JP2000305360A - Developing method, developing device, magnetic roll and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a good image density and image quality by preventing generation of an end void and a burr especially in a low contrast image. SOLUTION: In this developing method where developer is brought up to a developing sleeve, a magnetic brush is formed on the developing sleeve 43 and a latent image is visualized by having the developer come into a sliding contact with a latent image carrier, the magnetic brush is constituted so that its spikes get up uniformly in the longitudinal direction of the developing sleeve 43 and come into contact with the latent image carrier. Attenuation factor of magnetic density in a direction of a normal line of a main magnetic pole causing getting up of the spikes of the brush in a developing range is made so as to become >=40% and preferably >=50%. Since when the attenuation factor of the magnetic pole is made greater, the width of the getting-up of the spikes between standing and lying of the magnetic brush is made smaller, as a result the magnetic brush can stand short and with high density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for developing a developer on a so-called developing area on the surface of a developer carrier by raising (producing ears) a high image density and excellently producing a low-contrast image. The present invention relates to a developing method, a developing device for performing the developing method, a magnet roller disposed in the developing device, and an image forming apparatus equipped with the developing device.

[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, image information is stored on a latent image carrier such as a photosensitive drum or a photosensitive belt. An electrostatic latent image is formed, and a 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. The developer conveyed to the developing area causes ears to rise along the lines of magnetic force emitted from the main developing magnetic pole, and the chain of the developer contacts the surface of the latent image carrier so as to bend. Supplies toner while rubbing against the electrostatic latent image based on the relative linear velocity difference from the latent image carrier.

[0004]

However, in such a developing apparatus, the developing conditions for increasing the image density and the developing conditions for obtaining a low-contrast image are incompatible, and the developing device is not suitable for high-density areas. It is difficult to improve both the low concentration part and the low concentration part at the same time. That is, the developing conditions for increasing the image density include (i) reducing the developing gap, which is the distance between the latent image carrier and the developing sleeve, or (ii) increasing the developing area width. Can be On the other hand, developing conditions for obtaining a low-contrast image satisfactorily include (i ′) widening the developing gap or (i ′)
i ′) The width of the development area may be reduced. In other words, both development conditions are opposite and incompatible, and it is generally difficult to satisfy both conditions over the entire density range to obtain a good quality image.

For example, when importance is attached to a low-contrast image, an abnormal image referred to as a so-called "back-end blank portion" occurs in which a blank portion occurs at a cross portion of a solid line, a black solid portion, or a rear end portion of a halftone solid image. It's easy to do. Further, such a phenomenon that a horizontal line of a grid image formed with the same width becomes thinner than a vertical line, and a small point image such as one dot is not developed has occurred.

Consider the mechanism of such a phenomenon. As shown in FIG. 15, at a contact portion (developing nip) generated at a portion where the magnetic brush formed on the developing sleeve rubs against the latent image carrier, a linear velocity difference between the latent image carrier and the developing sleeve (vs. The above phenomenon occurs when there is a photoconductor linear velocity ratio). For example, when the linear speed ratio to the photosensitive member is set to 2.5 times, the developing sleeve moves 2.5 times faster than the latent image carrier. In addition, the half width of the developing main pole of the developing sleeve is 48.
The width of the developing nip when using a magnet of about ° was about 4 mm (experimental value), and the developing gap was 0.4 mm.

The latent image on the latent image carrier is formed into a toner image by a magnetic brush. When the latent image is developed in the developing nip shown in FIG. FIG. 16 showing the positional relationship between the standing and falling of the ear and the electrostatic latent image will be considered.

FIGS. 16A and 16B show the relationship between the surface potential of the electrostatic latent image and the developing bias, the position of the electrostatic latent image at the developing nip, and the movement of the magnetic brush before and after the developing nip. Although the developing sleeve is usually formed in a cylindrical shape, it is shown here as a flat one for convenience of explanation.

In FIG. 16A, the boundary between the background portion and the image portion of the electrostatic latent image is located substantially at the center of the nip. Since both the developing sleeve and the latent image carrier move in the same direction and the latent image carrier moving speed Sp <the developing sleeve moving speed Ss,
Assuming that the latent image carrier is relatively stationary, the movement of the magnetic brush is as follows. That is, the magnetic brush is H1
At the position, the contact between the latent image carrier and the carrier at the tip of the magnetic brush starts. At the position of H2, the magnetic brush moves by rubbing the background, at the position of H3, the magnetic brush passes through the image portion, at the position of H4, the tip falls, and the carrier at the tip of the magnetic brush separates from the latent image carrier. . The carrier at the tip of the magnetic brush that comes into contact with the latent image carrier between H1 and H4 passes through the nip with almost no change in the height position, but the carrier itself rotates while rotating.

FIGS. 17A to 17D are model diagrams showing the state of adhesion between the tip carrier and the toner in the magnetic brush between H1 and H4 shown in FIG. 16A. The magnetic brush position H1 corresponds to FIG. 17A, and the following H2 to H4 correspond to FIG.
b to FIG. 17d.

Since the magnetic brush position H1 is shortly after entering the nip, the toner is relatively uniformly attached around the carrier (FIG. 17a). Magnetic brush position H2
In this case, the electric field formed by the voltage of the developing bias Vb and the electrostatic potential of the background portion of the latent image carrier is a region having directionality from the latent image carrier side to the developing sleeve. It moves away, and the toner in the vicinity of the latent image carrier decreases as shown in FIG. 17B. In this state, the carrier moves while rolling in the nip,
As the nip width increases, the surface area of the carrier surface near the latent image carrier where toner is reduced increases.

At the magnetic brush position H3, the developing bias Vb
And the electric field formed by the electrostatic potential of the image portion of the latent image carrier becomes a region having directionality from the developing sleeve side to the latent image carrier, but the toner that has moved downward is instantaneously latent. It cannot adhere to the electrostatic image on the image carrier. In the meantime, the toner on the latent image carrier adhered to the latent image carrier by another magnetic brush that has passed the image portion first moves to the carrier side for the counter charge of the magnetic brush side carrier. "Move" occurs. FIG. 17C shows a state in which toner on the carrier surface at the leading end of the magnetic brush is increased and toner adhesion on the trailing end of the image portion of the latent image carrier is reduced.
It is.

