JP2006259533A - Electrostatic latent image developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of maintaining an appropriate toner charge amount, capable of giving good image properties over a prolonged period of time, and capable of suppressing toner flying-off and toner deposition on a developing roller. <P>SOLUTION: The developing device has: a developer comprising a magnetic toner and a magnetic carrier; a magnetic roller 16 which forms a brush of the developer; the developing roller 17 which forms a thin layer of the magnetic toner; and a photoreceptor 19 which holds an electrostatic latent image. In developing device, the magnetic roller 16 and the photoreceptor 19 are kept away from each other, the magnetic toner is made to fly to a surface of the photoreceptor to develop the electrostatic latent image, after the development, the voltage between the magnetic roller 16 and the developing roller 17 is varied to release a thin toner layer from the developing roller 17, and a fresh thin toner layer is formed again on the developing roller 17. A magnetic powder has been incorporated into the magnetic toner particles, the magnetic powder has an average particle diameter of 0.01-0.50 μm and an octahedron shape, each vertex and edge of the octahedron have a curved surface shape, and the magnetic powder has straight line portions at the periphery of a projected image of the octahedron. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic latent image developing device and an image forming apparatus, and in particular, a developer composed of magnetic toner and a magnetic carrier, a magnetic roller for charging the developer, and a developing roller for forming a thin layer of magnetic toner. A photosensitive member for holding the electrostatic latent image, and developing the electrostatic latent image by flying magnetic toner onto the surface of the photosensitive member in a state where the magnetic roller and the photosensitive member are separated from each other. The present invention relates to a so-called hybrid type developing device in which a voltage between the developing roller is changed, the thin layer is peeled off from the developing roller, and the thin layer is formed again on the developing roller.

  In an image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, and a composite machine thereof using an electrophotographic method, an electrostatic recording method, an electrostatic printing method, etc., first, a latent image holder The surface of the substrate is uniformly charged by charging means, and then exposed by exposure means such as a semiconductor laser or a light emitting diode to form an electrostatic latent image. Then, the electrostatic latent image is developed or reversely developed by developing means. To visualize the toner image. Next, the toner image is directly transferred to the surface of the printing material such as paper by a transfer unit, or transferred to the surface of the intermediate transfer body and then re-transferred to the surface of the printing material such as paper. A series of image forming steps is completed by fixing by the fixing unit. Development methods for developing an electrostatic latent image into a toner image are roughly classified into dry and wet methods. Currently, dry development methods are widely used.

  Also, the dry development method is based on the type of toner used, and a development method using magnetic toner in which magnetic powder is encapsulated in toner particles made of a binder resin (magnetic one-component development method, magnetic two-component development method). Etc.) and development methods using a non-magnetic toner not containing magnetic powder (non-magnetic one-component development method, non-magnetic two-component development method, etc.).

  In recent years, particularly in color machines, a developing method includes a magnetic roller for holding a two-component developer, and forming a thin layer on the developing roller from the developer held on the magnetic roller. A hybrid development system or the like, which is a development system that makes a latent image appear by moving toner from a thin toner layer on the developing roller to a photosensitive member with a gap between them, has attracted attention.

  In the hybrid development system, attention has been paid as a technology of an image forming system corresponding to high speed and high image quality, but in recent years, in order to increase the speed of a color machine, a plurality of photoconductors corresponding to the color of toner are used, and a transfer member is used. A tandem method in which a color image is formed in synchronization with the feeding of the image and color is superimposed on the transfer member has been attracting attention. Although this method has the advantage of being excellent in high speed, it has the disadvantage of increasing the size because the electrophotographic process members of each color must be arranged side by side.

  As a countermeasure, there has been proposed a small tandem image forming apparatus in which a compact image forming unit is arranged by narrowing the interval between the photosensitive members. In a miniaturized tandem image forming apparatus, it is advantageous to use a vertical developing device in order to minimize the size of the image forming unit in the width direction. That is, it is desirable in terms of layout that the developing device is arranged in the upper direction of the photosensitive member.

  In the small tandem hybrid development system, a non-contact development system with a gap between the photoreceptor and the developing roller allows the carrier to adhere to the photoreceptor, which has been a conventional two-component development system, and a photoreceptor using a magnetic brush. High image quality is possible without any scratches. In addition, a two-component developer method by mixing with a carrier is adopted as a charging method in the developing device, and the toner can be quickly charged to a desired charge amount even during high-density printing or continuous printing. In particular, it is effective for models with a small developer capacity due to space saving.

  However, in the tandem type hybrid development system, the developing roller inevitably comes to the lower side of the developing unit in order to reduce the size of the developing unit, and the developer is easily subjected to stress. Embedding becomes prominent, causing problems such as toner adhesion to the developing roller and image density reduction due to toner overcharging.

  Here, the toner adhesion to the developing roller due to charge-up will be described in detail. In the development layout of a small tandem hybrid development type color page printer, the toner with the desired charge amount is supplied from the magnetic roller to the development roller between the magnetic roller and the development roller, and at the same time, it is allowed to fly from the development roller to the photoreceptor. Instead, the toner remaining on the developing roller is collected, so that fresh toner is always supplied to the developing roller. To collect the toner remaining on the developing roller, bias control is performed together with scraping with a carrier held by the magnetic roller. However, due to the layout aimed at downsizing, it is necessary to move the toner from the developing roller to the magnetic roller against gravity, and if the toner is charged more than necessary and overcharged, the developing roller As a result, the particles are charged and agglomerated and the mirror image force on the developing roller is increased, so that the magnetic roller is not peeled off, and the toner adheres to the developing roller. As a result, the same toner always remains on the developing roller, the charge-up is accelerated, and the toner adheres to the roller. When the roller adhesion occurs, the adhered toner is difficult to be developed, and this portion leads to a serious image defect such as a decrease in image density or a ghost.

Patent Documents 1 and 2 disclose that the toner is peeled off from the developing roller by controlling the applied voltage between the developing roller and the supply roller as a countermeasure against the toner adhesion to the developing roller. However, the toner is completely pulled out. The toner cannot be peeled off, and when toner remains even in a small amount, the remaining toner serves as a base point and is charged up to develop roller adhesion. For this reason, the toner is required to have a charging characteristic that is difficult to charge up to prevent adhesion of the roller.
In the hybrid development system, it is common to use a non-magnetic toner. However, it has already been proposed to use a magnetic toner containing magnetic powder in order to prevent charge-up and toner scattering in the two-component developing method, and the developer consisting of carrier and toner is also used in the hybrid developing method. As in the case of the two-component development method, it was predicted that the effect of charge-up and toner scattering prevention could be obtained by using magnetic toner. In addition, particularly in the hybrid development method, the effect of scraping off the toner on the developing sleeve by the carrier on the magnetic roll is expected to be improved, and a good effect can be obtained in preventing the toner from adhering to the developing sleeve described above. Was expected to be.

At present, the magnetic powder contained in the toner includes a hexahedron (cube, cuboid) shape that is a convex polyhedron surrounded by six squares, and an octahedron shape that is a convex polyhedron surrounded by eight triangles. In general, polyhedral magnetic powder and spherical magnetic powder are used. However, magnetic toners using polyhedral magnetic powders tend to release charges from the sharp apexes of the magnetic powder exposed on the surface of the toner particles and the sharp ridges between adjacent surfaces, so that charge leakage occurs. It is more likely to occur than necessary. In addition, since the polyhedral magnetic powder has low fluidity and poor dispersibility in the binder resin, it is difficult to uniformly disperse it in the binder resin. For this reason, since the dispersion state of the magnetic powder in the individual toner particles is likely to vary, the ease of charging and the charge amount of the individual magnetic toners are also likely to vary. Therefore, the magnetic toner using the polyhedral magnetic powder is difficult to quickly rise, and the charge amount itself is low. As a result, the two-component developer is also used in the hybrid development method. There are problems such as toner scattering and toner dropping, and image defects such as image density reduction due to the one-component development portion. On the other hand, magnetic toners using spherical magnetic powder do not have sharp apexes or ridges, and charge is unlikely to be released from the magnetic powder exposed on the surface of the toner particles. . In addition, since the spherical magnetic powder is excellent in fluidity as compared with the polyhedral one, and is excellent in dispersibility in the binder resin, it can be easily dispersed uniformly in the binder resin. The dispersion of the magnetic powder in the magnetic toner can be prevented from varying, and the ease of charging and the amount of charge can be made uniform. On the contrary, since the charge is too easy to accumulate, when the carrier and the toner are repeatedly mixed, the toner is easily overcharged to a predetermined charge amount or more, so-called charge-up occurs. In addition, there is a problem that image defects such as a decrease in image density due to insufficient toner supply occur, and toner adhesion to the developing roller is also likely to occur.
In the hybrid development system, a carrier is used as a toner charging unit to form a two-component developer, and in the final development process, one-component jumping development is performed from the developing roller. In addition to avoiding this problem, it is necessary to adjust the charging characteristics of the toner so that the charge amount is suitable for one-component development. In addition, toner adhesion to the developing roller as described above must be avoided, and high charge control capability is required for the toner.

