JP2003043786A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of keeping excellent electrification property and image property by making electrification accelerating particles (m) exist by stabilizing the number of the electrification accelerating particles on the surface of a contact electrifying member 2 and simultaneously preventing developer left after transfer from being accumulated on the surface of the contact electrifying member as an image forming device where electrification is performed in a state where the electrification accelerating particles (m) intervenes between the contact electrifying member 2 and an image carrier 1. SOLUTION: The supply of the electrification accelerating particles is increased by forming a potential pattern whose resolution is lower than that of an outputted image from the image forming device on the image carrier 1 when an image is not formed, providing sequence to supply the electrification accelerating particles (m) to the potential pattern from a developing device 3, and making back contrast large by changing developing bias in the case of performing the sequence to supply the electrification accelerating particles when the image is not formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor,
The present invention relates to an image forming apparatus such as a copying machine or a printer that performs image formation by applying an image forming process including a step of uniformly charging an image carrier such as an electrostatic recording dielectric to a predetermined polarity and potential.

More specifically, a transfer type, cleanerless type image forming apparatus adopting a contact charging means using conductive particles (hereinafter referred to as charge promoting particles) as a charging means of an image bearing member. Regarding

[0003]

2. Description of the Related Art (a) Contact charging device 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 has a required polarity. A corona charger (corona discharger) has been used as a charging device for uniformly charging (including static elimination) the electric potential.

The corona charger is a non-contact type charging device. For example, the corona charger includes a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and the discharge opening is opposed to the body to be charged and arranged in a non-contact manner. Discharge current generated by applying a high voltage to the discharge electrode and the shield electrode (corona shower)
The surface of the body to be charged is exposed to the surface of the body to be charged in a predetermined manner.

In the contact charging device, an electrically conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type is brought into contact with a body to be charged, and a predetermined charging bias is applied to the contact charging member. Is applied to charge the surface of the image carrier to a predetermined polarity and potential.

Charging mechanism of contact charging (charging mechanism,
The charging principle) includes two types of charging mechanisms, a discharge charging mechanism and an injection charging mechanism (direct charging mechanism), and each characteristic appears depending on which one is dominant.

[Discharge Charging Mechanism] This is a mechanism in which the surface of the charged body is charged by the discharge phenomenon that occurs in the minute gap between the contact charging member and the charged body.

Since the discharge charging mechanism has a constant discharge threshold value between 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. Also,
Compared to the corona charger, the amount generated is much smaller, but in principle the generation of discharge products is unavoidable.
The harmful effects of active ions such as ozone are unavoidable.

[Injection Charging Mechanism] A mechanism for charging the surface of the member to be charged by directly injecting charges from the contact charging member into the member to be charged. Also called direct charging.

More specifically, a contact charging member having a medium resistance is brought into contact with a member to be charged, and charge is directly injected to the surface of the member to be charged without a discharge phenomenon, that is, basically no discharge is used. is there. Therefore, even if the applied voltage to the contact charging member is equal to or lower than the discharge threshold value, the charged body can be charged to a potential corresponding to the applied voltage. Since this injection charging mechanism does not generate ions, no harm is caused by discharge products.

However, since it is the injection charging, the contact property of the contact charging member to the member to be charged greatly affects the charging property.
Therefore, it is necessary to make the contact charging member more dense, have a large speed difference from the charged body, and contact the charged body more frequently.

The magnetic brush charging device is a charging means whose injection charging mechanism is dominant.

Also, for example, Japanese Patent Laid-Open No. 10-307454
A particle charging device disclosed in Japanese Patent No. 307459, which performs contact charging through non-magnetic / conductive fine particles (charged particles, charge promoting particles), is also a charging means in which the injection charging mechanism is dominant.

(B) Cleanerless (Toner Recycle System) In a conventional general transfer type image forming apparatus, the transfer residual developer (toner) remaining on the image carrier after transfer is transferred to a cleaner (cleaning device). Although the waste toner is removed from the surface of the image carrier to become waste toner, it is desirable that this waste toner does not come out from the viewpoint of environmental protection.

Therefore, the cleaner is eliminated, and the transfer residual developer on the image bearing member after transfer is removed from the image bearing member by "developing simultaneous cleaning" by the developing device and is collected and reused in the developing device. Less image forming apparatuses have also appeared.

Simultaneous development cleaning is a defoaming bias (potential difference between a DC voltage applied to the developing device and the surface potential of the image carrier) of the developer remaining on the image carrier after the transfer during the subsequent development process. Fogging removal potential difference Vback)
It is a method of collecting by. According to this method, the untransferred developer is collected by the developing device and reused in the subsequent steps, so that it is possible to eliminate the waste toner and reduce the troublesome maintenance. Further, since the cleaner is not used, there is a large space advantage, and the image forming apparatus can be significantly downsized.

(C) Contact charging system / transfer system / cleanerless image forming apparatus In the transfer system / cleanerless image forming apparatus, when the contact charging device is adopted as the charging means of the image carrier, the image carrier is contacted. Due to the effect of scattering the transfer residual developer by the charging member, positive ghost due to defective recovery of the transfer residual developer in the developing device can be suppressed. Since it is cleaner-less, there is an advantage that the surface of the image carrier is not damaged by the cleaning member that is in contact with and rubs against the surface of the image carrier.

Magnetic brush charging using a magnetic brush charging member having a magnetic brush portion in which conductive magnetic particles are magnetically restrained into a brush shape as a contact charging member is preferably used in a cleanerless process.

Further, Japanese Patent Laid-Open No. 10-307454 to 307
In the particle charging method disclosed in Japanese Patent Laid-Open No. 459, etc., in which the particles are contact-charged through the charging-promoting particles, the charging-promoting particles are externally added in advance to the developer of the developing device, and the particles are developed together with the developer (attached to the image carrier). In order to realize a cleanerless process, the charging-promoting particles are supplied to the contact charging member by the above method.

