JP2006243051A - Liquid developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid developing device capable of maintaining suitable printing quality regardless of the kind of a recording medium, having a simple control system and also achieving the reduction of the number of components. <P>SOLUTION: The liquid developing device 54 is equipped with: a developing roller 72 supplying liquid developer containing toner and insulating carrier liquid onto a photoreceptor drum 51 on which an electrostatic latent image is formed; a coating roller 73 supplying the liquid developer to the developing roller 72 so as to form the thin layer of the liquid developer on the surface of the developing roller 72; and a 2nd bias imparting circuit 78 imparting bias to the coating roller 73. A controller 100 controls the 2nd bias imparting circuit 78 so that the level of the bias imparted to the coating roller 73 may be changed in accordance with the kind of the recording medium to which a toner image obtained by making the electrostatic latent image on the photoreceptor drum 51 visible with the liquid developer is transferred. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid developing device employed in a copying machine, a facsimile machine, a printer, and the like.

  The liquid image forming apparatus provided with the liquid developing device is a high-grade system, and by using a liquid developer composed of fine toner and insulating carrier liquid, high quality printing equivalent to offset printing can be obtained, Also, a sufficient image density can be obtained with a small amount of toner.

  A conventional general liquid developing apparatus develops an electrostatic latent image formed on an image bearing member such as a photosensitive member (for example, a photosensitive drum) with a liquid developer in which toner is dispersed in an insulating carrier liquid. Like to do. That is, the liquid developing device includes a developing roller, a means for supplying a liquid developer to the developing roller, a developer storage tank for storing the liquid developer, and the like. Then, the liquid developer pumped up from the developer storage tank is supplied to the developing roller, and the liquid developer is supplied from the developing roller to the image carrier, and the supplied liquid developer causes the liquid developer on the image carrier. The electrostatic latent image formed on the surface is developed.

  By the way, in such a liquid developing apparatus, the liquid developer on the image carrier is directly or once temporarily applied to a recording medium (generally, paper is often used) by the action of an electric field. After being transferred to the transfer body, the toner image transferred to the intermediate transfer body is transferred. Therefore, the toner image finally transferred to the recording medium is easily affected by the material of the recording medium. That is, when the recording medium is a paper having a lot of irregularities on the surface, such as plain paper, and a high liquid absorption property, the transfer efficiency is extremely deteriorated when the amount of the insulating carrier liquid is small. Further, when the recording medium is a paper having low liquid absorbency and high smoothness such as coated paper, the toner image transferred to the recording medium is blurred (image flow) when the amount of the insulating carrier liquid is large. Cause.

In order to solve such a problem, in Japanese Patent Application Laid-Open No. 2004-228561, a recording used in a configuration in which the liquid developer in the developing container is supplied to the developing roller via the second supply roller and the first supply roller. The developer supply amount to the second supply roller is controlled by changing the developer film thickness on the first supply roller in accordance with the type of medium (paper). Further, in Patent Document 1, the peripheral speed difference between the second supply roller and the developing roller is adjusted at the same time, and the liquid developer is stretched by the peripheral speed difference, so that the film thickness of the liquid developer on the developing roller is increased. To change.
JP 2003-241520 A

  However, in Patent Document 1, in order to solve the above-described problem, the developer supply amount to the second supply roller is controlled by changing the developer film thickness on the first supply roller, and at the same time the second Since the peripheral speed difference between the supply roller and the developing roller is adjusted, the control system becomes complicated and the number of parts of the supply roller increases, resulting in an increase in cost.

  An object of the present invention is to provide a liquid developing apparatus that solves the above problems, can maintain a suitable print quality regardless of the type of recording medium, has a simple control system, and can reduce the number of components. There is to do.

  In order to solve the above problems, the invention described in claim 1 is a liquid developer carrier for supplying a liquid developer containing toner and an insulating carrier liquid to an image carrier on which an electrostatic latent image is formed. In a liquid developing apparatus comprising a supply means for supplying a liquid developer to the liquid developer carrier and forming a thin layer of the liquid developer on the surface of the liquid developer carrier, a bias is applied to the supply means. A bias applying means for applying, and a magnitude of the bias applied to the supplying means according to the type of the recording medium onto which the toner image in which the electrostatic latent image of the image carrier is visualized by the liquid developer is transferred. The gist of the present invention is a liquid developing apparatus comprising control means for controlling the bias applying means to be changed.

