JP2008070810A - Electrifying device, process unit and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing image quality deterioration due to a reversely electrified toner and a low-electrified toner in a transfer residual toner over a long period. <P>SOLUTION: The image forming apparatus includes: a photoreceptor; an optical writing unit for writing a latent image on the photoreceptor; a developing device for developing the latent image on the photoreceptor with the toner; and an electrifying device equipped with an electrifying brush roller for uniformly electrifying the surface of the photoreceptor with the endless movement of the own surface in contact with the photoreceptor on which the latent image is not written yet by the optical writing unit and a pre-electrification contact sheet 10Y coming in contact with the photoreceptor that is not uniformly electrified yet by the brush roller. A sheet having a plurality of grooves (dt) formed in the contact area of the surface thereof coming in contact with the photoreceptor while extending from the upstream end (sa) in the contact area to the downstream end (sb) or the side end (sc) in the contact area in the photoreceptor surface moving direction is used as the pre-electrification contact sheet 10Y. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging device that uniformly charges the surface of a latent image carrier while continuously moving the surface of a charging member abutted on the latent image carrier, and a process unit and an image forming apparatus using the same. is there.

  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 latent image carrier such as a photoreceptor uniformly charged by a charging device, 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 of such an image forming apparatus, the charging member and the latent image are supplied by supplying a charging bias to a charging member such as a charging roller or a charging brush roller that forms a charging nip by contact with the latent image carrier. A device that causes discharge between the carrier and the carrier is known.

  In an image forming apparatus using such a charging device, the transfer residual toner adhering to the surface of the latent image carrier after the transfer process is caused to enter the charging nip as the surface of the latent image carrier moves. There is. The transfer residual toner contains a relatively large amount of reversely charged toner that has been charged to a polarity opposite to that of the normal polarity, and low charge amount toner that is slightly charged to the normal polarity. Then, the reversely charged toner in the transfer residual toner that has entered the charging nip is electrostatically attracted to the charging member to which a charging bias including a voltage component having a polarity opposite to the normal polarity of the toner is applied. When the reversely charged toner accumulates on the charging member in this manner, image quality deterioration due to local charging failure of the latent image carrier eventually occurs. Further, the low charge amount toner in the transfer residual toner that has entered the charging nip passes through the charging nip, and is then conveyed again to the developing area where the developing device and the latent image carrier are opposed to each other. At this time, if the recharged low charge amount toner is located on the non-image portion of the latent image carrier, the toner is not recovered well in the developing device and remains on the non-image portion as it is. It will cause.

  On the other hand, Patent Document 1 describes the following image forming apparatus. In other words, the pre-charging contact member is brought into contact with the portion of the peripheral surface of the latent image carrier after passing through the transfer process and before entering the charging nip, while contacting the pre-charging contact member. The image forming apparatus applies a DC voltage having the same polarity as the normal polarity of the toner. In this configuration, the reverse charging toner in the transfer residual toner is charged to the normal polarity between the pre-charging contact member and the latent image carrier prior to entering the charging nip, whereby the charging member is reversely charged. It is possible to suppress the occurrence of image quality deterioration due to toner accumulation. Further, the low charge amount toner in the transfer residual toner is sufficiently charged with normal polarity between the pre-charging contact member and the latent image carrier. As a result, it is possible to suppress the occurrence of background contamination due to re-conveying the low charge amount toner to the development region.

JP 2005-62737 A

  However, in this image forming apparatus, the transfer residual toner blocked by the pre-charging contact member is located upstream of the contact portion between the pre-charging contact member and the latent image carrier on the surface moving direction of the latent image carrier. Let it stay. Then, the staying toner is gradually fixed in the vicinity of the entrance of the contact surface with the latent image carrier in the contact member before charging. When the toner is fixed in this manner, a defective discharge is caused at the fixed portion, and the reversely charged toner cannot be charged to the normal polarity. Then, the reversely charged toner can be accumulated intensively at the charging member location corresponding to the fixing location, or the low charge amount toner adhering to the latent image carrier location corresponding to the fixing location can be sufficiently charged. It becomes impossible to cause image quality degradation. As described above, in the image forming apparatus described in Patent Document 1, the toner blocked by the pre-charging contact member is fixed to the pre-charging contact member, thereby degrading the image quality due to the reversely charged toner or the low charged toner. The occurrence could not be suppressed stably over a long period of time.

