential measured by the potential measurement unit 23 are calculated and calculated. And a controller that adjusts charging of the liquid developer based on the difference.
[Selection] Figure 5

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a liquid developer having toner and carrier liquid, and a developer image developed by the developing device is transferred to a recording material and fixed. The present invention relates to an image forming apparatus and an image forming method for forming an image.

  Various wet image forming apparatuses that develop a latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent and visualize the electrostatic latent image have been proposed. The developer used in this wet image forming apparatus is one in which solids (toner particles) are suspended in a highly viscous carrier liquid having electrical insulation properties such as silicone oil, mineral oil, and edible oil. The toner particles are extremely fine with a particle diameter of around 1 μm. By using such fine toner particles, the wet image forming apparatus can achieve higher image quality than a dry image forming apparatus using powder toner particles having a particle diameter of about 7 μm.

  In an image forming apparatus using a liquid developer, a technique is known in which a charging roller or the like is provided on a developing roller, and the toner in the liquid developer applied to the developing roller is charged and compressed. According to this technique, it is possible to compensate for toner charge in the developer before development, and further compress the toner toward the developing roller, thereby improving toner mobility and suppressing toner adhesion to non-image areas. (Patent Document 1)

The developing roller is usually formed of a member typified by urethane rubber or the like, and has a resistance of about 10 ⁴ to 10 ⁸ Ω. Furthermore, since a surface layer member having high electrical resistance may be provided on the outermost surface of the developing roller, the charge applied from the outside by a toner charging corona or the like accumulates on the roller surface, and the potential of the developing roller surface increases. The phenomenon occurs. In this case, a phenomenon occurs in which the developing roller surface potential is higher than the developing bias.

  In the liquid developing method, a developing roller having an elastic layer and a photosensitive member are pressed against each other to form a developing nip, and toner particles are electrophoresed in the developing nip. Therefore, the difference between the developing roller surface potential and the photoreceptor surface potential (development contrast) dominates toner movement. When the developing roller surface potential fluctuates, the amount of toner movement changes sharply, resulting in a decrease in dot reproducibility and image quality uniformity.

  In order to deal with such a problem, in Patent Document 2, a potential measuring device is provided at a position after the developer charging device on the developing roller and after the developing nip, and applied to the developing roller by controlling the applied voltage of the developer charging device. An attempt is made to stabilize the surface of the formed liquid developer layer at a desired potential.

JP-A-9-185265 JP 2009-294490 A

However, in the potential measuring device described in Patent Document 2, only the potential of the liquid developer on the surface of the developing roller is measured. In such measurement, the charge accumulated on the liquid developer and the surface of the developing roller are measured. The accumulated charge is mixed and measured. Measurement of the charged state of the liquid developer layer itself in order to bring the liquid developer layer into an appropriate charged state, and further development that is separated from the potential of the liquid developer layer in order to suitably change the development contrast and inverse contrast. It is necessary to measure the surface potential of the roller.

  A developing apparatus according to the present invention includes a developer carrying member that carries a liquid developer containing toner and a carrier liquid and to which a developing bias is applied, and a charging unit that charges the liquid developer carried on the developer carrying member. And a first potential which is the potential of the developer carrying member at a position where the liquid developer is not carried, and the developer carrying member at a position where the liquid developer is carried and charged by the charging unit. A potential measurement unit that measures a second potential that is a potential of the first and second potentials, and calculates a difference between the first potential and the second potential measured by the potential measurement unit, and based on the calculated difference And a control unit that adjusts charging of the liquid developer.

  Furthermore, in the developing device according to the present invention, the control unit controls the developing bias to be applied to the developer carrier based on the first potential measured by the potential measuring unit.

  Furthermore, in the developing device according to the present invention, the potential measuring unit includes a potential detection member that detects a potential of the developer carrier at a position where the liquid developer of the developer carrier is carried, and the developer carrying member. The potential detection member measures the first potential when the body does not carry the liquid developer, and the second potential is applied to the potential detection member when the developer carrier carries the liquid developer. And a potential measurement control unit that measures the potential.

  Further, in the developing device according to the present invention, the potential measuring unit measures the potential of the developer carrying member at a position where the developer carrying member does not carry the liquid developer and at a position charged by the charging unit. A first potential detection member that measures the potential of the developer carrier at a position of the developer carrier that carries the liquid developer, and the first potential detection member. The first potential is detected and the second potential is detected by the second potential detection member.

The developing device according to the present invention further includes a cleaning member having a volume resistivity of 10 ³ to 10 ⁷ Ωcm for cleaning in contact with the developer carrier, and the cleaning member is applied to the developer carrier. It is assumed that a bias that is equal to or approximately equal to the applied bias is applied.

