JPH0233256Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a developing device for magnetic toner that develops an electrostatic latent image in a copying device using electrophotography or electrostatic recording.

[Prior Art] In electrophotographic copying machines and electrostatic printing devices, an electrostatic latent image is formed on the surface of a photoreceptor layer or dielectric layer, and this electrostatic latent image is magnetically transferred using a one-component magnetic toner. A method has been put into practical use in which a hard copy is obtained by developing the image using a brush method or the like and then directly fixing it or by transferring it onto a transfer sheet such as plain paper and then fixing it.

As mentioned above, in the so-called CPC method in which hard copies are obtained by direct fixation after development, magnetic toners have a coarse particle size distribution of about 5 to 50 μm and an average particle size of about 30 μm, and have low electrical resistance. So-called conductive materials are used,
Since the toner has good fluidity, there was no problem of toner aggregation within the developing device.
However, in the so-called PPC method that includes a transfer process, from the viewpoint of image quality stability and resolution,
The particle size distribution of the toner is narrow, ranging from 5 to 20 to 30 μm, and from the viewpoint of transferability, so-called semiconductive or insulating materials with high electrical resistance are used, which reduces the fluidity of the toner. Toner tends to aggregate within the developing device. In particular, in a normal developing device, the magnetic toner contained in the toner container is conveyed on a non-magnetic sleeve with its thickness regulated by a doctor member. A large force is applied, making toner agglomeration likely to occur.

As a conventional magnetic toner developing device, for example, one having a structure shown in FIG. 1 is known. In FIG. 1, a cylindrical sleeve 2 made of a non-magnetic material is rotatably disposed opposite a photosensitive drum 1 rotating in the direction of an arrow Z in the figure. A permanent magnet roll 3 is disposed within the sleeve 2 and includes a permanent magnet 4 having a plurality of magnetic poles on its surface fixed to a shaft 5. The magnetic toner 6 is contained in a toner tank 7, and a doctor member 8 is attached to the toner tank 7 to regulate the amount of magnetic toner conveyed on the sleeve.

In this developing device, for example, by fixing the permanent magnet roll 3 and rotating the sleeve 2 in the direction of arrow A in the figure, the magnetic toner 6 attracted to the sleeve 2 is conveyed from the doctor gap d toward the developing gap D. When reaching the development area D, a magnetic brush is formed there. The surface of the photoreceptor drum 1 is rubbed by the magnetic brush, and the surface of the photoreceptor drum 1 is rubbed.
An electrostatic latent image (not shown) formed thereon is developed.

According to the above-mentioned developing device, since the doctor member 8 is located approximately tangentially to the surface of the sleeve, as described in Japanese Patent Publication No. 56-33705, undesired toner is removed from the tip of the doctor member 8. Although accumulation can be prevented, and the horizontal length of the toner tank 6 is large, the toner storage capacity is large, but there are the following problems. That is, the surplus magnetic toner regulated by the doctor member 8 falls into the toner tank 7 along a path P as shown by the dashed line in the figure, and is deposited in the toner tank 7 . However, because the toner tank 7 is long, the toner falls near point Q, which is outside the range of the magnetic attraction of the permanent magnet roll (outside the arc shown by the solid line B in the figure), and this toner is not magnetized. As a result, the toner particles gather in the shaded area R in the figure and cause bridge development, which ultimately impedes toner conveyance.

[Purpose of the invention] The purpose of the invention is to solve the problems of the prior art described above and to provide a developing device for magnetic toner that can accommodate a relatively large amount of magnetic toner without insufficient toner transport. be.

[Summary] The magnetic toner developing device of the present invention includes: a permanent magnet roll having a plurality of magnetic poles on its surface; a cylindrical sleeve made of a non-magnetic material rotatably disposed around the permanent magnet roll; In the magnetic toner developing device, the magnetic toner developing device includes a toner tank that accommodates magnetic toner and is installed surrounding a part of the outer periphery of the sleeve, and a doctor member that regulates the amount of magnetic toner conveyed on the sleeve. A doctor member is positioned substantially tangentially and substantially perpendicularly to the surface of the sleeve, and a portion of the toner tank located below near the tip of the doctor member is within the range of the magnetic attraction force of the permanent magnet roll. The surface of the magnetic toner contained in the toner tank is located at a level substantially equal to or lower than the tip of the doctor member.

