JPH0225873A - Developing device - Google Patents

Abstract

PURPOSE:To prevent image troubles such as a tailing and a scattering by setting the change rate of the magnetic flux density of the horizontal magnetic field components of a developing pole at both edges of a developing area in correcting it so that it can be enlarged. CONSTITUTION:The developing pole is magnetize-set so that the absolute value of the density change rate of the horizontal magnetic field components at both edges of the developing area can be made into a maximum value. Namely, when a developing device is activated, a developer 10 made into a thin layer on the surface of a rotor 2 is carried to the close area of an electrostatic latent image carrier 1 and the rotor 2. The developer 10 is arranged in the close area of the rotor 2, it is napped by the magnetic field of a magnetic pole set so as to form both edges of the developing area in a position and the vicinity where the absolute value of the change rate of the density of the horizontal magnetic field components to the circumference direction distance of the rotor 2 is made into the maximum value, and a visible image is prepared according to the charge of an electrostatic latent image carried by the electrostatic latent image carrier 1. Thus, the adverse effects in an image preparation such as the tailing and scattering can be eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is utilized in the field of technology for developing electrostatic latent images with a developer, and in particular, a developing device that performs development by restraining the developer with magnetic force. Regarding.

[Prior Art] Conventionally, this type of developing device has an electrostatic latent image carrier and an electrostatic latent image carrier, which is disposed with its outer circumferential surface facing each other so as to form a close area with the electrostatic latent image carrier. It is composed of a non-magnetic rotating body that carries a magnetic developer. A predetermined area within the above-mentioned proximity area where the distance between the two outer peripheral surfaces facing each other is equal to or less than a certain value, that is, an area where the magnetic field strength is constant is defined as a development area.

In this case, as a means for supporting the developer on the surface of the rotating body, a magnetic field generating body including a plurality of magnets is fixedly installed inside the rotating body so that the magnetic poles are directed toward the outer peripheral surface of the rotating body. One of the plurality of magnets constituting the magnetic field generator is disposed in the vicinity of a position corresponding to the closest portion within the range of the vicinity of the electrostatic latent image body and the rotary body. The magnetization is set such that one magnetic pole on the outer circumferential surface of the rotating body has a maximum density point of a perpendicular magnetic field component (a magnetic field component perpendicular to the surface of the rotating body) approximately at the center of the developing area. This perpendicular magnetic field component magnetically restrains the developer on the outer circumferential surface of the rotating body within the range of the development area, forming a so-called "standing spike".
The developer is transferred to the electrostatic latent image carrier.

[Problems to be Solved by the Invention] However, in the conventional developing device, the density of the vertical magnetic field component of the magnet gradually decreases toward both ends of the developing area, and conversely, the density of the horizontal magnetic field component decreases toward both ends of the developing area. (The magnetic field component in the circumferential direction of the rotating body) gradually increases in density. The developer spikes become more inclined towards both ends of the formed image area, and various problems occur in the image developed in those areas. For example, this is called "tailing", and as the rotating body rotates, the developer extends linearly in a direction opposite to the direction of image formation (the direction of conveyance of the recording material on which the image is formed), creating a tail. This adversely affects image formation, such as a state in which developer particles appear to be floating, or a state in which the above-mentioned "tailing" (referred to as "splatter") is further worsened and developer particles are scattered near the periphery of the copied image.

FIG. 7 shows an enlarged view of the developing area at this time, showing the appearance of spikes of developer. In the figure, a developer 10 is carried on a developing sleeve 2.1 as a developer carrier. Further, an electrostatic latent image (represented by reference numeral 11 of negative polarity in FIG. 7) is carried on the photosensitive drum l serving as an electrostatic latent image carrier. Then, at the closest part between the photosensitive drum l and the developing sleeve 2 (in the case shown, the central part of the developing area), the developer 10 that has stood up on the developing sleeve 2 is moved toward the photosensitive drum l side by the electric attraction force. do. However, as you move from the center of the developing area to the non-developing areas at both ends, the spikes gradually become inclined due to the influence of the horizontal magnetic field component. This tendency is quite noticeable at both ends of the developing area as shown by reference numeral 12.For example, at the left side of the developing area shown in FIG. Some of the spikes of the developer lO are on the photosensitive drum 1.
Even though the distance between the developing sleeve 2 and the developing sleeve 2 tends to increase, the image forming direction A is generated on the rotating photosensitive drum 1 because it is electrically attracted to the photosensitive drum l in the direction of the arrow W. This deviation of the developer 10 causes the above-mentioned "tailing" which extends in a linear shape backwards on the copied image.

