JP2003207999A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To construct a cleaner-less system having stable electrifying property even to equipment whose processing speed is about 200 mm/s without causing the rise of production cost in an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer in which the electrifying means for an image carrier is a contact injection electrifying means using conductive particles and which adopts the cleaner-less system. <P>SOLUTION: By recovering and discharging the excessively supplied conductive particles 40 to a transfer member 4 while maintaining electrification uniformity by functional separation type sequence such as the discharge of toner from an electrifying member 2, the supply of the particles 40 from a developing means 3 and the recovery of the particles 40 by the transfer member 4, the member 2 can carry the proper amount of particles 40 so as to improve a light shielding white spot caused by the accumulation of the excessive amount of particles 40. <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 such as an electrophotographic copying machine or an electrophotographic printer, in which the charging means of the image carrier is a contact injection charging means using conductive particles, and a cleanerless system. It relates to the device.

[0002]

2. Description of the Related Art FIG. 11 is a diagram schematically showing a generally known general laser beam printer.

Reference numeral 1 denotes a photosensitive drum which is an image bearing member, and is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow a.

Reference numeral 2 is a charging roller as a charging member.
The photosensitive drum 1 is arranged in pressure contact with the photosensitive drum 1, and is rotated by the rotation of the photosensitive drum 1. S1 is a contact portion (charging portion) between the charging roller 2 and the photosensitive drum 1.

By applying a predetermined charging bias voltage (for example, a DC voltage of about 1 to 2 kv or a superimposed voltage of a DC voltage and an AC voltage) from the power source 13 to the charging roller 2, the surface of the photosensitive drum 1 is applied. Are uniformly contact-charged to a predetermined polarity and potential.

The uniformly charged surface of the photosensitive drum 1 is an exposing means (laser scanner) 8 as an information writing means.
By the laser beam L1 emitted from a, the reflecting member 8
b, an electrostatic latent image is formed on the photosensitive drum 1 by being scanned and exposed through the exposure window 6a.

The electrostatic latent image is visualized as a toner image by the developing device 3. Reference numeral 3a is a non-magnetic developing sleeve as a developer carrying member, and 3c is a multi-pole magnet roller contained in the developing sleeve 3a. The developing sleeve 3a is disposed in the opening of the developing device 3 on the side of the photosensitive drum 1 and is driven to rotate in the counterclockwise direction indicated by the arrow. The magnet roller 3c is non-rotatably fixed. Reference numeral 7 denotes a developer container connected to the developing device 3, in which a magnetic toner is contained as the developer t, and the toner is sequentially supplied to the developing device 3. Reference numeral 10 denotes a developer stirring member arranged in the developer container 7. The toner in the developing device 3 is adhered and carried on the surface of the developing sleeve 3a and is conveyed by the rotation of the developing sleeve 3a. Three
A regulating blade b regulates the layer thickness of the toner on the developing sleeve 3a to a predetermined value and charges the toner properly. A predetermined developing bias voltage (for example, a superimposed voltage of a DC voltage and an AC voltage) is applied from the power source 11 to the developing sleeve 3a, and the developing sleeve 3a carries the developing sleeve 3a on the developing portion D, which is an opposing portion of the developing sleeve 3a and the photosensitive drum 1. The carried toner makes the electrostatic latent image on the photosensitive drum 1 visible.

The toner image formed on the photosensitive drum 1 is
Electrostatic transfer is sequentially performed on a transfer target member (transfer sheet) P conveyed from a sheet feeding section (not shown) at a predetermined control timing to a contact section (transfer section) T between the photosensitive drum 1 and the transfer roller 4. . A predetermined transfer bias voltage is applied to the transfer roller 4 from the power supply 12.

The member P to which the toner image has been transferred at the transfer portion T is separated from the surface of the photosensitive drum 1 and is fixed by the fixing means 9.
The sheet is conveyed to, is fixed with the toner image, and is ejected.

The surface of the photosensitive drum 1 after the transfer target member is separated is cleaned by the cleaning blade 5a of the cleaning device 5 to remove the transfer residual toner, and is repeatedly used for image formation. 5b is a squi sheet.

The printer of this embodiment is of a process cartridge mounting / demounting type, and includes a photosensitive drum 1, a charging roller 2, a developing device 3 including a developer container 7, and a cleaning device 5.
The process cartridges 15 are compact and unitized into one unit, which is a process cartridge 15 that can be freely attached and detached.

Further, in recent years, the cleaning device 5 has been developed to further reduce the size of the process cartridge 15.
There is also an image forming apparatus in which a "cleanerless system" is implemented in which the transfer residual toner is removed and the developing device 3 collects the residual toner at the same time.

This cleanerless system is effective not only in reducing the size of the process cartridge, but is also preferable in terms of environmental protection because it does not discharge waste toner.

In this case, there has been known an example in which a cleanerless system is established by so-called contact development using an elastic developing sleeve so as to collect the transfer residual toner while the elastic developing sleeve collects and develops the toner. .

In addition, conventionally, the contact charging mechanism (charging mechanism, charging principle) includes: Discharge charging mechanism,
． Two types of charging mechanism, a direct injection charging mechanism, are known, and each has its advantages and disadvantages.

.. Discharge Charging Mechanism This mechanism charges the surface of the body to be charged by a discharge phenomenon that occurs in the minute gap between the contact charging member and the body to be charged. Since the discharge charging mechanism has a constant discharge threshold 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, although the ozone generation amount is remarkably smaller than that of the corona charger, generation of discharge products is unavoidable in principle. Further, the generated discharge product and the substance in the transfer material act on each other, which may cause a problem of "image deletion" in which formation of a latent image is hindered.

.. Direct injection charging mechanism In this system, the surface of the body to be charged is charged by directly injecting charge from the contact charging member into the body to be charged. It is also called direct charging, injection charging, or charge injection charging. More specifically, a medium-resistance contact charging member comes into contact with the surface of the member to be charged and directly injects the charge into the surface of the member to be charged without a 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 charged body can be charged to a potential corresponding to the applied voltage.

