JP2008275662A - Developing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a portion of developer carried on a developing roller, which projects from the width of output paper, from being give unnecessary stresses. <P>SOLUTION: The image forming apparatus 1 forms a toner image by sticking toner to an electrostatic latent image on the surface of a photoreceptor drum 10 by the developing device 13. In the developing device 13, two-component developer comprising toner components and magnetic carrier is carried on the surface of the developing roller 33 by magnetic field. A regulating member 35 for regulating the layer thickness of the developer comprises a shaft 36 and a blade 37, and a first regulating part K1, corresponding to paper width obtained when A3 size paper, is set with its shorter side at the top; and a second regulating part K2 obtained, when A4 size paper is set with its shorter side at the top are formed on the opposed sides in the longitudinal direction of the blade 37. By making the blade 37 inverted vertically by a motor 22, the first regulating part K1 and the second regulating part K2 are used for different purposes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic developing device and an image forming apparatus including the same.

  In an electrophotographic image forming apparatus, an image carrier on which an electrostatic latent image is formed, for example, the surface of a photosensitive drum is developed with toner. Recently, a two-component developer composed of a toner component and a magnetic carrier is often used. The two-component developer is carried on the developing roller by a magnetic field, and only the toner component is attached to the image carrier by an electric field. Examples of an image forming apparatus provided with such a developing device can be found in Patent Documents 1 and 2.

  In the developing device of the electrophotographic image forming apparatus, a regulating member is opposed to the developing roller in order to regulate the amount of toner supplied to the image carrier. The presence of the regulating member is indispensable, but on the other hand, the toner is subjected to mechanical stress due to its presence, and the deterioration is promoted.

The above problem has been recognized for a long time, and Patent Document 1 also describes means for solving it. In the apparatus described in Patent Document 1, the strength of the magnetic field generated in the restriction gap formed between the restriction member and the developing roller is adjusted according to the image printing rate to reduce mechanical stress on the toner. . Specifically, when continuously printing an image with a low printing rate, the magnetic field generating member in the developing roller is rotated by a predetermined amount to change the strength of the magnetic field in the regulation gap, thereby alleviating the stress applied to the developer. Patent Document 2 describes a device that changes the thickness of a regulating blade by individually moving a blade member in and out. This apparatus can also be used to reduce stress applied to the developer.
JP 2006-208579 A JP 2000-267436 A

  In an electrophotographic image forming apparatus, an image is usually formed on output paper (including a synthetic resin film) having two or more widths. The widths of the drums and rollers are determined according to the maximum output paper handled by the image forming apparatus.

  The developing roller carries the developer with the same width as that for the maximum width output paper even when an image is formed on the narrow output paper. The developer is stressed by the regulation gap, and suffers adverse effects such as desorption and embedding of the toner surface treatment agent, peeling of the carrier coating agent, and performance deterioration due to temperature rise. It can be said that the stress received when passing through the regulation gap is unavoidable for the developer within the width of the output paper, but it is excessive stress for the developer that protrudes from the width of the output paper and is collected without involving toner image formation. No one other than. In this way, as the cumulative amount of developer recovered simply by experiencing excessive stress increases, the developer as a whole deteriorates. Regarding this problem, neither the device described in Patent Document 1 nor the device described in Patent Document 2 has found a solution.

  The present invention has been made in view of the above points. The developer having a magnetic property is carried on the surface of the developing roller by a magnetic field, and the layer thickness of the carried developer is measured by a regulating member facing the developing roller with a predetermined regulating gap therebetween. In a developing device for supplying to an image carrier after regulating the amount of developer, an object is to prevent extra stress from being applied to the portion of the developer carried on the developing roller that protrudes from the width of the output paper. To do.

  (1) In order to achieve the above object, according to the present invention, a developer having magnetism is carried on the surface of a developing roller by a magnetic field, and the layer thickness of the carried developer is measured by a regulating member facing the developing roller with a predetermined regulating gap therebetween. In the developing device for supplying the image carrier to the image carrier, the width of a portion of the regulating member that forms the regulating gap between the developing roller and the output of the toner in the developer is transferred. It is characterized in that it can be changed according to the width of the paper.

  According to this configuration, among the developer carried on the surface of the developing roller, the developer at the location corresponding to the width of the output paper passes through the regular regulation gap, but the developer at the location protruding from there is more than that. Also, stress can be reduced by passing a wide gap. Therefore, even if the cumulative amount of developer collected without increasing the toner image increases, the deterioration of the developer is slow, and a stable toner image can be formed while maintaining the developer performance over a long period of time.

  (2) Further, in the developing device having the above-described configuration, the restricting member is rotatable around an axis parallel to the developing roller, and the restricting gap is formed between the developing roller and the developing roller according to a rotation angle. It is characterized in that the width of the portion to be different is different.

  According to this configuration, the width of the regulating member can be switched reliably and quickly by rotating the regulating member.

  (3) Further, the present invention is an image forming apparatus including the developing device having the above-described configuration.

