JPS60146274A - Developing device - Google Patents

Abstract

PURPOSE:To prevent effectively a sweeping phenomenon and a trailing phenomemon, and to obtain a distinct developing image by constituting so that a magnetic field of a magnetic pole installed in a visualized area of an electrostatic latent image becomes constant. CONSTITUTION:This device is constituted so that a magnet roll 13 is fixed and a developer holding member 12 is rotated. A magnetic blade 14 is provided in the vicinity of the surface of the holding member 12, the member 12 is rotated by an action of a magnetic field between the blade 14 and the N1 pole of the roll 13, also a toner 16 is coated to a thin layer, the toner 16 thin layer is carried to a developing area opposed to the surface of a photosensitive drum 11 by a rotation of the member 12, and a latent image is developed under an action of an electric field by an AC power source 17 and a DC power source 18. A magnetic field of a magnetic pole installed in an area for visualizing an electrostatic latent image, in magnetic poles of magnets is set to a specified range, that is to say, so that a width of a magnetic field of a value of 0.9-0.8 in case a peak value of the magnetic pole is set to ''1'' becomes >=45% and 65% of a half value width, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device, and more particularly to an electrophotographic developing device using a magnetic developer.

Normal U Blind Conventionally, as a method of visualizing an electrostatic latent image by holding 41 degrees of developer on a developer holding member by the magnetic force of a magnet installed inside the developer holding member, the developer layer was moved to the latent image bearing surface. A non-contact development method in which the developer is selectively flown onto the latent image bearing surface in an imagewise manner by the electric field of the electrostatic latent image without direct contact with the latent image.
In addition, a magnetic brush is formed using a conductive magnetic developer and brought into contact with the electrostatic latent image bearing surface to develop the image. A known magnetic brush method is known, in which the electrostatic latent image on the surface of a latent image carrier is developed by rotating the electrostatic latent image on the surface of the latent image carrier.

Among the various developing methods mentioned above, the Magne Dry method and the Magnetic Brush method are used to apply developer to the latent image bearing surface in the image area (the area where the final toner should stick) and the non-image area (the area where toner should not originally stick). Because the toner contacts the non-image areas without distinction (background area), toner sticks to non-image areas as well, making it impossible to avoid so-called background fog. However, in the non-contact developing method (for example, the method described in Japanese Patent Publication No. 41-9475), the toner layer and the electrostatic image bearing surface are developed without contacting each other and with a gap, which prevents background fog. 11-
In this respect, it is an extremely effective method.

However, in the contact development method, the electrostatic latent image is
Influenced by the magnetic field IE of a magnetic pole (hereinafter referred to as a developing magnetic pole) placed in a region to be visualized (hereinafter referred to as a developing area),
In particular, the image quality is affected by the magnetic field region below half the magnetic pole peak value. ” - If the region of the magnetic field greater than 1/2 (fl'i) is narrower than the half-width, there is a so-called sweep phenomenon in which the trailing edge of the solid image becomes darker, or a tail of toner scattered at the trailing edge of the solid image developing area. There was a problem in that a pulling phenomenon occurred and the image quality was significantly impaired.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a developing device for obtaining high-quality images free of sweep and trailing.

According to the present invention, in a developing device that visualizes an electrostatic latent image by bringing magnetic developer held on a developer holding member close to an electrostatic latent image carrier, developer holding Among the magnetic poles of the magnet included in the member, the magnetic field of the magnetic pole installed in the area where the electrostatic latent image is visualized is set within a specific range, that is, the peak of the magnetic pole (0.9 to 0.8 when Ffi is 1). (fi)
Since the magnetic field II is set to be 45% and 65% or more of the half-width, respectively, this type of developing device can form high-quality images without sweeping or trailing.

EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram of a developing device for magnetic developer to which the present invention is applied.

In FIG. 1, a photosensitive drum 11 as a latent image bearing member is shown.
The electrostatic latent image carried on the substrate is developed by the developing device of the present invention. A hopper 5 serving as a developer supply container contains a magnetic developer, that is, toner 16, and a developer holding member 12 containing a magnet roll 13 having a plurality of magnetic poles is provided below the hopper 5.

In this embodiment, the magnet roll 13 is fixed and the developer holding member 12'' rotates.A magnetic blade 14 is provided close to the surface of the developer holding member 12, and the magnetic blade 14 and the magnet, Troll 13 NIJ
As the developer holding member 12 rotates, a thin layer of toner 16 is coated on the developer holding member 12 due to the action of the magnetic field between the developer holding member 12 and the toner 16, which is exposed to light by the rotation of the developer holding member 12. It is carried to the developing area facing the surface of the drum 11, and the AC type @17 and the DC type Jul l
Under the action of the electric field by 8, the photosensitive drum 11, J-
Develop the latent image.