  The present invention has been made in view of the above background, and an object thereof is to provide the following charging device, and a process unit and an image forming apparatus using the charging device. That is, a charging device or the like that can suppress deterioration in image quality due to reversely charged toner or low-charged toner in the transfer residual toner for a longer 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. Developing means for developing the latent image with toner, and moving the surface of the latent image carrier in contact with the latent image carrier before the latent image is formed by the latent image forming means; A charging device having a charging member that uniformly charges the surface, a charging device that contacts the latent image carrier before being uniformly charged by the charging member, and a charging device that supplies a charging bias to the charging member In the charging device used in an image forming apparatus including a bias supplying unit and a pre-charging bias supplying unit that supplies a pre-charging bias to the pre-charging contact member, the latent image carrier is used as the pre-charging contact member. In the contact area of the surface contacting the That a groove leading to different ends from said upstream end in the abutting region extends from the upstream end of the abutting region of the surface moving direction of the carrier, it is characterized in that with.
According to a second aspect of the present invention, in the charging device of the first aspect, the pre-charging contact member is provided with a plurality of the grooves extending in parallel to each other. Is.
Further, in the charging device according to claim 1 or 2, an angle formed by an intersection of the direction perpendicular to the surface movement direction and the extending direction of the groove is 45 [°] or more in the charging device according to claim 1 or 2. [°] or less.
According to a fourth aspect of the present invention, in the charging device according to the third aspect, the angle is set to 60 [°] or more.
According to a fifth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the depth of the groove is 0.5 [μm] or more.
The invention according to claim 6 is the charging device according to any one of claims 1 to 5, wherein the pre-charging contact member has a volume resistivity of 10 ² [Ω · cm] or more and 10 ⁸ [Ω · cm. The following is used.
The invention of claim 7, in any one of the charging device of claims 1 to 6, as an abutment member before the charging, the surface resistance of the contact region 10 2 ^[Ω / cm ^2] or more, 10 ⁷ What is [Ω / cm ² ] or less is used.
According to an eighth aspect of the present invention, there is provided a latent image carrier for carrying a latent image, latent image forming means for forming a latent image on the latent image carrier, and developing the latent image on the latent image carrier with toner. Used in an image forming apparatus comprising: a developing unit configured to perform charging; and a charging unit configured to uniformly charge the latent image carrier before the latent image is formed by the latent image forming unit. The charging device according to any one of claims 1 to 7 is used as the charging unit in a process unit that is integrally attached to and detached from the image forming apparatus main body while holding the unit on a common holder. It is characterized by the fact that
According to a ninth aspect of the present invention, there is provided a latent image carrier for carrying a latent image, latent image forming means for forming a latent image on the latent image carrier, and developing the latent image on the latent image carrier with toner. The surface of the latent image carrier is uniformly charged while endlessly moving its surface abutted against the latent image carrier before the latent image is formed by the developing means. A charging member, a charging unit having a pre-charging contact member that contacts the latent image carrier before being uniformly charged by the charging member, a charging bias supply unit that supplies a charging bias to the charging member, 8. An image forming apparatus comprising a pre-charging bias supply unit that supplies a pre-charging bias to a pre-charging contact member, wherein the charging unit according to claim 1 is used as the charging unit. It is.
According to a tenth aspect of the present invention, in the image forming apparatus of the ninth aspect, the depth of the groove of the pre-charging contact member is 6% or more of the average particle diameter of the toner. To do.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, the depth of the groove is 12% or more of the average particle diameter of the toner.

  In these inventions, the groove provided in the contact area between the pre-charging contact member and the latent image carrier forms a gap between the pre-charging contact member and the latent image carrier, and the extending direction thereof. Is opened toward the upstream side of the surface movement direction of the latent image carrier. Then, the toner dammed upstream of the surface movement direction of the latent image carrier from the contact area is received in the groove through the opening, and then in the groove extending direction along with the surface movement of the latent image carrier. While moving, pull out from the opposite end of the groove. By moving the toner in such a groove, the contact area is quickly passed through the toner blocked by the pre-charging contact member, so that the amount of toner staying upstream of the contact area can be reduced. cut back. As a result, by suppressing the adhesion of the toner to the pre-charging contact member, it is possible to suppress the occurrence of image quality deterioration due to the reversely charged toner or the low charged toner in the transfer residual toner for a longer period of time.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color laser printer (hereinafter simply referred to as a printer) will be described.
First, a basic configuration of the printer according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a main part of the printer according to the present 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 have drum-shaped photoconductors 3Y, 3M, 3C, and 3K as latent image carriers, and developing devices 40Y, 4M, 4C, and 3K that individually correspond to these. ing. 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 process unit 1Y for Y of the four process units 1Y, M, C, and K together with the intermediate transfer belt 61 of the transfer unit (60 in FIG. 1). In the figure, a process unit 1Y for Y holds a photosensitive member 3Y, a charging brush roller 4Y, a neutralizing lamp (not shown), a developing device 40Y as developing means, etc. as a single unit in a common unit casing (holding body). Thus, it can be attached to and detached from the printer body.

