JP2006301503A - Image forming apparatus and method for adjusting transferability of image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently maintain secondary transferability and fixing ability which have trade-off relation and to restrain the discharge of carrier liquid by keeping the proper amount of content of carrier liquid in a toner image which largely affects the secondary transferability and the fixing ability even when an image forming condition is varied. <P>SOLUTION: A system control part 65 controls to primarily transfer an image pattern for detection to an intermediate transfer roller 7, to apply charge, to recover the carrier liquid, to detect concentration before secondary transfer, to secondarily transfer the image to transfer material, to detect the density of a toner image remaining after the secondary transfer, to decide what state is obtained, a state A, a state B or a state C by using a charge amount variable part 66, to set a current applying part 41 so that a discharge current may be increased to attain the state B when the state A is obtained, not to change the discharge current when the state B is obtained, and to set the current applying part 41 so that the discharge current may be decreased to attain the state B when the state C is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a transferability adjusting method for the image forming apparatus, and more particularly to a technique for improving the transferability of secondary transfer in the case of using a high-viscosity and high-concentration liquid developer.

  In an image forming apparatus such as a copying machine, a facsimile machine, or a printer, a latent image carrier (hereinafter referred to as liquid toner or toner) is dispersed by a liquid developer (hereinafter referred to as liquid toner or toner) in which toner is dispersed in an insulating liquid (hereinafter referred to as carrier liquid). The latent image formed on the photosensitive member is developed to form a visualized image (hereinafter referred to as a toner image). The toner image is primarily transferred onto the intermediate transfer member, and then transferred onto the recording medium. An electrophotographic apparatus using a liquid toner that is transferred to form an image is widely and generally used.

  In the electrophotographic apparatus using the liquid toner described above, a volatile or non-volatile carrier liquid is used as the carrier liquid for the liquid toner. When a volatile carrier liquid is used, the carrier liquid is volatilized and removed from the toner image by heating at the time of fixing, but a hydrocarbon-based solvent is usually used as the volatile carrier liquid. In view of the above, it is necessary to recover the volatilized solvent so as not to go out of the apparatus, and a large-scale recovery apparatus is required.

  On the other hand, in consideration of the influence on the environment, an image forming apparatus using liquid toner using a non-volatile carrier liquid that does not contain a component that volatilizes in the atmosphere has been proposed. In this image forming apparatus, instead of volatilizing and collecting the carrier liquid, a carrier liquid removing unit is provided to remove the non-volatile carrier liquid from the toner image portion and the non-image portion and collect it to adhere to the transfer material. Therefore, a method of reducing the amount discharged to the outside of the apparatus as much as possible is taken.

  In addition, the fixability of the toner image on the transfer material largely depends on the content ratio of the carrier liquid in the toner image, and the fixability should be reduced by reducing the carrier liquid content ratio, that is, reducing the amount of the carrier liquid in the toner layer as much as possible. Can be improved. This is because when a non-volatile carrier liquid is included in the toner image on the transfer material more than necessary, the toner resin is pressed and melted by the image fixing means composed of a pair of heat rollers. This is presumably because the carrier liquid present between the particles hinders the cohesive force and adhesive force acting between the toner resins, so that sufficient fixability cannot be obtained.

  Patent Document 1 includes a particle aggregating means for aggregating toner particles applied on a liquid toner carrier by an electric action, and a control means for controlling the strength of the electric action. There has been proposed a wet-type image forming apparatus that controls the strength of the electric action in accordance with the fraction and the electrical characteristics of the liquid toner. According to this patent document 1, the liquid toner coating film formed on the developing roller is given a charge to the toner particles, and an electric field is applied to agglomerate the liquid toner coating film. The carrier liquid can be removed while preventing the background fog and toner from being unevenly distributed and crushed.

  Patent Document 2 discloses a wet development in which at least one removal member for removing excess toner after development on the latent image carrier is provided on the downstream side of the surface of the liquid toner carrier in the moving direction of the latent image carrier. A device has been proposed. According to Patent Document 2, surplus carrier liquid can be removed from the latent image carrier and reused. As a result, it is possible to prevent the carrier liquid from being discharged outside the apparatus and cause an increase in printing cost, and it is possible to prevent deterioration of the fixability of the toner image due to the presence of excess carrier liquid in the toner layer.

  However, in the case of an image forming apparatus that uses an electrostatic transfer method for transferring from an intermediate transfer member to a transfer material, the carrier liquid removing means proposed in Patent Document 1 and Patent Document 2 can be used in the development process and the transfer process. If the removal of the carrier liquid from the liquid toner is repeated, the carrier liquid content in the toner layer on the intermediate transfer member is reduced, so that the secondary transfer rate to the transfer material is deteriorated. When the liquid toner has a considerably high solid content due to the removal of the carrier liquid, it becomes difficult to maintain the charging characteristics of the toner particles due to the lack of the carrier liquid, and the mobility of the toner particles due to the transfer electric field decreases, This is probably because transferability to the transfer material cannot be obtained sufficiently.

  As described above, the content of the carrier liquid in the toner image formed on the transfer material greatly affects the secondary transferability, so that the carrier liquid cannot be removed more than necessary and adheres to the transfer material. As a result, the amount of the carrier liquid consumed increases, resulting in an increase in printing cost, and further adversely affecting the image fixing property.

  The method of transferring the toner layer by compressing the toner layer with heating and pressurizing means and removing the carrier liquid from the toner layer to make the solid content ratio very high, and melting or semi-melting with heat is a transfer material. On the other hand, it is necessary to heat the intermediate transfer roller 7 and its peripheral portion while improving the transferability to the heat transfer, which is disadvantageous in increasing the consumption of heat energy and increasing the process speed.

JP 2000-214688 A JP 2001-228717 A

  In the unpublished Japanese Patent Application No. 2004-208019, the present inventors have proposed an image forming apparatus that suppresses the discharge of the carrier liquid while ensuring the secondary transfer property and the fixing property. However, it is difficult to avoid fluctuations in the viscosity and electrical characteristics of liquid toner depending on the surrounding environment, and the state after development in the developing unit (hereinafter referred to as “development”) due to change with time and fluctuation range of toner density. Therefore, there is a need for an image forming apparatus that suppresses the discharge of the carrier liquid while ensuring the secondary transfer property and the fixing property even if the image forming condition changes.

  The present invention maintains a proper amount of carrier liquid content in a toner image that greatly affects secondary transferability and fixability even when image forming conditions fluctuate. It is an object of the present invention to provide an image forming apparatus and a transferability adjusting method for an image forming apparatus that can maintain good image quality and fixing property and suppress discharge of a carrier liquid.

  According to a first image forming apparatus of the present invention, a latent image carrier and a latent image on the latent image carrier are developed using a high-viscosity high-concentration liquid developer in which toner is dispersed in a carrier liquid. An image forming apparatus comprising: a developing device that forms a toner image; an intermediate transfer member on which a toner image is primarily transferred from a latent image carrier; and a secondary transfer portion that secondarily transfers a charged toner image onto a transfer material. A charge applying unit configured to apply a charge to the toner image formed on the intermediate transfer member; a density detecting unit configured to detect a density of the toner image provided with the charge; and based on the detected density of the toner image. Charge amount varying means for varying the amount of charge imparted to the charge imparting means.

  According to a second image forming apparatus of the present invention, in the first image forming apparatus, the density detecting unit includes a pre-transfer density detecting unit that detects the density of the toner image to which the charge is applied before the secondary transfer, And a post-transfer density detecting means for detecting the density of residual toner in the toner image after the transfer.

