JP2010107897A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enlarge the uniform film thickness region of a liquid developer film, in a developing device where the liquid developer film is formed on a developer carrier using a first coating member and a second coating member. <P>SOLUTION: The developing device includes: the first coating member 34 which rotates and coats the liquid developer; the second coating member 35 which rotates in a direction reverse to that of the first coating member 34; the developer carrier 36 which rotates in the same direction as that of the second coating member 35; a contact member 352 which comes into contact with the liquid developer coated on the second coating member 35 by the first coating member 34; and a control part which switches the rotation circumferential speed ratio of the second coating member 35 with respect to the developer carrier 36 between a first rotation circumferential speed ratio and a second rotation circumferential speed ratio smaller than the first rotation circumferential speed ratio. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Various image forming apparatuses for developing and visualizing an electrostatic latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent as a carrier liquid have been proposed. The developer used in this image forming apparatus has solid components (toner particles) suspended in a highly viscous organic solvent (carrier liquid) having electrical insulation properties such as silicon oil, mineral oil, and edible oil. Is. These toner particles use very fine particles having a particle diameter of around 1 μm, and can achieve higher image quality than a conventional dry image forming apparatus using a particle diameter of 7 μm.

  As an image forming apparatus using such a liquid developer, for example, Patent Document 1 discloses a uniform liquid by adjusting the contact pressure of a blade contacting an anilox roller or adjusting the rotational speed of an anilox roller. An image forming apparatus in which a developer is applied to a developing roller to improve development efficiency is disclosed.

  Patent Document 2 discloses an image forming apparatus in which an intermediate roller is provided between a coating roller and a developing roller, and the intermediate roller rotates the coating roller in the same direction at a constant speed. According to this image forming apparatus, since the developing roller and the applying roller are not in direct contact with each other, wear and damage due to the concave portion formed on the surface of the applying roller is not caused, and mechanical stress applied to the developing roller is reduced. The life of the developing roller can be extended.

In such an image forming apparatus using a liquid developer, an application roller (anilox roller) having a recess on the surface is used for the purpose of efficiently pumping the liquid developer and accurately measuring the liquid developer. ing.
JP 2002-99151 A JP 2002-287513 A

  However, when a coating roller (anilox roller) having a concave portion formed on the surface in this way is used, a transfer pattern of the liquid developer is generated by the concave portion, and the film thickness of the liquid developer becomes nonuniform. appear. In particular, in Patent Document 2, as shown in a graph showing the relationship between the roller speed ratio between the developing roller and the intermediate roller described in FIG. 8 and the amount of liquid developer applied on the developing roller, A region having a speed ratio of 1.0 or less becomes a non-uniform region and cannot be used for image formation.

  In the image forming apparatus, the resolution of an image to be formed can be improved by reducing the amount of coating applied to the developing roller (thinning the film thickness of the liquid developer). In the image forming apparatus, the application amount, that is, the lower limit of the film thickness of the liquid developer is limited, and further higher resolution cannot be realized.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and an image forming apparatus that realize high resolution of a formed image by increasing the lower limit of the film thickness of a liquid developer formed on a developing roller. In addition, the film thickness of the liquid developer can be changed in accordance with the print setting, and can cope with various printing conditions from an image that emphasizes high resolution to an image that emphasizes image density.

  In order to solve the above-described problems, a developing device of the present invention is configured to rotate and apply a developer reservoir that stores a liquid developer having toner and carrier liquid, and the liquid developer that is stored in the developer reservoir. A first application member that contacts the first application member, a second application member that rotates in a direction opposite to the first application member, and a second application member that contacts the second application member, A developer carrier that rotates in the same direction and carries the liquid developer applied by the second application member, and abuts on the liquid developer applied to the second application member by the first application member The rotational peripheral speed ratio of the second application member with respect to the contact member and the developer carrying member is switched between a first rotational peripheral speed ratio and a second rotational peripheral speed ratio smaller than the first rotational peripheral speed ratio. And a control unit. .

  Furthermore, in the developing device of the present invention, the abutting member is a plate member, and abuts against the second application member at a surface portion.

  Furthermore, in the developing device of the present invention, the control unit switches the rotational peripheral speed ratio of the second coating member with respect to the developer carrier to a third rotational peripheral speed ratio that is larger than the first rotational peripheral speed ratio. It is.

  Furthermore, the developing device of the present invention includes a contact adjustment support portion that adjusts a contact pressure or a contact angle of the contact member with the second application member.

  Further, the image forming apparatus of the present invention includes a liquid developer concentration adjusting unit that adjusts a toner concentration of a liquid developer having toner and a carrier liquid, and the liquid development in which the toner concentration is adjusted by the liquid developer concentration adjusting unit. A transport section that transports the developer, a developer storage section that stores the liquid developer transported by the transport section, and a first application member that rotates and carries the liquid developer stored in the developer storage section A second application member that contacts the first application member and rotates in a direction opposite to the first application member; a developer carrier that contacts the second application member and rotates in the same direction as the second application member; And a developing unit having a contact member that contacts the liquid developer applied to the second application member by the first application member, a latent image carrier developed by the development unit, and the developer support Rotation of the second application member relative to the body The speed ratio, a first rotary peripheral velocity ratio, is characterized in that it has a control unit for switching into a smaller second rotational peripheral speed ratio than the first rotary peripheral velocity ratio.

  Furthermore, the image forming apparatus of the present invention has setting means for selecting a setting, and when the first setting is selected, the control unit selects the first rotational peripheral speed ratio and the second setting. Is selected, the second rotational peripheral speed ratio is selected.

  Furthermore, in the image forming apparatus according to the aspect of the invention, when the third setting is selected, the control unit sets a rotational peripheral speed ratio of the second coating member with respect to the developer carrying member to be higher than the first rotational peripheral speed ratio. The control is performed by switching to a large third rotational peripheral speed ratio.