If the direct injection charging mechanism is used as described above,
Since there is no generation of ions, there is a great advantage that no adverse effects are caused by the discharge products, and various applications have been filed.

For example, Japanese Patent Application Laid-Open No. 10-307454 proposes that conductive particles are interposed between the charging member and the photosensitive drum.

The conductive particles are conductive fine particles (charge promoting particles) for the purpose of assisting charging. For example, particle size 0.1-5
μm, volume resistance value of 1 × 10 ¹² Ω · cm or less, more preferably 1 × 10 ¹⁰ Ω · cm or less, metal oxide fine particles such as conductive zinc oxide, other conductive inorganic fine particles, a mixture with an organic substance, etc. Various conductive particles can be used.

In this proposal, as shown in FIG. 12, a supplying means 50 for the conductive particles 40 is provided upstream of the charging member 2 and the conductive particles 40 are supplied between the charging member 2 and the photosensitive drum 1 to directly charge the particles. The mechanism has been achieved.

Further, in JP-A-10-307455, conductive particles are contained in the developer, and the conductive particles supplied from the developing device to the photosensitive drum together with the toner are attached to the charging member to achieve the direct charging mechanism. There is.

At the same time, the above proposal achieves a cleanerless system by using a direct charging mechanism, which is effective for both environmental protection and miniaturization of the process cartridge.

In the cleanerless system, the positive toner and the positive external additive which are not negatively developed by the developing means, and the toner positively formed by the transfer means are adsorbed to the contact charging member to deteriorate the chargeability of the photosensitive drum. There was a problem of letting it.

To solve such a problem, Japanese Patent Laid-Open No. 9-325
According to Japanese Patent Laid-Open No. 607, a structure is provided in which a potential adjusting unit and a toner-disturbing rotating unit that comes into contact with the surface of the photosensitive member and rotates are disposed between the transfer unit and the charging unit, and the residual toner after transfer is stably collected at the time of development. Is proposed.

Further, in Japanese Patent Publication No. 63-43750, by applying a voltage having a polarity opposite to the charging polarity of the photoconductor to the charging device in the non-printing area, toner fragments having a polarity opposite to the charging polarity adhered to the charging device. It has been proposed to remove the like.

Further, in Japanese Patent Laid-Open No. 11-149205, in order to clean the transfer residual developer adhering to the surface of the contact charging member, a technique of applying a cleaning bias for cleaning the surface of the contact charging member during non-image formation. Is disclosed.

[0028]

However, in order to achieve direct injection charging by interposing conductive particles between the charging member and the photosensitive drum, another member is provided as in Japanese Patent Laid-Open No. 10-307454. In particular, further improvement is desired in terms of simplification of parts processing and manufacturing.

Further, as in Japanese Patent Laid-Open No. 10-307455, a system in which conductive particles are contained in a developer and the conductive particles are attached to a charging member together with toner from a developing device through a drum is simple. It is very preferable in that direct injection charging is achieved by the configuration. However, further improvement is desired in order to stably collect the residual toner on the photosensitive drum in the developing device and improve the completeness of the cleanerless system.

Further, as described above, in Japanese Patent Application Laid-Open No. 9-325607, which is an application for improving the charging property, the potential adjusting means is provided between the transfer means and the charging means, but the features of the cleanerless system are as follows. It is not preferable to provide a compact image forming apparatus having a simple configuration.

Further, as in Japanese Patent Publication No. 63-43750 and Japanese Unexamined Patent Publication No. 4-371972, it is an object to eject toner fragments of opposite polarity by controlling the voltage applied to the charging device in the non-printing area. Therefore, the same effect is exhibited with respect to an external additive having a reverse polarity contained in the developer.
However, as in Japanese Patent Laid-Open No. 10-307455, conductive particles are contained in the developer, and the conductive particles supplied from the developing device to the drum together with the toner are attached to the charging member to directly achieve the charging mechanism. In such a system, when the conductive particles have a polarity opposite to the charge polarity of the toner, it is difficult to maintain the chargeability by uniquely removing them, and further improvement is desired.

In Japanese Patent Laid-Open No. 11-149205, a cleaning bias in which an AC voltage for cleaning the surface of the charging member and a DC voltage are superimposed is applied during non-image formation, and the frequency of the AC voltage is 5 to 500 Hz. According to the technique disclosed in the above publication, cleaning unevenness occurs depending on the frequency of a device having a process speed of about 200 mm / s, and further improvement is desired with respect to a decrease in chargeability.

The present invention has been proposed in view of the above, and the charging means of the image carrier is a contact injection charging means using conductive particles, and a cleanerless system.
In an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, it is possible to construct a cleanerless system having stable chargeability even for a device having a process speed of about 200 mm / s without increasing the production cost. To aim.

[0034]

(1) First invention At least, an image carrier and an image carrier are formed by contacting the image carrier with conductive particles interposed therebetween to form a contact portion. A counter member, which is rotated by a counter, is charged to a predetermined potential, an information writing unit that forms an electrostatic latent image on the charged surface of the image carrier, and is arranged to face the image carrier, Image formation having a developer carrier that carries a developer and visualizes the electrostatic latent image as a toner image, and a transfer member that is in contact with the image carrier and transfers the formed toner image to a transfer target member. In the apparatus, the developer contains the conductive particles in the developer, and the developer carrying member collects the developer remaining on the image carrying member after transferring the toner image to the transfer target member. , The charging member transfers the toner image to the transfer target member After that, the conductive particles remaining on the image carrier are recovered, and the conductive particles are present in the contact portion between the charging member and the image carrier, and the non-printing operation of the image forming apparatus is performed. At least, at times. A bias including an AC component is applied to the charging member ,. Absolute value of direct current voltage applied to the developer carrier | V
The state in which dc | is made smaller than that during printing is maintained for a certain period of time ,. An image forming apparatus including a sequence for applying a bias having a reverse polarity to a normal polarity during a printing operation to the transfer member.

