JP2003270954A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus which can improve thin line reproducibility, prevent a rear end void phenomenon, and improve developing ability and image quality by preventing both of image density deterioration and toner deviation at a rear end. <P>SOLUTION: The following configuration is adopted in the image forming apparatus in which the magnetic force of a main magnetic pole for development is intensified, and the napping is shortened for the purpose of the improvement in the thin line reproducibility or the prevention of the rear end void phenomenon. That is, the opening width of the slot of a development sleeve 4 surface is set to be 0.1 (mm) to 0.2 (mm), an average in depth is set to be 0.1 (mm) to 0.2 (mm), and a groove pitch is set to be 0.4 (mm) to 0.6 (mm). Then, the volume averaged grain size of a carrier is set to be 40 (μm) to 60 (μm), comparatively small grain size. Thereby, image density does not run short even when the linear velocity of the development sleeve in a developing region is set to be 1.5 to 2.5 times of a photoreceptor linear velocity, which is comparatively low. <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 used for an image forming apparatus such as a copying machine, a printer and a FAX. 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 type 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 developing the electrostatic latent image with a developing device. In recent years, in carrying out such development, from the viewpoint of transferability, halftone reproducibility, stability of development characteristics with respect to temperature and humidity, etc., a two-component developer consisting of a toner and a carrier (hereinafter, simply referred to as "development The mainstream is to use a two-component developing method using "agent". 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. This magnet roller is for forming a magnetic field on the surface of the developing sleeve to make the developer stand up. By the relative movement of the developing sleeve with respect to the magnet roller, the developer that is erected on the surface of the developing sleeve is conveyed. In the development area,
The developer on the developing sleeve stands up along the lines of magnetic force emitted from the developing magnetic pole of the magnet roller. The brush-shaped 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 latent image carrier and the developing sleeve are to each other in the developing area, the higher the image density is easily obtained 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, if this distance is made close, the trailing edge of a black solid image or a halftone solid image will be white, so-called "rear white void".
There is a problem in that the image quality is deteriorated due to the phenomenon called ".

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 higher than the linear velocity of the latent image carrier. Yotsutte
The magnetic brush moves relative to the electrostatic latent image so as to rub against it while overtaking the electrostatic latent image on the latent image carrier. That is, the surface of the latent image carrier is rubbed so as to be sequentially overtaken by a plurality of magnetic brushes while passing through the developing area. Focusing on the electrostatic latent image portion (latent image trailing edge portion) on the latent image carrier corresponding to the image trailing edge position, a plurality of magnetic brushes that sequentially rub the latent image trailing edge portion are as follows. The toner supply capacity gradually decreases. The magnetic brush that rubs the trailing edge of the latent image carrier after moving into the developing area due to the movement of the latent image carrier surface is located on the non-latent image part located upstream of the latent image carrier surface moving direction on the latent image carrier. It has been facing. At the tip portion of such a magnetic brush, the toner drift that the toner adhering to the carrier surface moves to the developing sleeve side by the electrostatic force received from the non-latent image portion during the period facing the non-latent image portion. Has occurred. This toner drift
The longer the period facing the non-latent image portion, the more the process proceeds. Therefore, the closer the magnetic brush that rubs the trailing edge of the latent image on the downstream side of the developing area in the moving direction of the latent image carrier, the longer the period of time facing the non-latent image portion and the more the toner drifts and the carrier at the leading edge. The amount of toner on the surface is small and the toner supply capacity is small. Then, when the trailing edge portion of the latent image escapes from the developing area, the magnetic brush rubbing the trailing edge portion of the latent image is in a state where toner hardly exists on the carrier surface of the leading edge portion. The magnetic brush whose toner drift has progressed to such an extent electrostatically attracts the toner adhering to the trailing end portion of the latent image to the carrier surface of the magnetic brush tip portion to which the toner has not adhered. . As a result, regarding the trailing edge portion of the latent image, even if toner is once supplied by the magnetic brush in the developing area, there is almost no toner on the carrier surface before the toner leaves the developing area. It moves to the tip. As a result, trailing white spots and a decrease in fine line reproducibility are considered to occur.

The present applicant has proposed various inventions in order to suppress the trailing edge white spots and the deterioration of fine line reproducibility. For example, JP 2000-305360 A and JP 2000
-347506, JP 2001-5296 A, etc. According to these inventions, it is possible to improve the image quality of the developing device. 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 and the adjacent magnetic pole for making the developer stand in the developing area, and the half-value central angle of the main magnetic pole Etc. 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 has set the developing nip and the magnetic brush density (Japanese Patent Laid-Open No. 2001-278).
49) and the half-value angle width of the main pole (also referred to as the half-value center angle) (Japanese Patent Laid-Open No. 2001-134100).
We have also proposed an invention that realizes the improvement of image quality. According to these inventions, it has been confirmed that the developing efficiency can be improved, and the trailing edge white spot phenomenon and the fine line reproducibility can be improved.

Of the above publications, Japanese Patent Laid-Open No. 2000-3053
It is considered that the improvement of the developing efficiency, the trailing edge white spots, and the fine line reproducibility by the devices of JP-A No. 60, JP-A-2000-347506, and JP-A-2001-5296 are due to the following reasons. In FIG. 8A, the developing magnetic pole is 1
FIG. 10 is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing area in a conventional developing device including one magnetic pole P1. Also, FIG. 8 (b)
FIG. 3 is an explanatory diagram showing a shape of a magnetic brush made of a developer that is erected by receiving a magnetic force from a magnetic field formed by the developing magnetic pole P1 when viewed from the axial direction of the developing sleeve 4. FIG. 9A shows main magnetic poles P1b and 2 having one developing magnetic pole.
FIG. 6 is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing region in a developing device including one auxiliary magnetic pole P1a and P1c. Further, FIG. 9B shows a shape of a magnetic brush made of a developer that is erected by receiving a magnetic force from a magnetic field formed by these magnetic poles P1a, P1b, and P1c when viewed from the axial direction of the developing sleeve 4. It is an explanatory view shown.

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. Also,
There is also a magnetic pole P6 forming a magnetic field for transporting the developer drawn up onto the developing sleeve 4 to the developing area.
Since the magnetic poles P2 and P6 are arranged relatively far from the developing magnetic pole P1, the magnetic field distribution of the magnetic field in the developing area is as shown in FIG. It passes through a position relatively far from the surface of the sleeve. Then, the developer carried on the developing sleeve 4 and conveyed to the developing area stands up along the magnetic lines of force to form a magnetic brush, as shown in FIG. 8B.

On the other hand, in the developing device of the above publication, there are two auxiliary magnetic poles P1a and P1c as the S magnetic pole adjacent to the N magnetic pole P1b. The distance between the main magnetic pole P1b and these auxiliary magnetic poles P1a and P1c is shown in FIGS. 8 (a) and 8 (b).
It is smaller than the distance between the developing magnetic pole and the two magnetic poles P2 and P6 adjacent to the developing magnetic pole in the conventional developing device shown in FIG. For this reason, as shown in FIG. 9A, the magnetic force distribution of the magnetic field in the developing region is such that the magnetic line of force generated from the main magnetic pole P1b is larger than that of the magnetic pole generated from the main developing pole of the conventional developing device shown in FIG. 8A. It passes near the surface of the developing sleeve. Also, the main magnetic pole P1
More of the magnetic force lines emitted from b go to the two auxiliary magnetic poles P1a and P1c as the adjacent magnetic poles. As a result, the conventional developing device has the same number of magnetic force lines (hereinafter, referred to as "brushing magnetic force lines") that are in a direction close to the normal direction of the surface of the developing sleeve that is involved in the formation of the magnetic brush. Less than. The width (peak width) in the surface movement direction of the developing sleeve 4 where the magnetic field lines for spikes exist is also narrowed. Therefore, FIG. 8B and FIG.
As can be seen from the comparison with (b), the start position of the spikes of the developer conveyed to the developing area is the center of the developing sleeve surface moving direction in the developing area (hereinafter, simply referred to as “center ").). 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. That is, the developer on the developing sleeve 4 starts to stand up at a point closer to the center of the developing area than the conventional developing device, and ends the stand up. As a result, the period during which the magnetic brush on the developing sleeve 4 approaches or contacts the photosensitive drum 1 is shorter than that in the conventional developing device. Accordingly, when the latent image trailing edge portion moves out of the developing area due to the movement of the photosensitive drum surface, the magnetic brush rubbing the latent image trailing edge portion has come close to or in contact with the non-latent image portion until then. The existing period is shorter than that of the conventional developing device. Therefore, the degree of progress of toner drift of the magnetic brush rubbing the trailing end portion of the latent image on the photosensitive drum 1 when exiting the developing area can be reduced, and the trailing edge white spots and fine line reproducibility are improved as compared with the conventional developing device. Can be suppressed.

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 of the magnetic brush in the conventional apparatus exists) is the same as that in the above-mentioned publication. The device is smaller than conventional developing devices. 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 the device.

Further, when the developing device of the above publication is actually used, the amount of the developer conveyed to the developing area is smaller than the maximum amount of the developer which can stand up while passing through the developing area. Is set. That is, in the developing device of the above publication, although a longer magnetic brush can be originally formed, the length of the magnetic brush is regulated to be shorter by reducing the amount of the developer conveyed to the developing area. 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-mentioned 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. 9B, 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, if the developing device of the above publication is used, the brush density of the tip portion of the magnetic brush that contacts the photosensitive drum 1 can be made higher than that of the conventional developing device, as described above. Therefore, it is possible to prevent the amount of toner supplied to the latent image portion on the photosensitive drum 1 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 is attracted to the surface of the photoconductor drum by the electrostatic force generated between the carrier and the photoconductor drum 1. Has been found to occur. 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 photosensitive drum 1 moves relative to the surface of the photosensitive drum. However, the tip portion of the magnetic brush that contacts the surface of the photoconductor drum is often attracted to the surface of the photoconductor drum, and the rubbing operation is not performed on the surface of the photoconductor drum in many cases. Therefore, in the conventional developing device, even if the magnetic brush is rubbed (relatively moved) on the photoconductor drum 1, the effect of increasing the toner supply amount to the electrostatic latent image is small when the magnetic brush is not relatively moved. On the other hand, in the developing device disclosed in the above publication, the tip portion of the magnetic brush that comes into contact with the surface of the photoconductor drum can firmly rub against the surface of the photoconductor drum. This is because the tip portion of the magnetic brush that is in contact with the photosensitive drum 1 is located in a region where the magnetic flux density is higher and closer to the surface of the developing sleeve 4 than in the conventional device. This is because the binding force to the side is strong. Therefore, even if the rubbing width Pn becomes narrower than that of the conventional developing device, the amount of decrease in the amount of toner supplied to the latent image portion on the photosensitive drum 1 is small. The decrease in the amount of toner supplied to the latent image is due to the linear velocity ratio of the developing sleeve 4 to the linear velocity of the photosensitive drum 1 in the developing area (hereinafter,
It is possible to compensate by increasing the linear velocity ratio to the latent image carrier). Then, specifically, the linear velocity ratio is set to, for example, about 1.5 to 3.0.

