JP3647265B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer. More specifically, the present invention relates to a contact charging type image forming apparatus.
[0002]
[Prior art]
Conventionally, for example, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential (also a static elimination process). A corona charger (corona discharger) has been used as a charging device to be included.
[0003]
A corona charger is a non-contact type charging device. For example, a corona charger is provided with a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and a discharge opening is opposed to an image carrier as a charged body. The image carrier surface is charged to a predetermined level by exposing the image carrier surface to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.
[0004]
Recently, a contact charging device has been proposed and put to practical use as a charging device for an object to be charged such as an image bearing member because it has advantages such as low ozone and low power compared to a corona charger.
[0005]
The contact charging device contacts a charged object 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, and the charging member (contact charging member). A predetermined charging bias is applied to a contact charger (hereinafter referred to as a contact charging member) to charge the surface of the object to be charged to a predetermined polarity and potential.
[0006]
There are two types of charging mechanisms (1) discharge charging mechanism and (2) injection charging mechanism in the contact charging mechanism (charging mechanism, charging principle). Each charging mechanism depends on which is dominant. A characteristic appears.
[0007]
(1). Discharge charging mechanism
This is a mechanism for charging the surface of the member to be charged by a discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.
[0008]
Since the discharge charging mechanism has a constant discharge threshold value for the contact charging member and the member to be charged, it is necessary to apply a voltage larger than the charging potential to the contact charging member. Further, although the generation amount is remarkably smaller than that of the corona charger, it is unavoidable that a discharge product is generated in principle, and thus harmful effects due to active ions such as ozone are unavoidable.
[0009]
(2). Injection charging mechanism
This is a mechanism for charging the surface of the member to be charged by directly injecting the charge from the contact charging member to the member to be charged. It is also called direct charging, injection charging, or charge injection charging.
[0010]
More specifically, a medium-resistance contact charging member comes into contact with the surface of the member to be charged, and charge is directly injected into the surface of the member to be charged without going through a discharge phenomenon, that is, basically using no discharge. Therefore, even if the applied voltage to the contact charging member is an applied voltage that is equal to or lower than the discharge threshold, the object to be charged can be charged to a potential corresponding to the applied voltage. Since this injection charging mechanism does not involve the generation of ions, there is no adverse effect caused by the discharge product.
[0011]
However, since the charging is injection charging, the contact property of the contact charging member to the member to be charged greatly affects the charging property. Therefore, the contact charging member needs to be configured more densely, have a large speed difference from the object to be charged, and must be configured to contact the object to be charged more frequently.
[0012]
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.
[0013]
The roller charging is mainly performed by the discharge charging mechanism (1).
[0014]
The charging roller is made of a conductive or medium resistance rubber material or foam. In addition, there are those obtained by laminating these to obtain desired characteristics.
[0015]
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), but has a large frictional resistance, and is often driven by the photosensitive member or at a slight speed. Driven with a difference. Therefore, even if injection charging is attempted, a decrease in absolute charging ability, insufficient contact, uneven charging on the roller, and uneven charging due to the adherence of the photosensitive member cannot be avoided. The mechanism is dominant.
[0016]
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 photosensitive member charging potential obtained at that time.
[0017]
The charging characteristic in the case of conventional roller charging is represented by A. That is, charging starts after the discharge threshold of about −500V. Therefore, when charging to -500 V, apply a DC voltage of -1000 V, or in addition to a charging voltage of -500 V DC, apply an AC voltage with a peak-to-peak voltage of 1200 V so as to always have a potential difference greater than the discharge threshold. Thus, a method of converging the photoreceptor potential to the charging potential is common.
[0018]
More specifically, when the charging roller is brought into pressure contact with an OPC photoconductor having a thickness of 25 μm, the surface potential of the photoconductor starts to rise when a voltage of about 640 V or more is applied. Thereafter, the photosensitive member surface potential increases linearly with a slope of 1 with respect to the applied voltage. This threshold voltage is defined as the charging start voltage Vth.
[0019]
That is, in order to obtain the photoreceptor surface potential Vd required for electrophotography, the charging roller requires a DC voltage higher than that required, that is, Vd + Vth. A method of charging by applying only the DC voltage to the contact charging member in this way is referred to as a “DC charging method”.
[0020]
However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, and Vth fluctuates when the film thickness changes due to the photoconductor being scraped. It was difficult.
[0021]
Therefore, an AC component having a peak-to-peak voltage of 2 × Vth or more is added to a DC voltage corresponding to a desired Vd, as disclosed in Japanese Patent Laid-Open No. 63-149669, in order to further uniform charge. An “AC charging method” is used in which the superimposed voltage is applied to the contact charging member. This is for the purpose of smoothing the potential due to AC, and the potential of the charged body converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment.
[0022]
However, even in such a contact charging device, the essential charging mechanism is mainly based on a discharge charging mechanism and uses the discharge phenomenon from the contact charging member to the photosensitive member. In addition, the voltage applied to the contact charging member needs to have a value equal to or higher than the surface potential of the photoreceptor, and a trace amount of ozone is generated.
[0023]
Further, when AC charging is performed for uniform charging, further generation of ozone, generation of vibration noise (AC charging sound) between the contact charging member and the photosensitive member due to an AC voltage electric field, and surface of the photosensitive member due to discharge As a result, the deterioration and the like became remarkable, which was a new problem.
[0024]
B) Fur brush charging
Fur brush charging uses a member (fur brush charger) having a conductive fiber brush portion as a contact charging member, and the conductive fiber brush portion is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied. This is applied to charge the photoreceptor surface to a predetermined polarity and potential.
[0025]
The charge charging mechanism of the fur brush charging is dominated by the discharge charging mechanism (1).
[0026]
Fur brush chargers are available in fixed and roll types. A fixed type is a medium-resistance fiber folded into a base fabric and bonded to an electrode. The roll type is formed by winding a pile around a metal core. The fiber density is 100 / mm ² However, the contact property is still insufficient for sufficiently uniform charging by the injection charging mechanism, and the photosensitive member is mechanically charged for sufficiently uniform charging by the injection charging mechanism. As a configuration, it is necessary to have a speed difference that is difficult, which is not realistic.
[0027]
The charging characteristics of the fur brush charged when a DC voltage is applied are the characteristics shown in FIG. 4B. Accordingly, in the case of fur brush charging, both the fixed type and the roll type are charged using a discharge charging mechanism with a high charging bias applied.
[0028]
C) Magnetic brush charging
Magnetic brush charging uses a member (magnetic brush charger) having a magnetic brush portion formed in a brush shape by magnetically constraining conductive magnetic particles with a magnet roll or the like as a contact charging member, and the magnetic brush portion is to be charged. And a predetermined charging bias is applied to charge the surface of the photosensitive member to a predetermined polarity and potential.
[0029]
In the case of this magnetic brush charging, the charging mechanism of (2) is dominant as the charging mechanism.
[0030]
As the conductive magnetic particles constituting the magnetic brush portion, those having a particle diameter of 5 to 50 μm are used, and a sufficient speed difference from the photoconductor is provided, so that injection charging can be performed uniformly.
