JP2019101108A - Image forming apparatus - Google Patents

Abstract

To solve the problem that it is difficult to improve the transferability of a toner image in a transfer part, while stabilizing the rotation of a photoreceptor, in a cleanerless configuration.SOLUTION: An image forming apparatus 100 includes a controller circuit 23 which controls the rotational speed of at least one of a photoreceptive drum 1 and a transfer roller 8 and exposure means 7 which is arranged on the upstream side of a transfer part Nt and on the downstream side of developing means 5 in the rotational direction of the photoreceptive drum 1. In such a state that the photoreceptive drum 1 carrying a toner image is exposed by the exposure means 7, the controller circuit 23 controls the rotational speed of at least one of the photoreceptive drum 1 and the transfer roller 8, so that the rotational speed of the transfer roller 8 is lower than the rotational speed of the photoreceptive drum 1.SELECTED DRAWING: Figure 1

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus such as a copier, a printer or the like using an electrophotographic method.

  A conventional image forming apparatus using an electrophotographic method includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) carrying a toner image, and includes a charging step, an exposure step, a developing step, a transfer step, and a fixing step. To form an image on a transfer material such as paper or an OHP sheet. In the transfer step, the transfer material or the intermediate transfer is transferred from the photosensitive member at a transfer portion where the rotatable transfer member or intermediate transfer member (hereinafter referred to as transfer means) disposed at a position facing the photosensitive member abuts the photosensitive member. The toner image is electrostatically transferred to the body.

  Patent Document 1 discloses a so-called cleanerless configuration that does not have a cleaning member that contacts the photosensitive member and recovers the toner remaining on the photosensitive member after transferring the toner image from the photosensitive member to the transfer material. ing. In the cleaner-less configuration of Patent Document 1, the toner remaining on the photosensitive member is recovered by the developing unit after it moves with the rotation of the photosensitive member.

  In Patent Document 2, a speed difference is provided between the rotational speed of the photosensitive member and the rotational speed of the intermediate transfer member to reduce the physical adhesion of the toner to the photosensitive member, thereby transferring the photosensitive member to the intermediate transfer member. A configuration is disclosed that improves the transferability of transferring a toner image.

JP 2003-330252 A Patent No. 3997137

  In the cleanerless configuration, since the cleaning member in contact with the photosensitive member is not provided, the load for rotationally driving the photosensitive member is small compared to the conventional configuration. That is, in the cleanerless configuration, when the speed difference as shown in Patent Document 2 is provided to improve the transferability, the photosensitive member may be accompanied by the rotation of the transfer means, and the rotation of the photosensitive member may not be stabilized. is there.

  On the other hand, when the rotational speed of the transfer body is set slower than the rotational speed of the photosensitive body to provide a speed difference, it is possible to stabilize the rotational speed of the photosensitive body by preventing the photosensitive body from being taken by the transfer means. it is conceivable that. However, in this case, since the rotational speed of the transfer means is slower than the rotational speed of the photosensitive member, the toner image carried on the photosensitive member moves upstream with respect to the rotational direction of the photosensitive member at the transfer portion. That is, part of the toner image carried on the photosensitive member moves to the non-image portion where the potential different from the image portion carrying the toner image is formed on the surface of the photosensitive member. As a result, a part of the toner that should be transferred to the transfer material or the intermediate transfer member is not transferred to the transfer material or the intermediate transfer member, which may cause a transfer failure.

  In view of the above, it is an object of the present invention to improve the transferability of a toner image in a transfer portion while stabilizing the rotation of a photosensitive member in a cleanerless configuration.

  The present invention comprises a photosensitive member that is rotatable and carries a toner image, a first exposure unit that exposes the photosensitive member to form an electrostatic latent image on the photosensitive member, and is formed on the photosensitive member. Developing means for developing the electrostatic latent image with toner to form a toner image, and rotatable, in contact with the photosensitive member to form a transfer portion, and carried on the photosensitive member at the transfer portion An image forming apparatus comprising: transfer means for transferring a toner image, wherein the toner remaining on the photosensitive member after passing through the transfer portion can be recovered by the developing means, the rotational direction of the photosensitive member A second exposure unit disposed upstream of the transfer unit and downstream of the developing unit for exposing the photosensitive member, and the photosensitive member carrying a toner image by the second exposure unit Before exposing the body A control unit configured to control at least one of the rotational speed of the photosensitive member and the rotational speed of the transfer unit such that the rotational speed of the transfer unit is slower than the rotational speed of the photosensitive member; .

  According to the present invention, in the cleanerless configuration, the transferability of the toner image in the transfer portion can be improved while stabilizing the rotation of the photosensitive member.

FIG. 1 is a schematic cross-sectional view illustrating the configuration of an image forming apparatus according to a first embodiment. FIG. 1 is a block diagram of a first embodiment. 6 is a schematic graph illustrating the change in the potential of the photosensitive member when the photosensitive member is exposed by the second exposure unit in Example 1. In Example 1, it is a schematic diagram explaining the relationship of the various electric potential of the photoreceptor in the back and front exposed by a 2nd exposure means. In Example 1, it is a graph which shows transition of the transfer residual density when changing the electric current which flows to a photoreceptor from a transfer means. FIG. 7 is a schematic view illustrating the relationship between the potential of the photosensitive member and the occurrence of image defects in Example 1 and Comparative Example 3. FIG. 7 is a schematic view for explaining the relationship between the background potential of the photosensitive member after being exposed by the second exposure unit and the potential of the toner carried on the photosensitive member in Example 2; FIG. 10 is a schematic cross-sectional view for explaining the configuration of an image forming apparatus in another embodiment.

  Hereinafter, preferred embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, etc. of the components described in the following examples should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions, and the present invention It is not intended to limit the present invention to the following examples.