  According to a second aspect of the present invention, in the first aspect, the image forming apparatus further comprises selection input means for selectively inputting a type of the recording medium onto which the toner image is transferred, and the control means is based on a selection input of the recording medium of the selection input means. The bias applying means is controlled so as to change the magnitude of the bias applied to the supplying means.

  According to a third aspect of the present invention, in the first aspect, the control unit changes a magnitude of a bias applied to the supply unit according to monochrome printing or color printing and according to a type of the recording medium. The bias applying means is controlled as described above.

According to the first aspect of the present invention, when a bias is applied to the supply unit, the magnitude of the bias applied to the supply unit can be changed according to the type of the recording medium.
For example, if the recording medium is paper with low liquid absorbency and high smoothness, increasing the bias of the supply means causes more toner than the case where the bias of the supply means is reduced on the liquid developer carrier, and the insulating carrier A liquid developer having a small amount of liquid is transferred, and a liquid developer having a large amount of toner (that is, a solid component) is transferred to the image carrier. As a result, a toner image having a large amount of toner is formed on the image carrier, so that the toner image transferred to the recording medium can be free from blurring (image flow) and can have a suitable image quality, that is, printing. Quality can be maintained.

  On the other hand, when the recording medium is a paper with many irregularities on the surface, if the bias of the supply unit is reduced, the liquid developer carrier has less toner and more insulating carrier liquid than when the bias of the supply unit is increased. The liquid developer is transferred, and the liquid developer having a small amount of toner (that is, a solid component) and a large amount of the insulating carrier liquid is transferred to the image carrier. As a result, the image carrier forms a toner image with less toner and more insulating carrier liquid than when the bias of the supply means is increased. Therefore, the toner image transferred to the recording medium has more insulating carrier liquid. can do. As a result of the insulating carrier liquid of the liquid developer soaking into the recording medium more than when the bias of the supply means is increased, a suitable image quality, that is, printing quality can be maintained.

  According to the first aspect of the present invention, since it is only necessary to change the bias of the supply means in accordance with the type of the recording medium, the control system is simple, and it is not necessary to increase the number of supply rollers. There is an effect that the score can be reduced.

  According to the invention of claim 2, the bias of the supply means can be changed according to the type of the recording medium by the selection input of the recording medium of the selection input means. As a result, the effect of claim 1 can be easily achieved. realizable.

  According to a third aspect of the present invention, the control means applies the bias so as to change the magnitude of the bias applied to the supply means according to monochrome printing or color printing and according to the type of the recording medium. A suitable print quality can be obtained by controlling the means.

  Hereinafter, an embodiment in which a liquid developing apparatus of the present invention is applied to a liquid developing apparatus of a liquid image forming apparatus will be described with reference to FIGS. The liquid image forming apparatus can be used in a copying machine, a facsimile machine, a printer, and the like.

  As shown in FIG. 2, the liquid image forming apparatus includes a sheet feeding unit 1, a vertical conveyance path 2, a registration roller pair 3, a belt conveyance unit 4, a first image forming unit 5, a second image forming unit 6, and a second image forming unit 6. The image forming unit 7 includes a third image forming unit 7, a fourth image forming unit 8, a secondary transfer unit 9, a fixing unit 10, a discharge conveyance path 11, a discharge tray 14, and the like.

  The paper feed means 1 includes a paper feed cassette 1a and a pickup roller 1b, and transports the paper P in the paper feed cassette 1a to the vertical transport path 2 by the pickup roller 1b. The vertical conveyance path 2 conveys the conveyed paper P to the secondary transfer unit 9 via the registration roller pair 3. The paper P corresponds to a recording medium.

  The belt conveying 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 maintains an appropriate tension by the tension roller 44. In this state, the driving roller 41 receives driving force from a driving motor (not shown), and the outer peripheral speed of the photosensitive drum 51 as an image carrier in each image forming unit and the intermediate transfer belt 43 of the belt conveying unit 4. It is driven so that the outer peripheral speed is constant. The intermediate transfer belt 43 corresponds to an intermediate transfer member.

