JPH09319219A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain image quality in an initial condition over a long period and to reduce running costs by discharging development impurities which increase with the increment of the frequency of use. SOLUTION: A given bias voltages are applied to a developing roller 20 and a transfer unit 34 by a high voltage power sources 32 and 36, respectively. Potential and polarity control is exerted to the high voltage power sources 32 and 36 by a controller 16. When a refresh process is specified, a second developing bias voltage having a small absolute value is applied to the developing roller 20. As a result, toner electrified to an opposite polarity and sticking to the surface of the developing roller 20 is attracted to a photoreceptor 12. Further, a transfer bias voltage having the same polarity as that of the developing bias voltage is applied to the transfer unit 34. Thus, the toner electrified mainly to the opposite polarity, as impurity, is transferred to a transfer material 40 and discharged soon.

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,
In particular, for example, it is applied to a copying machine and a laser printer using an electrophotographic method, and collects untransferred toner remaining on the photoconductor at the same time as development by the potential difference between the surface potential of the photoconductor and the developing bias voltage. Regarding

[0002]

2. Description of the Related Art One example of this type of conventional technology is Japan Hard
It is disclosed in Copy '89 Proceedings (P143-146). That is, the toner is attached by reversal development to the portion where the surface potential of the photoconductor is attenuated by the exposure means, and the untransferred toner on the photoconductor is transferred to the developing unit by utilizing the potential difference between the surface potential of the photoconductor and the developing bias. It is designed to be electrostatically attracted.

In addition to the above-mentioned process, an example is provided in which charge removing means for removing charge from a photoconductor is provided before transfer of a toner image to improve transfer efficiency of the toner image and suppress generation of untransferred toner. Published Japanese Patent Application No. 63-63
-133179 gazette (G03G 21/00). Further, an example in which the rotation direction of the developing roller and the rotation direction of the photoconductor are made different, and the peripheral speed of the development roller is set to 1.2 times or more the peripheral speed of the photoconductor to improve the toner collecting ability. (JP-A-5-210300)
Another example has been proposed in which the amount of toner supplied to 1 cm ² of the surface of the photosensitive member in 1 ^second is regulated to form an effective cleaning electric field (JP-A-3-7972). In the conventional example in which such a cleaning step is omitted, there are advantages that the image forming apparatus itself can be downsized, and the toner that has been conventionally discarded can be reused.

[0004]

However, when the toner that has been disposed of as waste toner is reused for a long period of time, it is charged with a toner having a low charge amount, an uncharged toner, and a polarity opposite to the original charge polarity. The reverse polarity toner is gradually increased, and as a result, the average charge amount of the toner is decreased, and the toner is attached to the image background portion or the image edge portion is bleeding, resulting in an image defect. Further, since the thin toner layer formed on the developing roller is not uniformized, problems such as disturbance of a black image, deterioration of reproducibility of individual dots, and coupling of adjacent dots occur.

Therefore, in order to maintain the original performance of the image forming apparatus, conventionally, there is no means other than replacing the developing device including the developing roller and the like, and there is a drawback that the cost becomes high. Therefore, a main object of the present invention is to provide an image forming apparatus which eliminates developing impurities in the developing device, can be inexpensive, and can maintain the initial performance for a long period of time.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a charging means for uniformly charging a photoreceptor, an exposing means for forming an electrostatic latent image on the photoreceptor by an optical image corresponding to an original, and a charging polarity of the photoreceptor. The developing device is provided with a developer supplying unit that receives the developing bias voltage of the same polarity to reversely develop the electrostatic latent image, and a transfer unit that transfers the reversely developed developer image to a transfer material by a transfer bias voltage having a polarity opposite to the developing bias voltage. In an image forming apparatus, a developing bias voltage generating unit that generates a second developing bias voltage having an absolute value smaller than that of the developing bias voltage during a non-image forming operation, and a transfer bias voltage in synchronization with the second developing bias voltage. An image forming apparatus comprising a polarity switching means for switching to the same polarity as the developing bias voltage.

[0007]

When the image forming operation is not performed, that is, during the non-image forming operation, the photosensitive member is positively charged by the charging means. Then, the exposure unit is disabled, for example, and the second developing bias voltage is applied to the developer supplying unit by the developing bias generating unit. As a result, a large potential difference is generated between the photoconductor and the developer supply unit. Therefore, the development impurities existing in the developer supplying means move to the photoconductor side. In particular, a developer that is slightly charged to the opposite (negative) polarity is effectively adsorbed on the photoconductor. Also, in synchronization with the generation of the second developing bias voltage,
The polarity of the transfer bias voltage is set to the same polarity as the developing bias voltage by the polarity switching means. As a result, the developing impurities adsorbed on the surface of the photoconductor are transferred to the transfer material by the transfer means, and the transfer material passes through the fixing means and is discharged to the outside of the image forming apparatus.

