JP2007017583A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent toner particle accumulation by causing a liquid carrier recovery member on a photoreceptor to recover substantially only the liquid carrier whose fluidity is satisfactory, then pushing toner particles trapped by the recovery so that the toner particles do not accumulate. <P>SOLUTION: The image forming apparatus exerts control, such that a solid image is formed uniformly on the photoreceptor 16 during the stoppage of a printing operation, then the photoreceptor liquid carrier recovery member 22 recovers liquid carrier, a photoreceptor cleaning member 17 performs a sequence for recovering toner particles, and thereafter, the printing operation is stopped. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for developing an electrostatic latent image formed on a photoreceptor with liquid toner in which toner particles are dispersed in a carrier liquid.

  Conventionally, a thin film of liquid toner is formed on a developing roller, and carrier liquid and toner particles in the thin film are electrostatically transferred to an image portion of a latent image on a photosensitive member forming a nip portion with the developing roller. In an image forming apparatus that performs development in this way, when using high-concentration and high-viscosity liquid toner, toner particles adhere to a non-image portion on the photosensitive member that passes through the nip portion between the photosensitive member and the developing roller, and fog toner There remains a problem that the image remains fogged.

In order to solve this problem, there has been proposed an image forming apparatus in which a removing roller is provided on the photosensitive member, and a bias is applied to the removing roller to collect fog toner and excess carrier liquid on the photosensitive member. (Patent Document 1)
An outline of a conventional image forming apparatus will be described with reference to FIGS.

  In FIG. 11, 101 is a photosensitive member, 102 is a charging unit, 103 is an exposure unit, 104 is a developing device, 105 is a transfer device, and 106 is a removal roller. The photosensitive member 101 is rotationally driven at a constant speed by a driving unit (not shown). Then, after being charged by the charging unit 102, an electrostatic latent image is carried on the outer peripheral surface of the photoreceptor 101 by the exposure unit 103. Thereafter, the electrostatic latent image is developed by the developing device 104 and transferred to the transfer paper by the transfer device 105. The removal roller 106 is provided as a part of the developing device 104 by pressing the photosensitive member 101 with a toner layer interposed therebetween, and removes a part of the toner in the non-image area remaining as fog toner on the photosensitive member 101 by an electric field. belongs to.

FIG. 12 shows an example of setting potentials on the photoreceptor 101, the removing roller 106, the surface of the toner layer of the image portion, and the surface of the non-image portion. A bias voltage close to or higher than the surface potential of the image portion toner layer on the photosensitive member 101 is applied to the removal roller 106 so that the toner does not move from the developed toner layer to the removal roller 106. Therefore, the toner particles on the photoconductor 101 are not collected in the image portion, and only the carrier liquid is collected. In the non-image portion, the floating fog toner is moved to the removal roller 106 by an electric field generated by the difference between the non-image portion surface potential on the photoconductor 101 and the potential due to the bias voltage. Thereby, the fog toner is collected together with the carrier liquid.
JP 2002-287517 A

  In an image forming apparatus using a high-concentration and high-viscosity liquid toner, in a contact development system in which a developing roller and a photoconductor are in contact, fog toner may adhere to a non-image portion on the photoconductor. In the method of collecting the fog toner and the excess carrier liquid by providing the removal roller as in the prior art, the amount of fog toner collected by the removal roller increases when an image with many non-image portions is printed. By including the toner particles in the recovered liquid, the viscosity becomes high and the fluidity is poor as compared with the case where only the carrier liquid is recovered.

  On the other hand, in an image forming apparatus using liquid toner, the collected liquid collected in each collecting unit may be recycled and used again for printing. In order to recycle the recovery liquid of the conventional removal roller, it is necessary to transport the recovery liquid to a recovery tank or a supply destination. At this time, in consideration of miniaturization and simplification of the apparatus, it is preferable to transport the recovered liquid only by gravity, instead of forced transportation by a pump or the like. In the case of gravity transport, if only the carrier liquid is used, the fluidity is good and can be transported without problems. However, when toner particles are included, the toner particles are easily trapped in a pipe or the like and accumulated. There is a problem that clogging occurs when driving for a long time. As will be described below, the above-described problem occurs not only with high-concentration liquid toner but also with low-concentration liquid toner.

  FIG. 13 is a diagram showing dispersion due to three-dimensional repulsion, FIG. 14a is a diagram showing a state of toner solids with a solid content concentration of about 25%, and FIG. 14b is a diagram showing a state of toner solids with a solid content concentration of about 4%. . The dispersion of the high-viscosity, high-concentration liquid toner is achieved by the dispersion agent adhering to the particles extending into the carrier liquid, generating a three-dimensional repulsive force, and preventing the particles from contacting each other. For this reason, in a high concentration state during normal use, the particles maintain a uniform distance as shown in FIG. 14a, and a liquid with a uniform concentration is formed when viewed macroscopically.