[0031]
As indicated by C in the charging characteristic graph of FIG. 4, it is possible to obtain a charging potential substantially proportional to the applied bias.
[0032]
However, there are other disadvantages such as a complicated apparatus configuration and conductive magnetic particles constituting the magnetic brush portion falling off and adhering to the photoreceptor.
[0033]
Japanese Patent Laid-Open No. 6-3921 proposes a method of injecting charges into a charge holding member such as a trap level on the surface of a photoreceptor or a conductive particle of 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 photoreceptor surface potential, and ozone is not generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and this is an excellent charging system that is ozone-free and has low power compared to the roller charging system.
[0034]
D) Cleanerless (toner recycling system)
In a transfer type image forming apparatus, residual developer (toner) remaining on the photoreceptor after transfer (image carrier) is removed from the photoreceptor surface by a cleaner (cleaning device) to become waste toner. It is desirable that the toner does not come out from the viewpoint of environmental protection. Therefore, the cleaner is eliminated, and the transfer residual developer on the photosensitive member after transfer is removed from the photosensitive member by “development simultaneous cleaning” by the developing device, and is collected and reused in the developing device. Has also appeared.
[0035]
Simultaneous development cleaning refers to the developer remaining on the photoconductor after transfer during the subsequent development, that is, the photoconductor is subsequently charged and exposed to form a latent image, and the latent image is developed with a fog removal bias. (A fog removal potential difference Vback which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member). According to this method, the untransferred developer is collected by the developing device and reused after the next step. Therefore, waste toner can be eliminated and maintenance work can be reduced. Further, the cleanerless has a great advantage in terms of space, and the image forming apparatus can be greatly downsized.
[0036]
As described above, the cleaner-less system does not remove the transfer residual toner from the surface of the photosensitive member by a dedicated cleaner, but instead reaches the developing device via the charging unit and uses it again in the development process. When contact charging is used as the charging means for the body, there is a problem of how to charge the photosensitive body in a state where an insulating developer is interposed in the contact portion between the photosensitive body and the contact charging member. . In the above-described roller charging or fur brush charging, the transfer residual toner on the photosensitive member is diffused to be non-patterned, and charging by discharging by applying a large bias is often used. In magnetic brush charging, powder is used as the contact charging member, so there is an advantage that the magnetic brush portion of the conductive magnetic particles, which is the powder, can flexibly contact the photoconductor to charge the photoconductor, but the device configuration is complicated. That is, the harmful effect caused by dropping off of the conductive magnetic particles constituting the magnetic brush portion is great.
[0037]
E) Powder application to contact charging member
Japanese Patent Publication No. 7-99442 discloses a configuration in which powder is applied to a contact surface of a contact charging member with a surface of an object to be charged in order to prevent uneven charging and perform stable uniform charging. Although the contact charging member (charging roller) is driven to rotate (without speed difference driving), the generation of ozone products is much less than that of corona chargers such as Scorotron. The charging principle is mainly based on the discharge charging mechanism as in the case of the roller charging described above. In particular, in order to obtain more stable charging uniformity, a voltage obtained by superimposing an AC voltage on a DC voltage is applied, and therefore, more ozone products are generated due to discharge. Therefore, when the apparatus is used for a long period of time or when the cleanerless image forming apparatus is used for a long period of time, adverse effects such as image flow due to ozone products tend 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 and silica fine particles adhering to the surface of the charging means during repeated image formation for a long time is prevented. Therefore, it is disclosed that the 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, not the direct injection charging mechanism, and has the above-described problems due to discharge charging.
[0038]
[Problems to be solved by the invention]
As described in the section of the prior art above, in the conventional contact charging, the surface of the contact charging member is rough in order to perform the injection charging mechanism with a simple configuration using a charging roller or a fur brush as the contact charging member. Thus, intimate contact with the image carrier as a charged body is not ensured, and the injection charging mechanism is difficult.
[0039]
Therefore, in contact charging, even when a simple member such as a charging roller or a fur brush is used as the contact charging member, an injection charging mechanism that is more excellent in charging uniformity and stable for a long period of time is realized. Therefore, it is expected to realize an ozone-less injection charging mechanism with a simple configuration.
[0040]
Further, in a contact charging type and transfer type image forming apparatus that employs a contact charging device as a charging means for the image carrier, contamination of the contact charging member with the developer is also an inhibiting factor of the injection charging mechanism.
[0041]
That is, even in the case of an image forming apparatus provided with a dedicated cleaner for removing residual transfer residual developer on the surface of the image carrier after transfer, the residual transfer residual developer on the surface of the image carrier after transfer is 100% with the cleaner. A part of the residual developer that has not been removed passes through the cleaner and is carried to the charging part, which is the contact part between the contact charging member and the image carrier, and is attached to and mixed in the contact charging member. Developer contamination of the member occurs. Since the conventional developer is generally an insulator, the developer contamination of the contact charging member is a factor that causes charging failure.
[0042]
In particular, in a cleanerless image forming apparatus, a dedicated cleaner for removing the residual transfer residual developer on the surface of the image carrier after transfer is not used, so that the residual residual developer on the surface of the image carrier after transfer. Is carried by the image carrier surface as it is moved 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. In addition, the effect of charging inhibition by the transfer residual developer is large.
[0043]
Adhesive force between the contact charging member such as a charging roller and the developer is large, and even when a developer discharge bias is applied to the contact charging member, the developer is firmly attached to the contact charging member and sufficient chargeability is obtained. I couldn't.
[0044]
When charging failure occurs, the developer charging into the contact charging member further increases and the charging failure is intensified.
[0045]
In other words, here, the surface of the contact charging member is rough for injection charging with a simple contact charging member such as a charging roller, and the adhesion between the contact charging member and the developer is large, thereby causing contamination of the developer on the contact charging member. Inability to improve is a problem.
[0046]
In view of this, the present invention provides charging as a contact charging member for a contact charging type, transfer type image forming apparatus, or a contact charging type, transfer type, or cleanerless image forming apparatus that employs a contact charging unit as a charging means for an image carrier. Using simple members such as rollers and fur brushes, and regardless of developer contamination of contact charging members, ozoneless injection charging and cleanerless systems can be executed without problems at low applied voltage, and high-quality image formation is possible. The purpose is to maintain the image for a long period of time and to maintain high-quality image formation for a long period of time even after outputting an image with a high image ratio.
[0047]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0048]
(1) A charging step (process) for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, and developing the electrostatic latent image with a charged developer. In an image forming apparatus that performs image formation by applying an image forming process including a developing step and a transfer step of transferring a developer image on the image carrier to a recording medium, and the image carrier repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
b. Charge-promoting particles are mixed in the developer of the developing unit, and the charge-promoting particles are charged in the developing unit with the same polarity as the DC charging polarity of the contact charging device.
An image forming apparatus.