  The Y photoreceptor 3Y, 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 photoreceptor 3Y has a primary transfer nip (contact position with the intermediate transfer belt 61), a cleaning position (contact position with the cleaning blade 21Y), a pre-charging nip (pre-charging contact sheet), which will be described later. 10Y), charging nip (contacting position with charging brush roller 4Y), optical writing position, and developing area.

  The charging brush roller 4Y as a charging member includes a metal rotating shaft member 5Y that is rotatably received by a bearing (not shown), and a plurality of conductive flocked fibers 6Y that are erected on the surface thereof. Yes. Then, the front end side of each flocked fiber 6Y is slid against the photoreceptor 3Y while being driven to rotate counterclockwise in the figure by a driving means (not shown) around the rotation shaft member 5Y. The metal rotating shaft member 5Y is connected to a charging bias supply device made up of a power source, wiring, etc. (not shown), and thereby a charging bias made up of a superimposed voltage (a DC voltage is superimposed on an AC voltage) is applied. At the charging nip where the brush composed of the plurality of flocked fibers 6Y of the charging brush roller 4Y and the photoconductor 3Y contact or in the vicinity thereof, a discharge occurs between each flocked fiber 6Y and the photoconductor 3Y, and the photoconductor 3Y. Is uniformly charged to, for example, negative polarity.

  The surface of the photoreceptor 3Y after passing through a cleaning position (contact position with the cleaning blade 21Y), which will be described later, is in contact with the pre-charging contact sheet 10Y before being uniformly charged at the charging nip. Enter a pre-charging nip. The pre-charging contact sheet 10Y made of a conductive sheet is cantilevered, and the free end of the pre-charging contact sheet 10Y is directed to the downstream side of the surface of the photoconductor 3Y with respect to the surface of the photoconductor 3Y. It is in contact with the body 3Y. The pre-charging abutting sheet 10Y having the above-described configuration is charged with the same polarity as the toner charging polarity (the charging polarity of the photosensitive member and the polarity of the DC component of the charging bias) by a pre-charging bias supply means including a power source, wiring, etc. A pre-charging bias comprising a DC voltage of the same polarity). The reversely charged toner in the untransferred toner that has entered the pre-charging nip has a negative polarity due to discharge between the pre-charging contact sheet 10Y and the photoreceptor 3Y or charge injection from the pre-charging contact sheet 10Y. The polarity is sufficiently charged. Further, the low charge amount toner in the untransferred toner that has entered the pre-charging nip is also sufficiently charged to a negative polarity by discharge or charge injection. As a result, image quality deterioration due to reversely charged toner or low charge amount toner in the transfer residual toner can be suppressed.

  In this printer, a charging device that uniformly charges the peripheral surface of the photoreceptor 3Y is configured by the charging brush roller 4Y and a bearing (not shown) that rotatably supports the charging brush roller 4Y.

  A Y electrostatic latent image is formed on the surface of the Y photoconductor 3Y uniformly charged by the charging nip by optical scanning by the optical writing unit (50) described above. The toner is developed into a Y toner image by the Y developing device 40Y.

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

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

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

  The Y toner image developed in the development area is conveyed to the primary transfer nip for Y where the photoconductor 3Y and the intermediate transfer belt 61 come into contact with the rotation of the photoconductor 3Y. Intermediate transfer. Untransferred toner that has not been transferred onto the intermediate transfer belt 61 adheres to the surface of the photoreceptor 3Y after passing through the primary transfer nip. This transfer residual toner is removed from the surface of the photoreceptor 3Y by the drum cleaning device 20Y in which the cleaning blade 21Y is in contact with the photoreceptor 3Y. Then, the paper is discharged out of the drum cleaning device 20Y while being conveyed in a direction perpendicular to the drawing sheet as the recovery screw 22Y rotated by the drum cleaning device 20Y rotates. The discharged transfer residual toner is accommodated in a waste toner bottle (not shown).

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

  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.

