JP2014038259A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress abrasion of a photoreceptor by preventing unevenness in image density.SOLUTION: An image forming apparatus includes: a toner image holding body that holds a toner image; charging means for applying to a photoreceptor a superimposed voltage superimposed with a DC voltage and an AC voltage to uniformly charge the photoreceptor; latent image forming means for forming an electrostatic latent image on the surface of the charged photoreceptor; developing means for developing the electrostatic latent image formed on the photoreceptor with toner to form a toner image; transfer means for transferring the toner image formed on the photoreceptor onto a recording medium; cleaning means located downstream the transfer means for recovering an untransferred developer on the photoreceptor; environmental information detection means for detecting environmental information including a temperature or a humidity of the photoreceptor; and charge control means for controlling charging conditions of the charging means on the basis of the environmental information detected by the environmental information detection means.

Description

The present invention relates to an image forming apparatus.

There has been known an image forming apparatus capable of preventing filming of a photosensitive member by limiting the voltage and current of an AC component applied to a charging device according to the use environment and maintaining good image quality (Patent Document 1).

According to Patent Document 1, a temperature detection unit such as a thermistor is provided in the vicinity of the charging roller to detect the temperature in the vicinity of the charging roller, and the peak-to-peak value of the AC component applied to the charging roller according to the detected temperature. Is variable. In order to prevent charging failure at low temperatures, the peak-to-peak of the AC component is increased, and at high temperatures, peak-to-peak is decreased to prevent filming.

JP 2000-338751 A

  It is an object of the present invention to prevent image density unevenness and suppress photoreceptor wear.

In order to solve the above problem, an image forming apparatus according to claim 1,
A toner image holding body for holding a toner image;
Charging means for charging a uniform charge by applying a superimposed voltage in which a DC voltage and an AC voltage are superimposed on the photosensitive member;
Latent image forming means for forming an electrostatic latent image on the surface of the charged photoreceptor;
Developing means for developing the electrostatic latent image formed on the photoreceptor with toner to form a toner image;
Transfer means for transferring a toner image formed on the photoreceptor onto a recording medium;
A cleaning unit located downstream of the transfer unit and collecting untransferred developer on the photoreceptor;
Environmental information detecting means for detecting environmental information including temperature or humidity of the photoconductor;
Charging control means for controlling charging conditions of the charging means based on environmental information detected by the environmental information detecting means;
With
It is characterized by that.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
When the charging control means is a predetermined low-temperature and low-humidity environment or low-humidity environment, the AC voltage frequency and / or peak-to- Change the peak value,
It is characterized by that.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The charging unit includes a cleaning roller that rotates while being in pressure contact with the charging unit to clean the surface of the charging unit.
It is characterized by that.

According to the first and second aspects of the invention, image density unevenness can be prevented and photoconductor wear can be suppressed.
According to the third aspect of the present invention, the charging performance of the charging roller can be maintained over a long period of time.

2 is a schematic cross-sectional view illustrating an example of a schematic configuration of the image forming apparatus 1. FIG. 3 is a schematic diagram for explaining a function of an image forming unit in the image forming apparatus 1. FIG. It is a figure which shows the relationship between the alternating current value supplied to a charging roller, and the surface potential of a photoreceptor drum, and is a figure which shows a shoulder voltage. It is a figure for demonstrating the presumed mechanism in which the ghost resulting from the external additive which remained on the photoconductive drum generate | occur | produces. (A) is a graph showing the relationship between the AC current value supplied to the charging roller and the ghost, and (b) is a graph showing the relationship between the AC current value supplied to the charging roller and the contact angle of water on the surface of the photoreceptor. is there. It is a figure for demonstrating the contact angle of water. (A) is a graph showing the relationship between the frequency of the AC voltage applied to the charging roller and the ghost generated, and (b) is the relationship between the frequency of the AC voltage applied to the charging roller and the contact angle of water on the surface of the photosensitive drum. It is the graph which showed.

Next, the present invention will be described in more detail with reference to the drawings with reference to embodiments and specific examples. However, the present invention is not limited to these embodiments and specific examples.
Also, in the description using the following drawings, it should be noted that the drawings are schematic and the ratio of each dimension and the like are different from the actual ones, and are necessary for the description for easy understanding. Illustrations other than the members are omitted as appropriate.

