JPH0720716A - Developing device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a developing device which extends a developing region for making an image density high and simultaneously, whose manufacture is simple by arraying plural ferromagnetized blocks in the peripheral direction of a magnet roll, in a position where it faces an electrostatic latent image holder. CONSTITUTION:The part of the magnet roll 11 which faces the electrostatic latent image holder 40, is composed of the magnet blocks 12 and a resin part including a ferrite held between the magnet blocks 12, and the resin part is hardly magnetized, so that the distribution of the strength of a magnetic field in a developing region, has peaks on the magnet blocks 12. Therefore, the line of magnetic force is formed at the position where a developing roll 15 faces the electrostatic latent image holder 40 and the magnetic field having the strength suitable for development is formed in a wide area. Then, a magnetic brush is formed, the contact width of the magnetic brush with the electrostatic latent image holder 40 is made wide and the developing region is extended. Moreover, the magnetic brush is disturbed and reformed between the peaks, to make a development concentration high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device such as a copying machine and a printer using electrophotography and a method for manufacturing the same, and more particularly to a developing device capable of obtaining a high quality image at a sufficient density and its manufacturing. Regarding the method.

[0002]

2. Description of the Related Art In a conventional electrophotographic apparatus or electrostatic recording apparatus, a method of visualizing and developing a latent image on an electrostatic latent image carrier using a two-component developer composed of a non-magnetic toner and a magnetic carrier is known. well known. This method forms a magnetic brush in which magnetic carriers are connected in a spike shape on the developing roll, and by rotating the sleeve on the surface of the developing roll, the magnetic brush is moved to a position facing the electrostatic latent image holding member, The non-magnetic toner is transferred to the latent image on the electrostatic latent image holder.

A developing roll used in such a developing device is generally that shown in FIG. 8, and a magnet roll 61 and a sleeve 60 rotatable with respect to the developing roll form a major part. The magnet roll 61 is obtained, for example, by molding a powdered ferromagnetic material such as hard ferrite or a mixture of a powdered material of a ferromagnetic material and a binding material into a cylindrical shape, and its outer peripheral surface has a uniform axial direction. Multiple magnetic poles are provided in the circumferential direction. In addition, the magnet roll 61
A support shaft is fixed coaxially with the magnet roll at the center of the
Both ends of this support shaft are fixedly supported by the housing of the developing device. On the other hand, the sleeve 60 is made of a non-magnetic material such as aluminum alloy or stainless steel in the shape of a hollow cylinder, and is supported and rotatably driven by a support member rotatably mounted on the support shaft.

With such a structure, the two-component developer is attracted to the outer peripheral surface of the sleeve 60 by the magnetic action of the magnet roll 61, and a magnetic brush is formed. When the sleeve 60 is rotationally driven, the magnetic brush is conveyed to the developing area, and the electrostatic latent image is developed. At this time, as shown in FIG. 9, the magnetic brush on the sleeve 60 is formed on the sleeve along the magnetic lines of force generated by the S and N poles of the magnet roll 61 in the developing roll. In this figure, the distribution of the magnetic force lines is shown only in the magnetic pole portion facing the electrostatic latent image holder 40, but the other distributions have the same distribution. Since the magnetic field is strongest at the center position of the magnetic poles, as shown in FIG. 9, the bristles of the magnetic brush 63 on the sleeve 60 are formed such that the center position of the magnetic poles is the highest and the middle of the magnetic poles is the lowest.
Therefore, normally, the magnetic poles of the magnet roll 61 are arranged so that the development is performed at or near the highest point of the spikes.

In the developing process as described above, in order to increase the density of the image to be developed, a method of rotating the developing roll at a high speed, a method of narrowing the gap between the developing roll and the electrostatic latent image carrier, and a developing region And the like.
Among these methods, the method of rotating the developing roll at a high speed has a problem that the contamination in the machine is likely to occur due to the scattering of toner, and the method of narrowing the interval between the developing roll and the electrostatic latent image holding member, There is an inconvenience that the developer is easily pressed and solidified. On the other hand, the method of widening the development area has an advantage that there are few such inconveniences.

