JP2008102415A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of preventing toner particles existing in a nip area between an electric field applying roller and a developing roller from being stuck to either roller when stopping. <P>SOLUTION: The developing device is equipped with the developing roller 20Y developing a latent image formed on an image carrier 10Y with liquid developer, and the electric field applying roller 22Y applying electric field while abutting on the developing roller 20Y. When the developing roller 20Y and the electric field applying roller 22Y are stopped, the device operates in sequence that the liquid developer is accumulated in the nip between the developing roller 20Y and the electric field applying roller 22Y, and a difference between the work function of the surface material of the developing roller 20Y and that of the electric field applying roller 22Y is set to be ≤0.1 eV. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device for developing a latent image formed on an image carrier with a liquid developer and an image forming apparatus using the developing device.

  Various wet image forming apparatuses that develop a latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent and visualize the electrostatic latent image have been proposed. The developer used in this wet image forming apparatus suspends solids (toner particles) in a highly viscous organic solvent (carrier liquid) having electrical insulation properties such as silicon oil, mineral oil, and edible oil. The toner particles are extremely fine with a particle diameter of around 1 μm. By using such fine toner particles, the wet image forming apparatus can achieve higher image quality than a dry image forming apparatus using powder toner particles having a particle diameter of about 7 μm.

In such a wet image forming apparatus, a technique is known in which the toner component of the liquid developer is aggregated by performing a compaction action on the liquid developer layer supplied to the developing roller. More specifically, an electric field applying roller that is brought into contact with the surface of the liquid developer layer on the developing roller is provided, and the developing roller is rotated by rotating the electric field applying roller along with the developing roller that is driven to rotate. Contact is made over the entire surface of the liquid developer layer formed thereon. Furthermore, the electric field application roller causes an electrophoretic phenomenon in the charged toner particles in the liquid developer layer in accordance with a potential difference with the developing roller. At this time, the charged toner particles in the liquid developer layer are attracted to the developing roller having a lower potential than the electric field applying roller and are positively charged by the electric field applying roller and the developing roller. The charged charged toner particles are moved to the developing roller and gather on the developing roller side to form a liquid toner layer (see Patent Document 1 (Japanese Patent Laid-Open No. 9-185265)).
JP-A-9-185265

  When each roller rotates in a state where there is a liquid developer having a small carrier oil component between the electric field applying roller and the developing roller, a phenomenon occurs in which the roller surface is charged by friction between the rollers. When such a phenomenon occurs, the toner particles (solid content) of the liquid developer existing between the rollers tend to be attracted to either one of the rollers.

  As described above, when the toner particles (solid content) of the liquid developer are easily attracted to one roller due to charging of the roller surface, the toner particles are likely to be unevenly distributed on either the electric field application roller or the developing roller. It becomes a situation. Such a situation is particularly problematic when the image forming apparatus is stopped for a certain period of time. That is, when the image forming apparatus is stopped, the toner particles existing in the nip region between the electric field applying roller and the developing roller are fixed to one of the rollers. For this reason, in the cleaning operation at the initial operation when the operation of the image forming apparatus is resumed, the cleaning operation of the roller to which the toner particles are fixed must be strengthened more than the other roller. As a method of strengthening the cleaning operation in the roller, a method of adopting a stronger cleaning mechanism or a method of setting a longer cleaning operation time can be considered, but the former method causes an increase in the cost of the apparatus. In the latter method, the rise time of the image forming apparatus is increased.

  SUMMARY OF THE INVENTION The present invention is to solve the above-described problems. The invention according to claim 1 is directed to a developing roller for developing a latent image formed on an image carrier with a liquid developer, and abutting against the developing roller. An electric field applying roller for applying an electric field, and when the developing roller and the electric field applying roller are stopped, the liquid developer operates in a sequence in which the liquid developer stays between nips of the developing roller and the electric field applying roller, and The developing device is characterized in that the difference between the work function of the surface material of the developing roller and the work function of the surface material of the electric field applying roller is set to 0.1 eV or less.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein a developing roller cleaning blade for cleaning the developing roller and an electric field applying roller cleaning blade for cleaning the electric field applying roller are provided. It is characterized by being able to.

  The invention according to claim 3 is the developing device according to claim 2, wherein the developing roller cleaning blade and the electric field applying roller cleaning blade are the same member.

  According to a fourth aspect of the present invention, there is provided the developing device according to the second or third aspect, wherein a contact angle of the developing roller cleaning blade with respect to the developing roller and the electric field applying roller with respect to the electric field applying roller. The contact angle of the cleaning blade is equal.

  A fifth aspect of the present invention is an image forming apparatus using the developing device according to any one of the first to fourth aspects.

  According to the present invention, the difference between the work function of the surface material of the developing roller and the work function of the surface material of the electric field application roller is set to be 0.1 eV or less, and each is not charged by friction. When the image forming apparatus is stopped, it is possible to prevent the toner particles existing in the nip region between the electric field applying roller and the developing roller from adhering to one of the rollers. For this reason, it is not necessary to use a complicated cleaning mechanism for each roller, and it is not necessary to spend time for the cleaning operation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention. The developing devices 30Y, 30M, 30C, and 30K are arranged at the lower part of the image forming apparatus, and the intermediate transfer member 40 and the secondary transfer unit 60 Arranged at the top of the image forming apparatus.

  The image forming unit includes image carriers 10Y, 10M, 10C, and 10K, charging rollers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, 12C, and 12K (not shown). The exposure units 12Y, 12M, 12C, and 12K have an optical system such as a semiconductor laser, a polygon mirror, and an F-θ lens. The image bearing members 10Y, 10M, 10C, and 10K are provided by charging rollers 11Y, 11M, 11C, and 11K. Are uniformly charged and irradiated with a modulated laser beam based on the input image signal by the exposure units 12Y, 12M, 12C, and 12K, and charged image carriers 10Y, 10M, 10C, and 10K. An electrostatic latent image is formed thereon.

