JP2005077538A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a uniform thin toner layer by preventing excessive electrification and flocculation of toner in both end parts in the longitudinal direction of a rotating sleeve in a simple constitution in a developing device using magnetic one component developer (magnetic toner). <P>SOLUTION: A developing roll 23 is provided with a fixed magnet roll 23b on which a plurality of magnetic poles are formed along the circumferential direction, and the rotating sleeve 23a including the fixed magnet roll inside. The thickness of the magnetic toner formed on the rotating sleeve is restricted and made into the thin toner layer by a magnetic blade 24a extended in the axial direction of the developing roll, facing the rotating sleeve. On the surface side part of the magnetic blade facing the rotating sleeve, magnetic force concentrated parts (thin wall part) 241 to concentrate the magnetic force between the magnetic blade and the developing roll are formed on both end part sides of the magnetic blade in the axial direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device for developing an electrostatic latent image formed on an image carrier using a magnetic one-component developer (magnetic toner).

  In general, in a developing device using a magnetic one-component developer (magnetic toner (hereinafter simply referred to as toner)), a developing roller includes a fixed magnet roller having a plurality of magnetic poles magnetized and a rotating sleeve including the magnet roller. And a magnetic blade that is a toner layer thickness regulating member is provided to face the developing roller. The toner is charged to a predetermined polarity by friction with the rotating sleeve, and the charged toner adheres to the rotating sleeve and is conveyed as a toner layer.

  When the toner layer formed on the rotating sleeve passes through the magnetic blade, the toner close to the magnetic blade is caught by the magnetic blade, and the toner close to the rotating sleeve is attracted to the rotating sleeve by the magnetic attraction force. It goes to the photosensitive drum as an image carrier as a layer. Then, the toner thin layer that has reached the position (development position) facing the photosensitive drum flies to the electrostatic latent image formed on the photosensitive drum, and the electrostatic latent image is developed, A toner image is formed.

  In such a developing device, in order to uniformly form a toner thin layer (toner layer after toner layer thickness regulation), a toner layer thickness regulation member includes a magnetic blade and a magnet attached upstream in the rotational direction of the rotating sleeve. In addition, there is a magnetic blade in which a portion facing the rotating sleeve is formed in a thin edge shape (see Patent Document 1).

  On the other hand, in the image formation area (development area on the photosensitive drum), the toner consumption in this area is small because image formation is rarely performed near both ends in the longitudinal direction. For this reason, the toner is overcharged by friction at both end portions in the longitudinal direction of the rotating sleeve, and this often causes toner retention (aggregation) and disturbs the toner thin layer. A fog will occur. That is, if the thickness of the toner thin layer is disturbed and the toner thin layer becomes thick at both ends in the longitudinal direction of the rotating sleeve, the toner is likely to fly to the non-image forming area, and image fogging occurs. In particular, in a low humidity environment, triboelectric charges are likely to accumulate in the toner particles, and image fogging is likely to occur.

  In order to prevent such problems, metal soap is applied to the surface of the rotating sleeve corresponding to the sheet passing area of the photosensitive drum from the both ends of the maximum sheet passing size to the inside of the predetermined distance, and both ends of the rotating sleeve are In some cases, the toner is prevented from being overcharged to prevent image fogging (see Patent Document 2).

JP 2003-167426 A (paragraph (0041) to paragraph (0048), FIGS. 3 to 4) JP 2003-162143 A (paragraph (0036) to paragraph (0043), FIG. 6)

  In the developing device described in Patent Document 1, the magnetic blade facing the rotating sleeve is formed into a thin edge shape, the magnetic force is concentrated, and a strong magnetic force is generated between the blade tip (thin edge portion) and the rotating sleeve. The toner thin layer is not disturbed between the magnetic blade and the rotating sleeve, and a uniform toner thin layer having no roughness can be formed. However, even in this developing device, a special use, for example, a print output in which no image exists on both ends of the rotating sleeve is continuously repeated, or a high-speed image having a printing (copying) speed of 60 sheets or more per minute. When used in a forming apparatus and subjected to an extremely large amount of development processing exceeding 500,000 times, the toner may be overcharged due to friction at both ends in the longitudinal direction of the rotating sleeve. As a result, toner retention (aggregation) occurs, the toner thin layer is disturbed at both ends of the rotating sleeve, and there is a problem for further performance improvement that image fogging occurs during development.