  Therefore, magnetic powders having various particle shapes effective for the above-mentioned many problems have been studied by taking advantage of both spherical magnetic powder and polyhedral magnetic powder.

  For example, in Patent Documents 3, 4, and 5, the magnetic powder having a particle shape such that a vertex or a ridge line of a polyhedron such as the hexahedron or octahedron is chamfered by a plane smaller than each surface constituting the polyhedron. Is described. However, even in this magnetic powder, there is still a sharp ridgeline between the surface constituting the polyhedron and the chamfered small plane, and charges are easily released from this ridgeline, so the shape of the polyhedron is fundamentally There is a tendency similar to that of magnetic powder. When such magnetic powder is used, the charge leaks, and there is a risk of causing image defects such as a decrease in image density in the one-component development part and toner scattering in the two-component developer part. is there.

  Patent Document 6 discloses a magnetic powder having a particle shape in which each ridge line of a cube is curved. However, this magnetic powder has a curved surface as its ridgeline, and its apex is also curved, and there are no sharp vertices or ridgelines as charge discharge points. And the toner may be charged up to cause image defects such as a decrease in image density.

Patent Documents 7 and 8 disclose toner scattering and fog suppression as advantages of the two-component magnetic toner, but do not describe behavior during printing durability, and moreover, the magnetic powder shape is not described. The effect has not been confirmed, and there is a possibility that a stable charge amount cannot be obtained after printing.
As described above, it is difficult to effectively prevent toner adhesion to the developing sleeve while maintaining good image characteristics in hybrid development by adding magnetic powders of various shapes proposed so far. It is thought that. In particular, toner adhesion to the developing sleeve can be prevented at the present time by setting processes such as bias control. However, as the demands of the printer and copier continue to increase due to further market demand, It is easily guessed that there is a limit in control.
JP 7-72733 A JP 2001-109242 A Japanese Patent Laid-Open No. 11-153882 JP 2000-162817 A JP 2000-242029 A Japanese Patent Laid-Open No. 9-59024 JP-A-56-106249 JP 59-162563 A

  2. Description of the Related Art In recent years, copying machines and printers using electrophotography, electrostatic printing, and the like have been remarkably advanced in printing speed, machine size, and machine life. In addition, high performance, high image quality, and high durability are naturally demanded as performance. In order to obtain improved image characteristics and durability in accordance with the printing speed by increasing the printing speed, a toner having a stable charging characteristic is indispensable.

  However, in the so-called hybrid development method disclosed in Patent Documents 1 and 2, even if the magnetic powder disclosed in Patent Documents 3, 4, 5, and 6 is used, toner adhesion to the developing roller cannot be avoided. . In particular, in the tandem hybrid development system, if the developing device is downsized, the developing roller inevitably comes to the lower side of the developing device, and the developer is likely to be stressed. Embedding becomes prominent and problems such as toner adhesion to the developing roller and image density reduction due to toner overcharging occur.

  Accordingly, an object of the present invention is to maintain an appropriate toner charge amount, and as a result, good image characteristics can be obtained over a long period of time, and toner scattering and toner adhesion to the developing roller can be suppressed. A hybrid type developing device is provided. Here, the hybrid system means a developer composed of magnetic toner and a magnetic carrier, a magnetic roller for charging the developer, a developing roller for forming a thin layer of magnetic toner, and a photoreceptor for holding an electrostatic latent image. The electrostatic latent image is developed by flying magnetic toner onto the surface of the photoconductor with the magnetic roller and the photoconductor separated from each other, and the voltage between the magnetic roller and the developing roller is changed after development. The thin film is peeled off from the developing roller, and the thin layer is formed again on the developing roller.

  Another object of the present invention is to maintain an appropriate toner charge amount even in a small tandem type image forming apparatus that needs to move toner from a developing roller to a magnetic roller against gravity.

  A first means for solving the above-described problems includes a developer composed of a magnetic toner and a magnetic carrier, a magnetic roller for forming a spike of the developer, and a developing roller for forming a thin layer of the magnetic toner. And a photosensitive member for holding the electrostatic latent image, and the magnetic toner is allowed to fly to the surface of the photosensitive member in a state where the developing roller and the photosensitive member are spaced apart to develop the electrostatic latent image. In the developing device, magnetic powder is internally added to the magnetic toner particles, the average particle size of the magnetic powder is in the range of 0.01 to 0.50 μm, and the particle shape of the magnetic powder is 8 triangles. Is an octahedron that is a convex polyhedron surrounded by, and each vertex and ridge line of the octahedron is curved and has a straight line portion on the outer periphery of the projected image of the octahedron.

  The second means is that in the first means, 1 to 35% by mass of magnetic powder is internally added to the toner particles.

  The third means is that, in the first means, the photoconductor, the developing roller, and the magnetic roller are arranged in this order from the downward direction to the upward direction in the gravity direction.

  In the present invention, the magnetic powder contained in the two-component developer toner used in the hybrid development system is basically an octahedron that is a convex polyhedron surrounded by eight triangles, and each vertex and ridge line of the octahedron is Magnetic powder that has a curved surface and has a portion that can be regarded as a straight line on the outer periphery of the projected image is used. That is, in the development process, a thin toner layer is formed on the developing roller from the two-component developer held on the magnetic roller, and development is performed with a gap between the developing roller and the photoreceptor. System, that is, a hybrid developing system, the two-component developer used is composed of toner and carrier, the toner contains at least magnetic powder, and the magnetic powder is a convex polyhedron whose particle shape is surrounded by eight triangles The octahedron is a base, each vertex and ridge line of the octahedron is curved, and there is a portion that can be regarded as a straight line at the outer periphery of the projected image, and the average particle size is 0.01 to 0.50 μm. A magnetic toner for developing an electrostatic latent image, comprising magnetic powder. The magnetic powder having the above-mentioned particle shape has a curved vertex and no ridges or ridges that are easy to discharge charges, so that it is difficult to cause charge leakage when internally added to the toner. It is thought that you can. In addition, since the vertices and ridges of the polyhedron are curved as described above, this magnetic powder has excellent fluidity and dispersibility with respect to the resin, and can be easily dispersed uniformly in the resin. Therefore, it is considered that the dispersion state of the magnetic powder in each toner particle can be prevented from being varied, and the ease of charging and the charge amount of each magnetic toner can be made uniform. Moreover, since the basic shape of the magnetic powder is an octahedron, either the apex or the adjacent surface sandwiching the ridge line, or the adjacent ridge line sandwiching the apex must be included in the octahedron. The crossing is made at an acute angle of less than 90 °, and charges tend to concentrate on the apex where the surface or ridge line intersects at an acute angle or the ridge line where the surface intersects at an acute angle. However, it is possible to discharge charges at an appropriate rate mainly from the apexes and ridge lines where the charges tend to concentrate. Therefore, it is considered that charge-up can be made difficult to occur. However, even in the above-described particle shape, if the curvatures of the curved vertexes and ridge lines are too large, the effect of preventing the charge-up of the magnetic toner by discharging charges at an appropriate rate cannot be obtained. .

  Therefore, the inventor studied to define the range of the radius of curvature of the apex and the ridgeline formed into a curved surface from the projected image of the magnetic powder taken using, for example, a transmission electron microscope.

