JP2002182454A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize ozoneless implantation electrostatic charge with a low impressed voltage using a simple member, such as an electrostatic charging roller, as a contact electrostatic charging member 2 of an image forming device of a contact electrostatic charging system and to maintain good electrostatic chargeability in spite of a decrease in electrostatic charge acceleration particles (m) which are made to exist in an electrostatic charging section (a) and the contact electrostatic charging member 2 and permits the implantation electrostatic charge. SOLUTION: The electrostatic charge acceleration particles (m) having electrical conductivity for accelerating the electrostatic charge are interposed in a nip section (a) of the flexible contact electrostatic charging member 2 and an image carrying member 1. The electrostatic charging member moves at a speed difference with the image carrying member. The electrostatic charge acceleration particles (m) are added to a developer 31 of a developing means 3 and the electrostatic charge acceleration particles (m) are electrostatically charged to a polarity reverse from the polarity of the electrostatic charging voltage of the image carrying member 1 within the developing means 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a copying machine and a printer. More specifically, the present invention relates to a contact charging type image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential. A corona charger (corona discharger) has been used as a charging device for performing the treatment (including the charge removal treatment).

[0003] A corona charger is a non-contact type charging device, and includes, for example, a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and has a discharge opening facing an image carrier as a member to be charged. The image carrier is charged in a predetermined manner by exposing the surface of the image carrier to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.

Recently, many contact charging devices have been proposed and put into practical use as charging devices for a member to be charged such as an image carrier, because of their advantages such as low ozone and low power as compared with corona chargers. ing.

[0005] The contact charging device contacts a member to be charged such as an image carrier with a conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type or a blade type.
A predetermined charging bias is applied to this charging member (contact charging member / contact charger, hereinafter referred to as a contact charging member) to charge the surface of the charged body to a predetermined polarity and potential.

[0006] The contact charging mechanism (charging mechanism,
In the charging principle), two types of charging mechanisms, a discharge charging system and an injection charging system, coexist, and each characteristic appears depending on which is dominant.

[0007] Discharge Charging System (Discharge Charging Mechanism) This is a system in which the surface of a member to be charged is charged by a discharge phenomenon occurring in a minute gap between the contact charging member and the member to be charged.

Since the discharge charging system has a certain discharge threshold value for the contact charging member and the member to be charged, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Further, although the amount of generation is much smaller than that of the corona charger, it is in principle unavoidable to generate a discharge product, so that the harmful effects of active ions such as ozone are inevitable.

[0009] Injection Charging System (Direct Injection Charging Mechanism) This is a system in which the surface of the member to be charged is charged by injecting charges directly from the contact charging member to the member to be charged. It is also called direct charging, injection charging, or charge injection charging.

More specifically, a medium-resistance contact charging member is brought into contact with the surface of an object to be charged, and charge is injected directly to the surface of the object without going through a discharge phenomenon, that is, basically without using discharge. It is. Therefore, even when the voltage applied to the contact charging member is equal to or lower than the discharge threshold, the member to be charged can be charged to a potential corresponding to the applied voltage. Since this injection charging system does not involve generation of ions, no adverse effects are caused by the discharge products.

However, because of the injection charging, the contact property of the contact charging member with the member to be charged greatly affects the charging property.
Therefore, it is necessary to form the contact charging member more densely, have a large speed difference from the member to be charged, and contact the member to be charged more frequently.

A) Roller Charging In the contact charging device, a roller charging method using a conductive roller (charging roller) as a contact charging member is preferable in terms of charging stability, and is widely used.

In the roller charging, the charging mechanism is dominated by the discharge charging system.

The charging roller is made of a conductive or medium-resistance rubber or foam. In some cases, these are laminated to obtain desired characteristics.

The charging roller has elasticity in order to obtain a certain contact state with a member to be charged (hereinafter, referred to as a photosensitive member). Therefore, frictional resistance is large, and in many cases, the charging roller is driven by the photosensitive member. It is driven with a slight speed difference. Therefore, even if an attempt is made to perform injection charging, a reduction in absolute charging ability, insufficient contact properties, unevenness on rollers and uneven charging due to adherence of a photoconductor are inevitable. The system is dominant.

FIG. 4 is a graph showing an example of charging efficiency in contact charging. The horizontal axis represents the bias applied to the contact charging member, and the vertical axis represents the photoconductor charging potential obtained at that time.

The charging characteristic in the case of the conventional roller charging is represented by A. That is, charging starts after passing a discharge threshold of about -500V. Therefore, when charging to -500 V, a DC voltage of -1000 V is applied, or
A general method is to apply an AC voltage of 1200V between peaks so as to always have a potential difference equal to or greater than a discharge threshold in addition to the charging voltage of 00V DC, so that the photoconductor potential converges on the charging potential.

More specifically, when a charging roller is pressed against an OPC photosensitive member having a thickness of 25 μm, the surface potential of the photosensitive member increases when a voltage of about 640 V or more is applied. Start, and after that, slope 1 with applied voltage
, The photoconductor surface potential increases linearly. This threshold voltage is defined as charging start voltage Vth.

That is, in order to obtain the photosensitive member surface potential Vd required for electrophotography, the charging roller needs Vd + Vth
Therefore, a DC voltage higher than required is required. A method of applying only a DC voltage to the contact charging member to perform charging in this manner is referred to as a “DC charging method”.

However, in DC charging, since the resistance value of the contact charging member fluctuates due to environmental fluctuations and the like, and Vth fluctuates when the film thickness changes due to shaving of the photoreceptor, the potential of the photoreceptor changes to a desired value. It was difficult to value.

For this reason, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, a DC voltage corresponding to a desired Vd has a peak-to-peak voltage of 2 × Vth or more, as disclosed in JP-A-63-149669. An “AC charging method” in which a voltage on which an AC component is superimposed is applied to a contact charging member is used. This is for the purpose of effect of leveling the potential by AC, and the potential of the charged body is V V which is the center of the peak of the AC voltage.
It converges to d and is not affected by disturbances such as the environment.

However, even in such a contact charging device, since the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photosensitive member, the charging is applied to the contact charging member as described above. The voltage is required to be higher than the surface potential of the photoreceptor, and a small amount of ozone is generated.

When AC charging is performed for uniform charging, further generation of ozone, generation of vibration noise (AC charging noise) between the contact charging member and the photoreceptor due to the electric field of the AC voltage, and generation of discharge due to discharge. Deterioration of the surface of the photoreceptor becomes remarkable, and this is a new problem.

B) Fur Brush Charging In the fur brush charging, a member having a conductive fiber brush portion (fur brush charger) is used as a contact charging member.
The conductive fiber brush portion is brought into contact with a photoreceptor as a member to be charged, and a predetermined charging bias is applied to charge the photoreceptor surface to a predetermined polarity and potential.

In the fur brush charging, the charging mechanism is dominated by the discharge charging system.

As the fur brush charger, a fixed type and a roll type have been put to practical use. A fixed type is formed by folding a medium-resistance fiber into a base fabric and forming it in a pile shape and bonding it to an electrode. The roll type is formed by winding a pile around a cored bar. A fiber density of about 100 fibers / mm ² can be obtained relatively easily, but the contact property is still insufficient to perform sufficiently uniform charging by injection charging, and sufficiently uniform charging is performed by injection charging. It is necessary to make the speed difference such that it is difficult for the photoconductor to have a mechanical configuration, which is not practical.

The charging characteristics of this fur brush charging when a DC voltage is applied are as shown in FIG. 4B. Therefore, also in the case of the fur brush charging, in both the fixed type and the roll type, charging is performed by applying a high charging bias and using a discharge phenomenon.

C) Magnetic Brush Charging The magnetic brush charging uses a member (magnetic brush charger) having a magnetic brush portion formed by brushing conductive magnetic particles magnetically with a magnet roll or the like as a contact charging member. The magnetic brush portion is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied to charge the surface of the photosensitive member to a predetermined polarity and potential.