On the other hand, the developing device described in Patent Document 2 solves toner aggregation that occurs at both ends in the longitudinal direction of a blade as a toner regulating plate when toner is newly supplied to a new developing device that is not used. For this reason, metal soap is applied to the surface extending from the both ends of the maximum sheet passing size to the inside by a predetermined distance to prevent toner aggregation at both ends of the rotating sleeve. Further, this Patent Document 2 also describes the phenomenon of toner charge accumulation in the agglomerated portion described above in a low humidity environment.
However, the above-mentioned Patent Document 2 is intended for the countermeasure against initial failure of a new developing device in an unused state, and is intended for permanent solution by applying metal soap, and also for application to a high-speed machine or a long-life machine. Because it is not a thing, it is necessary to seek a further solution depending on the intended use.

Accordingly, the present invention provides a developing device capable of forming a uniform toner thin layer by preventing overcharging and aggregation of toner at both ends in the longitudinal direction of the rotating sleeve with a simple configuration in view of the problems of the prior art. The purpose is to do.
It is another object of the present invention to provide a developing device that is permanently effective in forming a uniform toner thin layer even for high-speed machines and long-life image forming apparatuses.

  Therefore, in order to solve such a problem, the present invention has a fixed magnet roller in which a magnetic one-component developer is used and a plurality of magnetic poles are formed along the circumferential direction, and a rotating sleeve that encloses the fixed magnet roller. A developing roller, a layer thickness regulating member that extends in the axial direction of the developing roller and faces the rotating sleeve to regulate the thickness of the magnetic one-component developer layer formed on the rotating sleeve to form a developer thin layer; A developing device that develops the electrostatic latent image formed on the image carrier with the developer thin layer to form a developed image, on the side of the layer thickness regulating member facing the rotating sleeve, A magnetic force concentrating portion for concentrating the magnetic force between the developing roller and the developing roller is formed on both end portions in the axial direction of the layer thickness regulating member.

  For example, the magnetic force concentrating portion is formed at both axial end portions of the layer thickness regulating member, and the axial inner end of the magnetic force concentrating portion is a recording medium on which a developed image on the image carrier is transferred. It is desirable to be located inside the widthwise end of the maximum size recording medium.

  Further, in the present invention, the side surface of the layer thickness regulating member located upstream in the rotation direction of the rotating sleeve is connected to the maximum magnetic field strength by the magnetic pole corresponding to the layer thickness regulating member and the central axis of the developing roller. It is preferable that it is positioned downstream of the line segment in the rotational direction.

  Further, in the present invention, a thin portion that is thinner than other portions of the layer thickness regulating member is formed at both axial end portions of the layer thickness regulating member, and the thin portion functions as the magnetic force concentration portion. Alternatively, acute edge edge portions may be formed at both axial end portions of the layer thickness regulating member so that the edge end portions function as the magnetic force concentration portions.

  As described above, in the developing device of the present invention, the magnetic force between the developing roller and the developing roller is concentrated on both sides of the layer thickness regulating member in the axial direction on the side facing the rotating sleeve of the layer thickness regulating member. Therefore, at both ends of the layer thickness regulating member, the developer layer on the rotating sleeve passes through the gap between the layer thickness regulating member and the rotating sleeve and is transported to the image carrier side, and the layer thickness regulating member is reduced. Since the magnetic toner is smoothly exchanged at both ends of the member, the developer can be prevented from being overcharged at both ends of the layer thickness regulating member with a simple configuration, and the developer thin layer is uniformly formed. be able to.

  In the present invention, the magnetic force concentrating portions are formed at both end portions in the axial direction of the layer thickness regulating member, and the inner end in the axial direction of the magnetic force concentrating portion is the maximum size of the recording medium on which the development image on the image carrier is transferred. Since it is located inside the end in the width direction of the medium, problems such as image fog do not occur on the recording medium during image formation.

  Furthermore, in the present invention, the side surface of the layer thickness regulating member located upstream in the rotation direction of the rotating sleeve is rotated more than the line segment connecting the maximum magnetic field strength by the magnetic pole corresponding to the layer thickness regulating member and the central axis of the developing roller. Since it is positioned on the downstream side in the direction, the developer can be effectively restrained by the layer thickness regulating member, so that the developer thin layer can be made more uniform.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, the developing device 10 shown is used in an image forming apparatus (experimental machine) such as a copying machine using an electrophotographic process assuming 80 sheets per minute (A4 lateral feed). After the surface of the photoconductor drum 11 (a-Si photoconductor) as an image carrier is uniformly charged by the charger 12, the surface of the photoconductor drum 11 is exposed according to the image data, and the surface of the photoconductor drum 11 is exposed. An electrostatic latent image is formed. The developing device 10 develops the electrostatic latent image on the photosensitive drum 11 with a magnetic one-component developer (magnetic toner) to form a toner image on the photosensitive drum 11.