[0008]

According to the present invention, the impurities remaining or mixed in the developing device can be discharged to the outside of the image forming device, so that the performance in the initial state can be maintained for a long time and the running cost can be suppressed. The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus 10 of the embodiment shown in FIG. 1 includes a photoconductor 12 which is an image carrier and rotates in the direction of the arrow.
The photoconductor 12 is, for example, a positively chargeable OPC photoconductor coated on a conductive base made of aluminum. A charger 14 is arranged on the left side of the photoreceptor 12, and the charger 1
As shown in FIG. 2, the power source 18 connected to the controller 16 controls the charge amount of the electric charges 4. That is, this charger 14 is, for example, a scorotron charger, and in order to protect the photoconductor 12, uneven electrostatic charge on the surface of the photoconductor 12 is prevented. Then, the photoconductor 12 is uniformly electrostatically charged by the charger 14.

A developing roller 20 is arranged below the photoconductor 12 so as to contact the photoconductor 12. The developing roller 20 is a developer (toner) for the photoconductor 12.
Therefore, the developing roller 20 constitutes a developer supplying means. Further, in relation to the developing roller 20, a supply roller 22 and a storage chamber 25 are arranged. An agitator 27 for agitating the toner and supplying the toner to the supply roller 22 is provided in the substantially center of the storage chamber 25.
Is arranged. Therefore, the toner stored or stored in the storage chamber 25 is supplied to the developing roller 20 by the supply roller 22. Then, on the surface of the developing roller 20, a toner thin layer whose thickness is regulated is formed by the supply roller 22 and the blade 24. It should be noted that the cartridge 2 detachably attached to the accommodation chamber 25
6 replenishes the toner.

An exposure device 28 is arranged on the lower right side of the photoconductor 12, and the optical image of the original formed by the exposure device 28 is incident on the photoconductor 12 via a mirror 30. Then, an electrostatic latent image is formed on the photoconductor 12 exposed by the original light image. The developing roller 20 and the supply roller 22
Receives a developing bias voltage from the high voltage power source 32, and the voltage and polarity of the high voltage power source 32 are controlled by the controller 16.

A transfer device 34 is arranged above the photoconductor 12, and a high voltage power supply 36 controlled by the controller 16 is connected to the transfer device 34. The transfer device 34 is
On the transfer material 40 such as paper conveyed by the paper feeder 38,
The toner image is electrostatically attracted. The toner on the transfer material 40 is
It is fixed to the transfer material 40 by the fixing device 42. In such an image forming apparatus 10, the electrophotographic process is
Repeated around the photoreceptor 12. That is, the charger 1
4, the photoconductor 12 is uniformly positively charged to, for example, about 1000 V, and an electrostatic latent image is formed by exposing the original image. This electrostatic latent image receives the developing bias voltage (for example, +400 V) from the high voltage power source 32, and the developing roller 2
Developed by 0. In this way, the toner on the developing roller 20 is charged to the same polarity as the charging polarity of the photoconductor 12. The developed toner image on the photoconductor 12 is transferred to the transfer device 34.
Is transferred to the transfer material 40. The transfer device 34
Is supplied with a transfer bias voltage having a polarity (negative polarity) opposite to that of the developing bias voltage. The transfer material 40 is peeled from the photoconductor 12 by a separator (not shown) and sent to the fixing device 42. The untransferred toner remaining on the photoconductor 12 without being transferred to the transfer material 40 is again guided to the charger 14 in a state of adhering on the photoconductor 12, and is uniformly charged (positive charge) together with the photoconductor 12. Is given.

Although such an electrophotographic process is repeated, the untransferred toner remaining on the photoconductor 12 is attracted in the direction opposite to the developing electric field by the background electric field formed by the developing roller 20 and the photoconductor 12. To be done. That is, when the toner is attached to the photoconductor 12 by reversal development as in this embodiment, the photoconductor 12 and the developing roller 2 are used.
0 has the same polarity, and the absolute value of each potential is, as shown in FIG. 3, the photoconductor charging potential> the developing bias potential>
It is related to the exposure potential. Therefore, the positively charged toner always receives the electrostatic force in the downward direction in FIG. As a result, the electrostatic latent image formed on the photoconductor 12 is visualized by the toner on the developing roller 20.
At this time, in the transfer process before that, the photoconductor 12
The untransferred toner remaining on the upper surface moves from the photoconductor 12 to the developing roller 20 contrary to the developing toner.

However, by repeating these series of steps, among the toners collected in the storage chamber 25, (1) a toner having a low charge amount, (2) a toner having no charge, and (3) ) Toner that exhibits charging property in the opposite polarity, and (4) Paper powder and dust of the transfer material 40 increase. The graph of FIG. 5 compares the toner charge amount in the initial state formed on the developing roller 20 with the toner charge amount after the endurance. By repeating the image formation and the recycling of the untransferred toner, the charge amount in the initial state shown in FIG. 5a becomes lower in average value and the toner charge becomes non-uniform as shown in FIG. 5b. Recognize. Therefore, as the frequency of use increases, the possibility of image failure increases.

