JP2773151B2 - Developing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention is used in the field of technology for developing an electrostatic latent image with a developer, and in particular, a developing device that performs development while restraining the developer with a magnetic force. About.

[Prior Art] Conventionally, this type of developing device has an electrostatic latent image carrier and an outer peripheral surface facing each other so as to form an area close to the electrostatic latent image carrier. And a non-magnetic rotating body that carries a magnetic developer. In the proximity region, a predetermined region in which the distance between the outer peripheral surfaces of the two adjacent surfaces is equal to or less than a predetermined value, that is, a region having a constant magnetic field strength is defined as a development region.

In this case, as a means for supporting the developer on the surface of the rotating body, a magnetic field generating body as a magnetic field generating means having a plurality of magnets such that one magnetic pole faces the outer peripheral surface side of the rotating body is fixedly installed inside the rotating body. I have. One of the plurality of magnets constituting the magnetic field generator is disposed in the range of the proximity area between the electrostatic latent image body and the rotator and near the position corresponding to the closest part. The magnetization is set such that one magnetic pole on the outer peripheral surface side of the rotating body has a maximum density point of a vertical magnetic field component (a magnetic field component perpendicular to the surface of the rotating body) substantially at the center of the developing region. This vertical magnetic field component magnetically constrains the developer on the outer peripheral surface of the rotating body within the range of the development area to form a so-called “spike”, and transfers the developer 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 horizontal magnetic field component ( The density of the magnetic field component parallel to the surface of the rotator gradually increases. As a result, the spikes of the developer are inclined toward both ends of the development area, so that various obstacles occur in the image developed in that part. For example, it is referred to as “tailing”, and the developer linearly extends in the direction opposite to the direction of image formation accompanying the rotation of the rotator (the direction of transport of the recording material on which an image is formed) and trails. The image formation has an adverse effect on the image formation, such as a state in which the developer particles appear to be scattered, and a state in which the "tailing", which is called "scattering", is further deteriorated, and the particles of the developer scatter to the periphery of the copied image.

FIG. 6 is an enlarged view of the development area at this time, showing the appearance of the ears of the developer. In FIG. 1, a developer 10 is carried on a developing sleeve 2 as a developer carrying member. Further, an electrostatic latent image (represented as a negative polarity of reference numeral 11 in FIG. 6) is carried on the photosensitive drum 1 as an electrostatic latent image carrier. At the closest portion between the photosensitive drum 1 and the developing sleeve 2 (in the case of the drawing, the central portion of the developing area), the developer which has risen on the developing sleeve 2
10 moves to the photosensitive drum 1 side under the electric suction force.
However, in the direction from the central part of the developing area to the non-developing areas at both ends, the ears gradually become inclined under the influence of the horizontal magnetic field component. This trend is referenced
As shown by reference numeral 12, it is quite noticeable at both ends of the development area. For example, in the left part of the developing area shown in FIG. 6, a part of the rising of the developer 10 inclined on the developing sleeve 2 has a large distance between the photosensitive drum 1 and the developing sleeve 2. Despite the tendency, the developer is electrically attracted to the photosensitive drum 1 in the direction of the arrow W, so that the developer 10 shifts in the image forming direction A on the rotating photosensitive drum 1. This displacement of the developer 10 is the above-mentioned “tailing” that extends linearly rearward on the copy image.

SUMMARY OF THE INVENTION An object of the present invention is to solve adverse effects on image formation, such as "tailing" and "scattering", of such a conventional developing device.

[Means for Solving the Problems] To achieve the above object, a developing device of the present invention comprises a non-magnetic cylinder in which a developing area is formed by an electrostatic latent image carrier and the electrostatic latent image carrier. In a developing device having a developer carrier and a magnetic field generating means provided in the developer carrier, the magnetic field generating means has a single magnetic pole in a development area,
The magnetic field on the developer carrier formed by the magnetic poles is such that the magnetic field component in the radial direction of the developer carrier substantially at the center of the development area has the maximum magnetic flux density, and the tangential direction of the surface of the developer carrier is Is present in the developing region, and the maximum value of the absolute value of the absolute value of the rate of change of the magnetic field component in the tangential direction on the surface of the developer carrier is 30 gauss / degree or more.

[Operation] When the developing device configured as described above is started, the developer thinned on the surface of the rotating body is transported to a region near the electrostatic latent image carrier and the rotating body. On the other hand, at least one of the magnetic poles disposed on the rotating body forms a developable area in an area near the electrostatic latent image carrier and the rotating body, and a magnetic field parallel to the rotating body surface formed by the magnetic pole. The components are set such that the maximum value of the absolute value of the density change rate with respect to the unit rotation angle of the rotator exists in the developable region. Therefore, the developer rises due to the magnetic field of the magnetic pole, and forms a visible image according to the charge of the electrostatic latent image carried on the electrostatic latent image carrier.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1A is a cross-sectional view showing the periphery of a developing sleeve as a developer carrier in a developing device as one embodiment of the present invention, and FIG. 1B is a developing sleeve of FIG. 1A. FIG. 3 is a diagram schematically illustrating a distribution state of a vertical magnetic field component in the proximity region formed by a photosensitive drum serving as an electrostatic latent image carrier formed by enlarging a proximity region.