As the residual toner on the image bearing member, in addition to the negative toner, there is also a toner made positive by a transfer process of applying a positive voltage. These residual toners are once collected and carried by the charging member by the charging member rotating on the counter with respect to the image carrier. Further, the toner on the charging member is rubbed by the rotation of the charging member to be made negative.

According to the present invention, by applying a bias containing an AC component to the charging member during the non-printing operation, the toner collected and negatively charged by the charging member is downstream of the contact portion between the charging member and the image carrier. Exhaled easily in the department.

Further, by keeping the absolute value | Vdc | of the DC voltage applied to the developing device smaller than that during the printing operation for a certain period of time, the dark potential Vd of the image bearing member and the potential Vdc of the developing device are Difference Vback = | Vd−Vd
c | can be large.

As a result, the toner that has been negatively rubbed by the friction with the charging member and has reached the developing portion downstream of the image carrier is Vb.
The effect of increasing ack is collected in the developing section.

At the same time, by increasing Vback, positive conductive particles are supplied to the image carrier.

The conductive particles on the image bearing member are collected and attached by the charging member that counter-rotates with respect to the image bearing member. However, the amount of the conductive particles that can be attached to the charging member has an upper limit as the saturated attachment amount. It has been decided. The amount of adhesion saturation depends on the structure of the charging member, and since conductive particles exceeding this amount cannot be carried on the charging member and stay on the image carrier, it is necessary to remove the excessively supplied conductive particles from the image carrier. There is.

In the present invention, in the non-printing operation, the conductive particles excessively supplied onto the image carrier are appropriately applied to the transfer member by applying a bias having a polarity opposite to the normal polarity during the printing operation. It can be collected on a transfer member. The collected conductive particles are discharged to the back side (back side of the paper) of the transfer target member by the transfer bias having the regular polarity applied to the transfer member in the next printing operation. This makes it possible to prevent the conductive particles from staying on the image carrier while supporting the conductive particles on the charging member.

Further, the charging member is rotating with respect to the image carrier by a counter. Since the charging property of the direct injection charging depends on the ratio of the peripheral speeds of the image carrier and the charging member, in order to obtain the same peripheral speed ratio as the reverse direction, in the forward direction, the rotation speed of the charging member is larger than that in the reverse direction. Become.

Therefore, rotating the charging member in the counter direction as in the present invention is more advantageous in terms of the number of rotations. The peripheral speed ratio described here is the peripheral speed ratio (%) = (peripheral speed of charging member−peripheral speed of image carrier) / peripheral speed of image carrier (× 100%). The peripheral speed of the image carrier is a positive value when the surface of the charging member moves in the same direction as the surface of the image carrier at the contact portion.

This peripheral speed ratio is preferably 120% or more. The peripheral speed is the speed at which the contact portion between the image carrier and the charging member passes, and in terms of charging property, the peripheral speed greatly differs depending on the width of the contact portion. In order to maintain the chargeability, it is desirable to take a value not less than the above peripheral speed ratio, but there is a problem that the photosensitive layer on the surface of the image carrier is scraped off due to the rubbing between the charging member and the image carrier. Therefore, it is desired to reduce the peripheral speed ratio by increasing the diameter of the charging member and decreasing the elasticity of the charging member. However, increasing the diameter of the charging member is not preferable because it causes a cost increase.
In addition, if the hardness of the charging member is reduced to obtain a sufficient width of the contact portion, the amount of deformation at the contact portion between the charging member and the image carrier increases, and the deformation cannot be recovered after being left for a long time. Excluding these, the lower limit of the peripheral speed of the charging member is preferably 60% or more.

(2) Second Invention In the above-mentioned first invention, the frequency of the bias including the AC component applied to the charging member is f> ps × R × 10 / [nip × (1 + R)] f: AC component Frequency (Hz) ps: Process speed (mm / s) R: Peripheral speed of charging member (× 100%) (The peripheral speed of the charging member is the image bearing surface of the charging member at the contact portion between the image carrier and the charging member. A positive value when moving in the direction opposite to the body surface) nip: an image forming apparatus characterized by setting the width (mm) of the contact portion where the charging member and the surface of the image carrier contact. Is.

In the present invention, M1 = ps × R / f represents unevenness on the surface of the charging member. On the other hand, M2 = nip
(1 + R) is the length of the charging member that rubs against each other while the surface of the image carrier passes through the contact portion. M1 / M2 is applied by applying bias including AC component to charging member,
It represents cleaning unevenness when cleaning the charging member. The ni
The length of p varies depending on the material of the charging member and the contact conditions, but is approximately 1.0 to 3.0 mm. This size depends on the amount of overlap between the image carrier and the charging member, and can be obtained by a simple graphic calculation from the positional relationship between the image carrier and the charging member and the outer diameter. However, as described above, the length of the nip differs depending on the material and the contact condition, and is actually longer than the length calculated by this graphic calculation due to the deformation of the elastic charging member. Therefore, here, ni is 1.5 times the overlap amount obtained in the previous figure calculation.
Define as p.

In the present invention, the size of M1 / M2 is 1
It is characterized in that it is / 10 or less. That is, [ps × R
/ F] / [nip (1 + R)] <1/10. In order to properly clean the charging member, it is necessary to make the size of M1 / M2 sufficiently small. M1 / M2 is 1
If it is larger than / 10, uneven charging occurs, which is not preferable. That is, f> [ps × R × 10] / [nip ×
By satisfying the condition of (1 + R)], the charging property can be maintained and the charging member can be cleaned well.

(3) Third Invention In the above first or second invention, the bias containing an AC component applied to the charging member changes from a low potential to a high potential with a sharp rise, and from a high potential to a low potential. An image forming apparatus having a sawtooth waveform having a gradual fall.

According to the present invention, since the bias applied to the charging member has a sharp rise from a low potential to a high potential, the negative toner particles adhering to the charging member form an image with the charging member. The particles are likely to be discharged to the image carrier downstream of the contact portion of the carrier.