  As a result, the curvature radius of the curved vertices and ridge lines is too large, the curved surfaces of adjacent vertices and ridge lines are connected, and there is no part that can be regarded as a straight line on the outer peripheral part of the projected image, The effect of preventing the charge-up of the magnetic toner is not obtained as in the case of a spherical toner, but each vertex and ridge line of the octahedron is a curved surface and has a portion that can be regarded as a straight line on the outer periphery of the projected image. The powder is composed of curved surfaces with ridgelines and vertices where adjacent surfaces intersect, but the curvature radius of the curved surface is smaller than that of spherical magnetic powder with the same particle size, so the charge concentrates. Charges can be released at an appropriate rate from easy apexes and ridges, and when the magnetic powder is encapsulated in magnetic toner, the charge leaks compared to using magnetic powder that does not have curved surfaces at the vertices or ridges. Wake up While Rinikuku, yet, found that it is possible to prevent the charge-up of the magnetic toner.

  Further, as a result of examining the size of the magnetic powder, the magnetic powder having an average particle size of less than 0.01 μm increases the ratio of the magnetic powder exposed on the surface of the toner, and discharges electric charges from the portion. There is a problem in that it occurs, causing insufficient charging and causing toner scattering. On the other hand, in the case of magnetic powder having an average particle size exceeding 0.50 μm, the ratio of the magnetic powder exposed on the surface of the toner is decreased, and appropriate discharge of charges from the portion is reduced, leading to charge up. As a result, the image density after durability is lowered. Therefore, it discovered that the average particle diameter of magnetic powder needs to be 0.01-0.50 micrometer.

  The binder resin, dye, pigment, charge control agent, fluidizing agent, external additive and the like in the present invention are not particularly limited. There are no particular restrictions on the carrier that can be used for all hybrid developing toners and that is necessary to obtain a two-component developer.

  According to the present invention, a hybrid system that can maintain an appropriate toner charge amount, as a result, can obtain good image characteristics over a long period of time, and can suppress toner scattering, toner adhesion to the developing roller, and the like. The developing device can be provided. The hybrid system is a developer composed of a magnetic toner and a magnetic carrier, a magnetic roller for charging the developer, a developing roller for forming a thin layer of magnetic toner, and a photoreceptor for holding an electrostatic latent image. The magnetic latent image is developed by flying magnetic toner on the surface of the photosensitive member with the magnetic roller and the photosensitive member separated from each other, and the voltage between the magnetic roller and the developing roller is changed after development. A developing system in which the thin layer is peeled off from the developing roller, and the thin layer is formed again on the developing roller.

  Further, according to the present invention, even in a small tandem type image forming apparatus that needs to move toner from the developing roller to the magnetic roller against gravity, an appropriate toner charge amount can be maintained, and toner scattering and developing roller can be maintained. Toner adhesion to the toner can be suppressed.

  Specifically, according to the present invention, the magnetic roller is added internally to the toner, thereby effectively preventing the toner overcharge, thereby preventing the toner roller from adhering to the developing roller and the magnetic roller. The toner can be removed from the developing roller to the magnetic roller while supplying the toner from the developing roller to the developing roller. As a result, new toner can always be supplied onto the developing roller. Furthermore, since the toner can hold the required charge amount while effectively preventing toner overcharge, the toner is prevented from scattering at the two-component developer portion held by the magnetic roller, and By holding the toner with the charge amount necessary for flying from the developing roller, which is a one-component developing portion, to the photoreceptor, it is possible to realize good image quality and image density. That is, it is possible to achieve the high charging performance required for the hybrid developing system toner having both the one-component developing portion and the two-component developing portion.

  More specifically, according to the present invention, the toner for the hybrid development system is based on an octahedron which is a convex polyhedron surrounded by eight triangles containing magnetic powder, and each vertex and ridge line of the octahedron. By using magnetic powder having a curved particle shape, it is possible to maintain an appropriate charge amount, and as a result, good image characteristics can be obtained over a long period of time, and toner scattering and a developing roller can be obtained. It is an object of the present invention to provide a toner that does not cause problems peculiar to the hybrid development method such as toner adhesion to the toner. That is, it is possible to provide a toner that has a rapid rise in toner charge amount and always has appropriate charging characteristics that do not charge up (overcharge).

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

FIG. 1 is a block diagram of the hybrid developing device of this embodiment.
First, the configuration of the hybrid developing device will be described with reference to FIG. The hybrid system is a developer composed of a magnetic toner and a magnetic carrier, a magnetic roller for charging the developer, a developing roller for forming a thin layer of magnetic toner, and a photoreceptor for holding an electrostatic latent image. The magnetic latent image is developed by flying magnetic toner on the surface of the photosensitive member with the magnetic roller and the photosensitive member separated from each other, and the voltage between the magnetic roller and the developing roller is changed after development. A developing system in which the thin layer is peeled off from the developing roller, and the thin layer is formed again on the developing roller.

  The toner container 11 supplies magnetic toner from the toner supply port 12. The magnetic toner is agitated by the mixers 13 and 14, is uniformly mixed with the magnetic carrier, and is charged. The magnetic roller 16 forms a spike (magnetic brush) of a magnetic carrier with a permanent magnet fixed inside, and attaches magnetic toner to the magnetic brush. The restriction blade 15 restricts the ears of the magnetic carrier to a certain height. The magnetic toner on the magnetic roller 16 is supplied to the developing roller 17 by a predetermined voltage. Thus, a thin layer of magnetic toner is formed on the developing roller 17. The developing roller 17 and the photoconductor 19 are separated from each other, and the magnetic toner flies toward the photoconductor 19 by the developing voltage, and the electrostatic latent image on the photoconductor 19 is developed. In order to form an electrostatic latent image, the photosensitive member 19 is uniformly charged by the charger 18 and then the image is exposed by the exposure device 20. The magnetic toner image carried on the photosensitive member is transferred onto a transfer material (copy paper or the like) conveyed by the transfer roller 21.

In FIG. 1, the developing roller 17 and the magnetic roller 16 are disposed obliquely above the photoconductor 19 to reduce the size of the photoconductor / developer system in the paper transport direction. In order to further reduce the size of the photoreceptor / developer system in the paper transport direction, the developing roller 17 and the magnetic roller 16 may be disposed vertically above the photoreceptor 19. In such an arrangement, the magnetic toner falls in the direction of gravity and is supplied to the developing roller 17 and is peeled off from the developing roller against the gravity.
Next, the operation of the developing device will be described.

  The developer composed of the toner and the carrier held on the surface of the magnetic roller 16 is held, and the toner is charged to an appropriate level while the developer is stirred and charged by the mixers 13 and 14. The developer passes through the regulating blade 15 and contacts the developing roller 17 with a constant layer thickness. The gap between the regulating blade 15 and the magnetic roller 16 is 0.3 to 1.5 mm, and the gap between the magnetic roller 16 and the developing roller 17 is similarly about 0.3 to 1.5 mm. The thin layer of toner on the developing roller 17 is set to a thickness of 6 to 50 μm, preferably 30 to 70 μm. This thickness is a value corresponding to about 5 to 10 layers of toner when the volume average particle diameter of the toner is 7 μm. The gap between the developing roller 17 and the photoreceptor 19 is 150 to 400 μm, preferably 200 to 300 μm. If it is smaller than 150 μm, it causes fogging. If it is larger than 400 μm, it becomes difficult to cause the toner to fly to the photoreceptor 19, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development.

FIG. 2 is a cross-sectional view of an example of an image forming apparatus including the hybrid developing device of the present embodiment.
First, the configuration of the image forming apparatus will be described with reference to FIG.
In this image forming apparatus, the paper transport belt 54 is disposed so that the recording paper from the paper feed cassette 53 can be transported toward the fixing device 59, and the black paper is disposed above the belt 54 that transports the recording paper. A developing device 50A, a yellow developing device 50B, a cyan developing device 50C, and a magenta developing device 50D are provided. These developing devices 50 (A, B, C, D) are developed in close proximity to the magnetic roller 1 (A, B, C, D) and the magnetic roller 1 (A, B, C, D), respectively. A roller 2 (A, B, C, D) is disposed, and a photosensitive member 3 (A, B, C, D) faces the developing roller 2, and a charging device is disposed around the photosensitive member 3. 56 (A, B, C, D) and exposure device 57 (A, B, C, D) are arranged.
Next, the operation of the image forming apparatus will be described.

