JPH09185257A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image of high image quality while preventing ozone pro duction as much as possible by using a photoreceptor of straight polarity, an uncontacted electrifying means, and a developer of straight polarity, carrying residual developer onto the photoreceptor after transfer, and recovering it via an electrifying position. SOLUTION: A photoreceptor drum 20 is made of a positively electrified material, for example, a positively electrified organic photoreceptor. An electrifier 40 is composed of a scorotron type electrifier used for positive electrification, and is arranged opposite the photoreceptor drum 20 without being in contact with it. By varying a bias voltage, a cleaning roller 42 once attracts residual toner 53 after transfer by a transfer roller 60, and discharges it onto the photoreceptive drum 20 with specific timing to return it to a developing unit 50. A developing roller 56 uses positively electrified toner 53, and develops an image and also recovers the residual toner 53. Thus, because, even if the residual toner 53 is carried by the photoreceptor drum 20, it does not stick to the electrifier 40, the image with high image quality can be formed and ozone productionhardly occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of electrophotographic image forming apparatuses such as laser beam printers, facsimiles, and copiers. Belongs to the technical field of image forming apparatuses that collect and collect.

[0002]

2. Description of the Related Art Conventionally, as a developing method in an electrophotographic image forming apparatus of this type, a conductive elastic roller is used as a developing roller for carrying toner, and the developing roller is pressed against a photosensitive drum to develop. The so-called impression development method for performing the above is widely adopted.

In recent years, development of an electrophotographic process which does not generate waste toner has been promoted in this type of developing system from the viewpoint of ecology. As one of such processes, the residual toner remaining on the photosensitive drum after transfer is carried to the developing device while being placed on the photosensitive drum at a timing that does not interfere with charging and latent image formation, and the developing device There is a so-called cleanerless process in which residual toner is collected and reused. By using this cleanerless process, it is not necessary to install a cleaning device such as a conventional cleaning blade, the photosensitive drum is not damaged by pressing the blade directly against the photosensitive drum, and the residual toner is compared. It can be returned to the developing device efficiently.

[0004]

Since the general demand for improving image quality is strong in the image forming apparatus, in the electrophotographic image forming apparatus, electrostatic latent image formation, development, etc. are properly performed. The charging process for charging is extremely important.

However, according to the above-mentioned conventional cleanerless process, since the residual toner is carried on the photosensitive drum, the residual toner must pass through the charging position where the charger faces the photosensitive drum. As a result, when a contact-type charger is used, the residual toner adheres to the contact portion of the charger with the photosensitive drum, which deteriorates the charging performance, resulting in a decrease in developing efficiency and a deterioration in output image quality. There was a problem of bringing it.

On the other hand, the non-contact type charger does not cause such a problem because residual toner does not adhere to the charger even in the cleanerless process. However, a negatively charged photosensitive drum, which is normally used in an electrophotographic image forming apparatus of this kind, is developed by using a negatively charged toner and a so-called scorotron charger which is a typical example of a non-contact type charger. However, there is a serious problem that the air existing in the space between the charger and the photosensitive drum is ionized and a large amount of ozone is generated. Further, there is a problem that the generated ozone causes deterioration of the negatively chargeable organic photoconductor and the like.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an image forming apparatus capable of forming a high quality image while preventing the generation of ozone as much as possible.

[0008]

In order to solve the above-mentioned problems, an image forming apparatus according to a first aspect of the present invention includes a positively charging photosensitive member, a driving unit for rotating the photosensitive member, and the rotating member. And a latent image forming unit for forming an electrostatic latent image on the positively charged photoconductor at a charging position so as to positively charge the photoconductor. Developing means for developing the formed electrostatic latent image with a developer charged to the same polarity as the photoreceptor to form a visible image on the photoreceptor, and recording the formed visible image The developing means further comprises a transfer means for transferring to a medium, and the developing means further places the residual developer remaining on the photoconductor after the transfer by the transfer means on the rotated photoconductor, and through the charging position. It is characterized in that it is configured to be collected.