  According to a third image forming apparatus of the present invention, in the second image forming apparatus, a carrier liquid recovery unit that recovers a carrier liquid from a toner image to which electric charges have been applied before secondary transfer is provided.

  According to a fourth image forming apparatus of the present invention, in the third image forming apparatus, the carrier liquid recovery means contacts the toner image and recovers the carrier liquid, and the carrier liquid recovery member is used as the toner image. A carrier liquid collecting member contacting / separating means for contacting / separating, and the charge amount varying means contacts / separates the carrier liquid collecting member to / from the intermediate transfer member by the carrier liquid collecting member contacting / separating means based on the detected toner image density. Let

  According to a fifth image forming apparatus of the present invention, in the third image forming apparatus, the carrier liquid recovery means contacts the toner image and recovers the carrier liquid, and the carrier liquid recovery member is used as the toner image. A carrier liquid collecting member contacting / separating means for contacting and separating, and storing a transfer material for bringing the carrier liquid collecting member into contact with the toner image and a transfer material for separating the carrier liquid collecting member from the toner image. When forming an image on a transfer material in which the member is brought into contact with the toner image, the carrier liquid collecting member is brought into contact with the toner image by the carrier liquid collecting member contacting / separating means, and the carrier liquid collecting member is separated from the toner image. When forming an image, the carrier liquid recovery means is separated from the toner image by the carrier liquid recovery member contacting / separating means.

  According to a sixth image forming apparatus of the present invention, in any one of the third to fifth image forming apparatuses, the charge amount varying unit is configured to charge the toner when the density of the toner image before the secondary transfer is lower than the threshold value. When the amount of charge applied from the applying unit is increased, and the density of the toner image before the secondary transfer is higher than the threshold value and the density of the toner image after the secondary transfer is higher than the threshold value, the charge applying unit If the toner image density before secondary transfer is higher than the threshold value and the toner image density after secondary transfer is lower than the threshold value, the charge is applied from the charge application unit. To maintain the amount of charge.

  According to a seventh image forming apparatus of the present invention, in any one of the first to sixth image forming apparatuses, the charge amount varying unit varies the charge amount based on the density of the toner image formed with the intermediate density pattern. To do.

  According to an eighth image forming apparatus of the present invention, in any one of the first to seventh image forming apparatuses, the charge applying unit includes a non-contact discharge member that discharges toward the toner image without contacting the toner image; Current applying means for varying the discharge current of the non-contact discharge member, and the charge amount varying means adjusts the charge amount by varying the discharge current in the current applying means.

  According to a ninth image forming apparatus of the present invention, in any one of the first to seventh image forming apparatuses, the charge applying unit includes a contact discharge member that contacts the toner image and discharges toward the toner image, and a contact discharge. Current applying means for changing the discharge current of the member, and the charge amount changing means adjusts the charge amount by causing the current applying means to change the discharge current.

  According to a tenth image forming apparatus of the present invention, in the ninth image forming apparatus, the contact discharge member has a surface moving body that moves the surface endlessly at a speed substantially equal to the surface moving speed of the intermediate transfer body.

  According to an eleventh image forming apparatus of the present invention, in the ninth or tenth image forming apparatus, the charge applying unit has a contact discharge member contacting / separating unit for contacting and separating the contact discharge member from the intermediate transfer member.

  According to a twelfth image forming apparatus of the present invention, in any of the ninth to eleventh image forming apparatuses, the charge applying unit has a cleaning unit for cleaning the surface of the contact discharge member, and the intermediate transfer is performed by the contact discharge member. Collect the carrier fluid on the body.

  According to the transferability adjusting method of the image forming apparatus of the present invention, a latent image carrier and a latent image on the latent image carrier are developed using a high-viscosity and high-concentration liquid developer in which toner is dispersed in a carrier liquid. A developing device for forming a toner image; an intermediate transfer member for primary transfer of the toner image from the latent image carrier; a charge applying means for applying a charge to the toner image formed on the intermediate transfer member; Transferability adjusting method for image forming apparatus, comprising: carrier liquid collecting means for collecting carrier liquid from secondary toner image before secondary transfer; and secondary transfer portion for secondary transfer of charged toner image to transfer material Then, a latent image having a detection image pattern is formed on the latent image carrier, and the latent image on the latent image carrier is developed using a high-viscosity and high-concentration liquid developer in which toner is dispersed in a carrier liquid. To form a toner image of the detection image pattern and The toner image for detection is primarily transferred from the carrier to the intermediate transfer member, the charge is applied to the detection toner image formed on the intermediate transfer member, and the carrier is applied from the detection toner image to which the charge is applied before the secondary transfer. The liquid is collected, the density of the detection toner image to which the charge is applied is detected before the secondary transfer, the detection toner image after the density detection is secondarily transferred to the transfer material, and the detection toner image after the secondary transfer. The residual toner density is detected, and if the density of the detection toner image before the secondary transfer is lower than the threshold value, the amount of charge applied to the toner image is increased, and the detection toner image before the secondary transfer When the density is higher than the threshold value and the density of the detection toner image after secondary transfer is higher than the threshold value, the amount of charge applied to the toner image is reduced, and the detection toner image before secondary transfer Is darker than the threshold and secondary transfer When the concentration of the detection toner images of thinner than the threshold value to maintain the amount of charge applied to the toner image.

  According to the image forming apparatus and the transferability adjusting method of the image forming apparatus of the present invention, the toner image is charged in order to efficiently recover the excess carrier liquid, and the charge amount is varied based on the density of the toner image. As a result, fluctuations in image forming conditions can be detected from changes in density, ensuring secondary transfer and fixing properties, and forming images with stable image quality while suppressing carrier liquid discharge. it can.

  As shown in the configuration diagram of FIG. 1, the image forming apparatus 1 according to the first embodiment includes a charging device 3, an exposure device 4, a liquid developing device 5, a photoconductor sweep device 6, and an intermediate device in order around the photoconductor 2. The transfer roller 7, the charge removal lamp 8, and the photoconductor cleaning device 9 are arranged to form an image forming unit, and around the intermediate transfer roller 7, a charge applying unit 10, a carrier liquid recovery unit 11, a secondary transfer roller 12, The intermediate transfer member cleaning device 13 and the density detection unit 14 are disposed, and a paper feeding unit 15, a fixing device 16, a paper discharge unit 17, and a control unit 18 are provided.

  The surface of the photoreceptor 2 as a latent image carrier that forms an image by reversal development is formed of a-Si, OPC, or the like, and is rotationally driven in a direction indicated by an arrow at a constant speed during image formation by a driving unit such as a motor. For example, the photoconductor 2 formed of a-Si has excellent durability and is not easily damaged even when a cleaning blade having high hardness is brought into contact therewith, so that a high-quality image free from abnormal images such as unwanted spots and streaks can be obtained. More preferable. The charging device 3 uniformly charges the surface of the photoreceptor 2 in the dark with a corona charger. The charging device 3 may have other forms such as a roller. The exposure device 4 forms an electrostatic latent image on the charged photoreceptor 2 by an LED array head, a laser scanning optical system, or the like.