When the amount of toner increases due to the reverse movement of the toner, the counter charge also decreases, and the toner that has moved downward becomes easier to move to the tip of the magnetic brush again. The toner becomes a normal development area toward the latent image carrier, and the toner that has moved backward can adhere to the latent image carrier again. This state is shown in FIG. 17d.

When the latent image sleeve and the latent image carrier relatively move with time and the rear end of the image portion approaches the magnetic brush position H4 as shown in FIG. 16b, the state shown in FIG. Ear falls. That is, considerable toner on the latent image carrier moves backward to the carrier side of the tip of the magnetic brush, and in a state where the amount of toner adhered to the image portion is reduced, the tip falls and the development is completed. This is the "back end blank area", which appears more prominently in halftone. Further, when developing with a higher linear velocity ratio, the impact force when the magnetic brush comes into contact with the latent image carrier is large, and the adhesive force between the carrier and the toner is reduced, so that the toner easily moves. ing. When this phenomenon occurs,
The trailing edge is jagged (wavy state)
Consider the mechanism.

The developer on the developing sleeve, which rotates around the fixed magnet, forms a magnetic brush along the line of magnetic force, and rises completely at a portion having a magnetic pole peak, and develops at a portion having a high tangential magnetic pole between the magnetic poles. It is along the sleeve surface, and is conveyed on the developing sleeve while repeating this. In particular, the above phenomenon is remarkable in a developer formed in a thin layer by a regulating member. When the magnetic brush enters the developing area, the developer conveyed along the surface of the developing sleeve between the developing main magnetic pole and the magnetic pole immediately before the main magnetic pole rises according to the main magnetic pole magnetic field and rises. To develop. Then, after the development, the magnetic brush which has fallen down in accordance with the magnetic field of the development main magnetic pole is transported to the downstream side on the surface of the development sleeve.

Here, if the rise of the magnetic brush in the longitudinal direction of the developing sleeve varies at the start of the rise of the magnetic brush according to the magnetic field of the developing main magnetic pole, the position at which the magnetic brush contacts the latent image carrier also varies. .
In other words, due to variations in the rise of the magnetic brush,
The state in which the magnetic brush reaches a complete rise at a position deviating from the peak portion of the main magnetic pole is scattered in the longitudinal direction of the sleeve, and the magnetic brushes adjacent in the longitudinal direction of the sleeve may be attracted, so they are individually separated. The ears are large, and the contact positions with the latent image carrier are irregular in the longitudinal direction of the sleeve and vary. Such a situation,
The same occurs after the magnetic brush rubs against the latent image carrier. As a result, as described above, the blank portion at the trailing edge of the image due to the counter charge generated by the toner drift phenomenon of the magnetic brush tip carrier becomes jagged as shown in FIG. 8B. On the other hand, if the magnetic brush that rises in accordance with the main magnetic pole magnetic field can achieve uniform rise in the sleeve longitudinal direction, the jagged shape at the rear end of the image should disappear as shown in FIG. is there.

Regarding the above-mentioned “back end blank area” phenomenon, as shown in FIG. 18, when an area density of about 5 mmφ is measured on a solid image of several cm square in a state of being applied to the back end, the condition shown in FIG. The result appears as the density characteristic at 2 (the developing nip width is about 4 mm). In the graph of FIG. 19, the vertical axis represents the rear end density of the solid image shown in FIG. 18, and the horizontal axis represents the developing sleeve moving speed Ss and the latent image carrier moving speed Sp.
It shows the speed ratio with the above. When the linear velocity ratio is further increased from, for example, about 1.1, the density in the portion other than the portion where the trailing edge white spot occurs increases, but the state shown in FIG.
Therefore, the trailing edge white spots become remarkable, and the width gradually widens, resulting in a large variation in the measured density results at the density measurement positions.

In order to eliminate the above drawbacks, a condition in which the behavior described with reference to FIGS. 16 and 17 does not change to the state shown in FIG. 17b is found, and the broken line in FIG.
As shown in the figure, a characteristic is obtained in which the trailing edge density does not decrease even when the linear speed ratio increases, or the trailing edge density increases as the linear speed ratio increases and toner supply increases. Find a way.

As a direction of improvement for eliminating the above-mentioned drawbacks, one way is to make the potential difference between the developing bias Vb and the background portion zero. Such a method is a practical improvement method because the toner has a charge amount distribution and needs to be set to a potential difference that does not cause background contamination in accordance with toner having a low charge amount that can cause background contamination. Can not be. Further, when a magnetic toner in which a magnetic substance is mixed with the toner is used, the toner is affected by the magnetic field on the developing sleeve side, and the movement by the electric field is slow, so that the state of FIG. However, toner adhesion to the image area on the latent image carrier is reduced, and the density of the entire image does not increase. It is difficult to do. Improving the carrier characteristics and the structure of the carrier surface will leave the possibility of an improved method, but considering durability etc., it is not practical to change the carrier just for this purpose, but a realistic improvement It cannot be the measure.

In order to ensure good image quality, it can be pointed out that factors such as the reproducibility of fine lines, especially the aspect ratio, the reproducibility of dots, and the uniformity of toner adhesion are taken into consideration.
This is an item that should be achieved together with the elimination of trailing white spots / jaggies.

In view of the above points, it is an object of the present invention to improve the image density and image quality of a low-contrast image by improving the occurrence of white spots / jaggies at the rear end.

[0022]

According to the present invention, a developer is pumped up to a developing sleeve, a magnetic brush is formed on the developing sleeve, and the latent image carrier is rubbed with the developer. In a developing method for visualizing an image, the problem can be solved by configuring the magnetic brush so as to raise ears uniformly in the longitudinal direction of the developing sleeve and to contact the latent image carrier. Alternatively, if the magnetic brush is configured to be uniformly spaced from the latent image carrier in the longitudinal direction of the developing sleeve so that the magnetic brush falls, the above problem can be solved more reliably. Here, "uniform" in the hot standing / falling
For example, when the carrier diameter is 50 μm, the amplitude of the ears of the magnetic brush in the longitudinal direction of the sleeve is about 2 mm, preferably about 1 mm.