Example 1
[Configuration of image forming apparatus]
FIG. 1 is a schematic cross-sectional view for explaining the configuration of the image forming apparatus 100 of the present embodiment, and FIG. 2 is a block diagram of a control system of the image forming apparatus 100 of the present embodiment. As shown in FIG. 2, the image forming apparatus 100 is connected to a personal computer 21 which is a host device. The operation start instruction from the personal computer 21 and the image signal are transmitted to a controller circuit 23 as a control unit built in the image forming apparatus 100. Then, the controller circuit 23 controls the various units to execute image formation in the image forming apparatus 100. The controller circuit 23 can control various units based on detection results input from various control units or information input to the image forming apparatus 100 by the user.

  As shown in FIG. 1, the image forming apparatus 100 of this embodiment has a photosensitive drum 1 which is rotatable and is a drum-shaped photosensitive member having an outer diameter of 20 mm. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed in the direction of the arrow R1 in response to the driving force from the driving source M. A developing unit 5 having a charging roller 2, a charging power source 3 for applying a voltage to the charging roller 2, an exposure unit 4 (first exposure unit), and a developing roller 5a as a developing member around the photosensitive drum 1 And are arranged. The developing means 5 contains toner, and the developing roller 5a carries the toner contained in the developing means 5 when a voltage having a polarity opposite to the regular charging polarity of the toner is applied from the developing power source 6. Is possible.

  At a position facing the photosensitive drum 1, a transfer roller 8 as a transfer unit that contacts the photosensitive drum 1 to form a transfer portion Nt is disposed. A fixing unit 14 is provided downstream of the transfer portion Nt with respect to the transfer direction of the transfer material P. The image forming apparatus 100 further includes a sheet feeding cassette 9 as a storage unit for storing a transfer material P such as paper or an OHP sheet, and a loading unit for loading the transfer material P discharged from the image forming apparatus 100 after an image is formed. And the paper discharge tray 17 as

  When the controller circuit 23 (shown in FIG. 2) receives an image signal, an image forming operation is started, and the photosensitive drum 1 is rotationally driven. During the rotation process, the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging roller 2 to which a voltage of a predetermined polarity (negative in this embodiment) is applied from the charging power source 3. Thereafter, exposure according to the image signal is performed by the exposure unit 4 to form an electrostatic latent image corresponding to the target image on the surface of the photosensitive drum 1. The electrostatic latent image is developed by the developing roller 5 a carrying toner at a developing portion G where the developing roller 5 a and the photosensitive drum 1 abut, and is visualized on the photosensitive drum 1 as a toner image.

  In this embodiment, the normal charging polarity of the toner contained in the developing means 5 is negative, and the electrostatic latent image is reversely developed by the toner charged to the same polarity as the charging polarity of the photosensitive drum 1 by the charging roller 2. ing. However, the present invention is not limited to this, and the present invention can be applied to an image forming apparatus that positively develops an electrostatic latent image with toner charged to a polarity opposite to that of the photosensitive drum 1. Further, in the present embodiment, a contact developing method is employed in which the developing roller 5a carrying toner is brought into contact with the photosensitive drum 1 to develop an electrostatic latent image. However, the invention is not limited to this, and a non-contact developing method such as a jumping developing method may be used.

  The toner image formed on the photosensitive drum 1 is supplied from the transfer power source 18 to the transfer roller 8 at the transfer portion Nt by applying a voltage of the reverse polarity (positive in this embodiment) to the regular charging polarity of the toner. The image is transferred onto a transfer material P fed from a paper cassette 9. The transfer material P conveyed to the transfer portion Nt is conveyed from the sheet cassette 9 toward the conveyance roller 11 by the feed roller 10 and then conveyed to the transfer portion Nt by the conveyance roller 11. Further, the transfer material P is held in the transfer portion Nt after its leading end is detected by a sensor (not shown) provided on the upstream side of the transfer portion Nt in the transport direction of the transfer material P, and the toner image is transferred from the photosensitive drum 1 Transcribed.

  The image forming apparatus 100 in this embodiment has a so-called cleanerless configuration in which the toner remaining on the photosensitive drum 1 is recovered by the developing unit 5 after the toner image is transferred from the photosensitive drum 1 to the transfer material P.

  In the cleaner-less configuration, the photosensitive drum 1 is disposed between the transfer portion Nt and the charging portion where the photosensitive drum 1 and the charging roller 2 are in contact with each other in the rotational direction of the photosensitive drum 1 (the direction of the arrow R1). No abutting blade is provided. Therefore, the toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt is charged to the negative polarity again when passing through the charging portion, and is then collected by the developing means 5 in the developing portion G.

  In the present embodiment, the contact charging method in which the photosensitive drum 1 is charged by the charging roller 2 in contact with the photosensitive drum 1 has been described. However, the present invention is not limited thereto. A non-contact charging method such as a corona charging method may be used. . Even in the image forming apparatus using the non-contact charging method, the toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt passes through the charging portion where the non-contact charging member and the photosensitive drum 1 face each other. At the same time, the toner is charged to the negative polarity again, and is collected by the developing means 5 at the developing portion G.

  Then, the transfer material P to which the toner image is transferred at the transfer portion Nt is conveyed to the fixing unit 14, and is fixed to the transfer material P by being heated and pressed by the fixing unit 14. The transfer material P after the toner image is fixed by the fixing unit 14 is discharged onto the paper discharge tray 17 by the paper discharge roller pair 16. In the image forming apparatus of the present embodiment, an image is formed on the transfer material P by the above operation.

<Configuration of Developing Unit 5>
As shown in FIG. 1, the developing means 5 includes a developing roller 5a as a developing member, a developing blade 5b in contact with the developing roller 5a, a supply roller 5c rotating in contact with the developing roller 5a, and a developing container 5d. , And contains toner. The developing roller 5a is in contact with the photosensitive drum 1 to form a developing portion G, and the developing portion G is rotationally driven in the direction of the arrow R2 so that the photosensitive drum 1 and the developing roller 5a rotate in the same direction. .