[0049]
(2) A charging step for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, and a development step for developing the electrostatic latent image with a charged developer. In an image forming apparatus that executes image formation 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 repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
b. The developing means is a regular developing means, in which the charge accelerating particles are mixed in the developer, and in the developing means, the charge accelerating particles are charged with a polarity different from that of the developer.
An image forming apparatus.
[0050]
(3) A charging step for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, and a development step for developing the electrostatic latent image with a charged developer. In an image forming apparatus that executes image formation 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 repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
b. The developing means is a reversal developing means, in which charge accelerating particles are mixed in the developer, and the charge accelerating particles are charged in the same polarity as the developer in the developing means.
An image forming apparatus.
[0051]
(4) Any one of (1) to (3), wherein the developing means also serves as a cleaning means for collecting the developer remaining on the image carrier after the developer image is transferred to the recording medium. The image forming apparatus described in 1.
[0052]
(5) The image forming apparatus according to any one of (1) to (4), wherein the charge accelerating particles are triboelectrically charged by rubbing against the developer and have a charge polarity.
[0053]
(6) The image forming apparatus according to any one of (1) to (4), wherein the member that frictionally charges the developer also serves as a member that charges the charge accelerating particles.
[0054]
(7) The charge accelerating particles have a particle size of ½ or less of the developer and a resistance value of 1 × 10. ¹² The image forming apparatus according to any one of (1) to (6), wherein the image forming apparatus is (Ω · cm) or less.
[0055]
(8) The charge accelerating particles have a particle size of ½ or less of the developer and a resistance value of 1 × 10. ^Ten The image forming apparatus according to any one of (1) to (6), wherein the image forming apparatus is (Ω · cm) or less.
[0056]
(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.
[0057]
(10) The image forming apparatus according to any one of (1) to (9), wherein the information writing means for forming an electrostatic latent image on the charging surface of the image carrier is an image exposure means.
[0058]
<Operation>
a) The charge accelerating particles are conductive particles for the purpose of assisting charging. In the contact charging, at least a nip portion between the charging member and the image bearing member is interposed between the charging accelerating particles to achieve uniform and stable direct charging. Realized. The charge promoting particles have a resistance value of 1 × 10 ¹² (Ω · cm) or less, more preferably 1 × 10 ^Ten The chargeability is not impaired by using (Ω · cm) or less. Further, by setting the particle size to ½ or less of the particle size of the developer, image exposure on the image carrier is not hindered.
[0059]
That is, by interposing the charge accelerating particles in the charging portion that is the nip portion between the image carrier and the contact charging member, the frictional effect of the particles increases the frictional resistance, and the speed difference with respect to the image carrier is left as it is. Even a charging roller that was difficult to hold and contact can be brought into contact with the surface of the image bearing member easily and effectively with a speed difference. At the same time, 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 more frequently.
[0060]
By providing a sufficient speed difference between the contact charging member and the image carrier, the chance of the charge accelerating particles contacting the image carrier at the nip portion between the contact charging member and the image carrier is greatly increased, and high contact is achieved. The charge accelerating particles present in the nip portion between the contact charging member and the image carrier can rub the image carrier surface without any gap so that charges can be directly injected into the image carrier. Contact charging of the image bearing member by the charging member is dominated by injection charging due to the presence of the charge accelerating particles.
[0061]
b) As a configuration for providing a speed difference, the contact charging member is rotationally driven or fixed to provide a speed difference with the image carrier. In the transfer type or transfer type / cleanerless image forming apparatus, it is preferable that the developer passed through the cleaner carried by the charging unit or the transfer residual developer in the case of cleanerless is temporarily applied to the contact charging member. In order to collect and level the target, it is desirable that the contact charging member is driven to rotate, and the rotation direction of the contact charging member rotates in the direction opposite to the moving direction of the image carrier surface. That is, injection charging can be performed preferentially by once separating and charging the residual developer on the image carrier by reverse rotation.
[0062]
Although it is possible to move the contact charging member in the same direction as the moving direction of the image carrier surface to give a speed difference, the charging property of injection charging is the ratio of the peripheral speed of the image carrier to the peripheral speed of the contact charging member. Therefore, in order to obtain the same peripheral speed ratio as in the reverse direction, the rotational speed of the contact charging member is larger in the forward direction than in the reverse direction. This is advantageous. The peripheral speed ratio described here is
Peripheral speed ratio (%) = (charging member peripheral speed−image carrier peripheral speed) / image carrier peripheral speed × 100
(The charging member peripheral speed is a positive value when the surface of the charging member moves in the same direction as the surface of the image carrier at the nip portion).
[0063]
c) In a cleanerless image forming apparatus, the residual developer remaining on the surface of the image carrier after transfer is held as it is by moving the surface of the image carrier to the charging portion which is the nip portion between the image carrier and the contact charging member. Carried.
[0064]
In this case, by bringing the contact charging member into contact with the image carrier with a speed difference, the pattern of the residual transfer developer is disturbed and destroyed, and the previous image pattern portion appears as a ghost in the halftone image. Nothing will happen.
[0065]
d) The developer that has been carried to the charging unit and has passed through the cleaner or the transfer residual developer in the case of cleanerless adheres to and mixes with the contact charging member. Conventionally, since the developer is an insulator, the adhesion / mixing of the transfer residual developer to the contact charging member is a factor that causes charging failure in charging of the image carrier.
[0066]
However, even in this case, since the charge accelerating particles are interposed in the charging portion, which is the nip portion between the image carrier and the contact charging member, the contact property of the contact charging member to the image carrier and the contact resistance can be maintained. Regardless of the contamination of the contact charging member with the residual transfer developer, the ozone-less direct charging can be stably maintained over a long period of time with a low applied voltage, and uniform chargeability can be provided.
[0067]
e) The developer adhering to and mixed in the contact charging member is gradually discharged from the contact charging member onto the image carrier, reaches the development site as the image carrier surface moves, and is simultaneously cleaned (collected) by the developing means (development). Toner recycling).
[0068]
In this case, since the charge promoting particles are carried on the contact charging member, the adhesion force between the contact charging member and the transfer residual developer adhering to and mixed with the contact charging member is reduced, and the contact charging member moves onto the image carrier. The developer discharge efficiency is improved.
[0069]
f) First, even if a sufficient amount of charge promoting particles are interposed in the charging portion, which is the nip portion between the image carrier and the contact charging member, or a sufficient amount of charge promoting particles is applied to the contact charging member. However, as the device is used, the charge accelerating particles are decreased from the charging portion or the charge accelerating particles are deteriorated.
[0070]
In the present invention, when the charge-promoting particles are decreased from the charging portion or the charge-promoting particles are deteriorated, and the chargeability is lowered, the charge-promoting particles mixed in the developer of the developing means are developed. Is attached to the surface of the image carrier where the charging property has been lowered at the portion, and is carried to the charging portion via the transfer portion as the image carrier surface moves, so that it is automatically supplied to the charging portion and the contact charging member. Good chargeability is maintained.
[0071]
The developer image on the image carrier is attracted and actively transferred to the recording medium side due to the effect of the transfer bias in the transfer portion, but the charge promoting particles on the image carrier are electrically conductive and thus move to the recording medium side. Does not move positively, 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.