The object of the present invention is to solve the adverse effects in image formation such as "tailing" and "splatter" that conventional developing devices have.

[Means for Solving the Problems] In order to achieve the above object, the developing device of the present invention includes an electrostatic latent image carrier and a rotating body as a developer carrier having a magnetic field generating member inside. The magnetic field generating body is arranged so as to form a proximate area having the closest portion between the outer circumferential surfaces, and the magnetic field generating body generates a maximum density point of a magnetic field component perpendicular to the surface of the rotating body at the closest portion of the rotating body. In a developing device, a developing device is provided with a magnetic pole at a position where the rotating body is exposed to the rotating body, carries magnetic developer on the surface of the rotating body, and performs development by forming the magnetic developer into a standing state by the perpendicular magnetic field component in the adjacent region, The horizontal magnetic field components formed by the magnetic poles form both ends of the developing area at and near a position where the absolute value of the rate of change in density with respect to the circumferential distance of the rotating body takes a maximum value.

It consists of

[Operation] When the developing device configured as described above is activated, the developer formed in a thin layer on the surface of the rotating body is transported to an area near the electrostatic latent image carrier and the rotating body. The developer is disposed in the vicinity of the rotating body, and is applied to both ends of the developing area at and near a position where the absolute value of the rate of change in the density of the horizontal magnetic field component with respect to the circumferential distance of the rotating body takes a maximum value. The electrostatic latent image bearing member carries the electrostatic latent image 1! A visible image is formed depending on the charge of the latent image.

[Example] Hereinafter, an example device of the present invention will be described based on the accompanying drawings.

FIG. 1(A) is a sectional view showing the periphery of a developing sleeve as a developer carrier in a developing device as an embodiment, and FIG. 1(B) is a sectional view of the developing sleeve of FIG. 1(A). FIG. 3 is an enlarged view of a close area formed by a photosensitive drum as an electrostatic latent image carrier, and schematically shows the distribution of perpendicular magnetic field components in the close area.

In FIG. 1(A), the developing sleeve 2 is disposed at a position facing the photosensitive drum 1 with a predetermined gap therebetween so as to be freely rotatable in the entrance direction. Inside the developing sleeve 2, a magnetic field generator 3 having four magnets a, b, c, and d around its periphery is fixedly installed at a predetermined position. Each magnet is arranged so that one of its pair of two magnetic poles faces the circumferential surface of the developing sleeve 2, with magnet a serving as a developing pole and magnet l serving as a developer regulating pole (café pole). , magnets C and d form developer transport poles, respectively.

Further, a blade 4 is disposed on the upper part of the developing sleeve 2 at a position facing the magnet 2 for regulating the height of the spikes of the developer 10 and thinning the developer in the developing sleeve 2. ing. A container 8 is disposed on the right side of the developing sleeve 2 with the left side of the developing sleeve 2 protruding from the opening, and is used to store the developer 10 to be supplied to the developing sleeve 2.
It becomes. Note that 2a is the center of rotation of the developing sleeve 2 and also the center of fixation of the magnetic field generator 3.

FIG. 1(B) shows an enlarged view of the adjacent area in FIG. 1(A), and in the same figure, the developing pole (in this example, the N pole) is the magnetic pole on the circumferential surface side of the magnet a. The distribution of the perpendicular magnetic field component is shown by the length of the arrow indicating the magnetic flux density at the circumferential surface position of the developing sleeve 2.

