JP2006071733A - Magnet roller, developing roller, development device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet roller by extrusion molding having high magnetic characteristics. <P>SOLUTION: The magnet roller 10 has a cylindrical magnet 2 formed by extrusion molding a resin composition containing 92 to 95wt% anisotropic magnetic powder and 8 to 5wt% polymeric material to a pipe form while applying a magnetic field thereto within a mold, wherein the storage elastic modulus of the resin composition at ordinary temperature is confined to ≤10 MPa. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnet roller used in an image forming apparatus such as a copying machine, a facsimile machine, and a printer, a developing roller having the magnet roller, a developing device having the developing roller, a process cartridge having the developing device, and the process cartridge. The present invention relates to an image forming apparatus.

  Many methods are known for the electrophotographic process. Most of them form an electrostatic latent image on a photoconductor, develop the electrostatic latent image with toner, and then use the toner. The developed electrostatic latent image is transferred onto paper or the like, and then the toner is fixed by heating or the like.

  Many methods are also known for developing with toner. One of them, the two-component development system, develops an electrostatic latent image on a photoreceptor by transporting a developer composed of toner and magnetic particles by a developing roller having a magnet roller as a magnetism generating member. It is. As a developing roller used in a two-component developing device, a developing roller in which a nonmagnetic cylindrical body is covered on the outer periphery of a magnet roller is known. The magnet roller is provided with a plurality of magnetic poles according to the configuration of the developing device. In the developing pole, the electrostatic latent image on the photosensitive member is developed by forming a spike on the nonmagnetic cylindrical body so that the developer follows the magnetic field lines, so that the developing ability is increased by increasing the peak magnetic flux density of the developing pole. The image density can be increased. Further, in the development area, it is desired to supply only the toner of the toner and carrier constituting the developer to the image area of the electrostatic latent image, but the carrier may also adhere to the photoconductor. The carrier is subjected to a magnetic force from the developing roller, an electric force from the photosensitive member, and a centrifugal force due to the rotation of the developing roller. The magnetic force is a force in a direction in which the magnetic force is attracted to the developing roller, and is a force in a direction in which the resultant force of the electric force and the centrifugal force is separated from the developing roller. The carrier needs to stay on the developing roller due to the magnetic force, but when the resultant force of the electric force and the centrifugal force becomes larger than the magnetic force, the carrier adheres to the photoconductor. This is a phenomenon called carrier adhesion. When the carrier adheres to the photoconductor, the carrier moves to the transfer body and paper together with the toner, adversely affects the transfer device and the fixing device, and reduces the reliability of the image forming apparatus. In order to prevent carrier adhesion, it is necessary to increase the magnetic force of the developing pole of the developing roller and its adjacent pole.

  Therefore, in order to improve the image quality and reliability of the image forming apparatus, it is effective to increase the magnetic characteristics of the developing pole of the developing roller and its adjacent pole, and the magnetic field generating member of the developing roller. It is effective for the magnet roller to have high magnetic characteristics.

  As a magnet used for the magnet roller, a sintered magnet is known for a long time, but a plastic magnet (see Patent Document 1) formed by extrusion molding a resin composition containing a polymer material and magnetic powder. A plastic magnet formed by injection molding a resin composition containing a polymer material and magnetic powder (see Patent Document 2) can be obtained in a relatively easy manner, and is now mainstream. Yes. Plastic magnets can obtain higher magnetic properties if the content of magnetic powder is increased. However, if the content of magnetic powder is increased, the viscosity of the resin composition increases and the moldability deteriorates, so magnetic powder is contained. Increasing the amount beyond a certain amount will not improve the magnetic properties. Due to these restrictions, the plastic magnet has a problem that it is difficult to obtain high magnetic characteristics as compared with the sintered magnet.

