JP5289834B2 - Charging control device, charging device and image forming apparatus - Google Patents

Description

  The present invention relates to a charge control device that controls the amount of charge of an object to be charged by electrons emitted by applying a voltage to an electron-emitting device, and a charging device including the same, and image formation including the charging device Relates to the device. In particular, in image formation of electrophotographic copying machines, printers, etc., a charge control device for controlling the amount of charge when the electrostatic latent image carrier is charged, a charging device equipped with the same, and further provided with the charging device The present invention relates to an image forming apparatus.

  In an image forming apparatus such as an electrophotographic copying machine or printer, the surface of a charged body is uniformly charged by various methods prior to forming an electrostatic latent image on the charged body such as a photoconductor.

  An example of a conventional charging method is a method using corona discharge. This method is a method in which the surface of the photoreceptor is charged by discharging from a very thin wire. However, in this method, a high voltage power source of about 4 to 10 kV is required to charge the surface of the photoreceptor. Furthermore, since a large amount of ozone is generated by the discharge from the wire, there is a problem that not only the human body is adversely affected but also the deterioration of the photoreceptor is accelerated. In order to solve such a problem, for example, Patent Document 1 and Patent Document 2 disclose corona chargers improved so as to reduce the amount of ozone generated.

  As another charging method, a method of charging the surface of a photoreceptor by a contact charging method has been put into practical use in recent years. In this method, since the surface of the photoconductor is charged by bringing a conductive member such as a conductive roller, brush, elastic blade, or carbon nanotube into contact with the surface of the photoconductor, the amount of ozone generated and the amount of power consumed Can be reduced.

  Among the charging methods using the contact charging method, a roller charging method using a conductive roller as a conductive member is currently widely used from the viewpoint of charging stability. In the roller charging method, a conductive elastic roller is brought into pressure contact with a photosensitive member, and a voltage is applied to the roller to charge the photosensitive member. However, when the photosensitive member is charged by the roller charging method and there is a minute defect (pinhole) on the surface of the photosensitive member, an abnormal amount of current is generated from the conductive elastic roller at the defective portion of the photosensitive member surface. A leak occurs. As a result, the surface of the photoconductor is damaged, which adversely affects image formation.

  As a charging method that further improves the problems that occur in such a roller charging method, there is known a method in which a secondary charging roller is added between a roller-shaped charging member (primary charging roller) for applying a voltage and a photosensitive member. (For example, see Patent Document 3). Here, the secondary charging roller plays a role of transporting charges from the primary charging roller to the photoconductor, and is provided to solve the problem of current leakage caused by pinholes on the surface of the photoconductor. However, in this method, since the photosensitive member is charged by a minute discharge generated in a narrow gap between the secondary charging roller and the photosensitive member, generation of ozone and NOx during charging cannot be suppressed completely.

  Further, for example, Patent Document 4 discloses a charging method using a contact charging method in which carbon nanotubes are applied as a conductive member. However, when carbon nanotubes are used as the conductive member, the carbon nanotubes are damaged by the pressure when the carbon nanotubes are pressed against the photoreceptor, and the charging ability is reduced.

  As yet another charging method, Patent Document 5 and Patent Document 6 disclose a charging method using an electron-emitting device having a MIS (metal-insulator-semiconductor) structure. In this electron-emitting device, an accelerating electric field of electrons is formed by a potential difference between an upper thin film electrode and a lower thin film electrode provided with a porous semiconductor layer interposed therebetween. Then, high-energy electrons generated by the formation of the acceleration electric field are emitted from the surface of the electron-emitting device, and the photoconductor is charged by the emitted electron-emitting device.

In the charging device including the electron-emitting device as described above, since negative ions are generated only using the electron attachment by the electrons emitted from the electron-emitting device, ozone or ozone is used as in the method using the discharge. NOx is not generated in principle. Non-patent document 1 discloses in detail the electron emission principle and formation method of the porous semiconductor layer made of a porous silicon thin film.
JP 9-114192 A (published May 2, 1997) JP 6-324556 A (published on November 25, 1994) JP 2001-296722 A (released on October 26, 2001) JP 2001-281964 A (published on October 10, 2001) JP 2001-331017 A (published on November 30, 2001) Japanese Patent Laying-Open No. 2001-357961 (released on December 26, 2001) “Light emission and new functions of quantum-size nanosilicon”, Nobuyoshi Koshida et al., Shingaku Technical Report, 1999-06: PP116-121 (1999)

  In general, an electron-emitting device is an element that obtains an electric current by applying a voltage. Therefore, in a charging device using an electron-emitting device, a voltage difference between the charging device and the photosensitive member is the same as in a corona discharge method or a roller charging method. When the charge amount of the charged body is controlled, the following problems occur.

  First, when the charge amount is controlled by the potential difference, it is necessary to continue to emit electrons until the potential difference between the charging device and the photosensitive member disappears. The electrons emitted from the charging device are attracted to the photosensitive member mainly by the electric field generated by the potential difference between the charging device and the photosensitive member, so that the charging speed decreases as the charging progresses and the potential difference becomes smaller and the electric field becomes weaker. Particularly in the atmosphere, since electrons are scattered by collision with gas, when the electric field is further weakened, the electrons do not reach the photoreceptor, and in the worst case, the photoreceptor cannot be charged to a desired potential.