  The developing devices 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, anilox rollers 32Y for supplying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K, The electrostatic latent images formed on the image carriers 10Y, 10M, 10C, and 10K are developed with liquid developers of respective colors.

  The intermediate transfer member 40 is an endless belt, and is stretched between the driving roller 41 and the tension roller 42, and is contacted with the image carriers 10Y, 10M, 10C, and 10K by the primary transfer portions 50Y, 50M, 50C, and 50K. It is rotationally driven by the driving roller 41 while in contact. The primary transfer units 50Y, 50M, 50C, and 50K are arranged such that the primary transfer rollers 51Y, 51M, 51C, and 51K are opposed to each other with the image transfer bodies 10Y, 10M, 10C, and 10K sandwiched between the intermediate transfer body 40 and the image transfer bodies 10Y, Using the contact position with 10M, 10C, and 10K as the transfer position, the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially superimposed and transferred onto the intermediate transfer body 40 to obtain a full-color toner. Form an image.

  As the intermediate transfer member 40, for example, a 200 μm-thick urethane rubber elastic layer (JIS-A 30 degrees) is formed on a 100 μm-thick polyimide base material layer, and further a 10 μm-thick fluororesin coat is formed thereon. A three-layer endless belt having a surface coat of layers is used. The volume resistance value of such a belt is about Log 10 Ωcm (resistance value of all layers).

  In the secondary transfer unit 60, a secondary transfer roller 61 is disposed opposite to the belt drive roller 41 with the intermediate transfer member 40 interposed therebetween, and a cleaning device including a secondary transfer roller cleaning blade 62 and a developer recovery unit 63 is disposed. The Then, at the transfer position where the secondary transfer roller 61 is disposed, a single color toner image or a full color toner image formed on the intermediate transfer body 40 is conveyed on the sheet material conveyance path L such as paper, film, cloth, etc. Transfer to recording medium.

  Further, a fixing unit (not shown) is disposed in front of the path 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. And fix.

  Further, the tension roller 42 stretches the intermediate transfer body 40 together with the belt driving roller 41, and the intermediate transfer body cleaning blade 46, developer recovery is the place where the tension roller 42 is stretched on the tension roller 42 of the intermediate transfer body 40. A cleaning device including the portion 47 is in contact with and disposed.

  Next, the image forming unit and the developing device will be described. FIG. 2 is a sectional view showing main components of the image forming unit and the developing device. 3 is a diagram for explaining compaction by the electric field applying roller 22Y, FIG. 4 is a diagram for explaining development by the developing roller 20Y, FIG. 5 is a diagram for explaining squeezing action by the image carrier squeeze roller 13Y, and FIG. 6 is an intermediate transfer member. It is a figure explaining the squeeze effect | action by the squeeze apparatus 52Y. Since the configurations of the image forming unit and the developing device for each color are the same, the following description is based on the yellow (Y) image forming unit and the developing device.

  The image forming unit includes a cleaning device including a latent image eraser 16Y, an image carrier cleaning blade 17Y, and a developer recovery unit 18Y, a charging roller 11Y, an exposure unit 12Y, and a developing device along the rotation direction of the outer periphery of the image carrier 10Y. A cleaning device including a developing roller 20Y of 30Y, an image carrier squeeze roller 13Y, an image carrier squeeze roller cleaning blade 14Y, and a developer recovery unit 15Y, which are associated with the development roller 20Y, is provided. In the developing device 30Y, the cleaning blade 21Y, the anilox roller 32Y, and the electric field applying roller 22Y are arranged on the outer periphery of the developing roller 20Y. An electric field application roller cleaning blade 23Y is provided on the outer periphery of the electric field application roller 22Y.

  Further, a part of the liquid developer supply roller 34Y and the anilox roller 32Y are accommodated in the liquid developer container 31Y. A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer body 40 at a position facing the image carrier 10Y, and an intermediate transfer body squeeze roller 53Y, a backup roller 54Y, and an intermediate transfer are disposed downstream in the moving direction. An intermediate transfer body squeeze device 52Y comprising a body squeeze roller cleaning blade 55Y and a developer recovery unit 56Y is disposed.

  The image carrier 10Y is a photosensitive drum made of a cylindrical member having a width wider than about 320 mm of the developing roller 20Y and a photosensitive layer formed on the outer peripheral surface. For example, the image carrier 10Y rotates in a clockwise direction as shown in FIG. To do. The photosensitive layer of the image carrier 10Y is composed of an amorphous silicon image carrier, and its surface potential is set to 550V. The charging roller 11Y is disposed upstream of the nip portion between the image carrier 10Y and the developing roller 20Y in the rotation direction of the image carrier 10Y, and a bias having the same polarity as the toner charging polarity is applied from a power supply device (not shown) to The carrier 10Y is charged. The exposure unit 12Y irradiates laser light onto the image carrier 10Y charged by the charging roller 11Y on the downstream side in the rotation direction of the image carrier 10Y with respect to the charging roller 11Y, thereby forming a latent image on the image carrier 10Y. To do.

  The developing device 30Y includes an electric field applying roller 22Y, a developer container 31Y that stores a liquid developer in a state where toner is dispersed in a carrier at a weight ratio of approximately 20%, a developing roller 20Y that carries the liquid developer, a liquid developer, and the like. An electric field applied to agglomerate the liquid developer carried on the anilox roller 32Y, the regulating blade 33Y, the supply roller 34Y, and the developing roller 20Y for stirring and maintaining the agent in a uniform dispersed state and supplying it to the developing roller 20Y. A developing roller cleaning blade 21Y for cleaning the roller 22Y and the developing roller 20Y is provided.

