JP2007322446A - Magnetic toner for two-component developer and image forming method using developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic one-component toner which maintains a moderate charge amount, can hold good image properties over a long period of time, effectively prevents dielectric breakdown in a photoreceptor while holding good image properties, and has such properties that the moderate charge amount can be obtained even in a state where a charge amount is less liable to rise, e.g., in a high temperature and high humidity environment, and to provide an image forming apparatus using the toner. <P>SOLUTION: The magnetic toner for a two-component developer comprising a magnetic toner and a carrier contains magnetic powder in a binder resin, wherein the particle form of the magnetic powder is based on a hexahedron which is a convex polyhedron defined by six quadrangles, each vertex of the hexahedron is curved, and the magnetic powder has a portion considered to be a straight line at a peripheral portion of its projected image. The toner has a saturation magnetization in a measurement magnetic field of 79.6 kA/m being 4.0-15.0 Am<SP>2</SP>/kg. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic toner for a two-component developer comprising a magnetic toner containing a magnetic powder in a binder resin and a carrier, and a latent image on a latent image carrier using the two-component developer. The present invention relates to an image forming method for visualizing the image.

  In an image forming apparatus such as a laser printer using an electrophotographic method, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these, first, the surface of the latent image holding member is uniformly charged by a charging means. Next, after exposure is performed by exposure means such as a semiconductor laser or a light emitting diode to form an electrostatic latent image, the electrostatic latent image is developed or reversed and developed by a developing means to be visualized as a 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.

  There are roughly two types of development methods for developing such an electrostatic latent image into a toner image. There are two types of development methods, dry and wet. Currently, dry development methods are widely used. This 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 (a one-component development method using magnetic toner alone, a magnetic toner) A two-component development method using a mixture of toner and magnetic carrier in a certain ratio), a development method using a non-magnetic toner not containing magnetic powder (a one-component development method using a non-magnetic toner alone, a non-magnetic toner And a two-component development method in which a magnetic carrier and a magnetic carrier are mixed at a certain ratio.

  Among these, in the two-component development method, fine toner particles are held on the surface of relatively large carrier particles made of iron powder, ferrite, etc. by the electric force generated by the friction caused by the mixing of both particles. When transported to the photoreceptor in the form of a brush and brought close to the electrostatic latent image, the attractive force in the latent image direction against the toner particles by the electric field formed by the electrostatic latent image overcomes the binding force between the toner particles and the carrier particles. The toner particles adhere to the electrostatic latent image and the electrostatic latent image is visualized.

  In the two-component development method, a non-magnetic toner that does not contain magnetic powder is mainly used. However, it has been known for a long time that a magnetic toner is used as a toner for a two-component developer. Describes that a toner containing magnetic powder in the toner is used. In other words, by incorporating magnetic powder in the toner for two-component developer, the problem of toner scattering or toner drop often caused by the two-component development method due to the magnetic attraction generated between the toner and the carrier is avoided. And fogging can be suppressed. In addition, toner overcharge and charge-up that occur when the toner is repeatedly mixed with the carrier can be prevented by charging leakage from the magnetic powder existing on the toner surface.

  On the other hand, in recent years, image forming apparatuses are required to increase the image forming speed, to reduce the size of the apparatus, and to extend the life of the entire apparatus, and among these, mainly to increase the image forming speed. In a high-speed machine adapted for business use, in order to prevent the resolution and image quality of the formed image from deteriorating as the printing speed increases, the toner charge amount is made easier to rise quickly than in the past, The charge amount is required to be more stable than in the past.

  In medium- and low-speed machines for small offices and general households that require miniaturization, the power is frequently turned on and off repeatedly, so magnetic toner is used to minimize the warm-up time after power on. It is required that the initial charge of the is good. In addition, regardless of the difference in image formation speed depending on the application, the image forming apparatus will continue to improve the resolution and quality of the formed image, improve the durability of the magnetic toner, and improve the stability against environmental fluctuations. Is required.

  For these reasons, magnetic toners are charged easily even in environments where the amount of charge tends to rise quickly and is difficult to be charged such as in a high temperature and high humidity environment, or in an environment that is excessively charged such as a low temperature and low humidity environment. Without causing a shortage or charge-up (overcharge), it is possible to always maintain an appropriate charge amount and maintain the appropriate charge amount over a long period of time, resulting in good image characteristics (high image density and no fogging, It has been demanded that it can be stably maintained under various temperature and humidity environments for a long time.

  In addition, as the machine speeds up and the service life is extended, the conventional toner scattering in the two-component developer, spent on the carrier (a phenomenon in which the toner component adheres and deposits on the surface of the carrier), and the magnetic brush on the photosensitive drum. Problems such as streaking are more likely to occur, and these problems are naturally required to be avoided. However, currently commonly used toners are becoming unable to fully satisfy these requirements in the flow of increasing the image forming speed and downsizing of the apparatus described above. Is the current situation.

  Among these, the streaks due to the magnetic brush with respect to the photosensitive drum as the latent image holding member is a problem that the photosensitive drum is streaked by keeping the magnetic brush in contact with the photosensitive member for a long period of time. That is, in the two-component development method, a magnetic brush is formed by a two-component developer on a magnetic roll facing the developing portion of the photosensitive drum, and development is performed by bringing the magnetic brush into contact with the photosensitive drum. This is a problem that occurs because the magnetic brush keeps in contact with the photosensitive member for a long period of time as the service life of the toner increases. Conventionally, this problem has been avoided by selecting a carrier. However, when magnetic powder is contained in the two-component toner, magnetic brush streaks are generated by the influence of the magnetic powder. There is a possibility.