  In addition, as described above, since the charging efficiency is reduced by scattering of electrons in the atmosphere, excessive electrons must be continuously emitted to compensate for the charging efficiency. In the corona discharge method, excess electrons are absorbed by the grid and the case of the charging device and do not come out of the charging device. However, in a charging device using an electron-emitting device, electron emission is performed regardless of the potential difference between the charging device and the photoreceptor. Since the amount is constant, the amount of electron emission emitted from the charging device does not decrease even if the potential difference is reduced. That is, a large amount of electrons that are not used for charging are emitted. Therefore, not only the emitted electrons are wasted, but also unexpected members other than the photoreceptor may be charged, and the electronic circuit of the peripheral device may be destroyed.

  The present invention has been made in view of the above problems, and the purpose thereof is to maintain the lifetime of the electron-emitting device even when, for example, an electron-emitting device that does not generate ozone or NOx is used. An object of the present invention is to provide a charge control device for efficiently charging a photoconductor, a charging device including the charge control device, and an image forming apparatus including the charging device.

  In order to solve the above-described problems, a charge control device according to the present invention is a charge control device that controls the charge amount of an object to be charged by electrons emitted by applying a voltage to an electron-emitting device. Based on the measurement means for measuring the amount of current in the emitter and the measurement result from the measurement means, the electron emitter is applied to the electron emitter so that the amount of electrons emitted from the electron emitter is constant. And a control means for controlling the voltage.

  According to the above configuration, the charging control device measures the amount of current in the electron-emitting device by the measuring unit. The control means controls the voltage applied to the electron-emitting device so that the amount of current of electrons emitted from the electron-emitting device becomes constant based on the measurement result from the measuring means. In this way, by monitoring the current amount of electrons emitted from the electron-emitting device and controlling in real time so that the current amount becomes constant, for example, an electron-emitting device that does not generate ozone or NOx is used. Even in such a case, it is possible to appropriately control the charge amount of the member to be charged. As a result, the member to be charged can be charged efficiently.

  In the charging control apparatus according to the present invention, the measuring means includes a first current measuring unit that measures the amount of current flowing into the electron-emitting device, and a current amount that is recovered without being emitted from the electron-emitting device. A second current measuring unit for measuring the current, and the control means makes the difference between the current amount measured by the first current measuring unit and the current amount measured by the second current measuring unit constant. The voltage applied to the electron-emitting device is preferably controlled.

  According to the above configuration, the amount of current flowing into the electron-emitting device and the amount of current recovered without being emitted from the electron-emitting device are measured. Then, by controlling the voltage applied to the electron-emitting device so that the difference between these current amounts is constant, the current amount of electrons emitted from the electron-emitting device can be kept constant. As a result, the charge amount of the member to be charged can be controlled more appropriately, so that the member to be charged can be charged efficiently.

  In order to solve the above-described problems, a charging device according to the present invention includes the charging control device and the electron-emitting device, and the electron-emitting device is at least partially insulated between the electrode substrate and the thin-film electrode. An electron acceleration layer composed of a body, and when a voltage is applied between the electrode substrate and the thin film electrode, electrons are accelerated in the electron acceleration layer and emitted from the thin film electrode. It is characterized by being.

  According to the above configuration, since it is not necessary to use discharge by using the electron-emitting device, the object to be charged can be charged without generation of harmful substances such as ozone. And since it has a charge control device that controls the amount of charge of the object to be charged by controlling the voltage applied to the electron emission element so as to keep the amount of current of electrons emitted from the electron emission element constant, It is possible to precisely control the charge amount of the object to be charged. In addition, since the voltage applied to the electron-emitting device is controlled so as not to generate useless electrons, the object to be charged can be charged to a desired charge amount with minimum electron emission. Therefore, it is possible to extend the lifetime of the device without placing an extra burden on the electron-emitting device. Furthermore, since at least a part of the electron acceleration layer is made of an insulator, heat dissipation and resistance value control in the electron-emitting device can be performed. As a result, the lifetime of the electron-emitting device can be extended and stable charging can be performed over a long period of time.

  In the charging device according to the present invention, the control unit controls the voltage applied to the electron-emitting device so that the amount of current of electrons emitted from the electron-emitting device is 0.25 μA to 20 mA. It is preferable that

  By controlling the amount of current of electrons emitted from the electron-emitting device to be 0.25 μA to 20 mA, an unnecessary amount of electrons are emitted from the electron-emitting device to cause unexpected charging, or conversely It is possible to prevent the charged amount of the object to be charged from being insufficient.

  Furthermore, in the charging device according to the present invention, the control means controls the voltage applied to the electron-emitting device so that a potential difference between the thin film electrode and the charged object is 1.5 kV to 4 kV. It is preferable that

  By controlling the potential difference between the thin film electrode of the electron-emitting device and the object to be charged to be 1.5 kV or more, it is possible to efficiently cause the electrons emitted from the electron-emitting device to reach the object to be charged, Diffusion does not waste electrons. Further, by controlling the potential difference between the thin-film electrode of the electron-emitting device and the member to be charged to be 4 kV or less, electrons can be emitted without causing corona discharge.

  In addition, the charging device according to the present invention preferably includes a plurality of the electron-emitting devices, and a plurality of the charge control devices that individually control the plurality of electron-emitting devices. In this way, by individually controlling the voltage applied to each of the plurality of electron-emitting devices, even if the characteristics of the electron-emitting devices vary due to the manufacturing method or deterioration over time, the amount of current of the emitted electrons is kept constant. Therefore, it is possible to prevent uneven charging from occurring on the member to be charged.

