JP2003207959A - Image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the life of an image forming apparatus by maintaining and recovering potential by electrification in the transfer type image forming apparatus of a cleaner-less system that an electrifying means 2 for an image carrier 1 is an electrifying means using conductive impalpable powder (m) and the conductive impalpable powder (m) is supplied to an abutting part (n) between the electrifying means 2 and the image carrier 1 from a developing means 3 through the image carrier 1. <P>SOLUTION: The current value of the image carrier is detected at the exposure time. When the detected value is equal to or under a fixed value, it is judged a situation is such that the electrified amount of the image carrier is low (potential by electrification is low), and then the potential by electrification is changed, the supply amount of the conductive powder (m) is increased or the apparatus is stopped in compliance with the situation. If the potential by electrification is not improved yet though the supply amount of the conductive powder (m) is tried to increase several times, the apparatus is allowed to perform the above-mentioned operation. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor,
The charging means for the image carrier such as the electrostatic recording dielectric is a charging means using conductive fine powder, and the conductive fine powder is replenished from the developing means to the contact portion between the charging means and the image carrier. The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a laser beam printer, and a process cartridge of a system that is performed via a carrier.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image is formed when an electrostatic latent image is formed on an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. A charging step for charging the carrier to a uniform potential is required, and a corona charging device (not in contact with the image carrier) has been widely used as the charging device. However, in the corona charging device, there are problems that a large amount of ozone is generated and that a high voltage of about 10 kV must be applied between the charging device and the image carrier, resulting in high cost.

As charging means for solving these problems,
In recent years, a so-called contact charging device has been proposed and put into practical use, in which a voltage is applied to a charging member that is in direct contact with the image carrier to uniformly charge the image carrier. However, this method is also the same as the above-mentioned corona charging device in that charging is performed by using the discharge phenomenon, and ozone is still generated although it is significantly suppressed as compared with the corona charging device.
This ozone produces nitric oxide (NOx), and when it adheres to the image carrier, its resistance is low and causes image defects due to poor charging.

Therefore, a charging process which does not have the above-mentioned problem of ozone generation and which can further lower the voltage applied to the charging device is proposed in Japanese Patent Laid-Open No. 6-3921.

A feature of this charging process is that the surface potential of the image carrier can be made approximately the same as the voltage applied to the charging device. This means that the surface of the image carrier in contact with the charging member can be used without using the discharge phenomenon. This is made possible by injecting charges into the image bearing member by directly exchanging charges with the image carrier.

As a charging device for realizing the injection charging process described above, a sponge roller charging device (Japanese Patent Laid-Open No. 10-307455, etc.) will be described here.

As shown in FIG. 4, this type, as a contact charging member, has a relatively low resistance conductivity in the empty space on the surface of the charging sponge roller 2 which contacts the image carrier 1 and rotates in the direction b. The fine powder m is attached. The charging sponge roller 2 rotates in the counter direction b with respect to the image carrier rotating direction a at the contact portion n with the image carrier 1, so that the charge is applied to the image carrier 1 from the charging sponge roller 2. By injecting, the image carrier 1 is charged to substantially the same potential as the potential of the charging sponge roller 2.

The conductive fine powder m is conductive fine particles for the purpose of assisting charging. For example, the particle size is 0.1 to 5 μm, the volume resistance value is 1 × 10 ¹² Ω · cm or less, and more preferably 1 × 10.
Various conductive fine powders of ¹⁰ Ω · cm or less such as metal oxide fine particles such as conductive zinc oxide, other conductive inorganic fine particles, and a mixture with an organic substance can be used.

In this system, a DC voltage of -600 V is applied to the charging sponge roller 2 by the power source S1. For this reason, the portion of the image carrier 1 that is in contact with the charging sponge roller 2 tends to have the same potential as this. At this time, charges are transferred from the charging sponge roller 2 over the energy barrier on the surface of the image carrier 1
If it is injected into the image carrier, the image carrier 1 is charged and cannot cross this energy barrier, or the charged sponge roller 2
When the image carrier 1 separates from the image carrier 1 and the charges move from the image carrier 1 to the charging sponge roller 2, charging does not occur. This phenomenon is largely due to the surface energy barrier of the image carrier 1 and the ability to retain charges, but when considered as a competitive reaction, the frequency with which the charging sponge roller 2 contacts the image carrier 1 becomes important. .

In order to increase the frequency, the conductive fine powder m is attached to the empty space on the surface of the charging sponge roller 2 to increase the adhesion between the charging sponge roller 2 and the image carrier 1, and the charging. It is effective to increase the number of times of contact with the image carrier 1 by increasing the relative speed by making the rotation direction b of the sponge roller 2 reverse to the traveling direction a of the image carrier 1. By doing so, the surface potential of the image carrier 1 becomes almost the same potential as -600 V applied to the charging sponge roller 2, and uniform charging without uneven charging is possible even in the micro portion.

