JPH11190930A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an ozonless injection electrification with a low impressed voltage by using such a simple member as an electrifying roller as a contact electrifying member in the case of a contact electrifying system and a transfer system and also to automatically supply electrification accelerating particles capable of realizing an injection electrification to the electrifying part and the contact electrifying member so as to prevent electrifying characteristic from lowering. SOLUTION: The electrification accelerating particles (m) for accelerating electrification and having electrical conductivity are made to exist at least a nip part (a) between the contact electrifying member 2 and an image carrier 1. The particles (m) are mixed in the developer 31 of a developing means 3, and the particles (m) are electrified inside the developing means 3 so that the particles (m) have a polarity by which the particles (m) are developed on the image carrier 1 part where electrifying property is lowered.

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,
The charging principle) includes two types: discharge charging mechanism and injection charging mechanism.
There are various types of charging mechanisms, and each characteristic appears depending on which one is dominant.

[0007] Discharge Charging Mechanism This is a mechanism in which the surface of the 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.

[0008] Since the discharge charging mechanism has a fixed discharge threshold 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 mechanism This is a mechanism in which the surface of the member to be charged is charged by injecting charge 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 mechanism does not involve generation of ions, no adverse effect is 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 discharging charging mechanism.

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 mechanism 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, the essential charging mechanism is mainly based on a discharge charging mechanism, and the discharge phenomenon from the contact charging member to the photosensitive member is used. As described above, the voltage applied to the contact charging member needs to be higher than the surface potential of the photoconductor, 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 mechanism.

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 the injection charging mechanism.
In order to perform sufficiently uniform charging by the injection charging mechanism, it is necessary to make the photoconductor have a speed difference that is difficult as 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 charging mechanism.

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 mechanism.

By using conductive magnetic particles having a particle diameter of 5 to 50 μm as a constituent of the magnetic brush portion and providing a sufficient speed difference from the photosensitive member, uniform charging can be achieved.

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 photoconductor (image carrier) after transfer is transferred to the surface of the photoconductor 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. Also, because it is cleaner-less, there are great advantages in terms of space,
The size of the image forming apparatus can be greatly 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 and fur brush charging, transfer residual toner on a photoreceptor is diffused to form a non-pattern, and a large bias is applied and discharge charging 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 In the contact charging device, in order to prevent charging unevenness and perform stable and uniform charging, a configuration in which powder is applied to the contact charging member with the surface in contact with the surface to be charged is particularly fair. 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 (photoreceptor), and generates ozone as compared with a corona charger such as a scorotron. Although the generation of an object is remarkably reduced, the charging principle is still mainly a discharge charging mechanism 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 in order to obtain more stable charging uniformity, generation of ozone products due to discharge is increased. Therefore, when using the device for a long time,
When a cleaner-less image forming apparatus is used for a long 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, charging inhibition due to toner particles or silica fine particles adhering to the surface of a charging unit during repeated image formation is prevented. Therefore, it is disclosed that a developer contains at least visible particles and conductive particles having an average particle size smaller than the visible particles. However, this contact charging is based on the discharge charging mechanism, and has the above-mentioned problem due to the discharge charging, not the direct injection charging mechanism.

[0038]

As described in the section of the prior art described above, conventionally, in the contact charging, in a simple configuration using a charging roller or a fur brush as a contact charging member, an injection charging mechanism is performed. However, 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 the injection charging mechanism was difficult.

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

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

That is, even in the case of an image forming apparatus provided with a dedicated cleaner for removing the residual transfer developer remaining on the surface of the image carrier after transfer, the residual developer remaining on the surface of the image carrier after 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. Since the conventional developer is generally an insulator, the developer contamination of the contact charging member is a factor that causes charging failure.

In particular, in a cleanerless image forming apparatus, since a dedicated cleaner for removing the residual transfer residual developer on the image carrier after transfer is not used, the residual transfer on the image carrier after transfer is not used. The residual developer is carried as it is by the movement of the image carrier to the charging portion, which is the contact portion between the image carrier and the contact charging member, 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 the developer is firmly adhered to the contact charging member even when a developer discharge bias is applied to the contact charging member. Could not get.

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

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.

Accordingly, the present invention relates to a contact charging system, a transfer system image forming apparatus employing a contact charging apparatus 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 the 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.

[0047]

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

(1) A charging step (stroke) of charging the image carrier to the image carrier, an information writing step of forming an electrostatic latent image on the charged surface of the image carrier, and a developing step of charging the electrostatic latent image Image formation is performed by applying an image forming process including a developing step of developing with a developer and a transfer step of transferring a developer image on the image carrier to a recording medium, and the image carrier is repeatedly subjected to image formation. The apparatus, comprising: a. A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein charge-promoting particles are mixed in a developer of a developing unit, and the charge-promoting particles are charged in the developing unit to the same polarity as a DC charging polarity of a contact charging device.

