JPH0344670A - Developing device - Google Patents

Abstract

PURPOSE:To effectively utilize magnetic field generated by a magnetic roller, to secure the sufficient conveying quantity of developer and to accomplish high-density development by spirally magnetizing the magnetic roller. CONSTITUTION:The magnetic roller 9 holds the supplied developer 8 with magnetic force and the conveying quantity of the developer is regulated to be proper by a conveying quantity regulating member 11. The roller 9 constitutes a magnetic circuit with a magnet 12 and a yoke 13. The developer 8 is conveyed by rotating the roller 9 in a state where the magnetic developer 8 is directly held on the roller 9 with leakage magnetic flux on the outer periphery of the magnet 12. By spirally magnetizing the roller 9, a magnetic brush is spirally formed and the vectors of the rotation and the revolution of the magnetic brush respectively have component in an axial direction, then effects for stirring and electrostatically charging the developer are enhanced and filming is prevented. Therefore, the sufficient conveying quantity of the developer is secured and the high-density development is accomplished.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a magnetic brush developing device.

[Prior Art] Conventional developing devices are known as magnetic brush developing devices (-component magnetic brushes and two-component magnetic brushes) and are made of rotatable non-magnetic and conductive materials such as stainless steel, aluminum, and brass. Inside the cylindrical developer conveying member (also referred to as a developer non-leave), there is a cylindrical magnetic roller magnetized with a plurality of uniform magnetic poles in the longitudinal direction. Therefore, the developer is held on the developer transport member and at least one of the magnetic roller and the developer transport member is rotated to transport the developer on the developer transport member.

FIG. 2 is a cross-sectional schematic view of a developer conveying member and a magnetic roller of a developing device in a conventional example. Conventional developing devices are known as magnetic brush developing devices (-component magnetic brushes and two-component magnetic brushes), which are rotatable non-magnetic and conductive cylindrical developing devices typically made of stainless steel, aluminum, or brass. The developer conveying member 17 (also referred to as a developing sleeve) has a cylindrical magnetic roller 19 magnetized to a plurality of 611 poles uniformly in the longitudinal direction, and the developer is transferred according to the magnetic field generated by the magnetic roller 19. The device holds the developer 8 on the conveying member 17 and rotates at least one of the magnetic roller 19 and the developer conveying member 17 to convey the developer 8 on the developer conveying member 17. 19 used a sintered ferrite magnet.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, it is necessary to uniformly magnetize the magnet in the longitudinal direction (axial direction) in order to eliminate uneven development density, but this is not easy. There wasn't. In addition, the number of magnetized poles of the magnetic roller is increased in order to reduce uneven development density due to the magnetic pole pitch of the magnetic roller, which is specific to images obtained when at least one of the developer transport member and the magnetic roller is rotated. In this case, sufficient leakage magnetic flux could not be secured on the developer transport member, causing problems in the transport of the developer.

Further, in the above-mentioned conventional technology, not only is the processing yield poor because the sintered magnet is brittle, but also it is difficult to reduce the size and weight of the magnetic roller because the thickness of the magnetic roller in the direction of magnetization cannot be reduced.

In addition, in the conventional technology described above, it is necessary to polish the outer diameter of the magnetic roller to obtain outer diameter accuracy and to arrange it with high precision across a small gap from the developer conveying member, which increases the number of man-hours and costs. This makes the developing device even more expensive as it is necessary to process the outer diameter of not only the magnetic roller but also the developer conveying member.In addition, the magnetic roller, the developer conveying member, and the parts and structures that support each of them have to be machined. The large number of parts made it difficult to make the developing device smaller and lighter.

The present invention is intended to solve these problems, and its purpose is to effectively utilize the magnetic field generated by the magnetic roller to ensure a sufficient amount of developer conveyance to achieve high developer density. The purpose of the present invention is to provide a developing device that can be obtained. Still another object is to provide a developing device that can reduce unevenness in developing density due to magnetic rollers and provide high print quality. Still another object is to provide a small and lightweight developing device. Still another object is to provide a low-cost developing device with fewer man-hours from manufacturing to assembly by having a developing device structure in which developer is directly conveyed on the surface of a magnetic roller.