[0020]

In an image forming apparatus using contact charging means using charging promoting particles as the charging means for the image bearing member, the contact between the contact charging member and the image bearing member is the surface of the contact charging member. Since the presence of the charge-accelerating particles compensates for this, if the proportion of the charge-accelerating particles on the surface of the contact charging member decreases, the chargeability may decrease. When the absolute number itself of the charge promoting particles adhering to the surface of the contact charging member is decreased, the ratio of the charge promoting particles on the surface of the contact charging member is decreased, resulting in deterioration of charging property and deterioration of image quality. There were challenges.

An object of the present invention is to solve the above problems, and in an image forming apparatus which performs charging by interposing charging accelerating particles between a contact charging member and an image carrier, the number of charging accelerating particles on the surface of the contact charging member. Is stably present, and at the same time, the developer remaining after transfer is prevented from accumulating on the surface of the contact charging member, thereby providing an image forming apparatus capable of maintaining good chargeability and image quality. .

[0022]

In an image forming apparatus which performs charging by interposing charge accelerating particles between a contact charging member and an image bearing member, by mixing the charge accelerating particles with a developer in a developing device, development is performed. When the charging accelerating particles are easily supplied from the apparatus, the charging accelerating particles are charged with the polarity opposite to that of the developer by rubbing against the developer and are supplied to the surface of the image carrier by the developing bias.

When the charge accelerating particles are supplied from the developing device to the surface of the image carrier, the developer is charged from the developing device to the image carrier because the charge accelerating particles are charged to the opposite polarity to the developer. There is a potential difference opposite to the development contrast potential difference supplied to the surface, that is, when the DC potential direction in the image carrier charging step is positive, the image carrier surface potential is the developer in the developing step. It is necessary that the potential is higher than the surface potential of the image carrier. In other words, "there is back contrast".

Further, since the charge promoting particles are likely to be concentrated in a place where the electric field strength is strong, they are supplied not only to the place where the back contrast potential difference exists, but also to the place where the electric field strength is strong. Therefore, the place where the electric field strength is large, that is,
It is possible to supply a large amount of charging promoting particles by forming a portion where the potential on the surface of the image carrier changes.

On the other hand, if the spatial frequency of the potential distribution formed on the surface of the image bearing member is too high, the effect of increasing the amount of charging promoting particles supplied from the developing device cannot be obtained.
Even if the potential distribution is higher than the image frequency that can be output by the image forming apparatus, the amount of charging promoting particles supplied from the developing apparatus does not increase. Therefore, in order to realize the sequence of increasing the supply amount of the charging promoting particles, the spatial frequency of the potential pattern formed on the surface of the image carrier must be equal to or lower than the image frequency that can be output by the image forming apparatus. .

In view of the above matters, the present invention is an image forming apparatus having the following configuration.

(1) A charging step of charging the image bearing body on the image bearing body, an information writing step of forming an electrostatic latent image on the charged surface of the image bearing body, and the electrostatic latent image is developed by a charged developer. In an image forming apparatus that executes an image formation by applying an image forming process including a developing step, a) a voltage is applied to a charging unit that charges the image carrier to form a nip portion with the image carrier. This is a contact charging device that charges the surface of the image bearing member with a flexible charging member, and at least the nip portion between the charging member and the image bearing member has electrically conductive charge promoting particles, and the charging member is the image bearing member. And b) the developer of the developing means contains toner and charge-accelerating particles, and adheres to the image carrier at the developing portion and after the toner image is transferred to the recording medium, the image carrier. Band in the developer remaining on top The charge-promoting particles are supplied to the nip portion between the charging member and the image carrier by carrying the accelerating particles, and c) the output image resolution of the image forming apparatus on the image carrier during non-image formation. Having a sequence for forming a potential pattern (potential distribution, latent image) having a resolution lower than that of the above, and supplying the charge accelerating particles to the latent image from within the developing device,
An image forming apparatus characterized by.

These features make it possible to provide a means for stably supplying the charge promoting particles from the developing device.

(2) In the above (1), it is possible to increase the supply of the charge promoting particles by increasing the back contrast (fog removing potential) when the sequence for supplying the charge promoting particles during non-image formation is performed. A characteristic image forming apparatus.

With this feature, it is possible to increase the amount of charge promoting particles supplied from the developing device.

(3) In the above (1) or (2),
By changing the voltage applied to the contact charging member,
An image forming apparatus characterized by forming a potential pattern on an image carrier during non-image formation by controlling a potential on the surface of the image carrier.

By using an existing process for forming a potential pattern on the surface of the image bearing member, it is possible to easily stabilize the supply of the charge promoting particles.

(4) In the above (1) or (2),
An image forming apparatus characterized in that a potential pattern on an image carrier is formed during non-image formation by controlling an information writing process for forming an electrostatic latent image on a charged surface of an image carrier during image formation. .

By using an existing process for forming a potential pattern on the surface of the image bearing member, it is possible to easily stabilize the supply of the charge promoting particles.

(5) Any one of (1) to (4) above
In the above, the developing bias at the time of performing the sequence of supplying the charge promoting particles at the time of non-image formation is higher than the lowest potential in the charge pattern formed on the surface of the image carrier (the charge potential direction of the image carrier is positive). An image forming apparatus characterized by the above.

That is, at the time of performing the sequence of supplying the charge promoting particles during non-image formation, the lowest potential distribution formed on the surface of the image carrier (when the charged potential direction of the image carrier is positive). ) The potential is controlled so as not to fall below the DC potential of the developing bias. Due to this feature, when the charge promoting particles are supplied from the developing device to the surface of the image carrier at the time of non-image formation, the developer causes the image carrier to It is possible to prevent the surface from being developed.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION <Embodiment 1> This embodiment is an image forming apparatus in which charge-promoting particles are used to contactly charge an image bearing member. By supplying from the device to the photosensitive drum, which is an image carrier, charging accelerating particles are supplied to the contact charging portion of the photosensitive drum through the surface of the photosensitive drum, and an AC bias is included in the contact charging member during non-image formation. It is characterized by forming a "potential pattern having a resolution lower than the output image resolution" by applying a voltage, and additionally having a charging promoting particle supply sequence for "increasing the back contrast".