  In order to obtain higher magnetic properties with plastic magnets that have limitations in increasing the magnetic powder content, molding is performed in a magnetic field using anisotropic magnetic powder, and the direction of the easy axis of magnetization of the magnetic powder is aligned ( (Orienting) is effective. Compared with a plastic magnet in which magnetic powder is not oriented, a magnetic characteristic in which magnetic powder is oriented is improved by about 70%. When injection molding is performed while applying a magnetic field, the melted material is fed into the mold, the magnetic powder is applied to orient the magnetic powder, and the viscosity is maintained in the mold until the orientation of the magnetic powder is maintained. Since it cools after hold | maintaining, magnetic powder can be easily orientated and the magnetic characteristic which material has can fully be utilized. However, in the case of a long length such as that used in a magnet roller, there is a problem in that the orientation of the magnetic powder tends to be different depending on the distance from the gate, and the deviation of the magnetic characteristics in the longitudinal direction tends to be large.

  When a resin composition containing a polymer material and magnetic powder is extruded while applying a magnetic field, the magnetic powder is not oriented unless the resin composition has a certain low viscosity in the region where the magnetic field is applied. The direction in which the resin composition is extruded and the direction in which the magnetic powder is oriented are orthogonal to each other, so that the oriented magnetic powder is likely to be disturbed, and therefore, it is generally difficult to obtain higher magnetic properties than injection molding. There was a problem.

When extruding while applying a magnetic field, the magnetic powder needs a certain degree of freedom so that the magnetization easy axes are aligned in the region where the magnetic field is applied. Moreover, it is necessary to hold the oriented magnetic powder until it is cooled from the region where the magnetic field is applied. Therefore, the polymer material is required to have an appropriate viscosity in a wide temperature range.
JP 10-104950 A JP 10-116714 A

  The present invention aims to solve this problem.

  That is, an object of the present invention is to provide an extrusion-molded magnet roller having high magnetic properties.

  In order to achieve the above-mentioned object, a first aspect of the present invention provides a resin composition containing 92 to 95% by weight of anisotropic magnetic powder and 8 to 5% by weight of a polymer material in a mold. A magnet roller having a cylindrical magnet that is extruded into a pipe shape while applying a magnetic field, wherein the resin composition has a storage elastic modulus at room temperature of 10 MPa or less.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, the polymer material is an olefin elastomer.

  The invention described in claim 3 is the invention described in claim 2, wherein the olefin-based elastomer is an ethylene ethyl acrylate copolymer containing 30% by weight or more of ethyl acrylate. It is what.

  The invention described in claim 4 is a developing roller characterized in that a rotatable nonmagnetic cylindrical body is disposed on the outer periphery of the magnet roller according to any one of claims 1 to 3.

  According to a fifth aspect of the present invention, in the developing device having at least a developing roller, a developer supply member, and a developer regulating member, the developing roller according to the fifth aspect is provided as the developing roller. Developing device.

  According to a sixth aspect of the present invention, there is provided a developing device having at least a developer carrier, a developer supply member, and a developer regulating member, and a process cartridge having a charging roller and an image carrier. A process cartridge comprising the developing device according to claim 5.

  According to a seventh aspect of the present invention, in an image forming apparatus having at least a process cartridge, an optical writing means, a transfer member, and a fixing device, the process cartridge according to the sixth aspect is provided as the process cartridge. The image forming apparatus.

  According to the invention described in claim 1, since the storage elastic modulus at room temperature of the resin composition is 10 MPa or less, even if the magnetic powder content in the resin composition is increased to 92% by weight or more, the magnetic property The degree of orientation of the powder does not decrease, and therefore a magnet roller with high magnetic properties can be obtained.

  According to the invention described in claim 2, since the polymer material is an olefin-based elastomer, it can have an appropriate viscosity in a wide temperature range. For this reason, when extrusion molding is performed while applying a magnetic field. In addition, it is possible to obtain a magnet roller having higher magnetic characteristics while minimizing the deterioration of magnetic characteristics, which is a problem.