(2) A charging step of charging the image carrier with the image carrier, an information writing step of forming an electrostatic latent image on the charged surface of the image carrier, and developing the electrostatic latent image with a charged developer In the image forming apparatus, an image forming process is performed by applying an image forming process including a transfer step of transferring a developer image on an image carrier to a recording medium, and the image carrier is repeatedly provided for image formation. a. A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein the developing means is a regular developing means, wherein charge-promoting particles are mixed into the developer, and the charge-promoting particles are charged to a polarity different from that of the developer in the developing means.

(3) A charging step of charging the image carrier with the image carrier, an information writing step of forming an electrostatic latent image on the charged surface of the image carrier, and developing the electrostatic latent image with a charged developer In the image forming apparatus, an image forming process is performed by applying an image forming process including a transfer step of transferring a developer image on an image carrier to a recording medium, and the image carrier is repeatedly provided for image formation. a. A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein the developing means is a reversal developing means, wherein charge-promoting particles are mixed in the developer, and the charge-promoting particles are charged to the same polarity as the developer in the developing means.

(4) The method according to (1) to (3), wherein the developing means also serves as a cleaning means for collecting the developer remaining on the image carrier after transferring the developer image to the recording medium. An image forming apparatus according to claim 1.

(5) The image forming apparatus according to any one of (1) to (4), wherein the charge-promoting particles have a charge polarity by frictional charging due to rubbing with the developer.

(6) The image forming apparatus according to any one of (1) to (4), wherein the member for frictionally charging the developer also serves as a member for charging the charge accelerating particles.

(7) The charge-promoting particles have a particle size of 1/2 or less of the developer and a resistance value of 1 × 10 ¹² (Ω · cm).
The image forming apparatus according to any one of (1) to (6), wherein:

(8) The charge-promoting particles have a particle size of 1/2 or less of the developer and a resistance value of 1 × 10 ¹⁰ (Ω · cm).
The image forming apparatus according to any one of (1) to (6), wherein:

(9) The image forming apparatus according to any one of (1) to (8), wherein the charging member is driven while maintaining a speed difference in a direction opposite to the moving direction of the image carrier. apparatus.

(10) The image according to any one of (1) to (9), wherein the information writing means for forming an electrostatic latent image on the charged surface of the image carrier is an image exposure means. Forming equipment.

<Operation> a) The charge-promoting particles are conductive particles for the purpose of assisting the charge. In contact charging, the charge-promoting particles are interposed at least in the nip portion between the charging member and the image carrier. Uniform and stable direct charging is realized. The charge-promoting particles have a resistance value of 1 × 10 ¹² (Ω · cm) or less, and more preferably 1 × 10 ¹⁰ (Ω · cm) or less, so that the chargeability is not impaired. In addition, the particle diameter is set to 1 of the particle diameter of the developer.
By setting the ratio to / 2 or less, image exposure on the image carrier is not hindered.

That is, by interposing the charge-promoting particles in the charging portion, which is the 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 particles have a large frictional resistance to the image carrier as it is. Even if the charging roller is difficult to contact with a speed difference, it can be easily and effectively brought into contact with the image carrier surface with a speed difference effectively. In addition to this, the contact charging member comes into close contact with the surface of the image carrier through 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 of contact of the charge promoting particles with the image carrier at the nip portion between the contact charging member and the image carrier is greatly increased. , So that the charge-promoting particles present in the nip 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 the contact charging of the image carrier by the contact charging member, injection charging is dominant due to the presence of the charge promoting particles.

B) As a configuration for providing a speed difference, a speed difference is provided from the image carrier by rotating or fixing the contact charging member. In a transfer-type or transfer-type / cleanerless image forming apparatus, it is preferable that the developer passed through the cleaner or the developer remaining after transfer in the case of the cleanerless state be 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 it is possible to move the contact charging member in the same direction as the moving direction of the surface of the image carrier to have a speed difference, the charging property 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 cleaner-less 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 at 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 by the charging unit and having passed through the cleaner or the transfer residual developer in the case of the cleaner-less case 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 poor charging in charging the image carrier.

