JP5435376B2 - Image forming apparatus - Google Patents

Description

  According to the present invention, at least one of the surface of the latent image carrier and the toner adhering to the surface is provided by a conductive member to which a bias is supplied while being in contact with the surface of the latent image carrier such as a photoconductor. The present invention relates to a process unit and an image forming apparatus that use a charging means for charging the toner.

  In general, an electrophotographic image forming apparatus forms an image by the following process. That is, first, an electrostatic latent image is formed by performing exposure scanning or the like on a uniformly charged latent image carrier such as a photosensitive member, and the electrostatic latent image is developed by a developing device. Next, the toner image obtained by development is directly transferred from the latent image carrier to a recording material such as transfer paper, or transferred to a recording member via an intermediate transfer material.

  As a charging device used in the image forming apparatus having such a configuration, the following is known. That is, by causing a discharge between the latent image carrier and the charging member while applying a charging bias to a charging member such as a charging roller which is a conductive member in contact with the surface of the latent image carrier, This is a charging device that uniformly charges the surface of the latent image carrier.

  In addition, a device that performs auxiliary charging, such as a charging device described in Patent Document 1, is also known. This type of charging device has an auxiliary charging member to which an auxiliary charging bias is applied, in addition to main charging means that mainly performs uniform charging of a latent image carrier such as a charging roller or a scorotron charging charger. Yes. The auxiliary charging member is brought into contact with a portion of the peripheral surface of the latent image carrier that moves endlessly, after passing through the transfer step and before entering the main charging step by the main charging means. . In such a configuration, the surface of the latent image carrier before being uniformly charged by the main charging unit is auxiliary charged in advance by discharging from the auxiliary charging member or charge injection, or the transfer residue adhered to the surface is preliminarily charged. The toner is charged to a normal charging polarity. As a result, the charging unevenness of the latent image carrier is suppressed, the occurrence of scumming due to the recharge of the low charge amount toner or the reverse charge toner to the development area, the low charge amount toner or the reverse charge toner is removed. The occurrence of contamination of the charging member due to transfer to the charging member by electrostatic force can be suppressed.

  In these charging devices, if the transfer residual toner adheres to the charging member or auxiliary charging member, which is a conductive member in contact with the latent image carrier, these members, the transfer residual toner and the surface of the latent image carrier Discharge and charge injection during the period are hindered. As a result, the main charging and the auxiliary charging are not performed satisfactorily and uneven charging occurs, or the transfer residual toner is not satisfactorily charged and scumming occurs. The background stain is a phenomenon in which toner adheres to the background portion (uniformly charged portion) of the latent image carrier.

  The present invention has been made in view of the above background, and an object thereof is to provide a process unit and an image forming apparatus using the following charging means. That is, it is a process unit or the like that can suppress the occurrence of uneven charging and soiling due to toner fixing to the conductive member over a long period of time.

In order to achieve the above object, a first aspect of the present invention provides a latent image carrier that carries a latent image, a latent image forming unit that forms a latent image on the latent image carrier, and a latent image carrier on the latent image carrier. At least one of the surface and the toner adhering to the surface by developing means for developing the latent image with toner and a conductive member to which a bias is supplied while contacting the surface of the latent image carrier An image forming apparatus including a charging unit that charges the surface of the latent image carrier in the surface movement direction of the latent image carrier without contacting the latent image carrier. The latent image bearing member is fixed to the support member in a state, and the region existing between the upstream end and the downstream end of the conductive member is supported by the elastic member fixed to the support member. The conductive member that is pressed toward the body The tensile breaking strength is 10 [MPa] or more, and is a value that is low enough to cause the conductive member to wear with sliding with the latent image carrier, and the contact between the conductive member and the latent image carrier is low. The contact pressure is 4 [kN / m ² ] or more and 15 [kN / m ² ] or less, and the pure water contact angle of the surface of the conductive member is 105 [°] or more. .
The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the latent image carrier is a cylindrical photoconductor, and the support member is curved along a curved surface of the photoconductor. It is characterized by being.
The invention according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein the latent image carrier has a surface having a pure water contact angle of 90 ° or more. To do.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, as the toner, 1 to 4 parts by weight of an external additive of the toner particles is added to the toner particles. , Is used.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a ratio of toner particles having a particle diameter of 5 [μm] or less to the total toner particles as the toner is 15 [%]. The following is used.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the charging unit is a region facing the conductive member in the entire area in the surface movement direction of the latent image carrier. And a charging member for uniformly charging a region downstream of the surface moving direction and upstream of the surface facing the developing unit. It is characterized by.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the conductive member is provided in the developing unit or a toner container that stores toner for replenishing the developing unit. It is fixed and detachable from the image forming apparatus main body separately from the latent image carrier .

In these inventions, as the present inventors have clarified through experiments to be described later, the conductive member having a tensile strength at break of 10 [MPa] or more and 40 [MPa] or less is compared with the latent image carrier. By setting the contact pressure to 4 [kN / m ² ] or more and 15 [kN / m ² ] or less, toner adhesion to the conductive member can be suppressed for a long period of time. Therefore, it is possible to suppress the occurrence of charging unevenness and scumming due to toner adhesion to the conductive member over a long period of time.

FIG. 2 is a schematic configuration diagram illustrating a main part of a printer according to a reference embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for K of the printer together with an intermediate transfer belt. The expansion block diagram which shows the process unit for K of a modification apparatus with an intermediate transfer belt. FIG. 3 is an enlarged configuration diagram illustrating an auxiliary charging member and a photosensitive member in a K process unit of a printer according to a first reference example. FIG. 3 is an enlarged configuration diagram illustrating a conductive sheet for K and a peripheral configuration thereof in the printer according to the embodiment. The graph which shows the relationship between the contact pressure of the photoreceptor and a conductive sheet in the printer which concerns on a reference form, and the position of a conductive sheet. 6 is a graph showing the relationship between the contact pressure between the photosensitive member and the conductive sheet and the position of the conductive sheet in the printer according to the embodiment . Enlarged view showing an auxiliary charging member for K in modified device of the printer according to the embodiment. FIG. 9 is a schematic configuration diagram illustrating a printer according to a third reference example. FIG. 2 is an enlarged configuration diagram showing a process unit for K of the printer together with a photoreceptor. The partial expansion perspective view which shows the same printer of the state which opened the housing upper cover from diagonally upward. FIG. 2 is a partially enlarged perspective view showing the printer in a state in which a process unit for K is pulled out from the inside of the printer body from an oblique upper side. FIG. 3 is an enlarged configuration diagram illustrating the process unit in a state where the process unit is pulled out from the printer body. The expansion block diagram which shows the process unit for K in the modification apparatus of the printer which concerns on a 3rd reference example.

Before describing an embodiment of an electrophotographic color laser printer (hereinafter simply referred to as “printer”) as an image forming apparatus to which the present invention is applied, a reference embodiment that is helpful in understanding the present invention will be described below. The printer will be described .
First, the basic configuration of the printer according to the reference embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a main part of a printer according to a reference embodiment. The printer includes four process units 1Y, M, C, and K for forming toner images of respective colors of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). An optical writing unit 50, a registration roller pair 54, a transfer unit 60, and the like are also provided. Subscripts Y, M, C, and K added to the end of each symbol indicate members for yellow, magenta, cyan, and black, respectively.

  The optical writing unit 50 serving as a latent image forming means includes a light source composed of four laser diodes corresponding to each color of Y, M, C, and K, a regular hexahedral polygon mirror, a polygon motor for rotationally driving this, and an fθ lens. , Lenses, reflection mirrors and the like. The laser light L emitted from the laser diode reaches any one of four photoconductors described later while being reflected by any one surface of the polygon mirror and deflected as the polygon mirror rotates. The surfaces of the four photosensitive members are optically scanned by the laser beams L emitted from the four laser diodes, respectively.

  The process units 1Y, 1M, 1C, and 1K are drum-shaped photoconductors 3Y, 3M, 3C, and 3K as latent image carriers, and developing devices 40Y, 4M, 4C, and 3K as developing units individually corresponding to these. It has a charging device. The photoreceptors 3Y, 3M, 3C, and 3K are rotationally driven in a clockwise direction in the drawing at a predetermined linear velocity by a driving unit (not shown). Then, it is optically scanned in the dark by an optical writing unit 50 that emits a laser beam L modulated based on image information sent from a personal computer (not shown) or the like, and static for Y, M, C, and K. Carries an electrostatic latent image.