  The liquid developing device 5 includes a developing roller 20, a coating roller 21 (Anix roller), an intermediate roller 22, a cleaning blade 23, and two stirring / conveying screws 24. The stirring / conveying screw 24 is a stirring / conveying means for the liquid developer. The application roller 21 is rotatably disposed in a developer storage tank that stores a liquid developer, forms a uniform pattern on the surface as an application member, and carries the liquid developer on the surface. The intermediate roller 22 is an intermediate application member that applies the liquid developer carried on the application roller 21 in contact with the development roller 20. The intermediate roller 22 has a function of contacting the surface of the application roller 21 and removing excess liquid developer on the surface, and serves as a doctor roller that regulates the amount of developer carried on the surface of the application roller 21. It also serves as a role. The cleaning blade 23 is a cleaning member formed of a metal blade or a rubber blade, and is in contact with the intermediate roller 22. The cleaning member may be a roller type other than the cleaning blade 23. The developing roller 20 applies the liquid developer applied from the intermediate roller 22 to the photoreceptor 2 and develops the toner image from the electrostatic latent image. The coating thickness of the liquid developer applied on the developing roller 20 is approximately in the range of about 5 to 20 μm.

  The developer is not a low-viscosity (about 1 cSt), low-concentration (about 1%) liquid developer using Isopar (registered trademark), which is generally commercially available, but a high-viscosity, high-concentration liquid. Developer is used. As the viscosity and concentration range of the developer, for example, it is preferable to use a developer having a viscosity of about 50 to 10,000 mPa · s and a concentration of about 5% to 40%. As the carrier liquid, a highly insulating material such as silicone oil, normal paraffin, IsoparM (registered trademark), vegetable oil, mineral oil, etc. can be used. It is preferable to use a highly non-volatile material that does not generate volatile components. The toner particle size of the liquid developer can be selected from submicron to about 6 μm according to the purpose.

  The photoconductor sweep device 6 includes a sweep roller 30, a cleaning blade 31, and a carrier recovery device 32. The sweep roller 30 is in contact with the photoconductor 2 on the downstream side in the rotation direction of the photoconductor 2 with respect to the liquid developing device 5 and removes excess developer from the toner image developed on the photoconductor 2. The sweep roller 30 is applied with a bias that generates an electric field that removes non-image area toner and that compresses image area toner on the photosensitive member 2. In addition, the sweep roller 30 may be provided with individual sweep rollers for generating each electric field as required. The cleaning blade 31 is formed of a urethane rubber blade or the like, contacts the sweep roller 30, and scrapes off excess toner and carrier liquid removed by the sweep roller 30. The carrier recovery device 32 recovers the carrier liquid scraped from the sweep roller 30 by the cleaning blade 31. The recovered carrier liquid is reused by a recycling apparatus.

  The intermediate transfer roller 7 is applied with a transfer bias and rotates while being in contact with the photosensitive member 2. The toner image formed on the photosensitive member 2 is primarily transferred to the intermediate transfer roller 7 at the contact portion with the intermediate transfer roller 7. The neutralizing lamp 8 removes residual potential remaining on the photoreceptor 2 after the primary transfer. The photoconductor cleaning device 9 removes the developer remaining on the photoconductor 2 after the primary transfer and prepares for the next image formation.

  The charge applying unit 10 includes a corona charger 40 and a current applying unit 41. The corona charger 40 applies a discharge current from the discharge wire and applies a charge having the same polarity as the charge polarity of the toner image toward the toner image primarily transferred onto the intermediate transfer roller 7. The current application unit 41 is a constant current power source that supplies a direct current to the discharge wire of the corona charger 40, and discharges the discharge wire with a set current value. The current application unit 41 is controlled so as to apply a charge only to a certain portion of the image on the intermediate transfer roller 7, and does not apply a charge to a portion where there is no image corresponding to the space between sheets, thus saving power consumption. can do. The voltage applied to the discharge wire by the current application unit 41 to flow the discharge current is preferably the same polarity as that of the toner, and is not limited to the DC voltage, but may be an AC voltage superimposed on the DC voltage. .

  The carrier liquid recovery unit 11 includes a carrier liquid recovery roller 33, a carrier liquid recovery power source 34, a cleaning blade 35, and a carrier recovery device 36. The carrier liquid recovery roller 33 is in contact with the intermediate transfer roller 7 on the downstream side in the rotational direction of the intermediate transfer roller 7 from the charge applying unit 10 and on the upstream side in front of the secondary transfer portion. Remove excess carrier liquid from the image.

  The carrier liquid recovery power source 34 applies a bias to the carrier liquid recovery roller 33 to generate an electric field that removes non-image area toner, and generates an electric field that compresses the image area toner on the intermediate transfer roller 7. The carrier liquid recovery roller 33 may be provided with individual sweep rollers for generating each electric field as required. The carrier liquid recovery roller 33 is required to have an elastic deformation function and conductivity for applying a bias voltage in order to ensure uniform contact with the intermediate transfer roller 7. The carrier liquid recovery roller 33 is made conductive by dispersing carbon or the like. It is preferable to use a rubber material having a softness of 70 degrees or less with a rubber hardness (JISA).

  The cleaning blade 35 is formed of a urethane rubber blade or the like, contacts the carrier liquid collection roller 33, and scrapes off excess toner and carrier liquid removed by the carrier liquid collection roller 33. The carrier recovery device 36 recovers the carrier liquid scraped from the carrier liquid recovery roller 33 by the cleaning blade 35. The recovered carrier liquid is reused by a recycling apparatus.

  The carrier liquid recovery roller 33 is provided with driving means for independently rotating the carrier liquid collection roller 33 so as to be able to rotate against the load of the cleaning blade 35 in contact therewith. By setting the rotation speed of the carrier liquid recovery roller 33 so that the surface of the carrier liquid recovery roller 33 and the surface of the intermediate transfer roller 7 are moved at substantially constant speed, the intermediate transfer roller 7 is relatively moved with respect to the toner. The velocity vector in the tangential direction can be avoided, and the leading edge of the image is blurred or the balance between the vertical and horizontal lines is poor regardless of the contact pressure between the carrier liquid recovery roller 33 and the intermediate transfer roller 7. This phenomenon can be avoided. Note that the surface of the carrier liquid recovery roller 33 and the intermediate transfer roller 7 can be adjusted so that the intermediate transfer roller 7 and the carrier liquid recovery roller 33 can be brought into contact with each other with a pressure that does not scrape off the toner on the intermediate transfer roller 7. The ability to remove the carrier liquid can be increased by rotating the moving direction between the surface and the surface in the opposite direction. That is, the rotational movement direction of the carrier liquid recovery roller 33 can be set according to the situation. The higher the rotational speed of the carrier liquid recovery roller 33, the higher the recovery capacity. However, there is a limit to the recovery capacity, and conversely, the recovery capacity decreases at a rotational speed of a certain level or more. It is desirable to set the rotation speed of the collection roller 33.

  The process of recovering the carrier liquid from the toner image that has passed through the charge applying unit 10 and the carrier liquid recovery unit 11 will be described with reference to the schematic diagram of FIG. As shown in the schematic diagram of FIG. 2A, the toner particle layer 42 on the intermediate transfer body 7 after the primary transfer receives a force pressed against the intermediate transfer roller 7 by the action of the electric field of the primary transfer, but is still a carrier. It is considered that the toner particles 44 are dispersed in the liquid 43, and the toner particle layer 42 has not reached a remarkable compression state. As shown in the schematic diagram of FIG. 2B, when the discharge current from the corona charger 40 flows toward the intermediate transfer roller 7, a charge 45 is applied to the toner particle layer 42, and the toner particles 44 are charged. It is considered that the carrier liquid 43 is squeezed out like a supernatant liquid on the upper side (surface) of the toner image due to the force by which the toner particle layer 42 is compressed toward the intermediate transfer roller 7 by the action of the discharge current. As shown in the schematic diagram of FIG. 2C, the carrier liquid collection roller 33 is squeezed to the upper side of the toner image by rotating in the same direction as the intermediate transfer roller 7 in contact with the toner image surface. The carrier liquid 43 adheres to the surface of the carrier liquid collection roller 33 and is collected. By applying a bias voltage having the same polarity as the charging characteristics of the toner particles 44 to the carrier liquid recovery roller 33 from the carrier liquid recovery power source 34, the toner particles 44 are prevented from adhering to the surface of the carrier liquid recovery roller 33. Can do.

