JP2001215798A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaner-less system image forming device in which developer left after transfer on an image carrier 1 after a transfer stage is removed and recovered by cleaning simultaneously with developing so as to be recycled, where faulty electrification and a faulty image are avoided by preventing the developer left after transfer from adhering to an electrifying means 2 and efficiently recovering the developer left after transfer by a developing means 4, and which makes the best use of the merit of a cleaner-less system. SOLUTION: The toner left after transfer is uniformized by a means 8 for uniformizing the toner left after transfer positioned on the downstream side of a transfer part (d), and processed to be electrified to have a normal polarity by a toner electrified amount control means 7 positioned on a more downstream side, whereby the electrified amount is made proper as soon as the surface of the image carrier 1 is electrified by the electrifying means 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cleaner-less transfer type image forming apparatus. More specifically, a cleaner-less cleaning device is used in which the developer (toner) remaining on the image carrier after the transfer process is removed and collected from the image carrier by simultaneous cleaning with development in the developing device and reused. The present invention relates to an image forming apparatus of the type.

[0002]

2. Description of the Related Art Conventionally, a transfer type image forming apparatus such as a copying machine, a printer, a facsimile or the like using a transfer type electrophotographic method has a photoreceptor which is a rotary drum type image carrier, and the photoreceptor. Device (charging step) for uniformly charging the photosensitive member to a predetermined polarity and potential, an exposure device (exposure step) as information writing means for forming an electrostatic latent image on the charged photosensitive member, A developing device (developing process) for visualizing the formed electrostatic latent image with toner as a developer, a transferring device (transfer process) for transferring the toner image from a photoreceptor surface to a transfer material such as paper, and after the transferring process And a fixing device (fixing step) for removing a small amount of residual toner on the photosensitive member and cleaning the surface of the photosensitive member, and a fixing device (fixing step) for fixing the toner image on the transfer material. Is Ri returns electrophotographic process (charging,
Exposure / development / transfer / cleaning) is applied and used for image formation.

The toner remaining on the photoreceptor after the transfer process is removed from the surface of the photoreceptor by the cleaning device and accumulates in the cleaning device to become waste toner. However, such a toner is disadvantageous in terms of environmental conservation and effective use of resources. It is desirable that no waste toner is generated.

Therefore, there is an image forming apparatus in which the transfer residual toner collected by the cleaning device, so-called waste toner, is returned to the developing device and reused.

Further, the cleaning device is abolished, and the transfer residual toner on the photoreceptor after the transfer process is removed and collected from the photoreceptor by "simultaneous development" in the developing device, and is reused. There is a forming device.

In the simultaneous cleaning with development, the transfer residual toner on the photoreceptor after the transfer is subjected to the subsequent development process, that is, the photoreceptor is charged and exposed to form an electrostatic latent image. A fog removing bias (fogging potential difference Vback, which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photoreceptor) during an image developing process, causes a portion of the photoreceptor surface not to be developed with toner (non-image This is a method in which the transfer residual toner existing in the section (part) is collected in the developing device. According to this method, since the transfer residual toner is collected in the developing device and reused for the development of the electrostatic latent image in the next and subsequent steps, waste toner is eliminated, and maintenance work is reduced. Can be. Further, being cleaner-less is advantageous for miniaturization of the image forming apparatus.

[0007]

A) As described above,
In a cleanerless image forming apparatus in which the transfer residual toner on the photoreceptor after the transfer process is removed and collected by a developing device at the same time as the cleaning at the same time as the cleaning and reused, the charging device of the photoreceptor contacts the photoreceptor to clean the photoreceptor surface. In the case of a contact charging device that performs a charging process, when the transfer residual toner on the photoconductor passes through the charging portion that is a contact nip portion of the photoconductor and the contact charging device, particularly the charging polarity of the transfer residual toner is a normal polarity. In this case, the toner, which has been inverted to the opposite polarity, adheres to the contact charging device, causing the contact charging device to become unacceptably contaminated with toner and causing charging failure.

That is, the toner as a developer contains a small amount of toner whose charge polarity is originally inverted to the polarity opposite to the normal polarity. In addition, there is a toner whose charge polarity is reversed to be affected by a transfer bias, a peeling discharge or the like, or a toner whose charge amount is reduced due to charge elimination, even if the toner has a normal charge polarity.

Therefore, the transfer residual toner includes a toner having a normal charge polarity, a reverse toner having a reverse polarity, and a toner having a small charge amount. It easily adheres to the contact charging device when passing through the charging portion that is the contact nip portion of the contact charging device.

B) Further, in order to remove and collect the transfer residual toner on the photoreceptor by simultaneous cleaning with the developing device, the transfer residual toner on the photoreceptor carried through the charging unit and carried to the developing unit. It is necessary that the charge polarity of the toner is a normal polarity and that the charge amount is a charge amount of the toner that can develop the electrostatic latent image on the photoconductor by the developing device. Inverted toner and toner with an inappropriate charge amount cannot be removed and collected from the photoreceptor to the developing device, causing a defective image.

C) Adhesion of the toner to the contact charging device of the above a) is carried out by mixing a toner having a normal charge polarity, a reverse charge polarity, and a small charge amount, which are carried from the transfer portion to the charging portion. The transfer residual toner on the photoreceptor is charged to the normal polarity by the toner charge amount control means so that the charge polarity is made uniform and the charge amount is made uniform.