In FIG. 5, the charging means for charging the image carrier 1 is an injection charging device using the above conductive fine powder m.
FIG. 1 is a schematic view of an example of a transfer type electrophotographic apparatus of a cleanerless system.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow a at a predetermined peripheral speed. Reference numeral 2 denotes a charging sponge roller as a contact charging member, which is brought into contact with the photosensitive member 1 with a predetermined pressing force to form a charging contact portion n having a predetermined width.
Reference numeral 21 is a conductive fine powder applicator for the outer peripheral surface of the charging sponge roller 2. The charging sponge roller 2 is indicated by the arrow b.
By being driven to rotate in the clockwise direction, conductive fine powder m is applied to the outer peripheral surface of the charging sponge roller.

That is, the charging sponge roller 2 is rotationally driven in the counter direction b with respect to the rotation direction a of the photoconductor 1 in the state where the conductive fine powder m is interposed at the charging contact portion n with the photoconductor 1, and the charging is performed. By applying a predetermined charging bias from the power source S1 to the sponge roller 2, the outer peripheral surface of the photoconductor 1 is uniformly injected and charged to have a predetermined polarity and potential.

Image exposure L is performed on the uniformly charged surface of the photoconductor 1 by an exposing means (a digital scanning exposing device such as a laser beam scanner, an image forming and projecting device for an original image, etc.) which is not shown. An electrostatic latent image corresponding to the exposure image pattern is formed on the uniformly charged surface of the photoconductor 1.

Then, the electrostatic latent image is visualized as a developer image (toner image) at the developing portion f by the developing sleeve 3-a of the non-contact jumping developing device 3. t is the developer (toner) accommodated in the developing device 3, and c is the developing sleeve 3.
The rotation direction of −a, S2 is a power source for applying a predetermined developing bias to the developing sleeve 3-a.

Then, the developer image is transferred to a contact portion g which is a contact portion between the photosensitive member 1 and the transfer roller 5-a of the transfer device 5.
, A transfer material P, which is a recording medium, is fed to the transfer contact portion g from a paper feeding portion (not shown) at a predetermined control timing.
Is transcribed to. d is the rotation direction of the transfer roller 5-a, S3
Is a power source for applying a predetermined transfer bias to the transfer roller 5-a.

Upon receiving the transfer of the developer image at the transfer contact portion g,
The transfer material P separated from the photoconductor 1 is introduced into a fixing device (not shown) to undergo image fixing, and is discharged as an image-formed product (print, copy).

After the transfer material is separated, the untransferred developer on the surface of the photosensitive member 1 is carried to the developing unit via the charging unit by the subsequent rotation of the photosensitive member 1, and is recovered by the developing device 3 by the simultaneous cleaning for developing. It

The conductive fine powder m has its charging polarity determined by the developer t.
By making the polarity opposite to that, the transfer roller 5-a does not transfer it to the transfer material P and leaves it on the photoconductor 1.
By collecting on the charging sponge roller 2, a new injection site is always obtained. Therefore, even if the developer t is accumulated on the charging sponge roller 2, if the conductive fine powder m is supplied more than that, it is possible to suppress the occurrence of charging failure.

Further, in this type, after the image on the photoconductor 1 is transferred by applying a positive voltage in the transfer process, the developer t remaining after the transfer is exposed to the conductive fine powder m subjected to the charging process and exposed to light. By being rubbed while passing between the body 1 and the body 1, it becomes possible to have a negative charge and to have an appropriate electric charge. Therefore, when passing through an area where the developing process is performed, the developing device does not pass through. It will be collected in 3. Therefore, it is possible to realize an electrophotographic process without a cleaner.

[0021]

In order to perform stable charging (keep the surface potential of the image carrier 1 constant) with the above structure, the conductive fine powder m is placed on the charging sponge roller 2 which is a charging member. A stable supply is essential. However, even if the conductive fine powder m is stably supplied onto the charging sponge roller 2, the surface potential of the image carrier 1 may be lowered. A typical example thereof is that the charging sponge roller 2, which is a charging member, deteriorates due to repeated energization, resulting in an increase in resistance and the like. Then, the surface potential of the image carrier 1 becomes lower than the voltage applied to the core metal of the charging sponge roller 2. This is because a current flows from the core metal of the charging sponge roller 2 to the image carrier 1 through the sponge roller at the time of charging, but if the resistance of the sponge roller portion is high, a voltage drop occurs in that portion, and the image carrier 1 and the sponge roller are This is because the electric potential of the contact portion is lowered. That is, when the surface potential of the image carrier 1 is lowered, there are at least two causes: an increase in the resistance value of the charging sponge roller 2 and an insufficient supply of the conductive fine powder m.

The present invention has been made in view of the above points, and when the surface potential of the image bearing member is lowered, it may be due to an increase in the resistance value of the charging member or an insufficient supply of the conductive fine powder. It is an object of the present invention to provide an image forming apparatus and a process cartridge capable of discriminating whether or not the above and taking appropriate measures depending on the cause.

[0023]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus and process cartridge characterized by the following configurations.

