JP2005202024A - Image forming method and magnetic monocomponent toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method capable of preventing the occurrence of dielectric breakdown in a surface of a photoreceptor in a magnetic monocomponent developing system using a thin layer amorphous silicon photoreceptor as a latent image carrier and using a cleaning blade as a means of cleaning a surface of the photoreceptor, and to provide a magnetic monocomponent toner for developing an electrostatic latent image. <P>SOLUTION: In the magnetic monocomponent developing system using an amorphous silicon photoreceptor whose film thickness is ≤30 μm as a latent image carrier and using a cleaning blade as a means of removing toner from a surface of the photoreceptor, the magnetic monocomponent toner containing at least 35-55 mass% of a magnetic powder and 1-10 mass% of a carbon black within toner particles is used as toner for developing an electrostatic latent image formed on the surface of the photoreceptor. <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. 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 addition, in the essential photoreceptor cleaning section, the material of the cleaning blade is not clearly described, but when an elastic blade with a simple (general) mechanism is used, the toner comes into contact and is frictionally charged. Charges that do not escape are accumulated in the toner, causing abnormal discharge (single point discharge, spark discharge) to the photoconductor, and destroying the photoconductor drum surface (charge generation layer, charge transfer layer). There is an extremely high possibility that defects that cannot be repaired (only defective images can be obtained) are generated.

  Further, Patent Document 7 proposes a toner in which free magnetic powder exists in order to prevent dielectric breakdown of the photoreceptor, and this free magnetic powder prevents leakage. However, there is a concern that the free magnetic powder adheres to the developing sleeve or adheres to the photoreceptor. It is well known that even if a very small amount of adhesion occurs, the adhered portion grows using the nucleus as a nucleus and causes a fatal image defect.

In Patent Document 8, it is said that the dielectric breakdown of the photoconductor can be suppressed by defining the film thickness of the photoconductor, but there is no special rule regarding the toner, which originally causes the dielectric breakdown. Therefore, when the toner having different characteristics is used, there is a concern again about the dielectric breakdown of the photosensitive member.
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 JP 2003-149857 A JP 2002-287391 A

  Accordingly, an object of the present invention is to develop a developing system based on 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 greening blade as means for cleaning the surface of the photosensitive member. The present invention provides an image forming method and a magnetic one-component toner for developing an electrostatic latent image that can prevent dielectric breakdown from occurring on the surface of the photoreceptor.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have the toner system contain at least magnetic powder and carbon black, which is a conductive material, 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 by adjusting the value to an appropriate range, and the present invention has been completed.

  That is, the image forming method of the present invention is based on a magnetic one-component developing system using an amorphous silicon photoconductor having a film thickness of 30 μm or less as a latent image holding member and using a cleaning blade as a cleaning means for removing toner from the surface of the photoconductor. In the image forming method, as a toner for developing the electrostatic latent image formed on the surface of the photoreceptor, a magnetic particle 1 containing at least 35 to 55% by mass of magnetic powder and 1 to 10% by mass of carbon black in toner particles. Component toner is used.

  The magnetic one-component toner of the present invention uses an amorphous silicon photosensitive member having a film thickness of 30 μm or less as a latent image holding member, and a magnetic one-component developing method using a cleaning blade as a cleaning means for removing the toner from the surface of the photosensitive member. In the toner, the toner particles contain at least 35 to 55% by mass of magnetic powder and 1 to 10% by mass of carbon black.

  In the present invention, as the magnetic one-component toner used in the development system, a toner containing a predetermined amount of magnetic powder in a binder resin and a predetermined amount of carbon black as a conductive agent is used. Conventionally, magnetic one-component toner contains magnetic powder, and if this magnetic powder is increased, the resistance of the toner can be reduced and dielectric breakdown of the photoreceptor can be prevented. Since it is necessary to contain a large amount of magnetic powder in order to prevent destruction, there is an adverse effect that the fixability as a toner is remarkably lowered and the image density is lowered. Therefore, in the present invention, not only the amount of magnetic powder is increased, but also carbon black is contained as a conductive agent, and by adjusting these contents to the optimum range, good fixability and image density can be obtained, and photosensitive properties can be obtained. It effectively prevents body breakdown.

  In other words, even if the toner collected near the tip of the cleaning blade rubs against the tip of the blade, the amount of charge can be kept low, and even if charged to some extent, it can be discharged before reaching the potential to cause dielectric breakdown. Therefore, it is possible to prevent dielectric breakdown of the surface of the photoreceptor due to toner overcharging. 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.

  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. As shown in FIG. 1, the image forming apparatus includes a developing system based on a magnetic one-component developing jumping system, 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 developability 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. This magnetic one-component toner is prepared by mixing a binder resin, magnetic powder, carbon black, and various toner compounding agents such as a colorant, a charge suppressing agent, and wax, and melting them using a kneader such as an extruder. After kneading, this is cooled, pulverized and classified. 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 above-described binder resin. The magnetic powder can also 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.