“First Embodiment”
(1) Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view showing the internal configuration of the image forming apparatus 1 according to this embodiment.
Hereinafter, the overall configuration and operation of the image forming apparatus 1 will be described with reference to the drawings.

  The image forming apparatus 1 includes a control device 10, a paper feeding device 20, a photosensitive unit 30, a developing device 40, a transfer device 50, and a fixing device 60. On the upper surface (Z direction) of the image forming apparatus 1, a discharge tray 1a for discharging and storing a sheet on which an image is recorded is formed.

The control device 10 includes a controller 11 that controls the operation of the image forming apparatus 1, an image processing unit 12 that is controlled by the controller 11, a power supply device 13, and the like. The power supply device 13 applies a voltage to a charging roller 32, a developing roller 42, a primary transfer roller 52, a secondary transfer roller 53, and the like which will be described later.
The image processing unit 12 converts print information input from an external information transmission apparatus (for example, a personal computer) into image information for forming a latent image, and outputs a drive signal to the exposure apparatus LH at a preset timing. To do. The exposure apparatus LH of the present embodiment is configured by an LED head in which LEDs (Light Emitting Diodes) are arranged in a line.

  A paper feeding device 20 is provided at the bottom of the image forming apparatus 1. The sheet feeding device 20 includes a sheet stacking plate 21, and a plurality of sheets P as recording media are stacked on the upper surface of the sheet stacking plate 21. The paper P loaded on the paper stacking plate 21 and whose position in the width direction is determined by a regulating plate (not shown) is pulled out one by one from the top by the paper pulling unit 22 (−X direction), and then registered. It is conveyed to the nip portion of the pair 23.

  The photoconductor unit 30 includes a photoconductor drum 31 that is provided in parallel above the paper feeding device 20 (in the Z direction) and serves as an image carrier that is rotationally driven. A charging roller 32, an exposure device LH, a developing device 40, a primary transfer roller 52, and a cleaning blade 34 are arranged along the rotation direction of the photosensitive drum 31. A cleaning roller 33 for cleaning the surface of the charging roller 32 is disposed opposite to and in contact with the charging roller 32.

The developing device 40 includes a developing housing 41 in which a developer is accommodated. In the developing housing 41, a developing roller 42 disposed to face the photosensitive drum 31, and a pair of augers 44 that stir and convey the developer to the developing roller 42 side obliquely below the back side of the developing roller 42, 45 is arranged. A layer regulating member 46 that regulates the layer thickness of the developer is disposed in proximity to the developing roller 42.
Each of the developing devices 40 is configured in substantially the same manner except for the developer contained in the developing housing 41, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The surface of the rotating photosensitive drum 31 is charged by the charging roller 32, and an electrostatic latent image is formed by the latent image forming light emitted from the exposure device LH. The electrostatic latent image formed on the photosensitive drum 31 is developed as a toner image by the developing roller 42.

The transfer device 50 includes an intermediate transfer belt 51 to which each color toner image formed on the photoconductive drum 31 of each photoconductor unit 30 is transferred, and each color toner image formed on each photoconductor unit 30 to the intermediate transfer belt. A primary transfer roller 52 that sequentially transfers (primary transfer) to 51 is provided. Further, the image forming apparatus includes a secondary transfer roller 53 that collectively transfers (secondary transfer) each color toner image superimposed and transferred onto the intermediate transfer belt 51 onto a sheet P as a recording medium.

Each color toner image formed on the photosensitive drum 31 of each photosensitive unit 30 is sequentially transferred onto the intermediate transfer belt 51 by the primary transfer roller 52 to which a predetermined transfer voltage is applied from the power supply device 13 or the like controlled by the controller 11. Electrostatic transfer (primary transfer) is performed to form a superimposed toner image in which toners of respective colors are superimposed.

The superimposed toner image on the intermediate transfer belt 51 is conveyed to a region (secondary transfer portion T) where the secondary transfer roller 53 is disposed as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper feeding device 20 to the secondary transfer unit T in accordance with the timing. A predetermined transfer voltage is applied to the secondary transfer roller 53 from the power supply device 13 or the like controlled by the controller 11, and the intermediate transfer belt 51 is fed to the sheet P fed from the registration roller pair 23 and guided by the conveyance guide. The upper multiple toner images are collectively transferred.