As is well known, the magnetic field of magnet a is formed in all directions with magnet a as the center. Therefore, a vertical magnetic field component and a horizontal magnetic field component are formed on the surface of the developing sleeve 2, and the direction of the developer spikes is determined by the vertical magnetic field component shown in the figure and the horizontal magnetic field component not shown. It's decided. Here, the horizontal magnetic field component is a magnetic field component in the direction of a tangent to the circumference of the sleeve.

By correcting the density distribution state of the horizontal magnetic field component of this development pole, it is possible to prevent the development caused by the slanted spikes of developer that occur at both ends of the development area, which is the problem of the conventional device mentioned above. can.

That is, the above-mentioned problem can be solved by correcting and setting the rate of change of the magnetic flux density of the horizontal magnetic field component of the development pole at both ends of the development area to be large.

In the following, a detailed description will be given of how the density distribution of the horizontal magnetic field component was formed in the development area in order to solve the problem in this embodiment. Therefore, first of all, we will clarify the maximum range that can be set as the developing area within the above-mentioned proximity area in the apparatus of this embodiment. Since it is a cylinder,
The developing area formed on the circumferential surface of the developing sleeve 2 will be explained in correspondence with the central angle with respect to the rotation center 2a of the developing sleeve 2.

Similar to FIG. 1(B), FIG. 2 shows the vicinity area between the developing sleeve 2 and the photosensitive tram l. Here, a line connecting the rotation center 2a of the developing sleeve 2 and the rotation center 1a of the photosensitive drum 1 is defined as a reference line, and a point on the developing sleeve 2 is defined as X. Distance X, where the intersections of this reference line and the outer circumferential surface of the developing sleeve 2 and the outer circumferential surface of the photosensitive drum l are respectively X and Y. Y is the shortest distance between the developing sleeve 2 and the photosensitive drum 1, and Xo is located at the center of the developing area.

In the vicinity of this position X0 in the circumferential direction, the density of the vertical magnetic field component of the above-mentioned development pole is approximately the maximum, and the horizontal magnetic field component is approximately the minimum, and this portion will be described below as the closest portion.

In the apparatus of this embodiment, which has the above-mentioned closest portion at approximately the center of the adjacent area, the developing speed is the limit for developing the electrostatic latent image on the photosensitive drum 1 with the developer on the developing sleeve z. The longest distance between sleeve 2 and photosensitive tram 1 is written in sentence a.
Let it be x.

this! Line segment X with length equal to l wax. A line segment X connecting the developing sleeve 2 and the surface of the photoreceptor 1 parallel to Yo,
Let Y□. As shown in FIG. 2, the line segments x and y exist at two positions sandwiching <XO, and are the longest facing distance between the opposing developing sleeve 2 and the photosensitive drum l within the developing range. In other words, these two line segments XtYt, X□Y,
It can be said that the circumferential range between the two is the range that can be set as the development area. Here, since the value of l wax changes depending on design conditions such as magnetic field strength, the maximum range (range in the circumferential direction) that can be set as the development area also changes accordingly. According to the results, usually fLwa
x≦2000 u, ■, and in many cases it is preferable to set it as the development area on that premise.

Next, the density distribution of the horizontal magnetic field component of the development pole in the development area will be explained. The angle α formed by the line segment connecting the circumferential arbitrary position X on the developing sleeve 2 shown in FIG. Also, the angle of the position xl from the reference line at this time is α
■Let it be ax.

Here, the development area is 1α if expressed by the angle α
It is within the range of wax l or less. Within the developing area represented by this angle α, the rotation center 2a of the developing sleeve 2 is expressed as the rate of change in density with respect to the circumferential distance of the rotating body.
The density change rate of the horizontal magnetic field component per unit central angle for
The development poles are magnetized so as to form both ends of the development area at the maximum absolute value of Gauss (7 degrees).

In other words, the center position between the two end positions 1tXt and L of the maximum range that can be set as the development area! ! Within the range surrounding x0, the development poles are magnetized so that positions at a predetermined distance from the center position to both sides are set as both ends of the development area. Furthermore, the third
As shown in the figure, if the density change line of the horizontal magnetic field component per unit center angle with respect to the center of one rotating body is less than 30 Gauss, image disturbances such as "tailing" and "splatter" are often observed to occur. Generally, it is preferable to set the magnetization so that the maximum absolute value of the density change rate is 30 Gauss/degree or more.

