JP2005227763A - Image forming method and magnetic one-component toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and a magnetic one-component toner for an electrostatic latent image development which can prevent an insulation destruction from occurring at the surface of a photosensor, in a development system by a magnetic one-component development method which employs an amorphous silicon photosensor of a thin layer as a latent image holder and a cleaning blade is used as a means to clean the surface of this photosensor. <P>SOLUTION: This is an image forming method by a magnetic one-component development method which employs an amorphous silicon photosensor whose film thickness is 10μm to 30μm as a latent image holder, and a cleaning blade is used as a cleaning means to remove toner from the surface of this photosensor. As a toner to develop an electrostatic latent image formed on the surface of the photosensor, a magnetic one-component toner which includes polyhedron-shaped magnetic powder whose volume resistivity is 4×10<SP>2</SP>(Ωcm) or more 1×10<SP>6</SP>(Ωcm) or less in its toner particles is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming method used in an electrophotographic method, an electrostatic recording method, an electrostatic printing method, and the like, and a dry magnetic one-component toner used therefor.

  In general, in electrophotography, electrostatic recording, etc., an electrostatic latent image formed by charging a latent image holding body made of a photoconductive photoreceptor, dielectric, etc. by corona charging, etc., and exposing it with a laser, LED, etc. Is visualized using a developer such as toner, or the electrostatic latent image is visualized by reversal development to obtain a high-quality image. Usually, toners applied in these development methods are kneaded by mixing a thermoplastic resin (binder resin) as a binder with a dye, a pigment as a charge control agent, a wax as a release agent, a magnetic material, and the like. The toner particles are pulverized and classified into toner particles having an average particle diameter of 5 to 15 μm. An inorganic fine powder such as silica or titanium oxide or an inorganic metal fine powder is externally added to the toner for the purpose of imparting fluidity to the toner, controlling charging of the toner, or improving the cleaning property.

  The dry development methods in various electrostatic copying systems currently in practical use include a two-component development system using a carrier such as toner and iron powder, and a magnetic one component containing a magnetic substance inside the toner without using a carrier. Development methods are known.

  Many developing methods for electrostatic latent images have been developed and put into practical use. For example, a number of development methods such as the magnetic brush method described in Patent Document 1, the cascade development method and the powder cloud method, and the fur brush development method described in Patent Document 2 are known. Among these, a magnetic brush method, a cascade method, and the like using a two-component developer mainly composed of toner and carrier are widely put into practical use. The method using these two-component developers can provide a relatively stable and high-quality image in the initial stage. However, when used over a long period of time, carrier deterioration occurs, that is, the spent phenomenon occurs. There are the common drawbacks that the imparting ability is lowered and a good quality image cannot be obtained over a long period of time, and the long-term durability is lacking because the mixing ratio of the toner and the carrier is difficult to keep constant.

  In order to avoid such drawbacks, various development methods using a one-component developer composed only of toner have been proposed, and among them, a magnetic one-component development method employing a magnetic toner is generally well known and utilized.

  As a developing method using a magnetic one-component toner, a developing method using a conductive magnetic toner disclosed in Patent Document 3 is known. In this method, a conductive magnetic toner is held on a cylindrical conductive developer carrier having magnetism inside, and is developed by bringing it 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 holding member and the surface of the sleeve, and electric charges are guided from the sleeve to the toner particles through this conductive path, and the electrostatic latent image The toner particles adhere to the image portion and are developed by the Coulomb force between the two. In this method, since the toner is conductive, it is difficult to electrostatically transfer the toner image on the latent image holding member to a printing medium (for example, plain paper) using an electric field, There are problems that it is difficult to obtain high image quality over a long period of time due to a trouble phenomenon derived from conductive toner in the process, and that there is a problem of electrical leakage destruction to the latent image holding member.

  A method using an insulating toner is proposed in Patent Document 4 and the like. This method is called a magnetic one-component development jumping method, and a developer carrier is provided opposite to the latent image carrier, and this developer carrier has a development sleeve containing a magnet roller. The toner is transported by the rotation of the developing sleeve, passed through the gap between the developing sleeve and the magnetic blade to form a thin toner layer, and the electrostatic latent image on the surface of the latent image holding member is developed with the charged toner. This method has advantages such as prevention of background fogging, and an excellent image can be obtained.

  Thus, by using the magnetic one-component developing method, the problem of lack of long-term durability with the two-component developer can be solved to some extent. Further, as a feature of the developing device used in such a developing method, it can be mentioned that it can have a very small and simple configuration.

  Although the present problems have been described mainly with respect to toner, background technology including an image forming apparatus will be described below. Currently, most printers have an organic photoconductor (OPC) mounted as a photoconductor, but those using amorphous silicon photoconductors (a-Si photoconductors) are also used as machines become more durable. Yes. The life of the O-PC is about 50,000 sheets, whereas the life of the a-Si photosensitive member is very durable at 500,000 sheets or more. This is because the film reduction rate on the surface of the a-Si photosensitive member is 1/100 or less of the OPC film reduction rate.

  For example, Patent Document 5 proposes an image forming method in which a cleaning blade is used as a cleaning means for a photoreceptor, a member thereof is formed of urethane rubber, and magnetic toner is used as a developer. According to this method, it is said that good cleaning can be achieved with a simple cleaning mechanism, a clear image can be formed, image defects such as fogging and image unevenness are not caused, and image density is not lowered. However, this method is not satisfactory in durability. Because the photoreceptor is an OPC drum, the surface of the soft OPC drum is easily damaged even if it is devised in terms of external additives, so that toner is embedded in the damaged photoreceptor surface and filming may occur. In other words, a defect that causes a fatal defect on the image, such as toner passing through the cleaning blade, occurs. This can also be seen from the fact that the durability evaluation of this image forming apparatus has only achieved about 150,000 sheets.

  On the other hand, the problem of using an a-Si photoconductor is that the a-Si photoconductor has a long film-forming time and the productivity is lowered, so that the cost is higher than that of OPC. Further, when the film thickness of the a-Si photosensitive member is increased, there is a problem that the image quality is deteriorated and halftone is difficult to be achieved. Therefore, the film thickness of a normal a-Si photosensitive member is 30 to 60 μm, but in recent years, in addition to the problem of cost, a thin film silicon drum of 30 μm or less is used from the viewpoint of reducing the film thickness and obtaining high resolution. Is starting to appear on the market.

  In addition, as a cleaning unit used in an image forming apparatus using an a-Si photosensitive member, there are a brush method and a blade method, but a blade method is selected in response to a compact product and a simplified mechanism. There are many things. Therefore, from the viewpoints of high durability, high resolution, and compact product, a system in which a thin film a-Si photosensitive drum and a cleaning blade are combined is often used.

  However, in an image forming apparatus using a thin-film a-Si photosensitive member and using a blade-type cleaning unit, the conventional magnetic one-component toner has a problem of abnormal images due to dielectric breakdown of the photosensitive member film. This becomes prominent when the a-Si photosensitive member is more susceptible to dielectric breakdown than OPC and has a thin film thickness. The location of dielectric breakdown is the blade ridge line (near the tip) where the drum is cleaned, and the toner accumulated there (the same toner that continues to stay, the external additive) is excessively charged by friction with the blade (overcharge) If it exceeds a certain upper limit, it is discharged at once. At that time, it is considered that the photoconductor is subjected to dielectric breakdown by one-point discharge (discharge to a very small area) toward the photoconductor. When this dielectric breakdown occurs, there is a problem that a black spot on the photoreceptor leaks, which is a defect that cannot be repaired, and the black spot appears remarkably on the image.

  On the other hand, in recent years, in the market of electrophotographic and electrostatic printing copiers and printers, the speed of printing, the miniaturization of machines, and the enhancement of durability of machine life are remarkably advanced. To achieve improved image characteristics and durability that match the printing speed by increasing the printing speed, toner with stable charging characteristics is indispensable and does not affect the steps of each process. There is a demand for a toner that has less influence on the photosensitive drum that determines the image quality.

  However, a conventional system using an a-Si photoreceptor or OPC, an electrostatic charge developer, and magnetic toner cannot sufficiently satisfy high resolution, high image quality, and high durability as described above. In other words, a system that satisfies the demands of the market has been obtained that combines toner that has stable charging characteristics over a long period of time and does not affect the process steps, and a photoreceptor that achieves long-term durability and high resolution. There is no current situation.