Further, the attenuation rate of the magnetic flux density in the normal direction of the main magnetic pole causing ears in the developing region is 40% or more, preferably 50% or more.
%, The above problem is solved. The increase in the attenuation rate of the magnetic pole means that the width of the spike between the rising and falling of the magnetic brush is reduced, and as a result, the magnetic brush rises short and densely.
Such a short and densely rising magnetic brush, when considered in the longitudinal direction of the sleeve, brings about uniform rise and fall. Increasing the damping rate can be realized by selecting the 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 2
It is preferable that the angle is set to 2 ° or less, preferably 18 ° or less.
The half-value width is a half value of the maximum normal magnetic force (apex) of the magnetic force distribution curve in the normal direction (for example, when the maximum normal magnetic force of a magnet made by the N pole is 120 mT (millitesla), the half value 50% is 60 mT, half value 8
(There is also an expression of 0%, in this case 96 mT)
Is the angular width of the portion pointing to

As one measure for reducing the half 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 was reduced, the spike position of the magnetic brush was closer to the main pole, the development nip itself was also narrowed, and good image density and image quality could be secured. It is preferable that an auxiliary magnetic pole for assisting the formation of the magnetic force of the main magnetic pole be formed between the main magnetic pole and the upstream and / or downstream transport magnetic poles in the developer transport direction. For this purpose, it is effective to dispose an auxiliary magnet on the upstream side and / or downstream side of the main magnet forming the main magnetic pole in the developer conveying direction. When the auxiliary magnetic pole is formed on the downstream side of the main magnetic pole, it is possible to prevent unevenness of the brush, which causes scavenging when the ear falls down in the short and uniform magnetic brush. Further, when the auxiliary magnetic pole is formed on the upstream side of the main magnetic pole, it is possible to prevent the brush from receiving a counter charge when the ears stand in the short and uniform magnetic brush.

The central angle of the magnet roller between the main magnet and the auxiliary magnet is 35 ° or less, preferably 30 ° or less; the half width of the auxiliary magnet is 40 ° or less, preferably 35 ° or less. Alternatively, it is preferable that the center angle of the magnet roller at the magnetic pole inflection point between the auxiliary magnet and the magnet for the developer carrying magnetic pole located further outside thereof be 120 ° or less, and more preferably 90 ° or less. In this case, regarding the half width and the lower limit of the central angle, since the magnets forming the respective angles have the size and shape, 0 ° is not practical, and is about 60 mT, which is the minimum magnetic force necessary for development. Is required. The main magnetic pole and the auxiliary magnetic pole are different from each other. It is advantageous if at least the magnet forming the main pole is made of a rare earth metal alloy.

[0026]

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 a photosensitive drum 1 serving as an electrostatic latent image carrier and a laser beam for forming a latent image on a uniformly charged surface are exposed. 3, a developing device 4 for forming a toner image by attaching a charged toner to a latent image on the drum surface, a transfer device 5 for transferring the formed toner image on the drum to recording paper 6, a residual toner on the drum And a static elimination lamp 8 for eliminating the residual potential on the drum. In such a configuration, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2 is formed with an electrostatic latent image by exposure 3 and a toner image is formed by the developing device 4. 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. The photosensitive drum 1 from which the residual toner has been removed is initialized by the discharge lamp 8, and is 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
If it is 0 μm, it is set to 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. In the present embodiment, it is preferable to set it to 10 times or less (0.55 mm). If the width is wider than this, it becomes difficult to obtain a desirable image density.

A doctor blade 45 for regulating 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 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, as shown in detail in FIG. 3, the developing main magnet P1b that causes the developer to spike in the developing region, and the main magnetic pole magnetic force forming auxiliary magnet P1 that assists the magnetic force generation of the main magnetic pole.
a, P1c, magnets P4 for pumping the developer onto the developing sleeve 43, 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. ing. Each of these magnets P1
b, P1a, P1c, P4, P5, P2 and P3 are arranged radially of the developing sleeve 43. In this example, the magnet roller body 44 is constituted by an eight-pole magnet, but the magnet (magnetic pole) 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. You may comprise 10 poles or 12 poles.

In particular, as shown in FIG.
Numeral 1 is composed of magnets having a small cross section arranged in order from P1a, P1b, and P1c from the upstream side. These magnets with small cross sections are made of rare earth metal alloy,
A samarium alloy magnet, particularly a samarium cobalt alloy magnet, can also be used. Maximum energy product in a typical iron neodymium boron alloy magnet of the rare earth metal alloy magnet is 358kJ / m ^3, the maximum energy product of iron neodymium boron alloy bond magnet 80 kJ / m
It is around ³ . With such a magnet, unlike the conventional magnet, the required magnetic force on the surface of the developing roller can be secured even if the size is considerably reduced. For conventional conventional ferrite magnets and ferrite bonded magnets, the maximum energy product is 36 kJ each.
/ M ^{3 and} around 20 kJ / m ³ . If it is permissible to increase the sleeve diameter, the half-width can be reduced by using a ferrite magnet or a ferrite bonded magnet to make the shape larger, or by making the magnet end facing the sleeve thinner. It is possible. Also,
In the present embodiment, the magnet is formed by a magnet having a small cross section. However, the magnet may be formed by a magnet roller formed by integral molding. Further, magnets other than the P1 pole group are integrally molded to form the P1 pole group individually. They may be integrated or formed simultaneously. The fan-shaped magnet may be formed by bonding to a magnet roller shaft.

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 as a pie chart graph, 8
A magnet having a normal magnetic force of 5 mT or more was used.
In this example, it was confirmed that no abnormal image such as carrier adhesion occurred by using a magnet having a magnetic force of 60 mT or more as the main magnetic pole magnetic force forming auxiliary magnet P1c on the downstream side of the main magnet P1b. When the magnetic force was smaller than this, carrier adhesion occurred. 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 or P1c. Can be. The magnets P1a, P1b,
The magnet width of P1c was 2 mm. At this time, the half width of P1b was 16 °.

