JP2009288676A - Electrifying device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent spread of an electrifying gap and the occurrence of uneven electrification/insufficient electrification at a longitudinal-direction center part of an electrifying roller caused by hardness and deflection of the electrifying roller. <P>SOLUTION: An electrifying device includes an image carrier, the electrifying roller to perform contactless electrification on the image carrier, and an electrifying cleaning member to clean the electrifying roller, wherein the electrifying cleaning member abuts on the electrifying roller and exerts pressing force in a direction where it goes toward the image carrier to the electrifying roller, and the pressing force to the electrifying roller at the center part of the electrifying cleaning member is larger than the pressing force at both ends of the electrifying cleaning member. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine for forming an image by an electrophotographic process, and a process cartridge employed in the image forming apparatus.

  Conventionally, as a charging device employed in this type of image forming apparatus, a contact-type charging roller that performs charging by bringing a charging roller into contact with the surface of an image carrier such as a photosensitive member or a non-contact roller charging-type charging roller. Are known.

  In an apparatus having a mechanism in which the charging cleaning member contacts and separates from the charging roller, when the charging cleaning member and the charging roller are in contact with each other and pressure is applied to the charging roller from the charging cleaning member, they are separated from each other, and the charging roller is charged with the charging cleaning member. In the case where no pressure is applied, it is difficult to make the charging gap between the charging roller and the charging cleaning member constant.

  The apparatus of the separation / contact mechanism has a layout in which the charging roller is arranged above the photosensitive member in the vertical direction, and the charging cleaning roller has an arrangement in which the charging roller is in contact with the charging roller by its own weight and rotates with the charging roller. In addition, there is a configuration in which the charging cleaning roller is disposed below the charging roller surface at a position below the virtual horizontal plane including the rotation center of the charging roller.

  Here, in the upper arrangement apparatus, the charging cleaning roller abuts on the photoconductor by its own weight, so the distance between the photoconductor and the charging roller does not increase at the center in the longitudinal direction. , The contact between the photosensitive member and the charging roller may increase at the center in the longitudinal direction. If the charging roller is separated from the photoreceptor, defects such as uneven charging or insufficient charging will occur. Therefore, a method is used in which the shaft of the charging cleaning roller is pressed with a constant applied pressure and brought into contact with the charging roller.

  In addition, the distance between the charging roller and the photosensitive member in the non-contact roller charging method needs to be adjusted with very high accuracy. However, in the same manner as described above, the interval between the photosensitive member and the charging roller is widened at the center portion in the longitudinal direction of the charging roller due to the hardness and bending of the charging roller.

  In Patent Document 1, when the charging roller is in contact with the surface of the charging roller below the virtual horizontal plane including the rotation center of the charging roller to clean the surface of the charging roller, the charging roller performs stable charging for a long period of time. The purpose is to obtain a good image. Therefore, a cleaner roller bearing holding member for holding the bearing for rotatably supporting the rotating shaft of the cleaner roller is integrally formed with the bearing for rotatably supporting the rotating shaft of the charging roller, and the cleaner roller bearing holding member provides a spring. Thus, the bearing of the cleaner roller is held so as to be movable in the direction in which the charging roller and the cleaner roller come into contact with and away from each other.

  In Patent Document 2, the cleaning operation of the charging unit is performed at an appropriate timing, the useless cleaning operation is eliminated, the running cost is reduced, the throughput is improved, and the image deterioration due to the contamination of the charging unit is surely prevented. An object of the present invention is to provide an image forming apparatus and an image forming method. For this reason, the photosensitive member that is rotationally driven, the charging unit that contacts the photosensitive member to charge the surface of the photosensitive member, and the charging unit can be separated from and contacted with each other, and the charging unit is cleaned by contacting the charging unit. Subsequently, an image forming apparatus including a charging cleaning unit that is separated from the charging unit and stands by is disclosed.

  However, in these apparatuses, the possibility that the distance between the central portion of the charging roller in the longitudinal direction and the photosensitive member is widened cannot be excluded.

