JP2009098327A - Magnet roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem involved in a magnet roller of conventional shaft integral type: the magnet roller is warped , the bending strengths of the shaft part and main body part of the magnet roller are decreased, or magnetic flux density in the axial direction of the roller suddenly is decreased locally due to a cooling speed difference between the peripheral part and central part of the roller, or the occurrence of a void or the like. <P>SOLUTION: The magnet roller is made of a mixture containing ferromagnetic powder and resin binder. This magnet roller is molded through a step in which at least a radially central part for the magnet roller is molded and a step in which a peripheral part for the main body of the magnet roller is molded. The contents of the ferromagnetic powder satisfy a following relation: the peripheral part of the main body of the magnet roller ≥ the radially central part of the magnet roller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnet roller used as a developing roller incorporated in an image forming apparatus such as a copying machine, a printer, or a facsimile. More particularly, the present invention relates to a shaft-integrated magnet roller having improved bending strength, warpage, and magnetic flux density.

Known magnet rollers include a magnet roller in which a magnet piece is arranged on the outer periphery of a shaft such as metal, or a shaft unit integrated magnet roller in which a shaft unit and a main body are integrated. In particular, the shaft-integrated magnet roller is widely used as a developing roller incorporated in an image forming apparatus, taking advantage of low cost. As a method of forming the shaft-integrated magnet roller, before injecting the molten resin magnet material into the cavity, the injection of the molten resin magnet material is started with the volume in the cavity being minimized, and the molten resin magnet is A method of forming a magnet roller by retreating a slide mold in accordance with material injection to increase a cavity volume (Patent Document 1), and a hollow cylindrical metal shaft in a magnet roller molding mold (in the cavity) Has been proposed (Patent Document 2) in which the same molten resin magnet material is injected into the hollow portion and the outer peripheral portion of the metal shaft in the cavity to form a magnet roller.
JP-A-11-138562 JP 2007-150005 A

However, Patent Document 1 is a method of simultaneously forming the radial center portion of the magnet roller and the outer peripheral portion of the main body, and cooling starts from the outer peripheral portion of the magnet roller due to the structure of this mold. It takes time to cool down, and as a result, the warp of the magnet roller and the strength of the central portion in the radial direction may be reduced, leading to the bending of the magnet roller. In some cases, voids are generated in the vicinity, and the magnetic flux density in the axial direction locally decreases rapidly.
For this reason, for example, it is difficult to use for a multifunction printer (MFP) or the like that requires durability (number of printed sheets 10 to 100 times that of a normal printer) compared to a normal printer.

  Further, Patent Document 2 injects the same molten resin into the hollow portion and the outer peripheral portion of a hollow cylindrical metal shaft, and similarly to Patent Document 1, there is a cooling delay in the hollow portion. Although there is a concern, the strength is maintained because the hollow cylindrical metal shaft is used, but the cost may be increased or the formability may be lowered.

The present invention provides a magnet roller obtained by molding a mixture containing at least a ferromagnetic powder and a resin binder, wherein the content of the ferromagnetic powder is:
Magnet roller main body outer periphery ≧ magnet roller radial center,
It is a magnet roller that satisfies the following relationship.

  The present invention also relates to a magnet roller obtained by molding a mixture containing at least a ferromagnetic powder and a resin binder, wherein the resin binder is different between the outer peripheral portion of the magnet roller and the central portion in the radial direction of the magnet roller. It is a magnet roller using

  Further, the present invention provides a magnet roller including a step of injecting a molten mixture containing a ferromagnetic powder and a resin binder into a cavity and molding by applying a magnetic field, and molding at least a central portion in the radial direction of the magnet roller; This is a magnet roller formed in two steps of forming the outer peripheral part of the main body of the magnet roller.

  Further, the present invention is a magnet roller using a resin binder whose hardness at the time of curing of the resin binder used in the central portion in the radial direction of the magnet roller is harder than that of the resin at the outer peripheral portion of the main body.