[Means for Solving the Problems] The developing device of the present invention has a cylindrical magnetic roller magnetized with a plurality of magnetic poles, and uses a magnetic field generated by the magnetic roller to transfer the developer onto the magnetic roller. In the developing device that transports the developer by holding and rotating a magnetic roller, the magnetic roller is helically magnetized.

Further, the developing device of the present invention is characterized in that the magnetic roller includes a rare earth magnet.

Furthermore, the developing device of the present invention is characterized in that the magnetic roller includes a shaped magnet.

Further, the developing device of the present invention is characterized in that the magnetic roller includes a magnet and a soft magnetic yoke inside the magnet.

Furthermore, the developing device of the present invention is characterized in that the molded magnet is a compression molded magnet, an injection molded magnet, or an extrusion molded magnet.

[Function] According to the above configuration of the present invention, by magnetizing the magnetic roller in a spiral shape, the rotation and revolution vectors of the magnetic brush each have a component in the longitudinal direction (axial direction).
The effects of developer agitation and developer charging can be enhanced, and furthermore, filming can be prevented.

In addition, by forming a magnetic roller using a rare earth magnet with high magnetic properties, multi-pole magnetization is possible, and sufficient magnetic properties can be obtained by making it into a thin cylindrical shape, and it is possible to suppress unevenness in development density. I can do it.

Furthermore, small and lightweight magnetic rollers can be constructed by forming magnetic rollers using rare earth magnets, and the magnets can be molded by injection molding, compression molding, or extrusion molding to achieve good dimensional accuracy and eliminate the need for post-processing. A magnetic roller can be constructed, and in particular, a soft magnetic yoke constituting a magnetic circuit can be incorporated inside the magnetic roller to improve mechanical strength and magnetic properties.

Further, according to the above-described configuration of the present invention, it is possible to configure a developing device with a simple structure by omitting the developer conveying member conventionally disposed on the outer peripheral side of the magnetic roller. Furthermore, since the developer is directly conveyed by the magnetic roller, the magnetic field generated by the magnetic roller can be utilized most effectively.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Embodiment FIG. 1 is a cross-sectional view of an image forming apparatus including a developing device according to an embodiment of the present invention. The latent image carrier 1 has an organic or inorganic photoconductive layer 3 coated on a conductive support portion 2 .

After the photosensitive layer 3 is charged using a charger 4 such as a corona charger, light emitted from a light source 5 is transferred to an imaging optical system 6 according to an image.
The photosensitive layer 3 is selectively irradiated with light through the photosensitive layer 3 to obtain a potential contrast and form an A i latent image on the photosensitive layer 3. on the other hand,
The developing device 7 charges the developer 8, which is an image forming body, and conveys it with a cylindrical magnetic roller 9 to form the latent image carriers 1 and 6!
The developer 8 is applied in accordance with the potential of the electrostatic latent image on the latent image carrier 1 and the bias voltage by the development bias voltage applying means 10 at the development gap portion where the i-type material roller 9 is close to the development gap.
The electrostatic latent image on the latent image carrier 1 is visualized using the developer 8. The developer 8 that has visualized the electrostatic latent image is transferred onto a recording paper 15 by a transfer device 14 using corona discharge, an electric field, pressure, or adhesive force, and the developer 8 is recorded by means such as pressure or heating. The developer 8 is fixed on the paper 15 to obtain a desired image on the recording paper 15. In the developing device shown in FIG. 1, the magnetic roller 9 holds the supplied developer 8 by magnetic force, and the conveyance amount regulating member 1
1 to transport the developer 8 while regulating the appropriate amount,
The magnetic roller 9 has a cylindrical shape and constitutes a magnetic circuit with a magnet 12 whose outer periphery is magnetized into a plurality of spiral poles and a soft magnetic cylindrical yoke 13, and leakage magnetic flux from the outer periphery of the magnet 12 causes 6!
This system transports the developer 8 by rotating the magnetic roller 9 while directly holding the i-type developer 8 on the magnetic roller 9. This allows for the most effective use of magnetic flux, and even with thin magnets, it is faster than conventional ones. A magnetic binding force of Note that in FIG. 1, arrows indicate the rotation direction of each member, but this does not limit the present invention.