  According to this configuration, an image forming apparatus that can perform stable image formation over a long period of time can be obtained.

  According to the present invention, among the developer carried on the surface of the developing roller, the developer at the location corresponding to the width of the output paper passes through the regulation gap of the regular width, but the developer at the location protruding from there is By passing a wider interval than that, it is possible to suppress deterioration of the developer without applying unnecessary stress to the developer collected without being involved in the formation of the toner image. Thus, a stable toner image can be formed while maintaining the developer performance for a long period of time.

  A first embodiment of the present invention is shown in FIGS. 1-5. FIG. 1 is a schematic configuration diagram of the image forming apparatus, FIG. 2 is a vertical sectional view of the developing device, FIGS. 3 and 4 are front views of the regulating member, and show different operation states, and FIG. It is a graph which shows correlation with the stress added to a developing agent.

  An image forming apparatus 1 shown in FIG. 1 is a printer. The image forming apparatus 1 forms an electrostatic latent image by exposing the charged surface of the photosensitive drum 10 to the photosensitive drum 10 that is an image carrier, the charging device 11 that uniformly charges the surface of the photosensitive drum 10, and the charged surface of the photosensitive drum 10. A transfer nip 14 is formed between the image writing device (laser scanning unit) 12, the developing device 13 that develops the electrostatic latent image on the surface of the photosensitive drum 10 as a toner image, and the photosensitive drum 10. A transfer roller 15 for transferring toner to the output paper, a cleaning device 16 for collecting toner remaining on the surface of the photosensitive drum 10 after toner transfer, a fixing device 17 for fixing the toner transferred to the output paper, and a transfer An output paper storage unit 18 that stores the output paper to be supplied to the nip 14, a paper discharge unit 19 that receives the output paper after toner fixing, and an output paper that is conveyed from the output paper storage unit 18 to the paper discharge unit That includes a transport unit 20, a control unit 21 which controls the whole operation. Conventionally known constituent elements other than the developing device 13 can be used as they are.

  Next, the structure of the developing device 13 will be described with reference to FIG. The structure of the developing device 13 is basically the same as that described in Patent Document 1, and the first stirring screw 31, the second stirring screw 32, and the developing roller 33 are arranged around the horizontal axis in the casing 30. It is pivotally supported. Rotational power is applied to the first stirring screw 31, the second stirring screw 32, and the developing roller 33 from an electric motor (not shown). A part of the developing roller 33 is exposed from the opening 34 of the casing 30 and faces the photosensitive drum 10.

  A regulating member 35 that regulates the layer thickness of the developer carried on the developing roller 33 is disposed on the developing roller 33. The restricting member 35 is obtained by attaching a magnetic or nonmagnetic blade 37 to the shaft 36, and when the shaft 36 is rotated by the electric motor 22, the blade 37 also rotates. The blade 37 forms a regulating gap 38 at a predetermined interval between the blade 37 and the developing roller 33.

  Inside the developing roller 33, five magnetic poles 40a, 40b, 40c, 40d, and 40e for generating a magnetic field outside the developing roller 33 are arranged. These magnetic poles are all composed of permanent magnets, in which the magnetic poles 40a, 40c, and 40d are S poles, and the magnetic poles 40b and 40e are N poles. The magnetic poles 40a, 40b, 40c, 40d, and 40e do not move, and the developing roller 33 rotates around the periphery.

  The image forming apparatus 1 has two types of output paper widths. One type is the width of a vertical A3 size paper, in other words, the width of a horizontal A4 size paper. The other type is the width of a vertical A4 size sheet. Two types of width restricting portions are formed on opposite sides of the blade 37 in the longitudinal direction so as to correspond to the width of the output paper.

  The entire one side of the blade 37 is the first restricting portion K1. The width of the first restricting portion K1 is slightly larger than the width of the vertical A3 sheet.

  The second restricting portion K2 is provided on the side opposite to the first restricting portion K1 so as to protrude from the central portion thereof. The width of the second restricting portion K2 is slightly larger than the width of the vertical A4 sheet. The spacing of the regulating gap 38 is 0.3 to 1 mm, and the protruding amount of the second regulating portion K2 is 0.1 to 0.3 mm.

  The distance from the axial center of the shaft 36 to the first restricting portion K1, in other words, the radius of the first restricting portion K1, and the distance from the axial center of the shaft 36 to the second restricting portion K2, in other words, the second restricting portion. The radii of the portions K2 are the same.

  The operation of the developing device 13 is as follows. As the photosensitive drum 10 rotates, the first stirring screw 31, the second stirring screw 32, and the developing roller 33 also rotate synchronously. The developer is pumped up on the surface of the developing roller 33 by the magnetic field of the magnetic pole 40e which is an N pole. When the developer adhering to the surface of the developing roller 33 reaches the regulation gap 38, the developer stands up like a brush by a magnetic field generated by the magnetic pole 40a which is the S pole. This is a so-called magnetic brush. The height of the magnetic brush is regulated by the blade 37.