  Furthermore, the present invention is a magnet roller in which a central portion in the radial direction of the magnet roller is formed without applying a low magnetic field (less than 240 K · A / m) or a magnetic field.

  The present invention is a magnet roller in which a permanent magnet (12) is embedded as an excitation source, and magnetic field application molding is performed.

  The magnet roller of the present invention is less likely to warp, and further improves the strength of the central portion in the radial direction of the magnet roller including the shaft portion, making it difficult for the magnet roller to break, and reducing the occurrence of voids. A sudden drop in the axial magnetic flux density can be prevented. Furthermore, since an expensive metal shaft or the like is not used, cost reduction can be expected.

  Next, the magnet roller of the present invention will be described in detail with an example.

  The present invention is a magnet roller formed in two steps, that is, a step of forming at least a radial center portion of the magnet roller and a step of forming the outer peripheral portion of the main body of the magnet roller.

  A shaft-integrated magnet roller is formed using a forming apparatus as shown in FIG. First, molten resin magnet material is injected while moving the slide mold A (1) in the direction of increasing the cavity volume, and the movement of the slide mold A (1) is stopped at a predetermined position, and the magnet roller The central portion in the radial direction is formed. Thereafter, while the slide mold B (2) is moved in the direction in which the cavity volume increases, the molten resin magnet material is injected, the movement of the slide mold B (2) is stopped at a predetermined position, and the magnet roller A shaft-integrated magnet roller as shown in FIG. 2 is formed.

  On the other hand, conventionally, as in the manufacturing method shown in FIG. 3, for example, a molten resin magnet material is injected while moving the slide mold C (11) in the direction in which the cavity volume increases, and the slide mold C is injected at a predetermined position. The movement of the mold C (11) was stopped, and the shaft portion and the main body portion of the magnet roller were formed. In such a conventional manufacturing method, the cooling rate in the vicinity of the outer peripheral portion of the main body portion and the cooling rate in the central portion in the radial direction of the magnet roller (near the shaft portion) are different, and as a result, the magnet roller is warped.

  In addition, a void is formed near the radial center of the magnet roller, the void adversely affects the magnetic characteristics, the uniformity of the magnetic flux density in the axial direction is reduced, and a local sudden magnetic flux density drop may occur. It was.

  Furthermore, the bending strength of the shaft portion may decrease due to the difference in the cooling rate and the generation of voids.

  Compared with the conventional manufacturing method, as described above, the present invention first forms only the central portion in the radial direction of the magnet roller, which is a portion corresponding to the shaft portion, so that the cavity volume is relatively small. As the filling rate is improved, the voids are drastically reduced, and only the central portion in the radial direction of the magnet roller is cooled, so that the cooling efficiency (speed) is improved and warpage can be prevented.

  In the case of molding only the central portion in the radial direction of the magnet roller, the magnetic field may be applied arbitrarily. When a magnetic field is applied, a magnetic field of 240 K · A / m to 2400 K · A / m may be applied (five locations). When emphasis is placed on improving magnetic characteristics, a desired magnetic field may be applied even in the step of forming the central portion in the radial direction of the magnet roller. Further, when importance is attached to the bending strength improvement of the shaft portion, a low magnetic field (less than 240 K · A / m) may be applied, or molding may be performed without applying a magnetic field. When a low magnetic field or no magnetic field is applied, the molten resin magnet material flowing in the cavity is not attracted in the direction of the applied magnetic field, the flow of the molten resin magnet material in the cavity is smooth, and the generation of voids is further suppressed. The

  When importance is attached to the improvement of the magnetic characteristics, as shown in FIG. 4, the permanent magnet (12) is embedded as an excitation source at a desired position of the slide mold B (2), and the orientation of the magnetic particles inside the shaft portion. The degree may be improved.

