JP2007206530A - Magnetic toner and image forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic toner that can prevent dielectric breakdown of an amorphous silicon photoreceptor, upon carrying out magnetic single component jumping development, using the amorphous silicon photoreceptor and the magnetic toner, and that ensures no variation in easy to charge properties and in a charge amount under an environment of less temperature or humidity influence, particularly, even in an environment, such as high temperature and high humidity environment where the toner is difficult to be charged, and that can continuously form proper images over a long period of time, and to provide an image forming method that uses the toner. <P>SOLUTION: The magnetic toner is constituted by using a magnetic powder having a particle form of an hexahedron as a base, having each vertex and ridge of the hexahedron in curved faces, having a portion considered as a straight line in the peripheral part of a projected image of the particle, having an average particle size of 0.01 to 0.50 μm, and having a volume resistivity of 1.0×10<SP>3</SP>(Ω cm) or larger to smaller than 1.0×10<SP>8</SP>(Ω cm). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic toner in which magnetic powder is contained in a binder resin, and an image forming method in which a latent image on a latent image carrier is visualized as a toner image using the magnetic toner.

  In an image forming apparatus such as a laser printer using an electrophotographic method, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these, first, the surface of the latent image carrier is charged uniformly by a charging means. Then, after exposing by an exposure means such as a semiconductor laser or a light emitting diode to form a latent image, the latent image is developed or reversed and developed by a developing means to be visualized as a toner image. Next, the toner image is directly transferred to the surface of the printed 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 printed material such as paper, and then the fixing means. In this way, a series of image forming steps is completed.

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

  Among them, in the magnetic one-component developing method, the magnetic toner is supplied while being thinned onto a toner carrier incorporating a fixed magnet so as to face the latent image carrier, and the latent image on the latent image carrier is converted into the magnetic image. Develop with toner. In addition, as a magnetic one-component developing method, there are a developing method using a magnetic toner having conductivity and a developing method called a magnetic one-component jumping developing method using an insulating magnetic toner, and the latter magnetic one-component developing method is currently available. Jumping development methods are widely used.

  In this magnetic one-component jumping development method, first, magnetic toner is triboelectrically charged by passing through a gap between a rotating toner carrier incorporating a fixed magnet and a magnetic blade disposed close to the toner carrier. Then, a thin layer of magnetic toner is formed on the surface of the toner carrier by being supplied to the surface of the toner carrier and held by the magnetic force of a built-in fixed magnet.

  The toner carrier is opposed to the latent image carrier so as not to come into contact with the formed thin layer, and a thin film formed on the toner carrier is formed by applying an AC or DC bias voltage. The magnetic toner charged from the layer is allowed to fly to the surface of the latent image carrier, and the latent image is visualized as a toner image.

  In this magnetic one-component jumping development method, an insulating magnetic toner is used, which is impossible when a conductive toner is 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 toner carrier while holding the magnetic toner by magnetic force, and can develop the latent image in a non-contact state with the latent 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 printed portion and the margin portion.

  As the latent image carrier used in the above magnetic one-component jumping development method, various organic and inorganic electrophotographic photoreceptors can be used as in the case of other development methods. An amorphous silicon photosensitive member in which an amorphous silicon photosensitive layer is formed on the conductive substrate 21 is suitable. This amorphous silicon photoreceptor has a high durability of about 10 times or more in terms of the number of images formed, for example, compared with an organic photoreceptor 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 of that of the organic photosensitive layer. It is a result obtained from this.

  However, the biggest disadvantage of the amorphous silicon photoreceptor is its low productivity. That is, the amorphous silicon photoreceptor is manufactured by forming an amorphous silicon photosensitive layer on the surface of the conductive substrate 21 by a vapor deposition method such as a CVD method. In such a vapor deposition method, a binder resin or the like is produced. Compared to an organic photosensitive layer formed by simply applying a coating solution containing, onto a conductive substrate 21 and drying, it takes a significantly longer time to form a photosensitive layer having a predetermined thickness, and vapor phase growth. Since the method is batch-type and cannot be continuously produced, productivity is inevitably lowered.

  Therefore, using the fact that the amorphous silicon photosensitive layer is less likely to wear than the organic photosensitive layer as described above, it is common to reduce the thickness of the amorphous silicon photosensitive layer and improve the productivity of the amorphous silicon photosensitive member. It's getting on. That is, the amorphous silicon photosensitive member having a thickness of 30 μm or less, which has been about 30 to 60 μm until now, and a thin film type amorphous silicon photosensitive member has begun to spread.

  The main merit of these thin-film amorphous silicon photoconductors is, of course, superior in productivity compared to conventional ones, but further, the merit that the resolution of the formed image is improved by making the film thinner. There is also.

  Also, after the toner image is transferred to the surface of the printed material such as paper, the toner remaining on the surface of the amorphous silicon photoconductor is removed by a cleaning unit. This cleaning unit forms an image with as few movable parts as possible. In order to reduce the size of the apparatus and simplify the mechanism, an elastic blade pressed against the surface of the amorphous silicon photoreceptor is suitable.

  After the toner image is transferred to the surface of the substrate, most of the magnetic toner remaining on the surface of the amorphous silicon photoreceptor is scraped off and removed from the surface of the photoreceptor by the elastic blade. That is, a part of toner particles, magnetic powder or resin pieces as fragments thereof, or external additives such as silica added to the magnetic toner in order to improve fluidity, chargeability, etc. It stays at the pressure contact portion with the amorphous silicon photoconductor. When these accumulated substances are rubbed with the elastic blade and the amorphous silicon photosensitive member for a long period of time, a so-called charge-up that overcharges more than a predetermined charge amount occurs, and the charge amount is a limit value, that is, amorphous. When the breakdown voltage value of the silicon photosensitive layer is exceeded, discharge (single point discharge) is performed toward a very small area of the photosensitive member, and the amorphous silicon photosensitive member may be dielectrically broken to cause an irreparable defect. This discharge is mainly generated at the ridge line portion of the tip portion of the elastic blade.

  Since the amorphous silicon photosensitive member is inherently vulnerable to dielectric breakdown, the dielectric breakdown is likely to occur. Therefore, when an amorphous silicon photoconductor, an elastic blade, and a magnetic toner are used and image formation by a magnetic one-component jumping development method is repeated, abnormal discharge (single point discharge, spark discharge) occurs in a short period of time due to the above mechanism. There is a risk that the silicon photoconductor will break down and cause defects. If image formation is continued using the amorphous silicon photoreceptor in which such a defect has occurred, the carrier blocking layer is destroyed at the defective portion and cannot be charged in the charging process. There is a problem of producing sunspots.

  This problem becomes a big problem especially in the amorphous silicon photoconductor of the thin film type. That is, the occurrence of defects in the amorphous silicon photosensitive layer due to dielectric breakdown largely depends on the needle withstand voltage (V) of the photoconductor, but the thin film type amorphous silicon photoconductor has a lower withstand voltage value than usual and the film thickness becomes smaller. The thinner the film, the easier it is for defects due to dielectric breakdown.

