JP2010139682A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for forming an image by developing an electrostatic latent image formed on a latent image carrier with charged toner carried on a toner carrier, which suppress wasteful toner consumption, and suppress an increase in torque at start-up and chip or the like of a peeling means. <P>SOLUTION: After performing an image forming process, application of developing bias Vb to a developing roller 7a is stopped. Thereafter, application of transfer bias Vt1 to an intermediate transfer belt 8a is continued for a fixed time, and then rotation of a photoreceptor 2 is stopped. The transfer bias Vt1 is DC potential to generate discharge between the photoreceptor 2 and the intermediate transfer belt 8a. While negatively charged particles existing between a developing position DP and a transfer position TP move to the transfer position TP, positive charge is applied to the negatively charged particles, so that the polarity thereof is inverted. When the photoreceptor 2 is stopped, only the positively charged particles remain. The positively charged particles function as lubricant at the next start-up, and the chip of a grinding blade 3 and the increase in driving torque of the photoreceptor 2 are prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an image forming apparatus and an image forming method for forming an image by developing an electrostatic latent image formed on a latent image carrier with a charged toner carried on a toner carrier.

In an image forming apparatus and an image forming method configured to develop an electrostatic latent image as a toner image on a latent image carrier and transfer the toner image to a transfer medium, in the image forming process, the latent image carrier There is a known problem that discharge products inevitably generated near the surface, external additives released from the toner, and the like adhere to the surface of the latent image carrier to inhibit image formation and reduce image quality. In order to solve such a problem, in the conventional image forming apparatus, a blade-like peeling means is brought into contact with the latent image carrier after the toner image is transferred to scrape off residual deposits on the latent image carrier. It is configured to be removed.

In such a conventional technique, the surface of the latent image carrier is prevented in order to prevent wear or chipping of the peeling means caused by the friction between the latent image carrier from which the residual deposit has been removed and the peeling means. In some cases, the toner is supplied to the slidable contact means so as to function as a lubricant. For example, in the technique disclosed in Patent Document 1, a toner band is periodically formed on a latent image carrier, and the blade is scraped off by the blade to prevent the blade from being damaged.

JP 2006-259524 A

The toner band formed in the above-described prior art uses toner only for functioning as a lubricant, leading to unnecessary increase in toner consumption. Further, even if the scraped-off toner is collected by the developing device, the toner is inevitably deteriorated and the life of the toner in the developing device is shortened.

Further, in the configuration in which the surface of the latent image carrier is brought into contact with the surface of the latent image carrier that circulates around the blade-like peeling means, residual deposits are removed from the surface of the latent image carrier at the end of the image forming process. In that state, the rotation stops, so that there is no toner as a lubricant at the next start-up, and there is a problem that the rotational torque of the latent image carrier at the start-up becomes large and the blade is easily chipped. It was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. In an apparatus and method for forming an image by developing an electrostatic latent image formed on a latent image carrier with a charged toner carried on the toner carrier, a wasteful invention is provided. An object of the present invention is to provide a technique capable of suppressing excessive toner consumption and suppressing increase in torque at start-up and chipping of a peeling means.

In order to achieve the above object, an image forming apparatus according to the present invention has a latent image carrier that circulates in a predetermined rotational direction and a surface of the latent image carrier that is not in contact with the surface of the latent image carrier at a predetermined charging position. The charging means for charging the toner to a potential having the same polarity as the normal charging polarity of the toner, and the potential of the surface of the latent image carrier charged at the latent image forming position downstream of the charging position in the rotation direction are attached to the toner. A latent image forming means for forming an electrostatic latent image on the surface of the latent image carrier by making the difference between an image portion to be applied and a non-image portion not to be attached, and downstream of the latent image forming position in the rotation direction. A toner carrying member disposed in a non-contact facing manner with respect to the latent image carrying member at a development position;
Developing means for carrying the charged toner on the surface of the toner carrying member and transporting it to the developing position and applying an alternating voltage as a developing bias to develop the electrostatic latent image as a toner image; Transfer means for transferring the toner image to the transfer medium by bringing the transfer medium into contact with the latent image carrier at a transfer position downstream from the development position, and peeling in the rotation direction downstream from the transfer position A peeling unit that slides on the surface of the latent image carrier at a position so as to peel off the residual deposits on the surface; and a control unit that controls each part of the apparatus to execute an image forming process, and the control unit includes the image After execution of the forming process, toner and a small amount of external additive released from the toner are applied to predetermined areas on the surface of the latent image carrier including the peeling position and the upstream area in the rotation direction. One Kutomo, the normal charging polarity of the toner is characterized by stopping the movement of the latent image bearing member remaining attached was in a state of being charged to the opposite polarity.

In the invention configured as described above, the latent image carrier after the completion of the image forming process adheres a toner or an external additive charged with a polarity opposite to the normal charging polarity, which is the original charging polarity of the toner, to the surface thereof. It has stopped in the state. Therefore, when the circular movement of the latent image carrier is resumed during the next image forming process, the adhered toner or external additive functions as a lubricant, and the rotational torque of the latent image carrier during startup is increased. The chipping of the peeling means can be prevented. In addition, a toner or an external additive that is charged with a normal charging polarity, which is the original charging polarity of the toner used, and that contributes to the development of an electrostatic latent image, but does not contribute to image formation with a polarity opposite to this is selectively used. Since the toner is adhered to the latent image carrier, the toner is not consumed unnecessarily.

In addition, in order to achieve the above object, the image forming method according to the present invention is arranged around the latent image carrier that circulates in a predetermined rotation direction at a predetermined charging position along the rotation direction. A charging means for charging the surface to the same potential as the normal charging polarity of the toner without contact with the surface of the carrier; and the latent image charged at the latent image forming position downstream of the charging position in the rotation direction. Latent image forming means for forming an electrostatic latent image on the surface of the latent image carrier by differentiating the potential of the surface of the image carrier between an image portion to which toner is attached and a non-image portion to which toner is not attached; and the rotation A toner carrying member disposed in a non-contact facing manner with respect to the latent image carrying member at a developing position downstream of the latent image forming position in the direction, and the toner carrying member carries charged toner on the surface thereof to carry out the development. To transport to a position A developing unit that develops the electrostatic latent image as a toner image by applying an alternating voltage as a developing bias, and a transfer medium is applied to the latent image carrier at a transfer position downstream of the developing position in the rotation direction. A transfer means for transferring the toner image to the transfer medium in contact with the surface and the surface of the latent image carrier at the peeling position downstream of the transfer position in the rotational direction to peel off the residual deposits on the surface; An image forming process is performed with the peeling means arranged in this order, and after the image forming process is performed, a predetermined area on the surface of the latent image carrier including the peeling position and an upstream area in the rotation direction. In addition, at least one of the toner and the external additive released from the toner is left to adhere in a state of being charged with a polarity opposite to the normal charging polarity of the toner to stop the movement of the latent image carrier. It is characterized in that to.

In the invention configured as described above, similarly to the above-described invention of the image forming apparatus, it is possible to prevent an increase in the rotational torque of the latent image carrier, the chipping of the peeling means, and the like while suppressing waste of unnecessary toner. .

In the present invention, the peeling means is configured such that an edge portion extending in a direction orthogonal to the rotation direction contacts the surface of the latent image carrier, and the transfer medium has a normal charging polarity of toner. A direct current potential having a reverse polarity and causing a discharge between the non-image portion of the latent image carrier and the transfer medium without causing a discharge between the image portion of the latent image carrier and the transfer medium is transferred. It may be applied as a bias.

According to such a configuration, the transfer medium has a polarity opposite to the normal charging polarity of the toner (hereinafter simply referred to as “
By applying a DC potential of “reverse polarity”, it is possible to transfer toner and external additives charged to a normal charge polarity to a transfer medium, while toners and external additives having a reverse polarity are latent images. It passes through the transfer position while remaining on the carrier. Further, by generating a discharge between the non-image portion of the latent image carrier and the transfer medium, it is possible to inject a charge having a reverse polarity into a toner or an external additive having a normal charge polarity and to reverse the polarity. Thereby, the charging polarity of the toner and the external additive attached on the latent image carrier can be controlled to the reverse polarity. Further, by bringing the peeling means into contact with the edge portion, the probability that the toner or the external additive slips through the contact position between the peeling means and the latent image carrier increases, so that the toner of the reverse polarity or the external additive is placed on the latent image carrier. The additive can be left efficiently.