  The image forming apparatus according to the present invention carries a latent image carrier on which a latent image is formed, an exposure unit for forming the latent image on the latent image carrier, and a liquid developer containing toner and carrier liquid. And a developer carrying body to which a developing bias is applied, and a charging unit that charges the liquid developer carried on the developer carrying body, and developing the latent image formed on the latent image carrying body with liquid development A developing portion that develops with the developer, a first potential that is the potential of the developer carrying member at a position where the liquid developer is not carried, and a position where the liquid developer is carried and charged by the charging unit. A potential measurement unit that measures the second potential of the developer carrying member, a difference between the first potential and the second potential measured by the potential measurement unit, and the calculated difference A control unit that adjusts the charge to the liquid developer based on It is an feature.

  Furthermore, in the image forming apparatus according to the present invention, the control unit controls the developing bias to be applied to the developer carrier based on the first potential measured by the potential measuring unit. .

Further, the image forming method according to the present invention charges the liquid developer containing the toner and carrier liquid carried on the developer carrying member, and the liquid developer carrying member at a position where the liquid developer is not carried. A first potential that is a potential and a second potential that is a potential of the developer carrying member at a position where the liquid developer is carried and charged by the charging unit; and The charging of the liquid developer is adjusted based on the difference between the second potentials, and the latent image formed on the latent image carrier is developed with the liquid developer carried on the developer carrier. It is what.

  According to the developing device of the present invention, on the developer carrying member, the potential at the position where the liquid developer is carried (second potential) and the potential at the position where the liquid developer is not carried (first potential). Based on the difference, the charged state of the liquid developer can be controlled to a suitable state.

  Further, by controlling the developing bias applied to the developer carrier based on the potential (first potential) at the position where the liquid developer is not carried, the actual surface potential of the developing roller is set to a predetermined value. It becomes possible to control. In addition, it is possible to maintain the development contrast and reverse contrast under suitable conditions.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating main components of an image forming unit and a developing unit according to the embodiment of the present invention. The figure which shows the relationship of the various electric potential with respect to the bias applied to a toner charger. FIG. 3 is a diagram illustrating a bias control configuration of a toner charger and a developing roller according to an embodiment of the present invention. The figure which shows arrangement | positioning of the electric potential detection member which concerns on embodiment of this invention. The figure which shows arrangement | positioning (enlargement) of the electric potential detection member which concerns on embodiment of this invention. The flowchart which shows the bias control processing which concerns on embodiment of this invention. The figure which shows the mode of the various electric potential transition which concerns on embodiment of this invention. The figure which shows the value of the various electric potential transition which concerns on embodiment of this invention. The figure which shows the charge amount by the difference in a toner color (cyan (C), black (Bk)). The figure which shows the favorable range of V2-V1 by the difference in a toner color. The figure which shows arrangement | positioning of the electric potential measurement part which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a main configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an image forming unit and a developing device for yellow (Y) color in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram illustrating a main configuration of (developing unit).

  As shown in FIG. 1, the image forming apparatus according to the present embodiment includes a transfer belt 40, four image forming units mainly including photoconductors 10Y, 10M, 10C, and 10K, and photoconductors 10Y, 10M, Four developing devices 30Y, 30M, 30C, 30K disposed corresponding to 10C, 10K (“latent image carrier” in the present invention), and 2 disposed on the right side of the transfer belt 40 in the drawing. The next transfer portion and a cleaning portion disposed on the left side of the transfer belt 40 in the drawing are configured.

  Hereinafter, the image forming unit and the developing devices 30Y, 30M, 30C, and 30K have the same configuration as the image forming unit and the developing device for each color, and therefore will be described based on the yellow (Y) image forming unit and the developing device. .

The developing unit 30Y is a device that develops a latent image formed on the photoreceptor 10Y with a liquid developer, and includes a developing roller 20Y, an intermediate roller 32Y, an anilox roller 33Y, and a liquid that stores the liquid developer. A toner charger 22Y for charging the toner on the developer container 31Y and the developing roller 20Y is a main component.

  A cleaning blade 21Y, an intermediate roller 32Y, and a toner charger 22Y are arranged on the outer periphery of the developing roller 20Y. The surface of the intermediate roller 32Y is in contact with the developing roller 20Y and the anilox roller 33Y, and an intermediate roller cleaning blade 34Y is disposed on the outer periphery thereof.