However, the transfer residual toner charged by the toner charge amount control means in order to prevent the toner from adhering to the contact charging device is compared with the charge amount of the toner capable of developing the electrostatic latent image on the photosensitive member. Because of its large size, it is difficult for the developing device to be removed and collected by simultaneous cleaning with development. In such a case, the toner remaining on the photoconductor overlaps with the next image, causing a defective image.

Further, with the diversification of user needs in recent years, a large amount of image data is transferred at a time by a continuous printing operation of an image having a high printing rate such as a photographic image, and a multi-developing method on a photoreceptor due to colorization. The occurrence of the residual toner further promotes the above-described problem.

Accordingly, the present invention relates to a cleaner-less image forming apparatus for removing and collecting and reusing a transfer residual developer on an image carrier after a transfer step by simultaneous cleaning with development, and relates to a transfer residual developer to a charging unit. In addition to preventing the adhesion of the developer, the developer remaining in the transfer unit is efficiently collected by the developing unit, so that there is no charging failure or defective image, and an image forming apparatus that utilizes the advantages of a cleaner-less system. The purpose is to provide.

[0015]

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

(1) Image carrier, charging means for charging the surface of the image carrier, information writing means for forming an electrostatic latent image on the charged image carrier, and supply of developer to the electrostatic latent image Developing means for visualizing the electrostatic latent image, transfer means for transferring the visualized developer image to a transfer material, and developer which is located upstream of the charging means and charges the developer on the image carrier surface Charge amount control means, and a residual developer image located upstream of the developer charge amount control means and downstream of the transfer means and remaining on the image carrier surface after transferring the developer image to a transfer material And a residual developer image equalizing means for uniformizing the residual developer image. The residual developer image remaining on the image carrier after the transfer of the developer image is uniformized by the residual developer image uniformizing means, and the uniformity is achieved. The developer remaining on the image carrier is charged to the normal polarity by the developer charge amount control means. Charged and, at the same time as charging the image bearing member surface by the charging unit, an image forming apparatus, characterized in that a proper charge quantity.

(2) The image forming apparatus according to (1), wherein the charging means is of a contact charging type.

(3) The image forming apparatus according to (1) or (2), wherein an oscillating electric field is applied to the charging means.

(4) The image forming apparatus according to any one of (1) to (3), wherein the information writing means is an exposure means.

(5) The image forming apparatus according to any one of (1) to (4), wherein the residual developer image uniforming means comprises an electrode portion having a potential difference with respect to the image carrier.

(6) Image carrier, charging means for charging the surface of the image carrier, information writing means for forming an electrostatic latent image on the charged image carrier, and supplying developer to the electrostatic latent image Developing means for visualizing the electrostatic latent image, transfer means for transferring the visualized developer image to a transfer material, and developer which is located upstream of the charging means and charges the developer on the image carrier surface Charge amount control means, and a residual developer image located upstream of the developer charge amount control means and downstream of the transfer means and remaining on the image carrier surface after transferring the developer image to a transfer material And a residual developer image equalizing means for uniformizing the residual developer image. The residual developer image remaining on the image carrier after the transfer of the developer image is uniformized by the residual developer image uniformizing means, and the uniformity is achieved. The developer remaining on the image carrier is charged to the normal polarity by the developer charge amount control means. Charging, charging the surface of the image carrier with the charging unit, and at the same time, setting the charging amount to an absolute value smaller than the absolute value of the charging amount when the charging process is performed by the developer charging amount control unit. Image forming apparatus.

(7) The image forming apparatus according to (6), wherein the charging means is of a contact charging type.

(8) The image forming apparatus according to (6) or (79), wherein an oscillating electric field is applied to the charging means.

(9) The image forming apparatus according to any one of (6) to (8), wherein the information writing means is an exposure means.

(10) The image forming apparatus according to any one of (6) to (9), wherein the residual developer image uniforming means comprises an electrode portion having a potential difference with respect to the image carrier. apparatus.

(11) Image carrier, charging means for charging the surface of the image carrier, information writing means for forming an electrostatic latent image on the charged image carrier, and supply of developer to the electrostatic latent image Developing means for visualizing the electrostatic latent image, transfer means for transferring the visualized developer image to a transfer material, and developer which is located upstream of the charging means and charges the developer on the image carrier surface Charge amount control means, and a residual developer image which is located upstream of the developer charge amount control means and downstream of the transfer means and remains on the carrier surface after transferring the developer image to a transfer material. Means for uniformizing the residual developer image, and for uniformizing the residual developer image remaining on the image carrier after the transfer of the developer image by the residual developer image uniformizing means. The developer remaining on the image carrier is developed by the developer charge amount controlling means. The charging process is performed with a charge amount of 2.2 times or more the charge amount of the developer after the step and at a normal polarity, and the surface of the image bearing member is charged by the charging unit. An image forming apparatus characterized in that the charge amount is 5 to 1.8 times.

(12) The image forming apparatus according to (11), wherein the charging means is of a contact charging type.

(13) The image forming apparatus according to (11) or (12), wherein an oscillating electric field is applied to the charging means.

(14) The image forming apparatus according to any one of (11) to (13), wherein the information writing means is an exposure means.

(15) The image forming apparatus according to any one of (11) to (14), wherein the residual developer image uniforming means comprises an electrode portion having a potential difference with respect to the image carrier. apparatus.