Specific methods for widening the developing area include a method of using a plurality of developing rolls and a method of widening the width of the magnetic pole, but the manufacturing cost of the apparatus is increased as much as possible without increasing the size of the apparatus. As a method of preventing the magnetic field, there is a method of providing a magnetic pole in the developing roll so that the strength of the magnetic field has a plurality of peaks in the developing region. This is disclosed in Japanese Examined Patent Publication No. 62-55149, in which two magnets are arranged in parallel in the developing roll at positions facing the electrostatic latent image holding member, with the magnetic poles oriented in the same direction and spaced in parallel. As
This is embodied by providing at least one recess in the magnet arranged in the developing area.

[0007]

However, the above-described conventional method of providing a plurality of magnetic field peaks in the developing region has the following problems. When two magnets are arranged in parallel, it takes time to fix the magnets in place, which leads to an increase in cost, and the air gap between the two magnets has a direction opposite to the originally intended magnetic field. A magnetic field is generated, so that toner adheres to a portion that should not be originally developed, and a clear image cannot be obtained.

Further, according to the means disclosed in Japanese Patent Publication No. 62-55149, the strength distribution of the magnetic field changes greatly depending on the size and shape of the recess, so that the recess is provided so as to obtain a predetermined strength distribution. There is a problem that a high-precision processing technique is required and the processing cost increases. In particular, when a strong magnetic field is required for development in the development area, a cylindrically shaped isotropic magnet material alone is not sufficient, and a block of anisotropic magnet material formed by sintering is used as an electrostatic latent material. It is necessary to embed it in a position facing the image carrier, but in order to make a highly accurate depression in this anisotropic block, it is necessary to polish the sintered magnet member, which is a time-consuming process. Will be required.

The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to lengthen a developing area to increase image density and to easily develop a developing device and The manufacturing method is provided.

[0010]

In order to solve the above problems, the developing device according to claim 1 is provided so as to face the electrostatic latent image holding member, and is rotationally driven in the circumferential direction. And a developing roll consisting of a hollow cylindrical sleeve and a cylindrical magnet roll fixedly supported inside the sleeve, forming a magnetic brush of two-component developer on the sleeve, and rotating the sleeve. In the developing device that conveys the two-component developer to the developing area facing the electrostatic latent image holding member by the above, and visualizes the latent image on the electrostatic latent image holding member,
A plurality of strongly magnetized blocks made of a magnet material are arranged in a circumferential direction of the magnet roll in a position facing the electrostatic latent image holding member, and a material forming the strongly magnetized block between the plurality of strongly magnetized blocks. It is assumed that a material that is less likely to be magnetized is inserted, and that the plurality of strongly magnetized blocks or the plurality of strongly magnetized blocks and the material interposed therebetween are magnetized to have the same polarity.

The invention according to claim 2 is the method for manufacturing a developing device according to claim 1, wherein a plurality of strongly magnetized blocks formed in a predetermined shape in a substantially cylindrical mold, Alternatively, a plurality of strongly magnetized blocks and a material interposed therebetween are fixed, and the other part of the mold is filled with a material that is harder to magnetize than the material forming the strongly magnetized block and solidified, and the filled material Is solidified before or after solidification to form a magnet roll, which is inserted into the sleeve and fixedly supported in the housing.

Further, the invention according to claim 3 is the method for manufacturing a developing device according to claim 1, wherein the developing device is substantially cylindrical and has the plurality of strong magnetization blocks or the plurality of strong magnetization blocks and these. A strong magnetization block molded into a predetermined shape by molding a material that is harder to magnetize than the strong magnetization block so as to have a recess corresponding to the shape of the material to be placed between the strong magnetization block and the material. , Or a plurality of strongly magnetized blocks and a material interposed therebetween, are mounted in the recesses and then magnetized to form a magnet roll, which is inserted into the sleeve and fixedly supported in the housing. It is characterized by that.