However, even in this case, since the charge accelerating particles are interposed in the charging portion which is a nip portion between the image bearing member and the contact charging member, the fine contact property and contact resistance of the contact charging member to the image bearing member are improved. Since the contact charging member can be maintained, the ozone-less direct charging can be stably maintained at a low applied voltage for a long period of time irrespective of contamination of the contact charging member by the transfer residual developer, 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 image carrier surface, reaches the developing site, and is simultaneously cleaned (collected) by the developing means. (Toner recycling).

In this case, since the charge promoting particles are carried on the contact charging member, the adhesive force 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 image bearing member to the image bearing member. The efficiency of discharging the developer upward is improved.

F) First, even if a sufficient amount of the charge-promoting particles is interposed in the charging portion, which is a nip portion between the image carrier and the contact charging member, or a sufficient amount of the charge-promoting particles is applied to the contact charging member. Even in such a case, the charge-promoting particles decrease from the charging section or the charge-promoting particles deteriorate with the use of the device, so that the chargeability decreases.

In the present invention, when the charge-promoting particles are reduced from the charging portion or the charge-promoting particles are deteriorated, and the chargeability is reduced, the charge-promoting particles mixed in the developer of the developing means are used. Particles adhere to the image carrier surface portion having reduced chargeability in the developing unit, and are carried to the charging unit via the transfer unit as the image carrier surface moves, so that the particles are automatically transferred to the charging unit and the contact charging member. Supplied, good chargeability is maintained.

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 charge promoting particles on the image carrier are conductive, the image is recorded. It is not positively transferred to the medium side, is substantially adhered and held on the image carrier, remains, and is carried to the charging unit via the transfer unit as the image carrier moves.

In this case, even in the case of an image forming apparatus provided with a cleaner, the transfer residual developer (including paper powder) remaining on the surface of the image carrier after the transfer and the transfer residual developer among the charge promoting particles are not changed. Most of the particles are recovered by a cleaner, but the charge-promoting particles have a smaller particle size than the developer, and thus easily pass through the cleaner. In the case of a cleaner-less image forming apparatus, the transfer residual developer and the charge accelerating particles remaining on the surface of the image carrier after transfer are carried to the charging section as they are.

That is, the charge-promoting particles are mixed with the developer of the developing means so that the charged particles have a polarity such that the charged particles are developed (adhesion of the charge-promoting particles to the image carrier) on the portion of the image carrier having reduced chargeability. The charged particles are charged in the developing means. In particular, . Charge-promoting particles are mixed in the developer of the developing means, and the charge-promoting particles are charged to the same polarity as the DC charging polarity of the contact charging device in the developing means. Alternatively, the developing means is a regular developing means, in which charge-promoting particles are mixed in the developer, and the charge-promoting particles are charged to a polarity different from that of the developer in the developing means. Alternatively, the developing means is a reversal developing means, in which the charge accelerating particles are mixed in the developer, and the charge accelerating particles are charged to the same polarity as the developer in the developing means, whereby the charge is accelerated from the charging section. When the chargeability is reduced due to a decrease in particles or deterioration of the charge-promoting particles, the charge-promoting particles mixed in the developer of the developing unit may cause the surface of the image bearing member having reduced chargeability in the developing unit. The toner adheres to the portion and is carried to the charging unit via the transfer unit along with the movement of the surface of the image carrier, and is automatically supplied to the charging unit and the contact charging member, thereby maintaining good charging properties.

G) Thus, the contact charging system, the transfer system,
Furthermore, with respect to a cleaner-less image forming apparatus, an ozone-less injection charging mechanism can be realized at a low applied voltage by using a simple member such as a charging roller or a fur brush as a contact charging member. The supply to the charging section and the contact charging member is automatically performed, and the developer, which is a charge inhibiting factor, is efficiently discharged from the contact charging member contaminated with the developer (toner), thereby providing good charging performance. 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 an image having a high image ratio is output, high-quality image formation can be maintained for a long period of time.

[0075]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIG. 1) FIG. 1 is a schematic structural diagram of an example of an image forming apparatus according to the present invention.

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

The printer of this embodiment is characterized in that regular development is used, and the charge accelerating particles mixed in the developer are charged to the polarity opposite to that of the developer by frictional charging with the developer.

(1) Overall Schematic Configuration of Printer of the Present Example [Image Carrier] 1 is a rotating drum type electrophotographic photosensitive member as an image carrier (charged member). The printer of this embodiment uses regular development, and the photoconductor 1 uses a positive 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 the charge promoting particles m in advance.
Exists.