In the following, the density distribution state of the vertical and horizontal magnetic field components formed by the developing pole of the apparatus of this embodiment will be specifically explained with reference to the drawings. FIG. 4 shows the density distribution of the vertical magnetic field component and the horizontal magnetic field component.

In addition, the solid line and the broken line in the figure show the density distribution of the vertical magnetic field component and the horizontal magnetic field component of the developing pole of the apparatus according to this embodiment, and the dashed-two dotted line and the dashed-dotted line indicate the vertical magnetic field of the developing pole of the conventional apparatus. component and horizontal magnetic field component.

The horizontal axis is located at an intermediate position between magnet a shown in FIG. The reference position θ is the position where the density is O Gauss. The binding is shown at an angle θ toward the downstream side (towards the developing pole) with respect to the rotation center 2a of the developing sleeve 2. The vertical axis represents the vertical magnetic field component density and the horizontal magnetic field component density G (Gauss) on the surface of the developing sleeve 2. In the figure, when comparing the perpendicular magnetic field component density of this example and the conventional device, it is found that the density of the vertical magnetic field component in the case of this example (solid line) is higher at the center position (double-dashed line) than in the conventional device (two-dot chain line).
The rate of change in density is relatively stable in the vicinity of the maximum density point S at the angle θ = 50 degrees (nearly 50 degrees), and the rate of change increases at positions a predetermined distance away from the center position on both sides. Also, when comparing the horizontal magnetic field component density, the device of this example (dashed line) is -
F. It can be seen that the rate of change in density is stable in the vicinity of the center position as the minimum density point, and that the rate of change becomes large at positions at the predetermined distance from the center position to both sides. In order to clarify the above relationship, the density (G (Gauss)) of the horizontal magnetic field component on the vertical axis in Fig. 4 is differentiated by the angle O, and
FIG. 5 shows the rate of change with respect to the angle θ on the vertical axis. Comparing the two, the rate of change is large at positions a predetermined distance from the center position to both sides, and the local maximum value (maximum value) and local minimum value (minimum value) are clear.

- As mentioned above, the development pole of the present embodiment apparatus is located at a predetermined distance from the center of the development area (i.e.,
This is because the absolute value of the density change rate of the horizontal magnetic field component is set to be maximum at the positions (positions that are both ends of the development area).

FIG. 6 is an enlarged view of the developing area of the apparatus of this embodiment, which has developing poles magnetized as described above, and shows the state of developer spikes. Both ends Nt of the development area,
Since the rate of change in the density of the vertical and horizontal magnetic field components is large at N, it is clear whether or not there is a spike at the edge of the development area. the result.

The developer particles that stand up vertically on the sleeve 2 are arranged in an orderly manner within the development area. As a result, the developer 10 is attracted and transferred to the photosensitive drum 1 without being disturbed, and image defects such as "tailing" and "splatter" do not occur.

Next, as another embodiment of the present invention, an apparatus in which a separating plate is provided between the developing sleeve 2 and the photosensitive drum 1 will be described. However, since the device of this embodiment has many of the same features as the device of the above-mentioned first embodiment, the isolation plate 14, which is a feature of this embodiment, is shown in FIG. The explanation will be omitted. In this embodiment, the device has a separating plate 14 to prevent the inclined letter agent at the end of the developing area from being involved in the development.
has been established. The separating plate 14 is connected to the developing sleeve 2 and the photoreceptor l such that the tip is located within the range of at least X, X.
The sleeve 2 is disposed in the longitudinal direction between the sleeve 2 and the sleeve 2. The material may be non-magnetic, depending on the properties of the developer used and surrounding materials.
It is possible to select magnetism, insulation, conductivity, etc. Regarding its shape, the tip may be pointed or rectangular as shown in FIG. When the tip of the separating plate 14 is installed near the end of the developing area as shown in Fig. 2, for example, in the case of a 2000 m thick wax, a polyethylene terephthalate or stainless steel plate with a thickness of 5 to 1500 IL at the base is used. can be used. In FIG. 2, the isolation plate 14 is provided only at the end of the development area on the downstream side in the rotational direction A of the developing sleeve 2, but it is also possible to provide it only on the upstream side, or it can be provided on the upstream and downstream sides. If the apparatus of this embodiment has a number of 0 or more, it is possible to more reliably prevent development due to spikes of developer having a large slope at the end of the development area.