  According to the inventors' investigation, the main cause of the charge-up causing such dielectric breakdown is the shape of magnetic powder added to the magnetic toner. The magnetic powder is currently a polyhedron such as a hexahedron (cube, cuboid) that is a convex polyhedron surrounded by six squares or an octahedron that is a convex polyhedron surrounded by eight triangles. In general, spherical magnetic powder and spherical magnetic powder are used.

  Among these, in the magnetic toner using the polyhedral magnetic powder, the magnetic toner is easily discharged from the sharp apex of the magnetic powder exposed on the surface of the toner particles and the sharp ridge line between adjacent surfaces. Even if the toner stays at the tip of the elastic blade and is rubbed for a long time, before the amorphous silicon photosensitive layer causes dielectric breakdown, the charged charge is discharged through the apex and ridgeline, and the toner particles are excessively charged. Can be prevented. Therefore, dielectric breakdown of the amorphous silicon photosensitive layer is unlikely to occur.

  However, magnetic toners using spherical magnetic powder do not have sharp apexes or ridges on the surface, so that it is difficult to release charges, and magnetic toner stays at the tip of the elastic blade and is rubbed for a long time. When charging, it tends to cause charge up. When the charge amount exceeds the withstand voltage value, the amorphous silicon photosensitive layer is dielectrically broken as described above, and minute black spots are generated in the subsequent formed image.

  Therefore, when the above-described thin film type amorphous silicon photoconductor, an elastic blade, and a magnetic toner containing a conventional spherical magnetic powder are combined, the amorphous silicon photoconductive layer is insulated in a very short time due to charge-up. There is a risk of destruction.

  For this reason, it is preferable to use a polyhedral magnetic powder in consideration only of prevention of charge-up, but this polyhedral magnetic powder has a sharp point of the magnetic powder exposed on the surface of the toner particles as described above. Charges are likely to be released from the apexes and sharp ridge lines between adjacent surfaces, and charge leakage is likely to occur. Polyhedral magnetic powder has low fluidity and poor dispersibility with respect to the binder resin, making it difficult to uniformly disperse in the binder resin. Therefore, the dispersion state of the magnetic powder in the individual toner particles tends to vary, and the ease of charging and the charge amount of the individual magnetic toners also vary.

  Therefore, the magnetic toner using the polyhedral magnetic powder is difficult to quickly rise, and the charge amount itself is low, and as a result, image defects such as a decrease in image density and occurrence of fogging are likely to occur. There's a problem. 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.

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

Patent Document 2 describes a magnetic powder having a particle shape in which each ridge line of a cube is curved. However, this magnetic powder has a curved surface as a ridgeline, and the vertices are also curved, and there are no sharp vertices or ridgelines as charge discharge points. In particular, the magnetic toner may be charged up at low temperatures and in low humidity environments, and image defects such as a decrease in image density may occur.
Japanese Patent Laid-Open No. 11-153882 Japanese Patent Laid-Open No. 9-59024

  For this reason, in the present invention, the magnetic powder is uniformly dispersed in the binder resin constituting the toner so that the chargeability and charge amount do not vary, and the charge leakage is less likely to occur and the charge amount is improved. It is excellent in both conflicting characteristics such as preventing the dielectric breakdown of the amorphous silicon photosensitive layer in a short period of time due to charge-up, preventing deterioration of image density and background fogging, A magnetic toner that can continue to form a good image for a longer period of time without fluctuation in the ease of charging and the amount of charge even in an environment that is difficult to be charged, such as a high-temperature, high-humidity environment, etc. An object is to provide an image forming method using the same.

  In order to solve the above-mentioned problem, as shown in FIG. 1, the present inventors are based on a hexahedron 1 that is a convex polyhedron surrounded by six quadrangles, and each vertex 2b and ridge line 2a of the hexahedron are curved. The use of magnetic powder 2 having a particle shape of

  The magnetic powder having the above-described particle shape does not have a sharp vertex or ridge line that easily releases charges because both the vertex and the ridge line are curved, and the vertex and ridge line of the polyhedron described in Patent Document 1 Compared with magnetic powder chamfered with a small flat surface, it is considered that leakage of electric charge can be made difficult when it is internally added to magnetic toner.

  In addition, since the magnetic powder has a curved surface at the apex and ridge line of the hexahedron as described above, it is excellent in fluidity and dispersibility with respect to the binder resin, and is uniformly dispersed in the binder resin. It is easy, and it is considered that the dispersion state of the magnetic powder in the individual toner particles can be prevented from being varied, and the ease of charging and the charge amount of the individual magnetic toner can be made uniform.

  In addition, as shown in FIG. 1, the magnetic powder has a hexahedral shape 1 as shown in FIG. 1, and the apex 2b or the ridge line 2a constituting the hexahedron 1 is a curved surface, and a portion that can be regarded as a straight line on the outer peripheral portion of the projected image. Since it has 2c, it can be made to discharge | release in a moderate ratio, without an electric charge concentrating on the vertex 2b and the ridgeline 2a.

  For this reason, it is considered that when encapsulated in magnetic toner, charge-up is unlikely to occur and the dielectric breakdown of the amorphous silicon photosensitive layer is prevented.

The present inventor also examined the volume resistivity value of the magnetic powder, and it is desirable that the value be 1.0 × 10 ³ (Ω · cm) or more and less than 1.0 × 10 ⁸ (Ω · cm). I found out. That is, even when a magnetic powder having a particle shape in which each vertex and ridge line of the hexahedron is curved on the basis of the hexahedron is used, the volume resistivity is less than 1.0 × 10 ³ (Ω · cm). As a result, electrical leakage current from the magnetic powder to the photosensitive drum is likely to occur, and even though the photosensitive drum can be prevented from being destroyed by charge-up, the amorphous silicon photosensitive layer is broken down by this leakage current, and the initial charge amount is small. In addition, the image density is low, and after the formation of a large number of images, both the charge amount and the image density may be lowered and the generation of minute black spots may occur.

On the contrary, if the volume resistivity exceeds 1.0 × 10 ⁸ (Ω · cm), the initial image density can be obtained, but the charge amount is remarkably increased after the formation of a large number of images, and the image density is lowered. At the same time, there is a tendency that a small black spot indicating that the amorphous silicon photosensitive layer is broken down due to the occurrence of ground fogging or charge-up occurs and the toner layer cannot be stably formed.

Therefore, the magnetic toner according to the present invention is a magnetic toner that develops a latent image formed by electrophotography on an amorphous silicon photoreceptor and contains magnetic powder in a binder resin,
The magnetic powder has a hexahedral shape as its basic particle shape, and each vertex and ridge line of the hexahedron is a curved surface and has a portion that can be regarded as a straight line on the outer periphery of the projected image, and an average particle diameter of 0.01 to 0. A magnetic toner having a volume resistivity of 1.0 × 10 ³ (Ω · cm) or more and less than 1.0 × 10 ⁸ (Ω · cm) at 50 μm.