  For example, Patent Document 6 introduces an example in which a latent image holding member made of stacked a-Si and a magnetic one-component toner are used. According to this method, it is said that the cleaning property can be improved and a good image can be stably formed many times without an image defect caused by a cleaning defect. In this method, organic fine particles are attached (externally added) to the magnetic toner so as to act as a spacer, but the organic fine particles have a very high charging ability and immediately cause charge-up by frictional charging. As a result, in the development process, the amount of toner in the appropriate charged area is reduced, causing image defects such as a decrease in image density, fogging, and image unevenness, and it is impossible to supply a stable and beautiful image over a long period of time. Can not. In the essential photoreceptor cleaning section, the material of the cleaning blade is not clearly described. However, when an elastic blade having a simple (general) mechanism is used, as shown in FIG. As the toner 31 accumulates near the tip of the cleaning blade 32 and is triboelectrically charged, the toner 31 accumulates a charge that does not escape, and an abnormal discharge (one-point discharge, spark discharge) 34 is generated on the photosensitive member 33 at a certain time. The possibility of destroying the surface of the photosensitive drum 33 (charge generation layer, charge transfer layer) and causing a defect that cannot be repaired (only a defective image can be obtained) becomes extremely high.

Patent Document 7 proposes a toner in which the angle of repose before and after the development process is defined. This method is expected to improve the toner replenishability and the image quality in order to facilitate the handling of the waste toner, but does not mention the influence of the waste toner on the photosensitive drum of the cleaning unit. It is unlikely that it will continue to provide high image quality while maintaining high durability.
US Pat. No. 2,874,063 US Pat. No. 2,618,552 U.S. Pat. No. 3,909,258 Japanese Patent Laid-Open No. 55-18656 Japanese Patent No. 2649363 Japanese Patent No. 2713716 Japanese Patent Laid-Open No. 11-265090

  Accordingly, an object of the present invention is to provide a magnetic one-component developing system using a thin layer amorphous silicon (a-Si) photosensitive member as a latent image holding member and using a cleaning blade as means for cleaning the surface of the photosensitive member. Another object of the present invention is to provide an image forming method capable of preventing dielectric breakdown from occurring on the surface of a photoreceptor and a magnetic one-component toner used therefor.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have made the toner particles contain polyhedral magnetic powder having a specific volume resistivity in a predetermined range in the toner particles. The inventors have found a new fact that it is possible to prevent dielectric breakdown from occurring on the surface of the photoreceptor, and have completed the present invention.

  Furthermore, the present inventors have adjusted the toner loose apparent density, that is, the fluidity of the toner to a predetermined range in the above development system, and the conductive metal oxide contained in the toner removed from the surface of the photoreceptor. The present inventors have completed the present invention by finding a new fact that it is possible to more reliably prevent dielectric breakdown from occurring on the surface of the photoreceptor by increasing the content of fine particles at a predetermined ratio compared to unused toner. It came to.

That is, the image forming method and the magnetic one-component toner of the present invention have the following configurations.
(1) An image forming method based on a magnetic one-component developing system using an amorphous silicon photoconductor having a film thickness of 10 μm to 30 μm as a latent image holding member and using a cleaning blade as a cleaning unit for removing toner from the surface of the photoconductor. As a toner for developing the electrostatic latent image formed on the surface of the photoreceptor, a polyhedron having a volume resistivity of 4 × 10 ² (Ω · cm) to 1 × 10 ⁶ (Ω · cm) in the toner particles. An image forming method using a magnetic one-component toner containing magnetic powder having a shape.
(2) The unused toner for developing the electrostatic latent image formed on the surface of the photoreceptor is externally added with at least one kind of conductive metal oxide fine particles. Image forming method.
(3) The unused toner for developing the electrostatic latent image formed on the surface of the photoreceptor has a loose apparent density (AD) adjusted to 0.490 g / cm ³ or more and 0.650 g / cm ³ or less, (2) The image forming method according to (2), wherein the waste toner removed from the surface of the photosensitive member contains conductive metal oxide fine particles in an amount satisfying the following formula (1).
[However, in the formula (1), the detection intensity (waste toner) means the detection intensity by the fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the waste toner. “Toner” indicates the intensity detected by fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the unused toner. ]
(4) A magnetic one-component toner used in a magnetic one-component developing system using an amorphous silicon photoconductor having a film thickness of 10 μm to 30 μm as a latent image holding member and using a cleaning blade as a cleaning means for removing toner from the surface of the photoconductor. The toner particles contain a polyhedral magnetic powder having a volume resistivity of 4 × 10 ² (Ω · cm) to 1 × 10 ⁶ (Ω · cm). Magnetic one component toner.
(5) The magnetic one-component toner according to (4), wherein at least one or more kinds of conductive metal oxide fine particles are externally added to the toner particles.
(6) The loose apparent density (AD) is 0.490 g / cm ³ or more and 0.650 g / cm ³ or less, and the conductivity contained in the waste toner removed from the surface of the photoreceptor by the cleaning blade at the time of the external addition. The magnetic single component according to (5), wherein the conductive metal oxide fine particles and the toner particles are stirred and mixed so that the content of the metal oxide fine particles satisfies the following formula (1): toner.
[However, in the formula (1), the detection intensity (waste toner) means the detection intensity by the fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the waste toner. “Toner” indicates the intensity detected by fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the unused toner. ]

  According to the inventions of (1) and (4), as the toner used in the development system, magnetic one-component toner containing magnetic powder having a polyhedral shape is used in the toner particles, so that the vicinity of the tip of the cleaning blade is used. When the toner accumulated in the toner rubs against the tip of the blade, the magnetic powder existing in the vicinity of the surface of the toner particles passes through the magnetic powder before reaching the potential at which the a-Si photosensitive drum causes dielectric breakdown. Therefore, it is possible to cause corona discharge at a low voltage, so that it is possible to prevent dielectric breakdown of the surface of the photoreceptor due to overcharging of the toner. That is, as compared with the spherical magnetic powder, the polyhedral magnetic powder used in the present invention can be gradually discharged from the protruding vertex because the vertex of the polyhedron is likely to protrude from the surface of the toner particles, Moreover, since it is a polyhedron, it is easily held in the toner particles (it is difficult to fall off). As a result, a clear image free from abnormalities such as black spots can be obtained. Furthermore, by preventing dielectric breakdown, it is possible to extend the life of the photoreceptor and reduce the cost. As described above, according to the present invention, it is possible to provide an image forming method and a magnetic one-component toner that can cope with high resolution, high image quality, high durability, and high speed.

  According to the inventions (2) and (5), at least one or more kinds of conductive metal oxide fine particles are externally added to control toner charging, toner fluidity, storage stability, cleaning properties, and the like. be able to. Further, these controls become more effective when fine particles such as colloidal silica and hydrophobic silica are used together with conductive metal oxide fine particles.

  According to the inventions of (3) and (6), the toner is suppressed from being frictionally charged by adjusting the fluidity of the toner to a predetermined range. In addition, when externally adding conductive metal oxide fine particles, by appropriately adjusting the stirring and mixing conditions such as the stirring and mixing time and the stirring speed during external addition so that many fine particles are not embedded excessively on the toner surface, The amount of conductive metal oxide fine particles (floating external additive) not firmly supported on the toner surface is adjusted. A part of this floating external additive remains on the surface of the photoconductor without being transferred together with the toner image when the toner image formed on the surface of the photoconductor is transferred to the transfer body or printing paper, and is discarded. The toner is conveyed to the cleaning blade together with the toner.

  As a result, the content of the conductive metal oxide fine particles contained in the waste toner is larger than that in the unused toner. Many conductive metal oxide fine particles conveyed to the cleaning blade in this way are interposed as spacers between the cleaning blade and the surface of the toner collected near the tip of the cleaning blade, so that the friction between the toner and the cleaning blade It becomes possible to suppress charging. Furthermore, since the conductive metal oxide fine particles have a lower electrical resistance than the toner, they function as a leak site for releasing electric charge, so that the electric charge is gradually released from the toner accumulated near the tip of the cleaning blade and overcharged. Can be prevented. As a result, it is possible to prevent dielectric breakdown of the surface of the photoreceptor due to overcharging of the toner, so that a clear image free from abnormalities such as black spots can be obtained. Furthermore, by preventing dielectric breakdown, it is possible to extend the life of the photoreceptor and reduce the cost.