  The anilox roller 33Y is in contact with a regulating member 35Y that adjusts the amount of liquid developer pumped from the developer reservoir 311Y. In the three-roller system using the intermediate roller 32Y as in the developing device of the present embodiment, the amount of liquid developer can be adjusted by the intermediate roller 32Y coming into contact with the anilox roller 33Y. It is also possible to adopt a configuration in which the restricting member 35Y is not provided.

  A liquid developer is supplied to the developer storage unit 311Y from a developer supply unit (not shown) via the transport path 723Y. In this embodiment, both end portions of the partition plate 313Y have a shape that is one step lower than the central portion, and the liquid developer is moved from the developer storage portion 311Y to the recovered liquid storage portion 312Y side at this one step lower portion. By overflowing, the liquid level of the developer reservoir 311Y is kept constant.

  In the recovery liquid storage unit 312Y, the recovery liquid containing the liquid developer overflowing from the developer storage unit 311Y and the liquid developer recovered by various blades is collected in the recovery auger 37Y by the recovery auger 37Y disposed therein. And is collected by the developer supply unit via the transfer path 721Y. The collected recovered liquid is adjusted in concentration by the developer replenishing section, and then supplied again via the transfer path 723Y so that it can be reused.

  The liquid developer contained in the developer container 31Y is a low-concentration (about 1 to 2 wt%) and low-viscosity volatile at room temperature using a conventionally used Isopar (trademark: exon) as a carrier. Is a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, in the liquid developer in the present invention, a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin is introduced into a liquid solvent such as an organic solvent, silicone oil, mineral oil, or edible oil. Viscoelasticity at a shear rate of 1000 (1 / s) at 25 ° C. with a high viscosity (HAAKE RheoStress RS600, added with a dispersant and having a toner solid content concentration of about 25%. 30 to 300 mPa · s Liquid developer.

  The anilox roller 33Y functions as an application roller that supplies and applies a liquid developer to the intermediate roller 32Y. This anilox roller 33Y is a cylindrical member, and is a roller having a concave and convex surface formed by grooves engraved finely and uniformly on the surface so as to easily carry the developer on the surface. The anilox roller 33Y supplies the liquid developer from the developer reservoir 311Y to the developing roller 20Y. During operation of the apparatus, as shown in the figure, the anilox roller 33Y rotates clockwise to apply the liquid developer to the intermediate roller 32Y.

  The regulating member 35Y is a metal blade having a thickness of about 200 μm, is placed on the surface of the anilox roller 33Y, regulates the film thickness and amount of the liquid developer carried and carried by the anilox roller 33Y, and develops The amount of the liquid developer supplied to the roller 20Y is adjusted.

The intermediate roller 32Y is a cylindrical member, and rotates counterclockwise like the developing roller 20Y and counter-contacts with the developing roller 20Y as shown in the drawing with the rotation axis as the center. Similar to the developing roller 20Y, the intermediate roller 32Y is configured by providing an elastic layer on the outer periphery of a metal inner core.

  An intermediate roller cleaning blade 34Y is disposed in contact downstream of the contact position between the intermediate roller 32Y and the developing roller 20Y. The liquid developer that has not been supplied to the developing roller 20Y is scraped off and stored in the developer container 31Y. It collects in the recovery liquid storage unit 312Y.

  The developing roller 20Y is a cylindrical member, and rotates counterclockwise around the rotation axis as shown in the figure. The developing roller 20Y is provided with an elastic layer such as polyurethane rubber, silicon rubber, NBR, or PFA tube on the outer periphery of an inner core made of metal such as iron. A developing bias is applied to the developing roller 20Y, and the developing bias is applied to the metal inner core.

  The developing roller cleaning blade 21Y is disposed downstream of the developing nip portion where the developing roller 20Y contacts the photoreceptor 10Y in the rotation direction of the developing roller 20Y, and scrapes off and removes the liquid developer remaining on the developing roller 20Y. . The developer remaining after development is scraped off and removed by the developing roller cleaning blade 21Y and dropped into the collected liquid storage unit 312Y in the developer container 31Y to be reused.

  The toner charger 22Y (“charger” in the present invention) is an electric field applying unit that increases the charging bias of the surface of the developing roller 20Y. The liquid developer conveyed by the developing roller 20Y is combined with the toner charger 22Y. An electric field due to corona discharge is applied and charged in a close position.

  The image forming unit is arranged in order along the rotation direction of the outer periphery of the photoconductor 10Y. Two corona chargers 11Y and 11Y ′, an exposure unit 12Y, a photoconductor squeeze device, a primary transfer unit 50Y, and a photoconductor It is constituted by a cleaning blade 18Y or the like. The image forming unit contacts the developing roller 20Y of the developing unit 30Y between the exposure unit 12Y and the first squeeze roller 13Y on the outer periphery of the photoreceptor 10Y.