(1) At least an image carrier, charging means for charging the image carrier, image information writing means for forming an electrostatic latent image on the charged surface of the image carrier, and toner for the electrostatic latent image. A developing means for making the toner image visible by means of a toner image, and a transferring means for transferring the toner image onto a recording medium, the image carrier is repeatedly used for image formation, and the charging means for charging the image carrier is A voltage is applied with a speed difference between the image carrier and the conductive powder interposed between the image carrier, and the developer of the developing means contains toner and conductive powder, The development of the electrostatic latent image on the image carrier is performed by the developer, and at least the contact portion between the charging member and the image carrier adheres to the image carrier at the developing unit and remains on the image carrier after transfer. Image type in which conductive powder contained in the agent is carried and intervened The apparatus has an image carrier current detection means for detecting a current generated by the image carrier by writing image information, the charging means is in an operating state, and the developing means and the transfer means are in a non-operating state. At some time, an electrostatic latent image is formed on the image carrier by the image information writing unit, and if the image carrier current amount detected by the image carrier current detection unit at that time is below a certain value, it is defective. An image forming apparatus having a control means for taking a means for preventing image generation.

(2) Means for preventing the generation of defective images are as follows:
The image forming apparatus according to (1) is characterized in that the charging voltage by the charging unit is changed.

(3) Means for preventing the generation of defective images are as follows:
The image forming apparatus described in (1) is characterized in that the supply of the conductive powder by the developing means is increased.

(4) The means for preventing the generation of defective images are
The image forming apparatus described in (1) is characterized in that the subsequent image forming operation is stopped.

(5) Means for preventing the generation of defective images are as follows:
“After increasing the supply of the conductive powder by the developing means, when the charging means is in the operating state again and the developing means and the transfer means are in the non-operating state, the image information writing means performs image formation. When the state in which the image carrier current when the electrostatic latent image is formed on the carrier is equal to or less than a predetermined value is repeated a predetermined number of times, the subsequent image forming operation is stopped ( The image forming apparatus according to 1).

(6) The image forming apparatus according to any one of (1) to (5), wherein the charging means is moved in a direction opposite to the moving direction of the image carrier while maintaining a speed difference.

(7) The image forming apparatus according to any one of (1) to (6), wherein the charging means includes a flexible member forming the contact portion.

(8) At least the image carrier, the charging unit, and the developing unit are provided in a frame body, and (1)
A process cartridge which forms a part of the image forming apparatus according to any one of (7) to (7) and is attachable to and detachable from the main body of the image forming apparatus.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic sectional view of an image forming apparatus showing an embodiment of the present invention. In the image forming apparatus of the embodiment, the charging means for the image carrier is a charging means using conductive fine powder, and the conductive fine powder is replenished from the developing means to the contact portion between the charging member and the image carrier. This is a transfer-type electrophotographic apparatus (laser beam printer) of a cleanerless system of a type that is performed via an image carrier.

(1) Overall Schematic Structure of Image Forming Apparatus This image forming apparatus includes an image carrier 1, an injection charging device 2, and a developing device (developing device) containing a mixture of a developer t and a conductive fine powder m. ) 3, a transfer device 5, a fixing device (fixing device) 6, an exposure device 7 and the like, and the image carrier 1,
A process cartridge 10 having an injection charging device 2 and a developing device 3 in a frame is attached to an image forming apparatus main body including the transfer device 5, the fixing device 6, and the exposure device 7.

The image (toner image) formed on the image carrier 1 in the latent image forming step and the developing step is fixed by the transfer roller 5-a of the transfer device 5 and the rotation direction d of the transfer roller 5-a. 6 is transferred to a transfer material P which is a recording medium sent in the direction of 6, and the image on the transfer material is fixed on the transfer material by the fixing device 6, and the transfer material on which the image is formed is the rotation direction e of the fixing device 6. Is discharged in the direction.

A) Image bearing member 1 The image bearing member 1 is an OPC photosensitive member (negative photosensitive member) having a diameter of 30 mm. Hereinafter referred to as a photoconductor. The photoconductor 1 is driven by a driving unit (not shown) in the clockwise direction of arrow a at 50 mm / sec.
It is driven to rotate at the peripheral speed (hereinafter referred to as process speed).

B) Injection charging device 2 The injection charging device 2 is a conductive elastic roller (hereinafter referred to as a charging roller) as a contact charging member, and rubber or foam as a flexible member is provided on the core metal 2-a. Medium resistance layer 2-
It is created by forming b. The medium resistance layer 2-b is formulated with a resin (for example, urethane), a conductive fine powder (for example, carbon black), a sulfiding agent, a foaming agent, etc., and is formed in a roller shape on the core metal 2-a. After that, the surface was polished as needed to prepare a charging roller 2 which was a conductive elastic roller having a diameter of 12 mm. When the roller resistance of the charging roller 2 of this example was measured, it was 10 ⁵ Ω (total load pressure 9.8 N, applied voltage 100 V).

Here, it is important that the charging roller 2 functions as an electrode. In other words, at the same time as providing a sufficient contact state with the photoconductor 1 as the member to be charged by providing elasticity,
It must have a low enough resistance to charge the moving photoreceptor 1. On the other hand, it is necessary to prevent voltage leakage when the photoconductor 1 has a defective portion such as a pinhole.