In FIG. 1A, a developing sleeve 2 is rotatably arranged in a direction A at a position facing the photosensitive drum 1 with a predetermined gap. Inside the developing sleeve 2, a magnetic field generator 3 having four magnets a, b, c, and d on its periphery is fixedly installed at a predetermined position. Each magnet is arranged so that one of the two magnetic poles forming a pair faces the peripheral surface of the developing sleeve 2, the magnet a serves as a developing pole, the magnet b serves as a developer regulating pole (cut pole), The magnets c and d form developer transport poles, respectively.

In addition, a blade 4 for regulating the height of the rising edge of the developer 10 to make the developer on the developing sleeve thinner is disposed at a position facing the magnet b above the developing sleeve 2. I have. On the right side of the developing sleeve 2 is a container 8 in which the left portion of the developing sleeve 2 is disposed so as to protrude at the opening, and stores a developer 10 to be supplied to the developing sleeve 2. 2a is the center of rotation of the developing sleeve 2 and the fixed center of the magnetic field generator 3.

FIG. 1 (B) is an enlarged view of the proximity region in FIG. 1 (A). In FIG. 1 (B), a developing pole (N pole in this embodiment) which is a magnetic pole on the peripheral surface side of the magnet a is shown. The vertical magnetic field component distribution is shown by the length of the arrow indicating the magnetic flux density at the peripheral surface position of the developing sleeve 2.

As is well known, the magnetic field of the magnet a is formed in all directions around the magnet a. Therefore, a vertical magnetic field component perpendicular to the surface and a horizontal magnetic field component parallel to the surface are formed on the surface of the developing sleeve 2, and the direction of the ears of the developer is the vertical magnetic field component shown in FIG. It is determined by a horizontal magnetic field component not shown. Here, the horizontal magnetic field component is a magnetic field component in a tangential direction on the circumference of the developing sleeve 2.

By correcting the density distribution state of the horizontal magnetic field component of the developing pole, it is possible to prevent the development caused by the inclined spikes of the developer occurring at both ends of the developing area, which has been pointed out as a problem of the conventional apparatus described above. it can.

That is, the above-mentioned problem is solved by correcting and setting the change rate of the magnetic flux density of the horizontal magnetic field component of the magnet a as the developing pole in the developable region.

Hereinafter, in this embodiment, how the density distribution of the horizontal magnetic field component is formed in the developing region in order to solve the problem will be described in detail. Therefore, first, the magnetization setting condition of the magnet a as the developing pole will be described. FIG. 3 shows the density distribution of the vertical magnetic field component and the horizontal magnetic field component.

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 the present embodiment, and the two-dot chain line and the one-dot chain line show the vertical magnetic field component of the developing pole of the conventional apparatus. And the horizontal magnetic field component.

The horizontal axis is at an intermediate position between the magnet a shown in FIG. 1 (A) and the magnet b located on the upstream side in the rotation direction A of the developing sleeve 2, and represents the vertical magnetic field component of the developing pole of the magnet a. The position at which the density becomes 0 Gauss is defined as a reference position θ _0, and the angle θ is shown downstream (developing pole side) with respect to the rotation center 2 a of the developing sleeve 2. The vertical axis represents the vertical magnetic field component density and the horizontal magnetic field component density on the surface of the developing sleeve 2 by G (Gauss).

The magnet a forms the maximum density point (point S, FIG. 3) of the magnetic field component perpendicular to the surface of the developing sleeve 2 at the closest contact point between the photosensitive drum 1 and the developing sleeve 2, and the developing sleeve 2 It is set so that the development area is formed at an angle of about 30 ° on the upstream side and the downstream side. The magnet a is further set so that the maximum value and the minimum value of the change amount of the magnetic flux density of the horizontal magnetic field component exist in the development area.

In addition, as shown in FIG. 2, when the amount of change in the density of the horizontal magnetic field component per unit center angle with respect to the center of the rotating body is 30 Gauss or less, the occurrence of image defects such as “tailing” and “scattering” often occurs. It has been confirmed that, in general, it is preferable to strengthen and set the maximum value of the absolute value of the density change rate to be 30 gauss / degree or more.

By the way, the developable region indicates a region where the developer on the developing sleeve 2 can develop the latent image on the photosensitive drum 1, and this developing region is the best condition in the following relationship. It became clear.

θ = 2 _cos ⁻¹ {[(d−G) / r] +1} (1) where θ (°) is a set angle of the developable area, and d
(Mm) is the photosensitive drum 1 which is the maximum density point of the vertical magnetic field component
And the closest distance between the surface facing distance of the developing sleeve 2 and the developing sleeve 2. G (mm) is a photosensitive drum 1 that can be developed.
And the surface facing distance of the developing sleeve 2. This G varies depending on conditions such as the type of developer, but is preferably about 2000 μm or less. Note that the relationship of the expression (1) is not limited to a cylindrical electrostatic latent image carrier or a developer carrier as in the present embodiment, but can be applied to, for example, a belt-shaped electrostatic latent image carrier or developer carrier. is there.

