JPH03186874A - Magnet roll - Google Patents

Abstract

PURPOSE:To provide a developing device which can make color development and has a higher resolution by specifying the outside diameter, inside diameter and length of a cylindrical magnet and radially providing anisotropy in the diametral direction thereof. CONSTITUTION:The magnet constituting body built in a cylindrical developer transporting member (sleeve) 1 consisting of a nonmagnetic material is formed by fixing the cylindrical magnet 2 having plural magnetic poles to a magnet support 3 and further fixing the same to a roll shaft 4. The cylindrical magnet 2 is integrally molded in the relation 2DL/d<2>>=1 in the outside diameter D, inside diameter d and length L and has the anisotropy radially in the diametral direction. The magnetic flux density on the surface of the developer transporting member is increased in this way, by which the content of the magnetic powder in the developer is decreased and the grain size of the magnetic powder is reduced. The developing device which can make color development and has the higher resolution is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnet roll used in magnetic brush developing devices such as copying machines and printers.

[Conventional technology]

A magnet roll used in a conventional developing device is, for example, a magnet structure in which a cylindrical sintered ferrite magnet is fixed to a roll shaft, which is built into a non-magnetic cylindrical developer conveying member and placed relative to the magnet. Those that are freely rotatable are widely used.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology has the following problems.

The magnets used in conventional magnet rolls are isotropic sintered ferrite magnets, which have low magnetic properties and cannot provide sufficient surface magnetic flux density on the developer transport member.

Therefore, in order to reliably restrain the developer on the conveyance unit assembly, development is performed using a developer containing a large amount of magnetic yJit. However, in order to increase the color and resolution of developing devices, it is necessary to reduce the amount of magnetic powder contained in the developer and to reduce the particle size of the magnetic powder in the developer. When such a developer is used for development using a conventional magnetic roll, it is difficult to obtain a clear image due to fogging in the background.

As a countermeasure to this problem, the following methods can be mentioned, for example, to increase the surface magnetic flux density of the magnet roll.

(1) Increase the thickness of the magnet molded body.

(2) A sintered ferrite magnet having anisotropy in one diameter direction as described in Japanese Patent Publication No. 60-37607 is fixed to a roll shaft.

Regarding (1), there is a problem in that it is difficult to reduce the size and weight of the magnet roll. Regarding (2),
The surface magnetic flux density of the magnetic pole must be adjusted in the anisotropic direction of the magnet and in other directions during magnetization, which has the problem of complicating the manufacturing process and poor productivity. In addition, since sintered magnets are used in both cases, there are problems in that the magnets are brittle and often crack and chip, and secondary processing such as cylindrical polishing is required to ensure dimensional accuracy.

In order to solve the above-mentioned problems of sintered magnets, magnet rolls using resin-bonded magnets (bond magnets) have also been devised. Some have a structure in which magnetic pieces are combined and fixed to the roll shaft. However, since this type of magnet roll also uses a ferrite bond magnet, it has low magnetic properties and has the problem that a sufficient surface magnetic flux density cannot be obtained. In addition, in terms of manufacturing, a step is required in which separate magnet pieces are assembled and integrated after molding, resulting in a problem of poor productivity.

As described above, when ferrite magnets are used in magnet rolls, there is a problem that their magnetic properties are low, but in addition to that, the temperature characteristics of the magnets are poor, so the developer density in the developing device is affected by changes in the surrounding temperature. There is also the problem that it changes with time.

From the above two points, the above problems can be solved by using a rare earth resin bonded magnet in which rare earth magnet powder with high magnetic properties is bonded with a resin instead of a ferrite magnet. However, 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 Both of these methods can mold a magnet having anisotropy by applying a magnetic field within the mold during forming. Cylindrical magnets with radial anisotropy are suitable as magnets for magnet rolls, but when molded using the above two methods, there are restrictions on the length of the molded product, and the length of the magnet is limited. Outer diameter (D
), inner diameter (d), and length (L) that satisfy the following relational expression can only be molded.