  Furthermore, the image forming apparatus of the present invention further includes a contact adjustment support unit that adjusts a contact pressure or a contact angle of the contact member with the second application member, and the control unit is configured by the setting unit. According to the selected setting, the contact pressure or the contact angle is adjusted by the contact adjustment support portion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a main configuration of an image forming apparatus according to an embodiment of the present invention. The four developing devices 30Y, 30M, 30C, and 30K are arranged at the lower part of the image forming unit with respect to the image forming unit arranged at the center of the image forming apparatus, and the intermediate transfer body 40, the secondary transfer unit ( The secondary transfer unit 60) is disposed above the image forming unit. Hereinafter, the image forming unit and the developing devices 30Y, 30M, 30C, and 30K will be described. However, since the configurations of the respective colors are the same, the alphabetical suffixes indicating the colors are omitted. Note that the image forming apparatus of the present embodiment is capable of forming a full-color image with four colors of YMCK, but is not limited to this embodiment, and may be an image forming apparatus that employs an appropriate number of colors such as a single color.

  The image forming unit includes an image carrier 10, a corona charger 11, an exposure unit 12, and the like. The exposure unit 12 includes an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. The exposure unit 12 irradiates the charged image carrier 10 with a laser beam modulated based on an input image signal, thereby statically. An electrostatic latent image is formed.

  The developing device 30 generally includes a developer container 31 that stores the liquid developer of each color, a supply roller 34 that applies the liquid developer from the developer container 31 to the intermediate roller 35, and the like. The electrostatic latent image formed on the image carrier 10 is developed. The intermediate transfer member 40 is configured by an endless belt or the like, is stretched around a drive roller 41 and a tension roller 42, and is rotationally driven by the drive roller 41 while being in contact with the image carrier 10 by the primary transfer unit 50. In the primary transfer unit 50, the image carrier 10 and the primary transfer backup roller 51 are arranged to face each other with the intermediate transfer member 40 interposed therebetween, and development is performed with the contact position of the image carrier 10 as the transfer position. The toner images of the respective colors on the image carrier 10 thus formed are sequentially superimposed and transferred onto the intermediate transfer member 40 to form a full color toner image.

  In the secondary transfer unit 60, a secondary transfer roller 61 is disposed to face the driving roller 41 with the intermediate transfer body 40 interposed therebetween. Further, a secondary transfer roller cleaning blade 62 is disposed in contact with the secondary transfer roller 61. Then, a recording medium such as a sheet, a film, or a cloth that transports a single-color toner image or a full-color toner image formed on the intermediate transfer body 40 through the sheet material transport path L at the transfer position on the secondary transfer roller 61. Transcript to.

  Further, a fixing unit (not shown) is disposed downstream of the sheet material conveyance path L, and a single color toner image or a full color toner image transferred onto a recording medium such as paper is fused to the recording medium such as paper. To fix. Further, the tension roller 42 stretches the intermediate transfer body 40 together with the drive roller 41, and the intermediate transfer body cleaning blade 46 abuts at a portion of the intermediate transfer body 40 that is stretched by the tension roller 42. Arranged.

  Next, an image forming unit and a developing device according to an embodiment of the present invention will be described. FIG. 2 is a cross-sectional view illustrating main components of the image forming unit and the developing device 30. Since the configurations of the image forming unit and the developing device for each color are the same, the description is based on the yellow (Y) image forming unit and the developing device, and the subscript alphabet is omitted.

  An image carrier cleaning roller 16, an image carrier cleaning blade 18, a corona charger 11, an exposure unit 12, a developing roller 36 of the developing device 30, and an image carrier are disposed on the outer periphery of the image carrier 10 along the rotation direction. A squeeze roller 13 is provided. Further, an image carrier cleaning roller cleaning blade 17 is disposed in contact with the image carrier cleaning roller 16. An image carrier squeeze roller cleaning blade 14 is disposed in contact with the image carrier squeeze roller 13 as an additional component.

  A primary transfer backup roller 51 of the primary transfer unit 50 is disposed along the intermediate transfer member 40 at a position facing the image carrier 10, and an intermediate transfer member squeeze roller 53 and an intermediate transfer roller are provided downstream in the moving direction. An intermediate transfer member squeeze device 52 including a transfer member squeeze backup roller 54 and an intermediate transfer member squeeze roller cleaning blade 55 is provided.

  The image carrier 10 is a photosensitive drum made of a cylindrical member that is wider than the developing roller 36 and has a photosensitive layer formed on the outer peripheral surface thereof. For example, the image carrier 10 rotates in a clockwise direction as shown in FIG. . The photosensitive layer of the image carrier 10 is composed of an organic image carrier or an amorphous silicon image carrier. The corona charger 11 is disposed upstream of the nip portion between the image carrier 10 and the developing roller 36 in the rotation direction of the image carrier 10 and is supplied with a voltage from a power supply device (not shown). Charge. The exposure unit 12 irradiates the image carrier 10 charged with the corona charger 11 with laser light on the downstream side in the rotation direction of the image carrier 10 with respect to the corona charger 11, so that the electrostatic latent image is applied to the image carrier 10. Form.

  The developing device 30 includes a developing roller 36, an intermediate roller 35, a supply roller 34, a developer container 31 that stores a liquid developer in which toner is dispersed in a carrier at a weight ratio of approximately 20%, and a developer. The main component is a toner compression corona generator 37 which performs a compaction action. On the outer periphery of the developing roller 36, a cleaning blade 361, an intermediate roller 35, and a toner compression corona generator 37 are disposed. The surface of the intermediate roller 35 is in contact with the developing roller 36 and the supply roller 34, and an intermediate roller cleaning blade 351 and a contact member 352 are disposed on the outer periphery thereof. A regulating blade 341 that adjusts the amount of liquid developer pumped from the developer reservoir 311 is in contact with the supply roller 34. The regulating blade 341 can be omitted because the intermediate roller 35 has a function of adjusting the amount of liquid developer by contacting the supply roller 34.

  In the liquid developer container 31, a developer reservoir 311 and a recovered liquid reservoir 313 are formed with a partition 312 serving as a wall. A conveyance screw 33 is accommodated in the developer storage unit 311, and a recovery screw 32 is accommodated in the developer recovery unit 313. The recovery liquid storage unit 313 is also provided with a recovery screw 32 that recovers the liquid developer that has not contributed to image formation.