Figure 2 shows the state of the developing magnetic pole and the lines of magnetic force in the developing area using polar coordinates.
The diametrical component of the magnetic flux density of l is designated by reference numeral 19. Furthermore, the state of the magnetic lines of force is indicated by reference numeral 20. Also, in this figure, the development area is A
It is shown in The toner 16 flies onto the photosensitive drum 11 in this development area and develops a latent image. The peak of this development area A changes depending on the difference between the latent image potential and the developer holding member potential applied to the developer holding member 12 by the AC power supply 17 and the DC power supply 18. In halftone development, the development area B becomes narrower as shown in .

Here, the diametrical component 19 of the magnetic flux density of the developing section J4S1
The relationship between the magnetic field lines 20 and the magnetic field lines 20 will be explained. Comparing a region where the magnetic field 1+ in a region with a magnetic flux density greater than half the peak value of the magnetic pole is wide as shown in Figure 3 and narrow as shown in Figure 4, the magnetic field lines in the narrower field have more circumferential direction components than in the wider field. is becoming more widespread. In other words, the magnetic field 1 in the region of -1- or more than half the magnetic pole peak value of the diametrical component 19 of the magnetic flux vFI degree
When 1J is narrow, the circumferential component of the magnetic field lines has a large radius in the development area A, and therefore,! - When the toner 16 flies between the photosensitive drum l'l and the developer holding member 12, it is more likely to receive force in the circumferential direction. In the non-contact development method, development is completed on the downstream side of the development area A, so a phenomenon occurs in which the developed image disappears toward the rear end in the direction of travel of the photosensitive drum ti. 1, the image scatters and trailing occurs during transfer to the transfer material. In particular, the sweep-up phenomenon is 1:1 with /＼-tone, and when the halftone development area becomes small as shown by B, the magnetic pole peak value is 0.9 to 1. 0.8 magnetic field 11]
is important. Conversely, if the magnetic field +lJ in this region is defined as a constant ratio to the half width, the magnetic field 111 in the 0.7 to 0.8 region will also be determined by itself, and all concentrations from /\-Ftone to black will be It has been found that it is possible to improve the image quality in images.

As shown in FIG. 3, when the magnetic field +l+ is wide in the region of half or more of the magnetic pole peak value of the diametrical component 19 of the magnetic flux density, the force that draws the toner in the circumferential direction is weak and the toner is swept together or Phenomena such as tailing do not occur.

Below, the table below shows 0.9 to 0 when the magnetic pole peak value is 1.
．． 8 shows the level of sweeping and trailing in the magnetic control with different magnetic fields [11].

As can be understood from this table, by setting the magnetic field +tJ of half-wave 1 or more wider than a predetermined value, the phenomenon of sweeping and trailing can be prevented.

L Mitate Lid Section.

As explained below, according to the present invention, by using the magnetic field described in the claims, it is possible to effectively prevent the sweeping phenomenon and trailing phenomenon that tend to occur in non-contact type developing devices. This makes it possible to form a clear developed image.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of the developing device of the present invention, FIG. 2 shows the state of the developing magnetic pole and lines of magnetic force in the developing area, and FIG. 3 shows a developing device having a magnetic flux density of 2 or more J-, half the peak value of the magnetic pole. Figure 4 shows the state of the developing magnetic pole and lines of magnetic force in the developing area when the magnetic field +1J in the area is wide, and shows the development in the developing area when the magnetic field I11 in the area having a magnetic flux density at half the peak value of the magnetic pole is narrow. Shows the state of magnetic poles and lines of magnetic force. Explanation of symbols 11: Photosensitive drum J1. 12: Developer holding member 13: Magnet roll, 14: Magnetic blade Figure 1 Figure 2 Section A Figure 4

Claims (1)

[Claims] In a developing device that visualizes an electrostatic latent image by bringing a magnetic developer held on a developer holding member close to an electrostatic latent image carrier, the magnetic developer is The magnetic field of the magnetic pole installed in the area where the electrolatent image is visualized is 0.9 to 0.8 when the peak value of the magnetic pole is 1.
The IJ of the magnetic field with the value of is 45% and 65% of the half ifi width, respectively.
% or more -1-.