  Then, the toner image on the photosensitive drum 11 is transferred to a recording sheet (not shown) by the transfer belt 13, the recording sheet is sent to a fixing unit (not shown), and the toner image transferred to the recording sheet is fixed. After that, the recording sheet is discharged to a discharge tray (not shown). The residual toner remaining on the photosensitive drum 11 is cleaned by the cleaning mechanism 14 and discarded in a waste toner container (not shown). The photosensitive drum 11 is neutralized by a static eliminator 15.

  2 and 3, the developing device 10 has a developing case 20 in which magnetic toner is accommodated, and the first and second stirring screws 21 and 22 are rotatable in the developing case 20. It is arranged. Then, the magnetic toner is conveyed to the developing roller 23 side while being agitated by the rotation of the first and second agitating screws 21 and 22.

  As shown in FIGS. 1 and 3, a toner layer thickness regulating member 24 is attached to the developing case 20, and the tip of the toner layer thickness regulating member 24 faces the surface of the developing roller 23 with a predetermined gap. The toner layer thickness regulating member 24 defines a toner thin layer on the developing roller 23 as described later. The developing roller 23 is disposed with a predetermined gap (gap) from the photosensitive drum 11. When the developing roller 23 reaches the developing position, the toner flies from the thin toner layer on the developing roller 23 toward the photosensitive drum 11, The electrostatic latent image on the photosensitive drum 11 is developed, and a toner image is formed on the photosensitive drum 11.

  The developing roller 23 includes a cylindrical rotating sleeve 23a made of a nonmagnetic material such as aluminum, and a fixed magnet roller (hereinafter simply referred to as a fixed magnet) 23b included in the rotating sleeve 23a. Is rotatably attached to the developing housing 20. Then, with the fixed magnet 23b fixed, the rotating sleeve 23a rotates around the fixed magnet 23b.

  In the example shown in FIG. 1, the fixed magnet 23 b is magnetized with four poles along the circumferential direction thereof, and the S pole (blade pole S 1), the photosensitive drum 11, An N pole (development pole N1) is arranged at an opposite position, and the S pole (S2) is located downstream of the development pole N1 in the rotation direction of the rotation sleeve 23a (indicated by a solid arrow in FIG. 1), and downstream of S2. The N pole (N2) is magnetized. As described above, the toner layer thickness regulating member 24 is disposed to face the rotating sleeve 23a (developing roller 23), and the toner layer thickness regulating member 24 has a magnetic blade 24a and a magnet 24b, and the magnet 24b. Is attached to the side surface of the magnetic blade 24a upstream of the magnetic blade 24a in the rotational direction of the rotary sleeve 23a (in the illustrated example, the magnet 24b is magnetized to the south pole on the rotary sleeve 23a side). The magnet 24b is not essential, and is omitted as necessary (the magnet 24b is not shown in FIG. 3).

  Referring to FIG. 4, FIG. 4 (a) is a diagram showing the magnetic blade 24a from the front, and FIG. 4 (b) is a diagram showing the magnetic blade 24a from the lower side (tip side). The magnetic blade 24a is a magnetic plate-like member (for example, magnetic stainless steel, specifically SUS430, etc.), and as shown in FIG. 4A, the lower side of the magnetic blade 24a (the side facing the developing roller 23). : Tip portion), the magnetic blade 24a is formed with thin portions 241 at the corners of both ends.

  As shown in FIGS. 4A and 4B, the thin portion 241 includes a thin plate portion 242 defined (formed) at both corners of the lower side portion of the magnetic blade 24a, and a slope continuous with the thin plate portion 242. As described above, the magnetic blade 24a is spaced apart from the rotating sleeve 23a by a predetermined distance (for example, 0.2 to 0.4 mm), for example, in the axial direction of the rotating sleeve 23a. It extends in parallel. When the thickness of the magnetic blade 24a is set to 2.0 mm, for example, the thickness of the thin plate portion 242 is set to 0.5 mm or more and 1.0 mm or less.