  The photoconductor 10Y is a photoconductor drum made of a cylindrical member having a photosensitive layer such as an amorphous silicon photoconductor formed on the outer peripheral surface, and rotates in the clockwise direction.

  The two corona chargers 11Y and 11Y ′ are arranged upstream of the nip portion between the photoconductor 10Y and the developing roller 20Y in the rotation direction of the photoconductor 10Y, and a voltage is applied from a power supply device (not shown) to thereby apply the photoconductor 10Y. Is corona charged. The exposure unit 12Y (“exposure unit” in the present invention) irradiates light on the photoconductor 10Y charged by the corona chargers 11Y and 11Y ′ on the downstream side in the rotation direction of the photoconductor 10Y from the corona charger 11Y. Then, a latent image is formed on the photoconductor 10Y.

  The photosensitive member squeeze device disposed on the upstream side of the primary transfer unit 50Y is disposed on the downstream side of the developing roller 20Y so as to face the photosensitive member 10Y. This photoconductor squeeze device is composed of a first squeeze roller 13Y, a second squeeze roller 13Y ′, and photoconductor squeeze roller cleaning blades 14Y and 14Y ′ made of an elastic roller member that slides in contact with the photoconductor 10Y. It has a function of collecting (squeezing) excess carrier liquid and originally unnecessary fog toner from the toner image developed on the body 10Y, and increasing the toner particle ratio in the visible image (toner image). Note that a bias (voltage) is applied to the photoconductor squeeze rollers 13Y and 13Y 'in order to attract fog toner to the photoconductor squeeze rollers 13Y and 13Y'.

The photoconductor squeeze roller cleaning blades 14Y and 14Y ′ are provided in contact with the photoconductor squeeze rollers 13Y and 13Y ′, and scrape off the collected liquid developer containing carrier liquid and fog toner to form a developer container. It is dripped at the collected liquid storage part 312Y in 31Y.

  The surface of the photoreceptor 10Y that has passed through the squeeze device including the first photoreceptor squeeze roller 13Y and the second photoreceptor squeeze roller 13Y 'enters the primary transfer unit 50Y. In the primary transfer portion 50Y, the developer image developed on the photoreceptor 10Y is transferred to the transfer belt 40 by the primary transfer backup roller 51Y. In the primary transfer portion 50Y, the toner image on the photoreceptor 10Y is transferred to the transfer belt 40 side by the action of the transfer bias applied to the primary transfer backup roller 51Y. Here, the photoconductor 10Y and the transfer belt 40 are configured to move at a constant speed, and the driving load of rotation and movement is reduced, and the disturbance effect on the visible toner image of the photoconductor 10Y is suppressed.

  On the downstream side of the primary transfer portion 50Y, the photoconductor cleaning blade 18Y that is in contact with the photoconductor 10Y cleans the liquid developer rich in carrier components on the photoconductor 10Y.

  The transfer belt 40 (transfer member) has a three-layer structure in which an elastic intermediate layer of polyurethane is provided on a polyimide base layer and a PFA surface layer is provided thereon. The transfer belt 40 is stretched by a belt driving roller 41 and a tension roller 42, and is used so that a toner image is transferred on the PFA surface layer side. In the image forming apparatus according to the present embodiment, the transfer belt 40 is used as a member for transfer. However, the transfer belt 40 is not limited to a belt, and various transfer members such as a roller and a drum may be employed.

  In the primary transfer portions 50Y, 50M, 50C, and 50K formed by the primary transfer backup rollers 51Y, 51M, 51C, and 51K facing each other with the photoconductors 10Y, 10M, 10C, and 10K and the transfer belt 40 interposed therebetween, The developed toner images of the respective colors on the photoconductors 10Y, 10M, 10C, and 10K are sequentially superimposed and transferred onto the transfer belt 40 with the contact position with the photoconductors 10Y, 10M, 10C, and 10K as the transfer position. A full-color toner image is formed on the belt 40.

  In the secondary transfer unit 60, the secondary transfer roller 61 is disposed opposite to the belt driving roller 41 with the transfer belt 40 interposed therebetween, and a secondary transfer portion (nip portion) is formed by both. In the secondary transfer unit, a single-color or full-color toner image formed on the transfer belt 40 is transferred to a transfer material such as a sheet, a film, or a cloth conveyed through the transfer material conveyance path L. Further, a fixing unit (not shown) is disposed downstream of the sheet material conveyance path L, and is fixed by applying heat or pressure to a single color toner image or a full color toner image transferred onto the transfer material.