  The first to fourth image forming units 5 to 8 shown in FIG. 2 are for black (BK), magenta (M), cyan (C), and yellow (Y) from the left side in the figure, and all have substantially the same configuration. Unit. Here, for convenience of explanation, the configuration of the first image forming means 5 on the left side in the drawing will be described with reference to FIG. In other image forming units, the same reference numerals are given to the same components as those of the first image forming unit 5.

  The first image forming unit 5 includes a photosensitive drum 51, a main charging device 52, an LPH (LED PRINT HEAD) 53, a liquid developing device 54, a primary transfer unit 55, a cleaning device 56, and a charge eliminating lamp 57. By assembling it into the completed casing, it becomes a single unit and is attached to an apparatus main body (not shown).

  The photosensitive drum 51 is an amorphous silicon drum and is charged by the main charging device 52 so that the dark potential at the developing position is about 600V. The LPH 53 irradiates the charged surface of the photosensitive drum 51 with light according to image information, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 51.

  The liquid developing device 54 stirs and mixes a liquid developer composed of toner and an insulating carrier liquid (hereinafter simply referred to as a carrier liquid) to a predetermined concentration, and the developing roller 72 sensitizes the liquid developer. A toner image is formed (developed) on the photosensitive drum 51 by applying to the electrostatic latent image of the portion irradiated with light of the photosensitive drum 51. The dark potential of the photosensitive drum 51 is set to 600V, the developing bias is set to 300V, and the post-exposure potential (bright potential) is set to 20V. That is, the dark potential corresponds to the white portion of the image, the post-exposure potential (bright potential) corresponds to the black portion of the image, and this difference is a so-called contrast potential. The toner image developed (developed) of 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 55. The primary transfer means 55 uses a transfer roller in this embodiment, and a voltage having a polarity opposite to the surface potential of the photosensitive drum 51 is set in a range of −200 to −1300 V and applied. Yes.

Here, the primary transfer unit 55 and the contact / separation mechanism S will be described.
The primary transfer means 55 is disposed so as to be movable between a transfer position and a retracted position separated from the transfer position. The transfer position is a position where the primary transfer unit 55 is pressed against the photosensitive drum 51 via the intermediate transfer belt 43. The retracted position is a position where the primary transfer means 55 has moved a predetermined amount from the transfer position in a direction away from the photosensitive drum 51. The intermediate transfer belt 43 maintains an appropriate tension by the tension roller 44, and is separated from the photosensitive drum 51 by the tension when the primary transfer means 55 is released.

  As shown in FIG. 1, the primary transfer means 55 is supported at the tip of an arm 110 that is swingably attached to a frame (not shown) of the apparatus main body. The base end of the arm 110 has a rotating shaft 111 that is swingably attached to the frame of the liquid image forming apparatus.

  The rotating shaft 111 is operatively connected to a primary transfer means drive motor (not shown), and the primary transfer means 55 is moved from the retracted position via the arm 110 by the rotation of the primary transfer means drive motor under the control of the control device 100. Movement between transfer positions is possible. Further, a tension coil spring 112 is attached to the arm 110 as an urging means attached to the frame of the apparatus main body. When a primary transfer means drive motor (not shown) is not driven to rotate, the tension coil spring 112 is not driven. Thus, the primary transfer means 55 can be positioned from the transfer position to the retracted position.

  The primary transfer means drive motor (not shown), the arm 110, the rotating shaft 111, and the tension coil spring 112 constitute a contact / separation mechanism S that makes the intermediate transfer belt 43 contact or separate from the photosensitive drum 51.

  The contact / separation mechanism S of the first to fourth image forming units 5 to 8 performs primary transfer of the first to fourth image forming units 5 to 8 under the control of the control device 100 described later in the full color image forming mode. A means drive motor (not shown) is driven to position each primary transfer means 55 at the transfer position.

  In the monochrome image forming mode, the primary transfer unit driving motor (not shown) of the first image forming unit 5 is driven to place the primary transfer unit 55 at the transfer position, and the second to fourth units. The primary transfer unit drive motor (not shown) of the image forming units 6 to 8 is not driven, and the primary transfer unit 55 is positioned at the retracted position. When the power of the apparatus main body is turned off, the primary transfer unit drive motors (not shown) of all the image forming units are not driven and all the primary transfer units 55 are positioned at the retracted position. Has been.

