JP4265208B2 - Image forming method and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming method and an electrophotographic image forming apparatus such as a copying machine or 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 rotationally driven photoconductor with a charger and then exposing it with an exposure device. Then, the electrostatic latent image is developed with toner from a developing device to form a toner image. The toner image is transferred directly or via an intermediate transfer member to a recording sheet, 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, so-called untransferred toner remaining on the photoreceptor without being transferred is removed by a cleaning member, and then the photoreceptor is charged again by a charger, and the next image forming process is executed.
[0003]
Currently, a blade that mechanically scrapes toner with a plate-like elastic rubber is frequently used as a cleaning member, and this is deeply related to the charging method of the charger. That is, a non-contact charger or an AC contact charger having a large amount of discharge generates a discharge with respect to the photoreceptor, so that ozone or nitrogen oxide adheres to the surface of the photoreceptor. Since ozone and nitrogen oxide cause image quality defects, it is necessary to remove the surface of the photoreceptor 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 the transfer residual toner but also ozone and nitrogen oxides is preferable, which contributes to the frequent use of blades. ing.
[0004]
However, the surface of the photoconductor is abraded due to the surface being scraped off, causing the life of the photoconductor to be shortened. In particular, in the case of an AC contact charger, there is a problem that the surface of the photoconductor is significantly worn because intense discharge is performed between the surface of the photoconductor and the charger.
[0005]
Therefore, in recent years, an attempt has been made to use a DC contact charger in which the 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 with toner or the like, and it is necessary to take measures such as removing the adhered toner.
[0007]
As a means for preventing the contact charger from being soiled, 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 retracting means for contacting and separating the charging roller is complicated in terms of mechanism, is expensive, and requires new power for retraction.
[0009]
There is also a method of coating the charging roller with a fluorine-based film so that foreign matters such as toner do not adhere, but the coating causes uneven charging on the photoreceptor. There is also a method of covering the surface layer in which the conductive material is dispersed and applying a voltage in which an AC voltage is superimposed on the DC voltage to prevent uneven charging. However, the cost increases by preparing an AC power supply. There is a problem that ozone is generated.
[0010]
Therefore, there is one 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, the charging roller whose surface layer is coated with a non-adhesive material is insufficient to prevent the charging roller from being soiled. If foreign matter adheres, the image quality is deteriorated due to charging failure.
[0012]
Therefore, when the image is not formed, there is a type in which foreign matters such as toner adhering to the charging member are electrostatically transferred to the photosensitive member by adjusting the voltage applied to the charging electrode of the charging member, and the charging member is cleaned ( (See Patent Document 3).
[0013]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-53413 (paragraph numbers 0009 to 0015, FIGS. 1 and 2)
[Patent Document 2]
Japanese Patent Laid-Open No. 06-266206 (paragraph numbers 007 to 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 the image is not formed, foreign substances such as toner adhering to the charging member are transferred in the direction of the photosensitive member. Therefore, if the voltage applied to the charging member is changed, the necessary potential difference with the developing device is maintained. Since the toner cannot be transferred to the non-image area or the carrier in the two-component developer is transferred to the surface of the photosensitive member, toner fog or BCO (Bead Carry Over) is generated. There is a problem that gets dirty. In this case, a method for avoiding the problem by retracting the developing device can be considered, but this increases the cost and becomes an obstacle to downsizing.
[0015]
In view of the above circumstances, the present invention allows the photosensitive member to be stably charged at low cost over a long period of time by cleaning the contact charging member while maintaining a predetermined potential difference with the developing device. 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 the image forming method of the present invention that achieves the above object, the image bearing member is charged to a predetermined charging potential by bringing a charging member into contact with the image bearing member moving in a predetermined direction. 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. In the image forming method of forming an image on a recording medium by removing the residual toner on the image carrier with a cleaning member and repeating the process of charging the image carrier to the charged potential again,
At a predetermined timing to repeat the above process, charging by the charging member to the non-image forming areas between the image forming areas where the toner image on the image carrier is formed is stopped and charging to the non-image forming areas is performed. The toner attached to the charging member is cleaned by causing the cleaning member to perform the cleaning.