  As described above, according to the present invention, it is possible to provide an image forming method and a magnetic one-component toner that can prevent dielectric breakdown from occurring on the surface of the photoreceptor and can cope with high resolution, high image quality, high durability, and high speed. .

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing the periphery of a photoreceptor of an image forming apparatus used in the image forming method of the present invention. This image forming apparatus includes a developing system based on a magnetic one-component developing jumping method, and uses a positively charged amorphous silicon (a-Si) photosensitive drum 11 as a latent image holding member. Around the a-Si photosensitive drum 11, a scorotron charger 12, an exposure body 13, a developing device 14, a transfer roller 15, a cleaning blade (cleaning means) 16 and a charge eliminating lamp (erase means) 17 are arranged.

  In this image forming apparatus, an a-Si photosensitive drum 11 is charged by a scorotron charger 12 and exposed to an optical signal converted based on print data to form an electrostatic latent image on the photosensitive drum 11. On the other hand, in the developing device 14, toner is conveyed by rotation of a developing sleeve 14a (developer carrying member) which is disposed opposite to the photosensitive drum 11 and has a magnet roller (not shown) therein. A thin toner layer is formed on the surface of the developing sleeve 14a by passing between a blade (not shown) and the developing sleeve. Then, toner is supplied from the thin toner layer onto the photosensitive drum 11, and the electrostatic latent image formed on the photosensitive drum 11 is developed.

  The developed toner image is transferred to a transfer material (printing paper or the like) by the transfer roller 15. On the other hand, the toner (waste toner) remaining on the surface of the photosensitive drum 11 without being transferred to the transfer material is removed by the cleaning blade 16. The waste toner temporarily stays near the tip of the cleaning blade 16 and is gradually pushed out by the subsequent waste toner so as to move toward a conveying member such as a screw roller (not shown) to a waste toner container (not shown). Be transported. Afterimage charges are removed from the surface of the photosensitive drum 11 from which the waste toner has been removed by the charge eliminating lamp 17.

  FIG. 2 is an enlarged cross-sectional view in which a part of the a-Si photosensitive drum 11 is enlarged. As shown in FIG. 2, it is preferable to use a photosensitive drum 11 having a plurality of layers in which a carrier blocking layer 20, a photosensitive layer 19, and a surface protective layer 18 are laminated on a conductive substrate 21. .

  In the present invention, unlike the conventional a-Si photosensitive drum, a thin-film a-Si photosensitive drum 11 is used. The film thickness of the photoreceptor 11 is 30 μm or less, preferably 10 to 30 μm. Here, in the present embodiment, the film thickness of the a-Si photosensitive drum 11 is the thickness from the surface of the conductive substrate 21 as a base material to the surface of the photosensitive drum 11, that is, the carrier blocking layer 20 and the photosensitive layer 19. And the total thickness of the surface protective layer 18.

  When the film thickness of the photoconductor drum 11 exceeds 30 μm, the moving speed of the heat carrier is increased, so that the dark decay characteristic (charge holding capacity per time of the photoconductive layer in the dark place) is deteriorated, and as a result, the surface of the photoconductor In this case, the latent image tends to flow in the direction of rotation of the photoconductor, which causes a decrease in resolution. It is known that not only the a-Si photosensitive member but also an organic photosensitive member (OPC), the resolution is improved as the photosensitive member is thinner. In terms of cost, the longer the film thickness of the photoconductor, the longer the film formation time, and the higher the probability of adhesion of foreign substances and the lower the yield. Therefore, the lower the total film thickness of the photoconductor, the lower the cost and the more stable the quality. To do. On the other hand, when the film thickness of the photosensitive drum 11 is less than 10 μm, there is a possibility that the charging ability as the photosensitive member is lowered and it is difficult to obtain a predetermined surface potential. Further, the laser beam is irregularly reflected on the surface of the conductive substrate 21, which may cause a problem that interference fringes are generated in the half pattern. Therefore, the film thickness of the photosensitive drum 11 is preferably in the range of 10 to 30 μm from the viewpoints of charging capability, pressure resistance, dark decay characteristics, manufacturing cost, and quality.

  As a more preferable embodiment of the photosensitive drum 11, the thickness of the surface protective layer 18 is 20000 mm or less, preferably 5000 to 15000 mm. When the thickness of the surface protective layer 18 is less than 5000 mm, the pressure resistance characteristic against the negative current flowing from the transfer roller 15 is lowered, and as a result, the SiC layer may be deteriorated at an early stage of 15000 sheets or less. On the other hand, when the thickness of the surface protective layer 18 exceeds 15000 mm, the film formation time becomes long, which is disadvantageous in terms of cost. Therefore, the thickness of the surface protective layer 18 is preferably in the range of 5000 to 15000 mm from the balance of charging ability, wear resistance, environmental resistance and film formation time.

  FIG. 3 is a graph showing the relationship between the film thickness of the photosensitive drum and the needle pressure resistance. As shown in FIG. 3, the breakdown voltage increases as the film thickness increases, and the breakdown voltage decreases as the film thickness decreases. Thus, the generation of black spots due to dielectric breakdown on the surface of the photoreceptor is largely dependent on the film thickness of the photoreceptor. Therefore, in the development system using the photosensitive drum 11 having a thin film thickness of 30 μm or less, there is a high possibility that dielectric breakdown occurs even at a low voltage. Therefore, the image forming method of the present invention that can prevent overcharging is particularly effective.

  The material (photosensitive layer material) constituting the photosensitive layer 19 is not particularly limited as long as it is amorphous silicon (a-Si). Preferable materials include inorganic materials such as a-Si, a-SiC, a-SiO, and a-SiON. Among these materials, a-Si is particularly suitable as a photosensitive layer material in the present embodiment in that it has a high resistance and a higher charging ability, abrasion resistance and environmental resistance can be obtained.

Moreover, when using a-SiC, it is good to use the thing of the ratio of Si and C (carbon) in a predetermined range. As such a-SiC, a-Si _1-X C _X (value of X is less than 0.3 to ₁ ), preferably a-Si _1-X C _X (value of X is 0.5 to 0). Less than .95). A-SiC in which the ratio of Si to C is in the above range has a particularly high resistance of 10 ¹² to 10 ¹³ Ωcm, and the flow of latent image charges in the direction of the photoconductor on the surface of the photoconductor is small. Excellent maintenance ability and moisture resistance.

In general, OPC has a surface resistance of the order of 10 ¹³ Ω / □, which is higher than the surface resistance of the a-Si photosensitive member (10 ⁸ Ω / □ order) and is difficult to break down. The a-Si photoreceptor is superior in wear resistance to OPC. Therefore, by using the image forming method of the present invention that can prevent overcharging in a development system using an a-Si photosensitive member, both prevention of dielectric breakdown and improvement of wear resistance can be achieved.

  The surface potential (charging potential) of the a-Si photosensitive drum 11 is in the range of +200 to + 500V, preferably in the range of +200 to + 300V. If the surface potential is less than +200, the developing electric field is insufficient and it is difficult to ensure the image density. On the other hand, when the surface potential exceeds +500, depending on the film thickness of the photosensitive drum 11, there is a problem that charging ability is insufficient, black spots due to dielectric breakdown are likely to occur, and the amount of ozone generated increases. In particular, when the film thickness of the photoconductor 11 is reduced, the charging ability of the photoconductor drum 11 tends to decrease correspondingly. Therefore, the surface potential of the surface of the a-Si photosensitive drum 11 is preferably in the above range from the viewpoint of the balance between the developing property and the charging ability of the photosensitive member.

  In the conventional image forming method, when the linear velocity of the photosensitive drum is increased, the toner is easily triboelectrically charged, so that dielectric breakdown is likely to occur. However, according to the present invention, when the linear velocity is high, for example, 400 to 500 mm / Even in the case of a large second, it is possible to suppress dielectric breakdown.

