JPH03116078A - Developing device - Google Patents

Abstract

PURPOSE:To execute the color conversion and to attain high resolution by using an extrusion molding magnet of a rare earth resin coupling type consisting of rare earth magnet powder and a thermoplastic resin such as a polyamide resin, etc., as a magnet roller. CONSTITUTION:A magnetic material roller 8 is an extrusion molding magnet of a rare earth resin coupling type consisting of rare earth magnetic powder consisting of a transition metal mainly composed of a rare earth element and cobalt, and a thermoplastic resin such as a polyamide resin, etc. Accordingly, a small sized and light weight magnetic material roller 8 in which wall thickness of a magnet formed body is thin can be constituted, and also, since the magnetic performance of the magnet is improved, the magnetic flux density on the surface of a developer carrying member 7 can be raised. In such a way, by decreasing the content of a magnetic material in a developer 11, and making a particle size of the magnetic material small, the color conversion and the high resolution of a developing device can be attained.

Description

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

[Prior Art] A conventional developing device, known as a magnetic brush developing device (-component magnetic brush and two-component magnetic brush), has a plurality of magnetic poles inside a rotatable non-magnetic cylindrical developer conveying member. It has a cylindrical magnetic roller magnetized to convey the developer on the developer conveying member according to the magnetic field generated by the magnetic roller, and the magnetic roller has a sintered ferrite magnet. was used.

[Problems to be Solved by the Invention] However, the above-mentioned prior art has the following problems.

That is, sintered ferrite magnets are generally used as magnets for magnetic rollers. Ferrite magnets have lower magnetic performance than rare earth magnets, so in order to obtain sufficient surface magnetic flux density on the developer conveying member, the thickness of the magnet molded body must be increased. However, the shape of the magnetic roller etc., 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.
In order to do this, it is difficult to obtain a surface magnetic flux density higher than the current surface magnetic flux density using a ferrite magnet with low magnetic performance. Furthermore, as mentioned above, in order to obtain the surface magnetic flux density, the thickness of the magnet molded body must be increased, making it difficult to make the magnetic roller smaller and lighter.Furthermore, it is difficult to make the magnetic roller smaller and lighter. However, even if the magnetic roller is rotated at high speed, the image obtained by developing the developer has a problem that unevenness in development density occurs due to the magnetic pole pitch of the magnetic roller.

Furthermore, since ferrite magnets have poor temperature characteristics, there is a problem in that the developing density of the developing device changes as the temperature changes.

From the above, there are many advantages to using a rare earth resin bonded magnet as a magnetic roller instead of a ferrite magnet, 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. In particular, when molding anisotropic long magnets in which magnetic powder is oriented in order to improve the magnetic performance of the magnet, there is a problem that conventional molding methods cannot be used.

The resin used for the rare earth resin bonded magnet is generally a thermosetting resin or a thermoplastic resin. However, in the case of thermosetting resin, a curing process for curing the resin is required during the magnet manufacturing process. As a result, the number of steps required during magnet molding increases, causing an increase in magnet molding costs.Furthermore, heat curing molding during extrusion molding makes it difficult to recycle defective products, which also causes an increase in costs. When rare earth magnet powder is used as the magnet powder, the amount increases compared to when a ferrite magnet is used, so reducing the molding cost is an important factor. In addition, thermosetting resins have the problem that they are difficult to mold because the resin tends to change in quality during molding.

Therefore, the present invention is intended to solve the above-mentioned problems, and its purpose is to reduce the content of magnetic material in the developer, and to improve colorization and high resolution by making the magnetic material finer particles. The goal is to provide a developing device with the highest possible performance. Another object of the present invention is to provide a developing device that is more stable in the environment in which the developing device is used, such as by reducing unevenness in developer density. Still another object is to provide a developing device having a small and lightweight magnetic rotor at a lower cost.