In the case of this magnetic brush charging, the charging mechanism is dominated by the injection charging system described above.

The use of conductive magnetic particles having a particle size of 5 to 50 μm as a constituent of the magnetic brush portion and providing a sufficient speed difference from the photosensitive member enables uniform direct charging.

As shown at C in the charging characteristic graph of FIG.
It is possible to obtain a charging potential substantially proportional to the applied bias.

However, there are other adverse effects, such as the complexity of the device configuration, and the fact that the conductive magnetic particles constituting the magnetic brush portion fall off and adhere to the photoreceptor.

Japanese Patent Application Laid-Open No. Hei 6-3921 proposes a method in which charge is injected into a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles in a charge injection layer to perform contact injection charging. . Since the discharge phenomenon is not used, the voltage required for charging is only the desired surface potential of the photoconductor, and no ozone is generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and the charging method is excellent in ozone-less and low power compared to the roller charging method.

D) Cleanerless (Toner Recycling System) In a transfer type image forming apparatus, a transfer residual developer (toner) remaining on a photoreceptor (image carrier) after transfer is transferred to the surface of the photoreceptor by a cleaner (cleaning device). The waste toner is removed from the toner, and it is desirable that the waste toner does not appear from the viewpoint of environmental protection. So I removed the cleaner,
A cleaner-less image forming apparatus has also emerged, in which the transfer residual developer on the photoreceptor after transfer is removed from the photoreceptor by "simultaneous development" by a developing device, and is collected and reused in the developing device. .

Simultaneous development cleaning means that the developer remaining on the photoreceptor after transfer is developed at the next and subsequent steps, that is, the photoreceptor is subsequently charged and exposed to form a latent image. This is a method of recovering by a fogging bias (fogging potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photoconductor). According to this method, the untransferred developer is collected in the developing device and reused after the next process, so that waste toner can be eliminated and troublesome maintenance can be reduced. In addition, the cleaner-less has a great advantage in terms of space, and the size of the image forming apparatus can be significantly reduced.

In the cleaner-less method, the transfer residual toner is not removed from the surface of the photoreceptor by a dedicated cleaner as described above, but is transferred to a developing device via a charging means and used again in the developing process. Therefore, when contact charging is used as the charging means of the photoconductor, how to charge the photoconductor in a state where an insulative developer is interposed in the contact portion between the photoconductor and the contact charging member is an issue. Has become. In the above-described roller charging or fur brush charging, transfer residual toner on a photoreceptor is diffused to form a non-pattern, and a large amount of bais is applied and charging by discharge is often used. In magnetic brush charging, since powder is used as a contact charging member, there is an advantage that the magnetic brush portion of the conductive magnetic particles as the powder can flexibly contact the photoconductor and charge the photoconductor, but the equipment configuration is complicated. That is, there is a large adverse effect due to the drop of the conductive magnetic particles constituting the magnetic brush portion.

E) Powder Coating on Contact Charging Member The contact charging device has a configuration in which powder is applied to the contact surface of the contact charging member with the surface to be charged in order to prevent charging unevenness and perform stable and uniform charging. As disclosed in Japanese Patent Application Laid-Open No. 7-99442, the contact charging member (charging roller) is driven to rotate (no speed difference driving) by the member to be charged (photosensitive member), and generates ozone as compared with a corona charger such as a scorotron. Although the generation of the object is remarkably reduced, the charging principle is still mainly the charging by the discharge as in the case of the roller charging described above. In particular, since a voltage obtained by superimposing an AC voltage on a DC voltage is applied to obtain more stable charging uniformity, the generation of ozone products due to discharge is increased. Therefore, when the apparatus is used for a long period of time or when the cleaner-less image forming apparatus is used for a long period of time, adverse effects such as image deletion due to ozone products are likely to appear.

Japanese Patent Application Laid-Open No. 5-150539 discloses that in an image forming method using contact charging, charge inhibition due to toner particles or silica fine particles adhering to the surface of the charging means during repeated image formation for a long time. It is disclosed that the developer contains at least visible particles and conductive particles having an average particle size smaller than the visible particles in order to prevent the development. However, this contact charging is due to the discharge charging mechanism, not the direct injection charging mechanism, and has the above-mentioned problem due to discharge charging.

[0039]

As described in the section of the prior art described above, conventionally, in contact charging, in a simple configuration using a charging roller or a fur brush as a contact charging member, it is difficult to perform injection charging. The surface of the contact charging member was rough, so that close contact with the image carrier as the member to be charged was not ensured, and injection charging was difficult.

Therefore, in the contact charging, even when a simple member such as a charging roller or a fur brush is used as the contact charging member, more excellent charging uniformity and stable injection charging over a long period of time are realized. It is expected that ozone-less injection charging can be realized with a simple configuration using an applied voltage.

In an image forming apparatus of a transfer type using a contact charging method employing a contact charging device as a charging means for the image carrier, contamination of the contact charging member with a developer is also a factor inhibiting injection charging. .

That is, even in the case of an image forming apparatus provided with a dedicated cleaner for removing the residual transfer residual developer on the surface of the image carrier after the transfer, the residual transfer developer remaining on the surface of the image carrier after the transfer is removed. Is not removed by 100%, and a part of the transfer residual developer passes through the cleaner and is carried to the charging portion, which is the contact portion between the contact charging member and the image carrier, and adheres to and mixes with the contact charging member. This causes developer contamination of the contact charging member. Conventionally, the developer is generally an insulator, so that the developer contamination of the contact charging member is a factor that causes poor charging.

In particular, in a cleaner-less image forming apparatus, a dedicated cleaner for removing the residual transfer developer remaining on the surface of the image carrier after transfer is not used. The residual developer is carried to the charging portion, which is the contact portion between the image carrier and the contact charging member, as it moves on the image carrier surface, and the contact charging member is contaminated with a larger amount of developer than in the case of an image forming apparatus having a cleaner. Therefore, the effect of charge inhibition by the transfer residual developer is large.

The adhesive force between the contact charging member such as a charging roller and the developer is large, and even when a developer discharge bias or the like is applied to the contact charging member, the developer is firmly adhered to the contact charging member and sufficient chargeability is obtained. Could not get.

When the charging failure occurs, the mixing of the developer into the contact charging member further increases, and the charging failure is intensified.

That is, here, in order to inject and charge with a simple contact charging member such as a charging roller, the surface of the contact charging member is rough, and the adhesion between the contact charging member and the developer is large, so that the development of the contact charging member is large. The problem is that the agent contamination cannot be improved.

Therefore, the present invention relates to an image forming apparatus employing a contact charging device as a charging means for an image carrier, and using a simple member such as a charging roller or a fur brush as a contact charging member and applying ozone-less injection at a low applied voltage. An object of the present invention is to realize charging and to perform high-quality image formation.

The present invention also relates to a contact charging system, a transfer system image forming apparatus employing a contact charger as a charging means of an image carrier, or a contact charging system, a transfer system, and a cleanerless image forming apparatus. Using a simple member such as a charging roller or fur brush as a member, and irrespective of the developer contamination of the contact charging member, the ozone-less injection charging and cleaner-less system can be performed without problems at a low applied voltage, and high quality It is an object of the present invention to maintain image formation for a long period of time and maintain high-quality image formation for a long period of time even after outputting an image having a high image ratio.

[0049]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) Image carrier, charging means for charging the image carrier, latent image forming means for forming an electrostatic latent image on the image carrier charged by the charging means, and the electrostatic latent image A developing means for developing the nip portion with a developer, wherein the charging means is provided with a flexible charging member to which a voltage is applied and forms a nip portion with the image carrier, and the nip portion The conductive particles are interposed, and the conductive particles are provided in the developing unit, are supplied from the developing unit to the image carrier, and are conveyed to the nip by the image carrier, and in the developing unit, An image forming apparatus, which is charged to a polarity opposite to a polarity of a voltage.

