JP2001312141A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a superior image where roughness is good, a void in a back end is prevented and a horizontal line is sufficiently reproduced. SOLUTION: In the image forming device where a magnetic brush is formed on a developer carrier and a latent image is visualized by having developer slid against a latent image carrier 1 and where the developer carrier 41 is constituted from a non magnetic sleeve 43 and a magnetic roller 44 that is installed fixed inside the sleeve, attenuation factor of the density of magnetic flux in a normal line direction of a main magnetic pole of the magnetic roller is more than 40% and the ratio of the distance between the latent image carrier and the developer carrier in a developing nip boundary to the closest distance between the latent image carrier and the developer carrier is less than 1.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus in which a developer is started up in a so-called developing area on the surface of a developer carrying member to perform a developing process.

[0002]

2. Description of the Related Art Generally, in an electrophotographic or electrostatic recording type image forming apparatus such as a copying machine, a printer, and a facsimile, a latent image carrier (hereinafter, referred to as an image carrier) including a photosensitive drum and a photosensitive belt. An electrostatic latent image corresponding to the image data is formed thereon, a developing operation is performed by a developing device, and a visible image is obtained. In performing the developing operation in this manner, transferability,
From the viewpoint of reproducibility of halftone and stability of development characteristics with respect to temperature and humidity, a magnetic brush development system using a two-component developer composed of a toner and a carrier has become mainstream. That is, in the developing device, the two-component developer causes brush chains on the developer carrier, and supplies the toner in the developer to the latent image portion on the latent image carrier in the developing area. . Here, the development area is a range where the magnetic brush rises on the developer carrier and is in contact with the latent image carrier.

The developer carrier is usually a sleeve (developing sleeve) formed in a cylindrical shape, and a magnet body (magnet roller) for forming a magnetic field so as to cause the developer to stand on the surface of the sleeve. Is provided inside the sleeve. When the ears are raised, the carrier is raised on the sleeve along the lines of magnetic force generated by the magnet roller, and the charged toner adheres to the carrier related to the raised ears. The magnet roller has a plurality of magnetic poles, and the magnets forming the respective magnetic poles are formed in a rod shape or the like. In particular, a developing main magnetic pole for starting up the developer is provided in the developing region on the sleeve surface. When at least one of the sleeve and the magnet roller moves, the developer that has raised ears on the sleeve surface moves. The developer conveyed to the developing area raises ears along the lines of magnetic force generated from the main developing magnetic pole, and the chain of the developer contacts the surface of the latent image carrier so as to bend. Performs toner supply (development) while rubbing against the electrostatic latent image based on the relative linear velocity difference from the latent image carrier.

[0004]

By increasing the distance or interval (hereinafter referred to as a developing gap) between the developer carrier and the closest contact point of the latent image carrier, the latent image carrier is rubbed by a magnetic brush. Since the force is reduced, a so-called trailing edge white spot phenomenon is unlikely to occur, and the reproducibility of the horizontal line is improved.
On the other hand, the so-called "edge effect" in which the amount of toner adhering to the edge of the latent image increases, the isolated point is unnecessarily developed, the line becomes thicker, and the solid area and the halftone area are emphasized. Further, an edge emphasis phenomenon in which the outside of the image becomes whiter becomes more noticeable. As a result, control of gradation reproduction becomes complicated.

On the other hand, when the developing gap is reduced, the edge effect at the time of development is reduced, and an image with less graininess can be obtained. However, the rubbing force of the magnetic brush is increased, and the effect of the reverse charge on the carrier is superimposed on it, resulting in trailing white spots and poor horizontal line reproducibility and dot dropout, resulting in direction dependency. The result is a strong image.

According to the present invention, even if the developing gap is made closer,
An object of the present invention is to provide an image forming apparatus which does not generate image noise such as the above-described trailing edge white spots, horizontal line reproducibility deterioration, and dot drop deterioration, has good roughness, and has excellent gradation reproducibility. .