  As described above, when combined with the amorphous silicon photoconductor and the magnetic toner of the present invention excellent in the effect of preventing the charge-up, the magnetic powder is uniformly dispersed in the binder resin constituting the toner, thereby facilitating charging and charging. Thin film type amorphous silicon that improves the charge amount and realizes a quick rise of the charge amount with no variation in the amount and prevents charge leakage, and improves the productivity and resolution of the formed image. While taking advantage of the photoconductor, it prevents the dielectric breakdown of the amorphous silicon photosensitive layer in a short period of time due to charge-up, is excellent in both conflicting properties, prevents image density reduction and background fogging, temperature and humidity environment In particular, even in high-temperature, high-humidity environments where charging is difficult, the ease of charging and the amount of charge remain unchanged for a longer period of time. Over and it is possible to provide an image forming method using a magnetic toner and it can continue to form a good image.

Further, in the image forming method according to the present invention using this magnetic toner, the particle shape of the magnetic powder contained in at least the binder resin is basically a hexahedron, and each vertex and ridge line of the hexahedron are curved and The projected image has a portion that can be regarded as a straight line, an average particle diameter of 0.01 to 0.50 μm, and a volume resistivity of 1.0 × 10 ³ (Ω · cm) to 1.0 × 10 ⁸ ( The magnetic toner is less than Ω · cm), and the magnetic toner is held on the surface of the rotating toner carrier with a built-in magnet and does not come into contact with the latent image carrier composed of the amorphous silicon photosensitive member. In this way, the surface is kept facing each other, the magnetic toner is allowed to fly on the surface of the amorphous silicon photosensitive member, and the latent image formed on the latent image carrier is developed with the magnetic toner.

  As described above, when the magnetic toner of the present invention is used in the image forming method, even when an elastic blade is used as a cleaning means for removing residual toner, The magnetic toner prevents dielectric breakdown of the amorphous silicon photosensitive layer in the cleaning section, and can take advantage of the advantages of the thin film type amorphous silicon photoconductor such as good productivity and improved resolution of the formed image. Thus, it is possible to provide an image forming method capable of continuously forming a good image.

  And, as the polyhedron that is the basis of the particle shape of the magnetic powder, when taking the vertex and ridge line into a curved surface shape, considering that the charges are released from the vertex and ridge line at an appropriate ratio, It is important that the particle shape is based on a hexahedron that is a convex polyhedron surrounded by six squares.

  Moreover, when the balance of an effect is considered, it is preferable that the average particle diameter of the said magnetic powder is 0.05-0.30 micrometers.

In addition, the smaller the volume resistivity value of the magnetic powder, the smaller the initial charge amount tends to be. Conversely, when the volume resistivity value is increased, the charge amount after forming a large number of images, particularly in a low temperature and low humidity test. There is a tendency to rise. For this reason, by setting the volume resistivity of the magnetic powder to 1.0 × 10 ⁴ (Ω · cm) or more and 1.0 × 10 ⁷ (Ω · cm), charge leakage in a wide range of environments In addition, it is possible to provide a magnetic toner capable of forming a good image over a longer period without causing dielectric breakdown of the amorphous silicon photosensitive layer due to charge-up.

  In consideration of imparting good magnetic properties to the magnetic toner, the magnetic powder is preferably added in an amount of 35 to 60 parts by mass with respect to 100 parts by mass of the binder resin.

  As described above, the magnetic toner according to the present invention and the image forming method using the magnetic toner are uniformly dispersed in the binder resin constituting the toner so that the chargeability and the charge amount do not vary, and the charge is not dispersed. It is excellent in both conflicting characteristics, such as preventing leakage and improving charge amount, realizing rapid rise of charge amount, and preventing dielectric breakdown of amorphous silicon photosensitive layer in a short period due to charge-up. , Prevents image density reduction and background fogging, and does not change the chargeability and charge amount even in difficult to charge environments such as temperature and humidity environments, especially high temperature and high humidity environments. A magnetic toner capable of continuously forming a good image and an image forming method using the magnetic toner can be provided.

  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. 2 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 magnetic toner, and FIG. 3 is a sectional view of a photosensitive drum 11 used in the present invention. In the drawing, around a photosensitive drum 11 made of amorphous silicon, there are a charger 12, an exposure device 13, a developing device 14 using magnetic toner according to the present invention, a transfer roll 15 as a transfer means, and a cleaning blade as a cleaning means. 16. A static elimination lamp 17 as a static elimination device is arranged along the rotation direction of the photosensitive drum 11, and a transfer material (not shown) such as paper or an OHP film is interposed between the photosensitive drum 11 and the transfer roll 15. A fixing device (not shown) is provided on the transfer material discharge path.

  As shown in FIG. 3, the amorphous silicon photosensitive member constituting the photosensitive drum 11 is 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. In addition, it may have a carrier blocking layer 20, a surface protective layer 18 and the like, and in the case of these multi-layered photosensitive layers, the total film thickness is preferably 30 μm or less. Such a thin film type amorphous silicon photoconductor is advantageous in that it is excellent in productivity and can form an image with high resolution.

  More specifically, when the film thickness of the photosensitive layer 19 exceeds 30 μm, the moving speed of the heat carrier is increased, so that the dark attenuation characteristic is deteriorated, and a latent image flow in a plane direction perpendicular to the thickness direction of the photosensitive layer 19 occurs. The resolution is reduced. Further, since the film formation time by the vapor phase growth method becomes longer, and the probability that foreign matter or the like adheres thereby increases and the yield deteriorates, the productivity of the photoreceptor decreases.

  On the other hand, if the film thickness is 30 μm or less, the occurrence of latent image flow is suppressed, so that a high-resolution image can be formed, and the film formation time is shortened and the yield is improved. Productivity is improved.

  The photosensitive layer 19 preferably has a thickness of 10 μm or more. If the film thickness is less than 10 μm, the charging ability as a photoreceptor may not be sufficiently obtained, and the laser beam for exposure may be irregularly reflected on the surface of the conductive substrate 21 to cause interference fringes in the half pattern. There is also.

  The amorphous silicon-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. it can. 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 photoconductive materials such as a-SiC, amorphous silicon-based materials such as a-SiC, a-SiO, and a-SiON. In particular, it is preferable to use a-SiC. In that case, the value of _x of Si _1-x C _x should be set to 0 <x ≦ 0.5, preferably 0.05 ≦ x ≦ 0.45. . 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.

Furthermore, when the amorphous silicon-based photosensitive layer 19 is formed by laminating a layer region (photoexcitation layer region) having an enhanced function of generating photocarriers and a layer region (carrier transporting layer region) having a function of transporting carriers. Both the photosensitivity and withstand voltage characteristics of the photoreceptor can be enhanced. At this time, in order to increase the generation efficiency of the photocarrier in the photoexcitation layer region, among the film formation conditions, (1) the film formation speed is set low, and (2) the dilution rate of the film formation component with H ₂ or He is set. It is preferable to form the film while taking measures such as increasing (3) the amount of the element to be doped is larger than that of the carrier transport layer region.