(2) The image forming apparatus according to (1), wherein the charging member moves at a speed difference with respect to the image carrier.

(3) The conductive particle according to (1) or (2), wherein the conductive particles are charged to a polarity opposite to the polarity of the voltage by rubbing with a developer in the developing unit. Image forming device.

(4) The developing means reversely develops the electrostatic latent image with a developer, and the conductive particles are attached to a non-image portion of the image carrier from the developing means. The image forming apparatus according to any one of (1) to (3).

(5) The image forming apparatus according to any one of (1) to (4), wherein the charging member has a foam on its surface.

(6) The image forming apparatus according to any one of (1) to (5), wherein the developing means is capable of collecting a developer on the image carrier.

(7) The image forming apparatus according to any one of (1) to (6), further comprising a transfer unit for transferring the developer image formed on the image carrier to a recording medium. .

<Operation> a) The conductive particles are conductive particles (charge promotion particles) for the purpose of assisting charging, and the conductive particles are interposed at least in the nip portion between the charging member and the image carrier in contact charging. By doing so, uniform and stable injection charging is realized. The conductive particles have a resistance value of 1 × 10 ¹² (Ω · cm) or less, more preferably 10 ¹⁰ (Ω · cm) or less, so that the chargeability is not impaired. Further, by setting the particle diameter to be not more than 1/2 of the particle diameter of the developer, it does not hinder image exposure on the image carrier.

That is, since conductive particles are interposed in the charging portion, which is a nip portion between the image carrier and the contact charging member, the frictional effect is large due to the lubricant effect of the particles, and the speed is higher than that of the image carrier as it is. Even if the charging roller has been difficult to contact with a difference, it can be easily and effectively brought into contact with the image carrier surface with a speed difference. At the same time, the contact charging member comes into close contact with the surface of the image carrier via the particles, and comes into contact with the surface of the image carrier at a higher frequency.

By providing a sufficient speed difference between the contact charging member and the image carrier, the chance that the conductive particles come into contact with the image carrier at the nip portion between the contact charging member and the image carrier is greatly increased. High contact properties can be obtained, and the conductive particles present in the nip portion between the contact charging member and the image carrier can directly inject charges into the image carrier by rubbing the image carrier surface without gaps, In contact charging of the image carrier by the contact charging member, injection charging is dominant due to the presence of conductive particles.

B) As a configuration for providing a speed difference, a contact charging member is rotated to provide a speed difference from the image carrier. In a transfer type or transfer type / cleanerless image forming apparatus, it is preferable that the developer carried through the cleaner or the transfer residual developer in the case of cleanerless, which is carried to the charging unit, is temporarily transferred to the contact charging member. It is desirable that the contact charging member be rotationally driven in order to collect and evenly collect the toner, and that the rotating direction of the contact charging member be rotated in a direction opposite to the moving direction of the surface of the image carrier. That is, it is possible to perform injection charging predominantly by once separating the remaining developer on the image carrier by reverse rotation and performing charging.

Although the contact charging member can be moved in the same direction as the moving direction of the surface of the image carrier to have a speed difference, the chargeability of the injection charging depends on the peripheral speed of the image carrier and the peripheral speed of the contact charging member. In order to obtain the same peripheral speed ratio as in the reverse direction, the rotational speed of the contact charging member is higher in the forward direction than in the reverse direction, so it is better to move the contact charging member in the reverse direction. This is advantageous in terms of rotation speed. The peripheral speed ratio described here is the peripheral speed ratio (%) = (the peripheral speed of the charging member−the peripheral speed of the image carrier) / the peripheral speed of the image carrier × 100. It is a positive value when moving in the same direction as the surface of the image carrier).

C) In a cleanerless image forming apparatus, the transfer residual developer remaining on the surface of the image carrier after transfer is moved to the charging portion which is a nip portion between the image carrier and the contact charging member. It is carried as it is.

In this case, by bringing the contact charging member into contact with the image carrier with a speed difference, the pattern of the transfer residual developer is disturbed and broken, and in the halftone image, the previous image pattern portion becomes ghost. Will not appear.

D) The developer carried through the cleaner and passed through the cleaner or the transfer residual developer in the case of cleaner-less adheres to and mixes with the contact charging member. Conventionally, since the developer is an insulator, the transfer residual developer adheres to the contact charging member.
The contamination is a factor that causes charging failure in charging the image carrier.

However, even in this case, since the conductive particles are interposed in the charging portion which is a nip portion between the image carrier and the contact charging member, the fine contact property and contact resistance of the contact charging member to the image carrier are maintained. Therefore, irrespective of contamination of the contact charging member by the transfer residual developer, ozone-less injection charging can be stably maintained at a low applied voltage for a long period of time, and uniform charging properties can be provided.

E) The developer adhering to and mixed into the contact charging member is gradually discharged from the contact charging member onto the image carrier, moves to the surface of the image carrier, and reaches the developing site. (Toner recycling).

In this case, since the conductive particles are carried on the contact charging member, the adhesion between the contact charging member and the transfer residual developer adhering to and mixing with the contact charging member is reduced, and the contact charging member is moved from the contact charging member onto the image carrier. Thus, the efficiency of discharging the developer to the surface is improved.

F) The conductive particles capable of being injected and charged as described above are placed in advance in a charging portion, which is a nip portion between the image carrier and the contact charging member, with a sufficient amount of the conductive particles interposed therebetween or in contact. Even if a sufficient amount of conductive particles are applied to the charging member, or if a conductive particle coating / supplying means is provided for the contact charging member, the conductive particles are reduced from the charging unit as the device is used, and the charged particles are injected. In some cases, the chargeability may decrease.

The image carrier can be frictionally charged to the same polarity as the charging voltage when the contact charging member and the image carrier are brought into contact with each other without conductive particles. However, even if the injection charging property is reduced due to the temporary decrease of the conductive particles interposed in the charging portion or the conductive particles applied to the surface of the contact charging member, the image carrier is still in contact with the image carrier of the contact charging member. The triboelectric charge having the same polarity as the polarity of the charging voltage is generated, so that the chargeability of the image carrier is hardly reduced. Thereby, good chargeability can be maintained.

That is, when the contact charging member comes into direct contact with the image carrier, the potential of the surface of the image carrier becomes the same polarity as the charging voltage due to frictional charging between the contact charging member and the image carrier. To rise. Therefore, even if there is a point of insufficient contact between the contact charging member and the image carrier in the vicinity of the point where the contact charging member and the image carrier are in direct contact (a point where the direct charging property is reduced), the charging property is hardly reduced as a whole.

G) In the present invention, in the transfer type image forming apparatus, conductive particles are added to the developer of the developing unit, and the conductive particles are charged in the developing unit with the polarity opposite to the polarity of the charging voltage of the image carrier. The developing means unit causes the conductive particles added to the developer to adhere to the image carrier, and is carried to the charging unit via the transfer unit as the image carrier surface moves. The conductive particles are automatically supplied to the charging section and the contact charging member to maintain good charging properties.

The developer image on the image carrier is attracted to the recording medium side by the influence of the transfer bias at the transfer portion and positively transitions. However, since the conductive particles on the image carrier are conductive, the recording medium is electrically conductive. Does not positively transfer to the side, remains substantially adhered and held on the image carrier, and is carried to the charging unit via the transfer unit as the image carrier surface moves.

In this case, even in the case of an image forming apparatus equipped with a cleaner, the transfer residual developer (including paper dust) remaining on the surface of the image carrier after transfer and the conductive transfer developer among the conductive particles are the same. Most of the particles are collected by the cleaner, but the conductive particles have a smaller particle size than the developer, and thus easily pass through the cleaner, and are carried to the charging section by the slip. In the case of a cleaner-less image forming apparatus, the transfer residual developer and the conductive particles remaining on the surface of the image carrier after the transfer are carried to the charging section as they are.