  The liquid developer accommodated in the developer container 31Y is a low concentration (about 1 to 2 wt%) and low viscosity with Isopar (trademark: exon) as a carrier, which is generally used, and is volatile at room temperature. It is not a volatile liquid developer having a property, but a non-volatile liquid developer having a high concentration and a high viscosity and having a non-volatile property at room temperature. That is, in the liquid developer in the present invention, a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin is introduced into a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a liquid developer having a high viscosity (about 30 to 10000 mPa · s) which is added together with a dispersant and has a toner solid content concentration of about 20%.

  Next, the anilox roller 32Y in this embodiment will be described. FIG. 7 is a view showing the external shape of the anilox roller. The anilox roller 32Y is a cylindrical member, and as shown in FIG. 7, is a roller having an uneven surface formed by fine and uniform spiral grooves on the surface so as to easily carry the developer on the surface. In the anilox roller 32Y, the spiral groove may have a lead angle of about 45 °, and the groove dimensions may be, for example, a groove pitch P of 127 μm and a groove depth D of 30 μm. The anilox roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. The diameter of the anilox roller 32Y is 20 mm. The bias voltage of +400 V, which is the same as that of the developing roller 20Y, is applied to the anilox roller 32Y.

When the anilox roller 32Y and the supply roller 34Y are in a counter-rotating state, a uniform liquid developer film can be formed from the supply roller 34Y to the anilox roller 32Y. Further, at least the surface of the supply roller 34Y is made of an elastic body, and the surface resistance is preferably about 10 ⁵ Ω · cm. If the anilox roller 32Y is configured to rotate in the opposite direction to the developing roller 20Y, a uniform liquid developer can be supplied from the anilox roller 32Y to the developing roller 20Y.

  The regulating blade 33Y is composed of an elastic blade whose surface is covered with an elastic body, a rubber portion made of urethane rubber or the like that comes into contact with the surface of the anilox roller 32Y, and a plate made of metal or the like that supports the rubber portion. Then, the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 32Y made of an anilox roller are regulated and adjusted, and the amount of the liquid developer supplied to the developing roller 20Y is adjusted.

  The developing roller 20Y is a cylindrical member having a width of about 320 mm, and rotates counterclockwise around the rotation axis as shown in FIG. The developing roller 20Y is provided with an elastic layer of urethane rubber (thickness 4 mm, hardness JIS-A 30 °) on the outer periphery of an inner core made of a metal such as iron, and a resin coating having a thickness of 100 μm on the elastic layer. Is provided. The developing roller 20Y has an outer diameter of 24 mm and a bias voltage of +400 V is applied to the ground.

  The electric field application roller 22Y is a cylindrical member, and is in the form of an elastic roller configured to cover the elastic body 22-1Y as in the developing roller 20Y as shown in FIG. 3, and the surface layer of the metal roller base is urethane. This is a structure in which an elastic layer of rubber (thickness 4 mm, hardness JIS-A 30 °) is provided, and a resin coat having a thickness of 100 μm is provided on the elastic layer. The electric field applying roller 22Y has an outer diameter of 20 mm and rotates clockwise in the opposite direction to the developing roller 20Y, for example, as shown in FIG. A bias voltage of +800 V is applied to the electric field applying roller 22Y with respect to the ground.

  The electric field applying roller 22Y is a means for increasing the charging bias on the surface of the developing roller 20Y. The developer conveyed by the developing roller 20Y is brought into sliding contact with the electric field applying roller 22Y as shown in FIGS. An electric field is applied from the electric field applying roller 22Y side toward the developing roller 20Y at the toner compression portion to be formed.

  With this electric field application roller 22Y, as shown in FIG. 3, the toner T uniformly dispersed in the carrier C is moved to the developing roller 20Y side to be aggregated to form a so-called toner compression state T ′. A portion of the toner T ″ that is not compressed by the toner is carried and rotated in the direction of the arrow in the drawing, scraped off by the electric field application roller cleaning blade 23Y, and merged with the developer in the reservoir 31Y and reused. The electric field applying roller cleaning blade 23Y will be described in detail in the second half, while the developer D carried on the developing roller 20Y and compressed by toner is transferred from the developing roller 20Y to the image carrier 10Y as shown in FIG. In the abutting development nip portion, development is performed corresponding to the latent image of the image carrier 10Y by applying a desired electric field, and the remaining development is developed. D is scraped off and removed by the developing roller cleaning blade 21Y.

  The image carrier squeeze device is disposed on the downstream side of the developing device 20Y so as to face the image carrier 10Y and collects the excess developer of the toner image developed on the image carrier 10Y. As shown in FIG. 5, an image carrier squeeze roller 13Y comprising an elastic roller member that covers the surface with an elastic member 13-1Y and rotates in sliding contact with the image carrier 10Y, and press-slidably contacts the image carrier squeeze roller 13Y. And a cleaning blade 14Y for cleaning the surface, and as shown in FIG. 5, the excess carrier C and the originally unnecessary fog toner T ″ are collected from the developer D developed on the image carrier 10Y, Has a function of increasing the toner particle ratio.

  In the image carrier squeeze roller 13Y, an elastic layer of urethane rubber (thickness 2 mm, hardness JIS-A 30 °) is provided on the surface layer of the metal roller base material, and PFA tubing (thickness 20 μm) is further provided on the elastic layer. The outer diameter is set to 14 mm. The resistance value of the image carrier squeeze roller 13Y is an actual resistance value of about Log 4Ω. A bias voltage of +150 V is applied to the image carrier squeeze device.