[0017]
As described above, when the charging member is cleaned, the non-image forming region is charged by the cleaning member and not charged by the charging member. Therefore, the charging member is attached 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-described object is an image carrier that moves in a predetermined direction to form a toner image, contacts the image carrier, and charges the image carrier to a predetermined charging voltage. The toner image obtained by developing the electrostatic latent image formed by exposing the charging member and the charged image bearing member with toner is brought into contact with the image bearing member at a predetermined position after being transferred to the transfer target. And a cleaning member that removes transfer residual toner on the image carrier, and finally, the toner image on the image carrier is transferred and fixed on a recording medium to form an image composed of a fixed toner image. In the image forming apparatus to
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 an image forming area on the image carrier where a toner image is formed, and the first image forming area is connected to the first image applying area. And a cleaning control unit for stopping the application of the voltage from the voltage application unit and applying a predetermined DC voltage from the second voltage application unit to clean the toner adhering to the charging member. To 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. Thus, the image carrier can be stably charged.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, 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 an image forming apparatus according to the first embodiment.
[0021]
The image forming apparatus shown in FIG. 1 is stretched between four image forming units 20a to 20b on which toner images of respective colors are formed, a driving roll 11, a driven roll 12, and a counter roll 13, and is provided with four image units. A nip portion is formed between the intermediate transfer belt 7 and the intermediate transfer belt 7 that circulates and moves while contacting each of the image forming units 20a to 20b, and the intermediate transfer belt 7. The intermediate transfer belts are formed from the image forming units 20a to 20b. 7, four primary transfer units 6 a to 6 b for primary transfer of the toner image, and a nip portion between the opposing roll 13 and the intermediate transfer belt 7 are formed, and the toner image is transferred from the intermediate transfer belt 7 to the recording medium. A secondary transfer device 9, a fixing device 8 for fixing the toner image on the recording medium onto the recording medium, and a belt cleaner for removing the 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 or a composite of urethane and a metal scraper can be used depending on the cleaning property.
[0023]
Each of the image forming units 20a to 20b includes a photosensitive drum 1a to 1d on which a toner image is formed, a contact charger 2a to 2d for uniformly charging the photosensitive drum 1a to 1d, and a uniformly charged photosensitive member. Exposure devices 3a to 3d for irradiating the drums 1a to 1d with exposure light to form electrostatic latent images, and a developing device 4a for developing the electrostatic latent images on the photosensitive drums 1a to 1d with toner to form toner images. And 4d and conductive fiber brushes 5a to 5d for removing residual toner remaining on the photosensitive drums 1a to 1d after the toner image is primarily transferred 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 applying unit 22 that applies an AC voltage or a DC voltage superimposed on the AC voltage to 5d, and the voltage applied from each of the first voltage applying unit 21 and the second voltage applying unit 22 are adjusted. And a cleaning control unit 23 for cleaning the contact chargers 2a to 2d by transferring the toner adhering to the contact chargers 2a to 2d to the photosensitive drums 1a to 1d.
[0025]
Photosensitive drums 1a to 1d of the present embodiment are cylindrical drums having a diameter of 30 mm, and in the infrared region composed of a polymer resin having polycarbonate as a binder and a triphenylamine-based charge transfer agent on the surface. A photosensitive organic photoreceptor is used, the contact charger is a conductive rubber molded into a roll, and 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), a spherical toner (polymerized toner) is used and an external additive is added, but is not limited thereto.
[0026]
When an image is formed using the image forming apparatus of the present embodiment, the photosensitive drums 1a to 1d are applied with a DC voltage of about minus 1 kV, for example, to the contact chargers 2a to 2d of the image forming units 20a to 20d. Electrostatic latent images are formed on the surfaces of the photosensitive drums 1a to 1d by charging the surface to minus 350 V and irradiating exposure light from the exposure devices 3a to 3d. Then, negatively charged toner from the developing devices 4a to 4d is attached to the electrostatic latent image and developed, and toner images are formed 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 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 transferred. The image is transferred to a recording medium such as paper by the secondary transfer unit 9 and fixed on the recording medium by the fixing unit 8. On the other hand, the untransferred 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. Further, the transfer residual toner remaining on the intermediate transfer belt 7 is removed by the belt cleaner 10.