In the invention described in claim 1, the strong magnetization block is made of a material that is strongly magnetized, and may be a ferromagnetic material having a high magnetic susceptibility or a powdery ferromagnetic material. It may be solidified with a binder or the like. Further, a plurality of strongly magnetized blocks made of a magnet material are arranged in the circumferential direction of the magnet roll in a position facing the electrostatic latent image holder, and between them are less likely to be magnetized than the magnet material forming the strongly magnetized block. Material must be inserted. The inserted material that is hard to be magnetized may be a material having a low magnetic susceptibility or a non-magnetic material. Further, a material containing a powdery magnetic material may be solidified, and by lowering the mixing ratio of the magnetic powder, it is possible to make it harder to magnetize than the material forming the strong magnetization block. Structurally, a part of a substantially cylindrical member that supports the strongly magnetized block may be inserted, or a material to be inserted between the strongly magnetized blocks may be sandwiched in advance, and this may be molded into a substantially cylindrical shape. It may be attached to the member.

[0014]

In the developing device according to claim 1, a plurality of strong magnetization blocks made of a magnetic material are arranged in the circumferential direction of the magnet roll at a position facing the electrostatic latent image holding member, and the strong magnetization blocks are arranged between them. A material that is harder to magnetize than the block is inserted,
And these are magnetized to the same polarity. Therefore,
The magnetic field strength distribution thus formed has a plurality of peaks as shown by the solid line in FIG. 2, for example, and has a single peak of the magnetic field strength (shown by the broken line in FIG. 2) in the development area. Can be lengthened. Also, since there is a weak magnetic field between the peaks of the magnetic field strength, the magnetic brush is temporarily disturbed here. Therefore, the chains of the magnetic carrier are rearranged in the magnetic brush which has already consumed the toner adhering to the vicinity of the brush tip during development, and the toner in the vicinity of the root of the magnetic brush also contributes to the development, so that a sufficient image density can be obtained. In addition, the strongly magnetized block is placed at a position facing the electrostatic latent image holder, and a material that is less magnetized than these is inserted between them, so by changing the material, size, or combination of these, development It is possible to obtain a strong magnetic field in a region and easily obtain a magnetic field having a predetermined intensity distribution.

In the method of manufacturing a developing device according to the second aspect, a plurality of strongly magnetized blocks formed in a predetermined shape in a substantially cylindrical mold, or a plurality of strongly magnetized blocks and a space between them. Since the material to be inserted is fixed and the other parts in the mold are filled with a material that is less magnetized than the material forming the strong magnetization block and solidified, it is possible to arrange a plurality of strong magnetization blocks at precise positions. This facilitates integration of the cylindrical member and the strongly magnetized block. In addition, since a magnetic field can be provided by applying a magnetic field before the filled material is solidified, if a resin material containing magnetic powder is used as the filled material, the magnetic powder will not generate magnetic field in the resin before curing. Oriented, the filled material can be strongly magnetized.

In the method of manufacturing the developing device according to the third aspect, a material that is less likely to be magnetized than the strong magnetization block is
A plurality of strongly magnetized blocks or a plurality of strongly magnetized blocks and a material to be inserted between them are provided with recesses at positions where the recesses are provided, and the recesses are molded into a substantially cylindrical shape. Since the strong magnetization blocks and the material interposed between them are mounted, it is possible to easily form the plurality of strong magnetization blocks and the magnetic poles made of a material that is hard to magnetize and interposed between them. Further, it is possible to easily provide the magnetic pole at another position of the substantially cylindrical member made of a material that is harder to be magnetized than the strong magnetization block.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a developing device which is an embodiment of the invention described in claim 1.