  The transfer material is supplied to the secondary transfer unit by a paper feeding device (not shown). The transfer material set in the paper feeding device is sent to the transfer material conveyance path L one by one at a predetermined timing. In the transfer material conveyance path L, the transfer material is conveyed to the secondary transfer portion by the gate rollers 101 and 101 ′, and the single color or full color toner image formed on the transfer belt 40 is transferred to the transfer material.

  The tension roller 42 stretches the intermediate transfer body 40 together with the drive roller 41, and a cleaning blade 46 that cleans the transfer belt 40 comes into contact with the tension roller 42 at a position stretched on the tension roller 42 of the intermediate transfer body 40. Arranged.

As described above, in the developing device 30Y and the image forming apparatus of the present embodiment, the liquid developer pumped up by the anilox roller 33Y is transferred to the intermediate roller 32Y that rotates with the roller, and the scraping interface is further developed by the developing roller 20Y that rotates counter. By uniforming, a uniform thin film of 4 to 10 μm is formed. Further, the toner charger 22Y provided opposite to the developing roller 20Y compensates for the charging of the liquid developer and is compressed toward the developing roller 20Y, so that extra toner adheres to the non-image area (fogging). ) And the uniformity in the image area can be improved.

  In this embodiment, as the toner charger 22Y, a device that charges the liquid developer by performing corona discharge, such as corotron and scorotron, is used. However, in addition to such a configuration, a charging roller may be used. . The charging / compression by the toner charger 22Y may be referred to as precharge.

  As shown in FIG. 2, around the developing roller 20Y, a potential measuring unit 23Y is disposed between the toner charger 22Y and the nip position between the developing roller 20Y and the photoreceptor 10Y. The surface potential (second potential) of the liquid developer immediately after the liquid developer is precharged by the potential measurement unit 23Y and immediately before the development, and the developing roller 20Y in a state where the liquid developer is not applied. The surface potential (first potential) can be measured.

  FIG. 3 is a diagram showing the relationship of various potentials with respect to the bias applied to the toner charger 22Y. The surface potential of the developing roller 20Y before precharging is substantially equal to the developing bias Vd applied to the developing roller 20Y (about 400 [V]). By increasing the bias applied to the toner charger 22Y, a second potential (hereinafter referred to as V2) which is the surface potential of the liquid developer layer, and a first potential (hereinafter referred to as the surface potential) of the developing roller 20Y itself. Both (V1) are higher than the developing bias. Here, the potential difference (V2−V1) between V2 and V1 can be considered as an increase in potential due to the charge applied to the liquid developer layer. Therefore, by measuring V2−V1, charging / compression of the liquid developer. The state can be determined. Furthermore, by measuring V1, it is possible to determine the potential contrast state during development.

  FIG. 4 is a diagram illustrating a bias control configuration of the toner charger and the developing roller according to the embodiment of the present invention. The potential measuring unit 23Y is disposed around the developing roller 20Y and between the toner charger 22Y and a nip formed by the developing roller 20Y and the photoreceptor 10Y. The potential measuring unit 23Y measures the potential (V2) of the liquid developer applied to the developing roller 20Y and the potential (V1) of the developing roller 20Y in a state where the liquid developer is not applied, and the central control unit 200 Output. A two-sensor method, a one-sensor method, or the like can be employed for the potential measurement unit 23Y, but a specific configuration such as the position of the sensor (potential detection member) will be described later.

  The central control unit 200 controls the high voltage power source 202 and the high voltage power source 201 based on V1 and V2. Here, the high voltage power source 202 controls the bias applied to the toner charger 22Y, and the high voltage power source 201 controls the developing bias applied to the developing roller 22Y. In particular, in this embodiment, the high-voltage power source 202 is controlled based on the difference between V2 and V1, and the charged state of the liquid developer on the developing roller 20Y is adjusted.

  FIG. 5 is a diagram for explaining the configuration of the potential measurement unit 23Y according to the embodiment of the present invention. A two-sensor system in which potential detection members 231Y and 232Y that measure the potential on the developing roller 20Y are disposed in at least two places is used for the potential measurement unit 23Y of the present embodiment. When a plurality of at least one of the first potential detection member 231Y and the second potential detection member 232Y are provided, the average of the measured potentials may be employed as V1 and V2.

The second potential detecting member 232Y can measure the potential (second potential) in the region where the liquid developer is applied on the developing roller 20Y, that is, the region corresponding to the uneven surface where the liquid developer is pumped up in the anilox roller 33Y. It is arranged at the position. Both the first potential detection member 231Y and the second potential detection member 232Y are sensors that detect the potential at a position facing each other in a non-contact manner.