<Operation> The present invention is directed to a cleaner-less type image forming apparatus in which a transfer residual developer (transfer residual toner) on an image carrier after a transfer step is removed and collected by a developing unit at the same time as a cleaning at the same time as development and reused. With respect to the forming apparatus, the distribution of the transfer residual developer on the image carrier is made uniform and the tribo is controlled, thereby obtaining the advantage of the cleaner-less system. The tribo of the transfer residual developer is controlled by the developer charge amount control means. The charging process is performed to a normal polarity, and an appropriate charging amount is obtained by a charging unit. A) The tribo of the transfer residual developer on the image carrier carried from the transfer unit to the charging unit is normalized by the developer charging amount control unit. B) charging the surface of the image bearing member to a predetermined potential by the charging unit while simultaneously preventing the transfer residual developer from adhering to the charging unit by performing the charging process to the polarity; Charged on By controlling the charge amount of the transfer residual developer to an appropriate charge amount that can develop the electrostatic latent image on the image carrier by the developing unit, the transfer residual developer can be efficiently collected by the developing unit. did.

C) In the above description, the proper charge amount of the transfer residual developer by the charging means is, more specifically, an absolute value smaller than the absolute value of the charge amount when the charge processing is performed by the developer charge amount control means. Is the charge amount. Further, the charge amount of the developer is 2.2 times or more larger than the charge amount of the developer after the developing means by the developer charge amount control means, and the charge treatment is performed to the normal polarity. The charge amount is 0.5 to 1.8 times the charge amount of the developer.

D) A residual developer image uniforming means is for transferring the pattern-shaped residual transfer developer image on the image carrier carried from the transfer section to the developer charge amount control means section, by applying the developer to the image carrier surface. This is a means for dispersing and distributing the data into non-patterned data. Specifically, the residual developer image pattern is scraped or disturbed by rubbing the image carrier surface with a rubbing member, thereby dispersing and distributing the developer on the image carrier surface. This is a method in which the developer of the residual developer image on the image carrier is collected by a collecting member, and the collected developer is re-attached to the image carrier in a dispersed distribution state.

The presence of the residual developer image uniformizing means ensures that the entire remaining charge of the transfer residual developer by the next developer charge amount control means is always sufficiently charged to the normal polarity, and that the transfer residual developer is removed. The adhesion to the charging means is effectively prevented. Further, since the residual developer image pattern is erased, generation of a ghost image of the residual developer image pattern is strictly prevented.

That is, when there is no means for equalizing the residual developer image, for example, when the transferability of the developer image is poor, such as a vertical line pattern developer image, environment, paper type (transfer paper), and color secondary color. The amount of developer of the pattern-shaped transfer residual developer image on the image carrier also increases, and the transfer residual developer image is carried to the developer charge amount control unit as it is, and the amount of the developer remains. When the developer concentrates on the portion, a phenomenon that the charge amount of the residual developer cannot be completely controlled by a part of the developer charge amount control means (toner charging failure phenomenon) occurs. → Poor charging → Fog image is generated. In addition, the residual developer image pattern remains and a ghost image is generated.

By providing the residual developer image uniforming means, as described above, the transfer residual developer image in the form of a pattern on the image carrier carried from the transfer section to the developer charge amount control means section becomes the developer. Even if the amount is large, the developer is dispersed and distributed on the surface of the image carrier and is not patterned, so that the developer does not concentrate on a part of the developer charge amount control means, and the developer charge amount The entire normal polarity charging process of the transfer residual developer by the control means is always sufficiently performed, and the adhesion of the transfer residual developer to the charging means is effectively prevented. Generation of a ghost image of the residual developer image pattern is also strictly prevented.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, an image forming apparatus (image recording apparatus) according to an embodiment will be described.

FIG. 1 is a schematic structural diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process, a contact charging type, a reversal developing type, a cleaner-less type, and an A3 size maximum sheet passing size.

(1) Overall Schematic Configuration of Printer a) Image Carrier 1 A rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. This photosensitive drum 1
Is a negatively chargeable organic photoconductor (OPC) having an outer diameter of 50 mm
, And is driven to rotate counterclockwise as indicated by an arrow at a process speed (peripheral speed) of 100 mm / sec around the center support shaft.

As shown in the schematic diagram of the layer structure in FIG. 2, this photosensitive drum 1 has a subbing layer on the surface of an aluminum cylinder (conductive drum base) 1a for suppressing light interference and improving the adhesiveness of the upper layer. 1b, a photocharge generation layer 1c, and a charge transporting layer 1d, which are sequentially coated from the bottom.

B) The charging means 2 is a contact charging device (contact charging device) as a charging device for uniformly charging the peripheral surface of the photosensitive drum 1, and in this example, a charging roller (roller charging device).

The charging roller 2 rotatably holds both ends of the cored bar 2a by bearing members (not shown), and urges the pressing roller 2e in the direction of the photosensitive drum 1a to press the surface of the photosensitive drum 1. The photosensitive drum 1 rotates in accordance with the rotation of the photosensitive drum 1. The pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a.

When a charging bias voltage under predetermined conditions is applied from a power source S1 to the core metal 2a of the charging roller 2, the peripheral surface of the rotating photosensitive drum 1 is contact-charged to a predetermined polarity and potential. In this example, the charging bias voltage for the charging roller 2 is a DC voltage (Vdc) and an AC voltage (Va).
c) is an oscillating voltage superimposed on

More specifically, DC voltage; -500 V AC voltage; frequency f1000 Hz, peak-to-peak voltage Vpp1
400 V, which is a vibration voltage in which a sine wave is superimposed, and the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to -500 V (dark potential Vd).

