JP2008276031A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which does not require complicated hardware and sequence for application of bias. <P>SOLUTION: The image forming apparatus includes a developing roller 20Y developing a latent image formed on an image carrier with liquid developer, a toner compression roller 22Y flocculating toner particles in the liquid developer on the developing roller 20Y on the surface of the developing roller 20Y, a constant-current power source connected to the toner compression roller 22Y, and a variable resistance means connected to the developing roller 20Y. The variable resistance means shows infinite resistance until the developing roller 20Y attains prescribed voltage, and changes resistance to limit the developing roller 20Y at the prescribed voltage when it attains the prescribed voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing roller that develops a latent image formed on an image carrier with a liquid developer, and in particular, toner compression that aggregates toner particles in the liquid developer on the developing roller on the surface of the developing roller. The present invention relates to a wet image forming apparatus using a liquid developer having a roller.

  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.

  The carrier liquid constituting the developer has a function of making the toner particles charged and further uniformly dispersed in addition to preventing the scattering of toner particles having a particle diameter of about 1 μm. It also has a role to make it easy to move by electric field action. As described above, the carrier liquid is an important component in toner storage, toner conveyance, development, and transfer processes, but also adheres to non-image areas, and excessive carrier liquid after development causes transfer disturbance and the like.

Therefore, on a roller such as a developing roller, toner particles uniformly dispersed in a carrier liquid are moved to the roller surface side by applying a bias to be aggregated (see, for example, Patent Document 1). Further, in the wet image forming apparatus, a bias is applied to a blade that is in contact with the developing roller, and solid components in the liquid developer are aggregated on the surface of the developing roller (see, for example, Patent Document 2). Further, the solid component in the liquid developer is aggregated on the surface of the developing roller by a corotron, a contact type discharge roller, or a non-contact type discharge roller (for example, see Patent Document 3).
JP 2000-56576 A JP 2004-258154 A JP 2005-234430 A

  By the way, in the wet image forming process, it is necessary to apply a bias for aggregating the toner particles on the surface of the developing roller as described above in addition to applying the bias to the photoconductor and the developing roller. There is a problem that a complicated bias application sequence is required before the start. Since such a complicated bias application sequence is required, there is a problem that the configuration and control of the power supply voltage for applying the bias are complicated.

  SUMMARY An advantage of some aspects of the invention is that an image forming apparatus according to the invention develops a latent image formed on an image carrier with a liquid developer, and a liquid developer on the developing roller. A toner compression roller for aggregating toner particles in the developing roller surface, a constant current power source connected to the toner compression roller, and variable resistance means connected to the development roller, the variable resistance means Is characterized in that an infinite resistance is exhibited until the developing roller reaches a predetermined voltage, and when the predetermined voltage is reached, the resistance changes so as to limit the developing roller at the predetermined voltage.

  The image forming apparatus according to the present invention further includes a capacitor unit in parallel with the variable resistor unit, and the capacitance of the capacitor unit is {(the nip between the developing roller and the toner compression roller, the developing roller, The creepage distance between the nip of the image carrier and the current value of the constant current source} / {(the moving speed of the developing roller surface) × (developing voltage)} is set.

  Further, in the image forming apparatus according to the present invention, the variable resistance means performs short-circuit control until a predetermined time has elapsed after the constant current power source is activated, and the predetermined time (the nip between the developing roller and the toner compression roller) And a creeping distance between the developing roller and the nip of the image carrier) / (developing roller surface moving speed) or more.

  The image forming apparatus according to the present invention also includes a developing roller for developing a latent image formed on an image carrier with a liquid developer, and toner particles in the liquid developer on the developing roller are aggregated on the surface of the developing roller. A toner compression roller, a constant current power source connected to the toner compression roller, an AC power source connected in series with the constant current power source, and variable resistance means connected to the developing roller, The variable resistance means has an infinite resistance until the developing roller reaches a predetermined voltage, and when the predetermined voltage is reached, the resistance changes so as to limit the developing roller at the predetermined voltage.

