JPH03122686A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a low-priced developing device whise number of processes from production to assembly is reduced by obtaining such structure that developer is directly conveyed on the surface of a magnetic roller. CONSTITUTION:The device is provided with the cylindrical magnetic roller 9 which is magnetized to have plural magnetic poles, and the developer 8 is held on the magnetic roller 9 with magnetic field generated by the magnetic roller 9 and it is conveyed by rotating the magnetic roller 9. Therefore, a devel oper conveying member which is disposed on the outer periphery side of the magnetic roller 9 in a conventional device is eliminated and the developing device with simple structure is constituted. Since the developer 8 is directly conveyed by the magnetic roller 9, the magnetic field generated by the magnetic roller 9 is the most effectively utilized. Thus, the number of processes from the production to the assembly thereof is reduced and the cost is made low.

Description

[Detailed description of the invention] [Industrial application field] 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. The cylindrical developer transporting member (also referred to as a developing sleeve) has a cylindrical magnetic roller magnetized with a plurality of magnetic poles inside it, and the magnetic roller moves the developer onto the developer transporting member according to the magnetic field generated by the magnetic roller. The device holds the developer and rotates at least one of a magnetic roller and a developer transporting member to transport the developer on the developer transporting member.

[Problem M to be Solved by the Invention] However, in the above-mentioned conventional technology, the outer diameter of the magnetic roller is polished to obtain outer diameter accuracy, and the magnetic roller is disposed with high precision across a small gap from the developer conveying member. This increases the number of man-hours and costs, and requires machining the outer diameter of not only the magnetic roller but also the developer conveying member, making the developing device even more expensive. In addition, there are many parts and components that support the magnetic roller, the developer conveying member, and each of them, which poses an obstacle to reducing the size and weight of the developing device. Furthermore, in order to reduce the unevenness of the developing temperature due to the magnetic pole pitch of the magnetic roller, which is specific to the image obtained when the magnetic roller is rotated, increasing the number of magnetized poles of the magnetic roller allows sufficient space on the developer conveying member. Leakage magnetic flux could not be secured, causing problems in developer transport.

Furthermore, the conventional developing device also has the following problems.

That is, sintered ferrite magnets are generally used as magnets for magnetic rollers. Since ferrite magnets have lower magnetic performance than rare earth magnets, the thickness of the magnet molded body must be increased in order to obtain a sufficient surface magnetic flux density on the developer conveying member. However, since the magnetic performance of ferrite magnets is essentially low, the surface magnetic flux density that can be obtained is limited. In order to achieve color development and high resolution in a developing device, it is necessary to reduce the content of magnetic material in the developer and to reduce the particle size of the magnetic material in the developer. However, at this time, the magnetic performance of the developer decreases, so to compensate for this it is necessary to increase the surface magnetic flux density of the magnetic roller. is difficult to obtain. Furthermore, as mentioned above, the wall thickness of the magnet molded body must be increased in order to obtain the surface magnetic flux density, which makes it difficult to make the magnetic roller smaller and lighter.
Furthermore, since it is difficult to increase the number of magnetic poles, it is difficult to use ferrite magnets when it is necessary to increase the number of poles in a magnet such as the magnetic roller of the present invention. Furthermore, since ferrite magnets have poor temperature characteristics, there is a problem in that the developing temperature of the developing device changes as the temperature changes.

From the above, using a rare earth resin bonded magnet with a magnetic roller instead of a ferrite magnet has many advantages, but this rare earth resin bonded magnet also has the following problems. .

The following two methods are commonly used for forming rare earth resin bonded magnets.

(1) Compression molding method (2) Injection molding method Among these methods, method (2) has a higher degree of freedom in the shape of the molded magnet than method (1), but even with method (2), the magnetic material roller It is difficult to mold the long magnets required for commercial magnets. Furthermore, when making magnets with a high degree of freedom in shape, thermoplastic resins that can be easily molded into various shapes are generally used. However, thermoplastic resins have poor heat resistance and a low glass transition temperature of 37. For example, nylon 12, which is often used in resin-bonded magnets, has a glass transition temperature of 37.
It is ℃. If the heat resistance, particularly the glass transition temperature, is low, distortion or distortion will occur in the magnet molded body in the magnetic rotor even under the usage environment of the developing device. The gap between the developer transport member and the magnet molded body must be made as small as possible in order to obtain as large a magnetic flux density as possible on the surface of the developer transport member, but since the magnet molded body deforms, the gap cannot be narrowed, and the magnet Performance cannot be demonstrated to its full potential. Furthermore, there is a problem in that the deformation of the magnet causes a change in the magnetic flux density on the developer conveying member.