[0007]

According to the present invention, a developer is pumped to a developer carrier, a magnetic brush is formed on the developer carrier, and the developer is slid on the latent image carrier. In an image forming apparatus that rubs the latent image into a visible image, the developer carrier includes a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is a developer magnetic pole, In an image forming apparatus including a developer carrying magnetic pole and a main magnetic pole for developing a developer, an attenuation rate of a magnetic flux density in a normal direction of the main magnetic pole is 40% or more, preferably 50% or more, and a latent image is formed. This problem can be solved by a configuration in which the ratio of the distance between the latent image carrier and the developer carrier at the development nip boundary to the closest distance between the carrier and the developer carrier is 1.5 or less. The decay rate is the difference between the peak value of the normal direction magnetic flux density on the sleeve surface and the peak value of the normal direction magnetic flux density at a distance of 1 mm from the sleeve surface. Is the ratio divided by. The increase in the attenuation rate of the magnetic pole means that the width of the spikes between the rise and fall of the magnetic brush is reduced, and as a result, the magnetic brush rises short and densely. The development nip is an area where the latent image carrier and the magnetic brush are in contact with each other, and the development nip boundary is the end of the area downstream of the nearest ground point between the latent image carrier and the developer carrier.

[0008] The increase of the attenuation factor can be realized by selecting a magnet forming the magnetic pole. Further, as described in the following embodiments, it has been experimentally found that a reduction in the half width of the magnetic pole increases the attenuation rate. The half width is 22 ° or less, preferably 18 °
It is preferable to configure the following. The half-value width is a half value (for example, N) of the highest normal magnetic force (apex) of the magnetic force distribution curve in the normal direction.
The maximum normal magnetic force of the magnet made by the poles is 120
In the case of mT (millitesla), half value 50% is 60 mT. The half width is also expressed as 80%, in this case 96 mT). As one measure for reducing the half-value width of the main magnetic pole, it is conceivable to form an auxiliary magnetic pole for assisting the formation of the magnetic force. When the half width is reduced, the position of the magnetic brush is closer to the main pole, and the developing nip itself is also reduced. The auxiliary magnetic pole is formed upstream and / or downstream of the main magnetic pole in the developer transport direction. It can be formed on either the upstream side or the downstream side, in addition to both the upstream side and the downstream side, and both have advantages.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on an example shown in the drawings. First, the entire photoconductor unit including the developing device according to the present invention will be described. In FIG. 1, a charging device 2 for charging the surface of the photosensitive drum 1, which is a latent image carrier, an exposure 3 comprising a laser beam for forming a latent image on a uniformly charged surface, A developing device 4 for forming a toner image by attaching a charged toner to the latent image on the drum surface; a transfer device 5 for transferring the formed toner image on the drum onto recording paper 6; and removing residual toner on the drum A cleaning device 7 for removing the residual potential on the drum and a discharge lamp 8 for removing the residual potential on the drum are arranged in this order. In such a configuration, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2
To form an electrostatic latent image, and the developing device 4 forms a toner image. The toner image is transferred from the surface of the photosensitive drum 1 to recording paper conveyed from a paper feed tray (not shown) by a transfer device 5 including a transfer belt or the like.
The recording paper electrostatically attached to the photosensitive drum at the time of this transfer is separated from the photosensitive drum 1 by a separation claw. The unfixed toner image on the recording paper is fixed on the recording paper by a fixing device. On the other hand, the toner remaining on the photosensitive drum without being transferred is removed and collected by the cleaning device 7. Photoconductor drum 1 from which residual toner has been removed
Is initialized by the static elimination lamp 8 and used for the next image forming process.

The construction of the developing device 4 will be described with reference to FIG. In the developing device 4, a developing roller 41, which is a developer carrier, is disposed so as to be close to the photosensitive drum 1. In the developing roller 41, a developing sleeve 43 formed of a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is rotated clockwise by a rotation drive mechanism (not shown). . A doctor blade 45 that regulates the height of the developer chain, that is, the amount of the developer on the developing sleeve, is provided on the upstream side of the developing area in the developer conveying direction (clockwise direction in the drawing).
Is installed. The doctor gap, which is the distance between the doctor blade 45 and the developing sleeve 43, is set to 0.4 mm. Further, a screw 4 for pumping the developer in the developing casing 46 to the developing roller 41 while stirring the developer in the developing casing 46 is provided in a region of the developing roller opposite to the photosensitive drum.
7 are installed.