  The carrier transport layer region mainly has a role of increasing the breakdown voltage of the photosensitive layer 19 and smoothly transporting carriers injected from the photoexcitation layer region to the conductive substrate 21. In this layer region, the photoexcitation layer is also used. Carrier generation is performed by light transmitted through the region, which contributes to improvement in photosensitivity of the photoconductor.

  As described above, the thickness of the amorphous silicon-based photosensitive layer 19 is preferably 5 to 30 μm. Among them, the thickness of the light absorption obtained from the absorption coefficient of this layer with respect to light of the exposure wavelength is particularly 0.1. It is preferable to set the thickness to which 2.0 μm is added. Further, when the photosensitive layer 19 is formed by laminating the photoexcitation layer region and the carrier transport layer region as described above, it is preferable to set the thickness of the photoexcitation layer region substantially equal to the light absorption depth.

  A carrier blocking layer 20 is preferably interposed between the photosensitive layer 19 and the conductive substrate 21. The carrier blocking layer 20 prevents the carrier from being injected from the conductive substrate 21 to the photosensitive layer 19 when the surface of the photoreceptor is in contact with the magnetic toner while a bias voltage is applied during development, so that the exposed portion and the non-exposed portion are exposed. It has the function of increasing the electrostatic contrast with the part to improve the image density and reducing background fog. As the carrier blocking layer 20, an inorganic insulating layer formed of a-SiC, a-SiO, a-SiN, a-SiON, a-SiCON or the like, or polyethylene terephthalate, Parylene (registered trademark), which are insulating, respectively. It is preferable to use an organic insulating layer formed of polytetrafluoroethylene, polyimide, polyfluoroethylenepropylene, polyurethane, epoxy resin, polyester, polycarbonate, cellulose acetate resin, or the like.

  In addition, the carrier blocking layer 20 has an insulating property and good adhesion to the conductive substrate 21 and the amorphous silicon-based photosensitive layer 19, and has a characteristic that it does not cause a large change in heating during the formation of the photosensitive layer 19. Desired. In consideration of such characteristics, the carrier blocking layer 20 is preferably formed of a-SiC. In order to make the a-SiC forming the carrier blocking layer 20 insulative, the amount of C contained in the carrier blocking layer 20 may be increased as compared with the photosensitive layer 19. The thickness of the carrier blocking layer 20 is preferably from 0.01 to 5 [mu] m, more preferably from 0.1 to 3 [mu] m.

  The surface of the photosensitive layer 19 is preferably covered and protected by a surface protective layer 18 made of an organic or inorganic insulating material. As a result, it is possible to prevent the surface of the photosensitive layer 19 from being oxidized during discharge by a charging means or the like and forming an oxide film that easily adsorbs discharge products, water molecules, and the like. In addition, the withstand voltage can be improved, and the wear resistance when repeatedly used can be improved. Among them, it is preferable to use a layer made of an a-Si insulating material such as a-SiC, a-SiN, a-SiO, a-SiCO, a-SiNO, and the like. In particular, it is preferable to use a-SiC.

When a-SiC is used for the surface protective layer 18, the amount of C contained in the surface protective layer 18 may be increased as compared with the photosensitive layer 19 in the same manner as in the carrier blocking layer 20. Specifically, the x value of Si _1-x C _x is preferably 0.3 ≦ x <1.0, and more preferably 0.5 ≦ x ≦ 0.95. Since the surface protective layer 18 made of a-SiC has a high volume resistivity of 10 ¹² to 10 ¹³ Ω · cm, the photoreceptor has less potential flow in the surface direction of the surface protective layer 18. As a result, the ability to maintain the latent image is enhanced, the moisture resistance is excellent, and the effect of suppressing the occurrence of image flow due to water absorption is excellent.

  Further, the high-resistance surface protective layer 18 prevents the injection of electric charges due to the bias through the magnetic toner, enhances the potential contrast between the exposed portion and the non-exposed portion, and attracts more magnetic toner to the surface. It also has a function of increasing the density of the toner image and sufficiently increasing the image density. Moreover, background fogging can also be suppressed. Furthermore, the withstand voltage of the photoreceptor can be increased.

  Further, the surface protective layer 18 formed of an insulating material other than a-SiC continues to trap optical carriers even after image formation, and there is a possibility that the residual potential cannot be erased reliably in a normal charge removal process. However, since the surface protective layer 18 formed of a-SiC effectively blocks positive charges from the surface but relatively easily passes negative charges from the conductive substrate 21, the residual potential after image formation. Can be effectively erased by a normal static elimination process, and there is an advantage that image formation can be performed continuously.

  Moreover, the surface protective layer 18 formed of a-SiC has good adhesion to the amorphous silicon-based photosensitive layer 19 such as a-SiC, and is excellent in wear resistance, environmental resistance, and the like. There is also an advantage that stable image formation can be performed over a long period of time. The surface protective layer 18 formed of a-SiC may form a gradient in the thickness direction in the amount of C in the layer, or may contain elements such as N, O, Ge, etc. together with C to be moisture resistant. Can be further increased.

  The thickness of the surface protective layer 18 is preferably 5000 to 20000 mm or less, and more preferably 5000 to 15000 mm. When the thickness is less than 5000 mm, the pressure resistance performance against the negative current flowing from the transfer unit is deteriorated particularly when the toner image is transferred, and the surface protective layer 18 may be deteriorated at an early stage. On the other hand, when it exceeds 20000 mm, the film formation time becomes long and the productivity of the photoreceptor may be lowered.

  The charging potential of the amorphous silicon photoconductor during image formation is not particularly limited, but it is preferable to charge the surface potential to be +200 to + 500V. When the surface potential is less than +200 V, the development electric field becomes insufficient, and therefore, there is a possibility that a good identification mark having a sufficiently high image density and excellent in accuracy when read by a reading device cannot be formed. Further, when the surface potential exceeds +500 V, the charging ability is insufficient depending on the film thickness of the photosensitive layer 19 and black spots due to dielectric breakdown are likely to occur. There is a possibility that the identification mark cannot be formed. Moreover, the problem that the generation amount of ozone increases also arises. In consideration of the balance between developability and charging ability, the surface potential is preferably +200 to +300 V, even within the above range.

  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 amorphous silicon photoconductor is transferred to a printing material such as paper. As a cleaning means for removing the residual toner by cleaning, it is preferable to use an elastic blade pressed against the surface of the amorphous silicon photoreceptor. 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 amorphous silicon photoreceptor is free from pressure marks.

  As the toner carrier, those made of various known materials can be used, and it is particularly preferable to use a toner carrier made of aluminum or stainless steel (stainless steel).