  The spent toner on the carrier is a phenomenon in which the toner component adheres and precipitates on the surface of the carrier, and the surface of the carrier is covered with the toner component and the original performance of the carrier cannot be obtained. Therefore, it can be considered as deterioration of the carrier. However, when the spent occurs, the image density is lowered and fogging occurs. In the worst case, the developer itself must be replaced. This spent is a problem that has conventionally occurred along with the extension of the life of the machine, and the possibility of the occurrence of the spent has become higher in recent years when the toner is being fixed at a low temperature. Further, when magnetic toner is used, not only the charging force with the carrier but also the magnetic restraining force is applied, so that the possibility of further occurrence is increased.

  Currently, the magnetic powder contained in the toner is a hexahedron (see FIG. 1B, cube, cuboid) that is a convex polyhedron surrounded by six squares, or a convex that is surrounded by eight triangles. Polyhedral magnetic powders such as octahedral ones (see FIG. 1C) and spherical magnetic powders (see FIG. 1A) are generally used. However, in magnetic toners using polyhedral magnetic powder, charges are more likely to be released from the sharp apex of the magnetic powder exposed on the surface of the toner particles and the sharp ridgeline between adjacent faces, and charge leakage is more than necessary. It is easy to happen. In addition, since the polyhedral magnetic powder has low fluidity and poor dispersibility with respect to the binder resin, it is difficult to uniformly disperse it in the binder resin. Therefore, the dispersion state of the magnetic powder in the individual toner particles is likely to vary, and 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 does not easily rise in charge amount, and the charge amount itself becomes low, resulting in problems such as toner scattering and toner dropping, and image defects such as fogging. There is a problem that it is likely to occur. In addition, since the ease of charging and the amount of charge are likely to vary depending on the temperature and humidity environment during image formation, the above-mentioned image defects are more likely to occur, particularly in environments that are difficult to charge, such as high temperatures and high humidity environments. There is also a problem.

  Furthermore, the magnetic toner using the polyhedral magnetic powder has a sharp apex of the magnetic powder exposed on the surface of the toner particles and a photoconductor that contacts as a magnetic brush due to a sharp ridge between adjacent surfaces. There is also a problem that the magnetic brush streak, which is difficult to generate with toner containing no magnetic powder, is generated instead. However, on the other hand, there is an advantage that the spent of the carrier can be effectively prevented by the polishing effect due to the sharp ridgeline or apex of the magnetic powder.

  On the other hand, magnetic toners using spherical magnetic powder do not have sharp apexes or ridges, prevent magnetic brushes from being exposed to the surface of the toner particles, and prevent magnetic brush damage to the photoreceptor. Compared with, it has excellent fluidity and excellent dispersibility in the binder resin, making it easy to disperse uniformly in the binder resin and preventing variation in the dispersion state of the magnetic powder in each magnetic toner. Thus, it is possible to make the chargeability and charge amount uniform.

  However, since magnetic toner using spherical magnetic powder does not have sharp apexes or ridges, it does not have the effect of preventing spent on the carrier, and it is not possible to remove magnetic powder exposed on the surface of toner particles. Charges are difficult to be released, and when the carrier and toner are repeatedly mixed because the charges are too easy to accumulate, the toner tends to overcharge more than a predetermined charge amount. There is a problem that an image defect typified by a decrease in density tends to occur.

Therefore, in order to take advantage of both the spherical magnetic powder and the polyhedral magnetic powder,
For example, Patent Document 1 describes a magnetic powder having a so-called chamfered particle shape with vertices and ridgelines of a polyhedron such as the hexahedron and octahedron being smaller than each plane constituting the polyhedron. Yes. However, even in this magnetic powder, there is still a sharp ridgeline between the polyhedron surface and the small chamfered plane, and charges are easily released from this ridgeline. As a result, image defects such as a decrease in image density and generation of ground fog may occur.

Patent Document 2 describes 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 a ridgeline, and the vertices are also curved, and there are no sharp vertices or ridgelines as charge discharge points. In particular, the magnetic toner may be charged up at low temperatures and in low humidity environments, and image defects such as a decrease in image density may occur.
Japanese Patent Laid-Open No. 11-153882 Japanese Patent Laid-Open No. 9-59024

  In recent years, the market for copiers and printers using electrophotography using two-component developers has been remarkably advanced in printing speed, machine size and machine life, and the required performance is also high. Resolution, high image quality, and high durability are becoming natural. Therefore, in order to obtain improved image characteristics and durability in accordance with the increased printing speed, a toner having stable charging characteristics and high performance is indispensable.

  Therefore, in view of the problems of the prior art, the present invention can obtain a good image characteristic (image density, fog) over a long period of time while maintaining an appropriate charge amount as a two-component developer, and those good It is possible to obtain image characteristics even in high-temperature and high-humidity environments and low-temperature and low-humidity environments, and to prevent toner scattering, carrier spent, and damage to the photoconductor drum by a magnetic brush over a long period of time. It is a problem to provide a highly durable two-component magnetic toner that can be used and an image forming method using the same.

  As a result of intensive studies to solve the above problems, the present invention has been completed by paying attention to the magnetic powder added to the toner for the two-component developer for the electrophotographic system adopting the two-component development method. That is, the inventor basically uses a hexahedron-shaped polyhedron that is a convex polyhedron surrounded by six squares as the magnetic powder contained in the toner for two-component developer, and each vertex and ridge line of the polyhedron has The use of magnetic powder having a curved particle shape was studied.

  As can be understood from the schematic diagram shown in FIG. 2, the magnetic powder is based on the hexahedron 1, and the vertex 2 b and the ridge 2 a are curved, and there are no sharp vertices or ridges that serve as charge discharge points. It is a feature. Even if the vertex 2b and the ridge line 2a are curved, the radius of curvature is too large and the curved surfaces of adjacent vertices and ridge lines are connected to each other, so that there is a portion that can be regarded as a straight line on the outer periphery of the projected image. However, the portion 2c that can be regarded as a straight line is left on the outer periphery of the projected image, and the feature as a hexahedron remains.

