JP2009198964A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that can effectively suppress nonuniform image density while allowing bend of a developing roller, and to provide an image forming apparatus. <P>SOLUTION: The developing device 10 includes: the developing roller 12 for supplying developer to an electrostatic latent image on a photoreceptor 2; and a supply roller 13 that brings the developing roller 12 into press-contact with the photoreceptor 2. The developing roller 12 has: a core bar 31 having cylindrical outer shape; and a resin layer 32 formed on the outer circumferential face of the core bar 31. The resin layer 32 is formed in such a manner that the middle part is thinner than both end parts in the lengthwise direction of the core bar 31. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing device that develops an electrostatic latent image on an image carrier using a developing roller, and an image forming apparatus having the developing device. More specifically, the present invention relates to a developing device and an image forming apparatus using a developing roller having a resin layer around a cored bar.

  Conventionally, in some developing devices using a developing roller, a supply roller, a regulating blade, or the like is brought into contact with the surface of the developing roller. In such a case, since the developing roller bends due to the contact pressure of each member during use, the distance between the developing roller and the image carrier may vary depending on the location in the longitudinal direction of the developing roller. . If the distance between the image carrier and the developing roller is different, the magnitude of the developing electric field varies accordingly, which causes uneven image density.

On the other hand, an image forming apparatus is disclosed in which members such as a supply roller and a regulating blade that are in contact with the developing roller are arranged on opposite sides with respect to the center of the developing roller (see, for example, Patent Document 1). ). In the apparatus of this document, it is said that the bending of the developing roller can be prevented by balancing the contact pressures of a plurality of members against the developing roller.
JP 2006-98854 A

  However, each member of the developing device has an appropriate arrangement, and it cannot always be arranged like the conventional image forming apparatus described above. Further, if the arrangement is made as described above, the entire image forming apparatus may be increased in size. That is, it is difficult to prevent the developing roller from being bent by adjusting the arrangement. Therefore, there has been a demand for a developing device that does not cause uneven image density even when the developing roller is slightly bent.

  The present invention has been made to solve the problems of the conventional developing device and image forming apparatus. That is, an object of the present invention is to provide a developing device and an image forming apparatus capable of effectively suppressing image density unevenness while allowing the developing roller to bend.

  In order to solve this problem, the developing device of the present invention includes a developing roller for supplying a developer to an electrostatic latent image on an image carrier, and the developing roller as an image carrier relative to the developing roller. A developing device having a supply roller that is pressed in a direction close to the developing roller, the developing roller having a cylindrical metal core and a resin layer provided at least in an image area on the outer peripheral surface of the metal core The resin layer is formed thinner in the central part than both end parts in the longitudinal direction of the cored bar.

  According to the developing device of the present invention, the developing roller has a resin layer formed on the surface of the core metal, and the thickness of the resin layer is thinner at the center than at both ends in the longitudinal direction of the developing roller. Has been. Therefore, the outermost peripheral shape of the developing roller is thick at both ends and thin at the center. In general, when the developing roller rotates while bending in use, the central portion of the core bar approaches the image carrier from both ends. Since the developing roller according to the present invention has a difference in thickness as described above, the distance between the outer peripheral surface and the image carrier can be prevented from being different between the central portion and both end portions. Therefore, image density unevenness can be effectively suppressed while allowing the developing roller to bend.

Furthermore, in the present invention, it is desirable that the thickness of the resin layer is continuously increased from the central portion in the image area toward both end portions.
With this arrangement, there is no portion where the outer diameter of the developing roller changes abruptly at least in the image area. Here, the image area is a range corresponding to a range in which an electrostatic latent image is formed on the image carrier in the longitudinal direction of the developing roller.

Further, in the present invention, it is desirable that the size of the gap between the developing roller and the image carrier does not exceed 200 μm.
Even with such a small gap, good results can be obtained according to the present invention.

  The present invention also provides an image carrier, a charging device that charges the surface of the image carrier, an exposure device that exposes the charged image carrier to form a latent image, and an electrostatic latent image on the image carrier. An image forming apparatus comprising: a developing roller for supplying a developer to the surface; and a supply roller that presses the developing roller toward the image carrier so that the developing roller is close to the image carrier. And a resin layer provided at least in the image area on the outer peripheral surface of the core metal, and the resin layer is formed thinner in the central part than both ends in the longitudinal direction of the core metal Also extends to forming equipment.

  According to the developing device and the image forming apparatus of the present invention, image density unevenness can be effectively suppressed while allowing the developing roller to bend.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a developing device having a developing roller and an image forming apparatus having the developing device.