  The developing sleeve 14a preferably has a ten-point average roughness Rz of 2.0 μm or more and 6.0 μm or less on the surface thereof. When the ten-point average roughness Rz is less than 2.0 μm, there is a possibility that the image density is lowered due to a decrease in toner conveying force. When Rz exceeds 6.0 μm, the image quality is deteriorated, and a leak from the protrusion on the surface of the sleeve 14a to the photosensitive drum 11 may occur, resulting in an image black spot and impairing the image quality. The ten-point average roughness Rz can be measured using, for example, a surface roughness measuring instrument “Surfcoder SE-30D” manufactured by Kosaka Laboratory.

  As a material used for the developing sleeve 14a, for example, aluminum, stainless steel (SUS), or the like can be used. In consideration of high durability, it is preferable to use SUS as a sleeve material, and for example, SUS303, SUS304, SUS305, SUS316 or the like can be used. In particular, it is more preferable to use SUS305 having weak magnetism and easy to process.

  The scorotron charger 12 includes a shield case, a corona wire, a grid, and the like. The charging width is 10 to 13 mm in the circumferential direction, 240 to 245 mm in the drum axis direction, and the distance between the corona wire and the grid is 5.3 to 3. It is preferable to set it to 6.3 mm. The distance between the grid and the photosensitive drum 11 is preferably 0.4 to 0.8 mm. When this distance is less than 0.4 mm, spark discharge may occur, and when it exceeds 0.8 mm, there is a problem that charging ability is lowered.

  The transfer roller 15 is in contact with the photosensitive drum 11, and is preferably driven to rotate at a linear speed difference of 3 to 5% with respect to the photosensitive drum 11. If this linear velocity difference is less than 3%, the transferability may be reduced, and there is a possibility that hollowing out may occur. On the other hand, if the linear velocity difference exceeds 5%, the slip between the transfer roll 15 and the photosensitive drum 11 becomes large and jitter. May increase.

  The material used for the transfer roller 15 is preferably foamed EPDM (ethylene-propylene-diene terpolymer foam). By using the foam in this manner, the toner contaminated in the case of a paper jam or the like enters the foamed bubbles, so that after the operation is resumed, the first paper can be prevented from being soiled. In addition, by using a foam material, it is not necessary to clean the transfer roller 15, and the cost can be reduced. The rubber hardness of the transfer roller 15 is preferably 35 ° ± 5 ° (Asuka C: Japan Rubber Association standard “SRIS-0101C type”). If the rubber hardness is less than 30 °, transfer failure occurs. If the rubber hardness is greater than 40 °, the nip with the photosensitive drum 11 becomes small, and the conveying force decreases.

  In this embodiment, a cleaning blade 16 is used as a cleaning unit for the surface of the photosensitive drum 11. The cleaning blade 16 is disposed downstream of the transfer roller 15 in the rotation direction of the photosensitive drum 11, and the tip of the cleaning blade 16 is in contact with the photosensitive drum 11. Thereby, waste toner remaining on the surface of the photosensitive drum 11 without being transferred to the transfer material can be removed.

  The cleaning blade 16 is preferably an elastic blade having elasticity. Thereby, it is possible to prevent the surface of the photosensitive drum 11 from being damaged. Examples of the elastic material include urethane rubber, silicone rubber, and elastic resin. The cleaning blade 16 is obtained by forming the elastic material into a blade shape or attaching an elastic material to the tip of a blade such as metal.

<Magnetic one component toner>
Next, the magnetic one-component toner of the present invention used in the above developing system will be described. The magnetic one-component toner is prepared by mixing a binder resin, magnetic powder, various toner compounding agents such as a colorant, a charge suppressing agent, and wax, and melt-kneading using a kneader such as an extruder. This is obtained by cooling, pulverizing and classifying. In addition, it is preferable to externally add at least one kind of conductive metal oxide fine particles to the toner particles. This magnetic one-component toner is used as a one-component developer for developing an electrostatic latent image formed on the surface of a photoreceptor. The volume average particle diameter of the toner particles is 5 to 15 μm, preferably about 5 to 10 μm.

  As the magnetic powder, conventionally known ones can be used. For example, ferrite, magnetite and other iron, cobalt, nickel and other metals or alloys exhibiting ferromagnetism, compounds containing these elements, or ferromagnetism An alloy that does not contain an element but becomes ferromagnetic when subjected to an appropriate heat treatment, chromium dioxide, or the like can be given. These magnetic powders may be fine powders having a volume average particle size of 0.1 to 1 μm, preferably 0.1 to 0.5 μm, and are uniformly dispersed in the toner particles described above. The magnetic powder can be used after being subjected to a surface treatment with a surface treatment agent such as a titanium coupling agent or a silane coupling agent.

In the present invention, the volume resistivity of the magnetic powder is 4 × 10 ² (Ω · cm) or more and 1 × 10 ⁶ (Ω · cm) or less, preferably 6 × 10 ² to 1 × 10 ⁵ . When the volume resistivity is less than 4 × 10 ² (Ω · cm), there is a possibility that the durability is lowered and the image density is lowered at high temperature and high humidity. On the other hand, if the volume resistivity exceeds 1 × 10 ⁶ (Ω · cm), the discharge effect of the magnetic powder may not be sufficiently obtained.

  The magnetic powder in the present invention is further characterized in shape, and the shape is not a spherical shape but a polyhedron such as a tetrahedron, a hexahedron, an octahedron, a 10-hedron, a dodecahedron having an edge, preferably It should be a hexahedron or an octahedron, more preferably an octahedron. Since the octahedron has a sharp apex, a larger discharge effect can be obtained. It is preferable that at least one vertex of the polyhedron protrudes (exposes) from the surface of the toner particles.

  In the measurement of the particle size and the shape of the magnetic powder, for example, transmission electron microscope (TEM) H-700H, H-800, H-7500 (all manufactured by Hitachi, Ltd.) or scanning electron microscope (SEM) S- Using 800 or S-4700 (both manufactured by Hitachi, Ltd.), images can be taken at 20000 to 200,000 times, and can be observed at an arbitrary magnification as a printing magnification of 1 to 10 times.

  FIG. 4 is an enlarged image of the toner particle surface according to the present invention by SEM, and FIG. 5 is an enlarged image of the conventional toner particle surface containing spherical magnetic powder by SEM. As shown in FIG. 4, many portions where the apex of the polyhedron protrudes are seen on the surface of the toner particles containing the polyhedral magnetic powder. On the other hand, as shown in FIG. 5, almost no protrusion of the magnetic powder is observed on the surface of the toner particles containing the spherical magnetic powder.

  The magnetic powder is contained in the toner particles in an amount of 40 to 60% by mass, preferably 45 to 55% by mass. Thereby, the electric charge can be more effectively discharged from the apex of the magnetic powder before the potential of the toner accumulated near the tip of the cleaning blade reaches the dielectric breakdown potential of the photosensitive member due to frictional charging with the blade. If the magnetic powder is used in a larger amount than the above range, the durability of the image density is lowered and the fixability tends to be extremely lowered. As more magnetic powder is added, the effect of preventing the dielectric breakdown of the photoreceptor is improved, but as described above, the fixing property is greatly lowered. If the amount is less than the above range, fog in the image density durability is likely to occur, and the conductivity of the toner particles is lowered, and the dielectric breakdown of the photosensitive member is likely to occur. In addition, since the magnetic powder has an effect of stably forming a thin toner layer on the developing sleeve, a stable thin toner layer cannot be formed when the amount of magnetic powder is small.

As the conductive metal oxide fine particles added to the toner, fine particles such as titanium oxide, alumina, and zinc oxide can be used. The conductive metal oxide fine particles may be externally added in the range of 0.3 to 3% by mass, preferably 0.5 to 2.0% by mass with respect to the toner particles. The volume average particle diameter of the conductive metal oxide fine particles is 1 μm or less, preferably 0.1 to 0.8 μm. The volume resistivity value of the conductive metal oxide fine particles is preferably 10 ⁰ to 10 ⁷ Ω · cm.

  In addition to the conductive metal oxide fine particles described above, fine particles such as colloidal silica and hydrophobic silica may be externally added to the toner particles as necessary. These fine particles are preferably added in an amount of 0.2 to 10% by mass based on the toner particles. Further, the volume average particle size of these fine particles is 1 μm or less, preferably 0.02 to 0.5 μm.

