JP2003215927A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents the deviation of toner to a rear end while achieves improvement of fine linear reproducibility, prevention of a white spot phenomenon at the rear end, prevention of the reduction of a density in an image and prevention of a poor image. <P>SOLUTION: A main magnetic pole position is deviated by 2(°) to the upstream of a development sleeve surface moving direction. Thus, the nap of a developer is turned to the upstream side by 2(°) compared with a conventional nap to thereby prevent the toner deviation to the rear end, which restricts agent accumulation at the rear end of a main magnetic pole. As the adverse effect of deviating the main magnetic pole position to the upstream of the development sleeve surface moving direction, the nap of the developer is deviated from a development nip too much to shorten a sliding time with a photoreceptor and also reduce a density at the center of the image owing to the shortage of a toner supply amount to an electrostatic latent image. Thus, the deviation range of the main magnetic pole position is made to be ≤6(°), the reduction of the density at the center of the image is evaded and, then, the excellent image is obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a fax machine. More specifically, the present invention relates to an image forming apparatus that develops a latent image on a latent image carrier by causing a developer to stand on the surface of the developer carrier in a developing region where the latent image carrier and the developer carrier face each other. .

[0002]

2. Description of the Related Art Generally, in an electrophotographic or electrostatic recording type image forming apparatus, an electrostatic latent image corresponding to image information is formed on a latent image carrier such as a photosensitive drum or a photosensitive belt. A visible image is obtained by subjecting the electrostatic latent image to development processing by a developing device. In recent years, when performing such development processing, transferability, halftone reproducibility,
From the viewpoint of stability of development characteristics against temperature and humidity, a two-component developer including a toner and a carrier (hereinafter,
Simply called "developer". The mainstream is to use a two-component developing method using). In the developing device using this two-component developing method, the developer is carried on the developer carrier in a brush shape and held, and is conveyed to the developing area where the developer carrier and the latent image carrier face each other. . Then, in the developing area, the brush-like developer is rubbed against the surface of the latent image carrier, and the toner in the developer is supplied to the electrostatic latent image portion on the latent image carrier to form the electrostatic latent image. A so-called brush-type development for developing is performed.

A developer carrying member in a developing device for carrying out such brush-type developing is usually composed of a cylindrical developing sleeve and a magnet roller provided inside the developing sleeve and having a plurality of magnetic poles. Has been done. Among them, the magnet roller is provided with a plurality of magnetic poles that form a magnetic field for causing the developer to stand on the surface of the developing sleeve.
Then, the developer that has stood up on the surface of the developing sleeve is conveyed as the surface of the developing sleeve that moves relative to the magnet roller moves. In the developing area, the developer on the developing sleeve stands up along the magnetic lines of force emitted from the main magnetic pole of the magnet roller. The brush-like developer that stands up in a bristles contacts the surface of the latent image carrier so as to bend as the surface of the developing sleeve moves, and supplies toner to the electrostatic latent image.

In such a developing device, it is known that the closer the distance between the latent image carrier and the developing sleeve is in the developing area, the higher the image density is likely to be and the less the edge effect is. Therefore, it is desirable that the latent image carrier and the developing sleeve be close to each other. However, when the two are brought close to each other, the trailing edge of a black solid image or a halftone solid image becomes white, so-called "rear white void".
There is a problem in that the image quality is deteriorated due to the phenomenon called ".

The cause of the occurrence of trailing white spots and the deterioration of the reproducibility of fine lines is considered as follows. Of the developer on the developing sleeve, only the tip portion of the magnetic brush that contacts the latent image carrier contacts the latent image carrier and contributes to the visualization of the electrostatic latent image. At this time, normally, the surface moving direction of the developing sleeve in the developing area is the direction along with the latent image carrier, and its linear velocity is set to be faster than the linear velocity of the latent image carrier. The electrostatic latent image on the latent image carrier is moved relative to the electrostatic latent image so as to rub against it. Therefore, when rubbing the rear end portion of the latent image carrier on the latent image carrier in the moving direction of the latent image carrier surface, the tip of the magnetic brush opposes the non-latent image part on the latent image carrier and then The rear end portion of the image is rubbed, and toner is supplied to the rear end portion of the latent image. At this time, at the tip of the magnetic brush, the toner adhering to the carrier surface is moved toward the developing sleeve side by the electrostatic force received from the non-latent image portion while facing the non-latent image portion on the latent image carrier. A phenomenon of moving (hereinafter, this phenomenon is referred to as "toner drift") occurs. As a result, when rubbing the trailing edge portion of the latent image on the latent image carrier, there is no toner on the carrier surface at the tip portion of the magnetic brush, and the toner adhering to the trailing edge portion of the latent image on the carrier surface. Adhere to. This is considered to cause trailing white spots and a decrease in reproducibility of fine lines.

[0006] The applicant of the present invention, in order to suppress the trailing edge white spots and the deterioration of the reproducibility of fine lines, discloses in JP-A-2000-305360 and 2000-347506 an improvement in the image quality of the above-mentioned developing device. An invention that can achieve the above is proposed. In the inventions proposed in these publications,
The attenuation rate of the magnetic flux density in the normal direction in the developing area, the angular interval between the main magnetic pole for advancing the developer in the developing area and the adjacent magnetic pole, and the like are defined as predetermined values. As a specific configuration, the above-mentioned developing magnetic pole is composed of one main magnetic pole including an N pole, and an S magnetic pole arranged so as to be close to the upstream side and the downstream side in the surface moving direction of the developing sleeve of the main magnetic pole. It is composed of two auxiliary magnetic poles. Furthermore, the applicant is
Auxiliary magnetic poles are formed between the main magnetic poles that raise the magnetic toner and the toner conveying magnetic poles (see JP 2001-5296A), and the developing nip and the magnetic brush density are set (see JP 2001-27849A). ) And the half-value angle width of the main pole (also referred to as the half-value center angle) (Japanese Patent Laid-Open No. 2001-13
4100 gazette) and the like to propose the invention for realizing the above-mentioned image quality improvement. According to these inventions, it has been confirmed that the developing efficiency can be improved, the reproducibility of fine lines, and the trailing edge blanking phenomenon can be improved.

Japanese Patent Laid-Open No. 2000-305360,
JP 2000-347506 A and JP 2001
With the apparatus of Japanese Patent No. 5296, etc., it is possible to improve the developing efficiency, improve the reproducibility of thin lines, and improve the trailing edge blank area phenomenon.
It is considered that this is due to the following reasons. FIG. 9A is an explanatory diagram showing the magnetic force distribution in the vicinity of the developing area in the conventional developing device in which the developing magnetic pole is one magnetic pole P1, and FIG. 9B is the magnetic field formed by the developing magnetic pole P1. FIG. 7 is an explanatory view showing a shape of a magnetic brush made of a developer that has been bristled when viewed from the axial direction of the developing sleeve 4.
Further, FIG. 10A shows that the main magnetic pole P1b has one developing magnetic pole.
FIG. 4B is an explanatory view showing a magnetic force distribution in the vicinity of the developing area in the developing device including the magnetic poles P1a, P1c and two auxiliary magnetic poles P1a, P1c. FIG. FIG. 6 is an explanatory diagram showing a shape of a magnetic brush made of a developer that has risen in a bristling shape when viewed in the axial direction of the developing sleeve 4.

In the conventional developing device, the S-pole magnetic pole adjacent to the N-pole developing magnetic pole is used to convey the developer in a region located downstream of the developing region in the surface moving direction of the developing sleeve 4. There is a magnetic pole P2 that forms a magnetic field, and a magnetic pole P6 that forms a magnetic field for transporting the developer drawn up on the developing sleeve 4 to the developing area. These magnetic poles P
2 and P6 are arranged relatively far from the developing magnetic pole P1, the magnetic force distribution of the magnetic field in the developing area is as shown in FIG.
As shown in (a), the magnetic force lines emitted from the developing magnetic pole P1 pass through a position relatively distant from the developing sleeve surface. Then, the developer carried on the developing sleeve 4 and conveyed to the developing area is, as shown in FIG. 9B,
The magnetic brush is formed along the magnetic lines of force.

On the other hand, in the developing device disclosed in the above publication, two S-pole auxiliary magnetic poles P1a and P1 adjacent to the N-pole main magnetic pole P1b are provided.
1c, the S pole is arranged closer to the N-pole main magnetic pole P1b as compared with the conventional developing device shown in FIGS. 9A and 9B. Therefore, the magnetic force distribution of the magnetic field in the developing region is as shown in FIG.
The magnetic field lines emitted from 1b pass near the surface of the developing sleeve. Here, most of the magnetic force lines emitted from the main magnetic pole P1b are directed to the two adjacent auxiliary magnetic poles P1a and P1c. Hereinafter, the number of "magnetic lines for spikes") is smaller than that of a conventional developing device in which the same number of magnetic lines of force is generated.
The width in the moving direction of the surface of the developing sleeve 4 where the magnetic field lines for spike formation exist (spike width) becomes narrow. for that reason,
The start position of the spike of the developer carried to the developing area while being carried on the surface of the developing sleeve 4 is the center of the developing sleeve surface moving direction in the developing area (hereinafter, simply “center”) in the developing area as compared with the conventional developing device. That said)). Further, similarly, the end position of the spike of the developer passing through the developing area while being carried on the surface of the developing sleeve 4 is closer to the center of the developing area than the conventional developing device.

In the conventional developing device, the developer on the developing sleeve 4 starts to stand at a point farther from the center of the developing area than the developing device of the above publication, as shown in FIG. 9 (b). Therefore, the non-latent image portion immediately after the trailing edge portion of the latent image on the photoconductor drum approaches or contacts and faces the non-latent image portion on the photosensitive drum for a longer period of time than the developing device disclosed in the above publication. Therefore, toner drift is likely to occur due to the electrostatic force from the non-latent image portion of the photosensitive drum 1. On the other hand, in the developing device of the above publication, as shown in FIG. 10B, the developer on the developing sleeve 4 starts to stand at a point closer to the center of the developing area than the conventional developing device. Therefore, the period in which the non-latent image portion immediately after the trailing edge portion of the latent image on the photoconductor drum is close to or in contact with the non-latent image portion is shorter than that in the conventional developing device, and thus the electrostatic force from the non-latent image portion of the photoconductor drum 1 is less likely to be received. . Therefore, toner drift is unlikely to occur, and it is possible to suppress trailing edge white spots and deterioration of fine line reproducibility. Further, the above-mentioned JP 2001-27849 A
In the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2001-134100 and Japanese Patent Laid-Open No. 2001-134100, it is possible to prevent trailing edge blank areas and improve image density.

