JP2007101745A - Magnetic monocomponent toner, and developing unit and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic monocomponent toner for electrostatic latent image development which is free of burying of an external additive in the toner surface even if the toner undergoes stress with age and thermal stress over a prolonged period of time, gives stable images free of voids because of excellent charge stability of the toner, prevents a filming phenomenon on a photoreceptor drum and dielectric breakdown due to leakage to the photoreceptor drum, and can ensure long-term stability of thin toner layer formation on a developing sleeve, and a developing unit and an image forming apparatus using the toner. <P>SOLUTION: The magnetic monocomponent toner contains a magnetic powder in at least a binder resin and has an externally added magnetic powder having a particle shape based on a polyhedron each vertex and edge of which have a curved surface shape, having a portion considered to be a straight line at the periphery of its projected image, and having a volume resistivity in a range of 10<SP>2</SP>-10<SP>9</SP>Ω cm. The ten-point average roughness Rz of a surface of a developing sleeve which has a built-in stationary magnet, holds the magnetic monocomponent toner on the surface and rotates is set to 2.0 to <6.0 μm, and an elastic blade is used as a cleaning means for a latent image carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, a magnetic powder is contained in a binder resin used in an image forming apparatus such as a laser printer utilizing an electrophotographic method, an electrostatic copying machine, a plain paper facsimile machine, and a composite machine thereof. The present invention relates to a magnetic one-component toner, a developing unit and an image forming apparatus that use the magnetic one-component toner to visualize a latent image on a latent image carrier into a toner 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 a latent image carrier (photosensitive body) is charged by a charging means. Uniformly charged, then exposed by an exposure means such as a semiconductor laser, a light emitting diode, etc. to form a latent image, and then the latent image is developed or reverse developed by a developing means to be visualized as a toner image; and This toner image is directly transferred to the surface of the printing material such as paper by the transfer means, or transferred to the surface of the intermediate transfer body and then re-transferred to the surface of the printing material such as paper, and then fixed by the fixing means. Thus, a series of image forming steps is completed.

  In general, as a toner used in these image forming processes, a thermoplastic resin as a binder (binder resin) is mixed with a dye, a pigment as a charge control agent, a pigment, a wax as a release agent, a magnetic material, and the like. Then, kneading, pulverization, and classification are performed to obtain toner particles having an average particle diameter of 5 to 15 μm. More generally, inorganic fine powders such as silica and titanium oxide and fine inorganic metal powders are externally added for the purpose of imparting fluidity to the toner, controlling charging of the toner, and improving cleaning properties.

  Development methods for developing a latent image on a latent image carrier into a toner image are roughly classified into a dry type and a wet type. Currently, a dry type development method is widely used. The dry development system is classified into a two-component development system using a carrier such as toner and iron powder and a one-component development system using no carrier, and further considering the type of toner used, a toner composed of a binder resin. Development method using magnetic toner with magnetic powder added to particles (magnetic one-component development method, magnetic two-component development method) and development method using non-magnetic toner without adding magnetic powder (non-magnetic one-component development method, non-magnetic development method) Magnetic two-component development system).

  Among them, the method using a two-component developer can provide a high-quality image relatively stably in the initial stage. However, when used over a long period of time, the spent phenomenon in which the toner component adheres and precipitates on the surface of the carrier ( Phenomenon), deterioration of the charge imparting ability of the carrier, resulting in a problem that a good quality image cannot be obtained over a long period of time, and it is difficult to keep the mixing ratio of the toner and the carrier constant. It has a drawback of lacking.

  On the other hand, in the one-component developing method using a one-component developer composed only of toner, the problem of lack of long-term durability in the two-component developer can be solved because no carrier is used. Can be made very small and simple. Among the one-component development systems, a magnetic one-component development system that employs a toner containing magnetic powder is generally well known and used.

  As a developing method using such a one-component magnetic toner, a developing method using a conductive magnetic toner disclosed in Patent Document 1 is known. In this method, a conductive magnetic toner is carried on a cylindrical conductive developer carrying member having magnetism therein, and developed by bringing the toner into contact with an electrostatic latent image. At this time, in the developing unit, a conductive path is formed by toner particles between the surface of the latent image carrier and the surface of the developing sleeve, and charges are guided from the sleeve to the toner particles through this conductive path. The toner particles adhere to the image portion and are developed by the Coulomb force between the portion and the portion.

  In this method, since the toner is conductive, there is a problem that it is difficult to electrostatically transfer the toner image on the latent image carrier to a printing medium (for example, plain paper) using an electric field, and each process. In other words, there is a problem that it is difficult to obtain high image quality over a long period of time due to a defect phenomenon derived from the conductive toner, and a problem of electrical leakage destruction to the latent image carrier.

  A method using an insulating toner is proposed in Patent Document 2. This method is called a magnetic one-component jumping method. A developer carrier having a developing sleeve (including a magnet roller) is provided opposite to the latent image carrier, and magnetic toner is held on the developing sleeve to hold a magnetic blade. The toner is charged to form a thin layer by passing the gap between the electrostatic latent image and the electrostatic latent image formed on the latent image carrier is developed with the charged toner.

  In this magnetic one-component jumping development system, since an insulating magnetic toner is used, a toner image is printed on the surface of a printed material such as paper by using an electric field, which was impossible when a conductive toner was used. In addition, the latent image carrier can be prevented from being destroyed by electrical leakage.

  Insulating magnetic toner is easy to be charged, can sufficiently rub against the developing sleeve while holding the magnetic toner by magnetic force, and can develop the latent image in a non-contact state with the latent image, so that the non-printing of the formed image There is also an advantage that an image having excellent image quality can be formed by preventing the occurrence of background fogging in which toner adheres to the portion and the margin.

  In recent years, since it is necessary to adapt to a strong demand for downsizing and energy saving of a developing machine, a toner having a fixing property at a lower energy has been demanded, and development of a toner using a resin having a low softening point, Toner using low melting point wax is being developed.

  In general, when a heating roll is used in a fixing process in which a non-printed material such as paper having a toner image transferred thereon is heated and fixed, the toner containing the low melting point wax is attached to the heating roll. This can reduce the occurrence of the offset phenomenon that smudges the copied image of the toner, and when the fixed toner image is rubbed with white paper, the toner image is partially broken and transferred to white paper (smudge). Advantages of improving fixability by improving the phenomenon that the fixed image is destroyed by a finger (finger mark) when the paper is peeled off after the paper has passed through the heating roll. There is.

  However, a toner containing such a low melting point wax has good release resistance because of its excellent release property from a heating roll, but it is bonded due to poor compatibility between the low melting point wax and the binder resin. Large domains of low melting point wax will be formed in the resin, and therefore the toner will be pulverized at the domain part during toner preparation, and the low melting point wax will be exposed on the surface, causing troubles in photoconductor drum filming. There's a problem. Further, if the toner is made to have a small particle size in order to realize high image quality, the amount of wax on the toner surface further increases, which becomes a more serious problem.

  In order to improve the above problems, for example, Patent Document 3 proposes a method for preventing toner aggregation due to thermal stress or aging stress by defining the rate of increase in the degree of aggregation due to heat storage. This method cannot solve the problem of photoconductor drum filming caused by wax.

  Further, Patent Document 4 in which magnetic powder is externally added has been proposed as a solution to the problem of photoconductor drum filming due to wax. However, when this toner is subjected to thermal stress or stress over time, the external additive becomes a toner particle. Since the fluidity is lowered due to being buried in the image, there is a problem that the resulting image has a void in the image.

  As the latent image carrier used in the magnetic one-component jumping development system, various organic and inorganic electrophotographic photoreceptors can be used as in the case of other development systems. In consideration, an a-Si photosensitive member in which an amorphous silicon (hereinafter abbreviated as a-Si) photosensitive layer is formed on a conductive substrate is preferable. This a-Si photosensitive member has a high durability of about 10 times or more in terms of the number of images formed, for example, compared with an organic photosensitive member having an organic photosensitive layer containing a pigment, a charge transport agent, or the like in a binder resin. This is because the speed at which the thickness of the photosensitive layer is reduced by rubbing against the substrate to be printed or the elastic blade described below is about 1/100 or less that of the organic photosensitive layer. This is because it is difficult to do.

  However, the greatest disadvantage of the a-Si photosensitive member is its low productivity. That is, the a-Si photosensitive member is manufactured by forming an a-Si photosensitive layer on the surface of a conductive substrate by a vapor phase growth method such as a CVD method. Compared to an organic photosensitive layer formed by simply applying a coating liquid containing a coating on a conductive substrate and drying it, it takes much longer to form a photosensitive layer having a predetermined thickness, and vapor phase growth is performed. Since the method is batch-type and cannot be continuously produced, productivity is inevitably lowered.

  Therefore, by utilizing the fact that the a-Si photosensitive layer is less likely to wear than the organic photosensitive layer as described above, the thickness of the a-Si photosensitive layer can be made smaller than before and the productivity of the a-Si photosensitive member can be improved. It is becoming common. That is, an a-Si photosensitive member having a thickness of 30 μm or less and a thin film type a-Si photosensitive member, which has been about 30 to 60 μm so far, is beginning to spread.

  Needless to say, the main merit of such a thin film type a-Si photoreceptor is that it is more productive than the conventional one, but further, the resolution of the formed image is improved when the film thickness is reduced. There are also benefits.

  On the other hand, after the toner image is transferred to the surface of the printed material such as paper, the toner remaining on the surface of the a-Si photosensitive member is removed by a cleaning unit. In order to reduce the size of the forming apparatus and simplify the mechanism, an elastic blade pressed against the surface of the a-Si photosensitive member is preferable.

  As an example of this, for example, Patent Document 5 uses an organic photoreceptor (OPC) as a photoreceptor, but uses a magnetic toner as a developer and a cleaning blade formed of urethane rubber. There has been proposed a method that can achieve good cleaning with a cleaning mechanism to form a clear image and does not reduce fogging, image unevenness, or image density.

  However, in the method disclosed in Patent Document 5, since the photoconductor is an organic photoconductor (OPC) drum as described above, the surface of the soft OPC drum is easily damaged regardless of how much an external additive is used. For this reason, the toner is embedded in the surface of the damaged photosensitive member to cause filming, or a problem that causes a fatal defect on the image such as the toner slipping through the cleaning blade occurs. This can be said from the fact that only 150,000 durability evaluations have been achieved.

  Patent Document 6 introduces an example in which a latent image carrier made of stacked a-Si and a magnetic one-component toner are used. According to this method, it is possible to improve the cleaning property, and it is possible to obtain an image forming method capable of stably forming a good image many times without an image defect caused by a cleaning defect. However, in the method introduced in Patent Document 6, organic fine particles are attached (externally added) to the magnetic toner so as to act as a spacer. However, the organic fine particles have a very high charging ability and are immediately charged by frictional charging. Causes a charge-up.

  As a result, in the development process, the amount of toner in an appropriate charged area is reduced, causing image defects such as a decrease in image density, fogging, and image unevenness. Therefore, there is a possibility that a stable and beautiful image cannot be supplied over a long period of time. In addition, although the material of the cleaning blade in the essential photoreceptor cleaning part is not clearly described, when an elastic blade of a simple (general) mechanism is used, while the toner comes into contact and frictionally charges, Charges that do not escape are accumulated in the toner, causing abnormal discharge (single-point discharge) to the photoreceptor, destroying the surface of the photoreceptor drum (charge generation layer, charge transport layer, etc.), and irreparable defects ( The possibility of causing a problem causing only a defective image) is extremely high.

  Further, Patent Document 7 proposes a toner containing free magnetic powder in order to prevent dielectric breakdown of the photoconductor. The free magnetic powder prevents leakage, but the released magnetic powder is developed. There is concern about adhesion to the sleeve, and there is also concern about adhesion to the photoreceptor. It is well known that when such a deposit occurs even in a very small amount, the deposit grows as a nucleus and causes a fatal image defect.

  In Patent Document 8, it is stated that the dielectric breakdown of the photoconductor can be suppressed by setting the film thickness of the photoconductor. Since no measures are taken with the toner that should have become, if a toner having different characteristics is used in the future, the dielectric breakdown of the photosensitive member is concerned again.

  In addition, the conventional inorganic metal fine powder is extremely hydrophilic due to the hydroxyl groups present on the surface. As a result, when added to the toner, the fluidity and charge rise characteristics of the toner change due to the influence of humidity, and printing durability. Adverse effects such as image quality and image density reduction.