The present invention is intended to solve these problems, and its purpose is to reduce the number of man-hours from manufacturing to assembly by creating a developing device structure that transports developer directly on the surface of a magnetic roller. The purpose of the present invention is to provide a low-cost developing device with less oxidation. Still another object is to provide a small and lightweight developing device. Still another object is to provide a developing device that can obtain a high-density development temperature by effectively utilizing the magnetic field generated by the magnetic roller to ensure a sufficient amount of developer to be conveyed. Still another object is to provide a developing device that can reduce unevenness in developer flow rate due to magnetic rollers and provide high print quality. Another object of the present invention is to provide a stable developing device with less unevenness in developing density due to environmental changes.

[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. The developer is conveyed by holding the developer and rotating a magnetic roller.

Further, the magnetic roller is a rare earth resin bonded magnet made of a rare earth magnetic powder made of a rare earth element (hereinafter referred to as R) and a transition metal mainly composed of cobalt, and a thermosetting resin such as an epoxy resin. It is characterized by being an extruded molded magnet.

Further, the rare earth magnetic powder is characterized in that it is a rare earth magnetic powder consisting of R, a transition metal mainly composed of iron, and boron.

[Function] 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 (magnet) can be most effectively utilized. Furthermore, by forming the magnetic roller using a rare earth magnet with high magnetic properties, it is possible to construct a small and lightweight magnetic roller. Also, compared to ferrite magnets, rare earth magnets
It has good temperature characteristics, and it is possible to reduce development temperature unevenness caused by temperature changes.

The rare earth resin bonded magnet used at this time requires a long magnet in order to be used as a magnetic roller. but,
It is difficult to mold the above-mentioned elongated magnet using conventional methods for molding rare earth resin-bonded magnets, and as a means to solve this problem, it is necessary to mold rare earth resin-bonded magnets by extrusion molding. Unlike conventional compression molding and injection molding, the extrusion molding method is continuous molding, so the length of the molded magnet can be formed as desired, and the molding cost during molding is also reduced. can be done. Also,
In the extrusion molding method, the dimensional accuracy of the molded magnet is good, and secondary processing of the magnet is mostly unnecessary, which also makes it possible to reduce the molding cost. Furthermore, by using a thermosetting resin as the resin for the resin-bonded magnet, the heat resistance, especially the glass transition temperature, is increased. This makes it possible to reduce the development temperature unevenness due to temperature.

Furthermore, thermosetting resins have good chemical resistance and can improve corrosion resistance.

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

[Embodiment] FIG. 1 is a cross-sectional schematic diagram of an image forming apparatus including a developing device in an embodiment of the present invention. The latent image carrier 1 has an organic or aqueous photoconductive photosensitive layer 3 coated on a conductive support portion 2 .

After the photosensitive M3 is charged using a charger 4 such as a corona charger, the light emitted from the light source 5 is transferred to an imaging optical system 6 according to the image.
The photosensitive layer 3 is selectively irradiated with light through the photosensitive layer 3 to obtain a potential contrast and form an electrostatic latent image on the photosensitive layer 3. On the other hand, the developing device 7 charges a developer 8, which is an image forming body, and transports the developer 8 with a cylindrical magnetic roller 9 to carry a latent image in a development gap where the latent image carrier 1 and the magnetic roller 9 are close to each other. The developer 8 is developed according to the electric potential of the electrostatic latent image on the latent image carrier 1 and the bias voltage applied by the developing bias voltage applying means 10, and the electrostatic latent image on the latent image carrier 1 is developed with the developer 8. It is something that can be visualized. 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 transports the developer 8 while regulating the amount by a transport amount regulating member 11. 9 is a cylindrical magnet 12 whose outer periphery is magnetized with multiple poles.
and a soft magnetic cylindrical yoke 13 constitute a magnetic circuit,
The magnetic developer 8 is held directly on the magnetic roller 9 by the magnetic flux leaking around the outer periphery of the magnet 12.
The magnetic flux is rotated to convey the developer 8, and magnetic flux can be used most effectively, and even with a thin magnet, a magnetic binding force greater than that of conventional magnets can be obtained. Note that in FIG. 1, arrows indicate the rotation direction of each member, but this does not limit the present invention.