FIG. 1 is a schematic structural model diagram of the image forming apparatus of this embodiment. The image forming apparatus of this embodiment is a copying machine or printer using a transfer type electrophotographic process, an injection charging system using charging accelerating particles, a laser beam scanning exposure system, a reversal development system, a cleanerless process cartridge system. .

(1) Description of Overall Schematic Structure of Image Forming Apparatus [Image Carrier] 1 is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image supporting member. The image forming apparatus of this embodiment uses reversal development and uses a negative photoconductor.

The photosensitive drum 1 of this embodiment is an OPC photosensitive member having a diameter of 30 mm, and is 200 mm / s in the clockwise direction of the arrow.
It is rotationally driven at a peripheral speed of ec (= process speed).

[Charging] 2 is a conductive elastic roller (charging roller) as a contact charging member which is brought into contact with the photosensitive drum 1.
Is. The surface of the contact charging member 2 is previously coated with charging accelerating particles m. A peripheral speed difference is provided between the photosensitive drum 1 and the contact charging member 2. In this embodiment, the contact charging member 2 is driven at a peripheral speed of 100% in the opposite direction (counter direction) to the rotation direction of the photosensitive drum 1 at the charging portion a which is the contact portion with the photosensitive drum 1.

A DC voltage of -620V is applied as a charging bias from the charging bias power source S1 to the contact charging member 2 so that the outer peripheral surface of the photosensitive drum 1 is uniformly charged to about -600V during image formation. ing. The charging mechanism is dominated by the injection charging mechanism.

In this embodiment, the applied voltage to the contact charging member 2 is variable between the image forming and non-image forming biases.
A DC voltage of V is applied, and during non-image formation, a frequency of 600 Hz, a peak-to-peak voltage of 100 V, DC
It has a sequence of applying a sinusoidal AC wave whose component is -620V.

As will be described later, the charge promoting particles m are also mixed in the developer 31 of the developing device 3 in a predetermined mixing ratio, and the charge promoting particles m mixed in the developer 31 at the surface of the photosensitive drum 1 at the time of development. And is carried to the charging section a and supplied. Further, even during non-image formation, a sequence for supplying the charging promoting particles m from the developing device to the surface of the photosensitive drum 1 is executed, and the particles are carried to the charging portion a and supplied.

FIG. 2 shows the charging / developing bias when the charging accelerating particle supply bias is applied in the sequence of supplying the charging accelerating particles m to the surface of the photosensitive drum 1 from the inside of the developing device during non-image formation in this embodiment.

[Exposure] With respect to the charged surface of the photosensitive drum 1, as information writing means in the exposure section b,
Laser beam scanning exposure L is performed by a laser beam scanner 10 including a laser diode and a polygon mirror.

The laser beam scanner 10 outputs a laser beam whose intensity is modulated corresponding to the time-series electric digital pixel signal of the target image information, and scans and exposes L the charged surface of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the target image information is formed on the outer peripheral surface of the photosensitive drum 1. In this embodiment, an electrostatic latent image having an image resolution of 600 dpi is formed.

[Current image] The electrostatic latent image is developed as a toner image by the reversal non-contact developing device 3 using a negative chargeable magnetic one-component insulating toner having an average particle diameter of 6 μm as the developer 31.

Reference numeral 32 denotes a diameter 16 which encloses the magnet 33.
mm non-magnetic developing sleeve, and this developing sleeve 3
2 is coated with the developer 31 and the distance from the surface of the photosensitive drum 1 is fixed to 500 μm.
Then, the developing bias voltage is applied to the developing sleeve 32 from the developing bias power source S2. The developer 31 is frictionally charged and has an electric charge by rubbing against the developing elastic blade 34. By applying a predetermined developing bias to the developing sleeve 32, the developing sleeve 3 is developed in the developing section c.
Two-component jumping development is performed between the photosensitive drum 1 and the photosensitive drum 1.

The developing bias is changed during image formation and during non-image formation, and during image formation, a rectangular AC wave having a frequency of 1.6 kHz, a peak-to-peak voltage of 1.7 kV and a DC component of -450 V is applied. When not forming an image, the frequency is 1.6 kHz.
z, peak-to-peak voltage is 1.7 kV, DC component is -200 V
The rectangular alternating current wave is applied.

[Transfer] On the other hand, a transfer material P serving as a recording material is supplied from a paper feeding unit (not shown), and the photosensitive drum 1 is brought into contact with the photosensitive material 1 with a predetermined pressing force.
It is introduced at a predetermined timing into the transfer portion d, which is a pressure contact contact portion with the medium resistance transfer roller 4.

A transfer bias applying power source S is applied to the transfer roller 4.
A predetermined transfer bias power source is applied from 3. In this embodiment, a transfer roller 4 having a roller resistance value of 5 × 10 ⁸ Ω was used, and transfer was performed by applying a DC voltage of + 3000V.

The transfer material P introduced into the transfer portion d is nipped and conveyed by the transfer portion d, and the developer image formed and carried on the surface of the photosensitive drum 1 is sequentially pushed by the electrostatic force with the surface of the transfer material P. Transferred by pressure.

[Fixing] The transfer material P, which has received the transfer of the developer image, is separated from the surface of the photosensitive drum 1 and is introduced into a fixing device 5 such as a heat fixing system to be fixed with the developer image to form an image. Items (prints, copies) are discharged outside the device.

