IMAGE FORMING SYSTEM

An image forming system includes: an image carrying element that is rotatably provided and carries an image; an image forming element that forms the image on the image carrying element using an image forming material containing at least an external additive; a transfer element that transfers the image carried by the image carrying element to a medium; a cleaning element having a plate shape, the cleaning element being disposed so that a leading end comes into contact with the image carrying element while being inclined in a direction opposite to a rotation direction of the image carrying element to clean a residue remaining on the image carrying element after a transfer operation by the transfer element; a maintenance element that forms, using the image forming element, a band-shaped maintenance image of the image forming material in a non-image formation region of the image carrying element, and regularly or irregularly supplies the maintenance image to the cleaning element in a state where the transfer operation by the transfer element is not performed; a microparticle application element that regularly or irregularly applies a microparticle having lubricity to the image carrying element; and a maintenance control element that controls an amount of the maintenance image by the maintenance element depending on an application state of the microparticle on the image carrying element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2023-084903 filed May 23, 2023.

BACKGROUND

(i) Technical Field

The present invention relates to an image forming system.

(ii) Related Art

Conventionally, devices disclosed in JP2006-313377A, JP2000-259011A, and JP2001-175090A, for example, are already known as this type of image forming system.

JP2006-313377A discloses an image forming device including an image carrier having a surface on which a toner image is formed, an intermediate transfer member that receives the toner image transferred from the image carrier and then transfers the toner image next, and a microparticle attaching device that attaches microparticles to the surface of the intermediate transfer member. The microparticle attaching device has a rotating brush and a rod member for brushing off excess microparticles, the rod member being supported so that the end of the bristle of the rotating brush is brought into contact with the rod member and the rod member is parallel to the rotating brush.

FIG.1of JP2000-259011A discloses an image recording device including an intermediate transfer member5ain contact with image carriers1K and1Y, an intermediate transfer member5bin contact with image carriers1M and1C, an intermediate transfer member6in contact with the intermediate transfer members5aand5b, and microparticle attachment devices20a,20b, and20cfor attaching microparticles having an average particle diameter three times or less the average particle diameter of primary particles to the surfaces of the intermediate transfer members5a,5b, and6.

JP2001-175090A discloses an image forming device including a control means for executing control to form a toner band (band-shaped toner image) crossing a specified region in the specified region which is at least a region not facing a recording sheet and outside a side end of the recording sheet in a feeding direction of the recording sheet in a transferable region of an intermediate transfer belt, when the width of the recording sheet in the feeding direction is narrower than a prescribed determination reference value.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate to an image forming system which can realize a maintenance process for a plate-shaped cleaning element without wastefully consuming an image forming material in a mode in which microparticles can be applied to an image carrying element.

According to an aspect of the present disclosure, there is provided an image forming system comprising: an image carrying element that is rotatably provided and carries an image; an image forming element that forms the image on the image carrying element using an image forming material containing at least an external additive; a transfer element that transfers the image carried by the image carrying element to a medium; a cleaning element having a plate shape, the cleaning element being disposed so that a leading end comes into contact with the image carrying element while being inclined in a direction opposite to a rotation direction of the image carrying element to clean a residue remaining on the image carrying element after a transfer operation by the transfer element; a maintenance element that forms, using the image forming element, a band-shaped maintenance image of the image forming material in a non-image formation region of the image carrying element, and regularly or irregularly supplies the maintenance image to the cleaning element in a state where the transfer operation by the transfer element is not performed; a microparticle application element that regularly or irregularly applies a microparticle having lubricity to the image carrying element; and a maintenance control element that controls an amount of the maintenance image by the maintenance element depending on an application state of the microparticle on the image carrying element.

DETAILED DESCRIPTION

⊙ Overview of Embodiments

FIG.1illustrates an overview of an embodiment of an image forming system to which the present invention is applied.

InFIG.1, the image forming system includes: an image carrying means1that is rotatably provided and carries an image G; an image forming means2that forms the image G on the image carrying means1using an image forming material containing at least an external additive; a transfer means3that transfers the image G carried by the image carrying means1to a medium S; a cleaning means4having a plate shape, the cleaning means4being disposed so that a leading end comes into contact with the image carrying means1while being inclined in a direction opposite to a rotation direction of the image carrying means1to clean a residue remaining on the image carrying means1after a transfer operation by the transfer means3; a maintenance means5that forms, using the image forming means2, a band-shaped maintenance image Gm of the image forming material in a non-image formation region NR (refer toFIG.2A) of the image carrying means1, and regularly or irregularly supplies the maintenance image Gm to the cleaning means4in a state where the transfer operation by the transfer means3is not performed; a microparticle application means6that regularly or irregularly applies a microparticle p having lubricity to the image carrying means1; and a maintenance control means7that controls an amount of the maintenance image by the maintenance means5depending on an application state of the microparticle p on the image carrying means1.

In such a technical aspect, the “image forming system” in the present application is not limited to a system constituted by a single device, but includes a system constituted by a plurality of devices.

The image carrying means1may be of any type that carries the image G formed by the image forming means, and may be an image forming and carrying means such as a photoconductor or a dielectric that directly forms and carries the image G, or may be an intermediate transfer means that intermediately carries the image G formed by the image forming and carrying means before the image G is transferred to the medium S.

In addition, the image forming means2is not limited to an electrophotographic type, and includes various types such as an electrostatic recording type using an ion flow as long as it forms an image using an image forming material containing at least an external additive.

Furthermore, the transfer means3may be appropriately selected as long as it transfers the image G carried on the image carrying means1to the medium S, and a mode of transferring an image under pressure using a transfer electric field is typical.

Furthermore, any type of the cleaning means4may be appropriately selected as long as it uses a mode (so-called blade cleaning system) in which a leading end of an elastic plate-shaped member is in contact with the image carrying means1in a state of being inclined in a direction opposite to the rotation direction of the image carrying means1.

In addition, the “band-shaped maintenance image Gm” by the maintenance means5may be one or a plurality of band-shaped images continuously extending along the width direction (corresponding to the intersecting direction intersecting with the rotation direction of the image carrying means1) of the image formation region (corresponding to an image forming region) GR (seeFIG.2A) of the image carrying means1, or may be a band-shaped image that discontinuously extends. Regarding the execution timing of maintenance operation by the maintenance means5, the maintenance operation may be executed regularly from the viewpoint of preventing the leading end of the cleaning means4from being turned up or worn, or may be irregularly executed by determining the maintenance timing from an image forming condition or the like by the image forming means2.

Further, a medium having various physical properties may be appropriately selected as the medium S. For example, in a case where a normal medium Sa such as plain paper is used as the medium S, the surface of the normal medium Sa is substantially smooth as illustrated inFIG.2B, so that the image G on the image carrying means1is easily transferred onto the normal medium Sa by a transfer electric field in the transfer region TR, and thus, a transfer failure is unlikely to occur. On the other hand, in a case where, for example, an embossed medium Sb is used as the medium S, the transferability of the image G on the image carrying means1tends to decrease due to the influence of the surface roughness (embossed surface) e of the embossed medium Sb as illustrated inFIG.2C. This is because the image G is less likely to be transferred to recessed portions than to protruding portions of the surface roughness e of the embossed medium Sb. In the present embodiment, in order to avoid such a situation, the microparticle application means6applies the microparticles p having lubricity onto the image carrying means1to improve the transferability of the image G when the embossed medium Sb is used. The “microparticle p” used herein may be appropriately selected as long as it has lubricity. If the external additive contained in the image forming material2of the image forming means2has lubricity, a material similar to the external additive can be used as the microparticle p, or a material different from the external additive may be used.

Furthermore, the maintenance control means7controls the maintenance operation of the maintenance means5in view of the application state of the microparticles p by the microparticle application means6(whether or not the microparticles p are applied or an application amount of microparticles p).

For example, when the microparticles p are not applied to the image carrying means1, a normal maintenance image Gm(0) may be produced as the maintenance image Gm using a normal amount of the image forming material, and the maintenance image Gm(0) may be supplied to a cleaning region CR at the leading end of the cleaning means4as illustrated inFIG.2D. In contrast, when, for example, the image carrying means1is applied with the microparticles p, the fact that a layer of the applied microparticles p functions as a part of the maintenance image Gm is focused. Specifically, as illustrated inFIG.2E, a special maintenance image Gm(1) which is smaller in amount than the normal maintenance image Gm(0) is generated as the maintenance image Gm, and the special maintenance image Gm(1) may be supplied together with the layer of microparticles p to the cleaning region CR at the leading end of the cleaning means4.

Next, a representative aspect or a preferable aspect of the image forming system according to the present embodiment will be described.

First, as a representative aspect of the maintenance control means7, there is an aspect of controlling an amount of the maintenance image by the maintenance means5(an amount of the image forming material used for producing the maintenance image Gm) to be different between under the condition that the microparticles p are applied and under the condition that the microparticles p are not applied, with an amount of the maintenance image by the maintenance means5under the condition that the microparticles p are not applied being defined as an upper limit. In this aspect, an amount of the maintenance image is changed depending on whether or not the microparticles p are applied.

Here, the reason why “an amount of the maintenance image by the maintenance means5under the condition that the microparticles p are not applied” is defined “as an upper limit” is to clearly exclude a mode in which an amount of the maintenance image is larger when the microparticles p are applied than when the microparticles p are not applied.