  The image forming apparatus according to the present invention further includes a capacitor unit in parallel with the variable resistor unit, and the capacitance of the capacitor unit is {(the nip between the developing roller and the toner compression roller, the developing roller, The creepage distance between the nip of the image carrier and the current value of the constant current source} / {(the moving speed of the developing roller surface) × (developing voltage)} is set.

  Further, in the image forming apparatus according to the present invention, the variable resistance means performs short-circuit control until a predetermined time has elapsed after the constant current power source is activated, and the predetermined time (the nip between the developing roller and the toner compression roller) And a creeping distance between the developing roller and the nip of the image carrier) / (developing roller surface moving speed) or more.

  According to the present invention, the image forming process of the liquid developing device is performed by a bias circuit including a combination of a constant current power source connected to the toner compression roller and a Zener diode or a constant voltage diode (variable resistance means for limiting with an upper limit voltage). The bias application sequence at the start is simplified.

  That is, when the constant current power source connected to the toner compression roller is turned on according to the image forming sequence of the wet image forming apparatus, the discharge between the toner compression roller and the development roller starts first, and the liquid developer on the development roller The solid component (toner particles) in the toner begins to aggregate on the surface of the developing roller, and as the discharge continues, the potential of the developing roller rises with a delay to reach a developable developing potential.

  In this way, simply by turning on the constant current power source, the solid components (toner particles) in the liquid developer are aggregated on the surface of the developing roller in advance, and then the potential of the developing roller rises with a delay to develop The potential of the developing roller does not reach a developable potential while the aggregation of solid components (toner particles) in the liquid developer is insufficient, so that the solid components (toner particles in the liquid developer are reached. ) Has reached a developing potential at which development is possible, and development is started, so that unnecessary solid components (toner particles) of the liquid developer are deposited on the image carrier at the start of development (fogging, abnormal image, toner) Troubles such as unnecessary consumption).

  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 image carriers 10Y, 10M, 10C, and 10K are in contact with image carrier squeeze rollers 13Y, 13M, 13C, and 13K that exert a squeeze action thereon, and around the developing rollers 20Y, 20M, 20C, and 20K. In addition, toner compression rollers 22Y, 22M, 22C, and 22K that provide a compaction effect are provided. The toner compression rollers 22Y, 22M, 22C, and 22K may be in contact with the developing rollers 20Y, 20M, 20C, and 20K, or may be kept in a non-contact state.

  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.

  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 toner compression 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, a cleaning blade 21Y, an anilox roller 32Y, and a toner compression roller 22Y are arranged on the outer periphery of the developing roller 20Y.

  A carrier amount adjusting blade 23Y is provided on the outer periphery of the toner compression 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 or the like. 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 a toner compression roller 22Y, a developer container 31Y that stores a liquid developer in which 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. Toner compression for bringing the liquid developer carried on the developing roller 20Y into a compaction state by stirring the agent to maintain a uniform dispersed state and supplying it to the developing roller 20Y, the regulating blade 33Y, the supply roller 34Y, and the liquid developer carried on the developing roller 20Y A developing roller cleaning blade 21Y for cleaning the roller 22Y and the developing roller 20Y is provided.

  FIG. 7 is a view showing the external shape of the anilox roller. The anilox roller 32Y and the supply roller 34Y are configured to rotate counter. 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.

  The liquid developer accommodated in the developer container 31Y is a non-volatile liquid developer having high concentration and high viscosity and non-volatility 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%.

  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.

  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 made of polyurethane rubber, silicon rubber, NBR or the like on the outer periphery of an inner core made of metal such as iron. The developing roller cleaning blade 21Y is made of rubber or the like that comes into contact with the surface of the developing roller 20Y. The developing roller 20Y is arranged downstream of the developing nip portion where the developing roller 20Y comes into contact with the image carrier 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the developing roller 20Y is scraped off and removed.

  The toner compression roller 22Y is a cylindrical member and is in the form of an elastic roller formed by covering an elastic body 22-1Y like the developing roller 20Y as shown in FIG. For example, as shown in FIG. 2, it rotates clockwise in the direction opposite to the developing roller 20Y. The toner compression roller 22Y has means for increasing the charging bias on the surface of the developing roller 20Y. The developer conveyed by the developing roller 20Y is slidably contacted by the toner compression roller 22Y as shown in FIGS. A bias electric field is applied from the toner compression roller 22Y side toward the developing roller 20Y at the toner compression portion that forms the toner image. This bias application will be described in detail later. If the toner compression function is effective, the toner compression roller 22Y may be configured not to contact the developing roller 20Y.