The longitudinal length of the charging roller 2 is 320 mm, and as shown in the schematic diagram of the layer structure in FIG.
It has a three-layer configuration in which a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are sequentially laminated from below on the outer periphery of a. The lower layer 2b is a foamed sponge layer for reducing charging noise,
Is a conductive layer for obtaining a uniform resistance as a whole of the charging roller, and a surface layer 2d is a protective layer provided to prevent a leak from occurring even if there is a defect such as a pinhole on the photosensitive drum 1. is there.

More specifically, the specifications of the charging roller 2 of this embodiment are as follows.

Core 2a: Stainless steel round bar 6 mm in diameter Lower layer 2b: Foamed EPDM of carbon dispersion, specific gravity 0.5
g / cm ³ , volume resistance value 10 ² to 10 ⁹ Ωcm, layer thickness 3.0 mm, length 320 mm middle layer 2c; NBR rubber dispersed with carbon, volume resistance value 10 ² to 10 ⁵ Ωcm, layer thickness 700 μm surface layer 2d A tin oxide and carbon dispersed in a fluororesin resin, a volume resistivity of 10 ⁷ to 10 ¹⁰ Ωcm, a surface roughness (JIS standard 10-point average surface roughness Ra), 1.5 μm
m, layer thickness 10 μm In FIG. 2, reference numeral 2f denotes a charging roller cleaning member, which is a cleaning film having flexibility in this embodiment. The cleaning film 2f is disposed in parallel with the longitudinal direction of the charging roller 2 and has one end fixed to a supporting member 2g that reciprocates by a fixed amount in the longitudinal direction. It is arranged to form a contact nip. The support member 2g is driven in a reciprocating motion by a predetermined amount in the longitudinal direction via a gear train by a drive motor of the printer, and the charging roller surface layer 2d is rubbed by the cleaning film 2f. As a result, contaminants adhering to the surface layer 2d of the charging roller (such as fine powder toner and external additives) are removed.

C) Information writing means 3 is an exposure device as information writing means for forming an electrostatic latent image on the surface of the charged photosensitive drum 1, and this example is a laser beam scanner using a semiconductor laser. . A laser beam modulated according to an image signal sent from a host device such as an image reading device (not shown) to the printer side is output to expose the uniformly charged surface of the rotating photosensitive drum 1 to an exposure position b.
, Laser scanning exposure L (image exposure) is performed. By the laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is reduced, so that an electrostatic latent image corresponding to the scanned and exposed image information is sequentially formed on the rotating photosensitive drum 1 surface. Go.

D) Developing means 4 is a developing device (developing device) as developing means for supplying a developer (toner) to the electrostatic latent image on the photosensitive drum 1 and visualizing the electrostatic latent image. This is a two-component magnetic brush developing type reversal developing device.

Reference numeral 4a denotes a developing container, and 4b denotes a non-magnetic developing sleeve. The developing sleeve 4b is rotatably disposed in the developing container 4a by exposing a part of its outer peripheral surface to the outside. Reference numeral 4c denotes a non-rotating fixed magnet roller inserted in the developing sleeve 4b, 4d denotes a developer coating blade, 4e denotes a two-component developer contained in the developing container 4a, and 4f denotes a bottom side in the developing container 4a. The provided developer agitating member, 4g, is a toner hopper, which stores toner for replenishment.

The two-component developer 4e in the developing container 4a is a mixture of a toner and a magnetic carrier.
Is stirred. In this example, the magnetic carrier has a resistance of about 10 ¹³ Ωcm and a particle size of about 40 μm. The toner is triboelectrically charged to a negative polarity by rubbing with the magnetic carrier.

The developing sleeve 4b is opposed to the photosensitive drum 1 while keeping the closest distance (referred to as S-Dgap) to the photosensitive drum 1 at 350 μm. The facing portion between the photosensitive drum 1 and the developing sleeve 4a is a developing portion c. The developing sleeve 4b is driven to rotate in a direction opposite to the direction in which the photosensitive drum 1 advances in the developing section c. A part of the two-component developer 4e in the developing container 4a is attracted and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 4b by the magnetic force of the magnet roller 4c in the sleeve, and is rotationally conveyed with the rotation of the sleeve. The developer coating blade 4d adjusts the thickness of the photosensitive drum 1 to a predetermined thin layer, and contacts the surface of the photosensitive drum 1 in the developing section c to rub the photosensitive drum surface appropriately. A predetermined developing bias is applied to the developing sleeve 4b from the power supply S2. In this example, the developing bias voltage for the developing sleeve 4b is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, it is an oscillating voltage obtained by superimposing a DC voltage; -350 V AC voltage;

The surface of the rotating developing sleeve 4b is coated as a thin layer, and the amount of toner in the developer conveyed to the developing section c is converted into an electrostatic latent image on the surface of the photosensitive drum 1 by the electric field generated by the developing bias. The electrostatic latent image is developed as a toner image by correspondingly selectively attaching. In the case of this example, the toner adheres to the light-exposed portion on the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

At this time, the charge amount of the toner developed on the photosensitive drum is -25 μC / g.

The developer thin layer on the developing sleeve 4b that has passed the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.