  The image carrier squeeze roller 13Y is basically rotated at the same speed as the image carrier 10Y. However, in order to adjust the recovery amount of the surplus carrier C, the form of rotation may be changed.

  The recovery capability of the surplus carrier C is set to a desired recovery capability based on the rotational direction of the image carrier squeeze roller 13Y and the relative peripheral speed difference of the surface of the image carrier squeeze roller 13Y with respect to the peripheral speed of the surface of the image carrier 10Y. When the image carrier 10Y is rotated in the counter direction, the recovery capability is increased. Further, even when the peripheral speed difference is set large, the recovery capability is increased, and this synergistic action is also possible.

  In this embodiment, as an example, as shown in FIG. 5, the image carrier squeeze roller 13Y is rotated with the image carrier 10Y at substantially the same peripheral speed, and the weight ratio from the developer D developed on the image carrier 10Y is increased. The excess carrier C of about 5 to 10% is collected to reduce both rotational driving loads and suppress the disturbance effect on the visible toner image of the image carrier 10Y. Excess carrier C and unnecessary fog toner T ″ collected by the image carrier squeeze roller 13Y are collected from the image carrier squeeze roller 13Y to the developer collecting unit 15Y by the action of the cleaning blade 14Y.

  In the primary transfer unit 50Y, the developer image developed on the image carrier 10Y is transferred to the intermediate transfer member 40 by the primary transfer roller 51Y. Here, the image carrier 10Y and the intermediate transfer member 40 are configured to move at a constant speed, reducing the driving load of rotation and movement, and suppressing the disturbance effect on the visible toner image of the image carrier 10Y. Yes. The primary transfer portion 50Y for the first color does not cause a color mixing phenomenon since it is the first primary transfer, but since the second and subsequent colors transfer different toner images onto the already transferred primary toner image portions and superimpose colors, the intermediate transfer body 40 is used. Due to the so-called reverse transfer phenomenon in which the toner moves from the image carrier 10 (M, C, K) to the image carrier 10 (M, C, K), the reverse transfer toner and the untransferred toner are mixed and are carried on the image carrier 10 (M, C, K) together with the excess carrier. Moved from the image carrier by the action of the cleaning blade 17 (M, C, K) and pooled.

  The intermediate transfer member squeeze device 52Y is disposed on the downstream side of the primary transfer unit 50Y, and removes excess carrier liquid from the intermediate transfer member 40 to increase the toner particle ratio in the visible image. In the stage where the carrier amount of the developer (toner dispersed in the carrier) transferred to the intermediate transfer body 40 by the transfer unit 50Y is secondarily transferred to the above-described final-stage sheet material and proceeds to the fixing process (not shown), In order to exhibit a preferable secondary transfer function and fixing function, excess carrier is further removed from the intermediate transfer body 40 when the approximate toner weight ratio of the desired dispersion state of the liquid developer does not reach about 40% to 60%. It is provided as a means. Similar to the image carrier squeeze device 52Y, the intermediate transfer member squeeze device 52Y has an intermediate transfer member squeeze roller 53Y composed of an elastic roller member that covers an elastic body and rotates in contact with the image carrier 40, and the intermediate transfer member 40. 6 includes a backup roller 54Y disposed opposite to the intermediate transfer member squeeze roller 53Y, a cleaning blade 55Y that presses and slides against the intermediate transfer member squeeze roller 53Y to clean the surface, and a developer recovery unit 56Y, as shown in FIG. As described above, it has a function of recovering excess carrier C and originally unnecessary fog toner T ″ from the developer D primarily transferred to the intermediate transfer body 40. The developer recovery section 56Y is provided with magenta magenta disposed downstream thereof. Also serves as a recovery mechanism for the carrier liquid recovered by the image carrier squeeze roller cleaning blade 14M. To have.

  In the intermediate transfer member squeeze roller 53Y, an elastic layer of urethane rubber (thickness 2 mm, hardness JIS-A 30 °) is provided on the surface layer of the metal roller base material, and PFA tubing (thickness 20 μm) is further provided on the elastic layer. The outer diameter is set to 14 mm. In the intermediate transfer member squeeze device 52Y, a bias voltage of +150 V is applied between the intermediate transfer member squeeze roller 53Y and the backup roller 54Y.

  The surplus carrier collecting ability can be set to a desired collecting ability by the relative circumferential speed difference of the surface of the intermediate transfer member squeeze roller 53Y with respect to the rotation direction of the intermediate transfer member squeeze roller 53Y and the moving speed of the intermediate transfer member 40. When the intermediate transfer member 40 is rotated in the counter direction, the recovery capability is increased, and even when the peripheral speed difference is set to be large, the recovery capability is increased, and this synergistic action is also possible. In this embodiment, as an example, the intermediate transfer member squeeze roller 53Y rotates with the intermediate transfer member 40 at substantially the same peripheral speed, and a weight ratio of about 5 to 10% from the developer primarily transferred to the intermediate transfer member 40 is obtained. The excess carrier and fog toner are collected to reduce both rotational driving loads and to suppress the disturbance effect on the toner image of the intermediate transfer member 40.

  The first color intermediate squeeze squeeze part is the first intermediate squeeze squeeze, so no color mixing phenomenon occurs. However, after the second color, a different toner image is transferred to the already transferred primary toner image part and overlaid. Therefore, when the toner is transferred from the intermediate transfer body 40 to the intermediate transfer body squeeze roller 53Y, the toner is mixed in color and carried and moved by the intermediate transfer body squeeze roller 53Y together with the excess carrier, and the intermediate transfer body squeeze roller is operated by the action of the cleaning blade. Collected from 53Y and pooled. Further, when the squeeze ability by the image carrier 40 at the primary transfer portion upstream of the intermediate transfer member squeeze process and the squeeze ability of the image carrier squeeze roller 53Y are performed with sufficient ability, not all primary transfer processes are necessarily performed. There is no need to provide an intermediate transfer member squeeze device on the downstream side.

