JP2003162160A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain high-quality image formation over a long term, and to maintain the high-quality image formation over a long term even after outputting an image having high image ratio by efficiently cleaning a contact electrifying member soiled by toner and further preventing the removed soiling substance from being transferred to transfer material at the image forming time in a contact electrifying type, transfer type and toner recycle system image forming apparatus. <P>SOLUTION: This image forming apparatus is provided with a developing means 4 developing an electrostatic latent image formed on an image carrier 1 by supplying the developer to the latent image and recovering the developer remaining on the image carrier 1 simultaneously and a transfer means 5 transferring the image developed on the image carrier 1 to transfer material P. Then, the polarity of bias applied to the transfer means 5 is switched at least once in an area where the transfer material does not exist at the transfer means part on the image carrier 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus (image recording apparatus) such as a copying machine, a laser beam printer, or a facsimile which applies electrophotography.

[0002]

2. Description of the Related Art Conventionally, for example, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric is made uniform in polarities and potentials at required points. A corona charger (corona discharger) has been used as a charging device for charging (including transfer).

The corona charger is a non-contact type charging device. For example, the 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 made to face an image carrier, which is a member to be charged. In this case, the surface of the image carrier is exposed to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode so that the surface of the image carrier is charged in a predetermined manner.

In recent years, contact charging devices have been proposed and put into practical use as charging devices for charged members such as image bearing members because they have advantages such as low ozone and low power compared to corona chargers. There is.

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

Charging mechanism of contact charging (charging mechanism,
In (charging principle), two types of charging mechanism (1) discharge charging mechanism and (2) direct charging mechanism coexist, and each characteristic appears depending on which one is dominant.

(1) Discharge Charging Mechanism This is a mechanism in which the surface of the charged member is charged by the discharge phenomenon that occurs in the minute gap between the contact charging member and the charged member. Since the discharge charging mechanism has a constant discharge threshold value between the contact charging member and the body to be charged, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Further, compared with a corona charger, the generation amount is remarkably small, but generation of a discharge product is unavoidable in principle, so that a harmful effect due to active ions such as ozone is unavoidable.

(2) Injection charging mechanism This is a mechanism in which charges are directly injected from the contact charging member to the charged body to charge the surface of the charged body. It is called direct charging or injection charging (hereinafter referred to as injection charging). More specifically, the contact charging member having a medium resistance contacts the body to be charged, and the charge is directly injected to the surface of the body to be charged without using the discharge phenomenon, that is, basically without using discharge.
Therefore, even if the applied voltage to the contact charging member is equal to or lower than the discharge threshold value, the member to be charged 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 directly charged, 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.

(A) Roller charging The contact charging device is preferably a roller charging device using a conductive roller (charging roller) as a contact charging member from the viewpoint of charging stability, and is widely used at present. In this roller charging, the charging mechanism is predominantly the discharge charging mechanism described in (1) above.

The charging roller is made of a conductive or medium-resistance rubber material or foam. Further, there is also one in which these are laminated to obtain desired characteristics. The charging roller is
Although it has elasticity in order to obtain a constant contact state with the charged body (hereinafter referred to as a photoconductor), the frictional resistance is large, and in many cases, the photoconductor is driven or slightly moved. Driven. Therefore, even if an attempt is made to directly charge, since the absolute charging ability is deteriorated, contact is insufficient, unevenness on the roller, and uneven charging due to adhered matter on the surface of the photoconductor are unavoidable, the charging mechanism of conventional roller charging is the discharge. The charging mechanism is dominant.

FIG. 6 is a graph showing the charging efficiency in contact charging. The horizontal axis represents the bias applied to the contact charging member, and the vertical axis represents the photoconductor charging potential obtained at that time.

In the case of conventional roller charging, the charging characteristic is represented by A. That is, charging starts after the discharge threshold of about -500V is exceeded. Therefore, when charging to -500V, apply a DC voltage of -1000V, or
In addition to the DC voltage of −500 V, a method of applying an AC voltage of 1200 V between peaks so as to always have a potential difference equal to or higher than the discharge threshold to converge the photoconductor potential to the charging potential is general.

More specifically, in the case where the charging roller is pressed against the OPC photosensitive member having a thickness of 25 μm to perform the charging process, the charging roller is about 64.
When a voltage of 0 V or higher is applied, the surface potential of the photoconductor starts to rise, and thereafter, the surface potential of the photoconductor linearly increases with a slope of 1 with respect to the applied voltage. Hereinafter, this threshold voltage is defined as the charging start voltage Vth. In other words, in order to obtain the photosensitive member surface potential Vd required for electrophotography, V is applied to the charging roller.
A DC voltage higher than required, that is, d + Vth, is required.

The system in which only the DC voltage is applied to the contact charging member in this way to charge the image carrier is called the "DC charging system". However, in the DC charging method, the resistance of the contact charging member fluctuates due to environmental changes and the Vth fluctuates when the film thickness changes due to the abrasion of the photoconductor as the image bearing member. Therefore, the potential of the photoconductor is changed. It was difficult to obtain the desired value.

For this reason, in order to further uniformize the charging, as disclosed in JP-A-63-149669, etc., a DC voltage corresponding to a desired Vd is provided with a peak-to-peak voltage of 2 × Vth or more. An "AC charging method" is used in which an oscillating voltage having a superposed AC component is applied to a contact charging member to charge the image carrier. This is for the purpose of leveling effect of the potential by AC, and the potential of the image carrier converges on Vd which is the center of the peak of the AC voltage, and is not affected by disturbance such as environment.

However, even in such a contact charging device, since the essential charging mechanism uses the discharge phenomenon from the charging member to the image carrier, the voltage required for charging as described above. Requires a value equal to or higher than the image carrier surface potential + discharge threshold value, and a small amount of ozone is generated. Also,
When AC charging is performed for uniform charging, further ozone is generated, vibration noise (AC charging sound) between the contact charging member and the photoconductor due to the electric field of the AC voltage, and deterioration of the photoconductor surface due to discharge. Etc. became remarkable and became a new problem.

(B) Fur brush charging In the fur brush charging, a member having a brush portion of a conductive fiber (a fur brush pair charger) is used as a contact charging member, and the conductive fiber brush portion is exposed as a photosensitive member. It contacts the body and applies a predetermined charging bias to charge the surface of the photoconductor to a predetermined polarity and potential.

As the fur brush charger, a fixed type and a roll type have been put into practical use. A fixed type is made by weaving medium resistance fibers into a base cloth and forming it into a pile and adhering it to the electrode. The roll type is formed by winding the pile around a core metal. A fiber density of about 100 fibers / mm ² can be obtained relatively easily, but the contact property is still insufficient for sufficient charging by direct charging, and sufficient uniform charging can be achieved by direct charging. Is not realistic because it is necessary to give a speed difference to the photoconductor so that it is difficult as a mechanical structure.

The charging characteristics of this fur brush charging when a DC voltage is applied have the characteristics shown in FIG. 6B. Therefore, in all cases of the fur brush charging, the fixed type, and the roll type, a high charging bias is applied and charging is performed using the discharge charging mechanism.

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

In the case of this magnetic brush charging, the charging mechanism described in (2) above is the dominant charging mechanism.

By using conductive particles having a particle diameter of 5 to 50 μm as the magnetic brush and providing a sufficient speed difference from the photosensitive member, uniform direct charging is possible.

As indicated by C in the charging characteristic graph of FIG.
It is possible to obtain a charging potential almost proportional to the applied bias.

However, there are problems that the device structure is complicated and that the conductive magnetic particles forming the magnetic brush fall off and adhere to the photoconductor.

Japanese Unexamined Patent Publication 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 conductive particles 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 surface potential of the photoconductor, and ozone is not generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and compared to the roller charging method, the charging method is ozoneless and has low power consumption.

