JPH09293609A - Extrusion technique of magnet roller in magnetic field and magnet roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the high magnetic force of a premolded item even if the manufacturing time of the molded item is shortened while the extrusion speed of an extruder is increased by a method wherein a resin material with a ferrite mixed therein is further molded on the outer periphery of the molded item, which is molded with a material with a ferrite mixed therein on a core axis and is orientated, making the position in the magnetic field orientation of the molded item coincide with the position in the magnetic field orientation of the outer peripheral layer of the molded item. SOLUTION: A core axis 10 is extruded from a crosshead metal mold, a resin material containing a ferrite is made to melt and is extruded by an extrucler and in an extrusion metal mold, the core axis 10 is put in a state that the molten material is applied on the periphery of the core axis 10 and the extrusion speed of the extruder and the core axis extrusion speed from the crosshead metal mold are adjusted to each other to extrude the core axis. Thereby, a molded item in a molten state is cooled and is formed into a press molded item 125. Then, a resin material mixed in with the same ferrire as the above ferrite is again applied and molded on the outer periphery of the molded item 125. In this case, for making the position in the magnetic field orientation of the molded item 125 coincide with the position in the magnetic field orientation of an outer peripheral layer 101, the shape of the molded item 125 is formed into a square and a triangular notch 121 for positioning the molded item 125 is provided in the square shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field extrusion method of a plastic magnet by extrusion molding and magnetic field orientation and magnetization, and a technical field relating to the magnet roller, and particularly to a developing roller in a developing device in a copying machine, The present invention relates to a toner replenishing roller and a cleaning roller for collecting toner remaining on the photoconductor.

[0002]

2. Description of the Related Art Conventionally, extrusion molding has been widely used as a method for manufacturing a plastic magnet roller. Among them, the integral molding method in which the core shaft is extruded with the plastic magnet material coated is mainly used.

As a molding method, in an extruder 1 as shown in FIGS. 1 and 2, a mixed material 5 of resin as a material of a plastic magnet and ferrite as a magnetic material is heated and melted from a material feeding hopper-2. The screw is pushed out to the extrusion die 7 which becomes the mold of the shape.

Further, the core shaft 10 has an inlet 11 for inserting the core shaft from the rear, a guide 12 aligned so that the position of the core shaft is the center, and further, a mixed material 5 melted by the extruder 1. The core shaft 10 is inserted into the extrusion mold 7 by using a crosshead mold 14 having an outlet 13 in which the clearance dimension with the core shaft is regulated so as not to flow backward from the extrusion mold 7.
As described above, the mixed material 5 is coated on the core shaft 10.

The pushing speed of the mixed material 5 and the pushing speed of the core shaft 10 are made to coincide with each other, and as shown in FIG.
The mixed material 5 covers the core shaft 10 in a gradually melted state, and a molded product 20 in a molten state is produced.

Next, in the molten state, the magnetic force generated by the magnetic field orientation coil 25 of the extruder in FIG. 2 is used to flow the molten magnetic product 20 into the orientation mold 27 using the yoke 26 which is a magnetic material. A magnetic field 33 is applied to the molded product as shown in FIG.

In the orienting mold 27, as shown in FIG. 5, a magnetic field coil 25 for generating a magnetic field has two north poles and two south poles.
The magnetic field coils 25 are arranged so as to surround the orienting die 27 by 90 ° in quadrupole orientation for each pole, and adjacent magnetic field coils 25 are arranged so as to form a pair of magnetic poles.

The magnetic field generated by the magnetic field orientation coil is generated by the magnetic material of the magnetic material incorporated in the orientation die 27 as shown in FIG.
The magnetic field loops 33 that propagate through the magnet 26 and flow from the N pole 30 to the adjacent S pole 31 are drawn, and the magnetic field loops 33 act on the mold forming portion 34. . The orientation die 27 is a combination of the yoke 26, which is a magnetic material, and the non-magnetic material 35. Since the magnetic field 33 generated by the orientation coil 25 propagates only in the yoke portion, the yoke is positioned. It is used as a magnetic field control because the size and direction of the magnetic field can be changed by changing the size of the magnetic field.

As a result, the ferrite, which was present in the molten mixed material shown in FIG. 6 without controlling the magnetic force, was subjected to a magnetic field as shown in FIG. Forms a vertical surface and is arranged with the south pole facing the north pole and the north pole surface facing the south pole. This arrangement of ferrite surfaces is called orientation, and the molten state of the molded article 20 has the magnetic force for the first time due to this orientation.

