JPH11311916A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electrification failure caused by soil of a contact electrifying member with toner and to ensure the formation of a satisfactory image over a long period, in the image forming device which develops and cleans simultaneously. SOLUTION: As an electrifying bias voltage, the overlap of a DC bias voltage and an asymmetrical AC bias having a different duty ratio is applied to the electrifying roller 2, disposed in contact with a photoreceptive drum 1, by an electrifying-bias application power source S1. This enables the uniform electrification of the surface of the photoreceptive drum 1 and the steady application of triboelectricity with a specific polarity to residual toner, and hence satisfactory simultaneous-development-and-cleaning. Thus, the electrifying roller 2 is prevented from being soiled with the residual toner.

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 a copying machine and a printer.

[0002]

2. Description of the Related Art FIG. 9 shows a schematic configuration of an electrophotographic copying machine as a conventional image forming apparatus.

In FIG. 1, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a "photosensitive drum") as an image carrier, which is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1. You. During the rotation process, the photosensitive drum 1 is subjected to static elimination exposure by the pre-exposure lamp 2,
After being subjected to uniform charging processing of a predetermined polarity and potential by a corona charger 3 as charging means, image exposure L by image exposure means (projection image formation exposure means of a document image, laser light scanning exposure means, etc.) not shown. As a result, the uniformly charged surface is selectively neutralized (or attenuated in potential) corresponding to the exposed image pattern, and an electrostatic latent image is formed. Then, the electrostatic latent image is developed as a toner image by the developing device 4 as a developing unit.

On the other hand, a transfer material P as a member to be transferred is fed between a photosensitive drum 1 and a corona charger 7 as a transfer means at a predetermined control timing from a paper feed mechanism (not shown). The toner image on the photosensitive drum 1 is electrostatically transferred to the front surface of the transfer material P by charging the back surface of P with a polarity opposite to that of the toner.

Next, the transfer material P is electrostatically separated from the surface of the photosensitive drum 1 by the separation charger 8, and is introduced into the fixing means 6, where the toner image is subjected to a fixing process and output as a copy or a print.

After the transfer of the toner image onto the transfer material P, the toner remaining on the surface of the photosensitive drum 1 that has not been transferred onto the transfer material P (hereinafter referred to as “residual toner”) is removed by cleaning means (cleaner) 5. For image formation.

In the above-described image forming apparatus, the charging means 3 for charging the photosensitive drum 1 is not a corona charger, but a contact charging type charger (magnetic brush charging, fur brush charging, roller charging, etc.). You can also. The contact-type charging device has an advantage that generation of ozone and the like can be reduced. Further, the transfer charger 7 can also be a transfer roller. Basically, an image is formed through a series of image forming processes of charging, exposure, development, transfer, fixing, and cleaning as described above.

In recent years, the size of such an image forming apparatus has been reduced. However, devices for performing the above-described image forming processes of charging, exposure, development, transfer, fixing, and cleaning have been downsized. There is a limit to miniaturization as a whole just by doing. Further, the above-mentioned residual toner is collected by the cleaner 5 as waste toner, but it is preferable that this waste toner is not generated from the viewpoint of environmental protection.

In view of this, an image forming apparatus of a so-called cleaner-less system in which the above-described cleaner 5 is removed and the developing device 4 performs simultaneous cleaning (recovery of residual toner) is developed.

Simultaneous development and cleaning means that the residual toner slightly remaining on the photosensitive drum 1 after the transfer of the toner image to the transfer material P is removed by applying a DC voltage applied to the developing device 4 at the time of development after the next process to the surface of the photosensitive drum 1. This is a method of collecting by fogging potential difference V _back which is a potential difference from the potential.

According to this method, since the residual toner is collected and reused after the next step, waste toner can be eliminated. Also, since there is no need to provide a cleaner 5 dedicated to cleaning, the advantage in terms of space is great,
The whole can be greatly reduced in size.

[0012]

However, in the above-described image forming apparatus, when the cleaner 5 is removed and the developing device 4 is cleaned at the same time as the developing operation, a positive ghost of the previous image is generated in a portion where there is no image in the period of the photosensitive drum. Has occurred.

This positive ghost is caused by the fact that the residual toner of the previous image could not be collected in the developing area or was insufficiently collected, so that the residual toner reached the transfer portion T, and the original toner on the surface of the transfer material P This is a phenomenon that occurs when the image is transferred to a white background.

One of the measures to prevent this positive ghost is as follows.

As a charging means, a contact charging device is used in place of the corona charger 3, and a DC voltage is applied to the contact charging member brought into contact with the photosensitive drum 1 to bring the photosensitive drum 1 to a predetermined polarity and a predetermined potential. The primary toner is charged, and the residual toner on the photosensitive drum 1 passing through the contact charging member is brought to the developing device 4 with the regular charging polarity. Thus, the above-described image defect (positive ghost) can be prevented.

However, also in this case, when a DC voltage is applied to the contact charging member and an image is output, poor charging due to toner contamination of the contact charging member occurs when only a few sheets are passed. As a result, the quality of the output image deteriorated.

Further, when a contact transfer member (for example, a transfer roller) which is arranged in contact with the surface of the photosensitive drum 1 is used as the transfer means, when the above-described positive ghost, cleaning failure, or jam of the transfer material P occurs. To
In some cases, the contact transfer member is contaminated by toner, which may cause image defects. Conventionally, in such a case, a method of transferring the contaminated toner to the photosensitive drum 1 by a cleaning bias to clean the contact charging member is generally performed. However, as described above, since the capability of simultaneous development and cleaning is insufficient, the developing device 4, the toner which cannot be collected again contaminates the contact charging member.