As a specific example of this aspect, there is an aspect of controlling an amount of the maintenance image to be smaller under a condition that the microparticles p are applied than under a condition that the microparticles p are not applied. In addition, in a case where the application amount of the microparticles p is sufficiently large, it is also possible to perform control such that the special maintenance image Gm(1) is not supplied under the condition that the microparticles p are applied.

As another representative aspect of the maintenance control means7, there is an aspect of performing control so that an amount of the maintenance image varies depending on the application amount of the microparticles p under the condition that the microparticles p are applied, with an amount of the maintenance image by the maintenance means5under the condition that the microparticles p are not applied being defined as an upper limit. In this aspect, an amount of the maintenance image is varied depending on an application amount of the microparticles p.

Specific examples of this aspect include an aspect of controlling an amount of the maintenance image to be smaller as the application amount of the microparticles p is greater under a condition that the microparticles p are applied and an aspect of controlling an amount of the maintenance image to be greater as the application amount of the microparticles p is smaller under a condition that the microparticles p are applied.

In addition, as a preferable aspect of the maintenance control means7, there is an aspect in which a detection means (not illustrated) capable of detecting an application state of the microparticles p is provided and the amount of the maintenance image is controlled on the basis of a detection result of the detection means. In this aspect, the application state of the microparticles p is detected by the detection means, and an amount of the maintenance image appropriate for the application state of the microparticles p is selected.

In this aspect, the detection means may be constituted by a reflective optical sensor disposed so as to face the application layer of the microparticles p.

In addition, as a preferable aspect of the microparticle application means6, there is an aspect in which the microparticles p having a particle diameter in a range of 30 nm to 150 nm are applied to the image carrying means1having a surface roughness Rz of 1.5 or less or a microgloss of 93 or more. In this aspect, from the viewpoint of reducing the adhesion force of the image G on the image carrying means1when the embossed medium Sb is used, an appropriate range is selected for the surface property of the image carrying means1and the particle diameter of the microparticles p.

In this aspect, the microparticle application means6may apply the microparticles p on the image carrying means1at a coverage of 10% to 50%. In this aspect, a preferable coverage of the microparticles p is selected in consideration of the fact that, even if the microparticles p are applied to the image carrying means1with a coverage of more than 50%, the adhesion force of the image G on the image carrying means1is not significantly reduced as compared with the case where the coverage is 50% or less.

Embodiments of the present invention will be described below in more detail with reference to the accompanying drawings.

⊙ First Embodiment

—Overall Configuration of Image Forming System—

FIG.3illustrates the overall configuration of an image forming system according to a first embodiment.

InFIG.3, an image forming system20is mounted in a device housing not illustrated, and includes an image forming engine21for forming images of a plurality of color components (four colors of yellow (Y), magenta (M), cyan (C), and black (K) in the present embodiment), a transfer device50for transferring the color component images formed by the image forming engine21onto a medium S, a fixing device70for fixing the color component images transferred in a transfer region TR of the transfer device50onto the medium S, and a medium conveyance system80for conveying the medium S to the transfer region TR of the transfer device50.

Configuration Example of Image Forming Engine

In the present embodiment, the image forming engine21includes image forming units22(to be specific,22ato22d) that form images of a plurality of color components, and a belt-shaped intermediate transfer member30that sequentially transfers (primary transfer) images G of the color components formed by the image forming units22, carries the images G, and conveys the images G to a transfer section where the images G are transferred to the medium S.

In the present embodiment, each of the image forming units22(22ato22d) employs, for example, an electrophotographic system and includes a drum-shaped photoconductor23as illustrated inFIGS.3and4. Each of the image forming units22includes, around the photoconductor23, a charging device24that charges the photoconductor23, an optical writing device25that writes an electrostatic latent image on the charged photoconductor23, a developing device26that develops the electrostatic latent image written on the photoconductor23with toner of each color component, and a photoconductor cleaning device27that removes toner remaining on the photoconductor23after an image is transferred to the intermediate transfer member30.

Although a charging roller, for example, is used as the charging device24in the present embodiment, a corotron, a scorotron, or the like may be appropriately selected. Although an LED array is used as the optical writing device25in the present embodiment, a laser scanning device or the like may be appropriately selected.

Any device may be appropriately selected as the developing device26as long as it uses a developer as an image forming material, and in the present embodiment, the developing device26employs a two-component development method. The developing device26includes a development housing261having an opening facing the photoconductor23, and a developing roller262disposed facing the opening of the development housing261. The developing device26stores a two-component developer containing toner (including an external additive) and a carrier in the development housing261. The developing device26agitates and conveys the developer by a pair of agitating/conveying members263so that the developer is carried on the developing roller262while charging the toner, and develops the electrostatic latent image on the photoconductor23with the toner. A collection member264returns the developer dropped from the developing roller262to the agitating/conveying member263.

In the present embodiment, the photoconductor cleaning device27includes a cleaning housing271that is open so as to face the photoconductor23, and an elastic plate-shaped cleaning member272is provided at an opening edge of the cleaning housing271with a support bracket273. Here, the cleaning member272is disposed in such a manner that a leading end thereof comes into contact with the photoconductor23in a state of being inclined in a direction opposite to the rotation direction of the photoconductor23, and scrapes residues remaining on the photoconductor23to clean the photoconductor23. Further, a leveling/conveying member274is provided at the bottom of the cleaning housing271to level the residue accommodated in the cleaning housing271and to convey the residue to the outside of the cleaning housing271toward a collection container (not illustrated) at the time of disposal. A guide member275guides the residue scraped off by the cleaning member272toward the leveling/conveying member274.

The intermediate transfer member30is stretched around plural tension rollers31to34, and for example, the tension roller31is used as a driving roller driven by a driving motor (not illustrated). The intermediate transfer member30is rotated by the driving roller.

In the present embodiment, the photoconductors23of the image forming units22are disposed so as to face the front surface of the intermediate transfer member30located between the tension rollers31and32, and primary transfer devices35such as transfer rollers that electrostatically transfer the images G formed on the photoconductors23to the intermediate transfer member30are disposed on the back surface of the intermediate transfer member30facing the photoconductors23.

Further, the intermediate transfer member30is provided with the intermediate-transfer-member cleaning device36on the surface located between the tension rollers31and34. The intermediate-transfer-member cleaning device36removes residues such as residual toner and paper dust on the intermediate transfer member30after the transfer of the image to the medium S.

In the present embodiment, the intermediate-transfer-member cleaning device36is disposed at a position of the intermediate transfer member30closer to the tension roller31on the downstream side in the rotation direction with respect to the transfer region TR (corresponding to the position of the tension roller34) of the transfer device50as illustrated inFIGS.3and4B. The intermediate-transfer-member cleaning device36includes a cleaning housing361that is open so as to face the front surface of the intermediate transfer member30, an elastic plate-shaped cleaning member362provided at the opening edge of the cleaning housing361with a support bracket363, and a counter roller364provided on the back surface of the intermediate transfer member30facing the cleaning member362. Here, the cleaning member362is disposed in such a manner that a leading end thereof comes into contact with the intermediate transfer member30in a state of being inclined in a direction opposite to the rotation direction of the intermediate transfer member30, and scrapes residues remaining on the intermediate transfer member30to clean the intermediate transfer member30. Further, the cleaning housing361includes a leveling/conveying member365that levels and conveys the accommodated residue, and a guide member366that guides the residue scraped off by the cleaning member362toward the leveling/conveying member365. It is obvious that another type of cleaning member such as a cleaning brush may be provided instead of the plate-shaped cleaning member362.

<Necessity of Maintenance Process>

In the present embodiment, the photoconductor cleaning device27and the intermediate-transfer-member cleaning device36include plate-shaped cleaning members272and362, respectively.

Taking the intermediate-transfer-member cleaning device36as an example, the cleaning member362is supported by the support bracket363in a cantilevered manner, and is disposed in a state of being inclined in a direction opposite to the moving direction (corresponding to the rotation direction) of the intermediate transfer member30as illustrated inFIGS.5A and5B. Therefore, the corner of the leading end of the cleaning member362on the free end side follows the moving direction of the intermediate transfer member30and comes into contact with the intermediate transfer member30in an elastically deformed state.

The residues such as toner remaining on the intermediate transfer member30are scraped off in the cleaning region by the cleaning member362.

Meanwhile, the toner TN often includes an external additive g around toner particles obtained by kneading and pulverizing a colorant in a resin binder such as polyester. Microparticles of silica (SiO2) such as colloidal silica, titanium oxide, alumina, or a fatty acid metal salt are used as the external additive g for the purpose of, for example, improving toner fluidity, adjusting an amount of triboelectric charge, and improving cleaning performance.

In this case, if a certain amount of residue such as toner remains on the intermediate transfer member30, a certain amount of residue reaches the corner of the leading end of the cleaning member362, so that a gap H between a contact portion CN of the cleaning member362and the intermediate transfer member30is filled with a dam DM constituted by the external additive g, and the residual toner TN can be dammed up by the dam DM constituted by the external additive g and scraped off, as illustrated inFIG.5B.

In contrast, if the amount of the toner TN remaining on the intermediate transfer member30is extremely small when, for example, an image with a low printing rate is continuously printed, the external additive g does not form a dam in the gap H between the contact portion CN of the cleaning member362and the intermediate transfer member30, so that the contact portion CN of the cleaning member362may have poor lubrication, and the remaining toner TN may pass through the contact portion CN of the cleaning member362, as illustrated inFIG.5C. In this case, the contact portion CN of the cleaning member362may be worn or the cleaning performance of the cleaning member362may be impaired.