  In the magnetic powder having the above particle shape, the vertex and the ridge line are both curved, and the portion where the magnetic powder is exposed from the toner is not a sharp vertex or ridge line, so this magnetic powder is contained in the magnetic brush of the two-component developer. Even if toner containing powder is present, it is not described in Patent Documents 1 and 2 because the photosensitive drum does not have a streak due to a magnetic brush and does not have sharp apexes or ridges that easily discharge charges. Compared to magnetic powder with chamfered vertices and ridge lines of a polyhedron, it is considered that charge leakage is less likely to occur when encapsulated in magnetic toner.

  In addition, the magnetic powder has a curved surface at the vertices and ridges of the polyhedron as described above. Therefore, the magnetic powder is excellent in fluidity and dispersibility with respect to the binder resin, and particularly when the magnetic powder is included. It is easy to uniformly disperse the toner particles in the toner particles, and the dispersion of the magnetic powder in each toner particle is prevented from being dispersed, and the ease of charging and the charge amount of each magnetic toner are made uniform. It is considered possible.

  Moreover, the magnetic powder has a hexahedral shape as shown in FIG. 2, but the apex or the ridge line constituting the hexahedron is a curved surface and has a portion that can be regarded as a straight line on the outer peripheral portion of the projected image. Therefore, the charges can be released at an appropriate rate without concentrating the charges on the vertices and ridge lines.

  For this reason, it is considered that charge-up can be made difficult to occur when encapsulated in magnetic toner.

Further, as a result of examining the magnetic characteristics of the toner containing these magnetic powders, the saturation magnetization of the toner containing the magnetic powders at a measured magnetic field of 79.6 kA / m (1 kQe) is less than 4.0 Am ² / kg. It has been found that the original effect of adding magnetic powder to the two-component toner cannot be obtained, and there is a problem that the occurrence of toner scattering cannot be effectively prevented. Further, when the toner saturation magnetization exceeds 15.0 Am ² / kg, when the magnetic binding force with the carrier is increased and a magnetic brush of a two-component developer is formed, the photosensitive portion is exposed by contact with the photosensitive drum in the development portion. Since magnetic brush streaks are attached to the body drum and the connection with the carrier becomes stronger, there is also a problem that the spent on the carrier is likely to occur.

  The inventor also examined the size of the magnetic powder. As a result, the magnetic powder having an average particle diameter of less than 0.01 μm increases the exposure ratio of the toner particles to the surface of the toner particles, and charges are released from the exposed magnetic powder, resulting in insufficient charging of the magnetic toner. On the other hand, the magnetic powder having an average particle diameter of more than 0.50 μm, on the other hand, reduces the rate of exposure on the surface of the toner particles and reduces the charge released from the exposed magnetic powder. As a result of charging up the magnetic toner, it has been found that there is a problem that the image density is lowered particularly when the image formation is repeated. Therefore, the average particle size of the magnetic powder is 0.01 to 0.50 μm. I found it necessary.

Therefore, the present invention is based on such knowledge,
In a magnetic toner for a two-component developer comprising a magnetic toner containing magnetic powder in a binder resin and a carrier,
The particle shape of the magnetic powder contained in the toner particles is based on a polyhedron, each vertex of the polyhedron is a curved surface, and has a portion that can be regarded as a straight line on the outer periphery of the projected image, and the magnetic field for measuring the toner The present invention proposes a magnetic toner for two-component developer, characterized in that the saturation magnetization at 79.6 kA / m is 4.0 to 15.0 Am ² / kg.

  Moreover, it is preferable that the polyhedron has a hexahedral shape that is a convex polyhedron surrounded by six quadrangles, and the average particle diameter of the magnetic powder is preferably 0.01 to 0.50 μm. The average particle diameter of the magnetic powder is a Martin diameter (equivalent circle diameter) measured for 300 magnetic powders photographed with a transmission electron microscope (magnification 10,000 times) magnified four times. Is the average value.

  As materials used for the magnetic toner for two-component developer in the present invention, known dyes, pigments, charge control agents, fluidizing agents, external additives, etc. can be used in addition to the binder resin. These materials are not particularly limited, and known materials that can be used for the two-component toner can be used, and the carrier necessary for forming the two-component developer is not particularly limited. However, considering the balance of the effect, the average particle size of the magnetic powder is preferably 0.05 to 0.35 μm, even within the above range. As the magnetic powder, in consideration of imparting good magnetic properties to the magnetic toner, 0.1 to 10 atomic% of Mn, Zn, Ni, Cu, Al, Ti, and Si with respect to Fe It is preferable to use a magnetite (triiron tetroxide) containing at least one element selected. For the same reason, the proportion of the magnetic powder in the toner particles is preferably 2.0 to 20% by mass.

  Further, when the magnetic toner of the present invention contains magnetic powder, for example, a binder resin, a magnetic material, a wax, a charge control agent, and other additives are sufficiently mixed by a mixer such as a Henschel mixer or a ball mill. The components are dispersed or dissolved in a melt-kneaded resin using a heat kneader such as a heating roll, kneader, or extruder to disperse or dissolve them. After cooling and solidification, pulverization and classification are performed. The desired external additive can also be obtained by sufficiently mixing with a mixer such as a Henschel mixer.

  With this configuration, the magnetic material according to the present invention has a uniform particle size distribution and is excellent in dispersibility in the binder resin, so that the chargeability of the toner can be stabilized. In addition, even when the average particle size of the toner is 10 μm or less when a ferrite carrier is used as the carrier, the charging uniformity is promoted and the aggregation property of the toner is reduced, and development such as improvement of image density and improvement of fog Improves. In particular, the effect is remarkable in a toner having a weight average particle diameter of 8.0 μm or less, and an extremely fine image can be obtained. A weight average particle diameter of 3.0 μm or more is preferable because a sufficient image density can be obtained. On the other hand, as the toner particle size is reduced, the release of the magnetic material is likely to occur. However, the magnetic powder having a number average particle size of 0.05 to 0.35 μm is 0.1 to 100 parts by weight of the binder resin. By using 10 parts by weight to form a magnetic toner having a volume average particle size of 3.0 to 10.0 μm, it has excellent adhesion to the binder resin, so that the magnetic substance is not easily released and troubles such as sleeve contamination are caused. It is suppressed.