  In the above description, urethane rubber (thickness 2.0 mm) is used for various cleaning blades and regulating blades.

  The movement of the developing roller 20Y and the electric field applying roller 22Y in the developing device of the present invention configured as described above will be described. FIG. 8 is a diagram showing drive timing, bias application timing, and development timing of the developing roller and electric field applying roller 22 in the developing device.

  In FIG. 8, (1) shows the rotational drive timing of the developing roller 20Y and the electric field applying roller 22Y, and (2) applies the bias voltages as described above to the developing roller 20Y and the electric field applying roller 22Y, respectively. The timing (3) indicates the timing at which the developing roller 20Y develops the latent image on the image carrier 10Y.

  In FIG. 8, the driving of the developing roller 20Y and the electric field applying roller 22Y is first started at time T1 in accordance with an input of a print command (not shown) to the image forming apparatus. Subsequently, at time T2, the bias voltage as described above is applied to both the developing roller 20Y and the electric field applying roller 22Y, and toner compression is performed in the nip region on the developing roller 20Y where the electric field applying roller 22Y is in sliding contact.

  T3 to T5 are timings when the developing roller 20Y develops the latent image on the image carrier 10Y. T4 is a timing at which the bias voltages of both the developing roller 20Y and the electric field applying roller 22Y are turned off. The timing immediately after the portion on the developing roller 20Y where toner compression has started at T2 passes through the nip portion between the developing roller 20Y and the image carrier 10Y is T3. Time T4 is set at such a timing that the compressed toner is sufficiently supplied to the nip portion between the developing roller 20Y and the image carrier 10Y until the end of development.

  At time T6, the driving of the developing roller 20Y and the electric field applying roller 22Y is stopped. Time T6 is set after a sufficient time has elapsed from time T4. This is because when the drive stop timing (T6) of the developing roller 20Y and the electric field applying roller 22Y and the bias voltage off timing (T4) of both the developing roller 20Y and the electric field applying roller 22Y are the same or close, This is to prevent the toner particles in the compaction state (toner compression state) from remaining in the nip region between the roller 20Y and the electric field application roller 22Y and sticking to the developing roller 22Y.

  The conventional problems in the developing device having the above operation timing will be described again with reference to FIG. FIG. 9 is a diagram schematically showing a nip region between a developing roller and an electric field applying roller of a conventional developing device. FIG. 9 shows a state after a predetermined time has elapsed since the development was completed at the operation timing of FIG. Note that the reference numerals given in FIG. 9 are the same as the reference numerals described as the configuration of the present invention.

  When the electric field applying roller 22Y and the developing roller 20Y rotate, a phenomenon occurs in which the roller surface is charged by friction between the rollers. When such a phenomenon occurs, the toner particles (solid content) of the liquid developer existing between the rollers tend to be attracted to either one of the rollers. When the toner particles (solid content) of the liquid developer are easily adsorbed to one of the rollers due to charging of the roller surface, the toner particles are likely to be unevenly distributed on either the electric field applying roller 22Y or the developing roller 20Y. turn into.

  Under such circumstances, when the development is completed at the operation timing of FIG. 8 and a predetermined time has elapsed, the toner particles T ′ existing in the nip region between the electric field applying roller 22Y and the developing roller 20Y are, for example, shown in FIG. As described above, it adheres to the developing roller 20Y side. Therefore, in the cleaning operation at the initial operation when the operation of the developing device is resumed, the cleaning operation of the roller to which the toner particles are fixed (for example, the developing roller 20Y in the example of FIG. 9) is changed to the other roller (FIG. 9). In the example, the electric field application roller 22) must be strengthened.

  In the developing device according to the embodiment of the present invention, in order to avoid the above, the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is 0.1 eV. Make sure that: Next, this work function will be described.

  The work function (Φ) is known as the energy required to extract electrons from the substance. The smaller the work function, the easier it is to emit electrons, and the larger the work function, the harder it is to emit electrons. Therefore, two materials with similar work function values are almost the same in terms of electron-donating property and electron-donating property. Therefore, when these two materials rub against each other, they can almost prevent their charging. it is conceivable that.

  The work function is measured by the following measurement method, and is quantified as energy (eV) for extracting electrons from the material, and the chargeability by contact between various materials can be evaluated. The work function is measured using a surface analyzer (AC-2, low energy electronic counting method manufactured by Riken Keiki Co., Ltd.). In the present invention, in the apparatus, a developing roller using a deuterium lamp and metal plating is set to an irradiation light amount of 10 nW, and for other measurements, the irradiation light amount is set to 500 nW, and monochromatic light is selected by a spectroscope. The sample is irradiated with a spot size of 4 mm square, an energy scanning range of 3.4 to 6.2 eV, and a measurement time of 10 sec / 1 point. Then, photoelectrons emitted from the surface of the sample are detected and processed using work function calculation software to obtain a work function value.

  When a surface material such as a photoconductor or a developing roller, which will be described later, is used as a sample, the surface material is cut to a width of 1 to 1.5 cm to obtain a measurement sample piece, and then placed on a specified position on the sample table. It fixes so that an irradiation surface may become smooth with respect to the direction where measurement light is irradiated. Thereby, the emitted photoelectrons are efficiently detected by the detector (photoelectron tube).

