JP2004191467A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus in which a contact electrifying member is cleaned while maintaining a predetermined potential difference between a development unit and the member. <P>SOLUTION: The image forming apparatus includes: a first voltage applying part 21 which applies voltage with which an image carrier 1 is electrified to an electrification voltage to the contact electrifying member 2; a second voltage applying part 22 which applies voltage of a predetermined level to a cleaning member 5; and a cleaning control part 23 that controls in such a manner that voltage from the first voltage applying part 21 is applied to an image formation area on the image carrier 1 where a toner image is formed, whereas voltage from the first voltage applying part 21 is stopped to be applied to an image non-formation area relative to the image formation area and a DC voltage of a predetermined level is applied from the second voltage applying part 22, thereby clearing away toner sticking to the electrifying member 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic image forming method and an electrophotographic image forming apparatus such as a copying machine and a laser beam printer.
[0002]
[Prior art]
Conventionally, in an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, and a facsimile, an electrostatic latent image is formed by uniformly charging a rotatably driven photoreceptor with a charger and exposing the same with an exposure device. Then, the electrostatic latent image is developed with a toner of a developing device to form a toner image. Then, the toner image is transferred to a recording sheet directly or via an intermediate transfer member, and the toner image on the recording sheet is fixed by a fixing device to form an image on the recording sheet. On the other hand, the so-called untransferred toner remaining on the photoconductor without being transferred is removed by the cleaning member, and then the photoconductor is charged again by the charger, and the next image forming process is executed.
[0003]
At present, a blade that mechanically scrapes toner with a plate-like elastic rubber is frequently used as a cleaning member, and this is closely related to a charging method of a charger. That is, a non-contact charger and an AC contact charger having a large amount of discharge generate a discharge between the photoconductor and ozone or nitrogen oxides adhere to the surface of the photoconductor. The ozone and nitrogen oxide cause image quality defects, so it is necessary to scrape off the photoreceptor surface to expose a clean surface. Therefore, when a non-contact charger or an AC contact charger is used, a member capable of removing not only transfer residual toner but also ozone and nitrogen oxide is preferable, and this is one of the causes of heavy use of the blade. ing.
[0004]
However, the surface of the photoreceptor is abraded by being scraped off, which causes the life of the photoreceptor to be shortened. In particular, in the case of an AC contact charger, a severe discharge occurs between the surface of the photoconductor and the charger, so that there is a problem that the surface of the photoconductor is significantly worn.
[0005]
For this reason, in recent years, an attempt has been made to use a DC contact charger in which discharge between the surface of the photoreceptor and the charger is relatively small, and fur brushes, sponge pads, and the like have been reviewed as cleaning members.
[0006]
However, the DC contact charger is easily contaminated by toner or the like, and it is necessary to take measures such as removing attached toner.
[0007]
As a means for preventing the contact charger from being stained, there is a means for preventing foreign matters such as toner from adhering to the charging roller by bringing the charging roller into and out of contact (see Patent Document 1).
[0008]
However, the retraction means for bringing the charging roller into and out of contact is mechanically complicated, costly, and requires new power for retraction.
[0009]
There is also a method of coating the charging roller with a fluorine-based coating so that foreign substances such as toner do not adhere thereto, but the coating causes uneven charging of the photoconductor. There is also a method of coating a surface layer in which a conductive substance is dispersed and applying a voltage in which an AC voltage is superimposed on a DC voltage to prevent uneven charging, but the cost is increased by preparing an AC power supply. There is a problem that ozone is generated.
[0010]
Therefore, there is a type in which a charging roller is coated with a non-adhesive surface layer and a high-voltage DC voltage is applied (see Patent Document 2).
[0011]
However, a charging roller whose surface layer is coated with a non-adhesive material is not enough to prevent the charging roller from being stained, and if foreign matter adheres, image quality will be deteriorated due to poor charging.
[0012]
Therefore, when an image is not formed, foreign matter such as toner attached to the charging member is electrostatically transferred to the photoconductor by adjusting the voltage applied to the charging electrode of the charging member, and the charging member is cleaned ( Patent Document 3).