  With this toner compression 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 has not been compressed with toner is carried and rotated in the direction of the arrow in the drawing, scraped off by the carrier amount adjusting blade 23Y, joined with the developer in the reservoir 31Y, and reused. On the other hand, the developer D, which is carried on the developing roller 20Y and compressed by toner, is applied to the image carrier 10Y by applying a desired electric field at the developing nip where the developing roller 20Y contacts the image carrier 10Y as shown in FIG. Are developed corresponding to the latent images of

  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, The recovery capability of the surplus carrier C is based on the rotational direction of the image carrier squeeze roller 13Y and the peripheral speed of the surface of the image carrier 10Y. The desired recovery capability can be set by the relative peripheral speed difference of the surface of the body squeeze roller 13Y. When the image carrier 10Y is rotated in the counter direction, the recovery capability is increased, and the peripheral speed difference is reduced. Even if it is set to a large value, the recovery capability is enhanced, and further, this synergistic action is 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 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 52, the intermediate transfer member squeeze device 52Y has an intermediate transfer member squeeze roller 53Y composed of an elastic roller member that covers the surface with an elastic member and rotates in sliding contact with the image carrier 40, and the image carrier 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. There.

  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 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 toner compression roller 22Y downstream of the nip portion with the anilox roller 32Y. A predetermined bias is applied to the developing roller 20Y, and a bias higher than that of the developing roller 20Y and having the same polarity as the charging polarity of the toner is applied to the toner compression roller 22Y. The bias application will be described later.

  Because of the bias application as described above, the toner particles in the liquid developer on the developing roller 20Y are aggregated and move toward the developing roller 20Y when passing through the nip with the toner compression roller 22Y as shown in FIG. . As a result, the toner particles are gradually combined and aggregated to form a film. 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 increased. Will improve.

  The image carrier 10Y is made of amorphous silicon, and after being charged by the charging roller 11Y upstream of the nip portion with the developing roller 20Y, a latent image is formed by the exposure unit 12Y. In the developing nip portion formed between the developing roller 20Y and the image carrier 10Y, the bias applied to the developing roller 20Y and the electric field formed by the latent image on the image carrier 10Y are as shown in FIG. Then, the toner particles T selectively move 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. By applying a bias having a polarity opposite to the charging characteristics of the toner particles to the primary transfer roller 51Y, the toner is primarily transferred from the image carrier 10Y to the intermediate transfer member 40, and only the carrier liquid is transferred to the image carrier 10Y. Remain. 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 predetermined bias is applied to 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. ing. 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, predetermined biases are respectively applied to the secondary transfer roller 61 and the belt driving roller 41, whereby the toner image on the intermediate transfer member 40 is transferred to a recording medium such as paper.

  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.

  Next, bias application in the developing devices 30Y, 30M, 30C, and 30K in the image forming apparatus according to the embodiment will be described in detail. FIG. 8 is a diagram schematically showing an outline of a bias circuit in the developing device. Since the configuration of the bias circuit of each color developing device is the same, the following description will be based on the yellow (Y) image forming unit and the developing device.

  As shown in FIG. 8, the toner compression roller 22Y is biased by a constant current source I that is grounded. The developing roller 20Y is connected to a grounded Zener diode ZD, and the image carrier 10Y is grounded.

  The Zener diode ZD connected to the toner compression roller 22Y is expected to function as a kind of variable resistance means. That is, such a Zener diode ZD exhibits an infinite resistance until the developing roller 20Y reaches a predetermined voltage, and functions as a variable resistor that limits the developing roller 20Y at the predetermined voltage when the predetermined voltage is reached. .

  The bias circuit according to the present invention configured as described above applies all biases to the toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y by the constant current source I connected to the toner compression roller 22Y. A sequence for applying a bias is also unnecessary.

