JP2007108200A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of removing toner particles which have come in the minute ruggedness of an intermediate transfer belt. <P>SOLUTION: A carrier liquid coating mechanism 90 is provided on the upstream side of a secondary transfer unit 80 on the intermediate transfer belt 70. Carrier liquid is applied to the intermediate transfer belt 70 from the carrier liquid coating mechanism when cleaning operation is performed. A secondary transfer roller 81 is constituted to rotate while making a speed difference from the intermediate transfer belt 70 when the cleaning operation is performed. Furthermore, bias having a polarity for moving the toner particles from the intermediate transfer belt 70 to the secondary transfer roller 81 is applied to the secondary transfer roller 81 side when the cleaning operation is performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on a photoreceptor with a liquid toner obtained by dispersing toner in a carrier liquid made of silicon oil, mineral oil, edible oil, or the like.

  2. Description of the Related Art Conventionally, a liquid developing type electrophotographic apparatus using a high-viscosity liquid toner in which a toner is dispersed in a carrier liquid made of silicon oil, mineral oil, edible oil, or the like is known. Whereas the dry toner particles have a particle size of 5 to 10 μm, the toner particles used in such a liquid development type electrophotography have a small particle size of 0.1 to 3 μm and have an elastic intermediate transfer member. When using, it may enter into the recess. In a liquid developing type electrophotographic apparatus, cleaning the toner particles that have entered the recesses in this way is one technical problem. FIG. 7 shows a state in which the toner particles 102 having a small particle diameter have entered the minute recesses of the elastic intermediate transfer member surface 101 together with the carrier liquid 103.

As means for solving such technical problems, Patent Document 1 (Japanese Patent Laid-Open No. 2001-109346) discloses an image carrying a developed image developed by a liquid developer in which toner is dispersed in a carrier liquid. Wet image forming apparatus comprising: a carrier; and a cleaning member that removes residual liquid developer from the surface of the image carrier after the visible image on the image carrier is transferred to the transfer member and cleans the surface The cleaning member is a member having an adhesion force larger than the adhesion force between the surface and the toner with respect to the toner in the residual liquid developer on the surface of the image carrier, and the cleaning member is There is disclosed a wet image forming apparatus that is disposed so as to be in contact with the surface to which the toner adheres.
JP 2001-109346 A

  By the way, in the wet image forming apparatus described in Patent Document 1, an adhesive is applied to the cleaning member in order to increase the adhesion between the cleaning member and the toner. The agent moves to the surface of the image carrier, and this pressure-sensitive adhesive may adsorb toner particles on the surface of the image carrier and cause image quality deterioration.

  Therefore, it is conceivable to use a blade made of rubber (for example, urethane rubber) as a cleaning member that does not use an adhesive, but as described in the known example of Patent Document 1, it has entered a recess on the surface of the image carrier. The toner is very difficult to collect by simply pressing the rubber blade against the surface of the image carrier. Then, the toner particles remaining on the surface of the image carrier without being collected gradually accumulate on the image carrier, moving over partial transfer defects and causing deterioration in image quality. In particular, when using a transfer belt provided with a low-hardness elastic layer as an image carrier in order to improve the transferability to paper, the surface can be kept sufficiently smooth with respect to the toner particle size. This problem is remarkable because it is difficult.

  The present invention is to solve the above-mentioned problems, and the invention according to claim 1 comprises a developing means for developing an electrostatic latent image formed on a photoconductor with a liquid toner in which a toner is dispersed in a carrier liquid, and A primary transfer means for transferring an image developed on the photosensitive member to an intermediate transfer medium; a secondary transfer means for transferring the image transferred to the intermediate transfer medium to a recording medium; and an image transferred to the recording medium. An image forming apparatus comprising: a fixing unit that heats and pressurizes and fixes the recording medium on the recording medium, and the secondary transfer unit includes a secondary transfer roller that opposes the intermediate transfer medium and presses the recording medium A carrier liquid applying mechanism for applying a carrier liquid to the intermediate transfer medium, means for applying a bias for moving toner from the intermediate transfer medium to the secondary transfer roller, the intermediate transfer medium, and the secondary transfer roller And rotate with a speed difference It means for, characterized in that the provided.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the secondary transfer roller is provided with a pressure changing mechanism capable of changing a pressure for pressing the intermediate transfer medium. It is characterized by that.