  The secondary transfer roller 12 is a secondary transfer unit disposed so as to face the intermediate transfer roller 7, and the intermediate transfer roller 12 is conveyed while sandwiching a transfer material in a secondary transfer region between the secondary transfer roller 7 and the intermediate transfer roller 7. 7 is secondarily transferred onto the transfer material. The intermediate transfer body cleaning device 13 removes residual toner remaining on the intermediate transfer roller 7 after the secondary transfer. Note that the secondary transfer means may have other methods besides the one using the secondary transfer roller 12 such as one using an electrostatic transfer method by corona discharge.

  The density detection unit 14 includes a pre-secondary transfer density detection unit 50 and a post-secondary transfer density detection unit 51. The pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit 51 are optical density sensors each having a light-emitting unit and a light-receiving unit, and irradiate light from the light-emitting unit to the part to be measured on the intermediate transfer roller 7. The optical density of the measured part is detected by detecting the reflected light from the measured part by the light receiving part, and the density is output in the form of a voltage value.

  The pre-secondary transfer density detector 50 and the post-secondary transfer density detector 51 are provided so as to detect the image density before and after the secondary transfer of the detection image pattern formed on the intermediate transfer roller 7. . That is, the pre-secondary transfer density detector 50 is provided upstream of the secondary transfer position of the intermediate transfer roller 7 (before the secondary transfer), and is formed on the photoreceptor 2 and then transferred to the intermediate transfer roller 7. Then, the density of the detection image pattern before the secondary transfer after passing through the charge applying unit 10 and the carrier liquid recovery unit 11 is detected. Further, the post-secondary transfer density detection unit 51 is provided downstream of the secondary transfer position of the intermediate transfer roller 7 (after the secondary transfer), and the intermediate transfer is performed after the detection image pattern is secondarily transferred to the transfer material. The density of the untransferred toner remaining on the roller 7 is detected. When the image density of the detection image pattern is low, the secondary transfer density detection unit 50 and the secondary transfer density detection unit 51 output a high voltage value because the amount of reflected light is large, and the image density of the detection image pattern is high. When the value is high, a low voltage value is output because the amount of reflected light is small.

  The paper feed unit 15 feeds transfer materials such as copy sheets and OHP sheets stacked on the paper feed tray by a paper feed roller, temporarily stops by a registration roller, and matches the position and timing of the toner image on the intermediate transfer roller 7. Then, the toner is fed to the contact portion between the secondary transfer roller 12 and the intermediate transfer roller 7.

  The fixing device 16 heats and pressurizes the transfer material onto which the toner image is secondarily transferred, fixes the toner image on the transfer material, and discharges the toner image to the paper discharge unit 17 as a printed matter. The fixing device 16 may be one using infrared heat fixing, oven heat fixing, solvent fixing, UV fixing, or the like, in addition to heat pressure fixing using a pair of heat rollers.

  As shown in the configuration diagram of FIG. 3, the control unit 18 includes an input / output unit 60, an image processing unit 61, an LD control unit 62, an engine controller 63, an operation unit 64, a system control unit 65, and a charge amount variable unit 66. Prepare. The input / output unit 60 inputs image data from the outside. The image processing unit 61 performs image processing to form an image of the input image data. The LD control unit 62 controls lighting of the light source of the exposure apparatus 4 according to the image data image-processed by the image processing unit 61. The engine controller 63 operates each component of the image forming apparatus 1 in accordance with the image forming operation. The operation unit 64 inputs an instruction for image formation.

  The system control unit 65 controls the overall operation of the image forming apparatus 1, forms an image based on the input image data, forms an image based on the detection image data, and optimizes the transfer rate. And a transferability adjusting method.

  The graph of FIG. 4 shows the relationship of the pattern image density after the secondary transfer when the halftone image area ratio of the image pattern is changed in each of the cases where the corona charger 40 is provided and not provided. At an intermediate density where the image area ratio is about 40 to 70%, a difference in image density due to the presence or absence of the corona charger 40 appears remarkably. This shows that when charge is applied to the toner image on the intermediate transfer roller 7 by the corona charger 40, the reproducibility of the image density in the image portion having a lower image area ratio is improved as compared with the solid image portion. Yes. That is, when the charge amount of the toner layer on the intermediate transfer roller 7 is not sufficient for the secondary transfer, the secondary transferability is easily deteriorated in a so-called dot image having a small individual image area. . Accordingly, the secondary transfer efficiency can be detected more accurately by measuring the image density of the intermediate density pattern. The intermediate density pattern may be any pattern as long as it is a pattern capable of obtaining a halftone density such as a halftone dot pattern or a line pattern. From the above examination, in this embodiment, an intermediate density pattern is used as the detection image pattern.

  The charge amount variable unit 66 receives the density of the image pattern for detection carried on the intermediate transfer roller 7 before the secondary transfer from the density detection unit 50 before the secondary transfer, and detects the density from the density detection unit 51 after the secondary transfer. After the image pattern is secondarily transferred to the transfer material, the density of toner remaining on the intermediate transfer roller 7 is input, and the current application unit 41 is controlled based on the two input densities to thereby reduce the discharge current generated by the corona charger 40. Make it variable.

  Here, the graph of FIG. 5 shows the relationship between the discharge current flowing from the corona charger 40 to the intermediate transfer roller 7 and the density detection results by the density detector 50 before secondary transfer and the density detector 51 after secondary transfer. As is apparent from the graph of FIG. 5, the secondary transfer density detector 50 and the secondary transfer according to the value of the discharge current supplied from the corona charger 40, that is, the amount of charge applied from the corona charger 40. The combinations of outputs from the post-density detector 51 are roughly classified into three states: state A, state B, and state C.

  In the state B, since the discharge current from the corona charger 40 is appropriate, the value of the secondary pre-transfer density detection unit 50 is stable and low regardless of the discharge current, and the detection value of the secondary post-transfer density detection unit 51 is high. stable.

  In the state A, since the discharge current from the corona charger 40 is not sufficient, sufficient charge is not given to the toner particles, the toner cannot be sufficiently compressed, and the image formed on the intermediate transfer roller 7 The toner is peeled off by the carrier liquid recovery roller 33, and the density before the secondary transfer is lowered. Further, in the state A, since the discharge current from the corona charger 40 is not sufficient, sufficient charge is not given to the toner particles, so that the secondary transfer rate is reduced, the residual toner after the secondary transfer is increased, and the secondary transfer is increased. The pattern density after transfer increases. Therefore, in the state A, the smaller the discharge current, the higher the detection value of the pre-secondary transfer density detection unit 50 and the lower the detection value of the post-secondary transfer density detection unit 51.

  In the state C, since the discharge current from the corona charger 40 is excessive, an excessive charge is applied to the toner on the image formed on the intermediate transfer roller 7 and the toner particles are strongly pressed against the surface of the intermediate transfer roller 7. The efficiency of transferring the toner particles to the transfer material side at the secondary transfer portion is lowered, and the pattern density after the secondary transfer is increased. Therefore, in the state C, the detection value of the pre-secondary transfer density detection unit 50 is stable, while the detection value of the post-secondary transfer density detection unit 51 decreases as the discharge current increases.