[0072]
In this case, even in the case of an image forming apparatus provided with a cleaner, most of the residual transfer developer (including paper dust) remaining on the surface of the image carrier after transfer and the charge accelerating particles are mostly residual transfer developer. Is collected by the cleaner, but the charge accelerating particles have a smaller particle size than the developer, and therefore easily pass through the cleaner and are carried to the charging unit by the slip. In the case of a cleanerless image forming apparatus, the residual developer remaining on the transfer and the charge accelerating particles remaining on the surface of the image carrier after transfer are carried directly to the charging unit.
[0073]
That is, the charge accelerating particles are mixed in the developer of the developing unit, and the charged particles are developed (attached to the image bearing member) on the image carrier portion where the chargeability is lowered. The charged particles are charged. In particular,
(1). Charge-promoting particles are mixed in the developer of the developing unit, and the charge-promoting particles are charged to the same polarity as the DC charging polarity of the contact charging device in the developing unit.
(2). Alternatively, the developing means is a regular developing means, in which charge accelerating particles are mixed in the developer, and in the developing means, the charge accelerating particles are charged with a polarity different from that of the developer.
(3). Alternatively, the developing means is a reversal developing means, in which charge accelerating particles are mixed in the developer, and in the developing means, the charge accelerating particles are charged to the same polarity as the developer.
As a result, when the charge-promoting particles are reduced from the charged portion or the charge-promoting particles are deteriorated, and the chargeability is lowered, the charge-promoting particles mixed in the developer of the developing unit are removed in the developing portion. It adheres to the surface of the image bearing member with reduced chargeability and is carried to the charging unit via the transfer unit along with the movement of the image bearing surface, so that it is automatically supplied to the charging unit and contact charging member. High chargeability is maintained.
[0074]
g) Thus, 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 for a contact charging method, a transfer method, or a cleanerless image forming apparatus. In addition, the charge-promoting particles that enable injection charging are automatically supplied to the charging portion and the contact charging member, and the developer is an inhibitor of charging from the contact charging member contaminated by the developer (toner). Can be efficiently discharged, and good chargeability can be stably maintained over a long period of time, injection charging and a toner recycling system can be executed without problems, and high-quality image formation can be maintained over a long period of time. Further, high-quality image formation can be maintained for a long time even after an image with a high image ratio is output.
[0075]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1> (FIG. 1)
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention.
[0076]
The image forming apparatus of this embodiment is a transfer type electrophotographic process use, contact charging type, cleanerless, process cartridge type laser printer.
[0077]
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 opposite polarity to the developer by frictional charging with the developer.
[0078]
(1) Overall schematic configuration of this example printer
[Image carrier]
Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image bearing member (charged member). The printer of this embodiment uses regular development, and the photosensitive member 1 uses a positive photosensitive member. The photoconductor 1 of this embodiment is an OPC photoconductor having a diameter of 30 mm, and is driven to rotate at a peripheral speed of 94 mm / sec in the clockwise direction of an arrow.
[0079]
[Charge]
Reference numeral 2 denotes a conductive elastic roller (charging roller) as a flexible contact charging member disposed in contact with the photoreceptor 1 with a predetermined pressing force. a is a charging nip portion between the photoreceptor 1 and the charging roller 2; The charging roller 2 is preliminarily coated with the charge promoting particles m on the outer peripheral surface thereof, and the charge accelerating particles m exist in the charging nip portion a.
[0080]
In this embodiment, the charging roller 2 is rotationally driven at a peripheral speed of 100% in the opposite direction (counter) to the rotation direction of the photosensitive member 1 in the charging nip portion a, and contacts the surface of the photosensitive member 1 with a speed difference. To do. A predetermined charging bias is applied to the charging roller 2 from the charging bias power source S1. As a result, the peripheral surface of the rotating photosensitive member 1 is uniformly contact-charged to a predetermined polarity and potential by the injection charging method. In this embodiment, a charging bias is applied to the charging roller 2 from the charging bias power source S1 so that the outer peripheral surface of the photoreceptor 1 is uniformly charged to about 700V.
[0081]
The charging roller 2, the charge accelerating particles m, injection charging, and the like will be described in detail in another section.
[0082]
[Exposure]
Then, scanning exposure L with a laser beam output from a laser beam scanner (not shown) including a laser diode, a polygon mirror, and the like is performed on the charged surface of the rotating photosensitive member 1. 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, and is applied to the outer peripheral surface of the rotating photosensitive member 1 by scanning exposure L with this laser beam. An electrostatic latent image corresponding to the target image information is formed.
[0083]
In the present embodiment, regular development is used, and in the scanning exposure L by the laser beam on the outer peripheral surface of the rotating photoconductor 1, the non-exposed portion is an image portion and the exposed portion is a non-image portion.
[0084]
[Current image]
Reference numeral 3 denotes a regular developing device, and the electrostatic latent image formed on the outer peripheral surface of the rotating photoconductor 1 is normally developed as a developer image (toner image) by the developing device 3.
[0085]
The developing device 3 of this example uses a non-magnetic one-component insulating developer (toner) having a negative charge average particle diameter of 7 μm as the developer 31.
[0086]
The developer 31 is externally added (mixed) with the charge accelerating particles m, and the external addition amount is 2 parts by weight with respect to 100 parts by weight of the developer in this embodiment.
[0087]
Reference numeral 32 denotes a non-magnetic developing sleeve having a diameter of 16 mm containing the magnet 33. The developing sleeve 32 is coated with the developer 31 (+ m) and the distance from the surface of the photosensitive member 1 is fixed to 500 μm. The developing bias voltage is applied to the developing sleeve 32 from the developing bias power source S2.
[0088]
The developer 31 (+ m) in the developing device is subjected to layer thickness regulation by the elastic blade (regulating blade) 34 in the process of being conveyed on the rotary developing sleeve 32, and is frictionally charged by sliding with the elastic blade 34. Have a charge.
[0089]
The development bias voltage is obtained by superimposing 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, and one-component jumping development is performed at the development site b between the development sleeve 32 and the photoreceptor 1. Make it.
[0090]
A developer adheres to a non-exposed portion which is an image portion of the electrostatic latent image on the surface of the rotating photosensitive member 1 so that the electrostatic latent image is normally developed.
[0091]
[Transfer]
Reference numeral 4 denotes a medium resistance transfer roller as a contact transfer means, which is brought into pressure contact with the photoreceptor 1 to form a transfer nip portion c. A transfer material P as a recording medium is fed to the transfer nip c from a paper feed 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 source S3. Thus, the developer image on the photosensitive member 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip c.
[0092]
The transfer roller 4 used in this example has a roller resistance value of 5 × 10, in which a medium resistance foam layer 42 is formed on a cored bar 41. ⁸ The transfer was carried out by applying a DC voltage of +2200 V to the cored bar 41. The transfer material P introduced into the transfer nip portion c is nipped and conveyed by the transfer nip portion c, and the developer image formed and supported on the surface of the rotary photosensitive member 1 is successively transferred to the surface side by electrostatic force and pressing force. Will be transcribed.