[0027]
For example, an AC voltage having a frequency of 3 kHz and a peak-to-peak voltage of 600 V is applied to the conductive fiber brushes 5a to 5d so that the bipolar toner generated during the primary transfer can be removed. Since the discharge start voltage (Vth) between the conductive fiber brushes 5a to 5d and the photosensitive drums 1a to 1d in this embodiment is about 650V, the peak voltage in each polarity is 300V so that no discharge occurs. Is set to
[0028]
Here, by applying an AC voltage to the conductive fiber brushes 5a to 5d, the residual transfer toner of both polarities remaining on the photosensitive drums 1a to 1d is removed. This is because toner having both polarities reciprocates between the photosensitive drums 1a to 1d and the conductive fiber brushes 5a to 5d due to electric field changes between the photosensitive drums 1a to 1d and the conductive fiber brushes 5a to 5d. This is probably because the conductive fiber brushes 5a to 5d are easily scraped off.
[0029]
In the present embodiment, the conductive fiber brushes 5a to 5d are used for the cleaning member, but the cleaning member is not limited to the conductive fiber brushes 5a to 5d, and may be any material having conductivity. . Further, although the present embodiment has been described based on a tandem type image forming apparatus using an intermediate transfer member, the image forming apparatus is not limited to this, and a single photosensitive drum may be used. Further, it may be a direct transfer type image forming apparatus.
[0030]
FIG. 2 is a diagram showing 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 (peak-to-peak 600V) applied to the conductive fiber brush.
[0032]
Here, the cleaning performance is such that 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 ) Was passed through a conductive fiber brush and the amount of toner passed was evaluated.
[0033]
As is apparent from the figure, the cleaning performance deteriorates because the floating state of the toner is not formed because the speed of the electric field change is slow when the frequency is 1 kHz or less, and the speed of the electric field change is too fast when the frequency is 10 kHz or more. It is guessed.
[0034]
Here, in this embodiment, the frequency of the alternating voltage applied to the conductive fiber brush is 3 kHz, but can be arbitrarily set as long as it is in the range of 1 kHz or more and 10 kHz or less.
[0035]
FIG. 3 is a diagram showing the potential when the image area and the inter image area of the photosensitive drum pass through the respective positions when executing the cleaning mode in which the toner attached to the contact charger is transferred to the photosensitive drum for cleaning. FIG. 3B shows a case where adjustment is performed by the cleaning control unit of the present embodiment, and FIG. 3A is a diagram showing a comparative example 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 area and the image forming area. .
[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 unit facing the photosensitive drum at the developing position. The third stage shows the voltage applied to the contact charger (FIG. 3B is the voltage applied from the first voltage application unit of the present embodiment), and the fourth stage and the fifth stage are: FIG. 3B shows a DC voltage and an AC voltage applied to the photosensitive drum cleaning member (FIG. 3B is 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 in order to charge the photosensitive drum, and toner having a reverse polarity charge, that is, a positive charge adheres to the contact charger.
[0039]
As shown in FIG. 3A, conventionally, when the reverse polarity charged toner adhering to the contact charger is cleaned, the contact charger corresponds to the inter-image area (the “image non-formation area” of the present invention). ), For example, plus 100 V is applied, and the potential of the inter-image area is made higher than the potential of the contact charger to remove the toner adhering to the contact charger as shown in the third stage. It is necessary to transfer to a photosensitive drum. Then, as shown in the first stage, the potential of the interimage area gradually increases at the development position. Therefore, in order to prevent the transfer from the developing unit to the photosensitive drum, the development roll shown in the second stage is used. Must be adjusted to follow the potential of the inter-image area at the development position so that the differential 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 toner is transferred from the developing roll. A high-concentration toner band due to, and a BCO band due to carrier transfer are generated. When these toner bands and BCO bands cannot be completely cleaned by the conductive fiber brush, they reach the contact charger and adhere.