  The charge amount variable unit 66 uses the actual pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit for the detection values of the pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit 51 in the state B. From the magnitude relationship of the detected values of 51, it is determined which state is state A, state B, or state C. If it is state A, the state is changed to state B by increasing the discharge current. And in state C, the discharge current is reduced to transition to state B.

  Specifically, the charge amount variable unit 66 discharges the detection values of the pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit 51 as shown in the control table 70a and the control table 70b of FIG. Whether to increase the current or decrease the discharge current is stored, and the detection values of the pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit 51 are applied to the control table to control the discharge current. More specifically, when the detection value Th1 of the concentration detector 50 before secondary transfer in the state B is 1.5V and the detection value Th2 of the concentration detector 51 after secondary transfer in the state B is 4.0V, the control is performed. The table 70a stores that the discharge current is increased if the detection value of the pre-secondary transfer density detector 50 is greater than 1.5V, that is, the state A, and the control table 70b detects the post-secondary transfer density detection. If the detected value of the part 51 is less than 4.0 V, that is, the state C, it is stored that the discharge current is reduced. The current application unit 41 gives priority to an increase in discharge current over a decrease in discharge current.

  As another specific example, the charge amount variable unit 66 includes a first comparison circuit 71, a second comparison circuit 72, and an appropriate value determination circuit 73 as shown in the circuit diagram of FIG. The first comparison circuit 71 compares the detection value Th1 = 1.5V of the secondary pre-transfer density detection unit 50 in the state B with the input from the actual pre-secondary transfer density detection unit 50, and performs the actual secondary transfer. If the input from the pre-density detector 50 is greater than 1.5V, a low signal that increases the discharge current is output. If the input from the actual pre-secondary transfer density detector 50 is 1.5V or less, a high signal is output. . The second comparison circuit 72 compares the detection value Th2 = 4.0V of the secondary post-transfer density detecting unit 51 in the state B with the input from the actual secondary post-transfer density detecting unit 51, and the actual secondary transfer. If the input from the post-density detector 51 is less than 4.0V, a low signal is output to reduce the discharge current. If the input from the actual post-secondary density detector 51 is 4.0V or higher, a high signal is output. To do. Appropriate value determination circuit 73 is configured by an AND circuit, and when both inputs from first comparison circuit 71 and second comparison circuit 72 are high signals, that is, in state B, the discharge current is appropriate. A high signal is output. The current application unit 41 increases the discharge current when a low signal that increases the discharge current is input from the first comparison circuit 71, and decreases the discharge current when the low signal that decreases the discharge current is input from the second comparison circuit 72. When the High signal is received from the appropriate value determination circuit 73, the current discharge current is maintained. The current application unit 41 gives priority to the signal for increasing the discharge current over the signal for decreasing the discharge current.

  A transferability adjustment method executed by the system control unit 65 will be described with reference to the flowchart of FIG. First, the system control unit 65 forms an image pattern for detection composed of an intermediate density pattern on the photosensitive member 2 in the same manner as a normal image forming method, and primarily transfers the image pattern to the intermediate transfer roller 7 (step S10). Next, the system control unit 65 applies a charge from the corona charger 40 to the detection image pattern on the intermediate transfer roller 7 by the current discharge current (step S11). Next, the system control unit 65 collects the carrier liquid from the detection image pattern on the intermediate transfer roller 7 by the carrier liquid collection unit 11 (step S12). Next, the system control unit 65 detects the density of the detection image pattern on the intermediate transfer roller 7 by the pre-secondary transfer density detection unit 50 (step S13). Next, the system control unit 65 secondarily transfers the detection image pattern of the intermediate transfer roller 7 to the transfer material sent out from the paper supply unit 15 at an appropriate timing by the secondary transfer roller 12 (step S14). Next, the system control unit 65 detects the density of the toner image remaining on the intermediate transfer roller 7 after the secondary transfer by the secondary transfer density detection unit 51 (step S15). Next, the system control unit 65 determines whether the state is the state A, the state B, or the state C by the charge amount variable unit 66. If the state is the state A, the system controller 65 increases the discharge current to the state B. In the state B, the current application unit 41 is set so as not to change the discharge current, and in the state C, the current application unit 41 is set so as to be in the state B by reducing the discharge current (step S16). .

  To be precise, since the appropriate amount of charge applied to the toner image from the corona charger 40 varies depending on the amount of toner, it is desirable to change the required amount of charge according to the image area ratio. Specifically, the image area ratio It is desirable to provide a control table for each image, or to change the reference voltage input to the first comparison circuit 71 and the second comparison circuit 72 for each image area ratio.

  It will be described that the transferability adjusting method of the present embodiment is effective even when the toner characteristics change with time. The graph of FIG. 9 shows the relationship between the discharge current flowing from the corona charger 40 to the intermediate transfer roller 7 and the density detection results by the density detector 50 before secondary transfer and the density detector 51 after secondary transfer. The state before the characteristics change, that is, the same state as in FIG. 5 is shown, and the solid line shows the state after the toner characteristics change with time.

  When the carrier liquid in the toner layer decreases with the passage of time, the detection value of the post-secondary transfer density detection unit 51 decreases as indicated by the solid line in the state C, and the state C region becomes wider and the appropriate region The region of the state B that is is narrowed. This is because the carrier liquid recovered by the carrier liquid recovery roller 33 increases as the discharge current increases, so that the carrier liquid at the time of secondary transfer becomes insufficient, the secondary transfer rate decreases, and the intermediate after the secondary transfer. This is because the toner remaining on the transfer roller 7 increases.

  When the charging characteristics of the toner deteriorate with time, the detection value of the pre-secondary transfer density detection unit 50 increases and the detection value of the pre-secondary transfer pattern density sensor 51 as shown by the solid line in the state A. Decreases, the state A region becomes wider, and the appropriate region, state B, becomes narrower. This is because when the discharge current is low, the amount of charge applied to the toner is small, so the amount of toner collected by the carrier liquid collection roller 33 increases and the density before secondary transfer decreases. Further, when the discharge current is low, the charge applied to the toner is small, so that the secondary transfer rate is lowered and the toner remaining on the intermediate transfer roller 7 after the secondary transfer is increased.

  Even when the toner characteristics change with time and the region of state B becomes narrower, the charge amount variable unit 66 is based on the changes in the pre-secondary transfer density detection unit 50 and the post-secondary transfer density detection unit 51. The state A and the state C can be detected, and the discharge current can be changed to transition to the state B.

  According to the image forming apparatus 1 of the present exemplary embodiment, the toner image is charged by compressing the toner, the excess carrier liquid is separated from the toner layer, and the excess carrier liquid is efficiently recovered from the toner image, thereby surplus. Therefore, it is possible to secure the toner fixability on the transfer material without adhering as much carrier liquid as possible to the transfer material. Therefore, it is possible to suppress the consumption of the carrier liquid and provide a high-quality image.

  According to the image forming apparatus 1 of the present embodiment, by detecting the toner density on the intermediate transfer roller 7 before and after the secondary transfer, the appropriate charge amount fluctuates in response to environmental changes and conditions. Even in this case, the amount of charge imparted from the charge imparting unit 10 to the toner image before the secondary transfer can be set to an appropriate value that enables good secondary transfer. The toner can be prevented from being peeled off and good secondary transfer can be maintained, and a stable image quality can be obtained.