  In order to prevent the influence of such environmental conditions as humidity, the surface of these inorganic metal fine powders is treated with a hydrophobizing agent or a polar group is introduced. For example, Patent Document 9 proposes a technique using a metal oxide treated with aminosilane as a polar group. Patent Document 10 proposes using a titanium compound treated with a silane coupling agent.

  Patent Document 11 discloses electrostatic latent image development in which abrasive fine particles such as alumina and zirconia are fixed to the surface of toner base particles, and the ratio between the particle size of the toner base particles and the particle size of the abrasive fine particles is controlled. Agents have been proposed. According to this method, an excellent polishing effect can be obtained on the surface of the photosensitive member, it is not necessary to incorporate a large system such as a cleaning brush, the apparatus can be miniaturized, and it is effective for image flow, image density, fog, etc. There is.

  However, in the above prior art, since the volume resistivity of inorganic metal oxides is high as a serious drawback, in the case of the magnetic one-component jumping development method, it is difficult to form a toner thin layer on the developing sleeve. In a usage environment where the charge is likely to increase such as in a low humidity environment, the toner thin layer formation failure is caused, and high resolution and high image quality have not been sufficiently satisfied in the initial and long term.

  Also, as a serious drawback, titanium oxide, zinc oxide, magnesium oxide, silicon carbide, etc. are generally used as the inorganic metal oxides conventionally used as external additives, but these usually have no magnetic force. In addition, when the developer is stirred for a long time in the developing device, it peels off from the toner particles, and the original function is not exhibited. That is, there was a problem in durability.

  In addition, attempts have been made to improve the flowability by changing the charge amount and specific resistance of the toner or increasing the particle size of the toner to improve the cleaning property, but generally satisfactory results have been obtained. Absent.

  Further, Patent Document 12 proposes to add octahedral magnetic powder as an external additive. As the magnetic powder, the spherical magnetic powder form shown in FIG. 3 (a) or the hexahedron (cube, cuboid) which is a convex polyhedron surrounded by the six squares shown in FIG. 3 (b). And polyhedral magnetic powders such as octahedral ones, which are convex polyhedrons surrounded by eight triangles shown in FIG. 3D, are generally used.

  In particular, in the case of polyhedrons having edges, such as octahedrons and hexahedrons (FIGS. 3B and 3D), the surface of the photoreceptor can be effectively polished by the edges of the magnetic powder externally added to the toner surface. Can be maintained without contamination. Therefore, although effective in solving the filming failure, charges are likely to be released from the sharp apex of the magnetic powder, and charge leakage is likely to occur.

  Therefore, the magnetic toner using the polyhedral magnetic powder has a problem that the charge amount is difficult to rise quickly and the charge amount itself is low, and as a result, image defects such as a decrease in image density and occurrence of background fog are likely to occur. is there. 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. Further, since the edge of the magnetic powder is too strong, scratches and the like are generated on the surface of the photoreceptor.

  On the other hand, in the magnetic toner using the spherical magnetic powder shown in FIG. 3A, the magnetic powder does not have a pointed apex, and it is difficult for the charge to be discharged, so that the charge leakage hardly occurs. However, toner using spherical magnetic powder as an external additive, on the other hand, tends to accumulate electric charge, so that, for example, when the toner is repeatedly rubbed in the gap between the developer holder and the magnetic blade, There is a problem that so-called charge-up that is overcharged more than the charge amount is likely to occur, and that charge-up is liable to cause image defects typified by a decrease in image density. In addition, poor toner thin layer formation on the developing sleeve, so-called layer unevenness, also occurs. Further, black spots are also generated due to a leak phenomenon to the photosensitive drum. In addition, the spherical magnetic powder has an advantage that scratches and the like are not generated on the surface of the photoconductor, but the effect cannot be exhibited as prevention of photoconductor drum filming due to insufficient polishing ability of the surface of the photoconductor.

U.S. Pat. No. 3,909,258 JP 55-18656 A, etc. JP-A-6-138893 JP-A-9-73186 Japanese Patent No. 2649363 Japanese Patent No. 2713716 JP 2003-149857 A JP 2002-287391 A JP-A-52-135739 Japanese Patent Laid-Open No. 10-3177 JP-A-5-181306 JP-A-2003-66647

  As described above, in the magnetic one-component jumping development method, the toner image can be transferred to the surface of the printing material such as paper by using an electric field, and can be sufficiently rubbed while being held by the magnetic force on the developing sleeve. It is easy to charge and can be developed in a non-contact state with the latent image, thereby preventing the occurrence of background fogging in which toner adheres to the non-printed and blank areas of the formed image and can form an image with excellent image quality. Have advantages.

  Further, by combining a thin film a-Si photosensitive member with excellent durability and improved resolution of the formed image and an elastic blade, there are few moving parts, and the image forming apparatus can be made compact by simplifying the mechanism. However, when an external additive is used to prevent photoconductor drum filming failure, the surface of the photoconductor drum (charge generation layer, charge transfer layer, etc.) is destroyed due to charge-up of the external additive, and thus an unrecoverable defect ( This can cause problems that cause only defective images to be obtained.

  In addition, when an inorganic metal oxide having a high volume resistivity is used as an external additive, it is difficult to form a toner thin layer on the developing sleeve in the case of the magnetic one-component jumping development method, particularly in a low temperature and low humidity environment. In the usage environment where the charge is likely to rise, there is a problem that the toner thin layer formation failure is caused and the high resolution and high image quality cannot be sufficiently satisfied in the initial and long term.

  In addition, inorganic metal oxides used as external additives generally do not have magnetic force, so if they are stirred for a long time in the developing device, they will peel off from the toner particles and will not be able to perform their original functions and will be durable. There is also a problem with sex.

  In addition, when magnetic powder is externally added to prevent photoconductor drum filming failure, the external additive is buried in the toner particles due to thermal stress or stress over time, and the image is lost in the image obtained by reducing fluidity. Furthermore, as an external additive, a hexahedron (cube, rectangular parallelepiped) that is a convex polyhedron surrounded by six squares, or a convex polyhedron surrounded by eight triangles is used as an external additive. When polyhedral magnetic powder such as octahedron is used, the charge amount is difficult to rise quickly and the charge amount itself becomes low. As a result, image defects such as a decrease in image density and occurrence of background fog are likely to occur, and magnetic properties are also reduced. Since the edge of the powder is too strong, there is a problem that the surface of the photoreceptor is damaged.

  Therefore, in the present invention, there is no buried external additive on the toner surface even when subjected to aging stress or thermal stress over a long period of time, and a stable image with excellent toner charging stability and no image void is obtained. Furthermore, electrostatic latent image development that can prevent long-term stability of the toner thin layer formation on the developing sleeve while preventing the photosensitive drum filming phenomenon, dielectric breakdown due to leakage to the photosensitive drum, etc. It is an object to provide a magnetic one-component toner for use, a developing unit using the toner, and an image forming apparatus.

  In order to solve the above-mentioned problems, the inventors have intensively studied. As a result, magnetic powder is used as an external additive for a magnetic one-component toner for developing an electrostatic latent image corresponding to a highly durable system. And a magnetic powder having a particle shape in which each vertex and ridge of the polyhedron are curved.

That is, the toner according to the present invention is
The latent image formed on the latent image carrier is developed by a magnetic jumping method so that the latent image is held on the surface of the developing sleeve facing the latent image carrier so that it does not come into contact with the latent image carrier. A magnetic one-component toner containing magnetic powder in at least a binder resin and externally adding magnetic powder,
Each of the externally added magnetic powders has a curved surface and a portion that can be regarded as a straight line on the outer periphery of the projected image, and the magnetic powder has a volume resistivity of 10 ² to 10 ⁹ Ω · cm. The magnetic mono-component toner is characterized by having a polyhedral shape.

  The particle shape of the magnetic powder for external addition of the polyhedron shape is an octahedron that is a convex polyhedron surrounded by eight triangles, each vertex and ridge line are curved, and a straight line is formed on the outer periphery of the projected image. It has a portion that can be considered.

  The external additive magnetic powder preferably has an average particle size of 0.01 to 0.50 μm, and the additive amount of the external additive magnetic powder is preferably 0.1 to 5.0% by mass. .

In addition, a developing unit using this magnetic one-component toner is
At least the binder resin contains magnetic powder, each vertex and ridge are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image, and the volume resistivity is 10 ² to 10 ⁹ Ω · cm. 10-point average of the surface facing the latent image carrier that forms a latent image by carrying a magnetic mono-component toner with externally added polyhedral magnetic powder in the range and incorporating a magnet roller inside A developing sleeve having a roughness Rz of 2.0 μm or more and less than 6.0 μm is provided, and a latent image formed on the latent image carrier by an electrophotographic method is developed by a magnetic jumping method.

Furthermore, the image forming apparatus
A latent image carrier, a toner carrier having a fixed magnet and a developing sleeve that faces the surface of the latent image carrier so as not to contact the latent image carrier, holds the magnetic one-component toner, and rotates. Means for causing the magnetic one-component toner held on the developing sleeve to fly to a latent image formed on the surface of the latent image carrier and developing it to form a toner image; An image forming apparatus comprising a cleaning means using an elastic blade for cleaning toner remaining after transferring an image to a recording medium,
The magnetic one-component toner contains at least a magnetic powder in a binder resin, and has a volume that has a portion that can be regarded as a straight line at the outer peripheral portion of the projected image, in which each particle shape is a polyhedron and each vertex and ridge are curved. Magnetic powder having a specific resistance in the range of 10 ² to 10 ⁹ Ω · cm is externally added, and the developing sleeve of the toner carrier has a ten-point average roughness Rz of 2.0 μm or more to less than 6.0 μm. It is characterized by being.

  In the preferred embodiment of the present invention, the latent image carrier is composed of an amorphous silicon photoconductor having a thickness of 10 to 30 μm.

  By configuring the magnetic one-component toner, the developing unit using the toner, and the image forming apparatus in this way, even if the toner accumulated on the photosensitive member cleaning blade is frictionally charged with the blade tip, the charge amount is kept low. The a-Si photosensitive member can be discharged before reaching a potential causing dielectric breakdown to prevent the occurrence of abnormal images due to the dielectric breakdown of the photosensitive member. Even if there are environmental fluctuations such as the environment and a short warm-up time, it is possible to ensure long-term stability of the toner thin layer formation on the developing sleeve.

  In addition, since the external additive is made of magnetic powder, it is easy to adhere to the toner due to its magnetic force. Inorganics that do not have a magnetic force, such as titanium oxide, zinc oxide, magnesium oxide, silicon carbide, etc., which have been conventionally used as external additives When the metal oxide is stirred for a long time in the developing device, it has been peeled off from the toner particles and has not performed its original function. However, the magnetic powder adheres firmly to the toner particles. Even if the developer is stirred in the developing device for a time, it does not fall off from the toner particles, and the initial performance can be maintained over a long period of time.

  In addition, the magnetic powder has a curved surface at each vertex and ridge line, but has a portion that can be regarded as a straight line on the outer periphery of the projected image, so that the drum filming phenomenon can be prevented by polishing the photoconductor at that portion, Even when subjected to aging stress or thermal stress over a long period of time, there is no buried external additive on the toner surface, and it is possible to obtain a stable image that is excellent in toner charging stability and does not cause image dropout. Thus, it is possible to provide a magnetic one-component toner for developing an electrostatic latent image, which can prevent dielectric breakdown due to leakage of the toner and ensure long-term stability of toner thin layer formation on the developing sleeve.

The binder resin, magnetic material, dye, pigment, charge adjusting agent and the like in the present invention are not particularly limited, and can be applied to all magnetic one-component toners for developing electrostatic latent images. Further, the volume resistivity of the magnetic powder for external addition is not limited to the above 10 ² to 10 ⁹ Ω · cm, preferably 10 ³ to 10 ⁸ Ω · cm, and more preferably 10 ⁴ to 10 ⁷ Ω · cm. The average particle size is preferably not only 0.01 to 0.50 μm but also 0.05 to 0.35 μm.

  As described above, the magnetic one-component toner according to the present invention, the developing unit using the same, and the image forming apparatus do not bury the external additive on the toner surface even when subjected to aging stress or thermal stress over a long period of time, and stabilize the charging of the toner. In addition, it is possible to obtain a stable image that does not cause image dropout, and to prevent photoconductor drum filming and dielectric breakdown due to leakage to the photoconductor drum. It is possible to ensure long-term stability of layer formation.