  Here, referring to FIG. 5, as described above, when the thin portions 241 are formed at both corners of the lower side portion of the magnetic blade 24a, on the both sides of the tip portion of the magnetic blade 24a, other than the tip portion of the magnetic blade 24a. As a result, the number of lines of magnetic force (that is, magnetic flux) generated between the magnetic blade 24a and the rotating sleeve 23a (that is, the developing roller 23) is reduced at the tip of the body. The density (see FIG. 5A) is smaller than the number of magnetic lines of force generated between the magnetic blade 24a and the developing roller 23 in the thin portion 241 (magnetic flux density: see FIG. 5B). That is, the magnetic flux density increases on both sides of the tip of the magnetic blade 24a.

  As a result, the magnetic lines of force are concentrated on both sides of the tip of the magnetic blade 24a, and the magnetic blade 24a and the rotating sleeve 23a are formed on both sides of the magnetic blade 24a in the longitudinal direction (axial direction of the developing roller 23). In the meantime, the magnetic binding force of the magnetic toner becomes stronger than the other part of the tip (the tip of the main body). As a result, at both ends of the magnetic blade 24a, the amount of the toner layer on the rotating sleeve 23a passing through the gap between the magnetic blade 24a and the rotating sleeve 23a and transported to the photosensitive drum 11 side is reduced (FIG. 6), the magnetic toner is smoothly exchanged at both ends of the magnetic blade 24a, so that overcharging of the magnetic toner at both ends of the magnetic blade 24a can be prevented, and a thin toner layer can be formed uniformly. Can do. This effect can be maintained even when copying 500,000 sheets while replenishing magnetic toner, and is also effective in a high-speed and long-life image forming apparatus.

  Here, referring to FIG. 7, FIG. 7 shows the magnetic blade 24a and the developing roller 23, the maximum sheet passing width (the maximum recording sheet width used in the image forming apparatus in which the developing device 10 is used), and the developing width. FIG. 6 is a diagram showing a relationship with (image forming area). The axial length (magnet width) L of the fixed magnet 23b is slightly longer than the developing width P, and the maximum sheet passing width Q is shorter than the developing width P. The axial length of the thin portion 241 is set such that the axial inner end of the thin portion 241 is positioned on the inner side from the axial end of the magnetic blade 24a to the end of the maximum sheet passing width Q. As a result, the magnetic flux density B along the axial direction of the developing roller 23 becomes maximum near the end portion of the maximum sheet passing width Q, and then gradually decreases to the inner end of the thin portion 241, and then is substantially flat. It becomes.

  When the axial length of the thin portion 241 is defined in this way, the toner thin layer corresponding to the end in the width direction of the recording paper becomes uniform when image formation is performed on the recording paper having the maximum sheet passing width. No image fogging occurs for the paper size.

  Referring now to FIG. 8, FIG. 8 shows the magnetic field distribution formed by the developing roller 23, the extension line of the upstream side surface of the magnetic blade 24a in the rotational direction (indicated by the solid line arrow) is indicated by R, and the blade When the line segment connecting the maximum value of the magnetic field formed by the magnetic pole S1 and the central axis of the developing roller 23 is denoted by S, the angle α defined by the extension line R and the line segment S is 3 ° to 10 °. Set to a range (preferably set to 8 °).

  That is, the side surface of the magnetic blade 24a located on the upstream side in the rotation direction of the rotation sleeve 23a is downstream in the rotation direction with respect to the line segment connecting the maximum magnetic field strength by the magnetic pole corresponding to the magnetic blade 24a and the central axis of the developing roller 23. Will be located.

  When the angle α is set in this way, the magnetic lines of force generated between the developing roller 23 and the magnetic blade 24a swell to the upstream side in the rotation direction of the developing roller 23, and the magnetic toner can be restrained favorably by the magnetic blade 24a. The toner thin layer can be made more uniform.

  In the above example, the example in which the thin portion 241 includes the thin plate portion 242 and the inclined surface 243 has been described. However, the shape of the thin portion 241 is not limited to the above example, and various shapes can be adopted. That is, both end portions of the tip end of the magnetic blade 24a may be made thinner than the other portions so that the magnetic flux density at both end portions of the magnetic blade 24a is increased. May be an edge portion of an acute angle shape (for example, a wedge shape), and the magnetic flux density at both ends of the tip of the magnetic blade 24a may be increased. Further, a magnet may be attached to both ends of the magnetic blade 24a so as to increase the magnetic flux density at both ends of the magnetic blade 24a. In any case, a magnetic force concentrating portion for concentrating the magnetic force may be formed at both ends of the tip of the magnetic blade 24a.

