JP4416467B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image by an electrophotographic method or an electrostatic recording method.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus performs uniform charging on an image carrier, and then performs image exposure by analog exposure or semiconductor laser or LED to form an electrostatic latent image on the image carrier. Such a toner image is visualized as a developer image (hereinafter referred to as “toner image”) by a developing device, and the toner image on the image carrier is transferred to a recording medium by a transfer unit to form an image. ing.

  FIG. 13 is a schematic configuration diagram showing a conventional electrophotographic image forming apparatus. This image forming apparatus is an image forming apparatus using a developing device that performs contact development by a reversal developing method using a non-magnetic one-component toner, and this image forming apparatus has a photosensitive drum 101 as an image carrier.

  The photosensitive drum 101 is provided with a photoconductive layer (not shown) such as OPC or a-Si on the surface of an aluminum cylinder, and is driven to rotate at a predetermined process speed in the direction of an arrow p.

  A charging roller 102 is disposed in contact with the photosensitive drum 101, and the surface of the photosensitive drum 101 is uniformly charged to, for example, -700V by the charging roller 102. Then, the surface potential of the exposed portion on the photosensitive drum 101 is attenuated to, for example, −200 V by image exposure with light modulated in accordance with the image signal output from the exposure device 103 on the charging surface of the photosensitive drum 101. Thus, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 101. For example, a semiconductor laser or an LED array is used for the image exposure.

  A developing roller 110 of the developing device 104 is disposed in contact with the photosensitive drum 101. The toner stored in the developing device 104 is frictionally charged by the regulating blade 112 that is in contact with the developing roller 110 as the developing roller 110 rotates in the q direction, and a thin layer is formed on the developing roller 110. After that, the photosensitive drum 101 and the developing roller 110 are conveyed to a developing site.

  After the electrostatic latent image formed on the photosensitive drum 101 is visualized by the toner conveyed by the developing roller 110, the toner image formed on the surface of the photosensitive drum 101 is transferred to a recording medium by the transfer unit 105. Then, the toner image is finally fixed on the recording medium by the fixing device 106 to form an image.

  Further, the transfer residual toner remaining on the surface of the photosensitive drum 101 after the toner image transfer is collected by a cleaning device or is not provided with a cleaning device (cleanerless) on the surface of the photosensitive member by “development simultaneous cleaning” by the developing device 104. And collected and reused in the developing device 104.

  The “development simultaneous cleaning” is a fog removal bias (DC voltage applied to the developing device 104) for residual toner remaining on the photosensitive member after the transfer at the time of development after the next step, that is, at the time of subsequent latent image development on the photosensitive drum 101. And the surface potential of the photosensitive member, and the surface potential of the photosensitive member is recovered by a fog removal potential difference Vback).

  According to this method, the residual toner remaining on the photoconductor after the transfer is collected by the developing device 104 and reused after the next step, so that waste toner can be eliminated and the printing running cost can be increased. Further, the cleaner-less has a great space advantage, and the image forming apparatus can be greatly downsized.

  Further, on the downstream side of the transfer unit 105, in order to improve the cleaning effect by the developing device 104, and to prevent image defects due to exposure disturbance during the next image forming process due to the transfer residual toner, an auxiliary such as a roller is provided. A member 107 is disposed in contact with the photosensitive drum 101.

  The conventional image forming apparatus performs image formation by repeating such operations.

  The non-magnetic one-component toner uses spherical toner particles for the main purpose of improving transferability. By forming such spherical toner particles by a polymerization method, toner particles having a smooth surface can be obtained.

  Further, it is common to coat the toner surface with an external additive. As the external additive, those having a particle diameter of 1/10 or less of the weight average diameter of the toner particles are used from the viewpoint of durability when added to the toner.

  Examples of such external additives include metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, etc.), nitrides (silicon nitride, etc.), carbides (silicon carbide, etc.), fatty acid metal salts ( Zinc stearate etc.), carbon black, silica etc. are used.

  By coating the surface of the toner with such an external additive, the fluidity of the toner can be improved, the releasability of the toner developed on the photosensitive drum from the photosensitive drum can be improved, and the triboelectric charge amount on the toner can be adjusted. It becomes possible.

  In recent years, market demand for higher image quality has increased, and it is necessary to reduce the particle size of toner used for development. However, in the conventional image forming apparatus, when the image forming operation of about 10,000 sheets is repeated, the smaller the toner particle diameter, the “reversal fog” in which the toner adheres to the non-image forming area on the photosensitive drum. Toner that does not have a charge amount falls without being held on the developing roller at the time of development, “bottom drop”, “charge failure” and “charging” in which the toner adheres to the charging roller and the photosensitive drum cannot be charged to a desired potential. There is a problem that a phenomenon such as “roller smear” is likely to occur, and an image defect occurs in which a desired image cannot be obtained.

  As a result of investigation by the present inventors, the above problems are caused by the fact that the external additive is embedded in the toner surface, so that the toner cannot maintain a desired charge amount and the toner shape is deformed. In addition, it has become clear that the toner is not able to obtain the desired uniform charge amount due to “toner deterioration”.

The cause investigation result of such “toner deterioration” will be described in more detail. In the conventional cleanerless image forming apparatus, the residual toner remaining on the photoreceptor after the transfer is collected by the developing device 104 and reused after the next process. Further, when the toner on the developing roller 110 is not used for developing the electrostatic latent image on the photosensitive drum 101, it is collected and reused by the developing device 104. For this reason, the reused toner passes many times through the contact portion between the rotating member such as the charging roller 102 and the developing roller 110 and the photosensitive drum 101. Here, the rotating bodies and the photosensitive drum are in contact with each other with a predetermined contact pressure and a predetermined peripheral speed difference. Therefore, the toner passing through the contact part is rubbed by the contact stress and the difference in peripheral speed at the contact part, and the friction force is applied to the toner existing in the contact part due to these two actions. Arise. Part of this frictional force is converted to heat, and the toner is softened.

  When the toner is softened, the toner receives the frictional force, so that the external additive that has covered the toner surface is embedded in the toner surface. Further, the toner is deformed. Such toner deterioration has a small surface area per toner in a toner having a small particle diameter, and therefore the ratio of the surface area of the deteriorated portion to the total surface area per toner even if deterioration occurs in one portion of the surface. large. In contrast, a toner having a large particle size has a large surface area per toner, so even if a portion of the surface deteriorates, the ratio of the surface area of the deteriorated portion to the total surface area per toner is small.

  For this reason, it has been clarified by investigation of the cause of the applicants that the smaller the particle diameter, the more easily the image defect is caused by the influence of toner deterioration.

  In addition to the problem of the occurrence of image defects, there is a demand for downsizing and cost reduction of image forming apparatuses. However, the contact developing type image forming apparatus using the non-magnetic one-component toner can easily obtain a good image with less fogging, but there are many parts in which the members are driven to contact each other. A large driving force is required for driving. For this reason, since it is necessary to use a high-torque motor, it has been difficult to reduce the size and price of the image forming apparatus.

  The present invention solves such problems of the conventional image forming apparatus, prevents the occurrence of toner deterioration even with a toner having a small particle size, and obtains a high-quality image satisfactorily over a long period of time. In addition, an object of the present invention is to provide an image forming apparatus that achieves downsizing of the apparatus.