In the developing sleeve 43, there is fixedly provided a magnet roller body (magnet roller) 44 for forming a magnetic field so as to cause the developer to spike on the peripheral surface of the developing sleeve 43. A carrier of the developer causes a chain-like spike on the developing sleeve 43 on the developing sleeve 43 along the normal magnetic field lines generated from the magnet roller body, and the charged toner is attached to the carrier having the chain-shaped spike. Thus, a magnetic brush is configured. The magnetic brush is transferred in the same direction as the developing sleeve 43 (clockwise as viewed in the figure) by the rotation of the developing sleeve 43.
The magnet roller body 44 has a plurality of magnetic poles (magnets). More specifically, a developing main magnet P1b that causes a developer spike in the developing region, main magnetic pole magnetic force forming auxiliary magnets P1a and P1c that assist in forming a magnetic force of the main magnetic pole, and a developing sleeve 4
A magnet P4 for pumping up the developer, magnets P5 and P6 for transporting the pumped developer to the development area, and magnetic poles P2 and P3 for transporting the developer in the area after development are provided on the surface 3. These magnets P1b, P1a, P1c, P4, P
5, P2 and P3 are arranged radially of the developing sleeve 43. In this example, the magnet roller body 44 is
Although it is constituted by pole magnets, the number of magnets (magnetic poles) is further increased between the P3 pole and the doctor blade 45 in order to improve the pumping property and the black solid image followability, thereby increasing the number of poles to 10 poles or 12 poles.
It may be composed of poles.

As can be understood from FIG.
The group P1 is arranged from the upstream side in the order of P1a, P1b, P1c.
It consists of a small magnet with a cross section. Small cross section
These magnets are made of rare earth metal alloy
Is a samarium alloy magnet, especially a samarium cobalt alloy
A gold-based magnet or the like can also be used. Rare earth metal alloy magnet
The largest iron-neodymium boron alloy magnet among stones
Energy product is 358kJ / m³And iron neodymium
Maximum energy product is 80kJ for boron alloy bonded magnet
/ M³Before and after. Conventional magnets
Unlike the development roller table, which is necessary even if the size is considerably reduced
Surface magnetic force can be secured. Conventional ordinary ferrite magnets and ferrites
The maximum energy product of each light-bonded magnet is 36
kJ / m ³Before and after, 20kJ / m³Before and after. sleeve
Ferrites where larger diameters are acceptable
Use a magnet or ferrite bonded magnet to increase the shape
Or narrow the magnet tip facing the sleeve side.
By doing so, it is possible to narrow the half width.
In this embodiment, the magnet is formed by a small cross section magnet.
However, it is formed by a magnet roller formed by integral molding.
The magnets other than the P1 pole group may be integrally molded to form the P1 pole.
Groups can be formed individually and integrated or formed simultaneously
No. For attaching a fan-shaped magnet to the magnet roller shaft
Therefore, it may be molded.

In this embodiment, a developing main magnet P1b, a magnet P4 for pumping the developer onto the developing sleeve 43, and a magnet P6 for transporting the pumped developer to the developing area.
And magnetic poles P2 and P3 for transporting the developer in the region after development form N poles, and main magnetic pole magnetic force forming auxiliary magnets P1a and P1c for assisting the magnetic force generation of the main magnetic pole, and a magnet for transporting the pumped developer. P5 forms the south pole. As can be understood from FIG. 3 in which the magnetic flux density in the normal direction was measured and shown in a pie chart graph, the main magnet P1b
A magnet having a normal magnetic force of 5 mT or more was used.
The magnetic force related to carrier adhesion is a tangential magnetic force. To increase this tangential magnetic force, it is necessary to increase the magnetic force of P1b, P1a, and P1c. Can be. The magnet width of the magnets P1b, P1a, P1c was 2 mm.
At this time, the half width of P1b was 16 °.

A region (developing nip) where the photosensitive drum and the magnetic brush are in contact with each other is formed at a portion where the developing roller 41 and the photosensitive drum 1 are opposed to each other. Although toner movement occurs between the image carrier and the magnetic brush and development is performed,
In contact development, movement of toner mainly occurs in the above-mentioned area.