  Of these, the toner carrier made of aluminum preferably has a 10-point average roughness of the surface of 5 to 10 μm. If the ten-point average roughness of the surface of the toner carrying member is less than 5 μm, the toner can be easily charged and the problem of overcharging occurs. That is, the thin layer becomes unstable, and layer unevenness at the time of installation is likely to occur, and the conveyance force is also reduced, so that the image density cannot be stably maintained and the image density is lowered. On the other hand, when the thickness exceeds 10 μm, the charge is not uniformly applied and the charge is insufficient, the image density is not stabilized, the toner layer is increased in thickness and the toner layer is disturbed by a slight impact, and random black spots are generated. May induce black spots on the image.

  In order to be able to form a good image without various image defects under a wide range of environments, the ten-point average roughness of the surface of the aluminum toner carrier is particularly 6.5 to 8. It is preferably 5 μm.

  Further, the toner carrier made of stainless steel (SUS) preferably has a 10-point average roughness of the surface of 2.5 to 8.0 μm. If the surface ten-point average roughness is less than 2.5 μm, the toner can be easily charged, resulting in the problem of overcharging. That is, it leads to destabilization of the thin layer, and the layer unevenness at the time of installation tends to occur. In addition, a decrease in conveying force causes a decrease in image density. However, stainless steel is extremely durable, so it won't be a big problem if the initial problems can be cleared.

  However, when stainless steel is used, it is difficult to earn a large Rz (ten-point average roughness) due to its hardness, and if the surface ten-point average roughness exceeds 8.0 μm, the productivity of the sleeve is extremely high. drop down. In addition, other surface parameters are affected, and for example, Sm (average interval of unevenness) becomes extremely large. That is, the charge is not uniformly applied, causing insufficient charge and lacking in image density stabilization. Further, the thickness of the toner layer increases, and the toner layer is disturbed by a slight impact to induce random black spots, and black spots appear on the image.

  The toner carrier is made of stainless steel, and in order to form a good image without various image defects under a wide range of environments while preventing these problems from occurring, the surface ten-point average roughness is in the above range. In particular, the thickness is preferably 3.5 to 5.5 μm.

  Examples of the stainless steel used for the toner carrier include stainless steel classified into SUS303, SUS304, SUS305, SUS316, and the like. SUS305 is particularly preferable because it is weak in magnetism and easy to process. The surface ten-point average roughness Rz of the toner carrier can be measured using a surface roughness measuring instrument [for example, Surfcoder SE-30D manufactured by Kosaka Laboratory Ltd.].

  In order to hold the latent image on the surface of the amorphous silicon photoconductor 11 as the latent image carrier, the surface of the photoconductor drum 11 is uniformly charged by the charger 12 using a scorotron charger or the like, as in the past. Thereafter, 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. Further, in order to transfer the toner image formed on the surface of the amorphous silicon photoconductor 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.

  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.

  The transfer roll 15 is preferably rotated with a linear velocity difference of 3 to 5% with respect to the surface of the photosensitive member in contact with the surface of the amorphous silicon photosensitive member. There is a possibility that the transferability of the toner image is deteriorated, resulting in a lack of characters and the like. .

In the image forming method of the present invention, the amorphous silicon photosensitive drum 11 as a latent image carrier, and a fixed carrier and a toner carrier (developing sleeve) on which a thin layer of magnetic toner is formed are rotated. 14 ₁ ) are opposed to each other while maintaining a distance so that the thin layer and the amorphous silicon photosensitive member do not contact each other, and the photosensitive layer 19 of the photosensitive drum 11 is uniformly charged by the charger 12, and then the exposure device 13. Then, 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 developed by a magnetic one-component jumping developer 14 using magnetic toner according to the present invention, and a toner image is formed on the surface of the photosensitive drum 11. 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.

  As described above, the magnetic powder 1 is the magnetic powder 1 having the hexahedron 2 as a basis and the apexes and ridges thereof being curved, and the average particle diameter needs to be 0.01 to 0.50 μm. It has been found that when the average particle size is less than 0.01 μm, the ratio of the magnetic powder exposed on the toner surface increases, and charges are released therefrom, leading to insufficient charging and resulting in a problem of image density reduction.

  On the other hand, in the case of magnetic powder having an average particle diameter exceeding 0.50 μm, the ratio of magnetic powder exposed on the toner surface is decreased, and the discharge of charge is reduced, leading to charge-up, resulting in the formation of a large number of images. After this, the effect of decreasing the image density and preventing the expected magnetic toner charge-up by adding magnetic powder is not obtained, and the dielectric breakdown of the amorphous silicon photosensitive layer is prevented. The problem that can not be.

  The average particle diameter of the magnetic powder is preferably 0.05 to 0.30 μm, more preferably 0.15 to 0.25 μm, even within the above range, considering the balance of effects. . The average particle size of the magnetic powder 1 is a value obtained by enlarging a photograph (magnification 10,000 times) taken with a transmission electron microscope 4 times and obtaining 300 pieces by the Martin diameter.

  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 made of magnetite is one in which each vertex and ridge line of the polyhedron are curved and have a portion that can be regarded as a straight line on the outer periphery of the projected image, and the average particle diameter is defined within the above range. However, 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 23.6 l hydroxide ^{(Fe 2+} in advance into the reaction vessel 1. Ferrous oxide containing ferrous hydroxide colloid by heating to 90 ° C. and adjusting the pH to 8-10 with a 3.4 N aqueous sodium hydroxide solution. A salt suspension is produced.

  Next, while maintaining the liquid temperature of the suspension at 90 ° C., air is blown to cause an oxidation reaction until the oxidation reaction rate of the ferrous salt reaches 60%.

  Next, an aqueous sulfuric acid solution was added to the upper suspension so that the pH was 6.5, and then air was blown into the suspension while maintaining the liquid temperature at 90 ° C. Generate.

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

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

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

  In addition, when performing the above synthesis reaction, various water-soluble metal compounds such as water-soluble silicates are added to an aqueous alkali hydroxide solution or an aqueous ferrous salt reaction solution containing ferrous hydroxide colloid, respectively. When added in a proportion of 0.1 to 10 atomic% with respect to Fe, the magnetic powder synthesized is Mn, Zn, It consists of magnetite containing at least one element selected from Ni, Cu, Al, Ti, and Si.

The ratio of the magnetic powder to 100 parts by weight of the binder resin is preferably 35 to 60 parts by weight, and more preferably 35 to 55 parts by weight. Is less than the rate that the range of the magnetic powder, because the effect of retaining a thin layer of the magnetic toner to the surface by the magnetic force of the fixed magnet incorporated in the developing sleeve 14 ₁ decreases, fogging occurs when the particular repeated image formation There is a risk. Further, if the blending proportion exceeds this range, conversely, the effect becomes stronger only for holding the thin layer of the magnetic toner to the developing sleeve 14 _first surface, the image density may decrease. In addition, since the content ratio of the binder resin is relatively reduced, there is a possibility that the fixing property of the magnetic toner on the surface of the printing material such as paper may be reduced or the durability may be reduced.