(D) Cleaner-less (toner recycling system) In a transfer type image forming apparatus, the transfer residual developer (toner) remaining on the photoconductor (image carrier) after transfer is exposed by a cleaner (cleaning device). Although the waste toner is removed from the body surface to become waste toner, it is desirable that this waste toner is not environmentally friendly. I lost the cleaner there,
A cleanerless image forming apparatus has also emerged in which the transfer residual developer on the photoconductor after transfer is removed from the photoconductor by "developing simultaneous cleaning" by the developing device and collected and reused in the developing device. .

Simultaneous development cleaning is a fog removal bias for the developer remaining on the photoconductor after transfer during development of the next step and after (fog removal which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor). Potential difference Vback)
It is a method of collecting by. According to this method, the untransferred residual developer is collected by the developing device and reused in the subsequent steps, so that the waste toner can be removed and the maintenance can be less troublesome. Further, since the cleaner is not used, there is a large space advantage, and the image forming apparatus can be significantly downsized.

The cleaner-less type does not remove the transfer residual toner from the surface of the photosensitive member by a dedicated cleaner as described above, but returns it to the developing device through the charging means and reuses it in the developing process. Therefore, when contact charging is used as the charging means of the photoconductor, the problem is how to charge the photoconductor in the state where the insulating developer is present in the contact portion between the photoconductor and the contact charging member. It has become. In the roller charging and the fur brush charging described above, the transfer residual toner on the photoconductor is often diffused to be non-patterned, and a large bias is applied to charge by discharge. Since powder is used as the contact charging member in magnetic brush charging, there is an advantage that the magnetic brush part of the conductive magnetic particles, which is the powder, can flexibly contact the photoconductor to charge the photoconductor, but the device configuration is complicated. To be. The harmful effect due to the dropping of the conductive magnetic particles forming the magnetic brush is great.

(E) Powder coating on the contact charging member In the contact charging device, in order to prevent uneven charging and to perform stable and uniform charging, the contact charging member is coated with powder on the contact surface with the surface to be charged. Although it is disclosed in Japanese Patent Publication No. 7-99442, the contact charging member is driven to rotate by the charged body, and the generation of ozone products is significantly reduced as compared with a corona charger such as a scorotron.
The charging principle is still based on the discharge charging mechanism as in the case of the roller charging described above. Particularly, in order to obtain more stable charging uniformity, a voltage in which an AC voltage is superimposed on a DC voltage is applied, so that the ozone products are more generated by the 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 deletion due to ozone products are likely to appear. Further, in Japanese Patent Application Laid-Open No. 5-150539, in an image forming method using contact charging, charging inhibition due to toner particles or silica fine particles adhering to the surface of a charging unit during repeated image formation for a long time is prevented. Therefore, it is disclosed that the developer contains at least developer particles and conductive particles having an average particle size smaller than the developer particles. However, this contact charging is due to the discharge charging mechanism, not the direct injection charging mechanism, and there is the above-mentioned problem due to the discharge charging.

[0031]

1) As described in the above-mentioned section of the prior art, in contact charging, direct charging is possible with a simple structure using a charging roller or a fur brush as a contact charging member. Since the surface of the contact charging member was rough, it was not possible to secure close contact with the image bearing member as the member to be charged, and direct charging was impossible.

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

2) Next, in the image forming apparatus of the toner recycling system, when a contact charging device is used as the charging means of the photosensitive drum, a cleaner dedicated to removing the transfer residual toner remaining on the surface of the image bearing member after transfer. Therefore, the transfer residual toner remaining on the surface of the image bearing member after transfer is carried as it is by the movement of the surface of the image bearing member to the charging portion, which is the contact portion between the image bearing member and the contact charging member, and the contact charging member serves as toner. Since the toner was contaminated, it was impossible to directly charge the toner because the transfer residual toner had a great influence of charge inhibition.

When the charging failure occurs, the amount of toner mixed in the contact charging member is further increased, and the charging failure is exacerbated.

3) As a measure against 2), when the toner or the like mixed in the contact charging member is discharged onto the photosensitive drum during non-image formation, it is recovered by the developing device after that.
The part that cannot be collected reaches the transfer portion. At this time, the transfer member is contaminated by the toner discharged onto the photosensitive drum. The contaminated transfer member contaminates the transfer material during the next image formation.

That is, when the discharging mechanism for discharging the toner or the like from the charging roller or the like is performed in order to prevent charging inhibition caused by the contamination by the transfer residual toner of the charging roller or the like, the contamination of the transfer member becomes a problem.

Therefore, the present invention relates to an image forming apparatus of a contact charging system, a transfer system and a toner recycling system, in which a simple member such as a charging roller or a fur brush is used as a contact charging member, and the contact charging is contaminated with toner. Efficient cleaning of members and prevention of transfer of cleaned contaminants to the transfer material during image formation enable ozone-less direct charging (injection charging) and toner recycling system with low applied voltage without any problems. The object is to maintain high-quality image formation 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.

[0038]

The present invention is an image forming apparatus having the following configuration.

(1) A developing means for supplying a developer to the electrostatic latent image formed on the image carrier to develop the electrostatic latent image and at the same time collecting the developer remaining on the image carrier, and the image carrier. In an image forming apparatus having transfer means for transferring an image developed on a transfer material to a transfer material, the polarity of the bias applied to the transfer means is switched at least once in a region where there is no transfer material on the transfer means portion on the image carrier. An image forming apparatus characterized by the above.

(2) The polarity of the bias applied to the transfer means after the polarity of the bias applied to the transfer means is switched at least once in the area on the image carrier where the transfer material is not present in the transfer means. The image forming apparatus according to (1), which has the same polarity as a print bias for transferring the image on the image carrier to the transfer material.

(3) After the transfer step by the transfer means, it has a storage means for temporarily storing the developer on the image carrier and a means for discharging the toner from the storage means onto the image carrier. The image forming apparatus according to (1) or (2), which is characterized.

(4) The toner is discharged from the storage means onto the image carrier in the area of the image carrier corresponding to the area where the transfer material is not present in the transfer means (3). The image forming apparatus according to item 1.

(5) After the area on the image carrier which has discharged the toner from the storage means passes through the transfer means,
The image forming apparatus according to (3) or (4), wherein the polarity of the bias applied to the transfer unit is switched at least once.

(6) After the area on the image carrier from which the toner has been discharged from the storage means has passed the transfer means,
The polarity of the bias applied to the transfer unit after the polarity of the bias applied to the transfer unit is switched at least once is the same as the print bias, (3) to (5) The image forming apparatus described.

(7) On the image carrier having no transfer material in the transfer means, while the area on the image carrier discharged from the storage means passes through the transfer member, it is applied to the transfer means. A bias having a polarity opposite to that of the print bias is applied, and after the area of the image carrier from which the toner is discharged from the storage unit passes through the transfer member, the image on the image carrier is printed with the print bias. The image forming apparatus according to any one of (3) to (6), characterized in that a bias having the same polarity as that of is applied.

(8) The bias having the same polarity as the print bias and the bias having the reverse polarity applied to the transfer means in the area of the image carrier corresponding to the area where the transfer material is not present in the transfer means are at least once. The image forming apparatus according to any one of (3) to (7), wherein the image forming apparatus is applied in a region other than a region where the toner is discharged from the storage unit.

(9) The transfer means is an elastic roller transfer means formed by an elastic member into a roller shape, and the elastic roller transfer means is pressed against the image carrier to form a pressure contact portion ( The image forming apparatus according to any one of 1) to 8).

(10) The polarity of the bias applied to the transfer means after the polarity of the bias applied to the transfer means is switched at least once in the area on the image carrier where the transfer material is not present in the transfer means. The image forming apparatus according to any one of (1) to (9), wherein the image forming apparatus has the same polarity as the print bias and is applied during at least one rotation of the transfer unit.

(11) The image forming apparatus according to any one of (3) to (10), characterized in that a voltage is applied to the storage means.

(12) A voltage whose voltage value temporally changes is applied to the storage means in an area on the image carrier corresponding to an area where there is no transfer material in the transfer means section ( The image forming apparatus according to any one of 3) to (11).