JP 2005-301216 A Japanese Patent No. 3832194

  Therefore, even when a charging roller with a roller is applied to the photosensitive member with a predetermined pressure to form a charging gap, the charging gap is prevented from widening in the central portion in the longitudinal direction of the charging roller due to the hardness and bending of the charging roller. Prevent shortages.

  The charging device according to the present invention includes an image carrier, a charging roller that performs non-contact charging with respect to the image carrier, and a charging cleaning member that cleans the charging roller. The charging cleaning member contacts the charging roller, It is advantageous that a pressing force is applied to the charging roller in the direction toward the image carrier so that the pressing force against the charging roller at the central portion of the charging cleaning member is greater than the pressing force at both ends of the charging cleaning member.

  The charging roller is installed below a horizontal line passing through the axis of the image carrier as viewed in a cross section perpendicular to the axis of the image carrier, and the charging cleaning member is a charging roller as viewed in a cross section perpendicular to the axis of the charging roller. It is advantageous to be installed below the horizontal line passing through the axis.

  Further, it is advantageous that the charging cleaning member is made of a melamine foam resin body at the contact portion with the charging roller, and the central portion of the charging cleaning member is compressed so as to have higher density and higher hardness than both ends. .

  Further, it is advantageous that the charging cleaning member is configured such that the contact portion with the charging roller is configured as a brush, and the hair density at the central portion is higher than the end portion.

  In addition, it is advantageous that the charging cleaning member is configured as a roller, and both end portions of the charging cleaning member are pressed against the charging roller by a spring member and rotate with the charging roller.

  The pressing force is made by spring members installed at both ends and the center of the charging cleaning member, and the number of spring members at the center is larger than the number of spring members at both ends, or the number of spring members at the center. The spring constant is advantageously greater than the spring constant of the spring member at both ends.

  In addition, it is advantageous that the process cartridge of the present invention has the charging device described above. Further, it is advantageous that the image forming apparatus of the present invention includes the charging device or the process cartridge.

  The charging device according to the present invention includes an image carrier, a charging roller that performs non-contact charging on the image carrier, and a charging cleaning member that cleans the charging roller. The charging cleaning member contacts the charging roller. The charging roller is pressed in the direction toward the image carrier, and the pressing force on the charging roller at the central portion of the charging cleaning member is larger than the pressing force at both ends of the charging cleaning member. Therefore, the charging gap between the image carrier and the charging roller can be made uniform over the entire length in the longitudinal direction without bending due to its own weight in the portion.

  The charging roller is installed below a horizontal line passing through the axis of the image carrier as viewed in a cross section perpendicular to the axis of the image carrier, and the charging cleaning member is a charging roller as viewed in a cross section perpendicular to the axis of the charging roller. By being installed below the horizontal line passing through the axis of the charging roller, it is possible to effectively prevent the charging gap from being widened at the center due to the weight of the charging roller.

  Further, the contact portion of the charging cleaning member with the charging roller is made of a melamine foam resin body, and the central portion of the charging cleaning member is compressed so as to have a higher density and higher hardness than both end portions, so that the central portion Increases the force applied to the charging roller, and wear over time due to friction on the surface of the melamine foamed resin is less likely to occur, and more stable cleaning can be maintained.

  In addition, the charging cleaning member is configured as a brush at the contact portion with the charging roller, and the flocking density in the central portion of the brush, which is likely to be worn, is higher than the end portion. And stable cleaning performance for a long time is guaranteed.

  Further, the charging cleaning member is configured as a roller, and both end portions of the charging cleaning member are pressed against the charging roller by a spring member and are rotated with the charging roller, so that a stable cleaning property can be maintained for a long time. At the same time, additional driving means for the charging cleaning member is omitted, and the number of parts and the cost can be reduced.