In the present embodiment, the charging roller 2 is driven to rotate at a peripheral speed of 100% in the direction (counter) opposite to the rotation direction of the photoconductor 1 in the charging nip portion a, and a speed difference with respect to the surface of the photoconductor 1 is generated. Hold and touch. Then, a predetermined charging bias is applied to the charging roller 2 from a charging bias power supply S1. As a result, the peripheral surface of the rotary photoreceptor 1 is uniformly contact-charged to a predetermined polarity and potential by the injection charging method. In this embodiment, the outer peripheral surface of the photosensitive member 1 is approximately 7
A charging bias is applied from a charging bias power supply S1 so that the charging process is uniformly performed at 00V.

The charging roller 2, the charge accelerating 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, the normal development is used, and in the scanning exposure L of the outer peripheral surface of the rotary photosensitive member 1 with the laser beam, the non-exposed portion is the image portion, and the exposed portion is the non-image portion.

[0107] [Current image] 3 is a regular developing device, and the electrostatic latent image formed on the outer peripheral surface of the rotary photosensitive member 1 is regularly developed as a developer image (toner image) by the developing device 3. .

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

The developer 31 is externally added (mixed) with the charge accelerating particles m. In this embodiment, the external addition amount is 2 parts by weight with respect to 100 parts by weight of the developer.

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 (+ m), 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.
2, a developing bias voltage is applied.

In the process of transporting the developer 31 (+ m) in the developing device on the rotary developing sleeve 32, the layer thickness is regulated by the elastic blade (regulating blade) 34, and the friction is caused by the rubbing with the elastic blade 34. It is charged and has a charge.

As the developing bias voltage, a DC voltage of 380 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superimposed.
One-component jumping development is performed at a development site b between the photoconductor 1 and the photoconductor 1.

The developer adheres to the non-exposed portion, which is the image portion of the electrostatic latent image on the surface of the rotating photosensitive member 1, and the electrostatic latent image is developed normally.

[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 the present embodiment is
Roller resistance value 5 × 1 with medium resistance foam layer 42 formed on 1
0 ⁸ Ω and a +2200 V DC voltage
The transfer was carried out by applying the voltage of 1 to 1. The transfer material P introduced into the transfer nip c is nipped and conveyed by the transfer nip c.
The developer image formed and carried on the surface of the rotary photoreceptor 1 is sequentially transferred to the surface side by electrostatic force and pressing force.

[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] The printer of this embodiment is
The three process devices of the photoreceptor 1, the contact charging member 2, and the developing device 3 are contained in a cartridge case, and the cartridge C is detachably mounted on the printer body in a lump. 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 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 middle resistance layer 22 is made of resin (for example, urethane),
It was formulated with conductive particles (for example, carbon black), a sulfide agent, a foaming agent, and the like, and formed on the cored bar 21 in a roller shape. Thereafter, the surface was polished as needed.

The roller resistance of the charging roller 2 of this embodiment was measured and found to be 100 kΩ. The roller resistance is adjusted so that a total pressure of 1 kg is applied to the metal core 21 of the charging roller 2.
With the charging roller 2 pressed against a 30 mm aluminum drum, 100 V was applied between the cored bar 21 and the aluminum drum, and measurement was performed.

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 -10
^{A 7} Ω resistor is desirable.

It is desirable that the surface of the charging roller 2 has micro unevenness so as to hold the charge accelerating 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.
M, urethane, NBR, silicone rubber, a rubber material in which a conductive substance such as carbon black or metal oxide is dispersed in IR or the like for resistance adjustment, or a foamed material 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 so as to be pressed against 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. It is.

(3) Charge-Promoting Particles m In this embodiment, the charge-promoting particles m which are previously coated on the outer peripheral surface of the charging roller 2 as the contact charging member and the charge-promoting particles m which are externally added to the developer 31 of the developing device 3 The conductive zinc oxide particles having a specific resistance of 10 ⁷ Ω · cm and an average particle size of 1.5 μm were used. There is no problem that the charge promoting particles exist not only in the state of primary particles but also in the state of aggregation of secondary particles. Whatever the state of aggregation,
The form is not important as long as the function as the charge promotion 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.

The resistance value of the charge accelerating particles m is 10 ¹² Ω · cm.
With the above, the chargeability was impaired. Therefore, the resistance value needs to be 10 ¹² Ω · cm or less, and more preferably 10 ¹⁰ Ω · cm or less. In the present embodiment, 1 × 10 ⁷ Ω · cm was used. The resistance was measured by a tablet method and normalized. That is, the bottom area 2.2
About 0.5 g of the powder sample was placed in a 6 cm ² cylinder, 15 kg of pressure was applied to the upper and lower electrodes, and at the same time, a voltage of 100 V was applied, the resistance was measured, and then the resistivity was normalized to calculate the specific resistance.