[Cleanerless] The transfer residual developer remaining on the surface of the photosensitive drum 1 after the transfer material is separated is removed from the surface of the photosensitive drum 1 by a dedicated cleaning device (cleaner) because the image forming apparatus is cleanerless. Without being carried, the photosensitive drum 1 is subsequently carried to the charging portion a and adheres to and is mixed with the contact charging member 2 (temporary recovery of the transfer residual developer by the contact charging member). Then, the transfer residual developer adhering to and mixed with the contact charging member 2 has its charging polarity adjusted to a normal polarity, and is electrostatically sequentially discharged from the contact charging member 2 to the photosensitive drum 1, and subsequently developed by the rotation of the photosensitive drum 1. It is carried to the section c and is collected and reused by the developing device 3 by simultaneous cleaning with development.

[Cartridge] In the image forming apparatus according to the present embodiment, the cartridge C includes the three process devices of the photosensitive drum 1, the contact charging member 2 and the developing device 3, and is attached / detached to / from the image forming apparatus main body at once. The device is a replaceable cartridge type device, but is not limited to this. 9 ・ 9
Shows a part of the process cartridge attachment / detachment guide / holding member on the image forming apparatus side.

Here, the process cartridge is a cartridge in which the charging means, the developing means or the cleaning means and the image carrier are integrally formed, and the cartridge can be attached to and detached from the main body of the image forming apparatus. Further, at least one of the charging unit, the developing unit, and the cleaning unit and the image carrier are integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. Further, at least the developing means image carrier is integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus.

(2) Operation sequence of image forming apparatus FIG. 3 is an operation sequence diagram of the image forming apparatus.

.. Pre-multi-rotation step: a start operation period (start operation period, warming period) of the image forming apparatus. When the main power switch is turned on, the main motor of the apparatus is driven to rotationally drive the photosensitive drum 1, and the preparatory operation of a predetermined process device is executed.

.. Pre-rotation step: A period during which the pre-printing operation is executed. This pre-rotation step is executed subsequent to the pre-multi-rotation step when a print signal is input during the pre-multi-rotation step. When no print signal is input, the drive of the main motor is once stopped to stop the rotation drive of the photosensitive drum 1 after the completion of the pre-multi-rotation process, and the apparatus is kept in a standby state until a print signal is input. Be done. When the print signal is input, the pre-rotation process is executed.

.. Printing process (image forming process, image forming process): When a predetermined pre-rotation process is completed, an image forming process is subsequently performed on the rotating photoconductor to transfer the developer image formed on the surface of the rotating photoconductor drum to a transfer material. And the fixing process of the developer image by the fixing unit is performed, and the image formed product is printed out.

In the case of the continuous printing (continuous printing) mode, the above printing process is repeated for a predetermined number of set prints.

.. Paper interval process: In the continuous print mode, the transfer material does not pass through the transfer part after the rear end of one transfer material passes through the transfer part and before the leading end of the next transfer material reaches the transfer part. It is a paper state period.

.. Post-rotation step: This is a period in which the main motor is continuously driven for a while after the final printing step of the transfer material is finished to drive the photosensitive drum 1 to rotate, and a predetermined post-operation is executed.

.. Standby: When a predetermined post-rotation process is completed, the driving of the main motor is stopped, the rotational drive of the photosensitive drum 1 is stopped, and the apparatus is kept in the standby state until the next print start signal is input.

In the case of printing only one sheet, after the printing is completed, the apparatus goes through a post-rotation step and goes into a standby state.

When the print start signal is input in the standby state, the apparatus shifts to the pre-rotation step.

The image forming is performed during the printing step, and the pre-multi-rotating step, the pre-rotating step, the sheet interval step, and the post-rotating step are non-image forming (non-image forming).

In FIG. 1, reference numeral 100 denotes a control circuit section which controls all the operations of the image forming apparatus.

(3) Contact charging member 2 The conductive elastic roller 2 as a contact charging member in this embodiment has a core metal 21 and a medium resistance layer 2 of rubber or foam.
It is created by forming 2. The medium resistance layer 22 is formed of resin (urethane in this embodiment), conductive particles (for example, carbon black), a sulfiding agent, a foaming agent and the like, and is formed on the cored bar 21 in a roller shape. Then, the surface was polished.

The resistance value of the contact charging member 2 was measured as follows. That is, the photosensitive drum 1 of the image forming apparatus is replaced with an aluminum drum. Thereafter, a voltage of 100 V was applied between the aluminum drum and the contact charging member 2, and the value of the current flowing at that time was measured to obtain the resistance value of the contact charging member 2.

The resistance value of the contact charging member 2 used in this example was 5 × 10 ⁶ Ω. This measurement has a temperature of 25 ° C and a humidity of 6
It was performed in an environment of 0%. Regarding this measurement environment, the same applies to other measurements in this embodiment and other embodiments.

The average cell diameter on the surface of the contact charging member 2 was 20 μm for each resistance value. The average cell diameter was measured by observation with an optical microscope.

(4) Charge accelerating particles m In this embodiment, the charge accelerating particles m have a specific resistance of 10 ⁷
Conductive zinc oxide particles having an Ω · cm and an average particle size of 1 μm were used.

The particle size is defined as the average particle size of the aggregate when the particles are formed as the aggregate.
To measure the particle size, 100 or more particles were extracted from observation by an optical or electron microscope, the volume particle size distribution was calculated with the maximum chord length in the horizontal direction, and the 50% average particle size was determined.

The resistance was measured by the tablet method and normalized. Approximately 0.5 g in a cylinder with a bottom area of 2.26 cm ^2.
The powder sample of No. 1 was put in, pressure of 147 N (15 kg) was applied to the upper and lower electrodes, a voltage of 100 V was applied at the same time, the resistance value was measured, and then normalized to calculate the specific resistance.