FIG. 3 is a general view of magnetization of a magnetic roller of a developing device in an embodiment of the present invention. When the axial magnetization width of the magnetic roller is d, and the helical pitch of the helical magnetization is p, p=2d, which indicates the case where the magnetic roller is apparently densely magnetized with multiple poles. There is. When actually magnetizing, it is possible to magnetize the entire circumference of the magnetic roller with one N pole and one S pole, and it is easy because it can be done while rotating the magnetic roller. By using a rare earth magnet with excellent magnetic properties for the magnetic roller, a thin cylindrical magnetic roller can be formed, and the wall thickness can be reduced to 0. It can be made as thin as about 5 mm, and sufficient magnetic flux on the surface of the magnetic roller can be ensured even when multi-pole magnetization is performed with the magnetization width being about as thick as the wall.

When the magnetic roller is magnetized in a spiral shape, the magnetic brush is formed in a spiral shape. Therefore, the rotation of the magnetic plan,
Since each of the revolution vectors has a component in the longitudinal direction (axial direction), it is possible to enhance the effects of developer stirring and developer charging, and to prevent filming. Further, even if the magnetization of each magnetic pole is not completely uniform, the unevenness in the image is not visually discernible because the unevenness is created randomly by rotating the magnetic roller.

FIG. 4 is a general view of magnetization of a magnetic roller of a developing device in another embodiment of the present invention. In this example, p>2d, and since the number of magnetized poles is small, magnetization is easy, and a large leakage magnetic field on the magnetic roller can be obtained.

When the magnetic roller is magnetized in a spiral, the magnetic brush is formed in a spiral. Therefore, the rotation and revolution vectors of the magnetic brush each have a component in the longitudinal direction (axial direction). It is possible to enhance the effect of charging the developer and prevent filming, and even if the magnetization of each magnetic pole is not completely uniform, by rotating the magnetic roller, each unevenness will occur randomly. Therefore, unevenness in the image cannot be visually identified.

FIG. 5 is a cross-sectional schematic diagram of a magnetic roller of a developing device according to an embodiment of the present invention, and shows a magnetic field distribution of developer on the outer peripheral surface of a cylindrical rare earth magnet 22 magnetized with multiple poles in the radial direction. The magnetic roller 21 has a soft magnetic yoke 23 mainly made of iron or the like arranged on the inner circumferential side of the magnet 22 by adhesive or other means to form a magnetic circuit. It is. Furthermore, a rare earth magnet is used for the magnet 22 to make the magnet 22 thinner and the weight of the magnet less than half that of the conventional magnet. Yoke 2 with multi-pole magnetization
3 can also be reduced in weight. In addition, after the soft magnetic yoke 23 is placed in a mold in advance during magnet molding, a magnetic material containing magnetic powder, resin, etc. is injection molded on the outer periphery of the soft magnetic yoke 23, and the magnet 22 and yoke 23 are integrally molded to form a magnetic roller. 2
1, it can be easily integrally molded as is known in plastic injection molding, and the wall thickness of the magnet can be reduced to 0. 5-2m
Sufficient mechanical strength can be obtained even when the thickness is as thin as m, and the deflection of the outer diameter portion of the magnetic roller 21 can be reduced, and fluctuations in the amount of developer conveyed and fluctuations in the development gap can be reduced. As the developer used in the present invention, all developers known as a -component magnetic brush developer and a two-component magnetic brush developer are applicable. Further, as the magnet material of the magnetic roller used in the present invention, known magnet materials such as ferrite magnets, alnico magnets, manganese aluminum magnets, and rare earth magnets can be used. In particular, atomic number 5
Fe
By using rare earth magnets containing 3D transition metals such as Ni and Co, it is possible to construct small and lightweight magnetic rollers that can obtain a high magnetic field even with a thin wall.
By using molded magnets that use not only sintering manufacturing methods but also compression molding, injection molding, and extrusion manufacturing methods, magnets can be made not only small and lightweight, but also have a high degree of freedom in shape and a large degree of freedom in magnetic field distribution. In addition, in the case of molded magnets, the yokes, etc. that make up the magnetic circuit can be formed integrally during molding.
Dimensional accuracy has been improved, such as reducing the runout of the outer diameter without any post-processing, and since no adhesive is used, variations in the magnetic resistance of the magnetic circuit are small, making the magnetic flux density on the magnet surface uniform and reducing the amount of developer conveyed due to variations in magnetic flux. It is possible to reduce fluctuations in the amount of development and fluctuations in the amount of development. Furthermore, since the magnet can be made thinner, even small-diameter magnets can be easily magnetized with multiple poles by arranging magnetizing yokes on the inside and outside. Fluctuations in conveyance amount and development amount can be reduced.