[Example] The details of the present invention will be explained below with reference to the drawings.

FIG. 2 is a sectional view showing an embodiment of the developing device of the present invention, and the same functional parts as in FIG. 1 are designated by the same reference numerals.

In Figure 2, an electrostatic latent image (not shown) on the surface.
A cylindrical sleeve 2 made of a non-magnetic material is rotatably disposed opposite a photoreceptor drum 1 having a cylindrical shape. Inside the sleeve 2 there is arranged a permanent magnet roll having a cylindrical permanent magnet 5 having a plurality of magnetic poles on its surface fixed around an axis 4 concentric with the sleeve.

Magnetic toner 6 is contained in toner tank 7 . A doctor member 8 that regulates the amount of magnetic toner conveyed on the sleeve is attached to the toner tank 7 so as to be positioned substantially tangentially and substantially perpendicularly to the surface of the sleeve 2 . Here, the toner tank 7 is
A portion (indicated by 7a in the figure) below the position corresponding to the vicinity of the tip of the doctor member 8 is formed so as to be located within the range of the magnetic attraction force of the permanent magnet roll 3. The surface of the magnetic toner 6 contained in the toner tank is at approximately the same level as the tip of the doctor member 8.

The operation of the developing device having the above configuration is as follows. First, by rotating the sleeve 2 and the permanent magnet roll 3 relative to each other, for example, by rotating only the sleeve 2 in the direction of arrow A in the figure, the magnetic toner 6 attracted to the sleeve 2 is conveyed in the same direction, and the doctor gap d ₁ to the developing gap _d2 . In the development area D, the electrostatic latent image is developed by rubbing the surface of the photoreceptor drum 1 with a magnetic brush formed there. After passing through the developing gap d ₂ , the magnetic toner 6 is conveyed in the direction of arrow A in the figure and returns to the toner tank 7 .

In this case, a part of the magnetic toner 6 attracted onto the sleeve 2 passes through the doctor gap d ₁ as described above, but most of the magnetic toner 6 is regulated by the doctor member 8 and passes through the doctor gap d 1 . The particles are deposited sequentially along the arrow E, and then fall downward from near the upper end of the doctor member 8, as shown by arrow E in the figure.
Since the toner tank 7 that receives the fallen magnetic toner 6 is within the range of the magnetic attraction force of the permanent magnet roll as described above, the excess magnetized magnetic toner 6 is attracted toward the sleeve 2. Therefore, the toner does not accumulate in the toner tank 7 and cause the bridging phenomenon.

Further, in the present invention, most of the magnetic toner 6 regulated by the doctor member 8 as described above falls between the inner wall of the toner tank 7 and the sleeve 2.
Therefore, even if impurities such as dust are mixed into the magnetic toner 6, it is unlikely that these impurities will fall directly onto the sleeve 2 and be transported to the developing area together with the magnetic toner attracted to the sleeve 2. Therefore, it is possible to effectively prevent white spots from occurring in the image.

In the above embodiment, the magnetic toner is conveyed by rotating only the sleeve 2, but it is preferable to further rotate the permanent magnet roll 3 in the same direction as the sleeve 2 at a higher speed. When the magnetic toner is conveyed by the rotation of the sleeve only, the magnetic toner is conveyed by the rotation of the sleeve and mainly by the frictional force with the sleeve, so the toner conveying force becomes strong (the Therefore, the amount of magnetic toner passing through the doctor gap increases, and a magnetic brush is formed whose peak height and valley height are both greater than the doctor gap. That is, in the case of sleeve rotation, the photosensitive drum is rubbed by a hard magnetic brush with high bristles, so the image quality tends to be hard. On the other hand, in the case of both rotations, the toner conveying force is stronger than in the case of magnetic rotation, but it is considerably weaker than in the case of sleeve rotation. Further, the toner conveyance speed is a value obtained by subtracting the revolution speed of the sleeve from the rotation speed due to the rotation of the magnet, and is relatively slow. In other words, in the case of both rotations, the toner conveying force is relatively strong, but the toner conveying speed is slow, so a magnetic brush with relatively high spikes is formed, but the magnetic brush makes soft contact with the photoreceptor drum. Therefore, good development can be performed.