  Furthermore, in the charging device according to the present invention, the plurality of electron-emitting devices are arranged in two or more rows along the longitudinal direction of the cylindrical object to be charged, and a gap between the electron-emitting devices in each row is provided. It is preferable that the adjacent rows are arranged so as not to overlap in the direction orthogonal to the longitudinal direction.

  As a result, the deterioration of charging characteristics and non-uniform charging due to the gap between the electron-emitting devices caused by arranging a plurality of electron-emitting devices in one column can be covered by charging by the electron-emitting devices in the other column. It is possible to achieve uniform charging of the member to be charged.

  In the charging device according to the present invention, it is preferable that the thin film electrode includes at least one of gold, carbon, nickel, titanium, and aluminum. As described above, since the thin film electrode contains a substance having a low work function, electrons accelerated in the electron acceleration layer can be efficiently tunneled, and more high-energy electrons can be emitted outside the electron-emitting device. it can.

  Further, in the charging device according to the present invention, it is preferable that the electron acceleration layer includes conductive fine particles made of a conductor coated with a first dielectric material and a second dielectric material.

  According to the above configuration, the electron accelerating layer includes the conductive fine particles made of the conductor coated with the first dielectric material, so that the electron-emitting device forms a multilayer MIM structure, and the electrode substrate and the thin film electrode By applying a voltage between the two, the electrons passing through the electron acceleration layer can be accelerated into ballistic electrons, and the electrons can be efficiently emitted through the thin film electrode.

  Moreover, the resistance value in an electron acceleration layer can be adjusted because an electron acceleration layer contains a 2nd dielectric material. Further, the second dielectric material can release heat generated in the process of electrons tunneling through the conductive fine particles repeatedly, so that the electron-emitting device can be prevented from being destroyed by heat.

  Since the charging device according to the present invention has the electron acceleration layer having the above-described configuration, electrons can be stably emitted at a low voltage even if the distance to the charged body is short. Thereby, it is possible to reduce the size of the charging device. Further, since electrons are emitted from the electron-emitting device in a planar shape, there is no electric field concentration, and the charging stability is excellent. Further, since there is no electric field concentration, there is no damage to the charged body due to arc discharge.

  In the charging device according to the present invention, it is preferable that the conductor includes at least one of gold, silver, platinum, nickel, and palladium. Thereby, it is possible to prevent the deterioration of the electron-emitting device due to the conductive fine particles being oxidized by oxygen in the atmosphere. Therefore, the lifetime of the electron-emitting device can be extended.

  Furthermore, in the charging device according to the present invention, the first dielectric material preferably contains at least one of an alcoholate, a fatty acid, and an alkanethiol. Thereby, it is possible to prevent element deterioration due to the growth of the first dielectric material due to oxidation of the conductive fine particles by oxygen in the atmosphere. Therefore, the lifetime of the electron-emitting device can be extended more effectively.

In the charging device according to the present invention, it is preferable that the second dielectric material contains at least one of SiO ₂ , Al ₂ O ₃ and TiO ₂ , or an organic polymer. Thus, since these highly insulating materials are contained in the second dielectric material, the resistance value of the electron acceleration layer can be adjusted to an arbitrary range.

  Furthermore, in the charging device according to the present invention, the film thickness of the first dielectric material is preferably thinner than the average diameter of the conductor. Thereby, electrons can be efficiently accelerated, and ballistic electrons can be generated efficiently.

  In the charging device according to the present invention, the second dielectric substance is preferably fine particles having an average diameter larger than the average diameter of the conductive fine particles, and the average particle diameter of the second dielectric substance at this time is 30. More preferably, it is -1000 nm. Accordingly, it is possible to efficiently release heat generated when electrons tunnel through the conductive fine particles, and it is possible to prevent the electron-emitting device from being destroyed by heat. Furthermore, the resistance value in the electron acceleration layer can be easily adjusted. The second dielectric material is layered and has a plurality of openings stacked in the current inflow direction of the electron-emitting device and penetrating in the inflow direction. It may be accommodated in the part. Thereby, the effect similar to the above is acquired.

  Furthermore, in the charging device according to the present invention, the average diameter of the conductive fine particles is preferably 10 nm or less. Thereby, since the average diameter of the conductive fine particles is equal to or less than the average free path of electrons in the conductor, the electrons can pass through the conductive fine particles without being scattered. As a result, ballistic electrons can be efficiently generated, and electrons having high energy can be emitted from the electron-emitting devices.

  In the charging device according to the present invention, the weight ratio of the second dielectric material in the electron acceleration layer is preferably 80 to 95 w%. As a result, the resistance value in the electron acceleration layer can be increased appropriately, and destruction of the electron-emitting device due to a large amount of electrons flowing at a time can be prevented.

  Furthermore, in the charger of the present invention, the electron acceleration layer preferably has a thickness of 30 to 1000 nm. Thereby, the tunnel between the conductive fine particles of electrons in the electron acceleration layer can be repeated an appropriate number of times. As a result, electrons can be emitted more efficiently.

  An image forming apparatus according to the present invention includes the above charging device. As a result, the object to be charged can be charged efficiently and uniformly, and an image can be formed appropriately.

