JP2007017793A - Toner supply roller and developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner supply roller capable of restraining the deflection of a developing roller with simple constitution so as to reduce image noise, and a developing device equipped therewith. <P>SOLUTION: The core bar 31 of the toner supply roller 3 is formed in inverted crown shape, and further the external shape of the toner supply roller 3 is formed to be straight by an elastic layer 32 covering the core bar 31. When the toner supply roller 3 is made to abut on the developing roller 2 whose external shape is formed to be straight, its press-contact force is weak in a center part in a shaft direction. Therefore, the deflection of the developing roller 2 is restrained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device used in an electrophotographic image forming apparatus and a toner supply roller used in the developing device.

  2. Description of the Related Art Conventionally, a developing device used in an electrophotographic image forming apparatus has a developing roller that conveys toner to an image carrier (for example, a photosensitive drum), and supplies toner onto the developing roller in contact with the developing roller. A toner supply roller that peels off toner remaining on the developing roller after development. The developing roller is rotatably supported by spacer members provided at both ends of the developing roller, and is disposed to face the photosensitive drum in the axial direction. Further, the toner supply roller is disposed so as to strongly contact the developing roller by a biasing member such as a spring.

  In this type of developing device, the gap between the developing roller and the image carrier needs to be uniform in the axial direction. However, the developing roller is configured such that both ends thereof are supported by a spacer member such as a roller. For this reason, when the toner supply roller or the like is always urged toward the image carrier, the central portion of the developing roller is bent toward the image carrier, and the gap between the developing roller and the image carrier becomes non-uniform. This gap non-uniformity causes image density unevenness in the axial direction.

As a technique paying attention to this problem, for example, Patent Document 1 discloses a technique in which the shape of the developing roller has an inverted crown shape in order to make the gap between the developing roller and the image carrier constant in the axial direction. ing.
JP 2000-194191 A JP-A-11-316496

  However, the conventional developing device described above has the following problems. That is, it is required that the gap between the developing roller and the photosensitive drum be uniform with high accuracy. However, as in the developing device disclosed in Patent Document 1, it is very difficult to make the gap uniform with high accuracy while bending the reverse crown-shaped developing roller. Specifically, there are concerns over design difficulties, variations in processing or assembly, variations in the amount of deflection due to environmental changes and continuous use, and the like.

  The present invention has been made to solve the problems of the conventional developing device described above. That is, an object of the present invention is to provide a toner supply roller and a developing device including the toner supply roller that can suppress the deflection of the developing roller with a simple configuration and reduce image noise.

  A toner supply roller for solving this problem is a toner supply roller that contacts a developing roller having a straight shape and supplies toner to the developing roller. It is characterized by having an elastic layer to be coated and having a straight outer shape.

  The developing device of the present invention is disposed opposite to the image carrier, and a developing roller that carries and transports toner toward the image carrier, abuts against the developing roller, and supplies toner to the developing roller. A developing device having a toner supply roller, the toner supply roller having an inverted crown-shaped cored bar and an elastic layer covering the cored bar. Both are characterized by a straight shape.

  That is, in the toner supply roller of the present invention, the core metal has an inverted crown shape, and the outer shape of the toner supply roller has a straight shape, that is, a cylindrical shape, by an elastic layer covering the core metal. When the toner supply roller is brought into contact with the straight developing roller, the pressure contact force is reduced at the central portion in the axial direction. For this reason, bending of the developing roller is suppressed. Further, since a straight developing roller can be used, the developing roller can be easily manufactured and the shape thereof can be processed with high accuracy. Further, unlike the conventional developing device, the developing roller is not intentionally bent for adjusting the gap. Therefore, the gap between the developing roller and the image carrier can be made uniform easily and with high accuracy.

  Further, since the press contact force at the central portion in the axial direction is weakened, the mechanical stress on the toner is reduced. For this reason, image noise such as background fogging is reduced. Furthermore, since the pressure contact force is weakened, the driving torque of the developing roller or the toner supply roller can be reduced.