  According to the invention described in claim 3, since the olefin elastomer is an ethylene ethyl acrylate copolymer containing ethyl acrylate in a proportion of 30% by weight or more, a filler is added to the resin composition containing the olefin elastomer. Formability can be ensured even with high filling, and for this reason, a magnet roller with higher magnetic properties without occurrence of abnormalities such as cracks can be obtained.

  According to the invention described in claim 4, since the rotatable nonmagnetic cylindrical body is disposed on the outer periphery of the magnet roller according to any one of claims 1 to 3, adhesion of the carrier is prevented. Therefore, it is possible to provide a developing roller that can achieve high image quality.

  According to the fifth aspect of the present invention, in the developing device having at least the developing roller, the developer supplying member, the developer layer regulating member, and the developer, the developing roller according to claim 4 as the developing roller. Therefore, high image quality can be achieved.

  According to the sixth aspect of the present invention, the process cartridge having at least the developing device, the photosensitive member, and the charging roller has the developing device according to the fifth aspect as the developing device. Is possible.

  According to the seventh aspect of the present invention, the image forming apparatus having at least the process cartridge, the optical writing unit, the transfer member, and the fixing device includes the process cartridge according to the sixth aspect. Image quality can be improved.

  FIG. 1 is a cross-sectional view of a developing roller showing an embodiment of the present invention. FIG. 2 is an explanatory diagram of a developing device showing an embodiment of the present invention. FIG. 3 is an explanatory diagram of a process cartridge showing an embodiment of the present invention. FIG. 4 is an explanatory diagram of an image forming apparatus showing an embodiment of the present invention. FIG. 5 is a graph showing the relationship between the temperature (° C.) of the resin composition and the storage elastic modulus in Example 1.

  In order to enhance the magnetic properties of the magnet roller, it is effective to increase the content of the magnetic powder in the resin composition to be extruded and to increase the degree of orientation of the magnetic powder. In order to enhance the magnetic properties of the magnet roller, it was studied to increase the content of magnetic powder in the resin composition to be extruded. As magnetic powder, strontium ferrite which is anisotropic ferrite was used. As the polymer material, an ethylene ethyl acrylate copolymer suitable for high filler filling was used. The content of ethyl acrylate, which is an amorphous component in the ethylene ethyl acrylate copolymer, was 25% by weight in order to ensure moldability. As a result, the magnetic characteristics of the magnet roller peak when the magnetic powder content in the resin composition is around 91.3 wt%, and it is understood that the magnetic characteristics of the magnet roller do not improve even if the content exceeds 91.3 wt%. It was. Therefore, the present inventors considered that when the content of the magnetic powder in the resin composition to be extruded is increased, the flexibility of the resin composition is lost, so that the magnetic powder is difficult to be oriented, In order to increase the degree of orientation of the magnetic component, it was investigated to increase the flexibility of the resin composition. Specifically, as the polymer material constituting the resin composition, an ethylene ethyl acrylate copolymer having an ethyl acrylate content increased to 35% by weight was used. When the ethyl acrylate content in the ethylene ethyl acrylate copolymer is increased, there is a concern that the shape stability is deteriorated due to being too flexible. However, by increasing the magnetic powder content, it was aimed to achieve an appropriate flexibility. As a result, the magnet roller magnetic characteristics were improved even when the magnetic characteristics were 92% by weight or more.

  According to the study by the present inventors, it has been found that even if the content of the magnetic powder in the resin composition to be extruded is increased, the magnetic characteristics of the magnetic roller will not be improved unless flexibility is secured. Therefore, as an index of flexibility, the viscoelastic characteristics of the molding material were evaluated, and attention was paid to the storage elastic modulus indicating the properties of the elastic component of the viscoelastic characteristics. Increasing the magnetic powder content tends to increase the storage modulus. When an ethylene ethyl acrylate copolymer having an ethyl acrylate content of 25% by weight is used as the polymer material, the magnetic properties in the resin composition are increased. When the powder content was 91.3% by weight, the storage elastic modulus reached 10 MPa. When an ethylene ethyl acrylate copolymer having an ethyl acrylate content of 35% by weight was used, the storage modulus reached 10 MPa when the magnetic powder content was 92.7% by weight. In any of the resin compositions, the magnet roller magnetic characteristics peaked around the storage elastic modulus reaching 10 MPa. Even if the content of the magnetic powder in the resin composition is increased to 92% by weight or more, if the content of the magnetic powder in the resin composition is 10 MPa or less, the degree of orientation of the magnetic powder does not decrease. Was found to have high magnetic properties.

