JPH0815988A - Developing roller in image forming device and its manufacture - Google Patents

Abstract

PURPOSE:To impart a rotational force to a carrier attracted on the surface of a photoreceptor and to prevent the carrier attraction by making the width of the magnetic density distribution curve small at the tip side in the direction along the peripheral direction of a sleeve roller in the area corresponding to the part for feeding the toner to the photoreceptor on the magnet roller. CONSTITUTION:The developing roller 4 is constituted so that different plural magnetic poles S1, N1, S2, S3 and N2 are arranged in this order in the peripheral direction inside the magnet roller 3 disposed in a stationary state inside the rotating sleeve roller 2. One magnetic pole N1 out of the magnetic poles is provided with the function for forming the developer into a napping state and this part becomes the carrier feeding area B. Then, the width of the magnetic density distribution curve E in the feeding area B is formed so as to become small on the tip side in the direction along the peripheral direction of the sleeve roller 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roller for an image forming apparatus such as an electrostatic photocopier, and more specifically, a two-component system having a toner roller and a magnet roller inside a sleeve roller. Developing roller for supplying the toner in the developer to the photoconductor by using the developer (generally, the toner is a non-magnetic substance and the carrier is a magnetic substance), and a manufacturing method thereof. Regarding

[0002]

2. Description of the Related Art A developing unit used in an image forming apparatus of this type, which uses a two-component system in which a toner and a carrier are mixed as a developer, has conventionally been a developing roller for supplying a toner to a photosensitive member, a toner. It has a stirring roller for stirring the carrier and a carrier, a supply roller for supplying the stirred developer to the developing roller, an ear cutting plate for regulating the developer adsorbed on the developing roller, a sensor for detecting the toner concentration, and the like.

As shown in FIG. 9, the developing roller 01 includes a magnet roller 02 and this magnet roller.
It is composed of a non-magnetic sleeve 03 that is fitted onto 02 so as to rotate counterclockwise. This magnet roller
02 is a plurality of magnetic poles N for supplying the developer to the photoconductor 04.
1, N2, S1, S2, S3. Each of the plurality of magnetic poles has a function of adsorbing and transporting the developer, and forming a magnetic brush in a state where the developer stands up at a portion approaching the photoconductor 04. The distribution of magnetic flux density between the magnetic poles is as shown in the same figure, and in the developing roller, the central portion on the left side of the drawing, that is, the region 05 corresponding to the N1 magnetic pole, that is, the developer stands up. In this state, the developer is supplied to the photoconductor 04 in the area where the magnetic brush is formed.

By the way, in this type of image forming apparatus, as is well known, the surface of the photosensitive member 04 is
For example, after positively (or negatively) charging, perform exposure,
Subsequently, the photosensitive member 04 is rotated to make the exposed area reach the developer supply area 05 facing the developing roller 01, and the negatively (or positively) charged toner is attached to the exposed area from the developing roller 01. The development is performed by. Further, the carrier is positively (or negatively) charged.

[0005]

However, in this type of image forming apparatus, a so-called toner fog phenomenon or a so-called carrier pulling phenomenon in which a carrier is attracted is sometimes observed on the surface of the photoconductor 04, and these phenomena are basically In addition to causing a defective image, it adversely affects other peripheral devices.

On the other hand, looking at the distribution curve 0E of the magnetic flux density in the developer supply region 05, as shown in FIG. 9, from the vicinity of the base near the sleeve to the radially outward side of the magnet roller 02. It is understood that there is a wide width in almost the entire region of the tip of the sleeve, and in particular, the tip has a distance in the rotational direction of the sleeve 03. That is, as shown in the schematic diagram of the flow of magnetic force lines in FIG. 10, the magnetic attractive force to the carrier in the supply region 05 is very high and low in any part of the magnetic flux density distribution curve 0E (FIG. 9) in the sleeve circumferential direction. It can be seen that there is no difference and they are almost even. In addition, the attraction direction of the magnet roller is substantially along the virtual line segment (normal line) 0P that connects the shaft cores of the photoconductor 04 and the magnet roller 02 at any part of the tip magnetic flux density distribution curve 0E. You can see that it is heading toward the axis of 02.