[0013]

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, is likely to occur. The inventors of the present invention have investigated the cause of occurrence of the toner near the trailing edge, and found that the amount of toner supplied to the latent image portion is increased by increasing the linear velocity ratio of the developing sleeve to the latent image carrier. I found out that there is. The cause of the toner near the trailing edge will be described in more detail below.

FIGS. 11A and 11B are views showing the mechanism of occurrence of the trailing edge toner deviation. This is because the developing magnetic pole has one main magnetic pole P1b and two auxiliary magnetic poles P1a and P1c.
FIG. 3 is a partially enlarged view of the vicinity of a developing area where a photosensitive drum and a developing sleeve face each other when developing is performed using the developing device including Further, this figure shows the state of the magnetic brush when the linear velocity ratio to the latent image carrier is increased as described above and development is performed. The tip of the ears of the developer carried to the developing area while being carried on the surface of the developing sleeve 4 comes into contact with the photosensitive drum 1. The photosensitive drum has an electrostatic latent image formed on a uniformly charged surface, which is exposed based on image information. Then, the tip of the brush of the developer which comes into contact with the electrostatic latent image in the developing area is slightly attracted by the toner adhering to the electrostatic latent image on the photoconductor drum, though it is not so large as in a conventional printer. Further, the carrier at the tip of the magnetic brush is polarized and attracted to the photosensitive drum. The surface of the photosensitive drum 1 is moving in the same direction at a slower speed than the surface of the developing sleeve 4. Therefore, FIG.
As shown in (a), the root of the magnetic brush advances along with the surface of the developing sleeve 4, but the tip of the magnetic brush is attracted to the surface side of the photosensitive drum and tends to be behind the moving speed of the surface of the developing sleeve 4. Development is performed in such a state, and the latent image rear end portion X located on the upstream side in the moving direction of the photosensitive drum surface.
Immediately before exiting from the developing area, the magnetic brush is overcrowded on the surface of the trailing edge X of the latent image, as shown in FIG. 11B. This is because when the trailing edge portion X exits the developing area, the leading end of the magnetic brush does not move with a delay because the upstream side in the moving direction of the photoconductor surface is a non-latent image portion. In such a state, when the linear velocity ratio of the latent image carrier to the developing sleeve becomes high, the magnetic brush carrying new toner successively develops latent images as compared with the case where the linear velocity ratio of the latent image carrier is low. The agent pool is generated in the vicinity of the rear end portion X and in the vicinity thereof. The agent pool becomes more remarkable as the linear velocity ratio to the latent image carrier increases. In addition, the main magnetic pole P1b has a strong magnetic force
In the case of the configuration in which the auxiliary magnetic pole is provided close to the main magnetic pole P1b, the agent density in the vicinity of the trailing edge of the latent image is likely to be higher than in the other configurations, and the agent pooling is remarkable. As a result, a larger amount of toner adheres to the trailing edge portion X of the latent image than the other latent image portions, and the image density is developed higher than that of the other latent image portions. When such trailing edge toner shift occurs, the edges of photos, pictures, print images, etc. become darker,
The resulting image will look unnatural and not smooth.

Therefore, in order to improve the reproducibility of fine lines and prevent the trailing edge blanking phenomenon, both the image density reduction and the trailing edge toner deviation are prevented in a structure in which the magnetic force of the developing main pole is strong and the spikes are short. This is where it is required. As a result, a better image can be formed as compared with the conventional case, and the image quality can be improved.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus as described below. That is, it is an object of the present invention to provide an image forming apparatus capable of improving the reproducibility of thin lines and preventing the trailing edge blank area phenomenon, and at the same time, preventing both the image density reduction and the trailing edge toner shift.

[0017]

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. Comprising a developer carrier for carrying and carrying a two-component developer, wherein the developer carrier is a developing area facing the latent image carrier, and the developing magnetic pole is arranged so as to face the developing area. A magnetic brush is formed by magnetically adsorbing the developer on the surface of the agent carrier, and in the developing region, 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. A developing device that moves the surface of the developer carrying member and rubs the surface of the latent image carrying member with the magnetic brush to develop a latent image on the latent image carrying member; and a surface of the developer carrying member. And a developer regulation that regulates the amount of developer conveyed to the development area at a predetermined interval. And a member, developing magnetic pole by the attenuation factor of magnetic flux density in the normal line direction of the developer carrying member surface caused outer surface of the developer carrying member of the developing region 40
[%] Or more, in the image forming apparatus, wherein the magnetic flux density generated by the developing magnetic pole in the developing region has a magnetic flux density in the normal direction of the surface of the developer carrying member on the surface of the developer carrying member is 100 to 200 [mT]. The volume average particle diameter of the magnetic particles is 40
[μm] or more and 60 [μm] or less, and a plurality of grooves extending in a direction orthogonal to the surface moving direction are provided on the surface of the developer carrier, and the surface moving direction of the grooves on the surface of the developer carrier. The opening width is 0.1 [mm] or more and 0.2 [mm] or less, and the average depth of the grooves is 0.1 [mm] or more and 0.2 [m].
m] or less, the pitch of the grooves in the surface moving direction on the surface of the developer carrier is 0.4 [mm] or more and 0.6 [mm] or less, and the linear velocity of the developer carrier in the developing region. Is set to be not less than 1.5 times and not more than 2.5 times the linear velocity of the latent image carrier. Here, the above-mentioned "attenuation rate" means the value obtained by the following mathematical formula 1. However, the peak value of the magnetic flux density (normal direction magnetic flux density) in the normal line direction of the developer carrying member surface generated on the surface of the developer carrying member by the developing magnetic pole is X. In addition, the peak value of the magnetic flux density in the normal direction at a position 1 [mm] away from the surface of the developer carrying member in the normal direction is defined as Y.