Then, the oriented molten product is
As shown in FIG. 8, the mixed material 5 is extruded from the orientation mold 27, the end portion is cut out, and the mixture material 5 is solidified by cooling to complete the magnet roller molded product as shown in FIGS. To do.

[0011]

In general extrusion molding, the initial state of the flow in a cross section perpendicular to the longitudinal direction of the flow path in the mold, that is, in the flow path cross section is as shown in FIG.
As shown in (a), there is no difference in flow velocity in the flow path cross section,
Even if it uniformly flows in the cross section of the flow path, the
As shown in (b), the flow velocity of the extruded mixed material 5 is high in the central portion 50 (the central portion of the vertical cross section with respect to the longitudinal direction of the flow channel), and becomes slower toward the flow channel wall surface 51. There is a phenomenon that there is a difference in the flow velocity.

This is because friction is generated between the molten resin material 20 and the flow passage wall surface 51, and the flow velocity becomes slow in the vicinity of the flow passage wall surface 51 due to the friction, and friction with the flow passage wall surface in the central portion 50. This is because the influence of is minimized and the flow velocity does not decrease.

This phenomenon becomes more remarkable as the viscosity of the material is lower, the extrusion speed is faster, and the difference between the mold temperature and the material temperature is larger.

In such a case, as shown in FIG. 11 (c), the inner central portion 50 due to the flow velocity difference when extruded from the mold.
There is a possibility that the molten material of (3) will be extruded quickly and will be divided into two parts in the longitudinal direction with the molten material of the outer flow path wall tube portion.

As described above, the center portion 50 of the flow is fast and the flow passage wall surface portion 51 is slow even in the cross section of the flow passage, so that the pressure is low in the center portion 50 and the flow passage wall surface portion 51 is As a result, a higher fluctuation occurs and
As shown in (b), the flow is inclined and disturbed.

As a result, the flow of the molten material 20 has been straightened by receiving the force in the traveling direction by the pushing force until now, and the flow is inclined by receiving the force in the central direction of the flow passage cross section. Or, a vortex is generated and the flow is disturbed.

The ferrite oriented by the magnetic field orientation mold 27 is oriented without being affected by the flow when the molten material 20 acts only in the traveling direction, that is, only in the force perpendicular to the magnetic field. However, the force in the cross section of the flow channel also acts to bend the flow or generate vortices, which causes the orientation to be inclined along the inclination of the flow, and the state where the orientation is disturbed by the turbulence of the flow. You can see the ferrite.

As a result, the magnetic force waveform of the molten molded product changes, and in particular, the magnetic force is reduced.

In the magnet roller thus formed in the extrusion molding section, the disturbance of the flow velocity disturbs the ferrite surface oriented by the magnetic field orientation die, so that the necessary magnetic force cannot be obtained.

Further, if the wall thickness of the molding portion is made thin so as not to disturb the flow velocity, both the central portion 50 and the wall portion 51 of the flow are strongly affected by the friction between the molten material 20 and the wall surface of the flow path. The flow velocity difference is small, the disorder of the ferrite surface is small, and the orientation is aligned. However, since the absolute amount of necessary ferrite is reduced, when a necessary magnetic force, especially a high magnetic force, is required, the magnetic force cannot be obtained and it may not be applicable.

From the above, it is difficult to form a plastic magnet roller of a thick pipe in particular, and it is often necessary to slow down the extrusion speed in order to solve these problems, which causes a problem that the manufacturing tact becomes long. .

Therefore, the problem to be solved by the present invention is to reduce the flow velocity difference between the resin on the outer side of the molding layer, that is, the flow path wall surface and the central portion at the time of molding the plastic magnet roller,
It is to provide an extrusion mold structure that can reduce the disorder of the orientation and realize a high magnetic force, which makes it possible to obtain an appropriate orientation even if the manufacturing tact is shortened while increasing the extrusion speed. And a magnetic field extrusion method for a particularly thick plastic magnet roller capable of obtaining a high magnetic force, and a plastic magnet roller having a high magnetic force with a proper orientation obtained by the manufacturing method. Is also to be provided.