This developing device 1 has an electrostatic latent image holder 4 capable of forming an electrostatic latent image on the surface due to a difference in charging potential.
And a cylindrical developing roller 15 that is provided to face the electrostatic latent image holding member 40 in the housing 2 so as to face the electrostatic latent image holding member 40 and to convey the developer by adsorbing the developer on the surface. Developer regulating member 3 for regulating the amount of developer on the roll 15
And have. A first stirring chamber 7 and a second stirring chamber 8 are provided inside the housing 2 along the axial direction of the developing roll 15, and the inside of the first stirring chamber 7 and the second stirring chamber 8 are provided. The stirring chamber 8 is provided with a first auger 5 and a second auger 6 which convey the developer while stirring.

The electrostatic latent image holding member 40 has a photoconductor (opc photoconductor) made of a polymer compound on the surface thereof, and is once uniformly charged to expose an image portion to form an electrostatic latent image. It is possible.

The developing roll 15 is composed of a magnet roll 11 having a plurality of magnetic poles in the circumferential direction and a non-magnetic hollow cylindrical sleeve rotatably supported around the magnet roll 11. The magnet roll 11 includes a cylindrical portion 11a made of resin containing powdery ferrite, and two magnet blocks 1 fixed to the cylindrical portion at a position facing the electrostatic latent image holding member.
2, 12 (strongly magnetized block). These magnet blocks 12 and 12 are formed by sintering powdery ferrite, and are magnetically anisotropic materials. A cylindrical portion 1 is provided between the two magnet blocks 12, 12.
The material forming 1a is inserted, and these two magnet blocks and the inserted material are magnetized to the same polarity to form a developing magnetic pole. Further, the magnet roll 11 forms a magnetic brush of a two-component developer, which is a mixture of magnetic carrier and toner, on the surface of the sleeve 10 by a magnetic field formed between adjacent magnetic poles, and the sleeve 10 rotates. Thus, the magnetic brush can be transported to the developing area. Such a developing roll 15 is arranged in the vicinity of the electrostatic latent image holding member 40, and the portions in which the surfaces thereof are close to each other form a developing area.

The developer regulating member 3 has a sleeve 1 at one end.
It is mounted so as to project close to the surface of No. 0, and regulates the amount of developer adsorbed on the surface of the sleeve 10 to form a uniform layer of developer.

The first stirring chamber 7 is provided substantially parallel to the developing roll 15 at a position facing the developing roll 15, and the developer can be supplied to the developing roll 15 by the rotation of the first auger 5. You can do it. The second stirring chamber 8 communicates with the first stirring chamber 7 at both ends in the axial direction of the developing roll, and the second auger 6 conveys the developer in the direction opposite to that of the first auger.

In the developing device as described above, the developer is the first
The magnetic carrier and the toner are sufficiently agitated by being conveyed so as to circulate in the agitating chamber 7 and the second agitating chamber 8. As a result, the toner is sufficiently charged and supplied to the surface of the developing roller 15. The developer supplied to the developing roll 15 is transferred to the sleeve 10 by the magnetic field of the magnet roll 11.
Form a magnetic brush on top. The magnetic brush is conveyed by the rotation of the sleeve 10, the developer amount is regulated by the developer regulating member 3, and then the magnetic brush is sent to the developing area. In the developing area, the toner is transferred to the electrostatic latent image holding member 40 for the image portion, and development is performed.

In this embodiment, the position of the magnet roll 11 facing the electrostatic latent image carrier 40 is composed of two magnet blocks 12 and a resin portion containing ferrite sandwiched between them, and the resin portion is Since it is harder to magnetize than the magnet block, the distribution of the magnetic field strength in the developing region has its peak on the magnet block. That is, the magnetic field strength distribution at the magnetic poles of the conventionally used cylindrical magnet roll has one peak as shown by the broken line A in FIG. The intensity distribution has a shape having two peaks as shown by the solid line B in FIG. Therefore, magnetic lines of force as shown in FIG. 3A are formed at the position where the developing roller faces the electrostatic latent image carrier 40, and a magnetic field having a strength suitable for development can be formed in a wider range than the conventional one. Is possible.
As a result, a magnetic brush as shown in FIG. 3B is formed, the contact width between the magnetic brush and the electrostatic latent image holding member is widened, and the developing region can be lengthened.