  The developer container 31 is connected to a transport unit that supplies the liquid developer to the developer storage unit 311. The transport unit pumps up the liquid developer whose concentration has been adjusted by the liquid developer concentration adjusting unit with a pump, and transports the liquid developer from the replenishing port provided in the developer container 31 to the liquid developer storage unit 311. The liquid developer conveyed to the developer storage unit 311 is volatile at room temperature at a low concentration (1 to 2 wt%) and low viscosity using Isopar (trademark: exon) as a carrier. Not a volatile liquid developer, but a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and high viscosity at room temperature, an organic solvent, silicon oil, mineral oil or It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) that is added to a liquid solvent such as edible oil together with a dispersant and has a toner solid content concentration of about 20%.

  The supply roller 34 as the first application member in the present invention has a function of supplying the liquid developer to the intermediate roller 35. The supply roller 34 is a cylindrical member, and is a roller in which a concave groove such as a spiral groove finely and uniformly engraved in a spiral shape is formed on the surface so as to easily carry the liquid developer on the surface. is there. The liquid developer pumped up by the groove of the recess is precisely measured by the abutting regulating blade 341 and supplied to the intermediate roller 35. During the operation of the apparatus, as shown in FIG. 2, the conveying screw 33 rotates clockwise to supply the liquid developer to the supply roller 34, and the supply roller 34 rotates clockwise to perform liquid development on the intermediate roller 35. Apply the agent.

  The restriction blade 341 is an elastic blade made of metal or having a surface covered with an elastic body. In the present embodiment, a rubber portion made of urethane rubber or the like that comes into contact with the surface of the supply roller 34 and a metal plate or the like that supports the rubber portion are configured. Then, the film thickness and amount of the liquid developer carried and conveyed by the supply roller 34 are regulated and adjusted, and the amount of liquid developer supplied to the intermediate roller 35 is adjusted. In place of the restriction blade 341, a restriction roller constituted by a roller may be used. In the present embodiment, the intermediate roller 35 has a function of adjusting the amount of liquid developer in the restriction blade 341 and the restriction roller. Therefore, the regulation blade 341 or the regulation roller may not be provided.

  The developing roller 36 as a developer carrier in the present invention is a cylindrical member, and rotates counterclockwise around the rotation axis as shown in FIG. The developing roller 36 is provided with an elastic layer such as polyurethane rubber, silicon rubber, NBR, or PFA tube on the outer periphery of an inner core made of metal such as iron. The developing roller cleaning blade 361 is made of rubber or the like that contacts the surface of the developing roller 36, and is disposed downstream of the developing nip portion where the developing roller 36 contacts the image carrier 10 in the rotation direction of the developing roller 36. The liquid developer remaining on the developing roller 36 is scraped off and removed.

  The intermediate roller 35 as the second application member in the present invention is a cylindrical member, and rotates counterclockwise like the developing roller 36 as shown in FIG. Counter abuts against. Similar to the developing roller 36, the intermediate roller 35 is configured by providing an elastic layer on the outer periphery of a metal inner core. A contact member 352 made of an elastic material such as PET film, urethane resin, or polyimide resin is in contact with the outer periphery of the intermediate roller 35 upstream of the contact position with the developing roller 36. The contact member 352 can eliminate or suppress the transfer pattern formed by the spiral groove 342 as the concave pattern.

  An intermediate roller cleaning blade 351 is provided downstream of the contact position between the intermediate roller 35 and the developing roller 36 and scrapes off the liquid developer that has not been supplied to the developing roller 36 and collects it in the recovered liquid storage unit 313.

  The toner compression corona generator 37 is an electric field applying means for increasing the charging bias on the surface of the developing roller 36, and the liquid developer conveyed by the developing roller 36 is subjected to an electric field at a position close to the toner compression corona generator 37. Is applied to compress the toner. The electric field applying means for compressing the toner may use a compaction roller or the like instead of the corona discharge of the corona discharger. Such a compaction roller is a cylindrical member and has a structure in which a conductive resin layer or a rubber layer is provided on the surface layer of a metal roller base material. For example, the compaction roller is rotated clockwise in the direction opposite to the developing roller 36. Good.

  On the other hand, the liquid developer carried on the developing roller 36 and compressed by toner corresponds to the electrostatic latent image on the image carrier 10 by a desired electric field at the development nip portion where the developing roller 36 contacts the image carrier 10. And developed. The developer that has not contributed to the development is scraped off by the developing roller cleaning blade 361 and dropped into the collected liquid storage unit 313 in the developer container 31. The dropped developer is adjusted in its concentration by the liquid developer concentration adjusting unit and supplied to the developer storing unit 311 again to be reused.

  The image carrier squeeze device disposed on the upstream side of the primary transfer is disposed on the downstream side of the developing roller 36 so as to face the image carrier 10, and excessively develops the toner image developed on the image carrier 10. An image carrier squeeze roller 13 made of an elastic roller member that covers an elastic body and rotates in contact with the image carrier 10, and is pressed and slidably contacted with the image carrier squeeze roller 13. And a cleaning blade 14 for cleaning the surface, and has a function of recovering excess carrier from the developer developed on the image carrier 10 and increasing the toner particle ratio in the visible image. In the present embodiment, one image carrier squeeze roller 13 is provided as the image carrier squeeze device before the primary transfer, but a plurality of image carrier squeeze rollers may be provided. In that case, the image carrier squeeze roller that contacts and contacts may be switched according to the state of the liquid developer.

  In the primary transfer unit 50, the developer image developed on the image carrier 10 is transferred to the intermediate transfer member 40 by the primary transfer backup roller 51. Here, the image carrier 10 and the intermediate transfer member 40 are moved at the same speed, thereby reducing the driving load of rotation and movement and suppressing the disturbance effect on the visible toner image of the image carrier 10. .

  The image carrier cleaning device is disposed downstream of the primary transfer unit 50 so as to face the image carrier 10, thereby cleaning the untransferred liquid developer and the untransferred liquid developer on the image carrier 10. . A bias voltage that attracts toner particles in the liquid developer is applied to the image carrier cleaning roller 16. For this reason, what is collected by the image carrier cleaning roller 16 is a liquid developer rich in solids containing a large amount of toner particles. The liquid developer rich in solid content collected by the image carrier cleaning roller 16 is scraped by the image carrier cleaning roller cleaning blade 17 in contact with the image carrier cleaning roller 16 and falls vertically downward.

