JPH08278701A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device which forms a satisfactory printed image having less fog even in transfer by a transfer fixing method. CONSTITUTION: A DC-overlap AC bias voltage having the opposite polarity of toner is applied to a developer supply roll 32 from an AC power source 52 and a DC power source 54, therefore normally-electrified toner flies from the developer supply roll 32 to a developing roll 36 with the rolls 32 and 36 uncontacted and toner having the opposite polarity and low-electrified toner hardly fly. The normally-electrified toner sticking to the developing roll 36 is carried to a developing area by the roll 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system has been widely spread. This electrophotographic image forming apparatus usually forms an electrostatic latent image on an image bearing member (for example, a photosensitive drum) configured in a drum shape, and is charged with a polarity opposite to that of the electrostatic latent image. This device is a device for obtaining a printed (copy) image by developing the electrostatic latent image with a developing agent (toner) and transferring and fixing the developed image directly or via a transfer drum or the like onto a sheet.

As a transfer method in this electrophotographic image forming apparatus, for example, an electric field is formed between an image carrier and a transfer material, and a developed image is electrostatically transferred to the transfer material by this electric field. Known are an electrostatic transfer method and a transfer fixing method in which a developed image is mechanically transferred onto a transfer target material by pressure or heat and pressure and is fixed at the same time (so-called Transfix). In the electrostatic transfer method, in addition to the transfer device, a fixing device for fixing the developed image transferred to the transfer material is required.
In the transfer fixing method, since transfer and fixing are performed by one transfer fixing device, the space is small accordingly, and although the transfer fixing method is superior to the electrostatic transfer method in this respect, as described below, The transfer fixing method is inferior to the electrostatic transfer method in terms of fogging of the print image formed on the transfer material.

As described above, the developing method in an electrophotographic image forming apparatus is generally performed by electrostatically developing an electrostatic latent image with a developer charged to a polarity opposite to that of the electrostatic latent image. It is to develop. The developer is usually charged so as to have a sufficient charge amount to electrostatically adhere to the electrostatic latent image (the developer thus charged is referred to as a normally charged toner). Some of them have an insufficient amount of charge for developing an electrostatic latent image (hereinafter referred to as low-charged toner), and those charged to the same polarity as the electrostatic latent image (hereinafter, reverse polarity). Polarized toner) may be present, and as a result, the opposite polarity toner mainly adheres to the periphery of the developed image to cause fogging in the developed image. Even if such fogging occurs on the image bearing member, as described above, the electrostatic fixing method electrostatically transfers the developed image on the image bearing member onto the transfer target material. That is, the developer (fog toner) around the developed image is hardly transferred to the transferred material, and only the developed image is selectively transferred to the transferred material. For this reason, in the electrostatic fixing method, the latitude for fogging of the developed image is wide, and even if the developed image on the image carrier has a considerable level of fogging, no fogging occurs in the image transferred and fixed on the transfer material. .

On the other hand, since the transfer fixing method is mechanical transfer, almost all of the fog toner on the image carrier is transferred and fixed on the transfer material. Therefore, the latitude for fogging of the developed image is narrow, and even if a little fogging occurs in the developed image on the image carrier, fogging occurs in the printed image. FIG.
1 shows a comparison of the results of visual inspection of the relationship between the fogging of the developed image on the image carrier and the fogging of the printed image in the electrostatic transfer method and the transfer fixing method.

The horizontal axis of FIG. 11 represents the degree of fogging of the developed image on the image carrier, and the larger the value, the more the fog. The vertical axis indicates the degree of fogging of the printed image,
The larger the value, the more the fog. Generally, the permissible level of fogging of a printed image is said to be 2.6 or less. As shown in FIG. 11, in the transfer fixing method, when the fogging of the developed image on the image carrier exceeds 2.0, Fogging exceeds the allowable level. On the other hand, in the electrostatic transfer method,
As described above, the latitude for the fogging of the developed image on the image carrier is wide, and the fogging of the developed image on the image carrier is about 1 or less.
The fogging of the printed image exceeds the allowable level only when the number exceeds 2. However, in order to reduce the fogging of the printed image not only by the transfer fixing method but also by the electrostatic transfer method, it is preferable to reduce the fogging of the developed image on the image carrier. The following techniques are known as techniques for reducing such fogging.