[0013]
[Patent Document 1]
JP-A-05-53413 (paragraph numbers 0009 to 0015, FIGS. 1 and 2)
[Patent Document 2]
JP-A-06-266206 (paragraph number 007 to paragraph number 008, FIG. 1)
[Patent Document 3]
JP-A-11-65238 (for example, paragraph number 0017 to paragraph number 0018, FIGS. 1 and 9)
[0014]
[Problems to be solved by the invention]
However, when an image is not formed, foreign matter such as toner attached to the charging member is transferred to the photosensitive member. Therefore, when the voltage applied to the charging member is changed, a necessary potential difference between the developing member and the developing device is maintained. And the toner in the non-image area is transferred to the non-image area, or the carrier in the two-component developer is transferred to the surface of the photoreceptor, causing toner fogging and BCO (Bead Carry Over). However, there is a problem that it becomes dirty. In this case, a method of avoiding the problem by retracting the developing device is conceivable, but it increases costs and hinders miniaturization.
[0015]
The present invention has been made in view of the above circumstances, and performs cleaning of a contact charging member while maintaining a predetermined potential difference between the developing device and the photoconductor. Another object of the present invention is to provide an image forming method and an image forming apparatus capable of obtaining a high-quality image.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the image forming method of the present invention comprises charging an image carrier to a predetermined charging potential by bringing a charging member into contact with an image carrier moving in a predetermined direction, and The electrostatic latent image formed by irradiating the body with exposure light is developed with toner to form a toner image on the image carrier, and the toner image is finally transferred and fixed on a recording medium. An image forming method for forming an image on a recording medium by removing a residual toner on the image carrier with a cleaning member and repeating a process of charging the image carrier again to the charging potential.
At a predetermined timing at which the above process is repeated, the charging of the non-image forming area between the image forming areas where the toner images on the image carrier are formed by the charging member and the charging of the non-image forming area are stopped. By causing the cleaning member to perform the cleaning, the toner attached to the charging member is cleaned.
[0017]
As described above, when cleaning the charging member, the charging of the non-image forming area is performed by the cleaning member, and the charging by the charging member is not performed. Therefore, the cleaning member adheres to the charging member due to a potential difference between the image carrier and the charging member. The toner can be cleaned.
[0018]
An image forming apparatus according to the present invention that achieves the above object moves an image carrier on which a toner image is formed in a predetermined direction, and contacts the image carrier to charge the image carrier to a predetermined charging voltage. A charging member, and a toner image obtained by developing the electrostatic latent image formed by exposing the charged image carrier with toner, is brought into contact with the image carrier at a predetermined position after the toner image is transferred to a transfer-receiving member. Forming a fixed toner image by transferring and fixing the toner image on the image carrier finally onto a recording medium, and a cleaning member for removing transfer residual toner on the image carrier. Image forming apparatus,
A first voltage application unit that applies a voltage at which the image carrier is charged to the charging voltage, to the contact charging member;
A second voltage application unit that applies a predetermined voltage to the cleaning member;
The first voltage application unit applies the voltage to the image forming area where the toner image is formed on the image carrier, and applies the first voltage to the non-image forming area between the image forming areas. A cleaning control unit for stopping application of the voltage from the voltage application unit and applying a predetermined DC voltage from the second voltage application unit to clean toner adhered to the charging member. I do.
[0019]
As described above, the cleaning control unit adjusts the voltage applied to the charging member and the voltage applied to the cleaning member, thereby cleaning the charging member while maintaining the potential difference between the developing device and the image carrier. Is performed, the image carrier can be stably charged.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an image forming method of the present invention and an image forming apparatus using the image forming method will be described.
(Embodiment 1)
FIG. 1 is a diagram illustrating the image forming apparatus according to the first embodiment.