In FIG. 3, the vertical magnetic field component density of the present embodiment is compared with that of the conventional device. In the case of the present embodiment (solid line), the center position (angle θ = around 50 degrees) is higher than that of the conventional device (two-dot chain line).
, The rate of change of density is relatively stable near the maximum density point S, and the rate of change increases at a position at a predetermined distance from the center position to both sides. Further, comparing the horizontal magnetic field component densities, the device of the present embodiment (broken line) has the above-mentioned center position as the minimum density point and the change rate of the density in the vicinity thereof is more stable than that of the conventional device (dashed line). It can be seen that the rate of change is greater at the position at the above-mentioned predetermined distance from the 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. 3 is differentiated by the angle θ, and the rate of change with respect to the angle θ is plotted on the vertical axis. FIG. Comparing the two, the change rate is large and the local maximum value (maximum value) and the local minimum value (minimum value) are clear at a position that is a predetermined distance from the center position to both sides. This is because, as described above, the developing pole of the present embodiment is set so that the absolute value of the density change rate of the horizontal magnetic field component is maximized at a position that is a predetermined distance from the center position of the developing area. .

FIG. 5 shows the state of the developer spikes in which the development area of the apparatus having the development poles whose magnetization is set as described above is enlarged. Both ends N ₁ and N _{2 of the} development area
Since the rate of change of the density of the vertical and horizontal magnetic field components is large, the presence or absence of ears at the end of the development area is clear. As a result, the developer that has risen vertically on the sleeve 2 is arranged neatly in the developing area. As a result, the developer 10 is suction-transferred to the photosensitive drum 1 without being disturbed, and does not cause image disturbance such as “tailing” and “scattering”.

The magnet provided in the magnetic field generating means of the device of the present invention described above can be widely applied, such as a ferrite sintered type and a resinous integral molding type. Also, the development pole magnetization need not be symmetrical with respect to the maximum density point of the vertical component as the center, but may be asymmetric with respect to the maximum density point.

[Effects of the Invention] As described above, the developing pole of the developing device according to the present invention is set such that a developable area is formed in the area near the electrostatic latent image carrier and the rotating body. At the developing pole, the magnetic field component in the radial direction of the developer carrier forms the maximum of the magnetic flux density at substantially the center of the developing region, and the maximum point of the absolute value of the change rate of the magnetic field component in the tangential direction on the surface of the developer carrier is Since the maximum value of the absolute value of the change rate of the magnetic field component in the tangential direction on the surface of the developer carrier is 30 gauss / degree or more in the development area, the density of the horizontal magnetic field component in the developable area Sharply changes, and the presence or absence of the ears of the developer can be clarified. Therefore, the situation in which development is performed by the inclined developer is eliminated, and image defects such as “tailing” and “splashing” which the conventional device has can be prevented, and the effect of always providing high-quality images can be obtained. Bring. The magnetic field generator can be manufactured by integral molding of a fixed magnet and a resin, and can be significantly reduced in cost and weight as compared with ferrite sintered type magnets, bonded type magnets, and embedded type magnets.

[Brief description of the drawings]

FIG. 1A is a schematic cross-sectional view of an apparatus according to an embodiment of the present invention,
FIG. 1 (B) is an enlarged view of a vertical magnetic field component density distribution in an adjacent area of FIG. 1 (A), and FIG. 2 is a view showing a change rate of a horizontal magnetic field component density and an image failure occurrence state. FIG. 3 is a diagram showing the density distribution of the vertical magnetic field component and the horizontal magnetic field component of the developing pole of the apparatus according to one embodiment of the present invention and the developing pole of the conventional apparatus, and FIG. 4 is FIG. FIG. 5 is a diagram showing the rate of change of the horizontal magnetic field component with respect to the center angle of the rotating body, FIG. 5 is a diagram showing the developing region of the apparatus of the present invention in an enlarged state, and FIG. FIG. 5 is a view showing a state of ears of the developer by enlarging a development region of FIG. DESCRIPTION OF SYMBOLS 1 ... Electrostatic latent image carrier (photosensitive drum) 2 ... Rotator for carrying developer (developing sleeve) 3 ... Magnetic field generating means 10 ... Developer a ... Magnet forming a developing magnetic pole

Claims (1)

(57) [Claims] An electrostatic latent image carrier, a developer carrier formed of a non-magnetic cylinder and forming a development area with the electrostatic latent image carrier;
A magnetic field generating means provided in the developer carrier, wherein the magnetic field generating means has a single magnetic pole in a developing area, and a magnetic field formed by the magnetic pole on the developer carrier is The magnetic field component in the radial direction of the developer carrying member has a maximum magnetic flux density at substantially the center of the developing region, and the maximum point of the absolute value of the change rate of the magnetic field component in the tangential direction on the surface of the developer carrying member is within the developing region. Wherein the maximum value of the absolute value of the change rate of the magnetic field component in the tangential direction on the surface of the developer carrying member is 30 gauss / degree or more.