JPH087500B2 - Development device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in the field of technology for developing with an electrostatic latent image and a developer, and in particular, a developing device for carrying out development by restraining the developer with a magnetic force. Regarding

[Prior Art] Conventionally, in this type of developing device, an electrostatic latent image carrier and an outer peripheral surface thereof are disposed so as to face each other so as to form a proximity area force with the electrostatic latent image carrier. And a non-magnetic rotating body carrying a developer having magnetism. In the proximity area, a predetermined area in which the distance between the outer peripheral surfaces facing each other is equal to or less than a certain value, that is, an area having a certain magnetic field strength is defined as a developing area.

In this case, as a means for carrying the developer on the surface of the rotating body, a magnetic field generator having a plurality of magnets is fixedly installed inside the rotating body so that one magnetic pole faces the outer peripheral surface side of the rotating body. One of the plurality of magnets forming the magnetic field generator is disposed in the vicinity of the position closest to the closest portion within the range of the proximity area between the electrostatic latent image body and the rotating body. , One magnetic pole on the outer peripheral surface side of the rotating body is a vertical magnetic field component in a substantially central portion of the developing area (magnetic field component perpendicular to the surface of the rotating body)
The magnetization is set so as to have a maximum density point of. This vertical magnetic field component magnetically restrains the developer on the outer peripheral surface of the rotating body within the range of the developing region to form a so-called "brush", 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 the both ends of the developing region, and conversely the horizontal magnetic field component. The density of (the magnetic field component in the circumferential direction of the rotating body) gradually increases. As a result, the spikes of the developer are inclined toward the both ends of the developing area, which causes various troubles in the image developed in that portion. For example, it is called “tailing”, and the developer linearly extends in a direction opposite to the image forming direction (conveying direction of the recording material on which the image is formed) along with the rotation of the rotating body, and the tail is drawn. The image formation is adversely affected by such a state as if it appears to be present or the above-mentioned "tailing" called "scattering" is further deteriorated and the developer particles are scattered to the peripheral portion of the copied image.

FIG. 7 shows a state in which the developing region at this time is enlarged and the spikes of the developer are raised. In the figure, the developer 10 is carried on the developing sleeve 2 as the developer carrying member. An electrostatic latent image (represented by a negative polarity of reference numeral 11 in FIG. 7) is carried on the photosensitive drum 1 as the electrostatic latent image carrier. Then, at the closest portion between the photosensitive drum 1 and the developing sleeve 2 (in the central portion of the developing area in the figure), the developer that stands on the developing sleeve 2
10 receives the electric attraction force and moves to the photosensitive drum 1 side.
However, as it goes from the central portion of the developing area to the non-developing areas on both ends, the spikes gradually incline due to the influence of the horizontal magnetic field component. This trend has a reference
As shown by 12, it appears considerably at both ends of the development area. For example, in the left side portion of the developing area shown in FIG. 7, a part of the spikes of the developer 10 inclined on the developing sleeve 2 tends to increase the distance between the photosensitive drum 1 and the developing sleeve 2. However, since the toner is electrically attracted to the photosensitive drum 1 in the arrow W direction, the developer 10 is displaced in the image forming direction A on the rotating photosensitive drum 1. This deviation of the development phase 10 is the above-mentioned "tailing" that extends linearly rearward on the copied image.

An object of the present invention is to solve the adverse effects in image formation such as "tailing" and "scattering" which the conventional developing device has.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the developing device of the present invention has a magnetic field generator inside and a developer carrier for carrying a magnetic developer and moving the developer carrier in a predetermined direction. A development having a developing magnetic pole facing the electrostatic latent image carrier so as to form a developing area of width, and the magnetic field generator forming a maximum magnetic flux density point of a vertical magnetic field component perpendicular to the surface of the developer carrier in the developing area. In the apparatus, the magnetic flux density distribution of the horizontal magnetic field component in the tangential direction on the surface of the developer carrier formed by the developing magnetic pole has a maximum value at or near the end position of the developing area.