The charge-accelerating particles m used in this embodiment are preferably colorless or white particles so as not to interfere with the latent image exposure. Further, if the particle size is not about 1/2 or less of the particle size of the developer (toner) 31, the image exposure may be blocked. Therefore, it must be smaller than this.

As the material of the charge promoting particles m, conductive zinc oxide particles were used in this embodiment, but the material of the particles is not limited to this, and conductive inorganic particles such as other metal oxides or Various conductive particles such as a mixture with an organic substance can be used.

(5) Developer 31 The developer 31 used in this example is a binder resin containing a styrene-acrylic copolymer as a main component and 60 magnetite.
Wt%, and 1 wt% of a metal complex salt of a monoazo dye as a negative charge control material, a magnetic one-component insulating toner having a volume resistivity of about 10 ¹³ Ω · cm, which is hydrophobized to impart fluidity. Externally added fine particles of 0.8% based on the weight of the developer were used.

The toner 31, which is a developer, is mixed with the charge promoting particles m, and the mixing amount is 2 parts by weight of the charge promoting particles with respect to 100 parts by weight of the developer. However, the mixing amount is not limited to this amount.

(6) Supply of Charge Accelerating Particles m to Contact Charging Member 2 In this embodiment, the injection charging mechanism is used as the charging mechanism of the photosensitive drum 1, and the surface of the conductive elastic roller 2 serving as the contact charging member is charged. By providing a speed difference between the conductive elastic roller 2 and the photosensitive drum 1 in a state where the accelerating particles m are present on the surface, the charging accelerating particles or the conductive elastic roller and the photosensitive drum surface are closely contacted, and Charge injection is performed on the surface.

In the injection charging mechanism in which the charge accelerating particles m are interposed, it is essential that the surface of the contact charging member 2 is coated with the charge accelerating particles m. However,
While the image forming apparatus is in operation, some of the charge promoting particles may fall off from the surface of the contact charging member. Therefore, a means for supplying the charging-promoting particles to the surface of the contact charging member when printing is required.

In this embodiment, as described above, the charge accelerating particles m are mixed with the developer 31 and supplied from the developing device 3 to the photosensitive drum 1, which is an image carrier, so that the photosensitive drum 1 is exposed through the surface of the photosensitive drum. A configuration is used in which the charging promoting particles m are supplied to the contact charging portion a of the drum 1.

That is, during image formation, the developing device 3
The charge accelerating particles m mixed in the developer 31 in the inside are the developer 3
1 adheres to the photosensitive drum 1 and is transferred to the surface of the photosensitive drum 1 when the electrostatic latent image is developed. Further, since the developer 31 is added with the negative charge control agent, the charge promoting particles m are frictionally charged with respect to the developer 31 and have a positive charge of opposite polarity. Therefore, the charge accelerating particles m in the developer 31 on the developing sleeve 32 are supplied to the surface of the photosensitive drum 1 from above the developing sleeve 32 due to the potential difference between the developing sleeve 32 and the surface of the photosensitive drum 1.

Since the charge accelerating particles m have charges of the opposite polarity to the developer 31, they are not substantially transferred to the transfer material P at the transfer portion d and are carried to the charging portion a, resulting in The contact charging member 2 is supplied and coated.

As described above, the charge accelerating particles m mixed with the developer 31 in the developing device 3 are rubbed with the developer or the developing blade in the developing device 3 to cause the developer 31.
Since it is charged with a polarity opposite to the charging polarity of, that is, a positive charge polarity, it receives an electric force on the negative potential side.
Therefore, when the potential of the surface of the photosensitive drum 1 is more negative than the potential of the developing bias applied to the developing sleeve 32, the charge promoting particles may be supplied from the inside of the developing device to the surface of the photosensitive drum. It will be possible.

In the case of the reversal developing device such as the printer in this embodiment, the charge promoting particles can be supplied to the dark potential portion on the surface of the photosensitive drum.

Further, since an arbitrary image pattern is usually printed at the time of image formation (at the time of printing), the ratio of the dark potential portion on the surface of the photosensitive drum at the time of image formation is not constant. Therefore, it is difficult to guarantee the charging property for a long period of time by supplying the charging promoting particles during image formation.

Therefore, in order to maintain the chargeability for a long period of time, it is necessary to supply the charge promoting particles from the developing device during non-image formation.

However, in the image forming apparatus, the non-image forming time is generally much shorter than the image forming time in order to increase the printing speed. That is, when the charging promoting particles are supplied during non-image formation, there is a problem that a large amount of charging promoting particles must be supplied within a short time.

In order to increase the supply amount of the charging promoting particles m from the developing device 3 to the photosensitive drum 1, it is effective to increase the potential difference in the negative potential direction of the photosensitive drum 1 with respect to the developing sleeve 32, that is, the back contrast potential difference. Is. It is possible to increase the supply amount of the charge promoting particles m by increasing the potential difference that works in the direction of supplying the charge promoting particles m having the polarity opposite to that of the developer 31 from the developing sleeve 32 onto the photosensitive drum 1. Becomes

In this embodiment, as shown in FIG. 2, the back contrast potential during image formation is 600 V-4.
50V = 150V. On the other hand, 600-2 when the charging promoting particle supply sequence is executed during non-image formation.
00 = 400V. In this way, the supply amount of the charging promoting particles is increased by increasing the potential difference such that the charging promoting particles m are supplied from the developing device 3 to the surface of the photosensitive drum 1.

In this embodiment, as shown in FIG. 2, the potential pattern formed on the surface of the photosensitive drum 1, that is, the potential applied to the contact charging member 2 is higher than the developing bias DC value at any position ( Positive charge potential direction). When the potential pattern formed on the surface of the photosensitive drum is lower than the DC value of the developing bias, the developer 31 is supplied from the developing device 3 to the photosensitive drum 1 during execution of the charging promoting particle supply sequence during non-image formation. There is. Therefore, the bias applied to the contact charging member 2 is always higher than the developing bias DC value (the charging potential direction is positive).
Is desirable.