  According to the charging control device of the present invention, the current amount of electrons emitted from the electron-emitting device is constant based on the measurement unit that measures the amount of current in the electron-emitting device and the measurement result from the measuring unit. Thus, since the control means for controlling the voltage applied to the electron-emitting device is provided, the object to be charged can be charged efficiently.

  Further, according to the charging device according to the present invention, the charge control device, and an electron-emitting device having an electron acceleration layer at least partly composed of an insulator between the electrode substrate and the thin film electrode, The charge control device controls the charge amount of the object to be charged by the electrons emitted by applying a voltage to the electron-emitting device. Therefore, the charge control device can efficiently charge the object without generating ozone or NOx. The body can be charged.

  An embodiment of a charging device according to the present invention will be described below with reference to FIGS. 1 and 2 are schematic views showing a charging device 1 according to an embodiment. As shown in FIGS. 1 and 2, the charging device 1 includes an electron-emitting device 2 and a charging control device 3 according to the present invention. The charging control device 3 according to the present invention includes an ammeter (first current measuring unit) 4 and an ammeter (second current measuring unit) 5 as an measuring unit for measuring the amount of current in the electron emitting device, and an electron emitting device. 2, and a control unit 7 that controls the drive power supply 6. The charging device 1 includes an electric field generating power source 11. Here, the electron-emitting device 2 includes an electrode substrate 8, an electron acceleration layer 9, and a thin film electrode 10, and the MIM is configured such that the electron acceleration layer 9 is positioned between the electrode substrate 8 and the thin film electrode 10. It has a structure.

  As shown in FIG. 1, in the charging device 1, the electron-emitting device 2 is installed so as to face the photoconductor (charged body) 12. The photoreceptor 12 is formed with a thickness of, for example, about 30 μm so as to cover the surface of the drum-shaped conductive support 13 made of aluminum or the like, and the conductive support 13 is grounded. The charging device 1 charges the photoconductor 12 by emitting electrons from the electron-emitting device 2 to the photoconductor 12.

  The electron-emitting device 2 is connected to ammeters 4 and 5 and a drive power supply 6, and the ammeters 4 and 5 and the drive power supply 6 are connected to the control unit 7. A voltage is applied between the electrode substrate 8 of the electron-emitting device 2 and the thin film electrode 10 by the driving power source 6, whereby electrons are emitted from the thin film electrode 10 side. The ammeters 4 and 5 each measure the amount of current in the electron-emitting device 2 in order to measure the amount of current of electrons emitted from the electron-emitting device 2. More specifically, the ammeter 4 is connected to the electrode substrate 8 of the electron-emitting device 2 and measures the current flowing into the electron-emitting device from the electrode substrate 8 side. The ammeter 5 is connected to the thin film electrode 10 of the electron-emitting device 2 and measures the amount of current recovered from the thin film electrode 10 without being emitted into the atmosphere.

  Then, the control unit 7 is applied to the electron-emitting device 2 by the driving power source 6 so that the amount of electrons emitted from the electron-emitting device 2 becomes constant based on the measurement results of the ammeters 4 and 5. The voltage is controlled in real time. That is, the control unit 7 determines the voltage applied to the electron-emitting device by the driving power source 6 so that the amount of current of electrons emitted from the electron-emitting device 2 is constant based on the measurement results of the ammeters 4 and 5. Is to control.

  In the present embodiment, the control unit 7 determines that the value obtained by subtracting the current amount measured by the ammeter 5 from the current amount measured by the ammeter 4, that is, the current amount of electrons emitted from the electron emitter 2 is constant. Thus, the voltage applied to the electron-emitting device 2 by the drive power supply 6 is controlled. In this way, by monitoring the current amount of electrons emitted from the electron-emitting device 2 and controlling it in real time, the charge amount of the photoconductor 12 can be appropriately controlled. As a result, the photoreceptor 12 can be charged efficiently.

  The relationship between the voltage applied to the electron-emitting device 2 by the driving power supply 6 and the emitted electrons generally has a relationship in which more electrons are emitted as the voltage is higher. However, the coefficient varies depending on various factors such as element characteristics, life, temperature, humidity, and atmospheric pressure. However, the control unit 7 may control the voltage applied to the electron-emitting device 2 by the drive power supply 6 so that the final electron emission amount after being affected by the influence is constant.

  Here, the control unit 7 controls the voltage applied to the electron-emitting device 2 by the driving power source 6 in real time based on the measurement results of the ammeters 4 and 5, thereby charging the photoconductor 12 at high speed and uniformly. This will be described more specifically.

  First, the potential on the surface of the photoreceptor 12 is expressed by the following formula (1).

  Here, V: surface potential of the photoconductor 12, Q: charge, C: capacitance of the photoconductor 12, ε: dielectric constant of the photoconductor 12 (= relative dielectric constant (εr) of the photoconductor 12 × vacuum dielectric) Ratio (ε0)), w: width of the photoconductor 12, a: radius of the conductive support 13, b: radius from the center of the conductive support 13 to the surface of the photoconductor 12 (= a + thickness of the photoconductor 12 ( d)).

  In addition, the charge received while the photoconductor 12 goes around

  Here, I is the electron emission current, n is the rotational speed (rpm) of the photoconductor 12, and v is the process speed.