Further, in the developing device of the above publication, N
Since the two S-pole auxiliary magnetic poles are arranged close to the main magnetic pole P1b of the pole, the magnetic lines of force in the developing area at the position away from the surface of the developing sleeve 4 in the normal direction thereof are the same as those in the conventional developing device. It becomes sparse compared to. Therefore, the normal-direction magnetic flux density in the developing area at a position distant from the surface of the developing sleeve 4 in the normal direction thereof (for example, a position where the tip portion of the magnetic brush in the conventional apparatus exists) is the same as that in the above-mentioned publication. The device is smaller than the conventional developing device. Therefore, in the developing device of the above publication, most of the developer constituting the magnetic brush is attracted to the vicinity of the surface of the developing sleeve 4 having a high magnetic flux density, and as shown in FIG. It is shorter than that of the developing device.

Further, when the developing device of the above publication is actually used, the amount of the developer supplied to the developing area is smaller than the maximum amount of the developer which can be bristled while passing through the developing area. Is set. That is, in the developing device of the above publication, a magnetic brush which is originally longer can be formed, but the amount of the developer supplied to the developing area is reduced and the length of the magnetic brush is regulated to be shorter. As a result, the tip portion of the magnetic brush is located in a region near the surface of the developing sleeve 4 where the magnetic flux density is high, and the tip portion of the magnetic brush has a higher brush density than the tip portion of the magnetic brush in the conventional developing device. Will be high. Then, the minimum gap (hereinafter, referred to as “developing gap”) Pg between the surface of the developing sleeve 4 and the surface of the photosensitive drum 1 is narrowed by the amount of the shortened magnetic brush, so that the developing sleeve 4 is made smaller than that of the conventional device. The photosensitive drum 1 can be rubbed with a high-density brush portion existing in a region having a high magnetic flux density close to the surface.

In the developing device of the above publication, as described above, the start point of the spike of the developer and the end point of the spike of the developer are closer to the center of the developing area than the conventional developing device. Therefore, as shown in FIG. 10B, the width (sliding width) Pn in the moving direction of the developing sleeve surface of the portion where the magnetic brush slides on the latent image carrier in the developing area is narrower than that of the conventional developing device. Become. Therefore, the amount of toner supplied to the latent image portion on the photosensitive drum 1 by the rubbing with the magnetic brush is smaller than that of the conventional developing device if the rubbing portion has the same brush density. However, when the developing device of the above publication is used, as described above, the brush density of the tip portion of the magnetic brush contacting the photosensitive drum 1 can be made higher than that of the conventional developing device, so that the latent image on the photosensitive drum 1 is formed. It is possible to prevent the amount of toner supplied to the portion from decreasing as compared with the conventional developing device. Further, as a result of the research conducted by the present inventors, in the conventional developing device, the carrier at the tip of the magnetic brush in the developing area receives the electrostatic force from the surface of the photosensitive drum 1 and the toner adhering to the surface. Then, it was found that the phenomenon of adsorption to the surface of the photoconductor drum occurred. More specifically, in the developing area of the conventional developing device, the developing sleeve side portion of the magnetic brush that does not contact the surface of the photoconductor drum 1 moves relative to the surface of the photoconductor drum, but contacts the surface of the photoconductor drum. In many cases, the tip portion of the magnetic brush is attracted to the surface of the photoconductor drum and the rubbing operation is not performed on the surface of the photoconductor drum. Therefore, in the conventional developing device, the magnetic brush is replaced by the photosensitive drum 1.
The amount of toner supplied to the electrostatic latent image is increased by sliding (relatively moving) the surface of the magnetic brush as compared with the case where the magnetic brush moves at a constant speed with respect to the surface of the photosensitive drum 1. The effect was small. On the other hand, in the developing device of the above publication, the tip portion of the magnetic brush that contacts the photoconductor drum 1 is located in a region having a higher magnetic flux density closer to the surface of the developing sleeve 4 than the conventional device, and therefore the tip portion is The constraining force acting on the carrier constituting the developing sleeve 4 is strong. Therefore, the tip portion of the magnetic brush that comes into contact with the surface of the photoconductor drum can firmly slide on the surface of the photoconductor drum. From the above, even if the sliding width Pn is narrower than that of the conventional developing device, the amount of toner supplied to the latent image portion on the photoconductor drum 1 is reduced in a small amount, and the linear velocity of the photoconductor drum 1 in the developing area is small. It is possible to compensate by increasing the linear velocity ratio of the developing sleeve 4 to Specifically, the linear velocity ratio is, for example, 1.5 to
It is about 3.0.

[0014]

However, when the structure of the developing device proposed in the above publication or the developing device provided in the image forming apparatus of the above publication is adopted, the image density at the trailing edge of the image is reduced. It has been found that the so-called trailing edge toner deviation, which is high, tends to occur. Then, the present inventor investigated the cause of occurrence of the toner near the trailing edge. It turned out to be related to

In all of the conventionally known structures including the above publications, the ratio of the linear velocity of the developing sleeve to the linear velocity of the latent image carrier in the developing region (hereinafter referred to as the linear velocity ratio of the developer carrier to the latent image carrier) will be described. ) Was set to 1.1 to 3.0 times, and practically set to 1.5 times to 3.0 times. Such setting of the linear velocity ratio is for sufficiently supplying toner to the latent image portion of the latent image carrier. The linear velocity ratio to this latent image carrier is 1,
That is, if the toner is made to be the same as the latent image carrier, the toner replenishment will be insufficient and the image density will decrease, and in addition, sufficient toner adhesion will not be obtained during normal image formation, and the image will be a blurred image. Therefore, even in an image forming apparatus using a developing device in which the magnetic force of the developing main pole is strong and the spikes are short in order to suppress trailing white spots and deterioration of reproducibility of fine lines, the linear velocity ratio to the latent image carrier is It is necessary to set the settings of as above.

However, as a result of making the linear velocity ratio to the latent image carrier larger than 1, the amount of developer supplied to the image portion increases, but
A large amount of developer is present at the rear end of the main pole. The cause is considered as follows. The ears of the developer carried to the developing area while being carried on the surface of the developing sleeve are
When its tip comes into contact with the latent image carrier, it is slightly attracted due to the bias of the latent image portion of the latent image carrier. By this, the developing magnetic poles P1a and P1 in the developing sleeve
The shape of the magnetic brush formed in accordance with the magnetic force received from the magnetic field formed by b and P1c is slightly different. Since the surface of the latent image carrier moves in the same direction at a slower speed than the surface of the developing sleeve, the tip of the magnetic brush is affected by the moving speed of the surface of the latent image carrier and tends to be delayed. Then, when the development is continued while the linear velocity ratio of the developing sleeve to the latent image carrier is larger than 1, in the developing area, the latent image carrier near the trailing edge of the latent image located upstream in the moving direction of the latent image carrier. Magnetic brushes face each other for a long time. The flow of the developer in the vicinity of the trailing edge of the latent image deteriorates, and an agent pool is generated.
The agent pool becomes more remarkable as the linear velocity ratio to the latent image carrier increases. In the case where the main magnetic pole has a strong magnetic force or the auxiliary magnetic pole is provided close to the main magnetic pole as described above, the agent density in the vicinity of the trailing edge of the latent image is higher than that in other configurations. It tends to be high, and agent accumulation is likely to occur. When the developer with sufficient toner is carried and carried on the surface of the developer carrier that moves faster than the surface linear velocity of the latent image carrier, the developer pool and the latent image on the surface of the latent image carrier By the edge effect of the edge, toner adheres to the edge of the latent image rear edge,
As a result, this portion is developed darker than other image portions. This is referred to as the trailing edge toner side in the development.
When the trailing edge of the toner is shifted, the edge portion of a copy of a photograph or a picture, a printed image, or the like becomes dark, resulting in an uncomfortable image without smoothness.

Therefore, in order to improve the reproducibility of fine lines and prevent the trailing edge blanking phenomenon, the magnetic force of the developing main pole is made strong and the spikes are shortened. Even in an image forming apparatus having a configuration in which the linear velocity ratio of the body to the latent image carrier is larger than 1, it is required to prevent the occurrence of the trailing edge toner deviation. As a result, it becomes possible to develop a better image than in the conventional case, and it is possible to improve the image quality.

The present invention has been made in view of the above background, and it is an object of the present invention to improve reproducibility of fine lines, prevent trailing edge white spots, prevent image density reduction, and prevent blurred images. It is an object of the present invention to provide an image forming apparatus capable of preventing the occurrence of the toner near the trailing edge in a configuration that can realize the above.

[0019]

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises a latent image carrier that carries an electrostatic latent image on its surface and moves, a toner and magnetic particles. And a developer carrying member carrying and carrying a two-component developer, the developer carrying member is provided on the surface of the developer carrying member by a developing magnetic pole facing the developing area where the developer carrying member faces the latent image carrying member. Is magnetically attracted to form a magnetic brush, and the surface of the developer carrier is moved in the developing area in the same direction as the surface moving direction of the latent image carrier and at a linear velocity higher than the linear velocity of the surface of the latent image carrier. And a developing device for developing the latent image on the latent image carrier by moving the magnetic brush and rubbing the surface of the latent image carrier with the magnetic brush. The amount of the developer conveyed to the developing area where the surface of the latent image bearing member is rubbed with the brush to develop is 6 ~95 [mg / cm ^2], image and the attenuation factor of magnetic flux density in the normal line direction of the developer carrying member surface by the developing magnetic pole occurring outside surface of the developer carrying member of the developing region 40% or more In the forming apparatus, the developer carrier surface position where the magnetic flux density in the normal direction of the developer carrier surface generated by the developing magnetic pole becomes the maximum value is set to the developer carrier surface and the latent image carrier surface. It is characterized in that it is shifted to the upstream side in the moving direction of the surface of the developer carrier with respect to the developing nip portion which is the closest position between the two. Here, the "attenuation rate of the magnetic flux density in the normal direction" means the peak value of the magnetic flux density in the normal direction generated on the surface of the developer carrier, and the normal line from the surface of the developer carrier. When the peak value of the magnetic flux density in the normal direction at a position 1 [mm] away in the direction is Y, it means the value obtained by the following mathematical formula 1.