  By externally adding the conductive metal oxide fine particles and, if necessary, fine particles such as silica to the toner particles, the fluidity, storage stability, cleaning properties, and the like of the toner can be controlled. For example, in order to improve the fluidity of the toner, the external addition amount of a fluidizing agent such as colloidal silica, hydrophobic silica, or alumina is increased, and the external addition amount of a polishing agent such as titanium oxide or alumina is within a predetermined range. What is necessary is just to adjust, to adjust the kind, shape, etc. of these external additives, or to combine these methods effectively.

In the magnetic one-component toner of the present invention, the loose apparent density (AD) is adjusted to 0.490 g / cm ³ or more and 0.650 g / cm ³ or less by adding the external additive to the toner particles. preferable. The loose apparent density (AD) is an index representing the fluidity of the toner. The smaller the AD, the lower the fluidity, and the larger the AD, the higher the fluidity. When AD is less than 0.490 g / cm ³ , the fluidity is lowered and the toner is easily charged up. On the other hand, if the AD exceeds 0.650 g / cm ³ , the fluidity becomes too high, and the toner slips through the cleaning blade, resulting in poor cleaning, or erroneous detection of the toner amount detection sensor in the developing unit. Or the toner charge amount decreases and the image density decreases.

  The loose apparent density (AD) is measured as follows. First, about 40 g of toner left in an environment of 23 ° C./60% RH for 24 hours is placed on a sieve, the toner is dropped while sweeping the entire surface of the sieve with a brush, and the toner is filled in the receiver over about 60 seconds. Thereafter, the toner is further dropped into the receiver, and the process ends after 90 seconds. Next, the toner piled up above the upper end of the receiver is quickly scraped off along the upper end of the receiver with a spatula. Next, the toner weight is weighed, and the loose apparent density is calculated using the following equation. In addition, as a measuring instrument used for this measurement, the thing according to the bulk measuring instrument described in JIS K5101 is used.

  The stirring and mixing device for externally adding the external additive to the toner particles is not particularly limited as long as the toner particles and the external additive can be stirred and mixed in a dry manner. For example, a Henschel mixer, a Nauter mixer, or the like is used. be able to. When external additives such as conductive metal oxide fine particles are externally added using these apparatuses, the conductive metal oxide in the waste toner removed from the surface of the photoreceptor 11 by the cleaning blade 16 in the above-described development system. It is necessary to stir and mix the conductive metal oxide fine particles with the toner particles so that the content of the fine particles satisfies the following formula (1).

  That is, when externally adding the conductive metal oxide fine particles, agitation and mixing conditions such as agitation and mixing time and agitation speed at the time of external addition so that many conductive metal oxide fine particles are not embedded excessively on the surface of the toner particles. Is adjusted moderately to adjust the amount of conductive metal oxide fine particles (floating external additive) not firmly supported on the surface of the toner particles. The amount of the floating external additive may be appropriately set according to the type and particle size of the conductive metal oxide fine particles used so as to satisfy the above formula (1).

  A part of the floating external additive remains on the surface of the photoconductor without being transferred together with the toner image formed on the surface of the photoconductor 11 and is transported to the cleaning blade 16 together with the waste toner. The content of the conductive metal oxide fine particles contained can be larger than that of the unused toner. Many conductive metal oxide fine particles transported to the cleaning blade 16 in this way can be interposed as spacers between the cleaning blade 16 and the toner surface collected near the tip of the cleaning blade 16. It is possible to suppress frictional charging between the cleaning blade 16 and the cleaning blade 16. Furthermore, since the conductive metal oxide fine particles have a lower electrical resistance than the toner particles, they function as leak sites for releasing electric charges, so that the electric charges are gradually released from the toner accumulated near the tip of the cleaning blade 16 and overcharged. Can be prevented. Thereby, it is possible to prevent discharge to the photoreceptor due to overcharging of the toner, and to prevent dielectric breakdown of the photoreceptor surface.

  On the other hand, when the conductive metal oxide fine particles are excessively embedded in the toner particles, the above-described effects cannot be obtained sufficiently. Further, the surface of the toner particles may be exposed, and charging aggregation may occur due to frictional charging between the toner particles, and the effect of the fluidizing agent may be lost.

  The detection intensity of the conductive metal oxide fine particles is measured, for example, as follows. First, about 5 mg each of unused toner and waste toner is weighed and formed into pellets having a diameter of about 5 cm with a press machine, and then using a fluorescent X-ray analyzer (for example, Model 3270 manufactured by Rigaku Corporation) The detected intensity data of the inorganic metal elements constituting the conductive metal oxide fine particles are respectively measured. X-ray fluorescence was measured at a voltage of 50 kV and a current of 50 mA using Rh as a target. Lithium fluoride was used as the spectroscopic crystal, and a proportional counter was used as the detector. The amount of titanium oxide contained in the toner can also be measured using the above fluorescent X-ray analysis. Specifically, since the amount of fluorescent X-rays derived from titanium element can be measured, the amount of titanium oxide can be determined.

  The material of the binder resin constituting the toner particles is not particularly limited. For example, styrene resin, acrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, polyvinyl chloride It is preferable to use thermoplastic resins such as resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, styrene-butadiene resins.

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

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

  Further, as the divalent or trivalent or higher carboxylic acid component, divalent or trivalent carboxylic acid, this acid anhydride or this lower alkyl ester is used, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid. Phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, Divalent carboxylic acids such as alkyl or alkenyl succinic acid such as n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid; , 4-Benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalene Recarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, Examples include trivalent or higher carboxylic acids such as 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empole trimer acid. Is done. Moreover, it is preferable that the softening point of a polyester-type resin is 80-150 degreeC, More preferably, it is 90-140 degreeC.

  Further, the binder resin may be a thermosetting resin. By introducing a partially crosslinked structure in this way, it is possible to further improve the storage stability, form retention, durability, etc. of the toner without deteriorating the fixability. Therefore, it is not necessary to use 100% of the thermoplastic resin as the binder resin, and a crosslinking agent may be added or a part of the thermosetting resin may be used.

  As the thermosetting resin, an epoxy resin, a cyanate resin, or the like can be used. Specifically, one or a combination of two or more of bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, cyanate resin, etc. Is mentioned.

  In the present invention, the glass transition point (Tg) of the binder resin is 50 to 65 ° C., preferably 50 to 60 ° C. When the glass transition point is lower than the above range, the obtained toners are fused with each other in the developing unit, and the storage stability may be lowered. Further, since the resin strength is low, there is a tendency that toner adheres to the photoreceptor. On the other hand, if the glass transition point is higher than the above range, the low-temperature fixability of the toner may be lowered. The glass transition point of the binder resin can be determined from the change point of specific heat using a differential scanning calorimeter (DSC). Specifically, it can be obtained by measuring an endothermic curve using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. In this case, put 10 mg of the measurement sample in an aluminum pan, use an empty aluminum pan as a reference, perform measurement at room temperature and humidity at a measurement temperature range of 25 to 200 ° C, and a temperature increase rate of 10 ° C / min. The glass transition point is obtained from the obtained endothermic curve.

  In the toner of the present invention, a pigment such as carbon black or a dye such as Acid Violet can be dispersed in the binder resin as a colorant in order to adjust the color tone, as in the known toner. Such a colorant is usually blended in an amount of 1 to 10 parts by mass per 100 parts by mass of the binder resin.

  Charge control agents are blended to remarkably improve the charge level and charge rise characteristics (an indicator of whether to charge to a constant charge level in a short time), and to obtain characteristics such as durability and stability. It is. That is, when the toner is positively charged for development, a positively chargeable charge control agent is added. When the toner is negatively charged for development, a negatively chargeable charge control agent is added.

  Such a charge control agent is not particularly limited. For example, specific examples of a positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4- Triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxa Azine compounds such as triazine, phthalazine, quinazoline, quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azin Light Brown GR, Azin-Kuklin BH / C, Azin-Dip Black EW and Ajindive Direct dyes composed of azine compounds such as rack 3RL; Nigrosine compounds such as nigrosine, nigrosine salts and nigrosine derivatives; acid dyes composed of nigrosine compounds such as nigrosine BK, nigrosine NB and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxyl Quaternary ammonium salts such as benzylamine, alkylamide, benzylmethylhexyldecylammonium and decyltrimethylammonium chloride, which may be used alone or in combination of two or more. It can also be used. In particular, the nigrosine compound is optimal for use as a positively chargeable toner from the viewpoint of obtaining a quicker start-up property.