Further, while the magnetic field strength distribution has two large peaks in the developing region, there is a weak magnetic field at the central part thereof, so that a gradient of the magnetic field is generated from this part toward both peak sides. That is, two magnet blocks 1
A repulsive magnetic field is generated between the two portions because they have the same polarity, and that portion has a weaker magnetic field than the other portions. Therefore,
When the magnetic brush on the sleeve 10 passes through this weak magnetic field, the magnetic brush temporarily collapses [the part indicated by symbol C in FIG. 3 (b)], and the magnetic brush that has already consumed toner that has adhered to the vicinity of the tip of the developing brush Since the toner is disturbed, it becomes possible for toners attached to areas other than the vicinity of the tips to contribute to the development, and the image density is further improved.

Next, a method of manufacturing the developing device, which is an embodiment of the invention described in claim 2, will be described. First, the ferrite was previously sintered 2
One magnet block 12, 12 is arranged at a predetermined position in a substantially cylindrical mold, and the other portion in the mold is filled with a molten resin containing powdered ferrite, and integrally molded into a cylindrical shape.
Before the resin is cured, as shown in FIG. 4, a plurality of magnetizing blades 51 are brought close to each other from the outer peripheral surface of the substantially cylindrical mold 50,
A plurality of magnetic poles are magnetized so as to be uniformly formed in the axial direction along the circumferential direction of the material molded into a cylindrical shape. At this time, the position where the two magnet blocks 12, 12 are provided is as shown in FIG.
The magnets 2, 12 and the material interposed therebetween are magnetized to the same polarity so as to form one magnetic pole. When magnetized in this manner, the magnet block 12 and the resin member containing ferrite between the magnet blocks 12 are materials that are magnetized more strongly, so that the magnetic field strength on the magnet blocks 12, 12 has two peaks. Have. Therefore, when such a magnet roll is arranged in the hollow cylindrical sleeve, the distribution of the magnetic field strength as shown by the solid line B in FIG. 2 can be formed on the sleeve 10 on the surface of the developing roll. Such a developing roll is arranged in the housing of the developing device, and the developing device is assembled. Note that the conventional method can be used for the other steps for manufacturing the developing device.

In the method of manufacturing the developing device as described above, 2
The distance x between the individual magnet blocks 12 and 12, the size of the strongly magnetized block 12 (length in each of the vertical and horizontal directions), and a material that is less likely to be magnetized than the magnet blocks 12 and the magnet blocks 12 interposed therebetween. The height of the two peaks, the width of the two peaks, and the size of the dip can be freely set by changing the type. Further, the number of peaks can be freely selected depending on the number of magnet blocks 12.

Next, another embodiment of the present invention will be described with reference to FIG. In this developing device, the magnet roll 31 is
It has a cylindrical portion 31a formed by sintering a material containing powdery ferrite and a binder, and two magnet blocks 32, 32 at a position facing the electrostatic latent image holder of this cylindrical portion 31a.
The magnetic material pieces 33, which are harder to be magnetized than the magnet blocks 32, 32, are fixed by being interposed between the two magnet blocks. These magnet blocks 32, 32 are formed by sintering powdery ferrite, and are magnetically anisotropic materials. These two magnet blocks and the material inserted between them are magnetized to the same polarity to form a developing magnetic pole.