In order to achieve the above object, the present invention provides:
A rotatable image carrier;
A developer carrier that rotates in contact with the image carrier, carries the developer, and visualizes and develops with the developer carrying an electrostatic latent image formed on the image carrier. ,
In the image forming apparatus for transferring the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image,
The developer carrier has a contact portion that contacts the image carrier,
In the case where the developer carrier and the image carrier are not in contact,
The curvature of the image carrier in the region to be the contact portion is
Greater than the curvature of the developer carrier in the region to be the contact portion,
The Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the developer carrier.
According to the present invention having such a configuration, both ends of the contact portion of the developer carrier are not deformed so as to be pushed out from the contact portion, and stress in the vicinity of both ends of the contact portion is reduced. Therefore, it is possible to reduce the frictional force that the toner present at the contact portion receives. For this reason, even when the toner has a small particle diameter, it is possible to prevent the toner from being deteriorated and to obtain a high-quality image favorably over a long period of time. Further, the load required for driving the image carrier or the developer carrier can be reduced even when the penetration amount when one of the image carrier or the developer carrier enters the other is kept constant. Therefore, the developer carrying member can be prevented from shaking and a good image can be obtained, and the apparatus can be miniaturized.
A rotatable image carrier;
Than the transfer means for transferring the developer image to the recording medium on the upstream side of the rotation direction of the image carrier relative to the charging means for rotating in contact with the image carrier and uniformly charging the image carrier. An auxiliary member provided on the downstream side in the rotation direction of the image carrier,
An image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by the transfer unit to form an image. ,
The auxiliary member has a contact portion that contacts the image carrier;
In the case where the auxiliary member and the image carrier do not contact,
The curvature of the image carrier in the region to be the contact portion is
Larger than the curvature of the auxiliary member in the region to be the contact portion,
The Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the auxiliary member.
A rotatable image carrier;
Than the transfer means for transferring the developer image to the recording medium on the upstream side of the rotation direction of the image carrier relative to the charging means for rotating in contact with the image carrier and uniformly charging the image carrier. An auxiliary member provided on the downstream side in the rotation direction of the image carrier,
An image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by the transfer unit to form an image. ,
The image carrier has a contact portion that contacts the auxiliary member;
In the case where the image carrier and the auxiliary member do not contact,
The curvature of the auxiliary member in the region to be the contact portion is
Larger than the curvature of the image carrier in the region to be the contact portion,
The Asker C hardness of the surface of the auxiliary member is higher than the Asker C hardness of the surface of the image carrier.
A rotatable image carrier;
Charging means for rotating in contact with the image carrier and uniformly charging the image carrier;
In an image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image.
The charging means has a contact portion that contacts the image carrier;
In the case where the charging means and the image carrier are not in contact,
The curvature of the image carrier in the region to be the contact portion is
Greater than the curvature of the charging means in the region to be the contact portion,
The Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the charging means.
A rotatable image carrier;
Charging means for rotating in contact with the image carrier and uniformly charging the image carrier;
In an image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image.
The image carrier has a contact portion that contacts the charging means;
In the case where the image carrier and the charging means do not contact,
The curvature of the charging means in the region to be the contact portion is
Larger than the curvature of the image carrier in the region to be the contact portion,
The Asker C hardness of the surface of the charging means is higher than the Asker C hardness of the surface of the image carrier.

The first rotating body ( one of the image bearing member or the rotating member that rotates in contact with the image bearing member) itself is not deformed and the second rotating body (the image bearing member or the rotating member ) is not deformed . Not only when entering the other) , but also entering the second rotating body while deforming the first rotating body itself, that is, both the first rotating body and the second rotating body are deformed. In this case, the contact portion is formed.

According to the present invention having such a configuration, when the first rotating body enters and contacts the second rotating body at the contact portion, the second rotating body at the contact portion. It is possible to reduce the stress applied to the surface. Therefore, it is possible to reduce the frictional force that the toner present at the contact portion between the image carrier and the rotating body receives from the image carrier and the rotating body. For this reason, even when the toner has a small particle diameter, it is possible to prevent the toner from being deteriorated and to obtain a high-quality image favorably over a long period of time. Further, since the driving force of the rotating body or the image carrier can be reduced, the image forming apparatus can be downsized.
Further, it is possible to prevent a problem that the deteriorated toner covers the surface of the charging unit and the image carrier cannot be charged to a desired charging potential, and a high-quality image can be obtained satisfactorily over a long period of time.

According to a preferred aspect of the present invention, the image carrier and the developer carrier are rotated in contact with each other with a relative speed difference. Further, the image carrier and the auxiliary member abut on and rotate with a relative speed difference. Further, the image carrier and the charging unit rotate in contact with each other with a relative speed difference.

  According to a preferred aspect of the present invention, the developer has a weight average particle diameter of 10 μm or less.

  According to such a configuration, a high-quality image can be obtained satisfactorily over a long period of time.

  Next, the “action” of the present invention will be described below with reference to FIGS.

  In FIG. 9, the “action” of the present invention will be described as a representative example, with a photosensitive drum as an image carrier and a developing roller as a developer carrier as a rotating member.

  FIG. 9 is a schematic diagram showing a contact portion between the photosensitive drum and the developing roller. The developing roller has a surface layer made of an elastic material such as rubber or sponge. On the other hand, the photosensitive drum is a rigid body in which a photosensitive layer of about 10 to 30 μm is provided on a metal cylinder. In the part where both are in contact, the photosensitive drum enters the developing roller and the developing roller is distorted to form a contact portion on the developing roller. Here, considering the frictional force at the contact portion, the photosensitive drum and the developing roller rotate with a peripheral speed difference, and therefore can be modeled as sliding friction.

  That is, the frictional force generated in the toner in the minute space of the contact portion is the friction coefficient μ determined by the material of the photosensitive drum and the developing roller, and the force received by the toner in the minute space of the contact portion, in other words, The product of the stress (pressure) p on the surface of the developing roller at the contact portion, expressed by μ × p. Here, the stress p has a distribution shown in FIG. 10 along the contact portion. Therefore, the total frictional force F generated in the toner in the contact portion is equal to a value obtained by integrating the stress p over the entire contact portion (shaded portion in FIG. 10) multiplied by the friction coefficient μ.

  Therefore, in order to reduce toner deterioration in the contact portion, it is effective to reduce the stress p in the contact portion. Here, in order to reduce the stress p, there is a method of lowering the hardness of the developing roller. However, if the hardness of the elastic layer is lowered, an image failure due to distortion of the developing roller at the contact portion or irreversible deformation of rubber due to neglecting. (Contact marks) may occur and there is a limit.

  FIG. 11 is a diagram illustrating the state of the contact portion. As illustrated, the photosensitive drum enters the developing roller to form the contact portion.

Here, as shown in FIG. 11A, S1 is a length along the circumferential direction at the contact portion of the developing roller in a state where the photosensitive drum has entered the developing roller. S2 is a region on the outer peripheral surface of the developing roller when the photosensitive drum does not enter the developing roller (a region that becomes the contact portion with the photosensitive drum when the photosensitive drum enters the developing roller). This is the circumferential length of the developing roller outer peripheral surface before deformation.

  As shown in FIG. 11B, when the diameter of the photosensitive drum is larger than the diameter of the developing roller, the S1 is shorter than the S2 (S1 <S2), and the elastic body at the contact portion of the developing roller becomes redundant, The elastic body is pushed out to both ends of the contact portion, and stress near both ends of the contact portion is increased.

On the other hand, as shown in FIG. 11C, when the diameter of the photosensitive drum is smaller than the diameter of the developing roller, S1 is longer than S2 (S1> S2), and both ends of the contact portion of the developing roller. As a result, the developing roller at the contact portion is pulled in the center direction of the contact portion, so that the stress near the end portion of the contact portion is reduced and the width of the stress distribution curve can be narrowed.

  The curvature at the contact portion between the photosensitive drum and the developing roller is equal to or larger than the curvature at the outer peripheral surface of the developing roller that becomes the contact portion when the photosensitive drum enters the developing roller. Thus, the relationship of S1> S2 can be established by appropriately setting the curvatures of the photosensitive drum and the developing roller.

  FIG. 12 is a diagram showing the stress distribution on the surface of the developing roller at the contact portion when the diameter of the developing roller is constant at 18 mm and the diameter of the photosensitive drum is changed to 20 mm, 18 mm, and 16 mm. As shown in FIG. 12, as the diameter of the photosensitive drum decreases, the force at both ends of the stress distribution can be reduced. As a result, the stress in the entire contact portion is reduced and the toner in the contact portion is reduced. It becomes possible to reduce the frictional force applied to.

  Accordingly, the shape of the stress distribution curve is controlled without changing the material of the photosensitive drum and the developing roller, and the frictional force at the contact portion is reduced to prevent toner deterioration and reduce the driving torque of the apparatus. It becomes possible.

  Note that when the hardness of the photosensitive drum and the developing roller is reversed, the effect is also reversed. Therefore, when the hardness of the developing roller is higher than the hardness of the photosensitive member, it is necessary to reduce the stress by increasing the diameter of the photosensitive drum and the diameter of the developing roller. In this case, even if the photosensitive drum is made elastic, since the diameter of the photosensitive drum is larger than the diameter of the developing roller, there is no possibility that the photosensitive drum surface is distorted at the contact portion, and a good image is formed.

  Further, in addition to the case where both of the above-described image carrier and rotating member are cylindrical rotating members, the belt-like image bearing member or rotating member is set as one side, and the cylindrical image bearing member or rotating member is set as the other side. Even in this case, the same effect can be obtained by setting the relationship between the hardness of the image carrier and the rotating member, the circumference of the contact portion, and the curvature as described above.

