JPH10171216A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a contact electrifying means, without any problem of the degradation of electrifiability and any trouble by holding an electrifying member in a second state without contacting with an image carrier, during at least a part of a period in an image nonforming process, in the process of operating an image forming device. SOLUTION: A position shifting means 3 for a magnetic brush member 2 shift-holds it in a first state of a fixed contact state with a photoreceptor 1 or a second state of a non-contact state. Then, during pre- or/and post-rotation processes in the operation process of a printer, the magnetic brush member 2 is shift-held in the second state of the non-contact state from the first state of the fixed contact state with the photoreceptor 1 by the position shifting means 3 controlled by a control circuit, so that toner remaining after a transfer, etc., which are stuck/infiltrated into the magnetic brush member 2 are transferred to the photoreceptor 1, to be removed. Thus, the magnetic brush member 2 as the electrifying member is kept in the non-contact state with the photoreceptor 1 as the image carrier, in a state where a voltage is applied on the member 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention charges an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, such as an electrophotographic device such as a laser beam printer or a copying machine, or an electrostatic recording device. Charging means, electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier, developing means for applying a toner of a developer to the electrostatic latent image for development, and transferring the toner image The present invention relates to an image forming apparatus that has an image forming process unit including a transfer unit that transfers to a material, and an image carrier repeatedly performs image forming.

More specifically, a cleaning means for collecting toner particles (transfer residual toner) remaining on the image carrier after transferring the toner image on the image carrier to a transfer material by a transfer means is provided in front of the charging means. There is no image forming device,
The charging unit is a contact charging unit that has a charging member that is in contact with the image carrier and to which a voltage is applied, and the image carrier is charged by a charge that is directly injected from the charging member into the image carrier. The present invention relates to an image forming apparatus in which a charging system in which injection charging is dominant is used.

[0003]

2. Description of the Related Art For convenience, a transfer type electrophotographic apparatus will be described as an example.

Conventionally, a transfer type electrophotographic apparatus generally has the following means configuration and image forming process. That is,
A rotating drum type is generally used as an image carrier,
Using an electrophotographic photoreceptor such as cadmium sulfide, zinc oxide, amorphous silicon, or an organic photoconductor, the surface of the photoreceptor is uniformly charged to a predetermined polarity and potential by a charging means, and the charged photoreceptor surface is imaged. An image is exposed by an exposure unit to form an electrostatic latent image corresponding to the exposed image, a developing unit attaches a toner of a developer to the electrostatic latent image and develops the toner image as a toner image, and the toner image is transferred by a transfer unit. The image is transferred to a transfer material. The transfer material on which the toner image has been transferred is subjected to a fixing process of the toner image by a fixing unit, and is discharged as an image formed product (copy, print). After the transfer of the toner image to the material to be transferred, the rotating photoreceptor is subjected to removal of untransferred toner by a cleaning unit (cleaner) and is repeatedly provided for image formation.

As a means for charging a photosensitive member as an image bearing member to be charged, a "corona charging system" charging means using a corona discharger has conventionally been generally used. In recent years, charging means of “contact charging method (direct charging method)” has been put to practical use because it has advantages such as low ozone and low power over corona charging method.

A) Corona charging method In this method, a corona discharger is disposed so as to face a photoconductor in a non-contact manner.
A high voltage (for example, DC 5) is applied to the discharge wire (metal wire).
-8 kV) to expose the surface of the photoreceptor to a corona shower that is generated, thereby charging the surface of the rotary photoreceptor to a predetermined polarity and potential.

However, in the corona charging method, or allowed to proceed image blurring or deterioration caused deterioration in the surface of the photoreceptor by corona products such as ozone and NO _x generated along with the corona discharge, contamination of the discharge wire image There is a problem that the quality is affected and white spots and black stripes are formed on the image.

In particular, an electrophotographic photosensitive member having a photosensitive layer mainly composed of an organic photoconductor has low chemical stability as compared with other selenium photosensitive members, amorphous silicon photosensitive members and the like.
Chemical reaction (mainly oxidation reaction) when exposed to corona products
Tend to occur and deteriorate easily. Therefore, when repeatedly used under corona charging, image blurring or deterioration in sensitivity due to the above-described deterioration, and a decrease in copy density due to an increase in residual potential, tend to shorten the printing (copying) life.

Further, in the corona charging, the electric current flowing toward the photoreceptor is only 5 to 30% of the electric power, most of the electric current flows to the shield plate, and the charging means has low power efficiency.

B) Contact charging method In the contact charging method, a conductive member whose resistance value is adjusted is provided as a charging member (charging member) in contact with a photosensitive member as a member to be charged without using a corona discharger. Then, by applying a voltage (charging bias) to the charging member, the surface of the photoreceptor is charged to a predetermined polarity and potential.

As the charging member, a conductive elastic roller type (charging roller), a conductive elastic blade type (charging blade), a magnetic brush type (magnetic brush member),
Various forms such as a fur brush type (fur brush member) can be used.

As a voltage application form to the charging member, for example, only a DC voltage Vdc of 1 to 2 kV is used.
C method "and an" AC superposition method "in which an alternating voltage Vac (a voltage whose voltage value changes periodically with time; hereinafter, referred to as an AC voltage) is superimposed on a DC voltage Vdc and applied to a charging member.
There is.

The contact charging method is different from the corona charging method,
There are advantages that the applied voltage can be reduced, the amount of corona products such as ozone generated is greatly reduced, and the power efficiency is good.

The contact charging includes "a system in which charging by the discharge phenomenon is dominant" (JP-A-57-178267, JP-A-56-104351, and JP-A-58-4804).
0566, JP-A-58-139156, JP-A-58-150975, etc.), "A system in which charging by direct injection (charging) of a charge to a surface to be charged is dominant (charge injection charging system) There is.

In this section b, a contact charging system in which charging by a discharge phenomenon is dominant will be described. When a conventional photoconductor is used as the image carrier, the photoconductor is charged by discharge in a minute space near a contact portion between the photoconductor and the charging member.

Therefore, even in a contact charging system in which charging by a discharge phenomenon is dominant, charging is performed by ionizing molecules in the air and flowing these ions to the surface of the photoreceptor, as in the corona charging system. No direct charge injection from the charging member to the photoreceptor surface is performed.

Naturally, the charging in such a charging mechanism largely depends on the surface shapes of the charging member and the photoreceptor as a member to be charged, and unevenness of each surface causes uneven charging.

Further, since the discharge occurs in the minute gap,
The movement of ions in a strong electric field causes significant damage to the photoreceptor, increases the amount of shaving, and reduces durability.

[0019] Compared to yet corona charging method, but orders of magnitude less, still image blurring occurs ozone, due to the occurrence of such NO _X.

In a contact charging system in which charging due to a discharge phenomenon is dominant, the DC system in which the voltage applied to the charging member is only the DC voltage Vdc is less uniform than the corona charging system. , And the occurrence of discharge breakdown of the photoconductor due to the direct application of voltage.