Japanese Unexamined Patent Publication No. 4-14078 discloses a technique in which the fogging of a print image that occurs during transfer and fixing is reduced by improving the materials of both the image carrier and the toner. In this technique, at the time of development, the materials of both the image carrier and the toner are selected in such a combination that the toner sandwiched between the image carrier and the developing roll is not charged to the opposite polarity even when the toner is frictionally charged. This is a technique for solving the problem that occurs when toner is sandwiched between the developing roll and the image carrier. However, this technology also produces reverse polarity toner,
Although the fogging of the developed image on the image carrier is reduced, the fusing of the printed image cannot be reduced to a satisfactory level by the transfer fixing method.

Japanese Unexamined Patent Publication (Kokai) No. 5-333582 describes a problem that fogging is likely to occur in a developed image on an image carrier due to the use of a polymerized toner spherically formed by polymerization. A technique for improving and solving the problem of good charging is disclosed. However, this technique cannot reduce the fog of a printed image to a satisfactory level by transfer using a mechanical adhesive force that does not rely on electrostatic force, such as Transfix.

Japanese Unexamined Patent Publication (Kokai) No. 4-242264 discloses a technique in which the material of the image carrier is devised to prevent fogging of a developed image on the image carrier. When a developed image formed by this technique is transferred onto a material to be transferred using an electrostatic transfer method to form a print image, fog can be reduced to a level that does not cause a problem, but it does not depend on electrostatic force such as Transfix. Fogging of printed images cannot be reduced by mechanical transfer.

The Electrophotographic Society of Japan, Vol. 19, No. 2, (198)
1) On pages 44 to 51, a layer of a normally charged toner is formed on a conductive developing roll by using a two-component developer having a non-magnetic toner and a magnetic carrier, and a fog of a developed image on an image carrier is formed. A technique for reducing the above is disclosed. In addition, JP-A-5
9-121077, JP-A-59-172662, JP-A-59-151173, JP-A-5-6.
Japanese Patent No. 6677 and Japanese Patent Laid-Open No. 3-113474 disclose
Image carrying is achieved by drawing out the advantages of a one-component developer that does not require a carrier and control of toner concentration, and the advantages of a two-component developer that can stably provide a uniform charge to the toner. Development techniques have been proposed to reduce fogging of a developed image on the body. According to these techniques, the biggest problem in using a one-component developer that has not been fully used due to the difficulty of handling it despite its many advantages, especially the non-magnetic one-component developer that is difficult to handle That is, it is possible to solve the uneven and unstable charging of the toner, and it is possible to reduce the reverse polarity toner and the low charging toner. Specifically, these techniques mix toner and magnetic particles with stirring,
After the toner is sufficiently charged, a magnetic brush is once formed with a mixture of the toner and magnetic particles, and the magnetic brush is rubbed against the developing roll to move the toner to the developing roll and convey the toner to the developing area. Is. However, in these technologies, magnetic particles and toner are mixed and agitated, or the magnetic brush is rubbed against the developing roll, so that the stress on the toner is large, and when pressure fixing toner or capsule toner is used. However, there is a problem that toner may be fixed in the developing device. In addition, when a magnetic brush is formed using normal heat fixing toner and the heat fixing toner is moved to the developing roll, the reverse polarity toner and low-charged toner that are generated are electrostatically attracted to the developing roll. However, when the magnetic brush rubs against the developing roll, mechanical force is applied to the opposite polarity toner and the low charge toner, so that not only the low charge toner but also the opposite polarity toner is slightly moved to the development roll. . As a result, reverse polarity toner or low-charged toner that causes fogging adheres to the developing roll,
If a developed image formed on the image bearing member using this developing roll is transferred by a transfer method such as Transfix that does not rely on electrostatic force, fogging occurs in the printed image.

Further, Japanese Laid-Open Patent Publication No. 56-69669 discloses a toner charging system in which a DC current is applied between a toner supply device for supplying toner to a developing roll and a developing roll to inject an electric charge into the toner. A developing device is disclosed. According to this developing device, a relatively large amount of reverse polarity toner or low-charged toner is present in the toner, and when the developed image developed by this developing device is transferred by a transfer method that does not rely on electrostatic force, such as Transfix. , Fogging occurs in the printed image.

[0012]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus which uses a transfer fixing method and can form a good print image with less fog.