According to the image forming apparatus of the first aspect,
The positively chargeable photoconductor is rotated by the driving means, and is first positively charged by the charging means at the charging position. Next, the latent image forming means forms an electrostatic latent image on the positively charged photoreceptor. Then, the developing means develops the formed electrostatic latent image with the developer charged to the positive polarity to form a visible image on the photoreceptor. Then, the visible image formed on the photoconductor is transferred to the recording medium by the transfer unit. Image formation is performed as described above. On the other hand, the residual developer remaining on the photoconductor after the transfer is placed on the rotated photoconductor and conveyed toward the developing means via the charging position. Then, when the residual developer returns to the developing means, the developing means collects the residual developer on the photoconductor. As described above, the residual developer is collected by the cleanerless method, and the developer collected by the developing means is reused for the subsequent development. Therefore, despite the residual developer being carried on the photoreceptor,
Since the charging means is positioned so as not to contact the photoreceptor,
The residual developer does not adhere to the charging means when passing through the charging position, and the charging performance of the charging means does not deteriorate due to the adhesion of the residual developer. At the same time, a positively charged photoconductor and a positively charged developer are used, and since charging is performed by a positive charging means such as a scorotron charger for positive charging, almost all ozone is generated. do not do.

An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the developing means includes a developing roller that develops with the developer and collects the residual developer. It is characterized by

According to the image forming apparatus of the second aspect,
In the developing means, development is performed and the residual developer is collected by one roller called a developing roller.
The development and the recovery may be performed in different cycles, or the development and the recovery may be performed at substantially the same time in the same cycle.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the developing means collects the developing-dedicated roller for developing with the developer and the residual developer. It is characterized in that it is provided with a recovery exclusive roller.

According to the image forming apparatus of claim 3,
In the developing means, the development-dedicated roller performs development, and the collection-dedicated roller collects the residual developer. The image forming apparatus according to claim 4 is the image forming apparatus according to any one of claims 1 to 3, wherein the residual developer is temporarily adsorbed before reaching the charging position, and a predetermined timing is reached. The developer dispersion means for discharging the temporarily adsorbed developer onto the photoconductor is further provided.

According to the image forming apparatus of the fourth aspect,
The residual developer is temporarily adsorbed by the developer dispersion means before it reaches the charging position. After that, at a predetermined timing at which the photosensitive member portion on which the residual developer is placed does not interfere with other processes such as charging, latent image formation, and development, the developer temporarily adsorbed by the developer dispersion means is developed. It is discharged from the agent dispersing means onto the photoconductor, is placed on the photoconductor, and is carried toward the developing means.

An image forming apparatus according to a fifth aspect is the image forming apparatus according to any one of the first to fourth aspects, wherein the charging means includes a scorotron charger for positive charging. And

According to the image forming apparatus of the fifth aspect,
Compared to the case where the photoconductor is positively charged with the positive polarity by the scorotron charger for positive charging and the photoconductor is negatively charged with the scorotron charger, the amount of ozone generated is, for example, about 1/10. Is reduced to.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 1, a laser beam printer 1 according to an embodiment of the present invention includes a main body case 2, a feeder unit 10 for feeding a sheet P for image formation, and exposure, development, and transfer for image formation. , A charging unit 70 for fixing the transfer image transferred from the photosensitive drum 20 to the sheet P to the sheet P, and a positively-charged photosensitive drum 20 as an example of the photoconductor in which the processes such as the collecting and the like are sequentially performed. And a paper discharge tray 77 for discharging the fixed paper P along the transport path PP.

The laser beam printer 1 is also provided with a driving means (not shown) for rotating the photosensitive drum 20, and on the photosensitive drum 20 rotated by the driving means in order along the periphery of the photosensitive drum 20. A laser scanner unit 30 as an example of a latent image forming unit for forming an electrostatic latent image on the surface, and the electrostatic latent image formed on the photosensitive drum 20 are positively charged as an example of a developer. A developing unit 50 having a developing roller 56 for developing with toner, and a transfer roller 6 as an example of a transfer unit for transferring the toner image developed on the photosensitive drum 20 onto the paper P.
0 and the photosensitive drum 20 after transfer by the transfer roller 60.
The residual toner remaining on the developing unit 5 is cleaned at a predetermined timing by using the photosensitive drum 20 by a cleanerless method.
A cleaning roller 42 as an example of a developer dispersing unit that temporarily adsorbs the residual toner in order to return it to 0, a static elimination lamp 41 for removing the residual potential remaining on the photosensitive drum 20 after the transfer, and a static elimination lamp 41 after the static elimination. A charging device 40 as an example of a charging unit for positively charging the photosensitive drum 20 so that an electrostatic latent image can be formed.