Although the embodiments have been described above, the present invention can be applied not only to the above embodiments but also to a wide range of developing devices such as electrophotography.
It is especially effective when applied to printers, copiers, facsimiles, and displays.

[Effects of the Invention] As described above, according to the present invention, since the magnetic roller is magnetized in a spiral manner, the rotation and revolution vectors of the magnetic brush can each have axial components, and the development It can enhance the effects of developer agitation and developer charging, and prevent filming.Also, by using a rare earth magnet as the magnet of the magnetic roller, the thickness of the magnet can be made thinner, and it can be magnetized with more poles. However, it is possible to provide a developing device that can obtain a magnetic field sufficient to hold and transport the developer.

Furthermore, by using a shaped magnet as the magnet of the magnetic roller, it is possible to construct an efficient magnetic circuit with fewer processing and assembly steps, good dimensional accuracy, and low magnetic resistance.

Furthermore, by using a magnetic roller structure that includes a soft magnetic yoke inside the magnet, an efficient magnetic circuit can be constructed and sufficient magnetic flux can be obtained to hold and transport the developer on the surface of the magnetic roller. can.

Furthermore, by using compression molded magnets, injection molded magnets, or extrusion molded magnets as magnets for magnetic rollers, it is possible to obtain magnetic rollers that require fewer processing and assembly steps, have good dimensional accuracy, and have excellent moldability even with thin walls. It is possible to obtain sufficient magnetic flux to hold and transport the developer on the surface of the magnetic roller.

Furthermore, by separately magnetizing the magnets of the magnetic roller, it is possible to provide a developing device that reduces unevenness in development density due to the magnetic roller and provides high print quality.

Furthermore, by holding and transporting the developer directly on a cylindrical magnetic roller magnetized with a plurality of magnetic poles, it is possible to provide a low-cost developing device with fewer man-hours from manufacturing to assembly. .

Further, since the structure is simplified, it is possible to provide a small and lightweight developing device. Furthermore, since the developer is conveyed by leakage magnetic flux on the surface of the magnetic roller, the developing device can effectively utilize the magnetic field generated by the magnetic roller to ensure a sufficient amount of developer to be conveyed and obtain a high developer density. A developing device that can provide sufficient magnetic properties to hold and transport developer even if the magnet is magnetized with multiple poles, reduces uneven development density due to magnetic rollers, and provides high print quality. can be provided.

As described above, the present invention has the excellent effect of providing a developing device that is small, lightweight, inexpensive, and capable of forming high-quality images.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional schematic diagram of an image forming apparatus including a developing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional schematic view of a developer conveying member and a magnetic roller of a developing device in a conventional embodiment. FIG. 3 is a general view of magnetization of a magnetic roller of a developing device in an embodiment of the present invention. FIG. 4 is a general view of magnetization of a magnetic roller of a developing device in another embodiment of the present invention. FIG. 5 is a cross-sectional schematic view of a magnetic roller of a developing device in an embodiment of the present invention. 8: Phenomenon symmetry J9.21: Magnetic roller 12.
22: Magnet 13.23 + yoke Figure 1 Latent image carrier 2 Figure 10 Funeral diagram 10 Funeral diagram

Claims (6)

[Claims] (1) A cylindrical magnetic roller magnetized with a plurality of magnetic poles is provided, the developer is held on the magnetic roller by a magnetic field generated by the magnetic roller, and the magnetic roller is rotated. A developing device for conveying the developer, wherein the magnetic roller is spirally magnetized. (2) When the magnetization width of the magnetic pole in the axial direction of the magnetic roller is d, and the helical pitch of the spiral magnetization is p, p≧2d is satisfied. developing device. (3) The developing device according to claim 2, wherein the magnetic roller includes a rare earth magnet. (4) The developing device according to claim 2 or 3, wherein the magnetic roller includes a shaped magnet. (5) The developing device according to claim 2, wherein the magnetic roller includes a magnet and a soft magnetic yoke inside the magnet. (6) The developing device according to claim 4, wherein the molded magnet is a compression molded magnet, an injection molded magnet, or an extrusion molded magnet.