  After forming the magnet roller radial center as described above, molten resin magnet material is injected while moving the slide mold B (2) in the direction of increasing the cavity volume, and 240K · A / m to 2400K. Orientation and magnetization while applying a magnetic field of A / m (5 places), stop the movement of the slide mold B (2) at a predetermined position, and form the outer peripheral part of the magnet roller in the radial direction. A shaft-integrated magnet roller as shown in FIG. Also in this case, as in the case of molding only the central portion in the radial direction of the magnet roller, since the cavity volume is relatively small compared to the conventional manufacturing method, the filling rate of the molten resin magnet material is improved, and voids are drastically reduced. A sudden drop in magnetic flux density can be prevented locally, a uniform axial magnetic flux density can be obtained, density unevenness of images and white spots can be prevented, and high image quality can be obtained.

  Further, the present invention is a magnet roller that satisfies the relationship of the outer peripheral portion of the magnet roller ≧ the central portion in the radial direction of the magnet roller in the content of the ferromagnetic powder.

  For example, when importance is attached to the bending strength improvement of the shaft part, the content of the ferromagnetic powder in the outer peripheral part of the magnet roller body is 90% by weight, the resin binder (including lubricant, stabilizer, etc.) is 10% by weight, The content of the ferromagnetic powder in the central portion in the radial direction of the magnet roller is 85% by weight, and the resin binder (including lubricant, stabilizer, etc.) is 15% by weight. In this manner, the bending strength can be improved by increasing the amount of the resin binder in the central portion in the radial direction of the magnet roller. In addition, carbon fiber, glass fiber, whisker, or the like may be added to the resin binder at the radial center of the magnet roller for the purpose of improving the strength. However, when these are added to the outer peripheral portion of the main body of the magnet roller, the bending strength is improved, but there is a case where the magnetic property is deteriorated.

  Further, in this magnet roller forming method, a shaft-integrated magnet roller is formed using a forming apparatus as shown in FIG. First, while moving the slide mold A in the direction in which the cavity volume increases, a molten resin magnet material is injected, the slide mold A stops moving at a predetermined position, and the radial center portion of the magnet roller is moved. Form. Then, while moving the slide mold B in the direction in which the cavity volume increases, the molten resin magnet material is injected, the slide mold B stops moving at a predetermined position, and the outer peripheral part of the magnet roller in the radial direction body And a shaft-integrated magnet roller as shown in FIG. 5 is formed.

  In the above invention, the following ferromagnetic powder and resin binder can be used as the magnet roller material.

Examples of the ferromagnetic powder include anisotropic ferrite magnetic powder having a chemical formula represented by MO.nFe ₂ O ₃ (n is a natural number). As M in the formula, one type or two or more types such as Sr, Ba or lead are appropriately selected and used.

  Further, as the ferromagnetic powder, anisotropic ferrite magnetic powder, isotropic ferrite magnetic powder, anisotropic rare earth magnetic powder (for example, SmFeN-based), and isotropic rare earth magnetic powder (for example, NdFeB-based) are used alone or in two types. You may mix and use the above. What is necessary is just to select suitably by the required magnetic flux density.

  Resin binders include polyamide resin, ethylene ethyl acrylate resin, polystyrene resin, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PPS (polyphenylene sulfide), EVA (ethylene-vinyl acetate copolymer), EVOH (ethylene-ethylene). 1 type or 2 or more types such as vinyl alcohol copolymer) and PVC (polyvinyl chloride), or thermosetting properties such as epoxy resin, phenol resin, urea resin, melamine resin, furan resin, unsaturated polyester resin and polyimide resin. One kind or two or more kinds of resins can be mixed and used.

  The content of the single magnetic powder or mixed magnetic powder shown above is preferably in the range of 50 to 95% by weight. If the content of the single magnetic powder or the mixed magnetic powder is less than 50% by weight, the magnetic properties of the magnet roller are lowered due to the lack of magnetic powder, making it difficult to obtain a desired magnetic force, and the content is 95% by weight. If it exceeds 1, the resin binder becomes insufficient and the moldability may be impaired.

  Additives include silane and titanate coupling agents as surface treatment agents for magnetic powders, polystyrene and fluorine lubricants that improve fluidity, stabilizers, plasticizers, or flame retardants. .