Residual toner on the surface of the photosensitive drum 31 is removed by the cleaning blade 34 and collected in a waste toner container (not shown). The surface of the photosensitive drum 31 is recharged by the charging roller 32. Residue that cannot be completely removed by the cleaning blade 34 and adheres to the charging roller 32 is captured on the surface of the cleaning roller 33 that rotates in contact with the charging roller 32.

The fixing device 60 includes an endless fixing belt 61 that rotates in one direction, and a pressure roller 62 that contacts the peripheral surface of the fixing belt 61 and rotates in one direction. A nip portion N (fixing region) is formed by the pressure contact region.
The sheet P on which the toner image is transferred in the transfer device 50 is conveyed to the fixing device 60 via the conveyance guide in a state where the toner image is not fixed. The toner image is fixed on the sheet P conveyed to the fixing device 60 by a pair of fixing belt 61 and pressure roller 62 by the action of pressure bonding and heating. The sheet P on which the fixed toner image is formed is guided by a conveyance guide and is discharged from a discharge roller pair 69 to a discharge tray 1 a on the upper surface of the image forming apparatus 1.

(2) Configuration and operation of image forming unit (2.1) Configuration of image forming unit FIG. 2 includes the photosensitive unit 30, the developing device 40, the transfer device 50, and the like in the image forming apparatus 1 of the present embodiment. It is a schematic diagram for demonstrating in more detail the function of an image creation part.

As shown in FIG. 2, the image forming unit is disposed around the photosensitive drum 31, and the charging roller 32 and the charging roller 32 are opposed to and in contact with the cleaning roller 33. On the downstream side of the charging roller 32, the exposure position of the exposure apparatus LH is set, and on the downstream side, the developing roller 42 is arranged to face. On the downstream side of the developing roller 42, a primary transfer roller 52 is disposed in contact with the intermediate transfer belt 51 in between to form a transfer portion. A cleaning blade 34 elastically contacts the downstream side of the transfer portion and the upstream side of the charging roller 32.

The control device 10 includes a power supply device 13 whose operation is controlled by the controller 11 and an environmental sensor 15 as an example of environmental information detection means. The controller 11 corresponds to an example of a charging control unit.
The power supply device 13 is controlled in operation by the controller 11 and applies a superimposed voltage in which a DC voltage and an AC voltage are superimposed on the charging roller 32.
Further, a superimposed voltage in which another DC voltage and an AC voltage are superimposed is applied to the developing roller 42, and another DC voltage is applied to the primary transfer roller 52 and the secondary transfer roller 53.

(2.2) Action of Image Forming Unit In the contact charging system using the charging roller 32, a superimposed voltage in which a DC voltage and an AC voltage for charging are superimposed is applied to the charging roller 32. Only by applying a DC voltage, a current flows only at a low resistance on the photosensitive drum 31, so that uniform charging cannot be performed. Further, when the surface of the photosensitive drum 31 is locally soiled, there arises a problem that only that portion is not charged. Therefore, the surface of the photosensitive drum 31 is charged by applying a superimposed voltage in which a DC voltage and an AC voltage are superimposed.

Further, when a superposed voltage in which a predetermined direct current voltage and an alternating current voltage are superposed is applied to the charging roller 32 disposed in contact with the photoconductor drum 31 that is rotationally driven, the surface potential of the photoconductor drum 31 is Even if an AC voltage (peak-to-peak: Vpp) of a certain value or more is applied to the charging roller 32, the voltage does not rise above a certain voltage (shoulder voltage) (saturation current value Iac0: see FIG. 3).

Actually, an optimum AC current value is set based on the shoulder voltage in order to cope with image quality and environmental fluctuations. For example, if the alternating current value is too large, there is a problem that the photosensitive drum 31 is worn. On the other hand, if it is too small, the uniformity of charging cannot be maintained, and image unevenness occurs when an image is formed.
For this reason, it is necessary to set the alternating current value to the minimum necessary optimum value. In the image forming apparatus 1 according to the present embodiment, the point A (Iac1) in FIG. 3 is set.