(13) The image forming apparatus according to any one of (3) to (12), wherein the voltage applied to the storage means has a voltage waveform in which an AC voltage is superimposed on a DC voltage. .

(14) The image forming apparatus according to any one of (3) to (13), wherein the storage means also serves as a charging means for charging the image carrier.

(15) The image forming apparatus according to any one of (3) to (14), wherein the storage means is an elastic roller storage means formed in a roller shape by an elastic member.

(16) The charging means for charging the image carrier is a charging means for forming a nip portion with the image carrier and charging via conductive particles (1) to (1)
The image forming apparatus according to any one of 5).

(17) The volume resistance value of the conductive particles is 10
The image forming apparatus according to (16), which has a resistance of ¹² Ω · cm or less.

(18) The volume resistance value of the conductive particles is 10
The image forming apparatus as described in (16) or (17), which is ¹⁰ Ω · cm or less.

[0057]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> (FIG. 1) FIG. 1 is a schematic structural model view of an example of an image forming apparatus according to the present invention. The image forming apparatus of the present embodiment is a laser printer using a transfer type electrophotographic process, a contact charging type, and a toner recycling system.

(1) Overall schematic configuration 1 of the printer is an image bearing member, and in this embodiment, a rotating drum type negative polarity OPC photosensitive member (negative photosensitive member, hereinafter referred to as photosensitive drum) having a diameter of 24 mm. The photosensitive drum 1 has a peripheral speed of 85 mm / sec (= process speed PS,
It is rotated at a constant speed (printing speed).

Reference numeral 2 denotes a conductive elastic roller (hereinafter referred to as a charging roller) as a contact charging member which is disposed in contact with the photosensitive drum 1 with a predetermined pressing force. Reference numeral n is a charging nip portion between the photosensitive drum 1 and the charging roller 2. The charging roller 2 has charge-accelerating particles m having conductivity on its outer peripheral surface.
It holds (carries) (conductive particles for the purpose of accelerating charging), and a charging nip portion n between the photosensitive drum 1 and the charging roller 2
The charging-promoting particles m are present at

The charging roller 2 is rotationally driven in the charging nip portion n in a direction (counter) opposite to the rotating direction of the photosensitive drum 1, and comes into contact with the surface of the photosensitive drum 1 with a speed difference (vs. process speed 80%). To do. Further, at the time of image recording by the printer, a predetermined charging bias is applied to the charging roller 2 from the charging bias applying power source S1. As a result, the peripheral surface of the rotary photosensitive drum 1 is uniformly contact charged by a direct charging (injection charging) method to a predetermined polarity and potential.

In this embodiment, when the image is recorded by the printer, the switch SW of the charging bias applying power source S1 is controlled to be switched to the A contact side so that the core metal 2a of the charging roller 2 is supplied with the DC power source S.
_{A DC} DC voltage of -700V is applied, and the surface of the rotary photosensitive drum 1 is directly charged to a voltage of about -700V which is substantially equal to the applied DC voltage (A mode).

The charging roller 2, the charging-promoting particles m, and the direct charging will be described in detail in another section.

Reference numeral 3 is a laser beam scanner (exposure device) including a laser diode, a polygon mirror and the like. The laser beam scanner 3 outputs a laser beam whose intensity is modulated corresponding to a time-series electric digital pixel signal of target image information, and scans and exposes L the uniformly charged surface of the rotary photosensitive drum 1 with the laser beam. . By this scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotary photosensitive drum 1.

Reference numeral 4 is a developing device. Charge accelerating particles m are added to the developer t. The electrostatic latent image on the surface of the rotating photosensitive drum 1 is reversely developed as a toner image at the developing portion a by the developing device 4. The developing device 4 will be described in detail in another section.

Reference numeral 5 denotes a medium resistance transfer roller as a contact transfer means, which is pressed against the photosensitive drum 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is fed to the transfer nip portion b from a paper feeding unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias applying power source S3. Then, the toner image on the photosensitive drum 1 side is sequentially transferred to the surface of the transfer material P fed to the transfer nip portion b.

The transfer material P introduced into the transfer nip portion b is nipped and conveyed through the transfer nip portion b, and the toner images formed and carried on the surface of the rotary photosensitive drum 1 are sequentially charged with electrostatic force on the surface side thereof. Transferred by pressing force.

Reference numeral 6 is a fixing device such as a heat fixing system. The transfer material P that has been fed to the transfer nip portion b and transferred with the toner image on the photosensitive drum 1 side is separated from the surface of the rotating photosensitive drum 1 and is introduced into the fixing device 6, where the toner image is fixed. It is ejected outside the apparatus as an image-formed product (print, copy).

The printer of the present embodiment is cleanerless, and the transfer residual toner remaining on the surface of the rotary photosensitive drum 1 after the toner image is transferred onto the transfer material P is not removed by a dedicated cleaner (cleaning device), and is exposed. As the drum 1 rotates, it reaches the developing portion a via the charging nip portion n, and is collected by the simultaneous developing cleaning in the developing device 4.
To be reused.

(2) Charging Roller 2 The charging roller 2 as a flexible contact charging member in this embodiment has a metal or foam medium resistance layer 2 on a core metal 2a.
It is created by forming b.

The medium resistance layer 2b is made of resin (for example, urethane),
It was formulated with conductive particles (for example, carbon black), a sulfiding agent, a foaming agent, etc., and formed into a roller shape on the core metal 2a. Then, if necessary, the surface is polished to a diameter of 18 mm,
A charging roller 2 which is a conductive elastic roller having a longitudinal length of 200 mm was prepared.

When the roller resistance of the charging roller 2 of this embodiment was measured, it was 100 kΩ. The roller resistance is φ so that a total pressure of 1 kg is applied to the core metal 2a of the charging roller 2.
In a state where the charging roller 2 was pressure-bonded to a 24 mm aluminum drum, 100 V was applied between the core metal 2a and the aluminum drum for measurement.

Here, the charging roller 2 which is a contact charging member.
Is important to function as an electrode. That is, it is necessary to impart elasticity to obtain a sufficient contact state with the charged body and at the same time have a resistance sufficiently low to charge the moving charged body. On the other hand, it is necessary to prevent voltage leakage when there is a low breakdown voltage defect site such as a pinhole on the charged body. When an electrophotographic photosensitive member is used as the member to be charged, 10 ⁴ to 10 ⁷ is required to obtain sufficient charging property and leak resistance.
A resistance of Ω is desirable.

It is desirable that the surface of the charging roller 2 has microscopic unevenness so as to hold the charge promoting particles m.

If the hardness of the charging roller 2 is too low, the shape is not stable, so that the contactability with the member to be charged is deteriorated, and if the hardness is too high, the charging nip portion n cannot be secured between the charging roller 2 and the member. In addition, since the micro contact property to the surface of the member to be charged is deteriorated, the Asker C hardness is preferably in the range of 25 to 50 degrees.

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

The charging roller 2 is arranged so as to be pressed against the photosensitive drum 1 as a member to be charged with a predetermined pressing force against elasticity, and in this embodiment, the charging nip portion n having a nip width of 2 to 3 mm is provided. It has been formed.

Further, in this embodiment, the charging roller 2 is moved in the charging nip portion n in the clockwise direction of the arrow at about 80% of the process speed so that the charging roller surface and the photosensitive member surface move in opposite directions at a constant speed. It was driven to rotate. That is, the surface of the charging roller 2 as the contact charging member has a speed difference with respect to the surface of the photosensitive drum 1 as the member to be charged.

(3) Developing Device 4 The developing device 4 of this embodiment is a reversal developing device using a one-component magnetic toner (negative toner) as the developer t. Charge accelerating particles m are added to the developer t.

Reference numeral 4a denotes a non-magnetic rotary developing sleeve as a developer carrying / conveying member which encloses the magnet roll 4b, and the developer t + m in the developing unit is the rotary developing sleeve 4
In the process of being conveyed on a, the regulation blade 4c receives the layer thickness regulation and the charge application.