And the image forming method forming method using the two-component developer is as follows:
At least the particle shape of the magnetic powder contained in the binder resin is based on a polyhedron, and each vertex and ridge line of the polyhedron are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image. A two-component developer comprising a magnetic toner and a carrier having a saturation magnetization of 4.0 to 15.0 Am ² / kg at a measurement magnetic field of 79.6 kA / m;
An image forming method comprising: causing a toner carrying body on which at least the magnetic toner into which electric charge is injected is carried to face a latent image carrying body, and developing an electrostatic image on the latent image carrying body with the magnetic toner. It is.

  This invention only includes an image forming method in which development is performed while a magnetic brush is formed on a development area facing a latent image carrier (photosensitive drum) by frictionally charging toner and a carrier on a development carrier (developing roller). The two-component developer conveying magnetic roll for charging the developer composed of carrier and toner while magnetically holding the toner, and transferring the toner from the conveying body using the magnetic brush and conveying bias of the magnetic roll, A developing roll that forms a thin layer of toner only on the surface, and a developing bias is applied to the closest position (developing position) between the developing roll and the latent image carrier to develop the latent image on the latent image carrier. The present invention can also be applied to an image forming apparatus having a hybrid developing device.

In this image forming method, a two-component developer composed of a carrier and the magnetic toner is formed in a brush shape using a magnetic field in a developing area where the toner carrier and the latent image carrier face each other (hereinafter referred to as magnetic). In the image forming method, the latent image on the latent image carrier is visualized as a toner image while the magnetic brush is rubbed against the surface of the latent image carrier.
The magnetic toner has magnetic toner particles containing at least a binder resin and magnetic powder, and the magnetic powder has an average particle diameter of 0.01 to 0.50 μm, and the particle shape is basically a polyhedron. In addition, each vertex and ridge line of the polyhedron is curved and has a portion that can be regarded as a straight line on the outer peripheral portion of the projected image.

  According to the present invention, the magnetic powder contained in the magnetic toner for two-component developer is basically a hexahedron, and the magnetic powder having a particle shape in which each apex and ridge line of the hexahedron is a curved surface. As a component toner, it has a charging characteristic that does not quickly charge up or charge up (overcharge) while maintaining an appropriate charge amount, and as a result, good image characteristics (image density, fog) can be obtained over a long period of time. At the same time, it is possible to obtain a toner that does not generate toner scattering, spent on carrier, magnetic brush streaks on the photosensitive drum, which is a problem peculiar to a two-component developer, and has a long life while maintaining good image characteristics. Even in the system, the various problems inherent to the two-component development method can be avoided and a highly durable magnetic toner for two-component developer and an image forming method can be obtained.

  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. 3 is a view showing an outline of the structure of an image forming apparatus provided with the magnetic brush developing device of the present invention. In the drawing, around the photosensitive drum 10 provided to be rotatable in the direction of the arrow, there are a charging device 25, an exposure mechanism 3, a magnetic brush developing device 4, a transfer device (not shown), a cleaning device 6, and a static eliminating device. 7 is arranged along the rotation direction of the photosensitive drum 1, and a transfer material 11 such as paper or an OHP film is passed between the photosensitive drum 10 and the transfer device, and on the discharge path of the transfer material 11. A fixing device (not shown) is provided.

  The photosensitive drum 10 is an inorganic photosensitive drum in which a photosensitive layer such as selenium or amorphous silicon is provided on a conductive substrate roller such as aluminum, or an organic material in which a charge generating agent or a charge transporting agent is dispersed in a binder resin. An organic photosensitive drum provided with a photosensitive layer is used. As the charging device 25, a roller-type contact charging device or a corona charger is used. By this charging device 25, the surface (photosensitive layer) of the photosensitive drum 10 is uniformly set to a predetermined polarity according to the type of the photosensitive layer. Is charged. The charging potential on the surface of the photoreceptor at this time is usually 200 to 1000 V (absolute value). Next, the image exposure mechanism 3 irradiates the surface of the photosensitive drum with dot light such as a laser beam corresponding to the original by reflected light of the original or an electric signal from a computer or the like, and the potential of the light irradiation portion is attenuated and static. An electrostatic latent image is formed.

  This electrostatic latent image is developed by a magnetic brush formed on the magnetic brush developer 4 using the present invention, and a toner image 15 is formed on the surface of the photosensitive drum 10. As the developer 35, a two-component developer composed of a magnetic carrier and a magnetic toner is used, and the developer 4 conveys the toner frictionally charged to a predetermined polarity in the form of a magnetic brush. The electrostatic latent image formed on the surface is developed, and a toner image 15 is formed on the surface of the photosensitive drum 10.

  The toner image 15 is transferred to the transfer material 11 as a transfer toner image 16 by a transfer device (not shown), conveyed to a fixing device (not shown), and fixed on the surface of the transfer material 11 by heat and pressure. . On the other hand, after the toner image 15 is transferred onto the transfer material 11 as the transfer toner image 16, the toner remaining on the surface of the photosensitive drum 10 is scraped and collected by the cleaning device 6 having a cleaning blade or the like. The surface charge of the photosensitive drum 10 is removed by light irradiation by the static eliminator 7, and the next image forming process is performed. The magnetic brush developing device 4 of the present invention is composed of a developing housing 30 filled with a developer 35, and in the developing housing 30, a developer conveying sleeve (facing the photosensitive drum 10) is provided. (Developing sleeve) 31 is disposed, and stirring paddles 32 a, 32 b, and 32 c are disposed in parallel with the developing sleeve 31 in the same direction.