[0093]
[Fixed]
Reference numeral 5 denotes a fixing device such as a heat fixing method. The transfer material P that has been fed to the transfer nip c and has received the transfer of the developer image on the side of the photoconductor 1 is separated from the surface of the rotary photoconductor 1 and introduced into the fixing device 5 to fix the developer image. Upon receipt, the image is discharged out of the apparatus as a print (print, copy).
[0094]
[cartridge]
In the printer of this embodiment, three process devices, that is, the photosensitive member 1, the contact charging member 2, and the developing device 3, are included in a cartridge case, and the cartridge C is detachably attached to the printer main body. The combination of process devices to be converted into cartridges is not limited to the above.
[0095]
(2) Charging roller 2
The charging roller 2 as a contact charging member in the present embodiment is formed by forming a middle resistance layer 22 of rubber or foam on a cored bar 21.
[0096]
The middle resistance layer 22 was formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and formed on the cored bar 21 in a roller shape. Thereafter, the surface was polished as necessary.
[0097]
The roller resistance of the charging roller 2 of this example was measured and found to be 100 kΩ. The roller resistance is measured by applying 100 V between the cored bar 21 and the aluminum drum in a state where the charging roller 2 is pressure-bonded to the φ30 mm aluminum drum so that the total pressure of 1 kg is applied to the cored bar 21 of the charging roller 2. did.
[0098]
Here, it is important that the charging roller 2 as a contact charging member functions as an electrode. In other words, it is necessary to provide a sufficient contact state with the member to be charged by providing elasticity, and at the same time to have a sufficiently low resistance to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a low-voltage defect site such as a pinhole is present in the member to be charged. When an electrophotographic photosensitive member is used as the member to be charged, 10 is necessary to obtain sufficient chargeability and leakage resistance. ^Four -10 ⁷ A resistance of Ω is desirable.
[0099]
It is desirable that the surface of the charging roller 2 has micro unevenness so that the charge accelerating particles m can be held.
[0100]
If the hardness of the charging roller 2 is too low, the shape is not stable, so that the contact with the member to be charged is deteriorated. If the hardness is too high, the charging nip portion a cannot be secured between the member and the member to be charged. Since the micro contact property to the surface of the member to be charged is deteriorated, the preferred Asker C hardness is 25 to 50 degrees.
[0101]
The material of the charging roller 2 is not limited to an elastic foam, but as an elastic material such as EPDM, urethane, NBR, silicone rubber, IR, etc., carbon black, metal oxide, etc. for resistance adjustment. Examples thereof include a rubber material in which a conductive material is dispersed and a foamed material of these materials. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance.
[0102]
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, and in this embodiment, a charging nip a having a width of several millimeters is formed.
[0103]
(3) Charge promoting particles m
In this embodiment, the specific resistance is 10 as the charge promoting particles m coated in advance on the outer peripheral surface of the charging roller 2 as the contact charging member and the charge promoting particles m externally added to the developer 31 of the developing device 3. ⁷ Conductive zinc oxide particles having an Ω · cm and an average particle diameter 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. In any aggregate state, the form is not important as long as the function as the charge promoting particles can be realized as the aggregate.
[0104]
The particle size was defined as the average particle size of the aggregate when the particles constituted an aggregate. For the measurement of the particle size, 100 or more samples were extracted from observation with an optical or electron microscope, the volume particle size distribution was calculated with the maximum horizontal chord length, and the 50% average particle size was determined.
[0105]
The resistance value of the charge promoting particles m is 10 ¹² When it was Ω · cm or more, the chargeability was impaired. Therefore, the resistance value is 10 ¹² Ω · cm or less, more preferably 10 ^Ten Must be Ω · cm or less. In this embodiment, 1 × 10 ⁷ The thing of ohm * cm was used. The resistance was measured by the tablet method and normalized. That is, the bottom area 2.26cm ² About 0.5 g of a powder sample was placed in the cylinder, and 15 kg of pressure was applied to the upper and lower electrodes. At the same time, a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.
[0106]
The charge accelerating particles m are desirably white or nearly transparent so as not to hinder the latent image exposure, and are therefore preferably non-magnetic. Further, considering that the charge accelerating particles are partially transferred from the photoreceptor to the recording material P, it is preferable that the color recording is colorless or white. Further, the image exposure may be blocked unless the particle size is about ½ or less of the particle size of the developer 31. Therefore, it is desirable that the particle diameter of the charge accelerating particles m is smaller than ½ of the particle diameter of the developer 31. As the lower limit of the particle size, 10 nm is considered to be the limit as a particle that can be stably obtained.
[0107]
In this embodiment, zinc oxide is used as the material for the charge accelerating particles m. However, the present invention is not limited to this, and other metal oxides such as alumina are mixed with conductive inorganic particles or organic substances, or the like. Various conductive particles such as those subjected to surface treatment can be used.
[0108]
In this embodiment, the charge accelerating particles m (zinc oxide particles) externally added to the developer 31 of the developing device 3 have a positive charge polarity opposite to that of the developer 31 due to the friction with the developer 31. Added. That is, the charge accelerating particles m are charged with a polarity opposite to that of the developer for normal development (= charged with the same polarity as the DC charging polarity of the contact charging device).
[0109]
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 photosensitive member 1 (= attached to the surface of the photosensitive member, and so on). ) 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 photosensitive member is on the negative side, that is, a region that is not charged.
[0110]
Here, the triboelectric charging characteristics between the charge promoting particles m and the developer 31 were measured as follows. That is, the charge-promoting particles m are put in a container coated with the developer 31 thermally melted on the inner surface, the container is shaken, and then the charge-promoting particles are sucked, and the amount of charge of the charge-promoting particles is measured. The charging characteristics were measured.
[0111]
(4) Injection charging
(1). By interposing the charge accelerating particles m in the charging nip a between the photosensitive member 1 as an image carrier and the charging roller 2 as a contact charging member, the frictional effect of the particles m increases the frictional resistance. Even a charging roller that has been difficult to contact with the body 1 with a speed difference is brought into contact with the surface of the photoreceptor 1 with a speed difference easily and effectively. In addition, the charging roller 2 comes into close contact with the surface of the photoconductor 1 through the particles m and comes into contact with the surface of the photoconductor 1 at a higher frequency.
[0112]
By providing a sufficient speed difference between the charging roller 2 and the photosensitive member 1, the chance of the charge accelerating particles m contacting the photosensitive member 1 at the charging nip portion between the charging roller 2 and the photosensitive member 1 is significantly increased. High contactability can be obtained, and the charge accelerating particles m existing in the charging nip portion a of the charging roller 2 and the photosensitive member 1 can slid the surface of the photosensitive member 1 without any gap so that charges can be directly injected into the photosensitive member 1. Thus, contact charging of the photoreceptor 1 by the charging roller 2 is dominated by the injection charging mechanism due to the presence of the charge accelerating particles m.