  On the other hand, the first potential detecting member 231Y is disposed at a position for detecting the potential (V1) of the region where the liquid developer is not applied on the developing roller 20Y. FIG. 6 shows details of the arrangement position of the first potential detection member 231Y. This figure is a side view in the vicinity of the end of the developing roller 20Y, and the first potential detection member 231Y is disposed at the position shown in the figure. The first potential detection member 231Y has a width L in the axial direction of the developing roller 20Y in a region where the liquid developer is not applied, a charging region by the toner charger 22Y, and the developing roller cleaning blade 21Y or the intermediate roller 32Y. It is arranged at a position included in the charge removal area. The first potential, that is, the surface potential of the developing roller 20Y itself can be measured at such a position.

In this embodiment, in order to improve the static elimination performance by the developing roller cleaning blade 21Y or the intermediate roller 32Y, the developing roller cleaning blade 21Y or the intermediate roller 32Y has a volume resistivity of 10 ³ to 10 ⁷ Ωcm or a surface resistivity. 10 ⁴
10 ¹¹ Ω / cm ² , and a developing bias Vd from a high voltage power source (not shown).
And an equal bias is applied. Since the charge from the toner charger 22Y accumulates on the surface of the developing roller 20Y, it is necessary to remove the charge every time the developing roller rotates once. Therefore, by configuring the developing roller cleaning blade 21Y or the intermediate roller 32Y with a resistance member within a predetermined range, the charge can be released from the contact portion with the developing roller. It becomes possible to make the surface potential of the developing roller 20Y immediately before charging substantially equal to the developing bias Vd.

  The width of the developing roller cleaning blade 21Y or the width of the intermediate roller 32Y, which is adjusted to a predetermined range of resistance in order to eliminate charges accumulated on the surface of the developing roller 20Y by precharging, is greater than the charging area (width) of the toner charger 22Y. Is also getting bigger. A bias lower than the developing bias Vd can be applied to the developing roller cleaning blade 21Y and the intermediate roller 32Y in order to enhance the charge eliminating effect of the charges accumulated on the surface of the developing roller 20Y.

  FIG. 7 is a flowchart showing a bias control process according to the embodiment of the present invention. The bias control process can be performed at an appropriate timing such as when the printing operation starts or during the printing operation. When this bias control process is started, first, the developing bias Vd applied to the developing roller 20Y and the bias Vw applied to the toner charger 22Y are set to initial values, and the developing roller 20Y, the intermediate roller 32Y, etc. are driven. Start (S102). When the liquid developer is applied on the developing roller 20Y and becomes in a stable state to some extent, the first potential V1 of the area where the liquid developer is not applied in the potential measurement unit 23Y, the area where the liquid developer is applied The second potential V2 is measured and the difference between them is obtained.

  This difference is the potential increase due to the charge applied to the liquid developer layer. When this potential increase is within a predetermined range, the charge amount of the liquid developer itself is in a suitable range. On the other hand, when the difference is out of the predetermined range, the charging amount of the liquid developer is adjusted to be within a suitable range by adjusting the bias applied to the toner charger 22Y of the liquid developer layer. Specifically, when the difference is smaller than the lower limit value of the predetermined range, the bias Vw applied to the toner charger 22Y is increased by a certain amount. If the difference is larger than the upper limit value in the predetermined range, the bias Vw applied to the toner charger 22Y is lowered by a certain amount. By repeating the processing of S103 and S105, the difference (V2−V1) is within a suitable range.

In the present embodiment, the surface potential of the developing roller 20Y itself is also controlled to be an appropriate value, and the development contrast and the reverse contrast are maintained under suitable conditions. In S104, whether or not the first potential indicating the surface potential of the developing roller 20Y is within a range of ± 5 [V] with respect to V1 ^* (appropriate value of V1) is determined to be an appropriate value. To be judged. If it is at an appropriate value, the bias control process is terminated (S101). On the other hand, if it is not an appropriate value, it is optimized by adjusting the developing bias Vd. Specifically, when V1 is larger than the appropriate value, the developing bias Vd is lowered, and when V1 is smaller than the appropriate value, the developing bias Vd is raised.

  When the developing bias Vd is changed in S106, the first potential V1 that is the surface potential of the developing roller 20Y and the second potential V2 that is the surface potential of the liquid developer are also affected. For this reason, in this embodiment, the difference (V2−V1) and V1 are both kept at appropriate values by repeatedly executing the processes after S103.