  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 diagram showing an outline of the structure of an image forming apparatus for carrying out the magnetic toner of the present invention and an image forming method using the same, and FIG. 2 is a photosensitive drum (electrostatic latent image carrier) 11 used in the present invention. FIG. 3 is a diagram showing the shape of the magnetic powder externally added to the toner, wherein (a) is spherical, (b) is a hexahedron, (d) is an octahedron, and (e) is a round octahedron. FIG. 4 is an electron micrograph showing an example of the magnetic powder used in the magnetic toner of the present invention, FIG. 5 is a graph showing the relationship between the film thickness of the amorphous silicon photoreceptor and the needle pressure resistance causing dielectric breakdown, and FIGS. 22 is a table summarizing the results of tests conducted at normal temperature, normal humidity environment, high temperature, high humidity environment, low temperature, and low humidity environment using Examples and Comparative Examples of the magnetic single component toner according to the present invention.

FIG. 1 is a diagram schematically showing the structure of an image forming apparatus for carrying out the magnetic toner of the present invention and an image forming method using the magnetic toner. A photosensitive drum (latent image carrier) 11 composed of amorphous silicon (hereinafter abbreviated as a-Si) is composed of a φ30 drum using positively charged a-Si as a photosensitive member. charger 12 with the exposure unit 13, an internal stationary magnet facing holds interval so as not to contact with the latent image bearing member has a toner carrier 14 ₁ which holds and rotates the toner to the surface A developing device 14, a transfer roll 15 as a transfer means, a cleaning blade (elastic body, rubber, etc.) 16 as a cleaning means, and a charge removal lamp 17 as a charge removal device are arranged along the rotation direction of the photosensitive drum 11. A transfer material (not shown) such as paper or an OHP film is passed between the drum 11 and the transfer roll 15, and a fixing device (not shown) is placed on the downstream transfer material discharge path. It is provided.

(Charger configuration)
The charger 12 used in the image forming apparatus of the present invention is, for example, a scorotron charger 12, which includes a shield case, a corona wire, and a grid. The charging width is 12.0 mm in the circumferential direction and 242 mm in the drum axis direction. Thus, the distance between the wire and the grid is preferably set to 5.8 mm. The distance between the grid and the a-Si photosensitive member is preferably 0.4 to 0.8 mm. If the distance is less than 0.4, there is a possibility of spark discharge, and if it is 0.8 mm or more, the charging ability is high. It will be lower.

(Configuration of a-Si Photosensitive Drum)
As the a-Si photosensitive member constituting the photosensitive drum 11, for example, as shown in FIG. 2, an a-Si photosensitive layer 19 is formed on the surface of a conductive substrate 21 formed in a predetermined shape such as a drum shape. A thin film type a-Si photosensitive member in which the thickness of the photosensitive layer 19 is 10 to 30 μm is particularly suitable.

  The a-Si-based photosensitive layer 19 includes a carrier blocking layer 20, in addition to a single layer or two or more photosensitive layers 19 that actually function as the photosensitive layer 19 on a roll of a conductive substrate 21 such as aluminum. It may have a surface protective layer 18 or the like, and in the case of these multi-layered photosensitive layers, the total film thickness is preferably in the range of 10 to 30 μm. Such a thin film type a-Si photosensitive member is advantageous in that it is excellent in productivity and can form a high-resolution image as described above.

(Photoreceptor film thickness)
In the present embodiment, the film thickness of the a-Si photoconductor means the film thickness from the surface of the substrate 21 to the surface of the photoconductor opposite to the substrate 21 in the a-Si photoconductor. , The total of the surface protective layer 18. In the a-Si photosensitive member of the present embodiment, the film thickness of the photosensitive layer 19 on the conductive substrate 21 is in the range of 10 to 30 μm because the charging ability as the photosensitive member is less than 10 μm. This is because it becomes difficult to obtain a predetermined surface potential, and the laser beam is irregularly reflected on the surface of the conductive substrate 21 to cause a problem that interference fringes are generated in the half pattern.

  On the other hand, when the film thickness of the photosensitive member is 30 μm or more, the moving speed of the heat carrier is increased, so that the dark attenuation characteristic is deteriorated. It will cause a drop. It is well known that not only the a-Si photoreceptor but also the OPC photoreceptor, the thinner the photoreceptor film, the higher the resolution. In terms of cost, the longer the film thickness, the longer the film formation time. The longer the film formation time, the higher the probability of adhesion of foreign substances and the like, and the worse the yield. Therefore, the thinner the film thickness of the photoconductor, the lower the cost and the more stable the quality.

  Therefore, the total film thickness of the photoreceptor is preferably used in the range of 10 to 30 μm or less in view of charging ability, withstand voltage, dark decay characteristics, manufacturing cost, and quality. More preferably, the thickness of the surface protective layer is preferably 20000 mm or less, more preferably 5000 to 15000 mm.

  This is because, when the thickness of the surface protective layer is less than 5000 mm, the pressure resistance characteristic is reduced with respect to the negative current flowing from the transfer roll, and as a result, the SiC layer is deteriorated at an early stage of 15000 sheets or less. This is because if the thickness of the surface protective layer exceeds 20000 mm, the film formation time becomes long and the cost becomes disadvantageous. Therefore, it is more preferable that the surface protective layer has a value in the range of 5000 to 15000 mm in terms of the balance between charging ability, wear resistance, environmental resistance, and film formation time.

  On the other hand, the occurrence of leak black spots on the a-Si photosensitive member in question largely depends on the needle pressure resistance (V) of the a-Si photosensitive member. That is, as shown in FIG. 5, the voltage required for dielectric breakdown increases as the film thickness increases, and the voltage required for dielectric breakdown decreases as the film thickness decreases. Therefore, when a thin film a-Si photosensitive member having a thickness of 30 μm or less is used, leakage to the photosensitive member becomes noticeable with a slight charge-up. In FIG. 5, the horizontal axis represents the film thickness of the a-Si photosensitive member, and the vertical axis represents the needle pressure resistance that causes discharge breakdown.

(Photoreceptor material)
The a-Si-based photosensitive layer 19 can be formed, for example, by a vapor phase growth method such as a glow discharge decomposition method, a sputtering method, an ECR method, or a vapor deposition method. You can also. Further, in order to adjust the characteristics of the photoreceptor, elements such as C, N, and O may be included, or a group 13 element or a group 15 element in the periodic table (long period type) may be included.

Specifically, the photosensitive layer 19 can be formed of various materials having a-Si photoconductivity such as a-SiC, a-SiO, and a-SiON in addition to a-Si. In particular, to use a-SiC Preferably, in which case the _{Si 1-x C} x of the value of x 0.3 ≦ x <1.0, more preferably set to 0.5 ≦ x ≦ 0.95 It is good. Within this range, the a-SiC layer can have a higher resistance than the a-Si layer while maintaining good carrier transport, and the photosensitivity characteristics of the photoreceptor can be improved. As group 13 elements and group 15 elements, B and P are desirable in that they are excellent in covalent bonding properties, can change semiconductor characteristics sensitively, and can provide excellent photosensitivity.

This is because such a-SiC has a high resistance of 10 < ¹² > to 10 < ¹³ > [Omega] cm, there is little flow of latent image charge in the direction of the photoreceptor surface, and the electrostatic latent image maintaining ability and moisture resistance are reduced. It is because it is also excellent.

(Characteristics to distinguish between OPC and amorphous silicon)
In general, an OPC photoreceptor has a surface resistance on the order of 10 ¹³ Ω / cm, which is extremely higher than that of an a-Si photoreceptor (on the order of 10 ⁸ Ω / cm), and is characterized by being difficult to break down. Therefore, the OPC photosensitive member is less susceptible to leak black spots.

(Photoreceptor surface potential)
The charging potential of the a-Si photoconductor during image formation is not particularly limited, but is preferably a value within the range of +200 to + 500V. When the surface potential of the photoreceptor is less than +200 V, the developing electric field is insufficient, and it is difficult to ensure the image density. On the other hand, when the voltage exceeds +500 V, there are problems that charging ability is insufficient depending on the film thickness of the photosensitive member, black spots are easily generated due to dielectric breakdown, or the amount of ozone generated is increased. In particular, when the film thickness is reduced, the charging ability of the photoreceptor tends to decrease correspondingly. Therefore, from the viewpoint of the balance between developability and the charging ability of the photoreceptor, the surface potential value is preferably set to a value within the range of +200 V to +500 V, and more preferably the surface potential is set to +200 V to +300 V.

(Developer)
Returning to FIG. 1 again, in the developing device 14 using the electrostatic latent image developing toner according to the present invention, a toner carrier comprising a developing sleeve provided facing the photosensitive member 11 and incorporating a magnet roller therein. 14 ₁ is arranged, a toner thin layer is carried on the surface of the toner carrier 14 ₁ , and a voltage supplied from an AC or DC bias power supply (not shown) as means for causing the toner to fly to the photoreceptor is applied. The electrostatic latent image formed on the photoconductor 11 is visualized as a toner image by the magnetic one-component jumping development method.

Developing sleeve surface of the toner carrying member 14 ₁ is roughened, and conveys the toner by the rotation of the toner carrying member, by passing the gap between the magnetic blade and the toner carrier 14 ₁ which is not shown, the toner carrying member 14 A toner thin layer is formed on the surface of ₁ . Developing sleeve surface of the toner carrier 14 _1, the ten-point average roughness Rz is less than or 2.0μm ~6.0μm. Here, if the ten-point average roughness Rz is less than 2.0 μm, the image density is not satisfied due to a decrease in the toner conveying force. On the other hand, if the thickness exceeds 6.0 μm, the image quality is deteriorated, and a leak from the protrusion on the sleeve surface to the photosensitive drum occurs, resulting in an image black spot and a loss of image quality. These ten-point average roughness Rz can be measured using a surface roughness measuring instrument manufactured by Kosaka Laboratory Ltd., Surfcoder SE-30D.

  As a material constituting the developing sleeve, for example, aluminum, SUS, or the like can be used. When considering high durability, it is preferable to use SUS as a sleeve material to be used, and for example, SUS303, SUS304, SUS305, SUS316, or the like can be used. Moreover, it is more preferable to use SUS305 which has weak magnetism and is easy to process.

(Transfer roll)
In order to hold the latent image on the surface of the a-Si photosensitive member 11 as a latent image carrier, the surface of the photosensitive drum 11 is uniformly charged with a charger 12 using a scorotron charger or the like as in the prior art. After that, exposure is performed by an exposure device 13 such as a semiconductor laser or a light emitting diode to remove the charge in the exposed portion. In order to transfer the toner image formed on the surface of the a-Si photoreceptor 11 onto the surface of the printing material, for example, a corona charger, a sawtooth electrode, a transfer roll, or the like is used, and the transfer roll 15 is particularly preferable. .

  The transfer roll 15 is preferably rotated with a linear velocity difference of 3 to 5% with respect to the surface of the photoconductor in a state where it is in contact with the surface of the a-Si photoconductor, and the linear velocity difference is less than 3%. In this case, there is a risk that the transferability of the toner image is deteriorated and characters are lost, and when it exceeds 5%, the slip amount with respect to the surface of the photosensitive member is increased, and the shift of the transferred image, so-called jitter may be increased. is there. As the transfer roll 15, for example, a roller made of a soft foam such as foamed EPDM is preferable. When a foam roller is used, the toner attached to the transfer roll when a paper jam or the like occurs is the foam. By entering the air bubbles, it is possible to prevent the back side of the printing material from being stained when the operation is resumed. Therefore, cleaning of the transfer roll becomes unnecessary, and the initial cost and running cost can be reduced. Further, the hardness of the transfer roll made of a soft foam is preferably 30 to 40 ° in terms of Asker C hardness. If it is softer than this range, there is a possibility that transfer failure may occur. If it is harder than the range, the nip between the photosensitive member and the photoconductor may be small, and the conveyance force of the substrate may be reduced.

(Cleaning device)
The toner remains on the surface of the photoconductor after the toner image formed on the surface of the photoconductor drum 11 composed of the a-Si photoconductor is transferred to a substrate such as paper. As the cleaning means 16 for cleaning and removing the residual toner, it is preferable to use an elastic blade pressed against the surface of the a-Si photosensitive member. As the elastic blade, various conventionally known elastic blades made of rubber, soft resin, or the like can be used. Specifically, for example, an elastic blade made of silicone rubber, fluorine rubber, urethane rubber, urethane resin or the like can be used. The elastic blade is preferably pressed at a linear pressure of 10 to 50 g / cm, considering that the magnetic toner is satisfactorily cleaned and the surface of the a-Si photoreceptor is free from pressure marks.