  The developing roller 5a has a multilayer structure in which an elastic layer having a base layer and a surface layer thereon is provided around a cylindrical body of aluminum, aluminum alloy or metal such as stainless steel. The base layer of the elastic layer is formed using rubber such as butadiene acrylonitrile rubber (NBR), ethylene-propylene-diene polyethylene (EPDM), silicone rubber, urethane rubber, etc., and the surface layer is formed using ether urethane or nylon etc. . However, the material of the elastic layer is not limited to these, and a foam such as sponge may be used for the base layer, and a rubber elastic layer may be formed on the surface layer. Also, the elastic layer may be a single-layer structure constituted only of a rubber elastic layer such as NBR, EPDM, urethane rubber or the like.

  The developing blade 5b has one end side (fixed end side) supported by the developing container 5d, and the vicinity of the tip of the other end side (free end side) is in contact with the outer peripheral surface of the developing roller 5a in a surface contact state. It is provided. The developing blade 5b is in contact with the developing roller 5a in a so-called counter direction in which the free end side is located upstream of the fixed end with respect to the contact portion with the developing roller 5a.

  In this embodiment, the developing blade 5b is formed by bonding or injection molding a polyamide elastomer as an elastic member to a phosphor bronze plate having a spring elasticity as a metal thin plate. The elastic member is in contact with the surface of the developing roller 5a with a predetermined linear pressure. The pressing force of the developing blade 5b against the developing roller 5a is maintained by the thin metal plate, and when the toner is a negatively chargeable toner, the polyamide elastomer of the elastic member applies an electric charge to the toner. The material of the thin metal plate is not particularly limited as long as it maintains the pressure contact force of the developing blade 5b, and the elastic member can be appropriately selected in consideration of the charging characteristics of the toner used. In addition, a thin metal plate having spring elasticity such as a stainless steel thin plate or a phosphor bronze thin plate may be brought into contact with the developing roller 5a without providing an elastic member.

  The supply roller 5c is disposed in contact with the development roller 5a, and the arrow shown in the figure so that the rotational direction of the development roller 5a and the supply roller 5c is opposite (counter direction) at the contact portion with the development roller 5a. It is rotationally driven in the R3 direction. The supply roller 5c uses a sponge structure or a fur brush structure in which fibers such as rayon and nylon are flocked on a core metal in consideration of supply of toner to the development roller 5a and peeling of toner from the development roller 5a. Is preferred. In the present embodiment, an elastic roller provided with a urethane foam on a cored bar is used as the supply roller 5c.

  The toner used in this embodiment is a nonmagnetic one-component developer, and the toner carried on the developing roller 5a is carried on the developing roller 5a by the mirror force by the charge of the toner and a slight van der Waals force. ing. Therefore, when the toner layer carried on the developing roller 5a is thick, the force acting between the toner in the upper layer portion of the toner layer and the developing roller 5a is weak, so the toner in the upper layer portion which can not be carried on the developing roller 5a Is scattered.

  For this reason, it is necessary to thinly regulate the toner layer carried on the developing roller 5a by the developing blade 5b, but it may be difficult to obtain sufficient image density by regulating the toner layer thinly. Therefore, in the present embodiment, by setting the rotational speed of the developing roller 5a faster than the rotational speed of the photosensitive drum 1, a sufficient image density is secured. The speed difference provided between the developing roller 5 a and the photosensitive drum 1 is preferably such that the rotational speed of the developing roller 5 a is 1.1 to 3 times the rotational speed of the photosensitive drum 1. In the present embodiment, the rotational speed of the developing roller 5 a is set to 1.3 times the rotational speed of the photosensitive drum 1.

  As the toner, a pulverized toner, or a chemical toner obtained by suspension polymerization, emulsion aggregation, dissolution suspension polymerization method or the like can be used. In this embodiment, spherical particles having a median particle diameter of 7 μm obtained by the suspension polymerization method are used, and silica particles having a primary particle diameter of about 15 nm with respect to the weight of the toner are used in order to secure the fluidity of the toner. A total of 0.5 copies are attached.

  In the image forming apparatus 100 of the present embodiment, the following conditions are suitable as the conditions of the electrostatic latent image formed on the photosensitive drum 1. In the case of using toner having a negative regular charge polarity, the potential of the non-image area (hereinafter referred to as background potential Vd) is preferably in the range of -500 to -1000V. The potential of the image portion where the maximum toner image density can be obtained (hereinafter referred to as latent image potential Vl) is preferably in the range of -50 to -200V. When a toner having a positive regular charge polarity is used, the background potential Vd is preferably in the range of +500 to +1000 V, and the latent image potential V1 at which the maximum toner image density can be obtained is preferably in the range of +50 to +200 V. . In the present embodiment, the image portion is an area on the photosensitive drum 1 on which the toner image corresponding to the image information is carried, and the non-image portion is a toner image corresponding to the image information on the photosensitive drum 1 Is an area that does not carry

  When the electrostatic latent image formed on the photosensitive drum 1 is developed with toner, a developing voltage Vdc, which is a DC voltage, is applied from the developing power supply 6 to the developing roller 5a. In the present embodiment, when the electrostatic latent image is formed under the above conditions, the following conditions are suitable as the conditions for the development voltage Vdc. That is, a range in which the development contrast potential | Vc | (hereinafter referred to as the potential | Vc |), which is a potential difference between the development voltage Vdc and the latent image potential Vl, is preferably 50 to 400V.

  Further, in the cleanerless configuration, the back contrast potential | Vb |, which is the potential difference between the developing voltage Vdc and the background potential Vd, in order to improve the recovery of the toner remaining on the photosensitive drum 1 by the developing means 5. It is preferable to increase the potential | Vb |). By increasing the potential | Vb |, the toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt is pulled back to the developing roller 5a. Can improve the recovery of From the above, in this embodiment, Vd = -900 V, Vl = -100 V, Vdc = -300 V, | Vc | = 200 V, | Vb | = 600 V.