Due to the non-uniformity of charging, a length of 2 to 200 mm and a width of 0.
It causes streak-like charging unevenness of about 5 mm or less, and causes white streaks (a phenomenon in which white streaks appear in solid black or halftone images) that occur in the case of the normal development system or black streaks that occur in the case of the reversal development system. Image defect.

As a solution to such a problem, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 3-149668, there is an AC superposition method in which a voltage applied to a charging member is superimposed on an AC voltage Vac on a DC voltage Vdc. This is to apply a pulsating voltage to the charging member by superimposing the AC voltage Vac on the DC voltage Vdc to perform uniform charging. In this case, in order to maintain image uniformity and prevent image defects such as white spots in the normal development mode, black spots and fog in the reversal development mode, the superimposed AC voltage is controlled by the discharge start voltage Vth ( A peak-to-peak potential difference Vpp (Peak) that is at least twice the applied voltage value of the charging member when a DC voltage is applied to the charging member to start charging of the member to be charged.
to peak (peak-to-peak).

In this AC superposition method, if the superimposed AC voltage is increased in order to prevent image defects, discharge breakdown occurs at a slight defect site inside the photoconductor due to the maximum applied voltage of the pulsating voltage. . In particular, when the photoconductor is an organic photoconductor having a low withstand voltage, this dielectric breakdown is remarkable. In this case, in the normal development system, the image becomes blank in the longitudinal direction of the contact portion, and in the reversal development system, black stripes occur. Further, when there is a pinhole, there is a problem that a portion there serves as a conduction path, current leaks, and the voltage applied to the charging member drops. Furthermore, since the discharge is caused in the minute gap, there is a problem that the damage to the photoconductor is large, the shaving amount of the photoconductor is large, and the durability is poor.

C) Charge Injection Charging System In order to solve these problems, a contact charging system (charge injection charging system) in which charging by direct injection (charging) of electric charge to the surface to be charged is dominant is used. It is being adopted.

The charge injection charging system uses a charging member and has a charge injection charging type as an object to be charged. In the case of an image bearing member, there is an ordinary organic photoreceptor having a surface layer in which conductive fine particles are dispersed on an organic photoreceptor. By using an amorphous silicon photoreceptor or the like, it is possible to obtain a charging potential substantially equal to the DC component of the bias applied to the charging member on the surface of the charging target.

In the charge injection charging, the surface of the image carrier is charged by applying only a DC voltage Vdc (V) from the charging member to the image carrier, and the DC voltage Vdc ( V) and the image carrier dark potential Vd (V)
Is a charging process that satisfies the following expression (1).

| Vdc−Vd | ≦ 200 (V) Equation (1) Since such charge injection charging does not use the corona discharge phenomenon for charging, the applied charging bias required for charging is substantially It is possible to achieve a completely ozone-free and low-power-consumption type charging that is only the desired surface potential of the member to be charged and does not generate ozone.

In Japanese Patent Application Laid-Open No. 6-3921, as a charge injecting layer, an S resin obtained by making an acrylic resin conductive on the surface of a photoreceptor with antimony dope as a conductive filler (conductive particles) is used.
There is a description that it is possible to apply and use a dispersion of nO ₂ .

As described above, it is possible to inject a charge by forming a layer in which conductive particles are dispersed in a resin on a surface layer of a photoreceptor, or by improving a charging member in a normal photoreceptor. The charging unevenness observed in the contact charging system in which the charging due to the discharge phenomenon is dominant disappeared, and the damage to the photoreceptor was reduced and the durability was improved. further,
Ozone, almost no generation of NO _X, eliminates the generation of image blur, the problem is greatly improved.

As the charging member in the case of the charge injection charging system, a magnetic brush member or a fur brush member is preferably used in terms of charging, contact stability and the like.

The magnetic brush member has a magnetic brush portion made of conductive magnetic particles (magnetic carrier for charging) magnetically constrained and supported by a supporting member also serving as a power supply electrode, and the magnetic brush portion is brought into contact with the member to be charged. Then, power is supplied to the supporting member. More specifically, the conductive magnetic particles are directly magnetically restrained and held as a magnetic brush portion on a magnet or a sleeve containing the magnet, and the magnetic brush member is covered while stopping or rotating the magnetic brush member. The object to be charged is charged by bringing it into contact with the object to be charged and applying a voltage.

The fur brush member has a conductive fiber brush portion carried on a carrier member also serving as a power supply electrode, and the conductive fiber brush portion is brought into contact with a member to be charged to supply power to the carrier member. .

Also, in the charge injection charging method, the charging bias applied to the charging member is an AC superposition method in which the AC voltage Vac is superimposed on the DC voltage Vdc, so that the charging is performed more than in the DC method in which only the DC voltage Vdc is applied. Is known to be more stable.

In the AC superposition system, the charge injection charging system is greatly different from the contact charging system in which the charging by the discharge phenomenon is dominant. The following formula (2) is used in the contact charging system in which the charging by the discharge phenomenon is dominant. )

[0035]

(Equation 2) Is satisfied, the charging becomes non-uniform, and the absolute value | Vdc−Vd | of the difference between the DC voltage Vdc (V) applied to the charging member and the dark potential Vd (V) of the photosensitive member serving as the image carrier becomes | Vdc− Vd | ≦ 200 (V) Expression (3) and / or the absolute value | V of the photoconductor dark potential Vd (V)
d | does not satisfy Expression (4). | Vd |> | Vpp / 2 | + | Vdc |-| Vth |

In the case of the AC superposition system and the charge injection charging system, the dark potential Vd (V) of the photoconductor is substantially equal to the applied DC voltage Vdc (V) even under the condition satisfying the expression (2). , (3) and (4) can be satisfied. That is, although the peak-to-peak voltage Vpp of the AC voltage Vac is smaller than twice the discharge start voltage Vth as shown in the equation (2), the dark potential Vd of the photoconductor and the applied DC voltage are shown in the equation (3). The difference from the voltage Vdc is within 200 V.

[0037]

In an image forming apparatus having no cleaning means in front of a charging means, for example, an image forming apparatus in a cleaning process in which a cleaning means also serves as a developing means, a contact charging means is used as a charging means for an image carrier. When adopted, the charging member (charging member) is a transfer residual toner, a developer external additive, etc. (hereinafter, referred to as a transfer residual toner, etc.)
When the charging member comes into contact with the surface of the image bearing member on which the image is carried, the charging member is contaminated by the adhesion of the transfer residual toner and the like.

When the contact charging of the image carrier is a system in which the charging due to the discharge phenomenon is dominant, the potential difference between the voltage Vdc applied from the charging member to the image carrier and the dark potential Vd of the image carrier is large. As a result, even if the transfer residual toner or the like adheres to the charging member, the adhered transfer residual toner or the like is easily detached electrically from the charging member side to the image carrier side, re-transferred, and removed from the charging member side. Accordingly, the charging member is excessively contaminated with transfer residual toner and the like, so that the charging property (charging performance) is improved.
Deterioration is naturally prevented.