  According to the present invention, the metal core has an inverted crown shape, and the outer shape of the toner supply roller has a straight shape. By causing the toner supply roller to abut on the straight-shaped developing roller, bending of the developing roller is suppressed. Therefore, image noise can be reduced.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to an electrophotographic image forming apparatus provided with a developing device for storing and supplying non-magnetic one-component toner.

  As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes a photosensitive drum 11 that is an image carrier, and uniformly charges the surface of the photosensitive drum 11 around the photosensitive drum 11. A charging device 12, an exposure device 13 for forming an electrostatic latent image on the surface of the photosensitive drum 11, and an electrostatic latent image on the photosensitive drum 11 for making a visible image (toner image). A developing device 14, a transfer device 15 for transferring the toner image on the photosensitive drum 11 to a sheet, and a cleaning device 16 for removing the transfer residual toner from the photosensitive drum 11 are arranged in the rotation direction of the photosensitive drum 11. Along with. Further, a timing roller 17 for adjusting the timing of conveying the sheet to the transfer position and a fixing device 18 for fixing the transferred toner image on the sheet are provided in the sheet conveying path. In this embodiment, the charging device 12, the transfer device 15, and the fixing device 18 are all roller-shaped. The cleaning device 16 uses a cleaning blade.

  Next, an image forming operation by the image forming apparatus 100 will be briefly described. The image forming apparatus 100 starts operation by receiving a start signal, image data, and the like. The photosensitive drum 11 is rotationally driven in the direction of the arrow in FIG. Then, it is uniformly charged by the charging roller at a position facing the charging device 12. Next, exposure is performed by the exposure device 13, and an electrostatic latent image based on the image data is formed on the surface.

  Next, when the electrostatic latent image reaches the position of the developing device 14, the toner charged by the electric field formed between the developing bias voltage applied to the developing roller and the electrostatic latent image on the photosensitive drum 11 moves. Then, the electrostatic latent image is developed with toner.

  On the other hand, the paper transported through the paper transport path is timed by the timing roller 17 to the front end position of the image, and is transported between the photosensitive drum 11 and the transfer device 15. Then, the toner image on the photosensitive drum 11 is transferred to a sheet by the transfer device 15. Further, the sheet holding the transferred toner image is further conveyed, and heat and pressure are applied by the fixing device 18 to fix the toner image on the sheet. Further, the transfer residual toner which is not transferred onto the sheet by the transfer device 15 and remains on the photosensitive drum 11 is scraped off by the cleaning device 16. Thereby, the image formation for one sheet is completed.

  Next, the developing device 14 will be described in detail. As shown in FIG. 2, the developing device 14 includes a developing container 1 that contains non-magnetic toner that is a one-component developer, a developing roller 2 that carries the toner and conveys the toner toward the photosensitive drum 11, Toner supply roller 3 for supplying toner to developing roller 2 and scraping off toner on developing roller 2, toner amount regulating member 4 for regulating the thickness of toner on developing roller 2, and toner for preventing toner leakage A leakage prevention seal 6 is provided. A power source 5 is connected to the developing roller 2 to apply a bias for development.

  In the developing device 14, the toner in the developing container 1 is transferred from the toner supply roller 3 to the development roller 2 by the potential difference between the toner supply roller 3 and the development roller 2 and the mechanical conveyance force of the toner supply roller 3 whose surface is foam. Transport. The toner supplied to the developing roller 2 is thinned while being frictionally charged by the toner amount regulating member 4 as the developing roller 2 rotates, and the electrostatic latent image is visualized at a portion facing the photosensitive drum 2. .

  The developing roller 2 is accommodated in the developing container 1 and a part thereof is exposed from the developing container 1 through the opening of the developing container 1. Further, as shown in FIG. 3, the developing roller 2 is disposed in contact with the photosensitive drum 11 by spacer members 8 such as rollers provided at both ends. The developing roller 2 is urged toward the photosensitive drum 11 because the toner supply roller 3 is in strong contact. For this reason, the developing roller 2 is configured to oppose with a slight gap (approximately 150 μm) along the longitudinal direction of the photosensitive drum 11. Further, as shown in FIG. 4, the developing roller 2 has a straight outer shape, that is, a cylindrical shape, and the diameter of the end portion is equal to the diameter of the central portion.