<Configuration of Transfer Roller 8>
As shown in FIG. 1, a rotatable transfer roller 8 as transfer means is in contact with the surface of the photosensitive drum 1 with a predetermined pressure (1 kgf in this embodiment) to form a transfer portion Nt. The transfer roller 8 is configured by providing an elastic layer formed of conductive rubber around the core metal, and rotates in synchronization with the rotation of the photosensitive drum 1 during image formation. The end of the core metal of the transfer roller 8 is connected to a pulse motor via a gear, and the transfer roller 8 has its rotational speed controlled by the controller circuit 23. In this embodiment, the rotational speed of the transfer roller 8 is set to 152 mm / sec, which is 5% slower than the rotational speed of the photosensitive member (160 mm / sec).

  Here, since the transfer roller 8 is softer than the photosensitive drum 1 and the contact area with the transfer material P at the transfer portion Nt is large, the moving speed of the transfer material P nipped by the transfer Nt is approximately equal to the rotational speed of the transfer roller 8 It will be the same. That is, the moving speed of the transfer material P in the transfer portion Nt is 5% slower than 160 mm / sec, which is the rotational speed of the photosensitive drum 1.

The electrical resistance value of the transfer roller 8 is preferably adjusted to 10 ⁶ to 10 ¹⁰ Ω. In the transfer roller 8 of this embodiment, the diameter of the elastic layer is φ14 mm, the diameter of the core metal is φ6 mm, and the thickness of the elastic layer is 4 mm over the entire longitudinal direction which is a direction intersecting the transfer direction of the transfer material P. It is set. The rubber of the elastic layer of the transfer roller 8 is a foam type NBR rubber, and the electric resistance value of the transfer roller 8 is 1.0 × 10 ^{8 in} a standard environment (room temperature 23 ° C., humidity 50%). It is Ω.

<Configuration of Exposure Unit 7>
Next, the configuration of the exposure unit 7 (second exposure unit) will be described. The exposure unit 7 is disposed upstream of the transfer portion Nt and downstream of the developing portion G with respect to the rotational direction of the photosensitive drum 1. The exposure unit 7 can discharge the background potential Vd of the photosensitive drum 1 by exposing the surface of the photosensitive drum 1 between the developing portion G and the transfer portion Nt in the rotational direction of the photosensitive drum 1. That is, the exposure unit 7 can change the background potential Vd of the photosensitive drum 1 before carrying the toner image by exposing the photosensitive drum 1 before passing through the transfer portion Nt.

  As the exposure means 7, an exposure means such as a laser scanner device, an LED print head system, an LED array system, a liquid crystal shutter array system or the like can be used. Alternatively, an LED lamp may be provided on the side of the main body of the image forming apparatus 100, and the surface of the photosensitive drum 1 may be irradiated through a light guide or the like. In the present embodiment, an LED array system is used as the exposure means 7.

  FIG. 3 is a schematic graph showing the relationship between the current Ie flowing through the exposure unit 7 and the background potential Vd ′ of the photosensitive drum 1 after exposure when the exposure unit 7 exposes the photosensitive drum 1. The control power supply is connected to the exposure unit 7. As the value of the voltage output from the control power supply is increased, the current Ie flowing through the exposure unit 7 is increased, and the light amount of the exposure unit 7 can be increased. In this embodiment, the background potential Vd 'after exposure by the exposure unit 7 is -500 V, as opposed to -900 V, which is the background potential Vd when the toner image is developed on the photosensitive drum 1 by the development unit 5. The light quantity of the exposure means 7 was adjusted.

  FIG. 4 (a) is a schematic view for explaining various potentials on the photosensitive drum 1 before being exposed by the exposure unit 7, and FIG. 4 (b) is for the photosensitive drum 1 after being exposed by the exposure unit 7. It is a schematic diagram explaining various electric potentials. As shown in FIG. 4 (b), although the exposing means 7 exposes almost the entire surface of the photosensitive drum 1, the light from the exposing means 7 is shielded by the toner at the position carrying the toner image. The image potential Vl hardly changes.

[Image evaluation]
In the present embodiment, image evaluation in the image forming apparatus 100 was performed using the following method. First, with respect to five transfer materials P, a halftone image with a 50% density toner was formed on the entire image area of the transfer material P. Then, among the five transfer materials P on which the halftone image is formed, when a linear image defect (hereinafter referred to as a horizontal stripe) occurs in the width direction intersecting the transfer material conveyance direction, the lateral stripes The numbers were visually counted and evaluated for the occurrence of image defects. As a standard of evaluation, among five transfer materials P, the one in which even one horizontal stripe did not occur was marked with ○, and the one in which horizontal stripe occurred was marked ×.

  Next, after the toner image is transferred to the transfer material P at the transfer portion Nt, the amount of toner remaining on the photosensitive drum 1 and the toner remaining on the photosensitive drum 1 are generated in the image formed on the subsequent transfer material P The level of image defect (ghost) was confirmed. In this embodiment, since the cleaner-less configuration is used, when the amount of toner remaining on the photosensitive drum 1 is excessively large, the transfer material P that is to be transferred onto the preceding transfer material P follows By being transferred to the image, an image defect called a ghost may occur.

  As the evaluation image pattern, with respect to the transport direction of the transfer material P, 10 dots long width horizontal lines were formed every 20 spaces at a resolution of 600 dpi. As the developing means 5, 70 g of toner was filled in the developing container 5d, and used after 5000 sheets of an image having an image printing rate of 1% were used. The evaluation of the ghost level is performed by visually evaluating the transfer material P on which the evaluation image pattern is formed, rank A where the ghost did not appear, rank B where the ghost slightly appeared, and where the ghost clearly appeared Was judged to be rank C. The ghost appears after the photosensitive drum 1 has rotated about one turn than the position of the longitudinal width horizontal line which should have been originally formed.

  Further, the density (transfer residual density) of the toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt was measured using the following method. First, the toner remaining on the photosensitive drum 1 is collected with a transparent tape, and after the collected transparent tape is attached to high quality paper, transparent using a Tokyo Denshoku reflection densitometer (DENSITOMETER TC-6DS / A30) The concentration of the amount of toner adhering to the tape was measured. Then, as a reference, one in which a transparent tape not attached with toner is pasted on high quality paper is also measured, and the density measured at this time is used as a reference density, the density of the transparent tape attached with toner and the reference density The residual transfer density was calculated from the difference.