[0021]
The image forming apparatus shown in FIG. 1 includes four image forming units 20 a to 20 b on which toner images of respective colors are formed, a driving roll 11, a driven roll 12, and an opposing roll 13, and four image units. An intermediate transfer belt 7 that circulates and moves while being in contact with each of the image forming units 20a to 20b, a nip portion is formed between the intermediate transfer belt 7 and each of the image forming units 20a to 20b. 7, a nip portion is formed between the opposing roll 13 and the intermediate transfer belt 7, and the toner image is transferred from the intermediate transfer belt 7 to a recording medium. A secondary transfer unit 9; a fixing unit 8 for fixing the toner image on the recording medium onto the recording medium; and a belt cleaning unit for removing transfer residual toner on the intermediate transfer belt 7. And a Na 10.
[0022]
Here, as the belt cleaner, a urethane blade, a metal scraper depending on cleaning properties, or a composite of urethane and a metal scraper can be used.
[0023]
Each of the image forming units 20a to 20b includes a photosensitive drum 1a to 1d on which a toner image is formed, contact chargers 2a to 2d for uniformly charging the photosensitive drums 1a to 1d, and a uniformly charged photosensitive body. Exposure devices 3a to 3d that irradiate exposure light to drums 1a to 1d to form electrostatic latent images, and developing devices 4a that form electrostatic latent images on photoconductor drums 1a to 1d with toner to form toner images. To 4d, and conductive fiber brushes 5a to 5d for removing transfer residual toner remaining on the photosensitive drums 1a to 1d after the primary transfer of the toner image to the intermediate transfer belt 7.
[0024]
Furthermore, in the present embodiment, the image forming apparatus includes a first voltage application unit 21 that applies a charging voltage for uniformly charging the photosensitive drums 1a to 1d to the contact chargers 2a to 2d, and the conductive fiber brushes 5a to 5d. The second voltage application unit 22 that applies an AC voltage or a DC voltage superimposed on the AC voltage to 5d, and the voltages applied from the first voltage application unit 21 and the second voltage application unit 22 are adjusted. A cleaning controller 23 for cleaning the contact chargers 2a to 2d by transferring the toner attached to the contact chargers 2a to 2d to the photosensitive drums 1a to 1d.
[0025]
The photoreceptor drums 1a to 1d of the present embodiment are cylindrical drums having a diameter of 30 mm. The surface of the photoreceptor drums 1a to 1d is composed of a polymer resin having polycarbonate as a binder and a triphenylamine-based charge transport agent. An organic photoreceptor with high sensitivity is used. The contact charger is made of conductive rubber formed into a roll. The conductive fiber brush is a mixed-woven brush of insulating 8 μm fine fibers and conductive nylon 30 μm. Is used, but is not limited to this. The toner has an average particle size of 6.5 μm and a spherical coefficient of 118 (ML). ² / A) is used, and an external additive is added, but the present invention is not limited to this.
[0026]
When an image is formed using the image forming apparatus of the present embodiment, a DC voltage of, for example, about -1 kV is applied to the contact chargers 2a to 2d of the image forming units 20a to 20d to form the photosensitive drums 1a to 1d. The surface is charged to minus 350 V, and exposure light is irradiated from the exposure devices 3a to 3d to form electrostatic latent images on the surfaces of the photosensitive drums 1a to 1d. Then, a negatively charged toner from the developing units 4a to 4d is attached to the electrostatic latent image and developed to form a toner image on the photosensitive drums 1a to 1d. The toner images formed on the photosensitive drums 1a to 1d of the image forming units 20a to 20d are sequentially multiplex-transferred onto the intermediate transfer belt 7 by the primary transfer units 6a to 6d, and the toner images on the intermediate transfer belt 7 are The image is transferred to a recording medium such as paper by the secondary transfer unit 9 and is fixed on the recording medium by the fixing unit 8. On the other hand, the transfer residual toner remaining on the photosensitive drums 1a to 1d is removed from the surfaces of the photosensitive drums 1a to 1d by the conductive fiber brushes 5a to 5d made of conductive fibers. The transfer residual toner remaining on the intermediate transfer belt 7 is removed by the belt cleaner 10.