  As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes four color image forming units 20 </ b> Bk, 20 </ b> C, 20 </ b> M, and 20 </ b> Y arranged along the intermediate transfer belt 1. Each of the image forming units 20Bk, 20C, 20M, and 20Y has a photoreceptor 2. Further, a charging device 21, an exposure device 22, a developing device 10, a primary transfer device 24, and a cleaner device 25 are disposed around the photoreceptor 2. Further, the intermediate transfer belt 1 is rotated as indicated by an arrow A in the drawing at the time of image formation. A secondary transfer device 26 is disposed downstream of the image forming units 20Bk, 20C, 20M, and 20Y in the rotational direction of the intermediate transfer belt 1.

  In this embodiment, toner images of respective colors are formed on the photoreceptor 2 by the image forming units 20Bk, 20C, 20M, and 20Y, respectively. Then, the images are sequentially transferred to the intermediate transfer belt 1 and toner images of respective colors are superimposed. The superimposed toner images are transferred onto the recording paper by the secondary transfer device 26.

  As shown in FIG. 2, the developing device 10 of the present embodiment is arranged to face the photosensitive member 2 and supplies developer to the electrostatic latent image on the photosensitive member 2. The developing device 10 includes a housing 11, a developing roller 12, a supply roller 13, a regulating blade 14, a charge removal sheet 15, and an elastic material 16. The developing roller 12, the supply roller 13, the regulating blade 14, and the elastic material 16 are disposed inside the housing 11.

  The developing roller 12 carries an appropriate amount of developer, faces the photoreceptor 2, and supplies the developer to the photoreceptor 2. In this embodiment, a non-magnetic one-component developer that does not use a carrier is used as the developer. The developing roller 12 is arranged in parallel to the photoreceptor 2 with a gap. In this embodiment, the size of the gap between the photosensitive member 2 and the developing roller 12 does not exceed 200 μm. The gap value is a design value defined by a DS roller provided between the roller shaft at the end of the developing roller 12 and the shaft of the photosensitive member 2. At the time of image formation, as indicated by an arrow in FIG.

  The supply roller 13 is for supplying the developer in the housing 11 to the development roller 12. The supply roller 13 is an elastic roller and is pressed against the developing roller in a direction perpendicular to the axis. Further, the supply roller 13 is rotated in the counter direction with respect to the developing roller 12 as shown by an arrow in FIG.

  The regulating blade 14 is for regulating the layer thickness of the developer carried on the developing roller 12 and charging the developer by rubbing. The regulating blade 14 is arranged in contact with the surface of the developing roller 12 on the downstream side with respect to the rotation of the developing roller 12 from the contact portion between the developing roller 12 and the supply roller 13.

  The neutralization sheet 15 is for neutralizing the developer remaining on the development roller 12 even after passing through the development area. The developing area is a range in which the developing roller 12 and the photosensitive member 2 face each other and the developer can be supplied from the developing roller 12 to the electrostatic latent image formed on the photosensitive member 2. For this reason, the static elimination sheet 15 is disposed in contact with the surface of the developing roller 12 on the downstream side of the rotation of the developing roller 12 with respect to the location where the developing roller 12 and the photosensitive member 2 face each other. In this embodiment, the static elimination sheet 15 is pressed against the developing roller 12 by an elastic material 16 fixed to the housing 11.

  In this embodiment, the developing roller 12 has a resin layer 32 provided on the outer periphery of a cored bar 31 as shown in FIG. As shown in FIG. 4, the cored bar 31 has a main body 31a and rotating shafts 31b formed at both ends thereof. The main body 31a and the rotating shaft 31b are arranged coaxially and are integrally formed. Of these, the main body 31a is a pipe material having a uniform outer diameter and thickness, and is preferably made of aluminum, for example. When the developing roller 12 is attached to the developing device 10 and used, the portion of the rotating shaft 31b of the cored bar 31 is held and receives a rotational driving force.

  As shown in FIG. 3, the resin layer 32 of the developing roller 12 is coated such that it is thick at the end in the longitudinal direction and thin at the center. The thickness of the resin layer 32 is symmetrical with respect to the central portion in the longitudinal direction in the figure, and is formed so as to be gradually different. Further, it is formed uniformly in the circumferential direction of the cored bar 31. In this figure, it is considerably exaggerated. As the material of the resin layer 32, a thermoplastic resin, a thermosetting resin, a photocurable resin, or the like is used. Among them, it is preferable to select a toner that has excellent toner releasability and is resistant to wear and scratches. In addition, this resin layer 32 will be in the state which hardly has elasticity by hardening after coating. Therefore, the developing roller 12 of this embodiment is a kind of hard roller.