FIG. 5 is a graph showing transition of the transfer residual density Dr when the current Itr flowing from the transfer roller 8 to the photosensitive drum 1 is changed. As shown in FIG. 5, in the evaluation of the transfer residual density in this embodiment, when a current is applied from the transfer roller 8 to the photosensitive drum 1 to transfer a solid image forming a toner image on the entire image area of the transfer material P. It set to current I ₀ (12 μA) at which the transfer residual density is minimum.

In addition, these image evaluations were performed in a standard environment of a room temperature of 23 ° C. and a humidity of 50%. Further, as the transfer material P, Vitality (a basis weight of 75 g / m ² ) manufactured by Xerox Corporation was used.

  Here, configurations of comparative examples 1 to 5 with respect to the configuration of the present embodiment will be described. In the following description, the same reference numerals are given to parts common to the present embodiment and the description will be omitted. Further, Table 1 is a table for explaining the results of the image evaluation in the present embodiment and Comparative Examples 1 to 5. The speed difference in Table 1 is the rotational speed of the transfer roller 8 with respect to the rotational speed of the photosensitive drum 1. The ratio is shown.

  As shown in Table 1, in Comparative Examples 1 and 2, the rotational speed of the transfer roller 8 is set substantially the same as the rotational speed of the photosensitive drum 1, and the rotational speed between the photosensitive drum 1 and the transfer roller 8 is set. It is set as the structure which does not provide a speed difference. In Comparative Example 1, the exposure unit 7 for exposing the photosensitive drum 1 at the time of transferring the toner image from the photosensitive drum 1 to the transfer material P at the transfer portion Nt is not provided. On the other hand, Comparative Example 2 is configured to include the exposure unit 7 that exposes the photosensitive drum 1 when the toner image is transferred from the photosensitive drum 1 to the transfer material P at the transfer portion Nt.

  In Comparative Example 3, the rotational speed of the transfer roller 8 is set 5% slower than the rotational speed of the photosensitive drum 1, and the photosensitive drum is transferred to the transfer material P from the photosensitive drum 1 at the transfer portion Nt. It is set as the structure which does not provide the exposure means 7 which exposes 1. In Comparative Examples 4 and 5, the rotational speed of the transfer roller 8 is set to a rotational speed (168 mm / sec) that is 5% faster than the rotational speed of the photosensitive drum 1. Further, in the comparative example 4, when transferring the toner image from the photosensitive drum 1 to the transfer material P at the transfer portion Nt, the exposing unit 7 for exposing the photosensitive drum 1 is not provided. On the other hand, Comparative Example 5 is configured to include the exposure unit 7 that exposes the photosensitive drum 1 when the toner image is transferred from the photosensitive drum 1 to the transfer material P at the transfer portion Nt.

  In Comparative Examples 1 and 2 in which the rotational speed of the transfer roller 8 is equal to the rotational speed of the photosensitive drum 1, the physical adhesion of the toner to the photosensitive drum 1 is reduced as compared with the configuration of the present embodiment. Have difficulty. As a result, as shown in Table 1, since the amount of toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt is relatively large, the ghost is slightly visible and the level of occurrence is given as Rank B. It was judged.

  Further, in Comparative Example 4 and Comparative Example 5 in which the rotational speed of the transfer roller 8 is increased by 5% with respect to the rotational speed of the photosensitive drum 1, the photosensitive drum 1 is rotated with the rotation of the transfer roller 8. Rotation became unstable and many horizontal stripes occurred. In the cleanerless configuration, since the collection member such as the blade contacting the photosensitive drum 1 is not provided, the rotational torque of the photosensitive drum 1 tends to be low. Therefore, when the rotational speed of the transfer roller 8 is set to be faster than the rotational speed of the photosensitive drum 1, the photosensitive drum 1 may be rotated by the rotation of the transfer roller 8 as in Comparative Examples 4 and 5.

  On the other hand, according to the configuration of the present embodiment, by setting the rotational speed of the transfer roller 8 to be slower than the rotational speed of the photosensitive drum 1, the rotation of the photosensitive drum 1 is braked relatively. Since the rotation of the drum 1 was stabilized, no lateral streaks occurred.

  FIG. 6 is a schematic view for explaining the relationship between the potential of the photosensitive drum 1 and the occurrence of an image defect when the toner image is transferred from the photosensitive drum 1 to the transfer material P in the transfer portion Nt. As shown in FIG. 6, when the rotational speed of the transfer roller 8 is relatively slow with respect to the rotational speed of the photosensitive drum 1, in the configuration of Comparative Example 3 in which the exposure unit 7 is not provided, the photosensitive drum rotates at the transfer portion Nt. The toner image relatively moves upstream with respect to the direction.

  That is, part of the toner image carried at the position where the latent image potential Vl is formed moves to the position where the background potential Vd is formed. Between the position where the background potential Vd is formed and the transfer roller 8, a potential difference larger than the potential difference formed between the position where the latent image potential Vl is formed and the transfer roller 8 is formed. Discharge through the layers is likely to occur. When a discharge occurs, the negative charge of the toner moved to the background potential Vd is lost, so the toner is not transferred to the transfer material P and remains on the photosensitive drum 1. When the width of the transfer portion Nt is about 4 mm and the speed difference between the transfer material P and the photosensitive drum 1 is 5%, a band shape in the range of about 0.2 mm (4 mm × 5%) with respect to the transfer direction of the transfer material P Toner remains.

  On the other hand, in the present embodiment, the background potential Vd of the photosensitive drum 1 is attenuated to the background potential Vd '(-500 V) at the transfer portion Nt due to the configuration in which the photosensitive drum 1 is exposed by the exposure unit 7. Thereby, the discharge generated between the position where the background potential Vd 'is formed and the transfer roller 8 can be suppressed. Furthermore, by providing a speed difference between the rotational speed of the photosensitive drum 1 and the rotational speed of the transfer material P, the physical adhesion of the toner to the photosensitive drum 1 at the transfer portion Nt is reduced, and the transferability is improved. It is possible to As a result, according to the configuration of the present embodiment, image defects such as horizontal stripes and ghosts did not occur.