In this case, when the image forming process is finished, after the supply of the developing bias to the toner carrier is stopped, the application of the transfer bias to the transfer medium is continued, and the surface of the latent image carrier The latent image carrier may be moved after a distance corresponding to the distance between the development position and the transfer position in step 1 to stop the circular movement of the latent image carrier. At the time when the application of the developing bias is completed, the toner of the normally charged polarity and the external additive that have been transferred from the toner carrier to the latent image carrier due to the application of the developing bias remain between the developing position and the transfer position. By doing so, all of such toner and external additives pass through the transfer position. At the transfer position, the charge polarity of the toner having the normal charge polarity is changed to the reverse polarity by the action of the transfer bias. As a result, only the toner and the external additive charged to the reverse polarity are applied to the latent image carrier after the stop. Can be left.

The toner carrier may carry on its surface a toner layer containing both contact toner that directly contacts the surface of the toner carrier and non-contact toner that does not directly contact the surface of the toner carrier. The contact toner is in direct contact with the surface of the toner carrying body because of its relatively high charge amount and strong adhesion to the surface of the toner carrying body. On the other hand, a toner with a low charge amount is easily discharged as a contact toner with a high charge amount and becomes a non-contact toner carried at a position away from the surface of the toner carrier. By carrying such a toner layer containing non-contact toner on the toner carrier, the toner with a low charge amount can be transferred from the toner carrier to the latent image carrier and adhered to the surface thereof. Since the toner with a low charge amount can be relatively easily reversed in its charge polarity, it can be made to function as the toner having the reverse polarity described above.

Also, a potential having a polarity opposite to the normal charging polarity of the toner is applied at a cleaning position downstream of the transfer position and upstream of the peeling position or downstream of the peeling position in the rotation direction. You may make it provide the cleaning means which contacts the contact member and removes the toner and external additive which were charged to the normal polarity on the latent image carrier. According to such a configuration, the toner of the normal charge polarity and the external additive remaining on the latent image carrier can be recovered and removed by contact with the contact member to which the electric potential of reverse polarity is applied, While the polarity can be reversed, the toner charged to the opposite polarity is not removed, so that only the toner of the opposite polarity and the external additive can be left on the latent image carrier.

The present invention is particularly effective when the volume average particle diameter of the toner is 5 μm or less. Such a small particle size toner has a strong adhesion to the latent image carrier in addition to its small particle size, and therefore it is not easy to remove it from the latent image carrier. In order to remove it reliably, it is necessary to bring the peeling means into contact with the latent image carrier at a sharp angle or to apply a high contact load. From the viewpoint of wear of the latent image carrier, damage to the peeling means, rotational torque, etc. Is more harmful. In the present invention, the toner on the latent image carrier is not removed, but the contact position by the peeling means is slipped through and remains, so the small toner particle size does not cause any disadvantage. . That is, the present invention exhibits particularly excellent effects when a small particle size toner is used.

FIG. 1 is a diagram schematically showing the main configuration of a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. In the image forming apparatus 1 of this example, image formation is performed using a non-magnetic one-component negatively charged toner. That is,
In this embodiment, the negative polarity is “regular charging polarity”. Of course, it is also possible to form an image using a positively charged toner having positive polarity as a normal charging polarity. In the following description, the image forming apparatus 1 is described as using negatively charged toner. However, when positively charged toner is used, the charging potential of each member described below may be reversed. In addition, the toner has toner base particles and external additives that are externally added to the toner base particles. In the following description, when simply referred to as “toner”, external additives are added to the toner base particles. Indicates the entire particle to which is added externally.

As shown in FIG. 1, the image forming apparatus 1 of this example includes a photoreceptor 2 on which an electrostatic latent image and a toner image are formed. The photosensitive member 2 is composed of a photosensitive drum, and a photosensitive layer having a predetermined thickness is formed on the outer peripheral surface of a cylindrical metal base tube in the same manner as a conventionally known photosensitive drum. A conductive tube such as aluminum is used for the metal base tube in the photoreceptor 2 and a conventionally known organic photoreceptor is used for the photosensitive layer.

Around the photoreceptor 2, a charger 5 that is a corona charger that charges the surface of the photoreceptor 2 to a predetermined potential, and exposure that forms an electrostatic latent image by exposing the surface of the photoreceptor 2 in accordance with an image signal. The unit 6, the developing unit 7 that visualizes the electrostatic latent image as a toner image, the transfer unit 8 to which the toner image is transferred, the discharge product (described later) adhering to the surface of the photoreceptor 2, etc. The polishing blade 3 and the cleaning roller 4 are rotated in the rotation direction D of the photosensitive member 2 in this order.
2 (clockwise in FIG. 1).

The charger 5 is not in contact with the surface of the photoreceptor 2, and a conventionally well-known and commonly used corona charger can be used as the charger 5. When a scorotron charger is used as the corona charger, a negative wire current Iw flows through the charge wire 5b of the scorotron charger, and a negative direct current (DC) grid charging bias Vg is applied to the grid 5a. Is done. The charger 5 is charged with corona discharge having the same polarity (negative polarity) as that of the toner by the charger 5, so that the surface potential of the photoreceptor 2 is set to a substantially uniform negative potential, more specifically, at the time of image formation. Potential Vo
Set to

The exposure unit 6 exposes the surface of the photoreceptor 2 with a light beam L in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal. More specifically, as shown in FIG. 2, an interface 11 is connected from an external device such as a host computer that generates an image signal.
When the image signal is given through 2, the image signal is subjected to a predetermined process by the image processing unit 111. This image signal is transferred to the exposure unit 6 via the CPU 101 that controls the operation of the entire apparatus. The exposure unit 6 exposes the surface of the photoconductor 2 by irradiating the light beam L in accordance with the image signal, and the exposed surface area (exposed portion) of the photoconductor 2 is neutralized and the surface is not exposed. It changes to a surface potential VL different from the region (non-exposed portion). Thus, an electrostatic latent image corresponding to the image signal is formed on the photoreceptor 2.

Toner is applied from the developing unit 7 to the electrostatic latent image thus formed, and the electrostatic latent image is developed with the toner. The developing unit 7 of the image forming apparatus 1 in this example is a non-contact developing type developing device in which the developing roller 7 a does not contact the photoreceptor 2. The developing roller 7a is a photosensitive member 2.
Are opposed to each other with a predetermined gap therebetween, and are rotationally driven in an arrow direction D7 in FIG.
A predetermined developing bias Vb is applied from the developing bias power supply 71 to the developing roller 7a. Although the structure of the developing unit 7 will be described in detail later, a conventionally known and non-contact developing device can also be used.

The transfer unit 8 is an endless belt capable of carrying a toner image on its surface, and has an intermediate transfer belt 8a that circulates in an arrow direction D8 in FIG. The intermediate transfer belt 8a is in contact with the surface of the photoreceptor 2 by 8b. Further, a transfer bias Vt1 having a polarity opposite to the toner charging polarity is applied to the intermediate transfer belt 8a from a transfer bias power source 81, and a toner image developed on the photoreceptor 2 by the action is applied to the intermediate transfer belt 8a. Transferred (primary transfer). The toner image transferred to the intermediate transfer belt 8a is secondarily transferred to a recording paper (not shown), and is permanently fixed on the recording paper by the fixing unit 9 and output.