  In this case, for example, with respect to the belt-shaped image carrier that is wound between a pair of pulleys and the rotating member that contacts the belt-shaped image carrier, the rotating member abuts on a portion of the belt-shaped image carrier that is wound around the pulley, and This includes both cases where the rotating member abuts against a flat belt portion between the pulleys.

  As described above, according to the image forming apparatus of the present invention, when one of the rotating member or the image carrier enters and contacts the other at the contact portion, the rotating member or the image carrier at the contact portion. It is possible to reduce the stress applied to the other surface of the toner, and it is possible to reduce the frictional force applied to the toner present at the contact portion between the image carrier and the rotating member. For this reason, even when the toner has a small particle diameter, it is possible to prevent the toner from being deteriorated and to obtain a high-quality image favorably over a long period of time. In addition, since the driving force of the rotating member and the image carrier can be reduced, power saving and downsizing of the image forming apparatus can be realized.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

  In FIG. 1, a central circular member 1 is a photosensitive drum as an image carrier. Above the photosensitive drum 1, a charging roller 2 is rotatably supported as a charging unit that contacts with a predetermined pressing force and uniformly charges the surface of the photosensitive drum 1. Further, a laser beam whose intensity is modulated in accordance with a time-series digital pixel signal of image information is output downstream of the charging roller 2 in the rotation direction of the photosensitive drum 1, and the photosensitive drum is irradiated with the laser beam. A laser beam scanner (exposure device) 3 including a laser diode, a polygon mirror, and the like that scans and exposes one charged surface and forms an electrostatic latent image corresponding to image information on the photosensitive drum 1 is disposed.

  The housing 4 disposed on the right side of the photosensitive drum 1 is a developing device that develops an electrostatic latent image formed on the photosensitive drum 1 to form a toner image. On the left side of the developing device 4 is a developing roller 8 that is a developer carrying member as a rotating member that is partly exposed from the developing device 4 and that the exposed portion is in contact with the photosensitive drum 1. Is rotatably supported. A transfer roller as a transfer means for transferring a toner image formed on the surface of the photosensitive drum 1 to a recording medium downstream of the contact portion between the developing roller 8 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. 5 is disposed in contact with the photosensitive drum 1. A cleaner 7 that collects residual toner remaining on the photosensitive drum 1 after the transfer is disposed downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1. In the drawing, a fixing device 6 for fixing the toner image transferred to the recording medium by the transfer roller 5 is disposed downstream of the contact portion between the photosensitive drum 1 and the transfer roller 5. Yes.

  The photosensitive drum 1 is a so-called negative-polarity OPC photosensitive member (negative photosensitive member) in which organic photosensitive is applied on an aluminum rotating drum having a diameter of 16 mm. The Asker C hardness of the photosensitive drum 1 was 100 degrees.

  Here, Asker C hardness is hardness measured using a spring type hardness meter Asker C (manufactured by Kobunshi Keiki Co., Ltd.). In the present invention, the load was measured as 1 kg.

  The photosensitive drum 1 is rotationally driven at a constant speed of 120 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The charging roller 2 is driven to rotate in a direction (counter) opposite to the rotation direction of the photosensitive drum 1 at a speed of about 80% of the surface speed of the photosensitive drum 1. Further, a voltage (about -1300 V) is applied to the charging roller 2 from a bias power source. With this configuration, the charging roller 2 uniformly charges the surface of the photosensitive drum 1 to a negative polarity (about −700 V).

  As shown in FIG. 1, the developing device 4 has an opening in the lower left part of the housing, and the developing roller 8 is rotatably supported so as to close the opening. Further, a peeling supply roller 11 is rotatably supported on the right side of the developing roller 8 so as to be in contact with the developing roller 8. Further, a regulating blade 12 for regulating the thickness of the toner layer adhering to the developing roller is arranged on the upper right side of the developing roller 8 so as to press the developing roller 8 in pressure contact therewith. A toner agitating member 13 is provided on the right side of the stripping supply roller 11 and includes a rotating plate having a rotating shaft in the center. A housing constituting the developing device 4 contains a nonmagnetic one-component insulating toner (negative toner) as a developer and an external additive covering the toner surface.

  The developing roller 8 is an elastic roller having a diameter of 18 mm obtained by molding EPDM rubber on a metal core having a diameter of 8 mm, and has an Asker C hardness of 45 degrees. The Asker C hardness is a value measured using a spring type hardness meter Asker C (manufactured by Kobunshi Keiki Co., Ltd.) in the same manner as described above.

  The diameter of the developing roller 8 is not particularly limited to this embodiment, and is appropriately selected from those having the same diameter as the photosensitive drum 1 (in this embodiment, a diameter of about 16 mm) or larger. It is possible.

  The Asker C hardness of the photosensitive drum 1 and the developing roller 8 is not particularly limited to this embodiment, and can be appropriately selected from those lower than the Asker C hardness of the photosensitive drum 1.

  The stripping supply roller 11 is an elastic body having a diameter of 16 mm obtained by molding a continuous foam made of urethane rubber on a metal core having a diameter of 5 mm, and has an Asker C hardness of 3 degrees. The Asker C hardness is measured in the same manner as in the developing roller 8.

  The developing roller 8 contacts the stripping supply roller 11 with an intrusion amount of 1 mm. The intrusion amount needs to be set so that the metal cores of the developing roller 8 and the peeling supply roller 11 do not come into contact with each other.

  The developing roller 8 is rotationally driven at a peripheral speed of 200 mm / sec in the direction of the arrow in FIG. 1 (counterclockwise in the figure). The stripping supply roller 11 is rotationally driven in the same direction as the developing roller 8 at a peripheral speed of 100 mm / sec. A DC voltage is applied to the developing roller 8 and the peeling supply roller 11 by a bias power source S2.

  In the image forming apparatus according to the first embodiment configured as described above, the toner in the developing device 4 is stirred by the stirring member 13 and supplied to the vicinity of the peeling supply roller 11. Then, the toner is conveyed to the developing roller 8 by the rotation of the peeling supply roller 11 and is carried on the surface of the developing roller 8. The toner carried on the developing roller 8 is regulated to a uniform thickness by the regulating blade 12 and charged to the negative electrode. The toner carried on the developing roller 8 with a uniform thickness is conveyed to a contact portion with the photosensitive drum 1, and when an electrostatic latent image is present on the surface of the photosensitive drum 1, the photosensitive drum 1. The toner adheres to the upper electrostatic latent image and the electrostatic latent image is visualized. On the other hand, when there is no electrostatic latent image on the surface of the photosensitive drum 1, it remains on the developing roller 8 and is returned to the developing device 4. The toner on the photosensitive drum 1 returned to the developing device 4 is peeled off from the photosensitive drum 1 by the peeling supply roller 11 and collected in the developing device 4.

  A positive transfer bias is applied to the transfer roller 5 by a bias power source S3 in order to transfer the toner adhering to the photosensitive drum 1 onto a recording sheet.

  The magnetic one-component insulating toner (negative toner) having a weight average particle diameter of 10 μm or less, preferably 4 μm to 10 μm is desirably used for improving image quality.

  The weight average particle diameter of the toner can be measured by various methods. In the present invention, Coulter Counter Multisizer II type (manufactured by Coulter) is used, and the measurement method is as follows: dispersed in 100 to 150 ml of 1% sodium electrolytic aqueous solution. 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as an agent, and 2 to 20 mg of toner as a measurement sample is further added thereto. Thereafter, the electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the toner volume and number are measured with the measuring device, and the volume distribution and the number distribution are determined from the measured values. calculate. Then, the weight average particle diameter of the toner is obtained from this value.

  An external additive for coating the toner surface is added to the toner. As the external additive, those having a particle diameter of 1/10 or less of the weight average diameter of the toner particles are used from the viewpoint of durability when added to the toner.

  Examples of such external additives include metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, etc.), nitrides (silicon nitride, etc.), carbides (silicon carbide, etc.), fatty acid metal salts ( Zinc stearate etc.), carbon black, silica etc. are used.

  The photosensitive drum 1 comes into contact with the developing roller 8 with an intrusion amount of 0.1 mm, and a contact portion is formed on the surface of the developing roller 8. The developing roller 8 is a rotating member having a diameter of 18 mm whose surface is made of an elastic body, and the diameter of the photosensitive drum 1 is 16 mm. Therefore, the developing roller 8 extends along the circumferential direction at the contact portion of the developing roller 8 with the photosensitive drum 1. The length is a contact portion with the photosensitive drum 1 when the photosensitive drum 1 enters the developing roller 8 on the outer peripheral surface of the developing roller 8 when the photosensitive drum 1 does not enter the developing roller 8. This is longer than the circumferential length in the region.