  According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the pressure for pressing the intermediate transfer medium is lowered by the pressure changing mechanism during the cleaning operation.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the photoconductor is used as the carrier liquid coating mechanism.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the pressure changing mechanism is operated during preliminary running before starting printing.

  According to the first aspect of the present invention, the carrier liquid is applied onto the intermediate transfer medium by the carrier liquid application mechanism, and the shear shear force is applied by the speed difference between the intermediate transfer medium and the secondary transfer roller. As a result, the irregularities on the surface of the intermediate transfer medium are spread and toner particles and the like are pushed out. Further, by applying a bias to the secondary transfer roller side, the toner particles on the intermediate transfer medium are attracted to the secondary transfer roller side, whereby the intermediate transfer medium can be cleaned.

  According to the second aspect of the present invention, since the pressure changing mechanism is provided, it is possible to set a pressure condition suitable for cleaning.

  According to the third aspect of the present invention, since the pressure for pressing the intermediate transfer medium is set low during the cleaning operation, the deterioration of the intermediate transfer medium can be prevented.

  According to the fourth aspect of the present invention, since the photosensitive member is used as the carrier liquid application mechanism, it is not necessary to provide a separate mechanism for applying the carrier liquid.

  According to the fifth aspect of the present invention, since the cleaning operation can be performed during the preliminary running before the start of printing, it is not necessary to turn the belt unnecessarily by starting the printing following the cleaning operation.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the first embodiment of the present invention. The developing units 50Y, 50M, 50C, and 50K are disposed in the lower part of the image forming apparatus, and the intermediate transfer belt 70 and the secondary transfer unit 80 are disposed in the upper part of the image forming apparatus.

  The intermediate transfer belt 70 is an endless belt stretched around belt drive rollers 82 and 85, and is rotationally driven while being in contact with the photoreceptors 20Y, 20M, 20C, and 20K. Four primary transfer units 60Y, 60M, 60C, and 60K including the intermediate transfer belt 70, the primary transfer backup rollers 61Y, 61M, 61C, and 61K and the photoconductors 20Y, 20M, 20C, and 20K are arranged on the intermediate transfer belt 70. The color liquid toners are sequentially superimposed and transferred to form a full color liquid toner image.

  The secondary transfer unit 80 includes a secondary transfer roller 81, a belt driving roller 82, a secondary transfer roller blade 83, and a secondary transfer roller cleaning liquid recovery unit 84, and a monochromatic liquid formed on the intermediate transfer belt 70. An apparatus for transferring a toner image or a full-color liquid toner image to a medium such as paper, film, or cloth.

  In the present invention, a carrier liquid application mechanism 90 is provided on the upstream side of the secondary transfer unit 80, so that the carrier liquid can be applied onto the intermediate transfer belt 70.

  A fixing unit (not shown) is a device for fusing a single color liquid toner image or a full color liquid toner image transferred on a medium such as paper to a medium such as paper to form a permanent image.

  In order to clean the carrier liquid and toner particles remaining on the intermediate transfer belt 70 after the secondary transfer, a belt cleaning blade 86 is in contact with the intermediate transfer belt 70 wound around the belt driving roller 85. The belt cleaning liquid recovery unit 87 is a mechanism for recovering the carrier liquid and toner particles scraped off by the belt cleaning blade 86.

  The developing units 50Y, 50M, 50C, and 50K have a function of developing a latent image with yellow (Y) liquid toner, magenta (M) liquid toner, cyan (C) liquid toner, and black (K) liquid toner, respectively. ing. As the yellow (Y) liquid toner, the magenta (M) liquid toner, the cyan (C) liquid toner, and the black (K) liquid toner, toners of various colors are dispersed in a carrier liquid.