Therefore, the present invention provides an image forming apparatus which performs cleaning at the same time as the image forming apparatus in which the toner is prevented from being contaminated by the contact charging member to perform good charging over a long period of time, thereby preventing the output image quality from deteriorating. It is intended to provide a device.

Another object of the present invention is to provide an image forming apparatus which performs simultaneous cleaning with development, in which image transfer is performed over a long period of time by preventing toner contamination of a contact transfer member, thereby preventing deterioration of output image quality. An object of the present invention is to provide a forming apparatus.

[0020]

According to the first aspect of the present invention, there is provided a charging means for charging the surface of an image carrier by a contact charging member, and a charging means for charging the surface of the image carrier after charging. An information writing unit that forms an electrostatic latent image; a developing unit that develops the electrostatic latent image as a toner image with a developer carried on a developer carrier; and an electric field that is formed between the image carrier and the developing unit. Transfer means for transferring a toner image on the image carrier to a transfer material, wherein the developing means also serves as a cleaning means for collecting residual toner remaining on the image carrier. The member includes a power supply that superimposes and applies a DC bias voltage and an asymmetrical alternating voltage having a different duty ratio as a charging bias voltage, and the image bearing member and the contact charging member are provided by the charging bias voltage. To form an alternating electric field asymmetric between,
At the same time that the image carrier is uniformly charged to a predetermined potential, a charge of a predetermined polarity is applied to the residual toner, and the residual toner having the charge is collected by the developing unit. .

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the developing system of the developing unit is a reversal developing system using a toner having the same polarity as the charging polarity of the image carrier. When a duty ratio of the alternating voltage is a ratio of turning on a bias having the same polarity as the charging polarity of the asymmetrical alternating voltage, the duty ratio is in a range of 60 to 90%.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the developing system of the developing unit is a regular developing system using a toner having a polarity opposite to a charging polarity of the image carrier. If the duty ratio of the alternating voltage is a ratio of turning on the same polarity side bias as the charging polarity of the asymmetrical alternating voltage, the duty ratio is in a range of 10 to 40%.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second, or third aspect, the toner particles contained in the developing means are toners produced by a polymerization method. I do.

According to a fifth aspect of the present invention, there is provided a charging means for charging the surface of an image carrier by a contact charging member, an information writing means for forming an electrostatic latent image on the surface of the image carrier after charging,
Developing means for developing the electrostatic latent image as a toner image with a developer carried on a developer carrier, and pressing a contact transfer member against the image carrier and pressing the contact transfer member between the image carrier and the contact member An image forming apparatus, comprising: transfer means for forming an electric field to transfer a toner image on the image carrier to a transfer material, wherein the developing means also serves as a cleaning means for collecting residual toner remaining on the image carrier. In the first aspect, at a predetermined timing during non-image formation, an electric field is formed between the contact charging member and the image carrier to transfer toner remaining on the contact charging member to the image carrier side. And a power supply for superimposing and applying a DC bias voltage and an asymmetrical alternating voltage having a different duty ratio as a charging bias voltage to the contact charging member. Therefore, an asymmetrical alternating electric field is formed between the image carrier and the contact charging member to uniformly charge the image carrier to a predetermined potential and at the same time impart a charge of a predetermined polarity to the residual toner. And a second step of recovering the residual toner to which the charge has been applied by the developing unit.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 (1) Schematic Configuration and Operation of Entire Image Forming Apparatus FIG. 1 shows an example of an image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of an electrophotographic laser beam printer. In a laser beam printer (hereinafter, referred to as an "image forming apparatus") shown in the figure, a contactless charging device is used as a charging means for charging the surface of the image carrier, and a cleanerless system which performs simultaneous development and cleaning as a developing means. Is adopted.

In the figure, A indicates a printer unit, and B indicates an image reading unit (image scanner).

In the image reading section B, reference numeral 13 denotes a platen glass fixedly disposed above the image reading section B. Manuscript G
Is placed on the upper surface of the platen glass 13 with the image side to be copied facing downward, and a document pressure plate (not shown) is placed over the platen. 14 is a document irradiation lamp 14
a, an image reading unit provided with a short focus lens array 14b, a CCD sensor 14c, and the like. When the copy button (not shown) is pressed, the image reading unit 14 moves from the home position indicated by a solid line to the right end in FIG. When it reaches the predetermined forward end point indicated by the broken line, it is driven backward and moves in the direction of arrow K2, and returns to the initial home position.

The image reading unit 14 is configured such that the downwardly facing image surface of the original G on the original platen glass 13 during the forward driving process thereof has the original illuminating lamp 14 a of the image reading unit 14.
The illumination scanning light is sequentially scanned in the direction of arrow K1, and the reflected light of the illumination scanning light on the document surface is imaged and incident on the CCD sensor 14c by the short focus lens eye 14b.

The CCD sensor 14c includes a light receiving section, a transfer section, and an output section. The light signal is converted into a charge signal in the CCD light receiving unit, and the transfer unit sequentially transfers the light signal to the output unit in synchronization with the clock pulse. The output unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the voltage signal. The analog signal obtained in this manner is subjected to well-known image processing, converted into a digital signal, and sent to the printer unit A.

That is, the image information of the original G is photoelectrically read by the image reading section B as a time-series electric digital pixel signal (image signal).

The printer section A includes a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image carrier. The photosensitive drum 1 has a predetermined peripheral speed around a center support shaft,
In the present embodiment, an arrow R with a rotation speed of 150 mm / s
It is driven to rotate in one direction.
The charging roller (contact charging member) 2 constituting the charging means receives a uniform negative charging process. Charging roller 2
Are arranged in contact with the photosensitive drum 1 to form a charging nip N between the photosensitive drum 1 and the photosensitive drum 1.
Along with the direction of arrow R1.
Further, the charging roller 2 has a charging bias application power source S1.
, A predetermined charging bias is applied, whereby the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential.