The polishing blade 3 is formed into a blade shape with an elastic material such as polyurethane resin, and the edge portion of the polishing blade 3 comes into contact with the surface of the photoconductor 2 in a so-called counter direction. The surface of the photoconductor 2 is polished by edge contact. To peel off the fixed matter. In this type of image forming apparatus, discharge products such as NOx (nitrogen oxide) generated by discharge caused by high voltage applied to each part, and external additives such as silica and titania released from the toner are photosensitive. There is a known problem that it adheres to the surface of the body in the form of a film and may hinder the image forming process. The polishing blade 3 has a function of rubbing and polishing such a fixed object to separate it from the surface of the photoreceptor 2.

The cleaning roller 4 has a brush roller 4a that is rotatably provided. The brush roller 4 a has a large number of brush hairs 4 b made of nylon, for example, and these brush hairs 4 b are disposed in contact with the surface of the photoreceptor 2. The brush roller 4a rotates and forwardly rotates the photosensitive member 2 (the direction of the tangential speed of rotation of the photosensitive member 2 at the contact portion between the photosensitive member 2 and the brush hair 4b and the tangential speed of rotation of the brush hair 4b). The direction is the same as the direction of), that is, so-called with rotation.

The brush roller 4a has a polarity opposite to the normal charging polarity of the toner, that is, a positive direct current (
DC) cleaning bias Vbr is applied. As a result, among the untransferred toner on the photoreceptor 2 and the external additive that have passed through the contact position with the intermediate transfer belt 8a, those charged to the normal charging polarity are attracted to the brush roller 4a and adhere to the brush bristles 4b. To do. As the cleaning roller 4, other conductive cleaning rollers such as a conductive rubber roller can be used in addition to the brush roller.

Further, the cleaning roller 4 has a cleaning blade 4c that comes into contact with the brush bristles 4b of the brush roller 4a. The cleaning blade 4c removes and collects transfer residual toner and external additives attached to the brush bristles 4b. The cleaning blade 4c includes
Conventionally known and commonly used cleaning blades can be used.

In the following description, the position at which the photosensitive member 2 and the charger 5 are opposed to each other is the charging position CP, the surface where the light beam L from the exposure unit 6 is irradiated to the surface of the photosensitive member 2 is the exposure position EP, and the photosensitive member 2.
And the developing roller 7a are opposed to the developing position DP, the contact position between the photoreceptor 2 and the intermediate transfer belt 8a is the transfer position TP, the position where the polishing blade 3 is in contact with the photoreceptor 2 is the peeling position SP, and the photoreceptor 2 The position at which the cleaning roller 4 abuts is referred to as a cleaning position BP. In this embodiment, these positions are provided in the above order from the upstream side to the downstream side in the rotation direction D2 of the photosensitive member 2.

FIG. 3 is a cross-sectional view showing the structure of the developing unit in this embodiment. In the developing unit 7, a supply roller 7 b is provided in a housing 72 that stores a nonmagnetic one-component toner T therein.
The developing roller 7a is pivotally mounted, the developing roller 7a is positioned opposite to the photosensitive member 2 with a predetermined gap at the developing position DP, and the rollers 7a and 7b are rotationally driven on the main body side. It is engaged with a portion (not shown) and rotates in a predetermined direction. The supply roller 7b is formed in a cylindrical shape by an elastic material such as foamed urethane rubber or silicon rubber. Further, the developing roller 7a is formed in a cylindrical shape by a metal base tube of a conductive material such as a metal such as copper, aluminum, stainless steel or an alloy. And two rollers 7a
, 7b rotate while being in contact with the toner, and the toner is rubbed against the surface of the developing roller 7a to form a toner layer having a predetermined thickness on the surface of the developing roller 7a.

The internal space of the housing 72 is partitioned into a first chamber 721 and a second chamber 722 by a partition wall 72a. Both the supply roller 7b and the developing roller 7a are provided in the second chamber 722, and the toner in the second chamber 722 flows and is agitated and supplied to the surface of the developing roller 7a as these rollers rotate.

In the developing unit 7, a regulating blade 76 for regulating the thickness of the toner layer formed on the surface of the developing roller 7a to a predetermined thickness is disposed. The regulating blade 76 includes a plate member 761 having elasticity such as stainless steel or phosphor bronze, and an elastic member 762 made of a resin member such as silicon rubber or urethane rubber attached to the tip of the plate member 761. ing. The rear end portion of the plate member 761 is fixed to the housing 72, and an elastic member 762 attached to the tip portion of the plate member 761 has a plate shape in the rotation direction D7 of the developing roller 7a shown by the arrow in FIG. The member 761 is disposed on the upstream side of the rear end portion. The elastic member 762 elastically contacts the surface of the developing roller 7a to form a restriction nip, and finally restricts the toner layer formed on the surface of the developing roller 7a to a predetermined thickness.

Further, the seal member 77 is pressed against the surface of the developing roller 7a on the housing 72 at a downstream side of the position facing the photosensitive member 2 (developing position DP) in the rotation direction D7 of the developing roller 7a.
Is provided. The seal member 77 is a band-shaped film formed of a flexible material such as polyethylene, nylon, or fluororesin, and extends along a direction X parallel to the rotation axis of the developing roller 7a. The seal member 77 is a short film orthogonal to the longitudinal direction X. One end in the hand direction is fixed to the housing 72, and the other end is in contact with the surface of the developing roller 7a. The other end is in contact with the developing roller 7a in the so-called trail direction so as to go downstream in the rotation direction D7 of the developing roller 7a, and the developing roller 7a that has passed through the position facing the photoreceptor 2 is contacted.
The toner remaining on the surface is guided into the housing 72 and the toner in the housing is prevented from leaking outside.

FIG. 4 is a view showing a developing roller and a partially enlarged view of the surface thereof. The developing roller 7a, the surface of which is formed of a metal tube made of a conductive material, is formed in a substantially cylindrical roller shape, and shafts 740 are provided coaxially with the roller at both ends in the longitudinal direction. A shaft 740 is pivotally supported by the developing device main body, and the entire developing roller 7a is rotatable. Development roller 7
a in the central portion 74a of the surface a, as shown in a partially enlarged view of FIG. 4 (in a dotted circle), a plurality of regularly arranged convex portions 741 and a concave portion 742 surrounding the convex portions 741 Is provided.

Each of the plurality of convex portions 741 protrudes toward the front side of the sheet of FIG.
The top surface of 1 forms part of a single cylindrical surface (envelope cylindrical surface) that is coaxial with the rotation axis of the developing roller 7a. Further, the concave portion 742 is a continuous groove surrounding the convex portion 741 in a mesh shape, and the entire concave portion 742 also has one cylindrical surface that is coaxial with the rotation axis of the developing roller 7a and different from the cylindrical surface formed by the convex portion. It is made. And the convex part 741 and the recessed part 742 surrounding it are shown.
Are connected by a gentle slope 743. That is, the inclined surface 743 has a component in the radial outward direction of the developing roller 7a, that is, in the direction away from the rotation axis of the developing roller 7a.

The developing roller 7a having such a structure can be manufactured by a manufacturing method using a so-called rolling process described in, for example, Japanese Patent Application Laid-Open No. 2007-140080. Thereby, regular and uniform uneven portions can be formed on the cylindrical surface of the developing roller 7a. Therefore, the obtained developing roller 7a can carry a uniform and optimum amount of toner on its cylindrical surface, and the rolling property (ease of rolling) of the toner on the cylindrical surface of the developing roller 7a is also uniform. Can be. As a result, it is possible to prevent poor local charging and conveyance of the toner and to exhibit excellent development characteristics. Further, since the concavo-convex portion is formed using a mold, unlike the general developing roller obtained by blasting, the obtained concavo-convex portion can have a relatively large tip width. Such uneven portions have excellent mechanical strength.
In particular, since the mechanical strength of the portion pressed by the mold is improved, the obtained concavo-convex portion has excellent mechanical strength as compared with that obtained by processing such as cutting. The developing roller 7a having such a concavo-convex portion can exhibit excellent durability. In addition, if the width of the tip of the convex part of the concave and convex part is relatively large, there is little change in shape even if it is worn out, so that the development characteristic is prevented from abruptly decreasing, and excellent development characteristics are exhibited over a long period of time. Can do.