[Means for Solving the Problems] The developing device of the present invention has a cylindrical magnetic roller magnetized with a plurality of magnetic poles inside a rotatable non-magnetic cylindrical developer conveying member, In a developing device that transports the developer on the developer transporting member according to a magnetic field generated by the magnetic roller, the magnetic roller is made of a transition metal mainly consisting of a rare earth element (hereinafter referred to as R) and cobalt. This is a rare earth resin bonded magnet made of rare earth magnetic powder and a thermoplastic resin such as polyamide resin, and is characterized by being an extrusion 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 configuration of the present invention, by forming the magnetic roller using a rare earth resin-bonded magnet with high magnetic performance, it is possible to create a small and lightweight magnetic roller with a thin magnet molded body. It becomes possible to configure. In addition, the improved magnetic performance of the magnet makes it possible to increase the magnetic flux density on the surface of the developer conveying member, thereby reducing the content of magnetic material in the developer and reducing the particle size of the magnetic material. By doing so, it is possible to make the developing device color and high resolution.If? becomes. In addition, rare earth magnets have better temperature characteristics than ferrite magnets, making it possible to reduce unevenness in developing temperature due to 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. However, 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. In addition, the extrusion molding method has good dimensional accuracy of the molded magnet, and secondary processing of the magnet is mostly unnecessary, which also makes it possible to reduce the molding cost. Furthermore, by using thermoplastic resin as the resin for resin-bonded magnets, it is possible to reduce molding costs by simplifying the molding process and making it possible to recycle the magnet compound. By reducing the weight, it becomes possible to provide a high-performance magnetic roller at a very low cost. Furthermore, due to the good moldability due to the use of thermoplastic resin, it is possible to provide this magnet relatively easily.

[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 example is an example of one-component development. In FIG. 1, reference numeral 1 denotes a latent image carrier, which has a photoconductive layer 3 coated on a conductive support 2. After the photosensitive layer 3 is charged to a predetermined potential using a charger 4, the light emitted from a light source 5 such as a laser is scanned using a rotating polygon mirror (not shown), and exposed to light by an imaging optical system 6. An electrostatic latent image is formed on the latent image carrier 1 by forming an image on the layer 3 to obtain a potential contrast.

On the other hand, 12 in the figure is a developing device and a developer (
Hereinafter, toner (hereinafter referred to as toner) 11 is charged and carried by a developer conveying member 7. The developer conveyance body 7 has a cylindrical magnetic roller 8 disposed inside a cylindrical non-magnetic sleeve 9 with a gap therebetween, and a conductive and flat plate adjacent to the developer conveyance body 7 as a conveyance amount regulating member. A shaped blade 10 is provided.

The toner 11 is held on the developer conveyance body 7 by the magnetic flux generated by the magnet roller 8, the conveyance amount is regulated by the blade 10, and the toner 11 is conveyed to the development gap portion 16 where the latent image carrier 1 and the developer conveyance body 7 are close to each other. to form a developing nip. In the development gap section 16, the toner 11 is developed on the latent image carrier 1 according to the electrostatic latent image and the development electric field by the development bias applying means 13 (connected between the conductive support section 2 and the sleeve 9). be done. Further, the visualized image is electrostatically transferred to a recording paper 15 or the like by a transfer device 14, and fixed by means such as pressure or heating to obtain a desired image.

Here, in FIG. 1, the potential of each part is 0 [V]- for the conductive support part 2 of the latent image carrier 1, and the sleeve 9
is set to -500 [V], and the gap between the latent image carrier 1 and the magnet roller 7 is set to 0.2 [mm].
l, the distance between the magnetic roller 7 and the blade is 0.
When set to 15 [mm], it became possible to form a toner image with high contrast and excellent temperature gradation.

It should be noted that the configuration shown in FIG. 1 does not limit the present invention, and the above-mentioned numerical values also do not limit the present invention. It goes without saying that all known developers can be used.

FIG. 2 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,
As a comparative example, when a thermosetting resin was used, it was cured and then cut to the final length to form a mag roll magnet.

More detailed examples will be shown below.