[0013]

In the image forming apparatus of the present invention for achieving the above object, an electrostatic latent image formed on an image carrier is charged to a polarity opposite to the polarity of the electrostatic latent image. In the image forming apparatus including a developing device that develops using the developed developer and a transfer fixing device that transfers the developed image developed by the developing device to a transfer material and fixes the image at the same time, 1) A developer supply member that rotates by carrying a developer on the outer peripheral surface. (2) A developer carried on the outer peripheral surface is sandwiched between the developer supply body and the developer, and the polarity of the electrostatic latent image is applied to the developer. A blade member for frictionally charging to the opposite polarity to (3) disposed in a state of being separated from the developer supply body,
A developer transport body that receives the developer supply from the developer supply body and transports the developer to a development area where the electrostatic latent image is developed. (4) A developer transport body from the developer supply body to the developer transport body. The present invention is characterized by comprising a bias applying means for applying a bias for supplying to the body to the developer supply body and the developer transport body.

Here, it is preferable to provide a collecting means for collecting the developer remaining in the developer carrying body after carrying the developer to the developing area.

[0015]

In the developer frictionally charged by the blade member, as described above, in addition to the normally charged toner having a sufficient charge amount to electrostatically adhere to the electrostatic latent image, the reverse polarity toner is used. And low-charged toner exist, and these reverse-polarity toners and low-charged toners may adhere to the periphery of the electrostatic latent image, causing fog in the developed image on the image carrier.
However, according to the present invention, by the bias applying means,
The developer supply member and the developer transfer member are arranged so that the normally charged toner of the developer frictionally charged by the blade member is supplied from the developer supply member to the developer transfer member, and the reverse polarity toner or the low charge toner is not supplied. A bias can be applied to. Therefore, the developer carrier supplies the normally charged toner to the developer carrier, and the developer carrier conveys the normally charged toner to the developing area. As a result, a high-quality developed image with reduced fog is formed on the image carrier,
When this developed image is transferred and fixed to the transfer material, a high-quality printed image with less fogging can be obtained. As described above, according to the image forming apparatus of the present invention, the normally-charged toner, which is preferable for forming a developed image, is not conveyed to the developing area, but the normally-charged toner, which is slightly present, is not conveyed to the developing area. It can be selectively supplied and conveyed to the developing area.

Further, since the developer transport body is arranged in a state of being separated from the developer supply body and the developer is electrostatically supplied from the developer supply body to the developer transport body by the bias applying means, The stress applied to the developer can be suppressed and the deterioration of the developer can be suppressed. Therefore, in the image forming apparatus of the present invention, it is possible to suppress the deterioration of the developer which is fixed by applying pressure like capsule toner which is easily fixed in the developing device.

Further, in the image forming apparatus of the present invention, the developer is frictionally charged by using the blade member. The frictional charging using the blade member will be described in comparison with the conventional charging by charge injection. In conventional charging by charge injection, as shown in FIG. 12A, a wide charge distribution is obtained, and a large amount of low-charged toner and reverse polarity toner is contained. On the other hand, in the triboelectrification by the blade member, as shown in FIG. 12B, most of the developer is charged to a level that can reduce the fogging of the developed image on the image carrier, and the low-charged toner and the reverse polarity toner are small. , The charge distribution is relatively sharp.

When the charging method by charge injection described above is applied to the present invention in place of the blade member, the proportion of the normally charged toner is low, so that when the normally charged toner is moved to the developer carrier, one of the developer supply members is used. The amount of the normally-charged toner that moves to the developer transport body due to the rotation decreases. When the low-charged toner or the opposite-polarity toner stays in the developer supply body for a long time, electric charge is injected and becomes a normally-charged toner, but it receives much stress. Further, in order to form a high-density developed image at a higher speed, the rotation speed of the developer supply body is increased, or a high voltage is applied to the developer supply body, so that a large amount of the normally charged toner can be conveyed quickly. When an attempt is made to move the toner to the body, a larger amount of toner of the opposite polarity moves to the developer transport body, or the Transfix
When the capsule toner and the soft low melting point toner used in the above are used, there is a problem in that they receive a lot of stress.