For this reason, in the present embodiment, a maintenance process of maintaining the cleaning member362by regularly or irregularly replenishing the external additive g to the contact portion CN of the cleaning member362is needed in order to suppress wear of the cleaning member362and a cleaning failure by the cleaning member362.

The above-described problem also occurs in the cleaning member272of the photoconductor cleaning device27, and the maintenance device also performs the maintenance process on the cleaning member272of the photoconductor cleaning device27.

The maintenance device that performs the maintenance process will be described later.

The transfer device50secondarily transfers the image G, which has been primarily transferred onto the intermediate transfer member30, onto the medium S as illustrated inFIGS.3and6A. In the present embodiment, the transfer device50includes a belt transfer module51obtained by stretching a transfer conveyance belt53around a plurality of tension rollers52(to be specific,52aand52b), the belt transfer module51being disposed so as to be in contact with the intermediate transfer member30. The transfer conveyance belt53is a semiconductive belt formed of a material such as chloroprene and having a volume resistivity of 106to 1012Ω·cm. The tension roller52awhich is one of the tension rollers is formed as an elastic transfer roller55. The elastic transfer roller55is disposed in pressure contact with the transfer region TR of the intermediate transfer member30with the transfer conveyance belt53therebetween, and the tension roller34of the intermediate transfer member30is disposed so as to face the elastic transfer roller55as a counter roller56serving as a counter electrode of the elastic transfer roller55. The transfer conveyance belt53forms a conveyance passage for the medium S from the position of the tension roller52ato the position of the tension roller52b. InFIG.3, a transfer cleaning device57cleans the transfer conveyance belt53.

In the present embodiment, the elastic transfer roller55has a structure in which the periphery of a metal shaft is covered with an elastic layer obtained by mixing carbon black or the like with urethane foam rubber or EPDM. A transfer bias Vt from a transfer power source59is applied to the counter roller56(also serving as the tension roller34in the present embodiment) via a conductive power supply roller58. The transfer power source59has a variable power source unit59aand a switch unit59bfor turning on and off the variable power source unit59a. On the other hand, the elastic transfer roller55(tension roller52a) is grounded via a metal shaft (not illustrated), and as illustrated inFIG.6B, a predetermined transfer electric field Et is formed between the elastic transfer roller55and the counter roller56, so that the image G on the intermediate transfer member30is transferred to the medium S.

Note that the tension roller52bis also grounded to prevent the transfer conveyance belt53from being charged. In addition, in consideration of the separation property of the medium S at the downstream end of the transfer conveyance belt53, it is effective to set the diameter of the tension roller52bon the downstream side to be smaller than the diameter of the tension roller52aon the upstream side, because the tension roller52balso serves as a separation roller.

The fixing device70includes a heat fixing roller71that is disposed in contact with the image-carrying surface of the medium S and that can be driven to rotate, and a pressure fixing roller72that is disposed in pressure contact with the heat fixing roller71so as to face the heat fixing roller71and rotates following the heat fixing roller71. The fixing device70allows an image carried on the medium S to pass through a pressure-contact region between the two fixing rollers71and72, thereby fixing the image by heat under pressure.

The fixing method performed by the fixing device70is not limited to the mode described in the embodiment, and a non-contact fixing method, a fixing method using a laser beam, or the like may be appropriately selected.

The medium conveyance system80has, for example, one medium supply container81from which the medium S can be supplied. The medium conveyance system80conveys the medium S supplied from the medium supply container81to the transfer region TR through a vertical conveyance path82extending in a substantially vertical direction and a horizontal conveyance path83extending in a substantially horizontal direction, then, conveys the medium S carrying the transferred image to a fixing region by the fixing device70via a conveyance belt84, and discharges the medium S to a medium discharge receiver (not illustrated) provided on a side of the device housing (not illustrated). In addition, the medium conveyance system80includes a position alignment roller86that aligns the position of the medium S and supplies the medium S to the transfer region TR, and further includes an appropriate number of conveyance rollers87in each of the conveyance paths82and83.

In the present embodiment, the medium S is discharged from one medium supply container81to the medium discharge receiver (not illustrated) through the vertical conveyance path82and the horizontal conveyance path83. However, the configuration is not limited thereto, and it is obvious that the design of the medium conveyance system80may be appropriately changed according to the specification of the image forming engine21. Examples of changes of the medium conveyance system80include: a mode of using a plurality of medium supply containers81; a mode in which a branch conveyance path that branches downward is provided at a section of the horizontal conveyance path83that is located downstream of the fixing device70in the medium conveyance direction, and a medium reversing mechanism is provided in the middle of the branch conveyance path to reverse and discharge the medium S into the medium discharge receiver; and a mode in which the medium S reversed by the above-described medium reversing mechanism is returned from the vertical conveyance path82to the horizontal conveyance path83through a return conveyance path (not illustrated), and an image is transferred onto the back surface of the medium S in the transfer region TR.

In the present embodiment, the intermediate transfer member30is provided with a microparticle application device100that applies microparticles having excellent lubricity to the surface of the intermediate transfer member30as illustrated inFIG.3.

The microparticle application device100is disposed, for example, at a portion of the intermediate transfer member30that is wound around the tension roller31. When a predetermined microparticle application condition is satisfied, the microparticle application device100applies microparticles onto the intermediate transfer member30so that the image G is carried on a microparticle application layer.

Examples of the microparticle application condition include a condition that the medium S to be used is an embossed medium such as embossed paper having surface roughness (embossed surface).

In the present embodiment, when the medium S is an embossed medium, there is a concern that the image G carried on the intermediate transfer member30is not easily transferred to the embossed medium due to the influence of the surface roughness of the embossed medium, so that a transfer failure is likely to occur. In order to address such a situation, the present embodiment aims to improve, under an image forming condition using an embossed medium as the medium S, the transferability of the image G to the embossed medium in such a manner that an appropriate amount of microparticles are applied onto the intermediate transfer member30, and the image G is carried on the microparticle application layer to reduce the adhesion force of the image G to the intermediate transfer member30.

In the present embodiment, the microparticles p may be appropriately selected as long as they have excellent lubricity. In the present embodiment, microparticles similar to those (for example, silica) that have already been used as an external additive of toner are used.

Examples of the reason why the material similar to the external additive of toner is used as the microparticle p as described above include the fact that the material is conventionally used as the external additive of toner and has high reliability, and the fact that, when the material is also used as the external additive, the material liberated from the toner is supplied to the intermediate transfer member30, and thus the effect of the microparticle can be maintained more stably.

Examples of the material that can be used for the microparticle p include, in addition to silica, fine inorganic powders such as titanium oxide, alumina, barium titanate, calcium titanate, strontium titanate, zinc oxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, chromium oxide, or red iron oxide, and fine organic powders such as polyacrylate, polymethacrylate, polymethyl methacrylate, polyethylene, polypropylene, polyvinylidene fluoride, or polytetrafluoroethylene. In view of environmental stability, the microparticles desirably have low hygroscopic properties, and when fine hygroscopic inorganic powders such as titanium oxide, alumina, or silica are used, they are desirably subjected to a hydrophobic treatment. The hydrophobic treatment for the fine inorganic powder can be carried out by reacting the fine inorganic powder with a silane coupling agent such as hexamethyldisilazane, dimethyldichlorosilane, decylsilane, dialkyldihalogenated silane, trialkylhalogenated silane, or alkyltrihalogenated silane, or a hydrophobic treatment agent such as dimethyl silicon oil at a high temperature.

The particle diameter of the microparticles p may be appropriately selected according to the surface properties of the intermediate transfer member30on which the microparticles are to be applied. In the present embodiment, the microparticles p having a particle diameter in the range of 30 nm to 150 nm are selected for the intermediate transfer member30having a surface roughness Rz of 1.5 or less or a microgloss of 93 or more.

The selection of the microparticles p is based on the results of Examples described later.

Configuration Example of Microparticle Application Device

In the present embodiment, the microparticle application device100includes: an application container101that is opened to face a portion of the intermediate transfer member30wound around the tension roller31; an application roller110that is disposed to face the opening of the application container101and is in contact with the intermediate transfer member30to apply the microparticles p; and a plate-shaped leveling member120that levels the application amount of a microparticle application layer pm applied on the intermediate transfer member30as illustrated inFIG.7A.

The application container101includes a storage portion102for storing the powdery microparticles p and supplying the microparticles p to the application roller110from a lower opening, the storage portion102being provided above the application roller110, a plate-shaped partition portion103provided below the application roller110so as to partition the space in the container, and a plate-shaped regulating portion104provided between the storage portion102and the partition portion103and disposed in contact with the application roller110on the side opposite to a contact portion with the intermediate transfer member30.

InFIG.7A, a sealing member102athat is in elastic contact with the application roller110is provided at the edge of the lower opening of the storage portion102, and a sealing member103athat is in elastic contact with the intermediate transfer member30is provided at the end of the partitioning portion103on the intermediate transfer member30side.