Therefore, no matter where in the magnetic flux density distribution curve 0E, the carrier is in a direction substantially along the line segment (normal line) 0P connecting the axis of the photoconductor 04 and the axis of the magnet roller 02. It receives a relatively strong magnetic attraction toward the magnet roller 03 side.

Looking at the carrier pulling phenomenon in more detail, for example, the photoconductor is positively charged, and the carrier is also positively charged by stirring and mixing with the toner. However, once the carrier was once adsorbed on the surface of the photoconductor 04, it was understood that what was originally positively charged was partially charged to the negative electrode on the photoconductor side. It is understood that most of the other components remain charged to the positive electrode.

Further, once the carrier is adsorbed on the surface of the photoconductor, a polarization phenomenon occurs due to so-called electrostatic induction, and the photoconductor side becomes the N pole, and the opposite side, that is, the developing roller side becomes the S pole. Exhibit a phenomenon.

Further, the toner is attached to the surface of the carrier by magnetic attraction and is supplied to the photosensitive member side. Observing how the toner adheres to the carrier,
It is understood that the toner does not adhere to the entire circumference of the carrier, and a relatively large amount of the toner non-adhered region remains on the surface of the carrier. That is, it can be seen that the toner still has a sufficient surface for adhering a large amount of toner.

In view of the phenomenon of carrier pulling and fogging, which has been heretofore seen in the prior art, the present invention shows that, as a result of various studies, the magnetic flux density distribution, the carrier and the toner are not generated by the conventional mechanical means. It is to provide a novel developing roller capable of easily preventing carrier pulling and fogging by making good use of the adhesion state of the toner, the property of the carrier at the time of pulling the carrier, and each of these phenomena.
The purpose of.

A second object of the present invention is to provide a method capable of efficiently manufacturing the developing roller in the image forming apparatus of the present invention.

[0013]

In order to achieve the above object, a developing roller in an image forming apparatus of the present invention has a magnet roller inside a sleeve roller, and uses a developer composed of toner and carrier. In the developing roller of the image forming apparatus that supplies the toner in the developer to the photoconductor, the magnetic flux density distribution curve in the area corresponding to the portion of the magnet roller that supplies the toner to the photoconductor has a circumference of the sleeve roller. It is characterized in that the tip side is narrowed in the direction along the direction.

A manufacturing method for achieving the second object is
In a method of manufacturing a developing roller of an image forming apparatus, which has a magnet roller inside a sleeve roller and uses a developer composed of toner and carrier, and supplies the toner in the developer to a photoconductor, a plurality of magnetic fields are generated. When forming a plurality of magnetic poles for adsorbing toner at a fixed position of the magnet roller according to the magnetic flux density distribution of the means, correspond to a portion between the plurality of magnetic poles that supplies toner to the photoconductor of the magnet roller. In order to narrow the magnetic flux density distribution curve in the region in which the leading end side is narrowed in the direction along the circumferential direction of the sleeve roller, the magnetic flux density distribution is regulated by using other magnetic field generating means. Is.

[0015]

With the developing roller in the image forming apparatus of the present invention constructed as described above, the magnetic flux density distribution curve in the region corresponding to the portion of the magnet roller for supplying the toner to the photosensitive member is calculated in the circumferential direction of the sleeve roller. Since the tip side is narrowed in the direction along, the width in the sleeve circumferential direction on the tip side of this magnetic flux density distribution curve is almost eliminated as shown in FIGS. As is also shown in the related art, it is wide in almost the entire region from the vicinity of the base near the sleeve to the tip end portion on the radially outer side of the magnet roller, and there is no property that the tip has a distance in the circumferential direction of the sleeve at all. Be understood.

That is, according to the conventional structure, the magnetic attractive force with respect to the carriers in the supply region is substantially uniform with no significant difference in height in any part of the magnetic flux density distribution curve in the sleeve circumferential direction. Contrary to what is seen, in the present invention, as shown in FIGS. 1 and 2, in the sleeve circumferential direction, the narrow central portion on the tip side is extremely high, and becomes as low as possible away from both sides thereof. From
While the magnetic attraction to the carrier at the narrow portion on the tip side is remarkably strong, if the magnetic attraction to the carrier is slightly shifted from the narrow central portion on the tip side in the sleeve circumferential direction, the magnetic attraction force to the carrier is increased. It can be said that it has a characteristic of being attenuated.