(Example 1) Table 1 shows the rare earth resin bond W i used in the magnetic roller.
It shows whether or not the ff stone can be formed. The resin used here was thermoplastic nylon 12, and the shape of the molded magnet was 18 mm in outer diameter and 16 mm in inner diameter. This is not possible using conventional methods for manufacturing rare earth resin-bonded magnets, or even if it is possible, it is very difficult. 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 1 Various thermoplastic resins were used as examples of the present invention, and epoxy resin, which is a thermosetting resin, was used as a comparative example. It was used. Table 2 shows the resins used.

The resins in Table 2 are the resins used in the comparative examples. Resins A to C are those used in conventional injection molding methods. Table 3 shows the results when these resins were used in extrusion molding. Sample 4 is the result when a thermosetting resin was used as a comparative example. First, regarding moldability, resin A-
When resin C, which has high heat resistance, is used, the moldability is slightly degraded due to the high molding temperature of the resin, but the moldability is good overall. In addition, the defective product No. 3
A front cycle was also possible. On the other hand, in the case of sample 4, which uses a thermosetting resin, during extrusion molding, the compound round was heated and melted in order to give fluidity to the magnetic compound. Molding was difficult because it increased due to deterioration. Next, regarding cost, when resin resin is used, a curing process is essential after extrusion molding, and the inclusion of this process increases the cost of molding the magnet. Furthermore, when resin resin is used, there is no recyclability, which also increases molding costs. On the other hand, when thermoplastic resin is used, there is no need for a curing process, and the final magnet molded body can be obtained by simply cutting the extrusion molded product, thereby reducing molding costs. Ta.

(Example 3) The relationship between the magnetic powder content in the toner, the image temperature, and the background fogging temperature was investigated by changing the type of magnet used in the magnet roller. The magnet used here is S as an example.
An m-Co-based anisotropic resin-bonded magnet, a Nd-Fe-B-based isotropic resin-bonded magnet, and a sintered ferrite magnet were used as a comparative example. 3m-Co and Nd-Fe-
The B-type magnets both had a magnetic powder content of 66vol%, thermoplastic nylon 12 was used as the resin, and both were made by extrusion molding. The magnetic performance of the magnet used here is an Sm-Go anisotropic magnet (hereinafter referred to as magnet 1).
), Nd-Fe-B isotropic magnet (hereinafter referred to as magnet 2), sintered ferrite magnet (hereinafter referred to as magnet 3), respectively (BH), □, 10MGOe, 7MGOe, 4M
It was GOe. The shape of the magnet used in the magnetic roller was 18 mm in outer diameter, 14 mm in inner diameter, and 216 mm in length. First, regarding the magnetic powder content of the developer and the image temperature of a solid image, sufficient values of OD values of 1.2 or more were obtained for all magnets 1 to 3 by adjusting the development bias voltage. When the magnetic roller No. 3 was used, it became difficult to form a magnetic brush when the magnetic powder content of the developer was less than 30 wt%, and it was difficult to further reduce the magnetic powder content. On the other hand, when a magnetic roller using magnets 1 and 2 is used, the magnetic powder content of the developer is 3.
It is possible to form a magnetic brush even with less than 0 wt%, and in the case of magnet 1, the developer contains magnetic powder fi 15
In the case of magnet 2, it was also possible to reduce the content to 18 wt%. Next, the relationship between the magnetic powder content (■) of the developer and the background image flux (fog) is almost unaffected by the adjustment of the developing bias voltage, and when magnet 3 is used, the magnetic powder content is 40 wt. % or less, developer adhesion occurred in the background area. When magnets 1 and 2 were used, it was possible to form images with small fog up to a magnetic powder content of about 25 wt%.

In particular, when Magnet 1 was used, it was possible to form images with less fog up to 20 wt%.