  A magnet having a plurality of magnetic poles is fixed inside the developing sleeve 31, and the developer is conveyed in the form of a magnetic brush by the rotation of the sleeve. Usually, the interval between the developing sleeve 31 and the photosensitive drum 10 is as follows. Generally, it is set to about 0.3 to 1.0 mm. Of course, the developing sleeve 31 may transport the developer by fixing the sleeve and rotating an internal magnet. A panning blade 33 is attached to the developing sleeve 31 at regular intervals (usually about 0.3 to 1.0 mm). That is, the developer pumped up by the developing sleeve 31 is blocked by the ear cutting blade 33, and is developed in the form of a magnetic brush adjusted to a certain ear length (the photosensitive drum 10 and the developing sleeve 31). The electrostatic latent image is developed in this portion.

  The stirring paddles 32a, 32b, and 32c are for mixing and stirring the developer 35 to sufficiently frictionally charge the toner in the developer 35. The blades of each paddle send the developer while stirring the developer in the axial direction. The adjacent paddles are partitioned by the partition 37 except for the central portion or both end portions. That is, while the developer 35 is stirred and fed in the axial direction by the plurality of stirring paddles 32a, 32b, and 32c, the developer 35 is taken in and out between the center or both ends of each paddle so that the frictional charging is performed efficiently. It has become. The developer (magnetic toner) 35 frictionally charged to a predetermined polarity in this way is pumped up by the developing sleeve 31, and the developer is conveyed to the developing area in the form of a magnetic brush whose ear length is adjusted by the ear cutting blade 33, The electrostatic latent image is developed.

  Further, a rectifying plate 40 is disposed in the vicinity of the above-described ear cutting blade 33, that is, on the side where the developer 35 is blocked by the blade 33. That is, the developer 35 blocked by the ear cutting blade 33 falls on the rectifying plate 40, smoothly flows on the guide plate 40a, is dropped on the stirring paddle 32b, is mixed and stirred again, and developed. Supplied to the sleeve 31.

  As the developing sleeve 31, those made of various known materials can be used, and it is particularly preferable to use a blasted stainless steel developer carrier.

  In the toner of the present invention, magnetic powder is blended in a binder resin to obtain a magnetic toner. The magnetic powder contained in the toner of the present invention is, for example, an octahedron that is a convex polyhedron surrounded by eight triangles, as shown by a dashed line in FIGS. 3A to 3C showing the case of an octahedron. 2 and having a particle shape in which the vertices 1b and ridges 1a of the octahedron 2 or the cubic shape are curved as shown by solid lines in the figure.

  Moreover, this magnetic powder needs to have an average particle diameter of 0.01 to 0.50 μm. When the average particle diameter is less than 0.01 μm, the ratio of the magnetic powder exposed on the toner surface increases, and the discharge of electric charge occurs from that portion, resulting in insufficient charging and toner scattering. On the other hand, the magnetic powder having an average particle diameter exceeding 0.50 μm reduces the ratio of the magnetic powder exposed on the surface of the toner, and reduces the appropriate discharge of charges from that portion, leading to charge-up. As a result, the image density is lowered after forming a large number of images.

  In consideration of the balance of the effects, the average particle diameter of the magnetic powder 1 is preferably 0.05 to 0.35 μm, more preferably 0.15 to 0.30 μm, even within the above range. .

  As magnetic powder, metals such as iron, cobalt, nickel, etc., alloys thereof, compounds containing these elements, or ferromagnetic elements that do not contain ferromagnetic elements, but exhibit ferromagnetism by appropriate heat treatment. In particular, an alloy made of chromium dioxide or the like is preferable, and 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.

  The cubic magnetic powder made of magnetite can be produced, for example, by the method described below.

That is, a ferrous salt aqueous solution 26.7 l sulfuric acid containing ^{Fe 2+} of 1.5 mol / liter, with respect to the prepared 3.4N aqueous sodium 23.6 l hydroxide ^{(Fe 2+} in advance into the reaction vessel 1. Ferrous oxide containing ferrous hydroxide colloid by heating to 90 ° C. and adjusting the pH to 8-10 with a 3.4 N aqueous sodium hydroxide solution. A salt suspension is produced.

  Next, while maintaining the liquid temperature of the suspension at 90 ° C., air is blown 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 air was blown into the suspension while maintaining the liquid temperature at 90 ° C. Generate.

  The produced magnetite particles are washed with water by a conventional method, filtered, dried, and then agglomerated magnetite particles are pulverized. Then, a magnetic powder composed of magnetite particles whose particle shape is basically a hexahedron and whose apexes and ridges are curved is synthesized.

  As a preferred range for carrying out the present invention, the pH during the first stage reaction is from 8 to 10, but if the pH during the first stage reaction is not maintained from 8 to 10, the hexahedral shape do not become. The hexahedron is produced by carrying out the first stage reaction in the range of 8 to 9.5.

  In this synthesis reaction, in order to adjust the curvature of the magnetic powder, the roundness varies depending on the reaction rate during the oxidation reaction of the first stage oxidation. When the amount is less than 50%, the edge appears, and when it exceeds 50%, the edge becomes round.

  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. When added in a proportion of 0.1 to 10 atomic% with respect to Fe, the magnetic powder synthesized is Mn, Zn, It consists of magnetite containing at least one element selected from Ni, Cu, Al, Ti, and Si.

  The ratio of the magnetic powder to 100 parts by mass of the resin is preferably 1.0 to 35 parts by mass, and more preferably 2.0 to 25 parts by mass. If the ratio of the magnetic powder is less than this range, the effect of holding the toner is reduced by the magnetic force of the fixed magnet built in the developer holder, so that fog may occur in the image and toner scattering is suppressed. I can't. On the other hand, if the blending ratio exceeds this range, the toner holding effect is too strong, and the image density may be lowered. In addition, since the content ratio of the binder resin is relatively reduced, there is a possibility that the fixability to the surface of the printing material such as paper may be reduced or the durability may be reduced.

  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, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allyl Phenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilyl mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyl Dimethylacetoxysilane, 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 one hydroxyl group bonded to a silicon atom, one for each siloxane unit located at the terminal, can also be used.