The charge accelerating particles m are desirably 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 charge accelerating particles are partially transferred from the photoreceptor to the recording material P, color recording is preferably colorless or white. Further, the particle size is also 1/1 of the particle size of the developer 31.
If it is less than about 2, image exposure may be interrupted. Therefore, the particle size of the charge promoting particles m is １ ／ of the particle size of the developer 31.
It is desirably smaller than the above. As the lower limit of the particle size,
10 nm is considered to be the limit as a stable particle.

In this embodiment, zinc oxide was used as the material of the charge accelerating 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 organic materials, or Various kinds of conductive particles such as those having been subjected to a surface treatment can be used.

In the present embodiment, the charge-promoting particles m (zinc oxide particles) externally added to the developer 31 of the developing device 3 are rubbed with the developer 31 to have a positive charge having a polarity opposite to that of the developer 31. Is added. That is, the charge accelerating particles m are charged to a polarity opposite to that of the developer for normal development (= charged to the same polarity as the DC charge polarity of the contact charging device).

In this embodiment, as described above, the charge accelerating particles m have a positive charge due to the rubbing with the developer 31 in the developing device 3 and are developed on the photoreceptor 1 (= adhered to the photoreceptor surface). The same applies hereinafter). That is, since the charge accelerating particles m have a polarity opposite to that of the developer 31, the charge accelerating particles m are developed in a region where the potential of the photoconductor is on the negative side, that is, in an uncharged region.

Here, the measurement of the triboelectric charging characteristic between the charge accelerating particles m and the developer 31 was performed as follows. That is,
The charge accelerating particles m are put in a container coated with the developer 31 by heat melting on the inner surface, and the container is shaken. Thereafter, the charge accelerating particles are sucked, and the amount of electric charge of the charge accelerating particles is measured. Was measured.

(4) Injection charging. By interposing the charge-promoting particles m in the charging nip portion a between the photoreceptor 1 as the image carrier and the charging roller 2 as the contact charging member, the frictional effect is large due to the lubricant effect of the particles m. Even if the charging roller is difficult to contact the body 1 with a speed difference,
It can be easily and easily brought into contact with the surface of the photoconductor 1 with a speed difference effectively and effectively, and the charging roller 2 is moved by the particles m through the surface of the photoconductor 1. , 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 opportunity for the charging promoting particles m to come into contact with the photosensitive member 1 at the charging nip portion between the charging roller 2 and the photosensitive member 1 is significantly improved. The charge accelerating particles m existing in the charging nip portion a of the charging roller 2 and the photoconductor 1 rub the surface of the photoconductor 1 without gaps, thereby charging the photoconductor 1. The direct charging can be performed, and the contact charging of the photoreceptor 1 by the charging roller 2 is controlled by the charging mechanism due to the presence of the charge promoting particles m.

As a structure for providing a speed difference, the charging roller 2 is driven to rotate or fixed, and a speed difference from the photosensitive drum 1 is provided. Preferably, the charging roller 2 is driven to rotate in order to temporarily recover 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 a 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 the conventional roller charging or the like, can be 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.

By previously supporting the charge promoting particles m on the surface of the charging nip portion a and the charging roller 2, the above-described direct charging performance can be exhibited without any trouble from the very beginning of use of the printer.

[0116] 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.

[0118] 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 charge accelerating particles m are interposed in the charging nip portion a between the photosensitive member 1 and the charging roller 2, the fine contact property and the contact resistance of the charging roller 2 to the photosensitive member 1 are maintained. Therefore, irrespective of contamination of the charging roller 2 by the transfer residual developer, ozone-less direct charging can be stably maintained at a low applied voltage for a long period of time, and uniform charging properties can be provided.

[0120] 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, the charge accelerating particles m
Is carried, the charging roller 2 and the
The adhesive force of the transfer residual developer mixed therein is reduced, and the efficiency of discharging the developer from the charging roller 2 onto the photosensitive member 1 is improved. As described above, during the development simultaneous cleaning, the toner remaining on the photoreceptor 1 after transfer is developed during the subsequent image forming process, that is, the photoreceptor is subsequently charged and exposed to form a latent image, and the latent image is developed. In some cases, the fogging bias of the developing device, that is, the fog removing potential difference Vba, which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member.
ck Is to be recovered. In the case of the reversal development as in the printer in this embodiment, the simultaneous cleaning of development involves applying the electric field for collecting the toner from the dark portion potential of the photoconductor to the developing sleeve and attaching the toner from the developing sleeve to the bright portion potential of the photoconductor. This is done by the action of an electric field.

. Further, the effect of improving the transfer efficiency of the developer from the photoconductor 1 side to the transfer material P side can be obtained by the presence of the charge promotion particles m substantially adhered and held on the photoconductor 1 surface.