The developer coated on the rotary developing sleeve 4a is conveyed by the rotation of the sleeve 4a to a developing portion (developing area) a which is a portion where the photosensitive drum 1 and the sleeve 4a face each other. Further, the developing bias applying power source S is applied to the sleeve 4a.
A developing bias voltage is applied from 2.

In this embodiment, the developing bias voltage is DC voltage: -500V AC voltage: peak-to-peak voltage 1600V, frequency 1.8kHz.
z, the superimposed voltage of a rectangular wave.

As a result, the electrostatic latent image on the photosensitive drum 1 side is reversely developed by the toner t.

A) Toner t: A one-component magnetic toner t, which is a developer, is prepared by mixing a binder resin, magnetic particles, and a charge control agent, kneading, pulverizing, and classifying, and further promoting charging. It is prepared by adding particles m, a fluidizing agent and the like as external additives. Weight average particle diameter (D4) of toner is 7μ
It was m.

B) Charge promoting particles m: In this example, as the charge promoting particles m, zinc oxide having a specific resistance of 10 ⁶ Ω · cm and an average particle size of 3 μm was used. And the charge promoting particles m
As a result, 1 part by weight was added to 100 parts by weight of the toner t after classification, and the mixture was uniformly dispersed by a mixer and housed in the developing device 4.

As the material of the charge accelerating particles m, various conductive particles such as conductive inorganic particles such as other metal oxides or a mixture with organic substances, or those subjected to surface treatment can be used.

The particle resistance needs to be 10 ¹² Ω · cm or less, preferably 10 ¹⁰ Ω · cm or less, in order to transfer charges through the particles.

The resistance was measured by the tablet method and normalized. That is, a powder sample of about 0.5 g was placed in a cylinder having a bottom area of 2.26 cm ² , 15 kg of pressure was applied to the upper and lower electrodes, and at the same time, a voltage of 100 V was applied to measure the resistance value and then normalized to obtain a specific resistance. Was calculated.

The particle size is 50 in order to obtain good charging uniformity.
μm or less is desirable. In the present invention, the particle size when the particles form an aggregate is defined as the average particle size of 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.

There is no problem that the charge promoting particles exist not only in the state of primary particles but also in the state of agglomeration of secondary particles. Whatever the aggregated state, the form is not important as long as the function as the charge promoting particles can be realized as the aggregate.

The charge accelerating particles are preferably white or nearly transparent so that they do not interfere with the latent image exposure particularly when they are used for charging the photoconductor, and thus are preferably non-magnetic. In addition, the charge-accelerating particles are transferred onto the recording material P
In consideration of the fact that a part of the image is transferred to the color recording medium, colorless or white color recording is desirable. Further, in order to prevent light scattering by particles at the time of image exposure, it is desirable that the particle size is equal to or smaller than the constituent pixel size. The lower limit of the particle size is 10n as a stable particle.
m is considered to be the limit.

(4) Transfer Roller 5 The transfer roller 5 comprises a cored bar made of SUS, aluminum or the like,
A structure in which a medium resistance elastic rubber layer having a volume resistance of about 1 × 10 ⁵ to 1 × 10 ¹² Ω · cm, for example, carbon black dispersed in EPDM, or a medium resistance elastic rubber layer such as NBR rubber is covered in a roller shape on the outer periphery thereof. Is taking. The outer diameter is about φ15 and the hardness is about 35 degrees when a 6N load is applied using an ASKER-C hardness meter. Both ends of the core can be rotated by bearings,
In addition, the bearing is pressed and supported by a spring material with a total weight of 7N so that the transfer roller 5 always contacts the photosensitive drum 1. The transfer roller 5 is driven and rotated.

(5) Direct charging a) The charge-accelerating particles m added to the developer t of the developing device 4 are suitable together with the toner at the developing portion a when the electrostatic latent image on the photosensitive drum 1 side is developed by the developing device 4. The amount shifts to the photosensitive drum 1 side.

The toner image on the photosensitive drum 1 is attracted to the transfer material P side by the influence of the transfer bias in the transfer nip portion b and positively transferred, but the charge promoting particles m on the photosensitive drum 1 are conductive. As a result, it is not positively transferred to the transfer material P side, and is substantially attached and retained on the photosensitive drum 1 and remains. Further, the presence of the charge promoting particles m substantially attached and held on the surface of the photosensitive drum 1 has an effect of improving the transfer efficiency of the toner image from the photosensitive drum 1 side to the transfer material P side.

In the cleanerless printer, the transfer residual toner remaining on the surface of the photosensitive drum 1 after transfer and the above-mentioned residual charging promoting particles m are stored in the charging nip portion n between the photosensitive drum 1 and the charging roller 2. Is carried as it is, and the charging-promoting particles m are supplied to the charging nip portion n and adhered / mixed to the charging roller 2.

Therefore, the photosensitive drum 1 and the charging roller 2
The contact charging of the photosensitive drum 1 is performed in the state where the charging accelerating particles m exist in the charging nip portion n.

B) Since the charging promoting particles m are present in the charging nip portion n between the photosensitive drum 1 and the charging roller 2, the frictional resistance is large due to the lubricant effect of the particles m, and the charging promoting particles m remain as they are with respect to the photosensitive drum 1. Even if it is difficult to contact the charging roller with a speed difference, it is necessary to easily and effectively contact the surface of the photosensitive drum 1 with a speed difference. In addition, the charging roller 2 comes into close contact with the surface of the photosensitive drum 1 through the particles m and comes into contact with the surface of the photosensitive drum 1 more frequently.

By providing a speed difference between the charging roller 2 and the photosensitive drum 1, the chances of the charging promoting particles m coming into contact with the photosensitive drum 1 at the nip portion between the charging roller 2 and the photosensitive drum 1 are significantly increased. A high contact property can be obtained, and the charge accelerating particles m existing in the nip portion between the charging roller 2 and the photosensitive drum 1 rub the surface of the photosensitive drum 1 without a gap so that the charge can be directly injected into the photosensitive drum 1. The direct charging (injection charging) is dominant in the contact charging of the photosensitive drum 1 by the charging roller 2 due to the interposition of the charging promoting particles m.

As a structure for providing the speed difference, the charging roller 2 is rotationally driven to provide the speed difference with the photosensitive drum 1. Preferably, in order to temporarily collect and level the transfer residual toner on the photosensitive drum 1 carried to the charging nip portion n on the charging roller 2, the charging roller 2 is rotationally driven, and the rotation direction is the photosensitive drum 1. It is desirable that the surface is rotated in the direction opposite to the moving direction of the surface. That is, it is possible to directly predominantly directly charge the transfer residual toner on the photosensitive drum 1 once by separating the residual toner on the photosensitive drum 1 by the reverse rotation.

Therefore, a high charging efficiency, which has not been obtained by the conventional roller charging or the like, can be obtained, and the charging potential almost equal to the voltage applied to the charging roller 2 can be applied to the photosensitive drum 1. Thus, the charging roller 2 serves as a contact charging member.
Even if the charging roller 2 is used, a voltage equivalent to the charging potential required for the photosensitive drum 1 is sufficient as the applied bias required for charging the charging roller 2, and a stable and safe contact charging method or device that does not use the discharge phenomenon is realized. can do.

Further, since the charging roller 2 is in contact with the photosensitive drum 1 with a speed difference, the pattern of the transfer residual toner from the transfer nip portion b to the charging nip portion n is disturbed and destroyed, In the halftone image, the previous image pattern portion will not appear as a ghost.

C) Even if the charging-promoting particles m fall off from the charging nip portion n or the charging roller 2 due to durability, the printer is operated so that the particles can be contained in the developer t of the developing device 4 as described above. Some charge promoting particles m are present on the photosensitive drum 1 at the developing portion a.
Surface and the surface of the photosensitive drum 1 moves to the charging nip portion n through the transfer nip portion b and the charging nip portion n.
Therefore, the good chargeability due to the presence of the charge promoting particles m in the charging nip portion n is stably maintained for a long time.

The charge accelerating particles that have fallen off the charging nip portion n or the charging roller 2 are collected by the developing device 4 at the developing portion a and mixed in the developer t for recycling.