  The toner supply roller 3 is accommodated in the developing container 1 and is in strong contact with the developing roller 2. The toner supply roller 3 is rotationally driven in the counter direction with respect to the developing roller 2.

  As shown in FIG. 5, the toner supply roller 3 includes a cored bar 31 and an elastic layer 32 that is located around the cored bar 31 and is made of a foam member. Specifically, in this embodiment, SUM (free cutting steel) in which the core metal 31 is plated is used. In addition, as the metal core 31, any metal that has been subjected to rust prevention treatment is applicable. Further, the diameter of the cored bar 31 is smaller at the center than at the end in the axial direction. That is, it has an inverted crown shape.

  As the material of the elastic layer 32, urethane foam is used. The elastic layer 32 may be a foamed member, and for example, silicon foam is applicable. The elastic layer 32 covering the metal core 31 is processed so that the outer shape of the toner supply roller 3 is a straight shape.

  In the toner supply roller 3 of this embodiment, the cored bar 31 has an inverted crown shape and the outer shape is a straight shape, so the thickness of the elastic layer 32 differs in the axial direction. Specifically, the thickness of the central portion in the axial direction is wider than the thickness of the end portion. For this reason, the pressing force at the central portion in the axial direction is small. Thereby, the bending of the developing roller 2 is avoided, and the uniformity of the gap between the developing roller 2 and the photosensitive drum 11 can be maintained even when the toner supply roller 3 is in contact.

[Evaluation of Embodiment]
Next, the evaluation result of the toner supply roller 3 of this embodiment will be described. In this evaluation, “magicolor2300DL” (hereinafter referred to as “evaluation machine”) manufactured by Konica Minolta Co., Ltd. was used, and the configuration of the toner supply roller was changed for evaluation.

  Specifically, the following was prepared as the configuration A (form of the present invention) of the toner supply roller. That is, as the shape of the cored bar, the diameter of the end (φA and φE in FIG. 5 and “reference diameter”) is 5 mm, and a quarter of the entire length from the end (φB in FIG. 5) The reference diameter is −30 μm, the half of the total length (φC in FIG. 5) is the reference diameter of −40 μm, and the 3/4 length (φD in FIG. 5) is the reference diameter of −30 μm. A supply roller having a diameter (φF in FIG. 5) of 11.5 mm, that is, a metal core having an inverted crown shape and an outer shape having a straight shape was prepared.

  On the other hand, as a configuration B (conventional form) of a toner supply roller as a comparative example, the following was prepared. That is, a straight cored bar (diameter 5 mm) and a straight toner supply roller (diameter 11.5 mm) were prepared.

  In addition, the following development roller configurations were prepared. That is, a rubber coat portion having a diameter of 16 mm and an outer shape having a straight shape was prepared.

The results are shown in Table 1.

  First, the density unevenness was evaluated. In this evaluation, ten solid images of cyan were printed, and the density difference in the CD direction (axial direction of the developing roller) at the center of the ten images was measured. For measurement of the density difference, a transmission densitometer “PROCESS MEASURMENT TD-904” manufactured by Macbeth was used. Then, 15 points were measured for each print sample, and it was determined that the difference between the highest density portion and the lower density portion was 0.1 or less (good), and if it was larger than 0.1, it was judged as bad (x). .

  As a result of this evaluation, in the configuration A (form of the present invention), the density difference was small (0.01 to 0.05), and good images with little density unevenness were obtained in most samples. On the other hand, in the configuration B (conventional form), the density difference was large (0.1 to 0.2), and density unevenness occurred in some samples.

  Next, the background fogging was evaluated. In this evaluation, 4500 test images with a printing rate of 5% were printed, and then a white solid image was printed, and the fogging amount of the background portion of the white solid image was visually evaluated. The evaluation standard was good (◯) if it could not be recognized visually, and bad (×) if it could be recognized.