  According to the image forming apparatus 1 of the present embodiment, when the viscosity and electrical characteristics of the liquid toner vary depending on the surrounding environment, the toner characteristics vary with time, and the variation range of the toner density varies. Even when the state after development by the liquid developing device 5, that is, when the image forming conditions are changed, the amount of charge applied from the charge applying unit 10 to the toner image before the secondary transfer is not fixed to a certain condition and is appropriate. Since the charge amount can be controlled, stable image quality can be obtained.

  An image forming apparatus 80 according to the second embodiment replaces the charge applying unit 10 having the corona charger 40 according to the first embodiment as shown in the configuration diagram around the intermediate transfer roller 7 in FIG. 81, a charge applying portion 84 having a cleaning blade 82 and a current applying portion 83 is provided. Other configurations are substantially the same as those of the image forming apparatus 80 of the first embodiment.

The non-contact discharge roller 81 has a conductive property having electrical characteristics such as a volume resistivity of 1 × 10 ⁻⁶ to 10 ⁻¹³ Ω · cm and a surface resistance of 1 × 10 ⁻⁶ Ω or more on a metal core. A cover layer is provided and configured. For the coating layer, a foamed conductive rubber composition or a conductive polyurethane foam containing a conductive material can be used. Examples of the rubber component constituting the foamed conductive rubber composition include ethylene-propylene-diene rubber (EPDM), chloroprene, chlorosulfonated polyethylene blended with a conductive material, and a copolymer rubber of epichlorohydrin and ethylene oxide. It is preferable to use a synthetic rubber material having a medium resistance, such as a foam obtained by blending a conductive material with a foamed rubber or a copolymer rubber of epichlorohydrin and ethylene oxide.

The non-contact discharge roller 81 is a non-contact type discharge roller, and thus does not necessarily have to be configured using elasticity, and is not limited to the above materials as long as the material satisfies electric characteristics. The non-contact discharge roller 81 has a function of improving the charging uniformity of the member to be charged, preventing leakage due to pinholes on the surface of the member to be charged, and preventing adhesion of toner particles and paper powder. In order to give it to the surface, the roller surface may be coated or coated with a coating tube as necessary. Specifically, the non-contact discharge roller 81 is provided with a thin (about 5 to 10 μm) polyamide resin coating film and a 15 μm thick fluororesin (including 4 wt% carbon) surface layer on the surface, and the surface resistance Is about 1 × 10 ⁻⁶ Ω. The non-contact discharge roller 81 may be provided with a dielectric coating such as a resin or an alumite layer on the core metal surface.

  As the installation condition of the non-contact discharge roller 81, it is desirable that the separation distance between the intermediate transfer roller 7 and the non-contact discharge roller 81 is 500 μm or less. There are several methods for maintaining the separation distance between the intermediate transfer roller 7 and the non-contact discharge roller 81. For example, a spacer roller that forms a thickness corresponding to the separation distance between the intermediate transfer roller 7 and the non-contact discharge roller 81 is provided in the non-image portion region at the axial end of the non-contact discharge roller 81. Press against the part.

  For example, when a charge is applied to a toner image by a corona charger, the corona charger has a configuration in which ions are generated by corona discharge. Therefore, it is necessary to flow the discharge current not only to the member to be charged but also to the casing member surrounding the charge wire. The current efficiency is poor and the setting range of the discharge current is not so large. On the other hand, the discharge of the non-contact discharge roller 81 is generated in the gap between the non-contact discharge roller 81 and the intermediate transfer roller 7, and almost all of the discharge current is applied to the toner layer on the intermediate transfer roller 7. Charge can be efficiently applied. Efficient charge application can reduce the amount of ozone generated during discharge.

  Since the non-contact discharge roller 81 is not in contact with the toner layer or the intermediate transfer roller 7, even when an elastic conductive rubber material is used as a member of the non-contact discharge roller 81, the non-contact discharge roller 81 is used as the intermediate transfer roller. Thus, it is possible to avoid problems such as permanent deformation, which becomes a problem when the apparatus is stopped for a long time while being in contact with 7.

  For example, when charge is applied to a toner image by a corona charger, the discharge of the charge wire becomes unstable due to adhesion of paper dust or discharge products to the discharge wire of the corona charger, and sufficient functions cannot be exhibited. Therefore, it is necessary to clean the charge wire regularly. On the other hand, when the non-contact discharge roller 81 is used as in this embodiment, the toner adhering to the non-contact discharge roller 81 as a charging member can be reduced, and the toner, carrier liquid, etc. on the intermediate transfer roller 7 are charged. A decrease in charging performance due to adhering to the member can be suppressed, and it can be used without providing a cleaning device. Even when the non-contact discharge roller 81 is used, it is impossible to completely eliminate the adhesion of foreign matters to the roller surface. Therefore, the non-contact discharge roller 81 can be driven to rotate and cleaned intermittently by the cleaning blade 82. desirable.

  The current application unit 83 causes a current to flow through the non-contact discharge roller 81 with the current value set from the charge amount variable unit 66 as in the current application unit 41 of the first embodiment. Note that the voltage applied to the non-contact discharge roller 81 by the current application unit 83 to cause the discharge current to flow is preferably the same polarity as the toner, and is not limited to the DC voltage, but is an AC voltage superimposed on the DC voltage. Also good.

  According to the image forming apparatus 80 of the second embodiment, by applying a charge to the toner image by the non-contact discharge roller 81, non-uniform discharge due to dirt can be avoided and discharged efficiently. The toner layer can be charged uniformly and stably.

  The image forming apparatus 90 according to the third embodiment includes the corona charger 40 according to the first embodiment as illustrated in the configuration diagram around the intermediate transfer roller 7 in FIG. 11 and the block diagram of the control unit 18 in FIG. 12. Instead of the charge application unit 10, a charge application unit 97 having a contact discharge roller 91, a cleaning blade 92, a carrier recovery device 93, a container 94, a contact / separation mechanism 95, and a current application unit 96 is provided. An approach / separation mechanism 98 is provided. Other configurations are substantially the same as those of the image forming apparatus 80 of the first embodiment.

  The contact discharge roller 91 is a contact type discharge member, and a material having substantially the same configuration and electrical characteristics as the non-contact discharge roller 81 can be used. Since the contact discharge roller 91 is in contact with the intermediate transfer roller 7 via a toner layer or a carrier liquid layer, a conductive rubber material (JISA) having a flexibility of 70 degrees or less is used as a material. It is desirable to use it. The configuration of the rubber material imparted with conductivity is the same as that of the coating layer of the second embodiment.

  It is desirable that the surface of the contact discharge roller 91 is as smooth as possible. This is because, when the surface of the contact discharge roller 91 is extremely uneven, the unevenness is transferred to the toner image and the toner image is crushed by the protrusion when the surface contacts the toner image surface, depending on the contact pressure. . Since the toner layer thickness on the intermediate transfer roller 7 is about 5 μm or less, and the surface roughness of the contact discharge roller 91 is preferably smoother than the thickness of the toner layer, the roller surface of the contact discharge roller 91 has ten locations. The average roughness Rz (JIS) is preferably 5 μm or less.

  Since the contact discharge roller 91 can reduce the voltage of the power source as compared with the corona charger, the amount of ozone generated due to the discharge process can be reduced. Since the contact discharge roller 91 can operate at a lower voltage than the non-contact discharge roller 81, the amount of ozone generated can be reduced. Since the contact discharge roller 91 is in contact with the intermediate transfer roller 7, the discharge gap can always be kept uniform and can be stably discharged.