At the time of development by such toner movement,
The so-called white spot phenomenon, in which the solid rear end portion is white, has become a problem. FIG. 4 is a conceptual diagram of the developing unit for explaining the cause of the trailing edge white spot. The image carrier (photoconductor) and the developer carrier (developing roller or developing sleeve) move in the directions of arrows a and b, respectively. The linear velocity is higher for the developer carrier. Therefore, the magnetic brush always develops while overtaking the electrostatic latent image formed on the image carrier. When the magnetic brush comes into contact with the non-image portion (background portion) on the upstream side of the developing area, the toner present at the tip of the magnetic brush receives a force in the developer carrier direction c due to the electric field in the developing area, and the image carrier Move away from the vicinity. Therefore, the longer the time that the magnetic brush contacts the non-image portion, the lower the toner concentration near the image carrier. When the magnetic brush moves to the downstream side of the developing area with the movement of the developer carrier and catches up with the image area, the tip of the magnetic brush having a low toner concentration shows the toner already developed and adhered to the image carrier by an arrow. Electrostatic suction in the direction of d. As a result, the amount of toner after the image decreases, while the toner concentration at the tip of the magnetic brush increases again. Even if the magnetic brush moves further downstream of the developing area, if the toner concentration is recovered, the toner will not be sucked from the image carrier. In such a state, there is no problem. However, if the contact between the magnetic brush and the image portion is short, the tip of the magnetic brush having a low toner density contacts the end portion (rear end) of the image portion, and the image carrier side in that range. As a result, an image having a blurred rear end portion is formed on the image carrier having passed through the developing area.

In the developing nip, the magnitude of the electric field formed differs between the point where the image carrier and the developer carrier are closest to each other and the point where the image carrier is farthest (boundary of the nip). For example, in this embodiment, if the drum diameter of the photosensitive drum 1 is set to 60 mm, the drum linear velocity is set to 240 mm / sec, the developing sleeve 43 is set to 20 mm in diameter, and the sleeve linear velocity is set to 600 mm / sec. The ratio of the sleeve linear speed to the drum linear speed is 2.5. When the developing gap, which is the distance between the photosensitive drum 1 and the developing sleeve 43, is 0.4 mm and the developing nip width is 4 mm, the photosensitive drum 1 and the developing sleeve 43 are 0.4 mm at the center of the nip and 0.67 at the nip boundary, and the electric field generated by the distance is about 1: 0.
It becomes 6. For this reason, on the downstream side of the developing nip, the toner is collected by the reverse charge on the carrier near the photosensitive drum.
The amount of toner adheres to the photoconductor drum due to the electric field, and the trailing edge white spot easily occurs as described above.

On the other hand, when the developing nip is narrowed and the ratio of the gap between the center of the nip and the boundary is close to 1,
As described above, the electric field intensity is not reduced even at the nip boundary portion, and the carrier does not substantially collect the toner developed on the photosensitive drum. For this reason, the phenomenon that the trailing edge is whitened out is eliminated. An experiment was performed to confirm this. The experimental conditions are shown in Table 1 below.

[0018]

[Table 1]

In the developing nip, a developing bias for transferring toner from the developing sleeve to the photosensitive drum is applied while the photosensitive drum and the developing sleeve are stopped, and an area where the toner adheres to the photosensitive drum is measured. Asked by that. That is, a bias is applied to the developing sleeve for about one second in a state where the photoconductor is not charged, the photoconductor is taken out, the width of the toner adhering in the moving direction of the photoconductor is measured, and it is defined as a nip width. . In addition, the nip boundary interval is defined by the diameter of the photosensitive drum, the diameter of the sleeve, the developing gap,
It was determined by calculation from the development nip. In either case,
The linear velocity of the developing sleeve is 2.
5 times. FIG. 5 shows the results. The horizontal axis of the graph in the figure is the developing gap at the center of the developing nip (distance between the photosensitive drum and the image carrier / developing sleeve and the developer carrier).
Is the ratio (interval ratio) of the nip boundary portion interval (distance between the photosensitive drum and the developing sleeve) of the nip boundary portion with respect to, and the vertical axis is a value obtained by visually ranking the trailing edge white spot level (no white spots at all). The unrecognizable level was 5, the most prominent level was 1, and the middle was ranked relatively).

As expected, the relationship between the interval ratio and the trailing edge white spot is clearly seen, and when the interval ratio exceeds 1.5, the trailing edge white spot becomes considerably noticeable, and the image quality is at a low level.
In addition, horizontal line reproducibility and dot uniformity are reduced, and a feeling of roughness is noticeable. From this result, if the ratio of the nip boundary portion interval to the development gap is 1.5 or less, an image without trailing white spots is formed. The same mechanism also improves horizontal line reproducibility and dot stability reproducibility.