  FIG. 2 is an enlarged configuration diagram showing the K process unit 1K of the four process units 1Y, 1M, 1C, and 1K together with the intermediate transfer belt 61 of the transfer unit (60 in FIG. 1). In the figure, a process unit 1K for K has a photosensitive unit 3K, a charging device, a neutralizing lamp (not shown), a developing device 40K as developing means, etc. held in a common unit casing (holding body) as one unit, The printer is detachable from the printer body.

  The photosensitive body 3K for K which is a charged body and a latent image carrier is coated with a photosensitive layer made of a negatively charged organic photophotoconductive substance (OPC) on the surface of a conductive base made of an aluminum base tube. The drum is about 24 [mm] in diameter and is driven to rotate in the clockwise direction in the drawing at a predetermined linear velocity by a driving means (not shown). As a result, the surface of the photosensitive member 3K sequentially passes through a primary transfer nip (contact position with the intermediate transfer belt 61), an auxiliary charging nip, a charging nip, an optical writing position, and a development area, which will be described later.

  The developing device 40K for K has a developing roller 42K that exposes a part of the peripheral surface from an opening provided in the casing 41K. The developing roller 42K, which is a developer carrying member, is rotatably supported by bearings (not shown) with shafts protruding from both ends in the longitudinal direction. The casing 41K contains K toner and is conveyed from the right side to the left side in the drawing by the agitator 43K that is driven to rotate. On the left side of the agitator 43K in the figure, a toner supply roller 44K that is driven to rotate counterclockwise in the figure by a driving means (not shown) is disposed. The roller portion of the toner supply roller 44K is made of an elastic foam such as sponge, and satisfactorily captures the K toner sent from the agitator 43K. The K toner thus captured is supplied to the developing roller 42K at the contact portion between the toner supply roller 44K and the developing roller 42K. The K toner carried on the surface of the developing roller 42K as the developer carrying member passes through the contact position with the regulating blade 45K as the developing roller 42K rotates in the counterclockwise direction in the drawing. After the layer thickness is regulated or frictional charging is promoted, the layer is transported to the developing area facing the photoreceptor 3K.

  In this developing area, negative K toner is applied from the developing roller 42K side between the developing roller 42K to which a negative developing bias output from a power source (not shown) is applied and the electrostatic latent image on the photoreceptor 3K. A developing potential for electrostatically moving to the latent image side acts. In addition, a non-development potential for electrostatically moving negative K toner from the background side to the development roller 42K acts between the developing roller 42K and the uniformly charged portion (background portion) of the photoreceptor 3K. The K toner on the developing roller 42K is separated from the developing roller 42K by the action of the developing potential and is transferred onto the electrostatic latent image on the photoreceptor 3K. By this transition, the electrostatic latent image on the photoreceptor 3K is developed into a K toner image.

  In this printer, a one-component developing method using a one-component developer containing K toner as a main component as a developer is adopted in the developing device 40K. However, a two-component developer containing K toner and a magnetic carrier is used. A two-component development method using

  The K toner image developed in the developing area is conveyed to the primary transfer nip for K where the photosensitive member 3K and the intermediate transfer belt 61 come into contact with the rotation of the photosensitive member 3K. Intermediate transfer. Untransferred toner that has not been transferred onto the intermediate transfer belt 61 adheres to the surface of the photoreceptor 3K after passing through the primary transfer nip. This transfer residual toner processing will be described later.

  The charging device includes a charging roller 7K that forms a charging nip by contacting the photosensitive member 3K while being driven to rotate counterclockwise in the drawing, an auxiliary charging member 10K that forms an auxiliary charging nip by contacting the photosensitive member 3K, and the like. Have. The charging roller 7K is formed by covering a peripheral surface of a metal rotating shaft member with a roller portion made of a material that exhibits conductivity and elasticity such as conductive rubber. A charging bias is applied to the rotating shaft member by charging bias supply means including a power source (not shown). By this application, a discharge is generated between the charging roller 7K and the photosensitive member 3K, so that the surface of the photosensitive member 3K is uniformly charged to the same polarity as the charging polarity of the toner.

  The auxiliary charging member 10K is obtained by covering the surface of an elastic portion 8K made of an elastic material such as sponge with a conductive sheet 9K made of a conductive material. Then, while being pressed toward the photoconductor 3K by the holder member, the portion of the peripheral surface of the photoconductor 3K passes through a primary transfer nip described later and before entering the charging nip. The sheet covering surface is in contact. The conductive sheet 9K is supplied with an auxiliary charging bias consisting of a DC voltage having the same polarity as the charging polarity of the toner or an AC voltage on which this DC voltage is superimposed by an auxiliary charging bias supply means including a power source (not shown). .

  Among the residual transfer toner adhering to the surface of the photoreceptor 3K after passing through the primary transfer nip, the amount of charge is not only the toner charged to the regular charge polarity but also the regular charge polarity. The low charge amount toner that is insufficient, the reversely charged toner that is charged to the opposite polarity, and the like are also included. Such untransferred toner enters the auxiliary charging nip as the photoreceptor 3K rotates. Then, the reversely charged toner in the transfer residual toner is sufficiently charged to the negative polarity, which is the normal polarity, by discharge between the auxiliary charging member 10K and the photosensitive member 3K or charge injection from the auxiliary charging member 10K. Further, the low charge amount toner in the transfer residual toner is also sufficiently charged to the negative polarity by discharge or charge injection.

  An electrostatic latent image for K is formed on the surface of the photosensitive member 3K for K uniformly charged by the charging nip by optical scanning by the optical writing unit (50) described above. A K toner image is developed by the K developing device 40K.

  As described above, the auxiliary charging member 10K has a role of sufficiently charging the low charge amount toner and the reversely charged toner in the transfer residual toner to the normal negative polarity. As a result, the toner contamination of the charging roller 7K, the charging unevenness of the photosensitive member 3K, the background contamination, the afterimage, and the like are suppressed.

  Specifically, the charging bias applied to the charging roller 7K is a negative polarity DC voltage or a superimposed voltage obtained by superimposing an AC voltage on the DC voltage. The charging roller 7K has a relatively negative polarity due to the application of the charging bias. In the charging nip, the photosensitive member 3K is charged with a negative polarity, but the negative value is smaller than the negative value of the charging roller 7K. For this reason, the low charge amount toner and the reversely charged toner contained in the transfer residual toner, as they are, are easily transferred from the surface of the photosensitive member 3K to the surface of the charging roller 7K at the charging nip and are likely to stay on the roller surface. ing. Therefore, the low charge amount toner and the reverse charge toner are sufficiently charged to the negative polarity upstream of the charging nip. By doing so, the transfer of toner from the photosensitive member 3K to the charging roller 7K at the charging nip and its entrance can be reduced, and toner contamination of the charging roller 7K can be suppressed. In addition, it is possible to suppress the occurrence of uneven charging of the photosensitive member 3K due to the fact that the discharge or charge injection is not performed satisfactorily at the toner smeared portion of the charging roller 7K, and the occurrence of a solid afterimage due to the uneven charging. Further, when a discharge is generated between the conductive sheet 9K of the auxiliary charging member 10K and the photosensitive member 3K, the photosensitive member 3K is assisted by the discharge prior to the main charging process of the photosensitive member 3K by the charging roller 7K. The charging unevenness can also be suppressed by charging.

  If low charge amount toner or reversely charged toner that has not been transferred to the charging roller 7K is transported to the development area, it becomes easy to cause background contamination. Due to the relationship between the background potential of the photoreceptor 3K and the potential (development bias) of the developing roller 42K, the low charge amount toner and the reversely charged toner cannot be transferred to the developing roller 42K in the developing region, and This is because it becomes easier to stay on the background. Therefore, the occurrence of background contamination can be suppressed by sufficiently charging the low charge amount toner and the reversely charged toner to the negative polarity by the auxiliary charging member 10K. Furthermore, toner contamination of the charging roller 7K due to transfer of a low charge amount toner or reversely charged toner to the charging roller 7K, generation of charging unevenness due to failure of good discharge at the location of toner contamination, and It is also possible to suppress the occurrence of a solid afterimage due to the uneven charging.