## EQU1 ## Attenuation rate [%] = {(X−Y) / X} × 100 In this way, the attenuation rate is increased to 40 [%] or more, and the developer conveyed to the developing area (developing nip area) The amount (developer supply amount) is set to 65 to 95 [mg / cm ² ] to be smaller than that of the conventional developing device. Then, by using a developing magnetic pole having a magnetic force in a common sense range, as shown in FIG. 10A, the magnetic force lines existing in the developing area are brought closer to the surface of the developer carrying member. Thereby, as described above, the length of the magnetic brush can be shortened and the density of the brush portion contacting the latent image carrier can be increased. In general, in order to maintain high image quality with respect to image density, etc., when the length and density settings of the magnetic brush are changed, the development parameters such as the linear velocity of the developer carrier in the development area and the development gap are changed accordingly. Will be set. In the image forming apparatus disclosed in the above-mentioned publication, which has been conventionally proposed, the latent image on the latent image carrier is usually rubbed with a larger amount of the developer, and the image is shown in FIGS. 9 (a) and 9 (b). In order to maintain the image density equal to or higher than the conventional one, the linear velocity ratio of the developer carrying member to the linear velocity of the latent image carrying member in the developing area is set to be high. As a result, the developing ability can be improved and the image density can be maintained. In the image forming apparatus according to claim 1, the magnetic pole density in the normal direction of the developing magnetic pole is set in such a configuration that the surface linear velocity of the developer carrier in the developing region is made higher than that of the latent image carrier. The surface position of the developer carrying member having the maximum value (hereinafter referred to as the magnetic pole density peak position of the developing magnetic pole) is the closest to both of the developing regions where the surface of the developer carrying member and the surface of the latent image carrying member are opposed to each other. The position is shifted to the upstream side in the moving direction of the surface of the developer carrying member with respect to the developing nip portion. As a result, the ears of the developer carried to the developing area while being carried on the surface of the developing sleeve are displaced toward the auxiliary magnetic pole P1c side from the magnetic pole density peak position formed by the main magnetic pole P1b of the developing magnetic pole. Therefore, the ears of the developer carried to the developing area are not attracted for a long time by the bias of the latent image portion of the latent image carrier, and the ears are completed under the influence of the auxiliary magnetic pole P1c. Therefore, conventionally, it is possible to avoid the generation of the agent pool near the trailing edge of the latent image, which is caused by the continuous development in the state where the linear velocity ratio of the developing sleeve to the latent image carrier is larger than 1. . An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the developer carrier comprises a non-magnetic sleeve and a plurality of magnetic poles fixedly arranged in the sleeve. Is composed of a main magnetic pole and an auxiliary magnetic pole arranged on both sides of the main magnetic pole.
[%] Or more and a half-value angle width of 25 [°] or less, the auxiliary magnetic pole has a magnetic flux density attenuation rate of 40 [%] or more in the normal direction of the developing sleeve surface, and the main magnetic pole and the auxiliary magnetic pole are The magnetic pole angle width is within 35 [°], the distance between the surface of the latent image carrier and the surface of the developing sleeve in the developing nip portion is set to 0.3 to 0.5 [mm], and The sleeve surface position at which the magnetic flux density in the normal direction of the sleeve surface generated by the main pole becomes the maximum is 2 [°] or more and 6 [°] or more on the upstream side in the sleeve surface moving direction with respect to the developing nip portion.
It is characterized in that the range is as follows. The above-mentioned "half-value angle width" means the two half-value points on the surface of the developer bearing member, which show the magnetic flux density which is half the maximum value of the magnetic flux density in the normal direction generated on the surface of the developer bearing member by the main magnetic pole. It refers to the angular width in the surface movement direction of the developer carrying member when viewed from the central axis of the developer carrying member. Further, the "magnetic pole angle width" means the developer carrier surface position where the magnetic flux density in the normal direction of the main magnetic pole becomes the maximum value and the developer carrier surface position where the magnetic flux density in the normal direction of the auxiliary magnetic pole becomes the maximum value. Is the angular width in the surface movement direction of the developer carrying member when viewed from the central axis of the developer carrying member. According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the developer has a fluidity of 30.
[Second / 50 g] or more and 50 [second / 50 g] or less. An image forming apparatus according to a fourth aspect is the image forming apparatus according to the second or third aspect, in which the fluidity of the magnetic particles, which is a component of the developer, is 20 [sec / 50 g] or more and 40 [sec / 50 g] or less. It is characterized by being. An image forming apparatus according to a fifth aspect is the image forming apparatus according to the second, third or fourth aspect, wherein the surface friction coefficient of the toner is 0.25 or more and 0.35 or less. The image forming apparatus according to claim 6 is the image forming apparatus according to claim 1,
In the image forming apparatus of No. 2, 3, 4, or 5, a toner treated with silicone oil is used as an external additive of the toner.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to a laser printer (hereinafter referred to as "printer") which is an electrophotographic image forming apparatus.
Say. The embodiment applied to the developing device of 1) will be described. FIG. 2 is a schematic configuration diagram of the entire printer according to the present embodiment. This printer has a photosensitive drum 1 as a latent image carrier. The surface of the photoconductor drum 1 is uniformly charged by a charging roller 50 as a uniform charging unit that contacts the photoconductor drum 1 while being rotationally driven in the direction of arrow A in the figure. After that, the optical writing unit 51 as a latent image forming means scans and exposes based on image information to form an electrostatic latent image on the surface of the photosensitive drum 1.
The uniform charging means and the latent image forming means may be different from the charging roller 50 and the optical writing unit 51. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 2 described later, and a toner image is formed on the photosensitive drum 1. The toner image formed on the photosensitive drum 1 serves as a transfer material that is conveyed from the paper feed cassette 54 through the paper feed roller 55 and the registration roller pair 56 by a transfer unit that includes a transfer belt 53 and serves as a transfer unit. It is transferred onto the transfer paper 52. The transfer paper 52 after the completion of transfer is fixed by a fixing unit 57 as a fixing unit.
Then, the toner image is fixed and discharged outside the apparatus. In addition,
The transfer residual toner remaining on the photosensitive drum 1 without being transferred is a cleaning unit 5 as a cleaning unit.
8 removes it from the surface of the photosensitive drum 1. Also,
The residual charge on the photoconductor drum 1 is removed by a charge eliminating lamp 59 as a charge eliminating means.

Next, the structure of the developing device 2 in this embodiment will be described. FIG. 3 is a schematic configuration diagram of a main device including the developing device 2 arranged around the photosensitive drum 1. The developing device 2 in the present embodiment is arranged such that the developing roller 3 as a developer carrying member is close to the photosensitive drum 1 via a developing gap having a predetermined interval. The developing roller 3 is provided with a cylindrical developing sleeve 4 made of a non-magnetic material such as aluminum, brass, stainless steel, and conductive resin, and a magnetic field for causing the developer to stand on the surface of the developing sleeve 4 inside. The magnetic roller 5 is provided as a magnetic field forming means for forming the magnetic field. The developing sleeve 4 rotates around the fixedly arranged magnet roller 5 in the counterclockwise direction in the drawing by a driving unit (not shown).

Further, the developing device 2 regulates the amount of developer adhering to the developing sleeve 4 on the upstream side in the surface moving direction of the developing sleeve 4 with respect to the developing area where the developing sleeve 4 and the photosensitive drum 1 face each other. A doctor blade 6 is provided. The doctor blade 6 regulates the height of the spikes of the developer that has stood on the developing sleeve 4. In this embodiment, the doctor gap, which is the distance between the doctor blade 6 and the developing sleeve 4, is set to 0.48 [mm]. Further, in the developing device 2, a screw 8 for pumping up the developer onto the developing sleeve 4 while stirring the developer is provided inside the developing casing 7 in a region of the developing roller 3 opposite to the photosensitive drum 1. .

In this embodiment, the photosensitive drum 1 having a diameter of 100 [mm] has a drum linear velocity of 33 in the developing area.
It is driven to rotate at 0 [mm / sec] and the diameter is 2
The developing sleeve 4 of 5 [mm] is rotationally driven so that the sleeve linear velocity in the developing area is 660 [mm / sec]. That is, in this embodiment, the linear velocity ratio of the sleeve linear velocity to the drum linear velocity is set to 2.0. Further, the development gap in this embodiment is set to 0.5 [mm]. The conventional development gap is generally set to about 10 times the carrier particle size, and is, for example, about 0.65 to 0.8 [mm] when the carrier particle size is 50 [μm]. On the other hand, in this embodiment, since the magnetic force of the main magnetic pole is larger than that of the conventional one, it is possible to set the carrier particle size to about 30 times. However, even in the present embodiment, if the development gap is made wider than about 30 times the carrier particle diameter, it becomes difficult to obtain a desired image density. According to the present embodiment, it is possible to obtain a desired image density even if the linear velocity ratio of the sleeve linear velocity to the drum linear velocity is reduced to 1.5.

Next, the magnetic field formed by the magnetic roller 5 will be described. FIG. 4 is a circle graph showing the distribution of the magnetic flux density in the normal direction of the surface (hereinafter, referred to as “normal direction magnetic flux density”) generated on the surface of the developing sleeve 4 by each magnetic pole of the magnet roller 5 by a solid line. Is. In order to create this pie chart, ADS Gauss meter (HGM-8
300) and ADS type A1 axial probe, and the results measured by these were recorded by a pie chart recorder. By the magnetic field generated by the magnet roller 5 having such a magnetic characteristic, the carrier in the developer stands on the developing sleeve 4 in a chain shape, and the toner is attached to the chain-shaped carrier by electrostatic force or the like. A magnetic brush is formed. The magnetic brush is conveyed in the surface moving direction of the developing sleeve 4 (counterclockwise direction in the drawing) as the surface of the developing sleeve 4 moves.