  As a result of the configuration described above, it is possible to reduce the frictional force that the toner present at the contact portion between the photosensitive drum 1 and the developing roller 8 receives.

  For this reason, it is possible to control the shape of the stress distribution curve without changing the material of the photosensitive drum and the developing roller, reduce the frictional force at the contact portion, and reduce the driving torque of the device and the toner deterioration. It becomes.

  When the hardness of the photosensitive drum and the developing roller is reversed, the effect is also reversed. Therefore, when the hardness of the developing roller is higher than the hardness of the photosensitive member, the frictional force at the contact portion can be reduced by making the diameter of the photosensitive drum larger than the diameter of the developing roller. In this case, even if the photosensitive drum is made elastic, since the diameter of the photosensitive drum is larger than the diameter of the developing roller, there is no possibility that the photosensitive drum surface is distorted at the contact portion, and a good image is formed.

  Next, in order to examine the performance of the image forming apparatus according to the present embodiment, the diameter of the photosensitive drum and the weight average particle diameter of the toner are changed, and after 10,000 image forming operations are repeated, “ Experiments were conducted to investigate the occurrence of “inversion fog” and “bottom drop”.

  Table 1 shows the conditions and results of the above experiment. In the experiment, when the diameter of the developing roller is constant at 18 mm and the diameter of the photosensitive drum is changed to 16 mm, 18 mm, and 20 mm, the weight average particle diameter of the toner is 4 μm, 7 μm, 10 μm, and 13 μm. This is an observation of the occurrence of “inversion fog” and “bottom drop”. Other configurations are the same as those of the image forming apparatus.

As is apparent from Table 1, when the photosensitive drum diameter> the developing roller diameter, image defects such as “reverse fogging” and “blur-off” occurred when the weight average particle diameter of the toner was 10 μm or less.
In the case of photosensitive drum diameter ≦ developing roller diameter, even if a toner of 10 μm is used, no image defect occurs. It can be seen that high-quality image output can be performed.

[Second Embodiment]
FIG. 2 is a schematic configuration diagram of an image forming apparatus according to the second embodiment of the present invention.

  In FIG. 2, the same members as those in the image forming apparatus according to the first embodiment are denoted by the same reference numerals. In the image forming apparatus according to the second embodiment, the hardness of the photosensitive member 10 is lower than that of the developing roller 80, and the curvature of the photosensitive member is set to be small.

  As shown in FIG. 3, the photoreceptor 10 is formed of an elastic body layer 10b made of urethane sponge on an aluminum shaft body 10a having a diameter of 12 mm, and a conductive film made of a resin film having a thickness of 50 μm deposited on the metal. Layer 10c is formed. Further, an organic photoreceptor layer 10d is applied as a thin film on the uppermost layer to form a rotating body made of an elastic body having a diameter of 20 mm as a whole. In this case, the Asker C hardness on the surface of the photoreceptor 10 is appropriately selected between 40 and 50 degrees. The elastic layer 10b can be appropriately selected from other foamed resins and low-hardness rubber materials in addition to the urethane sponge.

  The photosensitive member 10 is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The developing roller 80 is a rotating body made of a metal having a diameter of 18 mm and has an Asker C hardness of 100 degrees.

  The developing roller 80 is rotationally driven at a peripheral speed of 200 mm / sec in the direction of the arrow in FIG. 2 (counterclockwise in the figure).

  The developing roller 80 is brought into contact with the photoreceptor 14 with an intrusion amount of 0.1 mm and a constant nip width.

  With this configuration, the length along the circumferential direction of the contact portion of the photoconductor 10 with the developing roller 80 is the outer circumference of the photoconductor when the developing roller 80 does not enter the photoconductor 10. On the surface, the length of the developing roller 80 is longer than the length in the circumferential direction in a region that becomes a contact portion with the developing roller 80 when the developing roller 80 enters the photosensitive member 10.

  As a result, it is possible to reduce the frictional force that the toner present at the contact portion between the photoconductor 10 and the developing roller 80 receives.

  Since other configurations are the same as those of the image forming apparatus according to the first embodiment, description thereof will be omitted.

  Next, in order to examine the performance of the image forming apparatus according to the second embodiment, after the 10,000-sheet image forming operation was repeated by changing the diameter of the photoconductor and the weight average particle diameter of the toner. An experiment was conducted to investigate the occurrence of “inversion fogging” and “bottom drop”.

  Table 2 shows the conditions and results of the above experiment. In the experiment, when the diameter of the developing roller is constant at 18 mm and the diameter of the photosensitive member is changed to 20 mm and 16 mm, the “reversal fogging” of the image forming apparatus in which the weight average particle diameter of the toner is 4 μm, 7 μm, 10 μm, and 13 μm. ”Or“ dropping out ”is observed. Other configurations are the same as those of the image forming apparatus.

  As a result, it was found that when the photoconductor hardness is lower than the developing roller hardness, satisfactory image output can be performed even when a small diameter toner is used by setting the photoconductor diameter> the developing roller diameter as shown in Table 2.

  According to the image forming apparatus according to the first embodiment and the second embodiment, the frictional force at the contact portion between the developing roller and the image carrier in the nonmagnetic one-component contact development method is reduced, It becomes possible to reduce the driving torque of the apparatus and toner deterioration. Accordingly, it is possible to provide an inexpensive image forming apparatus, and it is possible to obtain a good image over a long period of time without deteriorating the toner even if a small diameter toner is used.

[Third Embodiment]
FIG. 4 is a schematic configuration diagram of an image forming apparatus according to the third embodiment of the present invention.

  The image forming apparatus of the present embodiment is a laser printer of a transfer type electrophotographic process, a contact charging method, and a toner recycling system. Therefore, in such a system, the transfer residual toner remaining on the surface of the photosensitive drum after image transfer is not removed by a dedicated cleaner (cleaning device), but passes through a contact portion with the charging roller 2 as the photosensitive drum rotates. Then, it reaches the contact portion with the developing roller, and is collected and reused in the developing device by simultaneous development cleaning.

  In FIG. 4, the central circular member 1 is a photosensitive drum as an image carrier. The roller 2 disposed above the photosensitive drum 1 is a conductive elastic roller as a charging unit that is brought into contact with the photosensitive drum 1 with a predetermined pressing force to charge the surface of the photosensitive drum 1. A transfer roller 5 is disposed below the photosensitive drum 1. An auxiliary roller 9, which is an auxiliary member as a rotating member, is disposed downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1 so as to contact the photosensitive drum 1.

  The auxiliary roller 9 unpatterns the residual toner remaining on the photosensitive drum 1 after being transferred onto the recording paper by the transfer roller 5, thereby preventing image defects due to exposure inhibition during the next image forming process due to the residual toner. At the same time, the residual toner is negatively charged by frictional charging at the contact portion between the photosensitive drum 1 and the auxiliary roller 9, thereby improving the recoverability of the residual toner. However, residual toner. Since friction is also received at the contact portion with the auxiliary roller (and charging roller), the deterioration of the toner is promoted and image defects such as fog are likely to occur as compared with the case where there is a cleaner.

  The photosensitive drum 1 is a so-called negative-polarity OPC photosensitive member (negative photosensitive member) in which organic photosensitive is applied on an aluminum rotating drum having a diameter of 20 mm. The Asker C hardness of the photosensitive drum 1 is 100 degrees.

  Here, the Asker C hardness was measured by the same method as the measuring method in the image forming apparatus according to the first embodiment.

  The photosensitive drum 1 is rotationally driven at a constant speed of 120 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The auxiliary roller 9 is an elastic roller having a diameter of 24 mm in which a semiconductive rubber layer is molded on the surface of a metal core having a diameter of 8 mm, and has an Asker C hardness of 15 degrees. Asker C hardness is a value measured in the same manner as described above.

  The auxiliary roller 9 is rotationally driven in the same direction as the photosensitive drum 1 at a constant speed of 100 mm / sec.

  The photosensitive drum 1 is brought into contact with the auxiliary roller 9 with an intrusion amount of 1.0 mm and a constant nip width. The amount of penetration of the photosensitive drum 1 into the auxiliary roller 9 is a value set appropriately so that the metal core of the auxiliary roller 9 does not contact the surface of the photosensitive drum 1.

