JP2001242711A - Developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner or developer from sticking to a developing sleeve, which happens to occur. SOLUTION: In this developing device, a developer carrier 41 is constituted of a non-magnetic sleeve 43 and a magnet roller 44 fixedly arranged in the sleeve 43, and the roller 44 is equipped with a developer drawing-up magnetic pole, a developer carrying magnetic pole and a main magnetic pole for the napping of the developer. The attenuation factor of the flux density of the main magnetic pole in a normal direction is >=40% and an irregular rugged pattern is formed on the surface of the sleeve 43.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in which a developer is hardly adhered when a developer is started up in a so-called developing area on a surface of a developer carrier and developed, and an image forming apparatus to which the developing device is attached. It is.

[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 information is formed thereon, and the developing device performs a developing operation to obtain a visible image.
In performing the developing operation as described above, from the viewpoints of transferability, reproducibility of halftone, stability of developing characteristics with respect to temperature and humidity, etc., a magnetic brush developing method using a two-component developer composed of a toner and a carrier is used. It is becoming 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 so as to follow the lines of magnetic force generated by the magnet roller, and the charged toner is attached 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. At this time, a groove extending in the longitudinal direction is formed on the surface of the developing sleeve, and the groove ensures the developer transportability. The surface may be subjected to unevenness treatment by sandblasting or the like instead of the groove. 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 the way, the distance or interval (hereinafter referred to as a developing gap) between the closest point between the developer carrier and the latent image carrier has a great influence on the image quality. That is, when the developing gap is wide, a so-called “edge-enhanced image” in which the amount of toner adhering to the edge of the latent image increases, and there is a problem that the image quality is reduced. One of the ways to reduce this phenomenon
First, a measure for narrowing the developing gap is often used. However, when the developing gap is narrowed, the developing electric field becomes large, so that the developing γ becomes high. If the development γ is too high, the gradation is deteriorated, and if the development γ is too low, it becomes difficult to obtain the maximum amount of adhesion. Therefore, the development γ has an optimum range.

Since the development γ is proportional to the sleeve linear velocity ratio (sleeve peripheral velocity / latent image carrier peripheral velocity), in order to reduce the development γ that has become too high, the rotation speed of the development sleeve is reduced to reduce the sleeve rotation speed. It is possible to reduce the linear velocity ratio and thereby obtain a desired development γ. However, when the sleeve linear velocity ratio is reduced in this way, the gradation is restored, but the developing ability is reduced. In the case of a developing sleeve having a longitudinal groove on the surface, the chain of the developer is concentrated on the groove, so that uneven toner adhesion occurs at a pitch corresponding to the groove. Therefore, the use of a sleeve that has been subjected to surface unevenness treatment is considered. However, a sleeve having surface irregularities formed by sandblasting or the like has a lower developer conveying force than a grooved sleeve, and when used with a small developing gap and a small sleeve linear velocity ratio, toner or developer adheres to the surface of the developing sleeve. Occurs.

When the sticking occurs, the rotational torque of the developing roller, which is a developer carrying member, increases, causing drive unevenness due to the gear pitch of a drive transmission system such as a developing drive gear, thereby causing banding. In addition, since drive unevenness is also generated in the latent image carrier, when forming a dot latent image by using a laser or the like, there is a problem that unevenness occurs in dot intervals and a similar banding image is generated. Further, if the image formation is continued as it is, there is a linear velocity difference between the latent image carrier and the developing sleeve,
The photosensitive layer of the latent image carrier is scraped, or driving of the latent image carrier is stopped, thereby causing a serious problem.

As another method for reducing the “edge-enhanced image”, using an AC bias as a developing bias is also known as an effective measure. By applying the AC bias, the electric resistance of the developer ear drops, the developing electrode becomes closer to the tip of the magnetic brush, and an effect of substantially reducing the developing gap (edge-improved image improvement) is obtained. . However, the development γ also increases at the same time, and it is necessary to reduce the sleeve linear velocity ratio in order to obtain the desired development γ, as in the case of the above-described gap narrowing. As a result, the same problem as in the above case occurs.

Here, the fixing mechanism will be described. The sticking is likely to occur when the regular developing gap width is reduced due to the shake of the image carrier and the shake of the developer carrier, or when the amount of the developer on the developer carrier exceeds the regular pumping amount. The pumping amount on the developer carrier is partially increased, and the increased amount of the developer is transferred to a developing nip (a contact portion generated at a portion where a magnetic brush formed on the developing sleeve rubs against the latent image carrier). )
Due to the stress generated in the narrow gap when passing through while being pressed inside the toner 1. The toner softens dynamically 2. The toner softens and melts thermally 3. The wax contained in the toner leaks out dynamically appear. Further, in such a state, if the developer conveying force on the surface of the developing sleeve is weak, the high-density developer that cannot pass through the developing nip slides on the surface of the sleeve, so that the toner is melted and fixed by frictional heat on the surface of the sleeve. Would.