[0027]
To the conductive fiber brushes 5a to 5d, for example, an AC voltage having a frequency of 3 kHz and a peak-to-peak voltage of 600 V is applied so that the bipolar toner generated at the time of the primary transfer can be removed. Since the discharge starting voltage (Vth) between the conductive fiber brushes 5a to 5d and the photosensitive drums 1a to 1d in the present embodiment is about 650 V, the peak voltage in each polarity is 300 V so that no discharge occurs. Is set to
[0028]
Here, by applying an AC voltage to the conductive fiber brushes 5a to 5d, bipolar transfer residual toner remaining on the photosensitive drums 1a to 1d is removed. This is because, due to an electric field change between the photosensitive drums 1a to 1d and the conductive fiber brushes 5a to 5d, the toner having both polarities reciprocates between the photosensitive drums 1a to 1d and the conductive fiber brushes 5a to 5d. It is considered that the conductive fiber brushes 5a to 5d are apt to be scraped off because of the floating state.
[0029]
In the present embodiment, the conductive member brushes 5a to 5d are used as the cleaning member. However, the cleaning member is not limited to the conductive member brushes 5a to 5d, and may be any member having conductivity. . Further, the present embodiment has been described based on the tandem type image forming apparatus using the intermediate transfer member, but the image forming apparatus is not limited to this, and may have one photosensitive drum. Further, a direct transfer type image forming apparatus may be used.
[0030]
FIG. 2 is a diagram illustrating the cleaning performance of the conductive fiber brush.
[0031]
In FIG. 2, the vertical axis represents the cleaning performance (%), and the horizontal axis represents the frequency of the AC voltage (600 V peak-to-peak) applied to the conductive fiber brush.
[0032]
Here, the cleaning performance is determined based on the toner patch having the same polarity as the charging polarity of the photosensitive drum and the toner patch having the opposite polarity (0.5 g / m 2). ² Was passed through a conductive fiber brush, and the amount of toner passing therethrough was measured.
[0033]
As is clear from the figure, when the frequency is 1 kHz or less, the speed of the electric field change is slow, and when the frequency is 10 kHz or more, the speed of the electric field change is too fast, so that the floating state of the toner is not formed. It is presumed.
[0034]
Here, in the present embodiment, the frequency of the AC voltage applied to the conductive fiber brush is set to 3 kHz, but can be set arbitrarily within a range of 1 kHz or more and 10 kHz or less.
[0035]
FIG. 3 is a diagram showing potentials when an image area and an inter-image area of the photosensitive drum pass through respective positions when a cleaning mode in which toner adhered to the contact charger is transferred to the photosensitive drum and cleaning is performed. FIG. 3B shows a case where the adjustment is performed by the cleaning control unit of the present embodiment, and FIG. 3A shows a comparative example which has been conventionally performed.
[0036]
Here, the image area means an image forming area where a toner image is formed on the photosensitive drum, and the inter-image area means an image non-forming area between the image forming areas. .
[0037]
In FIG. 3, the first stage shows the surface potential of the photosensitive drum at the developing position, and the second stage shows the potential (applied bias voltage) of the developing roll of the developing device facing the photosensitive drum at the developing position. , The third stage shows the voltage applied to the contact charger (FIG. 3B shows the voltage applied from the first voltage application unit of the present embodiment), and the fourth and fifth stages show FIG. 3B shows a DC voltage and an AC voltage applied to the cleaning member of the photosensitive drum (FIG. 3B shows a voltage applied from the second voltage application unit of the present embodiment).
[0038]
In the image forming area, a negative voltage is applied to the contact charger to charge the photosensitive drum, and the oppositely charged toner, that is, the positively charged toner adheres to the contact charger.