Briefly explaining the operation of the image forming apparatus according to the present invention, this image forming apparatus is an A4 33 ppm (linear speed 210 mm / s) printer as an example, and a positively charged a-Si photosensitive member having a φ30 as a latent image carrier. using somatic drum 11, and the a-Si photosensitive drum 11 rotates an internal stationary magnet, and the toner carrying member (developing sleeve) 14 ₁ a thin layer of the magnetic toner is formed on the surface, the toner holding the interval as thin layer and the a-Si photosensitive member on the bearing member 14 ₁ and does not contact by facing, after uniformly charging the photosensitive layer 19 of the photosensitive drum 11 by the charger 12, an exposure device In step 13, the surface of the photosensitive drum is irradiated with dot light 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 to form an electrostatic latent image.

This electrostatic latent image is toner thin layer carried on the toner carrier 14 ₁ surface as described above is, of the toner carrier 14 ₁ and is not shown is applied between the photoconductor AC or DC A toner image is formed on the surface of the photosensitive drum 11 by developing the magnetic single component jumping development method by flying to the photosensitive member 11 with a voltage from the bias power source. The toner image is transferred to a transfer material by a transfer roll 15, conveyed to a fixing device (not shown), and fixed on the surface of the transfer material by heat and pressure. On the other hand, after the toner image is transferred onto the transfer material, the toner remaining on the surface of the photosensitive drum 11 is scraped off and collected by a cleaning blade 16 constituting a cleaning device, and light emitted by a static elimination lamp 17 serving as a static elimination device. The surface charge is removed by irradiation, and the next image forming process is performed.

(Binder resin)
The toner of the present invention is obtained by dispersing various toner compounding agents such as a colorant in a binder resin, adding a magnetic powder therein, and externally adding the magnetic powder to the obtained toner. The kind of the binder resin used for the toner in the present invention is not particularly limited. For example, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyester resin, polyamide Resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether resin, N-vinyl resin, styrene-butadiene resin, and the like, and polystyrene resin and polyester resin are particularly preferable.

  More specifically, examples of the polystyrene-based resin include a styrene homopolymer and a binary or ternary copolymer of styrene and another monomer. Other monomers that can be copolymerized with styrene include, for example, p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl chloride, vinyl bromide, and fluoride. Vinyl halides such as vinyl; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, acrylic (Meth) acrylic acid esters such as n-octyl acid, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylonitrile, acrylic Other acrylic acid derivatives such as vinyl; 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- Examples thereof include N-vinyl compounds such as vinyl indole and N-vinyl pyrrolidone. These may be used alone or in combination of two or more with styrene.

  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. Among these, as the alcohol component, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Diols such as 1,5-pentanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,6-hexanediol, 1,8-octanediol Bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1, -Sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerin, diglycerin, 2-methylpropanthriol, 2-methyl-1 , 2,4-butanetriol, trimethylolethane, trimethylolpropane, trivalent or higher alcohols such as 1,3,5-trihydroxymethylbenzene and the like.

  The carboxylic acid component includes oxalic acid, 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, alkyl succinic acid (n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), alkenyl succinic acid (n-butenyl succinic acid, isobutenyl succinic acid) , N-octenyl succinic acid, n-dodecenyl succinic acid, isododecenyl succinic acid, etc.); 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid 2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene Recarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexane Tricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, trivalent or higher carboxylic acid such as empor trimer acid, and the like can be mentioned.

  Considering that the heat fixing means used in a normal image forming apparatus favorably fixes on the surface of a printed material such as paper, the polyester resin preferably has a softening point of 80 to 150 ° C, preferably 90 to 140 ° C. More preferably.

  It is preferable that a part of the binder resin has a crosslinked structure. By introducing a cross-linked structure in part, the storage stability, form retention, durability, etc. of the magnetic toner can be improved without deteriorating the fixability. In order to make a part of the binder resin have a crosslinked structure, a crosslinking agent may be added to crosslink the resin, or a thermosetting resin may be blended.

  Examples of the thermosetting resin include epoxy resins such as bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, and cyanate resin. 1 type, or 2 or more types.

  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. Further, since the strength of the resin is low, there is a possibility that the toner adheres to the surface of the latent image carrier and cannot be separated. On the other hand, when the glass transition temperature exceeds this range, the fixability on 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 the specific heat in the obtained endothermic curve by measuring at a normal temperature and a normal pressure at a temperature increase rate of 10 ° C./min.

  The toner of the present invention may contain various conventionally known additives such as colorants, charge control agents, and waxes. Among these, examples of the colorant include pigments such as carbon black and dyes such as acid violet in order to adjust the color tone. The proportion of the colorant in the toner particles is preferably about 0.5 to 5% by mass.

(Magnetic powder for internal addition)
The magnetic powder for external additives may be used as it is as the magnetic powder for internal addition. Or you may use a general well-known magnetic powder. For example, ferrite, magnetite and other iron, cobalt, nickel and other metals exhibiting ferromagnetism, alloys or compounds containing these elements, or ferromagnetic materials that do not contain ferromagnetic elements but are subjected to appropriate heat treatment. Examples thereof include an alloy that exhibits the above, chromium dioxide, and the like. These magnetic powders are uniformly dispersed in the toner binder in the form of fine powder having an average particle size of 0.1 to 1 μm, preferably 0.1 to 0.5 μm. May be a single substance or a surface treatment agent such as a titanium coupling agent or a silane coupling agent.

  The magnetic powder is preferably contained in the toner in an amount of 35 to 60% by mass, and preferably 40 to 60% by mass. If it exceeds 60% by mass, the image density tends to be low, and the fixability tends to extremely decrease. If it is less than 35% by mass, fog is deteriorated and image defects are caused.

(Charge control agent)
The charge control agent is blended in order to improve the charge level and charge rising characteristics of the magnetic toner (an index indicating whether the charge is charged to a constant charge level in a short time) and to improve durability and stability. There are two types of charge control agents, one that is positively charged and the other that is negatively charged, and either one is blended according to the charge polarity of the magnetic toner.

  Examples of the positive 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, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, Azine compounds such as quinazoline and quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azin Violet BO, Azine Direct dyes composed of sub-zine compounds such as Raun 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, Azin Deep Black 3RL; Nigrosine Compounds such as Nigrosine, Nigrosine Salt, Nigrosine Derivatives; Nigrosine BK , Nigrosine NB, nigrosine Z and other acid dyes; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride 1 type, or 2 or more types. In particular, a nigrosine compound is suitable as a positively chargeable toner because it can obtain a quicker charge rising characteristic.

  Moreover, as a positively chargeable charge control agent, a resin or oligomer having a quaternary ammonium salt, a resin or oligomer having a carboxylate, a resin or oligomer having a carboxyl group, or the like can be used. Specifically, polystyrene resin having quaternary ammonium salt, acrylic resin having quaternary ammonium salt, styrene-acrylic resin having quaternary ammonium salt, polyester resin having quaternary ammonium salt, carboxylate Polystyrene resin having carboxylate, acrylic resin having carboxylate, styrene-acrylic resin having carboxylate, polyester resin having carboxylate, polystyrene resin having carboxyl group, acrylic resin having carboxyl group 1 type, or 2 or more types, such as a styrene-acrylic resin having a carboxyl group and a polyester resin having a carboxyl group.

  In particular, a styrene-acrylic resin (styrene-acrylic copolymer) having a quaternary ammonium salt, carboxylate or carboxyl group as a functional group can easily adjust the charge amount to a value within a desired range. It is preferable in that it can be performed. Further, acrylic monomers constituting styrene-acrylic resin together with styrene are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, acrylic acid 2 Examples include (meth) acrylic acid alkyl esters such as ethylhexyl, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate.

  Furthermore, as the quaternary ammonium salt compound, 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) acrylates; 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 negatively chargeable charge control agent, for example, an organometallic complex or a chelate compound is effective, and among them, an acetylacetone metal complex, a salicylic acid metal complex or a salt is preferable, and a salicylic acid metal complex or salt is particularly preferable. Among these, examples of the acetylacetone metal complex include aluminum acetylacetonate and iron (II) acetylacetonate. Examples of the salicylic acid-based metal complex or salt include chromium 3,5-di-tert-butylsalicylate.

  The proportion of the charge control agent in the toner particles is preferably 0.1 to 15% by mass, more preferably 0.3 to 8.0% by mass, and 0.5 to 7.0% by mass. It is particularly preferred. If the ratio of the charge control agent is less than this range, it is difficult to impart a stable charging characteristic to the magnetic toner, and the image density may be lowered or the durability may be lowered. On the other hand, when the above range is exceeded, the magnetic toner tends to have environmental resistance, in particular, 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 possibility of causing background fogging or the charge control agent aggregated without being dispersed may contaminate the photoreceptor.

(wax)
Wax improves the fixability of the toner to the surface of the printed material such as paper, prevents the magnetic toner during fixing from adhering to the fixing roller of the image forming apparatus, improves the offset resistance, The toner adhering to the fixing roller or the like is blended in order to prevent the image smearing or the image smearing by reattaching to the surface of the printing material.

  Examples of the wax include olefin waxes such as polyethylene wax and polypropylene wax; plant waxes such as carnauba wax, rice wax and candelilla wax; mineral waxes such as montan wax; Fischer-Tropsch wax produced by the Tropsch method; Petroleum wax such as paraffin wax and microcrystalline wax; Ester wax; Teflon (registered trademark) wax selected from one or more Can be used.

  The proportion of the wax in the toner particles is preferably 1 to 5% by mass. If the ratio of the wax is less than this range, the effect of improving the offset property of the toner and preventing image smearing may be insufficient. There is a risk that the storage stability is lowered due to easy fusion.

<Electrostatic latent image developing toner>
(Magnetic powder for external additives)
As described above, the magnetic one-component toner of the present invention internally adds magnetic powder and externally adds magnetic powder. As shown in FIG. A magnetic powder is used whose particle shape is based on an octahedron and whose vertices and ridgelines of the polyhedron are curved and has a portion that can be regarded as a straight line on the outer periphery of the projected image.

  That is, this externally added magnetic powder is, for example, a photograph (projected image) of a magnetic powder based on octahedrons taken with a transmission electron microscope (TEM) as an example, as shown in FIG. The feature is that the ridgeline is curved and there are no sharp vertices or ridgelines that are the discharge points of charge. 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 to each other so that there is no 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 projected image, and the feature as an octahedron remains.

  Moreover, the said magnetic powder needs to be an average particle diameter of 0.01-0.50 micrometer. A magnetic powder having an average particle size of less than 0.01 μm has a high proportion of small particle size and strong cohesiveness, and the dispersibility during mixing cannot be improved and the effect of addition cannot be exhibited. That is, since the polishing force on the surface of the photosensitive drum is insufficient, the effect of preventing the photosensitive drum filming is insufficient.

  On the other hand, the magnetic powder having an average particle size exceeding 0.50 μm, on the contrary, has a large proportion of large particles and a wide particle size distribution, and a large proportion of both large particles and small particles. As a result, poor image quality occurs, it becomes difficult to uniformly adhere to the toner base surface, and the magnetic powder easily damages the photosensitive drum, so that the photosensitive drum is markedly damaged. Further, since the fluidity of the toner deteriorates, the toner thin layer formation on the sleeve is poor, and layer unevenness occurs.

  In consideration of the balance of the effects, 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. .

  The average particle size of the magnetic powder is the Martin diameter (equivalent circle diameter) measured for 300 magnetic powders photographed with a transmission electron microscope (magnification 10,000 times) magnified 4 times. Average value.

The volume resistivity of the magnetic powder is 10 ² to 10 ⁹ Ω · cm, preferably 10 ³ to 10 ⁸ Ω · cm, more preferably 10 ⁴ to 10 ⁷ Ω · cm. Is desirable. If the volume resistivity value is less than 10 ² Ω · cm, it is impossible to impart sufficient positive chargeability to the toner, causing a decrease in image density. Further, if it is 10 ⁹ Ω · cm or more, the charge amount is too high, and the durability is also charged up, resulting in a decrease in image density and deterioration in durability. Furthermore, excessive charge-up of the toner causes discharge breakdown to the a-Si photosensitive member, resulting in a black spot image.