As another example, as shown in FIG. 4, the main magnet P1c is formed only on the downstream side of the main magnet P1b.
Was arranged, the half-value width of the main magnet P1b did not change, but the magnetic force of the main magnetic pole (P1b portion) decreased by several percent. Since there was no main magnetic pole magnetic force forming auxiliary magnet (P1a) on the upstream side, it was confirmed that the magnetic force of the P1a portion was reduced to about 30 mT, but this portion is a portion that can be covered by the inlet seal, In such a configuration, since the portion is not exposed to the image forming unit, it is possible to supply the developer to the main magnetic pole without affecting the image. Further, it was confirmed that the half width was further reduced by reducing the width of the magnet. The half width of the main pole when using a magnet having a width of 1.6 mm was 12 °.

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. For comparison, FIG. 5 schematically shows details of the magnetic force of the conventional magnet roller. The measuring device used for the measurement was a Gauss meter manufactured by ADS (HGM)
-8300) and A1 type axial probe manufactured by ADS, and recorded by a pie chart recorder.

According to the observation by the magnet roller in this example, the magnetic flux density in the normal direction on the sleeve surface of the main magnetic pole P1b is 95%.
mT, the normal direction magnetic flux density at a portion 1 mm away from the sleeve surface was 44.2 mT, and the change in 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 53.
5%. 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 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, which is shorter than the magnetic brush (about 3 mm) formed by a conventional magnet roller, and has a denser brush. It is 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 (FIG. 5), the normal magnetic flux density on the sleeve surface of the main pole is 73 mT, and the normal magnetic flux density at a portion 1 mm away from the sleeve surface is 51.8 mT.
T, and the amount of change in 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%.

The main magnet P1 based on FIG. 3 showing the magnetic force distribution in the normal direction of the magnet roller according to the present invention and its magnitude is shown.
As can be seen from FIG. 6 again showing the positional relationship between b and the auxiliary magnets P1a and P1c, the half value when the maximum normal magnetic force of the main magnet is 95 mT is 47.5 mT, and the half value width is 22 °. It is. 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 half width of the main magnetic pole magnetic force forming auxiliary magnets P1a and P1c is set to 35 ° or less. The half width at this portion cannot be set relatively small as at the main pole because the half width of P2 and P6 located outside is large. Further, the included angle between the main magnetic pole magnetic force forming auxiliary magnets P1a and P1c on both sides of the main magnet P1b is set to 30 ° or less. In the above-described example in which the auxiliary magnetic pole is formed upstream and downstream of the main magnetic pole in the developer transport direction, the included angle is set to 22 ° in order to set the half width at the main magnetic pole to 16 °. Further, the included angle of the inflection point (0 mT: the point at which the magnetic force changes from the N pole to the S pole and the magnetic force changes from the S pole to the N pole) by the main magnetic pole magnetic force forming auxiliary magnets P1a and P1c and the magnets P2 and P6 outside the auxiliary magnet is set. 120 °
Do the following.

As a specific example, a diameter of 16 mm and a diameter of 20 mm
The magnetic flux density and the like of the FeNdB-bonded magnet roller according to the present invention in terms of diameter are shown in Table 1 in comparison with the magnet roller of the conventional configuration. The measurement of the magnet roller is performed by using the TS-10A type probe manufactured by ADS and the Gauss meter HGM-89 described above.
This was performed using 00S. The position of the Hall element in the measurement of the magnetic flux density in the normal and tangential directions is 0.5 m from the sleeve surface.
m.

[0038]

[Table 1]

Under the above conditions, the occurrence of a trailing edge white spot and a jagged shape are suppressed. In other words, by narrowing the half width of the main pole, the development and nip with a short magnetic brush are realized and the developing nip is narrowed, and the movement of the magnetic brush tip side toner to the root side shown in FIG. Since the rise and fall of the sleeve are made uniform in the longitudinal direction of the sleeve as much as possible, jagged shapes and white spots at the rear end of the image are less likely to occur.

FIG. 7 shows the relationship between the degree of uniformity of the magnetic brush ears and the rank of the trailing edge of the image. The degree of the uniformity of the magnetic brushes causing ears along the lines of magnetic force generated by the main magnetic pole is represented by the rank. ing. The smaller the rank number, the more the ears vary, and the larger the rank number, the more uniform the ears. It can be seen that the higher the degree of uniformity of the ears, the better the rank at the trailing edge of the image.

If the degree of uniformity of the magnetic brush is low, as shown in FIG. 8B, the magnetic brush at the portion in contact with the latent image carrier becomes non-uniform. In contrast, the distance of the toner that moves due to the electric charge in the non-image portion changes, and the toner density near the latent image carrier becomes non-uniform in the longitudinal direction. In addition, an image trailing edge white spot occurs in a state where the trailing edge of the image is wavy. Conversely, when the spike uniformity is good, as shown in FIG. 8A, when the magnetic brush contacts the latent image carrier uniformly in the longitudinal direction, the movement of the toner becomes uniform, and The occurrence of white spots can be suppressed. This is the same on the side where the magnetic brush is separated from the latent image carrier, and it is desirable that the magnetic brush be separated uniformly. When the magnetic brush comes out of the developing area, the brush spikes are developed in a uniform state in the sleeve longitudinal direction. When falling into the sleeve, the scavenge becomes uniform. When the magnetic brush causes the developing sleeve to fall down unevenly like a conventional magnet roller, there is a difference in the amount of scavenging, creating a state in which the magnetic brush sweeps the rear end of the image, causing abnormal images to occur. Will prompt you.

According to the present invention, the reproducibility of the horizontal line (especially, the securing of the aspect ratio), the reproducibility of the dots, and the uniformity of the toner adhesion are improved, as well as the occurrence of the occurrence of the trailing edge blank and the jagged shape. The image is shown in FIG. 9 and compared with FIG.

If the main magnetic pole is further controlled and only one row of carriers can contact the photoconductor, development can be performed with a nip width of [carrier particle diameter × linear velocity ratio (Ss / Sp)) or more. Becomes

The uniformity of the magnetic brush can be represented by a half width. FIG. 10 shows the relationship between the half width of the main magnetic pole and the uniformity of spikes of the magnetic brush. The smaller the half width, the better the uniformity of the magnetic brush ears. It is clear from FIG. 7 that the image is improved by making the ears uniform.