However, the system in which the contact charging of the image carrier is dominated by charging by direct injection of electric charge to the image carrier surface,
That is, in the case of the charge injection charging system, since the voltage Vdc applied from the charging member to the image carrier and the dark potential Vd of the image carrier are substantially the same, the transfer residual toner and the like adhered to the charging member are as described above. There is a problem in that the charging member is not removed as in the case but accumulates on the charging member, and the charging member is excessively contaminated with transfer residual toner or the like, thereby deteriorating the charging property.

Therefore, in the present invention, in an image forming apparatus having no cleaning means in front of the charging means, a contact charging means of a charge injection charging system as a charging means for an image carrier can be used without the above-mentioned problem, that is, a transfer residual of a charging member. It is an object of the present invention to provide an image forming apparatus which can be used without any trouble without the problem of deterioration of charging property caused by excessive contamination by toner or the like.

[0041]

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

(1) A rotating image carrier, a charging means for charging the image carrier, a latent image forming means for selectively removing a charge on the charged surface of the image carrier to form an electrostatic latent image, Developing means for developing the latent image as a toner image, transfer means for transferring the toner image to a transfer material, and toner remaining on the image carrier after the toner image on the image carrier is transferred to the transfer material by the transfer means An image forming apparatus that does not have a cleaning unit that collects particles before the charging unit, and the charging unit includes:
Contact charging means having a charging member which is in contact with the image carrier and to which a voltage is applied, wherein the charging of the image carrier is dominated by charge injection charging in which charges are directly injected from the charging member to the image carrier. In an image forming apparatus made by a charging system,
Means for switching between a first state in which the charging member is brought into contact with the image carrier and a second state in which the charging member is not in contact with the image carrier, wherein the charging member is used during a non-image forming process in an operation process of the image forming apparatus. The image forming apparatus is held in a second state in which the image carrier is not in contact with the image carrier during at least a part of the period.

(2) The charging member is not attached to the image carrier during the pre-rotation process or the post-rotation process, or during the pre-rotation process and the post-rotation process during the non-image formation process in the operation process of the image forming apparatus. The image forming apparatus according to (1), wherein the image forming apparatus is held in a second state of contact.

(3) The latent image forming means for selectively discharging the charged surface of the image carrier to form an electrostatic latent image is an image exposing means, which is described in (1) or (2). Image forming apparatus.

(4) The developing means is of a reversal developing type in which the electrostatic latent image is developed with a toner having the same polarity as the normal charging polarity for forming the electrostatic latent image on the image carrier. The image forming apparatus according to any one of (1) to (3).

(5) The method according to (4), wherein a bias having a potential between the dark portion potential and the bright portion potential of the electrostatic latent image on the image carrier is applied to the developer carrying conveyance member of the developing means. Image forming apparatus.

(6) The surface of the image carrier is charged by applying only DC voltage Vdc (V) from the charging member to the image carrier, and the DC voltage Vdc ( V) and the dark potential Vd (V) of the image carrier satisfy the following equation (1): | Vdc−Vd | ≦ 200 (V) (1) The image forming apparatus according to any one of (1) to (5).

(7) The image bearing member is an electrophotographic photosensitive member,
The surface of the photoconductor is charged by applying a voltage obtained by superimposing the alternating voltage Vac (V) on the DC voltage Vdc (V) from the charging member to the photoconductor, and the peak-to-peak voltage of the alternating voltage Vac (V) is applied. Vpp (V) is given by the following equation (2)

[0049]

(Equation 3) And the relationship between the applied DC voltage Vdc (V) and the photoconductor dark potential Vd (V) is expressed by the following equations (3) and (4): | Vdc−Vd | ≦ 200 (V) 3) | Vd |> | Vpp / 2 | + | Vdc | − | Vth | (1) to (5), which satisfy Expression (4). Image forming device.

<Operation> 1) As described above, in the case where the contact charging of the image bearing member is of the charge injection charging type in the image forming apparatus having no cleaning means in front of the charging means, contact with the image bearing member is performed. Since the voltage Vdc applied from the charged charging member (charging member) to the image carrier and the image carrier dark potential Vd are substantially the same, the transfer residual toner and the like adhering to the charging member are charged without being removed. As the charge accumulates on the member and the charged member becomes excessively contaminated with transfer residual toner and the like, the chargeability deteriorates.

2) However, even in the case of the charge injection charging system,
When a voltage is applied to the charging member by separating the charging member from the image carrier, a potential difference is generated between the charging member and the image carrier, and toner or the like adhering to and entering the charging member is electrically transferred to the image carrier side. It moves and is easily removed from the charging member.

3) Therefore, the present invention is directed to a case in which the image forming apparatus having no cleaning means in front of the charging means performs the contact charging of the image carrier by the charge injection charging method, the pre-rotation in the operation process of the image forming apparatus. During at least a part of a non-image forming process such as a process or a post-rotation process, the charging member is kept in a non-contact state with the image carrier while the voltage is applied. As a result, a potential difference is generated between the charging member and the image carrier as described in the above item 2), so that transfer residual toner and the like adhering to and mixing with the charging member are transferred to the image carrier side. It transfers electrically and is easily removed from the charging member.

The transfer residual toner and the like transferred from the charging member side to the image carrier side are removed and collected from the image carrier surface by the cleaning and developing means after charging by the simultaneous cleaning principle of development.

The charging member is brought into non-contact with the image carrier during at least a part of a non-image forming process such as a pre-rotation process or a post-rotation process in the operation of the image forming apparatus. During the forming process, the image forming is performed without any trouble by holding the charging member in a predetermined contact state with the image carrier and performing the charging process of the image carrier.

4) Therefore, in an image forming apparatus having no cleaning means in front of the charging means, even if the contact charging means of the charge injection charging system is adopted as the charging means for the image carrier, the image forming apparatus can be used. During at least a part of a non-image forming process such as a pre-rotation process and a post-rotation process in the operation process, the charging member is kept in a non-contact state with the image carrier while the voltage is applied while the voltage is being applied. The transfer residual toner and the like adhering to and mixed into the image bearing member can be electrically transferred to the image carrier side, and can be easily removed from the charging member, and the accumulation on the charging member can be prevented.

Accordingly, in an image forming apparatus having no cleaning means in front of the charging means, the contact charging means of the charge injection charging system as the charging means for the image carrier can be protected from excessive contamination due to transfer residual toner of the charging member. It can be used without any problem without the problem of the deterioration of the charging property caused by it.

[0057]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of the present example includes a transfer type electrophotographic process,
This is a cleaning-less laser beam printer in which a developing unit also functions as a charge injection contact charging system, a reversal developing system, and a cleaning unit.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier. Drum base 1 as conductive support
The photosensitive layer 11 is formed on the outer peripheral surface of the lens 0 and is driven to rotate at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow a around a support shaft. The photoreceptor 1 of this embodiment is a charge-injection chargeable / negatively chargeable photoreceptor. The layer configuration of the photoconductor 1 will be described in detail in section (3).