  Returning now, the transfer residual liquid developer that has not been transferred onto the photosensitive drum 51 is scraped off by the cleaning device 56 in the next process. The photosensitive drum 51 is neutralized by a neutralizing lamp 57 so as to reduce the residual potential on the surface and make it uniform, and thereafter, it is prepared for the next series of processes. The potential setting for image formation in this manner varies depending on the characteristics of the photosensitive drum 51, the toner performance, and the environment. The liquid image forming apparatus develops images corresponding to magenta, cyan, and yellow on the photosensitive drum by the second to fourth image forming units 6 to 8 in the same manner as the first image forming unit 5. A full-color image is formed by sequentially repeating the transfer onto the intermediate transfer belt 43 without transfer.

  Returning to FIG. 2 again, image formation after transfer will be described. In the present embodiment, the secondary transfer unit 9 includes a secondary transfer roller. The secondary transfer unit 9 is disposed at a secondary transfer position on the vertical conveyance path 2. The secondary transfer position is a position where the secondary transfer unit 9 faces the driving roller 41 and is pressed against the intermediate transfer belt 43. A secondary transfer bias is applied to the secondary transfer unit 9, and the paper P conveyed by the secondary transfer unit 9 from the intermediate transfer belt 43 through the vertical conveyance path 2 and the registration roller pair 3. A full-color image is secondarily transferred to the image. Thereafter, the paper P onto which the full color image has been secondarily transferred is separated from the intermediate transfer belt 43 and conveyed to the fixing unit 10. The fixing unit 10 includes a first fixing roller 10a and a second fixing roller 10b. Each fixing roller includes a fixing heater (not shown), and the identification fixing heater is controlled to a predetermined temperature necessary for fixing. Due to this temperature, a full-color image is fixed on the paper P that is pressed and passed by both rollers. The paper P is discharged to the discharge tray 14 via the discharge conveyance path 11 after being fixed by the fixing unit 10.

  The intermediate transfer cleaning unit 12 includes an intermediate transfer cleaning roller 12a, an intermediate transfer cleaning blade 12b, and the like in a cleaning case. The intermediate transfer cleaning roller 12a 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 by a drive motor (not shown). The intermediate transfer cleaning blade 12b counter-contacts the intermediate transfer belt 43 on the downstream side from the position of the intermediate transfer cleaning roller 12a in the moving direction of the intermediate transfer belt 43, thereby developing the transfer residual liquid on the intermediate transfer belt 43. The agent is recovered and removed.

Next, a specific configuration of the liquid developing device 54 will be described with reference to FIG.
The liquid developing device 54 according to this embodiment includes a liquid developer storage container 71 that stores the liquid developer 70. The liquid developer storage container 71 is provided with a developing roller 72 as a liquid developer carrier, a coating roller 73 as a supply means, a scooping roller 74, a doctor blade 75, and a developing cleaning blade 76. The developing roller 72, the application roller 73, and the scooping roller 74 are rotationally driven by a drive motor (both not shown) through a drive transmission mechanism including a gear train and the like.

The liquid developer 70 is adjusted so that precharged toner is dispersed at a high concentration in a carrier liquid which is an insulating, ie, electrically neutral, solvent such as silicon oil.
The toner contains a colorant, a resin (binder), and, if necessary, a charge control agent. The resin (binder) is adsorbed on the colorant and is well dispersed in the carrier liquid to give a positive or negative charge to the adsorbed colorant. In this embodiment, the toner is charged to a positive potential (positive) by the resin (binder). Examples of the carrier liquid include isoparaffinic solvents (for example, Isopar G (manufactured by Exxon)), higher fatty acid esters, silicon oil, and the like, but are preferably non-volatile. A part of the pumping roller 74 is immersed in the liquid developer 70, and the pumped liquid developer 70 is applied to the application roller 73.

  The amount of the liquid developer applied on the application roller 73 is measured by the doctor blade 75. Then, the application roller 73 applies a measured liquid developer 70 onto the development roller 72, thereby forming a thin layer of the liquid developer 70 on the development roller 72. In the developing area on the photosensitive drum 51, the latent image is developed and visualized by the liquid developer 70. Further, after development, the liquid developer 70 remaining on the developing roller 72 is removed from the developing roller 72 by the developing cleaning blade 76 and returned to the liquid developer storage container 71.