  The volume specific resistance value of the magnetic powder can be determined by applying a load of 1 kg and applying voltage DC10V using R8340A, ULTRA HIGH RESISTANCE METER manufactured by ADVANTEST.

Furthermore, the saturation magnetization of the magnetic powder is preferably in the range of 70 to 90 Am ² / kg when the measurement magnetic field is 795.8 kA / m. If it is less than 70 Am ² / kg, the magnetic binding force to the toner particles becomes weak, and during the durability, the externally added magnetic powder peels off from the toner particles and falls off, and the initial state cannot be maintained. On the other hand, if it exceeds 90 Am ² / kg, the magnetic binding force to the magnet sleeve is superior to the magnetic binding force to the toner particles, and as a result, the external additive magnetic powder is peeled off from the toner particles.

  The saturation magnetization of the magnetic powder can be measured using a vibrating sample magnetometer (VSM-P7-15 type: manufactured by Toei Kogyo Co., Ltd.).

  The amount of magnetic powder added to the toner base particles is preferably 0.1 to 5.0% by mass. When the addition amount is less than 0.1% by mass, the polishing force on the surface of the photosensitive drum is insufficient and a sufficient effect for preventing the photosensitive drum filming cannot be obtained. Further, the effect of suppressing the charge-up at the time of endurance is small, causing a decrease in image density, and at the same time, leak destruction to the photosensitive drum occurs, resulting in a black dot image. If the addition amount exceeds 5.0 mass%, scratches or the like on the photosensitive drum will be remarkably generated.

  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 magnetic powder comprising the magnetite, 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 periphery of the projected image, and the average particle diameter is defined within the above range, For example, it can be produced by the following method.

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 25.9 l hydroxide ^{(Fe 2+} in advance into the reaction vessel 1. In addition to 10 equivalents) and heated to 90 ° C. to produce a ferrous salt suspension containing ferrous hydroxide colloid while maintaining the pH at 10.5.

  Next, while maintaining the liquid temperature of the suspension at 90 ° C., 100 liters of air is blown in over 80 minutes to cause oxidation reaction until the ferrous salt oxidation reaction rate reaches 60%. . And after adding sulfuric acid aqueous solution to the upper suspension so that the pH becomes 6.5, while maintaining the liquid temperature at 90 ° C., 100 liters of air is blown for 50 minutes, Magnetite particles are generated in the suspension.

  Then, after adding a sodium hydroxide aqueous solution to the suspension containing the magnetite particles so that the pH becomes 10.5, 100 liters of air per minute is maintained for 20 minutes while maintaining the liquid temperature at 90 ° C. After blowing, 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. The shape of the magnetic powder can be controlled by adjusting the pH of the oxidation reaction when performing the above synthesis.

  In addition, when performing the above synthesis reaction, water-soluble various metal compounds such as water-soluble silicates are added to each metal in an aqueous alkali hydroxide solution or a ferrous salt reaction aqueous solution containing ferrous hydroxide colloid. In addition to the addition of 0.1 to 10 atomic% with respect to Fe, the pH of the liquid at the start of the aeration of the oxygen-containing gas in the first stage reaction is adjusted to 8.0 to 9.5. Then, the synthesized magnetic powder is composed of magnetite containing at least one element selected from Mn, Zn, Ni, Cu, Al, Ti, and Si at the predetermined ratio with respect to Fe described above. Become.

  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 obtaining charging stability against environmental fluctuations. . 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.

  In addition, the volume resistivity of magnetic powder can be changed by changing the type and amount of surface treatment agent such as titanium coupling agent, silane coupling agent, aluminum coupling agent, various fatty acids, It is adjusted by forming a coating layer of tin / antimony, francium, etc.

Furthermore, the saturation magnetization of the magnetic powder can be ^achieved by changing the content of Fe ²⁺ in the magnetic powder particles. In general, the saturation magnetization value increases as the Fe ²⁺ content increases. Further, when a different kind of metal other than Fe, for example, Zn is contained in the magnetic powder particles, the saturation magnetization value becomes large. On the other hand, the saturation magnetization value decreases when Ti is contained. In this way, the saturation magnetization value of the magnetic powder is adjusted.

  The present invention is described below. The binder resin, magnetic powder, charge control agent, wax, dye, pigment, fluidizing agent, external additive, etc. in the present invention can be used for all magnetic one-component toners for developing electrostatic latent images. There is no particular restriction.

(Manufacture of toner)
In the toner of the present invention, the above components are mixed using a stirring mixer such as a Henschel mixer, then kneaded using a kneader such as an extruder, then cooled, pulverized, and if necessary. It is manufactured by classification. Moreover, you may wet-mix said each component. The toner of the present invention thus produced preferably has a volume-based center particle size of 5 to 10 μm.

  In addition, the manufactured toner has improved fluidity and storage stability, cleaning properties indicating ease of cleaning removal from the surface of the latent image carrier, 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 hydrophobic silica, alumina, and titanium oxide. In the surface treatment, it is preferable to dry-mix the toner and the external additive. In particular, in order to prevent the external additive from being embedded in the surface of the toner particles, it is preferable to mix using a Henschel mixer or a Nauter mixer. preferable. The addition amount of the external additive is preferably 0.2 to 10.0% by mass with respect to the toner particles. Further, the external additive may be surface-treated with aminosilane, silicone oil, silane coupling agent (hexamethyldisilazane, etc.), titanium coupling agent, or the like, if necessary.

(Example)
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.

<< Examination of the shape of magnetic powder for external additives I >>
(Measurement of average particle size)
The photograph taken with a transmission electron microscope (magnification 10,000 times) was magnified four times, the Martin diameter (equivalent circle diameter) was measured for 300 magnetic powders photographed in the photograph, and the average value was obtained. The average particle size of the magnetic powder was used.

Example 1
(Synthesis of binder resin)
300 parts by mass of xylene are placed in a reaction vessel connected with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux tube, and the reaction vessel is heated while continuously introducing nitrogen from the nitrogen introduction tube, so that the liquid temperature becomes 170. While maintaining at ℃, 845 parts by mass of styrene, 155 parts by mass of n-butyl acrylate, and 8.5 parts by mass of di-tert-butyl peroxide were dissolved in 125 parts by mass of xylene in the above reaction vessel for 3 hours. After the completion of dropping, the mixture was further stirred for 1 hour at 170 ° C., and then the solvent was removed to produce a styrene-n-butyl acrylate copolymer as a binder resin.

(Manufacture of toner)
The magnetic powder for external addition is a convex polyhedron made of magnetite containing 1.1 atomic% of Zn with respect to Fe, and the particle shape is surrounded by eight triangles as shown in FIG. The toner base particle is a magnetic powder having an average particle diameter of 0.20 μm, which is based on an octahedron, and each apex and ridge line of the octahedron is curved and has a portion that can be regarded as a straight line on the outer peripheral portion of the projected image. In contrast, 2.0% was added for use. The volume resistivity value is 3 × 10 ⁵ Ω · cm.

The magnetic powder for internal addition is made of magnetite, which is Fe ₃ O ₄ (FeO · Fe ₂ O ₃ ). The particle shape is spherical as shown in FIG. 3A, and the average particle size is 0.20 μm. Some magnetic powder was used.

  49 parts by weight of the binder resin synthesized above, 45 parts by weight of the above magnetic powder, 3 parts by weight of Fischer-Tropsch wax (Sazole wax H1 manufactured by Sazol) as a release agent, and as a positive charge control agent 3 parts by mass of a quaternary ammonium salt (Bontron P-51 manufactured by Orient Chemical Co., Ltd.) was mixed using a Henschel mixer, kneaded using a twin screw extruder, cooled, and then roughly mixed using a hammer mill. Crushed. Next, the mixture was finely pulverized using a mechanical pulverizer and then classified using an airflow classifier to produce a toner having a volume-based center particle size of 8.0 μm.

(Comparative Example 1)
It is composed of magnetite having the same composition as that used in Example 1 as magnetic powder, and the particle shape is an octahedron that is a convex polyhedron surrounded by eight triangles, as shown in FIG. A toner having a volume-based center particle size of 8.0 μm, as in Example 1, except that the same amount of magnetic powder having an average particle size of 0.23 μm whose vertices and ridges are not curved is used. Manufactured.

(Comparative Example 2)
It is composed of magnetite having the same composition as that used in Example 1 as magnetic powder, and is based on an octahedron that is a convex polyhedron surrounded by eight triangles, and each vertex and ridge of the octahedron are curved. The volume-based center particle diameter is the same as in Example 1 except that the same amount of magnetic powder having an average particle diameter of 0.22 μm and having no portion that can be regarded as a straight line at the outer periphery of the projected image is used. A toner having a particle size of 8.0 μm was produced.

(Comparative Example 3)
It is an octahedron which is a convex polyhedron composed of magnetite having the same composition as that used in Example 1 as magnetic powder, and whose particle shape is surrounded by eight triangles, and its apexes and ridge lines constitute an octahedron. Toner having a volume-based center particle size of 8.0 μm, as in Example 1, except that the same amount of magnetic powder chamfered by a plane smaller than each surface and having an average particle size of 0.20 μm was used. Manufactured.

(Comparative Example 4)
The same amount of magnetic powder composed of magnetite having the same composition as used in Example 1 as a magnetic powder and having a particle shape of hexahedron and an average particle diameter of 0.20 μm as shown in FIG. A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 1 except for the above.

(Comparative Example 5)
The average particle diameter is made of magnetite having the same composition as that used in Example 1 as magnetic powder, the particle shape is a hexahedron, and the apex and ridge lines thereof are chamfered by a plane smaller than each surface constituting the hexahedron. A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 1 except that the same amount of 0.20 μm magnetic powder was used.

(Comparative Example 6)
The same amount of magnetic powder made of magnetite having the same composition as used in Example 1 as the magnetic powder, having a spherical particle shape and an average particle diameter of 0.22 μm as shown in FIG. A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 1 except that it was used.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a one-component magnetic toner for electrostatic latent image developer.

  Using this developer, initial image characteristics and durability were evaluated with a Kyocera page printer (FS-3830) equipped with an a-Si photoconductor, and photoconductor drum filming and photoconductor drum scratches were visually confirmed. In addition, charging characteristics were measured. A thin film a-Si photosensitive member having a film thickness of 14 μm was used as the latent image carrier.

(A) Normal temperature and humidity test After the above printer was allowed to stand for 8 hours in a normal temperature and humidity environment at a temperature of 20 ° C and a relative humidity of 65% RH, The following characteristics were evaluated.

(1) Image Density Using the above printer, the image density of the first image (initial image) on which a standard pattern with a printing rate of 5% is formed, and the printing rate after forming 100,000 images of ISO 4% original continuously. The image density of an image formed with a 5% standard pattern (post-endurance image) was measured using a Macbeth reflection densitometer (RD914 manufactured by Gretag Macbeth). An image density of 1.30 or higher was evaluated as acceptable, and an image density of less than 1.30 was evaluated as unacceptable.

(2) Ground fog The initial image formed in (1) and the blank portion of the post-durability image were observed, and the presence or absence of ground fog was evaluated according to the following criteria.
○: Ground fog was not seen at all.
Δ: Slight fog was observed.
X: Strong ground fog was observed.

(3) Toner charge amount:
During initial image formation and after continuous image formation, the charge amount μC / g of toner in the developer in the developer was measured using a charge amount measuring device [Q / M meter 210HS manufactured by TREK Co., Ltd.]. .

(4-1) Photoreceptor Drum Filming After 100,000 sheets of ISO 4% originals were continuously formed, the photoconductor drum was visually observed and the presence or absence of photoconductor drum filming was evaluated according to the following criteria.
○: No filming was observed.
Δ: Filming was slightly observed.
X: Strong filming was seen.

(5) Photosensitive drum scratch After 100,000 sheets of ISO 4% originals were continuously formed, the photoconductive drum was visually observed, and the presence or absence of scratches was evaluated according to the following criteria.
○: No scratch was observed.
Δ: Slight scratches were observed.
X: Many scratches were observed.

(B) High-temperature and high-humidity test The printer was allowed to stand for 8 hours in a high-temperature and high-humidity environment at a temperature of 33 ° C. and a relative humidity of 85% RH. Under the same conditions as in (1) to (5), image density and toner charge amount were measured, and background fogging, photoconductor drum filming, and photoconductor drum scratches were evaluated.