The image forming apparatus is a tandem type image forming apparatus, and a two-component developer including a toner and a carrier corresponding to each color such as yellow, cyan, magenta, and black is supplied to a developer container 51 (A, B, C, D) is supplied to each developing device 50, a magnetic brush is formed on the magnetic roller 1, and the toner is charged by stirring. The magnetic brush on the magnetic roller 1 is layer-regulated by a regulating blade, and the developing roller is driven by the potential difference between the DC voltage Vdc2 applied to the magnetic roller 1 and the constant DC bias voltage Vdc1 applied to the developing roller 2 and the AC voltage Vac. 2 is formed with a thin layer of toner only. Then, when a print start signal is received from a control circuit (not shown), first, the photosensitive member 3 composed of a positively charged organic photosensitive member (positive OPC) is charged to, for example, 400 V by the charger 56, and then, for example, 770 nm. By the exposure by the exposure device 57 using the LED having the wavelength, the post-exposure potential of the photosensitive member 3 becomes about 70 V, and a latent image is formed. The latent image is developed with the toner that has jumped from the toner layer on the developing roller 2 to the photosensitive member 3 by a constant DC bias voltage Vdc1 and an AC voltage Vac applied to the developing roller 2 to form a toner image. Then, the recording paper is fed from the paper feed cassette 53 and sent by the belt 54. When the recording paper reaches the photosensitive member 3, a transfer bias by the transfer device 58 (A, B, C, D) is applied. Then, the toner image is transferred to the recording paper, fixed by the fixing device 59, and discharged.
In order to perform stable development, it is preferable to move the toner thin layer from the developing roller to the magnetic roller side after development, and then re-form the toner thin layer from the magnetic roller onto the developing roller. Specifically, after the development is completed, as described above, development is performed by changing the DC voltage Vdc2 to the magnetic roller 1 (A, B, C, D) while applying the AC voltage Vac periodically according to the print data. A toner stripping process for collecting the toner layer on the roller with a magnetic brush and a subsequent toner layer re-forming process are performed.

Next, the relationship between each part of the image forming apparatus and the operation of the image forming apparatus will be described.
The exposure device 57 can use a semiconductor laser or an LED. When a positively charged organic photoconductor is used, a wavelength around 770 nm is effective, and when an amorphous silicon photoconductor is used, a wavelength around 685 nm is effective. When a positively charged organic photoconductor (positive OPC) is used, there is little generation of ozone, etc., and charging is stable. Especially, when a positive OPC with a single layer structure is used over a long period of time and the film thickness changes, the photosensitive characteristics. The image quality is stable and the image quality is stable. In addition, it is also possible to use an a-Si photoconductor. When used in a long-life system, the film thickness of the positive OPC is set to about 20 μm to 40 μm. In the case of 20 μm or less, when the film decreases and reaches 10 μm, black spots are noticeably generated due to dielectric breakdown. On the other hand, if the film thickness is thicker than 40 μm, the sensitivity is lowered and the image is lowered. The exposure device 57 may be a system using a semiconductor laser or LED. A wavelength near 770 nm is effective for positive OPC, and a wavelength near 685 nm is effective for an a-Si photoreceptor.

  The charger 56 charges the positively charged OPC3, which is an electrostatic latent image carrier, to 400V. Thereafter, when exposure is performed with an LED having a wavelength of 770 nm, the post-exposure potential is set to 70V. The primary OPC 3 is arranged with a space of about 250 μm with respect to the developing roller 2. No wire electrode or the like is used in this space. The surface of the developing roller 2 is a rotating body made of conductive aluminum. The material of the rotator may be a uniform conductor, and SUS, conductive resin coating, etc. can be applied. A DC voltage Vdc1 and an AC voltage Vac are superimposed and applied to this conductive rotor. Vdc1 is, for example, 100 v, and Vac is, for example, Vpp is 1.5 kv, frequency is 3.0 KHz, and Duty is 30%. The AC component waveform is preferably a rectangular wave. By applying these superimposed biases to the conductive rotator, the latent image on the latent electrostatic image bearing member has good developability and the toner layer recoverability with respect to the magnetic roller 1 is increased. Printing stability is improved. In order to stabilize the image density in continuous printing, it is necessary to periodically remove the toner from the developing roller and refresh.

  In order to supply sufficient toner to the latent image on the photosensitive member 3 without increasing the sheet interval, if the peripheral speed of the developing roller 1 is set to 1.5 times or more with respect to the photosensitive member 3, the toner can be removed in a short time. It can be put in and out. Further, when the magnetic roller 1 is set at a speed of 1 to 2 times that of the developing roller 2, the toner replacement is promoted. At this time, it is preferable that the rotating direction of the magnetic roller 1 is opposite to the developing roller 2.

  To replace the toner layer on the developing roller 2, the alternating current (Vac + Vdc 1) is applied at the end of development, and the DC voltage Vdc 2 of the magnetic roller 1 is changed to change the toner layer of the developing roller 2 to the magnetic layer on the magnetic roller 1. Collect on brush.

The amount of saturated toner in the toner layer is determined by the difference between Vdc2 and Vdc1. When Vdc1 is set to 150 V and the value of Vdc2 is set to 400 V, a toner layer of about 1.0 mg / cm ² is obtained on the second round of the developing roller. Adjustment of the toner layer is basically obtained by (Vdc2−Vdc1), but factors such as the charge amount of the toner and the magnetic pole strength of the magnetic roller may also contribute. The toner layer is varied by changing the value of Vdc2 according to the image data, whereby an image with a uniform density can be obtained. When performing high density printing continuously, it is advantageous to set the value of (Vdc2-Vdc1) slightly higher. If the toner layer is too thin at 0.5 mg / cm ² or less, the followability of the density when a high density image is continuous is lowered and image unevenness is likely to occur. On the other hand, if the toner layer exceeds 1.5 mg / cm ² and is too thick, the development ghost tends to be noticeable and the toner scattering tends to be noticeable. The toner layer thickness also depends on the charge amount of the toner. When the toner charge amount is as low as 10 μC / g or less, particularly 5 μC / g or less, the toner layer thickness increases and scattering increases. On the other hand, when the toner charge amount is 20 μC / g or more, the toner layer thickness becomes thin, the charge increases, and the developability of the toner decreases.

  The toner layer of the developing roller 2 is collected by the magnetic brush held by the magnetic roller 1, and new developer is carried to the developing roller 2 through the regulating blade.

  The developer is composed of a toner and a carrier, and the mixing ratio of the toner is 2 to 40% by weight, preferably 3 to 30% by weight, more preferably 4 to 25% by weight with respect to the total amount of the carrier and the toner. . When the mixing ratio of the toner is less than 2% by weight, the toner charge amount becomes high and a sufficient image density cannot be obtained, and when it exceeds 40% by weight, a sufficient charge amount cannot be obtained. The toner is scattered from the inside and contaminates the inside of the image forming apparatus, or toner fog occurs on the image. The two-component developer composed of toner and carrier forms a magnetic brush composed of toner and carrier on the magnetic roller 16, and the toner is agitated and charged by the mixers 13 and 14. The developer is layer-regulated by a regulating blade, and a thin layer of only toner is formed on the developing roller 17 by a potential difference between the magnetic roller 16 and the developing roller 17. The toner thin layer on the developing roller 17 varies depending on the resistance of the developer and the difference in rotational speed between the developing roller 17 and the magnetic roller 16, but can also be controlled by the above potential difference. When the potential difference is increased, the toner layer on the developing roller 17 is thickened, and when the potential difference is decreased, the toner layer is thinned. The range of potential difference is generally about 100 to 250 v.