When an electrophotographic photosensitive member is used as the member to be charged, 10 ⁴ to 10 ⁷ are required to obtain sufficient chargeability and leak resistance.
A resistance of Ω is desirable.

If the hardness of the charging roller 2 is too low, the shape of the charging roller 2 is not stable, so that the contact property with the photosensitive member 1 is deteriorated. If the hardness is too high, the charging contact portion n cannot be secured between the charging roller 2 and the photosensitive member 1. Not only this, but the microscopic contact property to the surface of the photosensitive member is deteriorated, and therefore, the Asker C hardness is preferably in the range of 25 to 50 degrees.

The material of the charging roller 2 is not limited to the elastic foam, but the material of the elastic body is EPD.
Examples thereof include M, urethane, NBR, silicone rubber, a rubber material in which a conductive material such as carbon black or a metal oxide is dispersed in IR or the like for resistance adjustment, or a material obtained by foaming these. In addition, especially without dispersing a conductive substance,
It is also possible to adjust the resistance by using an ion conductive material.

The charging roller 2 is a photosensitive member 1 as a member to be charged.
It is arranged in pressure contact with a predetermined pressing force against the elasticity. In this example, the peripheral speed is 75 mm in the clockwise direction of the arrow so that the charging roller 2 moves in the opposite direction (counter) to the charging roller surface and the photosensitive member surface at the charging contact portion n.
It was driven to rotate at / sec. That is, the surface of the charging roller 2 as the contact charging member has a speed difference with respect to the surface of the photoreceptor 1 as the image carrier.

A DC voltage of -620 V is applied as a charging bias from the charging bias applying power source S1 to the core metal 2-a of the charging roller 2. In this example, the surface of the photoconductor 1 is uniformly charged by the direct injection charging method to a potential (−600 V) which is almost equal to the voltage applied to the charging roller 2.

C) Exposure Device 7 The exposure device 7 is a laser beam scanner (exposure device) including a laser diode, a polygon mirror, and the like. This laser beam scanner outputs laser light whose intensity is modulated corresponding to the time-series electric digital pixel signal of the target image information, and scans and exposes L the uniformly charged surface of the rotating photoconductor 1 with the laser light. By this scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photoconductor 1.

D) Developing device 3 The electrostatic latent image on the surface of the rotating photoconductor 1 is developed as a toner image by the developing device 3. The developing device 3 of this example is a reversal developing device using a magnetic one-component insulating toner (negative toner) t as a developer.

Reference numeral 3-a is a non-magnetic rotary developing sleeve as a developer carrying / conveying member, in which a magnet roll 3-b is contained. The rotary developing sleeve 3-a is provided with a regulating blade 3-c and a developer container. The developer in 3-d is coated in a thin layer. The layer thickness of the developer toner is regulated by the regulation blade 3-c with respect to the rotary developing sleeve 3-a, and an electric charge is applied. The developer coated on the rotary developing sleeve 3-a is conveyed to the developing section (developing area section) f, which is an opposing section of the photoconductor 1 and the sleeve 3-a, by the rotation of the sleeve 3-a. A developing bias voltage is applied to the sleeve 3-a from a developing bias applying power source S2. The developing bias voltage is a DC voltage of -450V and a frequency of 1800H.
A rectangular AC voltage having z and a peak-to-peak voltage of 1200 V was superposed. As a result, the electrostatic latent image on the side of the photoconductor 1 is developed with the toner in the developing section f.

The developer is a mixture of toner t and conductive fine powder (charge assisting particles) m. The toner t is prepared by uniformly dissolving or dispersing a polymerizable monomer and a colorant (and optionally a polymerization initiator, a cross-linking agent, a charge control agent, and other additives) into a monomer composition, This monomer composition was prepared by a suspension polymerization method in which a continuous stabilizer (for example, an aqueous phase) containing a dispersion stabilizer was dispersed using an appropriate stirrer and a polymerization reaction was simultaneously performed. The fine powder m and the fluidizing agent are added as external additives. Toner t
Had a weight average particle diameter (D4) of 7 μm. As the conductive fine powder m, conductive zinc oxide particles having a particle diameter of 3 μm were used in this example. In this example, 1.5 parts by weight of the conductive fine powder m was externally added to 100 parts by weight of the toner t.

For the average particle size and particle size distribution of the toner, a Coulter counter TA-II type or a Coulter Multisizer (manufactured by Coulter Co.) is used, and an interface (manufactured by Nikkaki Co., Ltd.) for outputting number distribution and volume distribution and PC98
01 Connect a personal computer (made by NEC),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using first grade sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As the measuring method, the electrolytic aqueous solution 100 to 150 is used.
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) as a dispersant is added to ml, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample was suspended was subjected to dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toner particles of 2 μm or more were measured using the Coulter Counter TA-II model with an aperture of 100 μm as an aperture. The volume distribution and number distribution were calculated. Then, the volume-based weight average particle diameter (D4) determined from the volume distribution according to the present invention was determined.