[0039]
As shown in FIG. 3A, conventionally, when cleaning the oppositely charged toner adhered to the contact charger, the contact charger corresponds to the inter-image area (the "non-image forming area" of the present invention). 3), as shown in the third stage, for example, a voltage of +100 V is applied to make the potential of the inter-image area higher than the potential of the contact charger to remove the toner adhering to the contact charger. It is necessary to transfer to the photosensitive drum. Then, as shown in the first stage, at the developing position, the potential of the inter-image area gradually increases. Therefore, in order to prevent the transfer from the developing device to the photosensitive drum, the developing roller shown in the second stage Needs to be adjusted so as to follow the potential of the inter-image area at the developing position, so that the difference voltage does not change. However, it is not easy to adjust the potential of the developing roll shown in the second stage so as to follow the potential of the inter-image area at the developing position so that the differential voltage does not change. , And a BCO band due to carrier transfer. If these toner bands or BCO bands cannot be completely cleaned by the conductive fiber brush, they reach the contact charger and adhere to them.
[0040]
On the other hand, in the present embodiment, when executing the cleaning mode in which the toner adhering to the contact charger is transferred to the photosensitive drum, the cleaning control unit controls the voltage applied from the first voltage application unit to the contact charger. And the voltage applied to the conductive fiber brush from the second voltage applying unit is adjusted, and the potential in the image area (corresponding to the “image forming area” of the present invention) and the potential in the inter-image area at the developing position. And have the same potential. If the potential in the image area and the potential in the inter-image area are the same at the developing position, the potential difference between the potential of the developing roll and the potential before the execution of the cleaning mode is the same, as shown in FIG. Generation of a high-concentration toner band and a BCO band caused by carrier transfer can be avoided.
[0041]
Specifically, the cleaning control unit reduces the voltage applied from the first voltage application unit to the contact charger as shown in the third stage so that the toner is transferred from the contact charger to the inter-image area. By disconnecting from 1 kV to make the voltage zero and applying a DC voltage of minus 700 V to the conductive fiber brush from the second voltage applying part to the inter-image area in advance as shown in the fourth stage. The potential of the image area and the potential of the inter-image area at the developing position are both set to minus 350V.
[0042]
Here, the voltage applied from the first voltage application section to the contact charger is changed from -1 kV to zero, so that the toner of the contact charger is transferred to the photosensitive drum, but it is not necessarily required to be zero. . Further, a DC voltage of −700 V is applied to the conductive fiber brush from the second voltage applying unit while the AC voltage (peak-to-peak voltage 600 V, frequency 3 kHz) applied in the image area is applied. Although superimposed, it is not always necessary to apply the same AC voltage to the inter-image area when the cleaning mode is executed.
[0043]
As described above, by setting the voltage of the contact charger to 0 V, an electrostatic force for discharging the opposite polarity toner attached to the contact charger is formed, and the attached toner is transferred to the photosensitive drum. The reverse polarity toner discharged to the photoconductor drum is transferred onto the intermediate transfer belt by reversing the polarity of the bias voltage of the primary transfer unit from that at the time of the primary transfer, and is collected by the belt cleaner.
[0044]
In the present embodiment, the cleaning mode is executed in the inter-image area during printing. However, the cleaning mode may be executed after printing is completed, before printing is started, or after maintenance is finished.
[0045]
FIG. 4 is a diagram showing the relationship between the DC voltage applied to the contact charger and the photosensitive drum surface potential.
[0046]
4, the vertical axis represents the photosensitive drum surface potential (V), and the horizontal axis represents the DC voltage applied to the contact charger. The solid line in the drawing is a graph showing the relationship between the DC voltage applied to the contact charger and the surface potential of the photosensitive drum.
[0047]
As is apparent from the figure, the surface potential of the photoconductor drum is zero until the applied voltage of the contact charger is 650 V, but when it exceeds 650 V, discharge starts and the surface potential of the photoconductor drum rises linearly. Then, when the voltage applied to the contact charger becomes, for example, 1000 V, the surface potential of the photosensitive drum becomes 350, which coincides with the surface potential of the photosensitive drum shown in FIG.