  Examples of the thermoplastic resin suitable for the resin layer 32 include styrene resin, vinyl resin, polyethersulfone resin, polycarbonate resin, polyphenylene oxide resin, polyamide resin, fluorine resin, fiber resin, acrylic resin, and the like. . Examples of the thermo- and photo-curable resins include epoxy resins, polyester resins, alkyd resins, phenol resins, melamine resins, polyurethane resins, urea resins, silicone resins, polyimide resins, and the like. Also, a resin excellent in toner releasability such as silicon resin and fluorine resin is preferable. Furthermore, examples of the resin having excellent mechanical properties include polyethersulfone, polycarbonate, polyphenylene oxide, polyamide, phenol, polyester, polyurethane, styrene resin, and acrylic resin.

  Furthermore, it is preferable that the resin layer 32 has an appropriate volume resistivity. For this purpose, for example, conductive fine powder having a particle size of about 0.1 to 5 μm may be contained. Examples of the material to be included include metal powders such as conductive carbon black, aluminum, copper, nickel and silver, conductive metal oxides such as antimony oxide, indium oxide, titanium oxide, tin oxide and aluminum oxide, and metal shorts. Examples thereof include fiber, carbon fiber, and silicate fine powder. In addition, these addition amounts are preferably in the range of 0.1 to 400% by weight with respect to the resin. More preferably, it is in the range of 1 to 200% by weight.

  Examples of the method for forming the resin layer 32 include a dipping method, a spray coating method, a roll coater method, and a method of applying with a brush. The thickness in each method is adjusted as follows. In the dipping method, the speed can be increased by increasing the pulling speed and decreased by decreasing the speed. In the spray coating method, the coating time can be increased by increasing the coating time and decreased by decreasing the coating time. In the roll coater method, the thickness can be adjusted by adjusting the gap between the roll and the blade in contact with the roll.

  When an image is formed by the image forming apparatus of this embodiment, the rotating shaft 31b of the cored bar 31 is held and rotated. Further, the supply roller 13 does not contact the rotating shaft 31b but contacts only the main body 31a. For this reason, the central portion of the developing roller 12 is pressed by the supply roller 13 and is slightly bent toward the gap with the photoreceptor 2. The bending amount at this time is determined to some extent by the length and material of the developing roller 12, the pressure contact force of the supply roller 13, and the like. Therefore, in this embodiment, the difference between the thickness of the end portion of the resin layer 32 and the thickness of the central portion is set to the same size as this bending amount.

  By doing so, the gap between the developing roller 12 and the photosensitive member 2 in the bent state at the time of use becomes substantially equal at the central portion and the end portion in the axial direction. Note that, on the side of the developing roller 12 far from the photosensitive member 2, the difference in position between the central portion and the end portion is larger than that of the conventional one. However, the bending amount of the developing roller 12 is very small compared to the amount of elastic deformation of the supply roller 13, and the supply amount of the developer from the supply roller 13 to the developing roller 12 is sufficiently ensured.

  The inventors manufactured the developing roller 12 of this embodiment and conducted an experiment to confirm the effect. Next, the embodiment will be described. In this experiment, the coating liquid described below was created as the material of the resin layer 32. First, 10 parts by weight of fluorine-containing polyol (Daikin Kogyo Zefle: trade name), 8 parts by weight of conductive carbon black (Cabot), 10 parts by weight of silicon resin particles (average particle size 25 μm), butyl acetate 300 parts by weight of the mixture was dispersed by a disperser. To this dispersion, 50 parts by weight of reactive vinyl oil modified with carbinol at both ends (X-22-16-AS manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred. This is the main agent of the coating solution.

  Next, urethane-modified hexamethylene diisocyanate (Duranate manufactured by Asahi Kasei Kogyo Co., Ltd .: trade name) was blended with the main agent as a curing agent. The mixing ratio was adjusted so that the equivalent of the hydroxyl group in the main agent and the equivalent of the isocyanate group in the curing agent were 1: 1. This is a coating solution.

  The main body 31a of the core metal 31 was an aluminum pipe having a diameter of 12 mm and a wall thickness of 1.5 mm. Then, the above coating solution was coated using a coating apparatus by a dipping method. Then, as shown in FIG. 5, the speed at which the resin layer 32 is pulled up is adjusted so that the thickness of the resin layer 32 is about 100 μm at both ends of the main body 31a and about 10 μm at the thinnest part of the center.