  An outline of the circuit operation and sequence of bias application by the bias circuit will be described. When starting the image forming process in the image forming apparatus, the constant current source I is turned on. A current flows from the constant current source I to the toner compression roller 22Y, and then a discharge occurs from the toner compression roller 22Y to the developing roller 20Y. The electric charge discharged from the toner compression roller 22Y to the developing roller 20Y then flows into the Zener diode ZD. The Zener diode ZD exhibits an infinite resistance until reaching a predetermined voltage, and when reaching the upper limit voltage, the resistance changes so as to be limited by the upper limit voltage. In the present invention, the Zener diode ZD is referred to as variable resistance means. Other examples of devices having the same characteristics as the Zener diode ZD include constant voltage diodes and varistors.

  A bias application sequence in the bias circuit of the developing device configured as described above will be described with reference to the drawings. FIG. 9 is a diagram showing a bias application sequence of the bias circuit in the developing device. This figure shows a bias application sequence at the start of the image forming process (at the start of development), and a steady-state bias voltage in the latter half of the sequence is used when performing the image forming process continuously.

In FIG. 9, the horizontal axis indicates time, and the vertical axis indicates voltage or current. Hereinafter, description will be made along the time axis.
t0: The constant current power source I connected to the toner compression roller 22Y is turned on in cooperation with other image forming sequences in the image forming apparatus.
t1 to t2: Discharge between the toner compression roller 22Y and the developing roller 20Y starts, and solid components in the liquid developer on the developing roller 20Y start to aggregate on the surface of the developing roller 20Y.
t2 to t3: The potential of the developing roller 20Y rises with delay as the discharge continues.
After t3: The developing roller 20Y reaches a developing potential at which development is possible.

  As described above, in the present invention, it is necessary to provide independent bias application circuits for the toner compression roller, the development roller, and the image carrier in the developing device, and operate these bias application circuits in a predetermined order. In addition, the toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y are maintained at bias potentials at which development can be started only by turning on the constant current power source I connected to the toner compression roller 22Y. As a result, hardware and sequence for applying a complicated bias are not necessary.

  As described above, according to the present invention, the image of the liquid developing device is provided by the bias circuit including the combination of the constant current power source I connected to the toner compression roller 22Y, the Zener diode (variable resistance means), the constant voltage diode, and the like. The bias application sequence at the start of the formation process is simplified.

  That is, when the constant current power source I connected to the toner compression roller 22Y is turned on according to the image forming sequence of the wet image forming apparatus, the discharge between the toner compression roller 22Y and the development roller 20Y starts first, and the development roller 20Y The solid component (toner particles) in the upper liquid developer begins to aggregate on the surface of the developing roller 20Y, and the potential of the developing roller 20Y rises with delay as the discharge continues, reaching a developable developing potential.

  In this way, simply by turning on the constant current power supply I, solid components (toner particles) in the liquid developer are aggregated on the surface of the developing roller 20Y in advance, and then the potential of the developing roller 20Y is delayed and rises. However, since the developing potential reaches a developable potential, the potential of the developing roller 20Y does not reach the developable potential while the aggregation of the solid components (toner particles) in the liquid developer is insufficient, and the solid in the liquid developer. Since the development potential is reached when the components (toner particles) are aggregated, the development is started, so that unnecessary solid components (toner particles) of the liquid developer are deposited on the image carrier 10Y (fogging) at the start of development. , Abnormal images, unnecessary consumption of toner, etc.) will not occur.

  Next, another embodiment of the present invention will be described. FIG. 10 is a diagram schematically showing an outline of a bias circuit of a developing device in an image forming apparatus of another embodiment. Since the configuration of the bias circuit of each color developing device is the same, the following description will be based on the yellow (Y) image forming unit and the developing device.

  As shown in FIG. 10, the toner compression roller 22Y is biased by a grounded constant current source I, the developing roller 20Y is connected to the grounded Zener diode ZD and the capacitor C, and the image carrier 10Y is grounded. The

  The Zener diode ZD connected to the toner compression roller 22Y is expected to function as a kind of variable resistance means. That is, such a Zener diode ZD exhibits an infinite resistance until the developing roller 20Y reaches a predetermined voltage, and functions as a variable resistor that limits the developing roller 20Y at the predetermined voltage when the predetermined voltage is reached. . Other examples of devices having the same characteristics as the Zener diode ZD include constant voltage diodes and varistors.