  Further, a quaternary ammonium salt, a carboxylate, or a resin or oligomer having a carboxyl group as a functional group can also be used as a positively chargeable charge control agent. Specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylate Styrene 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 types or more, such as a styrene-acrylic resin having a carboxyl group and a polyester resin having a carboxyl group.

  In particular, a styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group is optimal from the viewpoint that the charge amount can be easily adjusted to a value within a desired range. In this case, preferred acrylic comonomers to be copolymerized with the styrene unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, Examples include (meth) acrylic acid alkyl esters such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate. As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate through a quaternization step is used. Examples of the derived dialkylaminoalkyl (meth) acrylate include di (amino) ethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like ( Lower alkyl) aminoethyl (meth) acrylate; dimethylmethacrylamide, dimethylaminopropylmethacrylamide are preferred. Further, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  For example, organometallic complexes and chelate compounds are effective as charge control agents exhibiting negative chargeability, such as aluminum acetylacetonate, iron (II) acetylacetonate, chromium 3,5-di-tert-butylsalicylate. In particular, acetylacetone metal complexes, salicylic acid metal complexes or salts are preferable, and salicylic acid metal complexes or salicylic acid metal salts are particularly preferable.

  The positively or negatively chargeable charge control agent described above may be contained in the toner in an amount of 1.5 to 15 parts by weight, preferably 2.0 to 8.0 parts by weight, more preferably 3.0 to 7.0 parts by weight (of the toner). The total amount is 100 parts by mass). If the amount of charge control agent added is less than the above range, it tends to be difficult to stably charge the toner to a predetermined polarity. When an electrostatic latent image is developed using this toner to form an image, the image density tends to decrease or the durability of the image density tends to decrease. In addition, the charge control agent tends to be poorly dispersed, causing so-called fogging, and the contamination of the photoconductor tends to be severe. On the other hand, if the charge control agent is used in a larger amount than the above range, environmental resistance, in particular, poor charging under high temperature and high humidity, poor image, etc., tend to cause defects such as photoconductor contamination. .

  The waxes used for improving the fixing property and the offset property are not particularly limited. For example, polyethylene wax, polypropylene wax, fluororesin (for example, “Teflon (registered trademark)” manufactured by DuPont) system Wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan wax, rice wax and the like are preferably used. Two or more of these waxes may be used in combination. By adding such wax, offset property and image smearing can be more efficiently prevented.

  The amount of the waxes described above is not particularly limited, but is preferably 1 to 5 parts by mass (the total amount of toner is 100 parts by mass). When the added amount of wax is less than 1 part by mass, there is a tendency that offset property and image smearing cannot be effectively prevented. On the other hand, when the amount exceeds 5 parts by mass, the toners are fused with each other, and the storage stability tends to be lowered.

  The binder resin, magnetic material, dye, pigment, charge control agent and the like in the magnetic one-component toner of the present invention are not particularly limited, and known materials can be appropriately selected and used. Further, since the dielectric breakdown of the surface of the photosensitive member is more likely to occur as the linear velocity of the photosensitive drum is higher, the image forming method and the magnetic one-component toner of the present invention are particularly suitable for an image forming apparatus having a high photosensitive drum linear velocity. It is.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited only to a following example.

[Examples 1-8, Comparative Examples 1-6]
54 parts by mass of binder resin, 40 parts by mass of magnetic powder, 3 parts by mass of release agent and 3 parts by mass of positive charge control agent were mixed with a Henschel mixer, melted and kneaded with a twin screw extruder, cooled, and hammer mill Coarsely pulverized. The coarsely pulverized product was further finely pulverized by a mechanical pulverizer and then classified by an airflow classifier to obtain magnetic toner particles having a volume average particle diameter of 8 μm. Next, 1 part by mass of silica (RA-200H manufactured by Nippon Aerosil Co., Ltd.) as an external additive and titanium oxide (EC-100 manufactured by Titanium Industry Co., Ltd., volume resistivity 12 Ω · cm) with respect to 100 parts by mass of the obtained toner particles 2) parts by mass, stirring and mixing with a Henschel mixer (stir mixing time: 5 minutes, rotation speed 2900 rpm), and attaching these external additives to the surface of the toner particles, Examples 1 to 8 and Magnetic one-component toners (magnetic one-component positively charged developer) of Comparative Examples 1 to 6 were prepared.

The details of each material constituting the toner particles are shown below.
Binder resin: Styrene acrylic copolymer (molecular weight (Mw) 47,000 (peaks 5,000, 931,000), molecular weight distribution (Mw / Mn) 29.0, tetrahydrofuran (THF) insoluble content 5%, glass transition Temperature (Tg) 58 ° C)
Mold release agent: Wax (Sazole Wax H1 from Sazol)
Positive charge control agent: quaternary ammonium salt (Orient Chemicals Bontron P-51)

The shape, volume resistivity, volume average particle diameter and specific surface area of the magnetic powder used are shown in Table 1 below. The volume resistivity value of the magnetic powder was determined as follows. First, 0.5 g of the particle powder was measured and subjected to pressure molding at a pressure of 1.37 × 10 ⁷ Pa (140 Kg / cm ² ) using a KBr tablet molding machine (manufactured by Shimadzu Corporation) to form a cylindrical shape. Samples to be measured were prepared. Next, after the sample to be measured was exposed to an environment of 25 ° C. and a relative temperature of 60% for 12 hours or more, the sample to be measured was set between stainless electrodes, and an electric resistance measuring device (model 4329A Yokogawa Hokushin Electric Co., Ltd.) The resistance value R (Ω) was measured by applying a voltage of 15 V. Next, the area A (cm ² ) and thickness t ₀ (cm) of the upper surface of the sample to be measured (cylindrical) are measured, and each measured value is substituted into the following equation to obtain the volume resistivity value ρ (Ω · cm )

  The developers of Examples 1 to 8 and Comparative Examples 1 to 6 were modified from a page printer FS-3800 (24 ppm (A4 size) manufactured by Kyocera Corporation) equipped with an a-Si photosensitive drum (film thickness: 14 μm). ) And a linear velocity of 147 mm / second), and a predetermined image evaluation pattern was printed on 50000 sheets of printing paper. The number of black spots on the 50,000th printed paper was counted using a dot analyzer (DA-5000S, manufactured by Oji Scientific Instruments). The measurement range of the black spot was an area of 5 mm × 210 mm in the A4 horizontal direction. The results are shown in Table 2 below. In remodeling the FS-3800, the developing roller was a stainless (SUS305) sleeve (surface roughness Rz = 4.5 μm) instead of the aluminum sleeve.

  The toner charge amount is obtained by mixing 4 parts by mass of toner particles and 100 parts by mass of a ferrite carrier (FK-150, manufactured by Powdertech) and triboelectrically charging for 10 minutes in a normal environment. (ΜC / g) was measured. Specifically, after the toner particles and the ferrite carrier are mixed in a normal temperature and normal humidity environment, the mixture is triboelectrically charged by stirring for 10 minutes in a ball mill, and about 100 mg of the developer is sampled and the charge amount is collected. Was measured using a charge amount measuring device (Q / M Meter210HS) manufactured by TREK, and the charge amount (μC / g) per gram of the developer was determined from the mass change at that time. The results are shown in Table 2 below.

Further, with respect to the developers of Examples 1 to 8 and Comparative Examples 1 to 6, initial image characteristics and durability were evaluated, and it was evaluated whether or not high-quality printing could be continuously provided for a long time. At the same time, the evaluation was also performed in a high temperature and high humidity environment. The results are shown in Table 2. In Table 2, “Initial”, “After 300,000 sheets” and “High temperature and high humidity” mean the following.
Initial: Evaluated with image immediately after toner installation
After 300,000 sheets: Evaluation with images after printing 300,000 (10,000 sheets / day) ISO4% originals continuously High temperature and high humidity: After leaving in an environmental test room at 35 ° C / 85% RH for about 8 hours Evaluation with initial image

  In Comparative Examples 3 and 6, the result of the black spot evaluation was too bad, so the evaluation after 300,000 sheets and high temperature and high humidity were not performed.