  The intermediate transfer body squeeze device 52 has an intermediate transfer body squeeze roller 53 formed of an elastic roller member that covers an elastic body and rotates in sliding contact with the intermediate transfer body 40, and the intermediate transfer body squeeze roller sandwiching the intermediate transfer body 40. 53, a backup roller 54 disposed opposite to the intermediate transfer member 53, and a cleaning blade 55 that presses and slides against the intermediate transfer member squeeze roller 53 to clean the surface. The surplus from the developer primarily transferred to the intermediate transfer member 40. It has a function to collect carriers and the like.

  The developing device and the image forming apparatus according to the embodiment of the present invention have been described above. Next, the supply roller 34 as the first application member used in the developing device and the image forming apparatus of the present invention will be described. FIG. 3 is a perspective view of the supply roller 34 used in the present invention, and an enlarged view of a part thereof. The supply roller 34 according to the present invention is provided with a concave pattern forming region at the center of the surface thereof, as indicated by the oblique lines in the figure. The concave pattern formation region is intended to accurately measure the liquid developer and improve the supply efficiency. In this embodiment, the spiral groove 342 is adopted. Without being limited to this embodiment, for example, various shapes and arrangements such as a pyramid shape for the recess shape or a lattice shape for the recess shape can be employed. As the supply roller 34 rotates, the recess forming pattern draws up the liquid developer and supplies it to the intermediate roller 35.

  Next, the state of the transfer pattern of the liquid developer by the concave pattern formed on the supply roller 34 will be described with reference to FIGS. FIG. 4A is a cross-sectional view of the developing device, and FIG. 4B is a diagram illustrating a state of a transfer pattern on each roller. FIG. 5 is a diagram for explaining a transfer pattern by the supply roller 34.

  4A is a cross-sectional view taken along a line AA ′ in FIG. 4B, and the thick lines described on the surfaces of the supply roller 34, the intermediate roller 35, and the developing roller 36 are drawn from the developer reservoir 311. FIG. This shows how the liquid developer pumped up is transferred. The configuration around each roller is omitted. First, the liquid developer stored in the developer storage unit 311 is pumped up by the supply roller 34 that rotates in the clockwise direction, rotates counterclockwise, and is supplied to the intermediate roller 35 that contacts the supply roller 34 in the forward direction. Is done. The liquid developer supplied to the intermediate roller 35 rotates counterclockwise and is supplied to the developing roller 36 that contacts the intermediate roller 35 in the opposite direction. Then, the liquid developer supplied to the developing roller 36 is supplied to the image carrier 10 (not shown) to form an image.

  Since the spiral groove 342 described with reference to FIG. 3 is formed on the surface of the supply roller 34 of the present embodiment, the liquid developer pumped up by the supply roller 34 is liquid on the surfaces of the intermediate roller 35 and the development roller 36. A developer transfer pattern is formed. The pattern transfer is shown in FIG. FIG. 4B is a view of FIG. 4A viewed from the direction indicated by symbol A, and shows the state of the transfer pattern on each roller. As shown in the figure, when the spiral groove 342 formed in the supply roller 34 has a downward-sloping pattern, the transfer pattern of the liquid developer on the surfaces of the intermediate roller 35 and the developing roller 36 is as shown in the figure. Specifically, a transfer pattern that rises to the right is formed on the surface of the intermediate roller 35 that contacts the supply roller 34 in the forward direction, and on the surface of the developing roller 36 that contacts the intermediate roller 35 in the opposite direction. However, a transfer pattern rising to the right is formed.

  FIG. 5 is a view for explaining the relationship between the relative speed of each roller and the state of the transfer pattern on each roller. FIG. 5A shows a transfer pattern on each roller when the rotational peripheral speed Vdr of the developing roller 36, the rotational peripheral speed Vmr of the intermediate roller 35, and the rotational peripheral speed Var of the supply roller 34 are equal. Here, the rotational peripheral speed refers to the speed in the tangential direction of each roller surface during rotation. As described with reference to FIG. 4, the transfer pattern formed on each roller is a transfer pattern indicated by diagonal lines in the present embodiment in which the concave pattern is a spiral groove.

Here, the acute angle formed by the supply roller 34 with the spiral groove 342 in the axial direction is θar, the acute angle formed by the transfer pattern of the intermediate roller 35 with the axial direction is θmr, and the acute angle formed by the transfer pattern of the developing roller 36 with the axial direction is θdr. Then, when the rotational peripheral speeds of the respective rollers are equal, the acute angles formed between the transfer patterns of the respective rollers and the axial direction thereof are equal, and the relation θar = θmr = θdr is established. The distance between the diagonal lines (pitch interval P _* ) in the direction perpendicular to the axis is equal to the pitch interval Par at the supply roller 34, the pitch interval Pmr at the intermediate roller 35, and the pitch interval Pdr at the developing roller 36. . Thus, when the rotational peripheral speeds of the rollers are equal, the pitch interval of the transfer pattern is equal to the pitch interval of the spiral grooves 352 formed in the supply roller 34. Usually, the pitch interval Par of the spiral groove 352 is set to an interval that takes into consideration that the film thickness of the liquid developer formed on the developing roller 36 is not non-uniform, so the pitch interval Par of the supply roller 34 and the developing roller When the pitch interval Pdr of 36 is equal, the developing roller 36 has no problem with the film thickness of the liquid developer.

  Next, with reference to FIG. 5B, when the rotational peripheral speed Vdr of the developing roller 36 is made faster than the rotational peripheral speed Vmr of the intermediate roller 35 and the rotational peripheral speed Var of the supply roller 34 (Vdr> Vmr = Var). ). When the film thickness of the liquid developer formed on the surface of the developing roller 36 is reduced, the roller (in this embodiment, the intermediate roller 35) that contacts the developing roller 36 with respect to the rotational peripheral speed Vdr of the developing roller 36 is reduced. The rotational peripheral speed is reduced. This is because the liquid developer is stretched by the difference in rotational peripheral speed. FIG. 5B shows a transfer pattern on each roller in such a case.