Another toner or carrier or the like starts to agglomerate in the softened and melted toner, and this portion serves as a nucleus to grow a fixed portion. There are cases where the sticking starts from approximately one location and gradually spreads in the circumferential direction, and cases where the growth occurs at a plurality of locations.

As another indirect factor, the toner concentration in the apparatus becomes high (when the P sensor is controlled in a low humidity environment or when a color material having a high toner concentration is used), the fluidity is reduced, and the aging of the developer is reduced. When the flowability is lowered due to an increase in the amount of floating toner having a reduced charge amount due to deterioration or a decrease in standing, fixation is likely to occur. In addition, especially when the sleeve surface roughness is reduced over time and the transportability of the developer is reduced, when the sleeve temperature is increased in a high-temperature environment or in continuous copying (eddy current), and when there is a lot of sleeve contamination, etc. Sticking easily occurs. In any case, as the relative speed difference between the developing sleeve and the carrier or toner increases, frictional heat is generated and the sticking is induced.

According to the present invention, in achieving high image quality,
It is an object of the present invention to provide a developing device that prevents the toner or developer from sticking to a developing sleeve, which may occur, and does not cause the above-described problem.

[0012]

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 a developing device for rubbing the latent image into a visible image, the developer carrier comprises a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used to draw up a developer magnetic pole, In a developing apparatus having a developer carrying magnetic pole and a main magnetic pole for developing a developer, the attenuation rate of the magnetic flux density in the normal direction of the main magnetic pole is 40% or more, preferably 50% or more, and the surface of the sleeve is The above problem is solved by forming an irregular concavo-convex pattern on the substrate. 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.
Increasing the attenuation rate of the magnetic pole means that the width of the magnetic brush during the rising and falling of the magnetic brush becomes smaller,
As a result, the magnetic brush rises short and densely.

An increase in 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.

The irregular pattern formed on the surface of the developing sleeve is performed by blasting. A typical blast treatment is a sand blast method, but a bead blast method can of course be used.

[0015]

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 structure 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 carrying member, is disposed so as to be close to the photosensitive drum 1, and a developing area where the photosensitive drum and the magnetic brush are in contact is provided on both opposing portions. Is formed. Developing roller 41
The developing sleeve 43 is formed by forming a non-magnetic material such as aluminum, brass, stainless steel, and conductive resin into a cylindrical shape.
Are rotated clockwise by a rotation drive mechanism (not shown). In this embodiment, the drum diameter of the photosensitive drum 1 is 60 mm, and the linear speed of the drum is 240 m.
m / sec, and the sleeve diameter of the developing sleeve 43 is 2
At 0 mm, the linear velocity of the sleeve is set to 600 mm / sec. Therefore, the ratio of the sleeve linear speed to the drum linear speed is 2.5. The developing gap, which is the distance between the photosensitive drum 1 and the developing sleeve 43, is set to 0.4 mm. Conventionally, the developing gap has a carrier particle size of 5
In the case of 0 μm, it is set to be about 0.65 mm to 0.8 mm, in other words, it is set to be 10 times or more of the developer particle diameter. If the width is wider than this, it is difficult to obtain a desirable image density.

A doctor blade 45 for regulating the height of the developer chain, ie, the amount of the developer on the developing sleeve, is provided on the upstream side of the developing area in the developer transport 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 47 for pumping the developer in the developing casing 46 to the developing roller 41 while stirring the developer in an area on the opposite side of the developing roller from the photosensitive drum is provided.

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 °.

As another example (second example), FIG. 4 shows an arrangement configuration of a magnet roller body having no auxiliary magnetic poles on the upper and lower sides of the main magnetic pole. Since the configuration itself of the developing device 4 and the photosensitive drum 1 is the same as that shown in FIG. 2 except for the arrangement of the magnet roller body, the same reference numerals are given and the description is omitted. The magnet roller body 44 'includes a developing main magnet P1 for raising the developer in the developing area, a magnet P4 for pumping the developer onto the developing sleeve 43, and a magnet P5 for transporting the pumped developer to the developing area. P6, and magnetic poles P2 and P3 for transporting the developer in the area after development. These magnets P1, P
4, 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. Alternatively, the number of magnets (magnetic poles) may be further increased and the number of poles may be increased to eight or more.

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. 5 shows a detail of the magnetic force in the first example.

Returning to FIG. 3, when considering the attenuation rate of the magnetic force density in the normal direction. 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 (HGM-8300) manufactured by ADS.
A1 type axial probe manufactured by ADS and recorded by a pie chart recorder.

According to the observation by 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 9
5 mT, the normal direction magnetic flux density at a portion 1 mm away from the sleeve surface was 44.2 mT, and the amount of change in the magnetic flux density was a magnetic force difference of 50.8 mT. 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 upstream 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 also be increased by bringing the main magnetic pole forming auxiliary magnet adjacent to the main magnetic pole closer to the main magnetic pole position (in the sleeve circumferential direction). 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.