The charge promoting particles m are used in the developing sleeve 3
When supplied to the surface of the photosensitive drum 1 from 2, it easily stays in a place where the electric field strength is high. In other words, not only where there is a back contrast potential difference, but also where there is an electric field on the surface of the photosensitive drum, the charge-accelerating particles m are retained and held there. Is easily supplied.

In particular, in the developing device for developing the developer (supplying the developer to the photosensitive drum) in a non-contact manner by applying an alternating electric field to the developing device 3 as in this embodiment, the photosensitive drum When the charge distribution on the surface is not constant, that is, when a potential pattern is created, an electric field is formed in the direction of enclosing the particles toward the surface of the photoreceptor. Therefore, particles are held in such a potential pattern and not collected by the developing device 3, resulting in an increase in the amount of particles supplied.

Therefore, by creating a finely varying potential distribution on the surface of the photosensitive drum 1 and forming a portion on the surface of the photosensitive drum 1 where the electric field strength is strong, more charging accelerating particles m are transferred from the developing device 3 to the photosensitive drum 1. It becomes possible to supply a large amount to the surface. That is, as shown in FIG. 2, due to the potential difference between the high-potential portion and the low-potential portion of the surface of the photosensitive drum, the force that tries to supply the charging-promoting particles m to the high-potential portion (the positive potential direction is positive) works. Therefore, it becomes possible to increase the supply amount of the charge promoting particles.

On the other hand, in general, the image forming apparatus cannot develop the developer for a latent image having a resolution higher than a predetermined image resolution. The same applies to the supply of the charge promoting particles, and if the spatial frequency of the potential distribution formed on the surface of the photosensitive drum is higher than the image resolution, the supply amount of the charge promoting particles cannot be increased.

When the injection charging method is used as in this embodiment, if an AC bias is applied to the contact charging member 2,
A potential distribution according to the AC bias is formed on the surface of the photosensitive drum. For example, process speed PS [mm /
s] and the frequency of the AC bias applied to the contact charging member 2 is f [Hz = cycle / s], the size of the potential pattern on the surface of the photosensitive drum formed by this AC bias is PS [mm / f] / f [cycle / s] = X [mm / cycle].

This X is the size of the potential pattern that can be developed by the image forming apparatus, that is, the size of the potential pattern at the maximum output resolution, in this embodiment 25.4 [mm / inch] / 600 [dot / inch] ≈. 0.04
If it is larger than 2 [mm / dot], it is possible to increase the supply amount of the electrification promoting particles.

Specifically, since the process speed is 200 [mm / s] in this embodiment, 200 / f> 0.042 may be satisfied.

That is, 200 / 0.042≈4800
If the frequency is equal to or lower than [Hz], it is possible to increase the supply amount of the charging promoting particles.

In this embodiment, since the AC bias of 600 [Hz] is applied to the contact charging member 2, it is possible to increase the supply amount of the charging promoting particles.

In this way, in this embodiment, by applying a voltage to the contact charging member 2 on the surface of the photosensitive drum during non-image formation, a potential pattern having a resolution lower than the output image resolution is formed. In addition, by increasing the back contrast in addition to this, the photosensitive drum 1
It is possible to supply the charging-promoting particles through the surface.

In this embodiment, the above-mentioned charging promoting particle supply sequence was executed in the pre-rotation step, the sheet interval step, and the post-rotation step, which are non-image forming steps. The charging promotion particle supply sequence may be executed even in the pre-multi-rotation step. The charging-promoting particle supply sequence should be executed during at least one step of the pre-multi-rotation step, the pre-rotation step, the sheet interval step, and the post-rotation step during non-image formation, or a part of that step. You can

[Comparative Example] The effect of the present invention will be confirmed by comparing the above-described actions with the comparative example. Here, Table 1
The four types of image forming apparatus shown in FIG.

Comparative Example 1: Image forming apparatus in which a potential pattern is not formed on the photosensitive drum during the charging promoting particle supply sequence performed during non-image formation Comparative Example 2: A potential pattern is formed, which is higher than the image resolution. Image forming apparatus having a potential pattern of frequency Comparative example 3: Image forming apparatus having the same back contrast during execution of the charging promoting particle supply sequence as in image formation An image forming apparatus that creates a potential pattern of frequency on the surface of the photosensitive drum but does not increase the back contrast.

[0107]

[Table 1]

Here, the charging property was evaluated by the deterioration of the ghost image.

Since the printers of Comparative Examples 1 to 4 and Example 1 perform image recording by the reversal developing system, the ghost here means a portion (toner) which is image-exposed in the first round of the photosensitive drum 1. This means that the image portion) has a shortage of withstand voltage in the second round of the photosensitive drum, so that the previous image pattern on the photosensitive drum is strongly developed and a ghost image is generated.

In these evaluations, one solid black image was printed on the entire surface, and the next image continuously produced was evaluated according to the following criteria.

X: A ghost is seen in the white background after solid black.

Δ: No ghost is seen in the white background portion after solid black, but a ghost pattern is seen in the halftone portion.

◯: No ghost can be seen in the white background portion after solid black, but a slight ghost pattern may be seen in the halftone portion.

⊚: No ghost pattern is seen in both the white background portion and the halftone portion after solid black.

Also from the results of this image evaluation, Comparative Examples 1 and 2
As described above, a potential pattern is not created on the photosensitive drum during the charging promotion particle supply sequence performed during non-image formation, or even if it is created, the potential pattern has a frequency higher than the image resolution. For those that do not, it is difficult to supply the charging-promoting particles during the durability, so that the charging property is deteriorated.

Further, although the potential pattern is not created as in Comparative Example 3, the one in which the back contrast is increased has a slight effect of maintaining the chargeability as compared with Comparative Examples 1 and 2, but the charge accelerating particles are still present. A decrease in the charging property due to a decrease in the supply amount of is not observed.