The toner containing the magnetic powder needs to contain the magnetic powder so that the saturation magnetization at the measurement magnetic field of 79.6 kA / m is 4.0 to 15 Am ² / kg. If it is less than this range, the original effect of containing the magnetic powder in the two-component toner cannot be obtained, and there is a problem that the occurrence of toner scattering cannot be effectively prevented. Also, if the toner saturation magnetization exceeds this range, the magnetic binding force with the carrier becomes too strong, and when a two-component developer magnetic brush is used, the photosensitive drum is magnetically contacted with the photosensitive drum at the development portion. You will end up with brush streaks. In addition, there is also a problem that the spent on the carrier is likely to occur due to the strong connection with the carrier. In consideration of effects and adverse effects, the saturation magnetization is more preferably 4.5 to 14.0 Am ² / kg.

The toner of the present invention can be obtained by dispersing various toner compounding agents such as a colorant in a binder resin. The type of binder resin used for the toner in the present invention is not particularly limited. For example, styrene resin, acrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, vinyl chloride It is preferable to use thermoplastic resins such as resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, styrene-butadiene resins.

  Examples of the polystyrene resin include a styrene homopolymer, and a binary or ternary or higher copolymer of styrene and another monomer. These may be used alone or in combination of two or more with styrene. As copolymerizable monomers, p-chlorostyrene; 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, propion Vinyl esters such as vinyl acrylate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, acrylic (Meth) acrylic acid esters such as phenyl acid, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; other acrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; Vinyl ethers such as nylmethyl 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, etc. N-vinyl compounds of These may be used alone or in combination of two or more with a styrene monomer.

  Examples of the polyester resin include various polyester resins obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component. As a component used when synthesizing a polyester-based resin, first, as a bivalent or trivalent or higher alcohol component, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol Diols such as polytetramethylene glycol; bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol And trivalent or higher alcohols such as 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, etc. .

  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 Phthalic 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, Divalent carboxylic acids such as alkyl or alkenyl succinic acid such as n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid; 4-benzenetricarboxylic acid (trimellitic acid) 1, 2, 5 Benzenetricarboxylic 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, empor 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 mass of the thermoplastic resin as the toner resin, and it is also preferable to add a cross-linking agent or 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.

  The glass transition temperature Tg of the binder resin is preferably 50 to 65 ° C, and more preferably 50 to 60 ° C. If the glass transition temperature is less than this range, the toner particles are likely to be fused with each other, and the storage stability may be lowered. In addition, since the strength of the resin is low, the resin adheres to the surface of the latent image holding member and does not come off, which may cause toner adhesion. On the other hand, when the glass transition temperature exceeds this range, the fixability to the surface of the substrate such as paper may be lowered.

  In addition, the glass transition temperature of binder resin can be calculated | required from the change point of specific heat in the endothermic curve measured, for example using the differential scanning calorimeter (DSC). Specifically, for example, a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. is used, and 10 mg of a measurement sample is put in an aluminum pan, and an empty aluminum pan is used as a reference, and a measurement temperature range of 25 to 200 ° C. The glass transition temperature of the binder resin can be determined from the change point of specific heat in the endothermic curve obtained by measuring at a temperature increase rate of 10 ° C./min and at normal temperature and normal pressure.

  Charge control agents are blended to remarkably 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 characteristics such as durability and stability. It is. That is, when the toner is positively charged for development, a positively chargeable charge control agent is added. When the toner is negatively charged for development, a negatively chargeable charge control agent can be added. .

  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; alkyl amides; benzylmethylhexyl decyl ammonium; 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, as a positively chargeable charge control agent, in particular, a styrene-acrylic resin (styrene-acrylic copolymer) having a quaternary ammonium salt, carboxylate or carboxyl group as a functional group has a desired charge amount. This is preferable in that it can be easily adjusted to a value within the range. 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 copolymerized with the styrene unit 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, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  As the charge control agent exhibiting negative chargeability, for example, an organometallic complex and a chelate compound are effective. Examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and chromium 3,5-di-tert-butylsalicylate. 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 proportion of the charge control agent in the toner particles is preferably 0.5 to 15% by mass, more preferably 0.5 to 8.0% by mass, and 0.5 to 7.0% by mass. Is particularly preferred. When the ratio of the charge control agent is less than this range, it is difficult to impart stable charging characteristics to the magnetic toner, and there is a possibility that the image density is lowered or the durability is lowered. In addition, since poor dispersion with respect to the binder resin is likely to occur, there is a risk that background fogging may occur, or the charge control agent aggregated without being dispersed may contaminate the photoreceptor. On the other hand, if the above range is exceeded, the magnetic toner tends to have environmental resistance, particularly charging failure and image failure under high temperature and high humidity. In addition, since poor dispersion with respect to the binder resin is likely to occur, there is a risk that background fogging may occur, or the charge control agent aggregated without being dispersed may contaminate the photoreceptor.

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

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

The toner of the present invention is obtained by mixing the above-described binder resin and various toner compounding agents such as a charge control agent, melt-kneading using a kneader such as an extruder, and then cooling, pulverizing and classifying the mixture. can get. The obtained toner particles have a volume average particle size of 5.0 to 10.0 [mu] m, preferably 5.0 to 10.0 [mu] m. If it is smaller than this, the fluidity is lowered and fogging is caused. If it is larger than this, the image quality will deteriorate.

  In addition, the manufactured magnetic toner improves the flowability, storage stability, cleaning properties indicating the ease of cleaning removal from the surface of the latent image holding member, etc. Surface treatment may be performed with fine particles (external additive, usually having an average particle size of 1.0 μm or less) such as silica, hydrophobic silica, alumina, titanium oxide and the like. For the surface treatment, it is preferable to dry-mix the magnetic toner and the external additive. In particular, in order to prevent the external additive from being embedded in the surface of the toner particles, mixing is performed using a Henschel mixer or a Nauter mixer. It is preferable to do this. The addition amount of the external additive is preferably 0.2 to 10.0% by mass with respect to the toner particles. The external additive may be surface-treated with aminosilane, silicone oil, silane coupling agent (hexamethyldisilazane, etc.), titanium coupling agent, or the like, if necessary.