The magnets to be disposed in the magnetic field generating body of the device of the present invention described above can be widely used, such as a sintered ferrite type or an integrally molded resin type. Further, the development pole magnetization setting does not need to be symmetrical with the maximum density point of the vertical component at the center, but may be asymmetrical.

[Effects of the Invention] As explained above, the developing poles of the developing device according to the present invention are magnetized so that the absolute value of the rate of change in density of the horizontal magnetic field component is the maximum value at both ends of the developing area. The density of the horizontal magnetic field component changes rapidly at both ends of the development area, making it possible to clearly see whether or not the developer is bristling.

Therefore, there is no longer a situation where the developer is slanted during development, and it is possible to prevent image defects such as "tailing" and "splatters" that were present in conventional devices, and it is possible to always provide high-quality images. The resulting magnetic field generator can be manufactured by integrally molding a fixed magnet and resin, making it possible to significantly reduce the cost and weight compared to ferrite sintered tabe magnets, bonded type magnets, and embedded type magnets. .

[Brief explanation of the drawing]

FIG. 1(A) is a schematic cross-sectional view of a device according to an embodiment of the present invention;
Fig. 1 (8) is an enlarged view of the adjacent region of Fig. 1 (A) to show the perpendicular magnetic field component density distribution in this region, and Fig. 2 is a diagram showing the density distribution of the perpendicular magnetic field component in the adjacent region of Fig. 1 (A). 3 is a diagram showing the relationship between the rate of change in the horizontal magnetic field component density and the state of occurrence of image disturbance, and FIG. A diagram showing the density distribution of the vertical magnetic field component and the horizontal magnetic field component of the developing pole of an embodiment of the invention and the developing pole of a conventional device. FIG. Figure 6 is a diagram showing the rate of change, and Figure 6 is an enlarged view of the development area of the device of the present invention to show the state of developer spikes. Figure 7 is an enlargement of the development area of the conventional device, showing the state of developer spikes. It is a diagram showing a standing state. l...... Electrostatic latent image carrier (photosensitive drum) 2
・・・・・・・・・・Developer carrying rotating body (developing sleeve) 3・・・・・・・・・Magnetic field generator 1t・・・・・・・・・Developer

Claims (4)

[Claims] (1) An electrostatic latent image carrier and a rotating body as a developer carrier having a magnetic field generating member inside are arranged so as to form a proximate region having the closest portion between the outer circumferential surfaces of both, The magnetic field generating body has a magnetic pole disposed at the closest portion of the rotating body at a position that produces a maximum density point of a magnetic field component perpendicular to the surface of the rotating body, and supports a magnetic developer on the surface of the rotating body, In a developing device that performs development by forming the magnetic developer into a spiked state using the perpendicular magnetic field component in the adjacent region, the horizontal magnetic field component formed by the magnetic pole has a density of A developing device characterized in that a position where the absolute value of the rate of change takes a maximum value and its vicinity form both ends of a developing area. (2) The developing device according to claim 1, wherein the density change rate of the horizontal magnetic field component with respect to the center angle of the rotating body at both ends of the developing area is 30 Gauss per degree or more. (3) The developing device according to claim 1 or 2, wherein in the developing region, the distance between the surfaces of the electrostatic latent image carrier and the rotating body is 2000 micrometers or less. (4) An isolation means for isolating the electrostatic latent image carrier and the rotating body is disposed near the end of the developing area in the close area formed by the electrostatic latent image carrier and the rotating body. The developing device according to any one of claims (1) to (3).