FIG. 5 is a cross-sectional view showing details of the structure of the developing roller surface. As shown in FIG. 5A, when the surface of the developing roller 7a is viewed from the cross-sectional direction, convex portions 741 projecting outward in the circumferential direction and concave portions 742 receding compared to this are alternately arranged. . Further, the convex portion 741 and the concave portion 74.
2 are connected by a slope 743. The dimension of the top surface of the convex portion 741 and the width of the concave portion 742 can be, for example, about 100 μm, but are not limited thereto. On the other hand, the height difference between the convex portion 741 and the concave portion 742, in other words, the depth of the groove-shaped concave portion 742 surrounding the convex portion 741, is set to a value larger than the volume average particle diameter Dave of the toner used. By doing so, it is possible to carry one or more layers of toner in the concave portion 742, and most of the carried toner does not protrude from the top surface of the convex portion 741, so that the regulating blade 76 and the seal member 77 It is possible to avoid deterioration such as peeling or deformation of the external additive due to rubbing.

More preferably, as shown in FIG. 5A, the depth of the concave portion 742 is set to be not less than twice the volume average particle diameter Dave (2Dave). By doing so, as shown in FIG. 5B, it is possible to carry two or more layers of toner in the concave portion 742 without protruding outward from the line connecting the top surface of the convex portion 742 (shown by a broken line). It becomes. In FIG. 5B, a white circle with a reference symbol T1 indicates toner (contact toner) that is in direct contact with the surface of the developing roller 7a. Further, the symbol T2 and the circle with hatching indicate the toner (non-contact toner) carried on the recess 742 without directly contacting the surface of the developing roller 7a. Two or more toner layers thus include both contact toner and non-contact toner. The non-contact toner T2 is easy to fly because the restraining force on the surface of the developing roller is weaker than the contact toner T1, and is effective in securing the image density by increasing the amount of toner flying. On the other hand, due to the weak binding force, there is also a problem that the developing roller 7a is likely to be separated from the surface of the developing roller 7a due to the airflow generated on the surface of the developing roller 7a and scattered.

The line connecting the top surfaces of the convex portions 742 indicated by broken lines in FIG. 5B indicates the top surface of each convex portion 741 as 1.
It is a curve on an envelope cylindrical surface when it is considered as a part of two cylindrical surfaces. The fact that the toner carried in the recess 742 does not exceed this line means that the toner is not exposed to the outside of the envelope cylindrical surface on the surface of the developing roller 7a. Therefore, the developing roller 7
Even if a strong air flow is generated on the surface of the developing roller 7a due to the rotation of a, the developing roller 7a
The toner carried at a position retracted from the surface is not affected, and even non-contact toner having a weak binding force to the developing roller is prevented from being separated and flying.

To carry the toner on the surface of the developing roller 7a as shown in FIG. 5B, FIG.
As shown in FIG. 4B, toner adhesion to the convex portion 741 is regulated by so-called edge regulation in which the upstream edge 762a of the elastic member 762 of the regulating blade 76 in the developing roller rotation direction D7 is brought into contact with the convex portion 741 of the developing roller 7a. To do. At the same time, a material having an appropriate elasticity may be selected as the elastic member 762 so that the elastic member 762 slightly protrudes toward the concave portion 742 at a position facing the concave portion 742. This restricts toner adhesion to the convex portion 741 and prevents the toner from being carried by the concave portion 742 beyond the envelope cylindrical surface.

As described above, a strong binding force to the developing roller 7a acts on the contact toner. Accordingly, it is considered that the contact toner has a relatively high resistance to airflow, and even if it is exposed to the outside of the envelope cylindrical surface, it is unlikely that the toner is detached. From this point of view, FIG.
As shown in d), the contact angle, contact load, etc. of the regulating blade 76 may be adjusted so as to allow toner adhesion of one layer or less to the convex portion 741.

However, the following effects can be obtained by carrying the toner only in the concave portion 742. First, in order to form a uniform toner layer on the convex portion 741, the regulating blade 76 and the convex portion 74 are used.
However, in order to carry the toner only in the concave portion 742, the toner on the convex portion 741 has only to be removed by bringing the regulating blade 76 and the convex portion 741 into contact with each other. Realization is relatively easy. Further, since the amount of toner to be conveyed is determined by the volume of the space generated in the gap between the regulating blade 76 and the recess 742, the toner conveyance amount can be stabilized.

There is also an advantage in terms of the good toner layer to be conveyed. That is, the convex portion 7
When the toner is carried on the toner 41, the toner is likely to be deteriorated due to the friction with the regulating blade 76. Specifically, there are problems such that the fluidity and chargeability of the toner are reduced, the toner is in a compacted state and agglomerates, and adheres to the developing roller 7a to cause filming. On the other hand, such a problem is unlikely to occur when the toner is carried on the concave portion 742 that does not receive much pressure from the regulating blade 76. Further, since the toner carried on the convex portion 741 and the toner carried on the concave portion 742 are greatly different in how they are slidably contacted with the regulating blade 76, it is expected that the variation in toner charge amount will increase. In addition, such a variation can be suppressed by carrying the toner only in the concave portion 742.

Particularly in recent years, there has been a demand for a smaller toner particle size and a lower fixing temperature in order to achieve higher definition of images and reduction in toner consumption and power consumption. It is possible to respond to various requests. In a small-diameter toner, the saturation charge amount is high in spite of a slow rise in charging, so that the toner carried on the convex portion 741 is in the concave portion 74.
2 tends to be significantly higher (overcharged) than the toner carried on the toner. Such a difference in charge amount appears in the image as a so-called development history. Further, in the low melting point toner, the toner is easily fixed to the toner or the developing roller 7a by rubbing. However, such a problem is unlikely to occur in the configuration of the present embodiment in which the toner is carried only in the concave portion 742.

In this embodiment, the particle diameter of the toner to be used is not particularly limited, but a particularly remarkable effect is exhibited when a toner having a volume average particle diameter Dave of 5 μm or less is used. Such a toner having a small particle diameter is difficult to fly from the developing roller 7a due to a strong van der Waals force due to its small particle diameter. Further, it is difficult to fly from the developing roller 7a due to a mirror image force that acts strongly on the developing roller 7a made of a conductive material. For this reason, the developing system of the present embodiment in which toner exceeding one layer is carried on the developing roller 7a and both the contact toner and the non-contact toner fly to contribute to the developing operation has a particularly excellent effect.

In addition, a toner having a volume average particle diameter of less than about 5 μm becomes stronger as a powder and behaves differently from a toner having a larger particle diameter. For example, since toner with a small particle diameter has a small mass, once scattered, it floats in the air for a long time, and may leak not only inside the apparatus but also outside the apparatus. Since the apparatus of this embodiment effectively suppresses toner scattering, such a problem does not occur even when toner having a small particle diameter is used.

Next, the toner applied to the image forming apparatus configured as described above will be described. In the image forming apparatus of this embodiment, the electrostatic latent image is developed using a non-magnetic one-component toner charged to a negative polarity. In the following, the negative polarity that is the original charging polarity of the toner is referred to as “regular polarity”,
The opposite positive polarity is referred to as “reverse polarity”. On the other hand, particles such as toner and external additive whose absolute charging polarity is positive polarity are referred to as “positively charged particles”, and particles such as toner and external additive whose charging polarity is negative are referred to as “negatively charged particles”. Therefore, the “positively charged toner” whose absolute charging polarity is positive is a “reversely charged toner” in the present embodiment. On the other hand, “negatively charged toner” having an absolute charging polarity of negative polarity is “regularly charged toner” in the present embodiment.

FIG. 6 is a diagram showing a toner charge amount distribution. This figure shows the result of measuring the charge amount distribution of the toner collected from the surface of the developing roller on the basis of the number. The toner used in this embodiment has a normal charging polarity of negative polarity, but as shown by the solid line in FIG. 6, the charging characteristics of the toner vary, and the charge amount distribution is generally a normal distribution. Some toners are not charged at all or are charged with a reverse polarity (in this case, positive polarity). Hereinafter, a toner having a small charge amount among toners charged to a regular charge polarity may be particularly referred to as “weakly charged toner”.