  The storage elastic modulus of the present invention is an elastic modulus measured by applying a certain strain to a sample using a commercially available VAR type rheometer [ReoExplorer (Reologica Instruments AB (Sweden))], and is well known in the art. It is a thing. The “storage modulus” of the present invention is obtained by heating a sample to 280 ° C., melting it, and sandwiching it between two plates having a diameter of 20 mm so as to have a thickness of 1 mm. Decrease to 30 degrees at 5 ° C./min and measure from strain at those temperatures. The “storage modulus” measured with this VAR rheometer is an index for evaluating the viscoelasticity of the resin composition to be extruded. In this specification, the elastic modulus measured with such a VAR rheometer is referred to as “storage elastic modulus”.

  The present invention has been made based on such knowledge. That is, as shown in FIG. 1, the magnet roller 10 of the present invention is obtained by applying a resin composition containing 92 to 95 wt% anisotropic magnetic powder and 8 to 5 wt% of a polymer material to a mold. A cylindrical magnet 2 is formed by extruding into a pipe shape while applying a magnetic field inside (not shown). And the storage elastic modulus in normal temperature of this resin composition shall be 10 Mpa or less. In FIG. 1, 1 is a shaft. Thus, when the storage elastic modulus at room temperature of the resin composition is 10 MPa or less, the degree of orientation of the magnetic powder does not decrease even when the magnetic powder content in the resin composition is increased to 92% or more. A magnet roller with high magnetic properties can be obtained.

  The anisotropic magnetic powder in the present invention is not particularly limited. For example, it is an anisotropic ferrite such as strontium ferrite that is inexpensive and easily available, or an alloy containing a rare earth element and a transition metal. It is. Such an alloy containing a rare earth element and a transition metal is (i) an R—Fe—B alloy (wherein R is at least one of rare earth elements containing Y), Typical examples include Nd—Fe—B alloys, Pr—Fe—B alloys, Nd—Pr—Fe—B alloys, Ce—Nd—Fe—B alloys, Ce—Pr—Nd—. Fe-B alloys, or those obtained by substituting part of Fe with other transition metals such as Co and Ni, or (b) Sm-Co alloys, rare earths mainly composed of Sm An element and a transition metal mainly containing Co are basic components, and typical examples thereof are SmCo5 and Sm2TM17 (wherein TM is a transition metal), Or (c) Sm—Fe—N alloy, rare earth mainly composed of Sm The element, a transition metal mainly containing Fe, is intended to be basic components and interstitial elements mainly containing N, As the typical, is Sm2Fe17N3 prepared by nitriding a Sm2Fe17 alloy.

  The polymer material is preferably an olefin-based elastomer. As described above, when the polymer material is an olefin-based elastomer, it can have an appropriate viscosity in a wide temperature range. For this reason, a decrease in magnetic properties which becomes a problem when extrusion molding is performed while applying a magnetic field. It is possible to obtain a magnet roller with higher magnetic characteristics while minimizing the above.

  Such an olefin-based elastomer is preferably an ethylene ethyl acrylate copolymer containing 30% by weight or more of ethyl acrylate. As described above, when the olefin elastomer is an ethylene ethyl acrylate copolymer containing 30% by weight or more of ethyl acrylate, the moldability can be improved even if the resin composition containing it is highly filled with a filler. Therefore, it is possible to obtain a magnet roller having higher magnetic properties without occurrence of abnormalities such as cracks. In addition, additives other than magnetic powder, such as a lubricant, can be added to the resin composition.