[0113]
As a configuration for providing a speed difference, the charging roller 2 is rotationally driven or fixed to provide a speed difference from the photosensitive drum 1. Preferably, in order to temporarily collect and level the transfer residual developer on the photosensitive member 1 carried to the charging nip part a by the charging roller 2, the charging roller 2 is driven to rotate, and the rotation direction of the photosensitive member 1 is the photosensitive member. It is desirable to configure to rotate in the direction opposite to the moving direction of one surface. That is, injection charging can be performed preferentially by once separating the residual developer on the photosensitive member 1 by reverse rotation and performing charging.
[0114]
Accordingly, high charging efficiency that cannot be obtained by conventional roller charging or the like can be obtained, and a charging potential almost equal to the voltage applied to the charging roller 2 can be applied to the photoreceptor 1. Thus, even when the charging roller 2 is used as the contact charging member, a voltage equivalent to the charging potential necessary for the photosensitive member 1 is sufficient as the bias applied to the charging roller 2 and stable and no discharge phenomenon is used. A safe contact charging method or apparatus can be realized.
[0115]
By previously supporting the charge accelerating particles m on the surface of the charging nip a or the charging roller 2, the direct charging performance can be exhibited without any problem from the very beginning of the use of the printer.
[0116]
(2). In the cleanerless image forming apparatus, the untransferred developer remaining on the surface of the photoreceptor 1 after the transfer is carried as it is to the charging nip portion a of the photoreceptor 1 and the charging roller 2 by the movement of the surface of the photoreceptor 1. .
[0117]
In this case, by bringing the charging roller 2 into contact with the photosensitive member 1 with a speed difference, the pattern of the residual transfer developer is disturbed and destroyed, and the previous image pattern portion appears as a ghost in the halftone image. Nothing will happen.
[0118]
(3). The untransferred developer carried to the charging nip a adheres to and mixes with the charging roller 2. Since the conventional developer is an insulator, the adhesion and mixing of the transfer residual developer to the charging roller 2 is a factor that causes a charging failure in charging the photosensitive member 1.
[0119]
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 close contact property and the contact resistance of the charging roller 2 to the photosensitive member 1 can be maintained. Regardless of contamination of the charging roller 2 by the residual transfer developer, ozone-less direct charging can be stably maintained over a long period of time with a low applied voltage, and uniform chargeability can be provided.
[0120]
(4). The transfer residual developer adhering to and mixed in the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive member 1 to reach the developing portion b along with the movement of the surface of the photosensitive member 1, and in the developing device 3 simultaneous cleaning (collection) (Toner recycling)
[0121]
In this case, since the charge accelerating particles m are carried on the charging roller 2, the adhesion force between the charging roller 2 and the transfer residual developer adhering to and mixing with the charging roller 2 is reduced. To Developer discharge efficiency is improved.
As described above, the simultaneous development cleaning is performed in the image forming process in which the toner remaining on the photoreceptor 1 after the transfer is continued, that is, the photoreceptor is continuously charged and exposed to form a latent image, and the latent image is developed. At this time, the image is recovered by the fog removal bias of the developing device, that is, the fog removal potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member. In the case of reversal development as in the printer in this embodiment, this simultaneous development cleaning is performed by attaching toner from the dark portion potential of the photosensitive member to the developing sleeve and from the developing sleeve to the bright portion potential of the photosensitive member. This is done by the action of an electric field.
[0122]
(5). Further, the presence of the charge accelerating particles m that are substantially adhered and held on the surface of the photosensitive member 1 also has an effect of improving the transfer efficiency of the developer from the photosensitive member 1 side to the transfer material P side.
[0123]
(5) Replenishment of the charge accelerating particles m to the charging nip a and the charging roller 2
First, even if a sufficient amount of the charge accelerating particles m are interposed in the charging nip portion a between the photoreceptor 1 and the charging roller 2, or a sufficient amount of the charge accelerating particles m are applied to the charging roller 2, As the apparatus is used, the charge accelerating particles m are decreased from the charging nip portion a and the charging roller 2 or the charge accelerating particles m are deteriorated.
[0124]
Therefore, when the charging property is lowered, it is necessary to replenish the charge accelerating particles m to the charging nip portion a and the charging roller 2.
[0125]
In this embodiment, when the charge accelerating particles m are reduced from the charging nip portion a or the charging roller 2 or the charge accelerating particles m are deteriorated, the charging property is lowered, and the developer of the developing device 3 is developed. The charge accelerating particles m mixed in 31 adhere to the surface of the photosensitive member 1 where the chargeability is lowered in the developing portion a, and are held in the charging nip portion a via the transfer portion c as the surface of the photosensitive member 1 moves. By being carried, it is automatically supplied to the charging roller 2 and the charging nip portion a, and good chargeability is maintained.
[0126]
The developer image on the photoconductor 1 is attracted and actively transferred to the recording medium side due to the influence of the transfer bias in the transfer portion c. However, since the charge promoting particles m on the photoconductor 1 have a low resistance value, the recording medium is used. It does not actively move to the side, but is substantially adhered and held on the photosensitive member 1 and remains and is carried to the charging nip portion a via the transfer portion c as the surface of the photosensitive member 1 moves.
[0127]
That is, in this embodiment, the charge promoting particles m are supplied by supplying the charge promoting particles m from the developing device 3. In the printer of this embodiment, regular development is used, and the charge accelerating particles m are frictionally charged with a polarity opposite to that of the developer 31 and have a positive charge. Therefore, development is performed on a region having a relatively negative potential on the photosensitive member 1, that is, a region that is not charged. Therefore, when the charge accelerating particles m are reduced or deteriorated from the charging nip part a or the charging roller 2 and a poorly charged part is generated, a large amount of charged accelerating particles are automatically replenished to the poorly charged part having a low potential. It becomes possible to do.
[0128]
As described above, in this embodiment, it becomes possible to automatically increase the replenishment amount for the portion where the charge promoting particles m are reduced or deteriorated.
[0129]
Thus, for a contact charging method, transfer method, and cleanerless image forming apparatus, ozoneless 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, thereby enabling injection charging. Supply of the charge accelerating particles m to the charging nip part a and the charging roller 2 is automatically executed, and the developer that is a charging inhibiting factor is efficiently discharged from the charging roller 2 contaminated with the developer, Good chargeability can be stably maintained over a long period of time, injection charging and a toner recycling system can be executed without problems, and high-quality image formation can be maintained over a long period of time. Further, high-quality image formation can be maintained for a long time even after an image with a high image ratio is output.
[0130]
If the amount of the charge accelerating particles m intervened in the charging nip a between the photosensitive member 1 as the image bearing member and the charging roller 2 as the contact charging member is too small, a sufficient lubricating effect due to the particles cannot be obtained. The friction between the roller 2 and the photosensitive member 1 is large, and it is difficult to drive the charging roller 2 to the photosensitive member 1 with a speed difference. That is, the driving torque becomes excessive, and the surface of the charging roller 2 and the photosensitive member 1 is scraped if it is forcibly rotated. Furthermore, the effect of increasing the contact opportunity by the particles may not be obtained, and sufficient charging performance cannot be obtained. On the other hand, when the amount of the inclusion is too large, dropping of the charge accelerating particles from the charging roller 2 is remarkably increased, which adversely affects image formation.