  8 and 9 show a specific example of the bias control process according to the embodiment of the present invention. Here, a case where cyan (C) toner is used as the liquid developer will be described as an example. When the development bias Vd before control (initial value) is 400 [V] and the bias applied to the toner charger 22 is Vw = 4.0 [kV], each potential measured by the potential measuring unit 23Y is V2. = 470 [V], V1 = 425 [V], and the difference V2−V1 = 45 [V].

  Here, the range of the difference (V2−V1) where the charged / compressed state of the toner in the liquid developer is a suitable condition is 30 to 60 [V]. The range of the difference is determined by various conditions such as the conductivity of the carrier oil used for the liquid developer, the characteristics of the resin or dispersant forming the toner, the charge control agent or the pigment, the volume resistivity and the surface resistivity of the developing roller. .

Before the control, the value of the difference (V2−V1) is 45 [V], which satisfies the condition, but the surface potential V1 of the developing roller 20Y is larger than the developing bias Vd, and the desired developing roller 20Y. 25 [V] higher than the surface potential V ^* . Accordingly, the developing bias is changed to Vd ′ = Vd−25 [V] = 375 [V] in order to set the surface potential V1 of the developing roller 20Y to a desired value 400 [V].

As a result of adjusting the developing bias Vd, V1 ′ = 410 [V] and V2 ′ = 475 [V] are obtained, and the difference is expanded to V2′−V1 ′ = 65 [V], which is outside the preferable condition. Further, V1 ′ is also out of the reference value. Therefore, the bias applied to the toner charger 22 is set to Vw ′ = 3.9 [V], and the discharge amount from the toner charger 22 is reduced, so that V1 ″ = 400 V and V2 ″ = 440 [V]. By setting the difference V2 ″ −V1 ″ = 40 [V], the surface potential V1 ″ of the developing roller 20Y and the difference V2 ″ −V1 ″ are both adjusted to a suitable range. A summary of the control results is shown in FIG.

  In the image forming apparatus using a plurality of colors as shown in FIG. 1, the range in which the difference (V2−V1) is good differs depending on the difference in the components contained in each color liquid developer. As color pigments for solid particles of each color, azo pigments and condensed polycyclic pigments for yellow (Y), azo pigments, condensed azo pigments and condensed polycyclic pigments for magenta (M), and phthalocyanines for cyan (C) High molecular organic compounds represented by pigments and condensed polycyclic pigments are used, and these Y, M, and C color liquid developers are known to have high insulation properties. On the other hand, in black (Bk), many inorganic pigments having conductivity represented by carbon black are used. Therefore, Y, M, C, and Bk have different conductivity as a liquid developer, and Bk liquid developer has higher electrical conductivity.

  FIG. 10 is a diagram showing the charge amount due to the difference in toner color (cyan (C), black (Bk)), and FIG. 11 is a diagram showing the good range of V2-V1 due to the difference in toner color. As shown in FIG. 10, when C and Bk are compared, V2 is lower for Bk when the same bias is applied by the toner charger 22. This is because even when the same amount of precharged charge is applied, Bk is less likely to accumulate charges on the surface of the liquid developer. Therefore, the range in which the difference (V2−V1) is favorable for Bk having high conductivity is higher than those of other colors (Y, M, C). In the bias control process, a range in which the difference (V2−V1) is suitable is determined in consideration of the difference in characteristics of the liquid developer.

  FIG. 12 is a diagram showing the arrangement of potential detection members according to another embodiment of the present invention. In FIG. 5, the two-sensor type potential measurement unit 23Y using the two potential detection members 231Y and 232Y has been described. However, the potential measurement unit 23Y may be configured by one potential detection member 230Y. In this case, as shown in the drawing, the potential detection member 230Y is disposed at a position where the potential at the position where the liquid developer is applied on the developing roller 20Y can be detected, like the second potential detection member 232Y of FIG. .

  In such a position, a process for measuring the potential (first potential) of the portion where the liquid developer is not applied is required. Accordingly, at the start of the printing operation, after a predetermined printing time has elapsed (for example, 1 hour), after a predetermined number of sheets have been printed (for example, 1000 pages), the printing operation is stopped, and the liquid development is performed in a period in which the liquid developer is not applied to the developing roller 20Y The surface potential of the developing roller 20Y not coated with the agent is detected and output as the first potential V1.

  In addition, during the printing operation, the developer coating is unnecessary at the positions corresponding to the transfer material (paper), and therefore various supply rollers (anilox roller 33Y or anilox roller 33Y and It is also possible to stop the intermediate roller 32Y) and measure the surface potential (first potential) of the developing roller 20Y not coated with the liquid developer.

  Note that although various embodiments have been described in this specification, embodiments configured by appropriately combining the configurations of the respective embodiments are also included in the scope of the present invention.