  The diameter of the auxiliary roller 9 is not particularly limited to this embodiment, and is appropriately selected from the same as the diameter of the photosensitive drum 1 (in this embodiment, a diameter of about 20 mm) or larger. It is possible. The Asker C hardness of the photosensitive drum 1 and the auxiliary roller 9 is not particularly limited to this embodiment, and can be appropriately selected from those lower than the Asker C hardness of the photosensitive drum.

  With the above configuration, the length of the auxiliary roller 9 along the circumferential direction at the contact portion with the photosensitive drum 1 is the outer circumference of the auxiliary roller 9 when the photosensitive drum 1 does not enter the auxiliary roller 9. On the surface, when the photosensitive drum 1 enters the auxiliary roller 9, it becomes longer than the length in the circumferential direction in a region that becomes a contact portion with the photosensitive drum 1.

  As a result, it is possible to reduce the frictional force that the toner present at the contact portion between the photosensitive drum 1 and the auxiliary roller 9 receives.

  Next, in order to investigate the performance of the image forming apparatus according to the third embodiment, after changing the diameter of the photoconductor and the weight average particle diameter of the toner and repeating the image forming operation for 10,000 sheets, An experiment was conducted to investigate the occurrence of “reverse fogging” and “charging roller contamination”.

  Table 3 shows the conditions and results of the above experiment. In the experiment, when the diameter of the photosensitive drum is constant at 20 mm and the diameter of the auxiliary roller 16 is changed to 16 mm and 24 mm, the “reversal” of the image forming apparatus in which the weight average particle diameter of the toner is 4 μm, 7 μm, 10 μm, and 13 μm. This is an observation of the occurrence of “fogging” and “charging roller contamination”. Other configurations are the same as those of the image forming apparatus according to the third embodiment.

  As a result, when the hardness of the auxiliary roller is lower than the hardness of the photosensitive drum, it is found that the effect can be obtained even when a small diameter toner is used by setting the diameter of the auxiliary roller ≧ the diameter of the photosensitive drum as shown in Table 3. It was.

  As described above, when the hardness of the photosensitive drum is higher than the hardness of the auxiliary roller, the frictional force generated on the toner in the contact portion between the photosensitive drum and the auxiliary roller is reduced by making the diameter of the photosensitive drum smaller than the diameter of the auxiliary roller. And toner deterioration can be reduced.

[Fourth Embodiment]
FIG. 5 is a schematic configuration diagram of an image forming apparatus according to the fourth embodiment of the present invention.

  In FIG. 5, the same members as those in the image forming apparatus according to the third embodiment are denoted by the same reference numerals. In the image forming apparatus according to the fourth embodiment, the hardness of the photoconductor 10 is lower than that of the auxiliary roller 90, and the curvature of the photoconductor is set to be small.

  The photoconductor 10 has the same configuration as the photoconductor in the first embodiment shown in FIG. 3, and an elastic body layer 10b made of urethane sponge is formed on a shaft body 10a made of aluminum having a diameter of 12 mm. A conductive layer 10c made of a dielectric resin film having a thickness of 50 μm and having a metal deposited on the surface is formed thereon. Further, an organic photoreceptor layer 10d is applied as a thin film on the uppermost layer, and an elastic photoreceptor having a diameter of 20 mm as a whole. Is formed. The Asker C hardness of the photoreceptor 10 in the fourth embodiment is 15 degrees. The Asker C hardness is a value measured in the same manner as in the first embodiment. The elastic layer 10b can be appropriately selected from other foamed resins and low-hardness rubber materials in addition to the urethane sponge.

  The photoreceptor 10 is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction indicated by an arrow in FIG.

  Further, the auxiliary roller 90 is a rigid roller having a diameter of 16 mm in which a thin elastic layer is formed on the surface of the metal core, and the Asker C hardness is 100 degrees.

  The diameter of the photosensitive member 10 is not particularly limited to this embodiment, and is appropriately selected from those having the same diameter as the auxiliary roller 90 (in this embodiment, a diameter of about 16 mm) or larger. It is possible. Further, the Asker C hardness of the photoconductor 10 and the auxiliary roller 90 is not particularly limited to this embodiment, and the Asker C hardness of the photoconductor 10 is lower than the Asker C hardness of the auxiliary roller 90. It is possible to select from those appropriately.

  The auxiliary roller 90 is rotationally driven at a peripheral speed of 200 mm / sec in the direction of the arrow in FIG. 2 (counterclockwise in the figure).

  The auxiliary roller 90 is brought into contact with the photoreceptor 10 with an intrusion amount of 1.0 mm and a constant nip width.

  With the above configuration, the length of the auxiliary roller 90 along the circumferential direction at the contact portion with the photoconductor 10 is the outer circumference of the photoconductor 10 when the auxiliary roller 90 does not enter the photoconductor 10. On the surface, the auxiliary roller 90 becomes longer than the circumferential length in a region that becomes a contact portion with the auxiliary roller 90 when the auxiliary roller 90 enters the photoconductor 10.

  As a result, it is possible to reduce the frictional force applied to the toner present at the contact portion between the auxiliary roller 90 and the photosensitive member 10.

  Since other configurations are the same as those of the image forming apparatus according to the third embodiment, description thereof will be omitted.

  In addition to the above embodiment, even in a configuration in which the hardness of the photosensitive member is lower than that of the auxiliary roller and the photosensitive member diameter and the auxiliary roller diameter are variously changed, the photosensitive member diameter <the auxiliary roller diameter. In this case, even when a toner having a weight average particle size of 10 μm or less is used, no image defect occurs after 10,000 sheets of image forming operation, and high-quality image output can be performed.

  Next, in order to investigate the performance of the image forming apparatus according to the fourth embodiment, after changing the diameter of the photoconductor and the weight average particle diameter of the toner and repeating the image forming operation for 10,000 sheets, An experiment was conducted to investigate the occurrence of “reverse fogging” and “charging roller contamination”.

  Table 4 shows the conditions and results of the above experiment. In the experiment, after the image forming operation of 10,000 sheets was repeated by the image forming apparatus according to the fourth embodiment and the image forming apparatus of the comparative example described below, occurrence of “reversal fog” and “charging roller smear” An experiment was conducted to investigate the situation.

  The photoconductor in the comparative example is a so-called negative-polarity OPC photoconductor (negative photoconductor) obtained by applying organic photosensitivity on an aluminum rotating drum having a diameter of 20 mm. In this case, the Asker C hardness of the photosensitive drum 1 is 100 degrees. The auxiliary roller in the comparative example is an elastic roller having a diameter of 16 mm in which a semiconductive rubber layer is molded on the surface of a metal core having a diameter of 8 mm, and has an Asker C hardness of 15 degrees.

  With respect to the image forming apparatuses of the above examples and comparative examples, the weight average particle diameter of the toner was changed within the range of 4 μm, 7 μm, 10 μm, and 13 μm, and the occurrence of “reversal fog” and “charging roller contamination” was observed. Is. The other configuration is the same as that of the image forming apparatus.

  As a result, as shown in Table 4, in the configuration in which the hardness of the photoconductor is higher than that of the auxiliary roller and the photoconductor diameter is large, when the toner weight average particle size is 10 μm or less, “reverse fogging” and “charging roller” An image defect factor such as “dirt” occurred. On the other hand, it has been found that image defects are less likely to occur even when 10 μm toner is used in a configuration in which the photoconductor has a lower hardness and a larger photosensitive drum diameter than the auxiliary roller.

  In the image forming apparatus according to the third embodiment and the fourth embodiment, the curvature having the lower hardness at the contact portion of the photosensitive drum (photosensitive member) and the auxiliary roller has a higher hardness. By making the curvature larger than this, the toner deterioration caused at the contact portion between the photosensitive drum (photoconductor) and the auxiliary roller is reduced, and even if a toner having a toner weight average particle size of 10 μm or less is used, it is good for a long period of time. Image output can be performed.

[Fifth Embodiment]
FIG. 6 is a schematic configuration diagram of an image forming apparatus according to the fifth embodiment of the present invention.

  The image forming apparatus of the present embodiment is a laser printer of a transfer type electrophotographic process, a contact charging method, and a toner recycling system, as in the third and fourth embodiments.