  The pressing force is made by spring members installed at both ends and the center of the charging cleaning member, and the number of spring members at the center is larger than the number of spring members at both ends, or the number of spring members at the center. Since the spring constant is larger than the spring constant of the spring member at both ends, the pressing force at the center can be increased by simple means, and the formation of a uniform charging gap over the entire length in the longitudinal direction and good cleaning properties are ensured. The

  Further, the process cartridge of the present invention has the above-described charging device, so that stable performance can be maintained over a long period of time. In addition, the image forming apparatus of the present invention includes the charging device or the process cartridge, so that stable performance can be maintained for a long time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a longitudinal side view schematically showing a color printer as an image forming apparatus. In the main body case 2 of the color printer 1, a printer engine 3, an optical writing device 4 that emits a light beam, a paper feed cassette 5 that is a recording medium storage unit that stores a recording medium P that is a transfer target, a toner image Are provided with a fixing device 6 for fixing the recording medium P to which toner has been transferred, a waste toner collecting container 7 for collecting waste toner generated after transferring the toner image, and the like.

  The printer engine 3 is a portion that forms a toner image and transfers the formed toner image to the recording medium P, and includes four photoconductors 8 (8Y, 8C, 8M, and 8K) that are image carriers, and each photoconductor 8. 9, a developing device 10, a cleaning device 11, a primary transfer roller 12, an intermediate transfer belt 13 that is an image carrier and a transfer target, a secondary transfer roller 14 that is a transfer device, and a cleaning device. It is comprised by the apparatus 15 grade | etc.,. Here, in the description of the present specification and drawings, Y, C, M, and K subscripts indicate yellow, cyan, magenta, and black colors, respectively, and these subscripts are omitted as necessary. .

The photoconductor 8 is formed in a cylindrical shape and is connected to a drive motor (not shown), and rotates around a center line by a drive force from the drive motor. A photosensitive layer on which an electrostatic latent image is formed is provided on the outer peripheral surface of the photoreceptor 8.
The charging roller 9 is disposed in contact with the outer peripheral surface of the photoconductor 8 or is disposed with a minute gap (charging gap) from the outer peripheral surface of the photoconductor 8. When a voltage is applied to the charging roller 9 from a power supply unit (not shown), corona discharge is generated between the charging roller 9 and the photoconductor 8, and the outer peripheral surface of the photoconductor 8 is made uniform. Charged.

The optical writing device 4 emits a light beam corresponding to the image data, and exposes the outer peripheral surface of the uniformly charged photoreceptor 8. By this exposure, an electrostatic latent image corresponding to the image data is formed on the outer peripheral surface of the photoreceptor 8.
The developing device 10 supplies toner to the photoreceptor 8. The supplied toner adheres to the electrostatic latent image formed on the outer peripheral surface of the photoconductor 8, and the electrostatic latent image on the outer peripheral surface of the photoconductor 8 is visualized as a toner image.

  The intermediate transfer belt 13 is a loop-shaped belt formed of a resin film or rubber as a base, and is wound around a drive roller 16, an entrance roller 17, and a tension roller 18, and is driven by a drive motor (not shown). When the connected driving roller 16 is driven to rotate, it rotates in the direction of arrow A. The entrance roller 17 and the tension roller 18 are driven to rotate by the frictional force with the intermediate transfer belt 13 as the intermediate transfer belt 13 rotates in the direction of arrow A.

  The primary transfer roller 12 is disposed on the inner peripheral surface side (inside the loop) of the intermediate transfer belt 13, and a toner image on each photoconductor 8 is applied by applying a transfer voltage to the primary transfer roller 12. Is transferred onto the intermediate transfer belt 13. The toner images formed on the respective photoreceptors 8 are sequentially transferred and superimposed on the intermediate transfer belt 13, and a color toner image is formed on the intermediate transfer belt 13.

  The cleaning device 11 cleans the outer peripheral surface of the photoconductor 8 after the toner image is transferred to the intermediate transfer belt 13. By this cleaning, toner, paper dust, and the like remaining on the outer peripheral surface of the photoreceptor 8 after the toner image is transferred to the intermediate transfer belt 13 are collected as waste toner.