[0040]
On the other hand, in this embodiment, when executing the cleaning mode in which the toner adhering to the contact charger is transferred to the photosensitive drum, the voltage applied to the contact charger from the first voltage application unit by the cleaning control unit. The voltage applied to the conductive fiber brush from the second voltage application 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 development 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 development position, the potential difference between the potential of the development roll is the same as that before executing the cleaning mode, and as shown in FIG. Generation of a high-concentration toner band and a BCO band due to carrier transfer can be avoided.
[0041]
Specifically, the cleaning control unit minus the voltage applied to the contact charger from the first voltage application unit, as shown in the third stage, so that the toner is transferred from the contact charger to the inter-image area. By cutting the voltage from 1 kV to zero and applying a DC voltage of minus 700 V from the second voltage application unit to the conductive fiber brush in advance in the inter-image area as shown in the fourth stage. The potential of the image area and the potential of the inter-image area at the development position are both set to minus 350V.
[0042]
Here, the voltage applied to the contact charger from the first voltage application unit is changed from minus 1 kV to zero so that the toner of the contact charger is transferred to the photosensitive drum. However, it is not necessarily required to be zero. . Further, a DC voltage of minus 700 V is applied to the conductive fiber brush while the AC voltage (peak-to-peak voltage 600 V, frequency 3 kHz) applied in the image region is applied from the second voltage application unit. Although superimposed, it is not always necessary to apply the same AC voltage in 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 toner of the reverse polarity attached to the contact charger is formed, and the attached toner is transferred to the photosensitive drum. The reverse polarity toner discharged to the photosensitive drum is transferred onto the intermediate transfer belt by reversing the polarity of the bias voltage of the primary transfer unit with respect to 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 the end of printing, before the start of printing, or after the end of maintenance.
[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]
In FIG. 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 figure is a graph showing the relationship between the DC voltage applied to the contact charger and the photosensitive drum surface potential.
[0047]
As is apparent from the figure, the surface potential of the photosensitive drum is zero until the applied voltage of the contact charger reaches 650 V, but discharge starts when the voltage exceeds 650 V, and the surface potential of the photosensitive drum rises linearly. When the applied voltage of the contact charger becomes 1000 V, for example, the surface potential of the photosensitive drum becomes 350, which matches the surface potential of the photosensitive drum shown in FIG.
[0048]
FIG. 5 is a diagram showing the relationship between the DC voltage superimposed on the AC voltage (peak-to-peak voltage 600 V, frequency 3 kHz) applied to the contact charger or the cleaning member and the photosensitive drum surface potential.
[0049]
In FIG. 5, the vertical axis represents the photosensitive drum surface potential (V), and the horizontal axis represents the DC voltage to be applied. The solid line in the figure is a graph showing the relationship between the DC voltage and the photosensitive drum surface potential.
[0050]
As is apparent from the figure, when the DC voltage is 700 V, the surface potential of the photosensitive drum is 350 V, which matches the surface potential of the photosensitive drum shown in FIG.
[0051]
Therefore, for example, if a 700 V DC voltage is superimposed and applied to a cleaning member to which an AC voltage of 600 V is applied, the photosensitive drum can obtain the same surface potential as when a 1000 V DC voltage is applied from the contact charger. Can do.
[0052]
Next, a second embodiment will be described.
[0053]
(Second Embodiment)
The second embodiment is different from the first embodiment in the voltage applied to the cleaning member, but the other points are common, so the difference will be described.
[0054]
In the second embodiment, the voltage applied from the second voltage application unit to the conductive fiber brush is the image area and the inter-image area when performing printing, and the image area when performing the cleaning mode of the contact charger. Is applied with an AC voltage with a peak-to-peak voltage of 1000 V and a frequency of 3 kHz, and a DC voltage of minus 450 V is superimposed on this AC voltage in the inter-image region 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 this 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 DC voltage to be applied. The solid line in the figure is a graph showing the relationship between the DC voltage and the photosensitive drum surface potential.
[0057]
As is apparent from the figure, when the DC voltage is 450 V, the surface potential of the photosensitive drum is 350 V, which matches the surface potential of the photosensitive drum shown in FIG.
[0058]
Therefore, for example, if a 450 V DC voltage is applied to a cleaning member to which an AC voltage of 1000 V is applied, the photosensitive drum can obtain the same surface potential as when a 1000 V DC voltage is applied from the contact charger. Can do.