Further, as described above, in this embodiment, since the toner is supported only on the concave portion 742 on the surface of the developing roller 7a and is not supported on the convex portion 741, the stress on the toner by the supply roller 7b and the regulating blade 76 is small. . Therefore, the variation in the charge amount due to the deterioration of the toner can be reduced, and a relatively narrow charge amount distribution can be obtained as shown by the broken line in FIG.

FIG. 7 is a diagram showing the relationship between potentials applied to the respective parts in this embodiment. The surface potential Vs of the photosensitive member 2 is charged by the charger 5 and then is neutralized at the exposed portion irradiated with the light beam L from the exposure unit 6 to become the potential VL, but not exposed. In the non-exposed portion, the potential Vo after dark decay is obtained. On the other hand, the developing bias Vb is a rectangular wave AC voltage as shown in FIG. 7, the maximum value on the positive side is represented by the symbol Vmax, the maximum value on the negative side is represented by the symbol Vmin, and the potential difference between them (corresponding to the amplitude) is represented by the symbol Vpp. To express. Further, the average potential of the developing bias is represented by the symbol Vave.

Of the repetition period Tc of the alternating current component of the developing bias Vb, the period in which the potential swings to the positive side is represented by the symbol Tp, the period in which the potential swings to the negative side is represented by the symbol Tn, and the waveform duty WD of the developing bias Vb is :
WD = Tp / (Tp + Tn) = Tp / Tc
Defined by As shown in FIG. 7, in this embodiment, the bias waveform is determined so that Tp> Tn, that is, the waveform duty WD is larger than 50%. This is because the non-exposed portion of the photosensitive member 2, that is, the original toner should be adhered, by making the period in which the normally charged toner flies from the photosensitive member 2 toward the developing roller 7a longer than the opposite period. This is because the normally charged toner adhering to the non-region is efficiently pulled back to the developing roller 7a side to suppress fogging.

Examples of numerical values of the potentials of the respective parts are shown below, but the numerical values disclosed here are merely examples that satisfy the requirements of the present invention, and the embodiment of the present invention is not limited to these numerical values. The non-exposed portion potential Vo of the photoreceptor 2 is typically (−500) V, but can be changed before and after that as will be described later. On the other hand, the exposed portion potential VL is a value determined by the characteristics of the photosensitive material, and here (−
100) V. The positive side maximum value Vmax and the negative side maximum value Vmin of the developing bias Vb are respectively (
+200) V, (−800) V. Therefore, the amplitude Vpp is 1000V. Since the waveform duty WD is 60%, the average potential Vave of the developing bias Vb is (−200).
V. The frequency of the developing bias Vb is 4 kHz.

The potential difference between the average value Vave of the developing bias Vb and the exposed portion potential VL of the photosensitive member 2 is a parameter generally called “contrast voltage” that affects the image density, and this is represented by the symbol Vco.
Represented by nt. On the other hand, the potential difference between the average value Vave of the developing bias Vb and the non-exposed portion potential Vo of the photosensitive member 2 is a parameter that has little influence on the image density but affects the amount of toner scattering and fogging at the developing position DP. Here, this potential difference is referred to as “reverse contrast voltage” and is represented by the symbol Vr.

In order to control the image density, it is necessary to make the contrast voltage Vcont variable. On the other hand, in order to stabilize the toner scattering and the amount of fogging, it is preferable to maintain a constant value for the reverse contrast voltage Vr. Therefore, in this embodiment, each parameter Vmax, Vmin, and WD of the developing bias Vb can be changed to control the average voltage Vave to obtain a desired image density, and the charging bias Vg is changed to the change in the average voltage Vave. The reverse contrast voltage Vr is maintained at a constant value by changing the non-exposed portion potential Vo of the photosensitive member 2 in conjunction with it.

The transfer bias Vt1 applied to the intermediate transfer belt 8a and the cleaning bias Vbr applied to the brush roller 4 are both (+300) V. However, there is no particular need to make these equal.

Next, an image forming process executed by the image forming apparatus configured as described above will be described. In the image forming process of the image forming apparatus 1, the charger 5 uniformly charges the surface of the photoreceptor 2, and the exposure unit 6 exposes the surface of the photoreceptor 2 to form an electrostatic latent image. Then, toner is applied from the developing unit 7 to the electrostatic latent image to be visualized as a toner image, which is primarily transferred to the intermediate transfer belt 8a and is secondarily transferred and fixed to a recording sheet (not shown). This completes the image forming process. In the following description, toner or external additive particles released from the toner and positively charged particles are collectively referred to as “positively charged particles”, and negatively charged particles are referred to as “negatively charged particles”.

FIG. 8 is a diagram schematically showing a phenomenon that occurs on the surface of the photoreceptor. At the development position DP, the electrostatic latent image is developed with toner by transferring charged toner from the developing roller 7a to the surface of the photoreceptor 2 on which the electrostatic latent image is formed. At this time, in principle, only a phenomenon in which negatively charged toner having normal polarity adheres to the exposed portion of the photoreceptor 2 should occur, but this is not necessarily the case. That is, a positively charged toner having a reverse polarity adheres to the exposed portion, or the toner adheres to a non-exposed portion where the toner should not be originally attached. Both positively charged and negatively charged toners may adhere to the non-exposed portion. The same applies to the external additive particles released from the toner.

As a result, as shown in FIG. 8, both the positively charged toner indicated by the hatched circle and the negatively charged toner indicated by the white circle are located downstream of the development position DP in the rotation direction of the photosensitive member 2 at D2. Is attached to the surface of the photoreceptor 2. Here, among the negatively charged particles, those having a relatively high charge amount are such that the alternating electric field formed at the developing position DP by the developing bias Vb pulls the toner back from the non-exposed portion of the photoreceptor 2 toward the developing roller 7a. Photoreceptor 2 for stronger action
However, there is a high possibility that weakly charged particles having a low charge amount will remain on the photosensitive member 2 without returning to the developing roller 7a. Therefore, weakly charged particles are mainly attached to the non-exposed portion of the photoreceptor 2. In particular, in this embodiment, since the toner with a low charge amount is positively carried on the developing roller 7a as a non-contact toner, the tendency becomes remarkable.

In this embodiment, the transfer bias Vt1 is applied to the intermediate transfer belt 8a that is in contact with the photosensitive member 2 at the transfer position TP located downstream of the development position DP. The transfer bias Vt1 is a positive potential, and the magnitude thereof is such that the potential difference between the intermediate transfer belt 8a and the exposed portion of the photoreceptor 2 does not exceed the discharge start voltage between the intermediate transfer belt 8a and the photoreceptor 2. Intermediate transfer belt 8a and photoreceptor 2
Is set to a value such that the potential difference from the non-exposed portion exceeds the discharge start voltage. In a photoconductor having a film thickness of 25 μm, which is a general apparatus configuration, the discharge start voltage is about 600 V, and the transfer bias Vt1
Is (+300) V, the potential difference from the exposed portion (-100 V) is 400 V, and the non-exposed portion (-
500V), the potential difference becomes 800V, which satisfies the above condition.

Under such conditions, discharge occurs from the intermediate transfer belt 8a toward the non-image portion of the photoreceptor 2. This discharge occurs at a position TP0 on the near side of the transfer position TP in the rotation direction D2 of the photosensitive member 2, and electric charges are also applied to particles such as toner and external additives attached to the non-exposed portion of the photosensitive member 2 due to this discharge. The positively charged particles are injected, and the charge amount of the positively charged particles is increased, while the weakly charged particles are reversed in polarity and become positively charged particles. Thus, most of the particles adhering to the non-exposed portion are positively charged particles. The positively charged particles having an increased charge amount adhere more firmly to the surface of the photoreceptor 2.