  The color toner image formed on the intermediate transfer belt 13 is transferred to the secondary transfer roller 14 at the timing when the recording medium P is sent to the transfer position where the intermediate transfer belt 13 and the secondary transfer roller 14 are in contact with each other. When the working voltage is applied, it is transferred to the recording medium P. The recording medium P is fed from the sheet feeding cassette 5 and is conveyed by the conveyance roller 19 and the registration roller 20, and is transferred to the fixing device 6 after the toner image is transferred. The recording medium P to which the toner image has been transferred is subjected to fixing processing by applying heat and pressure in the fixing device 6, and the toner image melted by this fixing processing is fixed to the recording medium P. The recording medium P for which the fixing process has been completed is discharged onto a discharge tray 21 formed on the upper surface of the main body case 2.

  The cleaning device 15 cleans the outer peripheral surface of the intermediate transfer belt 13 after the color toner image is transferred to the recording medium P. By this cleaning, toner, paper dust, and the like remaining on the outer peripheral surface of the intermediate transfer belt 13 after the toner image is transferred are collected as waste toner.

  The waste toner collection container 7 is a portion in which waste toner collected by the cleaning devices 11 and 15 is input from the cleaning devices 11 and 15 and the input waste toner is stored. The waste toner collection container 7 is detachably attached to the main body case 2, and is removed from the main body case 2 when the waste toner in the waste toner collection container 7 is almost full, and an empty waste toner collection container. 7 is attached.

  The photosensitive member 8 that is a component of the printer engine 3, the charging roller 9, the developing device 10 and the cleaning device 11 arranged around each photosensitive member 8 are unitized and housed in a case 22, and the process cartridge 23 ( 23Y, 23C, 23M, and 23K). Each process cartridge 23 is detachably mounted in the main body case 2. Since the photosensitive member 8, the charging roller 9, the developing device 10, and the cleaning device 11 are unitized as a process cartridge 23, replacement and maintenance work is facilitated, and the positional accuracy between the members is high. Therefore, the quality of the formed image can be improved. In the present embodiment, the photoconductor 8, the charging roller 9, the developing device 10, and the cleaning device 11 have been described by taking the process cartridge 23 as an example, but there are various process cartridge configurations. For example, at least one of the charging roller 9, the developing device 10, and the cleaning device 11 and the photoconductor 8 may be accommodated in a case and unitized.

FIG. 2 is a perspective view showing a state in which the side cover 24 provided on the main body case 2 is opened.
When the side cover 24 is opened, the printer engine 3 and the waste toner collection container 7 appear, and the process cartridge 23, the intermediate transfer belt 13 and the waste toner collection container 7 can be replaced and other maintenance can be performed. The intermediate transfer belt 13, the rollers 16, 17, 18 and the cleaning device 15 are housed in a belt case 13a and unitized.

  FIG. 6 shows the charging device and the charging gap G of the present invention. The charging device includes a charging roller 9 that is disposed to face the photoconductor 8 and extends substantially in parallel with the photoconductor. The charging roller 9 includes a cored bar 25 and a base material (not shown) made of a conductive resin or a rubber material provided around the cored bar 25. The charging roller 9 rotates in an appropriate direction during image formation. The charging roller 9 rotates in a direction in which a portion facing the photoconductor 8 moves in the same direction as the movement direction of the surface of the photoconductor. At this time, a charging voltage obtained by superimposing an AC voltage on a DC voltage is applied to the metal core 25 of the charging roller 9 by a power source (not shown), and the surface of the photoconductor 8 has a predetermined polarity due to the discharge generated at this time. For example, it is negatively charged.

At this time, a discharge product is generated by this discharge, and an abnormal image may be generated in the toner image formed on the photoconductor due to the discharge. Therefore, the charging roller 9 of this example is generated by the discharge. A photocatalyst layer (not shown) capable of decomposing the discharged product may be provided on the peripheral surface. As a photocatalyst substance constituting this photocatalyst layer, for example, titanium oxide, WO ₃ , ZnO, CdS, or the like can be used. The wavelength of the discharge light generated by the discharge phenomenon of the charging roller 9 covers a wide range from visible light (400 to 800 nm) to ultraviolet light (400 nm or more). At this time, since the surface of the charging roller 9 is coated with a photocatalytic substance capable of decomposing the discharge product, the photocatalyst is efficiently generated by the discharge light between the charging roller 9 and the photoconductor 8 without using any irradiation means. It is possible to decompose the discharge products such as O ₃ and NOx that are caused to react and adhere to the surface of the charging roller. Therefore, it is possible to effectively suppress or prevent the occurrence of an abnormal image in the toner image formed on the photoconductor.