Then, a laser beam output from a laser scanning unit (laser scanner) 3 as information writing means, that is, from the image reading unit B side to the printer unit A side, is sent to the uniformly charged surface of the photosensitive drum 1. The scanning exposure L by the laser light modulated in accordance with the image signal is performed, so that the electric charge in the laser-light irradiated portion is removed. In this way, an electrostatic latent image corresponding to the image information of the original G that is photoelectrically read by the image reading unit B is sequentially formed on the surface of the photosensitive drum 1.

The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by a developing device (developing means) 4. The developing device 4 has a rotatable developing sleeve 42 disposed opposite to the surface of the photosensitive drum 1.
A developing bias is applied to the electrostatic latent image by a developing bias applying power source S2, whereby toner is attached to the electrostatic latent image and developed as a toner image. The development in the present embodiment is a so-called reversal development in which toner is attached to a portion from which charge has been removed by the above-described exposure.

On the other hand, the transfer material P stored in the paper feed cassette 6 is fed one by one by a paper feed roller 7 and fed into the printer section A. It is supplied to a transfer nip T between the transfer roller 1 and a transfer roller (transfer means) 5. A transfer bias having a polarity opposite to that of the toner on the photosensitive drum 1 is applied to the transfer roller 5 from a transfer bias application power source S3 at a predetermined timing, and the surface of the transfer material P supplied to the transfer nip portion T is applied to the photosensitive drum 1 The toner image on the surface is electrostatically transferred.

The transfer material P to which the toner image has been transferred through the transfer nip portion T is sequentially separated from the surface of the photosensitive drum 1 and is conveyed to the fixing device 10 by the conveying device 9, where the toner image is heated and heated. Pressed and fixed on the surface, then
The paper is output as a copy or print on a paper discharge tray 12 by a paper discharge roller 11.

On the other hand, the photosensitive drum 1 after the transfer of the toner image
The toner remaining on the surface without being transferred to the transfer material P (residual toner) is removed by the developing device 4 as described later, and is used for the next image formation.

The description of the schematic configuration and operation of the entire image forming apparatus is now completed, and then each member will be described in detail.

(2) Photosensitive Drum (Image Carrier) In the present embodiment, as described above, the photosensitive drum 1 is used as an image carrier. As the surface layer of the photosensitive drum 1, an organic photosensitive member or the like can be used. As an example, in the present embodiment, a function-separated type OPC photosensitive drum is used, and the charge generation layer has a thickness of 0.2 μm.
And a polycarbonate having a hydrazone compound having a thickness of about 22 μm dispersed therein was used as a charge transport layer on the surface layer side.

(3) Laser Scanning Unit FIG. 2 shows a schematic configuration of the laser scanning unit 3. When the surface of the photosensitive drum 1 as a surface to be scanned is subjected to laser scanning exposure by the laser scanning unit 3, first, the solid-state laser element 32 is blinked at a predetermined timing by the light emission signal generator 31 based on the input image signal. ON / OFF). The laser light emitted from the solid-state laser element 32 is converted into a substantially parallel light beam by the collimator lens system 33, and further scanned in the direction of arrow K3 by the rotating polygon mirror 34 rotating at high speed in the direction of arrow R34. The fθ lens groups 35a, 35b and 35c form a spot image on the surface of the photosensitive drum 1. By such laser beam scanning, an exposure distribution for one image scan is formed on the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 is scrolled by a predetermined amount in each scan in a direction perpendicular to the main scanning direction. In this case, an exposure distribution according to the image signal is obtained on the surface of the photosensitive drum 1.

(4) Charging Roller The charging roller 2 as a contact charging member is of a well-known contact charging type, and is, for example, 100-200 μm and a volume resistivity of 10 ⁶ Ω · cm on a 3 mm thick elastic conductive rubber. A medium resistance layer having a thickness of about 10 μm and an anti-sticking layer of several tens μm (a nylon resin or the like) was further provided thereon. At this time, a metal rod such as stainless steel (SUS) was used as the core material, and the outer diameter of the charging roller itself was configured to be 12 mm in total. The charging roller 2 is brought into contact with the photosensitive drum 1 at a linear pressure of about 20 to 50 g / cm,
A charging nip N of about 2 mm was formed. The charging roller 2 is configured to rotate in the direction of the arrow R2 as the photosensitive drum 1 rotates in the direction of the arrow R1. Further, a charging bias in which an asymmetric alternating voltage is superimposed on a DC voltage of -600 V is applied to the charging roller 2 by a charging bias power supply S1.

Here, the asymmetrical alternating voltage refers to the one shown in FIG.
(A) a waveform obtained by changing the duty of a rectangular wave, (b) a waveform obtained by combining two sine waves having different frequencies on the plus side and the minus side of the voltage,
An asymmetrical alternating voltage such as a triangular pulse waveform as shown in (c) and a trapezoidal pulse waveform as shown in (d). In these figures, when minus is taken upward, V
_max is the negative maximum voltage, V _min is the negative minimum, V
_center is the average value of the above-mentioned maximum value V _max and minimum value V _min , V _rms indicates the effective value, and the effective value V _rms deviates from the average value V _center by applying an asymmetrical alternating voltage (these values are referred to as V _rms ). In the figure, it shifts to the minus side). In FIGS. 3A and 3B, all of them are shifted to the minus side. Also, in any of the waveforms (a) to (d), if the ratio of the time T ₋ during which the voltage is negative with respect to the effective value with respect to one cycle T is defined as the duty ratio, this duty ratio becomes 50 % Is set to exceed.