(5) Replenishment of Charge-Promoting Particles m to Charging Nip a and Charging Roller 2 First, even if a sufficient amount of charging-promoting particles m is interposed in the charging nip a between the photosensitive member 1 and the charging roller 2. Alternatively, even if a sufficient amount of the charge-promoting particles m is applied to the charging roller 2, the charge-promoting particles m become
When the charge accelerating particles m are deteriorated or the charge accelerating particles m deteriorate, the chargeability is reduced.

Therefore, when the chargeability is reduced,
Charge promoting particles m for the charging nip portion a and the charging roller 2
Need to be replenished.

In this embodiment, if the chargeability is reduced due to a decrease in the charge promotion particles m from the charge nip portion a or the charge roller 2 or a deterioration of the charge promotion particles m, the developing device 3 The charge accelerating particles m mixed in the developer 31 adhere to the surface of the photosensitive member 1 whose chargeability is reduced in the developing portion a, and the nip portion via the transfer portion c as the photosensitive member 1 moves. a, the toner is automatically supplied to the charging roller 2 and the charging nip part a, so that good chargeability is maintained.

The developer image on the photoreceptor 1 is attracted to the recording medium side by the influence of the transfer bias in the transfer portion c and is positively transferred, but the charge accelerating particles m on the photoreceptor 1 have a low resistance value. Does not positively transfer to the recording medium side, remains substantially adhered and held on the photoreceptor 1, and remains in the charging nip portion a via the transfer portion c as the photoreceptor 1 surface moves. Carried.

That is, in this embodiment, the charge accelerating particles m are supplied by supplying the charge accelerating particles m from within the developing device 3. In the printer of this embodiment, normal development is used, and the charge accelerating particles m are frictionally charged to a polarity opposite to that of the developer 31 and have a positive charge. Therefore, the photosensitive drum 1 is developed into a region having a relatively negative potential, that is, an uncharged region. Therefore, when the charge-promoting particles m are reduced or deteriorated from the charging nip portion a or the charging roller 2 and defective charging occurs, a large amount of the charge-promoting particles are automatically supplied to the charging defective portion having a lower potential. It is possible to do.

As described above, in this embodiment, the charge accelerating particles m
It is possible to automatically increase the replenishment amount for a portion that has decreased or deteriorated.

Thus, for a contact charging type, transfer type, and cleanerless image forming apparatus, ozone-less injection charging can be realized at a low applied voltage by using a simple member such as the charging roller 2 as a contact charging member. The supply of the charge-promoting particles m to the charging nip portion a and the charging roller 2 is automatically executed, and the developer, which is a factor inhibiting charging, is efficiently discharged from the charging roller 2 contaminated by the developer. As a result, good chargeability can be stably maintained for 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 for a long period of time. Further, even after an image having a high image ratio is output, high-quality image formation can be maintained for a long period of time.

If the amount of the charge-promoting 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 can be sufficiently obtained. In addition, the friction between the charging roller 2 and the photosensitive member 1 is large, and it is difficult to rotationally drive the charging roller 2 with a speed difference from the photosensitive member 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 detachment of the charge-promoting particles from the charging roller 2 increases remarkably, and adversely affects image formation. The intervening amount According to experiment 10 ³ / mm
^Two or more is desirable. 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 / m
The intervening amount of m 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 less than 5 × 10 ⁵ particles / mm ² , the amount of particles falling off can be kept low, and the adverse effect can be improved. When the abundance of the particles dropped on the photoreceptor 1 in the intervening amount range is measured, it is 10 ²
Since it was 10 ⁵ / mm ² , it is desired that the abundance having no adverse effect on image formation be 10 ⁵ / 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 photoconductor 1, but most of the particles existing on the photoconductor 1 before coming into contact with the charging roller 2 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 photosensitive drum 1 and the charging roller 2 is stopped without applying the charging bias, and
The surface of the charging roller 2 with a video microscope (O
LYMPUS OVM1000N) and a digital still recorder (DELTIS SR-3100). Regarding the charging roller 2, the charging roller 2 is
The slide glass was brought into contact with the slide glass under the same condition as that of the slide glass, and the contact surface was photographed from a rear surface of the slide glass with a video microscope at 10 or more places using a 1000-fold objective lens. 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 were present was measured using desired image processing software.
Also, the amount of the photoconductor 1 on the photoconductor 1 was photographed by the same video microscope and measured by performing the same processing. In other words, the amount of the charge-promoting particles m with respect to the developer 31 of the developing device 3 is set so that the amount of the charge-promoting particles m in the charging nip portion a becomes such an intervening amount. Generally, the amount of the charge accelerating particles m is 0.01 to 20 parts by weight based on 100 parts by weight of the developer (toner).