  Substituting equation (2) into equation (1), the relationship between V and I is

  That is, the following equation (4)

  It is represented by

  I is calculated from the desired charging potential V of the photoconductor 12 so that the above formula (4) is satisfied, and the value obtained by subtracting the measured value of the ammeter 5 from the measured value of the ammeter 4 is always I. The control unit 7 may control the voltage applied to the electron-emitting device 2 by the driving power source.

  For example, the target charge amount V is -200 V to -1 kV, the relative permittivity εr of the photoconductor 12 is 2 to 4, the width w of the photoconductor 12 is 250 mm to 500 mm, and the radius a of the conductive support 13 is 25 mm to 100 mm. If the thickness d of the photoreceptor 12 is 1 μm to 100 μm and the process speed v is 30 mm / sec to 1000 mm / sec, the required electron emission current I is −0.26 μA to −17.7 mA. That is, the charge amount is insufficient when the electron emission current I is −0.25 μA or less. In addition, even if some reduction in charging efficiency is taken into account, if the electron emission current I is -20 mA or more, the electrons become excessive, charging occurs in unnecessary portions, and the useless burden on the device increases, resulting in an increase in device life. Cause a decline. FIG. 8 shows a table summarizing the optimum range of the electron emission current I. As a more specific example, the target charge amount V is −650 V, the relative permittivity εr of the photoconductor 12 is 3, the width w of the photoconductor 12 is 330 mm, the radius a of the conductive support 13 is 30 mm, If the thickness d of the body 12 is 31.5 μm and the process speed v is 600 mm / sec, the required electron emission current I is −108 μA.

  By controlling the amount of current of electrons emitted from the electron-emitting device 2 to be constant as described above, the electron-emitting device 2 may be affected by environmental changes such as the life of the electron-emitting device 2, temperature / humidity, and contamination of the surface of the electron-emitting device 2. Stable charging is possible without being affected by changes in the characteristics of the electron-emitting device 2. Further, since it is assumed that all the emitted electrons are used for charging the photoconductor 12, no unnecessary electrons are generated. That is, since desired charging can be performed with minimum electron emission, the lifetime of the element can be extended without placing an extra burden on the electron-emitting element 2. Further, since all the emitted electrons are adsorbed by the photosensitive member 12, for example, when mounted on the image forming apparatus, other members are not charged, and there is no fear of destroying the kind of electric circuit.

  In an electron-emitting device using a conventional porous semiconductor layer, charge ring (electron trapping) is caused particularly when electrons are emitted into the atmosphere. As a result, the electrons charged in the nano-sized semiconductor fine particles (nano-silicon crystals) constituting the porous semiconductor layer suppress the acceleration of the electrons by making the electric field inside the porous semiconductor inhomogeneous and reduce the electron emission amount. There was a problem that. Such a problem appears more prominently when a high voltage is applied to the electron-emitting device in order to increase the charging speed, and the charging becomes unstable and the lifetime is shortened. According to the present invention, the voltage applied to the electron-emitting device is controlled so that the amount of electron current emitted from the electron-emitting device is constant, so that an unnecessarily high voltage is not applied to the electron-emitting device. The above-mentioned problem does not occur.

  Next, a detailed configuration of the electron-emitting device 2 will be described below with reference to FIG. As shown in FIG. 2, the electron-emitting device 2 includes an electrode substrate 8, an electron acceleration layer 9, and a thin film electrode 10. The electron acceleration layer 9 is formed so as to be sandwiched between the electrode substrate 8 and the thin film electrode 10. The electrode substrate 8 and the thin film electrode 10 are connected to a driving power source 6, and a voltage such as a direct current, a pulse waveform, a sine waveform, or a triangular waveform is applied between the electrode substrate 8 and the thin film electrode 10 by the driving power source 6. It has come to be. The electron acceleration layer 9 is at least partially made of an insulator. The electron-emitting device 2 accelerates and accelerates electrons between the electrode substrate 8 and the thin film electrode 10 (that is, the electron acceleration layer 9) by applying a voltage between the electrode substrate 8 and the thin film electrode 10. The emitted electrons are emitted from the thin film electrode 10.

  The charging device 1 includes an electric field generating power supply 11 in addition to the driving power supply 6. The electric field generating power source 11 is used to generate an electric field that attracts electrons emitted from the thin film electrode 10 to the photoconductor 12. The separation distance between the photosensitive member 12 and the thin film electrode 10 is not particularly limited as long as the electrons emitted from the thin film electrode 10 can reach the photosensitive member 12. For example, the separation distance is preferably 100 μm to 10 mm, and more preferably 100 μm to 2 mm.

  In the charging device 1, the electrode substrate 8 of the electron-emitting device 2 may be a metal substrate such as SUS, Ti, or Cu, or may be a semiconductor substrate such as Si, Ge, or GaAs. Further, when an insulating substrate such as a glass substrate is used, it can be used as the electrode substrate 8 by attaching a conductive substance such as a metal as an electrode to the interface on the electron acceleration layer 9 side.

  The thin film electrode 10 applies a voltage in the electron acceleration layer 9. Therefore, any material that can apply a voltage to the electron acceleration layer 9 can be used without particular limitation. However, it is preferable that the thin-film electrode 10 is configured so as to transmit and emit electrons accelerated in the electron acceleration layer 9 to high energy without loss of energy as much as possible. From this viewpoint, the thin film electrode 10 is more preferably formed of a material having a low work function and capable of forming a thin film. Examples of such a material include gold, carbon, titanium, nickel, and aluminum.