On the other hand, in the case of blade charging, as shown in FIG. 2, since the developer contains a large amount of normally charged toner, one rotation of the developer supply member causes a large amount of the normally charged toner to be transferred to the developer conveying member, resulting in a high charge. It can also be used for density development and high-speed development. Here, when the recovery means for recovering the developer remaining in the developer carrier after the developer is transported to the developing area is provided, the residual developer which may have an uneven charge amount is recovered,
The developer just supplied from the developer supplier can be conveyed to the developing area, and a developed image with stable fog and reduced for a long period is formed on the image carrier.

Further, when the image forming apparatus of the present invention is configured to electrostatically convey the developer from the developer conveying body to the developing area in a non-contact state, for example, stirring like a capsule toner which is fixed by pressure is agitated. Even if a developer which is very weak against stress such as is used, its deterioration can be suppressed.

[0021]

Embodiments of the image forming apparatus of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a schematic view showing a first embodiment of the image forming apparatus of the present invention. In the image forming apparatus 10, a heat-resistant dielectric belt 12 that rotates in the direction indicated by the arrow 12a is used as an image carrier. Around the dielectric belt 12, an ion head 14 for writing a latent image and a developing device are used. Bowl 3
0, a dielectric belt 12 having a heat generating means 16 for transfer fixing
A pair of rolls 18 sandwiching the sheet, a cooling fan 20 for air-cooling the dielectric belt 12, a cleaner 22 for removing the toner adhering to the dielectric belt 12, and a discharge lamp 24 for removing the electric charge of the dielectric belt 12 are arranged respectively. ing.

The developing device 30 includes a developer supply roll (an example of a developer supply member referred to in the present invention) 32 that carries toner on its surface and rotates, and a toner carried on the outer peripheral surface of the developer supply roll 32. A blade member 34 that is frictionally charged to have a polarity opposite to the polarity of the electrostatic latent image by being sandwiched between the blade member 34 and the outer peripheral surface;
A developing roll which is arranged in a state of being separated from the developer supply roller 32 and which conveys the toner supplied from the developer supply roller 32 to a developing region where the electrostatic latent image is developed (of the developer conveying body in the present invention). (Example) 36 and toner 38 inside
Is provided with a toner conveying member 40 that is triboelectrically charged and conveys the toner to the developer supply roll 32. The toner conveying member 40 is
A member 40a including a wire-shaped member or a paddle that conveys the toner to the vicinity of the toner supply roller is pressed against the toner supply roller 32, and the toner is sandwiched between the toner supply roller 32 to frictionally charge the toner. It is composed of a sponge-like soft member 40b that is conveyed to 32. The distance between the developing roll 36 and the dielectric belt 12 is kept at 0.1 to 0.5 mm. Between the developing roll 36 and the dielectric belt 12, a plurality of control electrodes 42 for controlling the flight of the toner are arranged so as not to hinder the flight of the toner.

As the developer supply roll 32, an aluminum cylinder whose surface is anodized, a cylinder made of phenol resin, or a cylinder whose metal surface is coated with a synthetic resin layer is used, and is shown by an arrow 32a. Rotate in the direction. The developer supply roll 32 is kept at a distance of about 0.1 to 0.5 mm with respect to the developing roll 36. The blade member 34 has a narrowed area in contact with the surface of the developer supply roll 32 so that the stress on the toner can be reduced as much as possible and the charge can be sufficiently applied to the toner. As shown in FIG. Thickness 0.05mm
The stainless steel plate 44 is attached to the fixing bracket 46, and the plate 44 is further attached with a silicon rubber 48 having a thickness of 1 mm.
It is a three-piece type blade in which

As the developing roll 36, similarly to the developer supplying roll 32, an aluminum cylinder whose surface is anodized, a cylinder made of phenol resin, or a cylinder having a synthetic resin layer formed on the metal surface is used. And rotates in the direction indicated by arrow 36a. The moving directions of the developing roller 36 and the dielectric belt 12 at the facing positions are the same in this embodiment, but they may be set to be opposite to each other. Further, the rotation direction of the developer supply roll 32 is preferably set so that the developer supply roll 32 and the development roll 36 rotate in opposite directions at a position where they face each other. The control electrode 42 is composed of a conductive wire having a diameter of 89 μm, is linearly arranged in a plurality of rows in the axial direction of the developing roll 36, and is supported by both ends (not shown) of the opening 31 a of the housing 31 to develop. Roll 36
It is located in the vicinity of. The control electrode 42
In place of the conductive wire, a plurality of openings larger than the average particle size of the toner particles may be formed in a thin metal plate, and an electrode group including a plurality of control electrodes may be formed on the surface of the developing roll 36. It may be embedded. The transfer / fixing roll pair 18 includes an elastic roll 18a disposed inside the dielectric belt 12 and a silicone roll having a thickness of 1 to 5 mm disposed outside the dielectric belt 12 and the outer peripheral surface. Coated roll 18b.