(6) Comparative Example Comparative Example A: A printer using no charge as the charge accelerating particles m in the printer of Example 1 Comparative Example B: A charge accelerating particle m in the printer of Example 1 In the printer of Comparative Example A, the charge accelerating particles m do not have a specific charge, and the charge is injected from the developing sleeve 32 of the developing device 3 to perform development. Done. In this case, when the charge promoting particles m are reduced or deteriorated from the charging nip portion a or the charging roller 2 and the chargeability is reduced, the development amount of the charge promoting particles m is not particularly increased. .

In the printer of Comparative Example B, when the chargeability was reduced, the development amount of the charge-promoting particles was also reduced, and the supply amount of the charge-promoting particles m to the charging nip portion a and the charging roller 2 was reduced. , And the chargeability continued to decrease.

In contrast to the printers of Comparative Examples A and B, in the printer of Example 1, when a charging failure occurs due to a decrease or deterioration of the charging promoting particles m in the charging nip portion a or the charging roller 2, the charging promoting particles are removed. Since the amount of development increases and the amount of the charge-promoting particles m supplied to the charging nip portion a and the charging roller 2 increases, the chargeability does not decrease.

Embodiment 2 (FIG. 2) This embodiment is characterized in that, in an image forming apparatus using reversal development, the charge accelerating particles are charged to the same polarity as the developer in the developing device. As a means for charging, the charge accelerating particles are charged using an elastic blade for charging the developer.

Specifically, for the printer of the first embodiment, as shown in FIG. A negative photoconductor was used as the image carrier 1; b. The outer peripheral surface of the photoconductor 1 is substantially -700 on the charging roller 2.
A charging bias was applied from a charging bias power supply S1 so as to be uniformly charged to V. c. The image exposure on the photoreceptor 1 is scanning exposure L using a laser beam as in the printer of the first embodiment. However, in this embodiment, since the reversal development system is used, the exposed portion is an image portion and the non-exposed portion is a non-image portion. Part d. The developing device 3 is a reversal developing device, and a developing bias voltage is obtained by superposing a DC voltage of −400 V and a rectangular AC voltage having a frequency of 1800 V and a peak-to-peak voltage of 1600 V, e. The charge promoting particles m previously coated on the outer peripheral surface of the charging roller 2 and the charge promoting particles m externally added to the developer 31 of the developing device 3 have a specific resistance of 10 ⁷ Ω · cm and an average particle diameter of 1.5.
using a dispersion of polyethylene in conductive zinc oxide particles of μm, f. The charge accelerating particles m
2 parts by weight based on 100 parts by weight of the developer
The charge promotion particles m are rubbed with the elastic blade 34,
Has a negative charge similarly to the developer 31 (= charged to the same polarity as the DC charging polarity of the contact charging device), g. The transfer bias was set to + 1800V.

A printer other than the printers a to g is the same as the printer of the first embodiment.

In the printer of this embodiment, the externally-charged particles m of the developer 31 of the developing device 3 are rubbed against the elastic blade 34 by a negative charge having the same polarity as the developer 31. have. For this reason, the photosensitive member 1 is developed in an incompletely charged portion (a region where the potential is on the positive side).

In this embodiment, the charge accelerating particles m
By developing from inside, the charge accelerating particles m are supplied. Since the charge accelerating particles m are negatively triboelectrically charged with the same polarity as that of the developer 31 by using the reversal development, the charge accelerating particles m are developed more toward the positive side.

Therefore, when the charge accelerating particles m are reduced or deteriorated from the charge nip portion a or the charge roller 2 and a defective charge portion is generated, the charge-defective portion having a positive potential is automatically applied to the charge-defective portion. It is possible to replenish a large amount of the charge accelerating particles.

As described above, in this embodiment, the charge accelerating particles m
It is possible to automatically increase the replenishment amount for a portion that has decreased or deteriorated.

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

In addition to the charging roller, the flexible contact charging member may be a fur brush charger. 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 injection charging mechanism in 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, the injection charging mechanism in contact charging can be 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 is formed by mixing and dispersing a lubricant such as tetrafluoroethylene resin (trade name: Teflon), a polymerization initiator, and the like, coating the mixture, and then performing photo-curing.

What is important as 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, for example, when the charge transport layer 15 is within the above-described resistance range, the same effect can be obtained.

Further, 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) As for the developing means 3, the developing method and structure are not limited to those of the embodiment.