By preliminarily supporting the charging-promoting particles m on the surface of the charging roller 2, the above-mentioned direct charging performance can be exhibited without any trouble from the very beginning of use of the printer.

D) Since the printer is cleanerless, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer is carried to the charging nip portion n between the photosensitive drum 1 and the charging roller 2 as it is by the movement of the photosensitive drum 1 surface. It is carried and adheres to and mixes with the charging roller 2.

Since the conventional toner is an insulator, the adhering / mixing of the transfer residual toner with respect to the charging roller 2 is a factor causing charging failure in charging the photosensitive drum.

However, even in this case, since the charging promoting particles m are present in the charging nip portion n between the photosensitive drum 1 and the charging roller 2, the close contact property and the contact resistance of the charging roller 2 to the photosensitive drum 1 are maintained. Therefore, regardless of contamination by the transfer residual toner on the charging roller 2, ozone-less direct charging can be stably maintained at a low applied voltage for a long period of time, and uniform charging property can be provided.

E) The transfer residual toner adhering to and mixed with the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 1 and reaches the developing portion a with the movement of the surface of the photosensitive drum 1, and the developing device 4 simultaneously performs the development. Cleaning (collection) (toner recycling). As described above, the simultaneous cleaning with the developing process is performed by developing the latent image by developing the latent image by continuously charging the photosensitive member with the toner remaining on the photosensitive member 1 after the transfer in the subsequent image forming process, that is, exposing the photosensitive member. At this time, it is recovered by the fog removing bias of the developing device, that is, the fog removing potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor. In the case of reversal development as in the printer of the present embodiment, this simultaneous cleaning of development causes the toner to adhere to the developing sleeve from the dark potential of the photoconductor to the developing sleeve and to the light potential of the photoconductor from the developing sleeve. It is made by the action of an electric field.

F) If the intervening amount of the charging promoting particles in the charging nip portion n between the photosensitive drum 1 as the image bearing member and the charging roller 2 as the contact charging member is too small, a sufficient lubricating effect by the particles can be obtained. However, the friction between the charging roller 2 and the photosensitive drum 1 is large and the charging roller 2 is not
It is difficult to drive the rotation with a speed difference. In other words, the driving torque becomes excessively large, and the surface of the charging roller 2 or the photosensitive drum 1 is scraped if it is forcibly rotated. Further, the effect of increasing contact opportunities due to the particles may not be obtained, and sufficient charging performance may not be obtained. On the other hand, if the intervening amount is too large, the fall of the charging promoting particles from the charging roller 2 remarkably increases, which adversely affects the image formation. According to experiments, it is desirable that the intervening amount is 10 ³ pieces / mm ² or more. When it is less than 10 ³ pieces / mm ² , sufficient lubrication effect and effect of increasing contact opportunity cannot be obtained, and charging performance is deteriorated.

More preferably, 10 ^{3 to} 5 × 10 ⁵ pieces / mm
The intervening amount of ² is preferred. If it exceeds 5 × 10 ⁵ particles / mm ² , the amount of the particles falling onto the photosensitive member 1 remarkably increases, and the exposure amount to the photosensitive drum 1 becomes insufficient regardless of the light transmittance of the particles themselves.

If it is 5 × 10 ⁵ particles / mm ² or less, the amount of particles that fall off can be suppressed to a low level, and the adverse effect can be improved. Since the photosensitive When measuring the abundance of the drum 1 on the falling particles 10 ² to 10 ⁵ / mm was ² in the intervening weight range. As the abundance on the no adverse effect imaging 10 ⁵ / mm ² or less is desired.

A method of measuring the intervening amount and the existing amount on the photosensitive drum 1 will be described. Although it is desirable to directly measure the interposition amount in the charging nip portion n between the charging roller 2 and the photosensitive drum 1, most of the particles existing on the photosensitive drum 1 before contacting the charging roller 2 contact while moving in the opposite direction. In the present invention, the amount of particles on the surface of the charging roller 2 immediately before reaching the charging nip portion n is defined as the intervening amount because the toner is peeled off by the charging roller 2. Specifically, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped without applying a charging bias, and the surfaces of the photosensitive drum 1 and the charging roller 2 are covered with a video microscope (OVM1000N made by OLYMPUS) and a digital still recorder (made by DERTIS). SR-31
It was taken at 00).

The charging roller 2 is brought into contact with the slide glass under the same conditions as when the charging roller 2 is brought into contact with the photosensitive drum 1, and the contact surface is formed from the back surface of the slide glass with a video microscope using a 1000 × objective lens. I took more than 10 shots.

In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of areas where particles exist was measured using desired image processing software.

The amount of existence on the photosensitive drum 1 was also measured by photographing the photosensitive drum 1 with the same video microscope and performing the same processing. The adjustment of the intervening amount is
It was performed by setting the blending amount of the charge accelerating particles m in the developer t of the developing device 4. Generally a developer (toner)
The charge-accelerating particles m are 0.01 to 2 with respect to 100 parts by weight of t.
It is 0 part by weight.

(6) Charging Roller Cleaning Mode In this embodiment, the transfer residual toner adhering to and mixed with the charging roller 2 which is a contact charging member, which is a factor that inhibits charging, is transferred to the image forming apparatus, for example, between sheets. In this case, a roller cleaning mode (contact charging member cleaning mode) for efficiently removing from the charging roller 2 at the time of non-image formation is provided, whereby the contamination level of the transfer roller residual toner on the charging roller 2 is always kept low, which is excellent. Maintains chargeability and image recording stably for a long time.

That is, the charging roller 2 as a contact charging member.
As the voltage application mode for the
A mode (non-roller cleaning mode) in which a DC voltage is applied to uniformly charge the photosensitive drum 1 as an image carrier, and a voltage in which a DC voltage and an AC voltage (cleaning bias) are superposed during non-image formation are applied. B mode (roller cleaning mode) is performed, and the frequency of the AC voltage in the B mode is approximately 5 to 500 Hz.

A) A mode In the present embodiment, during the image formation of the printer, the charging bias applying power source S is supplied by the sequence control circuit (not shown).
The switch SW of No. 1 is controlled to be switched to the A contact side, so that the core metal 2a of the charging roller 2 has a DC voltage of the DC power source SDC −7.
By applying 00V, the surface of the rotary photosensitive drum 1 is directly charged to a voltage of about -700V, which is substantially equal to the applied DC voltage, and image formation is executed.

B) B mode In the present embodiment, the switch SW of the charging bias applying power source S1 is controlled to be switched to the B contact side by the sequence control circuit (not shown) at the time of non-image forming of the printer during the sheet interval. , AC power supply SAC is connected in series to the DC power supply SDC, so that the core metal 2a of the charging roller 2 has a DC voltage of −700 V AC voltage: a peak-to-peak voltage of 200 V and a frequency of, for example, 200.
A superimposed voltage of Hz and a rectangular wave is applied.

In the B mode, the developing sleeve 4a of the developing device 4 has the same DC voltage as the image recording mode: -500V AC voltage: peak-to-peak voltage 1600V, frequency 1.8kHz.
The superimposed voltage of z and a rectangular wave was applied.

By maintaining these bias relationships, the toner accumulated on the charging roller 2 is developed on the photosensitive drum 1 (the toner on the charging roller 2 is discharged to the photosensitive drum 1 side), and the toner is further discharged. The back contrast of the developing device 4 can be collected.

That is, the chargeability can be maintained by efficiently removing the toner attached to the charging roller, which becomes a factor that inhibits charging, during non-image formation.

In this case, by supplying the charging promoting particles m to the charging roller 2, the releasability of the toner from the charging roller 2 is improved, that is, the releasability is increased.
The discharge of the toner on the charging roller 2 to the photosensitive drum 1 side is promoted, the charging roller 2 contaminated with the toner is efficiently cleaned, and the ozoneless direct charging and the toner recycling system can be executed without a problem with a low applied voltage. Therefore, it becomes possible to maintain high-quality image formation 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.