  The process unit 1K for K has been described, but the process units 1Y, 1M, and 1C for other colors have the same configuration as the process unit 1K for K, and thus description thereof is omitted.

  As the process units 1Y, 1M, 1C, and 1K, a so-called cleaner-less type is adopted. The cleanerless system is a system that executes an image forming process on a latent image carrier without using a dedicated means for cleaning and collecting transfer residual toner adhering on the latent image carrier such as the photoreceptor 3Y. That's it. Specifically, the dedicated means for cleaning and collecting means that after the transfer residual toner is separated from the latent image carrier, it is transported to the waste toner container and collected without being attached to the latent image carrier again. Or transported into the developing device for recycling. A cleaning blade that scrapes off the transfer residual toner from the latent image carrier is also included in the dedicated means.

  This cleaner-less method will be described in detail. The cleaner-less method is roughly classified into a scattering passing type, a temporary trapping type, and a combined type. Among these, the scattering passing type uses a scattering member such as a brush that rubs against the latent image carrier. Then, the residual image formed by the transfer residual toner existing on the surface of the latent image carrier after passing through the transfer process is scratched by the scattering member, so that the toner in the residual image is scattered, or the toner and the latent image carrier It weakens the adhesive force and promotes collection in the next process (collection of transfer residual toner in the development area). Thereafter, the transfer residual toner on the latent image carrier is electrostatically transferred to the development member such as the developing roller immediately before or in the developing region where the developing member such as the developing sleeve and the developing roller faces the latent image carrier. To collect in the developing device. Prior to this collection, the transfer residual toner passes through the optical writing position for writing the latent image. However, if the amount of transfer residual toner is relatively small, the latent image writing is not adversely affected. . However, if a reversely charged toner charged to a polarity opposite to the normal polarity is included in the transfer residual toner, it is not collected on the developing member, which causes background contamination. In order to suppress the occurrence of scumming due to the reversely charged toner, toner charging means for charging the transfer residual toner on the latent image carrier to the normal polarity is scattered by the transfer position (for example, the primary transfer nip) and the scattering member. It is desirable to provide it between the positions or between the scattering position and the development area. As the scattering member, a fixed brush having a plurality of flocked fibers made of conductive fibers affixed to a sheet metal or a unit casing, a brush roller in which a plurality of flocked fibers are erected on a metal rotating shaft member, and conductive A roller member (for example, a charging roller) having a roller portion made of sponge or the like can be used. The fixed brush has the advantage of being inexpensive because it can be configured with a relatively small amount of flocked fibers, but sufficient charging uniformity is required when it is also used as a charging member for uniformly charging the latent image carrier. You can't get it. On the other hand, the brush roller is preferable because sufficient charging uniformity can be obtained.

  In the temporary capture type in the cleanerless system, the transfer residual toner on the latent image carrier is temporarily captured by a capture member such as a rotating brush member that moves endlessly while the surface is in contact with the latent image carrier. Then, after the end of the print job or at the timing between sheets of the print job, the transfer residual toner on the capturing member is discharged and retransferred to the latent image carrier, and then electrostatically transferred to the developing member such as the developing roller. To collect in the developing device. In the above-mentioned scattering passing type, when a large amount of toner remains after transfer, such as when a solid image is formed or after a jam occurs, there is a risk of causing an abnormal image exceeding the recovery ability to the developing member, whereas temporary capture is performed. In the mold, the transfer residual toner captured by the capturing member is gradually collected on the developing member, and the occurrence of such an abnormal image can be suppressed.

  The combined type in the cleanerless system is a combination of the scattering passing type and the temporary trapping type, and has the best performance among the three types. Specifically, a rotating brush member that contacts the latent image carrier is used in combination as a scattering member and a capturing member. By applying only a DC voltage to the rotating brush member, etc., the rotating brush member, etc., can function as a scattering member, while the bias is switched from a DC voltage to a superimposed voltage as necessary, so that the rotating brush member can be used as a capturing member. Make it work.

  This printer employs a scattered and transmissive cleanerless system. Specifically, the photoreceptor 3Y contacts the front surface of the intermediate transfer belt 61 while rotating at a predetermined linear speed in the clockwise direction in the drawing to form a primary transfer nip for Y. . Then, the transfer residual toner on the photoconductor 3Y is scratched by the auxiliary charging member 10Y or the charging roller 7Y as a scattering member, thereby weakening the adhesion between the transfer residual toner and the photoconductor 3Y. Thereafter, in the developing area, the transfer residual toner on the photoreceptor 3Y is electrostatically transferred to the developing roller 42Y of the developing device 40Y and collected. At this time, if the transfer residual toner contains a large amount of low-charge toner or reverse-charge toner, they are not collected on the developing roller 42Y and cause soiling.

  In FIG. 1 shown above, a transfer unit 60 is disposed below the process units 1Y, M, C, and K for each color. The transfer unit 60 moves the endless intermediate transfer belt 61 endlessly in the counterclockwise direction in the drawing while being stretched by a plurality of stretching rollers. Specifically, the plurality of stretching rollers are a driven roller 62, a driving roller 63, four primary transfer bias rollers 66Y, M, C, K, and the like.

  The driven roller 62, the primary transfer bias rollers 66Y to 66K, and the drive roller 63 are all in contact with the back surface (loop inner peripheral surface) of the intermediate transfer belt 61. The four primary transfer bias rollers 66Y, 66M, 66C, and 66K are rollers in which a metal cored bar is covered with an elastic body such as a sponge, and Y, M, C, and K photoconductors 3Y. , M, C, and K to sandwich the intermediate transfer belt 61. As a result, the four primary bodies for Y, M, C, and K in which the four photoreceptors 3Y, M, C, and K and the front surface of the intermediate transfer belt 61 are in contact with each other with a predetermined length in the belt moving direction. A transfer nip is formed.

  A primary transfer bias that is constant current controlled by a transfer bias power source (not shown) is applied to the cores of the four primary transfer bias rollers 66Y, 66M, 66C, and 66K. As a result, transfer charges are applied to the back surface of the intermediate transfer belt 61 via the four primary transfer bias rollers 66Y, 66M, 66C, 66K, and the intermediate transfer belt 61 and the photoreceptors 3Y, M, A transfer electric field is formed between C and K. In this printer, the primary transfer bias rollers 66Y, 66M, 66C, and 66K are provided as the primary transfer means. However, a brush, a blade, or the like may be used instead of the rollers. A transfer charger or the like may be used.

  The Y, M, C, and K toner images formed on the photoreceptors 3Y, 3M, 3C, and 3K for each color are primarily transferred onto the intermediate transfer belt 61 in a primary transfer nip for each color. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 61.

  A secondary transfer bias roller 67 is in contact with the driving roller 63 on the intermediate transfer belt 61 from the belt front surface side, thereby forming a secondary transfer nip. A secondary transfer bias is applied to the secondary transfer bias roller 67 by a voltage applying means including a power source and wiring (not shown). As a result, a secondary transfer electric field is formed between the secondary transfer bias roller 67 and the grounded secondary transfer nip back roller 64. The four-color toner image formed on the intermediate transfer belt 61 enters the secondary transfer nip as the belt moves endlessly.

  The printer includes a paper feed cassette (not shown), and accommodates a recording paper bundle in which a plurality of recording papers P are stacked therein. Then, the uppermost recording paper P is sent out to the paper feed path at a predetermined timing. The fed recording paper P is sandwiched in a registration nip of a registration roller pair 54 disposed at the end of the paper feed path.

  The registration roller pair 54 rotates both rollers in order to sandwich the recording paper P sent from the paper feed cassette into the registration nip. However, as soon as the leading edge of the recording paper P is sandwiched, both rollers rotate. Stop. Then, the recording paper P is fed toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 61. At the secondary transfer nip, the four-color toner images on the intermediate transfer belt 61 are collectively transferred onto the recording paper P by the action of the secondary transfer electric field and the nip pressure, and become a full-color image combined with the white color of the recording paper P. .

  The recording paper P on which the full-color image is formed in this manner is discharged from the secondary transfer nip, and then sent to a fixing device (not shown) to fix the full-color image.

  The secondary transfer residual toner adhering to the surface of the intermediate transfer belt 61 after passing through the secondary transfer nip is removed from the belt surface by the belt cleaning device 68.