(C) Low-temperature, low-humidity test The printer was allowed to stand for 8 hours in a low-temperature, low-humidity environment at a temperature of 10 ° C. and a relative humidity of 20% RH. The image density and toner charge amount were measured under the same conditions as in (5), and background fogging, photoconductor drum filming, and photoconductor drum scratches were evaluated.

The above evaluation results are shown in Table 1 in FIG. 6 for the normal temperature and normal humidity test results, in Table 2 in FIG. 7 for the high temperature and high humidity test results, and in Table 3 in FIG. 8 for the low temperature and low humidity test results. In addition, the code | symbol in the particle | grain shape column of the magnetic powder in a table | surface is as follows.
Eight-circle: An octahedron having apexes and ridges that are curved and having a portion that can be regarded as a straight line on the outer periphery of the projected image.
Octagon: An octahedron shape whose vertices and ridge lines are not curved. Normal octahedron.
Eight-maru size: An octahedron shape with apexes and ridges being curved, and having a large radius of curvature of the curved surface and having no portion that can be regarded as a straight line at the outer periphery of the projected image.
Octahedral: An octahedron that is chamfered by a small flat surface with apexes and ridges.
Hexagon: normal hexahedron.
Hexa-face: A hexahedron with chamfered vertices and ridges on a small plane.
Sphere: Spherical.

  As can be seen from Tables 1 to 3 shown in FIG. 6 to FIG. 8, Comparative Example 1 using the magnetic powder that is octahedral and has no apex and ridges curved, and octahedral, The toner of Comparative Example 3 using magnetic powder with chamfered ridgelines on a small flat surface has an extremely small initial charge amount in any of normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity tests, and an image. Since the density was low, and background fogging occurred, and the fogging after durability deteriorated significantly, it was confirmed that leakage of charged charges was generated by the magnetic powder added to the toner. Further, filming of the photosensitive drum was not observed, but many scratches were generated.

  Similarly, the toner of Comparative Example 4 using hexahedral magnetic powder and Comparative Example 5 using hexagonal magnetic powder with chamfered vertices and ridges in a small plane are similarly used at normal temperature, normal humidity, high temperature, In any of the high humidity, low temperature, and low humidity tests, the initial charge amount is extremely small, the image density is low, and background fogging is occurring. It was confirmed that the charged magnetic charge leaked due to the added magnetic powder. Further, filming of the photosensitive drum was not observed, but many scratches were generated.

  Further, Comparative Example 2 using a magnetic powder which is octahedral and has a curved surface with vertices and ridgelines but has a curved surface with a too large radius of curvature and does not have a portion which can be regarded as a straight line on the outer periphery of the projected image. The toner of Comparative Example 6 using a spherical magnetic powder and the toner of Comparative Example 6 using a spherical magnetic powder significantly increased the charge amount after durability and decreased the image density in any of the normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity tests. In addition, since background fogging occurred, it was confirmed that there was no discharge from the magnetic powder internally added to the toner, and that charge-up occurred. Further, no scratches on the photosensitive drum were observed, but slight filming was observed.

  On the other hand, the toner of Example 1 using the magnetic powder having an octahedron shape and the apex and ridge lines being curved and having a portion that can be regarded as a straight line on the outer peripheral portion of the projected image is normal temperature and normal. In any of the humidity test, low temperature, low humidity test, and high temperature, high humidity test, the charge amount and image density after initial and endurance are maintained almost constant, and the occurrence of background fog is prevented, and a good image is obtained. It was confirmed that no scratches or filming occurred on the photosensitive drum.

(Examples 2-7, Comparative Examples 7-10)
<< Examination of magnetic powder shape for external additives II >>
It consists of magnetite having the same composition as that used in Example 1 as magnetic powder, and the shape of the particles is an octahedron that is a convex polyhedron surrounded by eight triangles, and its apexes and ridges are curved, The average particle diameter is 0.004 μm (Comparative Example 7), 0.014 μm (Example 2), 0.088 μm (Example 3), and 0.30 μm (implementation) having a portion that can be regarded as a straight line on the outer periphery of the projected image. Ex. 4), 0.37 μm (Example 5), and 0.63 μm (Comparative Example 8), except that the same amount of magnetic powder was used. A toner of 0.0 μm was produced.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a magnetic toner for electrostatic latent image one-component developer.

  Using this developer, a page printer (FS-3830) manufactured by Kyocera with an a-Si photosensitive member can provide initial image characteristics and durability in each environment of normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity as described above. In addition, the photosensitive drum filming and the photosensitive drum scratch were visually confirmed, and the charging characteristics were measured. A thin film a-Si having a film thickness of 14 μm was used as the latent image carrier.

  The results are shown in Tables 4 to 6 in FIGS. 9 to 11 together with the results of Example 1.

  As can be seen from Tables 4 to 6 shown in FIGS. 9 to 11, the average is an octahedron and the apex and ridge are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image. In the toner of Comparative Example 7 using magnetic powder having a particle size of less than 0.01 μm, the initial image density is less than 1.30 in each environment test, and the normal temperature, normal humidity test and The image density after endurance in the high temperature and high humidity test was also lower than 1.30. In addition, in the high-temperature and high-humidity test, background fogging occurred, and further, photoconductor drum filming occurred in each environment.

  Further, a comparative example using magnetic powder having an octahedron shape and a vertex and a ridge line having a curved surface and a portion that can be regarded as a straight line on the outer peripheral portion of the projected image, but whose average particle diameter exceeds 0.50 μm. The toner No. 8 was confirmed to have been charged up because the charge amount after durability increased in the test under each environment, the image density decreased, and background fogging occurred. There were also scratches on the drum.

  On the other hand, the shape is octahedral and the apex and ridge are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image, and the average particle diameter is 0.01 to 0.50 μm. In the toners of Examples 1 to 5 using magnetic powder, the charge amount and the image density after the initial and endurance are almost constant in any of normal temperature, normal humidity test, low temperature, low humidity test, and high temperature, high humidity test. It was confirmed that generation of background fog was prevented and a good image was formed.

  In addition, when each example is compared, the smaller the average particle diameter of the magnetic powder, the smaller the initial charge amount, and conversely, the larger the average particle diameter, the charge amount after the endurance particularly in the low temperature and low humidity test. Found a tendency to rise. And from this result, it was confirmed that the average particle diameter of the magnetic powder is preferably 0.05 to 0.35 μm, and more preferably 0.15 to 0.30 μm.

(Examples 6-9, Comparative Examples 9-10)
《Examination of magnetic powder for external additives III》
It consists of magnetite having the same composition as that used in Example 1 as magnetic powder, and the shape of the particles is an octahedron that is a convex polyhedron surrounded by eight triangles, and its apexes and ridges are curved, A volume resistivity value of 2 × 10 ¹ Ω · cm (Comparative Example 9), 5 × 10 ² Ω · cm (Example 6), and 7 × 10 ⁴ Ω having a portion that can be regarded as a straight line on the outer periphery of the projected image. Magnetics that are cm (Example 7), 1 × 10 ⁷ Ω · cm (Example 8), 3 × 10 ⁹ Ω · cm (Example 9), and 8 × 10 ¹⁰ Ω · cm (Comparative Example 10) A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 1 except that the same amount of powder was used.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a magnetic toner for electrostatic latent image one-component developer.

  Using this developer, an initial image characteristic and durability were evaluated at room temperature and humidity using a page printer (FS-3830) manufactured by Kyocera with an a-Si photoconductor, and the number of black spots on the photoconductor drum was confirmed. Furthermore, charging characteristics were measured. A thin film a-Si having a film thickness of 14 μm was used as the latent image carrier.

(6-1) The number of black spots on the photosensitive drum The dot printer (DA-5000S, manufactured by Oji Scientific Instruments) calculates the number of black spots generated by dielectric breakdown on the photosensitive drum when 100,000 sheets are printed by the page printer. And the number of dielectric breakdowns of the photosensitive film relative to the number of printed sheets, that is, the number of black spots on the printing paper was measured. The measurement range of the measured number of black spots was an area of 5 mm × 210 mm in the A4 horizontal direction.

  The results are shown in Table 7 of FIG. 12 together with the results of Example 1.

As can be seen from Table 7 in FIG. 12, Examples 1 and 6 to ^{9 in which} the volume resistivity of the magnetic powder is 5 × 10 ^{2 to} 3 × 10 ⁹ Ω · cm are all in the charge amount, the image density, and the fog. The black spots on the photosensitive drum are not generated. On the contrary, in Comparative Example 9 having a small resistance value of 2 × 10 ¹ Ω · cm, although black spots were not generated, fogging occurred at an early stage. This is because, since the volume resistivity of the magnetic powder is small, the initial charge amount is low and fogging occurs. However, the charge amount increases with continuous use, so fogging does not occur. Yes.

Further, in Comparative Example 10 having a large value of 8 × 10 ¹⁰ Ω · cm, black spots occurred and fogging occurred after durability. From this result, it was confirmed that the volume resistivity value of the magnetic powder is preferably 10 ² to 10 ⁹ Ω · cm, more preferably 10 ³ to 10 ⁸ Ω · cm.

(Examples 1 and 8, Comparative Examples 11 to 14)
《Examination of magnetic powder for external additives IV》
As a comparative example, the toners shown in Examples 1 and 8 were added and an external additive other than magnetic powder was added for examination. That is, as an external additive, titanium oxide having a volume resistivity of 3 × 10 ⁵ Ω · cm (Comparative Example 11), titanium oxide having a volume resistivity of 1 × 10 ⁷ Ω · cm (Comparative Example 12), and a volume resistivity of 3 Example 10 except that the same amount of abrasive such as × 10 ⁵ Ω · cm zinc oxide (Comparative Example 13) and 1 × 10 ⁷ Ω · cm zinc oxide (Comparative Example 14) was used. Thus, a toner having a volume-based center particle size of 8.0 μm was produced.

  1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Kogyo Co., Ltd.] is added to 100 parts by mass of the toner of each of the above Examples and Comparative Examples, and the mixture is mixed using a Henschel mixer. A magnetic toner for developer was obtained.

  Using this developer, a Kyocera page printer (FS-3830) equipped with an a-Si photoconductor is used to perform photoconductor drum filming, the number of black spots on the photoconductor drum, and adhesion of external additives to the toner surface at room temperature and humidity. Evaluation of observation was performed. A thin film a-Si having a film thickness of 14 μm was used as the latent image carrier.

(4-2) Photosensitive drum filming After forming 300,000 continuous images of ISO 4% originals, the photosensitive drum was visually observed, and the presence or absence of photosensitive drum filming was evaluated according to the following criteria.
○: No filming was observed.
Δ: Filming was slightly observed.
X: Strong filming was seen.

(6-2) Number of black spots on the photosensitive drum Using the above page printer, the number of black spots generated by dielectric breakdown on the photosensitive drum when 300,000 sheets were printed was calculated using a dot analyzer (DA-5000S, manufactured by Oji Scientific Instruments). ) To measure the number of dielectric breakdowns of the photosensitive film relative to the number of printed sheets, that is, the number of black spots on the printing paper. The measurement range of the measured number of black spots was an area of 5 mm × 210 mm in the A4 horizontal direction.

(7) Observation of adhesion of external additive on toner surface After forming 300,000 continuous images of ISO 4% originals, the toner in the developer is observed with a scanning electron microscope. Evaluated by criteria.
○: The external additive on the toner surface adheres in the same state as the initial state.
(Triangle | delta): The external additive on the toner surface has peeled off a little compared with the initial stage, and has fallen off.
X: The external additive on the toner surface is almost peeled off and dropped off compared to the initial stage.

  The evaluation results are shown in Table 8 of FIG. 13 together with the results of Example 1.

  From this table, Comparative Examples 11 to 14 in which inorganic metal oxides other than magnetic powder are externally added have a problem in durability because there is no holding force to the toner particles due to magnetic force, and external additives are added from the toner particles during durability. As a result, the initial performance cannot be maintained, and problems such as photoconductor drum filming, black spots, and adhesion of external additives to the toner surface have occurred. On the other hand, in Examples 1 and 8 using magnetic powder having a magnetic force, the external additive is easily held by the toner particles by the magnetic force, and the state can be maintained over a long period of time. The state is maintained as it is.