  The first bias applying circuit 77 is a circuit that applies a developing bias to the developing roller 72 based on a control command of the control device 100. In the present embodiment, a developing roller bias of 300 V is applied by the first bias applying circuit 77 based on a control command of the control device 100.

  The second bias applying circuit 78 as a bias applying unit is a circuit that applies a supply roller bias to the application roller 73 based on a control command of the control device 100. In the present embodiment, different sizes of bias can be applied to the application roller 73 based on the control command of the control device 100.

  A control device 100 as a control unit includes a CPU, a ROM, and a RAM (both not shown), and controls various devices of the liquid image forming apparatus of the present embodiment. Although not shown, the operation panel 101 is provided with a recording medium selection key and a print mode selection key. The recording medium selection key is used to select the type of paper P as a recording medium. The print mode selection key is used to select a monochrome image formation mode and a full color image formation mode. The operation panel 101 corresponds to selection input means for selecting and inputting the type of recording medium onto which the toner image is transferred.

  Based on the selection input of the recording medium selection key and the mode selection input of the print mode selection key provided on the operation panel 101, the control device 100 performs the following operations on the first bias application circuit 77 and the second bias application circuit 78. Each outputs a control command.

In the present embodiment, the control of the control device 100 in the case of full color image formation and monochrome image formation will be described.
In the case of full-color image formation, particularly when a non-volatile carrier liquid is used, transfer of the carrier liquid onto the intermediate transfer belt 43 is increased as compared with monochrome image formation. In the case of a volatile carrier liquid, it volatilizes after transfer to the intermediate transfer belt, and the amount is slightly reduced. However, compared to monochrome image formation, full color image formation is more suitable for intermediate transfer of carrier liquid. It is the same that the transfer onto the belt 43 increases.

  This is because in the present embodiment, monochrome image formation is performed by the first image forming unit 5, and image formation is not performed by the second to fourth image forming units 6 to 8. That is, in the case of monochrome image formation, in the second to fourth image forming units 6 to 8, the primary transfer unit 55 is located at the retracted position, and the intermediate transfer belt 43 is separated from the photosensitive drum 51. For this reason, in the second to fourth image forming units 6 to 8, the carrier liquid is not transferred onto the intermediate transfer belt 43. Conversely, in the case of full-color image formation, unlike the case of monochrome image formation, since primary transfer is performed in each image forming unit, the carrier liquid on the intermediate transfer belt 43 increases, and as a result, When the secondary transfer is performed on the paper P, the carrier liquid also increases. Therefore, in this state, the carrier liquid increases, and in the case of full-color image formation, the image quality (that is, print quality) is impaired.

  For this reason, the total amount of the carrier liquid primarily transferred onto the intermediate transfer belt 43 in the case of full-color image formation is the same as the amount of the carrier liquid primarily transferred onto the intermediate transfer belt 43 in the monochrome image formation mode. Alternatively, it is preferable that they are substantially the same because the image quality for the same type of recording medium is the same or similar in both modes (see the following formula).

Cb1 + Cc + Cm + Cy = (or≈) Cb2
Note that Cb1, Cc, Cm, and Cy are amounts of carrier liquid of the first to fourth image forming units 5 to 8 that are primarily transferred onto the intermediate transfer belt 43 in the case of full-color image formation. Cb2 is the amount of carrier liquid of the first image forming means 5 that is primarily transferred onto the intermediate transfer belt 43 in the case of monochrome image formation. Cb1, Cc, Cm, and Cy are values smaller than Cb2.

  Here, when the image is formed, the change in the amount of toner or carrier liquid conveyed from the application roller 73 to the development roller 72 changes the supply roller bias applied to the application roller 73 by the second bias applying circuit 78. Is possible. Accordingly, if the amount of toner or carrier liquid conveyed from the application roller 73 to the developing roller 72 changes, the amount of toner or carrier liquid of the first image forming means 5 that is primarily transferred onto the intermediate transfer belt 43 also changes. To do.

  In this embodiment, each image forming unit in the full-color image forming mode is configured so that the total amount of Cb1, Cc, Cm, and Cy in the full-color image forming mode is substantially the same as Cb2 in the monochrome image forming mode. The supply roller bias of the second bias applying circuit 78 is set. The supply roller bias is a value equal to or higher than the developing roller bias, and is a value equal to or higher than 300 V in the present embodiment.

