JP2005077540A - 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. 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. The magnetized pattern in the axial direction of the fixed magnet roll has a strong magnetic force part in which the magnetic force is stronger in a range specified beforehand than in other parts excluding the both end parts. <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.
Even when trying to prevent overcharging, it is extremely difficult to apply the metal soap uniformly. If the thickness of the metal soap partially varies (if it is not uniform), the charged state of the toner varies, and again the rotation sleeve There is a problem that it is impossible to prevent the toner from being overcharged at both ends in the longitudinal direction.

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, wherein the axial magnetized pattern of the fixed magnet roller is an axis of the fixed magnet roller. It has a high magnetic force part having higher magnetic force than other parts at both ends in the direction.

  In the present invention, the inner end in the axial direction of the high magnetic force portion is a predetermined distance from the end in the width direction of the maximum size recording medium among the recording media onto which the developed image on the image carrier is transferred. For example, the maximum magnetic force of the high magnetic force portion is more than 5% and less than 15% higher than the magnetic force of the other portion.

  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 desirable that it is positioned downstream of the line segment in the rotational direction.

  The axial length of the magnetized pattern is shorter than the axial length of the fixed magnet roller by a predetermined distance, and the axial length of the magnetized pattern is smaller than the width of the maximum size recording medium. long.

  As described above, in the developing device of the present invention, the axial magnetized pattern of the fixed magnet roller has high magnetic force portions having higher magnetic force than the other portions at both ends in the axial direction of the fixed magnet roller. As a result of concentration of magnetic force at both ends of the thickness regulating member, the developer layer on the rotating sleeve passes through the gap between the thickness regulating member and the rotating sleeve and is conveyed to the image carrier side at both ends of the layer thickness regulating member. As a result, the amount of generated toner is reduced, and the magnetic toner is smoothly exchanged at both ends of the layer thickness regulating member, thereby preventing overcharging of the developer at both ends of the layer thickness regulating member with a simple configuration. The developer thin layer can be formed uniformly.

  In the present invention, since the inner end in the axial direction of the high magnetic force portion is located inside the end in the width direction of the recording medium of the maximum size among the recording media onto which the developed image on the image carrier is transferred, image formation In this case, there is no problem such as image fogging on the recording medium.

  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, and an S pole (blade pole S <b> 1) in the vicinity of the toner layer thickness regulating member (for example, magnetic blade) 24. The N pole (developing pole N1) is disposed at a position facing the photosensitive drum 11, and the S pole (S2) is located downstream of the developing pole N1 in the rotation direction of the rotating sleeve 23a (shown by a solid arrow in FIG. 1). , N pole (N2) is magnetized downstream of S2. As described above, the toner layer thickness regulating member 24 is disposed to face the rotating sleeve 23a (developing roller 23).

  Here, referring to FIG. 4, FIG. 4 is a diagram showing an example of the axial magnetic force (magnetic field) intensity distribution (magnetization pattern) of the fixed magnet 23b in the developing roller 23. Now, the axial direction of the fixed magnet 23b is shown in FIG. When the length (magnet width) is L, the effective magnetization width (development width: image forming area) P of the fixed magnet roller 23b is shorter than the magnet width L. As shown in the figure, the axial magnetic field strength distribution B by the developing roller 23 suddenly rises from both ends of the fixed magnet 23b, and is almost flat thereafter, and the magnetization of the fixed magnet 23b is the axis shown in FIG. This is performed so as to obtain a direction magnetization distribution. The end portion of the effective magnetization width P is defined from the position where the axial magnetic field strength distribution becomes substantially flat.

  However, as shown in FIG. 4, when the axial magnetic field strength distribution B is defined, the axial magnetic field strength distribution B is flat (flat) over the entire effective magnetization width P. It is impossible to prevent the toner from being overcharged by friction at both ends in the longitudinal direction (axial direction). As a result, toner retention (aggregation) occurs, and the toner thin layer is formed at both ends of the rotating sleeve 23a. Will be disturbed and image fogging will occur during development.

  Here, in order to prevent the toner from being overcharged at both ends in the longitudinal direction of the rotating sleeve 23a as described above, an axial magnetic field strength distribution B 'is defined as shown in FIG. FIG. 5 shows the axial magnetic field strength distribution B ′ and 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 (effective magnetization width) in the developing roller 23. 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. As shown in the figure, the axial magnetic field strength distribution B 'rises rapidly from both ends of the fixed magnet 23b and reaches its maximum, and then gradually decreases and becomes flat.