The uniformly charged photosensitive drum 31 forms an electrostatic latent image by the latent image forming light emitted from the exposure device LH, and forms a toner image in a region facing the developing roller 42.
The toner image is formed by developing the latent image formed on the photosensitive drum 31 with a developer containing toner. Specifically, the developer carried on the surface of the developing roller 42 is brought into contact with a developer made into a magnetic brush, and an AC voltage is superimposed on a normal DC voltage and applied.
Incidentally, various external additives are used for toners used in electrophotography and the like in order to improve developability, fluidity, transferability, cleaning properties and the like.
In particular, an inorganic external additive having a relatively large particle size is used for primary transfer from the surface of the photosensitive drum 31 to the intermediate transfer belt 51 and secondary transfer from the intermediate transfer belt 51 to a sheet. An agent is added to the toner.

The toner image formed on the photosensitive drum 31 in this way is primarily transferred onto the intermediate transfer belt 51 by applying a predetermined transfer voltage (positive polarity) to the primary transfer roller 52.
The untransferred toner that is primarily transferred and remains on the surface of the photosensitive drum 31 is further driven to rotate and reaches the portion facing the cleaning blade 34. At this time, the toner and the external additive attached to the photosensitive drum 31 are scraped off by the cleaning blade 34.

The cleaning blade 34 elastically contacts the surface of the photoconductive drum 31 and can scrape off untransferred toner remaining on the surface without damaging the surface of the photoconductive drum 31, for example, urethane rubber. It is a member.
Accordingly, the elasticity changes depending on the surrounding environment of the photosensitive drum 31 to be used. As a result, the cleaning performance deteriorates in a low humidity environment even at a low temperature and low humidity environment or at room temperature, and is included in the untransferred toner. External additives may slip through.

For example, an inorganic external additive having a relatively large particle size directly attached to the photosensitive drum 31 passes through the cleaning blade 34 because the shape thereof is substantially spherical, and the charging roller 32 and the charging roller 32 rotate with the rotation of the photosensitive drum 31. To the opposite portion (charging nip portion).
As a result, more external additive remains on the surface of the image portion of the photosensitive drum 31 after being cleaned by the cleaning blade 34 as compared with the surrounding area.

(2.3) Generation Mechanism of Image Unevenness FIG. 4 is a diagram for explaining an estimation mechanism in which a ghost (image unevenness caused by the history of the previous image remaining) due to the external additive remaining on the photosensitive drum 31 occurs. FIG.
In the figure, 31a represents a charge generation layer of the photosensitive drum 31, 31b represents a charge transport layer of the photosensitive drum 31, T represents toner particles, and S represents an external additive.

The inorganic external additive having a relatively large particle size directly attached to the photosensitive drum 31 passes through the cleaning blade 34, and more external additive remains on the surface of the image portion of the photosensitive drum 31 as compared with the surrounding area. In this state, when the photosensitive drum 31 is charged again in the next image forming cycle, the external additive remaining on the surface of the image portion of the photosensitive drum 31 is charged together with the surface of the photosensitive drum 31. (See FIG. 4A).

In this state, when an electrostatic latent image is newly formed on the surface of the photosensitive drum 31 and developed, toner corresponding to the latent image should adhere to the surface of the photosensitive drum 31. The external additive remaining in the image portion of the previous image forming cycle is removed by rubbing with a magnetic brush of the developing roller 42 during development, for example, and replaced with toner (see FIG. 4B).
As a result, a potential difference occurs between the portion corresponding to the image portion of the previous image forming cycle and the portion that was a non-image portion in the previous image forming cycle, and corresponds to the latent image of the image portion of the previous image forming cycle. The portion becomes a high density portion and appears in the image, and image unevenness (ghost) occurs.

(2.4) Charging Control Therefore, in the image forming apparatus 1 according to the present embodiment, the environmental sensor 15 is provided as an environmental information detection unit that detects environmental information including the temperature or humidity of the photosensitive drum 31. The charging condition of the charging roller 32 is determined based on the detected temperature or humidity.
Specifically, when the environmental information detected by the environmental sensor 15 is a low temperature and low humidity environment or a low humidity environment even at room temperature, the AC voltage of the superimposed voltage applied to the charging roller 32 is not detected. The peak-to-peak (Vpp) is increased and the preset alternating current value is changed from Iac1 to Iac2 (see point B in FIG. 3).
The AC current value may be changed from Iac1 to Iac2 by increasing the frequency Fac of the AC voltage.