Next, image formation by the image forming apparatus 10 will be described. The surface of the dielectric belt 12 is uniformly discharged by the discharging lamp 24, and then the ion head 1
An electrostatic latent image is written on the dielectric belt 12 by 4. When the electrostatic latent image reaches the developing area, it is developed by the developing device 30, and the developed image is formed on the dielectric belt 12. The developed image is conveyed to the roll pair 18 while being superimposed on the recording medium 50. In the roll pair 18, the recording medium 50 is sandwiched between the rolls 18a and 18b, and the developed image is transferred and fixed onto the recording medium 50. The recording medium 50 that has passed the roll pair 18 is peeled off from the dielectric belt 12 and the copying is completed. On the other hand, the toner remaining on the dielectric belt 12 after the transfer and fixing is scraped off by the cleaner 22.

Next, the developing device 30 will be described in detail with reference to FIG. FIG. 2 is a partially enlarged view showing the developing device of the image forming apparatus of FIG. A non-magnetic single-component toner 38 that is fused and fixed to the recording medium 50 by heat is accommodated inside the developing device 30, and the toner 38 is conveyed to the developer supply roll 32 by the toner conveying member 40. The toner adhered to the developer supply roll 32 is triboelectrically charged when passing through the charging blade 34, the thickness of the layer is regulated, and the toner is carried to a position facing the developing roll 36. A DC superimposed AC bias voltage having a polarity opposite to the polarity of the toner is applied to the developer supply roll 32 from the AC power supply 52 and the DC power supply 54, and the developer supply roll 32 and the development roll 36 are not in contact with each other. The normally charged toner flies from the developer supply roll 32 to the developing roll 36, and the reverse polarity toner and the low charge toner hardly fly. The normally charged toner attached to the developing roll 36 is conveyed to the developing area by the developing roll 36. Further, a changeover switch 55 is provided between the AC power supply 52 and the DC power supply 54 to switch from the DC power supply 54 to the DC power supply 56 which applies a voltage for moving the toner on the developing roll 36 to the developer supply roll 32. There is.

A DC voltage is applied to the developing roller 36 from a DC power source 58 to form a potential between the developing roller 36 and the dielectric belt 12. In the developing area, an electric field is applied so that the normally charged toner moves to the dielectric belt 12. Is working. Further, a DC superimposed AC voltage is applied to the control electrode 42 from the AC power supply 60 and the DC power supply 62 to form an electric field in the surroundings,
The electric field causes the normally-charged toner on the developing roll 36 to fly and generate a cloud, and the normally-charged toner easily moves to the dielectric belt 12. The clouded normally charged toner flies in the electric field and adheres to the electrostatic latent image on the dielectric belt 12, whereby a developed image with less fogging is formed on the dielectric belt 12. By transferring and fixing the developed image, a print image with less fogging is formed.