By applying the charging bias as described above, the following is achieved. The surface of the photosensitive drum 1 is uniformly charged to approximately -600V. At this time, since the potential history before charging is also made uniform, the pre-exposure can be omitted. If there is a small amount of residual toner, the charge (tribo) polarity and the amount of charge can be controlled to predetermined values, and the residual toner adheres to the charging roller 2 to stain it. , Does not fly around.

The reason for the above is that the charging of the photosensitive drum 1 by the charging roller 2 occurs in the small gap portion G near the charging nip portion N as shown in FIG.
It is conceivable that the proportion depending on air discharge according to Schen's law is large. That is, according to the aerial discharge, once the discharge is generated and the photosensitive drum 1 is charged, a charged area having a certain width is formed, so that the DC voltage is applied to the charging roller 2 without applying an alternating voltage. When only the voltage is applied, the electric field near the charging nip N is weakened by the rotation of the photosensitive drum 1 until the above-mentioned charged area passes through the air discharge area near the charging nip N, and the next discharge occurs. A time that does not occur, a so-called discharge relaxation time occurs. On the other hand, if the alternating voltage is superimposed on the charging roller 2, the voltage exceeds the discharge threshold value near the charging nip N every time the voltage is alternated. charge by the charging roller 2 to 1 alternating frequency and alternating voltage upper and lower peaks of (V _max, V _min) intermediate value (=
V _center ) and no longer depends on the ratio (duty ratio) between T and T ₋ . Here, since the number of alternations of V _max and V _min is equal, it is considered that the surface potential of the photosensitive drum 1 converges to almost the V _center value, that is, −600 V.

On the other hand, the reason for the above is that the charge application of the residual toner t remaining on the photosensitive drum 1 is not caused by the aerial discharge as described above but by the charge injection in the charging nip N in FIG. It is thought to be caused. That is, in this case, the amount of charge injection is dependent on the V _rms is the effective value of the bias voltage applied to the charging roller 2, the triboelectric charge of the residual toner t is the application time of the alternating voltage, T and T _- of It can be controlled by the ratio (duty ratio). Although the reason why the charging roller 2 is not contaminated or scattered by the residual toner t is not fully understood, as a comparative example, the duty ratio of the alternating electric field is set to 50% (that is,
If the amount is plus or minus the same amount), a phenomenon occurs in which the residual toner t adheres to the charging roller 2 to cause contamination, and the toner scatters around in a cloud shape. From this point, it is considered that the electric field effect of separating the residual toner t from the charging roller 2 at the charging nip N and keeping the remaining toner t on the photosensitive drum 1 is caused by the long T ₋ . Note that specific charging bias conditions will be described later in detail.

(5) Developing Apparatus Generally, a method of developing an electrostatic latent image is such that non-magnetic toner is coated on a developing sleeve with a blade or the like, and magnetic toner is coated by a magnetic force and conveyed to a photosensitive drum. A non-contact development method (one-component non-contact development), a method of developing the toner coated as described above in contact with the photosensitive drum (one-component contact development), and a method of developing the toner particles. A method in which a mixture of magnetic carriers is used as a developer and transported by magnetic force to develop the photosensitive drum in contact with the photosensitive drum (two-component contact development); And two-component non-contact development.

In the present embodiment, a mixture of non-magnetic toner particles and magnetic carrier particles is used as a developer, and this developer is used as a magnetic brush or the like by a magnetic force on a developing sleeve 4a as a developing carrier. A two-component contact developing system is used in which the toner is held, transported to a developing unit, and brought into contact with the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image.

This is because it is advantageous in terms of improving the image quality and stability of the image and in terms of the mechanical retrievability of the magnetic brush when the residual toner on the photosensitive drum 1 is recovered.

FIG. 5 is a longitudinal sectional view showing a schematic structure of the developing device 4 of the two-component contact developing system (two-component magnetic brush development) used in the present embodiment.

In the figure, reference numeral 41 denotes a developing container, 42 denotes a developing sleeve as a developer carrier, and 43 denotes a developing sleeve 4.
A magnet roller 44 as a magnetic field generating means fixedly disposed in the inside 2; 44, a regulating blade for regulating the layer thickness of the developer carried on the surface of the developing sleeve 42; 45, a developer stirring / conveying screw; 41 is a two-component developer, which is a mixture of non-magnetic toner particles t and magnetic carrier particles c. Reference numeral 47 denotes a toner supply unit.

The developing sleeve 42 has a closest distance (gap) to the photosensitive drum 1 at least at the time of development.
The developing sleeve 42 is arranged so as to be
The developer magnetic brush thin layer 46a carried on the outer surface of the photosensitive drum 1 is set in contact with the surface of the photosensitive drum 1. The contact portion between the developer magnetic brush thin layer 46a and the photosensitive drum 1 is a developing portion (developing region) D.

The developing sleeve 42 is driven to rotate around the fixedly arranged magnet roller 43 at a predetermined rotational speed in the direction of arrow R4, and the developing sleeve 4
2 The developer 46 is applied to the outer surface by the magnetic force of the magnet roller 43.
Is formed. The magnetic brush is conveyed along with the rotation of the developing sleeve 42 in the direction of arrow R4, is regulated by a regulating blade 44, and is taken out of the developing container 41 as a developer magnetic brush thin layer 46a having a predetermined layer thickness to be developed by the developing unit D. To contact the surface of the photosensitive drum 1,
With the subsequent rotation of the developing sleeve 42, the developing sleeve 42 is returned and transported again into the developing container 41.