Since the bias applied to the charging member has a gradual fall from a high potential to a low potential, the positive conductive particles adhering to the charging member are discharged to the image carrier. It becomes difficult, and the charging member can hold the conductive particles necessary for charging the image carrier.

(4) Fourth invention In any one of the above-mentioned first to third inventions, the image bearing member is an image bearing member having a photosensitive layer, and is provided upstream of the charging member during the non-printing operation. An image forming apparatus, wherein the image carrier is exposed by a second exposure member provided.

According to the present invention, by lowering the potential of the image bearing member in front of the abutting portion, the development and recovery of the toner upstream of the charging member and the abutting portion of the image bearing member are accelerated, and the image bearing is carried out more effectively. It is possible to promote the negative tone of the toner remaining on the body.

(5) Fifth Invention In any one of the first to fourth inventions described above, the image forming is characterized in that the voltage applied to the charging means is only a DC component during the printing operation. Device.

According to the present invention, the voltage applied to the charging member during the printing operation is only the DC component, so that a large AC exceeding the discharge start voltage as in the conventionally known AC + DC contact charging system. The electric system circuit of the image forming apparatus main body can be simplified without requiring a voltage. Further, it is possible to further reduce a small amount of ozone products generated in the charging mechanism due to discharge of AC voltage + DC voltage.

(6) Sixth Invention The image forming apparatus according to any one of the first to fifth inventions, wherein the charging member is an elastic foam.

According to the present invention, the conductive particles can be surely carried on the contact portion between the image carrier and the contact charging member, and good contact charging can be performed on the image carrier. . (7) Seventh invention In any one of the first to sixth inventions, the image carrier is an image carrier having a photosensitive layer, and the information writing unit is an exposure unit. An image forming apparatus that does.

(8) Eighth invention In any one of the first to seventh inventions, the developer contains a toner having at least a binder resin and a magnetic material. The image forming apparatus according to the first aspect.

[0058]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment FIG. 1 is a schematic structural model view of an example of an image forming apparatus according to the present invention, in which the charging means of the image carrier is a contact injection charging means using conductive particles. It is also a cleanerless system electrophotographic laser beam printer.

The printer of this embodiment differs from the electrophotographic laser beam printer of FIG. 11 in the following points.

A. Removed the cleaning device and left it out b. Conductive particles 40 are applied to the charging roller 2 in advance. C. The charging roller 2 is rotated in the counter direction c at a contact portion S1 with the photosensitive drum 1 at a predetermined peripheral speed with respect to the rotation direction a of the photosensitive drum d. Applying only the DC component to the charging roller 2 as the charging bias voltage e. The developer (toner) t accommodated in the developer container 7 of the developing device 3 is mixed with the conductive particles 40 in a predetermined ratio in advance. Particles 40 are applied. Therefore,
Even in the initial cartridge 15, since the conductive particles 40 are present at the contact portion S1 between the photosensitive drum 1 and the charging roller 2, a predetermined charging bias voltage ( The surface of the photosensitive drum 1 can be uniformly charged to a dark potential (Vd) of about -600V by bringing the charging roller 2 to which a DC voltage of -620V is applied into contact with the photosensitive drum 1.

In the conventional example as shown in FIG. 11, the surface of the photosensitive drum is stably charged by applying a superimposed voltage of a normal DC voltage and an AC voltage to the charging roller 2, and a sand ground (toner on a white background) The image defect such as the flying phenomenon) was prevented. However, as described above, it is unavoidable in principle to generate a discharge product in such a discharge charging mechanism.

On the other hand, in this embodiment, since only the DC voltage is applied, the surface of the photosensitive drum can be charged without generating discharge products.

Now, the charging roller 2 will be described in detail. The charging roller 2 is formed by forming a medium resistance layer 2b of rubber or foam which is a flexible member on the cored bar 2a. The medium resistance layer 2b is a 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. After that, the surface was polished if necessary.

Further, the rotation direction c of the charging roller 2 is a counter direction with respect to the rotation direction a of the photosensitive drum 1 at the contact portion S1 between the charging roller 2 and the photosensitive drum 1, and the charging roller 2 is set at the peripheral speed difference. By rotating at a speed of 150%, most of the conductive particles 40 existing on the photosensitive drum 1 are peeled off. As a result, the conductive particles 40 supplied to the surface of the photosensitive drum 1 from the developing sleeve 3a described later.
Can be applied to the charging roller 2, and the conductive particles 40 are interposed between the charging roller 2 and the photosensitive drum 1 to realize direct injection charging.

By irradiating the laser beam L1 emitted from the exposing means 8a onto the photosensitive drum 1 charged as described above through the reflecting member 8b and the exposure window 6a, an electrostatic latent image is formed on the photosensitive drum 1. Form an image. At this time, the surface potential of the photosensitive drum 1 when the laser beam L1 is uniformly irradiated on the photosensitive drum 1 is set to the bright potential (VL = −150V).

The developing device 3 is 300 for the photosensitive drum 1.
The developing sleeve 3a, the blade 3b, the magnet roll 3c contained in the developing sleeve 3a, the power source 11 for supplying power to the developing sleeve 3a, and the like are provided. The developing sleeve 3a is an aluminum tube coated with a coating agent. The coating agent is a roughening agent (spherical carbon particles, particle size of about 10) for providing a binder (acrylic resin) with a pigment and an appropriate roughness on the surface.
μm and true density of 2.0 × 10 ³ kg / cm ³ ) are dispersed.

The spherical carbon particles used as the roughening agent can be obtained by a method such as phenol resin, naphthalene resin, furan resin, xylene resin, divinylbenzene polymer, styrene-divinylbenzene copolymer and polyacrylonitrile. Bulk mesophase pitch is coated on the surface of spherical resin particles by a mechanochemical method, and the coated particles are heat-treated in an oxidizing atmosphere and then fired in an inert atmosphere or in a vacuum to carbonize and / or graphitize, and to conduct electricity. The method of obtaining the spherical spherical carbon particles can be mentioned. The spherical carbon particles obtained by this method are more preferable because the graphitization makes the coated portion of the spherical carbon particles obtained have advanced crystallization, thereby improving the conductivity.