The evaluation method of each characteristic is as follows.
<Solid image density>
An image evaluation pattern was printed by the page printer in a room temperature and humidity environment (20 ° C., 65% RH). This image evaluation pattern was printed under the conditions of “initial”, “after 300,000 sheets”, and “high temperature and high humidity”. Subsequently, the obtained solid image was measured using a Macbeth reflection densitometer (RD914), and the density measurement was performed at nine places of a certain solid portion, and the average value (ID) was calculated. The image density was determined to be OK (good) when the ID was 1.30 or more.
<Uniformity of image density>
The uniformity of the image of the image evaluation pattern printed in the evaluation of the solid image density was evaluated by visual observation.
○: Uniformity is good.
Δ: Slightly uneven.
X: Unevenness is severe.
<Evaluation of background fog>
Evaluation was made by visually observing the image of the image evaluation pattern printed in the evaluation of the solid image density.
○: Fog is not seen.
Δ: Slight fogging occurs.
X: The fog is terrible.

  From Tables 1 and 2, in Comparative Examples 2 and 3, since high resistance magnetic powder was used, there was a tendency to be overcharged, and dielectric breakdown occurred in the photosensitive drum, resulting in many black spots. As a result, a minute black spot was developed even in the non-printing portion, and this became a fatal image defect. Further, as a result of the long-term durability test, the non-uniformity of the image was conspicuous, the fogging was particularly severe, the charge amount deviated from the appropriate development area, and the image density could not be maintained over a long period. In particular, in Comparative Example 3, since the leak to the drum started from the beginning of the black spot evaluation, the evaluation had to be interrupted. In Comparative Example 1, since the volume resistivity of the magnetic powder was too low, the durability was lowered and the image density was lowered at high temperature and high humidity.

  Further, according to Tables 1 and 2, in Comparative Examples 4, 5, and 6, since spherical magnetic powder was used, there was a tendency to be overcharged, and dielectric breakdown occurred in the photosensitive drum, resulting in many black spots. did. As a result, a minute black spot was developed even in the non-printing portion, and this became a fatal image defect. Further, as a result of a long-term durability test, the non-uniformity of the image was conspicuous, the fogging was particularly severe, the charge amount deviated from the development appropriate region, and the image density could not be maintained over a long period. In particular, in Comparative Example 6, since the leak to the drum started from the beginning of the black spot evaluation, the evaluation had to be interrupted. Another reason for the interruption was the poor level. Further, in Comparative Example 6, the toner charge amount distribution is broad and poorly charged (excessive charge), the cohesive force between the toners increases, and the toner thinness is less affected by the magnetic binding force from the blade. The stability of the layer was impaired.

  On the other hand, in Examples 1 to 8, clear images without black spots were obtained. This is considered to be because the charge-up of the toner itself can be suppressed by including in the toner magnetic powder having a small volume resistivity and a polyhedral shape, as can be seen from the charge amount of the toner. Further, in Examples 1 to 8, many apexes of the magnetic powder protruding from the toner particle surface as shown in FIG. 4 were confirmed. Further, in Examples 1 to 8, the toner thin layer on the sleeve can be stably formed over a long period of time, as well as having no adverse effect on the photosensitive drum, and high resolution and reproduction of fine lines can be achieved without causing fogging. High quality and high quality printing could be achieved. This is because the magnetic property value (especially the remanent magnetization value) increases due to the inclusion of magnetic powder with a small volume resistivity and a polyhedral shape, and the influence of the magnetic restraining force from the blade that regulates the toner thin layer. This is considered to be due to the fact that the toner thin layer has been promoted over a long period of time. Although not described in detail, the average toner charge amount on the sleeves of Examples 1 to 8 was stable at 2.0 to 6.0 μC / g from the initial stage to the evaluation under the environment after the durability test. This is because the toner itself is designed to be difficult to charge up.

  Considering these phenomena, it becomes as follows. Electric charges are generated in the toner due to friction between the cleaning blade and the toner surface. This is a phenomenon that occurs when any magnetic powder is contained. At this time, when the magnetic powder contained in the toner particles is spherical, the magnetic powder does not protrude from the surface of the toner particles (see FIG. 5). For this reason, electric discharge hardly occurs through the magnetic powder, and the toner is overcharged. Similarly, when the volume resistivity of the magnetic powder contained in the toner particles is high, discharge through the magnetic powder hardly occurs, and the toner is overcharged. When a certain critical point is reached, the accumulated charges are sparked at once through the magnetic powder, and a voltage exceeding the drum withstand voltage is applied to the photosensitive drum. At that moment, dielectric breakdown of the photosensitive layer on the surface of the photosensitive drum occurs.

  On the other hand, when the magnetic powder contained in the toner particles is a polyhedron (especially, the octahedron has a sharp apex and a large effect), the surface of the magnetic powder and the surface of the photosensitive drum are in a point-to-surface relationship, that is, inequality. Because of the electric field, an edge effect is obtained (discharge efficiency is increased), the top of the magnetic powder becomes a leak site, corona discharge is likely to occur, and the toner is prevented from being overcharged. Since it is gradually discharged, no discharge phenomenon exceeding the drum pressure resistance such as spark discharge occurs. Furthermore, when the volume resistivity of the magnetic powder contained in the toner particles is low, discharge through the magnetic powder is likely to occur, preventing the toner from being overcharged, that is, the charge in the toner particles is gradually discharged. Therefore, the discharge phenomenon exceeding the drum pressure resistance such as spark discharge does not occur.

[Examples 9 to 13 and Comparative Examples 7 to 12]
In the toner of Example 4, the addition amount and the addition conditions of the external additive were changed and the influence was investigated. The external additives used were silica and titanium oxide, which were the same as in Example 4. The same Henschel mixer 20B as in Example 4 was used for the external addition process, and the stirring speed was the same, 2900 rpm.

  Each developer of Examples 9 to 13 and Comparative Examples 7 to 12 was modified from a page printer FS-3800 (24 ppm (A4 size) manufactured by Kyocera Corporation) equipped with an a-Si photosensitive drum (film thickness: 14 μm). ) And a linear velocity of 147 mm / second), and a predetermined image evaluation pattern was printed on 50000 sheets of printing paper. The number of black spots on the 50,000th printed paper was counted using a dot analyzer (DA-5000S, manufactured by Oji Scientific Instruments). The measurement range of the black spot was an area of 5 mm × 210 mm in the A4 horizontal direction. The results are shown in Table 4. The loose apparent density and the detected intensity by fluorescent X-ray analysis shown in Table 4 were measured by the methods described above. The waste toner whose detected intensity was measured was collected at the front end of the cleaning blade of the page printer when printing of 50000 sheets was completed. In remodeling the FS-3800, the developing roller was a stainless (SUS305) sleeve (surface roughness Rz = 4.5 μm) instead of the aluminum sleeve.

  The toner charge amount is obtained by mixing 4 parts by mass of toner particles and 100 parts by mass of a ferrite carrier (FK-150, manufactured by Powdertech) and triboelectrically charging for 10 minutes in a normal environment. (ΜC / g) was measured. Specifically, after the toner particles and the ferrite carrier are mixed in a normal temperature and normal humidity environment, the mixture is triboelectrically charged by stirring for 10 minutes in a ball mill, and about 100 mg of the developer is sampled and the charge amount is collected. Was measured using a charge amount measuring device (Q / M Meter210HS) manufactured by TREK, and the charge amount (μC / g) per gram of the developer was determined from the mass change at that time. The results are shown in Table 4 below.

Further, with respect to the developers of Examples 9 to 13 and Comparative Examples 7 to 12, initial image characteristics and durability were evaluated, and it was evaluated whether or not high-quality printing could be continuously provided for a long period of time. At the same time, the evaluation was also performed in a high temperature and high humidity environment. The results are shown in Table 4. In Table 4, “initial”, “after 300,000 sheets”, and “high temperature and high humidity” mean the following.
Initial: Evaluated with image immediately after toner installation
After 300,000 sheets: Evaluation with images after printing 300,000 (10,000 sheets / day) ISO4% originals continuously High temperature and high humidity: After leaving in an environmental test room at 35 ° C / 85% RH for about 8 hours Evaluation with initial image

  In Comparative Example 11, the result of the black spot evaluation was too bad, and thus the evaluation after 300,000 sheets and high temperature and high humidity were not performed.