The magnet roller 5 in this embodiment is shown in FIG.
As shown in FIG. 3, three magnetic poles P1 are used as the developing magnetic poles that form a magnetic field for causing the developer to stand in the developing area.
a, P1b, P1c. These magnetic poles P1
The magnetic pole a, the magnetic pole P1b, and the magnetic pole P1c are arranged side by side in this order from the upstream side in the surface movement direction of the developing sleeve 4.
Each magnetic pole P1a, P1b, P1c is composed of a magnet having a small cross section. Generally, when the cross section of the magnet is made smaller, the magnetic force becomes weaker. Therefore, in the present embodiment, the three magnetic poles P1a, P1b, P1c are composed of magnets made of a rare earth metal alloy having a relatively strong magnetic force. Among the rare earth metal alloy magnets, a typical iron neodymium boron alloy magnet can obtain a maximum energy product of 358 [kJ / m ³ ], and an iron neodymium boron alloy bonded magnet has a maximum energy product of 80 [ It is possible to obtain the maximum energy product around kJ / m ³ ]. When such a rare earth metal alloy magnet is used, the maximum energy product is generally 36 [kJ / m].
³ ] and around 20 [kJ / m ³ ], ferrite magnets and ferrite bonded magnets were used, but a stronger magnetic force can be secured as compared with these magnets. Therefore, even if a magnet having a small cross section is used, the magnetic force on the surface of the developing sleeve 4 can be sufficiently secured. In this embodiment, the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by the three magnetic poles P1a, P1b, P1c forming the developing magnetic pole is set to be 100 to 200 [mT].

Further, in FIG. 4, the line indicated by the one-dot broken line shows the magnetic flux density in the normal direction at the position 1 [mm] away from the surface of the developing sleeve 4 in the normal direction thereof. In the present embodiment, the attenuation factor of the magnetic flux density in the normal direction is defined as X, which is the peak value of the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4, and is 1 in the normal direction from the surface of the developing sleeve 4.
Y of the peak value of the magnetic flux density in the normal direction at a position separated by [mm]
Means the value obtained by the above equation 1. For example, the magnetic flux density in the normal direction of the surface of the developing sleeve 4 is 100.
At [mT], when the magnetic flux density in the normal direction at a portion 1 [mm] away from the surface of the developing sleeve 4 is 80 [mT],
The attenuation rate is 20 [%].

Next, the magnetic pole arrangement of the magnetic roller 5 will be described. FIG. 5 is an explanatory diagram showing an arrangement of three magnetic poles P1a, P1b, P1c which are developing magnetic poles of the magnetic roller 5. The developing magnetic pole of the magnetic roller 5 is adjacent to the main magnetic pole P1b that mainly functions to make the developer in the developing area stand, and upstream and downstream of the main magnetic pole P1b in the surface moving direction of the developing sleeve 4. The auxiliary magnetic poles P1a and P1c, which have opposite polarities to the main magnetic pole P1b, are formed at the positions. In the present embodiment, the main magnetic pole P1b, the magnetic pole P4 that forms a magnetic field for drawing up the developer on the developing sleeve 4, and the magnetic field that conveys the drawn developer on the developing sleeve 4 to the developing area. Magnetic pole P6,
Further, the magnetic poles P2 and P3 that form a magnetic field for transporting the developer in an area located on the downstream side of the developing area in the surface moving direction of the developing sleeve 4 are constituted by N poles. The auxiliary magnetic poles P1a and P1c and the magnetic pole P5 that conveys the developer drawn onto the developing sleeve 4 are S poles. In this embodiment, as the main magnetic pole P1b, the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is 120.
A magnet of [mT] or more is used. The maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is 100 [mT] or more for both the auxiliary magnetic pole P1c and the main magnetic pole P1b located on the downstream side of the main magnetic pole P1b in the developing sleeve surface movement direction. For example, it has been confirmed that no abnormal image such as a carrier is attached on the photosensitive drum 1. vice versa,
If the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 in the main magnetic pole P1b and the auxiliary magnetic pole P1c is less than 100 [mT], carrier adhesion onto the photosensitive drum 1 occurs. Such carrier adhesion is more likely to occur as the tangential magnetic force on the surface of the developing sleeve 4 in the developing area is smaller, so it is important to increase the tangential magnetic force, but the main magnetic pole P1b or the auxiliary magnetic pole P1c should be made larger. If one of the magnetic poles is made sufficiently large, the occurrence of carrier adhesion can be sufficiently suppressed.

Further, the above-mentioned two auxiliary magnetic poles P1a, P1
1c is used to adjust the distribution of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 by the main magnetic pole P1c. Specifically, it is used for narrowing the half-value angular width which is the angular width between the half-value points in the developing sleeve surface moving direction viewed from the central axis of curvature of the surface of the developing sleeve 4 in the developing area, that is, the central axis of the developing sleeve 4. It Here, the half width at half maximum indicates the magnetic flux density that is half the maximum value of the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by the main magnetic pole P1c. 4 refers to the angular width in the surface movement direction of the developing sleeve 4 when viewed from the central axis of 4. Therefore, for example, when the maximum value of the magnetic flux density in the normal direction is 120 [mT], the half value angle width is 60 [mT], which is the half value of the magnetic flux density in the normal direction.
Is the angular width when the half value point on the surface of the developing sleeve 4 is viewed from the central axis of the developing sleeve 4. In this embodiment,
The magnetic characteristics and arrangement of the auxiliary magnetic poles P1a and P1c are set so that the half-value angle width of the main magnetic pole P1b is 25 [°] or less. Specifically, the width of the cross section of the magnets of the three magnetic poles P1a, P1b, and P1c forming the developing magnetic pole in the surface moving direction of the developing sleeve is set to 2 [mm]. The half-value angle width of the magnetic pole P1b is 16 [°].

FIG. 6A is an explanatory view showing the half value angular width in the case where the developing magnetic pole is composed of three magnetic poles P1a, P1b and P1c as in this embodiment, based on FIG. (B) is an explanatory view showing a half-value angle width when a developing magnetic pole is constituted by one magnetic pole P1 as in the conventional case. Figure 6
Comparing (a) and (b), the half-value angular width θ1 of the main magnetic pole P1b in the present embodiment shows that the auxiliary magnetic poles P1a and P1.
c, the half-value angle width θ ′ of the conventional single developing magnetic pole P1
It is narrower than 1. Here, it has been confirmed that an abnormal image occurs when the half-value angle width of the main magnetic pole P1b exceeds 25 [°].

In this embodiment, the auxiliary magnetic poles P1a,
As shown in FIG. 5, the half-value angle width of P1c is set to be 35 [°] or less. The positional relationship between the main magnetic pole P1b and the auxiliary magnetic poles P1a and P1c is such that the magnetic pole angle width between the main magnetic pole P1b and the auxiliary magnetic poles P1a and P1c is 35 [°] or less, as shown in FIG. Is set to. The magnetic pole angle width means each magnetic pole P1a, P1b, P1.
Each point on the surface of the developing sleeve 4 showing the maximum value of the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by c was viewed from the central axis of curvature of the surface of the developing sleeve 4 in the developing region, that is, the central axis of the developing sleeve 4. Development sleeve 4
Is the angular width of the surface moving direction. In the present embodiment, as described above, the half-value angle width of the main magnetic pole P1b is 16 [°].
Therefore, each auxiliary magnetic pole P1a with respect to the main magnetic pole P1b,
The magnetic pole angle width of P1c is 25 [°].

Further, in this embodiment, the developing magnetic poles P1a,
Among the inflection points at which the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by P1b and P1c is 0 [mT], two inflection points located on the most upstream side and the most downstream side in the surface moving direction of the developing sleeve 4 The angle width between them is set to 120 [°] or less. That is, as shown in FIG. 5, the angle width between the inflection points existing between the two auxiliary magnetic poles P1a and P1c and the magnetic poles P2 and P6 adjacent to the auxiliary magnetic poles P1a and P1c is 120 [°] or less. Has become.

In the above structure, the magnetic characteristics of the developing magnetic poles P1a, P1b, P1c in this embodiment were observed as shown below. Developing sleeve 4 of main pole P1b
The maximum value of the magnetic flux density in the normal direction on the surface of is 120
[mT], and the magnetic flux density in the normal direction is 55.8 [mT] at a position 1 [mm] away from the surface of the developing sleeve 4 that exhibits the highest value in the normal direction. The amount of change in magnetic flux density was 64.2 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this embodiment is 53.5 [%]. Further, the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the auxiliary magnetic pole P1a located on the upstream side of the main magnetic pole P1b in the developing sleeve surface moving direction is 100 [mT], and the developing sleeve showing the maximum value is shown. The magnetic flux density in the normal direction at a position 1 [mm] away from the surface of 4 in the normal direction is 53.3 [mT], and the change amount of the magnetic flux density in the normal direction is 46.7 [mT]. there were. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the auxiliary magnetic pole P1a in this embodiment is 46.7 [%]. The maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the auxiliary magnetic pole P1c located on the downstream side of the main magnetic pole P1b in the developing sleeve surface movement direction is 120 [mT], and the developing sleeve showing the maximum value is shown. 1 [m from the surface of 4 to the outside in the normal direction
The magnetic flux density in the normal direction at a distance of m] is 67.4 [mT]
And the amount of change in the magnetic flux density in the normal direction is 52.6 [m
T]. Therefore, the auxiliary magnetic pole P in the present embodiment
The attenuation rate of the magnetic flux density in the normal direction due to 1c is 43.8 [%]. In the conventional magnet roller 5 shown in FIG. 6B, for example, the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the developing magnetic pole P1 is 90 [mT],
The magnetic flux density in the normal direction at the position 1 [mm] away from the surface of the developing sleeve 4 showing the maximum value in the normal direction is 63.
9 [mT], and the change amount of the magnetic flux density in the normal direction is 2
It was 6.1 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this embodiment is 29 [%].
Becomes

The developing magnetic pole P having the magnetic characteristics as described above.
The developer stands up along the lines of magnetic force generated by the magnet roller 5 including the lapping rollers 1a, P1b, and P1c, and the developing sleeve 4
A magnetic brush is formed on the top. In this magnetic brush,
Only the brush portion formed by the magnetic field of the main magnetic pole P1b comes into contact with the surface of the photoconductor drum 1, which contributes to the visualization of the electrostatic latent image on the photoconductor drum 1. At this time, the length of the magnetic brush in the developing area is about 1 [mm], which is relatively short, and the density of the brush also becomes dense. The length of the magnetic brush referred to here is the length when the photoconductor drum 1 is removed. In reality, the developing gap is set to 0.5 [mm], so The length of the magnetic brush becomes shorter depending on its developing gap.