A developing bias in which a DC voltage and an alternating voltage are superimposed is applied between the developing sleeve 42 and the conductive drum substrate 1a of the photosensitive drum 1 by a developing bias applying power source S2. In the present embodiment, the potential setting of the photosensitive drum 1 is set to -600 V for the dark portion and -150 V for the bright portion, and the developing bias for the DC voltage is -450 V, the alternating voltage; the amplitude V _PP = 1500 V, and the frequency V _f = 200.
A developing bias of 0 Hz is applied, and in the developing section D, the toner particles t in the developer magnetic brush thin layer 46a on the developing sleeve 42 side are selectively adhered to the electrostatic latent image on the photosensitive drum 1 side. Is developed as a toner image.

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency increases, and the image becomes high quality.
Conversely, there is a danger that fogging is likely to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1.

The toner concentration (mixing ratio of the toner to the carrier) of the developer 46 in the developing container 41 gradually decreases as the toner is consumed for developing the electrostatic latent image. Developing container 4
When the toner concentration of the developer 46 in the first container 1 is detected by a detecting means (not shown) and decreases to a predetermined allowable lower limit concentration, the toner is supplied from the toner supply unit 47 to the developer 46 in the developing container 41 and the developing container 41 is supplied. The toner replenishment control is performed such that the toner concentration of the developer 46 in the inside is always kept within a predetermined allowable range.

The two-component developer 46 used in the present embodiment.
Is a toner particle t; titanium oxide is used in a weight ratio of 1 to a negatively charged toner having an average volume particle diameter of 6 μm manufactured by a pulverization method.
% Externally added Carrier c: A magnetic carrier having a saturation magnetization of 205 emu / cm ^{3 and} an average particle diameter of 35 μm was mixed at a weight ratio of 6:94.

Here, a method of measuring the toner particle size distribution in the present invention will be described.

As a measuring device, a Coulter counter TA-2 type (manufactured by Coulter Co., Ltd.) was used.
Interface to output volume average distribution (made by Nikkaki)
And CX-1 personal computer (manufactured by Canon Inc.), and the electrolyte is 1% Na using primary sodium chloride.
Adjust the aqueous Cl solution.

The measuring method is as follows.
A surfactant as a dispersant in ~ 150 ml, preferably
0.1 to 5 ml of an alkylbenzene sulfonate is added,
Further, 0.5 to 50 mg of a measurement sample is added.

The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and particles of 2 to 40 μm are dispersed by the above-mentioned Coulter Counter TA-2 using a 100 μ aperture as an aperture. The particle size distribution is measured to determine the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

The developer circulation system in the developing device 4 will be described. First, the developer 46 pumped by the N ₃ pole of the magnet roller 43 with the rotation of the developing sleeve 42 is regulated vertically disposed with respect to the developing sleeve 42 in the process of being transported from the S ₂ pole to the N ₁ pole. The developer magnetic brush thin layer 46 a is formed on the developing sleeve 42 by being regulated by the blade 44. Developer magnetic brush thin layer 46a which is a thin layer formed brush is formed by the conveyed to the developing main pole S ₁ of the developing unit D magnetic force.
The electrostatic latent image on the photosensitive drum 1 is developed as a toner image by the developer magnetic brush thin layer 46a formed in a spike shape, and also remains on the photosensitive drum 1 as residual toner in the above-described image forming step, and the charging roller The toner that has been normally charged (negatively charged) by 2 is collected on the developer magnetic brush thin layer 46 a on the developing sleeve 42. Thereafter, the developer on the developing sleeve 42 is returned into the developing container 41 by the repelling magnetic fields of the N ₂ pole and the N ₃ pole.

(6) Transfer Roller (Transfer Unit) In this embodiment, the transfer roller 5 is used as the transfer unit.
You are using The transfer roller 5 is in predetermined contact with the photosensitive drum 1 to form a transfer nip portion T as a transfer portion. The transfer roller 5 in the present embodiment has an outer diameter of 8 mm.
And a conductive elastic layer surrounding its outer peripheral surface, that is, urethane, EPDM
(Ethylene propylene dimethyl rubber) or the like to disperse a conductive material such as carbon, and the resistance value is 10 ⁵ to 10 ¹⁰ Ω ·
cm, and a conductive elastic layer formed of a foamed elastic material adjusted to about 20 to 50 degrees in Asker C hardness, and has an outer diameter of 16 mm. The transfer roller 5 is driven to rotate at a constant speed in the direction of the arrow R5 with the rotation of the photosensitive drum 1 in the direction of the arrow R1. At the time of transfer, a DC bias voltage of about +4 kV is applied as a transfer bias from a transfer bias applying power source S3 to the core metal of the transfer roller 5, and a negative polarity toner for forming a toner image is formed between the photosensitive drum 1 and the transfer roller 5. Electrostatic transfer is performed by forming a transfer electric field in a direction in which particles are transferred to the transfer material P.

(7) Simultaneous Cleaning with Development by Developing Device 4 (Recovery of Residual Toner) Residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. The residual toner not only reverses the charging polarity due to peeling discharge during transfer, injection of transfer charge, or the like, but also charges the surface of the photosensitive drum 1 after transfer slightly positively (approximately + several tens V). It often happens.

The toner having the polarity inverted as described above is
It is difficult to perform simultaneous development recovery in the developing device 4. In addition, since the photosensitive drum 1 whose potential has been inverted is to be charged, the difference between the voltage applied to the transfer roller 5 and the charged potential of the photosensitive drum 1 is increased, and the charging ability is reduced.