  However, in the state where the density is lowered like the fog toner collected by the squeeze roller, the particles come close to a distance where the three-dimensional repulsive force due to the dispersing agent becomes effective, so that the particles are segregated as shown in FIG. Furthermore, since the specific gravity of the carrier liquid and the toner solid content is different from about 0.84 and 0.90, respectively, the segregated particles are likely to be precipitated and easily trapped in the pipe.

  The present invention solves the above-mentioned problems, and collects a liquid having a good fluidity of only the carrier liquid on the carrier liquid recovery member on the photoreceptor so that the trapped toner particles are washed away so that the toner particles do not accumulate. The purpose is to do.

  The present invention solves the above-described problem, and includes a developing roller that carries liquid toner, a photosensitive member that forms a latent image with the liquid toner carried on the developing roller, and a photosensitive member that collects carrier liquid on the photosensitive member. In an image forming apparatus that includes a body carrier liquid recovery member and a photoreceptor cleaning member that collects toner particles on the photoreceptor, and forms and prints an image using a latent image formed on the photoreceptor, when the printing operation is stopped, A solid image is uniformly formed on the photoconductor, a carrier liquid is collected by the photoconductor carrier liquid collecting member, a toner particle is collected by the photoconductor cleaning member, and then a printing operation is stopped. It is characterized by having a control device for controlling as described above.

  Further, the control device controls to execute the sequence at the end of the printing operation.

  Further, the control device controls the developing roller bias to be set to be larger than that during normal printing during at least one rotation of the developing roller in the sequence.

  Further, the control device controls the photosensitive member and the intermediate transfer member to be separated during the sequence.

  Furthermore, the present invention is a method for solving the above-described problem, wherein when the printing operation is stopped, a solid image is uniformly formed on the photosensitive member, the carrier liquid is recovered by the photosensitive member carrier liquid recovery member, and the photosensitive member cleaning member is used. A sequence for collecting the toner particles is executed, and then the printing operation is stopped.

  Further, the sequence is executed at the end of the printing operation.

  Further, the developing roller bias is set to be larger than that during normal printing during at least one rotation of the developing roller in the sequence.

  Further, the photosensitive member and the intermediate transfer member are separated during the sequence.

  A developing roller carrying liquid toner, a photoconductor that forms a latent image with the liquid toner carried on the developing roller, a photoconductor carrier liquid collecting member that collects carrier liquid on the photoconductor, and toner particles on the photoconductor An image forming apparatus that forms and prints an image using a latent image formed on the photoconductor, and uniformly forms a solid image on the photoconductor when the printing operation is stopped. The photoconductor is provided with a control device that performs a sequence of collecting the carrier liquid with the photoconductor carrier liquid collecting member, collecting the toner particles with the photoconductor cleaning member, and then stopping the printing operation. The upper carrier liquid recovery member recovers a liquid having substantially good carrier fluidity, and the trapped toner particles are washed away, and the toner particles are stored. It is not necessary to.

  Further, by performing the sequence when the printing operation is stopped or ended, the toner particles collected during the printing operation can be pushed away. Also, providing a sequence when printing is not performed does not adversely affect the printing operation.

  Also, by setting the developing roller bias larger than that during normal printing during the sequence, the toner particles that have partially adhered to the surface of the developing roller over a long period of time are developed onto the photoreceptor, and the surface of the developing roller is clean. Can be reset.

  Further, by separating the photosensitive member from the intermediate transfer member during the sequence, toner particles developed on the photosensitive member are not transferred to the intermediate transfer member but are collected by the photosensitive blade, so that paper is wasted. There is no.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an image forming apparatus according to the present invention. 1 is an image forming apparatus, 2 is a developing device, 2Y is a yellow developing unit, 2M is a magenta developing unit, 2C is a cyan developing unit, 2K is a black developing unit, 60 is an intermediate transfer unit, 61 is an intermediate transfer belt, and 62 is an intermediate A transfer belt roller, 63 is a primary transfer roller, 70 is a secondary transfer unit, and 71 is a secondary transfer roller.

  The developing device 2 includes a yellow developing unit 2Y, a magenta developing unit 2M, a cyan developing unit 2C, and a black developing unit 2K as four developing units. In each of the developing units 2Y, 2M, 2C, and 2K, each color latent image is formed and developed with liquid toner as a developer of yellow Y, magenta M, cyan C, and black K, respectively. The detailed structure of the developing device 2 will be described later.

  The intermediate transfer unit 60 is arranged in an endless belt-like intermediate transfer belt 61, two intermediate transfer belt rollers 62 that stretch the intermediate transfer belt 61, and a position facing the developing device 2 inside the intermediate transfer belt 61. A primary transfer roller 63. The intermediate transfer unit 60 is for transferring the color toner images developed by the developing device 2 to the surface of the intermediate transfer belt 61. The intermediate transfer belt 61 is driven and rotated by one of the two intermediate transfer belt rollers 62.