In the present embodiment, a wedge-shaped gap105is formed between the application roller110and the regulating portion104, and a filling mechanism106for filling the wedge-shaped gap105with the microparticles p is provided in a part of the storage portion102. In the present embodiment, the storage portion102has a container side plate107that is contiguous to the regulating portion104and that is inclined like a slide at an angle θ of 45 degrees or more with respect to the horizontal direction. The filling mechanism106fills the wedge-shaped gap105with the microparticles p in such a manner that the container side plate107is supported so as to be swingable with respect to the regulating portion104with, for example, a hinge108, a rotating paddle109serving as a swing means is disposed in contact with a portion of the container side plate107away from the hinge108, and the container side plate107that is inclined like a slide is swung with the rotating paddle109at a predetermined angle α (for example, 10 degrees to 15 degrees).

Regarding the driving timing of the filling mechanism106, the filling mechanism106may be driven, for example, in synchronization with the rotation of the application roller110when the microparticle application device100is driven, but it is preferable to maintain the state in which the wedge-shaped gap105is filled with the microparticles p when the driving of the microparticle application device100is started. In this case, it is only sufficient that, after the end of the image forming operation by the image forming system20as illustrated inFIG.7B, for example, the filling mechanism106applies a vibration force to the container side plate107for a predetermined time to fill the wedge-shaped gap105with the microparticles p as illustrated inFIG.7C.

The filling mechanism106is not limited to the rotating paddle109, and may be appropriately changed in design. For example, the filling mechanism106may be configured such that a vibration motor (not illustrated) is directly or indirectly brought into contact with the outside of the container side plate107to propagate vibration, or such that the outside of the container side plate107is lifted by an eccentric cantilevered bar (not illustrated) and the cantilevered bar is rotated to repeat the contact and separation of the leading end of the cantilevered bar with the outside of the container side plate107to vibrate the container side plate107.

As illustrated inFIGS.7A and8A, the application roller110is an elastic roller having a large number of hemispherical recessed cells113on the surface thereof, and is produced by, for example, laminating an elastic layer112of urethane foam or the like around a metallic roller body111and forming many cells113on the surface of the elastic layer112by embossing.

In the present embodiment, it is sufficient that, since the cell113of the application roller110is required to carry the microparticles p therein, the cell has a diameter sufficiently larger than the particle diameter of the microparticles p, for example, 100 μm to 200 μm.

Further, in the present embodiment, the application roller110is disposed in elastic contact with the regulating portion104of the application container101. The distance d between the contact portion between the application roller110and the regulating portion104and the support point of the container side plate107(corresponding to the supporting point of rotation of the hinge108) is set to about 5 mm to 10 mm.

Further, the application roller110receives a driving force from a driving motor (not shown), and rotates in the same direction as the moving direction of the intermediate transfer member30at a portion facing the intermediate transfer member30. In this case, establishment of vr≠vb is needed where the rotation speed of the application roller110is vr and the rotation speed of the intermediate transfer member30is vb.

The operation process of the application roller110will be schematically described below.

In the present embodiment, the application roller110is elastically pressed against the regulating portion104at the contact portion between the application roller110and the regulating portion104. Thus, when the application roller110rotates with the microparticles p being filled in the wedge-shaped gap105, the regulating portion104has an effect of leveling and putting the microparticles p into the cells113of the application roller110as illustrated inFIGS.7A and8A. As a result, a large number of microparticles p are filled and carried in the cells113of the application roller110which has passed through the regulating portion104as indicated by <CARRY> inFIG.8B.

Next, when the cell113of the application roller110carrying the microparticles p reaches the contact portion with the intermediate transfer member30, a group of microparticles p1 in the group of microparticles p in the cell113at the portion facing an inlet comes into contact with the intermediate transfer member30as indicated by <CONTACT> inFIG.8B.

In this state, due to the speed difference between the rotation speed vr of the application roller110and the rotation speed vb of the intermediate transfer member30, the group of microparticles p in the cell113is pressed against the intermediate transfer member30, and the group of microparticles p1 in the group of microparticles p in the cell113at the position facing the inlet is going to adhere to the surface of the intermediate transfer member30, as indicated by <PRESS/SHEAR> inFIG.8B. Therefore, a shear force Fs associated with the speed difference acts on the boundary between the group of microparticles p1 in the cell113at the position facing the inlet and a group of the other microparticles p2, so that the group of microparticles p in the cell113is divided into two at the boundary.

Thereafter, when the cell113of the application roller110carrying the group of microparticles p passes through the contact portion with the intermediate transfer member30, the cell113moves to a position apart from the surface of the intermediate transfer member30as indicated by <SEPARATION> inFIG.8B. At this time, the group of microparticles p1 at a portion facing the inlet of the cell113is applied to the front surface of the intermediate transfer member30by the adhesion force, and the group of other microparticles p2 in the cell113remains carried in the cell113.

In the present embodiment, the leveling member120is fixed to a part of the application container101with a support bracket121as illustrated inFIGS.7A and8A. The leveling member120is formed of an elastic plate-shaped member, and is disposed such that the leading end thereof is in contact with the intermediate transfer member30while being inclined in a direction opposite to the moving direction of the intermediate transfer member30. In this configuration, the leveling member120needs to level the microparticle application layer pm applied on the intermediate transfer member30to a substantially uniform state, and to this end, an inclination angle β of the leveling member120with respect to the moving surface of the intermediate transfer member30is appropriately selected in a range of, for example, 5 degrees to 20 degrees. The inclination angle β is, for example, set to be smaller than the inclination angle of the cleaning member362of the intermediate-transfer-member cleaning device36so as to avoid excessive removal of the applied microparticles p.

As described above, in the present embodiment, the microparticle application layer pm applied on the intermediate transfer member30by the application roller110is substantially uniformly leveled by the leveling member120.

—Method for Detecting Application State of Microparticles—

In the present embodiment, an optical sensor130is provided as a detection means for detecting the application state of the microparticles p on the intermediate transfer member30. It is only sufficient that the optical sensor130is disposed so as to face the surface of the intermediate transfer member30. For example, the optical sensor130is disposed near an end of the intermediate transfer member30in an intersecting direction that intersects the rotation direction of the intermediate transfer member30in a region between tension rollers32and33as illustrated inFIGS.9A and9B.

As illustrated inFIG.9C, the optical sensor130includes, for example, a light emitting element132and a light receiving element133in a sensor housing131. The optical sensor130irradiates the surface of the intermediate transfer member30with light from the light emitting element132and detects reflected light from the intermediate transfer member30by the light receiving element133.

In the present embodiment, the optical sensor130detects the reflected light from the intermediate transfer member30with the light receiving element133in a state in which the microparticles p are not applied onto the intermediate transfer member30as illustrated inFIG.9C. On the other hand, in a state in which the microparticles p are applied onto the intermediate transfer member30, the optical sensor130detects the reflected light from the microparticle application layer pm on the intermediate transfer member30by the light receiving element133as illustrated inFIG.9D.

Here, the relationship between a microparticle coverage Bc (%) on the intermediate transfer member30and an output (V) of the optical sensor130was examined, and the following tendency was observed. Note that the optical sensor130having a wavelength of 940 nm was used, and SiO2having a particle diameter of 115 nm was used as the microparticles.

In this case, as illustrated inFIG.9E, the output of the optical sensor130has the maximum value when the microparticles p are not applied, and tends to gradually decrease as the microparticle coverage Bc increases. When the microparticle coverage Bc is 10% or more, the output of the optical sensor130is reduced to about ⅔ or less of the output when the microparticles p are not applied, and thus it is possible to clearly determine the state where the microparticles p are applied.

However, in the present embodiment, in a case where the microparticle coverage Bc exceeds 50%, the reduction rate of the output of the optical sensor130is extremely small, and the output of the optical sensor130has a value substantially the same as that in a case where the microparticle coverage Bc is 50%. This is presumed to be because, in a case where the microparticle coverage Bc increases, the reflection output decreases due to irregular reflection or a light confinement effect by the microparticles.

In the present embodiment, the output of the optical sensor130corresponds to the output of the light receiving element133, and the microparticle coverage Bc means the occupancy of the microparticles p in a predetermined reference region for the microparticle application layer pm applied on the intermediate transfer member30.

Therefore, in the present embodiment, since the output of the optical sensor130in a state where the microparticles p are applied is lower than the output of the optical sensor130in a state where the microparticles p are not applied, it is possible to determine whether or not the microparticles p are applied on the intermediate transfer member30by checking the output of the optical sensor130.

In particular, when the microparticle application layer pm is formed, the microparticle coverage Bc is preferably selected in the range of 10% to 50% in consideration of the output characteristics of the optical sensor130.

—Relationship Between Microparticle Coverage and Toner Adhesion Force—

As a result of examining the relationship between the microparticle coverage Bc and the toner adhesion force F in the present embodiment, the toner adhesion force F is the largest when the microparticles are not applied and tends to gradually decrease with an increase in the microparticle coverage Bc until the microparticle coverage Bc reaches or exceeds a certain value, as illustrated inFIG.10A. However, when the microparticle coverage Bc reaches or exceeds a certain value, the toner adhesion force F tends to increase again. This is presumed to be because, when the microparticle coverage Bc is equal to or greater than a certain value, the number of contact points between the microparticles p and toner TN increases, and the toner adhesion force F also increases with an increase in the van der Waals force, as indicated in the case of “application amount: excess” inFIG.10B.

Therefore, in the present embodiment, the microparticle coverage Bc in the vicinity of the minimum value at which the toner adhesion force F becomes the lowest as illustrated inFIG.10Ais selected to optimize the application amount of the microparticles. Note that the microparticle coverage Bc different from the microparticle coverage Bc used in the present embodiment may be obviously selected.