As the carrier, for example, a ferrite carrier having a volume resistivity of 10 ⁷ Ω · cm, a saturation magnetization of 70 Am ² / kg, and an average particle size of 35 μm is used. Examples of the high-magnetic force and low-resistance carrier include magnetite carrier, Mn-based ferrite, and Mn-Mg-based ferrite. These carriers may be used as they are, but they may be used after being surface-treated within a range not increasing the resistance. Further, the carrier used in the present invention is preferably coated on the surface with a resin for the purpose of increasing durability. Examples of the resin forming the coating layer include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polystyrene, acrylic (for example, polymethyl methacrylate), polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, Polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinylidene resins such as polyvinyl ether, and polyvinylidene resins; vinyl chloride-vinyl acetate copolymers; silicone resins composed of organosiloxane bonds or modified products thereof (for example, alkyd resins, polyester resins, epoxy resins) , Modified products by polyurethane, etc.); polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene Polyamides; polyesters; fluorine resin emissions such as polyurethane; polycarbonates; - urea amino resins such as formaldehyde resins, epoxy resins and the like. Further, the carrier used in the present invention may have a conductivity imparting material dispersed in the coating layer in order to control its volume resistivity. The conductivity imparting material to be dispersed may be a known material, and examples thereof include metals such as iron, gold and copper; iron oxides such as ferrite and magnetite; and pigments such as carbon black. Among these, in particular, by using a mixture of furnace black and acetylene black, which is one of the carbon blacks, it is possible to effectively adjust the conductivity by adding a small amount of conductive fine powder, and to further improve the wear resistance of the coating layer. An excellent carrier can be obtained. These conductive fine powders are preferably added in an amount of 2 to 30 parts by weight, more preferably 5 to 20 parts by weight, based on 100 parts by weight of the coating resin. In addition, a silane coupling agent, a titanium coupling agent, or the like may be added to the carrier coating layer for the purpose of improving the adhesion with the core particles or improving the dispersibility of the conductivity imparting agent. As a method for forming the coating layer, the coating layer forming liquid may be applied to the surface of the carrier core particle by means of a spraying method, a dipping method, or the like, as in the past. The thickness of the coating layer is 0.1 to 20 μm, preferably 0.2 to 5 μm. In the invention, the mixing ratio of the toner and the carrier when the two-component developer is used is preferably 2.0 to 20 parts by weight, more preferably 3.0 to 20 parts by weight with respect to 100 parts by weight of the carrier. 15 parts by weight. When the toner amount is below the above range, charge-up occurs. On the other hand, when the toner amount is above the above range, fogging and toner scattering occur.

As the developer, a carrier having a resistance of 10 ⁶ Ω · cm to 10 ⁹ Ω · cm, which plays a role of collecting and supplying toner, is used. The toner is peeled off with a magnetic brush, and the toner necessary for development is supplied. At this time, in order to increase the number of contact points with the toner, it is preferable to use a small diameter carrier having a volume average particle diameter of 40 μm or less and to increase the surface area of the carrier. At 10 ⁶ Ω · cm or less, a low-resistance carrier that places importance on recovery is effective as a countermeasure against development ghosts, but it is difficult to maintain development without causing fogging and providing accurate charging to the toner. Although it is possible to impart charging performance with a resistance of 10 ⁹ Ωcm or more that causes toner to scatter from the surface of the developing roller during a period of operation and cause contamination of a charger or an exposure unit (not shown). There was a problem that charging was likely to increase. By making the resistance value of the carrier appropriate, it is possible to recharge the charged toner again into the developing roller 17 while collecting the toner on the developing roller 17. The toner is controlled to 5 to 20 μC / g, prevents toner scattering and fogging, and does not leave a development history phenomenon on the developing roller 17 by developing with a low electric field, and is excellent in toner recoverability. Can be configured.

  As described above, the carrier used for constituting the developer in the present invention has a weight average particle diameter of 20 to 150 μm, preferably 20 to 100 μm, thereby increasing the toner concentration of the developer layer in the development region. Therefore, a good image having a high image density can be obtained even under development conditions on a high speed machine. The carrier core particles constituting the developer in the present invention may be known ones such as ferromagnetic metals such as iron, cobalt and nickel; alloys and compounds such as magnetite, hematite and ferrite; Examples include composites with resins.

  The charged toner is held in a thin layer on the developing roller 17 due to a potential difference between the magnetic roller 16 and the developing roller 17, and is developed by applying a bias in which direct current and alternating current are superimposed on the photoreceptor 19. . In order to prevent toner scattering, alternating current is applied immediately before development. The toner remaining on the development is not provided with a special device such as a scraping blade, and the magnetic brush on the magnetic roller 16 comes into contact with the toner layer on the developing roller 17. By changing the developer by stirring the developer in the mixer, the toner can be easily collected and replaced. At this time, since the width of the magnetic brush is a width for collecting the toner on the developing roller 17, the uncollected area can be surely eliminated by making the width of the developing roller 17 shorter than the width of the magnetic brush. By doing so, there is no toner adhering to the developing roller 17 outside the width of the magnetic brush, and toner scattering at both ends can be eliminated. As a method for accelerating the replacement of the developer, the rotation speed of the magnetic roller 16 is set to 1.0 to 2.0 times the speed of the developing roller 17, and the toner on the developing roller 17 is collected and appropriate. By supplying the developer set to the toner density to the developing roller 17, a uniform toner layer can be formed.

  Further, in order to maintain a uniform image density, the toner on the developing roller 17 is not subjected to a burden on the toner by applying the same potential between the developing roller 17 and the magnetic roller 16 at a time other than the development timing. It is also effective to collect the magnetic roller 16.

  When an a-Si photosensitive member is used as the photosensitive material for the photosensitive member 19, the post-exposure potential on the surface has a very low characteristic of 10v or less, but the saturation charging potential decreases when the film thickness is reduced. In addition, the withstand voltage leading to dielectric breakdown is reduced. On the other hand, the charge density on the surface of the photoreceptor 19 when a latent image is formed tends to improve and the development performance tends to improve. This characteristic is particularly remarkable when the dielectric constant is about 10 or less for an a-Si photoreceptor having a dielectric constant of about 10 or less, more preferably 20 μm or less. Development bias voltage Vdc1 can be developed with 150V or less, more preferably 100V or less, development AC voltage Vac component set to VP-P500 to 2000V and frequency set to 1 to 3 kHz. When a positively charged organic photoconductor (OPC) is used as the photoconductor 19, the photosensitive layer thickness is set to 25 μm or more to increase the amount of charge generation material added in order to make the residual potential 100 V or less. It is particularly important. In particular, OPC having a single-layer structure is advantageous because the charge generation material is added to the photosensitive layer, so that the sensitivity hardly changes even when the photosensitive layer is reduced. Even in this case, setting the developing bias Vdc1 to 400 V or less, more preferably 300 V or less is also preferable in terms of preventing a strong electric field from being applied to the toner. Setting the developing bias to be low in this way is effective for suppressing the dielectric breakdown of the thin film a-Si photosensitive member, preventing excessive charging of the toner, and suppressing the development history phenomenon. Further, a toner layer of 10 to 100 μm, preferably 30 to 70 μm is formed on the developing roller 17, and the gap between the developing roller 17 and the photoreceptor 19 is 150 to 400 μm, preferably 200 to 300 μm. A sharp image can be obtained by causing the toner to fly on the photoconductor 19 by an AC electric field.

FIG. 3 is a schematic diagram of the toner of this embodiment.
The toner 100 is obtained by dispersing the magnetic powder 101 and various toner compounding agents such as a colorant (not shown) in the binder resin 102. Further, an external additive 103 is applied to the surface of the toner 100 in order to control fluidity, storage stability, cleaning properties, and the like. The type of the binder resin 102 is not particularly limited. For example, a styrene resin, an acrylic resin, a styrene-acrylic copolymer, a polyethylene resin, a polypropylene resin, a vinyl chloride resin, and a polyester resin. It is preferable to use a thermoplastic resin such as a polyamide resin, a polyurethane resin, a polyvinyl alcohol resin, a vinyl ether resin, an N-vinyl resin, or a styrene-butadiene resin.

  In the toner 100 of the present invention, magnetic powder 101 is blended in a binder resin 102 to obtain a magnetic toner. As the magnetic powder 101, the particle shape is basically an octahedron that is a convex polyhedron surrounded by eight triangles, and each vertex and ridge of the octahedron are curved, and on the outer periphery of the projected image. Magnetic powder having a portion that can be regarded as a straight line is used.

FIG. 4 is a transmission electron microscope (TEM) photograph of the magnetic powder.
The magnetic powder 101 is based on an octahedron, and its vertex and ridge are curved, and there are no sharp vertices or ridges that serve as charge discharge points. Also, even if the vertices and ridgelines are curved, the radius of curvature is too large, and the curved surfaces of adjacent vertices and ridgelines are connected, so that there is no spherical part that can be regarded as a straight line on the outer periphery of the projected image As shown in FIG. 4, a portion that can be regarded as a straight line remains on the outer periphery of the projection image, and the characteristic as an octahedron remains.