  10Y (Hereinafter, Y is the same for the colors M, C, and K.) Photoconductor (latent image carrier), 11Y ... first corona charger, 11Y '... second corona charge , 12Y ... exposure unit (exposure unit), 13Y ... first squeeze roller, 13Y '... second squeeze roller, 14Y ... first squeeze roller cleaning blade, 14Y' ... second squeeze roller cleaning blade, 18Y ... photoconductor cleaning Blade, 20Y ... developing roller (developer carrier), 21Y ... developing roller cleaning blade, 22Y ... toner charger (charger), 23Y ... potential measuring unit, 230Y to 232Y ... potential detection member, 30Y ... developing unit (development) Device), 31Y ... developer container, 311Y ... developer reservoir, 312Y ... recovered liquid reservoir, 313Y ... finishing Plate, 32Y ... Intermediate roller, 33Y ... Anilox roller, 34Y ... Intermediate roller cleaning blade, 35Y ... Restriction member, 36Y ... Agitation auger, 37Y ... Collection auger, 40 ... Transfer belt, 41 ... Drive roller, 42 ... Tension roller, 50Y ... primary transfer unit, 51Y ... primary transfer backup roller, 60 ... secondary transfer unit, 61 ... secondary transfer roller, 62 ... secondary transfer roller cleaning blade, 63 ... secondary transfer unit collection / storage unit, 101, 101 '... Gate roller, 102 ... Transfer material guide, 200 ... Central control unit, 201, 202 ... High voltage power supply

Claims (8)

A developer carrier that carries a liquid developer containing toner and carrier liquid and to which a development bias is applied;
A charging unit for charging the liquid developer carried on the developer carrying member;
A first potential which is a potential of the developer carrying member at a position where the liquid developer is not carried, and a potential of the developer carrying member at a position where the liquid developer is carried and charged by the charging unit. A potential measuring unit that measures the second potential,
A controller that calculates a difference between the first potential and the second potential measured by the potential measuring unit, and adjusts charging of the liquid developer based on the calculated difference. A developing device.   The developing device according to claim 1, wherein the control unit controls the developing bias to be applied to the developer carrier based on the first potential measured by the potential measuring unit. The potential measurement unit includes a potential detection member that detects a potential of the developer carrier at a position where the liquid developer of the developer carrier is carried;
When the developer carrying member is not carrying a liquid developer, the potential detecting member measures the first potential, and when the developer carrying member is carrying a liquid developer, the potential detecting member is The developing device according to claim 1, further comprising: a potential measurement control unit that measures the second potential. The potential measuring unit includes:
A first potential detecting member that measures the potential of the developer carrying member at a position where the developer carrying member does not carry the liquid developer and is charged by the charging unit;
A second potential detecting member that measures the potential of the developer carrying member at a position of the developer carrying member carrying the liquid developer;
The developing device according to claim 1, wherein the first potential is detected by the first potential detection member, and the second potential is detected by the second potential detection member. A cleaning member having a volume resistivity of 10 ³ to 10 ⁷ Ωcm for cleaning in contact with the developer carrying member;
The developing device according to claim 1, wherein the cleaning member is applied with a bias that is equal to or substantially equal to a bias that is applied to the developer carrying member. A latent image carrier on which a latent image is formed;
An exposure unit that forms the latent image on the latent image carrier;
A latent image carrier having a developer carrier that carries a liquid developer containing toner and a carrier liquid and to which a developing bias is applied; and a charging unit that charges the liquid developer carried on the developer carrier. A developing unit for developing the latent image formed on the body with a liquid developer;
A first potential which is a potential of the developer carrying member at a position where the liquid developer is not carried, and a second developer carrying member at a position where the liquid developer is carried and charged by the charging unit. A potential measuring unit for measuring the potential of
A controller that calculates a difference between the first potential and the second potential measured by the potential measuring unit and adjusts charging of the liquid developer based on the calculated difference; An image forming apparatus.   The image forming apparatus according to claim 6, wherein the control unit controls the developing bias to be applied to the developer carrying member based on the first potential measured by the potential measuring unit. Charging a liquid developer containing toner and carrier liquid carried on the developer carrying member;
A first potential which is a potential of the liquid developer carrying member at a position where the liquid developer is not carried; and a position of the developer carrying member at a position where the liquid developer is carried and charged by the charging unit. A second potential which is a potential,
Adjusting the charging of the liquid developer based on the difference between the first potential and the second potential;
An image forming method comprising developing a latent image formed on a latent image carrier with a liquid developer carried on the developer carrier.

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