  The developing units 2Y, 2M, 2C, and 2K for the respective colors are arranged in the order of colors K, C, M, and Y from the upstream side in the rotation direction of the intermediate transfer belt 61 along the straight line portion of the intermediate transfer belt 61 of the intermediate transfer unit 60. It is installed. Of course, the developing units 2Y, 2M, 2C, and 2K can be arranged in any order other than that illustrated. In the image forming apparatus 1 configured as described above, the electrostatic latent image is first developed in the black K developing unit 2 </ b> K, and the black K toner image is transferred onto the surface of the intermediate transfer belt 61. Next, the electrostatic latent image is developed in the cyan C developing unit 2 </ b> C, and the cyan C toner image is transferred onto the black K toner image on the surface of the intermediate transfer belt 61. Similarly, the electrostatic latent image is developed in the developing unit 2M of magenta M, and the toner image of magenta M is transferred onto the surface of the intermediate transfer belt 61. Further, the electrostatic latent image is developed in the developing unit 2Y of yellow Y. Is developed, and a yellow Y toner image is superimposed and transferred onto the surface of the intermediate transfer belt 61. Thereafter, the respective color toner images transferred to the intermediate transfer belt 61 are combined, transferred onto a sheet by the secondary transfer roller 71 of the secondary transfer unit 70, and printed as a color toner image.

  Next, the developing device 2 will be described with reference to FIG. In the image forming apparatus 1, the developing device 2 includes a yellow developing unit 2Y, a magenta developing unit 2M, a cyan developing unit 2C, and a black developing unit 2K. Since the developing units have the same structure, the black developing unit 2K will be described as a representative here.

  FIG. 2 is a diagram showing the black developing unit 2K. 2K is a black developing unit, 3 is a toner supplying unit, 4 is a toner supplying roller, 5 is a toner regulating blade, 6 is a developing toner container, 7 is a developing unit, 8 is a developing roller, 9 is a developing roller blade, and 10 is a developing roller. A cleaning liquid recovery unit, 11 is a leveling unit, 12 is a leveling roller constituting a leveling means, 13 is a leveling roller blade constituting a leveling means cleaning member, 14 is a leveling means cleaning liquid recovery unit, and 15 Photosensitive unit, 16 is a photoconductor, 17 is a photoconductor blade constituting a photoconductor cleaning member, 18 is a photoconductor cleaning liquid recovery unit, 19 is a charging unit, 20 is an exposure unit, and 21 is a photoconductor carrier liquid recovery unit. Squeeze section 22 for squeezing rollers constituting the photosensitive member carrier liquid collecting means, and 23 squeezing constituting the cleaning member for the photosensitive member carrier liquid collecting means. Roller blades, 24 denotes a squeeze roller cleaning liquid collection portion constituting the photoconductor carrier liquid collecting means the cleaning liquid recovery section.

  The toner supply unit 3 includes a toner supply roller 4, a toner regulating blade 5, and a developing toner container 6. The toner supply roller 4 is a cylindrical member, and is an aniloc roller that rotates clockwise as viewed from the front of 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. FIG. 3 is a perspective view of the toner supply roller 4, and FIG. 4 is a diagram illustrating the groove pitch and groove depth of the toner supply roller 4.

  The toner regulating blade 5 is composed of a rubber portion made of urethane rubber or the like that contacts the surface of the toner supply roller 4 and a metal plate that supports the rubber portion, and scrapes off the liquid toner remaining on the toner supply roller 4. It is for removing. FIG. 5 shows a diagram in which the toner regulation blade 5 regulates the toner amount.

  The developing toner container 6 is a container such as a tank for storing the liquid toner scraped off by the toner regulating blade 5. Liquid toner is stored in the developing toner container 6 of the toner supply unit 3. The liquid toner is prepared by adding toner particles having an average particle diameter of 1 μm, in which a colorant such as a pigment is dispersed in a thermoplastic resin, together with a dispersant to a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. The toner solid content concentration is about 25%.

  The developing unit 7 includes a developing roller 8, a developing roller blade 9, and a developing roller cleaning liquid recovery unit 10. The developing roller 8 is a cylindrical member having a width of about 320 mm, and rotates counterclockwise around the central axis when viewed from the front of FIG. The developing roller is provided with an elastic body such as conductive urethane rubber, a resin layer, and a rubber layer on an outer peripheral portion of an inner core made of metal such as iron. The developing roller blade 9 is made of rubber or the like that comes into contact with the surface of the developing roller 8 and scrapes off and removes the liquid toner remaining on the developing roller 8. The developing roller cleaning liquid recovery unit 10 is a container such as a tank for storing liquid toner scraped off by the developing roller blade 9.