  In the developing device according to the embodiment of the present invention, based on the above measurement, the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is 0.1 eV or less. Was set to be.

Hereinafter, developing devices according to the present embodiment and comparative examples will be described. The developing roller 20Y is provided with an elastic layer of urethane rubber (thickness 4 mm, hardness JIS-A 30 °) on the outer periphery of an inner core made of a metal such as iron, and a resin coating having a thickness of 100 μm on the elastic layer. Is provided. As this 100 μm thick resin coat,
A: Conductive fluorine-modified acrylic resin → work function 5.20 eV
B: Conductive urethane resin (with fluorine additive) → work function 5.44 eV
C: Conductive urethane resin (no fluorine additive) → work function 5.38 eV
We prepared and compared them.

In the electric field application roller 22Y, an elastic layer of urethane rubber (thickness 4 mm, hardness JIS-A 30 °) is provided on the surface layer of the metal roller base material, and a resin coat having a thickness of 100 μm is further provided on the elastic layer. Structure. As this 100 μm thick resin coat,
A: Conductive fluorine-modified acrylic resin → work function 5.20 eV
B: Conductive urethane resin (with fluorine additive) → work function 5.44 eV
C: Conductive urethane resin (no fluorine additive) → work function 5.38 eV
We prepared and compared them.

  Table 1 shows the evaluation results of the developing devices according to this embodiment and the comparative example.

表１における評価は、本実施形態と比較例に係る現像装置を搭載した画像形成装置を所定時間停止させた後、画像形成を再開した最初の印刷紙によって評価を行った。評価基準は、紙端から５ｃｍの画像形成箇所と紙端から１５ｃｍの画像形成箇所における画像濃度が０．２以内であれば○として、０．２を超えれば×とした。表１に示されるように、現像ローラ２０Ｙの表面材質の仕事関数と電界印加ローラ２２Ｙの表面材質の仕事関数の差が０．１ｅＶ以下であるとき、良好な画像が得られることがわかる。

The evaluation in Table 1 was performed on the first printing paper on which image formation was resumed after stopping the image forming apparatus equipped with the developing devices according to the present embodiment and the comparative example for a predetermined time. The evaluation criteria were ◯ when the image density at the image forming portion 5 cm from the paper edge and the image forming portion 15 cm from the paper edge was within 0.2, and x when it exceeded 0.2. As shown in Table 1, it can be seen that when the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is 0.1 eV or less, a good image can be obtained.

  FIG. 10 is a diagram schematically showing a nip region between the developing roller and the electric field applying roller of the developing device according to the embodiment of the present invention. In the developing device of the present invention, since the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is set to 0.1 eV or less, a charging phenomenon occurs between the two. There seems to be little to do. Therefore, as in the nip region of FIG. 10, the toner particles T ′ are uniformly present in the nip region, and do not stick to one of the rollers.

  FIG. 11 is a view showing a cleaning blade particularly suitable for the developing device according to the embodiment of the present invention. FIG. 11 shows the developing roller 20Y, the developing roller cleaning blade 21Y, the electric field applying roller 22Y, and the electric field applying roller cleaning blade 23Y extracted in the developing device of the present invention.

  In the developing device according to the embodiment of the present invention, the developing roller cleaning blade 21Y is made of urethane having a blade thickness of 2.0 mm (hardness JIS-A 60 °), and the electric field application roller cleaning blade 23Y also has a blade thickness of 2. A urethane of 0 mm (hardness JIS-A 60 °) is preferable because the developing roller 20Y and the electric field applying roller 22Y have the same cleaning characteristics.

  Further, in the developing device according to the embodiment of the present invention, the particularly preferable arrangement of the cleaning blade is when the contact angle θ1 of the developing roller cleaning blade 21Y and the contact angle θ2 of the electric field application roller cleaning blade 23Y are substantially equal. In addition, the cleaning characteristics of both are equal, which is preferable. In the developing device according to the embodiment of the present invention, edge contact with contact angle θ1 = contact angle θ2 = 10 ° is used.

  The reference process speed is 210 mm / s for the rotation speed of the developing roller 20Y, the rotation speed of the image carrier 10Y, and the speed of the intermediate transfer body 40.

  As described above, according to the present invention, the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is set to be 0.1 eV or less, and each is charged by friction. Therefore, when the image forming apparatus is stopped, it is possible to prevent the toner particles existing in the nip region between the electric field applying roller 22Y and the developing roller 20Y from adhering to one of the rollers. . For this reason, it is not necessary to use a complicated cleaning mechanism for each roller, and it is not necessary to spend time for the cleaning operation.

  Next, the operation of the image forming apparatus of the present invention will be described. Subsequently, the image forming unit and the developing device will be described by taking the yellow image forming unit and the developing device 30Y among the four image forming units and the developing device as examples.

  In the developer container 31Y, the toner particles in the liquid developer have a positive charge. The liquid developer is agitated by the supply roller 34Y, and is pumped up from the developer container 31Y by rotating the anilox roller 32Y. It is done. At this time, for example, when +400 V is applied as a bias to the developing roller 20Y, a DC voltage of +400 V, which is the same bias, is applied to the anilox roller 32Y.

  In the liquid development image forming apparatus using the developer in which the toner is dispersed in the carrier of the present embodiment, the developer in which 20% of the toner is dispersed in 80% of the carrier by the approximate weight ratio is used. After the process, the toner weight ratio (solid content ratio) at the position immediately before the secondary transfer to the sheet material, that is, the so-called secondary transfer position is about 45% in the case of smooth paper such as coated paper, In this case, the control is performed with a target of around 55%, and around 60% in the case of rough paper with a coarse fiber fiber such as recycled paper. The developer initially stored in the developer container 31Y is in a state of being dispersed in the carrier at approximately a toner weight ratio of about 20%. However, in the case of development with a high image duty in the development on the image carrier 10Y, the toner In the case of development with a high consumption ratio of toner and a low image duty, the consumption ratio of toner is reduced. That is, the toner weight ratio of the developer stored in the developer container 31Y changes with the development of the image carrier 10Y, and this change is constantly monitored and the toner weight ratio is approximately 20%. It is necessary to maintain and control in a distributed state.