In order to maintain the toner concentration of the two-component developer 4e in the developing container 4a within a predetermined substantially constant range, the toner concentration of the two-component developer 4e in the developing container 4a is not The toner is detected by the density sensor, and the toner hopper 4g is driven and controlled in accordance with the detection information, and the toner in the toner hopper is supplied to the two-component developer 4e in the developing container 4a. The toner supplied to the two-component developer 4e is stirred by the stirring member 4f.

E) Transfer Means / Fixing Means 5 is a transfer device, and in this embodiment, a transfer roller. The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressing force, and the pressing nip portion is a transfer portion d. A transfer material (transfer member, recording material) P is fed to the transfer portion d from a paper feed mechanism (not shown) at a predetermined control timing.

The transfer material P fed to the transfer section d is conveyed while being sandwiched between the rotating photosensitive drum 1 and the transfer roller 5, and during this time, the transfer roller 5 is supplied from the power source S3 to the negative electrode having the normal charge polarity of the toner. In the present example, a transfer bias of +2 kV is applied to the transfer portion d
The toner image on the surface of the photosensitive drum 1 is sequentially electrostatically transferred onto the surface of the transfer material P which is nipped and conveyed.

The transfer material P to which the toner image has been transferred through the transfer section d is sequentially separated from the surface of the rotating photosensitive drum 1 and is conveyed to a fixing device 6 (for example, a heat roller fixing device) to fix the toner image. In response, it is output as an image forming product (print, copy).

(2) Cleanerless System and Toner Charge Control The printer of this embodiment is cleanerless and is dedicated to removing transfer residual toner slightly remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. No cleaning device is provided. The untransferred toner on the surface of the photosensitive drum 1 after the transfer is carried to the developing unit c through the charging unit a and the exposing unit b as the photosensitive drum 1 continues to be rotated, and the developing device 3 cleans (collects) the development at the same time. (Cleanerless system).

In the present embodiment, the developing sleeve 4b of the developing device 4 is rotated in the developing section c in the direction opposite to the traveling direction of the surface of the photosensitive drum 1 as described above. This is advantageous for collecting plate toner.

Since the untransferred toner on the surface of the photosensitive drum 1 passes through the exposure section b, the exposure process is performed on the untransferred toner. However, since the amount of the untransferred toner is small, there is no significant effect.

However, as described above, the transfer residual toner has a charge polarity of a normal polarity, a toner of a reverse polarity (reverse toner),
There is a mixture of toners having a small charge amount, and the reversal toner or the toner having a small charge amount adheres to the charging roller 2 when passing through the charging section a. Failure will occur.

In order to effectively carry out the simultaneous cleaning of the transfer residual toner on the surface of the photosensitive drum 1 by the developing device 3, the charge polarity of the transfer residual toner on the photosensitive drum carried to the developing section c is changed. It is necessary that the toner has a normal polarity and the charge amount is a charge amount of the toner that can develop the electrostatic latent image on the photosensitive drum by the developing device. Inverted toner and toner with an inappropriate charge amount cannot be removed and collected from the photosensitive drum to the developing device, which causes a defective image.

With the diversification of user needs in recent years, the above-described problem is caused by the generation of a large amount of untransferred toner at a time due to continuous printing operation of images having a high printing rate such as photographic images. It will further encourage them.

Therefore, in the present embodiment, at a position downstream of the transfer section d in the photosensitive drum rotation direction, the transfer residual toner (residual developer image) for uniformizing the transfer residual toner on the photosensitive drum 1 is uniform. Means 8 provided downstream of the transfer residual toner equalizing means 8 in the photosensitive drum rotation direction.
A toner (developer) charge amount control unit 7 is provided at a position upstream of the charging unit a in the rotation direction of the photosensitive drum to adjust the charge polarity of the transfer residual toner to a negative polarity which is a normal polarity.

By providing the untransferred toner uniforming means 8, the pattern-like untransferred toner on the photosensitive drum 1 carried from the transfer section d to the toner charge amount control means 7 is not affected even if the toner amount is large. Are dispersed and distributed on the surface of the photosensitive drum 1 and are unpatterned, so that the toner does not concentrate on a part of the toner charge amount control means 7, and the entire transfer residual toner by the toner charge amount control means 7 Thus, the normal polarity charging process is always sufficiently performed, and the adhesion of the transfer residual toner to the charging roller 2 is effectively prevented. Generation of a ghost image of the transfer residual toner image pattern is also strictly prevented.

Here, the triboelectric charge amount of the toner in the present invention can be measured, for example, as follows (blow-off method). FIG. 6 shows a schematic perspective view of an example of the frictional charge measuring device. Referring to the figure, a developer (toner only or a mixture of toner and carrier) whose frictional charge is to be measured is placed in a metal measuring container 82 having a conductive screen 83 at the bottom, and a metal lid 84 is provided. do. At this time, the weight of the entire measurement container 82 was weighed, and this was
(G).

Next, the suction device 81 (at least the measuring container 8)
2 is made of an insulator).
7 and adjust the air flow control valve 86 to set the pressure indicated by the vacuum gauge 85 to 2450 Pa. In this state, suction is sufficiently performed (about one minute) to remove the toner by suction. The potential of the electrometer 89 at this time is directly read and is set to V (volt). 88 is a capacitor, and its capacity is C (μF)
And Further, the weight of the entire measurement container 82 after suction is weighed and is defined as W2 (g). In this case, the triboelectric charge amount T (μC / g) of the toner in the developer is calculated as in the following equation.