[0023]

According to the present invention, a magnetic field orientation yaw is formed by molding a resin material in which ferrite is mixed around a core shaft.
In the magnetic field extrusion molding method of a plastic magnet roller that is created by orienting ferrite in the material using a magnetic field orientation mold, in the first step, as a pre-formed product, ferrite is placed on the core shaft by extrusion molding. A plastic magnet roller is created by molding and orienting the mixed material, and as the second step, a resin material mixed with ferrite is molded by extrusion molding on the outer periphery of the pre-molded product. The above-mentioned problems can be achieved by performing the magnetic field extrusion molding method of the magnet roller characterized by performing the magnetic field orientation so that the magnetic field orientation of the molded product and the magnetic field orientation of the outer peripheral layer are aligned. .

Further, since the magnetic force of the roller is largely influenced by the ferrite orientation on the surface, that is, the outer peripheral portion, ferrite powder having a high saturation magnetic flux density is used for the outer peripheral layer. Also,
There is a method of making the outer peripheral layer thinner than the pre-molded layer so as to eliminate the difference in the flow velocity of the outer peripheral layer.

[0025]

First, the flow velocity in the cross section of the flow channel is high in the central portion and becomes slower toward the wall surface portion of the flow channel. As shown in FIG.
A description will be given with the fluid flowing in the pipe divided into ~ 75.

When the fluid has no viscosity and friction does not occur in the contact portion between the wall surface of the flow path and the fluid, the fluid has no velocity difference in the cross section of the flow path, and each fluid element is
Proceed in the extrusion direction.

When a viscous fluid flows in the pipe, FIG.
As shown in FIG. 7, friction is generated at the contact portion between the pipe wall surface 79 and the fluid microelement 70 located inside by one due to the speed difference, and the force in the direction opposite to the fluid traveling direction between the contact portion layers, that is, the friction force 8
0 works.

The frictional force 80 reduces the velocity of the fluid element 70. Next, the speed of the fluid microelement 70 in contact with the wall surface of the flow path is reduced, so that a speed difference is generated between the fluid microelement 71 and the fluid microelement 71 located inside thereof.
In the same way, the frictional force 81 acts and the fluid element 71 also decelerates. However, the flow path wall surface and the fluid microelement 70 inside thereof
Since the speed difference between the fluid microelements 70 and 71 is smaller than the speed difference between and, the frictional force 81 is smaller than the frictional force 80, and the fluid element flowing inside is smaller than the fluid microelement flowing outside. Speed up.

Such a phenomenon continuously occurs from the wall surface portion of the flow passage toward the central portion, and the frictional force 84 between the adjacent fluid elements becomes smaller toward the center, so that the decrease in velocity is small. Become. Therefore, in the fluid element 74 flowing in the center and the fluid element 70 flowing in the vicinity of the flow path wall surface,
There will be a difference in flow velocity. In addition, such a difference in flow velocity increases as the cross section of the flow path increases.

Next, with the same initial flow velocity, the diameter of the flow tube is halved and the flow velocity difference is examined. As shown in FIG. 14, the fluid element 94 in the central portion of the flow is also close to the wall pipe, and the adjacent fluid element 9
It can be seen that the flow velocity is further affected by the friction with 3, 94 and the flow velocity is further reduced, and thus the flow velocity difference with the fluid element 90 near the flow tube wall is reduced.

Therefore, it is possible to obtain the magnetic force of the roller without disturbing the orientation of the ferrite when the forming layer is thinned and the forming is performed twice, that is, the preforming and the outer peripheral forming are divided. it is conceivable that.

Next, description will be made on matching the orientation positions of the pre-molded product and the outer peripheral layer. In the pre-molded product, the ferrite in the material is a 4-pole magnetic field coil 25 as shown in FIG.
It is oriented and magnetized by the magnetic field lines 33 that are generated.
FIG. 15 shows the magnetic force lines 100 of the pre-molded layer 99.

When the outer peripheral layer 101 is molded, the magnetic field lines 100 of the pre-molded product and the magnetic field lines 33 of the magnetic field orientation coil 25 for orienting the outer layer are not aligned with each other as shown in FIG. As a result, the orientation of the ferrite in the outer peripheral layer is disturbed, the magnetic field lines are disturbed, and the magnetic forces cancel each other out between N and S, resulting in a decrease in magnetic force.

Therefore, as shown in FIG. 17, by aligning the magnetic force lines 100 of the pre-molding 99 with the magnetic force lines 33 of the magnetic field orientation coil 25 for orienting the outer peripheral layer as shown in FIG. The magnetic force 33 generated in the roller due to the interaction between the magnetic force 33 and the magnetic force 100 from the pre-molding layer 99 can be effectively magnetized to a high magnetic force. Since it can be magnetized, a more stable magnetic force waveform can be obtained.