Next, the respective constituent elements of the laser beam printer 1 will be described in detail with reference to FIGS. 1 to 3. In FIG. 1, the feeder unit 10 includes a sheet pressing plate 11 having a width dimension substantially the same as that of the sheet P, which is disposed in the upper feeder section case 3 located at the rear end of the main body case 2. The paper pressing plate 11 is swingably supported at its rear end. A compression spring 12 is provided at the front end of the paper pressing plate 11, and the paper pressing plate 11 is elastically biased upward by the compression spring 12.
The paper pressing plate 11 includes a paper feed roller 13 extending in the left-right direction.
However, it is rotatably supported. The paper feed roller 13 is configured to be rotationally driven at a paper feed timing by a drive system (not shown). In the feeder unit 10, a paper feed cassette 14 capable of accommodating a plurality of sheets P of standard cut paper is detachably mounted in an inclined manner in the feeder case 3, and by rotation of the paper feed roller 13, Among the paper P stored in the paper feed cassette 14, the upper paper P is fed one by one. Further, the feeder unit 10 is provided with a separating member 15 below the paper feeding roller 13 in order to prevent double feeding of the paper P, and the separating member 15 is elastically attached to the paper feeding roller 13 by a compression spring 16. Being energized. A pair of registration rollers 17 and 18 that align the leading ends of the fed paper P are rotatably pivoted downstream of the paper feed roller 13 in the conveying direction (from the rear to the front in FIG. 1). There is.

In FIG. 1 and FIG. 2, the photosensitive drum 20
Is made of a positively chargeable material, for example, a positively chargeable organic photoreceptor. More specifically, as shown in FIG. 2, the photosensitive drum 20 has, for example, a cylindrical, cylindrical sleeve 21 made of aluminum as a main body, and has a predetermined thickness formed by dispersing a photoconductive resin in polycarbonate on an outer peripheral portion thereof. It is composed of a hollow drum on which a photoconductive layer 22 having a thickness (for example, about 20 μm) is formed, and is rotatably supported by the main body case 2 with the cylindrical sleeve 21 grounded. That is, the toner 53 charged to the positive polarity is developed by the reversal development method with respect to the electrostatic latent image of the positive polarity (positive charging) formed on the photosensitive drum 20. The photosensitive drum 20 is configured to be rotationally driven clockwise in a side view by a driving unit.

In FIG. 1, the laser scanner unit 3
Reference numeral 0 denotes a laser generator 31 disposed below the photosensitive drum 20, which generates a laser beam L for forming an electrostatic latent image on the photosensitive drum 20, and a polygon mirror (a pentahedron) driven to rotate. Mirror 32, a pair of lenses 33 and 34, and a pair of reflection mirrors 35 and 36. The laser scanner unit 30 is attached to the photosensitive drum 20.
Since the laser beam printer 1 is disposed below the laser beam printer 1, the laser beam printer 1 can be compact in size and can be emitted from the laser scanner unit 30 without interfering with sheet transportation. An electrostatic latent image can be formed on the photosensitive drum 20 with the laser light L.

The charger 40 is composed of a scorotron type charger for positive charging, which generates corona discharge from a charging wire made of tungsten or the like. In the present embodiment, a cleanerless system is adopted, but the charger 40 is arranged so as to face the photosensitive drum 20 in a non-contact manner so that the residual toner on the photosensitive drum 20 does not adhere to the charger 40. ing.

The charge eliminating lamp 41 is constituted by including a light source such as an LED (laser light emitting diode), an EL (Electro Luminescence), a fluorescent lamp or the like, and removes the electric charge remaining on the photosensitive drum 20 after the transfer (eliminating the charge). ), The residual charge affects the next electrostatic latent image,
It finally functions to prevent the image from appearing on the sheet P.