  Further, the present invention is a magnet roller using different resin binders in the outer peripheral part of the main body of the magnet roller and the radial center part of the magnet roller.

  For example, in the same manner as described above, when importance is attached to the bending strength improvement of the shaft portion, the content of the ferromagnetic powder in the outer peripheral portion of the magnet roller main body is 90% by weight, and the resin binder (including lubricant, stabilizer, etc.) is 10%. By using a resin binder whose hardness at the time of curing is harder than that of the resin at the outer periphery of the main body, the content of the ferromagnetic powder in the central portion in the radial direction of the magnet roller is 90% by weight The bending strength at the radial center of the magnet roller can be improved. Furthermore, in order to improve the strength of the central portion in the radial direction of the magnet roller, the content of ferromagnetic powder in the central portion in the radial direction of the magnet roller may be reduced, or carbon fiber, glass fiber, whisker, or the like may be added. .

  In addition, the magnet roller is formed in the same manner as described above by first forming the radial center portion of the magnet roller using a molding apparatus as shown in FIG. An outer peripheral part is formed, and a shaft-integrated magnet roller as shown in FIG. 6 is formed.

  For example, when a polyamide resin is used as the resin binder in the outer peripheral portion of the main body, the resin binder in the central portion in the radial direction may be a PPS (polyphenylene sulfide) resin, a modified polyphenylene ether (PPE) having a higher hardness when cured than the polyamide resin. ) Resin, polyetherimide (PEI) resin, polyethersulfone (PES) resin, etc. can be used alone or in admixture of two or more.

  In particular, when using a resin having a high hardness in the radial center portion, warpage may occur due to a difference in thermal expansion coefficient between the radial center portion and the outer peripheral portion of the main body, in order to prevent the warpage. Moreover, as the resin of the outer peripheral portion of the main body, an EEA resin, EVA resin, PVC resin, or the like having a low hardness at the time of curing is preferable.

  By using the shaft-unit-integrated magnet roll of the present invention, the strength of the central portion in the radial direction of the magnet roller including the shaft portion is improved and the bending strength is improved. Multifunction printers) can also be used at low cost.

  Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited thereto.

  In addition, the measuring method of the characteristic value used for this invention is as follows.

(Folding strength)
The obtained magnet roller is fixed as shown in FIG. 7, and the tip of a jig (head) that presses the shaft portion is R8 (manufactured by SUS303) using an autograph AGS-H manufactured by SHIMADZU. (Pressure jig lowering speed) was 50 mm / min, and the bending strength of the shaft part and the main body part was measured.

(Main pole magnetic flux density peak value, main pole axial direction magnetic flux density variation and ripple value)
The obtained magnet roller is supported at both ends of the magnet roller by 8 mm in the radial direction from the center of the magnet roller, and the tip of a Gauss meter probe (Bell magnetic flux density sensor) is installed at the center of the magnet roller axis. The magnet roller is rotated, the magnetic flux density in the circumferential direction of the magnet roller is measured, the magnetic flux density peak position of the main pole is detected, the axial magnetic flux density of the main pole is measured at that position, and the magnet roller body In the region excluding 10 mm in both axial directions, the difference between the maximum magnetic flux density and the minimum magnetic flux density was taken as the axial magnetic flux density variation, and the local magnetic flux density change rate (mT / mm: ripple) was measured. The ripple value is (local magnetic flux density variation mT) / (axial distance mm).