(2.5) Action / Effect of Charge Control Hereinafter, the action of charge control in the image forming apparatus 1 according to the present embodiment will be described.
FIG. 5A is a graph showing the relationship between the alternating current value Iac and the generated ghost when the alternating current value Iac is increased at a constant ratio from the saturated current value based on the saturated current value Iac0. is there.
ΔL * is a brightness difference between the normal image density portion and the ghost generation portion, and if ΔL * is close to 0, the brightness difference is low, and is preferably 0.5 or less.

FIG. 5B shows the contact angle of the AC current value Iac and the water on the surface of the photosensitive drum 31 when the AC current value Iac is increased at a constant ratio from the saturation current value based on the saturation current value Iac0. It is the graph which showed this relationship.
The contact angle decreases as the alternating current value Iac increases. It is known that a decrease in contact angle correlates with an increase in the amount of discharge products.

First, the contact angle α of water will be described with reference to FIG.
Under normal circumstances, since the surface of a substance (for example, the photosensitive layer on the photosensitive drum 31 or the nylon resin layer on the charging roller 32) is covered with a hydrophobic substance, it has a property of repelling water to some extent. is there.
The degree of repelling water can be expressed by the contact angle α between the water droplet and the substance surface. When the contact angle of water is large, it can be said that the water repellency is high. The contact angle α is, for example, 20 ° to 30 ° for an inorganic material such as glass, 70 ° to 90 ° for a general resin, and about 90 ° for a water-repellent silicone or fluororesin.

The contact angle θ of water can be measured by, for example, a droplet method described below. The solid-liquid interface / horizon between the solid (photosensitive drum 31 and charging roller 32 shown in the figure) and water W, the tangent to water W at the droplet end Wbottom, and the angle formed by these two lines is the contact angle of water. α. Further, a solid angle / horizontal line, a line connecting the droplet end Wbottom and the liquid vertex Wtop, and an angle formed by these two lines are defined as a measurement angle β. At this time, the contact angle α is twice the value of the measurement angle β, and the contact angle α can be measured using this.

The discharge product amount correlates with the contact angle of water on the photosensitive drum 31, and the contact angle α tends to decrease as the alternating current value Iac increases.
That is, as the alternating current value Iac increases, the frictional force on the surface of the photosensitive drum 31 increases, and the inorganic external additive having a relatively large particle diameter that passes through the cleaning blade 34 and directly adheres to the photosensitive drum 31 is obtained. The photosensitive drum 31 and the charging roller 32 are captured by the surface of the charging roller 32 that rotates in contact with the photosensitive drum 31 at a facing portion (charging nip portion) between the photosensitive drum 31 and the charging roller 32.

According to FIG. 5A, when the alternating current value Iac is increased at a rate of about 40% from the reference saturation current value Iac0, the brightness difference ΔL * between the normal image density portion and the ghost generation portion is 0. .5 or less, and the state cannot be recognized visually.
Note that since the alternating current value Iac is increased, the amount of discharge products is increased, and at this time, the contact angle α of water on the surface of the photosensitive drum 31 is reduced to approximately 65 ° (FIG. 5B). reference).

FIG. 7A is a graph showing the relationship between the frequency Fac of the AC voltage and the ghost generated when the frequency Fac of the AC voltage is increased.
FIG. 7B is a graph showing the relationship between the frequency Fac of the AC voltage and the contact angle of water on the surface of the photosensitive drum 31 when the frequency Fac of the AC voltage is increased.
The contact angle decreases as the alternating current value Iac increases. As a result, when the frequency Fac of the AC voltage is approximately 4.0 kHz or more, the brightness difference ΔL * between the normal image density portion and the ghost generation portion is 0.5 or less, and the state cannot be visually recognized.
If the AC current value Iac is increased, the surface of the photosensitive drum 31 is deteriorated due to the discharge due to the AC component, and the surface of the photosensitive drum 31 is rubbed with the cleaning blade 34, thereby promoting the wear of the surface of the photosensitive drum 31. May be.