  As a result of this evaluation, in the configuration A (form of the present invention), there was almost nothing that could be visually recognized, and a good image was obtained. On the other hand, in the configuration B (conventional form), visible objects were scattered, and background fogging occurred in some samples.

  From this evaluation result, it was found that density unevenness and background fogging were improved by making the core of the toner supply roller into an inverted crown shape and making the toner supply roller into a straight shape. In other words, it has been found that by forming the core of the toner supply roller in an inverted crown shape and providing a distribution of the pressure contact force between the toner supply roller and the development roller, the deflection of the development roller is reduced and density unevenness is improved. . In addition, it was found that the background fogging was improved because the pressure contact force at the central part in the axial direction was low.

  Note that the pressure contact force at the central portion in the axial direction is weakened by forming the core of the toner supply roller into an inverted crown shape. For this reason, it is possible to reduce the driving torque of the developing roller or the toner supply roller.

  As described above in detail, the developing device 14 according to the present embodiment includes the developing roller 2 having a straight outer shape, the toner supply roller 3 having a straight outer shape including the core 31 having a reverse crown shape and the elastic layer 32. To have. That is, by making the metal core 31 into an inverted crown shape, the pressure contact force with the developing roller 2 is reduced at the central portion in the axial direction. Therefore, the bending of the developing roller 2 is reduced, and the gap between the developing roller 2 and the photosensitive drum 11 can be made uniform. Therefore, the density unevenness in the axial direction is reduced, and high image quality can be achieved.

  Further, since the developing roller 2 itself has a straight outer shape, the processing of the developing roller 2 is facilitated. Of course, there are concerns about the difficulty in designing the pressure contact force to be uniform, the difficulty in processing the toner supply roller 3, and the change in the pressure contact force due to changes in the environment, etc. Therefore, high accuracy is not required as compared with the developing roller 2 that directly affects the electric field strength distribution due to the developing bias. That is, there is little influence on the image quality, and some variation is allowed as compared with the developing roller 2.

  Further, since the press contact force at the central portion in the axial direction is weakened, the mechanical stress on the toner is reduced. Therefore, image noise such as background fogging can be reduced. Furthermore, since the pressure contact force is weakened, the driving torque of the developing roller or the toner supply roller can be reduced.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention can be applied to various image forming apparatuses such as a color printer, a monochrome printer, a copier, and a facsimile.

  Further, although a roller-shaped photosensitive drum is used as the image carrier, a belt-shaped photosensitive belt may be used. In addition to the roller charging method, the charging device may use a corona discharge charging charger, blade, brush, or the like. The exposure apparatus may be a laser or LED. The transfer device may use a transfer charger in addition to the transfer roller. Alternatively, in addition to a method of directly transferring a toner image from a photosensitive member to a sheet, a method of providing an intermediate transfer member and performing transfer in two or more stages may be used. In addition to the cleaning blade, the cleaning device may be a cleaning brush, a cleaning roller, or a combination thereof. Alternatively, the transfer residual toner may be collected by a developing device. In addition to the fixing roller, the fixing device may use a fixing belt or a non-contact type.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a schematic configuration of a developing device according to an embodiment. It is a top view which shows arrangement | positioning of a photoconductor drum and a developing device. It is a figure which shows schematic structure of the developing roller concerning Embodiment. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a toner supply roller according to the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing container 2 Developing roller 3 Toner supply roller 31 Core metal 32 Elastic layer 11 Photosensitive drum 14 Developing device 100 Image forming apparatus

Claims (2)

In a toner supply roller that contacts a straight developing roller and supplies toner to the developing roller,
An inverted crown cored bar,
An elastic layer covering the cored bar,
A toner supply roller having a straight outer shape. A developing device having a developing roller disposed opposite to an image carrier and carrying and transporting toner toward the image carrier, and a toner supply roller that contacts the developing roller and supplies toner to the developing roller ,
The toner supply roller is
An inverted crown cored bar,
An elastic layer covering the core metal;
2. A developing device according to claim 1, wherein an outer shape of the developing roller and an outer shape of the toner supply roller are both straight.

Images