As described above, according to the method of extruding the magnet roller in the magnetic field described in claim 1 of the present invention, the forming layer is divided into a plurality of layers so as to prevent the orientation of the ferrite from being disturbed. The object can be achieved by matching the orientation positions of the molding layers.

Further, in the magnet roller molding in which the orientation position is aligned with the outer periphery of the inner pre-molded product and the ferrite-containing resin material is coated again and extruded, the magnetic force of the roller is the magnetic force of the ferrite of the outer peripheral layer 101. Pre-molded layer 9 orientation
It is more affected than the ferrite orientation of No. 9.

One of the reasons for this is that the magnetic performance of the magnet roller is judged by the magnitude of the magnetic force on the roller surface, and the orientation of the ferrite near the surface has a greater effect. The second reason is that if the thickness of the pre-molded layer and that of its outer peripheral layer are the same, the capacity of the material containing ferrite will be larger in the outer peripheral layer, and the magnetic force will be higher than in the inner pre-molded layer. .

Therefore, when the outer peripheral layer and the pre-molding layer have the same thickness, the outer peripheral layer 1 has the same thickness.
01 of the saturation magnetic flux density of the inner pre-molding layer 9
By setting the saturation magnetic flux density higher than 9, the high magnetic force can be obtained more effectively.

Further, by making the thickness of the outer peripheral layer smaller than the thickness of the pre-molding layer, the flow velocity difference in the cross section of the outer peripheral layer is reduced, and the disorder of ferrite orientation is suppressed.
High magnetic force can be obtained more efficiently. Further, if a high magnetic force can be obtained efficiently, it becomes easy to control the ferrite orientation in the magnet roller so as to obtain a desired magnetic force or a magnetic force waveform.

[0040]

EXAMPLE In the pre-molding, the structure of the extruder is as shown in FIGS. 1 and 2, and the members already used in the present invention and those which have been already explained will be explained in proportion.
As shown in FIG. 18, the cross-sectional shape 120 of the pre-molding is one side 1
Since the triangular notch 121 is formed in one corner of the 8 mm square, the extrusion die 7 and the magnetic field orientation die 27 are adapted to the shape. The thickness ratio between the pre-molded layer and the outer peripheral layer is about 1: 1.

The core shaft 10 having a diameter of 6 mm is used, and the inlet 11 and the outlet guide 1 of the crosshead mold 14 are used.
The size of 2 follows it. As the material, polypropylene is used as the resin material, strontium ferrite is used as the ferrite, and a lubricant is prescribed as the additive. Further, the mold is heated to near the melting temperature of the material, and the material is cooled in the mold so as not to solidify. First, the core shaft 10 is melted and extruded by the extruder 1 from the crosshead mold 14, and the melted material 20 is coated around the core shaft in the extrusion mold 7, and the extruder 1
The extrusion speed and the extrusion speed of the core shaft from the crosshead mold 14 are adjusted and extruded.

Next, as shown in FIG. 3, the molten material is molded into the external dimensions in the extrusion die 7, and the magnetic field orientation die 2 is formed.
Go to 7. In the magnetic field orientation mold 27, an orientation coil 25 for generating a magnetic field on the outside and a yoke 26, which is a magnetic material for causing the magnetic field to act on the molding material, are arranged as shown in FIG. The details of the alignment position and the alignment method are as described above.

By flowing the resin material containing ferrite therein, the surface of the ferrite is oriented perpendicular to the magnetic force lines 33. This is shown in FIGS. Finally, the melted molded product 20 is cooled by being extruded from the mold as shown in FIG. 5, and the pre-molded product 125 as shown in FIG. 19 is completed.

In the second step, the resin material 5 containing the same ferrite is again coated on the outer periphery of the pre-molded product 125,
Molding. The extrusion apparatus is the same as the pre-molding, but the outer peripheral layer 101 has a diameter of 30 mm.
The inner diameter of the extrusion die 7 and the magnetic field orientation die 27 is 3
The diameter of the circle is 0 mm. Crosshead mold 14 entrance 1
1. The inner diameter of the outlet guide 12 is set to the cross-sectional dimension 120 of the pre-molded product because the pre-molded product is inserted.

Further, when molding the outer peripheral layer 101, as shown in FIG.
As shown in FIG.
Since it is necessary to match the magnetic field orientation positions 102 of 1,
The shape of the pre-molded product 125 was square, and triangular notches 121 were provided for positioning.