  For each type of recording medium, the setting value of the supply roller bias of the second bias applying circuit 78 of each image forming means in the full color image forming mode can be obtained in advance by testing and stored as control information in a ROM (not shown). ing. Note that the setting value of the supply roller bias of the first image forming unit 5 at the time of monochrome image formation is smaller than the setting value of the supply roller bias in the full color image forming mode for each type of recording medium (paper). Is set.

  As the supply roller bias becomes larger than the developing roller bias, more toner is conveyed from the coating roller 73 to the developing roller 72, and conversely, the amount of carrier liquid is reduced. As a result, a large amount of toner that is a solid component is conveyed onto the photosensitive drum 51, and the amount of carrier liquid that is a liquid component is relatively reduced.

  On the other hand, the closer the supply roller bias is to the value of the developing roller bias, the less toner is transferred from the coating roller 73 to the developing roller 72, and the more the amount of carrier liquid is. As a result, a small amount of toner, which is a solid component, is transported onto the photosensitive drum 51, and the transport amount of carrier liquid, which is a liquid component, is relatively large.

Now, the operation of the liquid image forming apparatus configured as described above will be described.
Hereinafter, a case where the full color image forming mode is selected will be described.
First, when forming a full-color image, the type of recording medium to be used (the type of paper P) is selected and input in advance using the recording medium selection key on the operation panel 101, and the full-color image forming mode is selected and input using the printing mode selection key.

  The control device 100 controls the control target based on the selection input result. That is, the photosensitive drums 51 of the first to fourth image forming units 5 to 8 are uniformly charged to 600 V by the main charging device 52.

  Then, when each LPH 53 of each image forming unit irradiates the charged surface of each photosensitive drum 51 with light according to image information sent from the control device 100, the charge of the portion exposed to light is changed. It escapes and becomes a post-exposure potential (bright potential) of 20 V, and an electrostatic latent image is formed on the surface of the photosensitive drum 51.

  On the other hand, in the liquid developing device 54, the liquid developer 70 is pumped up by the scooping roller 74 and applied to the coating roller 73, and the coating amount is measured on the coating roller 73 by the doctor blade 75. Further, the supply roller bias is applied to the application roller 73 by the second bias applying circuit 78 based on a control command described later of the control device 100. Then, the application roller 73 applies a measured liquid developer 70 onto the development roller 72, thereby forming a thin layer of the liquid developer 70 on the development roller 72.

  In the developing roller 72, the developing roller bias is applied to 300 V by the first bias applying circuit 77 based on the control command of the control device 100. Then, due to the relationship between the developing roller bias and the post-exposure potential (bright potential) and dark potential on the photosensitive drum 51, the developing region on the photosensitive drum 51 is statically covered with a thin layer of the liquid developer 70. The electrostatic latent image is developed to obtain a toner image.

Further, after development, the liquid developer 70 remaining on the developing roller 72 is removed from the developing roller 72 by the developing cleaning blade 76 and returned to the liquid developer storage container 71.
On the other hand, the toner image on the photosensitive drum 51 is primarily transferred onto the intermediate transfer belt 43 by the primary transfer unit 55. In the case of full-color image formation, the liquid image forming apparatus develops the toner images corresponding to magenta, cyan, and yellow on the photosensitive drum as described above by each image forming unit, and sequentially repeats it on the intermediate transfer belt 43. A full color image is formed by transferring without deviation.

  The toner image on the intermediate transfer belt 43 is secondarily transferred by the secondary transfer unit 9 from the intermediate transfer belt 43 to the paper P conveyed through the vertical conveyance path 2 and the registration roller pair 3. Thereafter, the paper P onto which the full color image has been secondarily transferred is separated from the intermediate transfer belt 43 and conveyed to the fixing unit 10. The paper P is pressed against both rollers of the fixing unit 10 to perform a fixing process for a full-color image, and is discharged to the discharge tray 14 via the discharge conveyance path 11.

  By the way, in this embodiment, the control device 100 selects and inputs the type of recording medium to be used (the type of paper P) with the recording medium selection key of the operation panel 101, and selects the full-color image forming mode with the printing mode selection key. Have been entered.