As another example (second example), FIG. 6 shows an arrangement configuration of a magnet roller body having no auxiliary magnetic poles on the upstream and downstream sides of the main magnetic pole (Nos. 2, 5, and 8 in Table 1). Except for the magnet arrangement of the magnet roller body, the configuration itself of the developing device 4 and the photosensitive drum 1 is the same as that shown in FIG. The magnet roller body 44 ′ includes a developing main magnet P <b> 1 for causing the developer to spike in the developing area, and a developing sleeve 4.
A magnet P4 for pumping up the developer, magnets P5 and P6 for transporting the pumped developer to the development area, and magnetic poles P2 and P3 for transporting the developer in the area after development are provided on the surface 3. These magnets P1, P4, P5, P2 and P3
Are arranged in the radial direction of the developing sleeve 43. In the second example, the magnet roller body 44 ′ is constituted by six-pole magnets. However, in the same manner as in the above example, between the P3 pole and the doctor blade 45 in order to improve the pumping property and the black solid image followability. Further increase the number of magnets (magnetic poles) to 8
You may comprise more than poles.

As in the above-described example in which auxiliary magnets are provided on the upstream and downstream sides of the main magnet, the main magnet P1 forming the developing main pole is formed of a magnet having a small cross section. Although the magnet having a small cross section is made of a rare earth metal alloy, a samarium alloy magnet, in particular, a samarium cobalt alloy magnet can be used. When it is permissible to increase the sleeve diameter, it is possible to narrow the half-value central angle by forming a thin magnet end facing the sleeve using a ferrite magnet or a ferrite bond magnet.

In the second example, a magnet P4 for pumping the developer onto the developing sleeve 43, a magnet P6 for transporting the pumped developer to the development area, and a magnet P2 for transporting the developer in the area after development. , P3 form the north pole, and the developing main magnet P1 and the magnet P5 for transporting the pumped developer form the south pole. FIG. 7 shows the details of the magnetic force in the first example.

An experiment for confirming the elimination of the trailing edge white spot phenomenon in the configuration in which only one magnet is arranged between the photosensitive member and the developing sleeve was performed in the same manner as in the first example, and the experimental conditions were set in the above-mentioned table. Also described in 1.

Next, when considering the decay rate of the magnetic force density in the normal direction, return to FIG. The figure shows the normal magnetic force pattern, the solid line is a circular chart graph measuring the magnetic flux density on the surface of the developing sleeve, and the broken line measures the magnetic flux density in the normal direction at a distance of 1 mm from the surface of the developing sleeve. It is a pie chart graph. The measuring device used for the measurement was a Gauss meter manufactured by ADS (HGM-83).
00) and A1 type axial probe manufactured by ADS, and recorded by a pie chart recorder.

In the observation with the magnet roller in the first example,
The magnetic flux density in the normal direction on the sleeve surface of the main magnetic pole P1b is 95 mT, the magnetic flux density in the normal direction at a portion 1 mm away from the sleeve surface is 44.2 mT, and the variation of the magnetic flux density is 50.8 mT. It was a magnetic force difference. At this time, the attenuation rate of the magnetic flux density in the normal direction (the difference between the peak value of the magnetic flux density in the normal direction on the sleeve surface and the peak value of the magnetic flux density in the normal direction at a distance of 1 mm from the sleeve surface is calculated by the method on the sleeve surface. The ratio of the linear magnetic flux density divided by the peak value) is 5
3.5%. When the maximum normal magnetic force of the main magnet is 95 mT, the half value is 47.5 mT, and the half value width is 22 °. It was confirmed that an abnormal image was generated when the half width of the main magnetic pole was set to be larger than 22 °.