By changing the bias voltage, the cleaning roller 42 once absorbs the residual toner 53 remaining on the photosensitive drum 20 after the transfer by the transfer roller 60, and the next exposure, development, and development performed on the photosensitive drum 20. By discharging the absorbed residual toner 53 to the photosensitive drum 20 at a predetermined timing that does not hinder transfer or the like,
Remove the residual toner 53 from the photosensitive drum 20 to the developing unit 5
It is configured to return to 0. Cleaning roller 4
The reference numeral 2 is composed of a conductive elastic foamed material such as silicon rubber or urethane rubber to which a bias voltage can be applied. It should be noted that the cleaning roller 42 is designed so that the recovery can be efficiently performed by the cleanerless method.
However, instead of or in addition to the cleaning roller 42, a cleaning brush to which a bias for smoothing the residual toner on the surface of the photosensitive drum 20 is applied may be provided.

1 and 2, the developing unit 50
Includes a double-cylindrical toner box 51 detachably mounted in the developing unit case 4. The toner box 51 accommodates an agitator 52 that is driven to rotate and a positively charging toner 53 that has electrical insulation. In front of the toner box 51, a toner storage chamber 54 for storing the toner 53 supplied by the rotation of the agitator 52 through the toner supply port 51a formed in the toner box 51.
Are formed. In the toner storage chamber 54, a supply roller 55 is horizontally arranged in the longitudinal direction and is rotatably supported. Further, a developing roller 56 is horizontally arranged in the longitudinal direction and is rotatably supported so as to partition the front side of the toner storage chamber 54 and contact the supply roller 55 and the photosensitive drum 20, respectively.

The supply roller 55 is made of a conductive elastic foam material such as silicone rubber or urethane rubber, and the resistance value at the contact portion with the developing roller 56 is approximately 5 × 10 ⁴ to 1 × 10 5. It is set to ⁹ Ω.

The developing roller 56 is a conductive rigid roller made of silicon rubber, urethane rubber, or the like, and the resistance value from the central electrode to which the developing bias voltage is applied to the outer peripheral contact portion is about. 5 x 10 ⁴ to 1 x 1
It is set to 0 ⁷ Ω. The supply roller 55 and the developing roller 56 are configured to be rotationally driven clockwise by a drive mechanism.

The developing roller 56 is configured to perform development on the photosensitive drum 20 using the positively charged toner 53 and to collect the residual toner 53 returned to the photosensitive drum 20 by the cleaning roller 42.

More specifically, for example, for the photosensitive drum 20 in which the residual toner 53 remains about 10% of the toner amount before the transfer after the transfer, first, the residual toner 53 is removed by the laser scanner unit 30. The exposure should be performed so that the laser light reaches the bottom sufficiently. Next, in the developing unit 50, the residual toner 53 is attached to the unexposed portion of the photosensitive drum 20 by utilizing the potential difference between the exposed portion and the unexposed portion existing regardless of the presence of the residual toner 53 on the photosensitive drum 20. If so, the residual toner 53 is moved (collected) to the developing roller 56, and at the same time,
If the residual toner 53 has already adhered to the exposed portion of the photosensitive drum 20, it should be adhered (developed) as it is,
If the residual toner 53 does not adhere to the exposed portion of the photosensitive drum 20, the positively charged toner 53 is moved (developed) from the developing roller 56. That is, the developing unit 50 is configured so that the developing cycle and the collecting cycle are performed almost simultaneously.

Further, for example, as shown in FIG. 3, a collecting-dedicated roller 156 is provided adjacent to the side of the developing roller 56 near the laser scanner unit 30 to collect the residual toner 53 by the collecting-dedicated roller 156. The developing roller 56 may configure the developing unit 50 so as to function as a developing-only roller. In this case, the developing unit case 1
Reference numeral 04 is a shape for moving the residual toner 53 collected by the collection-dedicated roller 156 toward the supply roller 55 and the developing roller 56 by the rotation of the collection-dedicated roller 156.

Further, for example, a developing cycle and a collecting cycle are separately provided, and the bias voltage of the developing roller 56 with respect to the photosensitive drum 20 is changed for each cycle. The positively charged toner 53 is transferred from the roller 56 to the photosensitive drum 20.
The developing unit 50 may be configured so as to move (develop) to the exposed portion of (3) and apply a collecting bias voltage to move (collect) the residual toner 53 from the photosensitive drum 20 to the developing roller 56 in the collecting cycle.