In this embodiment, since spherical carbon particles are used as the roughening agent, it effectively acts on the surface roughness of the developing sleeve 3a. When the surface roughness of this example was measured, Ra was 1.7 μm.

The toner t containing the conductive particles 40 in the developer container 7 is conveyed to the photosensitive drum 1 by the rotational driving of the developing sleeve 3a. The rotation direction thereof is in the forward direction with respect to the rotational direction a of the photosensitive drum 1. It is the direction b, and is rotationally driven at a peripheral speed of 120% with respect to the drum peripheral speed.

A plate-like urethane rubber (thickness: 1.1 mm) is used for the regulating blade 3b for regulating and charging the toner on the developing sleeve 3a, and a linear pressure of about 49 N / m is applied to the developing sleeve 3a. Abutting. As a result, the styrene resin of the toner base is rubbed against the toner to be negatively charged.

In this embodiment, the developing device 3 having such a structure is carried and carried by applying a superimposed voltage of an AC voltage of about 1.2 kV and a DC voltage of -450 V from the power source 11 to the developing sleeve 3a. Photosensitive drum 1 with toner t
The electrostatic latent image above is visualized.

The toner image formed on the photosensitive drum 1 is
The photosensitive drum 1 and the transfer roller 4 are sequentially transferred onto an abutting portion (transfer portion) T of a transfer target member (transfer paper) P conveyed from a paper feeding portion (not shown) at a predetermined control timing. The transfer roller 4 rotates in the forward direction with the rotation of the photosensitive drum 1. The member P to which the toner image has been transferred at the transfer portion T is separated from the surface of the photosensitive drum 1 and is conveyed to the fixing unit 9 where the toner image is fixed and discharged.

The printer of this embodiment is cleanerless, and the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image to the transfer target member P is not removed by the cleaner, and the photosensitive drum 1 is rotated. The toner reaches the developing section D via the charging roller 2 and is simultaneously cleaned (collected) by the developing sleeve 3a during development (toner recycling process).

FIG. 2 is a diagram schematically showing how the toner t and the conductive particles 40 fly to the image portion and the non-image portion on the photosensitive drum surface in the developing portion D.

In this embodiment, the toner base is styrene resin.
Silica as an external additive that accelerates the charging of the toner
-Part of the matrix is 2 parts, the particle resistance of the conductive particles 40 is
10 ⁶Ω · cm, average particle size including secondary aggregate of 3 μm
Two parts of conductive zinc oxide particles are externally added.

To measure the average particle size and particle size distribution of the conductive fine powder 40, a liquid module was attached to a LS-230 type laser diffraction particle size distribution measuring device manufactured by Coulter Co., Ltd. in a measuring range of 0.04 to 2000 μm. It was measured. As a measuring method, a trace amount of a surfactant is added to 10 cc of pure water, 10 mg of a conductive fine powder sample is added thereto, and the mixture is dispersed for 10 minutes by an ultrasonic disperser (ultrasonic homogenizer), and then a measuring time of 90 The measurement was performed once per second and once, and the volume average particle diameter was calculated based on the result. The resistance of the conductive fine powder 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.

Since the conductive particles 40 tend to be weakly positive as an external additive, the external additive alone causes 800 V (| Vmin-Vd | =) from the developing sleeve 3a to the photosensitive drum 1 in the non-image area. | 200-(-60
It flies with a contrast of 0) |).

Further, the conductive particles 40 as an external additive may be attached to the toner t, so that 850 V (| VL-Vmax | = | -150) from the developing sleeve 3a to the photosensitive drum 1 is applied to the image portion. -(-10
It flies with a contrast of 00) |).

Since the conductive particles 40 flying on the photosensitive drum 1 are positive, most of them remain on the photosensitive drum 1 together with the transfer residual toner without being transferred to the transfer target member P by the transfer bias application. . By sufficiently supplying the conductive particles 40 to the charging roller 2, direct injection charging can be achieved.

As described above, in the present invention, how to uniformly supply the conductive particles 40 to the charging roller 2 via the photosensitive drum 1 becomes a major problem. If the conductive particles 40 are not supplied onto the charging roller 2, it is difficult to maintain the photosensitive drum dark potential Vd. If a large amount of toner adheres to the charging roller 2, the resistance of the toner impairs the charging uniformity and deteriorates the image quality. Therefore, it is important that the conductive particles 40 are uniformly supplied to the charging roller 2 and, at the same time, the toner adhered to the charging roller 2 is removed and collected by the developing device 3.

In this embodiment, the applied voltage to the charging roller 2 and the developing device 3 is controlled according to the timing chart as shown in FIG. Hereinafter, description will be sequentially made with reference to FIG. FIG. 6 is a diagram for supplementarily explaining the toner negative process by rubbing the charging roller, and FIGS. 7 and 8 are diagrams for supplementally explaining the toner recovery process by the developing device.

Process [P0] = printing operation During this period, the normal printing process is performed. When a printing start signal is input to the printer in the standby state, the photosensitive drum 1
The rotation drive of is started, the predetermined pre-rotation operation is executed,
When it is completed, the printing operation (printing process) starts.

In the printing process, first, only the DC voltage of -620 V is applied to the charging roller 2, and the transfer, development DC, and development AC bias are sequentially applied, and the latent image written on the photosensitive drum 1 by the exposure means. Is visualized and developed as a toner image. The toner image is transferred to the transfer target member P, the transfer target member P is conveyed to the fixing unit 9, and the toner image is fixed and discharged.

Process [P1] = non-printing operation (post-rotation), charging roller cleaning process When the above printing process is completed, the printer shifts to a predetermined post-rotational operation (non-printing operation), and then the rotation operation is completed. The rotation of the photosensitive drum 1 is stopped, and the printer is in the standby state until the next print start signal is input.