  As shown in FIG. 1, the developing roller 20 of the present invention is provided with a rotatable nonmagnetic cylindrical body 11 on the outer periphery of the magnet roller 10 according to any one of claims 1 to 3. Yes. The nonmagnetic cylindrical body is made of a nonmagnetic material such as aluminum or stainless steel (SUS). Aluminum is excellent in terms of workability and lightness. In the case of using aluminum, it is preferable to use A6063, A5056, and A3003. In the case of SUS, it is preferable to use SUS303, SUS304, and SUS316. Thus, when the rotatable nonmagnetic cylindrical body 11 is arranged on the outer periphery of the magnet roller 10 according to any one of claims 1 to 3, adhesion of the carrier can be prevented, and therefore In addition, it is possible to provide a developing roller that can achieve high image quality.

  As shown in FIG. 2, the developing device 30 of the present invention has at least a developing roller 20, a developer supply member 21, and a developer layer regulating member 22. The developing device 30 includes the developing roller according to claim 4 as the developing roller 23. Thus, when the developing roller according to claim 4 is provided as the developing roller 23, the developing device 30 capable of improving the image quality can be provided.

  As shown in FIG. 3, the process cartridge 40 of the present invention includes a developing roller 30, a developer supply member 21, a developing device 30 having at least a developer layer regulating member 22, a charging roller 24, and an image carrier 25. have. The process cartridge 40 includes the developing device according to claim 5 as the developing device 30. Thus, when the developing device according to claim 5 is provided as the developing device 30, the process cartridge 40 capable of improving the image quality can be provided.

  As shown in FIG. 4, the image forming apparatus 50 of the present invention includes at least a process cartridge 40, an optical writing unit 103, a transfer member 105, and a fixing device 117. The image forming apparatus 50 according to the present invention includes the process cartridge according to claim 6 as the process cartridge 40. As described above, when the process cartridge according to the sixth aspect is provided as the process cartridge 40, the image device 50 capable of improving the image quality can be provided. 4, 106 is a cleaning blade, 107 is a static elimination optical system, 113 is a toner supply unit, 114 is a registration roller, 115 is a toner recovery blade, and Reference numeral 117 denotes a toner carrying coil.

Example 1
A resin composition having 91.8% by weight of anisotropic strontium ferrite having an average particle size of 1.3 μm and 8.2% by weight of ethylene ethyl acrylate copolymer containing 35% by weight of ethyl acrylate. Extrusion molding is performed while applying a magnetic field to obtain a pipe-shaped magnet having a reference outer diameter of 16 mm, an inner hole reference diameter of 6 mm, and a length of 304 mm. The pipe-shaped magnet is demagnetized, and then the magnet A shaft (SMU22, electroless Ni plating) having an outer diameter of 6 mm was press-fitted into the inner hole of the roller. A magnet roller having desired magnetic characteristics at each pole is obtained by magnetizing a yoke to a pipe-like magnet into which the shaft is press-fitted. Next, the outer periphery of the magnet roller was covered with a nonmagnetic cylindrical body (A6063) having an outer diameter of 18 mm made of aluminum to obtain a developing roller. The storage elastic modulus, which is the viscoelastic characteristic of the magnet roller thus obtained, was measured based on the storage elastic modulus measurement method defined above, and the measurement results shown in FIG. 5 were obtained as a graph. According to this graph, the storage elastic modulus at room temperature was 9.25 [MPa]. And when the peak magnetic flux density which is a magnetic characteristic of a magnet roller was measured, it was 106 [mT].