Here, the rotation speed of the permanent magnet roll increases in proportion to the toner transport speed, and the magnetic brush also becomes larger. However, if the magnetic brush is too large, the cleaning effect will be strong, while if it is too small, it will not be able to reach the photoreceptor drum enough. Therefore, it is preferable to set the speed to be within a range of 5 to 20 times the circumferential speed of the drum. The circumferential speed of the sleeve is preferably in the range of 0.1 to 0.2 times the circumferential speed of the permanent magnet roll. The direction in which the toner is transported is preferably the same as the direction in which the photoreceptor drum moves.In the opposite case, a toner pool is formed on the downstream side of the toner transport direction in the developing area, and a portion of the toner pool that is away from the permanent magnet roll is formed in the developing area. The toner becomes unstable and fogging tends to occur.
Furthermore, if the developing gap D is too large, the toner pool formed on the upstream side of the developing gap will grow and the contact width between the photoreceptor drum and the magnetic toner will change, while if it is too small, the contact width between the magnetic brush and the drum will be changed. It is preferable to set the doctor gap d to 0.02 to 0.20 mm larger than the doctor gap d because contact cannot be made and the copy density decreases.

In the above embodiment, a cylindrical permanent magnet is used, but the permanent magnet is not limited to this, and for example, a block-shaped permanent magnet may be used. Further, the guide member may be manufactured separately from the doctor member and integrally connected to the doctor member.

[Effects] As described above, according to the magnetic toner developing device of the present invention, it is possible to prevent the bridging phenomenon of excess magnetic toner regulated by the doctor member, and to produce high quality products without white spots. You can get the image.

[Specific example] In FIG. 2, the diameter of the photoreceptor drum 1 is
Using a 120mmφ selenium drum, the circumferential speed is 150mm/
Rotated in sec. Sleeve 2 is made of stainless steel with an outer diameter of 32 mmφ and is rotated at 30 rpm.
The permanent magnet roll 2 consists of a barium ferrite magnet 4 with an outer diameter of 29.3 mmφ and symmetrical magnetization of 10 poles, which has a magnetic flux density of 700 G on a sleeve, fixed to the shaft 5, and is rotated for 500 r in the same direction as the sleeve. Rotated in pm. The doctor member 8 was arranged approximately vertically, and the doctor gap d was adjusted to 0.2 mm. Toner tank 7
, the radius of curvature of the inner wall of the circular arc portion 7a is
It was formed to have a diameter of 21 mm. However, in the above permanent magnet roll, approximately 10mm from the sleeve surface.
Its magnetic attraction works over a long distance.

Set development gap d ₂ to 0.3mm, D.C4000V/
When we made 10,000 copies using magnetic toner with a specific resistance of 10 Ω cm and a particle size of 10 to 20 μm, no toner transport defects occurred, and there were no white spots with a density of 1.2 or higher. Clear images with no fog or fog were obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a conventional magnetic toner developing device, and FIG. 2 is a sectional view showing an embodiment of the magnetic toner developing device of the present invention. 1... Photosensitive drum, 2... Sleeve, 3...
Permanent magnet roll, 6... Magnetic toner, 7... Toner tank, 8... Doctor member.

Claims (1)

[Claims for Utility Model Registration] 1. A permanent magnet roll having a plurality of magnetic poles on its surface, a cylindrical sleeve made of a non-magnetic material rotatably arranged around the permanent magnet roll, and an outer periphery of the sleeve. In a developing device for magnetic toner, the magnetic toner developing device has a toner tank for accommodating magnetic toner, which is installed surrounding a part of the sleeve, and a doctor member that regulates the amount of magnetic toner conveyed on the sleeve. The sleeve is positioned substantially tangentially and substantially perpendicularly to the surface of the sleeve, and a portion of the toner tank located below near the tip of the doctor member is located within the range of the magnetic attraction force of the permanent magnet roll. A developing device for magnetic toner, characterized in that the surface of the magnetic toner contained in the toner tank is at a level substantially equal to or lower than the tip of the doctor member. 2. The developing device for magnetic toner according to claim 1, wherein the permanent magnet roll is rotated in the same direction as the sleeve and at a higher speed than the sleeve.