As described above, in the present embodiment, it is possible to employ a system using various structures as a system for recovering the residual toner in the developing unit 50 using the developing roller 56 without a clayner.

As shown in FIG. 2, the developing unit case 4 of the developing unit 50 is provided with a toner storage chamber 54, and the toner storage chamber 54 is formed by providing a large upper space S above the supply roller 55. Has been done. For this reason, the toner 53 of the toner box 51 is not supplied to the toner supply port 51a.
Even when a large amount of toner is supplied to the toner storage chamber 54 via the toner, the toner 53 is not packed and solidified.
The toner 53 is always in powder form, its fluidity is maintained, and the toner supply by the supply roller 55 can be stabilized.

In FIG. 1 and FIG. 2, a thin plate-like elastic layer thickness regulating blade 57 made of stainless steel or phosphor bronze is attached downward to the developing unit case 4.

The bent portion 57a formed at the lower end of the layer thickness regulating blade 57 is in contact with the developing roller 56 in a pressed state, and is supplied from the supply roller 55 to be supplied to the developing roller 56.
The layer thickness of the toner 53 adhered to the surface of the toner layer in a layered manner is a predetermined thickness of about one layer (about 7 to 12 μm) by the layer thickness regulating blade 57.
m). That is, the toner amount on the developing roller 56 is configured to be 0.5 mg / cm ² or less. The layer thickness regulating blade 57 preferably has a radius of curvature of about 0.3 m, for example, so that the amount of toner on the developing roller 56 is set to about 0.4 mg / cm ^2.
m. The developing bias and the developing roller 56
The minimum required toner amount on the developing roller 56 is determined by the number of rotations of the developing roller 56, and for example, if the toner amount on the developing roller 56 is about 0.3 mg / cm ² , the developing bias and It is possible to perform development with a sufficient toner density by using the rotation speed of the developing roller 56. As described above, since the layer thickness of the toner layer is regulated by the layer thickness regulating blade 57 so as to form a layer having a toner amount of 0.5 mg / cm ² or less on the developing roller 56, the developing roller 5
The layer thickness of the toner 53 on 6 is 2 based on the toner particles.
It is less than one layer, that is, one layer or one layer is strong. As a result,
Most of the toner 53 is firmly rubbed by the developing roller 56 and the layer thickness regulating blade 57, and is sufficiently positively charged. Since the toner 53 on the developing roller 56 after the layer thickness regulation is one layer or a strong one layer, the toner 53 not subjected to the development does not accumulate on the contact portion with the photosensitive drum 20 and is developed. It adheres to the roller 56 and is collected.

The transfer roller 60 is provided so as to be in contact with the upper side of the photosensitive drum 20, is rotatably supported, and is made of a conductive elastic foam material such as silicon rubber or urethane rubber. The resistance value at the contact portion of the transfer roller 60 with the photosensitive drum 20 is about 1 × 10 ⁶ to 1 ×.
It is set to 10 ¹⁰ Ω. That is, the transfer roller 60 is
Since it is in contact with the surface of the photosensitive drum 20, its resistance value is increased so that the photoconductive layer 22 formed on the photosensitive drum 20 is not destroyed by the voltage applied to the transfer roller 60. The toner image on the photosensitive drum 20 is configured to be reliably transferred to the paper P.

The fixing unit 70 is provided on the downstream side of the photosensitive drum 20 in the conveying direction, and is composed of a heating roller 71 having a halogen lamp built therein and a pressing roller 72. The toner image transferred onto the lower surface of the paper P is heated. While being pressed, it is pressed and fixed on the paper P.

A pair of transport rollers 75 and a paper discharge tray 77 for transporting the paper are respectively provided on the downstream side of the fixing unit 70 in the transport direction. According to the present embodiment, as shown in FIG. 1, these paper feed rollers 13 that form a transport path PP (indicated by a dashed line in FIG. 1) for transporting the paper P fed from the paper feed cassette 14. The photosensitive drum 20, the fixing unit 70, and the paper discharge tray 77 are arranged in a substantially linear shape.