Therefore, as shown in FIG. 4 (A), among the carriers adsorbed on the photosensitive member 1, the position in the rotating direction of the photosensitive member is better than the position of the narrow portion on the tip side of the magnetic flux density distribution curve. The one on the side receives not only the magnetic attractive force (R1) to the developing roller side but also the force (T1) that is attracted upward (tangential direction) due to the influence of the direction of the magnetic force line. The resultant force (RF1) acts on the carrier D, and the carrier D is given a rotational force in the direction in which the resultant force (RF1) acts, that is, counterclockwise, and conversely the tip of the magnetic flux density distribution is sharp. As shown in FIG. 5 (A), the one on the lower side of the photosensitive member rotating direction than the partial existing position is
Similarly, not only the magnetic attraction (R2) to the developing roller side but also the force (T2) that is influenced downward by the direction of the magnetic force lines and is attracted downward (tangential direction) is received. (RF2) acts, and this resultant force (RF
Rotational force is applied in the working direction of 2), that is, in the clockwise direction. However, at this time, as described above, since the negative electrode on the carrier D side exists only in the local portion facing the photoconductor side, a slight rotational force is applied to the carrier as shown in FIGS. As shown in (B) above, the balance between the positive electrode on the photosensitive member side and the negative electrode on the carrier side up to now is destroyed all at once, and the carrier is peeled off within a short time.

Further, since a rotational force is applied to the carrier D to change its direction, the portion of the carrier surface on which the toner is not adhered is located closer to the surface of the photoconductor or closer to the surface of the photoconductor. The toner adhering to the non-exposed area on the surface of the photoconductor can be successfully attracted to the non-toner adhering portion of this carrier.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 7 is a schematic cross-sectional view showing a structure in the vicinity of a developing portion in an image forming apparatus such as an electrostatic photocopier having a developing device using a developing roller according to the present invention. ing.

In the electrostatographic copying machine of this embodiment, as shown in FIG.
As shown in FIG. 8, the photoconductor 1 is horizontally mounted inside the main body of the copying machine, and the developing roller 4 in which the magnet roller 3 is provided in a stationary state inside the rotating sleeve roller 2, the toner and the carrier. A stirring rotor 5 for mixing the above into a developer and a supply roller 6 for supplying the developer stirred by the stirring rotor 5 to the developing roller 4 are built in the developer accommodating case 7. A spike-cutting member (spike-off plate) 8 that regulates the height of the spikes of the developer on the developing roller 4, and the excess developer after the spike-cutting is diverted above the supply roller 6 to provide a toner replenishing device. A partition plate 10 for returning the toner to the toner replenishment section from 9 is provided, and a rectifying plate 11 is provided on the partition plate 10 at a predetermined interval in the rotation axis direction of the supply roller 6, and Plate 11 is toner More flow-down direction downstream side deviate to one side of the rotational axis direction is provided.

A toner concentration sensor S for driving the toner replenishing device 9 based on the detection of the concentration of the excess developer is provided in the vicinity of the ear cutting member 8 and agitates the developer dropped from the partition plate 10. Further, the developer is formed so as to be agitated by the agitating rotor 5 while being transported toward the other end side in the rotation axis direction.

The partition plate 10 has a chevron shape when viewed from the direction of the rotation axis of the supply roller 6, and the surplus developer cut off by the ear cutting member 8 while being pushed up by the supply roller 6 is moved upward or rearward. The swash plate portion 10a on the upstream side for recirculating the developer and the swash plate portion 10b on the downstream side for recirculating the developer having passed over the swash plate portion 10a toward the stirring rotor 5 obliquely rearward and downward are provided.

In FIG. 7, 12 is a toner replenishing roller arranged at the lower end of the toner replenishing device 9,
The toner inside is supplied to the stirring rotor 5.

As shown in FIG. 8, the developing roller 4 has a plurality of different magnet rollers 3 (five in the example shown in the drawing, but not shown) disposed inside the rotating sleeve roller 2 in a stationary state. There are various numbers of magnetic poles S1, N
1, S2, N2, S3 are arranged in this order in the circumferential direction, and one of these magnetic poles N1 has a function of forming a magnetic brush in a state in which the developer stands. As a matter of fact, this portion serves as the carrier supply region B.