  As the rotational speed of the transfer roller 8 is set slower with respect to the rotational speed of the photosensitive drum 1, the speed difference at the transfer portion Nt is greater, and the amount of toner remaining on the photosensitive drum 1 after passing through the transfer portion Nt is reduced. The effect of However, if it is set too late, violent rubbing may occur at the transfer portion Nt, and a phenomenon in which a line of a toner image transferred to the transfer material P may appear dusty (hereinafter, referred to as line bleeding) may occur. Table 2 shows the results of visual confirmation of the ghost generation level and the line bleeding generation level when the rotational speed of the transfer roller 8 with respect to the photosensitive drum 1 is changed.

  As shown in Table 2, when the rotational speed of the transfer roller 8 is lower than -0.5%, the effect of reducing the physical adhesion of the toner to the photosensitive drum 1 is sufficiently exhibited, and the ghost does not occur. On the other hand, when the rotational speed of the transfer roller 8 was decreased to -10%, the occurrence of line bleeding was confirmed although within an allowable range. Therefore, the rotational speed of the transfer roller 8 relative to the rotational speed of the photosensitive drum 1 is more preferably set to 0.5% or more and less than 10%.

  As described above, according to the configuration of the present embodiment, it is possible to improve the transferability when transferring a toner image from the photosensitive drum 1 to the transfer material P while stabilizing the rotation of the photosensitive drum 1. .

  In this embodiment, the rotational speed of the transfer roller 8 is controlled to be slower than the rotational speed of the photosensitive drum 1 by a pulse motor connected to the transfer roller 8. However, the present invention is not limited to this, as long as the rotational speed of the transfer roller 8 can be set slower than the rotational speed of the photosensitive drum 1, the control means may set the rotational speed of the photosensitive drum 1 and the rotational speed of the transfer roller 8 It is sufficient to control at least one. That is, only the rotational speed of the photosensitive drum 1 may be controlled by the control means to provide the speed difference, or the rotational speeds of both the photosensitive drum 1 and the transfer roller 8 may be controlled to provide the speed difference. .

(Example 2)
In the first embodiment, the background potential Vd ′ after exposure by the exposure unit 7 is −500 V with respect to −900 V, which is the background potential Vd when the toner image is developed on the photosensitive drum 1 by the development unit 5. The configuration for setting the current Ie flowing to the exposure unit 7 has been described. On the other hand, in the present embodiment, a configuration will be described in which the amount of light emitted from the exposure unit 7 to the photosensitive drum 1 is made variable by adjusting the current Ie flowing through the exposure unit 7. In the following description, parts that are the same as in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

  Table 3 is a table for explaining the values of the current Ie flowing through the exposure means 7 and the image evaluation results in Examples 1 to 2 and Modifications 5 and Comparative Examples 6 to 7. As shown in Table 3, in the present embodiment, the background potential Vd 'of the photosensitive drum 1 after exposure by the exposure unit 7 is set to -400 V by increasing the value of the current Ie compared to the first embodiment. ing. In the fifth modification, the background potential Vd ′ of the photosensitive drum 1 after exposure by the exposure unit 7 is set to −300 V by further increasing the value of the current Ie. The developing voltage Vdc in the present embodiment is -300 V, and in the configuration of the present embodiment and the fifth modification, the background potential Vd 'and the developing voltage Vdc have a relationship of background potential | Vd' | ≧ development voltage | Vdc | I meet.

  Further, in the configurations of Comparative Example 6 and Comparative Example 7, the exposure means is provided with a current Ie such that the absolute value of the background potential Vd 'of the photosensitive drum 1 after exposure by the exposure means 7 is smaller than the absolute value of the development voltage Vdc. It is flowing to 7. That is, in Comparative Examples 6 to 7, the background potential Vd ′ of the photosensitive drum 1 after being exposed by the exposure unit 7 and the developing voltage Vdc satisfy the relationship | background potential Vd ′ | <| development voltage Vdc | , The value of the current Ie flowing to the exposure means 7 is set.

  Furthermore, line sharpness was added to each item described in Example 1 as an evaluation item of image evaluation. When the line of the toner carried on the photosensitive drum 1 is broken, the boundary of the toner image is blurred and the line sharpness is reduced. The evaluation of the line sharpness is performed by visually evaluating the transfer material P on which the evaluation image pattern is formed, and rank A if it is equivalent to the sharpness of Example 1, and rank B if it is slightly inferior to Example 1. The rank C was judged to be far inferior to Example 1.

  As shown in Table 3, in the configurations of the present embodiment and the fifth modification, the line sharpness was at the same level as that of the first embodiment. The smaller the absolute value of the background potential Vd ', the smaller the potential difference between the position where the background potential Vd' is formed and the transfer roller 8. Therefore, the toner layer described in Example 1 is not an image. It is possible to suppress the discharge generated in the part shifted into the partial area. As a result, the transfer residual density also decreases and the transferability is improved.

  However, as shown in Comparative Example 6 and Comparative Example 7, when the absolute value of the background potential Vd 'after being exposed by the exposure unit 7 is too small, the line sharpness is inferior to that of Example 1. FIG. 7 is a schematic view for explaining the relationship between the background potential Vd ′ of the photosensitive drum 1 after being exposed by the exposure unit 7 and the line sharpness. Hereinafter, the conditions of the background potential Vd 'for maintaining the line sharpness satisfactorily will be described with reference to FIG. 7A and 7B, the potential Vt is the surface potential of the toner carried on the photosensitive drum 1 before being transferred to the transfer material P at the transfer portion Nt after being exposed by the exposure unit 7. Represents

  As shown in FIG. 7A, in the case of potential | Vt | <background potential | Vd '|, an electric field is formed in the direction to restrain the toner layer carried on the photosensitive drum 1, and therefore carried on the photosensitive drum 1. The toner image can be stably present. At this time, considering the electric field at the time of development, the potential | Vt | after passing the developing means 5 is always smaller than the developing voltage | Vdc |, so the potential | Vt | <the developing voltage | Vdc | . Therefore, the following effects can be obtained by controlling the value of the current Ie flowing through the exposure means 7 so as to satisfy the background potential | Vd ′ | ≧ developing voltage | Vdc | be able to. That is, even after being exposed by the exposure unit 7, the toner image can be stably carried on the photosensitive drum 1, and the line sharpness can be maintained well.