On the other hand, according to the present invention, as described above at the charging roller 2, the duty ratio of the alternating electric field, that is, the duty ratio which is the ratio of turning on the bias on the same polarity side as the charging polarity of the photosensitive drum is adjusted. By doing so, it becomes possible to control the tribo of the residual toner to an optimal state while maintaining good uniform charging property,
The above-mentioned simultaneous recovery of development can be favorably performed. As an example, using a rectangular charging bias as shown in FIG.
The frequency is 2 kHz, V _center is -600 V as described above, and the amplitude voltage V _PP (potential difference between V _max and V _min ) is 200.
0V, that is, the V _max -1600V, the V _min +4
00V, the duty ratio _- a (T to T ratio) of 70
%, The surface potential on the photosensitive drum 1 is almost −6.
The toner is uniformly charged to 00 V, and the tribo of residual toner after passing through the charging roller 2 (measured by directly suctioning from the surface of the photosensitive drum 1 by a suction method) is controlled to about −10 to −70 μC / g, and development is performed. Simultaneous development recovery was easily performed with the apparatus 4. In this state, about 5,000 prints were repeatedly performed. However, there was almost no contamination due to the adhesion of the toner to the charging roller 2, and the toner did not scatter around.

In the present embodiment, good results were obtained when the duty ratio was 60 to 90%. On the other hand, when the duty ratio was 60% or less, the toner was not properly collected in the developing device 4, and a ghost image and toner scattering at the charging section (near the charging roller 2) occurred. On the other hand, when the duty ratio is 90% or more, the photosensitive drum 1
Has been shifted to the negative side, and the potential convergence effect has also deteriorated.

<Second Embodiment> In the first embodiment described above, the so-called reversal developing method for developing the image exposure portion (light irradiation portion) of the electrostatic latent image on the photosensitive drum 1 has been described. In the second embodiment, a case where the present invention is applied to a so-called regular developing method for developing a non-exposed portion will be described.

This regular development system is a system generally used in a so-called analog copying machine for directly forming an image by the reflected light from the image surface of the original G when the original G is exposed. However, the main difference in the configuration from the first embodiment is that the charging polarity of the photosensitive drum 1 and the charging polarity of the toner, which have the same polarity in the first embodiment, are different from those of the first embodiment. 2 is a point of opposite polarity.

Therefore, in this embodiment, only this point will be described in detail, and description of the other portions will be omitted.

In order to carry out the above-mentioned regular developing method, only one of the polarity of the photosensitive drum 1 and the polarity of the toner in the first embodiment may be reversed.
Here, a case where the polarity of the photosensitive drum 1 is reversed (plus) will be described.

Specifically, an amorphous silicon drum having a positive charging polarity is used as the photosensitive drum 1,
The layer structure is such that Si-
A two-layer structure provided with a C protective layer was used.

The toner used was the same as that in the first embodiment, and the charging potential of the photosensitive drum was set at approximately +450 V. Further, the light portion potential (becoming the background potential) which is the exposed portion is +50.
V.

Since the polarity of the toner is the same as that of the first embodiment, the same polarity as that of the first embodiment can be used for the transfer bias. And The value of the transfer bias is increased by about 300 V to about +4.3 kV.
DC bias voltage.

Next, regarding the bias applied to the charging roller 2, the polarity of the DC bias voltage was inverted to + 500V. This takes into account dark decay from the charging of the amorphous silicon to the development position.

On the other hand, for the asymmetrical alternating voltage, FIG.
As shown in (a) to (d), the plus is taken above the vertical axis, the positive maximum value of the voltage is V _max , and the minimum value is V _min ,
V _center , V _rms (effective value), and the time during which the voltage is positive with respect to one cycle T are defined as T ₊ according to the first embodiment.

Here, in the normal development, since the polarity of the toner is negative in this embodiment, the ratio (duty) of the time T ₊ to T is set to be smaller than 50%. As a result, according to the same principle as described in the first embodiment, a uniform dark potential is always formed on the surface of the photosensitive drum 1 in accordance with the value of _Vcenter regardless of the duty ratio as the charging performance. The tribo is adjusted to a negative predetermined value in accordance with the duty ratio, and good development simultaneous recovery can be performed in the developing section.

As an example, by using the rectangular wave bias shown in FIG. 6A, the frequency is set to 2 kHz, and V _PP = V _max -V _{min is set} to 200.
By setting 0 V, V _max to +1500 V, V _min to -500 V, and the duty ratio to 30%, it is possible to perform excellent simultaneous recovery of development, and at this time, contamination of the charging roller 2 and endurance in the charging section are caused. No toner scattering occurred.

In the present embodiment, good results were obtained when the duty ratio was 10% to 40%. On the other hand, when the duty ratio was 40% or more, the toner was not properly collected in the developing device 4, and a ghost image and toner scattering at the charging unit occurred. At 10% or less, the charged potential of the photosensitive drum 1 shifts to the negative side,
There was a problem that the potential convergence effect also deteriorated.

Third Embodiment A third embodiment will be described below. In the present embodiment, in the image forming apparatuses of the first and second embodiments, the toner of the developer to be used is a toner generated by a polymerization method. The same is true. For similar places,
The description will not be repeated.

In the image forming apparatuses of the first and second embodiments, the toner produced by the pulverization method is used as the toner particles t of the developer 46. In the present embodiment, the average produced by the suspension polymerization method is used. A spherical toner having an average particle diameter of 20 mm and a weight ratio of 1% externally added to a spherical toner having a particle diameter of 6 μm was used.

The magnetic carrier c has a saturation magnetization of 2
A magnetic carrier having an average particle size of 35 μm with a particle size of 05 emu / cm ³ was used.

A mixture of the toner particles t and the carrier particles c at a weight ratio of 6:94 was used as the developer 46. Since the toner produced by the polymerization method has a nearly spherical shape, the external additive is uniformly coated. Therefore, the releasability from the photosensitive drum 1 is extremely good. Also, the charging roller 2
Re-charging can be performed more stably and uniformly.
Therefore, for example, when the transfer efficiency (the amount of toner per unit area transferred onto the transfer material P / the amount of toner per unit area on the photosensitive drum 1) is compared between the pulverized toner and the polymerized toner, the pulverized toner is 90%. % When the polymerized toner was used, which was as high as 97%. Further, fogging was better than that of the pulverized toner, and in the case of using the polymerized toner, fogging could be prevented even at V _back = 50V.