T (μC / g) = C × V / (W1−W2) The toner charge amount at the time of development is measured by collecting the toner from the surface of the photosensitive drum 1 and placing the toner in the measurement container 82.

The measurement of the charge amount of the transfer residual toner after passing through the toner charge amount control means 7 is performed by collecting the toner from the surface of the photosensitive drum 1 and putting it in a measurement container 82.

The measurement of the charge amount of the transfer residual toner after passing through the charging section a is performed by collecting the toner from the surface of the photosensitive drum 1 and placing the toner in a measurement container 82.

In this embodiment, the transfer residual toner equalizing means 8 and the toner charge amount controlling means 7 are brush-like members having appropriate conductivity, and the brush portion is brought into contact with the surface of the photosensitive drum 1. It is arranged. f denotes a contact portion between the transfer residual toner equalizing means 8 and the surface of the photosensitive drum 1. "e" is a contact portion between the toner charge amount control means 7 and the surface of the photosensitive drum 1.

The transfer residual toner equalizing means 8 is grounded, and a negative voltage is applied to the toner charge amount control means 7 from the power supply S4.

The transfer residual toner remaining on the photosensitive drum 1 after the transfer of the toner image to the transfer material P in the transfer section d is transferred to the transfer drum P by the subsequent rotation of the photosensitive drum 1.
Then, the toner reaches a contact portion f between the photosensitive drum 1 and the toner, and is once sucked by the transfer residual toner uniforming means 8. Here, since there is a limit to the amount of toner that can be held by the transfer residual toner equalizing means 8, after reaching the saturation state, the toner gradually separates and adheres to the surface of the photosensitive drum 1 and is conveyed. The adhesion state of the toner on the drum 1 surface, that is, the distribution of the toner adhering to the photosensitive drum 1 surface is made uniform.

The untransferred toner on the photosensitive drum surface uniformized by the untransferred toner uniforming means 8 is transferred to the photosensitive drum 1
Is rotated to reach a contact portion e between the toner charge amount control means 7 and the photosensitive drum 1, and the transfer residual toner on the photosensitive drum 1 passing through the toner charge amount control means 7 has a negative polarity whose charge polarity is the normal polarity. Aligned to.

By setting the charging polarity of the transfer residual toner to the negative polarity, which is the normal polarity, when the charging section a located further downstream charges the surface of the photosensitive drum 1 from above the transfer residual toner, The reflection power on the photosensitive drum 1 is increased,
This prevents the transfer residual toner from adhering to the charging roller 2.

For this reason, the amount of charge required for the transfer residual toner needs to be 2.2 times or more as compared with the amount of charge of the toner during development.

FIG. 3 shows the relationship between the voltage applied to the toner charge control means 7 and the toner charge after passing through the toner charge control means 7. When the voltage is not applied to the toner charge amount control means 7, as described above, the transfer residual toner is affected by the negative toner of the image portion, the positive toner of the non-image portion, and the positive voltage of the transfer. The charge amount is indefinite because the toner includes a toner whose polarity has been inverted to the positive polarity. Further, by applying a voltage to the toner charge amount control means 7, the toner charge amount after passing through the toner charge amount control means 7 increases, and it can be seen that the toner charge amount is saturated at a certain value or more. In the toner used in this example, the charge amount when saturated was -90 [mu] C / g.

Next, before the untransferred toner enters the charging section a,
FIG. 4 is a graph showing the relationship between the transfer residual toner charge amount and the amount of adhesion to the charging roller 2 when the transfer residual toner amount is set to 1.
Shown in It can be seen that the adhesion amount is reduced by increasing the charge amount of the transfer residual toner. At this time, the occurrence of a poorly charged image due to the adhesion of the transfer residual toner to the charging roller 2 occurred when the charge amount of the transfer residual toner was −55 μC / g or less.

Therefore, in order to prevent the transfer residual toner from adhering to the charging roller 2 and suppress the occurrence of a poorly charged image, the charge amount of the transfer residual toner is compared with the toner charge amount during development. It can be seen that more than two times is necessary.

In this embodiment, the voltage applied to the toner charge control means 7 is -800 V,
The charge amount of the transfer residual toner after passing through was set to −70 μC / g.

Next, the recovery of the transfer residual toner in the developing step will be described.

As described above, the developing device 4 is of a cleanerless type which cleans the transfer residual toner simultaneously with the development.
As described above, the charge amount of the developed toner on the photosensitive drum 1 is 125 μC / g in this embodiment. Here, the relationship between the transfer amount and the charge amount for the transfer residual toner to be collected in the developing device 4 under the developing conditions in the present embodiment is shown in Table 1.
Shown in

[0085]

[Table 1]

The toner charge amount for collecting the transfer residual toner on the photosensitive drum 1 to the developing device 4 is 0.5 to 1.8 as compared with the toner charge amount at the time of development (−25 μC / g).
It needs to be double.

However, as described above, in order to prevent the toner from adhering to the charging roller 2, the transfer residual toner charged to the negative polarity of −70 μC / g by the toner charge amount controller 7 is transferred to the developing device 4. It is necessary to remove static electricity in order to recover.

FIG. 5 shows the relationship between the toner charge amount after the toner on the photosensitive drum 1 having a charge amount of -70 μC / g has passed through the charging roller 2 and the Vpp of the AC voltage applied to the charging roller 2. Shown in It can be seen that the power is being received as the AC voltage Vpp is increased.