  The developing units 50Y, 50M, 50C, and 50K generally supply the developing toner containers 53Y, 53M, 53C, and 53K that store the liquid toners, and supply the color toners from the developing toner containers to the developing rollers 54Y, 54M, 54C, and 54K. Toner supply rollers 51Y, 51M, 51C, and 51K, and chargers 30Y, 30M, 30C, and 30K that charge the photoreceptors 20Y, 20M, 20C, and 20K, and an electrostatic latent image that is not shown in FIG. An exposure unit (the optical path of the exposure unit is 40Y, 40M, 40C, 40K).

  Since the developing units 50Y, 50M, 50C, and 50K have the same configuration, the developing unit 50K will be described below.

  As shown in FIG. 1, a charging unit 30K, an exposure unit, and a primary transfer unit 60K are mainly arranged along the rotation direction of the photoconductor 20K. The photoconductor 20K has a cylindrical base material and a photosensitive layer formed on the outer peripheral surface thereof, and can rotate around a central axis. In the present embodiment, the photoconductor 20K rotates clockwise.

  The charging unit 30K is a device for charging the photoconductor 20K. From an exposure unit (not shown), a latent image is formed on the charged photoconductor 20K by irradiating the laser with an optical path 40K. The exposure unit includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and irradiates a modulated laser onto the charged photoconductor 20K based on an input image signal.

  The developing unit 50K is a device for developing the latent image formed on the photoconductor 20K using black (K) liquid toner. Details of the developing unit 50K will be described later.

  The primary transfer unit 60K is a device for transferring the black liquid toner image formed on the photoreceptor 20K to the intermediate transfer belt 70.

  FIG. 2 is a cross-sectional view showing main components of the developing unit 50K. In FIG. 2, the developing toner container 53K contains liquid toner composed of toner and carrier liquid for developing the latent image formed on the photoreceptor 20K. The liquid toner stored in the developing toner container 53K is a low-concentration (about 1 to 2 wt%) and low-viscosity, which is generally used in the past, using Isopar (trademark: Exxon) as a carrier, and is volatile at room temperature. Is a non-volatile liquid toner having a high concentration and a high viscosity and having a non-volatile property at room temperature. That is, in the liquid toner according to the present embodiment, solid particles having an average particle diameter of 1.3 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin are used as an organic solvent, silicon oil, mineral oil, edible oil, or the like. It is a liquid toner having a high viscosity (about 30 to 10000 mPa · s) added to a liquid solvent together with a dispersant and having a toner solid content concentration of about 25%.

  Liquid toner is supplied from the developing toner container 53K to the developing roller 54K by the toner supply roller 51K. The toner supply roller 51K is a cylindrical member, and is an aniloc roller that rotates clockwise as shown in FIG. 2 and has fine and uniform spiral grooves formed on the surface. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm.

  The toner regulating blade 52K includes a rubber portion made of urethane rubber or the like that contacts the surface of the toner supply roller 51K, and a metal plate that supports the rubber portion, and scrapes off the liquid toner remaining on the toner supply roller 51K. To remove.

  The developing roller 54K is a cylindrical member having a width of about 320 mm, and rotates counterclockwise around the central axis as shown in FIG. The developing roller 54K is provided with an elastic body such as conductive urethane rubber, a resin layer, and a rubber layer on the outer periphery of an inner core made of metal such as iron. The developing roller 54K is provided with a developing roller blade 58K and a developing roller cleaning liquid recovery unit 59K. The developing roller blade 58K is made of rubber or the like that comes into contact with the surface of the developing roller 54K, and scrapes and removes the liquid toner remaining on the developing roller 54K. The developing roller cleaning liquid recovery unit 59K is a container such as a tank that stores the liquid toner scraped off by the developing roller blade 58K.

  The leveling roller 55K is a cylindrical member that rotates around a central axis and has a structure in which a conductive resin layer or a rubber layer is provided on the surface layer of the metal roller. As shown in FIG. 4, the rotation is clockwise in the direction opposite to the developing roller 54K. The leveling roller has means for increasing the charging bias on the surface of the developing roller 54K. The leveling roller blade 56K is made of rubber or the like that contacts the surface of the leveling roller 55K, and scrapes off and removes the liquid toner remaining on the leveling roller 55K. The leveling roller cleaning liquid recovery unit 57K is a container such as a tank for storing the liquid toner scraped off by the leveling roller blade 56K.