In FIG. 1, the toner 53 in the present embodiment is a non-magnetic one-component toner made of, for example, a pulverized toner or a polymerized toner made of styrene acryl or the like having a nearly spherical shape, and its particle size is 6 to 12 μm. It is a degree. The toner 53 is configured to include a base toner and silica as an example of an external additive (fluidity imparting agent) added to the base toner. The base toner is composed of, for example, resin, wax, carbon black, and CCA (for example, a charge control agent such as nigrosine or triphenylmethane), and its charging characteristic becomes positive due to the action of CCA. Silica, which is an example of an external additive, is a toner surface modifier, has an effect of increasing the fluidity of the toner 53, and generally has a charging property of being negatively charged. However, amino-modified silica and the like are known as positively-charged silica having a positively charged positive polarity. However, since positively chargeable silica generally does not have a sufficient fluidity improving effect, negatively chargeable silica having a small polarity is often used as an external additive. The difference between positively chargeable silica and negatively chargeable silica is positively chargeable silica when the charge amount of the toner when externally added to the base toner increases in the positive direction, and negative chargeable silica when the charge amount increases in the negative direction. The point is that In the present embodiment, since the toner 53 has such a configuration, the toner 53 is used as the layer thickness regulating blade 57 or the developing roller 56.
When the toner is in contact with the toner and is sufficiently rubbed, the charging characteristic of the CCA contained in the base toner becomes dominant and the toner 5
3 is positively charged, which is the charging characteristic of the base toner. On the other hand, when the toner 53 is lightly rubbed, the charging property of silica as an external additive exposed on the surface of the base toner becomes dominant, and the toner 53 is charged to the negative polarity which is the charging property of silica. To be done. In addition to the function of imparting fluidity, the external additive can be provided with functions of preventing toner blocking, improving cleaning properties, preventing scratches on the photosensitive drum, improving image density, and improving image quality. The external additives other than silica include fine powders of colloidal silica, titanium oxide, aluminum oxide (alumina), etc., but according to the present embodiment, not only the positively chargeable external additive, It is advantageous because even a negatively chargeable external additive can be used.

Next, the operation of the laser beam printer 1 configured as described above will be described with reference to FIGS. 1 and 4 to 7. In the present embodiment, it is assumed that the image is formed by the developing process of the reversal developing method.

In FIG. 1, the photosensitive drum 20 is rotationally driven in a clockwise direction in a side view by the driving means, and the supply roller 55 and the developing roller 56 are rotationally driven in a clockwise direction, respectively. As a result, the respective particles of the toner 53 are rubbed by the supply roller 55 and the developing roller 56, and the developing roller 56 of the layer thickness regulating plate 57, as shown in FIG.
The toner 53 that is positively charged due to the pressure friction on the toner 53 adheres to the electrostatic latent image formed on the photosensitive drum 20 by the laser light L and is developed by the reversal development method. .

In the present embodiment, the layer thickness regulating blade 57
As a result, a toner layer having a toner amount of 0.5 mg / cm ² or less is formed on the developing roller 56. Therefore, since the layer thickness of the toner 53 on the developing roller 56 is one layer or a little more than one layer, most of the toner is rubbed firmly on the developing roller 56 and the layer thickness regulating blade 57 and sufficiently charged. become.

Here, for example, as the transmission density (image density) necessary for the image formed on the paper P, for example, "2.
In order to obtain "0", as shown in FIG.
g / cm ² is required. To this end, as described above, the amount of toner on the developing roller 56 is set to about 0.4 mg / cm ² by the layer thickness regulating plate 57, while the developing efficiency is set to be slightly less than 100%. The peripheral speed of is about twice as high as the peripheral speed of the photosensitive drum 20. That is,
To prevent the developing roller 56 and the photosensitive drum 20 from directly contacting each other at the nip portion, the toner 53 is placed on the developing roller 56.
It should remain slightly due to van der Waals forces.

The charge amount of the toner 53 is about 25 μC / g in a low temperature and low humidity environment at a temperature of about 10 ° C. and a humidity of about 20%, and from a high temperature and high humidity environment of about 32 ° C. and a humidity of about 80%. It varies up to about 20 μC / g. Therefore, when the developing roller 56 is driven in the same rotation direction as the photosensitive drum 20, as shown in FIG. 6, whichever of the low temperature and low humidity environment indicated by the one-dot chain line and the high temperature and high humidity environment indicated by the two-dot chain line is shown. Even in the environment, a predetermined amount of developing toner (about 0.7
The effective developing bias voltage of the developing roller 56 is set to "about 200 V" so that 8 mg / cm ² ) can be obtained. At the same time, since the electrostatic latent image voltage, which is the voltage of the electrostatic latent image formed on the photosensitive drum 20, is “about 100 V”, the developing bias voltage of the developing power source E applied to the developing roller 56 is
It is set to "about 300V".