[0048]
FIG. 5 is a diagram showing a relationship between a DC voltage superimposed on an AC voltage (peak-to-peak voltage 600 V, frequency 3 kHz) applied to a contact charger or a cleaning member and a photosensitive drum surface potential.
[0049]
In FIG. 5, the vertical axis represents the photosensitive drum surface potential (V), and the horizontal axis represents the applied DC voltage. The solid line in the figure is a graph showing the relationship between the DC voltage and the surface potential of the photosensitive drum.
[0050]
As is clear from the figure, when the DC voltage is 700 V, the surface potential of the photosensitive drum becomes 350 V, which coincides with the surface potential of the photosensitive drum shown in FIG.
[0051]
Therefore, for example, if a DC voltage of 700 V is superimposed and applied to the cleaning member to which an AC voltage of 600 V is applied, the photosensitive drum obtains the same surface potential as when a DC voltage of 1000 V is applied from the contact charger. Can be.
[0052]
Next, a second embodiment will be described.
[0053]
(Second embodiment)
The second embodiment differs from the first embodiment in the voltage applied to the cleaning member, but has the other points in common. Therefore, the differences will be described.
[0054]
In the second embodiment, the voltage applied to the conductive fiber brush from the second voltage application unit is determined by the image area and the inter-image area when performing printing, and the image area when performing the cleaning mode of the contact charger. , An AC voltage having a peak-to-peak voltage of 1000 V and a frequency of 3 kHz is applied, and a DC voltage of minus 450 V is superimposed on this AC voltage in the inter-image area when the cleaning mode is performed.
[0055]
FIG. 6 shows the relationship between the DC voltage superimposed on the AC voltage (peak-to-peak voltage 1000 V, frequency 3 kHz) applied to the contact charger or the cleaning member of the present embodiment and the photosensitive drum surface potential. FIG.
[0056]
In FIG. 6, the vertical axis represents the photosensitive drum surface potential (V), and the horizontal axis represents the applied DC voltage. The solid line in the figure is a graph showing the relationship between the DC voltage and the surface potential of the photosensitive drum.
[0057]
As is apparent from the figure, when the DC voltage is 450 V, the surface potential of the photosensitive drum becomes 350 V, which coincides with the surface potential of the photosensitive drum shown in FIG.
[0058]
Therefore, for example, when a DC voltage of 450 V is superimposed and applied to the cleaning member to which an AC voltage of 1000 V is applied, the photosensitive drum obtains the same surface potential as when a DC voltage of 1000 V is applied from the contact charger. Can be.
[0059]
Also in the present embodiment, in the cleaning mode, the DC voltage is applied to the conductive fiber brush from the second voltage applying hand to the inter-image area in order to keep the photoconductor surface in the image area and the inter-image area at the developing position at the same potential. Are superimposed. However, even after the DC voltage is superimposed, there is no difference in using it as a charging device. However, even when the DC voltage is superimposed, the magnitude of the applied DC voltage is such that the peak of the voltage applied to the conductive fiber brush is over both polarities, and the magnitude of the applied DC voltage is the peak-to-peak voltage of the AC voltage. Is set to be equal to or less than 1/2. Therefore, even in the cleaning mode, the conductive fiber brush can remove the transfer residual toner having both polarities, so that further adhesion of the toner to the contact charger can be prevented.
[0060]
Next, effects of voltage adjustment by the cleaning control unit in the image forming apparatuses of the first embodiment and the second embodiment will be described.
[0061]
FIG. 7 is an experimental result showing the result of evaluating the image quality of an image formed when the amount of toner attached to the contact charger changes.
[0062]
In FIG. 7, the horizontal axis represents the amount of toner adhered to the contact charger (g / m 2). ² ), The vertical axis represents the image quality grade.
[0063]
Here, the image quality grade 0 has no defect at all, the image quality grade 1 has a very slight defect, the image quality grade 2 has a slight defect, the image quality grade 3 is acceptable, and the image quality grade 4 is unsightly. Occurrence and image quality grade 5 represent extremely remarkable occurrence, respectively. The image quality was evaluated with reference to “Optics, Vol. 12, No. 4, August 1983,“ Evaluation of Images in Copier ”, pp. 267 to 277”.