Next, a characteristic configuration of the printer will be described.
FIG. 3 is an enlarged plan view showing the pre-charging contact sheet 10Y from the contact surface side with the photoreceptor. A two-dot chain line in the figure indicates the photoconductor 3Y. Actually, the photoconductor 3Y is located on the front side in the drawing with respect to the pre-charging contact sheet 10Y indicated by a solid line. An arrow A indicates the direction of surface movement at the contact portion between the photoreceptor 3Y and the pre-charging contact sheet 10Y. An alternate long and short dash line L1 indicates the axial direction of the photoconductor 3Y, which is a direction orthogonal to the surface movement direction of the photoconductor 3Y at the contact portion as illustrated.

  A plurality of grooves dt extending in directions parallel to each other are provided on the contact surface of the pre-charging contact sheet 10Y with the photoreceptor 3Y. These grooves dt extend obliquely from the upstream end sa to the downstream end sb in the movement direction of the photoreceptor surface of the pre-charging contact sheet 10Y. Most of the grooves dt communicate with the downstream end sb starting from the upstream end sa, but some of the grooves dt communicate with the side end sc starting from the upstream end sa.

  FIG. 4 is a partial enlarged cross-sectional view showing the pre-charging contact sheet 10Y and the photoreceptor 3Y that are in contact with each other. This figure shows a fracture surface in a direction orthogonal to the photosensitive member surface movement direction. As shown in the figure, most of the area of the contact surface with the photoreceptor 3Y in the pre-charging contact sheet 10Y is in contact with the photoreceptor 3Y, but the pre-charging contact is provided at the position where the groove dt is provided. A gap is formed between the sheet 10Y and the photoreceptor 3Y. The gap is opened at one end in the length direction on the upstream side in the movement direction of the photosensitive member surface with respect to the contact portion between the pre-charging contact sheet 10Y and the photosensitive member 3Y. The pre-charging contact sheet 10Y receives the toner blocked at its upstream end (sa in FIG. 3) into the groove dt from its opening. Then, with the movement of the surface of the photosensitive member 3Y, the photosensitive member 3Y is moved in the extending direction of the groove dt, and is removed from the end opposite to the groove dt. For example, in FIG. 3 described above, in the case of the groove dt communicating from the upstream end sa to the downstream end sb, the toner received in the groove at the upstream end sa is discharged from the downstream end sb. Further, in the case of the groove dt communicating from the upstream end sa to the side end sc, the toner received in the groove at the upstream end sa is discharged from the side end sc. Due to the movement of the toner in the groove dt, the contact portion between the pre-charging contact sheet 10Y and the photoreceptor 3Y quickly passes through the toner blocked by the upstream end sa of the pre-charging contact sheet 10Y. By doing so, the amount of toner staying on the upstream side of the contact portion is reduced. As a result, by suppressing the sticking of the toner to the pre-charging contact sheet 10Y, it is possible to suppress the occurrence of image quality deterioration due to the reversely charged toner or the low charged toner in the transfer residual toner for a longer period of time.

  FIG. 3 shows an example in which the pre-charging contact sheet 10Y is brought into contact with the photosensitive member 3Y only in a partial region in a direction orthogonal to the surface movement direction. In such a configuration, a photosensitive region where the sheet does not contact is generated on both sides of the pre-charging contact sheet 10Y in the moving direction of the photosensitive member surface. The toner in the groove dt does not necessarily have to be guided to the downstream end sb of the pre-charging contact sheet 10Y, and even if the toner is guided to the regions on both sides (the side end sc in the example shown), It is possible to slip through the contact area. Therefore, as shown in the drawing, a part of the grooves dt may be communicated from the upstream end sa to the side end sc. On the other hand, when the pre-charging contact sheet 10Y is brought into contact with the entire area in the direction orthogonal to the surface movement direction with respect to the photoreceptor 3Y, all of the toner blocked by the upstream end sa is downstream. It is necessary to lead to the end sb. Therefore, in this case, it is necessary to extend all the grooves dt extending from the upstream end sa to the downstream end sc.

  Further, the example in which the groove dt is formed in the entire region of the contact surface of the pre-charging contact sheet 10Y (the surface on the side in contact with the photoreceptor 3Y) has been described. The groove dt may be formed only in the area of the surface that actually contacts the photoreceptor 3Y, that is, in the contact area. For example, the pre-charging contact sheet 10Y shown in FIG. 5 has a groove dt formed only in the contact area of the pre-charge contact sheet 10Y that actually contacts the photoconductor.