Example 1
As a magnet roller material of Figure 2, Nylon 6 resin in the resin binder (manufactured by Unitika A1015P) 10 wt% (lubricant, including the stabilizer), ferromagnetic powder anisotropic strontium ferrite (SrO · _6Fe 2 _{O 3} ) 90% by weight of powder (NF-350 manufactured by Nippon Valve Industry Co., Ltd.), these are mixed, melt-kneaded and formed into a pellet. As shown in FIG. 1 (a), the pellet is melted and injected from the gate port as shown in FIG. 1 while the cavity volume is minimum, and the slide mold A (1) is injected together with the molten resin magnet material. Is moved backward to increase the cavity volume, and orientation and magnetization is performed while applying a magnetic field of 240K · A / m to 2400K · A / m (5 locations), and the slide mold A (1) is moved to a predetermined position. It was made to retreat and the radial center part of the magnet roller including the shaft part was formed. Next, the pellet is injected in a molten state from a gate port different from the above, and the cavity volume is increased by retreating the slide mold B (2) along with the injection of the molten resin magnet material, and 240 K · A / Orientation and magnetization are performed while applying a magnetic field of m to 2400 K · A / m (5 locations), the slide mold B (2) is retracted to a predetermined position, and the outer periphery of the magnet roller body is formed. A magnet roller like 2 was obtained.

  The outer diameter of the outer peripheral part of the obtained magnet roller is φ13.6 mm, the outer diameter of both end shafts is φ5 mm, the axial length of the magnet roller main body is 320 mm, and the axial length of the magnet roller including both end shafts The thickness was 355 mm.

  With the measurement method described above, the bending strength of the shaft portion (radial center portion) and the main body portion (outer peripheral portion of the magnet roller) obtained, and the main pole magnetic flux density peak value, main pole axial magnetic flux density variation, and Ripple was measured. The measurement results are shown in Table 1.

  Here, the bending strength of the shaft portion (radial center portion) is preferably 100 N or more, and the bending strength of the main body portion (main body outer peripheral portion) is preferably 500 N or more. The main pole magnetic flux density peak value is preferably 80 mT or more. Moreover, the axial magnetic flux density variation is preferably 6 mT or less, and the local magnetic flux density reduction rate (ripple) in the axial direction is preferably 0.5 mT / mm or less.

（実施例２）
軸部を含むマグネットローラの径方向中心部の成形時に磁場を印加しない以外はすべて実施例１と同様に行った。測定結果を表１に示す。

(Example 2)
The same procedure as in Example 1 was performed except that no magnetic field was applied during molding of the radial center portion of the magnet roller including the shaft portion. The measurement results are shown in Table 1.

(Example 3)
The same procedure as in Example 1 was performed except that a permanent magnet was embedded as an excitation source at a desired position of the slide mold B (2). The measurement results are shown in Table 1.

Example 4
As a shaft material for the magnet roller of FIG. 8, 15 wt% of nylon 6 resin (A1015P manufactured by Unitika) is used as the resin binder, and anisotropic strontium ferrite (SrO.6Fe ₂ ) is used as the ferromagnetic powder. The same procedure as in Example 1 was carried out except that O ₃ ) powder (NF-350 manufactured by Nippon Valve Industry Co., Ltd.) was 85% by weight. The measurement results are shown in Table 1.

(Example 5)
The same procedure as in Example 1 was performed except that PPS resin (A900 manufactured by Toray Industries, Inc.) was used as the resin binder at the radial center of the magnet roller including the shaft. The measurement results are shown in Table 1.

(Example 6)
The same procedure as in Example 1 was performed except that PPS resin (Toray A503F1: with glass fiber) was used as the resin binder at the radial center of the magnet roller including the shaft. The measurement results are shown in Table 1.

(Comparative Example 1)
As shown in FIG. 3, while the slide mold C (11) is moved in the direction of increasing the cavity volume, the molten resin magnet material is injected, and the slide mold C (11) is moved at a predetermined position. All operations were performed in the same manner as in Example 1, except that the shaft portion (radially central portion) and the main body portion (main body outer peripheral portion) of the magnet roller were formed. The measurement results are shown in Table 1.

(Comparative Example 2)
15% by weight of nylon 6 resin (A1015P manufactured by Unitika) as a resin binder (including lubricant and stabilizer), anisotropic strontium ferrite (SrO.6Fe ₂ O ₃ ) powder as a ferromagnetic powder (NF-manufactured by Nippon Valve Industrial Co., Ltd.) 350) was changed to 85% by weight. The measurement results are shown in Table 1.