  Here, the internal structure of the electron acceleration layer 9 will be described below with reference to FIG. FIG. 3 is a cross-sectional view for explaining the structure of the electron-emitting device 2. As shown in FIG. 3, the electron acceleration layer 9 includes conductive fine particles 15 made of a conductor whose periphery is covered with a first dielectric material, and a second dielectric material 14. In the present embodiment, the first dielectric material is a coating material that coats conductive fine particles, metal fine particles are used as the conductor, and the conductive fine particles 15 are metal fine particles that have been coated with an insulating film. In the present embodiment, the second dielectric material 14 is a fine particle made of an insulator having an average particle diameter larger than the average particle diameter of the conductive fine particles 15. However, the configuration of the electron acceleration layer 9 is not limited to the one described above. For example, the second dielectric material 14 is formed in a sheet shape and is laminated between the electrode substrate 8 and the thin film electrode 10. And you may be comprised so that it may have a some opening part penetrated in the laminated | stacked direction. At this time, the conductive fine particles 15 are accommodated in the openings. Therefore, the electron acceleration layer 9 should just be comprised so that the electroconductive fine particles 15 and the 2nd dielectric material 14 may be mixed. It is preferable that at least two kinds of fine particles are present in the electron acceleration layer 9.

  Here, any metal species can be used as the metal species of the conductive fine particles 15 which are the metal fine particles coated with an insulating film on the operation principle of generating ballistic electrons. However, for the purpose of avoiding oxidative deterioration of the metal fine particles when operated at atmospheric pressure, the metal fine particles are preferably a metal that is not easily oxidized, and examples thereof include materials such as gold, silver, platinum, nickel, and palladium. In addition, any insulating coating can be used as the insulating coating of the conductive fine particles 15 which are metal particles coated with an insulating coating on the principle of operation of generating ballistic electrons. However, when the insulating film is covered with an oxide film of metal fine particles, there is a possibility that the thickness of the oxide film becomes thicker than a desired film thickness due to oxidative deterioration of the metal fine particles in the atmosphere. Therefore, for the purpose of avoiding oxidative deterioration of the metal fine particles when operated at atmospheric pressure, the insulating film is preferably an organic material, and examples thereof include materials such as alcoholate, fatty acid, and alkanethiol. The details of the principle of the generation of ballistic electrons will be described later. According to the principle, the diameter of the conductive fine particles 15 which are the metal particles coated with the insulating film is preferably 10 nm or less, and the thickness of the insulating film is thinner. It can be said that is more advantageous. Therefore, in the conductive fine particles 15, the insulating coating is preferably thinner than the average diameter of the metal fine particles.

The material of the second dielectric substance 14 that is fine particles made of an insulator can be used without particular limitation as long as it is an insulating material. However, it is preferable that the ratio of the second dielectric substance 14 with respect to all materials constituting the electron acceleration layer 9 is 80 to 95 w%. The number ratio of the second dielectric material 14 and the conductive fine particles 15 included in the electron acceleration layer 9 is about 2 to 300 conductive fine particles 15 for one second dielectric material 14. That is, when it is 1: 2 to 300, an appropriate resistivity and heat dissipation effect are obtained, which is preferable. The diameter of the second dielectric material 14 is preferably 5 to 1000 nm. Therefore, the material of the second dielectric substance 14 is preferably SiO ₂ , Al ₂ O ₃ , TiO ₂ or the like, or an organic polymer.

  The electron acceleration layer 9 has a stronger electric field as the layer thickness is thinner, and can accelerate electrons by applying a low voltage. However, since the electron acceleration layer 9 cannot be thinner than the average diameter of the second dielectric material 14, the electron acceleration layer 9 The layer thickness is preferably 5 to 1000 nm.

  Next, the principle of electron emission from the electron-emitting device 2 will be described with reference to FIG. FIG. 4 is a diagram showing an energy band of the electron acceleration layer 9 of the electron emitter 2. In the electron acceleration layer 9, as shown in FIG. 3, the conductive fine particles 15 are present so as to be in contact with each other to some extent. Therefore, in the portion where the conductive fine particles 15 are present, the insulator and the conductor are alternately arranged. It will exist. When a voltage is applied to the portion where the conductive fine particles 15 are present, the energy band diagram is as shown in FIG.

  As shown in FIG. 4, the electrons that have entered the electron acceleration layer 9 from the electrode substrate 8 by the electric field enter the insulating coating through a tunnel between the metal particles of the conductive fine particles 15 and the insulating coating. Since a high electric field is applied in the insulating film, the electrons are accelerated to obtain energy. The electrons that have penetrated the insulating coating then enter the conductive metal particles. The mean free path of electrons in the metal particles is 10 nm or more. However, by setting the radius of the conductive fine particles 15 that are the metal fine particles with insulating coating to 10 nm or less, the electrons do not collide with metal atoms and are not scattered. Pass through and penetrate into the next insulation coating. By repeating this, electrons gain high energy and become ballistic electrons. Finally, the electrons reach the thin film electrode 10.

  At this time, if the electrons have obtained energy equal to or higher than the work function of the thin film electrode 10, the electrons are emitted through the thin film electrode 10. Based on such a principle, the electron-emitting device 2 can emit electrons. At this time, if the conductive support 13 is grounded as shown in FIG. 1, electrons emitted from the electron-emitting device 2 are placed between the thin film electrode 10 and the conductive support 13 by the electric field generating power supply 11. The surface of the photoreceptor 12 is charged by being attracted by the generated electric field.