  In FIG. 3 shown above, θ is an angle formed by the intersection of the direction orthogonal to the photosensitive member surface movement direction (extending direction of the alternate long and short dash line L1) and the extending direction of the groove dt (hereinafter referred to as groove angle θ). ). When the groove angle θ is set to 0 [°], that is, when the groove dt is formed to extend in a direction perpendicular to the photosensitive member moving direction, the groove dt is communicated from the upstream end sa to the downstream end sb and the side end sc. Can not be made. Therefore, the groove angle θ needs to be larger than 0 [°]. It should be noted that four angles formed by the intersection of the direction perpendicular to the photoreceptor surface movement direction and the extending direction of the groove dt are actually generated, and two of these angles are symmetrical with each other (the angles are the same). Become. For this reason, there are two angles formed by the intersection of the direction perpendicular to the moving direction of the photosensitive member surface and the extending direction of the groove dt (in the case of 90 °, all four angles are equal). The groove angle θ represents the smaller one of these two angles.

  Although the pre-charging contact sheet 10Y in the Y process unit (1Y) has been described, the pre-charging contact sheet in the process units (1M, C, K) for other colors has the same configuration as that for Y. It has become.

  The inventors prepared a testing machine having the same configuration as the printer according to the embodiment shown in FIG. Further, as the pre-charging contact sheet for K, eight types having different groove dt depths (hereinafter referred to as groove depth D) and groove angles θ were prepared. Then, while sequentially replacing these eight types of pre-charging contact sheets mounted on the testing machine, a monochrome half chart (half-tone gradation image) of each sheet is 5% on 4,000 A4 sheets. Continuous printing was performed at an image area ratio (photosensitive temperature 22 to 25 ° C., environmental humidity 50 to 70%). Next, for each pre-charging contact sheet, the durability (toner adhesion resistance) of the pre-charging contact sheet was evaluated based on the result of magnifying and observing the 4000th printed image. Specifically, in the K process unit, the K reversely charged toner is applied to a local portion of the charging brush roller (a portion corresponding to the toner fixing to the sheet) due to the fixing of the K toner to the pre-charging contact sheet. As it accumulates, it is known that black stripes occur in the above-mentioned half chart. Therefore, the number of black stripes in the 4,000th printed image was confirmed, and 0 was evaluated as ◯, 1-2 were evaluated as Δ, and three or more were evaluated as ×. If it is Δ or more, it can be said that the toner fixing resistance is remarkably improved as compared with the conventional pre-charging contact sheet.

  The drum cleaning device was removed from the K process unit (1K) for the purpose of accelerating the life of the pre-charging contact sheet and the charging brush roller. As a result, the testing machine was a cleaner-less system. In such a configuration, the transfer residual toner on the photoconductor (3K) is not cleaned, and the entire amount enters the pre-charging contact nip and the charging nip. Thereafter, the toner is collected by the developing roller of the developing device (40K).

  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.

As the photoreceptor (3K), an undercoat layer having a thickness of 3 [μm], a charge generation layer having a thickness of 0.2 [μm], and a charge transport layer having a thickness of 23 [μm] are sequentially laminated on a drum. The one having an electrostatic capacity of 110 [pF / cm ² ] was used. During printing, the photoconductor having such a configuration was rotationally driven at a linear speed of 120 [mm / sec].

  As the charging brush roller, one having an outer diameter (φ) of 11 [mm] formed by brushing a plurality of conductive flocked fibers on a rotating shaft member having a diameter of 5 [mm] was used.

The charging bias applied to the charging brush roller includes a peak-to-peak voltage V _pp 1.0 [kV], a printing frequency 300 [Hz], a non-printing (inter-paper) frequency 10 [Hz], and a duty 45 A voltage obtained by superimposing a DC voltage Vdc of −500 [V] on an AC voltage of [%] was employed. By dropping 300 [Hz] at the time of printing to 10 [Hz] in the inter-paper area, it is possible to discharge the transfer residual toner captured by the charging brush roller to the photosensitive member. As described above, the discharged toner is collected from the photoreceptor to the developing roller. However, the low charge amount toner is difficult to collect. Even when the frequency is lowered to 10 [Hz], the reversely charged toner is not discharged from the charged brush roller, and therefore gradually accumulates on the charged brush roller.

As the pre-charging contact sheet, a conductive sheet having a thickness of 0.1 [mm] made of a material in which carbon powder as a conductive material is dispersed in polyvinylidene fluoroethylene (PVDF) was used. The volume resistance of this conductive sheet is 10 ⁵ [Ω · cm]. The surface resistance is 10 ² [Ω / □].