Note that the printer according to the reference embodiment uses negatively chargeable Y, M, C, and K toners. Then, after the photosensitive members 3Y, 3M, 3C, and 3K of the respective colors are uniformly charged to a negative polarity by the charging device, the negative potential of the electrostatic latent image obtained by the optical scanning is attenuated from the background portion. In this way, a negative-positive development system is adopted in which a negative polarity toner is attached to the electrostatic latent image whose potential is attenuated.

The inventors prepared a testing machine having the same configuration as the printer according to the reference embodiment shown in FIG. Then, the following test print experiment was performed using this testing machine. That is, in the test print, a charging bias having a DC voltage of −1100 [V] is applied to the charging roller 7K of the K process unit 1K. Further, an auxiliary charging bias composed of a negative polarity DC voltage is applied to the conductive sheet 9K. When test printing is performed under such conditions, the low charge amount toner and the reversely charged toner in the transfer residual toner are charged to minus of normal polarity by the auxiliary charging with the conductive sheet 9K, thereby suppressing the occurrence of soiling. be able to. In addition, before the main charging by the charging roller 7K, the photosensitive member 3K is auxiliary charged with an auxiliary charging bias lower than the charging bias, so that occurrence of charging unevenness can be suppressed.

As the test print, a print having a two-stage condition of printing first under the first condition and then printing under the second condition was performed. Under the first condition, an image area ratio of 100 [%] is applied while applying an auxiliary charging bias of −1500 [V] to the conductive sheet 9K abutted on the photoreceptor 3K with a contact pressure of 1 [kN / m ² ]. The monochrome solid test image was continuously printed on 500 sheets of A4 recording paper. By continuous printing under the first condition, it was confirmed that a large amount of untransferred toner was interposed between the conductive sheet 9K and the photosensitive member 3K in the K process unit 1K. Under the second condition, after the contact pressure between the conductive sheet 9K and the photosensitive member 3K is set to an arbitrary value, a charging bias having the same value as that in the first condition is applied, and −700 [V] is used as an auxiliary charging bias. A monochrome half chart (two-by-two halftone gradation image) was continuously printed on 500 sheets of A4 paper at an image area ratio of 5% while applying the DC voltage. A series of such test prints were performed for a plurality of types of conductive sheets 9K having different tensile breaking strengths while changing the contact pressure between the sheet and the photoreceptor 3K under the second condition.

  The tensile strength at break of the conductive sheet 9K was measured according to JIS-K-6897.

The contact pressure between the conductive sheet 9K and the photoreceptor 3K was measured as follows. That is, after attaching the pseudo-weighted converter to the test member, is pressed against the auxiliary charging member 10K of the printer according to the reference embodiment under the same conditions as in Reference form that the test member, measuring a load applied to the test member did. Based on the load and the contact area between the sheet and the test member, the contact pressure per unit area was calculated.

  As the toner (K), a toner obtained by a pulverization method with an average particle diameter adjusted to 8.5 [μm] and having an external additive added thereto was used.

  At the time of half-chart printing, each color photoconductor was rotated at a linear speed of 120 [mm / sec].

  As the charging brush roller of each color (for example, 7K), a roller having a diameter of 6 [mm] made of metal and having a roller portion covered with a conductive rubber layer (φ) 10 [mm] was used. .

As described above, as the conductive sheet 9K of the auxiliary charging member 10K, a plurality of types having different tensile rupture strengths were used, but their surface resistance and thickness were both 10 ⁵ [Ω / □], 0 .1 [mm]. These materials are all PTFE (polytetrafluoroethylene).

  As the elastic portion 8K of the auxiliary charging member 10K, a sponge made of 5 [mm] thick was used, and the auxiliary charging member 10K was brought into contact with the photoreceptor 3K so as to be compressed to a certain thickness. By adjusting the compression amount, the contact pressure between the conductive sheet 9K and the photoreceptor 3K was adjusted.

  In a plurality of print tests with different materials and contact pressures of the conductive sheet 9K, the conductive sheet 9K was removed from the process unit 1K after each second condition printing, and the presence or absence of toner adhesion to the surface was observed. . Then, the toner fixing property to the sheet was evaluated in two stages: x (toner fixing was observed at the center of the sheet in the moving direction of the photoreceptor surface) and ○ (toner fixing was not recognized). Moreover, about the abrasion loss of the electroconductive sheet 9K, it measured based on the profile of the surface shape using the laser microscope (VK-9500) by Keyence Corporation.

The results of the above experiment are shown in Table 1 below.

As shown in Table 1, as the conductive sheet 9K, a sheet having a tensile strength at break of 10 [MPa] or more and 40 [MPa] or less is used, and this is 4 [kN / m ² ] or more and 15 [kN / M ² ] with the contact pressure of the photosensitive member 3K, it is possible to obtain an acceptable result that the toner fixing property is good. In addition, when the evaluation result of the toner fixing property is “O” by other experiments, the present inventors have caused the image quality to be deteriorated even if the above half-chart continuous printing is performed 10,000 sheets or more. It has been confirmed that toner adhesion growth does not occur. That is, toner adhesion to the conductive sheet 9K can be suppressed for a long period of time.

When the tensile breaking strength of the conductive sheet 9K is less than 10 [MPa], even if the contact pressure is appropriate (4 to 15 kN / m ² ), the sheet is near the downstream end in the direction of movement of the photoreceptor surface. Toner adhesion was observed. This is presumably because the vicinity of the downstream end of the sheet was wavy due to good flexibility. Further, when the tensile breaking strength of the conductive sheet 9K is less than 40 [MPa], the evaluation result of the toner fixing property becomes “x”, as can be seen from the measurement result of the wear amount, the sheet slides with the photoreceptor 3K. This is because it does not wear moderately with rubbing. In other words, if the tensile breaking strength of the sheet is 10 to 40 [MPa], even if a slight amount of toner is fixed due to the sheet being appropriately worn with the friction with the photoreceptor 3K, Since the fixing portion is worn out immediately, toner fixing exceeding the allowable range does not occur.

When the contact pressure is less than 4 [kN / m ² ], even if the tensile breaking strength of the sheet is appropriate (10 to 40 MPa), it is not possible to obtain appropriate wear of the sheet due to insufficient contact pressure. Therefore, toner sticking exceeding the allowable range occurs. If the contact pressure exceeds 15 [kN / m ² ], even if the tensile strength at break of the sheet is appropriate (10 to 40 MPa), the toner is excessively pressed toward the sheet, Toner fusing is promoted, and toner fixation exceeding an allowable range occurs.

In view of the above experimental results, in the printer according to the reference embodiment, the tensile breaking strength is 10 [MPa] or more and 40 [MPa] as the conductive sheet of the auxiliary charging member of each color process unit 1Y, M, C, K. The following is used, and this is brought into contact with the photosensitive member with a contact pressure of 4 [kN / m ² ] or more.

  In the test print described above, the auxiliary charging member used is a method in which the conductive sheet is pressed against the photosensitive member by the elastic portion. However, according to other experiments conducted by the present inventors, the conductive sheet is used. The same results as in Table 1 were obtained even when a conductive blade having the same properties as in the above was cantilevered and brought into contact with the photoreceptor.

  Moreover, although the example which employ | adopted DC voltage as a charging bias was demonstrated, what superimposes AC voltage on DC voltage may be employ | adopted. Furthermore, although an example in which a DC voltage is used as the auxiliary charging bias has been described, a DC voltage superimposed with an AC voltage may be used.

The length in the moving direction of the photosensitive member surface (hereinafter referred to as auxiliary charging nip width) at the contact portion between the conductive sheet of the auxiliary charging member and the photosensitive member is preferably 2 [mm] or more. This is for the reason explained below. That is, when the auxiliary charging nip width is gradually reduced, if it starts to fall below 2 [mm], as shown in Table 2, the charge amount of the photosensitive member immediately after passing through the contact portion with the conductive sheet This is because the voltage starts to drop sharply and causes charging failure. Further, the charge amount of the toner adhering to the surface of the photoconductor immediately after passing through the contact portion also starts to rapidly decrease. In the experiment of Table 2, an auxiliary charging bias of −700 [V] is applied to the conductive sheet. The surface potential of the photoconductor immediately before entering the contact portion with the conductive sheet was measured with a surface potential meter (Trek Model 344 manufactured by Torek Co., Ltd.), and it was 0 to -50 [V]. Further, when the charge amount of the transfer residual toner adhering to the surface of the photosensitive member immediately before entering the contact portion was measured with a suction-type small charge amount measuring device (q / mmeter Model 210HS manufactured by Torek), 0 to 0.5. [-ΜC / g].