  The transfer pattern on the surface of the intermediate roller 35 is the same as in the case of FIG. 5A, and the acute angle θmr between the transfer pattern on the intermediate roller 35 and the axial direction is that the spiral groove 342 of the supply roller 34 is in the axial direction. Is equal to the acute angle θar. Further, the pitch interval Par in the supply roller 34 is equal to the pitch interval Pmr of the intermediate roller 35.

  On the other hand, the transfer pattern formed on the surface of the developing roller 36 whose rotational peripheral speed is set faster than that of the intermediate roller 35 is raised as compared with the transfer pattern on the intermediate roller 35 as shown in the figure. . Specifically, the acute angle θdr formed by the transfer pattern on the developing roller 36 with respect to the axial direction is larger than the other angles, and the pitch interval Pdr is enlarged as compared with the other angles. The increase in the pitch interval Pdr causes the film thickness of the liquid developer on the developing roller 36 to be non-uniform.

  As described above, the transfer pattern formation on each roller has been described for the supply roller 34 in which the spiral groove 342 is formed as a concave pattern. However, even when other shapes and arrangements are used for the concave pattern. It has been confirmed that the film thickness is not uniform due to the difference in rotational peripheral speed between the supply roller 34 and the intermediate roller 35. The present invention is characterized in that the contact member 352 is brought into contact with the liquid developer applied to the surface of the intermediate roller 35 in order to eliminate the uneven film thickness of the liquid developer due to the transfer pattern. . According to the present invention, even when the rotational peripheral speeds of the rollers are equal as shown in FIG. 5A, it is possible to improve the uniformity of the liquid developer film thickness.

  Now, the contact member 352 will be described in more detail with reference to FIGS. FIG. 6 is a diagram showing a state of contact between the intermediate roller 35 and the contact member 352, and FIG. 7 is a diagram showing a meniscus formed between the intermediate roller 35 and the contact member 352. 8 is a diagram showing the state of the liquid developer on the surface of the intermediate roller 35, and FIG. 9 is a graph showing the relationship between the roller rotation peripheral speed ratio Vmr / Vdr and the liquid developer film thickness.

  As described with reference to FIGS. 1 and 2, the contact member 352 is a member that contacts the intermediate roller 35 while the liquid developer applied by the supply roller 34 is applied to the developing roller 36. FIG. 6 is a view showing the contact state, and FIG. 7 is a view showing the meniscus of the liquid developer formed between the intermediate roller 35 and the contact member 352.

  The contact member 352 is made of a material such as PET, urethane resin, or polyimide resin, and is in contact with the intermediate roller 35 in the forward direction. In the present embodiment, a plate-like film made of PET is used.

  FIG. 7 shows how the liquid developer meniscus is formed by the surface tension between the intermediate roller 35 and the contact member 352. In the drawing, the surface of the intermediate roller 35 advances from the left to the right. The right side of the contact position between the intermediate roller 35 and the contact member 352 is the liquid developer inlet, and the left side is the outlet. A meniscus where the liquid developer stays is formed between the inlet and the outlet. The amount of the meniscus varies depending on factors such as the rotational peripheral speed of the intermediate roller 35, the viscosity of the liquid developer, the contact pressure of the contact member 352, and the contact angle.

  When the contact member 352 is a plate member and is in contact with the intermediate roller 35 at the front end portion thereof, the transfer pattern formed by the supply roller 34 is worn away, and the liquid developer passing performance at the contact portion is as follows. Getting worse. In addition, when the tip shape of the contact member 352 is rough, streaks are formed in the liquid developer after passing through the contact member 352, which causes the image to deteriorate.

  For this reason, in this embodiment, the front end portion of the contact member 352 is set to be longer than the contact portion between the contact member 352 and the intermediate roller 35, that is, the surface portion is not the front end portion of the contact member 352. I'm going to contact you. As a result, a meniscus is also formed in the vicinity of the exit of the contact portion, and the liquid developer is supplied also to the concave portion of the transfer pattern, so that the film thickness of the liquid developer can be made uniform. In this embodiment, it was confirmed that a uniform liquid developer surface can be obtained by setting the protruding amount of the tip portion to 500 μm or less.

  On the other hand, when the contact pressure of the contact member 352 is increased, the passage of the liquid developer is restricted and the value accurately measured by the supply roller 34 is deteriorated. For this reason, the contact pressure of the contact member 352 does not limit the passage of the liquid developer and needs to be sufficient to make the transfer pattern uniform. Specifically, it is preferable to set the contact pressure so that the meniscus of the liquid developer does not continue to increase at the contact portion entrance between the intermediate roller 35 and the contact member 352 when the intermediate roller 35 rotates. If the meniscus at the contact portion entrance continues to increase, the liquid developer accurately measured in the spiral groove 342 will be restricted. Further, the liquid developer that continues to increase at the entrance of the abutting portion causes dripping and causes contamination inside the apparatus.

  As described above, the contact pressure of the contact member 352 should not be increased so as to keep increasing the meniscus, but needs to be adjusted so as to remove the film thickness unevenness due to the transfer pattern. Further, since the amount of meniscus changes depending on various factors such as the type of liquid developer, the temperature inside the machine, and the rotational peripheral speed of the intermediate roller 35, a mechanical adjustment mechanism is provided on the contact member 352, It is preferable that the contact pressure can be adjusted. When the contact member 352 is a plate member as shown in FIG. 6, the contact member 352 is pivotally supported at the other end of the contact portion, or the contact member 352 itself is disposed close to or away from the intermediate roller 35. The contact pressure or the contact angle can be adjusted by the adjustment support portion. In the image forming apparatus, when the rotational peripheral speed of the intermediate roller 35 is variably controlled by various settings such as resolution, the adjustment mechanism of the contact member 352 may be automatically adjusted based on the various settings. Alternatively, it is conceivable to automatically adjust the adjustment mechanism in accordance with environmental changes such as temperature. Furthermore, it is also conceivable to provide a sensor for detecting the amount of meniscus and automatically adjust the adjustment mechanism based on the detected amount of meniscus.