  On the other hand, as shown in FIG. 7B, in the case of potential | Vt |> background potential | Vd '|, the potential difference between the potential Vt and the background potential Vd' causes the potential Vt to be between the background potential Vd '. An electric field E is formed in which the toner carried on the photosensitive drum 1 is pulled. As a result, part of the toner carried on the photosensitive drum 1 scatters to the position of the non-image portion where the background potential Vd 'is formed, making it difficult to maintain good line sharpness. As the absolute value of the background potential | Vd ′ | becomes smaller, the electric field E becomes stronger, so the degree of deterioration of the line becomes larger.

  According to the configuration of this embodiment, by controlling the current Ie flowing through the exposure unit 7 so that the absolute value of the background potential Vd 'becomes equal to or higher than the absolute value of the developing voltage Vdc, the toner transferability in the transfer portion Nt can be improved. The amount of light emitted from the exposure means 7 can be made variable while maintaining good. As a result, even when the setting of the development voltage Vdc and the various potentials of the photosensitive drum 1 change according to changes in the surrounding environment of the image forming apparatus 100, the cumulative number of sheets of the transfer material P, and image forming conditions, etc. The means 7 can perform exposure on the photosensitive drum 1 with an appropriate amount of light. This is to predict changes in various conditions from detection means such as an environment sensor provided in the image forming apparatus 100 and count data of the number of sheets to satisfy background potential | Vd ′ | ≧ developing voltage | Vdc | This can be achieved by controlling the exposure means 7.

  Further, in the present embodiment, the configuration has been described in which a DC voltage is applied as the development voltage Vdc. However, not only this, but also in AC development in which an AC voltage is superimposed on a developing voltage Vdc which is a DC voltage, line sharpness is well maintained by satisfying the relationship of background potential | Vd ′ | ≧ development voltage | Vdc | It is self-evident that it is possible.

(Other embodiments)
The above description is given based on the embodiment applied to the monochrome image forming apparatus, but the present invention is not limited to the above embodiment, and as shown in FIG. The present invention can be applied and similar effects can be obtained.

  FIG. 8 is a schematic cross-sectional view for explaining the configuration of the image forming apparatus 300 of this embodiment. As shown in FIG. 8, the image forming apparatus 300 according to the present embodiment includes an image forming unit SY, SM that forms an image of each color of yellow (Y), magenta (M), cyan (C), and black (K). , SC, and SK are arranged at one fixed interval. In the present embodiment, the configuration and operation of the image forming units SY, SM, SC, and SK are substantially the same except that the color of the image to be formed is different. Therefore, the configuration of the image forming apparatus 300 of this embodiment will be described below using the image forming unit SK.

  In the image forming apparatus 300 of the present embodiment, an image signal transmitted from an information device such as a personal computer (not shown) is received and analyzed in the image forming apparatus 300 and transmitted to control means (not shown). Then, an image forming operation is started in the image forming apparatus 300 by a control unit (not shown) controlling various units.

  The image forming unit SK includes a photosensitive drum 301K which is a drum-like photosensitive member, a charging roller 302K as a charging unit, and a developing roller 305K as a developing unit. Further, around the photosensitive drum 1, an exposure unit 304K as a first exposure unit and an exposure unit 307K as a second exposure unit are provided.

  When the image forming operation is started, the photosensitive drum 301 K is rotationally driven at a predetermined circumferential speed in the direction of the arrow R 31 in the drawing, and a predetermined potential with a predetermined polarity (negative in this embodiment) by the charging roller 302 K in the rotation process. Uniformly charged. Thereafter, exposure according to the image signal is received from the exposure unit 304K, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 301K. The electrostatic latent image formed on the surface of the photosensitive drum 301K is developed by the toner supplied from the developing roller 305K, and a toner image is formed on the photosensitive drum 301K.

  An endless intermediate transfer belt 308 as transfer means stretched by tension rollers 326a to 326c as tension members is disposed opposite to the photosensitive drum 301K, and the intermediate transfer belt 308 is in the direction of arrow R32 in the figure. Is driven to rotate. The intermediate transfer belt 308 is rotationally driven by transmitting the driving force from the drive source to any one of the tension rollers 326a to 326c, and the rotational speed of the intermediate transfer belt is equal to the driving force from the drive source. It is controlled by controlling the rotational speed of the transmitted roller. On the inner peripheral surface side of the intermediate transfer belt 308, a primary transfer roller 306K for pressing the intermediate transfer belt 308 against the photosensitive drum 301K is disposed. A primary transfer portion NtK is formed at a position where the intermediate transfer belt 308 pressed by the primary transfer roller 306K and the photosensitive drum 301K abut.

  The photosensitive drum 301K is on the upstream side of the primary transfer portion NtK and downstream of the developing portion where the developing roller 305K and the photosensitive drum 301K contact with respect to the rotational direction of the photosensitive drum 301K (direction of arrow R31). Exposure means 307 K for exposing the light. The exposure unit 307 K can discharge the background potential Vd of the photosensitive drum 301 K by exposing the photosensitive drum 301 K carrying the toner image formed by the developing roller 305.

  The toner image formed on the photosensitive drum 301K is primarily transferred from the photosensitive drum 301K to the intermediate transfer belt 308 in the process of passing through the primary transfer portion NtK. As described above, the toner images of the respective colors are primarily transferred to the intermediate transfer belt 308 at each of the image forming units SY, SM, SC, and SK, and toner images of a plurality of colors corresponding to the target color image are formed on the intermediate transfer belt 308. It is formed.