—Relationship Between Presence or Absence of Microparticles and Transfer Bias—

In the present embodiment, since the toner adhesion force F is different between when the microparticles are applied and when the microparticles are not applied, the transfer bias Vt of the transfer device50is selected so as to be different depending on whether or not the microparticles are applied.

For example, when the microparticles are not applied, the image G formed of the toner TN is carried on the intermediate transfer member30as illustrated inFIG.6B. Here, when the image quality was examined by changing the transfer bias, the image quality was the best when the transfer bias Vt was Vt0, and the image quality tended to deteriorate when the transfer bias Vt was set higher or lower than Vt0 as illustrated inFIG.10C.

When the microparticles p are applied with the predetermined microparticle coverage Bc, the image G formed of the toner TN is formed on the intermediate transfer member30with the microparticle application layer pm therebetween as illustrated inFIG.6C. When the image quality was examined by changing the transfer bias, the image quality was the best when the transfer bias Vt was Vt1 (<Vt0), and the image quality tended to deteriorate when the transfer bias Vt was set higher or lower than Vt1. It is to be noted, however, that it was confirmed that even when the transfer bias Vt0 at the time when the microparticles were not applied was selected at the time when the microparticles were applied, the image quality was better than that at the time when the microparticles were not applied.

Therefore, the transfer bias Vt at the time when the microparticles are applied may be set to the same value as the transfer bias Vt0 at the time when the microparticles are not applied, but the transfer bias Vt1 at which the image quality is the best at the time when the microparticles are applied is selected.

In the present embodiment, the control system of the image forming system20includes a control device140that is a microcomputer including various processors as illustrated inFIG.11. The “processor” used herein refers to a processor in a broad sense, and includes a general-purpose processor (for example, central processing unit (CPU)) or a dedicated processor (for example, a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a programmable logic device).

An operation panel150and the optical sensor130of the image forming system20are connected to the control device140. The control device140is connected to each control target (each image forming unit22, the intermediate transfer member30, a transfer power source59of the transfer device50, the microparticle application device100, and the like).

The operation panel150further includes a start switch (“start SW” inFIG.11)151for starting image formation by the image forming system20, a mode selection unit152for selecting one of various image forming modes (single-sided/double-sided printing mode, standard/high-quality printing mode, etc.), and a medium type instruction unit153for instructing the type (resistance, thickness, basis weight, size, whether or not embossing is performed, etc.) of the medium S. Regarding the type of the medium S, it is obvious that, for example, a detector which detects the type (resistance, thickness, size, whether or not embossing is performed, and the like) of the medium S may be installed in the medium supply container81or the conveyance path, and the type of the medium S may be acquired by the detector.

—Image Forming Process of Image Forming System—

Next, a procedure of the image forming process performed by the image forming system according to the present embodiment will be described.

First, when the start switch151is turned on, the image forming system20starts a print job based on the image forming mode selected by the mode selection unit152as illustrated inFIG.11. In this state, the medium S is supplied from the medium supply container81. On the other hand, in the image forming unit22, an image forming process for each color component image to be transferred to the medium S is performed, and the formed color component image moves to the transfer region TR via the intermediate transfer member30.

Thereafter, the medium S is conveyed to the transfer region TR through the horizontal conveyance path83, and a transfer operation is performed by the transfer device50. Then, the medium S to which each color component image has been transferred passes through the fixing device70, by which the image is fixed on the medium S.

In the present embodiment, the control device140executes a microparticle application control program illustrated inFIG.12to control the operation of applying the microparticles p onto the intermediate transfer member30.

InFIG.12, first, the control device140determines whether or not the medium S is an embossed medium based on instruction information from the medium type instruction unit153. Then, when the medium S is an embossed medium, the control device140sets a microparticle application amount, and executes the process of applying the microparticles p by the microparticle application device100. Regarding setting of the microparticle application amount, the microparticle coverage Bc in the vicinity of the minimum value at which the toner adhesion force F becomes the lowest as illustrated inFIGS.10A and10Bis selected in the present embodiment, although any value may be selected as appropriate.

When the medium S is not the embossed medium, it is determined whether or not there are any other conditions for microparticle application. When there are any other conditions for microparticle application, the control device140may set the microparticle application amount, and execute the process of applying the microparticles p. When there is no other condition for microparticle application, the control device140may not execute the process of applying the microparticles p.

Here, examples of the other conditions for microparticle application include a condition that rough paper or the like having a large amount of exposed paper fibers is used. In the present embodiment, the rough paper refers to, for example, paper (having roughness of about 10 μm to 30 μm) that has no roughness (about 30 μm or more) due to embossing and is rougher than electrophotographic paper.

—Maintenance Control Process of Cleaning Device—

The control device140executes a cleaning-device maintenance control program illustrated inFIG.12to perform a maintenance process on the photoconductor cleaning device27and the intermediate-transfer-member cleaning device36, thereby suppressing wear of the cleaning members272and362and cleaning failure by the cleaning members272and362.

InFIG.12, the control device140refers to information regarding the counted number of printed sheets and accumulation of image density to determine whether or not a condition requiring the maintenance process is established.

When the condition requiring the maintenance process is established, the control device140determines to execute the maintenance process. In contrast, when a condition not requiring the maintenance process is established, the control device140determines not to execute the maintenance process.

When determining to execute the maintenance process, the control device140identifies whether or not an object for maintenance is the intermediate-transfer-member cleaning device (illustrated as ITB cleaning device inFIG.13)36. When the object for maintenance is not the intermediate-transfer-member cleaning device36, the control device140executes a normal maintenance mode on the photoconductor cleaning device27that is the object for maintenance.

On the other hand, when the object for maintenance is the intermediate-transfer-member cleaning device36, the control device140determines whether or not the microparticles p are applied on the surface of the intermediate transfer member30from the output of the optical sensor130. When the microparticles p are not applied, the control device140executes the normal maintenance mode (seeFIGS.15A and15B) on the intermediate-transfer-member cleaning device36, and when the microparticles p are applied, the control device140executes a special maintenance mode on the intermediate-transfer-member cleaning device36(seeFIGS.15C to15E).

—Operation of Image Forming System—

<Normal Image Forming Mode (Image Forming Mode I)>

In the present embodiment, the image forming system20performs a normal image forming mode (image forming mode I) under a condition that the microparticles p are not applied on the intermediate transfer member30.

In the normal image forming mode (image forming mode I), the images G (to be specific, Ga to Gd) of the respective color components formed by the image forming units22(22ato22d) are sequentially primarily transferred to the respective image formation regions GR on the intermediate transfer member30, and are secondarily transferred to the medium S in the transfer region TR as illustrated inFIGS.11,14A, and14B. InFIG.14A, the image formation regions GR are discontinuously arranged with the non-image formation region NR therebetween. In addition, the image G of each color component is an image in which image elements of each color component are repeatedly described in a ladder pattern shape, and this schematically illustrates an image including the image elements of each color component. The same applies toFIG.14CandFIGS.15A and15C.

<Special Image Forming Mode (Image Forming Mode II)>

In the present embodiment, the image forming system20performs a special image forming mode (image forming mode II) obtained by adding an application process of applying the microparticles p to the normal image forming mode under a condition that the microparticles p are to be applied on the intermediate transfer member30.

In the special image forming mode (image forming mode II), the microparticle application device100applies the microparticles p to the entire region including the image formation regions GR and the non-image formation regions NR on the intermediate transfer member30according to a predetermined microparticle coverage Bc, and then the image forming units22(22ato22d) sequentially primarily transfer the images G of the color components to the image formation regions GR of the intermediate transfer member30as illustrated inFIGS.11,14C, and14D. Therefore, the image G of each color component produced by the corresponding image forming unit22is carried on the microparticle application layer pm on the intermediate transfer member30, and is secondarily transferred to the medium S (the embossed medium Sb in the present embodiment) in the transfer region TR.

At this time, the image G of each color component is carried on the intermediate transfer member30with the microparticle application layer pm therebetween, and thus, is easily transferred to the embossed medium Sb(S). Accordingly, the image G of each color component is appropriately transferred without being affected by the roughness of the embossed medium Sb.

In particular, in the present embodiment, the transfer bias Vt used in the transfer device50is changed to the transfer bias Vt1 that is optimum for the transfer condition when the microparticles are applied instead of the transfer bias Vt0 which is used during the normal image forming mode, and thus, it is possible to obtain image transferability of higher image quality than that in the case of using the transfer bias Vt0.

In the present embodiment, the control device140functions as a maintenance device serving as a maintenance means.

Under the condition that the microparticles p are not applied onto the intermediate transfer member30, the control device140performs the normal maintenance mode (maintenance mode I) as illustrated inFIGS.11,14,15A, and15B.

In the present embodiment, when a condition that requires the maintenance process on the predetermined cleaning members272and362is established, the control device140uses necessary devices (the charging device24, the optical writing device25, and the developing device26) of each image forming unit22to form a maintenance image Gm on an entire region or a part of each photoconductor23and supplies the maintenance image Gm to the cleaning members272and362to be maintained.

Here, examples of the condition requiring the maintenance process include a condition that an amount of toner remaining on the photoconductor23or the intermediate transfer member30is reduced to such an extent that the cleaning operation by the cleaning members272and362is impaired. This condition may be determined based on whether or not the accumulated image forming conditions and print number conditions of the print job reach a predetermined threshold.