At the transfer position TP, the intermediate transfer belt 8a to which the positive transfer bias Vt1 is applied is in contact with the surface of the photoconductor 2, so that negatively charged particles on the photoconductor 2 are transferred to the intermediate transfer belt 8.
Move to a. Negatively charged toner adhering to the exposed portion of the surface of the photoreceptor 2 is transferred to the intermediate transfer belt 8a as a toner image, but the negatively charged toner adhering to the non-exposed portion causes background fogging in the toner image. In this embodiment, since the polarity of the negatively charged particles in the non-exposed portion is reversed as described above, background fogging is suppressed.

On the other hand, the positively charged particles do not move to the intermediate transfer belt 8a due to the action of the positive transfer bias Vt1, but are sent further downstream while remaining on the photoreceptor 2. At the peeling position SP located downstream of the transfer position TP, the polishing blade 3 is in contact with the surface of the photoreceptor 2. The polishing blade 3 has a function of peeling off discharge products and the like that adhere to the surface of the photoconductor 2, but as will be described in detail later, the polishing blade 3 and the photoconductor 2 are hardly scraped off with respect to the toner on the photoconductor 2. The abutting method of the polishing blade 3 is managed so as to pass between the two. Therefore, the positively charged particles on the photoreceptor 2 pass through the peeling position SP and are sent to the cleaning position BP.

Since the positive polarity cleaning bias Vbr is also applied to the brush roller 4a in contact with the photosensitive member 2 at the cleaning position BP, there is no action of collecting positively charged particles adhering to the photosensitive member 2. In particular, by rotating the brush roller 4a with respect to the photoreceptor 2, the scraping action of the positively charged particles by the brush can be suppressed to a small level.

Due to the transfer efficiency being 100% or less, there are cases where negative transfer particles remaining after transfer remain on the surface of the exposed portion of the photoreceptor 2 that has passed the transfer position TP. Such negatively charged particles are given a positive charge by contact with the brush roller 4a and converted to positive polarity, or the brush hair 4
It is adsorbed by b and removed from the surface of the photoreceptor 2. In this manner, only the positively charged particles are attached to the surface of the photoreceptor 2 on the downstream side of the cleaning position BP. That is, the cleaning roller 4 has a function of adjusting the charging polarity of the toner or the like on the photoreceptor 2 to positive polarity (reverse polarity).

Since the positively charged particles are not in contact with each other, they do not adhere to the charger 5, pass through the charging position CP and the exposure position EP, and reach the developing position DP again. Since the positively charged particles whose charge amount has been increased in the course of rotation have already adhered to the surface of the photosensitive member 2 that has returned to the development position DP, the adhesion force exerted by the photosensitive member 2 is weakened, and new particles Adhesion is unlikely to occur. Furthermore, even if negatively charged particles adhere to the non-exposed portion due to reciprocating motion by an alternating electric field, the adhesion force of the photosensitive member 2 is reduced, so that it can be easily returned to the developing roller 7a by the electric field in the pull-back direction. become. That is, in this embodiment, the image forming process proceeds in a state in which a substantially constant amount of positively charged particles are always dispersed and adhered onto the photoreceptor 2.

Therefore, positively charged particles pass between the photosensitive member 2 and the polishing blade 3 one after another while the photosensitive member 2 repeatedly rotates as the image forming process proceeds. The positively charged particles function as a lubricant for reducing the friction between the two, and suppress wear of the photoconductor 2 and chipping of the polishing blade 3, and load torque of a motor (not shown) that drives the photoconductor 2 to rotate. Reduce.

Here, the toner carried on the surface of the developing roller 7a originally contains a certain amount of positively charged particles and is assumed to remain on the photosensitive member 2. However, as shown by the broken line in FIG. The same applies when the content ratio of the positively charged particles is extremely small. I mean,
Even if the content ratio of the positively charged particles is small, there is a variation in the charge amount. In this embodiment, the charge polarity of the weakly charged particles having a low charge amount is reversed at the transfer position TP and the cleaning position BP. This is because positively charged particles are generated.

Furthermore, in this embodiment, the photosensitive member 2 is stopped while the charged particles remain on the photosensitive member 2 as follows at the end of the image forming process, so that the normal image forming process can be performed correctly at the start of the next image forming process. The function as a lubricant by charged particles is exhibited.

FIG. 9 is a timing chart showing the operation of the image forming process. FIG. 10 is a diagram schematically showing the state of the surface of the photoreceptor after the rotation is stopped. As shown in FIG. 9, when an image formation command is given to the image forming apparatus 1 from the outside and the execution of the image forming process is started by the CPU 101, the rotation of the photosensitive member 2 is started. At substantially the same time, a cleaning bias Vbr is applied to the cleaning roller 4. Then, application of the developing bias Vb to the developing roller 7a and the transfer bias Vt1 to the intermediate transfer belt 8a are sequentially started. Here, the development of the electrostatic latent image is started by starting the application of the developing bias Vb, but the developed toner image is developed for the time Ta until the application of the transfer bias Vt1 is started. It is desirable that the time is shorter than the time from the position DP to the transfer position TP.

On the other hand, at the end of the image forming process, after the development bias Vb is turned off to complete the development, the transfer bias Vt1 is continuously applied for a predetermined time Tb while the photosensitive member 2 is rotated. This time Tb is preferably equal to or longer than the time required for the surface of the photosensitive member 2 at the development position DP to reach the transfer position TP when the application of the development bias Vb is completed. That is, when the distance between the development position DP and the transfer position TP along the surface of the photoconductor 2 is L1, and the peripheral speed of the surface of the photoconductor 2 is v,
Tb ≧ L1 / v
Is desirable. The reason is as follows.

While the developing bias Vb is applied to the developing roller 7a, the charged toner is flying at the developing position DP, and both positively charged particles and negatively charged particles can adhere to the photosensitive member 2. As a result, as shown in FIG. 8, positively and negatively charged particles adhere to the downstream side of the development position DP. In this embodiment, only positively charged particles that are not transferred to the intermediate transfer belt 7a need to be adhered to the photosensitive member 2, but immediately after the application of the developing bias Vb is stopped, the photosensitive member 2 is used.
When the rotation is stopped, negatively charged particles remain on the photoreceptor 2 between the development position DP and the transfer position TP.

Therefore, as described above, the application of the transfer bias Vt1 is continued for the time Tb after the application of the developing bias Vb is stopped, and then the rotation of the photosensitive member 2 is stopped. In this way, all negatively charged particles remaining between the development position DP and the transfer position TP reach the transfer position, and the negatively charged particles are converted to positive charge by the discharge by the transfer bias Vt1. Alternatively, the process proceeds to the intermediate transfer belt 8a. For this reason, the negatively charged particles do not remain on the photosensitive member 2 after the rotation is stopped.
As shown in FIG. 4, only the positively charged particles remain attached to the surface of the photoreceptor 2.

By doing so, the positively charged particles remaining on the photosensitive member 2 act as a lubricant with the polishing blade 3 even when the rotation of the photosensitive member 2 is started at the start of the next image forming process. Thus, an increase in starting torque and chipping or deformation of the polishing blade 3 are prevented.

Note that the cleaning bias Vbr applied to the cleaning roller 4 is preferably applied while the rotation of the photosensitive member 2 continues, but further, as shown in FIG. 9, the developing bias applied to the developing roller 7a. It is desirable to continue for a time Tc or longer after the application of Vb is stopped. Here, the time Tc corresponds to the development position DP and the cleaning position BP along the surface of the photosensitive member 2.
When the distance between and is L2,
Tc ≧ L2 / v
Is equal to or longer than the time until the surface of the photosensitive member 2 at the development position DP reaches the cleaning position BP at the end of application of the development bias Vb. By doing so, all of the negatively charged particles remaining on the photoreceptor 2 between the development position DP and the transfer position TP at the end of the application of the development bias Vb pass through the transfer position TP and the cleaning position BP. . In this way, only positively charged particles can remain on the photoreceptor 2 more reliably.