The evaluation method of each characteristic is as follows.
<Solid image density>
An image evaluation pattern was printed by the page printer in a room temperature and humidity environment (20 ° C., 65% RH). This image evaluation pattern was printed under the conditions of “initial”, “after 300,000 sheets”, and “high temperature and high humidity”. Subsequently, the obtained solid image was measured using a Macbeth reflection densitometer (RD914), and the density measurement was performed at nine places of a certain solid portion, and the average value (ID) was calculated. The image density was determined to be OK (good) when the ID was 1.30 or more.

<Uniformity of image density>
The uniformity of the image of the image evaluation pattern printed in the evaluation of the solid image density was evaluated by visual observation.
○: Uniformity is good.
Δ: Slightly uneven.
X: Unevenness is severe.

<Evaluation of background fog>
Evaluation was made by visually observing the image of the image evaluation pattern printed in the evaluation of the solid image density.
○: Fog is not seen.
Δ: Slight fogging occurs.
X: The fog is terrible.

  From Table 4, it can be seen that in Comparative Examples 7 to 12, black spots occurred in all, and dielectric breakdown occurred on the surface of the photosensitive drum. As described above, a fine black spot is developed even in a non-printing portion, and a fatal image defect occurs. From Table 4, Comparative Examples 7 to 12 also had problems in terms of image density, image density uniformity, and background fogging.

  In Comparative Examples 7, 10, and 11, since the stirring and mixing time of the external additive was made too long, much of the titanium oxide (conductive metal oxide fine particles) was embedded in the toner particles, and the floating external additive was reduced. This is considered to be because the titanium oxide was transferred to the printing paper together with the toner in the transfer step, and the titanium oxide interposed between the cleaning blade and the toner was reduced, thereby reducing the spacer effect.

  In particular, it was confirmed by visual observation before use that the toner of Comparative Example 11 was clearly deteriorated as a toner. The toner of Comparative Example 11 is in a state of being extremely easily charged due to the exposure of most of the toner particle surface. This not only provides an initial image density, but also causes a dielectric breakdown in the photosensitive layer of the photoreceptor. The overcharging that occurred occurred in the toner near the cleaning blade, resulting in the generation of an extremely large number of black spots.

  In Comparative Example 8, the amount of titanium oxide contained in the waste toner increased (the value of formula (1) exceeded 3.5), resulting in a decrease in toner fluidity and poor transfer residual toner collection. It can be considered that the toner stays in the vicinity of the cleaning blade and the toner is overcharged, causing dielectric breakdown in the photosensitive layer of the photosensitive drum.

  In Comparative Example 9, the AD value decreased because the amount of titanium oxide added was excessive. Therefore, as a result of conducting a long-term durability test, the charge amount deviated from the development suitability range, and the image density could not be maintained at a high density for a long time. Further, the non-uniformity of the image was conspicuous, and the background fogging was particularly remarkable. In addition, too much titanium oxide is present in the vicinity of the cleaning blade, so that the fluidity of the toner is reduced, the collection failure occurs, and the toner residence time is increased, resulting in overcharging of the toner and the photosensitive drum photosensitive. It is thought that dielectric breakdown occurred in the layer.

  In Comparative Example 12, since too much silica was added, the toner charge amount distribution was broad, and the toner was coherently charged (overcharged), increasing the cohesive force between the toners. As a result, the initial image characteristics were relatively good, but there was a problem in maintaining the image characteristics (density) during durability.

  On the other hand, in Examples 9 to 13, there was no dielectric breakdown on the surface of the photosensitive drum, and clear images without black spots were obtained. This is because, as a result of the loose apparent density (AD) of the toner satisfying a value within a predetermined range, the fluidity of the toner is not extremely deteriorated, the charging ability of the toner itself is suppressed, and the disposal is performed. Since the conductive metal oxide fine particles are present in a well-balanced manner in the toner, the conductive metal oxide fine particles are interposed as a spacer between the toner and the cleaning blade, so that frictional charging is suppressed, and the toner is overcharged. This is considered to be a suppressed result.

  The above phenomenon is considered as follows. The toner is charged due to friction between the cleaning blade and the toner surface. This is a phenomenon that occurs when any magnetic powder is contained. At this time, if the AD of the toner becomes extremely small or the conductive metal oxide fine particles in the waste toner decrease, the toner is charged due to friction, but the discharge hardly occurs, and the toner is overcharged. End up. Then, when the charged state reaches a certain critical point, the accumulated charge is sparked at once through the magnetic powder, a voltage exceeding the drum withstand voltage is applied to the surface of the photosensitive drum, and a black spot is generated at that moment.

  On the other hand, since the AD of the toner is within a predetermined range and the conductive metal oxide fine particles are sufficiently present in the waste toner, the toner can be prevented from being overcharged. In other words, the conductive metal oxide fine particles are present as a spacer between the toner and the cleaning blade, so that triboelectric charge is less likely to occur, and the conductive metal oxide does not accumulate excessively in the toner. It becomes easy to discharge gradually through oxide fine particles. In addition, it is considered that the presence of the conductive metal oxide fine particles makes it easy for the waste toner to be sent to the collection side (that is, the same toner is less likely to stay). Together, these factors do not cause a phenomenon like spark discharge that exceeds the drum pressure resistance.

1 is a schematic diagram illustrating an example of an image forming apparatus. It is a partial expanded sectional view which shows the laminated structure of an amorphous silicon photoconductor drum. It is a graph which shows the relationship between a photoconductor film thickness and needle pressure resistance. 3 is an enlarged image of the surface of toner particles according to the present invention by a scanning electron microscope (SEM). It is the enlarged image by the scanning electron microscope (SEM) of the surface of the conventional toner particle containing spherical magnetic powder. It is a conceptual diagram which shows the abnormal discharge phenomenon which arises in the conventional image forming method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 a-Si photosensitive drum 12 Scorotron charger 13 Exposed body 14 Developer 15 Transfer roll 16 Cleaning blade 17 Static elimination lamp 18 Surface protective layer 19 Photosensitive layer 20 Carrier blocking layer 21 Conductive substrate

Claims (6)

An image forming method based on a magnetic one-component developing method using an amorphous silicon photoconductor having a film thickness of 10 μm to 30 μm as a latent image holding member and using a cleaning blade as a cleaning unit for removing toner from the surface of the photoconductor,
As a toner for developing the electrostatic latent image formed on the surface of the photoreceptor, the toner particles have a polyhedral shape with a volume resistivity of 4 × 10 ² (Ω · cm) to 1 × 10 ⁶ (Ω · cm). An image forming method comprising using a magnetic one-component toner containing the magnetic powder.   2. The image formation according to claim 1, wherein the unused toner for developing the electrostatic latent image formed on the surface of the photosensitive member is externally added with at least one conductive metal oxide fine particle. Method. The unused toner for developing the electrostatic latent image formed on the surface of the photoreceptor has a loose apparent density (AD) adjusted to 0.490 g / cm ³ or more and 0.650 g / cm ³ or less,
3. The image forming method according to claim 2, wherein the waste toner removed from the surface of the photosensitive member contains conductive metal oxide fine particles in an amount satisfying the following formula (1).

[However, in the formula (1), the detection intensity (waste toner) means the detection intensity by the fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the waste toner. “Toner” indicates the intensity detected by fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the unused toner. ] A magnetic one-component toner used in a magnetic one-component developing system using an amorphous silicon photoconductor having a film thickness of 10 μm to 30 μm as a latent image holding member and using a cleaning blade as a cleaning means for removing toner from the surface of the photoconductor. ,
The toner particles contain a polyhedral magnetic powder having a volume resistivity of 4 × 10 ² (Ω · cm) or more and 1 × 10 ⁶ (Ω · cm) or less. .   The magnetic one-component toner according to claim 4, wherein at least one or more kinds of conductive metal oxide fine particles are externally added to the toner particles. The loose apparent density (AD) is 0.490 g / cm ³ or more and 0.650 g / cm ³ or less,
At the time of the external addition, the conductive metal oxide fine particles and the conductive metal oxide fine particles so that the content of the conductive metal oxide fine particles contained in the waste toner removed from the photoreceptor surface by the cleaning blade satisfies the following formula (1): 6. The magnetic one-component toner according to claim 5, wherein the toner particles are agitated and mixed.

[However, in the formula (1), the detection intensity (waste toner) means the detection intensity by the fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the waste toner. “Toner” indicates the intensity detected by fluorescent X-ray analysis of the metal element constituting the conductive metal oxide fine particles contained in the unused toner. ]