The length of the magnetic brush in the developing region can be made short and dense as described above, because the attenuation factor of the magnetic flux density in the normal direction is large as described above.
The magnetic flux density in the normal direction on the surface of the developing sleeve 4 is high,
Moreover, the magnetic flux density in the normal direction can be set to be low at a position 1 [mm] away from the surface of the developing sleeve 4. That is, since the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is high, the developer near the surface of the developing sleeve 4 is concentrated due to the action of a strong magnetic field, but is relatively separated from the surface of the developing sleeve 4. This is because the magnetic field is weak in some places and the developer cannot maintain the brush chain. Further, in this embodiment, the doctor gap is appropriately adjusted, and the amount of the developer carried on the developing sleeve 4 and conveyed to the developing nip region (developing region) (developer supply amount).
Is set to be as small as 65 to 95 [mg / cm ² ]. As a result, a magnetic brush which is originally longer can be formed, but the magnetic brush is restricted to be short due to the insufficient developer supply amount. Then, as a result of such a short regulation, the developing gap is set to 0.5 [mm], so that the photosensitive drum 1 is made to have a brush portion made of a developer concentrated near the surface of the developing sleeve 4 having a high magnetic flux density. The surface of can be rubbed.

From the above structure, in the present embodiment,
The width of the developing sleeve surface moving direction in the developing nip region where the magnetic brush formed by the main magnetic pole P1b contacts the photosensitive drum 1 is equal to or larger than the carrier particle diameter and is 2 [mm].
The following is relatively narrow. As a result, as described above, it is possible to form an image with high reproducibility of a thin image such as a horizontal thin line or a small dot without a trailing edge blank.

Next, the carrier of the developer used in this embodiment will be described. As the core material of the carrier, a known magnetic material having an average particle diameter of 30 to 100 [μm] can be used. As the magnetic material, for example,
Examples thereof include ferromagnetic metals such as iron, cobalt and nickel, alloys and compounds such as magnetite, hematite and ferrite.

Here, it has been confirmed by the examples described later that the magnetic characteristics of the carrier influence the influence of the magnetic field from the magnetic roller 5 on the carrier and greatly affect the developing characteristics and the transportability of the developer. ing. Specifically, the saturation magnetization value of the carrier is 90 × 10 ⁻⁷ × 4π [wb
.M / kg], the ears of the magnetic brush composed of toner and carrier on the developing sleeve 4 in the developing area become tight due to the action of the magnetic field received from the main pole P1b, and It was found that the reproducibility of gradation and halftone deteriorates. When the saturation magnetization value of the carrier is less than 50 × 10 ⁻⁷ × 4π [wb · m / kg], it becomes difficult to satisfactorily retain the toner and the carrier on the developing sleeve 4, and particularly the small particle size. When a developer composed of a carrier and toner is used, carrier adhesion to the photosensitive drum 1 and toner scattering are likely to occur. Therefore, in this embodiment, the saturation magnetization value is 50 to 90.
A carrier having a density of × 10 ^-7 × 4π [wb · m / kg] is used. As a result, particularly in the formation of a color image, it is possible to form an image having excellent image quality uniformity and gradation reproducibility. As the saturation magnetization value of the carrier mentioned here, the strength of magnetization of the carrier in a magnetic field of 3000 × 10 ³ / 4π [A / m] is used.

If the remanence value of the carrier and the strength of the coercive force are too large, the good transportability of the developer inside the developing casing 7 is hindered, and the image is blurred or the density is not uniform in the solid image. And the like are likely to occur, which is a factor of reducing the developing ability. In order to suppress such a decrease in developing ability, the residual magnetization value of the carrier is set to 10 × 10.
^-7 × 4π [wb · m / kg] or less, preferably 5 × 10 ^-7
× 4π [wb · m / kg] or less, more preferably substantially 0
Is desirable. The strength of the coercive force of the carrier is 40 × 10 ³ / 4π [A / m] or less, preferably 3
0 × 10 ³ / 4π [A / m] or less, more preferably 10
It is important that it is not more than × 10 ³ / 4π [A / m]. In addition, as the strength of the coercive force of the carrier here,
The strength of coercive force when placed in a magnetic field of 3000 × 10 ³ / 4π [A / m] is used.

Considering the above magnetic properties of the carrier, it is preferable to use ferrite as the core material of the carrier.

As the coating resin for the carrier, a general thermosetting silicone resin can be used.
Further, in the present embodiment, fine powder is added to the coating resin of the carrier for the purpose of adjusting the resistance value of the carrier and the like. It is preferable that Further, a coupling agent, particularly a silane coupling agent, can be used for the purpose of adjusting the charging characteristics of the carrier and improving the adhesion between the coating resin and the core material. For example, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-
Aminoethyl) aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane,
N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane,
Methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium Chloride, γ-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane (above, manufactured by Toray Silicon Co.), allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxy. Silane, dimethyldiethoxysilane, 1.3-divinyltetramethyldisilazane, methacryloxyethyldimethyl (3-trimethoxysilylpropyl) ammonium chloride ( On, and the like is manufactured by Chisso Corporation), and the like.

Next, the toner of the developer used in this embodiment will be described. As the toner in the present exemplary embodiment, toner manufactured by using a known method can be widely used. Specifically, for example, a mixture of a binder resin, a colorant, and a polarity control agent is melt-kneaded with a hot roll mill, cooled and solidified, and a product obtained by pulverizing and classifying the mixture can be used. . Moreover, you may include arbitrary additives as needed. In this embodiment, a toner having a weight average particle diameter in the range of 6 to 10 [μm] is used.
The weight average particle diameter of this toner can be measured by various methods, for example, using a Coulter counter. As this Coulter counter, for example, Coulter Counter II type (manufactured by Coulter Co.) can be used. Then, based on the measurement results obtained by such a Coulter counter, the weight average particle diameter of the toner can be obtained by analyzing characteristics such as number distribution and volume distribution. As the electrolytic solution used for the measurement with the Coulter counter, a 1% sodium chloride aqueous solution prepared by using primary sodium chloride can be used.

As the binder resin for the toner, any of those conventionally used as a binder resin for toner can be used. Specifically, polystyrene, polychlorostyrene, homopolymers of styrene such as polyvinyltoluene and its substitutes, styrene / p-chlorostyrene copolymers, styrene / propylene copolymers, styrene / vinyltoluene copolymers, Styrene / vinyl naphthalene copolymer, styrene / methyl acrylate copolymer, styrene / ethyl acrylate copolymer, styrene / butyl acrylate copolymer, styrene / octyl acrylate copolymer, styrene / methyl methacrylate copolymer Polymer, styrene / ethyl methacrylate copolymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethyl methacrylate copolymer, styrene / acrylonitrile copolymer, styrene / vinyl methyl ether copolymer, styrene / Vinyl ethyl ether copolymer, Ethylene / vinyl methyl ketone copolymer, styrene / butadiene copolymer, styrene / isoprene copolymer, styrene / acrylonitrile / indene copolymer, styrene / maleic acid copolymer, styrene / maleic acid ester copolymer, etc. Styrene-based copolymer, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester,
Polyvinyl butyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, and the like. Used alone or in combination of two or more.

As the colorant for the toner, all known colorants for toner can be used. As the black colorant, for example, carbon black, aniline black, furnace black, lamp black and the like can be used. Examples of cyan colorants that can be used include phthalocyanine blue, methyllen blue, Victoria blue, methyl violet, aniline blue, and ultramarine blue. As the magenta colorant, for example,
Rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake, etc. can be used. As the yellow colorant, for example, chrome yellow, benzidine yellow, Hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like can be used.

Further, in order to charge the toner more efficiently, a small amount of a charge imparting agent such as a dye / pigment and a polarity control agent may be contained. Examples of the polarity control agent include metal complex salts of monoazo dyes, nitrohumic acid and its salts, salicylic acid, naphthoic acid, and dicarboxylic acid Co and C.
A metal complex such as r or Fe, an organic dye, a quaternary ammonium salt or the like can be used.

As the other additives, silica fine particles, titanium oxide fine particles and the like are generally mentioned, but are not particularly limited. In this embodiment,
Fine particles treated with a silicone oil treatment agent are used as an additive. Examples of the fine particles include silica fine particles and titanium oxide fine particles. Specific examples of the silicone oil treating agent for silica fine particles include modified silicone oil having a reactive group in the molecule, hydrogen silicone oil, and fluorine-containing silicone oil.
Although it is preferable to use one or more species, it is also possible to use an unmodified silicone oil having no such active group in the molecule. The modified silicone oil having a reactive group in the molecule is a modified silicone oil containing at least one group selected from the group consisting of hydroxy group, carboxyl group, amino group, epoxy group, ether group and mercapto group in the molecule. More than one species are preferred. The viscosity of the silicone oil is preferably 5 to 15000 [cp] at room temperature.

Here, when a toner having a small particle size is used as in the present embodiment, since excessive charging due to rubbing is likely to occur, an increase in charge amount in continuous printing is suppressed, and counter charging is performed. Toner is likely to adhere to the non-image area. Therefore, in the present embodiment, fine particles of titanium oxide capable of enhancing the fluidity of the toner are contained for the purpose of controlling the charge amount of the toner. The amount of titanium oxide added is such that the specific surface area of titanium oxide to the total surface area of the toner measured by nitrogen adsorption by the BET method is 30
It is desirable to set it so as to be [m ² / g] or more, particularly in the range of 50 to 400 [m ² / g]. However, if the titanium oxide fine particles are added in a larger amount than the silica fine particles, the toner charge amount becomes insufficient. Therefore, the addition ratio of titanium oxide fine particles to silica fine particles is
It is desirable to set it to be 0.6 or less. The total amount of such fine powder added is 0.5 to 2 even for the toner.
[Wt%] is preferable.