The maintenance image Gm is produced separately from the normal image G and is supplied based on an amount required for the maintenance process of the cleaning members272and362. Since the maintenance image Gm is formed using developer in each developing device26, the maintenance image Gm has a shape pattern that does not wastefully consume the developer. In the present embodiment, the maintenance image Gm is formed as one or a plurality of band-shaped images (corresponding to so-called toner bands) TB continuously extending along an intersecting direction (for example, a width direction) intersecting the rotation direction of the photoconductor23or the intermediate transfer member30. The thickness, width, image density Cin, number, and the like of the band-shaped image TB may be appropriately selected. For example, the thickness, width, image density Cin, number, and the like of the band-shaped image TB may be appropriately selected in consideration of the configuration of, for example, one band-shaped image TB having a thickness equivalent to the thickness of a normal toner image (for example, 6 μm to 10 μm), a width of about 1 mm to 3 mm, and an image density Cin of about 50% to 100%.

Although the maintenance image Gm carried on the intermediate transfer member30includes the band-shaped images TB of all the color components of the image forming units22(22ato22d) inFIGS.15A and15A, the maintenance image Gm does not necessarily include the band-shaped images TB of all the color components and may include the band-shaped images TB of some of the color components.

In addition, it is only sufficient that the maintenance image Gm is formed over the entire width of the image formation region GR of the photoconductor23or the intermediate transfer member30. The maintenance image Gm is not limited to be continuously formed over the entire area of the image formation region GR in the width direction, and a plurality of divided band-shaped images may be discontinuously formed to cover the entire area of the image formation region GR in the width direction.

Furthermore, in the present embodiment, the image forming system20is configured to be able to execute the maintenance mode in parallel with the image forming mode, so that the maintenance image Gm is basically formed in the non-image formation region NR other than the image formation region GR. In the maintenance process for the photoconductor cleaning device27, the maintenance image Gm in the non-image formation region (not illustrated) on the photoconductor23is supplied to the photoconductor cleaning device27without being transferred to the intermediate transfer member30. On the other hand, in the maintenance process for the intermediate-transfer-member cleaning device36, the maintenance image Gm formed on the photoconductor23is transferred to the non-image formation region NR on the intermediate transfer member30, and then is supplied to the intermediate-transfer-member cleaning device36without being transferred to the medium S.

As described above, in the normal maintenance mode (maintenance mode I), the maintenance image Gm is forcibly supplied to the contact portion of the cleaning members272and362, so that a large amount of the external additive g included in the maintenance image Gm is supplied to the contact portion of the cleaning members272and362and accumulated as a dam DM, as illustrated inFIG.16A. Accordingly, the contact state between the contact portion of the cleaning member272and the photoconductor23and between the contact portion of the cleaning member362and the intermediate transfer member30is satisfactorily maintained, and the maintenance process for the cleaning members272and362is completed.

Under the condition that the microparticles p are to be applied onto the intermediate transfer member30, the control device140performs the special maintenance mode (maintenance mode II) on the intermediate-transfer-member cleaning device36as illustrated inFIGS.11,14,15C, and15D. Note that, in the present embodiment, only the normal maintenance mode I is executed for the photoconductor cleaning device27.

In the special maintenance mode (maintenance mode II), the control device140forms the maintenance image Gm as in the normal maintenance mode (maintenance mode I), but the width w2 of the band-shaped image TB as the maintenance image Gm is set to be smaller than the width w1 in the normal maintenance mode I. For this reason, the consumption amount of toner used for the maintenance image Gm is reduced.

Therefore, in the present embodiment, the maintenance image Gm is carried on the intermediate transfer member30on which the microparticle application layer pm is applied, and the maintenance image Gm and the microparticle application layer pm are forcibly supplied to the contact portion of the cleaning member362as illustrated inFIG.16B. At this time, the consumption amount of toner constituting the maintenance image Gm is smaller than that in the normal maintenance mode, and thus, the amount of the external additive g included in the maintenance image Gm is also small. However, the microparticles p included in the microparticle application layer pm compensate for the amount of the external additive g. Therefore, a large amount of the external additive g and the microparticles p equivalent to the external additive g are supplied to the contact portion of the cleaning member362and accumulated as the dam DM. Thus, the contact state between the contact portion of the cleaning member362and the intermediate transfer member30is maintained satisfactorily, and the maintenance process for the cleaning member362is completed.

Another Example of Special Maintenance Mode (Maintenance Mode II)

As another example of the special maintenance mode (maintenance mode II), it is also possible to use only the microparticle application layer pm as a substitute for the maintenance image without forming the maintenance image Gm in the maintenance process for the intermediate-transfer-member cleaning device36, as illustrated inFIG.15E. When the special image forming mode (image forming mode II) is executed, the microparticle application layer pm has already been formed on the intermediate transfer member30, and therefore, the microparticle application layer pm may be used as a substitute for the maintenance image. In addition, the microparticle application layer pm is not formed on the intermediate transfer member30during the execution of the normal image forming mode (image forming mode I). Therefore, when the special maintenance mode is performed, the microparticle application device100may be operated to form the microparticle application layer pm only in the non-image formation region NR on the intermediate transfer member30, and the formed microparticle application layer pm may be used as the maintenance image.

Another Configuration Example of Microparticle Application Device

In the present embodiment, the microparticle application device100, for example, is not limited to have the configuration described in the first embodiment, and it is obvious that the microparticle application device100may be changed in design, as appropriate, as in, for example, modification 1-1 or modification 1-2.

FIG.17illustrates a microparticle application device according to the modification 1-1.

InFIG.17, the microparticle application device100has a configuration different from that of the first embodiment, and is integrally incorporated in the intermediate-transfer-member cleaning device36.

In the present modification, the intermediate-transfer-member cleaning device36is provided in the vicinity of the tension roller31of the intermediate transfer member30on the upstream side of the tension roller31in the rotation direction. The intermediate-transfer-member cleaning device36includes a cleaning housing361that is open so as to face the front surface of the intermediate transfer member30, an elastic plate-shaped cleaning member362provided at the opening edge of the cleaning housing361with a support bracket363, and a counter roller364provided on the back surface of the intermediate transfer member30facing the cleaning member362. Furthermore, in the present modification, the cleaning housing361includes, in the lower portion thereof, a pair of leveling/conveying members365that levels and coveys the stored residues, and a brush-shaped second cleaning member367provided upstream of the plate-shaped cleaning member362in the rotation direction of the intermediate transfer member30. A counter roller368is provided on the back surface of the intermediate transfer member30facing the second cleaning member367.

The microparticle application device100is incorporated in an upper portion of the cleaning housing361of the intermediate-transfer-member cleaning device36.

As in the first embodiment, the microparticle application device100according to the present modification includes: an application container101that is opened to face a portion of the intermediate transfer member30wound around the tension roller31; an application roller110that is disposed to face the opening of the application container101and is in contact with the intermediate transfer member30to apply the microparticles p; a plate-shaped leveling member120that levels the application amount of the microparticle application layer pm applied on the intermediate transfer member30; and a microparticle attaching mechanism170that attaches the microparticles p to the surface of the application roller110.

In the present modification, unlike the first embodiment, the application container101is integrally formed in the upper portion of the cleaning housing361, and has a partition member160between the application roller110and the cleaning member362. The application roller110has substantially the same configuration as that in the first embodiment. In addition, the leveling member120is supported at the upper edge of the opening of the application container101with a support bracket121, and has substantially the same configuration as that of the first embodiment.

In particular, in the present modification, the microparticle attaching mechanism170is configured such that a block-shaped microparticle solid mass171produced by compression molding of a large number of microparticles is brought into contact with the application roller110on the side opposite to the contact portion with the intermediate transfer member30, and is pressed against the surface of the application roller110by a pressure spring172as a pressing means. According to the microparticle attaching mechanism170, the microparticles p are scraped off from the microparticle solid mass171at a contact portion between the application roller110and the microparticle solid mass171with the rotation of the application roller110, are leveled and filled into the recessed cells (not shown) of the application roller110, and are attached to the surface of the application roller110.

As a result, the application roller110reaches the contact portion with the intermediate transfer member30in a state of carrying the microparticles p on the surface thereof, and after being applied to the surface of the intermediate transfer member30, the microparticles p are leveled to a predetermined application amount by the leveling member120. In the present modification, even if some of the scraped microparticles p drop from the contact portion between the microparticle solid mass171and the application roller110, they are accumulated in a space partitioned by the partition member160.

Further, in the present modification, the microparticle application device100does not include the application container101described in the first embodiment (the storage portion102for storing powdery microparticles, the wedge-shaped gap105formed between the application roller110and the regulating portion104, and the filling mechanism106), but may use the application container101described in the first embodiment. Specifically, instead of the powdery microparticles p, the microparticle solid mass171(seeFIG.17) may be disposed in the storage portion102so as to be in contact with the application roller110or a scraping roller (not illustrated) provided separately from the application roller110, the microparticles p may be scraped from the microparticle solid mass171by the application roller110or the scraping roller, and the wedge-shaped gap105may be filled with the scraped powdery microparticles p.

FIG.18illustrates a microparticle application device according to the modification 1-2.

InFIG.18, the microparticle application device100includes an application container101for storing powdery microparticles p, an application roller110for applying the microparticles p to the intermediate transfer member30, and a leveling member120for leveling the microparticle application layer pm applied to the intermediate transfer member30as in the first embodiment, but differs from the first embodiment in the layout of the application roller110and the leveling member120and the method for attaching the microparticles p to the application roller110.