[0059]
Also in this embodiment, in the cleaning mode, in order to keep the image surface of the image area and the inter-image area at the development position at the same potential, a DC voltage is applied from the second voltage application hand to the conductive fiber brush in the inter-image area. Are superimposed. However, even after the DC voltage is superimposed, there is no difference in use as a charging device. However, even after superimposing the DC voltage, the magnitude of the applied DC voltage is the peak of the AC voltage and the two-peak voltage so that the peak of the voltage applied to the conductive fiber brush spans both polarities. Is set to be 1/2 or less. Therefore, even in the cleaning mode, the conductive fiber brush can remove the transfer residual toner having both polarities, so that further toner adhesion to the contact charger can be prevented.
[0060]
Next, an effect 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 a result of evaluating the image quality of an image formed when the amount of toner adhered to the contact charger is changed.
[0062]
In FIG. 7, the horizontal axis represents the amount of toner adhered to the contact charger (g / m ² ), The vertical axis represents the image quality grade.
[0063]
Here, image quality grade 0 has no defects, image quality grade 1 has very slight defects, image quality grade 2 has minor defects, image quality grade 3 is acceptable, and image quality grade 4 is unsightly. Occurrence and image quality grade 5 are extremely marked. Regarding image quality evaluation, “Optics Vol. 12 No. 4 (August 1983)“ Evaluation of Images in Copying Machines ”P267 to 277” was referred to.
[0064]
Now, when the allowable range of 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 0.1 (g / m ² ) You can see below.
[0065]
FIG. 8 is a diagram showing a result of detecting a change in the amount of toner adhering to the contact charging member every time printing is performed using the image forming apparatuses of the first embodiment and the second embodiment. is there.
[0066]
In FIG. 8, the vertical axis represents the amount of adhered toner (g / m ² ), And the horizontal axis represents the cumulative number of printed A4 plates (thousands).
[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 ♦ marks indicate changes in the amount of toner adhered to the image forming apparatus according to the first embodiment, and the black squares indicate comparisons. For this reason, the change in the amount of toner adhered to the image forming apparatus in the conventional example is shown.
[0068]
In the image forming apparatus according to the first embodiment, an AC voltage type having a peak-to-peak voltage of 600 V and a frequency of 3 kHz is applied to a conductive fiber brush that is a cleaning member. In the cleaning mode, a direct current is applied to an image non-formation region. Overlay minus 700V. In the image forming apparatus according to the second embodiment, an AC voltage type having a peak-to-peak voltage of 1000 V and a frequency of 3 kHz is applied to the conductive fiber brush that is a cleaning member. DC minus 450V is superimposed on.
[0069]
As is apparent from the figure, in the conventional example that does not have a cleaning mode for transferring the toner adhering to the contact charger to the photosensitive drum, when the number of printed sheets exceeds 30,000, the toner adhesion amount of the contact charger is 0. .1 (g / m ² ) Or more, and the image quality grade is at least 2 or more.
[0070]
On the other hand, in the image forming apparatus of the first embodiment, the toner adhesion amount of the contact charger is 0.1 (g / m) for at least 80,000 sheets. ² ) And the image quality grade is at least 1 or less. Further, the toner adhesion amount of the image forming apparatus according to the second embodiment is 0.1 (g / m) even if the contact toner exceeds 100,000 sheets. ² The influence 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 provided 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. It is confirmed that, by transferring the toner adhering to the contact charging member to the photosensitive drum side, the adhering toner is cleaned, thereby preventing the generation of the toner band and the BCO band due to the adhering toner. did it.
[0072]
The amount of toner adhered to the contact charging unit is smaller in the image forming apparatus in the second embodiment than in the image forming apparatus in the first embodiment. This is thought to be because 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 adhered to the contact charger in the cleaning mode is discharged, the photosensitive member is replaced with a cleaning member such as a conductive fiber brush instead of the contact charger. To provide a compact and low-cost image forming apparatus that can prevent the generation of toner bands and BCO bands and suppress contamination of contact chargers to obtain stable high image quality over a long period of time. Can do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus according to a first embodiment.