It is apparent from FIG. 11 that the trailing edge white spot rank is improved by reducing the half width.
11 can be derived from the relationship between FIG. 7 and FIG. 10. The smaller the half width, the higher the uniformity of the magnetic brush spikes (FIG. 10). As it goes up (FIG. 7), FIG.
The relationship as shown in FIG.

A state in which the spikes are uniform can be created by forming the main magnetic pole using a magnet roller having a high damping rate. 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). However, reducing the half width increases the amount of magnetic force flowing to the adjacent magnet and increases the distance from the sleeve surface. The magnetic flux density in the normal part at the bent portion is reduced. 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. Since the magnetic flux density is concentrated 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 for 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 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 half-width of the main pole is narrowed to realize rising and falling with a short magnetic brush, and the rising and falling are made uniform in the longitudinal direction of the sleeve. As shown in the curve, it was confirmed that the characteristics were not reduced even when the linear velocity ratio was increased (condition 1). Thus, it is possible to provide a developing device that realizes an improvement in image quality without occurrence of trailing edge whiteout / jagging.

Next, the application of the present invention will be extended to an electrophotographic color copying machine (hereinafter referred to as a color copying machine).
First, the schematic configuration and operation of the color copying machine will be described with reference to FIG. The color copier includes a color image reading device (hereinafter, referred to as a color scanner) 11, a color image recording device (hereinafter, referred to as a color printer) 12,
It is composed of a paper feed bank 13 and the like.

The color scanner 11 converts the image of the original 10 on the contact glass 101 into an illumination lamp 102, mirror groups 103a, 103b, 103c and a lens 104.
And color image information of the document 10 is read for each of red, green, and blue (hereinafter, referred to as R, G, and B) color separation lights, respectively, and an electrical image signal is output. Convert to Here, the color sensor 105
In this example, the image is composed of R, G, B color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three color images obtained by color separation of the image of the document 10. Based on the R, G, and B color separation image signal intensity levels obtained by the color scanner 11, a color conversion process is performed by an image processing unit (not shown), and black (hereinafter, referred to as Bk) and cyan (hereinafter, referred to as Bk). , C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y) color image data.

The operation of the color scanner 11 for obtaining the Bk, C, M, and Y color image data is as follows. The illumination lamp 102 receives a scanner start signal at the same timing as the operation of the color printer 12 described later.
An optical system including mirror groups 103a, 103b, 103c and the like scans the document 10 in the left direction of the arrow, and obtains one color image data for each scan. By repeating this operation four times in total, color image data of four colors is sequentially obtained. Then, each time the color printer 12 sequentially visualizes the images and superimposes them to form a final four-color full-color image.

The color printer 12 includes a photosensitive drum 20 as an image carrier, a writing optical unit 22, a revolver developing unit 23, an intermediate transfer device 26, a fixing device 27 and the like. The photosensitive drum 20 rotates in the counterclockwise direction indicated by an arrow, and around the photosensitive drum 20, a photosensitive member cleaning device 201, a static elimination lamp 202, a charger 203,
A potential sensor 204, a selected developing device of the revolver developing unit 23, a development density pattern detector 205, an intermediate transfer belt 261 of the intermediate transfer device 26, and the like are arranged.

The writing optical unit 22 includes:
The color image data from the color scanner 11 is converted into an optical signal, and optical writing corresponding to the image of the document 10 is performed, thereby forming an electrostatic latent image on the photosensitive drum 20. The writing optical unit 22 includes a semiconductor laser 221 as a light source, a laser emission drive control unit (not shown), a polygon mirror 222 and a rotation motor 223 thereof, and an f / θ lens 2.
24, a reflection mirror 225 and the like.

The revolver developing unit 23 includes:
Bk developing device 231K, C developing device 231C, M developing device 23
It comprises a 1M and Y developing unit 231Y, a revolver rotation drive unit which rotates each developing unit in a counterclockwise direction indicated by an arrow, and the like. Each developing device includes a developing sleeve that rotates by contacting a spike of developer with the surface of the photosensitive drum 20 to develop an electrostatic latent image, and a developer paddle that rotates to pump up and agitate the developer. It is composed of The toner in each developing unit 231 is negatively charged by stirring with the ferrite carrier, and a developing bias in which an AC voltage Vac is superimposed on a negative DC voltage Vdc by a developing bias power supply (not shown) is applied to each developing sleeve. The developing sleeve is biased to a predetermined potential with respect to the metal base layer of the photosensitive drum 20. In the standby state of the copying machine main body, the Bk developing unit 231K of the revolver developing unit 23 is set at the developing position, and when the copying operation is started, the color scanner 11 starts reading the Bk color image data at a predetermined timing. Then, based on the color image data, optical writing with a laser beam and formation of an electrostatic latent image are started (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk latent image. The same applies to C, M, and Y). The Bk developing sleeve is started to rotate before the leading end of the electrostatic latent image reaches the Bk developing position so that development can be performed from the leading end of the Bk latent image, and the Bk latent image is developed with BK toner. B
The developing operation of the k latent image area continues, and the rear end of the electrostatic latent image is Bk
Upon passing the developing position, the revolver developing unit 23 rotates until the developing device for the next color (normally, the C developing device in this example) immediately reaches the developing position. This is at least
The process is completed before the leading end of the electrostatic latent image based on the next image data arrives.

The revolver developing unit 23 will be described later in detail. The intermediate transfer device 26 includes an intermediate transfer belt 261, a belt cleaning device 262,
It comprises a paper transfer corona discharger (hereinafter referred to as a paper transfer device) 263 and the like. The intermediate transfer belt 261 is stretched around a drive roller 264a, a transfer opposed roller 264b, a cleaning opposed roller 264c, and a group of driven rollers.
The drive is controlled by a drive motor (not shown). The belt cleaning device 262 includes an entrance seal, a rubber blade, a discharge coil, an entrance seal, a mechanism for contacting and releasing the rubber blade, and the like. While the image of the fourth color is being transferred to the belt, the intermediate transfer belt 2 is
The entrance seal and the blade are kept apart from the surface of 61. The paper transfer unit 263 applies an AC voltage + DC voltage or a DC voltage by a corona discharge method, and collectively transfers the superimposed toner image on the intermediate transfer belt 261 to recording paper.