  As described above, in the charging device 1, the electron-emitting device 2 emits electrons into the atmospheric pressure, and the electrons reach the photoconductor 12 by an electric field. That is, since the charging device 1 generates electrons without using discharge, the photoreceptor 12 can be charged while suppressing generation of harmful substances such as ozone.

  In the present embodiment, the configuration including one electron-emitting device 2 has been described as an example. However, as illustrated in FIG. 5, the charging device 1 includes two or more electron-emitting devices 2 in a cylindrical shape. Alternatively, a linear arrangement may be employed in the longitudinal direction (width direction) of the photoconductor 12 having a shape. FIG. 5 is a schematic diagram illustrating a charging device 1 according to another embodiment. When the charge control device 3 is connected to each of the plurality of electron-emitting devices 2 and the charge control device 3 is driven so as to control the charge amount independently, only one electron-emitting device 2 is used. Compared to the above, it is less affected by variations in the electron emission characteristics depending on the area of the surface of the electron-emitting device 2 facing the photoreceptor 12, and uniform charging can be performed.

  As shown in FIG. 6, the charging device 1 may arrange two or more electron-emitting devices 2 in two or more rows in a straight line along the longitudinal direction of the photoreceptor 12. FIG. 6 is a schematic diagram illustrating a charging device 1 according to another embodiment. At this time, the gap between the electron-emitting devices 2 in each row is not overlapped in the direction perpendicular to the longitudinal direction of the photoconductor 12 between adjacent rows, that is, the gap is in the longitudinal direction of the photoconductor 12. It is preferable to arrange so that it may become alternate in the orthogonal direction. By arranging a plurality of electron-emitting devices 2 in a staggered manner in this way, it is possible to compensate for charging defects in the linear gaps in which they are aligned, and the effect of improving the charging uniformity of the photoconductor 12 is achieved. Occurs. In FIG. 6, the charge control device 3 is not shown, but the charge control device 3 is connected to each of the plurality of electron-emitting devices 2 in the same manner as the configuration shown in FIG. By independently controlling the amount of electrons emitted from the photoconductor 12, uniform charging of the photoconductor 12 can be realized.

  Next, the electric field generated by the electric field generating power supply 11 will be described. In general, if an electric field is present, all electrons are attracted to the electric field. Therefore, in the charging device 1, all the emitted electrons reach the photoconductor 12. However, as the photosensitive member 12 is charged, the electric field is weakened. When the surface of the photosensitive member 12 and the thin film electrode 10 of the electron-emitting device 2 finally become equipotential, the electric field disappears, and more electrons are transferred to the photosensitive member. No longer attracted to 12. In a scorotron charging device using a conventional discharge, the amount of charge is controlled using such a potential difference. That is, the potential applied to the thin-film electrode 10 of the electron-emitting device 2 by the electric field generating power source 11 needs to be at least equal to the target charge amount V of the photoreceptor 12.

  As described above, if the potential applied to the electron-emitting device 2 by the electric field generating power supply 11 is V, the potential of the photoconductor 12 finally becomes V. However, in reality, a certain amount of time is required for the photoreceptor 12 to be charged to the potential V. In particular, the charging speed decreases as the potential of the photoconductor 12 approaches V. Since the photosensitive member 12 is rotating, it is necessary to charge the photosensitive member 12 to a desired potential before the photosensitive member 12 passes just below the electron-emitting device 2.

  FIG. 7 shows an example in which the target charge amount V is −650 V, the relative permittivity εr of the photoconductor 12 is 3, the width w of the photoconductor 12 is 330 mm, the radius a of the conductive support 13 is 30 mm, FIG. 6 is a diagram showing the change with time of charging of the photoreceptor 12 when the thickness d of the body 12 is 31.5 μm, the process speed v is 600 mm / sec, and the electron emission current I is charged at −108 μA. The applied voltage of the electric field generating power supply 11 is −650 V, −1 kV, and −1.5 kV, and the ideal straight line is a straight line when the applied voltage of the electric field generating power supply 11 is −infinity. The length of the electron emitting element 2 in the rotation direction of the photoconductor 12 is 30 mm. Therefore, the time required for an arbitrary portion of the photoconductor 12 to pass directly under the electron emitting element 2 is 50 msec.

  As shown in FIG. 7, when the applied voltage of the electric field generating power supply 11 is −650V, it is still charged only to about −350V at the time of 50 msec, and it is understood that the charging amount is insufficient. On the other hand, when the applied voltage of the electric field generating power supply 11 is -1.5 kV, charging of -645 V, which is 99% or more of the desired potential, is obtained, which can be said to be sufficiently within the practical range. If the voltage is further increased, it approaches the ideal straight line, but on the other hand, if too much voltage is applied, corona discharge may occur. When corona discharge occurs, harmful substances such as ozone are generated, and a discharge current flows in addition to the electron emission current from the electron emitter 2, making it difficult to control the appropriate charge amount. Although depending on the shape of the discharge part and the state of electric field concentration, corona discharge is generally generated by applying a voltage of about ± 4 kV in the atmosphere, so the applied voltage of the electric field generating power supply 11 is preferably −4 kV or less. From the above, it is preferable to set the applied voltage of the electric field generating power supply 11 to a target charge amount V or more, more preferably −1.5 kV to −4 kV. FIG. 9 shows a table summarizing the optimum range of the potential difference between the thin film electrode and the charged body generated by the electric field generating power source 11.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible in the range shown to the claim. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  Since the charging device and the charging control device according to the present invention can efficiently charge the photoconductor without generating harmful substances such as ozone, the electrophotographic copying machine, printer, facsimile, etc. The image forming apparatus can be suitably used.