  Since 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, the toner concentration of the developer layer in the development region can be increased. A good image with 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.

  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; polyurethanes; polycarbonates; fluororesin etc. - urea amino resins such as formaldehyde resins, epoxy resins and the like.

  Further, in the carrier used in the present invention, a conductivity imparting material may be dispersed in the coating layer in order to control its volume resistivity. Application of the conductive material to be dispersed may be a conventionally 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. It became possible to obtain an excellent carrier. These conductive fine powders preferably have a particle size of about 0.01 to 10 μm, preferably 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 5.0 μm.

  In the present 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 mass, more preferably 3.0 to 20 parts by mass with respect to 100 parts by mass of the carrier. 15 parts by mass. When the amount of toner is less than the above range, charge up occurs and the image density decreases. On the other hand, fogging or toner scattering occurs when the above range is exceeded.

  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.

70 parts by mass of styrene-acrylic copolymer (low molecular weight peak molecular weight 8000, high molecular weight peak molecular weight 130, 500, glass transition point Tg 55.0 ° C.) as a binder resin, 15 parts by mass of magnetic powder, and wax as a release agent ( 5 parts by mass of Sazol Wax H1, manufactured by Sazol), 5 parts by mass of a quaternary ammonium salt (Bontron P-51, manufactured by Orient Chemical Co.) as a positive charge control agent, and 5 parts by mass of carbon black as a colorant in 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 has a hexahedral shape, which is a convex polyhedron surrounded by six quadrangles, and its apex 1b and ridge line 1a are curved and has an average particle size of 0.20 μm. It is powder.

A ferrous hydroxide colloid obtained by reacting a ferrous salt aqueous solution and a ferrous salt of the ferrous salt aqueous solution with 0.08 to 0.99 equivalent of an aqueous alkali hydroxide solution. A first-stage reaction in which an oxygen-containing gas is aerated in a ferrous salt reaction aqueous solution while heating in a temperature range of 70 to 100 ° C. to generate magnetite and nucleation particles are generated, and an iron oxidation reaction rate is 50 When the pH exceeds 10%, an alkali hydroxide solution is added to maintain the pH at 10, and the second stage reaction is performed by bubbling an oxygen-containing gas while heating to a temperature range of 70 to 100 ° C., and the particle shape is basically a hexahedron. As a result, magnetic iron oxide particles for toner composed of magnetite particles in which each ridge line 1a of the hexahedron is curved are obtained.

To the toner powder (magnetic toner) obtained above, 1.0 part by mass of titanium oxide (EC-100, manufactured by Titanium Industry Co., Ltd.) and 1.0 part by mass of silica (RA-200H, manufactured by Nippon Aerosil Co., Ltd.) The toner was adhered to the surface of the magnetic toner powder by a Henschel mixer (this toner is used as 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 9 were obtained. Table 1 shows the details. A two-component developer was obtained by mixing 10 parts by mass of the magnetic toner thus obtained with 100 parts by mass of a magnetic carrier (50 μm, manufactured by Powdertech) using a Nauta mixer.

  Using this two-component developer, a modified KM-1650, a Kyocera Mita digital copier that has been modified to a two-component development system in advance, the carrier spent, the magnetic brush streaks of the photoreceptor, the toner scattering state, the image characteristics, The developer charging characteristics were evaluated. In addition, the evaluation method of each characteristic is shown below, and the evaluation results are shown in Table 2. In addition, the code | symbol of the column of the particle shape of the magnetic powder in Table 1 is as follows.

  Six-circle: Cubic shape with vertices and ridges curved.

  Hexagonal shape: a cubic body and the vertices and ridges are not curved. Normal cube.

  6-plane: Cubic and chamfered with a small plane having apexes and ridgelines (see FIG. 7 of JP-A-11-153882).

  Octagon: An octahedron shape whose vertices and ridge lines are not curved. Normal octahedron (FIG. 1 (c)).

  Octahedral: An octahedron that is chamfered with a small plane having apexes and ridges (see FIG. 6 of Patent Document 3).

  Sphere: Spherical.

At the initial stage, an image evaluation pattern is printed by the copying machine as an initial image, and then 150,000 sheets of ISO 4% originals are continuously passed through, and the image evaluation pattern is printed again as a post-endurance image. Measurement was performed using a Macbeth reflection densitometer (RD914), and image characteristics were evaluated by visually observing fog. The image density was 1.30 or higher. The following criteria were used for fog evaluation.

○: No fogging is observed. Δ: Slight fogging is observed. X: Slight fogging is observed. The state of toner scattering from the developing unit is visually confirmed, and the following criteria are 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 toner scattered from the page printer exhaust fan The toner is attached to the paper transport path, and the image is soiled. The confirmation of the spent state by the toner to the carrier was confirmed for the developer after 150,000 sheets were continuously passed. . Specifically, the developer is placed on a 635 mesh sieve, suctioned from below to remove only the toner, the carrier remaining on the sieve is immersed in a THF solution, and the supernatant is measured by GPC and detected. The amount of toner adhering to the carrier was evaluated from the peak area. When the spent toner weight [mg] with respect to 1.0 g of the carrier reaches 0.50 mg / g or more, the image density and fogging are affected. Therefore, less than 0.50 mg / g was determined as OK.

  The state of the streak by the magnetic brush on the photosensitive drum was confirmed visually, and the following criteria were used for evaluation.