[Operation] When the developing device configured as described above is activated, the developer thinned on the surface of the rotating body is conveyed to the developing area. The developer is disposed in the developing region so that both ends of the developing region are formed at and near the position where the absolute value of the change rate of the density of the horizontal magnetic field component with respect to the circumferential distance of the rotating body has a maximum value. It stands by the magnetic field of the set magnetic pole,
A visible image is formed according to the charge of the electrostatic latent image carried by the electrostatic latent image carrier.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

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

In FIG. 1A, the developing sleeve 2 is disposed rotatably in the A direction 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, d in its peripheral portion is fixedly installed at a predetermined position. Each of the magnets is arranged such that one of the two magnetic poles forming the pair faces the peripheral surface of the developing sleeve 2. The magnet a is the developing pole, the magnet b is the developer regulating pole (cutting pole), The magnets c and d form the developer carrying poles, respectively.

Further, a blade 4 for regulating the height of spikes of the developer 10 and thinning the developer on the developing sleeve 2 is provided above the developing sleeve 2 at a position facing the magnet b. There is. The right side of the developing sleeve 2 is a container 8 in which the upper portion of the developing sleeve 2 is arranged in a projecting state at the opening and the developer 10 to be supplied to the developing sleeve 2 is accommodated. 2a is the rotation center 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 area in FIG. 1 (A). In FIG. 1 (B), the developing pole (N pole in this embodiment) which is the magnetic pole on the peripheral surface side of the magnet a is shown. The distribution of the vertical magnetic field component is indicated by the magnetic flux density at the peripheral surface position of the developing sleeve 2 by the length of the arrow.

As is well known, the magnetic field of the magnet a is formed in all directions centering on the magnet a. 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 spike of the developer is determined by the vertical magnetic field component shown in the drawing and the horizontal magnetic field component not shown. . here,
The horizontal magnetic field component is a magnetic field component in the direction of the tangent line on the circumference of the sleeve.

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 sloping spikes of the developer, which has been pointed out as a problem of the above-described conventional apparatus, which occurs at both ends of the developing area. it can.

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

In the following, 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 maximum range that can be set as the developing area in the above-mentioned proximity area in the apparatus of the present embodiment will be clarified. Prior to this, the developing sleeve 2 as the rotating body of the apparatus of the present embodiment has a substantially cylindrical shape. Therefore, the developing area formed on the peripheral surface of the developing sleeve 2 is
The description will be made in correspondence with the central angle of the developing sleeve 2 with respect to the rotation center 2a.

Similar to FIG. 1B, FIG. 2 shows a proximity area between the developing sleeve 2 and the photosensitive drum 1. Here, a line connecting the rotation center 2a of the developing sleeve 2 and the rotation center 1a of the photosensitive drum 1 is a reference line L, and a point on the developing sleeve 2 is X. The intersections of the reference line L and the outer peripheral surface of the developing sleeve 2 and the outer surface of the photosensitive drum 1 are defined as X ₀ and Y ₀ , respectively. distance
X ₀ Y ₀ is the shortest distance where the developing sleeve 2 and the photosensitive drum 1 face each other, and X ₀ is located at the center of the developing area.
In the vicinity of the position X ₀ in the circumferential direction, the density of the vertical magnetic field component of the above-described developing pole is almost maximum and the horizontal magnetic field component is almost minimum, and this portion will be described below as the closest portion.

In the apparatus of the present embodiment having the closest portion as described above in the approximate center of the proximity area, the development as the limit that allows the electrostatic latent image on the photosensitive drum 1 to be developed by the developer on the developing sleeve 2. The maximum distance between the sleeve 2 and the photosensitive drum 1 is lmax
And

A line segment connecting the developing sleeve 2 and the surface of the photoconductor 1 and having a length equal to this lmax and parallel to the line segment X ₀ Y ₀ is defined as X ₁ Y ₁ . This line segment X ₁ Y ₁ exists at two positions sandwiching X ₀ as shown in FIG. 2, and the developing sleeve 2 facing each other within the developable range.
Is the longest facing distance of the photosensitive drum 1. That is, it can be said that the circumferential range sandwiched between these two line segments X ₁ Y ₁ and X ₁ Y ₁ can be set as the development region. Here, since the value of lmax varies 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, but the test results of the present inventor According to the above, usually, lmax ≦ 2000 μm, and on the assumption that it is often preferable to set as the developing region.