It is a schematic diagram showing a charging device of the present invention according to an embodiment. It is a schematic diagram showing a charging device of the present invention according to an embodiment. It is sectional drawing which shows the internal structure of the electron-emitting element in the charging device of this invention which concerns on one Embodiment. It is a figure which shows the energy band of the electron acceleration layer of the electron-emitting element in the charging device of this invention which concerns on one Embodiment. It is a schematic diagram which shows the charging device of this invention which concerns on other embodiment. It is a schematic diagram which shows the charging device 1 of this invention which concerns on other embodiment. It is a figure which shows the time-dependent change of the charge of the photoreceptor by the charging device of this invention which concerns on one Embodiment. 3 is a table showing an optimum range of an electron emission current I. It is a table | surface which shows the optimal range of the electrical potential difference between a thin film electrode and a to-be-charged body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging device 2 Electron emission element 3 Charging control device 4 Ammeter (measuring means, first current measuring unit)
5 Ammeter (measuring means, second current measuring unit)
6 Drive Power Supply 7 Control Unit 8 Electrode Substrate 9 Electron Acceleration Layer 10 Thin Film Electrode 11 Electric Field Generating Power Supply 12 Photoconductor (Charged Object)
13 Conductive Support 14 Second Dielectric Material 15 Conductive Fine Particle

Claims (19)

A charge control device that controls the amount of charge of an object to be charged by electrons emitted by applying a voltage to an electron-emitting device,
Measuring means for measuring the amount of current in the electron-emitting device;
Based on the measurement results from the measuring means, so that the amount of current of electrons emitted from the electron-emitting device is constant, e Bei and control means for controlling a voltage applied to the electron-emitting device,
The measuring means includes a first current measuring unit that measures the amount of current flowing into the electron-emitting device, and a second current measuring unit that measures the amount of current recovered without being emitted from the electron-emitting device. Including
The control means controls the voltage applied to the electron-emitting device so that the difference between the current amount measured by the first current measurement unit and the current amount measured by the second current measurement unit is constant. charge control apparatus characterized by being turned. A charge control device according to claim 1 and the electron-emitting device.
The electron-emitting device has an electron acceleration layer at least partially composed of an insulator between the electrode substrate and the thin film electrode, and a voltage is applied between the electrode substrate and the thin film electrode, A charging device, wherein electrons are accelerated in the electron acceleration layer and emitted from the thin film electrode. The control means is configured to control a voltage applied to the electron-emitting device such that an amount of current of electrons emitted from the electron-emitting device is 0.25 μA to 20 mA. Item 3. The charging device according to Item 2 . The control means is configured to control a voltage applied to the electron-emitting device so that a potential difference between the thin film electrode and the member to be charged is 1.5 kV to 4 kV. Item 4. The charging device according to Item 2 or 3 . 5. The charging device according to claim 2 , comprising a plurality of the electron-emitting devices, and a plurality of the charge control devices that individually control the plurality of electron-emitting devices. . The plurality of electron-emitting devices are arranged in two or more rows along the longitudinal direction of the cylindrical body to be charged, and the gap between the electron-emitting devices in each row is between the adjacent rows in the longitudinal direction. The charging device according to claim 5 , wherein the charging device is arranged so as not to overlap in an orthogonal direction. The charging device according to claim 2 , wherein the thin film electrode includes at least one of gold, carbon, nickel, titanium, and aluminum. The electron acceleration layer is
Conductive particles made of a conductor coated with a first dielectric material;
The charging device according to claim 2 , further comprising a second dielectric substance. 9. The charging device according to claim 8 , wherein the conductor includes at least one of gold, silver, platinum, nickel, and palladium. The charging device according to claim 8 or 9 , wherein the first dielectric material includes at least one of an alcoholate, a fatty acid, and an alkanethiol. 11. The charging device according to claim 8 , wherein the second dielectric material includes at least one of SiO ₂ , Al ₂ O ₃ and TiO ₂ , or an organic polymer. . 12. The charging device according to claim 8 , wherein a film thickness of the first dielectric substance is thinner than an average diameter of the conductor. The charging device according to any one of claims 8 to 12 , wherein the second dielectric substance is fine particles having an average diameter larger than an average diameter of the conductive fine particles. 14. The charging device according to claim 13 , wherein the average particle diameter of the second dielectric material is 30 to 1000 nm. The second dielectric material is layered, and is stacked in the current inflow direction of the electron-emitting device, and has a plurality of openings that penetrate in the inflow direction.
The charging device according to claim 8 , wherein the conductive fine particles are accommodated in the opening. The charging device according to claim 8 , wherein an average diameter of the conductive fine particles is 10 nm or less. 17. The charging device according to claim 8 , wherein a weight ratio of the second dielectric material in the electron acceleration layer is 80 to 95 w%. 18. The charging device according to claim 8 , wherein the electron acceleration layer has a thickness of 30 to 1000 nm. An image forming apparatus comprising the charging device according to claim 2 .

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