(Example 10)
<Examination of the shape of magnetic powder for external additives V>
(Manufacture of toner)
As the magnetic powder for external addition, it is composed of magnetite containing 1.1 atomic% of Zn with respect to the same Fe used in Example 1, and the particle shape is 8 triangles as shown in FIG. The base is an octahedron that is a convex polyhedron surrounded by an octahedron, each vertex and ridge line of the octahedron is curved, and the projected image has a portion that can be regarded as a straight line, with an average particle diameter of 0.23 μm. Some magnetic powder was used by adding 2.0% to the toner base particles. The volume resistivity value is 7 × 10 ⁵ Ω · cm.

  As the magnetic powder for internal addition, magnetic powder having the same particle shape as in Example 1 as shown in FIG. 3A and having an average particle diameter of 0.20 μm is used. 49 parts by weight of binder resin, 45 parts by weight of the above magnetic powder, 3 parts by weight of Fischer-Tropsch wax (Sazol Wax H1 manufactured by Sazol) as a release agent, and a quaternary ammonium salt as a positive charge control agent [Bontron P-51 manufactured by Orient Chemical Co., Ltd.] 3 parts by mass were mixed using a Henschel mixer, kneaded using a twin screw extruder, cooled, and then roughly pulverized using a hammer mill. Next, the mixture was finely pulverized using a mechanical pulverizer and then classified using an airflow classifier to produce a toner having a volume-based center particle size of 8.0 μm.

(Comparative Example 15)
It consists of magnetite having the same composition as that used in Example 10 as magnetic powder, and its particle shape is an octahedron that is a convex polyhedron surrounded by eight triangles, as shown in FIG. A toner having a volume-based center particle size of 8.0 μm in the same manner as in Example 10 except that the same amount of magnetic powder having an average particle size of 0.26 μm and a ridge line that is not curved is used. Manufactured.

(Comparative Example 16)
It is composed of magnetite having the same composition as that used in Example 10 as magnetic powder. The particle shape is basically an octahedron that is a convex polyhedron surrounded by eight triangles, and each vertex and ridge line of the octahedron is curved. In addition, the same amount of magnetic powder having an average particle diameter of 0.25 μm that does not have a portion that can be regarded as a straight line on the outer peripheral portion of the projected image is used in the same manner as in Example 10, and the volume-based center particle. A toner having a diameter of 8.0 μm was produced.

(Comparative Example 17)
Each of the octahedrons is a convex polyhedron composed of magnetite having the same composition as that used in Example 10 as the magnetic powder and the particle shape is surrounded by eight triangles, and the apexes and ridge lines thereof constitute the octahedron. A toner having a volume-based center particle size of 8.0 μm, as in Example 10, except that the same amount of magnetic powder chamfered by a plane smaller than the surface and having an average particle diameter of 0.22 μm was used. Manufactured.

(Comparative Example 18)
As the magnetic powder, the same amount of magnetic powder consisting of magnetite having the same composition as used in Example 10 and having a particle shape of hexahedron and an average particle diameter of 0.22 μm as shown in FIG. 3B was used. A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 10.

(Comparative Example 19)
An average particle diameter composed of magnetite having the same composition as that used in Example 10 as magnetic powder, the particle shape being hexahedral, and the apexes and ridges thereof being chamfered by a plane smaller than each surface constituting the hexahedron A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 10 except that the same amount of magnetic powder having a particle size of 0.22 μm was used.

(Comparative Example 20)
The same amount of magnetic powder composed of magnetite having the same composition as that used in Example 10 as the magnetic powder, having a spherical particle shape and an average particle diameter of 0.24 μm as shown in FIG. A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 10 except that it was used.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a magnetic toner for electrostatic latent image one-component developer.

  Using this developer, the initial image characteristics and durability were evaluated by a Kyocera page printer (FS-3830 modified machine) equipped with an a-Si photosensitive member, and the state of the toner thin layer on the developing sleeve was also visually observed. Confirmation was made, and charging characteristics and fog were measured. In this modified machine, an amorphous silicon photoconductor having a film thickness of 14 μm was mounted, and Rz as a developing sleeve was replaced with a developing device using 4.0 μm SUS305.

  Image density, background fogging, and toner charge amount in a normal temperature and normal humidity test were measured in the same manner as described above.

(8-1) Toner Thin Layer State After 100,000 sheets of ISO 4% originals were continuously formed, the toner thin layer state on the developing sleeve was visually confirmed and evaluated using the following criteria.
○: A thin layer is uniformly formed and there is no unevenness.
(Triangle | delta): There exists a part with thick layer thickness.
X: Unevenness occurs.

  In the high-temperature, high-humidity test, low-temperature, and low-humidity test, the image density, ground fog, and toner charge amount were measured in the same manner as described above, and the toner thin layer state was evaluated.

  The above evaluation results are shown in Table 9 in FIG. 14 for the normal temperature and normal humidity test results, in Table 10 in FIG. 15 for the high temperature and high humidity test results, and in Table 11 in FIG. 16 for the low temperature and low humidity test results. In addition, the code | symbol in the particle | grain shape column of the magnetic powder in a table | surface is as above-mentioned.

  As can be seen from Tables 9 to 11 shown in FIGS. 14 to 16, octagonal and comparative example 15 using magnetic powder that does not have a curved surface of the apex and ridge, and octahedral, The toner of Comparative Example 17 using magnetic powder with chamfered ridgelines on a small flat surface has an extremely low initial charge amount and image density in any of normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity tests. The background fogging was low, and the fogging after the endurance was remarkably deteriorated. Therefore, it was confirmed that leakage of charged charges was caused by the magnetic powder internally added to the toner.

  Similarly, the toners of Comparative Example 18 using hexahedral magnetic powder and Comparative Example 19 using hexagonal magnetic powder with chamfered vertices and ridges on a small plane are similarly used at normal temperature, normal humidity, and high temperature. In the high humidity, low temperature, and low humidity tests, the initial charge amount was extremely small, the image density was low, and background fogging occurred and the background fogging after durability deteriorated significantly. It was confirmed that charging charge leaks due to the internally added magnetic powder.

  Furthermore, although it is octahedral and the vertex and the ridgeline are curved, the radius of curvature of the curved surface is too large, and the comparative example 16 uses magnetic powder that does not have a portion that can be regarded as a straight line on the outer periphery of the projected image. The toner of Comparative Example 20 using the spherical magnetic powder and the toner of Comparative Example 20 both have a significantly increased charge amount after durability in any of the normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity tests. Since the density decreased and background fogging occurred, it was confirmed that there was no discharge from the magnetic powder internally added to the toner, and that jersey up occurred. At the same time, the toner thin layer state deteriorated.

  On the other hand, the toner of Example 10 using the magnetic powder having an octahedral shape and having apexes and ridges curved and having a portion that can be regarded as a straight line on the outer peripheral portion of the projected image is normal temperature and normal. In all of the humidity test, low temperature, low humidity test, and high temperature and high humidity test, the charge amount and image density after initial and durability can be maintained almost constant, and the occurrence of background fogging is prevented and the toner thin layer state is also maintained. It was confirmed that a good image was formed without any problem.

(Examples 11 to 14, Comparative Examples 21 and 12)
<Examination of the shape of magnetic powder for external additives VI>
It is composed of magnetite having the same composition as that used in Example 10 as magnetic powder, and its particle shape is an octahedral shape that is a convex polyhedron surrounded by eight triangles, and its apex and ridge lines are curved. The average particle diameter is 0.005 μm (Comparative Example 21), 0.015 μm (Example 11), 0.092 μm (Example 12), and 0.35 μm (with a portion that can be regarded as a straight line on the outer periphery of the projected image) In the same manner as in Example 10 except that the same amount of magnetic powders of Example 13), 0.42 μm (Example 14), and 0.68 μm (Comparative Example 22) was used, the volume-based center particle size was A toner having a size of 8.0 μm was produced.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a magnetic toner for electrostatic latent image one-component developer.

  Using this developer, a page printer (FS-3830) manufactured by Kyocera with an a-Si photosensitive member can provide initial image characteristics and durability in each environment of normal temperature, normal humidity, high temperature, high humidity, low temperature, and low humidity as described above. In addition, the background fogging, the toner thin layer state, the photosensitive drum filming, and the photosensitive drum scratch were visually confirmed, and the charging characteristics were measured. The developing sleeve Rz used was 4.0 μm SUS305.

(4-3) Photosensitive drum filming
As described above, after 100,000 sheets of ISO 4% originals were continuously formed, the photosensitive drum was visually observed, and the presence or absence of photosensitive drum filming was evaluated according to the following criteria.
○: No filming was observed.
Δ: Filming was slightly observed.
X: Strong filming was seen.

(5) Photoreceptor Drum Scratch Similar to the above, after continuous image formation of 100,000 ISO 4% originals, the photoconductive drum was visually observed and evaluated for the presence or absence of a flaw according to the following criteria.
○: No scratch was observed.
Δ: Slight scratches were observed.
X: Many scratches were observed.

  The results are shown in Tables 12 to 14 of FIGS. 17 to 19 together with the results of Example 10.

  As can be seen from Tables 12 to 14 shown in FIGS. 17 to 19, the average of the octahedron shape, the apex and the ridge line being curved and having a portion that can be regarded as a straight line on the outer peripheral portion of the projected image. In the toner of Comparative Example 21 using magnetic powder having a particle size of less than 0.01 μm, the initial image density was less than 1.30 in each environment test, and the normal temperature, normal humidity test and In the high temperature and high humidity test, the image density after endurance was less than 1.30. In addition, in the high-temperature and high-humidity test, background fogging occurred, and further, photoconductor drum filming occurred in each environment.

  Further, a comparative example using magnetic powder having an octahedron shape and a vertex and a ridge line having a curved surface and a portion that can be regarded as a straight line on the outer peripheral portion of the projected image, but whose average particle diameter exceeds 0.50 μm. It was confirmed that the toner No. 22 was charged up because the charge amount after endurance increased, the image density decreased, and background fogging occurred in the test under each environment. At the same time, the toner thin layer condition deteriorated and scratches on the photosensitive drum occurred.

  On the other hand, the magnet has an octahedral shape, has apexes and ridges that are curved, has a portion that can be regarded as a straight line on the outer periphery of the projected image, and has an average particle diameter of 0.01 to 0.50 μm. As for the toners of Examples 10 and 11 to 14 using powder, the charge amount and the image density after the initial stage and after the endurance in any of normal temperature, normal humidity test, low temperature, low humidity test, and high temperature, high humidity test. It has been confirmed that a good image can be formed while maintaining a substantially constant image quality and preventing the occurrence of background fog.

  In addition, when each example is compared, the smaller the average particle diameter of the magnetic powder, the smaller the initial charge amount, and conversely, the larger the average particle diameter, the charging after endurance particularly at low temperature and low humidity tests. It was found that the amount tended to increase. And from this result, it was confirmed that the average particle diameter of the magnetic powder is preferably 0.05 to 0.35 μm, and more preferably 0.15 to 0.30 μm.

(Examples 15 to 28, Comparative Examples 23 to 32)
<Examination of the shape of magnetic powder for external additives VII>
It consists of magnetite of the same composition as used in Example 10 as magnetic powder, and the shape of the particles is an octahedron that is a convex polyhedron surrounded by eight triangles, and its vertices and ridges are curved, A volume resistivity value of 4 × 10 ¹ Ω · cm (Comparative Example 23), 3 × 10 ² Ω · cm (Example 15), and 4 × 10 ⁴ Ω having a portion that can be regarded as a straight line on the outer periphery of the projected image. Magnetics that are cm (Example 16), 8 × 10 ⁷ Ω · cm (Example 17), 1 × 10 ⁹ Ω · cm (Example 18), and 6 × 10 ¹⁰ Ω · cm (Comparative Example 24) A toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 10 except that the same amount of powder was used.

  In 100 parts by mass of the toners of the above examples and comparative examples, 1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.] and titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 0.0 part by mass was added and mixed using a Henschel mixer to obtain a magnetic toner for electrostatic latent image one-component developer.

  Using this developer, initial image characteristics and durability were evaluated at room temperature and humidity using a Kyocera page printer (FS-3830) equipped with an a-Si photosensitive member, and the state of the toner thin layer on the developing sleeve Were visually confirmed, and charging characteristics and background fogging were measured. The developing sleeve Rz used was SUS305 having a diameter of 4.0 μm.

  The results are shown in Table 15 of FIG. 20 together with the results of Example 10.