## EQU1 ## Attenuation rate [%] = {(X−Y) / X} × 100 Further, the image forming apparatus according to claim 2 is a latent image carrier that carries an electrostatic latent image on its surface and moves the surface. A developer carrier that carries and conveys a two-component developer composed of toner and magnetic particles, and the developer carrier is arranged in a developing area facing the latent image carrier so as to face the developing area. The developing magnetic pole magnetically attracts the developer to the surface of the developer carrier to form a magnetic brush, and in the developing region, the same direction as the surface moving direction of the latent image carrier and the linear velocity of the surface of the latent image carrier. A developing device for moving the surface of the developer bearing member at a linear velocity higher than that, rubbing the surface of the latent image bearing member with the magnetic brush, and developing the latent image on the latent image bearing member; A developer standard that opposes the surface of the developer carrier at a predetermined distance and regulates the amount of the developer conveyed to the developing area. And a half value point on the surface of the developer carrying member, which has a magnetic flux density which is half of the maximum magnetic flux density in the normal direction of the surface generated by the developing magnetic pole on the surface of the developer carrying member. The angle width between the half-value points in the surface moving direction of the developer carrier as viewed from the center axis of curvature of the developer carrier in the region is 25 [°] or less,
In the image forming apparatus, wherein the magnetic flux density of the magnetic flux generated by the developing magnetic pole in the developing area is 100 to 200 [mT] in the normal direction on the surface of the developer carrying member on the surface of the developer carrying member. Average particle size of 40 [μm] or more 6
0 [μm] or less, a plurality of grooves extending in a direction orthogonal to the surface moving direction are provided on the surface of the developer carrying member, and the opening width of the grooves on the surface of the developer carrying member in the surface moving direction. Is 0.1 [mm] or more and 0.2 [mm] or less, the average depth of the grooves is 0.1 [mm] or more and 0.2 [mm] or less, and the groove on the surface of the developer carrier is The pitch in the surface moving direction is 0.4 [mm] or more and 0.6 [mm] or less, and the linear velocity of the developer carrier in the developing area is 1.5 times or more the linear velocity of the latent image carrier. It is characterized in that it is 2.5 times or less. The image forming apparatus according to claim 3 is the image forming apparatus according to claim 1.
Or the dynamic resistance value of the magnetic particles is 8.0 [logΩ] or more and 9.0 [l
is less than or equal to ogΩ]. An image forming apparatus according to a fourth aspect is the image forming apparatus according to the third aspect, wherein the magnetic particles are composed of a core material and a coating layer that coats the surface of the core material, and the material forming the coating layer is poly. Consisting of coating resin containing siloxane resin and conductive fine particles,
The weight content of the conductive fine particles to the coating resin is set to 0.
It is characterized in that it is set to 04 [weight%] or more and 0.25 [weight%] or less. An image forming apparatus according to a fifth aspect is the image forming apparatus according to the first, second, third, or fourth aspect, in which the current value of the magnetic particles is 25 [μm] or more and 50 [μm] or less. To do. According to a sixth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, or fifth aspect, the toner has a weight average particle diameter of 6 [μm].
As described above, it is characterized by being 8 [μm] or less. In the image forming apparatus according to any one of claims 1 and 2, among the developing parameters that affect the developer transport amount or the toner transport amount to the developing area, the groove size and groove pitch on the developer carrier, and the volume average of magnetic particles. The particle size is limited as described above. Here, the size of the groove is substantially determined by the opening width and the depth on the surface of the developer carrying member. When grooves are provided on the surface of the developer carrier, irregularities occur on the surface of the carrier. The size and groove pitch of the grooves on the developer carrier affect the amount of developer conveyed to the developing area. When a groove is provided on the surface of the developer carrying member, when the surface of the developer carrying member passes through a position facing the developer regulating member, the carrier which is the root of the magnetic brush is caught in the groove and passes through. Therefore, the magnetic brush is less likely to be peeled off from the surface of the developer carrying member even when subjected to the stress at the time of restriction by the developer restricting member, and is more likely to pass through the restricting position by the developer restricting member than when the groove is not provided. Therefore, even if the regulation gap is the same as the conventional one, it is possible to increase the amount of developer conveyed to the developing area. The amount of the developer that can be carried on the surface of the developer carrier changes depending on the size and pitch of the groove provided on the developer carrier, and the image density also changes accordingly. If the opening width and depth are appropriate for the size of the magnetic particles, the amount of developer conveyed to the developing area can be increased. However, if the opening width is too large or too small, or if the depth is too shallow, the developer transport amount cannot be increased to a desired amount. Further, since the groove is provided on the surface of the developer carrying member, a dense magnetic brush can be formed in the developing area as compared with the case where the groove is not provided. The magnetic brush density varies not only with the amount of developer transported, but also with the presence or absence of grooves on the surface of the developer carrier. In the present invention, since a dense magnetic brush can be formed in the developing area, it is possible to increase the image density without increasing the linear velocity ratio of the developer carrier to the photoconductor, as compared with the case where no groove is provided. Become. However, if the opening width of the groove is too large or too small, or if the depth is too shallow, it may be unsuitable or insufficient for increasing the magnetic brush density [lines / cm ² ] and the density in the developing area may be increased. Magnetic brush cannot be formed. On the other hand, if the depth is too deep, it is difficult to form the groove on the sleeve surface, and the cost is too high to form the groove. Therefore,
It is desired that these are grooves in an appropriate range. Also,
Even if the groove pitch on the developer carrier is narrowed, the amount of developer conveyed can be increased. However, if the groove pitch on the developer carrying member is too narrow, the amount of developer conveyed becomes too large, and the amount of developer contributing to the formation of the magnetic brush becomes too large. As described above, the developing device used in the image forming apparatus of the present invention makes the amount of the developer conveyed to the developing region smaller than the maximum amount of the developer that can stand up while passing through the developing region. It is set. However, if the amount of developer conveyed is too large and approaches or exceeds the maximum amount at which ears can stand, magnetic particles may adhere to the latent image carrier or toner may easily scatter. Become. This is because the magnetic particles forming the tip portion of the magnetic brush cannot be retained by the magnetic force. Further, even if the volume average particle diameter of the magnetic particles is reduced, the amount of toner conveyed to the developing area is increased, and even if the linear velocity ratio of the developer carrier to the latent image carrier is suppressed, a large amount of toner is contained in the latent image. It can be supplied to increase the image density. This is because the surface area of the magnetic particles per unit weight is large and the amount of toner that can be attached to the magnetic particles per unit weight is large. However,
If the volume average particle diameter of the magnetic particles is too small, it will be difficult to retain the magnetic particles on the surface of the developer carrying member. For this reason, carrier adhesion is likely to occur in the non-image portion of the latent image carrier. Also,
When the volume average particle diameter of the magnetic particles is made too large, the following problems have been confirmed in addition to the decrease in image density. The density of the magnetic brush in the developing area becomes low, and the reproducibility of fine lines in the image is deteriorated and the gradation is deteriorated. Therefore, in the image forming apparatus of claim 1, the size of the groove on the developer carrying member, the groove pitch, and the volume average particle diameter of the magnetic particles are set in a relatively balanced manner, so that The development capability can be improved without increasing the linear velocity ratio to the latent image carrier. Specifically, the volume average particle diameter of the magnetic particles is set to a relatively small particle diameter of 40 [μm] or more and 60 [μm] or less, and the respective parameters are set as follows. The opening width in the surface moving direction of the groove formed on the surface of the developer carrying member is set to 0.1 [mm] or more and 0.2 [mm] or less, and the average depth of the groove is 0.1.
[mm] or more and 0.2 [mm] or less. However, the depth of the groove is almost uniform. Further, the groove pitch of such a size is 0.4 [mm] on the developer carrier.
As described above, it is formed to be relatively narrow at 0.6 [mm] or less. The opening width in the moving direction of the surface of the developer carrier is set to 0.1.
[mm] or more and 0.2 [mm] or less, the average depth of the groove is set to 0.
When the volume average particle size is 1 [mm] or more, the volume average particle size is 40
A proper amount of the developer of not less than [μm] and not more than 60 [μm] is introduced into the groove. As a result, a desired developer transport amount is ensured in the developing area. Further, by setting the depth of the groove to 0.2 [mm] or less, it is possible to prevent the groove from being formed on the surface of the sleeve, which makes it difficult to form the groove too much. Further, such a groove is formed on the developer carrier with a groove pitch of 0.4.
By forming so as to be not less than [mm] and not more than 0.6 [mm], the amount of developer conveyed to the developing area is increased as compared with the conventional case. Moreover, by setting the lower limit of the groove pitch to 0.4 [mm], the developer transport amount is prevented from becoming too large. Further, since the volume average particle diameter of the magnetic particles is 40 [μm] or more and 60 [μm] or less, which is a relatively small particle diameter, the surface area per unit weight of the magnetic particles can be made relatively large. As a result, the linear velocity ratio of the developer carrying member to the latent image carrying member is 1.5 times or more and 2.5 times or more, which is lower than the upper limit of the conventional one.
Make sure that the image density does not decrease even if it is double or less. With the above-mentioned settings, it is possible to prevent the image density from decreasing while suppressing the linear velocity ratio of the developer carrier to the latent image carrier in the developing area to the extent that the trailing edge of the toner does not occur. Details of this will be described in the embodiment. According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the attenuation factor is set to 40.
Instead of defining it as [%] or more, the angular width between half-value points is defined as 25 [°] or less. The angle width between half-value points is 25
Even when it is set to [°] or less, as in the case where the attenuation rate is set to 40 [%] or more, a magnetic brush having a short length and a high density of the brush portion contacting the latent image carrier is formed. be able to. Therefore, similarly to the image forming apparatus according to the first aspect, it is possible to improve the developing capability and the image quality.

[0018]

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. ) Is applied to the embodiment. Figure 2
FIG. 1 is a schematic configuration diagram of an entire printer according to this embodiment. This printer has a photosensitive drum 1 as a latent image carrier. The surface of the photosensitive drum 1 is uniformly charged by a charging roller 50 as a charging unit that comes into contact with the photosensitive 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 charging unit and the latent image forming unit may be different from the charging roller 50 and the optical writing unit 51.
The electrostatic latent image formed on the photoconductor drum 1 is developed by the developing device 2 as a developing unit described later, and a toner image is formed on the photoconductor 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. After the transfer is completed, the toner image is fixed on the transfer paper 52 by a fixing unit 57 that performs oilless fixing as a fixing unit, and is discharged to the outside of the machine. The transfer residual toner remaining on the photosensitive drum 1 without being transferred is removed from the surface of the photosensitive drum 1 by a cleaning unit 58 as a cleaning unit. The residual charge on the photosensitive drum 1 is
It is removed by the static elimination lamp 59 as a static elimination means.

Next, the structure of the developing device 2 in this embodiment will be described. FIG. 1 is a schematic configuration diagram of a main device including a 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 includes a cylindrical developing sleeve 4 made of a non-magnetic material such as aluminum, brass, stainless steel, and conductive resin. Further, inside the developing sleeve 4,
A magnetic roller 5 is provided as a magnetic field forming means for forming a magnetic field for causing the developer to stand on the surface of the magnetic roller. 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, in the developing device 2, a doctor blade 6 is provided 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. The doctor blade 6 serves as a developer regulating member that regulates the amount of the developer attached on the developing sleeve 4. In this embodiment, the doctor gap is set to 0.48 [mm], but it may be in the range normally provided. Generally, 0.40
It is often set in the range of not less than [mm] and not more than 0.6 [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 the present embodiment, the photosensitive drum 1 having a diameter of 100 mm has a drum linear velocity of 3 in the developing area.
It is rotationally driven so as to be 30 [mm / sec]. Further, the developing sleeve 4 having a diameter of 25 [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 developing 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 for example, if the carrier particle size is 50 [μm], it is 0.6.
It was about 5 [mm] or more and 0.8 [mm] or less. 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.

FIG. 3A is a perspective view showing a part of the developing sleeve 4 in the developing device of this embodiment.
FIG. 3B is an enlarged view of the surface of the developing sleeve 4.
On the surface of the developing sleeve 4 used in the present embodiment, a plurality of grooves 4a extending in a direction orthogonal to the surface moving direction of the developing sleeve 4, that is, in the axial direction of the developing sleeve.
Is provided. The width of the groove 4a, which is the opening width in the sleeve surface movement direction, is formed to be approximately 0.2 mm. The width of the groove is not limited to 0.2 [mm] and may be 0.1 [mm] or more and 0.2 [mm] or less. The average depth of the grooves is 0.1 [mm].
Then, the internal angle of the V-shape is 90 °. The depth of this groove is 0.1 [mm] or more and 0.2 [m] on average.
m] or less. Further, the groove pitch is generally set to 0.7 [mm] or more and 1.0 [mm] or less, but in the present embodiment, it is set to 0.5 [mm]. The groove pitch is 0.4 [mm] or more and 0.6 [m
m] or less. There is no problem even if these grooves have a difference in width and depth with respect to each other. Thereby, the apparent surface area of the developing sleeve 4 can be increased,
The magnetic brush can be held tightly even if a larger amount of developer is transported to the developing area than in the conventional case. Further, by providing such a groove 4a, at the position regulated by the doctor blade 6, the root of the magnetic brush is caught in the groove on the surface of the developing sleeve and passes through. Even if the magnetic brush is subjected to the stress caused by the doctor blade 6 at the time of regulation, the magnetic brush does not easily come off from the surface of the developing sleeve 4. Therefore, the amount of the developer per unit area of the surface of the sleeve 4 that can pass through the regulation position is larger than that in the case where the groove is not provided. In the developing area, the magnetic brush is also carried on the inclined surface, which is a groove on the surface of the developing sleeve 4, so that the brush density is higher than in the conventional case.

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. Due to the magnetic field generated by the magnet roller 5 having such magnetic characteristics, the carrier in the developer stands on the developing sleeve 4 in a chain shape, and 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 ]. Further, according to the iron neodymium boron alloy bonded magnet, the maximum energy product of about 80 [kJ / m ³ ] can be obtained. Generally, the maximum energy product is 3
Ferrite magnets, ferrite bond magnets, etc. of around 6 [kJ / m ³ ] and around 20 [kJ / m ³ ] are used. However, if a rare earth metal alloy magnet is used as in this embodiment, a stronger magnetic force can be secured as compared with these.
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 the present embodiment, the three magnetic poles P1a and P1 that form the developing magnetic poles.
The magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by b and P1c is set to 100 [mT] or more and 200 [mT] or less.

The line indicated by the one-dot broken line in FIG.
m] shows the magnetic flux density in the normal direction at a position apart from each other. In the present embodiment, the attenuation rate of the magnetic flux density in the normal direction means the value obtained by the above mathematical expression 1. At this time, in Formula 1, “X” indicates the peak value of the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4, and “Y” indicates the developing sleeve 4.
Indicates the peak value of the magnetic flux density in the normal direction at a position 1 [mm] away from the surface of the. For example, the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is 100 [mT].
Then, when the magnetic flux density in the normal direction in the 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 mainly composed of a main magnetic pole P1b which functions to make the developer in the developing area stand up and two auxiliary magnetic poles P1a and P1c. These auxiliary magnetic poles have polarities opposite to the main magnetic pole P1b at positions adjacent to the main magnetic pole P1b on the upstream side and the downstream side in the surface movement direction of the developing sleeve 4. In the present embodiment, the main magnetic pole P1b, the magnetic poles P2, P3, P4, and P
6 is composed of N poles. The magnetic poles P2 and P3 form a magnetic field for carrying the developer in a region located downstream of the developing region in the surface moving direction of the developing sleeve 4. The magnetic pole P4 is
A magnetic field for drawing up the developer is formed on the developing sleeve 4. The magnetic pole P6 forms a magnetic field for transporting the developer drawn up onto the developing sleeve 4 to the developing area. Further, the auxiliary magnetic poles P1a and P1c and the magnetic pole P5 that conveys the developer drawn up onto the developing sleeve 4.
Is composed of the S pole. In the present embodiment, the main pole P1
As b, a magnet having a maximum magnetic flux density in the normal direction on the surface of the developing sleeve 4 of about 120 [mT] is used.

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, the angle width between the half-value points in the developing sleeve surface movement direction viewed from the central axis of the curvature of the surface of the developing sleeve 4 in the developing area, that is, the central axis of the developing sleeve 4 (hereinafter, referred to as “half-value angular width”). Used for narrowing. Here, the half-value angular width refers to the angular width in the surface movement direction of the developing sleeve 4 when the two half-value points on the surface of the developing sleeve 4 are viewed from the central axis of the developing sleeve 4. The two half-value points are two points on the surface of the developing sleeve 4 showing 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 developing sleeve 4 by the main magnetic pole P1c. Therefore, for example, the maximum value of the magnetic flux density in the normal direction is 120 [m
In the case of T], the half value angular width is the angular width when the half value point on the surface of the developing sleeve 4 where the magnetic flux density in the normal direction is 60 [mT], which is the half value, is viewed from the central axis of the developing sleeve 4. . In the present embodiment, 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.
The magnetic properties and arrangement of are set. In particular,
Three magnetic poles P1a, P1b, P1c constituting the developing magnetic pole
The width of the cross section of the magnet in the moving direction of the developing sleeve surface is set to 2 [mm]. As a result, the half-value angle width of the main pole P1b in this embodiment is 16 [°].

FIG. 6A is an explanatory view showing the half-value angle width in the case where the developing magnetic pole is composed of the three magnetic poles P1a, P1b and P1c as in the present embodiment, based on FIG. Further, FIG. 6B is an explanatory diagram showing the half-value angle width in the case where the developing magnetic pole is composed of one magnetic pole P1 as in the conventional case.
Comparing FIGS. 6A and 6B, the half-value angle width θ1 of the main magnetic pole P1b in the present embodiment shows that the auxiliary magnetic pole P1a,
Due to P1c, the half-value angle width θ′1 of the conventional single developing magnetic pole P1 becomes narrower. Here, it has been confirmed that when the half-value angle width of the main magnetic pole P1b exceeds 25 [°], an abnormal image such as a trailing edge whiteout occurs.

Further, in this embodiment, the auxiliary magnetic poles P1a,
The full width at half maximum of P1c is 35 [°] as shown in FIG.
It is set as follows. The positional relationship between the main magnetic pole P1b and the auxiliary magnetic poles P1a and P1c is such that the arrangement angle width between the main magnetic pole P1b and the auxiliary magnetic poles P1a and P1c is 30 [°] or less, as shown in FIG. Is set to. The arrangement angle width means the following points on the surface of the developing sleeve 4 in the surface moving direction of the developing sleeve 4 when 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. Is the angular width of. Each point means a main magnetic pole P1b and two auxiliary magnetic poles P1.
1a and P1c are points 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. In the present embodiment, as described above, the main magnetic pole P1
Since the half-value angle width of b is 16 [°], the main magnetic pole P1b
The arrangement angle width of each auxiliary magnetic pole P1a, P1c with respect to
[°].

Further, in this embodiment, the developing magnetic poles P1a,
Among the inflection points where the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by P1b and P1c is 0 [mT], the angular width between the following two inflection points is 120 [°] or less. Has been done. The two inflection points are two inflection points located on the most upstream side and the most downstream side in the surface moving direction of the developing sleeve 4. That is, as shown in FIG. 5, the angular 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 and 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 was 55.8 [mT] at a position 1 [mm] away from the surface of the developing sleeve 4 showing the highest value in the normal direction. Therefore, the amount of change in the magnetic flux density in the normal direction is 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 upstream of the main magnetic pole P1b in the developing sleeve surface movement direction was 100 [mT]. Further, the magnetic flux density in the normal direction was 53.3 [mT] at a position 1 [mm] away from the surface of the developing sleeve 4 showing the maximum value in the normal direction. Therefore, the amount of change in the magnetic flux density in the normal direction is 46.7 [mT]. 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 was 120 [mT]. Further, the magnetic flux density in the normal direction was 67.4 [mT] at a position 1 [mm] away from the surface of the developing sleeve 4 showing the highest value in the normal direction. Therefore, the amount of change in the magnetic flux density in the normal direction is 52.6 [mT]. Therefore,
The attenuation rate of the magnetic flux density in the normal direction by the auxiliary magnetic pole P1c in this embodiment is 43.8 [%]. Note that FIG.
In the conventional magnet roller 5 shown in (b), 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 was 90 [mT]. In addition, the maximum value is 1 outside the surface of the developing sleeve 4 in the normal direction.
The magnetic flux density in the normal direction at a position separated by [mm] is 63.9.
It was [mT]. Therefore, the change amount of the magnetic flux density in the normal direction is 26.1 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this case is 29.
It 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
It is set to be about 1 [mm]. 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 reason why the length of the magnetic brush can be shortened in this way is that the attenuation factor of the magnetic flux density in the normal direction is large as described above. More specifically, the developing sleeve 4
Although the magnetic flux density in the normal direction on the surface is high, the magnetic flux density in the normal direction at a position 1 [mm] away from the surface of the developing sleeve 4 sharply decreases because of the high attenuation rate. Therefore, the developer near the surface of the developing sleeve 4 is concentrated due to the action of the strong magnetic field, but the magnetic field is weak at a position relatively far from the surface of the developing sleeve 4, so that the developer cannot maintain the brush chain. As a result, the length of the magnetic brush is shortened.

From the above configuration, in the present embodiment,
The width of the developing sleeve surface moving direction in the developing area of the portion where the magnetic brush formed by the main magnetic pole P1b contacts the photosensitive drum 1 is relatively narrow. More specifically, this width is equal to or larger than the carrier particle size and is 2 [mm].
It becomes the following. As a result, as described above, it is possible to form an image in which there is no trailing edge whiteout and horizontal thin lines have good reproducibility.

Next, the carrier of the developer used in this embodiment will be described. Carrier volume average particle size is 40 [μ
In the range of m] or more and 60 [μm] or less, the brush density of the tip portion of the magnetic brush in contact with the photoconductor drum 1 was high, and it was found from the experiments described later that there were no particular side effects. Explaining this, the carrier particle size greatly depends on the particle size distribution of the magnetic particles, but when the volume average particle size is less than 40 [μm], the number of carriers having a small particle size increases. Since such a carrier having a small diameter is difficult to be held on the developing sleeve 4, there is a phenomenon called carrier adhesion that moves and adheres to the surface of the photosensitive drum 1 in the developing area. Therefore, as the number of small-diameter carriers increases, carrier adhesion to the photosensitive drum 1 easily occurs. On the contrary, the volume average particle diameter of the carrier is 60 [μ
m], it becomes difficult to increase the brush density of the tip portion of the magnetic brush that comes into contact with the photosensitive drum 1, resulting in grainy image quality, and the phenomenon near the trailing edge of the toner easily occurs.

The dynamic resistance value of the carrier is
It is an index of the developing ability of the developer containing the carrier, and it has been found that the smaller the value is, the better the developing ability is. In fact, it has already been confirmed that the dynamic resistance value of the carrier can more accurately indicate the developing ability than the resistance value of the carrier measured when the cell is filled with the carrier by tapping or the like. Further, when developing is performed under the developing conditions of the present embodiment in a developing device in which the length of the magnetic brush is short and the brush portion in contact with the photosensitive drum 1 has a high density, the dynamic resistance value of the carrier affects the developing ability. It became clear by the experiment described later. This is independent of the linear velocity ratio of the developing sleeve 4 to the linear velocity of the photosensitive drum 1 in the developing area. As the developing ability, there is a phenomenon that the trailing edge of the toner is shifted. Specifically, if the dynamic resistance value of the carrier is lowered too much to increase the developing ability, the photosensitive drum 1
Adhesion of the carrier to the upper latent image portion may occur to cause an abnormal image, or abrasion resistance of the carrier may be reduced to shorten the life of the developer. On the other hand, if the dynamic resistance value of the carrier is set too high, the developing ability will be insufficient and the trailing edge toner will be deviated. From the experimental example described later, the dynamic resistance value of the carrier is 8.0 [logΩ] or more,
It was found that the following effects can be obtained when the range is 9.0 [logΩ] or less. That is, it is possible to suppress the carrier adhesion to the photosensitive drum 1 and to suppress the occurrence of the toner near the trailing edge while ensuring a high developing ability. Therefore, in this embodiment, a carrier having a dynamic resistance value of 8.0 [logΩ] or more and 9.0 [logΩ] or less is used.

Further, in general, the developer is subjected to mechanical and thermal stress in the developing device, the carrier coating layer is abraded, or the carrier adheres to the toner coating layer to charge the toner over time. Problems such as deterioration of quality occur. In order to suppress these problems and obtain a dynamic resistance value in the above-mentioned range, it is desirable to use a siloxane resin as a coating resin for the carrier and to contain conductive fine particles in the carrier. At this time, it is important to contain the conductive fine particles in an optimum ratio with respect to the coating resin of the carrier. Specifically, the content ratio of the conductive fine particles to the coating resin of the carrier is 0.
It is preferably from 04 to 0.25. This is important when developing with the developing conditions of this embodiment using a developing device in which the length of the magnetic brush is short and the density of the brush portion in contact with the photosensitive drum 1 is high.

Further, in order to obtain the dynamic resistance value in the above-mentioned range and to obtain a desired developer charge amount, it is necessary to set the current value of the magnetic particles in an appropriate range. When a carrier having a current value that is too low is used, the dynamic resistance value of the carrier becomes high, and the charging of the coating layer cannot be maintained. In order to reduce the dynamic resistance value, the conductive fine particle content ratio must be made very high. However, if the content ratio of the conductive fine particles is too high, the liquidity of the coating material dispersion liquid during production is deteriorated, and it becomes difficult to obtain a uniform coating layer. Then, the wear resistance of the carrier is reduced and the carrier becomes brittle. On the other hand, when the magnetic particles having an excessively high current value are used, the carrier dynamic resistance becomes low even if the conductive particles are not contained. When the dynamic resistance is low, the charging of the coating layer easily leaks. Then, the level of the charge amount of the developer becomes low, and problems such as background stain and toner scattering occur. Therefore, it is preferable to use the magnetic particles having a current value in the range of 25 to 50 μA.

The remanent magnetization value of the carrier and the strength of the coercive force are
If it is too large, the developer inside the developing casing 7
Good transportability was hindered, and the gradation of the image deteriorated
And the toner from the trailing edge may be generated.
Confirmed in the experimental example. Furthermore, the conclusion of our research
As a result, blurring of images and uneven density in solid images occur.
It became easy to do it, and it was also found to be a factor that reduces the developing ability
did. In order to suppress such problems,
Has a residual magnetization value of 10 × 10^-7× 4π [Wb · m / kg]
Below, preferably 5 × 10^-7× 4π [Wb · m / kg]
Below, it is more preferable that it is substantially 0. Well
Also, the coercive force of the carrier is 40 × 10 ³/ 4π
[A / m] or less, preferably 30 × 10³/ 4π [A /
m] or less, more preferably 10 × 10³/ 4π [A /
m] or less is important. In addition, the cap here
The strength of the rear coercive force is 3000 × 10³/ 4π
[A / m] Uses the strength of coercive force when placed in a magnetic field
is doing. Considering the above carrier magnetic characteristics,
It is preferable to use ferrite as the core material of the carrier.
Good The average particle size of the carrier core material used in the present invention is the above
As described above, a conventionally known magnetic substance of 40 to 60 μm is used.
To be done. For example, ferromagnetic gold such as iron, cobalt, nickel
Alloys such as genus and magnetite, hematite, ferrite
Alternatively, compounds and the like can be mentioned.

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 the particle size is about 5.0 [μm] or less. 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 Methoxysilane, hexamethyldisilazane, γ
-Anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, γ-
Chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane (above, manufactured by Torre Silicon Co.), allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldi Examples thereof include ethoxysilane, 1.3-divinyltetramethyldisilazane, methacryloxyethyldimethyl (3-trimethoxysilylpropyl) ammonium chloride (above, manufactured by Chisso Corporation).

The method of coating the coating layer on the core material is not particularly limited, and for example, a dip coating method, a spray coating method, a fluidized spray coating method using a flow coater, etc. can be used. Further, after coating the coating layer on the core material, the coating film is cured and dried. However, by performing heating or heating and humidification, the curing / drying treatment can be promptly completed.

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 the present embodiment, it is preferable to select a toner particle size corresponding to the above-mentioned carrier particle size so that a sufficient amount of toner can be held in the magnetic brush. This is because if the particle size of the toner is larger than that of the carrier having the small particle size as described above, the effect of the carrier surface area is not sufficiently exerted, and the amount of toner in the magnetic brush becomes small. On the other hand, if the particle diameter of the toner is too small, the amount of charge that can be held by one toner becomes too small, and the toner tends to be scattered by the centrifugal force due to the rotation of the developing sleeve. Therefore, in this embodiment, in order to secure a sufficient developing ability, the weight average particle diameter of the toner is 6.0.
[Μm] or more and 8.0 [μm]. This also makes it possible to maintain fine line reproducibility. 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, for example, the number distribution,
The weight average particle diameter of the toner can be obtained by analyzing characteristics such as volume distribution. As the electrolytic solution used in the measurement with a 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.
The method for producing these resins is not particularly limited, and any of bulk polymerization, solution polymerization, emulsion polymerization and suspension polymerization can be used.

Inorganic fine particles can be preferably used as the external additive of the toner. 1 of these inorganic particles
The secondary particle diameter is preferably 0.005 [μm] or more and 2 [μm] or less, and particularly 0.005 [μm] or more,
It is preferably 0.5 [μm] or less. Also BE
The specific surface area by T method is 20 [m ² / g] or more, 500
It is preferably not more than [m ² / g]. The usage ratio of the inorganic fine particles is 0.01% by weight or more of the toner, and 5
It is preferably [wt%] or less, particularly 0.01
It is preferably not less than [wt%] and not more than 2.0 [wt%]. Specific examples of the inorganic fine particles include, for example, silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, Diatomaceous earth, chromium oxide, cerium oxide, pengal, antimony trioxide, magnesium oxide,
Examples thereof include zirconium oxide, parium sulfate, barium carbonate, calcium carbonate, silicon carbide and silicon nitride. Examples of other polymer-based fine particles include, for example,
Soap-free emulsion polymerization, suspension polymerization, polystyrene obtained by dispersion polymerization, methacrylic acid ester, acrylic acid ester copolymer, silicone, benzoguanamine,
Polymer particles made of a polycondensation system such as nylon or a thermosetting resin can be used.

Further, by surface-treating the toner with a surface-treating agent to increase the hydrophobicity, it is possible to prevent deterioration of the flow characteristics and the charging characteristics even under high humidity. Examples of the surface treatment agent include a silane coupling agent, a silylating agent, a silane coupling agent having a fluorinated alkyl group, an organic titanate coupling agent, and an aluminum coupling agent.

Further, the toner may contain a cleaning property improving agent for improving the removal performance when removing the transfer residual toner remaining on the photosensitive drum 1. Examples of the cleaning property improver include zinc stearate, calcium stearate, and fatty acid metal salts such as stearic acid. Furthermore, for example, polymer fine particles produced by soap-free emulsion polymerization of polymethylmethacrylate fine particles, polystyrene fine particles and the like can be mentioned. The polymer particles have a relatively narrow particle size distribution and a volume average particle size of 0.
It is preferably from 01 [μm] to 0.5 [μm].

If desired, the toner may contain a charge control agent. As this charge control agent,
All known materials can be used. For example, nigrosine dye, triphenylmethane dye, chromium-containing metal complex dye, molybdic acid chelate pigment, rhodamine dye, alkoxy amine, quaternary ammonium salt (including fluorine-modified quaternary ammonium salt), alkylamide, Examples include phosphorus alone or a compound, tungsten alone or a compound, a fluorine-based activator, a salicylic acid metal salt, and a salicylic acid derivative metal salt. Specifically, the Nigrosine type dye Bontron 03, the quaternary ammonium salt Bontron P-51, the metal-containing azo dye Bontron S-34, the oxynaphthoic acid metal complex E-82, and the salicylic acid metal complex E. -84, E-89 of phenol-based condensate (above, manufactured by Orient Chemical Industry Co., Ltd.), quaternary ammonium salt molybdenum complex TP-302, TP-415 (above,
(Hodogaya Chemical Co., Ltd.), quaternary ammonium salt copy charge PSY VP2038, triphenylmethane derivative copy blue PR, quaternary ammonium salt copy charge NEG VP2036, copy charge
NX VP434 (above, manufactured by Hoechst), LRA-9
01, a boron complex LR-147 (manufactured by Nippon Kalit Co., Ltd.), copper phthalocyanine, perylene, quinacridone,
Examples thereof include azo pigments and other polymer compounds having functional groups such as sulfonic acid groups, carboxyl groups and quaternary ammonium salts.

Further, as the colorant added to the toner, all of the pigments and dyes conventionally used as the colorant for toner can be applied. Specific examples thereof include carbon black, lamp black, iron black, ultramarine blue, nigrosine dye, aniline blue, chalco oil blue, oil black and azo oil black. The amount of the colorant used is 1 part by weight or more and 10 parts by weight or less, preferably 3 parts by weight or more and 7 parts by weight or less.

The method for producing the toner may be a conventionally known method. First, a binder resin, a wax component, a colorant, and in some cases, a charge control agent and the like are mixed using a mixer or the like, and a heat roll, Knead using a kneader such as an extruder. Then, it can be solidified by cooling, crushed by crushing with a jet mill or the like, and then classified to obtain. To add inorganic powderless powder to this toner, use a super mixer,
A mixer such as a Henschel mixer may be used.

By the way, in the so-called slick development method in which the auxiliary magnetic pole is arranged close to the developing magnetic pole similar to the developing device used in the printer of the present embodiment, and the developing nip is set narrow, the image density tends to be low. Therefore, conventionally, the following settings have been made for the purpose of maintaining a high image density. That is, the linear velocity of the developing sleeve 4 in the developing area is 1.1 times or more the linear velocity of the photosensitive drum 1 and 3.0.
It is set to be not more than twice, and practically not less than 1.5 times and not more than 3.0 times so that high image density can be maintained. However, as a result of increasing the linear velocity of the developing sleeve in this manner, the agent pool is generated in the vicinity of the rear end portion of the main pole, and the edge portion of the rear end portion of the latent image is developed darker than other image portions. The phenomenon that the trailing edge of the toner is shifted occurs.

FIGS. 10 (a) and 10 (b) show a halftone image at four levels of image densities of 30, 41, 50, and 59%, respectively. FIG. 10A is a diagram schematically showing a state “X” in which the trailing edge toner shift is generated, and FIG. 10B is a diagram showing a state “◯” in which the trailing edge toner shift state is hardly generated. is there. 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. In developing the image which is the basis of this schematic diagram, first, the toner T1 and the carrier C1 are mixed to a toner concentration of 5 w [%], and the charge amount is 23 [μ].
1 kg of the developer of c / g] was used for the printer of the present embodiment shown in FIGS. Further, as described above, in each setting, the maximum value of the magnetic flux density in the normal direction of the main magnetic pole P1b is 120 [mT], and the attenuation rate of the magnetic flux density in the normal direction is 53.5 [%]. The half-value angle width of 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 set to 25 [°]. The development gap is set to 0.5 [mm]. 50 formed using the above printer
In the halftone dot image of [%], the rotation direction is 15
In the image area of [mm], the image density of the central part is 1.0
Then, when the image density at the edge portion is high, the toner near the trailing edge is generated. Also, the image density is set to 30,4.
Development was performed in four stages of 1, 50, 59 [%]. From this figure, as shown in FIG. 10A, 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. 10B, 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.

Here, the present inventors have found a structure for preventing both the image density reduction and the trailing edge toner deviation. Below, an experimental example for demonstrating the effect of the printer of the present embodiment will be described.

[Experimental Example] An experimental example performed by using the laser printer described in the above embodiment will be described below. First, the formulation and manufacturing method of the toners T1 to T4 and the carriers C1 to 9 used in the following experimental examples will be described.

(Preparation of Toner T1) A mixture of the materials shown in Table 1 below was thoroughly stirred and mixed in a Henschel mixer. Then, the mixture was heated and melted for about 30 minutes by a roll mill at a temperature of 80 ° C., cooled to room temperature, and the obtained kneaded product was pulverized and classified by a jet mill pulverizer to have a particle size of 6.5.
A classified toner having a particle size of [μm] was produced. This classification toner 1
To 100 parts of silica particles, 1.0 part of silica fine particles and 0.4 parts of titania fine particles were added and mixed at 1500 [rpm] with a Henschel mixer to obtain a toner T1. The weight average particle diameter of the toner T1 was 6.7 [μm].

[Table 1]

(Preparation of Toner T2) A mixture of the materials shown in Table 1 above was thoroughly stirred and mixed in a Henschel mixer. Then, the mixture was heated and melted for about 30 minutes by a roll mill at a temperature of 80 [° C.], cooled to room temperature, and the obtained kneaded product was pulverized and classified by a jet mill pulverizer to have a particle size of 7.5.
A classified toner having a particle size of [μm] was produced. This classification toner 1
To 00 parts, 0.87 part of silica fine particles and 0.35 part of titania fine particles are 1500 [rpm] in a Henschel mixer.
Toner T2 was obtained by adding and mixing. The weight average particle diameter of the toner T2 was 7.7 [μm].

(Preparation of Toner T3) The mixture of the materials shown in Table 1 above was thoroughly stirred and mixed in a Henschel mixer. Then, the mixture was heated and melted at a temperature of 80 ° C. for about 30 minutes by a roll mill, cooled to room temperature, and the obtained kneaded product was pulverized and classified by a jet mill pulverizer to have a particle size of 9.0.
A classified toner having a particle size of [μm] was produced. This classification toner 1
To 00 parts, 0.72 parts of silica fine particles and 0.29 parts of titania fine particles are 1500 [rpm] in a Henschel mixer.
Toner T3 was obtained by adding and mixing. The weight average particle diameter of the toner T3 was 9.1 [μm].

(Preparation of Toner T4) A mixture of the materials shown in Table 1 above was thoroughly stirred and mixed in a Henschel mixer. Then, the mixture was heated and melted at a temperature of 80 ° C. for about 30 minutes by a roll mill, cooled to room temperature, and the obtained kneaded product was pulverized and classified by a jet mill pulverizer to have a particle size of 5.5.
A classified toner having a particle size of [μm] was produced. This classification toner 1
To 00 parts, 1.18 parts of silica fine particles and 0.47 parts of titania fine particles are 1500 [rpm] in a Henschel mixer.
Addition and mixing were performed to obtain Toner T4. The weight average particle diameter of the toner T4 was 5.6 [μm].

(Preparation of Carrier C1) The formulations shown in Table 2 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid is applied to 100 by a spray air pressure of 0.4 [MPa] by a fluidized bed type coating device.
It was applied to the surface of 0 part of ferrite to form a coating layer on the surface of the ferrite. Then, the carrier C1 was produced by firing in an electric furnace at a temperature of 300 [° C.] for 2 hours. This ferrite has a volume average particle diameter of 55 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 30 [μA] 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 volume average particle diameter of this carrier C1 was 56 [μm], and its dynamic resistance value was 8.5 [logΩ].

[Table 2]

(Production of Carrier C2) The formulations shown in Table 2 above 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. After that, firing was performed for 2 hours in an electric furnace at a temperature of 300 [° C.] to produce a carrier C2. This ferrite has a volume average particle size of 45 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k].
g] and a current value of 30 [μA] was used. The volume average particle diameter of the carrier C2 is 47 [μ
m] and its dynamic resistance value is 8.5 [log
Ω].

(Production of Carrier C3) The formulations shown in Table 2 above 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. After that, firing was performed in an electric furnace at a temperature of 300 [° C.] for 2 hours to produce carrier C3. This ferrite has a volume average particle diameter of 60 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 30 [μA] was used. The volume average particle size of the carrier C3 is 60 [μ
m], and the dynamic resistance value is 8.6 [log
Ω].

(Production of Carrier C4) The formulations shown in Table 2 above 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. Then, the carrier C4 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has a volume average particle size of 35 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 30 [μA] was used. The volume average particle size of the carrier C4 is 37 [μ
m] and its dynamic resistance value is 8.4 [log
Ω].

(Production of Carrier C5) The formulations shown in Table 2 above were dispersed for 20 minutes with a homomixer 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. After that, firing was performed in an electric furnace at a temperature of 300 [° C.] for 2 hours to prepare carrier C5. This ferrite has a volume average particle diameter of 75 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 30 [μA] was used. The volume average particle diameter of the carrier C5 is 56 [μ
m] and its dynamic resistance value is 8.5 [log
Ω].

(Preparation of Carrier C6) The formulations shown in Table 3 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid is applied to 100 by a spray air pressure of 0.4 [MPa] by a fluidized bed type coating device.
It was applied to the surface of 0 part of ferrite to form a coating layer on the surface of the ferrite. Then, the carrier C6 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has a volume average particle diameter of 55 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 20 [μA] was used. The volume average particle diameter of the carrier C6 is 55 [μ
m] and its dynamic resistance value is 9.3 [log
Ω].

[Table 3]

(Preparation of Carrier C7) The formulations shown in Table 4 below were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid is applied to 100 by a spray air pressure of 0.4 [MPa] by a fluidized bed type coating device.
It was applied to the surface of 0 part of ferrite to form a coating layer on the surface of the ferrite. Then, the carrier C7 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has a volume average particle diameter of 55 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 60 [μA] was used. The volume average particle size of the carrier C7 is 57 [μ
m], and the dynamic resistance value is 7.7 [log
Ω].

[Table 4]

(Production of Carrier C8) The formulations shown in Table 5 below were dispersed by 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. Then, the carrier C8 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has a volume average particle diameter of 55 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 25 [μA] was used. The volume average particle diameter of the carrier C8 is 57 [μ
m] and its dynamic resistance value is 9.0 [log
Ω].

[Table 5]

(Preparation of Carrier C9) 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
Was applied to the surface of the ferrite in part to form a coating layer on the surface of the ferrite. Then, the carrier C9 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has a volume average particle diameter of 55 [μm] and a saturation magnetization value of 65 × 10 ⁻⁷ × 4π [Wb · m / k
g] and a current value of 50 [μA] was used. The volume average particle diameter of the carrier C9 is 57 [μ
m], and the dynamic resistance value is 8.2 [log
Ω].

[Table 6]

(Measurement method) Regarding the weight average particle diameter of the toner, in an electrolyte solution of 100 [ml] or more and 150 [ml] or less, 0.1 [ml] or more and 5 [ml] or less of a surfactant ( Alkylbenzene sulfonate), and the measurement sample is added thereto. Addition amount of measurement sample is 2 [m
g] or more and 20 [mg] or less. Then, the electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for 1 to 3 minutes by an ultrasonic disperser, and a Coulter Counter II type (manufactured by Coulter, Inc.) with an aperture of 100 [μm] is used to measure the volume by 2 to 2. The particle size distribution and the like of 40 [μm] was measured. The weight average particle diameter of the toner was obtained from this measurement result. Regarding the particle size distribution of the carrier, SRA type of Microtrac particle size analyzer (Nikkiso Co., Ltd.) was used and 0.7 [μ
m] and 125 [μm] or less were used. Regarding the carrier magnetic property, a BHU-60 type magnetization measuring device (manufactured by Riken measurement) was used as a measuring device. Then, the weighed carrier of about 1.0 [g] is packed in a cell having an inner diameter of 7 mmφ and a height of 10 [mm], set in the above measuring device, and the applied magnetic field is gradually increased to a maximum of 3000.
It was increased to × 10 ³ / 4π [A / m], and then the applied magnetic field was decreased. The hysteresis curve thus obtained was finally recorded on a recording paper, and the saturation magnetization value of the carrier, the residual magnetization of the carrier, and the coercive force of the carrier were obtained based on the recording results. 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 0 to 200 [V].
The current value at that time was detected by the ammeter 70. Based on the detection result, a graph was created in which the vertical axis represents voltage and the horizontal axis represents current value, 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 current value of the carrier was obtained by measuring the current value flowing from the surface of the conductive sleeve 61 to the ground when the applied voltage was 2000 [V] using a dynamic resistance value measuring device.

(Experimental Results) The toners T1 to T4 prepared as described above and one of the carriers C1 to C9 are combined, and 95 parts of the carrier is added to 5 parts of the toner to obtain a toner concentration of 5 [w%. ] Mixed in. This was heated at 46 [rpm] for 10 [minutes] with a Turbula mixer to obtain each developer. The developing device 2 used in this experimental example is the one described in the above-mentioned embodiment, the maximum value of the magnetic flux density in the normal direction of the main magnetic pole P1b is 120 [mT], and the attenuation rate of the magnetic flux density in the normal direction is Is 53.5 [%]. The half-value angle width of the main magnetic pole P1b is 16 [°]. Using these developers, Ricoh Co., Ltd. copy machine imagioMF
Development was carried out using a 7070 modified machine, and five points were evaluated: image density, background stain, image gradation, toner near the trailing edge, and carrier adhesion. For background stain and image density, 5000
The image density was evaluated at the initial stage of printing [sheets / day] and after printing 100,000 sheets. Evaluation of background dirt, gradation, and carrier adhesion is ranked by degree,
“O” was taken as a passing level, “Δ” was taken as an acceptable level, and “x” was taken as an unacceptable level. The image density is described as a numerical value, but if the density is 1.3 or more, the pass level is "○", if it is less than 1.3 and 1.25 or more, the acceptance level is "△", and if it is less than 1.25, the acceptance level is "x". Become. The evaluation of the toner near the rear edge is 50
Rotation direction 15 [mm] in halftone dot halftone image
In the image part of No. 3, the image density was divided into three ranks and evaluated based on the difference between the image density at the center and the image density at the edges. A density difference of 0.10 or less is “◯”, a density difference of more than 0.10 and less than 0.20 is “Δ”, and a density difference of 0.20 or more is “x”. The image density is a measurement result with a Macbeth densitometer RD914 in a range of 5φ. 10 (a) and 10 (b) show halftone images in four levels of image density of 30, 41, 50, 59 [%], respectively.
It is shown in. FIG. 10A is a diagram schematically showing a state X in which the trailing edge toner is shifted, and FIG. 10B is a state ◯ in which there is almost no trailing edge toner bias. This is a schematic representation of the state where the toner near the trailing edge is generated and the state where it is not generated so that the difference can be seen.

Table 7 shows Experimental Examples 1 to 17 using each developer.
Shows the characteristics of the developer. As the developer characteristics, the volume average particle diameter of the carrier [μm], the dynamic resistance [LogΩ], the ratio of conductive fine particles in the coating resin forming the carrier, the carrier current value [μA], and the toner weight average particle diameter [μm] are used. Indicated.

[Table 7]

The experimental results for each developer are shown in Table 8 below.

[Table 8]

As shown in Table 8 above, the pitch of the grooves formed on the surface of the No. 12 developing sleeve was 0.7.
When it was 5 [mm], the gradation became the unacceptable level “x”. Image density when printing 100,000 sheets is 1.21
It became an unacceptable level "x". Even when the pitch of the grooves of No. 11 is 0.75 [mm], the gradation is unacceptable level "x", and the image density when printing 100,000 sheets is 1.29, which is a relatively low value. there were. On the other hand, N
When the groove pitches of o and 18 were 0.35 [mm], which was relatively narrow, the image density when printing 100,000 sheets was 1.40, which was a pass level “◯”. However, the adhesion of the carrier was at an unacceptable level "x", the toner near the trailing edge was also at an unacceptable level "x", and scumming occurred and the unacceptable level was "x" at the time of printing 100,000 sheets. When the developer containing No. 15 and C5 having a carrier volume average particle diameter of 75 [μm] is used, the gradation is unacceptable level “×” and the image density is 1.27 when 100,000 sheets are printed. , Acceptable level "△"
However, it was a relatively low value. When the developer containing No. 14 and C4 having a carrier volume average particle diameter of 37 [μm] was used, carrier adhesion occurred and the level was unacceptable.

Incidentally, Whether carrier is attached to the photosensitive drum changes depending on the centrifugal force generated on the surface of the developing sleeve. In the present embodiment, as described above, the developing sleeve 4 having a diameter of 25 [mm] has a sleeve linear velocity in the developing area of 660 [mm / sec], that is, the rotation speed is 5
The drive is controlled at 04 [rpm]. At this time, if the centrifugal force is generated on the sleeve surface, carrier adhesion does not occur.

From the results of the above experimental example, in order to prevent the image density from being lowered and also to prevent the trailing edge toner from being shifted, the groove size, the groove pitch on the sleeve surface, and the volume average particle diameter of the carrier are as follows. It turns out that it can be achieved by setting the setting range. First, regarding the groove, the width is 0.1 [mm] or more and 0.2 [mm] or less, the average depth is 0.1 [mm] or more, and the groove pitch is 0.4 [mm] or more, It is to be 0.6 [mm] or less. Furthermore, the carrier volume average particle diameter is 40 [μm] or more and 60 [μm] or less. If the depth of the groove is deeper than 0.2 [mm], it is difficult to form the groove on the surface of the sleeve, and the cost for forming the groove is too high, which is not preferable. In Table 8 as well, in Nos. 1 to 10, 16 and 17 which satisfy all of these conditions, the image densities are all at the allowable level “Δ” or more, and the toner near the trailing edge is also the allowable level “Δ” or more. ing.

Considering this result, when the groove size is set in the above range, the groove pitch and the volume average particle diameter of the carrier influence the toner supply amount to the latent image,
This affects the image density. If the groove pitch on the developing sleeve is narrowed or the volume average particle diameter of the carrier is reduced, the toner supply amount increases. This is because the density of the magnetic brush on the surface of the developing sleeve can be increased by narrowing the groove pitch on the developing sleeve. Further, when the volume average particle size of the carrier is reduced, the surface area per unit weight of the carrier is increased,
This is because the toner adhesion amount per unit weight is increased and the toner supply amount can be increased. For these reasons, in this embodiment, the image density could be increased even if the linear velocity ratio of the developing sleeve to the photosensitive drum to the latent image carrier was suppressed to 2.5 times or less. Therefore, the linear velocity ratio of the developing sleeve to the latent image carrier relative to the photosensitive drum need not be larger than 2.5 times as in the conventional setting.
It is possible to prevent the occurrence of the toner near the trailing edge as compared with the case of making it larger than 2.5 times.

Further, further, in the above range, the adhesion of the carrier to the photosensitive drum was not less than the permissible level. Considering this result, the carrier particle size greatly depends on the particle size distribution of the magnetic particles, but when the volume average particle size is less than 40 [μm], the number of carriers having a small particle size increases. Since such a small-diameter carrier is difficult to be held on the developing sleeve 4, it is considered that the carrier adheres to the photosensitive drum 1. here,
Whether carrier is attached to the photosensitive drum changes depending on the centrifugal force generated on the surface of the developing sleeve. As in this embodiment, the developing sleeve 4 having a diameter of 25 [mm]
The sleeve linear velocity in the developing area is 660 [mm /
If the centrifugal force is the same as in the case of drive control in seconds, the volume average particle diameter is 40 [μm] and carrier adhesion does not occur. In order to more surely prevent the carrier adhesion to the non-image portion of the photoconductor drum which is caused by making the volume average particle diameter of the carrier too small, it is necessary to limit the range of the developing sleeve shape and the surface linear velocity. Good. In addition, Table 8 above
The volume average particle size of the carrier is 40
It has been found that when the thickness is less than [μm], toner scattering also occurs. In order to prevent this toner scattering, it is effective to set the volume average particle diameter of the carrier to 40 [μm] or more.

Further, as shown in Table 8 above, No. 16
When the developer containing the carrier C6 having a dynamic resistance value of 9.3 [logΩ] was used, the carrier adhesion to the surface of the photoconductor drum 1 became an unacceptable level “x”. Further, the image density was 1.33 at the initial stage and 1.24 at the time of printing 100,000 sheets, which was a relatively low value. Furthermore, the toner near the trailing edge is “Δ”. On the other hand, No. 17 carrier C7 having a dynamic resistance value of 7.7 [logΩ]
When a developer containing is used, the background stain when printing 100,000 sheets is “x”. According to the research conducted by the present inventors, the dynamic resistance value of the carrier is 8.0 [log
Ω] or more and 9.0 [logΩ] or less,
It was confirmed that the following effects could be obtained. That is, it is possible to suppress the carrier adhesion to the photosensitive drum 1, the background stain and the like, and also to solve the shortage of the image density to improve the image quality, and sufficiently suppress the occurrence of the toner near the trailing edge.

Further, as shown in No. 16 in Table 8 above, even if the material forming the coating layer of the carrier contains a polysiloxane resin, when the carrier C6 is used, the resin resin dynamic resistance value is 9. It became 3 [logΩ]. The carrier 6 has a weight content ratio of the conductive fine particles to the coating resin of 0.02 [w%]. At this time, the level of carrier adhesion was “x”, and the levels of the toner near the trailing edge and the gradation were both “Δ”. Also, No,
When the carrier C7 in which the weight content ratio of the conductive fine particles of 17 to the coating resin was 0.30 [w%] was used, the resin resin dynamic resistance value was 7.7 [log Ω]. At this time, the adhesion of the carrier to the surface of the photoconductor drum 1 became the unacceptable level "x", and the background stain at the time of printing 100,000 sheets became the unacceptable level "x". According to the research conducted by the present inventors, the weight content ratio of the conductive fine particles to the coating resin is 0.04 [w%] or more, 0.2
It was confirmed that the dynamic resistance value of the carrier can be set within a desired range within the range of 5 [w%] or less. In the printer of this embodiment, the desired range of the dynamic resistance value is 8.0 [lo] as described above.
It is not less than gΩ] and not more than 9.0 [logΩ].

In general, the developer is subjected to mechanical and thermal stress in the developing device and the carrier coating layer is abraded, or the carrier adheres to the toner coating layer to charge the toner over time. Problems such as deterioration of quality occur. Then, in order to suppress deterioration of developer durability due to wear of the carrier and spent, it is desirable to use a siloxane resin as a coating resin for the carrier. The carriers C1 to C9 used in the experimental examples all contain a silicone resin as a polysiloxane resin. Further, as proved by the experimental example, in order to obtain the dynamic resistance value in the above-mentioned range, it is important to contain the conductive fine particles in an optimum ratio with respect to the carrier coating resin.

In addition, No. 14 and No. 16 in Table 8 above
As shown in, when the carrier current value is 20 [μA],
The rank of carrier adhesion to the non-image area on the photoconductor surface is "x".
Became. If the ratio of the conductive fine particles is small like No. 16 among these, the dynamic resistance is 9.3 [lo].
gΩ] and it becomes high. On the other hand, No, 15 and No,
As shown in 17, when the carrier current value is 60 [μA], the following problems occur. In No. 17 and No. 17, when the conductive particles were contained, the dynamic resistance was lowered too much and the background stain was generated, and the rank became "x", and the carrier adhesion to the surface of the photosensitive drum also occurred "x". Became. And by the research of the present inventors,
It was confirmed that the following effects can be obtained when the carrier current value is 25 [μA] or more and 50 [μA] or less.
That is, the dynamic resistance is set in a desired range, that is, 8.0.
It is possible to set the range in the range from [logΩ] to 9.0 [logΩ]. In addition, the occurrence of carrier adhesion can be suppressed and the durability of the carrier can be improved. Therefore, in the printer of this embodiment,
A carrier having a current value of 25 [μA] or more and 50 [μA] or less is used.

Further, No. 10, No. 13 in Table 8 above
As shown in, when the developer containing the toner T4 having the toner weight average particle diameter of 5.6 [μm] was used, the background stain level was “Δ”. Specifically, in No. 10, “Δ” was obtained both at the initial stage and at the time of printing 100,000 sheets, and in No. 13 it was “◯” at the initial stage, but became “Δ” at the time of printing 100,000 sheets. Further, as shown in Nos. 9, 9, and 12, when the developer containing the toner T3 having the toner weight average particle diameter of 9.1 [μm] is used, the gradation of the image is “Δ”. there were. According to the research conducted by the present inventors, the toner has a weight average particle diameter of 6.0 [μm] or more and 8.0 [μm] or more.
It was confirmed that an image having no background stain and an excellent image gradation can be obtained as long as it is below. Further, it has been confirmed that if the weight average particle diameter of the toner is 8.0 [μm] or less, the fine line reproducibility of the image becomes good.