  By the way, in order to secure a minute gap G between the charging roller portion contributing to the discharge and the surface of the photosensitive member, as shown in FIG. 6, at least the charging roller 9 is arranged at an interval in the axial direction. Two annular roller portions 27 are provided on the charging roller 9, the diameter of the roller portion between these roller portions 27 is set to be smaller than the diameter of the roller portion 27, and each end in the longitudinal direction of the core metal 25 is a bearing 26. The roller 27 may be pressed against the surface of the photosensitive member 8 by applying pressure to the pressure spring 36. As a result, a substantially constant gap G can be ensured between the roller portion between the roller portions 27 and the surface of the photoreceptor. When the charging roller 9 is manufactured, the roller portion 27 may be formed integrally with another charging roller portion to form the protrusion, or the end portion that does not contribute to the discharge of the charging roller is covered with a tube, or The roller part 27 can also be formed by winding a tape.

  In order to rotationally drive the charging roller 9, for example, as shown in FIG. 6, a gear 40 fixed to the core metal 25 of the charging roller 9 is engaged with a gear 41 fixed to the shaft of the photosensitive member 8, and the gear 41 is motorized. By driving by means of (not shown), the photosensitive member 8 and the charging roller 9 can be rotated in conjunction with the rotation direction. Alternatively, the charging roller 9 may be lightly pressed against the photoconductor 8 by the pressurizing spring 36, and the charging roller 9 may be rotated around the photoconductor 8 by a frictional force between the two.

3 to 5 show an embodiment of the charging device of the present invention.
In the charging device of FIG. 3, a rectangular charging cleaning member 37 is used to clean the charging roller 9. The springs 38 are provided at three points on both ends and the center of the charging cleaning member 37, thereby pressing the charging cleaning member 37 against the charging roller 9. The other end of the spring is fixed, for example, inside the housing of the process cartridge (see FIG. 5). In this way, the pressure applied to the charging roller 9 near the center of the charging cleaning member 37 is increased by increasing the pressure by the spring 38 near the center rather than at both ends. The adjustment of the biasing force of the spring may be performed by increasing the number of springs 38 near the center rather than both ends, or using the spring 38 having a larger spring constant near the center than both ends, or a combination thereof. . Thereby, the spread of the charging gap G between the central portion of the charging roller 9 and the photosensitive member 8 can be prevented. Therefore, a uniform charging gap G is formed over the entire length of the charging roller 9, and charging unevenness and insufficient charging do not occur. Here, if the charging cleaning member 37 has a brush-shaped contact portion with the charging roller 9 and the hair density at the center is higher than that at the end (not shown), better cleaning properties can be obtained.

  In the charging device of FIG. 4, the charging cleaning member 37 is formed in a roller shape, and rotates with the charging roller 9 using both-end pressing by a spring 38. This rotation eliminates additional driving means for the charging cleaning member 37, leading to a reduction in parts and cost. Further, it is preferable that the charging cleaning member 37 is configured such that a contact portion with the charging roller 9 is formed of a melamine foamed resin body, and a central portion is harder than an end portion by compression. The lightweight melamine foam resin body is not easily affected by gravity, and the density of the member near the center from both ends is increased to a high density and high hardness by compression. The pressure on the charging roller 9 near the center of 37 is increased, and the formation of a uniform gap G over the entire length of the charging roller is ensured. Furthermore, since the density of the member in the vicinity of the center is set to a high density and high hardness, wear with time due to friction on the surface of the melamine foamed resin hardly occurs, and a stable cleaning property can be maintained.

  Further, it is preferable that the charging cleaning member 37 is formed as a brush at a contact portion with the charging roller 9 and the hair flocking density in the central portion where wear is likely to occur is increased (not shown). Thereby, there is little deterioration with time and stable cleaning property can be maintained.