  In consideration of the good dispersion of the magnetic powder in the binder resin, the surface treatment may be performed with a surface treatment agent such as a titanium coupling agent, a silane coupling agent, an aluminum coupling agent, or various fatty acids. Good. 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 having one hydroxyl group bonded to a silicon atom, one for each siloxane unit located at the terminal, can also be used.

  As the binder resin, 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-type resin, styrene-butadiene-type resin etc. are mentioned, Polystyrene-type resin and polyester-type resin are especially preferable.

  Examples of the polystyrene resin include a styrene homopolymer, and a binary or ternary or higher 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 surface of a printed material such as paper is satisfactorily fixed by a heat fixing unit used in a normal image forming apparatus, the softening point of the polyester resin is preferably 80 to 150 ° C., and preferably 90 to 140. More preferably, it is ° C.

  Part of the binder resin preferably 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 thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cycloaliphatic type epoxy resins, and other epoxy resins and cyanate resins. 1 type or 2 types or more are mentioned.

  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 does not leave. On the other hand, when the glass transition temperature exceeds this range, the fixability to the surface of the substrate such as paper may be lowered.

  In addition, the glass transition temperature of binder resin can be calculated | required from the change point of the 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, 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 is 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 endothermic curve obtained by measuring at normal temperature and normal pressure at a rate of 10 ° C./min.

  The magnetic toner of the present invention may contain various conventionally known additives such as a colorant, a charge control agent, and a wax. 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 content of the colorant is preferably about 1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  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 in accordance with the charging polarity of the magnetic toner.

  Examples of positively chargeable charge control agents 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. 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 content of the charge control agent is preferably 0.5 to 15 parts by weight, more preferably 0.5 to 8.0 parts by weight, based on the total amount of solids forming the magnetic toner. It is particularly preferably 5 to 7.0 parts by weight. When the content ratio is less than this range, it becomes difficult to impart stable charging characteristics to the magnetic toner, and there is a possibility that the image density is lowered or the durability is lowered. In addition, since poor dispersion with respect to the binder resin is likely to occur, there is a risk that background fogging may occur, or the charge control agent aggregated without being dispersed may contaminate the photoreceptor. On the other hand, if the content ratio exceeds the above range, the magnetic toner tends to cause environmental resistance, in particular, poor charging under high temperature and high humidity, image failure, and excessive charge control agent may contaminate the photoreceptor. There is also.

  Wax improves the anti-offset property by improving the fixability of magnetic toner to the surface of the printed material such as paper, or preventing the magnetic toner during fixing from adhering to the fixing roller of the image forming apparatus. The magnetic toner adhering to the fixing roller or the like is reattached to the surface of the printing material to contaminate the image and prevent image smearing.

  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 content of the wax is preferably 1 to 5% by weight in the total amount of solids forming the magnetic toner. If the content ratio is less than this range, the effect of improving the offset property of the magnetic toner or preventing image smearing may be insufficient. Conversely, if the content ratio exceeds this range, the toners are fused. And storage stability may be reduced.

  In the magnetic 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, cooled, further pulverized, and necessary. Manufactured by classifying accordingly. Moreover, you may wet-mix said each component. The magnetic toner of the present invention thus produced preferably has a volume-based center particle size of 5 to 10 μm.

  In addition, the produced magnetic toner is improved in the surface, if necessary, for example, colloidal, in order to improve fluidity, storage stability, cleaning property indicating ease of cleaning and removing from the surface of the latent image carrier. Surface treatment may be performed with fine particles (external additive, usually having an average particle size of 1.0 μm or less) such as silica, hydrophobic silica, alumina, titanium oxide and the like. For the surface treatment, it is preferable to dry-mix the magnetic toner and the external additive. In particular, in order to prevent the external additive from being embedded in the surface of the toner particle, the magnetic toner and the external additive are mixed using a Henschel mixer or a Nauter mixer. Is preferred. The amount of the external additive added is preferably 0.2 to 10.0 parts by weight with respect to 100 parts by weight of the magnetic toner. The external additive may be surface-treated with aminosilane, silicone oil, silane coupling agent (hexamethyldisilazane, etc.), titanium coupling agent, or the like, if necessary.

  As described above, the magnetic toner of the present invention is used for image formation in combination with an amorphous silicon photoconductor. At this time, the charge amount can be easily increased quickly and the charge amount can be improved due to the above-described characteristics of the particle shape. Because it is excellent in two contradictory properties to prevent the dielectric breakdown of the amorphous silicon photosensitive layer in a short period of time due to charge-up, it forms a good image over a long period of time in a wide range of environments It is possible to achieve a unique effect that it can continue.

  The average particle size of the magnetic powder is 4 times larger than that of a magnetic powder photographed with a transmission electron microscope [JSM-880 manufactured by JEOL Ltd.] (10,000 times magnification). Asked.

The volume resistivity was measured using ULTRA HIGH RESISTANCE METER (R8340A, manufactured by Advantest). In measurement, 10 g of magnetic powder was placed in a measuring cylindrical cell having a diameter of 25 mm under a condition of a temperature of 23 ° C. and a relative humidity of 50%, and a 1 kg load was applied and the measurement was performed at an applied voltage of 10V.
[Example 1]
First, as a binder resin, among molecular weight distributions measured by gel permeation chromatography, molecular weight distribution has peaks of molecular weight 8000 and molecular weight 130500, and styrene-acrylic copolymer having a glass transition temperature Tg of 55 ° C. A polymer was used.

The magnetic powder is made of magnetite, which is Fe ₃ O ₄ (FeO · Fe ₂ O ₃ ), and the shape of the particles is a hexahedron that is a convex polyhedron surrounded by six squares, and the apexes and ridges thereof are A magnetic powder having a curved surface and an average particle diameter of 0.20 μm was used.