Reference numeral 2 denotes a charging member as a charging member for the photoreceptor 1. In this embodiment, a sleeve rotating type magnetic brush member (magnetic brush charger) is used. S1 is a magnetic brush member 2
Is a charging bias application power supply. In the case of this embodiment, the peripheral surface of the rotary photoreceptor 1 is substantially
Contact charging is uniformly performed at 700 V by a charge injection charging method. The magnetic brush member 2 will be described in detail in section (4).

Numeral 3 is a position changing means for the magnetic brush member 2, which changes and maintains a first state in which the photosensitive member 1 is brought into predetermined contact with the photosensitive member 1 and a second state in which it is not in contact with the photosensitive member 1. For example, an elevating mechanism including an electromagnetic solenoid or the like for swinging the magnetic brush member 2 in the direction of coming and going with respect to the photoconductor 1 can be used.

Reference numeral 4 denotes a laser scanner as image exposure means, which is a laser beam modulated according to a time-series electric digital pixel signal of target image information input from a host device such as a computer, image reader, or word processor (not shown). L is output to scan and expose the uniformly charged surface of the rotary photoreceptor 1. As a result, an electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed on the surface of the rotating photoconductor 1. That is, the potential of the exposed portion irradiated with the laser beam drops on the surface of the rotating photoconductor 1 (bright portion potential), and corresponds to the exposure pattern by the contrast with the potential of the non-exposed portion not irradiated (dark portion potential). The formed electrostatic latent image is formed.

A developing device 5 develops the electrostatic latent image formed on the photosensitive member 1 as a toner image. This embodiment is a reversal developing device, which uses toner having the same polarity (negative in this embodiment) as the charging polarity of the photoconductor 1 and irradiates a laser beam of an electrostatic latent image formed on the surface of the rotating photoconductor 1 with the toner. Exposed part (bright part potential part)
And develops the electrostatic latent image as a toner image. Reference numeral 5a denotes a developing sleeve as a developer-carrying / transporting member which is driven to rotate in a counterclockwise direction indicated by an arrow, 5b denotes a fixed (non-rotating) magnet roller inserted and arranged in the developing sleeve, and T denotes two or one component. It is a magnetic developer. A developer layer is formed and held on the peripheral surface of the developing sleeve 5a by the magnetic force of the magnet roller 5b, and is conveyed to the developing section which is a part facing the photoconductor 1 by the rotation of the developing sleeve 5a. A predetermined developing bias is applied to the developing sleeve 5a from the power supply S2. As a result, the electrostatic latent image on the surface of the photoconductor 1 is reversely developed as a toner image by a contact developing method or a non-contact developing method.

In general, when an AC voltage is applied to the developing bias, the developing efficiency is increased, and the quality of the image becomes high, but fogging is liable to occur. Therefore, fog is usually prevented by providing a potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor 1. More specifically, a bias voltage having a potential between the potential of the exposed portion of the photoconductor 1 and the potential of the non-exposed portion is applied. The potential difference for preventing fogging is called a fogging potential (Vback). This potential difference prevents toner from adhering to a non-image area (non-exposed portion) on the surface of the photoconductor 1 during reversal development of the surface of the photoconductor 1. In addition, the cleaning-less image forming apparatus also collects the transfer residual toner on the surface of the photoconductor 1 (simultaneous cleaning with development).

Reference numeral 6 denotes a transfer roller having a resistance value adjusted as transfer means. A transfer material P such as paper is fed at a predetermined control timing from a paper feed unit (not shown) to a transfer nip portion, which is a pressure contact portion between the rotating photoreceptor 1 and the transfer roller 6, and is nipped and conveyed by the transfer nip portion. To go. While the transfer target material P is nipped and conveyed through the transfer nip portion, a predetermined transfer bias having a polarity opposite to that of the toner (positive in this example) is applied to the transfer roller 6 from the power source S3. Then, the toner image on the surface of the rotating photoconductor 1 is sequentially electrostatically transferred to the surface of the transfer material P.

The transfer material P to which the toner image has been transferred through the transfer nip portion is sequentially separated from the surface of the rotating photoreceptor 1 and is conveyed and introduced to the fixing device 7, where the toner image is heated and pressure-fixed and copied. Or it is discharged as a print.

The printer of this embodiment is cleaningless, and is disposed between the transfer means 6 and the charging means 2 to remove transfer residual toner from the surface of the photoconductor 1 after the transfer of the toner image onto the transfer material P. The exclusive cleaning device is omitted, and the transfer residual toner is collected by the developing unit 5 by the simultaneous cleaning with development.

If residual charge remains on the photoreceptor, it is better to remove the charge. Reference numeral 8 denotes an eraser lamp as a pre-exposure means provided for the purpose, and removes residual charges of the photoconductor by exposing the entire surface of the photoconductor 1 between the transfer means 6 and the charging means 2.

(2) Control of Contact and Separation of the Magnetic Brush Member 2 with respect to the Photoconductor 1 In the printer of this embodiment, the control circuit controls the pre-rotation process and / or the post-rotation process in the operation process of the printer shown in FIG. A first position changing means 3 for bringing the magnetic brush member 2 into contact with the photoreceptor 1 in a predetermined manner;
By changing the state from the state to the non-contact second state and holding the same, the transfer residual toner or the like adhering to and mixing with the magnetic brush member 2 is transferred to the photoconductor 1 and removed.

The operation of the printer shown in FIG. 2 is as follows.

A) Pre-multi-rotation process When the main power switch of the printer is turned on, the main motor of the printer is driven to rotate the photoreceptor, and the heater of the fixing device is energized to start up the heating process. This is a start-up (start-up) operation period (warming period) of the printer for performing the preparation operation of the device.

When the temperature of the fixing device rises to a predetermined temperature at which the toner image can be fixed, the driving of the main motor is temporarily stopped, the rotation of the photosensitive member 1 is stopped, and the printer receives a print start signal. Until the standby state is maintained. During this time, the temperature of the fixing device is adjusted to a predetermined temperature.

B) Pre-rotation process This is a period during which the main motor is driven again by the input of a print (print) start signal to drive the photoreceptor 1 to rotate again, and the printer executes a predetermined pre-print operation for a while.

C) Printing Process (Image Forming Process) When a predetermined pre-rotation process is completed, a printing process (image forming process, image forming process) of a predetermined sequence of charging, image exposure, development, transfer and the like for the rotating photosensitive member is subsequently performed. )
Is performed, and the printing process for the first sheet is performed.

In the case of the continuous printing (continuous printing) mode, the material to be transferred is continuously fed to the transfer nip portion, and the printing process for a predetermined number n is sequentially performed.

D) Paper-to-paper stroke In the continuous printing mode, the transfer is performed between the time when the rear end of one transfer material passes through the transfer nip portion and the time when the front end of the next transfer material reaches the transfer nip portion. This is a non-sheet passing state period of the transfer target material in the nip portion.

E) Post-rotation process The main motor continues to be driven for a while after the end of the last n-th printing process to rotate the photosensitive member 1 to execute a predetermined post-operation of the printer. Period.