  Further, since the abutting member 352 is used with its tip bent as shown in the drawing, the burden on the abutting member 352 increases as the abutting angle increases, and the bending may cause permanent deformation. Conceivable. When the contact member 352 is deformed, the expected contact pressure cannot be obtained, and the original function of the contact member 352 is not generated. Therefore, it is preferable to set the contact angle between the intermediate roller 35 and the contact member 352 to 30 ° or less.

  By bringing the contact member 352 into contact with the intermediate roller 35 under the contact conditions such as contact pressure and contact angle as described above, the transfer pattern is removed, and a uniform liquid developer film thickness is realized. It becomes possible. FIG. 8 shows the cross section of the liquid developer and the state of the surface before and after passing through the contact member 352. The liquid developer on the surface of the intermediate roller 35 before passing through the contact member 352 forms a noticeable oblique transfer pattern by the spiral groove 342. Further, the cross-section is such that mountain-shaped liquid developers are arranged at predetermined pitch intervals. If the gap in which the liquid developer is not applied becomes large, the liquid developer film thickness becomes non-uniform.

  On the other hand, the cross section after passing through the contact member 352 is in a state where the height of the mountain-shaped liquid developer is regulated and crushed in the lateral direction, and the gap where the liquid developer is not applied is filled. Therefore, the transfer pattern of the liquid developer on the surface of the intermediate roller 35 is reduced as compared with that before passing, as shown in the figure. Here, the embodiment for reducing the transfer pattern has been described, but preferably, the liquid developer film thickness is uniform in any part, that is, when the contact pressure is set so as to completely remove the transfer pattern. Good.

  For comparison between the film thickness of the liquid developer formed on the developing roller 36 when the contact member 352 is used and the same film thickness when the contact member 352 is not conventionally used, FIG. 3 is a graph showing the relationship between the peripheral speed ratio Vmr / Vdr and the liquid developer film thickness. The film thickness of the liquid developer formed on the developing roller 36 can be controlled by the difference in rotational peripheral speed between the developing roller 36 and the intermediate roller 35. By making the rotational peripheral speed of the developing roller 36 faster than the rotational peripheral speed of the intermediate roller 35, the film thickness of the developer can be reduced, and the rotational peripheral speed of the developing roller 36 can be set to the rotational peripheral speed of the intermediate roller 35. If the speed is slower than the speed, the liquid developer can be formed thicker.

  When the film thickness is reduced, conventionally, the roller rotation peripheral speed ratio Vmr / Vdr has a lower limit of about 1.1 because the liquid developer is unevenly generated due to the expansion of the pitch interval Pdr described with reference to FIG. I was trying. However, according to the present embodiment using the contact member 352, the lower limit can be lowered to about 0.7. As described above, in this embodiment, the range of the liquid developer film thickness control can be expanded. In particular, since a thinner film thickness can be realized as compared with the conventional case, a higher resolution image can be formed.

  Next, the length relationship of each roller and the structure located around each roller will be described with reference to FIGS. FIG. 10 shows a front view of each roller and its surrounding configuration, and FIG. 11 shows a cross-sectional view of each roller and its surrounding configuration. The front view of FIG. 10 is viewed from the direction of the arrow in the cross-sectional view of FIG. 11, and the cross-sectional view of FIG. 11 is the position between AA ′ in the front view of FIG. Yes.

  In FIG. 10, a recess pattern formation region is formed by a spiral groove 342 at the center of the supply roller 34. An axial length a (width a) of the concave pattern forming region is equal to the width of the liquid developer application region. The regulating blade 341 that contacts the supply roller 34 contacts the supply roller 34 over the entire width of the recess pattern forming region and accurately measures the liquid developer. Further, the regulation blade 341 is longer than the supply roller 34, and prevents excessive liquid developer adhering to the end of the supply roller 34 from being applied to the intermediate roller 35. In the present embodiment in which the liquid developer is indirectly applied to the developing roller 36 using the intermediate roller 35, the intermediate roller 35 functions as the regulating blade 341, and thus the regulating blade 341 is omitted. You can also.

  The transfer pattern of the liquid developer applied to the intermediate roller 352 is removed by the contact member 352. The length of the intermediate roller 35 in the axial direction is shorter than the length of the supply roller 34 in the axial direction and longer than the width a of the recess pattern forming region. Further, the length b (width b) of the contact member 352 with respect to the axial direction of the intermediate roller is longer than the width a of the recess pattern forming region. The liquid developer that has not been transferred to the developing roller 36 at the contact portion between the intermediate roller 35 and the developing roller 36 is collected by the intermediate roller cleaning blade 351. The length c (width c) of the intermediate roller cleaning blade 351 with respect to the intermediate roller axial direction is shorter than the axial length of the intermediate roller 35 and longer than the width b of the contact member 352. Even when the liquid developer flows out from the end portion of the contact member 352 due to the length relationship of the axial length of the intermediate roller 35, the width b of the contact member 352, and the width c of the intermediate roller cleaning blade 351. The intermediate roller cleaning blade 351 can collect the liquid ring and suppress the formation of the liquid ring.

  The axial length of the developing roller 36 and the width of the developing roller cleaning blade 361 are both longer than the width a of the recess pattern forming region. This length relationship enables image formation, and it is possible to collect the liquid developer that has not contributed to image formation.

  Next, the processing in the control unit when changing the amount of the liquid developer based on various settings will be described using the flow of printing control in FIG. First, when a print start command is issued from an information processing unit such as a computer (S100), the control unit determines whether or not the print setting selected by the setting unit is normal printing (S101). This setting may be made by referring to setting information set in advance in the control unit, or by asking which setting to print to the user at an appropriate interface every time printing is started. It is good to do.

  When normal printing (first setting) is selected, the rotation speed of the supply roller 34, the intermediate roller 35, the developing roller 36, and the like so that the reference amount of developer is applied to the developing roller 36. Is set and printing of input image information is started (S105). In a state where the reference amount of developer is applied to the developing roller 36 (reference state), for example, the roller rotation peripheral speed ratio Vmr / Vdr in FIG. In this case, the film thickness of the liquid developer on the developing roller 36 is about 6 μm.