On the other hand, in Comparative Example 4, by supplying a potential pattern having a frequency lower than the image resolution on the photosensitive drum during the charging promoting particle supply sequence performed at the time of non-image formation, the supplying amount of the charging promoting particles is increased. It can be seen that the chargeability can be increased and the chargeability is maintained.

In addition to this, by increasing the back contrast during the execution of the charging promoting particle supply sequence as in the first embodiment, the supply amount of the charging promoting particles can be further increased, and the charging property can be further maintained. It is possible to do.

As described above, in the present embodiment, a potential pattern having a frequency lower than the output image resolution is created on the surface of the photosensitive drum during non-image formation, and at the same time, the back contrast potential is increased to charge the surface of the photosensitive drum. The supply amount of the electrification promoting particles m to the part a was increased, and it was possible to maintain the electrification property for a long time.

<Embodiment 2> In this embodiment, an electric potential pattern is formed on the surface of the photosensitive drum 1 by operating the image exposure device (laser beam scanner) 10 during non-image formation, and the electric potential pattern is formed. This is characterized by increasing the supply amount of the electrification promoting particles.

The image forming apparatus of this embodiment is almost the same as the image forming apparatus used in the first embodiment, but the charging bias applied to the conductive elastic roller 2 which is the contact charging member is used during image formation and non-image formation. It is characterized in that a checkerboard-like potential pattern is formed on the surface of the photosensitive drum by weakly exposing the surface of the photosensitive drum using the image exposure device 10 without changing the time, and the supply amount of the charge promoting particles is increased. .

The charging device of this embodiment is almost the same as that of the first embodiment, except for the applied bias during non-image formation. The charging bias of this embodiment is approximately −6 on the outer peripheral surface of the photosensitive drum 1 during image formation as in the first embodiment.
A charging bias of −620V is applied from the charging bias power source S1 so that the charging process is uniformly performed to 00V. The same bias is applied during non-image formation. The charging bias applied during non-image formation is not limited to this, and a DC voltage of -720V is applied so that the outer peripheral surface of the photosensitive drum 1 is uniformly charged to approximately -700V during non-image formation. It doesn't matter.

The developing device of this embodiment is almost the same as that of the first embodiment, but the bias applied to the developing sleeve at the time of applying the charging accelerating particle supply bias at the time of non-image formation is the same as that at the time of image formation, and the frequency of 1. 6 kHz, peak-to-peak voltage is 1.
A rectangular AC wave of 7 kV and a DC component of -450 V is applied.

In this embodiment, when the image is not formed, the photosensitive drum surface is weakly exposed, and the output image resolution of the image forming apparatus of this embodiment is 6 with respect to the surface of the photosensitive drum.
A checkerboard-like potential pattern with 5 dots × 5 dots of 00 dpi as one unit is formed on the surface of the photosensitive drum. The potential pattern on the photosensitive drum after the exposure is shown in FIG. During non-image formation, the surface potential of the photoconductor is set to -700V, and the weakly exposed portion is set to -600V.

As shown in FIG. 4, in the present embodiment, the output image resolution of the image forming apparatus is 5 dots at 600 dpi.
A checkerboard-shaped electric potential pattern with a unit of × 5 dots is formed on the surface of the photosensitive drum. In this embodiment, the dark portion potential of the photosensitive drum is set to -700 V and the light exposure amount of the weakly exposed portion is set to -600 V during non-image formation. When non-image formation is performed, the drum potential when the photosensitive drum is averaged over a wide area is -650V which is just between -700V and -600V.

The back contrast potential at the time of image formation, that is, the fog removing potential is 600V-450V = 150.
V. On the other hand, 650V-450V = 20 during the execution of the charging promoting particle supply sequence performed during non-image formation.
The potential difference is 0 V, and the potential difference in the direction in which the particles charged with the positive charge polarity are supplied from the developing sleeve 32 onto the photosensitive drum 1 is large.

In addition to this back contrast potential difference, by forming such a checkerboard-like potential pattern on the surface of the photosensitive drum, a pattern in which the potential is changed over the entire surface of the photosensitive drum is created. ,
By forming a potential pattern having a resolution lower than the output image resolution as in the first embodiment, it is possible to increase the supply amount of the charging promoting particles.

As described above, in this embodiment, the image exposure apparatus 1
0 is used to create a potential pattern for increasing the supply amount of the charge promoting particles on the surface of the photosensitive drum during non-image formation. Due to this feature, it is possible to inexpensively realize the supply sequence of the charging promoting particles without requiring the AC bias power source used in the first embodiment.

In this embodiment, the checkerboard pattern is used as the weak exposure pattern during non-image formation, but the pattern is not limited to this, and may be a line image or a dot image, for example.

<Others> 1) The image carrier may be either a corona-charged material that is dominant or an injection-charged material that is dominant.

By providing a layer made of a material of 10 ⁹ to 10 ¹⁴ Ω · cm on the surface, the contact injection charging property can be made dominant. For example, it is an image carrier having a photosensitive layer and a surface layer, the surface layer being a resin layer (charge injection layer) in which conductive fine particles such as SnO ₂ are dispersed. Even when the charge injection layer is not used, the contact injection chargeability can be made dominant even when the charge transport layer of the photoreceptor is in the above resistance range. The same effect can be obtained by using an amorphous silicon photoconductor having a surface layer volume resistance of about 10 ¹³ (Ω · cm).

2) The image exposure apparatus 10 as the information writing means is not limited to the laser scanner of the embodiment, but may be LE.
It may be another digital exposure apparatus such as a D array apparatus, a combination apparatus of a light source and a liquid crystal shutter, or an analog exposure apparatus such as an image forming projection apparatus of a document image.