When the conductive particles are reduced from the charging section and the surface of the contact charging member, and the potential of the image carrier rises to the charging applied voltage side due to frictional charging of the contact charging member and the image carrier, the conductive particles from the developing means are discharged. Since the supply amount of the particles increases and more conductive particles are supplied to the charging unit and the contact charging member, the conductive particles can be applied again to the surface of the contact charging member. Therefore, the conductive particles adhered to the contact charging member do not continue to decrease, and it is possible to maintain good chargeability.

H) Thus, for the contact-charging type image forming apparatus, the ozone-less injection charging can be realized with a low applied voltage by using a simple member such as a charging roller or a fur brush as the contact charging member, and the injection charging can be performed. In the case where the conductive particles are reduced from the charging portion or the contact charging member, frictional charging of the same polarity as the charging voltage is generated on the image carrier by direct contact of the contact charging member, and further, a transfer type image forming apparatus. In the case of (1), the conductive particles added to the developer are supplied from the developing unit, so that the chargeability of the image carrier is small and good chargeability is maintained, and the contact that is contaminated by the developer is provided. The developer, which is an inhibitor of charging, is efficiently discharged from the charging member, and good charging performance can be stably maintained for a long period of time. The can be performed without any problems, a high-quality image formation can be over a long period of time maintaining. Further, even after outputting an image having a high image ratio, high-quality image formation can be maintained for a long period of time.

Since the polarity of the conductive particles is opposite to the polarity of the charging voltage, the conductive particles conveyed to the nip portion are easily carried by the charging member, so that good chargeability is maintained. Further, when the polarity of the conductive particles and the polarity of the developer are opposite, the conductive particles conveyed by the image carrier are difficult to be transferred to the recording medium, so that the amount of the conductive particles conveyed to the nip by the image carrier is reduced. Can be suppressed.

[0077]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference Example (FIG. 1) FIG. 1 is a schematic structural model diagram of an example of an image forming apparatus according to a reference example.

The image forming apparatus of this embodiment is a laser printer using a transfer type electrophotographic process, a contact charging type, a reversal developing type, a cleanerless type, and a process cartridge type.

Then, at least in the nip portion between the contact charging member and the image carrier, conductive particles having conductivity for accelerating the charging are interposed to realize injection charging. Is contacted without conductive particles, the image carrier is frictionally charged to the same polarity as the polarity of the charging voltage.

(1) Overall Schematic Configuration of the Printer [Image Carrier] 1 is a rotary drum type electrophotographic photosensitive member as an image carrier (charged body). The printer of this example uses reversal development, and the photoconductor 1 uses a negative photoconductor. The photoreceptor 1 of this embodiment is an OPC photoreceptor having a diameter of 30 mm, and is rotationally driven in a clockwise direction indicated by an arrow at a peripheral speed of 94 mm / sec.

[Charging] 2 is a conductive elastic roller (charging roller) as a flexible contact charging member disposed in contact with the photosensitive member 1 with a predetermined pressing force. Reference symbol a denotes a charging nip portion between the photoconductor 1 and the charging roller 2. The outer peripheral surface of the charging roller 2 is coated with and supported by conductive particles m in advance, and the conductive particles m are present in the charging nip portion a.

Reference numeral 7 denotes an apparatus for applying conductive particles to the charging roller 2. An appropriate amount of the conductive particles m is put in the coating container 71, and an appropriate amount of the conductive particles m is coated on the outer peripheral surface of the charging roller 2 rotated by the elastic blade 72.

In this embodiment, the charging roller 2 is driven to rotate at a peripheral speed of 100% in the direction opposite to the rotation direction of the photosensitive member 1 (counter) at the charging nip portion a, and has a speed difference with respect to the surface of the photosensitive member 1. Contact. And this charging roller 2
, A predetermined charging bias is applied from a charging bias power supply S1. As a result, the peripheral surface of the rotary photoconductor 1 is uniformly contact-charged to a predetermined polarity and potential by the injection charging method. In this example, the outer peripheral surface of the photoconductor 1 is substantially −700 on the charging roller 2.
V so as to be uniformly charged to V.
1 to apply a charging bias.

The charging roller 2, the conductive particles m, the injection charging and the like will be described in detail in another section.

[Exposure] Scanning exposure L is performed on the charged surface of the rotary photosensitive member 1 by a laser beam output from a laser beam scanner (not shown) including a laser diode, a polygon mirror, and the like. The laser beam output from the laser beam scanner is intensity-modulated in accordance with the time-series electric digital pixel signal of the target image information. An electrostatic latent image corresponding to the target image information is formed.

In this embodiment, reversal development is used, and in the scanning exposure L of the outer peripheral surface of the rotary photoreceptor 1 with a laser beam, the exposed portion is an image portion and the non-exposed portion is a non-image portion.

[0107] [Current image] 3 is a reversal developing device. The above-described electrostatic latent image formed on the outer peripheral surface of the rotary photoreceptor 1 has a developer (toner) adhered to an exposed portion by the developing device 3. The image is reversely developed as a developer image (toner image).

The developing device 3 of this embodiment uses a non-magnetic one-component insulating developer having a negative chargeability and an average particle diameter of 7 μm as the developer 31.

Reference numeral 32 denotes a diameter 16 containing the magnet 33.
mm of a non-magnetic developing sleeve.
2 is coated with the above-mentioned developer 31 and is rotated at the same speed as the photoconductor 1 with the distance from the surface of the photoconductor 1 fixed at 500 μm, and a developing bias voltage is applied to the developing sleeve 32 from a developing bias power source S2. .

In the process of being transported on the rotary developing sleeve 32, the developer 31 in the developing device is subjected to layer thickness regulation by an elastic blade (regulating blade) 34, and is frictionally charged by rubbing with the elastic blade 34, It has a charge.

The developing bias voltage is obtained by superimposing a DC voltage of -420 V and a rectangular AC voltage having a frequency of 1600 Hz and a peak-to-peak voltage of 1600 V.
One-component jumping development is performed at a development site b between the photoconductor 2 and the photoconductor 1.

[Transfer] Reference numeral 4 denotes a medium-resistance transfer roller as contact transfer means, which is brought into pressure contact with the photoreceptor 1 to form a transfer nip c. A transfer material P as a recording medium is supplied to the transfer nip c from a paper supply unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 4 from a transfer bias power supply S3. Thus, the developer image on the photoconductor 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip c.

The transfer roller 4 used in this example has a medium resistance foam layer 42 formed on a metal core 41 and has a roller resistance value of 5 × 10 ^8.
The transfer was performed by applying a DC voltage of +3000 V to the metal core 41. The transfer material P introduced into the transfer nip portion c is conveyed by nipping the transfer nip portion c, and the developer image formed and carried on the surface of the rotary photoreceptor 1 on its surface side is sequentially subjected to electrostatic force and pressing force. Is transcribed.

[Fixing] 5 is a fixing device such as a heat fixing method. The transfer material P fed to the transfer nip c and having received the transfer of the developer image on the photosensitive member 1 is separated from the surface of the rotating photosensitive member 1 and introduced into the fixing device 5 to fix the developer image. Then, the sheet is discharged out of the apparatus as an image formed product (print, copy).

[Cartridge] In the printer of this embodiment, the four process devices of the photosensitive member 1, the charging roller 2, the conductive particle coating device 7 for the charging roller, and the developing device 3 are contained in a cartridge case, and the printer body is It is a removable cartridge C as a whole. The combination of the process devices to be made into a cartridge is not limited to the above.

(2) Charging Roller 2 The charging roller 2 as a flexible contact charging member in this embodiment is formed by forming a medium resistance layer 22 of rubber or foam on a cored bar 21.