In the test print whose results are shown in Table 1, the auxiliary charging nip was set to 5 [mm]. However, as shown in Table 3 below, even with 2 [mm] and 8 [mm] Results equivalent to those in Table 1 can be obtained.

If the photosensitive member does not need auxiliary charging and only the transfer residual toner needs to be charged, an auxiliary charging bias of 300 to 500 [V] in absolute value is applied to the conductive sheet for the reason described below. It is desirable to apply. That is, the present inventors employ various values for the auxiliary charging bias applied to the conductive sheet, and output a test chart to 20,000 sheets of recording paper at each bias value to provide toner fill for the photoreceptor. The state of occurrence of toner (toner fixation) was examined. The experimental conditions at this time are as listed below.
The length of the auxiliary charging nip in the surface movement direction of the photosensitive member: 2 [mm].
Auxiliary charging nip pressure: 4 [kN / m ² ].
-Breaking strength of the conductive sheet: 40 [MPa].
Test chart: An image area ratio on A4 size recording paper is 50%.
Output environment: room temperature 23 [° C.]: humidity 50 [%].
-Chart output number: 20,000 sheets.
When an experiment was conducted under such conditions, as shown in Table 4 below, if the auxiliary charging bias is set in the range of 300 to 500 [V], even if 20,000 test charts are output, It was found that toner filming does not occur.

  As can be seen from Table 4, when the auxiliary charging bias is in the range of 300 to 500 [-V], the photosensitive member cannot be charged to a sufficient value, but for the transfer residual toner, a negative polarity which is a normal charging polarity. It can be seen that the surface is sufficiently charged (if 10 [−μC / g], the value is sufficient to avoid background contamination and charging roller contamination). Therefore, if auxiliary charging of the photoconductor is not required, it is possible to suppress the occurrence of toner filming on the photoconductor by setting the auxiliary charging bias in the range of 300 to 500 [V] in absolute value. It is. On the other hand, when the auxiliary charging bias is made larger than 500 [V] in absolute value, the photosensitive member can be sufficiently charged at the auxiliary charging nip, instead of between the conductive sheet and the photosensitive member. By causing the discharge to occur actively, filming due to toner fixation occurs on the surface of the photoreceptor.

  As the conductive sheet of the auxiliary charging member, it is desirable to use a sheet having a thickness of 50 [μm] to 2 [mm]. This is because when the thickness is less than 50 [μm], the durability required for a popular machine cannot be obtained. In addition, if the thickness exceeds 2 [mm], the sheet is insufficient in flexibility, resulting in poor adhesion between the sheet and the photoreceptor.

As the conductive sheet as the conductive member of the auxiliary charging member, it is desirable to use a sheet having a surface resistance of 10 ² [Ω / cm ² ] or more and 10 ⁸ [Ω / cm ² ] or less. If it is less than 10 ² [Ω / cm ² ], it is difficult to satisfactorily suppress uneven charging and soiling due to the fact that current flows between the sheet and the photoconductor and discharge between the two cannot be obtained. Because it becomes. Further, when the surface resistance exceeds 10 ⁸ [Ω / cm ² ], the discharge uniformity between the two begins to deteriorate remarkably, and it becomes difficult to satisfactorily suppress charging unevenness.

As the conductive sheet of the auxiliary charging member, it is desirable to use a sheet having a volume resistivity of 10 ² [Ω · cm] or more and 10 ⁶ [Ω · cm] or less. This is because the volume resistivity is preferably lower than the surface resistance from the viewpoint of discharge uniformity. In addition, if the volume resistivity is less than 10 ² [Ω · cm], a good current flows between the sheet and the photosensitive member, and a discharge between the two cannot be obtained.

  The surface roughness Ra of the conductive sheet of the auxiliary charging member is desirably 0.1 [μm] or more and 0.6 [μm] or less. This is because when the surface roughness Ra starts to be larger than 0.6 [μm], the toner is likely to stay, adhere and adhere rapidly to the concave portions in the fine unevenness of the surface. Further, when the surface roughness Ra starts to be smaller than 0.1, image smearing due to poor adhesion with the photosensitive member starts to occur rapidly.

  As the conductive sheet, it is desirable to use a sheet having a pure water contact angle of 105 [°] or more. This is because when the pure water contact angle starts to exceed 105 [°], toner fixation starts to occur rapidly. In addition, about a pure water contact angle, it is possible to measure by the droplet method (based on the instruction manual of the contact angle meter) using the contact angle meter CA-DT * A type made by Kyowa Interface Science Co., Ltd. .

  It is desirable to use a photoreceptor having a pure water contact angle of 90 [°] or more. This is because when the pure water contact angle begins to fall below 90 [°], toner adhesion to the photosensitive member starts to occur rapidly.

  As the toner, it is desirable to use toner in which an external additive of 1 to 4 parts by weight of toner particles is added to the toner particles. In such a toner, even if the toner enters the contact portion between the conductive sheet of the auxiliary charging member and the photosensitive member, an external additive is interposed between the toner particles and the conductive sheet to fix the toner to the conductive sheet. This is because it can be suppressed. In addition, when the addition amount of the external additive exceeds 4 parts by weight, an adverse effect due to the transfer of the external additive to various members starts to appear rapidly.

  Further, as the toner, it is desirable to use a toner having a ratio of toner particles having a particle diameter of 5 [μm] or less to all toner particles of 15 [%] or less. This is because when the ratio starts to exceed 15 [%], toner adhesion to the conductive sheet is likely to occur rapidly.

  As the photoreceptor, it is desirable to use one having a surface roughness Ra of 0.05 to 6. When the surface roughness Ra starts to be less than 0.05, image smearing due to spillage of the aggregated toner mass tends to occur rapidly. The agglomerated toner lump is a K toner blocked at the abutting portion between the conductive sheet 9K and the photosensitive member 3K and accumulated at the abutting portion entrance to form a lump. When this mass grows to some extent, it falls by gravity from the entrance of the contact portion and enters the K primary transfer nip. Then, it is attached to the recording paper P via the intermediate transfer belt 61 or directly, resulting in image smearing. This is because, when the surface roughness Ra starts to exceed 6, image quality deterioration due to the fixing of the external additive of the toner to the fine recesses on the surface of the photoreceptor starts to occur rapidly.

FIG. 3 is a schematic configuration diagram illustrating a modified apparatus of the printer according to the reference embodiment. This modified apparatus has a charging brush roller 4K as a charging member instead of the charging roller. The charging brush roller 4K includes a metal rotating shaft member 5K that is rotatably received by a bearing (not shown), and a plurality of conductive flocked fibers 6K that are erected on the surface thereof. Then, the front end side of each flocked fiber 6K is rubbed against the photoreceptor 3K while being driven to rotate counterclockwise in the figure by a driving means (not shown) around the rotation shaft member 5K. The metal rotating shaft member 5K is connected to a charging bias supply means made up of a power supply, wiring, etc. (not shown), thereby applying a charging bias made up of a superimposed voltage (a DC voltage is superimposed on an AC voltage). At or near the charging nip where the brush composed of the plurality of flocked fibers 6K of the charging brush roller 4K and the photosensitive member 3K come into contact, a discharge occurs between each flocked fiber 6K and the photosensitive member 3K, and the photosensitive member 3K. Is uniformly charged to, for example, negative polarity.

  This modified apparatus employs a temporary capture type cleanerless system. Specifically, in the above-described charging nip, a discharge is generated between the flocked fibers 6K and the photoconductor 3K, and the surface of the photoconductor 3K is uniformly charged with a negative polarity. At the same time, the transfer residual toner adhering to the photoreceptor 3K is transferred to the plurality of flocked fibers 6K by the action of the above-mentioned charging bias and temporarily captured. Then, after the end of the print job or timing between papers, the charging bias is switched from the superimposed voltage to the DC voltage, and the transfer residual toner captured on the flocked fiber 6K is retransferred onto the photoreceptor 3K. The toner is collected in the developing device 40K from the photosensitive member 3K through the developing roller 42K.