  Further, the capacitance C of the capacitor C connected to the toner compression roller 22Y satisfies the following formula.

C ≧ (L × I) / (v × Vd)
Here, L is the creeping distance between the nip between the developing roller 20Y and the toner compression roller 22Y and the nip between the developing roller 20Y and the image carrier 10Y, I is the current value of the constant current source, and v is the movement of the surface of the developing roller 20Y. The speed, Vd, is the developing voltage of the developing roller 20Y.

  According to this embodiment, the charging of the capacitor C with the constant current source is completed from the moving time from the nip that discharges (aggregates) on the developing roller 20Y to the nip that develops on the image carrier 10Y until the developing voltage is reached. And the solid component (toner particles) in the liquid developer does not reach a developable potential while the solid component (toner particles) in the liquid developer is insufficiently aggregated. ) Has reached a developing potential at which development is possible, and development is started. Therefore, unnecessary solid components (toner particles) of the liquid developer (fogging, abnormal image, No problems such as unnecessary consumption of toner) occur.

  Even in the bias circuit according to another embodiment configured as described above, all the bias application to the toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y is performed by the constant current source I connected to the toner compression roller 22Y. In addition, a sequence for applying a bias is not required.

  Next, another embodiment of the present invention will be described. FIG. 11 is a diagram schematically showing an outline of a bias circuit of a developing device in an image forming apparatus of another embodiment.

  As shown in FIG. 11, the toner compression roller 22Y is biased by a grounded constant current source I. The bias of the developing roller 20Y is controlled by an operational amplifier (operational amplifier) and a transistor Tr as shown in the figure. The reference voltage Vref is input to the inverting input terminal of the operational amplifier (operational amplifier), the voltage divided by R1 and R2 is input to the non-inverting input terminal, and the collector current of the transistor Tr is output from the operational amplifier (operational amplifier). To control. The image carrier 10Y is grounded.

  The control means including the operational amplifier (operational amplifier) and the transistor Tr connected to the toner compression roller 22Y is expected to function as a kind of variable resistance means. That is, the operational amplifier (operational amplifier) and the transistor Tr are short-circuit controlled when the constant current source I is initially turned on, and switched to constant voltage control after a predetermined time has elapsed.

  Such a predetermined time T is set as follows.

T ≧ L / v
Here, L is the creeping distance between the nip between the developing roller 20Y and the toner compression roller 22Y and the nip between the developing roller 20Y and the image carrier 10Y, and v is the moving speed of the surface of the developing roller 20Y.

  According to this embodiment, the potential increase of the developing roller 20Y is delayed. That is, the predetermined time T is defined such that the developing roller 20Y does not reach the developing potential at which the developing roller 20Y can develop until the aggregation of the toner particles by the toner compression roller 22Y ends.

Therefore, in this embodiment, while the aggregation of the solid components (toner particles) in the liquid developer is insufficient, the potential of the developing roller 20Y does not reach a developable potential, and the solid components (toner particles in the liquid developer). ) Has reached a developing potential at which development is possible, and development is started. Therefore, unnecessary solid components (toner particles) of the liquid developer (fogging, abnormal image, In the bias circuit according to the present invention configured as described above, the constant current source I connected to the toner compression roller 22Y causes the toner compression roller 22Y and the development roller 20Y. In addition to applying all the bias to the image carrier 10Y, a sequence for applying the bias is also unnecessary.

  An outline of the circuit operation and sequence of bias application by the bias circuit will be described. When starting the image forming process in the image forming apparatus, the constant current source I is turned on. A current flows from the constant current source I into the toner compression roller 22Y. Since the toner compression roller 22Y is controlled to be short-circuited for a predetermined time T, the potential of the developing roller 20Y remains unchanged. Next, when a predetermined time T elapses, the electric charge discharged from the toner compression roller 22Y to the developing roller 20Y increases the potential of the developing roller 20Y while charging the developing roller 20Y and the capacitor C, thereby developing the roller 20Y. To the development potential.