  When the magnetic brush that has passed through the regulation gap 38 moves to a position facing the photosensitive drum 10, the magnetic brush contacts the photosensitive drum 10 with a magnetic field by the magnetic pole 42 b that is an N pole, and an electrostatic latent image on the surface of the photosensitive drum 10 is obtained. Developing with toner forms a toner image.

  The developer that has not been used to form the toner image is collected in the developing device 13 by the magnetic pole 42c that is the S pole. Further, the developer is separated from the developing roller 33 by a magnetic field generated by the magnetic pole 42d which is also the S pole. Then, after being stirred and transported by the second stirring screw 32, it adheres to the developing roller 33 again by the magnetic field of the magnetic pole 42e.

  Here, when the width of the output paper is the vertical size of A4, as shown in FIG. 3, the second restricting portion K2 of the blade 37 faces downward and faces the developing roller 33. In this way, among the developer carried on the surface of the developing roller 33, the developer at the location corresponding to the width of the output paper passes through the regular regulation gap 38, and the layer thickness is regulated. However, the developer at the portion protruding from the passage passes through a gap wider than the regulation gap 38, and the stress received is reduced. Therefore, even when the cumulative amount of developer collected without increasing the toner image is increased, the deterioration of the developer is slow, and a stable toner image can be formed while maintaining the developer performance for a long period of time.

  When the width of the output paper is the vertical size of A3 or the horizontal size of A4, the motor 22 is driven to rotate the blade 37 and the blade 37 is turned upside down. When the first restricting portion K1 faces downward as shown in FIG. 4, the thickness of the entire developer carried on the developing roller 33 is restricted by the first restricting portion K1.

  There is a correlation as shown in the graph of FIG. 5 between the gap of the regulation gap and the stress received by the developer. As a measure for stress, the rotational torque of the developing roller was used.

  When the full width of the blade having a width of 315 mm was used as the restricting portion and the restricting gap was 0.55 mm, the rotational torque of the developing roller was measured and found to be 1.3 kgf · cm. When the width of the restriction gap of 0.55 mm was reduced to 225 mm, the restriction gap of the remaining part was increased to 0.7 mm, and the rotational torque of the developing roller was measured, it was 1.0 kgf · cm. The stress reduction rate was about 23%.

  A second embodiment of the present invention is shown in FIGS. 6-8. FIG. 6 is a vertical sectional view of the developing device, and FIGS. 7 and 8 are front views of the regulating member, showing different operating states.

  In the developing device 13 of the second embodiment, a roller 39 is used in place of the blade 37 as a component constituting the regulating member 35. At both end portions of the roller 39, a meat stealing portion 39a is provided in the half of the circumference, and the portion between them is the second restricting portion K2. The place where the meat stealing portion 39a is not provided becomes the first restricting portion K1. Other configurations are the same as those in the first embodiment.

  In the first embodiment, the blade 37 is turned upside down, and in the second embodiment, the roller 39 is turned upside down, and the first restricting portion K1 and the second restricting portion K2 are switched. And the switching means of the 2nd control part K2 is not limited to this. For example, a configuration in which a blade having the width of the first restricting portion K1 and a blade having the width of the second restricting portion K2 are separately prepared and used separately is possible. Further, it is possible to increase the width of the restricting portion so that paper widths other than “A3 portrait” and “A4 portrait” can be handled.

  Although the embodiments of the present invention have been described above, various modifications can be made without departing from the spirit of the invention. For example, a belt may be used as an image carrier instead of a drum.

  The present invention can be widely used in an image forming apparatus in which a two-component developer is attracted to a developing roller by a magnetic field.

Schematic configuration diagram of an image forming apparatus Vertical sectional view of the developing device Front view of restriction member A front view of the regulating member showing an operating state different from FIG. Graph showing the correlation between the gap of the regulation gap and the stress applied to the developer Vertical sectional view of the developing device according to the second embodiment Front view of regulating member according to second embodiment FIG. 7 is a front view of a regulating member according to the second embodiment and shows an operation state different from FIG.

Explanation of symbols

1 Image forming apparatus 10 Photosensitive drum (image carrier)
13 Developing Device 33 Developing Roller 35 Regulating Member 37 Blade 38 Regulating Gap 39 Roller

Claims (3)

In a developing device that supports a developer having magnetism on the surface of a developing roller with a magnetic field, and supplies the image bearing member with a layer thickness of the supported developer by a regulating member facing the developing roller with a predetermined regulating gap therebetween ,
The width of a portion of the regulating member that forms the regulating gap between the developing roller and the developing roller can be changed according to the width of the output paper onto which the toner in the developer is transferred. Developing device. The width of the part which forms the said control gap between developing rollers differs according to the rotation angle, The said control member can be rotated to the surroundings of an axis line parallel to the said developing roller, The width | variety of the part which forms the said control gap differs between development rollers. The developing device described. An image forming apparatus comprising the developing device according to claim 1.

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