And 49 parts by weight of the above-mentioned binder resin, 45 parts by weight of 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 [ 3 parts by weight of 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 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 magnetic toner having a volume-based center particle size of 8.0 μm.
[Comparative Example 1]
As the magnetic powder, magnetite having the same composition as that used in Example 1 is used, the particle shape is an octahedral shape that is a convex polyhedron surrounded by eight triangles, and the apex and ridge lines are not curved, A magnetic 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 magnetic powder having an average particle size of 0.20 μm was used.
[Comparative Example 2]
As the magnetic powder, magnetite having the same composition as that used in Example 1 is used, and the shape of the particles is an octahedron that is a convex polyhedron surrounded by eight triangles, and the apexes and ridges thereof are disclosed in Patent Document 1. As seen in FIG. 6 (b), the same amount of magnetic powder having an average particle diameter of 0.20 μm chamfered by a plane smaller than each face constituting the octahedron is used, and otherwise, Example 1 Similarly, a magnetic toner having a volume-based center particle size of 8.0 μm was produced.
[Comparative Example 3]
As the magnetic powder, magnetite having the same composition as that used in Example 1 was used. The magnetic powder having a cubic shape, the apex and ridge lines of which were not curved, and an average particle size of 0.20 μm was used. Otherwise, a magnetic toner having a volume-based center particle size of 8.0 μm was produced in the same manner as in Example 1.
[Comparative Example 4]
As the magnetic powder, magnetite having the same composition as that used in Example 1 is used, and the cubic shape is formed such that the particle shape is a cubic shape and the apexes and ridgelines thereof are shown in FIG. The same amount of magnetic powder having an average particle diameter of 0.20 μm chamfered by a plane smaller than each surface to be used is used, and the magnetic particle having a volume-based center particle diameter of 8.0 μm is the same as in Example 1 except that. A toner was produced.
[Comparative Example 5]
Magnetite having the same composition as that used in Example 1 was used as the magnetic powder, and the same amount of magnetic powder having a spherical particle shape and an average particle diameter of 0.20 μm was used. Otherwise, Example 1 was used. In the same manner as described above, a magnetic toner having a volume-based center particle size of 8.0 μm was produced.

  In each of the above examples and comparative examples, 100 parts by weight of magnetic toner and 1.0 part by weight of silica [RA-200H manufactured by Nippon Aerosil Industry Co., Ltd.], titanium oxide [EC-100 manufactured by Titanium Industry Co., Ltd.] 2 After adding 0.0 parts by weight and mixing using a Henschel mixer, a magnetic single component jumping development type page printer (FS-3830N manufactured by Kyocera Mita Co., Ltd.) equipped with an amorphous silicon photoconductor as a latent image carrier. Each of the following characteristics was evaluated during image formation.

An amorphous silicon photosensitive member having a total photosensitive layer thickness of 14 μm was used, and an elastic blade made of urethane rubber was used as a cleaning means. Further, as the toner carrier, a SUS305 product having a 10-point average roughness Rz of 5.0 μm on the surface was used.
(1) Image Density After forming a standard pattern with a printing rate of 5% using the above page printer, forming an image density of the first image (initial image) and 300,000 consecutive images of ISO 4% originals The image density of the image (post-endurance image) on which a standard pattern having a printing rate of 5% was formed was measured using a Macbeth reflection densitometer [RD914 manufactured by Gretag Macbeth Co., Ltd.].
(2) Ground fog The blank area of the initial image and the post-durability image formed in (1) above was 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) State of thin layer At the time of forming the initial image and the post-endurance image, the thin layer of toner formed on the surface of the toner carrier was observed, and the state was evaluated according to the following criteria.

  A: A thin thin layer having a uniform thickness and no defects or unevenness was formed.

  Δ: A thin part and a thick part were irregularly observed, but the formed image was not affected.

X: The thin part and the thick part were seen irregularly, and the formed image was affected.
(4) Toner charge amount During initial image formation and after endurance image formation, the toner charge amount μC / g in the toner thin layer formed on the surface of the toner carrier is measured by a charge amount measuring device [TREK (TREK ) Q / M meter 210HS]
(5) Cleanability The periphery of the amorphous silicon photoconductor during image formation after endurance and the formed image were observed. At the periphery of the amorphous silicon photoconductor, the toner was caught at the pressure contact portion of the elastic blade, and the surface of the photoconductor was Investigate the presence of defects such as adhesion of toner components and paper dust, scratches on the surface of the photoconductor, etc., and inspect the presence or absence of image defects associated with cleaning defects such as black streaks in the formed image, and evaluate the cleaning performance according to the following criteria did.

  ○: No defects were observed in the periphery of the photoreceptor and the formed image.

  Δ: A defect was observed around the photoreceptor, but no defect was observed in the formed image.

X: Defects were observed around the photoreceptor, and defects were also observed in the formed image.
(6) Image quality Photo obtained by forming the same photographic original after forming 300,000 consecutive images of the first photographic image (initial image) obtained by forming an image of a photographic original and ISO 4% original using the page printer. Images (post-endurance images) were observed, and each image quality was evaluated according to the following criteria.

  ○: There was no graininess and the image was uniform and fine.

  Δ: A part of the surface had a rough feeling and lacked uniformity, but it was in a practically acceptable range.

X: The whole surface had a rough feeling and was not uniform.
(7) Small black spots Using the modified page printer, a latent image corresponding to a solid black pattern is formed on the surface of the amorphous silicon photoconductor, developed into a toner image, and this toner image is then printed on paper. The image is transported to an elastic blade without being transferred to the surface, and after 50,000 sheets are continuously collected and removed from the surface of the amorphous silicon photosensitive member by the elastic blade, a blank image is output. The number of minute sunspots was measured using an analyzer [DA-5000S manufactured by Oji Scientific Instruments Co., Ltd.]. The black spot measurement range was 5 mm × 210 mm in the A4 horizontal direction.

  ○: 0, no minute black spots.

  (Triangle | delta): Although 1-20 pieces and a small black spot generate | occur | produced, it is the marginal range of background fog and has almost no influence on a formed image.

  X: 21 to 1000, a lot of minute black spots were generated and looked like black bands, and the formed image was affected.

XX: Since 1001 or more and a lot of minute black spots were generated, measurement was stopped.
(8) Image flow Using the page printer, 5000 images of ISO 4% originals were continuously formed, and then the page printer was left in a high temperature and high humidity environment at a temperature of 35 ° C. and a relative humidity of 85% RH for 12 hours. After the state was stabilized, a halftone and character document was imaged, the image was observed, and the presence or absence of image flow was evaluated according to the following criteria.

  ○: Both halftone and characters were reproduced well, and no image flow was seen.

  Δ: A slight blur was observed in the characters, but the image flow was within an allowable range.

X: The halftone was lost, characters were flowing, and the image flow was remarkable.
(A) Normal temperature and normal humidity test The above page printer was left in a normal temperature and normal humidity environment at a temperature of 20 ° C. and a relative humidity of 65% RH for 8 hours to stabilize the state, and then the same normal temperature and normal humidity environment. Among them, the characteristics (1) to (7) were evaluated.
(B) High-temperature and high-humidity test The above page 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. Among them, the tests of (1), (2) and (3) to (8) except for the state of (3) the thin layer were conducted to evaluate the characteristics.
(C) Low temperature and low humidity test The above page printer was allowed to stand in a low temperature and low humidity environment at a temperature of 10 ° C and a relative humidity of 20% RH for 8 hours to stabilize the state, and then in the same low temperature and low humidity environment. Each test of said (1)-(7) was done and the characteristic was evaluated.

  The above results are shown in Tables 1-6. In addition, the meaning of the code | symbol of the column of the particle shape of the magnetic powder in a table | surface is as follows.

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

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

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

  Octagon: An octahedron shape whose vertices and ridge lines are not curved. Normal octahedron.