When the predetermined post-rotation process is completed, the drive of the main motor is stopped and the rotation drive of the photosensitive member 1 is stopped.
The printer is kept in the standby state again until the next print start signal is input.

In the above, if a print start signal is input immediately after the previous multi-rotation process, the printing process is subsequently performed through the previous rotation process. In the case of printing only one sheet, the printing process is completed and the printer enters a standby state after a post-rotation process.

As described above, in the image forming apparatus of the cleaningless type, when the contact charging means is adopted as the charging means of the image carrier, the charging member is an image on which the transfer residual toner, the developer external additive and the like are placed. When the charging member comes into contact with the surface of the carrier, the charging member is contaminated by the adhesion of the transfer residual toner and the like. When the contact charging of the image carrier is a system in which the charging due to the discharge phenomenon is dominant, the potential difference between the voltage Vdc applied from the charging member to the image carrier and the image carrier dark potential Vd is large, Even if transfer residual toner adheres to the charging member,
The untransferred residual toner and the like are easily detached electrically from the charging member side to the image carrier side, re-transferred, and removed from the charging member side. The untransferred toner and the like retransferred to the image carrier side are removed and collected from the image carrier surface by the developing simultaneous cleaning principle in the developing unit. Therefore, it is naturally prevented that the charging member is excessively contaminated with the transfer residual toner or the like, thereby deteriorating the charging property. However, the contact charging of the image carrier is directly injected into the surface of the image carrier. In the case where the charging is dominant, that is, in the case of the charge injection charging system, the voltage Vdc applied from the charging member to the image carrier is substantially the same as the image carrier dark potential Vd. Adhered transfer residual toner and the like are not removed as in the case described above, but accumulate on the charging member, and the charging member is excessively contaminated with the transfer residual toner and the like, so that the chargeability is deteriorated.

However, even in the case of the charge injection charging method, when the charging member is separated from the image carrier and a voltage is applied to the charging member, a potential difference is generated between the charging member and the image carrier, causing the charging member to adhere to the charging member. The mixed toner and the like are electrically transferred to the image carrier side and are easily removed from the charging member.

Therefore, in the printer of this embodiment, a voltage is applied to the magnetic brush member 2 as a charging member during at least a part of a non-image forming process such as a pre-rotation process or a post-rotation process in the operation process of the printer. In this case, a potential difference is generated between the magnetic brush member 2 and the photosensitive member 1 even in the case of the charge injection charging method, so that the magnetic brush member 2 The transfer residual toner and the like adhering and mixing are electrically transferred to the photoconductor 1 side and easily removed from the magnetic brush member 2. The untransferred toner and the like transferred from the magnetic brush member 2 side to the photoconductor 1 side are removed and collected from the surface of the photoconductor 1 in the developing device 4 by the principle of simultaneous cleaning with development.

Therefore, in an image forming apparatus having no cleaning means in front of the charging means, even if the contact charging means of the charge injection charging system is adopted as the charging means for the image carrier, the image forming apparatus is not provided with a cleaning means. At least a part of the non-image forming process such as the rotation process and the post-rotation process, the charging member is kept in a non-contact state with the image carrier while the voltage is applied, so that the charging member adheres to and mixes with the charging member. The transfer residual toner and the like can be easily transferred from the charging member by electrically transferring the transfer residual toner to the image bearing member side, and the accumulation on the charging member can be prevented. The problem of deterioration is eliminated.

(3) Photoreceptor 1 The photosensitive layer 11 of the photoreceptor 1 has a single layer or a laminated structure.

In the case of a single-layer structure, generation and movement of photocarriers are performed in the same layer.

In the case of a stacked structure, a charge generation layer for generating photocarriers and a charge transport layer for moving carriers are stacked.

The thickness of the single-layer photosensitive layer is 5 to 1
00 μm is preferable, and 10 to 60 μm is more preferable.
The content of the charge generation material and the charge transport material is preferably from 20 to 80% by weight, more preferably from 30 to 70% by weight.

In the laminated photosensitive layer, the thickness of the charge generation layer is preferably 5 μm or less, more preferably 0.01 to 1 μm. The content of the charge generating material is preferably from 10 to 100% by weight, more preferably from 40 to 100% by weight. The thickness of the charge transport layer is preferably 5 to 100 μm,
μm is more preferred. The content of the charge transporting material is 20 to 8
0% by weight is preferable, and 30 to 70% by weight is more preferable.

FIGS. 3A to 3D show the photosensitive member 1 respectively.
FIG. 4 is a model diagram of a layer configuration example of FIG.

(A); photosensitive layer 11 on conductive support 10
The photosensitive layer 11 has a charge generation layer 1 in which a charge generation material (not shown) is dispersed and contained in a binder resin.
3 and a charge transport layer 14 containing a charge transport material (not shown). In this case, the charge transport layer 14
It is stacked on the charge generation layer 13.

(B): In this photosensitive member 1, unlike the case of (a), the charge transport layer 14 is laminated below the charge generation layer 13. In this case, the charge generation layer 13 may contain a charge transport material.

(C): Photosensitive layer 11 on conductive support 10
The photosensitive layer 11 contains a charge generation material and a charge transport material in a binder resin.

(D) Photosensitive layer 11 of photoreceptor 1 of (a)
(Or (b) or (c) of the photosensitive layer 11 of the photoreceptor 1) on which an overcoat layer 15 is further applied and formed. According to the study of the present inventors, it was possible to greatly improve the direct injection of charges by dispersing the conductive particles in the resin in the overcoat layer 15.

As the conductive support 10, a support having conductivity itself, for example, aluminum, aluminum alloy, stainless steel, etc. can be used. In addition, aluminum, aluminum alloy, indium oxide-tin oxide alloy and the like can be used. A conductive support or plastic having a layer formed by vacuum deposition, a support in which conductive fine particles (for example, carbon black, tin oxide, titanium oxide, silver particles, etc.) are impregnated with a suitable binder into plastic or paper, Plastic having a conductive binder or the like can be used.

An undercoat layer (adhesive layer) having a barrier function and an adhesive function is provided between the conductive support 10 and the photosensitive layer 11.
Can be provided. This undercoat layer improves the adhesion of the photosensitive layer, improves the coating properties, protects the support, covers defects of the support,
It is formed for the purpose of improving the charge injection property from the support and protecting the photosensitive layer against electrical breakdown. The undercoat layer can be formed of casein, polyvinyl alcohol, ethyl cellulose, ethylene-acrylic acid copolymer, polyamide, modified polyamide, polyurethane, gelatin, aluminum oxide, or the like. The thickness of the undercoat layer is preferably 5 μm or less, more preferably 0.2 to 3 μm.

Examples of the charge generating substance include phthalocyanine pigments, azo pigments, indigo pigments, polycyclic quinone pigments, perylene pigments, quinacridone pigments, azurenium salt pigments, pyrylium dyes, thiopyrylium dyes, squarylium dyes, cyanine dyes, xanthene dyes, and quinone imine dyes. , Triphenylmethane dye, styryl dye, selenium,
Selenium-tellurium, amorphous silicon, cadmium sulfide, zinc oxide and the like can be mentioned.