The medium resistance layer 22 is formulated with a resin (eg, urethane), conductive particles (eg, carbon black), a sulfide agent, a foaming agent, and the like. The medium resistance layer (elastic resin) so that the photosensitive member 1 is frictionally charged to the negative polarity (−) in the present example in the same polarity as the polarity of the charging voltage (without conductive particles).
Nylon was dispersed at 2% by weight therein to form a roller on the metal core 21. Thereafter, the surface was polished.

Here, the charging roller 2 as a contact charging member
Is important to function as an electrode. That is, it is necessary to obtain a sufficient contact state with the member to be charged by providing elasticity, and at the same time, it is necessary to have a resistance low enough to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a low withstand voltage defect site such as a pinhole is present in the member to be charged. When a photoreceptor for electrophotography is used as a member to be charged, 10 ⁴ to 10 ⁷ are required to obtain sufficient chargeability and leakage resistance.
A resistance of Ω is desirable.

It is desirable that the surface of the charging roller 2 has micro unevenness so as to hold the conductive particles m.

If the hardness of the charging roller 2 is too low, the shape is not stable and the contact with the member to be charged is deteriorated. If the hardness is too high, the charging nip a cannot be secured between the charging roller 2 and the member to be charged. However, the microscopic contact with the surface of the member to be charged is deteriorated, so that 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 an elastic foam.
Examples include M, urethane, NBR, silicone rubber, and rubber materials in which a conductive substance such as carbon black or metal oxide is dispersed in IR or the like for resistance adjustment, or foamed materials thereof. Also, without dispersing the conductive material,
It is also possible to adjust the resistance using an ion conductive material.

The charging roller 2 is disposed in pressure contact with the photosensitive drum 1 as a member to be charged with a predetermined pressing force against elasticity. In this embodiment, a charging nip portion a having a width of several mm is formed. is there.

The frictional charging polarity between the charging roller 2 and the photosensitive member 1 was measured as follows. That is, in the printer,
The developing device 3, the transfer roller 4, and the like are separated from the photoconductor 1, and only the charging roller 2 is brought into contact with the photoconductor 1. Thereafter, 0 V is applied to the charging roller 2 to rotate the photosensitive member 1 so that the charging roller 2 is driven to rotate. The state is continued for one minute, and the potential of the photoconductor 1 is measured. The triboelectric charging polarity between the charging roller 2 and the photoconductor 1 was measured based on the potential. All measurements were performed in an environment at a temperature of 25 ° C. and a humidity of 30%.

The resistance value of the charging roller 2 (hereinafter referred to as charging roller A) and the frictional charging polarity (offset potential (V); the frictional charging potential of the photosensitive member 1 caused by direct contact with the charging roller) in the above-described embodiment were measured. did. Table 1 shows the results.

The resistance value of the charging roller was measured as follows. The photoreceptor 1 of the printer is replaced with an aluminum drum. Thereafter, a voltage of 100 V was applied between the aluminum drum and the metal core 21 of the charging roller 2, and the value of the current flowing at that time was measured to determine the resistance value of the charging roller 2.

Further, as comparative examples, the following resistance values of the charging roller B and the charging roller C and the triboelectric charging polarity (offset potential (V)) were also measured.

Charging roller B: A charging roller having no medium resistance layer (elastic resin) containing nylon.

Charging roller C: A medium in which the medium resistance layer (elastic resin) of charging roller A contains 2% by weight of Teflon (registered trademark) (ethylene tetrafluoride resin) instead of nylon.

[0109]

[Table 1]

(3) Conductive Particles m In this example, the conductive particles m applied to the outer peripheral surface of the charging roller 2
And the specific resistance is 10 ⁷Ω · cm, average particle size 2.5μm
Was used.

There is no problem that the conductive particles are present not only in the form of primary particles but also in the form of aggregated secondary particles. Regardless of the state of aggregation, the form is not important as long as the function as conductive particles can be realized as an aggregate.

When the particles constitute an aggregate, the particle size is defined as the average particle size of the aggregate. The particle size is measured by observation using an optical or electron microscope.
More than 100 were extracted, the volume particle size distribution was calculated using the maximum chord length in the horizontal direction, and the 50% average particle size was determined.

When the resistance value of the conductive particles m was 10 ¹² Ω · cm or more, the chargeability was impaired. Therefore, if the resistance value is 10
^It is preferably ¹² Ω · cm or less, more preferably 10 ¹⁰ Ω · cm or less. In this example, 1 × 10 ⁷ Ω · cm was used. The resistance was measured by a tablet method and normalized. That is, about 0.5 g in a cylinder having a bottom area of 2.26 cm ^2.
The powder sample was put in, 15 kg of pressure was applied to the upper and lower electrodes, and at the same time, a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.

The conductive particles m are preferably white or nearly transparent so as not to hinder the exposure of the latent image, and are therefore preferably non-magnetic. Further, considering that the conductive particles are partially transferred from the photoreceptor to the recording material P, color recording is preferably colorless or white. Further, if the particle diameter is not more than about 1/2 of the particle diameter of the developer 31, image exposure may be interrupted. Therefore, it is desirable that the particle size of the conductive particles m be smaller than １ ／ of the particle size of the developer 31. The lower limit of the particle size is considered to be 10 nm as a limit so that the particles can be stably obtained.

In this example, zinc oxide was used as the material of the conductive particles m. However, the material is not limited to zinc oxide. In addition, a mixture of other metal oxides such as alumina with conductive inorganic particles or an organic material, or Various conductive particles such as those subjected to a surface treatment can be used.

(4) Injection charging. The conductive particles m are interposed in the charging nip portion a between the photosensitive member 1 serving as an image carrier and the charging roller 2 serving as a contact charging member. Even if it was difficult to contact the charging roller with a speed difference, the charging roller was easily and effectively brought into contact with the surface of the photoconductor 1 with a speed difference. As a result, the charging roller 2 comes into close contact with the surface of the photoconductor 1 via the particles m, and comes into contact with the surface of the photoconductor 1 more frequently.

By providing a sufficient speed difference between the charging roller 2 and the photosensitive member 1, the chance of the conductive particles m contacting the photosensitive member 1 in the nip portion between the charging roller 2 and the photosensitive member 1 is significantly increased. A high contact property can be obtained, and the conductive particles m present in the charging nip portion a of the charging roller 2 and the photoconductor 1 can directly inject charges into the photoconductor 1 by rubbing the surface of the photoconductor 1 without gaps. Thus, the contact charging of the photoconductor 1 by the charging roller 2 is dominated by the injection charging due to the presence of the conductive particles m.

As a configuration for providing a speed difference, the charging roller 2 is rotationally driven to provide a speed difference from the photosensitive drum 1. Preferably, the charging roller 2 is driven to rotate in order to temporarily collect and level the transfer residual developer on the photoconductor 1 carried to the charging nip portion a by the charging roller 2, and further, the rotation direction is It is desirable to configure so as to rotate in the direction opposite to the moving direction of one surface. That is, it is possible to perform the injection charging by dominating the transfer residual developer on the photoreceptor 1 once by reverse rotation to perform charging.

Accordingly, a high charging efficiency, which cannot be obtained by conventional roller charging or the like, is obtained, and a charging potential substantially equal to the voltage applied to the charging roller 2 can be applied to the photosensitive member 1. Thus, even when the charging roller 2 is used as the contact charging member, the applied bias necessary for charging the charging roller 2 is a voltage equivalent to the charging potential required for the photoreceptor 1 and is stable and does not use a discharge phenomenon. A safe contact charging system or device can be realized.