On the other hand, in the embodiment shown in FIG. 1, the developing bias voltage (400 V) is applied to the developing roller 20.
A second developing bias voltage having an absolute value smaller than that of the developing bias voltage is applied, and the transfer bias voltage is switched to the same polarity (positive polarity) as the developing bias voltage in synchronism with the second developing bias voltage. 12 can be adsorbed.

That is, as described above, the developing roller 20
The voltage of the high-voltage power supply 32 for applying the developing bias voltage to is selectively controlled by the controller 16.
Then, when a so-called refreshing process for discharging impurities is performed, the developing roller 2 is discharged from the high voltage power source 32.
With respect to 0, the second developing bias voltage (for example, 100 V) having a small absolute value is output. In addition, the controller 16 synchronizes the voltage polarity of the transfer bias voltage applied to the transfer device 34 with the output of the second developing bias voltage, and the polarity of the transfer bias voltage becomes the same polarity as the developing bias voltage. Can be switched. It should be noted that this refreshing step is performed, for example, by the controller 16 counting the number of development histories and periodically performing it according to the counted number, or at the same time as replacing the cartridge 26.

More specifically, this refreshing step will be described. The photoconductor 12 is positively charged to 1000 V by the charger 14, for example. Then, originally, an electrostatic latent image is formed on the photoconductor 12 by the exposing device 28, but during the operation of this refreshing step, the exposing step is disabled and the developing step is started. Then, as described above, as the second developing bias voltage applied to the developing roller 20,
For example, a bias voltage of about + 100V is applied.
Therefore, the potential difference between the surface potential of the photoconductor 12 and the developing roller 20 is about 900 V, which corresponds to about 1.5 times the potential difference in normal image formation.

Due to the large potential difference generated between the photoconductor 12 and the developing roller 20, the toner charged mainly to the negative polarity and adhering to the developing roller 20 is adsorbed to the photoconductor 12 as shown in FIG. It The toner on the photoconductor 12 is transferred to the transfer device 34 to which a positive transfer bias voltage is applied.
Is transferred to the transfer material 40. Then, the transfer material 40 passes through the fixing device 42, and thereafter, the image forming apparatus 10
It is discharged outside.

According to this embodiment, even the toner slightly attracted to the developing roller 20 and having a slightly opposite polarity can be removed. By performing this refreshing step, the average charge amount of the toner, which decreases as the usage frequency increases, as shown in FIG. 5b, can be restored to the charge amount shown in FIG. 5c after the recycling step. Further, as shown in FIG. 6, the second developing bias voltage is preferably about 100 V, and it can be seen that a good cleaning effect cannot be expected with a voltage having an absolute value smaller than that. Further, when the image formation is repeated without performing the refreshing step, an image defect occurs when the number of development history sheets reaches 5,000, whereas the above-mentioned refreshing step is performed once every 2,000 sheets. In the case of the above ratio, no image defect occurred up to about 30,000 sheets. In this way, the image forming apparatus 1
While maintaining the original performance of 0 for a long time,
The running cost can be minimized.

In the above-described embodiment, the electrophotographic process using the positively chargeable photoconductor 12 is carried out. However, a toner having the same polarity as that of the negatively chargeable photoconductor 12 is used, and the high voltage power source 18 is used. , 32 and 36, the same effect can be obtained even in the image forming apparatus in which all the voltage polarities are set in the opposite manner to the above-described embodiment. Also, it goes without saying that the optimum value of the absolute value of each bias potential differs depending on the electric resistance value of the components used and the like.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is an enlarged view showing a configuration of a main part of the embodiment shown in FIG.

FIG. 3 is an illustrative view showing a relationship between a charging potential, a developing bias potential and an exposure potential in a reversal developing method.

FIG. 4 is an illustrative view showing a relationship between a developing bias voltage controlled according to the embodiment of FIG. 1 and a charging potential.

5A and 5B are graphs showing toner charge amounts, in which FIG. 5A shows an initial state in a conventional technique, FIG. 5B shows a durability result in the conventional technique, and FIG. 5C shows a durability result in the embodiment of FIG. Show.

FIG. 6 is a graph showing a relationship between a second developing bias voltage controlled according to the embodiment of FIG. 1 and developing impurities.

[Explanation of symbols]

 10 ... Image forming apparatus 12 ... Photoconductor 14 ... Charging device 16 ... Controller 20 ... Developing roller 28 ... Exposure device 34 ... Transfer device 36 ... High voltage power source

Claims (1)

[Claims] 1. A charging unit for uniformly charging a photosensitive member, an exposing unit for forming an electrostatic latent image on the photosensitive member by an optical image according to an original, and a developing bias voltage having the same polarity as the charging polarity of the photosensitive member. In the image forming apparatus, a developer supply unit that receives the electrostatic latent image by reversal development, and a transfer unit that transfers the reversal developed developer image to a transfer material by a transfer bias voltage having a polarity opposite to the development bias voltage are provided. A developing bias voltage generating means for generating a second developing bias voltage having an absolute value smaller than that of the developing bias voltage during a non-image forming operation; and the transfer bias voltage in synchronization with the second developing bias voltage. An image forming apparatus comprising: polarity switching means for switching to the same polarity as the developing bias voltage.