As the conductive fine powder m having conductivity, conductive zinc oxide particles having a specific resistance of 10 ⁶ Ω · cm and an average particle size of 3 μm including secondary agglomerates were used in this example. As the material of the body m, various conductive particles such as conductive inorganic particles such as other metal oxides or a mixture with organic substances can be used.

The resistance measurement was performed by the tablet method and normalized.
I asked. That is, the bottom area is 2.26 cm ²Inside the cylinder
Put 0.5g of powder sample into the upper and lower electrodes of 147N (15k
g) Pressurization and at the same time applying a voltage of 100 V
The value was measured and then normalized to calculate the specific resistance.

E) Transfer Device 5 In the transfer device 5, reference numeral 5-a is a medium resistance transfer roller as a contact transfer means, and a transfer contact portion g is formed by pressing the photosensitive member 1 at a predetermined pressure. A transfer material P as a recording medium is fed to the transfer contact portion g from a paper feed portion (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied from the transfer bias applying power source S3 to the transfer roller 5-a. As a result, the toner image on the side of the photoconductor 1 is sequentially transferred to the surface of the transfer material P fed to the transfer contact portion g. That is,
The transfer material P introduced into the transfer contact portion g has the transfer contact portion g.
The toner images formed on and carried by the surface of the rotary photoconductor 1 are sequentially transferred by electrostatic force and pressing force.

The transfer material P, which has been fed to the transfer contact portion g and has received the toner image on the photosensitive member 1 side, is separated from the surface of the rotating photosensitive member 1 and introduced into the fixing device 6 to fix the toner image. The image is received and discharged as an image-formed product (print or copy) out of the apparatus.

F) Process Cartridge 10 In the image forming apparatus of the present embodiment described above, the photoconductor 1, the charging roller 2, and the developing device 3 are other parts (hereinafter referred to as the main body and the main body) constituting the image forming apparatus. The process cartridge 10 is formed by being combined with a housing independent of the main body (see FIG. 1) and is detachable from the main body.

G) Cleaner-less The image forming apparatus of this example is cleaner-less, and the transfer residual toner remaining on the surface of the rotary photosensitive member 1 after the toner image is transferred onto the transfer material P is not removed by the cleaner. Along with the rotation of 1, the developing portion f is reached via the charging contact portion n,
Simultaneous development cleaning (collection) is performed in the developing device 3 (toner recycling process).

By the way, the conductive fine powder m having conductivity contained in the developer t of the developing device 3 is exposed in a proper amount together with the toner when the electrostatic latent image on the side of the photoconductor 1 is developed by the developing device 3. Move to the body 1 side. The toner image on the photoconductor 1 is attracted and actively transferred to the transfer material P side at the transfer contact portion g due to the influence of the transfer bias, but the conductive fine powder m on the photoconductor 1 is conductive. Therefore, it is not positively transferred to the transfer material P side, and is substantially attached and retained on the photoconductor 1 and remains.

Since the image forming apparatus in the toner recycling process does not use a cleaner, the transfer residual toner remaining on the surface of the photosensitive member 1 after the transfer and the above-mentioned residual conductive fine powder m
Is carried as it is by the rotation of the photoconductor 1 to the charging end portion n of the photoconductor 1 and the charging roller 2 which is a contact charging member, and is attached to and mixed with the charge roller 2. Therefore, the contact charging of the photoconductor 1 is performed in the state where the conductive fine powder m exists at the contact portion n between the photoconductor 1 and the charging roller 2.

In the initial stage of printing, since the conductive fine powder is not supplied to the surface of the charging roller and charging cannot be performed, it is necessary to apply the conductive fine powder to the surface of the charging roller in advance.

Due to the presence of the conductive fine powder m, even if toner adheres to or mixes with the charging roller 2, it is possible to maintain the close contact property and the contact resistance of the charging roller 2 to the photosensitive member 1, and therefore the contact charging member. Is a simple member such as the charging roller 2, and the direct injection charging of the photoconductor 1 by the charging roller 2 can be performed regardless of the contamination of the charging roller 2 due to the transfer residual toner. That is, the charging roller 2 is in close contact with the photoconductor 1 through the conductive fine powder m,
The conductive fine powder m existing at the contact portion between the charging roller 2 and the photosensitive member 1 rubs the surface of the photosensitive member 1 without any gap, so that the charging roller 2 charges the photosensitive member 1 with the conductive fine powder m. As a result, stable and safe direct injection charging that does not use the discharge phenomenon becomes dominant, and high charging efficiency that cannot be obtained by conventional roller charging or the like is obtained, and a potential almost equal to the voltage applied to the charging roller 2 is obtained. Can be given to one.

The transfer residual toner adhering to and mixed with the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive member 1 and reaches the developing section along with the movement of the surface of the photosensitive member 1, and at the developing device 3 simultaneous cleaning for development ( Will be collected). Simultaneous development cleaning is carried out by developing the toner remaining on the photoconductor 1 after transfer in the subsequent image forming process, that is, by continuously charging and exposing the photoconductor to form a latent image and developing the latent image. The defoaming bias of the apparatus, that is, the fog-removing potential difference Vback, which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member, is used for recovery. In the case of reversal development as in the printer of this embodiment, this simultaneous development cleaning is performed by an electric field that collects toner from the dark part potential of the photoconductor to the developing sleeve and an electric field that attaches toner from the developing sleeve to the light part potential of the photoconductor. Is made by the action of.