FIG. 2 is a general view of a magnetic roller of a developing device according to another embodiment of the present invention, in which a developer is applied to the outer circumferential surface of a cylindrical rare earth magnet 22 that is magnetized into multiple poles in the radial direction. The magnetic roller 21 is configured to hold and convey the magnetic material according to the distribution, and a magnetic circuit is constructed by disposing a soft magnetic yoke 23 whose main component is iron or the like on the inner circumferential side of the magnet 22 by adhesive or other means. It is something. Furthermore, the weight of the yoke 23 is also reduced by using a rare earth magnet for the magnet 22 and making the magnet 22 thinner so that the weight of the magnet is less than half that of the conventional one, and the number of magnetized poles of the magnet 22 is multipolarized to 10 or more. I can do it.

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.

FIG. 3 shows the manufacturing process of the rare earth resin bonded magnet used in the magnet roller of the developing device of the present invention.

The rare earth magnetic powder, resin, and additives if necessary are weighed out to a desired mixing ratio and then mixed in a mixer such as a roll mill or extruder to create a compound. This compound is crushed into a size that can be easily fed into a molding machine, and then fed into an extrusion molding machine. The extruder used here was a single screw type extruder. The compound is heated in the extruder to melt the resin, which is then fed into a mold connected to the extruder. The compound is squeezed into the final shape in the mold, and an orienting magnetic field is applied at the tip of the mold to orient the magnet powder to the axis of easy magnetization, or it is cooled without orientation, and then released from the mold as a magnetic compact. being pushed out. At this time, if necessary, install a sizing device at the tip of the mold.

The extruded magnet is taken out and cut into appropriate lengths. After being cut, the magnet with oriented magnet powder is demagnetized,
If thermosetting resin is used, cure it.
Thereafter, it was cut to the final length to form a mag roll magnet.

More detailed examples will be shown below.

(Example 1) Table 1 shows whether or not a rare earth resin bonded magnet used for a magnetic roller can be molded. The resin used here was a thermosetting epoxy resin, and the molded magnet had an outer diameter of 20 mm and an inner diameter of 18. Particularly in the case of anisotropic magnets, it was impossible to mold them at all. However, with the extrusion molding method of the present invention, it was possible to mold not only isotropic magnets but also anisotropic magnets.

(Example 2) Investigating the effect of changing the type of resin in a rare earth resin bonded magnet Various thermosetting resins were used as examples of the present invention, and polyamide resin, which is a thermoplastic resin, was used as a comparative example. (Nylon 12) was used. Nylon 12 is commonly used as a resin for injection molding of resin-bonded magnets, and as a thermoplastic resin, it has excellent properties such as heat resistance, and as shown in Table 2, it is often used in magnetic rollers. When molding a long magnet, it is impossible or possible to use a resin that is either impossible or possible using conventional methods for manufacturing rare earth resin-bonded magnets. Second
The table shows the resins used. Resin E is the resin used in the comparative example. As can be seen from the table, thermosetting resins have excellent heat resistance.

Table 3 shows the water absorption, chemical resistance, and coefficient of thermal expansion of each resin.

Regarding the coefficient of thermal expansion, the value of thermosetting resin is generally lower than that of nylon 12. Therefore, the dimensional change due to temperature of the molded magnet can be reduced. It becomes possible to suppress changes in magnetic flux due to C.

In addition, dimensional changes in the magnet molded body during molding can be reduced, and the dimensional accuracy of the magnet molded body without secondary processing is 0.03 mm in outer diameter when made with epoxy resin and 0.07 mm in the case of nylon 12. Met. Therefore, compared to thermoplastic resins, it can be molded with good dimensional accuracy without secondary processing, and costs can be reduced. Furthermore, in terms of water absorption, thermosetting resins have low water absorption, which makes it possible to suppress dimensional changes under the usage environment. Because of these factors, dimensional accuracy during molding is good, and dimensional changes during use are small, so dimensional changes on the magnetic roller surface can be suppressed, thereby reducing uneven development due to environmental changes in the developing device. It became possible.