The charging roller cleaning process is executed during the post-rotation operation which is the non-printing operation. That is, also in this process, the charging roller 2 is counter-rotating with respect to the photosensitive drum 1. Here, the negative action of the residual toner after transfer will be described with reference to FIG. The charging roller 2 counter-rotates with respect to the photosensitive drum 1, so that the residual toner on the photosensitive drum 1 is scraped off by the charging roller 2. During this time, the charging roller 2 rubs the residual toner on the photosensitive drum 1 to make the positive residual toner negative. Further, in the upstream portion S2 of the contact portion between the charging roller 2 and the photosensitive drum, the toner negatively formed by the rubbing of the charging roller 2 is once developed on the photosensitive drum 1 due to the potential difference between the charging roller 2 and the photosensitive drum 1. As described above, when the charging roller 2 counter-rotates, it is immediately collected by the charging roller 2. In this way, the toner on the photosensitive drum 1 can be discharged negatively by rubbing the charging roller 2 and repeatedly collected by counter rotation, while discharging the toner upstream of the charging roller 2 to the downstream S3. Of.

Further, since the conductive particles 40 having a low resistance are interposed between the photosensitive drum 1 and the charging roller 2, electric charges are injected by the voltage applied to the charging roller 2, and the photosensitive drum 1 is properly charged. Can have

What is important here is that the negative toner is effectively discharged onto the photosensitive drum 1 in the downstream S3 of the contact portion of the charging member 2. If the negative toner is not conveyed to the photosensitive drum 1, the toner is accumulated on the charging roller 2, and the resistance of the toner resin increases the resistance of the charging roller. As a result, the injection charging property is deteriorated, and the photosensitive drum 1 cannot be stably and uniformly charged.

In this embodiment, the AC voltage (Vpp = 200V, f = 200 Hz) is applied to the charging roller 2 during post-rotation.
Is being applied. FIG. 4 shows an AC applied to the charging roller 2.
The waveform of the bias is schematically shown. In the figure, the AC bias applied to the charging roller 2 is characterized by having a sawtooth waveform having a sharp rise from a low potential to a high potential and a gradual fall from a high potential to a low potential. That is, when the potential of the charging roller 2 changes from a low potential to a high potential, it has a sharp rising edge. Then, the electric potential of the charging roller 2 rapidly changes with respect to the electric potential of the photosensitive drum 1, so that a potential contrast is likely to be formed, and the negatively charged toner on the charging roller 2 is easily developed on the photosensitive drum 1. That is, the negative toner can be effectively discharged to the photosensitive drum 1 in the downstream S3 of the contact portion of the charging member 2. On the contrary, when the potential of the charging roller 2 changes from a high potential to a low potential, the positive conductive particles 40 on the charging roller 2 are less likely to be developed on the photosensitive drum 1 because they have a gentle fall. That is, the conductive particles 40 are discharged from the charging roller 2 and do not hinder the injection charging property of the charging roller 2.

In this embodiment, the process speed is 200
mm / s, the length of the contact portion S1 is nip = 2 mm, and the AC voltage applied to the charging roller 2 is 650 Hz. Then, f = 650 (Hz)> ps × R × 10 / [nip × (1 + R)] = 200 (mm / s) × 1.5 (× 100%) × 10 / [(2 (mm) × (1 + 1) .5) (× 100%)] = 600, which is necessary for obtaining a good image without uneven charging.
The C voltage is secured.

In this embodiment, the value of the DC voltage applied to the charging roller 2 was not changed at the time of post-rotation, but the DC voltage can be changed if cleaning the charging roller 2 more effectively. Is also good.

As described above, the AC voltage is applied to the charging roller 2 at the time of post-rotation in order to clean the charging roller 2, but almost simultaneously with this, the developing DC voltage is lowered from -450V to -400V. A reverse polarity bias (-0.5 kV) is applied to the transfer applied voltage.

7 and 8 are views for explaining the process of collecting the toner particles discharged from the charging roller 2. In FIG. 7, the developing DC voltage Vdc has the same value as that in the printing operation. In this case, the toner particles on the photosensitive drum are unevenly distributed at the surface potential of the photosensitive drum of −500 V (= Vdc + Vpp / 2) due to the AC bias applied to the charging roller 2. Therefore, Vback = | Vd−Vdc | = | −500 − (− 45
0) | = 50 V, the conductive particles 40 in the developing device are supplied to the photosensitive drum 1 at the same time when they are collected in the developing device 3 with a contrast. However, the recovery process may be insufficient due to the adhesion force between the toner particles and the photosensitive drum 1 and the reflection force. Therefore, in this embodiment, the development D is performed during the non-printing operation.
The C voltage is lowered to Vdc = -400V. Therefore, Vback = | Vd−Vdc | = | −500 − (− 40
0) | = 100V, and the toner particles on the photosensitive drum 1 are more effectively collected by the developing device 3, and at the same time, more conductive particles 40 in the developing device 3 are supplied to the photosensitive drum 1 ( (See FIG. 8).

It is desirable that the conductive particles 40 supplied onto the photosensitive drum 1 be evenly distributed on the photosensitive drum 1 in the longitudinal direction. However, it is difficult to always keep the longitudinal uniformity of the developing device 3 constant over the life of the developing device. Therefore, the conductive particles 40 applied on the photosensitive drum 1 in a non-uniform manner may be excessively supplied at a specific portion. As a result, when the conductive particles 40 are excessively supplied to a specific position in the longitudinal direction, the conductive particles 40 are scraped by the charging roller 2 and excessively carried by the charging roller 2.

However, the amount of the conductive particles 40 that can be carried on the charging roller 2 has a saturation amount, and even if it is excessively supplied, it cannot be carried. Therefore, the excessively supplied conductive particles 40 cannot be carried on the charging roller 2 made of elastic foam, and are discharged downstream of the charging section. As a result, the aggregated conductive particles 40 of a visible size may prevent the formation of an electrostatic latent image on the photosensitive drum 1 in the exposed portion (hereinafter, this phenomenon will be referred to as "shading"). .