[0047]

Experimental Example An experimental example of the laser printer described in the above embodiment will be described below. First, the formulation and manufacturing method of the toners T1 to T5 and the carriers C1 to C6 used in the following experimental examples will be described.

(Preparation of Toner T1) A mixture of the respective materials shown in Table 1 below was thoroughly stirred and mixed in a Henschel mixer, and then heated and melted by a roll mill at a temperature of 80 ° C. for about 30 minutes to reach room temperature. The kneaded product obtained after cooling was pulverized and classified by a jet mill to produce a 6.5 [μm] classified toner. Then, for 100 parts of classified toner, 1.
Toner T1 was obtained by adding 0 part of silica fine particles and 0.4 part of titania fine particles and mixing them with a Henschel mixer rotating at 1500 [rpm]. The toner T1 had a weight average particle diameter of 6.7 [μm] and a surface friction coefficient of 0.30.

[Table 1]

(Preparation of Toner T2) A mixture of the materials shown in Table 2 below was thoroughly stirred and mixed in a Henschel mixer, and then heated and melted by a roll mill at a temperature of 80 ° C. for about 30 minutes to reach room temperature. The kneaded product obtained after cooling was pulverized and classified by a jet mill to produce a classified toner having a particle size of 6.5 [μm]. Then, to 100 parts of the classified toner, 1.0 part of silica fine particles and 0.4 part of titania fine particles were added and mixed by a Henschel mixer rotating at 1500 [rpm] to obtain toner T2. .
The toner T2 had a weight average particle diameter of 6.8 [μm] and a surface friction coefficient of 0.17.

[Table 2]

(Preparation of Toner T3) A mixture of each material shown in Table 3 below was thoroughly stirred and mixed in a Henschel mixer, and then heated and melted by a roll mill at a temperature of 80 ° C. for about 30 minutes to reach room temperature. The kneaded product obtained after cooling was pulverized and classified by a jet mill to produce a classified toner having a particle size of 6.5 [μm]. Then, to 100 parts of the classified toner, 1.0 part of silica fine particles and 0.4 part of titania fine particles were added and mixed by a Henschel mixer rotating at 1500 [rpm] to obtain toner T3. .
The toner T3 had a weight average particle diameter of 6.8 [μm] and a surface friction coefficient of 0.35.

[Table 3]

(Preparation of Toner T4) The mixture of the materials shown in Table 3 above was thoroughly stirred and mixed in a Henschel mixer, and then heated and melted by a roll mill at a temperature of 80 ° C. for about 30 minutes and cooled to room temperature. The kneaded material obtained later was pulverized and classified by a jet mill to produce a classified toner having a particle size of 6.5 [μm]. Then, to 100 parts of the classified toner, 1.0 part of silicone oil-treated silica fine particles and 0.4 part of titania fine particles were added, and 1500 [r
Toner T4 was obtained by mixing with a Henschel mixer rotating at pm]. The toner T4 had a weight average particle diameter of 6.8 [μm] and a surface friction coefficient of 0.31.

(Preparation of Toner T5) A mixture of the materials shown in Table 4 below was thoroughly stirred and mixed in a Henschel mixer, and then heated and melted by a roll mill at a temperature of 80 ° C. for about 30 minutes to reach room temperature. The kneaded product obtained after cooling was pulverized and classified by a jet mill to produce a classified toner having a particle size of 6.5 [μm]. Then, to 100 parts of the classified toner, 1.0 part of silica fine particles and 0.4 part of titania fine particles were added and mixed by a Henschel mixer rotating at 1500 [rpm] to obtain toner T5. .
The toner T5 had a weight average particle diameter of 6.8 [μm] and a surface friction coefficient of 0.43.

[Table 4]

(Preparation of Carrier C1) The formulations shown in Table 5 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, the coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.4 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
Firing was carried out for a period of time to prepare carrier C1. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ⁻⁷ × 4π [wb · m / kg], current value is 30 [μ
A] was used. The current value mentioned here indicates a current value that is conducted when the magnetic brush comes into contact with the photosensitive drum 1. The same applies to the following current values. The dynamic resistance value of the carrier C1 is 9.1 [Log
Ω], the fluidity was 32 [sec / 50 g].

[Table 5]

(Preparation of Carrier C2) The formulations shown in Table 6 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, the coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.4 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
The carrier C2 was produced by firing for a time. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ⁻⁷ × 4π [wb · m / kg], current value is 40 [μ
A] was used. The carrier C2 had a dynamic resistance value of 8.4 [LogΩ] and a fluidity of 17 [sec / 50 g].

[Table 6]

(Preparation of Carrier C3) The formulations shown in Table 7 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, the coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.4 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
Firing was carried out for a time to prepare carrier C3. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ^-7 × 4π [wb · m / kg], current value is 22 [μ
A] was used. The carrier C3 has a dynamic resistance value of 10.2 [LogΩ] and a fluidity of 45.
It was [second / 50 g].

[Table 7]

(Preparation of Carrier C4) The formulations shown in Table 8 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.1 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
Firing was carried out for a period of time to prepare carrier C4. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ⁻⁷ × 4π [wb · m / kg], current value is 30 [μ
A] was used. The carrier C4 had a dynamic resistance value of 9.3 [LogΩ] and a fluidity of 25 [sec / 50 g].

[Table 8]

(Production of Carrier C5) The formulations shown in Table 8 were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, the coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.6 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
Firing was carried out for a time to prepare carrier C5. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ⁻⁷ × 4π [wb · m / kg], current value is 25 [μ
A] was used. The carrier C5 had a dynamic resistance value of 9.8 [LogΩ] and a fluidity of 38 [sec / 50 g].

(Production of Carrier C6) The formulations shown in Table 9 below were dispersed for 20 minutes with a homomixer to prepare a coating layer forming liquid. Then, this coating layer forming liquid was applied to a fluidized bed type coating apparatus at a spray air pressure of 0.2 [MPa] to 1000
After coating on the surface of the ferrite part of the part and forming a coating layer on the ferrite surface, 2 in an electric furnace at a temperature of 300 [° C]
Firing was carried out for an hour to prepare carrier C6. This ferrite has a volume average particle size of 55 [μm] and a saturation magnetization value of 6
5 × 10 ⁻⁷ × 4π [wb · m / kg], current value is 35 [μ
A] was used. The carrier C6 had a dynamic resistance value of 8.5 [LogΩ] and a fluidity of 50 [sec / 50 g].

[Table 9]

(Measurement Method) Next, the method used for measuring the characteristics of the above-mentioned toner and carrier will be described. The surface friction coefficient of the toner is a full automatic friction manufactured by Kyowa Interface Science Co., Ltd., which is obtained by applying a load of 6 [t / cm ² ] to a toner having a mass of 3 [g] to make a disk-shaped pellet having a diameter of 40 [mm]. It was measured using a wear analyzer. As the contact at the time of this measurement, a point contact made of a 3 [mm] stainless steel ball was used. The volume average particle size of the carrier is measured by Microtrac particle size analyzer (Nikkiso Co., Ltd .:
The measurement was performed using an SRA type of LEEDS & NORTHRUP Type 7995) with a range setting of 0.7 to 125 [μm]. The dynamic resistance value of the carrier was measured using the dynamic resistance measuring device shown in FIG. This dynamic resistance measuring device includes a conductive sleeve 61, a doctor blade 62, a drive shaft 63, a variable DC power supply 64, a mount 65, a connecting member 66, a conductive contact member 67, an insulating support member 68, a drive motor 69, an ammeter. It is composed of 70 and the like. The conductive sleeve 61 is made of a non-magnetic and conductive cylindrical sleeve, and a magnet capable of changing the magnetic pole angle is provided inside the sleeve. The doctor blade 62 is made of a metal such as aluminum, and is fixed to the conductive sleeve 61 in an electrically floating state via an insulating support member 68. Further, the drive shaft 63 is attached to the conductive sleeve 61.
And a DC voltage is applied from the variable DC power supply 64 through the doctor blade 62. And
The current value flowing from the surface of the conductive sleeve 61 to the ground is measured by the ammeter 70 through the conductive contact member 67. Here, using this dynamic resistance measuring device, the voltage applied by the variable DC power supply 64 is changed in the range of 0 to 200 V, and the current value at that time is detected by the ammeter 70, and then based on the detection result. A graph was prepared by plotting voltage on the vertical axis and current value on the horizontal axis, and the slope of the graph was taken as the dynamic resistance value. In this measurement, the gap between the conductive sleeve 61 and the doctor blade 62 was 1 [mm], and the peripheral speed of the conductive sleeve 61 with respect to the doctor blade 62 was 600 [mm / sec]. The carrier fluidity is such that the temperature of the carrier is 2
After being left for 2 hours in an environment of 3 ± 3 [° C.] and humidity of 60 ± 10 [% RH], it is 50 based on JIS-Z2504.
The carrier of [g] was poured into a funnel, and the time when it dropped was measured.

Incidentally, the developing device 2 used in this experimental example.
As described above, under the condition that the attenuation rate of the magnetic flux density in the normal direction is 50 [%] or more, the magnetic brush is in a short and dense state. Therefore, as described above, The linear velocity is 1.1 with respect to the linear velocity of the photosensitive drum 1.
.About.3.0 times, practically 1.5 to 3.0 times, to maintain a high image density and suppress the generation of a blurred image. However, with this setting, as a result of the agent accumulation near the rear end of the main magnetic pole, the edge portion of the rear end portion of the latent image is developed darker than other image portions, that is, so-called rear end toner deviation. The phenomenon occurs.