The solvent used for the coating for the charge generating layer is selected from the solubility and dispersion stability of the resin and the charge generating material used. Examples of the organic solvent include alcohols, sulfoxides, ketones, ethers and esters. And aliphatic halogenated hydrocarbons or aromatic compounds.

As the charge transport material, hydrazone compounds, pyrazoline compounds, styryl compounds, oxazole compounds, thiazole compounds, triarylmethane compounds, polyarylalkane compounds and the like can be used.

The charge generation layer 13 is formed by adding the above-mentioned charge generation substance to a binder resin and a solvent in an amount of 0.3 to 4 times as much as a homogenizer, an ultrasonic wave, a ball mill, a vibration ball mill, a sand mill, an attritor, a roll mill, or the like. It is formed by well dispersing, applying and drying by a method. Its thickness is 5μ
m or less, particularly preferably in the range of 0.01 to 1 μm.

The charge transport layer 14 is generally formed by dissolving the above-described charge transport material and binder resin in a solvent and applying the solution. The mixing ratio of the charge transport material and the binder resin is 2: 1 to 1
It is about 1: 2. Examples of the solvent include ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, and chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride. . When applying this solution, for example, a dip coating method, a spray coating method, a coating method such as a spinner coating method can be used, and drying is performed at 10 ° C to 200 ° C.
Preferably at a temperature in the range of 20C to 150C for 5 minutes to 5 minutes.
The drying can be carried out for a period of time, preferably 10 minutes to 2 hours, under blast drying or still drying.

As the binder resin used to form the charge transport layer 14, an acrylic resin, a styrene resin,
A resin selected from polyester, polycarbonate resin, polyarylate, polysulfone, polyphenylene oxide, epoxy resin, polyurethane resin, alkyd resin, unsaturated resin, and the like is preferable. Particularly preferred resins include polymethyl methacrylate, polystyrene,
Examples include a styrene-acrylonitrile copolymer, a polycarbonate resin, and a diallyl phthalate resin.

The charge generation layer or the charge transport layer may contain various additives such as an antioxidant, an ultraviolet absorber and a lubricant. Further, on the photosensitive layer,
Further, an overcoat layer 15 can be applied as a protective layer.

As the overcoat layer 15, a medium resistance layer is preferably used. 1 × 10 ¹⁰ ~
1 × 10 ¹⁵ (Ω · cm), preferably 1 × 10 ¹¹
The volume resistance is about 5 × 10 ¹³ (Ω · cm). As a method of controlling the resistance to a medium resistance, there is a method of dispersing conductive particles in a binder, a method of using a binder having a medium resistance, and the like.

Here, a system in which conductive particles are dispersed in a binder will be described. As the conductive particles, ultrafine particles such as zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin-doped indium oxide, antimony and tantalum-doped tin oxide, and zirconium oxide may be used. it can. These metal oxides are used alone or in combination of two or more. When two or more kinds are mixed, they may be in the form of solid solution or fusion. Further, as the resin for the surface layer, commercially available polyester, polycarbonate, polyurethane, acrylic, epoxy, silicone, alkyd, vinyl chloride-vinyl acetate copolymer and the like can also be used. Investigations were made to further improve the intensity distribution and dispersibility. As a result, the conductive particles were dispersed in a photocurable acrylic monomer having two or more acryloyl groups in one molecule. By using the surface layer 15 formed by coating and photo-curing on the photosensitive layer 11,
Both the film strength and the dispersibility of the conductive particles can be dramatically improved.

(4) Charging Member a) Magnetic Brush Member 2 FIG. 4 is a schematic diagram of the configuration of the magnetic brush member 2 (magnetic brush charger) as a charging member. This embodiment is a sleeve rotating type.

The magnetic brush member 2 is fixed (non-rotating)
And a non-magnetic conductive sleeve 2b made of aluminum or the like, which is rotatably and concentrically fitted to the outer periphery of the magnet roll 2a, and is attached and held in a brush shape on the outer peripheral surface of the sleeve by the magnetic force of the magnet roll 3a inside the sleeve. The magnetic brush layer 2c is made of a magnetic carrier (magnetic particles) for charging such as Zn-Cu ferrite.

The magnetic brush member 2 is brought into contact with the photoreceptor 1 in a first state in which the magnetic brush layer 2c is in contact with the surface of the photoreceptor 1 by forming a charging nip portion N having a predetermined width, and in a non-contact state. It is arranged so that it can be switched between two states. Magnetic brush member 2
The switching between the first state and the second state is performed by switching means 3 controlled by a control circuit (not shown). The conversion means 3 can be appropriately configured, for example, such as a lifting / lowering mechanism including an electromagnetic solenoid or the like, which swings the magnetic brush member 2 toward and away from the photoconductor 1.

A predetermined charging bias is applied to the non-magnetic conductive sleeve 2b from the power supply S1, and the sleeve 2b is driven to rotate clockwise as indicated by an arrow b by driving means (not shown).

In the first state where the magnetic brush member 2 is in predetermined contact with the photosensitive member 1, the non-magnetic conductive sleeve 2
b, a predetermined charging bias is applied from a power source S1 and the surface of the rotating photosensitive member 1 is charged at a charging nip N
Is rubbed by the magnetic brush layer 2c and charged to a predetermined polarity / potential for contact charging.

In the printer according to the present embodiment, as described above, during the pre-rotation process or / and
And during the post-rotation process, the magnetic brush member 2 is switched to the non-contact second state with the photoreceptor 1 to be held.
The transfer residual toner and the like adhering to and mixing with the magnetic brush member are transferred to the photoconductor 1 and removed therefrom.

B) Fur brush member 2A The charging member may be a fur brush member (fur brush charger). FIG. 5 is a structural model diagram of an example of the fur brush member 2A. The fur brush member 2A of this example is
The fur brush layer 2e subjected to the conductive treatment is wound or adhered to a metal or other conductive core 2d.

As the material of the fur brush layer 2e, carbon, copper sulfide, a metal, a polymer which is conductively treated with a metal oxide, or the like is used. Rayon, acrylic, polypropylene, PET, polyethylene, or the like is used as the material of the polymer.

The fur brush member 2A is in contact with the photoreceptor 1 in the first state in which the fur brush layer 2e is in contact with the surface of the photoreceptor 1 by forming a charging nip portion N having a predetermined width, and in the non-contact state. It is arranged so that it can be switched between two states. The switching and holding of the fur brush member 2A between the first state and the second state are performed by the switching means 3 controlled by a control circuit (not shown), as in the case of the magnetic brush member 2 described above.

A predetermined charging bias is applied to the metal core 2d from the power supply S1, and the core metal 2d is driven to rotate clockwise as indicated by an arrow b by a driving means (not shown).