  As a comparative example, the same aluminum pipe and coating liquid as in the example were used and only the pulling speed was changed. That is, it was pulled up at a constant pulling speed throughout the entire axial direction. Specifically, it was pulled up at the slowest speed among the pulling speeds in the example. Thereby, the resin layer 32 having a thickness of 10 μm over the entire axial direction was formed.

  A modification was made by using a Magiccolor 5430 manufactured by Konica Minolta as an experimental machine and replacing the developing roller with that of this example or the comparative example. A solid image was formed with this modified machine, and the image density was examined. The image forming apparatus can adjust the image forming conditions so that the entire density is automatically adjusted with reference to the image density at the center or end in the main scanning direction. Therefore, Example 1 was obtained by using the developing roller of Example and adjusting the density with reference to the central portion in the main scanning direction. Further, Example 2 in which the density was adjusted using the developing roller of Example as the reference in the end portion in the main scanning direction was referred to as Example 2. Further, Comparative Example 1 was obtained by using the developing roller of the comparative example and adjusting the density with reference to the central portion in the main scanning direction. Comparative Example 2 was obtained by adjusting the density using the developing roller of the comparative example with reference to the end portion in the main scanning direction.

  The result of this experiment is shown in FIG. The solid line in the figure shows the results of Example 1 and Example 2. The result of Comparative Example 2 is shown by Comparative Example 1 and by the broken line. Example 1 and Example 2 had almost the same results. That is, in Examples 1 and 2, a substantially uniform concentration was obtained over the entire longitudinal direction. On the other hand, in Comparative Example 1, the image density was small at the end in the longitudinal direction. In Comparative Example 2, an extreme decrease in density was observed at the center in the longitudinal direction. This is because leakage has occurred because the distance between the developing roller and the photosensitive member 2 has become too small.

  As described above in detail, according to the developing device 10 of the present embodiment, the resin layer 32 having a different diameter in the longitudinal direction is formed on the developing roller 12. In particular, it is thinner at the center in the longitudinal direction than at the end. On the other hand, when the developing roller 12 is pressed toward the photosensitive member 2 by being pressed by the supply roller 13, the central portion in the longitudinal direction is closest to the photosensitive member 2 side. Therefore, by providing an appropriate difference in the thickness of the resin layer 32, the gap with the photoreceptor 2 when the developing roller 12 is bent can be made the same regardless of the position in the longitudinal direction. Thus, the developing device can effectively suppress unevenness in image density while allowing the developing roller to bend.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the type of resin used for the resin layer and the method for forming the resin layer are not limited to those described above. Further, the core metal is not limited to a pipe as long as it has a uniform thickness, and may be solid. For example, the resin layer 32 may contain a roughening material. Alternatively, after the resin layer 32 is formed, it may be roughened by polishing.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. It is a schematic block diagram of the developing device of this form. It is explanatory drawing which shows the developing roller of this form. It is a figure which shows the shape of a metal core. It is explanatory drawing which shows the thickness of the resin layer of a developing roller. It is explanatory drawing which shows image density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Photoconductor 10 Developing device 12 Developing roller 13 Supply roller 21 Charging device 22 Exposure device 31 Core metal 32 Resin layer 100 Image forming apparatus

Claims (4)

In a developing device comprising: a developing roller for supplying a developer to an electrostatic latent image on an image carrier; and a supply roller that presses the developing roller toward the image carrier in a direction to bring the developer roller closer to the image carrier.
The developing roller is
A metal core with a cylindrical outer shape,
A resin layer provided at least in the image area on the outer peripheral surface of the cored bar,
The developing device according to claim 1, wherein the resin layer is formed thinner in a central portion than both ends in a longitudinal direction of the cored bar. The developing device according to claim 1,
2. A developing device according to claim 1, wherein the thickness of the resin layer is continuously increased from the central portion to both end portions in the image area. In the developing device according to claim 1 or 2,
A developing device characterized in that the size of the gap between the developing roller and the image carrier does not exceed 200 μm. An image carrier, a charging device for charging the surface of the image carrier, an exposure device for exposing the charged image carrier to form a latent image, and developing an electrostatic latent image on the image carrier In an image forming apparatus comprising: a developing roller for supplying an agent; and a supply roller that presses the developing roller in a direction to bring the developing roller closer to the image carrier,
The developing roller is
A metal core with a cylindrical outer shape,
A resin layer provided at least in the image area on the outer peripheral surface of the cored bar,
The image forming apparatus according to claim 1, wherein the resin layer is formed thinner in the center than in the longitudinal direction of the cored bar.

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