The recording paper cassette 207 in the color printer 12 and the recording paper cassette 30 in the paper supply bank 13 are also provided.
Recording papers of various sizes are stored in a, 30b, and 30c.
Paper is fed and conveyed in the direction of the registration roller pair 29 by the paper feed rollers 28, 31a, 31b, 31c. Further, a manual tray 21 for manually feeding OHP paper or thick paper is provided on the right side of the printer 12 in the drawing.

When the image forming cycle is started in the above-described color copying machine, first, the photosensitive drum 20 is rotated counterclockwise as indicated by an arrow and the intermediate transfer belt 261 is rotated clockwise as indicated by an arrow by a drive motor (not shown). Is done. With the rotation of the intermediate transfer belt 261, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed, and finally the intermediate transfer belt 2 in the order of Bk, C, M, and Y
A toner image is formed superimposed on 61.

The Bk toner image is formed as follows. The charger 203 uniformly charges the photosensitive drum 20 with a negative charge to about -700 V by corona discharge. And
The semiconductor laser 221 performs raster exposure based on the Bk color image signal. When this raster image is exposed, in the exposed portion of the photosensitive drum 20, which is initially uniformly charged, the charge proportional to the exposure light amount disappears, and a Bk latent image is formed.
Then, when the negatively charged Bk toner on the Bk developing sleeve comes into contact with the Bk latent image, the toner does not adhere to the portion of the photosensitive drum 20 where the charge remains, and the portion without the charge, that is, the light is exposed. The Bk toner is adsorbed to the portion, and a Bk toner image similar to the electrostatic latent image is formed. Then, the Bk toner image formed on the photosensitive drum 20 is
The toner image is transferred from the photosensitive drum 20 to the intermediate transfer belt 261 by belt transfer onto the surface of the intermediate transfer belt 261 which is driven at a constant speed in contact with the photosensitive drum 20. ).

A small amount of untransferred residual toner on the photoconductor drum 20 is cleaned by the photoconductor cleaning device 201 in preparation for reuse of the photoconductor drum 20. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.

On the photosensitive drum 20 side, the process proceeds to the C image forming process after the Bk image forming process, and C image data reading by the color scanner 11 starts at a predetermined timing.
The formation of the C latent image is performed by the laser light writing based on the C image data. Then, after the rear end of the previous Bk latent image has passed and before the front end of the C latent image has reached, the rotating operation of the revolver developing unit 23 is performed, and the C developing device 2 is rotated.
31C is set at the development position, and the C latent image is developed with C toner. After the development of the C latent image area continues, when the rear end of the C latent image passes the development position, the Bk developing device 231B
As in the case of the above, the rotation operation of the revolver developing unit 23 is performed, and the next M developing device 231M is moved to the developing position. This is also completed before the leading end of the next M latent image reaches the developing position.

In the M and Y image forming steps, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those of the above-described steps Bk and C, and therefore the description is omitted.

The Bk, C, M, and Y toner images formed on the photosensitive drum 20 are sequentially aligned on the same surface of the intermediate transfer belt 261 to form a four-color superimposed toner image. In the next transfer step, the four color toner images are collectively transferred to the recording paper by the paper transfer unit 263.

At the time when the image forming operation is started, the recording paper is fed from either the recording paper cassette or the manual feed tray, and waits at the nip of the registration roller pair 29. Then, the intermediate transfer belt 26 is supplied to the paper transfer device 263.
When the leading edge of the toner image on the recording paper 1 is approaching, the registration roller pair 29 is driven so that the leading edge of the recording paper coincides with the leading edge of the toner image, and registration of the recording paper with the toner image is performed. Then, the recording paper is superimposed on the toner image on the intermediate transfer belt 261 and passes over the positive potential paper transfer unit 263. At this time, the recording paper is charged with a positive charge by the corona discharge current, and the toner image is transferred onto the recording paper. Subsequently, when the recording paper passes through a portion opposite to a separation static eliminator by an AC + DC corona (not shown) to be disposed on the left side in the drawing of the paper transfer device 263, the recording paper is neutralized, and peels off from the intermediate transfer belt 261. Move to the conveyor belt 211.

Then, the recording paper on which the four-color superimposed toner image has been collectively transferred from the surface of the intermediate transfer belt 261 is transferred to the conveyance belt 2.
The toner image is conveyed to the fixing device 27 at 11 and is fused and fixed at a nip portion between the fixing roller 271 and the pressure roller 272 controlled to a predetermined temperature, sent out of the apparatus main body by the discharge roller pair 32, and copied (not shown). Stacked face up on tray to get full color copy.

On the other hand, the surface of the photosensitive drum 20 after the belt transfer is cleaned by the photosensitive member cleaning device 201 (brush roller, rubber blade),
02, the charge is uniformly removed. Further, the surface of the intermediate transfer belt 261 after the transfer of the toner image onto the recording paper is cleaned by pressing the blade of the belt cleaning device 262 again by the blade contact / separation mechanism.

Next, the revolver developing unit 23 will be described. FIG. 13 shows each of the developing devices 231K and 231.
FIG. 9 is a cross-sectional view illustrating an internal structure of a revolver developing unit 23 in which C, 231M, and 231Y are integrated. Each of the developing units 231K, 231C, 2 of the revolver developing unit 23
31M and 231Y are respectively supported by stay members 242 in the shape of a hollow rectangular tube provided between front and rear end plates (not shown). Further, each of the developing devices 231K, 231C, 231
M and 231Y are the same type of developing device casing 2 respectively.
83K, 283C, 283M, 283Y.
Each of these developing unit casing parts 283K, 283C, 28
3M and 283Y contain a carrier as a developer and a two-component developer composed of toner of each color. In the illustrated example, the Bk developing device 2 containing the black toner and the carrier is located at the developing position facing the photosensitive drum 20.
At 31K, a Y developing device 231Y containing yellow toner and carrier, an M developing device 231M containing magenta toner and carrier, and a C developing device 231C containing cyan toner and carrier are arranged in a counterclockwise direction in the figure. .