2DL/d2<1 (Reference: Masayo Hamano, Abstracts of the 9th Injection Molding Technology and Application Development Lecture for High-Performance Plastic Magnets, Plastic Industry Technology Research Group, 1986) A radial magnetic field is created by guiding the magnetic flux passing through a circle (area πd2/4) whose diameter is the inner diameter of the cylindrical cavity of the mold to completely cross the side surface of the cylindrical cavity (area πDL). However, since the total amount of magnetic flux is determined by the inner diameter, the lateral area cannot be increased in order to generate a sufficient magnetic field to orient the magnet powder. Therefore, when manufacturing a magnet for a magnet roll using the above method, since there are restrictions on the length of the molded product, a plurality of magnets must be attached to the roll shaft. However, when the magnets are bonded together in this way, there is a problem that unevenness in image density occurs due to disturbance of the surface magnetic flux density at the joints of the magnets, and the magnet cannot be used as a developing device.

Therefore, the present invention solves the above problems.
The purpose is to provide a magnet roll that can be used in high-performance developing devices that can provide color and high resolution by reducing the content of magnetic powder in the developer and making the magnetic powder finer particles. It is in. Still another object is to provide a magnet roll that enables more stable development with less unevenness in development purulence under the environment in which the developing device is used. Still another object is to provide a small and lightweight magnet roll.

[Means to solve the problem]

The magnet roll of the present invention is a magnet roll having a cylindrical magnet structure magnetized with a plurality of magnetic poles inside a rotatable non-magnetic cylindrical developer conveying member. The cylindrical magnet to be formed has an outer diameter (hereinafter referred to as d), an inner diameter (hereinafter referred to as d), and a length (hereinafter referred to as d) having a relationship of 2DL/d2≧1, and is integrally molded, and It is characterized by having radial anisotropy in the radial direction.

Further, the cylindrical magnet is made of a molding raw material composed of magnet powder, an organic resin, and additives if necessary.
It is characterized by being manufactured by extrusion molding by passing through a mold to which a magnetic field is applied.

Further, the magnet powder is characterized in that it is a rare earth magnet powder made of a rare earth element and a transition metal mainly composed of cobalt, or a rare earth magnet powder made of a rare earth element, a transition metal mainly composed of iron, and boron.

[Effect]

According to the above configuration of the present invention, by using a rare earth resin bonded magnet with high magnetic properties, the magnetic flux density on the surface of the developer conveying member can be increased, and the content of magnetic powder in the developer can be reduced. In addition, by reducing the particle size of the magnetic powder, it becomes possible to provide color development devices and higher resolution. In addition, rare earth magnets have better temperature characteristics than ferrite magnets, which makes it possible to reduce unevenness in development flow rate due to temperature changes. Furthermore, it is possible to reduce the wall thickness of the magnet molded body and obtain a small and lightweight magnet roll.

The shape of the magnet used in the magnet roll of the present invention is an elongated cylindrical shape, which is difficult to mold using conventional methods for molding rare earth resin bonded magnets, and requires the use of extrusion molding. Unlike conventional compression molding and injection molding, the extrusion molding method is continuous molding, so the length of the magnet of the molded product can be arbitrarily determined. Furthermore, by applying a magnetic field within the mold during molding, it is also possible to mold a long cylindrical magnet having radial anisotropy in the radial direction, which has not been possible conventionally. In addition, the extrusion molding method has high productivity because it is continuous molding, and the molded product has good dimensional accuracy and almost no secondary processing of magnets is required, which reduces molding costs. is possible.

The organic resin that can be used in the present invention may be a thermoplastic resin or a thermosetting resin, and examples of the thermoplastic resin include plastics such as polyamide and polyphenylene sulfide (PPS), elastomers such as chlorinated polyethylene, and synthetic rubber. Examples of thermosetting resins include ethylenically unsaturated polyester resins and epoxy resins.

As additives, metal soaps (zinc stearate, calcium stearate, etc.), lubricants such as wax, and for the crosslinkable resins, additives that promote crosslinking reactions such as peroxides may also be used. can.

Hereinafter, the present invention will be described in detail based on examples.