  On the other hand, when the density priority state (third setting) is selected as the print setting (S102), the control unit applies the liquid developer increased by 20% with respect to the reference amount to the developing roller. Then, the rotational speeds of the supply roller 34, the intermediate roller 35, the developing roller 36, etc. are set (S103), and printing of the input image information is started (S105). In FIG. 9, when the roller rotational peripheral speed ratio Vmr / Vdr is set to about 1.8, the film thickness of the liquid developer is about 7.2 μm, and the amount of the liquid developer is increased by 20% compared to the reference state. Can do.

  Further, when the resolution priority state (second setting) is selected as the print setting (S102), the control unit applies the liquid developer reduced by 20% with respect to the reference amount to the developing roller 36. Then, the rotational speeds of the supply roller 34, the intermediate roller 35, the developing roller 36, etc. are set (S104), and printing of the input image information is started (S105). In FIG. 9, when the roller rotation peripheral speed ratio Vmr / Vdr is set to about 0.8, the film thickness of the liquid developer is about 4.2 μm, and the amount of the liquid developer is reduced by 20% compared to the reference state. be able to. In the resolution priority state in which the amount of the liquid developer was reduced by 20%, it was confirmed that reproducibility of 1200 dpi 50% halftone was ensured. As described above, in this embodiment, by bringing the contact member 352 into contact with the intermediate roller 35, the film thickness of the liquid developer formed on the developing roller 36 can be stably reduced. The priority state can be realized.

  As described above, in this embodiment, the three print settings are the reference state, the density priority state in which the amount of liquid developer is increased by 20%, and the resolution priority state in which the amount of liquid developer is reduced by 20%. The density priority state and the resolution priority state may be switchable in multiple stages by changing the amount of the liquid developer. At that time, because the image density does not change linearly and saturates at a constant value due to human visual characteristics, there is a certain limit to increasing the image density by increasing the amount of liquid developer applied. Therefore, in the density priority state, the amount of liquid developer is limited to about 25%.

  On the other hand, in the resolution priority state, if the amount of the liquid developer is set to be smaller than 20%, the amount of toner in the image portion is insufficient, causing a fixing failure and deterioration of toner embedding on paper, resulting in deterioration of image quality. Therefore, in this resolution priority state, the lower limit of the liquid developer reduction is set to 20%. As described above, various image quality can be realized within a range in which the amount of the liquid developer is increased or decreased by 20% from the reference state. In particular, in the present embodiment, it is possible to increase the range of higher resolution than in the past.

  Further, when the rotation speed of the intermediate roller 35 is changed in the density priority state and the resolution priority state, the meniscus of the liquid developer formed between the intermediate roller 35 and the contact member 352 according to the rotation speed is changed. The amount will also change. Therefore, the contact state of the contact member 352 may be changed according to the rotation speed 352 of the intermediate roller 35. As a change in the contact state of the contact member 352, it is conceivable to adjust the contact pressure pressure, contact angle, and the like with respect to the intermediate roller 35. As described with reference to FIG. The amount of meniscus at the inlet of the member 352 is adjusted so as not to continue to increase so that the amount of liquid developer accurately measured in the spiral groove 342 of the supply roller 34 does not decrease.

  Further, in the image forming apparatus that performs color printing using a plurality of developing devices 30 as shown in FIG. 1, the application amount of the liquid developer may be changed for each developing device 30 of each color. For example, in a color image, there are not many black solid image portions, and it is preferable to place importance on resolution for characters with a lot of black. Therefore, in the color image, in the reference state, the amount of the liquid developer in the black developing device 30K may be set to be smaller than that of the other color developing devices 30Y, 30M, and 30C.

  Next, another embodiment of the contact member 352 will be described with reference to FIGS. 13 and 14. In FIG. 6, the contact member 352 using a PET film has been described. However, as shown in FIGS. 13 and 14, the contact member 352 may have other shapes. The contact member 352 shown in FIG. 13 adopts a shape using a film formed in an endless tube shape. According to this shape, it was confirmed that more stable contact was obtained than a film formed in a plate shape.

  The contact member 352 shown in FIG. 14 employs a configuration in which both ends thereof are supported by two support members 353. According to this configuration, the positions of the two support members 353 can be independently adjusted, and the contact pressure and contact angle can be controlled more finely. 13 and 14, the contact member 352 contacts the intermediate roller 35 at its surface.

  Next, an embodiment for more reliably transferring toner particles will be described with reference to FIGS. In the present embodiment, toner particles are transferred by utilizing an electrostatic attraction force. FIG. 15 is a diagram illustrating a state in which a bias voltage is applied to each component, and FIG. FIG. 6 is a diagram illustrating a state of toner particle transfer between an intermediate roller and a contact member.

As shown in FIG. 15, the intermediate roller 35, the abutting member 352, and the developing roller 36 are connected to a power source as a bias applying unit, and are applied with predetermined voltages, Vor, Vfilm, and Vdr, respectively. The voltage Vor applied to the intermediate roller 35 and the voltage Vfilm applied to the contact member 352 are set to have a magnitude relationship such as Vor> Vfilm, for example. The applied voltage Vfilm to the contact member 352 may be connected to the ground instead of being connected to the power source, or may be in a magnitude relationship of Vor <Vfilm. By providing a potential difference between the intermediate roller 35 and the contact member 352 as described above, an electrostatic adsorption force is exerted between the two and the contact force of the contact member 352 is increased to make the liquid developer film thickness uniform. Can be achieved. Further, the electrostatic attraction force can be increased by optimizing the electric resistance value of the contact member 352. Specifically, it has been confirmed that the electrostatic adsorption force can be efficiently applied by setting the electric resistance value of the contact member 352 in the range of 10 ⁶ to 10 ¹² Ωcm. Further, the toner application can be efficiently performed by similarly providing the bias applying unit to the contact member 352 of the other embodiments described with reference to FIGS. 13 and 14.

  Further, the amount of toner particles transferred from the intermediate roller 35 to the developing roller 36 can be controlled by applying an electrostatic attraction force to the toner particles by the potential difference between the intermediate roller 35 and the developing roller 36. In the case of positively charged toner particles, by setting the potential to the relationship of Vdr <Vor, the toner particles are easily transferred to the developing roller 36 and the toner amount can be increased. If the potential is set in the relationship of Vdr> Vor, the toner particles are difficult to transfer and the amount of toner can be reduced.