  Since the contact discharge roller 91 is in contact with the toner layer on the intermediate transfer roller 7, unlike the non-contact discharge member, the contact discharge roller 91 can charge the toner particles and remove excess carrier liquid on the toner image. it can. The cleaning blade 92 cleans the carrier liquid adhering to the surface of the contact discharge roller 91 in the same manner as the cleaning blade 35 of the carrier liquid recovery roller 33. The carrier liquid recovery device 93 recovers and reuses the excess carrier removed by the cleaning blade 92. The container 94 has a contact discharge roller 91, a cleaning blade 92, and a carrier liquid recovery device 93 disposed therein.

  The contact discharge roller 91 is provided with driving means for independently rotating it so as to be able to rotate against the load of the cleaning blade 92 in contact therewith. Further, by setting the rotation speed of the contact discharge roller 91 so that the surface of the contact discharge roller 91 and the surface of the intermediate transfer roller 7 move at substantially constant speed, the intermediate transfer roller 7 is tangent to the toner relatively. It is possible to avoid having a velocity vector in the direction, and it is possible to avoid the phenomenon that the leading edge of the image is blurred or the balance between the vertical line and the horizontal line is poor.

  The contact / separation mechanism 95 includes a tension spring 100, a crank 101, an urging roller 102, and a solenoid 103. The tension spring 100 urges the contact discharge roller 91 in a direction away from the intermediate transfer roller 7 by pulling the container 94. The crank 101 is fixed so as to be rotatable at the center, and an urging roller 102 is connected to one end and the tip of a solenoid 103 is connected to the other end. The urging roller 102 is in contact with the container 94. The solenoid 103 presses the crank 101 in accordance with an instruction from the system control unit 65, thereby pressing the container 94 against the tensile force of the tension spring 100 by the urging roller 102 and pressing the contact discharge roller 91 against the intermediate transfer roller 7. The solenoid 103 pulls the crank 101 in accordance with an instruction from the system control unit 65 to move the biasing roller 102 away from the container 94, and the contact discharge roller 91 is moved from the intermediate transfer roller 7 by the tensile force of the tension spring 100. Release.

  The solenoid 103 presses the contact discharge roller 91 against the intermediate transfer roller 7 when the power supply of the image forming apparatus 90 is on, and the contact discharge roller 91 is pressed against the intermediate transfer roller when the power supply of the image forming apparatus 90 is off. Driven away from 7. By separating the contact discharge roller 91 from the intermediate transfer roller 7 while the image forming apparatus 90 is powered off, the contact discharge roller 91 using a conductive rubber material having elasticity remains in contact with the intermediate transfer roller 7. The image forming apparatus 90 is not stopped for a long time, and problems such as permanent deformation of the contact discharge roller 91 can be avoided.

  Similar to the current application unit 41 of the first embodiment, the current application unit 96 causes the current to flow through the contact discharge roller 91 with the current value set from the charge amount variable unit 66, thereby primary transfer onto the intermediate transfer roller 7. A charge having the same polarity as the charged polarity of the toner image is applied to the toner image. Note that the voltage applied to the contact discharge roller 91 by the current application unit 96 to cause the discharge current to flow is preferably the same polarity as that of the toner, and is not limited to a DC voltage, and may be a DC voltage superimposed with an AC voltage. Good.

  The contact / separation mechanism 98 provided in the carrier liquid recovery unit 11 pushes and pulls the container in which the carrier liquid recovery roller 33 is housed with the same configuration and timing as the contact / separation mechanism 95, whereby the carrier liquid recovery roller 33. Is pressed against or released from the intermediate transfer roller 7.

  According to the image forming apparatus 90 of the third embodiment, by applying a charge to the toner image from the contact discharge roller 91, it is possible to efficiently discharge, and to apply the charge uniformly and stably to the toner layer. be able to.

  The charge amount variable unit 66 determines whether or not the contact discharge roller 91 is brought into contact for each type of transfer material (paper type information) input from the input / output unit 60 or the operation unit 64, or the control table 70. May be selected. Specifically, on paper with a rough transfer material surface or paper with high carrier liquid absorbability, transfer efficiency may deteriorate significantly if the carrier liquid is removed more than necessary. When a material is selected and the carrier liquid is in a shortage state C, the carrier liquid recovery roller 33 may be separated from the intermediate transfer roller 7 to reduce the amount of carrier liquid removed to ensure transfer efficiency. If the transfer performance still does not improve sufficiently, it is possible to further reduce the amount of carrier liquid removed by separating the contact discharge roller 91 from the intermediate transfer roller 7. However, it is possible to select a more effective means depending on the situation, whether to use means for reducing the amount of carrier liquid removed or means for increasing the amount of charge applied by the contact discharge roller 91. Further, when the transfer material is made of a material that does not easily absorb oil, even if the carrier liquid is recovered by the carrier liquid recovery roller 33, the secondary transfer property is not easily lost. It is desirable to recover the carrier liquid as much as possible within a range that can be secured. As described above, the optimum transfer conditions can be automatically selected by inputting the paper type information to be used in advance.

  Note that the image forming apparatus 90 uses the contact discharge roller 91 as an example of the contact-type charge supply unit, but may use a discharge blade 110 as shown in FIG. The discharge blade 110 abuts on the toner layer on the intermediate transfer roller 7, is given a potential equal to that of the contact discharge roller 91 by the current application unit 95, and supplies charges to the toner layer by discharge. The discharge blade 110 is installed so as not to be in direct contact with the intermediate transfer roller 7 during normal image formation and to be insulated from the intermediate transfer roller 7 through the toner layer. In the wedge-shaped space 111 formed by the discharge blade 110 and the intermediate transfer roller 7, the discharge is performed when the distance between the discharge blade to which the constant voltage is applied and the intermediate transfer roller becomes a dischargeable distance, that is, the discharge Occurs upstream of the contact portion between the blade 110 and the toner layer in the rotational direction of the intermediate transfer roller 7.

As the material of the discharge blade 110, polyimide, polyamide, nylon (trademark) or the like can be used, and the volume resistivity of the material is preferably 1 × 10 ⁻⁶ Ω · cm or more. The surface of the discharge blade 110 is preferably smooth so as not to damage the toner layer, and the end of the discharge blade 110 is preferably free of irregularities. The hardness and thickness of the discharge blade 110 are preferably such that the toner layer is not damaged or scraped off. Specifically, the discharge blade 110 is formed of a polyimide film having a thickness of 50 μm and a volume resistivity of 1 × 10 ⁻⁶ Ω · cm, and is brought into contact with the rotation direction of the intermediate transfer roller 7. When a voltage of about 4 kV was applied to 110, the secondary transfer property was improved, and a high-quality image without omission could be obtained.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and substitutions can be made within the scope of the claims.