  Octahedral: An octahedron with chamfered vertices and ridges on a small plane.

  Sphere: Spherical.

From the experimental results shown in Table 1 to Table 6, the octagonal shape and the comparative example 1 using magnetic powder that does not have a curved surface at the apex and the ridgeline, and the octahedral shape, and the apex and the ridgeline are chamfered with a small plane. In each of the magnetic toners of Comparative Example 2 using the magnetic powder, the initial charge amount was small in the normal temperature and normal humidity test, the image density was low, and the background fogging occurred after the endurance. Has been confirmed to occur.

  In addition, the magnetic toner of Comparative Example 1 using a magnetic powder that has a cubic shape and the apex and ridge lines of which are not curved, and Comparative Example 4 that uses a magnetic powder that is cubic and chamfered with a small plane on the apexes and ridge lines. Similarly, in the normal temperature and normal humidity test, the initial charge amount was small, the image density was low, and the background fogging occurred after the endurance. Thus, it was confirmed that charge leakage occurred.

  In addition, it was confirmed that the magnetic toner of Comparative Example 2 was charged up due to the appearance of minute black spots, and that the amorphous silicon photosensitive layer was broken down. In the magnetic toner of Comparative Example 2, it is considered that the apex and the ridge line are chamfered by a plane smaller than each surface constituting the octahedron or the cube, and the sharp edge portion is eliminated, so that the charge cannot be discharged efficiently. .

  Further, the magnetic toner of Comparative Example 3 using spherical magnetic powder has a large initial charge amount in a normal temperature and normal humidity test, and the charge amount after durability is remarkably increased to lower the image density and cause fogging. In addition, since very small black spots were generated, it was confirmed that the dielectric breakdown of the amorphous silicon photosensitive layer was caused by the occurrence of charge-up.

On the other hand, the magnetic toner of Example 1 using the magnetic powder having a hexahedron shape and having a curved surface at the apex and the ridge line is any one of the normal temperature, normal humidity test, high temperature, high humidity test, and low temperature, low humidity test. In addition, since the charge amount and image density after the initial and endurance are almost constant, there is no background fogging, and there are no micro-spots. It was confirmed that good images can be formed over a long period of time in a wide range of environments without causing dielectric breakdown.
[Examples 2 to 5, Comparative Examples 6 and 7]
As the magnetic powder, magnetite having the same composition as that used in Example 1 is used, and the particle shape is a hexahedron shape that is a convex polyhedron surrounded by six squares, and the apexes and ridges thereof are curved. The average particle size is 0.008 μm (Comparative Example 4), 0.01 μm (Example 2), 0.05 μm (Example 3), 0.30 μm (Example 4), 0.50 μm (Example 5), A magnetic 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 the magnetic powder of 0.52 μm (Comparative Example 5) was used.

  The magnetic toner thus obtained was evaluated in the same various environments as in Example 1 using the same page printer as in Example 1. The results are shown in Tables 7 to 12 together with Example 1.

[Examples 6 to 9, Comparative Examples 8 and 9]
As the magnetic powder, magnetite having the same composition as that used in Example 1 is used, and the particle shape is a hexahedron shape that is a convex polyhedron surrounded by six squares, and the apexes and ridges thereof are curved. The volume resistivity value is 8.7 × 10 ² Ω · cm (Comparative Example 6), 4.2 × 10 ³ Ω · cm (Example 6), 6.1 × 10 ⁴ Ω · cm (Example 7). 6.8 × 10 ⁶ Ω · cm (Example 1), 2.6 × 10 ⁷ Ω · cm (Example 8), 8.9 × 10 ⁷ Ω · cm (Example 9), 3.1 × A magnetic 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 magnetic powder of 10 ⁸ Ω · cm (Comparative Example 7) was used.

  The magnetic toner thus obtained was evaluated in the same various environments as in Example 1 using the same page printer as in Example 1. The results are shown in Tables 13 to 18 together with Example 1.

As described above, the magnetic toner according to the present invention and the image forming method using the magnetic toner according to the present invention are uniformly dispersed in the binder resin constituting the toner so that the ease of charging and the charge amount vary. It does not occur, and it is difficult to cause leakage of electric charge, thereby improving the charge amount, realizing a rapid rise of the charge amount, and preventing the dielectric breakdown of the amorphous silicon photosensitive layer in a short period due to charge-up. Both of these characteristics are excellent, preventing image density reduction and background fogging, and the ease of charging and the amount of charge do not vary even in difficult-to-charge environments such as temperature and humidity environments, especially high temperature and high humidity environments. It is possible to provide a magnetic toner capable of continuing to form a good image for a longer period of time and an image forming method using the same.

  According to the present invention, it is possible to provide an image forming apparatus capable of continuously forming a good image over a long period of time using an amorphous silicon photoreceptor having high durability and a magnetic toner.

It is a schematic diagram which shows a shape of the magnetic powder of this invention. 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 photoconductive drum used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hexahedron 2a Ridge line 2b Vertex 2c Straight line part 11 Photosensitive drum 14 Developer 19 Amorphous silicon type photosensitive layer

Claims (5)

A magnetic toner that develops a latent image formed by electrophotography on an amorphous silicon photoreceptor and contains magnetic powder in a binder resin,
The magnetic powder is basically a hexahedron that is a convex polyhedron surrounded by six quadrangles, and each vertex and ridge line of the hexahedron are curved and a portion that can be regarded as a straight line on the outer periphery of the projected image. And having an average particle size of 0.01 to 0.50 μm and a volume resistivity value of 1.0 × 10 ³ (Ω · cm) or more and less than 1.0 × 10 ⁸ (Ω · cm). Magnetic toner.   The magnetic toner according to claim 1, wherein an average particle size of the magnetic powder is 0.05 to 0.30 μm. 4. The volume specific resistance value of the magnetic powder is 1.0 × 10 ⁴ (Ω · cm) or more and 1.0 × 10 ⁷ (Ω · cm). 5. The magnetic toner described in 1.   The magnetic toner according to claim 1, wherein the magnetic powder is added in an amount of 35 to 60 parts by mass with respect to 100 parts by mass of the binder resin. The particle shape of the magnetic powder contained in at least the binder resin is basically a hexahedron that is a convex polyhedron surrounded by six squares, and each vertex and ridge of the hexahedron are curved. In addition, there is a portion that can be regarded as a straight line on the outer periphery of the projected image, the average particle diameter is 0.01 to 0.50 μm, and the volume resistivity is 1.0 × 10 ³ (Ω · cm) or more and 1.0 × Having a magnetic toner that is less than 10 ⁸ (Ω · cm),
The magnetic toner has a built-in fixed magnet and is held on the surface of the rotating toner carrier. The magnetic toner is opposed to the latent image carrier made of an amorphous silicon photoconductor so as not to come into contact with the magnetic toner. An image forming method, wherein the latent image formed on the latent image carrier is developed with the magnetic toner by flying on the surface of the amorphous silicon photosensitive member.