According to experiments, the amount of intervention is 10 ^Three Piece / mm ² The above is desirable. 10 ^Three Piece / mm ² If it is lower, a sufficient lubrication effect and an effect of increasing the contact opportunity cannot be obtained, resulting in a decrease in charging performance.
More desirably 10 ^Three ~ 5x10 ^Five Piece / mm ² This amount of inclusion is preferred. 5 × 10 ^Five Piece / mm ² Exceeding this causes the particles to drop off to the photoconductor 1 significantly, resulting in insufficient exposure of the photoconductor 1 regardless of the light transmittance of the particles themselves. 5 × 10 ^Five Piece / mm ² In the following, the amount of dropped particles can be kept low, and the adverse effect can be improved. When the abundance of particles dropped on the photoreceptor 1 in the intervening amount range is measured, 10 is obtained. ² -10 ^Five Piece / mm ² Therefore, the abundance that is not harmful to image formation is 10 ^Five Piece / mm ² The following is desired:
[0131]
A method for measuring the intervening amount and the existing amount on the photoreceptor 1 will be described. It is desirable to directly measure the amount of intervening between the charging roller 2 and the charging nip portion a of the photosensitive member 1, but most of the particles existing on the photosensitive member 1 before contacting the charging roller 2 are moved in the opposite direction while contacting each other. 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 used as the amount of intervening. Specifically, rotation of the photosensitive drum 1 and the charging roller 2 is stopped in a state where no charging bias is applied, and the surfaces of the photosensitive member 1 and the charging roller 2 are video microscope (OLYMPUS OVM1000N) and a digital still recorder (manufactured by DELTAS). SR-3100). The charging roller 2 is in contact with the slide glass under the same conditions as the case where the charging roller 2 is in contact with the photosensitive member 1, and the contact surface of the charging roller 2 is 10 or more with a 1000 × objective lens from the back surface of the slide glass. I took a picture. 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. Further, the abundance on the photoconductor 1 was measured by photographing the photoconductor 1 with the same video microscope and performing the same processing.
In other words, the blending amount of the charge accelerating particles m with respect to the developer 31 of the developing device 3 is set so that the amount of the charge accelerating particles m in the charging nip portion a becomes such an intervening amount. Generally, the charge promoting particles m are 0.01 to 20 parts by weight with respect to 100 parts by weight of the developer (toner).
[0132]
(6) Comparative example
Comparative Example A: Printer using the printer of Example 1 having no charge as the charge promoting particles m
Comparative Example B: Printer using the printer of Example 1 having the same polarity as the developer 31 as the charge promoting particles m
In the printer of Comparative Example A, the charge accelerating particles m do not have a specific charge, and development is performed by charge injection from the developing sleeve 32 of the developing device 3. In this case, when the charge accelerating particles m are reduced or deteriorated from the charging nip portion a or the charging roller 2 and the chargeability is lowered, the development amount of the charge accelerating particles m is not particularly increased. .
[0133]
In the printer of Comparative Example B, when the chargeability decreases, the development amount of the charge accelerating particles also decreases, and the replenishment amount of the charge accelerating particles m to the charging nip portion a and the charging roller 2 decreases. Continued to decline.
[0134]
In contrast to these printers of Comparative Examples A and B, in the printer of Example 1, if a charging failure occurs due to the reduction or deterioration of the charge accelerating particles m in the charging nip part a or the charging roller 2, the development amount of the charge accelerating particles is reduced. The charge accelerating particles m to be supplied to the charging nip portion a and the charging roller 2 are increased, so that the chargeability is not lowered.
[0135]
<Example 2> (FIG. 2)
This embodiment is characterized in that, in an image forming apparatus using reversal development, the charge accelerating particles are charged in the same polarity as the developer in the developing device. As the charging means, the charge accelerating particles are charged by using an elastic blade for charging the developer.
[0136]
Specifically, for the printer of the first embodiment, as shown in FIG.
a. A negative photosensitive member was used as the image carrier 1,
b. A charging bias was applied to the charging roller 2 from the charging bias power source S1 so that the outer peripheral surface of the photosensitive member 1 was uniformly charged to approximately −700 V.
c. Image exposure on the photoreceptor 1 is scanning exposure L with 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. Part
d. The developing device 3 is a reversal developing device, and the developing bias voltage used was a superposition of a DC voltage of −400 V and a rectangular AC voltage with a frequency of 1800 V and a peak-to-peak voltage of 1600 V.
e. The specific resistance is 10 as 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. ⁷ Using polyethylene dispersed in conductive zinc oxide particles having an Ω · cm average particle size of 1.5 μm, f. The developer 31 of the developing device 3 is externally added with 2 parts by weight of the charge accelerating particles m with respect to 100 parts by weight of the developer, and the charge accelerating particles m are rubbed against the elastic blade 34 to develop the developer. Similar to 31, having a negative charge (= charged to the same polarity as the DC charging polarity of the contact charging device),
g. The transfer bias was + 1800V.
[0137]
A printer other than the above a to g is the same as that of the first embodiment.
[0138]
Thus, in the printer of this embodiment, the externally added charge promoting particles m have a negative charge having the same polarity as that of the developer 31 due to the friction with the elastic blade 34 in the developer 31 of the developing device 3. For this reason, the photosensitive member 1 is developed in an incompletely charged portion (region where the potential is on the positive side).
[0139]
In this embodiment, the charge accelerating particles m are supplied by developing the charge accelerating particles m from the developing device 3. Since reversal development is used and the charge accelerating particles m are triboelectrically charged to the negative polarity of the same polarity as the developer 31, the charge accelerating particles m are more developed on the positive side.
[0140]
Therefore, when the charge accelerating particles m are reduced or deteriorated from the charging nip portion a or the charging roller 2 and a defective charging portion is generated, the charging accelerating particles are automatically applied to the charging defective portion having a positive potential. It becomes possible to replenish a lot.
[0141]
As described above, in this embodiment, it becomes possible to automatically increase the replenishment amount for the portion where the charge promoting particles m are reduced or deteriorated.
[0142]
<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.
[0143]
In addition to the charging roller, the flexible contact charging member may be a fur brush charger or the like. Materials and shapes such as felt and cloth can also be used. Moreover, these can be laminated | stacked and it can also obtain more suitable elasticity and electroconductivity.
[0144]
2) In the charging mechanism for contact charging, the contact property of the contact charging member to the member to be charged greatly affects the charging property. Therefore, the contact charging member is configured to be denser, has a large speed difference from the charged body, and is configured to contact the charged body at a higher frequency.
[0145]
Further, an injection charging mechanism in contact charging can be made dominant 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.