In the B mode, the cleaning bias applied to the charging roller 2 is preferably set so that the difference between the potential of the photosensitive drum and the potential of the charging roller on the downstream side of the charging nip portion n in the moving direction of the photosensitive drum is large. It is more appropriate to set the bias according to the speed.

In the charging system by direct charging as in this embodiment, a potential approximately equal to the potential applied to the charging roller 2 which is the contact charging member is applied to the surface of the photosensitive drum 1 which is the charged member, so that the charging roller is charged. 2 and photosensitive drum 1
A potential difference is unlikely to occur between the two. Naturally, it is necessary to uniformly charge the surface of the photosensitive drum 1 during image recording, but it is necessary to apply an AC bias (cleaning bias) in the roller cleaning mode including non-image recording to generate a potential difference. Therefore, it is desirable to select the cleaning bias so that a potential difference is generated between the inside of the charging nip portion n and the downstream side in the moving direction of the photosensitive drum. For example, in this configuration, the charging nip portion n is 2 to 3 mm, and a frequency of 130 to 200 Hz or higher is suitable.

(7) Bias control of the transfer roller 5 at the time of non-image formation In the system of this embodiment, the transfer material P is cleanerless.
Toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image to the transfer residual toner is a dedicated cleaner (cleaning device).
It is not removed by the process described above and reaches the developing portion a via the charging roller as the photosensitive drum 1 rotates, and is collected and reused in the developing device 4 by simultaneous cleaning of development. Therefore, the residual toner that cannot be stored by the charging roller 1 and cannot be collected by the developing device 4 remains on the photosensitive drum 1. This residual toner gradually accumulates on the transfer roller during image formation at the initial stage of printing and in the non-sheet passing state during non-image formation, causing stains on the back of the paper. The roller resistance becomes high and the transfer bias becomes insufficient, which causes transfer failure. Therefore, it is necessary to prevent the residual toner from accumulating on the transfer roller in the non-sheet passing state.

Further, during continuous image formation such as continuous printing, the transfer residual toner adheres to the charging roller and gradually deteriorates the charging performance.
It is necessary to clean the charging roller during non-image formation. Therefore, it is necessary to clean the charging roller to prevent excessive accumulation of residual toner on the transfer roller when the residual toner on the photosensitive drum is relatively large.

Therefore, in the present embodiment, the timing chart shown in FIG. 2 is controlled in the non-sheet passing state (sheet interval) during non-image formation. The figure is based on the drum surface position.

When the image formation is completed and the non-image formation state is set, the bias applied to the charging roller 2 is set to A at the time of printing.
The mode is switched to the charging roller cleaning mode B mode. The time for the B mode was set to one round of the charging roller in order to discharge the toner evenly.

Most of the toner discharged from the charging roller 2 on the photosensitive drum 1 is collected by the developing device 4, but the discharged toner that cannot be collected goes to the transfer roller 5.

When the transfer roller 5 is reached, the transfer roller 5
Is a negative bias (in this embodiment, it is set to -1 kV)
Is applied to transfer the negative toner from the transfer roller 5 to the photosensitive drum 1 and the positive toner to the transfer roller. The minus bias application time is maintained for the area (about 130 mm in this embodiment) in which the toner discharged from the charging roller 2 is discharged onto the photosensitive drum.

After the area discharged onto the photosensitive drum has passed the transfer roller portion, the polarity of the transfer roller 5 is switched to the opposite polarity plus. In this embodiment, it is set to +1 kV. By doing so, the positive polarity toner once transferred onto the transfer roller 5 is transferred to the photosensitive drum 1.

At this time, the toner adheres to the transfer roller 2 (mainly negative polarity toner), though it is smaller than the ejection area. However, since the adhered amount is small and the print bias that is the transfer bias for transferring the toner image on the photosensitive drum 1 to the transfer material P is the same positive bias, the transfer to the back side of the paper does not occur during paper passing. . The toner held on the transfer roller 2 even during the paper passing is discharged again onto the photosensitive drum 1 when the next paper interval comes, so that the toner remains on the transfer roller 5 excessively even if the paper is continuously passed. It does not accumulate.

In other words, with these configurations, it is possible to realize a long-life cleanerless system in which charging failure, paper back stain, and transfer failure do not occur.

In this embodiment, the values of the negative bias and the positive bias are set to -1 kV and 1 kV, respectively, but the values are not limited to these values as long as the above-mentioned toner transfer effect can be obtained.

In the description of this embodiment, the control is performed as shown in the chart of FIG. In this embodiment, the charging roller 2
Since the area in the circumferential direction in which the toner discharged from the photosensitive drum 1 is transferred onto the photosensitive drum 1 is larger than the circumference of the transfer roller, the transfer roller makes several rounds while applying a negative bias, and the plus area is added to the entire circumference area of the transfer roller. The toner will be transferred. Therefore, the control of the transfer roller between the sheets is performed by applying a positive bias to the transfer for at least one rotation before the image formation, transferring the positive toner to the photosensitive drum and cleaning the transfer roller 5, and then forming the image. Need to move to.

In the present embodiment, the time for applying the positive bias is set to one rotation and the transfer roller 5 can be sufficiently cleaned, but the transfer roller cannot be completely cleaned due to the difference in the formulation of the toner and the transfer roller. In this case, it is preferable to additionally clean the circuit several times.

On the other hand, when the amount of accumulation in the transfer is small and there is a margin for the backside of the paper, the transfer roller cleaning is performed within one lap, and the number of paper interval control described in this embodiment is repeated. , You may gradually exhale.

When the outer circumference of the transfer roller is smaller than the area of the discharged toner on the photosensitive drum, the purpose is to clean the area. Therefore, it is not limited to one round of the transfer roller and may be within one round. .

Further, when the positive toner is further transferred from the transfer roller at the time of applying the sheet-to-paper transfer plus bias,
You may do more than one lap.

Further, the configuration is such that a negative bias is applied to the transfer roller 5 during a sheet interval, and then a positive bias is applied, and then the sheet of paper rushes into the transfer roller 5, which is as described above. This is because the toner is not transferred to the back of the paper. This is because if a small amount of negative toner is transferred to the back side of the paper such as when the amount of residual toner on the photosensitive drum 1 is sufficiently small and a small amount does not lead to dirt on the back side of the paper, a negative bias is applied after applying a positive bias. By doing so, the drum potential immediately before passing the transfer nip can be made negative, so it is advantageous to prevent the drum memory, which is an image defect due to insufficient charging caused by the photosensitive drum being positively charged. Therefore, it is preferable.

Further, in this embodiment, the discharging bias for one round of the charging roller is applied to clean the charging roller 2, but if the charging property is satisfied, the charging is performed within one cycle.
It is also possible to gradually exhale as the number of times of control between sheets described in this embodiment is repeated. For example, when the time between sheets is shorter than the drum area discharged by one rotation of the charging roller + the one rotation of the transfer roller, the time for one rotation of the transfer roller is secured as the time during which the discharge is not performed, and the other time is set. Alternatively, the toner on the charging roller may be discharged.
On the contrary, when the charging property is not satisfactory, the charging roller may be cleaned once or more times to secure the charging property.

Further, in the present embodiment, the charging roller cleaning is set between the sheets, however, during the rotation before the start of printing, the post-rotation after the end of printing, the power-on of the main body and the reset of the main body, etc. If it is carried out during rotation, the charging property can be further stabilized.

Further, when there is a margin in charging property, a configuration may be adopted in which the sheet interval is set once every several times.

Further, in the present embodiment, the discharging from the charging roller and the transfer sequence accompanied therewith are performed once between the sheets, but by performing a plurality of times, the cleaning effect can be further enhanced.

As described above, in this embodiment, the toner accumulated from the charging roller is discharged onto the photosensitive drum and collected by the developing device in a non-sheet passing state such as a sheet interval. After that, when the area comes to the transfer roller, a minus is applied to the transfer roller, and a plus is applied until the next sheet is passed after passing through. As a result, it is possible to form a good image that is free from charging defects and stains on the back of the paper during continuous paper feeding.