Next, the density distribution of the horizontal magnetic field component of the developing pole in the developing area will be described. The angle between the reference line L and the line segment connecting the arbitrary position X in the circumferential direction on the developing sleeve 2 in FIG. 2 and the rotation center 2a of the developing sleeve 2 is α. In addition, the angle of position X _{1 from} the reference line at this time is αma
Let x.

If the development area is represented by the angle α, then |
It is within the range of αmax | In the developing area represented by this angle α, the absolute rate of change in density (gauss / degree) of the horizontal magnetic field component per unit central angle with respect to 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 development poles are magnetized so that both ends of the development area are formed at the maximum value.

That is, within the range that encloses the central position X ₀ sandwiched by the positions X ₁ and X ₁ at both ends of the maximum range that can be set as the developing region, the positions that are a predetermined distance from the central position to both sides are the both ends of the developing region. Therefore, the developing pole is magnetized. As shown in Fig. 3, if the density variation of the horizontal magnetic field component per unit central angle with respect to the center of the rotating body is large below 30 Gauss, image defects such as "tailing" and "scattering" are confirmed. Therefore, it is generally preferable to set the magnetization so that the maximum value of the 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 described in detail with reference to the drawings. FIG. 4 shows the density distributions of the vertical magnetic field component and the horizontal magnetic field component.

The solid and broken lines in the figure show the density distributions 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 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 a horizontal magnetic field component.

The horizontal axis is 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 where the density is 0 gauss is defined as a reference position θ _o, and the angle θ is shown downstream (development pole side) 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 on the surface of the developing sleeve 2 by G (Gauss). In the figure, comparing the vertical magnetic field component densities of this embodiment and the conventional device, in the case of this embodiment (solid line), the central position (angle θ = near 50 degrees) is better than that of the conventional device (two-dot chain line). The rate of change of the density is relatively stable in the vicinity of the maximum density point S as the apex, and the rate of change becomes large at the position where the distance is a predetermined distance from the central position. Further, comparing the horizontal magnetic field component densities, the device of the present embodiment (dashed line) has a stable density change rate in the vicinity of the minimum density point at the central position as compared with the conventional device (dashed line). It can be seen that the rate of change increases at the position where the above-mentioned predetermined distance is from the position to both sides. In order to clarify the above relationship, the density of the horizontal magnetic field component (G (Gauss)) on the vertical axis in FIG. 4 is differentiated by the angle θ, and the rate of change with respect to the angle θ is plotted on the vertical axis. It is FIG.
Comparing the two, the rate of change is large and the maximum value (maximum value) and the minimum value (minimum value) are clear at the positions that are a predetermined distance from the center position to both sides. As described above, this is because the developing pole of the apparatus of this embodiment has an absolute value of the density change rate of the horizontal magnetic field component at a position at a predetermined distance from the center position of the developing region (that is, at both ends of the developing region). Is set to be maximum.

FIG. 6 shows the state of the spikes of the developer in which the developing area of the apparatus of this embodiment having the developing pole with the magnetization set as described above is enlarged. Both ends of development area N ₁ , N ₂
Since the rate of change in the density of the vertical and horizontal magnetic field components is large, the presence or absence of spikes at the edge of the developing area is clear. As a result, the developer that stands vertically on the sleeve 2 is arranged in an orderly manner in the developing area. As a result, the developer 10 is suction-transferred to the photosensitive drum 1 without being disturbed, and image defects such as "tailing" and "scattering" do not occur.