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

  As shown in Table 1, the pre-charging contact sheets of Nos. 1 to 5 were able to significantly improve the toner adhesion resistance than the conventional pre-charging contact sheets. On the other hand, the pre-charging contact sheets of Nos. 6 to 8 could not exhibit good toner adhesion resistance. This is for the reason explained below. That is, the pre-charging contact sheet of No. 6 had no grooves formed on the contact surface with the photosensitive member, as in the conventional sheet. In other words, since the pre-charging contact sheet did not have the groove which is a characteristic configuration of the present invention, the toner was fixed as in the conventional case. Further, the pre-charging contact sheet of No. 7 has a groove angle θ of 0 [°]. That is, unlike the present invention, the groove of the pre-charging contact sheet does not communicate with the upstream end of the contact area. For this reason, the toner blocked at the upstream end cannot be received in the groove, and the toner is fixed as in the conventional case. In addition, the pre-charging contact sheet of No. 8 has a groove angle θ of 40 [°], which is smaller than the pre-charging contact sheets of Nos. 1 to 5. Since the toner received in the groove moves in the groove extending direction along with the movement of the photosensitive member surface, the difference between the photosensitive member surface moving direction and the extending direction of the groove increases, that is, the groove angle θ decreases. The ability to discharge toner from the groove is reduced. From comparison between No. 1 to No. 5 and No. 8, it is considered that when the groove angle θ is 40 [°] or less, the toner in the groove cannot be discharged well.

  FIG. 6 is an enlarged configuration diagram showing a process unit 1Y for Y in the first modification example of the printer according to the embodiment. In the first modified apparatus, an elastic member 10Y made of an elastic material such as malt plane or sponge is pressed against the surface opposite to the contact surface of the pre-charging contact sheet 10Y, and the pre-charge contact sheet 10Y. Is pressed toward the photoreceptor 3Y. In such a configuration, the pre-charging contact sheet 10Y is brought into contact with the photoreceptor 3Y with a stronger pressure than in the case where the free end side of the pre-charging contact sheet 10Y supported by the cantilever is brought into contact with the photoreceptor 3Y. The adhesion between the sheet and the photoreceptor can be improved. The process units (1M, C, K) for other colors have the same configuration as that for Y.

  FIG. 7 is an enlarged configuration diagram showing a process unit 1Y for Y in the second modified example of the printer according to the embodiment. The process units (1M, C, K) for other colors have the same configuration as that for Y. In the second modified apparatus, a so-called cleaner-less system is adopted as in the above-described testing machine. 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 is. 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 (for example, 21Y in FIG. 2) 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, in the scatter-passing type, the transfer residual toner and the latent image carrier are separated by scratching the transfer residual toner on the latent image carrier using a scattering member such as a brush that rubs against the latent image carrier. Reduce adhesion. 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 having a roller portion made of a 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 case of the scattering-passing type described above, there is a possibility that image deterioration may occur due to exceeding the recovery ability to the developing member when the residual toner after transfer such as when a solid image is formed or after a jam occurs, is temporarily captured. In the mold, the transfer residual toner captured by the capturing member is gradually collected on the developing member, and the occurrence of such image deterioration can be suppressed.

  In the combined type in the cleaner-less method, the scattered passing type and the temporary capturing type are used in combination. 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.

  The second modified apparatus employs a temporary capture type cleaner-less 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, a discharge is generated between the flocked fiber 6Y and the photoreceptor 3Y, and the surface of the photoreceptor 3Y is uniformly charged to a negative polarity. At the same time, the transfer residual toner adhering on the photoreceptor 3Y is transferred to the plurality of flocked fibers 6Y 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 6Y is retransferred onto the photoreceptor 3Y. The toner is collected from the photoreceptor 3Y through the developing roller 42Y into the developing device 40Y.

  In the second modified apparatus having such a configuration, the amount of the transfer residual toner entering the pre-charging nip is much larger than that of the configuration including the dedicated cleaning unit, and thus the present invention is particularly effective.

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to each example is the same as that of the embodiment.
[First embodiment]
In the printer according to the first embodiment, the groove angle θ, which is an angle formed by the intersection of the direction orthogonal to the surface movement direction of the photoreceptor and the extending direction of the groove (dt), is 45 [°] or more and 90 [°] or less. In such a configuration, as can be seen from the comparison between Nos. 1 to 5 and No. 9 shown in Table 1, the toner adhesion resistance of the pre-charging contact sheet is rapidly increased by setting the groove angle θ too small. Deterioration can be avoided.

[Second Embodiment]
In the printer according to the second embodiment, the groove angle θ is set to 60 [°] or more. In this configuration, the toner adhesion resistance of the pre-charging contact sheet can be improved as compared with the case where the groove angle θ is smaller than 60 [°].