The normal magnetic flux density on the sleeve surface of the main magnetic pole magnetic force forming auxiliary magnet P1a located on the upstream side of the main magnetic pole P1b is 93 mT, and the normal magnetic flux density at a portion 1 mm away from the sleeve surface is: It was 49.6 mT, and the amount of change in magnetic flux density was a magnetic force difference of 43.4 mT. At this time, the attenuation rate of the magnetic flux density in the normal direction is 46.7%. The magnetic flux density in the normal direction on the sleeve surface of the main pole magnetic force forming auxiliary magnet P1c located downstream of the main pole P1b is 92 mT.
The magnetic flux density in the normal direction at a portion 1 mm away from the surface of the sleeve was 51.7 mT, and the amount of change in the magnetic flux density was a magnetic force difference of 40.3 mT. At this time, the attenuation rate of the magnetic flux density in the normal direction is 43.8%. In this example, in the magnetic brush formed along the lines of magnetic force generated on the magnet roller, only the brush portion formed on the main magnetic pole P1b is in contact with the photoconductor, and the electrostatic latent image on the photoconductor is visualized. . At this time, when measured in a state where the photoreceptor is not in contact, the length of the magnetic brush at that location is about 1.5 mm. It has become possible to create a state that has become. If the distance between the developer regulating member and the developing sleeve is the same as before, the amount of developer passing through the developer regulating member is the same, so the magnetic brush in the developing area is short and dense. Was confirmed. This phenomenon can be understood from the normal magnetic force pattern shown in FIG. 3. Since the normal magnetic flux density at a distance of 1 mm from the surface of the developing sleeve is greatly reduced, the magnetic brush forms a brush chain at a distance from the developing sleeve. Therefore, the magnetic brush is short and densely formed on the surface of the developing sleeve. Incidentally, in the conventional magnet roller, the magnetic flux density in the normal direction on the sleeve surface of the main magnetic pole is 73 mT, and 1 mm from the sleeve surface.
The magnetic flux density in the normal direction at the distant portion was 51.8 mT, and the amount of change in the magnetic flux density was a magnetic force difference of 21.2 mT. At this time, the attenuation rate of the magnetic flux density in the normal direction is 29%.

It has been found from experiments that the attenuation rate is increased by reducing the half width. The half width can be reduced by reducing the width of the magnet (width in the circumferential direction of the sleeve). For example, in the first example, the magnet width of the magnets P1b, P1a, and P1c is 2 mm,
The half width of P1b was 16 °, but the half width of the main pole was 12 ° for a 1.6 mm wide magnet. By narrowing the half width, the magnetic flux sneaking into adjacent magnets increases,
The normal magnetic flux density at a portion distant from the sleeve surface decreases. Between the magnet roller and the developing sleeve, there is a substantial gap based on the space required for the magnet roller to be fixed and the developing sleeve to rotate and the thickness of the developing sleeve, and the tangential magnetic flux density position is substantially equal to that of the developing sleeve. Because it concentrates on the sleeve side,
The normal magnetic flux density decreases as the distance from the sleeve surface increases.

When a magnet roller having a high damping rate is used, the magnetic brush is formed short and dense. On the other hand, in a conventional magnet roller having a low damping rate, the magnetic brush is formed long and sparsely. This is because a magnetic field formed by a magnet having a large attenuation rate is adjacent to a magnet (for example, P1a and P1c with respect to P1b).
The magnetic flux wraps in the tangential direction more than the magnetic flux spreads in the normal direction, and the magnetic flux density in the normal direction decreases. In addition, the magnetic brush is formed densely. For example, a magnet P1b having a high damping rate
When the magnetic brushes are formed to be short and adjacent to each other, they are more stable than those formed separately and elongated. With a conventional magnet roller having a low damping rate, the magnetic brush does not become short even if the amount of developer pumped is reduced, and the length is almost the same as that of the above-described magnetic brush.

The attenuation factor can be increased by moving the main magnetic pole forming auxiliary magnet adjacent to the main magnetic pole closer to the main magnetic pole position (in the circumferential direction of the sleeve). By doing so, the lines of magnetic force emitted from the main magnetic pole flow into the adjacent main magnetic pole forming auxiliary magnetic pole, and the number of magnetic lines of force increases.
The decay rate increases.

The carrier has a particle size of 50 μm.
The particle size was 100 μm and 15 μm for comparison.
When an image was formed using a 0-μm carrier (the other conditions were the same), in the latter, the density of the magnetic brush on the developing sleeve was reduced, the ears appeared strongly on the image, and the developing ability was reduced. When an image was produced with a 50 μm carrier having a small developing gap, the developing gap was 150 μm.
When the diameter was less than μm, ear marks became noticeable. Observing the developing nip, if the number of carriers stacked in the closest gap (developing gap) between the photoconductor and the developing sleeve is less than 3, the carrier closest to the photoconductor is also strongly bound directly by the magnet of the developing sleeve. As a result, the flexibility of the magnetic brush became extremely small, and as a result, it became clear that the magnetic brush did not move independently one by one and the magnetic brush behaved like a rod. As described above, the number of carriers constituting the magnetic brush is three or more between the developing sleeve and the photosensitive member when the carrier is arranged vertically, so that the magnetic brush has flexibility and the sliding force of the magnetic brush is increased. And the density of the developer on the developing sleeve is increased, so that a uniform image having no direction dependency can be obtained.