The developing roller has the same sleeve as that of the embodiment shown in FIG. Further, the developing device of this embodiment is the same as the developing device of the embodiment shown in FIG. 1 except for the above-mentioned magnet roll. In the developing device, the magnet blocks 32, 32
When the same magnetic field is applied between the magnet block 32 and the magnetic material piece 33 interposed therebetween, the magnet block 32 needs to be magnetized more strongly. In the present embodiment, the magnetic material piece 33 to be inserted is magnetized weaker than the magnet block 32 by adjusting the mixing ratio of ferrite which is a ferromagnetic material. Even in the developing device of this embodiment, the distribution of the magnetic force lines is as shown in FIG. 6 in the developing area, and the magnetic field strength distribution as shown by the solid line B in FIG. 2 is obtained. Therefore,
Similar to the developing device of the embodiment shown in FIG. 1, it is possible to obtain high density and good image quality.

Next, a method of manufacturing the developing device shown in FIG. 5, which is an embodiment of the invention described in claim 3, will be described. In this embodiment,
First, between the two magnet blocks 32 formed by sintering ferrite, a magnetic material piece 33 made of ferrite and a binder is formed.
And put them together. On the other hand, a substantially cylindrical magnetic material is molded by sintering a mixed material of powdered ferrite and a binder, and the peripheral surface of the cylindrical portion 31a is preliminarily adjusted to the shape of the magnet blocks 32, 32 and the magnetic material piece 33. To form a recess. Two magnet blocks 3 in this recess
2, 32 and the magnetic material piece 33 inserted between them are mounted and fixed.

After that, as shown in FIG. 7, a plurality of magnetizing blades 51 are brought close to each other from the outside of the peripheral surface of the substantially cylindrical magnetic material to form a plurality of magnetic poles along the circumferential direction of the cylindrically molded material. Magnetize as described. At this time, the two magnet blocks 3
As shown in FIG. 7 (b), the positions where the 2, 2 are provided are the same so that the two magnet blocks 32, 32 and the magnetic material piece 33 interposed between them form one magnetic pole. Magnetize with polarity. When magnetized in this manner, the magnet block 32 and the magnetic material piece 33 between the magnet block 32 and the magnet block 32 are magnetized.
Since it is a material that is more strongly magnetized, the magnetic field strength has two peaks on the magnet roll. Therefore, when such a magnet roll is placed in a hollow cylindrical sleeve,
A distribution of magnetic field strength as shown by the solid line B in FIG. 2 can be formed on the sleeve 30 on the surface of the developing roll. Such a developing roll is arranged in the housing of the developing device, and the developing device is assembled. Note that the conventional method can be used for the other steps for manufacturing the developing device.

Also, the distance x (the thickness of the magnetic material piece 33) between the magnet blocks 32 shown in FIG. 7B, the size of the magnet block 32 and the magnetic material piece 33 (the vertical and horizontal lengths), respectively. It is possible to freely set the heights of the two peaks, the widths of the two peaks, and the size of the depression by appropriately selecting the material and the like. Further, the number of peaks can be arbitrarily set depending on the number of magnet blocks 32 arranged.

[0033]

As described above, in the developing device according to the first aspect of the present invention, a plurality of strong magnetizations strongly magnetized in the circumferential direction of the magnet roll at a position facing the electrostatic latent image holding member. Since the blocks are arranged and a material that is less magnetized than the material forming the strong magnetization blocks is interposed between these strong magnetization blocks, the magnetic poles are located at the position facing the electrostatic latent image holder of the developing roll. The magnetic field strength distribution to be formed forms a plurality of peaks. Therefore, the developing region can be lengthened, and the magnetic brush is disturbed and reformed between the peaks, whereby the developing density can be increased. Therefore, even if a toner having a small particle size is used to obtain a high quality image, the development density can be increased without rotating the developing roll at a high speed, and an excellent image without fog can be obtained. Further, by appropriately selecting the strongly magnetized blocks and the material interposed therebetween, it is possible to easily adjust the magnitude and interval of the peak of the magnetic field strength in the developing region, and therefore these developing devices do not increase the cost. Can be manufactured.