The same study as in Embodiments 1 and 2 was conducted using such a polymerized toner. In this embodiment, in addition to the extremely small amount of residual toner,
Because of the high mold release property, when a configuration of a cleanerless system and simultaneous cleaning of development is adopted, the retrievability of residual toner is further improved, and no image defects occur.

The use of spherical toners such as those produced by the polymerization method has the effect of uniformizing the coating of the external additive on the toner and facilitating the movement of the toner by an electric field. Therefore, the present invention can be effectively implemented other than the two-component developing method using the magnetic carrier particles c used in the present embodiment. For example, in a one-component developing method without using a carrier, a toner is coated on a developing sleeve configured by providing a conductive elastic body on the surface, and the developing sleeve is brought into contact with the photosensitive drum 1. By using the spherical toner manufactured by the method described above, the simultaneous development and recovery method using the present invention can be effectively operated.

<Embodiment 4> In Embodiment 1, the embodiment in which the charging roller 2 which is a roller-type contact charging member is used has been described. However, as shown in FIG. As the member, a fixed blade type charging member can be used. The charging blade 20 has a back plate 21 made of a phosphor bronze plate having a free length (in the rotation direction of the photosensitive drum 1) of 20 mm and a thickness of 120 μm, on which an elastic conductive rubber layer having a thickness of about 1 mm is further provided. Thickness, medium resistivity of about 10 ⁶ Ω · cm, several tens μm on the outermost layer
m charging layer 2 consisting of an anti-sticking layer (eg, a nylon resin)
2 was used. The contact direction was forward with respect to the rotation direction of the photosensitive drum 1 (the direction of the arrow R1), and the linear pressure was set to several g / cm. Also in this method, the charging nip N and the discharge areas G ₁ and G ₂ near the charging nip can be formed.

Accordingly, the photosensitive drum 1 can be charged in the discharge areas G ₁ and G ₂ and the residual toner can be charged in the charging nip N.

In the present embodiment, the charging nip N
Of the transfer bias applying power supply S1
Good results were obtained under the same conditions as those in Embodiment 1 for applying the charging bias.

According to the configuration of the present embodiment, it is possible to make the entire image forming apparatus compact as compared with the case of the charging roller 2, and it is also possible to reduce the spring force of the back plate 21 and the abutment of the back plate 21. Depending on the method, the charging nip N, the discharge area G ₁ ,
There is an advantage that it can be to some extent freely adjust the G _2. Although FIG. 7 of the present embodiment shows an example in which the charging blade 20 is contacted in the forward direction, a certain distance (about several mm) between the charging nip N and the contact end is secured. in case of,
Even if the contact is made in the counter direction, the toner can be removed without accumulating, and the contact pressure can be stabilized.

Further, the fourth embodiment is particularly used by combining it with the polymerized (spherical) toner of the third embodiment.
The toner is easily rubbed off at the charging nip N,
Good results can be obtained.

<Embodiment 5> This embodiment relates to a method for cleaning the transfer roller 5 when the transfer roller 5 is contaminated by residual toner during a jam or the like. Here, the basic configuration will be described according to the first embodiment.

In FIG. 1, the transfer roller 5 may be directly contaminated by toner without the transfer material P, for example, due to paper feed jam. In this case, on the transfer roller 5, the residual toner having the normal polarity and the residual toner whose polarity is partially reversed due to a transfer electric field or the like are mixed and adhered.

Therefore, when the power is turned on again after the jam processing, as shown in FIG. 8, first, the positive and negative transfer biases are applied to the transfer roller 5 using the transfer bias applying power source S3 while the photosensitive drum 1 is rotating. Is applied alternately over one or more rotations of the transfer roller 5, whereby contaminated toner having positive and negative charges is transferred from the transfer roller 5 to the photosensitive drum 1. Here, the surface of the photosensitive drum 1 is charged to a normal dark potential (background potential in reversal development) by the charging roller 2 in advance, so that the positive and negative charges are generated by the action of the asymmetric alternating voltage described in the first embodiment. The contaminated toner having the above charge is uniformly recharged to the negative polarity. Next, by providing the second step of operating the developing device 4 under normal image forming conditions, the recharged contaminated toner is developed by the potential difference between the potential of the photosensitive drum 1 and the potential of the developing sleeve 42. Collected in the device 4.

Finally, the DC bias voltage as the bias voltage of the charging roller 2 is turned off, the surface of the photosensitive drum 1 is neutralized to approximately 0 V by the alternating bias, and the cleaning process is completed.

In the present embodiment, based on Embodiment 1, the charging potential of the photosensitive drum 1 is set to approximately -600 V during cleaning, and the DC voltage of the developing bias is -450 V, and an AC bias is applied thereto. The cleaning bias applied to the transfer roller 5 is −2 kV as the transfer (−) bias and +2 as the transfer (+) bias.
By using kV, the contaminated toner on the transfer roller 5 can be
The toner was collected in the developing device 4 via the photosensitive drum 1.

Note that the above-mentioned bias value is
Various other combinations can be used. For example, the DC bias voltage to the charging roller 2 is set to -1.
50V, DC bias voltage for development is 0V, etc.
The DC bias voltage to the charging roller 2 may be 0 V, and the DC bias voltage for development may be +150 V.

Although the present embodiment has been described with reference to the reversal developing method, it goes without saying that the present invention can be similarly applied to the case of the regular developing method as in the second embodiment.

Further, this cleaning step is executed at the time of non-image formation such as between transfer materials, for example, at the time of idle rotation in a pre-printing step or a post-printing step at the time of printing, other than at the time of jam clearance or power-on. be able to.