Next, a printer according to each reference example in which a more characteristic configuration is added to the printer according to the reference embodiment and the printer according to the embodiment will be described. Unless otherwise specified, the configuration of the printer according to each reference example and the printer according to the embodiment is the same as that of the reference embodiment.
[First Reference Example]
FIG. 4 is an enlarged configuration diagram illustrating the auxiliary charging member 10K and the photosensitive member 3K in the K process unit of the printer according to the first reference example. In this printer, the conductive sheet 9K of the auxiliary charging member 10K is not fixed to the elastic portion 8K. Instead, the support member 11K is cantilevered, and the conductive sheet 9K is brought into contact with the photoconductor 3K in such a posture that the free end side is directed to the downstream side in the moving direction of the photoconductor surface rather than the fixed end side. The elastic portion 8K is pressed toward the photoreceptor 3K.

  In such a configuration, the conductive sheet 9K is pulled in accordance with the rubbing with the photoconductor 3K, so that the conductive sheet 9K has a tight posture at the contact portion with the photoconductor 3K. Thus, the occurrence of sheet wrinkles at the contact portion is avoided, and the occurrence of charging unevenness due to wrinkles is eliminated.

[ Embodiment ]
In the printer according to the embodiment, as in the reference embodiment described above, a cylindrical member is used as the photosensitive member (3Y, M, C, K) as a latent image carrier. However, unlike the reference embodiment, as an elastic portion (for example, 8K in FIG. 2) that presses the conductive sheet toward the photoconductor, the surface facing the photoconductor is directed from both ends to the center in the moving direction of the photoconductor. A concavely curved shape is used.

FIG. 5 is an enlarged configuration diagram illustrating the conductive sheet 9K for K and the surrounding configuration thereof in the printer according to the embodiment. In the figure, an elastic portion 8K made of an elastic member such as sponge is fixed to the support member 11K that supports the auxiliary charging member. The surface of the elastic portion 8K facing the photosensitive member 3K is a concave curved surface that is curved with the same curvature as the photosensitive member 3K, and is in close contact with the cylindrical convex curved surface of the photosensitive member 3K. And the electroconductive sheet 9K is affixed on the concave curved surface of this elastic part 8K.

FIG. 6 is a graph showing the relationship between the contact pressure between the photosensitive member and the conductive sheet and the position of the conductive sheet in the printer according to the reference embodiment. FIG. 7 is a graph showing the relationship between the contact pressure between the photosensitive member and the conductive sheet and the position of the conductive sheet in the printer according to the embodiment . In the case of the printer according to the reference form, as shown in FIG. 6, the contact pressure of the conductive sheet at the upstream end and the downstream end in the moving direction of the photosensitive member surface is lower than that at the central portion. Become. This is because the amount of biting of the photoconductor with respect to the central portion of the elastic portion is larger than that of both end portions because the plane of the elastic portion is pressed against the convex curved surface of the photoconductor.

On the other hand, in the printer according to the embodiment , as shown in FIG. 7, the contact pressure with the photosensitive member is uniform from the upstream end to the downstream end of the conductive sheet. This is because the amount of biting of the photosensitive member into the elastic portion is uniform over the entire region from the upstream side toward the downstream side. Therefore, in the printer according to the embodiment , the contact pressure between the two can be made uniform over the entire contact portion between the photosensitive member and the conductive sheet.

FIG. 8 is an enlarged configuration diagram illustrating an auxiliary charging member for K in the modified apparatus of the printer according to the embodiment . In this modified apparatus, as the elastic portion 8K, a single one having a rectangular parallelepiped shape and having no concave curved surface is used. However, as the support member 11K, a member having a concave curved surface as shown in the figure is used, and the elastic portion 8K is fixed to the concave curved surface of the support member 11K and curved in accordance with the curved surface. The surface of the elastic portion 8K facing the photoconductor is a concave curved surface. In such a configuration, as the elastic portion 8K, a general-purpose member that does not have a concave curved surface is used, and the cost of the elastic portion 8K is reduced by combining with the support member 11K. The contact pressure can be made uniform by deforming into a concave shape.

[Second Reference Example]
In the printer according to the second reference example, the process unit for each color of Y, M, C, and K does not have a conductive sheet, an elastic portion, and an auxiliary charging member composed of these supporting members. . The auxiliary charging member is configured as an auxiliary charging unit configured to be detachable from the printer main body separately from the process unit. The auxiliary charging units for Y, M, C, and K hold the elastic portion 8K, the conductive sheet 9K, and the support member 11K similar to the printer according to the embodiment shown in FIG. It assists the body (not shown).

  In this configuration, the conductive sheet 9K can be replaced separately from the photoconductor, so that the running cost can be reduced as compared with the configuration in which the conductive sheet 9K is replaced together with the photoconductor.

[ Third reference example]
In the printer according to the third reference example, the auxiliary charging sheet is fixed as a process unit for each of the colors Y, M, C, and K, and is detachable from the printer main body separately from the photosensitive member. Something is used. In such a configuration, when the process unit in which the toner in the developing device runs out is replaced, the conductive sheet can be replaced at a suitable timing periodically by replacing the conductive sheet at the same time. If the toner container that contains toner to be replenished to the developing device is configured to be detachable from the printer main body separately from the developing device, the auxiliary charging member may be fixed to the toner container. desirable.

FIG. 9 is a schematic configuration diagram illustrating a printer according to a third reference example. In this figure, the printer includes four process units 1Y, 1M, 1C, and 1K for forming Y, M, C, and K toner images. These use different colors of Y, M, C, and K toners, but other than that, they have the same configuration and are replaced when the lifetime is reached. Taking a process unit 1K for forming a K toner image as an example, as shown in FIG. 10, as shown in FIG. 10, a developing device 40K, a conductive sheet 9K, an elastic portion 8K that presses this toward the photoreceptor 3K, and a charging member. It has a charging brush roller 12K and the like, and is attached to and detached from the printer body while being held in a unit casing as a common holding body.

  The photoconductor 3K shown in the figure is supported by a support (not shown) different from the process unit 1K, and remains in the printer body even when the process unit 1K is detached from the printer body.

  The charging brush roller 7K contacts the photoconductor 3K while rotating counterclockwise in the drawing by a driving unit (not shown), and uniformly charges the surface of the photoconductor 3K. The uniformly charged surface of the photosensitive member 3K is exposed and scanned with a laser beam to carry an electrostatic latent image for K. The electrostatic latent image for K is developed into a K toner image by a developing device 40K using K toner. Then, intermediate transfer is performed on an intermediate transfer belt described later.

  In FIG. 9, the other color process units (1Y, M, C) similarly form (Y, M, C) toner images on the photoreceptors (3Y, M, C), Intermediate transfer is performed on an intermediate transfer belt 61 described later.

  The developing device 40K includes a vertically long hopper that stores K toner (not shown) and a developing unit. In the hopper, an agitator 43K that is rotationally driven by a driving means (not shown), an agitation paddle 46K that is rotationally driven by a driving means (not shown) below, and rotationally driven by a driving means (not shown) below the vertical direction. A toner supply roller 44K is provided. The K toner in the hopper moves toward the toner supply roller 44K by its own weight while being stirred by the rotational drive of the agitator 43K and the stirring paddle 46K. The toner supply roller 44K has a metal cored bar and a roller portion made of foamed resin or the like coated on the surface thereof, and rotates while adhering K toner in the hopper portion to the surface of the roller portion. .

  In the developing section of the developing device 40K, a developing roller 42K that rotates while contacting the photoreceptor 3K and the toner supply roller 44K, and a thinning blade 45K that contacts the tip of the developing roller 42K are disposed. The K toner adhered to the toner supply roller 44K in the hopper is supplied to the surface of the development roller 42K at the contact portion between the development roller 42K and the toner supply roller 44K. When the supplied K toner passes through the contact position between the roller and the thinning blade 45K as the developing roller 42K rotates, the layer thickness on the roller surface is regulated. Then, the K toner whose layer thickness has been regulated adheres to the electrostatic latent image for K on the surface of the photosensitive member 3K in the developing region where the developing roller 42K and the photosensitive member 3K are in contact. By this adhesion, the electrostatic latent image for K is developed into a K toner image.

  The K process unit has been described with reference to FIG. 10, but the Y, M, and C process units 1Y, M, and C in FIG. , M, C toner images are formed.