FIG. 2 is a diagram showing the cleaning performance of a conductive fiber brush.
FIG. 3 is a diagram illustrating a potential when an image area and an inter-image area of a photosensitive drum pass through each position when executing a cleaning mode in which toner adhered to a contact charger is transferred to the photosensitive drum for cleaning. It is.
FIG. 4 is a diagram illustrating a relationship between a DC voltage applied to a contact charger and a photosensitive drum surface potential.
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.
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 this embodiment and the surface potential of the photosensitive drum. FIG.
FIG. 7 is an experimental result showing a result of evaluating the image quality of an image formed when the amount of toner adhered to the contact charger changes.
FIG. 8 is a diagram illustrating a result of detecting a change in the amount of toner adhered to a contact charging member every time 10 sheets are printed by performing printing using the image forming apparatuses of the first embodiment and the second embodiment. is there.
[Explanation of symbols]
1 Photosensitive drum
2 Contact charger
3 Exposure equipment
4 Developer
5 Conductive fiber brush
6 Primary transfer device
7 Intermediate transfer belt
8 Fixing device
9 Secondary transfer device
10 Belt cleaner
11 Drive roll
12 Followed roll
13 Opposite roll
20 Image forming unit
21 1st voltage application part
22 Second voltage application unit
23 Cleaning control unit

Claims (7)

An electrostatic latent image formed by bringing a charging member into contact 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, 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. In the image forming method of forming an image on a recording medium by repeating the process of charging the image carrier to the charged potential again,
In place of charging to the charging potential by the charging member to the image non-formation area between the image formation areas where the toner image on the image carrier is formed at a predetermined timing to repeat the process, the image non-formation By controlling the voltage of the charging member so that an electric field from the charging member to the non-image forming region is generated between the non-image forming region and the charging member while charging the region to the cleaning member. Cleaning the toner adhering to the charging member;
As for the charging of the image non-formation area by the cleaning member, the image non-formation area at the development position where development is performed after being brought into contact with the charging member and the image formation area at the development position have the same potential. An image forming method comprising: 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, and the charged image carrier is exposed to light. A developing unit that develops the electrostatic latent image with toner, and contacts the image carrier at a predetermined position after the developed toner image is transferred to the transfer material, and removes transfer residual toner on the image carrier. An image forming apparatus for forming an image composed of a fixed toner image by finally transferring and fixing a toner image on the image carrier onto a recording medium.
A first voltage application unit that applies a voltage to the charging member to charge the image carrier;
A second voltage application unit for applying a voltage to the cleaning member;
A voltage at which the image forming area is charged to a predetermined charging voltage is applied from the first voltage application unit to the image forming area on the image carrier where a toner image is formed. A predetermined DC voltage is applied from the second voltage application unit to the mutual non-image forming area, and an electric field from the charging member toward the non-image forming area is provided between the non-image forming area and the charging member. A cleaning control unit for controlling the first voltage application unit to generate and cleaning the toner adhering to the charging member,
The cleaning control unit, as the predetermined DC voltage applied from the second voltage application unit to the non-image forming region, passes through a contact region with the charging member and then is developed by the developing unit at a developing position. An image forming apparatus, wherein a non-image forming area and the image forming area at the development position are applied with a DC voltage having the same potential. The cleaning member has a brush roll made of conductive fibers,
The image forming apparatus according to claim 2, wherein the second voltage application unit applies the voltage to the brush roll. The second voltage application unit applies an AC voltage to the cleaning member, and applies an AC voltage superimposed with a DC voltage when the cleaning control unit cleans the toner. The image forming apparatus according to claim 2. The second voltage application unit applies an AC voltage whose peak-to-peak voltage is smaller than a voltage twice the discharge start voltage between the image carrier and the cleaning member. The image forming apparatus according to claim 4. The image forming apparatus according to claim 4, wherein the second voltage application unit applies an AC voltage having a frequency of 1 kHz or more and 10 kHz or less. The image forming apparatus according to claim 5, wherein the second voltage applying unit applies a DC voltage whose voltage is smaller than a half of a peak-to-peak voltage of the AC voltage. .

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