(Example 2)
A resin composition having 92.7% by weight of anisotropic strontium ferrite having an average particle size of 1.3 μm and 8.2% by weight of ethylene ethyl acrylate copolymer containing 35% by weight of ethyl acrylate. Extrusion molding is performed while applying a magnetic field to obtain a pipe-shaped magnet having a reference outer diameter of 16 mm, an inner hole reference diameter of 6 mm, and a length of 304 mm. The pipe-shaped magnet is demagnetized, and then the magnet A shaft (SMU22, electroless Ni plating) having an outer diameter of 6 mm was press-fitted into the inner hole of the roller. A magnet roller having desired magnetic characteristics at each pole is obtained by magnetizing a yoke to a pipe-like magnet into which the shaft is press-fitted. Next, the outer periphery of the magnet roller was covered with a nonmagnetic cylindrical body (A6063) having an outer diameter of 18 mm made of aluminum to obtain a developing roller. The storage elastic modulus, which is the viscoelastic property of the magnet roller thus obtained, was measured in the same manner as in Example 1. As a result, the storage elastic modulus was 9.57 [MPa], and the magnetic resistance of the magnet roller was When the peak magnetic flux density, which is a characteristic, was measured, the peak magnetic flux density was 107.3 [mT].

(Comparative Example 1)
A resin composition having 91.8% by weight of anisotropic strontium ferrite having an average particle diameter of 1.3 μm and 8.2% by weight of ethylene ethyl acrylate copolymer containing 25% by weight of ethyl acrylate. Extrusion molding is performed while applying a magnetic field to obtain a pipe-shaped magnet having a reference outer diameter of 16 mm, an inner hole reference diameter of 6 mm, and a length of 304 mm. The pipe-shaped magnet is demagnetized, and then the magnet A shaft (SMU22, electroless Ni plating) having an outer diameter of 6 mm was press-fitted into the inner hole of the roller. A magnet roller having desired magnetic characteristics at each pole is obtained by magnetizing a yoke to a pipe-like magnet into which the shaft is press-fitted. Next, the outer periphery of the magnet roller was covered with a nonmagnetic cylindrical body (A6063) having an outer diameter of 18 mm made of aluminum to obtain a developing roller. When the storage elastic modulus, which is the viscoelastic property of the magnet roller thus obtained, was measured in the same manner as in Example 1, the storage elastic modulus was 10.71 [MPa], and the magnet roller magnetic properties When the peak magnetic flux density as a characteristic was measured, the peak magnetic flux density was 99.5 [mT].

It is a top view of the developing roller showing an embodiment of the present invention. It is explanatory drawing of the developing device which shows one Embodiment of this invention. It is explanatory drawing of the process cartridge which shows one Embodiment of this invention. 1 is an explanatory diagram of an image forming apparatus showing an embodiment of the present invention. It is a graph which shows the relationship between the temperature (degreeC) of the resin composition in Example 1, and a storage elastic modulus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shaft 2 Cylindrical magnet 10 Magnet roller 11 Nonmagnetic cylindrical body 20 Developing roller 21 Developer supply member 22 Developer layer regulating member 24 Charging roller 25 Image carrier 30 Developing device 40 Process cartridge 50 Image forming apparatus

Claims (7)

  A cylindrical magnet formed by extruding a resin composition containing 92 to 95% by weight of anisotropic magnetic powder and 8 to 5% by weight of a polymer material into a pipe shape while applying a magnetic field in a mold. A magnet roller having a storage elastic modulus at room temperature of the resin composition of 10 MPa or less.   The magnet roller according to claim 1, wherein the polymer material is an olefin-based elastomer.   The magnet roller according to claim 2, wherein the olefin elastomer is an ethylene ethyl acrylate copolymer containing ethyl acrylate in a proportion of 30% by weight or more.   A developing roller comprising a rotatable nonmagnetic cylindrical body disposed on an outer periphery of the magnet roller according to claim 1.   A developing device having at least a developing roller, a developer supply member, and a developer regulating member, wherein the developing roller includes the developing roller according to claim 4.   A developing device having at least a developer carrying member, a developer supply member, a developer regulating member, and a process cartridge having a charging roller, wherein the developing device includes the developing device according to claim 5. Process cartridge.   7. An image forming apparatus comprising the process cartridge according to claim 6, wherein the process cartridge includes at least a process cartridge, an optical writing unit, a transfer member, and a fixing device.

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