Next, as another embodiment of the device of the present invention, the developing sleeve 2
An apparatus in which a separating plate is provided between the photosensitive drum 1 and the photosensitive drum 1 will be described. However, since the device of this embodiment shares much of it with the device of the first embodiment described above, the isolation plate 14 that is a feature of this embodiment is shown in FIG. 2 by a chain double-dashed line in FIG. The description is omitted. In the apparatus of this embodiment, the separating plate 14 is provided so that the inclined developer at both ends of the developing area does not participate in the development.
Was set up. The separating plate 14 is arranged in the longitudinal direction of the sleeve 2 between the developing sleeve 2 and the photoconductor 1 so that the tip thereof is located at least within the range of X ₁ X ₁ . The material is non-magnetic, magnetic, depending on the properties of the developer used and the surrounding materials.
Insulation, conductivity, etc. can be selected. As for the shape, the tip may have a pointed shape as shown in FIG. 2 or a rectangular shape. When the tip of the isolation plate 14 is installed near the edge of the developing area as shown in FIG. 2, for example, when lmax = 2000 μm, the thickness at the base is 5-15.
00 μm polyethylene terephthalate or stainless steel plate can be used. In FIG. 2, the isolation plate 14 is provided only on the downstream end of the developing area in the rotational direction A of the developing sleeve 2, but it may be provided only on the upstream side, or on the upstream and downstream sides. Is. According to the apparatus of this embodiment as described above, it is possible to more reliably prevent the development due to the spike of the developer having a large inclination at the end portion of the development area.

As the magnet arranged in the magnetic field generator of the device of the present invention described above, a ferrite sintered type, a resin integrally molded type, etc. can be widely applied. Also, the setting of the developing pole magnetization does not need to be symmetric with respect to the maximum density point of the vertical component as the center, and may be asymmetric.

[Advantages of the Invention] As described above, since the developing pole of the developing device according to the present invention is magnetized so that the absolute value of the density change rate of the horizontal magnetic field component has a maximum value at both ends of the developing region, The density of the horizontal magnetic field component changes abruptly at both ends of the developing area, so that the presence or absence of spikes of the developer can be made clear. Therefore, the situation in which the development is performed by the inclined developer is eliminated, and the image troubles such as “tailing” and “scattering” which the conventional apparatus has can be prevented, and the effect of always providing a high quality image can be obtained. Bring The magnetic field generator can be manufactured by integral molding of a fixed magnet and resin, a ferrite sintered type magnet, a laminated type,
Compared with embedded magnets, the price and weight can be reduced significantly.

[Brief description of drawings]

FIG. 1 (A) is a schematic sectional view of an apparatus according to an embodiment of the present invention,
FIG. 1 (B) is an enlarged view of the adjacent region of FIG. 1 (A) showing the vertical magnetic field component density distribution in that region, and FIG. 2 is a diagram of the developer carrier and the electrostatic latent image carrier. FIG. 3 is a diagram showing a proximity region and further showing the second embodiment by a chain double-dashed line, FIG. 3 is a diagram showing the relationship between the rate of change of the horizontal magnetic field component density and the image failure occurrence state, and FIG. The figure which shows the density distribution of the vertical magnetic field component and the horizontal magnetic field component of the developing pole of the Example apparatus and the developing pole of the conventional apparatus, FIG. 5 shows the rate of change with respect to the central angle of a rotating body about the horizontal magnetic field component of FIG. FIG. 6 is a diagram showing the developing area of the device of the present invention by enlarging the developing area, and FIG. 7 is the developing area of the conventional apparatus by enlarging the developing area of the developer. It is the figure shown. 1 ... Electrostatic latent image carrier (photosensitive drum) 2 ... Rotating member for carrying developer (developing sleeve) 3 ... Magnetic field generator 10 ... Developer a ... Magnet for forming developing magnetic pole

Claims (4)

[Claims] 1. A magnetic field generator is provided inside, and a developer carrying member carrying and moving a magnetic developer is opposed to the electrostatic latent image carrying member so as to form a developing region of a predetermined width in the moving direction, The magnetic field generator has a developing magnetic pole which forms a maximum magnetic flux density point of a vertical magnetic field component perpendicular to the surface of the developer carrier in the developing area, and in the tangential direction of the surface of the developer carrier formed by the developing magnetic pole. The developing device characterized in that the magnetic flux density distribution of the horizontal magnetic field component has a maximum value at or near the end position of the 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 central angle of the developer carrying member at both ends of the developing area is 30 gauss per degree or more. 3. The developing device according to claim 1, wherein in the developing area, the surface facing distance between the electrostatic latent image carrier and the developer carrier is 2000 μm or less. . 4. A separating means for separating the electrostatic latent image bearing member and the developer bearing member is disposed near the end of the developing area formed by the electrostatic latent image bearing member and the rotating member. The developing device according to any one of claims (1) to (3).