If the amount of the conductive particles m in the charging nip a between the photosensitive member 1 as the image carrier and the charging roller 2 as the contact charging member is too small, the lubricating effect of the particles cannot be sufficiently obtained. The friction between the charging roller 2 and the photoconductor 1 is large, and it is difficult to rotate the charging roller 2 with a speed difference between the photoconductor 1 and the photoconductor 1. In other words, the driving torque becomes excessively large, and the surface of the charging roller 2 and the surface of the photoconductor 1 will be scraped if they are rotated by force. Further, the effect of increasing the chance of contact by the particles may not be obtained, so that sufficient charging performance cannot be obtained. On the other hand, if the intervening amount is too large, the drop of the conductive particles from the charging roller 2 is remarkably increased, which adversely affects the image formation.

According to experiments, it is desirable that the intervening amount is not less than 10 ³ pieces / mm ² . If it is lower than 10 ³ / mm ² , a sufficient lubricating effect and an effect of increasing the contact chance cannot be obtained, and the charging performance is lowered.

More preferably, 10 ^{3 to} 5 × 10 ⁵ pieces / mm
The intervening amount of ² is preferred. If the number exceeds 5 × 10 ⁵ particles / mm ² , the particles drop off to the photoreceptor 1 significantly, resulting in insufficient exposure of the photoreceptor 1 irrespective of the light transmittance of the particles themselves. If it is 5 × 10 ⁵ particles / mm ² or less, the amount of particles falling off can be suppressed to a low level, and the adverse effect can be improved. When the abundance of the particles dropped on the photoreceptor 1 is measured in the range of the intervening amount, 10 ² to 1
Since the number was 0 ⁵ particles / mm ² , it is desired that the abundance without adverse effect on image formation be 10 ⁵ particles / mm ² or less.

A method for measuring the intervening amount and the abundance amount on the photoreceptor 1 will be described. It is desirable to directly measure the interposed amount between the charging roller 2 and the charging nip portion a of the photoreceptor 1, but most of the particles existing on the photoreceptor 1 before coming into contact with the charging roller 2 contact while moving in the opposite direction. In the present invention, the amount of particles on the surface of the charging roller 2 immediately before reaching the charging nip portion a is defined as the intervening amount. Specifically, the rotation of the photoconductor 1 and the charging roller 2 is stopped in a state where the charging bias is not applied, and the surfaces of the photoconductor 1 and the charging roller 2 are moved with a video microscope (OLY).
Images were taken with an OVM1000N manufactured by MPUS) and a digital still recorder (SR-3100 manufactured by DELTAS). Regarding the charging roller 2, the charging roller 2 is brought into contact with the slide glass under the same conditions as the contact with the photoreceptor 1, and the contact surface is viewed from the back of the slide glass with a video microscope at 10 or more locations using a 1000 × objective lens. Taken. In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where particles exist was measured using desired image processing software. Also, the amount of the photoconductor 1 on the photoconductor 1 was photographed with the same video microscope, and the same processing was performed and measured.

. In the cleaner-less image forming apparatus, the transfer residual developer remaining on the surface of the photoconductor 1 after the transfer is carried as it is to the charging nip portion a of the photoconductor 1 and the charging roller 2 by moving the surface of the photoconductor 1. .

In this case, by bringing the charging roller 2 into contact with the photosensitive member 1 with a speed difference, the pattern of the transfer residual developer is disturbed and broken, and in the halftone image, the previous image pattern portion becomes ghost. Will not appear.

. The transfer residual developer carried to the charging nip portion a adheres to and mixes with the charging roller 2. Conventionally, since the developer is an insulator, adhesion and mixing of the transfer residual developer with respect to the charging roller 2 is a factor that causes a charging failure in the charging of the photoconductor 1.

However, even in this case, since the conductive particles m intervene in the charging nip portion a between the photosensitive member 1 and the charging roller 2, the close contact property and contact resistance of the charging roller 2 to the photosensitive member 1 can be maintained. Therefore, irrespective of contamination of the charging roller 2 by the transfer residual developer, ozone-less injection charging can be stably maintained at a low applied voltage for a long period of time, and uniform charging properties can be provided.

[0128] The transfer residual developer adhering to and mixed into the charging roller 2 is gradually discharged from the charging roller 2 onto the photoreceptor 1 and reaches the developing site b with the movement of the photoreceptor 1 surface. (Toner recycling).

In this case, since the conductive particles m are carried on the charging roller 2, the adhesive force between the charging roller 2 and the transfer residual developer adhering to and mixing with the charging roller 2 is reduced, and
The efficiency of discharging the developer from the photoconductor 1 onto the photosensitive member 1 is improved.

As described above, the simultaneous cleaning for development is as follows.
The toner remaining on the photoreceptor 1 after the transfer is developed in a subsequent image forming process, that is, the photoreceptor is charged and exposed to form a latent image. That is, the toner is collected by a fog removal potential difference Vback, which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photosensitive member. In the case of reversal development as in the case of the printer in this example, this simultaneous development cleaning is performed by an electric field for collecting toner from the dark area potential of the photoconductor to the developing sleeve and an electric field for attaching toner from the developing sleeve to the light area potential of the photoconductor. Made by the action of

[0131] In addition, the transfer efficiency of the developer from the photoconductor 1 side to the transfer material P side is improved by the presence of the conductive particles m substantially adhered and held on the photoconductor 1 surface.

(5) Maintenance of Charging Property when Conductive Particles m Decrease First, even if a sufficient amount of conductive particles m is interposed in the charging nip portion a between the photosensitive member 1 and the charging roller 2, Even if a sufficient amount of the conductive particles m is applied to the charging roller 2, the conductive particles m will be
To decrease from. Further, even in the case where the conductive particle coating device 7 for the charging roller 2 is provided as in the present embodiment, the conductive nip may be charged even when the conductive particles m in the container 71 are consumed or due to malfunction of the coating device 7. Part a or charging roller 2
To decrease from.

The reduction of the conductive particles m from the charging nip portion a and the charging roller 2 causes a decrease in injection charging property. That is, the charging nip portion a between the charging roller 2 and the photosensitive member 1
In this case, the contact property between the two members 2 and 1 decreases, so that the photoconductor potential decreases near the photoconductor surface.

In this example, as described above, the photosensitive member 1
When the charging roller 2 and the photoconductor 1 are brought into contact with each other without the interposition of the conductive particles m, the photoconductor 1 is frictionally charged to the same polarity as the polarity of the charging voltage (minus in this example). Even if the charging property of the charging roller 2 is reduced due to the temporary decrease of the conductive particles m interposed in the charging nip portion a or the conductive particles m applied to the surface of the charging roller 2, the charging roller 2 is still in contact with the photosensitive member 1. Due to the occurrence of frictional charging of the same polarity as the polarity of the charging voltage of the photoconductor 1, the charging property of the photoconductor 1 is hardly reduced. Thereby, good chargeability can be maintained.

That is, when the charging roller comes into direct contact with the photoconductor 1, the potential of the photoconductor surface is the same as the charging voltage (minus) due to frictional charging between the charging roller 2 and the photoconductor 1. To rise. Therefore, even if there is a point of insufficient contact between the charging roller 2 and the photoreceptor 1 near the point where the charging roller 2 and the photoreceptor 1 are in direct contact (a point at which the injection charging property is reduced), the charging property is hardly reduced as a whole.

(6) Change in the amount of conductive particles attached to the surface of the charging roller and change in chargeability. In order to examine the change in the charging property when the amount of the conductive particles m deposited on the surface of the charging roller 2 changes, the amount of the charged particles m on the surface of the charging roller was selected from four types as shown in Table 2.
Was measured.

As a measure of the amount of the conductive particles m adhered to the surface of the charging roller, an area ratio indicating how much the surface of the charging roller was covered with the conductive particles m was used.

[0138]

[Table 2]

[0139] With respect to the charging roller having a different amount of the conductive particles attached as shown in Table 2 above, the charging roller is brought into contact with the photosensitive member 1 in a predetermined manner, 0 V is applied to the charging roller, and the photosensitive member is charged at the charging nip portion a. The photosensitive member 1 was rotated at a peripheral speed of 100% in the direction (counter) opposite to the rotating direction of the photosensitive member 1, and the photosensitive member surface potential (offset potential) after the photosensitive member 1 rotated one rotation was measured.