(8) Comparative Example Next, the image levels of the present invention and the comparative example will be shown. Continuous printing is performed with the configurations of the comparative example and the present example, and the tenth sheet and the first sheet are printed.
Image comparison was performed on the 000th sheet. Practical images with a printing rate of 5% are continuously printed and 600D is printed on the 10th and 1000th sheets.
A horizontal line image of 1 dot2space of PI was sampled to evaluate the charging property and the stain on the back of the paper.

First, the comparative examples 1 to 4 will be described below.

Comparative Example 1 Basically the constitution of this embodiment, but without the charging roller cleaning mode of this embodiment, without bias control of the transfer roller during non-image forming of this embodiment, instead of this It has the same polarity as the print bias between sheets and has a strength of 1
kV.

<Comparative Example 2> The configuration of this embodiment is basically the same, but without the charging roller cleaning mode of this embodiment, without bias control of the transfer roller during non-image formation of this embodiment,
Instead, the strength is -1kV with the polarity opposite to the print bias during the paper interval.

<Comparative Example 3> Although the configuration of this embodiment is basically the same, there is a charging roller cleaning mode of this embodiment, and there is no bias control of the transfer roller during non-image formation of this embodiment. It has the same polarity as the print bias between sheets and has a strength of 1
kV.

<Comparative Example 4> Although the configuration of this embodiment is basically the same, there is a charging roller cleaning mode of this embodiment, and there is no bias control of the transfer roller during non-image formation of this embodiment. It has the same polarity as the print bias during paper spacing,
1 kV.

As the evaluation items, the charging property and the stain on the back of the paper were evaluated.

The chargeability was judged by the number of white spots generated in the intermediate image. From a practical point of view, the number of white spots having a diameter of 0.3 mm or more was less than 50, and the presence of 50 or more was x. Furthermore, less than 30 were rated as ⊚ and less than 10 were rated as ☆.

The backside stain means that the black density of the recording material is measured by a reflection densitometer, and the difference is 4 with respect to the density of the recording material itself.
% Or more x, less than 4% o, and less than 3% o.

The reflection densitometer used in this case is TOKYO.
DENSHOTO METER made by DENSHOKU
PC6DS was used. Also, the comparison results are listed side by side with respect to Examples 2 and 3 below.

[0156]

[Table 1]

As shown in the above table, with the configuration of the first embodiment, it is possible to maintain high-quality image formation as compared with the conventional one for a long time, and to perform high-quality image formation even after outputting an image with a high image ratio. It can be maintained for a long period of time.

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

As the flexible contact charging member, in addition to the charging roller, a fur brush, felt, cloth or the like having a material and shape can be used. It is also possible to stack these to obtain more appropriate elasticity and conductivity.

2) As the waveform of the AC voltage (alternating voltage) applied to the contact charging member 2 and the developing sleeve 4a, a sine wave, a rectangular wave, a triangular wave or the like can be appropriately used. Further, it may be a rectangular wave formed by periodically turning on / off the DC power supply. Thus, as the waveform of the alternating voltage, a bias whose voltage value changes periodically can be used.

3) The image exposure means for forming an 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 type. Other light emitting elements such as image exposure and LEDs may be used, or a 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.

4) It is also possible to adjust the resistance of the surface of the photoconductor by providing a charge injection layer on the surface of the photoconductor as the image bearing member.

FIG. 3 is a schematic diagram of the layer structure of the photoconductor 1 having the charge injection layer 16 on the surface. That is, the photoconductor 1 comprises an aluminum drum base (Al drum base) 11, an undercoat layer 12,
Positive charge injection prevention layer 13, charge generation layer 14, charge transport layer 1
The charge injection layer 16 is applied to a general organic photoreceptor coated in the order of 5 to improve the charging performance.

The charge injection layer 16 is composed of a photo-curing acrylic resin as a binder and conductive particles (conductive filler).
SnO ₂ ultrafine particles 16a (diameter of about 0.03μ
m) A lubricant such as a tetrafluoroethylene resin (trade name Teflon), a polymerization initiator and the like are mixed and dispersed, and after coating, a film is formed by a photo-curing method.

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

Even when the charge injection layer 16 is not used as in this structure, the same effect can be obtained when the charge transport layer 15 is in the above resistance range.

Further, the volume resistance of the surface layer is about 10 ¹³ Ωcm.
The same effect can be obtained by using the amorphous silicon photoconductor or the like.

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

6) In the embodiment, the developing means 4 is described as an example of a reversal developing device using a one-component magnetic toner, but the developing device structure is not particularly limited. It may be a regular developing device.

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

8) An example of the method for measuring toner particle size will be described. As a measuring device, Coulter Counter TA-2
Interface (manufactured by Nikkaki) and CX that outputs number average distribution and volume average distribution using a mold (manufactured by Coulter)
-1 Connect a personal computer (made by Canon),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride.

As a measuring method, the electrolytic aqueous solution 100 to
Surfactant as a dispersant in 150 ml, preferably
Add 0.1 to 5 ml of alkylbenzene sulfonate, and add 0.5 to 50 mg of the measurement sample.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the Coulter counter TA-2 type was used to make a particle size of 2 to 40 μm using a 100 μ aperture as an aperture. The distribution is measured to obtain the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

<Embodiment 2> FIG. 4 shows a paper interval sequence of this embodiment.

The present embodiment is different from the first embodiment in that the toner is discharged from the charging roller 2 onto the photosensitive drum 1 and the developing device 4 collects the toner discharged from the charging roller 2 and then the developing device After the toner on the photosensitive drum 1 that has not been completely collected in No. 4 passes through the transfer nip, a positive (+1 kV) and a negative (−1 kV) bias of both polarities are applied to the transfer roller 5 at least once. .

In the structure of this embodiment, after the negative bias is applied, the positive bias is applied and each bias is applied for one round of the transfer roller. However, it is not limited to one rotation of the transfer roller, but when the number of rotations is one or more, the transfer roller 5 can be further cleaned, and the amount of toner remaining on the photosensitive drum 1 is small and the amount of toner attached to the transfer roller 5 is small. For example, the transfer roller should be within one round, and a sufficient effect can be obtained even if cleaning is performed little by little over several sheets of paper.

With such a structure, the positive and negative polar toners attached to the transfer roller 5 can be uniformly cleaned.

The comparative example is as described in Example 1.

The toner discharged from the charging roller at the time of non-image formation such as paper interval is not completely collected by the developing device 4, and the bias of the transfer roller 5 applied when passing through the transfer nip is a negative bias (-1 kV). However, this is because the toner discharged from the charging roller 2 is mainly negatively charged in the configuration of the present embodiment, and this negative toner is not attached to the transfer roller 5.
Conversely, when the discharged toner is positively charged, it is preferable to apply a positive bias.

The magnitude of the bias applied to each transfer (-1, 1 kV) is not limited to this as long as the toner on the transfer roller 5 can be sufficiently transferred to the photosensitive drum 1.

Further, while a negative bias is applied to the transfer roller 5 and then a positive bias is applied to the transfer roller 5 during the interval between the papers, the paper then rushes into the transfer roller 5. This is as described above. This is because the negative toner is not transferred to the inside of the paper. This is because if a small amount of negative toner is transferred to the back side of the paper such as when the amount of residual toner on the photosensitive drum 1 is sufficiently small and a small amount does not lead to dirt on the back side of the paper, a negative bias is applied after applying a positive bias. By doing so, since the drum potential immediately before passing the transfer nip can be made negative by doing so, it is advantageous to prevent the drum memory which is an image defect due to insufficient charging caused by the photosensitive drum 1 being positively charged. Therefore, it is preferable.

In the structure of this embodiment, it is possible to maintain high-quality image formation 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. .

<Embodiment 3> FIG. 5 is a diagram for explaining this embodiment. The general structure of this embodiment is the same as that of the first embodiment, and the description of the same points is omitted.