  The magnetic powder is contained in the toner particles in an amount of 35 to 55% by mass, preferably 40 to 53% by mass. 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.

In the toner of the present invention, it is necessary to contain carbon black as a conductive agent. The BET specific surface area of the carbon black is preferably 800 m ² / g or more, more preferably 900 m ² / g or more. This specific surface area is generally called a BET specific surface area by nitrogen adsorption, and can be measured using, for example, a 2200 type measuring device manufactured by Micromeritic. In addition to carbon black, examples of the conductive agent include metal oxides such as titanium oxide and tin oxide, and those doped with tin-antimony, but the conductivity is inferior to carbon black. In addition, carbon black is a highly effective conductive agent when dispersed in a polymer such as a binder resin because it is porous, has a large specific surface area, and has a structure called a unique structure. . Therefore, in the present invention, it is necessary to use carbon black as a conductive agent in order to prevent abnormal charging in the cleaning blade portion and perform appropriate discharge efficiently in order to prevent the dielectric breakdown of the photoreceptor.

  Carbon black is contained in the toner particles in an amount of 1.0 to 10.0% by mass, preferably 2.0 to 9.5% by mass. When the amount is less than the above range, the effect of imparting conductivity cannot be obtained even when carbon black is added. When the amount is large, dispersion in toner particles becomes difficult, and the effect of adding carbon black cannot be obtained. Even if the toner particles can be dispersed, the conductivity of the toner is increased too much and the charge amount is decreased too much, thereby causing image defects such as a decrease in image density and fogging.

  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 for adjusting the color tone or a dye such as Acid Violet can be dispersed in the binder resin as a colorant, 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), a 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.

  If necessary, fine particles (external additives) such as colloidal silica, hydrophobic silica, alumina, and titanium oxide may be externally added to the magnetic one-component toner of the present invention. The external additive is preferably added in an amount of about 0.2 to 10 parts by mass with respect to 100 parts by mass of the toner particles. The volume average particle size of the external additive is 1 μm or less, preferably 0.01 to 0.8 μm. By externally adding the external additive to the toner particles, the fluidity, storage stability, cleaning properties, and the like of the toner can be controlled. 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, but the external additive is embedded in the toner particles. It is preferable to use a Henschel mixer, a Nauter mixer or the like.

  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 to 5, Comparative Examples 1 to 4]
Table 1 shows the binder resin with the content shown in Table 1, 2.0 parts by weight of the release agent, 2.0 parts by weight of the positive charge control agent, the magnetic powder with the content shown in Table 1, and the conductive agent. Carbon black having the content shown was mixed with a Henschel mixer, melt-kneaded with a twin screw extruder, cooled, and coarsely pulverized with a hammer mill. 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, 1.0 part by mass of silica (RA-200H manufactured by Nippon Aerosil Co., Ltd.) and 2.0 parts by mass of titanium oxide (ST-100 manufactured by Titanium Industry Co., Ltd.) are added to 100 parts by mass of the obtained toner particles. The magnetic one-component toners of Examples 1 to 5 and Comparative Examples 1 to 4 are mixed by stirring and mixing with a Henschel mixer 20B (Mitsui Mining Co., Ltd.) and attaching these external additives to the surface of the toner particles. (Magnetic one-component positively charged developer) was prepared.

Details of the respective raw materials constituting the toner particles are shown below.
Binder resin: Put 300 parts of xylene into a reactor equipped with a thermometer, stirrer, and nitrogen inlet tube, and under a nitrogen stream, 845 parts of styrene and 155 parts of n-butyl acrylate mixed monomer and di-tert- Using a mixed solution of 8.5 parts of butyl peroxide (polymerization initiator) and 125 parts of xylene, the solution was added dropwise at 170 ° C. over 3 hours. After the dropwise addition, the mixture was reacted at 170 ° C. for 1 hour to complete the polymerization. Thereafter, the solvent was removed to obtain a binder resin.
Magnetic powder: holding power 5.0 kA / m when 796 kA / m is applied, saturation magnetization 82 Am ² / kg, residual magnetization 11 Am ² / kg, number average particle size 0.25 μm
Mold release agent: Wax (Sazole Wax H1 from Sazol)
Positive charge control agent: quaternary ammonium salt (Orient Chemicals Bontron P-51)
Conductive agent: Carbon black (Ketjen Black EC, manufactured by Lion Akzo, specific surface area 950m ² / g)

[Comparative Example 5]
A magnetic one-component toner (magnetic one-component positively charged developer) was prepared in the same manner as in Example 1 except that the toner particles contained tin oxide 5.0 (parts by mass) as a conductive agent instead of carbon black. Prepared.

[Comparative Example 6]
A magnetic one-component toner (magnetic one-component positively charged developer) was prepared in the same manner as in Example 1 except that the toner particles contained titanium oxide 5.0 (parts by mass) as a conductive agent instead of carbon black. Prepared.