[0064]
Now, when the allowable range of the image quality grade is set to grade 2 or less, as is apparent from the figure, the amount of toner adhered to the contact charger is reduced to 0.1 (g / m2). ² It can be seen that the following should be done.
[0065]
FIG. 8 is a diagram illustrating a result obtained by performing printing using the image forming apparatuses according to the first embodiment and the second embodiment, and detecting a change in the amount of toner attached to the contact charging member every time ten sheets are printed. is there.
[0066]
In FIG. 8, the vertical axis indicates the amount of the attached toner (g / m ² ), And the horizontal axis represents the cumulative number (thousands) of printed A4 plates.
[0067]
In the figure, the crosses indicate changes in the amount of toner adhered to the image forming apparatus according to the first embodiment, the triangles indicate changes in the amount of toner adhered to the image forming apparatus according to the first embodiment, and the black squares indicate comparisons. 1 shows the transition of the amount of toner adhered to the image forming apparatus in the conventional example.
[0068]
The image forming apparatus according to the first embodiment applies an AC voltage type having a peak-to-peak voltage of 600 V and a frequency of 3 kHz to a conductive fiber brush serving as a cleaning member. Superimpose minus 700V. Further, the image forming apparatus according to the second embodiment applies an AC voltage type having a peak-to-peak voltage of 1000 V and a frequency of 3 kHz to the conductive fiber brush which is a cleaning member. Is superimposed with DC minus 450V.
[0069]
As is apparent from the figure, in the conventional example having no cleaning mode for transferring the toner adhering to the contact charger to the photosensitive drum, when the number of prints exceeds 30,000, the toner adhering amount of the contact charger becomes zero. .1 (g / m ² ) Or higher, and the image quality grade is at least 2 or higher.
[0070]
On the other hand, the amount of toner adhered to the image forming apparatus of the first embodiment is 0.1 (g / m ² ), And the image quality grade is at least 1 or less. The amount of toner adhered to the image forming apparatus according to the second embodiment is 0.1 (g / m ² ), The effect on the image quality due to the toner adhesion of the contact charger is not a problem at all.
[0071]
As described above, when the cleaning mode is performed and the cleaning mode is executed, the cleaning control unit adjusts the voltage applied to the contact charging member and the voltage applied to the conductive fiber brush as the cleaning member. The toner attached to the contact charging member is transferred to the photosensitive drum side to remove the attached toner. According to the contact charging member of the present invention, it is confirmed that the toner band and the BCO band caused by the attached toner can be prevented. did it.
[0072]
The reason why the amount of toner adhered to the contact charging unit in the image forming apparatus according to the second embodiment is smaller than that in the image forming apparatus according to the first embodiment is that the cleaning member according to the second embodiment is different from the cleaning member according to the second embodiment. It is considered that the removal amount of the transfer residual toner due to is larger.
[0073]
【The invention's effect】
As described above, according to the image forming method and the image forming apparatus of the present invention, when the toner attached to the contact charger is discharged in the cleaning mode, the photosensitive member is replaced with a cleaning member such as a conductive fiber brush instead of the contact charger. To provide a small-sized, low-cost image forming apparatus capable of preventing a toner band or a BCO band from being generated by charging the toner and suppressing contamination of a contact charger, thereby obtaining stable and high image quality over a long period of time. Can be.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus according to a first embodiment.
FIG. 2 is a view showing the cleaning performance of a conductive fiber brush.
FIG. 3 is a diagram showing a potential when an image area and an inter-image area of the photosensitive drum pass through respective positions when a cleaning mode in which toner adhered to a contact charger is transferred to the photosensitive drum and cleaning is performed. It is.
FIG. 4 is a diagram showing a relationship between a DC voltage applied to a contact charger and a photosensitive drum surface potential.