  The regulating blade 33Y contacts the surface of the anilox roller 32Y, scrapes off the other liquid developer leaving the liquid developer in the concave and convex grooves of the anilox pattern formed on the surface of the anilox roller 32Y, and the developing roller The amount of liquid developer supplied to 20Y is regulated. By such regulation, the film thickness of the liquid developer applied to the developing roller 20Y is quantified so as to be about 6 μm. The liquid developer scraped off by the regulating blade 33Y falls back to the developer container 31Y due to gravity, and the liquid developer that has not been scraped off by the regulating blade 33Y falls in the uneven grooves on the surface of the anilox roller 32Y. It is accommodated and applied to the surface of the developing roller 20Y by being pressed against the developing roller 20Y.

  The developing roller 20Y applied with the liquid developer by the anilox roller 32Y contacts the electric field application roller 22Y downstream of the nip portion with the anilox roller 32Y. A bias of about +400 V is applied to the developing roller 20Y, and a bias of +800 V, which is higher than the developing roller 20Y and has the same polarity as the toner charging polarity, is applied to the electric field applying roller 22Y. Therefore, the toner particles in the liquid developer on the developing roller 20Y move toward the developing roller 20Y when passing through the nip with the electric field applying roller 22Y as shown in FIG. As a result, the toner particles are gently coupled to form a film, and when developing with the image carrier 10Y, the toner particles move from the developing roller 20Y to the image carrier 10Y quickly, and the image density is improved. To do.

  The image carrier 10Y is made of amorphous silicon. The surface of the image carrier 10Y is charged to about + 550V by the anti-static roller 11Y upstream of the nip portion with the developing roller 20Y, and then the latent image is set so that the potential of the image portion becomes + 25V by the exposure unit 12Y. An image is formed. In the developing nip portion formed between the developing roller 20Y and the image carrier 10Y, the bias + 400V applied to the developing roller 20Y and the latent image (image portion + 25V, non-image portion + 550V) applied to the image carrier 10Y. According to the formed electric field, as shown in FIG. 4, the toner particles T are selectively moved to the image portion on the image carrier 10Y, whereby a toner image is formed on the image carrier 10Y. Further, since the carrier liquid C is not affected by the electric field, as shown in FIG. 4, it is separated at the exit of the developing nip between the developing roller 20Y and the image carrier 10Y, and both the developing roller 20Y and the image carrier 10Y are separated. Adhere to. The image carrier 10Y that has passed through the development nip passes through the image carrier squeeze roller 13Y, and the excess carrier liquid C is removed as shown in FIG. 5 to increase the toner particle ratio in the visible image. The

  Next, the image carrier 10Y passes through the nip portion with the intermediate transfer body 40 in the primary transfer 50Y, and the primary transfer of the visible toner image to the intermediate transfer body 40 is performed. The primary transfer roller 51Y is applied with about −200 V having the opposite polarity to the charging characteristics of the toner particles, so that the toner is primarily transferred from the image carrier 10Y to the intermediate transfer member 40, and the carrier liquid is transferred to the image carrier 10Y. Only remains. On the downstream side in the rotation direction of the image carrier 10Y from the primary transfer portion, after the primary transfer, the electrostatic latent image in the image carrier 10Y is erased by the latent image eraser 16Y composed of a lamp or the like and remains on the image carrier 10Y. The carrier liquid is scraped off by the image carrier cleaning blade 17Y and recovered by the developer recovery unit 18Y.

  The toner image primarily transferred onto the intermediate transfer member 40 by the primary transfer unit 50Y passes through the intermediate transfer member squeeze device 52Y in order to scrape excess carriers on the intermediate transfer member 40. A bias of +150 V is applied between the intermediate transfer member squeeze roller 53Y and the intermediate transfer member squeeze backup roller 54Y of the intermediate transfer member squeeze device 52Y, and an electric field is generated to press the toner particles against the intermediate transfer member 40 side. I am letting. Therefore, toner particles are not collected on the intermediate transfer member squeeze roller 53Y as shown in FIG. 6, and only the carrier liquid that is not affected by the electric field is transferred between the intermediate transfer member 40 and the intermediate transfer member squeeze roller 53Y. Collected by crying.

  The toner image on the intermediate transfer member 40 then proceeds to the secondary transfer unit 60 and enters the nip portion between the intermediate transfer member 40 and the secondary transfer roller 61. The nip width at this time is set to 3 mm. In the secondary transfer unit 60, −1200 V is applied to the secondary transfer roller 61 and +200 V is applied to the belt driving roller 41, whereby the toner image on the intermediate transfer member 40 is a recording medium such as paper. Is transcribed.

  After passing through the secondary transfer unit 60, the intermediate transfer body 40 proceeds to the winding portion of the tension roller 42, the intermediate transfer body 40 is cleaned by the intermediate transfer body cleaning blade 46, and the primary transfer section 50 again. Head to.