Each developer of Examples 1 to 5 and Comparative Examples 1 to 6 is a page printer FS-3800 (24 ppm (A4 size), linear speed 147 mm / sec) manufactured by Kyocera Corporation, on which an a-Si photosensitive drum is mounted. Set in each developing unit, print a predetermined image evaluation pattern on printing paper, evaluate the dielectric breakdown state of the photoreceptor, image characteristics, developer charging characteristics and fixing characteristics, and thin layer on the developing sleeve The state was confirmed visually. The results are shown in Table 2. Moreover, the evaluation method of each characteristic is shown below.
<State of dielectric breakdown of photoconductor>
After printing an image evaluation pattern on 50,000 sheets of printing paper, the number of black spots on this 50,000th printing paper is counted using a dot analyzer (DA-5000S, manufactured by Oji Scientific Instruments), and the sensitivity to the number of printed sheets. The number of dielectric breakdowns of the body film was evaluated. The measurement range of the number of black spots measured was an area of 5 mm × 210 mm in the A4 horizontal direction.
<Image characteristics>
In a normal temperature and humidity environment (20 ° C, 65% RH), the initial image was printed with an image evaluation pattern by the above page printer, then 50,000 sheets were continuously fed and the image evaluation pattern was printed again. The thing was made into the image after endurance. These solid images were measured using a Macbeth reflection densitometer (RD914), and image characteristics were evaluated by visually observing fog. A case where the image density was 1.30 or more was determined to be OK (good). The following criteria were used for fog evaluation.
○: No fogging is observed. △: Some fogging is generated. ×: Fog is severe <Charging characteristics>
Regarding the charge amount of the toner, after magnetic toner and ferrite carrier (FK-150, manufactured by Powder Tech Co., Ltd.) are mixed in a normal temperature and humidity environment, they are triboelectrically charged by stirring for 10 minutes in a ball mill. The charge amount was measured using a charge amount measuring device (Q / M Meter 210HS) manufactured by TRek, and the charge amount μC / g per gram of the developer was determined from the mass change at that time.
<Fixing characteristics>
The fixing property of the magnetic toner was evaluated by controlling the fixing temperature of the page printer. Here, the minimum fixing temperature refers to the temperature of the fixing roller when the fixing rate exceeds 95%. Note that the fixing rate is when a 1 kg load is applied with a brass weight wrapped in cotton cloth, the solid image of the printed fixing evaluation pattern is rubbed 10 times, and the image density before and after rubbing is measured with a Macbeth reflection densitometer. Concentration ratio.
○: Fixing rate of 95% or more Δ: Fixing rate of 90% or more to less than 95% ×: Fixing rate of less than 90% The following criteria were used to evaluate the minimum fixing temperature.
○: Less than 150 ℃
Δ: higher than 150 ° C and lower than 160 ° C ×: higher than 160 ° C <Toner thin layer state>
The toner thin layer state on the developing sleeve was visually confirmed, and the following criteria were used for evaluation.
○: A thin layer is uniformly formed and there is no unevenness. Δ: There is a portion with a thick layer. ×: There is unevenness.

  In Comparative Examples 1 and 2, the content of the magnetic powder was outside the range of the present invention, but since carbon black was contained, the number of black spots was as small as 21 or less. However, in Comparative Example 1, since the amount of magnetic powder was small, fogging occurred and a toner thin layer could not be stably formed. In Comparative Example 2, since the amount of magnetic powder was too large, the fixability was remarkably lowered, and the magnetic binding force of the toner by the developing sleeve was increased, and the image density was lowered.

  In Comparative Examples 3 and 4, the content of carbon black as a conductive agent is not within a predetermined range, Comparative Example 3 has no effect of adding carbon black and a large amount of black spots are generated, and conversely in Comparative Example 4, the added amount is Since the amount was too large, the charging was abnormally reduced, the image density was low, fogging occurred, and the fixability was slightly deteriorated.

  In Comparative Examples 5 and 6, titanium oxide and tin oxide were used as the conductive agent instead of carbon black. However, when the addition amount was equivalent to that of carbon black, there was no effect of addition of these conductive agents, and the photoreceptor was insulated. Many sunspots that seem to have been destroyed occurred.

  On the other hand, in Examples 1 to 5, since carbon black was used as the conductive agent and the magnetic powder and carbon black were adjusted to appropriate contents, there were no problems in terms of image characteristics, toner thin layer, and black spots. In addition, the fixing property was excellent without deteriorating.

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.

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 (2)

An image forming method based on a magnetic one-component developing method using an amorphous silicon photoconductor having a film thickness of 30 μm or less 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 magnetic one-component toner containing at least 35 to 55% by mass of magnetic powder and 1 to 10% by mass of carbon black in toner particles is used. An image forming method. A magnetic one-component toner used in a magnetic one-component developing system using an amorphous silicon photosensitive member having a film thickness of 30 μm or less as a latent image holding member and using a cleaning blade as a cleaning means for removing toner from the surface of the photosensitive member,
A magnetic one-component toner characterized in that the toner particles contain at least 35 to 55% by mass of magnetic powder and 1 to 10% by mass of carbon black.

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