As shown in FIG. 1, the magnetic flux density distribution curve E in the region corresponding to the portion of the magnet roller 3 that supplies toner to the photoconductor 1, that is, the region corresponding to the supply region B. Is formed so that the tip side becomes narrow in the direction along the circumferential direction of the sleeve roller 2.

As a result, as shown in FIG. 2, the magnetic attraction of the magnet roller 3 with respect to the carrier in the supply area B becomes narrower on the tip side in the direction along the sleeve circumferential direction of the magnetic flux density distribution curve E. The central part is extremely high, and its suction direction is a virtual line segment (normal line) connecting the shaft cores of the photoconductor 1 and the magnet roller 3 to each other.
Since it is directed straight toward the axis of the magnet roller 3 along P, the magnetic attractive force R (see FIG. 3 (A)) on the carrier at the portion where the tip side is narrow is remarkably strong. However, on the contrary, the suction force becomes as low as possible as the tip end side moves away from both sides of the narrow central portion, and the suction direction is the normal line P.
The attraction force T1, T2, which goes toward the circumferential direction (tangential direction) by being influenced by the direction of the magnetic force lines, as well as the direction along the
[See each (B)]].
Therefore, when the tip side is slightly displaced from the narrow central portion in the sleeve circumferential direction, the magnetic attractive force on the carrier in the direction along the normal P is suddenly attenuated.

Therefore, the carrier D having the highest magnetic flux density distribution on the portion where the tip side of the magnetic flux density distribution curve E is narrow is, as shown in the schematic view of FIG. A line segment connecting the axis and the axis of the developing roller 4 (normal line)
It only receives a strong magnetic attractive force R toward the developing roller 4 side in a direction substantially along P.

However, among the carriers D adsorbed on the photoconductor 1, the carrier D located on the upper side of the photoconductor rotating direction Y than the position where the leading end side of the magnetic flux density distribution curve E is narrow is shown in FIG. As shown in the schematic view of (A), not only the magnetic attractive force R1 toward the developing roller 4 side but also the force T1 which is influenced upward by the direction of the magnetic force line and is attracted upward (tangential direction), The resultant force RF1 of both forces acts individually,
Carrier D is pulled in the direction of this resultant force RF1,
As a result, a rotational force, that is, a counterclockwise rotational force is given.

On the contrary, the carrier D on the tip side of the magnetic flux density distribution curve E on the lower side of the photosensitive member rotating direction Y from the position where the narrow portion is present is as shown in the schematic view of FIG. 5 (A). Similarly to the above, the magnetic attractive force R2 toward the developing roller 4 side as well as the force T2 which is influenced downward by the direction of the magnetic force lines and is attracted downward (tangential direction) is received. The resultant force RF2 acts on the carrier D.
Is pulled in the working direction, and as a result, a rotational force, that is, a clockwise rotational force is given.

However, at this time, as described above, since the negative electrode on the carrier side exists only in the local portion facing the photoconductor, only a slight rotational force is applied to the carrier as shown in FIG. As shown in (B) and the schematic view of FIG. 5 (B), the balance between the positive electrode on the photoconductor side and the negative electrode on the carrier side up to now is destroyed all at once, and the carrier D is peeled off within a short distance. I will end up. As a result, so-called carrier pulling can be effectively prevented.

Further, since a rotational force is applied to the carrier D to change its direction, the portion of the carrier surface on which the toner is not adhered is located on the surface side of the photoconductor or closer to the surface side of the photoconductor, so that the carrier can be easily moved. This allows the toner adhering to the non-exposed area on the surface of the photoconductor to be successfully attracted to the toner non-adhering portion of the carrier D. By this, so-called fogging can be effectively prevented.

Next, a method of manufacturing the magnet roller 3 will be described. The magnet roller 3 is integrally molded using a known material, for example, a mixture of magnetic powder and synthetic resin powder.

FIG. 6 is an enlarged sectional view of a magnetizing device for the magnet roller 3 formed as described above.
As shown in the drawing, the magnet roller 3 is provided with 13
The magnetic flux density distribution curve E in a region corresponding to N1 that is magnetically attached at the same time, that is, a region corresponding to the supply region B of the magnet roller 3 is the sleeve roller 2
It is formed so that the tip side becomes narrower in the direction along the circumferential direction.