Even if the conductive fine powder m falls off from the charging roller 2, the image forming apparatus is operated, so that the conductive fine powder m contained in the developer t of the developing device 3 is developed in the developing section. Due to the presence of the conductive fine powder m, the surface of the photosensitive body 1 is transferred to the charging contacting section n by the rotation of the photosensitive body 1 through the transfer contacting section g and continuously supplied to the charging roller 2. Good chargeability is stably maintained.

Thus, the contact charging method, the contact transfer method,
In the image forming apparatus of the toner recycling process, the charging roller is used as the contact charging member, and the ozoneless direct injection charging is stably maintained for a long period of time at a low applied voltage regardless of the contamination by the transfer residual toner of the charging roller 2. Therefore, it is possible to obtain an image forming apparatus having a simple structure and a low cost, which is capable of providing uniform charging property and is free from obstacles due to ozone products and obstacles due to poor charging.

(2) Defective Image Generation Preventing Means However, when a voltage is repeatedly applied to the charging roller 2 due to durability or the like, its electrical properties gradually change and the resistance value increases. When the resistance value of the charging roller 2 exceeds a proper range and becomes high, even if a predetermined voltage (-620 V in this embodiment) is applied to the photosensitive member 1, the voltage drop in the charging roller 2 causes the surface of the photosensitive member 1. The electric potential of does not reach -600V.

However, the increase in the resistance of the charging roller 2 is not the only reason why the potential of the photosensitive member 1 does not reach the predetermined value. That is, it is essential that the conductive fine powder m is stably supplied onto the charging roller 2 in order to perform stable injection charging in the apparatus of this embodiment, and the supply of the conductive fine powder m is successful. This is because there is a possibility that the electric potential of the photoconductor 1 does not reach a predetermined value because it has not been said. If there are a plurality of causes that the photoreceptor 1 does not reach the predetermined potential, the countermeasures are naturally different.

If the cause of the charging potential of the photosensitive member 1 not reaching the predetermined value is the increase in the resistance of the charging roller 2, the resistance value of the charging roller 2 may be lowered (specifically, the charging roller 2).
Will be replaced). On the other hand, when the cause of the charging potential of the photoconductor 1 not reaching the predetermined value is insufficient supply of the conductive fine powder m, the operation (sequence) may be performed to increase the supply of the conductive fine powder m.

The present invention has been made in view of the above points. When the surface potential of the photosensitive member 1 is lowered, it may be due to an increase in the resistance value of the charging roller 2 or insufficient supply of the conductive fine powder m. It is an object of the present invention to provide an image forming apparatus and a process cartridge capable of discriminating whether or not the cause is caused and taking appropriate measures according to the cause.

In the electrophotographic process, the photoconductor 1 is first charged, and the laser beam scanner 3 exposes the photoconductor 1 to the exposure, whereby the electric charge in the corresponding portion is attenuated and an electrostatic latent image is formed on the photoconductor 1. The charge attenuated from the surface of the photoconductor 1 during exposure is transmitted through the inner surface of the drum and the photoconductor current (image carrier current).
Flows to earth as.

Reference numeral 11 is an image carrier current detecting means (hereinafter referred to as an ammeter) for detecting the amount of the photoconductor current flowing to the ground. Information about the amount of current detected by the ammeter 11 is input to the control circuit unit 12 of the image forming apparatus.

When the initial (pre-exposure) potential of the photoconductor 1 used in this example was changed and the entire surface was exposed, the post-exposure potential and the photoconductor current were measured.
The exposure light amount is 8 mJ / m ² .

[0068]

[Table 1]

It can be seen from Table 1 that the potential of the photoconductor 1 before exposure can be detected by measuring the photoconductor current when the exposure light amount is constant. This is because the potential of the photoreceptor 1 after exposure is almost constant regardless of the fluctuation of the potential before exposure. Therefore, there is a relationship that the larger the current flowing from the photoconductor 1, the higher the photoconductor potential before exposure.

Based on Table 1, in this embodiment, the control circuit 1
2 indicates that the photoconductor current amount information input from the ammeter 11 is 2.3.
When it is less than μA, it is determined that the charging potential has not reached the predetermined value.

FIG. 2 is a control flowchart executed by the control circuit section 12 based on the photoconductor current detected by the ammeter 11 in this embodiment.

Before the image formation, the photosensitive member 1 is charged, the surface of the photosensitive member 1 is uniformly exposed by the laser beam scanner 3, and the current of the photosensitive member flowing at that time is measured by the ammeter 11.
As described above, when the value is less than 2.3 μA, the photoconductor 1
It can be detected that the charging potential of No. has not reached the predetermined value, but the cause cannot be specified.