Table 3 shows the measurement results of the charging roller A as the charging roller in this example and the charging rollers B and C as comparative examples.

[0141]

[Table 3]

In any one of the charging rollers A to C, as the amount of adhered conductive particles m increases (the amount of adhered particles 4 →
1) Since the area where the surface of the charging roller 2 and the surface of the photoreceptor 1 are in direct contact at the charging nip portion a is reduced, the charging 1
The offset potential in the cycle is decreasing.

In the charging roller A, which is the charging roller in this example, the photosensitive member 1 is charged (frictionally charged) on the negative side having the same polarity as the charging voltage.

In the charging roller B, the photosensitive member 1 is not frictionally charged, and in the charging roller C, the photosensitive member 1 is frictionally charged to the opposite polarity (plus) to the charging voltage.

. Table 4 shows the surface potential (V) of the photoconductor 1 after one round of charging when -700 V is applied to the charging roller.

[0146]

[Table 4]

[0147] In the above description, the potential of the photoconductor 1 after 10 rounds of charging was defined as a convergence potential (V), and the percentage of the potential in the first round of charging (hereinafter, referred to as the convergence rate) was measured. Table 5 shows the results.

[0148]

[Table 5]

In Table 5, the convergence potential V of the charging roller A is different from the bias applied to the charging roller (−700).
The reason why the surface potential becomes V) or more is that the potential of the photoconductor rises above the applied potential due to frictional charging between the photoconductor and the charging roller.

As can be seen from Tables 4 and 5, when the amount of the conductive particles attached to the charging roller is reduced (the amount of the attached particles 1 →
4) Since the chargeability decreases, the potential convergence rate in the first round of charge generally decreases.

However, the charging roller A, which is the charging roller in this example, having the opposite tendency of the offset potential, is stable irrespective of the attached amount of the conductive particles due to the combination of the injection charging property and the offset potential. The obtained charged potential can be obtained.

Conversely, when the chargeability and the offset potential tend to be the same as in the case of the charging roller C, the surface potential of the photosensitive member 1 obtained in the first round of charging increases when the amount of the conductive particles attached decreases. Will fluctuate.

Looking at the photoreceptor surface potential in the first cycle of charging, the charging rollers B and C, which are comparative examples, show a large change in the photoreceptor surface potential in the first round of charging when the amount of conductive particles deposited on the surface changes. Has been done.

On the other hand, when the charging roller A, which is the charging roller in this embodiment, is used, even if the amount of the conductive particles deposited on the surface of the charging roller changes, the surface potential of the photosensitive member during the first round of charging is changed. Stable chargeability was obtained with little change. Therefore, a good image can be obtained.

<Embodiment> (FIG. 2) FIG. 2 is a schematic structural diagram of an image forming apparatus according to an embodiment of the present invention.

The image forming apparatus of this embodiment is also a laser printer using a transfer type electrophotographic process, a contact charging system, a reversal developing system, a cleaner-less, and a process cartridge type, similarly to the printer of the above-described reference example (FIG. 1). .

Then, at least a charging nip portion a between the charging roller as a contact charging member and the photosensitive member 1 as an image carrier.
The charging roller 2 and the photoconductor 1 are brought into contact with each other without the conductive particles m when the charging roller 2 is brought into contact with the photoconductor 1 without the conductive particles m. Is characterized by being triboelectrically charged to the same polarity as

The printer of this embodiment is different from the printer of the reference example in that the conductive particle coating device 7 for the charging roller 2 is omitted, and instead, the conductive particles m are added to the developer 31 of the developing device 3. The conductive particles m are charged to the polarity opposite to the polarity of the charging voltage of the photoconductor 1 in the developing device, so that the conductive particles m added to the developer 31 adhere to the photoconductor 1 in the developing unit b. The conductive particles m are automatically supplied to the charging nip portion a and the charging roller 2 by being carried to the charging nip portion a via the transfer portion c along with the movement of the photoreceptor surface, thereby maintaining good chargeability. There is a feature in making it work. It is desirable that the charging roller 2 is first coated with the conductive particles m.

The other parts are the same as those of the printer of the reference example, so that the description will not be repeated.

The conductive particles m are conductive zinc oxide particles having a specific resistance of 10 ⁷ Ω · cm and an average particle size of 2.5 μm, as in the reference example.
Is added to the developer of the developing device 3 by 2 parts by weight based on 100 parts by weight of the developer. The external addition amount of the conductive particles m to the developer 31 is generally set to 0.01 to 20 parts by weight based on 100 parts by weight of the developer. By being rubbed with the developer 31 externally added to the developer 31, the developer 31 is charged to a polarity opposite to that of the developer 31, that is, a polarity opposite to the polarity of the charging voltage of the photoreceptor 1 (plus in this embodiment).

When the developing device 3 reversely develops the electrostatic latent image on the surface of the photosensitive member 1, the developer 31 adheres (develops) to the exposed portion which is an image portion, and the conductive particles m having the opposite polarity to the developer 31 Adhering (developing) to a non-exposed portion (white portion) which is a non-image portion.

The developer image on the photoreceptor 1 is attracted to the transfer material P side by the influence of the transfer bias in the transfer portion b and is positively transferred, but the conductive particles m on the photoreceptor 1 are conductive. Does not positively transfer to the transfer material P side, remains substantially adhered and held on the photosensitive member 1 and is carried to the charging nip portion a via the transfer portion b as the photosensitive member surface moves. In this case, the conductive particles m are supplied to the charging nip portion a and the charging roller 2.

The charging roller 2 used in this embodiment is frictionally charged similarly to the charging roller (charging roller A) of the reference example.
Has offset potential. Therefore, when the charging roller 2 and the surface of the photoconductor 1 come into direct contact with each other, the surface potential of the photoconductor 1 increases to the same side as the charging potential due to frictional charging. The present embodiment is characterized in that the conductive particles m used in the developing device 3 have a charge having a polarity opposite to the charge potential of the photoconductor in the developing device 3. Therefore, as the potential on the surface of the photoconductor 1 increases to the same polarity as the charged potential, the amount of development of the conductive particles from the developing device 3 increases.
That is, when the amount of the conductive particles m on the charging nip portion a and the surface of the charging roller 2 decreases, the supply amount of the conductive particles m from the developing device 3 increases.

As an example, Table 6 shows the adhesion amount of the conductive particles m on the surface of the charging roller 2 and the development amount of the conductive particles m in this embodiment. This measurement shows the photoconductor surface potential at the developing position b when ten solid white sheets are printed after removing the developing device 3. The measurement was performed by attaching an elastic blade downstream of the charging roller 2 so that the developer 31 or the conductive particles m did not exist on the surface of the charged photoconductor. The development amount of the conductive particles m was evaluated by counting the number of the conductive particles m on an enlarged photograph of the surface of the photoreceptor 1.

[0165]

[Table 6]

In Table 6, the surface potential (V) of the photoreceptor after charging is determined by applying a bias (−70) to the charging roller.
0 V) or higher because of frictional charging between the photoconductor and the charging roller.

Thus, in this embodiment, the charging nip a
When the conductive particles m on the surface of the charging roller 2 decrease, the supply amount of the conductive particles m from the developing device 3 increases, so that the conductive particles m adhering to the surface of the charging roller 2 hardly continue to decrease. At that time, the developing amount of the developer 31 is reduced contrary to the tendency of the conductive particles m. Therefore, the developer 31 does not easily adhere to the charging roller 2 and the chargeability is hardly reduced.

Therefore, in the image forming apparatus of this embodiment, the chargeability is hardly reduced, and a good image can be obtained.

<Others> 1) The charging roller 2 as a flexible contact charging member is not limited to the charging roller of the embodiment.