As described above, the outer peripheral layer 101 is molded by the same procedure as the pre-molding with the pre-molded product 125 as the core. The magnetic field orientation mold is magnetically oriented as shown in FIGS. 17 and 20, and is extruded from the mold to be cooled to be a finished product shown in FIG. FIG. 22 shows a flow velocity difference 130 in the magnetic field orientation mold in the case of collective molding. FIG.
3 shows a flow velocity difference 131 due to preforming and outer peripheral layer forming.
From this, by molding the material layer in two steps,
The difference in flow velocity 131 between the central part and the part near the tube wall is improved, the flow is turbulent, and the magnetic field orientation of ferrite is extruded with the flow being adjusted, and it is also oriented from the outside to the inside of the molded product. As a result, the magnetic force is high and a molded product having a stable magnetic force waveform can be obtained.

(Embodiment 2) As shown in FIG. 24, a cross section of a pre-molded product 125 was formed into a circle having a diameter of 18 mm, and a flat surface notch 135 was formed on one left side so as to be oriented during outer peripheral molding. . The thickness ratio between the pre-molded layer and the outer peripheral layer is 1: 1. Other than that, the molding apparatus and procedure are the same as in Example 1, but in Example 2, pre-molding 1
Since the shape of the outer peripheral molding is similar to that of No. 25, the resin flow of the molten material is uniform in the entire cross section, the flow velocity difference 132 is improved, and the orientation can be performed more effectively and easily.

(Embodiment 3) Since the magnetic force or the magnetic force waveform required for the magnet roller is the magnetic force generated on the surface of the roller, the orientation of the ferrite on the outside of the orientation of the ferrite on the inside of the roller It is important because the magnetic force due to influences.

Therefore, in this embodiment, in order to improve the magnetic force of the outer peripheral layer, the ferrite mixed in the outer peripheral layer 101 is formed into a rare earth magnet having a high saturation magnetic flux density. The strontium ferrite of the pre-molded layer has a saturation magnetic flux density of 4.5 K gauss and the rare earth magnet has a saturation magnetic flux density of 1
Since it is 0K gauss, the roller also has high magnetic force,
Further, it becomes possible to perform the alignment efficiently with a small magnetic field.

(Embodiment 4) In order to improve the magnetic field orientation of ferrite in the outer peripheral layer, the thickness of the outer peripheral layer 101 is made smaller than that of the pre-molding layer 99 to further reduce the flow velocity difference in the outer peripheral layer 101. Here is an example.

Since the ratio of the thickness of the outer peripheral layer to the thickness of the pre-molded layer is 1: 3, the diameter of the pre-molded article 125 shown in FIG. 22 is 24 mm, the thickness of the pre-molded layer 99 is 9 mm, and the outer peripheral layer 101 is Thickness of 3 mm, extrusion mold 7,
The inner diameter of the magnetic field orientation mold 27 was set in the same manner.

As a result, the flow velocity difference of the pre-molding layer 99 is 14
Although 0 becomes large, the flow velocity difference 141 of the outer peripheral layer 101 is further improved, and the orientation state of the ferrite on the roller surface is improved, so that the surface magnetic force of the roller is improved.

[0053]

According to the first aspect of the present invention, by performing the plastic magnet extrusion molding method in a magnetic field, it is possible to reduce the flow velocity difference of the material between the wall surface portion and the central portion of the molding portion, and disturb the magnetic field orientation of the roller. Since the stable orientation can be achieved even inside the roller, it is effective for increasing the magnetic force of the roller, and the magnetic force waveform control of the roller becomes easy.

When the plastic magnet according to the second aspect is extruded in a magnetic field, the difference in the flow velocity of the material between the wall surface portion and the central portion of the molding portion can be reduced.
Since the stable orientation can be achieved inside the roller layer without disturbing the magnetic field orientation of the roller, it is effective for increasing the magnetic force of the roller, and the magnetic force waveform of the roller can be more efficiently obtained. Can be controlled.

[Brief description of drawings]

FIG. 1 is a side view of an extrusion magnetic field orientation apparatus used in the present invention.

FIG. 2 is a front view of an extrusion magnetic field orientation apparatus used in the present invention.

FIG. 3 is a state diagram in which a molten material is coated on the core shaft.

FIG. 4 is a state diagram in which a molten material is magnetically oriented in a magnetic field orientation mold.

FIG. 5 is a state diagram of a magnetic field line loop generated from a magnetic field orientation coil.