[Third embodiment]
As can be seen from the comparison between No. 1 and No. 5 shown in Table 1 above, if the groove depth D is too small, the toner adhesion resistance of the pre-charging contact sheet can be improved satisfactorily. Disappear. Therefore, in the printer according to the third embodiment, the groove depth D is set to 0.5 [μm] or more. In such a configuration, compared to the case where the groove depth D is less than 0.5 [μm], the toner adhesion resistance of the pre-charging contact sheet can be improved.

[Fourth embodiment]
In the printer according to the fourth embodiment, the specific volume resistivity is 10 ² [Ω · cm] or more and 10 ⁸ [Ω · cm] or less as the pre-charging contact sheet of each color, and 10 ² [Ω / cm2] or more and 10 ⁷ [Ω / cm2] or less are used. The present inventors use the pre-charging contact sheet that exhibits such electric resistance characteristics, thereby avoiding a significant leakage of current from the pre-charging contact sheet to the photoreceptor due to the too low electrical resistance. It was confirmed by experiments that the transfer residual toner can be reliably charged to the normal polarity.

[Fifth embodiment]
In the printer according to the fifth embodiment, the groove depth D is set to 6% or more of the average particle diameter of the toner. In such a configuration, compared to the case where the groove depth D is less than 6% of the average particle diameter of the toner, the toner fixing resistance of the pre-charging contact sheet can be improved.

[Sixth embodiment]
In the printer according to the sixth embodiment, the groove depth D is set to 12% or more of the average particle diameter of the toner. In such a configuration, as indicated by numbers 1 to 5 in Table 1 (as revealed by experiments), good toner adhesion resistance cannot be obtained due to the groove depth D being too small. The situation can be avoided reliably.

  So far, an example of a so-called tandem printer that obtains a multicolor toner image by transferring the toner images of the plurality of process units 1Y, 1M, 1C, and 1K in an overlapping manner has been described. The present invention can also be applied to an image forming apparatus that forms the image. In this single system, a plurality of developing means for each color are arranged around a latent image carrier such as a photoconductor, and visible images of respective colors formed on the latent image carrier while sequentially switching the developing means to be used. Is transferred onto the intermediate transfer member in sequence. The present invention can also be applied to an image forming apparatus that forms only a single color image.

  As described above, in the printer according to the embodiment, the pre-charging contact sheet serving as the pre-charging contact member is provided with a plurality of grooves dt extending in parallel to each other. Compared to the case where only one is provided, the toner fixing resistance of the pre-charging contact member can be improved.

  In the printer according to the first embodiment, the groove angle θ, which is an angle formed by the intersection of the direction perpendicular to the surface movement direction of the photosensitive member as the latent image carrier and the extending direction of the groove dt, is set to 45 [ Since the angle is not less than 90 ° and not more than 90 °, as described above, it is possible to avoid abrupt deterioration of the toner fixing resistance of the pre-charging contact sheet due to setting the groove angle θ too small.

  In the printer according to the second embodiment, since the groove angle θ is set to 60 [°] or more, the resistance of the contact sheet before charging is more resistant than the case where the groove angle θ is made smaller than 60 [°]. The toner fixing property can be improved.

  Further, in the printer according to the third embodiment, since the groove depth D is 0.5 [μm] or more, the resistance against the pre-charging contact sheet is smaller than when the groove depth D is less than 0.5 [μm]. The toner fixing property can be improved.

In the printer according to the fourth embodiment, as the pre-charging contact sheet, a sheet having a volume resistivity of 10 ² [Ω · cm] or more and 10 ⁸ [Ω · cm] or less is used. Further, it is possible to reliably charge the transfer residual toner to the normal polarity while avoiding a significant leakage of current from the pre-charging contact sheet to the photoreceptor due to the electric resistance being too low. In addition, the surface resistance in the contact area of the contact surface with the photosensitive member is 10 ² [Ω / cm ² ] or more and 10 ⁷ [Ω / cm ² ] or less, so that charging due to the too low electric resistance. It is possible to reliably charge the transfer residual toner to the normal polarity while avoiding a significant leakage of current from the front contact sheet to the photoconductor.

  Further, in the printer according to the fifth embodiment, since the groove depth D is set to 6% or more of the average particle diameter of the toner, it is smaller than the case where the groove depth D is less than 6% of the average particle diameter of the toner. Thus, the toner adhesion resistance of the pre-charging contact sheet can be improved.