FIG. 5 shows a process cartridge in which the center of the charging cleaning member 37 is directly below the center of the charging roller 9. Basically, when the charging roller 9 is below the photoreceptor 8, the charging roller 9 is pressurized at both ends, but the charging gap G tends to widen in the center of the charging roller 9 due to its own weight. Therefore, as shown in the drawing, the charging roller 9 is installed below the horizontal line passing through the axis of the photoconductor 8 when viewed in a cross section perpendicular to the axis of the photoconductor 8, and the cross section perpendicular to the axis of the charging roller 9 is viewed. If the charging cleaning member 37 is installed below the horizontal line passing through the axis of the charging roller 9, the pressing of the charging cleaning member 37 against the charging roller 9 can be efficiently realized. Then, by using the above-mentioned means, the pressing force of the charging cleaning member 37 against the charging roller 9 is strengthened at the central portion rather than the longitudinal end portion, so that a desired pressing force can be ensured at the central portion. It can be kept uniform in the longitudinal direction.
As shown in FIG. 5, when the charging cleaning member 37 is directly below the charging roller 9, the central portion of the charging roller 9 receives force from the charging cleaning member 37 pressed by the spring 38 without waste. The spread of G can be suppressed most efficiently. Even if the charging cleaning member 37 is not located directly below the charging roller 9, it is pressed by the vertical component of the force applied by the charging cleaning member 37 to the charging roller 9 as long as it is disposed below the charging roller 9. The same effect as described above can be obtained.

1 is a longitudinal side view schematically showing a color printer as an image forming apparatus. The state which opened the side cover provided in the main body case is shown. 1 shows a charging device including a rectangular charging cleaning member for cleaning a charging roller. 1 shows a charging device including a roller-shaped charging cleaning member that rotates with a charging roller using both-end pressure by a spring. 1 shows a process cartridge provided with a charging cleaning member, a charging roller, a photoreceptor, and the like of the present invention. 1 shows a charging device and a charging gap G of the present invention.

Explanation of symbols

8 Photoconductor (image carrier)
9 Charging roller 26 Bearing 27 Roller part 36 Spring 37 Charging cleaning roller 38 Spring 40 Gear 41 Gear G Charging gap

Claims (8)

In a charging device including an image carrier, a charging roller that performs non-contact charging on the image carrier, and a charging cleaning member that cleans the charging roller.
The charging cleaning member is in contact with the charging roller and applies a pressing force to the charging roller in a direction toward the image carrier. The pressing force on the charging roller at the central portion of the charging cleaning member is a pressing force at both ends of the charging cleaning member. Charger characterized by being larger. The charging device according to claim 1,
The charging roller is installed below a horizontal line passing through the axis of the image carrier when viewed in a cross section perpendicular to the axis of the image carrier.
The charging device, wherein the charging cleaning member is installed below a horizontal line passing through the axis of the charging roller when viewed in a cross section perpendicular to the axis of the charging roller. The charging device according to claim 1 or 2,
The charging cleaning member is characterized in that the contact portion with the charging roller is made of a melamine foamed resin body, and the central portion of the charging cleaning member is compressed to have higher density and higher hardness than both ends. apparatus. The charging device according to claim 1.
The charging device is characterized in that the contact portion with the charging roller is configured as a brush, and the hair density in the central portion of the brush is higher than that of the end portion. In the charging device according to any one of claims 1 to 4,
A charging device, wherein the charging cleaning member is configured as a roller, and both ends of the charging cleaning member are pressed against the charging roller by a spring member, and rotate together with the charging roller. The charging device according to claim 1 or 2,
The pressing force is made by spring members installed at both ends and the center of the charging cleaning member, and the number of spring members at the center is larger than the number of spring members at both ends, or the spring constant of the spring member at the center. Is larger than the spring constant of the spring member at both ends.   A process cartridge comprising the charging device according to claim 1.   An image forming apparatus comprising the charging device according to claim 1 or the process cartridge according to claim 7.

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