(Comparative Example 3)
10% by weight of PPS resin (A900 manufactured by Toray Industries, Inc.) as the resin binder (including lubricant and stabilizer), anisotropic strontium ferrite (SrO.6Fe ₂ O ₃ ) powder as the ferromagnetic powder (NF-350 manufactured by Nippon Valve Corporation) ) Was performed in the same manner as Comparative Example 1 except that the content was 90% by weight. The measurement results are shown in Table 1.

  Comparing the bending strengths of the shaft portions (radially central portions) of Examples 1 to 6 and Comparative Examples 1 to 3, it can be seen that the shaft portion bending strength is improved in comparison with the comparative example.

  Moreover, when the bending strength of the main body part (main body outer peripheral part) of Examples 1 to 3 and Comparative Example 1 was compared, the bending strength of the shaft part (radial center) was improved in Examples 1 to 3, so that the main body It can be seen that the bending strength of the part (outer peripheral part of the main body) is also improved, and in the magnetic characteristics, the void in the central part in the radial direction of the magnet roller is reduced, and the magnetic pole axial direction magnetic flux density ripple and variation are improved. You can see that

  Furthermore, from Examples 4 to 6, by reducing the content of the ferromagnetic powder body in the shaft portion (radially central portion) or changing the resin binder, the shaft portion (radially central portion) and the main body portion ( It can be seen that the bending strength of the outer periphery of the main body is improved.

  As in Comparative Examples 2 and 3, when the content of the ferromagnetic powder body in the entire magnet roller is decreased, the bending strength of the shaft portion (radial center portion) and the main body portion (main body outer peripheral portion) is improved. It can be seen that the magnetic characteristics (main pole magnetic flux density peak value and main pole axial direction magnetic flux density variation) are reduced.

An apparatus (mold) for forming the magnet roller of the present invention. (A) is a state before injection of molten resin magnet material. (B) is the state of completion of injection of the molten resin magnet material into the shaft portion. (C) is a state in which the molten resin magnet material is completely injected into the main body. Magnetic roller perspective view of the present invention Conventional magnet roller molding equipment (mold) Apparatus (mold) for molding another magnet roller of the present invention Another magnet roller perspective view of the present invention Another magnet roller perspective view of the present invention Folding strength measuring device for shaft and main body of magnet roller

Explanation of symbols

1 Slide mold A
2 Slide mold B
3 Gate port 4 Molding space (shaft)
5 Molding space (main part)
6 Excitation source 7 Fixed mold 8 Moving mold 9 Magnet roller body outer peripheral part (main part)
10 Magnet roller center (shaft)
11 Slide mold C
12 Excitation source (permanent magnet)
13 Magnet roller center (shaft)
14 Magnet roller center (shaft)
15 head (pressure jig)
16 Magnet roller fixing jig 17 Folding strength measuring device base stand

Claims (6)

In a magnet roller obtained by molding a mixture containing at least a ferromagnetic powder and a resin binder, the content of the ferromagnetic powder is
Magnet roller main body outer periphery ≧ magnet roller radial center,
A magnet roller characterized by satisfying the following relationship.   In a magnet roller obtained by molding a mixture containing at least a ferromagnetic powder and a resin binder, a resin binder that is different between the outer peripheral portion of the magnet roller main body and the radial center of the magnet roller is used. Magnet roller to do.   In a magnet roller including a step of injecting a molten mixture containing a ferromagnetic powder and a resin binder into a cavity and molding by applying a magnetic field, at least a step of molding the central portion in the radial direction of the magnet roller, and an outer periphery of the magnet roller main body A magnet roller formed by two steps of forming a part.   3. The magnet roller according to claim 2, wherein the resin binder used at the central portion in the radial direction of the magnet roller is harder than the resin at the outer periphery of the main body.   5. The magnet roller according to claim 1, wherein the central portion in the radial direction of the magnet roller is formed without applying a low magnetic field (less than 240 K · A / m) or a magnetic field.   The magnet roller according to any one of claims 1 to 5, wherein a permanent magnet is embedded as an excitation source and molded by applying a magnetic field.

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