An AC voltage (frequency f 1000 Hz, frequency f 1000 Hz) is applied to the charging roller 2 to charge the peripheral surface of the photosensitive drum 1.
(Vpp 1400V), the transfer residual toner is subjected to AC static elimination. Therefore, the charging unit a
Is -30 [mu] C / g. In the developing step, the transfer residual toner on the photosensitive drum 1 on which the toner should not be developed is transferred to the developing device 4 for the above-described reason.
Will be collected.

In this way, the toner remaining amount transfer toner on the photosensitive drum 1 carried from the transfer section d to the charging section a is charged by the toner charge amount control means 7 so as to have a negative polarity, which is a normal polarity, and is charged. While the toner is prevented from adhering to the charging roller 2, the photosensitive drum 1 is charged to a predetermined potential by the charging roller 2, and at the same time, the transfer performed by the toner charge amount control means 7 to the negative polarity which is the normal polarity. By controlling the charge amount of the residual toner to an appropriate charge amount at which the developing device 4 can develop the electrostatic latent image on the photosensitive drum, the transfer residual toner can be efficiently collected in the developing device. In addition, it is possible to provide an image forming apparatus which is free from a charging failure and a defective image, and which makes use of the advantages of a cleanerless system.

<Embodiment 2> The structure of an image forming apparatus (printer) of the present embodiment is the same as that of the first embodiment.

The charge amount of the developer (toner) changes depending on the environment, the physical properties of the developer, and the like. In the present embodiment, the amount of toner charge on the photosensitive drum 1 after development is
A case of 35 μC / g, which is larger than -25 μC / g in Example 1, will be described.

The toner charge amount of the transfer residual toner after passing through the toner charge amount control means 7 is -90 μC / g. Therefore, in the charging section a, the transfer residual toner did not adhere to the charging roller 2 and no charging failure occurred.

The charge amount of the transfer residual toner after passing through the charging section a was -40 μC / g, and the toner was well collected in the developing device 4.

<Embodiment 3> The configuration of an image forming apparatus (printer) of the present embodiment is the same as that of the first embodiment.

A DC voltage may be applied to the transfer residual toner uniforming means 8. The transfer residual toner is once sucked by the transfer residual toner uniforming means. In this case, similarly to the above embodiment, there is a limit to the amount of toner that can be held by the transfer residual toner uniforming means 8, so that the toner gradually separates and adheres to the surface of the photosensitive drum 1 after reaching the saturation state. Although the toner is conveyed, the state of adhesion of the toner on the surface of the photosensitive drum 1, that is, the distribution of the toner attached to the surface of the photosensitive drum 1 is made uniform.

In the present embodiment, a DC voltage of -300 V was applied to the transfer residual toner uniforming means 8.

<Others> 1) The untransferred toner uniforming means 8 and the toner charge amount controlling means 7 are fixed brush-like members in the embodiment, but are arbitrary such as a brush rotating body, an elastic roller body, and a sheet-like member. It can be a member of the form.

2) The image carrier has a surface resistance of 10 ⁹ to 10 ¹⁴
It may be of a direct injection charging type provided with a charge injection layer of Ω · cm. Even when the charge injection layer is not used, the same effect can be obtained, for example, when the charge transport layer is in the above-described resistance range. An amorphous silicon photoreceptor whose surface layer has a volume resistance of about 10 ¹³ Ω · cm may be used.

3) As the flexible contact charging member, besides the charging roller, one having a shape and material such as a fur brush, felt, cloth and the like can be used. In addition, it is possible to obtain more appropriate elasticity, conductivity, surface properties and durability by combining various materials.

4) As a waveform of an alternating voltage component (AC component, a voltage whose voltage value changes periodically) of the oscillating electric field applied to the contact charging member and the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It is. It may be a rectangular wave formed by periodically turning on / off a DC power supply.

5) The image exposure means as the information writing means on the charged surface of the photoreceptor as the image carrier is not limited to the laser scanning means of the embodiment, but may be a digital exposure using a solid light emitting element array such as an LED. It may be a means. An analog image exposure unit using a halogen lamp, a fluorescent lamp, or the like as a document illumination light source may be used. In short, any device that can form an electrostatic latent image corresponding to image information may be used.

6) The image carrier may be an electrostatic recording dielectric or the like. In this case, after uniformly charging the dielectric surface,
The charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information.

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

In general, a method of developing an electrostatic latent image is to coat a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and to coat the magnetic toner with the developer carrying member. A method of applying an electrostatic latent image on the image carrier in a non-contact state by applying a magnetic force on the image carrier, conveying the image, and developing the electrostatic latent image (one-component non-contact development);
A method of applying the toner coated on the developer carrying member as described above to the image carrier in a contact state to develop an electrostatic latent image (one-component contact development); A method (two-component contact development) in which a mixture of the above is used as a developer (two-component developer) to be conveyed by magnetic force and applied in a contact state to an image carrier to develop an electrostatic latent image; The two-component developer is applied to the image carrier in a non-contact state to develop an electrostatic latent image (two-component non-contact development).

8) The transfer means is not limited to the roller transfer of the embodiment, but may be a blade transfer, a belt transfer, or another contact transfer charging system, or a non-contact transfer charging system using a corona charger. .

9) The present invention can be applied not only to the formation of a single-color image but also to an image forming apparatus for forming a multicolor or full-color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt.