Next, conditions for obtaining the above effects will be described. In order to realize the toner slipping at the contact position (peeling position SP) between the photosensitive member 2 and the polishing blade 3, the fluidity of the toner, the contact load of the polishing blade 3 on the photosensitive member 2, etc. Must satisfy a predetermined condition. This is because the effect of the present invention cannot be obtained if the toner on the photoreceptor 2 is scraped off by the polishing blade 3. The inventors of the present application conducted experiments while changing various combinations of toner and polishing blade materials, contact loads, etc., and found conditions for allowing toner to pass through satisfactorily.

The experiment is to measure the density of toner remaining on the photoreceptor 2 when toner particles are dispersed at a constant density on the surface of the photoreceptor 2 and the polishing blade 3 is brought into contact with the surface and rotated. . The parameters are the particle size (volume average particle size) of the toner, its circularity, the hardness of the polishing blade 3, the contact angle with the surface of the photoreceptor 2, the contact load, and the like.

The toner density on the photoreceptor 2 is the optical density (OD value) on the surface of the photoreceptor 2.
It was evaluated by. In the experiment for explaining the results below, the toner is adhered to the surface of the photoreceptor 2 having an OD value of about 0.1 alone until the OD value becomes about 0.5, and then the polishing blade 3
Was measured and the OD value of the surface of the photoreceptor 2 after rotating a certain amount was measured. If the toner is completely removed by the polishing blade 3, the measured value will be approximately 0.1. If not completely removed, the measured value should be 0.5. That is, it can be said that the closer the measured value is to the initial value 0.5, the better the toner slips between the photoreceptor 2 and the polishing blade 3.

The contact angle of the polishing blade 3 with respect to the surface of the photoreceptor 2 was changed between 7 degrees and 18 degrees, but there was almost no difference in the experimental results. Therefore, only the result when the contact angle is set to 12 degrees is shown below.

FIG. 11 is a diagram showing experimental results when the particle diameter and circularity of the toner are changed. Although it is considered preferable that the particle size of the toner is small for good slipping, FIG.
As shown in FIG. 3, it was found that the influence of the circularity of the toner is rather large. That is, toner having a circularity of 0.955 or more could be satisfactorily slipped through, including those having a relatively large particle diameter, if the contact load of the polishing blade 3 was 20 g / cm or less. In particular, when the circularity of the toner is 0.96 or more and the contact load of the polishing blade 3 is 20 g / cm or less, the OD value hardly decreases and it can be said that the toner slips very well. . On the other hand, with a toner having a low circularity, good results could not be obtained even when the contact load of the polishing blade 3 was adjusted.

FIG. 12 is a diagram showing experimental results when the hardness of the polishing blade is changed. The toner used has a circularity of 0.96. When the hardness of the polishing blade 3 was JIS-A hardness 85 degrees, when the blade contact load was 25 g / cm or less, there was almost no decrease in the OD value, and almost perfect slip-through could be realized. On the other hand, when a blade having a lower hardness was used, the OD value was hardly decreased if the blade contact load was 20 g / cm or less. However, when the contact load was increased, the OD value might be decreased. all right. Further, the lower the hardness, the more remarkable the decrease in the OD value. This is presumably because the low-hardness blade is elastically deformed and is in close contact with the surface of the photoreceptor 2 so that the toner on the photoreceptor 2 can be easily scraped off.

That is, in order to realize the slipping of the toner and to lubricate the photosensitive member 2 and the polishing blade 3, a highly fluid toner is used, and the high-hardness polishing blade 3 is applied to the photosensitive member with a low contact load. It is preferable to make it contact | abut 2 surface. More specifically, the circularity is 0 as the toner.
. 96 or more are used, and the contact load of the polishing blade 3 to the photosensitive member 2 is 25 g.
/ Cm or less, more preferably 20 g / cm or less. In particular, in order to obtain a high slip-through effect, it is desirable that the toner has a small particle diameter, for example, a volume average particle diameter of 5 μm.
m or less is desirable.

The polishing blade 3 preferably has a JIS-A hardness of 85 degrees or more. When using a material having a lower hardness, it is necessary to reduce the contact load on the photoreceptor 2 accordingly. For example, it is preferable to use a polishing blade having a JIS-A hardness of 65 degrees or more with a contact load of 20 g / cm or less.

As described above, in this embodiment, the toner has a volume average particle diameter of 4.5 μm and a circularity of 0.97.
The polishing blade 3 was made to abut on the photoreceptor 2 at a contact angle of 10 degrees and a contact load of 13 g / cm with a polyurethane rubber blade having a JIS-A hardness of 74 degrees.
According to such a configuration, the image forming process can be executed in a state where a substantially constant amount of positively charged particles are adhered on the photoreceptor 2, and the abrasion of the photoreceptor 2 by the polishing blade 3 and the polishing blade 3 Chipping and deformation could be suppressed. At the end of the image formation process,
By stopping the photoconductor 2 in accordance with the procedure shown in FIG. 9, it is possible to stop the photoconductor 2 with the positively charged particles remaining on the photoconductor 2, and this acts as a lubricant at the next start-up and performs photosensitivity. An increase in the starting torque of the body 2 could be prevented.

Even when the toner passes through between the photosensitive member 2 and the polishing blade 3 in this way, the effect of polishing the fixed matter such as a discharge product fixed on the surface of the photosensitive member 2 is not reduced. The point is confirmed by observing the surface of the photoreceptor 2.

FIG. 13 is a diagram showing a second embodiment of the image forming apparatus according to the present invention. In this figure, the same reference numerals as those in FIG. 1 are assigned to those having the same structure and function as the apparatus of the first embodiment described above. In the first embodiment shown in FIG. 1, the peeling position S is located downstream of the transfer position TP.
P is provided, and further, a cleaning position BP is provided downstream thereof. In contrast, FIG.
In the second embodiment, the positional relationship between the polishing blade 3 and the cleaning roller 4 is switched, and the cleaning position BP is disposed downstream of the transfer position TP, and the separation position SP is disposed downstream thereof. The advantages and disadvantages of the first and second embodiments are compared as follows.

In the first embodiment, the toner or the like that has passed through the polishing blade 3 is removed from the cleaning position BP.
Therefore, even if the toner is negatively charged by sliding with the polishing blade 3 at the peeling position SP, the charging polarity is applied by the cleaning roller 4 to which a positive cleaning bias is applied. Can be reversed or attached to the brush bristles 4b for recovery. For this reason, the negatively charged particles are not transported to the charging position CP and the developing position DP and do not cause background fogging. On the other hand, the untransferred toner that has not been transferred from the exposed portion of the photoreceptor 2 to the intermediate transfer belt 8a at the transfer position TP contacts the polishing blade 3 while remaining on the photoreceptor 2, so that the exposed portion and the non-exposed portion Due to the difference in the toner density, there is a possibility that the polishing effect will be different between the exposed part and the non-exposed part.

On the other hand, in the second embodiment, the transfer residual toner is collected by the cleaning roller 4, and therefore, the difference between the exposed portion and the non-exposed portion is small. However, since the negatively charged particles due to the rubbing with the polishing blade 3 are sent to the charging position CP as they are, the negatively charged particles whose charge amount is further increased by the charger 5 remain on the photoreceptor 2. If it is transferred to the intermediate transfer belt 8a, it causes background fogging.

Thus, while the second embodiment is advantageous from the viewpoint of obtaining a uniform polishing effect by the polishing blade 3, the first embodiment can be said to be more advantageous from the viewpoint of suppressing ground fog.

As described above, in each of the above-described embodiments, the photoreceptor 2, the charger 5, the exposure unit 6, the development unit 7, the transfer unit 8, and the polishing blade 3 are the “latent image carrier”, “charging” of the present invention, respectively. Means ”,“ latent image forming means ”,“ developing means ”,“ transfer means ”, and“ peeling means ”. Further, the developing roller 7a and the intermediate transfer belt 8a function as the “toner carrier” and “transfer medium” of the present invention, respectively.

In each of the above embodiments, the CPU 101 functions as the “control unit” of the present invention, while the cleaning roller 4 functions as the “cleaning unit” of the present invention.