〔Example〕

FIG. 1 is a sectional view showing one embodiment 0- of the magnet roll of the present invention. It has a structure in which a magnet structure is built in a cylindrical developer conveying part (hereinafter referred to as sleeve) 1 made of a non-magnetic material.

The magnet structure includes a cylindrical magnet 2 having a plurality of magnetic poles fixed to a magnet support 3, and further fixed to a roll shaft 4. The sleeve and the magnet structure are rotatable relative to each other.

FIG. 2 is a cross-sectional schematic view of an image forming apparatus including a developing device using the magnet roll of the present invention.

In FIG. 2, a latent image carrier is formed by coating a photoconductive layer 12 on a conductive support portion 11.

After the photosensitive layer 12 is charged to a predetermined potential by a charger 13, light emitted from a light source 14 such as a laser is scanned using a rotating polygon mirror or the like (not shown), and an imaging optical system 15 An image is formed on the photosensitive layer 12 to obtain a potential contrast, and an electrostatic latent image is formed on the latent image carrier. On the other hand, numeral 19 in the figure is a developing device, which charges a developer (hereinafter referred to as toner) 18, which is an image forming body, and transports it by a magnet roll 16 having a structure as shown in FIG. . Adjacent to the sleeve in the magnet roll 16 is a conductive and flat blade 17 that is a transport amount regulating member.
will be placed. The toner is held on the sleeve by the magnetic flux generated by the magnet structure in the magnet roll, the amount of toner conveyed is regulated by the blade 17, and the toner is conveyed to the developing gap portion 23 where the latent image carrier and the sleeve are close to each other. In the development gap section 23, the toner 18 is developed on the latent image carrier according to the electrostatic latent image and the development electric field by the development bias applying means 20 (connected between the conductive support section 11 and the sleeve). Ru. Further, the visualized image is transferred to the transfer device 2.
1, the image is electrostatically transferred onto a recording paper 22, etc., and fixed by means such as pressure or heating to obtain a desired image.

Here, in FIG. 2, the potential of each part was set so that if the electrically conductive support part 11 of the latent image carrier was O[V], the potential of the sleeve of the magnet roll was -500[V].

In addition, the gaps between the latent image carrier and the magnet roll 16 are
0.2 [mm] gap between magnet roll 16
The =12- gap between the blade 17 and the blade 17 was set to 0.15 [mm]. By setting in this way, it became possible to form a toner image with high contrast and excellent density gradation.

Note that the configuration in FIG. 2 does not limit the present invention,
Furthermore, the above-mentioned values are not intended to limit the present invention, and it goes without saying that all known developers such as one-component toner and two-component magnetic toner can be used as the developer. .

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

Rare earth magnet powder, organic resin, and additives if necessary are weighed and mixed to a desired mixing ratio, and then heated and kneaded with a kneading machine such as a roll mill or an extruder to a temperature higher than the melting temperature of the resin,
Create a compound. This compound is pulverized to 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 again in the extruder to melt the resin, and in this state it is fed into a mold connected to the extruder. In the mold, the compound is squeezed into the final shape. At the tip of the mold, an orienting magnetic field applied radially in the radial direction orients the magnet powder so that the axis of easy magnetization aligns with the direction of the magnetic field, cools it, and extrudes it from the mold as a compact magnet. The extruded magnet is taken out and cut into appropriate lengths. After being cut, the magnet was demagnetized, and when a thermosetting resin was used, the magnet molded body was cured, and then cut into the final length to form a magnet for a magnet roll. However, if a thermoplastic resin was used as the binder, the curing step was omitted.

More detailed examples will be shown below.

[Example 1] Sm-Co magnet powder, nylon 12 resin, and zinc stearate powder were mixed at a ratio of 92 wt%, 7.
After mixing and kneading so that the concentrations were 9 wt% and 0.1 wt%, they were extruded into a cylindrical shape while applying a magnetic field. This magnet will be referred to as magnet 1. In addition, a resin powder consisting of a mixture of Nd-Fe-B magnet powder, bisfu=14-enol A type epoxy, and novolac type epoxy, and calcium stearate powder and silica powder as additives were used at a ratio of 90 wt.
%, 9.4. wt%, mixed to be 0.6w7%,
After kneading, the mixture was extruded into a cylindrical shape while applying a magnetic field. This magnet will be referred to as magnet 2. The shape of the molded magnet is
Both magnet 1 and magnet 2 had an outer diameter of 18 mm, an inner diameter of 16 mm, and a length of 216 mm. These magnets were uniformly magnetized with 12 poles to produce a magnet roll. Table 1 shows the measurement results of the surface magnetic flux density of these magnet rolls.