When the image forming process is started under the voltage setting as described above, first, the charge eliminating lamp 41 is operated by the photosensitive drum 20.
After the upper residual charge is wiped out, the surface of the photosensitive drum 20 is uniformly charged by the charger 40 for positive charging to about +800 V as shown in FIG. Then, in this state, the laser light L emitted from the laser generator 31
Is a lens 33 while being main-scanned by the polygon mirror 32.
And 34 and reflection mirrors 35 and 36 to irradiate the photosensitive drum 20 to form an electrostatic latent image on the photosensitive drum 20. At this time, the voltage of the portion corresponding to the electrostatic latent image on the photosensitive drum 20 is changed by the irradiation of the laser light L.
For example, as shown in FIG. 7, the voltage drops to about + 100V. To the surface of the developing roller 56, as the developing bias voltage of, for example, about +300 V is applied as shown in FIG. 7, the toner 53 of positive polarity is attached with a layer thickness of more than one layer. 53 is not attracted to a charging voltage (about +800 V) higher than its own voltage, but is attracted to an electrostatic latent image voltage (about +100 V) lower than it, so that the toner 53 on the developing roller 56 is exposed to light. Only the electrostatic latent image formed on the drum 20 is attached and developed.

The toner image of the electrostatic latent image developed with the toner 53 is transferred onto the paper P by the transfer roller 60,
The fixing processing is performed by the fixing unit 70 and the sheet is discharged to the sheet discharge tray 77.

At this time, the transport path PP for transporting the paper P fed from the paper feed cassette 14 is formed in a substantially straight line,
Since the image is formed on the paper P while being conveyed by the substantially linear conveyance path PP, even if a thick paper such as a postcard or an envelope or an OHP film is used as the paper P, the paper P can be neatly and reliably formed. An image can be formed on.

On the other hand, in FIG. 1, the residual toner 53 which is not transferred to the sheet P when passing through the transfer roller 60 and remains on the photosensitive drum 20 is changed by changing the bias voltage of the cleaning roller 42 as described above. , And is once absorbed by the cleaning roller 42. Then, by changing the bias voltage of the cleaning roller 42 at a timing that does not interfere with the next exposure, development, transfer, etc. performed on the photosensitive drum 20, the residual toner 53 once absorbed is exposed from the cleaning roller 42. The photosensitive drum 20 is discharged to the drum 20 and is developed by the developing roller 56.
The upper residual toner 53 is collected by the cleanerless method.

As a result of the above, according to the laser beam printer 1 of the present embodiment, the residual toner 53 remains in the photosensitive drum 20.
Despite being carried in accordance with the rotation of the charging device 40, the charging device 40 is positioned so as not to contact the photosensitive drum 20. Therefore, the residual toner 53 does not adhere to the charging device 40 and the charging performance of the charging device 40 does not deteriorate. . Therefore, a high quality image can be formed on the paper P. At the same time, since the positively chargeable photosensitive drum 20 and the positively charged toner 53 are used and the charging is performed by the positive charging scorotron charger, most of the ozone due to the ionization of the air between the charger 40 and the photosensitive drum 20 is generated. Does not occur.

According to the above-mentioned embodiments, the toner is the non-magnetic one-component toner, but the two-component toner or the magnetic toner may be the positively-charged toner for the positively-charged photosensitive drum. If the same kind of effect can be expected. Further, although only the formation of a monochrome image has been described, the present invention effectively functions also when forming a color image. Further, although the developing roller 56 and the photosensitive drum 20 are configured to rotate in the same direction (move in opposite directions on their contact surfaces), these rollers rotate in opposite directions (same on both contact surfaces). It may be configured to move in the direction). Further, although the photoconductor is composed of the photoconductor drum, the same effect can be expected even if it is a belt-shaped photoconductor if it is made of a positively chargeable material. Furthermore, in the present embodiment, the laser beam printer has been described. However, in the case of an electrophotographic image forming apparatus using toner, a copying machine, a facsimile device, and the like are also provided as in the case of the present embodiment. The invention works effectively.