  The leveling unit 11 includes a leveling roller 12, a leveling roller blade 13, and a leveling roller cleaning liquid recovery unit 14. The leveling roller 12 is a cylindrical member, and preferably has a structure that rotates around a central axis and includes a conductive resin layer or a rubber layer on the surface layer of the metal roller. In this embodiment, the rotation direction is the direction opposite to the developing roller 8, but a speed difference may be provided with respect to the outer peripheral speed of the developing roller 8 to rotate in the driven direction. The leveling roller blade 13 is made of rubber or the like that comes into contact with the surface of the leveling roller 12 and scrapes and removes the liquid toner remaining on the leveling roller 12. The leveling roller cleaning liquid recovery unit 14 is a container such as a tank that stores liquid toner scraped off by the leveling roller blade 13.

  In this embodiment, the leveling roller 12 is used as the leveling means, but a corona charger may be used. In this case, the leveling roller blade 13 and the leveling roller cleaning liquid recovery unit 14 do not need to be provided. Further, the entire leveling portion 11 may not be provided.

  The photosensitive unit 15 includes a photoconductor 16, a photoconductor blade 17, and a photoconductor cleaning liquid recovery unit 18. The photosensitive member 16 is a cylindrical member having a width wider than about 320 mm of the developing roller 8 and having a photosensitive layer formed on the outer peripheral surface thereof, and rotates around a central axis. In this embodiment, it rotates clockwise as indicated by an arrow. The photoreceptor 16 is composed of an organic photoreceptor or an amorphous silicon photoreceptor. The photoconductor blade 17 is in contact with the surface of the photoconductor 16 and is made of rubber. The photoconductor blade 17 scrapes and removes the liquid toner remaining on the photoconductor 16. The photoconductor cleaning liquid recovery unit 18 is a container such as a tank for storing liquid toner scraped off by the photoconductor blade 17.

  The charging unit 19 and the exposure unit 20 are provided upstream of the nip portion between the photoconductor 16 and the developing roller 8. The charging unit 19 is a portion to which a bias having the same polarity as the liquid toner charging polarity is applied from a power supply device (not shown) and is charged by contacting the photosensitive member 16. The exposure unit 20 is charged by irradiating a laser. This is a portion for forming a latent image on the photosensitive member 16.

  The squeeze unit 21 includes a squeeze roller 22, a squeeze roller blade 23, and a squeeze roller cleaning liquid recovery unit 24. The squeeze roller 22 is a cylindrical member that is installed downstream of the nip portion between the photosensitive member 16 and the developing roller 8 and is wider than the width of about 320 mm of the developing roller 8, and is opposite to the photosensitive member 16 about the central axis. And an elastic roller having an elastic member such as conductive urethane rubber and a fluororesin surface layer disposed on the surface of the metal core. The squeeze roller blade 23 is in contact with the surface of the squeeze roller 22 and is made of rubber for scraping off and removing the liquid toner remaining on the squeeze roller 22. The squeeze roller cleaning liquid recovery unit 24 is a container such as a tank that stores liquid toner scraped off by the squeeze roller blade 23.

  In this embodiment, the squeeze roller is used as the photoconductor carrier liquid recovery member. However, the present invention is not limited to this.

  Next, the normal printing operation of the developing device 2 will be described. In the toner supply unit 3, the toner supply roller 4 rotates around the central axis to pump up the liquid toner stored in the developing toner container 6. The toner regulating blade 5 abuts on the surface of the toner supply roller 4, scrapes off other excess liquid toner while leaving the liquid toner in the groove formed on the surface of the toner supply roller 4, and supplies it to the developing roller 8. Regulate the amount of liquid toner. In the present embodiment, the liquid toner applied to the developing roller 8 is quantified so that the film thickness is about 6 μm. The liquid toner scraped off by the toner regulating blade 5 is dropped back into the developing toner container 6 by gravity. The liquid toner that has not been scraped off by the toner regulating blade 5 is accommodated in an uneven groove on the surface of the toner supply roller 4, and is applied to the surface of the developing roller 8 by being pressed against the developing roller 8. About +400 V is applied to the toner supply roller 4.

  In the developing unit 7, the developing roller 8 has a width of about 320 mm, and the surface speed in the circumferential direction rotates at about 250 mm / s. The developing roller 8 in which the liquid toner is applied to the toner supply roller 4 contacts the leveling roller 12 of the leveling unit 11 downstream of the nip portion with the toner supply roller 4. A bias of about +400 V is applied to the developing roller 8, and a bias higher than that of the developing roller 8 and having the same polarity as the charging polarity of the liquid toner is applied to the leveling roller 12. In the present embodiment, a bias of about + 800V is applied.