Specifically, as shown in the figure, the same number of soft iron electromagnetic yokes and electromagnetic coils are provided corresponding to the positions and the number of the plurality of magnetic poles, and the soft iron electromagnetic yokes 14a and the electromagnetic coils 14b are provided. Is a portion for magnetizing the magnet roller 3 with the N1 pole, a soft iron electromagnetic yoke 15a and an electromagnetic coil 15b for magnetizing the magnet roller 3 with the S1 pole, and a soft iron electromagnetic yoke 16a and an electromagnetic coil 16b for the magnet roller 3.
The portion for magnetizing the two poles, the soft iron electromagnetic yoke 17a and the electromagnetic coil 17b for magnetizing the magnet roller 3 with the S3 pole, and the soft iron electromagnetic yoke 18a and the electromagnetic coil 18b for magnetizing the magnet roller 3 with the S2 pole. It is a part.

In the soft iron electromagnetic yoke 14a and the electromagnetic coil 14b, the magnetic flux density distribution curve E in the area corresponding to the supply area B of the magnet roller 3 has a tip in the direction along the circumferential direction of the sleeve roller 2. It is provided so that the side is narrowed, and in the cross-sectional shape of the magnet roller 3 in the direction orthogonal to the axis, the tip, that is, the side facing the circumferential surface of the magnet roller 3, It is formed so sharply that it restricts the lines of magnetic force so that when the N1 pole is magnetized, the N1 pole has the above-described distribution.

As described above, the shape of the soft iron electromagnetic yoke 14a is sharper toward the tip, that is, on the side facing the circumferential surface of the magnet roller 3, in the cross-sectional shape in the direction orthogonal to the axis of the magnet roller 3. In addition to the above, the same operation and effect as described above can be obtained by making the entire width as thin as possible and forming a strip shape in the cross-sectional shape in the direction orthogonal to the axis of the magnet roller 3. it can.

In FIG. 6, 19 is a magnetic path yoke for connecting the magnetic paths of the respective electromagnetic yokes, and 20 is a resin spacer for supporting the magnet roller 3.

The magnet roller 3 manufactured as described above is then housed in the magnetizing device 13, and the magnetic poles N1, N2, S1, S2, S3 corresponding to the respective positions on the outer periphery thereof are magnetized, and in addition, The magnetic flux density distribution curve E in the area corresponding to the supply area B of the roller 3 is also formed such that the tip side becomes narrow in the direction along the circumferential direction of the sleeve roller 2. The magnetized magnet roller 3 is shown in FIG.
As shown in FIG. 8, after the shaft 21 made of, for example, stainless steel is press-fitted, it is housed and fixed inside the sleeve roller 2.

The magnet roller 3 is of a fixed type in the illustrated example, but is not necessarily limited to this structure, and a rotary type can also be used.

Further, although the magnetic poles are provided at five places and the arrangement thereof is also arranged in the order of S1, N1, S2, S3 and N2, various different forms are also adopted in this respect. Needless to say.

Further, it is needless to say that the types of magnetic poles and charging described in the embodiments are merely examples, and therefore the magnetic poles and charging may be completely opposite.

[0042]

As described above, according to the present invention, the magnetic flux density distribution curve in the region corresponding to the portion of the magnet roller for supplying the toner to the photosensitive member is set to the tip side in the direction along the circumferential direction of the sleeve roller. By making the width narrower, a rotational force can be applied to the carrier adsorbed on the surface of the photoconductor, so that the negative electrode (or positive electrode) on the carrier side exists only in the local portion facing the photoconductor side. Therefore, the balance between the positive electrode (or the negative electrode) on the side of the photoreceptor and the negative electrode (or the positive electrode) on the carrier side up to now is lost all at once, and the carrier is peeled off within a short time. by this,
So-called carrier pulling can be effectively prevented, and image defects can be prevented in advance.

By applying a rotational force to the carrier and changing its direction, the portion of the carrier surface on which the toner is not adhered can be easily directed toward the surface of the photoconductor or closer to the surface of the photoconductor. As a result, the toner adhering to the non-exposed area on the surface of the photoconductor can be successfully attracted to the toner non-adhering portion of this carrier. By this, so-called fogging can be effectively prevented.