In the contact charging method in which a voltage is applied to the charging roller to charge the photosensitive drum, the photosensitive drum is charged by a discharge generated in a small gap between the charging roller and the photosensitive drum. It is known that the starting voltage of the discharge generated in is defined by Paschen's law.

According to Paschen's law, the amount of discharge generated when an AC voltage is applied is larger than that when only a DC voltage is applied. For this reason, the surface of the photosensitive drum is deteriorated by sputtering due to electric discharge, and the smoothness of the surface of the photosensitive drum is lowered, resulting in an increase in the friction coefficient. The surface of the photosensitive drum having an increased coefficient of friction is easily worn by the cleaning blade, which not only shortens the life of the photosensitive drum, but also causes a problem that the film of the charging roll is reduced due to wear.

Therefore, the image forming apparatus 1 according to the present embodiment includes the environmental sensor 15 as environmental information detection means for detecting environmental information including the temperature or humidity of the photosensitive drum 31, and is based on the environmental information detected by the environmental sensor 15. Thus, the charging condition of the charging roller 32 is determined.
Specifically, when the environmental information detected by the environmental sensor 15 is a low temperature and low humidity environment or a low humidity environment even at room temperature, the AC voltage of the superimposed voltage applied to the charging roller 32 is not detected. The peak-to-peak (Vpp) is increased and the preset alternating current value is changed from Iac1 to Iac2 (see point B in FIG. 3).
On the other hand, the environmental information detected by the environmental sensor 15 indicates that the cleaning performance of the cleaning blade 34 is deteriorated, and external additives contained in the untransferred toner are easily slipped through. If it is, the preset alternating current value is maintained at Iac1.

Therefore, in a risk environment in which environmental information including temperature or humidity is detected and external additives are likely to slip through, the AC current value Iac or frequency of the charging roller 32 is changed (increased) to change the photosensitive drum. It is possible to prevent the occurrence of image unevenness (ghost) due to the external additive remaining on the toner 31 and to suppress the shortening of the life of the photoconductor unit 30 by using normal charging conditions in other environments. it can.

(2.6) Cleaning of Charging Roller The charging roller 32 captures the external additive that has passed through the cleaning blade 34 and adhered directly to the photosensitive drum 31 by contact rotation at the opposing portion (charging nip portion) of the photosensitive drum 31. However, the external additive trapped by the charging roller 32 is trapped on the surface of the cleaning roller 33 that rotates in contact with the charging roller 32 together with other residues that cannot be removed by the cleaning blade 34 and adhere to the charging roller 32. The

The cleaning roller 33 has a metal rotating shaft 33a and a polyurethane foam layer 33b as a porous elastic layer formed on the peripheral surface of the rotating shaft 33a.
Here, the charging roller 32 does not particularly have a drive source, and is driven to rotate as the photosensitive drum 31 in contact with the charging roller 32 rotates. Further, the cleaning roller 33 does not have a driving source in particular, and is driven to rotate as the charging roller 32 in contact with the cleaning roller 33 rotates.

The diameter of the charging roller 32 is, for example, 10 mm to 16 mm, and the diameter of the cleaning roller 33 is smaller than that of the charging roller 32 and is 6 mm to 12 mm. By determining the diameters of the charging roller 32 and the cleaning roller 33 in this way, the torque necessary for driving the cleaning roller 33 that rotates following the rotation of the charging roller 32 is reduced.

The charging roller 32 is applied with a superimposed voltage in which a predetermined DC voltage and an AC voltage are superimposed as described above. On the other hand, no bias voltage is applied to the cleaning roller 33, but the rotating shaft 32a of the charging roller 32 and the rotating shaft 33a of the cleaning roller 33 are rotatably supported by the same bearing, and the cleaning roller 33 is charged. The potential is the same as that of the roller 32.

The external additive adhering to the cleaning roller 33 is conveyed along with the rotation of the cleaning roller 33. During this time, van der Waals force acts strongly on the cleaning roller 33 and aggregates. In addition, the external additive tends to gather in the foamed holes existing on the surface of the foamed polyurethane layer 33b of the cleaning roller 33 and easily aggregate.