In the present modification, the application roller110and the leveling member120are disposed above a portion of the intermediate transfer member30which is stretched around the tension roller31.

Further, the application container101includes a storage portion102that is open so as to cover the right half surface of the application roller110inFIG.18and that stores the powdery microparticles p, a regulating portion104that is disposed in the storage portion102so as to be in contact with the application roller110in the vicinity of the lower portion of the application roller110, and a wedge-shaped gap105formed between the regulating portion104and the application roller110. An agitator165serving as an agitation member that agitates the accumulated microparticles p is provided above the wedge-shaped gap105in the storage portion102. An upper sealing member166that elastically comes into contact with the upper portion of the application roller110for sealing is provided at the upper edge of the opening of the storage portion102of the application container101, and a lower sealing member167that elastically comes into contact with the surface of the intermediate transfer member30for sealing is provided at the lower edge of the opening of the storage portion102.

As described above, according to the present modification, when the microparticles p are applied to the intermediate transfer member30, the application roller110and the agitator165may be rotated along with the rotation of the intermediate transfer member30. At this time, in the storage portion102of the application container101, the microparticles p in the storage portion102are filled in the wedge-shaped gap105by the rotation of the agitator165, and when the application roller110rotates in this state, the microparticles p are leveled and filled into the cells (not illustrated) of the application roller110by the regulating portion104at the contact portion between the application roller110and the regulating portion104. As a result, the application roller110reaches the contact portion with the intermediate transfer member30in a state of carrying the microparticles p on the surface thereof, and after being applied to the surface of the intermediate transfer member30, the microparticles p are leveled to a predetermined application amount by the leveling member120.

Θ Second Embodiment

An image forming system20according to the second embodiment is obtained by applying the aspect of the present invention to a mode in which an amount of microparticles applied to the intermediate transfer member30is changed in a plurality of stages, and basically has the same configuration as that of the first embodiment. However, the image forming system20is different from the first embodiment in control of applying microparticles to the intermediate transfer member30and the maintenance control of the intermediate-transfer-member cleaning device36.

In the present embodiment, the control device140(seeFIG.11) executes a microparticle application control program illustrated inFIG.19to control the operation of applying the microparticles p onto the intermediate transfer member30.

InFIG.19, first, the control device140determines whether or not the medium S is an embossed medium based on the instruction information from the medium type instruction unit153(seeFIG.11). In the determination process, when there are a plurality of types of embossed media depending on the depth, size, and the like of embossing, the types (for example, Sb1, Sb2, and Sb3) are identified.

In a case where the medium S is an embossed medium, a microparticle application amount MS (MS1, MS2, MS3) is set according to the type (Sb1, Sb2, Sb3) of the embossed medium, and the process of applying the microparticles p by the microparticle application device100is performed. Here, the microparticle application amount MS may be appropriately set, but in the present embodiment, the microparticle application amount MS is set to satisfy the relationship of MS1<MS2<MS3 on the basis of the microparticle coverage Bc on the intermediate transfer member30as illustrated inFIG.21.

In order to change the microparticle application amount MS, the application amount to the intermediate transfer member30by the application roller110may be changed by, for example, changing the rotation speed vr of the application roller110with respect to the rotation speed vb of the intermediate transfer member30to change the speed difference.

When the medium S is not the embossed medium, it is determined whether or not there are any other conditions for microparticle application. When there are any other conditions for microparticle application, the control device140may set the microparticle application amount, and execute the process of applying the microparticles p. When there is no other condition for microparticle application, the control device140may not execute the process of applying the microparticles p.

—Maintenance Control Process of Intermediate-Transfer-Member Cleaning Device—

The control device140(seeFIG.11) executes a program for maintenance control of the intermediate-transfer-member cleaning device illustrated inFIG.20to perform a maintenance process on the intermediate-transfer-member cleaning device36, thereby suppressing wear of the cleaning member362and cleaning failure by the cleaning member362. Note that the maintenance process in the normal maintenance mode is executed on the photoconductor cleaning device27in substantially the same manner as in the first embodiment.

InFIG.20, the control device140refers to information regarding the counted number of printed sheets and accumulation of image density to determine whether or not a condition requiring the maintenance process is established. When a condition requiring the maintenance process is established, the control device140determines to execute the maintenance process.

When determining to execute the maintenance process, the control device140determines whether or not the microparticles p are applied on the surface of the intermediate transfer member30from the output of the optical sensor130(seeFIG.9). When the microparticles p are not applied, the control device140executes the normal maintenance mode (seeFIGS.15A and15B) on the intermediate-transfer-member cleaning device36. In the present embodiment, when the output of the optical sensor130is less than a threshold TH1 corresponding to the microparticle application amount MS1, it is assumed that the microparticles p are not applied.

On the other hand, when the microparticles p are applied, the special maintenance mode is performed on the intermediate-transfer-member cleaning device36(seeFIGS.15C to15E).

The thresholds for the output of the optical sensor130corresponding to the microparticle application amounts MS1, MS2, and MS3 are defined as TH1, TH2, and TH3, respectively. In the present embodiment, when the output of the optical sensor130is equal to or greater than the threshold TH1 and less than the threshold TH2, a band-shaped image TB1 corresponding to the microparticle application amount MS1 is selected as the maintenance image Gm as illustrated inFIGS.20and21. When the output of the optical sensor130is equal to or greater than the threshold TH2 and less than the threshold TH3, a band-shaped image TB2 corresponding to the microparticle application amount MS2 is selected as the maintenance image Gm. Further, when the output of the optical sensor130is equal to or greater than the threshold TH3, a band-shaped image TB3 corresponding to the microparticle application amount MS3 is selected as the maintenance image Gm.

Given that the band-shaped image when the microparticles are not applied is defined as TB0, the relationship of TB0>TB1>TB2>TB3 is satisfied as illustrated inFIG.21regarding the supply amount of the maintenance image Gm.

As described above, in the special maintenance mode in the present embodiment, control is performed so that an amount of the maintenance image varies depending on the application amount of the microparticles under the condition that the microparticles are applied, with an amount of the maintenance image in the normal maintenance mode under the condition that the microparticles are not applied being defined as an upper limit.

More specifically, in the special maintenance mode, an amount of the maintenance image is controlled to be smaller as the application amount of the microparticles is larger under the condition that the microparticles are applied. In other words, in the special maintenance mode, an amount of the maintenance image is controlled to be larger as the application amount of the microparticles is smaller under the condition that the microparticles are applied.

Therefore, in the present embodiment, when the maintenance process is performed on the intermediate-transfer-member cleaning device36in a mode in which the application amount of the microparticles on the intermediate transfer member30varies, the amount of the maintenance image can be limited as much as possible by effectively using the microparticle application layer pm applied on the intermediate transfer member30, as compared with the case where the application amount of the microparticles is uniformly determined.

Although the microparticle application amount MS is changed stepwise in the present embodiment, it is obvious that, for example, the microparticle application amount may be continuously changed in accordance with the change curve of the microparticle coverage as illustrated inFIG.21, and an amount of the maintenance image in the special maintenance mode may be selected on the basis of the change.

FIG.22illustrates a main part of an image forming system according to a third embodiment.

Unlike the first and second embodiments, the image forming system20forms a single-color image with, for example, black toner inFIG.22.

InFIG.22, the image forming system20employs, for example, an electrophotographic method, and includes a drum-shaped photoconductor223. The image forming system20includes, around the photoconductor223, a charging device224that charges the photoconductor223, an optical writing device225that writes an electrostatic latent image on the charged photoconductor223, a developing device226that develops the electrostatic latent image written on the photoconductor223with toners of respective color components, a transfer device227that transfers the toner image formed on the photoconductor223onto a medium S, and a cleaning device228(including a plate-shaped cleaning member228a) that cleans off toner TN remaining on the photoconductor223.

In the present embodiment, a microparticle application device100is provided between the optical writing device225and the developing device226in the periphery of the photoconductor223, and microparticles are applied onto the photoconductor223in a case where the medium S is, for example, an embossed medium.

In the present embodiment, an operation panel250is connected to a control device240, and a medium type instruction unit253and the like are connected to the operation panel250. In addition to a normal image forming control process, the control device240performs a microparticle application control process on the photoconductor223, a maintenance control process on the cleaning device228, and the like, and appropriately controls the photoconductor223and each device around the photoconductor223.

The image forming system20includes a transfer power source229of the transfer device227.

In the present embodiment, the control device240performs control of application of microparticles onto the photoconductor223, and performs a maintenance process (normal maintenance process, special maintenance process) on the cleaning device228depending on the application state of the microparticles. The normal maintenance process and the special maintenance process are performed in substantially the same manner as those described in the first and second embodiments.

Although the image forming system in the present embodiment forms a single-color image, the image forming system20according to the present embodiment may be applied to, for example, an image forming system in which image forming units22(22ato22d, seeFIG.3) of respective color components are arranged so as to face a medium conveyance belt that conveys the medium S.