FIGS. 8A and 8B show halftone images at four levels of image densities of 30, 41, 50, and 59%, respectively. In FIG. 8A, the toner near the trailing edge occurs. The state X and FIG. 8B schematically show the state ◯ in which the state near the trailing edge toner hardly occurs. This is because it is difficult to quantify the evaluation of the toner near the trailing edge, so a schematic representation of the state where the toner near the trailing edge is generated and the state where it is not generated is shown so that the difference can be seen. Is. When developing the image which is the basis of this schematic diagram, first, the toner T1 and the carrier C1 are mixed in a toner concentration of 5 w [%], and 1 kg of a developer having a charge amount of 23 [μc / g] is used. And the printer of this embodiment shown in FIG. Also, as already mentioned, each setting is
The maximum value of the magnetic flux density in the normal direction of the main pole P1b is 120 [m
T], the attenuation factor of the magnetic flux density in the normal direction is 53.5 [%], and the half-value angle width of the main magnetic pole P1b is 16 [°]. Further, the attenuation rate of the magnetic flux density in the normal direction by the auxiliary magnetic pole P1a is 46.7 [%], and the attenuation rate of the magnetic flux density in the normal direction by the auxiliary magnetic pole P1c is 43.8 [%]. The arrangement angle width of the magnetic poles P1a and P1c is 25 [°]. The development gap is set to 0.5 [mm].
In the halftone halftone image of 50 [%] formed by using the above printer, in the image part of 15 [mm] in the rotation direction,
When the image densities at the central portion were 1.0 and the image densities at the edge portions were high, the toner near the trailing edge was generated. Further, development was carried out with four image density levels of 30, 41, 50, and 59%. From this figure, as shown in FIG. 8A, when the rank closer to the trailing edge toner is x, the density of the lower edge portion in the figure is higher than that of the central portion. On the other hand, as shown in FIG. 8B, when the rank near the trailing edge toner is ◯, the density at the lower edge portion in the figure is almost the same as that at the central portion. In addition, the middle of them is evaluated as rank Δ.

The present inventors have confirmed that by shifting the position of the main magnetic pole with respect to the developing nip portion to the upstream side in the moving direction of the surface of the developing sleeve, it is possible to prevent the trailing edge toner from shifting. Hereinafter, experimental examples according to the present invention will be described.

[Experimental Example 1] In Experimental Example 1, the main magnetic pole position with respect to the developing nip portion was shifted by 2 degrees to the upstream side in the moving direction of the developing sleeve surface up to a maximum of 8 degrees. Was examined. Figure 1
FIG. 4 is an explanatory diagram of main magnetic pole positions provided in the developing sleeve according to the present embodiment. Except for the movement of the relative position of the main magnetic pole P1b with respect to the developing nip portion, the same conditions and the same devices as those used for developing for each rank closer to the trailing edge toner were used. The results are shown in Table 10.

[Table 10] In Table 10, as for the main magnetic pole position, the sleeve surface position (hereinafter referred to as the main magnetic pole position) where the magnetic flux density in the direction normal to the developing sleeve surface generated by the main magnetic pole P1b has the highest value is upstream from the developing nip position in the developing sleeve surface moving direction. It is an angle indicating how many times it is shifted to the side, and is an angle between a line connecting the center of the developing sleeve and the center of the photosensitive drum and a line connecting the center of the developing sleeve and the main magnetic pole position. The density of the central portion of the image is shown by the density ratio with the density at the main magnetic pole position being 0 [°] as 1. From the above result, when the main magnetic pole position is shifted upstream in the developing sleeve surface movement direction, the trailing edge toner shift is gradually improved. When the main magnetic pole position is 4 [°] or more, the trailing edge toner bias rank is ◯, and when the main magnetic pole position is 2 [°] and the trailing edge toner bias rank is Δ, that is, (a) and (b) of FIG. Intermediate results. Further, the rank Δ or more closer to the trailing edge toner is an allowable range. However, as a side effect of shifting the position of the main magnetic pole upstream in the direction of movement of the surface of the developing sleeve, the brush of the developer shifts too much from the developing nip, and the rubbing time between the brush and the photosensitive drum 1 becomes too short, so that the toner on the electrostatic latent image is reduced. There is a tendency that the central portion of the image is also reduced due to a shortage of the supply amount of. Central image density is 0.9
~ 1.1 is an allowable range, preferably 0.95 to 1.05
Is desirable from the overall γ characteristic. To set the density of the central portion of the image to a preferable range, specifically, the main magnetic pole position may be 6 [°] or less, and at this time, the density of the central portion of the image becomes 0.9 or more. From the above, the range of the main magnetic pole position suitable for carrying out to prevent the trailing edge toner shift is from 2 [°] to 6 [°]
It is the following. Within this range, it is possible to achieve both prevention of the trailing edge toner shift and optimization of the image center density. still,
In the printer of this embodiment, the optimum condition of the main magnetic pole position is 4 ± 1 [°].

From the results of Experimental Example 1 above, by shifting the position of the main magnetic pole upstream by 2 to 6 [°] in the moving direction of the developing sleeve surface, the ears of the developer are 2 to 6 [°] upstream as compared with the conventional case. It was confirmed that it is possible to suppress the generation of the agent accumulation that has occurred at the rear end of the main pole facing toward the side, and at the same time, it is possible to form a good image without the density of the central portion of the image decreasing too much. ..

[Experimental Example 2] In Experimental Example 2, the following Table 11 is used.
The carrier and the toner shown in (1) were combined to evaluate the fluidity of the developer and the rank of the trailing edge toner. In Experimental Example 2, the main magnetic pole position was uniformly shifted 4 [°] upstream in the developing sleeve surface movement direction, and the same conditions and the same apparatus as those in Experimental Example 1 were used except for the developer used.

[Table 11] In Table 11, the fluidity of the developer is the time during which 50 [g] of the developer flows down the funnel, and the measurement is based on JIS.
Based on -Z2504, the sample is allowed to stand in an environment of a temperature of 23 ± 3 [° C.] and a humidity of 60 ± 10 [%] for 2 hours and then measured. The fluidity is a cohesive property of a developer and a carrier, and is a value showing the fluidity of the developer in this experimental example. A developer having a small value shows a characteristic that it easily moves (flows) in a free-flowing state even when the other conditions are the same. On the contrary, the developer having a large value is difficult to flow, and the ears of the developer formed on the developing sleeve are also hard to move. If the fluidity of the developer that has passed through the doctor blade is large, the movement of the developer between the photosensitive drum 1 and the developer drum 1 is slow, and it is easy to form an agent pool. Easier to do. On the other hand, a developer having a low fluidity easily moves between the developing sleeve 4 and the photoconductor drum 1 even when the developer passing amount and the magnetic force are the same, and exhibits a behavior as when the developer density is small. As a result, agent accumulation is less likely to occur, and the toner near the trailing edge is lessened, but the developing ability tends to decrease and the image density also decreases. From the results in Table 11 above, when the main magnetic pole position is shifted to the upstream side and the developer fluidity is in the range of 30 to 50 [sec / 50 g], both the image density and the prevention of the trailing edge toner shift are compatible. Can be better satisfied. When the toner charge amount is in the normal charge amount range (20 to 30 [μC / g]), the developer fluidity is almost determined by the carrier fluidity. With the charge amount in this range, the developer fluidity is around carrier fluidity + 10 [μC / g]. Therefore, it can be said that if the fluidity of the carrier is in the range of 20 to 40 [sec / 50 g], it is possible to better satisfy both the image density and the prevention of the trailing edge toner shift.

[Experimental Example 3] In Experimental Example 3, the surface friction coefficient of the toner was variously changed, and the trailing edge of the toner and the density of the central portion of the image in each case were examined. In particular,
C1 is used as the carrier, and the same conditions and the same apparatus as those used for developing by the rank closer to the rear end toner are used, except that the surface friction coefficient of the toner used is changed by changing the toner from T1 to T5. I was there. Here, the surface friction coefficient of toner indicates the slipperiness of the toner surface, and the lower the value, the more slippery the toner surface. The toner used in this experimental example is an oilless toner, and W
The ax is dispersed, which is common as a monochrome toner. Here, if a large amount of dispersed Wax oozes out on the toner surface, Wax adheres to the carrier to reduce the charging ability, and if too much Wax oozes out, the image density will decrease over time. On the other hand, when the wax is small, the releasability at the time of fixing is deteriorated and an abnormal phenomenon occurs at the fixing. In order to avoid these phenomena, it has been confirmed that there is no problem if the toner surface friction coefficient is within the range of 0.15 to 0.45. Table 12 shows the experimental results.

[Table 12] From the results shown in Table 12, when the toner surface friction coefficient is large, the developing efficiency is good, but the trailing edge toner is liable to occur. N
From the results of o, 4 and 5, it is understood that the toner surface friction coefficient should be 0.35 or less in order to prevent the trailing edge toner deviation. Although not shown in the table, No,
When 1, the image density was too low. If the toner surface friction coefficient is small, the toner near the trailing edge is reduced, but the developing ability is lowered and the image density is lowered. In order to avoid a decrease in image density, the toner surface friction coefficient may be 0.25 or more. When the toner surface friction coefficient is in the range of 0.25 to 0.35, the image density is also in the preferable range while preventing the trailing edge toner shift.

Here, the toner surface friction coefficient is mainly determined by the amount of the wax that is internally added to the toner that oozes out to the surface. Changes depending on the dispersion state of. Wax having a small dispersion state does not easily exude, and the cohesiveness of the developer is deteriorated. On the other hand, Wax having a large dispersion state easily exudes to the toner surface due to the influence of heat, and loosens the cohesiveness of the developer. The developer having a loose cohesive property allows the developer to move smoothly between the photosensitive drum 1 and the sleeve, thereby reducing the amount of developer accumulated. It can be said that the condition that the cohesiveness is mild is preferable under the condition that the image density does not deteriorate as described above. As a method of controlling the surface friction coefficient of the toner, there is a method of controlling the size of the raw material particle diameter of Wax to a predetermined size. Further, No. 4 and N using toners T3 and T4 made of the same material are used.
Compared with No. 3 and No. 3, the developer using the toner T4 to which the silica treated with silicone oil of No. 3 is externally added is
The friction coefficient of the toner surface is smaller than that of the developer using the toner T3 that does not use silica treated with silicone oil as the external additive of the toner. Then, it can be seen that the flowability of the developer is reduced, which is effective in preventing the trailing edge toner from deviating. Further, by using silica fine particles treated with a silicone oil treatment agent as an additive, it is possible to reduce the abrasion of the photosensitive drum 1 due to the silica fine particles.