  In FIG. 6, a circular member 1 at the center is a photosensitive drum as an image carrier. Reference numeral 2 denotes a charging roller as a charging unit that is a rotating member that is brought into contact with the photosensitive drum 1 with a predetermined pressing force and charges the surface of the photosensitive drum 1. In the figure, a housing 4 disposed on the right side of the photosensitive drum 1 is the developing device that develops an electrostatic latent image formed on the photosensitive drum 1 to form a toner image. A developing roller 8 is rotatably supported on the left side of the developing device 4 so that a part of the developing device 4 is exposed from the developing device 4 and the exposed portion is in contact with the photosensitive drum 1. A transfer roller 5 is disposed below the photosensitive drum 1.

  The photosensitive drum 1 is a so-called negative-polarity OPC photosensitive member (negative photosensitive member) in which organic photosensitive is applied on an aluminum rotating drum having a diameter of 20 mm. The Asker C hardness of the photosensitive drum 1 was 100 degrees.

  Here, the Asker C hardness was measured by the same method as the measuring method in the image forming apparatus according to the first embodiment.

  Further, the photosensitive drum 1 is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The charging roller 2 is formed by molding an elastic body made of EPDM having a thickness of 3.5 mm on a conductive core having a diameter of 8 mm, and covering it with a hydrin rubber having a thickness of 500 μm to prevent leakage. A thin film surface layer made of a resin resin of a fluorine compound that assists the charging of the toner is formed. The elastic roller has a laminated structure with a diameter of 24 mm as a whole. The charging roller 2 has an Asker C hardness of 20 degrees. Here, the Asker C hardness was measured by the same method as the measuring method in the image forming apparatus according to the first embodiment.

The diameter of the charging roller 2 is not particularly limited to this embodiment, and is appropriately selected from those having the same diameter as the photosensitive drum 1 (in this embodiment, a diameter of about 20 mm) or larger. It is possible.

  The Asker C hardness of the photosensitive drum 1 and the charging roller 2 is not particularly limited to this embodiment, and the Asker C hardness of the charging roller 2 is lower than the Asker C hardness of the photosensitive drum 1. It is possible to select appropriately.

  The charging roller 2 is rotationally driven at a peripheral speed of 150 mm / sec in the direction of the arrow in FIG. 6 (counterclockwise in the figure). Further, a DC voltage of about -1300 V is applied to the charging roller 2 by a bias power source S1. The surface of the photosensitive drum 1 is uniformly charged at about −700 V by the charging roller 2.

  The photosensitive drum 1 is brought into contact with the charging roller 2 with an intrusion amount of 1.0 mm and a constant nip width.

  With the above configuration, the toner image formed on the photosensitive drum 1 is transferred onto the recording paper at the nip portion between the transfer roller 5 and the photosensitive drum 1. The transfer residual toner remaining on the photosensitive drum 1 after the transfer is charged to a weak positive polarity by the transfer roller 5, and is rotated between the charging roller 2 and the photosensitive drum 1 as the photosensitive drum 1 rotates. It is conveyed to the contact part (charging nip part). The untransferred toner conveyed to the charging nip is returned to negative polarity by friction between the charging roller 2 and the photosensitive drum 1.

  Thereafter, the untransferred toner present in the image forming area on the photosensitive drum is conveyed to a contact portion between the developing roller 8 and the photosensitive drum 1 as the photosensitive drum 1 rotates. In order to visualize the latent image on the photosensitive drum 1 in the next developing step together with the toner conveyed from the developing device 4 via the developing roller 8 by the action of an electric field that urges the toner from the developing roller 8 to the photosensitive drum 1. Used again.

  On the other hand, the untransferred toner existing in the non-image forming area on the photosensitive drum passes through the developing roller 8 from the photosensitive drum 1 by the action of an electric field that urges the toner from the photosensitive drum 1 to the developing roller 8. And collected by the developing device 4. By repeating such an operation, image formation is performed.

  Therefore, with the above configuration, the length of the charging roller 2 along the circumferential direction at the contact portion with the photosensitive drum 1 is the charging roller 2 when the photosensitive drum 1 does not enter the charging roller 2. Is longer than the circumferential length in a region that becomes a contact portion with the photosensitive drum 1 when the photosensitive drum 1 enters the charging roller 2.

  As a result, it is possible to reduce the frictional force that the toner present at the contact portion between the charging roller 2 and the photosensitive drum 1 receives.

  Next, in order to examine the performance of the image forming apparatus according to the fifth embodiment, the radius of the photosensitive drum is constant, the radius of the charging roller and the weight average particle diameter of the toner are changed, and 10,000 sheets After repeating the image forming operation, an experiment was conducted to examine the occurrence of “reverse fogging”, “blurring drop”, and “charging failure”.

  Table 5 shows the conditions and results of the above experiment. In the experiment, when the diameter of the photosensitive drum is constant at 20 mm and the diameter of the charging roller is changed to 16 mm, 20 mm, and 24 mm, the weight average particle diameter of the toner is 4 μm, 7 μm, 10 μm, and 13 μm. This is an observation of the occurrence of “reversal fogging”, “charging roller dirt”, and “charging failure”.

  As a result, when the hardness of the charging roller is lower than the hardness of the photosensitive drum, as shown in Table 5, even when a small-diameter toner is used by setting the photosensitive drum diameter ≦ the charging roller diameter, In addition, it was found that good image output can be performed without causing “charging failure”.

  In the present embodiment, the photosensitive drum rotates clockwise in FIG. 6 at 100 mm / sec, and the charging roller rotates counterclockwise at 150 mm / sec. Therefore, the relative speed of both is 50 mm / sec. is there. The inventors of the present invention have made a similar investigation under a condition range of a relative speed of 500 mm / sec or less. As a result, in the configuration where the diameter of the photosensitive drum> the diameter of the charging roller, an image failure occurs when the toner particle size is small and the relative speed is high. However, when the photosensitive drum radius is equal to or smaller than the charging roller radius, even when a toner of 10 μm or less is used, an image defect does not occur and a good image is obtained.

  As described above, when the hardness of the photosensitive drum is higher than the hardness of the charging roller, the friction generated on the toner in the contact portion between the photosensitive drum and the charging roller is reduced by making the diameter of the photosensitive drum smaller than the diameter of the charging roller. The force can be reduced and toner deterioration can be reduced. Therefore, even in a small particle size toner that is easily affected by deterioration, it is possible to prevent the occurrence of image defects such as “reversal fogging”, “charging roller dirt”, and “charging failure”.

[Sixth Embodiment]
FIG. 7 is a schematic configuration diagram of an image forming apparatus according to the sixth embodiment of the present invention.

  In FIG. 7, the same members as those in the image forming apparatus according to the fifth embodiment are denoted by the same reference numerals. In the image forming apparatus according to the sixth embodiment, the hardness of the photosensitive member 10 is lower than that of the charging roller 20, and the curvature of the photosensitive member is set to be small.

  The photoconductor 10 has the same configuration as the photoconductor in the first embodiment shown in FIG. 3, and an elastic body layer 10b made of urethane sponge is formed on an aluminum shaft 10a having a diameter of 6 mm. A conductive layer 10c made of a dielectric resin film having a thickness of 50 μm and having a metal vapor-deposited surface is formed thereon, and an organic photoreceptor layer 10d is applied as a thin film on the uppermost layer. It is an elastic photoconductor having a diameter of 20 mm. The photoreceptor 10 has an Asker C hardness of 20. Asker C hardness is a value measured in the same manner as described above. The elastic layer 10b can be appropriately selected from other foamed resins and low-hardness rubber materials in addition to the urethane sponge.

  The photoreceptor 10 is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The charging roller 20 is formed by forming a resistance layer made of 500 μm hydrin rubber for preventing leakage on the surface of the metal core, and further forming a thin film surface layer having a thickness of 30 μm made of a fluororesin resin resin for assisting the charging of the toner. This is a roller having a laminated structure having a diameter of 16 mm as a whole. The charging roller 2 has an Asker C hardness of 100 degrees.

  The diameter of the photoreceptor 10 is not particularly limited to this embodiment, and is appropriately selected from the same as the diameter of the charging roller 20 (in this embodiment, a diameter of about 16 mm) or larger. It is possible. Also, the Asker C hardness of the charging roller 20 and the photoreceptor 10 is not particularly limited to this embodiment, and the Asker C hardness of the photoreceptor is lower than the Asker C hardness of the charging roller 20. It is possible to select as appropriate.

  The charging roller 20 is rotationally driven at a peripheral speed of 150 mm / sec in the direction of the arrow in FIG. 7 (counterclockwise in the figure).

  The charging roller 20 is brought into contact with the photosensitive member 10 with an intrusion amount of 1.0 mm and a constant contact width.