Then, next, a conductive fine powder supply sequence is executed in order to investigate the reason why the potential of the photosensitive member 1 does not reach the predetermined value. This sequence is performed by changing the potential of the DC component of the developing bias. More specifically,
The potential of the DC component of the developing bias during normal image formation is-
Although it is 450 V, the back contrast (difference between the photoconductor dark portion potential and the developing potential) is increased by setting this to −350 V. This sequence utilizes the fact that the conductive fine powder m has a polarity opposite to that of the developer. By doing so, the amount of the conductive fine powder m supplied from the developing device 3 to the photoconductor 1 is increased. Can be made. Of course, during the execution of the conductive fine powder supply sequence, it is necessary to keep the photoconductor 1 at the dark potential, so that the exposure operation is not performed.

From the viewpoint that the conductive fine powder m is uniformly supplied to the charging roller 2, this conductive fine powder supply sequence is at least the time for the charging roller 2 to make one revolution (about 0.5 in this embodiment). Second) need to be done.

After that, the photoconductor current is measured again by the same procedure as described above, and if the photoconductor potential is restored, the image forming operation is started. If the photoconductor potential has not reached the predetermined value, it is determined that the resistance value of the charging roller 2 has increased, and the image forming operation is stopped to prevent the occurrence of a defective image. In this case, the control circuit unit 12 displays a message to that effect on a display unit (not shown) to prompt replacement of the charging roller 2. A warning prompting replacement of the charging roller 2 may be displayed on the display unit without stopping the image forming operation.

As described above, when the surface potential of the photoconductor 1 decreases, it is determined whether it is due to the increase in the resistance value of the charging roller 2 or the insufficient supply of the conductive fine powder m, and It is possible to provide an image forming apparatus and a process cartridge that can take appropriate measures depending on the cause.

It is needless to say that the above-described embodiment is merely an example, and modifications can be made without changing the gist of the present invention. For example, in this embodiment, the photoconductor 1
In the above description, the operation of detecting whether or not the charging potential is normal is performed before image formation. However, in order to prepare for the next operation, it may be performed after image formation, or in continuous printing, it may be performed between sheets. good. Also, not every movement,
You may perform it every fixed number of sheets, every fixed time, etc. Of course, a combination of these may be used.

(Second Embodiment) When the amount of the conductive fine powder m on the charging roller 2 is significantly insufficient, the charging performance cannot be sufficiently restored by executing the conductive fine powder supply sequence only once. Can also be considered. Therefore, the reason why the potential of the photoconductor 1 does not reach the predetermined value for the first time is that the potential of the photoconductor 1 does not reach the predetermined value even if the conductive fine powder supply sequence is executed a plurality of times. The reliability of the device can be improved by determining that the temperature is rising.

Since the image forming apparatus of this embodiment is the same as that of the first embodiment, the repetitive description will be omitted. FIG. 3 is a control flowchart performed by the control circuit unit 12 based on the photoconductor current detected by the ammeter 11 in this embodiment.

When the photosensitive body current is detected, the conductive fine powder supply sequence is operated, and when the photosensitive body potential is restored to a predetermined value after the first conductive fine powder supply sequence, the image forming operation is performed. The operation is the same as in the first embodiment. However, if the photoconductor potential does not reach the predetermined value again after this first conductive fine powder supply sequence, the subsequent image forming operation is not performed, but the conductive fine powder supply sequence is operated again to expose the photosensitive material. It is again detected whether the body potential has reached a predetermined value. It is determined that the resistance value of the charging roller has risen for the first time when the 1) conductive fine powder supply sequence and 2) the photoconductor current detection are repeated a predetermined number of times and the photoconductor potential still does not reach the predetermined value. At the same time, the image forming operation is stopped in order to prevent the occurrence of a defective image. In this example, the predetermined number of times was three times.

Therefore, according to this embodiment, when the surface potential of the photoconductor 1 is lowered, it is highly accurate whether it is due to the increase of the resistance value of the charging roller 2 or the insufficient supply of the conductive fine powder m. It is possible to provide an image forming apparatus and a process cartridge which can be discriminated in step 1 and take appropriate action depending on the cause.

(Third Embodiment) When the charging potential is lowered, the charging potential can be restored by changing the charging voltage applied to the charging roller 2.

Since the image forming apparatus of this embodiment is the same as that of the first embodiment, the repetitive description will be omitted. The charge potential of the photoconductor can be estimated by detecting the photoconductor current and comparing it with Table 1. Therefore, the charge potential of the photoconductor is changed to a predetermined value by changing the charge voltage by an amount that is less than the predetermined value. Can be recovered up to. For example, when the detection value of the photoconductor current is 2.0 μA, the charging potential is −580 from Table 1.
Since it is estimated to be V, the absolute value of the charging voltage is 20V.
You can add it on top.

If the photoconductor potential does not reach the predetermined value (the photoconductor current does not reach the predetermined value) even if the charging voltage is changed, the charging voltage may be changed again. Also the first
It may be carried out in combination with the conductive fine powder supply sequence described in the above embodiment.

Therefore, according to the present embodiment, when the surface potential of the photoconductor 1 is lowered, the charge potential of the photoconductor 1 can be restored to a predetermined value by changing the charging voltage, and a defective image is formed. It is possible to provide an image forming apparatus and a process cartridge that do not generate.