From the above results, by setting the toner surface friction coefficient within the range of 0.25 to 0.35, it is possible to prevent the trailing edge toner from deviating while keeping the image density within the preferable range.

As described above, in the present embodiment, as is clear from Experimental Example 1, the main magnetic pole position is shifted to the upstream side in the developing sleeve surface moving direction with respect to the developing nip portion, so that the main magnetic pole is generated at the rear end. Further, it is possible to suppress the generation of the agent accumulation, prevent the trailing edge toner from deviating, and form a good image. Further, in the present embodiment, the developing magnetic pole is composed of the main magnetic pole and the auxiliary magnetic poles arranged on both sides of the main magnetic pole, whereby the time during which the same magnetic brush rubs the surface of the photosensitive drum can be shortened. Therefore, it is possible to suppress the occurrence of trailing white spots and the deterioration of fine line reproducibility. Further, by setting the main magnetic pole so that the attenuation rate of the magnetic flux density in the normal direction is 50 [%] or more and the half-value angle width is 25 [°] or less, the magnetic brush can be shortly and closely raised, and rises on the developing sleeve surface. It is designed to bring about uniform fall. Further, by setting the half-value angle width to be narrow in this way, it is possible to narrow the developing nip and easily control the rising position of the magnetic brush to a preset position. Also, by setting the attenuation rate of the magnetic flux density in the normal direction of the auxiliary magnetic pole to be 40% or more, it is possible to prevent the magnetic brush raised by the auxiliary magnetic pole from coming into contact with the photosensitive drum. Furthermore, by setting the magnetic pole angle width between the main magnetic pole and the auxiliary magnetic pole to be within 35 [°] and not wider than this, the half width of the main magnetic pole sandwiched between the auxiliary magnetic poles can be narrowed. In addition, the distance between the latent image carrier and the developing sleeve 4 in the developing nip portion (hereinafter referred to as the developing gap) is 0.3 to 0.5 [m.
m], and even if the development gap, doctor gap, etc. change within the practical tolerance range due to normal processing accuracy and mounting accuracy, the image density is effectively stable within the parameter range that is normally set. ID and the like can be maintained.
Further, as is clear from Experimental Example 1, the main magnetic pole position is set to 2 to the upstream side in the developing sleeve surface moving direction with respect to the developing nip portion.
By shifting by 6 [°], it is possible to suppress the generation of the agent pool that has occurred at the rear end of the main magnetic pole, and it is possible to form a good image without the density of the central portion of the image decreasing too much. . Further, as is clear from Experimental Example 2, by satisfying the developer fluidity in the range of 30 to 50 [sec / 50 g], it is possible to better satisfy both the image density and the trailing edge toner shift prevention. You can Further, when the toner charge amount is within a normal charge amount range (20 to 30 [μC / g]), the developer fluidity is almost determined by the carrier fluidity, so that the carrier fluidity is 20 to 40 [sec / sec. It can be said that both of the image density and the prevention of the trailing edge toner deviation can be better satisfied in the range of 50 g]. Further, as is clear from Experimental Example 3, the toner surface friction coefficient is 0.25.
Within the range of 0.35 to 0.35, it is possible to prevent the trailing edge toner shift and to set the image density to a preferable range, and it is possible to better satisfy both the image density and the trailing edge toner shift prevention. it can. Also, as is clear from Experimental Example 3,
By using silica fine particles treated with a silicone oil treatment agent as an additive, the fluidity of the developer can be reduced without changing the material and mixing ratio of the developer, and the fluidity of the developer can be controlled. It will be easy. This is effective in preventing the trailing edge toner from deviating. Further, it is possible to reduce the abrasion of the photosensitive drum 1 due to the silica fine particles.

[0070]

According to the image forming apparatus of the present invention, the vicinity of the rear end portion of the latent image caused by the continuous development in the state where the linear velocity ratio of the developing sleeve to the latent image carrier is larger than 1. Since it is possible to avoid the occurrence of the accumulation of the agent in the configuration, it is possible to improve the reproducibility of fine lines, prevent the trailing edge whiteout phenomenon, prevent the image density from decreasing, and prevent the occurrence of blurred images. In addition, there is an excellent effect that it is possible to prevent the trailing edge of the toner. In particular, claim 2
According to the image forming apparatus of No. 1, the practical numerical value range shows how much the development density peak position can be shifted from the development nip portion to the upstream side in the sleeve surface moving direction to prevent the toner rear end deviation. It has the excellent effect of being targeted.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main pole position provided in a developing sleeve according to the present invention.

FIG. 2 is a schematic configuration diagram of the entire printer according to the embodiment.

FIG. 3 is a schematic configuration diagram around a photosensitive drum of the printer.

FIG. 4 is a pie chart showing the distribution of magnetic flux density in the normal direction generated on the surface of the developing sleeve by each magnetic pole of the magnet roller of the printer.

FIG. 5 is an explanatory diagram showing an arrangement of three magnetic poles that form a developing magnetic pole of the magnetic roller.

FIG. 6A is an explanatory diagram showing a half-value angle width when a developing magnetic pole is composed of three magnetic poles. (B) is an explanatory view showing a half value angular width in the case where a developing magnetic pole is constituted by one magnetic pole.

FIG. 7 is a schematic configuration diagram of a measuring device for measuring a dynamic resistance value of a carrier.

FIG. 8A is a halftone image showing a state X in which the trailing edge of the toner is deviated, in a four-step image density. (B) is a halftone image showing the state ◯ in which the trailing edge of the toner is not generated, at four levels of image density.

FIG. 9A is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing region in a conventional developing device in which the developing magnetic pole is composed of one magnetic pole. FIG. 3B is an explanatory view showing the shape of the magnetic brush made of the developer that has risen in the magnetic field formed by the developing magnetic pole when viewed from the axial direction of the developing sleeve in the developing device.

FIG. 10A is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing area in a developing device in which a developing magnetic pole includes one main magnetic pole P1b and two auxiliary magnetic poles P1a and P1c. FIG. 3B is an explanatory view showing the shape of the magnetic brush made of the developer that has risen in the magnetic field formed by the developing magnetic pole when viewed from the axial direction of the developing sleeve in the developing device.

[Explanation of symbols]

1 photoconductor drum 2 Development device 3 developing roller 4 Development sleeve 5 magnetic roller 6 doctor blade 7 Development casing 8 screws 50 charging roller 51 Optical writing unit 52 Transfer paper 53 Transfer belt P1b Main pole P1a, P1c Auxiliary magnetic pole

Continued front page    (72) Inventor Naoto Shimoda             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Yuji Suzuki             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Akihiro Ito             3 Shinmei-do, Nakameisei, Shibata-cho, Shibata-gun, Miyagi Prefecture             Number one F-term (reference) 2H005 AA00 AA08 BA00 CA12                 2H031 AC08 AC11 AC14 AC15 AC18                       AC19 AC20 AD03 AD05 AD15                       BA05 BA09 DA01

Claims (6)

[Claims] 1. A latent image carrier that carries an electrostatic latent image on its surface and moves, and a developer carrier that carries and conveys a two-component developer consisting of toner and magnetic particles. The developer is magnetically attracted to the surface of the developer carrier by a developing magnetic pole facing the developing region where the carrier is opposed to the latent image carrier to form a magnetic brush, and the magnetic brush of the latent image carrier is formed in the developing region. The surface of the latent image carrier is moved by moving the surface of the developer carrier at a linear velocity which is the same as the surface moving direction and is higher than the linear velocity of the surface of the latent image carrier, and the surface of the latent image carrier is rubbed by the magnetic brush. And a developing device for developing the latent image on the latent image carrier, which is carried by the developer carrier and is conveyed to a developing area for developing by rubbing the surface of the latent image carrier by the magnetic brush. The amount of developer used is 65
˜95 [mg / cm ² ], an image in which the attenuation rate of the magnetic flux density in the normal direction of the surface of the developer carrier, which is generated outside the surface of the developer carrier in the developing area by the developing magnetic pole, is 40% or more In the forming apparatus, the developer carrier surface position where the magnetic flux density in the normal direction of the developer carrier surface generated by the developing magnetic pole becomes the maximum value is set to the developer carrier surface and the latent image carrier surface. The image forming apparatus is characterized in that it is shifted to the upstream side in the moving direction of the surface of the developer carrier with respect to the developing nip portion which is the closest position between the two. 2. The image forming apparatus according to claim 1, wherein the developer carrier comprises a non-magnetic sleeve and a plurality of magnetic poles fixedly arranged in the sleeve, the developing magnetic pole being a main magnetic pole and the developing magnetic pole. The auxiliary magnetic poles are arranged on both sides of the main magnetic pole, and the main magnetic pole has a magnetic flux density attenuation rate of 50% or more in the normal direction to the surface of the developing sleeve and a half-value angle width of 25.
[°] or less, the auxiliary magnetic pole has a magnetic flux density attenuation rate of 40 [%] or more in the normal direction to the surface of the developing sleeve, and the magnetic pole angle width between the main magnetic pole and the auxiliary magnetic pole is within 35 [°]. Yes, the distance between the surface of the latent image carrier and the surface of the developing sleeve in the developing nip portion is set to 0.3 to 0.5 [mm], and the surface of the sleeve caused by the main magnetic pole is measured. The position of the sleeve surface where the magnetic flux density in the linear direction becomes the maximum value is set in the range of 2 [°] or more and 6 [°] or less on the upstream side in the sleeve surface moving direction with respect to the developing nip portion. A characteristic image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the fluidity of the developer is 30 [sec / 50 g] or more and 50 [sec / 50 g] or less. 4. The image forming apparatus according to claim 2, wherein the fluidity of the magnetic particles, which is a constituent element of the developer, is 20.
An image forming apparatus characterized in that it is not less than [second / 50 g] and not more than 40 [second / 50 g]. 5. The image forming apparatus according to claim 2, 3 or 4, wherein the surface friction coefficient of the toner is 0.25 or more and 0.35 or less. 6. The image forming apparatus according to claim 1, 2, 3, 4, or 5, wherein an external additive of the toner treated with silicone oil is used.