  The axial magnetic field strength distribution B ′ is maximum between the end portion of the developing width P and the end portion of the maximum sheet passing width Q, and the end portion of the maximum sheet passing width Q is the axial direction magnetic field strength distribution B ′. Is positioned outside the flat state (that is, the end portion of the maximum sheet passing width Q is positioned between the position where the axial magnetic field strength distribution B ′ is flat and the maximum value). Is).

  In other words, the position where the axial magnetic field strength distribution B ′ is flat is represented by “e”, and the distance from the end of the development width P to the position “e” is represented by c (mm). The distance d (mm) from the end to the position “e” is equal to or less than the distance c, and the end of the maximum sheet passing width Q is positioned between the position “e” and the end of the developing width P. The distance c is, for example, 20 mm. Now, the magnetic force at the central portion of the axial magnetic field strength distribution B ′ (that is, the axial central portion of the fixed magnet 23b) is a (mT), and the maximum value of the magnetic force is b ( mT), the maximum value of the magnetic force in the range of the distance c is positioned in the range of 5 <{(ba) / a} × 100 <15 (%). In other words, the magnetic field strength distribution B 'in the axial direction has a magnetic force at both ends exceeding 5% and less than 15% than the central portion (a portion where the magnetic field strength distribution is flat).

  As described above, when the axial magnetic field strength distribution (magnetization pattern) of the fixed magnet 23b is defined, the other part of the tip of the toner layer thickness regulating member 24 (on the both sides of the tip of the toner layer thickness regulating member 24) The magnetic field strength is different from that of the main body tip, and the number of lines of magnetic force generated between the toner layer thickness regulating member 24 and the rotating sleeve 23a (that is, the developing roller 23) at the main body tip (that is, the developing roller 23). (Magnetic flux density: see FIG. 6A) is the number of lines of magnetic force generated between the toner layer thickness regulating member 24 and the developing roller 23 on both sides of the tip of the toner layer thickness regulating member 24 (magnetic flux density: FIG. 6B). Smaller than reference). That is, the magnetic flux density becomes high on both sides of the front end portion of the toner layer thickness regulating member 24.

  As a result, the lines of magnetic force are concentrated on both sides of the front end portion of the toner layer thickness regulating member 24, and the toner layer thickness is formed on both sides of the toner layer thickness regulating member 24 in the longitudinal direction (axial direction of the developing roller 23). The magnetic binding force of the magnetic toner is stronger between the regulating member 24 and the rotating sleeve 23a than the other part (the front end part of the main body).

  As a result, at both ends of the toner layer thickness regulating member 24, the toner layer on the rotating sleeve 23a passes through the gap between the toner layer thickness regulating member 24 and the rotating sleeve 23a and is conveyed to the photosensitive drum 11 side. The amount is reduced (see FIG. 7), and the magnetic toner is smoothly exchanged at both ends of the toner layer thickness regulating member 24, so that the magnetic toner is overcharged at both ends of the toner layer thickness regulating member 24. The toner thin layer can be formed uniformly. 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.

  According to an experiment, when the magnetic force in the range of the distance c is 5% or less higher than the magnetic force in the center portion, overcharging of the magnetic toner is prevented at both ends of the toner layer thickness regulating member 24. On the other hand, if it is 15% or more, the amount of magnetic toner drawn up increases, and the magnetic toner hardly moves on the back side of the toner layer thickness regulating member 24 (downstream in the rotation direction of the rotation sleeve 23a). It was found that the toner charge amount becomes unstable.

  Referring now to FIG. 8, FIG. 8 shows a magnetic field distribution (vertical direction) formed by the developing roller 23, and an extension of the upstream side surface of the toner layer thickness regulating member 24 in the rotational direction (shown by a solid line arrow). When a line is indicated by R and a line segment connecting the maximum value of the magnetic field formed by the blade magnetic pole S1 and the central axis of the developing roller 23 is indicated by S, the angle α defined by the extension line R and the line segment S is It is set in a range of 3 ° to 10 ° (preferably, set to 8 °. See also FIGS. 6A and 6B).

  That is, the side surface of the toner layer thickness regulating member 24 located upstream in the rotation direction of the rotation sleeve 23 a is a line segment connecting the maximum magnetic field strength by the magnetic pole S 1 corresponding to the toner layer thickness regulating member 24 and the central axis of the developing roller 23. It is located on the downstream side in the rotational direction. When the angle α is set in this way, the magnetic lines of force generated between the developing roller 23 and the toner layer thickness regulating member 24 swell to the upstream side in the rotation direction of the developing roller 23, and the toner layer thickness regulating member 24 causes the magnetic toner. The toner thin layer can be made more uniform.