Further, in the method for manufacturing the developing roller in the image forming apparatus according to the present invention, the magnetic flux density distribution curve in the region corresponding to the portion of the magnet roller for supplying the toner to the photosensitive member is set in the circumferential direction of the sleeve roller. Although the magnetic flux density distribution is regulated by using other magnetic field generating means in order to narrow the tip side in the direction along the same direction, it is the same as the magnetizing device inevitably adopted in this magnet roller. Since it employs a magnetizing device, it can be used to magnetize other magnetic poles at once in a magnet roller, as compared with, for example, devices that prevent carrier pulling and fogging by using other mechanical means. In addition, the magnetic flux density distribution curve in the area corresponding to the supply area can be narrowed on the front end side in the direction along the circumferential direction of the sleeve roller, which enables highly efficient manufacturing and, at the same time, increases the added value. The split those comprising on the attained also the manufacturing cost, the structure is simple, there is an advantage that does not lead to increase in size of the apparatus.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a magnetic flux density distribution of a developing roller according to an embodiment of a developing roller and its manufacturing method in an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram showing the flow of magnetic lines of force in the supply region of the developing roller, showing an embodiment of the developing roller and its manufacturing method in the image forming apparatus of the present invention.

FIG. 3 is an explanatory view of the operation of an embodiment of the developing roller and its manufacturing method in the image forming apparatus of the present invention.

FIG. 4 is an explanatory view of the operation, showing an embodiment of the developing roller and its manufacturing method in the image forming apparatus of the present invention.

FIG. 5 is an explanatory view of the operation, showing an embodiment of the developing roller and its manufacturing method in the image forming apparatus of the present invention.

FIG. 6 is a sectional view of a magnetizing device for manufacturing the developing roller, showing an embodiment of the developing roller and the manufacturing method thereof in the image forming apparatus of the present invention.

FIG. 7 is a schematic cross-sectional view of a developing device using the developing roller, showing an embodiment of the developing roller and the manufacturing method thereof in the image forming apparatus of the present invention.

FIG. 8 is a partial enlarged cross-sectional view of the vicinity of the developing roller, showing an embodiment of the developing roller and its manufacturing method in the image forming apparatus of the present invention.

FIG. 9 is an explanatory diagram showing a magnetic flux density distribution of a conventional developing roller.

FIG. 10 is a schematic diagram of a flow of magnetic force lines in a supply area of a conventional developing roller.

[Explanation of symbols]

1-photoreceptor, 2-sleeve roller, 3 ... magnet roller, 4-developing roller, 13-magnetizing device, 14a-soft iron electromagnetic yoke, 14b-electromagnetic coil, B-supply area, D-carrier, E-magnetic flux Density distribution curve, P-normal line, R, R1, R2-normal magnetic attraction, T1, T2-tangential magnetic attraction,
RF1, RF2-combined force.

Claims (3)

[Claims] 1. A magnet roller is provided inside a sleeve roller, and a developer composed of toner and carrier is used.
In the developing roller of the image forming apparatus that supplies the toner in the developer to the photoconductor, the magnetic flux density distribution curve in the area corresponding to the portion of the magnet roller that supplies the toner to the photoconductor has a circumference of the sleeve roller. A developing roller in an image forming apparatus, wherein a front end side is narrowed in a direction along the direction. 2. A magnet roller is provided inside the sleeve roller, and a developer comprising toner and carrier is used.
In a method of manufacturing a developing roller of an image forming apparatus that supplies toner in the developer to a photoconductor, a plurality of magnetic poles for adhering the toner to a fixed position of the magnet roller by a magnetic flux density distribution of a plurality of magnetic field generating means. When forming the magnetic flux density distribution curve in the region corresponding to the portion of the magnet roller that supplies toner to the photoconductor between the plurality of magnetic poles, the tip side in the direction along the circumferential direction of the sleeve roller. A method of manufacturing a developing roller in an image forming apparatus, wherein the magnetic flux density distribution is regulated by using another magnetic field generating means in order to narrow the width. 3. The other magnetic field generating means employs an electromagnetic yoke and an electromagnetic coil made of metal, and the electromagnetic yoke is sharper toward its tip end in a sectional shape along a direction orthogonal to the axis of the magnet roller. Is it trapezoidal,
The method for manufacturing a developing roller in an image forming apparatus according to claim 2, wherein the whole is formed in a narrow strip shape.