(Example 4) Using a developing device as shown in FIG.
8 [emu/gl), 4 wt% of carbon black, and about 1 wt% of other additives before addition, the number average particle diameter was 8 μm and the saturation magnetization was 26 emu/g.
Using a one-component magnetic developer, the development bias voltage is -50
The image was developed by applying 0 V and transferred and fixed onto plain paper to form an image.

Here, as the magnet roller, magnets 1 and 2 were used as an example of the present invention, and magnet 3 was used as a comparative example. When magnets 1 and 2 are used, a magnetic brush sufficient to transport the developer 1 is formed on the developer transport member 2, and the maximum O
With a D value of 1.5, a high-contrast image with no fog in the background was obtained, and a resolution of 600 DPI was obtained, allowing even small characters of about 3 points to be formed accurately. 0 again,
When magnet 1 is used for a small pixel of 5 mm square, approximately 1
When magnet 2 was used, an area gradation of approximately 64 gradations was obtained. On the other hand, when the magnet 3 is used, a magnetic brush is formed on the developer transport member 2 to transport the developer 1, and a high density image with a maximum OD value of 1.5 in the solid image area can be obtained. Excessive fogging occurred in some areas, resulting in only low-quality images.

(Example 5) Using a developing device as shown in FIG. 1, developer 1 was added to a polyester resin with ferrite particles (
The composition was a mixture of 30 wt% of saturation magnetization (88 [emu/g]), 4 wt% of cyan colorant, and about 1 wt% of other ingredients before addition, and the number average particle diameter was 6 μm and the saturation magnetization was 26 emu/g.
Using a u/g one-component magnetic developer, the image was developed by applying a developing bias voltage of -450 V, and then transferred and fixed onto plain paper to form an image. Here, as the magnet roller, magnets 1 and 2 were used as an example of the present invention, and magnet 3 was used as a comparative example. When magnets 1 and 2 are used, a magnetic brush of cyan developer is formed on the developer transport member 2, resulting in a high contrast image with less color turbidity, a maximum OD value of 1.5, and no background fog. Obtained. Similar results were also obtained when yellow developer and magenta colorant were used instead of cyan colorant. On the other hand, when the magnet 3 is used, a magnetic brush is formed on the developer conveying member 2, and an image with a maximum OD value of 1.5 and a high hot water density in the solid image area can be obtained, but a dark spot with almost no gradation is obtained. I could only get low quality images.

[YA Ming Effect] As described above, according to the present invention, a rare earth resin-bonded extrusion-molded magnet made of rare earth magnet powder and a thermoplastic resin such as a polyamide resin is used as the magnet roller, so that the developer By reducing the content of the magnetic material therein or reducing the particle size of the magnetic material, it becomes possible to provide color development devices and higher resolution.

In addition, by extrusion-molding thermoplastic resin as the resin for resin-bonded magnets, it becomes easier to mold and manufacture high-performance magnet roller magnets that enable color development and high-resolution development devices. This makes it possible to provide a magnetic roller with good performance. In addition, good productivity and simplification of the manufacturing process,
The compound's good recyclability makes it possible to provide high-performance magnetic rollers at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a developing device in an embodiment of the present invention. FIG. 2 is a schematic diagram of the manufacturing process of the rare earth resin bonded magnet used in the magnet roller of the developing device of the present invention. 7, developer conveyor 8, magnet roller 1゜developer (toner)

Claims (2)

[Claims] (1) A rotatable non-magnetic cylindrical developer conveying member has a cylindrical magnetic roller magnetized with a plurality of magnetic poles inside the rotatable non-magnetic cylindrical developer conveying member, and the developer In a developing device that conveys the developer on a conveying member, the magnetic roller contains a rare earth element (hereinafter, R
It is a rare earth resin/resin bond type magnet made of a rare earth magnetic powder made of a transition metal mainly composed of cobalt and a thermoplastic resin such as a polyamide resin, and is characterized by being an extrusion molded magnet. Developing device. (2) The developing device according to claim 1, wherein the rare earth magnetic powder is a rare earth magnetic powder consisting of R, a transition metal mainly composed of iron, and boron.