In the first state in which the fur brush member 2A is in predetermined contact with the photosensitive member 1, the power supply S is applied to the cored bar 2d.
A predetermined charging bias is applied from 1 and the surface of the rotating photoreceptor 1 is rubbed by the fur brush layer 2e in the charging nip portion N by the rotation and driven to be charged and contact-charged to a predetermined polarity and potential.

In the case of the fur brush member 2A, similarly to the case of the magnetic brush member 2, the fur brush member 2A is attached to the photosensitive member 1 during the pre-rotation process and / or the post-rotation process in the printer operation process. By transferring and holding the non-contact second state, the transfer residual toner and the like adhering to and entering the fur brush member is transferred to the photoconductor 1 and removed.

(5) Examples and Comparative Examples a) Photoreceptor 1 used An aluminum cylinder of φ30 mm × 260.5 mm was used as a support 10, and a polyamide resin (trade name: Amilan CM8000, manufactured by Toray Co., Ltd.) was placed on the aluminum cylinder 5 wt. % Methanol solution was applied by a dipping method to provide a 0.5 μm undercoat layer.

Next, in the following structural formula, the diffraction angle 2θ ± 0.2 ° in the X-ray diffraction spectrum of CuKα is 9.0, 1
Strong peaks at 4.2, 23.9, 27.1 °

[0118]

Embedded image 4 parts (parts by weight, the same applies hereinafter) of titanyl oxophthalocyanine pigment, 2 parts of polyvinyl butyral resin BX-1 (manufactured by Sekisui Chemical Co., Ltd.), and 80 parts of cyclohexanone were added to φ
The mixture was dispersed for 4 hours by a sand mill using 1 mm glass beads. Ethyl acetate (100 parts) was added to this dispersion and applied onto the undercoat layer to form a charge generation layer.

Next, the following structural formula

[0120]

Embedded image Was dissolved in 100 parts of monochlorobenzene. 10 parts of the compound of formula (I) and 10 parts of bisphenol Z-type polycarbonate (trade name: Z-200, manufactured by Mitsubishi Gas Chemical) were dissolved. This solution was applied on the charge generation layer and dried with hot air at 105 ° C. for 1 hour to form a 20 μm charge transport layer.

As the overcoat layer, the following structural formula

[0122]

Embedded image Antimony-doped tin oxide ultrafine particles 5 (25 parts) of which was surface-treated (treatment amount 7%) by the following structural formula
0 copies,

[0123]

Embedded image Ethanol (150 parts) was dispersed in a sand mill for 66 hours. Further, 20 parts of polytetrafluoroethylene fine particles (average particle size: 0.18 μm) were added and dispersed. Thereafter, 2-methylthioxanthone 3 was used as a photopolymerization initiator.
Parts, 9 parts of a photopolymerization initiation aid represented by the following structural formula was dissolved to prepare a preparation liquid.

[0124]

Embedded image Using this prepared solution, a film is formed on the charge transport layer by a dip coating method, photocured for 60 seconds at a light intensity of 160 W / cm ² with a high pressure mercury lamp, and then dried with hot air at 120 ° C. for 2 hours. To obtain a surface layer.

At this time, the thickness of the obtained surface layer was 3 μm. In addition, the dispersibility of the surface layer preparation liquid was good, and the surface layer surface was a uniform surface without unevenness.

B) Charging member used Magnetic Brush Member 2 The sleeve rotating type magnetic brush member 2 shown in FIG.

As the magnetic particles, Zn having an average particle size of 25 μm was used.
-Cu ferrite particles and Zn-Cu with an average particle size of 10 µm
Ferrite particles are mixed at a weight ratio of 1: 0.05, and an average particle size of 25 μm having a peak at each average particle size position
The magnetic particles obtained by coating the ferrite particles with a medium resistance resin layer were used.

The coated magnetic particles were coated on the sleeve 2b to a thickness of 1 mm to form and hold the magnetic brush layer 2c.

The first state of the magnetic brush member 2 is to maintain the gap between the sleeve 2b and the photosensitive member 1 at about 500 μm, thereby forming the charging nip portion N having a width of about 5 mm on the magnetic brush layer 2c to form the photosensitive member. It was in a state of contacting one surface.

In the second state, the gap between the sleeve 2b and the photosensitive member 1 is maintained at about 1 mm, so that the magnetic brush layer 2
c was floated substantially from the surface of the photoreceptor 1 to be in a non-contact state.

The sleeve 2b is rotated so that the surface of the sleeve moves in the opposite direction at the charging nip N at twice the peripheral speed of the surface of the photosensitive member, so that the photosensitive member 1 and the magnetic brush layer 2c are uniformly formed. Contact was made.

The resistance of the magnetic brush member 2 was 5 × 10 ⁵ (Ω) from the current value when an aluminum cylinder was brought into contact with the photosensitive member 1 and 100 V was applied.

[0133] Fur brush member 2A The fur brush member 2A of FIG. 5 described above. As a material of fur brush, conductive rayon fiber REC manufactured by Unitika Ltd.
-C was used.

C) An LBP-NX (laser beam printer) manufactured by Canon Inc. was modified to use the photoconductor of the above item a) as a photoconductor, and the magnetic brush member 2 or fur brush member of the above b) as a charging member. 2A is used to form a charge injection contact charging system and a cleaning-free laser beam printer. According to the present invention, the charging member 2 or 2A is connected to the photosensitive member 1 during the pre-rotation process and / or the post-rotation process in the printer operation process. The contact state is changed to the non-contact second state,
The initial state of the photoconductor potential and the state after printing 10,000 sheets (10K) were measured when printing was performed by transferring the transfer residual toner and the like to the photoconductor 1 and removing it (Example 1). 9).

As a comparative example, the charging member 2 or 2A
The initial state of the photoconductor potential and the state after printing 10,000 sheets (10K) were measured when the first state was kept in contact with the photoconductor 1 (Comparative Examples 1 to 3).

The results are shown in Table 1. As is evident from the results in Table 1, in Examples 1 to 9 according to the present invention, the photoconductor potential after printing 10,000 sheets is maintained at substantially the same potential as at the initial stage, and there is no deterioration in chargeability. This is because even in the case where the contactless charging means of the charge injection charging method is adopted as the charging means of the image bearing member in the image forming apparatus of the cleaningless system, the charging operation is performed during the pre-rotation process or the post-rotation process in the operation process of the device. During at least a part of the non-image forming process, such as during the non-image forming process, the charging member is kept in a non-contact state with the image carrier while the voltage is applied, so that the charging member adheres to the charging member.
The mixed transfer residual toner and the like can be electrically transferred to the image carrier side and easily removed from the charging member to prevent accumulation on the charging member, and the charging property caused by excessive contamination of the charging member by the transfer residual toner and the like. This is because the deterioration of the situation has been resolved.

On the other hand, in each of Comparative Examples 1 to 3, the photoconductor potential after printing 10,000 sheets is much worse than in the initial stage. This is because the transfer residual toner and the like cannot be easily removed from the charging member and accumulates on the charging member, so that the charging member is excessively contaminated with the transfer residual toner and the like.