[0108]

As described above, according to the present invention, there is provided a cleaner-less type image forming apparatus which removes, collects, and reuses a transfer residual developer on an image carrier after a transfer step by simultaneous cleaning with development. By preventing the transfer residual developer from adhering to the charging unit and efficiently collecting the transfer residual developer in the developing unit, there is no charging failure or defective image, and a cleaner-less system is provided. An image forming apparatus utilizing the advantages can be provided.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a layer configuration of a photosensitive drum and a charging roller.

FIG. 3 is a diagram showing a relationship between a voltage applied to a toner charge amount control unit and a charge amount of a transfer residual toner.

FIG. 4 is a diagram showing the relationship between the charge amount of the transfer residual toner and the toner adhesion amount to the charging roller.

FIG. 5 is a diagram illustrating a relationship between a toner charge amount after passing through a charging roller and an applied AC voltage Vpp.

FIG. 6 is a schematic perspective view showing a triboelectric charge amount measuring device.

[Explanation of symbols]

1. Photosensitive drum (image carrier), 2. Charging roller, 3
..Laser beam scanner, 4 developing device, 5 transfer roller, 6 fixing device, 7 toner charge amount control means (developer charge amount control means), 8 transfer residual toner uniforming means (Residual developer image uniforming means), S1 to S4 ... bias voltage application power supply

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Motoki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H003 AA12 BB13 CC05 CC06 DD03 2H077 AA37 AC16 AE08

Claims (15)

[Claims] An image carrier, a charging unit for charging a surface of the image carrier, an information writing unit for forming an electrostatic latent image on the charged image carrier, and a developer for supplying a developer to the electrostatic latent image. Developing means for visualizing the electrostatic latent image; transfer means for transferring the visualized developer image to a transfer material; and developer charging for charging the developer on the surface of the image carrier which is located upstream of the charging means. An amount control unit, and a residual developer image that is located upstream of the developer charge amount control unit and downstream of the transfer unit and remains on the image carrier surface after transferring the developer image onto a transfer material. Means for uniformizing the residual developer image, and a method for uniformizing the residual developer image remaining on the image carrier after the transfer of the developer image by the residual developer image uniformizing means. The developer remaining on the image carrier is brought to the normal polarity by the developer charge amount control means. An image forming apparatus, comprising: performing a charging process; charging the surface of the image carrier by the charging unit; 2. An image forming apparatus according to claim 1, wherein said charging means is of a contact charging type. 3. An image forming apparatus according to claim 1, wherein an oscillating electric field is applied to said charging means. 4. An image forming apparatus according to claim 1, wherein said information writing means is an exposure means. 5. An image forming apparatus according to claim 1, wherein said residual developer image uniforming means comprises an electrode portion having a potential difference with respect to said image carrier. 6. An image carrier, charging means for charging the surface of the image carrier, information writing means for forming an electrostatic latent image on the charged image carrier, and supplying developer to the electrostatic latent image Developing means for visualizing the electrostatic latent image; transfer means for transferring the visualized developer image to a transfer material; and developer charging for charging the developer on the surface of the image carrier which is located upstream of the charging means. An amount control unit, and a residual developer image that is located upstream of the developer charge amount control unit and downstream of the transfer unit and remains on the image carrier surface after transferring the developer image onto a transfer material. Means for uniformizing the residual developer image, and a method for uniformizing the residual developer image remaining on the image carrier after the transfer of the developer image by the residual developer image uniformizing means. The developer remaining on the image carrier is brought to the normal polarity by the developer charge amount control means. Charging, charging the surface of the image carrier with the charging unit, and at the same time, setting the charging amount to an absolute value smaller than the absolute value of the charging amount when the charging process is performed by the developer charging amount control unit. Image forming apparatus. 7. An image forming apparatus according to claim 6, wherein said charging means is of a contact charging type. 8. An image forming apparatus according to claim 6, wherein an oscillating electric field is applied to said charging means. 9. An image forming apparatus according to claim 6, wherein said information writing means is an exposure means. 10. An image forming apparatus according to claim 6, wherein said residual developer image uniforming means comprises an electrode portion having a potential difference with respect to said image carrier. 11. An image carrier, charging means for charging the surface of the image carrier, information writing means for forming an electrostatic latent image on the charged image carrier, and supplying developer to the electrostatic latent image. Developing means for visualizing the electrostatic latent image; transfer means for transferring the visualized developer image to a transfer material; and developer charging for charging the developer on the surface of the image carrier which is located upstream of the charging means. An amount control unit, which is located upstream of the developer charge amount control unit and downstream of the transfer unit, and uniformizes the residual developer image remaining on the carrier surface after transferring the developer image onto a transfer material. A residual developer image uniformizing means, and a residual developer image remaining on the image carrier after transfer of the developer image is homogenized by the residual developer image uniformizing means. The developer remaining on the image carrier is removed by the developer The charging process is performed with a charge amount of 2.2 times or more the charge amount of the developer after the step and at a normal polarity, and the surface of the image bearing member is charged by the charging unit. An image forming apparatus characterized in that the charge amount is 5 to 1.8 times. 12. An image forming apparatus according to claim 11, wherein said charging means is of a contact charging type. 13. An image forming apparatus according to claim 11, wherein an oscillating electric field is applied to said charging means. 14. An image forming apparatus according to claim 11, wherein said information writing means is an exposure means. 15. An image forming apparatus according to claim 11, wherein said residual developer image uniforming means comprises an electrode portion having a potential difference with respect to said image carrier.