  Based on the type of recording medium selected and input and the full-color image forming mode, the control device 100 reads out control information stored in the ROM, and based on this control information, the second bias applying circuit of each image forming means. 78 is controlled. That is, in each liquid developing device 54, the supply roller bias corresponding to the type of recording medium selected (type of paper P) is applied to the coating roller 73 by the second bias applying circuit 78 in the full color image forming mode. Is applied.

Here, when the type of the recording medium selected and input is coated paper, 450 V is applied to the application roller 73 as the supply roller bias.
In this case, since the supply roller bias applied to the application roller 73 is larger than the type of recording medium selected and input as compared with plain paper described later, the toner conveyed from the application roller 73 to the development roller 72 is larger. On the contrary, the amount of carrier liquid decreases. The layer thickness of the thin layer formed on the developing roller 72 is measured by the doctor blade 75 on the coating roller 73 and is constant, and thus is a solid component with respect to the photosensitive drum 51. A large amount of toner is transported, and the transport amount of the carrier liquid, which is a liquid component, is relatively small.

  Then, the toner image formed by developing with the liquid developer conveyed from the developing roller 72 to the photosensitive drum 51 is primary-transferred onto the intermediate transfer belt 43 including the toner and the carrier liquid, and the secondary transfer is performed. By means 9, the secondary transfer is performed on the paper P from the intermediate transfer belt 43.

  Therefore, when a coated paper having low liquid absorbency and high smoothness is selectively input as a recording medium, the primary and secondary transferred toner images have many solid components and liquid components. Fewer toner images. As a result, when coated paper is used, bleeding (image flow) can be eliminated, and a suitable image quality, that is, print quality can be obtained.

Here, when the type of the recording medium selected and input is plain paper, 350 V is applied to the application roller 73 as the supply roller bias.
In this case, since the supply roller bias applied to the application roller 73 is smaller than the type of the recording medium selected and input as compared with the above-described coated paper, the toner conveyed from the application roller 73 to the development roller 72 is less. On the contrary, the amount of carrier liquid increases. The layer thickness of the thin layer formed on the developing roller 72 is measured by the doctor blade 75 on the coating roller 73 and is constant, and thus is a solid component with respect to the photosensitive drum 51. The toner is transported in a small amount, and the transport amount of the carrier liquid which is a liquid component is relatively increased.

  Then, the toner image formed by developing with the liquid developer conveyed from the developing roller 72 to the photosensitive drum 51 is primary-transferred onto the intermediate transfer belt 43 including the toner and the carrier liquid, and the secondary transfer is performed. By means 9, the secondary transfer is performed on the paper P from the intermediate transfer belt 43.

  Therefore, when plain paper, which has a lot of irregularities on the surface and has high liquid absorption, is selected and input as the recording medium, the toner images that are primary and secondary transferred have few solid components and liquid components. This results in a toner image with a large amount of toner.

  Therefore, by impregnating the plain paper with a large amount of carrier liquid, the toner can reach the concave portion of the plain paper, and as a result, there is no transfer failure that does not allow the toner to reach the concave portion, and the transfer efficiency. The image quality, that is, the print quality can be maintained.

  Next, a case where the monochrome image forming mode is selected and input will be described. The monochrome image forming mode will be described with a focus on differences from the full-color image forming mode.

  First, when forming a monochrome image, the type of recording medium to be used (the type of paper P) is selected and input in advance using the recording medium selection key on the operation panel 101, and the monochrome image forming mode is selected and input using the print mode selection key. And the control apparatus 100 controls a control object based on this selection input result.

  In this case, the control device 100 drives the primary transfer unit drive motor (not shown) of the first image forming unit 5 to position the primary transfer unit 55 at the transfer position, and the remaining image forming units of the other image forming units. Unlike the full-color image forming mode, the primary transfer unit driving motor (not shown) is not driven and the primary transfer unit 55 is positioned at the retracted position.

  When coated paper is selected and input, the first image forming unit 5 outputs a control command based on the control information stored in the ROM from the control device 100 to the second bias applying circuit 78, and the second bias. The application circuit 78 is different in that a supply roller bias of 400 V is applied to the application roller 73.

  Therefore, in the monochrome image forming mode, in the liquid developing device 54, the supply roller bias is made smaller at the developing roller 72 than at the time when the coated paper is selected and input in the full color image forming mode. For this reason, the carrier liquid, which is a liquid component transported onto the photosensitive drum 51 from the application roller 73 via the developing roller 72, is transported more than in the color image forming mode, and transport of toner that is a solid component is performed. The amount is relatively small.