Since the internal structure of each of the four developing units is exactly the same, the internal structure of the Bk developing unit 231K at the developing position will be described below with reference to FIG. Are the same reference numerals as those in the Bk developing device, and are Y, Magenta, and cyan developing devices.
Reference numerals with subscripts of M and C are shown in the figure, and the description thereof is omitted.

As shown in FIG. 13, a developing roller 284 as a developer carrying member provided in the developing device is disposed so as to be close to the photosensitive drum 20 as a latent image carrying member. A developing region is formed in the facing portion. On the developing roller 284, a developing sleeve 285 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). Provided. In this example, the photosensitive drum 2
The drum diameter of 0 is set to 90 mm, and the drum linear velocity is set to 200 mm / sec. The sleeve diameter of the developing sleeve 285 is set to 30 mm, and the linear velocity of the sleeve is set to 240 mm / sec. Therefore, the ratio of the sleeve linear speed of the developing sleeve 285 to the drum linear speed of the photosensitive drum 20 is 1.2. The photosensitive drum 20 and the developing sleeve 2
The developing gap, which is an interval from the distance 85, is set to 0.4 mm.

In the developing sleeve 285, there is fixedly provided a magnet roller body 286 for forming a magnetic field so that the developer rises on the surface of the developing sleeve 285. At this time, the carrier constituting the developer causes a chain-like spike on the developing sleeve 285 along the lines of magnetic force generated from the magnet roller body 286, and the carrier that spikes in the chain-like form. The magnetic brush is formed by the charged toner being attached. This magnetic brush is used for the developing sleeve 2
With the rotation transfer of 85, the transfer is performed in the same direction (clockwise) as the developing sleeve 285. The magnet roller body 286 has a plurality of magnetic poles. More specifically, as shown in detail in FIG. 14, a developing main magnetic pole P1b for raising a developer in a developing area portion, main magnetic pole forming auxiliary members P1a and P1c for assisting formation of a developing main magnetic pole magnetic force, and a developing sleeve 285 are provided. Magnetic pole P for pumping up developer
4, P5, magnetic poles P6, P7, P8 for transporting the pumped developer to the development area, and magnetic poles P2, P3 for transporting the developer in the area after development. These magnetic poles P1b, P1a, P1c, P4, P5, P6, P7, P
8, P2 and P3 are arranged radially of the developing sleeve 285. Table 2 shows the magnetic flux density and the like of the FeNdB-bonded magnet roller according to the present invention with the diameter of 30 mm in comparison with the magnet roller having the conventional configuration.

[0071]

[Table 2]

The magnet roller 286 is composed of 10 poles. However, in order to improve the pumping property and the black solid image followability, the number of magnetic poles is further increased between the P3 pole and the doctor blade. Is also good. Regarding the shape of the magnet, the sectional shape of each magnet inside the magnet roller may be square, but other shapes such as a fan shape and a bamboo ring shape are also conceivable.

The measurement of the magnet roller is performed by using the above-described TS-10A type probe manufactured by ADS, Gauss meter HGM-89.
This was performed using 00S. The position of the Hall element in the measurement of the magnetic flux density in the normal and tangential directions is 0.5 m from the sleeve surface.
m.

In the developing device having the developing roller having the above-described configuration, the amount of the developer carried on the developing roller 284 and conveyed to the portion facing the photosensitive drum 20 is regulated in the developing device casing 283K. A blade blade 287, a first conveying screw 288 that conveys the negative part of the developer regulated by the doctor blade 287 and pressed into the developing device casing from the rear to the front along the central axis direction, and the central axis. A second transport screw 289 that transports the developer in a direction opposite to the first transport screw 288 along the direction is provided. A toner concentration sensor for detecting the toner concentration of the developer contained in the developing device casing 283K is provided in the developing device casing 283K below the second conveying screw 289.

[0075]

According to the present invention, the rise and fall with a short magnetic brush can be realized to narrow the developing nip, and the rise and fall can be made uniform in the longitudinal direction of the sleeve. Occurrence of white spots and jagged shapes at the trailing edge, as well as the generation of fine line images, and the reduction of point image thinning phenomena can be suppressed to suppress the occurrence of abnormal images, increase image density, and reduce low-contrast images. It can be good.

[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 diagram showing a magnetic force distribution when the magnet P1a is missing.

FIG. 5 is a diagram showing a magnetic force distribution of a conventionally known developing roller for comparison.

FIG. 6 is a diagram illustrating an angular positional relationship between a main magnet and a main magnetic pole magnetic force forming auxiliary magnet.

FIG. 7 is a graph rank-wise illustrating the relationship between the degree of spike uniformity of the magnetic brush and the degree of white spots at the rear end of an image.

8A and 8B are conceptual diagrams showing a state in the longitudinal direction of the developing sleeve according to the presence or absence of a trailing edge white spot, where FIG. 8A is a view using a magnetic brush according to the present invention, and FIG. 8B is a view using a conventional magnetic brush. It is.

FIG. 9 is an image diagram showing the size of a developing gap and a nip in a developing area in the present invention.

FIG. 10 is a graph showing a relationship between a half width of a main magnetic pole and a degree of spike uniformity of a magnetic brush.

FIG. 11 is a graph showing the relationship between the half width of a main pole and the degree of white spots on the trailing edge of an image.

FIG. 12 is a schematic configuration diagram of a color copying machine as an image forming apparatus according to the present invention.

FIG. 13 is a partial schematic configuration diagram of a revolver developing unit as a developing device according to the present invention.

FIG. 14 is a diagram showing a magnetic force distribution of a developing roller in the revolver developing unit of FIG. 10 and its magnitude.

FIG. 15 is an image diagram showing conventionally known developing gaps and nip sizes for comparison.

FIG. 16 shows the behavior of toner adhering to a carrier in a magnetic brush in a development nip in terms of a positional relationship with an electrostatic latent image, and shows the surface potential of the electrostatic latent image and the electrostatic latent image at the nip The position state and the movement of the magnetic brush in the nip are indicated by a and b, respectively.