  9, the optical writing unit 50 is disposed above the process units 1Y, M, C, and K in the vertical direction. The optical writing unit 50, which is a latent image writing device, optically scans the photoreceptors 3Y, 3M, 3C, and 3K in the process units 1Y, M, C, and K with laser light L emitted from a laser diode based on image information. To do. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 3Y, 3M, C, and K. The optical writing unit 50 is a photosensitive member that passes through a plurality of optical lenses and mirrors while polarizing a laser beam (L) emitted from a light source in a main scanning direction with a polygon mirror that is rotationally driven by a polygon motor (not shown). Is irradiated. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the process units 1Y, 1M, 1C, and 1K, a transfer unit 60 that is endlessly moved in the counterclockwise direction in the drawing while an endless intermediate transfer belt 61 is stretched is disposed. In addition to the intermediate transfer belt 61, the transfer unit 60 serving as a transfer unit includes a driving roller 63, a driven roller 62, four primary transfer bias rollers 66 Y, M, C, K, a secondary transfer bias roller 67, and a belt cleaning device 68. Further, a cleaning backup roller 69 is provided.

  The intermediate transfer belt 61 is stretched by a driving roller 63, a driven roller 62, a cleaning backup roller 69, and four primary transfer bias rollers 66Y, 66M, 66C, and 66K disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the driving roller 63 that is driven to rotate in the counterclockwise direction in the figure by a driving means (not shown).

  The four primary transfer rollers 66Y, 66M, 66C, and 66K sandwich the intermediate transfer belt 61 that is moved endlessly in this manner between the photoreceptors 3Y, 3M, C, and K. By this sandwiching, primary transfer nips for Y, M, C, and K where the front surface of the intermediate transfer belt 61 and the photoreceptors 3Y, 3M, 3C, and 3K come into contact are formed.

  Below the transfer unit 60 in the vertical direction, a paper feed cassette 30 that stores a plurality of recording sheets P in a bundle of sheets is slidably attached to the printer housing. In the paper feed cassette 30, a paper feed roller 30a is brought into contact with the top recording paper P of the paper bundle, and the recording paper is rotated by rotating it in a counterclockwise direction in the drawing at a predetermined timing. P is sent out toward the paper feed path 31.

  A registration roller pair 54 is disposed near the end of the paper feed path 31. The registration roller pair 54 stops the rotation of both rollers as soon as the recording paper P delivered from the paper feed cassette 30 is sandwiched between the rollers. Then, rotation driving is resumed at a timing at which the sandwiched recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 61 in the above-described secondary transfer nip, and the recording paper P is directed to the secondary transfer nip. Send it out.

  The four-color toner image on the intermediate transfer belt 61 brought into close contact with the recording paper P at the secondary transfer nip is secondarily transferred onto the recording paper P under the influence of the secondary transfer electric field and nip pressure, and the recording paper Combined with the white color of P, a full color toner image is obtained. The recording paper P having a full-color toner image formed on the surface in this way is separated from the secondary transfer roller 67 and the intermediate transfer belt 61 by the curvature when passing through the secondary transfer nip. Then, the toner is fed into a fixing device 34 described later via a post-transfer conveyance path 33.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 61 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 68 which is in contact with the front surface of the intermediate transfer belt 61. A cleaning backup roller 69 disposed inside the loop of the intermediate transfer belt 61 backs up the cleaning of the belt by the belt cleaning device 68 from the inside of the loop.

  The fixing device 34 forms a fixing nip by a fixing roller 34a containing a heat source such as a halogen lamp (not shown) and a pressure roller 34b that rotates while contacting the fixing roller 34a with a predetermined pressure. The recording paper P fed into the fixing device 34 is sandwiched between the fixing nips such that the unfixed toner image carrying surface is brought into close contact with the fixing roller 34a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The recording paper P discharged from the fixing device 34 passes through the post-fixing conveyance path 35 and then reaches a branch point between the paper discharge path 36 and the pre-reversal conveyance path 71. On the side of the post-fixing conveyance path 35, a switching claw 72 that is rotationally driven about a rotation shaft 72a is disposed. By the rotation, the vicinity of the end of the post-fixing conveyance path 35 is closed. Or open it. At the timing when the recording paper P is sent out from the fixing device 34, the switching claw 72 stops at the rotational position indicated by the solid line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is opened. Therefore, the recording paper P enters the paper discharge path 36 from the conveyance path 35 after fixing, and is sandwiched between the rollers of the paper discharge roller pair 37.

  When the single-sided print mode is set by an input operation to an operation unit including a numeric keypad (not shown) or a control signal sent from a personal computer (not shown), the recording sandwiched between the paper discharge roller pair 37 is performed. The paper P is discharged out of the machine as it is. Then, it is stacked on the stack portion that is the upper surface of the upper cover 80 of the housing.

  On the other hand, when the duplex printing mode is set, the trailing edge of the recording paper P conveyed through the paper discharge path 36 while the front end is sandwiched between the paper discharge roller pair 37 passes through the post-fixing conveyance path 35. The switching claw 72 is rotated to the position indicated by the alternate long and short dash line in FIG. At substantially the same time, the paper discharge roller pair 37 starts to rotate in the reverse direction. Then, the recording paper P is conveyed while the rear end side is directed to the top, and enters the pre-reversal conveyance path 71.

  The side portion of the printer is a reversing unit 70 that can be opened and closed with respect to the housing body by rotating about a rotation shaft 70a. When the paper discharge roller pair 37 rotates in the reverse direction, the recording paper P enters the pre-reversal conveyance path 71 of the reversing unit 70 and is conveyed from the upper side to the lower side in the vertical direction. Then, after passing through between the rollers of the pair of reverse conveying rollers 73, it enters the reverse conveying path 74 that is curved in a semicircular shape. Furthermore, while the upper and lower surfaces are reversed as the sheet is conveyed along the curved shape, the traveling direction from the upper side in the vertical direction to the lower side is also reversed, and conveyed from the lower side in the vertical direction toward the upper side. Is done. Thereafter, the toner enters the secondary transfer nip again through the above-described paper feed path 31. Then, after the full color image is collectively transferred to the other surface, the post-transfer conveyance path 33, the fixing device 34, the post-fixation conveyance path 35, the paper discharge path 36, and the paper discharge roller pair 37 are sequentially passed. And discharged outside the machine.

  The reversing unit 70 described above has an external cover 75 and a rocking body 76. Specifically, the external cover 75 of the reversing unit 70 is supported so as to rotate about a rotation shaft 70a provided in the housing of the printer main body. By this rotation, the outer cover 75 opens and closes with respect to the housing together with the swinging body 76 held therein. As shown by the dotted line in the drawing, when the outer cover 75 is opened together with the swinging body 76 therein, the paper feed path 31 formed between the reversing unit 70 and the printer main body, the secondary transfer nip, and after the transfer. The conveyance path 33, the fixing nip, the post-fixing conveyance path 35, and the paper discharge path 36 are vertically divided into two and exposed to the outside. Thereby, jammed paper in the paper feed path 31, the secondary transfer nip, the post-transfer conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 can be easily removed.

  The swing body 76 is supported by the external cover 75 so as to rotate about a swing shaft (not shown) provided in the external cover 75 in a state where the external cover 75 is opened. When the swinging body 76 is opened with respect to the outer cover 75 by this rotation, the pre-reversal conveyance path 71 and the reverse conveyance path 74 are vertically divided into two and exposed to the outside. As a result, the jammed paper in the pre-reversal conveyance path 71 and the reverse conveyance path 74 can be easily removed.

  An upper cover 80 of the printer casing is supported so as to be rotatable about a shaft member 81 as indicated by an arrow in the figure, and is opened with respect to the casing by rotating counterclockwise in the figure. It becomes a state. And the upper opening of a housing is exposed greatly.

  In this printer, as shown in the figure, each process unit is disposed above the intermediate transfer belt 61, and the optical writing unit 50 is further disposed thereon, so that each process unit is attached to and detached from the printer body. At this time, it is necessary to retract the optical writing unit 50 from directly above each process unit. Therefore, in this printer, as shown in FIG. 11, the optical writing unit 50 is supported by the lower surface of the upper cover 80, and the optical writing unit 50 is retracted from above each process unit as the upper cover 80 is opened. It is supposed to let you. In such a configuration, as shown in FIG. 12, by opening the upper cover 80, the process units of the respective colors can be exposed from the maintenance inspection opening that faces upward in the vertical direction at the upper end of the printer body. In this state, the process unit (1K in the illustrated example) in the printer main body is gripped and pulled upward in the vertical direction, so that the process unit can be pulled out from the printer main body as illustrated.