FIG. 5 is a diagram showing the relationship between a DC voltage superimposed on an AC voltage (peak-to-peak voltage of 600 V, frequency of 3 kHz) applied to a contact charger or a cleaning member and a photoconductor drum surface potential.
FIG. 6 shows a relationship between a DC voltage superimposed on an AC voltage (peak-to-peak voltage of 1000 V, frequency of 3 kHz) applied to a contact charger or a cleaning member of the present embodiment and a photosensitive drum surface potential. FIG.
FIG. 7 is an experimental result showing the result of evaluating the image quality of an image formed when the amount of toner attached to the contact charger changes.
FIG. 8 is a diagram illustrating a result obtained by performing printing using the image forming apparatuses according to the first embodiment and the second embodiment, and detecting a change in the amount of toner adhered to the contact charging member each time ten sheets are printed. is there.
[Explanation of symbols]
1 Photoconductor drum
2 Contact charger
3 Exposure equipment
4 Developing device
5 conductive fiber brush
6 Primary transfer unit
7 Intermediate transfer belt
8 Fixing device
9 Secondary transfer unit
10 Belt cleaner
11 Drive roll
12 Follower roll
13 Opposing roll
20 Image forming unit
21 1st voltage application part
22 Second voltage applying unit
23 Cleaning control unit

Claims (8)

An electrostatic latent member formed by contacting the charging member with an image carrier moving in a predetermined direction to charge the image carrier to a predetermined charging potential and irradiating the charged image carrier with exposure light. The image is developed with toner to form a toner image on the image carrier, and the toner image is finally transferred and fixed on a recording medium, and the residual toner on the image carrier is removed by a cleaning member. An image forming method for forming an image on a recording medium by repeating a process of charging the image carrier to the charging potential again,
At a predetermined timing of repeating the above process, the charging of the non-image forming area between the image forming areas where the toner image on the image carrier is formed by the charging member is stopped, and the charging to the non-image forming area is stopped. An image forming method, wherein the cleaning member is used to clean toner adhered to the charging member. 2. The image forming method according to claim 1, wherein the non-image forming area charged by the cleaning member and the image forming area charged by the charging member have the same potential. An image carrier that moves in a predetermined direction to form a toner image, a charging member that contacts the image carrier and charges the image carrier to a predetermined charging voltage, and exposes the charged image carrier. The toner image obtained by developing the electrostatic latent image formed by the toner with the toner is transferred to a transfer receiving member, and is brought into contact with the image holding member at a predetermined position to remove transfer residual toner on the image holding member. A cleaning member, wherein the toner image on the image carrier is finally transferred and fixed on a recording medium to form an image composed of a fixed toner image.
A first voltage applying unit that applies a voltage at which the image carrier is charged to the charging voltage, to the contact charging member;
A second voltage application unit that applies a predetermined voltage to the cleaning member;
The voltage is applied from the first voltage application unit to the image forming area on the image carrier where the toner image is formed, and the first voltage is applied to the non-image forming area between the image forming areas. A cleaning control unit for stopping application of the voltage from the voltage application unit and applying a predetermined DC voltage from the second voltage application unit to clean toner adhered to the charging member. Image forming apparatus. The cleaning member has a brush roll made of conductive fibers,
The image forming apparatus according to claim 3, wherein the second voltage applying unit applies the voltage to the brush roll. The second voltage applying unit applies an AC voltage to the cleaning member, and applies an AC voltage on which a DC voltage is superimposed when the cleaning control unit cleans the toner. The image forming apparatus according to claim 3, wherein: The second voltage applying unit applies an AC voltage having a peak-to-peak voltage smaller than a voltage twice as high as a discharge starting voltage between the image carrier and the cleaning member. The image forming apparatus according to claim 5, wherein 6. The image forming apparatus according to claim 5, wherein the second voltage applying unit applies an AC voltage having a frequency of 1 kHz or more and 10 kHz or less. 7. The image forming apparatus according to claim 6, wherein the second voltage applying unit applies a DC voltage whose voltage is smaller than half the peak-to-peak voltage of the AC voltage. .

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