Further, the flexible contact charging member may be a fur brush charger or the like in addition to the charging roller. Materials and shapes such as felt and cloth can also be used.
It is also possible to obtain a more appropriate elasticity and conductivity by laminating them.

2) In the direct injection charging in the contact charging, the contact property of the contact charging member with the member to be charged greatly affects the charging property. Therefore, the contact charging member is formed more densely, has a large speed difference from the member to be charged, and comes into contact with the member to be charged more frequently.

By providing a charge injection layer on the surface of the member to be charged and adjusting the resistance of the surface of the member to be charged, direct injection charging in contact charging can be made dominant.

FIG. 3 is a schematic diagram of the layer structure of the photoreceptor 1 provided with the charge injection layer 16 on the surface. That is, the photoreceptor 1 has an undercoat layer 12 on an aluminum drum base (Al drum base) 11,
Positive charge injection prevention layer 13, charge generation layer 14, charge transport layer 1
The charge performance is improved by applying the charge injection layer 16 to a general organic photoreceptor coated in the order of No. 5.

The charge injection layer 16 is formed by adding a photo-curable acrylic resin as a binder to conductive particles (conductive filler).
SnO ₂ ultrafine particles 16a (having a diameter of about 0.03 μm)
m) A film formed by mixing and dispersing a lubricant such as a tetrafluoroethylene resin (trade name: Teflon (registered trademark)), a polymerization initiator, and the like, coating, and forming a film by a photocuring method.

An important point for the charge injection layer 16 is the resistance of the surface layer. In the charging method by direct injection of electric charges, the electric charges can be transferred more efficiently by lowering the resistance of the object to be charged. On the other hand, when used as a photoconductor, it is necessary to hold the electrostatic latent image for a certain time,
The volume resistance value of the charge injection layer 16 is 1 × 10 ⁹ to 1 ×.
A range of 10 ¹⁴ (Ω · cm) is appropriate.

Even when the charge injection layer 16 is not used as in the present configuration, the same effect can be obtained, for example, when the charge transport layer 15 is within the above resistance range.

Furthermore, the volume resistance of the surface layer is about 10 ¹³ Ω · c
The same effect can be obtained by using an amorphous silicon photoreceptor of m.

3) A for the contact charging member and the developing device
As the AC voltage waveform when the C voltage (alternating voltage) component is applied, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating voltage.

4) The image exposing means for forming an electrostatic latent image is not limited to the laser scanning exposing means for forming a digital latent image as in the embodiment, but is a general analog type. Other light-emitting elements such as an image exposure or LED may be used, and any device that can form an electrostatic latent image corresponding to image information, such as a combination of a light-emitting device such as a fluorescent lamp and a liquid crystal shutter, may be used.

The image carrier 1 may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a desired electrostatic latent image.

5) The developing means 3 is a non-magnetic 1 in the embodiment.
Although the description has been made with reference to the reversal development using the component insulating developer,
The configuration of the developing unit 3 is not particularly limited.
Regular developing means may be used.

6) The image forming apparatus may be a direct type image forming apparatus in which photosensitive paper or electrostatic recording paper is used as an image carrier, and the surface thereof is contact-charged to form an image without a transfer step. .

The transfer type image forming apparatus may also be provided with a cleaner for removing transfer residual developer, paper dust and the like from the surface of the image carrier after transfer.

7) In the transfer type image forming apparatus, the recording medium to which the developer image is transferred from the image carrier 1 may be an intermediate transfer body such as a transfer drum.

8) An example of a method for measuring the particle size of the developer (toner) 31 will be described. As a measuring device, a Coulter Counter TA-2 type (manufactured by Coulter) was used, and an interface (manufactured by Nikkaki) for outputting a number average distribution and a volume average distribution and a CX-1 personal computer (manufactured by Canon) were connected. Use 1st grade sodium chloride solution
% NaCl aqueous solution is prepared.

The measuring method is as follows.
A surfactant as a dispersant in 150 ml, preferably
0.1 to 5 ml of an alkylbenzene sulfonate is added, and 0.5 to 50 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 using an ultrasonic disperser, and the particle size of 2 to 40 μm was measured using the Coulter Counter TA-2 using a 100 μ aperture as an aperture. The distribution is measured to determine the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

[0188]

As described above, according to the present invention, it is possible to perform ozone-less injection charging at a low applied voltage by using a simple member such as a charging roller or a fur brush as a contact charging member for an image forming apparatus of a contact charging system. It can be realized, and by supplying the conductive particles added to the developer from the developing means, the chargeability of the image carrier is little reduced, good chargeability is maintained, and contact charging contaminated by the developer is achieved. Efficiently discharges the developer, which is a charge inhibition factor, from the member,
Good chargeability can be stably maintained over a long period of time, the injection charging and toner recycling system can be executed without any problem, and high-quality image formation can be maintained over a long period of time. Further, even after outputting an image having a high image ratio, high-quality image formation can be maintained for a long period of time.

Since the polarity of the conductive particles and the polarity of the charging voltage are opposite, the conductive particles conveyed to the nip portion are easily carried by the charging member, so that good chargeability is maintained. Further, when the polarity of the conductive particles and the polarity of the developer are opposite, the conductive particles conveyed by the image carrier are difficult to be transferred to the recording medium, so that the amount of the conductive particles conveyed to the nip by the image carrier is reduced. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus of a reference example.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 3 is a schematic diagram of a layer configuration of an example of a photoreceptor having a charge injection layer on a surface.

FIG. 4 is a graph showing charging characteristics.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier, charged object) 2 charging roller (contact charging member) 3 developing device 31 developer (toner) m conductive particles (charge promoting particles) 4 transfer roller 5 fixing device 7 conductive particle coating device P transfer Material C Process cartridge S1 to S3 Bias power supply

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasunori Kono 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H077 AA37 AC16 AD06 AD13 AD23 AD36 AE03 AE05 DB08 DB14 EA13 EA16 GA03 GA17 2H134 GA01 GB02 HF13 2H200 FA02 FA13 GA14 GA16 GA23 GA34 GA46 GA49 GA57 GA59 GB22 GB25 GB37 HA02 HA03 HA28 HB12 HB17 HB23 HB43 HB45 HB46 HB47 HB48 JA02 JA23 JA23 JA26 JA28 MA03 MA04 MA12 MA14 MB06 MC02 MC06 NA09 NA09

Claims (7)

[Claims] An image carrier; a charging unit configured to charge the image carrier; a latent image forming unit configured to form an electrostatic latent image on the image carrier charged by the charging unit; A developing means for developing with a developer, wherein the charging means is provided with a flexible charging member to which a voltage is applied and forms a nip with the image carrier, and the nip has The conductive particles are interposed, and the conductive particles are provided in the developing unit, are supplied to the image carrier from the developing unit, are conveyed to the nip by the image carrier, and have the voltage in the developing unit. An image forming apparatus characterized in that the image forming apparatus is charged to a polarity opposite to the polarity. 2. The image forming apparatus according to claim 1, wherein the charging member moves at a speed difference with respect to the image carrier. 3. The image forming apparatus according to claim 1, wherein the conductive particles are charged to a polarity opposite to the polarity of the voltage by rubbing with a developer in the developing unit. . 4. The image forming apparatus according to claim 1, wherein the developing unit reversely develops the electrostatic latent image with a developer, and the conductive particles are attached to a non-image portion of the image carrier from the developing unit. Item 4. The image forming apparatus according to any one of Items 1 to 3. 5. The image forming apparatus according to claim 1, wherein the charging member has a foam on a surface thereof. 6. The image forming apparatus according to claim 1, wherein the developing unit is capable of collecting a developer on the image carrier. 7. The image forming apparatus according to claim 1, further comprising a transfer unit configured to transfer a developer image formed on the image carrier to a recording medium.