○: no streaks or scratches △: minute streaks can be confirmed on the photoreceptor, but there is no effect on the image ×: streaks can be clearly confirmed on the photoreceptor, and also can be confirmed as unevenness in the image

As can be seen from Table 2, in Examples 1 to 3 in which the magnetic powder is hexahedral and the apexes and ridges are curved, the saturation magnetization is in the range of 5.0 to 13.8 Am ² / kg. In addition to showing good image characteristics due to the effect of the magnetic powder, there were no problems with spent to the carrier, magnetic brush streaks on the photoreceptor, and toner scattering. This good characteristic is maintained even after 150,000 sheet printing durability evaluation, and it can be seen that the toner has a long life.
Saturation magnetization 8.4Am 2 / ^kg at a octahedral Comparative Example using a magnetic powder 1 and the saturation magnetization is 8.2Am 2 / In ^kg there is usually the vertexes and edges at cubical not a curved surface Comparative Example 3 which is a cube (FIG. 1 (b) hexagonal), Comparative Example 2 which uses chamfered octahedral magnetic powder whose saturation magnetization is 8.1 Am ² / kg, and whose saturation magnetization is 7. In the comparative example 4 of the vertical surface where the apex and the ridgeline are chamfered with a small plane although it is 7 Am ² / kg, since the magnetic powder having a shape with a sharp apex or ridgeline is used, it is durable. Later, magnetic brush streaks occurred on the photoreceptor.

Moreover, although the saturation magnetization of the magnetic powder was 7.9 Am ² / kg, in the comparative example 5 having a spherical shape (FIG. 1 (a)), spent was generated, and fogging due to it was observed after durability. Further, in Comparative Example 6 in which the magnetic powder is a hexahedron and the apex and ridge are curved, as in Examples 1 to 3, but the saturation magnetization is as small as 2.6 Am ² / kg, the toner and carrier The magnetic attraction force generated during the process prevents the problem of toner scattering or toner dropping and suppresses the generation of fog, so that the effect originally obtained by adding magnetic powder cannot be obtained, and slight fog occurs. It was seen.

Then, in Comparative Example 7 in which the magnetic powder is a hexahedron and the apex and ridge lines are curved like the first to third examples, and the saturation magnetization is as large as 16.5 Am ² / kg, the saturation magnetization is conversely Since the toner was too high, the magnetic binding force of the toner with the carrier was too strong, streaks were generated on the photosensitive member by the magnetic brush, and spent on the carrier was also generated for the same reason.

From these results, the minimum value of the saturation magnetization of the toner is 3.2 Am at a magnetic field of 79.6 kA / m when the magnetic powder has a hexahedral shape and the apex and ridge are curved. ² / kg, greater than the maximum value it can be seen that it is preferable to 4.0～15.0Am ² / kg in the range of less than 16.8Am ² / kg.

  As described above, according to the present invention, the magnetic powder contained in the toner for two-component developer is based on a polyhedron, and the magnetic powder having a particle shape in which each vertex and ridge line of the polyhedron are curved. As a two-component toner, it has a charging characteristic that does not cause a quick rise in charge amount or charge-up (overcharge) while maintaining an appropriate charge amount, and as a result, good image characteristics (image density, fog) can be obtained over a long period of time. In addition, it is possible to obtain a toner that does not generate toner scattering, spent on the carrier, magnetic brush streaks on the photosensitive drum, which is a problem peculiar to the two-component developer, while maintaining good image characteristics, Even in a system with a long service life, various problems inherent to the two-component development method can be avoided and a highly durable magnetic toner for two-component developer and an image forming method can be obtained. .

It is a figure which shows the example of the shape of the magnetic powder contained in a toner, The figure (a) is spherical, the figure (b) is a hexahedron, The figure (c) shows the shape of an octahedron. It is a schematic diagram which shows an example of the magnetic powder used with the magnetic toner of this invention. 1 is a view showing an outline of a structure of an image forming apparatus including a magnetic brush developing device of the present invention.

Explanation of symbols

1 Hexahedron
2 Magnetic powder 2a contained in the toner of the present invention 2a edge 2b vertex 2c linear portion

Claims (5)

In a magnetic toner for a two-component developer comprising a magnetic toner containing magnetic powder in a binder resin and a carrier,
The magnetic powder particle shape is based on a hexahedron that is a convex polyhedron surrounded by six squares, each vertex of the hexahedron is curved and has a portion that can be regarded as a straight line on the outer periphery of the projected image, A magnetic toner for a two-component developer, wherein the toner has a saturation magnetization of 4.0 to 15.0 Am ² / kg at a measurement magnetic field of 79.6 kA / m.   2. The magnetic toner for two-component developer according to claim 1, wherein the magnetic powder has an average particle size of 0.01 to 0.50 [mu] m. At least the hexahedron that is a convex polyhedron surrounded by six quadrangles, and the magnetic powder contained in the binder resin is basically a hexahedron, and each vertex and ridge of the hexahedron are curved and the outer periphery of the projected image And a two-component developer comprising a magnetic toner and a carrier whose saturation magnetization at a measurement magnetic field of 79.6 kA / m is 4.0 to 15.0 Am ² / kg. ,
An image forming method comprising: causing a toner carrying member on which at least the magnetic toner into which charge has been injected is carried to face a latent image carrying member, and developing an electrostatic charge image on the latent image carrying member with the magnetic toner. . A two-component developer composed of a carrier and the magnetic toner is formed in a brush shape (hereinafter referred to as a magnetic brush) using a magnetic field in a developing region where the toner carrier and the latent image carrier face each other. In an image forming method of developing a latent image on a latent image carrier into a toner image while rubbing a brush on the surface of the latent image carrier,
The magnetic toner is magnetic toner particles containing at least a magnetic powder in a binder resin, and the magnetic powder has an average particle diameter of 0.01 to 0.50 μm and a particle shape of six squares. An image forming method characterized by comprising a hexahedron that is an enclosed convex polyhedron, and each vertex and ridge line of the hexahedron are curved and have a portion that can be regarded as a straight line at the outer periphery of the projected image.   5. The image forming method according to claim 3, wherein an average particle diameter of the magnetic powder is 0.01 to 0.50 μm.