[0138]

[Table 1] (6) Others 1) The image exposure means as information writing means on the charged surface of the image carrier is not limited to the laser scanning exposure means for forming a digital latent image as shown in the embodiment. An analog image exposure means using a halogen lamp, a fluorescent lamp, or the like as a light source may be used, another light emitting element such as an LED array may be used, or a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used. Any device can be used as long as it can form an electrostatic latent image corresponding to image information.

2) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly primary charged, the charged surface is selectively neutralized by a neutralization means such as a static elimination needle head or an electron gun to write and form an electrostatic latent image corresponding to the target image information. I do.

3) The method and means for developing the electrostatic latent image with toner are arbitrary. A reversal development system or a normal development system may be used.

4) Magnetic brush member 2 as charging member
Is not limited to the sleeve rotating type of the embodiment, but may be a type in which the magnet roll 2a rotates,
The surface of a is subjected to a conductive treatment as a power supply electrode, if necessary, and further a resistive layer is applied, and magnetic particles are directly magnetically constrained on the outer peripheral surface of the magnet roll 2a to form and hold a magnetic brush layer 2c. In this case, the magnet roll 2a may be rotated. A non-rotating type magnetic brush member may be used.

The fur brush member 2A can also be of a type that does not rotate.

As the charging member, in addition to the magnetic brush member 2 and the fur brush member 2A, an arbitrary member such as a roller or a plate made of a conductive elastic member is selectively used according to the specifications and the form of the image forming apparatus. It is possible.

5) The transfer means is not limited to the roller transfer of the embodiment, but may be any transfer means such as blade transfer or corona discharge transfer. Further, the present invention can be applied not only to single-color image formation but also to an image forming apparatus for forming a multi-color or full-color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt.

6) The image forming process of the image forming apparatus is not limited to that of the embodiment but may be arbitrary. Further, other auxiliary process equipment may be added as needed.

It is also possible to use a process cartridge detachable type in which any process equipment such as the image carrier 1, the charging member 2, the developing device 4 and the like can be collectively attached to and detached from the image forming apparatus main body.

7) In the AC superposition method in which the AC voltage Vac is superimposed on the DC voltage Vac on the charging member, the AC voltage Va
As the waveform c, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. The AC voltage may be, for example, a rectangular wave formed by periodically turning on and off a DC power supply. As described above, a bias whose voltage value periodically changes can be used as the AC voltage.

8) In the printer operation process shown in FIG.
The non-image formation is also performed during the pre-multi-rotation process and the sheet interval. Also in this case, the charging member is held in the second state in which the charging member is not in contact with the image carrier, and the toner attached and mixed on the charging member side is transferred to the image carrier side. Then, it can be collected by the developing means.

The noncontact second contact of the charging member with the image carrier
The state is such that the charging member is completely separated from the image carrier, and even if the charging member is not completely separated, a potential difference is generated between the charging member and the toner adhering to the charging member to the image carrier. This includes the state in which

[0150]

As described above, according to the present invention, in the image forming apparatus of the cleaningless system, the contact charging unit of the charge injection charging system is used as the charging unit of the image carrier by the transfer residual toner of the charging member. An image forming apparatus which can be used without any problem without deterioration of charging property due to excessive contamination and which can stably maintain high image quality for a long period of time can be configured.

[Brief description of the drawings]

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

FIG. 2 is an operation process of the image forming apparatus.

FIGS. 3A to 3D are model diagrams each showing a layer configuration example of a photoreceptor;

FIG. 4 is a schematic diagram of a configuration of an example of a magnetic brush member as a charging member.

FIG. 5 is a structural model diagram of an example of a fur brush member as a charging member.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image carrier (electrophotographic photoreceptor) 2.2 A charging member (magnetic brush member / fur brush member) 3 charging member position changing unit 4 image exposure unit (laser beam scanner) 5 developing unit (reversal developing device) 6 transfer Means (transfer roller) 7 Fixing means 8 Pre-exposure means S1 to S3 Bias application power supply 10 Conductive support 11 Photosensitive layer 13 Charge generation layer 14 Charge transport layer 15 Overcoat layer

Claims (7)

[Claims] 1. A rotating image carrier, a charging device for charging the image carrier, a latent image forming device for selectively removing a charged surface of the image carrier to form an electrostatic latent image, and the electrostatic latent image Developing means for developing the image as a toner image, transfer means for transferring the toner image to a transfer material, and toner particles remaining on the image carrier after the toner image on the image carrier is transferred to the transfer material by the transfer means An image forming apparatus having no cleaning means in front of the charging means, wherein the charging means is a contact charging means having a charging member to which an image carrier is contacted and to which a voltage is applied; In the image forming apparatus, the charging of the body is performed by a charging system in which charge injection charging in which charge is directly injected from the charging member to the image carrier is dominant, wherein the charging member is brought into contact with the image carrier. In the first state and the second state, which is non-contact The charging member is held in a second state in which the charging member is not in contact with the image carrier during at least a part of a non-image forming process in an operation process of the image forming apparatus. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the charging member is not in contact with the image carrier during a pre-rotation process, a non-image formation process, a post-rotation process, or during the pre-rotation process and the post-rotation process. The image forming apparatus according to claim 1, wherein the image forming apparatus is held in the second state. 3. The image forming apparatus according to claim 1, wherein the latent image forming means for selectively removing the charge on the charged surface of the image carrier to form an electrostatic latent image is an image exposing means. apparatus. 4. The developing means is of a reversal developing type for developing an electrostatic latent image with a toner having a charge having the same polarity as a normal charge polarity for forming an electrostatic latent image on an image carrier. The image forming apparatus according to claim 1, wherein: 5. The image forming apparatus according to claim 4, wherein a bias having a potential between a dark portion potential and a bright portion potential of the electrostatic latent image on the image carrier is applied to the developer carrying conveyance member of the developing means. Image forming device. 6. A DC voltage Vd from a charging member to an image carrier.
The surface of the image carrier is charged by applying only c (V), and the relationship between the DC voltage Vdc (V) applied from the charging member to the image carrier and the dark potential Vd (V) of the image carrier is obtained. The image forming apparatus according to claim 1, wherein the following formula (1) is satisfied: | Vdc−Vd | ≦ 200 (V) (1) 7. The image bearing member is an electrophotographic photosensitive member, and the charging member supplies the photosensitive member with a DC voltage Vdc (V) and an alternating voltage Vdc.
The surface of the photoreceptor is charged by applying a voltage on which ac (V) is superimposed, and the peak of the alternating voltage Vac (V)
The two-peak voltage Vpp (V) is calculated by the following equation (2). And the relationship between the applied DC voltage Vdc (V) and the photoconductor dark potential Vd (V) is expressed by the following equations (3) and (4): | Vdc−Vd | ≦ 200 (V) 3) | Vd |> | Vpp / 2 | + | Vdc | − | Vth | (4), wherein Expression (4) is satisfied. apparatus.