  With this configuration, the length along the circumferential direction of the contact portion of the photoconductor 10 with the charging roller 20 is such that the charging roller 20 does not enter the photoconductor 10. On the outer peripheral surface, the length becomes longer than the length in the circumferential direction in a region that becomes a contact portion with the charging roller 20 when the charging roller 20 enters the photoreceptor 10.

  As a result, it is possible to reduce the frictional force that the toner present at the contact portion between the charging roller 20 and the photosensitive member 10 receives.

  Since other configurations are the same as those of the image forming apparatus according to the fifth embodiment, description thereof is omitted.

  In addition to the above embodiment, the hardness of the photosensitive member is lower than that of the charging roller, and the charging roller diameter is smaller than the photosensitive member diameter even when the photosensitive member diameter and the charging roller diameter are variously changed. In this case, even when a toner having a weight average particle size of 10 μm or less is used, no image defect occurs after 10,000 sheets of image forming operation, and high-quality image output can be performed.

  Next, in order to examine the performance of the image forming apparatus according to the sixth embodiment, the hardness of the photoconductor and the hardness of the charging roller are changed with respect to the weight average particle diameter of the toner to obtain 10,000 sheets. After repeating the image forming operation, an experiment was conducted to examine the occurrence of “reverse fogging”, “blurring drop”, and “charging failure”.

  Table 6 shows the conditions and results of the above experiment. In the experiment, after the image forming operation of 10,000 sheets was repeated by the image forming apparatus according to the sixth embodiment and the image forming apparatus of the comparative example described below, “reverse fogging”, “bottom dropping”, and “ An experiment was conducted to investigate the occurrence of “charge failure”.

  The photoconductor in the comparative example is a so-called negative-polarity OPC photoconductor (negative photoconductor) obtained by applying organic photosensitivity on an aluminum rotating drum having a radius of 10 mm. In this case, the Asker C hardness of the photoreceptor 1 is 100 degrees.

Further, the auxiliary roller in the comparative example has an EP of 3.5 mm in thickness on a conductive core having a radius of 8 mm.
An elastic body made of DM is molded, and a hydrin rubber having a thickness of 500 μm is coated thereon to prevent leakage, and a thin film surface layer made of a fluororesin resin resin that assists in imparting charging to the toner is formed thereon. The elastic roller has a laminated structure with a diameter of 16 mm as a whole. The charging roller 2 has an Asker C hardness of 20 degrees.

  With respect to the image forming apparatuses of the above-mentioned examples and comparative examples, the weight average particle diameter of the toner is changed in the range of 4 μm, 7 μm, 10 μm, and 13 μm, and “reversal fogging”, “blur-off”, and “charging failure” This is an observation of the state of occurrence. The other configuration is the same as that of the image forming apparatus.

  As a result, as shown in Table 6, in the configuration in which the hardness of the photoconductor is higher than that of the charging roller and the diameter of the photoconductor is large, when the toner weight average particle size is 10 μm or less, “reversal fog” and “bottom” Drop "and" charge failure "occurred. On the other hand, in a configuration where the hardness of the photoconductor is lower than that of the charging roller and the diameter of the photoconductor is large, even if toner of 10 μm or less is used, image defects do not occur, and high-quality image output can be performed. I understood that I could do it.

[Seventh Embodiment]
FIG. 8 is a schematic configuration diagram of an image forming apparatus according to the seventh embodiment of the present invention.

  In FIG. 8, the same members as those in the image forming apparatus according to the seventh embodiment are denoted by the same reference numerals. In the image forming apparatus according to the seventh embodiment, the photosensitive member has an endless belt shape.

  In the photoconductor 17 according to the seventh embodiment, a conductive layer made of a dielectric resin film having a thickness of 50 μm, the surface of which is metal-deposited, is formed on a base of an endless belt having an elastic layer. The organic photoreceptor layer is applied in a thin film, and the endless elastic photoreceptor is 4 mm thick as a whole. The photoreceptor 17 has an Asker C hardness of about 25 degrees. The Asker C hardness is a value measured in the same manner as in the other embodiments.

  The endless belt-like photoconductor 17 is stretched between a pair of pulleys 18 having a radius of 4 mm, and the radius of curvature of the portion wound around the pulley is 8 mm. The photosensitive member 17 is driven by the rotation of the pulley 18.

  The photosensitive member 17 is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction indicated by an arrow in FIG.

  The charging roller 20 is formed by molding a resin layer made of hydrin rubber having a thickness of 3 mm for preventing leakage on the surface of a metal core having a radius of 3 mm, and further comprising a resin compound of fluorine compound for assisting the charging of the toner on the upper layer. A thin film surface layer having a film thickness of 30 μm is formed, and a roller having a laminated structure having a radius of 6 mm as a whole. The charging roller 2 has an Asker C hardness of about 50 degrees.

  The Asker C hardness of the charging roller 20 and the photoreceptor 17 is not particularly limited to this embodiment, and the Asker C hardness of the photoreceptor 17 is lower than the Asker C hardness of the charging roller 20. It is possible to select appropriately.

  The charging roller 20 is rotationally driven at a peripheral speed of 150 mm / sec in the direction of the arrow in FIG. 2 (counterclockwise in the figure).

  As shown in FIG. 8, the charging roller 20 contacts a portion of the photosensitive member 17 wound around the pulley 18 with a curvature radius of 8 mm, and the intrusion amount is 1.0 mm and has a constant nip width. Is done.

  With this configuration, the length along the circumferential direction of the contact portion of the photoconductor 17 with the charging roller 20 is the outer circumference of the photoconductor 17 when the charging roller 20 does not enter the photoconductor 17. On the surface, when the charging roller 20 enters the photoconductor 17, it becomes longer than the circumferential length in the region that becomes the contact portion with the charging roller 20.

  As a result, it is possible to reduce the frictional force that the toner present at the contact portion between the charging roller 20 and the photoconductor 17 receives. For this reason, even when a toner having a weight average particle size of 10 μm or less is used, no image defect occurs after 10,000 sheets of image forming operation, and high-quality image output can be performed.

  In addition to the seventh embodiment, even when the charging roller 20 contacts the non-rolled portion between the pulleys 18 of the photoconductor 17, the radius of curvature of the charging roller 20 is 6 mm, and the photoconductor 17 Therefore, the length of the photosensitive member 17 along the circumferential direction at the contact portion with the charging roller 20 does not allow the charging roller 20 to enter the photosensitive member 17. In this case, the outer circumferential surface of the photoconductor 17 is longer than the circumferential length in the region that becomes the contact portion with the charging roller 20 when the charging roller 20 enters the photoconductor 17, thereby obtaining the same effect. I can do it.

  Next, in order to investigate the performance of the image forming apparatus according to the seventh embodiment, the hardness of the photosensitive member and the hardness of the charging roller are changed with respect to the weight average particle diameter of the toner, and 10,000 sheets After repeating the image forming operation, an experiment was conducted to examine the occurrence of “reverse fogging”, “blurring drop”, and “charging failure”.

  Table 7 shows the conditions and results of the above experiment. In the experiment, after the image forming operation of 10,000 sheets was repeated by the image forming apparatus according to the seventh embodiment and the image forming apparatus of the comparative example described below, “reverse fogging”, “bottom dropping”, and “ An experiment was conducted to investigate the occurrence of “charge failure”.

  In the photoconductor in the comparative example, a conductive layer made of a dielectric resin film having a thickness of 50 μm, the surface of which is metal-deposited, is formed on a base of an endless belt having an elastic layer, and an organic photoconductor layer is further formed as the uppermost layer. Is an endless elastic photoconductor having a thickness of 4 mm as a whole. The photoreceptor has an Asker C hardness of about 50 degrees. The Asker C hardness is a value measured in the same manner as in the other embodiments. Incidentally, the hardness of the photoconductor of the comparative example is adjusted by changing the hardness of the elastic body.

  The endless belt-like photoconductor is wound and driven between a pair of pulleys as in the seventh embodiment.

  Further, the photoconductor in the comparative example is rotationally driven at a constant speed of 100 mm / sec in the clockwise direction, which is the same direction as the photoconductor 17 in FIG.

  Further, the charging roller in the comparative example is formed by forming a resistance layer made of hydrin rubber having a thickness of 3 mm for preventing leakage on the surface of a metal core having a radius of 3 mm, and further, a fluororesin resin resin for assisting the charging of the toner on the upper layer. A thin film surface layer having a thickness of 30 μm is formed, and a roller having a laminated structure with a radius of 6 mm as a whole is formed. The charging roller 2 has an Asker C hardness of about 25 degrees. Incidentally, the hardness of the charging roller of the comparative example is adjusted by changing the hardness of the elastic body.