  Incidentally, as shown in FIG. 4, the axial magnetic field distribution B is defined, the magnetic force in the flat part is changed, and the layer thickness of the toner thin layer after passing through the toner layer thickness regulating member 24 is measured. The results shown in (1) were obtained. In FIG. 9, the gap between the toner layer thickness regulating member 24 and the developing roller 23 is 0.3 mm, and the angle α is 5 °.

As shown in FIG. 9, when the magnetic force (ear-cutting magnetic force) in the axial magnetic field distribution B is increased, the layer thickness is reduced. For example, the ear-cutting magnetic force is 850 G, 900 G, 1000 G (1G = 10 ⁻⁴ T). And the layer thicknesses become 130 μm, 100 μm, and 80 μm, respectively. That is, if the axial magnetic force is increased over the entire fixed magnet 23b, the toner thin layer becomes thin and cannot cope with the change in image density (the margin is reduced).

  On the other hand, as described with reference to FIG. 5, if the axial magnetic field distribution B ′ is defined, overcharging of the magnetic toner at both ends of the magnetic blade can be prevented, and portions excluding both ends of the axial magnetic field distribution B ′ ( Since it is not necessary to increase the magnetic force of the central portion), the thickness of the toner thin layer is not reduced and the margin can be increased.

  In a developing device using a magnetic one-component developer, the axial magnetized pattern of the fixed magnet roller 23b has a magnetic force within a predetermined range at both ends in the axial direction of the fixed magnet roller 23b than other portions excluding the both ends. Therefore, the magnetic force is concentrated on both ends of the toner layer thickness regulating member 24, and the toner layer on the rotating sleeve 23a is formed at both ends of the toner layer thickness regulating member 24. The amount transported to the photosensitive drum 11 side through the gap between the toner layer thickness regulating member 24 and the rotating sleeve 23a is reduced, and the magnetic toner is smoothly exchanged at both ends of the toner layer thickness regulating member 24. It will be. As a result, toner can be prevented from being overcharged at both ends of the toner layer thickness regulating member 24 with a simple configuration, and a thin toner layer can be formed uniformly. An electrophotographic apparatus such as a copying machine, a printer, or a facsimile machine can be used. The present invention can be applied to prevention of image defects in an image forming apparatus using a process. 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 example of the axial direction magnetization pattern (magnetic field strength distribution) of a fixed magnet roller. It is a figure which shows the axial direction magnetization pattern (magnetic field strength distribution) of the fixed magnet roller used in Example 1 of the developing device according to the present invention. 2A and 2B are diagrams illustrating magnetic lines of force between the magnetic blade and the developing roller, in which FIG. 1A is a cross-sectional view illustrating magnetic lines of force at a central portion of the magnetic blade, and FIG. 2B is a cross-sectional view illustrating magnetic lines of force at both ends of the magnetic blade; FIG. 3 is a cross-sectional view conceptually illustrating toner regulation at both ends of a magnetic blade in the first embodiment of the developing device according to the present invention. It is a figure which shows the angle relationship between a magnetic blade and the largest magnetic field strength in Example 1 of the developing device by this invention. FIG. 5 is a diagram showing a change in the thickness of the toner thin layer when the magnetic force is changed in the magnetization pattern shown in FIG. 4.

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 (magnetic blade)
23a Rotating sleeve 23b Fixed magnet roller

Claims (5)

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; And a layer thickness regulating member that regulates the thickness of the magnetic one-component developer layer formed on the rotating sleeve so as to face the rotating sleeve, thereby forming a developer thin layer. In a developing device that develops an electrostatic latent image with the developer thin layer to form a developed image,
2. The developing device according to claim 1, wherein the axial magnetized pattern of the fixed magnet roller has high magnetic force portions having a higher magnetic force than other portions at both ends in the axial direction of the fixed magnet roller.   The axially inner end of the high magnetic force portion is positioned inside a predetermined distance from the widthwise end portion of the maximum size recording medium of the recording medium onto which the developed image on the image carrier is transferred. The developing device according to claim 1, wherein   3. The developing device according to claim 2, wherein the maximum magnetic force of the high magnetic force part is more than 5% and less than 15% higher than the magnetic force of the other part.   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.   The axial length of the magnetized pattern is shorter than the axial length of the fixed magnet roller by a predetermined distance, and the axial length of the magnetized pattern is longer than the width of the maximum size recording medium. The developing device according to claim 1, wherein:

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