In the above embodiment, the case where the polarity of the residual toner is controlled to the normal polarity, that is, the negative polarity by the charging roller 2 has been described.
Since the second step is performed in a non-image forming state, there is no need to perform simultaneous development at the time of collection by the developing device 4. Therefore, for example, the duty ratio of the alternating bias applied to the charging roller 2 is set to 10 to 40%, the residual toner is charged to a positive polarity, and the values of the developing DC bias voltage and the charging DC bias voltage are appropriately adjusted. Alternatively, the residual toner in the developing device 4 may be collected by shifting the developing DC bias voltage in the minus direction from the photosensitive drum potential.

[0099]

As described above, according to the present invention,
A simple configuration in which a DC bias voltage and an asymmetrical alternating bias voltage having different duty ratios are superimposed and applied as a charging bias voltage to a contact charging member arranged in contact with the image carrier, so that the surface of the image carrier is made uniform. Charging and stable application of a tribo of a predetermined polarity to the residual toner can be performed, and good simultaneous cleaning with development can be performed. Thereby, the charging failure caused by the contamination of the contact charging member by the residual toner is prevented,
Good images can be formed over a long period of time.

Even when the contact transfer member is contaminated with residual toner, after transferring the residual toner on the contact transfer member to the image carrier, the contact charging member is charged with a DC bias voltage as a charging bias voltage. With a simple configuration in which an asymmetrical alternating bias voltage having a different duty ratio is superimposed and applied, uniform charging of the surface of the image carrier and stable application of a predetermined polarity to the residual toner can be performed. Cleaning at the same time as development can be performed. As a result, it is possible to effectively prevent image defects and transfer material back contamination caused by contamination of the contact transfer member with the residual toner for a long period of time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram showing a configuration of an optical system according to the first embodiment.

FIGS. 3A, 3B, 3C, and 3D are diagrams illustrating asymmetric charging biases according to the first embodiment; FIGS.

FIG. 4 is a diagram for describing the application of charge to residual toner in the first embodiment.

FIG. 5 is a longitudinal sectional view illustrating a schematic configuration of a developing device according to the first embodiment.

FIGS. 6A, 6B, 6C, and 6D are diagrams showing asymmetric charging biases according to the second embodiment. FIG. 9 is an explanatory diagram of an asymmetric charging bias according to the second embodiment of the present invention.

FIG. 7 is a diagram for explaining how a charge is applied to residual toner in the fourth embodiment.

FIG. 8 illustrates an operation in Embodiment 5;

FIG. 9 is a longitudinal sectional view illustrating a schematic configuration of the image forming apparatus according to the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging means (contact charging member, charging roller) 3 Information writing means (laser operation part) 4 Developing means (developing device) 5 Transfer means (contact transfer member, transfer roller) 20 Charging means ( (Contact charging member, charging blade) 46 Developer P Transfer material S1 Power supply (Charging bias application power supply) S2 Development bias application power supply S3 Transfer bias application power supply

Claims (5)

[Claims] A charging unit configured to charge the surface of the image carrier with a contact charging member; an information writing unit configured to form an electrostatic latent image on the surface of the image carrier after charging; Developing means for developing as a toner image with a developer carried on the body, transfer means for forming an electric field between the image carrier and transferring the toner image on the image carrier to a transfer material, In the image forming apparatus, wherein the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier, the contact charging member is provided with an asymmetrical alternating current having a duty ratio different from a DC bias voltage as a charging bias voltage. A power supply for superimposing and applying a voltage, wherein an asymmetrical alternating electric field is formed between the image carrier and the contact charging member by the charging bias voltage, and the image carrier is made uniform at a predetermined potential. Simultaneously with the collector, the residual toner by applying a predetermined polarity charge, the residual toner charge is imparted and recovered by the developing means, that the image forming apparatus according to claim. 2. The developing system of the developing means is a reversal developing system using a toner having the same polarity as the charging polarity of the image carrier, and turns on a bias on the same polarity side as the charging polarity of the asymmetrical alternating voltage. The image forming apparatus according to claim 1, wherein the duty ratio is in a range of 60% to 90%, where a duty ratio is a duty ratio of the alternating voltage. 3. The developing system of the developing means is a regular developing system using a toner having a polarity opposite to the charging polarity of the image carrier, and turns on a bias having the same polarity as the charging polarity of the asymmetrical alternating voltage. 2. The image forming apparatus according to claim 1, wherein the duty ratio is in a range of 10 to 40%, where a ratio is a duty ratio of the alternating voltage. 4. The image forming apparatus according to claim 1, wherein the toner particles accommodated in the developing unit are toners generated by a polymerization method. 5. A charging unit for charging the surface of the image carrier by a contact charging member, an information writing unit for forming an electrostatic latent image on the surface of the image carrier after charging, and a developer carrying the electrostatic latent image. Developing means for developing a toner image with a developer carried on a body, and pressing the contact transfer member against the image carrier and forming an electric field between the image carrier and the contact member to form the image carrier A transfer means for transferring the upper toner image onto a transfer material, wherein the developing means also serves as a cleaning means for collecting residual toner remaining on the image carrier; In the first step, the toner remaining on the contact charging member is transferred to the image carrier side by forming an electric field between the contact charging member and the image carrier; versus A power supply for superimposing and applying a DC bias voltage and an asymmetrical alternating voltage having a different duty ratio as a charging bias voltage, wherein the charging bias voltage causes an asymmetrical alternating electric field between the image carrier and the contact charging member. And charging the image carrier to a predetermined potential at the same time as applying a charge of a predetermined polarity to the residual toner, and collecting the residual toner with the charge by the developing unit. 2. An image forming apparatus comprising: