JP2003223051A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the adhesion of a carrier to a latent image carrier and to obtain a high image density while improving the reproducibility of a thin line and restraining a rear end void phenomenon in an image forming apparatus (a high-speed machine) whose image forming speed is high. <P>SOLUTION: A magnetic brush is formed by napping developer on a developing sleeve 4 by a main magnetic pole being an N pole and two auxiliary magnetic poles being S poles arranged to be opposed to a developing area where the sleeve 4 and a photoreceptor drum 1 are mutually opposed in the developing area, and it rubs to develop an electrostatic latent image on the drum 1. In the developing device, the length of the magnetic brush is short and the density of the edge part of the magnetic brush coming into contact with the latent image carrier is made high, so that the rear end void phenomenon is restrained but the linear velocity of the sleeve 4 must be made high with reference to that of the drum 1 in order to maintain the high image density. Therefore, the carrier easily adheres to the drum 1, but the adhesion of the carrier is restrained by using the carrier whose saturation magnetization value is within a specified range. <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 a developing device used in an image forming apparatus such as a copying machine, a printer and a fax machine, and an image forming apparatus equipped with the developing device. More specifically, the present invention relates to a developing device and an image forming apparatus for developing a latent image on a latent image bearing member by causing a developer to stand on the surface of the developer bearing member in a developing area where the latent image bearing member and the developer bearing member face each other. It is a thing.

[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 developing area, the developer on the developing sleeve stands up along the magnetic lines of 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 distance between the latent image carrier and the developing sleeve is in the developing area, the higher the image density is likely to be and the less the edge effect is. Therefore, it is desirable that the latent image carrier and the developing sleeve be close to each other. However, if this distance is made close, a phenomenon called so-called "rear edge whiteout" occurs, in which the trailing edge of a black solid image or a halftone solid image becomes white, or the fine line reproducibility deteriorates. However, the problem that the image quality is deteriorated occurs.

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. That is, the magnetic brush that slides the trailing edge of the latent image after moving into the developing area by moving the surface of the latent image carrier is a non-latent image located on the upstream side in the moving direction of the surface of the latent image carrier. It is the one facing the part.
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 progresses as the period of time facing the non-latent image portion increases. 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 applicant of the present invention, in order to suppress trailing edge white spots and deterioration of fine line reproducibility, JP-A-2000-305360, JP-A-2000-347506, and JP-A-2001.
In Japanese Patent Laid-Open No. 5296, there is proposed an invention capable of improving the image quality of the above-mentioned 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 is
Setting of developing nip and magnetic brush density
No. 27849), a half-value angle width of the main magnetic pole (also referred to as a half-value central angle) is set (Japanese Patent Laid-Open No. 2001-134100), and other inventions are proposed to realize image quality improvement. 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. 2000-30536
The developing efficiency can be improved and the trailing edge white spot phenomenon and the fine line reproducibility can be improved by the devices described in JP-A No. 0, JP-A 2000-347506, and JP-A 2001-5296 for the following reasons. It is considered to be a thing. Figure 7
FIG. 6A is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing area in a conventional developing device in which the developing magnetic pole is one magnetic pole P1. Further, FIG. 7B is an explanatory view showing the shape of the magnetic brush made of the developer that is erected by receiving the magnetic force from the magnetic field formed by the developing magnetic pole P1 when viewed from the axial direction of the developing sleeve 4. is there. In FIG. 8A, the developing magnetic pole is 1
FIG. 6 is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing area in a developing device including one main magnetic pole P1b and two auxiliary magnetic poles P1a and P1c. Further, FIG. 8B shows these magnetic poles P1.
FIG. 6 is an explanatory diagram 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, P1b, and P1c when viewed in the axial direction of the developing sleeve 4.

In the conventional developing device, the S-pole magnetic pole adjacent to the N-pole developing magnetic pole is used to convey the developer in a region located downstream of the developing region in the surface moving direction of the developing sleeve 4. There is a magnetic pole P2 that forms a magnetic field. 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 at positions relatively distant from the developing magnetic pole P1, the magnetic field distribution of the magnetic field in the developing region is such that the magnetic force lines emitted from the developing magnetic pole P1 are as shown in FIG. 7A. 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. 7B.

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. 7 (a) and 7 (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. Therefore, as shown in FIG. 8A, the magnetic force distribution of the magnetic field in the developing region is such that the magnetic line of force from the main magnetic pole P1b is larger than that of the magnetic pole from the main developing pole of the conventional developing device shown in FIG. 7A. 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. 7 (b) 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 the conventional developing device. Therefore, in the developing device of the above publication, most of the developer constituting the magnetic brush is attracted to the vicinity of the surface of the developing sleeve 4 having a high magnetic flux density, and as shown in FIG. It is shorter than that of the developing device.

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

In the developing device of the above-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. 8B, 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. From the above, even when the sliding width Pn is narrower than that of the conventional developing device, the linear velocity ratio of the developing sleeve 4 to the linear velocity of the photosensitive drum 1 in the developing area is increased to supply the electrostatic latent image. It is possible to secure a sufficient amount of toner.

[0013]

However, in order to increase the linear velocity ratio, there are a method of decreasing the linear velocity of the photosensitive drum 1 and a method of increasing the linear velocity of the developing sleeve 4.
Since the former method reduces the image forming speed, the latter method is generally adopted. However, if the linear velocity of the developing sleeve 4 is increased in this way, the centrifugal force acting on the developer adhering to the developing sleeve increases. for that reason,
The carrier constituting the magnetic brush is easily released from the magnetic brush due to an impact when the magnetic brush made of the developer comes into contact with the photosensitive drum 1. A phenomenon called carrier adhesion occurs in which the released carrier adheres to the photosensitive drum 1. When this phenomenon occurs,
The adhered carrier adhered on the photosensitive drum 1 disturbs the image or causes missing dots in the image. As a result, not only the problem that the image quality is deteriorated but also the problem that the components arranged around the photosensitive drum 1 are damaged may occur. Further, the linear velocity of the photosensitive drum 1 in the developing area is 300 [mm /
An image forming apparatus (high speed machine), which has a high image forming speed set to a value of not less than 2 seconds and not more than 600 [mm / second], is now widespread. In such an image forming apparatus, the linear velocity of the developing sleeve 4 becomes higher, and the centrifugal force acting on the developer adhering to the developing sleeve becomes higher. Therefore,
In such a high-speed machine, the above-mentioned problems are likely to occur.

Further, as a result of the research conducted by the present inventors, in the conventional developing device, the carrier at the tip of the magnetic brush in the developing area receives the electrostatic force from the photosensitive drum 1 and is attracted to the surface of the photosensitive drum. It turned out that the phenomenon that occurs occurs.
More specifically, in the conventional developing device, the magnetic brush is rubbed (relatively moved) on the surface of the photosensitive drum 1 to move the magnetic brush at a constant speed relative to the surface of the photosensitive drum 1. It was trying to increase the amount of toner supplied to the electrostatic latent image. In the developing area at this time, the developing sleeve side portion of the magnetic brush that is not in contact with the surface of the photosensitive drum 1 is relatively moved with respect to the surface of the photosensitive drum. However, the tip portion of the magnetic brush that comes into contact with 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, there is a problem that the effect of increasing the amount of toner supplied to the electrostatic latent image by rubbing (relatively moving) the magnetic brush on the surface of the photosensitive drum 1 is small. Such a problem can occur even when the developing device of the above publication is used, in which the length of the magnetic brush described above is short and the density of the brush portion in contact with the photosensitive drum 1 is high. Therefore, in the developing device of the above publication, even when the linear velocity ratio of the developing sleeve 4 to the linear velocity of the photosensitive drum 1 in the developing region is increased to maintain the image density similar to the conventional one, the phenomenon described above causes The effect is small.

The present invention has been made in view of the above problems, and an object thereof is to obtain a linear velocity of the latent image carrier in the developing area of 300 [mm / sec] or more and 600 [mm / sec] or more.
[Second] or less, in an image forming apparatus (high speed machine) having a high image forming speed, it is possible to suppress the adhesion of carriers to the latent image carrier while improving the fine line reproducibility and suppressing the trailing edge blank area It is possible to provide a developing device and an image forming apparatus capable of achieving high image density.

[0016]

[Means for Solving the Problems] To achieve the above object
According to the invention of claim 1, a developer containing toner and magnetic particles.
On the surface of the developer carrier that moves on the surface and the electrostatic latent
The image is held on the surface and the latent image carrier moving on the surface faces
In the developing area, the current
The image magnetic pole causes the developer on the developer carrier to stand up.
A magnetic brush is formed on the developer carrying member to carry the developer.
The same direction as the surface moving direction of the latent image carrier in the developing area.
And the surface transfer at a linear velocity higher than the linear velocity on the surface of the latent image carrier.
The surface of the latent image carrier with the magnetic brush.
In a developing device for rubbing to develop the latent image on the latent image carrier
The linear velocity of the developer carrying member in the developing area is
500 [mm / sec] or more and 1200 [mm / sec] or less
Is carried by the above developer carrier and conveyed to the developing area.
The amount of developer is 65 [mg / cm²] More than 95 [mg
/ Cm²] And the above-mentioned development area is
Of the magnetic flux generated on the outside of the surface of the developer carrier
Attenuation rate of magnetic flux density in the body surface normal direction is 40%
The above is caused by the developing magnetic pole in the developing area.
The developer carrier on the surface of the developer carrier of the magnetic flux
Magnetic flux density in the normal direction of the surface is 100 [mT] or more 200
[MT] or less, and the saturation magnetization value of the magnetic particles is 6
0x10 ^-7× 4π [Wb · m / kg] or more 90 × 10^-7
It is characterized by being less than × 4π [Wb · m / kg]
It is a thing. Here, the above-mentioned "attenuation rate" refers to the developing magnetic pole.
Therefore, the developer carrier surface generated on the developer carrier surface
Of the magnetic flux density in the normal direction of
The peak value as X, and from the surface of the developer carrier in the normal direction
Peak value of magnetic flux density in the normal direction at a position 1 mm away
Where Y is the value obtained by the following formula 1.
It

## EQU1 ## Attenuation rate [%] = {(X−Y) / X} × 100 Further, according to the invention of claim 2, a developer carrying toner and magnetic particles is carried on the surface and carried on the surface. The developer on the developer carrying member is provided by a developing magnetic pole arranged so as to oppose the developing region in the developing region where the body and the latent image carrying member carrying the electrostatic latent image on the surface and moving on the surface face each other. To form a magnetic brush on the developer carrying member, and the developer carrying member is in the developing region in the same direction as the surface moving direction of the latent image carrying member and at the linear velocity of the latent image carrying member surface. In the developing device for developing the latent image on the latent image carrier by moving the surface at a linear velocity higher than that of the developer and rubbing the surface of the latent image carrier with the magnetic brush. The linear velocity of the carrier is 500 [mm / sec] or more and 1200 [mm / sec] or less, The amount of the developer carried on the body is transported to the developing area, 65 [mg / cm ^2] or more 95
[Mg / cm ² ] or less, and the surface of the developer carrying body has a magnetic flux density which is half of the maximum magnetic flux density in the normal direction of the surface of the developer carrying body generated on the surface of the developer carrying body by the developing magnetic pole. When the upper half value point is viewed from the center axis of curvature of the surface of the developer carrying member in the developing area, the angular width between the half value points in the surface moving direction of the developer carrying member is 25.
[°] or less, and the magnetic flux density of the magnetic flux generated by the developing magnetic pole in the developing area on the surface of the developer carrying member in the normal direction of the developer carrying member is 100 [mT] or more 2
It is not more than 00 [mT] and the saturation magnetization value of the magnetic particles is not less than 60 × 10 ⁻⁷ × 4π [Wb · m / kg] and not less than 90 ×
It is characterized by being 10 ⁻⁷ × 4π [Wb · m / kg] or less. The invention of claim 3 is the same as claim 1
Alternatively, in the developing device of No. 2, the static resistance value of the magnetic particles is 12 [logΩ] or more and 14 [logΩ] or less. According to a fourth aspect of the present invention, in the developing device according to the first, second or third aspect, the fluidity of the magnetic particles is 20 [sec / 50 g] or more and 40 [sec / 5.
0 g] or less. Also,
According to a fifth aspect of the present invention, in the developing device according to the fourth aspect, the toner has a charge amount of 10 [μC / g] or more and 40 [μC / g] or more.
g] or less. According to a sixth aspect of the present invention, a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, a latent image on the latent image carrier is developed with toner and magnetic particles. An image forming apparatus comprising a developing means for developing with a developer and a transfer means for transferring a toner image on the latent image carrier onto a transfer material, wherein the latent image carrier and the developer provided on the developing means. The linear velocity of the latent image carrier in the developing area facing the carrier is 3
00 [mm / sec] or more and 600 [mm / sec] or less,
As the developing means, the developing device according to claim 1, 2, 3, 4 or 5 is used. In the developing device of the first aspect, the attenuation rate of the magnetic flux density in the normal direction outside the developer carrier in the developing area is 40% or more. In order to increase the attenuation rate in this way, for example, as in the developing device of the above publication, one main pole composed of an N pole and an S pole arranged in proximity to both sides of the main pole in the developing sleeve surface movement direction. A developing magnetic pole composed of two auxiliary magnetic poles is used. The polarities of the main magnetic pole and the auxiliary magnetic pole may be opposite to each other, and the developing magnetic pole may be the S pole and the auxiliary magnetic pole may be the N pole. In addition to increasing the attenuation rate in this way, the amount of developer conveyed to the developing area (developer supply amount) is higher than the maximum amount of developer that can stand up while passing through the developing area. Reduce. Specifically, 65 [mg / cm ² ] or more and 95 [mg
/ Cm ² ]. As a result, as described above, the length of the magnetic brush can be shortened and the density of the brush portion contacting the latent image carrier can be increased. Here, among the image forming apparatuses that are currently widespread, there are many high-speed machines in which the linear velocity of the latent image carrier is set to 300 [mm / sec] or more and 600 [mm / sec] or less. In such an image forming apparatus, when 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 latent image carrier is high as described above, the development with respect to the latent image carrier linear velocity in the developing area is performed. It is necessary to increase the linear velocity of the agent carrier. This is to maintain high image density. In particular,
It is necessary to set the linear velocity of the developer bearing member substantially to about 1.5 to 2.0 times the linear velocity of the latent image bearing member. mm / sec] or more 12
It is necessary to increase the speed to about 00 [mm / sec] or less. However, when the linear velocity of the developer bearing member is high in this way, as described above, the centrifugal force acting on the developer attached to the developer bearing member increases, and a phenomenon called carrier attachment to the latent image bearing member occurs. Occurs. In particular, in the developing device having the high attenuation rate as in the developing device of the present invention, the force of restraining the magnetic particles (carriers) by the magnetic force at the tip portion of the magnetic brush is relatively weak.
Therefore, the carrier at the tip of the magnetic brush is easily attached to the latent image carrier, and the carrier is likely to be attached. As a result of repeated research, the present inventors have determined that the magnetic flux density of the magnetic flux generated by the developing magnetic pole in the developing region on the surface of the developer carrying member in the normal direction of the developer carrying member is 100 [mT] or more.
When the magnetic particle (carrier) constituting the developer has a saturation magnetization value of 60 × 10 ⁻⁷ × 4π [Wb ·
It was confirmed that the phenomenon of carrier adhesion can be suppressed by setting m / kg] or more (60 [emu / g] or more). The details will be described in Experimental Example 1 described later. If a carrier having a saturation magnetization value in such a range is used, the magnetic flux density in the normal direction is 100 [mT] or more and 200 [mT] or less and the attenuation rate is 40 [%].
In the developing area having a magnetic field as described above, the carrier restraining force at the tip of the magnetic brush can be made sufficiently larger than the force acting on the carrier toward the latent image carrier. That is,
According to the developing device of the present invention, the developer carrier acting on the carrier at the tip of the magnetic brush is more than the combined force such as the centrifugal force applied by the surface movement of the developer carrier and the electrostatic force received from the surface of the latent image carrier. The binding force by the magnetic force to the body side can be increased. Therefore, the number of carriers attached to the latent image carrier can be reduced. Here, when the saturation magnetization value of the magnetic particles is less than 60 × 10 ⁻⁷ × 4π [Wb · m / kg],
In the developing device of the present invention which performs the developing in the developing region where the magnetic field is formed, the restraining force of the carrier by the magnetic force becomes insufficient. Therefore, carrier adhesion to the latent image carrier cannot be sufficiently suppressed. Moreover, the saturation magnetization value of the magnetic particles is 90 × 10 ⁻⁷ × 4π [Wb · m / kg] (90
Beyond [emu / g]), the result is that the carrier restraining force in the developing region where the above-mentioned magnetic field is formed is too strong. Therefore, the magnetic brush composed of the toner and the carrier on the developer carrying member has a tightly erected state, which deteriorates the gradation and halftone reproducibility of the image. From the above, in the developing device according to claim 1, the above-mentioned magnetic field is formed in the developing area, and the saturation magnetization value is 60 × 10 ⁻⁷ × 4π.
[Wb · m / kg] or more 90 × 10 ⁻⁷ × 4π [Wb · m
/ Kg] or less. As a result, it is possible to suppress the carrier adhesion to the latent image carrier. It is preferable to use ferrite as the core material of the carrier that can suitably obtain such a saturation magnetization value. Further, conventionally, as described above, the brush portion contacting the surface of the latent image carrier in the developing area is attracted to the surface of the latent image carrier, and the electrostatic latent image on the latent image carrier is rubbed by the magnetic brush. The effect of increasing the amount of toner supplied to the image was small. On the other hand, according to the developing device of the present invention, since the carrier constituting the tip portion of the magnetic brush has a high binding force as described above, the brush portion contacting the surface of the latent image carrier has a latent image carrier surface. The rubbing operation can be performed firmly against.
Therefore, the effect of increasing the amount of toner supplied to the electrostatic latent image on the latent image carrier by rubbing the magnetic brush can be enhanced. Further, in the developing device of claim 2, the attenuation rate is set to 4
Instead of setting it to 0% or more, set the angular width between half-value points to 25
It is different from the constitution of the developing device of the above-mentioned claim 1 in that it is set to [°] or less. Even when the angular width between the half-value points is 25 [°] or less, the length of the magnetic brush that is short and contacts the latent image carrier is similar to the case where the attenuation rate is 40 [%] or more. It is possible to form a magnetic brush having a high density at the tip portion. Therefore, as in the developing device according to the first aspect, it is possible to suppress the carrier adhesion to the latent image carrier and increase the toner supply amount to the electrostatic latent image on the latent image carrier. The image forming apparatus according to claim 6 is
The linear velocity of the latent image carrier in the developing area is 300 [mm /
The image forming speed is set to be higher than 600 seconds and lower than 600 [mm / second]. Since the image forming apparatus according to claim 6 is equipped with the developing device according to any one of claims 1 to 5, the carrier adhesion to the latent image carrier can be suppressed and the electrostatic latent image on the latent image carrier can be suppressed. The toner supply amount can be increased.

[0017]

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. The transfer paper 52 after the completion of transfer is fixed by a fixing unit 57 as a fixing unit.
Then, the toner image is fixed and discharged outside the apparatus. In addition,
The transfer residual toner remaining on the photosensitive drum 1 without being transferred is a cleaning unit 5 as a cleaning unit.
8 removes it from the surface of the photosensitive drum 1. Also,
The residual charge on the photoconductor drum 1 is removed by a charge eliminating lamp 59 as a charge eliminating means.

Next, the structure of the developing device 2 in this embodiment will be described. FIG. 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, the developing device 2 regulates the amount of the developer adhering to the developing sleeve 4 on the upstream side in the surface moving direction of the developing sleeve 4 with respect to the developing area where the developing sleeve 4 and the photosensitive drum 1 face each other. A doctor blade 6 as a developer regulating member is provided. The doctor gap, which is the distance between the doctor blade 6 and the developing sleeve 4, affects the amount of developer supplied to the developing area. Although the doctor gap is set to 0.48 [mm] in the present embodiment, it may be set within the range of 0.35 [mm] or more and 0.5 [mm] or less. 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 to 30 [mm / sec], and the developing sleeve 4 having a diameter of 25 [mm] is rotationally driven so that the sleeve linear velocity in the developing region is 660 [mm / sec]. There is. That is, in this embodiment, the linear velocity ratio of the sleeve linear velocity to the drum linear velocity is set to 2.0. The developing gap in this embodiment is 0.5.
It is set to [mm]. The conventional developing gap is generally set to about 10 times the carrier particle size, and for example, if the carrier particle size is 50 [μm], 0.65 [m
It was about m] or more and 0.8 [mm] or less. On the other hand, in this embodiment, the magnetic force of the main pole is larger than that of the conventional one,
It is also possible to set about 30 times the carrier particle size. 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.

Next, the magnetic field formed by the magnetic roller 5 will be described. FIG. 3 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 be 100 [mT] or more and 200 [mT] or less.

The line indicated by the one-dot broken line in FIG. 4 is 1 [m from the surface of the developing sleeve 4 in the normal direction thereof.
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. 4 is an explanatory diagram showing the arrangement of the three magnetic poles P1a, P1b, P1c that are the 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 region stand up, and two auxiliary magnetic poles P1a having a polarity opposite to that of the main magnetic pole P1b.
It is composed of P1c. Two auxiliary magnetic poles P1a and P1c
Are arranged adjacent to the main pole P1b on the upstream side and the downstream side in the surface movement direction of the developing sleeve 4. In this embodiment, the main magnetic pole P1b and the magnetic pole P that forms a magnetic field for drawing up the developer on the developing sleeve 4.
4, a magnetic pole P6 that forms a magnetic field for transporting the developer drawn up onto the developing sleeve 4 to the developing area, and
A magnetic pole P that forms a magnetic field for transporting the developer in a region located downstream of the developing region in the surface moving direction of the developing sleeve 4.
2 and P3 are constituted by N poles. The auxiliary magnetic poles P1a and P1c and the magnetic pole P5 that conveys the developer drawn onto the developing sleeve 4 are S poles. In this embodiment, as the main magnetic pole P1b, the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is about 120.
A magnet of [mT] is used. And the main pole P1
If the auxiliary magnetic pole P1c and the main magnetic pole P1b located on the downstream side of the developing sleeve surface movement direction of b have a magnetic flux density in the normal direction of 100 [mT] or more, by using a carrier having a saturation magnetization value described later. It has been confirmed that no abnormal image such as carrier adhered on the photosensitive drum 1 is generated. Such carrier adhesion is more likely to occur as the tangential magnetic force on the surface of the developing sleeve 4 in the developing area is smaller. Therefore, it is important to increase the magnetic force in the tangential direction, but if one of the main magnetic pole P1b and the auxiliary magnetic pole P1c is made sufficiently large, the occurrence of carrier adhesion can be sufficiently suppressed.

Further, the above-mentioned two auxiliary magnetic poles P1a, P1
1c is used to adjust the distribution of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 by the main magnetic pole P1c. Specifically, 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 width at half maximum indicates the magnetic flux density that is half the maximum value of the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by the main magnetic pole P1c. 4 refers to the angular width in the surface movement direction of the developing sleeve 4 when viewed from the central axis of 4. Therefore, for example, 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], and as a result, the half-value angle width of the main magnetic pole P1b is 16 [°] in this embodiment.

FIG. 5A is an explanatory view showing the half-value angular 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. FIG. 5B is an explanatory diagram showing the half-value angular width in the case where the developing magnetic pole is composed of one magnetic pole P1 as in the conventional case. Figure 5
Comparing (a) and (b), the half-value angular width θ1 of the main magnetic pole P1b in the present embodiment shows that the auxiliary magnetic poles P1a and P1.
c, the half-value angle width θ ′ of the conventional single developing magnetic pole P1
It is narrower than 1. Here, it has been confirmed that 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 the present 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 angular 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 indicates 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 P1b and the two auxiliary magnetic poles P1a and P1c.
The respective angular widths in the surface movement direction of the developing sleeve 4 when the respective points on the surface are 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. In the present embodiment, as described above, the main magnetic pole P
Since the half-value angle width of 1b is 16 [°], the main magnetic pole P1
The arrangement angle width of each auxiliary magnetic pole P1a, P1c with respect to b is 2
It is set to 5 [°].

Further, in this embodiment, the developing magnetic poles P1a,
Of the inflection points at which the magnetic flux density in the normal direction generated on the surface of the developing sleeve 4 by P1b and P1c is 0 [mT], the two inflection points located on the most upstream side and the most downstream side in the surface moving direction of the developing sleeve 4. The angle width between them is 120 [°] or less. That is, as shown in FIG.
Two auxiliary magnetic poles P1a and P1c and each auxiliary magnetic pole P1a and P1
The angle width between the inflection points existing between the magnetic poles P2 and P6 adjacent to 1c is 120 [°] or less.

In the above structure, the magnetic characteristics of the developing magnetic poles P1a, P1b, P1c in this embodiment were observed as shown below. Developing sleeve 4 of main pole P1b
The maximum value of the magnetic flux density in the normal direction on the surface of is 120
[MT], and the magnetic flux density in the normal direction 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 was 64.2 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this embodiment is 53.5 [%].
Further, the maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the auxiliary magnetic pole P1a located upstream of the main magnetic pole P1b in the developing sleeve surface movement direction is 100 [mT], and the developing sleeve showing the maximum value is shown. The magnetic flux density in the normal direction at a position 1 [mm] away from the surface of No. 4 in the normal direction was 53.3 [mT]. Therefore, the amount of change in the magnetic flux density in the normal direction was 46.7 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this embodiment is 46.7 [%]. The maximum value of the magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the auxiliary magnetic pole P1c located on the downstream side of the main magnetic pole P1b in the developing sleeve surface movement direction is 120 [mT], and the developing sleeve showing the maximum value is shown. 1 from the surface of 4 to the outside in the normal direction
The magnetic flux density in the normal direction at a position separated by [mm] is 67.4.
It was [mT]. Therefore, the amount of change in the magnetic flux density in the normal direction was 52.6 [mT]. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this embodiment is 43.8 [%]. In the conventional magnet roller 5 shown in FIG. 5B, for example, the maximum magnetic flux density in the normal direction on the surface of the developing sleeve 4 of the developing magnetic pole P1 is 90 [mT]. The magnetic flux density in the normal direction was 63.9 [mT] at a position 1 [mm] away from the surface of the developing sleeve 4 in the normal direction. Therefore, the change amount of the magnetic flux density in the normal direction is 26.1 [mT].
Met. Therefore, the attenuation rate of the magnetic flux density in the normal direction by the main magnetic pole P1b in this case is 29 [%].

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. The reason is that the magnetic flux density in the normal direction on the surface of the developing sleeve 4 is high, but the attenuation factor 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. For this reason, 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. is there. Further, in this embodiment, the doctor gap is appropriately adjusted so that the amount of the developer carried on the developing sleeve 4 and conveyed to the developing area (the developer supply amount) is 65.
It is set so as to be as small as [mg / cm ² ] or more and 95 [mg / cm ² ] or less. As a result, a magnetic brush which is originally longer can be formed, but the magnetic brush is restricted to be short due to the insufficient developer supply amount. Then, as a result of such a short regulation, the developing gap is set to 0.5 [mm], so that the photosensitive drum 1 is made to have a brush portion made of a developer concentrated near the surface of the developing sleeve 4 having a high magnetic flux density. The surface of can be rubbed.
In the present embodiment, the developing gap is set to 0.5 [mm], but it may be in the range of 0.3 [mm] or more and 0.5 [mm] or less. Within this range, the surface of the photosensitive drum 1 can be rubbed with the brush portion made of the developer densely gathered near the surface of the developing sleeve 4 having a high magnetic flux density.

From the above configuration, in the present embodiment,
The width of the developing area in the moving direction of the developing sleeve surface of the portion where the magnetic brush formed by the main magnetic pole P1b contacts the photosensitive drum 1 is not less than the carrier particle diameter and not more than 2 [mm], which is relatively narrow. . As a result, as described above, it is possible to form an image with high reproducibility of a thin image such as a horizontal thin line or a small dot without a trailing edge blank.

Next, the developer carrier used in this embodiment will be described. A known magnetic material can be used as the core material of the carrier. Examples of the magnetic material include ferromagnetic metals such as iron, cobalt and nickel, alloys and compounds such as magnetite, hematite and ferrite. Here, it has been confirmed by experimental examples and the like described later that the magnetic characteristics of the carrier influence the influence of the magnetic field from the magnetic roller 5 on the carrier and greatly affect the developing characteristics and the transportability of the developer. In this embodiment, the saturation magnetization value is 60 × 10 ⁻⁷ × 4π [W for the purpose of suppressing carrier adhesion and increasing image density.
b · m / kg] or more 90 × 10 ⁻⁷ × 4π [Wb · m / k
g] or less carrier is used. The saturation magnetization value of the carrier mentioned here is 3000 × 10 ³ /
The magnetization intensity of carriers in a 4π [A / m] magnetic field is used. Further, as the carrier in the present embodiment, those having an average particle size of 20 [μm] or more and 100 [μm] or less, preferably 20 [μm] or more and 80 [μm] or less are used. As a result, the toner density in the developer in the developing area can be increased, and even when applied to an image forming apparatus having a high image forming speed, that is, a high linear velocity of the latent image carrier, a high image density can be maintained, A good image can be obtained. Considering the above magnetic properties of the carrier, it is preferable to use ferrite as the core material of the carrier.

Further, as the coating resin for the carrier, a general thermosetting type silicone resin can be used.
In the present embodiment, the static resistance value of the carrier is 12 [l
Fine powder is added to the coating resin of the carrier for the purpose of adjusting the resistance value of the carrier so as to be not less than 14 [log Ω]. This fine powder preferably has a particle size of about 0.01 [μm] or more and 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, hexamethyldisilazane,
γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, γ
-Chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane (all manufactured by Toray Silicon Co., Ltd.), allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyl. Diethoxysilane, 1,3-divinyltetramethyldisilazane, methacryloxyethyldimethyl (3-
Trimethoxysilylpropyl) ammonium chloride (above, manufactured by Chisso Corporation) and the like can be mentioned.

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

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

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

As other additives, silica fine particles, titanium oxide fine particles and the like can be mentioned as general ones, but they are not particularly limited. In this embodiment,
Fine particles treated with a silicone oil treatment agent are used as an additive. Examples of the fine particles include silica fine particles and titanium oxide fine particles. Specific examples of the silicone oil treating agent for silica fine particles include modified silicone oil having a reactive group in the molecule, hydrogen silicone oil, and fluorine-containing silicone oil.
Although it is preferable to use one or more species, it is also possible to use an unmodified silicone oil having no such active group in the molecule. The modified silicone oil having a reactive group in the molecule is a modified silicone oil containing at least one group selected from the group consisting of hydroxy group, carboxyl group, amino group, epoxy group, ether group and mercapto group in the molecule. More than one species are preferred. The viscosity of this silicone oil is 5 [cp] or more and 1500 at room temperature.
It is preferably 0 [cp] or less. If silica fine particles treated with a silicone oil treatment agent are used as an additive, abrasion of the photosensitive drum 1 due to the silica fine particles can be reduced.

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

Hereinafter, four experimental examples performed using the laser printer described in the above embodiment will be described. First, the formulation and manufacturing method of the toner T and the carriers C1 to C8 used in the following experimental examples will be described.

(Preparation of Toner T) A mixture of the respective materials shown in Table 1 below was thoroughly mixed by stirring in a Henschel mixer. Then, it was heated and melted for about 30 minutes by a roll mill at a temperature of 80 [° C.] and cooled to room temperature. The kneaded material thus obtained was pulverized and classified by a jet mill to obtain 6.5 [μ
The amount of fine particles of 4 [μm] or less is 60 [%]
The following classified toner was produced. Then, for 100 parts of the classified toner, 1.0 part of silica fine particles and 0.
Toner T was obtained by adding 4 parts of titania fine particles and mixing them with a Henschel mixer rotating at 1500 [rpm]. The weight average particle diameter of the toner T is 6.7.
It was [μm].

[Table 1]

(Production 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 an average particle size of 55 [μm],
A saturation magnetization value of 40 × 10 ⁻⁷ × 4π [Wb · m / kg],
A current value of 22 [μA] and a fluidity of 25 [sec / 50 g] were 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 carrier C1 has a static resistance value of 16.2 [logΩ], a fluidity of 29 [sec / 50 g], and a saturation magnetization value of 4
It was 0 × 10 ⁻⁷ × 4π [Wb · m / kg]. The carrier C1 has been used conventionally.

[Table 2]

(Preparation of Carrier C2) 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. 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 an average particle size of 55 [μm],
The one having a saturation magnetization value of 60 × 10 ⁻⁷ × 4π [Wb · m / kg] was used. The average particle size of the carrier C2 is 55.
[Μm] and its saturation magnetization value is 60 × 10 ⁻⁷ × 4π
It was [Wb · m / kg].

[Table 3]

(Production of Carrier C3) The formulations shown in Table 3 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. As the ferrite, one having an average particle size of 55 [μm] and a saturation magnetization value of 90 × 10 ⁻⁷ × 4π [Wb · m / kg] was used. The average particle size of the carrier C3 is 55 [μ
m] and its saturation magnetization value is 90 × 10 ⁻⁷ × 4π [W
b · m / kg].

(Production of Carrier C4) 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. Then, the carrier C4 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], a current value of 60 [μA], and a fluidity of 25 [sec / 50 g]. I used the one. The static resistance value of this carrier C4 is 12.4 [lo].
gΩ], its fluidity is 29 [sec / 50 g], and its saturation magnetization value is 75 × 10 ⁻⁷ × 4π [Wb · m / kg].
Met.

(Production of Carrier C5) 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. After that, firing was performed in an electric furnace at a temperature of 300 [° C.] for 2 hours to prepare carrier C5. As the ferrite, one having an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], and a current value of 30 [μA] was used. The carrier C5 has a static resistance value of 13.8 [logΩ] and a fluidity of 35.
[Sec / 50 g] and its saturation magnetization value is 75 × 10 ⁻⁷
It was × 4π [Wb · m / kg].

[Table 4]

(Production of Carrier C6) The formulations shown in Table 3 above were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid was applied to a fluidized bed type coating apparatus at a spray air pressure of 0.1 [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 C6 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], a current value of 30 [μA], and a fluidity of 20 [sec / 50 g]. I used the one. The static resistance value of this carrier C6 is 13.8 [lo].
gΩ], its fluidity is 25 [sec / 50 g], and its saturation magnetization value is 75 × 10 ⁻⁷ × 4π [Wb · m / kg].
Met.

(Production of Carrier C7) The formulations shown in Table 3 above were dispersed in a homomixer for 20 minutes to prepare a coating layer forming liquid. Then, this coating layer forming liquid was applied to a fluidized bed type coating device at a spray air pressure of 0.6 [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 C7 was produced by firing in an electric furnace at a temperature of 300 ° C. for 2 hours. This ferrite has an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], a current value of 30 [μA], and a fluidity of 30 [sec / 50 g]. I used the one. The static resistance value of this carrier C7 is 13.8 [lo].
gΩ], its fluidity is 42 [sec / 50 g], and its saturation magnetization value is 75 × 10 ⁻⁷ × 4π [Wb · m / kg].
Met.

(Production of Carrier C8) The formulations shown in Table 3 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 0.3 [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 340 [° C.] for 2 hours to prepare carrier C8. This ferrite has an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], a current value of 30 [μA], and a fluidity of 25 [sec / 50 g]. I used the one. The static resistance value of this carrier C8 is 13.8 [lo
gΩ], its fluidity is 33 [sec / 50 g], and its saturation magnetization value is 75 × 10 ⁻⁷ × 4π [Wb · m / kg].
Met.

(Production of Carrier C9) The formulations shown in Table 3 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 0.3 [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 260 [° C.] for 2 hours to prepare carrier C9. This ferrite has an average particle size of 55 [μm], a saturation magnetization value of 75 × 10 ⁻⁷ × 4π [Wb · m / kg], a current value of 30 [μA], and a fluidity of 25 [sec / 50 g]. I used the one. The static resistance value of this carrier C9 is 13.8 [lo].
gΩ], its fluidity is 33 [sec / 50 g], and its saturation magnetization value is 75 × 10 ⁻⁷ × 4π [Wb · m / kg].
Met.

(Measurement Method) Next, the method used for measuring the characteristics of the above-mentioned toner and carrier will be described. Regarding the saturation magnetization value of the carrier, 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 obtained based on the recording result was taken as the saturation magnetization value of the carrier. The average particle size of the carrier is measured by Microtrac particle size analyzer (Nikkiso Co., Ltd .: LEE).
SRA of DS & NORTHRUUP Type7995)
Type was used. This measurement is 0.7 [μm] or more 12
The range setting was 5 [μm] or less. The fluidity of the carrier or developer is the time required for 50 g of the carrier or developer to drop from the pores. The measurement is J
Based on IS-Z2504, the temperature of the sample is 23 [° C] ±
2 in an environment of 3 [° C] and humidity of 60 [%] ± 10 [%]
It went after leaving for an hour. The static resistance value of the carrier was measured using the static resistance measuring device shown in FIG. This static resistance measuring device includes a cell 60, two electrodes 61 and 62 connected to the cell 60, a power supply 63 that applies a voltage between the electrodes 61 and 62, and the electrodes 61 and 6.
It is composed of an ammeter 64 for measuring the current flowing between the two electrodes and a voltmeter 65 for measuring the voltage generated between these electrodes 61, 62. When measurement is performed using this static resistance measuring device, the carrier or the developer B is added to the cell 60.
After charging the carrier, when the voltage is applied from the power supply 63, the carrier or the developer B
The static resistance value of In this measurement, the electrodes 61 and 62 contacting the carrier or the developer B filled in the cell 60
Area was about 4.0 [cm ² ]. The distance d between the two electrodes 61 and 62, that is, the thickness d of the carrier or the developer B in the current direction was about 2 [mm]. The weight of the upper electrode 62 was 275 [g]. And power supply 6
The voltage applied from 3 was 500V. In this measurement, since the carrier or the developer B is a powder, the filling rate of the cell 60 is likely to change, and the static resistance value may change due to the change of the filling rate, so caution is required. The weight average particle diameter of the toner is obtained by using a Coulter Counter II type (manufactured by Coulter Co.) and analyzing the characteristics such as number distribution and volume distribution based on the measurement results to obtain the weight average particle diameter of the toner. It was As the electrolytic solution used in this measurement, a 1% sodium chloride aqueous solution prepared by using primary sodium chloride was used.

[Experimental Example 1] Like the developing device 2 used in this experimental example, the attenuation rate of the magnetic flux density in the normal direction is 40% or more, and the developer supply amount is 65 [mg / cm ² ] And 95 [mg / cm ² ] or less, the magnetic brush becomes short and dense. Therefore, the linear velocity of the developing sleeve 4 in the developing area is 1.1 to 3.0 times the linear velocity of the photosensitive drum 1, and practically about 1.5 to 2.
It is necessary to set 0 times, maintain a high image density, and suppress the generation of a blurred image. However, when such a high linear velocity ratio is set, since the linear velocity of the developing sleeve 4 is generally increased, the problem of carrier adhesion to the photosensitive drum 1 arises as described above. Therefore, in Experimental Example 1, the relationship between the saturation magnetization value of the carrier and the carrier adhesion to the photosensitive drum 1 is confirmed.

In this Experimental Example 1, the toner T and the carrier C are used.
Toner concentration is 5 [wt%] by mixing 1 to C3.
Two developers were prepared. The developing device 2 used in this experimental example is the one described in the above-mentioned embodiment, and the maximum value of the magnetic flux density in the normal direction of the main magnetic pole P1b is 120 [mT].
Is. The attenuation rate of the magnetic flux density in the normal direction is 53.
5 [%], and the half-value angle width of the main magnetic pole P1b is 16
[°]. Further, in this experimental example, the ratio of the linear velocity (660 [mm / sec]) of the developing sleeve 4 to the linear velocity (330 [mm / sec]) of the photosensitive drum 1 in the developing area is set to 2.0. There is. Then, 1 [kg] of the developer of this experimental example was put into the developing device 2, and ten halftone images were printed on the entire surface of A4 size (horizontal) paper by the laser printer according to the above-described embodiment. When the carrier adheres to the photoconductor drum 1, white dot-like dot omissions (hereinafter referred to as “white omissions”) occur in the halftone image. The number of white spots was counted, and the average number of white spots per sheet was used as a characteristic value for evaluation. If the average number of white spots per sheet is 15 or less, carrier adhesion is sufficiently within a permissible range at a practical level. The experimental results in this experimental example are as shown in Table 5 below.

[0055]

[Table 5]

As shown in Table 5 above, the saturation magnetization value is 40
Carrier C1 with × 10 ^-7 × 4π [Wb · m / kg]
When using a developer containing, the average number of white spots per sheet is 2
It was 5.8. On the other hand, the saturation magnetization value is 60 × 1
0 ^-7 × 4π [Wb · m / kg] and 90 × 10 ^-7 × 4π
Carrier C2 and carrier C having [Wb · m / kg]
When a developer containing No. 3 was used, the average number of white spots per sheet was 9.6 and 4.3, respectively. Therefore, the saturation magnetization value is at least 60 × 10 ⁻⁷ × 4π [Wb · m / kg]
When a carrier having a density of 90 × 10 ⁻⁷ × 4π [Wb · m / kg] or less is used, the saturation magnetization value is 60 × 10 ^−7.
It was confirmed that the carrier adhesion to the surface of the photosensitive drum 1 was reduced as compared with the case of using the carrier of less than × 4π [Wb · m / kg].

Considering this result, the carrier contained in the developer on the developing sleeve 4 forms a magnetic brush in the developing area, but the attenuation rate is as high as 53.5% as in the present embodiment. . Therefore, the magnetic force is applied to the carrier forming the tip portion of the magnetic brush by the developing sleeve 4.
The restraint force for restraining to the side is relatively weak. Here, to the carrier in the developing area, a combined force toward the photosensitive drum 1 side such as a centrifugal force applied by the surface movement of the developing sleeve 4 or an electrostatic force received from the surface of the photosensitive drum 1 or the toner attached to the surface. Is added. The carrier C1 has a saturation magnetization value of 40 × 10 ⁻⁷ × 4π [Wb · m /
kg], which is relatively low. Therefore, the restraining force of the carrier C1 on the developing sleeve 4 side is lost to the combined force such as the centrifugal force and the electrostatic force on the photosensitive drum 1 side. As a result, it is considered that most of the carrier C1 forming the tip portion of the magnetic brush moved to the photosensitive drum 1 side and adhered thereto. On the other hand, the saturation magnetization value is 60 × like carrier C2 and carrier C3.
When it is relatively high such as 10 ⁻⁷ × 4π [Wb · m / kg] or more, the binding force of the carrier to the developing sleeve 4 side may overcome the combined force such as centrifugal force and electrostatic force to the photosensitive drum 1 side. it can. As a result, it is considered that the carrier C1 forming the tip portion of the magnetic brush was able to be sufficiently suppressed from moving to and adhering to the photosensitive drum 1 side. The saturation magnetization value of the carrier is 90 × 10 ⁻⁷ × 4π [Wb · m /
If it exceeds [kg], the binding force of the carrier in the developing area becomes too strong. For this reason, it was confirmed that the magnetic brush on the developing sleeve 4 was tightly erected, and the gradation and halftone reproducibility of the image were deteriorated.

As described above, according to the first experimental example, the saturation magnetization value of the carrier is 60 × 10 ⁻⁷ × 4π [Wb · m / kg] or more.
It was confirmed that the carrier adhesion to the photosensitive drum 1 can be sufficiently suppressed by setting it to 0 × 10 ⁻⁷ × 4π [Wb · m / kg] or less. As a result, image quality deterioration such as dot omission due to the carrier attached to the photoconductor drum 1 and the photoconductor drum 1
It has been found that the damage of the parts arranged around the can be reduced.

[Experimental Example 2] In Experimental Example 2, the toner T
The carrier C1, the carrier C4, and the carrier C5 were mixed to prepare two developers having a toner concentration of 5 [wt%]. In this experimental example, a laser printer equipped with the same developing device 2 as in Experimental Example 1 was used for each developer, 10 images were printed in the same manner as in Experimental Example 1, and the average number of blank areas was 1 sheet. Based on the evaluation. The experimental results in Experimental Example 2 are shown in Table 6 below.

[0060]

[Table 6]

As shown in Table 6 above, the static resistance value was 16.
When the developer containing the carrier C1 of 2 [logΩ] was used, the average number of white spots per sheet was 25.8. On the other hand, static resistance values of 12.4 [logΩ] and 13.
When using the developer containing the carrier C4 and the carrier C5 having 8 [logΩ], the average number of white spots per sheet was 8.7 and 12.6, respectively. As a result of the research conducted by the present inventors, the static resistance value is 12 [logΩ] or more.
When a carrier having a relatively low static resistance value of [log Ω] or less is used, carrier adhesion to the surface of the photosensitive drum 1 is reduced as compared with the case of using a carrier having a static resistance value of more than 14 [log Ω]. It was confirmed to do.

Considering this result, the carrier in the developing region is subjected to the centrifugal force applied by the surface movement of the developing sleeve 4 and the electrostatic force received from the surface of the photosensitive drum 1. This electrostatic force serves to attract the carrier forming the magnetic brush toward the photoconductor drum 1 side. Here, the carrier forming the tip portion of the magnetic brush comes close to the surface of the photoconductor drum, so that the surface of the carrier facing the surface of the photoconductor drum is charged with the charges existing on the surface of the photoconductor drum 1. The opposite charge will be induced. As a result, the carrier receives the electrostatic force from the surface of the photoconductor drum and is attracted to the photoconductor drum 1 side. The strength of this electrostatic force increases as the amount of charge induced on the carrier surface increases. Carrier C1
Since the static resistance value is 16.2 [logΩ], which is relatively high, the amount of charge induced on the carrier surface by the surface charge of the photosensitive drum 1 is relatively high. Therefore, the electrostatic force that acts on the carrier C1 from the surface of the photosensitive drum is relatively large, and the force that pulls the carrier C1 toward the photosensitive drum 1 side is large. Therefore, the binding force of the carrier C1 toward the developing sleeve 4 side due to the magnetic force is lost to the combined force of the centrifugal force and the electrostatic force toward the photoconductor drum 1 side, and most of the carrier C1 forming the magnetic brush tip portion are photoconductor drums. It is considered that it moved to the 1 side and adhered. On the other hand, like the carrier C4 and the carrier C5, the static resistance value is 12 [logΩ] or more and 14 [log
Ω] or less, the charge amount induced on the carrier surface by the surface charge of the photosensitive drum 1 becomes relatively low. Therefore, from the surface of the photoconductor drum to the carrier C4,
The electrostatic force acting on C5 is relatively small. Therefore, the force that pulls the carriers C4 and C5 toward the photosensitive drum 1 side becomes small. As a result, the restraining force of the carrier C1 on the developing sleeve 4 side can overcome the combined force such as centrifugal force and electrostatic force on the photosensitive drum 1 side. Therefore,
It is considered that the carrier constituting the tip portion of the magnetic brush was able to be sufficiently suppressed from moving and adhering to the photosensitive drum 1 side. Incidentally, in order to reduce the static resistance value of the carrier, it is necessary to thin the coating layer of the carrier. Therefore, when it is attempted to obtain a carrier having a static resistance value of less than 12 [logΩ], the life of the carrier is shortened and carrier charging becomes unstable because the coating layer of the carrier is too thin. As a result, the latent image on the photoconductor drum 1 was disturbed, and it was confirmed that a good image could not be obtained over time.

As described above, it has been confirmed by this Experimental Example 2 that the carrier adhesion to the photosensitive drum 1 can be more effectively suppressed when the static resistance value of the carrier is set to 12 [logΩ] or more and 14 [logΩ] or less. . As a result, image quality deterioration such as dot omission due to the carrier attached to the photosensitive drum 1,
It was found that damage to the parts arranged around the photoconductor drum 1 can be further reduced.

[Experimental Example 3] In Experimental Example 3, the toner T
And the carriers C5 to C7 were mixed to prepare two developers having a toner concentration of 5 [wt%]. In this experimental example, for each developer, the same developing device 2 as in Experimental example 1 is used.
Using a laser printer provided with, 10 images were printed in the same manner as in Experimental Example 1 described above, and evaluation was performed based on the average number of blank areas. The experimental results in Experimental Example 3 are shown in Table 7 below.

[0065]

[Table 7]

As shown in Table 7, when the developer containing the carrier C6 having the carrier fluidity of 25 [sec / 50 g] was used, the average number of white spots per sheet was 14.8. In contrast, the carrier fluidity is 35 [sec / 50
g] and 42 [sec / 50 g], the average number of white spots per sheet was 12.6 and 8.4, respectively, when the developer containing carrier C5 and carrier C7 was used. As a result of the research conducted by the present inventors, it was confirmed that when the carrier fluidity is low, the carrier is likely to adhere to the photosensitive drum 1. Then, the present inventors have found that when the carrier fluidity is in the range of 20 [seconds / 50 g] or more and 40 [seconds / 50 g] or less, the carrier to the surface of the photoconductor drum 1 is maintained while maintaining high image quality. It was confirmed that the adhesion can be effectively reduced.

Considering this result, even when the same magnet roller 5 is used, the length of the magnetic brush changes and the density of the magnetic brush changes depending on the developer fluidity and the carrier fluidity, so that the magnetic brush The hardness also changes and the image quality is greatly affected. That is, if the carrier has a low fluidity and the developer is free-flowing, the spikes are weakened and the magnetic brush becomes soft to improve the image quality. However, the liquidity of the carrier is 2
When it is lower than 0 [sec / 50 g], carrier adhesion to the photosensitive drum 1 is likely to occur and the image density is low. On the other hand, when the fluidity of the carrier exceeds 40 [sec / 50 g] and the fluidity of the developer becomes poor, the magnetic brush becomes hard and dense, and the gradation of the image and the reproducibility of halftone deteriorate. It is considered that this is because the hard and dense brush portion strongly rubs the photosensitive drum.

As described above, according to Experimental Example 3, if the carrier fluidity is set to 20 [sec / 50 g] or more and 40 [sec / 50 g] or less, carrier adhesion to the photosensitive drum 1 can be effectively suppressed, and It was confirmed that good image quality with high image density and excellent gradation was obtained. In addition, the relationship between the fluidity of the developer and the fluidity of the carrier is as described above in the carrier C.
Judging from 1 to C9, the average fluidity of the developer is 9.8 [sec / 50 g] greater than the fluidity of the carrier. Therefore, the carrier fluidity is 30
[Sec / 50 g] or more and 50 [sec / 50 g] or less, preferably 30 [sec / 50 g] or more and 45 [sec / 50 g] or less, the carrier adhesion to the photosensitive drum 1 is suppressed in the same manner as above. At the same time, it is possible to obtain good image quality with high image density and excellent gradation and halftone reproducibility.

[Experimental Example 4] In Experimental Example 4, the toner T
The carrier C8 and the carrier C9 were mixed to prepare two developers having a toner concentration of 5 [wt%].
At this time, the toner charge amount of the developer containing the carrier C8 was 10.2 [μC / g], and the toner charge amount of the developer containing the carrier C9 was 39.7 [μC / g]. The fluidity of each developer was 43 [sec / 50 g]. In this experimental example, a laser printer equipped with the same developing device 2 as in Experimental Example 1 was used for each developer, 10 images were printed in the same manner as in Experimental Example 1, and the average number of blank areas was 1 sheet. Based on the evaluation. This Experimental Example 4
The experimental results in Table 1 are as shown in Table 8 below.

[0070]

[Table 8]

As shown in Table 8 above, when the developer containing the carrier C9 having the toner charge amount of 39.7 [μC / g] was used, the average number of white spots per sheet was 11.3. .. On the other hand, the toner charge amount is 10.2 [μC /
When the developer containing the carrier C8 of g] was used, the average number of white spots per sheet was 7.9. As a result of the research conducted by the present inventors, it was confirmed that when the charge amount of the toner is large, the carrier is likely to adhere to the photosensitive drum 1. The present inventors have found that the toner charge amount is 10
It has been confirmed that when the thickness is in the range of [μC / g] or more and 40 [μC / g] or less, carrier adhesion to the surface of the photosensitive drum 1 can be effectively reduced while maintaining high image quality.

Considering this result, an electrostatic force attracting the toner adhering to the photosensitive drum 1 to the photosensitive drum 1 side acts on the carrier in the developing area. Since this electrostatic force becomes stronger as the toner charge amount increases, it is considered that when the toner charge amount increases, the carrier is attracted to the photosensitive drum 1 side and carrier adhesion easily occurs. Here, if the toner has a low charging ability and the toner has a charge amount smaller than 10 [μC / g], the attraction force between the toner and the carrier becomes too small, and the toner tends to scatter. Further, in the developing area, the toner lacks the ability to move to the electrostatic latent image portion on the photosensitive drum 1, resulting in a low image density. On the other hand, the charging ability of the toner is high,
If the charge amount of the toner exceeds 40 [μC / g], the attraction force between the toner and the carrier becomes too large, and the toner becomes difficult to separate from the carrier. Therefore, the carrier moves to the photosensitive drum 1 together with the toner in the developing area, and the carrier is likely to be attached.

As described above, according to Experimental Example 4, if the charge amount of the toner is set to 10 [μC / g] or more and 40 [μC / g] or less, carrier adhesion to the photosensitive drum 1 can be suppressed more effectively. It has been found that good image quality can be obtained without causing toner scattering and image density reduction.

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 the photosensitive drum 1 as a latent image carrier that carries and moves its surface.
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 developing sleeve 4 in the developing region, in which the latent image on the photosensitive drum 1 is developed by moving the surface at a linear velocity higher than the linear velocity and rubbing the surface of the photosensitive drum 1 with a magnetic brush. The speed is 500 [mm / sec] or more and 1200 [mm / sec] or less, and the amount of the developer carried on the developing sleeve 4 and conveyed to the developing area (developer supply amount) is 65 [mg / cm ² ]. more than 95 or less [mg / cm ^2], the magnetic flux density in the main pole P1b and the auxiliary magnetic pole P1a, developing sleeve surface normal direction of the magnetic flux generated on the surface outside of the developing sleeve 4 in the developing region by P1c And a decay rate of 40% or more, the main pole P1b and the auxiliary magnetic pole P1a in the developing area, the normal flux density of the developing sleeve surface in the developing sleeve on the surface of the magnetic flux generated by P1c is 100 [mT] to 200
[MT] or less and the saturation magnetization value of the carrier is 60 × 1.
0 ^-7 × 4π [Wb · m / kg] or more 90 × 10 ^-7 × 4π
Since it is [Wb · m / kg] or less, the length of the magnetic brush is short and the density of the brush portion in contact with the latent image carrier can be increased, as described in Experimental Example 1 above. It is possible to improve the property and to suppress the trailing edge blanking phenomenon, and it is possible to sufficiently increase the binding force of the carrier that constitutes the tip portion of the magnetic brush. Therefore, it is possible to suppress the carrier adhesion to the photosensitive drum 1. You can Also,
In the present embodiment, the main magnetic pole P1b and the auxiliary magnetic pole P1.
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 normal direction of the developing sleeve surface generated on the surface of the developing sleeve 4 by a and P1c is viewed from the central axis of curvature of the developing sleeve surface in the developing area. Since the angular width (half-value angular width) between the half-value points in the surface moving direction of the developing sleeve 4 is 25 [°] or less, the magnetic brush of the magnetic brush is the same as when the attenuation rate is 40 [%] or more. The length of the carrier is short, and the density of the brush portion in contact with the latent image carrier is high, so that the reproducibility of fine lines can be improved and the trailing edge whiteout phenomenon can be suppressed. Since the binding force can be sufficiently increased, it is possible to suppress the carrier adhesion to the photosensitive drum 1. Further, in the present embodiment, since the static resistance value of the carrier is 12 [logΩ] or more and 14 [logΩ] or less, as described in Experimental Example 2 above, it is more effective to attach the carrier to the photosensitive drum 1. Can be suppressed to. As a result, it is possible to further reduce image quality deterioration such as dot omission due to the carrier attached to the photoconductor drum 1 and damage to parts arranged around the photoconductor drum 1. Further, in the present embodiment, the carrier fluidity is 20 [sec / 50 g] or more and 40 or more.
Since it is less than [sec / 50 g], as described in Experimental Example 3, it is possible to effectively suppress the carrier adhesion to the photosensitive drum 1. Further, it is possible to obtain good image quality with high image density and excellent gradation and halftone reproducibility. At this time, the toner charge amount is 10 [μC / g] or more and 40 [μC]
/ G] or less, carrier adhesion to the photoconductor drum 1 can be suppressed more effectively, as described in Experimental Example 4 above. Further, it is possible to obtain a good image quality without causing the toner scattering and the image density reduction. In the present embodiment, the photosensitive drum 1 as a latent image carrier,
An optical writing unit 51 as a latent image forming means for forming a latent image on the photosensitive drum 1, and a developing means for developing the latent image on the photosensitive drum 1 with a developer containing toner and carriers as magnetic particles. The developing device 2 described above is used as a developing device of a laser printer as an image forming apparatus having a transfer unit as a transfer device for transferring a toner image on the photosensitive drum 1 onto a transfer paper 52 as a transfer material. Since the length of the magnetic brush is short, and the density of the brush portion in contact with the latent image carrier can be increased, it is possible to improve reproducibility of fine lines and suppress the trailing edge whiteout phenomenon, and Since the binding force of the carrier forming the tip portion of the brush can be sufficiently increased, it is possible to suppress the carrier adhesion to the photosensitive drum 1.

[0075]

According to the first and second aspects of the invention, the linear velocity of the developer carrying member in the developing area is set to 500 [mm / sec] or more and 1200 [mm / sec] or less, and the length of the magnetic brush is set. Is short, and the binding force of the carrier constituting the tip portion of the magnetic brush can be sufficiently increased in the magnetic field formed in the developing area in the developing device in which the density of the brush portion in contact with the latent image carrier is high. , The linear velocity of the latent image carrier in the developing area is 100 [mm / sec] or more and 300 [mm
/ Second] or less], it is possible to suppress carrier adhesion to the latent image carrier while maintaining a high image density in an image forming apparatus (medium speed machine) having a relatively high image forming speed. It has an excellent effect. Further, claims 1 and 2
According to the invention, since the binding force of the carrier forming the tip portion of the magnetic brush is strong, the tip portion of the magnetic brush that comes into contact with the surface of the latent image carrier can rub firmly on the surface of the latent image carrier, and the magnetic brush There is also an excellent effect that it is possible to improve the effect of increasing the amount of toner supplied to the electrostatic latent image on the latent image carrier by the rubbing, and to obtain a high image density. Further, according to the invention of claim 6, the linear velocity of the latent image bearing member in the developing area is 300 [mm / sec] or more and 600 [mm /
[Second] or less, and an image forming apparatus having a relatively high image forming speed is used with a developing apparatus having a short magnetic brush length and a high density of a brush portion in contact with the latent image carrier. Even in the case of carrying out, there is an excellent effect that the carrier adhesion to the latent image bearing member can be suppressed and a high image density can be obtained.

[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. 3 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. 4 is an explanatory diagram showing an arrangement of three magnetic poles that form a developing magnetic pole of the magnetic roller.

FIG. 5A 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. 6 is a schematic configuration diagram of a measuring device for measuring a static resistance value of a carrier.

FIG. 7A is an explanatory diagram showing a magnetic force distribution in the vicinity of a developing area 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. 8A 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.

[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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 501 501 G03G 9/10 352 361 (72) Inventor Zhu Ji 1-3 Nakamagome, Ota-ku, Tokyo No. 6 In Ricoh Co., Ltd. (72) Inventor Koji Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Inventor Akihiro Ito 3 Meindo, Shinmei-do, Shibata-cho, Shibata-gun, Miyagi Prefecture 1F term (reference) 2H005 BA01 BA06 BA07 CA12 CB18 EA01 EA02 FA02 2H031 AB02 AC11 AC15 AC18 AC19 AC20 AD03 AD05 BA08 BA09 2H077 AC02 AC12 AD02 AD06 AD13 BA07 EA03 EA16

Claims (6)

[Claims] 1. A developing device in which a developer carrying member carrying a developer containing toner and magnetic particles on its surface and moving on the surface and a latent image carrying member carrying an electrostatic latent image on its surface and moving on the surface face each other. In the region, the developer on the developer carrying member is made to stand up by a developing magnetic pole arranged so as to face the developing region to form a magnetic brush on the developer carrying member. In the developing area, the surface 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,
In the developing device for rubbing the surface of the latent image bearing member with the magnetic brush to develop the latent image on the latent image bearing member, the linear velocity of the developer bearing member in the developing area is 500 [m.
m / sec] or more and 1200 [mm / sec] or less, and the amount of the developer carried by the developer carrying member and conveyed to the developing area is 65 [mg / cm ² ] or more and 95 [mg / cm ² ] And the attenuation rate of the magnetic flux density of the magnetic flux generated by the developing magnetic pole on the outside of the surface of the developer carrying member in the developing region is 40 [%] or more,
The magnetic flux density of the magnetic flux generated by the developing magnetic pole in the developing area on the surface of the developer carrying member in the normal direction on the surface of the developer carrying member is 100 [mT] or more and 200 [mT] or less, and the magnetic particles are saturated. Magnetization value is 60 × 10 ^-7 × 4
π [Wb · m / kg] or more 90 × 10 ⁻⁷ × 4π [Wb ·
m / kg] or less. 2. A developing device in which a developer carrying member carrying a developer containing toner and magnetic particles on its surface and moving on the surface and a latent image carrying member carrying an electrostatic latent image on its surface and moving on the surface face each other. In the area, the developer on the developer carrying member is erected by a developing magnetic pole arranged so as to face the developing area to form a magnetic brush on the developer carrying member. In the developing area, the surface 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,
In the developing device for rubbing the surface of the latent image bearing member with the magnetic brush to develop the latent image on the latent image bearing member, the linear velocity of the developer bearing member in the developing area is 500 [m.
m / sec] or more and 1200 [mm / sec] or less, and the amount of the developer carried by the developer carrying member and conveyed to the developing area is 65 [mg / cm ² ] or more and 95 [mg / cm ² ] And the half-value point on the surface of the developer carrying body, which is half the maximum magnetic flux density in the direction normal to the surface of the developer carrying body caused by the developing magnetic pole on the surface of the developer carrying body, 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 magnetic flux generated by the developing magnetic pole in the developing area on the surface of the developer carrying member in the normal direction on the surface of the developer carrying member is 100 [mT] or more and 200 [mT] or less, and the magnetic particles are saturated. Magnetization value is 60 × 10 ^-7 × 4
π [Wb · m / kg] or more 90 × 10 ⁻⁷ × 4π [Wb ·
m / kg] or less. 3. The developing device according to claim 1, wherein the static resistance value of the magnetic particles is 12 [logΩ] or more and 14 [l.
The developing device is characterized in that 4. The developing device according to claim 1, 2, or 3,
The fluidity of the magnetic particles is 20 [sec / 50 g] or more 40
A developing device characterized by being less than [second / 50 g]. 5. The developing device according to claim 4, wherein the charge amount of the toner is 10 [μC / g] or more and 40 [μC / g] or less. 6. A latent image carrier, a latent image forming means for forming a latent image on the latent image carrier, and a latent image on the latent image carrier is developed with a developer containing toner and magnetic particles. In an image forming apparatus including a developing unit and a transfer unit that transfers a toner image on the latent image carrier onto a transfer material, the latent image carrier and the developer carrier provided in the developing unit are provided. The linear velocity of the latent image carrier in the opposing developing area is 300.
An image forming apparatus having a developing rate of not less than [mm / sec] and not more than 600 [mm / sec] and using the developing device of claim 1, 2, 3, 4 or 5 as the developing means.