  Next, the squeeze function of the secondary transfer roller 61 will be described. The sheet material is supplied in accordance with the timing at which the toner image overlaid on the intermediate transfer body 40 reaches the secondary transfer portion, and the toner image is secondarily transferred to the sheet material to proceed to a fixing step (not shown). When the final image formation on the sheet material is completed, but a sheet material supply trouble such as a jam occurs, the toner image is transferred in contact with the secondary transfer roller 61 without the sheet material interposed therebetween. Causes backside contamination. The secondary transfer roller 61 according to the present embodiment uses a plurality of photoconductors as means for improving the secondary transfer characteristics following the non-smooth sheet material surface, even if the surface is a non-smooth sheet material due to fibers or the like. An elastic roller having a surface coated with an elastic body for the same purpose as the elastic belt employed in the intermediate transfer body 40 that sequentially transfers the formed toner images, sequentially carries them, and carries them together to carry out secondary transfer onto the sheet material. It is composed. The secondary transfer roller cleaning blade 62 is provided as a means for removing the developer (toner dispersed in the carrier) transferred to the secondary transfer roller 61, collects the developer from the secondary transfer roller 61, and is pooled. . Note that the pooled developer is in a mixed color state and may contain foreign matters such as paper dust.

  Next, the cleaning device for the intermediate transfer member 40 will be described. When a sheet material supply trouble such as a jam occurs, not all the toner images are transferred to the secondary transfer roller 61 and collected, and a part remains on the intermediate transfer body 40. Further, even in a normal secondary transfer process, the toner image on the intermediate transfer member 40 is not 100% secondary transferred and transferred to the sheet material, and a secondary transfer residue of several percent occurs. The two types of unnecessary toner images are collected and pooled by an intermediate transfer member cleaning blade 46 and a developer recovery unit 47 disposed downstream in the moving direction of the intermediate transfer member 40 for the next image formation.

  In the image forming apparatus of the present invention, the difference between the work function of the surface material of the developing roller 20Y and the work function of the surface material of the electric field applying roller 22Y is set to be 0.1 eV or less. Therefore, each of them is not charged by friction, and therefore, when the image forming apparatus is stopped, the toner particles existing in the nip region between the electric field applying roller 22Y and the developing roller 20Y are fixed to one of the rollers. Can be prevented. For this reason, it is not necessary to use a complicated cleaning mechanism for each roller, and it is not necessary to spend time for the cleaning operation.

1 is a diagram illustrating main components constituting 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. It is a figure explaining the compaction by the electric field application roller 22Y. It is a figure explaining the development by the developing roller 20Y. It is a figure explaining the squeeze effect | action by the image carrier squeeze roller 13Y. It is a figure explaining the squeeze effect | action by the intermediate transfer body squeeze apparatus 52Y. It is a figure which shows the external appearance shape of an anilox roller. FIG. 4 is a diagram illustrating drive timing, bias application timing, and development timing of a development roller and an electric field application roller 22 in the development device. It is a figure which shows typically the nip area | region between the developing roller and electric field application roller of the conventional developing device. It is a figure which shows typically the nip area | region between the developing roller and electric field application roller of the developing device which concerns on embodiment of this invention. It is a figure which shows the cleaning blade especially suitable in the developing device which concerns on embodiment of this invention.

Explanation of symbols

10Y, 10M, 10C, 10K ... image carrier, 11Y, 11M, 11C, 11K ... charging roller, 12Y, 12M, 12C, 12K ... exposure unit, 13Y ... image carrier squeeze roller, 14Y: Image carrier squeeze roller cleaning blade, 15Y: Developer recovery unit, 16Y: Latent image eraser, 17Y: Image carrier cleaning blade, 18Y ... Developer recovery unit, 20Y, 20M, 20C, 20K ... developing roller, 21Y ... developing roller cleaning blade, 22Y ... electric field applying roller, 23Y ... electric field applying roller cleaning blade, 30Y, 30M, 30C, 30K ... developing device , 31Y, 31M, 31C, 31K ... developer container, 32Y, 32M, 32C, 32K ... Aniloc Slurers, 31Y, 31M, 31C, 31K ... developer container, 33Y ... regulating blade, 34Y ... supply roller, 40 ... intermediate transfer member, 41, 42 ... belt drive roller, 45. ..Developer recovery unit, 46 ... intermediate transfer member cleaning blade, 47 ... developer recovery unit, 50Y, 50M, 50C, 50K ... primary transfer unit, 51Y, 51M, 51C, 51K ... Primary transfer backup roller, 52Y, 52M, 52C, 52K ... Intermediate transfer member squeeze unit, 53Y ... Intermediate transfer member squeeze roller, 54Y ... Intermediate transfer member squeeze backup roller, 55Y ... Intermediate transfer member squeeze Roller cleaning blade, 56Y ... developer recovery unit, 60 ... secondary transfer unit, 61 ... secondary transfer roller, 2 ... secondary transfer roller cleaning blade 63 ... developer collecting section

Claims (5)

A developing roller that develops the latent image formed on the image bearing member with a liquid developer; and an electric field applying roller that contacts the developing roller and applies an electric field, and when the developing roller and the electric field applying roller are stopped It operates in a sequence in which the liquid developer stays between the nip between the developing roller and the electric field applying roller, and the difference between the work function of the surface material of the developing roller and the work function of the surface material of the electric field applying roller is 0. A developing device, wherein the developing device is set to be 1 eV or less. The developing device according to claim 1, further comprising: a developing roller cleaning blade that cleans the developing roller; and an electric field applying roller cleaning blade that cleans the electric field applying roller. The developing device according to claim 2, wherein the developing roller cleaning blade and the electric field application roller cleaning blade are the same member. 4. The developing device according to claim 2, wherein a contact angle of the developing roller cleaning blade with respect to the developing roller is equal to a contact angle of the electric field applying roller cleaning blade with respect to the electric field applying roller. . An image forming apparatus using the developing device according to claim 1.

Images