In Table 1, magnets 3, 4, and 5 each represent a comparative example. The magnet 3 is made by injection molding a raw material having the same composition as the magnet 1 while applying a magnetic field. However, in order to obtain a molded product with sufficient magnetic properties using the injection molding method, the two molded products must have an outer diameter of 18 mm, an inner diameter of 16 mm, and a length of 6 mm. Therefore, the magnet roll has this shape. Thirty-six magnets were glued together and used. The magnet 4 is Sm-Co
system magnet powder and epoxy resin, each = 15- Table 1 * Surface magnetic flux density difference in the axial direction of the magnet roll (maximum value -
The mixture was mixed and kneaded so that the ratio of the difference in the minimum value (minimum value) was 98 wt% and 2 wt%, and compressed while applying a magnetic field. In the compression molding method, as in the injection molding method, in order to obtain a molded product with sufficient magnetic properties, the shape of the molded product must be 18 mm in outer diameter, 16 mm in inner diameter, and 4 mm in length. 54 of these magnets were glued together and used. The magnet 5 is a conventionally used sintered ferrite magnet. However, the shape of the magnet is 18 mm in outer diameter and 6 m in inner diameter.
m, and the length is 216 mm. The surface magnetic flux density in the table was measured on the surface of a sleeve with an outer diameter of 20 mm. As is clear from Table 1, by using a rare earth magnet instead of a ferrite magnet, it is possible to obtain a large surface magnetic flux density even if the magnet is made thinner and lighter. Furthermore, it can be seen that the difference in surface magnetic flux density in the axial direction is large in the magnet rolls using magnets produced by injection molding and compression molding (magnet 3.4). This is because there is a large change in surface magnetic flux density at the bonded portion of the magnet. In contrast, the magnet roll of the present invention has excellent uniformity of surface magnetic flux density.

[Example 2] Next, using the magnetic roll produced in Example 1, the relationship between the magnetic powder content in the toner, the image flow rate of a solid image, and the image density of the background area was investigated. First, regarding the magnetic powder content of the toner and the image density of the solid image, by adjusting the developing bias voltage, a sufficient value of OD value of 1.2 or more can be obtained with the magnet roll using magnets 1.2 and 5. Ta.

However, when a magnet roll using magnets 3 and 4 was used, unevenness in image density was noticeable at the joint portion of the magnets. As described in Example 1, this is due to the disturbance in the surface magnetic flux density at the joint portion of the magnet. Furthermore, even if a magnetic roll using the magnet 5 is used, it becomes difficult to form a magnetic brush when the magnetic powder content of the toner becomes 30 wt% or less, and it is difficult to further reduce the magnetic powder content. there were. On the other hand, when a magnetic roll using magnets 1 and 2 is used, it is possible to form a magnetic brush even if the magnetic powder content of the toner is 30 wt% or less, and the magnetic powder content can be reduced to 16 wt%. It was possible. Next, the relationship between the magnetic powder content of the toner and the background area image roughness is almost unaffected by the adjustment of the developing bias voltage, and when the magnet 5 is used, the magnetic powder content is 40 wt%. Below this, developer adhesion (fogging) 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 8-25 wt%.

[Example 3] Using a developing device as shown in FIG. 2, toner 18
The composition is a mixture of styrene-acrylic resin, 30 wt% of ferrite particles (saturation magnetization: 88 e mu / g), 4 wt% of carbon black, and about 1 wt% of the additive, and has a saturation magnetization with a number average particle diameter of 8 μm. 26
Using a one-component magnetic toner of emu/g, a developing bias voltage of -500 V was applied to develop the image and transfer and fix it onto plain paper to form an image.