  Therefore, the toner particles on the developing roller 8 move to the developing roller 8 side when passing through the nip portion with the leveling roller 12, and the toner solid content concentration of the liquid toner adhering to the leveling roller 12 is 25% or less. Therefore, the toner solid content concentration of the liquid toner adhering to the developing roller 8 is 25% or more. Accordingly, the toner particles are loosely coupled on the developing roller 8, the toner moves quickly, the image density is improved, the pattern corresponding to the groove of the toner supply roller 4 is erased, and the liquid toner film thickness is made uniform. And the toner is carried. Next, the developing roller 8 that has passed through the nip portion with the leveling roller 12 contacts the photoconductor 16.

  The leveling roller blade 13 abuts the surface of the leveling roller 12 downstream of the nip portion between the leveling roller 12 and the developing roller 8 and scrapes off excess liquid toner adhering to the surface of the leveling roller 12. The liquid toner is leveled by gravity and dropped into the roller cleaning liquid recovery unit 14 and recovered.

  In the photosensitive unit 15, the photosensitive member 16 charges the surface to about +600 V by applying about +5.5 kV to the wire of the corona charger by the charging unit 19 upstream of the nip portion with the developing roller 8, and then the exposure unit 20, a latent image is formed so that the potential of the image portion is about + 25V. At the nip where the developing roller 8 and the photosensitive member 16 are in contact, the bias is about +400 V applied to the developing roller 8 and an image portion lower than the bias applied to the developing roller 8 formed by the latent image on the photosensitive member 16. According to an electric field of about +25 V and a non-image portion of about +600 V higher than the bias applied to the developing roller 8, the toner particles selectively move to the image portion on the photoconductor 16 to form a latent image having the same width as the developing roller 8. To do. However, fog toner is also generated in the non-image area, and some toner particles are attached. Further, since the carrier liquid is not affected by the electric field, it is separated at the exit of the nip portion between the developing roller 8 and the photosensitive member 16 and adheres to both the developing roller 8 and the photosensitive member 16.

  The developing roller blade 9 abuts on the surface of the developing roller 8 downstream of the nip portion with the photosensitive member 16, scrapes off excess liquid toner adhering to the surface of the developing roller 8, and the liquid toner is removed by gravity. It falls into the cleaning liquid recovery unit 10 and is recovered.

  After passing through the nip portion with the developing roller 8, the photosensitive member 16 contacts the squeeze roller 22 with a surface potential of about + 150V for the image portion and about + 550V for the non-image portion. The squeeze roller 22 is applied with about +300 V which is a bias between the image portion and the non-image portion, and an electric field is generated in the direction to press the toner particles against the photosensitive member 16. The toner particles are not collected on the roller 22 but remain attached to the photoreceptor 16 and are not affected by the electric field, and the carrier liquid is separated at the exit of the nip portion between the photoreceptor 16 and the squeeze roller 22. An electric field in the direction in which the fog toner is collected by the squeeze roller 22 is generated for the non-image portion. Therefore, the carrier liquid is collected by the squeeze roller 22 and is not affected by the electric field. 22 at the nip exit.

  The carrier liquid containing excess fog toner collected by the squeeze roller 22 and adhered to the surface is scraped off by the squeeze roller blade 23 that contacts the surface of the squeeze roller 22 downstream of the nip portion with the photosensitive member 16. The carrier liquid containing the fog toner falls to the squeeze roller cleaning liquid recovery unit 24 by gravity and is recovered.

  The photoreceptor 16 that has passed through the nip portion with the squeeze roller 22 forms a clean image with no toner particles adhering to the non-image portion, and forms the nip portion with the primary transfer backup roller 63 via the intermediate transfer belt 61. To do. The primary transfer backup roller 63 is applied with about -200 V having the opposite polarity to the charging characteristics of the toner particles, and the toner particles on the photosensitive member 16 are primarily transferred to the intermediate transfer belt 61 and are transferred to the photosensitive member 16. Only the carrier liquid remains. The carrier liquid remaining on the photoconductor 16 is scraped off by the photoconductor blade 17 in contact with the surface of the photoconductor 16 downstream of the primary transfer backup roller 63 via the intermediate transfer belt 61 and the nip, and the carrier liquid is It is dropped and collected in the photosensitive member cleaning liquid collecting unit 18 by gravity.

  Next, two embodiments of the recycling mechanism of the liquid toner collected in the squeeze roller cleaning liquid collecting unit 24 and the developing roller cleaning liquid collecting unit 10 will be described.

  FIG. 6 is a diagram illustrating a first embodiment of the recycling mechanism. Reference numeral 25 denotes a recycling unit, 26 denotes a toner tank, 27 denotes a first pump, 28 denotes a carrier liquid tank, 29 denotes a first valve, 30 denotes a concentration adjusting tank, 31 denotes an agitator, and 32 denotes a second pump.