FIG. 4 is a timing chart showing changes in the DC component of the bias applied to the developer supply roll 32 and the development roll 36 and the timing of image formation. A DC superimposed AC voltage is applied to the developer supply roll 32,
As the DC component, different voltages are applied by the changeover switch 55. Approximately 0.2 seconds before the developing process starts (time t1), the developing roll 36 and the developer supply roll 3
2 is started, a voltage of −400V is applied from the DC power source 54 to the developer supply roll 32, and the developing roll 3
A voltage of −200 V is applied to the 6 from the DC power source 58,
As a result, the normally charged toner on the developer supply roll 32 moves to the developing roll 36 and a toner layer is formed. In addition to the normally charged toner, the reverse polarity toner and the low charged toner are also attached to the developer supply roll 32.
-4 for the developer supply roll 32 and the developing roll 36, respectively
Since the voltages of 00V and -200V are applied, only the normally charged toner moves to the developing roll 36 due to this potential difference. The time from the end of the developing process (time t2) to the start of the next developing process (time t4) is about 0.5 seconds, and this time is two rotations or more of the developing roll 36. Within a time corresponding to the first one rotation, the changeover switch 55 switches to the DC power supply 56 to set the voltage applied to the developer supply roll 32 to -100V. At this time, the potential difference between the developing roll 36 and the developer supplying roll 32 is 100 in absolute value.
V, the electric field between the developing roll 36 and the developer supplying roll 32 is opposite to that when the toner layer is formed, and the developing roll 3
The toner on 6 moves to the developer supply roll 32. Here, applying the voltage in this manner is called a reverse DC bias mode. Next, in order to prepare for the second developing step, the voltage of the developer supply roll 32 is returned to -400V (at time t
3) As a result, the formation of the toner layer on the developing roll 36 is started. The second development process is completed (time t5)
After that, the voltage to the developer supply roll 32 is switched again, and the toner on the development roll 36 is transferred to the developer supply roll 32.
Move to. Needless to say, the above steps may be repeated when an image is formed on a plurality of sheets. In this embodiment, the AC component applied to the developer supply roll 32 has a frequency of 2 kHz and Vp-p1 kV, the AC component applied to the control electrode 42 has a frequency of 2 kHz and Vp-p1 kV, and the DC voltage is -150 V. is there. Further, when the power is turned on, the reverse DC bias mode continues for 7 seconds, not only the toner on the developing roll 36 moves to the developer supply roll 32, but also the toner attached to the control electrode 42 is attracted to the developing roll 36. Then, the control electrode 42 is cleaned. By performing the reverse DC bias mode, toner that does not easily move to the electrostatic latent image and remains on the developing roll 36 and has a high charge amount to reduce the developing efficiency, or toner that adheres to the control electrode 42 and reduces the developing efficiency is used. It can be removed and more stable development performance can be maintained.

In this embodiment, the dielectric belt is used as the image carrier, but a heat-resistant photosensitive belt may be used. In this case, instead of the ion head, a charger and a laser ROS for writing an electrostatic latent image ( Raster Output Sc
aner) is used. Also, instead of laser ROS, L
ED or document reflected light (analog) may be used. The shape of the image carrier is not limited to the belt and may be a drum.
As the developer, a magnetic one-component developer or a two-component developer including a non-magnetic toner and a magnetic carrier can be used. In this case, as the developer supply roll 32, one having a built-in magnet and coated with a phenol resin or the like, or an aluminum sleeve whose surface is roughened by blasting is used. Further heat causes Trnsfi
Needless to say, the pressure fixing toner can be used instead of the pair of rolls 18 for fixing x by fixing with pressure. Further, in Transflx, since the transfer rate is very high, it is possible to omit the cleaner 22 so as not to generate waste toner.

[Second Embodiment] FIG. 5 is a schematic view showing a second embodiment of the image forming apparatus of the present invention. Image forming apparatus 7
Reference numeral 0 designates a photosensitive drum 72 having a cylindrical aluminum surface coated with an amorphous silicon film and rotating in a direction indicated by an arrow 72a, and a photosensitive drum arranged around the photosensitive drum 72 in the order of image forming processes. A charging roll 74 that uniformly charges 72, a laser ROS (not shown) that oscillates a laser 76 for forming an electrostatic latent image, and a developing device 7.
8, a transfer / fixing roll 80, a cleaner 82 for removing toner adhering to the photosensitive drum 72, and the photosensitive drum 7
A charge eliminating lamp 84 for removing the second electric charge is provided.

The developing device 90 contains a pressure fixing capsule toner 86, and is provided with a developer supply roll 92, a blade member 94 and a developing roll 96 as in the first embodiment. The transfer / fixing roll 80 is in pressure contact with the photosensitive drum 72. The cleaner 82 has a metal blade 82a inside, and the blade 82a contacts the photosensitive drum 72 at a constant angle, and the toner remaining on the photosensitive drum 72 is mechanically scraped off.

Next, an image forming procedure by the image forming apparatus 70 will be described. The surface of the photosensitive drum 72 is uniformly charged by the charging roll 74, and an electrostatic latent image is formed on the surface of the photosensitive drum 72 by a laser ROS (not shown). The formed electrostatic latent image is developed by the developing device 90 with the capsule toner 86 to form a developed image on the photosensitive drum 72. The developed image is transferred onto the recording medium 50 supplied between the photosensitive drum 72 and the transfer fixing roll 80 by pressure and is fixed at the same time. After the transfer and fixing, the toner remaining on the photosensitive drum 72 is scraped off by the cleaner 82. Further, the charge on the surface of the photosensitive drum 72 is removed by the charge eliminating lamp 84, and one image forming cycle is completed.