  The magnetic powder 101 needs to have an average particle size of 0.01 to 0.50 μm. The magnetic powder 101 having an average particle diameter of less than 0.01 μm has an increased ratio of exposure on the surface of the toner 100 and discharge of the exposed magnetic powder 101 results in insufficient charging of the magnetic toner. There is a problem of lowering. On the other hand, the magnetic powder having an average particle diameter exceeding 0.05 μm, on the contrary, the ratio of exposure to the surface of the toner particles is reduced, and the charge released from the exposed magnetic powder is reduced, leading to charge up of the magnetic toner. .

  In consideration of the balance of chargeability, the average particle diameter of the magnetic powder is preferably 0.05 to 0.35 μm, more preferably 0.15 to 0.30 μm, even within the above range. preferable. The average particle diameter of the magnetic powder is a Martin diameter (equivalent circle diameter) measured for 300 magnetic powders photographed by magnifying a photograph taken with a transmission electron microscope (magnification 10,000 times) four times. Is the average value.

  As the magnetic powder 101, a metal exhibiting ferromagnetism such as iron, cobalt, nickel, or an alloy thereof, a compound containing these elements, or a ferromagnetic element that does not contain a ferromagnetic element but is subjected to an appropriate heat treatment. In particular, an alloy made of chromium dioxide or the like can be used, and among them, a magnetic powder made of ferrite or magnetite is preferable. In particular, in consideration of imparting good magnetic properties to the magnetic toner, the magnetic powder is from 0.1 to 10 atomic% of Mn, Zn, Ni, Cu, Al, Ti, and Si with respect to Fe. It is preferable to use magnetic powder formed of magnetite containing at least one selected element. It consists of said magnetite, and each vertex and ridgeline of the octahedron are curved and have a portion that can be regarded as a straight line on the outer peripheral portion of the projected image, and the average particle diameter is defined within the above range.

The magnetic powder 101 can be manufactured, for example, by the following method. That is, 26.7 L of a ferrous sulfate aqueous solution containing 1.5 mol / L of Fe ²⁺ was prepared in advance in a reaction vessel, 25.9 L of a 3.4 N aqueous sodium hydroxide solution (1.10 equivalent to Fe ²⁺ ). In addition to heating to 90 ° C., a ferrous salt suspension containing ferrous hydroxide colloid is produced while maintaining the pH at 10.5. Next, while maintaining the liquid temperature of the suspension at 90 ° C., 100 L of air is blown in over 80 minutes to cause an oxidation reaction until the oxidation reaction rate of the ferrous salt reaches 60%. Next, an aqueous sulfuric acid solution was added to the upper suspension so that the pH was 6.5, and then 100 L of air was blown in for 50 minutes while maintaining the liquid temperature at 90 ° C. To generate magnetite particles in the suspension. Then, after adding an aqueous sodium hydroxide solution to the suspension containing the magnetite particles so that the pH becomes 10.5, 100 L of air is applied for 20 minutes while maintaining the liquid temperature at 90 ° C. Then, the produced magnetite particles are washed with water by a conventional method, filtered and dried, and then the aggregates of the magnetite particles are pulverized. Then, a magnetic powder composed of magnetite particles whose particle shape is based on an octahedron and whose apexes and ridges are curved is synthesized. In addition, when performing the above synthesis reaction, various water-soluble metal compounds such as water-soluble silicates are added to an aqueous alkali hydroxide solution or an aqueous ferrous salt reaction solution containing ferrous hydroxide colloid, respectively. In addition to 0.1 to 10 atomic percent of Fe in terms of metal, the pH of the liquid at the start of the aeration of the oxygen-containing gas in the first stage reaction is 8.0 to 8.0. When adjusted to 9.5, the magnetic powder synthesized is at least one selected from Mn, Zn, Ni, Cu, Al, Ti, and Si at the predetermined ratio described above with respect to Fe. It consists of magnetite containing elements.

  The ratio of the magnetic powder to 100 parts by weight of the resin is preferably 1.0 to 35 parts by weight, and more preferably 2.0 to 25 parts by weight. If the ratio of the magnetic powder is less than this range, the effect of containing the magnetic powder cannot be obtained. On the other hand, if the blending ratio exceeds this range, the effect of retaining the toner becomes too strong, and the image density may be lowered. Further, since the content ratio of the binder resin is relatively reduced, the fixability to the surface of the printed material such as paper may be lowered, or the durability may be lowered. The magnetic powder may be subjected to a surface treatment with a surface treatment agent such as a titanium coupling agent, a silane coupling agent, an aluminum coupling agent, or various fatty acids in consideration of being well dispersed in the binder resin. . Of these, silane coupling agents are preferred, and specific compounds thereof include, for example, hexamethyldisilazane, trimethylsilane, trimethylcrawler silane, trimethylethoxysilane, dimethyl dicrollasilane, methyltriclorasilane, allyldimethylcrawlersilane, Allylphenyl dicrolla silane, benzyl dimethyl crawler silane, bromomethyl dimethyl crawler silane, α-crawler ethyl tricola silane, β-crawler ethyl tricola silane, crawler methyl dimethyl crawler silane, triorganosilyl mercaptan, trimethylsilyl mercaptan, triorganosilyl Acrylate, vinyldimethylacetoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, diphenylethoxysilane , Hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and the like. Further, dimethylpolysiloxane having 2 to 12 siloxane units in one molecule and having one hydroxyl group bonded to a silicon atom, one for each siloxane unit located at the terminal, can also be used.

  More specifically, the polystyrene resin may be a homopolymer of styrene or a copolymer with another copolymerizable monomer copolymerizable with styrene. Examples of copolymerizable monomers include p-crawler styrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride; vinyl acetate and propion. Vinyl esters such as vinyl acid vinyl, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-crawler ethyl acrylate, (Meth) acrylic esters such as phenyl acrylate, alpha-crawler methyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; other acrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidene N-vinyl compounds such as These may be used alone or in combination of two or more with a styrene monomer.

  Moreover, as the polyester resin, any resin obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component can be used. The following are mentioned as a component used when synthesize | combining a polyester-type resin. First, dihydric or trihydric or higher alcohol components include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1, Diols such as 4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, hydrogen Bisphenols such as added bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrola, 1,4-sorbitan, Entaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerola, diglycerola, 2-methylpropanetriol, 2-methyl-1,2,4-butane Examples include trivalent or higher alcohols such as triol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

  As the divalent or trivalent or higher carboxylic acid component, a divalent or trivalent carboxylic acid, an acid anhydride or a lower alkyl ester thereof is used. Maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalate Acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n- Divalent carboxylic acids such as alkyl or alkenyl succinic acid such as octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid and isododecenyl succinic acid; -Benzenetricarboxylic acid (trimellitic acid), 1,2,5-ben Tricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl -2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empole trimer acid Examples thereof include trivalent or higher carboxylic acids and the like. Moreover, it is preferable that the softening point of a polyester-type resin is 110-150 degreeC, More preferably, it is 120-140 degreeC.

  The binder resin may be a thermosetting resin. By introducing a partially crosslinked structure in this way, it is possible to further improve the storage stability, form retention, and durability of the toner without deteriorating the fixability. Therefore, it is not necessary to use 100 parts by weight of the thermoplastic resin as the toner resin, and it is also preferable to add a crosslinking agent or to partially use a thermosetting resin. Therefore, an epoxy resin, a cyanate resin, or the like can be used as the thermosetting resin. More specifically, one or more of bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, cyanate resin, etc. Combinations are listed. Moreover, in this invention, it is preferable that the glass transition point (Tg) of binder resin is 50-65 degreeC, More preferably, it is 50-60 degreeC. When the glass transition point is lower than the above range, the obtained toners are fused with each other in the developing device, and the storage stability is lowered. Further, since the resin strength is low, there is a tendency that toner adheres to the photoreceptor. Further, when the glass transition point is higher than the above range, the low-temperature fixability of the toner is lowered. In addition, the glass transition point of binder resin can be calculated | required from the change point of specific heat using a differential scanning calorimeter (DSC). More specifically, it was obtained by measuring an endothermic curve using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. 10 mg of a measurement sample was put in an aluminum pan, an empty aluminum pan was used as a reference, a measurement temperature range of 25 to 200 ° C., a temperature increase rate of 10 ° C./min. The glass transition point was determined from the obtained endothermic curve.