  Further, in the printer according to the sixth embodiment, since the groove depth D is set to 12 [%] or more of the average particle diameter of the toner, it is compared with the case where the groove depth D is less than 6 [%] of the average particle diameter of the toner. Further, the toner adhesion resistance of the pre-charging contact sheet can be improved.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram showing a process unit for Y of the printer together with an intermediate transfer belt. FIG. 3 is an enlarged plan view showing a pre-charging contact sheet of the process unit from a contact surface side with a photoreceptor. FIG. 3 is a partially enlarged cross-sectional view showing the pre-charging contact sheet and the photoconductor that are in contact with each other. FIG. 3 is an enlarged plan view showing a pre-charging contact sheet in which a groove is provided only in a contact region with a photoreceptor. The expansion block diagram which shows the process unit for Y in a 1st modification apparatus. The expansion block diagram which shows the process unit for Y in a 2nd modification apparatus.

Explanation of symbols

1Y, M, C, K: Process unit 3Y, M, C, K: Photoconductor (latent image carrier)
4Y: charging brush roller (charging member)
5Y: Rotating shaft member 6Y: Flocked fiber 10Y: Pre-charging contact sheet (pre-charging contact member)
dt: groove 40Y, M, C, K: developing device (developing means)
50: Optical writing unit (latent image forming means)
60: Transfer unit (transfer means)

Claims (11)

A latent image carrier for carrying a latent image;
Latent image forming means for forming a latent image on the latent image carrier;
Developing means for developing the latent image on the latent image carrier with toner;
A charging member that uniformly charges the surface of the latent image carrier while moving its surface endlessly in contact with the latent image carrier before the latent image is formed by the latent image forming means; and A charging device having a pre-charging contact member that contacts the latent image carrier before being uniformly charged by the charging member;
Charging bias supply means for supplying a charging bias to the charging member;
In the charging device used in an image forming apparatus comprising a pre-charging bias supply means for supplying a pre-charging bias to the pre-charging contact member,
The pre-charging contact member extends from the upstream end of the contact area in the surface movement direction of the latent image carrier to the contact area of the surface that contacts the latent image carrier and the upstream end of the contact area. Is a charging device using a groove provided to a different end. The charging device according to claim 1.
A charging device using a plurality of the grooves extending in parallel directions as the pre-charging contact member. The charging device according to claim 1 or 2,
A charging device, wherein an angle formed by an intersection between a direction perpendicular to the surface moving direction and an extending direction of the groove is set to 45 [°] or more and 90 [°] or less. The charging device according to claim 3.
A charging device characterized in that the angle is set to 60 [°] or more. The charging device according to any one of claims 1 to 4,
A charging device characterized in that the depth of the groove is 0.5 [μm] or more. The charging device according to any one of claims 1 to 5,
A charging device using a pre-charging contact member having a volume resistivity of 10 ² [Ω · cm] or more and 10 ⁸ [Ω · cm] or less. The charging device according to any one of claims 1 to 6,
A charging device using a pre-charging contact member having a surface resistance of 10 ² [Ω / cm ² ] or more and 10 ⁷ [Ω / cm ² ] or less in the contact region. A latent image carrier for carrying a latent image, a latent image forming means for forming a latent image on the latent image carrier, a developing means for developing the latent image on the latent image carrier with toner, and the latent image formation The image forming apparatus includes a charging unit that uniformly charges the latent image carrier before the latent image is formed by the unit, and holds at least the latent image carrier and the charging unit on a common holder. In the process unit that is integrally attached to and detached from the image forming apparatus main body as one unit,
A process unit using the charging device according to claim 1 as the charging means. A latent image carrier for carrying a latent image;
Latent image forming means for forming a latent image on the latent image carrier;
Developing means for developing the latent image on the latent image carrier with toner;
A charging member that uniformly charges the surface of the latent image carrier while moving its surface endlessly in contact with the latent image carrier before the latent image is formed by the latent image forming means; and A charging means having a pre-charging contact member that contacts the latent image carrier before being uniformly charged by the charging member;
Charging bias supply means for supplying a charging bias to the charging member;
In an image forming apparatus comprising: a pre-charging bias supply unit that supplies a pre-charging bias to the pre-charging contact member;
An image forming apparatus using the charging device according to claim 1 as the charging unit. The image forming apparatus according to claim 9.
The depth of the groove of the pre-charging contact member is 6% or more of the average particle diameter of the toner. The image forming apparatus according to claim 10.
An image forming apparatus, wherein the depth of the groove is 12% or more of the average particle diameter of the toner.

Images