(Example 3) A developing device as shown in FIG. 1 was composed of a molded magnet with an outer diameter of 20 mm and an inner diameter of 18 mm, and a yoke with an outer diameter of 18 mm and an inner diameter of 16 mm that constituted a magnetic circuit therein. However, when using a ferrite magnet as a comparative example, the thickness of the magnet was 4 mm and the outer diameter of the yoke was 12 mm.
And so. Table 4 shows the magnets used here. Magnet 1~
The magnets up to No. 4 were extruded magnets bonded with rare earth resin, and the amount of magnet powder filled was 65vol%. Magnets 1.2.4 were radially anisotropic magnets and magnet 3 was an isotropic magnet.

Magnet 5 was a sintered ferrite magnet. Among these, magnet 4.5 is a comparative example of the present invention. The surface magnetic flux in the table represents the surface magnetic flux density on the surface of the magnet roller when each magnet is used in the magnet roller of the present invention Table 4 *: unit G. At this time, the rare earth resin bonded magnet was magnetized with 40 multi-poles, and the ferrite magnet was magnetized with 16 poles. When a ferrite magnet was magnetized further, a surface magnetic flux of 700G or more could not be obtained.As is clear from Table 1, by using a rare earth resin bonded magnet, the amount of magnet used can be reduced and the surface magnetic flux can be reduced. It was possible to obtain an increase. Furthermore, when resin E, which is a thermoplastic resin, is used as the resin, the surface magnetic flux is reduced compared to when a thermosetting resin is used. This is thought to be because the magnetic powder deteriorated during molding due to the high molding temperature when thermoplastic resin was used. When a magnetic roller was created using these magnets, a surface magnetic flux of 500 G or more was obtained for magnets 1 to 5, so that sufficient developer spikes and conveyance amount were obtained. Furthermore, when image formation was performed using the developing device shown in Fig. 1, magnets 1 to 4
If the magnetic roller is moved at a linear velocity that is more than twice the linear velocity of the latent image carrier, unevenness in the developing temperature becomes almost invisible to the naked eye, and images with high density and contrast can be stably formed. We were able to. On the other hand, when the magnet 5 is used, if the magnetic roller is moved at a linear velocity that is more than twice the linear velocity of the latent image carrier, uneven development can be visually confirmed, and an image with high contrast cannot be obtained at too high a temperature. I couldn't do it.

Next, when a developing device using magnet 1.4 described above was installed in an environment with temperature changes and development was performed, it was found that when magnet 1 using thermosetting resin was used, the developed density was almost invisible by visual inspection. Although no unevenness was observed, when the magnet 4 made of thermoplastic resin was used, unevenness in developer density was visually observed as the temperature changed.

[Effects of the Invention] As described above, according to the present invention, by holding and conveying the developer directly on a cylindrical magnetic roller magnetized with a plurality of magnetic poles, the number of man-hours from manufacturing to assembly can be reduced. Therefore, it is possible to provide a low-cost developing device with a small amount of damage. Also,
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 achieve high-temperature development density. A developing device that can provide sufficient magnetic properties to hold and transport developer even when the magnet is magnetized with multiple poles, reduces uneven development density due to magnetic rollers, and provides high print quality. can be provided. Further, it is possible to provide a developing device that is stable against changes in the environment.

Furthermore, by using a rare earth resin bonded magnet as the magnet of the magnetic roller, it is possible to provide a developing device that can obtain a magnetic field sufficient to hold and transport the developer even if the thickness of the magnet is reduced. .

Furthermore, by using an extruded 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. I can do it.

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, and FIG. 2 is a schematic diagram of a magnetic roller of a developing device according to another embodiment of the present invention. FIG. 3 is a diagram showing the manufacturing process of the rare earth resin bonded magnet used in the magnet roller of the developing device of the present invention. 8: Developer 9.21: Magnetic roller 12.22: Magnet 13, 23: Above yoke

Claims (3)

[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 configured to transport the developer. (2) The magnetic roller is a rare earth resin bonded magnet made of a rare earth magnetic powder made of a rare earth element (hereinafter referred to as R) and a transition metal mainly composed of cobalt, and a thermosetting resin such as an epoxy resin; 2. The developing device according to claim 1, wherein the developing device is a molded magnet formed by extrusion molding. (3) The developing device according to claim 1 or 2, wherein the rare earth magnetic powder is a rare earth magnetic powder consisting of R, a transition metal mainly composed of iron, and boron.