Further, in order to maintain the transfer rate, the central axis of the transfer fixing roll 80 is inclined by 0.4 with respect to the central axis of the photosensitive drum 72, and the recording medium 50 and the photosensitive drum 72.
There is a slight slip between and. The transfer / fixing roll 80 is provided on the photosensitive drum 72 by a pressing unit (not shown).
With a load of 2000 N (about 200 kgf), the pressure is evenly applied.

Inside the developing device 78, a capsule toner 86 containing magnetic powder is contained, and the toner is carried by the toner carrying member 98 to the developer supply roll 92. The conveyed toner is attracted by the magnetic force of a magnet (not shown) built in the developer supply roll 92, moves on this surface as the developer supply roll 92 rotates, and is triboelectrically charged by the blade member 94. Then, a toner layer is formed. In this toner layer, there are not only the normally charged toner but also the opposite polarity toner and the lowly charged toner. However, as will be described later, the normally charged toner is supplied to the developer supply roll 92 and the developing roll 96, respectively. A bias is applied so as to move. The normally charged toner that has moved to the developing roll 96 is conveyed to the developing area as the developing roll 96 rotates. Bias is applied to each of the developing roll 96 and the photoconductor drum 72, and the normally charged toner flies in the form of a cloud and adheres to the electrostatic latent image on the photoconductor drum 72 to form a developed image with less fogging. To be done. By transferring and fixing the developed image, a print image with less fogging is formed.

Bias applying means for applying a bias to the developer supply roll 92 and the developing roll 96 respectively include those shown in FIGS. 6, 7 and 8. The bias applying means shown in FIG. 6 applies a DC voltage (−500 V) to the developer supply roll 92 using the DC power supply 100, and applies a DC superimposed AC voltage to the developing roll 96 using the DC power supply 102 and the AC power supply 104. (Frequency 2 kHz, V
p-p2kV, _VDC ; -250) is applied to vibrate the normally-charged toner so that the developer supply roll 92
Is a means for facilitating the separation from the developer and for moving the normally charged toner from the developer supply roll 92 to the developing roll 96. The normally charged toner that has moved to the developing roll 96 is conveyed to the developing area as the developing roll 96 rotates. In the photosensitive drum 72, the image portion is -100V and the non-image portion is -500V.
Similarly to the case where the normally charged toner is charged to V from the developer supply roll 92 to the developing roll 96, the normally charged toner is moved only to the image portion due to the toner vibration effect of the AC voltage and the potential difference, and the photoconductor is A developed image with less fog is formed on the drum 72.

In the bias applying means of FIG. 7, the developer is supplied.
Directly connected to the roll 92 by the AC power supply 106 and the DC power supply 108.
An AC voltage is applied. Alternate to developing roll 96
DC weight AC voltage is generated by the power supply 110 and the DC power supply 112.
Apply. AC voltage applied to the developer supply roll 92
The AC voltage applied to the developing roll 96 does not cancel each other out.
Use a combination of frequencies with greatly different periods
Or applying an AC voltage with a phase shift
Ingenuity is required. In this embodiment, the developer supply roll 9
2 frequency 8kHz, Vp-p600V, V_DC-40
By applying 0 V DC superimposed AC voltage, the developing roll 96 is rotated.
Wave number 2.5 kHz, Vp-p2 kV, V _DC-200V
A DC weight AC voltage was applied.

The bias applying means shown in FIG. 8 is configured to apply to the developer supply roll 92 a bias in which an AC voltage having a frequency higher than the frequency of the AC voltage applied to the developing roll 96 and a DC voltage are superposed. In this embodiment, the developer supply roll 92 has a frequency of 2 k from the AC power supply 114.
Hz, the AC voltage Vp-p2kV, from the AC power supply 116, frequency 30 Hz, superimposed with a DC voltage of V _DC -400 V from an AC voltage and a DC power supply 118 of Vp-p500V. This waveform is schematically shown in FIG. AC voltage from the AC power source 114 (frequency 2 kHz) is applied to the developing roll 96.
z, Vp-p2kV), -20 from the DC power supply 120
A bias on which a DC voltage of 0 V was superimposed was applied.