  Charge control agents are formulated (internally added) in order to significantly improve the charge level and charge rise characteristics (an indicator of whether to charge to a constant charge level in a short time) and to obtain excellent durability and stability characteristics. Or externally added). That is, when the toner 100 is positively charged for development, a positively chargeable charge control agent is added. When the toner 100 is negatively charged for development, a negatively chargeable charge control agent may be added. it can.

  The charge control agent is not particularly limited. For example, specific examples of the positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, Metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6- Oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1, Azine compounds such as 2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, quinoxaline; Direct dyes composed of azine compounds such as DE FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azin Light Brown GR, Azin-Kuklin BH / C, Azin Dep Black EW and Azin Dee Black 3RL; Nigrosine Nigrosine compounds such as nigrosine salts and nigrosine derivatives; acid dyes comprising nigrosine compounds such as nigrosine BK, nigrosine NB and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; benzylmethylhexyldecylammonium Quaternary ammonium salts such as decyltrimethylammonium chloride can be exemplified, and these can be used alone or in combination of two or more. In particular, the nigrosine compound is optimal for use as a positively chargeable toner from the viewpoint of obtaining a quicker start-up property. Further, a quaternary ammonium salt, a carboxylate, or a resin or oligomer having a carboxyl group as a functional group can also be used as a positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylic acid Styrene resin with salt, acrylic resin with carboxylate, styrene-acrylic resin with carboxylate, polyester resin with carboxylate, polystyrene resin with carboxyl group, acrylic with carboxyl group 1 type, or 2 or more types, such as resin, the styrene-acrylic resin which has a carboxyl group, and the polyester-type resin which has a carboxyl group, are mentioned. In particular, a styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group is optimal from the viewpoint that the charge amount can be easily adjusted to a value within a desired range. In this case, preferred acrylic comonomers to be copolymerized with the styrene units include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, Examples include (meth) acrylic acid alkyl esters such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate. As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate through a quaternization step is used. Examples of the derived dialkylaminoalkyl (meth) acrylate include di (amino) ethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like ( Lower alkyl) aminoethyl (meth) acrylate; dimethylmethacrylamide, dimethylaminopropylmethacrylamide are preferred. Further, a hydroxy group-containing polymerizable monomer such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, N-methylol (meth) acrylamide or the like can be used in combination during polymerization.

  As the charge control agent exhibiting negative chargeability, for example, organometallic complexes and chelate compounds are effective. Examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and 3,5-di-tert-butylsalicylate chromium. In particular, acetylacetone metal complexes, salicylic acid metal complexes or salts are preferable, and salicylic acid metal complexes or salicylic acid metal salts are particularly preferable. The positively or negatively chargeable charge control agent described above is generally in an amount of 0.5 to 15 parts by weight, preferably 0.5 to 8.0 parts by weight, most preferably 0.5 to 7.0 parts by weight. And is preferably contained in the toner (the total amount of toner is 100 parts by weight). If the addition amount of the charge control agent is smaller than the above range, it tends to be difficult to stably charge the toner to a predetermined polarity, and the electrostatic latent image is developed using the toner to develop an image. When forming, there is a tendency that the image density is lowered and the durability is lowered. In addition, poor dispersion of the charge control agent tends to occur, and there is a tendency that the contamination of the photoreceptor becomes severe. On the other hand, when the charge control agent is used in a larger amount than the above range, it tends to cause defective charging and image defects, and defects such as photoconductor contamination tend to occur.

  The waxes used for improving the fixing property and the offset property are not particularly limited. For example, polyethylene wax, polypropylene wax, Teflon wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan It is preferable to use wax, rice wax or the like. Two or more of these waxes may be used in combination. By adding such wax (internal addition or external addition), offset property and image smearing can be more efficiently prevented.

  The waxes described above are not particularly limited, but it is generally preferable that the wax is blended in an amount of 1 to 5 parts by weight with respect to 100 parts by weight of the total amount of toner. If the addition amount of the wax is less than 1 part by weight, there is a tendency that the offset property and image smearing cannot be effectively prevented. On the other hand, if the amount exceeds 5 parts by weight, the toners are fused. Storage stability tends to decrease.

  Further, the magnetic toner 100 of the present invention can contain a colorant for use as a black toner for forming a monochrome image or as a black toner for forming a color image. The colorant to be used is not particularly limited, and examples thereof include black pigments. These colorants are usually blended in an amount of 1 to 20 parts by weight, preferably 3 to 15 parts by weight, per 100 parts by weight of the binder resin.

  Examples of the black colorant include carbon black such as acetylene black, run black, and aniline black.

  The toner 100 of the present invention is prepared by mixing the above-described binder resin and various toner compounding agents such as a charge control agent and magnetic powder, melt-kneading using a kneader such as an extruder, and cooling and grinding the mixture. And obtained by classification. The obtained toner particles preferably have an average particle diameter of 5.0 to 10.0 μm. If it is smaller than this, the fluidity is lowered, and if it is larger than this, the image quality is lowered. In the toner of the present invention, the surface of the toner particles can be treated with colloidal silica, hydrophobic silica, titanium oxide, alumina, silicon carbide or the like for the purpose of maintaining the fluidity and storage stability of the toner. In addition, these external additives may be subjected to surface treatment such as aminosilane, chicone oil, hexamethyldisilazane, titanate coupling agent, and silane coupling agent, if necessary. The fine particle external additive is used to improve fluidity, storage stability, cleaning properties and the like by surface treatment of the toner. The silica fine particles and titanium oxide are externally added by dry mixing with magnetic toner. This stirring and mixing is performed so that the external additive fine particles are not embedded in the toner 100. Or a nauter mixer.

  Hereinafter, the present invention will be described based on examples. Needless to say, the following description exemplifies the present invention, and the scope of the present invention is not limited to the following description without any particular reason.

  As binder resin, 75 parts by weight of styrene-acrylic copolymer (low molecular weight peak molecular weight 8000, high molecular weight peak molecular weight 130,000, glass transition point Tg 55 ° C.), 12 parts by weight of magnetic powder, and wax as a release agent ( 4 parts by weight of Sazol Wax H1, manufactured by Sazol), 4 parts by weight of a quaternary ammonium salt (Bontron P-51, manufactured by Orient Chemical Co.) as a positive charge control agent, and 5 parts by weight of carbon black as a colorant are added to a Henschel mixer. After mixing, the mixture was melt kneaded with a twin screw extruder, cooled, and coarsely pulverized with a hammer mill. Further finely pulverized by a mechanical pulverizer was classified by an airflow classifier to obtain a toner having a volume average particle size of 7.0 μm. The magnetic powder used is an octahedral shape, which is a convex polyhedron surrounded by eight triangles, and its apex and ridge are curved.

  A ferrous hydroxide colloid obtained by reacting a ferrous salt aqueous solution with 0.08 to 0.99 equivalent of an alkali hydroxide aqueous solution with respect to the ferrous salt of the ferrous salt aqueous solution. The first stage reaction in which an oxygen-containing gas is passed through a ferrous salt reaction aqueous solution while heating in a temperature range of 70 to 100 ° C. to generate magnetite to produce nuclei particles, and the iron oxidation reaction rate is 50%. When it exceeded, the pH was adjusted to 10 or more by adding an alkali hydroxide solution, and the second stage reaction was performed by aeration of an oxygen-containing gas while heating to a temperature range of 70 to 100 ° C., and the particle shapes were hexahedral and octahedral. From the above, magnetic iron oxide particles for toner composed of magnetite particles in which each ridge line of the hexahedron and octahedron is curved are obtained.

  In addition, as a binder resin, 300 parts of xylene was placed in a reactor equipped with a thermometer, a stirrer, and a nitrogen introduction tube, and under a nitrogen stream, 820 parts of styrene and 180 parts of n-butyl acrylate were mixed with dimer and dimer. -Tert-butyl peroxide (polymerization initiator) was dropwise added at 170 ° C. over 2 hours using a mixed solution of 8.0 parts and 125 parts of xylene. After dripping, it was made to react at 170 degreeC for 1 hour, and superposition | polymerization was completed. Thereafter, the solvent was removed to obtain a styrene-acrylic copolymer resin A.