1 is a configuration diagram of an image forming apparatus according to a first embodiment. FIG. 4 is a schematic diagram illustrating a process of collecting a carrier liquid from a toner image. It is a block diagram of the control part of 1st Embodiment. It is a graph which shows the relationship between a halftone image area ratio and the density after secondary transfer. 6 is a graph showing a relationship between a discharge current and a toner image density. It is a figure which shows the example of the content of a control table. It is a figure which shows the structural example of the specific circuit of a charge amount variable part. It is a flowchart of a transferability adjustment method. It is a graph which shows the time change of the relationship between the discharge current and the density of the toner image. FIG. 6 is a configuration diagram around an intermediate transfer roller of an image forming apparatus according to a second embodiment. FIG. 10 is a configuration diagram around an intermediate transfer roller of an image forming apparatus according to a third embodiment. FIG. 10 is a block diagram of a control unit of an image forming apparatus according to a third embodiment. It is a block diagram of an image forming apparatus using a discharge blade.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Image forming apparatus, 2; Photoconductor, 3; Charging apparatus, 4; Exposure apparatus, 5: Liquid developing apparatus,
6; photoconductor sweep device, 7; intermediate transfer roller, 8; static elimination lamp,
9; photoconductor cleaning device, 10; charge applying unit, 11; carrier liquid recovery unit,
12; secondary transfer roller; 13; intermediate transfer member cleaning device; 14; density detector;
15; paper feeding unit, 16; fixing device, 17; paper discharge unit, 18; control unit, 20; developing roller,
21; coating roller, 22; intermediate roller, 23; cleaning blade,
24; stirring / conveying screw, 30; sweep roller, 31; cleaning blade,
32; Carrier recovery device 33; Carrier liquid recovery roller 34; Carrier liquid recovery power supply;
35; Cleaning blade, 36; Carrier recovery device, 40; Corona charger,
41; current application unit, 42; toner particle layer, 43; carrier liquid, 44; toner particles,
45; electric charge, 50; concentration detector before secondary transfer, 51; concentration detector after secondary transfer,
60; input / output unit, 61; image processing unit, 62; LD control unit, 63; engine controller,
64; operation unit 65; system control unit 66; charge amount variable unit 70a; control table;
70b; control table 71; first comparison circuit 72; second comparison circuit
73; appropriate value determination circuit; 80; image forming apparatus; 81; non-contact discharge roller;
82; Cleaning blade; 83; Current application unit; 84; Charge application unit;
90; Image forming apparatus, 91; Contact discharge roller, 92; Cleaning blade,
93; carrier recovery device; 94; container; 95; contact / separation mechanism; 96; current application unit;
97; Charge applying portion, 98; Contact / separation mechanism, 100; Tensile spring, 101; Crank,
102; urging roller; 103; solenoid; 110; discharge blade;
111; a wedge-shaped space.

Claims (13)

A latent image carrier;
A developing device for developing a latent image on the latent image carrier using a high-viscosity high-concentration liquid developer in which toner is dispersed in a carrier liquid to form a toner image;
An intermediate transfer member on which the toner image is primarily transferred from the latent image carrier;
An image forming apparatus comprising: a secondary transfer unit that secondary-transfers the toner image to which a charge has been applied to a transfer material;
Charge applying means for applying charge to the toner image formed on the intermediate transfer member;
Density detecting means for detecting the density of the toner image to which electric charge is applied;
An image forming apparatus comprising: a charge amount varying unit configured to vary a charge amount applied to the charge applying unit based on the detected density of the toner image.   The density detection means includes a pre-transfer density detection means for detecting the density of the toner image to which electric charge has been applied before secondary transfer, and a post-transfer density detection for detecting the density of residual toner in the toner image after secondary transfer. And an image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, further comprising a carrier liquid recovery unit that recovers a carrier liquid from the toner image to which electric charges have been applied before secondary transfer. The carrier liquid recovery means includes a carrier liquid recovery member that contacts the toner image to recover the carrier liquid, and a carrier liquid recovery member contact / separation means that contacts and separates the carrier liquid recovery member from the toner image,
The image forming apparatus according to claim 3, wherein the charge amount varying unit causes the carrier liquid recovery member contacting / separating unit to contact / separate the intermediate transfer body based on the detected density of the toner image. . The carrier liquid recovery means includes a carrier liquid recovery member that contacts the toner image to recover the carrier liquid, and a carrier liquid recovery member contact / separation means that contacts and separates the carrier liquid recovery member from the toner image,
The transfer material for contacting the carrier liquid recovery member with the toner image and the transfer material for separating the carrier liquid recovery member from the toner image are stored, and the transfer material for contacting the carrier liquid recovery member with the toner image When the image is formed on the transfer material, the carrier liquid recovery member contacting / separating means is brought into contact with the toner image, and the carrier liquid recovery member is formed on a transfer material spaced from the toner image. 4. The image forming apparatus according to claim 3, wherein the carrier liquid collecting member is separated from the toner image by the carrier liquid collecting member contacting / separating means.   The charge amount varying unit increases the amount of charge applied from the charge applying unit when the density of the toner image before secondary transfer is lower than a threshold value, and the density of the toner image before secondary transfer is increased. When the density of the toner image after the secondary transfer is higher than the threshold and the density of the toner image after the secondary transfer is higher than the threshold, the amount of charge applied from the charge applying unit is reduced to reduce the density of the toner image before the secondary transfer. 6. The charge amount applied from the charge applying unit is maintained when the toner image is darker than a threshold value and the density of the toner image after the secondary transfer is lower than the threshold value. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the charge amount varying unit varies the charge amount based on a density of a toner image formed with an intermediate density pattern. The charge applying unit includes a non-contact discharge member that discharges toward the toner image without contacting the toner image, and a current application unit that varies a discharge current of the non-contact discharge member,
The image forming apparatus according to claim 1, wherein the charge amount varying unit adjusts a charge amount by varying a discharge current in the current application unit. The charge applying unit includes a contact discharge member that contacts the toner image and discharges toward the toner image, and a current application unit that varies a discharge current of the contact discharge member,
The image forming apparatus according to claim 1, wherein the charge amount varying unit adjusts a charge amount by varying a discharge current in the current application unit.   The image forming apparatus according to claim 9, wherein the contact discharge member includes a surface moving body that moves the surface endlessly at a speed substantially equal to a surface moving speed of the intermediate transfer body.   The image forming apparatus according to claim 9, wherein the charge applying unit includes a contact discharge member contacting / separating unit that contacts and separates the contact discharge member from the intermediate transfer member.   12. The charge applying unit according to claim 9, wherein the charge applying unit includes a cleaning unit that cleans a surface of the contact discharge member, and the carrier liquid on the intermediate transfer member is collected by the contact discharge member. Image forming apparatus. A latent image carrier, a developing device that develops the latent image on the latent image carrier using a high-viscosity, high-concentration liquid developer in which toner is dispersed in a carrier liquid, and the latent image; An intermediate transfer member on which the toner image is primarily transferred from the carrier, a charge applying unit for applying charge to the toner image formed on the intermediate transfer member, and a secondary transfer from the toner image to which the charge is applied A transferability adjusting method for an image forming apparatus, comprising: a carrier liquid recovery unit that recovers a carrier liquid before; and a secondary transfer unit that secondary-transfers the charged toner image to a transfer material,
A latent image of a detection image pattern is formed on the latent image carrier,
The latent image on the latent image carrier is developed using a high-viscosity and high-concentration liquid developer in which toner is dispersed in a carrier liquid to form a toner image having a detection image pattern.
Primary transfer of the detection toner image from the latent image carrier to an intermediate transfer member,
Giving electric charge to the toner image for detection formed on the intermediate transfer member,
The carrier liquid is collected before the secondary transfer from the detection toner image to which the electric charge is applied,
Detecting a density before secondary transfer of the toner image for detection to which a charge is applied;
Secondary transfer the toner image for detection after density detection to a transfer material,
Detecting the density of residual toner in the detection toner image after secondary transfer;
If the density of the detection toner image before the secondary transfer is lower than the threshold, the amount of charge applied to the toner image is increased, and the density of the detection toner image before the secondary transfer exceeds the threshold. If the density of the toner image for detection after secondary transfer is higher than the threshold value, the amount of charge applied to the toner image is reduced, and the density of the toner image for detection before secondary transfer is the threshold. A transferability adjusting method for an image forming apparatus, which maintains a charge amount applied to a toner image when the density of the toner image for detection after secondary transfer is lower than a threshold value.

Images