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, each numerical value shown in the description of the above embodiment is merely an example, and the present invention is not limited thereto. In addition, the cleaning bias applied to the cleaning roller 4 may be not only a direct current potential as in the above embodiment, but also an alternating current potential superimposed on the direct current potential. In this case, the average potential of the cleaning bias may be opposite to the normal charging polarity of the toner.

The above-described embodiment is a so-called negative latent image type image forming apparatus in which toner is attached to a region of the charged surface of the photosensitive member 2 from which the electric charge has been removed by exposure. The region (exposed portion) is the “image portion” in the present invention to which the toner is to be attached, while the non-exposed region (non-exposed portion) is the “non-image portion” in the present invention. However, the present invention can also be applied to a so-called positive latent image type image forming apparatus in which toner is attached to a region where charge is generated by exposure. In this case, the exposed area on the photoconductor is the “image area”, and the unexposed area is the “non-image area”. In this embodiment, negatively charged toner is used. However, the present invention can be applied to an image forming apparatus using positively charged toner. In this case, the potential relationship of each part may be reversed from the above.

Further, the image forming apparatus of the above embodiment is an apparatus that forms an electrostatic latent image by exposing the uniformly charged surface of the photosensitive member 2 by the exposure unit 6, but the surface of the charged latent image bearing member is formed. As long as an electrostatic latent image can be formed, a latent image forming unit other than that by exposure as described above may be used.

Further, the surface structure of the developing roller 7a in the present embodiment is a convex portion 7 having a substantially rhombic top surface.
41 and a concave portion 742 provided so as to surround it are regularly arranged, but the shape of the convex portion and the surface structure of the developing roller are not limited thereto. In addition to this, for example, a structure in which a large number of dimples are provided on a substantially smooth envelope cylindrical surface or a structure in which a spiral groove is provided can be used. The present invention can also be applied to the case of using a developing roller having a roughened surface by blasting that has been conventionally used.

In the above embodiment, the number of the developing units 7 is not particularly mentioned. However, the present invention is not limited to a color image forming apparatus in which a plurality of developing units are mounted on a rotatable rotary developing unit, or a plurality of developing units are intermediate-transferred. The present invention can be suitably applied to a so-called tandem type image forming apparatus arranged around a medium, a monochrome image forming apparatus that includes only one developing unit and forms a monochrome image, and the like.

1 is a diagram schematically showing the main configuration of a first embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. FIG. 3 is a cross-sectional view showing a structure of a developing unit in this embodiment. The figure which shows the image development roller and the elements on larger scale of the surface. Sectional drawing which shows the detail of the structure of the developing roller surface. FIG. 4 is a diagram illustrating a toner charge amount distribution. The figure which shows the relationship of the electric potential provided to each part in this embodiment. The figure which shows typically the phenomenon which arises on the surface of a photoreceptor. 6 is a timing chart showing an operation of an image forming process. The figure which shows typically the state of the photoreceptor surface after rotation stop. The figure which shows the experimental result when changing the particle size and circularity of a toner. The figure which shows the experimental result when changing the hardness of a grinding | polishing blade. FIG. 4 is a diagram illustrating a second embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

2 ... photosensitive body (latent image carrier), 3 ... polishing blade (peeling means), 4 ... cleaning roller (cleaning means), 5 ... charger (charging means), 6 ... exposure unit (latent image forming means), 7 DESCRIPTION OF SYMBOLS Developing unit (developing unit) 7a Developing roller (toner carrier) 8 Transfer unit (transfer unit) 8a Intermediate transfer belt (transfer medium) 101 CPU (control unit) 741 Projection 742 ... Recess, BP ... Cleaning position, CP ... Charging position, DP ... Developing position, EP ... Exposure position (latent image forming position), SP ... Peeling position, TP
... Transfer position

Claims (7)

A latent image carrier that circulates in a predetermined rotational direction;
Charging means for charging the surface to a potential having the same polarity as the normal charging polarity of the toner at a predetermined charging position without contacting the surface of the latent image carrier;
By making the potential of the surface of the latent image carrier charged at a latent image forming position downstream of the charging position in the rotation direction different between an image portion to which toner is attached and a non-image portion to which toner is not attached. Latent image forming means for forming an electrostatic latent image on the surface of the latent image carrier;
And a toner carrying member disposed in a non-contact facing manner with respect to the latent image carrying member at a developing position downstream of the latent image forming position in the rotation direction, and the toner carrying member carries charged toner on the surface thereof. Developing means for transporting to the developing position and applying an alternating voltage as a developing bias to develop the electrostatic latent image as a toner image;
Transfer means for transferring the toner image to the transfer medium by bringing the transfer medium into contact with the latent image carrier at a transfer position downstream of the development position in the rotation direction;
A peeling means that slides on the surface of the latent image carrier at a peeling position downstream of the transfer position in the rotation direction and peels off the residual deposit on the surface;
Control means for controlling each part of the apparatus and executing an image forming process,
After the execution of the image forming process, the control means has at least one of toner and an external additive released from the toner in a predetermined area on the surface of the latent image carrier including the peeling position and the upstream area in the rotation direction. In the state of being charged with a polarity opposite to the normal charging polarity of the toner to stop the movement of the latent image carrier. The peeling means has an edge portion extending along a direction orthogonal to the rotation direction, and the edge portion is in contact with the surface of the latent image carrier,
The transfer medium has a polarity opposite to the normal charging polarity of the toner, and does not cause discharge between the image portion of the latent image carrier and the transfer medium, and the non-image portion of the latent image carrier and the transfer The image forming apparatus according to claim 1, wherein a direct-current potential that causes electric discharge with the medium is applied as a transfer bias. The control means stops the supply of the developing bias to the toner carrier when finishing the image forming process, and then continues to apply the transfer bias to the transfer medium, while the latent image carrier 3. The circular movement of the latent image carrier is stopped after the latent image carrier is moved by a distance corresponding to a distance between the development position and the transfer position on the surface.
The image forming apparatus described in 1. The toner carrier carries on its surface a toner layer containing both a contact toner that is in direct contact with the surface of the toner carrier and a non-contact toner that is not in direct contact with the surface of the toner carrier.
4. The image forming apparatus according to any one of items 3 to 3. Contact with a potential opposite to the normal charging polarity of the toner at a cleaning position downstream of the transfer position and upstream of the peeling position or downstream of the peeling position in the rotational direction. 5. The image forming apparatus according to claim 1, further comprising a cleaning unit that contacts the member to remove the toner and the external additive charged to the normal polarity on the latent image carrier. The image forming apparatus according to claim 1, wherein a volume average particle diameter of the toner is 5 μm or less. Around the latent image carrier that circulates in a predetermined rotation direction, along the rotation direction,
Charging means for charging the surface to a potential having the same polarity as the normal charging polarity of the toner at a predetermined charging position without contacting the surface of the latent image carrier;
By making the potential of the surface of the latent image carrier charged at a latent image forming position downstream of the charging position in the rotation direction different between an image portion to which toner is attached and a non-image portion to which toner is not attached. Latent image forming means for forming an electrostatic latent image on the surface of the latent image carrier;
A toner carrying member disposed in a non-contact facing manner with respect to the latent image carrying member at a developing position downstream of the latent image forming position in the rotation direction, the toner carrying member carrying charged toner on the surface thereof; Developing means for transporting to the developing position and applying an alternating voltage as a developing bias to develop the electrostatic latent image as a toner image;
Transfer means for transferring the toner image to the transfer medium by bringing the transfer medium into contact with the latent image carrier at a transfer position downstream of the development position in the rotation direction;
An image forming process is performed by arranging in this order with a peeling unit that slides on the surface of the latent image carrier at a peeling position downstream of the transfer position in the rotation direction and peels off the residual deposits on the surface. Moreover,
After execution of the image forming process, at least one of the toner and the external additive released from the toner is applied to a predetermined region of the surface of the latent image carrier including the peeling position and the upstream region in the rotation direction. An image forming method, wherein the latent image carrier is stopped by remaining attached in a state of being charged to a polarity opposite to the charged polarity.

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