Reference numeral 7 denotes a storage roller, which is located on the downstream side of the transfer roller 5 with respect to the rotating direction of the photosensitive drum, is in contact with the photosensitive drum 1, and rotates in the counter direction with respect to the rotating direction of the photosensitive drum. The storage roller 7 has the same structure as the charging roller 2.

A bias similar to that of the charging roller 5 is applied to the storage roller 7, and by controlling the bias value, the transfer residual toner is collected from the surface of the photosensitive drum, or the storage roller 7 has a residual toner. The accumulated toner can be discharged to the surface of the photosensitive drum.

The bias sequence in this embodiment is applied at the same position on the upper surface of the photosensitive drum in consideration of the time lag between the storage roller 7 and the charging roller 2 on the photosensitive drum 1 along the photosensitive drum surface. The bias sequence of the charging roller 2 was the same as that of the charging roller 2 except that it was started. The bias sequence is equivalent to that described in Example 1. The storage roller 7 serves as a charging auxiliary member mainly for collecting transfer residual toner during image formation. Charging roller 2
In the case of (1), since the amount of transfer residual toner adhered during image formation is drastically reduced, it serves as a saving auxiliary member mainly for charging.

With such a configuration, it becomes possible to maintain high-quality image formation 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.

The comparative example is as described in Example 1.

Further, in this embodiment, the storage roller 7 has substantially the same structure as that of the charging roller 2 and applies the same bias to collect and discharge the transfer residual toner. The configuration may be modified, and is not limited to the configuration of this embodiment.

Further, since the storage roller 7 is in contact with the photosensitive drum 1 and rotates in the counter direction with respect to the rotation direction of the photosensitive drum, the transfer residual toner on the photosensitive drum 1 is rotated in the nip of the storage roller 7. The transfer residual toner is dammed near the outlet, and as a result, it is scattered.

When the amount of transfer residual toner is small, it is possible to obtain only the mechanical leaflet effect of the storage roller 7 without reducing the cost of the high-voltage substrate.

Charging roller 2 and storage roller 7 of this embodiment
On the other hand, although the bias sequence described in the first embodiment is used, a higher quality image can be formed by using the bias sequence described in the second embodiment.

[0193]

As described above, according to the present invention, in the image recording apparatus of the contact charging system, the transfer system and the toner recycling system, a simple member such as a charging roller or a fur brush is used as the contact charging member. In addition, the contact charging member contaminated by the toner is efficiently cleaned, and the cleaned contaminants are prevented from transferring to the transfer material during image formation, so that ozone-less direct charging (injection charging) and toner can be performed at a low applied voltage. The recycling system can be executed without problems, high-quality image formation can be maintained for a long time, and high-quality image formation can be maintained for a long time even after outputting an image with a high image ratio.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating control according to the first embodiment of the present invention.

FIG. 3 is a layer configuration model diagram of an example of a photoconductor having a surface on which a charge injection layer is provided.

FIG. 4 is a diagram illustrating control according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of a third embodiment of the present invention.

FIG. 6 is a diagram showing charging characteristics.

[Explanation of symbols]

1. Photosensitive drum 2. Charging roller 3. Laser beam scanner 4. Developer 4a. Development sleeve t. Developer (toner) m. Charge promoting particles (conductive particles) 5. Transfer roller 6. Fixing device 7. Savings roller P. Transfer material

Continued front page    (72) Inventor Shuji Moriya             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Koichi Otaka             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Michihito Yamazaki             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Kenichi Ogawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA22 DC04 DE01 DE07 DE09                       EA03 ED01 ED03 ED16 ED24                       ED27 EE02 EF06                 2H077 AA37 AC11 AC16 AD02 AD06                       DB12 DB15 GA03                 2H200 FA02 FA14 GA23 GA44 GB11                       GB37 HA02 HA21 HA28 HB12                       HB17 HB22 HB46 HB47 HB48                       JA02 JA27 JA28 JA29 JA30                       JB10 LB03 LB15 LB17 LB18                       LB38 LB39 MB04 MC01 NA02                       NA06 PA05 PA10 PA18 PA22                       PB12 PB36

Claims (18)

[Claims] 1. A developing unit for supplying a developer to an electrostatic latent image formed on an image bearing member to develop the electrostatic latent image and collecting the developer remaining on the image bearing member at the same time, and to the image bearing member. In an image forming apparatus having a transfer unit that transfers a developed image to a transfer material, in a region where the transfer member on the image carrier does not have the transfer material, the polarity of the bias applied to the transfer unit is switched at least once. An image forming apparatus characterized by. 2. The polarity of the bias applied to the transfer means after the polarity of the bias applied to the transfer means is switched at least once in a region where there is no transfer material in the transfer means section on the image carrier, The image forming apparatus according to claim 1, wherein the image forming apparatus has the same polarity as a print bias for transferring the image on the image carrier to the transfer material. 3. A storage means for temporarily storing the developer on the image carrier after the transfer step by the transfer means, and a means for discharging the toner from the storage means onto the image carrier. The image forming apparatus according to claim 1 or 2. 4. The toner is discharged from the storage unit onto the image carrier in a region of the image carrier corresponding to a region where the transfer unit has no transfer material. The image forming apparatus described. 5. The polarity of the bias applied to the transfer means is switched at least once after the area on the image carrier from which the toner has been discharged from the storage means has passed through the transfer means. Alternatively, the image forming apparatus according to item 4. 6. After the area on the image carrier from which the toner has been discharged from the storage means has passed through the transfer means, the polarity of the bias applied to the transfer means is switched at least once and then applied to the transfer means. The image forming apparatus according to claim 3, wherein the polarity of the bias to be applied is the same as the polarity of the print bias. 7. On the image carrier having no transfer material in the transfer means section, while the area on the image carrier discharged from the storage means passes through the transfer member, it is applied to the transfer means. The bias applies a bias having a reverse polarity to the print bias, and after the area of the image carrier from which the toner is discharged from the storage unit has passed through the transfer member,
7. A bias having the same polarity as the print bias is applied to the image on the image carrier.
The image forming apparatus according to any one of 1. 8. A bias having the same polarity and a reverse polarity to the print bias applied to the transfer means in the area of the image carrier corresponding to the area where there is no transfer material in the transfer means are at least once, respectively. The image forming apparatus according to any one of claims 3 to 7, wherein the image forming apparatus is applied in a region other than a region where the toner is discharged from the storage unit. 9. The transfer means is an elastic roller transfer means formed by an elastic member into a roller shape, and the elastic roller transfer means is pressed against the image carrier to form a pressure contact portion. The image forming apparatus according to any one of 1 to 8. 10. The polarity of the bias applied to the transfer means after switching the polarity of the bias applied to the transfer means at least once in a region where the transfer means on the image carrier has no transfer material, The image forming apparatus according to claim 1, wherein the image forming apparatus has the same polarity as the print bias and is applied during at least one rotation of the transfer unit. 11. The image forming apparatus according to claim 3, wherein a voltage is applied to the storage means. 12. A voltage having a temporally varying voltage value is applied to the storage means in an area on the image carrier corresponding to an area where there is no transfer material in the transfer means. The image forming apparatus according to any one of 3 to 11. 13. The image forming apparatus according to claim 3, wherein the voltage applied to the storage means has a voltage waveform in which an AC voltage is superimposed on a DC voltage. 14. The storage means also functions as a charging means for charging the image carrier.
The image forming apparatus according to any one of 1. 15. The image forming apparatus according to claim 3, wherein the storage means is an elastic roller storage means formed in a roller shape by an elastic member. 16. The charging means for charging the image carrier is a charging means for forming a nip portion with the image carrier and charging via conductive particles. The image forming apparatus described. 17. The volume resistance value of the conductive particles is 10 ¹² Ω.multidot.
The image forming apparatus according to claim 16, wherein the image forming apparatus has a size of not more than cm. 18. The volume resistance value of the conductive particles is 10 ¹⁰ Ω.multidot.
It is below cm, The claim 16 or 17 characterized by the above-mentioned.
The image forming apparatus according to item 1.