  The toner tank 26 is a tank that stores high-concentration replenishment toner having a solid concentration of about 35%, and is connected to the concentration adjustment tank 30 via a pipe and a first pump 27. The first pump 27 is a pump for supplying high-concentration replenishment toner from the toner tank 26 to the concentration adjustment tank 30. The carrier liquid tank 28 is a tank that stores a carrier liquid of liquid toner, and is connected to the concentration adjustment tank 30 via a pipe and a first valve 29. The first valve 29 is a valve that opens and closes when supplying the carrier liquid.

The density adjustment tank 30 includes the liquid toner collected by the squeeze roller cleaning liquid collecting unit 24, the liquid toner collected by the developing roller cleaning liquid collecting unit 10, and
For example, the high-concentration toner supplied from the toner tank 26 and the carrier liquid supplied from the carrier liquid tank 28 are stored to adjust the density. In this embodiment, the developing roller cleaning liquid recovery unit 10 is also used.

  The agitator 31 is a member that continuously agitates the liquid toner in the concentration adjusting tank 30. The second pump 32 is a pump for supplying the liquid toner adjusted in the density adjusting tank 30 to the developing toner container 6.

  Next, the operation of the first embodiment of the recycling mechanism will be described. The liquid toner recovered by the squeeze roller cleaning liquid recovery unit 24 is gravity transported to the concentration adjustment tank 30 through the pipe. Further, the liquid toner scraped off from the developing roller 8 by the developing roller blade 9 is also gravity transported to the density adjusting tank 30. The collected liquid toner is continuously stirred by the agitator 31 in the concentration adjusting tank 30. The density of the liquid toner in the density adjusting tank 30 is measured at any time by a density measuring mechanism (not shown). The liquid toner in the density adjusting tank 30 is adjusted to about 25% by appropriately adding the high density toner in the toner tank 26 or the carrier liquid in the carrier liquid tank 28 according to the result of density measurement. The liquid toner adjusted to about 25% is supplied to the developing toner container 6 by the second pump 32 as necessary.

  Here, the case where high density toner is supplied to the density adjustment tank 30 means that a lot of toner particles are consumed by printing a large number of high density images having a high image rate, and the toner particles are not much consumed by the developing roller blade 9. This is a case where the liquid toner in the concentration adjusting tank 30 is not collected and has a low concentration. Further, when the carrier liquid is supplied to the density adjustment tank 30, the amount of toner particles consumed is reduced by printing many low density images having an image rate of several percent, and the developing roller blade 9 increases the density. This is a case where the toner is collected and the liquid toner in the concentration adjusting tank 30 has a high concentration.

  The carrier liquid remaining on the photoconductor 16 is collected by the photoconductor blade 17 downstream of the nip portion between the photoconductor 16 and the primary transfer backup roller 63 via the intermediate transfer belt 61. For this reason, toner particles of different colors may be mixed in the recovered liquid due to reverse transfer or the like, and the recovered liquid is discarded without being recycled.

  FIG. 7 is a diagram showing a second embodiment of the recycling mechanism. Reference numeral 25 denotes a recycling unit, 26 denotes a toner tank, 27 denotes a first pump, 28 denotes a carrier liquid tank, 29 denotes a first valve, 30 denotes a concentration adjusting tank, 31 denotes an agitator, 32 denotes a second pump, 33 denotes a third pump, Reference numeral 34 denotes a separation device, 35 denotes a low concentration liquid tank, and 36 denotes a second valve. Members common to those in the first embodiment are given common reference numerals, and description thereof is omitted.

  The third pump 33 is a pump for supplying the liquid toner collected by the developing roller cleaning liquid collecting unit 10 to the separation device 34. The separation device 34 is a device that separates the liquid toner collected by the developing roller cleaning liquid collection unit 10 into a high-concentration liquid and a low-concentration liquid, and a detailed structure thereof will be described later. The low concentration liquid tank 35 is connected to the carrier liquid tank 28, the squeeze roller cleaning liquid recovery unit 24, and the separation device 34, and stores low concentration liquid toner. The second valve 36 is a valve provided between the low concentration liquid tank 35 and the concentration adjustment tank 30.

  FIG. 8 shows the structure of the separation device. Reference numeral 37 denotes a motor, and 38 denotes a mesh. The separation device 33 separates the toner particles by centrifugal force using the difference that the specific gravity of the toner particles is about 0.90 while the specific gravity of the carrier liquid is 0.84. The separation device 34 is rotated by a motor 37 at a high speed of about 5000 rpm, for example. In this state, the liquid toner recovered by the developing roller cleaning liquid recovery unit 10 is sent to the separation device 34 by the third pump 33. The liquid toner sent to the separation device 34 is moved upward by the force of the third pump 33 and is separated from the high-concentration toner liquid on the outside and the low-concentration toner liquid on the inside by the centrifugal force. At this time, the plurality of meshes 38 installed in the separation device 34 suppresses fluctuations in the liquid level due to rotation, so that a good separation effect can be obtained. The liquid toner reaching the top is separated into a high-concentration liquid and a low-concentration liquid, and the high-concentration liquid is discharged into the concentration adjustment tank 30 and the low-concentration liquid is discharged into the low-concentration liquid tank 35.