6) The image forming apparatus of the present invention may be provided with a cleaner for removing transfer residual developer and paper dust from the surface of the image carrier after transfer.

7) The recording medium on 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 a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the particle size of 2 to 40 μm was measured with 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.

[0160]

As described above, according to the present invention, for a contact charging system, a transfer system, and a cleanerless image forming apparatus, a simple member such as a charging roller or a fur brush is used as a contact charging member. Ozone-less injection charging can be realized with a low applied voltage, and the supply of the charge-promoting particles that enable injection charging to the charging unit and the contact charging member is automatically executed, and the contact that is contaminated with the developer (toner) is also performed. The developer, which is an inhibitor of charging, can be efficiently discharged from the charging member to maintain good charging performance stably for a long period of time. Image formation can be maintained for a long time. Further, even after an image having a high image ratio is output, high-quality image formation can be maintained for a long period of time.

[Brief description of the drawings]

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

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

 DESCRIPTION OF SYMBOLS 1 Photoreceptor (image carrier, charged object) 2 Charging roller (contact charging member) 3 Developing device (regular developing device or reversal developing device) 31 Developer (toner) m Charge promotion particles 4 Transfer roller 5 Fixing device P Transfer Material C Process cartridge S1 to S3 Bias application power supply

Claims (10)

[Claims] A charging step of charging the image carrier with the image carrier; an information writing step of forming an electrostatic latent image on the charged surface of the image carrier; and developing the electrostatic latent image with a charged developer. In an image forming apparatus, an image forming process is performed by applying an image forming process including a developing step and a transfer step of transferring a developer image on an image carrier to a recording medium, and the image carrier is repeatedly used for image formation. . A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein charge-promoting particles are mixed in a developer of a developing unit, and the charge-promoting particles are charged in the developing unit to the same polarity as a DC charging polarity of a contact charging device. 2. A charging step of charging an image carrier on an image carrier, an information writing step of forming an electrostatic latent image on a charged surface of the image carrier, and developing the electrostatic latent image with a charged developer. In an image forming apparatus, an image forming process is performed by applying an image forming process including a developing step and a transfer step of transferring a developer image on an image carrier to a recording medium, and the image carrier is repeatedly used for image formation. . A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein the developing means is a regular developing means, wherein charge-promoting particles are mixed into the developer, and the charge-promoting particles are charged to a polarity different from that of the developer in the developing means. 3. A charging step of charging the image carrier with the image carrier, an information writing step of forming an electrostatic latent image on the charged surface of the image carrier, and developing the electrostatic latent image with a charged developer. In an image forming apparatus, an image forming process is performed by applying an image forming process including a developing step and a transfer step of transferring a developer image on an image carrier to a recording medium, and the image carrier is repeatedly used for image formation. . A voltage is applied to a charging unit for charging the image carrier,
A contact charging device for charging an image carrier surface by a flexible charging member forming a nip portion with the image carrier, wherein the charging member moves with a speed difference with respect to the image carrier, and at least the charging member and the image carrier And a nip portion having conductive particles for accelerating electrification for promoting electrification, b. An image forming apparatus, wherein the developing means is a reversal developing means, wherein charge-promoting particles are mixed in the developer, and the charge-promoting particles are charged to the same polarity as the developer in the developing means. 4. The image forming apparatus according to claim 1, wherein said developing means also serves as a cleaning means for collecting the developer remaining on the image carrier after transferring the developer image onto a recording medium. An image forming apparatus according to any one of the preceding claims. 5. The method according to claim 1, wherein the charge accelerating particles are frictionally charged by rubbing with the developer and have a charge polarity.
5. The image forming apparatus according to any one of claims 1 to 4. 6. The image forming apparatus according to claim 1, wherein the member that frictionally charges the developer also functions as a member that charges the charge accelerating particles. 7. The charge-promoting particles having a particle diameter of 1% of the developer.
The image forming apparatus according to any one of claims 1 to 6, wherein the resistance value is equal to or less than / 2 and the resistance value is equal to or less than 1 × 10 ¹² (Ω · cm). 8. The charge-promoting particles whose particle size is one of that of the developer.
The image forming apparatus according to any one of claims 1 to 6, wherein the resistance value is equal to or less than / 2 and the resistance value is equal to or less than 1 × 10 ¹⁰ (Ω · cm). 9. The image forming apparatus according to claim 1, wherein the charging member is driven while maintaining a speed difference in a direction opposite to a moving direction of the image carrier. 10. The image forming apparatus according to claim 1, wherein the information writing means for forming an electrostatic latent image on the charged surface of the image carrier is an image exposure means.