Here, as the magnet roll, magnets 1 and 2 were used as examples of the present invention, and magnet 5 was used as a comparative example. When magnets 1 and 2 are used, a magnetic brush sufficient to convey the toner 18 is formed on the sleeve of the magnet roll 16, and a high-contrast image with no fog in the background can be obtained with a maximum OD value of 1.5. A resolution of 600 DP was achieved, allowing accurate formation of even small characters of about 3 points. In addition, a small pixel 1 of 0.5 mm square
9-, area gradation of approximately 100 gradations was obtained. On the other hand, when magnet 5 was used, only the developing bias voltage was changed to 400 cm, and image formation was performed under the same conditions. In this case, a magnetic brush sufficient to convey the toner 18 is formed on the sleeve of the magnet roll 16, and an image with a maximum OD value of 1.5 and a high temperature in the solid image area is obtained, but there is an excessive amount in the background area. Fog occurred and only images of low quality were obtained.

[Example 4] Using a developing device as shown in FIG. 2, toner 18
30wt of ferrite particles with good optical transparency (saturation magnetization 88 e mu / g) are added to polyester resin.
%, cyan colorant 4wt%, other additives approximately 1wt%
Using a single-component magnetic toner with a number average particle diameter of 6 μm and a saturation magnetization of 26 e mu / g, a developing bias voltage of -450 V was applied to develop the toner, which was then transferred and fixed onto plain paper to form an image. Ta. Here, as the magnet roll, magnets 1 and 2 are used as an example of the present invention.
Magnet 5 was used as a comparative example. When magnets 1 and 2 are used, a magnetic brush of cyan developer is formed on the sleeve of the magnet roll 16, resulting in less color turbidity, a maximum OD value of 1.5, and high contrast with no background fog. An image was obtained, and area gradation of about 64 gradations was obtained even with small pixels of 0.5 mm square. Similar results were also obtained when yellow colorant and magenta colorant were used. On the other hand, when the magnet 5 is used, a magnetic brush is formed on the sleeve of the magnet roll 16,
Although a high-density image with a maximum OD value of 1.5 in the solid image portion was obtained, only a dark, low-quality image with low gradation was obtained.

〔Effect of the invention〕

As described above, according to the present invention, the outer diameter D, the inner diameter d, and the length L are integrally molded with the relationship of 2DL/d2≧1, and are radially anisotropic in the radial direction. By using a magnet roll using a rare earth resin bonded cylindrical magnet in the developing device, the content of magnetic material in the toner can be reduced, and the particle size of the magnetic material can be reduced. This has the excellent effect of making it possible to use a developing device in color and with higher resolution. Therefore, it can be widely applied to developing devices such as electrophotography, and is particularly effective when applied to printers, copying machines, facsimile machines, and displays.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a magnet roll in an embodiment of the present invention. FIG. 2 is a cross-sectional schematic diagram of a developing device in an embodiment of the present invention. FIG. 3 is a diagram showing the manufacturing process of the resin-bonded magnet used in the magnet roll of the present invention. that's all

Claims (3)

[Claims] (1) In a magnet roll having a cylindrical magnet structure magnetized with a plurality of magnetic poles inside a rotatable non-magnetic cylindrical developer conveying member, the cylindrical magnet forming the magnet structure is Outer diameter (hereinafter referred to as D),
Inner diameter (hereinafter referred to as d) and length (hereinafter referred to as L)
2DL/d^2≧1, the magnetic roll is integrally molded, and has radial anisotropy in the radial direction. (2) The cylindrical magnet was manufactured by extrusion-molding a molding raw material consisting of magnet powder, an organic resin, and, if necessary, additives, by passing it through a mold to which a magnetic field was applied. Claim 1 characterized in that
Magnetic roll as described. (3) A claim characterized in that the magnet powder is a rare earth magnet powder made of a rare earth element and a transition metal mainly composed of cobalt, or a rare earth magnet powder made of a rare earth element, a transition metal mainly composed of iron, and boron. The magnetic roll according to item 2.