  The photosensitive member 20K is a cylindrical member having a width wider than about 320 mm of the developing roller 54K and having a photosensitive layer formed on the outer peripheral surface thereof, and rotates clockwise around the central axis as shown in FIG. The photosensitive layer of the photoreceptor 20K is composed of an organic photoreceptor or an amorphous silicon photoreceptor.

  Around the photoreceptor 20K, a photoreceptor blade 21K and a photoreceptor cleaning liquid recovery unit 22K are arranged. The photoreceptor blade 21K is in contact with the surface of the photoreceptor 20K, is made of rubber, and scrapes off and removes the liquid toner remaining on the photoreceptor 20K. The photoreceptor cleaning liquid recovery unit 22K is a container such as a tank that stores liquid toner scraped off by the photoreceptor blade 21K.

  The charger 30K is provided upstream of the nip portion between the photoconductor 20K and the developing roller 54K. The charger 30K is applied with a bias having the same polarity as the liquid toner charging polarity from a power supply device (not shown), and charges the photosensitive member 20K. On the charged photosensitive member 20K, an exposure unit (not shown) By irradiating the laser beam, a latent image is formed. The formed latent image is developed by the developing roller 54K and transferred to the intermediate transfer belt 70 in the primary transfer unit 60K.

  Next, the operation of the image forming apparatus of the present invention will be described. Subsequently, the developing unit will be described by taking the developing unit 50K of the four developing units as an example.

  The liquid toner in the developing toner container 53K has a toner solid content concentration of 25%, and the toner particles have an average particle size of 1.3 μm and a positive charge. The liquid toner is pumped up from the developing toner container 53K as the toner supply roller 51K rotates. The toner regulating blade 52K abuts on the surface of the toner supply roller 51K, scrapes off other excess developer while leaving the developer in the groove formed on the surface of the toner supply roller 51K, and supplies it to the development roller 54K. Regulate the amount of liquid toner. By such regulation, the liquid toner applied to the developing roller 54K is quantified so that the film thickness is about 6 μm. The liquid toner scraped off by the toner regulating blade 52K is dropped back into the developing toner container 53K by gravity. The liquid toner that has not been scraped off by the toner regulating blade 52K is accommodated in an uneven groove on the surface of the toner supply roller 51K, and is applied to the surface of the developing roller 54K by being pressed against the developing roller 54K.

  The developing roller 54K coated with the liquid toner by the toner supply roller 51K contacts the leveling roller 55K downstream of the nip portion with the toner supply roller 51K. A bias of about +400 V is applied to the developing roller 54K, and a bias having a polarity higher than that of the developing roller 8 and the same polarity as the charging polarity of the liquid toner is applied to the leveling roller 55K. In the present embodiment, a bias of about +600 V is applied to the leveling roller 55K. Therefore, the toner particles in the liquid toner on the developing roller 54K move toward the developing roller 54K when passing through the nip with the leveling roller 55K. As a result, the toner particles are gently coupled to form a film, and when developing on the photoconductor, the toner particles move from the developing roller 54K to the photoconductor 20K quickly, and the image density is improved.

  The photoreceptor 20K is made of amorphous silicon, and the surface is charged to about +600 V by applying about +5.5 kV to the wire of the corona charger 30K upstream of the nip portion with the developing roller 54K. A latent image is formed so that the potential of the portion becomes + 25V. In the developing nip portion formed between the developing roller 54K and the photoconductor 20K, a bias + 400V applied to the developing roller 54K and a latent image (image portion + 25V, non-image portion + 600V) applied to the photoconductor 20K are formed. According to the electric field, the toner particles selectively move to the image portion on the photoconductor 20K. Thereby, an image is formed on the photoreceptor 20K. Since the carrier liquid is not affected by the electric field, it is separated at the exit of the developing nip between the developing roller 54K and the photoconductor 20K and adheres to both the developing roller 54K and the photoconductor 20K.