  With respect to the image forming apparatuses of the above-mentioned examples and comparative examples, the weight average particle diameter of the toner is changed in the range of 4 μm, 7 μm, 10 μm, and 13 μm, and “reversal fogging”, “blur-off”, and “charging failure” This is an observation of the state of occurrence. The other configuration is the same as that of the image forming apparatus.

  As a result, as shown in Table 7, in the configuration in which the hardness of the photosensitive member is higher than that of the charging roller and the radius of the photosensitive member is large, when the toner weight average particle diameter is 10 μm or less, “reversal fog” and “bottom” Drop "and" charge failure "occurred. On the other hand, in a configuration in which the photoconductor has a lower hardness than the charging roller and the photoconductor has a large radius, even if toner of 10 μm is used, image defects do not occur and high-quality image output can be performed. I understood.

  Even when a non-circular photoconductor is used as described above, the hardness of the photoconductor is lower than that of the charging roller and the curvature of the photoconductor 17 at the contact portion is such that the charging roller 20 enters the photoconductor 17. By making the curvature equal to or larger than the curvature in the region to be the contact portion of the photoconductor 17 in the case where the contact is not made, the frictional force generated in the toner in the contact portion can be reduced, and toner deterioration can be suppressed. Even in the case of a small particle size toner which is easily affected by the above, it is possible to prevent image defects such as “reversal fog” and “blurring” and charging failure.

  In the present embodiment, the case where the photosensitive member is in the shape of a belt has been exemplified. However, even when the charging member is in the shape of a belt or when both the photosensitive member and the charging member are in the shape of a belt, the curvature of a member having a lower hardness among the two. By making the radius larger than the other radius of curvature, the frictional force and frictional heat generated in the toner in the contact portion can be reduced, and toner deterioration can be reduced.

  According to the image forming apparatuses according to the fifth embodiment, the sixth embodiment, and the seventh embodiment, toner deterioration that occurs at the contact portion between the photosensitive drum (photoconductor) and the charging member is reduced. Therefore, it is possible to provide a charging device and a cleanerless image forming apparatus that can perform good image formation over a long period of time.

In this specification, the case of using a non-magnetic one-component negatively charged toner has been described. However, the present invention is not particularly limited to this. For example, the same effect can be obtained with either a magnetic one-component toner or a positively charged toner.

  In addition, the toner shape is not limited to spherical or pulverized, and the effect can be obtained with any shape of toner.

  In each of the above embodiments, the reversal development method has been described as an example, but the same effect can be obtained regardless of reversal and normal development.

  In each of the above-described embodiments, the rotation direction of the rotating member such as the auxiliary member is illustrated in the contact portion in the reverse direction with respect to the rotation direction of the image carrier. The effect of can be obtained.

  Further, even when the shape of the image carrier and the auxiliary member is not a cylinder as in each of the above embodiments, it satisfies that the member having a higher hardness at the contact portion is larger than the curvature of the member having a lower hardness. If so, the same effect can be obtained.

  Further, the contact developing type image forming apparatus using the non-magnetic one-component toner can easily obtain a good image with less fogging, while there are many parts in which the members are driven to contact each other. However, according to the image forming apparatus of the present invention, it is not necessary to use a high torque motor, and the image forming apparatus can be downsized.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an image forming apparatus according to the second embodiment of the present invention. FIG. 3 is a sectional view of an image carrier (photosensitive member). FIG. 4 is a schematic configuration diagram of an image forming apparatus according to the third embodiment of the present invention. FIG. 5 is a schematic configuration diagram of an image forming apparatus according to the fourth embodiment of the present invention. FIG. 6 is a schematic configuration diagram of an image forming apparatus according to the fifth embodiment of the present invention. FIG. 7 is a schematic configuration diagram of an image forming apparatus according to the sixth embodiment of the present invention. FIG. 8 is a schematic configuration diagram of an image forming apparatus according to the seventh embodiment of the present invention. FIG. 9 is a schematic view of a contact portion between the photosensitive drum and the developing roller. FIG. 10 is a stress distribution diagram at the contact portion between the photosensitive drum and the developing roller. FIG. 11 is a diagram illustrating a state of a contact portion between the photosensitive drum and the developing roller. FIG. 12 is a stress distribution diagram at the contact portion when the outer diameter of the photosensitive drum is changed. FIG. 13 is a schematic configuration diagram of a conventional image forming apparatus.

Explanation of symbols

1 Image carrier (photosensitive drum)
2 Charging means (charging roller)
4 Developing device 5 Transfer means (transfer roller)
8 Developer carrier (developing roller)
9 Auxiliary member (auxiliary roller)
10 Image carrier (photoreceptor)
17 Image carrier (photoreceptor)
20 Charging means (charging roller)
80 Developer carrier (developing roller)
90 Auxiliary member (auxiliary roller)

Claims (9)

A rotatable image carrier;
A developer carrier that rotates in contact with the image carrier, carries the developer, and visualizes and develops with the developer carrying an electrostatic latent image formed on the image carrier. ,
In the image forming apparatus for transferring the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image,
The developer carrier has a contact portion that contacts the image carrier,
In the case where the developer carrier and the image carrier are not in contact,
The curvature of the image carrier in the region to be the contact portion is
Greater than the curvature of the developer carrier in the region to be the contact portion,
An image forming apparatus, wherein the Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the developer carrier. A rotatable image carrier;
Than the transfer means for transferring the developer image to the recording medium on the upstream side of the rotation direction of the image carrier relative to the charging means for rotating in contact with the image carrier and uniformly charging the image carrier. An auxiliary member provided on the downstream side in the rotation direction of the image carrier,
An image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by the transfer unit to form an image. ,
The auxiliary member has a contact portion that contacts the image carrier;
In the case where the auxiliary member and the image carrier do not contact,
The curvature of the image carrier in the region to be the contact portion is
Larger than the curvature of the auxiliary member in the region to be the contact portion,
An image forming apparatus, wherein the Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the auxiliary member. A rotatable image carrier;
Than the transfer means for transferring the developer image to the recording medium on the upstream side of the rotation direction of the image carrier relative to the charging means for rotating in contact with the image carrier and uniformly charging the image carrier. An auxiliary member provided on the downstream side in the rotation direction of the image carrier,
An image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by the transfer unit to form an image. ,
The image carrier has a contact portion that contacts the auxiliary member;
In the case where the image carrier and the auxiliary member do not contact,
The curvature of the auxiliary member in the region to be the contact portion is
Larger than the curvature of the image carrier in the region to be the contact portion,
The image forming apparatus according to claim 1, wherein an Asker C hardness of a surface of the auxiliary member is higher than an Asker C hardness of a surface of the image carrier. A rotatable image carrier;
Charging means for rotating in contact with the image carrier and uniformly charging the image carrier;
In an image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image.
The charging means has a contact portion that contacts the image carrier;
In the case where the charging means and the image carrier are not in contact,
The curvature of the image carrier in the region to be the contact portion is
Greater than the curvature of the charging means in the region to be the contact portion,
An image forming apparatus characterized in that the Asker C hardness of the surface of the image carrier is higher than the Asker C hardness of the surface of the charging means. A rotatable image carrier;
Charging means for rotating in contact with the image carrier and uniformly charging the image carrier;
In an image forming apparatus that visualizes an electrostatic latent image formed on the image carrier with a developer, and transfers the visualized developer image on the image carrier to a recording medium by a transfer unit to form an image.
The image carrier has a contact portion that contacts the charging means;
In the case where the image carrier and the charging means do not contact,
The curvature of the charging means in the region to be the contact portion is
Larger than the curvature of the image carrier in the region to be the contact portion,
The image forming apparatus according to claim 1, wherein an Asker C hardness of the surface of the charging unit is higher than an Asker C hardness of the surface of the image carrier.   The image forming apparatus according to claim 1, wherein the image carrier and the developer carrier are in contact with each other and rotated with a relative speed difference.   The image forming apparatus according to claim 2, wherein the image carrier and the auxiliary member are rotated in contact with each other with a relative speed difference.   The image forming apparatus according to claim 4, wherein the image carrier and the charging unit rotate in contact with each other with a relative speed difference.   The image forming apparatus according to claim 1, wherein the developer has a weight average particle diameter of 10 μm or less.

Images