  A bias application sequence in the bias circuit of the developing device configured as described above will be described with reference to the drawings. FIG. 12 is a diagram showing a bias application sequence of the bias circuit in the developing device. FIG. 12 is a diagram illustrating a bias application sequence of an image forming apparatus according to another embodiment. This figure shows a bias application sequence at the start of the image forming process (at the start of development), and a steady-state bias voltage in the latter half of the sequence is used when performing the image forming process continuously.

In FIG. 12, the horizontal axis indicates time, and the vertical axis indicates voltage or current. Hereinafter, description will be made along the time axis.
t0: The constant current power source I connected to the toner compression roller 22Y is turned on while cooperating with other image forming sequences in the image forming apparatus.
t1 to t2: Discharge between the toner compression roller 22Y and the developing roller 20Y starts, and solid components (toner particles) in the liquid developer on the developing roller 20Y start to aggregate on the surface of the developing roller 20Y.
t3: After the predetermined time (T = t3-t0) has elapsed, the short circuit of the variable resistance means is opened, switching to constant voltage control, and the potential of the developing roller 20Y rises with delay as the discharge continues.
t4: A development potential that can be developed is reached.

  As described above, in the present invention, it is necessary to provide independent bias application circuits for the toner compression roller, the development roller, and the image carrier in the developing device, and operate these bias application circuits in a predetermined order. In addition, the toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y are maintained at bias potentials at which development can be started only by turning on the constant current power source I connected to the toner compression roller 22Y. As a result, hardware and sequence for applying a complicated bias are not necessary.

  Next, another embodiment of the present invention will be described. FIG. 13 is a diagram schematically showing an outline of a bias circuit of a developing device in an image forming apparatus of another embodiment. Since the configuration of the bias circuit of each color developing device is the same, the following description will be based on the yellow (Y) image forming unit and the developing device.

  As shown in FIG. 13, in this embodiment, the toner compression roller 22Y is biased by a grounded constant current source I and an AC power supply AC, and the developing roller 20Y is connected to a grounded Zener diode ZD to carry an image. The body 10Y is grounded.

  The Zener diode ZD connected to the toner compression roller 22Y is expected to function as a kind of variable resistance means. That is, such a Zener diode ZD exhibits an infinite resistance until the developing roller 20Y reaches a predetermined voltage, and functions as a variable resistor that limits the developing roller 20Y at the predetermined voltage when the predetermined voltage is reached. .

  Even with the bias circuit in the present invention provided with the AC power supply AC as described above, all the biases of the toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y are connected by the constant current source I connected to the toner compression roller 22Y. In addition to the application, the sequence for applying the bias is also unnecessary.

An outline of the circuit operation and sequence of bias application by the bias circuit will be described. When starting the image forming process in the image forming apparatus, the constant current source I is turned on. A current flows from the constant current source I to the toner compression roller 22Y, and then a discharge occurs from the toner compression roller 22Y to the developing roller 20Y. The electric charge discharged from the toner compression roller 22Y to the developing roller 20Y then flows into the Zener diode ZD. The Zener diode ZD exhibits an infinite resistance until reaching a predetermined voltage, and when reaching the upper limit voltage, the resistance changes so as to be limited by the upper limit voltage. In the present invention, the Zener diode ZD is referred to as variable resistance means. Other examples of devices having the same characteristics as the Zener diode ZD include constant voltage diodes and varistors.
The electric charge discharged from the toner compression roller 22Y to the developing roller 20Y flows into the variable resistance means. The variable resistance means exhibits an infinite resistance until reaching a predetermined voltage, and when reaching the upper limit voltage, the resistance changes so as to be limited by the upper limit voltage. Examples of devices having such characteristics include constant voltage diodes and varistors.

  The AC power supply AC used in the present embodiment has an effect of stabilizing the discharge of the toner compression roller 22Y. Further, for example, control with a microcomputer may be performed so that the amplitude of the AC power supply AC is adjusted so that a constant current flows through the constant current power supply I.

  Note that the second embodiment in which the capacitor C is provided or the third embodiment in which a comparator and a transistor are provided is combined with the present embodiment that is also biased by the AC power supply AC. Are also included in the scope of the present invention.