Therefore, in the present embodiment, it is said that the transfer roller 4 collects a part of the conductive particles 40 so as not to cause the light shielding and ejects the conductive particles 40 to the back surface (back side of the paper) of the transfer target member P during the printing operation. Do the process.

In this embodiment, the transfer roller 4 is
A reverse bias of 500V is applied. Photosensitive drum 1
And the transfer roller 4 is in contact at the contact position T. At the contact position T, the drum surface potential is approximately −600 V and the voltage applied to the transfer roller 4 is −500 V, so that the transfer roller 4 and the photosensitive drum 1 are approximately equal in potential. However, the excessive positive conductive particles 40 adhering to the photosensitive drum 1 at the contact position T
It is separated into the photosensitive drum 1 and the transfer roller 4 by the physical adhesive force and the mirroring force. That is, a part of the conductive particles 40 having an excessive positive property is collected by the transfer roller 4.

Here, the voltage applied to the transfer roller 4 is −
Explain that it is 500V. FIG. 5 is a diagram schematically showing the surface potential on the photosensitive drum 1 with respect to the voltage applied to the transfer roller 4 contacting the photosensitive drum 1. In the figure, A indicates that the conductive particles 40 are present in the contact portion T between the transfer roller 4 and the photosensitive drum 1, and B in the figure indicates the conductive particles 40 in the contact portion T between the transfer roller 4 and the photosensitive drum 1. This is the case where 40 is not present. As you can see in Figure 5, A
Then, the surface potential of the photosensitive drum increases linearly from the discharge start voltage Vth. On the other hand, in B, charge injection to the photosensitive drum 1 is started from a value smaller than the discharge start voltage,
At the discharge start voltage Vth, the surface potential of the photoconductor becomes Vo. Therefore, when a voltage higher than the discharge start voltage Vth is applied to the transfer roller 4 to which the conductive particles 40 adhere, the surface potential on the photosensitive drum 1 may become higher than a predetermined dark potential of the photosensitive drum. Therefore, -500V is adopted as a value that allows positive particles to be adsorbed to the transfer roller 4 and a predetermined dark potential of the photosensitive drum can be obtained.

The conductive particles 40 collected on the transfer roller 4 are discharged to the back side of the transfer target member by applying a positive bias in the next printing operation process [P0].
In this way, since it is possible to supply an appropriate amount of the conductive particles 40 to the charging roller 2, it is possible to prevent image defects such as light shielding.

As described above, by applying the cleaning bias to the charging roller 2, the toner on the charging roller 2 is satisfactorily conveyed to the photosensitive drum 1. Further, by lowering the developing DC voltage, the transported toner can be collected and at the same time, the conductive particles 40 can be supplied onto the photosensitive drum 1. Further, by applying a predetermined reverse bias to the transfer roller 4, the conductive particles 40 excessively supplied on the photosensitive drum 1 can be collected and discharged to the back side of the transfer target member in the next printing process.

A good cleanerless system can be constructed by performing the above-described process during the post-rotation.

In this embodiment, the above-described process is performed at the time of post-rotation, but if necessary, at the time of starting the printer,
It may be applied at the time of pre-rotation and at the time of sheet interval.

<Second Embodiment> FIG. 9 is a schematic view showing the present embodiment. The outline of this embodiment is the same as that of the first embodiment. As shown in the first embodiment, the charging roller 2
Is counter-rotated with respect to the photosensitive drum 1, the residual toner on the photosensitive drum 1 is scraped off by the charging roller 2, and the residual toner is rubbed, so that the positive residual toner becomes negative. Further, the toner negatively formed by the rubbing of the charging roller 2 is once developed on the photosensitive drum 1 due to the potential difference between the charging roller 2 and the photosensitive drum 1. However, as described above, the charging roller 2 is immediately rotated by the counter rotation. It is collected by the charging roller 2. In this way, the toner on the photosensitive drum 1 is conveyed to the downstream S3 while the toner on the upstream side of the charging roller 2 is made negative while the toner on the photosensitive drum 1 is negatively moved by rubbing the charging roller 2 and is repeatedly collected by counter rotation. .

In order to further promote the development and recovery of the toner on the upstream side of the contact portion between the charging roller 2 and the photosensitive drum 1, in this embodiment, the toner is placed downstream of the transfer roller 4 and upstream of the charging roller 2. An exposure unit 60 is provided.

FIG. 10 is a diagram schematically showing the potential of the photosensitive drum 1 after being exposed by the pre-exposure means 60 and the bias applied to the charging roller 2. In the same figure, by exposing the transferred photosensitive drum 1 by the pre-exposure means 60, the surface potential of the photosensitive drum 1 is approximately a bright potential (VL), so the potential difference from the charging roller 2 becomes large. Here, the charging roller cleaning bias (Vdc = -620V, Vpp = 200V, f = 600)
Hz) is applied to the charging roller 2 when the charging voltage is Vmax before the contact portion with the photosensitive drum 1.
Therefore, the toner is easily developed on the photosensitive drum 1. As a result, the development and recovery of the toner in front of the abutting portion is accelerated, and it is possible to more effectively promote the negative toner remaining on the photosensitive drum.

<Others> 1) The contact charging member is not limited to the one shown in the embodiment.

2) As the waveform of the AC voltage component of the bias applied to the developing member, 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 the electrostatic latent image may be a laser scanning exposure means for forming a digital latent image, or an ordinary analog image exposure or LE.
Other light emitting elements such as D may be used, or a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter, etc.
It does not matter if it can form an electrostatic latent image corresponding to image information.

4) The image carrier 1 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.

5) The structure of the developing means 3 is not particularly limited.

6) The member to which the toner image is transferred from the image carrier 1 may be an intermediate transfer member such as a transfer drum.