Example

In this example, a device based on Revoria Press PC1120 manufactured by FUJIFILM Business Innovation Corp. was used. The evaluation environment is 22° C./55%, and the process speed is 524 mm/s. Regarding toner, YMC each have a specific gravity of 1.1 and a particle diameter of 4.7 μm, and K has a specific gravity of 1.2 and a particle diameter of 4.7 μm. The toner mass per area (TMA) of YMC was set to 3.3 g/m2and the TMA of K was set to 3.7 g/m2. The primary transfer device35was an elastic roller with φ28having a volume resistance of 7.7 log Ω and an Asker C hardness of 30°. The primary transfer current was set to 54 μA. As the intermediate transfer member30, an intermediate transfer belt obtained by dispersing carbon in polyimide was used, the intermediate transfer belt having a volume resistivity of 12.5 log Ωcm. The intermediate-transfer-member cleaning device36has, as a cleaning member, a plate-shaped cleaning blade made of urethane rubber and having a thickness of 2 mm, the cleaning blade being in contact with the surface of the intermediate transfer belt at a setting angle of 22° and a linear pressure of 2.3 gf/mm.

The transfer device50employed a belt transfer module51in which a rubber belt with φ40 having a thickness of 450 μm and a volume resistance of 9.2 log Ω as the transfer conveyance belt53was wound around the elastic transfer roller55with ϕ28 having a volume resistance of 6.3 log Ω and was stretched between the elastic transfer roller55and a separation roller with φ20. An elastic roller with φ28 having an Asker C hardness of 53° and a surface resistance of 7.3 log Ω/□ was used as the counter roller56provided via the intermediate transfer member30.

Further, as the microparticles, SiO2having a particle diameter of 115 nm was used, and as the application roller110, a urethane sponge roller with φ28 having an Asker C hardness of 15° was used. The urethane sponge roller carrying the microparticles was brought into contact with the intermediate transfer member30with an amount of bite of 0.5 mm and rotated at a peripheral speed ratio of 1.5 with respect to the intermediate transfer member30, thereby applying the microparticles onto the surface of the intermediate transfer member30. The amount of microparticles applied to the intermediate transfer member30was adjusted by the amount of microparticles carried by the urethane sponge roller.

—Relationship Between Application Amount of Microparticles and Amount of Maintenance Image—

J paper (non-coated paper, 82 gsm) manufactured by FUJIFILM Business Innovation Corp. was used as a medium, and cleaning failure for the intermediate transfer member when image/non-image charts illustrated inFIGS.15A and15A, for example, were output in 1kpv on the J paper was checked by changing the application amount of microparticles and the amount of toner band that is a band-shaped image as the maintenance image.

Specifically, the application amount of microparticles was classified into “microparticles not applied, 0%”, “microparticles applied with coverage of 10%”, and “microparticles applied with coverage of 40%”, and the amount of toner band was classified into “no band”, “band of 1%”, “band of 4%”, and “band of 10%”.

Here, the amount of toner band (wt %) is per color, and is a value obtained by conversion with a case where a single color is solidly printed on all over the surface of A4 paper being defined as 100%.

The results are shown inFIG.23.

FIG.23suggests that, as the application amount of microparticles increases, the cleaning failure can be suppressed even when the amount of toner band is small.

—Relationship Between Particle Diameter of Microparticles, Toner Adhesion Force, and Image Transferability—

When the microparticles are applied onto the intermediate transfer member30according to the present example, the surface roughness of the microparticle application layer changes depending on the particle diameter of the microparticles.

The used intermediate transfer belt had a surface roughness Rz of 1.5 or less or a microgloss of 93 or more when the surface property of the intermediate transfer member30on which the microparticles were not applied was measured.

The relationship between the surface roughness (corresponding to the particle diameter of the microparticles) [nm] of the microparticle application layer and the toner adhesion force to the surface of the intermediate transfer member30(hereinafter referred to as toner adhesion force) [kPa] was examined, and the results shown inFIG.24were obtained. Here, the toner adhesion force is expressed as follows. Specifically, compressed air is blown from a glass nozzle to the toner layer on the surface of the intermediate transfer member30while increasing the pressure, and the air pressure at the timing at which the toner layer is separated is used as the adhesion force (alternative characteristic).

Further, based on the results shown inFIG.24, the relationship between the toner adhesion force [kPa] and the transferability grade was examined, and the results shown inFIG.25were obtained. Here, the transferability grade is obtained in such a manner that the microparticle application layer corresponding to the toner adhesion force is applied on the intermediate transfer belt, a predetermined image/non-image chart is carried on the microparticle application layer, and image quality when the chart is transferred to embossed paper as an embossed medium is visually checked. The smaller the numerical value of the transferability grade, the better the transferability to the embossed medium.

It is understood fromFIG.25that, when the toner adhesion force is equal to or less than a predetermined threshold L (in this example, 10 kPa is selected), the transferability grade with respect to embossed medium is good.

It is understood fromFIG.24that, when the particle diameter range of the microparticles having the toner adhesion force equal to or less than the threshold L (10 kPa) is examined, the particle diameter range from 30 nm to 115 nm is preferable.

Thus, it is understood that the main effect of the microparticle application is to reduce the adhesion force between the toner and the surface of the intermediate transfer member30and improve the image transferability.

It is to be noted, however, that the particle diameter of the microparticles is preferably selected in an appropriate range from 30 nm to 115 nm.

The microparticles within the appropriate range have a size that allows the microparticles to enter the gap H (seeFIG.5B) between the contact portion of the cleaning member362of the intermediate-transfer-member cleaning device36and the intermediate transfer member30, and therefore have an effect of preventing a cleaning failure. On the other hand, when the particle diameter of the microparticles is large, the microparticles do not enter the gap H between the contact portion of the cleaning member362and the intermediate transfer member30, and thus, do not provide the effect of preventing a cleaning failure. When the particle diameter of the microparticles is smaller than 30 nm, the microparticles p that have entered the gap H easily pass through the contact portion, and the amount of microparticles passing through the contact portion increases. This destabilizes the contact state, and also allows toner TN to pass through, and thus, not preferable.

—Relationship Between Particle Diameter of Microparticles and Amount of Maintenance Image—

As in the above case, cleaning failure for the intermediate transfer member when the image/non-image charts were output on J paper (non-coated paper, 82 gsm) in 1kpv was checked by changing the particle diameter of the microparticles and the amount of toner band that is a band-shaped image as the maintenance image.

To be specific, the particle diameter of the microparticles was classified into “microparticles not applied”, “SiO2with 500 nm applied”, “SiO2with 100 nm applied”, and “SiO2with 37 nm applied”, and the amount of toner band was classified into “no band”, “band of 1%”, “band of 4%”, and “band of 10%”.

The results are shown inFIG.26.

It is suggested that, when the microparticles SiO2having a particle diameter in the range of 30 nm to 115 nm and having a good transferability grade are used, the effect of reducing the amount of toner band is observed with respect to the case where the microparticles are not applied, but the effect is not observed when the particle diameter size is increased.

An image forming system comprising: an image carrying element that is rotatably provided and carries an image; an image forming element that forms the image on the image carrying element using an image forming material containing at least an external additive; a transfer element that transfers the image carried by the image carrying element to a medium; a cleaning element having a plate shape, the cleaning element being disposed so that a leading end comes into contact with the image carrying element while being inclined in a direction opposite to a rotation direction of the image carrying element to clean a residue remaining on the image carrying element after a transfer operation by the transfer element; a maintenance element that forms, using the image forming element, a band-shaped maintenance image of the image forming material in a non-image formation region of the image carrying element, and regularly or irregularly supplies the maintenance image to the cleaning element in a state where the transfer operation by the transfer element is not performed; a microparticle application element that regularly or irregularly applies a microparticle having lubricity to the image carrying element; and a maintenance control element that controls an amount of the maintenance image by the maintenance element depending on an application state of the microparticle on the image carrying element.

The image forming system according to (((1))), wherein the maintenance control element performs control so that the amount of the maintenance image by the maintenance element differs between under a condition that the microparticle is applied and under a condition that the microparticle is not applied, with the amount of the maintenance image by the maintenance element under the condition that the microparticle is not applied being defined as an upper limit.

The image forming system according to (((2))), wherein the maintenance control element performs control so that the amount of the maintenance image is smaller under the condition that the microparticle is applied than the amount of the maintenance image under the condition that the microparticle is not applied.

The image forming system according to (((2))) or (((3))), wherein the maintenance control element performs control so that the maintenance image is not supplied under the condition that the microparticle is applied.

The image forming system according to (((1))), wherein the maintenance control element performs control so that the amount of the maintenance image varies depending on an application amount of the microparticle under a condition that the microparticle is applied, with the amount of the maintenance image by the maintenance element under a condition that the microparticle is not applied being defined as an upper limit.

The image forming system according to (((5))), wherein the maintenance control element performs control so that the amount of the maintenance image is smaller as the application amount of the microparticle is larger under the condition that the microparticle is applied.

The image forming system according to (((5))), wherein the maintenance control element performs control so that the amount of the maintenance image is larger as the application amount of the microparticle is smaller under the condition that the microparticle is applied.

The image forming system according to any one of (((1))) to (((7))), wherein the maintenance control element includes a detection element capable of detecting an application state of the microparticle, and controls the amount of the maintenance image on the basis of a detection result of the detection element.

The image forming system according to (((8))), wherein the detection element includes a reflective optical sensor disposed facing an application layer of the microparticle.

The image forming system according to any one of (((1))) to (((9))), wherein the microparticle application element applies the microparticle having a particle diameter within a range of 30 nm to 150 nm onto the image carrying element having a surface roughness Rz of 1.5 or less or a microgloss of 93 or more.

The image forming system according to (((10))), wherein the microparticle application element applies the microparticle to the image carrying element with a coverage in a range of 10% to 50%.