[0146]
FIG. 3 is a layer configuration model diagram of the photosensitive member 1 having the charge injection layer 16 provided on the surface. That is, the photosensitive member 1 is generally coated on an aluminum drum substrate (Al drum substrate) 11 in the order of an undercoat layer 12, a positive charge injection preventing layer 13, a charge generation layer 14, and a charge transport layer 15. The charge performance is improved by applying the charge injection layer 16 to the organic photoreceptor.
[0147]
The charge injection layer 16 is made of SnO as conductive particles (conductive filler) on a photo-curable acrylic resin as a binder. ₂ Ultrafine particles 16a (diameter is about 0.03 μm), a lubricant such as tetrafluoroethylene resin (trade name: Teflon), a polymerization initiator, and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method.
[0148]
An important point as the charge injection layer 16 is the resistance of the surface layer. In the charging method by direct injection of charges, charges can be exchanged more efficiently by reducing the resistance on the charged object side. On the other hand, since the electrostatic latent image needs to be held for a certain time when used as a photoconductor, the volume resistance value of the charge injection layer 16 is 1 × 10 6. ⁹ ~ 1x10 ¹⁴ A range of (Ω · cm) is appropriate.
[0149]
Even when the charge injection layer 16 is not used as in this configuration, for example, the same effect can be obtained when the charge transport layer 15 is within the above resistance range.
[0150]
Furthermore, the volume resistance of the surface layer is about 10 ¹³ The same effect can be obtained by using an amorphous silicon photoreceptor having Ω · cm.
[0151]
3) As an AC voltage waveform when an AC voltage (alternating voltage) component is applied to the contact charging member or the developing device, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, it may be a rectangular wave formed by periodically turning on / off a DC power source. In this way, a bias that changes the voltage value periodically can be used as the waveform of the alternating voltage.
[0152]
4) The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means for forming a digital latent image as in the embodiment, but a normal analog image exposure or Other light emitting elements such as LEDs may be used, and any combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used as long as it can form an electrostatic latent image corresponding to image information.
[0153]
The image carrier 1 may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly primary-charged to a predetermined polarity and potential, and then selectively neutralized by a neutralizing means such as a static elimination needle head or an electron gun to write and form a target electrostatic latent image.
[0154]
5) Of course, the developing means 3 is not limited to the developing system and configuration of the developing means 3 as well.
[0155]
6) The image forming apparatus of the present invention may be provided with a cleaner that removes the transfer residual developer and paper dust from the surface of the image carrier after transfer.
[0156]
7) The recording medium that receives the developer image transferred from the image carrier 1 may be an intermediate transfer body such as a transfer drum.
[0157]
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 Inc.) was used, and an interface (manufactured by Nikka) and a CX-1 personal computer (manufactured by Canon) that output number average distribution and volume average distribution were connected, and electrolysis was performed. Prepare 1% NaCl aqueous solution using primary sodium chloride.
[0158]
As a measuring method, a surfactant, preferably 0.1 to 5 ml of alkylbenzene sulfonate, is added to 100 to 150 ml of the electrolytic aqueous solution, and 0.5 to 50 mg of a measurement sample is further added.
[0159]
The electrolyte in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the particle size distribution of 2 to 40 μm particles is measured using the 100 μ aperture as the aperture by the Coulter Counter TA-2 type. Then, the volume average distribution is obtained. The volume average particle diameter is obtained from the obtained volume average distribution.
[0160]
【The invention's effect】
As described above, according to the present invention, a contact charging method, a transfer method, and a cleaner-less image forming apparatus are used as a contact charging member by using a simple member such as a charging roller or a fur brush at a low applied voltage. Injecting electrification can be realized, and charging acceleration particles that enable injecting electrification are automatically supplied to the charging portion and the contact charging member, and charged from the contact charging member contaminated by the developer (toner). The developer, which is an inhibitory factor, can be efficiently ejected, and good chargeability can be stably maintained over a long period of time. The injection charging mechanism and the toner recycling system can be executed without problems, and high-quality image formation can be achieved over a long period of time. Can be maintained across. Further, high-quality image formation can be maintained for a long time even after an image with a high image ratio is output.
[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 model diagram of a layer structure of an example of a photoreceptor having a charge injection layer on the surface.
[Chart 4] Charging characteristic graph
[Explanation of symbols]
1 Photoconductor (image carrier, charged body)
2 Charging roller (contact charging member)
3 Development device (regular development device or reversal development device)
31 Developer (Toner)
m Charge accelerating particles
4 Transfer roller
5 Fixing device
P transfer material
C Process cartridge
S1 to S3 Bias applied power supply

Claims (10)

A charging step for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, a development step for developing the electrostatic latent image with a charged developer, an image carrier In an image forming apparatus that executes image formation by applying an image forming process including a transfer step of transferring a developer image on a body to a recording medium, and the image carrier repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
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 with the same polarity as a DC charging polarity of a contact charging device. A charging step for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, a development step for developing the electrostatic latent image with a charged developer, an image carrier In an image forming apparatus that executes image formation by applying an image forming process including a transfer step of transferring a developer image on a body to a recording medium, and the image carrier repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
b. An image forming apparatus, wherein the developing means is a regular developing means, and charge-promoting particles are mixed in the developer, and the charge-promoting particles are charged in a polarity different from that of the developer in the developing means. A charging step for charging the image carrier on the image carrier, an information writing step for forming an electrostatic latent image on the charging surface of the image carrier, a development step for developing the electrostatic latent image with a charged developer, an image carrier In an image forming apparatus that executes image formation by applying an image forming process including a transfer step of transferring a developer image on a body to a recording medium, and the image carrier repeatedly provides images,
a. The charging means for charging the image carrier is a contact charging device in which a voltage is applied and the surface of the image carrier is charged by a flexible charging member that forms a nip portion with the image carrier. The charging member is attached to the image carrier. In contrast, the particles are moved with a speed difference, and at least in the nip portion between the charging member and the image carrier, the charge-promoting particles having conductivity for promoting charging are interposed,
b. An image forming apparatus, wherein the developing means is a reversal developing means, and the charge accelerating particles are mixed in the developer, and the charge accelerating particles are charged in the same polarity as the developer in the developing means. 4. The image according to claim 1, wherein the developing means also serves as a cleaning means for collecting the developer remaining on the image carrier after the developer image is transferred to the recording medium. Forming equipment. The image forming apparatus according to claim 1, wherein the charge accelerating particles are triboelectrically charged by rubbing with a developer and have a charge polarity. 5. The image forming apparatus according to claim 1, wherein the member for frictionally charging the developer also serves as a member for charging the charge accelerating particles. 7. The charge promoting particle according to claim 1, wherein the particle size of the charge accelerating particle is 1/2 or less of that of the developer, and the resistance value is 1 × 10 ¹² (Ω · cm) or less. The image forming apparatus described. 7. The charge promoting particle according to claim 1, wherein the particle size of the charge accelerating particle is 1/2 or less of that of the developer, and the resistance value is 1 × 10 ¹⁰ (Ω · cm) or less. The image forming apparatus described. 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 charging surface of the image carrier is an image exposure means.

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