As described above, according to the present embodiment, the developing sleeve 4 as a developer carrying member carrying the developer containing the toner and the carrier as the magnetic particles on the surface and moving the surface, and the electrostatic latent image on the surface. A main magnetic pole P1 as a developing magnetic pole arranged in a developing area facing a photosensitive drum 1 as a latent image carrier that carries and moves its surface in opposition to the developing area.
b and the auxiliary magnetic poles P1a and P1c make the developer on the developing sleeve 4 stand up to form a magnetic brush, and the developing sleeve 4 is in the developing region in the same direction as the surface moving direction of the photosensitive drum 1 and on the surface of the photosensitive drum. Of the main magnetic pole P1b and the auxiliary magnetic pole P1a, the surface of the photosensitive drum 1 is rubbed by the magnetic brush to develop the latent image on the photosensitive drum 1, P1c
The magnetic flux density on the surface of the developing sleeve 4 in the developing area is 40% or more in the direction of the developing sleeve surface normal, and the magnetic flux generated by the developing magnetic pole in the developing area develops on the surface of the developing sleeve. The magnetic flux density in the normal direction of the sleeve surface is 100 to 200 [mT], and the volume average particle diameter of the carrier is 40 [μm] or more, 6
0 [μm] or less, the developing sleeve has a plurality of grooves on its surface extending in a direction orthogonal to the surface moving direction of the developing sleeve, and the opening width of the grooves in the surface moving direction on the surface of the developing sleeve. Is 0.1 [mm] or more and 0.2 [mm]
Below, the average depth of the groove is 0.1 [mm] or more and 0.2 [m
m] or less, a plurality of groove pitches is 0.4 [mm] or more and 0.6
[Mm] or less and the linear velocity of the developing sleeve in the developing region is 1.5 times or more and 2.5 times or less than the linear velocity of the photoconductor drum. It is possible to improve the developing ability and the image quality by preventing the toner from being shifted toward the trailing edge. Further, in this embodiment, the main magnetic pole P1b and the auxiliary magnetic poles P1a and P1c.
When the half-value point on the surface of the developing sleeve in which the magnetic flux density is half the maximum magnetic flux density in the direction normal to the surface of the developing sleeve 4 due to Since the angular width between the half-value points (half-value angular width) in the surface movement direction of the developing sleeve 4 is 25 [°] or less, the attenuation factor is 40.
As in the case of [%] or more, the length of the magnetic brush is short, and the density of the brush portion in contact with the latent image carrier becomes high, so that the trailing edge whiteout phenomenon and the deterioration of fine line reproducibility are suppressed. Can be planned. Further, the magnetic flux density of the magnetic flux generated by the developing magnetic poles in the developing region in the direction normal to the surface of the developing sleeve on the surface of the developing sleeve is 100 to 200 [mT]. Has a plurality of grooves extending in a direction orthogonal to each other,
The plurality of groove pitches is 0.4 [mm] or more and 0.6 [mm] or less, and the opening width of the grooves on the surface of the developing sleeve in the surface moving direction is 0.1 [mm] or more and 0.2 [mm]. ] Or less, and the average groove depth is 0.1 [mm] or more and 0.2 [m
m] or less and the volume average particle diameter of the carrier is 40
The linear velocity of the developing sleeve in the developing area is not less than 1 [μm] and not more than 60 [μm].
Since it is 5 times or more and 2.5 times or less, it is possible to prevent both a decrease in image density and a shift toward the trailing edge toner, as confirmed in the above experimental example. Further, in the present embodiment, since the dynamic resistance value of the carrier is 8.0 [logΩ] or more and 9.0 [logΩ] or less, the following effects can be obtained as confirmed in the above experimental example. That is, since the dynamic resistance value is not lowered too much, it is possible to suppress the carrier adhesion to the photoconductor drum 1 to improve the image quality and prevent the background stain. Also, the dynamic resistance value is not raised too much. As a result, it is possible to prevent the linear velocity ratio of the developing sleeve to the latent image carrier from being raised too much, it is possible to sufficiently suppress the occurrence of the toner near the trailing edge, and it is also effective in eliminating the insufficient image density. Further, in the present embodiment, a polysiloxane resin is used as the material for forming the carrier coating layer, and the weight content of the conductive fine particles to the coating resin is 0.04 [wt%] or more and 0.25 or more.
[Weight%] or less. As a result, as confirmed in the above experimental examples and the like, it is possible to suppress the deterioration of the developer durability due to the wear of the carrier and the spent, and to make the dynamic resistance value of the carrier within a desired range, thereby improving the image quality. it can. Further, in the present embodiment, the carrier current value is set to 25 [μA] or more and 50 [μA] or less, so that the following effects can be obtained as confirmed in the above experimental examples and the like. That is, it becomes possible to set the dynamic resistance value in the range of 8.0 [logΩ] or more and 9.0 [logΩ] or less, and it is possible to suppress the occurrence of carrier adhesion and also to improve the durability of the carrier. become. Further, in this embodiment, the weight average particle diameter of the toner is 6.0 [μ
Since it is set to m] or more and 8.0 [μm] or less, the following effects can be obtained as confirmed in the above experimental examples. That is, it is possible to prevent the background stain that occurs when the weight average particle diameter of the toner is too small. In addition to this, it is possible to prevent deterioration of fine line reproducibility and image gradation which occur due to too large a toner weight average particle diameter, and it is possible to obtain a high quality image.

[0082]

According to the image forming apparatus of the first and second aspects, it is possible to prevent the image density from decreasing without increasing the linear velocity ratio of the developer bearing member to the latent image bearing member too much. by this,
It is possible to improve the fine line reproducibility and prevent the trailing edge blank area phenomenon, and at the same time, prevent both the image density reduction and the trailing edge toner shift.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram around a photosensitive drum of a printer according to a first embodiment.

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

FIG. 3A is a perspective view showing a part of a developing sleeve of a developing device used in the printer. (B) is an enlarged view of the surface of the developing sleeve.

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 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 a magnetic brush made of a developer that is erected by receiving a magnetic force from a magnetic field formed by a developing magnetic pole when viewed from the axial direction of the developing sleeve in the developing device.

FIG. 9A 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 and two auxiliary magnetic poles. FIG. 3B is an explanatory view showing the shape of a magnetic brush made of a developer that is erected by receiving a magnetic force from a magnetic field formed by a developing magnetic pole when viewed from the axial direction of the developing sleeve in the developing device.

FIG. 10A is a halftone image showing the state X in which the trailing edge of the toner is deviated, at four levels of image density. (B) is a halftone image at four image densities showing a state ◯ in which the toner near the trailing edge is almost absent.

FIGS. 11A and 11B are views showing a mechanism of occurrence of toner near the trailing edge.

[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

Front page continued (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 9/10 361 (72) Inventor Yuji Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72 ) Inventor Zhu Bai 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Inventor Akihiro Ito 1F term at Shinmeidou, Nakameisei, Shibata-cho, Shibata-gun, Miyagi 2H005 BA06 BA07 CA12 CB18 DA09 EA01 EA05 2H031 AB02 AC10 AC15 AC18 AC19 AC20 AC30 AD03 AD05 BA08 BA09 2H077 AB02 AC02 AC12 AD02 AD06 AD13 BA07 EA03 EA16 FA01

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. In a developing area where the carrier is opposed to the latent image carrier, a magnetic brush is formed by magnetically adsorbing the developer on the surface of the developer carrier by a developing magnetic pole arranged so as to be opposed to the developing area. Then, the surface of the developer carrier is moved 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 the magnetic brush moves the surface of the latent image carrier. A developing device that develops a latent image on the latent image carrier by rubbing the surface thereof and a surface of the developer carrier are opposed to each other at a predetermined distance to regulate the amount of the developer conveyed to the developing area. A developer regulating member, and the developing magnetic poles are provided outside the surface of the developer carrier in the developing area. The attenuation rate of the magnetic flux density in the direction normal to the surface of the developer carrying body is 40% or more, and the magnetic flux generated by the developing magnetic pole in the developing area is more than that of the surface of the developer carrying body on the surface of the developer carrying body. Normal direction magnetic flux density is 1
In an image forming apparatus having a diameter of 100 to 200 [mT], the volume average particle diameter of the magnetic particles is 40 [μm] or more and 60 [μm] or more.
m] or less, a plurality of grooves extending in a direction orthogonal to the surface moving direction are provided on the surface of the developer carrying member, and the opening width of the grooves on the surface of the developer carrying member in the surface moving direction is 0. 1 [mm] or more and 0.2 [mm] or less, the average depth of the groove is 0.1 [mm] or more and 0.2 [mm] or less, and the surface movement of the groove on the surface of the developer carrying member. 1. The pitch in the direction is 0.4 [mm] or more and 0.6 [mm] or less, and the linear velocity of the developer bearing member in the developing area is 1.5 times or more the linear velocity of the latent image bearing member. An image forming apparatus characterized by being 5 times or less. 2. 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 composed of toner and magnetic particles. In a developing area where the carrier is opposed to the latent image carrier, a magnetic developer is magnetically adsorbed to the surface of the developer carrier by a developing magnetic pole arranged so as to be opposed to the developing area to form a magnetic brush. Then, the surface of the developer carrying member is moved at the same linear velocity as the surface moving direction of the latent image bearing member and at a linear velocity higher than the linear velocity of the surface of the latent image bearing member, and the magnetic brush moves the surface of the latent image bearing member. A developing device that rubs the surface to develop the latent image on the latent image carrier and a surface of the developer carrier are opposed to each other at a predetermined distance to regulate the amount of the developer conveyed to the developing area. A developer regulating member, which is formed on the surface of the developer carrier by the developing magnetic pole. The half point on half of the developer carrying member surface as the magnetic flux density of up to magnetic flux density in the linear direction,
The angle width between the half-value points in the surface moving direction of the developer carrier as viewed from the center axis of curvature of the surface of the developer carrier in the developing region is 25 [°] or less, The magnetic flux density of the generated magnetic flux on the surface of the developer carrying member in the direction normal to the surface of the developer carrying member is 100 to 20.
In the image forming apparatus of 0 [mT], the volume average particle diameter of the magnetic particles is 40 [μm] or more and 60 [μm] or more.
m] or less, a plurality of grooves extending in a direction orthogonal to the surface moving direction are provided on the surface of the developer carrying member, and the opening width of the grooves on the surface of the developer carrying member in the surface moving direction is 0. 1 [mm] or more and 0.2 [mm] or less, the average depth of the groove is 0.1 [mm] or more and 0.2 [mm] or less, and the surface movement of the groove on the surface of the developer carrying member. 1. The pitch in the direction is 0.4 [mm] or more and 0.6 [mm] or less, and the linear velocity of the developer bearing member in the developing area is 1.5 times or more the linear velocity of the latent image bearing member. An image forming apparatus characterized by being 5 times or less. 3. The image forming apparatus according to claim 1, wherein the magnetic particles have a dynamic resistance value of 8.0 [log].
Ω] or more and 9.0 [log Ω] or less. 4. The image forming apparatus according to claim 3, wherein the magnetic particles are composed of a core material and a coating layer coating the surface of the core material, and the material forming the coating layer contains a polysiloxane resin. It is composed of a coating resin and conductive fine particles, and the weight content ratio of the conductive fine particles to the coating resin is 0.04.
An image forming apparatus characterized by being set to [weight%] or more and 0.25 [weight%] or less. 5. The image forming apparatus according to claim 1, 2, 3, or 4, wherein the magnetic particles have a current value of 25 [μm] or more and 50 [μm] or more.
m] or less. 6. The image forming apparatus according to claim 1, 2, 3, 4, or 5, wherein the toner has a weight average particle diameter of 6 [μm] or more and 8 [μm] or more.
m] or less.