Further, except for using a mixed solution of 730 parts of styrene, 270 parts of n-butyl acrylate, 1.5 parts of di-tert-butyl peroxide and 125 parts of xylene, the same as the binder resin B described above. Polymerization was performed to obtain a styrene-acrylic copolymer resin B.
A mixture of the copolymer resins A and B obtained at a ratio of 75:25 was used as the binder resin.

  To the toner powder obtained above, 1.0 part by weight of titanium oxide (EC-100, manufactured by Titanium Industry Co., Ltd.), 1.0 part by weight of silica (RA-200H, manufactured by Nippon Aerosil Co., Ltd.), and Henschel mixer The toner was adhered to the surface of the magnetic toner powder (this is the toner used in the developer of Example 1). In addition, a toner powder was produced in the same manner as the toner of Example 1 except that only the magnetic powder was changed, and toners used for the developers of Examples 2 to 5 and Comparative Examples 1 to 8 were obtained.

  A two-component developer was obtained by mixing 10 parts by weight of the magnetic toner thus obtained with 100 parts by weight of a magnetic carrier (50 μm, manufactured by Powdertech) using a Nauta mixer.

  The particle size distribution of the toner was measured using a Coulter Counter Multisizer 3 (manufactured by Beckman Coulter). Isoton II (manufactured by Beckman Coulter, Inc.) was used as the electrolyte, and a 100 μm aperture was used as the aperture. Specifically, 10 mg of a measurement sample is added to a solution obtained by adding a small amount of a surfactant to the electrolytic solution, a dispersion treatment is performed using an ultrasonic disperser, and the solution in which the measurement sample is dispersed is measured using the measurement device. A volume distribution of the sample particle size was obtained.

  The carrier particle size distribution is measured using a laser diffraction / scattering type particle size distribution measuring device LA-920 (manufactured by Horiba, Ltd.) as a measuring device and using ethanol as a dispersion solvent at a range setting of 5 to 100 μm. Thus, a volume distribution of the particle size of the carrier was obtained.

Using this two-component developer, a Kyocera Mita page printer FS-C5016N remodeling machine adopting a hybrid development system (up to 16 print speeds per minute up to 20 sheets), the above mentioned for the black development part A two-component developer was added, and the toner scattering state, roller adhesion state, image characteristics, and developer charging characteristics were evaluated in a normal temperature and humidity environment of 20 ° C. and 65%. The evaluation results are shown in Tables 1 and 2.

  Regarding the charging characteristics shown in Tables 1 and 2, the charge amount of the magnetic toner in the developing unit of the printer was measured using a suction type charge amount measuring device (Q / M Meter 210HS) manufactured by TREK, and the weight change at that time was measured. The charge amount μC / g per gram of toner was determined. It should be noted that the charge amount measured after the image was formed with the developer using the page printer and the image for initial image characteristic evaluation was output was measured after the initial charge amount and 100,000 sheets were continuously passed. The charged amount was taken as the charged amount after durability.

  For the image density evaluation in Tables 1 and 2, an initial image is printed by printing the image evaluation pattern with the page printer at the initial stage, and then 100,000 sheets of ISO 4% original is continuously fed, and the image evaluation pattern is printed again. Each image was measured using a Macbeth reflection densitometer (RD914), and the image density was 1.30 or more. K.

Regarding the toner scattering states in Tables 1 and 2, the state of toner scattering from the developing unit was confirmed visually, and the following criteria were used for evaluation.
○: No toner scattering △: Some toner scattering occurs and the inside of the printer is dirty, but there is no effect on the image ×: Toner scattering occurs and the toner scattered from the exhaust fan of the page printer It is discharged out of the machine, and toner adheres to the paper transport path and stains the image.

The sleeve adhesion shown in Tables 1 and 2 (the state where the toner 100 adheres to the developing roller 17) was visually confirmed, and the following criteria were used for evaluation.
○: No toner adherence to the roller Δ: Some roller adherence has occurred, but there is no significant effect on the image ×: Roller adherence has occurred, and the density reduction of the part where the adhesion has occurred is also seen in the image Be

Table 1 is a table showing the evaluation results of the shape and charge amount, image density, toner misery, and sleeve adhesion (toner adhesion to the developing roller 17) of the magnetic powder 101. According to Table 1, good results were obtained for all the evaluation items only when the magnetic powder 101 having the “eight-circle” shape was used. Here, the symbols in the column of magnetic powder particle shape in Table 1 are as follows.
Eight-circle: An octahedron shape with vertices and ridges curved.
Octagon: An octahedron shape whose vertices and ridge lines are not curved. Normal octahedron.
Octahedral: An octahedron with chamfered vertices and ridges on a small plane.
Vertical-angle: It is a cubic body and its vertices and ridges are not curved. Normal cube.
Elevation-plane: Cubic shape with vertices and ridges chamfered by a small plane.
Standing-circle: A cubic shape with vertices and ridges curved.
Sphere: Spherical.

  Table 2 is a table showing evaluation results of the average particle diameter and charge amount of the magnetic powder 101, image density, toner misery, and sleeve adhesion (toner adhesion to the developing roller 17). According to Table 2, good results were obtained for all the evaluation items when the average particle size of the magnetic powder 101 was in the range of 0.05 to 0.37 μm.

  According to Tables 1 and 2, in Examples 1 to 5, good image characteristics were exhibited until after printing due to the effect of the magnetic powder, no roller adhesion occurred, and there was no problem with toner scattering. In Comparative Examples 1 to 4, since the magnetic powder having a shape with a vertex is used, the rising of the charge amount is poor, and toner scattering occurs in the two-component developer portion on the magnetic roller. In Comparative Examples 5 and 6, the battery was charged up after the endurance, and the image density significantly decreased as the toner adhered to the developing roller. In Comparative Examples 7 and 8, the particle size was small and large, the former had a low charge amount and toner scattering occurred, and the latter was charged up and roller adhesion occurred.

  INDUSTRIAL APPLICABILITY The present invention can be used for image forming apparatuses such as laser printers, electrostatic copying machines, plain paper facsimile machines, and multi-function machines using electrophotography, electrostatic recording, and electrostatic printing. it can.

It is a block diagram of the hybrid developing device of this embodiment. 1 is a cross-sectional view of an example of an image forming apparatus including a hybrid developing device of the present embodiment. FIG. 3 is a schematic diagram of a toner according to an exemplary embodiment. 3 is a transmission electron micrograph of magnetic powder internally added to toner.

Explanation of symbols

1 (A, B, C, D) Magnetic roller 2 (A, B, C, D) Developing roller 3 (A, B, C, D) Photoconductor 11 Toner container 12 Toner supply port 13, 14 Mixer 15 Regulating blade 16 Magnetic roller 17 Developing roller 18 Charger 19 Photoconductor 20 Exposure device
21 Transfer roller 50 (A, B, C, D) Developing device 53 Paper feed cassette 54 Paper transport belt 56 (A, B, C, D) Charger 57 (A, B, C, D) Exposure device 59 Fixing device

Claims (3)

A developer comprising a magnetic toner and a magnetic carrier;
A magnetic roller that forms a spike of the developer;
A developing roller for forming a thin layer of the magnetic toner;
A photosensitive member carrying an electrostatic latent image,
In the developing device for developing the electrostatic latent image by causing the magnetic toner to fly onto the surface of the photosensitive member in a state where the developing roller and the photosensitive member are separated from each other,
Adding magnetic powder into the magnetic toner particles,
The average particle size of the magnetic powder ranges from 0.01 to 0.50 μm,
The particle shape of the magnetic powder is an octahedron that is a convex polyhedron surrounded by eight triangles,
Each vertex and ridge line of the octahedron is curved.
A developing device having a linear portion on an outer peripheral portion of the projected image of the octahedron.   2. The developing device according to claim 1, wherein 1 to 35% by mass of magnetic powder is internally added to the toner particles.   2. The developing device according to claim 1, wherein the photosensitive member, the developing roller, and the magnetic roller are arranged in this order from the bottom to the top along the direction of gravity.

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