As can be seen from Table 15 of FIG. 20, Examples 10 and 15 to 18 in which the volume resistivity of the magnetic powder is 3 × 10 ² to 1 × 10 ⁹ Ω · cm are all in the charge amount, the image density, and the fog. The toner thin layer state on the developing sleeve was also good. On the contrary, in Comparative Example 23 having a small resistance value of 4 × 10 ¹ Ω · cm, the toner thin layer state was good, but fogging occurred at an early stage for the same reason as in Comparative Example 9. Further, in Comparative Example 24 having a large value of 6 × 10 ¹⁰ Ω · cm, the toner thin layer on the developing sleeve was disturbed, and fogging occurred after durability. From this result, the volume resistivity value of the magnetic powder is preferably 10 ² to 10 ⁹ Ω · cm, more preferably 10 ³ to 10 ⁸ Ω · cm, and more preferably in the range of 10 ⁴ to 10 ⁷ Ω · cm. It was confirmed that it is more preferable to be within.

(Examples 10, 17, 25, Comparative Examples 25-36)
《Examination of magnetic powder for external additives VIII》
As a comparative example, studies other than magnetic powder were performed. That is, as an external additive, titanium oxide having a volume resistivity of 7 × 10 ⁵ Ω · cm (Comparative Example 25), titanium oxide having a volume resistivity of 8 × 10 ⁷ Ω · cm (Comparative Example 26), and volume resistivity Other than using the same amount of abrasive such as zinc oxide having a value of 7 × 10 ⁵ Ω · cm (Comparative Example 27) and zinc oxide having a volume resistivity of 8 × 10 ⁷ Ω · cm (Comparative Example 28). Produced a toner having a volume-based center particle size of 8.0 μm in the same manner as in Example 10.

  1.0 part by mass of silica [RA-200H manufactured by Nippon Aerosil Kogyo Co., Ltd.] is added to 100 parts by mass of the toner of each of the above Examples and Comparative Examples, and the mixture is mixed using a Henschel mixer. A magnetic toner for developer was obtained.

  Using this developer, the state of the toner thin layer on the developing sleeve and the adhesion of the external additive on the toner surface were observed with a Kyocera page printer (FS-3830) equipped with an a-Si photosensitive member at room temperature and humidity. . The developing sleeve Rz used was SUS305 having a diameter of 4.0 μm.

(8-2) Toner Thin Layer State After forming 300,000 continuous images of ISO 4% originals, the toner thin layer state on the developing sleeve was visually confirmed and evaluated using the following criteria.
○: A thin layer is uniformly formed and there is no unevenness.
(Triangle | delta): There exists a part with thick layer thickness.
X: Unevenness occurs.

(9) Observation of adhesion of external additive on toner surface After forming 300,000 consecutive images of ISO 4% original, the toner in the developer is observed with a scanning electron microscope, and the presence or absence of external additive adhesion on the toner surface is as follows. Evaluation based on the criteria.
○: The external additive on the toner surface adheres in the same state as the initial state.
(Triangle | delta): The external additive on the toner surface has peeled off a little compared with the initial stage, and has fallen off.
X: The external additive on the toner surface is almost peeled off and dropped off compared to the initial stage.

  The results are shown in Table 16 of FIG. 21 together with the results of Example 10.

  From this table, in Comparative Examples 25 to 28 in which inorganic metal oxides other than magnetic powder are externally added, there is a problem in durability because there is no holding force to the toner particles due to magnetic force, and external additives are added from the toner particles during durability. As a result, the initial performance cannot be maintained, and there are problems in both the toner thin layer state and adhesion of external additives on the surface. On the other hand, the magnetic powder having a magnetic force is easily held by the toner particles due to its effect, and can maintain the state for a long time, and as a result, the initial state can be maintained as it is after the endurance.

Further, using the toner formulation of Example 10, the toner thin layer state, the initial image density, and the leak black spot when the Rz of the developing sleeve was changed were evaluated, and the results are shown in Table 17 of FIG. Regarding the leak black spots in this evaluation, the number of black spots with a diameter of 0.1 mm or more existing on the white image when a white image is output by the page printer at the initial time in a normal temperature and humidity environment (20 ° C., 65% RH). Evaluated. For evaluation, the following criteria were used.
○: The number of black spots is zero.
Δ: The number of black spots is less than 5.
X: The number of black spots is 5 or more.

  It can be seen from Table 17 in FIG. 22 that the Rz of the developing sleeve that does not disturb the formation of the toner thin layer on the developing sleeve and does not cause a leak black spot is optimally 2.0 μm or more and less than 6.0 μm.

From the above results, the magnetic one-component toner according to the present invention is based on a polyhedron having a particle shape of octahedron as an externally added magnetic powder, each vertex and ridge are curved, and a straight line is formed on the outer periphery of the projected image. The magnetic powder has an average particle diameter of 0.01 to 0.50 μm and a volume resistivity of 10 ² to 10 ⁹ Ω · cm, preferably 10 ³ to 10 ⁸ Ω · cm, More preferably, it is found to be in the range of 10 ⁴ to 10 ⁷ Ω · cm.

  In addition, an image forming apparatus for forming an image using a magnetic one-component toner to which magnetic powder is externally added uses a thin film a-Si having a film thickness of 30 μm or less as a latent image carrier, and the latent image carrier. The body is cleaned by an elastic blade, and toner is transported by rotation of a developing sleeve having a rough surface with a built-in magnet roller, and passes through the gap between the magnetic blade and the developing sleeve, thereby developing the sleeve. It is optimal to use a magnetic one-component jumping method in which a toner thin layer is formed on the surface and developed, and the ten-point average roughness Rz of the surface of the developing sleeve should be 2.0 μm or more to less than 6.0 μm. Is preferred.

  According to the present invention, it is possible to obtain a stable image that is excellent in charging stability of a toner and that does not cause a void in an image even when subjected to stress over time or thermal stress over a long period of time. It is possible to provide a magnetic one-component toner for developing an electrostatic latent image that can prevent dielectric breakdown due to leakage and also ensure long-term stability of toner thin layer formation on the developing sleeve, and can provide a high-quality image over a long period of time. A development unit and an image forming apparatus that can be provided can be provided.

1 is a diagram showing an outline of the structure of an image forming apparatus for carrying out a magnetic toner of the present invention and an image forming method using the magnetic toner. It is sectional drawing of the photoconductor drum (electrostatic latent image carrier) used for this invention. 2A and 2B are diagrams illustrating the shape of magnetic powder externally added to a toner, where FIG. 3A is a spherical shape, FIG. 2B is a hexahedron, FIG. 3D is an octahedron, and FIG. 2 is an electron micrograph showing an example of magnetic powder used in the magnetic toner of the present invention. It is the graph which showed the relationship between the film thickness of an amorphous silicon photoreceptor, and the needle | hook pressure resistance which causes a dielectric breakdown. 6 is a table summarizing the results of tests in a normal temperature and normal humidity environment using Example 1 of the magnetic toner according to the present invention and Comparative Examples 1 to 6. 6 is a table summarizing the results of tests in a high temperature and high humidity environment using Example 1 of the magnetic toner according to the present invention and Comparative Examples 1 to 6. 6 is a table summarizing the results of tests in a low temperature and low humidity environment using Example 1 of the magnetic toner according to the present invention and Comparative Examples 1 to 6. 6 is a table summarizing the results of tests conducted at room temperature and humidity using Examples 1 to 5 and Comparative Examples 7 and 8 of the magnetic toner according to the present invention. 6 is a table summarizing the results of tests in high temperature and high humidity environments using Examples 1 to 5 and Comparative Examples 7 and 8 of the magnetic toner according to the present invention. 6 is a table summarizing the results of tests in low temperature and low humidity environments using Examples 1 to 5 and Comparative Examples 7 and 8 of the magnetic toner according to the present invention. 4 is a table summarizing the results of tests conducted at room temperature and humidity using Examples 1 and 6 to 9 and Comparative Examples 9 and 10 of the magnetic toner according to the present invention. 6 is a table summarizing the results of tests conducted at room temperature and humidity using Examples 1 and 8 and Comparative Examples 11 to 14 of the magnetic toner according to the present invention. 7 is a table summarizing the results of tests in a normal temperature and humidity environment using Example 10 and Comparative Examples 15 to 20 of the magnetic toner according to the present invention. 10 is a table summarizing the results of tests in a high temperature and high humidity environment using Example 10 and Comparative Examples 15 to 20 of the magnetic toner according to the present invention. 10 is a table summarizing the results of tests in a low temperature and low humidity environment using Example 10 and Comparative Examples 15 to 20 of the magnetic toner according to the present invention. 6 is a table summarizing the results of tests conducted at normal temperature and humidity using Examples 10 to 14 and Comparative Examples 21 and 22 of magnetic toner according to the present invention. 6 is a table summarizing the results of tests in high temperature and high humidity environments using Examples 10 to 14 and Comparative Examples 21 and 22 of magnetic toner according to the present invention. 10 is a table summarizing the results of tests in low temperature and low humidity environments using Examples 10 to 14 and Comparative Examples 21 and 22 of magnetic toner according to the present invention. 6 is a table summarizing the results of tests in normal temperature and normal humidity environments using Examples 10 and 15 to 18 and Comparative Examples 23 and 24 of the magnetic toner according to the present invention. 4 is a table summarizing the results of tests conducted at normal temperature and humidity using Examples 10 and 17 and Comparative Examples 25 to 28 of the magnetic toner according to the present invention. A table summarizing the results of evaluating and testing the toner thin layer state, the initial image density, and the leak black spot when the Rz of the developing sleeve is changed at room temperature and normal humidity using Example 10 of the magnetic toner according to the present invention. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Charging device 13 Exposure device 14 Developing device 14 ₁ Developer carrying body (developing sleeve)
15 Transfer roll 16 Cleaning means 17 Static elimination device

Claims (7)

The latent image formed on the latent image carrier is developed by a magnetic jumping method so that the latent image is held on the surface of the developing sleeve facing the latent image carrier so that it does not come into contact with the latent image carrier. A magnetic one-component toner containing magnetic powder in at least a binder resin and externally adding magnetic powder,
Each of the externally added magnetic powders has a curved surface and a portion that can be regarded as a straight line on the outer periphery of the projected image, and the magnetic powder has a volume resistivity of 10 ² to 10 ⁹ Ω · cm. Magnetic single-component toner characterized by having a polyhedral shape.   The shape of the magnetic powder for external addition of the polyhedron is an octahedron that is a convex polyhedron surrounded by eight triangles, and each vertex and ridge are curved and the portion that can be regarded as a straight line on the outer periphery of the projected image The magnetic one-component toner according to claim 1, wherein   3. The magnetic one-component toner according to claim 1, wherein the magnetic powder for external addition has an average particle diameter of 0.01 to 0.50 μm.   The magnetic one-component toner according to any one of claims 1 to 3, wherein an amount of the magnetic powder for external additive added is 0.1 to 5.0% by mass. At least the binder resin contains magnetic powder, each vertex and ridge are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image, and the volume resistivity is 10 ² to 10 ⁹ Ω · cm. 10-point average of the surface facing the latent image carrier that forms a latent image by carrying a magnetic mono-component toner with externally added polyhedral magnetic powder in the range and incorporating a magnet roller inside A development having a developing sleeve having a roughness Rz of 2.0 μm or more and less than 6.0 μm, and developing a latent image formed on the latent image carrier by an electrophotographic method by a magnetic jumping method unit. A latent image carrier, a toner carrier having a fixed magnet and a developing sleeve that faces the surface of the latent image carrier so as not to contact the latent image carrier, holds the magnetic one-component toner, and rotates. Means for causing the magnetic one-component toner held on the developing sleeve to fly to a latent image formed on the surface of the latent image carrier and developing it to form a toner image; An image forming apparatus comprising a cleaning means using an elastic blade for cleaning toner remaining after transferring an image to a recording medium,
The magnetic one-component toner contains at least a magnetic powder in a binder resin, and has a volume that has a portion that can be regarded as a straight line at the outer peripheral portion of the projected image, in which each particle shape is a polyhedron and each vertex and ridge are curved. Magnetic powder having a specific resistance in the range of 10 ² to 10 ⁹ Ω · cm is externally added, and the developing sleeve of the toner carrier has a ten-point average roughness Rz of 2.0 μm or more to less than 6.0 μm. An image forming apparatus.   8. The developing unit or the image forming apparatus according to claim 6, wherein the latent image carrier is composed of an amorphous silicon photoconductor having a thickness of 10 to 30 [mu] m.

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