FIG. 9 shows the relationship of the potential difference between the developer supply roll 92 and the developing roll 96 by the bias applying means shown in FIGS. As shown in FIG. 9, the potential difference (toner supply contrast) 130 between the developer supply roll 92 and the development roll 96 is 200V. The potential difference (developing contrast) 140 between the image portion of the photosensitive drum 72 and the developing roll 96 is 100V.

Although the electrostatic latent image writing laser ROS is used in this embodiment, an LED may be used, or analog original reflected light may be used. As the image carrier, an aluminum surface coated with an amorphous silicon film was used, but the image carrier is not limited to this, and may be a dielectric substrate or a photosensitive layer formed on the surface of a conductive substrate. In addition, it is sufficient that the surface has sufficient strength to withstand the pressure required for pressure transfer fixing. For example, a dielectric drum having an anodized aluminum surface, or an aluminum surface coated with an inorganic film such as silicon nitride or silicon carbide by a method such as plasma CVD may be used. When the dielectric drum is used, the charger is not required and the electrostatic latent image writing head is used as the latent image writing means. As an electrostatic latent image writing head,
Arranged with a constant gap in the axial direction of the dielectric drum,
It is preferable that the irradiation of ions output in the axial direction can be independently controlled for each pixel. Further, the developer, the transfer fixing method, and the image bearing member are not limited to those described above,
A combination of transfer fixing using magnetic, non-magnetic, pressure fixing toner, thermal transfer fixing using heat fixing toner, belt, drum and the like may be used. Further, it goes without saying that the present invention can be applied to color.

[0040]

As described above, according to the image forming apparatus of the present invention, since the normally charged toner is selectively conveyed to the developing area, a developed image with less fog is formed on the image carrier, and this developing is performed. By transferring and fixing the image on the transfer material, a printed image with less fogging can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of an image forming apparatus of the present invention.

2 is a partially enlarged view showing a developing device of the image forming apparatus of FIG.

FIG. 3 is a perspective view showing a blade member of the image forming apparatus of FIG.

FIG. 4 is a timing chart showing changes in the DC component of the bias applied to the developer supply roll 32 and the development roll and the timing of image formation.

FIG. 5 is a schematic view showing a second embodiment of the image forming apparatus of the invention.

FIG. 6 is a schematic view showing an example of bias applying means.

FIG. 7 is a schematic view showing another example of bias applying means.

FIG. 8 is a schematic view showing still another example of bias applying means.

FIG. 9 is a graph showing a potential difference between a developer supply roll and a developing roll.

FIG. 10 is a graph showing a waveform of a voltage applied to a developer supply roll.

FIG. 11 is a graph showing the relationship between the fogging of a developed image on the image carrier and the fogging of a print image by comparing the electrostatic transfer method and the transfer fixing method.

12A is a graph showing a charge distribution by charge injection, and FIG. 12B is a graph showing a charge distribution by a blade member.

[Explanation of symbols]

10, 70 Image forming apparatus 12 Dielectric belt 18 Roll pair 30 Developer 32, 92 Developer supply roll 34, 94 Blade member 36, 96 Development roll 52, 104, 106, 110, 114, 116 AC power supply 54, 58, 100, 102, 108, 112, 11
8,120 DC power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gouji Nagao 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (1)

[Claims] 1. A developing device for developing an electrostatic latent image formed on an image bearing member with a developer charged to a polarity opposite to the polarity of the electrostatic latent image; and a developing device developed by the developing device. An image forming apparatus including a transfer fixing device that transfers the developed image to a transfer material and fixes the developed image at the same time, wherein the developing device holds a developer on an outer peripheral surface and rotates, and the outer peripheral surface. And a blade member for frictionally charging the developer carried on the outer peripheral surface with the developer and frictionally charging the developer to a polarity opposite to the polarity of the electrostatic latent image, and in a state of being separated from the developer supply body. A developer transport body which is disposed and receives the developer supplied from the developer supply body and conveys the developer to a developing area where the electrostatic latent image is developed; and a developer transport body which transfers the developer from the developer supply body. A bias for supplying to the developer transport body is applied to the developer supply body and the developer. An image forming apparatus characterized in that with a bias applying means for applying to the Okukarada.