  Next, the operation of the second embodiment of the recycling mechanism will be described. The liquid toner recovered by the squeeze roller cleaning liquid recovery unit 24 is gravity transported to the low concentration liquid tank 35 through the pipe. The liquid toner scraped from the developing roller 8 by the developing roller blade 9 passes through the third pump 33 and the separation device 34, and the low concentration liquid is conveyed to the low concentration liquid tank 35 and the high concentration liquid is conveyed to the concentration adjustment tank 30. The carrier liquid tank 28 is connected to the low-concentration liquid tank 35 via the first valve 29, and when the low-concentration liquid in the low-concentration liquid tank 35 is insufficient, the carrier liquid tank 28 is supplied with a low concentration from the carrier liquid tank 28 as necessary. A carrier liquid is appropriately supplied to the liquid tank 35.

  The liquid toner in the concentration adjustment tank 30 is continuously stirred by the agitator 31. The density of the liquid toner in the density adjusting tank 30 is measured at any time by a density measuring mechanism (not shown). The liquid toner in the concentration adjusting tank 30 is adjusted to about 25% by appropriately adding the high concentration toner in the toner tank 26 or the low concentration liquid in the low concentration liquid tank 35 according to the result of the concentration measurement. The liquid toner adjusted to about 25% is supplied to the developing toner container 6 by the second pump 32 as necessary.

  Next, the liquid toner, that is, the prevention sequence according to the embodiment of the present invention will be described. In the embodiment of the present invention, a control device (not shown) controls to start the liquid toner, that is, the prevention sequence when the normal printing operation is stopped or ended. First, as in the normal printing operation, the toner supply roller 4 supplies liquid toner to the developing roller 8. Next, the photosensitive member 16 is charged by the charging unit 19 and exposed to the exposure unit 20 to form a latent image.

  Subsequently, the photosensitive member 16 has a solid image or a 100% solid image in the entire width of the effective image area at the nip portion with the developing roller 8 for about 200 mm in the paper feed direction (A4 horizontal feed for one page). An image portion of about 3 turns is formed with about 20 mm. At this time, the developing roller bias is set to about +600 V, and the toner particles adhering to the surface of the developing roller 8 are more easily moved to the photoconductor 16 than usual.

  Next, the photoreceptor 16 forms a nip portion with the squeeze roller 22 downstream of the nip portion with the developing roller 8. At the nip portion between the photoconductor 16 and the squeeze roller 22, an electric field is generated in the image portion developed on the photoconductor 16 in a direction in which the toner particles are pressed against the photoconductor 16. Instead, a liquid with substantially good fluidity of only the carrier liquid is recovered and falls due to gravity, and only the carrier liquid is stored in the squeeze roller cleaning liquid recovery unit 24.

  Therefore, only the carrier liquid flows through the piping connected from the squeeze roller cleaning liquid recovery unit 24 to the concentration adjusting tank 30 or the low concentration liquid tank 35, and the trapped toner particles are pushed away, and the piping, It is possible to prevent toner particles from accumulating in the valve or the pump, that is, to prevent clogging.

  During the liquid toner, that is, the prevention sequence, the photoconductor 16 and the intermediate transfer belt 61 are separated from each other, and the toner particles of the solid image developed on the photoconductor 16 are not transferred to the intermediate transfer belt 61 but are collected by the photoconductor blade 17. Therefore, there is no need to transfer it wastefully.

  FIG. 9 is a diagram showing a solid image pattern. The solid image does not need to print 100% solid data, and may be a uniform image pattern in a grid pattern with an on-paper image density of 1.0 or more and a full width of the effective image area of 1 on 1 off. . The image density is a single color density for each of yellow Y, magenta M, cyan C, and black K with a density measuring standard ANSI-A, a light source D50, and a viewing angle of 2 degrees using a density measuring apparatus SpectroEye manufactured by GretagMacbeth. Was measured.

  FIG. 10 shows the relationship between the image density on paper and the toner solid content collected by the squeeze roller when printing the image pattern, by printing a uniform image pattern with different image ratios using cyan C toner. Results are shown. It can be seen that when the on-paper image density is a pattern of 1.0 or more, the squeeze roller recovery liquid contains almost no toner solids, and a liquid with excellent fluidity of only the carrier is recovered. Here, the toner solid content concentration is determined by placing 2 g of toner liquid on a filter paper (Advantech Toyo No. 2), flowing the carrier with ISOPER-G 100 g, and then sucking and drying all day and night, and the weight of solid content remaining on the filter paper ( The solid content concentration (x / 2) is calculated by measuring x).