The aggregated external additive adhering to the cleaning roller 33 reaches the nip portion with the charging roller 32 again as the cleaning roller 33 rotates, and the elasticity of the polyurethane foam layer 33 b as the porous elastic layer of the cleaning roller 33 is reached. It is urged outward by force and ejected from the surface of the cleaning roller 33.

The external additive ejected from the cleaning roller 33 is transferred and attached to the charging roller 32 this time. The external additive attached to the charging roller 32 is transported to the charging nip portion facing the photosensitive drum 31 as the charging roller 32 rotates, and further transferred and attached to the photosensitive drum 31. Thereafter, the external additive adhering to the photosensitive drum 31 is collected by, for example, the developing device 40 or is primarily transferred to the intermediate transfer belt 51, and the external additive remaining in the image portion of the previous image forming cycle. The form as an additive is not maintained.

As described above, in this embodiment, the external additive transferred and attached from the charging roller 32 to the cleaning roller 33 aggregates on the cleaning roller 33 and then returns to the charging roller 32 again.
For this reason, the external additive captured by the cleaning roller 33 does not accumulate and cause clogging, and the cleaning performance of the cleaning roller 33 can be maintained over a long period of time. Therefore, the surface of the charging roller 32 is maintained without being contaminated by the external additive, and the charging performance of the charging roller 32 can be maintained over a long period of time.

In the image forming apparatus 1 according to the present embodiment, the external additive that passes through the cleaning blade 34 by driving the charging roller 32 under the charging condition determined based on the environmental information detected by the environment sensor 15 is charged by the charging roller 32. Complement. Therefore, it is possible to prevent the occurrence of image unevenness (ghost) due to the previous image forming cycle.
Under other circumstances in which the external additive is difficult to pass through the cleaning blade 34, normal charging conditions are used to prevent the life of the photosensitive unit 30 from being shortened. In addition, the external additive that has passed through the cleaning blade 34 is supplemented. The surface of the charging roller 32 is cleaned with the cleaning roller 33 that rotates in contact with the charging roller 32 to maintain the charging performance of the charging roller 32 over a long period of time.

As mentioned above, although embodiment concerning this invention was explained in full detail, this invention is not limited to the said embodiment, A various change is made within the range of the summary of this invention described in the claim. Is possible.
In this embodiment, the image forming apparatus 1 is a so-called tandem type, but is not limited thereto. In addition, the color image forming apparatus including a plurality of developing devices has been described. However, the present invention is not limited to this. For example, a monochrome image forming apparatus can also be applied.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Control apparatus 11 ... Controller 12 ... Image processing part 13 ... Power supply device 15 ... Environmental sensor 20 ... Paper feeding apparatus 30 ... Photoconductor Unit 31 ... Photosensitive drum 32 ... Charging roller 33 ... Cleaning roller 34 ... Cleaning blade 40 ... Developing device 42 ... Developing roller 50 ... Transfer device 51 ... Intermediate transfer Belt 52... Primary transfer roller 53... Secondary transfer roller 60.

Claims (3)

A toner image holding body for holding a toner image;
Charging means for charging a uniform charge by applying a superimposed voltage in which a DC voltage and an AC voltage are superimposed on the photosensitive member;
Latent image forming means for forming an electrostatic latent image on the surface of the charged photoreceptor;
Developing means for developing the electrostatic latent image formed on the photoreceptor with toner to form a toner image;
Transfer means for transferring a toner image formed on the photoreceptor onto a recording medium;
A cleaning unit located downstream of the transfer unit and collecting untransferred developer on the photoreceptor;
Environmental information detecting means for detecting environmental information including temperature or humidity of the photoconductor;
Charging control means for controlling charging conditions of the charging means based on environmental information detected by the environmental information detecting means;
With
An image forming apparatus. When the charging control means is a predetermined low-temperature and low-humidity environment or low-humidity environment, the AC voltage frequency and / or peak-to- Change the peak value,
The image forming apparatus according to claim 1. The charging unit includes a cleaning roller that rotates while being in pressure contact with the charging unit to clean the surface of the charging unit.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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