  In a developing device using a magnetic one-component developer, the magnetic force between the developing roller 23 is applied to the side of the layer thickness regulating member (magnetic blade) 24a facing the rotating sleeve 23a and to both ends in the axial direction of the magnetic blade 24a. Since the magnetic force concentrating portion for concentrating is formed, the toner layer on the rotating sleeve passes through the gap between the magnetic blade 24a and the rotating sleeve 23a at both ends of the magnetic blade 24a, and the photosensitive drum 11 side. The amount of toner transferred to the both ends of the magnetic blade 24a is reduced, and the magnetic toner is smoothly exchanged at both ends of the magnetic blade 24a. With a simple configuration, overcharging of the toner at both ends of the magnetic blade 24a can be prevented, As a result of being able to form a thin toner layer uniformly, an electrophotographic process such as a copying machine, a printer, or a facsimile machine is used. It can be applied to prevent image defects in the image forming apparatus. In particular, it is effective as a developing device having a long life even when employed in a high-speed machine of 80 sheets per minute (A4 lateral feed).

1 is a diagram illustrating a developing device according to a first embodiment of the present invention together with a photosensitive drum. FIG. It is a figure which shows the developing roller used in Example 1 of the developing device by this invention from upper direction with a stirring screw. It is sectional drawing which shows the relationship between a developing roller and a magnetic blade. It is a figure which shows the magnetic blade used in Example 1 of the image development apparatus by this invention, (a) is a figure shown from the front, (b) is a figure shown from the lower side (front end side). It is a figure which shows the magnetic force line between the magnetic blade and developing roller shown in FIG. 4, (a) is sectional drawing which shows the magnetic force line in the center part of a magnetic blade, (b) is a cross section which shows the magnetic force line in the both ends of a magnetic blade FIG. FIG. 5 is a cross-sectional view conceptually showing toner regulation at both ends when the magnetic blade shown in FIG. 4 is used. FIG. 5 is a diagram for explaining a relationship between a thin portion of the magnetic blade shown in FIG. 4 and a maximum sheet passing width. FIG. 5 is a diagram showing an angular relationship between the magnetic blade shown in FIG. 4 and the maximum magnetic field strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing device 11 Photoconductor drum 12 Charger 13 Transfer belt 14 Cleaning mechanism 21, 22 Agitating screw 23 Developing roller 24 Toner layer thickness regulating member 23a Rotating sleeve 23b Fixed magnet roller 24a Magnetic blade 241 Thin portion

Claims (6)

A magnetic one-component developer is used, a developing roller having a fixed magnet roller having a plurality of magnetic poles formed along the circumferential direction, a rotating sleeve containing the fixed magnet roller, and extending in the axial direction of the developing roller; A layer thickness regulating member that faces the rotating sleeve and regulates the thickness of the magnetic one-component developer layer formed on the rotating sleeve to form a developer thin layer, and is formed on an image carrier. In a developing device that develops a latent image with the developer thin layer to form a developed image,
A magnetic force concentrating portion for concentrating the magnetic force between the developing roller and the developing roller is formed on the side of the layer thickness regulating member facing the rotating sleeve. A developing device.   The developing device according to claim 2, wherein the magnetic force concentration portion is formed at both axial end portions of the layer thickness regulating member.   The magnetic force concentrating portion extends in the axial direction of the developing roller, and the inner end in the axial direction of the magnetic force concentrating portion is the width of the maximum recording medium among the recording media onto which the developed image on the image carrier is transferred. The developing device according to claim 2, wherein the developing device is located on an inner side than a direction end portion.   The side surface of the layer thickness regulating member located upstream in the rotation direction of the rotating sleeve is rotated more than the line segment connecting the maximum magnetic field strength by the magnetic pole corresponding to the layer thickness regulating member and the central axis of the developing roller. The developing device according to claim 1, wherein the developing device is located downstream in the direction. Thin portions that are thinner than other portions of the layer thickness regulating member are formed at both axial ends of the layer thickness regulating member,
2. The developing device according to claim 1, wherein the thin portion functions as the magnetic force concentration portion. At both ends in the axial direction of the layer thickness regulating member, an acute-angled edge end is formed,
2. The developing device according to claim 1, wherein the edge end portion functions as the magnetic force concentration portion.

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