  By performing the sequence of the above embodiment, the squeeze roller 22 on the photosensitive member recovers a liquid having substantially good fluidity of only the carrier liquid, and thereby the concentration adjusting tank 30 or the low concentration is recovered from the squeeze roller cleaning liquid recovery unit 24. The toner particles trapped in the pipe, valve, pump, etc. connected to the liquid tank 35 are pushed away, and the toner particles are not accumulated in the pipe, valve, pump, etc.

  Further, by performing the sequence when the printing operation is stopped or ended, the toner particles collected during the printing operation can be pushed away. Also, providing a sequence when printing is not performed does not adversely affect the printing operation.

  Further, by setting the developing roller bias larger than that during normal printing during the sequence, the toner particles partially adhered to the surface of the developing roller 8 are developed on the photosensitive member 16 by a long operation, and the developing roller 8 The surface can be reset cleanly.

  Further, by separating the photosensitive member 16 and the intermediate transfer member 61 during the sequence, the toner particles developed on the photosensitive member 16 are not transferred to the intermediate transfer member 61 and are collected by the photosensitive blade 17, which is useless. There is no need to do transcription.

The figure which shows the image forming apparatus of this invention Diagram showing development unit Perspective view of toner supply roller Diagram showing groove pitch and groove depth of toner supply roller Diagram of toner regulation blade regulating toner amount The figure which shows 1st Embodiment of a liquid toner recycling mechanism. The figure which shows 2nd Embodiment of a liquid toner recycling mechanism. Diagram showing separation device Diagram showing solid print pattern The figure which shows the relationship between the image density and the toner density of the squeeze roller recovery liquid A diagram showing a conventional image forming apparatus The figure which shows the example of electric potential setting of the conventional image forming apparatus The figure which shows dispersion | distribution by the three-dimensional repulsion of a toner, The figure which shows the state of toner solid content of a squeeze roller collection | recovery liquid

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Developing apparatus, 3 ... Toner supply part, 4 ... Toner supply roller, 5 ... Toner control blade, 6 ... Developing toner container, 7 ... Developing part, 8 ... Developing roller, 9 ... Developing roller blade DESCRIPTION OF SYMBOLS 10 ... Developing roller cleaning liquid recovery part, 11 ... Leveling part, 12 ... Leveling roller, 13 ... Leveling roller blade, 14 ... Leveling roller cleaning liquid recovery part, 15 ... Photosensitive part, 16 ... Photoconductor, 17 DESCRIPTION OF SYMBOLS ... Photoconductor blade, 18 ... Photoconductor cleaning liquid collection part, 19 ... Charging part, 20 ... Exposure part, 21 ... Squeeze part, 22 ... Squeeze roller, 23 ... Squeeze roller blade, 24 ... Squeeze roller cleaning liquid collection part, 25 Recycler, 26 ... toner tank, 27 ... first pump, 28 ... carrier liquid tank, 29 ... first valve, 30 ... concentration adjusting tank, 31 ... agitator 32 ... second pump, 33 ... third pump, 34 ... separation device, 35 ... low concentration liquid tank, 36 ... second valve, 37 ... motor, 38 ... mesh, 60 ... intermediate transfer unit, 61 ... intermediate transfer belt 62 ... Intermediate transfer belt roller, 63 ... Primary transfer roller, 70 ... Secondary transfer unit, 71 ... Secondary transfer roller

Claims (8)

A developing roller carrying liquid toner; a photoreceptor that forms a latent image with the liquid toner carried on the developing roller; a photoreceptor carrier liquid collecting member that collects carrier liquid on the photoreceptor; And a photoconductor cleaning member that collects toner particles, and forms a solid image uniformly on the photoconductor when the printing operation is stopped in an image forming apparatus that forms and prints an image using a latent image formed on the photoconductor And a control device that controls to recover the carrier liquid with the photoconductor carrier liquid recovery member, execute a sequence of recovering toner particles with the photoconductor cleaning member, and then stop the printing operation. An image forming apparatus. The image forming apparatus according to claim 1, wherein the control device controls the sequence to be executed at the end of a printing operation. The image forming apparatus according to claim 1, wherein the control device controls the developing roller bias to be set larger than that during normal printing during at least one rotation of the developing roller in the sequence. The image forming apparatus according to claim 1, wherein the control device controls the photosensitive member and the intermediate transfer member to be separated during the sequence. When the printing operation is stopped, a solid image is uniformly formed on the photosensitive member, the carrier liquid is collected by the photosensitive member carrier liquid collecting member, and the toner particles are collected by the photosensitive member cleaning member, and then the printing operation is performed. An image forming method characterized by stopping. The image forming method according to claim 5, wherein the sequence is executed at the end of a printing operation. 7. The image forming method according to claim 5, wherein the developing roller bias is set larger than that during normal printing during at least one rotation of the developing roller in the sequence. The image forming method according to claim 5, wherein the photosensitive member and the intermediate transfer member are separated from each other during the sequence.

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