In the examples described so far, an electrostatic latent image is formed by scanning a photosensitive drum with a laser beam by a rotating polygon mirror. However, the invention is not limited to this, and a large number of light sources such as LEDs are arranged in an array. Optical writing elements arranged in a line may be used.

[0033]

According to the present invention, a sufficiently strong electric field strength can be maintained even at the boundary of the developing region, so that a visible image can be faithfully formed with respect to the latent image, the roughness is good, and the rear end is good. It is possible to obtain an image free from white spots, horizontal lines, fading around the character portion, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a photoconductor unit including a developing device according to the present invention.

FIG. 2 is a detailed configuration diagram of a developing device in FIG.

FIG. 3 is a diagram showing a magnetic force distribution of a developing roller and its magnitude in the developing device according to the present invention.

FIG. 4 is a conceptual diagram of a developing unit for explaining a cause of a trailing edge white spot.

FIG. 5 is a graph illustrating a relationship between a ratio of a developing nip boundary portion interval to a developing gap and a degree of trailing edge white spots.

FIG. 6 is a detailed configuration diagram of a developing device provided with a magnet roller body having another arrangement configuration.

7 is a diagram corresponding to FIG. 3 and showing a magnetic force distribution of the developing roller in the developing device of FIG. 6 and its magnitude.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 4 Developing device 41 Developing roller 43 Developing sleeve 44 Magnet roller body

Claims (7)

[Claims] 1. An image forming device that draws a developer to a developer carrier, forms a magnetic brush on the developer carrier, and rubs the developer on the latent image carrier to visualize the latent image. In the apparatus, the developer carrier includes a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for a developer pumping magnetic pole, a developer carrying magnetic pole, and a main part for developing a developer. In the image forming apparatus having the magnetic pole, the attenuation rate of the magnetic flux density in the normal direction of the main magnetic pole is 40% or more, and the latent image at the developing nip boundary with respect to the closest distance between the latent image carrier and the developer carrier. An image forming apparatus, wherein the ratio of the distance between the image carrier and the developer carrier is 1.5 or less. 2. An image forming step of drawing a developer to a developer carrier, forming a magnetic brush on the developer carrier, and rubbing the developer on the latent image carrier to visualize the latent image. In the apparatus, the developer carrier includes a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for a developer pumping magnetic pole, a developer carrying magnetic pole, and a main part for developing a developer. In an image forming apparatus having a magnetic pole, the half width of the main magnetic pole is 22 ° or less, and the latent image carrier
An image forming apparatus, wherein a ratio of a distance between a latent image carrier and a developer carrier at a development nip boundary to a closest distance between the developer carriers is 1.5 or less. 3. An image forming step of drawing a developer to a developer carrier, forming a magnetic brush on the developer carrier, and rubbing the developer on the latent image carrier to visualize the latent image. In the apparatus, the developer carrier includes a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for a developer pumping magnetic pole, a developer carrying magnetic pole, and a main part for developing a developer. An image forming apparatus having a magnetic pole, comprising: an auxiliary magnet for assisting the formation of a magnetic force of the main magnetic pole; and a latent image carrier at a developing nip boundary with respect to a closest distance between the latent image carrier and the developer carrier. An image forming apparatus, wherein the ratio of the distance between the agent carriers is 1.5 or less. 4. The image forming apparatus according to claim 3, wherein the auxiliary magnet is disposed upstream and / or downstream of a main magnet forming the main magnetic pole in a developer conveying direction. 5. The image forming apparatus according to claim 3, wherein the polarity of the main magnetic pole and the polarity of the auxiliary magnetic pole are different from each other. 6. The magnet according to claim 3, wherein the magnet forming the main magnetic pole is made of a rare earth metal alloy.
6. The image forming apparatus according to claim 5, 7. The method according to claim 1, wherein the closest distance between the latent image carrier and the developer carrier is set to be at least three times the average particle size of the carrier particles. An image forming apparatus according to claim 1.