In the method for manufacturing a developing device according to claim 2 or 3, a plurality of strongly magnetized blocks, a material interposed between them, and a substantially cylindrical magnetic material that supports the strongly magnetized blocks are molded, Since they are integrated and then magnetized, it becomes possible to easily form a magnetic pole having a plurality of peaks of magnetic field strength in a portion facing the electrostatic latent image holding member. The device can be manufactured at a low cost by a simple process.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a developing device which is an embodiment of the invention described in claim 1. FIG.

FIG. 2 is a diagram showing a distribution of magnetic field strength in a developing area of the developing device shown in FIG.

FIG. 3 is a diagram for explaining the distribution of magnetic force lines and the state of formation of magnetic brushes in the developing area of the developing device shown in FIG.

FIG. 4 is a process for manufacturing the developing device shown in FIG.
It is a figure which shows the state which magnetizes a magnet roll.

FIG. 5 is a schematic configuration diagram showing a developing device that is another embodiment of the invention described in claim 1.

FIG. 6 is a diagram illustrating a distribution state of magnetic force lines in a developing area of the developing device shown in FIG.

7 is a process for manufacturing the developing device shown in FIG.
It is a figure which shows the state which magnetizes a magnet roll.

FIG. 8 is a diagram showing a distribution of lines of magnetic force in a developing area of a conventional developing device.

FIG. 9 is a view showing a formation state of a magnetic brush formed in a developing area of a conventional developing device.

[Explanation of symbols]

 1, 21 Developing device 2, 22 Housing 3, 23 Developer regulating member 4, 24 Paddle 5, 25 1st auger 6, 26 2nd auger 7 1st stirring chamber 8 2nd stirring chamber 10, 30 Sleeve 11, 31 Magnet roll 12, 32 Magnet block (strongly magnetized block) 15 Developing roll 33 Magnetic material piece 40 Electrostatic latent image holder 63 Magnetic brush

Claims (3)

[Claims] 1. A hollow cylindrical sleeve which is provided so as to face the electrostatic latent image holding member and is rotationally driven in the circumferential direction, and a cylindrical magnet roll which is fixed and supported inside the sleeve. And a magnetic brush of a two-component developer is formed on the sleeve,
In a developing device that conveys a two-component developer to a developing area facing the electrostatic latent image holding member by the rotation of the sleeve to visualize the latent image on the electrostatic latent image holding member, A plurality of strong magnetization blocks made of a magnetic material are arranged in a circumferential direction at a position facing the image carrier, and a material that is harder to be magnetized than the material forming the strong magnetization blocks is interposed between the plurality of strong magnetization blocks. The developing device is characterized in that the plurality of strongly magnetized blocks or the plurality of strongly magnetized blocks and the material interposed therebetween are magnetized to have the same polarity. 2. The method for manufacturing a developing device according to claim 1, wherein a plurality of strongly magnetized blocks or a plurality of strongly magnetized blocks formed in a predetermined shape in a substantially cylindrical mold. The material to be inserted is fixed between the mold and the other part of the mold is filled with a material that is harder to be magnetized than the material forming the strong magnetization block to be solidified, and before or after the filled material is solidified. A method of manufacturing a developing device, which comprises magnetizing to form a magnet roll, which is inserted into a sleeve and fixedly supported in a housing. 3. The method of manufacturing a developing device according to claim 1, wherein the plurality of strongly magnetized blocks, or the plurality of strongly magnetized blocks and a material interposed therebetween are arranged in a substantially cylindrical shape. A strong magnetic block or a plurality of strong magnetic blocks molded into a predetermined shape by molding a material that is harder to magnetize than the strong magnetic block so as to have a concave portion corresponding to the shape of the arranged one. After a material inserted between these is mounted in the recess, it is magnetized to form a magnet roll, and the magnet roll is inserted into the sleeve and fixedly supported in the housing. Production method.