FIG. 6 is a phase diagram of ferrite in the material when it is not magnetically oriented.

FIG. 7: Phase diagram of ferrite in magnetic field oriented material

FIG. 8 is a view showing the completion of the roller, in which the magnetic field-oriented molding roller is extruded from the mold and cooled.

[Figure 9] Roller finished product cross section

[Figure 10] Front view of the finished roller

FIG. 11 is a state diagram until the ferrite orientation is disturbed by the flow velocity difference and the ferrite is extruded.

FIG. 12 is a model diagram of the flow when there is no flow velocity difference between the fluids in the flow tube.

FIG. 13 is a model diagram in which friction is generated between each fluid element in the flow tube and a difference in flow velocity is generated.

FIG. 14 is a model diagram showing that the difference in flow velocity is small.

FIG. 15 is a state diagram in which the ferrite of the pre-molding layer is oriented.

FIG. 16 is a state diagram showing that the outer peripheral layer is magnetically oriented without the alignment position of the pre-molding layer and the outer peripheral layer being aligned.

FIG. 17 is a state diagram showing that the peripheral layer is magnetically oriented by aligning the alignment position of the pre-molding layer with the alignment position of the outer peripheral layer.

FIG. 18 is a cross-sectional view of preforming in Example 1 of the present invention.

FIG. 19: Pre-molded product in Example 1 of the present invention

FIG. 20 is a state diagram showing the extrusion molding of the outer peripheral layer on the pre-molded product.

FIG. 21 is a finished product diagram of the roller in the first embodiment of the present invention.

22 (a) is a sectional view of a die for batch molding in the present invention. FIG. 22 (b) is a state diagram showing a flow velocity difference in a die for batch molding in the present invention.

23A is a sectional view of the inside of the mold according to the first embodiment of the present invention. FIG. 23B is a state diagram showing the flow velocity difference in the mold of the first embodiment according to the present invention.

FIG. 24A is a sectional view of the inside of a mold according to the second embodiment of the present invention. FIG. 24B is a state diagram showing a flow velocity difference inside the mold of the second embodiment according to the present invention.

[Explanation of symbols]

7 Extrusion Die, 10 Core Shaft, 14 Cross Head Die, 20 Molded Layer 25 in Melt State Magnetic Field Orientation Coil, 2
6 yokes, 27 magnetic field orientation mold, 30 magnetic field orientation coil N pole, 31 magnetic field orientation coil S pole, 33 magnetic field lines in magnetic field orientation mold, 99 pre-molding layer, 100 magnetic field lines of pre-molding layer, 101 outer peripheral layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Nakamura 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Kyota Hizuka 1-3-6 Nakamagome, Ota-ku, Tokyo In stock company Ricoh (72) Inventor Kenji Narita 1-3-6 Nakamagome, Ota-ku, Tokyo Stock company Ricoh (72) Inventor Kenichi Ishiguro 1-3-6 Nakamagome, Tokyo Ota-ku Inside Ricoh

Claims (4)

[Claims] 1. A plastic magnet roller is extruded in a magnetic field by molding a resin material in which ferrite is mixed around a core shaft and orienting the ferrite in the material using a magnetic field orientation yoke and a magnetic field orientation die. In the molding method, in the first step, as a pre-molded product, a plastic magnet roller is created by molding and orienting a material mixed with ferrite on the core shaft by extrusion molding, and as a second step, the pre-molded product is prepared. Further, a resin material mixed with ferrite is molded by extrusion molding on the outer periphery of the molded product, and magnetic field orientation is performed so that the magnetic field orientation of the pre-molded product and the magnetic field orientation of the outer peripheral layer are matched at that time. Extrusion molding method in a magnetic field of a magnet roller. 2. A magnet roller according to claim 1, wherein the saturation magnetic flux density of the ferrite mixed in the material of the outer peripheral layer of the pre-molding is equal to or higher than the saturation magnetic flux density of the ferrite of the pre-molding layer. Extrusion molding method in magnetic field. 3. A resin mixture material in which ferrite is mixed is extruded on a core shaft to form a pre-molding magnet roller by magnetic field molding, and a resin mixture material in which ferrite is similarly mixed is extruded on the outer periphery thereof by magnetic field molding. The magnet roller is characterized in that the magnetic field orientations of the pre-molding layer and the outer peripheral layer are arranged in the same direction at that time for molding. 4. The magnet roller according to claim 3, wherein the saturation magnetic flux density of the mixed material is higher in the outer peripheral layer than in the preforming layer.