  In the embodiment in which the capacitor C connected in parallel with the variable resistance means is provided with the AC power supply AC bias, the capacitor C bypasses the AC current flowing from the AC power supply and also has the effect of stabilizing the development bias to DC. Have.

  As described above, according to the present invention, it is necessary to provide independent bias application circuits for the toner compression roller, the development roller, and the image carrier in the developing device, and to operate these bias application circuits in a predetermined order. The toner compression roller 22Y, the developing roller 20Y, and the image carrier 10Y are kept at a bias potential at which development can be started by simply turning on the constant current power source I connected to the toner compression roller 22Y. Therefore, hardware and sequence for applying a complicated bias are not necessary.

  Although various embodiments have been described above, embodiments configured by arbitrarily combining the components of the respective embodiments are also included in the present invention.

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 toner compression 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. It is a figure which shows typically the outline of the bias circuit in a developing device. It is a figure which shows the bias application sequence of the bias circuit in a developing device. It is a figure which shows typically the outline of the bias circuit of the image development apparatus in the image forming apparatus of other embodiment. It is a figure which shows typically the outline of the bias circuit of the image development apparatus in the image forming apparatus of other embodiment. It is a figure which shows the bias application sequence of the image forming apparatus of other embodiment. It is a figure which shows typically the outline of the bias circuit of the image development apparatus in the image forming apparatus of other embodiment.

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 ... toner compression roller, 23Y ... carrier amount adjusting blade, 30Y, 30M, 30C, 30K ... developing device, 31Y, 31M, 31C, 31K ... Developer container, 32Y, 32M, 32C, 32K ... Anilox roller 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, 62 ... Next transfer roller cleaning blade, 63 ... developer collecting section

Claims (6)

A developing roller for developing the latent image formed on the image carrier with a liquid developer;
A toner compression roller for aggregating toner particles in the liquid developer on the developing roller on the surface of the developing roller;
A constant current power source connected to the toner compression roller;
Variable resistance means connected to the developing roller,
The variable resistance means has an infinite resistance until the developing roller reaches a predetermined voltage, and when the predetermined voltage is reached, the resistance changes so as to limit the developing roller at the predetermined voltage. Image forming apparatus. Having capacitor means in parallel with the variable resistance means;
The capacitance of the capacitor means is
{(Creepage distance between the nip between the developing roller and the toner compression roller and the nip between the developing roller and the image carrier) × (current value of the constant current source)} / {(the moving speed of the developing roller surface) × (Development voltage)}
The image forming apparatus according to claim 1, wherein the image forming apparatus is set as described above. The variable resistance means performs short-circuit control until a predetermined time after the constant current power supply is activated,
The predetermined time is
(Creepage distance between the nip of the developing roller and the toner compression roller and the nip of the developing roller and the image carrier) / (velocity of the developing roller surface)
The image forming apparatus according to claim 1, wherein the image forming apparatus is set as described above. A developing roller for developing the latent image formed on the image carrier with a liquid developer;
A toner compression roller for aggregating toner particles in the liquid developer on the developing roller on the surface of the developing roller;
A constant current power source connected to the toner compression roller;
An AC power supply connected in series with the constant current power supply;
Variable resistance means connected to the developing roller,
The variable resistance means has an infinite resistance until the developing roller reaches a predetermined voltage, and when the predetermined voltage is reached, the resistance changes so as to limit the developing roller at the predetermined voltage. Image forming apparatus. Having capacitor means in parallel with the variable resistance means;
The capacitance of the capacitor means is
{(Creepage distance between the nip between the developing roller and the toner compression roller and the nip between the developing roller and the image carrier) × (current value of the constant current source)} / {(the moving speed of the developing roller surface) × (Development voltage)}
The image forming apparatus according to claim 4, wherein the image forming apparatus is set as described above. The variable resistance means performs short-circuit control until a predetermined time after the constant current power supply is activated,
The predetermined time is
(Creepage distance between the nip of the developing roller and the toner compression roller and the nip of the developing roller and the image carrier) / (velocity of the developing roller surface)
The image forming apparatus according to claim 4, wherein the image forming apparatus is set as described above.

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