FIG. 17 is a model diagram showing the state of adhesion between the carrier at the tip of the magnetic brush and the toner in FIG.
Correspond to the magnetic brush positions H1, H2, H3, and H4, respectively.

FIG. 18 is a diagram showing a solid image used for observing a trailing edge white spot.

FIG. 19 is a graph illustrating a relationship between a moving speed of a developing sleeve, a speed ratio of a moving speed of a photoconductor, and an image density.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 4 developing device 41 developing roller 43 developing sleeve 44 magnet roller body 45 doctor blade 47 screw

Claims (27)

[Claims] 1. A developing method for drawing a developer to a developing sleeve, forming a magnetic brush on the developing sleeve, and rubbing the developer against a latent image carrier to visualize the latent image, comprising: A developing method, wherein a brush is uniformly raised in the longitudinal direction of a developing sleeve and comes into contact with a latent image carrier. 2. A developing method for drawing a developer to a developing sleeve, forming a magnetic brush on the developing sleeve, and rubbing the developer against a latent image carrier to visualize the latent image, A developing method characterized in that the brush is evenly separated from the latent image carrier in the longitudinal direction of the developing sleeve and causes falling of the ear. 3. A developing method for drawing a developer to a developing sleeve, forming a magnetic brush on the developing sleeve, and rubbing the developer against a latent image carrier to visualize the latent image. Forming an auxiliary magnetic pole for assisting the formation of a magnetic force of a main magnetic pole for raising the magnetic field. 4. An auxiliary magnetic pole for assisting formation of a main magnetic pole magnetic force is formed between a main magnetic pole for starting a developer and a conveying magnetic pole on an upstream side and / or a downstream side in a developer conveying direction. Item 4. The developing method according to Item 3. 5. A developing device for drawing a developer to a developing sleeve, forming a magnetic brush on the developing sleeve, and rubbing the developer against a latent image carrier to visualize the latent image, A developing device wherein the brush uniformly raises in the longitudinal direction of the developing sleeve and comes into contact with the latent image carrier. 6. A developing device for drawing a developer to a developing sleeve, forming a magnetic brush on the developing sleeve, and rubbing the developer against a latent image carrier to visualize the latent image, A developing device wherein a brush is uniformly separated from a latent image carrier in a longitudinal direction of a developing sleeve, and causes a fall of an ear. 7. A developer carrier for visualizing a latent image includes a non-magnetic sleeve and a magnet roller fixedly disposed in the sleeve, wherein the magnet roller draws up a magnetic pole of the developer and transports the developer. A developing device comprising a magnetic pole and a main magnetic pole for developing a developer, wherein an attenuation rate of a magnetic flux density in a normal direction of the main magnetic pole is 40% or more. 8. The developing device according to claim 7, wherein the magnet forming the main magnetic pole is made of a rare earth metal alloy. 9. A developer carrier for visualizing a latent image, comprising a non-magnetic sleeve and a magnet roller fixedly arranged in the sleeve, wherein the magnet roller draws up a developer magnetic pole, and transports the developer. A developing device comprising a magnetic pole and a main magnetic pole for developing a developer, wherein the half width of the main magnetic pole is 22 ° or less. 10. A developer carrier for visualizing a latent image, comprising a non-magnetic sleeve and a magnet roller fixedly disposed in the sleeve, wherein the magnet roller draws up developer magnetic poles, and transports the developer. What is claimed is: 1. A developing device comprising: a magnetic pole; and a main magnetic pole for developing a developer, comprising: an auxiliary magnet for assisting formation of a magnetic force of the main magnetic pole. 11. The developing device according to claim 10, wherein the auxiliary magnet is arranged upstream and / or downstream of a main magnet forming the main magnetic pole in a developer conveying direction. 12. The developing device according to claim 11, wherein a center angle of the magnet roller by the main magnet and the auxiliary magnet is set to 35 ° or less. 13. The developing device according to claim 10, wherein the auxiliary magnet has a half width of 40 ° or less. 14. The magnetic roller according to claim 11, wherein the center angle of the magnet roller at the magnetic pole inflection point between the auxiliary magnet and the magnet for the developer carrying magnetic pole located further outside thereof is 120 ° or less. The developing device as described in the above. 15. The developing device according to claim 10, wherein the main magnetic pole and the auxiliary magnet have different magnetic poles. 16. The magnet according to claim 1, wherein the magnet forming the main magnetic pole is made of a rare earth metal alloy.
The developing device according to any one of 0 to 15. 17. A magnet roller comprising a main magnetic pole for a developer spike, which is a magnet roller constituting a developer carrying member mounted on a developing device, comprising: a damping rate of a magnetic flux density in a normal direction of the main magnetic pole. Is 40% or more. 18. The magnet according to claim 17, wherein the magnet forming the main pole is made of a rare earth metal alloy.
4. The magnet roller according to 1. 19. A magnet roller comprising a main magnetic pole for developing a developer in a developing region, wherein the half width of the main magnetic pole is 22. ° or less. 20. A magnet roller constituting a developer carrier mounted on a developing device, comprising: an auxiliary magnet for assisting formation of a magnetic force of a main magnetic pole for developing a developer in a developing area. Magnet roller. 21. The magnet roller according to claim 20, wherein the auxiliary magnet is arranged upstream and / or downstream of a main magnet forming the main magnetic pole in a developer conveying direction. 22. The magnet roller according to claim 21, wherein the central angle of the magnet roller by the main magnet and the auxiliary magnet is set to 35 ° or less. 23. The magnet roller according to claim 20, wherein the auxiliary magnet has a half width of 40 ° or less. 24. The method according to claim 21, wherein a center angle of the magnet roller at a magnetic pole inflection point between the auxiliary magnet and a magnet for a developer carrying magnetic pole located outside the auxiliary magnet is 120 ° or less. The described magnet roller. 25. The magnet roller according to claim 20, wherein the main magnetic pole and the auxiliary magnet have different magnetic poles. 26. The magnet roller according to claim 20, wherein at least the magnet forming the main magnetic pole is made of a rare earth metal alloy. 27. An image forming apparatus comprising the developing device according to claim 5.