[0111]

As described above, according to the present invention, the charging means of the image bearing member is the contact injection charging means using the conductive particles, and the cleanerless system, the electrophotographic copying machine, the electrophotography. In an image forming apparatus such as a printer, a function separation type sequence such as discharging toner from a charging member, supplying conductive particles from a developing unit, and collecting conductive particles by a transfer member allows excessive charging while maintaining charging uniformity. The conductive particles thus formed can be collected and discharged to the transfer member. As a result, the charging member can carry an appropriate amount of conductive particles, and the light-shielding white spots due to the accumulation of an excessive amount of conductive particles are improved. Then, it is possible to construct a cleanerless system having a stable charging property even for equipment having a process speed of about 200 mm / s without increasing the production cost.

[Brief description of drawings]

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

FIG. 2 is a diagram schematically showing how toner and conductive particles fly in an image area and a non-image area on a photosensitive drum surface in a developing section.

FIG. 3 is a control timing chart diagram.

FIG. 4 is a waveform diagram of a charging applied voltage.

FIG. 5 shows a case where a conductive cloth is present in the contact portion between the transfer roller and the photosensitive drum (A) and a case where no conductive cloth is present (B).
FIG. 6 is a diagram schematically showing the relationship of the surface potential on the photosensitive drum with respect to the voltage applied to the transfer roller.

FIG. 6 is an explanatory diagram of a residual toner negative conversion process, a development simultaneous recovery process, and a conductive particle supply process.

FIG. 7 is an explanatory diagram of a simultaneous development recovery process.

FIG. 8 is an explanatory diagram of a simultaneous development collection process.

FIG. 9 is an explanatory diagram of a residual toner negative conversion process, a development simultaneous recovery process, and a conductive particle supply process of the image forming apparatus according to the second embodiment.

FIG. 10 is a diagram schematically showing the potential of the photosensitive drum after being exposed by the pre-exposure unit and the bias applied to the charging roller.

FIG. 11 is a schematic configuration model diagram of an image forming apparatus of a conventional example.

FIG. 12 is an explanatory diagram of a conductive particle supply unit for the charging roller.

[Explanation of symbols]

1. ． ． Photosensitive drum, 2. ． ． Charging roller, 3a. ． ．
Developing roller, 3b. ． ． Development blade, 4. ． ． Transfer roller, 5a. ． ． Cleaning blade, 5b. ． ． Squishy sheet, 7. ． ． Toner container, 8a. ． ． Exposure means, 8b. ． ． Folding reflection member, 9. ． ． Fixing means,
10. ． ． Developer stirring member, 11, 12, 13. ． ． Power supply, 40. ． ． Conductive particles, 50. ． ． Conductive particle supplying means, 60. ． ． Pre-exposure means, P. ． ． Transferred member (recording medium)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 9/08 101 (72) Inventor Hiroyuki Oba 3 chome Shimomaruko, Ota-ku, Tokyo No. 30-2 Canon Inc. (72) Inventor Masahiro Yoshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Incorporated Canon Inc. (72) Junichi Kato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-terms (reference) 2H005 AA02 AA08 CB07 DA07 DA09 FA06 2H027 DA38 EA01 EA05 ED09 2H073 BA04 BA13 BA43 CA02 CA13 2H077 AC16 AD06 AD13 AD36 AE03 BA03 EA16 FA01 GA00 2H200 FA18 GA23 GA54 GA21 GA46 GA49 GA49 GA46 GA49 GA52 HB12 HB22 HB45 HB48 JA02 JA28 LA19 LA20 MA03 MA04 MA14 NA02 NA03 NA09

Claims (8)

[Claims] 1. A contact portion is formed by contacting at least the image carrier with the image carrier with conductive particles interposed therebetween, and the contact part is rotated with respect to the image carrier by a predetermined potential. A charging member for electrically charging the image bearing member, an information writing unit for forming an electrostatic latent image on the charging surface of the image bearing member, and a charging member arranged so as to face the image bearing member and carrying a developer. A developer carrier for visualizing the toner image as a toner image,
In an image forming apparatus having a transfer member that is in contact with the image carrier and transfers the formed toner image to a transfer target member, the developer contains the conductive particles in the developer, The body collects the developer remaining on the image bearing member after transferring the toner image to the transferred member, and the charging member transfers the toner image onto the image bearing member after transferring the toner image to the transferred member. The remaining conductive particles are collected, and the conductive particles are present in the contact portion between the charging member and the image carrier, and at least during the non-printing operation of the image forming apparatus. A bias including an AC component is applied to the charging member ,. Absolute value of direct current voltage applied to the developer carrier | V
The state in which dc | is made smaller than that during printing is maintained for a certain period of time ,. An image forming apparatus including a sequence for applying a bias having a polarity opposite to a normal polarity during a printing operation to the transfer member. 2. The frequency of the bias including the AC component applied to the charging member is f> ps × R × 10 / [nip × (1 + R)] f: Frequency of the AC component (Hz) ps: Process speed (mm / s) R: peripheral speed of the charging member (× 100%) (the peripheral speed of the charging member is a positive value when the surface of the charging member moves in the direction opposite to the surface of the image carrier at the contact portion between the image carrier and the charging member). Nip: The image forming apparatus according to claim 1, wherein the width (mm) of the contact portion where the charging member and the surface of the image carrier contact each other is set. 3. A bias having an AC component applied to the charging member has a sawtooth waveform having a sharp rising from a low potential to a high potential and a gradual falling from a high potential to a low potential. The image forming apparatus according to claim 1 or 2, which is characterized in that. 4. The image bearing member is an image bearing member having a photosensitive layer, and the image bearing member is exposed by a second exposure member provided upstream of the charging member during the non-printing operation. The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein the voltage applied to the charging means is only a DC component during the printing operation. 6. The image forming apparatus according to claim 1, wherein the charging member is an elastic foam. 7. The image forming apparatus according to claim 1, wherein the image bearing member is an image bearing member having a photosensitive layer, and the information writing unit is an exposing unit. 8. The image forming apparatus according to claim 1, wherein the developer includes a magnetic developer containing at least a binder resin and a toner having a magnetic material.