(Others) 1) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the primary surface of the dielectric surface is uniformly charged to a predetermined polarity and potential, the target electrostatic latent image is written and formed by selectively neutralizing with a neutralizing means such as a neutralizing needle head or an electron gun.

2) The recording medium to which the toner image is transferred from the image carrier may be an intermediate transfer member such as a transfer drum.

[0088]

As described above, according to the present invention, the charging means of the image carrier is a charging means using conductive fine powder, and the conductivity of the contact portion between the charging means and the image carrier is high. In a transfer-type image forming apparatus of a cleanerless system, in which replenishment of fine powder is performed from a developing means via an image carrier, an image carrier current is detected when the surface potential of the image carrier is lowered ,. By repeating the conductive fine powder supply sequence as appropriate, it is determined whether it is due to the increase in the resistance value of the charging member or the insufficient supply of conductive powder, and appropriate action is taken according to the cause. Take ,. The charge potential of the image carrier is restored by changing the charge voltage.
An image forming apparatus and a process cartridge that do not generate a defective image can be provided. In addition, the life of the device can be extended.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a control flowchart showing the operation of the image forming apparatus in the first embodiment.

FIG. 3 is a control flowchart showing the operation of the image forming apparatus according to the second embodiment.

FIG. 4 is an explanatory view of contact injection charging means using conductive fine powder.

FIG. 5 is a schematic configuration model diagram of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Charging roller (injection charging device, contact charging member), 3 ... Developing device, 5 ... Transfer device, 6 ... Fixing device, 7 ... Laser beam scanner, 10 ... Process cartridge, 11 ... Image carrier Body current detection means, 12 ... Control circuit section, S1 to S3 ... High-voltage power supply, P ... Transfer material (recording medium), m ... Conductive fine powder

Continued front page    (72) Inventor Hiroshi Sato             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Yasushi Shimizu             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Masahiro Yoshida             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H005 AA08 CB07                 2H027 DA02 DA16 DE05 DE07 DE10                       EA01 EC06 ED02 ED03 ED08                       EF08 EF10                 2H077 AA37 AC12 AC16 AD06 AD13                       AD36 BA09 EA13                 2H200 FA18 GA16 GA23 GA28 GA30                       GA34 GA46 GA57 GA59 GB37                       HA03 HA21 HA29 HB12 HB22                       HB45 HB46 HB47 HB48 JA02                       JB10 MA03 MA08 MA12 MA14                       MA20 MB06 MC02 NA02 PA06                       PB04 PB38

Claims (8)

[Claims] 1. At least an image carrier, a charging unit that charges the image carrier, an image information writing unit that forms an electrostatic latent image on a charged surface of the image carrier, and the electrostatic latent image by toner. The image carrier has a developing unit that visualizes it as a toner image and a transfer unit that transfers the toner image to a recording medium. The image carrier is repeatedly used for image formation, and the charging unit that charges the image carrier is the image. A voltage is applied with a speed difference between the image carrier and a carrier, and a conductive powder is applied between the carrier and the image carrier, and the developer of the developing unit contains toner and conductive powder. The development of the electrostatic latent image on the carrier is performed by the developer, and at least the contact portion between the charging member and the image carrier,
In an image forming apparatus in which a conductive powder contained in the developer that is attached to the image carrier in the developing section and remains on the image carrier after transfer is carried and intervenes, the image carrier is written by writing image information. An image carrier current detecting means for detecting a current generated by the body, and when the charging means is in an operating state and the developing means and the transfer means are in a non-operating state, an image is written by the image information writing means. Control for forming an electrostatic latent image on a carrier and providing means for preventing the generation of a defective image when the amount of current of the image carrier detected by the image carrier current detection means at that time is below a certain value An image forming apparatus comprising means. 2. The image forming apparatus according to claim 1, wherein the means for preventing the generation of the defective image is to change the charging voltage by the charging means. 3. The image forming apparatus according to claim 1, wherein the means for preventing the generation of the defective image is to increase the supply of the conductive powder by the developing means. 4. The image forming apparatus according to claim 1, wherein the means for preventing the generation of the defective image is to stop the subsequent image forming operation. 5. A means for preventing the generation of a defective image is, “After the supply of the conductive powder by the developing means is increased, the charging means is in the operating state again, and the developing means and the transfer means are In the non-operating state, the image carrier current when the electrostatic latent image is formed on the image carrier by the image information writing means is equal to or less than a certain value ''. The image forming apparatus according to claim 1, wherein the image forming operation is stopped. 6. The image forming apparatus according to claim 1, wherein the charging unit is moved in a direction opposite to a moving direction of the image carrier while maintaining a speed difference. 7. The image forming apparatus according to claim 1, wherein the charging unit includes a flexible member that forms the contact portion. 8. An image forming a part of the image forming apparatus according to claim 1, wherein at least the image carrier, the charging unit, and the developing unit are provided in a frame body. A process cartridge that can be attached to and detached from the main body of the forming device.