[0051]

According to the image forming apparatus of the first aspect, the developer collected by the cleanerless system can be reused for the subsequent development. At this time, since the residual developer does not adhere to the charging means, the charging performance of the charging means does not deteriorate, and high quality image formation is possible. At the same time, the effect that almost no ozone is generated can be obtained.

According to the image forming apparatus of the second aspect,
Development and recovery can be done with one roller,
The developing unit can be downsized, and the residual developer can be efficiently collected by the cleanerless method. Further, at this time, if the development and the recovery are performed in separate cycles, it is possible to recover the residual developer by the cleanerless system by using a relatively simple structure, and the development is performed in the same cycle. If the collecting and the collecting are performed almost at the same time, it is not necessary to spend time for the collecting, and the image can be quickly formed as a whole.

According to the image forming apparatus of claim 3,
Since the residual developer is recovered by the recovery-dedicated roller, the residual developer can be recovered more reliably by using a relatively simple structure.

According to the image forming apparatus of the fourth aspect,
Since the residual developer can be carried to the developing means at a predetermined timing by the developer dispersing means, the residual developer can be collected by the cleanerless method so as not to interfere with charging, latent image formation, development and the like.

According to the image forming apparatus of the fifth aspect,
Since the positive charging is performed by the scorotron charger for positive charging, the amount of ozone generated can be reduced to, for example, about 1/10 of that in the case where the photoconductor is negatively charged by the scorotron charger.

As a result, according to the present invention, it is possible to realize an electrophotographic image forming apparatus capable of reducing the amount of ozone generated and forming a high quality image.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a laser beam printer according to an embodiment of the present invention.

FIG. 2 is an enlarged side view of a developing unit and a photosensitive drum portion of the laser beam printer of FIG.

FIG. 3 is an enlarged side view of a developing unit and a photosensitive drum portion showing a modified example of the developing unit that can be used in the laser beam printer of FIG.

FIG. 4 is an enlarged side view of a developing unit of the laser beam printer of FIG.

5 is a characteristic diagram showing a relationship between a developing toner amount and a transmission density in the laser beam printer of FIG.

6 is a characteristic diagram showing a relationship between an effective bias voltage and a developing toner amount in the laser beam printer of FIG.

7 is an explanatory diagram showing the potential of each part of the development processing by the reversal development method performed in the laser beam printer of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser beam printer 10 ... Feeder unit 13 ... Paper feeding roller 14 ... Paper feeding cassette 20 ... Photosensitive drum 30 ... Laser scanner unit 42 ... Cleaning roller 50 ... Developing unit 53 ... Toner 55 ... Supply roller 56 ... Developing roller 57 ... Layer Thickness control blade 60 ... Transfer roller 70 ... Fixing unit 77 ... Paper discharge tray 156 ... Collection-dedicated roller

Claims (5)

[Claims] 1. A positively chargeable photoconductor, a driving means for rotating the photoconductor, and a non-contact facing arrangement at the charging position for positively charging the rotated photoconductor. Charging means, a latent image forming means for forming an electrostatic latent image on the positively charged photoconductor, and a developer charged with the formed electrostatic latent image to the same polarity as the photoconductor. And a transfer unit for transferring the formed visible image onto a recording medium, the developing unit further transferring the image by the transfer unit. After that, the residual developer remaining on the photosensitive member is placed on the rotated photosensitive member and is collected via the charging position. 2. The image forming apparatus according to claim 1, wherein the developing unit includes a developing roller that develops with the developer and collects the residual developer. 3. The image according to claim 1, wherein the developing means includes a developing-dedicated roller for developing with the developer and a collecting-dedicated roller for collecting the residual developer. Forming equipment. 4. A developer dispersion means for temporarily adsorbing the residual developer before reaching the charging position, and discharging the temporarily adsorbed developer onto the photoconductor at a predetermined timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 5. The image forming apparatus according to claim 1, wherein the charging unit includes a scorotron charger for positive charging.