  The photosensitive member 20K that has passed through the developing nip portion passes through the nip portion with the intermediate transfer belt 70, and primary transfer is performed. The primary transfer backup roller 61K is applied with about -200 V having the opposite polarity to the charging characteristics of the toner particles, and the toner on the photoreceptor 20K is primarily transferred to the intermediate transfer belt 70, and only the carrier liquid is applied to the photoreceptor 20K. Remains. The carrier liquid remaining on the photoconductor 20K is scraped off by the photoconductor blade 21K downstream of the primary transfer unit and collected by the photoconductor cleaning liquid collection unit 22K.

  After the primary transfer, the intermediate transfer belt 70 proceeds to the secondary transfer unit 80 and enters the nip portion between the intermediate transfer belt 70 and the secondary transfer roller 81. In the secondary transfer unit 80, -1000V is connected to the secondary transfer roller 81, and the belt driving roller 82 is connected to the ground so as to be maintained at 0V. The layer is transferred to a medium such as paper.

The toner image transferred to a medium such as paper is then made into a permanent image by fusing the single color liquid toner image or full color liquid toner image transferred onto the medium in a fixing unit (not shown).
(Cleaning operation 1)
Next, the cleaning operation in the first embodiment of the present invention will be described.

  As described in the column of the problem to be solved by the invention, when the intermediate transfer belt 70 having elasticity is used, the toner particles may enter a minute recess of the intermediate transfer belt 70. In order to solve this problem, in the present embodiment, first, the carrier liquid is applied onto the intermediate transfer belt 70 by the carrier liquid application mechanism 90.

  The intermediate transfer belt 70 is made of an urethane rubber elastic layer of 200 μm and a total thickness of 280 μm on an 80 μm polyimide base material. The intermediate transfer belt 70 has a surface roughness of 2.9 μm, a volume resistance of 8.2 × 10 9 Ω · cm, and a relative dielectric constant of 4.0.

  FIG. 3 is a diagram showing a detailed configuration of the carrier liquid coating mechanism 90 according to the first embodiment of the present invention. As shown in the figure, a carrier liquid application mechanism 90 is disposed upstream of the secondary transfer roller 81, and this carrier liquid application mechanism 90 abuts against the intermediate transfer belt 70 and applies a carrier liquid to the carrier liquid application roller 91. A carrier liquid application backup roller 92, a carrier liquid storage unit 96 that stores the carrier liquid, a carrier liquid supply roller 93 that supplies the carrier liquid from the carrier liquid storage unit 96 to the carrier liquid application roller 91, and a carrier to the intermediate transfer belt 70. It comprises a carrier liquid supply roller blade 94 for adjusting the liquid application amount.

  In the normal state, the carrier liquid application roller 91 is separated from the intermediate transfer belt 70, but when the intermediate transfer belt 70 is cleaned, it is brought into contact with the intermediate transfer belt 70 to apply the carrier liquid. The amount of carrier liquid applied to the intermediate transfer belt 70 is about 2 μm to 20 μm in terms of the thickness of the carrier liquid. This is because when the amount of carrier liquid is 2 μm or less, the amount of carrier liquid is too small, and the dirt attached to the belt is difficult to diffuse, and when the amount of carrier liquid is 20 μm or more, the effect of diffusion of dirt into the carrier liquid is not. It depends on the fact that the carrier liquid is not wasted and is wasted. In the present embodiment, the amount of carrier liquid applied to the intermediate transfer belt 70 is 5 μm in terms of the thickness of the carrier liquid.

  In the present invention, the carrier liquid coating mechanism 90 makes the carrier liquid rich on the intermediate transfer belt 70, applies a shear shear force by the secondary transfer roller 81, deforms the minute irregularities of the intermediate transfer belt 70, and further performs the secondary transfer. By applying a bias to the roller 81 side, the toner particles that have entered the minute concave portion of the intermediate transfer belt 70 are attracted to the secondary transfer roller 81 side, thereby cleaning the upper surface of the intermediate transfer belt 70. In more detail, each part is operated as follows.

  During the operation of the normal image forming apparatus, the secondary transfer roller 81 rotates with the intermediate transfer belt 70 at a constant speed. The nip contact pressure between the secondary transfer roller 81 and the intermediate transfer belt 70 is set to 0.8 kgf / cm.

  On the other hand, during the cleaning operation, before the intermediate transfer belt 70 coated with the carrier liquid reaches the secondary transfer unit 80, the speed of the secondary transfer roller 81 is increased from the normal speed to 1.5 times speed. Change and drive. At this time, the rotation direction and contact pressure of the secondary transfer roller 81 are set in the same manner as in normal printing. At the same time, −1000 V is applied to the secondary transfer roller 81.

  The speed difference between the intermediate transfer belt 70 and the secondary transfer roller 81 is preferably in the range of 50 to 600 mm / s. This is because the shearing force is weak at 50 mm / s or less and a cleaning effect cannot be obtained, and the shearing force is too large at 600 mm / s or more, and the elastic intermediate transfer member is deteriorated.

  In this way, the toner particles adhering to the intermediate transfer belt 70 are recessed as the irregularities on the surface of the intermediate transfer belt 70 are deformed by shear shearing by the secondary transfer roller 81 at the nip of the secondary transfer portion. The toner is peeled off from the toner image and further moved to the secondary transfer roller 81 side. Further, since the secondary transfer roller 81 rotates faster than the intermediate transfer belt 70, the carrier liquid amount adhering to the intermediate transfer belt 70 side and the carrier liquid amount adhering to the secondary transfer roller 81 side are the latter. More, the cleaning effect will be higher.

  The carrier liquid and toner particles collected on the secondary transfer roller 81 side are scraped off by the secondary transfer roller blade 83 and collected by the secondary transfer roller cleaning liquid collection unit 84.

  Such a cleaning operation can be performed at any timing that does not affect image formation.

  The carrier liquid application time by the carrier liquid application mechanism 90 can be set arbitrarily, but it is preferable to perform one round of the intermediate transfer belt 70 by a single cleaning operation. This is to prevent a difference from the cleaning portion from appearing in the image on the paper because an uncleaned portion is formed on the intermediate transfer belt 70.

As a modification, FIG. 4 illustrates a case where the rotation of the secondary transfer roller 81 is rotated in the direction opposite to that during the normal printing operation. By reversing the rotation of the secondary transfer roller 81 in this way, it becomes easy to obtain a large shearing force, and the amount of carrier liquid that moves to the secondary transfer roller 81 side also increases, so that the cleaning effect is achieved. Becomes higher. In this modified example, the secondary transfer roller blade 88 and the secondary transfer roller cleaning liquid recovery unit 89 are provided below the secondary transfer roller 81.
(Cleaning operation 2)
Next, a cleaning operation in the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing main components constituting the image forming apparatus according to the second embodiment of the present invention. In this embodiment, the carrier liquid coating mechanism 90 is omitted by providing the carrier liquid on the intermediate transfer belt 70 from the photoconductor 20. At this time, any photoconductor of 20Y, 20M, 20C, and 20K may be used as the photoconductor 20 for supplying the carrier liquid, so that a notable limitation is avoided. As described above, in the second embodiment, since the photosensitive member is used as the carrier liquid application mechanism, it is not necessary to provide a separate mechanism for applying the carrier liquid.

  The intermediate transfer belt 70 is made of an urethane rubber elastic layer of 200 μm and a total thickness of 280 μm on an 80 μm polyimide base material. The intermediate transfer belt 70 has a surface roughness of 2.9 μm, a volume resistance of 8.2 × 10 9 Ω · cm, and a relative dielectric constant of 4.0.

  In this embodiment, during the cleaning operation, the contact pressure of the nip between the secondary transfer roller 81 and the intermediate transfer belt 70 is made smaller than the contact pressure during normal printing. This is because the optimum condition for cleaning can be set by reducing the contact pressure, and the deterioration of the intermediate transfer belt 70 can be prevented.

  During normal printing, the contact pressure of the nip between the secondary transfer roller 81 and the intermediate transfer belt 70 is set to 0.3 to 4 kgf / cm. This is because, at 0.3 kgf / cm or less, the intermediate transfer belt 70 having elasticity does not deform so as to correspond to the deformation of the paper asperities, and the transferability is reduced. This is because the bending pressure of the roller is induced and the contact pressure is not uniform in the axial direction. On the other hand, during the cleaning operation of the present invention, the contact pressure is preferably set to 0.05 to 1 kgf / cm. This is because if 0.05 kgf / cm or less, the shearing shear force is weak and the cleaning effect cannot be obtained, and if it is 1 kgf / cm or more, the shearing shear force is too large and the intermediate transfer belt 70 having elasticity is deteriorated. is there.

  In this embodiment, the secondary transfer roller 81 is a mechanism for changing the contact pressure of the nip between the secondary transfer roller 81 and the intermediate transfer belt 70 between normal printing and cleaning operation. A pressure changing mechanism for changing the pressure for pressing the intermediate transfer belt 70 is provided.

  In the second embodiment of the present invention, the outline of the operation at the time of cleaning is as follows. First, the carrier liquid is applied onto the intermediate transfer belt 70 by performing white printing from the photoreceptor 20. Next, as in the previous embodiment, by applying a speed difference between the intermediate transfer belt 70 and the secondary transfer roller 81, a shear shear force by the secondary transfer roller 81 is applied to the intermediate transfer belt 70. By deforming minute irregularities of the intermediate transfer belt 70 and applying a bias to the secondary transfer roller 81 side, toner particles that have entered the minute recesses of the intermediate transfer belt 70 are moved to the secondary transfer roller 81 side. The intermediate transfer belt 70 is cleaned by drawing it. As described above, the second embodiment of the present invention has an effect that the cleaning operation of the present invention can be performed without particularly providing the carrier liquid coating mechanism 90.

  The speed difference between the intermediate transfer belt 70 and the secondary transfer roller 81 is preferably in the range of 50 to 600 mm / s. This is because the shearing force is weak at 50 mm / s or less and a cleaning effect cannot be obtained, and the shearing force is too large at 600 mm / s or more, and the elastic intermediate transfer member is deteriorated.

  FIG. 6 shows a cleaning sequence diagram showing how each unit operates in order to perform the cleaning operation as described above. In this sequence diagram, it is assumed that the cleaning operation is performed as preliminary running before the start of image printing. If the cleaning operation is performed during the preliminary running before the start of image printing in this way, the cleaning can be performed without unnecessary rotation by starting the printing.

Hereinafter, this cleaning sequence will be described. First, the belt driving rollers 82 and 85 are started to rotate, and the intermediate transfer belt 70 is started to be driven. (See FIG. 11E) At this time, charging of the photoconductor 20 is started at the same time. (See FIG. 11A.) Since the exposure unit is off in the initial stage, no latent image is formed on the photoconductor 20. (Refer to FIG. 11B.) Further, the pressure that causes the secondary transfer roller 81 to contact the intermediate transfer belt 70 by the pressure changing mechanism is 0.2 kgf / cm, which is lower than 1.5 kgf / cm during normal printing. . (See FIG. 11 (f)) The speed of the secondary transfer roller 81 is a normal speed. (See Fig. 11 (g))
Next, a developing bias is applied at the timing when the leading end of the charging portion of the photoconductor 20 reaches the nip with the developing roller 54. (See FIG. 11 (c)) Since no latent image is formed on the photoconductor 20, white solid printing is performed. As a result, the carrier liquid is applied from the photoconductor 20 to the intermediate transfer belt 70. During this time, the primary transfer bias is not applied. (See FIG. 11 (d))
The speed of the secondary transfer roller 81 is switched to the normal double speed immediately before the white solid print front end on the intermediate transfer belt 70 reaches the secondary transfer unit 80. (See FIG. 11 (g)) At the same time, -1000 V is applied to the secondary transfer roller. After the switching, when the time required for the intermediate transfer belt 70 to make one revolution has elapsed, the speed of the secondary transfer roller 81 is returned to the normal speed, and the pressure for bringing the secondary transfer roller 81 into contact with the intermediate transfer belt 70 is set to 1 during normal printing. .5 kgf / cm. (See FIGS. 11 (f) and 11 (g))
After white printing is performed for one turn of the intermediate transfer belt 70, a normal image forming operation is started. (See FIG. 11B) A primary transfer bias is applied immediately before the leading edge of the image formed on the photoconductor 20 reaches the primary transfer unit. After that (see FIG. 11D), a normal image forming operation is performed.

  As described above, the example in which the cleaning sequence is performed during the preliminary running before the start of image printing has been described. In addition to performing the cleaning sequence before starting the image printing in this way, the cleaning sequence may be performed while the printing operation is not performed. Alternatively, a cleaning sequence may be performed after the end of the printing operation.

Further, as in the first embodiment, the rotation direction of the secondary transfer roller 81 may be reverse to the normal rotation as shown in FIG. The reverse rotation makes it easy to obtain a large shearing force, and the amount of carrier liquid that moves toward the secondary transfer roller 81 increases, so that the cleaning effect is enhanced.

1 is a diagram illustrating main components constituting an image forming apparatus according to a first embodiment of the present invention. It is sectional drawing which showed the main components of the developing unit. It is a figure which shows the detailed structure of the carrier liquid application mechanism 90 of this invention. It is a figure which shows a structure when a piezoelectric ceramic element is used as an example of a vibration application member. It is a figure which shows the main components which comprise the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a cleaning sequence diagram showing how each unit operates to perform a cleaning operation. FIG. 6 is a diagram illustrating a state in which toner particles have entered a concave portion of an intermediate transfer member having elasticity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vibration application member, 11 ... Piezoelectric ceramic element, 12 ... Stainless steel plate, 13 ... Base plate, 14 ... Vibration member holding member 20Y, 20M, 20C, 20K ... Photoconductor 21K ... Photoconductor blade, 22K ... Photoconductor cleaning liquid recovery units 30Y, 30M, 30C, 30K ... Corona chargers 40Y, 40M, 40C, 40K ... Exposure unit optical paths 50Y, 50M, 50C, 50K ... Development units 51Y, 51M, 51C, 51K ... Toner supply rollers 53Y, 53M, 53C, 53K ... Development toner containers 54Y, 54M, 54C, 54K ... Development rollers 52K ... Toner regulating blade , 55K, leveling roller, 56K, leveling roller blade, 57K, leveling roller blade cleaning liquid recovery unit, 8K: developing roller blade, 59K: developing roller cleaning liquid recovery unit 60Y, 60M, 60C, 60K ... primary transfer unit 61Y, 61M, 61C, 61K ... primary transfer backup roller 70: intermediate Transfer belt 80 ... secondary transfer unit 81 ... secondary transfer roller 82 ... belt drive roller 83 ... secondary transfer roller blade 84 ... secondary transfer roller cleaning liquid recovery unit , 85... Belt drive roller, 86... Belt cleaning blade, 87... Belt cleaning liquid recovery unit, 88... Secondary transfer roller blade, 89. ... Carrier liquid application mechanism, 91 ... Carrier liquid application roller, 92 ... Carrier liquid application backup roller, 93 Carrier liquid supply roller, 94... Carrier liquid supply roller blade, 95... Carrier liquid storage unit 101... Intermediate transfer belt (intermediate transfer body) surface, 102. liquid

Claims (5)

Developing means for developing an electrostatic latent image formed on the photoreceptor with liquid toner obtained by dispersing toner in a carrier liquid;
Primary transfer means for transferring an image developed on the photoreceptor to an intermediate transfer medium;
Secondary transfer means for transferring the image transferred to the intermediate transfer medium to a recording medium;
Fixing means for heating and pressurizing the image transferred to the recording medium and fixing the image on the recording medium,
In the image forming apparatus, wherein the secondary transfer unit includes a secondary transfer roller that presses the recording medium so as to face the intermediate transfer medium.
A carrier liquid application mechanism for applying a carrier liquid to the intermediate transfer medium;
Means for applying a bias for moving toner from the intermediate transfer medium to the secondary transfer roller;
Means for rotating the intermediate transfer medium and the secondary transfer roller with a speed difference;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the secondary transfer roller is provided with a pressure changing mechanism capable of changing a pressure for pressing the intermediate transfer medium. The image forming apparatus according to claim 2, wherein the pressure for pressing the intermediate transfer medium is lowered by the pressure changing mechanism during a cleaning operation. 4. The image forming apparatus according to claim 1, wherein the photoconductor is used as the carrier liquid coating mechanism. The image forming apparatus according to claim 4, wherein the pressure changing mechanism is operated during preliminary running before starting printing.

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