Assuming that the peak position of the magnetic flux density of the main magnetic pole (developing pole) is 0 ° in the magnet roller body (also referred to as the mag roller of the present application) shown in FIG. 2, the magnetic force is as shown by the solid line in FIG. However, in the case of a conventional magnet roller body (also referred to as a conventional mag roller), it is indicated by a dotted line. In FIG. 7, the relationship between the magnetic force and the sliding amount of the developer on the sleeve shows that the larger the magnetic force, the smaller the sliding amount. The sliding amount of the present mag roller is smaller than that of the conventional mag roller. This presupposes that the friction coefficient of the sleeve surface is the same, but the relationship between the surface roughness Rz, which has a positive correlation with the friction coefficient, and the slip amount is as shown in FIG. In the conventional mag roller, the slip amount increases when the surface roughness Rz decreases, but in the mag roller of the present invention, since the magnetic force is strong, the slip amount is small even when the surface roughness is small, and as a result, the sleeve does not stick.

FIG. 9 is a graph showing a result of examining a limit point at which sleeve sticking occurs in relation to a developing gap and a developer pumping amount. With the conventional mag roller, when the developing gap is reduced, the amount of the developer pumped up cannot be increased because the sleeve is likely to stick.However, with the mag roller of the present application, the amount of the developer pumped is larger than the conventional one. Does not occur, it is possible to achieve a narrow developing gap which is essential for high image quality.

By using the magnet roller body according to the present invention, the carrier receives a strong magnetic force from the developing poles (P1b pole, P1 pole), so that the surface roughness of the sleeve is reduced and the transportability of the developer is reduced. Even when the sleeve surface does not slip easily, the generation of frictional heat can be suppressed. That is, the developer transportability at the developing nip portion where the sticking occurs is increased, and the sleeve hardly slips on the sleeve surface, so that sticking due to frictional heat is eliminated. Therefore, a blasted sleeve in which the developer transportability of the sleeve surface is inferior to that of the grooved sleeve can be used at a low sleeve linear velocity ratio. The blast treatment includes, for example, a sand blast method and a bead blast method, and any of the treatment methods can be used for forming the surface unevenness of the present invention.

Even when the linear velocity ratio was lowered to reduce the development γ increased by applying the AC bias, the sleeve was not fixed. Specifically, the linear velocity ratio is 1.2, Vpp =
0.8 Kv, f = 4.5 kHz, development gap = 0.3
When the drawing amount was 5 mm and the pumping amount was 0.08 mg / cm ² , no sticking occurred and the image quality was good.

[0034]

According to the present invention, the spike width between the rising and falling of the magnetic brush is small, the magnetic brush is short, the linear velocity ratio of the sleeve is reduced, and the developing gap is narrowed. The stress of the developer sandwiched between the developer carrier and the image carrier is small, so that the developer accumulation and the adhesion of the magnetic brush hardly occur.

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

5 is a diagram corresponding to FIG. 3 and showing the magnetic force distribution of the developing roller in the developing device of FIG. 4 and the magnitude thereof.

FIG. 6 is a graph showing a change in magnetic force when the magnetic flux density peak of the main magnetic pole is set to 0 ° in the magnet roller body of the first example according to the present invention and the magnet roller body of the conventional configuration.

FIG. 7 is a graph showing the relationship between the magnetic force and the amount of sliding of the developer on the sleeve when the friction coefficient of the surface of the developing sleeve is the same.

FIG. 8 is a graph showing the relationship between the surface roughness of the developing sleeve and the amount of sliding of the developer on the sleeve.

FIG. 9 is a graph showing a sticking occurrence region depending on the magnitude of a developing gap and a developer pumping amount.

[Explanation of symbols]

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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobutaka Takeuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock inside Ricoh Company (72) Inventor Nobuo Takami 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Osamu Ariizumi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Company (reference) 2H031 AB02 AB09 AC08 AC10 AC11 AC13 AC19 AC20 AD03 CA09

Claims (7)

[Claims] 1. A developing device which draws a developer onto 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. The developer carrier comprises a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for picking up a magnetic pole of the developer, a magnetic pole for conveying the developer, and a main magnetic pole for raising the developer. The developing device according to claim 1, wherein an attenuation rate of a magnetic flux density in a normal direction of the main pole is 40% or more, and an irregular concavo-convex pattern is formed on a surface of the sleeve. 2. A developing device which draws up a developer onto 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. The developer carrier comprises a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for picking up a magnetic pole of the developer, a magnetic pole for conveying the developer, and a main magnetic pole for raising the developer. The half-width of the main pole is 22 ° or less, and an irregular pattern is formed on the surface of the sleeve. 3. A developing device which draws up a developer onto 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. The developer carrier comprises a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, and the magnet roller is used for picking up a magnetic pole of the developer, a magnetic pole for conveying the developer, and a main magnetic pole for raising the developer. A developing device comprising: an auxiliary magnet that assists in forming a magnetic force of the main magnetic pole; and an irregular pattern formed on a surface of the sleeve. 4. The developing device 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 developing device according to claim 1, wherein the irregular pattern is formed by sandblasting. 6. The developing device according to claim 5, wherein said latent image is developed with an alternating electric field. 7. An image forming apparatus comprising the developing device according to claim 1.