  In the image forming apparatus 300, with respect to the rotational direction of the photosensitive drum 301K, a recovery member such as a blade abutting on the photosensitive drum 301K is from the primary transfer portion NtK to the charging portion where the photosensitive drum 301K contacts the charging roller 302K. Not provided. That is, the image forming unit SK has a cleanerless configuration. Therefore, the toner remaining on the photosensitive drum 301K after passing through the primary transfer portion NtK is charged to the negative polarity again when passing through the charging portion, and then in the developing portion where the developing roller 5a and the photosensitive drum 1 abut. The toner is collected by the developing means 5.

  A secondary transfer roller 320 is disposed opposite to the tension roller 326a via an intermediate transfer belt 308 as a transfer unit, and a transfer portion is disposed at a position where the intermediate transfer belt 308 and the secondary transfer roller 320 abut. The second transfer portion Nt3 is formed. The secondary transfer roller 320 is connected to the transfer power source 330, and a control unit (not shown) controls the transfer power source 330 to apply a voltage to the secondary transfer roller 320 to transfer the intermediate transfer belt 308 to the transfer material P. The toner images of a plurality of colors are secondarily transferred.

  The transfer material P stacked on the sheet feeding cassette 309 is fed from the sheet feeding cassette 309 by the sheet feeding roller 311 in accordance with the timing when the toner images of a plurality of colors formed on the intermediate transfer belt 308 reach the secondary transfer portion Nt3. The sheet is fed and conveyed to the secondary transfer portion Nt3. The transfer material P on which the toner images of a plurality of colors are secondarily transferred in the secondary transfer portion Nt 3 is heated and pressed in the fixing unit 314, and the toners of the respective colors are melt mixed and fixed to the transfer material P. Thereafter, the transfer material P is discharged by the discharge roller 316 onto the discharge tray 310 as a stacking unit.

  In such a color image forming apparatus 300 as well, by providing a speed difference between the rotational speed of the photosensitive drum 301 and the rotational speed of the intermediate transfer belt 308, the physical adhesion of toner on the photosensitive drum 301 is reduced. It is possible. Thereby, it is possible to improve the transferability when transferring the toner image from the photosensitive drum 301 to the intermediate transfer belt 308.

  Further, as in the first embodiment and the second embodiment, the rotational speed of the intermediate transfer belt 308 is set slower with respect to the rotational speed of the photosensitive drum 301, and the photosensitive drum 301 is exposed by the exposure unit 307. You can get That is, it is possible to improve the transferability at the time of transferring the toner image from the photosensitive drum 301 to the intermediate transfer belt 308 while stabilizing the rotation of the photosensitive drum 301.

Reference Signs List 1 photosensitive drum 5 developing unit 4 exposure unit 7 exposure unit 8 transfer roller 23 controller circuit Nt transfer portion P transfer material

Claims (11)

A photosensitive member that is rotatable and carries a toner image, a first exposure unit that exposes the photosensitive member to form an electrostatic latent image on the photosensitive member, and an electrostatic latent formed on the photosensitive member Developing means for developing an image with toner to form a toner image, and rotatable, are in contact with the photosensitive member to form a transfer portion, and transfer the toner image carried on the photosensitive member at the transfer portion An image forming apparatus including: transfer means for transferring the toner, and the toner remaining on the photosensitive member after passing through the transfer portion can be collected by
A second exposure unit disposed upstream of the transfer unit and downstream of the developing unit with respect to the rotational direction of the photosensitive member and exposing the photosensitive member; and toner by the second exposure unit Among the rotational speed of the photosensitive member and the rotational speed of the transfer means, the rotational speed of the transfer means is slower than the rotational speed of the photosensitive body in a state where the photosensitive body carrying an image is exposed. An image forming apparatus comprising: control means for controlling at least one of the control means;   A charging unit is provided for charging the photosensitive member, and a blade is provided in contact with the photosensitive member between the transfer unit and the position where the photosensitive member and the charging unit are opposed with respect to the rotational direction of the photosensitive member. The image forming apparatus according to claim 1, wherein the image forming apparatus is not provided.   The control means controls the rotational speed of the transfer means to be lower than 0.5% to less than 10% of the rotational speed of the photosensitive body, among the rotational speeds of the photosensitive body and the transfer means. The image forming apparatus according to claim 1, wherein at least one is controlled.   The second exposure unit responds to the image information by exposing the photosensitive member carrying a toner image according to the image information after passing the position where the developing unit and the photosensitive member face each other. The image forming apparatus according to any one of claims 1 to 3, wherein a potential Vd of a non-image portion not carrying a toner image is changed.   The control means can change the amount of light emitted from the second exposure means to the photosensitive member by controlling the value of the current flowing to the second exposure means. 5. An image forming apparatus according to item 4. A developing power source that applies a voltage Vdc to the developing unit to develop the electrostatic latent image formed on the photosensitive member with toner;
The control unit is configured to control the current flowing through the exposure unit such that the absolute value of the potential Vd ′ which is changed from the potential Vd by being exposed by the second exposure unit becomes equal to or greater than the absolute value of the voltage Vdc. The image forming apparatus according to claim 4, wherein the value is controlled.   The control means controls the rotational speed of the transfer means such that the rotational speed of the transfer means is slower than the rotational speed of the photosensitive member. Image forming apparatus as described.   8. The image forming apparatus according to claim 7, wherein the transfer unit is an elastic roller including a cored bar and a conductive elastic layer formed around the cored bar.   9. The image forming apparatus according to claim 8, further comprising a pulse motor connected to the transfer unit, wherein the control unit controls the rotational speed of the transfer unit by controlling the pulse motor.   The transfer means is a transfer belt which is stretched and rotated on a plurality of stretching rollers at a position facing the photosensitive member, and the transfer belt is connected to any one of the plurality of stretching rollers. The image forming apparatus according to claim 7, wherein the image forming apparatus is rotationally driven in response to a driving force from a driving source. 11. The image forming apparatus according to claim 10, wherein the control unit controls the rotational speed of the transfer belt by controlling the rotational speed of the roller that drives the transfer belt to rotate.

Images