  Although not shown in the figure, a configuration may be adopted in which an electrostatic attraction force is applied to the toner particles by providing a potential difference between the intermediate roller 35 and the supply roller 34. The present embodiment is characterized in that a potential difference is provided between the abutting member 352 and the intermediate roller 35, and between these intermediate roller 35 and the developing roller 36, and between the supply roller 34 and the intermediate roller 35. There is no need to provide a bias applying means.

  Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and embodiments configured by appropriately combining the configurations of the respective embodiments also fall within the scope of the present invention. Is.

1 is a cross-sectional view illustrating main components of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating main components of an image forming unit and a developing device. The perspective view of the supply roller which concerns on embodiment of this invention. FIG. 2 is a cross-sectional view of a developing device according to an embodiment of the present invention, and a diagram illustrating a transfer pattern. The figure explaining the transfer pattern by a supply roller. The figure explaining the mode of contact of an intermediate roller and a contact member. The figure which shows the meniscus formed between an intermediate | middle roller and a contact member. The figure which shows the mode of the liquid developer in the intermediate roller surface. The graph which shows the relationship between roller rotational peripheral speed ratio Vmr / Vdr and a liquid developer film thickness. The front view of each roller and its surrounding structure. Sectional drawing of each roller and its surrounding structure. The flowchart which shows a printing process. The figure which shows the contact member which concerns on other embodiment of this invention. The figure which shows the contact member which concerns on other embodiment of this invention. The schematic diagram which shows the mode of the bias voltage application to an intermediate | middle roller, a developing roller, and a contact member. FIG. 6 is a schematic diagram showing toner movement by applying a bias voltage.

Explanation of symbols

10 (Y, M, C, K) ... image carrier, 11 (Y, M, C, K) ... corona charger, 12 (Y, M, C, K) ... exposure unit, 13Y ... image carrier squeeze Roller, 14Y ... Image carrier squeeze roller cleaning blade, 16Y ... Image carrier cleaning roller, 17Y ... Image carrier cleaning roller cleaning blade, 18Y ... Image carrier cleaning blade,
30 (Y, M, C, K) ... developing apparatus, 31 (Y, M, C, K) ... developer container, 311Y ... developer storage part, 312Y ... partition part (wall part), 313Y ... recovered liquid storage Part, 32Y ... recovery screw, 33Y ... conveying screw, 34Y ... supply roller, 341Y ... regulating blade, 342Y ... spiral groove, 35Y ... intermediate roller, 351Y ... intermediate roller cleaning blade, 352Y ... contact member, 36Y ... developing roller 361Y ... developing roller cleaning blade, 37Y ... toner compression corona generator,
40 ... Intermediate transfer member, 41 ... Driving roller, 42 ... Tension roller, 46 ... Intermediate transfer member cleaning blade,
50 (Y, M, C, K) ... primary transfer portion, 51 (Y, M, C, K) ... primary transfer backup roller, 52 (Y, M, C, K) ... intermediate transfer member squeeze device, 53 ... Intermediate transfer member squeeze roller, 54 ... Intermediate transfer member squeeze backup roller,
60 ... secondary transfer unit, 61 ... secondary transfer roller, 62 ... secondary transfer roller cleaning blade

Claims (8)

A developer reservoir for storing a liquid developer having toner and carrier liquid;
A first application member for rotating and applying the liquid developer stored in the developer storage unit;
A second application member that contacts the first application member and rotates in a direction opposite to the first application member;
A developer carrier that contacts the second application member and rotates in the same direction as the second application member and carries the liquid developer applied by the second application member;
A contact member that contacts the liquid developer applied to the second application member by the first application member;
A controller that switches a rotational peripheral speed ratio of the second application member with respect to the developer carrying member between a first rotational peripheral speed ratio and a second rotational peripheral speed ratio that is smaller than the first rotational peripheral speed ratio; A developing device comprising:   The developing device according to claim 1, wherein the abutting member is a plate member and abuts against the second application member at a surface portion.   3. The control unit according to claim 1, wherein the control unit switches a rotation peripheral speed ratio of the second application member with respect to the developer carrying member to a third rotation peripheral speed ratio that is larger than the first rotation peripheral speed ratio. Development device.   The developing device according to claim 1, further comprising a contact adjustment support portion that adjusts a contact pressure or a contact angle of the contact member with the second application member. A liquid developer concentration adjusting unit for adjusting the toner concentration of the liquid developer having toner and carrier liquid;
A transport unit configured to transport the liquid developer whose toner concentration is adjusted by the liquid developer concentration adjusting unit;
The developer storage unit that stores the liquid developer transported by the transport unit, the first application member that rotates and supports the liquid developer stored in the developer storage unit, and the first application member A second application member that contacts and rotates in a direction opposite to the first application member; a developer carrier that contacts the second application member and rotates in the same direction as the second application member; and the first application member. A developing section having a contact member that contacts the liquid developer applied to the second application member;
A latent image carrier to be developed by the developing unit;
A control unit that switches and controls a rotational peripheral speed ratio of the second coating member with respect to the developer carrying member between a first rotational peripheral speed ratio and a second rotational peripheral speed ratio that is smaller than the first rotational peripheral speed ratio; And an image forming apparatus. Having setting means for selecting settings;
6. The control unit according to claim 5, wherein the control unit selects the first rotational peripheral speed ratio when the first setting is selected, and selects the second rotational peripheral speed ratio when the second setting is selected. Image forming apparatus.   When the third setting is selected, the control unit controls the rotation peripheral speed ratio of the second application member with respect to the developer carrying member to a third rotation peripheral speed ratio that is larger than the first rotation peripheral speed ratio. The image forming apparatus according to claim 6. A contact adjustment support portion for adjusting a contact pressure or a contact angle of the contact member to the second application member;
The image forming apparatus according to claim 6, wherein the control unit adjusts the contact pressure or the contact angle by the contact adjustment support unit according to the setting selected by the setting unit.

Images