  FIG. 13 is an enlarged configuration diagram showing the K process unit 1K in a state of being pulled out from the printer main body. In the figure, the process unit 1K has a swing bracket 15K that is swingably held in the casing of the developing device 40K, and the charging brush roller 12K, the conductive sheet 9K, and the elastic portion 8K are swung. The bracket 15K is supported.

  As shown in FIG. 10, when the process unit 1K is mounted in the printer body, the photosensitive member 3K is placed between the charging brush roller 12K and the developing roller 42K that are in contact with the photosensitive member 3K. positioned. When the process unit 1K is removed from the printer main body, the photosensitive member 3K is retracted from between the charging brush roller 12K and the developing roller 42K. Then, the swinging bracket 15K urged toward the developing roller 42K by a spring (not shown) slightly rotates in the counterclockwise direction in the figure about the swinging shaft. Then, as shown in FIG. 13, the swing bracket 15K moves to the right in the figure by approximately the size of the photosensitive member, and the size of the process unit 1K is reduced.

  When the process unit 1K is mounted in the printer main body, the swing bracket 15K is opened as the photosensitive member enters between the free end of the swing bracket 15K and the developing roller 42K. Accordingly, as shown in FIG. 10, the photosensitive member 3K is positioned between the charging brush roller 12K on the swing bracket 15K and the developing roller 42K.

FIG. 14 is an enlarged configuration diagram showing a K process unit 1K in the modified apparatus of the printer according to the third reference example. In this modified apparatus, not only the photoconductor but also the charging brush roller are attached to and detached from the printer main body separately from the process unit 1K. When the process unit 1K is removed from the printer main body, the charging brush is removed. The roller and the photoreceptor are retracted from the unit.

  So far, a printer employing a cleanerless process unit has been described. However, a configuration is provided in which a cleaning unit is provided for removing untransferred toner from the surface of the photoreceptor after passing through the primary transfer nip and before entering the charging nip. In addition, the present invention can be applied.

As described above, in the printer according to the reference embodiment, the length of the auxiliary charging nip, which is a contact portion between the latent image carrier and the conductive member, in the photosensitive member surface moving direction is 2 [mm] or more. For this reason, it is possible to suppress the occurrence of poor charging of the photoconductor immediately after passing through the auxiliary charging nip, and it is possible to suppress the occurrence of background contamination due to the charging failure of the transfer residual toner after passing through the auxiliary charging nip.

Further, in the printer according to the reference embodiment, a conductive sheet that is a conductive member uses a sheet having a surface resistance of 10 ² [Ω / cm ² ] or more and 10 ⁸ [Ω / cm ² ] or less. For the reasons described above, it is possible to suppress the occurrence of uneven charging and soiling due to a good current flow between the conductive sheet and the photosensitive member. Furthermore, it is possible to suppress the occurrence of uneven charging of the photosensitive member due to poor uniformity of discharge between the conductive sheet and the photosensitive member.

Further, in the printer according to the reference embodiment, as the conductive sheet, one having a volume resistivity of 10 ² [Ω · cm] or more and 10 ⁶ [Ω · cm] or less is used. Thus, the uniformity of discharge from the conductive sheet can be kept good.

In the printer according to the reference embodiment, since the conductive sheet having a pure water contact angle of 105 [°] or more is used as the conductive sheet, the life of the sheet is reduced by fixing the toner to the conductive sheet. Can be suppressed.

Further, in the printer according to the reference embodiment, if the auxiliary charging bias supply unit serving as the bias supply unit is configured to supply an auxiliary charging bias having an absolute value of 300 [V] or more and 500 [V] or less to the conductive sheet. In a device that does not require charging of the photosensitive member at the auxiliary charging nip, the auxiliary charging bias is increased while appropriately charging the low power failure amount toner or the reverse charging toner in the transfer residual toner to the normal polarity at the auxiliary charging nip. It is possible to avoid the occurrence of toner filming on the surface of the photosensitive member due to passing.

Further, in the printer according to the first reference example, the conductive sheet is placed in such a posture that the free end side is directed to the downstream side in the surface movement direction of the photoconductor rather than the fixed end side of the conductive sheet that is cantilevered by the support member. Since it is in contact with the photoconductor, it is possible to suppress the occurrence of uneven charging of the photoconductor due to generation of wrinkles on the conductive sheet for the reasons described above.

In the printer according to the embodiment , a cylindrical member is used as the photosensitive member, and a concave curve in which a surface facing the photosensitive member is recessed from both ends in the moving direction of the peripheral surface of the photosensitive member toward the central side. Since the conductive sheet is pressed toward the photosensitive member by the elastic portion formed of the elastic member, for the reason described above, over the entire contact portion between the photosensitive member and the conductive sheet, Both contact pressures can be made uniform.

In the modified apparatus of the printer according to the embodiment , since the elastic portion is fixed to the concave curved surface of the support member having the concave curved surface, for the reason described above, the elastic portion itself is concave curved. While reducing the cost by using a general-purpose one having no surface, it is possible to make the contact pressure uniform by deforming the surface of the elastic portion facing the photosensitive member into a concave shape by combining with a support member. it can.

Further, in the printer according to the second reference example, the conductive sheet and the supporting member that supports the conductive sheet are held as a unit on a common holding body (casing) so that it can be attached to and detached from the printer main body separately from the photoconductor. Therefore, the running cost can be reduced as compared with the configuration in which the conductive sheet is replaced together with the photosensitive member.

Further, in the printer according to the third reference example, the conductive sheet is fixed to the developing device as developing means and is detachable from the printer main body separately from the photosensitive member. The conductive sheet can be periodically replaced at a proper timing.

1Y, M, C, K: Process unit 3Y, M, C, K: Photoconductor (latent image carrier)
4K: charging brush roller (charging member, part of charging device)
7K: Charging roller (charging member, part of charging device)
9K: Conductive sheet (conductive member, part of charging device)
10K: auxiliary charging member (part of charging device)
11K: support member 40Y, M, C, K: developing device (developing means)
50: Optical writing unit (latent image forming means)
60: Transfer unit (transfer means)

JP 2005-62737 A

Claims (7)

A latent image carrier that carries a latent image, a latent image forming unit that forms a latent image on the latent image carrier, a developing unit that develops the latent image on the latent image carrier with toner, and the latent image carrier An image forming apparatus comprising: a conductive member to which a bias is supplied while being in contact with a surface of a body; and a charging unit that charges at least one of the surface and toner attached to the surface,
The upstream end and the downstream end in the surface movement direction of the latent image carrier in the conductive member are fixed to the support member in a state where they are not in contact with the latent image carrier,
A region existing between the upstream end and the downstream end of the conductive member is pressed toward the latent image carrier by an elastic member fixed to the support member;
The tensile breaking strength of the conductive member is 10 [MPa] or more, and is a value that is low enough to cause the conductive member to wear with sliding with the latent image carrier,
The contact pressure between the conductive member and the latent image carrier is 4 [kN / m ² ] or more and 15 [kN / m ² ] or less,
An image forming apparatus, wherein the contact angle of pure water on the surface of the conductive member is 105 [°] or more. The image forming apparatus according to claim 1,
The latent image carrier is a cylindrical photoconductor,
An image forming apparatus, wherein the support member is curved along a curved surface of the photoreceptor. The image forming apparatus according to claim 1 or 2,
An image forming apparatus using the latent image carrier having a surface having a pure water contact angle of 90 ° or more. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising: a toner particle having an additive of 1 to 4 parts by weight of the toner particle added to the toner particle. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising: a toner having a particle diameter of 5 [μm] or less and a ratio of toner particles to all toner particles of 15 [%] or less. The image forming apparatus according to claim 1,
The charging unit is located downstream of the region facing the conductive member in the surface movement direction of the latent image carrier in the surface movement direction and further from the region facing the developing unit. An image forming apparatus comprising a charging member for uniformly charging an upstream region in the surface moving direction. The image forming apparatus according to claim 1,
The conductive member is fixed to the developing means or a toner container that contains toner to be replenished to the developing means, and can be attached to and detached from the image forming apparatus main body separately from the latent image carrier. An image forming apparatus .

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