As a result, the toner image on the photoconductive drum 51 is primarily transferred onto the intermediate transfer belt 43 including the toner and the carrier liquid, and is secondarily transferred onto the paper P by the secondary transfer unit 9.
Accordingly, when a coated paper having a low liquid absorbency and a high smoothness is selected and input as a recording medium, the second bias applying circuit 78 is set in the second color application mode in accordance with a control command from the control device 100 in the full color image forming mode. A supply roller bias having a small value is applied to the application roller 73. For this reason, the primary and secondary transferred toner images are toner images with more liquid components and fewer solid components than in the case of coated paper in the full-color image forming mode. However, as will be described later, the toner image has less liquid components and more solid components than the case of plain paper in the monochrome image forming mode. As a result, even in the monochrome image forming mode, when coated paper is used, blurring (image flow) can be eliminated, and favorable image quality, that is, print quality can be obtained.

  When plain paper is selected and input, the first image forming unit 5 outputs a control command based on the control information stored in the ROM from the control device 100 to the second bias applying circuit 78, and the second bias. The application circuit 78 is different in that a supply roller bias of 300 V is applied to the application roller 73.

  In the monochrome image forming mode, when plain paper is selected and input, the supply roller bias is set to a smaller value than when coated paper is selected and input. For this reason, in the monochrome image forming mode, as compared with the case where the coated paper is selected and input, the toner as the solid component is transported less and the carrier liquid is transported more.

  For this reason, in the monochrome image forming mode, the carrier liquid can be soaked in the plain paper so that the toner can reach the concave portion on the surface of the plain paper, and as a result, the toner does not reach the concave portion. Therefore, the transfer efficiency can be increased, and the image quality, that is, the print quality can be maintained.

  In the present embodiment, in each of the monochrome image forming mode and the full-color image forming mode, the amount of the carrier liquid in the first to fourth image forming units 5 to 8 is Cb1 + Cc + Cm + Cy≈Cb2. The second bias applying circuit 78 applies a supply roller bias to the application roller 73.

  That is, by changing the supply roller bias applied to the application roller 73 in accordance with both the monochrome image formation mode and the full color image formation mode (in accordance with monochrome printing and color printing), the same recording medium can be obtained. Image quality (that is, print quality) can be obtained.

  Furthermore, also in monochrome printing and color printing, there is an effect that a suitable image quality (that is, print quality) can be always obtained by changing the supply roller bias to the application roller 73 according to the type of the recording medium. .

The present invention is not limited to the above embodiment, and may be modified to the following configuration.
In the above embodiment, the scooping roller 74 is provided, but a scooping pump may be used instead of the scooping roller 74.

1 is a schematic view of a liquid developing apparatus according to an embodiment embodying the present invention. 1 is a schematic view of a liquid image forming apparatus to which a liquid developing device of the present invention is applied.

Explanation of symbols

51. Photosensitive drum (image carrier)
54 ... Liquid developing device 72 ... Developing roller (liquid developer carrier)
73 ... Application roller (supply means)
78 ... Second bias applying circuit (bias applying means)
100: Control device (control means)
101 ... Operation panel (selection input means)

Claims (3)

A liquid developer carrier that supplies a liquid developer containing toner and an insulating carrier liquid to an image carrier on which an electrostatic latent image is formed; a liquid developer that is supplied to the liquid developer carrier; In a liquid developing apparatus comprising a supply means for forming a thin layer of the liquid developer on the surface of the developer carrying member,
Bias applying means for applying a bias to the supply means;
The bias application is performed so as to change the magnitude of the bias applied to the supply unit according to the type of the recording medium onto which the toner image in which the electrostatic latent image of the image carrier is visualized by the liquid developer is transferred. A liquid developing apparatus comprising control means for controlling the means. A selection input means for selecting and inputting the type of recording medium onto which the toner image is transferred;
2. The bias applying unit according to claim 1, wherein the control unit controls the bias applying unit to change a magnitude of a bias applied to the supply unit based on a selection input of a recording medium of the selection input unit. Liquid developing device.   The control means controls the bias applying means so as to change the magnitude of the bias applied to the supplying means according to monochrome printing or color printing and according to the type of the recording medium. The liquid developing device according to claim 1.

Images