3) The image carrier is not limited to the photoconductor, but may be an electrostatic recording dielectric or the like. In this case, an electrostatic latent image is formed by selectively removing electricity by using a uniformly charged magnetic brush contact charging device of the embodiment or an image carrier surface as an electricity writing means such as an electricity removal needle array or an electron gun. To do.

4) The developing system of the developing device is arbitrary. Generally, in the method of developing an electrostatic latent image, non-magnetic toner is coated with a blade or the like on a developer carrying and conveying member such as a sleeve, and magnetic toner is magnetically coated on the developer carrying and carrying member. A method of developing an electrostatic latent image by applying it in a non-contact state to the image carrier by carrying it by coating with force (one-component non-contact development), and coating on the developer carrying member as described above. A method in which toner is applied in contact with an image carrier to develop an electrostatic latent image (one-component contact development), and a mixture of magnetic carrier with toner particles is used as a developer (two-component developer). To be used as a magnetic material and conveyed by magnetic force to be applied in contact with an image carrier to develop an electrostatic latent image (two-component contact development)
And a method of developing the electrostatic latent image by applying the developer to the image carrier in a non-contact state (two-component non-contact development).

5) The transfer means 4 is not limited to roller transfer,
Belt transfer, corona discharge transfer, pressure transfer, etc. are optional.

6) An image forming apparatus for forming not only a single color image but also a multicolor image or a full color image by multiple transfer using an intermediate transfer means such as a transfer drum or a transfer belt may be used.

[0137]

As described above, according to the present invention, in an image forming apparatus using a charging device for performing injection charging by using charge promoting particles, the charge promoting particles are mixed with the developer in the developing device to carry out image carrying. By supplying the charging-promoting particles to the body surface from the developing device, the charging-promoting particles are supplied to the contact charging member surface through the image bearing member surface. In order to prevent the resulting decrease in chargeability, the charge-accelerating particles are supplied from the developing device during non-image formation, and the method has a resolution lower than the output image resolution during image formation on the image carrier surface during non-image formation. It has a sequence to increase the supply amount of electrification promoting particles by creating a certain potential pattern,
Further, it is characterized in that the back contrast is increased during execution of the sequence to increase the supply amount of the charge promoting particles from the developing device to the image carrier.

With this feature, it is possible to supply a large amount of charge promoting particles from the developing device to the surface of the image carrier, and it is possible to prevent a decrease in chargeability due to a decrease in the supply amount of charge promoting particles. It is possible to maintain good chargeability.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a charging / developing bias when a charging promoting particle supply bias is applied in a charging promoting particle supply sequence executed during non-image formation.

FIG. 3 is an operation sequence of the image forming apparatus

FIG. 4 is a schematic diagram of a checkerboard-like potential pattern formed on a photosensitive drum in a charging promoting particle supply sequence performed during non-image formation in Example 2.

[Explanation of symbols]

1 ... Image carrier (photoreceptor), 2 ... Contact charging member (conductive elastic roller), m ... Charging promotion particles, 3 ... Developing device, 31 ... Developer, 4 ... Transfer roller, 5 ..Fixing device, C..Process cartridge, 10..Laser scanner (image exposure device), L..Image exposure, 100 ..
Control circuit part, a ... Charging part, b ... Exposure part, c ... Development part, d ... Transfer part, P ... Transfer material, S1 ... Primary charging bias power supply, S2 ... Development bias power supply, S3 ..Transfer bias power supply

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Harumi Ishiyama             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Norio Takahashi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA38 EA01 EA05 EC03 ED03                       ED06 ED07 EE02 EF06 EF07                       EF11                 2H073 AA03 BA04 BA13 CA02 CA03                       CA22                 2H200 GA18 GA23 GA33 GA34 GA49                       GB37 HA02 HA21 HA29 HB12                       HB17 HB22 HB45 HB46 HB47                       HB48 JA02 JB10 LA23 MA08                       MB01 MB06 MC01 MC15 MC18                       NA02 NA04 PA05 PA11 PA19

Claims (5)

[Claims] 1. A charging step of charging an image bearing body on an image bearing body, an information writing step of forming an electrostatic latent image on a charged surface of the image bearing body, and the electrostatic latent image is developed with a charged developer. In an image forming apparatus that executes an image formation by applying an image forming process including a developing step, a) A charging unit that charges the image carrier is applied with a voltage and is flexible to form a nip portion with the image carrier. Is a contact charging device that charges the surface of the image bearing member with a conductive charging member, and at least the nip portion between the charging member and the image bearing member has conductive charge promoting particles, and the charging member is attached to the image bearing member. And b) the developer of the developing means contains toner and charge accelerating particles, and adheres to the image carrier at the developing section and is transferred onto the image carrier after transfer of the toner image to the recording medium. Of charge in the developer remaining in the developer When the child is carried, the charging accelerating particles are supplied to the nip portion between the charging member and the image carrier, and c) when the image is not formed on the image carrier more than the output image resolution of the image forming apparatus. An image forming apparatus having a sequence of forming a potential pattern having a low resolution and supplying charging accelerating particles to the potential pattern from inside a developing device. 2. The supply of charging promoting particles according to claim 1, wherein the developing bias is changed to increase the back contrast when the sequence of supplying charging promoting particles during non-image formation is performed. An image forming apparatus characterized by. 3. An image forming apparatus according to claim 1, wherein the potential pattern on the image carrier is formed during non-image formation by controlling the voltage applied to the charging member. 4. The information writing step of forming an electrostatic latent image on the charged surface of an image carrier during image formation according to claim 1 or 2, whereby the potential pattern on the image carrier during non-image formation is changed. An image forming apparatus characterized by performing formation. 5. The developing bias used in the sequence for supplying the charge-accelerating particles at the time of non-image formation is the lowest potential in the potential pattern formed on the surface of the image carrier according to any one of claims 1 to 4. The image forming apparatus is higher than the above (when the charging potential direction of the image carrier is positive).